Juraj Alföldi

Structural and solution properties of corn cob heteroxylans

The main structural features of the l-arabino-(4-O-methyl-d-glucurono)-d-xylan (AGX) from corn cobs were evaluated by means of methylation analysis and 13C-NMR spectroscopy. The heteroxylan consisted of water-soluble and water-insoluble xylan molecules differing in the amount and proportion of non-regularly distributed side chains. Single α-(1 → 2)-linked 4-O-methyl-d-glucopyranosyl uronic acid units and α-(1 → 3)-linked l-arabinofuranose residues, as well as 2-O-β-d-xylopyranosyl-α-l-arabinofuranose moieties constituted the side chains. GPC analysis of the water-soluble fractions coupled with viscometry and light-scattering was used to characterise the molecular weight distribution (MWD) and to establish the Mark-Houwink relationship. The flow properties of aqueous dispersions of the water-soluble and water-insoluble fractions were discussed in relation to their structural properties.

Galactoglucomannan from the secondary cell wall of Picea abies L. Karst.

The fine structural features of alkali-extracted galactoglucomannan composed of D-galactose, D-glucose and D-mannose in a 1:8:33 mole proportion from the secondary cell walls of Picea abies L. Karst have been determined. Compositional and methylation analyses of the polymer, partial acid hydrolysis, as well as 1H and 13C NMR measurements of the polymer and products of partial acid hydrolysis confirmed a beta-(1-->4)-linked backbone of galactoglucomannan containing the segments of mannosyl residues (Man2, Man3, Man4, etc.) interrupted with the segments having both mannose and glucose residues, as well as the segments in which D-Glcp units can be adjacent to each other (Glc2). Further, the low content of branching points (approximately 3%) at the positions of 0-6, 0-3 and 0-2 of mannosyl and 0-6 and 0-3 of glucosyl residues, but preferably of mannosyl ones, indicates the presence of short side-chains terminated at position 0-6 predominantly by D-galactose units as single stubs.

An acetylated galactoglucomannan from Picea abies L. Karst

A water-soluble galactoglucomannan composed of D-galactose, D-glucose, and D-mannose in 1:3:17 mole proportion has been isolated from the secondary cell walls of Picea abies L. Karst. About 33% of the polysaccharide units were substituted by acetyl groups. Structural studies of the polymer indicated a beta-(1-->4)-linked glucomannopyranosyl backbone with a low content of branch points at O-6 of mannosyl and glucosyl residues. A preference for mannosyl groups indicates the presence of a single D-galactosyl unit side-chain. About half of the mannose residues were O-acetylated at C-2 and C-3 in 1.7:1 mole proportion.

Chemical and 13C-n.m.r. studies of an arabinogalactan from Larix sibirica L.

Abstract An arabinogalactan isolated from the wood of Larix sibirica L. was investigated by methylation analysis, partial hydrolysis, enzymic oxidation, and 13 C-n.m.r. spectroscopy. The structural conclusions arrived at by 13 C-n.m.r. spectroscopy were consistent with the data from methylation analysis. The polysaccharide is highly branched and similar in structure to those of arabino-3,6-galactans isolated from other Larix species.

Modification of corn cob meal with quarternary ammonium groups

Abstract Corn cob meal was modified with quarternary ammonium groups and subsequently extracted with 80% ethanol, water, and 5% NaOH. The fractions obtained had lower polydispersities, M w values, and yields than unmodified material. The yields are lower than those obtained on bagasse under the same conditions. The modification caused the drastic degradation of the ethanol-lignin (EL) fraction. The one-step extraction with NaOH/H2O2 gave 28·8% yield of material (calculated on the starting material) which contained 12·0% Klason lignin, and had the highest polydispersity (4·3, M w = 9540 ). The water-soluble fractions consisted of arabinoglucuronoxylan and alkali-soluble fractions of xylan without other sugar moieties. The water-soluble fraction from NaOH/H2O2 extraction contained arabinoglucuronoxylan with modified arabinose and 4-O- methyl- d -glucuronic acid units. By this method higher yields could be obtained than on bagasse treated by the sequential extraction.

Cyclodextrin derivative of hyaluronan

Conversion of hyaluronan (HA) to its β-cyclodextrin derivative (HA-β-CD) was accomplished by direct coupling of β-cyclodextrin (β-CD) molecules with carboxylic acid groups of the HA macromolecule. The intermolecular dehydration, yielding the HA-β-CD derivative, was performed by the action of diethyl azodicarboxylate and triphenylphosphine under mild, neutral conditions. The physico-chemical characteristics of the novel (bio)material, determined both in solution and solid state, were compared with those of native HA. The specific action of a hyaluronidase was exploited to advantage in studying the depolymerization kinetics of the two types (HA and HA-β-CD) of macrobiomolecules.

Modification of pectin with UV-absorbing substitutents and its effect on the structural and hydrodynamic properties of the water-soluble derivatives

Citrus pectin with a low degree of methyl esterification (LMP) and its deesterified form, potassium pectate (KP), were modified with a low amount of UV-absorbing substituents. For this purpose, two different substitution reactions were used (a) alkylation of hydroxyl groups with p-carboxybenzyl bromide in aqueous alkali and (b) alkylation of the carboxylate group with benzyl bromide in the DMSO/TBAI/catalyst system. Chemical and spectroscopic methods reveal a low degree of substitution (DS<0.1) for the derivatives. The hydrodynamic properties were assessed by analytical ultracentrifugion, viscometry, and HPGPC. The results indicate that the introduction of small amounts of p-carboxybenzyl ether groups practically had no effect on the hydrodynamic properties in the case of KP, whereas, it was accompanied with a decrease of the molecular mass for LMP. The degradation was more pronounced during the benzyl esterification of LMP. The results confirmed that LMP is susceptible to chain cleavage due to I²-elimination during both modification reactions. However, KP seems to be more tolerant of the reaction conditions. © 2002 Elsevier Science Ltd. All rights reserved.

A new approach to the synthesis of rare thiazino[6,5-b]indol-4-one derivatives. First total synthesis of the indole phytoalexin cyclobrassinon

Abstract The first synthesis of the indole phytoalexin cyclobrassinon and some of its analogues, possessing a thiazino[6,5- b ]indol-4-one tricyclic ring system was performed starting from 1-substitued 2-chloroindole-3-carboxaldehydes. The route employed the intramolecular Et 3 N-mediated or photochemical nucleophilic substitution of a chlorine atom in the 2-position of the indole ring with a sulfur atom as a key step. Examination of biological activity against the selected tumor cell lines, bacteria and fungi revealed no expressive activity of synthesized compounds.

A 13C-n.m.r. study of the alkaline degradation products of polysaccharides

Abstract Thirteen products of alkaline degradation of polysaccharides have been examined by 13 C-n.m.r. spectroscopy. The main product of the alkaline degradation of l -arabino-(4- O -methyl- d -glucurono)- d -xylan was the sodium salt of 3-deoxy-2- C -hydroxymethyltetronic (xyloisosaccharinic) acid. l -Arabino-(4- O -methyl- d -glucurono)- d -xylan and (4- O -methyl- d -glucurono)- d -xylan were degraded in alkaline media by the elimination of l -arabinose and 4- O -methyl- d -glucuronic acid residues. The first step in the elimination of the 4- O -methyl- d -glucuronic acid residue was the loss of MeO-4 and the formation of a 4,5-double bond. The presence of a 3-deoxyaldonic acid end-unit in the polysaccharide was also found.

Stereochemistry of the hydrolysis of glycosidic linkage by endo-β-1,4-xylanases of Trichoderma reesei

Methyl β‐d‐xylotrioside was used as a non‐reducing substrate to investigate the stereochemistry of hydrolysis of, β‐1,4‐xylopyranosidic linkage by purified endo‐β‐1,4‐xylanases (EC 3.2.1.8) of Trichoderma reesei, employing 1H NMR spectroscopy. The fungus produces one acidic species (pI 4.8–5.5), designated as EXI, and one alkaline species (pI 8.5–9.0), designated as EXII. Both enzymes were found to cleave the xylotrioside predominantly to methyl β‐d‐xyloside and xylobiose. Monitoring of the intensity of the H‐1 signals of α‐ and β‐xylobiose during the time course of hydrolysis clearly showed that both enzymes liberate the β‐anomer of xylobiose, i.e. a product with anomeric configuration identical with that of the cleaved glycosidic linkage. This means that both EXI and EXII belong to the so‐called retaining glycanases that utilize the double displacement reaction mechanism of hydrolysis.