Roxithromycin Impurity C (Erythromycin oxime)

Roxithromycin Impurity C is a structurally related byproduct derived from erythromycin via oxime formation at the C-9 ketone, resulting in a 14-membered macrolide lactone core conjugated with cladinose and desosamine sugars. The oxime functional group introduces a nitrogen-hydroxyl moiety, altering the parent drug's pharmacophore while retaining the characteristic polyene macrolactone scaffold. This impurity arises during synthetic processes involving roxithromycin's methylation, serving as a critical HPLC reference standard for impurity profiling in quality control.