Pyrene based Schiff bases: Synthesis, crystal structure, antibacterial and BSA binding studies

Comparative study on Antibacterial efficacy of a series of chromone sulfonamide derivatives against drug-resistant and MDR-isolates

Sulfonamide derivatives have numerous pharmaceutical applications having antiviral, antibacterial, antifungal, antimalarial, anticancer, and antidepressant activities. The structural flexibility of sulfonamide derivatives makes them an excellent candidate for the development of new multi-target agents, although long-time exposure to sulfonamide drugs results in many toxic impacts on human health. However, sulfonamides may be functionalized for developing less toxic and more competent drugs. In this work, sulfonamides including Sulfapyridine (a), Sulfathiazole (b), Sulfamethoxazole (c), and Sulfamerazine (d) are used to synthesize Schiff bases of 7-hydroxy-4-methyl-2-oxo-2H-chromene-8-carbalde-hyde (1a-1d). The synthesized compounds were spectroscopically characterized and tested against hospital isolates of three Gram-positive (Methicillin-resistant Staphylococcus aureus PH217, Ampicillin-resistant Coagulase-negative Staphylococcus aureus, multidrug-resistant (MDR) Enterococcus faecalis PH007R) and two Gram-negative bacteria (multidrug-resistant Escherichia coli, and Salmonella enterica serovar Typhi), compared to the quality control strains from ATCC (S. aureus 29213, E. faecalis 25922, E. coli 29212) and MTCC (S. Typhi 734). Two of the four Schiff bases 1a and 1b are found to be more active than their counterpart 1c and 1d; while 1a have showed significant activity by inhibiting MRSA PH217 and MDR isolates of E. coli at the minimum inhibitory concentration (MIC) of 150 μg/mL and 128 μg/mL with MBC of 1024 µg/mL, respectively. On the other hand, the MIC of 1b was 150 μg/mL against both S. aureus ATCC 29213 and Salmonella Typhi MTCC 734, compared to the control antibiotics Ampicillin and Gentamycin. Scanning electron microscopy demonstrated the altered surface structure of bacterial cells as a possible mechanism of action, supported by the in-silico molecular docking analysis.

Integrated Approach to Interaction Studies of Pyrene Derivatives with Bovine Serum Albumin: Insights from Theory and Experiment

This work aimed to investigate the interaction of bovine serum albumin with newly synthesized potent new pyrene derivatives (PS1 and PS2), which might prove useful to have a better antibacterial character as found for similar compounds in the previous report [Low et al. Bioconjugate Chemistry2014, 12, 2269−2284]. However, to date, binding studies with plasma protein are still unknown. Steady-state fluorescence spectroscopy and lifetime fluorescence studies show that the static interaction binding mode and binding constants of PS1 and PS2 are 7.39 and 7.81 [K_b × 10⁵ (M^–1)], respectively. The experimental results suggest that hydrophobic forces play a crucial role in interacting pyrene derivatives with BSA protein. To verify this, molecular docking and molecular dynamics simulations were performed to predict the nature of the interaction and the dynamic behavior of the two compounds in the BSA complex, PS1 and PS2, under physiological conditions of pH = 7.1. In addition, the free energies of binding for the BSA-PS1 and BSA-PS2 complexes were estimated at 300 K based on the molecular mechanics of the Poisson–Boltzmann surface (MMPBSA) with the Gromacs package. PS2 was found to have a higher binding affinity than PS1. To determine the behavior of the orbital transitions in the ground state geometry, we found that both compounds have similar orbital transitions from HOMO–LUMO via π → π* and HOMO–1–LUMO+1 via n → π*, which was included in the FMO analysis. A cytotoxicity study was performed to determine the toxicity of the compounds. Based on the MD study, the stability of the compounds with BSA and the dynamic binding modes were further revealed, as well as the nature of the binding force components involved and the important residues involved in the binding process. From the binding energy analysis, it can be assumed that PS2 may be more active than PS1.

A Review on the Antimicrobial Activity of Schiff Bases: Data Collection and Recent Studies

Schiff bases (SBs) have extensive applications in different fields such as analytical, inorganic and organic chemistry. They are used as dyes, catalysts, polymer stabilizers, luminescence chemosensors, catalyzers in the fixation of CO₂ biolubricant additives and have been suggested for solar energy applications as well. Further, a wide range of pharmacological and biological applications, such as antimalarial, antiproliferative, analgesic, anti-inflammatory, antiviral, antipyretic, antibacterial and antifungal uses, emphasize the need for SB synthesis. Several SBs conjugated with chitosan have been studied in order to enhance the antibacterial activity of chitosan. Moreover, the use of the nanoparticles of SBs may improve their antimicrobial effects. Herein, we provide an analytical overview of the antibacterial and antifungal properties of SBs and chitosan-based SBs as well as SBs-functionalized nanoparticles. The most relevant and recent literature was reviewed for this purpose.

Visible-light driven regioselective synthesis, characterization and binding studies of 2-aroyl-3-methyl-6,7-dihydro-5H-thiazolo[3,2-a]pyrimidines with DNA and BSA using biophysical and computational techniques

In recent times, fused azaheterocycles emerged as impressive therapeutic agents. Binding studies of such azaheterocycles with biomolecules is an important subject for pharmaceutical and biochemical studies aiming at the design and development of new drugs. Fused heterocyclic scaffolds, such as thiazolopyrmidines have long been used in the pharmaceutical industry for the treatment of various diseases. In this study, we have accomplished a regioselective synthesis of 2-aroyl-3-methyl-6,7-dihydro-5H-thiazolo[3,2-a]pyrimidines by the reaction of tetrahydropyrimidine-2(H)-thione with α-bromo-1,3-diketones, generated in situ from 1,3-diketones and NBS, using visible light as an inexpensive, green and renewable energy source under mild reaction conditions with wide-ranging substrate scope. The regioisomer was characterized unambiguously by 2D-NMR [1H-13C] HMBC and [1H-13C] HMQC spectroscopy. In silico toxicity data analysis showed the low toxicity risks of the synthesized compounds. Computational molecular docking studies were carried out to examine the interaction of thiazolo[3,2-a]pyrimidines with calf-thymus DNA (ct-DNA) and Bovine Serum Albumin (BSA). Moreover, different spectroscopic approaches viz. steady-state fluorescence, competitive displacement assay, UV-visible and circular dichroism (CD) along with viscosity measurements were employed to investigate the binding mechanisms of thiazolo[3,2-a]pyrimidines with DNA and BSA. The results thus obtained revealed that thiazolo[3,2-a]pyrimidines offer groove bindings with DNA and showed moderate bindings with BSA.