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.

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, ß-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.

Spiro[benzoxazine-piperidin]-one derivatives as chitin synthase inhibitors and antifungal agents: Design, synthesis and biological evaluation.

Four series of spiro[benzoxazine-piperidin]-one derivatives were designed and synthesized. Their inhibition percentages against chitin synthase and antifungal activities were evaluated. Based on the preliminary biological assays, the series of derivatives containing α, ß-unsaturated carbonyl fragment which had moderate to excellent CHS inhibitory activity and antifungal activity were further researched. In this series of compounds, eight out of twenty-one compounds had good to excellent inhibitory activity against chitin synthase with an inhibition percentage value above 60% at the concentration of 300 µg/mL. Among them, compounds 9a, 9o, 9s and 9t showed excellent chitin synthase inhibitory activity with IC50 values of 0.14 mM, 0.11 mM, 0.10 mM and 0.16 mM, respectively, which were equal to that of the control drug (polyoxin B). The results of sorbitol protection assays and evaluation of antifungal activity against micafungin-resistant fungi further proved that the target of these synthesized compounds was chitin synthase. The antifungal activity evaluation showed that compounds 9a, 9d, 9h, 9s and 9t had broad-spectrum antifungal activity in vitro and their antifungal activities are equal to those of fluconazole and polyoxin B. The result of combination use showed this series of compounds combined with fluconazole had additive or synergistic effects. In addition, compounds 9a, 9o and 9t showed good antifungal activity against fluconazole-resistant C. albicans and fluconazole-resistant C. neoformans variants. Consequently, the results showed that these compounds were chitin synthase inhibitors and antifungal agents and had significant activity against drug-resistant fungal variants.

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

A series of novel spiro-quinolinone derivatives were designed and synthesized and their structures were confirmed by spectroscopic methods. The enzymatic experiments showed that all the seventeen synthesized compounds had inhibition potency against chitin synthase, among them five compounds had excellent inhibition potency that equal to that of polyoxin B. The Kinetic parameters of enzymatic assays indicated that these compounds were non-competitive inhibitors of chitin synthase. The antimicrobial experiments displayed that the synthesized compounds had selectively and broad-spectrum antifungal activity in vitro Among them, two compounds had stronger antifungal activity against C. albicans than that of fluconazole meanwhile five others compounds showed antifungal activity against C. albicans being equal to that of fluconazole. Moreover, there are four or five compounds that possessed antifungal activities against C. neoformans, A. fumigatus and A. flavus as high as fluconazole had, respectively. The sorbitol protection assay and evaluation of antifungal activity against micafungin-resistant strain further verified that these compounds possessed antifungal activity through inhibiting the synthesis of chitin of cell wall. The evaluation of antifungal activity against others drug-resistant fungi variants showed these designed compounds had significant antifungal activity against these tested variants. The combination use experiments exhibited that the synthesized compounds had synergistic effects or additive effects with current used drugs in clinic. These results demonstrated that these synthesized compounds were chitin synthase inhibitors and had selective and broad-spectra antifungal activities.

Design, synthesis and biological evaluation of novel diazaspirodecanone derivatives containing piperidine-4-carboxamide as chitin synthase inhibitors and antifungal agents.

A series of novel 2-oxo-(1-oxo-2,8-diazaspiro[4.5]decane-8-yl)ethylpiperidine carboxamide derivatives were designed, synthesized and characterized by 1H NMR, 13C NMR and HRMS spectroscopy. All eighteen newly prepared compounds were evaluated for their inhibition against chitin synthase (CHS) and antifungal activities in vitro. The enzyme assay revealed that compound 5h showed excellent inhibitory activity against CHS with IC50 value of 0.10 mM, and the compounds 5b, 5d and 5q showed good inhibition against chitin synthase with IC50 values of 0.13 mM, 0.18 mM and 0.15 mM, respectively, while IC50 value of ployoxin B was 0.08 mM. Meanwhile, the others of these compounds exhibited moderate inhibition potency against chitin synthase. The antifungal assay showed compound 5h had excellent antifungal activity compared with the control drugs fluconazole and polyoxin B against these tested strains including C. albicans, A. fumigatus, C. neoformans and A. flavus. Its excellent antifungal activity was consistent with its excellent chitin synthase inhibition. Compound 5k and 5l against C. albicans were comparable with fluconazole, and they showed strong antifungal potency against A. flavus with MIC values of 0.07 mmol/L and 0.13 mmol/L respectively. Compound 5m had similar MIC value against A. fumigatus to fluconazole. The phenomenon that compounds 5b, 5d and 5q that showed good enzymatic inhibition didn't exert good antifungal activity, while compounds 5k, 5l and 5m that showed moderate chitin synthase inhibition exhibited excellent antifungal activity was discussed. Furthermore, the trial of drug combination showed that compounds had synergistic effects or additive effects with fluconazole against tested fungi which also verified that these designed compounds targeted different targets from that of fluconazole. Additionally, the antibacterial trial showed that all synthesized compounds had little potency against tested bacteria strains. These results indicated that the designed compounds were potential chitin synthase inhibitors and had selectively antifungal activities.