Dextrans are neutral, water soluble polysaccharides that are extracellularly produced from saccharose by Leuconostoc bacteria (L. mesenteroides and L. dextranicum). Native dextrans have a high molecular weight and consist only of α-D-glucose. By acidic hydrolysis and fractionated precipitation also dextrans with a lower molecular weight can be obtained. They are currently applied in medicin e.g. as substitute for blood plasm, osmotherapeutic agent and additive for radio-opaque substances. Further potent applications of dextrans arise based on their biocompatibility. They can for instance be used as coatings for magnetic nanoparticles, coatings for sensor surfaces (left picture, sensor on the left uncoated, on the right coated) or as scaffolds for tissue engineering.
A key derivative in our department is the carboxymethyl dextran (CMD), which can be synthesized by esterification with chloracetic acid in a mixture of alcohol and an aqueous solution of sodium hydroxide. By variation of the reaction conditions the degree of substitution can be adjusted to DS = 0.7 - 1.7. Due to the carboxyl groups CMD is applicable for immobilization of aminogroup-containing biomolecules, active agents or linkers. Besides it can be used as educt for further functionalizations. By reaction with diamines bifunctional dextran derivatives can be prepared that possess both carboxyl and aminogroups.
Another interesting dextran derivative is aminodextran (AMD), which can be synthesized by partial periodate cleavage and subsequent reductive amination. By variation of the reaction parameters the degree of substitution can be adjusted. Also dextran derivatives with fluorescence markers (right picture) can be synthesized by periodate cleavage and reductive amination. A reaction of AMD with glycidyl methacrylate leads to cross-linkable dextran derivatives that are basic materials for the formation of stable hydrogels.
Dr. Kerstin Wagner