Application of bioorganometallic B12 in green organic synthesis

Bioorganometallic structure found in coenzyme B₁₂ is a key component in B₁₂-dependent enzymatic reactions in natural enzymes. Cleavage of a cobalt-carbon bond in organometallic B₁₂ compound provide reactive intermediate for molecular transformations. Application of the bioorganometallic B₁₂ in organic synthesis have been developed using natural vitamin B₁₂ as well as synthetic vitamin B₁₂ derivatives as a bioinspired catalyst in organic solvent. Vitamin B₁₂ derivatives composed of corrinoid structure should form stable organometallic compound having a cobalt-carbon bond. Using the unique property of the organometallic vitamin B₁₂ derivatives, various catalytic reactions have been developed in synthetic organic chemistry. The dual catalytic system of vitamin B₁₂ derivatives and photocatalyst, such as Ru(II) polypyridyl complex or titanium oxide, could construct light-driven molecular transformations. The B₁₂-dependent enzymes mimic reactions, such as the dechlorination of organic halides and the radical mediated isomerization reactions, catalytically proceed in the dual catalyst system. Electroorganic syntheses mediated by the vitamin B₁₂ derivatives have been developed as green molecular transformations. The redox active vitamin B₁₂ derivatives shows a unique catalysis in the electroorganic synthesis, such as alkene and alkyne reductions.

Visible light-driven Giese reaction with alkyl tosylates catalysed by nucleophilic cobalt

The scope of the Giese reaction is expanded using readily available alkyl tosylates as substrates and nucleophilic cobalt(i) catalysts under visible-light irradiation. The reaction proceeds preferentially with less bulky primary alkyl tosylates. This unique reactivity enables the regio-selective Giese reaction of polyol derivatives.

We report an efficient approach for the Giese reaction with abundant alkyl tosylates as alkyl radical sources using a nucleophilic cobalt catalyst under visible-light irradiation.

Visible Light-Driven, One-pot Amide Synthesis Catalyzed by the B12 Model Complex under Aerobic Conditions

A visible light responsive catalytic system with the B₁₂ complex as the catalyst and [Ir(dtbbpy)(ppy)₂ ]PF₆ as the photosensitizer was developed. It provides a convenient and efficient way to synthesize amides. Based on this method, trichlorinated organic compounds were converted into amides in the presence of an amine under aerobic conditions at room temperature in a one-pot procedure. Various trichlorinated organic compounds and an amine source, such as primary, secondary, and cyclic amines, have been evaluated for this transformation, providing the expected products in moderate to excellent yields. Notably, product formation depended on the reaction atmosphere where the amide was obtained under aerobic conditions while partially dechlorinated products were obtained under anaerobic conditions. As this protocol is free from hazardous reagents, extra additives, noble metals, and dangerous gas, the present method provides a novel and efficient approach for amide synthesis under mild and easily controlled conditions.

CO2 capture and sequestration in stable Ca-oxalate, via Ca-ascorbate promoted green reaction

The increase in the amount of carbon dioxide (CO₂) emissions related to many anthropic activities is a persistent and growing problem. During the last years, many solutions have been set out, none of them being the ultimate one. Investigators agree on the need of a synergic approach to the problem, in terms of many complementary methods of sequestration that, combined with the reduction of production, will be able to decrease the concentration of the CO₂ in the atmosphere. In this work, we explore the use of a green reaction to trap the CO₂ into a stable crystalline phase (weddellite) resorting to a multidisciplinary approach. CO₂ is reduced and precipitated as calcium oxalate through vitamin C as a sacrificial reductant. Calcium oxalate crystals obtained show a startling good quality that increases their already great stability over a wide chemical and physical conditions' range.

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

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.

Organic dye-catalyzed radical ring expansion reaction

Herein, we reported an attractive method for synthesizing medium-sized rings that are catalyzed by erythrosine B under fluorescent light irradiation. This synthetic approach featured mild conditions, a facile procedure, a broad substrate scope, and moderate-to-good yields.

Herein, we reported an attractive method for synthesizing medium-sized rings that are catalyzed by erythrosine B under fluorescent light irradiation.

Impact of the corrin framework of vitamin B12 on the electrochemical carbon-skeleton rearrangement in comparison to an imine/oxime planar ligand; tuning selectivity in 1,2-migration of a functional group by controlling electrolysis potential

Among the coenzyme B₁₂-dependent enzymes, methylmalonyl-CoA mutase (MMCM) catalyzes the carbon-skeleton rearrangement reaction between R-methylmalonyl-CoA and succinyl-CoA. Diethyl 2-bromomethyl-2-phenylmalonate, an alkyl bromide substrate having two different migrating groups (phenyl and carboxylic ester groups) on the β-carbon, was applied to the electrolysis mediated by a hydrophobic vitamin B₁₂ model complex, heptamethyl cobyrinate perchlorate in this study. The electrolysis of the substrate at -1.0V vs. Ag-AgCl by light irradiation afforded the simple reduced product (diethyl 2-methyl-2-phenylmalonate) and the phenyl migrated product (diethyl 2-benzyl-2-phenylmalonate), as well as the electrolysis of the substrate at -1.5V vs. Ag-AgCl in the dark. The electrolysis of the substrate at -2.0V vs. Ag-AgCl afforded the carboxylic ester migrated product (diethyl phenylsuccinate) as the major product. The selectivity for the migrating group was successfully tuned by controlling the electrolysis potential. We clarified that the cathodic chemistry of the Co(III) alkylated heptamethyl cobyrinate is critical for the selectivity of the migrating group through mechanistic investigations and comparisons to the simple vitamin B₁₂ model complex, an imine/oxime-type cobalt complex.

Synthesis and characterization of [Cu(salen)]2 coordination nano-assembly by a green and simple method

Hierarchical structured microplates consisting of nanoparticles were grown based on a self-assembly approach via a hydrothermal synthesis route without using any additive. Experimental parameters, such as reaction temperature, time and solvent play crucial roles in determining the morphology of final product. The nanoscale shape and macroscopically assembled architecture of [Cu(salen)]2 {salen = N,N′-bis(salicylidene)1,2-ethyelenediimine} crystals were totally controlled by preparation conditions for crystal growth. The synthesized [Cu(salen)]2 hierarchical architectures were characterized with UV-Vis, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermogravimetric (TGA) analyses. The thickness of the fabricated plates changes from 25 nm to 3.5 μm. The as-prepared nanoplates are actually composed of nanoparticles with diameters under 100 nm. Furthermore, the formation mechanism of the microplates decorated with nanorods has also been discussed, based on the influence of the kinetics of nucleation and crystal growth.

Small alterations in cobinamide structure considerably influence sGC activation

Specially designed B-ring-modified cobalamin derivatives were synthesized and tested as potential activators of soluble guanylyl cyclase (sGC). Herein, we disclose the influence of substituents at the c- and d-positions in hydrophilic and hydrophobic cobyrinic acid derivatives on their capacities to activate sGC. The presence of the amide group at c-/d-position in cobyrinic acid derivatives strongly influence the level of sGC activation. Removal of the d-position altogether has a profound effect for hydrophobic compounds. In contrast, little differences were observed in hydrophilic ones.

Bioinspired catalytic reactions with vitamin B12 derivative and photosensitizers

As part of a study directed toward design of good catalytic systems based upon a hydrophobic vitamin B12, heptamethyl cobyrinate perchlorate, we describe the preparation of various nanomaterials using the vitamin B12 derivative and photosensitizers. Examples include vitamin B12-hyperbranched polymers (HBPs), human serum albumin (HSA) containing vitamin B12 derivatives, a vitamin B12-titanium dioxide hybrid catalyst, a vitamin B12-Ru complex combined system, and a vitamin B12-rose bengal combined system. These bioinspired materials have the potential as catalytic systems for the degradation of organic halide pollutants and for molecular transformations via radical intermediates during irradiation by UV or visible light, and offer a variety of applications that are of great interest in terms of green chemistry.

Photoinduced electron transfer promoted radical ring expansion and cyclization reactions of α-(ω-carboxyalkyl) β-keto esters

Photoinduced electron transfer (PET) promoted decarboxylation of α-(ω-carboxyalkyl) β-keto esters undergoes radical ring expansion and cyclization reactions. This mild and environmentally friendly method can provide one-carbon expanded γ-keto esters and bicyclic alcohols, and the product distribution is strongly dependent on the length of the alkyl chain containing the terminal carboxylate group.

Vitamin B₁₂ derivatives as activators of soluble guanylyl cyclase

Various newly prepared and previously known vitamin B₁₂ derivatives have been studied as potential soluble guanylyl cyclase (sGC) activators. All compounds tested were found to activate the sGC enzyme, although to differing extents. The best results were obtained with the derivatives synthesized from c-lactone and possessing aliphatic amides in the c- and d-positions.