Fatty acids, long-chain commonly occurring forms

Figure 12.5 Cholesterol ester. Cholesterol is a derivative of the cyclopentanoper-hydrophenanthrene condensed ring system and is therefore a member of the group of compounds called steroids. It often occurs esterified at position 3 with a long chain fatty acid, which may be saturated or unsaturated and commonly contains 16 or 18 carbon atoms. Steroids that form esters in this way are more correctly called sterols.

In general, acid chlorides and acid anhydrides are too reactive to occur naturally, and nitriles are rare in nature. Esters and amides, on the other hand, are very common. Many esters have pleasant odors, often sweet or fruity, and are responsible for the fragrant odors of fruits and flowers. They are components of many flavorings, both natural and artificial. For example, isopentyl acetate has a strong banana odor, and methyl bu-tanoate is used as an artificial rum flavoring. Typical fats are triesters formed from long-chain fatty acids and the triol glycerol. 

A common chemical property of polyunsatured fatty acids, which are needed to maintain animals in healthy condition, seems to be cis double bonds at the w6 and w9 positions [14]. Important essential fatty acids in the diet are linoleic (18 2w6) and a-linoleic (18 3w3) acids, which both occur in plants. In the mammalian organism, these fatty acids can be desaturated and elongated to form the derived essential fatty acids, dihomo-y-linolenic acid (20 3w6), arachidonic acid (20 4 6) and timnodonic acid (20 5to3), the three precursor acids of prostaglandins (Fig. 2, see also Fig. 11). The derived essential fatty acids can also be obtained in the diet. Arachidonic and dihomo-y-linolenic acids occur in animal tissues timnodonic acid in fish. The mammalian organism cannot introduce double bonds at the co3 and <06 positions of long-chain fatty acids, which partly explains why fatty acids of the w3 and w6 series must be provided in the diet (see refs. 15-18 for reviews). These fatty acids are also essential to man, however, deficiency states can only be induced by... 

Fats have another important commercial value based on their abihty to react with sodium hydroxide, NaOH, commonly known as lye. When a fat combines with NaOH, an add-base reaction caiied saponification occurs, and a sait and water form. This salt is made up of molecules that have long carboxyhc acid chains and is called soap. A molecule of soap has a charged ionic head and a nonpolar hydrocarbon tail. This structure allows the ionic head of a soap molecule to dissolve in water and the nonpolar tail to dissolve in nonpolar greases. This property gives the soap its cleaning ability. The chemistry of this reaction is also used as a way of classifying Upids. Lipids that react with a base to form soap are caUed saponifiable lipids, which include fats, oils, and fatty acids. 

E,aphylla wax contained triterpenoids in amounts of 31%,beside the common wax lipids. In this wax the alcohols -amyrin, a-amyrin,lupeol and also simiarenol were found. With the exception of simiarenol the first triterpenols occured free as well as esterified with long chain fatty acids and with acetic acid,too,and they were found also in form of their ketones. The publications of further Euphorbia wax triterpenoids are in preparation. All Euphorbia waxes show qualitative and quantitative species specific compositions of triterpenoids,which are not in agreement with triterpenoids described from the latex in most cases (2). 

---