Stabilizing intramolecular cobalt–imidazole coordination with a remote methyl group in the backbone of a cofactor B12–protein model

Abstract

This communication describes the stabilizing effect (ΔΔG° = −4 kJ mol⁻¹) of a remote methyl group in the backbone of a cobalamin–enzyme mimic on intramolecular imidazole–cobalt coordination. For this purpose, two B₁₂ derivatives with an appended imidazole base were synthesized and analysed with spectrophotometric pH titrations. Qualitative conformation analysis of the backbone structure suggests that a thermodynamically unfavoured gauche interaction in the base-off form of a model containing an (R)-configured CH₃ group at position C176 of the linker between the corrin ring and the terminal imidazole ligand steers the base toward cobalt coordination.