Evaluation of analogues of furan-amidines as inhibitors of NQO2.

Inhibitors of the enzyme NQO2 (NRH: quinone oxidoreductase 2) are of potential use in cancer chemotherapy and malaria. We have previously reported that non-symmetrical furan amidines are potent inhibitors of NQO2 and here novel analogues are evaluated. The furan ring has been changed to other heterocycles (imidazole, N-methylimidazole, oxazole, thiophene) and the amidine group has been replaced with imidate, reversed amidine, N-arylamide and amidoxime to probe NQO2 activity, improve solubility and decrease basicity of the lead furan amidine. All compounds were fully characterised spectroscopically and the structure of the unexpected product N-hydroxy-4-(5-methyl-4-phenylfuran-2-yl)benzamidine was established by X-ray crystallography. The analogues were evaluated for inhibition of NQO2, which showed lower activity than the lead furan amidine. The observed structure-activity relationship for the furan-amidine series with NQO2 was rationalized by preliminary molecular docking and binding mode analysis. In addition, the oxazole-amidine analogue inhibited the growth of Plasmodium falciparum with an IC50 value of 0.3 µM.

Boron-Based Inhibitors of the NLRP3 Inflammasome.

NLRP3 is a receptor important for host responses to infection, yet is also known to contribute to devastating diseases such as Alzheimer's disease, diabetes, atherosclerosis, and others, making inhibitors for NLRP3 sought after. One of the inhibitors currently in use is 2-aminoethoxy diphenylborinate (2APB). Unfortunately, in addition to inhibiting NLRP3, 2APB also displays non-selective effects on cellular Ca2+ homeostasis. Here, we use 2APB as a chemical scaffold to build a series of inhibitors, the NBC series, which inhibit the NLRP3 inflammasome in vitro and in vivo without affecting Ca2+ homeostasis. The core chemical insight of this work is that the oxazaborine ring is a critical feature of the NBC series, and the main biological insight the use of NBC inhibitors led to was that NLRP3 inflammasome activation was independent of Ca2+. The NBC compounds represent useful tools to dissect NLRP3 function, and may lead to oxazaborine ring-containing therapeutics.

Analgesic Effects of 5-Alkyloxy-4-amino-2(5H)-furanones as Cholecystokinin-2 Antagonists.

4-Amino-2(5H)-furanones were synthesized in high yields over two synthetic steps from readily available mucochloric acid. These 5-alkyloxy-4-amino-2(5H)-furanones were screened in a ([125]) I-CCK-8 radioligand receptor binding assay for CCK2 affinity and novel active ligands in the nanomolar range were identified. SAR was optimized leading to the cyclohexyl derivative 25 with an IC50 of 27 nM. Furanone 18 was obtained as a stable crystalline material with an IC50 of 85 nM, but had a higher CCK2 selectivity. It was subsequently tested in the isolated guinea pig ileum assay with sulfated CCK8 , and the CCK antagonizing properties of the ligand were confirmed. The CCK2 selective antagonist 18 was found to potentiate analgesia in the tail flick assay in mice, for the strong opiate morphine, the partial opiate agonist tramadol and the tricyclic antidepressant desimipramine.

Caesium bis(5-bromosalicylaldehyde thiosemicarbazonato-κ3O,N,S)ferrate(III): supramolecular arrangement of low-spin FeIII complex anions mediated by Cs+ cations.

The synthesis and crystal structure determination (at 293 K) of the title complex, Cs[Fe(C(8)H(6)BrN(3)OS)(2)], are reported. The compound is composed of two dianionic O,N,S-tridentate 5-bromosalicylaldehyde thiosemicarbazonate(2-) ligands coordinated to an Fe(III) cation, displaying a distorted octahedral geometry. The ligands are orientated in two perpendicular planes, with the O- and S-donor atoms in cis positions and the N-donor atoms in trans positions. The complex displays intermolecular N-H...O and N-H...Br hydrogen bonds, creating R4(4)(18) rings, which link the Fe(III) units in the a and b directions. The Fe(III) cation is in the low-spin state at 293 K.

Fe(III) in a low-spin state in caesium bis[3-ethoxysalicylaldehyde 4-methylthiosemicarbazonato(2-)-κ3O2,N1,S]ferrate(III) methanol monosolvate.

The synthesis and crystal structure (at 100 K) of the title compound, Cs[Fe(C11H13N3O2S2)2]·CH3OH, is reported. The asymmetric unit consists of an octahedral [Fe(III)(L)2](-) fragment, where L(2-) is 3-ethoxysalicylaldehyde 4-methylthiosemicarbazonate(2-) {systematic name: [2-(3-ethoxy-2-oxidobenzylidene)hydrazin-1-ylidene](methylamino)methanethiolate}, a caesium cation and a methanol solvent molecule. Each L(2-) ligand binds through the thiolate S, the imine N and the phenolate O atoms as donors, resulting in an Fe(III)S2N2O2 chromophore. The O,N,S-coordinating ligands are orientated in two perpendicular planes, with the O and S atoms in cis positions and the N atoms in trans positions. The Fe(III) cation is in the low-spin state at 100 K.

Fluorescent probe for detection of bacteria: conformational trigger upon bacterial reduction of an azo bridge.

Using biomimetic chemical reduction or Clostridium perfringens cell extract containing azoreductase, the dimer-fluorescent probe 2,4-O-bisdansyl-6,7-diazabicyclooct-6-ene, which possesses a conformationally constrained cis-azo bridge, is reduced to the tetra-equatorial 2,4-O-bisdansyl-cyclohexyl-3,5-bisammonium salt which exhibits fluorescence indicative of a dansyl monomer.

In-vitro and in-vivo antivenin activity of 2-[2-(5,5,8a-trimethyl-2-methylene-decahydro-naphthalen-1-yl)-ethylidene]-succinaldehyde against Ophiophagus hannah venom.

OBJECTIVES: Curcuma zedoaroides A. Chaveerach & T. Tanee, locally known as Wan-Paya-Ngoo-Tua-Mia, is commonly used in the North-Eastern part of Thailand as a 'snakebite antidote'. The aim of this study was to isolate the active compound from the rhizome of C. zedoaroides, to determine its structure and to assess its antagonistic activity in vitro and in vivo against King cobra venom. METHODS: The active compound was obtained from C. zedoaroides by extraction with acetone followed by purification using column chromatography; its X-ray structure was determined. Its inhibition of venom lethality was studied in vitro in rat phrenic nerve-hemidiaphragms and in vivo in mice. KEY FINDINGS: The acetone extract of the Curcuma rhizomes contained a C20 dialdehyde, [2-(5,5,8a-trimethyl-2-methylene-decahydro-naphthalen-1-yl)-ethylidene]-succinaldehyde, as the major component. The isolated curcuma dialdehyde was found active in vitro and in vivo for antivenin activity against the King cobra venom. Using isolated rat phrenic nerve-hemidiaphragm preparations, a significant antagonistic effect on the inhibition of neuromuscular transmission was observed in vitro. Inhibition on muscle contraction, produced by the 4 microg/ml venom, was reversed by 2-16 microg/ml of Curcuma dialdehyde in organ bath preparations over a period of 2 h. Mice intraperitoneally injected with 0.75 mg/kg venom and dialdehyde at 100 mg/kg had a significantly increased survival time. Injection of Curcuma dialdehyde (100 mg/kg) 30 min before the subcutaneous injection of the venom resulted in a 100% survival time after 2 h compared with 0% for the control group. CONCLUSIONS: The in vitro and in vivo evaluation confirmed the medicinal use of traditional snake plants against snakebites. The bioactivity is linked to an isolated molecule and not a result of synergistic effects of a mixture. The active compound was isolated and the structure fully elucidated, including its stereochemistry. This dialdehyde is a versatile chemical building block and can be easily obtained from this plant source.

Conformational analysis of the natural iron chelator myo-inositol 1,2,3-trisphosphate using a pyrene-based fluorescent mimic.

myo-Inositol phosphates possessing the 1,2,3-trisphosphate motif share the remarkable ability to completely inhibit iron-catalysed hydroxyl radical formation. The simplest derivative, myo-inositol 1,2,3-trisphosphate [Ins(1,2,3)P(3)], has been proposed as an intracellular iron chelator involved in iron transport. The binding conformation of Ins(1,2,3)P(3) is considered to be important to complex Fe(3+) in a 'safe' manner. Here, a pyrene-based fluorescent probe, 4,6-bispyrenoyl-myo-inositol 1,2,3,5-tetrakisphosphate [4,6-bispyrenoyl Ins(1,2,3,5)P(4)], has been synthesised and used to monitor the conformation of the 1,2,3-trisphosphate motif using excimer fluorescence emission. Ring-flip of the cyclohexane chair to the penta-axial conformation occurs upon association with Fe(3+), evident from excimer fluorescence induced by pi-pi stacking of the pyrene reporter groups, accompanied by excimer formation by excitation at 351 nm. This effect is unique amongst biologically relevant metal cations, except for Ca(2+) cations exceeding a 1 : 1 molar ratio. In addition, the thermodynamic constants for the interaction of the fluorescent probe with Fe(3+) have been determined. The complexes formed between Fe(3+) and 4,6-bispyrenoyl Ins(1,2,3,5)P(4) display similar stability to those formed with Ins(1,2,3)P(3), indicating that the fluorescent probe acts as a good model for the 1,2,3-trisphosphate motif. This is further supported by the antioxidant properties of 4,6-bispyrenoyl Ins(1,2,3,5)P(4), which closely resemble those obtained for Ins(1,2,3)P(3). The data presented confirms that Fe(3+) binds tightly to the unstable penta-axial conformation of myo-inositol phosphates possessing the 1,2,3-trisphosphate motif.

Fluorescent probe: complexation of Fe3+ with the myo-inositol 1,2,3-trisphosphate motif.

Natural myo-inositol phosphate antioxidants containing the 1,2,3-trisphosphate motif bind Fe(3+) in the unstable penta-axial conformation.

2-(3-Hydroxypropyl)isoindoline-1,3-dione: competition among hydrogen-bond acceptors.

The title compound, C(11)H(11)NO(3), has two molecules in the asymmetric unit, which differ in the orientation of their side-chain OH groups, allowing them to form intermolecular O-H...O hydrogen bonds to different acceptors. In one case, the acceptor is the OH group of the other molecule, and in the other case it is an imide O=C group. This is the first example in the N-substituted phthalimide series in which independent molecules have different types of acceptor. Molecular-orbital calculations place the greatest negative charge on the OH group.

Novel reaction products from the hypervalent iodine oxidation of hydroxylated stilbenes and isoflavones.

Novel reaction pathways for the hypervalent iodine-mediated oxidation of bioactive phenols containing extended conjugated pi-systems are described. Oxidation of 4-hydroxystilbenes in methanol using a hypervalent iodine-based oxidant led to the formal 1,2-addition of methoxy groups across the central stilbene double bond. Treatment of the structurally related 4-hydroxyisoflavone with di(trifluoroacetoxy)iodobenzene leads to the surprising formation of 2,4'-dihydroxybenzil. Potential mechanisms for these new reaction pathways are discussed, and the X-ray crystal structure of 2,4'-dihydroxybenzil is presented. In contrast, oxidation of the corresponding 3-hydroxystilbenes and 3-hydroxyisoflavone led to conventional dienone oxidation products. The antitumour implications of these oxidation processes are briefly highlighted; the novel 4-substituted phenolic oxidation products were found to be inactive in terms of in vitro antitumour cellular activity, whereas the 3-substituted phenol products gave novel agents with potent and enhanced antitumour activity in the HCT 116 cancer cell line.

Quinols as novel therapeutic agents. 2.(1) 4-(1-Arylsulfonylindol-2-yl)-4-hydroxycyclohexa-2,5-dien-1-ones and related agents as potent and selective antitumor agents.

A series of substituted 4-(1-arylsulfonylindol-2-yl)-4-hydroxycyclohexa-2,5-dien-1-ones (indolylquinols) has been synthesized on the basis of the discovery of lead compound 1a and screened for antitumor activity. Synthesis of this novel series was accomplished via the "one-pot" addition of lithiated (arylsulfonyl)indoles to 4,4-dimethoxycyclohexa-2,5-dienone followed by deprotection under acidic conditions. Similar methodology gave rise to the related naphtho-, 1H-indole-, and benzimidazole-substituted quinols. A number of compounds in this new series were found to possess in vitro human tumor cell line activity substantially more potent than the recently reported antitumor 4-substituted 4-hydroxycyclohexa-2,5-dien-1-ones(1) with similar patterns of selectivity against colon, renal, and breast cell lines. The most potent compound in the series in vitro, 4-(1-benzenesulfonyl-6-fluoro-1H-indol-2-yl)-4-hydroxycyclohexa-2,5-dienone (1h), exhibits a mean GI(50) value of 16 nM and a mean LC(50) value of 2.24 muM in the NCI 60-cell-line screen, with LC(50) activity in the HCT 116 human colon cancer cell line below 10 nM. The crystal structure of the unsubstituted indolylquinol 1a exhibits two independent molecules, both participating in intermolecular hydrogen bonds from quinol OH to carbonyl O, but one OH group also interacts intramolecularly with a sulfonyl O atom. This interaction, which strengthens upon ab initio optimization, may influence the chemical environment of the bioactive quinol moiety. In vivo, significant antitumor activity was recorded (day 28) in mice bearing subcutaneously implanted MDA-MB-435 xenografts, following intraperitoneal treatment of mice with compound 1a at 50 mg/kg.

Synthesis and cytotoxicity of a novel 1-alkylaminomethyl-2,4-diaryl-butadiene-1,3 fragment integrated within cyclohex(pent)enes.

A group of 1-alkylaminomethyl-2-aryl-3-arylidenecyclohex(pent)enes 3a-n with a 1-alkylaminomethyl-2,4-diaryl-1,3-butadiene fragment and a group of their congeners 3-alkylaminomethyl-1,2-diarylcyclohexene 7a-f have been synthesised for the first time. The conjugated system in 1-alkylaminomethyl-2-aryl-3-arylidenecyclohex(pent)enes 3a-n was unambiguously confirmed by X-ray crystallography. Cytotoxicity tests revealed that 3a-n possess inconsistent cytotoxicity against cancer cells, not their congeners 7a-f.