Melanocortin receptor-specific peptides

A cyclic peptide of Formula (I):

• or a pharmaceutically acceptable salt thereof,
• wherein:
• R1 is —NH—C(═O)— or —C(═O)—NH—;
• R2 is —H or —CH2—, wherein if R2 is —CH2—, then R2 forms with R3 a pyrrolidine ring, wherein the pyrrolidine ring is optionally substituted with —OH;
• R3 is —(CH2)2— if R2 is —CH2—, and otherwise R3 is selected from the group consisting of:
• —(CH2)1-4NH2, CH3, —CH(CH3)2, —C(CH3)3, —CH2OH, —CH(OH)CH3, —(CH2)1-2CONH2, —CH2(imidazole), —(CH2)1-2CO2H, —CH2OBz, —CH(CH3)OBz, —CH2Ph(CONH2), —(CH2)2NHCOCH3, —(CH2)3NHC(═NH)NH2 and —(CH2)2SO2CH3;
• R4a, R4b and R4c are each independently selected from the group consisting of:
• —H, —Cl, —F, —CN, —OH, —CF3, —CH3, —OCH3, —NO2, -Ph and —NH2, with the provisos that at least one of R4a, R4b and R4c is not hydrogen and that R4a, R4b and R4c cannot all be —Cl, —CH3 or —OCH3
• R5 is —OH or —N(R6a)(R6b);
• R6a and R6b are each H;
• x is 1 to 4;
• and
• y is 1 to 4.