The invention relates to peptides with general formula (I), X1CTX2X3X4CX5 (I) where X1 is: M, F, V, A, I, and X2 is: R, K, and X3 is: K, R, L, A and X4 is: L, G, M, A, W, Y, and X5 is: W, Y, L, M, N, E, G; and their pharmaceutically acceptable salts, esters and prodrugs. The invention also relates to pharmaceutical preparations and kits containing them, and to screening and isolation procedures containing them, and to their use in the production of pharmaceutical preparations.