Title Isomerization of Saccharides in Subcritical Aqueous Alcohols

Isomerization of Saccharides in Subcritical Aqueous Alcohols( Title Dissertation_全文 ) Author(s) Gao, Da-Ming Citation 京都大学 Issue Date 2016-03-23 URL https://doi.org/10.14989/doctor.k19754 Right 許諾条件により本文は2016-10-01に公開 Type Thesis or Dissertation Textversion ETD Kyoto University Isomerization of Saccharides in Subcritical Aqueous Alcohols Da-Ming Gao 2016 Contents General Introduction ··········································································1 Chapter 1 Kinetics of Sucrose Hydrolysis in a Subcritical Water-ethanol Mixture 1.1. Introduction ·····················································································4 1.2. Materials and Methods ········································································4 1.3. Results and Discussion ········································································5 1.4. Conclusions ··················································································· 11 Chapter 2 Kinetic Analysis for the Isomerization of Glucose, Fructose, and Mannose in Subcritical Aqueous Ethanol 2.1. Introduction ···················································································12 2.2. Materials and Methods ······································································12 2.3. Results and Discussion ······································································13 2.4. Conclusions ···················································································20 Chapter 3 Promotion or Suppression of Glucose Isomerization in Subcritical Aqueous Straight- and Branched-chain Alcohols 3.1. Introduction ···················································································21 3.2. Materials and Methods ······································································21 3.3. Results and Discussion ······································································22 3.4. Conclusions ···················································································27 Chapter 4 Kinetic Effect of Alcohols on Hexose Isomerization under Subcritical Aqueous Conditions 4.1. Introduction ···················································································28 4.2. Materials and Methods ······································································28 4.3. Results and Discussion ······································································28 4.4. Conclusions ···················································································37 I Chapter 5 Production of Rare Sugars from Common Sugars in Subcritical Aqueous Ethanol 5.1. Introduction ···················································································38 5.2. Materials and Methods ······································································38 5.3. Results and Discussion ······································································39 5.4. Conclusions ···················································································46 Chapter 6 Solubility of D-Galactose, D-Talose, and D-Tagatose in Aqueous Ethanol at Low Temperature 6.1. Introduction ···················································································47 6.2. Materials and Methods ······································································47 6.3. Results and Discussion ······································································48 6.4. Conclusions ···················································································49 Chapter 7 Production of Keto-disaccharides from Aldo-disaccharides in Subcritical Aqueous Ethanol 7.1. Introduction ···················································································50 7.2. Materials and Methods ······································································50 7.3. Results and Discussion ······································································52 7.4. Conclusions ···················································································63 Concluding Remarks ·············································································64 References ·····························································································67 Acknowledgements ················································································74 List of Publications ················································································75 II General Introduction Saccharides, which are also interchangeably called “carbohydrates” or “sugars”, are a group of marvelous and abundant bestowals from nature and have a variety of vital functions to all of the living creatures. For human beings, a common use of saccharides is to provide energy since human appeared despite unknowing what saccharide is. Research on the molecular level about saccharides did not begin until the nineteenth century. Since then, the physiological functions of saccharides were gradually discovered beyond as sources and stores of energy. Saccharides were found as an important constituent of cells as supporting tissue or displaying on the surface of cells playing critical roles in cell interactions [1,2]. Saccharides also can conjugate with proteins to form glycoproteins to alter protein structure and function [3]. In recent decades, many previously unknown physiological functions of saccharides were discovered as supplements or sugar-based medicines for various illnesses. In particular, rare sugars (also called “rare saccharides”), which were defined as the sugars that are rare in nature, are found possessing many important physiological functions [4]. Among the rare saccharides, rare ketoses such as D-tagatose, D-xylulose, D-ribulose, cellobiulose, maltulose, lactulose, and melibiulose have attracted the most attentions in the scientific research fields of health and synthetic chemistry. Because D-tagatose has low energy (almost 0 kJ/g of food energy) and can be used as a drug to control type-2 diabetes and obesity, it can be used as a sweetener substitute for sucrose [5,6]. Besides, dietary restriction of energy by the intake of D-tagatose reduces the incidence of neoplastic lesions and significantly extends the maximum life span [5]. D-Xylulose is not only an energy resource for growth but also can be used in the pharmaceutical chemistry [4]. Intake of lactulose can promote the growth of Bifidobacterium [7,8] and has been proved to be used as drugs in treatment of many diseases such as hepatic encephalopathy and chronic constipation [8–10]. There are few reports on the physiological effects of D-ribulose, cellobiulose, and melibiulose because of the difficulty in their production and high cost. D-Ribulose is an important material to synthesize nucleosides [11]. Aldose-ketose isomerization is considered as the most important method to prepare these ketoses and has been significantly progressed despite that the ketose formation is not thermodynamically favorable because the formation of ketose is endothermic. Among the possible isomers, only D-glucose, D-mannose, D-galactose, D-xylose, D-ribose, L-arabinose, 1 lactose, and melibiose are naturally abundant. Free cellobiose and maltose are not abundantly found in nature, but they can be easily obtained by hydrolyzing cellulose and starch, respectively [12]. The conversion of these abundant saccharides to rare ketoses has become necessary and attracted much attention. These monosaccharides and disaccharides can be isomerized to the corresponding C-2 ketoses by alkali-catalyzed, metal-catalyzed, and enzymatic isomerizations. Biotransformations of abundant saccharides to rare saccharides have been performed primarily using aldose-ketose isomerases, epimerases, and polyol dehydrogenases [13]. Enzymatic isomerization can afford high selectively and even high yield of products. Nevertheless, the operating temperature cannot be largely elevated to accelerate the reaction and improve the reaction equilibrium to avoid denaturation of the enzymes. The metal-catalyzed isomerization is complex and the product distribution strongly depends on the type of substrate, cosolvent, metal ions, and carrier of metal ions in heterogeneous isomerization [14–20]. The post-treatment of homogeneous metal-catalyzed isomerization and the preparation and recovery of the heterogeneous catalyst are often tedious, which usually result in low final yield or high cost of the desired product. In alkali-catalyzed isomerization, glucose-type (2,3-threo-type) monosaccharides could be easily isomerized to the corresponding C-2 ketoses such as isomerization of glucose to fructose; however, mannose-type (2,3-erythro-type) monosaccharides were isomerized to the C-2 ketoses in low yields [21–24]. Among these methods, only alkali-catalyzed isomerization was considered as versatile and was exclusively applied to produce a limited number of ketoses for the commercial demand suffering from low yields and many by-products. This has the implication that many rare ketoses are not readily accessible, which consecutively hindered researches of this class of saccharides and restricted the potential applications. Therefore, it is necessary to develop a new method to synthesize these rare ketoses simply and efficiently, preferably by one-step isomerization. It was reported that the isomerization of monosaccharides occurred in subcritical water. Subcritical water, which is defined as the water remaining liquid state under pressurized conditions between the atmospheric boiling point and critical temperature, possesses properties of high ion product

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