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.