C-24 stereochemistry of marine sterols: (22E)-24-ethyl-24-methylcholesta-5, 22-dien-3β-ol and 24-ethyl-24-methylcholest-5-en-3β-ol

Abstract

The C-24 configurations of (22E)-24-ethyl-24-methylcholesta-5,22-dien- 3β-ol (1) and 24-ethyl-24-methylcholest-5-en-3β-ol (2), isolated from the Colombian Caribbean sponge Topsentia ophiraphidites, were determined to be R and S, respectively, by comparing their NMR data with those of stereodefined (24R)-and (24S)-samples that were synthesized in routes involving the orthoester Claisen rearrangement of Δ23-22-allylic alcohols. This is the first synthetic study where the Claisen rearrangement is used to introduce a C-24 quaternary center in a stereospecific manner with acceptable yield. X-ray analysis of 1 conirmed these stereochemical assignments. © 2011 Sociedade Brasileira de Química.