Dihydromalvalic acid

Figure 5.1 Structures of naturally occurring cyclic fatty acids. I, Cyclopropane acids a, 9,10-methylenehexadecanoic acid b, 11,12-methyleneoctadecanoic (lactobacillic) acid c, 8,9-methy-leneheptadecanoic (dihydromalvalic) acid d, 9,10-methyleneoctadecanoic (dihydrosterculic) acid. II, Mycolic (2-alkyl-3-hydroxy) acid. Ill, Cyclopropene acids a, 9,10-methyleneoctadec-9-enoic (sterculic) acid b, 8,9-methyleneheptadec-8-enoic (malvalic) acid. IV, Cyclopentenyl acids a, ll-cyclopent-2-enyl-undecanoic (hydnocarpic) acid b, 13-cyclopent-2-enyl-tridecanoic (chaulmoogric) acid c, 13-cyclopent-2-enyl-tridec-6-enoic (gorlic) acid. V a, 11-cyclohexyl-undecanoic acid b, 11-cycloheptylundecanoic acid.

While the transformation of oleic acid to dihydrosterculic acid and desaturation of the latter to sterculic acid were clearly established, the route of biosynthesis of the homologous cyclopropanoid and cyclopropenoid fatty acids could not be deduced from the results of experiments with seedlings and seed slices (Johnson et al., 1967 Hooper and Law, 1965). It appeared likely that dihydromalvalic acid was the immediate precursor of malvalic acid (Johnson et al., 1967), but it was not apparent whether dihydromalvalic acid was formed from a heptadecenoic acid or by a-oxidation of dihydrosterculic acid. The latter possibility appeared more likely in view of the labeling pattern of sterculic and malvalic acids isolated from H. syriacus seedlings that had been incubated with [l- C]acetate (Smith and Bu Lock, 1964). 

From the results obtained with callus cultures it was concluded, though not unequivocally established, that a-oxidation of dihydrosterculic to dihydromalvalic acid, and of stercuiic to malvalic acid, occurred without activation of the cyclopropanoid and cyclopropenoid fatty acids (Yano et al., 1972a). It appears that a-oxidation is the major or even the only pathway for the oxidation of fatty acids in these callus cultures (Yano et al., 1972a). 

Figure 5.14. Analysis of kapok seed oil methyl esters after reaction with silver nitrate in anhydrous methanol, on a glass WCOT column coated with Carbowax 20M, maintained at 190°C with hydrogen as carrier gas [99]. Abbreviations 18 CA, dihydromalvalic acid 19 CA, dihydrosterculic acid 18 CM, methoxy derivatives of malvalic acid 19 CM, methoxy derivatives of sterculic acid 18 CC, enone derivatives of malvalic acid 19 CC, enone derivatives of sterculic acid. (Reproduced by kind permission of the authors and of Analytical Chemistry, and redrawn from the original paper).

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