Lipids

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

2. 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

3. 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]

4. 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

5. 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.

6. 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

7. 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

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

9. 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’

10. 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 • eg peanut oil • may contain essential fatty acids (linoleic acid, arachidonic acid required in prostaglandin formation)

11. 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

12. 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)

13. 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

14. 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

15. 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)

16. Almond oil • FromPrunus 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

17. 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

18. Animal products • Cod and Halibut liver oils • 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

19. 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) 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

20. 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

21. 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

22. [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

23. [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

24. Cocoa seeds • 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

25. 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

26. 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

27. 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

28. Monoterpene components • Hydrocarbons • Alcohols

29. Aldehydes • all produced via the terpenoid pathway • Ketones Citral

30. Esters • Oxides

31. Sesquiterpenes (C15) Hydrocarbons Phenols Phenolic esters Anethole

32. 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

33. 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

34. [3] Pinaceae Pine, juniper • 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

35. 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

36. 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

37. Uses 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

38. 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

39. [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)

40. [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)