Design, Synthesis And Structure-activity Relationship Study Of β-secretase Inhibitors

Alzheimer's disease (AD), the neurodegenerative disorder, is the most common cause of dementia. It is characterized pathologically by the presence of intracellular neurofibrillary tangles(NFTs)and extracellular amyloid plaques. The current treatments temporarily alleviate the cognitive symptoms of the illness but cannot stop or slow down neuronal cell death or brain deterioration.Acording to the amyloid hypothesis, accumulation of amyloid peptides(Aβ) in the brain which is the main component of senile plaques result in neuronal toxicity and cell death. Aβis produced fromβ-amyloid precursor protein (β-APP) by the sequential cleavage of theβ-andγ-secretase.β-secretase (β-amyloid cleaving enzyme-1, BACE1) has being considered to be an attractive therapeutic target for the treatment and prevention of AD.Even though theβ-secretase inhibitors OM99-1,OM99-2 and OM00-3 have high affinity to the target, their molecular mass is over 900 Da and these compounds are belong to polypeptide structure and insufficient of drug-likeness. During the develepment process ofβ-secretase inhibitors, the breakthrough was that Shawn J. Stachel from Merck develeped sulfamide substituted isophthalic acid derivatives in 2004. One of these derivatives, CTS-21166, has been ongoing phase II clinical trials..Based on the crystal structure of BACE1 and the structure-function relationship of BACE1 inhibitors , with the assistance of computer-aided drug design, two types of target compounds were designed. Then the compounds, which would be synthesized in this study, were selected by molecular docking (Surflex Model of Sybyl 8.1 program) against active site of BACE1. Finally, twenty target compounds of isothiazolone substituted isophthalic acid derivatives were synthesized. The purity of these compounds determined by HPLC was over 90 %. The structures of these compounds had been confirmed by 1H-NMR and MS.Synthetic routes of three key intermediates were investigated and optimized. In the course of synthesizing these compounds, the synthetic conditions for isothiazolone substituted isophthalic acid, Suzuki coupling reaction and hydroxyethyl- amine intermediates were emphatically explored.Time-resolved fluorescence (TRF) was used to evaluate the inhibitory activity of these compounds againstβ-secretase. Inhibitory activity of ten target compounds against Aβ40 production was determined on APP/BACE1 double transfection CHO cell. The results showed that four compounds of type V had high inhibitory activities against BACE1 with inhibitiory rate of more than 70% at the concentration of 1μmol·L -1. Compound Va had an IC50 value of 13.7 nmol·L -1. Its inhibitiory rate against Aβ40 production on APP/BACE1 double transfection CHO cell was 19.6% at the concentration of 50 nmol·L -1. Eight compounds of type VI had high inhibitory activities against BACE1. Especially compound VIc had an IC50 value of 8.1 nmol·L -1,which inhibitiory rate against Aβ40 production on APP/BACE1 double transfection CHO cell was 43.7% at the concentration of 10 nmol·L -1. Compound VId had an IC50 value of 73.7 nmol·L -1,which inhibitiory rate against Aβ40 production on APP/BACE1 double transfection CHO cell was 58.3% at the concentration of 10 nmol·L -1. Three compounds had more potent inhibitory activities against Aβ40 production on APP/BACE1 double transfection CHO cell than positive control compound, and they are ongoing for the animal model evaluation.Compounds designed and synthesized in this study were evaluated in the molecular and cellular level . The structure-function relationship were summarized. All the work could guide the future research of designing and synthesizing novol BACE1 inhibitors which could pass the blood-brain barrier with high inhibitory activity and selectivity.