Roxithromycin EP Impurity I

(3R,4S,5S,6R,7R,9R,11S,12R,13S,14R, E) -6- (((2S,3R,4S,6R) -4- (dimethylamino) -3- ((2-methoxyethoxy) methoxy) -6-methyltetrahydro-2H-pyran-2-yl) oxy) -14-ethyl-7,12,13-trihydroxy-4- (((2R,4R,5S,6S) -5-hydroxy-4-methoxy-4,6-dimethyltetrahydro-2H-pyran-2-yl) oxy) -10- (((2-methoxyethoxy) methoxy) imino) -3,5,7,9,11,13-hexamethyloxacyclotetradecan-2-one