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.

MALDI-MS provides a rapid and sensitive analysis of large biomolecules such as proteins and nucleic acids. However, oligo- and polysaccharides are less sensitive in MS analysis partly due to their neutral and hydrophilic nature to cause low ionization efficiency. In this study, four types of oligosaccharides including aldoses, aminoaldoses, alduronic acids and α-keto acids were modified by appropriate tags at the reducing termini to improve their ionization efficiency. Bradykinin (BK), a vasoactive nonapeptide (RPPGFSPFR), containing two arginine and two phenylalanine residues turned out to be an excellent MS signal enhancer for maltoheptaose, GlcNAc oligomers and oligogalacturonic acids. In the MALDI-TOF-MS analysis using 2,5-dihydroxybenzoic acid (2,5-DHB) as the matrix, the GalA4-BK and GalA5-BK conjugates prepared by reductive amination showed the detection limit at 0.1 fmol, i.e. ∼800-fold enhancement over the unmodified pentagalacturonic acids. The remarkable MS enhancement was attributable to the synergistic effect of the basic arginine residues for high proton affinity and the hydrophobic property phenylalanine residues for facile ionization. A tetrapeptide GFGR(OMe) and an arginine linked phenylenediamine (H(2) N)(2) Ph-R(OMe) were thus designed to act as potent tags of oligosaccharides in MS analysis. Interestingly, concurrent condensation and lactonization of α2,8-linked tetrasialic acid (SA4) was carried out with (H(2) N)(2) Ph-R(OMe) to obtain a quinoxalinone derivative, which showed > 200-fold enhancement over unmodified SA4 in the MALDI-TOF-MS analysis.

Analysis. -Under the mild conditions, a number of functional groups is tolerated. Glycosidic bonds are not cleaved and racemization does not occur. Aldo-naphthimidazoles are highly fluorescent what is useful for the research in glycochemistry and glycobiology. -(LIN, C.; LAI, P.-T.; LIAO, S. K.-S.; HUNG, W.-T.; YANG*, W.-B.; FANG, J.-M.; J.