The Identification of cis-11,12-Methylene-2-hydroxyoctadecanoic Acid from Thiobacillus thiooxidans

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 14 C-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.