Crystal structure of tolazoline hydrochloride (priscoline), an α-adrenergic antagonist

Abstract

The crystal and molecular structure of tolazoline hydrochloride (priscoline), an α-adrenergic antagonist which is clinically used as a vasodilating drug, has been studied by X-ray diffraction methods. The results show that the imidazole group is involved in a protonation process, the positive charge being dispersed over both nitrogen atoms of the imidazole ring, and the molecule adopts a biplanar conformation with an angle of 89.3(2)° between the phenyl and imidazole rings—an orientation which seems to be relevant for their interaction at the receptor site. Critical sites for the interaction of the adrenergic dihydroimidazoles with the α-receptors are discussed.