Reduction of various ketones by red algae

The reduction of acetophenone derivatives, (+)- and (-)-camphorquinones and steroidal ketones using red algae (Cyanidios-chyzon 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 (-)-3S- exo-hydroxycamphor 5d as the major product with high stereoselectivity in high yield. In addition, it was found that reduction of 5 alpha-androstane-3,17-dione 8a gave the 3ot-OH isomer (3 alpha-OH/3 beta-OH = 76/24) with high stereoselectivity. Overall it was found that C. merolae and C. caldarium were able to reduce various substrates. @ 2006 Elsevier Ltd. All rights reserved.