Double Ligand Transfer Reaction Research Articles

Initial evaluation of 99m Tc-tricarbonyl-cyclopentadienyl fatty acids derivatives as SPECT tracers for myocardium.

Fatty acids are myocardial metabolic agent for detecting myocardial ischemia and infraction. However, no 99m Tc-labeled fatty acids had potential use in clinical practice. In this study, 99m Tc-CpTT-10-oxo-para-PPA (1d), 99m Tc-CpTT-11-oxo-para-PPA (2d), 99m Tc-CpTT-12-oxo-para-PPA (3d), 99m Tc-CpTT-11-oxo-ortho-PPA (4d), and 99m Tc-CpTT-11-oxo-meta-PPA (5d) were synthesized by a double ligand transfer reaction, and their biological behaviors were investigated. Compound 2d achieved good heart to blood ratio (3.39 at 5min after intravenous), and 2d showed high-heart uptake of 6.20%ID/g at 5minutes after injection. Compound 3d displayed a prolonged retention in the myocardium (1.43%ID/g at 60min after injection). Radioactivity accumulation in the lungs, spleen, and blood was eliminated rapidly. In vivo, metabolite analysis presented that compound 6d may be metabolite of 2d through β-oxidation in tissue. Unfortunately, the biodistribution studies of 1d, 2d, 3d, 4d, and 5d showed fast heart clearance and poor heart to liver ratios, which suggested that the 5 99m Tc-labeled fatty acid analogues cannot be used for diagnosis.

Synthesis and biological evaluation of fatty acids conjugates bearing cyclopentadienyl-donors incorporated [99mTc/Re(CO)3]+ for myocardical imaging

Four 99mTc-labeled fatty acid analogs, 1b, 2b, 3b, 4b were synthesized by a double ligand transfer reaction and theirs potential were investigated. The radiochemical yield of the radiotracers was from 11.7% to 30.3% (no decay corrected). Those compounds were found to be chemically stable when incubated in SD rat serum for 3 h at 37 °C. The biodistribution studies in mice showed that high radioactivity accumulated of Tc-99m complexes were observed, followed by moderate clearance from the heart. The maximum heart/blood ratio was 5.7 at 15 min postinjection of 1b. Metabolite analysis showed 1b was not metabolized by β-oxidation in the heart. These results suggest that 1b may be a promising radiotracer for evaluation of myocardial viability.

Long-chain rhenium and technetium glucosamine conjugates

A series of five glucosamine-conjugated organometallic complexes of the tricarbonyl cores of technetium-99m and rhenium were made. Glucosamine was derivatized at the C-2 nitrogen with long chain alkyl spacers linked to either pyridyl-tert-nitrogen-phenol tridentate chelates or cyclopentadienyl ligating groups. The metal complexes of the tridentate ligands were formed by refluxing with [Re(CO)(3)(H(2)O)(3)]Br, or with a base and [(99m)Tc(CO)(3)(H(2)O)(3)](+). These ligands were found to be competent chelates in binding the [(99m)Tc(CO)(3)](+) core as radiolabeling yields ranged from 87 to 93% and the resulting complexes are stable to cysteine and histidine challenges for 24 h. The cyclopentadienyl analogues were formed using a double ligand transfer reaction for the rhenium complexes and a single ligand transfer for the technetium-99m complexes. All five rhenium complexes were tested as substrates of hexokinase; two of these complexes were tested as hexokinase inhibitors and they were found to be competent inhibitors, suggesting that they may be able to interact with hexokinase. MTT cytotoxicity studies were performed and the complexes tested were found to be non-toxic to the concentrations tested (100 microM or 1 mM). GLUT-1 mediated cell uptake studies were performed on all five technetium-99m complexes, and their cell entry was found to parallel their lipophilicities, suggesting that cellular uptake is by passive diffusion and is not mediated by GLUT-1.

16-Cyclopentadienyl Tricarbonyl 99mTc 16-Oxo-hexadecanoic Acid: Synthesis and Evaluation of Fatty Acid Metabolism in Mouse Myocardium

We synthesized 16-cyclopentadienyl tricarbonyl 99mTc 16-oxo-hexadecanoic acid (99mTc-CpTT-16-oxo-HDA, 1) and investigated its potential as a radiotracer for evaluating fatty acid metabolism in myocardium. Radiotracer 1 was synthesized in 22.6 +/- 6.3% decay-corrected yield by a double ligand transfer reaction between the ferrocene adduct of methyl hexadecanoate ( 2) and Na99mTcO 4 in the presence of Cr(CO)6 and CrCl3, followed by hydrolysis of the methyl ester group. Radiotracer 1 was found to be chemically stable (99% at 6 h) when incubated in human serum. A tissue distribution study in mice showed that high radioactivity accumulated in heart (9.03%ID/g at 1 min and 5.41%ID/g at 5 min postinjection) with rapid clearance and that heart to blood uptake ratios increased with time (2.13 at 5 min and 3.76 at 30 min postinjection). Metabolite analysis of the heart tissues using a simple extraction method showed that 99mTc-CpTT-4-oxo-butyric acid was detected as the major radioactive metabolite by HPLC, suggesting that 1 is metabolized to 99mTc-CpTT-4-oxo-butyric acid via beta-oxidation in myocardium.

Diastereoselectivity at chiral metal center of half-sandwich-type ruthenium complexes with planar-chiral cyclopentadienyl ligands in multiple ligand transfer reaction

The triple ligand transfer reaction between planar-chiral cyclopentadienyl–ruthenium complexes [Cp′Ru(NCMe) 3][PF 6] ( 1) (Cp′ = 1-(COOR 2)-2-Me-4-R 1C 5H 2; R 1 = Me, Ph, t-Bu) and iron complexes CpFe(CO)(L)X ( 2) (L = PMe 3, PMe 2Ph, PMePh 2, PPh 3; X = I, Br) resulted in the formation of metal-centered chiral ruthenium complexes Cp′Ru(CO)(L)X ( 3) in moderate yields with diastereoselectivities of up to 68% de. The configurations of some major diastereomers were determined to be S Cp ∗ R Ru ∗ by X-ray crystallography. The diastereoselectivity of 3 was under kinetic control and not affected by the steric effect of the substituents on the Cp′ ring of 1 and the phosphine of 2. Although the double ligand transfer reaction between [Cp′Ru{P(OMe) 3}(NCMe) 2][PF 6] ( 7) and CpFe(CO) 2X ( 8) produced Cp′Ru{P(OMe) 3}(CO)X ( 9), the selectivity at the ruthenium center was low.

Design and Synthesis of Functionalized Cyclopentadienyl Tricarbonylmetal Complexes for Technetium-94m PET Imaging of Estrogen Receptors

Cyclopentadienyl tricarbonylmetal (CpTM, M = Re, (94m)Tc) complexes, some based on a typical nonsteroidal estrogen, were prepared with the aim of developing technetium- and rhenium-labeled imaging agents for estrogen receptor (ER) positive breast tumors. CpT[(94m)Tc] compounds with simple cyclopentadienyl substituents were first synthesized using a modified double ligand transfer reaction. The in vivo biodistribution of one of these CpT[(94m)Tc] complexes was determined by tissue dissection and microPET imaging. Novel C-ring substituted analogues of cyclofenil, a nonsteroidal compound known to bind the ER, were also prepared, and their ER binding was measured. Because of their low ER affinity, however, labeling and imaging studies of these compounds were not pursued. It is notable that the highest ER binding analogue, a CpTRe cyclofenil derivative, could be synthesized from the corresponding ferrocenyl cyclofenil analogue by the double ligand transfer reaction. This further demonstrates the versatility of the double ligand transfer reaction and indicates that the synthesis of technetium and rhenium radiolabeled agents for breast tumor imaging and therapy is also likely to be successful.

8-cyclopentadienyltricarbonyl 99mtc 8-oxooctanoic acid: a novel radiotracer for evaluation of medium chain fatty acid metabolism in the liver.

8-Cyclopentadienyltricarbonyl 99mTc 8-oxooctanoic acid (99mTc-CpTTOA; 1a) was synthesized for evaluation of medium chain fatty acid metabolism in the liver. 99mTc-CpTTOA was prepared in high radiochemical yield (50-63%) by a double ligand transfer reaction of methyl 8-ferrocenyl-8-oxooctanoate and Na99mTcO4 in the presence of CrCl3 and Cr(CO)6, followed by hydrolysis. This radiotracer was shown to be stable (>90% at 6 h) when incubated with human serum. Aqueous extraction of the radioactivity from the liver and blood samples of mice suggested that 99mTc-CpTTOA was mainly metabolized via beta-oxidation in the liver, and the radioactivity was retained longer in CCl4-treated mice than in control mice, possibly due to impaired beta-oxidation in the former. Planar images of rats injected with 99mTc-CpTTOA showed accumulation of the radioactivity in the liver, kidneys, and bladder with rapid hepatic clearance as a function of time. Analysis of the metabolites from the liver and urine samples of rats further supported that 99mTc-CpTTOA was metabolized to 4-cyclopentadienyltricarbonyl 99mTc 4-oxobutanoic acid (99mTc-CpTTBA; 1c) via beta-oxidation. The results suggested that this radiotracer might be of valuable use in the evaluation of fatty acid metabolism in the liver.

Synthesis and biological evaluation of tc-99m-cyclopentadienyltricarbonyltechnetium-labeled octreotide

Octreotide was labeled at its N-terminus with Tc-99m-cyclopentadienyltricarbonyltechnetium, and the biodistribution of the labeled conjugate was studied in adult female Sprague–Dawley rats. The synthesis began with the preparation of Tc-99m-(methoxycarbonylcyclopentadienyl)tricarbonyltechnetium from Tc-99m-pertechnetate using a novel double ligand transfer reaction; it was completed in a total of five steps, with an 8% overall radiochemical yield (15% decay-corrected). The 99mTc-cyclopentadienyltricarbonyltechnetium-labeled octreotide conjugate ( 99mTc-CpTT-octreotide) showed receptor-mediated uptake in the pancreas and adrenals, which was blocked (80% and 93%, respectively) by excess unlabeled octreotide. These studies illustrate a new method for labeling a peptide with Tc-99m through an organometallic linkage that is stable, nonpolar, and low molecular weight; it complements labeling approaches that utilize inorganic metal complexes.

Protein and peptide labeling with (cyclopentadienyl)tricarbonyl rhenium and technetium.

A method for labeling proteins and peptides with (methoxycarbonyl cyclopentadienyl)tricarbonyl rhenium and technetium is described. The precursors used for this labeling are conveniently produced from perrhenate and pertechnetate, respectively, using a double ligand transfer reaction. For labeling the lysine residues of the model protein bovine serum albumin, the technetium methyl ester was saponified and then transformed into its N-hydroxysuccinimidyl ester. For the labeling of the model peptides leucine enkephalin, substance P, oxytocin, and the tumor imaging/therapy candidate octreotide, the rhenium methyl ester was saponified and activated using either 1-hydoxybenzotriazole or 1-hydroxy-7-azabenzotriazole. The activation and peptide-coupling reactions were followed using reversed-phase (C18) HPLC and yields averaged approximately 70%.