Replacement of the cobalt center of vitamin B₁₂ by nickel: Nibalamin and nibyric acid prepared from metal-free B₁₂ 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 B₁₂. Described here is Nibl, synthesized by incorporation of a Ni^II ion into the metal-free B₁₂ 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.