Equine Metabolites of Norethandrolone: Synthesis of a Series of 19-Nor-17α-pregnanediols and 19-Nor-17α-pregnanetriols

Abstract

A range of 19-nor-17α-pregnanediols and 19-nor-17α-pregnanetriols have been synthesized and used to confirm the structures of major equine urinary metabolites of the synthetic anabolic steroid norethandrolone (1). 19-Nor-5α,17α-pregnane-3α,17β-diol (2), 19-nor-5α,17α-pregnane-3β,17β-diol (4), 19-nor-5β,17α-pregnane-3α,17β-diol (6), and 19-nor-5β,17α-pregnane-3β,17β-diol (7) were prepared by stereoselective reduction of the 3-ene-4-one of norethandrolone. The 19-nor-5α,17α-pregnane-3β,16α,17β-triol (8) and 19-nor-5α,17α-pregnane-3β,16β,17β-triol (9) were prepared from 19-nortestosterone (11) by multistep processes in which the critical step involved Grignard additions to 16-acetoxy-17-ones. The triols (20R)-19-nor-5α,17α-pregnane-3β,17β,20-triol (22) and (20S)-19-nor-5α,17α-pregnane-3β,17β,20-triol (23) were prepared from norethindrone (24) by initial selective A-ring reduction, then subsequent modification of the 17-ethynyl group. By comparison of these compounds with post-administration equine urine samples it was possible to establish A-ring reduction with 3β,5α stereochemistry as well as non-stereospecific 16-hydroxylation and 20-hydroxylation as significant metabolic pathways affecting norethandrolone in the horse.