The Alkaloids of Vincetoxicum officinale

Platonova et al. (6) have reported the isolation from Antitoxicum funebre Boiss. and Kotschy of the alkaloid antofine, C23H25O3N (mp 213°-215°), containing three methoxy groups. Pailer and Streicher (5) have suggested that their alkaloid A from Vincetoxicum officinale Moench could be identical with antofine. Both A and tylophorine were isolated from this plant. 

Alkaloid A has the molecular formula C23H25O3N and three methoxyl groups. Its UV-spectrum is very similar to that of tylophorine. The IR-spectrum shows the absence of NH or OH. The mass spectrum of A shows a molecular ion peak at m/e 363 and a base peak at m/e 294 (M-69), a behavior parallel to that of tylophorine which shows a molecular ion peak at m/e 393 and a base peak at m/e 324, probably by the fragmentation depicted below  

The presence of a phenanthroindolizidine ring system can be assumed on the basis of the UV- and mass-spectra. Oxidation of the alkaloid with alkaline hydrogen peroxide yielded m-hemipinic acid as the only isolable product. On the basis of its IR-spectrum and biogenetic considerations, the methoxyl groups can be assigned to the 2,3,6- or 3,6,7-positions on the phenanthroindolizidine system leading to the alternate structures XVa and XVI. It is of interest that racemic forms of both the possible structures have already been synthesized (12, 18). 

The phenanthroindolizine alkaloids can be visualized as arising by the condensation of two molecules of dihydroxyphenylalanine or one molecule of dihydroxypheny]alanine and one of t3Tosine (or their equivalents, the corresponding benzoyl acetic and phenyl pyruvic acids) with ornithine (or its equivalent, y-aminobutyraldehyde). 

The joint occurrence of tylophorine and tylocrebrine with the seco-phenanthroindolizidine alkaloid septicine (XXI) in Ficus septica (4) lends support to the biogenetic scheme outlined above. It is also of interest that septicine is transformed to a mixture of tylophorine and tylocrebrine on UV-irradiation. It is quite possible that the amorphous base (mp 125°-130°), of Chopra et al. 10) is in fact septicine. 

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