Peptide compositions

An isolated polypeptide of the following structural Formula (I):

• or a pharmaceutically acceptable salt thereof,
• wherein:
• R1 is —H, or a C1-C6 acyl;
• R2 is —NR3R4, or —OR5 wherein R3, R4, and R5 are each independently is-H or a C1-C6 alkyl;
• A1 Nle;
• A2 and A8 is each independently an amino acid residue selected from Cys, hCys, Glu, or Dpr, wherein A2 and A8 are pairwise selected so as to be able to form a covalent bond between their respective side chains;
• A3 is an amino acid residue selected from Ala, Tle, Val, Leu, Ile, Cha, Pro, Ser, Thr, Lys, Arg, His, Phe, Gln, Sar, Gly, Asn, Aib, or
• A3 is absent, or
• A3 is residue Y, wherein Y is an amino acid selected from amino acids represented by the following structural formulas
• wherein:
• R11 and R12, each independently, is H, —CH3, phenyl, or benzyl;
• R21, R22, R23, and R24, each independently is H, —CH3, —CF3, phenyl, benzyl, F, Cl, Br, I, —OCH3, or —OH;
• R31, R32, R33, R34, R41, R42, and R43, each independently is H, —CH3, —CF3, phenyl, benzyl, F, Cl, Br, I, —OCH3, or —OH;
• A4 is absent or an optionally substituted His;
• A5 is an optionally substituted Phe
• A6 is Arg;
• and
• A7 is Trp,
• wherein any amino acid residue is either in L- or in D-configuration.