A terpenoid and two steroids from the flowers of Mammea siamensis

Two steroids, β-sitosterol and stigmasterol (of their mixture in an approximate ratio 1:1) and a terpenoid, friedelin, were isolated from a chloroform extract of Mammea siamensis flowers by means of chromatographic techniques. Chemical structures of the isolated compounds were identified by direct comparison of their spectroscopic data with those reported in the literature and by comparing their TLC patterns with those of authentic samples. The preliminary biological acitvities, such as antimicrobial activity (disc diffusion method), DPPH-radical scavenging and brine shrimp lethality effects of various solvent extracts from M. siamensis flowers were examined. The chloroform extract of M. siamensis flowers showed antibacterial effects on Staphylococcus aureus and Bacillus subtilis with inhibition zone of 7.8 and 9.0 mm, respectively. A methanol extract exhibited inhibition zone (6.0 mm) for B. subtilis. However, neither extract affected the growth of either Escherichia coli or Candida albicans. Both the chloroform and the methanol extract did not show antioxidative effect in DPPH radical-scavenging assay, whereas they exhibited lethality effects on brine shrimps with LC50 value of 5.2 and 43.2 μg/ml, respectively. Neither the mixture of β-sitosterol and stigmasterol, or friedelin showed any effect on brine shrimps.