Mersicarpine, an unusual tetracyclic dihydroindole alkaloid incorporating a seven-membered imine ring

A novel dihydroindole derivative, viz., mersicarpine, incorporating a novel tetracyclic carbon skeleton, containing a seven-membered imine ring, was obtained from a Malayan Kopsia species. The structure was established by spectroscopic analysis and a possible biogenetic pathway from a leuconolam precursor is presented.