A77 1726 physiologically active metabolite of the immunosuppressive drug leflunomide (Cat. No.1972-10, 50). A77 1726 Inhibits the activity of dihydroorotate dehydrogenase and of protein tyrosine kinases. A77 1726 Blocks TNF-mediated NF-κB activation in a dose- and time-dependent manner. A77 1726 Also inhibits the activity of COX-2 in vitro and in vivo.