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Galactose dialdehyde as potential protein cross-linker: proof of principle.
Combined enzymatic oxidation of D-galactose by D-galactose oxidase [EC 1.1.3.9] in water, amination with butylamine, and oxalic acid catalyzed Amadori rearrangement in methanol yielded 1,6-bis(butylamino)-1,6-dideoxy-erythro-hexo-2,5-diulose, demonstrating how in situ formed galacto-hexodialdose can be used to cross-link protein residues. The various species formed during this three-step conversion are present as bicyclic structures in solution as established by 13C labeling and in situ NMR spectroscopy of the reaction mixtures. Using protein (gelatin) instead of butylamine, distinct Amadori product formation was observed using 99% enriched D-(1-(13)C)- and D-(2-(13)C)-galactose.
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