scholarly journals Difficulties to Determine the Absolute Configuration of Guaiaretic Acid

2018 ◽  
Vol 13 (8) ◽  
pp. 1934578X1801300
Author(s):  
Alfredo R. Ortega ◽  
Eleuterio Burgueño-Tapia ◽  
Pedro Joseph-Nathan
Keyword(s):  
Symmetric Space ◽  
Single Crystal ◽  
Absolute Configuration ◽  
Structure Elucidation ◽  
Carbon Chain ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
The Absolute ◽  
Stereogenic Center

An account of the difficulties to determine the absolute configuration (AC) of guaiaretic acid (1a), using contemporary methodology, is described in commemoration of the century of its structure elucidation. In fact, the herein studied molecule was the derived diacetate 1b, since the natural lignan slowly decomposes upon manipulation. Single crystal X-ray diffraction of 1b demonstrated the structure, but calculation of Flack and Hooft parameters to know the AC was unsuccessful since the crystals were triclinic, P-1, which is a centro-symmetric space group. In turn, manual band to band comparison of experimental and DFT B3LYP/DGDZVP calculated VCD spectra of 1b allowed ascertaining its AC, although automatic comparison using the Compare VOA software was not very successful. This behavior is associated to the fact that the studied molecule has a sole stereogenic center located on the acyclic portion of a carbon chain possessing two quite similar substituents. The behavior is discussed in relation to cases where the molecular flexibility also generates a very large number of conformers.

Euryachins A and B, a new type of diterpenoids from Eurya chinensis with potent NO production inhibitory activity

RSC Advances ◽  
2016 ◽  
Vol 6 (89) ◽  
pp. 85958-85961 ◽  
Author(s):  
Jia-Ling Song ◽  
Yao Yuan ◽  
Hai-Bo Tan ◽  
Jie-Wei Wu ◽  
Ri-Ming Huang ◽  
...  
Keyword(s):  
Single Crystal ◽  
Absolute Configuration ◽  
Inhibitory Activity ◽  
No Production ◽  
X Ray Diffraction ◽  
X Ray ◽  
New Type ◽  
The Absolute

Euryachins A (1) and B (2), new typediterpenoid euryamanes, were isolated from the branches of Eurya chinensis. The absolute configuration of 1 was determined by single-crystal X-ray diffraction. Both 1 and 2 exhibited significant NO production inhibitory activity.

Heterocladol, a halogenated selinane sesquiterpene of biosynthetic significance from the red alga Laurencia filiformis: Its isolation, crystal structure andabsolute configuration

1977 ◽  
Vol 30 (12) ◽  
pp. 2679 ◽  
Author(s):  
R Kazlauskas ◽  
PT Murphy ◽  
RJ Wells ◽  
JJ Daly ◽  
WE Oberhansli
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Absolute Configuration ◽  
Red Alga ◽  
Ring Closure ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Annular Ring

The structure and absolute configuration of heterocladol, C15H26BrClO (6), have been determined by single-crystal X-ray diffraction methods. This compound is the first example of a selinane skeleton reported from Laurencia species and its structure can be rationalized in terms of a trans-annular ring closure of a germacradiene. The colourless crystals are monoclinic, space group P21, with a 11.852, b 14.486, c 10.932 Ǻ, β 119.6�, Z4.

scholarly journals Memorial Issue Dedicated to Dr. Howard D. Flack: The Man behind the Flack Parameter

Chemistry ◽  
2021 ◽  
Vol 3 (3) ◽  
pp. 818-820
Author(s):  
Catherine E. Housecroft ◽  
Katharina M. Fromm
Keyword(s):  
Single Crystal ◽  
Absolute Configuration ◽  
Molecular Species ◽  
Crystalline Material ◽  
Special Issue ◽  
X Ray Diffraction ◽  
X Ray ◽  
Memorial Issue ◽  
The Absolute ◽  
Absolute Structure

This Special Issue of Chemistry is dedicated to Dr. Howard D. Flack (1943–2017), a renowned crystallographer who transformed the way in which, by using single crystal X-ray diffraction, we are able to determine the absolute structure of a crystalline material, and thereby determine the absolute configuration of molecular species within the material [...]

Vibrational circular dichroism and single crystal X-Ray diffraction analyses of [Ir(bzq)2(phen)]+ (bzq = benzo[h]quinoline; phen = 1,10-phenanthroline): absolute configuration and role of CH–π interaction in molecular packing

2017 ◽  
Vol 46 (13) ◽  
pp. 4397-4402 ◽  
Author(s):  
Kazuyoshi Takimoto ◽  
Yutaka Watanabe ◽  
Shigeki Mori ◽  
Hisako Sato
Keyword(s):  
Circular Dichroism ◽  
Single Crystal ◽  
Absolute Configuration ◽  
Molecular Packing ◽  
Vibrational Circular Dichroism ◽  
X Ray Diffraction ◽  
X Ray ◽  
The Absolute ◽  
Circular Dichroïsm

The absolute configuration of a cationic iridium(iii) complex was determined in solution and solid by vibrational circular dichroism and X-ray diffraction analyses.

Crystal structure of aristoserratine

1983 ◽  
Vol 36 (5) ◽  
pp. 1037 ◽  
Author(s):  
IRC Bick ◽  
MA Hai ◽  
VA Patrick ◽  
AH White
Keyword(s):  
Crystal Structure ◽  
Circular Dichroism ◽  
Single Crystal ◽  
Absolute Configuration ◽  
Circular Dichroism Spectrum ◽  
X Ray Diffraction ◽  
Relative Configuration ◽  
X Ray ◽  
The Absolute ◽  
Circular Dichroïsm

The crystal structure of the alkaloid aristoserratine,* C20H24N2O, has been determined by single-crystal X-ray diffraction methods at 295 K, the structure being refined to a residual of 0.034 for 1107 independent 'observed' reflections. Crystals are monoclinic, P21, a 14.836(5), b 8.568(3), c 6.633(3) �, β 98.05(3)�, Z 2. The relative configuration is established and, by inference, by comparison of the circular dichroism spectrum with that of aristoteline, the absolute configuration is assigned.

The Absolute Structure of Latifoline

1992 ◽  
Vol 45 (2) ◽  
pp. 451 ◽  
Author(s):  
CCJ Culvenor ◽  
MF Mackay
Keyword(s):  
Single Crystal ◽  
Absolute Configuration ◽  
Crystallographic Analysis ◽  
Salt Hydrate ◽  
Space Group ◽  
X Ray ◽  
Orthorhombic Crystals ◽  
The Absolute ◽  
Absolute Structure

The absolute structure of latifoline, a pyrrolizidine diester alkaloid of retronecine and latifolic and angelic acids, has been defined by single-crystal X-ray crystallographic analysis of the hydrobromide salt hydrate. Orthorhombic crystals of C20H27NO7.HBr.H2O belong to the space group P 2′2′2′ with a 7.279(1), b 17.898(3), c 17.922(2) � and V 2334-9(8) � 3 . The structure has been refined to an R index of 0.054 for 1725 observed terms. The absolute configuration has been assigned by comparison with that of retronecine and also determined independently by X-ray examination of selected Bijvoet pairs. Our results have shown that the absolute structure of latifolic acid is 13S,14R,19S (2R,3S,4S in latifolic acid numbering), and not the stereoisomer reported recently by Roitman and Wong.

scholarly journals Molecular Structure and Its Inverse: The Mystery of Their Origins, the Enigma of Their Detection

2021 ◽  
pp. 45-51
Author(s):  
Sosale Chandrasekhar
Keyword(s):  
Absolute Configuration ◽  
Anomalous Dispersion ◽  
X Rays ◽  
X Ray Diffraction ◽  
Dispersion Method ◽  
X Ray ◽  
X Ray Crystallography ◽  
The Absolute ◽  
Dispersion Technique ◽  
Stereogenic Center

The origins of the molecular-chiral homogeneity that is the very basis of life remain a tantalizing mystery. Molecular chirality itself is manifest in its interaction with radiation, particularly as optical activity, although an intriguing alternative technique based in X-ray crystallography is being increasingly employed. Thus, X-ray diffraction with anomalous dispersion is currently believed to lead to the absolute configuration of a stereogenic center, the ultimate goal of structural chemistry. However, despite its apparently unerring consistency, the fundamental basis of the anomalous dispersion technique is itself enigmatic. This is because it is unclear how the technique not only distinguishes two enantiomeric lattices but also assigns the absolute configuration: all, apparently, in the absence of an external chiral influence! Indeed, as argued previously, it is highly likely that the technique succeeds because the X-rays employed are circularly polarized, itself a possible consequence of parity violation. All the same, the question of how the absolute configuration is assigned remains, as the chiral sense of the putative circular polarization of the X-rays is unknown. It is argued herein that the anomalous dispersion method is essentially based in the chirality of X-rays that must have entered–although unbeknownst as such–into the calculations leading to the absolute configuration. In fact, the enigma surrounding the anomalous dispersion method derives from uncertainties concerning the theory of X-ray diffraction itself, thus leading to the apparently inescapable conclusion that both methods are essentially empirical — but without detracting from the brilliance of the scientific achievements that led to these methods.          

scholarly journals Indole type akuammiline from Vinca erecta: Crystal structure of 10-OAc-Akuammine

2019 ◽  
Vol 10 (4) ◽  
pp. 345-349 ◽  
Author(s):  
Shahobiddin Adizov ◽  
Bakhodir Tashkhodjaev
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Absolute Configuration ◽  
Indole Alkaloids ◽  
Acyl Derivative ◽  
Crystal Data ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
X Ray

Single crystal X-ray diffraction has established the absolute configuration of the indole alkaloids from Vinca erecta such as akuammiline-o-acyl derivative of akuammine with a 3D stable polycyclic framework. Crystal data for C24H28N2O5: orthorhombic, space group P212121 (no. 19), a = 7.349(3) Å, b = 16.099(5) Å, c = 17.323(5) Å, V = 2049.5(12) Å3, Z = 4, T = 293(2) K, μ(CuKα) = 0.789 mm-1, Dcalc = 1.376 g/cm3, 1742 reflections measured (7.496° ≤ 2Θ ≤ 119.792°), 1742 unique (Rsigma = 0.0374) which were used in all calculations. The final R1 was 0.0608 (I > 2σ(I)) and wR2 was 0.1680 (all data). The polycyclic framework of the well-known picrinine and akuammine is compared. The ether bridges located in different positions of the framework and forming five-membered cycles do not change the conformation of the polycyclic akuammiline framework. In V. erecta alkaloids, the exomethylene fragment (C18-C19=C20-C21) of the polycyclic backbone always takes on the E-condition.

Confirmation of the absolute configuration of Stachybotrin C using single-crystal X-ray diffraction analysis of its 4-bromobenzyl ether derivative

2018 ◽  
Vol 71 (6) ◽  
pp. 584-591 ◽  
Author(s):  
Yu Kuroda ◽  
Keiko Hasegawa ◽  
Keiichi Noguchi ◽  
Kazuhiro Chiba ◽  
Keiji Hasumi ◽  
...  
Keyword(s):  
Single Crystal ◽  
Diffraction Analysis ◽  
Absolute Configuration ◽  
X Ray Diffraction ◽  
X Ray ◽  
Ether Derivative ◽  
The Absolute

Crystal structure of an inclusion complex between chiral monoaza-15-crown-5 and S(–)-1-phenyl-ethyl ammonium percholorate

2003 ◽  
Vol 218 (5) ◽  
Author(s):  
Süheyla Özbey ◽  
F. B. Kaynak ◽  
M. Toğrul ◽  
N. Demirel ◽  
H. Hoşgören
Keyword(s):  
Crystal Structure ◽  
Inclusion Complex ◽  
Single Crystal ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
New Type

AbstractA new type of inclusion complex, S(–)-1 phenyl ethyl ammonium percholorate complex of R-(–)-2-ethyl - N - benzyl - 4, 7, 10, 13 - tetraoxa -1- azacyclopentadecane, has been prepared and studied by NMR, IR and single crystal X-ray diffraction techniques. The compound crystallizes in space group

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