Compound of formula (I): ##STR00001## wherein: R.sub.1 represents aryl, heteroaryl or alkyl which is optionally substituted, or a group of formula --(CO)--CR.sub.6R.sub.7NR.sub.8R.sub.9 wherein R.sub.6, R.sub.7, R.sub.8 and R.sub.9 are as defined in the description, R.sub.2 represents hydrogen or alkyl, R.sub.3 represents hydrogen or optionally substituted alkyl, R.sub.4 represents a saturated or unsaturated, 7- to 15-membered bicyclic system or optionally substituted alkyl, or R.sub.3 and R.sub.4, together with the carbon atom carrying them, form a saturated or unsaturated, 3- to 18-membered, mono-, bi- or tri-cyclic system optionally containing one or more hetero atoms selected from O, S and N and optionally substituted, n represents 1 or 2, Ar represents aryl or heteroaryl, R.sub.5 represents amino, guanidino, cyano or amidino which is optionally substituted, its optical isomers, and also addition salts thereof with a pharmaceutically acceptable acid. Medicinal products containing the same which are useful in pathological conditions involving activated protein C.