Conformational features of acyclonucleosides: structure of acyclovir, an antiherpes agent

Abstract

Crystals of acyclovir belong to the space group P21/n, and the cell dimensions are a = 25.459(1), b = 11.282 (1), c = 10.768(1) Å, β = 95.16(1)°. Intensity data were measured on a diffractometer and the structure was determined by direct methods. The asymmetric unit was found to contain three independent molecules of acyclovir and two molecules of water. Least-squares refinement, which included all hydrogen atoms, converged at R = 0.053 for 3970 observed reflections. In two of the molecules the side chain is partially folded, while in the third one it is fully extended. The glycosidic torsion angles are in the range 91.4–104.3°. The conformational features are compared with those in other known acyclonucleosides. They are also examined in relation to the behavior of acyclonucleosides and acyclonucleotides in various enzymatic systems, including those related to antiviral activities.