Relationship between conformation and antiviral activity - IV. 5- Ethyl- 2'-deoxyuridin and 5-ethyl-2'-deoxycytidine

5-Ethyl-2'-deoxyuridine (EtdUrd), though a potent inhibitor of herpes simplex virus (HSV) replication, is rapidly catabolized to produce an inactive pyrimidine base by thymidine and/or uridine phosphorylases. 5- Ethyl-2'-deoxycytidine (EtdCyd) was synthesized to confer metabolic stability and thus improve efficacy against systemic HSV infections. EtdCyd was inactive against HSV in the presence or absence of deaminase inhibitors in VERO cells up to 2 mM. The relationship between molecular conformation and antiherpes activity for EtdUrd and EtdCyd is discussed.