1. Hydrocarbons and derivatives
Pharmacognosy I
Mosul University/ College of Pharmacy
L.A. Dilbreen Barzanji

2. Hydrocarbons and derivatives
Hydrocarbons contain carbon and hydrogen only and, from these by the addition of functional groups and by interaction, all other natural compounds can theoretically be derived.
In particular class of compounds such as volatile oils, the components of any one member may be synthetically related (e.g. menthol and menthone in oil of peppermint) although because of their different functional groups they may undergo different sets of chemical reactions and posses different pharmacological properties.
Among most common functional groups are carboxylic acids, alcohols, ketones, aldehydes and phenols; biochemical interactions produce esters, lactones etc.

3. Monobasic acids
Organic acids posses one or more carboxyl groups and a monobasic acid may be represented as RCOOH.
The high frequency of the biochemical occurrence of the carboxyl group means that acids are found in all living organisms and as derivatives of all the major metabolic groups.

4. 1- C1-C6 monocarboxylic acids
In the free state they are not found abundantly in nature but occur scattered throughout the plant kingdom in the esterified form as a feature of some volatile oils, resins, fats, coumarin derivatives and alkaloids.
e.g. formic acid, acetic acid, propionic acids, etc.

6. 2- Fatty acids
These acids are important as components of plant oils (acyl lipids) in which they occur as esters with the trihydric alcohol glycerol.
Most are C10-C20 straight-chain monocarboxylic acids with an even number of carbon atoms.
Over 200 have been isolated from natural sources but relatively few are ubiquitous in their occurrence. They may be saturated (e.g. palmitic or stearics) or unsaturated (e.g. oleic acid).
Less commonly they are cyclic compounds such the prostaglandins.
The characteristic acid of castor oil, ricinoleic acid (hydroxyoleic acid) has both a hydroxyl group and an unsaturated double bond.
The polyunsaturated acids have received much attention in recent years both regarding their role in dietary fats and as medicinal.

8. 3- Aromatic acids
Two common aromatic acids are benzoic acid and cinnamic acid (unsaturated side chain), which are widely distributed in nature and often occur free and combined in considerable amounts in drugs such as balsams.
Truxillic acid, a polymer of cinnamic acid, occurs in coca leaves.
Other related acids of fairly common occurrence are those having Phenolic or other groupings in addition to a carboxyl group; such are: salicylic acid (o-hyrdoxy benzoic acid). Similarly derived from cinnamic acid, one finds caffeic acid (p-hydroxy cinnamic acid).
Acids having an alcohol group example is shikimic acid, an important intermediate metabolite. Shikimic acid has itself acquired recent pharmaceutical importance as the starting material for the semisynthesis of the antiviral drug oseltamivir (Tamiflu®) for use against bird infections in human.

10. Dibasic and Tribasic acids
Oxalic acid, (COOH)2, forms the first of a series of dicarboxylic acids which include malonic acid, CH2(COOH)2, and succinic acid, (CH2)2(COOH)2. Closely related malonic acid is the unsaturated acid fumaric acid, COOH-CH=CH-COOH.
Malic acid contains an alcohol group and has the formula COOH-CH2-CHOH-COOH. It is found in fruits such as apples and tamarinds.
The tribasic acids, citric, isocitric and aconitic are closely related to one another.
Citric acid is abundant in front juices. It forms part of the Kreb’s cycle.

12. Alcohols
Alcohols posses one or more hydroxyl groups and exist naturally in either the free state or combined as esters.
The are classed according to the number of hydroxyl groups presents: monohydric, dihydric, trihydric and polyhydric-four or more.
The remainder of the molecule may be saturated, unsaturated, aliphatic or aromatic.

13. Monohydric aliphatic alcohols
Lower members of the series are found principally combined as esters e.g. methyl salicylate in oil of wintergreen and methyl and ethyl esters responsible for some fruit aromas.
Esterified long-chain alcohols are constituents of some pharmaceutically important animal waxes and include cetyl alcohol (C16H33OH), ceryl alcohol (C26H53OH) and mericyl alcohol (C30H61OH). Such alcohols are also participate in the formation of esters which are constituents of leaf waxes, e.g. Carnuba wax which contain merocyl cerotate.

14. Monohydric terpene alcohols
These are alcohols associated with that large group of compounds which arise from mevalonic acid and have isoprene as a fundamental structural unit.
Pharmacognistically they are particularly evident as constituents of volatile oils namely:
Non-cyclic terpene alcohols e.g. geraniol in rose
Monocyclic terpene alcohol e.g. menthol in peppermint oil
Dicyclic terpene alcohol

15. Monohydric aromatic alcohol
Benzyl alcohol and cinnamyl alcohol occur both free and as esters of benzoic and cinnamic acids in balsams such as Tolu and Peru balsams.

16. Dihydric alcohols
Dihydric alcohols or glycols are compounds containing two hydroxyl groups.
The dihydric alcohol panaxadiol is component of ginseng (panax) plant.

17. Trihydric alcohols
An important example is glycerol, an essential component of fixed oils and fats.

18. Polyhydric aliphatic alcohols
They are alcohols with four or six hydroxyl groups.
Such as the hexahydric sugar alcohol (e.g. sorbitol, mannitol).

19. Esters
Many types of esters are known, and those formed by an acetylation of an alcoholic group are very common and are found in many biosynthetic groups of metabolites including volatile oils, e.g. linalyl acetate in lavender.
Esters which invlolve aromatic acids such as benzoic and cinnamic acids with corresponding alcohols are sometimes found associated with free acids, other volatile metabolites and resins, in such products as balsams.
A number of alklaoids (e.g. atropine and reserpine) are esters.

20. A particular important group of esters from the pharmaceutical viewpoint is that compromising the lipids or fatty esters. These involves a long-chain fatty acid of type described earlier and alcohol such as glycerol and the higher monohydric alcohols.
The term ‘lipid’ includes not only fixed oils, fats and waxes (simple lipids), but also phosphatides and lecithins (complex lipids), which may contain phosphorus and nitrogen in addition to carbon, hydrogen and oxygen.

21. Fats and fixed oils
As agricultural crops, seeds used for the extraction of fixed oils rate in importance second only to cereals.
Fixed oils are also obtained from fruit pericarps.
A naturally occurring mixture of lipids such as olive oil or oil of theobroma may be either liquid or soild and the terms ‘oil’ and ‘fat’ have, therefore, no very precise significance.
Coconut oil , for example, leave the tropic as an oil and arrive in western Europe as solid.
Even an oil such as olive oil will largely solidify in cold weather.

22. In general, acylglycerols involving saturated fatty acids are solid and those of unsaturated acids are liquids.
When both types are present, as in crude cod-liver oil, cooling results in the deposition of saturated acylglycerols such as stearin. In most medicinal cod-liver oils these solid materials are removed by freezing and filtration.

23. Waxes
The term ‘wax’ applied to those natural mixtures containing appreciable quantities of esters derived from higher monohydric alcohols of the methyl alcohols series combined with fatty acids.
In this series of alcohols the members change from liquids to solids, become less soluble and have higher melting points with increase in molecular weight. The first solid of the series is dodecyl alcohol, C12H25OH.
Waxes include vegetable products such as carnauba wax and animal products such as spermaceti, bees wax and ‘wool-fat’.

24. Although waxes are abundant in nature, a limited number only are of commercial importance.
An important practical difference between fats and waxes is that fats may be saponified by means of either aqueous or alcoholic alkali but waxes are only saponified by alcoholic alkali.
This fact is used for detection of fats when added as adulterants to waxes (e.g. for detecting the fat ‘Japan wax’ as an adulterant in beeswax).