Tricyclic Pyrazolo[1,5-d][1,4]benzoxazepin-5(6H)-one Scaffold Derivatives:Synthesis And Biological Evaluation As ChE Inhibitors

Alzheimer's disease?AD?is a chronic neurodegenerative disease that is characterized by progressive deterioration of memory and other cognitive functions.Cholinesterase as the main therapeutic target for AD.BuChE inhibitors can reduce or avoid adverse reactions caused by AChE inhibitors.The development of potent,selective BuChE inhibitors has the potential advantage of increasing acetylcholine levels in advanced AD.Inourrecentwork,anoveltricyclicscaffoldofpyrazolo[1,5-d][1,4]benzoxazepin-5?6H?-one was found to be a selective hMAO-B inhibitor,which are used alone or in combination to treat Alzheimer's and Parkinson's diseases.To develop novel cholinesterase inhibitor,this tricyclic scaffold was screened ChEs inhibitory activities,but they showed weak inhibitory activities for AChE and BuChE.When 2-aryl group of the tricyclic scaffold was substituted by methyl group,this tricyclic scaffold exhibited moderate inhibitory activities for ChE and weak inhibitory activitiesforMAO.Accordingtoourrecentworks,pyrazolo[1,5-d][1,4]benzoxazepin-5?6H?-one derivatives?3a?3s?were synthesized according to the protocol outlined.The key intermediate 2-pyrazoline derivatives?1?were obtained by the cyclization reaction of excess hydrazine hydrate with the styrene ketones,which were prepared through Claisen-Schmidt condensation of substituted salicylaldehyde with acetone.The acylation of compound 1 with?-bromoacyl chloride were2-pyrazoline-1-ethanone derivatives?2?.The title compounds 3a?3s were obtained through the cyclization reaction of compound 2 in the present of NaHCO₃ catalysis in ethanol.Compounds 3t-3x were synthesized according to the literature procedure.To further study a possible influence of chirality at C-6 on ChEinhibitory activity,two enantiomersofcompound3oweresynthesizedbytheacylation of2-bromo-4-chloro-6-?3-methyl-4,5-dihydro-1H-pyrazol-5-yl?phenol with chiral pure2-chloropropionic acid and subsequent cyclization reaction.A series of tricyclic pyrazolo[1,5-d][1,4]benzoxazepin-5?6H?-onederivatives were evaluated as acetylcholinesterase?ACh E?and butyrylcholinesterase?BuChE?inhibitors.Some derivatives showed selective BuChE inhibitory activity,which was influenced by the volumes of the substituted groups at the C6 position and halogen substituents at the benzene ring of tricyclic scaffold.Among them,compounds 3f and 3o with dihalogen and 6-ethyl substituent showed the most potent activity(IC₅₀=2.95,2.04?M,and mixed-type,non-competitive inhibition against BuChE,respectively).Eutomer?6R?-3o exhibited better BuChE inhibitory activity than?6S?-3o.Compound 3o exhibited nontoxic,good ADMET properties,and remarkable neuroprotective activity.It can provide a reference direction for the later novel tricyclic framework modification.The results of this study have certain significance for the exploration of new selective BuChE inhibitors.