Synthesis of 3-amino-ribofuranans having 1,5-alpha and -beta structures by selective ring-opening polymerization of a 1,4-anhydro-3-azido-3-deoxy-alpha-D-ribopyranose derivative

Ring-opening polymerization of a new anhydro ribose-type monomer, 1,4-anhydro-3-azido-3-deoxy-2-O-tert-butyldimethylsilyl-alpha-D-ribopyranose (A3ASR), was investigated. The monomer was synthesized from 1,4-anhyro-alpha-D-xylopyranose by three steps comprising Walden inversion at the C3 position into ribose configuration. Ring-opening polymerization of A3ASR by Lewis acid catalysts such as boron trifluoride etherate and stannic chloride gave a stereoregular 3-azido-3-deoxy-2-O-tert-butyldimethylsilyl-(1-->5)-alpha-D-ribofuranan having specific rotations of +246 similar to +271 deg . dm(-1) . g(-1) . cm(3) and number-average molecular weights of 18,7 x 10(3) similar to 25,1 x 10(3). When the polymerization was carried out by antimony pentachloride at 0 degrees C, the resulting polymer exhibited a negative specific rotation of -6 deg . dm(-1) . g(-1) . cm(3) and the C1 absorption in the C-13 NMR spectrum shifted downfield to 107,5 ppm, suggesting that the polymer might consist of 1,5-beta furanosidic unit. The reduction of the azido group of the 1,5-alpha and 1,5-beta furanosidic polymers into amino group and subsequent desilylation gave 3-amino-3-deoxy-(1-->5)-alpha- and -beta-D-ribofuranans, respectively. In addition, copolymerization of A3ASR with 1,4-anhydro-2,3-di-O-tert-butyldimethyls-alpha-D-ribopyranose (ADSR) in various feeds was performed by boron trifluoride etherate as catalyst to give copolymers with different monomeric components. The structural analysis of the homopolymers and copolymers was examined by means of H-1 and C-13 NMR spectroscopies, IR spectroscopy, and optical rotation.