Benzothieno[3,2-b]quinolinium and 3-(phenylthio)quinolinium compounds: Synthesis and evaluation 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.

Synthesis of indolo- and benzothieno[3,2-c]quinolines via POCl3 mediated tandem cyclization of o-alkynylisocyanobenzenes derived from o-alkynyl-N-phenylformamides

A synthesis of indolo[3,2-c]quinolines and benzothieno[3,2-c]quinolines has been developed employing o-alkynyl-N-phenylformamide derivatives as the substrates. The reaction proceeded via a tandem process involving POCl3‒assisted intramolecular cyclization of the firstly formed...

Isothiourea-catalysed enantioselective annulation of 2-aminobenzothiophenes with α,β-unsaturated anhydrides

An isothiourea-catalysed asymmetric Michael/lactamization cascade reaction of 2-aminobenzothiophenes and α,β-unsaturated anhydrides for the enantioselective synthesis of benzothienopiperidones with high stereoselectivities was developed.

Metal-free switchable ortho/ipso-cyclization of N-aryl alkynamides: divergent synthesis of 3-selenyl quinolin-2-ones and azaspiro[4,5]trienones

A selenium radical triggered switchable ortho/ipso-cyclization cascade of N-aryl alkynamides has been devised under metal-free conditions to access 3-selenyl quinolin-2-ones and 3-selenospiro[4,5]trienones in high yields (up to 98%).

AlCl3-Catalyzed Intramolecular Cyclization of N-Arylpropynamides with N-Sulfanylsuccinimides: Divergent Synthesis of 3-Sulfenyl Quinolin-2-ones and Azaspiro[4,5]trienones

Switchable ortho/ipso-cyclization of N-arylpropynamides induced with N-sulfanylsuccinimides as general sulfur reagents is reported. In the presence of MeOH, para-fluoro N-arylpropynamides exclusively undergo the ipso-cyclization to give 3-sulfenyl azaspiro[4,5]trienones. Two kinds of bioactive heterocycles, benzothieno-[3,2-b]quinoline and -[2,3-c]quinolone, have been directly and efficiently prepared from the corresponding sulfenylated products.

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.

Design, synthesis, and evaluations of antifungal activity of novel phenyl(2H-tetrazol-5-yl)methanamine derivatives

Fungal infections pose a continuous and serious threat to human health and life. The intrinsic resistance has been observed in many genera of fungi. Many fungal infections are caused by opportunistic pathogens that may be endogenous (Candida infections) or acquired from the environment (Cryptococcus and Aspergillus infections). So, new therapeutic strategies are needed to combat various fungal infections. Fluconazole shows good antifungal activity with relatively low toxicity and is preferred as first line antifungal therapy, but it has suffered from severe drug resistance. So, there is a need to design novel analogues by modification of fluconazole-like structure. A novel series of phenyl(2H-tetrazol-5-yl)methanamine derivatives were synthesized by reaction of α-amino nitrile with sodium azide and ZnCl2 in presence of isopropyl alcohol. They were evaluated for antifungal activity against Candida albicans and Aspergillus niger and subjected to docking study against 1EA1.

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.

Preliminary antifungal and cytotoxic evaluation of synthetic cycloalkyl[b]thiophene derivatives with PLS-DA analysis

A series of 2-[(arylidene)amino]-cycloalkyl[b]thiophene-3-carbonitriles (2a-x) was synthesized by incorporation of substituted aromatic aldehydes in Gewald adducts (1a-c). The title compounds were screened for their antifungal activity against Candida krusei and Criptococcus neoformans and for their antiproliferative activity against a panel of 3 human cancer cell lines (HT29, NCI H-292 and HEP). For antiproliferative activity, the partial least squares (PLS) methodology was applied. Some of the prepared compounds exhibited promising antifungal and proliferative properties. The most active compounds for antifungal activity were cyclohexyl[b]thiophene derivatives, and for antiproliferative activity cycloheptyl[b]thiophene derivatives, especially 2-[(1H-indol-2-yl-methylidene)amino]- 5,6,7,8-tetrahydro-4H-cyclohepta[b]thiophene-3-carbonitrile (2r), which inhibited more than 97 % growth of the three cell lines. The PLS discriminant analysis (PLS-DA) applied generated good exploratory and predictive results and showed that the descriptors having shape characteristics were strongly correlated with the biological data.

δ-Carbolines and their ring-opened analogs: synthesis and evaluation against fungal and bacterial opportunistic pathogens

Previous studies have indicated that the δ-carboline (2) ring system derived from the natural product cryptolepine (1) may represent a pharmacophore for anti-infective activity. This paper describes the design and synthesis of a small library of substituted δ-carbolines and the evaluation of the anti-fungal and anti-bacterial activities. An evaluation of the anti-bacterial activity of a previously reported library of ring-opened analogs was also conducted to provide an opportunity to test the hypothesis that both group of compounds may have the same biological target. Results indicate that against a selected group of fungal pathogens, substituted δ-carbolinium analogs displayed higher potency and several fold lower cytotoxicity than cryptolepine the parent natural product. Both the δ-carbolinium compounds and their ring-opened analogs, exhibited equally high anti-bacterial activity against the selected pathogens and especially against the gram positive bacteria evaluated.

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

Ring-opened benzothieno[3,2-b]quinolinium salts (3) were designed and synthesized with substitution on the thiophene moiety. In vitro screenings were carried out against fungal pathogens including Cryptococcus neoformans, Candida albicans, Candida glabrata, Candida krusei and Aspergillus fumigatus. In all, by replacing the N-methyl group (2) with N-ω-phenylpentyl or ω-cyclohexylpentyl group to form substituted 3-(phenylthio)quinolinium compounds produced remarkable potencies, as high as 300-fold (cf, cryptolepine (1)=250 μg/mL vs 11p=0.8 μg/mL for C. albicans) over the starting tetracyclic parent. In addition, all the N-ω-cyclohexylpentyl analogs produced superior activity against all the microorganisms tested than the N-ω-phenylpentyl substituted compounds. The potential of these compounds to induce toxicity in Vero cells was also investigated and the majority of them showed lower or no cytotoxicity at 10 μg/mL than amphotericin B, the gold standard in antifungal drug development. For instance, the trifluoromethyl substituted analogs (11n-p) have selectivity indices over 2-fold better than those of amphotericin B in C. neoformans. Overall, this ring-opened scafford of benzothienoquinolines, with substitution on the thiophenyl moiety, serves as a new lead for further development.

Identification of 3-phenylaminoquinolinium and 3-phenylaminopyridinium salts as new agents against opportunistic fungal pathogens

Previous studies on the indoloquinoline alkaloid, cryptolepine (2), revealed that it has antii-nfective properties among other activities. Using Structure-activity relationship (SAR) techniques, several ring-opened analogs of cryptolepine (3-phenylaminopyridinium and 3-phenylaminoquinolinium derivatives) were designed to improve the potency and lower the cytotoxicity shown by several of the precursor agents. Results indicate that these ring-opened analogs constitute new anti-infective agents with over a 100-fold potency and several fold lower cytotoxicity than cryptolepine from which they are derived.