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Hydrocarbons and derivatives
Pharmacognosy I
Mosul University/ College of Pharmacy
L.A. Dilbreen Barzanji
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.
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.
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.
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.
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.
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.
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.
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.
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:
1. Non-cyclic terpene alcohols e.g. geraniol in rose
2. Monocyclic terpene alcohol e.g. menthol in
peppermint oil
3. Dicyclic terpene alcohol
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.
Dihydric alcohols
• Dihydric alcohols or glycols are compounds
containing two hydroxyl groups.
• The dihydric alcohol panaxadiol is component
of ginseng (panax) plant.
Trihydric alcohols
• An important example is glycerol, an essential
component of fixed oils and fats.
Polyhydric aliphatic alcohols
• They are alcohols with four or six hydroxyl
groups.
• Such as the hexahydric sugar alcohol (e.g.
sorbitol, mannitol).
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.
• A particular important group of esters from the
pharmaceutical viewpoint is that compromising
the lipids or fatty esters. These involves a longchain 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.
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.
• In general, acylglycerols involving saturated
fatty acids are solid and those of unsaturated
acids are liquids.
• When both types are present, as in crude codliver 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.
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’.
• 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).