A guanine derivative with an acyclic side chain, 2-hydroxyethoxymethyl, at position 9 has potent antiviral activity [dose for 50% inhibition (ED(50)) = 0.1 muM] against herpes simplex virus type 1. This acyclic nucleoside analog, termed acycloguanosine, is converted to a monophosphate by a virus-specified pyrimidine deoxynucleoside (thymidine) kinase and is subsequently converted to acycloguano...