O-Oligosaccharidyl-1-amino-1-deoxyalditols as intermediates for fluorescent labelling of oligosaccharides

Reducing monosaccharides were efficiently converted to stable 1-amino-1-deoxyalditols (=glycamines; distinguished from glycosylamines by mass-spectrometry) during incubation at 20 °C in saturated aqueous NH4HCO3 containing NaCNBH3. Potentially useful by-products included a novel, fully-reduced dimer (the corresponding secondary glycamine) and several relatively long-lived, unreduced products. With increasing incubation time, monomers exceeded dimers. Reducing disaccharides and oligosaccharides underwent similar reactions at their reducing termini; the yield of dimers decreased with increasing oligosaccharide Mr. The O-oligosaccharidyl-1-amino-1-deoxyalditols (OADs) obtained by reductive amination of oligosaccharides reacted readily with lissamine rhodamine sulfonyl chloride to yield OAD–sulforhodamine conjugates linked by a stable sulfonamide bond. Conditions for this reaction were optimised (borate buffer, pH 9.0–9.5). The highly fluorescent OAD–sulforhodamine products were purified on a C18 cartridge. They were electrophoretically immobile at pH 2.0 and 6.5, and migrated towards the anode in borate buffer, pH 9.4. The OAD–sulforhodamines were amenable to TLC and were excellent substrates for enzymic transglycosylation and for glycosylhydrolase action.

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