Uncarines

In 1966, Johns and Lamberton [45] showed that equilibration of uncarine C and uncarine D in acidic and basic solutions resulted in C-3 isomerizations. Further investigations [46,47] revealed that equilibration of e.g. uncarine C in an aqueous acetic acid solution (50%) resulted in four isomers, namely uncarine C (64), D (65), E (66) and F (67), Fig. 

Ratios of 40 40 10 10 were obtained for uncarine C, D, E and F. These were demonstrated to be true equilibrium ratios by treating each isomer under analogous conditions the ratios were the same. 

Rauniticine oxindole A (77) Rauniticine pseudoindoxyl (77) Tetrahydroalstonine (77) Tetrahydroalstonine A/-oxide (77) Uncarine A (77)... 

The root bark of an uncharacterized Uncaria species from Peru contains67 pteropodine, isopteropodine, speciophylline, uncarine F, and isomitraphylline. 

The presence of an oxindole nucleus in mitraphylline is established by the results of zinc dust distillation. The basic products include isoquinoline and 3,4-diethylpyridine, while the neutral fraction affords 3-spirocyclopropano-oxindole (IV), mp 179°-181° (55, 56). This degradation product is of the greatest importance in this series of alkaloids it was first obtained from the calcium oxide distillation of rhynchophyllic acid (19), and has since been obtained by zinc dust distillation of uncarine-A (58), by hydrogenation and pyrolysis of uncarine-A methiodide (59), and by zinc dust distillation of formosanine (uncarine-B) (60). The structure of this neutral degradation product was first proposed by Wenkert and Reid (61), who pointed out that its properties were very similar to those... 

Independently, Nozoye (10) also proposed structure VI for mitraphylline, on the basis of the identity of its UV-spectrum and the close similarity of its IR-spectrum (except in the fingerprint region) with those of formosanine (uncarine-B), for which the constitution VI had already been proposed. 

The stem, wood, and bark of Uncaria kawaJcamii contain the two isomeric alkaloids, uncarine-A and uncarine-B, C21H24N2O4 (30, 31), the highest proportion of alkaloids (1.48%) occurring in the bark (31). Uncarine-B has been identified with formosanine (28, 33), which was isolated earlier from Ourouparia formosana (21, 32). The chemical behavior of uncarine-A and formosanine is identical in all respects, and their relationship as stereoisomers is shown by their ready interconversion and equilibration, which frequently hinders the separation and purification of individual isomers. Thus, uncarine-A in hot dilute acetic acid yields formosanine, and the reverse transformation can be achieved by heating formosanine with ether, until it has all been isomerized into the more soluble uncarine-A. Some formosanine is even obtained when uncarine-A is recovered from its hydrochloride, or from the hydrochloride of the related amino acid, by methylation with diazomethane (59). 

Uncarine-A and formosanine are monoacidic bases, which contain one... 

As in the case of mitraphylline, a re-examination of the available evidence, together with some new experimental data, led to the adoption of the constitution VI for uncarine-A and formosanine. Reduction of... 

Now formosanine and uncarine-A possess comparable stabilities, since,... 

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