Factor B-IN-8 (Compound (3R,4R)-15) is a potent, selective, and orally active inhibitor of Factor B, demonstrating an IC50 value of 10.2 nM. It effectively blocks the interaction between Factor B and C3b, thus preventing the formation of the C3 convertase (C3bBb). Additionally, Factor B-IN-8 hinders the deposition of the membrane attack complex (MAC) along the alternative pathway with an IC50 of 59.3 nM. This compound reduces the cleavage of Factor B protein and lessens the deposition of complement C3d in the glomeruli and renal tubules. Factor B-IN-8 is applicable in the research of arthritis and paroxysmal nocturnal hemoglobinuria (PNH).