Synthesis, solution and crystal structure of the coenzyme B(12) analogue Co(ß)-2'-fluoro-2',5'-dideoxyadenosylcobalamin.

ABSTRACT

Crystal structure analyses have helped to decipher the mode of binding of coenzyme B12 (AdoCbl) in the active site of AdoCbl-dependent enzymes. However, the question of how such enzymes perform their radical reactions is still incompletely answered. A pioneering study by Gruber and Kratky of AdoCbl-dependent glutamate mutase (GLM) laid out a path for the movement of the catalytically active 5'-deoxyadenosyl radical, in which H-bonds between the protein and the 2'- and 3'-OH groups of the protein bound AdoCbl would play a decisive role. Studies with correspondingly modified coenzyme B12-analogues are of interest to gain insights into cofactor binding and enzyme mechanism. Here we report the preparation of Coß-2'-fluoro-2',5'-dideoxyadenosylcobalamin (2'FAdoCbl), which lacks the 2'-OH group critical for the interaction in enzymes. 2'FAdoCbl was prepared by alkylation of cob(I)alamin, obtained from the electrochemical reduction of aquocobalamin. Spectroscopic data and a single crystal X-ray analysis of 2'FAdoCbl established its structure, which was very similar to that one of coenzyme B12. 2'FAdoCbl is a (19)F NMR active mimic of coenzyme B12 that may help to gain insights into binding interactions of coenzyme B12 with AdoCbl-dependent enzymes, proteins of B12 transport and of AdoCbl-biosynthesis, as well as with B12-riboswitches.