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 (4 S )‐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 ( IC 50 =8.3 μ M ) 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 ( IC 50 >100 μ M for 1 – 6 or >30 μ M for 7 ).