lecture 33 - lipids introduction [compatibility mode]
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PHARM. DChemical Pharmacognosy- I
Lecture 33May 25th, 2011
LIPIDSINTRODUCTION
M.M. AhsanAhsan KhalidKhalid,, B.PharmB.Pharm, Pharm. D, Pharm. DM.PhilM.Phil Scholar (RIPS/RIU)Scholar (RIPS/RIU)
HIPSHIPS--HUKICHUKIC
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LIPIDS
Simple: fixed oils, fats, waxes
Complex: Phosphatides, lecithins may contain P, N as well as C, H, O
widely distributed in plant and animal kingdom in all living cells
sometimes accumulate to be commercially useful plants - food reserve (fruit and seeds)
animals insulation, energy sources, protection
Lipids are a broad group of naturally occurring moleculeswhich includes fats, waxes, sterols, fat-soluble vitamins (suchas vitamins A, D, E and K), monoglycerides, diglycerides,phospholipids, and others. The main biological functions of
lipids include energy storage, as structural components of cellmembranes, and as important signaling molecules.
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Fixed oils & fats
Esters of glycerol: 3 fatty acids may be involved => triglyceride (main
component of oils and fats) some may exist as free acids
[Fish oils may have 12 fatty acids which vary]
Any substance that is liquid at ambienttemperatures and is hydrophobic but soluble inorganic solvents.Oils have a high carbon and hydrogen content andare nonpolar substances.
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Simple triglyceride (triacylglycerol)
all fatty acid groups the same
-> yields 3molecules ofpalmatic acid
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Saturated or unsaturated:
unsaturated acids: oleic, linoleic, linolenic, palmitolinic
saturated acids: palmitic, myristic, stearic
Fatty acid content determines properties
large amount of saturated -> solid at room temp.
large amount of unsaturated -> liquid at room temp.
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most vegetable products contain a high number oftriglycerides with unsaturated fatty acids liquid
most animal products opposite
where large number of unsaturated fatty acids readilyoxidizes
eg whale, fish oils, linseed
Expect a good (fixed) oil to be:
odourless, tastleless and non-volatile
soluble in a lipid solvent
fairly readily air-oxidized -> rancid oil (depending ondegree of saturation)
leave a permanent grease stain on filter paper
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Determination of structure
By hydrolysis or saponification in 2 ways:
i) Alkaline hydrolysis with KOH splits triacylglycerol into parent glycerol and releases all
fatty acids
arrangement of fatty acids is unknown ii) Can use an enzyme (pancreatic lipase)
hydrolyses two outer glycerides
and then remove final group with KOH
Detecting fatty acids
GLC not volatile so have to form a methyletherand separate them by chain length
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Chemical tests solubility
freezing point, melting point
refractive index (and sometimes optical rotation)
density
volatile acidity, unsaponifiable matter, acetyl value
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Waxes
Wax refers to a class of chemical compounds that are plasticnear ambient temperatures. Characteristically, they melt above45 C (113 F) to give a low viscosity liquid. Waxes are insolublein water but soluble in organic, nonpolar solvents
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Waxes
contain appreciable quantities of esters derived from higher monohydric alcohols (one OH
group) of the methyl (1y) alcohol series
combined with fatty acids (C16 C32)
Most are solids at room temperature can only be saponified by alcoholic alkali
often contain free acids, hydrocarbons, free alcohols and sterols
saponification and acid values higher, iodine values lower
Commercially important examples Vegetable: carnuba
Animal: spermaceti, beeswax, wool fat
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Uses
Readily absorbed through skin ointments
Protect from entry of water eg cod liver oil, linseed oil
Vehicles for injections
Waxes in enteric coatings
Pharmacological substances vitamin A and D in cod liver oil
Food source E.g peanut oil
may contain essential fatty acids (linoleic acid, arachidonic acidrequired in prostaglandin formation)
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EXAMPLES: Olive oil
salad oil, sweet oil
From ripe fruits of Oleo europoea(Oleaceae)
Mediterranean, California native of Palestine, known in Egypt in 7th
century B.C., introduced into Spain early on
pale yellow with greenish tinge
(chlorophyll and carotene)
bland, slight odour, goes pasty/cloudy at10oC
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tested for absence of arachis oil, cotton-seed oil, sesame
oil, peanut oil and tea-seed oil (Camellia sasanqua)
Composition:
high iodine value, low acid value
Uses salad oil, soaps, plasters
manufacture of parenteral preparations (low acid value, free ofwater)
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Arachis oil
From seeds of Arachis hypogaea(Leguminosae) -groundnut
cultivated in tropical Africa, India, Brazil, southern USA
and Australia worlds 4th largest source of a fixed oil
seeds contain 40-50% oil
fruits shelled by a machine kernels difficult to express; crushed and cooked at low
pressure seed cake fed to cattle
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Composition:
oleic acid ~ 60% linoleic acid 24% palmitic acid 9% arachidonic acid
GU3, GSU2 like olive oil
acid and saponification values similar to olive oil
if fatty acids are separated (hydrolysis) the
presence of arachidonic acid gives a meltingpoint >710C used as a test for adulteration of olive oil
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Castor oil
From seeds of Ricinus communis(Euphorbiaceae)
India, Africa, Europe
Contains ricinoleic acid 91%, glycerides GU3 must be free of ricin
pale yellow, very viscous, acrid tasting
soluble in ethanol (unlike most oils) due to so much
hydroxy- acid
Used in toothpaste, nail varnish remover, lubricantindustry and pharmacy (as derivatives)
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Almond oil
From Prunus amygdalus v. amara(bitter used inpharmacy), v. dulcis(sweet)
native to Far East, grown in Mediterranean, N.California
Oil is highly unsaturated with oleic acid 77%, linoleic acid 17% 83% GU 3, 17% GSU2
Bitter almond oil also contains amygdalin (glycoside)
which decomposes to benazldehyde + HCN
Used in pharmacy in oily injections and ointments prone to oxidation so has to be kept air-free or goes rancid
transfer to smaller bottle to exclude air
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Theobroma oil
Cocoa butter
From seeds of Theobroma cacao(Sterculaceaea)
Central America, also cultivated in Brazil, W.Africa(Nigeria)
Solid oil
high steric and palmitic acid content (35%, 25%), oleic acid 3% melting point 31-350C low iodine value because saturated most expensive commercial fixed oil (adulterated)
Mainly used in suppositories
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Animal products
Cod and Halibut liver oils
mixed triglycerides, mainly unsaturated C16-22 acidsand decahexanoic acid
Used for Vitamin A and D content (halibut > cod)
Beeswax
yellow and white from honeycomb
simple esters of 1y alcohols with a high degree ofmyricyl palmitate (80%) (C15H31OOC30H61)
ester:acid ratio value 3.3-4.2
Used in paraffin ointment, plasters and enteric coating
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Carnuba wax
an adulterate of beeswax From the cuticle of the South American palm
Copenicia cerifera
Used in tablet coatings
Spermaceti
From the head of sperm (Physeter macrocephalus)and bottle-nosed whales (Hyperodon rostratus) justabove right nostril) 500lb from 1 whale
simple esters of cetyl alcohol CH3(CH2)4CH2OH cetyl palmitate, cetyl myistate 90-93%
no longer used pharmaceutically, can be replaced byjojoba oil
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Wool fat
From the wool of sheep (Ovis aries) Complex composition:
esters of cholesteryl and isocholesteryl + estolidic32-33%
esters of normal aliphatic alcohols with fatty acids48-49%
Used as an emollient base for creams andointments
major component of most ointments
melting point 30-42oC
readily absorbed through skin
absorbs twice its own weight in water so makes anemulsion
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Extraction
enzymes in cells can break down oils in
cells
some oils highly unsaturated and easilyoxidized heat in air > rapid oxidation
[1] Cold expression
[2] Steam treatment + expression
[3] Solvent extraction
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[1] Cold method
Castor beans
roll to break down testa winnow to separate seed coat from seed
Olives
put into press light pressure applied
gives the 1st
grade oil used in pharmacy oil washed to remove pigment floats to the top and is skimmed off 30-40% oil recovered not economical
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[2] Steam treatment + expression
material left over from [1] undergoes steamtreatment repressed to get 2nd fraction of oil
[3] Solvent extraction
to get 100% of oil out
last portion gives a low grade used to industrial paintsetc
left with high protein+fibre fed to animals once ricinremoved
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Cocoa seeds
fat is solid so cant cold express use hot expression with steam treatment oil is a byproduct of the cocoa industry
Cod liver and halibut
livers heated by steam process in an inertatmosphere mixture separated by centrifugation oil dried in drying towers gives a clear bright highly refined oil
cooled to 0oC to remove saturated stearic fats leaves polyunsaturated triglycerides standardised for vitamin content stored in airtight containers in the dark
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Spermacetin
ensure well separated from normal triglycerides
washed with alkali
Wool fat has to be cleaned up
acidified to precipitate waxes
free fatty acids removed by forming salts
wax extracted with acetate product can be bleached to give light yellow colour or
left as dark yellow wax
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Volatile oils
A concentrated hydrophobic liquid containing volatile aroma compoundsfrom plants. Essential oils are also known as volatile oils, ethereal oils oraetherolea, or simply as the "oil of" the plant from which they wereextracted, such as oil of clove. An oil is "essential" in the sense that itcarries a distinctive scent, or essence, of the plant.
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Volatile oils
different from fixed
components of plants that are highly odiferous
generally occur as they are
secreted in oil cells in specialised structures ducts, cavities, glandular hairs
frequently associated with other substances gums, resins (resinify on exposure to air)
mainly terpenoid some phenol ethers and phenols
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Terpenoids
based on the 5C isoprene unit
Monoterpenes
most important, most volatile
di-, tri-, sesquiterpenes also important
contain 2 condensed 5C units head-tail most formed from geranyl pyrophosphate
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Monoterpene components
Hydrocarbons
Alcohols
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Aldehydes
all produced via the terpenoid pathway
Ketones
Citral
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Esters
Oxides
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Sesquiterpenes (C15)
Class of terpenes that consist of three isopreneunits
Hydrocarbons Phenols Phenolic
esters
Anethole
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Chemical and physical properties
volatile liquids with no colour keep in amber bottles with minimum air
odour
asymetric centres, isomers with optical activity only one isomer occurs naturally
refractive index normally high is a means to characterise the oil
miscible in water and soluble in organic solvents
more soluble if contains OH fatty acids reasonably heat stable
can be steam distilled
tend to be used as solvents for resins
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Families
Economically only a few family groups arecommercially useful
[1] LabiataeLavender, Mentha Sp.
large number, tend to hybridise oil occurs in special organs
synthesized in glandular trichomes (mint)
burst easily releasing oil
[2] UmbelliferaeFruits (best if ripe): anise, caraway, fennel, coriander
steam distill to remove oils
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[3] PinaceaePine, juniper
found in resin ducts in outer old xylem or bark released when bark removed
[4] RutaceaeCitrus fruits
typical ductless sacs in outer part of fruit rind found at various depths before albino layer (white bitter pithy
part) oil is there under pressure and will burst open when rasped less stable, need more care
[5] LauraceaeCinnamon, camphor from region immediately below bark
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Method of extraction
Depends where oils lies and its stability
Steam distillation gentle, herb + water heated and oil
distilled over
Water distillation wood chips in chamber and heated until
water distills over crushed sample must be stable
Raw plant material, consisting ofthe flowers, leaves, wood, bark,roots, seeds, or peel, is put intodistillation apparatus over water.
As the water is heated, thesteam passes through the plantmaterial, vaporizing the volatilecompounds.
The vapors flow through a coil,
where they condense back toliquid, which is then collected inthe receiving vessel.
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Solvent extractionMost flowers contain too little volatile oil to undergoexpression and their chemical components are too delicateand easily denatured by the high heat used in steamdistillation.Instead, a solvent such as hexane or supercritical carbondioxide is used to extract the oils. Extracts from hexaneand other hydrophobic solvent are called concretes, whichare a mixture of essential oil, waxes, resins, and other
lipophilic (oil soluble) plant material.
Cold expressionMost citrus peel oils are expressed mechanically, or cold pressed(similar to olive oil extraction).
Due to the relatively large quantities of oil in citrus peel and low costto grow and harvest the raw materials, citrus-fruit oils are cheaperthan most other essential oils.
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Usesas inhalations, orally, gargles, mouthwashes, trans-dermally
[1] Flavours & carminatives
Labiatae Mentha piperita(peppermint oil)
50-75% menthol, also contains menthone etc used mainly in toothpastes
Mentha spicata(spearmint oil) 50-75% L-carvone some minor components similar to peppermint but major
components differ giving different smell and taste Lavendura officinalis(lavender oil)
35-45% linalyl acetate, also geraniol, limonene, cineole some varieties have a lower % so other compound
characteristics dominate growing environment will affect quality
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Rutaceae
Citrus oils D-limonene 90%, citral 4% + esters, pinene, d-limonene (small
amount) high proportion of limonene desirable but a lot is removed after isolation by distillation under
reduced pressure leaves oil high in citral which deteriorates on storage giving
a turpentine odour
Citrus flower oils no citral, other constituents that give a different odour and
flavour of orange flower oil used in confectionary
Umbelliferae
Pimpinella anisum(anise), Foeniculum vulgare(fennel) 90% anethole some fennel variaties contain fenchone giving a bitter taste
Carum carvi(carraway) carvone
Coriandum sativum(coriander) 60-80% linalool
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[2] Local stimulants and antiseptics(containing phenols)
Pinaceae
Pinus paulastrus
destructive distillation
phenol p-cresol
Juniperus oxycedrus cadenine
CloveSyzygium aromaticum
eugenol 82%
used on sore teeth to deaden pain
Eucalyptus oil 1,8-cineole 70%
(sesquiterpene)
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[3] Perfumes
Rose oil
Rosa gallica, R. damescena trans-geraneol
and isomer cis-nerol
Lavender oil
Citrus oil
[4] Insect repellant
Citronella oil from grass
[5] Starting materials
Turpentine (for synthesis of other compounds)