Methyl ricinoleate (
1) was treated with bromine and the dibromo derivative (
2) was reacted with ethanolic KOH under ultrasonic irradiation to give 12-hydroxy-octadec-9-ynoic acid upon acidification with
dil. HCl. The latter compound was methylated with BF
3/methanol to give methyl 12-hydroxy-octadec-9-ynoate (
3). Compound
3 was treated with methanesulfonyl chloride in the presence of triethylamine in CH
2Cl
2 to give methyl 12-mesyloxy-octadec-9-ynoate (
4). Reaction of methyl 12-mesyloxy-octadec-9-ynoate with aqueous KOH under ultrasonic irradiation (20 kHz) gave (11
E)-octadecen-9-ynoic acid (
5, santalbic acid, 40%) and (11
Z)-octadecen-9-ynoic acid (
6, 60%) on acidification with dil. HCl. These isomers were separated by urea fractionation. The
13C nuclear magnetic resonance (NMR) spectroscopic properties of the methyl ester and the triacylglycerol (TAG) esters of these
enynoic fatty acid isomers were studied. The carbon shifts of the unsaturated carbon nuclei of the methyl ester of the
E-isomer were unambiguously assigned as 88.547 (C-9), 79.287 (C-10), 109.760 (C-11), and 143.450 (C-12) ppm while the unsaturated
carbon shifts of the (
Z)-enynoate isomer appeared at 94.277 (C-9), 77.561 (C-10), 109.297 (C-11), and 142.668 (C-12) ppm. In the
13C NMR spectral analysis of the TAG molecules of type AAA containing either the (
Z)-or (
E)-enyne fatty acid, the C-1 to C-6 carbon atoms on the α- and β-acyl positions were differentiated. The unsaturated carbon
atoms in the α- and β-acyl chains were also resolved into two signals except that of the C-11 olefinic carbon. Sandal (
Santalum album) wood seed oil (a source of santalbic acid) was separated by silica chromatography into three fractions. The least polar
fraction (7.2 wt%) contained TAG which had a random distribution of saturated and unsaturated fatty acids, of which oleic
acid (69%) was the predominant component. The second fraction (3.8 wt%) contained santalbic acid (58%) and oleic acid (28%)
together with some other normal fatty acids. Santalbic acid in this fraction was found in both the α- and β-acyl positions
of the glycerol “backbone”. The most polar fraction (89 wt%) consisted of TAG containing santalbic acid only. The distribution
of the various fatty acids on the glycerol “backbone” was supported by the results from the
13C NMR spectroscopic analysis.
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