Alkaloids of Pedicularis macrochila

Chemistry of Natural Compounds
1976.0

Abstract

From the epigeal part of Pedicularis macrochila collected in the gorge of the R. Dzhetyagus on June 8, 1972, we have obtained 0.18% of total alkaloids, from which we have isolated plantagonine [1], noractinidine [2], and a base CnH13NO3 with mp 380-382°C, Rf 0.91 [in the butyl acetate-chloroform (9: 1) system]. The latter proved to be identical with gentiananine [3]. The IR spectrum of the base [λmax 219,265 nm (log ε 3.69, 3.76)] is characteristic for pyridine alkaloids. In the IR spectrum of gentiananine there are absorption bands for the lactone of a carbonyl group at 1735 cm⁻¹ and for an aromatic ring at 1600 cm⁻¹. On the basis of its UV and IR spectra, gentiananine has the skeleton of gentianine [4]. The NMR spectrum of gentiananine (CCl4, δ scale) has signals at 3.38ppm (3H, singlet, methoxy group) and 2.25 and 1.78 ppm (3H and 3H, singlets, C-methyl groups), and in the weak-field region (6.0-10.0 ppm) there are no signals of protons. Consequently, in the base all the aromatic protons have been replaced. In the NMR spectra of pyridine alkaloids substituents present in the α position are revealed in weaker fields than those in the β position. On this basis it may be concluded that one of the C-methyl groups in gentiananine is present in the α position and the other in the β position. Thus, structures (I) and (II) are possible for gentiananine. On the basis of the biogenesis of the gentian alkaloids [5], (I) is the more probable.

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