Synthesis of brassinosteroids analogues from laxogenin and their plant growth promotion.

Four steroid saponins (2-5) and three derivatives (6-8) were synthesised from laxogenin. Four of them were new compounds: (25R)-3β-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyloxy)-5α-spirostan-6-one (3), (25R)-3β-(β-D-galactopyranosyloxy)-5α-spirostan-6-one (5), 3β,16-diacetyl-26-hydroxy-5α-cholestan-6,22-dione (6) and 16-acetyl-3β,26-dihydroxy-5α-cholestan-6,22-dione (7). All the compounds showed plant growth-promoting activity in the radish hypocotyl elongation and cotyledon expansion bioassay. Above all, 2 and 6 were found to be more active.