RESUMEN
Phytochemical investigation of the roots of Walsura trichostemon, a Thai medicinal plant, provided a new tirucallane, 3-epimesendanin S 12-acetate (1), together with four known compounds, 3-epimesendanin S (2), meliasenin G (3), ß-sitosterol (4) and ß-sitosterol glucoside (5). Their structures were characterized by intensive spectroscopy including 1 D and 2 D NMR, UV, IR and MS spectrometric analysis. The isolated compounds were evaluated for antibacterial and acetylcholinesterase inhibitory activities. Compounds 1-2 showed antibacterial activity against Bacillus cereus and Bacillus subtilis with MIC values ranging from 16-128 µg/mL. In addition, compound 3 was active against Pseudomonas aeruginosa and Escherichia coli with MIC values of 64 and 128 µg/mL, respectively.