Roxithromycin EP Impurity CC37H68N2O13FR166227(3R,4R,5R,6S,7R,9S,10E,11S,12R,14S)-6-[(2S)-4-(dimethylamino)-3-hydroxy-6-methyl-tetrahydropyran-2-yl]oxy-14-ethyl-7,12,13-trihydroxy-10-hydroxyimino-4-[(2R,5S)-5-hydroxy-4-methoxy-4,6-dimethyl-tetrahydropyran-2-yl]oxy-3,5,7,9,11,13-hexamethyl-oxacyclotetradecan-2-one