A Versatile Strategy for Screening Custom-Designed Warhead-Armed Cyclic Peptide Inhibitors

Demand for peptide-based pharmaceuticals has been steadily increasing, but only limited success has been achieved to date. To expedite peptide-based drug discovery, we developed a general scheme for cell-based screening of cyclic peptide inhibitors armed with a user-designed warhead. We combined unnatural amino acid incorporation and split intein-mediated peptide cyclization techniques and integrated a yeast-based colorimetric screening assay to generate a new scheme that we call the custom-designed warhead-armed cyclic peptide screening platform (CWCPS). This strategy successfully discovered a potent inhibitor, CY5-6Q, that targets human histone deacetylase 8 (HDAC8) with a K_D value of 15 nM. This approach can be a versatile and general platform for discovering cyclic peptide inhibitors.     

Electrochemical behaviour of the LiF-(CaF2)-La2O3 system

The electrochemical behaviour of the LiF-La₂O₃ and LiF-CaF₂-La₂O₃ systems was investigated by means of cyclic voltammetry. Several types of working electrodes (spectrographic pure graphite, W, Mo, Ni, Cu) were used. It was found that chemical reactions take place in the system during the dissolution of lanthanum oxide. The reduction of lithium cations occurred at the most positive potential from the species formed in the melt on ‘inert’ cathodes (W, Mo). The reactive cathodes (Cu, Ni) allowed the lanthanum deposition with depolarisation.     

Synthesis,crystal structure and biological activities of dehydroacetic acid complexes of Ru(II) and Ru(III) containing PPh3/AsPh3

A series of Ru(II) and Ru(III) complexes of the types [RuX(CO)(EPh₃)₂L] (X = H, E = P; X = Cl, E = P or As) and [RuX₂(EPh₃)₂L] (X = Cl, E = P or As; X = Br, E = As, L = monoanion of dehydroacetic acid) have been synthesized in order to explore their biological activities, such as DNA-binding and antibacterial activity. The complexes were characterized by analytical and spectroscopic techniques. The crystal and molecular structure of [RuCl₂(AsPh₃)₂(L)] has been determined by single crystal XRD. The cyclic voltammograms of the complexes in acetonitrile displayed either quasi-reversible or irreversible redox couples based on the metal centre. The ligand, dehydroacetic acid (DHA) and its metal complexes were tested against five pathogenic bacteria. Absorption titration and cyclic voltammetric studies revealed that the complexes interact with Herring Sperm ds DNA through different binding modes to different extents.     

Redox-active antifungal cobalt(II) and copper(II) complexes with sterically hindered o-aminophenol derivatives

Co(II) complexes with 4,6-di(tert-butyl)-2-aminophenol (HL^I) and 2-anilino-4,6-di(tert-butyl)phenol (HL^II) have been synthesized and characterized by means of physico-chemical methods. The compounds HL^I and HL^II coordinate in their singly deprotonated forms and behave as bidentate O,N-coordinated ligands; their low-spin Co(II) complexes are characterized by CoN₂O₂ coordination modes and square planar geometry. Both the free ligands and their Co(II) and Cu(II) complexes (we have produced and characterized the latter before) exhibit a pronounced antifungal activity against Aspergillus niger, Fusarium spp., Mucor spp., Penicillium lividum, Botrytis cinerea, Alternaria alternata, Sclerotinia sclerotiorum, Monilia spp., which in a number of cases is comparable with that of Nystatin and Terbinafine or even higher. The reducing properties of the ligands and their metal(II) complexes, as well as their antifungal activities, were found to decrease in the order: Cu(L^I)₂ > Cu(L^II)₂ ? Co(L^I)₂ > Co(L^II)₂ > HL^I > HL^II.     

Copper recovery by polymer enhanced ultrafiltration (PEUF) and electrochemical regeneration

In this work, the removal of Cu²⁺ from a synthetic effluent has been tested by means of polymer enhanced ultrafiltration (PEUF), using partially ethoxylated polyethylenimine (PEPEI) as water-soluble polymer. Overall, the two necessary steps of a hypothetical continuous process, metal retention (in total recirculation and discontinuous mode) and polymer regeneration (in discontinuous mode), have been confronted individually. On the one hand, the values of temperature (T), transmembrane pressure (ΔP), metal–polymer ratio and pH that maximize both, permeate fluxes and rejection coefficients, have been obtained by ultrafiltration tests, reaching Cu²⁺ retention coefficients higher than 97%. On the other hand, the polymer regeneration step has been carried out by the electrochemical technique, which consists in the metal electrodeposition on the cathode of an electrochemical cell. In a first step, cyclic voltammetries have been carried out to assure the polymer does not suffer any oxidation or reduction process. From these tests, a cathodic working potential has been selected to minimize hydrogen evolution reaction (−0.7 V vs. Ag/AgCl). Working at this voltage in deposition tests, a pH of 3.3 has been selected from experiments at different pH values. This pH is less extreme than the pH necessary if this step was carried out chemically (pH 2).     

Structural characteristics and cyclic voltammetric behaviour of Sonogel-Carbon tyrosinase biosensors. A detailed comparative study of three immobilization matrixes

Structural characteristics an cyclic voltammetry of three amperommetric biosensors based on immobilization of tyrosinase on a Sonogel-Carbon electrode for detection of phenols are described. Cyclic voltammetry was applied to study the electrochemical behaviour of the electrode and the electrochemical reaction on the electrode surface. Scanning electron microscopy, X-ray energy dispersive spectroscopy and atomic force microscopy were used for the structure characterization of the electrode surface, enzyme film and polymers coatings. The influence of additive-protective polymers, such as polyethylene glycol and perfluorinated-Nafion ion-exchanger on the surface of the biosensor were explored.     

Site selectivity in the reactions of the hexanuclear platinum cluster [Pt6(mu-PtBu2)4(CO)6][CF3SO3]2

The previously reported hexanuclear cluster [Pt(6)(mu-PtBu(2))(4)(CO)(6)](2+)[Y](2) (1-Y(2): Y=CF(3)SO(3) (-)) contains a central Pt(4) tetrahedron bridged at each of the opposite edges by another platinum atom; in turn, four phosphido ligands bridge the four Pt-Pt bonds not involved in the tetrahedron, and, finally, one carbonyl ligand is terminally bonded to each metal centre. Interestingly, the two outer carbonyls are more easily substituted or attacked by nucleophiles than the inner four, which are bonded to the tetrahedron vertices. In fact, the reaction of 1-Y(2) with 1 equiv of [nBu(4)N]Cl or with an excess of halide salts gives the monochloride [Pt(6)(mu-PtBu(2))(4)(CO)(5)Cl](+)[Y], 2-Y, or the neutral dihalide derivatives [Pt(6)(mu-PtBu(2))(4)(CO)(4)X(2)] (3: X=Cl; 4: X=Br; 5: X=I). Moreover, the useful unsymmetrically substituted [Pt(6)(mu-PtBu(2))(4)(CO)(4)ICl] (6) was obtained by reacting equimolar amounts of 2 and [nBu(4)N]I, and the dicationic derivatives [Pt(6)(mu-PtBu(2))(4)(CO)(4)L(2)](2+)[Y](2) (7-Y(2): L=(13)CO; 8-Y(2): L=CNtBu; 9-Y(2): L=PMe(3)) were obtained by reaction of an excess of the ligand L with 1-Y(2). Weaker nitrogen ligands were introduced by dissolving the dichloride 3 in acetonitrile or pyridyne in the presence of TlPF(6) to afford [Pt(6)(mu-PtBu(2))(4) (CO)(4)L(2)](2+)[Z](2) (Z=PF(6) (-), 10-Z(2): L=MeCN; 11-Z(2): L=Py). The "apical" carbonyls in 1-Y(2) are also prone to nucleophilic addition (Nu(-): H(-), MeO(-)) affording the acyl derivatives [Pt(6)(mu-PtBu(2))(4)(CO)(4)(CONu)(2)] (12: Nu=H; 13: Nu=OMe). Complex 12 is slowly converted into the dihydride [Pt(6)(mu-PtBu(2))(4)(CO)(4)H(2)] (14), which was more cleanly prepared by reacting 3 with NaBH(4). In a unique case we observed a reaction involving also the inner carbonyls of complex 1, that is, in the reaction with a large excess of the isocyanides R-NC, which form the corresponding persubstituted derivatives [Pt(6)(mu-tPBu(2))(4)(CN-R)(6)](2+)[Y](2), (15-Y(2): R=tBu; 16-Y(2) (2-): R=-C(6)H(4)-4-C triple bond CH). All complexes were characterized by microanalysis, IR and multinuclear NMR spectroscopy. The crystal and molecular structures of complexes 3, 5, 6 and 9-Y(2) are also reported. From the redox viewpoint, all complexes display two reversible one-electron reduction steps, the location of which depends both upon the electronic effects of the substituents, and the overall charge of the original complex.     

Crystal-packing-induced antiferromagnetic interactions of metallocenes: cyanonickelocenes, -cobaltocenes, and -ferrocenes

The cyano-substituted metallocenes [M(C5H4CN)2] (M=Fe, 1; Co, 2; Ni 3) and [M(C5Me5)(C5H4CN)] (M=Fe, 4; Co, 5; Ni, 6) were synthesized in yields up to 58 % by treating K(C5H4CN) or Tl(C5H4CN) with suitable transition-metal precursors. Cyclic voltammetry indicated that the oxidation and reduction potentials of all the cyanometallocenes were shifted to positive values by up to 0.8 V. Single-crystal X-ray structure analysis showed that 1 had eclipsed ligands, formed planes in the lattice, and--unlike usual metallocenes--lined up in stacks perpendicular to these planes. Powder X-ray studies established that 1 and 2 are isotypic. The 1H and 13C NMR spectra were recorded for all the new compounds. Signal shifts of up to delta=1500 ppm were recorded for the paramagnetic molecules 2 and 3 and were, at a given temperature, strikingly different for solution and solid-state spectra. These results pointed to antiferromagnetic interactions as a consequence of molecular ordering in the lattice, as confirmed by magnetic measurements. The temperature-dependent susceptibilities were reproduced by Heisenberg spin-chain models (H=-J sum n- 1 i=1 SiSi+1), thus yielding J=-28.3 and -10.3 cm(-1) for 2 and 3, respectively, whereas J=-11.8 cm(-1) was obtained for 3 from the Ising spin-chain model. In accordance with molecular orbital (MO) considerations, much spin density was found to be delocalized not only on the cyclopentadienyl ligand but also the cyano substituents. The magnetic interaction was interpreted as a Heitler-London spin exchange and was analyzed based on how the interaction depends on the singly occupied MOs and the shift of parallel metallocenes relative to each other.     

Quantitative conformational study of redox-active [2]rotaxanes, part 1: Methodology and application to a model [2]rotaxane

This paper reports a novel methodology for the conformational analysis of [2]rotaxanes. It combines NMR spectroscopic (COSY, NOESY and the recently reported paramagnetic line-broadening and suppression technique) and electrochemical techniques to enable a quantitative analysis of the co-conformations of interlocked molecules and the conformations of their components. This methodology was used to study a model [2]rotaxane in solution. This [2]rotaxane consists of an axle that incorporates an electron-poor, doubly positively charged viologen that threads an electron-rich crown ether. It has been shown that the axle of the [2]rotaxane in its dicationic state adopts a folded conformation in solution and the crown ether is localised at the viologen moiety. Following a one-electron reduction of viologen, the paramagnetic radical cation of the [2]rotaxane retains its folded conformation in solution. The data also demonstrate that in the radical cation the crown ether remains localised at the viologen, despite its reduced affinity for the singly reduced viologen. The combined quantitative NMR spectroscopic and electrochemical characterisation of the electromechanical function of the model [2]rotaxane in solution provides an important reference point for the study of switching in structurally related bistable [2]rotaxanes, which is the subject of the second part of this work.     

Electrogenerated chemiluminescence: an oxidative-reductive mechanism between quinolone antibiotics and tris(2,2'-bipyridyl)ruthenium(II)

The cyclic voltammetry and electrogenerated chemiluminescent (ECL) reactions of a series of quinolone and fluoroquinolone antibiotics were investigated in a flow injection analysis (FIA) system. 7-Piperazinyl fluoroquinolone antibiotics were found to participate as a coreactant in an oxidative-reductive ECL mechanism with tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) as the luminescent reagent. The reaction mechanism was investigated in order to understand and optimize the processes leading to light emission. The optimal conditions included a solution pH ∼7 at a flow rate of 3.0 mL min⁻¹ with no added organic modifier and application of 1.2 V vs. a Pt quasi-reference electrode (QRE). Fluoroquinolones containing a tertiary distal nitrogen on the piperazine ring, such as enrofloxacin and ofloxacin, reacted to produce more intense ECL than those with a secondary nitrogen, such as ciprofloxacin and norfloxacin. The method linear range, precision, detection limits, and sensitivity for the detection of enrofloxacin and ciprofloxacin were compared to that of tripropylamine. The method was applied to the determination of the ciprofloxacin content in a pharmaceutical preparation. The assay is discussed in terms of its analytical figures of merit, ease of use, speed, accuracy and application to pharmaceutical samples.