Indazole- and Indole-5-carboxamides: Selective and Reversible Monoamine Oxidase B Inhibitors with Subnanomolar Potency

Discovery of novel benzimidazole derivatives as selective and reversible monoamine oxidase B inhibitors for Parkinson's disease treatment

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta. The development of novel scaffolds for human monoamine oxidase B (hMAO-B) inhibitors with reversible properties represents an important strategy to improve the efficacy and safety for PD treatment. In the current work, we have devised and assessed two innovative derivative series serving as hMAO-B inhibitors. These series have utilized benzimidazole as a scaffold and strategically incorporated a primary amide group, which is recognized as a pivotal pharmacophore in subsequent activity screening and reversible mode of action. Among these compounds, 16d has emerged as the most potent hMAO-B inhibitor with an IC50 value of 67.3 nM, comparable to safinamide (IC50 = 42.6 nM) in vitro. Besides, 16d demonstrated good selectivity towards hMAO-B isoenzyme with a selectivity index over 387. Importantly, in line with the design purpose, 16d inhibited hMAO-B in a competitive and reversible manner (Ki = 82.50 nM). Moreover, 16d exhibited a good safety profile in both cellular and acute toxicity assays in mice. It also displayed ideal pharmacokinetic properties and blood-brain barrier permeability in vivo, essential prerequisites for central nervous system medicines. In the MPTP-induced PD mouse model, 16d significantly alleviated the motor impairment, especially muscle relaxation and motor coordination. Therefore, 16d, serving as a lead compound, holds instructive significance for subsequent investigations regarding its application in the treatment of PD.

Benzodioxane Carboxamide Derivatives As Novel Monoamine Oxidase B Inhibitors with Antineuroinflammatory Activity

In this study, a series of N-phenyl-2,3-dihydrobenzo[b][1,4]dioxine-6-carboxamide derivatives were designed, synthesized, and evaluated for their inhibitory activities against human MAO-B (hMAO-B). The structure-activity relationship (SAR) was investigated and summarized. Compound 1l (N-(3,4-dichlorophenyl)-2,3-dihydrobenzo[b][1,4]dioxine-6-carboxamide) showed the most potent inhibitory activity with an IC50 value of 0.0083 μM and the selectivity index (IC50 (hMAO-A)/IC50 (hMAO-B)) was >4819. Kinetics and reversibility studies confirmed that compound 1l acted as a competitive and reversible inhibitor of hMAO-B. Molecular docking studies revealed the enzyme-inhibitor interactions, and the rationale was provided. Additionally, compound 1l could effectively inhibit the release of NO, TNF-α, and IL-1β in both LPS- and Aβ1-42-stimulated BV2 cells and attenuate the cytotoxicity induced by Aβ1-42. Since compound 1l exhibited low neurotoxicity, we believe that the hit compound with dual activities of inhibiting MAO-B and antineuroinflammation could be further investigated as a novel potential lead for future studies in vivo.

Design and Synthesis of Indazole-Indole Hybrid via tert-Butyl Nitrite Mediated Cascade Diazotization/Isomerization/Cyclization

In this report, a tert-butyl nitrite (TBN)-mediated straightforward metal-free approach has been presented for the synthesis of a diverse range of C-3-substituted indazole-indole hybrids using readily accessible 2-(indolin-3-ylidenemethyl)aniline derivatives. This strategy is proposed to occur via a diazonium salt intermediate that is capable of cascade isomerization and intramolecular C-N bond formation through a 5-endo-dig cyclization to achieve a wide variety of indazole-indole hybrids in good yields.

Quinoline-sulfonamides as a multi-targeting neurotherapeutic for cognitive decline: in vitro, in silico studies and ADME evaluation of monoamine oxidases and cholinesterases inhibitors

Alzheimer's disease (AD) is a multifactorial irreversible neurological disorder with multiple enzymes involved. In the treatment of AD, multifunctional agents targeting cholinesterase (ChE) and monoamine oxidase (MAO) inhibitors have shown promising results. Herein, a series of novel quinoline-sulfonamides (a1-18) were designed and synthesized as a dual inhibitor of MAOs and ChEs. The in vitro results showed that compounds a5, a12, a11, and a6 exhibited the most potent compounds against specific enzymes. They had IC50 value 0.59 ± 0.04 for MAO-A, 0.47 ± 0.03 for MAO-B, 0.58 ± 0.05 for BChE and 1.10 ± 0.77 for AChE μM respectively. Furthermore, kinetic studies revealed that these compounds are competitive. Molecular docking studies enhanced the understanding of the in silico component, unveiling critical interactions, specifically the hydrogen bonding interaction, π-π, π-alkyl, π-amid and π-sulfur interactions between the ligand and enzymes. These findings suggest that compounds a5, a6, a11, a12, a15, and a18 may be potent multifunctional candidates for AD treatment.

Superiority of the Triple-Acting 5-HT6R/5-HT3R Antagonist and MAO-B Reversible Inhibitor over 5-HT6R Antagonist Intepirdine in Alleviation of Cognitive Deficits in Rats

The multifactorial origin and neurochemistry of Alzheimer's disease (AD) call for the development of multitarget treatment strategies. We report a first-in-class triple acting compound that targets serotonin type 6 and 3 receptors (5-HT-Rs) and monoamine oxidase type B (MAO-B) as an approach for treating AD. The key structural features required for MAO-B inhibition and 5-HT6R antagonism and interaction with 5-HT3R were determined using molecular dynamic simulations and cryo-electron microscopy, respectively. Bioavailable PZ-1922 reversed scopolamine-induced cognitive deficits in the novel object recognition test. Furthermore, it displayed superior pro-cognitive properties compared to intepirdine (a 5-HT6R antagonist) in the AD model, which involved intracerebroventricular injection of an oligomeric solution of amyloid-β peptide (oAβ) in the T-maze test in rats. PZ-1922, but not intepirdine, restored levels of biomarkers characteristic of the debilitating effects of oAβ. These data support the potential of a multitarget approach involving the joint modulation of 5-HT6R/5-HT3R/MAO-B in AD.

An efficient method to access spiro pseudoindoxyl ketones: evaluation of indoxyl and their N-benzylated derivatives for inhibition of the activity of monoamine oxidases

A simple, metal-free approach was developed to obtain novel pseudoindoxyl derivatives. The reaction was mediated by tBuOK on tetrahydrocarbazole 8 in dimethyl sulfoxide (DMSO) at room temperature through the hydroxylation of the indole double bond and a subsequent pinacol-type rearrangement. Spiro pseudoindoxyl compounds and their N-benzylated derivatives were assessed for their inhibitory activities against monoamine oxidase (MAO) enzymes. Based on half-maximal inhibitory concentration (IC50) values, 13 compounds were found to have higher inhibitory activity against MAO-B than against MAO-A. With regard to MAO-B inhibition, 11f showed the best inhibitory activity, with an IC50 value of 1.44 μM, followed by 11h (IC50 = 1.60 μM), 11j (IC50 = 2.78 μM), 11d (IC50 = 2.81 μM), and 11i (IC50 = 3.02 μM). Compound 11f was a competitive inhibitor with a Ki value of 0.51 ± 0.023 μM. In a reversibility experiment using dialysis, 11f showed effective recovery of MAO-B inhibition similar to that of safinamide. These experiments suggested that 11f was a potent, reversible, and competitive inhibitor of MAO-B activity.

Repurposing of FDA-approved drugs as dual-acting MAO-B and AChE inhibitors against Alzheimer's disease: An in silico and in vitro study

An in silico consensus molecular docking approach and in vitro evaluations were adopted in the present study to explore a dataset of FDA-approved drugs as novel multitarget MAO-B/AChE agents in the treatment of Alzheimer's disease (AD). GOLD 5.3 and Glide were employed in the virtual assessments and consensus superimpositions of the obtained poses were applied to increase the reliability of the docking protocols. Furthermore, the top ranked molecules were subjected to binding free energy calculations using MM/GBSA, Induced fit docking (IFD) simulations, and a literature review. Consequently, the top four multitarget drugs were examined for their in vitro MAO-B and AChE inhibition effects. The consensus molecular docking identified Dolutegravir, Rebamipide, Loracarbef and Diflunisal as potential multitarget drugs. The biological data demonstrated that most of the docking scores were in good correlation with the in vitro experiments, however the theoretical simulations in the active site of MAO-B identified two false-positives - Rebamipide and Diflunisal. Dolutegravir and Loracarbef were accessed as active MAO-B inhibitors, while Dolutegravir, Rebamapide and Diflunisal as potential AChE inhibitors. The antiretroviral agent Dolutegravir exhibited the most potent multitarget activity - 41% inhibition of MAO-B (1 μM) and 68% inhibition of AChE (10 μM). Visualizations of the intermolecular interactions of Dolutegravir in the active sites of MAO-B and AChE revealed the formation of several stable hydrogen bonds. Overall, Dolutegravir was identified as a potential anti-AD drug, however further in vivo evaluations should be considered.

Bioisosteric replacement based on 1,2,4-oxadiazoles in the discovery of 1H-indazole-bearing neuroprotective MAO B inhibitors

Following a hybridization strategy, a series of 5-substituted-1H-indazoles were designed and evaluated in vitro as inhibitors of human monoamine oxidase (hMAO) A and B. Among structural modifications, the bioisostere-based introduction of 1,2,4-oxadiazole ring returned the most potent and selective human MAO B inhibitor (compound 20, IC₅₀ = 52 nM, SI > 192). The most promising inhibitors were studied in cell-based neuroprotection models of SH-SY5Y and astrocytes line against H₂O₂. Moreover, preliminary drug-like features (aqueous solubility at pH 7.4; hydrolytic stability at acidic and neutral pH) were assessed for selected 1,2,4-oxadiazoles and compared to amide analogues through RP-HPLC methods. Molecular docking simulations highlighted the crucial role of molecular flexibility in providing a better shape complementarity for compound 20 within MAO B enzymatic cleft than rigid analogue 18. Enzymatic kinetics analysis along with thermal stability curves (T_m shift = +2.9 °C) provided clues of a tight-binding mechanism for hMAO B inhibition by 20.

2,1-Benzothiazine - (quinolin/thiophen)yl hydrazone frameworks as new monoamine oxidase inhibitory agents; synthesis, in vitro and in silico investigation

Two series of new 2,1-benzothiazine derivatives have been synthesized by condensation of 4-hydrazono-1-methyl-3,4-dihydro-1H-benzo[c][1,2]thiazine 2,2-dioxide (5) with 2-chloroquinoline-3-carbaldehydes and acetylthiophenes to acquire new heteroaryl ethylidenes 7(a-f) and 9(a-k) in excellent yields. After characterization by FTIR, ¹H NMR, ¹³C NMR and elemental analyses, the newly synthesized analogues were investigated against monoamine oxidase enzymes (MAO A and MAO B). The titled compounds exhibited activity in the lower micromolar range among which 9e was the most potent compound against MAO A with IC₅₀ of 1.04 ± 0.01 μM whereas 9h proved to be the most potent derivative against MAO B with an IC₅₀ value of 1.03 ± 0.17 μM. Furthermore, in vitro results were further endorsed by molecular docking studies to determine the interaction between the potent compounds and the enzyme active site. These newly synthesized compounds represent promising hits for the development of safer and potent lead molecules for therapeutic use against depression and other neurological diseases.

Novel indazole skeleton derivatives containing 1,2,3-triazole as potential anti-prostate cancer drugs

In this study, a novel batch of indazole containing 1,2,3-triazole agents were designed and synthesized. The antiproliferative activity of target compounds in four human cancer cells, PC-3 (human prostate cancer cell), MCF-7 (human breast cancer cell), HepG-2 (human hepatoma cell) and MGC-803 (human gastric cancer cell), was evaluated by thiazole blue (MTT). In the antiproliferative activity screening, we were surprised to find that most compounds have specific cytotoxicity to PC-3 cancer cells. In particular, 9a has an IC₅₀ value of 4.42 ± 0.06 μmol/L against PC-3 cell. Cloning experiments showed that 9a could inhibit the formation of PC-3 cancer cell clone in a dose-dependent manner. Through cell cycle arrest experiment, we found that compound 9a can block the cell cycle in G2/M phase and inhibit cell proliferation. Finally, by evaluating the safety of compound 9a, we noticed that it showed fairly good safety both in vivo and in vitro. Overall, based on the biological activity evaluation and safety, analogue 9a can be viewed as a potential lead compound for further development of novel anti-prostate cancer drug.

Molecular dynamics and 3D-QSAR studies on indazole derivatives as HIF-1α inhibitors

Hypoxia-inducible factor (HIF) is a transcriptional factor which plays a crucial role in tumour metastasis thereby responsible for development of various forms of cancers. Indazole derivatives have been reported in the literature as potent HIF-1α inhibitor via interaction with key residues of the HIF-1α active site. Taking into consideration the role HIF-1α in cancer and potency of indazole derivative against HIF-1α; it was considered of interest to correlate structural features of known indazole derivatives with specified HIF-1α inhibitory activity to map pharmacophoric features through Three-dimensional quantitative structural activity relationship (3D-QSAR) and pharmacophore mapping. Field and Gaussian based 3D-QSAR studies were performed to realize the variables influencing the inhibitory potency of HIF-1α inhibitors. Field and Gaussian- based 3D-QSAR models were validated through various statistical measures generated by partial least square (PLS). The steric and electrostatic maps generated for both 3D-QSAR provide a structural framework for designing new inhibitors. Further; 3D-maps were also helpful in understanding variability in the activity of the compounds. Pharmacophore mapping also generates a common five-point pharmacophore hypothesis (A₁D₂R₃R₄R₅_4) which can be employed in combination with 3D-contour maps to design potent HIF-1α inhibitors. Molecular docking and molecular dynamics (MD) simulation of the most potent compound 39 showed good binding efficiency and was found to be quite stable in the active site of the HIF-1α protein. The developed 3D-QSAR models; pharmacophore modelling; molecular docking studies along with the MD simulation analysis may be employed to design lead molecule as selective HIF-1α inhibitors for the treatment of Cancer.

Highly Potent, Selective, and Competitive Indole-Based MAO-B Inhibitors Protect PC12 Cells against 6-Hydroxydopamine- and Rotenone-Induced Oxidative Stress

Monoamine oxidase B (MAO-B) is responsible for dopamine metabolism and plays a key role in oxidative stress by changing the redox state of neuronal and glial cells. To date, no disease-modifying therapy for Parkinson's disease (PD) has been identified. However, MAO-B inhibitors have emerged as a viable therapeutic strategy for PD patients. Herein, a novel series of indole-based small molecules was synthesized as new MAO-B inhibitors with the potential to counteract the induced oxidative stress in PC12 cells. At a single dose concentration of 10 µM, 10 compounds out of 30 were able to inhibit MAO-B with more than 50%. Among them, compounds 7b, 8a, 8b, and 8e showed 84.1, 99.3, 99.4, and 89.6% inhibition over MAO-B and IC₅₀ values of 0.33, 0.02, 0.03, and 0.45 µM, respectively. When compared to the modest selectivity index of rasagiline (II, a well-known MAO-B inhibitor, SI > 50), compounds 7b, 8a, 8b and 8e showed remarkable selectivity indices (SI > 305, 3649, 3278, and 220, respectively). A further kinetic study displayed a competitive mode of action for 8a and 8b over MAO-B with Ki values of 10.34 and 6.63 nM. Molecular docking studies of the enzyme-inhibitor binding complexes in MAO-B revealed that free NH and substituted indole derivatives share a common favorable binding mode: H-bonding with a crucial water "anchor" and Tyr326. Whereas in MAO-A the compounds failed to form favorable interactions, which explained their high selectivity. In addition, compounds 7b, 8a, 8b, and 8e exhibited safe neurotoxicity profiles in PC12 cells and partially reversed 6-hydroxydopamine- and rotenone-induced cell death. Accordingly, we report compounds 7b, 8a, 8b, and 8e as novel promising leads that could be further exploited for their multi-targeted role in the development of a new oxidative stress-related PD therapy.

Discovery of 3,4-dichloro-N-(1H-indol-5-yl)benzamide: A highly potent, selective, and competitive hMAO-B inhibitor with high BBB permeability profile and neuroprotective action

Since there is no disease-modifying treatment discovered yet for Parkinson's disease (PD), there is still a vital need to develop novel selective monoamine oxidase B (MAO-B) inhibitors as promising therapeutically active candidates for PD patients. Herein, we report the design, synthesis, and full characterization of new twenty-six indole derivatives as potential human MAO-B (hMAO-B) selective inhibitors. Six compounds (2i, 3b-e, and 5) exhibited low micromolar to nanomolar inhibitory activities over hMAO-B; compared to our recently reported N-substituted indole-based lead compound VIII (hMAO-B IC₅₀ = 777 nM), compound 5 (3,4-dichloro-N-(1H-indol-5-yl)benzamide) exhibited 18-fold increase in potency (IC₅₀ = 42 nM). A selectivity study over hMAO-A revealed an excellent selectivity index of compound 5 (SI > 2375) with a 47-fold increase compared to rasagiline (II, a well-known MAO-B inhibitor, SI > 50). A further kinetic evaluation of compound 5 over hMAO-B showed a reversible and competitive mode of inhibition with K_i value of 7 nM. Highly effective permeability and high CNS bioavailability of compound 5 with P_e = 54.49 × 10^-6 cm/s were demonstrated. Compound 5 also exhibited a low cytotoxicity profile and a promising neuroprotective effect against the 6-hydroxydopamine-induced neuronal cell damage in PC12 cells, which was more effective than that of rasagiline. Docking simulations on both hMAO-B and hMAO-A supported the in vitro data and served as further molecular evidence. Accordingly, we report the discovery of compound 5 as one of the most potent indole-based MAO-B inhibitors to date which is noteworthy to be further evaluated as a promising agent for PD treatment.

Small-Molecule Inhibitors of Reactive Oxygen Species Production

Reactive oxygen species (ROS) are involved in physiological cellular processes including differentiation, proliferation, and apoptosis by acting as signaling molecules or regulators of transcription factors. The maintenance of appropriate cellular ROS levels is termed redox homeostasis, a balance between their production and neutralization. High concentrations of ROS may contribute to severe pathological events including cancer, neurodegenerative, and cardiovascular diseases. In recent years, approaches to target the sources of ROS production directly in order to develop tool compounds or potential therapeutics have been explored. Herein, we briefly outline the major sources of cellular ROS production and comprehensively review the targeting of these by small-molecule inhibitors. We critically assess the value of ROS inhibitors with different mechanisms-of-action, including their potency, mode-of-action, known off-target effects, and clinical or preclinical status, while suggesting future avenues of research in the field.

Discovery of N-(1-(3-fluorobenzoyl)-1H-indol-5-yl)pyrazine-2-carboxamide: a novel, selective, and competitive indole-based lead inhibitor for human monoamine oxidase B

Herein, two new series of N-substituted indole-based analogues were rationally designed, synthesized via microwave heating technology, and evaluated as noteworthy MAO-B potential inhibitors. Compared to the reported indazole-based hits VI and VII, compounds 4b and 4e exhibited higher inhibitory activities over MAO-B with IC₅₀ values of 1.65 and 0.78 µM, respectively. When compared to the modest selectivity index of rasagiline (II, a well-known MAO-B inhibitor, SI > 50), both 4b and 4e also showed better selectivity indices (SI > 60 and 120, respectively). A further kinetic evaluation of the most potent derivative (4e) displayed a competitive mode of inhibition (inhibition constant (K_i)/MAO-B = 94.52 nM). Reasonable explanations of the elicited biological activities were presented via SAR study and molecular docking simulation. Accordingly, the remarkable MAO-B inhibitory activity of 4e (N-(1-(3-fluorobenzoyl)-1H-indol-5-yl)pyrazine-2-carboxamide), with its selectivity and competitive inhibition, advocates its potential role as a promising lead worthy of further optimization.

Indazole as a Privileged Scaffold: The Derivatives and their Therapeutic Applications

BACKGROUND

Heterocyclic compounds, also called heterocycles, are a major class of organic chemical compound that plays a vital role in the metabolism of all living cells. The heterocyclic compound, indazole, has attracted more attention in recent years and is widely present in numerous commercially available drugs. Indazole-containing derivatives, representing one of the most important heterocycles in drug molecules, are endowed with a broad range of biological properties.

METHODS

A literature search was conducted in PubMed, Google Scholar and Web of Science regarding articles related to indazole and its therapeutic application.

RESULTS

The mechanism and structure-activity relationship of indazole and its derivatives were described. Based on their versatile biological activities, the compounds were divided into six groups: anti-inflammatory, antibacterial, anti-HIV, antiarrhythmic, antifungal and antitumour. At least 43 indazole-based therapeutic agents were found to be used in clinical application or clinical trials.

CONCLUSION

This review is a guide for pharmacologists who are in search of valid preclinical/clinical drug compounds where the progress of approved marketed drugs containing indazole scaffold is examined from 1966 to the present day. Future direction involves more diverse bioactive moieties with indazole scaffold and greater insights into its mechanism.

Design and synthesis of novel 3,4-dihydrocoumarins as potent and selective monoamine oxidase-B inhibitors with the neuroprotection against Parkinson's disease

The monoamine oxidase-B (MAO-B) inhibitors with neuroprotective effects are better for Parkinson's disease (PD) treatment, due to the complicated pathogenesis of PD. To develop new hMAO-B inhibitors with neuroprotection, a novel series of 3,4-dihydrocoumarins was designed as selective and reversible hMAO-B inhibitors to treat PD. Most compounds showed potent and selective inhibition for hMAO-B over hMAO-A with IC₅₀ values ranging from nanomolar to sub-nanomolar. Among them, compound 4d was the most potent hMAO-B inhibitor (IC₅₀ = 0.37 nM) being about 20783-fold more active than iproniazid, and exhibited the highest selectivity for hMAO-B (SI > 270,270). Kinetic studies revealed that compound 4d was a reversible and competitive inhibitor of hMAO-B. Neuroprotective studies indicated that compound 4d could protect PC12 cells from the damage induced by 6-OHDA and rotenone. Besides, compound 4d did not exhibit acute toxicity at a dose up to 2500 mg/kg (po), and could cross the BBB in parallel artificial membrane permeability assay. More importantly, compound 4d was able to significantly prevent the motor deficits in the MPTP-induced PD model. These results indicate that compound 4d is an effective and promising candidate against PD.

Accelerating the identification of subtype selective inhibitors via Three-Dimensional Biologically Relevant Spectrum (BRS-3D): The monoamine oxidase subtypes as a case study

Subtype-selective drugs are of great therapeutic importance as they are expected to be more effective and with less side-effects. However, discovery of subtype selective inhibitors was hampered by the high similarity of the binding sites within subfamilies. In this study, we further evaluated the applicability of "Three-Dimensional Biologically Relevant Spectrum (BRS-3D)" for the identification of subtype-selective inhibitors. A case study was performed on monoamine oxidase, which has two subtypes related to distinct diseases. The inhibitory activity against MAO-A/B of 347 compounds experimentally tested in this research was reported. Compound M124 (5H-thiazolo[3,2-a]pyrimidin-5-one) with IC₅₀ less than 100 nM (SI = 23) was selected as a probe to investigate the structure selectivity relationship. Similarity search led to the identification of compound M229 and M249 with IC₅₀ values of 7.4 nM, 4 nM and acceptable selectivity index over MAO-A (M229 SI > 1351, M249 SI > 2500). The molecular basis for subtype selectivity was explored through docking study and attention based DNN model. Additionally, in silico ADME properties were characterized. Accordingly, it is found that BRS-3D is a robust method for subtype selectivity in the early stage of drug discovery and the compounds reported here can be promising leads for further experimental analysis.

Xylariaopyrones E-I, five new α-pyrone derivatives from the endophytic fungus Xylariales sp. (HM-1)

Five new α-pyrones, xylariaopyrones E-I (1-5), along with three known analogues (6-8) were isolated from the cultivation broth of the endophytic fungus Xylariales sp. (HM-1). The structures of the new compounds including their absolute configurations were elucidated by comprehensive spectroscopic methods and quantum ECD calculations. Xylariaopyrone E (1) is the first example of α-pyrone derivative with a novel [3, 2, 0] bridge ring system via a ketal function group in the side chain. In bioactivity assays, xylariaopyrones E-G (1-3) showed moderate inhibiting activities against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa with MIC values from 25.4 to 64.5 μg/mL, whereras xylariaopyrone G (3) exhibited significant inhibition of monoamine oxidase B with an IC₅₀ value of 15.6 μmol/L. Xylariaopyrone H (4) and the known compound 7 showed moderate toxicity against brine shrimp larvae with inhibition rates of 42.8% and 44.5%, respectively.

Synthesis of Indolyl Pyrazole Scaffolds as Potential Anti-cancer Agents and their Molecular Modelling Studies

Background::

Indole and pyrazoles are one of the prime structural units in the field of medicinal chemistry and have been reported to exhibit a variety of biological activities specifically anti-cancer. In view of their medicinal significance, we synthesized a conjugate of the two moieties to get access to newer and potential anti-cancer agents.

Methods:

Indolyl pyrazoles [3-(1,3-diphenyl-1H-pyrazol-4-yl)-2-(1-methyl-1H-indole-3-carbon yl)acrylonitriles] (4a-l) were synthesized by adopting simple and greener protocol and all the synthesized derivatives were docked against Bcl-2 protein and the selected chemical moieties were screened for their cytotoxicity by using the MTT assay.

Results: :

All the synthesized compounds were docked against BCL-2 protein in order to understand their binding pattern. Among the 12 compounds docked, 4d, 4f, 4h, 4j, and 4l compounds exhibited better protein binding interactions and the same were screened for their anti-cancer activity against A549 (lung) cancer cell lines at a concentration of 100 μM using Doxorubicin as standard. Substitutions such as N-benzyl, N-ethyl groups and halogen groups such as Br, Cl on indole ring showed moderate activity against A-549 cell lines.

Conclusion::

Among the 5 indolyl pyrazole derivatives screened, compounds 4h and 4j showed significantly better activity with an IC50 of 33.12 and 34.24 μM, respectively. Further, structural tweaking of the synthesized new chemical entities may lead to potential hit/lead-like molecules.

Dual Target Ligands with 4-tert-Butylphenoxy Scaffold as Histamine H3 Receptor Antagonists and Monoamine Oxidase B Inhibitors

Dual target ligands are a promising concept for the treatment of Parkinson's disease (PD). A combination of monoamine oxidase B (MAO B) inhibition with histamine H₃ receptor (H₃R) antagonism could have positive effects on dopamine regulation. Thus, a series of twenty-seven 4-tert-butylphenoxyalkoxyamines were designed as potential dual-target ligands for PD based on the structure of 1-(3-(4-tert-butylphenoxy)propyl)piperidine (DL76). Probed modifications included the introduction of different cyclic amines and elongation of the alkyl chain. Synthesized compounds were investigated for human H₃R (hH₃R) affinity and human MAO B (hMAO B) inhibitory activity. Most compounds showed good hH₃R affinities with K_i values below 400 nM, and some of them showed potent inhibitory activity for hMAO B with IC₅₀ values below 50 nM. However, the most balanced activity against both biological targets showed DL76 (hH₃R: K_i = 38 nM and hMAO B: IC₅₀ = 48 nM). Thus, DL76 was chosen for further studies, revealing the nontoxic nature of DL76 in HEK293 and neuroblastoma SH-SY5Ycells. However, no neuroprotective effect was observed for DL76 in hydrogen peroxide-treated neuroblastoma SH-SY5Y cells. Furthermore, in vivo studies showed antiparkinsonian activity of DL76 in haloperidol-induced catalepsy (Cross Leg Position Test) at a dose of 50 mg/kg body weight.

Iodine-Catalyzed Synthesis of 3-Arylthioindoles Employing a 1-Aryltriazene/CS2 Combination as a New Sulfenylation Source

A practical approach for the regioselective synthesis of 3-arylthioindoles has been accomplished using a combination of 1-aryltriazene/CS₂ as a new sulfenylation source. The methodology employs molecular iodine as a catalyst and is compatible with a variety of structurally diverse reactants.

Synthesis, crystal structures, antiproliferative activities and reverse docking studies of eight novel Schiff bases derived from benzil

Eight novel Schiff bases derived from benzil dihydrazone (BDH) or benzil monohydrazone (BMH) and four fused-ring carbonyl compounds (3-formylindole, FI; 3-acetylindole, AI; 3-formyl-1-methylindole, MFI; 1-formylnaphthalene, FN) were synthesized and characterized by elemental analysis, ESI-QTOF-MS, ¹H and ¹³C NMR spectroscopy, as well as single-crystal X-ray diffraction. They are (1Z,2Z)-1,2-bis{(E)-[(1H-indol-3-yl)methylidene]hydrazinylidene}-1,2-diphenylethane (BDHFI), C₃₂H₂₄N₆, (1Z,2Z)-1,2-bis{(E)-[1-(1H-indol-3-yl)ethylidene]hydrazinylidene}-1,2-diphenylethane (BDHAI), C₃₄H₂₈N₆, (1Z,2Z)-1,2-bis{(E)-[(1-methyl-1H-indol-3-yl)methylidene]hydrazinylidene}-1,2-diphenylethane (BMHMFI) acetonitrile hemisolvate, C₃₄H₂₈N₆·0.5CH₃CN, (1Z,2Z)-1,2-bis{(E)-[(naphthalen-1-yl)methylidene]hydrazinylidene}-1,2-diphenylethane (BDHFN), C₃₆H₂₆N₄, (Z)-2-{(E)-[(1H-indol-3-yl)methylidene]hydrazinylidene}-1,2-diphenylethanone (BMHFI), C₂₃H₁₇N₃O, (Z)-2-{(E)-[1-(1H-indol-3-yl)ethylidene]hydrazinylidene}-1,2-diphenylethanone (BMHAI), C₂₄H₁₉N₃O, (Z)-2-{(E)-[(1-methyl-1H-indol-3-yl)methylidene]hydrazinylidene}-1,2-diphenylethanone (BMHMFI), C₂₄H₁₉N₃O, and (Z)-2-{(E)-[(naphthalen-1-yl)methylidene]hydrazinylidene}-1,2-diphenylethanone (BMHFN) C₂₅H₁₈N₂O. Moreover, the in vitro cytotoxicity of the eight title compounds was evaluated against two tumour cell lines (A549 human lung cancer and 4T₁ mouse breast cancer) and two normal cell lines (MRC-5 normal lung cells and NIH 3T3 fibroblasts) by MTT assay. The results indicate that four (BDHMFI, BDHFN, BMHMFI and BMHFN) are inactive and the other four (BDHFI, BDHAI, BMHFI and BMHAI) show severe toxicities against human A549 and mouse 4T₁ cells, similar to the standard cisplatin. All the compounds exhibited weaker cytotoxicity against normal cells than cancer cells. The Swiss Target Prediction web server was applied for the prediction of protein targets. After analyzing the differences in frequency hits between these active and inactive Schiff bases, 18 probable targets were selected for reverse docking with the Surflex-dock function in SYBYL-X 2.0 software. Three target proteins, i.e. human ether-á-go-go-related (hERG) potassium channel, the inhibitor of apoptosis protein 3 and serine/threonine-protein kinase PIM1, were chosen as the targets. Finally, the ligand-based structure-activity relationships were analyzed based on the putative protein target (hERG) docking results, which will be used to design and synthesize novel hERG ion channel inhibitors.

Novel Diels-Alder Type Adducts from Morus alba Root Bark Targeting Human Monoamine Oxidase and Dopaminergic Receptors for the Management of Neurodegenerative Diseases

In this study, we delineate the human monoamine oxidase (hMAO) inhibitory potential of natural Diels–Alder type adducts, mulberrofuran G (1), kuwanon G (2), and albanol B (3), from Morus alba root bark to characterize their role in Parkinson’s disease (PD) and depression, focusing on their ability to modulate dopaminergic receptors (D₁R, D_2LR, D₃R, and D₄R). In hMAO-A inhibition, 1–3 showed mild effects (50% inhibitory concentration (IC₅₀): 54‒114 μM). However, 1 displayed moderate inhibition of the hMAO-B isozyme (IC₅₀: 18.14 ± 1.06 μM) followed by mild inhibition by 2 (IC₅₀: 57.71 ± 2.12 μM) and 3 (IC₅₀: 90.59 ± 1.72 μM). Our kinetic study characterized the inhibition mode, and the in silico docking predicted that the moderate inhibitor 1 would have the lowest binding energy. Similarly, cell-based G protein-coupled receptors (GPCR) functional assays in vector-transfected cells expressing dopamine (DA) receptors characterized 1–3 as D₁R/D_2LR antagonists and D₃R/D₄R agonists. The half-maximum effective concentration (EC₅₀) of 1–3 on DA D₃R/D₄R was 15.13/17.19, 20.18/21.05, and 12.63/‒ µM, respectively. Similarly, 1–3 inhibited 50% of the DA response on D₁R/D_2LR by 6.13/2.41, 16.48/31.22, and 7.16/18.42 µM, respectively. A computational study revealed low binding energy for the test ligands. Interactions with residues Asp110, Val111, Tyr365, and Phe345 at the D₃R receptor and Asp115 and His414 at the D₄R receptor explain the high agonist effect. Likewise, Asp187 at D₁R and Asp114 at D_2LR play a crucial role in the antagonist effects of the ligand binding. Our overall results depict 1–3 from M. alba root bark as good inhibitors of hMAO and potent modulators of DA function as D₁R/D_2LR antagonists and D₃R/D₄R agonists. These active constituents in M. alba deserve in-depth study for their potential to manage neurodegenerative disorders (NDs), particularly PD and psychosis.

Synthetic approaches and pharmaceutical applications of chloro-containing molecules for drug discovery: A critical review

At present more than 250 FDA approved chlorine containing drugs were available in the market and many pharmaceutically important drug candidates in pre-clinical trials. Thus, it is quite obvious to expect that in coming decades there will be an even greater number of new chlorine-containing pharmaceuticals in market. Chlorinated compounds represent the family of compounds promising for use in medicinal chemistry. This review describes the recent advances in the synthesis of chlorine containing heterocyclic compounds as diverse biological agents and drugs in the pharmaceutical industries for the inspiration of the discovery and development of more potent and effective chlorinated drugs against numerous death-causing diseases.

Design and Synthesis of Novel Cytotoxic Indole-Thiosemicarbazone Derivatives: Biological Evaluation and Docking Study

In this work, two novel series of indole-thiosemicarbazone derivatives were designed, synthesized, and evaluated for their cytotoxic activity against MCF-7, A-549, and Hep-G2 cell lines in comparison to etoposide and colchicine as the reference drugs. Generally, the synthesized compounds showed better cytotoxicity towards A-549 and Hep-G2 than MCF-7. Among them, (2E)-2-{[2-(4-chlorophenyl)-1H-indol-3-yl]methylidene}-N-(4-methoxyphenyl)hydrazinecarbothioamide (8l) was found to be the most potent compound against A-549 and Hep-G2, at least three times more potent than etoposide. The morphological analysis by the acridine orange/ethidium bromide double staining test and flow cytometry analysis indicated that compound 8l induced apoptosis in A-549 cells. Moreover, molecular docking methodology was exploited to elucidate the details of molecular interactions of the studied compounds with putative targets.

Inhibitor structure-guided design and synthesis of near-infrared fluorescent probes for monoamine oxidase A (MAO-A) and its application in living cells and in vivo

A series of near-infrared fluorescent probes based on inhibitor (clorgyline) structure-guided design were synthesized for the specific detection of MAO-A in cells and in vivo.

Preparation of spiro[imidazolidine-4,3′-indolin]-2′-imines via copper(i)-catalyzed formal [2 + 2 + 1] cycloaddition of 3-diazoindolin-2-imines and triazines

We report a facile and efficient synthesis of spiro[imidazolidine-4,3′-indolin]-2′-imines via a copper(i)-catalyzed cascade reaction of 3-diazoindolin-2-imines with 1,3,5-triazines.

4-tert-Pentylphenoxyalkyl derivatives - Histamine H3 receptor ligands and monoamine oxidase B inhibitors

The synthesis and biological activity of 4-tert-pentylphenoxypropyl derivatives are described in this manuscript. All compounds (except one) showed human histamine H₃ receptor affinity with K_i values below 760 nM. The inhibitory activity toward human monoamine oxidase B (hMAO B) was evaluated using a fluorometric Amplex-Red assay, and most of the compounds were effective in the submicromolar range. Among them, 1-(3-(4-tert-pPentylphenoxy)propyl)pyrrolidine (5) exhibited hMAO B inhibitory activity with an IC₅₀ value of 4.5 nM. In addition, hMAO B inhibition by 5 was shown to be non-competitive and reversible. Further, recently described potent histamine H₃ receptor ligands - 4-tert-pentylphenoxyalkyl derivatives (with a 4-8 carbon spacer) - were evaluated for hMAO B inhibitory activity, and some of them displayed activity in the submicromolar range. Selected compounds were also tested for human MAO A (hMAO A) inhibitory potencies and exhibited no activity. Moreover, molecular modeling studies were carried out for tested compounds to explain their molecular mechanism of hMAO B inhibition and the selectivity of compounds for hMAO B over hMAO A.

A facile route to 1H- and 2H-indazoles from readily accessible acyl hydrazides by exploiting a novel aryne-based molecular rearrangement

Herein we report the transformation of readily synthesised acyl hydrazides into 2-hydrazobenzophenones via a novel molecular rearrangement pathway using aryne chemistry. The developed reaction protocol is performed under relatively mild conditions and is tolerant of a wide variety of functional groups, and the 2-hydrazobenzophenone products provide access to both 1H- and 2H-indazoles from a single intermediate.

Indazole derivatives and their therapeutic applications: a patent review (2013-2017)

INTRODUCTION

Indazoles are heterocyclic moieties rarely found in nature. They are nitrogen containing chemical compounds composed of a pyrazole ring condensed with a benzene ring. Various indazole derivatives have been described with a wide variety of biological activities. This has aroused great interest in the development of novel indazole based therapeutic agents.

AREAS COVERED

Forty-two patents published within the last 5 years (2013-2017) describing derivatives with the indazole scaffold and their therapeutic applications were analysed.

EXPERT OPINION

The indazole scaffold is of great pharmacological importance as it forms the basic structure of a large number of compounds with potential therapeutic value. Derivatives have been found to possess promising anticancer and anti-inflammatory activity and have also found application in disorders involving protein kinases (aside from cancer) and neurodegeneration. The compounds where mechanism of action is defined can afford new molecules with biological and therapeutic properties.

Synthesis, characterization, monoamine oxidase inhibition, molecular docking and dynamic simulations of novel 2,1-benzothiazine-2,2-dioxide derivatives

In this research work, we report the synthesis and biological evaluation of two new series of 1-benzyl-4-(benzylidenehydrazono)-3,4-dihydro-1H-benzo[c] [1,2]thiazine 2,2-dioxides and 1-benzyl-4-((1-phenylethylidene)hydrazono)-3,4-dihydro-1H-benzo[c][1,2]thiazine 2,2-dioxides. The synthetic plan involves the mesylation of methyl anthranilate with subsequent N-benzylation of the product. The methyl 2-(N-benzylmethylsulfonamido)benzoate was subjected to cyclization reaction in the presence of sodium hydride to obtain 1-benzyl-1H-benzo[c][1,2]thiazin-4(3H)-one 2,2-dioxide which was treated with hydrazine hydrate to get corresponding hydrazone precursor. Finally, the titled compounds were obtained by reaction of hydrazone with various substituted aldehydes and ketones. The synthesized derivatives were subjected to carry out their inhibition activities against monoamine oxidases along with modelling investigations to evaluate their binding interactions and dynamic stability during the docking studies. The inhibition profile of potent compounds was found as competitive for both the isozymes. The compounds were more selective inhibitors of MAO-A as compared to MAO-B. Moreover, drug likeness profile of the derivatives was evaluated to have an additional insight into the physicochemical properties. The molecular dynamic simulations predicted the behaviour of amino acids with the active site residues.

Convenient synthesis of 2-amino-3-(arylthio)indoles via the Rh-catalyzed reaction of 3-diazoindol-2-imines with thioesters

2-Amino-3-(arylthio)indoles were conveniently synthesized via the Rh(ii)-catalyzed C–S/N–C coupling reaction between 3-diazoindol-2-imines and thioesters.

Unprotected Indazoles Are Resilient to Ring-Opening Isomerization: A Case Study on Catalytic C-S Couplings in the Presence of Strong Base

Indazoles represent a privileged scaffold in medicinal chemistry. In the presence of strong base, however, N-protected indazoles are prone to an undesirable ring-opening reaction to liberate o-aminobenzonitriles. By employing unprotected indazoles with a free N-H bond, isomerization is averted because the heterocycle is deprotonated in situ. We herein report functional group-tolerant and robust C-S couplings of bromoindazoles with thiols of varying electronic nature in the presence of lithium bis(trimethylsilyl)amide at elevated temperatures.