The Constituents of Naucleadiderrichii. Part III. Indole-Pyridine Alkaloids

Abstract

Six alkaloids isolated from the bark of Naucleadiderrichii have been shown to have structures that contain both indole and pyridine units. Because of the small amounts available of each constituent, investigation of structure has been confined mainly to the application of spectroscopic techniques; these have shown that all of these alkaloids belong to the novel indole-pyridine class, and have led us to propose structures or part structures with varying degrees of confidence for each of the alkaloids. Structure 1 was deduced for naucledine, C18H15N3O2, and confirmed by synthesis. Its spectroscopic characteristics indicate that nauclederine, C19H19N3O2, has structure 3, but this has not yet been confirmed by synthesis. Evidence is presented that nauclechine, C21H21N3O3, has part structures 6 and 7, and it is suggested that these can be incorporated in structure 8. A working hypothesis for the structure of nauclexine, C18H17N3O2, is represented by 9. Two alkaloids, ND-363C, C21H21N3O3, and ND-305B, C19H19N3O, are closely related, the latter being formally derived from the former by removal of a carbomethoxy group; each appears to exist as an equilibratible pair of isomers containing an indolic (substituted β-carboline) and a pyridine part linked together in a manner which may incorporate a spiro carbinolamine ether (as in 12) that can form ring-opened or solvated derivatives in some solvents.