Three new alkaloids from the leaves of Uncaria rhynchophylla

Three new alkaloids, 2′-O-β-d-glucopyranosyl-11-hydroxyvincoside lactam (1), 22-O-demethyl-22-O-β-d-glucopyranosylisocorynoxeine (2), and (4S)-corynoxeine N-oxide (3) were isolated from the leaves of Uncaria rhynchophylla, together with four known tetracyclic oxindole or indole alkaloids, isocorynoxeine N-oxide (4), rhynchophylline N-oxide (5), isorhynchophylline N-oxide (6), and dihydrocorynantheine (7), and an indole alkaloid glycoside, strictosidine (8). The structures of 1 - 3 were elucidated by spectroscopic methods including UV, IR, ESI-TOF-MS, 1D- and 2D-NMR, as well as CD experiments. The activity assay showed that 8 (IC₅₀=8.3 mm) exhibited potent inhibitory activity on lipopolysaccharide(LPS)-induced nitrogen monoxide (NO) release in N9 microglia cells. However, only weak inhibitory activities were observed for 1 - 7 (IC₅₀>100 μm for 1 - 6 or >30 mm for 7).