Clickable VitaminB12 Derivative

A clickable vitaminB12 derivative possessing the azide functionality at the 5-position was synthesized by means of a two-step procedure on the gram scale. The reaction of cobalamin with mesyl chloride (MsCl) afforded the 5-OMs derivative, which was subsequently transformed to the desired 5-azide, the structure of which was confirmed using X-ray analysis. It proved to be reactive in the azidealkyne 1,3-dipolar cycloaddition reaction to give substituted triazoles in high yields. A study of the reaction conditions and the scope of the process are reported.