Melohenines A and B, two unprecedented alkaloids from Melodinus henryi.

A phytochemical study on Melodinus henryi has led to the isolation of two novel alkaloids, melohenines A (1), a monoterpenoid indole alkaloid with additional skeletal carbons arranged compactly in eight rings, and melohenine B (2), an alkaloid with an unprecedented 6/9/6/6 tetracyclic ring system regarded as a key intermediate from indole to quinoline alkaloids. Their structures were elucidated by means of spectroscopic methods and further confirmed by X-ray diffraction analysis.