Knut Lundquist

Analysis of Lignin Products by Fluorescence Spectroscopy

Hydrolyse eines Birkensulfatzel ls toffes Ein Birkensulfatzellstoff mit einem DP-Wert von 850 und einem -Cellulosegahlt von 90,5 wurde nach den oben beschriebenen Bedingungen hydrolysiert. Der Kristallinitätsindex nahm bei dieser Behandlung von 54 auf 74,5 zu. Auch hier konnte man feststellen, daß durch heterogene Hydrolyse die röntgenamorphen Bereiche nicht voll entfernt werden konnten und daß die Röntgenkristallinität des Hydrolyseproduktes weit unter dem Wert der Hydrocellulose aus BaumwollLinters liegt. Es konnte ferner nachgewiesen werden, daß die Hydrocellulose verschiedene Fraktionen enthält, die große Unterschiede im Ordnungszustand aufweisen.

Reassignment of relative stereochemistry at C-7 and C-8 in arylcoumaran neolignans

Abstract 1 H NMR spectral characteristics of synthetic trans and cis arylcoumarans and their acetates which are related to 8-5′ neolignans are given. This information is used to reassign structures to neolignans reported in nine papers, from the cis to the trans 7-aryl-8-hydroxymethyl configurations, and to neolignans in six papers in which no assignments were made. Thus far, there is no evidence for the occurrence of 8-5′ neolignans with a cis configuration in nature.

Investigation of the acid-catalysed alkylation of lignins by means of NMR spectroscopic methods

The acid-catalysed (catalyst, 0.15 M p-toluenesulfonic acid in the reaction medium) alkylation of lignins with rnethano) or ethanol in dioxane (alcohol-dioxane (2:1)) at 30°C has been studied by NMR spectroscopic methods. Complete alkylation required 4—6 days and resulted in the introduction of about one alkoxyl group in every second phenylpropane unit. The alkylation can be explained by etherification of benzy) alcohols (and, to a minute extent, cinnamyl alcohols), reetherification of benzyl ethers, esterification of carboxylic acids and formation of acetals from benzaldehydes, cinnamaldehydes and glyceraldehyde-2-aryl ethers. The methodology used permitted the conclusion that reactions other than alkylation occurred to only a minor extent. The wine-red colour acquired by the reaction mixture from lignin alkylation could be related to the occurrence of cinnamaldehyde groups. According to model compound studies, alkylation of arylglycerol-ß-aryl ethers resulted in a mixture of the erythro (60%) and threo (40%) forms of the benzyl ethers.

On the distribution of the diastereomers of the structural elements in lignins: the steric course of reactions mimicking lignin biosynthesis

SummaryStereochemical studies on the formation of the diastereomers of arylglycerol-β-aryl ether structures during lignin biosynthesis have been carried out with model compounds. The addition of water to quinone methides of the β-syringyl ether type gives arylglycerol β-syringyl ethers with a predominance of the erythro isomer when the pH of the medium is low. Since erythro forms of arylglycerol β-syringyl ethers are prevalent in hardwood lignins, this indicates that the pH of the medium in which lignin biosynthesis occurs is lower than has been assumed until now. Equilibration studies with non-phenolic model compounds of the arylglycerolβ-guaiacyl ether and β-syringyl ether types under acidolysis conditions indicate that the erythro predominance observed in the syringyl ethers in lignins does not correspond to equilibrium conditions. A remarkable resistance to acidolysis is observed in the model compounds of etherified syringylglycerol β-syringyl ether type.

The chemical structure of extracellular lignin released by cultures of Picea abies

Abstract Fractionation, size exclusion chromatography, thioacidolysis and 13C NMR of released suspension culture lignin (RSCL)produced by Picea abies sh

Distribution of erythro and threo forms of different types of β‐O‐4 structures in aspen lignin by 13C NMR using the 2D INADEQUATE experiment

Carbon–carbon connectivity spectra of 13C‐enriched aspen lignin recorded using the 2D INADEQUATE experiment revealed cross peaks which can be assigned to four types of arylglycerol β‐aryl ethers (β‐O‐4 structures): erythro forms of arylglycerol β‐syringyl ethers, threo forms of arylglycerol β‐syringyl ethers, erythro forms arylglycerol β‐guaiacyl ethers and threo forms of arylglycerol β‐guaiacyl ethers. The intensities of the cross peaks suggest larger amounts of β‐syringyl ethers than β‐guaiacyl ethers. The erythro isomers dominate among the β‐syringyl ethers. Erythro and threo forms of β‐guaiacyl ethers are present in similar amounts.

Synthesis of cinnamaldehydes, esters of cinnamic acids and acylals of cinnamaldehydes by oxidation of arylpropenes with 2,3-dicyano-5,6-dichlorobenzoquinone (DDQ)

Abstract 1-Arylpropenes and 3-arylpropenes give cinnamaldehydes (yield≈ 80%) on oxidation with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) in the presence of water. The conversion to aldehydes is promoted by electron-donating groups at the aromatic ring. On DDQ oxidation in the presence of methanol, methyl esters of cinnamic acids are the predominant products. DDQ oxidation of 1- or 3-(3,4-dimethoxyphenyl)-1-propene in the presence of acetic acid gives an acylal [the diacetate of ( E )-3-(3,4-dimethoxyphenyl)-2-propene-1,1-diol].

Trametes versicolor ligninase: Isozyme sequence homology and substrate specificity

The substrate specificity of three ligninase isozymes from the white‐rot fungus Trametes versicolor has been investigated using stereochemically defined synthetic dimeric models for lignin. The isozymes have been found to attack non‐phenolic β‐O‐4 as well as β‐1 lignin model compounds. This finding confirms the classification of the isozymes from T. versicolor as ligninases. The amino‐terminal residues of the three isozymes from T. versicolor have been determined using Edman degradation. Minor differences found between the sequences suggest the existence of several structural genes for ligninase in T. versicolor. Comparisons have been made with the sequences of three previously reported ligninases from Phanerochaete chrysosporium, another lignin‐degrading fungus. One of the sequences from P. chrysosporium is distinctly more similar to the T. versicolor isozymes than to the other two sequences from P. chrysosporium.

On the Occurrence of β-1 Structures in Lignins

Abstract 1H NMR spectral evidence for the occurrence of β-1 structures in lignins it presented. The number of β-1 side chains may be 1–2% in spruce lignin and perhaps as much as 5% in birch lignin.

Revisiting the mechanism of beta-O-4 bond cleavage during acidolysis of lignin. Part 3: Search for the rate-determining step of a non-phenolic C6-C3 type model compound

Abstract The rate-determining step of a C6-C3 dimeric non-phenolic β-O-4 type lignin model compound, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)propane-1,3-diol (veratrylglycerol-β-guaiacyl ether, VG), was evaluated under acidolysis conditions (0.2 mol/l HBr in 82% aqueous 1,4-dioxane at 85°C) by comparing the disappearances between VG and the corresponding compound labeled at the β-position of VG, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)(2–2H)propane-1,3-diol. The disappearance of VG occurred more rapidly than that of the latter compound, and a primary kinetic isotope effect was clearly observed. This result indicates that the C-H bond at the β-position of VG is broken in the rate-determining step. Two possible mechanisms are presented as the rate-determining step: (1) A base abstracts the β-proton of a benzyl cation-type intermediate produced from VG affording an enol ether compound, 2-(2-methoxyphenoxy)-3-(3,4-dimethoxyphenyl)prop-2-en-1-ol; (2) The hydride transfers from the β- to the α-position of the benzyl cation. It was confirmed that both mechanisms certainly exist and that the latter seems to contribute more than has generally been considered.