Study On The Synthesis Of Tetrabenzylglucopyranose And Tetrabenzyl Galactopyranose

D-glucose and D-galactose are common monosaccharids and widely exist in the nature. They are both aldohexoses, which leads to their similar physicochemical properties, and C4 epimers, which makes different physicochemical characteristics. In consequence, the synthetic techniques of their corresponding derivatives have similarities and special adjustments are needed to achieve optimum process parameters.2,3,4,6-tetra-O-benzyl-a-D-glucopyranose and 2,3,4,6-tetra-O-benzyl-a-D-galacto-pyranose are prepared through Fischer glycosidation, Williamson etherification and selective hydrolysis of D-glucose and D-galactose respectively. Each reaction intermediates and differences between D-glucose and D-galactose derivatives in configuration, yield and quality and causes of the above differences were investigated.This paper improves Williamson etherification by using sodium hydroxide instead of sodium hydride in sodium alkoxide method and reflux dewatering to promote reaction equilibrium, which makes the reaction carried out completely by using lower amount of alkoxide and benzyl etherifying agent and enhance reaction safety and ensures reaction yield over 95%. All the above techniques explored are effective for preparation of both methyl-2,3,4,6-tetra-O-benzyl-a-D-glucopyranose and methyl-2,3,4,6-tetra-O-benzyl-α-D-galactopyranose.This paper raises the selective hydrolysis selectivity by using propionic acid instead of common acidic acid as reaction solvent to create greater solubility difference between raw material and product. Based on the optimization of operation parameters, the yield of methyl-2,3,4,6-tetra-O-benzyl-a-D-glucopyranose is improve from 40%(lit.) to 65%. Hydrolysis proceeds smoothly in the above method to give a yellow syrup which is consists of 2,3,4,6-tetra-O-benzyl-α-D-galactopyranose isomers.The synthetic process explored in this paper for 2,3,4,6-tetra-O-benzyl-a-D-glucopyranose and 2,3,4,6-tetra-O-benzy-a-D-galactopyranose embodies high yield, good safety, and it is friendly to environment and fit for industrial application.