Linolenic

The linolenic acid series, C H2n-602, with three double bonds. 

The unsaturated fatty acids, linoleic [60-33-3] and linolenic [463-40-17, contain two and three double bonds and are considered beneficial components of the diet. The double bond is an essential ingredient for human nutrition when it is in the correct position on the fat molecule. Humans are unable to insert the double bond at the omega-3 and -6 position. Therefore, fatty acids containing double bonds at these positions are essential in the diet, including linoleic and linolenic acids. They are accordingly described as essential fatty acids (EFA) (23). 

Multiply unsaturated linolenic and linoleic acid residues make triglycerides more vulnerable to oxidative degradation than oleic acid which is relatively stable. It is therefore desirable to hydrogenate the most unsaturated residues selectively without production of large quantities of stearic (fully saturated) acid. The stepwise reduction of an unsaturated oil may be visualized as ... 

Additional evidence indirectly supports the reversibiUty of reaction 2. The addition of oxygen to a highly conjugated radical is readily reversible even at 40°C according to a study of the isomerization of methyl linolenate hydroperoxides in the presence of 02 (95). 

Type of oil Palmitic Stearic Olei Linoleic Linolenic Arachidic glc Wijs... 

Homogeneous and heterogenous catalysts which selectively or partially hydrogenate fatty amines have been developed (50). Selective hydrogenation of cis and trans isomers, and partial hydrogenation of polyunsaturated moieties, such as linoleic and linolenic to oleic, is possible. 

Fig. 2. (a) The basis for prostaglandin nomenclature, where the letters A—F and J define principal families (b) defines the side chains for PG derived from dihomo-y-linolenic acid (c) PG2 derived from arachidonic acid and (d), PG derived from eicosapentaenoic acid. 

Detailed accounts of the biosynthesis of the prostanoids have been pubUshed (14—17). Under normal circumstances arachidonic acid (AA) is the most abundant C-20 fatty acid m vivo (18—21) which accounts for the predominance of the prostanoids containing two double bonds eg, PGE2 (see Fig. 1). Prostanoids of the one and three series are biosynthesized from dihomo-S-linolenic and eicosapentaenoic acids, respectively. Concentrations ia human tissue of the one-series precursor, dihomo-S-linolenic acid, are about one-fourth those of AA (22) and the presence of PGE has been noted ia a variety of tissues (23). The biosynthesis of the two-series prostaglandins from AA is shown ia Eigure 1. These reactions make up a portion of what is known as the arachidonic acid cascade. Other Hpid products of the cascade iaclude the leukotrienes, lipoxins, and the hydroxyeicosatetraenoic acids (HETEs). Collectively, these substances are termed eicosanoids. 

Lipids. Representative fatty acid compositions of the unprocessed triglyceride oils found in the four oilseeds are given in Table 4 (see Fats and FATTY oils). Cottonseed, peanut, and sundower oils are classified as oleic—linoleic acid oils because of the high (>50%) content of these fatty acids. Although the oleic and linoleic acid content of soybean oils is high, it is distinguished from the others by a content of 4—10% of linolenic acid, and hence is called a linolenic acid oil. 

The polyunsaturated aliphatic monocarboxyhc acids having industrial significance include sorbic, linoleic, linolenic, eleostearic, and various polyunsaturated fish acids (Table 3). Of these, only sorbic acid (qv) is made synthetically. The other acids, except those from tall oil, occur naturally as glycerides and are used mosdy in this form. 

Shorthand notations have been developed to avoid repetitive systematic names of unsaturated fatty acids. Eor example, linolenic or (7j -9,i7j -12-,i7j -15-octadecatrienoic acid can be represented by 18 3(9, 12, 15 ). The Greek letter A has been used to indicate presence and position of double bonds, eg a fatty acid, but it should never be used in a systematic name. An equally inappropriate but popular designation is derived by counting... 

Conjugation as well as geometric and positional isomerization occur when an alkadienoic acid such as linoleic acid is treated with a strong base at an elevated temperature. CycHc fatty acids result from isomerization of linolenic acid ia strong base at about 250°C (58). Conjugated fatty acids undergo the Diels-Alder reaction with many dienophiles including ethylene, propylene, acryUc acid, and maleic anhydride. 

FIG. 23-36 Product compositions of tbe first-order sequence of fatty acids Linolenic Linoleic Oleic Stearic. 

Fig. 35 Fluorescence scan of the dansyl semicadavende denvatives of 1 behenic acid 2 erucic acid, 3 steanc acid, 4 oleic acid, 5 linoleic acid, 6 linolenic acid...

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