HYDROXYLATION OF THE NATIVE BRASSINOSTEROIDS 24-EPICASTASTERONE AND 24-EPIBRASSINOLIDE BY THE FUNGUS CUNNINGHAMELLA-ECHINULATA

24-Epicastasterone and 24-epibrassinolide, two naturally occurring phy tohormones of the brassinosteroid type, were transformed by the fungus Cunninghamella echinulata to give the corresponding 12beta-hydroxylat ed compounds. The structures of these compounds were determined by spe ctroscopic methods, especially heterocorrelated two-dimensional nuclea r magnetic resonance investigations. In the rice lamina inclination te st the 12beta-hydroxylation lowered the bioactivity at 0.1 ppm to 10% in comparison with that of the corresponding parent hormones. The desc ribed hydroxylations represent the first biotransformations of native brassinosteroids.