Development of Oxadiazole-Sulfonamide-Based Compounds as Potential Antibacterial Agents

Synergistic antimicrobial activity, MD simulation studies and crystal structure of natural alcohol motif containing novel substituted cinnamates

A series of natural alcohols motif containing novel substituted cinnamates were developed and screened against five bacterial strains namely, Enterococcus faecal (E. faecalis), Escherichia coli (E. coli), Bacillus subtilis (B. subtilis), Pseudomonas aeruginosa (P. aeruginosa) and Klebsiella pneumonieae (K. pneumonieae). Among all cinnamates, YS17 was identified with 100% bacterial growth inhibition across the panel, except in E. faecalis with MIC values of 0.25 mg/mL against B. subtilis and P. aeruginosa whereas 0.125, 0.5 and 1 mg/mL against E. coli, K. pneumonieae and E. faecalis, respectively. The growth inhibitory property of YS17 was further validated by disk diffusion, synergistic study and in vitro toxicity assays. Interestingly, YS17 exhibits synergistic effect in combination with the standard drug Ampicillin (AMP). The single crystal structure analysis of YS4 and YS6 was also performed which reconfirmed their proposed structures. Molecular docking visualized significant non-covalent interactions between E. coli MetAP and YS17 and the structural and conformational changes were further analysed using MD simulation studies. Overall, the study provided a suitable core for further synthetic alterations for their optimization as an antibacterial agent. Communicated by Ramaswamy H. Sarma.

New Copper Complexes with Antibacterial and Cytotoxic Activity

The discovery of a new non-toxic metal complex with biological activity represents a very active area of research. Two Cu+2 complexes, [Cu4(L1)4(OH)4(DMF)2(H2O)] (C1) (HL1 = N-(5-ethyl-[1,3,4]-thiadiazole-2-yl)-benzenesulfonamide) and [Cu(L2)2(phen)(H2O)] (C2) (HL2 = N-(5-(4-methylphenyl)-[1,3,4]-thiadiazole-2-yl)-naphtalenesulfonamide), with two new ligands were synthesized. The X-ray crystal structures of the complexes were determined. In both complexes, Cu+2 is five-coordinated, forming a CuN2O3 and CuN4O chromophore, respectively. The ligands act as monodentate, coordinating the metal ion through a single Nthiadiazole atom; for the two complexes, the molecules from the reaction medium (phenantroline, dimethylformamide and water) are also involved in the coordination of Cu+2. The complexes have a distorted square pyramidal square-planar geometry. The compounds were characterized by FT-IR and UV-Vis spectroscopy. Using the microdilution method, the antibacterial activity of the complexes was determined against four Gram-positive and two Gram-negative bacteria, with Gentamicin as the positive control. Cytotoxicity studies were carried out on two tumor cell lines (HeLa, DLD-1) and on a normal cell line (HFL1) using the MTT method and Cisplatin as a positive control. Flow cytometric assessment of apoptosis induced by the complexes on the three cell lines was also performed. Both complexes present in vitro biological activities but complex C2 is more active.

Acrylonitrile adducts: design, synthesis and biological evaluation as antimicrobial, haemolytic and thrombolytic agent

In this work, five acrylonitrile adducts were screened for antibacterial activity against Gram-positive Bacillus subtilis, Microbial Type Culture Collection and Gene Bank (MTCC 1305) and Gram-negative Escherichia coli (MTCC 443). Synthesis was followed by aza-Michael addition reaction, where the acrylonitrile accepts an electron pair from the respective amines and results in the formation of n-alkyliminobis-propionitrile and n-alkyliminopropionitrile under microwave irradiation. Characterization of the compounds were performed using Fourier Transform Infrared (FTIR), Proton Nuclear Magnetic Resonance (¹H NMR) and Electrospray Ionisation Mass Spectrometry (ESI-MS). The particle size characterization was done by Dynamic Light Scattering (DLS) technique. The antibacterial study showed higher inhibition rate for both Gram-positive and Gram-negative bacteria. The antibacterial ability was found to be dose dependent. The minimum inhibitory concentration against both bacteria were found to be 1, 3, 0.4, 1, 3 µl/ml for E. coli and 6, 6, 0.9, 0.5, 5 µl/ml for B. subtilis. Time-kill kinetics evaluation showed that the adducts possess bacteriostatic action. Further it was evaluated for high-throughput in vitro assays to determine the compatibility of the adducts for drug delivery. The haemolytic and thrombolytic activity was analysed against normal mouse erythrocytes. The haemolytic activity showed prominent results, and thereby projecting this acrylonitrile adducts as potent antimicrobial and haemolytic agent.

Synthesis, spectral characterization of pyrazole derived Schiff base analogs: molecular dynamic simulation, antibacterial and DNA binding studies

We have synthesized the pyrazole-bearing Schiff base derivatives (5a-5e) and (6a-6h) then the structural confirmation was supported by various spectral analyses. The antibacterial activity of all analogs was screened against bacterial strains Staphylococcus aureus, Bacillus subtilis, Enterococcus faecalis, Escherichia coli, Klebsiella pneumonieae and Pseudomonas aeruginosa. In comparison to the reference drug ciprofloxacin, the lead analogs 5c and 6c showed potent activity, with MIC values of 64 µg/mL against E. coli and B. subtilis. Compound 5c showed a moderate effect with a MIC value of 128 µg/mL against B. subtilis, P. aeruginosa and K. pneumonieae, while compound 6c was against E. coli and P. aeruginosa. Furthermore, the compounds 5c and 6c displayed groove binding mode towards CT-DNA by absorption, emission, competitive fluorescence studies using EtBr, CD and time-resolved fluorescence studies. Thermodynamic parameters of analogs 5c and 6c with CT-DNA were also calculated at 298, 303 and 308K temperatures by UV-visible spectroscopy. The molecular docking studies give the docking score for all compounds with PDB codes: 1BNA and 2XCT. The MD simulation study of analogs 5c and 6c was also carried out. The pharmacokinetic and ADME properties were calculated for all of the synthesized analogs (5a-5e) and (6a-6h).Communicated by Ramaswamy H. Sarma.

New Ni(II) and Pd(II) complexes bearing derived sulfa drug ligands: synthesis, characterization, DFT calculations, and in silico and in vitro biological activity studies

In the present study, the synthesis of six new Ni(II) and Pd(II) complexes with three derived sulfamethoxazole drug ligands is reported. The coordination mode, geometry, and chemical formula of all the synthesized compounds have been determined by elemental analysis, mass spectrometry, emission atomic spectroscopy, conductivity measurements, magnetic susceptibility, FTIR, TGA, 1H-NMR, electronic absorption spectroscopy, SEM-EDX along with DFT calculations. The Schiff Base ligands were found to be bidentate and coordinated to the metal ions through sulfonamidic nitrogen and oxazolic nitrogen atoms leading to a square planar geometry for palladium (II) while a distorted octahedral geometry around Nickel (II) ion was suggested. Biological applications of the new complexes including in vitro antimicrobial, antioxidant and anticancer properties were investigated. The results showed that the new metal (II) compounds exhibit remarkable antibacterial inhibition activity against both Gram-positive and Gram-negative bacteria, in addition to noticeable DPPH free radical scavenging activity. The in vitro cytotoxicity assay of the complexes against cell lines of chronic myelogenous leukaemia (K562) showed promising potential for the application of the coordination compounds in antitumor therapy. Subsequently, to evaluate the pharmaceutical potential of the metal-containing compounds, pharmacokinetics and toxicity were studied by ADMET simulations while interactions between the complexes and bacterial proteins were evaluated by molecular docking.

Design, Synthesis and Mechanistic Studies of Novel Isatin-Pyrazole Hydrazone Conjugates as Selective and Potent Bacterial MetAP Inhibitors

Methionine aminopeptidases (MetAPs) are attractive drug targets due to their essential role in eukaryotes as well as prokaryotic cells. In this study, biochemical assays were performed on newly synthesized Isatin-pyrazole hydrazones (PS1-14) to identify potent and selective bacterial MetAPs inhibitors. Compound PS9 inhibited prokaryotic MetAPs, i.e., MtMetAP1c, EfMetAP1a and SpMetAP1a with Ki values of 0.31, 6.93 and 0.37 µM, respectively. Interestingly, PS9 inhibited the human analogue HsMetAP1b with Ki (631.7 µM) about ten thousand-fold higher than the bacterial MetAPs. The in vitro screening against Gram-positive (Enterococcus faecalis, Bacillus subtilis and Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa, Klebsiella pneumonia and Escherichia coli) bacterial strains also exhibited their antibacterial potential supported by minimum bactericidal concentration (MBC), disk diffusion assay, growth curve and time-kill curve experiments. Additionally, PS6 and PS9 had synergistic effects when combined with ampicillin (AMP) and ciprofloxacin (CIP) against selective bacterial strains. PS9 showed no significant cytotoxic effect on human RBCs, HEK293 cells and Galleria mellonella larvae in vivo. PS9 inhibited the growth of multidrug-resistant environmental isolates as it showed the MIC lower than the standard drugs used against selective bacterial strains. Overall, the study suggested PS9 could be a useful candidate for the development of antibacterial alternatives.

Target-Based Virtual Screening of Natural Compounds Identifies a Potent Antimalarial With Selective Falcipain-2 Inhibitory Activity

We employed a comprehensive approach of target-based virtual high-throughput screening to find potential hits from the ZINC database of natural compounds against cysteine proteases falcipain-2 and falcipain-3 (FP2 and FP3). Molecular docking studies showed the initial hits showing high binding affinity and specificity toward FP2 were selected. Furthermore, the enzyme inhibition and surface plasmon resonance assays were performed which resulted in a compound ZINC12900664 (ST72) with potent inhibitory effects on purified FP2. ST72 exhibited strong growth inhibition of chloroquine-sensitive (3D7; EC₅₀ = 2.8 µM) and chloroquine-resistant (RKL-9; EC₅₀ = 6.7 µM) strains of Plasmodium falciparum. Stage-specific inhibition assays revealed a delayed and growth defect during parasite growth and development in parasites treated with ST72. Furthermore, ST72 significantly reduced parasite load and increased host survival in a murine model infected with Plasmodium berghei ANKA. No Evans blue staining in ST72 treatment indicated that ST72 mediated protection of blood–brain barrier integrity in mice infected with P. berghei. ST72 did not show any significant hemolysis or cytotoxicity against human HepG2 cells suggesting a good safety profile. Importantly, ST72 with CQ resulted in improved growth inhibitory activity than individual drugs in both in vitro and in vivo studies.