Contrast enhancement agents and method of use thereof

1. A contrast agent composition, comprising:

a pharmaceutically acceptable carrier or excipient; and

a metal-complex derived from a metal and a ligand having a structure (XXXI):

wherein R 1 , R 2 , R 3 , R′ 1 , R′ 2 , and R′ 3 , are independently at each occurrence hydrogen, or a C 1 -C 3 alkyl group;

R 4 and R′ 4 are independently at each occurrence hydrogen or a C 1 -C 3 alkyl group; and n is an integer between 0 and 4;

R 5 and R′ 5 are independently at each occurrence hydrogen or a group selected from the group consisting of C 1 -C 30 aliphatic radicals, C 3 -C 30 cycloaliphatic radicals, C 2 -C 30 aromatic radicals; and m is an integer between 0 and 10; and

Y comprises a polyethylene glycol (PEG) moiety; and wherein the metal is Fe, Mn, Ga, In, Gd, W, Ta, or B.

2. The contrast agent composition of claim 1 , wherein at least one of the R 5 and R′ 5 of the ligand is independently at each occurrence a hydrogen, an ethyl, a trichloroethyl, a beta-cyanoethyl, a trimethylsilyl ethyl, butyldimethylsilyl, trimethylsilyl, methoxyethoxymethyl (MEM), a 2-(trimethylsilyl)ethoxymethyl (SEM), a tetrahydropyranyl (THP), a triisopropylsilyl (TIPS), a tert-butyl (t-Bu), a tert-butyldiphenylsilyl (TBDPS), a benzyloxymethyl (BOM), a methylthiomethyl (MTM) or a combination thereof.

3. The contrast agent composition of claim 1 , wherein at least one of the R 5 and R′ 5 of the ligand is independently at each occurrence a methoxyethoxymethyl (MEM) group.

4. The contrast agent composition of claim 1 , wherein R 1 , R 2 , R 3 , R 4 , and R 5 are the same as R 1 ′, R 2 ′, R 3 ′, R 4 ′, and R 5 ′ of the ligand, respectively.

5. The contrast agent composition of claim 1 , wherein the polyethylene glycol moiety has an average molecular weight greater than about 2000 daltons and less than or equal to about 30,000 daltons.

6. The contrast agent composition of claim 1 , wherein the polyethylene glycol moiety has an average molecular weight in a range from about 5000 daltons to about 10,000 daltons.

7. The contrast agent composition of claim 1 , wherein the ligand has a structure XXXIII-A:

8. The contrast agent composition of claim 1 , wherein the ligand has a structure XXXIII-B:

9. The contrast agent composition of claim 1 , wherein the metal is iron.

10. The contrast agent composition of claim 1 , wherein the contrast agent composition is suitable for injection into a mammalian subject.

11. The contrast agent composition of claim 1 , wherein the contrast agent composition is suitable for injection into a human subject.

12. The contrast agent composition of claim 1 , wherein the metal-complex is characterized by an average aqueous hydrodynamic diameter (DH), as determined by dynamic light scattering, in a range from about 2 nm to about 500 nm.

13. The contrast agent composition of claim 12 , wherein the metal-complex is characterized by its ability to form a stable aqueous solution that exhibits no substantial change in the aqueous hydrodynamic diameter (D H ) as determined by dynamic light scattering after one or more of a tangential flow filtration, dialysis, ultrafiltation, or storage for one week at room temperature.

14. The contrast agent composition of claim 1 , wherein the contrast agent composition is suitable for use in magnetic resonance (MR), nuclear or X-ray imaging.

15. The contrast agent composition of claim 1 , wherein the carrier or excipient is an isotonic aqueous medium.

16. The contrast agent composition of claim 1 , wherein the carrier or excipient is at physiological pH.

17. A contrast agent composition suitable for injection into a mammalian subject, comprising:

a pharmaceutically acceptable carrier or excipient; and

a metal-complex having a structure (XXXXII):

wherein R 1 , R 2 , R 3 , R′ 1 , R′ 2 , and R′ 3 are independently at each occurrence hydrogen, or a C 1 -C 3 alkyl group;

R 4 and R′ 4 are independently at each occurrence a hydrogen or a C 1 -C 3 alkyl group; n is an integer between 0 and 4; m is an integer between 0 and 10; and

Y comprises a polyethylene glycol (PEG) moiety; and wherein the M is Fe, Mn, Ga, In, Gd, W, Ta, or B.

18. The contrast agent composition of claim 17 , wherein the polyethylene glycol moiety has an average molecular weight greater than about 2000 daltons and less than or equal to about 30,000 daltons.

19. The contrast agent composition of claim 17 , wherein the metal-complex is a racemate, a single enantiomer, an enantiomerically enriched composition, or a mixture of diastereomers.

20. The contrast agent composition of claim 17 , wherein the metal-complex has a structure XXXXIV

21. A contrast agent composition, comprising:

a pharmaceutically acceptable carrier or excipient; and

a metal-complex derived from a metal and a ligand having structure (XXX):

wherein R 1 , R 2 , R 3 , R 4 , R 8 , R′ 1 , R′ 2 , R′ 3 , R′ 4 and R 8 ′ are independently at each occurrence hydrogen or a C 1 -C 3 alkyl group;

R 5 and R′ 5 are independently at each occurrence hydrogen or a group selected from the group consisting of C 1 -C 30 aliphatic radicals, C 3 -C 30 cycloaliphatic radicals, C 2 -C 30 aromatic radicals; n is an integer between 0 and 4; m is an integer between 0 and 10;

R 7 and R′ 7 are independently at each occurrence a phosphonic acid group or a phosphonate group; and

Y comprises a polyethylene glycol (PEG) moiety; and wherein the metal is Fe, Mn, Ga, In, Gd, W, Ta, or B.