Syntheis of methyl (20R,22E)- and (20S,22E)-3-Oxochola-1,4,22-trien-24-oate

摘要

Methyl (22E)-3-oxochola-1,4-22-trien-24-oate(4;C_(25)J_(34)O_3) is a naturally occurring steroid with unknown configuration at C(20).Starting from the (20S)-3-oxo-23,24-dinorchol-4-en-22-al(1a),we prepared both diastereoisomeric methyl esters 4a and 4b by a three-step procedure(Scheme).In the case of 4b,the initial epimerization of aldehyde 1a was followed by completion of the sequence and then separation via fractional crystallization to afford prue (20R)-methyl ester 4a and its (20S)-diastereomer 4b.Only the analytical data of the (20S)-compounds 4b were in good agreement with those reported for the natural product.