Photodecomposition of a new 1,4-dihydropyridine: furnidipine.

The photodecomposition of new 1,4-dihydropyridine, furnidipine (CRE-319); [2,6-dimethyl-4-(2-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid 3-tetrahydrofurfuryl 5-methyl diester) was studied by voltammetric, UV-vis spectrophotometric, and HPLC technique with three different light conditions (artificial daylight, UV light, and room daylight). The artificial daylight photodecomposition of furnidipine follows 0.5-order kinetics as assessed by the above-mentioned techniques. Furthermore, the daylight photoderivative was isolated and identified by NMR and IR as 2,6-dimethyl-4-(2-nitros-ophenyl)pyridine-3,5-dicarboxylic acid 3-tetrahydrofurfuryl 5-methyl diester. Quantitative kinetic data for the UV photodecomposition of furnidipine cannot be obtained due to both the high rate of degradation (< 1 min) and intermediate reactions. However, polarographic, spectroscopic, and chromatographic evidence permits us to identify this photoproduct as 2,6-dimethyl-4-(2-nitrophenyl)pyridine-3,5-dicarboxylic acid 3-tetrahydrofurfuryl 5-methyl diester. Polarography was the most useful technique to assess the photodegradation of this drug from the qualitative point of view, and quantitative kinetic data were similar to those obtained by HPLC and UV-vis spectroscopy.