Design,Synthesis And Bioactivity Evaluation Of Nitazoxanide-based Derivatives As Novel Anti-alzheimer’s Disease (AD) Agents,and Discovery Of Novel Purine Nucleoside Derivatives As Phosphodiesterase 2(PDE2) Inhibitors

There are two parts in my dissertation:Part 1,design,synthesis and bioactivity evaluation of nitazoxanide-based derivatives as novel anti-Alzheimer’s disease(AD)agents.AD is a progressive neurodegenerative disorder and characterized by memory dysfunction and congnitive impairment.The two typical hallmark lesions of AD are amyloid senile plaques(SPs)and neurofibrillary tangles(NFTs)that made of accumulated β-amyloid(A(3)peptides and abnormally hyperphosphorylated tau protein,respectively.Due to the complicated pathogenesis of AD,there are still no effective drugs in clinic that can halt or slow down the disease progression,while the current available therapies provide only limited symptomatic relief.More and more studies suggest that the autophagy deficits may also contribute to the pathogenesis of various neurodegenerative diseases including AD,and symptoms of AD could be improved by enhancing autophagy.Herein,an in-house library of old drugs was screened to identy novel anti-AD agents,and we dertermined that a clinical drug nitazoxanide could promote Aβ clearance and inhibit the hyperphosphorlation of Tau protein.Further results revealed that nitazoxanide could inhibit the phosphorylation of serine 757 of Unc-51-like kinase 1(ULK1)by inhibiting the phosphorylation of mammalian target of rapamycin(mTOR),thereby promoting autophagy.Then,a total of 67 derivatives based on nitazoxanide were designed,synthesized and their inhibitory abilities of phosphorylation of p70 ribosomal protein S6 kinase(p70S6K)——the direct downstream substrate of mTOR——were tested by a-screen assay.Among them,17 compounds exhibited strong inhibitory activity with the inhibitory rate of more than 75%at 20 μM,and most of these 17 compounds also displayed good blood-brain barrier(BBB)permeability.For compounds B21 and B30 with optimal p70S6K phosphorylation and BBB permeability,we identified that B21 could inhibit the phosphorylations of mTOR and ULK1 by Western blot method,thus enhancing the level of autophagy in cells.Although B30 could inhibit the phosphorylations of AKT and mTOR,its inhibitory effect on phosphorylation of ULK1 was not significant and it can not be determined whether it can enhance autophagy.In addition,compound B21 could significantly promote Aβ clearance and effectively inhibit Tau phosphorylation.The result of anti-AD activity study in vivo revealed that compound B21 could significantly improve memory and cognitive impairment in APP/PS1 double transgenic AD model mice.Meanwhile,the in vitro hERG potassium channel inhibitory assay indicated that compound B21 showed good safety.Altogether,considering the good anti-AD activity of compound B21 in vivo,compound B21 can be further developed as a novel anti-AD drug candidate.Part 2,discovery of novel purine nucleoside derivatives as phosphodiesterase 2(PDE2)inhibitors.PDE2 has received much attention for the potential treatment of central nervous system(CNS)diseases and pulmonary hypertension.Although several PDE2 inhibitors have been reported recently,none of them have reached the market yet.In our previous study,an in-house library of old drugs was investigated by the method of structure-based virtual screening,thus an FDA-approved drug clofarabine was found to be a moderate PDE2 inhibitor(IC50 = 3.12±0.67μM).The previous structural modification had led to the discovery of compounds 22 with a～10 folds enhancement of activity(IC50 = 0.32±0.04 μM).Herein,further optimization of 22 was carried out to improve the PDE2 inhibitory activity,and 12 derivatives were designed,synthesized and tested with biological assays.The results showed that the IC50 values of three compounds(C1,C2,C3)were less than 1 μM,and the most potent compound C2 with IC50 value of 0.29±0.03μM was identified.In consideration of the structural similarities among compound 22 and C2,the following molecular docking and molecular dynamic simulations made it clear that 22 could interact with the unique hydrophobic pocket of PDE2 by forming extra van der Waals interactions with hydrophobic residues such as Leu770,Thr768,Thr805 and Leu809,which might contribute to its enhancement of PDE2 inhibition.In summery,these potential compounds reported in this dissertation and the available structure-activity relationships might bring significant instruction for further development of potent PDE2 inhibitors.