Vobasine-type alkaloid

The chemical conversion of alkaloids of the vobasine type into those of the ervatamine type can readily be effected, using a modified Polonovski reaction. This involves formation of an N-oxide and its rearrangement, using trifluoroacetic anhydride as reagent. Dregamine (65) has been converted into 20-epi-ervatamine... 

Four vobasine-type bisindole alkaloids 1—4 were isolated from... 

LeuconoUne (141) (Figure 22), the first example of ebuman—vobasine-type bisindole alkaloids, was isolated from the stem bark of Malayan... 

Four macroline—vobasine-type bisindole alkaloids, perhentisines A—C (201—203) and lumutinine E (204), were isolated from the stem bark of Malaysian Alstonia angustifolia (Apocynaceae). In addition, bisindole... 

In contrast to the many Aspidosperma-Aspidosperma type bisindoles found in the leaf extract of the Malaysian T. divaricata vide infra), the stem extract provided only one bisindole, conodusarine (509), which was of the iboga-vobasine type 309). The spectral data indicated that conodusarine (509) is constituted from the union of 3-vobasinyl and 3-oxovoacangine moieties via a 3-11 bond. The presence of the latter alkaloid in the same plant provided additional support for the assignment. 

These 2-acyl indole alkaloids are peculiar in that there are three carbon atoms between the indole nucleus and the N, atom. These alkaloids are thought to be biosynthesized from vobasine-type 2-acyl indole alkaloids. 

Applying the Potier-Polonovski reaction, vobasine-type indole alkaloids such as vobasine, dregamine, and tabernaemontanine could be transformed into dehydroervatamine, 20-epiervatamine, and ervatamine, respectively (70). 

Spectral and X-ray crystallographic analysis has established the structure of the major alkaloid (0.11%) of S. erichsonii stem bark from French Guiana, erichsonine, as (13). It is a vobasine-type base, evidently related to 16- pi-affinine, and is of a type that has not previously been found in Strychnos species (338). 

A characteristic of the genera Callichilia, Conopharyngia, Gabunia, Stemmadenia, Tabernaemontana, and Voacanga of the Apocynaceae family is the presence of bisindole alkaloids of the voacamine type, the prototype of this group being voacamine itself. All these alkaloids are composed of a vobasine-like [vobasine,... 

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... 

The third alkaloid of Capuronetta elegans, capuvosine (225), is a bisindole alkaloid of new type in which a vobasine unit is attached to one of dihydrocleavamine type. Indeed, fission of capuvosine by means of hydrochloric acid results in the formation... 

---