Anti-herpes simplex virus activity of substituted 1-hydroxyacridones

5-Chloro-1,3-dihydroxyacridone, 1, is a potent and selective inhibitor of Herpes Simplex Virus Type-1 (HSV-1).(1) Substituted 1,3-dihydroxyacridones represent a new class of nonnucleoside HSV-1 inhibitors, and biochemical studies indicate a novel mechanism of action for 1, although the target is not yet defined.(2) With the goal of lead optimization, analogues of 1 were synthesized in an effort to describe the structure-activity relationships between 1 and its hypothetical binding site. Modifications of key functional groups led to the identity of several features of I that were important for activity. In the process, a more expedient and reliable synthesis of 1 and its analogues was developed. Analogues were evaluated against HSV-1 and HSV-2 using a viral plaque-elimination assay for viral inhibition of HSV-1 and HSV-2, and effects on replication of the host cell were also measured in order to assess a therapeutic index (TI) of selectivity. Several new analogues with significant antiviral activity were identified, including 5-methoxy-1,3-dihydroxyacridone (11), which inhibits replication of several HSV-2 strains with a mean ED50 of 0.7 muM and a TI range of 25-60-fold.