title: D-Penturonic acids: solution studies of stable-isotopically enriched compounds by 1H- and 13C-n.m.r. spectroscopy.
abstract: Methyl D-pentofuranosides were prepared by Fischer glycosidation of the aldopentoses D-arabinose, D-lyxose, D-ribose, D-xylose, and 2-deoxy-D-erythro-pentose, and oxidized with O2 over a platinum oxide catalyst to give the corresponding methyl D-pentofuranosiduronic acids. After purification by anion-exchange chromatography, these glycosides were hydrolyzed to give the corresponding D-penturonic acids [D-arabinuronic acid (1), D-lyxuronic acid (2), D-riburonic acid (3), D-xyluronic acid (4), and 2-deoxy-D-erythro-penturonic acid (5)] in 80% yield based on the starting pentofuranoside. 1-13C-Substituted D-aldopentoses were used to prepare D-(1-13C)penturonic acids. Aqueous solutions of the 1-13C-substituted penturonic acids, studied over a range of pH values by 13C-n.m.r. spectroscopy, were found to contain alpha- and beta-furanoses, acyclic aldehyde and hydrate, and/or hydrated 2,5-lactone. The ratio of D-riburonic acid anomers was most sensitive to solution pH (alpha/beta = 0.49 and 1.2 at pH 1.9 and 4.9, respectively). The values of the 1H and 13C chemical shifts, and 1H-1H. 13C-1H, and 13C-13C spin-coupling constants, were determined by 1H-(300, 500, and 620 MHz) and 13C-(75 MHz) n.m.r. spectroscopy with the aid of 2-D 13C-1H chemical shift correlation maps, 2-D 1H-1H COSY data, and 13C substitution, and were compared to those determined previously for structurally-related furanose rings. Isomerization of the penturonic acids at pH 5.0 and 50 degrees gave the corresponding 4-pentulosonic acids.
authors.affiliation: Department of Chemistry and Biochemistry, University of Notre Dame, Indiana 46556.
authors.forename: J A
authors.initials: JA
authors.lastname: Wu
authors.forename: A S
authors.initials: AS
authors.lastname: Serianni
mesh_terms: D002247:Carbon Isotopes; D002384:Catalysis; D006027:Glycosides / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D009682:Magnetic Resonance Spectroscopy; D010084:Oxidation-Reduction; D011522:Protons; D012996:Solutions; D013329:Structure-Activity Relationship; D014574:Uronic Acids / Q000737:chemistry*
chemical_list: D002247:Carbon Isotopes; D006027:Glycosides; D011522:Protons; D012996:Solutions; D014574:Uronic Acids