Design, synthesis of tri‐substituted pyrazole derivatives as promising antimicrobial agents and investigation of structure activity relationships

Synthesis and biological evaluation of antibacterial activity of novel clarithromycin derivatives incorporating 1,2,3-triazole moieties at the 4''- and 11-OH positions

Bacterial infection is still one of the diseases that threaten human health, and bacterial drug resistance is widespread worldwide. As a result, their eradication now largely relies on antibacterial drug discovery. Here, we reveal a novel approach to the development of 14-membered macrolide antibiotics by describing the design, synthesis, and evaluation of novel clarithromycin derivatives incorporating 1,2,3-triazole moieties at the 4''- and 11-OH positions. Using chemical synthesis, 35 clarithromycin derivatives were prepared, and their antibacterial properties were profiled. We found that compounds 8e-8h, 8l-8o, 8v, and 19d were as potent as azithromycin against Enterococcus faecalis ATCC29212. Furthermore, compounds 8c, 8d, 8n, and 8o showed slightly improved antibacterial activity (2-fold) against Acinetobacter baumannii ATCC19606 when compared with azithromycin and clarithromycin. In addition, compounds 8e, 8f, 8h, 8l, and 8v exhibited excellent antibacterial activity against Staphylococcus aureus ATCC43300, Staphylococcus aureus PR, and Streptococcus pneumoniae ER-2. These compounds were generally 64- to 128-fold more active than azithromycin, and 32- to 128-fold more active than clarithromycin. The results of molecular docking indicated that compound 8f may bind to the nucleotide residue A752 through hydrogen-bonding, hydrophobic, electrostatic, or π-π stacking interactions. The predicted ClogP data suggested that higher values of ClogP (>6.65) enhanced the antibacterial activity of compounds such as 8e, 8f, 8h, 8l, and 8v. The determination of the minimum bactericidal concentration showed that most of the tested compounds were bacteriostatic agents. From this study of bactericidal kinetics, we can conclude that compound 8f had a concentration- and time-dependent effect on the proliferation of Staphylococcus aureus ATCC43300. Finally, the results of the cytotoxicity assay showed that compound 8f exhibited no toxicity at the effective antibacterial concentration.

Synthesis and characterization of new functionalized chitosan and its antimicrobial and in-vitro release behavior from topical gel

Recently, chitosan and its derivatives have been gaining more attention due to their high integration into various biomedical applications. Herein, a new chitosan derivative was prepared by linking the chitosan (Cs) with a novel heterocyclic compound, Benzoimidazolyl-thiadiazole (BzimTD) to form Cs-BzimTD. The synthesis of the new chitosan derivative was confirmed by Fourier-Transform Infrared (FT-IR) spectroscopy, proton nuclear magnetic resonance (¹H NMR), thermogravimetric (TGA-DTG) analysis, elemental analysis, and UV-Visible spectrophotometer. Data showed the high efficacy of functionalized Cs-BzimTD to inhibit the growth of pathogenic microbes, Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans, with inhibition zones of 15.3 ± 0.6 - 9.2 ± 0.3 mm. Also, Cs-BzimTD was applied in a topical gel formulation by using two different polymers, Carbopol 940 (CP) and Carboxymethyl Cellulose (CMC) to form three gel formulations: Cs-BzimTD-CP, Cs-BzimTD-CMC, and Cs-BzimTD-CP-CMC. The new gels were checked for physical appearance, viscosity, Cs-BzimTD release, pH, spread-ability, and drug content. The results showed that all formulations were clear, transparent, and homogeneous with non-irritant pH values for skin (6.4 - 6.8). The spread-ability was found in the range of 7.1 - 9.4 g.cm/s. The Cs-BzimTD-CP formula showed the maximal Cs-BzimTD content percentage (86.5%) and the Cs-BzimTD release varied from 89.9 to 81.6% after 8 h depending on the gel formulation, with a maximum release achieved for Cs-BzimTD-CMC.

Isocoumarins: a new class of selective carbonic anhydrase IX and XII inhibitors

Isocoumarins, isomeric to comarins which act as effective carbonic anhydrase (CA, EC 4.2.1.1) inhibitors, were investigated for the first time as inhibitors of this enzyme. A series of 3-substituted and 3,4-disubstituted isocoumarins incorporating phenylhydrazone, 1-phenyl-pyrazole and pyrazolo-substituted pyrimidine trione/thioxo-pyrimidine dione moieties were investigated for their interaction with four human (h) CA isoforms, hCA I, II, IX and XII, known to be important drug targets. hCA I and II were not inhibited by these compounds, whereas hCA IX and XII were inhibited in the low micromolar range by the less bulky derivatives. The inhibition constants ranged between 2.7–78.9 µM against hCA IX and of 1.2–66.5 µM against hCA XII. As for the coumarins, we hypothesise that the isocoumarins are hydrolysed by the esterase activity of the enzyme with formation of 2-carboxy-phenylacetic aldehydes which act as CA inhibitors. Isocoumarins represent a new class of CA inhibitors.

Antimicrobial activities of spirooxindolopyrrolidine tethered dicarbonitrile heterocycles against multidrug resistant nosocomial pathogens

BACKGROUND

Microbial infections together with rising drug resistance pose a threat to immunocompromised individual. In this perspective, compounds with spirooxindolopyrrolidine play a significant role in research on antimicrobial drug delivery research owing to their various pharmaceutical activities. Spiroheterocyclic compounds are present in number of medications as active motif due to their exceptional structural properties which enable for easy interaction with the protein of the biological target. Inspired by this biological precedent encouraged to synthesize a new class of dispirooxindole fused pyrrolidine heterocycles via a three-component cycloaddition strategy.

MATERIALS AND METHODS

The new class of structurally intriguing spirooxindolopyrrolidines were synthesized through three component cycloaddition process and the structure of products were assigned through spectroscopic analysis. The newly synthesized compounds were assessed for their antimicrobial sensitivity test with standard Kirby Bauer method with common drugs.

RESULTS

The structurally unexplored hybrid heterocycles fused spirooxindolopyrrolidine exhibited excellent antimicrobial activity against the common nosocomial microbial pathogens. Of four compounds, the compound bearing a chlorine atom on the aryl ring (4a) exhibited significant antimicrobial activity (zone of inhibition: 9.00 ± 1.00-17.00 ± 0.35 mm and MIC: 16.00-256.00 μg/mL) against selected nosocomial infection causing microbial pathogens. Hence, the compound 4a has been considered as an effective drug of interest in therapeutic field for compacting infectious diseases causing pathogens.

CONCLUSION

With an aim of developing more effective and economically more affordable antimicrobial leads with a unique mechanism of action, we have designed and synthesized structurally diverse spirooxindolopyrrolidine tethered hybrids that has been assayed against multidrug resistant nosocomial pathogens. The regioisomer having chloro substituted on the phenyl ring showed potent activity when compared to standard drug. Future studies are required to explicate the pharmacological properties of new hybrid heterocycles that have been synthesized in our laboratory for the novel therapeutic development.

Exploration of brominated Plastoquinone analogs: Discovery and structure-activity relationships of small antimicrobial lead molecules

In the fight with the antimicrobial resistance, our continuous effort to find quinone analogs with higher inhibitory activity has previously led us to the promising Plastoquinone analogs. The 1,4-quinone moiety substituted with alkoxy substituent(s) plays an important role in the field of antimicrobial and anticancer drug discovery and development. Thus, an extensive series of 1,4-quinones, substituted in different positions with a variety of alkoxy substituents, has been designed, synthesized, and evaluated for their antimicrobial activity. Here, we describe the synthesis of brominated Plastoquinone analogs (BrPQ1-15) based on the dimethyl-1,4-quinone scaffold by employing two different paths. We also present here the in vitro antimicrobial activity of these analogs (BrPQ1-15) against a panel of pathogenic organisms. These studies resulted in several new selective antibacterial inhibitors and gave valuable insights into the structure-activity relationships. Among all the analogs studied, two analogs BrPQ1 with a methoxy substituent and BrPQ14 with a cyclic dioxy stand out as the most promising antibacterial molecules against Staphylococcus aureus and Staphylococcus epidermidis. Afterwards, two analogs were selected for a further investigation for biofilm evaluation. Finally, molecular docking studies for BrPQ1 and BrPQ14 with probable target S. aureus PNPase (5XEX) and predictive ADMET studies were also carried out.

Design, synthesis and structure-activity relationships of novel N11-, C12- and C13-substituted 15-membered homo-aza-clarithromycin derivatives against various resistant bacteria

Bacterial infections are still the main significant problem of public health in the world, and their elimination will greatly rely on the discovery of antibacterial drugs. In the processes of our searching for novel macrolide derivatives with excellent activity against sensitive and resistant bacteria, three series of novel N11-, C12- and C13-substituted 15-membered homo-aza-clarithromycin derivatives were designed and synthesized as Series A, B and C by creatively opening the lactone ring of clarithromycin (CAM), introducing various 4-substituted phenyl-1H-1,2,3-triazole side chains at the N11, C12 or C13 position of CAM and macrolactonization. The results from their in vitro antibacterial activity demonstrated that compounds 20c, 20d and 20f displayed not only the most potent activity against S. aureus ATCC25923 with the MIC values of 0.5, 0.5 and 0.5 µg/mL, but also greatly improved activity against B. subtilis ATCC9372 with the MIC values of less than or equal to 0.25, 0.25 and 0.25 µg/mL, respectively. In particular, compound 11g exhibited the strongest antibacterial effectiveness against all the tested resistant bacterial strains and had well balanced activity with the MIC values of 4-8 µg/mL. Further study on minimum bactericidal concentration and kinetics confirmed that compound 11g possessed a bacteriostatic effect on bacterial proliferation. Moreover, the results of molecular docking revealed an potential additional binding force between compound 11g and U790 in addition to the normal binding force of macrolide skeleton, which may explain why this compound performed the most potent activity against resistant bacteria. The results of cytotoxic assay indicated that compounds 20c, 20d and 20f were non-toxic to human breast cancer MCF-7 cells at its effective antibacterial concentration.