Abstract
Abstract A polar fatty acid has been observed as a component of an ornithine-containing lipid of Thiobacillus thiooxidans. A comparison of thin layer chromatographic mobilities of reference compounds to those of the natural acid and its derivatives suggested that the acid was a 2-hydroxy fatty acid. The presence of a cyclopropane function in the acid was indicated by 14C-labeling experiments and infrared spectroscopy. Mass spectrometry of the methyl ester and the acetylated methyl ester of the natural acid provided a molecular weight for the acid. Equivalent chain lengths were determined for the natural acid, the acid obtained by oxidative decarboxylation of the natural acid with permanganate, and the acids derived through reductive ring cleavage of the cyclopropane group in the ester of the oxidatively decarboxylated natural acid. The mass spectral data, the equivalent chain length determinations, and the permanganate oxidation study clearly indicated that the acid possessed an 18-carbon chain with a methylene bridge and a 2-hydroxyl function. The equivalent chain length determinations further suggested that the cyclopropane group had the cis configuration. Mass spectrographic analysis of the branched chain esters obtained by reductive cleavage of the ester which was in turn derived through oxidative decarboxylation of the natural acid allowed the assignment of the 11,12 position for the cyclopropane group. Based on these data, the polar acid is proposed to be cis-11,12-methylene-2-hydroxyoctadecanoic acid.
Highlights
Chromatogruphic Isolation and Characterization-When subjected to methanolysis, the ornithine-containing lipid of T. thiooxidans yielded a diethyl ether-soluble product (I) which exhibited thin layer chromatography properties that were identical to those of methyl esters of 2-hydroxy fatty acids
Adding 5.4 units for the acetoxy group, 1.Ounit for the carbon atom lost through decarboxylation, and 18.8 for this acid, one obtains 25.2 units. This value is identical to the equivalent chain length determined for the acetylated derivative of methyl-HFA. These results provided strong evidence for the conclusion that HFA is a 2-hydroxy fatty acid and indicated that olefinic linkages were absent in the molecule, since no dicarboxylic acids were detected among the oxidation products
The presence of a ring structure such as a cyclopropane group in HFA seemed quite certain since the indicated molecular weights were two mass units less than that expected for a saturated, 19-carbon normal or branched chain, hydroxy, or acetoxy fatty acid
Summary
Chromatogruphic Isolation and Characterization-When subjected to methanolysis, the ornithine-containing lipid of T. thiooxidans yielded a diethyl ether-soluble product (I) which exhibited thin layer chromatography properties that were identical to those of methyl esters of 2-hydroxy fatty acids. The 2-acetoxy group appears to increase the equivalent chain length of normal fatty acid methyl esters by 5.4 units in the gas-liquid chromatography system employed.
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