A method of regioselectively and stereoselectively synthesizing forskolin (8,13-epoxy-1 alpha ,6 beta ,7 beta ,9 alpha -tetrahydroxylabd-14-en-11-one) from 9-deoxyforskolin (8,13-epoxy-1 alpha ,6 beta ,7 beta ,-trihydroxylabd-14-en-11-one) with a good yield is described. In a preferred embodiment, it comprises an enol ether formation from 8,13-epoxy-1 alpha ,6 beta ,7 beta -trihydroxylabd-14-en-11-one-6,7-carbonate, oxidation of the enol ether with a suitable peroxy acid to obtain 11,12-dehydro-8,13-epoxy-11-methoxy-1 alpha ,6 beta ,7 beta ,9 alpha -tetrahydrolabd-14-ene-6,7-carbon ate and hydrolysis of the latter under an acidic condition to obtain 8,13-epoxy-1 alpha ,6 beta ,7 beta ,9 alpha -tetrahydroxylabd-14-en-11-one-6,7-carbonate. As an alternative way of protecting the two hydroxy groups at carbon-6 and carbon-7, they may also be converted to dimethyl acetal during the synthetic sequence. Four compounds produced in the synthetic scheme as intermediates, namely, 9,11-dehydro-8,13-epoxy-11-methoxy-1 alpha ,6 beta ,7 beta -trihydroxy-labd-14-ene-6,7-carbonate and 11,12-dehydro-8,13-epoxy-11-methoxy-1 alpha ,6 beta ,7 beta ,9 alpha -tetrahydroxylabd-14-ene-6,7-carb onate and the corresponding dimethyl acetal compounds are believed to be novel.
展开▼
