compounds useful in treating hypercholesterolemia and atherosclerosis having the formula ## str1 ## wherein x is oxygen or sulfur , het is a monocyclic heterocyclic group having three hetero atoms selected from nitrogen , oxygen and sulfur , and r 1 , r 2 and r 3 are hydrogen , flourine , chlorine , bromine , a straight or branched alkyl group having from 1 to 6 carbon atoms , a straight or branched alkoxy group having from 1 to 6 carbon atoms , substituted or unsubstituted benzoyl , substituted or unsubstituted benzoyl , substituted or unsubstituted phenyl , amino or substituted amino or a carboxy group .