Steroid conformations in solid and solution: stereoselective synthesis of (20S)- and (20R)-[20-methyl-labelled]-20-methylpregn-5-ene-3β,17α,20-triol

Abstract

Addition of isotopically labelled methylmagnesium bromide followed by reduction with lithium aluminium hydride of 17α-hydroxypregnenolone 3-acetate and 16α,17α-epoxypregnenolone acetate gave, respectively, (20S)- and (20R)-[20-¹³CH₃]-,[20-C³H₃]-, and [20-C²H₃]-20-methylpregn-5-ene-3β,17α,20-triol (99% for S, 93% for R) owing to conformational localization of the 20-carbonyl group to positions of opposite chirality caused by neighbouring substitution.