| Polysaccharides are a class of biological macromolecules that are as important as proteins and nucleic acids.They play an important role in the cellular environment,including the cell recogization,cell migration and adhesion,etc.Polysaccharides are widely distributed in animals,plants and microorganisms.Among them,fungal polysaccharides are a class of polysaccharides isolated from fungal fruit bodies,mycelium and fermentation broth.A large number of pharmacological studies show that these polysaccharides have antibacterial and antiviral effects,anticancer effects,antioxidant effects and immune regulation effects.The two fungal polysaccharides that we are concerned about in this dissertation are galactomannans from Antrodia cinnamomea and Aspergillus fumigatus.Antrodia cinnamomea is a precious medicinal fungus unique in Taiwan area.It can be used to treat various diseases,including liver disease,abdominal pain,drug poisoning,diarrhea,skin itching,high blood pressure and cancer.Polysaccharides have been identified as one of the main pharmacological active ingredients in Antrodia cinnamomea.They have liver protection,anti-angiogenesis,anti-oxidation,immune regulation,anti-inflammatory and anti-tumor activities.Studies have found that Antrodia cinnamomea galactomannan is a class of polysaccharides with important biological activity,which can significantly enhance the phagocytosis and bactericidal ability of mouse macrophages,stimulate immune activity and reduce the risk of severe inflammation.Therefore,this glycan can be used as a drug candidate for the development of nutritional supplements and adjuvants for various diseases.Aspergillus fumigatus is one of the most common airborne fungal pathogens that can cause severe and often fatal invasive aspergillosis in immunocompromised patients.Studies have found that the main carbohydrate antigen produced by Aspergillus fumigatus is galactomannan,which can induce host-specific responses.In clinical practice,medical personnel usually use the detection of this polysaccharide antigen circulating in the patient’s serum to diagnose invasive aspergillosis.In view of the important biological activity and potential application value of the above-mentioned two fungal galactomannans,as well considering the naturally extracted polysaccharides having some shortcomings such as micro-inhomogeneity,poor purity,and large structural changes,this dissertation aims to prepare related oligosaccharide fragments with specific and defined structural characteristics through chemical synthesis,which will lay the foundation for the systematic study of the corresponding structure-activity relationship.This dissertatipon mainly includes the following three parts:In the first chapter,we presented a brief overview of fungal polysaccharides,focusing on the various functions and applications of fungal polysaccharides.At the same time,we introduced the two fungal galactomannan polysaccharides from Antrodia cinnamomea and Aspergillus fumigatus,and reviewed the important biological functions and synthesis progress of the two fungal polysaccharides.The second chapter introduced the chemical synthesis and preliminary bioactivity evaluation of the oligosaccharide fragments related to Antrodia cinnamomea galactomannose.We synthesized two tetrasaccharides ACP-2,ACP-3 and the hexasaccharide ACP-4 through[2+2]and[2+2+2]glycosylation strategies,and obtained the hexasaccharide ACP-5 through catalytic hydrogenation.In the synthesis of the tetrasaccharides ACP-2 and ACP-3,we used the trichloroacetimidate ester as donor for glycosylation reaction,and constructed α-configuration glycosidic bonds through the neighboring group participation effect of acyl groups on C-2 postions and the solvent effect of ethyl ether.Therefore,the fully protected tetrasaccharides ACP-14 and ACP-17 were prepared in high yield,and all protecting groups were then removed and the azide group was reduced to the amino group to obtain the target tetrasaccharide molecules ACP-2 and ACP-3.During the synthesis of the hexasaccharide ACP-4,we used the characteristic of trityl group to selectively protect the primary hydroxyl group to construct the monosaccharide module ACP-19,which was further glycosylated with the thioglycoside donor and the trichloroacetimidate donor.Similarly,the neighboring group participation effect and the solvent effect of ether ensured the specificity of the glycosidic bond configuration.Finally,we evaluated the role of five oligosaccharide fragments ACP-1,2,3,4 and 5 on the proliferation and phagocytosis of mouse mononuclear macrophage leukemia cell progenitor 264.7,and found that the tetrasaccharide ACP-3,the hexasaccharide ACP-5 and the octasaccharide ACP-1 have relatively good activity.Among of them,the Antrodia cinnamomea galactomannan backbone segment ACP-3 exhibited the best bioactivity.Thus,we speculated that the immune activity of the Antrodia cinnamomea galactomannan might be determined by the main carbohydrate chain structure.The third chapter introduced the chemical synthesis of the tetrasaccharide fragment related to Aspergillus fumigatus galactomannan.We synthesized the tetrasaccharide AFP-1 through the[1+1+1+1]assembly strategy.During the synthesis process,we constructed monosaccharide modules AFP-3 and AFP-4 with D-galactopyranose as the strating material,and constructed monosaccharide module AFP-5 with mannose module AFP-6 as the starting material.Glycosylation reaction was carried out through the pre-activation assembly method.During its synthesis,the β-configuration of the glycosidic bond was ensured through the neighboring group participation effect of the C-2 benzoyl group.First,the monosaccharide donor AFP-3 was fully activated by the pre-activation reagent(p-toluenesulfur chloride),then glycosylated with the monosaccharide acceptor AFP-4 to obtain the disaccharide AFP-14.Next,AFP-14 was pre-activated again,and then glycosylated with AFP-4 to yield the trisaccharide AFP-15.Thereafter,AFP-15 was activated and coupled with the mannose receptor AFP-5 to obtain the fully protected tetrasaccharide AFP-16.Finally,all the protecting groups are removed from AFP-16 and the azide group was reduced to the amino group to produce the target molecule AFP-1. |
