Chemical constituents from Melodinus axillaris W. T. Wang and their chemotaxonomic significance

A phytochemical investigation on the aerial parts of Melodinus axillaris resulted in the isolation and identification of 14 indole alkaloids and 2 other compounds. The 14 alkaloids were readily classified as an unusual aspidosperma (1), aspidosperma (2–9), quinolone (10 and 11), eburnamine (12 and 13) and condylocarpan (14) types. Melaxillarine (1) was an unusual aspidosperma-type alkaloid with a contracted E ring, and was identified by means of spectroscopic analysis, including HRESIMS, and 1D and 2D NMR experiments. Compounds 1, 4, 7–9, 11 and 15–16 were isolated from this plant for the first time, while the 1, 9 and 15–16 were reported from Melodinus species for the first time. Compounds 1 and 9 could be considered as chemotaxonomic markers for M. axillaris. The chemotaxonomic significance and distribution of these compounds in Melodinus genus were discussed.