Constituents of Naucleadiderrichii. Part VII. Synthesis of nauclederine, naucleonine, and naucleonidine; spectroscopic evidence for the structures of 3α-dihydrocadambine and two other constituents

Abstract

Evidence is advanced concerning the structures of six N. diderrichii alkaloids, based on synthetic and spectroscopic studies. The synthesis of nauclederine, 2, provides support for the structural assignment made earlier. Synthesis has shown that the structures previously assigned to the alkaloids designated ND-305B and ND-363C are incorrect; this, however, has led to revised structures (19 and 20) for these alkaloids, now named naucleonine and naucleonidine, respectively, and these have been established by synthesis. Based on this study and an examination of data obtained previously, a tentative proposal is made for the structure 21 of another constituent of the plant, designated ND-363B. Spectroscopic studies have allowed a structure 22 to be advanced for the glycosidic alkaloid, which was shown to be identical with the alkaloid 3α-dihydrocadambine obtained by Brown and Fraser. Based on this study and a reexamination of data reported previously, structure 25 is tentatively proposed for another constituent of the plant, designated ND-370.