Synthesis of diastereomers of 3α,7α,12α,24-tetrahydroxy- and 3α,7α,24-trihydroxy-5β-cholestan-26-oic acids and their structures

Add time:07/24/2019    Source:sciencedirect.com

Four stereoisomers of 3α,7α,12α,24-tetrahydroxy-5β-cholestan-26-oic acids were synthesized as possible intermediates of the side-chain degradation step of bile acid biosynthesis. 3α,7α,12α-Trihydroxy-5β-cholest-25-en-24-one prepared by thermolysis of β-ketosulfoxide was reduced to the (24R)- and (24S)-allylic alcohols by reduction with sodium borohydride. Each isomeric alcohol was subjected to hydroboration and oxidation to give (25R)- and (25S)-3α,7α,12α,24,26-pentahydroxy-5β-cholestanes. The separated four stereoisomers were converted into the corresponding 26-carboxylic acids. The stereoisomers of 3α,7α,24-trihydroxy-5β-cholestan-26-oic acids were synthesized in the same manner. To establish the stereochemistry of these carboxylic acids, the chemical transformation of methyl 3α,7α,12α-trihydroxy- and 3α,7α-dihydroxy-5β-cholest-24-en-26-oates into the above stereoisomers and the reductive dehydroxylation of the 24-hydroxyl group into known 3α,7α,12α,26-tetrahydroxy- and 3α,7α,26-trihydroxy-5β-cholestanes are described. The applications of spectroscopic methods (circular dichroism and 1H nuclear magnetic resonance) to elucidation of the stereochemistry are also discussed.

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