Stereochemistry in the formation of 9-hydroxy-10,12-octadecadienoic acid and 13-hydroxy-9,11-octadecadienoic acid from linoleic acid by fatty acid cyclooxygenase.

9-Hydroxy-10,12-octadecadienoic acid and 13-hydroxy-9,11-octadecadienoic acid are formed from linoleic acid upon incubation with the microsomal fraction of homogenates of the sheep vesicular gland (Hamberg, M. and Samuelsson, B. (1967) J. Biol. Chem. 242, 5344-5354. This communication is concerned with the stereochemical aspects of the conversion. The ratio between the 9- and 13-hydroxy isomers was 77:23. Steric analysis of the individual isomers showed that the hydroxyl group of both isomers had mainly the L configuration, i.e. 9L:9D, 79:21 and 13L:13D, 9- and 13-hydroxyoctadecadienoates which had largely lost the tritium label (6% and 7% retention of tritium relative to precursor, respectively) showing that the hydrogen which is removed from C-11 during the conversion has the L (pro-S) configuration.