Some chemical and analytical aspects of polysaccharide modifications. III. Formation of branched-chain, soluble chitosan derivatives

Abstract

Specific attachment of carbohydrates to the 2-amino functions of chitosan transforms this water-insoluble, linear polymer into branched-chain water-soluble derivatives. Facile conversions can be achieved by reductive alkylation using sodium cyanoborohydride and any aldehyde or keto sugar, by Schiff base formation, or by amidation reactions using carboxylic acid or lactone derivatives. Experimental results are presented for a series of mono-, di-, tri-, and polysaccharides, including D-glucose, IV-acetylglucosamine, D-glucosamine, D-galactose, D-galactosamine, D-fructose, D-glucoheptonic acid 7-lactone, lactose, cellobiose, maltose, melibiose, maltotriose, streptomycin sulfate, C6-o(de/iydo-cycloheptamylose, and dextran. These procedures facilitate the preparation of polymer derivatives with a variety of comblike, treelike, and other branching types. Many of these products are amenable to further, specific chemical modifications; this is demonstrated by the introduction, via galactose oxidase treatment, of C-6 aldehyde functions into the pendant galactose residues of derivatives 8 and 13. The synthetic chitosan derivatives exhibit a number of useful and uncommon properties in terms of their solution characteristics. Thus, aqueous solutions of derivative 8 were compatible with a wide range of salts, and derivatives 11 and 13 were stable in 50% aqueous ethanol. Derivative 8 formed inclusion complexes with iodine, lactose, and 4-oxo-2,2,6,6-tetramethylpiperidine-l-oxyl. Solubility modifications were accomplished by coreaction of hydrophilic (lactose) and hydrophobic (various alkyl) residues, affording products, such as 24, which were soluble in both aqueous and organic media. Reductive alkylation of chitin afforded the 1-deoxylactit-l-yl derivative 27, which was water insoluble but formed sols in water and several organic solvents. Factors affecting the solution behavior of chitosan and its branched derivatives have been evaluated and mechanisms have been discussed for solute interactions and conformational transitions.

Chitosan: some pharmaceutical and biological aspects - an update

“…Involvement of tight junctions was visualised by confocal scanning microscopy using tight junctional proteins occludin and ZO-1. An increased transport of compounds was obtained in the acidic medium where the pH was less or in the order of the pKa of chitosan (Yalpani & Hall, 1984). Each value represents the meanps.d., n l 3 ; *significantly different from control (P 0.05) ; †significantly different from all other treatments in the group (P 0.05) ; nd, not determined due to the insolubility of chitosan salts ; value in parentheses, absorption enhancement ratio ; P app , apparent permeability coefficient.…”

Novel metal chelating chitosan derivative: attachment of iminodiacetate moieties via a hydrophilic spacer group

“…Chitosan has been modified in order to prepare controlled solubility derivatives (3,4), metal sequestrants (5-7), drug carriers (8), and immobilization supports (ref. 2, pp.…”

“…443-444). Although our main efforts have been directed toward controlled solubility compounds (3,4), we felt that our experience in chitosan modification could be exploited in the synthesis of metal chelating, controlled solubility conjugates.…”

Modication of Heterocyclic Amino Acids: Histidine and Tryptophan

“…The role of the alcohol is to solubilise the aldehyde component, which can often be hydrophobic. This procedure has been used with many different carbonyl components, including reducing monosaccharides, disaccharides, ketosugars, other oxidised sugars, and noncarbohydrate carbonyls [136]. Aldehydes bearing straight-chain alkyl groups with chain lengths from C 3 -C 12 have been used [155].…”