Onychopetalum amazonicum

The structure of onychine, an alkaloid of Onychopetalum amazonicum that has hitherto been formulated as (33), must be revised to (34). Both structures have been synthesized the former was found to be different from onychine and the latter identical with it.33 Three stereospecific syntheses of sesbanine (35) have been reported. In one, 4-(methoxycarbonyl)nicotinic acid is the starting point (Scheme 3).34 The other two both start from 4-methylnicotinonitrile, one35 leading to ( )-sesbanine and the other to the (+)-enantiomer.35 10-Deoxyses-banine has also been synthesized, by a route which appears applicable to the alkaloid itself.37... 

Onychine (135) was first described as a natural product in 1976, when its isolation from Onychopetalum amazonicum (Annonaceae) was reported (83), and its structure was given as 4-methyl-l-azafluoren-9-one (158) on the basis of elemental analysis and high-resolution MS, as well as UV, IR, and H-NMR spectra. As in all the azafluorenone alkaloids discovered to date, the complex UV spectrum is reminiscent of that of fluoren-9-one, and the H-NMR spectrum clearly indicates the presence of a 2,3-disubstituted 4-methylpyridine moiety. The immediate conclusion, therefore, is that onychine is either l-methyl-4-azafluoren-9-one (135) or 4-methyl-l-azafluoren-9-one (158), which is supported by the spectral properties of the secondary alcohol obtained by reduction of the ketone group and of the acetylation and hydrogenolysis products of this... 

Tetrahedron Letters, 1978, 2723), whereas onychine (103) from Onychopetalum amazonicum is based on a 2- benzoyl -pyridine sub-structure (J. Koyama et al.. Heterocycles, 1979, 12, 1017). 

Investigation of the trunk wood of Onychopetalum amazonicum yielded the structurally new alkaloid onychine, l-aza-4-methylfluorenone (XIV.163), and it was suggested that its biosynthesis involves phenylalanine and mevalonate in an interesting pathway leading to the pyridine nucleus. 

The few alkaloids devoid of an isoquinohne skeleton are onychine (1) from Onychopetalum amazonicum eupolauridine (2), a naphthyridine alkaloid, althou it is considered as a product of degradation of an oxoaporphine, Hriodenine annomontine (3) and methoxyannomontine (4), first examples of a new class of pyrimi-... 

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