Viral infections selected from the group consisting of herpes simplex virus, varicella zoster virus, respiratory syncytial virus and cytomegalovirus can be treated by administering to the host a therapeutically effective amount of a compound of formula I or a pharmaceutically acceptable salt thereof; ##STR1##

wherein Y, Ra, and R1 are as defined herein. The compounds and salts can also be used to inhibit viral replication of these viruses in cells.