Melanin-concentrating hormone analogs

1. An optionally substituted peptide having the structure:

wherein X 6 is an optionally present amino acid that, if present, is either arginine or des-amino-arginine;

X 7 is cysteine;

X 8 is either methionine, alanine, or norleucine;

X 9 is either leucine or alanine;

X 10 is either glycine, alanine, leucine, norleucine, serine, sarcosine, gamma-aminobutyric acid, D-leucine, D-alanine, D-norleucine, D-asparagine, D-serine, β-alanine, phenylglycine, D-2-cyclohexyl-alanine, or D-phenylalanine;

X 11 is either arginine, alanine, N-methyl-arginine, homoarginine, citrulline, norleucine, or flitroarginine;

X 12 is valine or alanine;

X 13 is either phenylalanine, tyrosine, D-(p-benzoylpbenylalanine), (1′)- and (2′)-naphthylalanine, cyclohexylalanine, or mono and multi-substituted phenylalanine wherein each substituent is independently selected from the group consisting of O-alkyl, alkyl, OH, NO 2 , NH 2 , F, I, and Br;

X 14 is arginine;

X 15 is alanine, proline or sarcosine;

X 16 is either cysteine or D-cysteine;

X 17 is an optionally present amino acid that, if present, is either tryptophan or tyrosine,

Z 1 is an optionally present protecting group that, if present, is covalently joined to the N-terminal amino group;

Z 2 is an optionally present protecting group that, if present, is covalently joined to the C-terminal carboxy group;

or a labeled derivative of said peptide wherein said label is a detectable label selected from the group consisting of luminescent, enzymatic and radioactive;

or a pharmaceutically acceptable salt of said peptide or of said labeled derivative;

provided that one or more of the following groups are present:

X 6 is des-amino-arginine;

X 10 is either D-alanine, D-leucine, D-asparagine, D-norleucine, D-serine, β-alanine, phenylglycine, D-2-cyclohexyl-alanine, or D-phenylalanine, and

X 11 is nitroarginine, citrulline, norleucine, or homoarginine.

2. The peptide of claim 1 , wherein one or more of the following groups are present:

X 10 is either D-alanine, D-leucine, D-asparagine, D-norleucine, D-serine, β-alanine, phenylglycine, D-2-cyclohexyl-alanine, or D-phenylalanine, and

X 11 is nitroarginine, citrulline, norleucine, or homoarginine.

3. The peptide of claim 1 , wherein X 17 is not present.

4. The peptide of claim 3 , wherein

X 6 is arginine;

X 8 is methionine;

X 9 is leucine;

X 12 is valine;

X 13 is either phenylalanine, (2′)napthylalanine, p-fluoro-phenylalanine, or cyclohexylalanine; and

X 15 is proline or sarcosine.

5. The peptide of claim 4 , wherein X 10 is either D-alanine, D-serine or D-asparagine.

6. The peptide of claim 3 , wherein X 6 is an optionally present amino acid that, if present, is arginine, Z 1 is —C(O)CH 3 and Z 2 is —NH 2 .

7. The peptide of claim 4 , wherein Z 1 is —C(O)CH 3 and Z 2 is —NH 2 .

8. The peptide of claim 5 , wherein Z 1 is —C(O)CH 3 and Z 2 is —NH 2 .

9. The peptide of claim 1 , wherein said peptide is either SEQ ID 12, 13, 15, 16, 17, 18, 19, 20, 25, 26, 34, 35, or 36.

10. The peptide of claim 1 , wherein said peptide is either SEQ ID NO: 13, 18, 19, 35 or 36.

11. The peptide of claim 1 , wherein said peptide is SEQ ID NO: 36.

12. The peptide of claim 1 , wherein said peptide is not labeled.

13. The peptide of claim 1 , wherein said labeled derivative said peptide, is said peptide containing either a luminescent, enzymatic or radioactive label.

14. The peptide of claim 1 , wherein a radiolabel is present.

15. The peptide of claim 4 , wherein said peptide is flat labeled.

16. The peptide of claim 4 , wherein said labeled derivative of said peptide, is said peptide containing either a luminescent, enzymatic or radioactive label.

17. The peptide of claim 4 , wherein a radiolabel is present.

18. The peptide of claim 5 , wherein said peptide is not labeled.

19. The peptide of claim 5 , wherein said labeled derivative of said peptide, is said peptide containing either a luminescent, enzymatic or radioactive label.

20. The peptide of claim 5 , wherein a radiolabel is present.