Circularly polarized luminescence of Sm (III) and Eu (III) complexes with chiral ligand (R/S)-BINAPO.

Luminescent lanthanide (III) ions have been exploited for circularly polarized luminescence (CPL) for decades. However, very few of these studies have involved chiral samarium (III) complexes. Complexes are prepared by mixing axial chiral ligands (R/S))-2,2'-bis(diphenylphosphoryl)-1,1'-binaphthyl (BINAPO) with europium and samarium Tris (trifluoromethane sulfonate) (Eu (OTf)3 and Sm (OTf)3 ). Luminescence-based titration shows that the complex formed is Ln((R/S)-BINAPO)2 (OTf)3 , where Ln = Eu or Sm. The CPL spectra are reported for Eu((R/S)-BINAPO)2 (OTf)3 and Sm((R/S)-BINAPO)2 (OTf)3 . The sign of the dissymmetry factors, gem , was dependent upon the chirality of the BINAPO ligand, and the magnitudes were relatively large. Of all of the complexes in this study, Sm((S)-BINAPO)2 (OTf)3 has the largest gem  = 0.272, which is one of the largest recorded for a chiral Sm3+ complex. A theoretical three-dimensional structural model of the complex that is consistent with the experimental observations is developed and refined. This report also shows that (R/S)-BINAPO are the only reported ligands where gem (Sm3+ ) > gem (Eu3+ ).

In Vitro Antiviral Activity and Resistance Profile of the Next-Generation Hepatitis C Virus NS3/4A Protease Inhibitor Glecaprevir.

Glecaprevir (formerly ABT-493) is a novel hepatitis C virus (HCV) NS3/4A protease inhibitor (PI) with pangenotypic activity. It inhibited the enzymatic activity of purified NS3/4A proteases from HCV genotypes 1 to 6 in vitro (half-maximal [50%] inhibitory concentration = 3.5 to 11.3 nM) and the replication of stable HCV subgenomic replicons containing proteases from genotypes 1 to 6 (50% effective concentration [EC50] = 0.21 to 4.6 nM). Glecaprevir had a median EC50 of 0.30 nM (range, 0.05 to 3.8 nM) for HCV replicons containing proteases from 40 samples from patients infected with HCV genotypes 1 to 5. Importantly, glecaprevir was active against the protease from genotype 3, the most-difficult-to-treat HCV genotype, in both enzymatic and replicon assays demonstrating comparable activity against the other HCV genotypes. In drug-resistant colony selection studies, glecaprevir generally selected substitutions at NS3 amino acid position A156 in replicons containing proteases from genotypes 1a, 1b, 2a, 2b, 3a, and 4a and substitutions at position D/Q168 in replicons containing proteases from genotypes 3a, 5a, and 6a. Although the substitutions A156T and A156V in NS3 of genotype 1 reduced susceptibility to glecaprevir, replicons with these substitutions demonstrated a low replication efficiency in vitro Glecaprevir is active against HCV with most of the common NS3 amino acid substitutions that are associated with reduced susceptibility to other currently approved HCV PIs, including those at positions 155 and 168. Combination of glecaprevir with HCV inhibitors with other mechanisms of action resulted in additive or synergistic antiviral activity. In summary, glecaprevir is a next-generation HCV PI with potent pangenotypic activity and a high barrier to the development of resistance.

Induction of Circularly Polarized Luminescence from Europium by Amino Acid Based Ionic Liquids.

Materials that emit circularly polarized light have application in several important industries. Because they show large optical activity and emit sharp visible light transitions, europium complexes are often exploited in applications that require circularly polarized luminescence (CPL). Chiral and coordinating ionic liquids based on prolinate, valinate, and aspartate anions are used to induce CPL from a simple achiral europium triflate salt. The sign of the induced CPL is dependent on the handedness (l vs d) of the amino acid anion. Comparison of the CPL spectra in ionic liquid with proline and valine vs aspartate shows that the number of carboxylate groups in the amino acid anion influences the europium coordination environment. DFT calculations predict a chiral eight-coordinate Eu(Pro)4- structure in the prolinate ionic liquid and a chiral seven- or eight-coordinate Eu(Asp)33- structure in the aspartate ionic liquid.

Chiral discrimination by ionic liquids: impact of ionic solutes.

Chiral ionic liquids hold promise in many asymmetric applications. This study explores the impact of ionic solutes on the chiral discrimination of five amino acid methyl ester-based ionic liquids, including L- and D-alanine methyl ester, L-proline methyl ester, L-leucine methyl ester, and L-valine methyl ester cations combined with bis(trifluoromethanesulfonimide) anion. Circularly polarized luminescence spectroscopy was used to study the chiral discrimination by measuring the racemization equilibrium of a dissymmetric europium complex, Eu(dpa)3(3-) (where dpa = 2,6-pyridinedicarboxylate). The chiral discrimination measured was dependent on the concentration of Eu(dpa)3(3-) and this concentration-dependence was different in each of the ionic liquids. Ionic liquids with L-leucine methyl ester and L-valine methyl ester even switched enantiomeric preference based on the solute concentration. Changing the cation of the Eu(dpa)3(3-) salt from tetrabutylammonium to tetramethylammonium ion also affected the chiral discrimination demonstrated by the ionic liquids.

Modifications of C-2 on the pyrroloquinoline template aimed at the development of potent herpesvirus antivirals with improved aqueous solubility.

A series of C-2 pyrroloquinoline analogs designed to improve aqueous solubility were examined for herpesvirus polymerase and antiviral activity. Several analogs were identified that maintained the antiviral activity of the previous development candidate against HCMV, HSV-1 and VZV, but with significantly improved aqueous solubility.

The design and development of 2-aryl-2-hydroxy ethylamine substituted 1H,7H-pyrido[1,2,3-de]quinoxaline-6-carboxamides as inhibitors of human cytomegalovirus polymerase.

Discovery efforts were focused on identifying a non-nucleoside antiviral for treating infections caused by human cytomegalovirus (HCMV) with equal or better potency and diminished toxicity compared to current therapeutics. This Letter describes the HCMV DNA polymerase inhibition and in vitro antiviral activity of various 2-aryl-2-hydroxy ethylamine substituted 1H,7H-pyrido[1,2,3-de]quinoxaline-6-carboxamides.

Study of SF6 adsorption on graphite using infrared spectroscopy.

We report an experimental study of adsorbed monolayers of SF(6) on graphite using infrared reflection absorption spectroscopy supplemented by ellipsometry. The asymmetric S-F stretch mode nu(3) near 948 cm(-1) in the gas is strongly blueshifted in the film by dynamic dipole coupling. This blueshift is very sensitive to the intermolecular spacing in the SF(6) layer. We convert the measured frequency nu(3) to a lattice spacing a, using a self-consistent field calculation, calibrated by the frequency in the commensurate phase. The resolution in lattice spacing is 0.002 A, although there is a larger systematic uncertainty associated with nondynamic-dipole contributions to the frequency shift. We map the commensurate-incommensurate transition, a transition between two incommensurate phases, and the melting transition. These results are compared to previous x-ray data. We provide a new determination of the layer critical point (156 K), the layer condensation line down to 110 K, and the spreading pressure at saturation in this temperature range.

Controlling cellular distribution of drugs with permeability modifying moieties.

Phenotypic screening provides compounds with very limited target cellular localization data. In order to select the most appropriate target identification methods, determining if a compound acts at the cell-surface or intracellularly can be very valuable. In addition, controlling cell-permeability of targeted therapeutics such as antibody-drug conjugates (ADCs) and targeted nanoparticle formulations can reduce toxicity from extracellular release of drug in undesired tissues or direct activity in bystander cells. By incorporating highly polar, anionic moieties via short polyethylene glycol linkers into compounds with known intracellular, and cell-surface targets, we have been able to correlate the cellular activity of compounds with their subcellular site of action. For compounds with nuclear (Brd, PARP) or cytosolic (dasatinib, NAMPT) targets, addition of the permeability modifying group (small sulfonic acid, polycarboxylic acid, or a polysulfonated fluorescent dye) results in near complete loss of biological activity in cell-based assays. For cell-surface targets (H3, 5HT1A, ß2AR) significant activity was maintained for all conjugates, but the results were more nuanced in that the modifiers impacted binding/activity of the resulting conjugates. Taken together, these results demonstrate that small anionic compounds can be used to control cell-permeability independent of on-target activity and should find utility in guiding target deconvolution studies and controlling drug distribution of targeted therapeutics.

PARP1 Trapping by PARP Inhibitors Drives Cytotoxicity in Both Cancer Cells and Healthy Bone Marrow.

PARP inhibitors have recently been approved as monotherapies for the treatment of recurrent ovarian cancer and metastatic BRCA-associated breast cancer, and ongoing studies are exploring additional indications and combinations with other agents. PARP inhibitors trap PARP onto damaged chromatin when combined with temozolomide and methyl methanesulfonate, but the clinical relevance of these findings remains unknown. PARP trapping has thus far been undetectable in cancer cells treated with PARP inhibitors alone. Here, we evaluate the contribution of PARP trapping to the tolerability and efficacy of PARP inhibitors in the monotherapy setting. We developed a novel implementation of the proximity ligation assay to detect chromatin-trapped PARP1 at single-cell resolution with higher sensitivity and throughput than previously reported methods. We further demonstrate that the PARP inhibitor-induced trapping appears to drive single-agent cytotoxicity in healthy human bone marrow, indicating that the toxicity of trapped PARP complexes is not restricted to cancer cells with homologous recombination deficiency. Finally, we show that PARP inhibitors with dramatically different trapping potencies exhibit comparable tumor growth inhibition at MTDs in a xenograft model of BRCA1-mutant triple-negative breast cancer. These results are consistent with emerging clinical data and suggest that the inverse relationship between trapping potency and tolerability may limit the potential therapeutic advantage of potent trapping activity. IMPLICATIONS: PARP trapping contributes to single-agent cytotoxicity of PARP inhibitors in both cancer cells and healthy bone marrow, and the therapeutic advantage of potent trapping activity appears to be limited.

Synthesis of 4-oxo-4,7-dihydrofuro[2,3-b]pyridine-5-carboxamides with broad-spectrum human herpesvirus polymerase inhibition.

A versatile synthesis of 4-oxo-4,7-dihydrofuro[2,3-b]pyridine-5-carboxylate esters has been developed which has lead to the identification of a new series of non-nucleoside inhibitors of human herpesvirus polymerases HCMV, HSV-1, EBV, and VZV with high specificity compared to human DNA polymerases.

Deep Eutectic Solvents for Induced Circularly Polarized Luminescence.

Materials that emit circularly polarized light have application in several important industries. Deep eutectic solvents (DES) with chiral components are attractive as solvents of luminescent lanthanides for the development of chiral light-emitting materials. Deep eutectic solvents are prepared with combinations of tetrabutylammonium (or tetrabutylphosphonium) chloride as hydrogen bond acceptor (HBA) and amino acids, l-and d-glutamic acid, l-proline, and l-arginine as hydrogen bond donor (HBD). A racemic mixture of dissymmetric lanthanide (europium, terbium, and samarium) complexes is dissolved in the DES to measure the induced circularly polarized luminescence (CPL). This resulted in green, orange, and red CPL with a sign that is dictated by the enantiomer of the amino acid in the DES. Thermodynamic measurements show that changing the salt from tetrabutylammonium to tetrabutylphosphonium leads to a 50% increase in the enthalpy and entropy of chiral discrimination. This study demonstrates the capability of chiral DES as a solvent for chiral light-emitting materials and the ability to control this capability through the choice of HBA and HBD.

4-Oxo-4,7-dihydrothieno[2,3-b]pyridines as non-nucleoside inhibitors of human cytomegalovirus and related herpesvirus polymerases.

A novel series of 4-oxo-4,7-dihydrothieno[2,3-b]pyridine-5-carboxamides have been identified as potential antivirals against human herpesvirus infections resulting from human cytomegalovirus (HCMV), herpes simplex virus type 1 (HSV-1), and varicella-zoster virus (VZV). Compounds 10c and 14 demonstrated broad-spectrum inhibition of the herpesvirus polymerases HCMV, HSV-1, and VZV. High specificity for the viral polymerases was observed compared to human alpha polymerase. The antiviral activity of 10c and 14, as determined by plaque reduction assay, was comparable or superior to that of existing antiherpes drugs, ganciclovir (for HCMV) and acyclovir (for HSV-1 and VZV). Drug resistance to compound 14 correlated to point mutations in conserved domain III of the herpesvirus DNA polymerase, but these mutations do not confer resistance to existing nucleoside therapy. In addition, compound 14 maintained potent antiviral activity against acyclovir-resistant HSV-1 strains. Substitution to the pyridone nitrogen (N7) was found to be critical for enhanced in vitro antiviral activity.

Mechanistic Dissection of PARP1 Trapping and the Impact on In Vivo Tolerability and Efficacy of PARP Inhibitors.

UNLABELLED: Poly(ADP-ribose) polymerases (PARP1, -2, and -3) play important roles in DNA damage repair. As such, a number of PARP inhibitors are undergoing clinical development as anticancer therapies, particularly in tumors with DNA repair deficits and in combination with DNA-damaging agents. Preclinical evidence indicates that PARP inhibitors potentiate the cytotoxicity of DNA alkylating agents. It has been proposed that a major mechanism underlying this activity is the allosteric trapping of PARP1 at DNA single-strand breaks during base excision repair; however, direct evidence of allostery has not been reported. Here the data reveal that veliparib, olaparib, niraparib, and talazoparib (BMN-673) potentiate the cytotoxicity of alkylating agents. Consistent with this, all four drugs possess PARP1 trapping activity. Using biochemical and cellular approaches, we directly probe the trapping mechanism for an allosteric component. These studies indicate that trapping is due to catalytic inhibition and not allostery. The potency of PARP inhibitors with respect to trapping and catalytic inhibition is linearly correlated in biochemical systems but is nonlinear in cells. High-content imaging of γH2Ax levels suggests that this is attributable to differential potentiation of DNA damage in cells. Trapping potency is inversely correlated with tolerability when PARP inhibitors are combined with temozolomide in mouse xenograft studies. As a result, PARP inhibitors with dramatically different trapping potencies elicit comparable in vivo efficacy at maximum tolerated doses. Finally, the impact of trapping on tolerability and efficacy is likely to be context specific. IMPLICATIONS: Understanding the context-specific relationships of trapping and catalytic inhibition with both tolerability and efficacy will aid in determining the suitability of a PARP inhibitor for inclusion in a particular clinical regimen.

Broad-spectrum antiviral activity of PNU-183792, a 4-oxo-dihydroquinoline, against human and animal herpesviruses.

We identified a novel class of 4-oxo-dihydroquinolines represented by PNU-183792 which specifically inhibit herpesvirus polymerases. PNU-183792 was highly active against human cytomegalovirus (HCMV, IC(50) value 0.69 microM), varicella zoster virus (VZV, IC(50) value 0.37 microM) and herpes simplex virus (HSV, IC(50) value 0.58 microM) polymerases but was inactive (IC(50) value >40 microM) against human alpha (alpha), gamma (gamma), or delta (delta) polymerases. In vitro antiviral activity against HCMV was determined using cytopathic effect, plaque reduction and virus yield reduction assays (IC(50) ranging from 0.3 to 2.4 microM). PNU-183792 antiviral activity against both VZV (IC(50) value 0.1 microM) and HSV (IC(50) ranging from 3 to 5 microM) was analyzed using plaque reduction assays. PNU-183792 was also active (IC(50) ranging 0.1-0.7 microM) in cell culture assays against simian varicella virus (SVV), murine cytomegalovirus (MCMV) and rat cytomegalovirus (RCMV). Cell culture activity was compared with the appropriate licensed drugs ganciclovir (GCV), cidofovir (CDV) and acyclovir (ACV). PNU-183792 was also active against both GCV-resistant and CDV-resistant HCMV and against ACV-resistant HSV. Toxicity assays using four different species of proliferating mammalian cells indicated PNU-183792 was not cytotoxic at relevant drug concentrations (CC(50) value >100 microM). PNU-183792 was inactive against unrelated DNA and RNA viruses indicating specificity for herpesviruses. In animals, PNU-183792 was orally bioavailable and was efficacious in a model of lethal MCMV infection.

Electronic State Structure and Optical Properties of Tb(oda)(3)(3)(-) Complexes in Trigonal Na(3)[Tb(oda)(3)].2NaClO(4).6H(2)O Crystals.

Polarized optical absorption and emission measurements are used to locate and assign 95 crystal-field energy levels split out of the 4f( )(8) electronic configuration of Tb(3+) in single crystals of Na(3)[Tb(oda)(3)].2NaClO(4).6H(2)O (where oda denotes an oxydiacetate ligand). The absorption measurements span the 235-490 nm wavelength range, and the emission measurements span the 485-685 nm wavelength range. The combined absorption and emission spectra measurements provide access to the energy-level structures of 46 different 4f( )(8)[SL]J multiplet manifolds of Tb(3+) (all multiplet manifolds with baricenter energies <42 400 cm(-)(1) above ground). The site symmetry of the Tb(3+) ions in Na(3)[Tb(oda)(3)].2NaClO(4).6H(2)O is D(3), and the point-group symmetry of the tris-terdentate Tb(oda)(3)(3)(-) coordination complexes is also D(3). The Tb(oda)(3)(3)(-) complexes are chiral, and they exist in just one, fully resolved enantiomeric form in single crystals of Na(3)[Tb(oda)(3)].2NaClO(4).6H(2)O. The crystals exhibit strong chiroptical activity in their absorption and emission spectra, and results obtained from both circularly polarized and linearly polarized optical spectra measurements are used in making transition line assignments. The energy-level data acquired from the spectroscopic measurements are analyzed in terms of a model Hamiltonian that includes consideration of both isotropic and nonisotropic 4f electron/crystal-field interactions, and the interaction parameters derived from this analysis are discussed and then compared with those obtained for other Na(3)[Ln(oda)(3)].2NaClO(4).6H(2)O systems and for Tb(3+) in other crystalline hosts.

Chiroptical study of chiral discrimination by amino acid based ionic liquids.

The chiral discrimination ability of amino acid based chiral ionic liquids is studied using chiroptical luminescence techniques. A racemic mixture of dissymmetric europium tris(2,6-pyridinedicarboxylate) complexes are dissolved in five chiral ionic liquids, including l- and d-alanine methyl ester bis(trifluoromethanesulfonimide), l-leucine methyl ester bis(trifluoromethanesulfonimide), l-proline methyl ester bis(trifluoromethanesulfonimide), and tetrabutylammonium l-alanate. Circularly polarized luminescence spectra are measured for the samples over the 283-323 K temperature range. Analysis of the spectroscopic results shows that the amino acid methyl ester chiral ionic liquids show discrimination with a preference (handedness) that corresponds to the stereoisomer (l- vs d-). Most of the chiral ionic liquids show enthalpically dominated discrimination, but l-leucine methyl ester bis(trifluoromethanesulfonimide) shows entropically dominated chiral discrimination.

Intermolecular chiral recognition processes probed by chiroptical luminescence.

Enantiopreferential energy transfer processes between dissymmetric lanthanide and transition metal complexes dissolved in acetonitrile are studied using chiroptical luminescence techniques. The energy donors (luminophores) in this study are a racemic mixture of Ln(dpa)3 (3-) complexes (where Ln = Eu3+ or Tb3+ and dpa = 2,6-pyridinedicarboxylate), and the energy acceptors (quenchers) are an enantiomerically-resolved population of Co(R,R-chxn)3 3+ (where R,R-chxn = trans-1R,2R-diaminocyclohexane) complexes. The luminophores are dissolved in acetonitrile as (NEt4)3[Ln(dpa)3] (where NEt(4) = tetraethlylammonium) and (NBu4)[Ln(dpa)3] (where NBu4 = tetrabutylammonium) salts. The unquenched luminescence lifetimes are reported for both Eu(dpa)3 (3-) and Tb(dpa)3 (3-) in acetonitrile over the range 263-333 K, and these results are compared to luminescence lifetimes in aqueous solution. Time-resolved chiroptical luminescence measurements of enantiopreferential quenching kinetics are reported for samples with Eu(dpa)3 (3-) and Co(R,R-chxn)3 3+ in acetonitrile over 263-333 K range. These results are analyzed using a phenomenological quenching kinetics model, and the results are compared to results in aqueous solution. These comparisons show that the overall Eu-Co luminescence quenching efficiency is reduced in acetonitrile vs. aqueous samples, because the salts of (NX4)3[Eu(dpa)3] are not completely dissociated in acetonitrile. However, the enantiopreference exhibited is identical in acetonitrile vs. aqueous solution.

Infrared spectroscopic study of C(2)F(6) monolayers and bilayers on graphite.

We report an experimental study of adsorbed films of C(2)F(6) on graphite by using infrared reflection absorption spectroscopy supplemented by ellipsometry. The vibrational C-F stretch modes nu(5) (parallel to the molecular axis) and nu(7) (perpendicular) in the film are strongly blueshifted by dynamic dipole coupling, and these shifts are sensitive to lattice spacing and molecular tilt. The relative strength of the absorption peaks mainly depends on the tilt angle relative to the surface normal. We use the strength data to estimate the tilt angle across the known monolayer phases, information that is difficult to obtain by other techniques. Although only the surface-normal component of the induced dipole moment appreciably couples to the external infrared field, surface-parallel components contribute to the intralayer coupling and hence to the frequency shifts for tilted molecules. Comparison to model calculations for a range of herringbone tilt configurations allows us to draw conclusions regarding the pattern of tilt azimuths. On this basis, we offer a revised interpretation of the origin of the Ising-type ordering transition found by Arndt et al. [Phys. Rev. Lett. 80, 1686 (1998)] in heat capacity measurements. Our phase boundaries for monolayer phases above 80 K are in good agreement with earlier results of the Saarbrucken group. We identify three distinct bilayer phases near saturation in isothermal pressure scans from ellipsometric steps and spectroscopic signatures. In temperature scans, we find evidence for several monolayer phases more dense than the well-established 2 x 2 commensurate phase and for a stable trilayer phase below about 60 K.