Synthesis and Structure of Dimephosphone Pyridinoylhydrazones with Antimycobacterial Activity

Nicotinoyl- and isonicotinoylhydrazones of 2-dimethoxyphosphoryl-2-methylpentan-4-one (the active ingredient of the medicinal preparation Dimephosphone) were synthesized. It was shown that crystals of both hydrazones contained a single spatial form of the E C=N isomer. The dimephosphone pyridinoylhydrazones existed in slightly polar and polar solvents as a mixture of two amide conformers of a single E C=N isomer. This was due to hindered rotation of the molecular fragments around the (O=)C–N amide bond. The ratio of conformers was determined by the solvent and the time of solution preparation. Both hydrazones possessed low toxicity and high antimycobacterial activity.