Ra Pharmaceuticals, Inc. is a United States-based clinical-stage biopharmaceutical company. The Company focuses on the development of therapeutics for diseases of complement dysregulation and a range of orphan indications. It utilizes small molecules and peptide approaches to address pathological targets in the complement cascade. It has leveraged the Extreme Diversity peptide chemistry platform to develop a portfolio of products that selectively inhibit the complement system and other immune targets. Its main program, RA101495, is a macrocyclic peptide inhibitor of complement component 5 (C5), which is in Phase I stage of development for the treatment of paroxysmal nocturnal hemoglobinuria (PNH). RA101495 binds a site on the C5 protein to inhibit cleavage into C5a and C5b, thereby preventing red blood cell lysis by inhibiting the production and assembly of the membrane attack complex (MAC). RA101495 is being developed as an alternative to eculizumab therapy for patients with PNH.