As one of the most important three natural big molecules, Polysaccaride is widely used in medicine, food and some other fields.A class of Endo glycosidases has been found which have a good effection in catalytic synthesis of polysaccharides, for which can identified the oxazoline structure of disccharides.Enzymatic synthesis requires a structure with an oxazoline as its substrate,this thesis synthesize respectively obtain disaccharide glycoside substrate by chemical way.First of all,i protect the-OH of glucose with acetylation, then using bromine replace the 1-OAc to obtain the donor.This monosaccharide easily hydrolyzed, require to keep in low temperature storage, also we should boil away the water inside with toluene before we use it;Then next,when i use the glucosamine hydrochloride as the material of disaccharide acceptor, i should keep other-OH in protecting but 4-OH;So using phthalates in protecting the amino,and the acetyl protecting hydroxy.Introducing the benzyl in the 1 position selectively.Delete the acetyl so i can connect the 4-OH and the 5-OH by benzaldehyde dimethyl acetal,leaving only the 3-OH to protect with benzyl.Utilizing the triethylsilane(Et3SiH) to selectively open the loop to gain the 4-OH disaccharide receptor.Finally,i synthesize the the disaccharide with silver trifluoromethanesulfonate(AgOTf).We also intent to add some function groups acetylenyl at the second position of acceptor.So i use the coupling agent EDC to couple the alkyne acid with NHS. Deprotected disaccharide can use DMC, Et3 N reacting in strong alkaline water.After purificating we obtain the oxazoline disaccharide.Then you can use Endo-A-glucosidase catalytic synthesize polysaccharides. |