Benidipine Impurity 70

(R) -5- ((((R) -1-benzylpiperidin-3-yl) oxy) carbonyl) -2,6-dimethyl-4- (3-nitrophenyl) -1,4-dihydropyridine-3-carboxylic acid and (S) -5- ((((S) -1-benzylpiperidin-3-yl) oxy) carbonyl) -2,6-dimethyl-4- (3-nitrophenyl) -1,4-dihydropyridine-3-carboxylic acid