Peptide-based multimeric targeted contrast agents

1. A purified peptide comprising the amino acid sequence: P*-Y*-X 1 *-L* (SEQ ID NO:1), wherein:

P* is a proline or its non-natural derivative 4-hydroxyproline;

Y* is a tyrosine or its non-natural derivative substituted at the 3 position with a moiety selected from the group consisting of F, Cl, Br, I, and NO 2 ;

provided that at least one of said P* or Y* is said non-natural derivative of the respective amino acid;

X 1 * is G or a non-natural derivative of G selected from the group consisting of cyclohexylglycine, allylglycine, 2-indanylglycine, tert-butylglycine, N-(4-phenylbutyl)glycine, N-decylglycine, phenylglycine, propargylglycine, and the d isomer of glycine; or D or a non-natural derivative of D selected from the group consisting of β-connected aspartic acid (bD), N-methylaspartic acid, and the d isomer of aspartic acid; and

L* is a leucine or a non-natural derivative of leucine selected from the group consisting of N-methylleucine, Norleucine, tert-leucine, and the d isomer of leucine.

2. A purified peptide according to claim 1 , wherein X 1 * is G or D and wherein L* is leucine.

3. A purified peptide comprising the amino acid sequence:

X 1 -X 2 -C-P*-Y*-X 3 -L-C-X 4 -X 5 -X 6 (SEQ ID NO:2), wherein:

P* is a proline or its non-natural derivative 4-hydroxyproline;

Y* is a tyrosine or its non-natural derivative substituted at the 3 position with a moiety selected from the group consisting of F, Cl, Br, I, and NO 2 ;

provided that at least one of said P* or Y* is said non-natural derivative of the respective amino acid;

X 1 is selected from the group consisting of W, Y, F, S, Bip, Hx, Dpr, Cy, Gu, Ad, Hfe, 3-Pal, 4-Pal, DopaMe2, nTyr, dW, dF, F(3/4*), and Y(3*), wherein F(3/4*) is a phenylalanine substituted at either the 3 or the 4 position with a moiety selected from the group consisting of CH 3 , CF 3 , NH 2 , CH 2 NH 2 , CN, F, Cl, Br, I, Et, and OMe, and wherein Y(3*) is a tyrosine substituted at the 3 position with a moiety selected from the group consisting of F, Cl, Br, I, and NO 2 ;

X 2 is selected from the group consisting of E, H, dE, S, H(Bzl), 2-Pal, Dpr, and Th;

X 3 is selected from the group consisting of G and D;

X 4 is selected from the group consisting of H, F, Y, and W;

X 5 is selected from the group consisting of I, L, V, N, Bpa, Bal, Hfe, Nle, Tle, Nval, Phg, Cha, Taz, Fua, Th, 4-Pal, and F(3/4*), wherein F(3/4*) is a phenylalanine substituted at either the 3 or the 4 position with a moiety selected from the group consisting of CF 3 , Et, iPr, and OMe; and

X 6 is selected from the group consisting of N, Q, I, L, and V, or X 6 is not present.

4. A purified peptide according to claim 3 , wherein P* is proline or 4-hydroxyproline, and Y* is tyrosine or said non-natural derivative of tyrosine substituted at the 3 position with Cl.

5. The purified peptide of claim 3 or 4 , the peptide further capable of forming a disulfide bond under non-reducing conditions.

6. The purified peptide of claim 5 , the peptide comprising a disulfide bond.

7. The purified peptide of claim 6 , the peptide having a specific binding affinity for fibrin.

8. A purified peptide of claim 4 comprising an amino acid sequence selected from the group consisting of:

                             (SEQ ID NO:4)

W-dE-C-P(4-OH)-Y(3-Cl)-G-L-C-W-I-Q

                             (SEQ ID NO:5)

Y-dE-C-P(4-OH)-Y(3-Cl)-G-L-C-Y-I-Q

                             (SEQ ID NO:6)

Y-dE-C-P(4-OH)-Y(3-Cl)-G-L-C-W-I-Q

                             (SEQ ID NO:7)

W-dE-C-P(4-OH)-Y(3-Cl)-G-L-C-Y-I-Q

                             (SEQ ID NO:8)

W-dE-C-P(4-OH)-Y(3-Cl)-D-L-C-W-I-Q

                             (SEQ ID NO:9)

Y-dE-C-P(4-OH)-Y(3-Cl)-D-L-C-Y-I-Q

                            (SEQ ID NO:10)

Y-dE-C-P(4-OH)-Y(3-Cl)-D-L-C-W-I-Q

                            (SEQ ID NO:11)

W-dE-C-P(4-OH)-Y(3-Cl)-D-L-C-Y-I-Q

                            (SEQ ID NO:12)

F(4-OMe)-H-C-P(4-OH)-Y(3-Cl)-D-L-C-H-I-L

                            (SEQ ID NO:13)

Y-H-C-P(4-OH)-Y(3-Cl)-G-L-C-W-I-Q

                            (SEQ ID NO:14)

W-dE-C-P-Y(3-Cl)-G-L-C-W-I-Q

                            (SEQ ID NO:15)

W-dE-C-P(4-OH)-Y-G-L-C-W-I-Q, and

                            (SEQ ID NO:16)

F-H-C-P(4-OH)-Y(3-Cl)-D-L-C-H-I-L.

9. The purified peptide of claim 8 , the peptide further capable of forming a disulfide bond under non-reducing conditions.

10. The purified peptide of claim 9 , the peptide comprising a disulfide bond.

11. The purified peptide of claim 10 , the peptide having a specific binding affinity for fibrin.

12. A compound comprising the peptide of claim 1 linked to a thrombolytic agent.

13. A purified peptide comprising the amino acid sequence: C-P*-Y*-X 1 -L-C (SEQ ID NO:3), wherein:

X 1 is G or D,

P* is proline or its non-natural derivative 4-hydroxyproline;

Y* is tyrosine or its non-natural derivative substituted at the 3 position with

a moiety selected from the group consisting of F, Cl, Br, I, and NO 2 ;

provided that at least one of P* or Y* is said non-natural derivative of the respective amino acid.

14. The purified peptide according to claim 13 , the peptide further capable of forming a disulfide bond under non-reducing conditions.

15. The purified peptide according to claim 14 , the peptide comprising a disulfide bond.

16. The purified peptide of claim 15 , the peptide having a specific binding affinity for fibrin.

17. A compound comprising the peptide of claim 13 , linked to a thrombolytic agent.