Optimization of 3-(phenylthio)quinolinium compounds against opportunistic fungal pathogens

Structural Simplification of Cryptolepine to Obtain Novel Antifungal Quinoline Derivatives against Phytopathogenic Fungi

A series of quinoline derivatives were designed and synthesized by the structural simplification of cryptolepine and evaluated for their fungicidal activity against six phytopathogenic fungi. Most of these compounds exhibited remarkable activities against Botrytis cinereain vitro. Among them, compounds A18 and L01 showed superior antifungal activity. Significantly, compared to cryptolepine, compound A18 exhibited broad-spectrum inhibitory activities against B. cinerea, Sclerotinia sclerotiorum, Rhizoctonia solani, Phytophthora capsica, Magnaporthe oryzae, and Fusarium graminearum with the respective EC₅₀ values of 0.249, 1.569, 3.915, 0.505, 0.246, and 4.999 μg/mL. Compound L01 displayed the best antifungal activity against B. cinerea with an EC₅₀ value of 0.156 μg/mL. Preliminary mechanistic studies showed that compound A18 could inhibit spore germination, affect the permeability of the cell membrane, increase the content of reactive oxygen species, and affect the morphology of hyphae and cells. Moreover, compound A18 showed excellent in vivo protective effect against B. cinerea, which was more potent than pyrimethanil and equitant to cryptolepine. These results evidenced that compound A18 displayed superior fungicidal activities and could be a potential fungicidal candidate against plant fungal diseases.

Electrochemical Selective C3-Thiolation of Quinolines

An electrochemical method has been developed to achieve C3-thiolation of quinoline compounds. This new strategy highlights the maximum atom economy, direct conversion and also the use of simple and readily...

Design, Synthesis, and Antifungal Evaluation of Cryptolepine Derivatives against Phytopathogenic Fungi

Inspired by the widely antiphytopathogenic application of diversified derivatives from natural sources, cryptolepine and its derivatives were subsequently designed, synthesized, and evaluated for their antifungal activities against four agriculturally important fungi Rhizoctonia solani, Botrytis cinerea, Fusarium graminearum, and Sclerotinia sclerotiorum. The results obtained from in vitro assay indicated that compounds a1-a24 showed great fungicidal property against B. cinerea (EC₅₀ < 4 μg/mL); especially, a3 presented significantly prominent inhibitory activity with an EC₅₀ of 0.027 μg/mL. In the pursuit of further expanding the antifungal spectrum of cryptolepine, ring-opened compound f1 produced better activity with an EC₅₀ of 3.632 μg/mL against R. solani and an EC₅₀ of 5.599 μg/mL against F. graminearum. Furthermore, a3 was selected to be a candidate to investigate its preliminary antifungal mechanism to B. cinerea, revealing that not only spore germination was effectively inhibited and the normal physiological structure of mycelium was severely undermined but also detrimental reactive oxygen was obviously accumulated and the normal function of the nucleus was fairly disordered. Besides, in vivo curative experiment against B. cinerea found that the therapeutic action of a3 was comparable to that of the positive control azoxystrobin. These results suggested that compound a3 could be regarded as a novel and promising agent against B. cinerea for its valuable potency.

Imidazolylchromanones containing non-benzylic oxime ethers: synthesis and molecular modeling study of new azole antifungals selective against Cryptococcus gattii

A series of imidazolylchromanone oximes containing phenoxyethyl ether moiety, as found in omoconazole, were synthesized and evaluated against yeasts (Candida albicans and Cryptococcus gattii) and filamentous fungi (Aspergillus fumigatus and Exophiala dermatitidis). Although the title compounds showed marginal activity against filamentous fungi but all of them exhibited potent activity against C. gattii (MIC values ≤4 μg/mL). Among them, (3-chlorophenoxy)ethyl analog 7c with MIC value of 0.5 μg/mL was the most potent compound. Further molecular docking studies provided a better insight into the binding of designed compounds within the homology modeled active site of CnCYP51 (Cryptococcus CYP51-14α-demethylase).

Structure-activity relationship (SAR) and preliminary mode of action studies of 3-substituted benzylthioquinolinium iodide as anti-opportunistic infection agents

Opportunistic infections are devastating to immunocompromised patients. And in especially sub-Saharan Africa where the AIDS epidemic is still raging, the mortality rate was recently as high as 70%. The paucity of anti-opportunistic drugs, the decreasing efficacy and the development of resistance against the azoles and even amphotericin B have stimulated the search for new drugs with new mechanisms of action. In a previous work, we showed that a new chemotype derived from the natural product cryptolepine displayed selective toxicity against opportunistic pathogens with minimal cytotoxicity to normal cells. In this manuscript, we report the design and synthesis of substituted benzylthioquinolinium iodides, evaluated their anti-infective properties and formulated some initial structure-activity relationships around phenyl ring A from the original natural product. The sensitivity of the most potent analog 10l, to selected strains of C. cerevisiae was also evaluated leading to the observation that this scaffold may have a different mode of action from its predecessor, cryptolepine.

CoMFA studies and in vitro evaluation of some 3-substituted benzylthio quinolinium salts as anticryptococcal agents

The 3-dimensional quantitative structure-activity relationship (3D-QSAR) molecular modeling technique or comparative molecular field analysis (CoMFA) has been used to design analogs of the natural product cryptolepine (1). Twenty-three compounds with their in vitro biological activities (IC50 values) against Crytococcus neoformans were used to generate the training set database of compounds for the CoMFA studies. The cross-validated q(2), noncross-validated r(2), and partial least squares (PLS) analysis results were used to predict the biological activity of 11 newly designed test set compounds. The best CoMFA model produced a q(2) of 0.815 and an r(2) of 0.976 indicating high statistical significance as a predictive model. The steric and electrostatic contributions from the contour map were interpreted from the color-coded contour plots generated from the PLS model and the active structural components for potency against C. neoformans were determined and validated in the test set compounds. The 3-substituted benzylthio quinolinium salts (4) that make up the test set were synthesized and evaluated based on the predicted activity from the CoMFA model and the results produced a good correlation between the predicted and experimental activity (R=0.82). Thus, CoMFA has served as an effective tool to aid the design of new analogs and in this case, it has aided the identification of compounds equipotent with amphotericin B, the gold standard in antifungal drug design.