Lecture 33 - Lipids Introduction [Compatibility Mode]

8/3/2019 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)

Lecture 33 - Lipids Introduction [Compatibility Mode]

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