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991.
992.
993.
Handschuh S Goldfuss B Chen J Gasteiger J Houk KN 《Journal of computer-aided molecular design》2000,14(7):611-629
Binding mode calculations for complexes between an artificial paracyclophane receptor and digoxins, cholic acids as well as cortisone steroids show encapsulation of different ring combinations. Docking experiments were performed between the 26-10 antibody and digoxins. Coordination affinity arises from hydrophobic desolvation and van der Waals interactions rather than from hydrogen bonds. The specificity and affinity arises mainly from shape complementarity. Computed binding free energies and Kohonen neural network computations both point to physicochemical and structural similarities of natural antibodies and artificial receptors. 相似文献
994.
Johann Schinnerl Elisabeth Kaltenegger Thomas Pacher Srunya Vajrodaya Otmar Hofer Harald Greger 《Monatshefte für Chemie / Chemical Monthly》2005,136(9):1671-1680
Summary. Three new pyrroloazepine type alkaloids, stichoneurines A and B and 6-hydroxycroomine were isolated from the lipophilic root extracts of Stichoneuron caudatum and Stemona tuberosa collected in Thailand together with the already known croomine, tuberostemonine, and tuberostemonine A. The structures were elucidated by spectroscopic methods including H/H-COSY, HMQC, and HMBC. Information on the relative stereochemistries and conformational behaviour was obtained by analysis of the NOESY spectra. The formation of pyrroloazepine alkaloids in the genus Stichoneuron is reported for the first time and supports its affiliation to the family Stemonaceae. The occurrence of two different types of alkaloids, of the tuberostemonine and croomine series, in different geographical provenances of Stemona tuberosa is of special chemosystematic interest and may contribute to a more natural species delimitation within that complex group. 相似文献
995.
Dimethylformamide dimethylacetal () and 3-hydroxycarboxylic acids () react with formation of esters () and olefins (). Evidence is provided that is generated via an E1/E2-type fragmentation of a zwitterionic intermediate . (Scheme 1). 相似文献
996.
In course of chromium(II) mediated additions of relatively complex allylic bromides to aldehydes (Hiyama-Nozaki allylation) radical intermediates have been observed. From these findings a new mechanism of the allylation is derived. 相似文献
997.
Caemelbecke EV Will S Autret M Adamian VA Lex J Gisselbrecht JP Gross M Vogel E Kadish KM 《Inorganic chemistry》1996,35(1):184-192
The electrochemistry and spectroscopic properties of three iron corroles were examined in benzonitrile, dichloromethane, and pyridine containing 0.1 M tetra-n-butylammonium perchlorate or tetra-n-ethylammonium hexafluorophosphate as supporting electrolyte. The investigated compounds are represented as (OEC)Fe(IV)(C(6)H(5)), (OEC)Fe(IV)Cl, and (OEC)Fe(III)(py), where OEC is the trianion of 2,3,7,8,12,13,17,18-octaethylcorrole. Each iron(IV) corrole undergoes two one-electron reductions and two or three one-electron oxidations depending upon the solvent. Under the same solution conditions, the iron(III) corrole undergoes a single one-electron reduction and one or two one-electron oxidations. Each singly oxidized and singly reduced product was characterized by UV-vis and/or EPR spectroscopy. The data indicate a conversion of (OEC)Fe(IV)(C(6)H(5)) and (OEC)Fe(IV)Cl to their iron(III) forms upon a one-electron reduction and to iron(IV) corrole pi cation radicals upon a one-electron oxidation. The metal center in [(OEC)Fe(III)(C(6)H(5))](-) is low spin (S = (1)/(2)) as compared to electrogenerated [(OEC)Fe(III)Cl](-), which contains an intermediate-spin (S = (3)/(2)) iron(III). (OEC)Fe(III)(py) also contains an intermediate-spin-state iron(III) and, unlike previously characterized (OEC)Fe(III)(NO), is converted to an iron(IV) corrole upon oxidation rather than to an iron(III) pi cation radical. Singly oxidized [(OEC)Fe(IV)(C(6)H(5))](*)(+) is the first iron(IV) tetrapyrrole pi cation radical to be isolated and was structurally characterized as a perchlorate salt. It crystallizes in the triclinic space group P&onemacr; with a = 10.783(3) ?, b = 13.826(3) ?, c = 14.151(3) ?, alpha = 78.95(2) degrees, beta = 89.59(2) degrees, and gamma = 72.98(2) degrees at 293 K with Z = 2. Refinement of 8400 reflections and 670 parameters against F(o)(2) yields R1 = 0.0864 and wR2 = 0.2293. The complex contains a five-coordinated iron with average Fe-N bond lengths of 1.871(3) ?. The formulation of the electron distribution in this compound was confirmed by M?ssbauer, X-ray crystallographic, and magnetic susceptibility data as well as by EPR spectroscopy, which gives evidence for strong antiferromagnetic coupling between the iron(IV) center and the singly oxidized corrole macrocycle. 相似文献
998.
Johann G. Leipoldt Stephen S. Basson Andreas Roodt Walter Purcell 《Transition Metal Chemistry》1987,12(3):209-212
Summary The preparation and characterization of salts of the [ReO2(CN)4]3–, [ReO(OH)(CN)4]2–, [ReO(H2O)(CN)4]–, [Re2O3(CN)8]4– and [ReO(NCS)(CN)4]2– species are described. The nature of the protonation reactions of [ReO2(CN)4]3– was established by the successful isolation of these salts. 相似文献
999.
Summary The key step in the preparation of 6-deoxy-1,2-O-isopropylidene--L-talofuranose (7) and 6-deoxy-1,2-O-isopropylidene--L-idofuranose (13) is the selective exchange of the 6-O-mesyl rest of 3-O-acetyl-5,6-O-dimesyl-1,2-O-isopropylidene--D-allofuranose (4) and 3-O-acetyl-5,6-O-dimesyl-1,2-O-isopropylidene--D-glucofuranose (10) by acetate group (potassium acetate/18-crown-6).
Ein neuartiger und präparativ nützlicher Zugang zu 6-Desoxy-1,2-O-isopropyliden--L-talofuranose und 6-Desoxy-1,2-O-isopropyliden--L-idofuranose
Zusammenfassung Schlüsselschritt bei der Herstellung von 6-Desoxy-1,2-O-isopropyliden--L-talofuranose (7) und 6-Desoxy-1,2-O-isopropyliden--L-idofuranose (13) ist der selektive Austausch der primären Mesyl-Gruppe in 3-O-Acetyl-5,6-O-dimesyl-1,2-O-isopropyliden--D-allofuranose (4) und 3-O-Acetyl-5,6-O-dimesyl-1,2-O-isopropyliden--D-glucofuranose (10) durch den Acetat-Rest in Gegenwart von Kaliumacetat/Kronen-Ether.相似文献
1000.
Gerd Bader Tuja Danzandarjaa Karl Hiller Gottfried Reznicek Johann Jurenitsch Monika Golly Harald Schrder Manfred Schubert-Zsilavecz Ernst Haslinger 《Helvetica chimica acta》1994,77(7):1861-1868
A new saponin, O-α-D -arabinopyranosyl-(1→6)-O-[α-L -rhamnopyranosyl-(1→2)]-O-[β-D -xylopyranosyl-(1→3)]-β-D -glucopyranosyl arjunolate ( 1 ) was isolated from the flowers of Heteropappus biennis (LDB .) TAMAMSCH . The structure was established mainly by a combination of 1D selective and 2D NMR techniques like COSY, TOCSY, ROESY, HMQC, and HMBC. Molecular-modelling calculations showed that the oligosaccharide chain is rather rigid. Six minimum structures are discussed. 相似文献