Synthesis and biological activity of three new 5a-hydroxy spirostanic brassinosteroid analogues

Three new spirostanic brassinosteroid analogues have been synthesized for the first time from diosgenin: (25R)-2alpha,3alpha-epoxy-5alpha-hydroxyspirostan-6-one (3), (25R)-2beta,3alpha,5alpha-trihydroxyspirostan-6-one (5) and (25R)-2beta-methoxy-3alpha,5alpha-dihydroxyspirostan-6-one (6). In the radish hypocotyl elongation and cotyledon expansion bioassay compound 3 showed plant growth promoting activity whereas 6 was shown to be phytotoxic.Três novos análogos espirostânicos de brassinosteróides foram sintetizados pela primeira vez a partir de diosgenina: (25R)-2alfa,3alfa-epoxi-5alfa-hidroxiespirostan-6-ona (3), (25R)-2beta,3alfa,5alfa-triidroxiespirostan-6-ona (5) e (25R)-2beta-metoxi-3alfa,5alfa-diidroxiespirostan-6-ona (6). A substância 3 mostrou acentuada atividade promotora de crescimento vegetal no bioensaio de elongação do hipocótilo e expansão do cotilédone de rabanete, enquanto a substância 6 mostrou-se fitotóxica