SEQUENTIAL OXYGENATION OF LINOLEIC-ACID IN THE FUNGUS GAEUMANNOMYCES-GRAMINIS - STEREOCHEMISTRY OF DIOXYGENASE AND HYDROPEROXIDE ISOMERASE REACTIONS

Linoleic acid is sequentially oxygenated to (7S,8S)-dihydroxylinoleic acid by dioxygenase and hydroperoxide isomerase activities present in the fungus Gaeu-mannomyces graminis (Brodowsky, I. D., Hamberg, M., an d Oliw, E. H., J. Biol. Chem. 267, 14738-14745 (1992)). Linoleic acids stereospecifically deuterated at C-7 and C-8 were prepared by biologi cal desaturation of the corresponding stearates and used to determine the stereochemistry of the hydrogen abstractions occurring in the diox ygenase- and hydroperoxide isomerase-catalyzed reactions. The dioxygen ase reaction was found to involve stereospecific abstraction of the pr o-S hydrogen from C-8 followed by antarafacial insertion of dioxygen t o produce (8R)-hydroperoxylinoleic acid. The hydroperoxide isomerase r eaction consisted of conversion of (8R)-hydroperoxylinoleic acid into (7S,8S)-dihydroxylinoleic acid by stereospecific elimination of the pr o-S hydrogen from C-7 and intramolecular suprafacial insertion of oxyg en at C-7. Accordingly, during the conversion of linoleic acid into (8 R)-hydroperoxylinoleic acid, the absolute configuration of C-8 was inv erted, while the conversion of (8R)-hydroperoxylinoleic acid into (7S, 8S)-dihydroxylinoleic acid occurred with retention of absolute configu ration at C-7. (C) 1994 Academic Press, Inc.