Optical and geometric isomers of some fatty acids with vicinal hydroxy groups

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Abstract
Racemic threo-9,10-dihydroxypalmitic acid was resolved by means of the brucine salts into the optically active forms. Levorotatory threo-11,12-dihydroxyeicosanoic acid was obtained from the corresponding racemate by crystallization of the ephedrine salts.The conformation of the geometric isomers of certain dihydroxy long-chain acids and their derivatives was studied by means of nuclear magnetic resonance spectra. There was a small but significant difference in the chemical shift of the CH protons in the ( ± )-threo acid as compared with those in the ( ± )-erythro acid. This was observed in 9,10-dihydroxypalmitic, 9,10-dihydroxystearic, and 11,12-dihydroxyeicosanoic acids. A similar but larger difference in the chemical shift (0.49 p.p.m.) was observed for the CH protons in the O-isopropylidene derivatives of the same acids. These differences are discussed and correlated with the stereochemistry of the dihydroxy acids and the corresponding 1,3-dioxolanes.cis-( + )-12,13-Epoxyoleic acid was isolated from the seed oil of Vernonia colorata. ( − )-threo-12,13-Dihydroxyoleic acid was prepared from the oil of V. cinerea.

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