Aspidospermine group

In a reinvestigation of the minor alkaloids of A. quebrachoblanco, whose presence had already been indicated by Hesse (59) in 1882 (Vol. II), Biemann et al. (28, 51a) were able to isolate by a combination of alumina and gas chromatography about twenty compounds. The identification or structure determination of fifteen of these by mass spectrometry was described. Six belonged to the aspidospermine group and four of these were the known compounds, aspidospermine (II), deacetylaspido-spermine (VI), V.,-methyldeacetylaspidospermine (XLI), and (— )-pyri-folidine (XLVI). The three last-named had not previously been encountered in nature, VI and XLI having been prepared from aspidospermine (II) and vallesine (XXXVIII) (38, 39, 25). (— )-Pyrifolidine is identical with O-methylaspidocarpine (XLVI) which has been prepared... 

The three alkaloids named in the title (XXXII, XXXIII, and XXXIV) are respectively the A -formyl, -acetyl, and -propionyl derivatives of aspidospermidine (Section II, E). Demethoxypalosine (XXXIV) has been isolated from Aspidosperma limae (40) and A. discolor (40a) and was characterized as an iVa-acyldihydroindole by its UV-spectrum (Table III) and IR-absorption at 5.89 p. A strong band in the IR-spectrum at 13.1 p indicated an unsubstituted benzene ring. The foregoing information was confirmed and the substance was shown to belong to the aspidospermine group by NMR- and mass spectrometry. In the NMR-spectrum (Table IV) the 17-proton absorption is found at 8.13 well downfield from the three-proton multiplet due to the other aromatic protons which is centered at 7.07 8. This shift is due to the proximity of the carbonyl group of the iVa-propionyl group. In the aliphatic part of the spectrum, absorptions which are characteristic of the... 

The simplest of the phenolic members of the aspidospermine group, demethylaspidospermine (XXXVII), has been found in A. discolor (40a). It was isolated as its crystalline perchlorate (25) from which the oily free... 

In the case of the aspidospermine group (Section II), the nature of the carbon skeleton was elucidated for aspidospermine only, the structures of the other members of the group following by correlation with this alkaloid, either directly or mass spectrometrically. Although mass spectrometry alone suggested the structure CXVII for the skeleton of some Aspidosperma alkaloids, the final proof of CXVII rests on both... 

Aspidofractinine (146), the parent member of this third large subgroup of alkaloids of the aspidospermine group, does not occur widely, and the only recent report of its occurrence is in the stem bark and root bark of Hunteria elliottii Pichon (12). Its Na-methyl (147) and Na-methyl-14,15-didehydro (148) derivatives are new alkaloids, which have been found in the roots of Vinca sardoa (67). The ester alkaloids occur much more widely, and several new sources have been reported for (—)-kopsinine (149), (-)-venalstonine (150), (-)-venalstonidine (151), and several minor alkaloids (152-160) (Table I). Of the six reported isolations of 15a-hydroxykopsinine (154), one (16) does not spedfy the configuration of the hydroxyl group. Since it is described as a known alkaloid, it is presumed to be 15a-hydroxykopsinine, because 15/3-hydroxykopsinine is unknown as a natural product. 

During the past two decades the total synthesis of the aspidospermine group of alkaloids has attracted considerable attention from numerous organic chemists, and virtually all the subgroups of alkaloids have now )delded to synthesis. Several routes of exceptional ingenuity have been developed, as well as notable attempts to mimic the presumed biosynthesis of the alkaloids in the laboratory. Most of the outstanding work of recent years was stunmarized in Volume SO (4) hence, the present account will not attempt to be exhaustive, but will nevertheless include all the salient references. 

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