Structures and Synthesis of 4a-Homo-7,19-dinorsteroids, X-Ray Crystallography and NMR Spectroscopy

1999 ◽  
Vol 64 (12) ◽  
pp. 2019-2034 ◽  
Author(s):  
Alexander Kasal ◽  
Miloš Buděšínský ◽  
Jan Pelnař ◽  
Michael A. Bruck ◽  
Michael F. Brown
Keyword(s):  
Nmr Spectroscopy ◽  
Absolute Configuration ◽  
Starting Material ◽  
Nmr Analysis ◽  
X Ray Diffraction ◽  
X Ray ◽  
X Ray Crystallography ◽  
Leaving Group ◽  
The Absolute ◽  
Related Compounds

X-Ray diffraction revealed the absolute configuration of 4aβ-methyl-4a-homo-7,19-dinor- 5α,10α-androstane-3,17-dione. Detailed NMR analysis suggested that the 5α configuration existed in the starting material, 3β-acetoxy-4a-methylidene-4a-homo-7,19-dinor- 5α-androst-9-en-17-one, and related compounds. Thus 5-methyl-5β-estr-9-ene derivatives with a leaving group in position 6β were found to react with nucleophiles to form rearranged 4a-homo-7,19-dinorandrostane derivatives with a 5α configuration.

DETERMINATION OF THE ABSOLUTE CONFIGURATION OF NEW PIPERIDIN-4-ONE DERIVATIVE FROM Pellacalyx saccardianus BY NOESY SPECTROSCOPY

2016 ◽  
Vol 78 (3-2) ◽  
Author(s):  
Salam Ahmed Abed ◽  
Hasnah Mohd Sirat
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Nmr Spectroscopy ◽  
Magnetic Resonance ◽  
Absolute Configuration ◽  
X Ray ◽  
X Ray Crystallography ◽  
The Absolute ◽  
Nuclear Overhauser ◽  
Nuclear Magnetic

A new alkaloid, pellacalyxin was isolated from the leaves of Pellacalyx saccardianus of Rhizophoraceae family. Pellacalyxin was analyzed using nuclear Overhauser spectroscopy (NOESY) nuclear magnetic resonance (NMR) technique to determine the absolute configuration. The analysis of absolute configuration of pellacalyxin was supported by X-ray crystallography. 1H-1H NOESY NMR spectroscopy exhibited that pellacalyxin possesses two chiral centers (3S) and (6R).

Transition Metal Allyls, V. The Preparation and Structure of [NiX(PmenthylR1R2)(η3-allyl)] Complexes

1984 ◽  
Vol 39 (8) ◽  
pp. 1139-1150 ◽  
Author(s):  
H. Brandes ◽  
R. Goddard ◽  
P. W. Jolly ◽  
C. Krüger ◽  
R. Mynott ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Transition Metal ◽  
Absolute Configuration ◽  
Phosphorus Atom ◽  
Optically Active ◽  
X Ray ◽  
X Ray Crystallography ◽  
The Absolute ◽  
Active Centres

A number of adducts formed by reacting [NiX(η3-allyl)]2 complexes with optically active tert.- phosphines, in which optically active centres are found both at the phosphorus atom and in a substituent, have been isolated and their structures investigated in solution by NMR spectroscopy. The absolute configuration of the phosphine in [NiCl{Pm enthyl(Me)But}(η3-C3H5)] has been determ ined by X-ray crystallography. The relevance of the results to the nickel-catalyzed asymmetric codimerisation of alkenes is discussed.

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 N-Benzyl-3,5-dideoxy-3,5-imino-1,2-O-isopropylidene-β-L-lyxofuranose

2012 ◽  
Vol 68 (8) ◽  
pp. o2410-o2410
Author(s):  
David S. Edgeley ◽  
Sarah F. Jenkinson ◽  
Gabriel Lenagh-Snow ◽  
Catherine Rutherford ◽  
George W. J. Fleet ◽  
...  
Keyword(s):  
Absolute Configuration ◽  
Title Compound ◽  
Ring System ◽  
Starting Material ◽  
X Ray ◽  
X Ray Crystallography ◽  
Compound C ◽  
Relative Stereochemistry ◽  
The Absolute

X-ray crystallography confirmed the formation, structure and relative stereochemistry of the title compound, C15H19NO3, which contains a sterically congested four-membered azetidine ring system. The absolute configuration was determined by the use of L-arabinose as the starting material.

Alkaloids of Rauvolfia salicifolia GRISEB species

1982 ◽  
Vol 47 (11) ◽  
pp. 2912-2921 ◽  
Author(s):  
Patricia Sierra ◽  
Ladislav Novotný ◽  
Zdeněk Samek ◽  
Miloš Buděšínský ◽  
Ladislav Dolejš ◽  
...  
Keyword(s):  
Absolute Configuration ◽  
Cd Spectroscopy ◽  
X Ray Diffraction ◽  
X Ray ◽  
The Absolute

From the endemic Cuban species Rauvolfia salicifolia GRISEB nine alkaloids were isolated of which the following seven had been already described: (+)-ajmalidine (I), (-)-reserpiline (II), (-)-isoreserpiline (III), (-)-isocarapanaubine (IV), (-)-ajmalicine (V), (+)-vellosimine (VI), and (+)-yohimbine (VII). The structure of (-)-raucubaine (VIII) had been previously determined by X-ray diffraction and the structure of the alkaloid (-)-raucubainine (IX) was suggested on the basis of its conversion to (-)-raucubaine (VIII). The absolute configuration of (-)-raucubaine and (-)-raucubainine was elucidated by CD spectroscopy.

scholarly journals Absolute Configuration of Cembrane Diterpenoids from Bursera multijuga

2014 ◽  
Vol 9 (9) ◽  
pp. 1934578X1400900 ◽  
Author(s):  
Juan D. Hernández-Hernández ◽  
Hugo A. García-Gutiérrez ◽  
Luisa U. Román-Marín ◽  
Yunuen I. Torres-Blanco ◽  
Carlos M. Cerda-García-Rojas ◽  
...  
Keyword(s):  
Molecular Modeling ◽  
Absolute Configuration ◽  
2D Nmr ◽  
Vibrational Circular Dichroism ◽  
Conformational Preference ◽  
X Ray Diffraction ◽  
X Ray ◽  
The Absolute ◽  
First Time ◽  
Good Agreement

The stems of Bursera multijuga afforded (-)-(1 S,3 E,7 R,8 R,11 E)-7,8-epoxycembra-3,11-dien-1-ol (1) and its acetate 2, together with cembrene A (3), nephthenol (4), and cembrenol (5). The structures of 1 and 2 were elucidated by 1D and 2D NMR, HRESIMS, and X-ray diffraction. The conformational preference of flexible 1 was studied by molecular modeling at the DFT B3LYP/DGDZVP level of theory. Good agreement between calculated and experimental vibrational circular dichroism curves established the absolute configuration of 1. This is the first time that cembrane derivatives have been isolated from the genus Bursera.

The synergy of different solid-state techniques to elucidate the supramolecular assembly of two 1H-benzotriazole polymorphs

2019 ◽  
Vol 21 (36) ◽  
pp. 19879-19889
Author(s):  
María Mar Quesada-Moreno ◽  
Juan Ramón Avilés-Moreno ◽  
Juan Jesús López-González ◽  
Fco. Javier Zúñiga ◽  
Dolores Santa María ◽  
...  
Keyword(s):  
Solid State ◽  
Quantum Chemical Calculations ◽  
Absolute Configuration ◽  
Quantum Chemical ◽  
Supramolecular Structure ◽  
Supramolecular Assembly ◽  
X Ray ◽  
X Ray Crystallography ◽  
The Absolute

4aα (chiral) and 4aβ (achiral) polymorphs of 1H-benzotriazole are studied by X-ray crystallography, SSNMR, IR, Raman, VCD, and quantum chemical calculations. The absolute configuration of the supramolecular structure of 4aα polymorph is determined.

Synthese und Absolute Konfiguration von (+)-1-Amino-2-propanthiol·HCl / Synthesis and Absolute Configuration of ( + )-1-Amino-2-propanethiol · HCl

1987 ◽  
Vol 42 (5) ◽  
pp. 617-622 ◽  
Author(s):  
Sigurd Elz ◽  
Martin Dräger ◽  
Hans-Joachim Sattler ◽  
Walter Schunack
Keyword(s):  
Nmr Spectroscopy ◽  
Absolute Configuration ◽  
X Ray ◽  
Single Diastereomer ◽  
Important Intermediate ◽  
The Absolute ◽  
C Nmr

)-4a-The structure of (-)-5-methyl-2-phenylthiazolidine (( -)-4a), an intermediate in the synthesis of (+)-1-amino-2-propanethiol · HCl ((+)-2 · HCl), was elucidated by 1H and 13C NMR spectroscopy. In contrast to earlier findings it was shown that the important intermediate ( -)-4a is not a single diastereomer but represents a 1:1 mixture of (2R,5Sand ((2S,5S)-4a-diastereomers. The absolute configuration of the (2S,3S)-di-O-(4-toluoyl)tartrate of the disulfide (5) derived from (+)-2 · HCl was determined to be (S,S) using X-ray technique.

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