General methods of synthesis of indole alkaloids. XIII. Oxindole alkaloid models

Abstract

The synthesis of oxytryptophol and oxindoloindolizidine esters and methyl ketones is described. The determination of the stereochemistry of the acyl derivatives by 1H and 13C nmr spectral means is portrayed.

Eudistomin U and Isoeudistomin U, New Alkaloids from the Carribean Ascidian Lissoclinum fragile

“…The honrar spectrum of ( 158.63) was located between two nitrogen atoms like in a pyrrolo [2,3-d] pyrimidine (18) or -carboline ring ( 152.2) ( 14), a deshielded value corresponding to the lack of a ß-shielding effect due to the nitrogen atom N-2 in the ß-carboline ring. With such a structure, the other deshielded carbon value (6 138.31 for C-4b) was in agreement with those found for indole alkaloids possessing an unsaturated double bond [e.g., pandoline ( 19)1 or unsaturated functionalities [rhyncophylline derivatives (20)] in an a orientation from the NH group. Therefore, a dihydro a-carboline moiety was proposed for 2 to account for these features.…”

Reactions of 1-carboethoxytetrahydrocarbazole chloroindolenine

“…The choice of 5 as the diene part added a considerable amount of flexibility, as the oxygenated character of the resulting cycloadduct provides numerous possibilities for further modifications. 8 The desired substrate 6 was prepared readily and in high yield from 1 and 5. Surprisingly, however, 6 resisted any attempt to effect the desired cycloaddition to produce 7; in fact, compound 6, when heated in a sealed NMR tube (CeDe), remained unchanged up to temperatures of 230°.…”