Abstract: A compound of formula (I): ##STR1## In which: R.sub.1 represents linear or branched (C.sub.1 -C.sub.6) alkyl,X represents oxygen or sulfur,R.sub.2 represents optionally substituted alkyl, alkoxy, optionally substituted phenyl, optionally substituted cycloalkyl, 4-(2,3-dithiacyclopent-1-yl)butyl, pyridyl or optionally substituted amino or any one of the groups as defined in the description,R.sub.3 represents hydrogen or cycloalkyl, formyl, optionally substituted phenyl, pyridyl or optionally substituted alkyl,the isomers thereof, the addition salts thereof with a pharmaceutically acceptable acid or base, and medicinal compounds containing them are useful for the treatment of chronic or cellular ischemia.