Coronaridine-type alkaloids

Sri Lankan plants of the genus Tabemaemontana have also yielded 14 coronaridine-type alkaloids. Both species investigated, namely, T. dichotoma... 

In an extensive study of indole alkaloids from Tabernaemontana dichotoma, Perera and co-workers reported the isolation and characterization of eight bisindole alkaloids of the vobasine-coronaridine type (90,93). Of these, the previously known alkaloids tabernamine (173), voacamine (175), and 3 R/S-hydroxyvoacamine (178) were identified from their spectral characteristics and co-TLC with authentic samples (91). UV, IR, and XH NMR data of three of the bisindole alkaloids indicated a close structural relationship to tabernamine (173), and the XH NMR of one of these alkaloids was identical to that of tabernamine, except that the signal at 6 2.62 ppm due to the N-Me group was missing. The MS and IR spectroscopic data... 

Another type of rearrangement ensues if the ATb-oxide (219) is treated with a nucleophile. This reaction can be applied to the partial synthesis of bisindole alkaloids (q.v.), but in most cases a by-product is obtained. In the simple example in which the nucleophile is acetate, the product obtained is the pentacyclic compound (222), in which the intermediate fragmentation product has cyclized on to Aa. Analogous compounds can also be obtained starting with dihydrocatharanthine or coronaridine. ... 

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