The invention relates to compounds of the formula I ##STR00001## in which R1, R2, X, A, B and Y1 to Y4 have the meanings indicated in the claims, and/or a pharmaceutically acceptable salt and/or a prodrug thereof. Because of their properties as inhibitors of chemokine receptors, especially as CXCR2 inhibitors, the compounds of the formula I and the pharmaceutically acceptable salts and prodrugs thereof are suitable for the prevention and treatment of chemokine mediated diseases.