the unchanged drug with a 1,4-dihydropyridine structure was oxidized with nitrous acid to its pyridine anlogue , which was stable for gas chromatography , and subjected to mass spectrometry at m/e 134 ( nicardipine ) and m/e 137 ( n-d3-methyl derivative ) .
C0012315
dihydropyridine
C0028005
nicardipine