4-Methylcyanocobalamin is a methylated cobamide derivative featuring a corrin ring system with a cyanide ligand at the cobalt center and a methyl substitution at position 4 of the lower axial chain. This compound retains the 17,20-butanediol moiety and adenosyl phosphate group characteristic of cyanocobalamin but exhibits a structural modification via the 4-methyl group, altering its redox and coordination properties. The methyl substitution introduces steric hindrance, reducing enzymatic activity compared to the parent vitamin B12. Synthetically derived as a byproduct during cobalamin alkylation processes, it serves as an HPLC reference standard for impurity profiling in cyanocobalamin formulations.
