Preparation of (5 alpha,13 alpha)-D-azasteroids as key precursors of a new family of potential GABAA receptor modulators

Reagent-controlled regiodivergent ring expansions of steroids

Ring expansion provides a powerful way of introducing a heteroatom substituent into a carbocyclic framework. However, such reactions are often limited by the tendency of a given substrate to afford only one of the two rearrangement products or fail to achieve high selectivity at all. These limitations are particularly acute when seeking to carry out late-stage functionalization of natural products as starting points in drug discovery. In this work, we present a stereoelectronically controlled ring expansion sequence towards selective and flexible access to complementary ring systems derived from common steroidal substrates. Chemical diversification of the reaction intermediate affords over 100 isomerically pure analogs with spatial and functional diversity. This regiodivergent rearrangement, and the concept of using chiral reagents to affect regiocontrol in chiral natural products, should be broadly applicable to late-stage natural product diversification programs.

Late-stage diversification of natural products is an important starting point for drug discovery. Here, the authors use chiral reagents to perform the regiocontrolled ring expansion of steroid precursors and achieve more than 100 isomerically pure analogs with spatial and functional diversity.

Synthesis of novel 13α-18-nor-16-carboxamido steroids via a palladium-catalyzed aminocarbonylation reaction

13α-18-nor-16-Carboxamido steroids were synthesized via a palladium-catalyzed aminocarbonylation reaction of the corresponding iodoalkenes. The starting material was an unnatural 13α-16-keto steroid, obtained by a Wagner-Meerwein rearrangement of a 16α,17α-epoxide in the presence of [BMIM][BF4]. The 13α-16-keto steroid was converted to a mixture of 16-iodo-16-ene and 16-iodo-15-ene derivatives in two steps by Barton's methodology. Aminocarbonylation of the steroidal alkenyl iodides was carried out using different primary and secondary amines as nucleophiles. The products, 16-carboxamido-16-ene and 16-carboxamido-15-ene derivatives, were obtained in good yields and were characterized by (1)H and (13)C NMR, IR and MS. The reduction of the above two unsaturated carboxamides resulted in the same product, 17α-methyl-16α-carboxamido-androstane.

Recent advances in azasteroids chemistry

Modified steroids have attracted a great deal of attention these last years. Their preparation is a stimulating challenge to the organic chemist, often demanding development of new and generally useful reactions. Moreover, the biological properties of modified steroids have proved to be of interest. The recent development in the partial and total syntheses of azasteroids is herein described.

Steroids: reactions and partial synthesis

This article reviews the progress in the chemistry of the steroids that was published between January and December 2003. The reactions and partial synthesis of estrogens, androgens, pregnanes, cholic acid derivatives, cholestanes and vitamin D analogues are covered. There are 152 references.