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Conformational effects due to stereochemistry and C3-substituents in xylopyranoside derivatives as studied by NMR spectroscopy

In English

Författare

Summary, in English

Glycosaminoglycans contain a beta-D-xylopyranose residue at its reducing end, which links the polysaccharide to the protein in proteoglycans. 2-Naphthyl beta-D-xylopyranosides have shown inhibition of tumor growth and we herein investigate conformation and dynamics of compounds structurally and stereochemically modified at the C3 position as well as the influence of solvent. The 3-deoxygenated compound, the 3-C-methyl-substituted beta-D-xylopyranoside, beta-D-ribopyranoside, the 3-C-methyl-substituted beta-D-ribopyranoside as well as 2-naphthyl beta-D-xylopyranoside were analyzed by NMR spectroscopy. Conformational equilibria were dependent on the solvent of choice, either methanol-d(4) or chloroform-d, with mainly C-4(1) and C-1(4) conformations present but also skew conformations to some extent. Intramolecular hydrogen bonding was concluded to be important for the 3-C-methyl-substituted beta-D-xylopyranosides in the non-polar solvent. Dynamic NMR (DNMR) spectroscopy was carried out for the 3-deoxygenated compound, which at 25 degrees C in methanol-d(4) exists with equally populated states of the C-4(1) and the C-1(4) conformations, but at -100 degrees C only a few percent is present of the latter. Using C-13 NMR detection for DNMR, resonance lines were shown to broaden at -40 degrees C and to sharpen again below -90 degrees C, without the emergence of a second set of NMR resonances, a typical behavior for an unequally populated equilibrium. The enthalpy and entropy activation barriers were calculated and resulted in Delta H-double dagger = 47.3 kJ mol(-1) and Delta S-double dagger = 54 J mol(-1) K-1.

Publiceringsår

2014

Språk

Engelska

Sidor

8031-8035

Publikation/Tidskrift/Serie

Organic and Biomolecular Chemistry

Volym

12

Issue

40

Dokumenttyp

Artikel i tidskrift

Förlag

Royal Society of Chemistry

Ämne

  • Chemical Sciences

Status

Published

ISBN/ISSN/Övrigt

  • ISSN: 1477-0539