Photochemical stability of 4′-azido-2′-deoxy-2′-methylcytidine hydrochloride: structural elucidation of major degradation products by LC-MS and NMR analysis

► The stability of a new 4′-azido-2′-deoxy nucleoside analog was investigated. ► The azide moiety induced drug degradation upon exposure to light. ► Photolysis products were identified by LC-MS and NMR analysis. ► Three main photodegradation pathways were unraveled.