Ring-Opening Polymerization of a 1,4-Anhydro Xylose Derivative Having an Azido Group and Synthesis of Stereoregular 3-Amino-3-deoxy-(1→5)-α- d -xylofuranan

A new 1,4-anhydro pentose monomer having an azido group, 1,4-anhydro-3-azido-2- O -benzyl-3-deoxy-α- d -xylopyranose (A3ABX), was synthesized by benzylation of 1,4-anhydro-α- d -ribopyranose at the C2 hydroxyl group and subsequent trifluoromethylsulfonylation at the C3 hydroxyl group, followed by S N 2 replacement of the trifluoromethylsulfonyl group with the azido group with lithium azide. Ring-opening polymerization of A3ABX was attempted with Lewis acid catalysts such as boron trifluoride etherate, phosphorus pentafluoride, and antimony pentachloride at different temperatures between −60 and −20 °C. Boron trifluoride etherate catalyst gave a polymer with a positive specific rotation and with a single C1 absorption at 99 ppm in the 13 C NMR spectrum, indicating that the resulting polymer had a stereoregular 1,5-α furanosidic structure. When the polymerization was carried out by antimony pentachloride at −60 °C, the polymer obtained had a negative specific rotation and the C1 absorption shifted downfield to around 107 ppm, suggesting that the polymer might be composed of a 1,5-β furanosidic unit. Reduction of the azido group to an amino group and the benzyl group to a hydroxyl group gave 3-amino-3-deoxy-(1→5)-α- d -xylofuranan. The structural analysis of the polysaccharides was performed by means of high-resolution 1 H and 13 C NMR spectroscopies including the two-dimensional spectra of H−H COSY, NOESY, and FGHMQC.