Design, synthesis, and biological evaluation of novel spiro[pyrrolidine-2,3′-quinolin]-2′-one derivatives as potential chitin synthase inhibitors and antifungal agents

Assessment of novel 1,2,3,4-tetrahydroquinoline-triazole hybrids compounds as inhibitors of E. coli DNA GyraseB: in vitro and in silico investigation

Ten novel 1,2,3,4-tetrahydroquinolone-triazole compounds (denoted as 6a-6j) were synthesized using click chemistry. These compounds were thoroughly characterized using various analytical techniques, such as FT-IR, mass spectrometry,1H NMR, and 13C NMR. To gather a deeper understanding regarding structural properties of the synthesized compounds, we conducted Density Functional Theory (DFT) studies employing the B3LYP/6-311G (d,p) methodology. These calculations allowed us to evaluate important properties such as the HOMO-LUMO energy gap, chemical potential (µ), electrophilicity (ω), chemical hardness (η), dipole moment (Debye), and total energy (a.u.) for the synthesized hybrids. Moving on to the practical application of these hybrids, we evaluated in vitro antimicrobial inhibitory potential against two gram-positive and two gram-negative strains, and three fungal strains. Obtained outcomes revealed a range of antibacterial activity, with some compounds exhibiting excellent to moderate efficacy. Compounds 6b and 6i showed a very good result with a MIC of 12.5 μg/mL compared to standard Ciprofloxacin (MIC 25 μg/mL), demonstrating strong antibacterial activity against E. coli among the 6a-6j compounds. Furthermore, in silico docking validated our compounds' interaction with E. coli DNA gyrase B. Further, a 200 ns simulation revealed that the promising compounds maintained stability within the binding cavity, with RMSD values below 3 Å, and exhibited reduced structural fluctuations compared to the Apo protein, as evidenced by lower average RMSF values in the ligand-protein complexes. Additionally, an in silico ADME study assessed the drug-likeness of the hybrids, offering insights for future drug development.

Spirocyclic compounds: potential drug leads in the fight against Mycobacterium tuberculosis

TB drug discovery needs scientists' attention since drug resistance in TB, including extensively drug-resistant TB (XDR-TB) and multidrug-resistant TB (MDR-TB), is a major healthcare concern. Since millions of fatalities from tuberculosis are recorded each year, there is an urgent need to discover new anti-tubercular medications that will either eradicate or control the disease. Spiro compounds have garnered a lot of attention in medicinal chemistry these days because of various biological activities mainly because of their adaptability and structural resemblance to significant pharmacophores. This article overviews the synthesis and activity of spirocyclic compounds as anti-tubercular agents. Both synthesized and naturally occurring spiro chemicals exhibit antitubercular properties. The promising antitubercular potential shown by some of the spirocyclic compounds has attracted scientists to explore them further to develop molecules with improved pharmacodynamic and pharmacokinetic properties and new mechanisms of action with enhanced safety and efficacy in tuberculosis. The current review covers the exploration of spiro compounds from the year 2004 to 2024 for the combat of Tuberculosis. This review gives the comprehensive advancements in this scaffold which would help the logical design of powerful, less toxic, and more effective spirocyclic anti-TB medicinal molecules.

Novel spiro[indoline-3,2'thiazolo[5,4-e]pyrimido[1,2-a] pyrimidine] derivatives as possible anti-dermatophytic and anti-candidiasis agent

A novel series of 5'-benzylidene-3'-phenylspiro[indoline-3,2'-thiazolidine]-2,4'(1H)-diones 6a-d and spiro[indoline-3,2'-thiazolo[5,4-e]pyrimido[1,2-a]pyrimidin]-2(1H)-one 9a-d derivatives have been synthesized. All the newly synthesized compounds were evaluated for antifungal and anti-candidiasis activity by using Disc Diffusion and Modified Microdilution methods. The antimicrobial experiments have shown that the synthesized compounds demonstrated broad-spectrum antifungal activity in vitro. Among them, compounds 9a-9d had stronger antifungal activity against Trichophyton rubrum, Trichophyton mentagrophytes, and Candida albicans; compounds 6a-d also showed significant antifungal activity against selected fungal strains as compared to ketoconazole, the reference antifungal drug. The evaluation of antifungal activity against drug-resistant fungal variants showed that the designed compounds had significant antifungal activity against the tested variants. The combination of compounds (6a-d) and (9a-d) exhibited that the synthesized compounds had synergistic effects or additive effects. These results demonstrated that the synthesized compounds were putative chitin synthase inhibitors exhibiting broad spectrum antifungal activities. The present results indicate that novel spiro pyrimidine derivatives can be used as an active pharmaceutical ingredient for novel drug candidate for treatment of dermatophytosis and other fungal agents.

Novel spiro[pyrrolidine-2,3'-quinoline]-2'-one derivatives containing piperazine fragment as potential chitin synthase inhibitors and antifungal agents: Design, synthesis and biological evaluation

A series of spiro[pyrrolidine-2,3'-quinoline]-2'-one derivatives were designed and synthesized for the discovery of novel antifungal drugs. The bioactivities of all derivatives were screened by evaluating their inhibitory effects against chitin synthase (CHS) and antimicrobial activities in vitro. Enzyme inhibition experiments showed that all the synthesized compounds inhibited the chitin synthase. Compounds 4d, 4k, 4n and 4o showed inhibitory effects against CHS with IC50 values which were close to that of the control drug (polyoxin B). The results of enzyme kinetics experiment showed that these compounds were non-competitive inhibitors of chitin synthase (Ki of compound 4o is 0.14 mM). Antimicrobial experiments showed that these compounds exhibited moderate to excellent antifungal activity against pathogenic fungal strains while the compounds showed little potency against bacteria. Among them, compounds 4d, 4f, 4k and 4n showed stronger antifungal activities against C. albicans than those of fluconazole and polyoxin B. Compounds 4f, 4n and 4o showed better antifungal activities against A. flavus than those of fluconazole and polyoxin B. Compound 4d showed similar activity to that of fluconazole and stronger activity than those of polyoxin B against C. neoformans and A. fumigatus. It is also showed that these compounds have the potency against drug-resistant fungal variants. The results of sorbitol protection assay and evaluation of antifungal activity against micafungin-resistant strains experiment further illustrated that these compounds inhibited the synthesis of chitin of fungal cell wall. Drug combination experiments showed that these compounds had synergistic or additive effects when combined with fluconazole or polyoxin B. The synergistic effects with polyoxin B further confirmed the compounds were non-competitive inhibitors of chitin synthase. Additionally, docking studies showed that these compounds had strong affinity with chitin synthase from C. albicans (CaChs2). These results indicate that the target of these synthesized compounds is chitin synthase, and these compounds had excellent antifungal activity while possessed the potency against drug-resistant fungal variants.

Novel quinolin-2(1H)-one analogues as potential fungicides targeting succinate dehydrogenase: design, synthesis, inhibitory evaluation and molecular modeling

BACKGROUND

Succinate dehydrogenase is an important target of fungicides. Succinate dehydrogenase inhibitors (SDHIs) have widely been used to combat destructive plant pathogenic fungi because they possess efficient and broad-spectrum antifungal activities and as well as unique mode of action. The research and development of novel SDHIs have been ongoing.

RESULTS

Thirty-six novel quinolin-2(1H)-one derivatives were designed, synthesized and characterized. The single crystal structure of compound 3c was determined through the X-ray diffraction of single crystals. The bioassay results displayed that most compounds had good antifungal activities at 16 μg mL-1 against Rhizoctonia cerealis, Erysiphe graminis, Botrytis cinerea, Penicillium italicum and Phytophthora infestans. Compounds 6o, 6p and 6r had better antifungal activities than the commercialized fungicide pyraziflumid against Botrytis cinerea. Their half maximal effective concentration (EC50 ) values were 0.398, 0.513, 0.205 and 0.706 μg mL-1 , respectively. Moreover, the inhibiting activities of the bioactive compounds were tested against succinate dehydrogenase. The results indicated that they possessed outstanding activities. Compounds 6o, 6p and 6r also exhibited better inhibiting activities than pyraziflumid against succinate dehydrogenase. Their half maximal inhibitory concentration (IC50 ) values were 0.450, 0.672, 0.232 and 0.858 μg mL-1 , respectively. The results of molecular dynamic (MD) simulations indicated that compound 6r displayed stronger affinity to succinate dehydrogenase than pyraziflumid.

CONCLUSION

The results of the present study displayed that quinolin-2(1H)-one derivative could be one scaffold of potential SDHIs and will provide some valuable information for the research and development of new SDHIs. © 2022 Society of Chemical Industry.

Exploration of Baicalein-Core Derivatives as Potent Antifungal Agents: SAR and Mechanism Insights

Baicalein (BE), the major component of Scutellaria Baicalensis, exhibited potently antifungal activity against drug-resistant Candida albicans, and strong inhibition on biofilm formation. Therefore, a series of baicalein-core derivatives were designed and synthesized to find more potent compounds and investigate structure-activity relationship (SAR) and mode of action (MoA). Results demonstrate that A4 and B5 exert a more potent antifungal effect (MIC80 = 0.125 μg/mL) than BE (MIC80 = 4 μg/mL) when used in combination with fluconazole (FLC), while the MIC80 of FLC dropped from 128 μg/mL to 1 μg/mL. SAR analysis indicates that the presence of 5-OH is crucial for synergistic antifungal activities, while o-dihydroxyls and vic-trihydroxyls are an essential pharmacophore, whether they are located on the A ring or the B ring of flavonoids. The MoA demonstrated that these compounds exhibited potent antifungal effects by inhibiting hypha formation of C. albicans. However, sterol composition assay and enzymatic assay conducted in vitro indicated minimal impact of these compounds on sterol biosynthesis and Eno1. These findings were further confirmed by the results of the in-silico assay, which assessed the stability of the complexes. Moreover, the inhibition of hypha of this kind of compound could be attributed to their effect on the catalytic subunit of 1,3-β-d-glucan synthase, 1,3-β-d-glucan-UDP glucosyltransferase and glycosyl-phosphatidylinositol protein, rather than inhibiting ergosterol biosynthesis and Eno1 activity by Induced-Fit Docking and Molecular Dynamics Simulations. This study presents potential antifungal agents with synergistic effects that can effectively inhibit hypha formation. It also provides new insights into the MoA.

Design, synthesis and biological evaluation of novel spiro-quinazolinone derivatives as chitin synthase inhibitors and antifungal agents

A series of spiro-quinazolinone scaffolds were constructed based on the bioactivity of quinazolinone and the inherent feature of spirocycle to design novel chitin synthase inhibitors that possess mode of action different from that of the currently used antifungal agents. Among them, the spiro[thiophen-quinazolin]-one derivatives containing α, β-unsaturated carbonyl fragments had shown inhibitory activities against chitin synthase and antifungal activities. The enzymatic experiments showed that among the sixteen compounds, compounds 12d, 12g, 12j, 12l and 12m exhibited inhibitions against chitin synthase with IC₅₀ values of 116.7 ± 19.6 μM, 106.7 ± 14.2 μM, 102.3 ± 9.6 μM, 122.7 ± 22.2 μM and 136.8 ± 12.4 μM, respectively, which were comparable to that of polyoxin B (IC₅₀ = 93.5 ± 11.1 μM). The assays of enzymatic Kinetic parameters showed that compound 12g was a non-competitive inhibitor of chitin synthase. The antifungal assays showed that compounds 12d, 12g, 12j, 12l and 12m exhibited a broad-spectrum of antifungal activity against the four strains tested in vitro. In which, compounds 12g and 12j had stronger antifungal activity against four tested strains than that of polyoxin B and similar to that of fluconazole, while compounds 12d, 12l and 12m showed antifungal activity comparable to that of polyoxin B against four tested strains. Meanwhile, compounds 12d, 12g, 12j, 12l and 12m exhibited good antifungal activity against fluconazole-resistant and micafungin-resistant fungi variants with MIC values ranging from 4 to 32 μg/mL while the MIC values of reference drugs were above 256 μg/mL. Furthermore, the results of drug-combination experiments showed that compounds 12d, 12g, 12j, 12l and 12m had synergistic or additive effects with fluconazole or polyoxin B. The results of sorbitol protection experiment and the experiment of antifungal activity against micafungin-resistant fungi further demonstrated that these compounds target chitin synthase. The result of cytotoxicity assay showed that compound 12g had low toxicity toward human lung cancer A549 cells and the ADME analysis in silico displayed that compound 12g possessed promising pharmacokinetic properties. The molecular docking indicated that compound 12g formed multiple hydrogen bond interactions binding to chitin synthase, which might be conductive to increasing the binding affinity and inhibiting the activity of chitin synthase. The above results indicated that the designed compounds were chitin synthase inhibitors with selectivity and broad-spectrum antifungal activity and could be act as the lead compounds against drug-resistant fungi.