Cytotoxic Triterpenoid Alkaloids from Buxus microphylla

Five new triterpenoid alkaloids, buxmicrophyllines E−I (1−5), and six known ones (6−11) were isolated from the leaves and stems of Buxus microphylla. The structures of compounds 1−5 were elucidated by NMR and MS spectroscopic analysis, and the relative stereochemistry of 5 was determined by single-crystal X-ray crystallography. Compounds 3 and 9 were cytotoxic against HepG2 cells, with IC50 values of 0.89 and 0.78 μM, and compounds 2, 3, 7, 8, and 9 were cytotoxic against K562 cells, with IC50 values of 2.95, 4.44, 1.70, 5.61, and 0.37 μM, respectively.