Aporphinoids

The aporphinoid alkaloid PO-3 (129) was also prepared by intermolecular benzyne cycloaddition between 1-methylene isoquinolines 148 and arynes derived from 147 (Scheme 53). The alkaloid was finally isolated by means of preparative thin layer chromatography (91JOC2984). 

H. Guinaudeau, M. Leboeuf, and A. Cav6, J. Nat. Prod. 47,565 (1984). Dimeric aporphinoid alkaloids. Cites 23 new dimeric alkaloids and 8 related synthetic derivatives for 1979-1984 48 references. 

M. Shamma and H. Guinaudeau, Tetrahedron 40, 479S (1984). Biosynthesis of aporphinoid alkaloids. In addition to monomeric alkaloids, discusses proaporphine- and aporphine-benzyliso-quinoline dimers, dimeric oxidized aporphines, and types derived by catabolism of benzyliso-quinoline-derived dimers. 

Aporphinoids are by far the most abundant alkaloids in this genus and also, generally speaking, in the family Annonaceae. Guatteria has proved to be a rich source of unusual structures of this general type. Aporphines have been reviewed in Volume 24 of this treatise (3) and elsewhere (4-7), and a review on aporphinoids of the Annonaceae has just been published (8). For this reason we address the structures and chemistry of only a few alkaloids of this type that have not been included in the Kametani and Honda review (5). 

Goudotianine was obtained from the Colombian species G. goudotiana (29). The structure 126, proposed as a poster in London in 1984, rests primarily on the H-NMR spectrum associated with NOE results. The placement of the A-ring hydroxyl group at C-2 rather than C-3 is based on the anticipated instability of an aporphinoid with both C-3 and C-9 phenolic groups. This structure has not been confirmed until now. 

A number of structural types that have been found in Guatteria species and occasionally in other genera of the Annonaceae appear to be related biogenetically to the aporphinoids. The lack of experimental proof of this derivation, which is discussed in a later section (see Section V), makes it advisable to consider these compounds separately. 

The possible origins of highly conjugated lactam groups has been discussed above in connection with the biogenesis of dielsiquinone (134). Similar considerations may be applicable to dielsine (137), dielsinol (138), and 2,7(or 6)-dimethoxy-6(or 7)hydroxyonychine (166, 167). In the case of the latter compound, as with dielsiquinone, the methoxyl group at C-2 can be traced back to a hypothetical 4-methoxylated aporphinoid precursor. 

With the foregoing caveat in mind, and considering the alkaloids found in higher concentrations, Guatteria seems to be on the whole a rather typical an-nonaceous genus characterized by the almost universal presence of aporphinoids. These compounds are often accompanied by unexceptional berbines and/or pro-toberberines as well as occasional monomeric benzylisoquinolines. 

The year under review has witnessed the isolation and structural elucidation of no less than nine new aporphines, as well as of five aporphine-benzylisoquinoline dimers. Two of these five aporphine-benzylisoquinolines, namely kalashine and khyberine, are the first such dimers known to be substituted at C-l 1 of the aporphine moiety. Thallium(m) trifluoroacetate is an oxidizing agent which effects the cyclization of tetrahydrobenzylisoquinolines to aporphines in satisfactory yields.1 A listing of aporphinoid alkaloids has appeared.2... 

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