Crystal Structures of Antiarrhythmic Drug Disopyramide and Its Salt with Phthalic Acid

Disopyramide (DPA) is as a class IA antiarrhythmic drug and its crystallization from cyclohexane at ambient condition yields lower melting form crystals which belong to the monoclinic centrosymmetric space group P21/n, having two molecules in an asymmetric unit. Crystal structure analysis of pure DPA revealed closely associated aggregates via amide–amide dimer synthon through N–H∙∙∙O hydrogen bond whereas second amide N–H engaged intramolecular N–H∙∙∙N with N-nitrogen 2-pyridine moieties. Crystallization phthalic acid (PA) 1: 1 stoichiometric molar ratio acetone yielded block shape 1:1 DPA_PA salt. Its X-ray single crystal formation salt by transfer acidic proton one carboxylic groups PA tertiary amino chain moiety (N3-nitrogen atom) molecules. comprising protonated PA¯ anion (hydrogen phthalate counterion) unit linked C–H∙∙∙O bonds. Pure were further characterized differential calorimetric analysis, thermal gravimetric powder x-ray diffraction infrared spectroscopy.