Cellulose is the most abundant polysaccharide on earth and it is relatively a simple homopolymer with three hydroxyl groups, differing only subtly in reactivity. The position of substitution has a powerful influence on physical properties of cellulose derivatives. To better understand the structure and property relationships of cellulose derivatives, it is critical to have all homopolymers related to important cellulose ethers and esters available. However, regiocontrol in cellulose chemistry is still a difficult, mostly unconquered frontier. In this dissertation, the main objective is to develop novel synthetic methods to synthesize regioselectively substituted cellulose derivatives including cellulose ethers and esters, and apply advanced characterization tools to understand structure and its influence on properties, which will give us deep insights into the composition of more random commercial derivatives, maximizing the content of advantageous monosaccharides. Several strategies to regioselectively synthesize cellulose derivatives are discussed in detail. The obtained regioselective cellulose derivatives were fully characterized analytically. Structure-property relationships of these regioselectively substituted cellulose derivatives were also studied. / Ph. D.

New methods were developed for the regioselective synthesis of new classes of cellulose derivatives with properties that could help improve the delivery of pharmaceutical drugs within the human body. The specific synthetic targets of this research were regioselectively carboxylated and regioselectively aminated cellulose derivatives. While different avenues to the carboxylated cellulose were ultimately explored without success, a new method for the synthesis of selectively <i>O</i>-acylated 6-amino-6-deoxy-cellulose esters was devised. A key reaction that enabled the synthesis of the new cellulose derivatives described in this dissertation was the one-pot conversion of microcrystalline cellulose to 6-bromo-6-deoxy-cellulose esters. This reaction resulted in the highly selective displacement of the primary hydroxyl groups attached to the 6-carbon (<i>C</i>-6) on each anhydroglucose unit (AGU) in cellulose with bromide, with little or no bromination occurring at carbons 2 and 3 (<i>C</i>-2 and <i>C</i>-3). The brominated cellulose was then completely esterified by adding acetic, propionoic, or butyric acid anhydride to the reaction solution. The reaction products were readily soluble in many common organic solvents, including acetone, dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, and chloroform. It was shown that the bromides could be converted to iodides under Finkelstein reaction conditions. The presence of halides at <i>C</i>-6 allows a variety of new functional groups to be regioselectively introduced to cellulose via nucleophilic substitution. In one case, the 6-bromo-6-deoxy-cellulose esters were reacted with sodium cyanide to produce regioselectively synthesized cellulose nitriles. These compounds were synthesized with the idea that they could be converted to regioselectively carboxylated cellulose derivatives as an alternative pathway to the rhodium-catalyzed carbonyl insertion reactions also attempted in this research. However, the cellulose nitriles were highly susceptible to alkaline degradation, and conversion to the carboxylated cellulose was not achieved. The 6-bromo-6-deoxy-cellulose esters were also reacted with sodium azide to successfully produce 6-azido-6-deoxy-cellulose esters. The azide groups were then reduced to amines using the Staudinger reaction. This very mild and selective reaction allowed the conversion of the azides to amines in the presence of the ester groups still attached to the cellulose backbone. Such derivatives could have properties useful for a range of biomedical applications, including the delivery of anionic drugs. / Ph. D.

Polysaccharides are one of the most abundant and diverse families of natural polymers, and have an incredibly wide range of natural functions including structural reinforcement, energy storage, aqueous rheology modification, and communication and identity. Application of native polysaccharides like cellulose as sustainable materials is limited by some inherent drawbacks such as insolubility in common solvents including water, and poor dimensional stability. To increase their functionality and utility, researchers have sought to tailor the chemical and physical properties of cellulose and other polysaccharides using a variety of chemical modification techniques, resulting in a number of important, useful commercial derivatives. Because of their greater biocompatibility and biodegradability, and low immunogenicity, naturally derived cationic polymers including cationic polysaccharide derivatives are very attractive candidates for biomedical applications, due to the fact that they are capable of binding with anionic biomolecules, such as nucleic acids and certain proteins, via electrostatic interactions. However, there are relatively few practical synthetic methods reported for their preparation. We demonstrated a useful and efficient strategy for cationic polysaccharide salt preparation by reaction of 6-bromo-6-deoxypolysaccharides such as 6-bromo-6-deoxycellulose esters with pyridine or 1-methylimidazole exclusively at the C-6 position, resulting in high degrees of substitution (DSs). These permanently cationic polysaccharide derivatives have been demonstrated to dissolve readily in water, and bind strongly with a hydrophilic and anionic surface. Availability of these cationic polysaccharides will facilitate structure-property relationship studies for biomedical uses including drug delivery and bioelectronics applications. We also extended the chemistry, reacting 6-imidazolo-6-deoxycellulose with propane sultone, leading to a new synthetic pathway to zwitterionic cellulose derivatives. In addition to cationic and zwitterionic derivatives, we found a simple, efficient route to carboxyl-containing polysaccharide derivatives from curdlan esters via regioselective ring-opening reactions catalyzed by triphenylphosphine (Ph3P) under mild conditions. Curdlan, a polysaccharide used by the food industry and in biomedical applications, was employed as starting material for preparing these carboxyl-containing derivatives by a reaction sequence of bromination, azide displacement and ring-opening reaction with cyclic anhydrides, affording high conversions. These modification techniques have been demonstrated to display essentially complete regio- and chemo-selectivity at C-6. These novel polysaccharide-based materials starting from abundant and inexpensive curdlan are promising for some applications such as amorphous solid dispersion (ASD) oral drug delivery. / Ph. D.

Curdlan, a (1,3)-linked linear homopolysaccharide composed of beta-D-glucan, is produced by the bacterium Alcaligenes faecalis var. myxogenes. Several strategies to synthesize chemically modified curdlan derivatives have been reported, but there have been few reports of regioselective functionalization at specific positions of the curdlan backbone, especially of aminated curdlan derivatives which have remarkable potential in biomedical and pharmaceutical applications. We demonstrate herein the design, synthesis and characterization of a family of regioselectively aminated curdlan derivatives including 6-deoxy-6-(bromo/azido/amino/amido/ammonium) curdlans starting from 6-bromo/azido-6-deoxycurdlan. A key reaction that enabled the whole synthesis of new curdlan derivatives at C-6 described in this dissertation was the highly selective bromination of curdlan. The resultant 6-bromo-6-deoxycurdlan, prepared with high regioselectivity, was treated with trialkylamines or heterocyclic amines to produce a range of water-soluble curdlan ammonium salts. The bromide was then nucleophilically displaced by sodium azide to produce the versatile precursor 6-azido-6-deoxycurdlan. Its water solubility was enhanced either by the incorporation of hydrophilic trioxadecanoate esters into O-2/4 positions or by the borohydride reduction to afford 6-amino-6-deoxycurdlan. The iminophosphorane intermediate generated during Staudinger reactions was further investigated for subsequent syntheses: i) 6-amino or 6-amido-6-deoxycurdlan by in situ reaction with water or excess carboxylic anhydride, ii) 6-monoalkylamino curdlan by reductive amination using aldehydes and sodium cyanoborohydride, and iii) 6-dialkylamino-/tri-alkylammoniocurdlans by reacting with methyl iodide. Such derivatives could have properties useful for a range of biomedical applications, including interactions with proteins, encapsulation of drugs, and formulation with genes or other biological compounds. / Ph. D.

We now report an in depth analysis of the successful in vitro enzymatic synthesis of PHB utilizing the three-enzyme system from the bacteria Cupriavidus necator. Using HPLC methodology developed in this laboratory, and by adding each enzyme in a step-wise manner, we follow each individual stage in the three-enzyme route for PHB synthesis and delineate all stoichiometric relationships. We report the construction of the first metabolic model developed specifically for analyzing in vitro enzymatic PHB synthesis. We developed a hands-on student laboratory for culturing, producing, isolating, and purifying the bacterial biopolyesters PHB. We now report the first structural characterizations of iso-CoA, acetyl-iso-CoA, acetoacetyl-iso-CoA, and beta-hydroxybutyryl-iso-CoA using MS, MS/MS, and homo- and hetero-nuclear NMR analyses.We describe HPLC methodology to separate the isomers of several iso-CoA-containing compounds and report the first examples of iso-CoA-containing compounds acting as substrates in enzymatic acyl-transfer reactions. We describe a simple regioselective synthesis of iso-CoA from CoA. We also demonstrate a plausible mechanism, which accounts for the existence of iso-CoA isomers in commercial preparations of CoA-containing compounds. Herein we report that phenylaminoethyl selenide compounds protect DNA from peroxynitrite-mediated single-strand breaks. The mechanism of protection against peroxynitrite mediated DNA damage was investigated by HPLC. The chemistry of the reaction between peroxynitrite and HOMePAES was investigated using HPLC and HPLC/MS. The unique chemistry of the reaction between peroxynitrite and HOMePAES was investigated using HPLC and HPLC/MS. We report the development of novel CDB derivatives, which are selective COX-II inhibitors. A series of compounds were assayed with an in vitro colorimetric inhibitor screening and with a whole blood ELISA screening and the results indicate that MST is a selective inhibitor of COX-II.