Total synthesis of (+)-conagenin

The first total synthesis of (+)-conagenin, a novel immunomodulator produced by Streptomyces roseosporus, has been achieved in highly stereo- and enantioselective manner. The carboxylic acid moiety was synthesized starting with asymmetric aldol reaction of propiophenone with acetaldehyde followed by in situ syn-selective NaBH4 reduction. The amino acid moiety was synthesized based upon Et(2)AlCl catalyzed cyclization of the epoxy trichloroacetimidate prepared from (S)-methylglycidol. Condensation of both moieties and alkaline hydrolysis led to (+)-conagenin. (C) 1996 Elsevier Science Ltd.