Melohemsines A-I, melodinus-type alkaloids from Melodinus hemsleyanus

Abstract

Nine new melodinus-type alkaloids, melohemsines A-I (1–9), together with eight known ones were isolated from Melodinus hemselyanus. The structures of the new alkaloids, including their absolute configurations, were elucidated on the basis of comprehensive spectroscopic and electronic circular dichroism (ECD) analyses and X-ray diffraction. Compound 1 is the first melodinus-type alkaloid with a 6/6/5/5/6/3 hexacyclic ring skeleton system. Compounds 2–3 are the first natural melodinus-type alkaloids with a reduction in two carbon units at C-20.