Proaporphines, reduced

Several groups have examined the 13C spectra of the aporphine alkaloids (6, 7, 38-40) examples are found in Fig. 10. The chemical shift assignments (Table X) for the aliphatic carbon atoms of rings B and C were made by comparison to laudanosine (28) (6) and to the reduced proaporphines (41). In the case of caaverine (49) a comparison with (+)-lirmidine (50) revealed the P deshielding effect of the TV-methyl group on C-5 and C-6a and the shielding of C-7 by a y effect. 

The 13C chemical shifts of several reduced (61-64) and nonreduced (65, 66) proaporphine alkaloids (Fig. 11 and Table XI) have been reported by Ricca and Casagrande (41). The authors studied several pairs of diastereo-mers and found the 13C chemical shifts to be sensitive to the relative stereochemistry in these compounds. 

The structure of imenine (72 R1 = R2 = OMe, R3 = R4 = Me, R5 = H), the first ketoaporphine alkaloid to have a substituent in the heterocyclic ring, was elucidated mainly by AT-ray analysis.92 The absolute configuration of S-( + )-isoboldine isolated from Corydalis pallida var. tenuis was assigned on the basis of o.r.d. and c.d. studies interestingly, all alkaloids isolated from this species belong to the S-series.97 The structure of the reduced proaporphine jaculadine... 

Mass spectrometry (22, 96,181, 530, 531) and NMR spectroscopy (65, 69,181,209,431) have been recorded. The UV spectra of the dienone alkaloids differ in the extinction maxima (proaporphine alkaloids at 220 nm (e 24800) and 285 nm (c 3000) promorphinane alkaloids 230 nm (e 24,000) and 285 nm (e 7500)). IR Spectroscopy reveals characteristic frequencies of the cross-conjugated dienone at 1655, 1630, and 1613 cm"i. On polarography the proaporphine and the promorphinane dienone compoimds are reduced (335) at a half-wave potential similar to that of aromatic aldehydes. 

Indole and isoquinoline alkaloids continue to play a dominant role. The apor-phinoids, comprising proaporphines, aporphines and related dimers, are treated separately, partly in order to reduce the burden on contributors aristolactams and aristolochic acids, which have not been reviewed since 1961, also are discussed in this chapter. This year the quinolizidine alkaloids, including the sesquiterpenoid Nuphar bases and the appropriate Lythraceae alkaloids, as well as azaphenalenes of plant and insect origin are reviewed together. Amaryllidaceae, Erythrina, imidazole, purine and peptide alkaloids are omitted from this volume, but it is expected that the chemistry of these groups covering the period 1974—1976 will be surveyed in Volume 7. 

This material is supplementary to The Alkaloids, Vol. XII, p. 349. t The proaporphine alkaloids of the cyclohexadienone type or those with a partially reduced ring D occur not only in the Papaveraceae but in many other plant families, such as Euphorbiaceae, Lauraceae, Menispermaceae, Monimiaceae, and Nymphaceae (1,393). Their widespread occurrence permits a study of the isolation and the synthesis of these compounds on a large scale. 

The products of the sodium borohydride reduction of (-)-mecambrine (20b) and of the catalytic hydrogenation of the same alkaloid and (—)-roemeramine (22a) were studied and, on the basis of the ORD curves and H NMR spectra, the relative configurations of these two alkaloids and of four stereoisomeric dihydromecambrinols 22b and 22c were established (418). Casagrande et al. (203) studied the synthesis of ( )-glaziovine (20a) and the stereochemistry of partially reduced proaporphine products (20, 412,446). 

The PMR spectra of several reduced proaporphines have been recorded both in deuteriochloroform and in pyridine-dg. PMR chemical shifts for 8,9-dihydroglaziovine in deuteriochloroform are shown below. The CMR spectra of fifteen reduced proaporphines have been recorded. 

Several homoaporphines and reduced homoproaporphines have recently been isolated from members of the Liliaceae, mostly by the Russian school. The assigned structures are reproduced below. However, in the case of the reduced proaporphines, the data available are fragmentary, and some of the stereochemical assignments still remain to be made or to be confirmed. 

The C-11 hydroxyl was tentatively assigned as being axial. Kesselringine shows negative CD Cotton effects at 250 and 300 nm, and a positive effect at 220 nm. By analogy with the reduced proaporphines, the absolute configuration of kesselringine was assumed to be as shown. ... 

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