[Constitution] A tricyclic heterocyclic compound represented by general formula (I) wherein R¹ and R² represent each hydrogen, lower alkyl, lower alkoxy, halogen or halogenated lower alkyl; R³ represents hydrogen or lower alkyl; R⁴ represents substituted phenyl or naphthyl; R⁵ represents hydrogen or lower alkyl; A represents lower alkylene; B represents -O- or -S-; and n represents 0 or 1. [Effect] It is excellent in the inhibition of acyl-CoA-cholesterol acyltransferase (ACAT) and is useful for treating or preventing arteriosclerosis.
Constitution Tricyclic heterocyclyl compounds having a general formula (I): ##STR1## wherein: R.sup.1 and R.sup.2 each represents H, a lower alkyl or lower alkoxy group, a halogen atom or halogeno-lower alkyl; R.sup.3 represents H or a lower alkyl group; R.sup.4 represents a substituted phenyl or naphthyl group; R.sub.5 represents H or a lower alkyl group; A represents a lower alkylene group; B represents an --O-- or --S-- group; and n is 0-1. Effect The compounds have an excellent activity in the inhibition of acyl-CoA: cholesterol acyltransferase (ACAT) and are useful for the treatment and prophylaxis of atherosclerosis.