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 q², noncross-validated r², 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 q² of 0.815 and an r² 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.     

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.     

Synthesis and cytotoxic activity of pyrazino[1,2-b]-isoquinolines, 1-(3-isoquinolyl)isoquinolines, and 6,15-iminoisoquino[3,2-b]-3-benzazocines

A series of pyrazino[2,1-b]isoquinoline and 6,15-iminoisoquino[3,2-b]-3-benzazocine compounds related to renieramycins, cribrostatin 4, and phthalascidin was synthesized and their in vitro cytotoxic activities were evaluated against three human cancer cell lines. Pyrazino[2,1-b]isoquinolines, 6,15-iminoisoquino[3,2-b]-3-benzazocines, and other more complex octacyclic compounds have been obtained and derived to precursors of iminium ion species. Hydrogenolysis of the lactam function in pentacyclic compounds gave 1-(3-isoquinolyl)isoquinolines. The micromolar cytotoxic activity of representative structures was apparently uninfluenced by the ability to generate intermediates which would permit covalent bonding to DNA.     

Synthesis and antibiofilm evaluation of 3-hydroxy-2,3-dihydroquinazolin-4(1H)-one derivatives against opportunistic pathogen Acinetobacter baumannii

The emergence of multidrug resistant microorganisms has triggered the impending need for new aitimicrobial strategies. The antivirulence strategy with the benefite of alleviating the drug resistance becomes the focus of research. In this study, 22 quorum sensing inhibitors were synthesized by mimicking the structure of autoinducer and acinetobactin and up to 34% biofilm inhibition was observed with 5u. The biofilm inhibition effect was further demonstrated with extracellular polysaccharides inhibition and synergism with Gentamycin sulphate.     

Synthesis and evaluation of thiophene-based guanylhydrazones (iminoguanidines) efficient against panel of voriconazole-resistant fungal isolates

A series of new thiophene-based guanylhydrazones (iminoguanidines) were synthesized in high yields using a straightforward two-step procedure. The antifungal activity of compounds was evaluated against a wide range of medicaly important fungal strains including yeasts, molds, and dermatophytes in comparison to clinically used drug voriconazole. Cytotoxic properties of compounds were also determined using human lung fibroblast cell line and hemolysis assay. All guanylhydrazones showed significant activity against broad spectrum of clinically important species of Candida spp., Aspergillus fumigatus, Fusarium oxysporum, Microsporum canis and Trichophyton mentagrophytes, which was in some cases comparable or better than activity of voriconazole. More importantly, compounds 10, 11, 13, 14, 18 and 21 exhibited excellent activity against voriconazole-resistant Candida albicans CA5 with very low minimal inhibitory concentration (MIC) values <2 μg mL⁻¹. Derivative 14, bearing bromine on the phenyl ring, was the most effective compound with MICs ranging from 0.25 to 6.25 μg mL⁻¹. However, bis-guanylhydrazone 18 showed better selectivity in terms of therapeutic index values. In vivo embryotoxicity on zebrafish (Danio rerio) showed improved toxicity profile of 11, 14 and 18 in comparison to that of voriconazole. Most guanylhydrazones also inhibited C. albicans yeast to hyphal transition, essential for its biofilm formation, while 11 and 18 were able to disperse preformed Candida biofilms. All guanylhydrazones showed the equal potential to interact with genomic DNA of C. albicans in vitro, thus indicating a possible mechanism of their action, as well as possible mechanism of observed cytotoxic effects. Tested compounds did not have significant hemolytic effect and caused low liposome leakage, which excluded the cell membrane as a primary target. On the basis of computational docking experiments using both human and cytochrome P450 from Candida it was concluded that the most active guanylhydrazones had minimal structural prerequisites to interact with the cytochrome P450 14α-demethylase (CYP51). Promising guanylhydrazone derivatives also showed satisfactory pharmacokinetic profile based on molecular calculations.     

Synthesis of new 1-[2-Azido-2-(2,4-dichlorophenyl)ethyl]-1H/-imidazoles and in vitro evaluation of their antifungal activity

New 1-[2-azido-2-(2,4-dichlorophenyl)ethyl]-1H/-imidazole were synthesized by nucleophilic substitution of various tertiary alcohols with azide anion in presence of boron trifluoride-diethyl etherate. Their antifungal activity was evaluated against Candida albicans, Candida glabrata, Aspergillus fumigatus and an azole-resistant petite mutant of C. glabrata. Preliminary SAR results are discussed.     

Synthesis and evaluation of isosteres of N-methyl indolo[3,2-b]-quinoline (cryptolepine) as new antiinfective agents

Isosteres of cryptolepine (1) were synthesized and evaluated for their antiinfective activities. Overall, the sulfur isostere, 5-methyl benzothieno[3,2-b]quinolinium salt (5b), was equipotent to 1 and has shown no cytotoxicity at 23.8 microg/mL. Compound 5b was also found to have a broad spectrum of activity. Both the carbon and oxygen isosteres were less potent than cryptolepine. A limited library of 2-substituted analogs of 5b has been synthesized and evaluated in antifungal screens but did not show increase in potency compared to the unsubstituted 5b. Similarly, evaluation of tricyclic benzothieno[3,2-b]pyridines while showing promise in individual screens did not produce an overall increase in potency. Overall, the evaluation of the activities of 5b compared with standard antifungal/anti-protozoal agents suggests that the benzothienoquinoline scaffold could serve as a lead for optimization.     

Synthesis and evaluation of cis-hexahydropyrrolo[3,2-b]pyrrol-3-one peptidomimetic inhibitors of CAC1 cysteinyl proteinases

A stereoselective synthesis of functionalised cis-hexahydropyrrolo[3,2-b]pyrrol-3-ones has been developed through Fmoc and Cbz-protected intermediates 5 and 6. Building blocks 5 and 6 were prepared via the intramolecular cyclisation of anti-epoxide 17. The intramolecular reaction occurred exclusively through the anti-epoxide to provide the 5,5-cis-fused bicycle, whereas the syn-epoxide, which theoretically would provide the 5,5-trans-fused bicycle, remained unchanged. These experimental observations are consistent with a key design element that we have introduced within this novel bicyclic ketone scaffold. Our bicyclic design strategy provides chiral stability to the bridgehead stereocentre that is situated alpha to the ketone because the cis-fused geometry is both thermodynamically and kinetically stable. Building blocks 5 and 6 have been utilised in both solid phase and solution phase syntheses of peptidomimetics 22, 36-40, which exhibit potent in vitro inhibition against a range of CAC1 cysteinyl proteinases. Compound 22, a potent and selective inhibitor of human cathepsin K exhibited good primary DMPK properties along with promising activity in an in vitro cell-based human osteoclast assay of bone resorption.     

Synthesis and QSAR studies on hypotensive 1-[3-(4-substituted phenylthio) propyl]-4-(substituted phenyl) piperazines

A series of 1-[3-(4-substituted phenylthio) propyl]-4-(substituted phenyl) piperazines has been synthesized and evaluated for hypotensive activity. The QSAR studies indicate that resonance and hydrophobic parameters of the aryl substituents are important for hypotensive activity. The similar role of resonance parameter in describing the variance of 5-HT(2A) receptor binding affinities of these compounds suggests a possible role of 5-HT(2A) receptors in mediating the hypotensive action of title compounds.     

Synthesis of New 9-glycosyl-4,9-dihydropyrano [3,4-b]indole-1(3H)-ones as Antibacterial Agents

A series of new 9-glycosyl-4,9-dihydropyrano[3,4-b]indole-1(3H)-ones 3 was synthesized in moderate to low yields. 4,9-Dihydropyrano[3,4-b]indole-1(3H)-ones (1) were coupled with different acetobromoglycopyranoses 2 in refluxing toluene in the presence of silver oxide to afford one coupling product of the respective N-glycosides. α-L-Arabinopyranosides 3j and 3m were the most active glycosides among the tested compounds against certain Gram positive and Gram negative bacterial strains.     

Benzofuro[3,2-d]pyrimidines inspired from cercosporamide CaPkc1 inhibitor: Synthesis and evaluation of fluconazole susceptibility restoration

In a context of growing resistance to classical antifungal therapy, the design of new drugs targeting alternative pathways is highly expected. Benzofuro[3,2-d]pyrimidine derivatives, derived from (?)-cercosporamide, were synthesized and evaluated as potential Candida albicans PKC inhibitors in the aim of restoring susceptibility to azole treatment. Co-administration assay of benzofuropyrimidinedione 23 and fluconazole highlighted a synergistic effect on inhibition of cell growth of a Candida albicans resistant strain.     

Synthesis of 3-(alpha- and beta-D-arabinofuranosyl)-6-chloro-1,2,4-triazolo[4,3-b]pyridazine

Di-O-isopropylidene- and O-methanesulfonyl-protected 1-C-(6-chloro-1,2,4-triazolo[4,3-b]pyridazin-3-yl)pentitols were prepared in three to four steps from D-galactose, D-glucose, D-mannose, and 2,3:5,6-di-O-isopropylidene-alpha-D-mannofuranose. Acid-catalysed treatment of (1S)- and (1R)-1-C-(6-chloro-1,2,4-triazolo[4,3-b]-pyridazin-3-yl)-2,3:4,5-di-O-isopropylidene-1-O-methanesulfonyl-D-arabinitols in refluxing 1,2-dimethoxyethane furnished 3-(alpha- and beta-D-arabinofuranosyl)-6-chloro-1,2,4-triazolo[4,3-b]pyridazine, respectively. Several structures, including the structure of the 3-(beta-D-arabinofuranosyl)-6-chloro-1,2,4-triazolo[4,3-b]pyridazine, were also determined by single-crystal X-ray diffraction analysis.     

Synthesis,antidepressant evaluation and QSAR studies of novel 2-(5H-[1,2,4]triazino[5,6-b]indol-3-ylthio)-N-(substituted phenyl)acetamides

In search for novel antidepressants, a series of 2-(5H-[1,2,4]triazino[5,6-b]indol-3-ylthio)-N-(substituted phenyl)acetamides was synthesized and screened for potential antidepressant activity by tail suspension test (TST) in mice. Number of synthesized compounds exhibited impressive antidepressant activity, measured in terms of percentage decrease in immobility duration (%DID). QSAR analysis was also undertaken which correlated three parameters FOSA, PISA, and glob with biological activity.     

Synthesis and anticancer evaluation of 3-aryl-6-phenylimidazo[2,1-b]thiazoles

A series of new 3,6-diphenylimidazo[2,1-b]thiazole derivatives (4a–l) are synthesized and evaluated for their anticancer activity. Some of the synthesized compounds have shown potent anti-proliferative activity against HeLa, MDA-MB-231, A549 and THP1 human cancer cell lines. Among the active compounds, 3-(3-trifluoromethylphenyl)-6-phenylimidazo[2,1-b]thiazole (4j) has caused significant cytotoxicity in HeLa cells, with IC₅₀ as low as 6.5 μM. Compound 4j has induced caspase-3 and caspase-8 activation, leading to an apoptotic cell death. FACS analysis has revealed that compound 4j arrests cells in G0/G1 phase. The presence of 3-(3-trifluoromethylphenyl)- or 3-(3-chlorophenyl)-substituent, in that order, on the 6-phenylimidazo[2,1-b]thiazole impacts more positively than other aryl-substituents, on the anti-proliferative properties of these compounds.     

Synthesis and biological evaluation of 3-functionalized 2-phenyl- and 2-alkylbenzo[b]furans as antiproliferative agents against human melanoma cell line

The key function of microtubules and mitotic spindle in cell division make them attractive targets in anticancer therapy. In the present study, functionalized in 3 position 2-phenyl- and 2-alkylbenzo[b]furans were synthesized and evaluated as antitumor agents. Among the synthesized derivatives 13a, 13b and 14 exhibited the most potent antiproliferative activity against human melanoma A375 cell line with IC₅₀ values of 2.85 µM, 0.86 µM, 0.09 µM, respectively. The most promising compound defined was 14 with three methoxy groups in the 3-aroyl substituent and 7-methoxy group in 2-phenylbenzo[b]furan skeleton. Tubulin polymerization assay, confocal microscopy imaging and flow cytometry analysis revealed that 2-phenyl-3-aroylbenzo[b]furans (13a, 13b and 14) inhibited tubulin polymerization leading to disruption of mitotic spindle formation, cell cycle arrest in G2/M phase and apoptosis.     

Antimycobacterial activity: synthesis of novel 3-(substituted phenyl)-6,7-dimethoxy-3a,4-dihydro-3H-indeno[1,2-c]isoxazole analogues

In this study, a series of novel 3-(substituted phenyl)-6,7-dimethoxy-3a,4-dihydro-3H-indeno[1,2-c]isoxazole analogues were synthesized and evaluated for antimycobacterial activity against Mycobacterium tuberculosis (MTB) H₃₇Rv and isoniazid resistant M. tuberculosis (INHR-MTB). All the newly synthesized compounds were showing moderate to high inhibitory activities. The compound 6,7-dimethoxy-3-(4-chloro phenyl)-4H-indeno[1,2-c]isoxazole (4b) was found to be the most promising compound, active against MTB H₃₇Rv and INHR-MTB with minimum inhibitory concentrations of 0.22 and 0.34 μM.     

Synthesis of 3-(3-pyridyl)- and 3-(3-benzo[b]thienyl)-D-alanine

The DL-arylamino acid ethyl ester derivatives of beta-(3-pyridyl)-DL-alanine, and beta-(3-benzo[b]thienyl)-DL-alanine were synthesized by diethyl acetamidomalonate condensation with the respective arylmethyl halides followed by partial hydrolysis to the monoethyl ester and decarboxylation. Each derivative was enzymatically resolved to a separable mixture of the corresponding N-acetyl-L-amino acid and the unchanged D amino acid derivative. Acidic hydrolysis of the latter gave the corresponding D-amino acid, the optical purity of which was established by HPLC analysis of the 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl isothiocyanate (GITC) derivative. The free D amino acids were converted to D-BOC derivatives by reaction with di-tert-butyldicarbonate in tert-butyl alcohol, water and sodium hydroxide.     

Synthesis, stereochemistry and in vitro antimicrobial evaluation of novel 2-[(2,4-diaryl-3-azabicyclo[3.3.1]nonan-9-ylidene)hydrazono]-4-phenyl-2,3-dihydrothiazoles

2-[(2,4-Diaryl-3-azabicyclo[3.3.1]nonan-9-ylidene)hydrazono]-4-phenyl-2,3-dihydrothiazoles (3a-3k) have been synthesized by the cyclization of 2-[(2,4-diaryl-3-azabicyclo[3.3.1]nonan-9-one thiosemicarbazones with phenacyl bromide and characterized by analytical (melting point and elemental analysis) and spectral (IR, (1)H NMR, (13)C NMR, D(2)O exchange, NOESY and mass) techniques. The novel Hantzsch products (3a-3k) were screened for their in vitro antibacterial and antifungal activities against some selected microorganisms. Structure activity relationship (SAR) for the reported compounds was studied by comparing their MIC values with standard drugs (Streptomycin and Amphotericin B). The results show that 3e against Escherichia coli and Cryptococcus neoformans3i against Bacillus Subtilis, 3b against Aspergillus flavus, and 3k against Rhizopus sp. were found to show significant growth inhibition.     

Synthesis and cytotoxic evaluation of certain 4-(phenylamino)furo[2,3-b]quinoline and 2-(furan-2-yl)-4-(phenylamino)quinoline derivatives

Certain 4-(phenylamino)furo[2,3-b]quinoline and 2-(furan-2-yl)-4-(phenylamino)quinoline derivatives were synthesized and evaluated in vitro against the full panel of NCIs 60 cancer cell lines. The preliminary results indicated these tricyclic 4-(phenylamino)furo[2,3-b]quinolines were more cytotoxic than their corresponding 2-(furan-2-yl)-4-(phenylamino)quinoline isomers. For the 4-(phenylamino)furo[2,3-b]quinolines, compounds 2a and 3d are two of the most potent with a mean GI50 value of 0.025 microM in each case. Inactivity of 2b and 2c (positional isomers of 2a) indicated that both electronic environment, and the distance between intercalating pharmacophore and H-bond-donating MeO group are important. For the 2-(furan-2-yl)-4-(phenylamino)quinoline isomers, compound 12 (a mean GI50 of 4.36 microM), which bears a para-COMe substituent, is more active than its meta-substituted counterpart 13 (10.5 microM). However, the electron-donating MeO substituent is preferred at the meta-position, and the cytotoxicity for the meta-substituted derivatives decreased in the order: MeO derivative 14b (3.05 microM) > oxime 16 (6.85 microM) > ketone 13 (10.5 microM) > methyl oxime 18 (20.6 microM).