The structure of an unknown yellow base from Menisperum dauricum DC. (Menispermaceae) was determined to be 5, 6, 9-trimethoxy-7H-dibenzo [de, h] quinolin-7-one (1) by spectral data and total synthesis. It was named menisporphine and the skeletal name"oxoisoaporphine"was proposed for this new type of alkaloid. The biosynthesis route of oxoisoaporphine-type alkaloids in plants is suggested.
