what is provided is epo mimetic peptide derivatives defined as formula and their pharmaceutical salts , the preparation thereof , wherein r 1 , r 2 , r 3 , r 4 , r 5 , n 1 , n 2 are defined as described in description . a composition comprising of an epo mimetic peptide derivative defined as formula and its pharmaceutical salt . the uses of the derivatives and their pharmaceutical salts , as well as the uses of the compositions described above in treatment of diseases characterized by a deficiency of epo or a low or defective red blood cell population . r 1 — r 2 — n1 — r 3 — n2 — r 4 — r 5