Reactions of Enolic Biotin Models

Article abstract of DOI:10.1246/bcsj.58.2801

In order to delineate the mechanism of biotin-dependent carboxylation reactions, the following model experiments have been carried out.In reactions of carbonate derivatives such as methyl chloroformate with 2-ethoxy-2-imidazoline (1), a putative enolic biotin model, or 2-imidazolidinone (2), the former showed a much higher reactivity to provide the methoxycarbonylated 1 (3).Reactions of 3 with benzenethiolate, cyclohexylamine and carbanions have also been investigated as a model of transcarboxylation from N-carboxybiotin to an acceptor substrate.Only carbanions attack the carbonyl carbon of 3, leading to rupture of the C-O bond, but not of the N-C bond.A net "carboxyl" transfer was effected with 1-methoxycarbonylimidazole (9) as a donor substrate.Implications of these results in biotin catalysis are discussed.