Saponins from the bark of Nephelium maingayi

Activity-guided fractionation of the bark of Nephelium maingayi, collected in Indonesia, led to the isolation of six new saponins (1-6). The aglycon of 4 was determined to be a new compound, 7alpha-methoxyerythrodiol, and those of 1-3 and of 5 and 6 were identified as erythrodiol and maniladiol (16beta-hydroxyamyrin), respectively. The structures of 1-6 were determined on the basis of spectral data interpretation, and the absolute configurations of their component monosaccharides were determined as their thiazolidine derivatives after acid hydrolysis. Of the isolates, only compounds 1 and 5 showed very weak cytotoxic activity against a panel of human tumor cell lines.