Novel N-oxide derivatives of benzyltetrahydroisoquinoline alkaloid from the tubers of Stephania viridiflavens H.S. Lo et M. Yang

► Minor chemical constituents of a Chinese medicinal plant. ► Two new N-oxide derivatives of benzyltetrahydroisoquinoline alkaloid. ► Structures comfirmed by spectroscopic methods together with partial synthesis. ► N-oxide derivatives showed more potent cytotoxicity than corresponding free base.