Synthesis and biological evaluation of some 4-(6-substituted-1,3-benzothiazol-2-yl)amino-1,3-thiazole-2-amines and their Schiff bases

Recent Advances on the Antimicrobial Activities of Schiff Bases and their Metal Complexes: An Updated Overview

Schiff bases represent a valuable class of organic compounds, synthesized via condensation of primary amines with ketones or aldehydes. They are renowned for possessing innumerable applications in agricultural chemistry, organic synthesis, chemical and biological sensing, coating, polymer and resin industries, catalysis, coordination chemistry, and drug designing. Schiff bases contain imine or azomethine (-C=N-) functional groups which are important pharmacophores for the design and synthesis of lead bioactive compounds. In medicinal chemistry, Schiff bases have attracted immense attention due to their diverse biological activities. This review aims to encompass the recent developments on the antimicrobial activities of Schiff bases. The article summarizes the antibacterial, antifungal, antiviral, antimalarial, and antileishmanial activities of Schiff bases reported since 2011.

Antimicrobial Activity of Novel Ni(II) and Zn(II) Complexes with (E)-2-((5-Bromothiazol-2-yl)imino)methyl)phenol Ligand: Synthesis, Characterization and Molecular Docking Studies

In order to address the challenges associated with antibiotic resistance by bacteria, two new complexes, Ni(II) and Zn(II), have been synthesized using the conventional method based on Schiff base ligand (E)-2-((5-bromothiazol-2-yl) imino) methyl) phenol. The Schiff base ligand (HL) was synthesized using salicylaldehyde and 5-(4-bromophenyl)thiazol-2-amine in both traditional and efficient, ecologically friendly, microwave-assisted procedures. The ligand and its complexes were evaluated by elemental analyses, FTIR spectroscopy, UV-Vis spectroscopy, nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA) and magnetic susceptibility. The ligand and its complexes were tested for antibacterial activity against three Gram-positive bacteria (Staphylococcus aureus ATCC 25923, Methicillin-resistant Staphylococcus aureus ATCC 43300 and Enterococcus faecalis ATCC 29212) and three Gram-negative bacteria (Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 25922 and Klebsiella pneumoniae ATCC 700603). The findings demonstrate the potent activity of the ligand and its complexes against selective bacteria but the Ni(II) complex with MIC values ranging from 1.95 to 7.81 µg/mL outperformed all other compounds, including the widely used antibiotic Streptomycin. Furthermore, the docking study provided evidence supporting the validity of the antimicrobial results, since the Ni complex showed superior binding affinity against to E. coli NAD synthetase, which had a docking score (-7.61 kcal/mol).

Network Analysis Guided Designing of Multi-Targeted Anti-Fungal Agents: Synthesis and Biological Evaluation

During the ongoing pandemic, there have been increasing reports of invasive fungal disease (IFD), particularly among immunocompromised populations. Candida albicans is one of the most common clinical pathogenic microorganisms which have become a serious health threat to population either infected with Covid-19 or on treatment with immunosuppressant's/broad-range antibiotics. Currently, benzothiazole is a well explored scaffold for anti-fungal activity, especially mercapto substituted benzothiazoles. It is reported that exploring the 2nd position of benzothiazoles yield improved anti-fungal molecules. Therefore, in the current study, lead optimization approach using bioisosteric replacement protocol was followed to improve the anti-fungal activity of an already reported benzothiazole derivative, N-(1,3-benzothiazole-2-yl)-2-(pyridine-3-ylformohydrazido) acetamide. To rationally identify the putative anti-candida targets of this derivative, network analysis was carried out. Complexes of designed compounds and identified putative targets were further analyzed for the docking interactions and their consequent retention after the completion of exhaustive MD simulations. Top seven designed compounds were synthesized and evaluated for in-vitro anti-fungal property against Candida, which indicated that compounds 1.2c and 1.2f possess improved and comparable anti-fungal activity to N-(1,3-benzothiazole-2-yl)-2-(pyridine-3-ylformohydrazido) acetamide and Nystatin, respectively.

Thiazole Ring-A Biologically Active Scaffold

BACKGROUND

Thiazole is a good pharmacophore nucleus due to its various pharmaceutical applications. Its derivatives have a wide range of biological activities such as antioxidant, analgesic, and antimicrobial including antibacterial, antifungal, antimalarial, anticancer, antiallergic, antihypertensive, anti-inflammatory, and antipsychotic. Indeed, the thiazole scaffold is contained in more than 18 FDA-approved drugs as well as in numerous experimental drugs.

OBJECTIVE

To summarize recent literature on the biological activities of thiazole ring-containing compounds Methods: A literature survey regarding the topics from the year 2015 up to now was carried out. Older publications were not included, since they were previously analyzed in available peer reviews.

RESULTS

Nearly 124 research articles were found, critically analyzed, and arranged regarding the synthesis and biological activities of thiazoles derivatives in the last 5 years.

Synthesis of biologically active derivatives of 2-aminobenzothiazole

The minireview considers the current trends in the synthesis of some biologically active compounds based on 2-aminobenzothiazole. The presented information covers publications of the last five years.

Modern Approaches to the Synthesis and Transformations of Practically Valuable Benzothiazole Derivatives

The review is devoted to modern trends in the chemistry of 2-amino and 2-mercapto substituted benzothiazoles covering the literature since 2015. The reviewed heterocycles belong to biologically active and industrially demanded compounds. Newly developed synthesis methods can be divided into conventional multistep processes and one-pot, atom economy procedures, realized using green chemistry principles and simple reagents. The easy functionalization of the 2-NH2 and 2-SH groups and the benzene ring of the benzothiazole moiety allows considering them as highly reactive building blocks for organic and organoelement synthesis, including the synthesis of pharmacologically active heterocycles. The review provides a summary of findings, which may be useful for developing new drugs and materials and new synthetic approaches and patterns of reactivity.

Synthesis and Biological Activity of Some Aminothiazole Derivatives as Antileishmanial Agents

Background:

Leishmaniasis is a major health problem which is caused by the protozoan parasite of the genus Leishmania. Cutaneous leishmaniasis is one type of leishmaniasis and selflimited in most of the cases. However, when the lesions come with scars, they make a deep lifelong stigma. Despite being WHO's research priority, the optimum treatment for this disease has not been found yet. The current study aimed to synthesize and assess the activity of some new aminothiazole compounds against Leishmania major-induced cutaneous leishmaniasis in BALB/c mice.

Methods:

Eight new aminothiazole derivatives were synthesized and their chemical structures were characterized by spectral data 1H-NMR spectroscopy, Mass spectrophotometry and elemental analysis. L. major parasites were inoculated into the tail base of BALB/c mice and the induced lesions were treated every other day with three different doses of the synthesized compounds against meglumine antimoniate as the drug reference for two weeks. Size of the lesions was observed for three weeks and the collected data were analyzed by SPSS software. Also, these compounds are docked into the active site of 14- α-demethylase as the targets in the treatment of leishmaniasis.

Results:

Among the synthesized aminothiazole derivatives, compounds 1, 2, 3, 4, and 7 had good leishmanicidal effects. Docking binding energies showed that the synthesized compounds could act as inhibitors for 14- α-demethylase.

Conclusions:

Among the synthesized compounds, compound 3, (N-((4-chlorophenyl)(phenyl) methyl)thiazol-2-amine) was the most promising one which deserves future studies for the treatment of leishmaniasis.

Synthesis and In Vitro Antibacterial Evaluation of Schiff Bases Derived FROM 2-Chloro-3-Quinolinecarboxaldehyde

Background: Design, identification, and synthesis of new antimicrobial agents along with preventive proceedings are essential to confront antibiotic-resistant pathogenic bacteria. Heterocyclic Schiff bases are biologically important compounds whose antimicrobial potentials have been proven to bacterial and fungal pathogens. Objectives: In this study, some quinoline Schiff bases were synthesized from condensation of 2-chloro3-quinolinecarboxaldehyde and aniline derivatives. Their inhibitory activities were evaluated against 6 gram-positive and 2 gram-negative bacterial pathogens. Methods: Disc diffusion, broth microdilution, and time-kill tests were applied according to the CLSI guidelines to determine IZD, MIC, and MBC values. Results: 2-Chloro-3-quinolinecarboxaldehyde Schiff bases could inhibit the growth of bacteria with IZDs of 7.5-19.8 mm, MICs of 256-2048 μg mL-1, and MBCs of 512 to ≥2048 μg mL-1. Conclusion: Moderate antibacterial effects were observed with heterocyclic Schiff bases. Complexation and structural changes can improve their antimicrobial properties.

Synthesis and Antidepressant Activity Profile of Some Novel Benzothiazole Derivatives

Within the scope of our new antidepressant drug development efforts, in this study, we synthesized eight novel benzothiazole derivatives 3a–3h. The chemical structures of the synthesized compounds were elucidated by spectroscopic methods. Test compounds were administered orally at a dose of 40 mg/kg to mice 24, 5 and 1 h before performing tail suspension, modified forced swimming, and activity cage tests. The obtained results showed that compounds 3c, 3d, 3f–3h reduced the immobility time of mice as assessed in the tail suspension test. Moreover, in the modified forced swimming tests, the same compounds significantly decreased the immobility, but increased the swimming frequencies of mice, without any alteration in the climbing frequencies. These results, similar to the results induced by the reference drug fluoxetine (20 mg/kg, po), indicated the antidepressant-like activities of the compounds 3c, 3d, 3f–3h. Owing to the fact that test compounds did not induce any significant alteration in the total number of spontaneous locomotor activities, the antidepressant-like effects of these derivatives seemed to be specific. In order to predict ADME parameters of the synthesized compounds 3a–3h, some physicochemical parameters were calculated. The ADME prediction study revealed that all synthesized compounds may possess good pharmacokinetic profiles.