Quinoline ligands and metal complexes for diagnosis and therapy

The present invention relates to novel ligands for forming metal complexes that absorb or fluoresce in the visible or near-infrared (NIR) region of the electromagnetic spectrum, new complexes incorporating such ligands, process for preparing such complexes, and methods of imaging or therapy using such agents. More particularly, the present invention specifically pertains to novel metal complexes derived from quinoline based heterocyclic N.sub.2 O.sub.3, N.sub.3 O.sub.3, N.sub.3 O.sub.4, N.sub.3 O.sub.5 and N.sub.2 OS ligands, and are useful as general imaging, diagnostic, or therapeutic agents employing optical, nuclear medicine, or magnetic resonance procedures.

FIELD OF THE INVENTION
 The present invention relates to diagnosis and therapy within the field of
 biomedical optics. More particularly, the invention relates to novel
 ligands for forming metal complexes that absorb or fluoresce in the
 visible or near-infrared (NIR) region of the electromagnetic spectrum, new
 complexes incorporating such ligands, process for preparing such
 complexes, and methods of imaging or therapy using such agents.
 BACKGROUND OF THE INVENTION
 The field of biomedical optics is growing rapidly due to distinct
 advantages over other imaging modalities such as X-ray CT, MRI, nuclear
 medicine, or ultrasound (J. C. Hebden and D. T. Delpy. Diagnostic Imaging
 with Light, The British Journal of Radiology, 1997, 70, S206-S214; G.
 Freiherr. The Light Stuff: Optical Imaging in Medical Diagnostics, Medical
 Devices & Diagnostic Industry, 1998, 40-46). Compounds absorbing or
 emitting in the visible or NIR region of electromagnetic spectrum are
 potentially useful for tomographic imaging, endoscopic examination,
 photodynamic therapy, optoacoustic imaging, and sonofluourescene
 techniques. Furthermore, compounds absorbing or emitting in the
 appropriate visible region can be used to generate singlet oxygen and have
 been shown to be effective for photodynamic therapy of certain types of
 tumors.
 Metal ions continue to play a major role in diagnostic and therapeutic
 medicine. For example, radionuclide metal complexes derived from both
 transition and lanthanide elements are being used extensively in
 diagnostic and therapeutic nuclear medicine procedures, paramagnetic
 complexes are being used extensively in magnetic resonance imaging
 procedures, and platinum complexes have long been used as cancer
 chemotherapeutic agents. Recently, metal complexes that absorb or emit in
 the visible or near-infrared (NIR) region have made a significant impact
 in the field of biomedical optics and have a great potential for
 photodiagnostic and phototherapeutic applications (J. N. Demas and B. A.
 DeGraff. Design and Applications of Highly Luminescent Transition Metal
 Complexes, Analytical Chemistry, 1991, 63, 829-837; M. P. Houline et al.
 Spectroscopic Characterization and Tissue Imaging Using Site-Selective
 Polyazacyclic Terbium (III) Chelates, Applied Spectroscopy, 1996, 50(10),
 1221-1228; J. R. Lakowicz et al. Development of Long-Lifetime Metal-Ligand
 Probes for Biophysics and Cellular Imaging, Journal of Fluorescence, 1997,
 7, 17-25; F. J. Steemers et al. Near-Infrared Luminescence of Yb.sup.3+,
 Nd.sup.3+, and Er.sup.3+ Azatriphenylene Complexes, Tetrahedron Letters,
 1998, 39, 7583-7586; G. E. Keifer and D. J. Bornhop. Fluorescent Chelates
 as Visual Tissue Specific Imaging Agents, U.S. Pat. No. 5,922,867, 1999).
 Examples of suitable metal ions for optical applications include Cr(III),
 Os(II), Ru(II), Ni(II), Eu(III), Tb(III), Lu(III), Yb(III), Er(III), and
 Nd(III). Eu(III), and Tb(III) are particularly preferred because of
 favorable absorption and emission properties in visible and NIR regions.
 The key requirements for design of novel metal complexes for optical
 diagnostic and therapeutic application are: (a) strong absorption and
 emission in the visible or NIR region; (b) high thermodynamic, kinetic,
 and photo stability; (c) low toxicity; (d) water solubility; and (e)
 conjugation capability for targeted delivery to particular tissues or
 organs. Free metal ions are generally quite toxic; they need to be
 administered in the form of complexes with complexing agents (ligands) in
 order to deliver them to specific organs and to alleviate toxicity.
 Electronic property, toxicity, stability, and tissue specificity are
 greatly affected by the nature of the complexing agents (ligands). Various
 physicochemical and pharmacokinetic factors have to be considered in order
 to render the metal complex safe and effective. Electronic requirements
 for enabling the metal ion (transition and lanthanide) to absorb or emit
 in the visible or NIR region are well established and essentially involve
 incorporation of metal into highly polarizable .pi.-electron rich,
 multidentate ligand systems. Energy transfer from aromatic donors
 (referred to as "antennae") to the lanthanide metal ion directly bounded
 to the donor group results in large increase in lanthanide fluorescence
 (S. I. Weissman, Journal of Chemical Physics, 1942, 10, 214; B. Alpha et
 al. Energy Transfer Luminescence of Europium (III) and Terbium (III)
 Cryptates of Macrobicyclic Polypyridine Ligands, Angewandte Chemie
 International Edition in English, 1987, 26(3), 266-267; J. B. Lamture et
 al. Luminescence Properties of Terbium (III) Complexes with 4-Substituted
 Dipiclolinic Acid Analogues, Inorganic Chemistry, 1995, 34, 864-869). In
 contrast, simple lanthanide metal salts or lanthanide ions coordinated to
 polyaminocarboxylate ligands wherein the aromatic donors are not directly
 attached exhibit very weak fluorescence in aqueous media (A. Abusaleh and
 C. F. Meares. Photochemistry and Photobiology, 1984, 39, 763-769).
 Long-wavelength fluorescence of transition metal complexes generally
 occurs via metal-to-ligand charge transfer (MCLT) interactions (Z. Murtaza
 and J. R. Lakowicz. Long-lifetime and Long-wavelength Osmium (II) Metal
 Complexes Containing Polypyridine Ligands. Excellent Red Fluorescent Dyes
 for Biophysics and for Sensors, SPIE, 1999, 3602, 309-315).
 Toxicity of metal complexes is greatly affected by the nature of the
 ligands. Since in vivo release of free metal ions from the complex is a
 major cause of toxicity, thermodynamic and kinetic stability are critical
 requirements for the design of novel ligands. The thermodynamic stability
 constant indicates the affinity of totally unprotonated ligand for a metal
 ion. The conditional stability constant indicates the stability of the
 complex under physiological pH. Ion selectivity of the ligand toward the
 desired metal ion over other endogenous metal ions such as zinc, iron,
 magnesium, and calcium, determines the rate of release of the metal ion
 into the vascular or extracellular space. The released metal ion is
 capable of crossing the blood-brain barrier and thereby perturbing the
 neurophysiology. Therefore, in vivo reaction kinetics are also a major
 factor in the design of stable complexes and complexes with structural
 features that make in vivo transmettlation reactions proceed much slower
 than the biological clearance of the intact metal complexes would be
 predicted to have low toxicities (W. Cacheris et al., Magnetic Resonance
 Imaging, 1990, 8, 467; Oksendal et al., Journal of Magnetic Resonance
 Imaging, 1993, 3, 157). Thus, a need continues to exist for new and
 structurally diverse metal complexes for use as imaging, diagnostic, or
 therapeutic agents employing optical procedures.
 SUMMARY OF THE INVENTION
 Thermodynamically and kinetically stable metal complexes can be achieved
 with a proper choice of ligands systems. Transition metal ions generally
 require soft donors such as thiols and phosphines, whereas lanthanide ions
 require hard donors such as carboxylates or amines. However, unsaturated
 heterocyclic bases such as pyridines, imidazoles, and the like are
 excellent coordinators to both types of metal ions. Numerous pyridine,
 quinoline, and imidazole based metal complexes have been prepared and many
 of them have been conjugated to bioactive carriers such as immunoglobulins
 (R. Rajagopalan et al. Preparation, Characterization, and Biological
 Evaluation of Technetium (V) and Rhenium (V) Complexes of Novel
 Heterocyclic Tetradentate N.sub.3 S Ligands, Bioconjugate Chemistry, 1997,
 8, 407-415; J. B. Lamture and T. G. Wensel. A Novel Reagent for Labeling
 Macromolecules with Intensely Luminescent Lanthanide Complexes,
 Tetrahedron Letters, 1993, 34(26), 4141-4144). The present invention
 specifically pertains to novel quinoline based heterocyclic N.sub.2
 O.sub.3, N.sub.3 O.sub.3, N.sub.3 O.sub.4, and N.sub.2 OS ligands that are
 suitable for complexing metal ions, and are useful as general imaging,
 diagnostic, or therapeutic agents employing optical, nuclear medicine, or
 magnetic resonance procedures. The principal advantages of this invention
 are: (a) the metal ion is directly bounded to the "antenna" portion of the
 molecule, and (b) the entire complex is rigid. Both of these factors are
 expected to contribute to significant enhancement of absorption and
 luminescence properties compared to those metal complexes where the
 antenna is either located remote from the metal ion or has considerable
 degrees of freedom.
 DETAILED DESCRIPTION OF THE INVENTION
 The present invention provides new and structurally diverse compositions
 comprising complexing agents (ligands) of the general Formula 1,
 ##STR1##
 wherein R.sup.1 to R .sup.5 may the same or different and are selected from
 the group consisting of hydrogen, C1-C10 alkyl, --OH, C1-C10
 polyhydroxyalkyl, C1-C10 alkoxyl, C1-C10 alkoxyalkyl, --SO.sub.3 H,
 --(CH.sub.2).sub.m --CO.sub.2 H and --NR.sup.6 R.sup.7 ; R.sup.6 and
 R.sup.7 may the same or different and are selected from the group
 consisting of hydrogen, C1-C10 alkyl, C1-C10 aryl, and C1-C10
 polyhydroxyalkyl; m ranges from 0 to 10; A.sup.1 is selected from the
 group consisting of --OH, --CO.sub.2 H, --N(R.sup.8)(R.sup.9), --SPg
 --CONHR.sup.10 and --HNCOR.sup.11 ; R.sup.8 and R.sup.9 may the same or
 different and are selected from the group consisting of hydrogen, C1-C10
 alkyl, C1-C10 aryl, C1-C10 polyhydroxyalkyl, --(CH.sub.2).sub.m CO.sub.2 H
 and --(CH.sub.2).sub.2 --N(CH.sub.2 CO.sub.2 H).sub.2 ; R.sup.10 is
 selected from the group consisting of hydrogen, C1-C10 alkyl, C1-C10 aryl,
 C1-C10 polyhydroxyalkyl and --(CH.sub.2).sub.2 --SPg; R.sup.11 is selected
 from the group consisting of hydrogen, C1-C10 alkyl, C1-C10 aryl, C1-C10
 polyhydroxyalkyl and --CH(R.sup.12)--SPg; R.sup.12 is selected from the
 group consisting of hydrogen, C1-C10 alkyl, C1-C10 aryl, C1-C10
 polyhydroxyalkyl, --(CH.sub.2).sub.m CO.sub.2 H and --(CH.sub.2).sub.n
 NH.sub.2 ; n varies from 1 to 10; B.sup.1 is selected from the group
 consisting of --CHR.sup.13 and --CH(R.sup.14)CH(R.sup.15); R.sup.13 to
 R.sup.15 may be the same or different and are defined in the same manner
 as R.sup.12 ; C.sup.1 is selected from the group consisting of hydrogen,
 C1-C10 alkyl, C1-C10 aryl, C1-C10 polyhydroxyalkyl, C1-C10 alkoxyl, C1-C10
 alkoxyalkyl, --(CH.sub.2).sub.m CO.sub.2 H, --CH.sub.2 CH.sub.2
 --N(CH.sub.2 CO.sub.2 H).sub.2, --(CH.sub.2).sub.2 --SPg and
 --COCH(R.sup.16)--SPg; R.sup.16 is defined in the same manner as R.sup.12
 ; D.sup.1 is selected from the group consisting of hydrogen, C1-C10 alkyl,
 C1-C10 aryl, hydroxyl, C1-C10 polyhydroxyalkyl, C1-C10 alkoxyl, C1-C10
 alkoxyalkyl, --(CH.sub.2).sub.m CO.sub.2 H, and --CH.sub.2 CH.sub.2
 --N(CH.sub.2 CO.sub.2 H).sub.2 ; and Pg may be hydrogen or a protecting
 group selected from the group consisting of t-butyl, benzyl, benzoyl,
 2,4-dimethoxybenzyl, trityl, tetrahydropyranyl, C1-C10 acyl, C1-C10
 alkoxyalkyl, and C1-C10 alkoxycarbonyl.
 In a preferred embodiment, ligands according to the present invention have
 the general formula of Formula 1 above wherein R.sup.1 to R.sup.5 are
 selected from the group consisting of hydrogen, --OH, C1-C10 alkoxyl,
 --(CH.sub.2).sub.m --CO.sub.2 H, and --N(R.sup.6)(R.sup.7); A.sup.1 is
 selected from the group consisting of --OH, --N(R.sup.8)(R.sup.9), and
 --HNCOR.sup.11 ; B.sup.1 is --CHR.sup.13 ; C.sup.1 is selected from the
 group consisting of hydrogen, C1-C10 alkyl, --(CH.sub.2).sub.m CO.sub.2 H,
 --CH.sub.2 CH.sub.2 --N(CH.sub.2 CO.sub.2 H).sub.2, and
 --COCH(R.sup.16)--SPg; D.sup.1 is selected from the group consisting of
 hydrogen, C1-C10 alkyl, C1-C10 polyhydroxyalkyl, --(CH.sub.2).sub.m
 --CO.sub.2 H, and --CH.sub.2 CH.sub.2 --N(CH.sub.2 CO.sub.2 H).sub.2 ; and
 Pg is selected from the group consisting of C1-C10 acyl,
 tetrahydropyranyl, C1-C10 alkoxyalkyl, and C1-C10 alkoxycarbonyl.
 In a further preferred embodiment, ligands according to the present
 invention have the general formula of Formula 1 above wherein R.sup.1 to
 R.sup.5 are hydrogens; A.sup.1 is --OH or --N(CH.sub.2 CO.sub.2 H).sub.2 ;
 B.sup.1 is --CH.sub.2 --; C.sup.1 is selected from the group consisting of
 --CH.sub.2 --CO.sub.2 H, --CH.sub.2 CH.sub.2 --N(CH.sub.2 CO.sub.2
 H).sub.2, and --COCH.sub.2 --SPg; D.sup.1 is selected from the group
 consisting of hydrogen, C1-C10 alkyl, and --CH.sub.2 --CO.sub.2 H; and Pg
 is selected from the group consisting of benzoyl, tetrahydropyranyl, and
 methoxycarbonyl.
 The present invention also provides structurally diverse compositions
 comprising metal complexes of the general formula of Formula 2 formed by
 coordination of an appropriate metal ion to the ligands derived from
 Formula 1 shown above,
 ##STR2##
 wherein R.sup.17 to R.sup.21 may the same or different and are defined in
 the same manner as R.sup.1 ; A.sup.2 is selected from the group consisting
 of --O.sup.-, --CO.sub.2.sup.-, --N(R.sup.8)(R.sup.9), --SPg
 --CON(R.sup.10), and --NCOR.sup.11 ; R.sup.8 and R.sup.9 may the same or
 different and are selected from the group consisting of hydrogen, C1-C10
 alkyl, C1-C10 aryl, C1-C10 polyhydroxyalkyl, --(CH.sub.2).sub.m
 CO.sub.2.sup.-, and --(CH).sub.2 --N(CH.sub.2 CO.sub.2.sup.-).sub.2 ;
 R.sup.10 is selected from the group consisting of hydrogen, C1-C10, alkyl,
 C1-C10 aryl, C1-C10 polyhydroxyalkyl, and --(CH.sub.2).sub.2 --S; R.sup.11
 is selected from the group consisting of hydrogen, C1-C10 alkyl, C1-C10
 aryl, C1-C10 polyhydroxyalkyl, and --CH(R.sup.12)--S.sup.31 ; R.sup.12 is
 selected from the group consisting of hydrogen, C1-C10 alkyl, C1-C10 aryl,
 C1-C10 polyhydroxyalkyl, --(CH.sub.2).sub.m CO.sub.2.sup.- and
 --(CH.sub.2).sub.n NH.sub.2.sup.- ; m ranges from 0 to 10 n varies from 1
 to 10; B.sup.2 is selected from the group consisting of --CHR.sup.13 and
 --CH(R.sup.14)CH(R.sup.15); R.sup.13 to R.sup.15 may be the same or
 different and are defined in the same manner as R.sup.12 ; C.sup.2 is
 selected from the group consisting of hydrogen, C1-C10 alkyl, C1-C10 aryl,
 C1-C10 polyhydroxyalkyl, C1-C10 alkoxyl, C1-C10 alkoxylalkyl,
 --(CH.sub.2)mCO.sub.2.sup.-, --CH.sub.2 CH.sub.2 --N(CH.sub.2
 CO.sub.2.sup.-).sub.2, --(CH.sub.2).sub.2 --S.sup.-, and
 --COCH(R.sup.16)--S.sup.- ; R.sup.16 is defined in the same manner as
 R.sup.12, D.sup.2 is selected from the group consisting of hydrogen,
 C1-C10 alkyl, C1-C10 aryl, hydroxyl, C1-C10 polyhydroxyalkyl, C1-C10
 alkoxyl, C1-C10 alkoxylalkyl, --(CH.sub.2).sub.m CO.sub.2.sup.-, and
 --CH.sub.2 CH.sub.2 --N(CH.sub.2 CO.sub.2.sup.-).sub.2 and M is a metal
 ion having an atomic number of .sub.24 to 31, 42 to 49, 58-71, or 74-83.
 In a preferred embodiment, the complexes according to the present invention
 have the general formula of Formula 2 above wherein R.sup.17 to R.sup.21
 are selected from the group consisting of hydrogen, --O.sup.-, C1-C10
 alkoxyl, --(CH2).sub.m --CO.sub.2.sup.- ; and --N(R.sup.6)(R.sup.7);
 A.sup.2 is selected from the group consisting of --O.sup.- ;
 --N(R.sup.8)(R.sup.9), and --HNCOR.sup.11 ; B.sup.2 is --CHR.sup.13 ;
 C.sup.2 is selected from the group consisting of hydrogen, C1-C10 alkyl,
 --(CH.sub.2)mCO.sub.2.sup.-, --CH.sub.2 CH.sub.2 --N(CH.sub.2
 CO.sub.2.sup.-).sub.2, and --COCH(R.sup.16)--S.sup.- ; D.sup.2 is selected
 from the group consisting of hydrogen, C1-C10 alkyl, C1-C10
 polyhydroxyalkyl, --(CH.sub.2)mCO.sub.2.sup.-, and --CH.sub.2 CH.sub.2
 --N(CH.sub.2 CO.sub.2.sup.-).sub.2 and M is a metal ion having an atomic
 number of 24 to 28, 31, 42 to 45, 49, 62-65, 71, 75, 76, or 83.
 In a further preferred embodiment, the complexes according to the present
 invention have the general formula of Formula 2 above wherein R.sup.17 to
 R.sup.21 are hydrogens; A.sup.2 is --O.sup.- or --N(CH.sub.2
 CO.sub.2.sup.-).sub.2 ; B.sup.2 is --CH.sub.2 --; C.sup.2 is selected from
 the group consisting of --CH.sub.2 --CO.sub.2.sup.-, --CH.sub.2 CH.sub.2
 --N(CH.sub.2 CO.sub.2.sup.-).sub.2, and --COCH.sub.2 --S.sup.- ; D.sup.2
 is selected from the group consisting of hydrogen, C1-C10 alkyl, and
 --CH.sub.2 --CO.sub.2.sup.- ; and M is a metal ion having an atomic number
 of 24-26, 28, 31, 43, 44, 49, 62-65, 71, 75, or 76.
 The compositions of the invention are suitable for use with a variety of
 other modalities including X-rays, magnetic resonance, and radiographic
 imaging. Electron donating and electron releasing groups at various
 positions in the ligands of Formula 1 and the metal complexes Formula 2
 provide an opportunity to alter the absorption and emission properties of
 the molecule thereby enhancing the optical utility of these molecules.
 Also, these additional functionalities afford the capability of
 conjugation to biomolecules and synthetic polymers for selective delivery
 to various organs or tissues of interest. The term biomolecule refers to
 all natural and synthetic molecules that play a role in biological
 systems. Biomolecules include hormones, amino acids, peptides,
 peptidomimetics, proteins, nucleosides, nucleotides, nucleic acids,
 carbohydrates, lipids, albumins, mono- and polyclonal antibodies, receptor
 molecules, receptor binding molecules, synthetic polymers, and aptamers.
 Specific examples of biomolecules include inulins, prostaglandins, growth
 factors, growth factor inhibitors like somatostatin, liposomes, and
 nucleic acid probes. Example of synthetic polymers include polylysine,
 polyaspartic acid, polyarginine, aborols, dendrimers, and cyclodextrins.
 The advantages of biomolecules include enhance tissue targeting through
 specificity and delivery. The specific targeting of effector molecules to
 a particular tissue, such as tumor, using antibodies is well known in the
 art (see Halpern et al., Diagnostic Imaging, 1983, 40). Coupling of
 bifunctional ligands and complexes to biomolecules can be accomplished by
 several known methods (see Hnatowich et al., Science, 1983, 220, 613).
 The complexes of the present invention may vary widely depending on the
 contemplated application. For diagnostic imaging of areas of lesion,
 fluorescent compounds absorbing and emitting in the near infrared (NIR)
 region, i.e. 650-900 nm, are desirable. For monitoring blood clearance or
 for endoscopic examination of lesions, dyes absorbing and emitting in the
 region of 350-950 nm, preferably 600-900 nm, are desirable. Similarly, the
 carrier molecules may also vary widely. For blood persistent agents,
 albumin or methylated serum albumin is preferable. For renal function
 measurements, polysaccharides or anionic polypeptides are desirable. For
 endoscopic examination of lesions, antibodies, peptides, or carbohydrates
 directed against specific cell surface markers are preferred.
 Diagnostic compositions comprising the compounds of the invention are also
 provided. Methods of performing diagnostic procedures with compositions of
 the invention are also disclosed. The method comprises administering an
 effective amount of a composition of the invention contained in a
 pharmaceutically acceptable formulation to a patient either systemically
 or locally to the organ or tissue to be studied. It is believed that the
 novel compositions of the present invention have broad clinical utility,
 which includes, but is not limited to, diagnostic imaging of tumors, of
 inflammation (both sterile and bacterial), and of impaired vasculature;
 laser guided endoscopic examination of sites of lesion; and photodynamic
 and chemotherapy of tumors or infection.
 The novel compositions of this invention can be formulated into diagnostic
 or therapeutic compositions for enteral, parenteral, or oral
 administration. These compositions contain an effective amount of the
 metal complexes along with conventional pharmaceutical carriers and
 excipients appropriate for the type of administration contemplated. These
 compositions may also include stabilizing agents selected from the class
 consisting of mono- or polycarboxylic acids, mono- or polyamines, mono- or
 polynucleotides, mono or polysaccharides, amino acids, and peptides. For
 example, parenteral administration advantageously contains a sterile
 aqueous solution or suspension of the complexes whose concentration ranges
 from about 1 nM to about 0.5 M. Preferred parenteral formulations have a
 concentration of 1 .mu.M to 10 mM. Such solutions also may contain
 pharmaceutically acceptable buffers, emulsifiers, surfactants, and,
 optionally, electrolytes such as sodium chloride. Concentrations of the
 metal complexes of this invention in formulations for enteral
 administration may vary widely as is well-known in the art. In general,
 such formulations are liquids which include an effective amount of the
 complexes in aqueous solution or suspension. Such enteral composition may
 optionally include buffers, surfactants, emulsifiers, thixotropic agents,
 and the like. Compositions for oral administration may also contain
 flavoring agents and other ingredients for enhancing their organoleptic
 qualities. The diagnostic compositions are administered in doses effective
 to achieve the desired diagnostic or therapeutic objective. Such doses may
 vary widely depending upon the particular complex employed, the organs or
 tissues to be examined, the equipment employed in the clinical procedure,
 and the like.

The following examples illustrate specific embodiments of this invention.
 As would be apparent to skilled artisans, various changes and
 modifications are possible and are contemplated within the scope of the
 invention described.
 EXAMPLE 1
 Preparation of the Quinoline Ligand (Formula 3)
 ##STR3##
 A mixture of 2-aminomethyl-8-hydroxyquinoline hydrochloride (Chem-Master
 International) (2.1 g, 10 mmol), t-butyl bromoacetate (3.9 g, 20 mmol),
 diisopropylethylamine (3.9 g, 30 mmol), and sodium iodide (0.15 g, 1 mmol)
 in dimethoxyethane (20 mL) was heated under reflux for 2 hours. The
 reaction mixture was poured onto water and extracted with ethyl acetate
 (3.times.30 mL). The combined organic layers were washed with water
 (3.times.50 mL), dried (Na.sub.2 SO.sub.4), filtered, and the filtrate
 evaporated in vacuo to furnish 2.2 g of the diester as a red gum. .sup.1
 H-NMR (CDCl.sub.3) .delta.8.17 (s, 1H), 7.60 (d, 1H), 7.40 (d, 1H), 7.35
 (m, 2H), 7.15 (d, 1H), 4.18 (s, 2H), 3.50 (s, 4H); .sup.13 C-NMR
 (CDCl.sub.3) .delta.165.7, 152.7, 147.2, 137.8, 122.4, 117.4, 112.8,
 105.0, 76.4, 55.0, 50.9, 23.3.
 The diester obtained above was treated with 96% formic acid (20 mL) and
 kept at ambient temperature for 24 hours. Excess formic acid was removed
 by evaporation in vacuo and the brown residue was treated with water (25
 mL), and filtered hot (gravity filtration). Upon cooling, the product
 crystallized as a red solid which was filtered and dried to furnish 1.1 g
 of the ligand of Formula 3. .sup.1 H-NMR (DMSO-d.sub.6) .delta.9.45
 (broad, 2H), 8.15 (d, 1H), 7.77 (d, 1H), 7.28 (m, 2H), 7.10 (d, 1H), 4.15
 (s, 2H), 3.50 (s, 4H); .sup.13 C-NMR (DMSO-d.sub.6) .delta.172.5, 158.1,
 152.8, 137.4, 136.4, 127.9, 127.0, 121.5, 117.6, 111.3, 59.7, 54.5;
 electrospray mass spectrum, m/Z=291 (M+H).
 EXAMPLE 2
 Preparation of the Chromium Complex (Formula 4)
 ##STR4##
 A solution of the ligand of Formula 3 (145 mg, 0.5 mmol) and chromium
 acetylacetonate (175 mg, 0.5 mmol) in dimethylformamide (2 mL) was treated
 with two drops of water and two drops of 96% formic acid and the entire
 mixture was heated at 100-120.degree. C. for 24 hours. After cooling the
 reaction mixture to ambient temperature, the solution was poured onto
 ethyl ether. The brown precipitate was collected by filtration, washed
 with ether, dried, and recrystallized from propanol to give the chromium
 complex of Formula 4 as a brown solid.
 EXAMPLE 3
 Hypothetical Preparation of the Iron Complex (Formula 5)
 ##STR5##
 A solution of the ligand of Formula 3 (145 mg, 0.5 mmol) and iron
 acetylacetonate (177 mg, 0.5 mmol) in dimethylformamide (2 mL) is treated
 with two drops of water and the entire mixture is heated at
 100-120.degree. C. for 16 hours. After cooling the reaction mixture to
 ambient temperature, the solution is poured onto ethyl ether. The
 precipitate is collected by filtration and is purified by either
 recrystallization or C-18 reverse phase chromatography to give the iron
 complex of Formula 5.
 EXAMPLE 4
 Preparation of Ruthenium Complex (Formula 6)
 ##STR6##
 A solution of the ligand of Formula 3 (145 mg, 0.5 mmol) and ruthenium
 acetylacetonate (199 mg, 0.5 mmol) in dimethylformamide (2 mL) was treated
 with two drops of water and the entire mixture was heated at
 100-120.degree. C. for 16 hours. After cooling the reaction mixture to
 ambient temperature, the solution was poured onto ethyl ether. The brown
 precipitate was collected by filtration, washed with ether, dried, and
 recrystallized from propanol to give the ruthenium complex of Formula 6 as
 a black solid.
 EXAMPLE 5
 Preparation of the Quinoline Ligand (Formula 7)
 ##STR7##
 A mixture of 2-chloromethyl-8-hydroxyquinoline hydrochloride (Chem-Master
 International) (0.69 g, 3 mmol), ethylenediamine-N,N,N'-triacetic acid
 tri(t-butyl)ester (10.8 g, 3 mmol), diisopropylethylamine (0.78 g, 6
 mmol), and sodium iodide (0.15 g, 1 mmol) in dimethoxyethane (10 mL) was
 heated under reflux for 4 hours. The reaction mixture was poured onto
 water and extracted with ether (3.times.30 mL). The combined organic
 layers were washed with water (3.times.50 mL), dried (Na.sub.2 SO.sub.4),
 filtered, and the filtrate evaporated in vacuo to furnish the triester
 which was purified by silica gel chromatography using chloroform-methanol
 (9:1) as eluent. .sup.1 H-NMR (CDCl.sub.3) .delta.8.10 (d, 1H), 7.61 (d,
 1H), 7.32 (m, 2H), 7.08 (d, 1H), 4.08 (s, 2H), 3.42 (s, 4H), 3.38 (s, 4H),
 2.83 (bs, 4H); .sup.13 C-NMR (CDCl.sub.3) .delta.170.6, 158.0, 152.1,
 137.4, 136.3, 127.5, 127.1, 122.1, 117.5, 112.8, 109.9, 80.9, 80.8, 60.4,
 56.1, 55.8, 52.5, 51.8.
 The triester obtained above (820 mg) was treated with 96% formic acid (10
 mL) and heated at 80-90.degree. C. for 15 minutes and thereafter kept at
 ambient temperature for 24 hours. Excess formic acid was removed by
 evaporation in vacuo and the residue was triturated with acetone (50 mL).
 The solid was collected by filtration and dried to give 520 mg of the
 ligand of Formula 7 as a pale pink solid. .sup.1 H-NMR (DMSO-d.sub.6)
 .delta.8.15 (d, 1H), 7.60 (d, 1H), 7.32 (m, 2H), 7.05 (d, 1H), 4.25 (s,
 2H), 3.42 (s, 4H), 3.38 (s, 4H), 2.80 (bs, 4H); .sup.13 C-NMR
 (DMSO-d.sub.6) .delta.172.4, 171.3, 156.2, 152.8, 137.3, 136.6, 127.8,
 127.2, 121.4, 117.6, 111.2, 59.3, 55.0, 54.8, 51.7, 50.9; electrospray
 mass spectrum, m/Z=392 (M+H).
 EXAMPLE 6
 Preparation of Europium Complex (Formula 8)
 ##STR8##
 A mixture of the ligand of Formula 7 (780 mg, 2 mmol) and europium oxide
 (352 mg, 1 mmol) in deionized, distilled water (10 mL) was heated under
 reflux for 72 hours. The mixture remained heterogeneous throughout the
 heating period. The precipitate was filtered, washed with water and dried
 to give the europium complex of Formula 8 as an off-white solid.
 EXAMPLE 7
 Hypothetical Preparation of Lutetium Complex (Formula 9)
 ##STR9##
 A mixture of the ligand of Formula 7 (798 mg, 2 mmol) and lutetium oxide
 (398 mg, 1 mmol) in deionized, distilled water (10 mL) is heated under
 reflux for 24 hours. The solution is filtered through fine porosity
 sintered glass funnel to remove undissolved impurities and the filtrate is
 poured onto acetone (200 mL). The precipitate is collected, washed with
 acetone, and dried. The crude lutetium complex of Formula 9 is purified by
 C-18 reverse phase chromatography.
 EXAMPLE 8
 Preparation of Iron Complex (Formula 10)
 ##STR10##
 A solution of the ligand of Formula 7 (391 mg, 1 mmol) in 1N sodium
 hydroxide was treated with ferric chloride hexahydrate (269 mg, 1 mmol)
 and the entire mixture was stirred at ambient temperature for 16 hours.
 The dark reaction mixture was filtered and the filtrate washed with
 ice-cold water and dried. The U.V. spectrum showed intense bands at 455 nm
 and 596 nm. The mass spectrum showed the correct molecular ion for the
 iron complex of Formula 10, m/Z=445 (M+H).
 EXAMPLE 9
 Hypothetical Preparation of the Gadolinium Complex (Formula 11)
 ##STR11##
 A mixture of the ligand of Formula 7 (780 mg, 2 mmol) and gadolinium oxide
 (362 mg, 1 mmol) in deionized, distilled water (10 mL) is heated under
 reflux for 24 hours. The solution is filtered through fine porosity
 sintered glass funnel to remove undissolved impurities and the filtrate is
 poured onto acetone (200 mL). The precipitate is collected, washed with
 acetone, and dried. The crude gadolinium complex of Formula 11 is purified
 by C-18 reverse phase chromatography.
 EXAMPLE 10
 Preparation of the Quinoline Ligand (Formula 12)
 ##STR12##
 A mixture of 2-chloromethyl-8-hydroxyquinoline hydrochloride (1.05 g, 5
 mmol), di-t-butyl
 3,10-bis(t-butoxycarbonylmethy)-3,6,10-triazadodecanedioate (1.78 g, 1
 mmol), diisopropylethylamine (3.87 g, 20 mmol), and sodium iodide (0.15 g,
 1 mmol) in dimethoxyethane (10 mL) was heated under reflux for 4 hours.
 The reaction mixture was poured onto water and extracted with ethyl ether
 (3.times.20 mL). The combined organic layers were washed with water
 (3.times.20 mL), dried (Na.sub.2 SO.sub.4), filtered, and the filtrate
 evaporated in vacuo to furnish the tetraester which was purified by silica
 gel chromatography using chloroform-methanol (9:1). The yield of the pale
 brown tetraester was 1.8 g. .sup.1 H-NMR (CDCl.sub.3) .delta.8.02 (d, 1H),
 7.61 (d, 1H), 7.38 (m, 2H), 7.25 (d, 1H), 7.15 (d, 1H), 3.95 (s, 2H), 3.42
 (bs, 8H), 2.90 (m, 4H), 2.72 (bs, 4H), 1.21 (s, 48H); .sup.13 C-NMR
 (CDCl.sub.3) .delta.170.6, 158.7, 152.1, 137.4, 136.2, 127.5, 127.0,
 122.0, 117.5, 112.8, 109.9, 80.8, 60.8, 56.1, 53.0, 51.8, 28.1.
 The tetraester obtained above was treated with 96% formic acid (10 mL) and
 kept at ambient temperature for 24 hours. The reaction mixture was poured
 onto acetone (200 mL) and solid was collected by filtration and dried to
 furnish the ligand of Formula 12 as an off-white solid. .sup.1 H-NMR
 (DMSO-d.sub.6) .delta.8.32 (d, 1H), 7.58 (d, 1H), 7.38 (m, 2H), 7.05 (d,
 1H), 4.58 (bs, 2H), 3.37 (bs, 8H), 3.12 (bs, 4H), 3.00 (bs, 4H); .sup.13
 C-NMR (DMSO-d.sub.6) .delta.173.0, 153.1, 152.4, 137.2, 136.6, 137.0,
 127.8, 127.7, 121.3, 117.4, 111.5, 58.0, 55.6, 51.7, 49.7; elecctrospray
 mass spectrum, m/Z=493 (M+H).
 EXAMPLE 11
 Preparation of the Europium Complex (Formula 13)
 ##STR13##
 A mixture of the ligand of Formula 12 (984 mg, 2 mmol) and europium oxide
 (352 mg, 1 mmol) in deionized, distilled water (10 mL) was heated under
 reflux for 24 hours. The solution was filtered through a fine porosity
 sintered glass funnel to remove undissolved impurities and the filtrate
 was poured onto acetone (200 mL). The yellow-orange solid precipitate, a
 crude europium complex of Formula 13, was collected, washed with acetone,
 and dried.
 EXAMPLE 12
 Hypothetical Preparation of the Lutetium Complex (Formula 14)
 ##STR14##
 A mixture of the ligand of Formula 12 (984 mg, 2 mmol) and lutetium oxide
 (398 mg, 1 mmol) in deionized, distilled water (10 mL) is heated under
 reflux for 24 hours. The solution is filtered through fine porosity
 sintered glass funnel to remove undissolved impurities and the filtrate is
 poured onto acetone (200 mL). The precipitate is collected, washed with
 acetone, and dried. The crude lutetium complex of Formula 14 is purified
 by C-18 reverse phase chromatography.
 EXAMPLE 13
 Hypothetical Preparation of the Chromium Complex (Formula 15)
 ##STR15##
 A mixture of the ligand of Formula 12 (390 mg, 1 mmol) and chromium
 acetylacetonate (350 mg, 1 mmol) in dimethylformamide (3 mL) is treated
 with two drops of water and the entire mixture was heated at
 100-120.degree. C. for 24 hours. After cooling the reaction mixture to
 ambient temperature, the solution is poured onto ethyl ether. The
 precipitate is collected by filtration, washed with ether, and dried. The
 crude chromium complex of Formula 15 is purified by crystallization or
 C-18 reverse phase chromatography.
 EXAMPLE 14
 Hypothetical Preparation of Gadolinium Complex (Formula 16)
 ##STR16##
 A mixture of the ligand of Formula 12 (780 mg, 2 mmol) and gadolinium oxide
 (362 mg, 1 mmol) in deionized, distilled water (10 mL) is heated under
 reflux for 24 hours. The solution is filtered through a fine porosity
 sintered glass funnel to remove undissolved impurities and the filtrate is
 poured onto acetone (200 mL). The precipitate is collected, washed with
 acetone, and dried. The crude gadolinium complex of Formula 16 is purified
 by C-18 reverse phase chromatography.
 EXAMPLE 15
 Preparation of the Quinoline Ligand (Formula 17)
 ##STR17##
 A mixture of 2-aminomethyl-8-hydroxyquinoline hydrochloride (1.05 g, 5
 mmol) N-succinimidyl S-tetrahydropyranylmercaptoacetate (1.37 g, 5 mmol),
 and triethylamine (0.51 g, 5 mmol) in acetonitrile (15 mL) was heated
 under reflux for 2 hours. The reaction mixture was poured onto water and
 extracted with methylene chloride (3.times.20 mL). The combined organic
 layers were washed with water and dried (MgSO.sub.4) to give the ligand of
 Formula 17 as an orange gum which was sufficiently pure for complexation
 purposes. .sup.1 H-NMR (CDCl.sub.3) .delta.8.42 (broad, 1H), 8.20 (d, 1H),
 7.41 (d, 1H), 7.35 (m, 2H), 7.18 (d, 1H), 4.95 (dd, 1H), 4.82(dd, 1H),
 4.73 (dd, 1H), 4.00 (m, 1H), 3.78 (m, 1H), 3.57 (d, 1H), 3.35 (d, 1H),
 2.10-1.55 (m, 6H); .sup.13 C-NMR (CDCl.sub.3) .delta.169.6, 154.1, 152.1,
 137.0, 136.9, 127.5, 127.4, 120.2, 117.8, 110.9, 83.7, 65.5, 44.7, 35.2,
 30.8, 25.0, 21.6.
 EXAMPLE 16
 Preparation of Rhenium Complex (Formula 18)
 ##STR18##
 A mixture of the ligand of Formula 17 (332 mg, 1 mmol), triethylamine (2
 drops), and oxodichlorobis(triphenyl)phosphinoethoxyrhenium (880 mg, 1
 mmol) in ethanol (5 ml) was heated under reflux for 6 hours. The
 precipitate was collected by filtration and the crude rhenium complex of
 Formula 18 was purified by recrystallization.
 While the invention has been disclosed by reference to the details of
 preferred embodiments of the invention, it is to be understood that the
 disclosure is intended in an illustrative rather than in a limiting sense,
 as it is contemplated that modifications will readily occur to those
 skilled in the art, within the spirit of the invention and the scope of
 the appended claims.