Formation of [17-2H]androsta-5,16-dien-3beta-ol from [17,21,21,21]pregnenolone by the microsomal fraction of boar testis.

After incubation of [17,21,21,21-2H4]pregnenolone, which had been synthesized from nonlabeled pregnenolone by base-catalyzed exchange procedure, with the microsomal fraction of boar testis, [17-2H]androsta-5,16-dien-3beta-ol was identified as a metabolite. The identification has been performed by gas chromatography-mass spectrometry of the metabolite and of its hydrogenation product. Conclusive evidence on the location of the 2H atom at C-17 has been obtained by transforming the metabolite to androsta-4,16-dien-3-one and then to androst-4-ene-3,17-dione and by proving that the former compound contained a 2H atom while the latter did not. The result indicates that, in boar testis, androsta-5,16-dien-3beta-ol is synthesized from pregnenolone by a pathway in which 17 alpha-hydrogen atom of pregnenolone is retained throughout the reaction, excluding 17 alpha-hydroxypregnenolone and 3beta-hydroxyandrost-5-en17-one as intermediates.