The synthesis of emimycin, 5-substituted emimycin analogues and the corresponding ribo- and 2'-deoxyribonucleoside derivatives is described. Emimycin, its 5-substituted congeners and the ribonucleoside derivatives are completely devoid of antiviral activity against RNA viruses. In contrast, some of the 2'-deoxyribosyl emimycin derivatives are potent inhibitors of the replication of herpes simplex virus-1 and varicella-zoster virus, lacking cytotoxicity.