Site-selective oxidation of vitamin B12 using 2-iodoxybenzoic acid

Reaction of vitamin B 12 (B 12 ) with excess 2-iodoxybenzoic acid and 2-hydroxypyridine leads to selective oxidation of the 5′-hydroxyl group of the ribose tail of B 12 in a 30% isolated yield. The acid derivative was purified in one step by HPLC chroma­tography and characterized by MALDI-TOF mass spectrometry, 1 H NMR and 2D (HSQC and HMBC) NMR. The new carboxylic acid derivative is perfectly suited to make stable amide-based B 12 bioconjugates.