The absolute optical configurations of the isomeric 9,10-epoxystearic, 9,10-dihydroxystearic and 9,10,12-trihydroxystearic acids

Abstract

The absolute optical configuration of (−)-cis-9,10-epoxystearic acid has been verified as being L. Here (−)-erythro-9,10-dihydroxystearic acid, isolated from castor oil, was converted by stereospecific reactions to (+)-cis-9,10-epoxystearic acid and was thereby proved to be D-9,D-10-dihydroxystearic acid. Removal of the D-12-hydroxy group from the higher meltingerythro-9,10,12-trihydroxystearate derived from ricinoleic acid, after protection of the glycol group, gave the L-9,L-10-dihydroxystearate derivative. This proved the high melting diastereoisomer to be L-9,L-10,D-12-trihydroxystearate and directly verified the supposition that the higher melting, arsenite-complexing diastereoisomer of such oxidation pairs has thetrans-10,12-diol grouping. On this basis, the higher meltingthreo-trihydroxystearate from ricinoleate must be D-9,L-10,D-12-trihydroxystearate and removal of the 12-hydroxy group must give D-9,L-10-dihydroxystearate which proved to be the levorotatory enantiomer. The dextrorotatory L-9,D-10-dihydroxystearate was transformed by stereospecific reactions to (+)-trans-9,10-epoxystearic acid, thereby defining the absolute configurations oftrans-9,10-epoxystearic acids. On the basis of these results conclusions may be drawn as to the stereospecificity and site of action of enzymes which hydrate 9,10-epoxystearic acids.