Pyridin-4-on-Nueleosid+: Stabilisierung der Struktur im Kristall und in wäßriger Lösung / Pyridine-4-on Nucleoside: Stabilisation of the Structure in the Crystal and in Aqueous Solution

Abstract

Abstract C10H13NO5 • H2O is monoclinic, space group P2i with a = 773.7 pm, b = 814.6 pm, c= 932.6 pm, β = 109.36° at 143 K, Z = 2. The crystal structure has been refined to R =0.031 with 1340 counter reflections. Features of this nucleoside include an orientation of the base at the glycosidic bond N(l)-C(l') in the anii-range (52.5°), a ribosyl moiety in the C(2')-endo(S) conformation and in contrast to many other nucleosides a trans arrange-ment at C(4')-C(5'). This unusual conformation is stabilized by a distinct H-bonding scheme including the water molecule and the oxygen of the adjacent pyridin-4-on ring system. NMR data indicate on the other side that in solution the conformation of the nucleoside is anti/g + similar to that of other pyrimidine nucleosides. The 5'-OH group replaces the water molecule in the crystal. The preferred anti position of the base cannot be explained by an interaction of H(2,6) of the base with the 5'-OH group or the C(4) oxygen. Both protons which couple with H(3,5) coalesce in a single sharp doublet. Water entropy seems to be the decisive factor for the stabilization of the anti/g+ conformation in aqueous solution.