FD-IN-1 (Compound 12) is an orally bioavailable and selective?factor D?(FD) inhibitor with an?IC50?of 12 nM. Complement FD, a highly specific S1 serine protease, plays a central role in the alternative complement pathway of the innate immune system. FD-IN-1 also inhibits factor XIa (FXIa) and Tryptase β2 with IC50s of 7.7 and 6.5 μM, respectively