The structure of papaverine in solution as determined by H nuclear magnetic relaxation methods

Abstract

Hydrogen relaxation in the papaverine molecule in CDCI3 solution has been studied so as to derive the conformation about the C 1-CH2 bond. This was done for papaverine itself, in which the resonances of H 5 and H 8 were reassigned on the basis of noesy spectra, and in the 7-OC2H3 analogue, the spectrum of which confirms the reassignment. The value for the torsional angle C 8a-C 1-CH2-C lays between 70 and 92°, in good agreement with those found in crystals of papaverine, its hydrochloride, and the related alkaloid isosevanine (all in the range 68-94°). Conformational energy calculations show a broad energy minimum over the range 60-70°. The 6, 7-methylenedioxy analogue of papaverine has esse..