α-Mangostin has been reported to possess a broad range of pharmacological effects including potent cholinesterase inhibition, but the development of α-mangostin as a potential lead compound is impeded by its toxicity. The present study investigated the impact of simple structural modification of α-mangostin on its cholinesterase inhibitory activities and toxicity toward neuroblastoma and liver cancer cells. The dialkylated derivatives retained good acetylcholinesterase (AChE) inhibitory activities with IC50 values between 4.15 and 6.73 µM, but not butyrylcholinesterase (BChE) inhibitory activities, compared with α-mangostin, a dual inhibitor (IC50 : AChE, 2.48 µM; BChE, 5.87 µM). Dialkylation of α-mangostin produced AChE selective inhibitors that formed hydrophobic interactions at the active site of AChE. Interestingly, all four dialkylated derivatives of α-mangostin showed much lower cytotoxicity, being 6.4- to 9.0-fold and 3.8- to 5.5-fold less toxic than their parent compound on neuroblastoma and liver cancer cells, respectively. Likewise, their selectivity index was higher by 1.9- to 4.4-fold; in particular, A2 and A4 showed improved selectivity index compared with α-mangostin. Taken together, modification of the hydroxyl groups of α-mangostin at positions C-3 and C-6 greatly influenced its BChE inhibitory and cytotoxic but not its AChE inhibitory activities. These dialkylated derivatives are viable candidates for further structural modification and refinement, worthy in the search of new AChE inhibitors with higher safety margins.
With the fading of 'one drug-one target' approach, Multi-Target-Directed Ligands (MTDL) has become a central idea in modern Medicinal Chemistry. The present study aimed to design, develop and characterize a novel series of 4-(Diethylamino)-salicylaldehyde based thiosemicarbazones (3a-p) and evaluates their biological activity against cholinesterase, carbonic anhydrases and α-glycosidase enzymes. The hCA I isoform was inhibited by these novel 4-(diethylamino)-salicylaldehyde-based thiosemicarbazones (3a-p) in low nanomolar levels, the Ki of which differed between 407.73 ± 43.71 and 1104.11 ± 80.66 nM. Against the physiologically dominant isoform hCA II, the novel compounds demonstrated Kis varying from 323.04 ± 56.88 to 991.62 ± 77.26 nM. Also, these novel 4-(diethylamino)-salicylaldehyde based thiosemicarbazones (3a-p) effectively inhibited AChE, with Ki values in the range of 121.74 ± 23.52 to 548.63 ± 73.74 nM. For BChE, Ki values were obtained with in the range of 132.85 ± 12.53 to 618.53 ± 74.23 nM. For α-glycosidase, the most effective Ki values of 3b, 3k, and 3g were with Ki values of 77.85 ± 10.64, 96.15 ± 9.64, and 124.95 ± 11.44 nM, respectively. We have identified inhibition mechanism of 3b, 3g, 3k, and 3n on α-glycosidase AChE, hCA I, hCA II, and BChE enzyme activities. Hydrazine-1-carbothioamide and hydroxybenzylidene moieties of compounds play an important role in the inhibition of AChE, hCA I, and hCA II enzymes. Hydroxybenzylidene moieties are critical for inhibition of both BChE and α-glycosidase enzymes. The findings of in vitro and in silico evaluations indicate 4-(diethylamino)-salicylaldehyde-based thiosemicarbazone scaffold to be a promising hit for drug development for multifactorial diseases like Alzheimer's disease.
The resistance status of Selangor Aedes aegypti (Linnaeus) larvae against four major groups of insecticides (i.e., organochlorines, carbamates, organophosphates and pyrethroids) was investigated. Aedes aegypti were susceptible against temephos (organophosphate), although resistance (RR50 = 0.21-2.64) may be developing. The insecticides susceptibility status of Ae. aegypti larvae were found heterogeneous among the different study sites. Results showed that Ae. aegypti larvae from Klang, Sabak Bernam and Sepang were susceptible against all insecticides tested. However, other study sites exhibited low to high resistance against all pyrethroids (RR50 = 1.19-32.16). Overall, the application of synergists ethacrynic acid, S.S.S.- tributylphosphorotrithioate and piperonyl butoxide increased the toxicity of insecticides investigated. However, the application failed to increase the mortality to susceptible level (>97%) for certain populations, therefore there are chances of alteration of target site resistance involved. Biochemical assays revealed that α-esterase, (Gombak, Kuala Langat, Kuala Selangor and Sabak Bernam strains) β-esterase (Klang and Sabak Bernam strains), acetylcholinesterase (Kuala Selangor and Sabak Bernam strains), glutathione-S-transferase (Kuala Selangor and Sabak Bernam strains) and mono-oxygenases (Gombak, Hulu Langat, Hulu Selangor and Kuala Langat strains) were elevated. Spearman rank-order correlation indicated a significant correlation between resistance ratios of: DDT and deltamethrin (r = 0.683, P = 0.042), cyfluthrin and deltamethrin (r = 0.867, P =0.002), cyflyuthrin and lambdacyhalothrin (r = 0.800, P =0.010), cyfluthrin and permethrin (r = 0.770, P =0.015) deltamethrin and permethrin (r = 0.803, P =0.088), propoxur and malathion (r = 0.867, P = 0.002), malathion and temephos (r = 0.800, P = 0.010), etofenprox and MFO enzyme (r = 0.667, P =0.050). The current study provides baseline information for vector control programs conducted by local authorities. The susceptibility status of Ae. aegypti should be monitored sporadically to ensure the effectiveness of current vector control strategy in Selangor.
Centella asiatica (C. asiatica) is one of the medicinal plants that has been reported to exert comprehensive neuroprotection in vitro and in vivo. In view of this, the present study was performed to investigate the effect of ethanolic extract of C. asiatica, designated as raw-extract of C. asiatica (RECA) in reducing the acetylcholinesterase (AChE), inflammations, and oxidative stress activities via both in vitro (SH-SY5Y and RAW 264.7 cells) and in vivo (Sprague Dawley rats). Quantitative high-performance liquid chromatography analysis reveals that RECA contains a significantly high proportion of glycosides than the aglycones with madecassoside as the highest component, followed by asiaticoside. Treatment of SH-SY5Y cells with RECA significantly reduced the AChE activity in a concentration-dependent manner with an IC50 value of 31.09 ± 10.07 µg/mL. Furthermore, the anti-inflammatory and antioxidant effects of RECA were evaluated by lipopolysaccharides (LPS)-stimulated RAW 264.7 cells. Our results elucidated that treatment with RECA significantly suppressed the level of pro-inflammatory cytokine/mediators and oxidative stress released in a concentration-dependent manner. Interestingly, these patterns of inhibition were consistent as observed in the LPS-induced neuroinflammation Sprague Dawley rats' model. The highest concentration used in the two models presented the most significant results. Herein, our findings strongly suggest that RECA may offer therapeutic potential for the treatment of Alzheimer's disease through inhibiting the AChE, inflammation, and oxidative stress activities.
Substitution of hazardous and often harmful organic solvents with "green" and "sustainable" alternative reaction media is always desirous. Ionic liquids (IL) have emerged as valuable and versatile liquids that can replace most organic solvents in a variety of syntheses. However, recently new types of low melting mixtures termed as Deep Eutectic Solvents (DES) have been utilized in organic syntheses. DES are non-volatile in nature, have sufficient thermal stability, and also have the ability to be recycled and reused. Hence DES have been used as alternative reaction media to perform different organic reactions. The availability of green, inexpensive and easy to handle alternative solvents for organic synthesis is still scarce, hence our interest in DES mediated syntheses. Herein we have investigated Biginelli reaction in different DES for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones. Monoamine oxidases and cholinesterases are important drug targets for the treatment of various neurological disorders such as Alzheimer's disease, Parkinson's disease, depression and anxiety. The compounds synthesized herein were evaluated for their inhibitory potential against these enzymes. Some of the compounds were found to be highly potent and selective inhibitors. Compounds 1 h and 1c were the most active monoamine oxidase A (MAO A) (IC50 = 0.31 ± 0.11 µM) and monoamine oxidase B (MAO B) (IC50 = 0.34 ± 0.04 µM) inhibitors respectively. All compounds were selective AChE inhibitors and did not inhibit BChE (<29% inhibition). Compound 1 k (IC50 = 0.13 ± 0.09 µM) was the most active AChE inhibitor.
Alzheimer's disease (AD) is a prevalent neurodegenerative disorder, which affected 35 million people in the world. The most practiced approach to improve the life expectancy of AD patients is to increase acetylcholine neurotransmitter level at cholinergic synapses by inhibition of cholinesterase enzymes. A series of unreported piperidone grafted spiropyrrolidines 8(a-p) were synthesized and evaluated in vitro for their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities. Therein, compounds 8h and 8l displayed more potent AChE enzyme inhibition than standard drug with IC50 values of 1.88 and 1.37 µM, respectively. Molecular docking simulations for 8l possessing the most potent AChE inhibitory activities, disclosed its interesting binding templates to the active site channel of AChE enzymes. These compounds are remarkable AChE inhibitors and have potential as AD drugs.
Heterocyclic molecules have been frequently investigated to possess various biological activities during the last few decades. The present work elaborates the synthesis and enzymatic inhibition potentials of a series of sulfonamides. A series of 1-arylsulfonyl-4-Phenylpiperazine (3a-n) geared up by the reaction of 1-phenylpiperazine (1) and different (un)substituted alkyl/arylsulfonyl chlorides (2a-n), under defined pH control using water as a reaction medium. The synthesized molecules were characterized by 1H-NMR, 13C-NMR, IR and EI-MS spectral data. The enzyme inhibition study was carried on α-glucosidase, lipoxygenase (LOX), acetyl cholinesterase (AChE) and butyryl cholinesterase (BChE) enzymes supported by docking simulation studies and the IC50 values rendered a few of the synthesized molecules as moderate inhibitors of these enzymes where, the compound 3e exhibited comparatively better potency against α-glucosidase enzyme. The synthesized compounds showed weak or no inhibition against LOX, AChE and BChE enzymes.
A series of 2'-hydroxy- and 2'-hydroxy-4',6'-dimethoxychalcones was synthesised and evaluated as inhibitors of human acetylcholinesterase (AChE). The majority of the compounds were found to show some activity, with the most active compounds having IC50 values of 40-85 µM. Higher activities were generally observed for compounds with methoxy substituents in the A ring and halogen substituents in the B ring. Kinetic studies on the most active compounds showed that they act as mixed-type inhibitors, in agreement with the results of molecular modelling studies, which suggested that they interact with residues in the peripheral anionic site and the gorge region of AChE.
Alzheimer's disease (AD) is a progressive neurodegenerative disorder with multiple factors associated with its pathogenesis. Our strategy against AD involves design of multi-targeted 2-substituted-4,5-diphenyl-1H-imidazole analogues which can interact and inhibit AChE, thereby, increasing the synaptic availability of ACh, inhibit BuChE, relieve induced oxidative stress and confer a neuroprotective role. Molecular docking was employed to study interactions within the AChE active site. In silico ADME study was performed to estimate pharmacokinetic parameters. Based on computational studies, some analogues were synthesized and subjected to pharmacological evaluation involving antioxidant activity, toxicity and memory model studies in animals followed by detailed mechanistic in vitro cholinesterase inhibition study. Amongst the series, analogue 13 and 20 are the most promising multi-targeted candidates which can potentially increase memory, decrease free radical levels and protect neurons against cognitive deficit.
Currently, nano-formulated mosquito larvicides have been widely proposed to control young instars of malaria vector populations. However, the fate of nanoparticles in the aquatic environment is scarcely known, with special reference to the impact of nanoparticles on enzymatic activity of non-target aquatic invertebrates. In this study, we synthesized CdS nanoparticles using a green protocol relying on the cheap extract of Valoniopsis pachynema algae. CdS nanoparticles showed high toxicity on young instars of the malaria vectors Anopheles stephensi and A. sundaicus. The antimalarial activity of the nano-synthesized product against chloroquine-resistant (CQ-r) Plasmodium falciparum parasites was investigated. From a non-target perspective, we focused on the impact of this novel nano-pesticide on antioxidant enzymes acetylcholinesterase (AChE) and glutathione S-transferase (GST) activities of the mud crab Scylla serrata. The characterization of nanomaterials was carried out by UV-vis and FTIR spectroscopy, as well as SEM and XRD analyses. In mosquitocidal assays, LC50 of V. pachynema-synthesized CdS nanoparticles on A. stephensi ranged from 16.856 (larva I), to 30.301μg/ml (pupa), while for An. sundaicus they ranged from 13.584 to 22.496μg/ml. The antiplasmodial activity of V. pachynema extract and CdS nanoparticles was evaluated against CQ-r and CQ-sensitive (CQ-s) strains of Plasmodium falciparum. IC50 of V. pachynema extract was 58.1μg/ml (CQ-s) and 71.46μg/ml (CQ-r), while nano-CdS IC50 was 76.14μg/ml (CQ-s) and 89.21μg/ml (CQ-r). In enzymatic assays, S. serrata crabs were exposed to sub-lethal concentrations, i.e. 4, 6 and 8μg/ml of CdS nanoparticles, assessing changes in GST and AChE activity after 16days. We observed significantly higher activity of GST, if compared to the control, during the whole experiment period. In addition, a single treatment with CdS nanoparticles led to a significant decrease in AChE activity over time. The toxicity of CdS nanoparticles and Cd ions in aqueous solution was also assessed in mud crabs, showing higher toxicity of aqueous Cd ions if compared to nano-CdS. Overall, our results underlined the efficacy of green-synthesized CdS nanoparticles in malaria vector control, outlining also significant impacts on the enzymatic activity of non-target aquatic organisms, with special reference to mud crabs.
Garcinia parvifolia belongs to the same family as mangosteen (Garcinia mangostana), which is known locally in Sabah as "asam kandis" or cherry mangosteen. The present study was conducted to determine the phytochemicals content (total phenolic, flavonoid, anthocyanin, and carotenoid content) and antioxidant and acetylcholinesterase inhibition activity of the flesh and peel of G. parvifolia. All samples were freeze-dried and extracted using 80% methanol and distilled water. For the 80% methanol extract, the flesh of G. parvifolia displayed higher phenolic and flavonoid contents than the peel, with values of 7.2 ± 0.3 mg gallic acid equivalent (GAE)/g and 5.9 ± 0.1 mg rutin equivalent (RU)/g, respectively. Anthocyanins were detected in the peel part of G. parvifolia but absent in the flesh. The peel of G. parvifolia displayed higher total carotenoid content as compared to the flesh part with the values of 17.0 ± 0.3 and 3.0 ± 0.0 mg β-carotene equivalents (BC)/100 g, respectively. The free-radical scavenging, ferric reducing, and acetylcholinesterase inhibition effect of the flesh were higher as compared to the peel in both extracts. These findings suggested that the edible part of G. parvifolia fruit has a potential as a natural source of antioxidant and anti-Alzheimer's agents.
Context Dodonaea viscosa (L.) Jacq (Sapindaceae) has been used in traditional medicine as antimalarial, antidiabetic and antibacterial agent, but further investigations are needed. Objective This study determines the antioxidant and anticholinesterase activities of six compounds (1-6) and two crystals (1A and 3A) isolated from D. viscosa, and discusses their structure-activity relationships. Materials and methods Antioxidant activity was evaluated using six complementary tests, i.e., β-carotene-linoleic acid; DPPH(•), ABTS(•+), superoxide scavenging, CUPRAC and metal chelating assays. Anticholinesterase activity was performed using the Elman method. Results Clerodane diterpenoids (1 and 2) and phenolics (3-6) - together with three crystals (1A, 3A and 7A) - were isolated from the aerial parts of D. viscosa. Compound 3A exhibited good antioxidant activity in DPPH (IC50: 27.44 ± 1.06 μM), superoxide (28.18 ± 1.35% inhibition at 100 μM) and CUPRAC (A0.5: 35.89 ± 0.09 μM) assays. Compound 5 (IC50: 11.02 ± 0.02 μM) indicated best activity in ABTS assay, and 6 (IC50: 14.30 ± 0.18 μM) in β-carotene-linoleic acid assay. Compounds 1 and 3 were also obtained in the crystal (1A and 3A) form. Both crystals showed antioxidant activity. Furthermore, crystal 3A was more active than 3 in all activity tests. Phenol 6 possessed moderate anticholinesterase activity against acetylcholinesterase and butyrylcholinesterase enzymes (IC50 values: 158.14 ± 1.65 and 111.60 ± 1.28 μM, respectively). Discussion and conclusion This is the first report on antioxidant and anticholinesterase activities of compounds 1, 2, 5, 6, 1A and 3A, and characterisation of 7A using XRD. Furthermore, the structure-activity relationships are also discussed in detail for the first time.
In recent decade, the entrance of α-N-heterocyclic thiosemicarbazones derivates (Triapne, COTI-2 and DpC) in clinical trials for cancer and HIV-1 has vastly increased the interests of medicinal chemists towards this class of organic compounds. In the given study, a series of eighteen new (3a-r) 3-ethoxy salicylaldehyde-based thiosemicarbazones (TSC), bearing aryl and cycloalkyl substituents, were synthesized and assayed for their pharmacological potential against carbonic anhydrases (hCA I and hCA II), cholinesterases (AChE and BChE) and α-glycosidase. The hCA I isoform was inhibited by these novel 3-ethoxysalicylaldehyde thiosemicarbazone derivatives (3a-r) in low nanomolar levels, the Ki of which differed between 144.18 ± 26.74 and 454.92 ± 48.32 nM. Against the physiologically dominant isoform hCA II, the novel compounds demonstrated Kis varying from 110.54 ± 14.05 to 444.12 ± 36.08 nM. Also, these novel derivatives (3a-r) effectively inhibited AChE, with Ki values in the range of 385.38 ± 45.03 to 983.04 ± 104.64 nM. For BChE was obtained with Ki values in the range of 400.21 ± 35.68 to 1003.02 ± 154.27 nM. For α-glycosidase the most effective Ki values of 3l, 3n, and 3q were with Ki values of 12.85 ± 1.05, 16.03 ± 2.84, and 19.16 ± 2.66 nM, respectively. Moreover, the synthesized TCSs were simulated using force field methods whereas the binding energies of the selected compounds were estimated using MM-GBSA method. The findings indicate the present novel 3-ethoxy salicylaldehyde-based thiosemicarbazones to be excellent hits for pharmaceutical applications.
A facile stereoselective synthesis of novel dispiro indeno pyrrolidine/pyrrolothiazole-thiochroman hybrids has been achieved by 1,3-dipolar cycloaddition of azomethine ylides, generated in situ from ninhydrin and sarcosine/thiaproline, on a series of 3-benzylidenethiochroman-4-ones. The synthesised compounds were screened for their antimycobacterial, anticancer and AchE inhibition activities. Compound 4l (IC50 1.07μM) has been found to exhibit the most potent antimycobacterial activity compared to cycloserine (12 times), pyrimethamine (37 times) and ethambutol (IC50 <1.56μM) and 6l (IC50=2.87μM) is more active than both cycloserine (4 times) and pyrimethamine (12 times). Three compounds, 4a, 6b and 6i, display good anticancer activity against CCRF-CEM cell lines. Compounds 6g and 4g display maximum AchE inhibitory activity with IC50 values of 1.10 and 1.16μmol/L respectively.
Cognitive impairments and cholinergic dysfunctions have been well reported in old age disorders including Alzheimer's disease (AD). d-galactose (D-gal) has been reported as a senescence agent while aluminium act as a neurotoxic metal, but little is known about their combined effects at different doses. The aim of this study was to establish an animal model with cognitive impairments by comparing the effects of different doses of co-administrated D-gal and aluminium chloride (AlCl3). In this study male albino wistar rats were administered with D-gal 60 mg/kg.bwt intra peritoneally (I.P) injected and AlCl3 (100, 200, or 300 mg/kg.bwt.) was orally administered once daily for 10 consecutive weeks. Performance of the rats were evaluated through behavioural assessments; Morris water maze (MWM) and open field tests (OFT); histopathological examination was performed on the hippocampus; moreover biochemical measurements of acetylcholinesterase (AChE) and hyperphosphorylated tau protein (p-tau) were examined. The results of this experiment on rats treated with D-gal 60 + AlCl3 200 mg/kg.bwt showed near ideal cognitive impairments. The rats exhibited an obvious memory and learning deficits, marked neuronal loss in hippocampus, showed increase in AChE activities and high expression of p-tau within the tissues of the brain. This study concludes that D-gal 60 + AlCl3 200 mg/kg.bwt as the ideal dose for mimicking AD like cognitive impairments in albino wistar rats. It is also crucial to understand the pathogenesis of this neurodegenerative disease and for drug discovery.
The heterocyclic compounds have been extensively reported for their bioactivity potential. The current research work reports the synthesis of some new multi-functional derivatives of 2-furoic piperazide (1; 1-(2-furoyl)piperazine). The synthesis was initiated by reacting the starting compound 1 with 3,5-dichloro-2-hydroxybenzenesulfonyl chloride (2) in a basic, polar and protic medium to obtain the parent sulfonamide 3 which was then treated with different electrophiles, 4a-g, in a polar and aprotic medium to acquire the designed molecules, 5a-g. These convergent derivatives were evaluated for their inhibitory potential against α-glucosidase, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes. Acarbose was used as a reference standard for α-glucosidase inhibition while eserine for AChE and BChE inhibition. Some of the synthesized compounds were identified as promising inhibitors of these three enzymes and their bioactivity potentials were also supported by molecular docking study. The most active compounds among the synthetic analogues might be helpful in drug discovery and development for the treatment of type 2 diabetes and Alzhiemer's diseases.
A high-performance thin-layer chromatography (HPTLC) method combined with effect-directed-analysis (EDA) was developed to screen the antioxidant, neuroprotective and antidiabetic effects in essential oils derived from lavender flower, lemon myrtle, oregano, peppermint, sage, and rosemary leaves (Lamiaceae family). HPTLC hyphenated with microchemical (DPPH•, p-anisaldehyde, and ferric chloride) derivatizations, was used to evaluate antioxidant activity, presence of phytosterols and terpenoids, and polyphenolic content, while the combination with biochemical (α-amylase and acetylcholine esterase (AChE) enzymatic) derivatizations was used to asses α-amylase and AChE inhibitory activities. The superior antioxidant activity of oregano leaf extract is attributed to the presence of high levels of aromatic compounds, like polyphenolic acids. The strongest α-amylase inhibition was observed in lemon myrtle and rosemary plus extracts due to the presence of monoterpenes. Rosemary and sage extracts exhibit the highest AChE inhibition activity, with 1 μL essential oils being more potent than the recommended daily dose of donepezil. This superior neuroprotection was attributed to the presences of di- and triterpenes that displayed strong AChE inhibition and antioxidant potential in DPPH• free radical assay. Antioxidant activity was related to phenolic content (R = 0.49), while α-amylase inhibitory activity was positively related to antioxidant activity (R = 0.20) and terpenoid/sterol content (R = 0.31). AChE inhibitory activity was correlated (R = 0.80) to the combined effect of phenolics and terpenoids. Thus, the superior AChE inhibitory and neuroprotection potential of rosemary and sage essential oils could be attributed to joint effects of main phenolic and terpene constituents. The hyphenated HPTLC method provided rapid bioanalytical profiling of highly complex essential oil samples.
Butyrylcholinesterase is a serine hydrolase that catalyzes the hydrolysis of esters in the body. Unlike its sister enzyme acetylcholinesterase, butyrylcholinesterase has a broad substrate scope and lower acetylcholine catalytic efficiency. The difference in tissue distribution and inhibitor sensitivity also points to its involvement external to cholinergic neurotransmission. Initial studies on butyrylcholinesterase showed that the inhibition of the enzyme led to the increment of brain acetylcholine levels. Further gene knockout studies suggested its involvement in the regulation of amyloid-beta, a brain pathogenic protein. Thus, it is an interesting target for neurological disorders such as Alzheimer's disease. The substrate scope of butyrylcholinesterase was recently found to include cocaine, as well as ghrelin, the "hunger hormone". These findings led to the development of recombinant butyrylcholinesterase mutants and viral gene therapy to combat cocaine addiction, along with in-depth studies on the significance of butyrylcholinesterase in obesity. It is observed that the pharmacological impact of butyrylcholinesterase increased in tandem with each reported finding. Not only is the enzyme now considered an important pharmacological target, it is also becoming an important tool to study the biological pathways in various diseases. Here, we review and summarize the biochemical properties of butyrylcholinesterase and its roles, as a cholinergic neurotransmitter, in various diseases, particularly neurodegenerative disorders.
An increase in dementia numbers and global trends in population aging across the world prompts the need for new medications to treat the complex biological dysfunctions, such as neurodegeneration associated with dementia. Alzheimer's disease (AD) is the most common form of dementia. Cholinergic signaling, which is important in cognition, is slowly lost in AD, so the first line therapy is to treat symptoms with acetylcholinesterase inhibitors to increase levels of acetylcholine. Out of five available FDA-approved AD medications, donepezil, galantamine and rivastigmine are cholinesterase inhibitors while memantine, a N-methyl d-aspartate (NMDA) receptor antagonist, blocks the effects of high glutamate levels. The fifth medication consists of a combination of donepezil and memantine. Although these medications can reduce and temporarily slow down the symptoms of AD, they cannot stop the damage to the brain from progressing. For a superior therapeutic effect, multi-target drugs are required. Thus, a Multi-Target-Directed Ligand (MTDL) strategy has received more attention by scientists who are attempting to develop hybrid molecules that simultaneously modulate multiple biological targets. This review highlights recent examples of the MTDL approach and fragment based strategy in the rational design of new potential AD medications.