In certain embodiments, the macrocyclic compounds have the following structure:

[Image Omitted]

wherein X₁, X₂, X₃, and X₄are N; W₁, W₂, and W₃are each independently O or S; Y₁, Y₂, Y₃, and Y₄are each independently pendant donors comprising N, wherein N has a lone pair of electrons (e.g., amino, benzimidazole, imidazole, aniline, pyrazoyl, triazole, benzotriazole, and the like), or a pendant donor comprising O, wherein O has at least one lone pair of electrons but preferably two or three lone pairs (e.g., ketone, alcohol, alkoxide, carboxylic acid, amide, phenol or phenoxide, or a deprotonated form of the foregoing, such as, for example, a carboxylate ion, an imidazolate ion, a pyrazolate ion or an oxide, including an alkoxide or a phenoxide; m₁, m₂, m₃, and m₄are each independently 0, 1, or 2; n₁, n₂, n₃, and n₄are each independently 1 or 2; and R₁, R₂, and R₃are each independently substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl or substituted or unsubstituted alkyl group, wherein R₁, R₂, and R₃are not substituted by a pendant donor, wherein the alkyl segment of the alkyl-Y chain (alkyl-Y₁, alkyl-Y₂, alkyl-Y₃and/or alkyl-Y₄) may each independently be substituted (e.g., Structure a or Structure b) or unsubstituted (Structure c or Structure d). For Structures a-f, the pendent may have either R or S configuration at the chiral carbon:

[Image Omitted]

This paragraph is hereinafter referred to as “Scheme I.”

In an embodiment, the disclosure provides macrocyclic compounds having the structures and definitions set forth in Scheme I with the proviso that when the above macrocyclic compounds have the structures labeled I-XVI in Scheme II, one combination or any combination of the provisos for Structures I-XVI apply.

In another embodiment, any or all of alkyl-Y₁, alkyl-Y₂, alkyl-Y₃, and alkyl-Y₄may each independently be any of Structures 1-19 as defined in Scheme III.

Examples of suitable macrocyclic compounds include:

[Image Omitted]

- where R₁, R₂, and R₃each independently is substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl or substituted or unsubstituted alkyl group, where R₁, R₂, and R₃are not substituted by pendant donors; and when the macrocyclic core has Structure I, Z₁is H or one of the pendant groups in Scheme III and Z₂and Z₃each independently is a pendant group (e.g., one of the pendant groups in Scheme III);
- when the macrocyclic compound has Structure II, III, VII, VIII, IX or XV, Z₁and Z₂each independently is a pendant group (e.g., one of the pendant groups in Scheme III);
- when the macrocycle has Structure VI, XI or XIV, Z₁and Z₃each independently is a pendant group (e.g., one of the pendant groups in Scheme III);
- when the macrocycle has Structure XVI, Z₁is a pendant group (e.g., one of the pendant groups in Scheme III);
- when the macrocycle has Structure IV, Z₄is a pendant group (e.g., one of the pendant groups in Scheme III) and Z₁, Z₂and Z₃each independently is H or is a pendant group (e.g., one of the pendant groups in Scheme III), provided that at most two of Z₁, Z₂and Z₃is H;
- when the macrocycle has Structure V, Z₁and Z₂each independently is H or a pendant group (e.g., one of the pendant groups in Scheme III) and Z₃is a pendant group (e.g., one of the pendant groups in Scheme III);
- when the macrocycle has Structure X, Z₁and Z₃each independently is a pendant group (e.g., one of the pendant groups in Scheme III) and Z₂is H or a pendant group (e.g., one of the pendant groups in Scheme III);
- when the macrocycle has Structure XII, Z₄is a pendant group (e.g., one of the pendant groups in Scheme III) and Z₁, Z₂and Z₃each independently is H or a pendant group (e.g., one of the pendant groups in Scheme III), provided that at most two of Z₁, Z₂, and Z₃is H;
- when the macrocycle has Structure XIII, Z₁and Z₃each independently is a pendant group (e.g., one of the pendant groups in Scheme III) and Z₂is H or a pendant group (e.g., one of the pendant groups in Scheme III);
- wherein for all Structures I-XVI, each of Z₁, Z₂, Z₃and Z₄, as applicable, are selected independently of each other. This paragraph is hereinafter referred to as “Scheme II.”

The macrocyclic compound has at least one pendant donor on the macrocyclic core. For example, the pendant donor can have the following structure:

[Image Omitted]

wherein Q₁and Q₂are each independently —H, —OCH₃, —CO₂H, or —CH₂CO₂G₄, G₄is H, C₁to C₁₂substituted or unsubstituted alkyl groups of linear or branched structure or PEG group (—CH₂CH₂O—)_n(n=1-12, e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12), Q₃is H, C₁to C₁₂substituted or unsubstituted alkyl groups of linear or branched structure or PEG group (—CH₂CH₂O—)_n(n=1-12, e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12), Q₄and Q₅are each independently —H, —OCH₃, —CO₂H, or substituted or unsubstituted alkyl groups of linear or branched structures, A is a substituted or unsubstituted alkyl group of linear or branched structure with C₁to C₁₂or is a substituted or unsubstituted aryl group or naturally occurring (e.g., glycine) or synthetic amino acid or analog thereof. Some pendant donors, such as, for example, carboxylic acid, alcohol, imidazole or pyrazole, may deprotonate when complexed with Fe(III) or at certain pH values. Such protonated and deprotonated forms are within the scope of the disclosure. For example, the pendant donor is a carboxylate ion, an imidazolate ion, a pyrazolate ion, or an oxide (e.g., an alkoxide or a phenoxide). This paragraph is hereinafter referred to as “Scheme III.”

The macrocyclic compound may comprise one or more ancillary pendant groups. The ancillary pendant group (s) may be one or more coordinating ancillary pendant groups and/or one or more non-coordinating ancillary pendant groups.

A non-coordinating ancillary pendant group does not have a heteroatom that can bind to the Fe(III) metal ion to form a five-membered or six-membered chelate. Non-limiting examples of non-coordinating ancillary pendant groups include benzyl groups, phenyl groups, and other aromatic (e.g., aryl) groups that have one or more methylene group attached to aromatic group or no methylene groups), alkyl groups (both branched and linear groups), and the like. Other non-limiting examples of non-coordinating ancillary pendant groups include biphenyl, napthyl, anthracenyl, pyridyl, quinolyl, methyl, ethyl, isopropyl, n-propyl, ethyl methoxyether, PEG derivatives (polyethylene glycol), and the like.

Non-limiting examples of coordinating ancillary pendant groups (e.g., which is a third pendent group when two are already hydroxyl propyl) include oxygen or nitrogen donors that form five or six-membered chelates such as, for example, amides, carboxylates, alcohols or phenols, or derivatives of triazole, imidazole, pyrazole, picolyl, pyridine, alkylamines, aminopyridine, aminophenol, aniline, and the like. Some of these groups may deprotonate when bound to Fe(III).

A macrocyclic complex comprising one or more non-coordinating ancillary pendant group may have an open coordination site (have open coordination). A macrocyclic complex comprising one or more coordinating ancillary pendant group may not have an open coordination site (have closed coordination).

In an embodiment, the subject disclosure provides macrocyclic compounds having the structures and definitions set forth in Schemes II-IV,

[Image Omitted]

- where any or all of the following provisos apply when the macrocycle has structure II: when Z₁=Z₂=Structure 1, R₁≠methyl, ethyl, isopropyl, n-hexyl or Structure i, ii, iii, or iv; when Z₁=Z₂=Structure 7, R₁≠Structure v or vi; when Z₁=Z₂=Structure 9, R₁≠ethyl; when Z₁=Z₂=Structure 12, R₁≠ethyl; when Z₁=Z₂=Structure 16 when Q₄=t-butyl and Q₅=OCH₃or when Q₄=Q₅=t-butyl, R₁≠ethyl or isopropyl; when Z₁=Z₂=Structure 15, R₁≠methyl;
- where any or all of the following provisos apply when the macrocycle has Structure III: when Z₁=Structure 16 when Q₄=t-butyl and Q₅=OCH₃or when Q₄=Q₅=t-butyl, Z₂≠Structure 16 when Q₄=t-butyl and Q₅=OCH₃or when Q₄=Q₅=t-butyl;
- where any or all of the following provisos apply when the macrocycle has Structure V: when Z₁=Z₂=Z₃=Structure 17, R₁≠methyl, ethyl, n-propyl, n-butyl, n-dodecyl, or Structure ii, xiii, xv, ix, xvi or xix; when Z₁=Z₂=Z₃=structure 2, R₁≠Structure xvii or xx; when Z₁=Z₂=Z₃=Structure 1, R₁≠methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-octyl, n-decyl, n-octadecyl (C₁₈) or Structure ii, x, xi, xii, xiii, xiv or xvii;
- where any or all of the following provisos apply when the macrocycle has Structure VI: when Z₁=Z₃=Structure 1, R₁=R₂≠methyl, Structure ii, x, or xi; when Z₁=Z₃=Structure 9, R₁=R₂≠methyl; when Z₁=Z₃=Structure 18, R₁=R₂≠methyl; when Z₁=Z₃=Structure 16 when Q₄=Q₅=methyl or t-butyl, R₁=R₂≠methyl; when Q₄=H and Q₅=Br, R₁=R₂≠methyl; when Z₁=Z₃=Structure 15, R₁=R₂≠methyl; when Z₁=Z₃=Structure 17, R₁=R₂≠methyl;
- where any or all of the following provisos apply when the macrocycle has Structure XI: when Z₁=Z₂=Structure 1, R₁=R₂≠methyl;
- where any or all of the following provisos apply when the macrocycle has Structure XIII: when Z₁=Z₂=Z₃=Structure 7, R₁≠methyl;
- where any or all of the following provisos apply when the macrocycle has Structure XV: when Z₁=Z₂=Structure 1, Rid methyl; when Z₁=Z₂=Structure 3, Rid methyl; when Z₁=Z₂=Structure 4, R₁=R₂≠methyl; when Z₁=Z₂=Structure 1, R₁=R₂≠methyl; when Z₁=Z₂=Structure 5, R₁=R₂≠methyl; when Z₁=Z₂=Structure 7, R₁=R₂≠methyl; when Z₁=Structure 3 and Z₂=Structure 9, R₁=R₂≠methyl; when Z₁=Z₂=Structure 9, R₁=R₂≠methyl; when Z₁=Z₂=Structure 17, R₁=R₂≠methyl; when Z₁=Z₂=Structure 18, R₁=R₂≠methyl;
- where any or all of the following provisos apply when the macrocycle has Structure XVI: when Z₁=Structure 1, R₁=R₂=R₃methyl; when Z₁=Structure 3, R₁=R₂=R₃methyl; when Z₁=Structure 4, R₁=R₂=R₃methyl; when Z₁=Structure 5, R₁=R₂=R₃methyl; when Z₁=structure 7, R₁=R₂=R₃methyl; when Z₁=structure 15, R₁=R₂=R₃methyl.

In one embodiment, the subject disclosure provides macrocyclic compounds having the structures and definitions set forth in Schemes II-IV, where any or all of the following provisos apply when the macrocycle has Structure I: when Z₁=Z₂=Structure 1, Z₃≠Structure 1; when Z₁=Z₂=Structure 2, Z₃≠Structure 2; when Z₁=Z₂=Structure 3, Z₃≠Structure 3; when Z₁=Z₂=Structure 6, Z₃≠Structure 6; when Z₁=Z₂=Structure 7, Z₃≠Structure 7; when Z₁=Z₂=Structure 9, Z₃≠Structure 9; when Z₁=Z₂=Structure 11, Z₃≠Structure 11; when Z₁=Z₂=Structure 12, Z₃≠Structure 12; when Z₁=Z₂=Structure 13 when Q₁=Q₂=H, Z₃≠Structure 13 when Q₁=Q₂=H; when Z₁=Z₂=Structure 15, Z₃≠Structure 15; at most two of Z₁, Z₂or Z₃=Structure 16 when i) Q₄=Q₅=t-butyl, ii) Q₄=Q₅=OCH₃, iii) Q₄=t-butyl and Q₅=OCH₃or iv) Q₄=OCH₃and Q₅=t-butyl; when Z₁=H, Z₂≠Structure 1; when Z₁=H, Z₂≠Structure 7; when Z₁=H, Z₂≠Structure 9; when Z₁=H, Z₂≠Structure 13; when Z₁=Z₂=Structure 1, Z₃≠Structure 15; when Z₁=Structure 1 and Z₂=H, Z₃≠Structure 16 when Q=t-butyl;

- where any or all of the following provisos apply when the macrocycle has Structure III: when Z₁=Structure 1, Z₂≠Structure 1; when Z₁=Structure 17, Z₂≠Structure 17;
- where any or all of the following provisos apply when the macrocycle has Structure IV: when Z₁=Z₂=Z₃=Structure 1, Z₄≠Structure 1; when Z₁=Z₂=Z₃=Structure 2, Z₄≠Structure 2; when Z₁=Z₂=Z₃=Structure 3, Z₄≠Structure 3; when Z₁=Z₂=Z₃=Structure 6, Z₄≠Structure 6; when Z₁=Z₂=Z₃=Structure 7, Z₄≠Structure 7; when Z₁=Z₂=Z₃=Structure 9, Z₄≠Structure 9; when Z₁=Z₂=Z₃=Structure 11, Z₄≠Structure 11; when Z₁=Z₂=Z₃=Structure 12, Z₄≠Structure 12; when Z₁=Z₂=Z₃=Structure 15, Z₄≠Structure 15; when Z₁=Z₂=Z₃=Structure 16, Z₄≠Structure 16; when Z₁=Z₂=Z₃=Structure 17, Z₄≠Z₁, Z₄≠Structure 17; when Z₁=Z₂=Z₃=Structure 1, Z₄≠H; when Z₁=Z₂=Z₃=Structure 2, Z₄≠H; when Z₁=Z₂=Z₃=Structure 3, Z₄≠H; when Z₁=Z₂=Z₃=Structure 6, Z₄≠H; when Z₁=Z₂=Z₃=Structure 7, Z₄≠H; when Z₁=Z₂=Z₃=Structure 17, Z₄≠H; when Z₁=Z₂═H and Z₃=Structure 1, Z₄≠Structure 1; Z₁=Z₂=H and Z₃=structure 2, Z₄structure 2; when Z₁=Z₂=H and Z₃=Structure 3, Z₄≠Structure 3; when Z₁=Z₂=H and Z₃=Structure 6, Z₄≠Structure 6; when Z₁=Z₂=H and Z₃=Structure 7, Z₄≠Structure 7; when Z₁=Z₂=H and Z₃=Structure 17, Z₄≠Structure 17; when Z₁=Z₃=H and Z₂=Structure 1, Z₄≠Structure 1; when Z₁=Z₃=H and Z₂=Structure 2, Z₄≠Structure 2; when Z₁=Z₃=H and Z₂=Structure 3, Z₄≠Structure 3; when Z₁=Z₃=H and Z₂=Structure 6, Z₄≠Structure 6; when Z₁=Z₃=H and Z₂=Structure 7, Z₄≠Structure 7; when Z₁=Z₃=H and Z₂=Structure 17, Z₄≠Structure 17; when Z₁=Z₃=Structure 6 and Z₂=Structure 3, Z₄≠Z₂; when Z₁=Z₃=Structure 7 and Z₂=Structure 3, Z₄≠Z₂; when Z₁=Z₃=Structure 1 and Z₂=Structure 3, Z₄≠Z₂; when Z₁=Z₂=Z₃=Structure 1, Z₄≠Structure 3; when Z₁=Z₂=Z₃=Structure 1, Z₄≠Structure 17; when Z₁=Z₂=Z₃=Structure 1, Z₄≠Structure 6; when Z₁=Z₂=Z₃=Structure 1, Z₄≠Structure 7; when Z₁=Z₂=Z₃=Structure 1, Z₄≠Structure 9; where any or all of the following provisos apply when the macrocycle has Structure V: when Z₁=Z₂=Structure 1, Z₃≠Structure 1; when Z₁=Z₂=Structure 3, Z₃≠Structure 3; when Z₁=Z₂=Structure 6, Z₃≠Structure 6; when Z₁=Z₂=Structure 9, Z₃≠Structure 9; when Z₁=Z₂=Structure 17, Z₃≠Structure 17; when Z₁=Structure 1 and Z₂═H, Z₃≠Structure 1; when Z₁=Structure 3 and Z₂═H, Z₃≠Structure 3; when Z₁=Structure 6 and Z₂═H, Z₃≠Structure 6;
- where any or all of the following provisos apply when the macrocycle has Structure VII: when Z₁=Structure 1, Z₂≠Structure 1; when Z₁=Structure 2, Z₂≠Structure 2; when Z₁=Structure 6, Z₂≠Structure 6;
- where any or all of the following provisos apply when the macrocycle has Structure IX: when Z₁=Structure 1, Z₂≠Structure 1; when Z₁=Structure 6, Z₂≠Structure 6; Z₁=Structure 7, Z₂≠Structure 7;
- where any or all of the following provisos apply when the macrocycle has Structure X: when Z₁=Z₃=Structure 1, Z₂≠Structure 1; when Z₁=Z₃=Structure 3, Z₂≠Structure 3; when Z₁=Z₃=Structure 7, Z₂≠Structure 7; when Z₁=Z₃=Structure 1, Z₂≠H;
- where any or all of the following provisos apply when the macrocycle has Structure XII: when Z₁=Z₂=Z₃=Structure 1, Z₄≠Structure 1; when Z₁=Z₂=Z₃=Structure 3, Z₄≠Structure 3; when Z₁=Z₂=Z₃=Structure 6, Z₄≠Structure 6; when Z₁=Z₂=Z₃=Structure 7, Z₄≠Structure 7; when Z₁=Z₂=Z₃=Structure 9, Z₄≠Structure 9; when Z₁=Z₂=Z₃=Structure 12, Z₄≠Structure 12; when Z₁=Z₂=Z₃=Structure 15, Z₄≠Structure 15; when Z₁=Z₂=Z₃=Structure 17, Z₄≠Structure 17; when Z₁=Z₂=Z₃=Structure 7, Z₄≠H; when Z₁=Z₂=Z₃=Structure 3, Z₄≠H; when Z₁=Z₃=H and Z₂=Structure 1, Z₄≠Structure 1; when Z₁=Z₃=H and Z₂=Structure 7, Z₄≠Structure 7; when Z₁=Z₃=H and Z₂=Structure 14, Z₄≠Structure 14; when Z₁=Z₂=H and Z₂=Structure 1, Z₄≠Structure 1; when Z₁=Z₂=Z₃=H, Z₄≠Structure 7; when Z₁=Z₂=Z₃=H, Z₄≠Structure 9; when Z₁=Z₂=Z₃=H, Z₄≠Structure 14; when Z₁=Z₂=Z₃=H, Z₄≠Structure 17.

In an embodiment, the subject disclosure provides macrocyclic compounds having the structures and definitions set forth in Scheme I with the proviso that when the macromolecule has Structure A, at most two of Y₁, Y₂and Y₃is

[Image Omitted]

In certain embodiments, Fe(III) cation is complexed to the macrocyclic compound. In certain other embodiments, Fe(III) cation is not complexed to the macrocyclic compound. The Fe(III) may be complexed to the macrocycle as shown herein.

As previously noted, some pendant donors, such as, for example, carboxylic acid, alcohol, imidazole or pyrazole may deprotonate when complexed with Fe(III). Their corresponding carboxylate ions, imidazolate ions, pyrazolate ions, triazolate ions or oxides (e.g., alkoxide or phenoxide) are within the scope of the disclosure.

In an embodiment, the subject disclosure provides Fe(III) complex comprising Fe(III) complexed with a macromolecule having a structure set forth in Schemes II-IV, as defined in Schemes II-IV.

In another embodiment, the subject disclosure provides Fe(III) complexes comprising Fe(III) complexed with a macromolecule having a structure set forth in Schemes II-IV, as defined in Schemes II-IV, where any or all of the following provisos apply when the macromolecule has Structure I: when Z₁=Z₂=Structure 1, Z₃≠Structure 1; when Z₁=Z₂=Structure 2, Z₃≠Structure 2; when Z₁=Z₂=Structure 3, Z₃≠Structure 3; when Z₁=Z₂=Structure 4, Z₃≠Structure 4; when Z₁=Z₂=Structure 6, Z₃≠Structure 6; when Z₁=Z₂=Structure 7, Z₃≠Structure 7; when Z₁=Z₂=Structure 11, Z₃≠Structure 11; when Z₁=Z₂=Structure 12, Z₃≠Structure 12; when Z₁=Z₂=Structure 15, Z₃≠Structure 15; at most two of Z₁, Z₂, or Z₃=Structure 16 when Q₄=Q₅=t-butyl, ii) when Q₄=Q₅=OCH₃, iii) when Q₄=t-butyl and Q₅=OCH₃and iv) when Q₄=OCH₃and Q₅=t-butyl; Z₃≠Structure 16 when Q₄=Q₅=t-butyl, ii) when Q₄=Q₅=OCH₃, iii) when Q₄=t-butyl and Q₅=OCH₃and iv) when Q₄=OCH₃and Q₅=t-butyl; when Z₁=Z₂=Structure 17, Z₃≠Structure 17; when Z₁=Z₂=Structure 1, Z₃≠Structure 15; when Z₁=Structure 1 and Z₂=H, Z₃≠Structure 16 when Q=t-butyl; when Z₁=Z₂=Structure 15, R methyl; where any or all of the following provisos apply when the macromolecule has Structure IV: when Z₁=Z₂=Z₃=Structure 1, Z₄≠Structure 1; when Z₁=Z₂=Z₃=Structure 7, Z₄≠Structure 7; when Z₁=Z₂=Z₃=Structure 1, Z₄≠Structure 3; when Z₁=Z₂=Z₃=Structure 1, Z₄≠Structure 7; when Z₁=Z₂=Z₃=Structure 1, Z₄≠Structure 17; when Z₁=Z₂=Z₃=Structure 1, Z₄≠H; when Z₁=Structure 7, Z₂≠Structure 7;

- where any or all of the following provisos apply when the macromolecule has Structure XII: when Z₁=Z₂=Z₃=Structure 1, Z₄≠Structure 1; when Z₁=Z₂=Z₃=H, Z₄≠Structure 1; when Z₁=Z₂=Z₃=H, Z₄≠Structure 3; when Z₁=Z₂=Z₃=H, Z₄≠Structure 7; where when the macromolecule has Structure XVI and Z₁=Z₂=Z₃=methyl, Z₄≠Structure 1.

In an embodiment, Fe(III) complex comprising Fe(III) complexed with a macromolecule having a structure set forth in Scheme I with the proviso that when the macromolecule has Structure A, at most two of Y₁, Y₂and Y₃is

[Image Omitted]

The Fe(III) complex may have a bound water, hydroxide, or no bound water or hydroxide ligands. However, without being bound by any theory, it is believed that desirable agents have an open coordination site for binding water or anions.

In an embodiment, the subject disclosure provides a macromolecule having a structure set forth in Schemes II-IV, as defined in Schemes II-IV, with the proviso that when the macromolecule has Structure IV and Z₁, Z₂and Z₄=Structure 1, Z₃≠Structure 6. In another embodiment, the subject disclosure provides Fe(III) complex comprising Fe(III) complexed with a macromolecule having a structure set forth in Schemes II-IV, as defined in Schemes II-IV, with the proviso that when the macromolecule has Structure IV and Z₁, Z₂and Z₄=deprotonated Structure 1, i.e.,

[Image Omitted]

Z₃≠Structure 6. In still another embodiment, the subject disclosure provides Fe(III) complex comprising Fe(III) complexed with a macromolecule having a structure set forth in Schemes II-IV, as defined in Schemes II-IV, with the proviso that when the macromolecule has Structure IV and Z₁, Z₂and Z₄=deprotonated Structure 1, Z₃deprotonated Structure 6, i.e.,

[Image Omitted]

In yet another embodiment, the subject disclosure provides a macromolecule having a structure set forth in Schemes II-IV, as defined in Schemes II-INT, with the proviso that when the macromolecule has Structure IV and Z₁=Z₂=Z₃=deprotonated Structure 1, Z₄≠Z₁.

Certain pendants may have more than one N or O donor atom (e.g., pyrazole or imidazole, carboxylate or carboxylic acid) although generally only one is coordinated to metal ion.

A macrocyclic compound can have various pendant groups and combinations of pendant groups. When more than one pendant donor is present, they may be the same or different.

In various examples, the macrocyclic core has 1, 2, 3, or 4 nitrogen atoms, 1, or 2 oxygen atoms and/or 1, or 2 sulfur atoms. For example, the macrocyclic core has 6, 7, 8, 9, or 10 carbons. For example, the macrocyclic core has from 9 to 16 atoms, including all ranges and integers there between, where at least one of the atoms in the macrocyclic core is a heteroatom, such as N. In another embodiment, at least two of the atoms in the macrocyclic core are heteroatoms, such as, for example, N. In various examples, there are 2, 3, 4, or 5 carbon atoms separating the heteroatoms in the macrocyclic core. The one or more carbons in the macrocyclic core can be unsubstituted (e.g., —CH₂—) or substituted (e.g., —CHR—, or —CR₂—, where the R groups are, for example, alkyl groups or aryl groups (e.g., benzyl groups) as described herein), provided that at least one carbon in the macrocyclic core is substituted with a pendant donor. For example, they can be substituted with the substituents disclosed herein. In another embodiment, the macrocyclic core comprises at least two heteroatoms, each of which is independently N or O, which are separated from each other by at least two carbon atoms.

The pendant groups can be covalently attached to a macrocyclic core (e.g. at a nitrogen): especially for cyclen(III), cyclam (VII), TACN (I).

Macrocyclic compounds can be macrocyclic ligands. The macrocyclic ligands described herein stabilize the trivalent iron (Fe(III)) state. The coordination geometry is designed for desirable binding of Fe(III) in comparison to Fe(II) to maintain the Fe(III) oxidation state, for example, under biologically relevant conditions. Stabilization of the Fe(III) state (e.g., E_o<0 mV vs. NHE) also serves to inhibit the production of reactive oxygen species that occur through reduction to the Fe(II) state of the complex.

It is desirable that the Fe(III) center is stabilized relative to Fe(II) so that there is no reaction with biological reductants to produce reactive oxygen species (ROS) (see, e.g., FIG. 11). Such redox-inactive (under biological conditions) Fe(III) centers have negative redox potentials versus NHE. Examples of macrocyclic complexes of the present with macrocyclic core and pendant groups that produce stabilized Fe(III) include, but are not limited to, 1,4,9-triazacyclononane macrocyclic core and alcohol pendent groups that become deprotonated upon binding of Fe(III) (see, e.g., FIG. 6).

In various examples, a macrocyclic compound or compound of the present disclosure exhibits a reduction potential (E_o) of less than 0 mV vs. normal hydrogen electrode (NHE) in aqueous solution at a biologically relevant pH (e.g., a pH of 6.5-7.5 or 7.2-7.4, including all 0.1 pH values and ranges therebetween). In various other examples, a macrocyclic compound or compound of the present disclosure exhibits a reduction potential (E_o) of at least −100, at least −150, at least −200, at least −300, at least −400, at least −500, or at least −600 mV vs. normal hydrogen electrode (NHE) in aqueous solution at a biologically relevant pH (e.g., a pH of 6.5-7.5 or 7.2-7.4, including all 0.1 pH values and ranges therebetween). In various other examples, a macrocyclic compound or compound of the present disclosure exhibits a reduction potential (E_o) of less than 0 to −600 mV vs. normal hydrogen electrode (NHE) in aqueous solution at a biologically relevant pH (e.g., a pH of 6.5-7.5 or 7.2-7.4, including all 0.1 pH values and ranges therebetween).

The shortening of the T₁relaxation times of the protons of water by the Fe(III) complexes, T₁relaxivity, is promoted by both innersphere water and outersphere water interactions. Accordingly, in various examples, macrocyclic complexes and compounds of the present disclosure comprise one or more pendant donor groups that can hydrogen bond to water through heteroatoms such as, for example, oxygen or nitrogen (see, e.g., FIG. 1).

Non-limiting examples of such pendant donor groups are pendent alcohol groups that deprotonate to alkoxide groups (see, e.g., FIGS. 2, 3, 4, and 7). In addition, in various examples, macrocyclic compounds and compounds of the present disclosure comprise an open coordination site, which may bind water (see, e.g., FIGS. 5 and 6). These water ligands may ionize to form hydroxide ligands at neutral pH (see, e.g., FIGS. 8 and 9), for example, as shown by, pH-potentiometric titrations (see, e.g., FIG. 12). It may desirable that the water ligands are rapidly exchanging. Rate constants for innersphere water exchange is dependent on both the magnetic field strength of the scanner and also on the rotational correlation time of the contrast agent which is related to size. For clinical MRI scanners with field strengths of 3 Tesla, the following is desirable. In various examples, for a molecule with a rotational correlation time of about 1-4 nanoseconds, the exchange rate constant for the contrast agents is from 10⁵s⁻¹to 10⁹s⁻¹or greater than 2×10⁵s⁻¹. In various examples, for a molecule with a rotational correlation time of about 0.1 to 0.2 nanoseconds, the exchange rate constant for the contrast agents is from 10⁶s⁻¹to 10⁹s⁻¹. Evidence for rapidly exchanging water ligands is shown by variable temperature ¹⁷O NMR spectroscopy studies (see, e.g., FIG. 10). The reduced transverse relaxation times (T_2r) is approximated by measurement of the linewidth of the ¹⁷O resonance.

Coordination chemistry of Fe(III) is dependent on the coordination number. The macrocyclic compounds of the present disclosure have donor groups which can be part of the macrocyclic core, also referred to as macrocycle donors, and donor groups can be part of the substituents (e.g., pendant groups) on the macrocyclic core, also referred to as pendant donors. When Fe(III) is complexed to a macrocyclic compound of the present disclosure, 4 to 7 donors are complexed to the metal ion center. In an embodiment, the macrocyclic core can have from 2 to 4 donors and from 2 to 4 pendant donors. In various embodiments, there are 2 macrocycle donors and 3 pendant donors, 2 macrocycle donors and 4 pendant donors, 3 macrocycle donors and 2 pendant donors, 3 macrocycle donors and 3 pendant donors, 3 macrocycle donors and 4 pendant donors, 4 macrocycle donors and 2 pendant donors, 4 macrocycle donors and 3 pendant donors.

Examples of suitable macrocyclic compounds include:

[Image Omitted]

In an embodiment, the compounds of the present disclosure can have more than one macrocyclic core tethered together (i.e., covalently bound) via a linker group (e.g., aromatic groups), one or more macrocyclic compound of the present disclosure, a polymer, a dendrimer, or peptide.

It is desirable to produce an oligomeric molecule with a rotational correlation time of approximately 1 to 4 nanoseconds for effective contrast agent at field strengths of 3 Tesla to 7 Tesla. For example, linking three macrocyclic Fe(III) complexes together, e.g. through the functionalized benzene by using click chemistry (shown below), is expected to produce a compound (and produces a compound for the compound shown below) that will have a rotational correlation time which has a value which is intermediate between a macrocyclic complex, such as, for example, Fe(TACO) and a molecule linked or bound to a large protein.

Linkers may have multiple fused aromatic groups such as, for example, anthracene, or carbazole or linked through the nitrogens of triazacyclononane or tetraazacyclododecane. There may be a direct attachment to the macrocyclic nitrogen donor of the contrast agent (e.g., as shown below) or there may be an intervening methylene group (e.g., as shown for Fe₂(DT-meta)).

[Image Omitted]

Linkers may have one or more coordinating groups or be non-coordinating.

One or more macrocyclic compound may be covalently bound to a protein, such as, for example, human serum albumin, which is the predominant protein in the blood. This approach is considered to slow the rotational correlation time and increase the relaxivity of the tethered macrocyclic compound(s) (e.g., at field strengths of 3 Tesla) and to increase the residency time of the contrast agent in the blood.

Peptides may be used to link (tether) two or more iron complexes together. In this approach, the complexes are, for example, linked through the carboxy or amino terminus of the peptide. A peptides may have one or more sequences that allow for targeting to other biopolymers such as, for example, fibrin targeting peptides.

A compound may be a dendrimer with a plurality of pendant macrocyclic complexes. For example, dendrimers based on ethylenediamine cored PAMAM dendrimers will be prepared where PAMAM is polyamidoamine with 4 up to 36 chelates. The iron complexes will be attached either through click chemistry or by coupling of carboxylic acid group to the terminal amines of the PAMAM.

Polymeric contrast agents may be made by, for example, using click chemistry as described for the complexes containing triazole linkers or, alternatively, by radical polymerization (as shown below). In this approach, a styrene functionality is put in place of a benzyl group and the macrocyclic ligand is incorporated into the polymer. This approach is also amenable with macrocyclic compounds such as, for example, the TOB type TACN macrocyclic compound.

[Image Omitted]

In the above reaction, the resulting polymer may be reacted with a source of Fe(III), such as, for example, FeCl₃, to provide a compound of the present disclosure that can be used as an MRI contrast agent.

For tumor uptake and retention, the size of the molecule containing the contrast agent is important. In addition, given that the magnitude of the T₁relaxivity increases proportionally with the number of iron complexes and also increase with the size of the molecule, or more precisely the rotational correlation time (τ_c), the use of multiple tethered macrocyclic complexes should increase contrast. This can be accomplished by the formation of dimeric or oligomeric Fe(III) complexes with three macrocyclic compounds as shown below. For example, the compound can have the following structures:

[Image Omitted]

Alternatively, the macrocyclic compounds may be linked in the following manner to form dinuclear complexes in scheme below.

[Image Omitted]

Alternatively, the complex can be attached to a polymeric structure (e.g., water-soluble polymers such as, for example, polyesters, polylactides, polylactide-polystryene copolymers, and the like), for example, as shown below by using click chemistry.

[Image Omitted]

The following are examples of Fe(III) complexes, and are within the scope of the disclosure.

[Image Omitted]

In various embodiments, the macrocyclic compounds, macrocyclic complexes, or compounds of the disclosure are a salt, a partial salt, a hydrate, a polymorph, or a stereoisomer, or a mixture thereof. For example, the macrocyclic compound, macrocyclic complex, or compound is present as a racemic mixture, a single enantiomer, a single diastereomer, or mixture of diastereomers. In certain embodiments, after complexation of the metal ion, the macrocyclic complexes or compounds are present as mixtures of diastereomers and/or conformers which can be determined by NMR. The diastereomers may arise from the conformation of the macrocyclic core and the directionality of the substituents on the macrocyclic core.

The compounds of the disclosure can have innersphere water or alternatively, a hydroxide ligand. In an embodiment the compounds have one innersphere ligand (q) which contributes to relaxivity as in Eq. 1.

R
1

=

R
1

S
⁢
S

+

R
1

I
⁢
S

Equation
⁢

1

R
1
IS

=

q
/

[

H
2

⁢
O

]

T

1
⁢
m

+

τ
m

Equation
⁢

2

Eq. 1 shows that relaxivity has contributions from bound water (innersphere, IS) and second-sphere (SS) (outersphere) water. Eq. 2 predicts that greater numbers of bound water molecules and rapid ligand exchange rate constants (short lifetimes for bound water (Tm)) are advantageous. Notably r₁, the parameter used to characterize relaxivity, has units of mM⁻¹s⁻¹, and is obtained from a plot of T_1obs(s⁻¹) versus contrast agent concentration. There is an analogous relationship for second-sphere waters although the number and residence time is not well defined. The R₁and R₂relaxivity (from T₁and T₂relaxation rate constants at 4.7 T at 37° C. is shown for several complexes in FIG. 13 and FIG. 14. Data on a 3 Tesla MRI scanner are shown in FIG. 21. Table 1 summarizes R₁and R₂relaxivity data for several Fe(III) complexes.

TABLE 1

T₁Relaxivity of Fe(III) complexes at neutral pH, Hepes buffer, 37° C.

on a 4.7 Tesla MRI scanner. HSA is human serum albumin.

R₁(mM^-1s^-1)

Complex
R₁(mM^-1s^-1)
with HSA
R₂(mM^-1s^-1)
R₂with HSA

Fe(GUAC)
0.015
0.41
1.05
6.5

Fe(NOKA)
2.0
2.5
4.8
1.3

Fe(TACO)
1.3
1.4
1.7
2.0

Fe(TOB)
2.5
3.4
4.3
4.9

Fe(STHP)
0.074
0.53
1.2
3.9

Fe(TOM)
0.45
1.3
2.7
2.5

Structures of certain complexes in Table 1.

[Image Omitted]

It is desirable that the ratio of the T₁to T₂relaxivity (R₁/R₂) of a macrocyclic complex or compound of the present disclosure are close to one (unity). R₂, the transverse relaxivity, is by definition always larger than R₁, the longitudinal relaxivity. In various examples, Fe(III) contrast agents of the present disclosure have desirably low R₂to give R₁/R₂ratios close to one, for example, as shown in Table 1. In various examples, a macrocyclic complex or compound of the present disclosure have R₁/R₂ratios of 0.5 to 0.2 or 0.8 to 0.6. These data demonstrate the desirability of the TACN ligand, alcohol pendents and an open coordination site, for example, in Fe(TOB) or Fe(MeOxyBz) in comparison to certain complexes with no open coordination site for the mononuclear complexes such as Fe(AmBz), or Fe(TOTO). (see, e.g., Table 2).

TABLE 2

T₁relaxivity at 4.7 T, 37° C., at pH 7.4, 100 mM NaCl, 37° C. with

6 mM human serum albumin (HSA).

Complex alone
Complex + HSA

Fe(MeOxyBz)
2.3
3.13

Fe(AmBz)
0.80
1.23

Fe(TOTO)
0.56
1.13

Fe(ToTzB)
0.87
1.09

Fe(TON)
—
0.93

Fe₂(DT-meta)
—
2.91

Fe₂(DT-ortho)
—
3.60

Fe₂(TONO)
—
1.10

Structures of certain complexes in Table 2.

[Image Omitted]

Tables 1 and 2 show that desirable interaction of the Fe(III) complex with water molecules can enhance relaxation of the protons of the water. Without being bound by any particular theory, it is considered that exchange of innersphere water with bulk water is an important mechanism for proton relaxivity.

This shows that optimization of the interaction of the Fe(III) complex with water molecules to enhance relaxation of the protons of the water is important. Without being bound by any theory, exchange of innersphere water with bulk water is thought to be a dominant mechanism for proton relaxivity in Gd(III) complexes. However, Fe(III) is a much smaller metal ion than Gd(III) (0.78 Å vs. 1.25 Å, respectively). The shorter M−H distance in bound water of Fe(III) compared to Gd(III) suggests that the relative efficiency of the outersphere versus innersphere contributions may differ for the two metal ion complexes.

There are three mechanisms that contribute to paramagnetic relaxation of associated water (1/T_1m): the scalar (contact) contributions, dipole-dipole contributions and Curie spin relaxation. The most important of these for the longitudinal relaxation considered here is the dipole-dipole contribution (1/T₁DD). At field strengths of 1.5 T or greater, 1/T₁DD is defined as shown in Eq. 3 where S is the spin quantum number, ω_His the Larmor frequency of the proton, r_MHis the metal ion-proton distance and γ_His the proton gyromagnetic ratio, ge is the electronic g factor, μ_Bis the Bohr magneton, and μ_ois the permittivity of a vacuum. Notably, the 1/T₁DD term increases (higher relaxivity) with larger total spin (S) which favors Gd(III) over Fe(III). However, the shorter distance of the paramagnetic Fe(III) center to water protons (r_MH) favors Fe(III) proton relaxation, especially given the 1/r⁶dependence.

1

T
1

D
⁢
D

=

2

1
⁢
5

⁢

(

μ
0

4
⁢
π

)

⁢

γ
H
2

⁢

g
e
2

⁢

μ
B
2

⁢

S
⁡
(

S
+
1

)

r

M
⁢
H

6

[

3
⁢

τ
c

1
+

ω
H
2

⁢

τ
c
2

]

Equation
⁢

3

1

τ
c

=

1

τ
R

+

1

T

1
⁢
e

+

1

τ
m

Equation
⁢

4

The correlation time (τc) for the dipolar relaxation mechanism is influenced by different processes including the lifetime of the bound water (1/τ_m), the rotational motion of the contrast agent (1/τ_R) and the longitudinal relaxation of the unpaired electrons (1/T_1e). Although any of these three processes can contribute, their importance depends on the strength of the magnetic field. Much of the literature is focused on the importance of these processes at low field strength (<1 T). Under these conditions, the rotational processes or electronic relaxation times may be limiting, and τ_mshould be in a narrow range close to 10 ns (k_ex=10⁸s⁻¹). However at higher field strengths (≥1.5 T), simulations show that the optimal τ_mhas a larger range (1-100 ns) and rotational motions should have values intermediate between small molecules and proteins. An important parameter is T_1e, the electronic relaxation time. A long T_1efor Fe(III) may result from complexes that have a high degree of symmetry, leading to little zero field splitting and slow relaxation of the electronic state. Also, the coordination sphere needs to favor high spin (S=5/2) and not low spin S=½ Fe(III).

Studies to determine whether a metal complex has a bound water can involve the collection of variable temperature ¹⁷O NMR data. The data were obtained using a Varian 400 MHz NMR spectrometer with a broad band probe (FIG. 10). Since the ¹⁷O isotope has a low natural abundance, each complex was dissolved into a solution of water enriched with H₂¹⁷O such that the peak measured by the NMR would be larger and therefore easier to detect visually. NMR studies were performed at various temperatures for each complex studied. The temperature ranges for each compound tested were between 10° C. and 80° C., or 283K and 353K. In order to obtain the desired complex solubility of 45 mM for these measurements, the pH range studied was 3-5. The temperature dependent transverse relaxation data were fit to various equations via a least squares fit analysis using Scientist for Windows version 3.0. First, it is known that complexes with an open coordination site, obey the Swift-Connick equation, as shown in equation 5a:

1

T

2
⁢
r

=

π

P
m

*

(

Δ
⁢

v

o
⁢
b
⁢
s
⁢
e
⁢
r
⁢
v
⁢
e
⁢
d

-

Δ
⁢

v

s
⁢
o
⁢
l
⁢
v
⁢
e
⁢
n
⁢
t

)

=

1

τ
m

*

(

T

2
⁢
m

-
1

+

T

2
⁢
m

-
1

*

τ
m

-
1

+

Δ
⁢

ω
m
2

)

(

T

2
⁢
m

-
1

+

τ
m

-
1

)

2

+

Δ
⁢

ω
m
2

+

1

T

2
⁢
os

⁢

where
⁢

1

T

2
⁢
r

Equation
⁢

5
⁢
a

is the reduced transverse relaxation rate, P_mis the molar fraction of bound water and (Δv_observed−Δv_solvent) is the difference in line widths between H₂¹⁷O with and without complex present. Since the observed line widths can be measured using NMR spectroscopy, and P_Mcan be calculated in advance, they are the measurable quantities in the equation. In addition,

1

τ
m

is residence time of the bound water molecules, T_2m⁻¹is the transverse relaxation rate of the bound water and Δω_mis the chemical shift difference between bound and bulk water. The T_2OSis a term taking into account the hydrogen bonding of ligand atoms to bulk water.

In the complexes studied at the temperature ranges in which data were recorded and analyzed,

T

2
⁢
m

-
1

⁢

and
⁢

1

T

2
⁢
os

can be neglected and the Swift-Connick equation is reduced to equation 5b. In conjunction, since reduced transverse relaxation rates are often quite large, taking the natural logarithm of both sides of the equation allows for better scaling and simpler representation of the data, as shown in equation 5c:

1

T

2
⁢
r

=

π

P
m

*

(

Δ
⁢

v

o
⁢
b
⁢
s
⁢
e
⁢
τ
⁢
v
⁢
e
⁢
d

-

Δ
⁢

v

s
⁢
o
⁢
l
⁢
v
⁢
e
⁢
n
⁢
t

)

=

1

τ
m

*

Δ
⁢

ω
m
2

τ
m

-
2

+

Δω
m
2

.

Equation
⁢

5
⁢
b

ln
⁡
(

1

T

2
⁢
r

)

=

ln
⁡
(

1

τ
m

*

Δ
⁢

ω
m
2

τ
m

-
2

+

Δω
m
2

)

.

Equation
⁢

5
⁢
c

The inverse bound water residence time, and the chemical shift difference between bound and bulk water are each represented by equations 6a and 6b, respectively:

1

τ
m

=

k

e
⁢
x

=

k
b

*
T

h

*

exp
⁡
(

Δ
⁢

S
‡

R

-

Δ
⁢

H
‡

R
⁢
T

)

.

Equation
⁢

6
⁢
a

Δω
m

=

g
L

⁢

μ
b

⁢

S
⁡
(

S
+
1

)

⁢
B

T

⁢

(

A
ℏ

)

.

Equation
⁢

6
⁢
b

In equation 6a, k_exis the water exchange rate constant at the coordination site and is the inverse of the bound water residence time. k_bis Boltzmann's constant, h is Planck's constant, T represents absolute temperature, ΔS^‡ and ΔH^‡ represent the activation entropy and enthalpy, respectively. In equation 6b, g_Lis the isentropic Lande factor, μ_bis the magnetic moment, S represents the total spin state, B represents the applied magnetic field, and

(

A
ℏ

)

represents the hyperfine coupling constant. In equation 6b, the isentropic Lande factor, magnetic moment, spin state, magnetic field, and hyperfine coupling constant terms are consolidated into a single parameter which is solved for in the treatment of the data. This consolidation reduces equation 6a to a simple inverse temperature dependence and the simplified constant is represented by the constant C. This approach was used to determine the exchange rate constants for the bound water of Fe(TOB) as shown in FIG. 10 of 2×10⁶s⁻¹.

The macrocyclic compounds of the present disclosure are thermodynamically stable and/or kinetically inert towards dissociation. In an embodiment, the macrocyclic compounds are thermodynamically stable and kinetically inert towards dissociation. In an embodiment, the kinetic inertness of the macrocyclic compounds of the present disclosure can be described using a rate constant for dissociation. In an embodiment, the macrocyclic donors and pendant donors do not dissociate appreciably from the metal center (e.g., 1% or less, 0.1% or less, or 0.01% or less dissociation is observed) for up to 24 hours at neutral pH in the presence of 1) 25 mM carbonate, 0.40 mM phosphate, 100 mM NaCl, pH 7.2; 2) pH 4, 100 mM NaCl; or 3) with 5-fold excess ZnCl₂, 100 mM NaCl, pH 7.2.

In an embodiment, Fe(III) is high-spin S= 5/2. For effective T₁(longitudinal) relaxation, a paramagnetic spin state is needed. In order to keep Fe(III) in the high-spin state, the ligand (or crystal) field splitting must not be too large. If the crystal field splitting is larger than the pairing energy, a low spin (S=½) state will result. Fe(III) is readily maintained in a high-spin paramagnetic state with a range of ligand donor groups, especially containing anionic oxygen donors.

Examples of desirable macrocyclic complexes and compounds are shown below. These Fe(III) complexes may have an open coordination site for a water ligand, two alcohol pendants and a third pendant which is sterically bulky. Ancillary pendant groups such as, for example, aryl groups (e.g., benzyl groups and substituted benzyl groups, such as, for example, methoxy-benzyl groups, and fused ring aryl groups) or alkyl groups (e.g., branched alkyl groups) are particularly effective. Some may have two or more Fe(III) centers such as Fe₂(DT-para). The coordinatively saturated complexes, Fe(ToTzB) and Fe(AmBz) have relatively high relaxivity that may be enhanced by attachment of larger ancillary pendants to slow rotational correlation times.

[Image Omitted]

It is desirable that the electronic relaxation time of the high-spin Fe(III) center is sufficiently long (e.g., greater than 3×10¹¹s), that it is not the limiting factor in the correlation time constant as expressed in equation 4 at field strengths of 1.5 Tesla or greater. This can be accomplished by, for example, using macrocyclic ligands that produce high symmetry at the Fe(III) center such as, for example, Fe(TACO), Fe(NOKA), and Fe(TOB). It is desirable that the zero field splitting factor (D) is small given that (T_1e)⁻¹is directly proportional to D²for high-spin Fe(III) complexes in an axially distorted complex.

It is desirable that the Fe(III) complex remain in the trivalent oxidation state and not be reduced by, for example, peroxide, superoxide, ascorbate, or by glutathione at concentrations present in the extracellular medium of cells such as, for example, mammalian cells (e.g., human cells). Normally, a redox potential more negative than zero mV (<0 mV) versus NHE is sufficient. If the complex were to be reduced to Fe(II) and the Fe(II) complex and the complex has a positive redox potential versus NHE, reactive oxygen species may be produced, for example, as shown in FIG. 8. For example, [Fe(EDTA)]—has a redox potential of approximately 300 mV and produces ROS as shown by the assay in FIG. 11.

For use in methods of the disclosure, the compounds described herein can be administered as pharmaceutical preparations. Accordingly, they can be provided in a variety of compositions, and can be combined with one or more pharmaceutically acceptable carriers. Some examples of pharmaceutically acceptable carriers can be found in: Remington: The Science and Practice of Pharmacy (2005) 21st Edition, Philadelphia, PA Lippincott Williams & Wilkins. The composition can be provided as a liquid, a solution, or a solid, and may be provided in combination with any suitable delivery form or vehicle, examples of which include but are not limited to caplets, capsules, tablets, an inhalant or aerosol, etc.

Various methods known to those skilled in the art may be used to introduce the compositions of the disclosure to an individual. These methods include but are not limited to intravenous, intramuscular, intracranial, intrathecal, intradermal, subcutaneous, and oral routes. In an embodiment, the composition is administered intravenously.

The necessary solubility of the complexes depends on their effectiveness in producing contrast. For Fe(III) T₁contrast agents that have good relaxivity, the complexes need 100 μM-2 mM solubility. However, other additives such as human serum albumin (has) or meglumine may be used to increase solubility and/or increase relaxivity. Addition of HSA (e.g., 35 mg/mL) to some of the Iron(III) complexes produces higher T₁relaxivity as shown in Table 1 and 2). Solubility is generally measured in aqueous solution at near neutral pH (e.g., 6.5 to 7.5, including all 0.1 pH values and ranges therebetween) in 100 mM NaCl with 25 mM carbonate and 0.4 mM phosphate. The dose of the composition to be used will necessarily be dependent upon the needs of the individual to whom the composition of the disclosure is to be administered. These factors include, but are not necessarily limited to the weight, age, sex, and medical history of the individual. Shown in FIGS. 15, 16, 17, 18, 19, 20 are data from in vivo MRI studies done in mice. The contrast agent, Fe(TOB) was injected at 0.20 mL of 6.3 mM Fe-TOB-HSA (10.5 mg of HAS or two equivalents of megluamine). T₁relaxivity differences in tissue over a 30 minute period show that the highest signal is observed in the kidney cortex. A second in vivo study carried out with Fe(NOKA) shows that a contrast agent that lacks a water ligand does not perform as well in vivo. Fe(TOB) also produces contrast of brain tumors in mice (FIG. 20).

In an aspect, the present disclosure provides imaging methods using the macrocyclic complexes and compounds described herein. The imaging methods use magnetic resonance imaging methods. Non-limiting examples of such methods include, Magnetic Resonance Imaging (MRI).

Specifically, the macrocyclic compounds of the present disclosure, which are complexed to Fe(III), can be used as T₁MRI contrast agents. These complexes may have properties that change with alterations in pH. Such properties make these complexes useful for mapping pH to enable better therapeutic treatment of diseases such as, for example, cancer, stroke and heart disease.

The imaging methods of the present disclosure can be used to image a cell, tissue, organ, vasculature, or a part thereof. The cell, tissue, organ, vasculature can be a part of an individual. By “individual” it is meant a human or non-human animal (e.g., cow, pig, mouse, rat, cat, dog, or other agricultural, pet, or service animal, and the like). In an embodiment, the disclosure provides a method to obtain an image of at least a portion of a cell, tissue, organ, or vasculature comprising the steps of: contacting a cell, tissue, organ, or vasculature with the compounds of the present disclosure, and imaging at least a portion of the cell, tissue, organ, or vasculature to obtain an image of the portion of cell, tissue, organ, or vasculature. At least part of a cell, tissue, or organ can be alive or dead. Likewise, the individual can also be alive or deceased.

In an embodiment, the macrocyclic complex compound is used as a Fe(III) T₁MRI contrast agent. This contrast is produced by T₁weighted imaging to give positive contrast in the region where the iron complexes accumulate. The complexes are high-spin Fe(III) under biologically reducing conditions with either innersphere and/or outersphere water interactions that give a decrease in the T₁relaxation times of bulk water protons.

In this application, the use of the singular form encompasses the plural and vice versa.

The macrocyclic compounds of the present disclosure can be prepared, for example, as described in the Experimental Details. The following examples are presented to illustrate the present disclosure. They are not intended to be limiting in any manner. Those skilled in the art will recognize that routine modifications to these embodiments can be made which are intended to be within the scope of the disclosure.

The following Statements describe various examples of macrocyclic compounds, macrocyclic complexes, compounds, and compositions of the present disclosure, and uses thereof:

Statement 1. A macrocyclic compound of the present disclosure comprising: a macrocyclic core of the present disclosure (e.g., a macrocyclic core comprising from 9 to 15 atoms, where at least one of the atoms in the macrocyclic core is a N atom, at least two carbon atoms separate a heteroatom selected from the group consisting of: N atom, O atom, or S atom) and one or more pendant groups of the present disclosure, where the one or more pendant groups are substituents on (e.g., covalently bound to) the macrocyclic core (e.g., one or more pendant groups having the following structure:

[Image Omitted]

or an anionic (e.g., deprotonated) analog thereof or a stereoisomer thereof, where Q₁and Q₂are each independently H, OCH₃, CO₂H, or CH₂CO₂G₄, G₄is H, C₁to C₁₂substituted or unsubstituted alkyl groups of linear or branched structure or PEG group (—CH₂CH₂O—)_n(n=1-12), Q₃is H, C₁to C₁₂substituted or unsubstituted alkyl groups of linear or branched structure or PEG group (—CH₂CH₂O—)_n(n=1-12), Q₄and Q₅are each independently H, OCH₃, CO₂H, or substituted or unsubstituted alkyl groups of linear or branched structures, A is a substituted or unsubstituted alkyl group of linear or branched structure with C₁to C₁₂or is a substituted or unsubstituted aryl group, or an amino acid, a salt, a partial salt, a hydrate, a polymorph, or a stereoisomer thereof.

Statement 2. A macrocyclic complex comprising a high-spin Fe(III) cation complexed to a macrocyclic core is a macrocyclic compound of the present disclosure (e.g., a macrocyclic compound according to Statement 1), and/or at least one pendant group substituent of the macrocyclic compound, or a salt, a partial salt, a hydrate, a polymorph, or a stereoisomer thereof, where the macrocyclic compound exhibits a negative redox potential (e.g., a redox potential of less than 0 vs. normal hydrogen electrode (NHE) in aqueous (e.g., water) solution at a biologically relevant pH (e.g., 6.5-7.5 or 7.2-7.4)).

Statement 3. A macrocyclic compound or complex according to Statements 1 or 2, where at least one or all of the one or more pendant groups is covalently bound to a N on the macrocyclic core.

Statement 4. A macrocyclic complex according to Statements 2 or 3, where the macrocyclic complex has at least one open coordination site.

Statement 5. A macrocyclic complex according to any one of Statements 2-4, where the macrocyclic complex has at least one water or at least one hydroxide complexed to the high-spin Fe(III) cation.

Statement 6. A macrocyclic compound or macrocyclic complex according to any one of Statements 1-5, where at least one of the pendant groups is substituted at a benzylic position or any carbon the alkyl group leading to the heteroatom of the pendant group.

Statement 7. A macrocyclic compound or macrocyclic complex according to any one of Statements 1-6, where the macrocyclic core is a cyclen moiety, a cyclam moiety, or TACN moiety.

Statement 8. A macrocyclic complex according to any one of Statements 2-4, where the macrocyclic complex comprises a TACN moiety and at least one (e.g., one or two) anionic pendant groups.

Statement 9. A macrocyclic complex according to Statement 8, where the anionic pendants are individually chosen from carboxylate pendants, imidazolate pendants, pyrazolate pendants, alkoxide pendants, and phenoxide pendants.

Statement 10. A macrocyclic complex according to Statement 8 or 9, where the macrocyclic complex further comprises a coordinating pendant group or a non-coordinating pendant.

Statement 11. A macrocyclic compound or macrocyclic complex according to any one of Statements 1-10, where the macrocyclic core has one of the following structures:

[Image Omitted]

- where X₁, X₂, X₃, and X₄are N; W₁, W₂, and W₃are each independently O or S; Y₁, Y₂, Y₃, and Y₄are each independently pendant donors comprising N, where N has a lone pair of electrons (e.g., amino, benzimidazole, imidazole, aniline, pyrazoyl, triazole, benzotriazole), or a pendant donor comprising O, where O has at least one lone pair of electrons but preferably two or three lone pairs (e.g., ketone, alcohol, alkoxide, carboxylic acid, amide, phenol or phenoxide, or a deprotonated form of the foregoing, such as a carboxylate ion, an imidazolate ion, a pyrazolate ion or an oxide, including, for example, an alkoxide or a phenoxide); m₁, m₂, m₃, and m₄are each independently 0, 1, or 2; n₁, n₂, n₃, and n₄are each independently 1 or 2; and R₁, R₂, and R₃are each independently substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl or substituted or unsubstituted alkyl group, where R₁, R₂, and R₃are not substituted by a pendant donor, where the alkyl segment of the alkyl-Y chain (alkyl-Y₁, alkyl-Y₂, alkyl-Y₃and/or alkyl-Y₄) may each independently be substituted (e.g., Structure a or Structure b) or unsubstituted (Structure c or Structure d). For Structures a-f, the pendent may have either R or S configuration at the chiral carbon:

[Image Omitted]

Statement 12. A macrocyclic compound or complex according to any one of Statements 2-11, where the macrocyclic core has the following structure:

[Image Omitted]

- where R₁, R₂, and R₃each independently=substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl or substituted or unsubstituted alkyl group, where R₁, R₂, and R₃are not substituted by pendant donors; and when the macrocycle has Structure I, Z₁=H or one of the pendant groups in Scheme III and Z₂and Z₃each independently=one of the pendant groups in Scheme III;
- when the macrocycle has Structure II, III, VII, VIII, IX or XV, Z₁and Z₂each independently=one of the pendant groups in Scheme III; when the macrocycle has Structure VI, XI or XIV, Z₁and Z₃each independently=one of the pendant groups in Scheme III;
- when the macrocycle has Structure XVI, Z₁=one of the pendant groups in Scheme III; when the macrocycle has Structure IV, Z₄=one of the pendant groups in Scheme III and Z₁, Z₂and Z₃each independently=H or one of the pendant groups in Scheme III, provided that at most two of Z₁, Z₂and Z₃=H;
- when the macrocycle has Structure V, Z₁and Z₂each independently=H or one of the pendant groups in Scheme III and Z₃=one of the pendant groups in Scheme III;
- when the macrocycle has Structure X, Z₁and Z₃each independently=one of the pendant groups in Scheme III and Z₂=H or one of the pendant groups in Scheme III; when the macrocycle has Structure XII, Z₄=one of the pendant groups in Scheme III and Z₁, Z₂and Z₃each independently=H or one of the pendant groups in Scheme III, provided that at most two of Z₁, Z₂, and Z₃=H;
- when the macrocycle has Structure XIII, Z₁and Z₃each independently=one of the pendant groups in Scheme III and Z₂=H or one of the pendant groups in Scheme III; where for all Structures I-XVI, each of Z₁, Z₂, Z₃and Z₄, as applicable, are selected independently of each other.
  
  Statement 13. A macrocyclic compound or complex according to any one of Statements 2-12, where the macrocyclic core has the following structure:

[Image Omitted]

Statement 14. A macrocyclic compound or complex according to any one of Statements 2-13, where the macrocyclic compound has one of the following structures:

[Image Omitted]

Statement 15. A compound comprising one or more macrocyclic groups (e.g., macrocyclic complex groups) tethered together (e.g., covalently linked) by a linker group or a polymer, a dendrimer, a protein, or a peptide, comprising one or more pendant macrocyclic groups (e.g., macrocyclic complex groups) covalently linked (e.g., bound) to the polymer, the dendrimer, the protein, or the peptide, where each of the individual macrocyclic groups (e.g., macrocyclic complex groups) are derived from a macrocyclic compound of the present disclosure (e.g., a macrocyclic compound according to any one of Statements 1-14).

Statement 16. A compound or polymer according to Statement 15, where the compound has the following structure:

[Image Omitted]

Statement 17. A compound or polymer according to Statement 15, where the polymer has the following structure:

[Image Omitted]

Statement 18. A composition comprising one or more macrocyclic compound and/or one or more macrocyclic complex of the present disclosure (e.g., one or more macrocyclic compound according to Statements 1 and/or one or more macrocyclic complex according to any one of Statements 2-14) and/or one or more compound of the present disclosure (e.g., a compound according to any one of Statements 15-17) and a pharmaceutically acceptable carrier.

Statement 19. A composition according to Statement 18, where the composition further comprises human serum albumin and/or meglumine.

Statement 20. A method to obtain an image of at least a portion of a cell, organ, vasculature or tissue comprising: contacting the cell, organ, vasculature, or tissue with one or more macrocyclic compound and/or one or more macrocyclic complex of the present disclosure (e.g., one or more macrocyclic compound according to Statement 1 and/or one or more macrocyclic complex according to any one of Statements 2-14) and/or one or more compound of the present disclosure (e.g., a compound according to any one of Statements 15-17), and imaging at least a portion of the cell, organ, vasculature, or tissue to obtain an image of the portion of a cell, organ, vasculature, or tissue, where the image is obtained by using magnetic resonance.

Statement 21. A method according to Statement 20, where the cell, organ, vasculature, or tissue is part of an individual.

Statement 22. A method according to Statement 20 or 21, where the image is obtained using magnetic resonance imaging (MM).

Statement 23. A method according to any one of Statements 20-22, where the macrocyclic compound(s) and/or compound(s) is/are a T₁agent or T₁agents.

EXPERIMENTAL DETAILS

General procedure for synthesis of disubstituted TACN (1,4,7-triazacyclononane) ligands. Other synthetic procedures are shown in FIGS. 27, 28, 29, 30.

TACN-Protection: N,N-Dimethylformamide dimethylacetal (304 mg, 2.55 mmol, 1.1 equiv) was added to a solution of TACN (300 mg, 2.32 mmol) in chloroform (2 mL) and toluene (8 mL). The solution was stirred at room temperature for 12 hours. The solvent was evaporated under reduced pressure to yield an oily product. This crude product was used in the next synthesis without further purification. ESI-MS (m/z) of 1,4,7-triazatricyclo[5.2.1.04,10]decane (tacn orthoamide), calculated: 140.1 [M+H+] (100%).

Protected TACN alkylations. The crude TACN-orthoamide product isolated above was dissolved in dry THF (5 mL) and Ar(g) was bubbled through this solution for 5 minutes to produce an inert atmosphere. Halogenated reagents were added to this solution either directly or pre-dissolved in 1 mL dry THF. These reagents may include one of the following including: benzyl bromide, iodomethane, propargyl bromide, 1-Bromo-2-(2-methoxy-ethoxy)ethane, 4-(bromomethyl)-1,1′-biphenyl, ethyl 4-(bromomethyl)-benzoate or benzyl chloromethyl ether. Solutions were stirred for 1-7 days depending on the chosen reagent. The product precipitated from solution, which was then filtered and washed with diethyl ether (3×15 mL). If the product did not precipitate, such as is the case with 1-Bromo-2-(2-methoxy-ethoxy)ethane, solvent was removed under pressure to yield a crude product which can be utilized in the next synthesis without further purification.

Deprotection of alkylated protected TACN derivatives. Products of the previous synthesis were dissolved in 12 M HCl/MeOH 1:1 solution or KOH solution. The solution was refluxed overnight. After the solution was allowed to cool to room temperature, purification of products was carried out by one of two methods. To isolate the free-base form of the product, the pH of the solution was adjusted to 12 (in the case of KOH deprotection, no adjustment is needed) and product was extracted using chloroform (3×10 mL). Chloroform layers were combined and solvent removed under pressure. To isolate the product as HCl salt, solvent was evaporated under pressure and crude HCl salt was dissolved in ethanol (5 mL). 12 M HCl was added to the solution (1-2 mL) and solvent was evaporated under pressure to yield product.

Propyl alcohol donor group addition. One of the monoalkylated products (free base form) described in the paragraph above was dissolved in ethanol, water, or an ethanol/water mixture. (S)-(−) propylene oxide was added to the solution and stirred for 12 hours. Solvent was removed under pressure to yield the crude product. Purification of final ligands was performed using column chromatography, chloroform/methanol 100/0 to 50/50. Alternatively, (R)-(+) propylene oxide may be used instead of (S)-(−) propylene oxide to give the macrocycle with pendent groups of an opposite chirality.

General Procedure for forming Fe(III) TACN derivatives. The ligand described immediately above was dissolved in ethanol and FeCl₂·4H₂O was added to the solution. The solution was heated to 40° C. and allowed to stir for 1 hour. After the solution was allowed to cool to RT, diethyl ether was added until product precipitates. The product was filtered and washed with diethyl ether (3×20 mL). Alternatively, an equivalent of FeCl₃, was added to a stirred solution of the ligand in acetonitrile along with two equivalents of trimethylamine. Diethyl ether was added until the product precipitated.

SPECIFIC EXAMPLES

Synthesis of TOB ligand. Synthesis of 1,1′-(7-benzyl-1,4,7-triazonane-1,4-diyl)bis(propan-2-ol). In a 10 mL round-bottom flask, 1-Benzyl[1,4,7]-triazacyclononane (0.127 g, 0.5795 mmol) was dissolved in 5.0 mL absolute ethanol. To this solution was added (S)-(−)-propylene oxide (2.9 mmol, 5.0 eq). After the solution was stirred at RT for 2 days the solvent was removed under pressure to yield an oily crude product. The crude product was then dissolved in diethyl ether and precipitate removed through filtration. The filtrate was dried under pressure to yield 1,1′-(7-benzyl-1,4,7-triazonane-1,4-diyl)bis(propan-2-ol) as a clear oil (0.1657 g, 0.4942 mmol, 85%). ESI-MS: m/z=336.3 [M+H]+. ¹H NMR (400 MHz, CD3OD); δ 1.09 (d, 6H, J=6), 2.25-2.94 (m, 16H), 3.55-3.83 (m, 4H), 7.15-7.44 (m, 5H). ¹³C NMR (75 MHz, CDCl₃): δ 19.9, 54.4, 55.2, 62.7, 63.8, 66.4, 127.1, 128.2, 129.6, 139. To the TOB ligand in acetonitrile was added one equivalent of FeCl₃, two equivalents of triethylylamine and the reaction was stirred overnight. Diethyl ether was added until the product precipitated. The precipitate was isolated and washed with diethyl ether and dried under vacuum. Yield 35%. ESI-MS: m/z=389.2 [M]⁺, 425.0 [M+H+Cl]⁺. Wash with diethyl ether. Dry under vacuum. Yield 35%. ESI-MS: m/z=389.2 [M]⁺, 425.0 [M+H+Cl]⁺.

Synthesis of TON ligand. Benzyl deprotection was performed by Pd/C (10%) catalyst. 30 mg Pd/C (10%) in 5 mL methanol 1 mL water was added into the ligand solution. The air was removed from the solution under argon gas for 30 minutes. Catalytic hydrogenation was performed for 3 days with vigorous shaking on a Parr hydrogenator at room temperature under hydrogen atmosphere. The mixture was filtrated over celite to remove the catalyst from the reaction solution and (1,4,7-triazonane-1,4-diyl)bis(propan-2-ol) (TON ligand) was obtained. ESI-MS (m/z), calculated: 246.3 [M+H³⁰] (100%). The solution was dried by placing flask on a rotoevaporator.

Synthesis of NODAC (2,2′-(1,7-dioxa-4,10-diazacyclododecane-4,10-diyl) diacetic acid). A mass of 0.122 grams (0.701 mmol) of 4,10-Diaza-12-crown 4-ether and 0.0987 grams (0.714 mmol) of potassium carbonate were added into 5 mL of acetonitrile and stirred a round bottom flask at room temperature. To the stirring mixture, 0.2848 grams (1.46 mmol) of tert-butyl bromoacetate was slowly added by pipette. The solution continued to stir for four hours. Next the solution was filtered, removing any undissolved potassium carbonate and the filtrate was put under vacuum to remove the solvent, leaving behind a yellow oil. The oil was dissolved in 3 mL of dichloromethane and 1 mL of trifluoroacetic acid and allowed to stir at room temperature overnight. Next, the solvent was removed by vacuum, and the remaining white solid was washed in a 50:50 ether-methanol mixture, and filtered for collection. The yield of the product was 0.1822 grams (0.628 mmol, 89.5%). ¹H NMR (300 MHz) ppm: 4.004 (s, pendent CH₂, 4H), 3.760 (t, O—CH₂, 8H), 3.535 (s, ring N—CH₂, 8H). ESI-MS:m/z=347.2 [M+2Na—H)]⁺, 375.0 [M+2Na+K—2H+]⁺).

Synthesis of Fe(III)NODAC complex. A mass of 0.1108 grams (0.381 mmol) of 2,2′-(1,7-dioxa-4,10-diazacyclododecane-4,10-diyl) diacetic acid was dissolved in 3 mL of water and stirred into solution, adding small aliquots of a 1 M NaOH until a pH of 6 was reached. Next, 0.1028 grams (0.380 mmol) of iron(III)chloride hexahydrate was added to the solution and stirred overnight. Acetonitrile was added into the solution and centrifuged to form a precipitate. The precipitate was repeatedly washed and centrifuged with ether to remove water, then allowed to dry under vacuum. A red solid was obtained. Yield, 0.0601 grams of [Fe(III){NODAC)OH] was obtained (0.139 mmol, 36.6%). ESI-MS: m/z=384.1 ([M+NaOH—2H]⁺).

Synthesis of NODOH (2,2′-(1,7-dioxa-4,10-diazacyclododecane-4,10-diyl) bis(propan-2-ol). A mass of 102.6 mg (0.589 mmol) of 4,10-Diaza-12-crown 4-ether was dissolved in 4 mL ethanol and stirred in a round bottom flask. A large excess of S-propylene oxide (0.400 mL, 0.332 g, 5.716 mmol) was added to the solution and stirred for three days at room temperature. Solvent was removed under vacuum to yield a yellow oil product (0.0603 g, 0.207 mmol, 35.1%). ¹H NMR (300 MHz) ppm: 3.75 (m, CH, 2H), 3.48 and 3.33 (t, O—CH₂, 8H), 2.69 and 2.49 (t, N—CH₂(ring), 8H), 2.34 and 3.24 (t, N—CH₂pendent, 4H), 1.00 (d, CH3, 6H). ESI-MS:m/z=291.3 [M+H]+, 313.3 [M+Na]+.

Synthesis of Fe(NODOH). A mass of 0.0796 grams of NODOH was dissolved in ethanol and added to a round bottom flask. Next 0.0548 grams of FeCl