Heavy vitamin B12 derivatives

A process for preparing a heavy vitamin B12 having a mass shift of at least +7 over unlabelled vitamin B12, the process including:

• providing 13C-labelled 5,6-dimethylbenzimidazole having seven or more 13C atoms and optionally one or more 2H atoms,
• providing cobinamide dicyanide, and
• forming the heavy vitamin B12 from the 13C-labelled 5,6-dimethylbenzimidazole and the cobinamide dicyanide in the presence of a bacterium,
• wherein the heavy vitamin B12 comprises seven 13C atoms located in the dimethylbenzimidazole moiety and is a compound of formula (I):
• or a pharmaceutically acceptable salt, hydrate, solvate, or prodrug thereof,
• wherein R is 5′-deoxyadenosyl, OH, H2O, CH3, or CN.