Greener synthesis of indolizine analogues using water as a base and solvent: study for larvicidal activity against Anopheles arabiensis

Design, synthesis and characterization of ethyl 3-benzoyl-7-morpholinoindolizine-1-carboxylate as anti-tubercular agents: In silico screening for possible target identification

A thorough search for the development of innovative drugs to treat tuberculosis, especially considering the urgent need to address developing drug resistance, we report here a synthetic series of ethyl 3-benzoyl-7-morpholinoindolizine-1-carboxylate analogues (5a-o) as potent anti-tubercular agents. These morpholino-indolizines were synthesized by reacting 4-morpholino pyridinium salts, with various electron-deficient acetylenes to afford the ethyl 3-benzoyl-7-morpholinoindolizine-1-carboxylate analogues (5a-o). All synthesized intermediate and final compounds are characterized by spectroscopic methods such as 1H NMR, 13C NMR and HRMS and further examined for their anti-tubercular activity against the M. tuberculosis H37Rv strain (ATCC 27294-American type cell culture). All the compounds screened for anti-tubercular activity in the range of 6.25-50 μM against the H37Rv strain of Mycobacterium tuberculosis. Compound 5g showed prominent activity with MIC99 2.55 μg/mL whereas compounds 5d and 5j showed activity with MIC99 18.91 μg/mL and 25.07 μg/mL, respectively. In silico analysis of these compounds revealed drug-likeness. Additionally, the molecular target identification for Malate synthase (PDB 5CBB) is attained by computational approach. The compound 5g with a MIC99 value of 2.55 μg/mL against M. tuberculosis H37Rv emerged as the most promising anti-TB drug and in silico investigations suggest Malate synthase (5CBB) might be the compound's possible target.

Synthesis, characterization and larvicidal studies of ethyl 3-benzoyl-7-(piperidin-1-yl)indolizine-1-carboxylate analogues against Anopheles arabiensis and cheminformatics approaches

According to WHO, in 2021, there was an estimation of 247 million malaria cases from 84 malaria-endemic countries. Globally an estimated count of 2 billion malaria cases and 11.7 million deaths due to malaria were recorded in the past two decades. Further, the emergence of drug-resistant mosquitos threatens mankind. Therefore, the development of newer larvicidal agents is the need of the hour. This research identifies a new series of variably substituted indolizines for their effectiveness in controlling Anopheles arabiensis larvae through larvicidal activity. The series of Ethyl 3-benzoyl-7-(piperidin-1-yl)indolizine-1-carboxylate analogues (4a-j) were synthesized by reacting 4-(piperidin-1-yl)pyridine, phenacyl bromides with ethyl propiolate via 1, 3-dipolar cycloaddition and the green metrics of the process are reported. All the newly synthesized compounds were characterized by spectroscopic techniques such as 1H NMR,13C NMR, FT-IR, and HRMS. The larvicidal effectiveness of the newly synthesized compounds was assessed against Anopheles arabiensis. Among the compounds studied, namely 4c, 4d, 4e, and 4f, displayed the most notable larval mortality rates within the series, reaching 73%, 81%, 76%, and 71% respectively, in contrast with the negative control acetone. In comparison, the standard Temephos exhibited a mortality rate of 99% at the same concentration. Furthermore, computational approaches including molecular docking and molecular dynamics simulations identified the potential targets of the series compounds as the larval Acetylcholinesterase (AChE) enzyme and the Sterol Carrier Protein-2 (SCP-2) protein. However, it is essential for these computational predictions to undergo experimental validation.Communicated by Ramaswamy H. Sarma.

1,2,3-Triazolyl-tetrahydropyrimidine Conjugates as Potential Sterol Carrier Protein-2 Inhibitors: Larvicidal Activity against the Malaria Vector Anopheles arabiensis and In Silico Molecular Docking Study

Alteration of insect growth regulators by the action of inhibitors is becoming an attractive strategy to combat disease-transmitting insects. In the present study, we investigated the larvicidal effect of 1,2,3-triazolyl-pyrimidinone derivatives against the larvae of the mosquito Anopheles arabiensis, a vector of malaria. All compounds demonstrated insecticidal activity against mosquito larvae in a dose-dependent fashion. A preliminary study of the structure-activity relationship indicated that the electron-withdrawing substituent in the para position of the 4-phenyl-pyrimidinone moiety enhanced the molecules' potency. A docking study of these derivatives revealed favorable binding affinity for the sterol carrier protein-2 receptor, a protein present in the intestine of the mosquito larvae. Being effective insecticides against the malaria-transmitting Anopheles arabiensis, 1,2,3-triazole-based pyrimidinones represent a starting point to develop novel inhibitors of insect growth regulators.

Acetic Acid-Catalyzed Regioselective C(sp2)-H Bond Functionalization of Indolizines: Concomitant Involvement of Synthetic and Theoretical Studies

An atom economical and environmentally benign protocol has been developed for the regioselective C(sp²)-H bond functionalization of indolizines. The acetic acid-catalyzed cross-coupling reaction proceeds under metal-free conditions, producing a wide range of synthetically useful indolizine derivatives. The present protocol showed good functional group tolerance and broad substrate scope in good to excellent yields. Quantum mechanical investigation using density functional theory (DFT) has played a crucial role in understanding that acetic acid is the key player in determining the actual pathway as the catalyst and its ultrafast nature. Different pathways involving inter- and intramolecular proton transfer, with or without acetic acid, were investigated. Calculated results revealed that a proton shuttle mechanism is involved for the least energetic, most favorable acetic acid-catalyzed pathway. Furthermore, regioselectivity has also been explained theoretically.

4-Aryl-1,4-Dihydropyridines as Potential Enoyl-Acyl Carrier Protein Reductase Inhibitors: Antitubercular Activity and Molecular Docking Study

BACKGROUND

Tuberculosis remains one of the most deadly infectious diseases worldwide due to the emergence of multi-drug resistance (MDR) and extensively drug resistance (XDR) strains of Mycobacterium tuberculosis (MTB).

AIMS

Currently, available drugs are getting resistant and toxic. Hence, there is an urgent need for the development of potent molecules to treat tuberculosis.

MATERIALS AND METHODS

Herein, the screening of a total of eight symmetrical 1,4-dihydropyridine (1,4- DHP) derivatives (4a-4h) was carried out for whole-cell anti-TB activity against the susceptible H37Rv and MDR strains of MTB.

RESULTS AND DISCUSSION

Most of the compounds exhibited moderate to excellent activity against the susceptible H37Rv. Moreover, the most promising compound 4f (against H37Rv) having paratrifluoromethyl phenyl group at 4-position and bis para-methoxy benzyl ester group at 3- and 5- positions of 1,4-dihydropyridine pharmacophore, exhibited no toxicity, but demonstrated weak activity against MTB strains resistant to isoniazid and rifampicin. In light of the inhibitory profile of the title compounds, enoyl-acyl carrier protein reductase (InhA) appeared to be the appropriate molecular target. A docking study of these derivatives against InhA receptor revealed favorable binding interactions. Further, in silico predicted ADME properties of these compounds 4a-4h were found to be in the acceptable ranges, including satisfactory Lipinski's rule of five, thereby indicating their potential as drug-like molecules.

CONCLUSION

In particular, the 1,4-DHP derivative 4f can be considered an attractive lead molecule for further exploration and development of more potent anti-TB agents as InhA inhibitors.

Anti-tubercular activity and molecular docking studies of indolizine derivatives targeting mycobacterial InhA enzyme

A series of 1,2,3-trisubstituted indolizines (2a-2f, 3a-3d, and 4a-4c) were screened for in vitro whole-cell anti-tubercular activity against the susceptible H37Rv and multidrug-resistant (MDR) Mycobacterium tuberculosis (MTB) strains. Compounds 2b-2d, 3a-3d, and 4a-4c were active against the H37Rv-MTB strain with minimum inhibitory concentration (MIC) ranging from 4 to 32 µg/mL, whereas the indolizines 4a-4c, with ethyl ester group at the 4-position of the benzoyl ring also exhibited anti-MDR-MTB activity (MIC = 16-64 µg/mL). In silico docking study revealed the enoyl-acyl carrier protein reductase (InhA) and anthranilate phosphoribosyltransferase as potential molecular targets for the indolizines. The X-ray diffraction analysis of the compound 4b was also carried out. Further, a safety study (in silico and in vitro) demonstrated no toxicity for these compounds. Thus, the indolizines warrant further development and may represent a novel promising class of InhA inhibitors and multi-targeting agents to combat drug-sensitive and drug-resistant MTB strains.

Crystallography, Molecular Modeling, and COX-2 Inhibition Studies on Indolizine Derivatives

The cyclooxygenase-2 (COX-2) enzyme is an important target for drug discovery and development of novel anti-inflammatory agents. Selective COX-2 inhibitors have the advantage of reduced side-effects, which result from COX-1 inhibition that is usually observed with nonselective COX inhibitors. In this study, the design and synthesis of a new series of 7-methoxy indolizines as bioisostere indomethacin analogues (5a-e) were carried out and evaluated for COX-2 enzyme inhibition. All the compounds showed activity in micromolar ranges, and the compound diethyl 3-(4-cyanobenzoyl)-7-methoxyindolizine-1,2-dicarboxylate (5a) emerged as a promising COX-2 inhibitor with an IC₅₀ of 5.84 µM, as compared to indomethacin (IC₅₀ = 6.84 µM). The molecular modeling study of indolizines indicated that hydrophobic interactions were the major contribution to COX-2 inhibition. The title compound diethyl 3-(4-bromobenzoyl)-7-methoxyindolizine-1,2-dicarboxylate (5c) was subjected for single-crystal X-ray studies, Hirshfeld surface analysis, and energy framework calculations. The X-ray diffraction analysis showed that the molecule (5c) crystallizes in the monoclinic crystal system with space group P 2₁/n with a = 12.0497(6)Å, b = 17.8324(10)Å, c = 19.6052(11)Å, α = 90.000°, β = 100.372(1)°, γ = 90.000°, and V = 4143.8(4)ų. In addition, with the help of Crystal Explorer software program using the B3LYP/6-31G(d, p) basis set, the theoretical calculation of the interaction and graphical representation of energy value was measured in the form of the energy framework in terms of coulombic, dispersion, and total energy.

Investigation of Antifungal Properties of Synthetic Dimethyl-4-Bromo-1-(Substituted Benzoyl) Pyrrolo[1,2-a] Quinoline-2,3-Dicarboxylates Analogues: Molecular Docking Studies and Conceptual DFT-Based Chemical Reactivity Descriptors and Pharmacokinetics Evaluation

Candida albicans, an opportunistic fungal pathogen, frequently colonizes immune-compromised patients and causes mild to severe systemic reactions. Only few antifungal drugs are currently in use for therapeutic treatment. However, evolution of a drug-resistant C. albicans fungal pathogen is of major concern in the treatment of patients, hence the clinical need for novel drug design and development. In this study, in vitro screening of novel putative pyrrolo[1,2-a]quinoline derivatives as the lead drug targets and in silico prediction of the binding potential of these lead molecules against C. albicans pathogenic proteins, such as secreted aspartic protease 3 (SAP3; 2H6T), surface protein β-glucanase (3N9K) and sterol 14-alpha demethylase (5TZ1), were carried out by molecular docking analyses. Further, biological activity-based QSAR and theoretical pharmacokinetic analysis were analyzed. Here, in vitro screening of novel analogue derivatives as drug targets against C. albicans showed inhibitory potential in the concentration of 0.4 µg for BQ-06, 07 and 08, 0.8 µg for BQ-01, 03, and 05, 1.6 µg for BQ-04 and 12.5 µg for BQ-02 in comparison to the standard antifungal drug fluconazole in the concentration of 30 µg. Further, in silico analysis of BQ-01, 03, 05 and 07 analogues docked on chimeric 2H6T, 3N9K and 5TZ1 revealed that these analogues show potential binding affinity, which is different from the therapeutic antifungal drug fluconazole. In addition, these molecules possess good drug-like properties based on the determination of conceptual Density Functional Theory (DFT)-based descriptors, QSAR and pharmacokinetics. Thus, the study offers significant insight into employing pyrrolo[1,2-a]quinoline analogues as novel antifungal agents against C. albicans that warrants further investigation.

Inhibitory activities of indolizine derivatives: a patent review

INTRODUCTION

Indolizines are structural isomers with indoles. Although several indole-based commercial drugs are available in the market, none of the indolizine-based drugs are available up-to-date. Natural and synthetic indolizines have a wide-range of pharmaceutical importance such as antitumor, antimycobacterial, antagonist, and antiproliferative activities. This prompted us to search and collect all possible data about the pharmacological importance of indolizine to open an avenue to the researchers in exploring more medicinal applications of such biologically important compounds.

AREAS COVERED

The current review article covers the advancements in the biological and pharmacological activities of indolizine-based compounds during the last decade. The covered areas of this work involved anticancer, anti-HIV-1, anti-inflammatory, antimicrobial, anti-tubercular, larvicidal, anti-schizophrenia, CRTh2 antagonist's activities in addition to enzymatic inhibitory activity.

EXPERT OPINION

The discovery of indolizine drugs will be a major breakthrough as compared with their widely available drug-containing indole isosteres. Major work collected here was focused on anticancer, anti-tubercular, anti-inflammatory, and enzymatic inhibitory activities. The SAR study of the reported biologically active indolizines is summarized throughout the review whenever highlighted to the rationale the behavior of inhibitory action. Several indolizines with certain functions provided great enhancement in the therapeutic activities comparing with reference drugs.

Structural investigation of methyl 3-(4-fluoro-benzo-yl)-7-methyl-2-phenyl-indolizine-1-carboxyl-ate, an inhibitory drug towards Mycobacterium tuberculosis

The title compound, C24H18FNO3, crystallizes in the monoclinic centrosymmetric space group P21/n and its mol-ecular conformation is stabilized via C-H⋯O intra-molecular inter-actions. The supra-molecular network mainly comprises C-H⋯O, C-H⋯F and C-H⋯π inter-actions, which contribute towards the formation of the crystal structure. The different inter-molecular inter-actions have been further analysed via Hirshfeld surface analysis and fingerprint plots.

Larvicidal Activities of 2-Aryl-2,3-Dihydroquinazolin -4-ones against Malaria Vector Anopheles arabiensis, In Silico ADMET Prediction and Molecular Target Investigation

Malaria, affecting all continents, remains one of the life-threatening diseases introduced by parasites that are transmitted to humans through the bites of infected Anopheles mosquitoes. Although insecticides are currently used to reduce malaria transmission, their safety concern for living systems, as well as the environment, is a growing problem. Therefore, the discovery of novel, less toxic, and environmentally safe molecules to effectively combat the control of these vectors is in high demand. In order to identify new potential larvicidal agents, a series of 2-aryl-1,2-dihydroquinazolin-4-one derivatives were synthesized and evaluated for their larvicidal activity against Anopheles arabiensis. The in silico absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties of the compounds were also investigated and most of the derivatives possessed a favorable ADMET profile. Computational modeling studies of the title compounds demonstrated a favorable binding interaction against the acetylcholinesterase enzyme molecular target. Thus, 2-aryl-1,2-dihydroquinazolin-4-ones were identified as a novel class of Anopheles arabiensis insecticides which can be used as lead molecules for the further development of more potent and safer larvicidal agents for treating malaria.

Anti-Tubercular Activity of Substituted 7-Methyl and 7-Formylindolizines and In Silico Study for Prospective Molecular Target Identification

Novel series of diversely substituted indolizines were designed, synthesized, and evaluated for their in vitro anti-mycobacterial activity against H37Rv and multi-drug-resistant (MDR) strains of Mycobacterium tuberculosis (MTB). Many compounds exhibited significant inhibitory activity against MTB H37Rv strains. Indolizines 2d, 2e, and 4 were also found to be active against MTB clinical isolates with multi-resistance to rifampicin and isoniazid. Indolizine 4 was identified as the most promising anti-mycobacterial agent, displaying minimum inhibitory concentration (MIC) values of 4 and 32 μg/mL against H37Rv and MDR strains, respectively. Furthermore, an in silico study was carried out for prospective molecular target identification and revealed favorable interactions with the target enzymes CYP 121, malate synthase, and DNA GyrB ATPase. None of the potent molecules presented toxicity against peripheral blood mononuclear (PBM) cell lines, demonstrating their potentiality to be used for drug-sensitive and drug-resistant tuberculosis therapy.

Design, synthesis, and structural elucidation of novel NmeNANAS inhibitors for the treatment of meningococcal infection

Neisseria meningitidis is the primary cause of bacterial meningitis in many parts of the world, with considerable mortality rates among neonates and adults. In Saudi Arabia, serious outbreaks of N. meningitidis affecting several hundreds of pilgrims attending Hajj in Makkah were recorded in the 2000–2001 season. Evidence shows increased rates of bacterial resistance to penicillin and other antimicrobial agents that are used in the treatment of the meningococcal disease. The host’s immune system becomes unable to recognize the polysialic acid capsule of the resistant N. meningitidis that mimics the mammalian cell surface. The biosynthetic pathways of sialic acid (i.e., N-acetylneuraminic acid [NANA]) in bacteria, however, are somewhat different from those in mammals. The largest obstacle facing previously identified inhibitors of NANA synthase (NANAS) in N. meningitidis is that these inhibitors feature undesired chemical and pharmacological characteristics. To better comprehend the binding mechanism underlying these inhibitors at the catalytic site of NANAS, we performed molecular modeling studies to uncover essential structural aspects for the ultimate recognition at the catalytic site required for optimal inhibitory activity. Applying two virtual screening candidate molecules and one designed molecule showed promising structural scaffolds. Here, we report ethyl 3-benzoyl-2,7-dimethyl indolizine-1-carboxylate (INLZ) as a novel molecule with high energetic fitness scores at the catalytic site of the NmeNANAS enzyme. INLZ represents a promising scaffold for NmeNANAS enzyme inhibitors, with new prospects for further structural development and activity optimization.

Computational, crystallographic studies, cytotoxicity and anti-tubercular activity of substituted 7-methoxy-indolizine analogues

Indolizines are heteroaromatic compounds, and their synthetic analogues have reportedly showed promising pharmacological properties. In this study, a series of synthetic 7-methoxy-indolizine derivatives were synthesised, characterised and evaluated for in vitro whole-cell anti-tuberculosis (TB) screening against susceptible (H37Rv) and multi-drug-resistant (MDR) strains of Mycobacterium tuberculosis (MTB) using the resazurin microplate assay method. The cytotoxicity was evaluated using the MTT assay. In silico molecular-docking study was conducted for compounds 5a-j against enoyl-[acyl-carrier] protein reductase, a key enzyme of the type II fatty acid synthesis that has attracted much interest for the development of novel anti-TB compounds. Thereafter, molecular dynamic (MD) simulation was undertaken for the most active inhibitors. Compounds 5i and 5j with the methoxy functional group at the meta position of the benzoyl group, which was at the third position of the indolizine nucleus, demonstrated encouraging anti-TB activity against MDR strains of MTB at 16 μg/mL. In silico studies showed binding affinity within the range of 7.07-8.57 kcal/mol, with 5i showing the highest binding affinity. Hydrogen bonding, π-π- interactions, and electrostatic interactions were common with the active site. Most of these interactions occurred with the catalytic amino acids (Pro193, Tyr158, Phe149, and Lys165). MD simulation showed that 5j possessed the highest binding affinity toward the enzyme, according to the two calculation methods (MM/PBSA and MM/GBSA). The single-crystal X-ray studies of compounds 5c and 5d revealed that the molecular arrangements in these two structures were mostly guided by C-H···O hydrogen-bonded dimeric motifs and C-H···N hydrogen bonds, while various secondary interactions (such as π···π and C-H···F) also contributed to crystal formation. Compounds 5a, 5c, 5i, and 5j exhibited no toxicity up to 500 μg/mL. In conclusion, 5i and 5j are promising anti-TB compounds that have shown high affinity based on docking and MD simulation results.

Larvicidal study of tetrahydropyrimidine scaffolds against Anopheles arabiensis and structural insight by single crystal X-ray studies

A series of methyl or ethyl 4-(substitutedphenyl/pyridyl)-6-methyl-2-oxo/thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate (HPM) analogues 4a-g were synthesized and evaluated for larvicidal activity against Anopheles arabiensis. These newly synthesized compounds were characterized by spectral studies such as FT-IR, NMR (¹ H and ¹³ C), LC-MS, and elemental analysis. The conformational features and supramolecular assembly of molecules 4a, 4b, and 4e were further analyzed from single crystal X-ray study. The larvicidal activity of these tetrahydropyrimidine pharmacophore series was analyzed based on their relative substituents. Among the synthesized HPM analogous from the series, compounds 4d and 4e both having electron withdrawing chlorine group on phenyl ring at the fourth position of the tetrahydropyrimidine pharmacophore exhibited the most promising larvicidal activity.

Efficient synthesis and characterization of novel indolizines: exploration of in vitro COX-2 inhibitory activity and molecular modelling studies

Novel indolizine scaffolds as COX-2 inhibiting agents.

Molecular modeling studies and anti-TB activity of trisubstituted indolizine analogues; molecular docking and dynamic inputs

A series of trisubstituted indolizine analogues has been designed as a result of a fragment-based approach to target the inhibition of mycobacterial enoyl-acyl carrier protein reductase. Anti-tuberculosis (TB) screening of the characterized compounds by a resazurin microplate assay method revealed that ethyl group at second position of indolizine nucleus exhibited activity against susceptible and multidrug-resistant strains of Mycobacterium tuberculosis at concentration of 5.5 and 11.3 μg/mL, respectively. A molecular docking study was also conducted to evaluate the stability of the active compounds, and compound with ethyl substitution at second position of indolizine nucleus showed the highest free binding energy of ΔG -24.11 (kcal/mol), a low clash score of 3.04, and high lipo score of -13.33. Indolizine analog with ethyl substitution at second position demonstrated Molecular Mechanics/Generalized Born Surface Area (-23.85 kcal/mol). Two molecular dynamics studies were computed (100 ps and 50 ns) to calculate the relationship between the potential and kinetic energies of the active anti-TB compound with time and temperature. The discovery of this lead may have a positive impact on anti-TB drug discovery.

Synthesis and characterization of a novel series of 1,4-dihydropyridine analogues for larvicidal activity against Anopheles arabiensis

The new-fangled bis(4-substituted benzyl) 4-(4-substitued phenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate derivatives were synthesized by the union of substituted aryl aldehyde, tert-butyl acetoacetate, ammonium carbonate with 4-substituted benzyl alcohol via Hantzsch ester synthesis in aqueous medium under catalyst-free conditions. The newly synthesized compounds were characterized by spectroscopic techniques such as IR, NMR (¹ H and ¹³ C), ESI mass, elemental analysis, and single-crystal X-ray diffraction. The characterized title compounds were evaluated for the larvicidal activity against Anopheles arabiensis by standard WHO larvicidal assay method using Temephos as standard at 4 μg/ml. The title compounds bis(4-methoxybenzyl) 2,6-dimethyl-4-(4-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate and bis(4-chlorobenzyl) 2,6-dimethyl-4-(4-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate exhibited promising larvicidal activity at 65.6% and 72.2%, respectively, when compared with the standard compound at 98.9%.

Application of primary halogenated hydrocarbons for the synthesis of 3-aryl and 3-alkyl indolizines

A transition-metal-free synthetic route to 3-aryl and 3-alkyl indolizines from electron-deficient alkenes, pyridines and primary halogenated hydrocarbons is reported for the first time using a tandem reaction.