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Zuzana Kotková - Ph.D. Thesis: MRI Contrast Agents for Modern Applications 1 Abstract Over the last few decades, Magnetic Resonance Imaging (MRI) has become one of the most powerful medicinal methods for the diagnosis of various diseases (Fig. A1a ). In several types of examinations, contrast agents (CAs) are used to increase the quality of images (Fig. A1b ). These contrast agents are usually based on paramagnetic metal complexes of macrocyclic ligands. In dependence on the measured nuclei, two basic groups of CAs are considered - 1 H MRI CAs and, recently, also 19 F "hot-spot" CAs. The 1 H MRI CAs are based on Gd3+ complexes of macrocyclic ligands with one water molecule coordinated to the central metal ion (Fig. A1c ) and the effect of the CAs is to shorten the relaxation times of water protons. (a) (b) (c) Fig. A1: Illustrative pictures for Magnetic Resonance Imaging (MRI) method; (a) whole body MRI tomograph,* (b) an example of MR head scans with the use of MRI CA** and (c) schematic general structure of a contrast agent based on Gd3+ complex of macrocyclic ligands (for more details see the Thesis, section 1.3.3, Fig. 18). * https://www.ottawaheart.ca/test-procedure/cardiac-mri (Accessed 25 Febr. 2023) ** https://affordablemri.com/mri-explained (Accessed 25 Febr. 2023) The shortening of relaxation...

In the last years, radioisotopes of heavy elements from the bottom of the Periodic Table have been increasingly used in nuclear medicine with focus on alpha-therapy. These large metal ions demand ligands fulfilling their special requirements. Complexes of polyazamacrocyclic ligands have been used in radiomedicine for a long time as diagnostic and therapeutic agents. This work aims to con- tribute to understanding of coordination chemistry of large macrocycles toward large metal ions. Thus, this work deals with structural studies, formation and decomplexation kinetics of Ln(III)-H4pyta complexes employing X-ray solid-state and solution NMR/UV-Vis spectroscopic data. The H4pyta is a 18-membered hexaazamacrocycle formed by two pyridine units and four amine groups which are modified with four acetate pendant arms. In the solid state, several isomeric complexes were structu- rally characterized. Large Ln(III) ions form decacoordinated species with two and two acetates on each side of the macrocyclic N6-plane. Small Ln(III) binds the ligand in a nonadentate fashion with one pendant non-coordinated. In the middle of lanthanide series, both isomers were characterized for several Ln(III) ions. Formation of the complexes takes place in a three-step mechanism with fast formation of an out-of-cage intermediate...

Currently, a number of methods, both diagnostic and therapeutic, find use in the field of nuclear medicine. The importance of macrocyclic ligands, capable of coordination of ions of employed metal radionuclides, is rising for both mentioned areas. Great potential lies in the area of the so-called theragnostics, i.e., drugs with both diagnostic and therapeutic functions. This thesis makes the first steps towards the concept of a theranostic ligand containing two macrocyclic coordinating centres, each individually optimised for coordinating radioisotopes of one metal ion. The coordination of Ga(III), currently used in diagnostics, is provided in the studied model system by a nine-membered macrocycle with phosphinate pendant arms. The coordination of Lu(III), currently used for radiotherapy, is provided by a twelve-membered macrocycle with phosphinate pendant arms. The results of the NMR measurements in this thesis show that the studied model system behaves in agreement with requirements placed upon the conceived drug. A macrocyclic ligand L1e, optimised for coordination of Lu(III), was prepared with the intended use in the synthesis of the proposed drug. H-phosphinic acids and a derivative of cyclene were also prepared as precursor compounds for a series of bifunctional ligands L1a - L1e. Keywords...

Macrocyclic ligands have been used in radiomedicine for a long time. These ligands have been studied mainly in terms of complexation of heavy metal ions and possible use of these com- plexes in diagnostics and radiotherapy. Recent studies have highlighted the potential use of actinium-225 as an alpha-emitting radionuclide. This isotope is suitable for a precise treatment of micrometastases as it emits a cascade of high-energy but short-range alpha radiation. Due to the high linear energy transfer of the emitted particles, the tumor cells at a given location in the patient's body are completely destroyed. This work deals with the preparation and char- acterization of 18-membered polyazamacrocyclic ligands that can be used for complexation of this radioisotope. The prepared substances were characterized by potentiometry, NMR, MS and EA. Thermodynamic data of the complexes of these ligands with "model" heavy metal ions (Ca2+ , Sr2+ and Ba2+ ) were obtained using potentiometry. For cerium(III) complexes with prepared ligands, the pH-dependent kinetics of their formation were studied, and the results of these measurements indicate the possibility of using these ligands in radiomedicine. Keywords: macrocyclic ligands, heavy metal complexes, radiotherapy 1

Currently, modified electron transport metaloproteins with presence ion Cu(II) in their active site are most commonly used to study kinetics of electron transfer. One of the most studied model protein is cupredoxin azurin from P. aeruginosa with standard redox potential approximately 310-360 nm (depends on experimental conditions and techniques). Ion Cu(II) in azurin is coordinated by the side chain atoms of His46 , His117 , Cys112 , Met121 and carbonyl of Gly45 . The aim of this work was to prepare macrocyclic ligand, 1-[1H-imidazol-2- yl)methyl]-1,4,7-triazacycklononanu (LIM ), which would be able to form stable complexes with both of copper ions Cu(II) and Cu(I). Such as macrocyclic complexes could be utilized as low molecular models of active sites in proteins. The ligand was prepared using five-step synthesis employing protection of macrocycle, reduction and subsequent bromation of 1H- imidazol-2-karbaldehyd, and following alkylation reaction. Deprotection of macrocycle revealed final product of ligand. All reaction intermediates and prepared ligand were characterized by NMR and MS. Potentiometric titrations determined ligand protonation constant (log K1 = 10,62, log K2 = 6,65, log K3 = 4,91), which describe acid-base properties of a ligand in an aqueous solution. Similarly, the coordination...

Selective protection of functional groups is a commonly used method which is used in multistep synthesis. Pentaerythrityltetraamine (PEA) is substance with four amino groups and substances with one to three selectively protected amino groups were prepared. Protections by t-butyloxycarbonyl (Boc) which is stable under neutral and basic conditions and can be deprotected in the acidic conditions, and with benzyloxycarbonyl (Cbz) which is stable under acidic and basic conditions and can be eliminated by hydrogenation was tested. Separation and purification of the protected amines was done by chromatography. Selectively protected PEA can be also prepared by indirect path by stepwise reduction of pentaerythrityltetraazide. Pentaerythritylmonoamine-triazide is prepared two-phase reduction and the amino group of the monoamine is protected with Boc or Cbz.

Conclusions In my PhD project I synthesized two new polydentate macrocyclic ligands, the monofunctional DO3A-pyNO and the bifunctional DO3A-pyNO-C. Both compounds are based on the design of DOTA, with one of the acetate pendant arms being replaced with a pyridine-Noxide arm. This structural modification has a tremendous influence on chemical properties of the lanthanide(III) complexes of these compounds. The water exchange rate in the gadolinium(III) complexes is significantly accelerated in comparison with the complexes of DOTA. In fact, the values are almost optimal for use of the Gd(III) complexes as contrast agents for magnetic resonance imaging. Besides, the complexes exist exclusively in the form of square antiprismatic isomers. I investigated the complexes by various physico-chemical techniques in solution and in solid state, in order to elucidate the relationship between their structure and properties. On the basis of these results I found an explanation to the unexpectedly fast water exchange rate observed on the squareantiprismatic isomers. I established a synthetic protocol that can be used for the attachment of the bifunctional ligand DO3A-pyNO-C to any amine-bearing molecule. I prepared a series of conjugates with polyamidoamine dendrimes and a conjugate with per-6-amino--cyclodextrine and...