Lipids Anna Drew with grateful acknowledgement for inspirational teaching received at The School of Pharmacy, University of London

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 or ‘fatty esters’ are an important group long chain fatty acid + alcohols eg glycerol

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]

Simple triglyceride (triacylglycerol) all fatty acid groups the same Mixed triglyceride fatty acid groups different more usual in nature -> yields 3 molecules of palmatic acid

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.

Expect a good (fixed) oil to be: most vegetable products contain a high number of triglycerides with unsaturated fatty acids – liquid most animal products – opposite where large number of unsaturated fatty acids readily oxidizes 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 on degree of saturation) leave a permanent grease stain on filter paper

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 methylether and separate them by chain length

Chemical tests solubility freezing point, melting point refractive index (and sometimes optical rotation) density volatile acidity, unsaponifiable matter, acetyl value

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’

Uses readily absorbed through skin protect from entry of water 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 eg peanut oil may contain essential fatty acids (linoleic acid, arachidonic acid required in prostaglandin formation)

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 at 10oC

high iodine value, low acid value Uses 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 of water)

Arachis oil From seeds of Arachis hypogaea (Leguminosae) - groundnut cultivated in tropical Africa, India, Brazil, southern USA and Australia world’s 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

acid and saponification values similar to olive oil 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 melting point >710C used as a test for adulteration of olive oil

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, lubricant industry and pharmacy (as derivatives)

Almond oil From Prunus amygdalus v. amara (bitter – used in pharmacy), v. dulcis (sweet) native to Far East, grown in Mediterranean, N.California Oil is highly unsaturated with oleic acid 77%, linoleic acid 17% 83% GU3, 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

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% GS2U 52% melting point 31-350C low iodine value because saturated most expensive commercial fixed oil (adulterated) Mainly used in suppositories

Animal products Cod and Halibut liver oils Beeswax mixed triglycerides, mainly unsaturated C16-22 acids and 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 of myricyl palmitate (80%) (C15H31OOC30H61) ester:acid ratio value 3.3-4.2 Used in paraffin ointment, plasters and enteric coating

Carnuba wax Spermaceti 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) just above 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 by jojoba oil

Wool fat From the wool of sheep (Ovis aries) Complex composition: esters of cholesteryl and isocholesteryl + estolidic 32-33% esters of normal aliphatic alcohols with fatty acids 48-49% Used as an emollient base for creams and ointments major component of most ointments melting point 30-42oC readily absorbed through skin absorbs twice its own weight in water so makes an emulsion

Extraction enzymes in cells can break down oils in cells some oils highly unsaturated and easily oxidized – heat in air –> rapid oxidation [1] Cold expression [2] Steam treatment + expression [3] Solvent extraction

[1] Cold method Castor beans Olives 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

[2] Steam treatment + expression material left over from [1] undergoes steam treatment 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 paints etc left with high protein+fibre – fed to animals once ricin removed

Cocoa seeds Cod liver and halibut fat is solid so can’t 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 inert atmosphere 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

Spermacetin Wool fat 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

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

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

Monoterpene components Hydrocarbons Alcohols

Aldehydes all produced via the terpenoid pathway Ketones Citral

Esters Oxides

Sesquiterpenes (C15) Hydrocarbons Phenols Phenolic esters Anethole

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

Families Economically only a few family groups are commercially useful [1] Labiatae Lavender, Mentha Sp. large number, tend to hybridise oil occurs in special organs synthesized in glandular trichomes (mint) burst easily releasing oil [2] Umbelliferae Fruits (best if ripe): anise, caraway, fennel, coriander found in “vittae” in the outer layer is characteristic steam distill to remove oils

[3] Pinaceae [4] Rutaceae [5] Lauraceae Pine, juniper Citrus fruits found in resin ducts in outer old xylem or bark released when bark removed [4] Rutaceae Citrus 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] Lauraceae Cinnamon, camphor from region immediately below bark

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 Cold expression citrus fruit oil (lemon, orange, bergamot) rasping process breaks oil sacs in rind pour cold water over and then separate oil and water

Destructive distillation Enfleurage petals (rose) placed between glass sheets covered in sheep or pig fat oil seeps into fat and can be extracted with methanol Destructive distillation produces a different product from the one started with pine and juniper heated to exclude air over aqueous part - wood naphtha (ethanol and crude acetic acid) to attract juniper oil non-aqueous part – resin (pine tar) to attract C5-C20 molecules including monoterpenes like a fractional distillation Menthol and camphor nearly solid at room temperature can isolate by freezing oils out cheaper to synthesize camphor but generally extracted from plants camphor

Uses [1] Flavours & carminatives Labiatae as 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

Rutaceae Umbelliferae Citrus oils Citrus flower 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

[2] Local stimulants and antiseptics (containing phenols) Pinaceae Pinus paulastrus destructive distillation phenol p-cresol Juniperus oxycedrus cadenine Clove Syzygium aromaticum eugenol 82% used on sore teeth to deaden pain Eucalyptus oil 1,8-cineole 70% (sesquiterpene)

[4] Insect repellant, antimating device [3] Perfumes Rose oil Rosa gallica, R. damescena trans-geraneol and isomer cis-nerol Lavender oil Citrus oil [4] Insect repellant, antimating device Citronella oil from grass doesn’t work well [5] Starting materials Turpentine (for synthesis of other compounds)