The regioselective Cu(I)-catalyzed 1,3-dipolar cycloaddition of 17α- and 17β-azidoandrost-5-en-3β-ol epimers (3b and 5b) with different terminal alkynes afforded novel 1,4-substituted triazolyl derivatives (8a-k and 9a-k). For the preparation of 5'-iodo-1',2',3'-triazoles (8m-n and 9m-n), an improved method was developed, directly from steroidal azides and terminal alkynes, in reaction mediated by CuI and ICl as iodinating agents. Acetolysis and subsequent hydrolysis of 8n and 9n yielded 5'-hydroxy-1',2',3'-triazoles 8o and 9o. The inhibitory effect of 8a-o, 9a-o, 3, and 5 on rat testicular C17,20-lyase was investigated by means of an in vitro radioincubation technique. The results revealed that the C-17 epimers of steroidal triazoles influence the C17,20-lyase effect. Inhibitors were found only in the 17α-triazolyl series (8a-o), whereas in the C-17 azide pair the 17β compound (5b) was more potent.
Keywords: 17α- and 17β-azido-androst-5-ene; Azide-alkyne cycloaddition; Chemoselectivity; Inhibitory effect.
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