Ring-opening polymerization of a 1,4-anhydro xylose derivative having an azido group and synthesis of stereoregular 3-amino-3-deoxy-(1->5)-alpha-D-xylofuranan

A new 1,4-anhydro pentose monomer having an azido group, 1,4-anhydro-3-azido-2-O-benzyl-3-deoxy-alpha-D-xylopyranose (A3ABX), was synthesized by benzylation of 1,4-anhydro-alpha-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 degrees C. Boron trifluoride etherate catalyst gave a polymer with a positive specific rotation and with a single C1 absorption at 99 ppm in the C-13 NMR spectrum, indicating that the resulting polymer had a stereoregular 1,5-alpha furanosidic structure. When the polymerization was carried out by antimony pentachloride at -60 degrees 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-beta 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)-alpha-D-xylofuranan. The structural analysis of the polysaccharides was performed by means of high-resolution H-1 and C-13 NMR spectroscopies including the two-dimensional spectra of H-H COSY, NOESY, and FGHMQC.