The Quebrachamine Group

Several new sources of quebrachamine (5) (10-16) and, particularly, voaphylline (conoflorine, 6) (15,17-34) have been found in recent years. Other known alkaloids encountered in recent extractions include vincadine (7) (35,36), 14,15-didehydro-epivincadine (8) (37), rhazidine (9) (38), and 12-methoxyvoaphylline (10) (39-41). New alkaloids include quebrachamine hydroxyindolenine (strictanol, 11), which has been found in the fruits (42) and leaves (43) of R. stricta, and voaphylline hydroxyindolenine (12), for which five sources have been reported (20,22,27,34,44). In common with many other hydroxyindolenine derivatives of easily oxidized alkaloids, these may well prove to be artifacts of the extraction process. Ervayunine (13), the enantiomer of voaphylline, occurs in the roots of Ervatamia yunnanensis 

Two new alkaloids, ervatinine and stapfinine, have been extracted from the leaves of E. coronaria, a species endemic in Pakistan, which is used in the indigenous system of medicine for the treatment of ophthalmia, in the treatment of wounds, and as an anthelmintic. The structures of both alkaloids were deduced from their mass and nuclear magnetic resonance (NMR) spectra. Ervatinine (16) is an ll-hydroxy-5-oxovoaphylline of unknown stereochemistry (47), and stapfinine (17a) appears to have the relative stereochemistry of 5-hydroxyvoaphylline. Again, the configuration of the hydroxyl group is unknown (48). 

Two further relatives of voaphylline have been obtained from the leaves of the double-flowering variety of T. divaricata (49). These are voafinine (17b) and A a-methylvoafinine (17c), whose structures were deduced mainly from an examination of their NMR spectra. 

Three incompletely characterized alkaloids in the quebrachamine group are among the 45 alkaloids isolated from the root bark of T. chippii Stapf (30). Alkaloids TC-A and TC-C gave identical mass spectra, which were in turn identical with that exhibited by synthetically prepared (l SjlS )-voaphyllinediol (18) (50,51). Alkaloids TC-A and TC-C are therefore regarded as (14R,155)-voaphyllinediol and (145,15S)-voaphyllinediol (19 and 18), but in view of the trace amounts of alkaloid isolated, it was not possible to determine which was which. Alkaloid TC-B contains an additional oxygen atom (mass spectrum), probably as a hydroxyl group attached to C-19, the most frequently substituted position in this group of alkaloids. It is therefore tentatively formulated as 20 (30). 

The remaining alkaloid in this group, hyderabadine, is similarly oxidized at positions 14 and 15, and also at C-18. It occurs in the leaves of E. coronaria (52) and is formulated as the pentacyclic ether 21 of undetermined stereochemistry, on the basis of its NMR and mass spectra. 

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Two new structural variants in the quebrachamine group have been encountered recently. Voaharine (22), a constituent of T. divaricata, is clearly obtained by oxidation of voaphylline (6), followed by rearrangement. Its structure was established by X-ray crystallographic analysis 24). 

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