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991.
Axel Trefzer Carsten Fischer Sigrid Stockert Lucy Westrich Eva Künzel Ulrich Girreser Jürgen Rohr Andreas Bechthold 《Chemistry & biology》2001,8(12):520-1252
BACKGROUND: The genetic engineering of antibiotic-producing Streptomyces strains is an approach that became a successful methodology in developing new natural polyketide derivatives. Glycosyltransferases are important biosynthetic enzymes that link sugar moieties to aglycones, which often derive from polyketides. Biological activity is frequently generated along with this process. Here we report the use of glycosyltransferase genes isolated from the landomycin biosynthetic gene cluster to create hybrid landomycin/urdamycin oligosaccharide antibiotics. RESULTS: Production of several novel urdamycin derivatives by a mutant of Streptomyces fradiae Tü2717 has been achieved in a combinatorial biosynthetic approach using glycosyltransferase genes from the landomycin producer Streptomyces cyanogenus S136. For the generation of gene cassettes useful for combinatorial biosynthesis experiments new vectors named pMUNI, pMUNII and pMUNIII were constructed. These vectors facilitate the construction of gene combinations taking advantage of the compatible MunI and EcoRI restriction sites. CONCLUSIONS: The high-yielding production of novel oligosaccharide antibiotics using glycosyltransferase gene cassettes generated in a very convenient way proves that glycosyltransferases can be flexible towards the alcohol substrate. In addition, our results indicate that LanGT1 from S. cyanogenus S136 is a D-olivosyltransferase, whereas LanGT4 is a L-rhodinosyltransferase. 相似文献
992.
Carsten D. Siebert 《Chemie in Unserer Zeit》2004,38(5):320-324
The couples benzene‐thiophene, benzene‐pyridine, thiophene‐furane represent prominent examples of bioisosterism in drug research. These cycles are aromatic and similar of expansion and electronical properties (isostere). The concept of bioisosterism includes also the replacement of substituents and atoms in pharmacologically active compounds. Selected drugs are shown to introduce into this important principle of rational drug design. 相似文献
993.
Narumol Vachirapatama Miroslav Macka Brett Paull Carsten Mü nker Paul R. Haddad 《Journal of chromatography. A》1999,850(1-2):257-268
A method for the simultaneous separation and determination of Nb(V) and Ta(V) as ternary complexes formed with 4-(2-pyridylazo)resorcinol (PAR) and citrate was developed using ion-interaction reversed-phase high-performance liquid chromatography on a C18 column. Method parameters, such as pre-column complex formation conditions and composition of the complexes were investigated using spectrophotometry and HPLC. Under the optimum conditions, the Nb(V) and Ta(V) complexes were eluted within 12 min with a mobile phase of methanol–water (32:68, v/v) containing 5 mM acetate, 5 mM TBABr and 5 mM citrate buffer at pH 6.5, with detection at 540 nm. A typical separation efficiency was 33 000 and 20 000 theoretical plates per metre for Nb(V) and Ta(V), respectively. The relative standard deviation of retention times for the Nb(V) and Ta(V) complexes were 0.16% and 0.17% and for peak areas were 0.28% and 1.36%, respectively. The detection limits (signal-to-noise ratio=3) for Nb(V) and Ta(V) were 0.4 ppb and 1.4 ppb, respectively. Results obtained for standard reference rock samples agreed well with certified values and results obtained by inductively coupled plasma MS. 相似文献
994.
Werner-Michael Kulicke Ulf Reinhardt Gerald G. Fuller Oliver Arendt 《Rheologica Acta》1999,38(1):26-33
Sodium carboxymethylcellulose (NaCMC) in solution represents a complex rheological system, since it forms aggregates and
associations and hence higher-level structures and, depending on the synthesis, is only found in a molecularly dispersed form
in exceptional cases. Rheo-mechanical investigations of the viscoelasticity showed that the Cox-Merz rule is not fulfilled.
The aim was therefore to examine whether rheo-optics could be employed to provide more detailed conclusions about the parameters that influence the flow behavior of NaCMC than
has hitherto been available with mechanical methods. The flow birefringence, Δn
′, rises as the degree of polymerization increases, and exhibits the same dependence on molar mass as does the viscosity: Δn
′∝M
w
3.4. As the degree of polymerization increases while the shear rate remains constant, the polymer segments become more distinctly
aligned in the direction of shear. Hence increasing the degree of polymerization also affects the solution structure, i.e.
the interaction of the molecules with one another. The stress-optical rule only applies to a limited extent for this system.
The stress-optical coefficient, C, is almost independent of the shear rate, but is strongly influenced by the concentration and attains a limiting value of
3 × 10−8 Pa−1. C was determined for a polymer in dilute solution and the curve obtained also enabled transitions in the solution structure to be recognized.
Received: 1 May 1998 Accepted: 5 October 1998 相似文献
995.
996.
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998.
Carsten von Hnisch 《无机化学与普通化学杂志》2001,627(1):68-72
New GaE and InE Four Membered Ring Compounds: Syntheses and Crystal Structures of [Et2InE(SiMe3)2]2 and [GaCl(P t Bu2Me)E(SiMe3)]2 (E = P, As) Et3In · PR3 (R = Et, iPr) reacts with H2ESiMe3 under liberation of C2H6 and EH3 to form the cyclic compounds [Et2InE(SiMe3)2]2 ( 1 a : E = P, 1 b : E = As). 1 consists of a planar four membered In2E2 ring in which the indium and phosphorus or arsenic atoms are four coordinated. In contrast, the phosphorus/arsenic atoms in [GaCl(PtBu2Me)E(SiMe3)]2 ( 2 a : E = P, 2 b : E = As) only have the coordination number three. 2 results from the reaction of GaCl3 · PtBu2Me with As(SiMe3)3 or Li2PSiMe3 respectively, and displays a folded four membered Ga2E2 ring as central structural motif. 1 and 2 have been characterised by single crystal X‐ray diffraction analysis as well as 1H and 31P{1H} NMR spectroscopy. 相似文献
999.
1000.
We show that an adaptive conforming finite element method for the solution of a variational inequality of the second kind, as model of one implicit time step of the primal problem of plasticity with positive hardening, yields the energy reduction property and the R -linear convergence of the stresses. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献