C-25 prochirality in the fragmentation reaction catalysed by fucosterol epoxide lyase from the silkworm, Bombyx mori

Abstract

The fate of the diastereotopic methyl groups on the prochiral C-25 centre of fucosterol epoxide and isofucosterol epoxide during enzymatic conversion into desmosterol has been investigated. Incubation of stereospecifically ¹³C-labelled fucosterol (24R, 28R)-epoxides and isofucosterol (24R, 28S)-epoxides with a cell-free preparation obtained from the guts of larvae of the silkworm, Bombyx mori, followed by ¹³C NMR analysis of the product has shown that the reaction is stereospecific, where the pro-S and pro-R methyl groups of the epoxides turn stereospecifically into (Z)- and (E)-methyl groups of desmosterol, respectively.