Replacement of the Cobalt Center of Vitamin B 12 by Nickel: Nibalamin and Nibyric Acid Prepared from Metal‐Free B 12 Ligands Hydrogenobalamin and Hydrogenobyric Acid

The (formal) replacement of Co in cobalamin ( Cbl ) by Ni II generates nibalamin ( Nibl ), a new transition‐metal analogue of vitamin B 12 . Described here is Nibl , synthesized by incorporation of a Ni II ion into the metal‐free B 12  ligand hydrogenobalamin ( Hbl ), itself prepared from hydrogenobyric acid ( Hby ). The related Ni II  corrin nibyric acid ( Niby ) was similarly synthesized from Hby , the metal‐free cobyric acid ligand. The solution structures of Hbl , and Niby and Nibl , were characterized by spectroscopic studies. Hbl features two inner protons bound at N2 and N4 of the corrin ligand, as discovered in Hby . X‐ray analysis of Niby shows the structural adaptation of the corrin ligand to Ni II ions and the coordination behavior of Ni II . The diamagnetic Niby and Nibl , and corresponding isoelectronic Co I corrins, were deduced to be isostructural. Nibl is a structural mimic of four‐coordinate base‐off Cbls , as verified by its ability to act as a strong inhibitor of bacterial adenosyltransferase.