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Title: Preparation of novel chitin derivatives via homogeneous method
Keywords: chitin, chitosan, chemical, modification, anticoagulant
Issue Date: 17-Nov-2006
Source: ZOU YUQUAN (2006-11-17). Preparation of novel chitin derivatives via homogeneous method. ScholarBank@NUS Repository.
Abstract: Chemical modification of chitin and chitosan was investigated under homogeneous conditions. Anticoagulation activity of the obtained chitin and chitosan derivatives were investigated.A homogeneous synthetic method via SN2 reaction was established for chitin to prepare C-6 substituted chitin derivatives. Tosyl-chitin was used as the active intermediate, while sodium salts of ethyl hydroxybenzoate, diethylmalonate and diethylphosphite were applied as nucleophiles. Three chitin derivatives that showed good solubility or swellability in DMSO or dimethyl acetamide (DMAc) were obtained. Subsequent hydrolysis of the chitin-ester derivatives with tert-butoxide in DMSO generated 6-O-carboxyphenyl-chitin and 6-deoxy-di(carboxy)methyl-chitin, which showed good water solubility. A homogeneous synthetic method was established to prepare sulfated-chitins. Sulfur trioxide-pyridine complex was used as the sulfating reagent, while 5% of Lithium chloride/Dimethyl acetamide (LiCl/DMAc) was used as the reaction solvent system. 6-O-sulfated-chitins and 3, 6-O-disulfated-chitins with different degrees of substitution were obtained. The reaction temperature proved critical for controlling the regio-selectivity of the sulfation. The anticoagulation property of sulfated-chitins was evaluated by activated partial thromboplastin time (APTT), thrombin time (TT) and prothrombin time (PT) assays. The degree of sulfation (D.S.) closely correlated to the anticoagulation activity of sulfated-chitins, the higher the D.S., the higher the anticoagulation activity. The high anticoagulation activity of 3, 6-O-disulfated-chitin was attributed to the presence of the 3, 6-O-sulfate groups (36S) on the sugar ring.A novel chitosan-based photocrosslinable anticoagulant was synthesized via the itaconylation of sulfated-chitosan. Swelling ability, enzymatic degradation and anticoagulation activity of the hydrogel was investigated. Fully sulfated-chitosan was prepared in DMAc by using sulfur-trioxide-pyridine complex as sulfating reagent. The subsequent itaconylation of sulfated-chitosan was conducted in 1:1 methanol/water solution. The anticoagulation activity of itaconyl-sulfated-chitosan increased markedly compared to that of sulfated-chitosan. The increased anticoagulation activity was attributed to the introduction of the carboxylic group, verified with succinyl and glutaryl sulfated-chitosan. The subsequent photocrosslinking of itaconyl-sulfated-chitosan yielded the corresponding anticoagulant hydrogel. The itaconyl-sulfated-chitosan hydrogel showed an extent of anticoagulation activity with respect to APTT and TT, which was attributed to the antithrombogenic nature of the hydrogel.In conclusion, chemical derivatization of chitin and chitosan under homogeneous conditions have been investigated. The resulting sulfated-chitin and chitosan derivatives have great potential as anticoagulant and blood-contact materials.
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