Synthesis and activity evaluation of new 11α-hydroxybrassinosteroids

Six new brassinosteroid analogues bearing an 11α-OH functionality on the 24-epi skeleton have been synthesized. Thus, 11α-hydroxy-24- epiteasterone, 11α-hydroxy-24-epicastasterone, 11α-hydroxy-24- epibrassinolide, and their 22S,23S diastereoisomers have been prepared from ergosterol acetate in 11, 15 and 16 synthetic steps respectively. The compounds have been evaluated for brassinosteroid activity by means of the rice lamina inclination test (RLIT). The results showed that, although these compounds are less active than their dehydroxylated counterparts are, they still follow the general activity sequence previously observed in brassinosteroid field. Both facts suggest that the presence of a hydrophobic area between the two polar ends of the molecule is advantageous for good brassinosteroid activity.