6-Amino-5-azacytidine

6-Amino-5-azacytidine is a 5-azapurine nucleoside derivative characterized by a six-membered pyrimidine ring fused to a furanose sugar, with a nitrogen atom at position 5 of the pyrimidine and an amino substituent at position 6. This compound arises as a synthetic byproduct during Azacytidine production due to nucleophilic attack at the 6-position during cytosine ring formation. The 5-aza substitution enhances nucleophilicity, promoting side reactions that yield the 6-amino variant. Structurally, it differs from Azacytidine by the additional amino group, which alters hydrogen bonding and tautomeric behavior. This impurity is employed as an HPLC reference standard for quantifying process-related impurities in Azacytidine drug substance batches.