Dextran modification

A method with an enormous potential for dextran modification is the homogeneous one-pot synthesis after in situ activation of the carboxylic acids with CDI, which is a rather well known technique in general organic chemistry and was published in 1962 [ 197]. It is especially suitable for the functionalisation of the biopolymers, because during conversion the reactive imidazolide of the acid is generated and only CO2 and imidazole are formed as by-products (Fig. 29). 

Table 11 Summary of etherification reactions used most frequently for dextran modification...

Fig. 2.5 Dextran modification via cationic substitution which present alkyl chains of varying length...

For the methacrylation of polysaccharides, several examples of dextran modification have been reported, for instance using maleic anhydride (5 methacryloyl chloride (6) or glycidyl methacrylate (7) as modifiers. Here we report the use of 2-[(l-imidazolyl) formyloxyjethyl methacrylate (HEMA-Im) as an efficient and more convenient agent for the methacrylation of polysaccharides (8). 

This paper concentrates on the identification of the structural unit of the condensation product between sucrose and organo-stannane. As in the ease of dextran modification, the product contains a mixture of units including those depicted as to 7. 

A number of other polysaccharides, such as glycogen, dextran, chitin, etc., possess interesting structures for chemical modification [103,104]. Dextran has been used as a blood plasma substitute. Although it can be converted to films and fibers, chitin s relatively small resource restricts its commercialization. 

Phase-Transfer-Catalyzed Modification of Dextran Employing Dibutyltin Dichloride and Bis(cyclopentadienyl)titanium Dichloride... 

Dextran was chosen to study for the following reasons. First, it is water soluble allowing three dimensional modification employing aqueous solution and classical interfacial condensation routes. Second, it is readily available in industrial quantities. Third, it is available in a range of molecular weight allowing product modification to be studied as a function of dextran chain size. Fourth, it is generally considered to be an under-utilized natural feedstock. 

An underlying assumption is that dextran is a representative polysaccharide and that results derived from its study can be applied to other polysaccharides. Effected modifications are intended to occur throughout the dextran material rather than only at the surface. This is achieved by employing solutions containing dissolved dextran. 

Recently Carraher, Naoshima and coworkers effected the modification of polysaccharides employing organostannanes and bis(cyclopenta-dienyl)titanium dichloride, BCTD (20-25). Here we report the modification of dextran employing the interfacial condensation technique using various phase transfer agents utilizing BCTD and dibutyltin dichloride, DBTD. 

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. 

The following protocol illustrates the modification of a dextran polymer with chloroace-tic acid. 

The following protocols make use of the compounds adipic acid dihydrazide and carbohy-drazide to derivatize molecules containing aldehydes, carboxylates, and alkylphosphates. The protocols are applicable for the modification of proteins, including enzymes, soluble polymers such as dextrans and poly-amino acids, and insoluble polymers used as micro-carriers or chromatographic supports. 

Dextran derivatives containing carboxyl- or amine-terminal spacer arms may be prepared by a number of techniques. These derivatives are useful for coupling amine- or carboxylate-containing molecules through a carbodiimide-mediated reaction to form an amide bond (Chapter 3, Section 1). Amine-terminal spacers also can be used to create secondary reactive groups by modification with a heterobifunctional crosslinking agent (Chapter 5). 

This type of modification process has been used to form sulfhydryl-reactive dextran polymers by coupling amine spacers with crosslinkers containing an amine reactive end and a thiol-reactive end (Brunswick et al., 1988 Noguchi et al., 1992). The result was a multivalent sulfhydryl-reactive dextran derivative that could couple numerous sulfhydryl-containing molecules per polymer chain. 

Protocol for the Modification of Dextran with Chloroacetic Acid... 

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