Learning from B₁₂ enzymes: biomimetic and bioinspired catalysts for eco-friendly organic synthesis

Abstract

Cobalamins (B12) play various important roles in vivo. Most B12-dependent enzymes are divided into three main subfamilies: adenosylcobalamin-dependent isomerases, methylcobalamin-dependent methyltransferases, and dehalogenases. Mimicking these B12 enzyme functions under non-enzymatic conditions offers good understanding of their elaborate reaction mechanisms. Furthermore, bio-inspiration offers a new approach to catalytic design for green and eco-friendly molecular transformations. As part of a study based on vitamin B12 derivatives including heptamethyl cobyrinate perchlorate, we describe biomimetic and bioinspired catalytic reactions with B12 enzyme functions. The reactions are classified according to the corresponding three B12 enzyme subfamilies, with a focus on our recent development on electrochemical and photochemical catalytic systems. Other important reactions are also described, with a focus on radical-involved reactions in terms of organic synthesis.

Learning From Vitamin B12‐Mediated Reactions: Cobalt(III)−Carbon‐Assisted Catalytic C−H Difluoroacylation of (Hetero)Arenes through Controlled‐Potential Electrolysis

“…Cobalt−carbon complexes are among the most studied organometallic bonds . These complexes act as important synthetic intermediates that can be cleaved homolytically by photolysis, electrolysis, or thermolysis to generate Co(II) and carbon‐centered radicals.…”

Vitamin B12 Enables Consecutive Generation of Acyl and Alkyl Radicals from One Reagent

“…[49] To provide sufficient solubility hydrophobic vitamin B 12 derivative (CN)(H 2 O)Cby(OMe) 7 (3) was selected as a catalyst. The formation of desired product 14 in only 30 % yield and the presence of by-products indicated a number of competing reactions, including: dehalogenation (15), generation of only alkyl radical (16), reduction (17) Interestingly, the structure of products 15 and 16, the lack of halide and the presence of thioester moiety respectively, suggests that alkyl radicals generate faster than acyl ones.…”

“…[8][9][10][11][12][13][14] Of particular importance are Co complexes that mimic native reactivity of vitamin B 12 (1, cobalamin) (Figure 1, Scheme 1). [15][16][17][18] These are represented by cobaloxime (2) [19] and heptamethyl cobyrinate ((CN)(H 2 O)Cby(OMe) 7, 3) which is a derivative of vitamin B 12 that have been already successfully applied to radical-processes. [15,20] Catalytic activity of these compounds is inherently connected with the central Co(III) ion and its ability to access +1 Mechanistic studies reveal that alkyl corrins forms at much higher rate than the respective acyl derivatives enabling selective reactions with activated olefins.…”

The Merger of Photoredox and Cobalt Catalysis

“…The reduction of protons into molecular hydrogen is an indispensable transformation in artificial photosynthesis and, in that context, the combination of visible-light-driven photocatalysts and cobalt complexes has been intensively studied [39]. In addition, early contributions on biomimetic chemistry regarding vitamin B12 and its model compounds under photochemical conditions [40,41] should also be regarded as pioneering work in cobalt/ photoredox cooperative catalysis. Despite these precedents and recent developments in cobalt/photoredox cooperative catalysis, to the best of our knowledge there is still no review that focuses on this topic from the perspective of synthetic chemistry.…”