Stereochemistry, proaporphines

Coyhaiquine (107), C26H27N05, from Berberis empetrifolia Lam. (Ber-beridaceae), although not formally a bis alkaloid, appears to be derived by in vivo degradation of a proaporphine-benzylisoquinoline. NMR spin decoupling experiments assigned the chemical shifts of the 6a, 7a, and 7(3 hydrogens. NOE experiments then showed a 3% enhancement of the 7a-H on irradiation of the 8-H, establishing the indicated syn stereochemistry (64). 

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. 

New proaporphine alkaloids are (-l-)-isocrotsparinine (1), (-I-)-N-methyliso-crotsparinine (2), and ( )-tetrahydroglaziovine (3), all obtained from Croton spar-siflorus. The stereochemistry of crotsparinine has been defined as in structure (4). Jacularine and Base-E, two minor alkaloids previously isolated from C. linearis have been assigned stereo formulas, with the former being enantiomeric with (1), and the latter being represented by (5)/... 

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). 

Proaporphine-BeHzylisoquinoline Dimers.—The first known proaporphine-benzylisoquinoline dimer, pakistanamine (112), has been isolated from Berber is baluchistanica Ahrendt (Berberidaceae). Dienone-phenol rearrangement of pakistanamine (112) using dilute hydrochloric acid gave rise to the phenolic aporphine-benzylisoquinoline dimer (113), and O-methylation of this product with diazomethane provided 00-dimethylpakistanine (114) of known structure and stereochemistry. ... 

The fragmentation process in the mass spectra of proaporphines is strongly dependent on the character of the spiranoid ring D, as well as on the substitution pattern in the aromatic ring A and the relative stereochemistry. Cleavage patterns should, therefore, be compared only among structurally close analogs. 

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