A compound of the formula R--CH.sub.2 --O--W and its pharmaceutically acceptable salts wherein R is a purine, a substituted purine, a pyrimidine or a substituted pyrimidine, wherein the substituents on the purine or pyrimidine are selected from amino, hydroxyl, halogen, thiol or alkylthiol wherein the alkyl moiety of the alkylthiol has 1 to 6 carbon atoms; and W is ##STR1## The compounds have antiviral activity.