20-Nitroaminopregn-5-en-3-yl acetate (13a), 17-nitroamino-5-androstan-3-yl acetate (14), and 12-nitroamino-(25R)-5-spirostan-3-yl acetate (15a) have been prepared by nitrosation of the corresponding oximes, followed by reduction with sodium borohydride. The 23-nitro-imine (12), obtained by reaction of sarsasapogenin acetate (10) with nitrous acid and boron trifluoride–diethyl ether complex, was similarly reduced to give 23R-nitroamino-(20S,22S,25S)-5-spirostan-3-yl acetate (16). Denitroamination of (13a) was achieved by treatment with acetic anhydride and pyridine to give the acetates of pregna-5,20-dien-3-ol (17), pregn-5-ene-3,20-diol (18), 17-methyl-D-homo-androst-5-ene-3,17a-diol (19), and 17-methyl-12a-methylene-c(12a)-homo-18-norandrost-5-en-3-ol (20). Under the same conditions the nitro-amine (14) afforded the acetates of 5-androst-16-en-3-ol (27a), 17-methyl-18-nor-5-androst-12-en-3-ol (28a), 17-methyl-18-nor-5-androst-13(17)-en-3-ol (29a), and 17-methyl-18-nor-5-androst-13-en-3-ol (30a). Denitroamination of (15a) took place through the expected c-nor-D-homo rearrangement producing 14 (13 12H)abeo-(25R)-5-spirost-13(18)-en-3-yl acetate (31) in high yield and a minor amount of 14(13 12)abeo-(25R)-5-spirost-12-en-3-yl acetate (32). The trans-stereochemistry of the -hydrogen-elimination produced in the denitroamination of (16) was established by using labelled sarsasapogenin (10) biosynthesized by Agave attenuata from [2-14C,(4R)-4-3H] mevalonic acid.

This work was supported by the Investigation Programme of the Comisión Asesora de Investigación Científica y Técnica.

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