Synthesis of Two Possible Diastereoisomers of the Epoxy Lactone Proposed for Epoxyrollin A

Abstract

Syntheses of two possible stereoisomeric epoxy lactones (20S, 21R)- and (20R, 21S)-1 that have been proposed for epoxy-rollin A, a structural representative of biosynthetic precursors of tetrahydrofuran annonaceous acetogenins, are described. Protected dihydroxy compound 4, which is the latent epoxy moiety of (20S, 21R)- and (20R, 21S)-1, was prepared by an 8-step sequence via Sharpless asymmetric dihydroxylation, starting from allyl alcohol 6. Preparation of γ-lactone moiety 5 was conducted by the method reported earlier. A palladium-catalyzed cross coupling reaction of 4 with 5 gave enyne 3, which, by a 3-step sequence, was converted into (20S, 21R)- and (20R, 21S)-1. The ¹³C-NMR and mass spectraldata of the two synthetic diastereoisomers are not in accordance with those recorded for epoxyrollin A. Consequently, the structure of epoxyrollin A needs to be revised.