Preliminary Study On The Structural Modification And Multi-target Anti-Alzheimer’s Disease Acitivities Of Active Component Of Polygala Xanthone

Objective:Alzheimer’s Disease（AD）is the most common form of dementia.As people ages,the prevalence of AD also increases,which seriously threatens the health of the elderly,and at the same time brings a heavy burden on their families and the society.AD has become the focus of world attention.However,the pathogenic mechanism of AD is complex,which greatly slows down the development of anti-AD drugs.At present,the only marketed drugs for treating AD are acetylcholinesterase inhibitors and N-methyl-D-aspartate receptor antagonists that target a single target.Although they can alleviate the symptoms of patients,they cannot effectively prevent the progress of AD.Therefore,Multi-target-directed ligands（MTDLs）have become a hot spot in the research of new anti-AD drugs.Polygala is a traditional Chinese medicine.It is widely used in the treatment of learning and memory disorders,dementia,neurasthenia,cancer and other symptoms.Xanthones are active ingredient in Polygala.Studies have shown that xanthones have neuroprotective and cholinesterase inhibitory effects.The purpose of this thesis is to modify the structure of 1,3-dihydroxyxanthone which commonly exist in Polygala and study the potential as MTDLs of their derivatives.Methods:Firstly,1,3-dihydroxyxanthone was synthesized by condensation reaction,and tertiary amine groups were introduced through nucleophilic substitution reaction.Four kinds of xanthone derivatives were synthesized and characterized by MS,¹H NMR,¹³C NMR,elemental analysis and melting point.The computer-assisted prediction method was used to evaluate the blood-brain barrier（BBB）permeability of the compounds.The spectrophotometric method was then used to study the chelating ability and stoichiometric ratio of the compounds to Cu（II）and Fe（III）.A series of metal complexes of compounds 1-4with Zn（II）and Cu（II）were synthesized by stirring the mixtures at room temperature,and the structure of the complexes was preliminarily characterized by IR and ¹H NMR.Secondly,Ellman’s method was used to study the inhibitory activities and the inhibitory types of compounds 1-4 on Acetylcholinesterase（ACh E）and Butylcholinesterase（Bu Ch E）.Semi-flexible molecular docking was also used to study the binding abilities of compounds1-4 and cholinesterase.Finally,Fenton reaction and pyrogallol autoxidation reaction were used to study the anti-oxidant abilities of compounds 1-4.Results:1.Four kinds of xanthone derivatives were synthesized,and their structures were characterized.The prediction results showed that the chemical properties of compounds 1-4are similar to donepezil.They have good absorption and permeability,and can penetrate BBB.2.In the metal chelating ability experiment,compounds 1-4 can all chelate Cu（II）and Fe（III）,and the stoichiometric ratio are both 2:1.In the synthesis experiments of metal complexes,a series of metal complexes of compounds 1-4 were synthesized.And the results of spectra analysis showed that in all of the structures of the metal complexes metal ions were coordinated with the compounds throng both 1-hydroxyl oxygen and carbonyl oxygen.3.Cholinesterase inhibition activity experiments showed that all of compounds 1-4 had good inhibitory effects on ACh E.And compound 2 had the strongest inhibitory effect on ACh E(IC₅₀=2.403±0.002μM),but a relatively lower inhibitory effect on Bu Ch E(IC₅₀=31.221±0.002μM),which indicated that compound 2 can selectively inhibit ACh E.Compound 4 had the same inhibitory capacity for Bu Ch E(IC₅₀=2.816±0.004μM)and ACh E(IC₅₀=2.615±0.004μM),and both were in the micromolar range,so compound 4 was a dual inhibitor.The complex of compound 2 and Cu（II）had better inhibitory effect on ACh E than the single compound 2(IC₅₀=0.934±0.002μM).Enzyme kinetics experiments showed that compound 2 and compound 4 were mixed inhibitors.The results of molecular docking experiments showed that all compounds 1-4 combined with both the catalytic active site（CAS）and peripheral anionic site（PAS）of ACh E,which was consistent with the in vitro results.4.The experimental results of scavenging hydroxyl radicals showed that compounds1-4 had a strong scavenging effect on hydroxyl radicals,and their scavenging capabilities were in the micromolar range and were stronger than that of vitamin C.Compound 2 had the strongest scavenging ability,and the scavenging ability was enhanced after coordination with Cu（II）.The results of scavenging superoxide radicals scavenging experiments showed that the scavenging ability of compound 2 and compound 4 were better than vitamin C.Conclusion:We have synthesized four new xanthone derivatives,all of which have good absorption and permeability.In vitro activity test results show that 1-4 has good inhibitory effect on cholinesterase.In addition,these compounds also have strong metal chelating ability and antioxidant activity.Compound 2 has the highest inhibitory activity on acetylcholinesterase,the highest selective inhibitory effect on acetylcholinesterase,and the strongest antioxidant activity.In particular,after coordination with metal,compound 2shows better biological activity due to the synergistic effect.Therefore,compounds 1-4,especially compound 2,especially compound 2,have the potential to be developed as new drugs against Alzheimer’s disease.