The assignment of the configuration for α-hydroxy acid esters using a CEC strategy

2016 ◽  
Vol 14 (23) ◽  
pp. 5258-5262 ◽  
Author(s):  
Ruixue Peng ◽  
Lili Lin ◽  
Yuheng Zhang ◽  
Wangbin Wu ◽  
Yan Lu ◽  
...  
Keyword(s):  
Absolute Configuration ◽  
Hydroxy Acid ◽  
H Nmr ◽  
Nmr Method ◽  
The Absolute ◽  
Acid Esters

A simple and efficient 1H NMR method for determining the absolute configuration of chiral α-hydroxy acid esters using a CEC strategy with a chiral N,N′-dioxide-scandium(iii) complex was developed.

scholarly journals A New Bisabolene from Stevia tomentosa

2011 ◽  
Vol 6 (9) ◽  
pp. 1934578X1100600
Author(s):  
Alejandro Valdez-Calderón ◽  
J. Martín Torres-Valencia ◽  
J. Jesús Manríquez-Torres ◽  
René Velázquez-Jiménez ◽  
Mario A. Gómez-Hurtado ◽  
...  
Keyword(s):  
Absolute Configuration ◽  
Coupling Constants ◽  
Spectral Studies ◽  
Dihedral Angles ◽  
Model Compounds ◽  
H Nmr ◽  
Aerial Parts ◽  
The Absolute

The new sesquiterpene (1 R,2 R,3 R,6 R,7 S)-1-acetoxy-2,3-dmydroxy-2,3-dihydrobisabolene (3) together with ten known terpenes and three known flavonoids were isolated from the aerial parts and from the roots of Stevia tomentosa. The structure of 3 follows from spectral studies, the relative chirality at C-3 follows from 1H NMR coupling constants comparison with the corresponding calculated values obtained by applying a generalized Karplus-type relationship to the dihedral angles of model compounds, and the absolute configuration is assumed in analogy to known (2 R,3 R,6 R,7 S)-2,3-epoxy-2,3-dihydrobisabolen-1-one (2).

scholarly journals Absolute Stereochemistry of the β-Hydroxy Acid Unit in Hantupeptins and Trungapeptins

2016 ◽  
Vol 11 (1) ◽  
pp. 1934578X1601100 ◽  
Author(s):  
Deepak Kumar Gupta ◽  
Gary Chi Ying Ding ◽  
Yong Chua Teo ◽  
Lik Tong Tan
Keyword(s):  
Amino Acid ◽  
Structural Feature ◽  
Absolute Configuration ◽  
Hydroxy Acid ◽  
Hplc Analysis ◽  
The Absolute ◽  
Absolute Stereochemistry ◽  
Common Structural Feature ◽  
Acid Unit

The β-hydroxy/amino acid unit is a common structural feature of many bioactive marine cyanobacterial depsipeptides. In this study, the absolute stereochemistry of the β-hydroxy acid moieties in hantupeptins and trungapeptins were determined through their synthesis and HPLC analysis of the Mosher ester derivatives. Synthesis of two3-hydroxy-2-methyloctanoic acid (Hmoa) stereoisomers, (2 S,3 R)-Hmoa and (2 S,3 S)-Hmoa, were achieved using diastereoselective asymmetric method and the retention times of all four Hmoa isomers were established indirectly by RPLC-MS analysis of their Mosher ester derivative standards. Based on the retention times of the standards, the absolute configuration of the Hmoa unit in hantupeptin C (3) and trungapeptin C (6) was assigned as (2 R,3 S)- and (2 S,3 R)-Hmoa, respectively. The use of the Mosher's reagents, coupled with HPLC analysis, provided a viable alternative to the absolute stereochemical determination of β-hydroxy acid units in depsipeptides.

Structure of isosilerolide, relative and absolute configuration of silerolide and lasolide - Sesquiterpenic lactones of new stereoisomeric type of eudesmanolides

1986 ◽  
Vol 51 (4) ◽  
pp. 903-929 ◽  
Author(s):  
Miroslav Holub ◽  
Miloš Buděšínský ◽  
Zdenka Smítalová ◽  
David Šaman ◽  
Urszula Rychłewska
Keyword(s):  
Absolute Configuration ◽  
X Ray Diffraction ◽  
X Ray ◽  
H Nmr ◽  
Nmr Data ◽  
Chemical Correlation ◽  
The Absolute

On the basis of spectroscopic, particularly 1H NMR data, isosilerolide was assigned structure I, including the absolute configuration. The structure was confirmed by X-ray diffraction. Isosilerolide represents a new stereoisomeric type of natural eudesmanolides, characterized as 5βH, 6αH, 7αH, 10αCH3-eudesman-6,12-olide. As shown by the chemical correlation of isosilerolide (I) with silerolide (III) and lasolide (X), the latter two natural lactones belong to this stereoisomeric group of eudesmanolides. Analysis of models and 1H NMR data shows that structures of some eudesman-6,12-olides, published by other authors, should be corrected.

Sesquiterpenic lactones of Inula aschersoniana JANKA var. aschersoniana species

1990 ◽  
Vol 55 (6) ◽  
pp. 1562-1567 ◽  
Author(s):  
Ełżbieta Błoszyk ◽  
Miloš Buděšínský ◽  
Włodzimierz M. Daniewski ◽  
Eva Pešková ◽  
Bohdan Drożdż ◽  
...  
Keyword(s):  
Absolute Configuration ◽  
Cd Spectroscopy ◽  
H Nmr ◽  
Aerial Parts ◽  
The Absolute

Aerial parts of species Inula aschersoniana JANKA var. aschersoniana have been shown to contain parthenolide (I), costunolide diepoxide (III) and the hitherto undescribed inusoniolide (IV) whose structure, including the absolute configuration, was determined using 1H NMR and CD spectroscopy.

scholarly journals A Novel Acylated Anthocyanin with a Linear Trisaccharide from Flowers of Convolvulus althaeoides

2015 ◽  
Vol 10 (11) ◽  
pp. 1934578X1501001 ◽  
Author(s):  
Luis Cabrita
Keyword(s):  
Absolute Configuration ◽  
Complete Characterization ◽  
H Nmr ◽  
Chromatographic Techniques ◽  
Maldi Tof ◽  
The Absolute

An acylated anthocyanin trioside was isolated from pink flowers of Convolvulus althaeoides using a combination of chromatographic techniques. On the basis of MS (MALDI-TOF) and NMR (1H NMR, 1H-1H COSY, 1D TOCSY, HSQC, HMBC, 13C CAPT) its structure was determined as cyanidin 3- O-[6- O-(4- O-(6- O-( E-caffeoyl)-β-D-glucopyranosyl)-α-L-rhamnopyranosyl)-β-D-glucopyranoside]-5- O-β-D-glucopyranoside. The absolute configuration of the aldose enantiomer moieties was determined from the separation of the corresponding thiazolidine diastereoisomer derivatives by HPLC-DAD. This is a novel trisaccharide within the flavonoids, and the first complete characterization of a linear glucosyl-rhamnosyl-glucoside (4′-glucosylrutinoside) within the anthocyanins. Whilst acylation of rhamnose moieties in position 4 is quite common, the occurrence in anthocyanins of a glycosylated rhamnose is a unique trait. Although many complex anthocyanins have been found amongst the Convolvulaceae, the genus Convolvulus had not yet been surveyed for anthocyanins and thus this account could be of significance within the current chemotaxonomy of this family.

scholarly journals Stereochemistry of Two Hydroxybiflavanonols from Garcinia cola Nuts

1987 ◽  
Vol 42 (7-8) ◽  
pp. 855-857 ◽  
Author(s):  
Johann Sonnenbichler ◽  
Ifeanyi Madubunyi ◽  
Hugo Scheer
Keyword(s):  
Nmr Spectroscopy ◽  
Absolute Configuration ◽  
Room Temperature ◽  
H Nmr ◽  
The Absolute

The absolute configuration of two hydroxybiflavanonols from Garcinia cola nuts have been determined by CD and 500 MHz 1H NMR spectroscopy. Additionally the occurrence of atrop-isomers at room temperature as the consequence of rotational hindrance in the molecules could be demonstrated.

Determination of the absolute configuration of the fragments composing the phytotoxin phomalide

1997 ◽  
Vol 75 (3) ◽  
pp. 314-317 ◽  
Author(s):  
M. Soledade C. Pedras
Keyword(s):  
Absolute Configuration ◽  
Capillary Column ◽  
Acid Methyl Ester ◽  
Isopropyl Ester ◽  
H Nmr ◽  
Acid Methyl ◽  
The Absolute ◽  
Amino Acid Methyl Ester ◽  
Unambiguous Assignment

The absolute configurations of the residues constituting phomalide (1) were determined on the products resulting from acidic hydrolysis. The configurations of the amino acids Val and Leu were determined as (S) and (R), respectively, by chiral GC analysis (Chirasil-Val capillary column), employing N-trifluoroacetyl (TFA) amino acid methyl ester derivatives. The configurations of the hydroxy acids O-Phe and O-Leu were determined as (S) by 1H NMR of the Mosher's esters of the isopropyl ester derivatives. The method described allowed for the unambiguous assignment of the absolute configuration of the α-amino and α-hydroxy acid residues composing phomalide (1). Keywords: absolute configuration, depsipeptide, Mosher's ester.

Determination of the absolute stereochemistry of the fungal metabolite (R)-(−)-2-(4′-hydroxyphenyl)-2-hydroxyethanoic acid (pisolithin B)

1991 ◽  
Vol 69 (5) ◽  
pp. 772-778 ◽  
Author(s):  
Youla S. Tsantrizos ◽  
Kelvin K. Ogilvie
Keyword(s):  
Absolute Configuration ◽  
Lithium Aluminum Hydride ◽  
Optical Rotation ◽  
Aluminum Hydride ◽  
Lithium Aluminum ◽  
Fungal Metabolite ◽  
H Nmr ◽  
The Absolute ◽  
Absolute Stereochemistry

The antifungal antibiotic pisolithin B (p-hydroxymandelic acid, 2-(4′-hydroxyphenyl)-2-hydroxyethanoic acid, 1a) was shown to have the absolute (R) configuration. The stereochemistry was established via comparison of its optical rotation to that of its synthetic (R) and (S) enantiomers. The synthetic samples were prepared by the stereospecific reduction of the prochiral α-keto acid, p-hydroxybenzoylformic acid (2-(4′-hydroxyphenyl)-2-oxoethanoic acid, 2a), with (R) or (S)-2,2′-dihydroxy-1,1′-binaphthyl lithium aluminum hydride (BINAL-H). The absolute configuration and enantiomeric purity of both products were determined using the 1H NMR of their isobutyl esters in the presence of the chiral solvating agent (R)-(−)-2,2,2-trifluoro-1-(9-anthryl)ethanol. Key words: pisolithin B, p-hydroxymandelic acid, antifungal, absolute configuration.

Oxetanes from Photocycloaddition of 2-Aminopropenenitriles to Methyl Phenylglyoxylate and Benzils

2006 ◽  
Vol 61 (3) ◽  
pp. 301-310 ◽  
Author(s):  
Christiane van Wolven ◽  
Dietrich Döpp ◽  
Gerald Henkel
Keyword(s):  
Single Crystal ◽  
Absolute Configuration ◽  
Structure Determination ◽  
Benzene Solution ◽  
X Ray ◽  
H Nmr ◽  
The Absolute ◽  
Layer Chromatography ◽  
Preparative Layer Chromatography

Abstract By irradiation of methyl phenylglyoxylate (1) in benzene solution in presence of equimolar amounts of 2-aminopropenenitriles H2C=C(NR2)CN (3a - e, NR2 = morpholino, 1-pyrrolidinyl, 1-piperidinyl, hexamethyleneimino, heptamethyleneimino) the corresponding 2R∗,3R∗ head-to-head oxetanes 4a - e were obtained in moderate yields (11 - 52%) along with 2 - 28% of rac-dimethyl 2,3- diphenyltartrate (2). In presence of (S)-2-(2-methoxymethylpiperidin-1-yl)propenenitrile ((+)-3g) 1 is transformed into 26% of 2 and 33% of a mixture of diastereomeric oxetanes 4g,4’g in a ratio of 1.4 : 1 which could be improved to 2.5 : 1 by preparative layer chromatography. The absolute configuration of the major diastereomer 4g was unambiguously confirmed by a single crystal X-ray structure determination to be 2R,3R,2’S. Analogous photoadditions to benzil (5a), 4,4’-bis-(trifluoromethyl)benzil (5b) and 4,4’-dichlorobenzil (5c) with (+)-3g and its lower homologue (S)-2-(2-methoxymethylpyrrolidin- 1-yl)propenenitrile ((-)-3f) gave oxetanes only in low yield as detected by 1H NMR. Byproducts arise from competitive symmetrical α-cleavage of 5.

Sign in / Sign up

Export Citation Format

Share Document