Synthesis and biological evaluation of 1,3,4-thiadiazole analogues as novel AChE and BuChE inhibitors

Comparison of HPLC, HPTLC, and In Silico Lipophilicity Parameters Determined for 5-Heterocyclic 2-(2,4-Dihydroxyphenyl)-1,3,4-thiadiazoles

The 5-heterocyclic 2-(2,4-dihydroxyphenyl)-1,3,4-thiadiazoles were obtained as potential biologically active compounds. Lipophilicity is one of the most important physicochemical properties of compounds and was already taken into account during the drug candidates design and development. The lipophilicity of compounds was determined using the computational (log P) and chromatography (log kw, RMw) methods. The experimental ones included the reverse-phase column high performance liquid chromatography RP (HPLC) with C8, C18, phosphatidylcholine (IAM), and cholesterol stationary phases and the thin layer chromatography (RP-HPTLC) with C8 and C18 stationary phases and various organic modifiers under the isocratic conditions. Descriptive statistics, correlation, and PCA analyses were used to compare the obtained results. For lipophilicity estimation of the tested compounds by HPTLC, dioxane and MeOH seem to be particularly beneficial as organic modifiers. The chromatographic lipophilicity parameters log kw (RMw) were well correlated and highly redundant (85%) compared with those calculated. Most compounds possess lipophilicity parameters within the recommended range for drug candidates.

A Series of Biguanide Ligands and Their Cu(II) Complexes: Cholinesterase Inhibitory and Antimicrobial Properties

In this work, a series of biguanide hydrochloride salts and their Cu(II) complexes were synthesized and screened for their acetyl/butyryl choline esterase inhibitory and antimicrobial properties. The structures of the synthesized compounds were characterised by common spectroscopic and analytical methods. Biguanide compounds showed considerably lower inhibitory activity compared to the reference drugs donepezil and galantamine. On the other hand, complexation of the biguanide compounds with Cu(II) resulted in dramatic increase in the inhibitory activity. The Cu(II) complexes showed AChE inhibitory activity with the IC50 values of 21.29±0.95-82.53±0.20 μM and those values are comparable to that of donepezil (IC50 : 18.54±1.03 μM). The synthesised compounds were also screened for their antimicrobial activity towards gram positive (+) and gram negative (-) bacteria. Compounds (12.50 mg/mL) showed important antibacterial properties with inhibition zones of 8-28 mm diameter against gram-positive and gram-negative microorganisms. Compounds A03 and A08 exhibited more antimicrobial properties towards E. coli than standard antibiotics amikacin and gentamicin.

Rivastigmine-Bambuterol Hybrids as Selective Butyrylcholinesterase Inhibitors

Selective butyrylcholinesterase inhibitors are considered promising drug candidates for the treatment of Alzheimer's disease. In this work, one rivastigmine-bambuterol hybrid (MTR-1) and fourteen of its analogues were synthesized, purified, and characterized. In vitro cholinesterase assays showed that all the compounds were more potent inhibitors of BChE when compared to AChE. Further investigations indicated that MTR-3 (IC50(AChE) > 100,000 nM, IC50(BChE) = 78 nM) was the best compound in the series, showing high butyrylcholinesterase selectivity and inhibition potency, the potential to permeate the blood-brain barrier, and longer-lasting BChE inhibition than bambuterol. These compounds could be used to discover novel specific BChE inhibitors for the treatment of Alzheimer's disease.

Thiadiazole – A promising structure in design and development of anti-Alzheimer agents

The design and development of effective multitargeted agents in treating Alzheimer disease (AD) has always been a hot topic in the field of drug discovery. Since AD is a multifactorial disorder, various key hidden players such as deficit of acetylcholine (ACh), tau-protein aggregation, and oxidative stress have been associated with the incidence and progress of AD. In pursuit of improving efficacy and expanding the range of pharmacological activities of current AD drugs, the molecular hybridization method is also used intensively. Five-membered heterocyclic systems such as thiadiazole scaffolds have previously been shown to have therapeutic activity. Thiadiazole analogs as an anti-oxidant compound have been known to include a wide range of biological activity from anti-cancer to anti-Alzheimer properties. The suitable pharmacokinetic and physicochemical properties of the thiadiazole scaffold have introduced it as a therapeutic target in medicinal chemistry. The current review portrays the critical role of the thiadiazole scaffold in the design of various compounds with potential effects in the treatment of Alzheimer's disease. Furthermore, the rationale used behind hybrid-based design strategies and the outcomes achieved through the hybridization of Thiadiazole analogs with various core structures have been discussed. In addition, the data in the present review may help researchers in the design of new multidrug combinations that may provide new options for the treatment of AD.

Biologically Potent Benzimidazole-Based-Substituted Benzaldehyde Derivatives as Potent Inhibitors for Alzheimer's Disease along with Molecular Docking Study

Twenty-one analogs were synthesized based on benzimidazole, incorporating a substituted benzaldehyde moiety (1-21). These were then screened for their acetylcholinesterase and butyrylcholinesterase inhibition profiles. All the derivatives except 13, 14, and 20 showed various inhibitory potentials, ranging from IC50 values of 0.050 ± 0.001 µM to 25.30 ± 0.40 µM against acetylcholinesterase, and 0.080 ± 0.001 µM to 25.80 ± 0.40 µM against butyrylcholinesterase, when compared with the standard drug donepezil (0.016 ± 0.12 µM and 0.30 ± 0.010 µM, against acetylcholinesterase and butyrylcholinesterase, respectively). Compound 3 in both cases was found to be the most potent compound due to the presence of chloro groups at the 3 and 4 positions of the phenyl ring. A structure-activity relationship study was performed for all the analogs except 13, 14, and 20, further, molecular dynamics simulations were performed for the top two compounds as well as the reference compound in a complex with acetylcholinesterase and butyrylcholinesterase. The molecular dynamics simulation analysis revealed that compound 3 formed the most stable complex with both acetylcholinesterase and butyrylcholinesterase, followed by compound 10. As compared to the standard inhibitor donepezil both compounds revealed greater stabilities and higher binding affinities for both acetylcholinesterase and butyrylcholinesterase.

Cholinesterases Inhibition, Anticancer and Antioxidant Activity of Novel Benzoxazole and Naphthoxazole Analogs

Benzoxazole and naphthoxazole fused systems are found in many biologically active molecules. Novel benzoxazole and naphthoxazole analogs functionalized by the 2,4-dihydroxyphenyl moiety were designed, obtained and evaluated as a broad spectrum of biological potency compounds. Sulfinylbis[(2,4-dihydroxyphenyl)methanethione] or its analogs and 2-aminophenols or 1-amino-2-naphthol were used as starting reagents. 4-(Naphtho[1,2-d][1,3]oxazol-2-yl)benzene-1,3-diol was identified as the most promising compound of the nanomolar activity against AChE (IC₅₀ = 58 nM) of the mixed-type inhibition and of the moderate activity against BChE (IC₅₀ = 981 nM). The higher antiproliferative potency against a panel of human cancer cell lines for naphtho[1,2-d][1,3]oxazoles than for benzoxazoles was found. The activity of the analog with chlorine atom was in the range of 2.18-2.89 µM (IC₅₀) against all studied cells and it is similar to that of cisplatin studied comparatively. Moreover, this compound was not toxic at this concentration to human normal breast cells and keratinocytes. For some compounds it also has proved antioxidant properties at the level of IC₅₀ = 0.214 µM, for the most active compound. The lipophilicity of all compounds, expressed as log p values, is within the range recommended for potential drugs. The biological activity profile of the considered analogs and their lipophilic level justify the search for agents used in AD or in anticancer therapy in this group of compounds.

Progress and Development of Carbazole Scaffold Based as Potential Anti- Alzheimer Agents Using MTDL Approach

Abstract:

Alzheimer’s is a neurodegenerative disease (NDs) found in old age people with associated most common symptom dementia. MTDLs (Multi-Target Direct Ligand strategy) is based on a combination of two or more bioactive pharmacophores into a single molecule and this phenomenon has received a great attention in the new era of modern drug discovery and emerging as a choice to treat this complex Alzheimer’s disease (AD). In last fifteen years, many research groups designed, and synthesized new carbazole integrated molecules linked with other bioactive pharmacophores like thiazoles, carvedilol, α- naphthylaminopropan-2-ol, tacrine, ferulic acid, piperazine, coumarin, chalcones, stilbene, benzyl piperidine, adamantane, quinoline, phthalocyanines, α-amino phosphonate, thiosemicarbazones, hydrazones, etc. derivatives using MTDLs approach to confront AD. The present review entails the scientific data on carbazole hybrids as potential Anti-Alzheimer activities from 2007 to 2021 that have shown potential anti-Alzheimer activities through multiple target pathways thereby promising hope for new drug development to confront AD.

Inhibitory potential of nitrogen, oxygen and sulfur containing heterocyclic scaffolds against acetylcholinesterase and butyrylcholinesterase

Heterocycles are the key structures in organic chemistry owing to their immense applications in the biological, chemical, and pharmaceutical fields. Heterocyclic compounds perform various noteworthy functions in nature, medication, innovation etc. Most frequently, pure nitrogen heterocycles or various positional combinations of nitrogen, oxygen, and sulfur atoms in five or six-membered rings can be found. Inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes is a popular strategy for the management of numerous mental diseases. In this context, cholinesterase inhibitors are utilized to relieve the symptoms of neurological illnesses like dementia and Alzheimer's disease (AD). The present review focuses on various heterocyclic scaffolds and their role in designing and developing new potential AChE and BChE inhibitors to treat AD. Moreover, a detailed structure-activity relationship (SAR) has been established for the future discovery of novel drugs for the treatment of AD. Most of the heterocyclic motifs have been used in the design of new potent cholinesterase inhibitors. In this regard, this review is an endeavor to summarize the biological and chemical studies over the past decade (2010-2022) describing the pursuit of new N, O and S containing heterocycles which can offer a rich supply of promising AChE and BChE inhibitory activities.

Green and four-component cyclocondensation synthesis and in silico docking of new polyfunctionalized pyrrole derivatives as the potential anticholinesterase agents

Synthesis of new substituted pyrrole scaffolds containing substituted thiadiazol-2-amine moiety was successfully developed through one-pot and multi-component tandem condensation reaction utilizing of triethyl ammonium hydrogen sulfate ([Et3NH][HSO4]) ionic liquid as a green media under solvent-free conditions. The chemical structures of all newly synthesized compounds were fully characterized by spectroscopic methods (IR, ¹H NMR, ¹³C NMR) and elemental analyzes. The molecular docking studies were also performed to predict the possible binding sites of the derivatives on the active site gorge of cholinesterase enzymes (AChE and BuChE). The results showed that all the seventeen derivatives interact with the enzymes with high affinity and among them 7d and 7f possess the greatest ability to bind to AChE and BuChE, respectively.

Novel Coumarin-Thiadiazole Hybrids and Their Cu(II) and Zn(II) Complexes as Potential Antimicrobial Agents and Acetylcholinesterase Inhibitors

A series of coumarin-thiadiazole hybrids and their corresponding Cu(II) and Zn(II) complexes were synthesized and characterized with the use of spectroscopic techniques. The results obtained indicate that all the coumarin-thiadiazole hybrids act as bidentate chelators of Cu(II) and Zn(II) ions. The complexes isolated differ in their ligand:metal ratio depending on the central metal. In most cases, the Zn(II) complexes are characteristic of a 1:1 ligand:metal ratio, while in the Cu(II) complexes the ligand:metal ratio is 2:1. All compounds were tested as potential antibacterial agents against Gram-positive (Staphylococcus aureus, Staphylococcus epidermidis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacterial strains demonstrating activities notably lower than commercially available antibiotics. The more promising results were obtained from the assessment of antineurodegenerative potency as all compounds showed moderate acetylcholinesterase (AChE) inhibition activity.

Exploring indole-based-thiadiazole derivatives as potent acetylcholinesterase and butyrylcholinesterase enzyme inhibitors

Indole based thiadiazole derivatives (1-18) were synthesized and evaluated for their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibition. The IC₅₀ values of the synthesized analogues ranging between 0.17 ± 0.05 to 33.10 ± 0.6 μM against (AChE) and 0.30 ± 0.1 to 37.60 ± 0.6 μM against (BChE) enzymes. Among the series compounds 8 (IC₅₀ = 0.17 ± 0.05 μM) (IC₅₀ = 0.30 ± 0.1 μM), 9 (IC₅₀ = 0.30 ± 0.05 μM) (IC₅₀ = 0.60 ± 0.05 μM) and 10 (IC₅₀ = 1.30 ± 0.1 μM) (IC₅₀ = 2.60 ± 0.1) were found to be the most potent analogues bearing para, ortho, and meta-fluoro substitutions on phenyl ring attached to thiadiazole. In addition, all the synthesized scaffolds were characterized by using ¹H NMR, ¹³C NMR spectroscopy, and high-resolution Mass Spectrometry (HR-MS). To apprehend the binding mode of interaction of the most potent synthesized derivatives, a molecular docking study was performed.

Biological evaluation and molecular docking of novel 1,3,4-thiadiazole-resorcinol conjugates as multifunctional cholinesterases inhibitors

Two series of novel 1,3,4-thiadiazole-resorcinol conjugates were efficiently synthesized and evaluated as cholinesterases inhibitors. N-Butyl- and N-chlorophenyl-5-amino-1,3,4-thiadiazol-2-yl)benzene-1,3-diols were identified as the most promising compounds of low nanomolar activity against AChE (IC₅₀ = 29-76 nM) and moderate activity against BuChE. The inhibition mechanism studies proved that the compounds are mixed type inhibitors. The docking simulations showed great affinity of the compounds for both enzymes. The modelled amine derivatives exhibited a similar arrangement in the catalytic anionic site of AChE similar to that of tacrine. The thiadiazole ring interacted with Trp84 and the phenyl groups created π-π stacking interactions with the residue - Phe330. The compounds showed better inhibition of the in vitro self-induced Aβ (1-42) aggregation than that compared with curcumin as well as antioxidant properties similar to those of quercetin. They exhibited metal ion chelating properties, acceptable cytotoxicity in vitro and favourable ADMET profile determined in silico.

Design, synthesis and biological assessment of acridine derivatives containing 1,3,4-thiadiazole moiety as novel selective acetylcholinesterase inhibitors

A novel series of acridine derivatives containing substituted thiadiazol-2-amine moiety was synthesized via multi-component condensation reaction of dimedone, aromatic aldehyde and 5-aryl-1,3,4-thiadiazol-2-amines in the presence of LaCl₃ as a catalyst under solvent-free conditions. Anticholinesterase (AChE and BuChE) activity evaluation of the derivatives showed that all the derivatives are capable of inhibiting both enzymes and are highly selective towards AChE. Among them, the ability of 4i and 4d with respective IC₅₀ values of 0.002 and 0.006 µM to inhibit AChE was higher than the reference compound tacrine (IC₅₀ = 0.016 µM). The kinetics studies demonstrated that 4i and 4d inhibit AChE through a competitive/non-competitive mixed mechanism. The HEPG2 cell viability assay evidenced that 4i and 4d significantly exhibit lower hepatotoxicity compared with tacrine. Blind docking experiments performed on TcAChE (PDB ID: 2ACE) indicated that an unknown site is preferred for binding by all the derivatives over classic binding site of the enzyme, site 1 (CAS/PAS). Identification of the residues by protein structure alignment confirmed that this site is site 2 which was recently recognized as a new allosteric site of hAChE. The binding modes of 4i and 4d were also investigated using local docking studies on site 1 and site 2.

ESIPT-Related Origin of Dual Fluorescence in the Selected Model 1,3,4-Thiadiazole Derivatives

In our previous work, we discussed the emergence of the dual fluorescence phenomenon in selected compounds from the group of 1,3,4-thiadiazoles. The results obtained in a number of experimental studies, supported by [TD]DFT calculations, clearly indicated that the phenomenon of dual fluorescence stemmed from an overlap of several factors, including the correct conformation of the analyzed molecule and, very significantly in this context, aggregation effects. Where those two conditions were met, we could observe the phenomenon of intermolecular charge transfer (CT) and the emergence of electronic states responsible for long wave emissions. However, in light of the new studies presented in this paper, we were able, for the first time, to provide a specific theory for the effect of dual fluorescence observed in the analyzed group of 1,3,4-thiadiazoles. We present the results of spectroscopic measurements conducted for two selected analogues from the 1,3,4-thiadiazole group, both in polar and non-polar solvents, which clearly evidence (as we have already suspected in the past, albeit have not shown in publications to date) the possibility of processes related to emission from the tautomer formed in the process of excited state intramolecular proton transfer, which is responsible for the long-wavelength emissions observed in the selected analogues. The presented results obtained with the use of UV-Vis, fluorescence (stationary and time-resolved), FTIR, and Raman spectroscopy, as well as from calculations of dipole moment changes between the ground and excited state with the use of two derivatives with different structures of the resorcylic system, corroborated our standing hypothesis. At the same time, they excluded the presence of ground state keto forms of the analyzed analogues unless necessitated by the structure of the molecule itself. In this case, aggregation factors enhance the observed effects related to the dual fluorescence of the analyzed compounds (by way of AIE-aggregated induced emissions).

Structural Features of 1,3,4-Thiadiazole-Derived Ligands and Their Zn(II) and Cu(II) Complexes Which Demonstrate Synergistic Antibacterial Effects with Kanamycin

Classical synthetic protocols were applied for the isolation of three novel 1,3,4-thiadiazole derivatives which were then complexed with the biologically important Cu(II) and Zn(II) ions. All free ligands and their corresponding complexes were characterized using a number of spectroscopic techniques including Ultraviolet-visible (UV–vis), Fluorescence, Infrared (FT-IR), tandem liquid chromatography-mass (LC-MS), X-ray diffraction (XRD), and Nuclear Magnetic Resonance (NMR) spectroscopy (¹H, ¹³C, HSQC, HMBC). The results obtained are consistent with the formation of dihydrate complexes, in which the chelation of the metal ion occurs via one of the thiadiazole nitrogen atoms and the deprotonated hydroxyl group of the neighboring resorcynyl moiety. The Zn(II) complexes utilize a 1:1 ligand–metal ratio, while in the Cu(II) complexes the ligand–metal ratio is 2:1. Although the antibacterial testing identified moderate activity of the compounds against the tested bacterial strains and additionally modest antioxidant activity, a strong synergistic antibacterial effect against Staphylococcus aureus, using concomitant treatment of thiadiazole derivatives with the commercial antibiotic kanamycin, was observed. The most active thiadiazole derivative demonstrated a minimal inhibitory concentration (MIC) of 500 μg/mL while it was 125 μg/mL in the presence of kanamycin. Moreover, in the presence of few thiadiazole derivatives the MIC value of kanamycin decreased from 0.39 μg/mL to 0.5 μg/mL. The antioxidant activity (IC₅₀) of the most active thiadiazole derivative was determined as 0.13 mM which was nearly three-fold lower compared to that of TROLOX (0.5 mM).

Identify Compounds' Target Against Alzheimer's Disease Based on In-Silico Approach

BACKGROUND

Alzheimer's disease swept every corner of the globe and the number of patients worldwide has been rising. At present, there are as many as 30 million people with Alzheimer's disease in the world, and it is expected to exceed 80 million people by 2050. Consequently, the study of Alzheimer's drugs has become one of the most popular medical topics.

METHODS

In this study, in order to build a predicting model for Alzheimer's drugs and targets, the attribute discriminators CfsSubsetEval, ConsistencySubsetEval and FilteredSubsetEval are combined with search methods such as BestFirst, GeneticSearch and Greedystepwise to filter the molecular descriptors. Then the machine learning algorithms such as BayesNet, SVM, KNN and C4.5 are used to construct the 2D-Structure Activity Relationship(2D-SAR) model. Its modeling results are utilized for Receiver Operating Characteristic curve(ROC) analysis.

RESULTS

The prediction rates of correctness using Randomforest for AChE, BChE, MAO-B, BACE1, Tau protein and Non-inhibitor are 77.0%, 79.1%, 100.0%, 94.2%, 93.2% and 94.9%, respectively, which are overwhelming as compared to those of BayesNet, BP, SVM, KNN, AdaBoost and C4.5.

CONCLUSION

In this paper, we conclude that Random Forest is the best learner model for the prediction of Alzheimer's drugs and targets. Besides, we set up an online server to predict whether a small molecule is the inhibitor of Alzheimer's target at http://47.106.158.30:8080/AD/. Furthermore, it can distinguish the target protein of a small molecule.

Biological Evaluation, Molecular Docking, and SAR Studies of Novel 2-(2,4-Dihydroxyphenyl)-1H- Benzimidazole Analogues

In the present study, new 4-(1H-benzimidazol-2-yl)-benzene-1,3-diols, modified in both rings, have been synthesized and their efficacies as acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitors have been determined. The modified Ellman’s spectrophotometric method was applied for the biological evaluation. The compounds showed strong (IC₅₀ 80–90 nM) AChE and moderate (IC₅₀ 5–0.2 µM) BuChE inhibition in vitro. Some compounds were effective toward AChE/BuChE, exhibiting high selectivity ratios versus BuChE, while the other compounds were active against both enzymes. The structure–activity relationships were discussed. The compounds inhibited also in vitro self-induced Aβ(1–42) aggregation and exhibited antioxidant properties. The docking simulations showed that the benzimidazoles under consideration interact mainly with the catalytic site of AChE and mimic the binding mode of tacrine.

SAR-mediated Similarity Assessment of the Property Profile for New, Silicon-Based AChE/BChE Inhibitors

A set of 25 novel, silicon-based carbamate derivatives as potential acetyl- and butyrylcholinesterase (AChE/BChE) inhibitors was synthesized and characterized by their in vitro inhibition profiles and the selectivity indexes (SIs). The prepared compounds were also tested for their inhibition potential on photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. In fact, some of the newly prepared molecules revealed comparable or even better inhibitory activities compared to the marketed drugs (rivastigmine or galanthamine) and commercially applied pesticide Diuron®, respectively. Generally, most compounds exhibited better inhibition potency towards AChE; however, a wider activity span was observed for BChE. Notably, benzyl N-[(1S)-2-[(tert-butyldimethylsilyl)oxy]-1-[(2-hydroxyphenyl)carbamoyl]ethyl]-carbamate (2) and benzyl N-[(1S)-2-[(tert-butyldimethylsilyl)oxy]-1-[(3-hydroxyphenyl)carbamoyl]ethyl]-carbamate (3) were characterized by fairly high selective indexes. Specifically, compound 2 was prescribed with the lowest IC50 value that corresponds quite well with galanthamine inhibition activity, while the inhibitory profiles of molecules 3 and benzyl-N-[(1S)-2-[(tert-butyldimethylsilyl)oxy]-1-[(4-hydroxyphenyl)carbamoyl]ethyl]carbamate (4) are in line with rivastigmine activity. Moreover, a structure-activity relationship (SAR)-driven similarity evaluation of the physicochemical properties for the carbamates examined appeared to have foreseen the activity cliffs using a similarity-activity landscape index for BChE inhibitory response values. The 'indirect' ligand-based and 'direct' protein-mediated in silico approaches were applied to specify electronic/steric/lipophilic factors that are potentially valid for quantitative (Q)SAR modeling of the carbamate analogues. The stochastic model validation was used to generate an 'average' 3D-QSAR pharmacophore pattern. Finally, the target-oriented molecular docking was employed to (re)arrange the spatial distribution of the ligand property space for BChE and photosystem II (PSII).

Utility of 5-(furan-2-yl)-3-(p-tolyl)-4,5-dihydro-1H-pyrazole-1-carbothioamide in the synthesis of heterocyclic compounds with antimicrobial activity

Background

Pyrazolines show different biological activities. In recent years, interest in the chemistry of hydrazonoyl halides has been renewed. 1,3,4-Thiadiazoles are one of the most common heterocyclic pharmacophores with a wide range of biological activities.

Results

Ethyl 2-(5-(furan-2-yl)-3-(p-tolyl)-4,5-dihydro-1H-pyrazol-1-yl)-4-methyl-thiazole-5-carboxylate, 2-(5-(furan-2-yl)-3-(p-tolyl)-4,5-dihydro-1H-pyrazol-1-yl)thiazol-4(5H)-one, and 1-(2-(5-(furan-2-yl)-3-(p-tolyl)-4,5-dihydro-1H-pyrazol-1-yl)-4-methylthiazol-5-yl)ethan-1-one were synthesized from the reaction of 5-(furan-2-yl)-3-(p-tolyl)-4,5-dihydro-1H-pyrazole-1-carbothioamide with different halogenated compounds. Thiazole, 1,3,4-thiadiazole and pyrano[2,3-d]thiazole derivatives were also synthesized. The structures of the newly synthesized compounds were elucidated based on elemental analysis, spectral data, and alternative synthetic routes whenever possible. Additionally, the newly synthesized compounds were screened for antimicrobial activity against various microorganisms.

Conclusions

A new series of novel functionalized 1,3,4-thiadiazoles, 1,3-thiazoles, and pyrazoline-containing moieties were synthesized using hydrazonoyl halides as precursors and evaluated for their in vitro antibacterial, and antifungal activities. The antimicrobial results of the examined compounds revealed promising results and some derivatives have activities similar to the references used.

Electronic supplementary material

The online version of this article (10.1186/s13065-019-0566-y) contains supplementary material, which is available to authorized users.

Novel Benzene-Based Carbamates for AChE/BChE Inhibition: Synthesis and Ligand/Structure-Oriented SAR Study

A series of new benzene-based derivatives was designed, synthesized and comprehensively characterized. All of the tested compounds were evaluated for their in vitro ability to potentially inhibit the acetyl- and butyrylcholinesterase enzymes. The selectivity index of individual molecules to cholinesterases was also determined. Generally, the inhibitory potency was stronger against butyryl- compared to acetylcholinesterase; however, some of the compounds showed a promising inhibition of both enzymes. In fact, two compounds (23, benzyl ethyl(1-oxo-1-phenylpropan-2-yl)carbamate and 28, benzyl (1-(3-chlorophenyl)-1-oxopropan-2-yl) (methyl)carbamate) had a very high selectivity index, while the second one (28) reached the lowest inhibitory concentration IC₅₀ value, which corresponds quite well with galanthamine. Moreover, comparative receptor-independent and receptor-dependent structure–activity studies were conducted to explain the observed variations in inhibiting the potential of the investigated carbamate series. The principal objective of the ligand-based study was to comparatively analyze the molecular surface to gain insight into the electronic and/or steric factors that govern the ability to inhibit enzyme activities. The spatial distribution of potentially important steric and electrostatic factors was determined using the probability-guided pharmacophore mapping procedure, which is based on the iterative variable elimination method. Additionally, planar and spatial maps of the host–target interactions were created for all of the active compounds and compared with the drug molecules using the docking methodology.

Structure-activity study of fluorine or chlorine-substituted cinnamic acid derivatives with tertiary amine side chain in acetylcholinesterase and butyrylcholinesterase inhibition

In this study, a series of new fluorine or chlorine-substituted cinnamic acid derivatives that contain tertiary amine side chain were designed, synthesized, and evaluated in acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibition. The results show that almost all the derivatives containing tertiary amine side chain (compounds 4a-9d) exhibit moderate or potent activity in AChE inhibition. By contrast, their parent compounds (compounds 3a-3f) in the absence of tertiary amine moitery exhibit poor inhibitory activity against AChE. For the compounds containing pyrroline or piperidine side chain, the bioactivity in AChE inhibition is much intense than those containing N,N-diethylamino side chain. The chlorine or fluorine substituted position produces a significant effect on the bioactivity and selectivity in AChE inhibition. Most of the compounds that contain para-substituted fluorine or chlorine exhibit potent activity against AChE and poor activity against BChE, while ortho-substituted analogs show the opposite effect. It is worth noticing that the compounds containing N,N-diethylamino side chain are exceptions to this pattern. Among the newly synthesized compounds, compounds 6d are the most potent in AChE inhibition (IC₅₀ = 1.11 ± 0.08 μmol/L) with high selectivity for AChE over BChE (selectivity ratio: 46.58). An enzyme kinetic study of compounds 6d suggests it produces a mixed-type inhibitory effect in AChE.

Structure-activity relationship investigation of coumarin-chalcone hybrids with diverse side-chains as acetylcholinesterase and butyrylcholinesterase inhibitors

Chalcones containing tertiary amine side-chains have potent activity as acetylcholinesterase (AChE) inhibitors. However, the effects of the location of the tertiary amine groups as well as of other groups on AChE and butyrylcholinesterase (BChE) activity have not been reported. Here, we report the synthesis and testing of 36 new coumarin-chalcone hybrids (5d-7j, 9d-11f, 12k-13m) against AChE and BChE. The nature and position of the chalcone substituents had major effects on inhibitory activity as well as selectivity for AChE over BChE. Compounds with para-substituted chalcone fragments in which the substituents were choline-like had potent activity against AChE and poor activity against BChE, while ortho-substituted analogs exhibited an opposite effect. Replacement of the terminal amine groups by amide, alkyl or alkenyl groups abrogated activity. Compound 5e showed potent inhibitory activity [Formula: see text]) and good selectivity for AChE over BChE (ratio 27.4), and a kinetic study showed that 5e exhibited mixed-type inhibition against AChE. Computational docking results indicate that 5e binds to Trp 279, Tyr334 and Trp 84 in AChE, but only to Trp 82 in BChE. Overall, the results show that coumarin-chalcone hybrids with choline-like side-chains have promising activity and selectivity against AChE and be promising therapeutic leads for Alzheimer's disease.

Structure-activity relationship investigation of benzamide and picolinamide derivatives containing dimethylamine side chain as acetylcholinesterase inhibitors

A series of benzamide and picolinamide derivatives containing dimethylamine side chain (4a–4c and 7a–7i) were synthesised and evaluated for acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activity in vitro. Structure–activity relationship investigation revealed that the substituted position of dimethylamine side chain markedly influenced the inhibitory activity and selectivity against AChE and BChE. In addition, it seemed that the bioactivity of picolinamide amide derivatives was stronger than that of benzamide derivatives. Among them, compound 7a revealed the most potent AChE inhibitory activity (IC₅₀: 2.49 ± 0.19 μM) and the highest selectivity against AChE over BChE (Ratio: 99.40). Enzyme kinetic study indicated that compound 7a show a mixed-type inhibition against AChE. The molecular docking study revealed that this compound can bind with both the catalytic site and the peripheral site of AChE.

Thiadiazole inhibitors: a patent review

INTRODUCTION

Four isomeric structures of thiadiazole motifs have outstanding pharmacological inhibitory applications are reported in this review. Thiadiazole nucleus is present in several biologically active natural products and commercial drugs. Most of thiadiazoles reported herein are emphasized to have broad spectrum of medicinal activities. Areas covered: This review represents the recent inhibitory activities of thiadiazole isomeric scaffolds and their broad-spectrum biological applications published as full texts during 2010-2016 as well as the patents published during 2005-2016. The inhibition areas covered included anti-inflammatory, antimicrobial, antitumor, antioxidant, antitubercular, antiviral, antileishmanial, anticonvulsant, herbicidal and algicidal activities in addition to enzymes, human platelet aggregation and neuroprotective inhibitors. Expert opinion: This survey revealed very interesting data about the applications of thiadiazoles, where some synthetic or natural thiadiazole derivatives were components of drugs available in the market. Many thiadiazole derivatives can be considered as lead compounds for drug synthesis. The most inhibitory active 1,3,4-thiadiazole compounds are those incorporating secondary alkyl(aryl)amido- and/or benzylthio(mercapto) groups at positions 2 and 5. Several thiadiazole derivatives demonstrated higher antibacterial, antitumor and antiviral activities than the standard drugs. Some thiadiazole derivatives exhibited high selective enzymes inhibitory activities based on the electronic properties of the substituents at positions 2 or 5.

Tertiary amine derivatives of chlorochalcone as acetylcholinesterase (AChE) and buthylcholinesterase (BuChE) inhibitors: the influence of chlorine, alkyl amine side chain and α,β-unsaturated ketone group

A new series of tertiary amine derivatives of chlorochalcone (4a∼4l) were designed, synthesized and evaluated for the effect on acetylcholinesterase (AChE) and buthylcholinesterase (BuChE). The results indicated that all compounds revealed moderate or potent inhibitory activity against AChE, and some possessed high selectivity for AChE over BuChE. The structure–activity investigation showed that the substituted position of chlorine significantly influenced the activity and selectivity. The alteration of tertiary amine group also leads to obvious change in bioactivity. Among them, IC₅₀ of compound 4l against AChE was 0.17 ± 0.06 µmol/L, and the selectivity was 667.2 fold for AChE over BuChE. Molecular docking and enzyme kinetic study on compound 4l suggested that it simultaneously binds to the catalytic active site (CAS) and peripheral anionic site (PAS) of AChE. Further study showed that the pyrazoline derivatives synthesized from chlorochalcones had weaker activity and lower selectivity in inhibiting AChE compared to that of chlorochalcone derivatives.

Molecular docking studies and biological evaluation of 1,3,4-thiadiazole derivatives bearing Schiff base moieties as tyrosinase inhibitors

1,3,4-Thiadiazole derivatives bearing Schiff base moieties were designed, synthesized, and their tyrosinase inhibitory activities were evaluated. Some compounds displayed potent tyrosinase inhibitory activities, especially, 4-(((5-mercapto-1,3,4-thiadiazol-2-yl)-imino)methyl)-2-methoxy-phenol (14) exhibited superior inhibitory effect to the other compounds with an IC₅₀ value of 0.036μM. The structure-activity relationships (SARs) were preliminarily discussed and docking studies showed compound 14 had strong binding affinity to mushroom tyrosinase. Hydroxy might be the active groups. The inhibition kinetics study revealed that compounds (13 and 14) inhibited tyrosinase by acting as uncompetitive inhibitors. The LD₅₀ value of the compound 14 was 5000mg/kg.

Synthesis and Antimicrobial Activity of Some New Thiadiazoles, Thioamides, 5-Arylazothiazoles and Pyrimido[4,5-d][1,2,4]triazolo[4,3-a]pyrimidines

A novel series of 1,3,4-thiadiazoles, 5-arylazothiazoles and hexahydropyrimido-[4,5-d][1,2,4]triazolo[4,3-a]pyrimidines were synthesized via reaction of hydrazonoyl halides with each of alkyl carbothioates, carbothioamides and 7-thioxo-5,6,7,8-tetrahydropyrimido-[4,5-d]pyrimidine-2,4(1H,3H)-diones in the presence of triethylamine. The structures of the newly synthesized compounds were established based on their spectral data, elemental analyses and alternative synthetic routes whenever possible. Also, the newly synthesized compounds were screened for their antimicrobial activity against various microorganisms.

Synthesis and antiproliferative activity of some N'-substituted 2,4-dihydroxybenzothiohydrazides

The paper shows that new N'-substituted 2,4-dihydroxybenzocarbothiohydrazides are able to inhibit the in vitro proliferation of human tumor cell lines. The compounds were prepared by the reaction of sulfinylbis[(2,4-dihydroxyphenyl)methanethione] (STB) or its analogs with the hydrazines. The panel of N'-substitution included aryl, pyridinyl and pyrimidinyl rings. The highest antiproliferative activity for N'-(4-(4-chlorophenyl)-6-(trifluoromethyl)pyrimidin-2-yl)-5-ethyl-2,4-dihydroxybenzothiohydrazide (5b) was found. The antiproliferative potency of some compounds was similar to that of cisplatin. Analogs with the Et substituent on benzenediol moiety displayed higher potency than with the unsubstituted one. The influence of N'-substitution on antiproliferative activity of compounds was discussed.

Ameliorative effects of amide derivatives of 1,3,4-thiadiazoles on scopolamine induced cognitive dysfunction

The present study reports the effect of amide derivatives of 1,3,4-thiadizoles on scopolamine induced deficit cholinergic neurotransmission and oxidative stress serving as promising leads for the therapeutics of cognitive dysfunction. Fourteen compounds (2c-8d) have been synthesised and evaluated against behavioural alterations using step down passive avoidance protocol and morris water maze and at a dose of 0.5 mg/kg with reference to the standard, Rivastigmine. All the synthesised compounds were evaluated for their in vitro acetylcholinesterase (AChE) inhibition at five different concentrations using mice brain homogenate as the source of the enzyme. Biochemical estimation of markers of oxidative stress (lipid peroxidation, superoxide dismutase, glutathione, plasma nitrite, catalase) has also been carried out to assess the role of synthesised molecules on the oxidative damage induced by scopolamine. The compounds 5c, 6c and 8c displayed appreciable activity with an IC50 value of 3 μM, 3.033 μM and 2.743 μM, respectively towards acetylcholinesterase inhibition. These compounds also decreased scopolamine induced oxidative stress, thus serving as promising leads for the amelioration of oxidative stress induced cognitive decline. The molecular docking study performed to predict the binding mode of the compounds also suggested that these compounds bind appreciably with the amino acids present in the active site of recombinant human acetylcholinesterase (rhAChE). The results indicated that these compounds could be further traversed as inhibitors of AChE and oxidative stress for the treatment of cognitive dysfunction.

Synthesis and anticancer evaluation of 1,3,4-oxadiazoles, 1,3,4-thiadiazoles, 1,2,4-triazoles and Mannich bases

A series of 5-(pyridin-4-yl)-N-substituted-1,3,4-oxadiazol-2-amines (3a-d), 5-(pyridin-4-yl)-N-substituted-1,3,4-thiadiazol-2-amines (4a-d) and 5-(pyridin-4-yl)-4-substituted-1,2,4-triazole-3-thiones (5a-d) were obtained by the cyclization of hydrazinecarbothioamide derivatives 2a-d derived from isonicotinic acid hydrazide. Aminoalkylation of compounds 5a-d with formaldehyde and various secondary amines furnished the Mannich bases 6a-p. The structures of the newly synthesized compounds were confirmed on the basis of their spectral data and elemental analyses. All the compounds were screened for their in vitro anticancer activity against six human cancer cell lines and normal fibroblast cells. Sixteen of the tested compounds exhibited significant cytotoxicity against most cell lines. Among these derivatives, the Mannich bases 6j, 6m and 6p were found to exhibit the most potent activity. The Mannich base 6m showed more potent cytotoxic activity against gastric cancer NUGC (IC50=0.021 µM) than the standard CHS 828 (IC50=0.025 µM). Normal fibroblast cells WI38 were affected to a much lesser extent (IC50>10 µM).

Synthesis, Characterisation and Acetylcholinesterase-Inhibition Activities of 5-benzyl-1,3,4-thiadiazol-2-amine Derivatives

Four 5-benzyl-1,3,4-thiadiazol-2-amine derivatives were synthesised from phenylacetic acid derivatives. The structures of the 5-benzyl-1,3,4-thiadiazole derivatives were characterised by NMR spectroscopy and X-ray crystallography. The acetylcholinesterase-inhibition activities were also tested. Among the four compounds, 5- (4-bromobenzyl)-1,3,4-thiadiazol-2-amine showed the best acetylcholinesterase-inhibition activity with an IC50 of 49.86 μM. The docking study performed with AUTODOCK demonstrated that this compound could interact with the catalytic active site of acetylcholinesterase.

Synthesis, biological evaluation and molecular modeling studies of phthalazin-1(2H)-one derivatives as novel cholinesterase inhibitors

A series of donepezil analogues based on phthalazin-1(2H)-one scaffold was studied as hChEIs. The biological results revealed that the structural modifications proposed significantly affected ChE inhibitory potency as well as selectivity AChE/BuChE.

Influence of Solvent Polarizability on the Keto-Enol Equilibrium in 4-[5-(naphthalen-1-ylmethyl)-1,3,4-thiadiazol-2-yl]benzene-1,3-diol

This work presents spectroscopic studies of the keto-enol equilibrium induced by solvent polarizability in 4-[5-(naphthalen-1-ylmethyl)-1,3,4-thiadiazol-2-yl]benzene-1,3-diol a strong antiproliferative and anticancer thiadiazol derivative. Electronic absorption, steady state and time resolved fluorescence, and infrared spectroscopies were applied to investigate the keto and enol forms of this compound in a series of polar and non-polar solvents. The enol form dominates in polar solvents while, surprisingly, the keto form dominates in non-polar solvents with high average electric dipole polarizability e.g. n-alkenes. The electronic absorption spectrum of this derivative is more dependent on spatially averaged electric dipole polarizability of the solvent than on Kirkwood's correlation or on Lorenz-Lorenz electric polarizability. By analogy of n-alkanes to the alkyl parts of lipids, one can expect that the transformation of 1,3,4-thiadiazoles to the keto form may be facilitated in the hydrophobic core of the lipid membrane. Such a transition may be of great practical importance for the design of biologically active pharmaceutics, which are able to interact with the hydrophobic regions of cell membranes in a specific manner.

Design, synthesis and preliminary structure-activity relationship investigation of nitrogen-containing chalcone derivatives as acetylcholinesterase and butyrylcholinesterase inhibitors: a further study based on Flavokawain B Mannich base derivatives

In order to study the structure-activity relationship of Flavokawain B Mannich-based derivatives as acetylcholinesterase (AChE) inhibitors in our recent investigation, 20 new nitrogen-containing chalcone derivatives (4 a-8d) were designed, synthesized, and evaluated for AChE inhibitory activity in vitro. The results suggested that amino alkyl side chain of chalcone dramatically influenced the inhibitory activity against AChE. Among them, compound 6c revealed the strongest AChE inhibitory activity (IC50 value: 0.85 μmol/L) and the highest selectivity against AChE over BuChE (ratio: 35.79). Enzyme kinetic study showed that the inhibition mechanism of compound 6c against AChE was a mixed-type inhibition. The molecular docking assay showed that this compound can both bind with the catalytic site and the peripheral site of AChE.

Synthesis, in vitro anticancer and antimycobacterial evaluation of new 5-(2,5-dimethoxyphenyl)-1,3,4-thiadiazole-2-amino derivatives

A series of 2,5-disubstituted-1,3,4-thiadiazole derivatives 5a-5l, 7a-7e and 9 have been synthesised and screened for in vitro antimycobacterial activity against Mycobacterium smegmatis MC-155. In addition these compounds have also been screened for cytotoxic activity against cancer cell lines HT-29, MDA-MB-231 by MTT colorimetric assay. The compounds are well characterized by spectral analysis viz. (1)H NMR, (13)C NMR, FT-IR, mass and HRMS. Screening results indicate that compounds 5g, 7a possess good antitubercular activity with MIC value 65.74 and 40.86, respectively, compounds 5g, 7a, 7b, 7d, 7e and 9 displayed promising cytotoxic activity against the cell lines tested. 5g and 7a stand out to be potent antimycobacterial and anticancer agents among the tested series. Further the title compounds were also tested on human normal cells HEK293T and are found to be safer with lesser cytotoxicity. It is interesting to observe that compound 5g has come out to be safer, potent anticancer and antimycobacterial agent.

Preparation, anticholinesterase activity, and docking study of new 2-butenediamide and oxalamide derivatives

Several new oxalamide and 2-butenediamide derivatives have been designed, synthesized and evaluated as the acetyl- and butyryl-cholinesterase inhibitors for Alzheimer's disease. The enzyme inhibitory activity of the synthesized compounds was measured using Ellman's colorimetric method. It was revealed that compound 1a (N,N'-bis-(4-chloro-benzyl)-N,N'-diphenyl-oxalamide) showed maximum activity against BuChE with a half maximal inhibitory concentration (IC50) = 1.86 µM and compound 2a (but-2-enedioic acid bis-[(4-chloro-benzyl)-phenyl-amide]) exhibited optimum AChE (IC50 = 1.51 µM) inhibition with a high-selectivity index. To better understand the enzyme-inhibitor interaction of the most active compounds towards cholinesterase, molecular modelling studies were carried out. Docking simulations revealed that inhibitors 1a and 2a targeted both the catalytic active site and the peripheral anionic site of 1ACJ and 1P0I.