Macrophyllionium and Macrophyllines A and B, Oxindole Alkaloids from Uncaria macrophylla

An unusual oxindole alkaloid inner salt, macrophyllionium (1), and a pair of new tetracyclic oxindole alkaloids, macrophyllines A (2) and B (3), together with six known alkaloids, were isolated from the aerial parts of Uncaria macrophylla. Corynantheidine (8) exhibited moderate cytotoxicity against HL-60 and SW480 cells with IC(50) values of 13.96 and 23.28 mu M, respectively. Dihydrocorynantheine (9) exhibited significant vasodilating activity against phenylephrine-induced contraction in rat thoracic aorta rings (IC(50) = 6.73 mu g/mL). In addition, compounds 2, 6, and 9 showed weak inhibitory action on KO-induced contraction.