Synthesis of novel pregnane-based 20-carboxamides via palladium-catalysed aminocarbonylation

Abstract

20-Carboxamidopregnene derivatives, such as 3β-acetoxy-5α-pregn-20-ene-20-carboxamides and 5α-pregn-20-ene-20-carboxamides were synthesized from the widely accessible 3β-acetoxy-pregn-5,16-dien-20-one (PDA) using selective hydrogenation, hydrazine and iodoalkene formation, as well as palladium-catalysed aminocarbonylation. The 20-iodo-20-ene derivatives, obtained from the corresponding 20-keto derivatives via their hydrazones, served as substrates. 23 new 20-carboxamides were obtained using various N-nucleophiles ranging from simple primary amines to α-amino acid esters. The novelty of this methodology lies in the application of facile, moderate or high-yielding reactions to obtain otherwise hardly accessible steroidal 20-carboxamides of pharmaceutical importance. In other words, instead of the enzymatic or synthetic degradation of e.g., sterols or cholanic acids, functionalization of the basic skeleton (a ‘building-up’ approach) was used.