The synthesis of phenylalanine-derived C5-substituted rhodanines and their activity against selected methicillin-resistant Staphylococcus aureus (MRSA) strains

Can a Small Change in the Heterocyclic Substituent Significantly Impact the Physicochemical and Biological Properties of (Z)-2-(5-Benzylidene-4-oxo-2-thioxothiazolidin-3-yl)acetic Acid Derivatives?

Rhodanine-3-acetic acid derivatives are attractive compounds with versatile effects. What is very important is that compounds of this type have many biological properties. They are tested, among others, as fluorescent probes for bioimaging and aldose reductase inhibitors. Rhodanine-3-acetic acid derivatives also have antibacterial, antifungal and anticancer activity. The presented work demonstrates that a slight change in the five-membered heterocyclic substituent significantly affects the properties of the compounds under consideration. Three rhodanine-3-acetic acid derivatives (A-1-A-3) were obtained in the Knoevenagel condensation reaction with good yields, ranging from 54% to 71%. High thermal stability of the tested compounds was also demonstrated above 240 °C. The absorption and emission maxima in polar and non-polar solvents were determined. Then, the possibility of using the considered derivatives for fluorescence bioimaging was checked. Compounds A-1 and A-2 were successfully used as fluorescent dyes of fixed cells of mammalian origin. In addition, biological activity tests against bacteria and fungi were carried out. Our results showed that A-1 and A-2 showed the most excellent antimicrobial activity among the newly synthesized compounds, especially against Gram-positive bacteria.

Design, dynamic docking, synthesis, and in vitro validation of a novel DNA gyrase B inhibitor

Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-intermediate-resistant Staphylococcus aureus (VRSA) are among the WHO's high priority pathogens. Among these two, MRSA is the most globally documented pathogen that necessitates the pressing demand for new classes of anti-MRSA drugs. Bacterial gyrase targeted therapeutics are unique strategies to overcome cross-resistance as they are present only in bacteria and absent in higher eukaryotes. The GyrB subunit is essential for the catalytic functions of the bacterial enzyme DNA Gyrase, thereby constituting a promising druggable target. The current study performed a structure-based virtual screening to designing GyrB target-specific candidate molecules. The de novo ligand design of novel hit molecules was performed using a rhodanine scaffold. Through a systematic in silico screening process, the hit molecules were screened for their synthetic accessibility, drug-likeness and pharmacokinetics properties in addition to its target specific interactions. Of the 374 hit molecules obtained through de novo ligand design, qsl-304 emerged as the most promising ligand. The molecular dynamic simulation studies confirmed the stable interaction between the key residues and qsl-304. qsl-304 was synthesized through a one-step chemical synthesis procedure, and the in vitro activity was proven, with an IC₅₀ of 31.23 µg/mL against the novobiocin resistant clinical isolate, Staphylococcus aureus sa-P2003. Further studies on time-kill kinetics showed the bacteriostatic nature with the diminished recurrence of resistance. The on-target gyrB inhibition further proved the efficacy of qsl-304.Communicated by Ramaswamy H. Sarma.

Synthesis and Evaluation of Chiral Rhodanine Derivatives Bearing Quinoxalinyl Imidazole Moiety as ALK5 Inhibitors

BACKGROUND

TGF-β signaling pathway inhibition is considered an effective way to prevent the development of several diseases. In the design and synthesis of TGF-β inhibitors, a rhodanine compound containing a quinoxalinyl imidazole moiety was found to have strong antimicrobial activity.

OBJECTIVE

The purpose of this work was to investigate the antimicrobial activity of other chiral rhodanine TGF-β inhibitors synthesized.

METHODS

Two series of 3-substituted-5-((5-(6-methylpyridin-2-yl)-4-(quinoxalinyl-6-yl)- 1H-imidazol-2-yl)methylene)-2-thioxothiazolin-4-ones (12a-h and 13a-e) were synthesized and evaluated for their ALK5 inhibitory and antimicrobial activity. The structures were confirmed by their 1H NMR, 13C NMR, and HRMS spectra. All the synthesized compounds were screened against Gram-positive strains, Gram-negative strains, and fungi.

RESULTS

Among the synthesized compounds, compound 12h showed the highest activity (IC50 = 0.416 μM) against ALK5 kinase. Compound 12h exhibited a good selectivity index of > 24 against p38α MAP kinase and was 6.0-fold more selective than the clinical candidate, compound 2 (LY-2157299). Nearly all the compounds displayed high selectivity toward both Gram-positive and Gram-negative bacteria. They also showed similar or 2.0-fold greater antifungal activity (minimum inhibitory concentration [MIC] = 0.5 µg/mL) compared with the positive control compounds Gatifloxacin (MIC = 0.5 µg/mL) and fluconazole (MIC = 1 µg/mL).

CONCLUSION

The findings suggest that the synthesized rhodanine compounds have good ALK5 inhibitory activity and can be used for further research and development as potential antifungal drugs.

Diaryl Ether: A Privileged Scaffold for Drug and Agrochemical Discovery

Diaryl ether (DE) is a functional scaffold existing widely both in natural products (NPs) and synthetic organic compounds. Statistically, DE is the second most popular and enduring scaffold within the numerous medicinal chemistry and agrochemical reports. Given its unique physicochemical properties and potential biological activities, DE nucleus is recognized as a fundamental element of medicinal and agrochemical agents aimed at different biological targets. Its drug-like derivatives have been extensively synthesized with interesting biological features including anticancer, anti-inflammatory, antiviral, antibacterial, antimalarial, herbicidal, fungicidal, insecticidal, and so on. In this review, we highlight the medicinal and agrochemical versatility of the DE motif according to the published information in the past decade and comprehensively give a summary of the target recognition, structure-activity relationship (SAR), and mechanism of action of its analogues. It is expected that this profile may provide valuable guidance for the discovery of new active ingredients both in drug and pesticide research.

Synthesis, biological evaluation of benzothiazole derivatives bearing a 1,3,4-oxadiazole moiety as potential anti-oxidant and anti-inflammatory agents

Twenty benzothiazole derivatives bearing a 1,3,4-oxadiazole moiety were synthesized and evaluated for their anti-oxidant and anti-inflammatory activities. Among these compounds, 8h and 8l were appeared to have high radical scavenging efficacies as 0.05 ± 0.02 and 0.07 ± 0.03 mmol/L of IC₅₀ values in ABTS⁺ bioassay, respectively. In anti-inflammatory tests, compound 8h displayed good activity with 57.35% inhibition after intraperitoneal administration, which was more potent than the reference drug (indomethacin). Molecular modeling studies were performed to investigate the binding mode of the representative compound 8h into COX-2 enzyme. In vitro enzyme study implied that compound 8h exerted its anti-inflammatory activity through COX-2 inhibition.

Antibacterial properties of 5-substituted derivatives of rhodanine-3-carboxyalkyl acids. Part II

Two series of rhodanine-3-acetic and rhodanine-3-propionic acids derivatives having benzylidene and cinnamylidene substituents with additional electron donating and withdrawing groups at the C-5 position, were synthesised. The structures of the obtained derivatives were confirmed by spectroscopic methods and their lipophilicity was screened. The crystal structures were determined for selected compounds. The antibacterial activity of the derivatives was depended on the type of carboxyalkyl group in the N-3 position and on the type of the substituent in the C-5 position. The derivatives of rhodanine-3-propionic acid demonstrated the highest activity against Gram-positive bacteria. However, none of tested derivatives showed activity against Gram-negative bacteria and yeast. We believe that the presence of the N,N-diethylamine group in the aromatic system and the number of carbon atoms in the carboxyalkyl group is more significant for the biological activity than the fact that the benzylidene or cinnamylidene substituent was present at the C-5 position.

Drug screening of rhodanine derivatives for antibacterial activity

Introduction: Bacteriological infections are a major risk to human health. These include all hospital and public-acquired infections. In drug discovery, rhodanines are privileged heterocyclic frameworks. Their derivatives possess strong anti-bacterial activity and some of them have shown potent activity against multidrug-resistant pathogens, both under in vitro and in vivo conditions. To treat multi-drug resistant pathogens, the development of novel potent drugs, with superior anti-bacterial efficacy, is paramount. One avenue which shows promise is the design and development of novel rhodanines.Areas covered: This review summarizes the status on rhodanine-based derivatives and their anti-bacterial activity, based on published research over the past six years. Furthermore, to facilitate the design of novel derivatives with improved functions, their structure-activity relationships are assessed with reference to their efficacy as anti-bacterial agents and their toxicity.Expert opinion: The pharmacological activity of molecules bearing a rhodanine scaffold needs to be very critically assessed in spite of considerable information available from various biological evaluations. Although, some data on structure-activity relationship frameworks is available, information is not adequate to optimize the efficacy of rhodanine derivatives for different applications.

Promising antibacterial agents against multidrug resistant Staphylococcus aureus

Rapid emergence of multidrug resistant Staphylococcus aureus infections has created a critical health menace universally. Resistance to all the available chemotherapeutics has been on rise which led to WHO to stratify Staphylococcus aureus as high tier priorty II pathogen. Hence, discovery and development of new antibacterial agents with new mode of action is crucial to address the multidrug resistant Staphylococcus aureus infections. The egressing understanding of new antibacterials on their biological target provides opportunities for new therapeutic agents. This review underlines on various aspects of drug design, structure activity relationships (SARs) and mechanism of action of various new antibacterial agents and also covers the recent reports on new antibacterial agents with potent activity against multidrug resistant Staphylococcus aureus. This review provides attention on in vitro and in vivo pharmacological activities of new antibacterial agents in the point of view of drug discovery and development.

Design, synthesis, biological evaluation, and molecular modeling studies of rhodanine derivatives as pancreatic lipase inhibitors

A series of rhodanine-3-acetic acid derivatives were synthesized via Knoevenagel condensation of rhodanine-3-acetic acid with various substituted aromatic aldehydes. The synthesized derivatives were screened in vitro for understanding the inhibitory potential towards pancreatic lipase (PL), a key enzyme responsible for the digestion of dietary fats. Derivative 8f exhibited a potential inhibitory activity towards PL (IC₅₀ = 5.16 µM), comparable to that of the standard drug, orlistat (0.99 µM). An increase in the density of the aromatic ring resulted in potential PL inhibition. The enzyme kinetics of 8f exhibited a reversible competitive-type inhibition, similar to that of orlistat. Derivative 8f exhibited a MolDock score of -125.19 kcal/mol in docking studies, and the results were in accordance with their PL inhibitory potential. Furthermore, the reactive carbonyl group of 8f existed at a distance adjacent to Ser152 (≈3 Å) similar to that of orlistat. Molecular dynamics simulation (10 ns) of the 8f-PL complex revealed a stable binding conformation of 8f in the active site of PL (maximum root mean square displacement of ≈2.25 Å). The present study identified novel rhodanine-3-acetic acid derivatives with promising PL inhibitory potential, and further lead optimization might result in potent PL inhibitors.

Recent Highlights on the Synthesis of Pyrazoles with Antimicrobial Activity

Background:

Heterocyclic compounds containing nitrogen atoms such as pyrazoles have a long history and applicability in the field of medicinal chemistry. Many compounds containing pyrazole moiety have been reported in the available literature for their prominent biological activities, including antimicrobial activity against different microorganisms. Over the years, there has been a concern with the many health problems associated with the dramatic increase of microbial infections and resistance to standard drugs, so there is a need for the development of more effective antimicrobial agents. Pyrazoles and their derivatives are promising candidates to bypass these problems with good safety profiles, and there is a wide range of synthetic methodologies for their obtainment. This review aims to compact a literature survey (2012-2017) very informative and helpful for researchers who wish to study or continue the development of new, potent and broad-spectrum antimicrobial compounds.

Methods:

This review encompasses reports on the synthesis and antimicrobial evaluation of synthetic pyrazoles from the year 2012 to 2017, which were extracted from bibliographic databases such as PubMed, scielo, sciencedirect, scifinder, and scopus. The main keywords in our search were “pyrazole” and “antimicrobial activity”, in which we made efforts to include synthetic and biological methodologies that can be useful for laboratories of different levels of infrastructure. Moreover, inclusion/ exclusion criteria was applied to select quality reports which could demonstrate different tools of antimicrobial evaluation, focusing on the advances made in the area, such as evaluation in silico and exploration of the possible mechanism of action for active compounds.

Results:

Thirty-four papers were included in this work, which was displayed chronologically from the year 2012 to 2017 in order to enhance the advances made in the area, with at least five reports from each year. We found that the most commonly tested bacterial strains are Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, and from the year 2016 onwards Mycobacterium tuberculosis. The most common tested fungal strains are Candida albicans, Aspergillus flavus, and Aspergillus niger. The majority of articles expressed the antimicrobial results as a zone of inhibition, leading to the determination of the Minimum Inhibitory Concentration (MIC) and a probable mechanism of action for the most prominent compounds, considering cytotoxicity. Aromatic aldehydes and ketones are key reactants to obtain important precursors for the synthesis of pyrazoles, such as chalcones, together with alkyl or phenylhydrazines and thiosemicarbazide. A great variation in the reported MICs was found as there is no standard maximum limit, but many compounds exhibited antimicrobial activity comparable or better than standard drugs, from which 10 reports active compounds with MIC lower than 5 μg mL-1.

Conclusion:

The findings of this work support the importance of pyrazole moiety in the structure of antimicrobial compounds and the versatility of synthetic methodologies to obtain the target products. Results clearly indicate that they are attractive target compounds for new antimicrobial drugs development. We hope that this information will guide further studies on continuing the search for more effective, highly active antimicrobial agents.

Structural optimization and antibacterial evaluation of rhodomyrtosone B analogues against MRSA strains

Methicillin-resistant Staphylococcus aureus (MRSA) infections are well-known as a significant global health challenge. In this study, twenty-two congeners of the natural antibiotic rhodomyrtosone B (RDSB) were synthesized with the aim of specifically enhancing the structural diversity through modifying the pendant acyl moiety. The structure-activity relationship study against various MRSA strains revealed that a suitable hydrophobic acyl tail in the phloroglucinol scaffold is a prerequisite for antibacterial activity. Notably, RDSB analogue 11k was identified as a promising lead compound with significant in vitro and in vivo antibacterial activities against a panel of hospital mortality-relevant MRSA strains. Moreover, compound 11k possessed other potent advantages, including breadth of the antibacterial spectrum, rapidity of bactericidal action, and excellent membrane selectivity. The mode of action study of compound 11k at the biophysical and morphology levels disclosed that 11k exerted its MRSA bactericidal action by membrane superpolarization resulting in cell lysis and membrane disruption. Collectively, the presented results indicate that the novel modified RDSB analogue 11k warrants further exploration as a promising candidate for the treatment of MRSA infections.

Synthesis and antibacterial activity of new (2,4-dioxothiazolidin-5-yl/ylidene)acetic acid derivatives with thiazolidine-2,4-dione, rhodanine and 2-thiohydantoin moieties

A series of new (2,4-dioxothiazolidin-5-yl/ylidene)acetic acid derivatives with thiazolidine-2,4-dione, rhodanine and 2-thiohydantoin moiety (28–65) were synthesized by the reaction of (2,4-dioxothiazolidin-5-yl/ylidene)acetic acid chlorides with 5-(hydroxybenzylidene) thiazolidine-2,4-dione, rhodanine and 2-thiohydantoin derivatives. Obtained compounds (28–65) were tested on reference strains of Gram-positive bacteria and ones of the Gram-negative bacteria. The antibacterial activity of target compounds was determined by broth microdilution method. These derivatives showed antibacterial activity generally against Gram-positive bacterial strains. Most active compounds possess MIC = 3.91 mg/L. Our results suggest that presence of electron-withdrawing substituent at phenyl ring is favorable while geometry of molecule does not play important role in antibacterial response. It was confirmed the lack of direct influence of substitution pattern at phenyl ring on antibacterial activity of closely related compounds of series 1–3. The antibacterial activity of some compounds was similar or higher than the activity of commonly used reference drugs such as oxacillin and cefuroxime.

Antibacterial properties of 5-substituted derivatives of rhodanine-3-carboxyalkyl acids

A series of rhodanine 3-carboxyalkanoic acid derivatives possessing 4′-(N,N-dialkyl-amino or diphenylamino)-benzylidene moiety as a substituent at the C-5 position were synthesised and their antibacterial activity was screened. All the rhodanine derivatives showed bacteriostatic or bactericidal activity to the reference gram-positive bacterial strains, but lack of activity to the reference Gram-negative bacterial strains and yeast strains was observed.

Revisiting Greek Propolis: Chromatographic Analysis and Antioxidant Activity Study

Propolis is a bee product that has been extensively used in alternative medicine and recently has gained interest on a global scale as an essential ingredient of healthy foods and cosmetics. Propolis is also considered to improve human health and to prevent diseases such as inflammation, heart disease, diabetes and even cancer. However, the claimed effects are anticipated to be correlated to its chemical composition. Since propolis is a natural product, its composition is consequently expected to be variable depending on the local flora alignment. In this work, we present the development of a novel HPLC-PDA-ESI/MS targeted method, used to identify and quantify 59 phenolic compounds in Greek propolis hydroalcoholic extracts. Amongst them, nine phenolic compounds are herein reported for the first time in Greek propolis. Alongside GC-MS complementary analysis was employed, unveiling eight additional newly reported compounds. The antioxidant activity study of the propolis samples verified the potential of these extracts to effectively scavenge radicals, with the extract of Imathia region exhibiting comparable antioxidant activity to that of quercetin.

Discovery of novel cinnamylidene-thiazolidinedione derivatives as PTP-1B inhibitors for the management of type 2 diabetes

Synthesis, biological evaluation,in silicobinding affinity prediction and 3D-QSAR studies of cinnamylidene-thiazolidinedione derivatives was performed as inhibitors of PTP-1B.

Prevention and treatment of Staphylococcus aureus biofilms

S. aureus colonizes both artificial and tissue surfaces in humans causing chronic persistent infections that are difficult to cure. It is a notorious pathogen due to its antibiotic recalcitrance and phenotypic adaptability, both of which are facilitated by its ability to develop biofilms. S. aureus biofilms challenge conventional anti-infective approaches, most notably antibiotic therapy. Therefore there is an unmet need to develop and include parallel approaches that target S. aureus biofilm infections. This review discusses two broad anti-infective strategies: (1) preventative approaches (anti-biofilm surface coatings, the inclusion of biofilm-specific vaccine antigens); and (2) approaches aimed at eradicating established S. aureus biofilms, particularly those associated with implant infections. Advances in understanding the distinct nature of S. aureus biofilm development and pathogenesis have led to growing optimism in S. aureus biofilm targeted anti-infective strategies. Further research is needed however, to see the successful administration and validation of these approaches to the diverse types of infections caused by S. aureus biofilms from multiple clinical strains.

Design, synthesis and biological evaluation of 4-benzoyl-1-dichlorobenzoylthiosemicarbazides as potent Gram-positive antibacterial agents

Twelve 4-benzoyl-1-dichlorobenzoylthiosemicarbazides have been tested as potential antibacterials. All the compounds had MICs between 0.49 and 15.63 µg/ml toward Micrococcus luteus, Bacillus cereus, Bacillus subtilis and Staphylococcus epidermidis indicating, in most cases, equipotent or even more effective action than cefuroxime. In order to clarify if the observed antibacterial effects are universal, further research were undertaken to test inhibitory potency of two most potent compounds 3 and 11 on clinical isolates of Staphylococcus aureus. Compound 11 inhibited the growth of methicillin-sensitive S. aureus (MSSA) at MICs of 1.95-7.81 µg/ml, methicillin-resistant S. aureus (MRSA) at MICs of 0.49-1.95 µg/ml and MDR-MRSA at MIC of 0.98 and 3.90 µg/ml, respectively. Finally, inhibitory efficacy of 3 and 11 on planktonic cells and biofilms formation in clinical isolates of S. aureus and Haemophilus parainfluenzae was tested. The majority of cells in biofilm populations of MSSA and MRSA were eradicated at low level of 3, with MBICs in the range of 7.82-15.63 µg/ml.

A simple and green procedure for the synthesis of 5-arylidenerhodanines catalyzed by diammonium hydrogen phosphate in water

A simple and efficient procedure for the synthesis of 5-arylidenerhodanines by condensation of aromatic aldehydes with rhodanine in water using diammonium hydrogen phosphate as catalyst is described. The procedure offers several advantages including environmentally friendly, mild reaction conditions, short reaction times, high yields, and simple experimental and work-up procedures.

Synthesis and biological evaluation of (E)-1-(substituted)-3-phenylprop-2-en-1-ones bearing rhodanines as potent anti-microbial agents

Herein, we report the design, syntheses and in vitro anti-microbial activity of two series of rhodanines with chalcone moiety. Anti-microbial tests showed that some of the synthesized compounds exhibited good inhibition (MIC = 1-8 µg/mL) against multi-drug-resistant Gram-positive organisms, including methicillin resistant and quinolone-resistant Staphylococcus aureus, in which the compound 4g was found to be the most potent with minimum inhibitory concentration (MIC) value of 1 µg/mL against two methicillin-resistant S. aureus.

Design and synthesis of L- and D-phenylalanine derived rhodanines with novel C5-arylidenes as inhibitors of HCV NS5B polymerase

Hepatitis C virus (HCV) NS5B polymerase is a key target for anti-HCV therapeutics development. Herein, we report the synthesis and in vitro evaluation of anti-NS5B polymerase activity of a molecular hybrid of our previously reported lead compounds 1 (IC50=7.7 μM) and 2 (IC50=10.6 μM) as represented by hybrid compound 27 (IC50=6.7 μM). We have explored the optimal substituents on the terminal phenyl ring of the 3-phenoxybenzylidene moiety in 27, by generating a set of six analogs. This resulted in the identification of compound 34 with an IC50 of 2.6 μM. To probe the role of stereochemistry towards the observed biological activity, we synthesized and evaluated the D-isomers 41 (IC50=19.3 μM) and 45 (IC50=5.4 μM) as enantiomers of the l-isomers 27 and 34, respectively. The binding site of compounds 32 and 34 was mapped to palm pocket-I (PP-I) of NS5B. The docking models of 34 and 45 within the PP-I of NS5B were investigated to envisage the molecular mechanism of inhibition.

Recent pharmacological developments on rhodanines and 2,4-thiazolidinediones

Thiazolidines are five-member heterocyclic having sulfur, nitrogen, and oxygen atoms in their ring structure and exhibiting potent as well as wide range of pharmacological activities. In this minireview, recent updates on synthesis and pharmacological evaluations of molecules based on 2,4-thiazolidine and rhodanine are discussed.

Synthesis and antibacterial evaluation of rhodanine-based 5-aryloxy pyrazoles against selected methicillin resistant and quinolone-resistant Staphylococcus aureus (MRSA and QRSA)

With an intention to synergize the anti-bacterial activity of 5-aryloxy pyrazole and rhodanine derivatives, eight series of hybrid compounds have been synthesized and evaluated for their antibacterial activity. The majority of the synthesized compounds showed good inhibitory activity against selected methicillin resistant and quinolone-resistant Staphylococcus aureus (MRSA, QRSA) with minimum inhibitory concentration (MIC) values in the range of 1-32 μg/mL. The cytotoxicity test suggests that these compounds exhibited in vitro antibacterial activity at non-cytotoxic concentrations. These studies therefore suggest that rhodanine-based 5-aryloxy pyrazoles are interesting scaffolds for the development of novel Gram-positive antibacterial agents.

Small change in structure leads to large difference in protein photocleavage: two porphyrins bearing rhodanine-based pendants

Two 5,10,15,20-tetraphenylporphyrins with one phenyl group anchored to a rhodanine-terminated side chain, RhD-TPP and RhDCOOH-TPP, were designed and synthesized, and their protein photocleavage activities were investigated using bovine serum albumin (BSA) as a model protein. Both porphyrins exhibit similar absorption spectra, fluorescence spectra, fluorescence quantum yields, and singlet oxygen ((1)O(2)) quantum yields in organic solvents due to their structure similarity. They also show similar binding affinities and binding sites toward BSA. However, RhD-TPP is nearly inactive in protein photocleavage while RhDCOOH-TPP can lead to distinct photocleavage of BSA under the same experimental conditions. Such a difference may be attributed to the different binding modes of the two porphyrin derivatives toward BSA, though the apparent binding affinities and the binding sites are similar, and consequently a great difference in the (1)O(2) quantum yields of the two porphyrins bound on BSA. The presence of the COOH group in RhDCOOH is proposed to play an important role, leading to less hydrophobic character and additional interactions towards BSA.