Efficient Regioselective Synthesis of Novel Water-Soluble 2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium Derivatives by Annulation Reactions of 8-quinolinesulfenyl Halides

Regioselective synthesis of novel 2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium derivatives has been developed by annulation reactions of 8-quinolinesulfenyl halides with vinyl chalcogenides (vinyl ethers, divinyl sulfide, divinyl selenide and phenyl vinyl sulfide) and tetravinyl silane. The novel reagent 8-quinolinesulfenyl bromide was used in the annulation reactions. The influence of the substrate structure and the nature of heteroatoms on the direction of the reactions and on product yields has been studied. The opposite regiochemistry was observed in the reactions with vinyl chalcogenides and tetravinyl silane. The obtained condensed heterocycles are novel water-soluble functionalized compounds with promising biological activity.

Tuning the selectivity of N-alkylated styrylquinolinium dyes for sensing of G-quadruplex DNA

Selective and sensitive detection of G-quadruplex DNA structures is an important issue and attracts extensive interest. To this end, numerous small molecular fluorescent probes have been designed. Here, we present a series of N-alkylated styrylquinolinium dyes named Ls-1, Ls-2 and Ls-3 with varying side groups at the chain end. We found that these dyes exhibited different binding behaviors to DNAs, and Ls-2 with a sulfonato group at the chain end displayed sensitivity and selectivity to G-quadruplex DNA structures in vitro. The characteristics of this dye and its interaction with G-quadruplex DNA were comprehensively investigated by means of UV-vis spectrophotometry, fluorescence, circular dichroism and molecular docking. Furthermore, confocal fluorescence images and MTT assays indicated dye Ls-2 could pass through membrane and enter the living HepG2 cells with low cytotoxicity.

Synthesis and Antimicrobial Activity of Sulfur Derivatives of Quinolinium Salts

A novel method for cleavage of the dithiine ring in 5,12-(dimethyl)-thioqinantrenium bis-chloride 1 "via" reaction with sodium hydrosulfide leads to 1-methyl-3-mercaptoquinoline-4(1H)-thione 2. Further transformation of thiol and thione functions of compound 2 leads to a series of sulfide and disulfide derivatives of quinolinium salts 4 and 6. 1-Methyl-4-chloro-3-benzylthioquinoline chloride 8 was obtained by N-alkylating 4-chloro-3-benzylthioquinoline using dimethyl sulfate. Antimicrobial activity of the obtained compounds was investigated using six Gram-positive and six Gram-negative bacterial strains, as well as Candida albicans yeast. Greater activity was demonstrated towards Gram-positive strains. MIC values for compounds and with benzylthio 4d and benzoylthio 4f substituents in 3-quinoline position were found to be in the 0.5-1 μg/mL range, at a level similar to that of ciprofloxacin (reference). Compounds 4d and 4f also demonstrated interesting antifungal properties (MIC = 1).

Photoinduced apoptosis using a peptide carrying a photosensitizer

A novel molecule, TatBim-Alexa, consisting of the HIV1 Tat cell-penetrating peptide, the Bim apoptosis-inducing peptide, and Alexa Fluor 546 was synthesized for photoinducion of apoptosis. The Alexa Fluor 546 was used as a photosensitizer and covalently attached at the C-terminus of TatBim peptide by the thiol-maleimide reaction. Photo-dependent cytosolic internalization of TatBim-Alexa and photo-dependent apoptosis using TatBim-Alexa were demonstrated in several kinds of mammalian cells including human cancer cell lines.

Selective Inhibition of the Mitochondrial Permeability Transition Pore Protects against Neurodegeneration in Experimental Multiple Sclerosis

The mitochondrial permeability transition pore is a recognized drug target for neurodegenerative conditions such as multiple sclerosis and for ischemia-reperfusion injury in the brain and heart. The peptidylprolyl isomerase, cyclophilin D (CypD, PPIF), is a positive regulator of the pore, and genetic down-regulation or knock-out improves outcomes in disease models. Current inhibitors of peptidylprolyl isomerases show no selectivity between the tightly conserved cyclophilin paralogs and exhibit significant off-target effects, immunosuppression, and toxicity. We therefore designed and synthesized a new mitochondrially targeted CypD inhibitor, JW47, using a quinolinium cation tethered to cyclosporine. X-ray analysis was used to validate the design concept, and biological evaluation revealed selective cellular inhibition of CypD and the permeability transition pore with reduced cellular toxicity compared with cyclosporine. In an experimental autoimmune encephalomyelitis disease model of neurodegeneration in multiple sclerosis, JW47 demonstrated significant protection of axons and improved motor assessments with minimal immunosuppression. These findings suggest that selective CypD inhibition may represent a viable therapeutic strategy for MS and identify quinolinium as a mitochondrial targeting group for in vivo use.

New class of 2-aryl-6-chloro-3,4-dihydroisoquinolinium salts as potential antifungal agents for plant protection: synthesis, bioactivity and structure-activity relationships

Thirty-four new 2-aryl-6-chloro-3,4-dihydroisoquinolin-2-ium bromides were synthesized, and their structures were elucidated by spectroscopic analysis. Antifungal activities against Alternaria alternate, Curvularia lunata and Valsa mali were evaluated by the mycelium linear growth rate method. SAR was discussed also. All compounds showed some activity against each of the fungi at 25 μg/mL. Compared to azoxystrobin, a commercial fungicide, 31 out of 34 test compounds showed higher inhibition rates against C. lunata and 10 were more effective against A. alternate and V. mali. Compounds 5-4, 5-2 and 5-34 showed the highest activity against A. alternate (EC50 = 10.3 μg/mL), C. lunata (EC50 = 4.6 μg/mL) and V. mali (EC50 = 3.9 μg/mL), respectively, superior to azoxystrobin (EC50 = 12.8, 71.9, 37.2 μg/mL). Compound 5-4 displayed good activities against each of the fungi with EC50 of 10.3, 4.7, and 18.0 μg/mL while 5-34 displayed excellent activities against V. mali (EC50 = 3.9 μg/mL) and C. lunata (EC50 = 5.8 μg/mL). The SAR showed that the type and position of substituents on the C-ring had significant effects on the activity. Generally, the presence of 2'-F, 4'-F or 2'-CH3 could significantly improve the activities, whereas OH, OMe, NO2 or CF3 groups decreased the activities. Thus, it was concluded that the present research provided a new series of 2-aryl-6-chloro-3,4-dihydroisoquinolin-2-iums with excellent antifungal potency, and the results were of importance for the structure optimization design, synthesis and development of more potent isoquinoline antifungal agents.

Mechanistic studies on regioselective dephosphorylation of phosphate prodrugs during a facile synthesis of antitumor phosphorylated 2-phenyl-6,7-methylenedioxy-1H-quinolin-4-one

Phosphorylation of 2-(3-hydroxy-5-methoxyphenyl)-6,7-methylenedioxy-1H-quinolin-4-one (1) afforded diphosphate 2. We found that, upon treatment with methanol under mild conditions, 2 can undergo facile and highly regioselective dephosphorylation to give the monophosphate 3, with a phosphate group remaining on the phenyl ring. The details of the dephosphorylation process were postulated and then probed by LC-MS and HPLC analyses. Furthermore, as a preliminary study, the water soluble monophosphate prodrug 4 was tested for antitumor activity against a MCF-7 xenograft nude mice model.

Synthesis, crystal structure, and spectroscopic properties of new stilbazolium salt with enlarged π-conjugated system

A new stilbazolium dye 4-{(E)-2-[4-(dimethylamino)naphthalen-1-yl]ethenyl}-1-methylquinolinium iodide monohydrate (DANSQI) having enlarged π-conjugated system was synthesized and characterized by X-ray diffraction, IR, Raman, UV-Vis, Fluorescence, (1)H- and (13)C NMR spectroscopy. Quantum chemical calculations were performed to obtain electronic structure and vibrational data, using DFT. The crystals are monoclinic, space group P21/n, with a=8.0751(14), b=25.839(4), c=10.9031(15) Å, V=2141.4(6) Å(3), and Z=4 (at 300(2) K). The unit cell contains four molecules of the dye, participating in weak intermolecular interactions. The cation is nearly flat with a deviation of the planarity of 5.08 (1)°. The dye investigated is the first stilbazolium iodide containing water molecule in the solid state therefore the N-dimethylamino group declines significantly from planarity, as indicated by C13N1C2C3 torsion angle of 16.08°. The dye studied shows solvatochromism of 84 nm in visible region and very large Stokes shift up to 253 nm. The intensity of fluorescence bands strongly depends on solvent polarity.

Further studies on bis-charged tetraazacyclophanes as potent inhibitors of small conductance Ca(2+)-activated K+ channels

Previously, quinolinium-based tetraazacyclophanes, such as UCL 1684 and UCL 1848, have been shown to be extraordinarily sensitive to changes in chemical structure (especially to the size of the cyclophane system) with respect to activity as potent non-peptidic blockers of the small conductance Ca(2+)-activated K(+) ion channels (SKCa). The present work has sought to optimize the structure of the linking chains in UCL 1848. We report the synthesis and SKCa channel-blocking activity of 29 analogues of UCL 1848 in which the central CH2 of UCL 1848 is replaced by other groups X or Y = O, S, CF2, CO, CHOH, CC, CHCH, CHMe to explore whether subtle changes in bond length or flexibility can improve potency still further. The possibility of improving potency by introducing ring substituents has also been explored by synthesizing and testing 25 analogues of UCL 1684 and UCL 1848 with substituents (NO2, NH2, CF3, F, Cl, CH3, OCH3, OCF3, OH) in the 5, 6 or 7 positions of the aminoquinolinium rings. As in our earlier work, each compound was assayed for inhibition of the afterhyperpolarization (AHP) in rat sympathetic neurons, an action mediated by the SK3 subtype of the SKCa channel. One of the new compounds (39, R(7) = Cl, UCL 2053) is twice as potent as UCL 1848 and UCL 1684: seven are comparable in activity.

Synthesis and in vitro antimicrobial activity of 1-methyl-3-sulfonylthio-4-aminoquinolinium chlorides

Synthesis and in vitro antimicrobial activity (MIC) of novel 1-methyl-3-sulfonylthio-4-aminoquinolinium chlorides 2 are described. Compounds 2 were obtained in the reaction of 1-methyl-4-aminoquinolinium 3-thiolates 1 with sulfonyl chlorides. Antimicrobial activity of compounds 2 was investigated using Gram-positive Staphylococcus aureus, Staphylococcus saprophyticus, Staphylococcus epidermidis, Micrococcus luteus, Enterococcus faecalis, Bacillus subtilis, Corynebacterium pseudodiphtericum and Gram-negative Escherichia coil, Klebsiella pneumoniae, Proteus vulgaris, Serratia marcescens, Citrobacter freundii, Pseudomonas aeruginosa strains as well as Candida albicans. The investigated compounds exhibited growth-inhibitory activity towards Gram-positive bacteria in the 4-64 microg/mL range whereas that towards Gram-negative bacteria covered the 128-1024 microg/mL range. The highest activity was shown by compound 2c, featuring a phenylsulfonylthio substituent in the 3-quinoline position and a 4-chlorophenylamine group in the position 4. All of the investigated compounds 2 showed antifungal activity in the 32-128 microg/mL range. Correlations between antimicrobial activity and chemical structure of the tested compounds were observed.

Biomimetic Total Synthesis and Antimicrobial Evaluation of Anachelin H

The first biomimetic total synthesis of the iron chelator anachelin H isolated from the cyanobacterium Anabaena cylindrica is reported. A first generation approach delivered one enantiomeric series of the polyketide fragment. Comparison of the 1H NMR data suggested the relative configuration of this anachelin fragment. The relative and absolute configuration of anachelin H was then established by total synthesis. A second generation approach involved the enzymatic conversion of N,N-dimethyltyramine to the anachelin chromophore. It was demonstrated that the enzyme tyrosinase is activated by the product during this reaction, the anachelin chromophore can serve as a tyrosinase activator. Anachelin H was evaluated against a panel of eleven bacterial and fungal pathogens, and moderate antibiotic activity (32 microg/mL) against Moraxella catarrhalis was found.

Vibrational spectroscopic studies of an organic non-linear optical crystal 8-hydroxyquinolinium picrate

8-hydroxyquinolinium picrate (8-HQP) was synthesized by the addition of equimolar quantities of 8-hydroxyquinoline (8-HQ) and picric acid (PA). Single crystals were grown from N,N dimethyl formamide (DMF) by restricted evaporation method at room temperature. The solubility of 8-HQP was determined in different solvents at various temperatures. The structural characterization of the grown crystals was carried out by X-ray diffraction. Vibrational modes were classified on the basis of group theoretical analysis and the spectral bands were compared with those of parent compounds in order to propose a tentative assignment by recording FT-IR, FT-Raman and polarized Raman spectra in different crystal orientations. The crystal possess lower cut-off at 230 nm and good transparency as confirmed by optical transmittance studies.

Synthesis and Biological Evaluation of N-Substituted Quinolinimides, as Potential Ligands for in Vivo Imaging Studies of δ-Opioid Receptors

We report here the syntheses of N-substituted quinolinimide derivatives displaying sufficient affinity and high selectivity for delta-opioid receptors. Among 9-subsituted derivatives, one showed much higher selectivity for the delta receptor in binding assays than the delta antagonist methylnaltrindole (6: Ki = 42 nM; micro/delta and kappa/delta > 238 on rat brain membranes) and antagonist properties. This compound was labeled with carbon-11 (t1/2 = 20.4 min) as a potential radioligand for the noninvasive assessment of delta opioid receptors in vivo with positron emission tomography (PET). A high yielding radiosynthesis of [11C]-6, based on the [11C]methyl introduction on the pyridine moiety by a Stille reaction, was described (radiochemical yield = 60 +/- 10%, specific activities = 0.8 to 1.5 Ci/micromol). The in vivo pharmacological profile in rats indicated that the radiotracer crossed the blood-brain barrier but was not stable and underwent rapid degradation in both plasma and brain. No specific binding was consequently revealed.

Isocyanide Addition to Pyridinium Salts. Efficient Entry into Substituted Nicotinonitrile Derivatives

The addition of isocyanides to pyridinium salts is studied. The process takes place efficiently when a carboxamido group is present in the 3 position of the pyridine ring. The outcome of the reaction involves the stabilization of the nitrilium intermediate by the amide, which suffers a mild dehydration, leading regioselectively to beta-cyano-gamma-carbamoyl-1,4-dihydropyridines. In this way, a variety of nicotinamide derivatives were carbamoylated. Extension to quinolinium, isoquinolinium, and N-acylpyridinium salts is also reported. [reaction: see text]

(Q)SAR studies to design new human choline kinase inhibitors as antiproliferative drugs

Most of the signal transduction pathways are mediated by protein kinases regulating every aspect of cell function. Mutations which deregulate their expression or their function or both result in cancers. Therefore, protein kinase inhibitors have become the focus of development of new therapies for cancer. A comprehensive review of Choline kinase (ChoK) was published by us in 2003. Since then, molecular information of ChoK inhibitors has been accumulated. In this review, we intend to summarize the new lines of evidence that will include the design of the most active antiproliferative agents so far described against ChoK. Studies have been aimed at the establishment of structure-activity relationships and the structural parameters that define ChoK inhibitory and antiproliferative activities of a set of twenty-five acyclic biscationic pyridophane and forty acyclic biscationic quinolinephane compounds. The corresponding QSAR equation was obtained for the whole set of bisquinolinium compounds for the antiproliferative activity, taking into consideration the electronic parameter sigma(R) of R(4), the molar refractivity (MR) of R(8), and the lipophilic parameters clog P and pi(linker). The most potent antiproliferative agent shows an IC(50) = 0.45 microM, predicted by the QSAR equation, whilst its experimental value is IC(50) = 0.20 microM. Finally, toxicity assays were performed for the most promising compounds because of their interesting antiproliferative activities [IC(50 HT-29) = 0.70, 0.80, 1.50 and 1.90 microM] and low toxicity [LD(50) = 16.7, 12.5, > 25 and > 20 mg/kg of mouse]. These biological activities justify further analysis for antitumoral assays under in vivo conditions.

7-Dialkylamino-1-alkylquinolinium Salts: Highly Versatile and Stable Fluorescent Probes

7-Dialkylamino- and 7-alkylsulfenyl-1-alkylquinolinium salts have been synthesized using a novel synthetic approach. The key intermediate, 7-fluoro-1-methylquinolinium iodide, was shown to possess high reactivity toward nitrogen and sulfur nucleophiles, and the kinetics of this nucleophilic aromatic substitution reaction was investigated. A wide variety of compounds were synthesized and characterized spectroscopically. High fluorescence quantum yields were observed, and this was attributed to the rigid molecular architecture. The thermal and photochemical stability of a number of compounds was investigated, and it was demonstrated that 7-dialkylamino-1-methylquinolinium salts have superior stability compared to a number of hemicyanine dyes and rigid charge-transfer probes. Based on the high quantum yields, the large Stokes shifts, and in particular, the high thermal and photochemical stability, it is concluded that 7-dialkylamino-1-methylquinolinium salts are excellent color-shifting, mobility-sensitive fluorescent probes for polymer characterization and other demanding applications.

On the Use of Nonfluorescent Dye Labeled Ligands in FRET-Based Receptor Binding Studies

The efficiency of fluorescence resonance energy transfer (FRET) is dependent upon donor-acceptor proximity and spectral overlap, whether the acceptor partner is fluorescent or not. We report here on the design, synthesis, and characterization of two novel pirenzepine derivatives that were coupled to patent blue VF and pinacyanol dyes. These nonfluorescent compounds, when added to cells stably expressing enhanced green fluorescent protein (EGFP)-fused muscarinic M1 receptors, promote EGFP fluorescence extinction in a time-, concentration-, and atropine-dependent manner. They display nanomolar affinity for the muscarinic receptor, determined using either FRET or classical radioligand binding conditions. We provide evidence that these compounds behave as potent acceptors of energy from excited EGFP with quenching efficiencies comparable to those of analogous fluorescent bodipy or rhodamine red pirenzepine derivatives. The advantages they offer over fluorescent ligands are illustrated and discussed in terms of reliability, sensitivity, and wider applicability of FRET-based receptor binding assays.

Synthesis and evaluation of the bis-nor-anachelin chromophore as potential cyanobacterial ligand

The cyanobacterial metabolite anachelin, postulated to serve as a biological ligand to Fe (siderophore), is composed of a fascinating blend of polyketide, peptide, and alkaloid building blocks. In particular, the latter consists of a N,N-dimethyltetrahydroquinolinium fragment, of which the biosynthesis is unknown. To investigate the role of this permanently positively charged fragment, we developed a synthesis of both the anachelin chromophore and its bis-nor derivative lacking the N,N-dimethyl groups starting from suitably protected nitro-DOPA in six and five steps, respectively, and in 50-64% overall yield. Both compounds were then compared for their chemical behavior toward oxidation. It was found that the bis-nor-anachelin chromophore is readily oxidized in solution in the presence of air, with a clear dependence of the rate of oxidation on the pH value. In addition, we could demonstrate that the enzyme tyrosinase, postulated to serve as key catechol oxidase in the biosynthesis of anachelin, also oxidized the bis-nor-hydroquinonamine derivative. Last, Fe(III) was shown to be an effective oxidant for the bis-nor-anachelin chromophore, resulting in all cases in the corresponding aminoquinone. In stark contrast, the anachelin chromophore resisted oxidation under various conditions surveyed (i.e., mediated by air, by tyrosinase, and by Fe(III)). In particular, Fe(III) was readily complexed by the anachelin chromophore, and the resulting complexes were characterized. In conclusion, these experiments demonstrate that the bis-nor-anachelin chromophore is unlikely to serve as cyanobacterial ligand, due to its instability toward oxidation. Moreover, the permanent quaternary ammonium group in anachelin renders the alkaloid chromophore much more stable against oxidation and thus results in its use as ligand for Fe(III).

Symmetrical Bis-Quinolinium Compounds: New Human Choline Kinase Inhibitors with Antiproliferative Activity against the HT-29 Cell Line

Studies have been aimed at the establishment of structure-activity relationships that define choline kinase inhibitory and antiproliferative activities of 40 bisquinolinium compounds. These derivatives have electron-releasing groups at position 4 of the quinolinium ring. It is found that the enzymatic inhibition is closely related to the size of the linker, the 3,3'-biphenyl moiety being the most suitable. On the other hand, the antiproliferative activity against the HT-29 cancer cell line is less influenced by the linker type and by substituent R(4). The corresponding QSAR equation was obtained for the whole set of compounds for the antiproliferative activity, the electronic parameter sigma(R) of R(4), the molar refractivity of R(8), and the lipophilic parameters clog P and pi(linker). The most potent antiproliferative agent so far described is 40 for which an IC(50) = 0.45 microM was predicted by the QSAR equation, while its experimental value is IC(50) = 0.20 microM.

Quinolinium salt as a potent inhibitor of lymphocyte apoptosis

The synthesis of several quinolinium salts and related compounds and their ability to inhibit glucocorticoid-induced apoptosis in murine thymocytes are described. Interestingly, 1-[2-methoxyimino-2-(4-pyrrolidin-1-yl-phenyl)ethyl]quinolinium bromide (11) showed a potent protective effect with an EC(50) of 0.013 microM, which was at least 300-fold more potent than the reference compound pifithrin-alpha.

Total Synthesis of Anachelin H

[structure: see text] The first total synthesis of anachelin H is reported. Starting from L-Ser, a stereodivergent synthesis of the polyketide fragment resulting in all possible diastereoisomers is described. The alkaloid peptide fragment is prepared via a tellurium-mediated oxidative aza annulation as the key step. Coupling of the fragments gave synthetic anachelin H, which was found to be identical to a sample of the natural product, thus confirming the configuration by total synthesis.

Ophthalmic glucose monitoring using disposable contact lenses--a review

We have developed a range of disposable and colorless tear glucose sensing contact lenses, using off-the-shelf lenses embedded with new water soluble, highly fluorescent and glucose sensitive boronic acid containing fluorophores. The new lenses are readily able to track tear glucose levels and therefore blood glucose levels, which are ideally suited for potential use by diabetics. The fluorescence responses from the lenses can be monitored using simple excitation and emission detection devices. The novelty of our approach is two fold. Firstly, the notion of sensing extremely low glucose concentrations in tears, which track blood levels, by our contact lens approach, and secondly, the unique compatibility of our new glucose signaling probes with the internal mildly acidic contact lens environment. The new lenses are therefore ideal for the non-invasive and continuous monitoring of tear glucose, with about 15-min response time, and a measured shelf life in excess of 3 months. In this review article, we show that fluorescence based signaling using plastic disposable lenses, which have already been industrially optimized with regard to vision correction and oxygen/analyte permeability etc, may a notable alternative to invasive and random finger pricking, the most widely used glucose monitoring technology by diabetics.

Groove-binding unsymmetrical cyanine dyes for staining of DNA: syntheses and characterization of the DNA-binding

Two new crescent-shaped unsymmetrical cyanine dyes have been synthesised and their interactions with DNA have been investigated by different spectroscopic methods. These dyes are analogues to a minor groove binding unsymmetrical cyanine dye, BEBO, recently reported by us. In this dye, the structure of the known intercalating cyanine dye BO was extended with a benzothiazole substituent. To investigate how the identity of the extending heterocycle affects the binding to DNA, the new dyes BETO and BOXTO have a benzothiazole group and a benzoxazole moiety, respectively. Whereas BEBO showed a heterogeneous binding to calf thymus DNA, linear and circular dichroism studies of BOXTO indicate a high preference for minor groove binding. BETO also binds in the minor groove to mixed sequence DNA but has a contribution of non-ordered and non-emissive species present. A non-intercalative binding mode of the new dyes, as well as for BEBO, is further supported by electrophoresis unwinding assays. These dyes, having comparable spectral properties as the intercalating cyanine dyes, but bind in the minor groove instead, might be useful complements for staining of DNA. In particular, the benzoxazole substituted dye BOXTO has attractive fluorescence properties with a quantum yield of 0.52 when bound to mixed sequence DNA and a 300-fold increase in fluorescence intensity upon binding.

Chloride-sensitive fluorescent indicators

Three fluorescent halide-sensitive quinolinium dyes have been produced by the reaction of the 6-methylquinoline heterocyclic nitrogen base with methyl bromide, methyl iodide, and 3-bromo-1-propanol. The quaternary salts, unlike the precursor molecule, are readily water soluble and the fluorescence intensity of these salts is reduced in the presence of aqueous chloride, bromide, and iodide ions, allowing halide solution concentrations to be determined using well-known Stern-Volmer kinetics. One of the dyes, dye 1, has a chloride Stern-Volmer constant of 255 mol(-1) dm(3) which is more than twice that of SPQ [6-methoxy-N-(3-sulfopropyl)quinolinium] used in recent physiological measurements to measure intracellular chloride levels. The dyes have been characterized using steady-state fluorescence spectroscopy and are compared to three similar dyes based on the 6-methoxyquinoline nucleus, reported earlier by the authors, and also to dyes reported by Krapf et al. (Anal. Biochem. 169, 142-150, 1988). The interference of aqueous anions and the potential for using these dyes in biological halide-sensing applications are discussed.

Synthesis, molecular modeling, and pharmacological testing of bis-quinolinium cyclophanes: potent, non-peptidic blockers of the apamin-sensitive Ca(2+)-activated K(+) channel

The synthesis and pharmacological testing of two series of novel bis-quinolinium cyclophanes as blockers of the apamin-sensitive Ca(2+)-activated K(+) (SK(Ca)) channel are presented. In these cyclophanes the two 4-aminoquinolinium groups are joined at the ring N atoms (linker L) and at the exocyclic N atoms (linker A). In those cases where A and L contain two or more aromatic rings each, the activity of the compound is not critically dependent upon the nature of the linkers. When A and L each have only one benzene ring, the blocking potency changes dramatically with simple structural variations in the linkers. One of these smaller cyclophanes having A = benzene-1,4-diylbis(methylene) and L = benzene-1, 3-diylbis(methylene) (3j, 6,10-diaza-1,5(1,4)-diquinolina-3(1,3),8(1, 4)-dibenzenacyclodecaphanedium tritrifluoroacetate, UCL 1684) has an IC(50) of 3 nM and is the most potent non-peptidic SK(Ca) channel blocker described to date. Conformational analysis on the smaller cyclophanes using molecular modeling techniques suggests that the differences in the blocking potencies of the compounds may be attributable to their different conformational preferences.

Synthesis and characterization of dual-wavelength Cl--sensitive fluorescent indicators for ratio imaging

The fluorescence of quinolinium-based Cl- indicators such as 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ) is quenched by Cl- by a collisional mechanism without change in spectral shape. A series of "chimeric" dual-wavelength Cl- indicators were synthesized by conjugating Cl--sensitive and -insensitive chromophores with spacers. The SPQ chromophore (N-substituted 6-methoxyquinolinium; MQ) was selected as the Cl--sensitive moiety [excitation wavelength (lambdaex) 350 nm, emission wavelength (lambdaem) 450 nm]. N-substituted 6-aminoquinolinium (AQ) was chosen as the Cl--insensitive moiety because of its different spectral characteristics (lambdaex 380 nm, lambdaem 546 nm), insensitivity to Cl-, positive charge (to minimize quenching by chromophore stacking/electron transfer), and reducibility (for noninvasive cell loading). The dual-wavelength indicators were stable and nontoxic in cells and were distributed uniformly in cytoplasm, with occasional staining of the nucleus. The brightest and most Cl--sensitive indicators were alpha-MQ-alpha'-dimethyl-AQ-xylene dichloride and trans-1, 2-bis(4-[1-alpha'-MQ-1'-alpha'-dimethyl-AQ-xylyl]-pyridinium)ethyl ene (bis-DMXPQ). At 365-nm excitation, emission maxima were at 450 nm (Cl- sensitive; Stern-Volmer constants 82 and 98 M-1) and 565 nm (Cl- insensitive). Cystic fibrosis transmembrane conductance regulator-expressing Swiss 3T3 fibroblasts were labeled with bis-DMXPQ by hypotonic shock or were labeled with its uncharged reduced form (octahydro-bis-DMXPQ) by brief incubation (20 microM, 10 min). Changes in Cl- concentration in response to Cl-/nitrate exchange were recorded by emission ratio imaging (450/565 nm) at 365-nm excitation wavelength. These results establish a first-generation set of chimeric bisquinolinium Cl- indicators for ratiometric measurement of Cl- concentration.

On the concept of a bivalent pharmacophore for SKCa channel blockers: synthesis, pharmacological testing, and radioligand binding studies on mono-, bis-, and tris-quinolinium compounds

The dissociation equilibrium constants (Kd values) of dequalinium (2) and the monoquinolinium compounds 1a and 1b have been determined from competition equilibrium radioligand binding with [125I]apamin on rat brain synaptic plasma membranes (SPMs). Dequalinium binds to the channel with 2 orders of magnitude higher affinity than 1a or 1b, suggesting that both quinolinium groups are needed for potent and selective SKCa channel blockade. The trisquinolinium compound 3 (1,1'-[5-[4-(4- aminoquinolinium-1-yl)but-1-yl]non-4-en-1,9-diyl]-bis-(4- aminoquinolinium)) has been synthesized and tested for inhibition of the afterhyperpolarization of rat sympathetic neurones and on the binding assay. Compound 3 shows approximately one order of magnitude higher potency than 2, being the most potent non-peptidic SKCa channel blocker reported so far (Kd approximately 30 nM). The higher affinity of 3 compared with 2 may be due to direct binding of the third quinolinium group to the channel or may arise from a reduction of the unfavorable entropy of binding via an increase of the "local concentration" of quinolinium groups.

Discovery of 6,11-ethano-12,12-diaryl-6,11-dihydrobenzo[b]quinolizinium cations, a novel class of N-methyl-D-aspartate antagonists

6,11-Ethano-12,12-diaryl-6,11-dihydrobenzo[b]quinolizinium cations 8, a novel class of N-methyl-D-aspartate (NMDA) antagonists acting at the phencyclidine site, have been identified. Structure-activity relationship studies around the lead compound 8a led to the identification of 12g (WIN 67870-2), one of the most potent compounds in this series. Compound 12g has a Ki = 1.8 +/- 0.2 nM vs [3H]TCP binding, has 700-fold selectivity for binding to the open state of the NMDA receptor-ionophore, and was devoid of MK-801- and PCP-like behavioral effects in rats. Compound 12g was neuroprotective in cultured mouse cortical neurons and exhibited antiischemic activity in a rat middle cerebral artery occlusion/reperfusion model of focal ischemia.

Isocyanines and pseudoisocyanines as a novel class of potent noradrenaline transport inhibitors: synthesis, detection, and biological activity

Noradrenaline, the neurotransmitter of the sympathetic nervous system, is removed from the extracellular space by both neuronal and extraneuronal transport mechanisms. In the past, further investigation of the extraneuronal type of noradrenaline transporter was severely hampered by the lack of potent inhibitors. Here, we describe the synthesis of various novel noradrenaline transport inhibitors which belong to the chemical class of isocyanine and pseudoisocyanine dyes. The biological activity of these compounds was investigated in a tissue culture system (Caki-1 cells). 1,1'-Diisopropyl-2,4'-cyanine, 1,1'-diethyl-2,2'-cyanine, and 1-ethyl-1'-isopropyl-2,2'-cyanine turned out as the most potent inhibitors of the extraneuronal noradrenaline transport known so far. At 100 nmol/L, these compounds diminished extraneuronal noradrenaline transport by about 95%. Their IC50's were below 20 nmol/L. In addition, a rapid and sensitive method (based on HPLC with fluorometric detection) to measure these compounds in body fluids is reported.

Compounds with positive inotropic activity, IV: Synthesis of N-methoxyquinolinium salts and their effects in heart muscles

N-Methoxyquinolinium salts 3 are prepared as potential cardiotonic agents by alkylation of the corresponding N-oxides 2 synthesized by two different methods. 1. Oxidation of some quinoline derivatives 1 using 30% H2O2 or 3-chloroperbenzoic acid. 2. Nitration of the quinoline-N-oxides 2a, 2c, and 2m. Preparation of 2h and 2k requires subsequent nucleophilic ipso-substitution of the nitro group. The compounds 3 are tested for positive inotropic activity on isolated left atria and papillary muscles from guinea-pig. Structure activity relationships indicate that the effect depends on the N-methoxy group of the target compounds as well as on the presence of an electron-withdrawing substituent.

Synthesis of cell-impermeable Cl-sensitive fluorescent indicators with improved sensitivity and optical properties

Quinolinium compounds have been used as Cl-sensitive fluorescent indicators in cells and cell-free membrane fractions. To improve Cl sensitivity and for conjugation via nucleophilic reaction, the compounds 6-methoxy-N-(n-aminoalkyl)quinolinium bromide hydrochloride (AAQ) with alkyl chain lengths (n) of 2 (AEQ), 3 (APQ), and 4 (ABQ) were synthesized. AAQ was water soluble, fluorescent, and quenched by Cl. The Stern-Volmer constants (KCl) for quenching of protonated AEQ, APQ and ABQ by Cl were 354, 322, and 272 M-1, respectively, higher than KCl for 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ; 118 M-1). To eliminate pH-dependent fluorescence, 6-methoxy-N-(3-trimethylammoniumpropyl)quinolinium dibromide (TMAPQ) was synthesized (KCl, 310 M-1). To red shift fluorescence excitation and emission spectra, 6-phenyl-N-(3-trimethylammoniumpropyl) quinolinium dibromide (phenyl-TMAPQ) (emission 475 nm) and N-(3-trimethylammoniumpropyl)phenanthridinium dibromide (TMAPP) (excitation 380 nm) were synthesized. AEQ and ABQ were conjugated with neutral dextran activated by cyanogen bromide to give indicator-to-dextran mole ratios of 5 to 20. KCl values at pH 7.4 were 132 (AEQ-dextran) and 237 M-1 (ABQ-dextran). To construct a single molecule with Cl-sensitive and insensitive moieties, the bichromophores 6-methoxy-N-(n-dansylsulfonamidoalkyl)quinolinium with alkyl chains of two and four were synthesized. The new Cl-sensitive indicators were used for measurement of intracellular Cl activity and for the labeling of endocytic vesicles in 3T3 fibroblasts and T84 cells. Our results indicate that N-substitution of quinoline with positively charged moieties gives increased Cl sensitivity, and extension of ring conjugation gives indicators with red-shifted fluorescence spectra.

6-methoxy-N-(3-sulfopropyl)quinolinium; dextran; fibroblast

Submitted on December 20, 1990

Accepted on June 10, 1991

Structure-activity relationships of chloride-sensitive fluorescent indicators for biological application

The application of the quinoline derivative 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ) to the measurement of membrane transport of chloride in biological systems was reported recently (N.P. Illsley and A.S. Verkman (1987) Biochemistry 26, 1215-1219). To understand the structure-activity relationships of compounds with chloride-sensitive fluorescence properties, 19 structural analogs of SPQ having a single quaternized nitrogen heteroatom were synthesized and characterized. The effect of variations in ring structure, length of sulfoalkyl chain, position of ring substituent, and nature of ring substituent were examined. For each compound, the water solubility, octanol:water partition coefficient, absorbance and fluorescence spectra, fluorescence lifetime, and Stern-Volmer constants (Kq) for quenching by a series of anions were measured. All compounds were quenched by chloride, bromide, iodide, and thiocyanate, but not by cations, sulfate, phosphate, nitrate, or by pH (5-8); several compounds were quenched slightly by bicarbonate (Kq = 8-12 M-1). High chloride sensitivity (Kq greater than 50 M-1) required the presence of a quinoline backbone substituted with electron-donating groups such as methyl and methoxy, but did not depend on length of the sulfoalkyl chain or on the position of ring substituents (positions 2-7). All compounds with high chloride sensitivity had fluorescence excitation spectra in the ultraviolet (excitation maximum less than 350 nm) and fluorescence lifetimes greater than 15 ns. These results establish a set of guidelines for synthesis of chloride-sensitive fluorescent indicators tailored for specific biological applications.

Synthesis and antileukemic activity of 2-(2-methylthio-2-aminovinyl)-1-methylquinolinium iodides

Reaction of 2-bis(2-methylthio)vinyl-1-methylquinolinium iodide with several heterocyclic aliphatic amines at 30-70 degrees resulted in replacement of one methylthio group to give the title compounds. Reaction with pyrrolidine gave an unidentified product lacking sulfur. Antileukemic screening against P-388 lymphocytic leukemia showed positive activity only with the 6-methyl-morpholino derivative, whereas the 6-unsubstituted morpholino derivative was inactive. This result is in contrast to previous testing results with the 2-bis(2-methylthio)vinyl compounds where both 6-substituted and 6-unsubstituted derivatives showed activity.

Antileukemic activity of 2-bis(2-methylthio)vinyl-1-methylquinolinium iodides

Reaction of 1-methylquinolinium-2-dithioacetic acid zwitterions with excess methyl iodide in dimethylformamide gave the corresponding bis(2-methylthio)vinyl derivatives. These compounds were more soluble in both aqueous and organic media than the dithioacetic acid zwitterions but showed comparable antileukemic activity in mice. Reaction with morpholine converted a bis(2-methylthio)vinyl derivative almost quantitatively to the 2-mono(methylthio)-2-morpholino derivative. Leukemia cell culture studies of the 6-methyl derivative showed no effect on cell cycle processes.

4-Acetoxy-1,2,3,4-tetrahydro-2,2-dimethyl-6,7-methylenedioxyisoquinolinium iodide, an acetylcholine analog

4-Acetoxy-1,2,3,4-tetrahydro-2,2-dimethyl-6,7-methylenedioxyisoquinolinium iodide, an analog of acetylcholine, was synthesized and a pharmacological profile of its GI effects was compiled. The agent inhibited dog colonic contraction in response to pelvic nerve stimulation and to acetylcholine. In rats, the compound markedly reduced gastric acid output and the volume of gastric secretions. The lack of inhibition of chromodacryorrhea production in response to carbachol indicates a lack of anticholinergic action. The agent failed to affect the acute inflammatory response of the rat hindpaw in response to carrageenan. The precursor of the compound was ineffective in the pharmacological tests.

6-substituted 1-methylquinolinium-2-dithioacetic acid zwitterions: antileukemia activity

Condensation of the anhydro bases derived from 6-substituted 1-methylquinaldinium iodides with carbon disulfide provided the 2-dithioacetic acid zwitterions. Since 1.6-dimethylquinolinium-2-dithioacetic acid zwitterion previously showed appreciable activity against P-388 lymphocytic leukemia in mice, a series of analogs with other 6-substituents was synthesized to assess the importance of substitution in this position. Both electron-donating and electron-attracting 6-substituents gave compounds with antileukemia activity. The 6-unsubstituted analog had only marginal activity.

Pyridinium- and quinolinium-2-dithioacetic acid zwitterions: antiradiation and anticancer activities

Pyridinium-, quinolinium-, and one pyrimidinium-2-dithioacetic acid zwitterions were prepared by condensation of the N-methyl heterocyclic anhydro bases with carbon disulfide. Reaction of the 2-methylpyridine methiodide anhydro base with carbon disulfide resulted in replacement of the 2-methyl group to give the 1-methylpyridinium-2-dithioacetic acid zwitterion. The 1,6-dimethylquinolinium-2-dithioacetic acid zwitterion showed appreciable anticancer activity against P-388 lymphocytic leukemia in mice, but the other zwitterions tested showed no activity. No antiradiation activity was found for 1-methyl-pyridinium-2-dithioacetic acid zwitterion.

Potent reversible anticholinesterase agents. Bis- and mono-N-substituted benzoquinolinium halides

A number of bis- and mono-N-substituted benzoquinolinium salts and their analogues were prepared and evaluated as inhibitors of acetylcholinesterase (AcChE) and butyrylcholinesterase (BuChE). These compounds were also used to help identify some of the morphologic characteristics of the surface at or near the active sites of the cholinesterases. The shape, size, configuration, and conformation of the onium moieties of the quaternary ammonium compounds were found to be the important factors in their anticholinesterase activity. A high concentration of the positive charge of the quaternary ammonium compound is not a critical factor for the cholinesterase inhibitory activity. The order of decreasing potency of cholinesterase inhibition of the benzoquinolinium compounds was found to be acridinium greater than phenanthridinium greater than 5,6-benzoquinolinium greater than 7,8-benzoquinolinium. The inhibitory activity of the monobenzoquinolinium halides against cholinesterases is influenced by the N-substituent. A bis-quaternary ammonium compound with a flexible bridge that links the two nitrogen atoms was found to be more potent in inhibiting AcChE and less potent in inhibiting BuChE than a bis-quaternary ammonium compound with a rigid bridge. The acridinium and phenanthridinium derivatives of the benzoquinolinium compounds are very potent reversible inhibitors against both AcChE and BuChE.