Reduction of various ketones by red algae

Abstract

The reduction of acetophenone derivatives, (+)- and (−)-camphorquinones and steroidal ketones using red algae ( Cyanidioschyzon merolae 10D and Cyanidium caldarium) was investigated. It was found that fluoro, chloro and bromo acetophenone derivatives 1a– i were reduced with good enantioselectivity. On the contrary, reduction of methyl and methoxy acetophenone 1j– o showed low enantioselectivity. The reduction followed Prelog’s rule, giving the ( S)-alcohols in all cases. Moreover, (+)- camphorquinone 5a was reduced to give (−)-3 S- exo-hydroxycamphor 5d as the major product with high stereoselectivity in high yield. In addition, it was found that reduction of 5α-androstane-3,17-dione 8a gave the 3α-OH isomer (3α-OH/3β-OH = 76/24) with high stereoselectivity. Overall it was found that C. merolae and C. caldarium were able to reduce various substrates.