5-benzothiazepine skeleton were synthesized and their vasodilating, antihypertensive, and plateletaggregation-inhibitoryactivities were investigated. (-)-cis-3-Acetoxy-5-[2-(di-methylamino) ethyl]-2,3-dihydro-8-methyl-2-(4-methylphenyl)-1,5-benzothiazepin- 4(5H)-one ((-)-13e) was selected for further studies as a potent inhibitor of platelet aggregation.