Structure-Based Evolution of Subtype-Selective Neurotensin Receptor Ligands

Subtype-selective agonists of the neurotensin receptor NTS2 represent a promising option for the treatment of neuropathic pain, as NTS2 is involved in the mediation of μ-opioid-independent anti-nociceptive effects. Based on the crystal structure of the subtype NTS1 and previous structure–activity relationships (SARs) indicating a potential role for the sub-pocket around Tyr11 of NT(8–13) in subtype-specific ligand recognition, we have developed new NTS2-selective ligands. Starting from NT(8–13), we replaced the tyrosine unit by β²-amino acids (type 1), by heterocyclic tyrosine bioisosteres (type 2) and peptoid analogues (type 3). We were able to evolve an asymmetric synthesis of a 5-substituted azaindolylalanine and its application as a bioisostere of tyrosine capable of enhancing NTS2 selectivity. The S-configured test compound 2 a, [(S)-3-(pyrazolo[1,5-a]pyridine-5-yl)-propionyl¹¹]NT(8–13), exhibits substantial NTS2 affinity (4.8 nm) and has a nearly 30-fold NTS2 selectivity over NTS1. The (R)-epimer 2 b showed lower NTS2 affinity but more than 600-fold selectivity over NTS1.     

Urethanases for the Enzymatic Hydrolysis of Low Molecular Weight Carbamates and the Recycling of Polyurethanes

Enzymatic degradation and recycling can reduce the environmental impact of plastics. Despite decades of research, no enzymes for the efficient hydrolysis of polyurethanes have been reported. Whereas the hydrolysis of the ester bonds in polyester-polyurethanes by cutinases is known, the urethane bonds in polyether-polyurethanes have remained inaccessible to biocatalytic hydrolysis. Here we report the discovery of urethanases from a metagenome library constructed from soil that had been exposed to polyurethane waste for many years. We then demonstrate the use of a urethanase in a chemoenzymatic process for polyurethane foam recycling. The urethanase hydrolyses low molecular weight dicarbamates resulting from chemical glycolysis of polyether-polyurethane foam, making this strategy broadly applicable to diverse polyether-polyurethane wastes.     

Combining the Advantages of Tetrazoles and 1,2,3‐Triazoles: 4,5‐Bis(tetrazol‐5‐yl)‐1,2,3‐triazole, 4,5‐Bis(1‐hydroxytetrazol‐5‐yl)‐1,2,3‐triazole,and their Energetic Derivatives

In the development of new energetic materials, the main challenge is the combination of high energy content with chemical and mechanical stability, two properties that are often contradictory. In this study, the syntheses and comprehensive characterizations of 4,5‐bis(tetrazole‐5‐yl)‐1,2,3‐triazole and the novel 4,5‐bis(1‐hydroxytetrazole‐5‐yl)‐1,2,3‐triazole, as well as their energetic properties, are presented, combining the advantages of the more energetic tetrazole and the more stable 1,2,3‐triazole rings. Nitrogen‐rich salts of both compounds were synthesized to investigate their detonation performances and combustion behavior calculated by computer codes for potential application in erosion‐reduced gun propellant mixtures due to their high nitrogen content. The structures of several of the compounds were studied by single‐crystal X‐ray diffraction and, especially in the case of 4,5‐bis(tetrazol‐5‐yl)‐1,2,3‐triazole, revealed the site of deprotonation.     

Multifunctional Polyoxometalate Platforms for Supramolecular Light-Driven Hydrogen Evolution**

Multifunctional supramolecular systems are a central research topic in light-driven solar energy conversion. Here, we report a polyoxometalate (POM)-based supramolecular dyad, where two platinum-complex hydrogen evolution catalysts are covalently anchored to an Anderson polyoxomolybdate anion. Supramolecular electrostatic coupling of the system to an iridium photosensitizer enables visible light-driven hydrogen evolution. Combined theory and experiment demonstrate the multifunctionality of the POM, which acts as photosensitizer/catalyst-binding-site^[1] and facilitates light-induced charge-transfer and catalytic turnover. Chemical modification of the Pt-catalyst site leads to increased hydrogen evolution reactivity. Mechanistic studies shed light on the role of the individual components and provide a molecular understanding of the interactions which govern stability and reactivity. The system could serve as a blueprint for multifunctional polyoxometalates in energy conversion and storage.     

π-Extended Diaza[7]helicenes by Hybridization of Naphthalene Diimides and Hexa-peri-hexabenzocoronenes

The synthesis of an unprecedented, π-extended hexabenzocorene (HBC)-based diaza[7]helicene is presented. The target compound was synthesized by an ortho-fusion of two naphthalene diimide (NDI) units to a HBC-skeleton. A combination of Diels–Alder and Scholl-type oxidation reactions involving a symmetric di-NDI-tolane precursor were crucial for the very selective formation of the helical superstructure via a hexaphenyl-benzene (HPB) derivative. The formation of the diaza[7]helicene moiety in the final Scholl oxidation is favoured, affording the symmetric π-extended helicene as the major product as a pair of enantiomers. The separation of the enantiomers was successfully accomplished by HPLC involving a chiral stationary phase. The absolute configuration of the enantiomers was assigned by comparison of circular dichroism spectra with quantum mechanical calculations.     

Characterization of Aldehyde Dehydrogenases Applying an Enzyme Assay with In Situ Formation of Phenylacetaldehydes

Herein, different dehydrogenases (DH) were characterized by applying a novel two-step enzyme assay. We focused on the NAD(P)⁺-dependent phenylacetaldehyde dehydrogenases because they produce industrially relevant phenylacetic acids, but they are not well studied due to limited substrate availability. The first assay step comprises a styrene oxide isomerase (440 U mg^?1 _protein) which allows the production of pure phenylacetaldehydes (>70 mmol L^?1) from commercially available styrene oxides. Thereafter, a DH of interest can be added to convert phenylacetaldehydes in a broad concentration range (0.05 to 1.25 mmol L^?1). DH activity can be determined spectrophotometrically by following cofactor reduction or alternatively by RP-HPLC. This assay allowed the comparison of four aldehyde dehydrogenases and even of an alcohol dehydrogenase with respect to the production of phenylacetic acids (up to 8.4 U mg^?1 _protein). FeaB derived from Escherichia coli K-12 was characterized in more detail, and for the first time, substituted phenylacetaldehydes had been converted. With this enzyme assay, characterization of dehydrogenases is possible although the substrates are not commercially available in sufficient quality but enzymatically producible. The advantages of this assay in comparison to the former one are discussed.     

Protein-Templated Fragment Ligations—From Molecular Recognition to Drug Discovery

Protein-templated fragment ligation is a novel concept to support drug discovery and can help to improve the efficacy of protein ligands. Protein-templated fragment ligations are chemical reactions between small molecules (“fragments”) utilizing a protein's surface as a reaction vessel to catalyze the formation of a protein ligand with increased binding affinity. The approach exploits the molecular recognition of reactive small-molecule fragments by proteins both for ligand assembly and for the identification of bioactive fragment combinations. In this way, chemical synthesis and bioassay are integrated in one single step. This Review discusses the biophysical basis of reversible and irreversible fragment ligations and gives an overview of the available methods to detect protein-templated ligation products. The chemical scope and recent applications as well as future potential of the concept in drug discovery are reviewed.     

Validated determination of eight antibiotic substance groups in cattle and pig muscle by HPLC/MS/MS

The described multimethod is suited for the determination of 53 substances of eight antibiotic groups-tetracyclines, quinolones, macrolides, sulfonamides, diphenylsulfones, diamino-pyrimidine derivatives, pleuromutilines, and lincosamides-in cattle and pig muscle. All substances were analyzed simultaneously with the same sample preparation and in one HPLC/MS/MS run. The validation of the multimethod was successfully accomplished with the help of an alternative in-house validation concept requiring only 48 experiments. The substances were validated at concentrations of 0.25, 0.5, 1.0, 1.5, and 2.0 x MRL (maximum residue limit) or 5, 10, 20, 30, and 40 microg/kg for substances without an MRL. The calculated relevant validation parameters were based on and comply with the requirements of Commission Decision 2002/657/EC, i.e., the decision limit, detection capability, repeatability, within-laboratory reproducibility, and recovery. The robustness of the method was demonstrated by varying seven factors of the analytical procedure. Several proficiency tests were carried out successfully to provide evidence for the applicability of the method.     

Unexpected stable dimerisation of an anionic imidopyrrolecarboxylate in polar solution

The imidopyrrolecarboxylate 3(-) unexpectedly forms stable dimers (K(ass) = 130 M(-1) in CHCl(3)/DMSO, 1?:?1, v/v) despite the fact that two anions have to interact. The dimer is more stable than an analogous neutral amidopyrrolecarboxylic acid dimer (K(ass) < 10 M(-1)) underlining the importance of charged H-bonds compared to neutral ones.     

Characterization and Stability Study of Immobilized PQQ‐Dependent Aldose Dehydrogenase Bioanodes

In this paper, glucose oxidizing bioanodes employing immobilized PQQ‐dependent aldose dehydrogenase were prepared and characterized. The enzyme was immobilized on carbon paper in two different polymeric systems: tetrabutylammonium bromide (TBAB) modified Nafion and butanal modified chitosan. Characterization of the bioanodes included electron microscopy, electrochemical evaluation, as well as stability and leaching studies. Results indicate that the operational degradation was the same but the long term storage stability is better in the case of modified Nafion. The performance of the modified Nafion immobilized bioanodes stayed at 70 % of the initial value after 60 days of storing at 4 °C and 25 °C. Compared to TBAB modified Nafion immobilized bioanodes, butanal modified chitosan immobilized bioanodes showed 50 % activity after eight weeks storage at 4°C and one week storage at 25 °C. However, the electrochemical properties of modified chitosan were better.