50-Carboxycyanocobalamin

50-Carboxycyanocobalamin is a structurally modified corrinoid derivative featuring a carboxylic acid substituent at the 50-position of the cyanocobalamin core. This impurity retains the characteristic cobalt-coordinated corrin ring and axial cyanide ligand but incorporates an oxidized carboxyl group, likely arising from electrophilic oxidation of a methyl or hydroxyl moiety in the parent compound. The substitution disrupts the native cobalamin coordination geometry, altering its redox and spectroscopic properties. This compound serves as an HPLC reference standard for quantifying degradation-related impurities in cyanocobalamin pharmaceutical formulations.