Cobalt Catalyst Determines Regioselectivity in Ring Opening of Epoxides with Aryl Halides

Ring-opening of epoxides furnishing either linear or branched products belongs to the group of classic transformations in organic synthesis. However, the regioselective cross-electrophile coupling of aryl epoxides with aryl halides still represents a key challenge. Herein, we report that the vitamin B₁₂/Ni dual-catalytic system allows for the selective synthesis of linear products under blue-light irradiation, thus complementing methodologies that give access to branched alcohols. Experimental and theoretical studies corroborate the proposed mechanism involving alkylcobalamin as an intermediate in this reaction.

Alkyl Halides as Substrates for Photocatalytic Minisci-Type C–H Alkylation of Hetarenes

Alkyl halides are readily available starting materials for various synthetic transformations, including Minisci-type C–H functionalizations of hetarenes. The existing methods, however, often require harsh reaction conditions, such as the use of acids, sacrificial electron donors, or radical precursors in excess amounts. Here, we outline recent developments in this field and we highlight our group̓s efforts to achieve fully catalytic photoredox Minisci-type alkylations supported by noncovalent interactions under mild aqueous conditions.

Vitamin B12 transports modified RNA into E. coli and S. Typhimurium cells

Specifically designed, antisense oligonucleotides are promising candidates for antibacterial drugs. They suppress the correct expression of bacterial genes by complementary binding to essential sequences of bacterial DNA or RNA. The main obstacle in fully utilizing their potential as therapeutic agents comes from the fact that bacteria do not uptake oligonucleotides from their environment. Herein, we report that vitamin B12 can transport oligonucleotides into Escherichia coli and Salmonella typhimurium cells. 5'-Aminocobalamin with an alkyne linker and azide-modified oligonucleotides enabled the synthesis of vitamin B12-2'OMeRNA conjugates using an efficient "click" methodology. Inhibition of protein expression in E. coli and S. Typhimurium cells indicates an unprecedented transport of 2'OMeRNA oligomers into bacterial cells via the vitamin B12 delivery pathway.

5′-Vitamin B12 derivatives suitable for bioconjugation via the amide bond

Vitamin B₁₂ derivatives bearing either the amino or the carboxylic group at the 5′-position were synthesised hence enabling conjugation of therapeutics to vitamin B₁₂via the amide bond.

Photoinduced Vitamin B12-Catalysis for Deprotection of (Allyloxy)arenes

Vitamin B₁₂ is a natural cobalt complex that, while reduced to the "supernucleophilic" Co(I) form, can easily react with electrophiles via an S_N2 mechanism. It is also shown to react via an S_N2' mechanism with allylic compounds allowing for photochemical deprotection of (allyloxy)arenes. A sustainable alternative to commonly used noble metal-catalyzed deprotection reactions is presented.

Electrochemistry and catalytic properties of amphiphilic vitamin B12 derivatives in nonaqueous media

The reduction pathway of cobalester (CN)Cble, an amphiphilic vitamin B12 derivative, was investigated in organic solvents under electrochemical conditions and compared with mono- and dicyanocobyrinates. The redox characteristics were determined using cyclic voltammetry and spectroelectrochemical methods. The presence of a nucleotide moiety in B12-derivative impedes the in situ formation of dicyano-species thus facilitating the (CN)Co(iii) to Co(i) reduction. The (CN)Cble shows stepwise reduction to Co(i) via (CN)Co(ii). The reduction of (CN)Co(ii)/Co(i) was found to depend on cyanide-solvent exchange equilibrium with weakly coordinating solvents and bulky peripheral chains promoting intact (CN)Co(ii) species existence. The studied complexes were also utilized as catalysts in bulk electrolysis of benzyl bromide affording bibenzyl in very good yield.

Cobalt(i)-catalysed CH-alkylation of terminal olefins, and beyond

Cobalester, a natural nontoxic vitamin B₁₂ derivative, was found to catalyse unusual olefinic sp² C–H alkylation with diazo reagents as a carbene source instead of the expected cyclopropanation.

Vitamin B12catalysed reactions

This tutorial review focuses on cobalamin as a natural, nontoxic, environmentally benign cobalt catalyst for synthetically useful organic reactions.

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.

An amphiphilic, catalytically active, vitamin B12 derivative

The reaction of vitamin B₁₂ with DMF-DMA and MeOH as a nucleophile affords cobalester, the first amphiphilic cobalamin derivative which is able to catalyze C–C bond forming reactions.

Synthesis of New Hydrophilic and Hydrophobic Cobinamides as NO-Independent sGC Activators

Herein, the synthesis of novel hydrophobic and hydrophilic cobinamides via aminolysis of vitamin B12 derivatives that activate soluble guanyl cyclase (sGC) is presented. Unlike other sGC regulators, they target the catalytic domain of sGC and show higher activity than (CN)2Cbi.