Chemoenzymatic Synthesis of Pleiogenone A: An Antiproliferative Trihydroxyalkylcyclohexenone Isolated from Pleiogynium timorense.

The first total synthesis of polyhydroxylated cyclohexenone 1, isolated from Pleiogynium timorense and named pleiogenone A, is reported that also serves as a proof of structure and absolute configuration. Enzymatic dihydroxylation of benzoic acid with R. eutrophus B9 provided enantiomerically pure diene diol 6. Elaboration of the carboxylate moiety to the alkyl side chain was followed by singlet oxygen cycloaddition to furnish an endoperoxide whose reduction with thiourea led to cyclitol 19. Several protective operations were required before oxidation and the final extension of the side chain by a Wittig reaction. After final deprotection of the acetonide functionality the desired pleiogenone A (1) was obtained in 14 operations from benzoic acid.