Three steroids (spinasterol, spinasterone, and spinasterol glucopyranosyl) were isolated from the stem of the Amazonian plant Moutabea guianensis. Their structures were determined on the basis of NMR analysis and by comparison with spectroscopic data found in the literature. The allelopathic activities of the three substances were evaluated against two common weeds of the Amazon region, Mimosa pudica ('malicia') and Senna obtusifolia ('mata-pasto'). The substance spinasterol glucopyranosyl was the most active in the radicle growth bioassay, inhibiting Senna obtusifolia in 75%; spinasterol inhibited the development of hypocotyl of Senna obtusifolia in 22%, and spinasterone and spinasterol inhibited 10% of the seed germination of the species Mimosa pudica. These results showed that the difference of substitutes at the C-3 position of the steroids can influence allelopathic activity: the glicosyl group at the C-3 position enhanced the inhibition of hypocotyl growth of the species Mimosa pudica, compared to the hydroxilated and carbonylated steroid. This is the first chemical and allelopathic study with Moutabea guianensis.
Moutabea guianensis; Polygalaceae; allelopathy; Senna obtusifolia; Mimosa pudica
