A new chiral synthesis of bullfrog bile sterol 5β-ranol

Abstract

(24R)-27-Nor-5β-cholestane-3α,7α ,12α,24,26-pentol (5β-ranol) has been synthesised by the Wittig olefinic coupling of a steroidal module and a side-chain module followed by reduction and deprotection. The steroidal module is derived from cholic acid by a one-carbon degradation of the side chain to produce norcholic acid followed by the loss of a second carbon in an iododecarboxylation and then synthesis of the triphenylphosphonium iodide. The side-chain module is derived from (S)-(-)-butane-1,2,4-triol by benzylidene protection of the 2,4-diol followed by Swern oxidation to the aldehyde. This general synthetic scheme could be used to produce a range of bile sterols with the (24R)-hydroxy moiety which may have significant hepatoprotective activity against liver damage induced by free radicals or reactive metabolites.