|
| ||
|
|
||
Absolute Configuration (absolute + configuration)
Selected AbstractsBoron-Based Diastereomerism and Enantiomerism in Imine Complexes , Determination of the Absolute Configuration at Boron by CD SpectroscopyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 31 2008Manfred Braun Abstract Boron turns out to be a stable stereogenic center in imine complexes of aryl and alkyl boronates. Diastereomerically pure complexes 7a,c are obtained from chiral imine ligands 5a,b that are derived from the amino alcohol (R)- 4. The configuration at the boron atom is determined by crystal structure analyses. Racemic boronates 10a,c, available from a condensation of aryl boronic acids 6 with the achiral imine ligand 9, can be separated into stable enantiomers by HPLC on a chiral column. The racemization barrier ,G, has been determined to amount to 105,115 kJ,mol,1. The comparison of calculated and measured CD spectra permits to assign unambiguously the absolute configuration to boron in the enantiomeric boronate-imine complex 10a.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Tetra- tert -butyltrioxabicyclo[3.3.1]nonadienedicarboxylic Acid: Optical Resolution, Absolute Configuration and Application in Chiral DiscriminationEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2008Jennifer Kremsner Abstract The enantiopure bridged bis-dioxine 4, a dissymmetric dicarboxylic acid exhibiting axial chirality, can easily be synthesized and serve as host for separating and/or transporting chiral guest molecules. Racemic 4 gives with (R)- and (S)-1-phenylethylamine the corresponding pure diastereomeric salts 7 and 8. The absolut configuration of the diacid 4 in the diastereomeric salt 7 containing (R)-1-phenylethylamine was confirmed to be R by X-ray crystal structure analysis, which also confirmed its concave nature. Release of the acid-sensitive pure enantiomers (R)- 4 as well as (S)- 4 was achieved conveniently by use of dry flash-chromatography on silica. The CD spectrum shows a positive Cotton effect of the (S)-enantiomer at 206 nm. The enantiomeric purity was proved by 1H NMR discrimination of the diastereomeric salts with (R,R)-1,2-bis(4-methoxyphenyl)ethane-1,2-diamine as the base. The dicarboxylic acid (R)- 4 can be used as chiral auxiliary as demonstrated by the difficult resolution of racemicN,N,-di- tert -butyl-1,2-bis(4-methoxyphenyl)ethane-1,2-diamine 9.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Synthesis and Absolute Configuration of (+)-Pseudodeflectusin: Structural Revision of Aspergione BEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2006Fumiyo Saito Abstract We report herein the total synthesis and determination of the absolute configuration of (+)-pseudodeflectusin. The total synthesis of (+)-pseudodeflectusin starting from o -anisic aid was achieved in 11 total steps with an overall yield of 2.0,%. The 1H- and 13C NMR spectroscopic data of our synthetic pseudodeflectusin was identical to that of the natural compound. The absolute configuration of (+)-pseudodeflectusin was determined by chiral HPLC and X-ray crystallographic analyses. We also synthesized the proposed structure of aspergione B, whose 1H- and 13C NMR spectroscopic data is identical to that of pseudodeflectusin. The 1H- and 13C NMR spectra of our synthetic aspergione B were different from those of the natural compound reported by Proksch et al. Our results confirm that aspergione B and pseudodeflectusin are, in fact, the same compound.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] First Asymmetric Synthesis and Determination of the Absolute Configuration of a Lignan Isolated from Virola sebiferaEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2005Dieter Enders Abstract The first asymmetric synthesis of a lignan isolated from the seeds of Virola sebifera, one of the most widely spread Myristicaceae species in Brazil, in four steps (48,% overall yield) and with excellent stereoselectivity (de, ee , 96,%) is described. The key step is the asymmetric Michael addition of a lithiated enantiopure ,-amino nitrile to an enone, followed by ,-methylation and cleavage of the amino nitrile. The absolute configuration of the naturally occurring 1,4-diketone was determined by polarimetry as well as by CD spectroscopy and quantum chemical calculations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] ,N-Stereogenic Quaternary Ammonium Salts' from L -Amino Acids: Synthesis, Separation, and Absolute ConfigurationHELVETICA CHIMICA ACTA, Issue 4 2009Hua-Fang Wu Abstract Diastereoisomeric linear and cyclic ,N-chiral quaternary ammonium salts' (QASs) were efficiently synthesized from corresponding L -amino acids in high yields. The diastereoisomers of each pair of ,N-chiral QASs' were successfully separated. The absolute configurations of these QASs were determined predominately by X-ray single-crystal analysis. The 1H-NMR data of ,N-chiral QASs' provided characteristic information on the configuration of the N-chiral center. ,N-Chiral QASs' exemplified by [N(R)]- 2a and [N(S)]- 2a are stable in protic and aprotic solvents within a broad pH and temperature range. [source] Total Synthesis of Auripyrones,A and B and Determination of the Absolute Configuration of Auripyrone,B,ANGEWANDTE CHEMIE, Issue 13 2010Ichiro Hayakawa Dr. Mit Aldol zum Erfolg: Eine diastereoselektive Aldolreaktion mit 2,6-Diethyl-3,5-dimethyl-4-pyron war der Schlüsselschritt in der Totalsynthese der Auripyrone,A und B. Die stereochemischen Verhältnisse und die absolute Konfiguration von Auripyron,B wurden ebenfalls bestimmt. [source] Total Synthesis and Absolute Configuration of Macrocidin,A, a Cyclophane Tetramic Acid Natural Product,ANGEWANDTE CHEMIE, Issue 5 2010Tomohiro Yoshinari Der stereokontrollierte Zugang zum Cyclophangerüst von Macrocidin,A ist zum ersten Mal gelungen. Die Schlüsselschritte sind: die iridiumkatalysierte asymmetrische Hydrierung ohne Spaltung der C-I-Bindung, die Makrolactambildung durch intramolekulares Abfangen eines Ketens und die Lacey-Dieckmann-Cyclisierung zum Aufbau des Tetramsäurerings. [source] Stereoselective Synthesis of (+)-Paeonilide (I) and Confirmation of Its Absolute Configuration.CHEMINFORM, Issue 37 2006Chenying Wang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Complete Stereochemistry of Neamphamide A (I) and Absolute Configuration of the ,-Methoxytyrosine Residue in Papuamide B.CHEMINFORM, Issue 1 2006Naoya Oku No abstract is available for this article. [source] Absolute Configuration of Side Chains of Polyhydroxylated Steroidal Compounds from the Starfish Henricia derjugini.CHEMINFORM, Issue 36 2005N. V. Ivanchina No abstract is available for this article. [source] Total Synthesis of (+)-(S)-Angustureine and the Determination of the Absolute Configuration of the Natural Product Angustureine.CHEMINFORM, Issue 30 2005Chumpol Theeraladanon Abstract For Abstract see ChemInform Abstract in Full Text. [source] One-Pot Synthesis of Helical Aromatics: Stereoselectivity, Stability Against Racemization, and Assignment of Absolute Configuration Assisted by Experimental and Theoretical Circular Dichroism.CHEMINFORM, Issue 12 2005Masashi Watanabe Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis, Structure, and Absolute Configuration of a New Cyclopropanic Compound Derived from the Sesquiterpene ,-Himachalene.CHEMINFORM, Issue 8 2005Hossni Ziyat Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis of Marine Sponge Alkaloid Hachijodine B (Ia) and a Comment on the Structure of Ikimine B (Ib) and on the Absolute Configuration of Niphatesine D (Ic).CHEMINFORM, Issue 31 2004Stuart P. Romeril No abstract is available for this article. [source] Lipase-Catalyzed Remote Kinetic Resolution of Quaternary Carbon-Containing Alcohols and Determination of Their Absolute Configuration.CHEMINFORM, Issue 9 2004Dai Sig Im Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis and Absolute Configuration of Cordiaquinone K, Antifungal and Larvicidal Meroterpenoid Isolated from the Panamanian Plant, Cordia curassavica.CHEMINFORM, Issue 50 2003Arata Yajima No abstract is available for this article. [source] Optically Active Telluronium Imides: Optical Resolution, Absolute Configuration, and Mechanism of Racemization.CHEMINFORM, Issue 49 2003Toshio Shimizu No abstract is available for this article. [source] Total Synthesis and Absolute Configuration of the Novel Microtubule-Stabilizing Agent Peloruside A.CHEMINFORM, Issue 32 2003Xibin Liao Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis and Absolute Configuration of (-)-Chettaphanin I and (-)-Chettaphanin II.CHEMINFORM, Issue 22 2003I. S. Marcos No abstract is available for this article. [source] Determination of Absolute Configuration of Decipinone, a Diterpenoid Ester with a Myrsinane-Type Carbon Skeleton, by NMR Spectroscopy.CHEMINFORM, Issue 44 2002Amir Reza Jassbi No abstract is available for this article. [source] ChemInform Abstract: Absolute Configuration of D2 -Symmetric Fullerene C84.CHEMINFORM, Issue 33 2002Filipp Furche Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Wedekind,Fock,Havinga Salt Me(Et)N+(All)PhI - ×CHCl3 as Historically the First Object for Absolute Asymmetric Synthesis: Spontaneous Resolution, Structure and Absolute Configuration.CHEMINFORM, Issue 28 2001Remir G. Kostyanovsky Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Asymmetric Synthesis and Determination of the Absolute Configuration of FK584, an Agent for the Treatment of Overactive Detrusor.CHEMINFORM, Issue 20 2001Kazuhiko Take Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Synthesis of Enantiopure Sulfonimidamides and Elucidation of Their Absolute Configuration by Comparison of Measured and Calculated CD Spectra and X-Ray Crystal Structure DeterminationCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2010Christin Worch Abstract Straightforward syntheses of enantiopure N -benzoyl- and N - tert -butyloxycarbonyl-protected sulfonimidamides, which can be used as building blocks in newly designed catalysts, are presented. Key synthetic step is a dynamic resolution of a racemic sulfinic acid sodium salt. All subsequent transformations proceed stereospecifically. The absolute configurations at the sulfur atoms of both sulfonimidamides were determined by comparison of measured and calculated CD spectra. An X-ray crystal structure determination of a sulfonimidoylguanidine derivative confirmed this result. [source] Determination of the Absolute Configurations of Natural Products via Density Functional Theory Calculations of Vibrational Circular Dichroism, Electronic Circular Dichroism, and Optical Rotation: The Iridoids Plumericin and Isoplumericin.CHEMINFORM, Issue 37 2007P. J. Stephens Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] New Macrocycles with Planar Chirality,Synthesis and Determination of Absolute ConfigurationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2006Jaros, aw Kalisiak Dr. Abstract A versatile system for preparing macrocyclic compounds with planar chirality is presented. In this system chiral diazacoronands are synthesized readily from lariat-type diesters 13 and 14 and unsymmetrical diamines 7, 8, 12, 15, and 16 under non-high-dilution conditions. The title compounds were subjected to structural analysis by X-ray crystallography and circular dichroism spectroscopy, and absolute configurations for two representative examples (compounds 2 and 3) were assigned by molecular modeling. The correctness of the theoretical approach was verified by the crystallographic results obtained experimentally. [source] Absolute configuration of eremophilane sesquiterpenes from Petasites hybridus: Comparison of experimental and calculated circular dichroism spectraCHIRALITY, Issue 3 2010Antje Bodensieck Abstract In-depth conformational analyses of 10 known eremophilane (= (1S,4aR,7R,8aR)-decahydro-1,8a-dimethyl-7-(1-methylethyl)napththalene) sesquiterpenes, 1,10, from Petasites hybridus were performed with molecular mechanics as well as density functional theory methods. Electronic transition energies and rotational strengths of these eight eremophilane lactones and two petasins were calculated by time-dependent density functional theory (B3PW91/TZVP). The absolute configurations of the constituents could be assigned by comparison of their simulated and experimental circular dichroism (CD) spectra in methanol as (4S,5R,8S,10R) (1, 2), (2R,4S,5R,8S,10R) (3, 4, 5), (2R,4S,5R,8R,9R,10R) (6), (2R,4S,5R,8R,10R) (7, 8), and (3R,4R,5R) (9, 10). Single-crystal X-ray diffraction data of 8,-hydroxyeremophilanolide ((8S)-8-hydroxyeremophil-7(11)-en-12,8-olide) (1) served as starting point for the theoretical conformational calculations of the 8,-epimers of the eremophilane lactones. Experimental CD spectra as well as 1H NMR spectra of compound 1 in methanol were considerably dependent on sample concentration. Chirality, 2010. © 2009 Wiley-Liss, Inc. [source] Absolute configuration of the thyroid hormone analog KAT-2003 as determined by the 1H NMR anisotropy method with a novel chiral auxiliary, M,NP acidCHIRALITY, Issue 1 2004Toshihiro Nishimura Abstract The absolute configuration of the chiral thyroid hormone analog KAT-2003 (+)- 2, showing hypocholesterolemic activities, decreases of hepatic triglyceride contents with lowering cardiac side effects, and significant inhibitory effect for the second primary hepatocellular carcinoma, was determined as S by the 1H NMR anisotropy method using a novel chiral auxiliary, 2-methoxy-2-(1-naphtyl)propionic acid (M,NP acid). Chirality 16:13,21, 2004. © 2003 Wiley-Liss, Inc. [source] Absolute configuration and conformational analysis of a degradation product of inhalation anesthetic Sevoflurane: A vibrational circular dichroism studyCHIRALITY, Issue 8 2002Feng Wang Abstract 1,1,1,3,3-pentafluoro-2-(fluoromethoxy)-3-methoxypropane, compound B, is a product obtained in the degradation of the anesthetic Sevoflurane. Enantiopure (+)- B was investigated using vibrational circular dichroism (VCD). Experimental absorption and VCD spectra of (+)- B in CDCl3 solution in the 2,000,900 cm,1 region are compared with the ab initio predictions of absorption and VCD spectra obtained from density functional theory using B3LYP/6-31G* basis set for different conformers of (S)-1,1,1,3,3-pentafluoro-2-(fluoromethoxy)-3-methoxypropane. This comparison indicates that (+)- B is of the (S)-configuration in CDCl3 solution, in agreement with previous literature results. Our results also indicate that this compound adopts six predominant conformations in CDCl3 solution. Chirality 14:618,624, 2002. © 2002 Wiley-Liss, Inc. [source] Enzyme-Catalysed Synthesis and Absolute Configuration Assignments of cis -Dihydrodiol Metabolites from 1,4-Disubstituted BenzenesCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2007Derek Abstract A series of ten cis -dihydrodiol metabolites has been obtained by bacterial biotransformation of the corresponding 1,4-disubstituted benzene substrates using Pseudomonas putida UV4, a source of toluene dioxygenase (TDO). Their enantiomeric excess (ee) values have been established using chiral stationary phase HPLC and 1H,NMR spectroscopy. Absolute configurations of the majority of cis -dihydrodiols have been established using stereochemical correlation and X-ray crystallography and the remainder have been tentatively assigned using NMR spectroscopic methods but finally confirmed by circular dichroism (CD) spectroscopy. These configurational assignments support and extend the validity of an empirical model, previously used to predict the preferred stereochemistry of TDO-catalysed cis -dihydroxylation of ten 1,4-disubstituted benzene substrates, to more than twenty-five examples. [source] | |||||||||||||||||||||||||||||||