Synthesis and Ambiphilic Reactivity of Metalated Diorgano-Phosphonite Boranes

Unprecedented metalated phosphonite boranes were prepared from PH-substituted precursors and silyl amides. Although potassium derivatives were thermally stable and could even be isolated and structurally characterised, lithiated analogues proved to be unstable towards self-condensation under cleavage of LiOR at ambient temperature. Reaction studies revealed that the metalated phosphonite boranes exhibit ambiphilic character. Their synthetic potential as nucleophilic building blocks was demonstrated in the synthesis of the first stannylated phosphonite representing a new structural motif in phosphine chemistry.     

Absolute Configuration of Pharmaceutical Research Compounds Determined by X‐ray Powder Diffraction

The absolute configuration of active pharmaceutical ingredients (APIs) was determined by generating salts of the active pharmaceutical ingredient (API) with counterions of known chirality, and determining the crystal structures by X‐ray powder diffraction. This approach avoids the (often tedious) growth of single crystals, and is successful with very limited quantities of material (less than 1 mg). The feasibility of the method is demonstrated on five examples, and its limitations are discussed as well.     

Effects of blue light irradiation on human dermal fibroblasts

Previous studies have reported that separately from UV-radiation also blue light influences cellular physiology in different cell types. However, little is known about the blue light action spectrum. The purpose of this study was to investigate effects of blue light at distinct wavelengths (410, 420, 453, 480 nm) emitted by well defined light-emitting-diodes on viability, proliferation and antioxidative capacity of human dermal fibroblasts. We found that irradiation with blue light (410, 420 nm) led to intracellular oxidative stress and toxic effects in a dose and wavelength dependent manner. No toxicity was observed using light at 453 nm and 480 nm. Furthermore, blue light (410, 420, 453 nm) at low doses reduced the antioxidative capacity of fibroblasts. At non-toxic doses, irradiations at 410, 420 and 453 nm reduced proliferation indicating a higher susceptibility of proliferating fibroblasts to blue light. Our results show that blue light at different wavelengths may induce varying degrees of intracellular oxidative stress with different physiological outcome, which could contribute to premature skin photoaging. On the other hand, the use of blue light due to its antiproliferative and toxic properties may represent a new approach in treatment and prevention of keloids, hypertrophic scars and fibrotic skin diseases.     

Synthesis of <Emphasis Type="Italic">O</Emphasis>-[2-[<Superscript>18</Superscript>F]fluoro-3-(2-nitro-1<Emphasis Type="Italic">H</Emphasis>-imidazole-1-yl)propyl]tyrosine ([<Superscript>18</Superscript>F]FNT]) as a new class of tracer for imaging hypoxia

For detection of hypoxic tumor tissue, all radiotracers synthesized until now, are based on the concept that cellular uptake is being controlled by diffusion. As a new approach, we chose the concept to have the tracer hypothetically transported into the cells by well known carrier systems like the amino acid transporters. For this purpose, radiosynthesis of O-[2-[¹⁸F]fluoro-3-(2-nitro-1H-imidazole-1yl)propyl]tyrosine ([¹⁸F]FNT]) was carried out from methyl 2-(benzyloxycarbonyl)-3-(4-3-(2-nitro-1H-imidazol-1-yl)-2-(tosyloxy)propoxy) phenyl)propanoate via no-carrier-added nucleophilic aliphatic substitution. After labelling, 81 ± 0.9% of labelled intermediate i.e. methyl 2-(benzyloxycarbonyl)-3-(4-(2-[¹⁸F]fluoro-3-(2-nitro-1H-imidazole-1-yl)propoxy) phenyl)propanoate was obtained at 140 °C. At the end of radiosynthesis, [¹⁸F]FNT was obtained in an overall radiochemical yield of 40 ± 0.9% (not decay corrected) within 90 min in a radiochemical purity of >98% in a formulation ready for application in the clinical studies for PET imaging of hypoxia.     

Deuterium-labelled N-acyl-L-homoserine lactones (AHLs)--inter-kingdom signalling molecules--synthesis, structural studies, and interactions with model lipid membranes

N-Acyl-l-homoserine lactones (AHLs) are synthesized by Gram-negative bacteria. These quorum-sensing molecules play an important role in the context of bacterial infection and biofilm formation. They also allow communication between microorganisms and eukaryotic cells (inter-kingdom signalling). However, very little is known about the entire mechanism of those interactions. Precise structural studies are required to analyse the different AHL isomers as only one form is biologically most active. Theoretical studies combined with experimental infrared and Raman spectroscopic data are therefore undertaken to characterise the obtained compounds. To mimic interactions between AHL and cell membranes, we studied the insertion of AHL in supported lipid bilayers, using vibrational sum-frequency-generation spectroscopy. Deuterium-labelled AHLs were thus synthesized. Starting from readily available deuterated fatty acids, a two-step procedure towards deuterated N-acyl-l-homoserine lactones with varying chain lengths is described. This included the acylation of Meldrum’s acid followed by amidation. Additionally, the detailed analytical evaluation of the products is presented herein.     

Axial ligand and spin-state influence on the formation and reactivity of hydroperoxo-iron(III) porphyrin complexes

The present study focuses on the formation and reactivity of hydroperoxo-iron(III) porphyrin complexes formed in the [Fe(III)(tpfpp)X]/H(2)O(2)/HOO(-) system (TPFPP=5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphyrin; X=Cl(-) or CF(3) SO(3)(-)) in acetonitrile under basic conditions at -15 °C. Depending on the selected reaction conditions and the active form of the catalyst, the formation of high-spin [Fe(III)(tpfpp)(OOH)] and low-spin [Fe(III)(tpfpp)(OH)(OOH)] could be observed with the application of a low-temperature rapid-scan UV/Vis spectroscopic technique. Axial ligation and the spin state of the iron(III) center control the mode of O-O bond cleavage in the corresponding hydroperoxo porphyrin species. A mechanistic changeover from homo- to heterolytic O-O bond cleavage is observed for high- [Fe(III)(tpfpp)(OOH)] and low-spin [Fe(III)(tpfpp)(OH)(OOH)] complexes, respectively. In contrast to other iron(III) hydroperoxo complexes with electron-rich porphyrin ligands, electron-deficient [Fe(III)(tpfpp)(OH)(OOH)] was stable under relatively mild conditions and could therefore be investigated directly in the oxygenation reactions of selected organic substrates. The very low reactivity of [Fe(III)(tpfpp)(OH)(OOH)] towards organic substrates implied that the ferric hydroperoxo intermediate must be a very sluggish oxidant compared with the iron(IV)-oxo porphyrin π-cation radical intermediate in the catalytic oxygenation reactions of cytochrome P450.     

Monitoring on-chip Pictet-Spengler reactions by integrated analytical separation and label-free time-resolved fluorescence

High-throughput screening for optimal reaction conditions and the search for efficient catalysts is of eminent importance in the development of chemical processes and for expanding the spectrum of synthetic methodologies in chemistry. In this context we report a novel approach for a microfluidic chemical laboratory integrating organic synthesis, separation and time-resolved fluorescence detection on a single microchip. The feasibility of our integrated laboratory is demonstrated by monitoring the formation of tetrahydroisoquinoline derivatives by Pictet-Spengler condensation. After on-chip reaction the products and residual starting material were separated enantioselectively on the same chip. On-chip deep UV laser-induced fluorescence detection with time-correlated single photon counting was applied for compound assignment. The system was utilized to screen reaction conditions and various substrates for Pictet-Spengler reactions on-chip. Finally, the microlab was successfully applied to investigate enantioselective reactions using BINOL-based phosphoric acids as organocatalysts.     

Laccase Encapsulation in ZIF-8 Metal-Organic Framework Shows Stability Enhancement and Substrate Selectivity

CgL1 laccase from Corynebacterium glutamicum was encapsulated into the metal-organic framework (MOF) ZIF-8 which was synthesized in a rapid enzyme friendly aqueous synthesis, the fastest in situ encapsulation of laccases reported to date. The obtained enzyme/MOF, i. e. laccase@ZIF-8 composite showed enhanced thermal (up to 70 °C) and chemical (N,N-dimethylformamide) stability, resulting in a stable heterogenous catalyst, suitable for high temperature reactions in organic solvents. Furthermore, the defined structure of ZIF-8 produced a size selective substrate specificity, so that substrates larger than the pore size were not accepted. Thereby, 2’-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) was used to verify that the enzyme is immobilized inside the MOF versus the outside surface. The enzyme@MOF composite was analyzed by atomic absorption spectroscopy (ASS) to precisely determine the enzyme loading to 2.1 wt%.