Provided are compounds of the formula: ##STR00001## wherein R.sup.N1 is a substituent of formula G.sup.1--NX.sup.1X.sup.2, wherein G.sup.1 is an optionally further substituted alkylene, which optionally forms, together with R.sup.N2, a cyclic group, and each of X.sup.1 and X.sup.2 is independently H or an N-substituent, or X.sup.1 and X.sup.2 together form a heterocyclic ring, or X.sup.1 together with G.sup.1 forms a cyclic group and X.sup.2 is H or an N-substituent; and each of Z.sup.1, Z.sup.2, Z.sup.3 and Z.sup.4 is H or a substituent, or two of Z.sup.1, Z.sup.2, Z.sup.3 and Z.sup.4 together form an optionally substituted ring, and further wherein at least one of Z.sup.1, Z.sup.2, Z.sup.3 and Z.sup.4 is other than H, and salts thereof, pharmaceutical compositions and methods of using the compounds. The compounds have antiviral activity.