Photodegradation kinetics of lodenafil carbonate, structure elucidation of two major degradation products using UPLC-MS/MS and in vitro cytotoxicity

Abstract

The photostability of lodenafil carbonate was studied and some degradation products were observed. A stability-indicating liquid chromatography method for the determination of lodenafil carbonate was used to determine the kinetics of photodegradation. The identification of two major photodegradation products was performed by an isocratic ultra performance liquid chromatography-tandem mass spectrometry method (UPLC-MS/MS). UPLC-MS/MS was carried out on a Waters® Acquity Ultra Performance LC system coupled to a Micromass® Quadrupole Time of Flight tandem mass spectrometer equipped with an electrospray ionization interface in positive ion mode. The column applied was Acquity UPLC® BEH C18; the mobile phase consisted of a mixture of methanol–formic acid 0.1% pH 4.0 (55 : 45, v/v) at a flow-rate of 0.4 mL min⁻¹ and UV detection at 290 nm. The photodegradation of lodenafil carbonate followed first-order reaction kinetics and the kinetic parameters of degradation rate constant and t_90% were calculated. Under photodegradation conditions, ion products were detected at m/z 393 (DP-1) and at m/z 377 (DP-2). The product DP-1 is 4-ethoxy-3-(1-methyl-7-oxo-3-propyl-6,7-dihydro-1H-pyrazolo [4,3-d]pyrimidin-5-yl)-benzenesulfonic acid and DP-2 probably is 4-ethoxy-3-(1-methyl-7-oxo-3-propyl-6,7-dihydro-1H-pyrazolo [4,3-d]pyrimidin-5-yl) benzenesulfinic acid. The degraded samples of lodenafil carbonate were also evaluated in order to determine the in vitro cytotoxicity against mononuclear cells.