Rudolf Toman

Polysaccharides from the roots of the marsh mallow (Althaea officinalis L.): Structure of an arabinan

Abstract A water-soluble l -arabinan isolated from the mucous material of the roots of the marsh mallow ( Althaea officinalis L.) has a highly branched structure of ∼90 α- l -arabinofuranosyl residues variously linked by (1→5), (1→3), and (1→2) bonds. Some of the l -arabinosyl groups are involved in branches through O-2, O-3, and O-5. There was good agreement between the results obtained by chemical and 13 C-n.m.r.-spectroscopic methods. The polymer has essentially the same structural features as those found for l -arabinans isolated from other plant sources.

Regioselective enhancement of the nucleophilicity of the hydroxyl groups in methyl α-l-rhamnopyranoside by complexation with tin(II) chloride

Abstract A tentative mechanism for complexation, and a possible model of a tin(II)chloride—methyl glycoside intermediate complex, have been established largely from analysis of methyl ethers formed on methylation of methyl α- l -rhamnopyranoside and its monomethyl ethers by diazomethane in the presence of a catalytic amount of tin(II) chloride in selected solvents. The complex is mainly formed through displacement of molecules of the donor solvent coordinated to a tin(II) atom by the favorably cis -disposed, hydroxyl groups of the sugar moiety. The spatial arrangement of the hydroxyl groups plus the distribution of atomic charges at the individual oxygen atoms of hydroxyl groups of the methyl glycoside were found to be the main factors responsible for the selectivity observed. The effect of selected solvents on the stability and/or ability to participate in the formation of the foregoing intermediate complex could not be satisfactorily clarified.

Mass spectrometry of the positionally isomeric, monobenzyl ethers of methyl glycopyranosides

Abstract The electron-impact, mass-spectrometric behavior of all theoretically possible, positionally isomeric monobenzyl ethers of methyl pento-, hexo-, and 6-deoxy-hexo-pyranosides is described, on the basis of 70- and 12-eV mass spectra. O-deuterium-labeling experiments, elemental composition, and metastable-transition measurements. The semiempirical MNDO quantum-chemical method was used for calculation of both the geometrical parameters (bond lengths, bond angles, and dihedral angles) and the distribution of net charges in the cyclic and acyclic forms of the abundant [C4H7O3]+ and [C5H9O4]+ ions. The results obtained show that the cyclic structures of both ions are the more stable. Differences in the fragmentation of the compounds studied have been applied for establishing criteria that permit simple and unambiguous localization of the benzyl group in monobenzyl ethers of methyl glycopyranosides.