Synthesis of manool-related labdane diterpenes as platelet aggregation inhibitors

Enantioselective total synthesis of the labdane diterpene (-)-1, was achieved starting from the R-(-)-enantiomer of the Wieland-Miescher ketone (3). The enantiomer (+)-1 was obtained by partial synthesis via microbial transformation of sclareol (24). These results established that the natural compound (+)-1, a platelet aggregation inhibitor, has a normal absolute stereochemistry like that of manool (2). The B-norlabdane-related compound 44 was also synthesized using a novel ring contraction reaction.