scholarly journals Light-Atom Structures: Absolute Configuration Determination and Beyond

2014 ◽  
Vol 70 (a1) ◽  
pp. C965-C965
Author(s):  
Jürgen Graf ◽  
Michael Ruf ◽  
Holger Ott ◽  
Bruce Noll ◽  
Séverine Freisz ◽  
...  
Keyword(s):  
Absolute Configuration ◽  
Quality Data ◽  
Liquid Gallium ◽  
Light Atom ◽  
Reliable Determination ◽  
X Ray ◽  
Anomalous Signal ◽  
The Absolute ◽  
Absolute Structure

The determination of the absolute configuration for light-atom structures is central to research in pharmaceuticals and natural-product synthesis [1]. In the absence of elements heavier than silicon, it is often problematic to make a significant assignment of absolute configuration. Traditionally, heavy-atom derivatives were prepared which have a stronger anomalous signal compared to the native compound. However, this is not always feasible. The assignment of the absolute structure of pure organic compounds has become somewhat easier with the advent of high-intensity microfocus sources [2], as the increased flux density improves the anomalous signal through improvements in counting statistics. In order to maximize the anomalous signal, X-ray sources with Cu anodes are usually used for the absolute structure determination. However, these data are usually limited to a maximum resolution of about 0.80 Å. High-brilliance microfocus X-ray sources with Mo targets enable the collection of high quality data beyond 0.40 Å within a reasonable amount of time. This allows not only a more accurate modelling of the electron density by using aspherical scattering factors, but also enables a reliable determination of the absolute structure, despite the significantly lower anomalous signal obtained with Mo Kα radiation. With the recently introduced liquid-Gallium-jet X-ray source unprecedented beam intensities can be achieved [3]. The shorter wavelength of Ga Kα compared to Cu Kα slightly weakens the anomalous signal of a typical light-atom structure. However, due to the shorter wavelength, the highest resolution for the liquid metal-jet source is typically at about 0.70 Å, compared to about 0.80 Å for Cu Kα. Hence, about 50% more unique reflections can be recorded. This clearly improves the structural model and the quality of the Flack parameter. Selected results on the absolute structure and charge density determinations for light-atom structures will be presented.

scholarly journals Preparative-scale HPLC Resolution of Metallacyclic η3-Allyltricarbonyliron Complexes and Determination of the Absolute Configuration by X-Ray Crystal Structure Analysis

1999 ◽  
Vol 23 (9) ◽  
pp. 578-579
Author(s):  
Rainer Schobert ◽  
Hermann Pfab ◽  
Jutta Böhmer ◽  
Frank Hampel ◽  
Andreas Werner
Keyword(s):  
Crystal Structure ◽  
Silica Gel ◽  
Structure Analysis ◽  
Absolute Configuration ◽  
Crystal Structure Analysis ◽  
Preparative Scale ◽  
X Ray ◽  
The Absolute

Racemates of (η3-allyl)tricarbonyliron lactone complex Fe(CO)3{η1:η3-C(O)XCH2CHCMeCH2} 1a (X = O) and (η3-allyl)tricarbonyliron lactam complex 2a (X = NMe) are resolved on a preparative scale by HPLC on cellulose tris(3,5-dimethylphenyl)carbamate/silica gel RP-8 and the absolute configuration of (-)-2a is determined by X-ray crystal structure analysis.

Étude conformationnelle de cétopipérazines: (I) 3R-méthyl-6-carbéthoxy-2 oxopipérazine, (II) 3R-[p-hydroxybenzyl]-6-carbéthoxy-2 oxopipérazine: I, II en solution et structure cristalline de II

1987 ◽  
Vol 65 (6) ◽  
pp. 1308-1312 ◽  
Author(s):  
André Michel ◽  
Guy Evrard ◽  
B. Norberg
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Absolute Configuration ◽  
Structure Determination ◽  
Opiate Receptor ◽  
Receptor Level ◽  
X Ray ◽  
Diastereomeric Mixture ◽  
The Absolute

The synthesis of the title compounds has been described recently. It was anticipated that the product would be a diastereomeric mixture. Surprisingly, only one isomer was obtained. The present work is an attempt to find the conformationnal properties accounting for those observations. X-ray structure determination of 3R-[p-hydroxybenzyl]-6-carbethoxy-2-oxopiperazine shows that the molecule adopts a folded conformation and that the absolute configuration at C6 is [R]. Investigation in solution using 1H nuclear magnetic resonance shows the existence of three conformers and discusses the relative populations. Those findings are also relevant in terms of the activity of such compounds at the opiate receptor level.

The use of Mo Kα radiation in the assignment of the absolute configuration of light-atom molecules; the importance of high-resolution data

2014 ◽  
Vol 70 (4) ◽  
pp. 660-668 ◽  
Author(s):  
Eduardo C. Escudero-Adán ◽  
Jordi Benet-Buchholz ◽  
Pablo Ballester
Keyword(s):  
High Resolution ◽  
Crystal Structures ◽  
Structure Determination ◽  
Great Majority ◽  
Data Sets ◽  
Light Atom ◽  
High Resolution Data ◽  
The Absolute ◽  
Absolute Structure

Recent studies have confirmed the usefulness of the Hooft and Parsons methodologies for determination of the absolute crystal structures of enantiopure light-atom compounds using CuKα radiation. While many single-crystal diffractometers used for small-molecule structure determination are equipped with molybdenum anodes, use of data from such instruments for the absolute structure determination of light-atom crystal structures is rarely documented and has often been found to be unsuccessful. The Hooft and Parsons methodologies have been applied to 44 data sets obtained from single crystals containing light-atom molecules of known chirality using Mo Kαradiation. Several factors influencing the calculation of accurate and precise values for the Hooft and Parsons parameters obtained from these data sets have been identified, the inclusion of high-resolution diffraction data being particularly important. The correct absolute structure was obtained in all cases, with the standard uncertainties of the final absolute structure parameters below 0.1 for the great majority.

scholarly journals Cannabidiol revisited

IUCrData ◽  
2017 ◽  
Vol 2 (2) ◽  
Author(s):  
Tobias Mayr ◽  
Tobias Grassl ◽  
Nikolaus Korber ◽  
Volker Christoffel ◽  
Michael Bodensteiner
Keyword(s):  
Absolute Configuration ◽  
Structure Determination ◽  
High Quality ◽  
Acta Cryst ◽  
X Ray ◽  
Radiation Sources ◽  
Wavelength Radiation ◽  
The Absolute ◽  
Absolute Structure ◽  
Intensity Radiation

The crystal structure of cannabidiol, C21H30O2, {systematic name: 2-[(1R,6R)-3-methyl-6-(prop-1-en-2-yl)cyclohex-2-enyl]-5-pentylbenzene-1,3-diol}, was determined earlier by Joneset al.[(1977).Acta Cryst.B33, 3211–3214] and Ottersen & Rosenqvist [(1977).Acta Chem. Scand.B31, 749–755]. In both investigations, the absolute configuration is given asR,R, referring to Mechoulamet al.[(1967.J. Am. Chem. Soc.89, 4552–4554]. In the latter, the absolute configuration was identified by chemical means. Using the advantages of modern single-crystal X-ray diffractometers such as area detectors and high-intensity radiation sources, a high-quality structure determination including the absolute configuration was possible and is shown in this work. Furthermore, the rather uncommon CuKβ wavelength radiation was applied for the structure determination, which confirmed the absolute structure to beR,R.

Conclusive Determination of the Absolute Configuration of Chiral C60-Fullerenecis-3 Bisadducts by X-ray Crystallography and Circular Dichroism

2005 ◽  
Vol 117 (15) ◽  
pp. 2302-2305 ◽  
Author(s):  
Shunsuke Kuwahara ◽  
Kazuhiro Obata ◽  
Kazuhiro Yoshida ◽  
Takatoshi Matsumoto ◽  
Nobuyuki Harada ◽  
...  
Keyword(s):  
Circular Dichroism ◽  
Absolute Configuration ◽  
X Ray ◽  
X Ray Crystallography ◽  
The Absolute ◽  
Circular Dichroïsm

Relative and Absolute Structure Assignments of Alkenes Using Crystalline Osmate Derivatives for X-Ray Analysis

2019 ◽  
Author(s):  
Alexander S. Burns ◽  
Charles dooley ◽  
Paul R. Carlson ◽  
Joseph W. Ziller ◽  
Scott Rychnovsky
Keyword(s):  
Absolute Configuration ◽  
Osmium Tetroxide ◽  
Heavy Atom ◽  
Crystallographic Analysis ◽  
Enol Ethers ◽  
X Ray ◽  
Silyl Enol Ethers ◽  
Absolute Structure ◽  
Structure Of Liquid

<div><div><p>Osmium tetroxide and TMEDA form stable crystalline adducts with alkenes. The structure of liquid alkenes can be determined through X-ray analysis of these derivatives. Osmium, a heavy atom, facilitates the crystallographic analysis and the determination of the absolute configuration using common Mo X-ray sources. The utility of this method for assigning structures and absolute configurations was demonstrated on a number of unsaturated substrates that include simple alkenes, enones, enol ethers, and silyl enol ethers.</p></div></div>

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