Prodrug design for the potent cardiovascular agent Nω-hydroxy-L-arginine (NOHA): synthetic approaches and physicochemical characterization

N(ω)-Hydroxy-L-arginine (NOHA)--the physiological nitric oxide precursor--is the intermediate of NO synthase (NOS) catalysis. Besides the important fact of releasing NO mainly at the NOS-side of action, NOHA also represents a potent inhibitor of arginases, making it an ideal therapeutic tool to treat cardiovascular diseases that are associated with endothelial dysfunction. Here, we describe an approach to impart NOHA drug-like properties, particularly by wrapping up the chemically and metabolically instable N-hydroxyguanidine moiety with different prodrug groups. We present synthetic routes that deliver several more or less highly substituted NOHA derivatives in excellent yields. Versatile prodrug strategies were realized, including novel concepts of bioactivation. Prodrug candidates were primarily investigated regarding their hydrolytic and oxidative stabilities. Within the scope of this work, we essentially present the first prodrug approaches for an interesting pharmacophoric moiety, i.e., N-hydroxyguanidine.     

Thermal study of mononuclear Pd(II) complexes of the type [Pd(X)<Subscript>2</Subscript>(Rtu)(PPh<Subscript>3</Subscript>)] (X = Cl,SCN; Rtu = <Emphasis Type="Italic">N</Emphasis>-methylthiourea, <Emphasis Type="Italic">N</Emphasis>-phenylthiourea)

The synthesis, spectroscopic characterization, and thermal analysis of the compounds [Pd(X)₂(mtu)(PPh₃)] (X = Cl⁻ (1), SCN⁻ (2); mtu = N-methylthiourea; PPh₃ = triphenylphosphine) and [Pd(X)₂(phtu)(PPh₃)] (X = Cl⁻ (3), SCN⁻ (4); phtu = N-phenylthiourea) are described. The thermal decomposition of the compounds occurs in two, three, or four stages and the final decomposition products were identified as Pd⁰ by X-ray powder diffraction. The thermal stability order of the complexes is 4 > 3>2 > 1.     

Steric, electronic, and secondary effects on the coordination chemistry of ionic phosphine ligands and the catalytic behavior of their metal complexes

The effects of introducing ionic functionalities in phosphine ligands on the coordination chemistry of these ligands and the catalytic behavior of the corresponding metal complexes are reviewed. The steric and electronic consequences of such functionalizations are discussed. Apart from these steric and electronic effects, the presence of charged groups often leads to additional, supramolecular interactions that occur in the second coordination sphere of the metal complex, such as intramolecular, interligand hydrogen bonding and Coulombic repulsion. These interactions can significantly alter the behavior of the phosphine ligand in question. Such effects have been observed in phosphine-metal association/dissociation equilibria, ligand substitution reactions, and stereoisomerism in phosphine-metal complexes. By drawing general conclusions, this review offers an insight into the coordination and catalytic behavior of phosphine ligands containing ionic functionalities and their corresponding metal complexes.     

Identification of sulfoquinovosyldiacyglycerides from Phaeodactylum tricornutum by matrix-assisted laser desorption/ionization QTrap time-of-flight hybrid mass spectrometry

The pharmaceutical industry is interested in identifying novel target compounds. Due to their versatile pharmacological activities (e.g. antiviral, anti-carcinogen and immunosuppressive) sulfoquinovosyldiacylglycerides (SQDGs) are potential drug candidates. The present publication deals with the purification and structural characterization of SQDGs from three different strains of Phaeodactylum tricornutum. Besides detection of SQDGs (sn-1: C16:1/sn-2: C16:0 and sn-1: C20:5/sn-2: C16:0), two novel 2'-O-acylsulfoquinovosyldiacylglyerides (Ac-SQDGs, sn-1: C16:0/ sn-2: C16:0/2' C20:5 and sn-1: C20:5/sn-2: C16:0/2' C20:5) were identified by using matrix-assisted laser desorption/ionization (MALDI) QTrap time-of-flight (ToF) hybrid mass spectrometry (MS) with multistage MS(n). The analytical method enables the sn-position verification of fatty acids (MS(2)) as well as the confirmation of the regioposition of eicospentanoic acid at the sulfoquinovose (MS(3)).     

Thioamide quenching of intrinsic protein fluorescence

Thioamides quench tryptophan and tyrosine fluorescence in a distance-dependent manner and thus can be used to monitor the binding of thioamide-containing peptides to proteins. Since thioamide analogs of the natural amino acids can be synthetically incorporated into peptides, they can function as minimally-perturbing probes of protein/peptide interactions.     

Oxido-pincer complexes of copper(II) - An EXAFS and EPR study of mono- and binuclear [(pydotH2)CuCl2]n (n = 1 or 2)

The oxido-pincer ligand pydotH₂ (2,6-bis(1-hydroxy-1-o-tolyl-ethyl-η²O,O′)pyridine) forms two different Cu^II containing complexes when prepared from anhydrous CuCl₂. A combination of EPR spectroscopy and EXAFS allowed to structurally characterise the light-green dimer of the formula [(pydotH₂)CuCl(μ-Cl)₂ClCu(pydotH₂)] and the penta-coordinate olive-green monomer [(pydotH₂)CuCl₂]. The molecular entities imply that the ligand remains protonated upon coordination. When dissolved in DMF both compounds form monomeric species [(pydotH₂)CuCl₂(DMF)] which could be characterised in detail by EPR, UV-Vis/NIR spectroscopy and electrochemical measurements. The assignments were supported by comparison with Cu^II complexes of the related ligands 2,6-bis(hydroxymethyl)pyridine (pydimH₂) and 2,6-bis(1-hydroxy-1-methyl)pyridine (pydipH₂).     

Synthesis and Structure Determination of Ag5HgSbO6, Comparison with AgHg3SbO6 and Ag5Pb2O6

From solid state reactions of Ag₂O, HgO, and Sb₂O₃ at high temperatures under elevated oxygen pressures a new silver mercury antimonate, Ag₅HgSbO₆, has been obtained. According to a single crystal structure determination Ag₅HgSbO₆ crystallizes in space group P$\bar{3}$ 1c (no. 163) with a = 5.9263(4), c = 12.3023(7) Å, V = 374.18(4) ų, Z = 2, 498 independent reflections, R1 = 0.030, wR2 = 0.059 (I ≥ 2 σ (I). Ag₅HgSbO₆ consists of HgSbO₆ layers, analogous to BiI_3, which are separated by Kagome nets formed by Ag⁺ ions. Perpendicular to these layers and along the c axis linear strings of Ag⁺ ions run through the large voids of the layers. Accordingly, Ag₅HgSbO₆ adopts the Ag₅Pb₂O₆ type of structure where the lead positions are occupied by mercury and antimony alternatingly. The finding of mercury in octahedral coordination, particularly besides the lower charged Ag⁺ cations in linear coordination, which is also highly preferred by Hg²⁺ ions, is rather unexpected. Ag₅HgSbO₆ starts to decompose at 450 °C and, in contrast to subvalent and metallic Ag₅Pb₂O₆, the new compound is charge balanced and semiconducting (ρ = 5.7 Ωcm at ambient temperature, E_a = 0.047 eV).     

Quantization and fractional quantization of currents in periodically driven stochastic systems. II. Full counting statistics

We study Markovian stochastic motion on a graph with finite number of nodes and adiabatically periodically driven transition rates. We show that, under general conditions, the quantized currents that appear at low temperatures are a manifestation of topological invariants in the counting statistics of currents. This observation provides an approach for classification of topological properties of the counting statistics, as well as for extensions of the phenomenon of the robust quantization of currents at low temperatures to the properties of the counting statistics which persist to finite temperatures.     

Metal induced folding: synthesis and conformational analysis of the lanthanide complexes of two 44-membered hydrazone macrocycles

Six new lanthanide complexes of two 44-membered macrocycles have been prepared and characterised in solution. An analysis of the conformations of the free macrocycles and their lanthanide complexes both in solution (2D NMR) and in solid state (X-ray crystallography) demonstrate that the complexation induces changes in folding of the macrocycles.