Silylation reaction of dextran: effect of experimental conditions on silylation yield, regioselectivity, and chemical stability of silylated dextrans.
The controlled synthesis of biodegradable copolymers of dextran grafted with aliphatic polyesters first requires the preparation of polysaccharide derivatives soluble in organic solvents. Silylation of dextran can thus lead to such organosoluble derivatives and allows the polymerization of cyclic esters initiated from the nonsilylated OH functions. Silylation of dextran was studied in DMSO by different reactants such as 1,1,1,3,3,3-hexamethyldisilazane (HMDS) in the presence of various catalysts and N,O-bis(trimethylsilyl)acetamide (BSA). According to the silylating agent and the used experimental conditions, it was possible to obtain highly or totally silylated dextrans. In parallel, an investigation of the chemical stability of the dextran chain during silylation was performed. Thus, it was found that, when used at 50 degrees C, HMDS with or without catalysts gives a relatively high silylation yield and does not alter the dextran chain length, whereas at 80 degrees C, dextran degradation was observed. BSA is a very good silylating agent, which allows reaching 100% silylation even at 50 degrees C but provokes the degradation of the polysaccharide chains. The work was completed by a study of the reactivity order of the glucosidic OH functions toward silylation reaction. This order was found to be (OH(2) > OH(4) > OH(3)) as already reported for other reactions. 2D-NMR of highly silylated dextrans demonstrated that they are constituted of both quantitatively silylated glucose units and two types of disilylated ones.
Nouvel
Cécile
C
Laboratoire de Chimie-Physique Macromoléculaire (LCPM), UMR CNRS-INPL 7568, Groupe ENSIC, 1 rue Grandville, BP 451, 54001 Nancy Cedex, France.
Dubois
Philippe
P
Dellacherie
Edith
E
Six
Jean-Luc
JL
D003911:Dextrans / Q000737:chemistry*; D004121:Dimethyl Sulfoxide; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D012821:Silanes / Q000737:chemistry*
D003911:Dextrans; D012821:Silanes; D004121:Dimethyl Sulfoxide