Determination of chemical shifts in 6-condensed syringylic lignin model compounds

Holzforschung ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Lucas Lagerquist ◽  
Jani Rahkila ◽  
Patrik Eklund

Abstract A small library of 6-substituted syringyl model compounds with aliphatic, carboxylic, phenylic, benzylic alcohols and brominated substituents were prepared. The influence of the substituents on the chemical shifts of the compounds was analyzed. All of model compounds showed a characteristic increase in the 13C NMR chemical shift of the methoxy group vicinal to the substitution. This 13C NMR peak and its corresponding correlation peak in HSQC could potentially be used to identify 6-condensation in syringylic lignin samples.

1987 ◽  
Vol 52 (8) ◽  
pp. 1985-1991 ◽  
Author(s):  
Jan Schraml ◽  
Jaan Past ◽  
Jüri Puskar ◽  
Tõnis Pehk ◽  
Endel Lippmaa ◽  
...  

Selective heteronuclear (Si-C) INADEQUATE method has been successfully used to assign all 29Si chemical shifts in six pertrimethylsilylated lignin model compounds. Empirical assignment of the lines in the region δ = 23-25 to trimethylsilyl esters of carboxylic compounds has been confirmed. Selectivity of the method permits unambiguous assignment to trimethylsiloxy groups which differ by their position on the benzene ring only. The assignment is possible despite that 29Si-13C two-bond coupling constants (2·1-3·0 Hz) are of comparable magnitude with the three-bond coupling constants (1-2·3 Hz). The chemical shifts of trimethylsiloxy groups on the benzene ring are sensitive to substituent effect to such an extent that their assignment cannot rely on an empirical rule but requires experimental method such as the one used here.


1999 ◽  
Vol 77 (4) ◽  
pp. 481-494 ◽  
Author(s):  
Huiping Qin ◽  
T Bruce Grindley

The C-polysaccharide is an antigen common to all known serotypes of Streptococcus pneumoniae bacteria and is a potential target for vaccine preparation. The final uncertainty in the structure of its repeating unit, a pentasaccharide phosphate containing two phosphorylcholine side chains, has been resolved by determining the configuration of ribitol. Assignment of configuration was performed by synthesis of the two trisaccharide phosphate fragments that have either D- or L-ribitol at their centers and comparison of their 1H and 13C NMR spectral data with that of the natural polysaccharide. The syntheses employed common synthons added in different orders to an asymmetrically substituted chiral ribitol derivative to obtain opposite chiralities in the ribitol segments. The data for the trisaccharide containing D-ribitol was almost identical to that of the natural material while that for the trisaccharide containing L-ribitol differed significantly. In particular, the chemical shift differences between the two protons of the primary carbons of ribitol units directly attached to the β-2-acetamido-2-deoxy-galactopyranosyl residue were 0.10, 0.12, and 0.33 ppm, in the natural polysaccharide, the D-ribitol-containing trisaccharide, and the L-ribitol-containing trisaccharide, respectively. The average difference between the 13C NMR chemical shifts of corresponding ribitol carbons from the natural polysaccharide and the D-ribitol-containing trisaccharide phosphate was 0.034 ppm. This evidence indicates that ribitol in the C-polysaccharide has the D-configuration and that a very similar mixture of conformations in the ribitol portions is present for the natural polysaccharide and the D-ribitol-containing trisaccharide phosphate.Key words: C-polysaccharide, Streptococcus pneumoniae, ribitol, dibutylstannylene acetal, determination of configuration.


Holzforschung ◽  
2004 ◽  
Vol 58 (4) ◽  
pp. 355-362 ◽  
Author(s):  
T. Kishimoto ◽  
A. Ueki ◽  
H. Takamori ◽  
Y. Uraki ◽  
M. Ubukata

Abstract In order to investigate the delignification mechanism during high-boiling solvent (HBS) pulping, softwood HBS lignin samples from todo fir (Abies sachalinensis) were analyzed by 1H–13C correlation NMR spectroscopy (HMQC). Nine lignin model compounds that may represent the substructures in HBS lignin were prepared. The 1H and 13C NMR spectral data were compared with HBS lignin samples. The HMQC spectra of HBS lignin samples showed the disappearance of β-O-4 structures. Introduction of a pulping solvent into lignin was plainly observed with new signals in aliphatic regions. Only the erythro β-1 structure was detected in softwood milled wood lignin from todo fir by HMQC spectra. The β-1 structure was very reactive and probably produced the stilbene structure. The β-β and β-5 structures remained in HBS lignin. The 4-O-5 structure was successfully detected by HMQC spectra, and it was found to be stable under the conditions used.


Holzforschung ◽  
1992 ◽  
Vol 46 (2) ◽  
pp. 127-148 ◽  
Author(s):  
Mariza G. Drumond ◽  
Dorila Piló Veloso ◽  
Stela D. Santos Cota ◽  
Sergio A. Lemos de Morais ◽  
Evandro A. do Nascimento ◽  
...  

1997 ◽  
Vol 13 (3) ◽  
pp. 227-249 ◽  
Author(s):  
Sandra A. Vestri Alvarenga ◽  
Jean Pierre Gastmans ◽  
Gilberto do Vale Rodrigues ◽  
Vicente de Paulo Emerenciano

This work describes the creation of heuristics rules based on13C-NMR spectroscopy that characterize several skeletal types of diterpenes. Using a collection of 2745 spectra we built a database linked to the expert system SISTEMAT. Several programs were applied to the database in order to discover characteristic signals that identify with a good performance, a large diversity of skeletal types. The heuristic approach used was able to differentiate groups of skeletons based firstly on the number of primary, secondary, tertiary and quaternary carbons, and secondly the program searches, for each group, if there are ranges of chemical shifts that identifies specific skeletal type. The program was checked with 100 new structures recently published and was able to identify the correct skeleton in 65 of the studied cases. When the skeleton has several hundreds of compounds, for example, the labdanes, the program employs the concept of subskeletal, and does not classify in the same group labdanes with double bounds at different positions. The chemical shift ranges for each subskeletal types and the structures of all skeletal types are given. The consultation program can be obtained from the authors.


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