Cancentrine

In the spectrum of the cancentrine model compound [171] one of the methoxyl group of protons absorbs at low frequency (5 3-38) compared with absorption for the other methoxyl protons at <5 3 85, 3-85, and 3 90. This low frequency signal was assigned to the 7-methoxyl protons. In the hydrogenated derivative the lowest frequency methoxyl proton absorption is at <5 3-65. The low frequency aromatic proton absorption ((56-59) in [171] was assigned to the 8-proton. Both low frequency shifts are attributed to the shielding effects of ring c. (127)... 

Details of the structure proof of cancentrine (28) have appeared (14), and the absolute configuration has been determined by X-ray study of a derivative (15). 

The chemistry of the cancentrine family of alkaloids has been reviewed (16,17). (Also see 10-oxocancentrine, Section II,C,85.)... 

C36H34N207 Tetradehydrolimacine Tetradehydrolimacusine Cancentrine O-Methylpunjabine Stepinonine... 

Cancentrine (43) is a complex alkaloid that embodies within its structure a modified codeine skeleton and a cularine skeleton. Its 13C spectrum along with that of some derivatives was studied (36) in order to obtain chemical... 

The spectrum ofcancentrine was interpreted primarily by comparison with the previously discussed spectra of cularine and the morphine alkaloids, particularly codeine. The assignments of C-10, C-15, C-16, and the NCH3 of cancentrine followed by analogy from the corresponding carbon atoms of codeine and were confirmed by the off-resonance spectrum. The high-field... 

The aromatic carbon atoms of the morphine moiety of cancentrine were assigned by comparison to codeine (32, 33). For example, C-4 was assigned to 145.1 ppm because of its low intensity. Since this carbon atom does not have any neighboring protons to provide dipolar relaxation, it therefore should have a longer Tx and a lower intensity because of partial saturation owing to the short delay between the rf pulses. The similar chemical shifts of C-l 1, C-l 2, and C-30 did not allow unambiguous assignments to be made. 

A similar analysis of the cularine portion of cancentrine resulted in the tentative assignment of the remaining aromatic carbon atoms (36). The signals at 194.0, 160.1, and 104.3 ppm were assigned to C-l, C-25, and C-24, respectively. The assignment of the oxygenated carbon atoms can at best be considered tentative. 

These data were used to good advantage in the structural elucidation of 10-oxocancentrine (44). Other physical data had suggested that the new alkaloid differed from cancentrine only at C-10. To provide additional support for these observations the 13C spectrum of 10-oxocancentrine and the model compounds, codeinone (45) and 10-oxocodeinone (46), were recorded. In the latter the carbonyl group at C-10 appears at 190.4 ppm. This change in functionality caused a deshielding of carbons C-9, C-14, C-3, and C-12 relative to codeinone. 

In the aliphatic region of the 10-oxocancentrine spectrum the signal at 20.4 ppm corresponding to C-10 in cancentrine was absent. Both C-9 and C-14 were deshielded as in the model discussed above. These results confirmed the location of the carbonyl at C-10 in oxocancentrine. The assignments made to the quaternary aromatic and carbonyl carbons were considered to be tentative by the authors. 

The structure of a most unusual dimeric benzylisoquinoline alkaloid, cancen-trine (316 R = H), has been elucidated almost forty years after it was originally isolated from Dicentra canadensis.263 The n.m.r. spectrum of cancentrine showed signals corresponding to three aromatic methoxy-groups and one iV-methyl group. Analysis of its hydrochloride and paper electrophoresis studies indicated the presence of one basic and one non-basic nitrogen. Hofmann degradation... 

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