1 H, 13 C and 15 N NMR spectroscopic characterization of unexpected degradation products of the nifedipine analogue bis(2‐cyanoethyl) 2,6‐dimethyl‐4‐(2‐nitrophenyl)‐1,4‐dihydro‐3,5‐pyridinedicarboxylate

In the course of saponification experiments with bis(2‐cyanoethyl) 2,6‐dimethyl‐4‐(2‐nitrophenyl)‐1,4‐dihydro‐3,5‐pyridinedicarboxylate ( 1 ), an analogue of the calcium channel blocker nifedipine, three unexpected degradation products were isolated. The compounds were identified as 3‐(2‐acetamido‐1‐carboxy‐1‐propenyl)‐1‐hydroxy‐2‐indolecarboxylic acid ( 3 ), 9‐hydroxy‐1,3‐dimethyl‐β‐carboline‐4‐carboxylic acid ( 4 ) and 6‐hydroxy‐2,4‐dimethyl‐5‐oxo‐5,6‐dihydrobenzo[ c ][2,7]naphthyridine‐1‐carboxylic acid ( 6 ). The structures of these compounds were deduced from one‐ and two‐dimensional 1 H, 13 C and natural abundance 15 N NMR experiments ( 1 H, 1 H‐COSY, gs‐HSQC, gs‐HMBC, 15 N gs‐HMBC), and corroborated by comparison of their NMR data with the respective data for structurally similar compounds. Copyright © 2002 John Wiley & Sons, Ltd.