ashish gajera b. pharm. project roll no 14

AANNTTII--DDIIAABBEETTIICC AAGGEENNTTSS

Project submitted for the Partial fulfillment for the degree of

BBAACCHHEELLOORR OOFF PPHHAARRMMAACCYY

In the faculty of Pharmaceutical Sciences,Bharati Vidyapeeth Deemed University, Pune.

By

Ashish Lavjibhai Gajera

Bharati Vidyapeeth Deemed University,

POONA COLLEGE OF PHARMACY,

Erandawane, Pune – 411 038, INDIA.

2009-2010

CERTIFICATE

This is to certify that the work presented in the project entitled

‘‘AAnnttii--ddiiaabbeettiicc AAggeennttss’’For the degree of

BBaacchheelloorr ooff PPhhaarrmmaaccyy

has been carried out by Ashish Lavjibhai Gajera in Bharati

Vidyapeeth Deemed University, Poona College of Pharmacy,

Pune, under, under the guidance of Prof. Dr. V. M. Kulkarni of

Bharati Vidyapeeth Deemed University, Poona College of

Pharmacy, Pune.

Date : /04/2010

Place : Pune

Dr. K. R. Mahadik Principal, Poona College of Pharamcy,Bharati Vidyapeeth Deemed University, Erandwane, Pune-411 038

CERTIFICATE

This is to certify that the work presented in the project entitled

‘‘AAnnttii--ddiiaabbeettiicc AAggeennttss’’For the degree of

BBaacchheelloorr ooff PPhhaarrmmaaccyy

has been carried out by Ashish Lavjibhai Gajera in Bharati

Vidyapeeth Deemed University, Poona College of Pharmacy,

Pune, under my guidance and to my satisfaction. This report

is now ready for examination. Such materials, as obtained

from other sources have been duly acknowledged in the

project.

Date : /04/2010

Place : Pune

Prof. Dr. Vithal M. Kulkarni,Research Guide,Professor Emeritus,Poona College of Pharmacy,Erandwane, Pune-411 038 .

ACKNOWLEDGEMENT

I take this opportunity to express the deep sense of gratitude to my adored research

guide Dr. V. M. Kulkarni, Emeritus Professor, Poona College of Pharmacy, Pune who

continues to support my aspiration with lots of love and encouragement. I consider myself

privileged to work under his generous guidance because I got the newer creative dimensions,

thinking and analyzing capacity, positive attitude, which has always helped me in making

things simple and pragmatic too. I will always remain indebted to him.

My sincere thanks and remembrance to our Vice Chancellor Dr. S. S. Kadam, and our

Principal Dr. K .R. Mahadik for their constant support, valuable suggestions and for making

available the infrastructure with all the sophisticated instruments. I owe my special thanks to

Dr. S. R. Dhaneshwar, Dr. S. H. Bhosale, Dr. (Mrs.) S. S. Dhaneshwar and Dr. (Mrs.) J. R.

Rao for their kind support and dynamic co-operation. I also wish to thank all the faculty

members of Poona College of Pharmacy for providing the mandatory and scholastic inputs

during my course venture.

Special thanks to my Ph. D senior Shah Ujashkumar for his constant support to

complete this project.

I would like to express my heartfelt gratitude to God, grandparents, my parents

& my brother Ashwinbhai & Dayabhabhi and sister Anuradhdidi & Artididi, jiju

Ghanshyamkumar & Parimalkumar and sweet Isha & Manthan for their love, affection,

care, courage, and confidence to complete this project work. I cannot adequately express my

deep sense of gratitude and heartfelt emotions for my family, who blessed me with their good

wishes relieving all type of distress from me.

I am thankful to all those who have directly or indirectly extended their help towards

this project.

Thankful I ever remain……

Date:

Place: Pune Ashish Lavjibhai Gajera

INDEX

1. Introduction 1-15

1.1 Pre-diabetes 1

1.2 Diabetes 1

1.3 Etymology 6

1.4 Epidemiology 6

1.5 Insulin and diabetes mellitus 7

1.6 Pathophysiology of diabetes 8

1.7 Signs and Symptoms 9

1.8 History 11

2. Literature Review 16-38

2.1 History 16

2.2 Oral antidiabetic agent (Clinically used) 18

2.3 Oral antidiabetic agent (Clinically not used) 20

3. Classification of Anti-Diabetic Drug 39-40

4. Insulin 41-46

4.1 Discription 42

4.2 Variants of Insulin products 42

5. Secretagogues 47-77

5.1 K+ ATP 47

5.1.1 Sulfonylureas 47

5.1.2 Meglitinide 60

5.2 GLP-I analogues 63

5.3 Protein Tyrosin Phosphate 1β inhibitors 65

5.4 Dipeptidyl peptidase-4 inhibitors 72

6. Sensitizers 78-89

6.1 Biguanide 78

6.2 Thiazolidinedione 82

6.3 PPAR modulator 87

7. Other Insulin Analogues 90-95

7.1 Animal insulin 90

7.2 Chemically and enzymatically modified insulin 91

7.3 Non hexameric insulin analogues 91

7.4 Shifted isoelectric point insulin 91

7.5 Carcinogenicity 92

8. Other analogues 96-103

8.1 α-Glucosidase inhibitor 96

8.2Amylin 100

8.3 Sodium-glucose transport proteins 102

9. Other Drugs 104

10. Natural antidiabetic agent 106

11. References 107

LISTS OF FIGURE

No Title Page No

1.1 Normal insulin signaling pathways 8

1.2 Complications of diabetes mellitus 10

4.1 Primary structure of proinsulin, depicting cleavage sites to produce

insulin.

41

4.2 Insulin structure 42

5.1 Classification of PTP 66

5.2 Role of PTP-1β in insulin signaling 67

5.3 Structure of PTP-1β showing main sites 68

5.4 Structure of PTP-1β showing simultaneous dephosphorylation of

insulin receptor

69

5.5 Dipeptidyl peptidase-4 inhibitor 72

6.1 PPAR α and γ pathways. 87

8.1 Amino acid sequence of Amylin with disulfide bridge and cleavage

sites of insulin degrading enzyme indicated with arrows

100

ANTI-DIABETIC AGENTS

Page 1

DIABETES1. INTRODUCTION1-20

1.1 Pre-diabetes

Prediabetes is a stage between normal and diabetes stage. It is an alarming sign for

upcoming diabetes or a chance to change your future. Universally, numerous terms are

given like, Borderline Diabetes, Chemical Diabetes, Touch of Diabetes etc. The term

Prediabetic was given by the US Department of Health And Human Services on 27th

march 2002 with an intention to create awareness and convey seriousness of the condition.

Also, they motivated people to option for appropriate treatment and lifestyle modification.

According to that 17 million US citizens are diabetic and 16 millions are prediabetic. It

defines it as a stage before the development of diabetes, with normal glucose tolerance, but

with an increased risk of developing diabetes in near future.

Prediabetes is a condition when your blood sugar level triggers higher than normal,

but not so high that we can justify it as type 2 diabetes. According to the Centers for

Disease Control and Prevention, 41 million U.S. adults aged 40 to 74 have prediabetes.

And the same reports from, The American Academy of Pediatrics show that, one of every

10 males and one of every 25 females have prediabetes aged from 12 to 19 years.

1.2 Diabetes

Diabetes is a disease in which levels of blood glucose, also called blood sugar, are

above normal. People with diabetes have problems converting food to energy. Normally,

after a meal, the body breaks food down into glucose, which the blood carries to cells

throughout the body. Cells use insulin, a hormone made in the pancreas, to help them

convert blood glucose into energy.

People develop diabetes because the pancreas does not make enough insulin or

because the cells in the muscles, liver and fat do not use insulin properly, or both. As a

result, the amount of glucose in the blood increases while the cells are starved of energy.

Over the years, high blood glucose, also called hyperglycemia, damages nerves and blood


Page 2

vessels, which can lead to complications such as heart disease, stroke, kidney disease,

blindness, nerve problems, gum infections, and amputation.

As per global projections by International Diabetes Federation (IDF), the number

of diabetes patients has risen sharply in recent years. While in 1985, 30 million people had

diabetes worldwide; the number rose to 150 million in 2000, 285 million in 2010 and is

estimated to be 435 million - 7.8% of the adult world population by 2030.India has the

highest number of diabetics in the world. By next year, the country will be home to 50.8

million diabetics, making it the world's unchallenged diabetes capital. And the number is

expected to go up to 87 million -8.4% of the country's adult population -- by 2030.

Diabetes mellitus is a common disease in the all over world.The crude prevalence

rate of diabetes in urban areas is about 9% and that the prevalence in rural areas has also

increased to around 3% of the total population. If one takes into consideration that the total

population of India is more than 1000 million then one can understand the sheer numbers

involved. Taking an urban-rural population distribution of 70:30 and an overall crude

prevalence rate of around 4%, at a conservative estimate, India is home to around 40

million diabetics and this number is thought to give India the dubious distinction of being

home to the largest number of diabetics in any one country. Diabetes prevalence has

increased steadily in the last half of this century and will continue rising among U.S.

population. It is believed to be one of the main criterions for deaths in United States, every

year. This diabetes information hub projects on the necessary steps and precautions to

control and eradicate diabetes, completely.

Diabetes is a metabolic disorder where in human body does not produce or

properly uses insulin, a hormone that is required to convert sugar, starches, and other food

into energy. Diabetes mellitus is characterized by constant high levels of blood glucose

(sugar). Human body has to maintain the blood glucose level at a very narrow range,

which is done with insulin and glucagon. The function of glucagon is causing the liver to

release glucose from its cells into the blood, for the production of energy.

There are three main types of diabetes:

Type 1 diabetes

Type 2 diabetes

Gestational diabetes


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1.2.1 Type 1 Diabetes

The insulin-dependent diabetes mellitus (IDDM), normally takes place when the β-

cells of the prevailing pancreatic islets of Langerhans are destroyed, perhaps by an

autoimmune, mechanism, as a consequence of which the ‘insulin production’ in vivo is

overwhelmingly insufficient. Subjects undergoing such abnormalities in biological

functions may show appreciable metabolic irregularity that may ultimately lead to develop

diabetic β-ketoacidosis together with other manifestations of acute diabetes.

Therapeutically Type-I diabetes is largely treated with insulin.

1.2.2 Type 2 Diabetes

The noninsulin-dependent diabetes mellitus (NIDDM), i.e., type 2 diabetes, is

most abundantly linked with obesity in its adult patients largely. In such a situation, the

insulin levels could be either elevated or normal; and therefore, in short, it is nothing but a

disease of abnormal ‘insulin resistance’. However, it has been duly observed that the

impact of the disease is relativel milder, occasionally leaving to β-ketoacidosis and may

also be accompanied by certain other degenerative phenomena in vivo. The etiology of the

condition bears a strong genetic hereditar; and, hence, insulin therapy may not prove to be

quite effective.

1.2.3 Gestational Diabetes

Some women develop gestational diabetes late in pregnancy. Although this form of

diabetes usually disappears after the birth of the baby, women who have had gestational

diabetes have a 40 to 60 percent chance of developing type 2 diabetecs within 5 to 10

years. Maintaining a reasonable body weight and being physically active may help prevent

development of type 2 diabetes.

About 3 to 8 percent of pregnant women in the United States develop gestational

diabetes. As with type 2 diabetes, gestational diabetes occurs more often in some ethnic

groups and among women with a family history of diabetes. Gestational diabetes is caused

by the hormones of pregnancy or a shortage of insulin. Women with gestational diabetes

may not experience any symptoms.

Type 1 and Type 2 diabetes impede a person’s carefree life. When breakdown of

glucose is stopped completely, body uses fat and protein for producing the energy. Due to

this mechanism symptoms like polydipsia, polyuria, polyphegia, and excessive weightloss


Page 4

can be observed in a diabetic. Desired blood sugar of human body should be between 70

mg/dl -110 mg/dl at fasting state. If blood sugar is less than 70 mg/dl, it is termed as

hypoglycemia and if more than 110 mg /dl, it’s hyperglycemia.

Diabetes is the primary reason for adult blindness, end-stage renal disease (ESRD),

gangrene and amputations. Overweight, lack of exercise, family history and stress increase

the likelihood of diabetes. When blood sugar level is constantly high it leads to kidney

failure, cardiovascular problems and neuropathy. Patients with diabetes are 4 times more

likely to have coronary heart disease and stroke. Gestational diabetes is more dangerous

for pregnant women and their fetus.

Though, Diabetes mellitus is not completely curable but, it is controllable to a great

extent. So, you need to have thorough diabetes information to manage this it successfully.

The control of diabetes mostly depends on the patient and it is his/her responsibility to take

care of their diet, exercise and medication. Advances in diabetes research have led to

better ways of controlling diabetes and treating its complications.

1.2.4 Other specific types:

1. Genetic defects of beta cell function

Chromosome 20q, HNF-4α (MODY1)

Chromosome 7p, glucokinase (MODY2)

Chromosome 12q, HNF-1α (MODY3)

Chromosome 13q, insulin promoter factor (MODY4)

Chromosome 17q, HNF-1β (MODY5)

Chromosome 2q, neurogenic differentiation1/b-cell ebox

transactivator 2 (MODY6)

Mitochondrial DNA

2. Genetic defects in insulin action

Type 1 insulin resistance

Leprechaunism

Rabson-mendenhall syndrome

Lipoatrophic diabetes


Page 5

3. Diseases of exocrine pancreas

Pancriatitis

Trauma/pancreatectomy

Neoplasia

Cystic fibrosis

Hemochromatosis

Fibrocalculous pancreatopathy

4. Endocrinopathies

Acromegaly

Cushing’s syndrome

Glucagonoma

Pheochromocytoma

Hyperthyroidism

Somatostatinoma

Aldosteronoma

5. Drug or chemical induced

Vacor

Pentamidine

Nicotinic acid

Glucocorticoids

Thyroid hormone

Diazooxide

Β-Adrenergic agonists

Thiazides

Dilantin

Interferon

6. Infections

Congenital rubella

Cytomegalovirus


Page 6

7. Uncommon forms of immune mediated diabetes

Stiff-man syndrome

Klinefelter’s syndrome

Turner’s syndrome

Wolfram’s syndrome

Friedeich’s ataxia

Huntington’s chorea

Laurence-Moon-Biedel syndrome

Porphyria

Prader-Willi syndrome

1.3 Etymology

The word diabetes was coined by Aretaeus (81–133 CE) of Cappadocia. The word

is taken from Greek diabaínein, and literally means “passing through,” or “siphon”.

"Mellitus" comes from the Greek word "sweet". Apparently, the Greeks named it thus

because the excessive amounts of urine diabetics produce (when blood glucose is too high)

attracted flies and bees because of the glucose content. The ancient Chinese tested for

diabetes by observing whether ants were attracted to a person's urine; medieval European

doctors tested for it by tasting the urine themselves, a scene occasionally depicted in

Gothic reliefs.The word became diabetes from the English adoption of the medieval Latin,

diabetes. In 1675, Thomas Willis added mellitus to the name (Greek mel “honey,” sense

‘honey sweet’) when he noted that a diabetic’s urine and blood has a sweet taste (first

noticed by ancient Indians).

It is probably important to note that passing abnormal amounts of urine is a

symptom shared by several diseases (most commonly of the kidneys), and the single word

diabetes is applied to many of them. The most common of them are diabetes insipidus and

the subject of this article, diabetes mellitus.

1.4 Epidemiology

Diabetes mellitus is a disease that occurs worldwide and the incidence is higher in

relatives of diabetes, people older than 45 years and those who are currently or were obese.

Studies of identical twins show greater than 94% concordance for developing NIDDM.


Page 7

Furthermore, there is a high prevalence of NIDDM in offspring’s of parents with the

disease and also in siblings of affected individuals. Persons more than 20 % over ideal

body weight also have a greater risk of developing NIDDM. In addition, previously

identified impaired glucose tolerance, gestational diabetes, hypertension or significant

hyperlipidemias are associated with an increased risk of NIDDM.

1.5 Insulin and diabetes mellitus

Insulin is a 58-kDa polypeptide hormone produced by pancreatic islets of

langerhance regulating, in vivo, the storage, release, and utilization of nutrient energy,

carbohydrate in the form of glucose, fat and protein, in response to the changing supply

and demand.

The major metabolic actions of insulin include:

Promotion of uptake and storage of glucose in liver and muscle in the form of

glycogen.

Suppression of hepatic glycogenolysis and gluconeogenesis.

Increasing the rate of glucose oxidation in muscle.

Suppression of lipolysis and the release of fatty acid from adipose tissue.

Enhancing triglyceride synthesis and storage and de novo lipogenesis from

carbohydrate in liver and fat.

Promotion of amino acid uptake and protein synthesis in muscle.

Regulation of gene transcription.

Insulin initiates its actions by binding to the cell surface receptors on target cells

(mostly liver, muscle, fat). The receptor is a glycoprotein complex (350000MW)

consisting of two - and two -subunits linked by disulfide bridges. The -subunits are

entirely extracellular and contain the insulin binding domain, while -subunits are

transmembrane proteins that posses tyrosine protein kinase activity.


Page 8

After insulin is bound the receptors aggregate and are rapidly internalized.

Tyrosine kinase gets autophosphorylated and also phosphorylates other substrates so that a

signaling cascade is initiated and biological response ensues.

Figure 1.1: Normal Insulin Signaling Pathways

1.6 Pathophysiology of diabetes:

Although several pathogenic processes may be involved in the development of

diabetes, the vast majority of cases fall in to two categories: type 1 and type 2 Diabetes

Mellitus. There are genetic and environmental components in both types of DM. Type 1

DM occurs usually due to genetic predisposition and immune mediated destruction of

pancreatic islet β-cells with consequent loss of insulin secretion followed by prediabetes

and overt diabetes.


Page 9

Type 2 DM results from a combination of relative deficiency in insulin production

from the beta cell and insulin resistance at the target cell (liver, muscle and fat). Owing to

heterogeneous nature of NIDDM and two major pathogenic factors influence one another,

it is difficult to determine which of the two is initializing factor and what is relative

contributions to the development of glucose intolerance.

1.7 Signs and symptoms:

Onset of type 1 DM is sudden and characterized by polyurea, polydipsia,

polyphagia, weight loss, decreased muscle strength, irritability and perhaps a return of

bed-wetting. The presentation may be ketosis. The clinical presentation of type 2 diabetes

mellitus may be insidious onset of weight loss, nocturia, vascular complication, decreased

or blurred vision, fatigue, anemia or signs and symptoms of neuropathy. The diagnosis of

diabetes mellitus is based on the documentation of elevated fasting blood glucose, elevated

blood glucose two hours postprandly, or an abnormal glucose tolerance test.

Complication:

A well control diabetic is less labile to ketosis and infections. It is now certain that

good control of glycemia mitigates the serious microvascular complications, retinopathy,

nephropathy and cataract. Too light control of glycemia can increase the frequency of

attacks of hypoglycemia.

Diabetic ketoacidosis is caused by insulin deficiency and an increase in catabolic

hormones, leading to hepatic overproduction of glucose and ketone bodies. Hyperglycemia

causes a profound osmotic diuresis leading to dehydration and electrolyte loss, particularly

of sodium and potassium. The metabolic acidosis forces hydrogen ions into cells,

displacing potassium ions, which may be lost in urine or through vomiting. The signs and

symptoms include polyuria, weight loss, thirst, abdominal pain, nausea, and vomiting.

Hypotension, hypothermia and air hunger may also be present.

Nonketotic hyperosmolar coma is characterized by severe hyperglycemia (>50

mmol/l) without significant hyperketonemia or acidosis. This condition usually affects

elderly patients, many with previously undiagnosed diabetes. Mortality is over 40%.


Page 10

Fig 1.2: Complications of Diabetes mellitus

Diabetic retinopathy is the most common cause of blindness in adults between 30

and 65 years of age in developed countries. Clinical features of diabetic retinopathy

include microaneurysms, retinal haemmorhages, hard exudates, soft exudates and fibrosis.

Cataracts also are associated with the disease.

Diabetic neuropathy occurs mainly due to axonal degeneration of both myelinated

and unmyelinated fibres (Axonal shrinkage, Axonal fragmentation; regeneration),


Page 11

thickening of schwan cell basal lamina, patchy segmental demyelination and abnormalities

in intraneural capillaries. This is relatively early and common complication affecting

approximately 30% of diabetic patients.

Diabetic foot occurs as a result of trauma in the presence of neuropathy and / or

peripheral vascular disease, with infection occurring as a secondary phenomenon

following ulceration of protective epidermis. In most cases all the three components are

involved but sometimes neuropathy or ischaemia may predominate.

In Diabetic nephropathy pathologically the first changes (at the time of

microalbuminurea) are thickening of glomerular basement membrane and accumulation of

matrix material in the mesangium. Subsequently, nodular deposits are characteristic, and

glomerulosclerosis worsens (time of heavy proteinurea) glomeruli are progressively lost

and renal function deteriorates.

1.8 History

Diabetes mellitus is known to the human beings many years ago mainly from

prehistoric times. In earlier day, a clinical diagnosis of diabetes was an invariable death

sentence, more or less quickly. Even non-progressing type 2 diabetes was left

undiagnosed. But with the discovery of insulin, its treatment is made possible. Diabetes

was first identified by Egyptians about 3500 years ago. It has been explained in the

medical books of the ancient civilizations of Egypt, Greece, Indian, Rome and China. In

the ancient books it has been mentioned that the disease is associated with polyuria,

polydipsia, polyphagia, etc. A Roman citizen has described diabetes as a melting down of

the flesh and limbs into urine. Moreover, the Charaka and Sushruta well known Ayurvedic

physician, described that the diabetic patients’ passes sweet urine in large amount that is

rain of honey.

So, They have named Diabetes mellitus as “Madhumeha”. Thereafter, we can say

diabetes has been recognized since antiquity, and its treatments were known since the

middle ages. But the etiopathogensis of diabetes occurred mainly in the 20thcentury. The

ancient Chinese have tested for diabetes by observing whether ants were attracted to a

person’s urine or not. Medieval European doctors have tested for diabetes, by testing the

urine of diabetic patients themselves, a scene occasionally depicted in Gothic relief, and

they named it “sweet urine disease”.


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1552 B.C. Earliest known record of diabetes mentioned on 3rd

Dynasty Egyptian papyrus by physician Hesy-Ra;

mentions polyuria (frequent urination) as a symptom.

1st Century A.D. Diabetes described by Arateus as 'the melting down of

flesh and limbs into urine.'

164 A.D. Greek physician Galen of Pergamum mistakenly

diagnoses diabetes as an ailment of the kidneys.

Up to 11th

Century

Diabetes commonly diagnosed by 'water tasters,' who

drank the urine of those suspected of having diabetes;

the urine of people with diabetes was thought to be

sweet-tasting. The Latin word for honey (referring to

its sweetness), 'mellitus', is added to the term diabetes

as a result.

16th Century Paracelsus identifies diabetes as a serious general

disorder.

Early 19th

Century

First chemical tests developed to indicate and measure

the presence of sugar in the urine.

late 1850s French physician, Priorry, advises diabetes patients to

eat extra large quantities of sugar as a treatment.

1870s French physician, Bouchardat, notices the

disappearance of glycosuria in his diabetes patients

during the rationing of food in Paris while under siege

by Germany during the Franco-Prussian War;

formulates idea of individualized diets for his diabetes

patients.

19th Century French researcher, Claude Bernard, studies the

workings of the pancreas and the glycogen metabolism

of the liver.

Czech researcher, I.V. Pavlov, discovers the links

between the nervous system and gastric secretion,

making an important contribution to science's

knowledge of the physiology of the digestive system.


Page 13

Late 19th Century Italian diabetes specialist, Catoni, isolates his patients

under lock and key in order to get them to follow their

diets.

1869 Paul Langerhans, a German medical student, announces

in a dissertation that the pancreas contains contains two

systems of cells. One set secretes the normal pancreatic

juice, the function of the other was unknown. Several

years later, these cells are identified as the 'islets of

Langerhans.'

1889 Oskar Minkowski and Joseph von Mering at the

University of Strasbourg, France, first remove the

pancreas from a dog to determine the effect of an

absent pancreas on digestion.

1900-1915 'Fad' diabetes diets include: the 'oat-cure' (in which the

majority of diet was made up of oatmeal), the milk diet,

the rice cure, 'potato therapy' and even the use of

opium!

1908 German scientist, Georg Zuelzer develops the first

injectible pancreatic extract to suppress glycosuria;

however, there are extreme side effects to the

treatment.

1910-1920 Frederick Madison Allen and Elliot P. Joslin emerge as

the two leading diabetes specialists in the United

States. Joslin believes diabetes to be 'the best of the

chronic diseases' because it was 'clean, seldom

unsightly, not contagious, often painless and

susceptible to treatment.'

1913 Allen, after three years of diabetes study, publishes

Studies Concerning Glycosuria and Diabetes, a book

which is significant for the revolution in diabetes

therapy that developed from it.

1919 Frederick Allen publishes Total Dietary Regulation in


Page 14

the Treatment of Diabetes, citing exhaustive case

records of 76 of the 100 diabetes patients he observed,

becomes the director of diabetes research at the

Rockefeller Institute.

1919-20 Allen establishes the first treatment clinic in the USA,

the Physiatric Institute in New Jersey, to treat patients

with diabetes, high blood pressure and Bright's disease;

wealthy and desperate patients flock to it.

October 31, 1920 Dr. Banting conceives of the idea of insulin after

reading Moses Barron's 'The Relation of the Islets of

Langerhans to Diabetes with Special Reference to

Cases of Pancreatic Lithiasis' in the November issue of

Surgery, Gynecology and Obstetrics. For the next year,

with the assistance of Best, Collip and Macleod, Dr.

Banting continues his research using a variety of

different extracts on de-pancreatized dogs.

Summer 1921 Insulin is 'discovered'. A de-pancreatized dog is

successfully treated with insulin.

December 30,

1921

Dr. Banting presents a paper entitled 'The Beneficial

Influences of Certain Pancreatic Extracts on Pancreatic

Diabetes', summarizing his work to this point at a

session of the American Physiological Society at Yale

University. Among the attendees are Allen and Joslin.

Little praise or congratulation is received.

1940s Link is made between diabetes and long-term

complications (kidney and eye disease).

1944 Standard insulin syringe is developed, helping to make

diabetes management more uniform.

1955 Oral drugs are introduced to help lower blood glucose

levels.

1959 Two major types of diabetes are recognized: type 1

(insulin-dependent) diabetes and type 2 (non insulin-


Page 15

dependent) diabetes.

1960s The purity of insulin is improved. Home testing for

sugar levels in urine increases level of control for

people with diabetes.

1970 Blood glucose meters and insulin pumps are developed.

Laser therapy is used to help slow or prevent blindness

in some people with diabetes.

1983 First biosynthetic human insulin is introduced.

1986 Insulin pen delivery system is introduced.

1993 Diabetes Control and Complications Trial (DCCT)

report is published. The DCCT results clearly

demonstrate that intensive therapy (more frequent

doses and self-adjustment according to individual

activity and eating patterns) delays the onset and

progression of long-term complications in individuals

with type 1 diabetes.

1998 The United Kingdom Prospective Diabetes Study

(UKPDS) is published. UKPDS results clearly identify

the importance of good glucose control and good blood

pressure control in the delay and/or prevention of

complications in type 2 diabetes.


Page 16

2. LITERATURE SURVEY21-39

2.1 History

The discovery of insulin in 1922 by Benting, Best, Mac Leod and Collip,

confirmed on the one hand the role of pancreas as an endocrine gland and the part it plays

in the pathogenesis of diabetes, a fact which had also been indicated initially by the

research of Minkowisky and of Hedon. Insulin was isolated in the crystalline form by Abel

in 1926. On the other hand it provided many diabetic patients with an effective form of

treatment allowing them to lead almost normal lives.

It is immediately apparent that insulin did not cure diabetes, that its beneficial

effects did not last more than a few hours, that injections needed to be repeated throughout

the day and that such treatment would have to be carried out immediately. It was also

shown that insulin was rapidly inactivated when it was administered via the digestive tract.

Attempts to treat human diabetes by orally administered pharmacological agents

like synthalins and their derivatives, were made between 1925 to 1930, these substances

were quickly abandoned by their advocates however because of their variability, the

appearance of toxic side effects and of the uncertainty concerning their mode of action.

After the earlier therapeutic failures of the synthalins, attempts were made

to prolong the 6-8 hour effects of the single injection of soluble insulin to obviate the

necessity for repeated injections. This was done by coupling the hormone to zinc and then

to certain protamines, which are other agents, prolonging the effects of ordinary insulin,

producing protamine-zinc-insulin (PZI), which after a single injection could maintain

effects for 24 hrs in certain cases, longer.

Between 1939 and 1942, the therapeutic use of the sulfonamide increased dramatically and

the drugs were assessed end tried in the treatment of many infectious diseases.

NH2S

N N

SO2NHCH3

CH3

VK-57 (2254RP)

P-amino-benzene-sulfonamide-isopropyl-thiadiazole (VK-57) was synthes -ized in

1941 by Von Kennel and Kimming. This drug had shown a certain in vitro inhibitory


Page 17

effect on multiplication of the typhoid bacillus. After oral doses of 2254RP some patients

died from obscure causes, which were only elucidated later when the hypoglycemic action

of the sulfonamide became clear, it was strongly suggested that they died from severe and

prolonged hypoglycemia.

Several experiments were done in different animal models to explain the

hypoglycemic effect of sulfonamide. It was postulated that sulfonamide act by stimulating

the beta cells of the islets and liberate in to the blood an accumulated quantity of

endogenous insulin (insulin secretory action).

SO2NHCONHCH2CH2CH2CH3NH2

Carbutamide (BZ55)

German workers published that a new sulfonamide i.e.1-butyl-3-sulfonylurea

(carbutamide or BZ55) was more active than 2254 RP as hypoglycemic agent. 2254 RP

and carbutamide have a NH2 group in the para position on the benzene ring and because of

this have a bacteriostatic action, which could be considered unnecessary if not a major

disadvantage.

In 1956, a group of german workers published the experimental and clinical

results obtained by using a sulfonamide with its NH2 group in the para position replaced

by CH3 group but with the reminder of the molecule possessing a structure identical to that

of carbutamide. This substance D860, 1-butyl-3-tolyl-sulfonylurea (tolbutamide) which

did not have bacteriostatic action and retained the hypoglycemic and antidiabetic

properties of 2254RP and carbutamide.

CH3 SO2NHCONHCH2CH2CH2CH3

Tolbutamide


Page 18

2.2 Oral Antidiabetic Agents (Clinically used)

1) Sulfonylureas:

Since 1956 till present sulfonylureas class of compounds are used for the treatment

of diabetes mellitus. Modifications were made to improve the potency of the compounds

and avoid toxic effects. A wide variety of structural modifications have been carried out on

the original Carbutamide, tolbutamide, chlorpropamide type sulfonylureas which led to

tolazamide, gliclizide, acetohexamide, gibornuride, glimidine, tolcyclamide etc. These

sulfonylureas were termed as first generation sulfonylureas. Further research in this area

led to potent antidiabetic agent, glibenclamide (gliburide, glibiride, and glybencyclamide,

HB-419) and other compounds like glipizide, glisepoxide, gliquidone, glypentide etc,

which are termed as second-generation sulfonylureas.

A-SO2-NH-B

First generation sulfonylureas:

First generation sulfonylureas are less potent and act at higher dose. Some of useful

compounds and their structures are:

Cl SO2NHCONHCH2CH2CH3

Chlorpropamide

CH3 SO2NHCONH N

Tolazamide

SO2NHCONHOMe

Acetohexamide


Page 19

SO2NHCONHCH3 N

Gliclizide

Second-generation sulfonylureas:

Second generation sulfonylureas are very potent compounds and their dose is low.

Some examples are as follows:

SO2NHCONHCONHCH2CH2

OMe

Cl

Glibenclamide

SO2NHCONHN

CONHCH2CH2

N

CH3

Glipizide

2) Biguanides:

The only nonsulfonylurea drugs, which have proven useful in antidiabetic therapy,

are the biguanides17, which can be used either alone or in combination with sulfonylureas.

Only three agents are marketed at the present time (Metformin, Chenformin and

Buformin).

C

NH

NHN C

NH

NH2

CH3

CH3

Metformin

C

NH

NHNH C

NH

NH2H2CH2C

Phenformin (Chenformin)


Page 20

C

NH

NHNH C

NH

NH2H3CH2CH2CH2C

Buformin

Two factors have recently emerged which adversely affect the use of biguanides.

Phenformin was one of the drugs examined in the university group Diabetes program

(UGDP) study and as in the case of tolbutamide, enhanced cardiovascular mortality was

observed instead of the anticipated beneficial effects. These findings were judged to be

severe enough to warrant an early termination of phenformin study. Again, the conclusion

of the UGDP study group have aroused controversy, and its conclusions have been

questioned. It is certainly interesting that a group from England found a reduced incidence

of myocardial infarction in a 5-year study of phenformin and that another group found a

slight but insignificant beneficial effects of phenformin on survival in patients with

coronary heart disease. It is therefore not clear at this time whether the use of phenformin

is associated with increased cardiovascular mortality only in diabetes or whether the

findings with phenformin can be generalized to other biguanides.

2.3 Oral Antidiabetic Agents (Clinically not used)

1) Carboxylic Acids:

An interesting newer structure is meglitinide (HB-669), which is related to

Glibenclamide, with a carboxyl group replacing the acidic sulfonylurea function. HB-669

and its higher homologue (HB-093) are insulin releasers although their potency is much

more than that of Glibenclamide and more in the range of tolbutamide. It should be

interesting to see whether or not will prove efficacious in man. Similarly, a benzoic acid

derivative has hypoglycemic properties, and the S-enantiomer is more potent than R-

enantiomer. This suggest that the high potency side chain of both sulfonylureas and

benzoic acids interact at the same receptor.


Page 21

Cl

OMe

CONHCH2CH2 COOH

Meglitinide

Cl

OMe

CONHCH2CH2 CH2CH2COOH

HB-669

2) Benzoic Acid Derivatives: (S-enantiomer)

F

OMe

CH3

HNHCOCH2 COOH

Salicylates have been used long ago to improve glucose control in diabetes,

possibly via their insulin-releasing or antilipolytic effects. However, high doses are

required and the clinical benefits appear to be marginal.

OH

COOH

OH

COOH

CH3

The benzoic acid derivatives have been reported to stimulate glucose utilization,

but it apparently had side effects and caused tachyphylaxis in animals.


Page 22

Cl

COOH

N

3-Mercaptopicolinic acid and several derivatives are apparently gluconeogenesis

inhibitors, which lower glucose levels in animals.

N

SH

COOH

3) Heterocyclic Carboxylic Acid:

A series of heterocyclic carboxylic acids and their metabolic precursors generated

some excitement a few years ago because these antilipolytic compounds lowered blood

glucose in diabetics.

4) Heterocyclic Acids:

ON

CH3

COOH

5) Metabolic precursors of above Heterocyclic Acids:

NH

N

CH3

CH3

ON

CH3

CH3

6) Aliphatic Carboxylic Acids:

Among aliphatic carboxylic acids, dichloroacetic acid in the form of its

diisopropylammonium or sodium salt, has been shown to lower blood glucose and to

remedy the lactate elevations found after phenformin treatment.


Page 23

7) Dichloroacetic Acid:

Cl2CHCOOH

8) Diisopropyl Derivative:

HOOCCOCH2COOH

9) Oxirane Carboxylic Acid:

Oxirane carboxylic acid and its methyl esters are reported to be inhibitors of

carnitine acyl transferase and to be hypoglycemic in fasted, diabetic, or fat fed animals, by

enhancing peripheral glucose oxidation.

O

H29C14 COOH

O

H29C14 COOCH3

NH2

COOH

COOH

10) Amidines and Guanidines:

Among non-acidic hypoglycemic agents, there are several intriguing guanidines

and amidines. Pirogliride, although its structure is somewhat reminiscent of biguanides, is

reported to have a different activity profile and mechanism of action.

N

N N N

CH3

Pirogliride

Cetpiperalone is piperazine derivative related to cyclic guanidines and has the

potency range of tolbutamide, is probably an insulin releaser.


Page 24

NHNNH

NH

O

Cetpieralone

A series of alpha alkoxy amidines. Displayed hypoglycemic and nutiuretic activity

in animals, but poor separation of activity from toxicity exhibited by these compounds

prevented clinical studies.

NH

NH3CH2CO

-Alkoxy amidines

11) Fatty acid Oxidation Inhibitors:

Its use as orally effective hypoglycemic compounds has its roots in Randles

glucose-fatty acid cycle first proposed in the 1960’s. This hypothesis recognized the

reciprocal relationship that exists between fat and carbohydrate metabolism. A reduction

in fatty acid oxidation should enhance carbohydrate utilization and consequently lower

blood glucose levels.

12) Carnitine Palmitoyl Transferase (CPT):

Most inhibitors of this enzyme reported in the literature are long chain fattyacyl

CoA analogues. The two most thoroughly characterized CPT inhibitors are TDGA (2-

tetradelylglycidate) and its methyl ester (MeTDGA) and POCA

(chlorophenylpentyoxirane carboxylate).

O

CH3(CH2)13 COOH

O

COOH

Cl


Page 25

Emeriamine is a carnitine analogue, which has significant hypoglycemic effects in

fasted rats and several other animal models. Another novel compound, 2-(3-

methylcinnamylhydrazono) propionate (MCHP) apparently inhibits the translocation of

long chain fattyacyl carnitines across the mitochondrial membrane but has little or no

effect on either CPT or CPT ІІ.

CH3 N

CH3

CH2

CH3

CH CH2 COOH

Emeriamine

HC CH2

CH3

NH NCOOH

CH3

MCHP

13) Hydrazinopropionic Acids:

Over 20 years ago, monoamine oxidase inhibitors of the hydrazine type were

proposed as supplementary hypoglycemic agents for the treatment of diabetes mellitus.

They found two hydrazine analogues, (2-phenylethylhydra-zino) and 2-

(cyclohexylethylhydrazino) propionic acids (PEHP and CHEHP, respectively), with

increased hypoglycemic activity and reduced toxicity.

H2C NH NCOOH

CH3H2C

Both compounds at dose of between 145 and 800 μmol / kg (30 and 170 mg / kg,

respectively) significantly lowered blood glucose in 48 hours fasted guinea pigs, rats and

hamster. Glucose lowering effects were also observed in 12 hr fasted diabetic mice.


Page 26

H2C NH NCOOH

CH3H2C

PEHP

Another novel hypoglycemic agent AS-6, is derived from ascochlorin which was

first discovered in the filter cake of the fermented broth of the fungus. Ascochytavivia

Libert. AS-6, the 4-0-carboxymethylated derivative of ascochlorin, is a more potent

hypoglycemic agent and is more readily absorbed.

OH

CH3

Cl

O

CH3

O

CH3

CH3

OHC

CH2

COOH

AS-6

14) β-Adrenergic agonist:

The utility of β-Adrenergic agonists as hypoglycemic agents has been surprising,

since acute administration of isoproterenol (isoprenaline) or the more selective β2-agonist,

terbuteline, caused deterioration in glycemic control in humans.

CH

OH

CH2NH CH C

H2

COOCH3

CH3

BRL-26830

New β-adrenergic agonists have been designed for their utility in treatment of

obesity and NIDDM, as opposed to the traditional antiasthematic β2-agonists. A subset of

β-adrenergic receptors that dose not fall clearly in to either β1 or β2 has been described in

rat brown adipose tissue. Selective activation of this receptor, by chronic administration of


Page 27

BRL-26830 to genetically obese (57 BL/6, ob/ob) mice, stimulated the metabolic activity

of brown adipose tissue, elevated caloric consumption and resulted in a highly significant

reduction in weight gain.

A second β-adrenergic agonist with potential utility in the improvement of insulin

sensitivity is Ro-16-8714. When obese mice (C57BL/6J, ob/ob) received this agent for 15

days, glycosuria rapidly diminished and blood glucose was normalized, while circulating

insulin levels were not altered.

CH CH2

OH

CH CH2

OH

N CH

OH

NH2

O

CH2 CH2

Ro-16-8714

15) Anorectic agents:

Weight loss in the treatment of obese NIDDM is often an effective means of

achieving improved glycemic control. When diet therapy alone is inadequate to initiate the

weight reduction program variety of anorectic agents are available for short-term therapy.

Two of the agents, mazindol and fenfluramine, may also possess activities which improve

glucose control independent of the weight loss they reduce.

CH CH2

OH

CH CH2

OH

N CH

OH

NH2

O

CH2 CH2

Mazindol

Ciclizindol, a drug structurally related to mazindole, also stimulated glucose uptake

in to human skeletal muscle in both the presence and absence of insulin.


Page 28

N

NOH

Cl

Ciclazindol

Fenfluramine is an anorectic agent structurally similar to amphetamine, but with a

mechanism of action relating to its 5-hydroxytryptamine- agonistic activity, which

distinguishes a from the amphetamine class of drugs.

CH NH CH2 CH3

CH3

CH2

CF3

Fenfluramine

16) Steroids:

Dehydroepiandrosterone (DHEA) is a major secretory product of the adrenal

cortex, which ameliorates several metabolic abnormalities found in obese, insulin resistant

rodents.40 Substantial improvement in glucose metabolism in insulin resistant rodents, has

been demonstrated with chronic dosing of DHEA and its metabolites. Although DHEA

produces pronounced changes in glucose metabolism and insulin sensitivity, three

metabolic products of DHEA, 3-tetrahydroxyetiocholanolone (tetra-ET), 3-α-

hydroxyetiocholano lone (Beta- ET), β-hydroxyetiocholanolone (β-ET) and DHEA sulfate,

are more potent hypoglycemic agents.

O

OH

O

OH

DHEA 3-α-hydroxyetiocholanolone


Page 29

O

OH

3-β-hydroxyetiocholanolon

17) Miscellaneous Agents:

The anorectic agent fenfluramine has been shown to improve glucose tolerance and to

lower fasting blood sugar in diabetes in numerous studies. A fenfluramine analogue, 780

SE has also been shown to improve tolerance in insulin-independent diabetics, Potential of

insulin mediated glucose utilization in the periphery has also been postulated as the

mechanism of action.

CH2 CH NH CH2 CH3

CH3

CF3

Fenfluramine

CH2 CH

CH3

CF3NHCH2CH2O

H

CO

780 SE

The hypoglycemic agent halofenate at a dose of 500-1500 mg daily reduces the

requirements for sulfonylureas in diabetics, and this effect seems to be mediated by

interference with the metabolism of the sulfonylurea and not by a direct hypoglycemic

effect.


Page 30

Cl

OCF3NH

COOH

COCH3

Halofenate

The hypoglycemic drug clofibrate on the other hand, which also transiently

potentiates the effects of sulfonylureas at a dose of 1000 mg bid, has been shown to lower

fasting and postprandial glucose in diabetics when given alone in a 7 day study,

supposedly by increasing insulin sensitivity; however; it had no effect on fasting blood

glucose in longer term (48 weeks) studies.

Cl

O

CH3

CH3

COOCH2CH3

Clofibrate

Experiments in normal subjects suggested that the glycosidase and amylase

inhibitor acarbose (BAY 5421, 60), used at about 75 mg, should be of value in decreasing

postprandial blood glucose peaks.

O

O

OH OH

CH3

O

OO

OH OH OH OH

OH

HOCH2HOCH2

OH

OH OH

HOCH2

NH

Acarbose

A study in diabetics showed that addition of 6 times 50 mg of daily to the usual

sulfonylurea or insulin regimen led to a further decrease in blood glucose values.

Somatostatin a tetrapeptide which was originally isolated from hypothalamus, but which

occurs also in the D-cell of the pancreas, suppresses the secretion of growth harmone,

glucagons and insulin dependent diabetics, but caused only a transient hypoglycemia


Page 31

followed by hyperglycemia in NIDDM. Analogues of such as are of value in management

of diabetes.

H-Ala-Gly-Cys-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Thr-Ser-Cys-OH

2,4-Thiazolidinediones:

A recent new class of oral hypoglycemic drugs thiazolidinediones was found to be

effective against noninsulin dependent diabetes mellitus. Its development started many

years ago and still a lot of work is left with this class of compounds.

In 1980 Kawamatsu, Y.; Saraie, E. found that ethyl 2-chloro-3-[4-(2-methyl-2-

phenylpropoxy) phenyl] propionate (AL-294) was effective against hyperglycemia and

hyperlipidemia in genetically obese and diabetic mice, yellow KK, which develop glucose

and lipid dismetabolism associated with severe insulin resistance.

CH3

CH3

CH2O CH2

CH

Cl

COOCH2CH3

AL-294

In 1982 Shohda, Takashi.; Kawamatsu, Y. from Takeda Chemical Industries Ltd.

Osaka, Japan developed a series of compounds containing 4-(2-methyl-2-phenylpropoxy)

benzyl moity and evaluated their hypoglycemic and hypolipidemic activities with

genetically obese and diabetic mice, yellow KK. Among these compounds 5-[4-(2-methyl-

2-phenylpropoxy) benzyl] thiazolidine-2, 4-dione (AL-321) was found to possess

hypoglycemic and hypolipidemic activities higher than AL-294.

CH3

CH3

CH2O NHS

O

O

AL-321

1 2 3 4 5 6 7 8 9 10 11 12 13 14


Page 32

In the same year more than 100 5-substituted thiazolidine-2, 4-dione were prepared

and their hypoglycemic and hypolipidemic activities were evaluated with genetically

obese and diabetic mice, yellow KK. Among these compounds 5-{4-[2-(3-pyridyl) ethoxy]

benzyl} benzyl] thiazolidine-2, 4-dione (ADD-3878, ciglitazone) exhibited most favorable

activity.

NHS

O

O

OCH2

CH3

ADD-3878 (Ciglitazone)

In 1982 Shohda, T; Kawamatsu, Y. from Takeda Chemical Industries Ltd. and

Senju Pharmaceutical Co., Ltd. Japan synthesized and evaluated thiazolidine-2, 4-dione

having substitution at 5-position for Aldose Reductase Inhibitors.

In 1984 Shohda, T; Kawamatsu, Y. of Takeda Chemical Industries Ltd. Osaka,

synthesized compounds having hydroxy and an oxo moity on the cyclohexane ring of

ciglitazone to clarify the structure of the metabolites of ciglitazone and for studies of their

pharmacological properties. Of the metabolites identified, 5-[4-(t-3-hydroxy-1-

cyclohexylmethoxy) benzyl] thiazolidine-2, 4-dione exhibited extremely potent

antidiabetic activity compared to ciglitazone.

NHS

O

O

OR

R=…

CH

2

CH3

O

CH2

CH3

OH

CH2

CH3

OH

CH

2

CH3O

4’-oxo cis-4’-ol trans-4’-ol 3’-oxo


Page 33

CH2

CH3

OH

CH2

CH3O

CH2

CH3OH

CH2

CH3

OH

trans-3’-ol 2’-oxo 2’-ol cis3’-ol

In 1986 Meguro, K; Fugita, T.; Shohda, T. of Takeda Chemical Industries Ltd.

Osaka, Got a US patent (4,687,777) as well as European patent (0193256) for some

thiazolidedione derivatives of formula given as (A) exhibited blood sugar and lipid

lowering activity in mammals.

NNH

S

O

O

O

C2H5

(A)

In 1989 Yoshioka, T.; Fujita, T; Kanai T. et al. at Sankyo Co., Ltd. Japan

investigated series of hindered phenols hypolipidemic and/or hypoglycemic agents with

ability to inhibit lipid peroxidation. Among the compounds of this series (f)-5-[4-[(6-

hydroxy-2, 5, 7, 8-tetramethylchroman-2-yl) methoxy]-benzyl]-2, 4-thiazolidinedione

(CS-045) was found to have all of our expected properties and was selected as a candidate

for further development as a hypoglycemic and hypolipidemic agent.

NHS

O

O

O

O

OH

Troglitazone (CS-045)

In 1990 Zask, A.; McCaleb, M. L. of Wyeth-Ayerst Research, New Jersey

synthesized a series of (naphthalenylsulfonyl)- 2, 4-thiazolidinedione and evaluated for

antihyperglycemic activity in insulin-resistant, genetically diabetic db/db mouse model of

non-insulin dependent diabetes mellitus (NIDDM). The best analogue (AY-31637) was

equipotent to ciglitazone.


Page 34

NHS

O

O

SO2

(AY-31637)

In 1991 Clark, D. A.; Goldstein, S. W of Central Research, Pfizer, Groton

synthesized Dihydrobenopyran and dihydrobenzofuran thiazolidedione-2, 4-diones. These

compounds represent conformationally restricted analogues of novel hypoglycemic

ciglitazone. Among the compounds of this series englitazone (CP-68722, CP-72466) was

proved to be efficacious in terms of activity.

NHS

O

O

O

Englitazone (CP-68722, CP-72466)

In 1991 Ammos, Y; Shohda, T. synthesized various analogues of Pioglitazone

(AD-4833, U-72107). Several 5- [4-(2-(2-pyridyl) ethoxy] benzylidine]-2,4-

thiazolidinediones were equipotent to pioglitazone however; the thia analogues and

benzylidine heterocycles had decreased activity.

NHS

O

O

O

N

Pioglitazone (AD-4833, U-72107)

In 1992 Shohda, T.; Fugita. T. of Takeda Chemical Industries Ltd. Osaka,

synthesized a series of 5- [4-(2-(2-pyridyl) ethoxy] benzylidine]-2, 4-thiazolidinediones as

modification of the novel antidiabetic Pioglitazone (AD-4833, U-72107). Among the

compounds synthesized 5- [4-(2-(5-methyl-2-phenyl-4-oxazolyl) ethoxy] benzy]-2,4-


Page 35

thiazolidinedione (B) exhibited the most potent activity, more than 100 times that of

pioglitazone.

NHS

O

O

O(CH2)nYN

XR1 R2

(B)

In 1994 Barrie, C. C.; Thurlby, P. L. from SmithKline Beecham Pharmaceuticals,

UK synthesized a series of [[-(Hetro cyclyl amino) alkoxy] benzyl –2,4-

thiazolidinedionesantihyperglycemic activity together with effects on hemoglobin content

was performed in genetically obese C57 B1/6 ob/ob mice. From these studies BRL 49653

has been selected for further evaluation.

N

N NHS

O

O

O

CH3

BRL 49653

In 1998 Lohray, B. B.; Rajagopalan, R. of Dr. Reddy’s Research Foundation,

Hyderabad, India synthesized a series of [[(heterocyclyl) ethoxy] benzyl]-2,4-

thiazolidinediones. Many of these compounds have shown superior euglycemic and

hypolipidemic activity compared to troglitazone (CS045). The indole analogue DRF-2189

was found to be more potent insulin sensitizer, compared to BRL-49653 in genetically

obese C57BL/6J-ob/ob and 57BL/KS-db/db mice.

N NHS

O

O

O

DRF-2189


Page 36

In 1999 Lohray, B. B.; Rajagopalan, R. Dr. Reddy’s research foundation,

Hyderabad, India synthesized substituted pyridyl- and quinolinyl-containing 2, 4-

thiazolidinediones having cyclic amine as a linker and evaluated hypoglycemic and

hypolipidemic activity and compared with BRL-49653. Among all the salts evaluated, the

maleate salt of unsaturated TZD (5a) was found to be euglycemic and hypolipidemic

compound.

NN

NHS

O

O

O

(5a)

In 1999 Nomura, M.; Miyachi, H. of Kyorin Pharmaceutical Company, Japan

prepared a series of (3-substituted benzyl) thiazolidine-2, 4-dione which led to the

identification of (KRP-297) as a candidate for the treatment of diabetes mellitus.

NHS

O

O

CH2

O

CH2

HCH3OCF3

KRP-297

In 2000 Oguchi, M.; Fugita, T. of Sankyo company, Ltd., and sankyo pharma

research institute, California designed and synthesized a series of Imidazopyridine

thiazolidine-2, 4-diones and evaluated for its effect on Insulin induced 3T3-L1 adipocyte

differentiation invitro and its hypoglycemic activity in genetically diabetic KK mouse in

vivo.

N

NN

R3

R4

R2

R1

NHS

O

O

O


Page 37

R1= H, Me, Et, Ph, 4-Cl-C6H4CH2, R2= H, Me, Cl, OH, etc

R3= H, Cl, Br, CF3, R4= = H, Me

In 2003 Desai, R. C.; Berger, J. P.; Kwan, L. of Merck Research Laboratories,

USA synthesized a number of potent 5-aryl thiazolidine-2, 4-diones and performed

efficacy studies which showed them superior to rosiglitazone in correcting hyperglycemia

and hypertriglyceridemia.

NHS

O

O

OO

O

5-aryl thiazolidine-2, 4-diones

In 2004 Bhatt, A. B.; Srivastava, A. K. from CDRI, Lucknow synthesized a

number of thiazolidinedione derivatives having carboxylic ester appendage at N-3 and

evaluated their hypoglycemic activity. N-carboalkoxymethylthiazolidine-2, 4-diones was

selected as core structure with substituted benzylidine and benzyl and heteroaryl

derivatives.

NS

O

O

ROX

OZ

N-carboalkoxymethylthiazolidine-2, 4-diones

R=C6H5OH, C6H5CF3, C6H5CH3, C6H5Cl etc.

X=CH2CH3, CH3

Z=Single Bond, Double Bond

Iqbal, Javed. of Dr. Reddy’s Laboratories, Hyderabad, India designed TZD

derivatives, which can reduce plasma glucose with less adipogenesis. The SAR of these

TZD derivatives gave Balaglitazone which has 70% of PPAR- transactivation compared to

rosiglitazone and showed partial agonism in competitive binding assay. Balaglitazone has


Page 38

shown good efficacy in db/db and ob/ob mice models at 3mg/kg. In zucker fa/fa rats it

shows insulin sensitization effects by 70% reduction in insulin and 80% reduction in free

fatty acids at 3mg/kg dose. Balaglitazone is now in phase-II clinical trials.

The literature, found for this class of drugs shows that there is a lot of advancement

in the development of a novel analogues of thiazolidinedione for the treatment of

noninsulin dependent diabetes mellitus and it is also clear that there has been abundant

research activity in this field globally. Several approaches have been attempted and some

new approaches are still emerging.


Page 39

3. CLASSIFICATION

1. Insulin

2. Secretagogues

2.1. Sulfonylureas

2.2. Meglitinides

3. Sensitizers

3.1. Biguanides

3.2. Thiazolidinediones

4. Alpha-glucosidase inhibitors

5. Peptide analogs

5.1. Incretin mimetics

5.1.1. Glucagon-like peptide (GLP) analogs and agonists

5.1.2. Gastric inhibitory peptide (GIP) analogs

5.1.3. Protein Tyrosin Phosphate 1β inhibitors

5.2. DPP-4 inhibitors

5.3. Amylin analogues


Page 40

Oral anti-diabetic drugs and Insulin analogs

Insulin

Sensitizers

BiguanidesMetformin ·Buformin‡ ·Phenformin‡

TZDs (PPAR)Pioglitazone · Rivoglitazone† · Rosiglitazone· Troglitazone‡

Dual PPAR agonists

Aleglitazar† · Muraglitazar§ · Tesaglitazar§

Secretagogues

K+ ATP Sulfonylureas

1stgeneration: Acetohexamide·Carbutamide ·Chlorpropamide· Gliclazide · Tolbutamide· Tolazamide2nd generation: Glibenclamide( Glyburide) · Glipizide· Gliquidone · Glyclopyramide3rd generation: Glimepiride

Meglitinides/Glinides

Nateglinide · Repaglinide· Mitiglinide

GLP-1 analogs Exenatide · Liraglutide · Albiglutide†

DPP-4 inhibitors

Alogliptin† ·Linagliptin† · Saxagliptin · Sitagliptin· Vildagliptin

Analogs/other insulins

. fast acting : (Insulin lispro · Insulin aspart · Insulin glulisine) · Short acting : (Regular insulin)· long acting : (Insulin glargine · Insulin detemir) · Inhalable insulin (Exubera)‡ · NPH insulin

Other

α-glucosidase inhibitors

Acarbose · Miglitol · Voglibose

Amylinanalog Pramlintide

SGLT2inhibitor

Dapagliflozin† · Remogliflozin† · Sergliflozin†

OtherBenfluorex · Tolrestat‡

‡ Withdrawn from market. CLINICAL TRIALS:

† Phase III.

§ Never to phase III

Table No. 1- Oral anti-diabetic drugs and Insulin analogs


Page 41

4. INSULIN

Sanger (in 1950s) put forward the primary structure of insulin as below in Figure.

Figure 4.1 Primary structure of proinsulin, depicting cleavage sites to produce

insulin.

The above Figure has the following Salient Features, namely:

(1) Proinsulin is the immediate precursor to insulin in the single-chain peptide.

(2) Proinsulin folds to adopt the ‘correct orientation of the prevailing ‘disulphide

bonds’ plus other relevant conformational constraints whatsoever on account of its primary

structure exclusively.

(3) Proinsulin in reality, has a precursor of its own, preproinsulin–a peptide, that

essentially comprises of hundreds of ‘additional residues’.

(4) At an emerging critical situation the insulin gets generated from proinsulin due

to the ensuing cleavage of proinsulin at the two points indicated. This eventually produces

20

20


Page 42

insulin, that comprises of a 21-residue A chain and strategically linked with two disulphide

bonds ultimately to a 30-residue B chain. Interestingly, these bondages between the two

aforesaid residual chains ‘A’ and ‘B’ are invariably oriented almost perfectly and correctly

by virtue of the prempted nature of proinsulin folding.

4.1 Description

Insulin is a hormone produced by the beta cells in the islets of Langerhans in the

pancreas.

Figure 4.2 Insuline structure

Insulin is used medically to treat some forms of diabetes mellitus. By reducing the

concentration of glucose in the blood, insulin is thought to prevent or reduce the long-term

complications of diabetes, including damage to the blood vessels, eyes, kidneys, and

nerves.

4.2 Variants of Insulin Products

There are a number of variants of insulin products that are available as follows:

4.2.1. Insulin Injection

4.2.1.1 Synonyms: Regular Insulin; Crystalline Zinc Insulin

It is available as a sterile, acidified or neutral solution of insulin. The solution has a

potency of 40, 80, 100 or 500 USP Insulin Units in each ml.

4.2.1.2 Mechanism of Action

It is a rapid-action insulin. The time interval from a hypodermic injection of this

drug until its action may be observed ranges between 1/2 to an hour. It has been observed

that the duration of action is comparatively short but evidently a little longer than the


Page 43

plasma half-life that stands at nearly 9 minutes. Importantly, the duration of action is not

linearly proportional to the size of the dose, but it is a simple function of the logarithm of

the dose i.e., if 1 unit exerts its action for 4 hours then 10 units will last 8 hours. In usual

practice the duration is from 8 to 12 hour after the subcutaneous injection, which is

particularly timed a few minutes before the ingestion of food so as to avoid any possible

untoward fall in the prevailing blood-glucose level.

4.2.2. Isophane Insulin Suspension

4.2.2.1 Synonyms: Isophane Insulin; Isophane Insulin Injection; NPH Insulin; NPH Iletin

The drug is a sterile suspension of Zinc-insulin crystals and protamine sulphate in

buffered water for injection, usually combined in such a fashion that the ‘solid phase of the

suspension’ essentially comprises of crystals composed of insulin, protamine*, and zinc.

Each mL is prepared from enough insulin to provide either 40, 80, or 100 USP Insulin

units of insulin activity.


The drug exerts its action intermediate acting insulin for being insoluble and

obtained as repository form of insulin. In reality, the action commences in 1–1.5 hour,

attains a peak-level in 4 to 12 hour, and usually lasts upto 24 hours, with an exception that

‘human isophane insulin’ exerts a rather shorter duration of action. It is, however, never to

be administered IV.

4.2.2.3 Note: Incidence of occasional hypersensitivity may occur due to the presence of

‘protamine’.

4.2.3. Insulin Zinc Suspension

It is invariably obtained as a sterile suspension of insulin in buffered water for

injection, carefully modified by the addition of zinc chloride (ZnCl2) in such a manner that

the ‘solid-phase of the suspension’ comprises of a mixture of crystalline as well as

amorphous insulin present approximately in a ratio of 7 portions of crystals and 3 portions

of amorphous substance. Each mL is obtained from sufficient insulin to provide either 40,

80, or 100 USP Insulin Units of the Insulin Activity.


Page 44


It has been duly observed that the ‘amorphous zinc-insulin component’ exerts a

duration of action ranging between 6–8 hours, whereas the ‘crystalline zinc-insulin

component’ a duration of action more than 36 hour, certainly due to the sluggishness and

slowness with which the larger crystals get dissolved. However, an appropriate dosage of

the 3 : 7 mixture employed usually displays an onset of action of 1 to 2.5 hour and an

intermediate duration of action which is very near to that of ‘isophane insulin suspension’

(24 hour), with which preparation this drug could be employed interchangeably without

any problem whatsoever. However, it must not be administered IV. The major advantage

of ‘zinc insulin’ is its absolute freedom from ‘foreign proteinous matter’, such as : globin,

or protamine, to which certain subjects are sensitive.

4.2.4. Extended Insulin Zinc Suspension

4.2.4.1 Synonyms: Ultra-Lente Iletin; Ultralente Insulin/Ultratard


The actual ‘crystalline profile’ in this specific form are of sufficient size to afford

a slow rate of dissolution. It is found to exert its long-acting action having an onset of

action ranging between 4 to 8 hours, an optimal attainable peak varying between 10-30

hours, and its overall duration of action normally in excesss of 36 hours, which being a

little longer than that of Protamine Zinc Insulin.

4.2.4.3 Note: Because the drug is free of both protamine and other foreign proteins, the

eventual incidence of allergic reactions gets minimized to a significant extent.

4.2.5. Prompt Insulin Zinc Suspension

4.2.5.1 Synonyms: Semi-Lente Iletin ; Semitard

The drug is usually a sterile preparation of insulin in ‘buffered water for injection’,

strategically modified by the addition of zinc chloride (ZnCl2) in such a manner that the

‘solid phase of the prevailing suspension’ is rendered amorphous absolutely. Each mL of

this preparation provides sufficient insulin either 40, 80, or 100 USP Insulin Units.


Page 45


The zinc-insulin in this particular form is a mixture of amorphous and extremely

fine crystalline materials. As a result, the drug serves as a rapid-acting insulin with an

onset of 1 to 1.5 hour, an attainable peak of 5-10 hours, and a duration of action ranging

between 12-16 hours.

4.2.5.3 Note: Since this specific form of insulin is essentially free of any foreign proteins,

the incidence of allergic reactions is found to be extremely low.

4.2.6. Lispro Insulin

4.2.6.1 Synonyms: Human Insulin Analog; Humalog

It is a human insulin analogue of r DNA origin meticulously synthesized from a

special nonpathogenic strain of E. coli, genetically altered by the addition of the gene for

insulin lispro ; Lys (B28), Pro (B29). In fact, the prevailing amino acids at position 28 and

29 of human insulin have been reversed altogether.


The drug is very rapid-acting insulin which may be injected conveniently just

prior to a meal. It exhibits an onset of action within a short span of 15 minutes besides

having a relatively much shorter peak ranging between 0.5 to 1.5 hour, and having

duration of action varying between 6 to 8 hours in comparison to the ‘regular insulin

injection’.

4.2.7. Protamine Zinc Insulin Suspension

4.2.7.1 Synonyms: Zinc Insulin ; Protamine Zinc Insulin Injection ; Protamine Zinc and

Iletin

The drug is a sterile suspension of insulin in buffered water for injection, that has

been adequately modified by the addition of zinc chloride (ZnCl2) and protamine sulphate.

The protamine sulphate is usually prepared from the sperm or from the mature testes of

fish belonging to the genus Oncorhynchus Suckley or Salmo Linne (Family : Salmonidae).

Each mL of the suspension prepared from sufficient insulin to provide wither 40, 80, or

100 USP Insulin Units.


Page 46


The drug exerts a long-acting action having an onset of action of 4 to 8 hour, a

peak at 14 to 24 hour, and a duration of action nearly 36 hour. As a result this drug need

not be administered with any definite time relation frame to the corresponding food intake.

Besides, it should not be depended upon solely when a very prompt action is required,

such as : in diabetic acidosis and coma. Since the drug possesses an inherent prolonged

action, it must not be administered more frequently than once a day. It has been duly

observed that ‘low levels’ invariably persists for 3 o 4 days; and, therefore, the dose must

be adjusted at intervals of not less than 3 days. It is given by injection, normally into the

loose subcutaneous tissue.

4.2.7.3 Note: The drug should never be administered IV.


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5. Secretagogues

5.1 K+ ATP

5.1.1 Sulfonylureas

The sulfonylurea hypoglycemic agents are basically sulphonamide structural

analogues but they do not essentially possess any ‘antibacterial activity’ whatsoever. In

fact, out of 12,000 sulfonylureas have been synthesized and clinically screened, and

approximately 10 compounds are being used currently across the globe for lowering

blood-sugar levels significantly and safely. The sulfonylureas may be represented by the

following s

Salient Features: The salient features of the ‘sulfonylureas’ are as given below :

(1) These are urea derivatives having an arylsulfonyl moiety in the 1 position and

an aliphatic function at the 3-position.

(2) The aliphatic moiety, R’, essentially confers lipophilic characteristic properties

to the newer drug molecule.

(3) Optimal therapeutic activity often results when R’ comprises of 3 to 6 carbon

atoms, as in acetohexamide, chlorpropamide and tolbutamide.

(4) Aryl functional moieties at R’ invariably give rise to toxic compounds.

(5) The R moiety strategically positioned on the ‘aromatic ring’ is primarily

responsible for the duration of action of the compound.

5.1.1.1 SAR of Sulfonylureas

Certain substituents when placed at para position in benzene ring tend to

potentiate the activity, e.g. halogens, amino, acetyl, methyl, methylthio and

trifluoromethyl groups.


Page 48

The size of terminal nitrogen along with its aliphatic subsituent R, determines

lipophilic properties of the molecules. Optimum activity results when R

consists of 3 to 6 carbon atoms.

The nature of para subsituents in benzene ring (-x-) appears to govern the

duration of action of the compound.

Aliphatic subsituents (R) at the terminal nitrogen may also be replaced by an

alicyclic and hetrocyclic ring.

hypoglycemic activity can be related to the nature of sulfonyl grouping.

Replacement of a metabolically easily oxidize group, like a CH3 group by a less

readily oxidize chlorine was used to transform the short actingtolbutamide into long acting

chlorpropamide, with a half life six fold greater than its parent.

However, these agents are now divided into two sub-groups, namely:

(a) 1st generation sulfonylureas

(b) 2nd generation sulfonylureas

These two aforesaid classes of sulfonylureas will be further separated by:

First-generation agents

o tolbutamide (Orinase)

o acetohexamide (Dymelor)

o tolazamide (Tolinase)

o chlorpropamide (Diabinese)

Second-generation agents

o glipizide (Glucotrol)

o glyburide (Diabeta, Micronase, Glynase)

o glimepiride (Amaryl)

o gliclazide (Diamicron)


Page 49

Tolbutamide

Tolbutamide is a first generation potassium channel blocker, sulfonylurea oral

hypoglycemic drug sold under the brand name Orinase. This drug may be used in the

management of type II diabetes if diet alone is not effective. Tolbutamide stimulates the

secretion of insulin by the pancreas. Since the pancreas must synthesize insulin in order for

this drug to work, it is not effective in the management of type I diabetes. It is not

routinely used due to a higher incidence of adverse effects compared to newer second

generation sulfonylureas, such as glyburide.

Mechanism of Action

The drug usually follows the major route of breakdown ultimately leading to the

formation of butylamine and p-toluene sulphonamide respectively. Importantly, the

observed hypoglycemia induced by rather higher doses of the drug is mostly not as severe

and acute as can be induced by insulin; and, therefore, the chances of severe hypoglycemic

reactions is quite lower with tolbutamide ; however, one may observe acute refractory

hypoglycemia occasionally does take place. In other words, refractoriness to it often

develops.

Structure

Systemic (IUPAC) Name

N-[(butylamino)carbonyl]-4-methylbenzenesulfonamide

Chemical data

FORMULA C12H18N2O3S

MOLECULAR MASS 270.35 g/mol

Pharmacokinetic data

METABOLISM Hepatic (CYP2C19-mediated)

PROTEIN BINDING 96 %

HALF LIFE 4.5 to 6.5 hours

EXECRETION Renal


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Side Effects

1. Hypoglycemia

2. Weight gain

3. Hypersensitivity- Cross-allergicity with sulfonamide

4. Drug Interactions (especially first generation drugs): Increase Hypoglycemia with

cimetidine, Insulin, salicylates, sulfonamides.

Synthesis of Tolbutamide

Procedure

First of all toluene is treated with chlorosulfonic acid to yield p-toluenesulphonyl

chloride, which on treatment with ammonia gives rise to the formation of p-

toluenesulphonamide. The resulting product on condensation with ethyl chloroformate in

the presence of pyridine produces N-p-toluenesulphonyl carbamate with the loss of a mole

of HCl. Further aminolysis of this product with butyl amine using ethylene glycol

monomethyl ether as a reaction medium loses a mole of ethanol and yields tolbutamide. It

is mostly beneficial in the treatment of selected cases of non-insulin-dependent diabetes

melitus (NIDDM). Interestingly, only such patients having some residual functional islet

β-cells which may be stimulated by this drug shall afford a positive response. Therefore, it


Page 51

is quite obvious that such subjects who essentially need more than 40 Units of insulin per

day normally will not respond to this drug.

Acetohexamide

Structure


4-acetyl-N-(cyclohexylcarbamoyl)benzenesulfonamide

Chemical data

FORMULA C15H20N2O4S



It lowers the blood-sugar level particularly by causing stimulation for the release of

endogenous insulin.

Mechanism of Action

The drug gets metabolized in the liver solely to a reduced entity, the corresponding

α-hydroxymethyl structural analogue, which is present predominantly in humans, shares

the prime responsibility for the ensuing hypoglycemic activity.

Synthesis of Acetohexamide


Page 52

SAR of Acetohexamide

It is found to be an intermediate between ‘tolbutamide’ and ‘chlorpropamide’ i.e.,

in the former the cyclohexyl ring is replaced by butyl moiety and p-acetyl group with

methyl group ; while in the latter the cyclohexyl group is replaced by propyl moiety and

the p-acetyl function with chloro moiety. Acetohexamide is metabolized in the liver to a

reduced from, the α-hydroxyethyl derivative. This metabolite, the main one in human,

possesses hypoglycemic activity. Acetohexamide is intermediate between tolbutamide and

chlorpropamide in potency and duration of effect on blood sugar level.

Tolazamide

Structure


N-[(azepan-1-ylamino)carbonyl]-4-methylbenzenesulfonamide

Chemical data

FORMULA C14H21N3O3S



HALF LIFE 7 hours

EXECRETION Renal (85%) and fecal (7%)

Mechanism of Action

Based on the radiactive studies it has been observed that nearly 85% of an oral

dose usually appears in the urine as its corresponding metabolites which were certainly

more water-soluble than the parent tolazamide itself.


Page 53

Synthesis of Tolazamide

Chlorpropamide

Structure


1-[(p-Chlorophenyl)-Sulphonyl]-3-propyl urea

Chemical data

FORMULA C10H13ClN2O3S


HALF LIFE 36 hours

Chlorpropamide is a drug in the sulphonylurea class used to treat type 2 diabetes

mellitus. It is a long-acting sulphonylurea. It has more side effects than other

sulphonylureas and its use is no longer recommended.


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Synthesis of Chlorpropamide

Procedure

The interaction between p-chlorobenzenesulphonamide and phenyl isocyanate in

equimolar concentrations under the influence of heat undergoes addition reaction to yield

the desired official compound.

The therapeutic application of this drug is limited to such subjects having a history

of table, mild to mderately severe diabetes melitus who still retain residual pancreatic β-

cell function to a certain extent.

Mechanism of Action

The drug is found to be more resistant to conversion to its corresponding inactive

metabolites than is ‘tolbutamide’; and, therefore, it exhibits a much longer duration of

action. It has also been reported that almost 50% of the drug gets usually excreted as

metabolites, with the principal one being hydroxylated at the C-2 position of the propyl-

side chain.

Glipizide

STRUCTURE


N-(4-[N-(cyclohexylcarbamoyl)sulfamoyl]phenethyl)-5- methylpyrazine-2-carboxamide

Chemical data

FORMULA C21H27N5O4S




Page 55

BIOAVAIBILITY 100% (regular formulation),90% (extended release)

PROTEIN BINDING 98 -99 %

METABOLISM Hepatic hydroxylation

HALF LIFE 2 to 4 hr

EXECRETION Renal and fecal

ROUTE Oral

Glipizide is an oral medium-to-long acting anti-diabetic drug from the sulfonylurea

class. It is classified as a second generation sulfonylurea, which means that it undergoes

enterohepatic circulation. The structure on the R2 group is a much larger cyclo or aromatic

group compared to the 1st generation sulfonylureas. This leads to a once a day dosing that

is much less than the first generation, about 100 fold.

Mechanism of Action

The primary hypoglycemic action of this drug is caused due to the fact that it

upregulates the insulin receptors in the periphery. It is also believed that it does not exert a

direct effect on glucagon secretion. The drug gets metabolized via oxidation of the

cyclohexane ring to the corresponding p-hydroxy and m-hydroxy metabolites. Besides, a

‘minor metabolite’ which occurs invariably essentially involves the N-acetyl structural

analogue that eventually results, from the acetylation of the primary amine caused due to

the hydrolysis of the amide system exclusively by amidase enzymes.

Synthesis of Glipizide


Page 56

Procedure

Glipizide may be prepared by the condensation of 4-[2-(5-methyl-2-pyrazine-

carboxamido)-ethyl] benzenesulphonamide with cyclohexylisocyanate in equimolar

proportions. It is employed for the treatment of Type 2 diabetes mellitus which is found to

be 100 folds more potent than tolbutamide in evoking the pancreatic secretion of insulin. It

essentially differs from other oral hypoglycemic drugs wherein the ensuing tolerance to

this specific action evidently does not take place.

Note : The drug enjoys two special status, namely:

(a) Treatment of non-insulin dependent diabetes mellitus (NIDDM) since it is

effective in most patients who particularly show resistance to all other hypoglycemic drugs

;

(b) Differs from other oral hypoglycemic drug because it is found to be more

effective during eating than during fasting.

Gliclazide

Gliclazide is an oral hypoglycemic (anti-diabetic drug) and is classified as a

sulfonylurea.

SAR of Gliclazide

Gliclazide is very similar to tolbutamide, with the exception of the bicyclic

hetrocyclic ring found in gliclazide. The pyrrolidine increases its lipophilicity over that of

tolbutamide, which increases its half life. Even so, the p-methyl is susceptible to the same

Structure


N-(hexahydrocyclopenta[c]pyrrol-2(1H)-ylcarbamoyl)-4-methylbenzenesulfonamide

Chemical data

FORMULA C15H21N3O3S



Page 57

oxidative metabolic fate as observed for tolbutamide, namely, it will be metabolized to a

carboxylic acid.

Synthesis of Gliclazide

Glimepiride

Structure


3-ethyl-4-methyl-N-(4-[N-((1r,4r)-4-methylcyclohexylcarbamoyl)sulfamoyl]phenethyl)-2-oxo-2,5-dihydro-

1H-pyrrole-1-carboxamide

Chemical data

FORMULA C24H34N4O5S



PROTEIN BINDING >99.5%

HALF LIFE 5 hours

EXECRETION Urine and Fecal

ROUTES Oral


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Mechanism of Action

The drug is found to be metabolized primarily through oxidation of the alkyl side

chain attached to the pyrrolidine nucleus via a minor metabolic path that essentially

involves acetylation of the amine function.

Synthesis of Glimepiride

SAR of Glimepiride

The only major distinct difference between this drug and glipizide is that the

former contains a five-membered ‘pyrrolidine ring’ whereas the latter contains a six-

membered ‘pyrazine ring’. It is metabolise primarily through oxidation of the alkyl side

chain of the pyrrolidine, with a minor metabolic route involving acetylation of the amine.

Glibenclamide

Structure


Page 59


5-chloro-N-(4-[N-(cyclohexylcarbamoyl)sulfamoyl]phenethyl)-2-methoxybenzamide

Chemical data

FORMULA C23H28ClN3O5S



PROTEIN BINDING Extensive

METABOLISM Hepatic hydroxylation (CYP2C9-mediated)

HALF LIFE 1.5 to 5 hours

EXECRETION Renal and Biliary

ROUTES Oral

Glibenclamide (INN), also known as glyburide (USAN), is an anti-diabetic drug in

a class of medications known as sulfonylureas. It is mostly used for Type 2 diabetes

melitus. It is found to be almost 200 times as potent as tolbutamide in evoking the release

of insulin from the pancreatic islets. However, it exerts a rather more effective agent in

causing suppression of fasting than postprandial hyperglycemia.

Synthesis of Glibenclamide


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SAR of Glyburide

The SAR of Glyburide and Glypizzide are discussed below :

DRUG pKa Potency Compared to Tolbutamide

Glipizide 5.9 100 times more potent

Glyburide 5.3 200 times more potent

Obviously the presence of ‘R’ in glyburide potentiates the hypoglycemic activity

200 times, whereas the heterocylic nucleus in glipizide potentiates 100 times in

comparison to tolbutamide. It is 2nd generation oral hypoglycemic agent. The drug has a

half life elimination of 10 hours, but its hypoglycemic effects remains for up to 24 hours.

Mechanism of Action

The drug gets absorbed upto 90% when administered orally from an empty

stomach. About 97% gets bound to plasma albumin in the form of a weak-acid anion; and

therefore, is found to be more susceptible to displacement by a host of weakly acidic drug

substances. Elimination is mostly afforded by ‘hepatic metabolism’. The half-life ranges

between 1.5 to 5 hours, and the duration of action lasts upto 24 hours.

5.1.2 Meglitinide

Metaglinides are nothing but non sulphonylurea oral hypoglucemic agents

normally employed in the control and management of type 2 diabetes (i.e, non-insulin-

dependent diabetes mellitus, NIDDM). Interestingly, these agents have a tendency to show

up a quick and rapid onset and a short duration of action. Just like the ‘sulphonylureas’,

they also exert their action by inducing insulinrelease from the prevailing functional


Page 61

pancreatic β-cells. Importantly the mechanism of action of the ‘metaglinides’ is observed

to differ from that of the ‘sulphonylureas’.

In fact, the mechanism of action could be explained as under:

(a) Through binding to the particular receptors in the β-cells membrane that

ultimately lead to the closure of ATP-dependent K+ channels, and

(b) K+ channel blockade affords depolarizes the β-cell membrane, which iN turn

gives rise to Ca2+ influx, enhanced intracellular Ca2+, and finally stimulation of insulin

secretion.

Based on the altogether different mechanism of action from the two aforesaid

‘sulphonylureas’ there exist two distinct, major and spectacular existing differences

between these two apparently similar categories of ‘drug substances’, namely :

(i) Metaglinides usually produe substantially faster insulin production in comparison

to the ‘sulphonyl ureas’, and, therefore, these could be administered in-between meals by

virtue of the fact that under these conditions pancreas would produce insulin in a relatively

much shorter duration, and

(ii) Metaglinides do not exert a prolonged duration of action as those exhibited by the

‘sulphonylureas’. Its effect lasts for less than 1 hour whereas sulphonylureas continue to

cause insulin generation for several hours.

Repaglinide

Structure


(S)-(+)-2-ethoxy-4-[2-(3-methyl-1-[2-(piperidin-1-yl)phenyl]butylamino)-2-oxoethyl]benzoic acid

Chemical data

FORMULA C27H36N2O4



BIOAVAIBILITY 56 % (oral)

PROTEIN BINDING >98 %


Page 62

METABOLISM Hepatic oxidation and glucuronidation (CYP3A4-

mediated)

HALF LIFE 1 hr

EXECRETION Fecal (90%) and renal (8%)

ROUTES Oral

It is used in the control and management of Type-2 diabetes mellitus. It must be

taken along with meals.

Mechanism of Action

The drug is found to exert its action by stimulating insulin secretion by binding to

and inhibiting the ATP-dependent K+ channels in the β-cell membrane, resulting

ultimately

in an opening of Ca+2 channels. It gets absorbed more or less rapidly and completely from

the GI tract; and also is exhaustively metabolized in the liver by two biochemical

phenomena, such as:

(a) Glucuronidation; and

(b) Oxidative biotransformation. Besides, it has been established that the hepatic

cytochrome P-450 system 3A4 is predominantly involved in the ultimate metabolism of

repaglinide.

SAR of Repaglinide

Repaglinide represents a new class of nonsulfonylurea oral hypoglycemic agent.

With a fast onset and short duration of action, the medication should be taken with meals.

It is oxidized by CYP 3A4, and the carboxylic acid may be conjugated to inactive

compounds. Less than 0.2 % is excreated unchanged by kidney, which may be an

adventage for elderly patients who are renally impaired.

Side effects

The most common side effects involves hypoglycemia, resulting in headache, cold

sweats, anxity, and changes in mental state.


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Nateglinide

Structure


(R)-2-(4-isopropylcyclohexanecarboxamido)-3-phenylpropanoic acid

Chemical data

FORMULA C19H27NO3




HALF LIFE 1.5 hr

Nateglinide (INN, trade name Starlix) is a drug for the treatment of type 2 diabetes.

Nateglinide was developed by the Swiss pharmaceutical company Novartis.

Nateglinide belongs to the meglitinide class of blood glucose-lowering drugs.

Dosage

Nateglinide is delivered in 60mg & 120mg tablet form.

5.2 GLP-I analogs

5.2.1 Glucagon-like peptide-1 hormons

It is the incretin hormone acting via GLP-1 receptor (a G-protein coupled receptor).

When blood glucose levels are high this hormone stimulates insulin secretion and

biosynthesis and inhibits glucagon release leading to reduce hepatic glucose output. In

addition it serves as an “ileal brake”, slowing gastric emptying and reducing appetite.

GLP-1 has a no. of effects on regulation of β-cell mass: stimulation of replication and

growth and inhibition of apoptosis of existing β-cells and neogenesis of new β-cells from


Page 64

precursors. Thus, GLP-1 therapy for the treatment of type 2 diabetes is an area of active

research.

There are two sub-classes of GLP-1 in clinical development .One is natural GLP-1

and the other is exendin-4, a peptide agonist isolated from the venom of lizard and is more

potent than natural GLP-1.

Exenatide (AC2993) is a peptide consist of 39 amino acid approved recently

developed by Lilly and Amylin & used for treatment of diabetes. Liraglutide (NN2211), is

under phase ΙΙ clinical trial by Novo Nordisk, CJC1131 is under phase I / ΙΙ clinical trial

by Conjuchem, ZP10 is under phase I / ΙΙ clinical trial by Zealand.

Glucagon-like peptide-1 analogs are a new class of drug for treatment of type 2

diabetes. One of their advantages is that they have a lower risk of causing hypoglycemia.

Exenatide

Structure

Chemical data

FORMULA C184H282N50O60S


METABOLISM Proteolysis

HALF LIFE 2.4 hr

EXECRETION renal/proteolysis

ROUTES subcutaneous injection

Exenatide (INN, marketed as Byetta) is one of a new class of medications (incretin

mimetics) approved (Apr 2005) for the treatment of diabetes mellitus type 2. (It is not

approved for use in diabetes mellitus type 1). It is manufactured by Eli Lilly and

Company.

Exenatide is administered as a subcutaneous injection (under the skin) of the

abdomen, thigh, or arm, 30 to 60 minutes before the first and last meal of the day.


Page 65

Albiglutide

Albiglutide is a drug under investigation by GlaxoSmithKline for treatment of type

2 diabetes. It is a dipeptidyl peptidase-4-resistant glucagon-like peptide-1 dimer fused to

human albumin. It has a half life of 6 to 7 days (longer than exenatide or liraglutide).

5.3 Protein Tyrosin Phosphate 1β inhibitors

Phosphatases are the enzyme which remove phosphate group from the substrate

process known as dephosphorylation. Protein tyrosine phosphatase (PTP) is the enzyme

acts by dephosphorylation of the tyrosine kinase.Tyrosine phosphorylation of proteins is a

fundamental mechanism for the control of cell growth and differentiation. It is reversible

and governed by the opposing activities of protein tyrosine kinases (PTKs), which catalyse

phosphorylation and protein tyrosine phosphatases (PTPs), which are responsible for

dephosphorylation. Defective or inappropriate operation of these network leads to aberrant

tyrosine phosphorylation, contributing to the development of many diseases like cancer

and diabetes. Phosphorylation is reversible. PTPs are the enzymes play an important role

in cellular signaling. PTPs are the enzymes not only function as negatively but also

positively i.e. they are not only the cause of a disease they are used in the treatment of

diseases.

PTPs can be divided into three major subfamilies – tyrosine-specific, dualspecific

and low molecular weight phosphatases. The dual-specific phosphatase utilizes the protein

substrate that contains pTyr as well as pSer and pThr. Several PTPs have been implicated

as negative regulators of the insulin signalling pathway; these include TC-PTP, SHP-2,

PTEN, PTP-LAR, and PTP-1B. PTP-1β is a cytosolic phosphates consisting of a single

catalytic domain. PTPs are divided into 2 classes:

a) Non transmembrane.

b) Transmembrane type or Receptor type


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Fig.5.1 Classification of PTP

5.3.1 Protein tyrosine phosphatase-1β ( PTP-1β)

PTB-1β a founding member of PTPase with 435 amino acid residues was first

purified from human placental tissue in 1988 and first crystallized in 1994. PTP-1β

belongs to non transmembrane class of enzymes. PTP-1β is an abundant enzyme

expressed in nearly all tissues where it is localized primarily on intracellular membranes

by a C-terminal sequence. PTP-1β acts as negative regulator of insulin signalling. It acts

by causing dephosphorylation of insulin receptor. It also causes negative regulation of

insulin signaling. It is involved in type-2 diabetes & obesity. It has been shown mice

lacking PTP-1β show enhance insulin activity, resistant to development of obesity. In

vitro, it is a non-specific PTP and dephosphorylates a wide variety of substrates. In vivo, it

is involved in down regulation of insulin signalling by dephosphorylation of specific

phosphotyrosine residues on the insulin receptor. Administration of PTP-1β antisense

oligonucleotides to diabetic obese mice reduces plasma glucose and brings insulin level to

normal. PTP-1β knockout mice have shown increased insulin sensitivity and decreased

weight gain after a high fat diet. All these evidences help to validate PTP-1β as a


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keynegative regulator of insulin signal transduction and a potential therapeutic target in the

treatment of NIDDM and obesity.

5.3.2 Role of PTP-1β in Insulin & Leptin signaling

Binding of insulin to insulin receptor α-subunit induces conformational change in β-

subunit which in turns activates insulin receptor tyrosine kinase which causes

phosphorylation of insulin receptor substrate which is responsible for down stream

signaling through recruitment of appropriate signal transducers which is responsible for

various effect exerted by insulin (Fig.5.2). It has been shown recently that PTP-1β

negatively regulates leptin receptor signaling in a murine neuronal subline.PTP-1β acts to

block leptin signaling by dephosphorylating jleptinanus kinase (jak)- 2. Leptin is a key

adipokine regulating food intake & energy expenditure. It is likely that the resistance to

diet induced obesity is due, atleast in part, to increased leptin ssenstivity in the PTP-1β

knockout mice.

Fig.5.2: Role of PTP-1B in insulin signaling


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5.3.3 Structure of PTP-1β

Red:Catalytic site ,(His214-Arg221); Blue: second aryl phosphate binding siteYellow :( Tyr46-Arg47-Asp48) , Magenta: (Asp181 and Phe182)

Fig.5.3: Structure of PTP-1β showing main sites

The active site of PTP-1β contains a common structural motif His–Cys–Ser–Ala–

Gly–Ile–Gly–Arg, forming a rigid, cradle like structure that coordinates to the aryl

phosphate moiety of the substrate. It contains an active site nucleophile, Cys 215. It also

contain second aryl phosphate binding site. In the above structure, red is main catalytic

active site which is from His 214 –Arg 221, in the blue is contain second aryl phosphate

binding site, in the yellow is YRD loop which play an important role in substrate binding,

and in the magenta is Wpd loop which contain Asp181 & Phe 182 which is full of water

and responsible for hydrogen bonding interactions. The dephosphorylation of tyrosine

takes place via two steps. In the first step there is a nucleophilic attack on the substrate

phosphate by the sulphur atom of Cys, coupled with protonation of tyrosyl leaving group

by Asp181 acting as a general acid.

This leads to the formation of cysteinyl phosphate intermediate. The second step

mediated by Glu262 and Asp181, leads to the hydrolysis of catalytic intermediate and

release of phosphate.


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PTP-1β has been closely structurally correlated with other members of PTP family

especially TC-PTP. PTP-1β causes simultaneous dephosphorylation of phosphorylated

1162 & 1163 residue of insulin receptor thus causing inhibition of insulin signalling while

other PTP s does not causes simultaneous dephosphorylation thus has important role in

insulin signaling.

Fig.5.4: Structure of PTP-1β showing simultaneous dephosphorylation of insulin receptor


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5.3.4 PTP-1β Inhibitors

Phosphatase LAR, CD45, SHP-2, cdc25c and T-cell PTP (TCPTP) share 50–80%

homology in the catalytic domain with PTP-1β, which presents a challenging task of

achieving selectivity, especially over TCPTP. Thus it was necessary for the inhibitors to

interact with the regions outside the catalytic site in order to be selective. A non-catalytic

phosphotyrosine-binding site was identified, which seems to be ideal since it is close to the

catalytic site and is less homologous between the PTP-1β and TCPTP when the amino acid

sequences were compared. Hence targeting both the sites simultaneously may show good

activity and selectivity against PTP-1 β. PTPase have been inhibited experimentally using

a variety of mechanisms and chemical entities. PTPase can be inhibited by chemical

inactivation of the active site cysteine residue common to all members of the family. This

inactivation may occur via an oxidative mechanism initiated by reactive species such as

pervanadate and peroxides e.g. Most of early PTP-1β inhibitors are phosphate-based and

the most studied phosphate-based PTP-1β inhibitors are difluorophosphonates e.g. This

difluorophosphonate group was introduced as a nonhydrolyzable phosphotyrosine mimetic

in 1992 by Burke and coworkers.2-(Oxalylamino)-benzoic acid (OBA) e.g. was identified

as a general, reversible and competitive inhibitor of severalPTPase using a scintillation

proximity-based high throughput screening by workers at Novo Nordisk.

High-throughput screening has allowed the identification of several more PTP-1β

inhibitor classes having various mechanisms of action. Pyridazine derivatives such as were

identified at Biovitrum potencies in a low micromolar range (5.6μM) and over 20 fold

selectivity over TC-PTP. Hydroxyphenylazole derivatives such as with IC50 value in the

micromolar range, were claimed by Japan Tobacco. A series of azolidinediones e.g., and

phenoxyacetic acid based PTP1β inhibitors e.g., have been reported by American Home

Products. More recently a group at Hoffmann-LaRoche described novel

pyrimidotriazinepiperidine analogues e.g., with oral glucose lowering effect in ob/ob mice.

The inhibition of PTP1β by this class of compounds presumably involves the oxidation of

the active site. Alpha-bromoacetophenone derivatives act as potent PTP inhibitors by

covalently alkylating the conserved catalytic cysteine in the PTP active site.

Derivatization of the phenyl ring with a tripeptide Gly–Glu–Glu29 resulted in potent,

selective inhibitors against PTP-1β cysteine of PTP1β to the corresponding sulfenic acid.


Page 71


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Despite good biological target validation, designing PTP-1β inhibitors as oral agent

is challenging because of the highly charged nature of the catalytic domain of the target.

Furthermore the development of selective, potent and bioavailable inhibitors of PTP-1β

will be a formidable challenge although some of the groundwork has now been laid out.

5.4 Dipeptidyl peptidase-4 inhibitor

Inhibitors of Dipeptidyl peptidase 4 also called as DPP-4 inhibitors, are a class of

oral hypoglycemics that block DPP-4. They can be used to treat diabetes mellitus type 2.

The first agent of the class - sitagliptin - was approved by the FDA in 2006.

Sitagliptin entered the Australian drug market in late 2007 for the treatment of difficult-to-

control diabetes mellitus type 2.

Their mechanism of action is thought to result from increased Incretin levels (GLP-

1 and GIP), which inhibit glucagon release, the effect of which, in turn, decreases blood

glucose, but, more significant, increases insulin secretion and decreases gastric emptying.

Figure No.5.5 Dipeptidyl peptidase-4 inhibitor

The role of DPP-4, GLP-1 in glucose homeostasis. Following meal ingestion, the

incretin hormones, intact (active) GLP-1 and GIP, released from gut endocrine cells and


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function to lower blood glucose levels by stimulating glucose-dependent insulin release

from pancreatic β-cells (GLP-1 and GIP) and suppressing glucose-dependent glucagon

release from pancreatic α-cells (GLP-1). However, once released into the circulation,

incretin hormones are rapidly inactivated and degraded by plasma protease enzyme DPP-

4. DPP-4 inhibitors like sitagliptin inhibit breakdown of incretin hormones, thereby

increasing active GLP-1 and GIP levels and promoting fasting and postprandial glycemic

control.

5.4.1 Examples

Drugs belonging to this class are:

sitagliptin (FDA approved 2006, marketed by Merck & Co. under the trade name

Januvia),

vildagliptin (marketed in the EU by Novartis under the trade name Galvus),

Saxagliptin (being developed by Bristol-Myers Squibb, AstraZeneca and Otsuka

Pharmaceutical Co.),

linagliptin (being developed by Boehringer Ingelheim),

Alogliptin (developed by Takeda Pharmaceutical Company, whose FDA

application for the product is currently suspended as of June 2009).

Berberine, the common herbal dietery supplement, too inhibits dipeptidyl peptidase-4,

which at least partly explains its anti-hyperglycemic activities.

5.4.2 Possible cancer risk

Although extensive long-term, pre-clinical studies of the major DPP-4 inhibitors

has failed to show any evidence of potential to cause tumors in laboratory animals, there

was one in-vitro (i.e., test tube) study that has raised some questions. In theory, DPP-4

inhibitors may allow some cancers to progress, since DPP-4 appears to work as a

suppressor in the development of cancer and tumours.


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Alogliptin

Structure


2-({6-[(3R)-3-aminopiperidin-1-yl]-3-methyl-2,4-dioxo-

3,4-dihydropyrimidin-1(2H)-yl}methyl)benzonitrile

Chemical data

FORMULA C18H21N5O2


ROUTES Oral

Alogliptin (codenamed SYR-322) is an investigational anti-diabetic drug in the

DPP-4 inhibitor class, being developed by Takeda Pharmaceutical Company. Takeda has

submitted a New Drug Application for alogliptin to the U.S. Food and Drug

Administration, after positive results from Phase III clinical trials.FDA submission

suspended or withdrawn June 2009 needing more data.

Linagliptin

Structure


8-[(3R)-3-aminopiperidin-1-yl]-7-(but-2-yn-1-yl)-3- methyl-1-[(4-methylquinazolin-2-yl)methyl]-3,7-

dihydro-1H-purine-2,6-dione

Chemical data

FORMULA C25H26N8O2


ROUTES Oral


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Linagliptin (BI-1356, expected trade name Ondero) is a DPP-4 inhibitor developed

by Boehringer Ingelheim undergoing research for type II diabetes. It is currently in a Phase

III clinical trial.

Saxagliptin

Saxagliptin (rINN), previously identified as BMS-477118, is a new oral

hypoglycemic (anti-diabetic drug) of the new dipeptidyl peptidase-4 (DPP-4) inhibitor

class of drugs. It was developed by Bristol-Myers Squibb. In June 2008, it was announced

that Onglyza would be the trade name under which saxagliptin will be marketed. The FDA

approved Onglyza on July 31, 2009. Dipeptidyl peptidase-4's role in blood glucose

regulation is thought to be through degradation of GIP and the degradation of GLP-1.

Bristol-Myers Squibb announced on 27 December 2006 that Otsuka

Pharmaceutical Co. has been granted exclusive rights to develop and commercialize the

compound in Japan. Under the licensing agreement, Otsuka will be responsible for all

development costs, but Bristol-Myers Squibb retains rights to co-promote saxagliptin with

Otsuka in Japan. Further, on 11 January 2007 it was announced that Bristol-Myers Squibb

and AstraZeneca would work together to complete development of the drug and in

subsequent marketing.

Structure


(1S,3S,5S)-2-[(2S)-2-amino-2-(3-hydroxy-1-adamantyl)

acetyl]-2-azabicyclo[3.1.0]hexane-3-carbonitrile

Chemical data

FORMULA C18H25N3O2



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Sitagliptin

Structure


(R)-4-oxo-4-[3-(trifluoromethyl)-5,6-dihydro[1,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl]-1-(2,4,5-

trifluorophenyl)butan-2-amine

Chemical data

FORMULA C16H15F6N5O



BIOAVAIBILITY 87 %


METABOLISM Hepatic (CYP3A4- and CYP2C8-mediated)

HALF LIFE 8 to 14 hour

EXECRETION Renal (80%)

ROUTES Oral

Sitagliptin (INN; previously identified as MK-0431, trade name Januvia) is an oral

antihyperglycemic (anti-diabetic drug) of the dipeptidyl peptidase-4 (DPP-4) inhibitor

class, Sitagliptin being the only second generation DPP-4 inhibitor currently available in

the USA. This enzyme-inhibiting drug is used either alone or in combination with other

oral antihyperglycemic agents (such as metformin or a thiazolidinedione) for treatment of

diabetes mellitus type 2. The benefit of this medicine is its lower side-effects (e.g., less

hypoglycemia, less weight gain) in the control of blood glucose values. Exenatide (Byetta)

also works by its effect on the incretin system.

Mechanism of Action

Sitagliptin works to competitively inhibit the enzyme dipeptidyl peptidase 4 (DPP-

4). This enzyme breaks down the incretins GLP-1 and GIP, gastrointestinal hormones that

are released in response to a meal. By preventing GLP-1 and GIP inactivation, GLP-1 and


Page 77

GIP are able to potentiate the secretion of insulin and suppress the release of glucagon by

the pancreas. This drives blood glucose levels towards normal. As the blood glucose level

approaches normal, the amounts of insulin released and glucagon suppressed diminishes

thus tending to prevent an "overshoot" and subsequent low blood sugar (hypoglycemia)

which is seen with some other oral hypoglycemic agents.

Vildagliptin


(S)-1-[N-(3-hydroxy-1-adamantyl)glycyl]pyrrolidine-2-carbonitrile

Chemical data

FORMULA C17H25N3O2


SYNONYMS (2S)-1-{2-[(3-hydroxy-1-

adamantyl)amino]acetyl}pyrrolidine-2-carbonitrile


BIOAVAIBILITY 85 %

PROTEIN BINDING 9.3 %

METABOLISM Mainly hydrolysis to inactive metabolite; CYP450

not appreciably involved

HALF LIFE 2 to 3 hr

EXECRETION Renal

ROUTES Oral

Vildagliptin (previously identified as LAF237, trade name Galvus) is a new oral

anti-hyperglycemic agent (anti-diabetic drug) of the new dipeptidyl peptidase-4 (DPP-4)

inhibitor class of drugs. Vildagliptin inhibits the inactivation of GLP-1 and GIP by DPP-4,

allowing GLP-1 and GIP to potentiate the secretion of insulin in the beta cells and

suppress glucagon release by the alpha cells of the islets of Langerhans in the pancreas.

Vildagliptin has been shown to reduce hyperglycemia in type 2 diabetes mellitus.

Novartis has since withdrawn its intent to submit vildagliptin to the FDA, as of

July 2008. The Food and Drug Administration had demanded additional clinical data

before it could approve vildagliptin including extra evidence that skin lesions and kidney

impairment seen during an early study on animals have not occurred in human trials.


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6. Sensitizers

6.1 Biguanide

Biguanide can refer to a molecule, or to a class of drugs based upon this molecule.

Biguanides can function as oral antihyperglycemic drugs used for diabetes mellitus or

prediabetes treatment. They are also used as antimalarial drugs. The disinfectant

polyaminopropyl biguanide (PAPB) features biguanide functional groups.

6.1.2 Examples of biguanides:

Metformin - widely used in treatment of diabetes mellitus type 2

Phenformin - withdrawn from the market in most countries due to toxic effects

Buformin - withdrawn from the market due to toxic effects

6.1.3 Mechanism of action

The mechanism of action of biguanides is not fully understood. However, in

hyperinsulinemia, biguanides can lower fasting levels of insulin in plasma. Their

therapeutic uses derive from their tendency to reduce gluconeogenesis in the liver, and, as

a result, reduce the level of glucose in the blood. Biguanides also tend to make the cells of

the body more willing to absorb glucose already present in the blood stream, and there

again reducing the level of glucose in the plasma.

Structure


Diguanide, 2-carbamimidoylguanidine

Chemical data

FORMULA C2H7N5



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Metformin

Structure


N,N-dimethylimidodicarbonimidic diamide

Chemical data

FORMULA C4H11N5

MOLECULAR MASS 129.164 g/mol (free)

165.63 g/mol (HCl)

SYNONYMS 1,1-dimethylbiguanide


BIOAVAIBILITY 50 to 60% under fasting conditions

METABOLISM None

HALF LIFE 6.2 hours

EXECRETION Active renal tubular excretion by OCT2

ROUTES Oral

It is used as an oral antihyperglycemic drug for the management of Type 2 diabetes

mellitus. It is invariably recommended either as monotherapy or as an adjunct to diet or

with a sulphonylurea (combination) to reduce blood-glucose levels.

Mechanism of Action

The drug is found to lower both basal and postprandial glucose. Interestingly, its

mechanism of action is distinct from that of sulphonylureas and does not cause

hypoglycemia. However, it distinctly lowers hepatic glucose production, reduces intestinal

absorption of glucose, and ultimately improves insulin sensitivity by enhancing

appreciably peripheral glucose uptake and its subsequent utilization. The drug is mostly

eliminated unchanged in the urine, and fails to undergo hepatic metabolism.


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Synthesis of Metformin

Procedure

Metformin hydrochloride (N,N-dimethylimidodicarbonimidic diamide

hydrochloride) is an oral antihyperglycemic drug used in the management of diabetes. It is

usually prepared from the reaction between dimethylamine hydrochloride and dicyano

diamide at 120-140 oC in 4 hrs time with 69% yield. In designing ecofriendly synthesis of

the target molecule, the starting materials are made to react by modifying the reaction

conditions in such a way that the by-products and wastes are eliminated and also the use of

organic solvents is minimized.Thin layer chromatography (TLC) has been reported as a

tool for reaction optimization in microwave assisted synthesis. This method has been used

to modify a conventional procedure for an efficient synthesis of metformin hydrochloride

by simply spotting of the reaction mixture on a TLC plate and then subjecting it to

microwave irradiation.

Formulations

Metformin is sold under several trade names, including Glucophage XR, Riomet,

Fortamet, Glumetza, Obimet, Dianben, Diabex, and Diaformin. Metformin IR (immediate

release) is available in 500 mg, 850 mg, and 1000 mg tablets, all now generic in the US.

Buformin

Structure


N-butylimidocarbonimidic diamide


Page 81

Buformin is an anti-diabetic drug of the biguanide class, it is chemically related to

metformin, and phenformin. It was withdrawn from the market in most countries due to a

high risk of causing lactic acidosis. This drug is still used in some countries, such as

Romania and Spain. It is marketed by German pharmaceutical company Grünenthal.

Phenformin

Structure


2-(N-phenethylcarbamimidoyl)guanidine

Chemical data

FORMULA C10H15N5


Phenformin is an anti-diabetic drug from the biguanide class. It was marketed as

DBI by Ciba-Geigy but was withdrawn from most markets in the late 1970s due to a high

risk of lactic acidosis, which was fatal in 50% of cases.

Chemical data

FORMULA C6H15N5



EXECRETION Renal

ROUTES Oral

LEGAL STATUS Withdrawn in most countries


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6.2 Thiazolidinedione

The medication class of thiazolidinedione (also called glitazones) was introduced

in the late 1990s as an adjunctive therapy for diabetes mellitus (type 2) and related

diseases.

6.2.1 Mode of action

Thiazolidinediones or TZDs act by binding to PPARs (peroxisome proliferator-

activated receptors), a group of receptor molecules inside the cell nucleus, specifically

PPARγ (gamma). The ligands for these receptors are free fatty acids (FFAs) and

eicosanoids. When activated, the receptor migrates to the DNA, activating transcription of

a number of specific genes.

Genes upregulated by PPARγ can be found in the main article on peroxisome

proliferator-activated receptors.

By activating PPARγ:

Insulin resistance is decreased

Adipocyte differentiation is modified

VEGF-induced angiogenesis is inhibited

Leptin levels decrease (leading to an increased appetite)

Levels of certain interleukins (e.g. IL-6) fall

Adiponectin levels rise

6.2.2 Synthesis of N-substituted 2, 4-thiazolidinediones from oxazolidinethiones

A novel reaction has been found between oxazolidinethione and bromoacetyl

bromide to afford N-substituted 2,4-thiazolidinediones through an intramolecular

nucleophilic substitution reaction. Interestingly a step of elimination was carried out in

trisubstituted oxazolidinethiones forming a double bond.


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6.2.3 Members of the class

The chemical structure of thiazolidinedione

Chemically, the members of this class are derivatives of the parent compound

thiazolidinedione, and include:

Rosiglitazone (Avandia)

Pioglitazone (Actos)

Troglitazone (Rezulin), which was withdrawn from the market due to an increased

incidence of drug-induced hepatitis.

6.2.4 Uses

The only approved use of the thiazolidinediones is in diabetes mellitus type 2.

It is being investigated experimentally in polycystic ovary syndrome (PCOS), non-

alcoholic steatohepatitis (NASH), psoriasis, autism, and other conditions.

Several forms of lipodystrophy cause insulin resistance, which has responded

favorably to thiazolidinediones. There are some indications that thiazolidinediones provide

some degree of the protection against initial stages of the breast carcinoma development.

Pioglitazone

STRUCTURE


(RS)-5-(4-[2-(5-ethylpyridin-2-yl)ethoxy]benzyl)thiazolidine-2,4-dione


Page 84

Chemical data

FORMULA C19H20N2O3S



PROTEIN BINDING >99 %

METABOLISM liver (CYP2C8)

HALF LIFE 3–7 hours

EXECRETION In bile

ROUTES Oral

Pioglitazone is a prescription drug of the class thiazolidinedione (TZD) with

hypoglycemic (antihyperglycemic, antidiabetic) action. Pioglitazone is marketed as

trademarks Actos in the USA and UK, Glustin in Europe, Zactos in Mexico by Takeda

Pharmaceuticals & Piozer in Pakistan by Hilton Pharmaceuticals. Actos was the tenth-best

selling drug in the U.S. in 2008, with sales exceeding $2.4 billion.

Side effects

Pioglitazone can cause fluid retention and peripheral edema. As a result, it may

precipitate congestive heart failure (which worsens with fluid overload in those at risk). It

may cause anemia. Mild weight gain is common due to increase in subcutaneous adipose

tissue. In studies, patients on pioglitazone had a slightly increased proportion of upper

respiratory tract infection, sinusitis, headache, myalgia and tooth problems.

Rivoglitazone

Structure


(RS)-5-{4-[(6-methoxy-1-methyl-1H-benzimidazol-2-yl) methoxy]benzyl}-1,3-thiazolidine-2,4-dione

Chemical data

FORMULA C20H19N3O4S



Page 85

Rivoglitazone (INN) is a thiazolidinedione undergoing research for use in the

treatment of type 2 diabetes. It is being developed by Daiichi Sankyo Co.

Rosiglitazone

STRUCTURE


(RS)-5-[4-(2-[methyl(pyridin-2-yl)amino]ethoxy)benzyl]thiazolidine-2,4-dione

Chemical data

FORMULA C18H19N3O3S



BIOAVAIBILITY 99 %

PROTEIN BINDING 99.8 %

METABOLISM Hepatic (CYP2C8-mediated)

HALF LIFE 3 – 4 hours

EXECRETION Renal (64%) and fecal (23%)

ROUTES Oral

Rosiglitazone is an anti-diabetic drug in the thiazolidinedione class of drugs. It is

marketed by the pharmaceutical company GlaxoSmithKline as a stand-alone drug

(Avandia) and in combination with metformin (Avandamet) or with glimepiride

(Avandaryl). Annual sales peaked at approx $2.5bn in 2006. The drug's patent expires in

2012.

Some reports have suggested that rosiglitazone is associated with a statistically

significant risk of heart attacks, but other reports have disagreed, and the controversy has

not been resolved. Concern about adverse effects has reduced the use of rosiglitazone

despite its important and sustained effects on glycemic control.


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Side effects

Heart disease, Bone fractures, Eye damage, Hepatotoxicity

Troglitazone

Structure


5-(4-[(6-hydroxy-2,5,7,8-tetramethylchroman-2-yl)methoxy]benzyl)thiazolidine-2,4-dione

Chemical data

FORMULA C24H27NO5S


HALF LIFE 16-34 hours

Troglitazone (Rezulin, Resulin or Romozin) is an anti-diabetic and

antiinflammatory drug, and a member of the drug class of the thiazolidinediones. It was

developed by Daiichi Sankyo Co.(Japan). It was introduced and manufactured by Parke-

Davis in the late 1990s but turned out to be associated with an idiosyncratic reaction

leading to drug-induced hepatitis. Evaluating FDA medical officer Dr. John Gueriguian

had disapproved it due to high liver toxicity. But the FDA stripped Gueriguian of his post

and discarded his report under successful corporate pressure to approve the drug.

It was withdrawn from the United Kingdom market (sailing by Glaxo) on

December 1997.after,from the USA market on 21 March 2000, and from the Japan

markets(introduced and manufactured by Sankyo.Co.) soon afterwards.

Mode of action

Troglitazone, like the other thiazolidinediones (pioglitazone and rosiglitazone),

works by activating PPARs (peroxisome proliferator-activated receptors). Troglitazone is


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a ligand to both PPARα and - more strongly - PPARγ. Troglitazone also contains an α-

tocopheroyl moiety, potentially giving it vitamin E-like activity in addition to its PPAR

activation. It has been shown to reduce inflammation: troglitazone use was associated with

a decrease of nuclear factor kappa-B (NFκB) and a concomitant increase in its inhibitor

(IκB). NFκB is an important cellular transcription regulator for the immune response.

6.3 PPAR modulator41-45

Figure 6.1 PPAR α and γ pathways.

PPAR modulators are drugs which act upon the peroxisome proliferator-activated receptor.

6.3.1 PPAR α/γ dual agonist

These agents are shown to ameliorate the hyperglycemia and hyperlipidmia

associated with type 2 diabetes. In addition to their benefit on lipids the activation of

PPARα may mitigate the weight gain induced by PPARγ activation .So this dual agonist is

supposed to provide additive and possibly synergistic effects.

First literature report of a balanced PPAR α/γ dual agonist was KRP-297 (MK-

767), a TZD derivative that was reported to bind PPARα and PPARγ with an affinity of

approx.0.230 and 0.33 μM respectively and to trans activate PPARα and PPARγ with

potencies of 1.0 and 0.8 μM followed by phenylpropionic acid based PPAR α/γ dual


Page 88

agonists Tesaglitazar (AZ-242) by Astra Zeneca, reportedly in phase III clinical trial,

Ragaglitazar (DRF-2725) by Dr. Reddy’s Research foundation, reportedly completed

phase ΙΙ clinical trial but clinical development being terminated due to an incidence of

bladder tumors in rodents. LY-510925 is a result of collaborative effort of Ellily Lilly and

Ligand pharmaceuticals, Muraglitazar (BMS –298585) is disclosed by Cheng et al.

Aleglitazar

Structure

Chemical data

FORMULA C24H23NO5S

MOLECULAR MASS 437.50812 gm/mol

Aleglitazar is a peroxisome proliferator-activated receptor agonist (hence a PPAR

modulator ) with affinity to PPARα and PPARγ, which is being developed by Hoffmann–

La Roche for the treatment of type II diabetes. It is currently in phase II clinical trials.

Muraglitazar

Structure


N-[(4-methoxyphenoxy)carbonyl]-N-{4-[2-(5-methyl-2-phenyl-1,3-oxazol-4-yl)ethoxy]benzyl}glycine

Chemical data

FORMULA C29H28N2O7



Page 89

Muraglitazar (proposed tradename Pargluva) is a peroxisome proliferator-activated

receptor agonist with affinity to PPARα and PPARγ.

The drug had completed phase III clinical trials, however in May, 2006 Bristol-

Myers Squibb announced that it had discontinued further development.

Tesaglitazar

Structure


(2S)-2-Ethoxy-3-[4-[2-(4-methylsulfonyloxyphenyl)ethoxy]phenyl]propanoic acid

Chemical data

FORMULA C20H24O7S

MOLECULAR MASS 408.46 gm/mol

Tesaglitazar is a peroxisome proliferator-activated receptor agonist with affinity to

PPARα and PPARγ, proposed for type 2 diabetes.

The drug had completed several phase III clinical trials, however in May, 2006

AstraZeneca announced that it had discontinued further development.


Page 90

7. Other insulin analogs

An insulin analog is an altered from of insulin, different from any occurring in

nature, but still available to the human body for performing the same action as human

insulin in terms of glycemic control. Through genetic engineering of the underlying DNA,

the amino acid sequence of insulin can be changed to alter its ADME (absorption,

distribution, metabolism, and excretion) characteristics. Officially, the U.S. Food and Drug

Administration (FDA) refers to these as "insulin receptor ligands", although they are more

commonly referred to as insulin analogs.

These modifications have been used to create two types of insulin analogs: those

that are more readily absorbed from the injection site and therefore act faster than natural

insulin injected subcutaneously, intended to supply the bolus level of insulin needed after a

meal; and those that are released slowly over a period of between 8 and 24 hours, intended

to supply the basal level of insulin for the day. Insulin analog was first manufactured by

Eli Lilly and Company.

7.1 Animal insulin

The amino acid sequence for insulin is almost the same in different mammals.

Porcine insulin has only a single amino acid variation from the human variety, and bovine

insulin varies by three amino acids. Both are active on the human receptor with

approximately the same strength. Prior to the introduction of biosynthetic human insulin,

insulin derived from sharks was widely used in Japan. Even insulin from some species of

fish may be effective in humans. Non-human insulins can cause allergic reactions in a tiny

number of people, as can genetically engineered "human" insulin. Synthetic "human"

insulin has largely replaced animal insulin. With the advent of high-pressure liquid

chromatography (HPLC) equipment, the level of purification of animal-sourced insulins

has reached as high as 99%, whereas the purity level of synthetic human insulins made via

recombinant DNA has only attained a maximum purity level of 97%, which raises

questions about the claim of synthetic insulin's purity relative to animal-sourced insulin

varieties.


Page 91

7.2 Chemically and enzymatically modified insulins

Before biosynthetic human recombinant analogues were available, porcine insulin

was chemically converted into human insulin. Chemical modifications of the amino acid

side chains at the N-terminus and/or the C-terminus were made in order to alter the ADME

characteristics of the analogue. Novo Nordisk was able to enzymatically convert porcine

insulin into 'human' insulin by removing the single amino acid that varies from the human

variety, and chemically adding the correct one.

7.3 Non hexameric insulin analogs

Unmodified human and porcine insulins tend to complex with zinc in the blood,

forming hexamers. Insulin in the form of a hexamer will not bind to its receptors, so the

hexamer has to slowly equilibrate back into its monomers to be biologically useful.

Hexameric insulin delivered subcutaneously is not readily available for the body when

insulin is needed in larger doses, such as after a meal (although this is more a function of

subcutaneously administered insulin, as intravenously dosed insulin is distributed rapidly

to the cell receptors, and therefore, avoids this problem). Zinc combinations of insulin are

used for slow release of basal insulin. Basal insulin is the amount the body needs through

the day excluding the amount needed after meals. Non hexameric insulins were developed

to be faster acting and to replace the injection of normal unmodified insulin before a meal.

7.4 Shifted isoelectric point insulins

Normal unmodified insulin is soluble at physiological pH. Analogues have been

created that have a shifted isoelectric point so that they exist in a solubility equilibrium in

which most precipitates out but slowly dissolves in the bloodstream and is eventually

excreted by the kidneys. These insulin analogues are used to replace the basal level of

insulin, and may be effective over a period of about 24 hours. However, some insulin

analogues, such as insulin detemir, bind to albumin rather than fat like earlier insulin

varieties, and results from long-term usage (e.g. more than 10 years) have never been

released.


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7.5 Carcinogenicity

All insulin analogs must be tested for carcinogenicity, as insulin engages in cross-

talk with IGF pathways, which can cause abnormal cell growth and tumorigenesis.

Modifications to insulin always carry the risk of unintentionally enhancing IGF signalling

in addition to the desired pharmacological properties.

Insulin aspart

Chemical data

FORMULA C256H381N65O79S6


ROUTES Subcutaneous

Insulin aspart (marketed by Novo Nordisk as "NovoLog/NovoRapid") is a fast

acting insulin analogue. It was created through recombinant DNA technology so that the

amino acid, B28, which is normally proline, is substituted with an aspartic acid residue.

This analogue has increased charge repulsion, which prevents the formation of hexamers,

to create a faster acting insulin. The sequence was inserted into the yeast genome, and the

yeast expressed the insulin analogue, which was then harvested from a bioreactor.

The components of insulin aspart are as follows: Metal ion – zinc (19.6 ug/mL)

Buffer – disodium hydrogen phosphate dihydrate (1.25 mg/mL) Preservative – m-cresol

(1.72 mg/mL) and phenol (1.50 mg/mL) Isotonicity agent – glycerin (16 mg/mL) and

sodium chloride (0.58 mg/mL). The pH of insulin aspart is 7.2-7.6.

According to JDRF, insulin aspart was approved for marketing in the United States

by the Food and Drug Administration in June 2000.

Insulin glargine


Recombinant human insulin

Chemical data


MOLECULAR MASS 6063 g/mol

ROUTES Subcutaneous


Page 93

Insulin glargine, marketed by Sanofi-Aventis under the name Lantus, is a long-

acting basal insulin analogue, given once daily to help control the blood sugar level of

those with diabetes. Its advantage is that it has a duration of action of 24 hours, with a

"less peaked" profile than NPH. Thus, it more closely resembles the basal insulin secretion

of the normal pancreatic beta cells. Sometimes, in type 2 diabetes and in combination with

a short acting sulfonylurea (drugs which stimulate the pancreas to make more insulin), it

can offer moderate control of serum glucose levels. In the absence of endogenous

insulin—Type 1 diabetes, depleted type two (in some cases) or latent autoimmune diabetes

of adults in late stage—Lantus needs the support of fast acting insulin taken with food to

reduce the effect of prandially derived glucose. It is fasting glucose elevation which more

significantly affects HbA1c and thus determines the progression of the long-term

complications of diabetes mellitus.

Insulin detemir

Structure

Chemical data


MOLECULAR MASS 5913 gm/mol


BIOAVAIBILITY 60% (when administered s.c.)

HALF LIFE 5-7 hours

ROUTES Subcutaneous


Page 94

Insulin detemir is a long-acting human insulin analogue for maintaining the basal

level of insulin. Novo Nordisk markets it under the trade name Levemir. It is an insulin

analogue in which a fatty acid (myristic acid) is bound to the lysine amino acid at position

B29 . It is quickly resorbed after which it binds to albumin in the blood through the fat

acid at position B29. It then slowly dissociates from this complex.

Insulin lispro

Chemical data



Insulin lispro (marketed by Eli Lilly and Company as "Humalog") is a fast acting

insulin analogue; it was the first insulin analogue.

Insulin glulisine

Chemical data


MOLECULAR MASS 5823 gm/mol

ROUTES Subcutaneous

Insulin glulisine is a rapid-acting insulin analogue that differs from human insulin

in that the amino acid asparagine at position B3 is replaced by lysine and the lysine in

position B29 is replaced by glutamic acid. Chemically, it is 3B-lysine-29B-glutamic acid-

human insulin, has the empirical formula C258H384N64O78S6 and a molecular weight of

5823. It was developed by Sanofi-Aventis and sold under the trade name Apidra. When

injected subcutaneously, it appears in the blood earlier and at higher concentrations than

human insulin. When used as a meal time insulin, the dose should be given within 15

minutes before a meal or within 20 minutes after starting a meal.

NPH insulin

NPH insulin; also known as Humulin N, Novolin N,Novolin NPH, NPH Lletin II,

and isophane insulin, marketed by Eli Lilly and Company under the name Humulin N, is

an intermediate-acting insulin given to help control the blood sugar level of those with


Page 95

diabetes. NPH stands for Neutral Protamine Hagedorn and was created in 1936 when

Nordisk formulated "isophane" porcine insulin by adding Neutral Protamine to regular

insulin. It was dubbed Neutral Protamine Hagedorn or NPH.

This is a suspension of crystalline zinc insulin combined with the positively

charged polypeptide, protamine. When injected subcutaneously, it has an intermediate

duration of action, meaning longer than that of regular insulin, but shorter than ultralente,

glargine or detemir.


Page 96

8. Other analogs

8.1 α-Glucosidase inhibitor

α-Glucosidase inhibitors are oral anti-diabetic drugs used for diabetes mellitus type

2 that work by preventing the digestion of carbohydrates (such as starch and table sugar).

Carbohydrates are normally converted into simple sugars (monosaccharides), which can be

absorbed through the intestine. Hence, alpha-glucosidase inhibitors reduce the impact of

carbohydrates on blood sugar.

8.1.1 Examples and differences

Examples of alpha-glucosidase inhibitors include:

Acarbose- Precose

Miglitol - Glyset

Voglibose

Even though the drugs have a similar mechanism of action, there are subtle

differences between acarbose and miglitol. Acarbose is an oligosaccharide, whereas

miglitol resembles a monosaccharide. Miglitol is fairly well-absorbed by the body, as

opposed to acarbose. Moreover, acarbose inhibits pancreatic alpha-amylase in addition to

alpha-glucosidase.

8.1.2 Natural α glucosidase inhibitors

Research has shown the culinary mushroom Maitake (Grifola frondosa) has a

hypoglycemic effect. The reason Maitake lowers blood sugar is due to the fact the

mushroom naturally contains a alpha glucosidase inhibitor.

8.1.3 Mechanism of action

Alpha-glucosidase inhibitors are competitive, reversible inhibitors of pancreatic α-

amylase and membrane-bound intestinal α-glucosidase hydrolase enzymes. Acarbose, the

first α-glucosidase inhibitor discovered, is a nitrogen-containing pseudotetrasaccharide,

while miglitol is a synthetic analog of 1-deoxynojirimycin. The mechanism of action of

these inhibitors is similar but not identical. They bind competitively to the oligosaccharide

binding site of the α-glucosidase enzymes, thereby preventing enzymatic hydrolysis.

Acarbose binding affinity for the α-glucosidase enzymes is: glycoamylase > sucrase >


Page 97

maltase > dextranase. Acarbose has little affinity for isomaltase and no affinity for the α-

glucosidase enzymes, such as lactase. Miglitol is a more potent inhibitor of sucrase and

maltase that acarbose, has no effect on α-amylase, but does inhibit intestinal isomaltose.

The major side effects of the α-glucosidase inhibitors are related to gastrointestinal

disturbances. These occur in approximately 25-30% of diabetic patients, and include

flatulence, diarrhea, bloating, and abdominal discomfort. Daily dose of acabose and

miglitol is 25-100mg.

8.1.4 SAR of α-Glucosidase inhibitors

An extensive search for α-Glucosidase inhibitors from microbial cultures led to the

isolation of acarbose from an actinomycete. Extensive structure activity investigations

revealed that active α-glucosidase inhibitors have a common pharmacophore, comprising a

substituted cyclohexane ring and a 4,6-dideoxy-4-amino-D-glucose unit known as

carvosine. It appears that the secondary amino group of this core structure prevents an

essensial carboxyl group of the α-glucosidase from protonating the glycosidic oxygen

bonds of the substrate. Most recently, screening programs of small molecules have yielded

several other α-glucosidase inhibitors resembling simple amino sugar as miglitol and

voglibose.

Acarbose

Structure


(2R,3R,4R,5S,6R)-5-{[(2R,3R,4R,5S,6R)-5- {[(2R,3R,4S,5S,6R)-3,4-dihydroxy-6-methyl- 5-

{[(1S,4R,5S,6S)-4,5,6-trihydroxy-3- (hydroxymethyl)cyclohex-2-en-1-yl]amino} tetrahydro-2H-pyran-2-

yl]oxy}-3,4-dihydroxy- 6-(hydroxymethyl)tetrahydro-2H-pyran-2-yl]oxy}- 6-(hydroxymethyl)tetrahydro-

2H-pyran-2,3,4-triol


Page 98

Chemical data

FORMULA C25H43NO18



BIOAVAIBILITY Extremely low

METABOLISM Gastrointestinal tract

HALF LIFEca 2 hours

EXECRETION Renal (less than 2%)

ROUTES Oral

It is used in the control and management of Type 2 diabetes mellitus.

Mechanism of Action

The drug, which is obtained from the microorganism Actinoplane utahensis, is

found to a complex oligosaccharide that specifically delays digestion of indigested

carbohydrates, thereby causing in a smaller rise in blood glucose levels soonafter meals. It

fails to increase insulin secretion; and its antihyperglycemic action is usually mediated by

a sort of competitive, reversible inhibition of pancreatic α-amylase membrane-bound

intestinal α-glucosidase hydrolase enzymes. The drug is metabolized solely within the GI

tract, chiefly by intestinal bacteria but also by diagestive enzymes.

Miglitol

Structure


(2R,3R,4R,5S)-1-(2-hydroxyethyl)-2-(hydroxymethyl)piperidine-3,4,5-triol

Chemical data

FORMULA C8H17NO5



BIOAVAIBILITY Dose-dependent


Page 99

PROTEIN BINDING Negligible (<4.0%)

HALF LIFE 2 hours

EXECRETION Renal (95%)

ROUTES Oral

It also lowers blood-glucose level.

Mechanism of Action

It resembles closely to a sugar, having the heterocyclic nitrogen serving as an

isosteric replacement of the ‘sugar oxygen’. The critical alteration in its structure enables

its recognition by the α-glycosidase as a substrate. The ultimate outcome is the overall

competitive inhibition of the enzyme which eventually delays complex carbohydrate

absorption from the ensuing GI tract.

Voglibose

Structure


(1S,2S,3R,4S,5S)-5-(1,3-dihydroxypropan-2-ylamino)-1-(hydroxymethyl)cyclohexane-1,2,3,4-tetraol

Chemical data

FORMULA C10H21NO7


Voglibose (trade name Voglib, marketed by Mascot Health Series) is an alpha-

glucosidase inhibitor used for lowering post-prandial blood glucose levels in people with

diabetes mellitus. Postprandial hyperglycemia (PPHG) is primarily due to first phase

insulin secretion. Alpha glucosidase inhibitors delay glucose absorption at the intestine

level and thereby prevent sudden surge of glucose after a meal. There are three drugs

which belong to this class, acarbose, miglitol and voglibose, of which voglibose is the

newest. Voglibose scores over both acarbose and miglitol in terms of side effect profile.


Page 100

8.2 Amylin

8.2.1 Islet amyloid polypeptide

Figure No. 8.1 Amino acid sequence of amylin with disulfide bridge and cleavage sites of

insulin degrading enzyme indicated with arrows

Amylin, or Islet Amyloid Polypeptide (IAPP), is a 37-residue peptide hormone

secreted by pancreatic β-cells at the same time as insulin (in a roughly 1:100

amylin:insulin ratio).

8.2.2 Pharmacology

Synthetic amylin, or pramlintide (brand name Symlin), was recently approved for

adult use in patients with both diabetes mellitus type 1 and diabetes mellitus type 2. Insulin

and pramlintide, injected separately but both before a meal, work together to control the

post-prandial glucose excursion.

Amylin is degraded in part by insulin-degrading enzyme.

8.2.3 Receptors

There appears to be at least three distinct receptor complexes that bind with high

affinity to amylin. All three complexes contain the calcitonin receptor at the core, plus one

of three receptor activity-modifying proteins, RAMP1, RAMP2, or RAMP3.


Page 101

Pramlintide

Structure

Chemical data




BIOAVAIBILITY 30-40%

PROTEIN BINDING Approximately 60%

METABOLISM Renal

HALF LIFE Approximately 48 minutes

ROUTES Subcutaneous

Pramlintide acetate (Symlin) is a relatively new adjunct treatment for diabetes

(both type 1 and 2), developed by Amylin Pharmaceuticals.

Side effects

The major side effects reported for pramlintide consist of mild to moderate nausea,

with sever nausea appearing in patients using large doses of the drug. The nausea may

decrease on continued use of the drug. The rate of hypoglysemia appears to be quite low.

Design and structure

Since, native human amylin is highly amyloidogenic and potentially toxic, the

strategy for designing pramlintide was to substitute residues from rat amylin, which is not

amyloidogenic (but would presumably retain clinical activity). Proline residues are known

to be structure-breaking residues, so these were directly grafted into the human sequence.

Amino acid sequences:

Pramlintide:KCNTATCATQRLANFLVHSSNNFGPILPPTNVGSNTY-(NH2)

Amylin:KCNTATCATQRLANFLVHSSNNFGAILSSTNVGSNTY-(NH2)

Rat amylin: KCNTATCATQRLANFLVRSSNNFGPVLPPTNVGSNTY-(NH2)


Page 102

8.3 Sodium-glucose transport proteins

Sodium-dependent glucose cotransporters are a family of glucose transporter found

in the intestinal mucosa of the small intestine (SGLT1) and the proximal tubule of the

nephron (SGLT2 and SGLT1). They contribute to renal glucose reabsorption.

Dapagliflozin

Structure


(2S,3R,4R,5S,6R)-2-[4-chloro-3-

(4-ethoxybenzyl)phenyl]-6-(hydroxymethyl) tetrahydro-2H-pyran-3,4,5-triol

Chemical data

FORMULA C21H25ClO6


SYNONYMS (1S)-1,5-anhydro-1-C-{4-chloro-3- [(4-

ethoxyphenyl)methyl]phenyl}-D-glucitol

ROUTES Oral

Dapagliflozin is an experimental drug being studied by Bristol-Myers Squibb in

partnership with AstraZeneca as a potential treatment for type 1 and 2 diabetes. Although

dapagliflozin's method of action would operate on either type of diabetes or other

conditions resulting in hyperglycemia, the current clinical trials specifically exclude

participants with Type 1 diabetes.

Method of action

Dapagliflozin inhibits subtype 2 of the sodium-glucose transport proteins (SGLT2),

which is responsible for at least 90% of the glucose reabsorption in the kidney. Blocking

this transporter causes blood glucose to be eliminated through the urine.


Page 103

Remogliflozin etabonate


5-methyl-4-[4-(1-methylethoxy)benzyl]-1-(1-methylethyl)-1H-pyrazol-3-yl 6-O-(ethoxycarbonyl)-β-D-

glucopyranoside

Chemical data

FORMULA C26H38N2O9


ROUTES Oral

Remogliflozin etabonate is a proposed drug for the treatment of type 2 diabetes

being investigated by GlaxoSmithKline.

Method of action

Remogliflozin inhibits the sodium-glucose transport proteins, which are

responsible for glucose reabsorption in the kidney. Blocking this transporter causes blood

glucose to be eliminated through the urine.

Sergliflozin etabonate


2-(4-methoxybenzyl)phenyl 6-O-(ethoxycarbonyl)-β-D-glucopyranoside

Chemical data

FORMULA C23H28O9


ROUTES Oral

Sergliflozin etabonate is an investigational anti-diabetic drug being developed by

GlaxoSmithKline.

Method of action

Sergliflozin inhibits subtype 2 of the sodium-glucose transport proteins (SGLT2),

which is responsible for at least 90% of the glucose reabsorption in the kidney. Blocking

this transporter causes blood glucose to be eliminated through the urine.


Page 104

9. Other Drugs

Tolrestat

Structure


N-{[6-methoxy-5-(trifluoromethyl)-1-naphthyl]carbothioyl}-N-methylglycine

Chemical data

FORMULA C16H14F3NO3S


Tolrestat is an aldose reductase inhibitor which was approved for the control of

certain diabetic complications.

It was discontinued by Wyeth in 1997 because of the risk of severe liver toxicity

and death. It was sold under the tradename Alredase.

Synthesis of Tolrestat


Page 105

Benfluorex


(RS)-2-({1-[3-(trifluoromethyl)phenyl]propan- 2-yl}amino)ethyl benzoate

Chemical data

FORMULA C19H20F3NO2


EXECRETION Renal

ROUTES Oral

Benfluorex is an anorectic and hypolipidemic agent. Clinical studies have shown it

may improve glycemic control and decrease insulin resistance in people with poorly

controlled type 2 diabetes. It is marketed in France as an adjuvant antidiabetic.

On 18 December 2009 the European Medicines Agency (EMEA) has

recommended the withdrawal of all medicines containing benfluorex in the European

Union, because their risks, particularly the risk of heart valve disease (fenfluramine-like

cardiovascular side-effects), are greater than their benefits. Benfluorex is structurally

related to fenfluramine.

Synthesis of Benfluorex


Page 106

10. Natural antidiabetic agent

10.1 Traditional plant treatments for diabetes

A study was made of the effects on glucose homeostasis in normal

and streptozotocin (induced) diabetic mice of eleven plants that have been used as

traditional treatments for diabetes. The mice were given diets containing dried leaves from

the following plants: agrimony (Agrimonia eupatoria), alfalfa (Medicago sativa),

blackberry (Rubus fructicosus), celandine (Chelidonium majus), eucalyptus (Eucalyptus

globulus), lady's mantle (Alchemilla vulgaris), and lily of the valley (Convallaria majalis);

seeds of coriander (Coriandrum sativum); dried berries of juniper (Juniperus communis);

bulbs of garlic (Allium sativum) and roots of liquorice (Glycyrhizza glabra). The study

concluded that "The results suggest that certain traditional plant treatments for diabetes,

namely agrimony, alfalfa, coriander, eucalyptus and juniper, can retard the development of

streptozotocin diabetes in mice".

10.2 Mushrooms

Research has shown the Maitake mushroom (Grifola frondosa) has

a hypoglycemic effect, and may be beneficial for the management of diabetes. The reason

Maitake lowers blood sugar is due to the fact the mushroom naturally acts as an alpha

glucosidase inhibitor.Other mushrooms like Reishi, Agaricus blazei, Agrocybe

cylindracea and Cordyceps have been noted to lower blood sugar levels to a certain extent,

although the mechanism is currently unknown.

10.3 Aloe vera

Oral administration of aloe vera might be a useful adjunct for lowering blood

glucose in diabetic patients as well as for reducing blood lipid levels in patients with

hyperlipidaemia. Ten controlled clinical trials were found to reach that conclusion in four

independent literature searches. However, caveats reported in each study led the

researchers to conclude that aloe vera's clinical effectiveness was not yet sufficiently

defined in 1999.


Page 107

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