Introduction of various functionalities into polysaccharides using alkynyl ethers as precursors: Pentynyl dextrans

Following the concept of using O-alkynyl glycans as key precursors of functional polysaccharides, dextran derivatives with nearly the same distritbution pattern, but various functional groups – for common (bio)conjugation reactions, molecular recognition, and antioxidant activity – have been prepared. Pentynyl dextran well characterized with respect to the degree of substitution (DS 0.43) and the distribution of alkynyl groups to the various OH of the glucosyl unit, was further modified by 1,3-dipolar cycloaddition of various functionalized azides, thus introducing amino, hydroxy, thiol, and carboxyl groups with good to quantitative yield. Besides these functional groups, biotin and tocopherol were introduced with about 60% conversion of alkyne groups. Biotinylated dextran was demonstrated to bind specifically to fluorophor-labeled streptavidin, while glucose linked tocopherol did not show loss of antioxidant activity. Formation of triazole derivatives was proved by ATR-IR and NMR spectroscopy, and after methanolysis of the dextran, by ESI mass spectrometry. Degree of conversion was estimated from 1H NMR spectra, decrease of pentynyl groups in the product mixture analyzed by GLC, and elemental analysis.

► Pentynyl dextran (PyD) with degree of substitution (DS) 0.43 with known substituent distribution was used as starting material for defined functionalized dextrans. ► Functional groups including biotin and tocopherol were introduced by cycloaddition of various azides to PyD. ► Biotinylated dextran binds specifically to fluorophor-labeled streptavidin. ► Tocopherol azide grafted on dextran chain retains its antioxidant capacity. ► Products were characterized by GLC, elemental analysis, ATR-IR and NMR spectroscopy.