meso-Brominated nitrosylcobinamides: Nitric oxide release and oxidation by dioxygen.

[Display omitted] • Efficient synthesis methods for meso-brominated aquacyanocobinamide and aquahydroxocobinamide. • meso-Bromination alters the aerobic stability of NOCbi in the presence of ligands. • Slower NO release from the meso-brominated NOCbi suggests milder hypotensive effects. • meso-Modification represents a valuable tool for modifying the properties of corrinoids as NO donors. This study explores the modification of nitrosylcobinamide, explicitly focusing on meso-bromination, and its impact on the dissociation rate of nitric oxide (NO). meso-Brominated aquahydroxocobinamide was efficiently synthesized from meso-brominated cyanocobalamin via hydrolysis, followed by decyanation step. Its reaction with Angeli's salt produces meso-brominated nitrosylcobinamide (NOCbi-Br). NOCbi-Br exhibits stability in the presence of dioxygen comparable to that of the unmodified NOCbi in neutral aqueous solutions. However, in the presence of L-histidine the oxidation of NOCbi-Br by dioxygen is significantly slower than unmodified NOCbi, indicating potential differences in ligand affinities. Furthermore, the rate constant for NO release from NOCbi-Br was lower than that of unmodified NOCbi, suggesting that meso-bromination strengthens the Co(II)–NO bond. These findings underscore the utility of meso-modification in tailoring the properties of corrinoids as nitric oxide donors, with potential implications for therapeutic applications. [ABSTRACT FROM AUTHOR]