Two novel bibenzyls from Dendrobium trigonopus

Two novel bibenzyl trigonopols A(1) and B(2), together with seven known compounds, gigantol (3), tristin (4), moscatin (5), hircinol (6), naringenin (7), 3-(4-hydroxy-3-methoxyphenyl)-2-propen-l-ol (8), and (-)-syringaresinol (9), have been isolated from the stems of Dendrobium trigonopus, of which compounds 6, 8, and 9 were isolated for the first time from this species. The structures of two new compounds were elucidated as threo-22-(17-hydroxyl-9-(3-hydroxyl-4-methoxy- phenethyl)-13,16,18-trimethoxy-21H-benzo[c]chromen-21-yl)ethane-22, 23-diol (1) and 9-(4-hydroxyl-3-methoxy-phenethyl)-17-(21-hydroxyl-20-methoxy-phenyl) chroman-11, 16-diol (2) on the basis of spectroscopic methods. Trigonopol A was found to exhibit antiplatelet aggregation activity in vitro with 67.55% inhibitory ration at 1.4337 x 10(-3) M.