8-Chloroguanosine: solid-state and solution conformations and their biological implications

Publisher Website
Google Scholar
Abstract
The 3-dimensional structure of 8-chloroguanosine dihydrate was determined by X-ray crystallography. The crystals belong to the orthorhombic space group P21212, and the cell dimensions are a = 4.871 (1) .ANG., b = 12.040 (1) .ANG., and c = 24.506 (1) .ANG.. The structure was determined by direct methods, and least-squares refinement, which included all H atoms, converged at R = 0.031 for 1599 observed reflections. The conformation about the glycosidic bond is syn with .chi.CN = -131.1.degree.. The ribose ring has a C(2'')-endo/C-(1'')-exo (2T1) pucker, and the gauche+ conformation of the -CH2OH side chain is stabilized by an intramolecular O-(5'')-H .cntdot. .cntdot. .cntdot. N(3) H- bond. Conformational analysis by means of 1H NMR spectroscopy showed that, in dimethyl sulfoxide, the sugar ring exhibits a marked preference for the C(2'')-endo conformation (.apprx. 70%) and a conformation about the glycosidic bond predominantly syn (.apprx. 90%), hence similar to that in the solid state. However, the conformation of the exocyclic 5''-CH2OH group exhibits only a moderate preference for the gauche+ rotamer (.apprx. 40%), presumably due to the inability to form the intramolecular H- bond to N(3) in a polar medium. The conformational features are examined in relation to the behavior of 8-substituted purine nucleosides in several enzymatic systems, with due account taken of the steric bulk and electronegativities of the 8-substituents.

This publication has 23 references indexed in Scilit: