Abstract: Use of a compound of the formula wherein Base is thymine, Cytosine, adenine or guanine, or a physiologically acceptable salt thereof, for therapeutic or prophylactic control or treatment of retrovirus infections, including HIV, and hepatitis B virus infections and to a method for such treatment, especially for AIDS.

Abstract: Antivirally active compounds of formula (I), wherein R.sup.1 is hydrogen, hydroxy, mercapto or amino; R.sup.2 is hydrogen, hydroxy, fluoro, chloro or amino; R.sup.3 and R.sup.4 are independently selected from (II), (III), amino, hydroxy or an ether or ester residue thereof, or R.sup.3 together with R.sup.4 is (IV), wherein M is hydrogen or a pharmaceutically acceptable counterion; and n is 1 or 2; with the proviso that, when R.sup.2 is amino and R.sup.3 and R.sup.4 are hydroxy, R.sup.1 is not hydroxy and in addition, when n=1, R.sup.1 is not hydrogen, and pharmaceutically acceptable salts thereof; processes for preparation of said compounds, a pharmaceutical composition comprising said compounds, methods for treatments of virus infections as well as use of compounds of formula (I) without the proviso for the manufacture of a medicament for treatment of AIDS.