Hydrogenobinamide and nibinamide - metal-free ligand and Ni(II)-analogue of the vitamin B¹² precursor cobinamide

Abstract

The replacement of cobalt in vitamin B₁₂ derivatives by other transition metals is a formal path to non-natural corrins. Here, we describe nibinamide (Nibi), the novel Ni(II)-analogue of the natural B₁₂ -derivative cobinamide (Cbi), and its synthesis from the metal-free ligand of Cbi, hydrogenobinamide (Hbi), both isolated as tetrafluoroborate salts. Aqueous solutions of the metal-free corrin Hbi are strongly fluorescent, whereas its Ni(II)-complex Nibi is non-luminescent. The solution structures of Hbi and of Nibi were characterized by hetero-nuclear NMR-spectroscopy. The Ni(II)-corrin Nibi was deduced to be roughly iso-structural to cob(I)inamide (Cbi^I) and to house a diamagnetic d⁸-metal-ioniso-electronic to Co^I in Cbi^I. The chemically robust Nibi is, thus, a structural mimic of enzyme-activated and reduced biosynthetic precursors of vitamin B¹² and a B¹²
-antimetabolite potentially functioning as a specific inhibitor of B^12-biosynthesis.

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ORCID for Andrew D. Lawrence: orcid.org/0000-0002-5853-5409

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