Synthesis of fluorescent probe – carbohydrate conjugates

Abstract

A new type of luminescent label has been synthesized and a range of carbohydrates has been derivatized with various fluorescent probes. Amine-containing labels were readily transformed with chloroacetylchloride into the corresponding fluorescent chloroacetamide reagents 1–4. Suitably blocked monosaccharides containing either a free thio 9, hydroxyl 11, or carboxyl 17 functionality have been conjugated with (a) 4-chloroacetamido labels 1 and 2, (b) with 4-aminobenzophenone 5, and (c) with 1-dimethyl-1-aminonaphthalene-5-sulfonylchloride 21, to form the fluorescent carbohydrate conjugates 10, 16, 18, and 20. Direct derivatization of the unblocked disaccharides 22 and 23 was achieved by reductive amination with amines 5 and 7 and sodium cyanoborohydride affording the 1-deoxyglycit-1-yl derivatives 24–26, which were characterized by 13C nmr spectroscopy. The synthesis of fluorescent polysaccharides is exemplified by the condensation of 9-anthraldehyde with chitosan either via Schiff 's base formation to afford 32, or via reductive alkylation to form 33.