Hydrazide Conjugated Oligoguluronates
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Advances reported in the field of amphiphilic block copolymers in recent years has demonstrated that predetermined structures can be formed from the self-organizing of amphiphilic molecules at interfaces or in solutions. Alginates are abundant, generally biocompatible and have numerous applications due to desirable physicochemical properties.The aim of this master thesis was to prepare hydrazide-activated guluronate oligomers (Gn-ADH), and diblock conjugates (Gn-ADH-Gn) from reactions with guluronate oligomers (Gn) and adipic acid dihydrazide (ADH). Gn-ADH are interesting for future preparation of glycoconjugates and block copolymers, while Gn-ADH-Gn were prepared for the purpose of establishing a protocol that could be further developed to prepare heteropolymeric conjugates at a later time.Hydrazide-activated oligomers (Gn-ADH) were prepared from the reaction with gu- luronate oligomers (Gn) of varying degree of polymerization (n) and ADH (1:10 molar ratios of ADH). 2-Picoline borane was used as the reducing agent in the reactions. The reaction products were separated by size exclusion chromatography (SEC), and the main products were further characterized by proton nuclear resonance spectroscopy (1H-NMR). The target products were formed in good yield.Diblock conjugates (Gn-ADH-Gn) were also prepared from the reaction with Gn and ADH for varying degree of polymerization (n), using the same protocol as for the prepa- ration of Gn-ADH, except 0.5 molar equivalent of ADH was used. The target products were formed, but the yield was observed to change with the DP of the oligomer. An initial study of the e↵ect of oligomer concentration on the yield of diblock conjugates was performed, which indicated that the yield of diblock conjugates could be increase by using an optimal molar concentration of the oligomer.Diblock conjugates were also prepared from the reaction with maltooligomers (Glcn) and ADH, the reactions were aimed to function positive controls. The 1H-NMR spectrum of Glcn-ADH-Glcn revealed a difference in the signals from ADH observed compared to the signals observed for Gn-ADH-Gn. A small study of the acid-base properties of hydrazide conjugated oligoguluronates was performed, revealing changes in the 1H-NMR spectra of Gn-ADH and Gn-ADH-Gn after adjusting the pH.A method was developed to study the kinetics of the reaction with Gn and ADH using high-performance anion-exchange chromatography (HPAEC), in tandem with a pulsed amperometric detector (PAD). The formation of Gn-ADH was studied for n = 5 and 10, and the the reaction times were shown to increase from 10 - 12 h to 25 - 30 h, for the increase in DP from 5 to 10, respectively. The formation of Gn-ADH-Gn was studied using the same method, for n = 4 and 10, and the reaction time increased from 8 - 10 h to 80 - 100 h, respectively. The method also revealed background reduction of Gn by PicBH3 for all reactions, indicative of sub-optimal reaction conditions. The reaction with G5, and both reactions with G10, were shown to occur according to first order kinetics with respect to both reactants, and the rate constants of the reactions were estimated using an iterative model.