Monoamine Oxidase Inhibitor from Uncaria rhynchophylla

A methanol soluble extract from the dried hooks and stems of Uncaria rhynchophylla showed a strong inhibitory activity against monoamine oxidase in mouse brain. Using a bioassay-guided purification of this extract, a known type alkaloid, harman (1), was obtained as an active constituent. In addition, five known indole alkaloids, isocorynoxeine (2), isorhynchophylline (3), corynoxeine (4), cadambine (5), and (6), were isolated and found to be weakly active or inactive.