Sesquiterpenic lactones of the Inula caspica BLUME species

1990 ◽  
Vol 55 (6) ◽  
pp. 1568-1579 ◽  
Author(s):  
Sergazy M. Adekenov ◽  
Miloš Buděšínský ◽  
Metram A. Abdikalikov ◽  
Coblandy M. Turdybekov ◽  
David Šaman ◽  
...  
Keyword(s):  
Absolute Configuration ◽  
Cd Spectroscopy ◽  
X Ray Diffraction ◽  
Relative Configuration ◽  
X Ray

From Inula caspica BLUME (Compositae) were isolated 3β-hydroxy-2α-senecioyloxyisoalantolactone (I), whose structure was confirmed by X-ray diffraction and completed by determination of its absolute configuration, and britannin (II) whose relative configuration was determined by X-ray diffraction and absolute configuration by CD spectroscopy.

Structure of laserolide and isolaserolide: Revision of constitution and determination of relative and absolute configuration

1985 ◽  
Vol 50 (8) ◽  
pp. 1878-1887 ◽  
Author(s):  
Miroslav Holub ◽  
Miloš Buděšínský ◽  
Zdenka Smítalová ◽  
David Šaman ◽  
Urszula Rychłewska
Keyword(s):  
Diffraction Analysis ◽  
Absolute Configuration ◽  
Cd Spectroscopy ◽  
X Ray Diffraction ◽  
Physical Methods ◽  
X Ray

The position of the ester groups in sesquiterpenic lactones laserolide (I) and isolaserolide (II) has been revised and its relative and absolute configuration determined by chemical and physical methods (NMR and CD spectroscopy). The structure I was confirmed by X-ray diffraction analysis. Laserolide (I) is the first germacranolide found in the Umbelliferae family, isolaserolide (II) is the first representative of new stereostructural group of elemanolides - 5βH,6αH,7αH,10αCH3-elema-1,3-dien-6,12-olides.

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 Determination of the absolute stereostructure of a cyclic azobenzene from the crystal structure of the precursor containing a heavy element

2016 ◽  
Vol 12 ◽  
pp. 2211-2215 ◽  
Author(s):  
Reji Thomas ◽  
Nobuyuki Tamaoki
Keyword(s):  
Cd Spectroscopy ◽  
Chiral Molecules ◽  
X Ray Diffraction ◽  
X Ray ◽  
Heavy Atoms ◽  
Unambiguous Determination ◽  
The Common ◽  
The Absolute ◽  
Reverse Method

Single crystal X-ray diffraction has been used as one of the common methods for the unambiguous determination of the absolute stereostructure of chiral molecules. However, this method is limited to molecules containing heavy atoms or to molecules with the possibility of functionalization with heavy elements or chiral internal references. Herein, we report the determination of the absolute stereostructure of the enantiomers of molecule (E)-2, which lacks the possibility of functionalization, using a reverse method, i.e., defunctionalization of its precursor of known stereostructure with bromine substitution (S-(−)-(E)-1). A reductive debromination of S-(−)-(E)-1 results in formation of one of the enantiomers of (E)-2. Using a combination of HPLC and CD spectroscopy we could safely assign the stereostructure of one of the enantiomers of (E)-2, the reduced product R-(−)-(E)-1.

Coordination Chemistry of N-(2-Hydroxybenzyl)-(S)-amino Acids. Absolute Configuration of LAMBDA-mer-R,R-[Co(ohb-(S)-Ala)2]- Anion

1997 ◽  
Vol 62 (8) ◽  
pp. 1205-1213 ◽  
Author(s):  
Svetlana Pakhomova ◽  
Jan Ondráček ◽  
František Jursík
Keyword(s):  
Absolute Configuration ◽  
Diffraction Method ◽  
Cd Spectroscopy ◽  
X Ray Diffraction ◽  
Aromatic Rings ◽  
Molecular Mechanics Calculations ◽  
X Ray ◽  
Bond Network ◽  
Twist Boat ◽  
C Nmr

The crystal and molecular structure of the Ag[Co(ohb-(S)-Ala)2] . 5 H2O have been determined by X-ray diffraction method. The crystals are hexagonal with a = b = 9.039(0.002) Å, c = 24.896(0.006) Å, space group P3221, and Z = 3. Each Ag+ counterion coordinated by one water molecule which is a part of hydrogen bond network, is bonded to aromatic rings. The anion adopts LAMBDA-mer absolute configuration. Mer geometry is in accord with the molecular mechanics calculations. Since CD spectroscopy does not reflect configurational chirality, the absolute configuration has been determined by the X-ray structure analysis and assigned using chirality descriptors. The arrangements at the chiral centers are R for both N atoms. The two five-membered rings each assume envelope conformation with C1 and C2 atoms exceptionally deviated (0.378(7) and 1.210(7) Å) from the N-Co-O plane. Both six-membered rings have delta twist boat conformations. The complex described has been also characterized by the electronic and 13C NMR spectroscopies.

scholarly journals Absolute configuration of naturally occurring glabridin

2013 ◽  
Vol 69 (11) ◽  
pp. 1212-1216 ◽  
Author(s):  
Charlotte Simmler ◽  
Frank R. Fronczek ◽  
Guido F. Pauli ◽  
Bernard D. Santarsiero
Keyword(s):  
Absolute Configuration ◽  
X Ray Diffraction ◽  
Data Set ◽  
X Ray ◽  
Naturally Occurring ◽  
Nmr Data ◽  
Stereochemical Analysis ◽  
Medium Pressure Liquid Chromatography ◽  
Species Specific

The title compound {systematic name: 4-[(3R)-8,8-dimethyl-3,4-dihydro-2H-pyrano[2,3-f]chromen-3-yl]benzene-1,3-diol, commonly named glabridin}, C20H20O4, is a species-specific biomarker from the rootsGlycyrrhiza glabraL. (European licorice, Fabaceae). In the present study, this prenylated isoflavan has been purified from an enriched CHCl3fraction of the extract of the root, using three steps of medium-pressure liquid chromatography (MPLC) by employing HW-40F, Sephadex LH-20 and LiChroCN as adsorbents. Pure glabridin was crystallized from an MeOH–H2O mixture (95:5 v/v) to yield colorless crystals containing one molecule per asymmetric unit (Z′ = 1) in the space groupP212121. Although the crystal structure has been reported before, the determination of the absolute configuration remained uncertain. Stereochemical analysis, including circular dichroism, NMR data and an X-ray diffraction data set with Bijvoet differences, confirms that glabridin, purified from its natural source, is found only in a C3Rconfiguration. These results can therefore be used as a reference for the assignment of the configuration and enantiopurity of any isolated or synthetic glabridin sample.

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