PCSK9-IN-15 (compound 5) is a potent inhibitor of proprotein convertase subtilisin/kexin 9 ( PCSK9 , K D <200 nM). PCSK9 is involved in cholesterol metabolism and regulates levels of low-density lipoprotein cholesterol (LDL-C) in the blood. PCSK9- in -15 can be used to study cholesterol-lowering and dyslipidemia.