Vitamin B12 enzymes, involving the cobalt species as a catalytic center, mediate various isomerization reactions accompanied by carbon-skeleton rearrangements. In order to simulate the catalytic functions of vitamin B12 as exerted in the hydrophobic active sites of enzymes concerned, we have been dealing with hydrophobic vitamin B12 derivatives, which have ester groups in place of the peripheral amide moieties of the naturally occurring vitamin B12. In this work, the carbon-skeleton rearrangements as mediated by hydrophobic vitamin B12 derivatives were investigated under electrochemical conditions. The controlled-potential electrolyses of alkyl halides with various electron-withdrawing groups were carried out, and the electrochemical carbon-skeleton rearrangements proceeded effectively via formation of anionic intermediates. These reactions can also be applied to the ring-expansion reactions. We have prepared a novel vitamin B12 derivative, [Cob(II)7Phe(OBzl)]ClO4, having phenylalanine residues on the peripheral side chains. [Cob(II)7Phe(OBzl)]ClO4 effectively catalyzed 1,2-migration of the carboxylic ester in 1-bromo-2,2-bis(ethoxycarbonyl)propane at - 1.0 V vs. SCE under irradiation conditions. A strapped hydrophobic vitamin B12 was prepared in order to change the enantioselectivity, and the controlled-potential electrolysis of a racemic alkyl halide was carried out in the presence of vitamin B12 derivatives. Product analyses and computational calculations suggested that the stability of alkylated complexes dominated the enantioselectivity of reduction products.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry