The structure of yatein. Determination of the positions, and configurations of benzyl groups in lignans of the 2,3-dibenzylbutyrolactone type

1982 ◽  
Vol 47 (2) ◽  
pp. 644-663 ◽  
Author(s):  
Juraj Harmatha ◽  
Miloš Buděšínský ◽  
Antonín Trka
Keyword(s):  
Absolute Configuration ◽  
Nmr Spectra ◽  
Optical Rotation ◽  
Shift Reagent ◽  
Complete Analysis ◽  
Nmr Spectrum ◽  
H Nmr ◽  
Determination Of Absolute Configuration ◽  
Erroneous Interpretation

The structure of yatein isolated from Libocedrus yateensis has been determined as (2R, 3R)-2-(3,4,5-trimethoxybenzyl)3-(3,4-methylenedioxybenzyl)butyrolactone (Ia). The assignment of individual signals of the 1H NMR spectrum of yatein and further lignans of the 2,3-dibenzyl-butyrolactone type is discussed and supported by the use of a lanthanide shift reagent and by mass spectrometry of deuterated derivatives IIa, IIb. A method of determination of absolute configuration of the centres C(2) and C(3) of these 2,3-dibenzylbutyrolactone lignans on the basis of a combination of information obtained from 1H NMR spectra and optical rotation is proposed. The erroneous interpretation of the ORD and CD spectra used in some instances for the determination of absolute configuration of these substances, as well as the often repeated error in the assignment of benzyl and C(2)-H, C(3)-H protons in 1H NMR spectra of trans-lignans is also discussed. A complete analysis of the 1H NMR spectra permitted the proposition of the preferred conformation for trans and cis isomer Ia and Ib.

21,22-Disubstituted 18α,19βH-Ursane Derivatives with Oxabicyclooctane System in Ring E

1993 ◽  
Vol 58 (1) ◽  
pp. 173-190 ◽  
Author(s):  
Eva Klinotová ◽  
Jiří Klinot ◽  
Václav Křeček ◽  
Miloš Buděšínský ◽  
Bohumil Máca
Keyword(s):  
Spectral Data ◽  
Spin Systems ◽  
Coupling Constants ◽  
Complete Analysis ◽  
Nmr Spectrum ◽  
Proton Proton ◽  
H Nmr ◽  
Proton Coupling ◽  
C Nmr

Reaction of 3β-acetoxy-21,22-dioxo-18α,19βH-ursan-28,20β-olide (IIIa) and 20β,28-epoxy-21,22-dioxo-19α,19βH-ursan-3β-yl acetate (IIIb) with diazomethane afforded derivatives XII-XIV with spiroepoxide group in position 21 or 22, which were further converted into hydroxy derivatives XV and XVII. Ethylene ketals VIII-X were also prepared. In connection with the determination of position and configuration of the functional groups at C(21) and C(22), the 1H and 13C NMR spectral data of the prepared compounds are discussed. Complete analysis of two four-spin systems in the 1H NMR spectrum of bisethylenedioxy derivative Xb led to the proton-proton coupling constants from which the structure with two 1,4-dioxane rings condensed with ring E, and their conformation, was derived.

The 1H NMR spectra and the conformation of 1,6-anhydro-β-D-hexopyranoses and their triacetates

1979 ◽  
Vol 44 (6) ◽  
pp. 1949-1964 ◽  
Author(s):  
Miloš Buděšínský ◽  
Tomáš Trnka ◽  
Miloslav Černý
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
Shift Reagent ◽  
Point Of View ◽  
Coupling Constants ◽  
Lanthanide Shift Reagent ◽  
Pyranose Ring ◽  
H Nmr ◽  
Vicinal Coupling Constants

The 1H NMR spectra of 1,6-anhydro-β-D-hexopyranoses and their triacetates, measured in hexadeuteriodimethyl sulfoxide or deuteriochloroform, confirmed the existence of these compounds in 1C4(D) conformations, with the pyranose ring partly planarized in dependence on the configuration of the substituents in positions C(2), C(3) and C(4). The effects of the substituents on the chemical shifts and the adjusted relationship for the dependence of vicinal coupling constants on the torsion angle are discussed in detail from the point of view of the determination of the configuration and the conformation of 1,6-anhydro-β-D-hexopyranoses and their derivatives. The 1H NMR spectra of triacetates were also measured in the presence of the lanthanide shift reagent, tris(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione) europium (III) [Eu.(FOD)3].

Determination of Absolute Configuration Using Optical Rotation Calculated Using Density Functional Theory

2002 ◽  
Vol 4 (26) ◽  
pp. 4595-4598 ◽  
Author(s):  
P. J. Stephens ◽  
F. J. Devlin ◽  
J. R. Cheeseman ◽  
M. J. Frisch ◽  
C. Rosini
Keyword(s):  
Density Functional Theory ◽  
Absolute Configuration ◽  
Density Functional ◽  
Optical Rotation ◽  
Functional Theory ◽  
Determination Of Absolute Configuration
Sign in / Sign up

Export Citation Format

Share Document