Biological Activities of Biosynthetically-related Congeners of Brassinolide

Biological activity of intermediate steroids in the biosynthesis of brassinolide was examined by the rice-lamina inclination test and wheat-leaf unrolling test. In both bioassays, biological activity of intermediates increased according to the order in the biosynthetic pathway. The introduction of a hydroxyl group in the side chain (C-22), the step of 6-oxocampestanol to cathasterone, strikingly enhanced the activity. The activities of teasterone, 3-dehydroteasterone, and typhasterol were almost the same. Relative activities in the rice-lamina inclination test were as follows: 6-oxocampestanol (0.002), cathasterone (1), teasterone (20), castasterone (240), and brassinolide (1200).