d-Penturonic acids: solution studies of stable-isotopically enriched compounds by 1H- and 13C-n.m.r. spectroscopy
作者:Jian Wu、Anthony S. Serianni
DOI:10.1016/0008-6215(91)80112-z
日期:1991.3
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-C-13-Substituted D-aldopentoses were used to prepare D-(1-C-13)penturonic acids. Aqueous solutions of the 1-C-13-substituted penturonic acids, studied over a range of pH values by C-13-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 H-1 and C-13 chemical shifts, and H-1-H-1, C-13-H-1, and C-13-C-13 spin-coupling constants, were determined by H-1-(300, 500, and 620 MHz) and C-13-(75 MHz) n.m.r. spectroscopy with the aid of 2-D C-13-H-1 chemical shift correlation maps, 2-D H-1-H-1 COSY data, and C-13 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.