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CARBOHYDRATES

Presented by; M Pharm (Pharmaceutical Chemistry) students Gunturu .Aparna

Akshintala. Sree Gayatri

Thota. Madhu latha

Kamre. Sunil

Daram. Sekhar

University college of pharmaceutical sciences

Department of pharmaceutical chemistry

Acharya Nagarjuna University

Guntur

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CARBOHYDRATES

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Cells of organisms - plants, fungi, bacteria.

Insects, animals - produce a large variety of organic compounds.

Many substances were obtained anciently, e.g. foodstuffs, building materials, dyes, medicinals, and other extracts from nature.

INTRODUCTION OF NATURAL PRODUCTS:

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Oils & Fats, Terpenoids Prostaglandins Alkaloids, Vitamins Flavanoids Steroids Carbohydrates Lignins lignans Proteins Nucleic acid Antibiotics pigments

EXAMPLES OF NATURAL PRODUCTS

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CARBOHYDRATES

Carbohydrates are the most abundant organic compounds in the plant world.

They act as storehouses of chemical energy (glucose, starch, glycogen); are the components of supportive structures in plants (cellulose), crustacean shells (chitin) and connective tissues in animals (acidic polysaccharides) and are essential components of nucleic acids (D-ribose and 2-deoxy-D-ribose).

Carbohydrates make up about three fourths of the dry weight of

plants. .

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Animals (including humans) get their carbohydrates by eating plants, but they do not store much, what they consume.

Less than 1% of the body weight of animals is made up of carbohydrates. For a photosynthesis, an endothermic reductive condensation of carbon dioxide requiring light energy and the pigment chlorophyll.

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Simple Sugars

MonosaccharidesDisaccharides

Complex Carbohydrates

StarchGlycogenCellulose (a form of fiber)

CLASSIFICATION OF CARBOHYDRATES

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A. Structure and Nomenclature The general formula CnH2nOn

with one of the carbons being the carbonyl group of either an aldehyde or a ketone.

The most common monosaccharides have three to eight carbon atoms.

The suffix-ose indicates that a molecule is a carbohydrate, and the prefixes tri-, tetr-, pent-, and so forth indicate the number of carbon atoms in the chain.

Monosaccharide containing an aldehyde group are classified as aldoses; those containing a ketone group are classified as ketoses.

A ketose can also be indicated with the suffix ulose; thus, a five- carbon ketose is also termed a Pentulose.

Monosaccharides

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Another type of classification scheme is based on the hydrolysis of certain carbohydrates to simpler carbohydrates i.e. classifications based on number of sugar units in total chain.

Monosaccharides: single sugar unit

Disaccharides: two sugar units

Oligosaccharides: 3 to 10 sugar units

Polysaccharides: more than 10 units

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Sucrose (C12H22O11) + H2O acid or certain enzyme Glucose (C6H12O6) + Fructose (C6H12O6)

MonosaccharidesDisaccharides

Monosaccharides cannot be converted into simpler carbohydrates by hydrolysis. Glucose and fructose are examples of monosacchides is Sucrose, however, is a disaccharide-a compound that can be converted by hydrolysis into two monosaccharides.

There are only two trioses: the aldotriose glyceraldehyde and the ketotriose dihydroxyacetone

Glyceraldehyde(an aldotriose)

CHO

CHOH

CH2OH

CH2OH

C

CH2OH

O

Didroxyacetone(a ketotriose)

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We will consider the stereochemistry of carbohydrates by focusing largely on the aldoses with six or fewer carbons.

The aldo hexoses have four asymmetric carbons and therefore exist as 24 or 16 possible stereo isomers.

These can be divided into two enantiomeric sets of eight diastereomers.

B. Stereochemistry and Configuration

HOH2C

OH

HC

OH

HC

OH

HC

HC

OH

CH

O

Aldohexosesfour asymmetric carbons

24 = 16 stereoisomers

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Similarly, there are two enantiomeric sets of four diastereomers (eight stereoisomers total) in the aldopentose series. Each diastereomer is a different carbohydrate with different properties, known by a different name.

The aldoses with six or fewer carbons are given as Fischer projections. Be sure you understand how to draw and interpret Fischer projections, as they are widely used in carbohydrate chemistry.

Each of the monosaccharides has an enantiomer. For example, the two enantiomers of glucose have the following structures: HC

OHH

HHO

OHH

OHH

CH2OH

HC

HO H

H OH

HO H

HO H

CH2OH

O

Enantiomers of glucose

D - L -

O

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It is important to specify the enantiomers of carbohydrates in a simple way.

Suppose you had a model of one of these glucose enantiomers in your hand. You could, of course, use the R,S system to describe the configuration of one or more of the asymmetric carbon atoms.

A different system, however, was in use long before the R,S system was established.

The D,L system, which came from proposals made in 1906 by M. A. Rosanoff, is used for this purpose.

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Glyceraldehydes contains a chiral center and therefore exists as a pair of enantiomers.

C. Fischer Projection Formulas:

Glyceraldehyde is a common name; the IUPAC name for this monosaccharide is 2,3-dihydroxypropanal.

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Chemists commonly use two-dimensional representations called Fischer projections to show the configuration of carbohydrates.

Following is an illustration of how a three-dimensional representation is converted to a Fischer projection.

CHO

CH OH

CH2OH

CHO

C HHO

CH2OH

(R)-Glyceraldehyde (S)-Glyceraldehyde

4 C 3

1

2

4 C 2

1

3

(S) (R)

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The horizontal segments of a Fischer projection represent bonds directed toward you and the vertical segments represent bonds directed away from you. The only atom in the plane of the paper is the chiral center.

CHO

HO H

H OH

H OH

CH2OH

CHO

H OH

HO H

H OH

CH2OH

CHO

HO H

HO H

H OH

CH2OH

CHO

H OH

H OH

H OH

CH2OH

D-(-)-ribose(2R,3R,4R)

D-(-)-arabinose(2S,3R,4R)

D-(+)-xylose(2R,3S,4R)

D-(-)-lyxose(2S,3S,4R)

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CHO

H OH

H OH

CH2OH

CHO

HO H

H OH

CH2OH

D-(-)-Erythrose D-(-)-Threose

CHO

H OH

H OH

H OH

CH2OH

D-(-)-Ribose

H

OH

O

OH

H2C

HO

H

O

OH

H2C

HO

OH

H

OH

O

OH

CH2

OH

HO4

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2(R),3(R),4(R),5-tetrahydroxypentanal

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Even though the R,S system is widely accepted today as a standard for designating configuration, the configuration of carbohydrates as well as those of amino acids and many other compounds in biochemistry is commonly designated by the D,L system proposed by Emil Fischer in 1891.

At that time, it was known that one enantiomer of glyceraldehyde has a specific rotation of + 13.5; the other has a specific rotation of -13.5.

D. D-and L- Monosaccharides:

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Fischer proposed that these enantiomers be designated D and L (for dextro and levorotatory) but he had no experimental way to determine which enantiomer has which specific rotation.

Fischer, therefore, did the only possible thing-he made an arbitrary assignment.

He assigned the dextrorotatory enantiomer an arbitrary configuration and named it D-glyceraldehyde. He named its enantiomer L-glyceraldehyde.

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Fischer could have been wrong, but by a stroke of good fortune he was correct, as proven in 1952 by a special application of X-ray crystallography.

D- and L-glyceraldehyde serve as reference points for the assignment of relative configuration to all other aldoses and ketoses.

CHO

CH OH

CH2OH

D-Glyceraldehyde[]D = +13.5

CHO

C HHO

CH2OH

25L-Glyceraldehyde

[]D = -13.525

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The reference point is the chiral center farthest from the carbonyl group. Because this chiral center is always the next to the last carbon on the chain, it is called the penultimate carbon.

A D-monosaccharide has the same configuration at its penultimate carbon as D-glyceraldehyde (its-OH is on the right when written as a Fischer projection); an L-monosaccharide has the same configuration at its penultimate carbon as L-glyceraldehyde.

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NAMES AND FISCHER PROJECTIONS FOR ALL D- ALDOTETROSES, PENTOSES, AND HEXOSES.

CHO

CH OH

CH2OH

*

D-Glyceraldehyde

CHO

H OH

H OH*

CH2OH

CHO

HO H

H OH*

CH2OH

D-Erythrose D-Threose

CHO

H OH

H OH

H OH*

CH2OH

CHO

HO H

H OH

H OH*

CH2OH

CHO

H OH

HO H

H OH*

CH2OH

CHO

HO H

HO H

H OH*

CH2OH

D-Ribose D-Arabinose D-Xylose D-Lyxose

CHO

OHH

OHH

OHH

OH*H

CH2OH

CHO

HHO

OHH

OHH

OH*H

CH2OH

CHO

OHH

HHO

OHH

OH*H

CH2OH

CHO

HHO

HHO

OHH

OH*H

CH2OH

CHO

OHH

OHH

HHO

OH*H

CH2OH

CHO

HHO

OHH

HHO

OH*H

CH2OH

CHO

OHH

HHO

HHO

OH*H

CH2OH CHO

H OH*

H OH

H OH

HO H

CH2OH

D-Allose D-Altrose D-Glucose D-Mannose D-Gulose D-TaloseD-GalactoseD-Idose

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Three main disaccharides: sucrose maltose

lactose

All are isomers with molecular formula C12H22O11

On hydrolysis they yield 2 monosaccharide. which soluble in water Even though they are soluble in water, they are

too large to pass through the cell membrane.

Disaccharides

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Is a sugar used at home Also known as the cane sugar When hydrolyzed, it forms a mixture of

glucose and fructose

Sucrose

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Formation of sucrose

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Commonly known as malt sugar. Present in germinating grain. Produced commercially by hydrolysis of

starch.

Maltose

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Formation of maltose

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Commercially known as milk sugar. Bacteria cause fermentation of lactose

forming lactic acid. When these reaction occur ,it changes the

taste to a sour one.

Lactose

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Formation of lactose

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Glycosidic linkage between glucose

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Sucrose and maltose will ferment when yeast is added because yeast contains the enzyme sucrase and maltase.

Lactose will not ferment because yeast does not contain lactase.

Fermentation

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The chemical reactions of these sugars can be used to distinguish them in the laboratory.

If you have 2 test tubes containing a disaccharide, C12H22O11.

To determine if it is sucrose lactose or maltose.

We can use the alkaline Cu complex reaction of glucose and the principle of fermentation.

Testing for disaccharides

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Polysaccharides are large molecules containing 10 or more monosaccharide units. Carbohydrate units are connected in one continuous chain or the chain can be branched.

1. Storage polysaccharides contain only -glucose units. Three important ones are starch, glycogen, and amylopectin.

2. Structural polysaccharides contain only -glucose units. Two important ones are cellulose and chitin. Chitin contains a modified -glucose unit

Polysaccharides

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Amylose and amylopectin—starch

Starch is a mixture of amylose and amylopectin and is found in plant foods.

Amylose makes up 20% of plant starch and is made up of 250–4000 D-glucose units bonded α(1→4) in a continuous chain.

Long chains of amylose tend to coil. Amylopectin makes up 80% of plant starch and is

made up of D-glucose units connected by α(1→4) glycosidic bonds.

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Glycogen is a storage polysaccharide found in animals.

Glycogen is stored in the liver and muscles.

Its structure is identical to amylopectin, except that α(1→6) branching occurs about every 12 glucose units.

When glucose is needed, glycogen is hydrolyzed in the liver to glucose.

Glycogen

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Structural Polysaccharides

Cellulose

Cellulose contains glucose units bonded (1→4).

This glycosidic bond configuration changes the three-dimensional shape of cellulose compared with that of amylose.

The chain of glucose units is straight. This allows chains to align next to each other to form a strong rigid structure.

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Cellulose is an insoluble fiber in our diet because we lack the enzyme cellulase to hydrolyze the (1→4) glycosidic bond.

Whole grains are a good source of cellulose.

Cellulose is important in our diet because it assists with digestive movement in the small and large intestine.

Some animals and insects can digest cellulose because they contain bacteria that produce cellulase.

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Chitin

Chitin makes up the exoskeleton of insects and crustaceans and cell walls of some fungi.

It is made up of N-acetyl glucosamine containing (1→4) glycosidic bonds.

It is structurally strong. Chitin is used as surgical thread that

biodegrades as a wound heals. It serves as a protection from water in insects. Chitin is also used to waterproof paper, and in

cosmetics and lotions to retain moisture.

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Polysaccharides

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Heparin: Heparin is a medically important

polysaccharide because it prevents clotting in the bloodstream.

It is a highly ionic polysaccharide of repeating disaccharide units of an oxidized monosaccharide and D-glucosamine. Heparin also contains sulfate groups that are negatively charged.

It belongs to a group of polysaccharides called glycosaminoglycans.