Compounds of formula (I) and pharmaceutically acceptable salts thereof: ##STR1## wherein R.sub.1 is hydroxy, amino, chloro or OR.sub.7 wherein R.sub.7 is C.sub.1-6 alkyl, phenyl or phenyl C.sub.1-2 alkyl either of which phenyl moieties may be substituted by one or two substituents selected from halo, C.sub.1-4 alkyl or C.sub.1-4 alkoxy; R.sub.2 amino or, when R.sub.1 is hydroxy or amino, R.sub.2 may also be hydrogen; X is --CH.sub.2 CH.sub.2 -- or a moiety of structure (a), (b) or (c): ##STR2## wherein n is 1 or 2; m is 0, 1 or 2; and R.sub.3 is hydrogen or acyl; R.sub.4 is a group of formula: ##STR3## wherein R.sub.5 and R.sub.6 are independently selected from hydrogen, C.sub.1-6 alkyl and optionally substituted phenyl; having antiviral activity, processes for their preparation and their use as pharmaceuticals.