The concept of privileged structures in rational drug design: focus on acridine and quinoline scaffolds in neurodegenerative and protozoan diseases

Quinoline Derivatives: Promising Antioxidants with Neuroprotective Potential

Quinoline has been proposed as a privileged molecular framework in medicinal chemistry. Although by itself it has very few applications, its derivatives have diverse biological activities. In this work, 8536 quinoline derivatives, strategically designed using the CADMA-Chem protocol, are presented. This large chemical space was sampled, analyzed and reduced using selection and elimination scores that combine their properties of bioavailability, toxicity and manufacturability. After applying several filters, 25 derivatives were selected to investigate their acid-base, antioxidant and neuroprotective properties. The antioxidant activity was predicted based on the ionization potential and bond dissociation energies, parameters directly related to the transfer of hydrogen atoms and of a single electron, respectively. These two mechanisms are typically involved in the radical scavenging processes. The antioxidant efficiency was compared with reference compounds, and the most promising antioxidants were found to be more efficient than Trolox but less efficient than ascorbate. In addition, based on molecular docking simulations, some derivatives are expected to act as inhibitors of catechol-O methyltransferase (COMT), acetylcholinesterase (AChE) and monoamine oxidase type B (MAO-B) enzymes. Some structural insights about the compounds were found to enhance or decrease the neuroprotection activity. Based on the results, four quinoline derivatives are proposed as candidates to act as multifunctional antioxidants against Alzheimer's (AD) and Parkinson's (PD) diseases.

Derivatives of 9-phosphorylated acridine as butyrylcholinesterase inhibitors with antioxidant activity and the ability to inhibit β-amyloid self-aggregation: potential therapeutic agents for Alzheimer's disease

We investigated the inhibitory activities of novel 9-phosphoryl-9,10-dihydroacridines and 9-phosphorylacridines against acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and carboxylesterase (CES). We also studied the abilities of the new compounds to interfere with the self-aggregation of β-amyloid (Aβ42) in the thioflavin test as well as their antioxidant activities in the ABTS and FRAP assays. We used molecular docking, molecular dynamics simulations, and quantum-chemical calculations to explain experimental results. All new compounds weakly inhibited AChE and off-target CES. Dihydroacridines with aryl substituents in the phosphoryl moiety inhibited BChE; the most active were the dibenzyloxy derivative 1d and its diphenethyl bioisostere 1e (IC50 = 2.90 ± 0.23 µM and 3.22 ± 0.25 µM, respectively). Only one acridine, 2d, an analog of dihydroacridine, 1d, was an effective BChE inhibitor (IC50 = 6.90 ± 0.55 μM), consistent with docking results. Dihydroacridines inhibited Aβ42 self-aggregation; 1d and 1e were the most active (58.9% ± 4.7% and 46.9% ± 4.2%, respectively). All dihydroacridines 1 demonstrated high ABTS•+-scavenging and iron-reducing activities comparable to Trolox, but acridines 2 were almost inactive. Observed features were well explained by quantum-chemical calculations. ADMET parameters calculated for all compounds predicted favorable intestinal absorption, good blood-brain barrier permeability, and low cardiac toxicity. Overall, the best results were obtained for two dihydroacridine derivatives 1d and 1e with dibenzyloxy and diphenethyl substituents in the phosphoryl moiety. These compounds displayed high inhibition of BChE activity and Aβ42 self-aggregation, high antioxidant activity, and favorable predicted ADMET profiles. Therefore, we consider 1d and 1e as lead compounds for further in-depth studies as potential anti-AD preparations.

Facile access to 3-sulfonylquinolines via Knoevenagel condensation/aza-Wittig reaction cascade involving ortho-azidobenzaldehydes and β-ketosulfonamides and sulfones

Quinoline-based sulfonyl derivatives, and especially sulfonamides, are relevant and promising structures for drug design. We have developed a new convenient protocol for the synthesis of 3-sulfonyl-substituted quinolines (sulfonamides and sulfones). The approach is based on a Knoevenagel condensation/aza-Wittig reaction cascade involving o-azidobenzaldehydes and ketosulfonamides or ketosulfones as key building blocks. The protocol is appropriate for both ketosulfonyl reagents and α-sulfonyl-substituted alkyl acetates providing the target quinoline derivatives in good to excellent yields.

Design, synthesis and biological evaluations of quinolone amides against African trypanosomiasis with improved solubility

The human African trypanosomiasis is a devastating parasitic infection, which is caused by the protozoan Trypanosoma brucei and transmitted by the bite of the tsetse fly. An untreated infection usually results in death and only few drugs with significant drawbacks are currently available for treatment. Previous investigations revealed the quinolone amide MB007 as a lead compound with an excellent selectivity for T. b. brucei. Here, new quinolone amides were synthesized for deeper insights into the structure-activity relationship. Furthermore, the aqueous solubility of the compounds was analyzed, as the poor solubility of previous quinolone amides impeded in vivo studies for target identification. The biological evaluation led to the new lead structure 9f, which exhibits a promising in vitro activity against T. b. brucei (IC50 = 22 nM) and showed no cytotoxicity against macrophages. Moreover, compounds 10b and 10c were discovered, which possessed an improved solubility combined with a decent selectivity.

Quinolinyl β-enaminone derivatives exhibit leishmanicidal activity against Leishmania donovani by impairing the mitochondrial electron transport chain complex and inducing ROS-mediated programmed cell death

OBJECTIVES

Previously, a series of side chain-modified quinolinyl β-enaminones was identified to possess significant activity against chloroquine-sensitive or -resistant Plasmodium falciparum and Brugia malayi microfilariae. The present study evaluates in vitro and in vivo activity of the series against Leishmania donovani and reports their mode of action.

METHODS

The in vitro activity of 15 quinolinyl β-enaminone derivatives against Leishmania promastigotes and amastigotes was assessed by luciferase assay. The reduction of organ parasite burden was assessed by Giemsa staining in L. donovani-infected BALB/c mice and hamsters. Intracellular Ca2+ and ATP level in active derivative (3D)-treated promastigotes were determined by fluorescence and luminescence assays. Flow cytometry was performed to determine loss of mitochondrial membrane potential (MMP) using JC-1 dye, reactive oxygen species (ROS) generation using 2',7'-dichlorodihydrofluorescein diacetate (DCFDA) dye, phosphatidylserine externalization by Annexin V-FITC staining and cell-cycle arrest by propidium iodide (PI) staining.

RESULTS

Compounds 3A, 3B and 3D showed significant in vitro efficacy against L. donovani with IC50 < 6 µM and mild cytotoxicity (∼75% viability) at 25 µM on J774 macrophages. 3A and 3D at 50 mg/kg and 100 mg/kg reduced parasite burden (>84%) in infected mice and hamsters, respectively, whereas 3D-treated animals demonstrated maximum parasite burden reduction without organ toxicity. Mode-of-action analysis revealed that 3D induced apoptosis by inhibiting mitochondrial complex II, reducing MMP and ATP levels, increasing ROS and Ca2+ levels, ultimately triggering phosphatidylserine externalization and sub-G0/G1 cell-cycle arrest in promastigotes.

CONCLUSIONS

Compound 3D-mediated inhibition of L. donovani mitochondrial complex induces apoptosis, making it a promising therapeutic candidate for visceral leishmaniasis.

Antimicrobial and antioxidant activities of Streptomyces species from soils of three different cold sites in the Fez-Meknes region Morocco

The increasing demand for new bioactive compounds to combat the evolution of multi-drug resistance (MDR) requires research on microorganisms in different environments in order to identify new potent molecules. In this study, initial screening regarding the antimicrobial activity of 44 Actinomycetes isolates isolated from three soil samples from three different extremely cold sites in Morocco was carried out. Primary and secondary screening were performed against Candida albicans ATCC 60,193, Escherichia coli ATCC 25,922, Staphylococcus aureus ATCC 25,923, Bacillus cereus ATCC 14,579, other clinical MDR bacteria, and thirteen phytopathogenic fungi. Based on the results obtained, 11 active isolates were selected for further study. The 11microbial isolates were identified based on morphological and biochemical characters and their molecular identification was performed using 16S rRNA sequence homology. The UV-visible analysis of dichloromethane extracts of the five Streptomyces sp. Strains that showed high antimicrobial and antioxidant (ABTS 35.8% and DPPH 25.6%) activities revealed the absence of polyene molecules. GC-MS analysis of the dichloromethane extract of E23-4 as the most active strain revealed the presence of 21 volatile compounds including Pyrrolopyrazine (98%) and Benzeneacetic acid (90%). In conclusion, we studied the isolation of new Streptomyces strains to produce new compounds with antimicrobial and antioxidant activities in a cold and microbiologically unexplored region of Morocco. Furthermore, this study has demonstrated a significant (P < 0.0001) positive correlation between total phenolic and flavonoid contents and antioxidant capacity, paving the way for the further characterization of these Streptomyces sp. isolates for their optimal use for anticancer, antioxidant, and antimicrobial purposes.

Structural Characterization of Multicomponent Crystals Formed from Diclofenac and Acridines

Multicomponent crystals containing diclofenac and acridine (1) and diclofenac and 6,9-diamino-2-ethoxyacridine (2) were synthesized and structurally characterized. The single-crystal XRD measurements showed that compound 1 crystallizes in the triclinic P-1 space group as a salt cocrystal with one acridinium cation, one diclofenac anion, and one diclofenac molecule in the asymmetric unit, whereas compound 2 crystallizes in the triclinic P-1 space group as an ethanol solvate monohydrate salt with one 6,9-diamino-2-ethoxyacridinium cation, one diclofenac anion, one ethanol molecule, and one water molecule in the asymmetric unit. In the crystals of the title compounds, diclofenac and acridines ions and solvent molecules interact via N–H⋯O, O–H⋯O, and C–H⋯O hydrogen bonds, as well as C–H⋯π and π–π interactions, and form heterotetramer bis[⋯cation⋯anion⋯] (1) or heterohexamer bis[⋯cation⋯ethanol⋯anion⋯] (2). Moreover, in the crystal of compound 1, acridine cations and diclofenac anions interact via N–H⋯O hydrogen bond, C–H⋯π and π–π interactions to produce blocks, while diclofenac molecules interact via C–Cl⋯π interactions to form columns. In the crystal of compound 2, the ethacridine cations interact via C–H⋯π and π–π interactions building blocks, while diclofenac anions interact via π–π interactions to form columns.

Quinoline-Based Materials: Spectroscopic Investigations as well as DFT and TD-DFT Calculations

Quinoline derivatives such as 15,15-difluoro-[1,3,2] diaazaborininodiquinoline (DDP) and 15,15-difluoro-[1,3,2] diaazaborininodiquinoline acetonitrile (DDPA) have a range of biological and medical activities. So, it is vital to shed light on these compounds in terms of their optical properties supported by quantum calculations. The absorption and emission spectra of studied compounds were measured within the laboratory, whereas the quantum calculations were performed utilizing the density functional theory (DFT) calculations. Additionally, the time-dependent density functional theory (TD-DFT) was applied for the comparison of some sensible results with the theoretical ones. The molecular structures of these compounds were presented via applying chemical analysis techniques. The electronic absorption spectra of DDP and DDPA molecular structures were monitored through an experiment in hosts such as carbon tetrachloride (CCl4), chloroform (CHCl3), methylene dichloride (CH2Cl2), acetone, and dimethyl sulfoxide (DMSO). Also, the influence of pH on the absorption spectra of the DDP molecule was studied. The molecular structures of these quinoline derivatives have been optimized via utilizing the B3LYP/6-31G (d) level of theory. The electronic absorption and emission spectra of the DDP compound in gas, THF, and DMSO have been calculated utilizing TD-DFT at the CAM-B3LYP/6-31G ++(d, p) level.

Synthesis of Proposed Structure of Aaptoline B via Transition Metal-Catalyzed Cycloisomerization and Evaluation of Its Neuroprotective Properties in C. Elegans

A concise synthesis of the proposed structure of aaptoline B, a pyrroloquinoline derived from a marine sponge, was accomplished. A key feature of this synthesis is the versatile transition metal-catalyzed cycloisomerization of N-propargylaniline to construct a quinoline skeleton. However, the spectral data of the synthesized aaptoline B did not agree with those of previous studies. The structure of the synthesized aaptoline B was confirmed using a combined 2D NMR analysis. Furthermore, we assessed the possible neuroprotective potential of aaptoline B using the C. elegans model system. In this study, aaptoline B significantly improved the viability and the morphology of dopaminergic neurons of nematodes under MPP+ exposure conditions. We also found that MPP+-induced motor deficits in nematodes were efficiently restored by aaptoline B treatment. Our findings demonstrate the neuroprotective effects of aaptoline B against MPP+-induced dopaminergic neuronal damage. Further studies are underway to explain its pharmacological mechanism.

Biological Evaluation and Mechanistic Studies of Quinolin-(1H)-Imines as a New Chemotype against Leishmaniasis

Leishmaniasis is one of the most challenging neglected tropical diseases and remains a global threat to public health. Currently available therapies for leishmaniases present significant drawbacks and are rendered increasingly inefficient due to parasite resistance, making the need for more effective, safer, and less expensive drugs an urgent one. In our efforts to identify novel chemical scaffolds for the development of antileishmanial agents, we have screened in-house antiplasmodial libraries against axenic and intracellular forms of Leishmania infantum, Leishmania amazonensis, and Leishmania major. Several of the screened compounds showed half-maximal inhibitory concentrations (IC₅₀s) against intracellular L. infantum parasites in the submicromolar range (compounds 1h, IC₅₀ = 0.9 μM, and 1n, IC₅₀ = 0.7 μM) and selectivity indexes of 11 and 9.7, respectively. Compounds also displayed activity against L. amazonensis and L. major parasites, albeit in the low micromolar range. Mechanistic studies revealed that compound 1n efficiently inhibits oxygen consumption and significantly decreases the mitochondrial membrane potential in L. infantum axenic amastigotes, suggesting that this chemotype acts, at least in part, by interfering with mitochondrial function. Structure-activity analysis suggests that compound 1n is a promising antileishmanial lead and emphasizes the potential of the quinoline-(1H)-imine chemotype for the future development of new antileishmanial agents.

Recent advancements in anti-leishmanial research: Synthetic strategies and structural activity relationships

Leishmaniasis is a parasitic neglected tropical disease caused by various species of Leishmania parasite. Despite tremendous advancements in the therapeutic sector and drug development strategies, still the existing anti-leishmanial agents are associated with some clinical issues like drug resistance, toxicity and selectivity. Therefore, several research groups are continuously working towards the development of new therapeutic candidates to overcome these issues. Many potential heterocyclic moieties have been explored for this purpose including triazoles, chalcones, chromone, thiazoles, thiosemicarbazones, indole, quinolines, etc. It is evident from the literature that the majority of anti-leishmanial agents act by interacting with key regulators including PTR-I, DHFR, LdMetAP1, MAPK, 14 α-demethylase and pteridine reductase-I, etc. Also, these tend to induce the production of ROS which causes damage to parasites. In the present compilation, authors have summarized various significant synthetic procedures for anti-leishmanial agents reported in recent years. A brief description of the pharmacological potentials of synthesized compounds along with important aspects related to structural activity relationship has been provided. Important docking outcomes highlighting the possible mode of interaction for the reported compounds have also been included. This review would be helpful to the scientific community to design newer strategies and also to develop novel therapeutic candidates against leishmaniasis.

An Overview of Privileged Scaffold: Quinolines and Isoquinolines in Medicinal Chemistry as Anticancer Agents

Cancer is one of the most difficult diseases and causes of death for many decades. Many pieces of research are continuously going on to get a solution for cancer. Quinoline and isoquinoline derivatives have shown their possibilities to work as an antitumor agent in anticancer treatment. The members of this privileged scaffold quinoline and isoquinoline have shown their controlling impacts on cancer treatment through various modes. In particular, this review suggests the current scenario of quinoline and isoquinoline derivatives as antitumor agents and refine the path of these derivatives to find and develop new drugs against an evil known as cancer.

Advancements in the synthesis of fused tetracyclic quinoline derivatives

Fused tetracyclic systems containing a quinoline nucleus represent an important class of heterocyclic bioactive natural products and pharmaceuticals because of their significant and wide-spectrum biological properties. Several of these compounds have been obtained with diverse pharmacological and biological activities, such as antiplasmodial, antifungal, antibacterial, potent antiparasitic, antiproliferative, anti-tumor and anti-inflammatory activities. This information will be beneficial for medicinal chemists in the field of drug discovery to design and synthesize new fused tetracyclic quinolines as potent therapeutical agents. This review article provides a comprehensive report regarding the methods developed for the synthesis of fused tetracyclic quinolines reported so far (till October 2019). The article includes synthesis by one-pot domino reaction, microwave synthesis using a catalyst, using ionic liquids, photocatalytic synthesis (UV radiation), Pfitzinger reaction, I2-catalyzed cyclization reaction, Wittig reaction, cascade reaction, imino Diels-Alder reaction, Friedel-Crafts reaction, CDC reaction, solvent-free reactions and using small chiral organic molecules as catalysts. To the best of our knowledge, this is the first review focused on the synthesis of fused tetracyclic quinolines along with mechanistic aspects.

Design of new quinolin-2-one-pyrimidine hybrids as sphingosine kinases inhibitors

Sphingosine-1-phosphate is now emerging as an important player in cancer, inflammation, autoimmune, neurological and cardiovascular disorders. Abundance evidence in animal and humans cancer models has shown that SphK1 is linked to cancer. Thus, there is a great interest in the development new SphK1 inhibitors as a potential new treatment for cancer. In a search for new SphK1 inhibitors we selected the well-known SKI-II inhibitor as the starting structure and we synthesized a new inhibitor structurally related to SKI-II with a significant but moderate inhibitory effect. In a second approach, based on our molecular modeling results, we designed new structures based on the structure of PF-543, the most potent known SphK1 inhibitor. Using this approach, we report the design, synthesis and biological evaluation of a new series of compounds with inhibitory activity against both SphK1 and SphK2. These new inhibitors were obtained incorporating new connecting chains between their polar heads and hydrophobic tails. On the other hand, the combined techniques of molecular dynamics simulations and QTAIM calculations provided complete and detailed information about the molecular interactions that stabilize the different complexes of these new inhibitors with the active sites of the SphK1. This information will be useful in the design of new SphK inhibitors.

Privileged Structures in the Design of Potential Drug Candidates for Neglected Diseases

Background:

Privileged motifs are recurring in a wide range of biologically active compounds that reach different pharmaceutical targets and pathways and could represent a suitable start point to access potential candidates in the neglected diseases field. The current therapies to treat these diseases are based in drugs that lack of the desired effectiveness, affordable methods of synthesis and allow a way to emergence of resistant strains. Due the lack of financial return, only few pharmaceutical companies have been investing in research for new therapeutics for neglected diseases (ND).

Methods:

Based on the literature search from 2002 to 2016, we discuss how six privileged motifs, focusing phthalimide, isatin, indole, thiosemicarbazone, thiazole, and thiazolidinone are particularly recurrent in compounds active against some of neglected diseases.

Results:

It was observed that attention was paid particularly for Chagas disease, malaria, tuberculosis, schistosomiasis, leishmaniasis, dengue, African sleeping sickness (Human African Trypanosomiasis - HAT) and toxoplasmosis. It was possible to verify that, among the ND, antitrypanosomal and antiplasmodial activities were between the most searched. Besides, thiosemicarbazone moiety seems to be the most versatile and frequently explored scaffold. As well, phthalimide, isatin, thiazole, and thiazolidone nucleus have been also explored in the ND field.

Conclusion:

Some described compounds, appear to be promising drug candidates, while others could represent a valuable inspiration in the research for new lead compounds.

Synthesis of 3-aryl-2-phosphinoimidazo[1,2-a]pyridine ligands for use in palladium-catalyzed cross-coupling reactions

3-Aryl-2-phosphinoimidazo[1,2-a]pyridine ligands were synthesized from 2-aminopyridine via two complementary routes. The first synthetic route involves the copper-catalyzed iodine-mediated cyclizations of 2-aminopyridine with arylacetylenes followed by palladium-catalyzed cross-coupling reactions with phosphines. The second synthetic route requires the preparation of 2,3-diiodoimidazo[1,2-a]pyridine or 2-iodo-3-bromoimidazo[1,2-a]pyridine from 2-aminopyridine followed by palladium-catalyzed Suzuki/phosphination or a phosphination/Suzuki cross-coupling reactions sequence, respectively. Preliminary model studies on the Suzuki synthesis of sterically-hindered biaryl and Buchwald-Hartwig amination compounds are presented with these ligands.

Synthesis, Biological Evaluation, Structure-Activity Relationship, and Mechanism of Action Studies of Quinoline-Metronidazole Derivatives Against Experimental Visceral Leishmaniasis

In our efforts to identify novel chemical scaffolds for the development of antileishmanial agents, a series of quinoline-metronidazole hybrid compounds was synthesized and tested against the murine model of visceral leishmaniasis. Among all synthesized derivatives, 15b and 15i showed significant antileishmanial efficacy against both extracellular promastigote (IC₅₀ 9.54 and 5.42 μM, respectively) and intracellular amastigote (IC₅₀ 9.81 and 3.75 μM, respectively) forms of Leishmania donovani with negligible cytotoxicity toward the host (J774 macrophages, Vero cells). However, compound 15i effectively inhibited the parasite burden in the liver and spleen (>80%) of infected BALB/c mice. Mechanistic studies revealed that 15i triggers oxidative stress which induces bioenergetic collapse and apoptosis of the parasite by decreasing ATP production and mitochondrial membrane potential. Structure-activity analyses and pharmacokinetic studies suggest 15i as a promising antileishmanial lead and emphasize the importance of quinoline-metronidazole series as a suitable platform for the future development of antileishmanial agents.

Copper-catalyzed cross-dehydrogenative coupling between quinazoline-3-oxides and indoles

A novel and simple protocol for the synthesis of 4-(indole-3-yl)quinazolines via cross-dehydrogenative coupling of quinazoline-3-oxides and indoles under an air atmosphere has been developed.

To Loop or Not to Loop: Influence of Hinge Flexibility on Self-Assembly Outcomes for Acridine-Based Triazolylpyridine Chelates with Zinc(II), Iron(II), and Copper(II)

Coordination-driven self-assembly has been established as an effective strategy for the efficient construction of intricate architectures in both natural and artificial systems, for applications ranging from gene regulation to metal-organic frameworks. Central to these systems is the need for carefully designed organic ligands, generally with rigid components, that can undergo self-assembly with metal ions in a predictable manner. Herein, we report the synthesis and study of three novel organic ligands that feature 3,6-disubstituted acridine as a rigid spacer connected to two 2-(1,2,3-triazol-4-yl)pyridine "click" chelates through hinges of the same length but differing flexibility. The flexibility of these "three-atom" hinges was modulated by i) moving from secondary to tertiary amide functional groups and ii) replacing an sp² amide carbon with an sp³ methylene carbon. In an effort to understand the role of hinge flexibility in directing self-assembly into mononuclear loops or dinuclear cylinders, the impact of these changes on self-assembly outcomes with zinc(II), iron(II), and copper(II) ions is described.

New amyloid beta-disaggregating agents: synthesis, pharmacological evaluation, crystal structure and molecular docking of N-(4-((7-chloroquinolin-4-yl)oxy)-3-ethoxybenzyl)amines

In the journey towards the development of potent multi-targeted ligands for the treatment of Alzheimer's disease, a series of Aβ aggregation inhibitors having quinoline scaffold were designed utilizing computational biology tools, synthesized and characterized by various spectral techniques including single-crystal X-ray crystallography. Organic syntheses relying upon convergent synthetic routes were employed. Investigations via ThT fluorescence assay, electron microscopy and transmission electron microscopy revealed the synthesized derivatives to exhibit Aβ self-aggregation inhibition. Molecules 5g and 5a showed the highest inhibitory potential, 53.73% and 53.63% at 50 μM respectively; higher than the standard Aβ disaggregating agent, curcumin. Molecules 5g and 5a disaggregated AChE-induced (58.26%, 47.36%) Aβ aggregation more than two fold more than the standard drug-donepezil (23.66%) and inhibited Cu²⁺-induced Aβ aggregation. A docking study significantly showed their interaction with key residues of Aβ and the results were in accordance with the study. Besides, these compounds also exhibited potential antioxidant activity (5a, 2.7240 Trolox equivalent by ORAC assay) and metal chelating property. Furthermore, the stoichiometric ratio of Cu (ii)-5a and Cu(ii)-5g complexes were found by Job's method (0.5 : 1 for 5a and 0.8 : 1 for 5g). In silico ADMET profiling showed these derivatives to have drug like properties with very low toxicity effects in the pharmacokinetic study. Overall, these results displayed a multi-activity profile with promising Aβ aggregation inhibition and antioxidation and metal chelation activity that could be helpful for developing new multifunctional agents against Alzheimer's disease.

Synthesis, Structure, Chemical Stability, and In Vitro Cytotoxic Properties of Novel Quinoline-3-Carbaldehyde Hydrazones Bearing a 1,2,4-Triazole or Benzotriazole Moiety

A small library of novel quinoline-3-carbaldehyde hydrazones (Series 1), acylhydrazones (Series 2), and arylsulfonylhydrazones (Series 3) bearing either a 1,2,4-triazole or benzotriazole ring at position 2 was prepared, characterized by elemental analyses and IR, NMR, and MS spectra, and then subjected to in vitro cytotoxicity studies on three human tumor cell lines: DAN-G, LCLC-103H, and SISO. In general, compounds 4, 6, and 8 substituted with a 1,2,4-triazole ring proved to be inactive, whereas the benzotriazole-containing quinolines 5, 7, and 9 elicited pronounced cancer cell growth inhibitory effects with IC50 values in the range of 1.23⁻7.39 µM. The most potent 2-(1H-benzotriazol-1-yl)-3-[2-(pyridin-2-yl)hydrazonomethyl]quinoline (5e) showed a cytostatic effect on the cancer cell lines, whereas N′-[(2-(1H-benzotriazol-1-yl)quinolin-3-yl)methylene]-benzohydrazide (7a) and N′-[(2-1H-benzotriazol-1-yl)quinolin-3-yl)methylene]-naphthalene-2-sulfonohydrazide (9h) exhibited selective activity against the pancreas cancer DAN-G and cervical cancer SISO cell lines. Based on the determined IC50 values, the compound 5e seems to be leading compound for further development as anticancer agent.

Development of a Focused Library of Triazole-Linked Privileged-Structure-Based Conjugates Leading to the Discovery of Novel Phenotypic Hits against Protozoan Parasitic Infections

Protozoan infections caused by Plasmodium, Leishmania, and Trypanosoma spp. contribute significantly to the burden of infectious diseases worldwide, causing severe morbidity and mortality. The inadequacy of available treatments calls for cost- and time-effective drug discovery endeavors. To this end, we envisaged the triazole linkage of privileged structures as an effective drug design strategy to generate a focused library of high-quality compounds. The versatility of this approach was combined with the feasibility of a phenotypic assay, integrated with early ADME-tox profiling. Thus, an 18-membered library was efficiently assembled via Huisgen cycloaddition of phenothiazine, biphenyl, and phenylpiperazine scaffolds. The resulting 18 compounds were then tested against seven parasite strains, and counter-screened for selectivity against two mammalian cell lines. In parallel, hERG and cytochrome P450 (CYP) inhibition, and mitochondrial toxicity were assessed. Remarkably, 10-((1-(3-([1,1'-biphenyl]-3-yloxy)propyl)-1H-1,2,3-triazol-5-yl)methyl)-10H-phenothiazine (7) and 10-(3-(1-(3-([1,1'-biphenyl]-3-yloxy)propyl)-1H-1,2,3-triazol-4-yl)propyl)-10H-phenothiazine (12) showed respective IC₅₀ values of 1.8 and 1.9 μg mL^-1 against T. cruzi, together with optimal selectivity. In particular, compound 7 showed a promising ADME-tox profile. Thus, hit 7 might be progressed as an antichagasic lead.

Base-Controlled Regioselective Functionalization of Chloro-Substituted Quinolines

We prepared a number of di- and trifunctionalized quinolines by selective metalation of chloro-substituted quinolines with metal amides followed by reaction with different electrophiles. Metalation of the C-3 position of the quinolinic ring with lithium diisopropylamide at -70 °C is easy to achieve, whereas reaction with lithium-magnesium and lithium-zinc amides affords C-2 or C-8 functionalized derivatives in a regioselective fashion. These complementary methods could be rationalized by DFT calculations and are convenient strategies toward the synthesis of bioactive quinoline derivatives such as chloroquine analogues.

Synthesis of thieno[2,3-c]acridine and furo[2,3-c]acridine derivatives via an iodocyclization reaction and their fluorescence properties and DFT mechanistic studies

In this paper, we report the novel synthesis of thieno[2,3-c]acridine and furo[2,3-c]acridine derivatives via intramolecular iodocyclization reaction. The thieno[2,3-c]acridine derivatives exhibited blue fluorescence in hexane.

Preparation of pyrrolizinone derivatives via sequential transformations of cyclic allyl imides: synthesis of quinolactacide and marinamide

A facile synthetic route toward the preparation of pyrrolizinone derivatives has been developed and applied for the synthesis of quinolactacide/marinamide.

Antiparasitic Lead Discovery: Toward Optimization of a Chemotype with Activity Against Multiple Protozoan Parasites

Human African trypanosomiasis (HAT), Chagas disease, and leishmaniasis present a significant burden across the developing world. Existing therapeutics for these protozoal neglected tropical diseases suffer from severe side effects and toxicity. Previously, NEU-1045 (3) was identified as a promising lead with cross-pathogen activity, though it possessed poor physicochemical properties. We have designed a library of analogues with improved calculated physicochemical properties built on the quinoline scaffold of 3 incorporating small, polar aminoheterocycles in place of the 4-(3-fluorobenzyloxy)aniline substituent. We report the biological activity of these inhibitors against Trypanosoma brucei (HAT), T. cruzi (Chagas disease), and Leishmania major (cutaneous leishmaniasis) and describe the identification of N-(5-chloropyrimidin-2-yl)-6-(4-(morpholinosulfonyl)phenyl)quinolin-4-amine (13t) as a promising inhibitor of L. major proliferation and 6-(4-(morpholinosulfonyl)phenyl)-N-(pyrimidin-4-yl)quinolin-4-amine (13j), a potent inhibitor of T. brucei proliferation with improved drug-like properties.

Energy efficient Pfitzinger reaction: a novel strategy using a surfactant catalyst

A novel ultrasound assisted synthetic route catalysed by a surfactant for the synthesis of quinolone-4-carboxylic acid.

Synthesis and biological evaluation of novel N-arylidenequinoline-3-carbohydrazides as potent β-glucuronidase inhibitors

Thirty N-arylidenequinoline-3-carbohydrazides (1-30) have been synthesized and evaluated against β-glucuronidase inhibitory potential. Twenty four analogs showed outstanding β-glucuronidase activity having IC50 values ranging between 2.11±0.05 and 46.14±0.95 than standard d-saccharic acid 1,4 lactone (IC50=48.4±1.25μM). Six analogs showed good β-glucuronidase activity having IC50 values ranging between 49.38±0.90 and 80.10±1.80. Structure activity relationship and the interaction of the active compounds and enzyme active site with the help of docking studies were established. Our study identifies novel series of potent β-glucuronidase inhibitors for further investigation.

A convenient approach to an advanced intermediate toward the naturally occurring, bioactive 6-substituted 5-hydroxy-4-aryl-1H-quinolin-2-ones

An advanced intermediate for the total synthesis of the 5-hydroxy-4-aryl-3,4-dihydro-1H-quinolin-2-one natural products and a 3,4-bisdesoxy analog of peniprequinolone were synthesized.

Rational approach to an antiprion compound with a multiple mechanism of action

Background: The main pathogenic event of prion disorders has been identified in the deposition of the disease-associated prion protein (PrPSc), which is accompanied by metal dyshomeostasis. Results: The multitarget-directed ligand 1, designed by combining a heteroaromatic prion recognition motif to an 8-hydroxyquinoline metal chelator, has been developed as a potential antiprion disease-modifying agent. Importantly, 1 was found to effectively clear PrPSc from scrapie-infected cells, and, at the same time, inhibit metal-induced prion aggregation and reactive oxygen species generation. 1 was also characterized in terms of pharmacokinetic properties in a preliminary in vitro investigation. Conclusion: Compound 1 has emerged as a suitable lead candidate against prion diseases and as a good starting point for a further optimization process.

Approaches for discovering anti-prion compounds: lessons learned and challenges ahead

INTRODUCTION

Recent years have witnessed major advances in our understanding of the molecular bases of prion diseases. These studies not only highlight the protein misfolding as a potential initiator of a neurodegenerative process, they also provide a foundation for considering whether such a process can be common to many neurodegenerative diseases, including Alzheimer's disease. This makes prion diseases a sort of prototype of neurodegenerative disease, endowed with some intrinsic positive features in terms of drug development. Thanks to the fact that disappearance of the scrapie protein can serve as a clear readout of drug efficiency, phenotypic approaches have high potential for prion disease drug discovery.

AREAS COVERED

In this review, the authors discuss phenotypic screening and how it lends itself to drug repositioning. Furthermore, they discuss the advantages of working with a molecule with proven safety, tolerability and drug-like properties in combination with a reliable phenotypic screening and how it could improve the success rate for prion drug development. They also provide examples of several interesting candidates that have been identified using this approach, including quinacrine, astemizole, guanabenz and doxycycline.

EXPERT OPINION

The availability of persistently scrapie-infected murine neuroblastoma cells has greatly helped to identify compounds that inhibit prion formation. However, a human neuronal model infected with the human isoform would ultimately serve as the ideal disease model toward the discovery of effective drugs.

Metal-free domino one-pot protocols for quinoline synthesis

Metal-free domino one-pot protocols for quinoline synthesis have been reviewed.

Synthesis of functionalized 3-, 5-, 6- and 8-aminoquinolines via intermediate (3-pyrrolin-1-yl)- and (2-oxopyrrolidin-1-yl)quinolines and evaluation of their antiplasmodial and antifungal activity

(3-Pyrrolin-1-yl)- and (2-oxopyrrolidin-1-yl)quinolines were prepared via cyclization of diallylaminoquinolines and 4-chloro-N-quinolinylbutanamides, respectively, as novel synthetic intermediates en route to N-functionalized 3-, 5-, 6- and 8-aminoquinolines with potential biological activity. (3-Pyrrolin-1-yl)quinolines were subjected to bromination reactions, and the reactivity of (2-oxopyrrolidin-1-yl)quinolines toward lithium aluminum hydride and methyllithium was assessed, providing an entry into a broad range of novel functionalized (pyrrolidin-1-yl)- and (hydroxyalkylamino)quinolines. Antiplasmodial evaluation of these novel quinolines and their functionalized derivatives revealed moderate micromolar potency against a chloroquine-sensitive strain of the malaria parasite Plasmodium falciparum, and the two most potent compounds also showed micromolar activity against a chloroquine-resistant strain of P. falciparum. Antifungal assessment of (hydroxyalkylamino)quinolines revealed three compounds with promising MIC values against Rhodotorula bogoriensis and one compound with potent activity against Aspergillus flavus.