Conventional and Microwave-Assisted Synthesis, Antitubercular Activity, and Molecular Docking Studies of Pyrazole and Oxadiazole Hybrids

Microwave-assisted protocol towards synthesis of heterocyclic molecules: a comparative analysis with conventional synthetic methodologies (years 2019-2023): a review

Microwave-assisted protocols have become extensively accepted across various scientific and technological domains because of their numerous advantages, shorter reaction times, higher yields, and often milder reaction conditions. In this review, we focus on the synthesis of N, O, and S-containing heterocyclic structural cores, crucial in the development of pharmaceuticals, agrochemicals, and materials science following through conventional and microwave method via eliminating the side products and enhances the product yield that is nowadays the biggest barrier for a synthetic chemist. The major findings emphasizes the substantial advantages of microwave-assisted techniques over conventional synthetic protocols. This comparative study underscores the potential of microwave-assisted techniques to revolutionize heterocyclic compound synthesis, providing insights into optimizing reaction conditions and expanding the scope of chemical synthesis in industrial applications.

In silico drug design strategies for discovering novel tuberculosis therapeutics

INTRODUCTION

Tuberculosis remains a significant concern in global public health due to its intricate biology and propensity for developing antibiotic resistance. Discovering new drugs is a protracted and expensive endeavor, often spanning over a decade and incurring costs in the billions. However, computer-aided drug design (CADD) has surfaced as a nimbler and more cost-effective alternative. CADD tools enable us to decipher the interactions between therapeutic targets and novel drugs, making them invaluable in the quest for new tuberculosis treatments.

AREAS COVERED

In this review, the authors explore recent advancements in tuberculosis drug discovery enabled by in silico tools. The main objectives of this review article are to highlight emerging drug candidates identified through in silico methods and to provide an update on the therapeutic targets associated with Mycobacterium tuberculosis.

EXPERT OPINION

These in silico methods have not only streamlined the drug discovery process but also opened up new horizons for finding novel drug candidates and repositioning existing ones. The continued advancements in these fields hold great promise for more efficient, ethical, and successful drug development in the future.

Novel Antitubercular Agents: Design, Synthesis, Molecular Dynamic and Biological Studies of Pyrazole - 1,2,4-Triazole Conjugates

Mycobacterium tuberculosis (Mtb) has numerous cell wall and non-cell wall mediated receptors for drug action, of which cell wall mediated targets were found to be more promising because of their pivotal role in bacterial protection and survival. Herein, we reported the design and synthesis of a series of pyrazole-linked triazoles based on the reported structural features of promising drug candidates that target DprE1 receptors through a Structure-based drug design (SBDD) approach (6a-6j and 7a-7j). The synthesized compounds were evaluated for their in-vitro antitubercular activity against virulent strains of Mtb H37Rv. In-silico studies revealed that most compounds exhibit binding interactions with crucial amino acids like Lys418, Tyr314, Tyr60, and Asp386 at DprE1. Furthermore, the protein-ligand (7j) shows appreciable stability compared to innate protein in a 100 ns molecular dynamic simulation study. In-vitro MAB assay revealed that 14 compounds exhibit significant antitubercular activity with minimum inhibitory concentration (MIC) of the 3.15-4.87 μM of the 20 compounds tested. An in-vitro cytotoxicity study on normal cell lines (MCF10) revealed safe compounds (IC50 values:341.85 to 726.08 μM). Hence, the present study opens the development of new pyrazole-linked triazoles as probable DprE1 inhibitors.

Synthesis, Antifungal Ergosterol Inhibition, Antibiofilm Activities, and Molecular Docking on β-Tubulin and Sterol 14-Alpha Demethylase along with DFT-Based Quantum Mechanical Calculation of Pyrazole Containing Fused Pyridine-Pyrimidine Derivatives

Multidrug-resistant fungal infections have become much more common in recent years, especially in immune-compromised patients. Therefore, researchers and pharmaceutical professionals have focused on the development of novel antifungal agents that can tackle the problem of resistance. In continuation to this, a novel series of pyrazole-bearing pyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione derivatives (4a-4o) have been developed. These compounds have been screened against Candida albicans, Aspergillus niger, and Aspergillus clavatus. The synthesized compounds were characterized by well-known spectroscopic techniques, i.e., IR, 1H NMR, 13C NMR, and mass spectrometry. In vitro antifungal results revealed that compound 4n showed activity against C. albicans having MIC value of 200 μg/mL. To know the plausible mode of action, the active derivatives were screened for anti-biofilm and ergosterol biosynthesis inhibition activities. The compounds 4h, 4j, 4k, and 4n showed greater ergosterol biosynthesis inhibition than the control DMSO. To comprehend how molecules interact with the receptor, studies of molecular docking of 4k and 4n have been performed on the homology-modeled protein of β-tubulin. The molecular docking revealed that the active compounds 4h, 4j, 4k, 4l, and 4n interacting with the active site amino acid of sterol 14-alpha demethylase (PDB ID: 5v5z) indicate one of the possible modes of action of ergosterol inhibition activity. The synthesized compounds 4c, 4e, 4h, 4i, 4j, 4k, 4l, and 4n inhibited biofilm formation and possessed the potential for anti-biofilm activity. DFT-based quantum mechanical calculations were carried out to optimize, predict, and compare the vibration modes of the molecule 4a.

Design, synthesis, antimicrobial activity, DFT, and molecular docking studies of pyridine-pyrazole-based dihydro-1,3,4-oxadiazoles against various bacterial and fungal targets

Antimicrobial resistance which is increasing at an alarming rate is a severe public health issue worldwide. Hence, the development of novel antibiotics is an urgent need as microbes have developed resistance against available antibiotics. In search of novel antimicrobial agents, a convenient route for the preparation of substituted 3-(1-phenyl-3-(p-tolyl)-1H-pyrazol-4-yl)-1-(2-phenyl-5-(pyridin-3-yl)-1,3,4-oxadiazol-3(2H)-yl)prop-2-en-1-ones (6a-6o) has been adopted by using pyridine-3-carbohydrazide and various aromatic aldehydes. The newly synthesized compounds were characterized by using various spectral techniques, for example, IR, 1 H NMR, 13 C NMR, and mass spectroscopy. Synthesized hybrids were studied for in vitro antimicrobial potency against various bacterial and fungal strains. Antibacterial results revealed that compounds 6e, 6h, 6i, 6l, and 6m were found to be most active against bacterial strains as they showed minimum inhibitory concentration (MIC) value of 62.5 μg/mL while compounds 6d, 6e, and 6h showed MIC value of 200 μg/mL against Candida albicans. The quantum parameters that relate to the bioavailability of the compounds were computed, followed by docking with different bacterial and fungal targets like sortase A, dihydrofolate reductase, thymidylate kinase, gyrase B, sterol 14-alpha demethylase. The experimental and computational results are in good agreement.

Synthesis, Characterization, Antitubercular Activity, and Molecular Docking Studies of Pyrazolylpyrazoline-Clubbed Triazole and Tetrazole Hybrids

To increase the antitubercular potency, we synthesized a series of novel pyrazolylpyrazoline derivatives (9a-p) using the one-pot multicomponent reaction of the substituted heteroaryl aldehyde (3a,b), 2-acetyl pyrrole/thiazole (4a,b), and substituted hydrazine hydrates (5-8) in the presence of base NaOH as a catalyst in ethanol as the solvent at room temperature. Substituted heteroaryl aldehyde (3a,b) was synthesized from 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-methyl-carbaldehyde on protection with ethylene glycol followed by treatment with 4-amino triazole/5-amino tetrazole and then deprotection using acid. The salient features of the green protocol are the one-pot reaction, shorter reaction time, and straightforward workup procedure. All of the compounds were tested against Mycobacterium tuberculosis H₃₇Rv, wherein compounds 9i, 9k, 9l, 9o, and 9p were found to be most effective. The structures of newly synthesized compounds were determined using spectral methods. Furthermore, molecular docking investigations into the active site of mycobacterial InhA yielded well-clustered solutions for these compounds' binding modalities producing a binding affinity in the range from -8.884 to -7.113. Theoretical results were in good accord with the observed experimental values. The docking score of the most active compound 9o was found to be -8.884, and the Glide energy was -61.144 kcal/mol. and it was found to accommodate well into the active site of InhA, engaging in a network of bonded and nonbonded interactions.

Oxadiazole: A highly versatile scaffold in drug discovery

As a pharmacologically important heterocycle, oxadiazole paved the way to combat the problem associated with the confluence of many commercially available drugs with different pharmacological profiles. The present review focuses on the potential applications of five-membered heterocyclic oxadiazole derivatives, especially 1,2,4-oxadiazole, 1,2,5-oxadiazole, and 1,3,4-oxadiazole, as therapeutic agents. Designing new hybrid molecules containing the oxadiazole moiety is a better solution for the development of new drug molecules. The designed molecules may accumulate a biological profile better than those of the drugs currently available on the market. The present review will guide the way for researchers in the field of medicinal chemistry to design new biologically active molecules based on the oxadiazole nucleus. Antitubercular, antimalarial, anti-inflammatory, anti-HIV, antibacterial, and anticancer activities of various oxadiazoles have been reviewed extensively here.

A Review of the Recent Development in the Synthesis and Biological Evaluations of Pyrazole Derivatives

Pyrazoles are five-membered heterocyclic compounds that contain nitrogen. They are an important class of compounds for drug development; thus, they have attracted much attention. In the meantime, pyrazole derivatives have been synthesized as target structures and have demonstrated numerous biological activities such as antituberculosis, antimicrobial, antifungal, and anti-inflammatory. This review summarizes the results of published research on pyrazole derivatives synthesis and biological activities. The published research works on pyrazole derivatives synthesis and biological activities between January 2018 and December 2021 were retrieved from the Scopus database and reviewed accordingly.

Microwave-assisted organic synthesis, antimycobacterial activity, structure-activity relationship and molecular docking studies of some novel indole-oxadiazole hybrids

Multidrug-resistant tuberculosis (MDR-TB) is a severe threat to mankind because most drugs are ineffective in inhibiting tubercular strains. Due to the increase of MDR-TB, many first and second-line drugs are ineffective against tubercular strains. To combat the resistance of currently accessible drugs, structural changes must be made on a regular basis. Thus, in the search for new antimycobacterial drugs, a series of 1-(2-(1H-indol-3-yl)-5-phenyl-1,3,4-oxadiazol-3(2H)-yl)-3-phenylprop-2-en-1-ones (5a-o) have been developed, synthesized, characterized, and screened for antimycobacterial activity. The synthetic approach includes imine generation and cyclization using both conventional and microwave methods to create hybrid molecules with indole and oxadiazole motifs. The set of synthesized compounds have demonstrated some promising activity against tubercular strains of Mycobacterium tuberculosis (ATCC 25177) and M. bovis (ATCC 35734). Compound 5l inhibited M. bovis strain 100% in 10 µg/mL concentration, while compound 5m inhibited M. tuberculosis strain 90.4% in 30 µg/mL concentration. Molecular docking study against mycobacterial enoyl reductase (InhA) could provide well-clustered solutions to the binding modes and affinity for these molecules as compound 5l showed glide score of -12.275 and glide energy of -54.937 kcal/mol.