Indole alkaloids from Ervatamia orientalis. III. The configurations of the ethyl side chains of dregamine and tabernaemontanine and some further chemistry of the vobasine group

Abstract

Evidence is presented to show that the configurations of the ethyl side chains of dregamine and tabernaemontanine are the reverse of the original assignments, i.e. the correct structures are (2) and (3) respectively. Dregamine readily forms the 16-epimer (6) from treatment with sodium methoxide; two neutral products from similar treatment of tabernaemontanine are assigned the epimeric structures (7) and (8). Evidence for the mode of formation of the methine products of Hofmann degradation of dregamine and vobasine (1) is presented and the stereochemistry of these products is assigned on the basis of chemical correlations with taberpsychine (23).