Keywords: Dihydroorotate dehydrogenase (DHODH) inhibitors; X-ray-crystallography; Autoimmune diseases; Leflunomide; Brequinar; Bioisosterism; human dihydroorotate dehydrogenase; (hDHODH); l-dihydroorotate; (DHO); orotate; (ORO); reduced flavin mononucleotide; (FMNH