Synthesis and bioactivity evaluation of brassinosteroid analogs

Four new analogs of 28-homocastasterone have been synthesized and completely characterized for the first time from stigmasterol. (22R,23R,24S)-3 beta-acetoxy-22,23-dihydroxy-5 alpha-stigmastan-6-one (17), (22R,23R,24S)-3 beta-bromo-22,23-dihydroxy-5 alpha-stigmastan-6-one (18), (22R,23R,24S)-3 beta-acetoxy-5,22,23-trihydroxy-5 alpha-stigmastan-6-one (20), and (22R,23R,24S)-3 beta-bromo-5,22,23-trihydroxy-5 alpha-stigmastan-6-one (21), were obtained through a synthetic route based on regioselective Delta(5) epoxidation. Compounds 17 and 18, bearing a 5 alpha H moiety, were prepared through a reductive opening of the 5 beta,6 beta epoxy precursor, and compounds 20 and 21, analogs with a 5 alpha OH moiety were obtained by hydrolytic opening of a mixture of 5 alpha,6 alpha and 5 beta,6 beta epoxy precursors. Known compounds 19 and 22 were also obtained following the described synthetic routes, respectively. The new compounds were tested with the traditional auxin-like bioassay for brassinosteroids with 19 and 22 as standards. All compounds were comparatively evaluated for their inhibitory effect on the replication of DNA (HSV-1) virus. (C) 2000 Elsevier Science Inc. All rights reserved.