Compounds of the formula: ##STR1## wherein R.sup.1 is alkoxycarbonyl, aralkoxycarbonyl, alkanoyl, aralkanoyl, heterocyclylcarbonyl or a group of the formula: ##STR2## R.sup.2 is alkyl, cycloalkylalkyl or aralkyl; R.sup.3 is hydrogen and R.sup.4 is hydroxy or R.sup.3 and R.sup.4 together are oxo; R.sup.5 is alkoxycarbonyl or alkylcarbamoyl; R.sup.6 and R.sup.7 together are trimethylene or tetramethylene optionally substituted by alkyl or on adjacent carbon atoms by tetramethylene; R.sup.8 is alkoxycarbonyl, aralkoxycarbonyl, alkanoyl, aroyl, aralkanoyl or heterocyclylcarbonyl; and R.sup.9 is alkyl, cycloalkyl, cycloalkylalkyl, aralkyl, cyanoalkyl, carbamoyl-alkyl, alkylthioalkyl, alkoxyalkyl or alkoxycarbonylalkyl: and pharmaceutically acceptable acid addition salts of those compounds of formula I which are basic, inhibit aspartyl proteases of viral origin and can be used in the form of medicaments for the prophylaxis or treatment of viral infections. They can be manufactured according to generally known methods.