Synthesis of dextran

The investigation of the chemical modification of dextran to determine the importance of various reaction parameters that may eventually allow the controlled synthesis of dextran-modified materials has began. The initial parameter chosen was reactant molar ratio, since this reaction variable has previously been found to greatly influence other interfacial condensations. Phase transfer catalysts, PTC s, have been successfully employed in the synthesis of various metal-containing polyethers and polyamines (for instance 26). Thus, the effect of various PTC s was also studied as a function of reactant molar ratio. 

J. F. Robyt and S. H. Eklund, Stereochemistry involved in the mechanism of action of dextransucrase in the synthesis of dextran and the formation of acceptor products, Bioorg. Chem., 11 (1982) 115-132. 

Fig. 1 (a) Synthesis of dextran-spermine conjugates, (b) Fluorescence micrographs of dextran-spermine compared to common transfection reagents in HEK293 and NIH3T3 cells. Adapted with permission from [38]. 2002 American Chemical Society... 

Synthesis of Dextran Esters with Bioactive Moieties (Prodrugs)... 

Fig. 8 Synthesis of dextran via a cationic ring-opening polymerisation of 1,6-anhydro-2,3,4-tri-0-allyl-/J-D-glucopyranose (path A) and l)6-anhydro-2,3,4-tri-0-benzyl-/J-D-glucopyranose path B) [84,85]...

Fig. 20 Synthesis of dextran methacrylate usable for the formation of hydrogels after photo-initiated cross-linking [175]...

Nevertheless, the reagent is still used for a large number of esterification reactions of dextran. The synthesis of dextran amino acid esters is achieved by conversion of the polysaccharide in DMSO with the N-ben-zyloxycarbonyl protected acids for 48 h at 20 °C using DCC and pyridine. 0-(N-B enzyloxycarbonylglycyl) dextran with DS 1.1, 0-(AT-benzyloxycarbo-nyl-aminoenanthyl) dextran with DS 2.2, and 0-(N-acelyl-i,-histidinyl)dcx-tran with DS 1.1 are accessible. Deprotection was achieved with oxalic acid and Pd/C [190,191],... 

In 1861, Louis Pasteur1 reported a polysaccharide that was produced from sucrose. In 1874, Scheubler2 determined its empirical formula and named it dextran. The formation of polysaccharide (dextran) was observed as the result of bacterial transformation of sucrose solutions into viscous solutions, gels, and/or flocculent precipitates.3 The synthesis of dextran from sucrose by a cell-free... 

Thus, in the 1940s and 50s, the primer mechanism was assumed for the synthesis of dextran.52 5369,70 This mechanism was strengthened in the 1970s when Germaine et a/.71-73 found that the addition of dextran to digests of Strep, mutans dextransu-crase increased the rate of dextran synthesis. They found that the rate reached a maximum when the average size of the added dextran was 30 glucose residues.7172... 

Thus, it was determined that the mechanism of action of the acceptors is one of terminating dextran synthesis by the release of the glucosyl and dextranyl units from the covalent enzyme intermediate rather than one of priming the synthesis of dextran. 

Control of the Synthesis of Dextran and Acceptor Product and the Efficiencies of Different Acceptors... 

Even though the reaction scheme is complex, attempts have been made to model the reaction and develop kinetic equations. Mooser et al.lu developed kinetic equations for a limited case based on the primer mechanism. Reh et a/.145 developed kinetic equations for the synthesis of dextran and for the maltose acceptor reaction based on the two-site insertion mechanism. Likewise, Boker et al,146 developed a kinetic equation for the formation of the fructose acceptor product, leucrose, based on the two-site insertion mechanism that included an acceptor site. An equation was derived for the overall reaction rate that was a function of the consumption of sucrose by dextran formation and acceptor-product formation. 

As stated earlier (see p. 342), study of the cell-free, enzymic synthesis of dextran was initiated by Hehre and Sugg They demonstrated the ability of a cell-free extract of Leuconostoc mesenteroidea to catalyze the formation of dextran. The over-all reaction was represented by equation (1). In addi-... 

The following mechanism is a slight modification of the scheme proposed by Bovey for explaining the enzymic synthesis of dextran. The step con-... 

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