Preparation and modification of cellooligosaccharides

Graduation date: 2003Cellooligosaccharides are the reaction intermediates produced during the\ud hydrolysis of cellulose to glucose. Hence, they have the same chemical structure as\ud cellulose, just shorter chain lengths. Cellooligosaccharides up to DP eight are\ud soluble in water. The soluble cellooligosaccharides can be used "as is" in the food\ud industry as non-digestible oligosaccharides and in the laboratory as representative\ud substrates for cellulolytic enzymes. The soluble cellooligosaccharides may also be\ud chemically modified for use in the laboratory, in this case serving as affinity ligands,\ud reporter groups, or model substrates.\ud A number of methods are available for the separation of\ud cellooligosaccharides differing only with respect to DP. This type of separation is\ud relevant to both laboratory and industrial applications. A new approach to the chromatographic separation of cellooligosacchandes is presented in this thesis. It is\ud shown that cellulose stationary phases, in conjunction with ethanol-water mobile\ud phases, may be used for cellooligosaccharide fractionation. The system appears to\ud behave as an affinity/partition system, with retention times increasing as the DP of\ud the cellooligosaccharides increase. The feasibility of using such a chromatographic\ud system for the "clean-up" of cellooligosaccharide mixtures is demonstrated.\ud The relative merit of different chromatographic approaches putatively used for the\ud fractionation of cellooligosaccharides was determined. Affinity-, adsorption-, ion-mediated-\ud and molecular exclusion-approaches were tested. Adsorption\ud chromatography, using a charcoal-celite stationary phase, was the most generally\ud applicable method for the preparation of near gram quantities of pure\ud cellooligosaccharides. Cellulose-based affinity/partition chromatography was found\ud to be the least time consuming and most economical method for the preparation of\ud cellotetraose and cellopentaose.\ud Studies using chemically modified cellooligosaccharides are typically limited\ud to derivatives whose aglycone group is conjugated to the reducing end of the sugar.\ud This is because the chemistry involved in modifying the reducing end is typically\ud much easier than that involved in selectively modifying other sites on the\ud oligosaccharides. A portion of the studies presented herein was aimed at exploring\ud approaches for the modification of the non-reducing end of cellooligosaccharides.\ud Methyl 6-O-p-nitrobenzoyl-β-D-glucoside was synthesized by reacting methyl 4,6-O-p-nitrobenzylidine-β-Dglucoside with N-bromosuccinimide. This method has\ud potential as a general method for the modification of the reducing terminus of\ud oligosaccharides, including, cellooligosaccharides