Synthesis and bioactivity of 6 alpha- and 6 beta-hydroxy analogues of castasterone

The reduction of castasterone with sodium in ethanol produced chiefly the k nown 6 alpha -hydroxy stereoisomer, whereas reduction with sodium borohydri de in methanol afforded mainly the novel 6 beta -epimer. Both compounds sho wed variable bioactivity through four separate assays via the rice leaf lam ina inclination bioassay. However, when treated with an appropriate statist ical program to remove outliers, the averaged results clearly indicated tha t the two 6-hydroxy epimers possess comparable and significant bioactivity, which is, however, lower than that of castasterone or brassinolide. When a pplied together with 1000 ng of the auxin, indole-3-acetic acid (IAA), the activity of both the 6 alpha and 6 beta hydroxy epimers was enhanced by ca. one order of magnitude across a wide range of doses. (C) 2000 Elsevier Sci ence Ltd. All rights reserved.