Synthesis Study Of Human Milk Oligosaccharide DSLNT

Human milk is the best nutrition source for newborns.It is mainly composed of fat,protein.human milk oligosaccharides(HMOs)and other trace elements.The content of human milk oligosaccharides(HMOs)are about 10 g/L.HMOs are the third most important nutrient components in milk,their content in animal milk is extremely low,and they are the most typical biomark of human milk.Human milk oligosaccharide is a mixture composed of more than 150 kinds of oligosaccharides.According to the difference of the main chain structure,human milk oligosaccharides can be divided into two groups,milk series and milk new series.Studies have shown that human milk oligosaccharides can directly function in newborns without being metabolized,including promoting the proliferation of probiotics in the intestine,inhibiting the attachment of pathogens and toxins,regulating cellular immune responses,promoting neonatal brain development.and reducing certain incidence of these diseases and so on.The content of human milk oligosaccharides are varied according to the genes,environment,and physical development.Human milk oligosaccharides have diverse structures and limited sources.Therefore.it is impossible to add all human milk oligosaccharides to formula milk powder.Usually,galactooligosaccharides(GOS)and fructo-oligosaccharides(FOS)are added as surrogates of human milk oligosaccharides but.obviously.GOS and FOS can not replace the important biological functions of human milk oligosaccharides.Necrotizing enterocolitis(NEC)is a serious intestinal disease that mainly occurs in premature infants.The incidence of NEC in very low births(weight less than 1500 g)is 15%,and the fatality rate is as high as 30%.Moreover,there will be serious sequelae after recovery.NEC is the main cause of death in the neonatal intensive care unit(NICU).This disease develops rapidly and lacks characteristic clinical manifestations.There is not good treatment method yet.In clinical observations,it was found that infants fed with formula milk are 10 times more likely to suffer from NEC than those fed with human milk.Obviously,certain components in human milk play important roles.In 2012.researchers found the disialvllacto-N-tetraose(DSLNT)in human milk oligosaccharides can prevent neonatal mice from suffering from NEC through the neonatal mouse model is.Further studies found that DSLNT could help neonates from suffering from NEC only when its concentration is higher than 310 mg/L.Currently DSLNT is directly extracted from a large amount of human milk,its source is limited and the purity is not high.Enzymatic synthesis lacks the key acetylglucosamine α2-6 sialyl glycosyltransferase This greatly limits related research on its biological significance.Therefore,how to obtain DSLNT and its derivatives with a single structure has become an important issue.I attempt to synthesize the DSLNT on a large scale by chemical method.The first chapter briefly introduces the important biological functions of human milk oligosaccharides and current synthesis of human milk oligosaccharides.The second chapter conducts preliminary literature research on the protective group of amino groups in glucosamine,and N,N-diacetyl group is used as the amino protecting group.The retro-synthesis analysis of DSLNT is carried out.First,the core tetrasaccharide is designed by a one-pot strategy,and the 6OAc protection of glucosamine and the 3-O-TBS of galactose are removed,and then the two sialic acid residues are installed in one step,and the protecting group is finally removed to obtain the DSLNT.The third chapter is the synthesis.The core tetrasaccharide is synthesized by the one-pot method,initially 3-3 is used as the donor and 2-6 is used as the acceptor.It was found that no expected product was formed and both donor and acceptor were hydrolyzed,I next switched to a stepwiselysynthesis from the reducing end to the non-reducing end.Glucosamine 2-11 was used as the donor and lactose 1-4 was used as the acceptor.The p-TolSCl/AgOTf was selected for the glycosylation and trisaccharide 1 was obtained with a yield of 81%.DDQ was selected as the oxidizing reagent to remove 2-naphthylmethyl group in 75%in a PBS-buffer.However,an orthoester is generated when the galactose 3-3 is used as the donor for the[1+3]glycosylation.A more reactive galactose donor 3-7 was used in the presence of NIS/TfOH and the tetrasaccharide was successfully preparedat-78℃ with a 79%yield.When the O-TBS protective group at position 34 of galactose was removed,acyl migration occurred,which reduced the overall yield.Finally,the 2-position benzoyl group of the terminal galactose was removed together to generate a 5hydroxyl substrate to react with 2.5 equivalents of sialic acid donor 5-1,although a large number of 6 sugar products were detected in mass spectrometry,due to the close polarity of each product,it is difficult to separate pure products to verify the structure by conventional column chromatography.