Vladimír Kováčik

Mass spectrometry of uronic acid derivatives

Electron impact mass spectra of a series of aldobiouronic and pseudoaldobiouronic acid per-0-methyl derivatives and of the corresponding 4,5-unsaturated analogues, found normally among the products of methylation of uronic acid containing disaccharides as a result of methylation accompanying &elimination, have been studied. Using labelling experiments, metastable transition measurements and high resolution mass spectrometry, the fragmentation mechanisms of substances of this class have been deduced. Application of the information to the structure elucidation of this type of compound is discussed. It is concluded that from the mass spectra alone it is possible to determine the molecular weight, the cycle masses as well as the mode of linkage between the monomeric units. The appearance potentials of ions formed by cleavage of the glycosidic linkages have also been determined and the energetic differences encountered in the fission of the glycosidic linkages of various types of uronic acid containing oligosaccharides are discussed.

Low Temperature Thermolysis of Lignins - I. Reactions of ß—O—4 Model Compounds

Two pairs of model compounds of arylglyceroland arylglycol-j3-guaiacyl ether type, representing phenolic and non-phenolic variant of 0-O-4 structure, were heated in atmosphere of own decomposition products at rate 10 °C/min. up to 275 and 315 °C, for phenolic and non-phenolic derivatives, respectively. On the basis of qualitative and quantitative analysis of the thermolyzates by rneans of chromatography and mass spectrometry, the role of the following reactions is discussed: 1. cleavage of 0-ether linkage presumably via oxirane intermediate 2. a, 0-dehydration 3. cleavage of Cß-Cy bond presumably via oxetane intermediate 4. formation of -0Condensed Structures and 5. cleavage of C^-C^ bond. In the phenolic series, thermal transformations of hypothetical oxirane intermediate are the most representative reaction. In the non-phenolic series, thermal stability is considerably increased, and a, ßdehydration and Cß-Cy cleavage become the most characteristic feature of the thermolysis.

Loss of internal 1 → 6 substituted monosaccharide residues from underivatized and Per-O-methylated trisaccharides

The fragmentation behavior of [M + H]+ ions of a series of underivatized and per-O-methylated trisaccharides having 1 → 6 linked residues, of which one or two is a deoxy-fluoro or deoxy residue and thus has a unique mass, has been studied by using collision-induced dissociation fast-atom bombardment mass spectrometry. In addition to the usual fragment ions resulting from glycosidic bond cleavage, fragment ions were observed which must have been generated following an unusual rearrangement process which can be rationalized in terms of the loss of an internal monosaccharide residue.

Mass spectrometry of uronic acid derivatives Part IV. The fragmentation of methyl ester methyl glycosides of methylated aldotriouronic acids

Abstract The mass spectra of methyl ester methyl glycosides of methylated uronic acids, methyl ester methyl glycosides of methylated aldobiouronic acids of different types, and of methyl ester methyl glycosides of acetylated aldobiouronic acids having 4- O -methyl- d -glucuronic acid as the acidic component were obtained. Fragmentation patterns of these compounds, characteristic features of their mass spectra, and their importance for analytical applications are discussed.

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.

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.

The stepwise synthesis of an aldopentaouronic acid derivative related to branched (4-O-methylglucurono)xylans

Abstract Benzylation of methyl 2,3-anhydro-4- O -[2- O -benzyl-3,4-di- O -(β- D -xylop yranosyl]-β- D -xylopyranosyl]-β- D -ribopyranoside ( 1 ) afforded the crystalline. fully benzylated tetrasaccharide derivative 2 . The octa- O -benzyl derivative 3 , having only HO-2 unsubstituted, obtained by treatment of 2 with benzyl alcoholate anion in benzyl alcohol, was allowed to react in dichloromethane with methyl 2,3-di- O -benzyl- 1-chloro-1-deoxy-4- O -methy]-α,β-glucopyranuronate in the presence of silver perchlorate and triethylamine to give the branched, 4- O -methyl-α- D -glucuronic acid-containing pentasaccharide derivative 4a as the major product. Subsequent debenzylation afforded the aldopentaouronic acid derivative 5a , which contains all the basic structural features of branched, hardwood (4- O -methylglucurono)xylans. The structure of 5a was confirmed by analysis of its 13 C-n.m.r. spectrum and the mass-spectral fragmentation pattern of the corresponding fully methylated derivative 6a .

Structural analysis by mass spectrometry of oligosaccharides related to xylans

Abstract Fully methylated, xylan-type oligosaccharides, namely, positionally and inter-glycosidically isomeric O - D -xylopyranosyl-β- D -xylopyranoses (xylobioses, 2–7 ), a complete series of O -β- D -xylopyranosyl(l →4)- O -β- D -xylopyranosyl-β- D -xylopyranoses (xylotrioses, 8 , 9 , 11 , 12 , and 14 ), a branched β- D -xylotetraose ( 15 ), and α- D -xylopyranosyl β- D -xylopyranoside ( 1 ), have been studied by 70- and 12-eV mass spectrometry. By using high-resolution techniques metastable-transition measurements, ion species formed through hitherto unknown fragmentation-processes have been found for the (1→1)- and (1→3)-linked disaccharides 1 , 4 , and 5 . Based on the qualitative and quantitative differences in the fragmentations, criteria for unambiguous determination of the positional mode of linkage in xylobioses are proposed. Similarly, by studying the fragmentation of xylotriose ( 10 ) labelled in the side-chain with tri-deuteriomethyl groups, the fragmentation-pathways for xylotrioses have been clarified. A new fragmentation series has been discovered in the fission of trioses 13 and 14 having a D -xylopyranosyl group attached to O-3 of the nonreducing end of the basic (1→4)-linked skeleton. Within the series of di- and tri-saccharides studied, the criteria proposed permit reliable determination of any of the theoretically possible branching points. The basic possibilities for structural analysis by mass spectrometry of related pentose tetraoses are also shown.

Identification of methyl O-methyl-D-xylofuranosides by mass spectrometry

Abstract The fragmentation of methyl O -methyl- D -xylofuranosides under conditions of electron-impact mass spectrometry has been studied and compared with that of fully methylated methyl pentofuranosides. Characteristic differences in fragmentation of the differently substituted methyl O -methyl- D -xylofuranosides have been found which permit unambiguous assignment of both the number and the location of the methyl groups. Thus, compounds in this series can be identified without derivatization prior to the analysis. The g.l.c.-m.s. technique can be conveniently used to identify the products of methanolysis of methylated polysaccharides.

1,3-Thiazino[6,5-b]indol-4-one derivatives. The first synthesis of indole phytoalexin cyclobrassinon

Abstract The first synthesis of indole phytoalexin cyclobrassinon in six steps, in 12% overall yield and some of its analogues, possessing a 1,3-thiazino[6,5- b ]indol-4-one tricyclic ring system was performed, starting from 2-chloroindole-3-carboxaldehyde and employing the intramolecular Et 3 N-mediated nucleophilic substitution of a chlorine atom in the 2-position of an indole ring with sulfur as a key step.