(103)Rhodium(III) complexes derived from seven acyclic tetradentate N(2)S(2) ligands (one diaminedithiol and six diaminedithioether ligands) have been synthesized and characterized. Structural variations in the ligand include the length of carbon backbone between the coordinating atoms (222; 232; 323; 333), the presence or absence of gem-dimethyl groups α to sulfur, and the nature of the organic moiety on the sulfurs (hydrogen, p-methoxybenzyl and methyl). For each ligand, the formation of cis and/or trans dichloro isomeric complexes was assessed. Two complexes have been further characterized by single crystal X-ray diffraction. Preparation of the (103)Rhodium(III) complexes was conducted and overall radiochemical yields, in vitro stability and log D(7.4) values were measured. From these studies, the ligand with the 232 chain length, gem-dimethyl groups and the methyl thioether (L4) emerged as a preferred ligand for formation of rhodium complexes with trans geometry and highest radiochemical yields.
Therapeutic radiopharmaceuticals are drugs designed to destroy the cancer cell with ionizing radiation. Unlike conventional chemotherapy and radiation therapy, therapeutic radiopharmaceutical destroys the cancer cells selectively without damaging the normal tissue. These radiopharmaceuticals can be small organic/inorganic molecules or they could be antibodies, peptides or hormones that have a radioisotope attached to them. In this project a potential peptide based radiopharmaceutical was designed and synthesized. This radiopharmaceutical involved a specially designed peptide Bombesin(7-14) that can directly recognize various cancer cells (e.g., small lung, breast and prostate cancers). 105Rhodium (a radioactive isotope of the element rhodium) was used as a radiation source due to its ideal nuclear and chemical properties. To attach the Rhodium-105 to the peptide, a chemical compound (acyclic diaminodithioether) was used. In order to find the ideal ligand for Rhodium-105, several analogues of acyclic diaminodithioether ligands were synthesized and their Rh(III) complexes were prepared and analyzed. The coupling studies of the optimum acyclic diaminodithioether ligand to the Bombesin(7-14) was accomplished. Finally, the attachment of the Rhodium-105 was performed to obtain the potential peptide base radiopharmaceutical.
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