Received: 16 March 2021 Revised: 05 May 2021 Accepted: 15 May 2021 DOI: 10.22034/ecc.2021.229705.1168 FULL PAPER Role of pyridazine analogs as acetylcholinesterase inhibitor: An approach for management of alzheimer’s disease Saad Alghamdia | Mohammad Asifb,* aLaboratory Medicine Department, Faculty of Alzheimer's disease (AD) is a neurodegenerative disorder causing Applied Medical Sciences, Umm Al-Qura failure of cognitive aptitude and performance irregularities, University, Makkah, 21955, Saudi Arabia resulting in degradation of cerebral and psychological activities. bGlocal School of Pharmacy, Glocal University, AD is presently a main health trouble and it is the third-major Mirzapur Pole, Saharanpur, Uttar Pradesh, India reason of casualty in the developed nations after cardiac and cancer diseases. The physiological pathway of this disorder remains almost unknown. The present curative advances to AD pursue the cholinergic theory. The acetylcholinesterase (AChE) enzyme has an essential role in the therapy of AD. The AChE- inhibitors have been developed into the leading approach for the advance of anti-ADs. Some AChE-inhibitors, like donepezil, tacrine, rivastigmine and ensaculin have shown progress in memory and cognitive actions. However, ensaculin is a coumarin analog that has prevented or lowered the progressive neurodegeneration. Several considerations support that some pyridazine analogs act as AChE and BuAChE inhibitors. *Corresponding Author: KEYWORDS Mohammad Asif Acetyl-cholinesterase; alzheimer's disease; butyryl- Tel.: +91-9897088910 cholinesterase; neurodegenerative; pyridazine derivatives. Introduction the patient death [3]. The improvement in life expectancy and the reality that occurrence of Alzheimer's disease (AD) is a AD enhances with age can contribute to neurodegenerative disorder, differentiated by handling it [4]. Despite various works, many the failure of cognitive capacity and rigorous features of the etiology and physiological behavior deformities, which eventually lead to paths of the AD remain unclear. The common degradation of cerebral and psychological present drug treatment advances to AD follow actions [1]. Three key phases can be the cholinergic theory [5-7]. distinguished in AD [2]. The first phase of In recent years, large numbers of amnesia, memory loss, engages early short- pyridazine derivatives have been reported to term memory loss and also short of significant possess almost all type pharmacological artlessness. In the second phase of confusion, activities viz. analgesic, anti-inflammatory, uncertainty, the patient displays time and antipyretics, antiulcer, anticancer, liberty confusion, mental uncertainty, and antimicrobial, antifeedant, herbicidal, alters in character. The third phase of antiphlogistics, antisecretory, anxiolytics, dementia occupies the totally mental inability sedative-hypnotics, antidepressants, and dependence of the patient. While AD itself tranquilizers, anticonvulsants, is not lethal, mental problems related with AD, immunosuppressant, anti-Alzheimer, GABA generally bacterial or viral infections, lead to antagonists, and some other useful Eurasian Chem. Commun. 3(2021) 435-442 http:/echemcom.com P a g e | 435 P a g e | 436 S. Alghamdi and M. Asif pharmacological activities. Various pyridazine agents [8,9]. Some anti-AChE drugs, like derivatives are also used as intermediates of donepezil, rivastigmine, tacrine, and ensaculin drugs and agrochemicals. The cardiovascular have been reported to play a role in enhancing activities of pyridazine compounds are very in memory and cognitive activities [10], and well known such as antiplatelets, were used as anti-AD agent (Figure 1). antihypertensive, antithrombotics, However, ensaculin is a coumarin analog that vasodilators, antiarrhythmics, cardiotonic, β- stops or slows down the progressive neuro- blockers, and hypocholesterolemic [8-10]. degeneration. Some pyridazine analogs act as The acetylcholinesterase (AChE) has AChE and butyrylcholinesterase (BuAChE) established extensive awareness as a drug inhibitors. Ensaculin contain benzopyran with design as anti-AD agent. The AChE inhibitor is a substituted piperazine moiety and used as an a primary strategy for the progress of anti-AD anti-AD drug [11,12]. CH3 O CH3 N OCH3 H3CO O N O O NH2 N N OCH3 O O CH3 N Dopanezil Tacrine Ensaculin Rivastigmin FIGURE 1 Some acetylcholinesterase (AchE) inhibitors used as anti-alzheimer's drugs (anti-AD) The anti-Alzheimer activity of pyridazine sulphonyl]-2-[4-(aryl)-piperazine]- compounds pyridazin3(2H)-one-2-yl- acetohydrazide/propionohydrazides. Three series of coumarins with The weak, reversible, and competitive phenylpiperazine substitution have been AChE-inhibiting action of minaprine (IC50=85 designed as potential anti-AD drugs [13]. µM on rat striatum AChE, 3-amino-6- Additionally, a large number of pyridazine phenylpyridazines (1) were tested as AChE analogs have interesting biological activities inhibitor. In relation to minaprine, the main like antibacterial, antiviral, antifungal, basics for high AChE inhibition are: analgesic, anti-convulsant, anti-inflammatory, (i) existence of a middle pyridazine ring, antimalarial, anti-platelets, anti-tuberculosis, (ii) requiring a lipophilic cationic head, and anticancer, etc. Some aryl-pyridazines having (iii) modification of a 2-5 carbon distance hetero-cycles, such as furan, pyridine, indole, between pyridazine moiety and cationic head. oxadiazole, triazole, and imidazole, thiadiazole The 3-[2-(1-benzylpiperidin-4-yl) rings have attracted special attention of ethylamino]-6-phenylpyridazine (2) showed researchers [14-23]. However, the an IC50 of 0.12 µM on AChE and strong anti- pharmacological evaluation of pyridazines as AChE inhibitor activity, 5000-time more AChE and BuAChE inhibitors is an extension of effective than minaprine. Some pyridazines the effort to develop newer and effective anti- act as AChE inhibitors. Structural alterations AD agents [24,25]. The above mentioned were attained on four dissimilar parts of pharmacologically active pyridazines [26, 27] compound 2 with subsequent remarks. and research efforts [28] to recognize new (i) Introduction of a lipophilic group in the drugs may be valuable in designing of AChE pyridazine moiety at C-5 position is favorable and BuAChE inhibitors like N'-[(4-aryl) Role of pyridazine analogs as acetylcholinesterase … P a g e | 437 for the AChE-inhibitory activity and The indeno-pyridazine compound was 12- AChE/BuChE selectivity, time more potent inhibitor on AChE compared (ii) Different substitutes of the C-6 phenyl ring with compound 2. Moreover, 3-[2-(1- are probable and led to equal or more effective benzylpiperidin-4-yl)ethylamino]-5-methyl- compounds, and 6-phenylpyridazine (3) is 100-times more (iii) The isosteric variants of the benzyl- selective AChE (BuChE/AChE ratio of 24) than piperidine moiety are critical to the efficiency. tacrine for human [29,30] (Figure 2). N N N N N H2N N N N N N H H 1 2 3 FIGURE 2 The 3-[(β-morpholino ethyl)amino]-4- chlorophenyl-benzal)hydrazones of 3-(6-(4- methyl-6-phenylpyridazine (minaprine) (4) is fluorophenyl)-pyridazin3(2H)-on-2-yl) an AChE inhibitor. The 3-Benzidino-6(4- propionohydrazide exhibited a very good chlorophenyl) pyridazine (BCP) (5) and AChE inhibitory action. All other compounds minaprine have a central pyridazine moiety. also exhibited significant BuAChE inhibitory The actions of BCP on late rectifier potassium action [33]. Some ethyl-6-[(aryl piperazine]- ions (K+) current and transitory outward K+ pyridazin-3(2H)one-2-ylpropionate and 6- ions current in isolated rat hippocampus [(arylpiperazine]-pyridazin-3(2H)one-2-yl pyramidal neurons, BCP, inhibited both propionohydrazides exhibited AChE and currents. The BCP potentially inhibits both BuAChE inhibitory action. The 6-Substituted- currents in rat hippocampus pyramidal pyridazin-3(2H)one-2-yl propionates neurons [31]. exhibited significant AChE and BuAChE Several N’-[(4-aryl)sulphonyl]-2-[4-(aryl)- inhibitory action. The 6-[4-(3-Trifluoromethyl piperazine]-pyridazin-3(2H)-one-2-yl-aceto phenyl)-piperazine]-pyridazin-3(2H)-one-2- hydrazide/propionohydrazides may be ylpropionate exhibited most active compound important in designing and developing AChE AChE and BuAChE inhibitor actions and and BuChE inhibitors. The AChE and BuAChE showed inhibitory action close to the inhibition of pyridazine analogs was galantamine and did not show any selectivity determined in-vitro by using galantamine as a between the two enzymes [28]. reference drug. Some compounds exhibited Some 6-substituted-pyridazin-3(2H)one-2- inhibitory actions close to galantamine at 25, propyl-3-(substituted or nonsubstituted 50, 100, 200μg/mL dos levels. The N’-[(4- benzal) hydrazones showed significant AChE aryl)sulphonyl]-2-[4-(aryl)- inhibitory action. None of the compounds piperidine/piperazine]-pyridazin-3(2H)one- exhibited BuChE inhibitory action. These 2yl-acetohydrazide/propionohydrazides, compounds exhibited AChE inhibitors with which have CF3 group on para position of AChE or BuChE selectivity [25]. The 2,6- phenyl sulfonyl ring, enhanced the anti-AChE disubstituted pyridazinone was an AChE action [32]. Some substituted or non- inhibitor and displayed high AChE inhibitory substituted benzalhydrazones of 3-(6- action and AChE or BuChE selectivity. The 6- substituted-pyridazin3(2H)-on-2-yl) ortho-tolylamino and N-ethyl-N- propionohydrazides exhibited AChE and isopropylacetamide substituted piperidine BuChE inhibitor activities. Only (4- exhibited