2,3,5-Tri-epi-brassinolide : preparation and biological activity in rice lamina inclination test

Abstract With a view to attaining more precise information on the biological activity of 2,3,5-tri- epi -brassinolide analogs, 2,3,5-tri- epi -brassinolide was prepared from 2,3-di- epi -brassinolide by direct epimerization at C-5. Biological activity of 2,3,5-tri- epi -brassinolide in the rice lamina inclination test was nil even at 1 μg/plant by the single application technique, while with co-application of indole-3-acetic acid, the activity was ca 1/1000th that of brassinolide, reconfirming that the A/B trans -fused ring junction of brassinosteroids is an essential structural factor for high biological activity.