CONFORMATION OF CIS-4-HYDROXY-PRAZIQUANTEL AND ITS CRYSTAL AND MOLECULAR-STRUCTURE

The crystal structure of racemic cis-4-OH-PZQ-the main metabolite of the anthelmintic drug Praziquantel-has been determined by X-ray analysis and refined to R = 0.064. In the unit cell there are two independent molecules, but with a similar conformation. The molecules of the same enantiomer (joined by H-bonds) form in the crystal a column along a-axis direction. Molecular mechanics calculations indicate that the conformation in the solid state does not correspond to the energy minimum and there are two lower energy conformations. Thus, in solutions these two conformers can most probably exist. Their concentration in solutions depends on the solvent polarity and the value of the dipole moment for the respective form of the molecule.