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 μM) 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 μM for 7).