EQUILIBRIA OF THE ANOMERIC AND RING FORMS OF AMMONIUM 3-DEOXY-D-MANNO-OCTULOSONATE IN DEUTERIUM-OXIDE

The tautomeric composition of a solution of ammonium 3-deoxy-d-manno-octulosonate (KDO, 1a) in D2O at 28° was assessed by means of 13 C-F.t.-n.m.r. spectroscopy. The results revealed the presence of 6̃0 and 11 % of the α and β anomers of the pyranose, and 20 and 9 % of the two furanoses, and suggested, but did not unequivocally prove, that the major furanose form is the α anomer. To facilitate interpretation of the spectral results for 1, ammonium 3,5-dideoxy-d-arabino(or ribo)-octulosonate (3a) was prepared by the reaction of 5-deoxy-d-erythro-pentose with sodium oxalacetate at pH 11. A chromatographically homogeneous, noncrystalline sample of 3 was obtained by lyophilization, and characterized as its (4-nitrophenyl)hydrazone (m.p. 162-163°). The 13C-n.m.r. spectrum of a solution of 3a in D2O revealed it to be substantially all in the α-pyranose form. No signals were obtained for the possible 1,4-lactone of 3. As the 1,5-lactone and furanose forms are impossible for 3, it exhibited no signals analogous to those attributed to furanoid 1. On the basis of these results for 3, the two lactone forms of 1 were excluded from consideration, and the three pairs of 13C-n.m.r. signals observed at ≈45, 86, and 104 p.p.m. were assigned to the furanose forms of 1. © 1979.