Structure-activity relationship studies of sulfonylpiperazine analogues as novel negative allosteric modulators of human neuronal nicotinic receptors

Studies on Methylpyrazole-Substituted Benzimidazoles to Target Helicobacter pylori Infection through HpIMPDH Inhibition

The prevalence of Helicobacter pylori infection has been increasing rapidly due to the genetic heterogeneity and antibacterial resistance shown by the bacteria, affecting over 50% of the world population and over 80% of the Indian population, in particular. In this regard, novel drug targets are currently being explored, one of which is the crucial metabolic enzyme inosine-5'-monophosphate dehydrogenase (IMPDH) involved in the de novo nucleotide biosynthesis pathway, in order to combat the infection and devise efficient therapeutic strategies. The present study reports the development of methylpyrazole-substituted benzimidazoles as small molecule inhibitors of H. pylori IMPDH with a nanomolar range of enzyme inhibition. A set of 19 small molecules have been designed, synthesized, and further evaluated for their inhibitory potential against H. pylori IMPDH using in silico, in vitro, biochemical, and biophysical techniques. Compound 7j was found to inhibit H. pylori IMPDH with an IC50 value of 0.095 ± 0.023 μM, which is close to 1.5-fold increase in the inhibitory activity, in comparison to the previously reported benzimidazole-based hit C91. Moreover, kinetic characterization has provided significant insights into the uncompetitive inhibition shown by these small molecules on H. pylori IMPDH, thus providing details about the enzyme inhibition mechanism. In conclusion, methylpyrazole-based small molecules indicate a promising path to develop cheap and bioavailable drugs to efficiently treat H. pylori infection in the coming years, in comparison to the currently available therapy.

Recent Advances in the Discovery of Nicotinic Acetylcholine Receptor Allosteric Modulators

Positive allosteric modulators (PAMs), negative allosteric modulators (NAMs), silent agonists, allosteric activating PAMs and neutral or silent allosteric modulators are compounds capable of modulating the nicotinic receptor by interacting at allosteric modulatory sites distinct from the orthosteric sites. This survey is focused on the compounds that have been shown or have been designed to interact with nicotinic receptors as allosteric modulators of different subtypes, mainly α7 and α4β2. Minimal chemical changes can cause a different pharmacological profile, which can then lead to the design of selective modulators. Experimental evidence supports the use of allosteric modulators as therapeutic tools for neurological and non-neurological conditions.

Ultrasound-Assisted Synthesis and In Silico Modeling of Methanesulfonyl-Piperazine-Based Dithiocarbamates as Potential Anticancer, Thrombolytic, and Hemolytic Structural Motifs

Piperazine-based dithiocarbamates serve as important scaffolds for numerous pharmacologically active drugs. The current study investigates the design and synthesis of a series of dithiocarbamates with a piperazine unit as well as their biological activities. Under ultrasound conditions, the corresponding piperazine-1-carbodithioates 5a–5j were synthesized from monosubstituted piperazine 2 and N-phenylacetamides 4a–4j in the presence of sodium acetate and carbon disulfide in methanol. The structures of the newly synthesized piperazines were confirmed, and their anti-lung carcinoma effects were evaluated. A cytotoxic assay was performed to assess the hemolytic and thrombolytic potential of the synthesized piperazines 5a–5j. The types of substituents on the aryl ring were found to affect the anticancer activity of piperazines 5a–5j. Piperazines containing 2-chlorophenyl (5b; cell viability = 25.11 ± 2.49) and 2,4-dimethylphenyl (5i; cell viability = 25.31 ± 3.62) moieties demonstrated the most potent antiproliferative activity. On the other hand, piperazines containing 3,4-dichlorophenyl (5d; 0.1%) and 3,4-dimethylphenyl (5j; 0.1%) rings demonstrated the least cytotoxicity. The piperazine with the 2,5-dimethoxyphenyl moiety (5h; 60.2%) showed the best thrombolytic effect. To determine the mode of binding, in silico modeling of the most potent piperazine (i.e., 5b) was performed, and the results were in accordance with those of antiproliferation. It exhibits a similar binding affinity to PQ10 and an efficient conformational alignment with the lipophilic site of PDE10A conserved for PQ10A.

Identification of Cyclic Sulfonamides with an N-Arylacetamide Group as α-Glucosidase and α-Amylase Inhibitors: Biological Evaluation and Molecular Modeling

Diabetes mellitus (DM), a complicated metabolic disorder, is due to insensitivity to insulin function or reduction in insulin secretion, which results in postprandial hyperglycemia. α-Glucosidase inhibitors (AGIs) and α-amylase inhibitors (AAIs) block the function of digestive enzymes, which delays the carbohydrate hydrolysis process and ultimately helps to control the postprandial hyperglycemia. Diversified 2-(3-(3-methoxybenzoyl)-4-hydroxy-1,1-dioxido-2H-benzo[e][1,2]thiazin-2-yl)-N-arylacetamides were synthesized and evaluated for their in vitro inhibitory potential against α-glucosidase and α-amylase enzymes. The compounds with chloro, bromo and methyl substituents demonstrated good inhibition of α-glucosidase enzymes having IC50 values in the range of 25.88-46.25 μM, which are less than the standard drug, acarbose (IC50 = 58.8 μM). Similarly, some derivatives having chloro, bromo and nitro substituents were observed potent inhibitors of α-amylase enzyme, with IC50 values of 7.52 to 15.06 μM, lower than acarbose (IC50 = 17.0 μM). In addition, the most potent compound, N-(4-bromophenyl)-2-(4-hydroxy-3-(3-methoxybenzoyl)-1,1-dioxido-2H-benzo[e][1,2]thiazin-2-yl)acetamide (12i), was found to be a non-competitive and competitive inhibitor of α-glucosidase and α-amylase enzymes, respectively, during kinetic studies. The molecular docking studies provided the binding modes of active compounds and the molecular dynamics simulation studies of compound 12i in complex with α-amylase also showed that the compound is binding in a fashion similar to that predicted by molecular docking studies.

Site-Selective Cross-Coupling of Polyhalogenated Arenes and Heteroarenes with Identical Halogen Groups

Methods to functionalize arenes and heteroarenes in a site-selective manner are highly sought after for rapidly constructing value-added molecules of medicinal, agrochemical, and materials interest. One effective approach is the site-selective cross-coupling of polyhalogenated arenes bearing multiple, but identical, halogen groups. Such cross-coupling reactions have proven to be incredibly effective for site-selective functionalization. However, they also present formidable challenges due to the inherent similarities in the reactivities of the halogen substituents. In this Review, we discuss strategies for site-selective cross-couplings of polyhalogenated arenes and heteroarenes bearing identical halogens, beginning first with an overview of the reaction types that are more traditional in nature, such as electronically, sterically, and directing-group-controlled processes. Following these examples is a description of emerging strategies, which includes ligand- and additive/solvent-controlled reactions as well as photochemically initiated processes.

Synthesis and α-Glucosidase Inhibition Activity of 2-[3-(Benzoyl/4-bromobenzoyl)-4-hydroxy-1,1-dioxido-2H-benzo[e][1,2]thiazin-2-yl]-N-arylacetamides: An In Silico and Biochemical Approach

Diabetes mellitus (DM) is a chronic disorder and has affected a large number of people worldwide. Insufficient insulin production causes an increase in blood glucose level that results in DM. To lower the blood glucose level, various drugs are employed that block the activity of the α-glucosidase enzyme, which is considered responsible for the breakdown of polysaccharides into monosaccharides leading to an increase in the intestinal blood glucose level. We have synthesized novel 2-(3-(benzoyl/4-bromobenzoyl)-4-hydroxy-1,1-dioxido-2H-benzo[e][1,2]thiazin-2-yl)-N-arylacetamides and have screened them for their in silico and in vitro α-glucosidase inhibition activity. The derivatives 11c, 12a, 12d, 12e, and 12g emerged as potent inhibitors of the α-glucosidase enzyme. These compounds exhibited good docking scores and excellent binding interactions with the selected residues (Asp203, Asp542, Asp327, His600, Arg526) during in silico screening. Similarly, these compounds also showed good in vitro α-glucosidase inhibitions with IC₅₀ values of 30.65, 18.25, 20.76, 35.14, and 24.24 μM, respectively, which were better than the standard drug, acarbose (IC₅₀ = 58.8 μM). Furthermore, a good agreement was observed between in silico and in vitro modes of study.

Identification of N-phenyl-2-(phenylsulfonyl)acetamides/propanamides as new SLC-0111 analogues: Synthesis and evaluation of the carbonic anhydrase inhibitory activities

As a front-runner selective CA IX inhibitor currently in Phase Ib/II clinical trials, SLC-0111 has been herein exploited as a lead molecule for development of new different sets of N-phenyl-2-(phenylsulfonyl)acetamides/propanamides incorporating different functionalities; primary sulfonamide (5a-f), free carboxylic (8a, 8d), ethyl ester (8b, 8e), acetyl (8c, 8f) and nitro (10a, 10b), as potential carbonic anhydrase (CA, EC 4.2.1.1) inhibitors. All the prepared analogues have been examined for their CA inhibitory activities towards four human (h) isoenzymes, hCA I, II, IX and XII. Interestingly, replacement of SLC-0111 ureido linker with the flexible sulfonyl acetamide linker, as well as linker branching and elongation strategies successfully enhanced the inhibitory action toward hCA IX isoform, such as in sulfones 5a-d and 5f which displayed better activity than SLC-0111. Furthermore, sulfonamide-based sulfone (5f) and carboxylic acid-based sulfones (8a and 8d) demonstrated interesting selectivity toward the tumor-related hCA IX isoform over both hCA I and hCA II, which suggests them as promising candidates for further development as potential anticancer candidates. Thereafter, the anti-proliferative action for sulfones 5f, 8a and 8d was examined against breast (MCF-7) and colon (HCT-116) cancer cell lines. Also, sulfone 5f was further assessed for its impact on the cell cycle progression and apoptosis in HCT-116 cells.

Synthesis and antibacterial activity of novel myricetin derivatives containing sulfonylpiperazine

Myricetin derivatives containing sulfonylpiperazine were synthesized and their structures were confirmed by NMR and HRMS. The antibacterial activity results indicated that some compounds showed good antibacterial activity against Xanthomonas oryzaepv. oryzae (Xoo), Xanthomonas axonopodispv. citri (Xac) and Ralstonia solanacearum (Rs). Among them, compounds 4m and 4p revealed excellent antibacterial activities against Rs with a concentration for 50% of maximal effect (EC50) value of 4 and 4 μg/mL, which were better than the control drugs bismerthiazol (13 μg/mL) and thiodiazole-copper (185 μg/mL). As observed using scanning electron microscope (SEM), these compounds act by causing folding and deformation of the bacterial surface, resulting in incomplete bacterial structure, so as to achieve the goal of bacteriostasis. The myricetin derivatives synthesized are expected to guide the research direction of new antibacterial agents.

Rational modifications, synthesis and biological evaluation of new potential antivirals for RSV designed to target the M2-1 protein

Respiratory syncytial virus (RSV) is the main cause of lower respiratory tract diseases in infants and young children, with potentially serious and fatal consequences associated with severe infections. Despite extensive research efforts invested in the identification of therapeutic measures, no vaccine is currently available, while treatment options are limited to ribavirin and palivizumab, which both present significant limitations. While clinical and pre-clinical candidates mainly target the viral fusion protein, the nucleocapsid protein or the viral polymerase, our focus has been the identification of new antiviral compounds targeting the viral M2-1 protein, thanks to the presence of a zinc-ejecting group in their chemical structure. Starting from an anti-RSV hit we had previously identified with an in silico structure-based approach, we have designed, synthesised and evaluated a new series of dithiocarbamate analogues, with which we have explored the antiviral activity of this scaffold. The findings presented in this work may provide the basis for the identification of a new antiviral lead to treat RSV infections.

Synthesis and cytotoxicity of thieno[2,3-b]pyridine and furo[2,3-b]pyridine derivatives

Forty seven thieno[2,3-b]pyridines-2-carboxamides, furo[2,3-b]pyridines-2-carboxamides and tetrahydrothieno[2,3-b]quinolones-2-carboxamides derivatives were synthesized and tested for their antiproliferative activity against the NCI-60 cell lines. The 5-keto-tetrahydrothieno[2,3-b]quinolones-2-carboxamides (series 17) were found to have the greatest activity, with the compound containing a 3-methoxyphenylcarboxamide (compound 17d) being the most active, with GI50 values in the low nanomolar range against a range of cell lines, in particular the melanoma cell line MDA-MD-435 (GI50 - 23 nM) and the breast cancer cell line MDA-MB-468 (GI50 - 46 nM). Molecular modelling of series 17 against phosphoinositide specific-phospholipase C reveals that the side chains of the amino acids His356, Glu341, Arg549 and Lys438 are involved in hydrogen bonding with the ligands as well as a lipophilic pocket is occupied by the phenyl carboxamide moiety.

Discovery of benzamide analogs as negative allosteric modulators of human neuronal nicotinic receptors: pharmacophore modeling and structure-activity relationship studies

The present study describes our ongoing efforts toward the discovery of drugs that selectively target nAChR subtypes. We exploited knowledge on nAChR ligands and their binding site that were previously identified by our laboratory through virtual screenings and identified benzamide analogs as a novel chemical class of neuronal nicotinic receptor (nAChR) ligands. The lead molecule, compound 1 (4-(allyloxy)-N-(6-methylpyridin-2-yl)benzamide) inhibits nAChR activity with an IC₅₀ value of 6.0 (3.4-10.6) μM on human α4β2 nAChRs with a ∼5-fold preference against human α3β4 nAChRs. Twenty-six analogs of compound 1 were also either synthesized or purchased for structure-activity relationship (SAR) studies and provided information relating the chemical/structural properties of the molecules to their ability to inhibit nAChR activity. The discovery of subtype-selective ligands of nAChRs described here should contribute significantly to our understanding of the involvement of specific nAChR subtypes in normal and pathophysiological states.

Alkaloids from Microcos paniculata with cytotoxic and nicotinic receptor antagonistic activities

Microcos paniculata is a large shrub or small tree that grows in several countries in South and Southeast Asia. In the present study, three new piperidine alkaloids, microgrewiapines A-C (1-3), as well as three known compounds, inclusive of microcosamine A (4), 7'-(3',4'-dihydroxyphenyl)-N-[4-methoxyphenyl)ethyl]propenamide (5), and liriodenine (6), were isolated from cytotoxic fractions of the separate chloroform-soluble extracts of the stem bark, branches, and leaves of M. paniculata. Compounds 1-6 and 1a (microgrewiapine A 3-acetate) showed a range of cytotoxicity values against the HT-29 human colon cancer cell line. When evaluated for their effects on human α3β4 or α4β2 nicotinic acetylcholine receptors (nAChRs), several of these compounds were shown to be active as nAChR antagonists. As a result of this study, microgrewiapine A (1) was found to be a selective cytotoxic agent for colon cancer cells over normal colon cells and to exhibit nicotinic receptor antagonistic activity for both the hα3β4 and hα4β2 receptor subtypes.

Defining the putative inhibitory site for a selective negative allosteric modulator of human α4β2 neuronal nicotinic receptors

Neuronal nicotinic receptors (nAChRs) have been implicated in several diseases and disorders such as autism spectrum disorders, Alzheimer's disease, Parkinson's disease, epilepsy, and nicotine addiction. To understand the role of nAChRs in these conditions, it would be beneficial to have selective molecules that target specific nAChRs in vitro and in vivo. Our laboratory has previously identified a novel allosteric site on human α4β2 nAChRs using a series of computational and in vitro approaches. At this site, we have identified negative allosteric modulators that selectively inhibit human α4β2 nAChRs, a subtype implicated in nicotine addiction. This study characterizes the allosteric site via site-directed mutagenesis. Three amino acids (Phe118, Glu60, and Thr58) on the β2 subunit were shown to participate in the inhibitory properties of the selective antagonist KAB-18 and provided insights into its antagonism of human α4β2 nAChRs. SAR studies with KAB-18 analogues and various mutant α4β2 nAChRs also provided information concerning how different physiochemical features influence the inhibition of nAChRs through this allosteric site. Together, these studies identify the amino acids that contribute to the selective antagonism of human α4β2 nAChRs at this allosteric site. Finally, these studies define the physiochemical features of ligands that influence interaction with specific amino acids in this allosteric site.