Here, we describethe discovery of compound 9 (GLPG3667), a reversibleand selective TYK2 adenosine triphosphate competitive inhibitor indevelopment for the treatment of inflammatory and autoimmune diseases.The preclinical pharmacokinetic profile was favorable, and TYK2 selectivitywas confirmed in peripheral blood mononuclear cells and whole bloodassays. Here, TYK2 is linked to autoimmune disease.