Using molecular iodine in direct oxidative condensation of aldoses with diamines: an improved synthesis of aldo-benzimidazoles and aldo-naphthimidazoles for carbohydrate analysis.

A practical method has been developed for conversion of unprotected and unmodified aldoses to aldo-benzimidazoles and aldo-naphthimidazoles. Using iodine as an oxidant or promoter in acetic acid solution, a series of mono-, di-, and trialdoses, including those containing carboxyl and acetamido groups, undergo an oxidative condensation reaction with o-phenylenediamine or 2,3-naphthalenediamine at room temperature to give the aldo-benzimidazole and aldo-naphthimidazole products in high yields. No cleavage of the glycosidic bond occurs under such mild reaction conditions. The composition analysis of saccharides is realized by the HPLC analysis of the fluorescent naphthimidazole derivatives.