Synthesis of ribosylhopane, the putative biosynthetic precursor of bacterial triterpenoids of the hopane series

A versatile, efficient route to ribosylhopane with control over all asymmetric carbon atoms of the side-chain is presented. The synthesis is based on two chain elongations starting from diploptene by subsequent additions of two acetylenic moieties. In a key step a keto-propiolate is stereoselectively reduced to the corresponding hydroxy-propiolate by means of a chiral oxazaborolidine assisted hydroboration. This synthetic protocol represents a useful tool for the access to natural and unnatural bacteriohopanepolyol derivatives of biological interest as well as to labeled ribosylhopane and bacteriohopanetetrol for biosynthetic studies. (C) 1999 Elsevier Science Ltd. All rights reserved.