Stability of new analgesic active compound, pyrrolo-[3,4-c]pyridine derivative, in aqueous solutions.

The kinetics of hydrolysis of 4-ethoxy-2-[2-hydroxy-3-(4-phenyl-1-piperazinyl)]propyl-2,3-dihydro-6-methyl-1,3-dioxo-1H-pyrrolo[3,4-c]pyridine (III) in aqueous solutions at 333, 343, 353 and 363 K over the pH range 0.4-5.0 was investigated. The decomposition was observed by means of the HPLC method. A sample solution was chromatographed on octadecyl-packed column (LiChrosorb 100 RP-18 column 250 x 4.0 mm I.D., dp 5 microm) using a mixture of acetonitrile and phosphate buffer (pH 2, 0.01 mol/L) as an eluent (45:55, v/v--phase A or 30:70, v/v--phase B). The UV detection was performed at a wavelength of 239 nm. The stability of compound III was found to be dependent on pH. The pH-rate profile indicated specific acid- and base-catalyzed reactions as well as spontaneous water-catalyzed degradation. The ionic strength effect, the pKa value (2.9; 6.0), the pHmin value (2.1) and thermodynamic parameters of the reaction (energy of activation (Ea), enthalpy (DeltaH(not equal to)) and entropy (DeltaS(not equal to were determined.