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91.
92.
Bringmann G Haagen Y Gulder TA Gulder T Heide L 《The Journal of organic chemistry》2007,72(11):4198-4204
Streptomyces cinnamonensis DSM 1042 produces the polyketide-isoprenoid compound furanonaphthoquinone I (FNQ I) and isoprenylated phenazines, predominantly endophenazine A. However, the recently identified biosynthetic gene cluster for these compounds only contains a single gene for a mevalonate pathway enzyme, that is, a putative mevalonate kinase gene. This is in strong contrast to all Streptomyces strains examined so far, where all six genes encoding the mevalonate pathway enzymes are clustered in a single operon of 6.8 kb and, thus, raised the question about the biosynthetic origin of the isoprenoid moieties of FNQ I and endophenazine A. In this study, we investigated the incorporation of [13C2]acetate and [2-13C]glycerol into FNQ I and endophenazine A. The results unequivocally prove that the isoprenoid building blocks of both compounds are predominantly formed via the mevalonate pathway (approximately 80%) but that the MEP pathway (approximately 20%) contributes to the biosynthesis of these molecules, too. In actinomycetes, this is the first experimentally proven example of the utilization of both biosynthetic routes for the formation of one single secondary metabolite. The incorporation pattern of [2-13C]glycerol was consistent with a "reverse" prenyl transfer, that is, with the formation of a C-C bond from C-3 of GPP to the polyketide nucleus of FNQ I. 相似文献
93.
Jürgen M. Kolos Sebastian Pomplun Sascha Jung Benedikt Rieß Patrick L. Purder Andreas M. Voll Stephanie Merz Monika Gnatzy Thomas M. Geiger Ingrid Quist-Lkken Jerome Jatzlau Petra Knaus Toril Holien Andreas Bracher Christian Meyners Paul Czodrowski Vera Krewald Felix Hausch 《Chemical science》2021,12(44):14758
Methyl groups can have profound effects in drug discovery but the underlying mechanisms are diverse and incompletely understood. Here we report the stereospecific effect of a single, solvent-exposed methyl group in bicyclic [4.3.1] aza-amides, robustly leading to a 2 to 10-fold increase in binding affinity for FK506-binding proteins (FKBPs). This resulted in the most potent and efficient FKBP ligands known to date. By a combination of co-crystal structures, isothermal titration calorimetry (ITC), density-functional theory (DFT), and 3D reference interaction site model (3D-RISM) calculations we elucidated the origin of the observed affinity boost, which was purely entropically driven and relied on the displacement of a water molecule at the protein–ligand–bulk solvent interface. The best compounds potently occupied FKBPs in cells and enhanced bone morphogenic protein (BMP) signaling. Our results show how subtle manipulation of the solvent network can be used to design atom-efficient ligands for difficult, solvent-exposed binding pockets.Enhancement by displacement. A single methyl group displaces a water molecule from the binding site of FKBPs, resulting in the most potent binders known, outperforming the natural products FK506 and rapamycin in biochemical and cellular assays. 相似文献
94.
Aromatic azides with hindered amine light stabilizer (HALS) residues or hydrophilic groups such as glucose, sucrose and dextrine residues were synthesized and used for surface modification of polyolefins. By UV‐irradiation nitrenes were formed, which are able to react with polyolefin surfaces. By photochemical immobilization of the carbohydrates hydrophilicity of PE and PP was strongly increased (surface tensions > 44mN/m). Light stability of PP surfaces modified with HALS azides was comparable with PP, stabilised with Tinuvin 770. Bulk modification of ethylene‐propylene and ethylene‐octene copolymers was achieved by grafting nitrenes formed by thermal decomposition of azido benzoic acid. In a circulating air oven up to 1.55 wt% amino benzoic acid residues could be bonded covalently to ethylene‐propylene‐copolymers, less than half of it to ethylene‐octene‐copolymers. Reactive extrusion resulted in grafting yields of more than 50% for both types of copolymers. 相似文献
95.
96.
97.
Alejandro Saenz Tanja Asthalter Wolf Weyrich 《International journal of quantum chemistry》1997,65(3):213-223
For the first time, an analytical and efficient algorithm for the evaluation of spherically averaged reciprocal form factors B(s)=〈B( s )〉Ω using Gauss-type basis functions is presented. The spherically averaged Compton profile is available by Fourier transformation of the reciprocal form factor. The algorithm has been successfully implemented in connection with the quantum chemistry codes GAMESS and CRYSTAL92, which perform Hartree–Fock calculations for molecules and solids. In addition, an analytical algorithm for the direct evaluation of spherically averaged Compton profiles and the moments 〈pν〉 (ν≥−1) via the momentum density is proposed for Gauss-type basis functions. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65 : 213–223, 1997 相似文献
98.
Pr(BO2)3 and PrCl(BO2)2: Two Praseodymium meta‐Borates in Comparison Single‐crystalline PrCl(BO2)2 can be obtained by the reaction of praseodymium, Pr6O11 and PrCl3 with a small excess of B2O3 in evacuated silica tubes after seven days at 850 °C. If NaCl is additionally used as flux, single crystals of Pr(BO2)3 dominate the main product. Both praseodymium(III) meta‐borates are air and water stable. The crystals of PrCl(BO2)2 emerge as long, thin, pale green needles which tend to severe twinning due to their fibrous habit. The crystal structure (triclinic, P1¯; a = 420.56(4), b = 655.42(7), c = 808.34(8) pm, α = 82.361(8), β = 89.173(9), γ = 71.980(7)°, Z = 2) exhibits zigzag chains {[(B1)ot1/1Oe2/2(B2)Ot1/1Oe2/2]2−} (≡ {[BO2]−}) of corner‐linked [BO3]3− triangles with syndiotactic orientation of the terminal oxygen atoms which are running parallel to the [100] direction. The Pr3+ cations are surrounded by three Cl− and seven O2− anions with the shape of a tetracapped trigonal prism. The green, transparent crystals of Pr(BO2)3 (monoclinic, C2/c; a= 984.98(9), b = 809.57(8), c = 641.02(6) pm, β = 126.783(9)°, Z = 4) appear either lath‐shaped or rather spherical. In the crystal structure the B3+ cations reside both in trigonal planar as well as in tetrahedral coordination of oxygen atoms. Both types of borate polyhedra ([BO3]3− and [BO4]5−) are linked via corners to form chains of the composition {[(B2)‐Ot1/1Oe2/2(B1)Oe4/2(B2)Ot1/1Oe2/2]3−} (≡ {[BO2]−}) which run parallel [101]. The coordination sphere of the Pr3+ cations consists of ten oxide anions which build up a bicapped square antiprism. 相似文献
99.
Klaus Albert Markus Dachtler Tobias Glaser Heidi Hndel Tanja Lacker Gtz Schlotterbeck Sabine Strohschein Li-Hong Tseng Ulrich Braumann 《Journal of separation science》1999,22(3):135-143
The hyphenation of chromatographic separation techniques with NMR spectroscopy is one of the most powerful and time-saving methods for the separation and structural elucidation of unknown compounds and molecular compositions of mixtures. Most of the routinely used NMR flow-cells have detection volumes between 40–180 μL for conventional separations with analytical columns, and the newest designs employ detection volumes in the order of 200 nL for capillary separations. The low flow rates used in capillary chromatography permit the use of deuterated solvents. Unequivocal structural assignment of unknown chromatographic peaks is possible by two-dimensional stopped-flow capillary HPLC-NMR experiments. 相似文献
100.
Tobat P.I. Saragi Christoph Schmidt Tanja Weis Arno Ehresmann 《Journal of magnetism and magnetic materials》2009,321(14):2204-2209
The surface and interface morphology and magnetization characteristics of Co70Fe30 thin films deposited on bare glass and p-Si/SiO2 substrates and on conjugated polymer poly(3-hexylthiophene-2,5-diyl) (P3HT) thin films on such substrates have been studied by atomic force microscopy and magneto-optic Kerr effect. It was found that the average absolute magnitude of the coercive field of Co70Fe30 correlates with the roughness of the underlayer prior to Co70Fe30 deposition. P3HT deposited on p-Si/SiO2 substrates possesses an increased surface roughness as compared to the p-Si/SiO2 surface, but displays a decreased surface roughness as compared to the one of a bare glass substrate. 相似文献