Technetium-99m N,N'-bis(2-mercapto-2-methylpropyl)-2-aminobenzylamine: technetium-99m complexes of a novel bis(aminoethanethiol) ligand

Electrophilically Activated Nitroalkanes in Synthesis of 3,4-Dihydroquinozalines

Nitroalkanes activated with polyphosphoric acid serve as efficient electrophiles in reactions with various nucleophilic amines. Strategically placed second functionality allows for the design of annulation reactions enabling preparation of various heterocycles. This strategy was employed to develop an innovative synthetic approach towards 3,4-dihydroquinazolines from readily available 2-(aminomethyl)anilines.

MO tripeptide diastereomers (M=99/99mTc, Re): models to identify the structure of 99mTc peptide targeted radiopharmaceuticals

Biologically active molecules, such as many peptides, serve as targeting vectors for radiopharmaceuticals based on 99mTc. Tripeptides can be suitable chelates and are easily and conveniently synthesized and linked to peptide targeting vectors through solid-phase peptide synthesis and form stable TcVO complexes. Upon complexation with [TcO]3+, two products form; these are syn and anti diastereomers, and they often have different biological behavior. This is the case with the approved radiopharmaceutical [99mTcO]depreotide ([99mTcO]P829, NeoTect) that is used to image lung cancer. [99mTcO]depreotide indeed exhibits two product peaks in its HPLC profile, but assignment of the product peaks to the diastereomers has proven to be difficult because the metal peptide complex is difficult to crystallize for structural analysis. In this study, we isolated diastereomers of [99TcO] and [ReO] complexes of several tripeptide ligands that model the metal chelator region of [99mTcO]depreotide. Using X-ray crystallography, we observed that the early eluting peak (A) corresponds to the anti diastereomer, where the Tc=O group is on the opposite side of the plane formed by the ligand backbone relative to the pendant groups of the tripeptide ligand, and the later eluting peak (B) corresponds to the syn diastereomer, where the Tc=O group is on the same side of the plane as the residues of the tripeptide. 1H NMR and circular dichroism (CD) spectroscopy report on the metal environment and prove to be diagnostic for syn or anti diastereomers, and we identified characteristic features from these techniques that can be used to assign the diastereomer profile in 99mTc peptide radiopharmaceuticals like [99mTcO]depreotide and in 188Re peptide radiotherapeutic agents. Crystallography, potentiometric titration, and NMR results presented insights into the chemistry occurring under physiological conditions. The tripeptide complexes where lysine is the second amino acid crystallized in a deprotonated metallo-amide form, possessing a short N1-M bond. The pKa measurements of the N1 amine (pKa approximately 5.6) suggested that this amine is rendered more acidic by both metal complexation and the presence of the lysine residue. Furthermore, peptide chelators incorporating a lysine (like the chelator of [TcO]depreotide) likely exist in the deprotonated form in vivo, comprising a neutral metal center. Deprotonation possibly mediates the interconversion process between the syn and anti diastereomers. The N1 amine group on non-lysine-containing metallopeptides is not as acidic (pKa approximately 6.8) and does not deprotonate and crystallize as do the metallo-amide species. Three of the tripeptide ligands (FGC, FSC, and FKC) were radiolabeled with 99mTc, and the individual syn and anti isomers were isolated for biodistribution studies in normal female nude mice. The main organs of uptake were the liver, intestines, and kidneys, with the FGC compounds exhibiting the highest liver uptake. In comparing the diastereomers, the syn compounds had substantially higher organ uptake and slower blood clearance than the anti compounds.

99mTc Complexes with activated ester functions; ligands comprising a 3,4-diamino-benzoate backbone

Preformed (99m)Tc chelates with an activated ester function are useful for the gentle labeling of proteins (precomplexation route). In this context, new heterobifunctional ligands derived from 2,3,5,6-tetrafluorophenyl (TFP) 3,4-diamino-benzoates (OC1, OC3, OC4) were synthesized. Their corresponding (99m)Tc-complexation and protein-conjugation characteristics were elucidated and compared with the results previously reported using 2,3,5,6-tetrafluorophenyl N-(S-benzoylthioacetyl)glycylglycyl-p-aminobenzoate (OC2). The reaction temperatures and the reaction time markedly influenced complexation yields. Compared with OC2, the (99m)Tc-chelate formation with OC1 and OC4 was more effective, showing radiochemical yields of 60% and 70% within 20 min, respectively. Owing to steric hindrance, the complexation of OC3, however, did not exceed 10%. No-carrier-added (99m)Tc complexes were conjugated at pH 10 with the anti-EGF-receptor monoclonal antibody MAb425, resulting in labeling yields of 14% for (99m)Tc-OC1 and 7% for (99m)Tc-OC4 after incubating for 20 min at 30 degrees C. Increasing the temperature to 40 degrees C improved these results by 14% and 3%, respectively. As compared with (99m)Tc-OC2, which provides the chelating substituent at the 4-phenyl position only, the application of 3,4-phenyl substituents proved less appropriate for protein conjugation. However, the 3,4-diaminobenzoate backbone may be attractive for an alternative design of novel (99m)Tc N2S2 or N3S complexes, because they show excellent complexation characteristics.

Biphenyls labeled with technetium 99m for imaging β-amyloid plaques in the brain

Formation and accumulation of excess aggregates of beta-amyloid (Abeta) plaques in the brain are critical factors contributing to the development and progression of Alzheimer's disease (AD). There is an urgent need for in vivo imaging agents that can specifically demonstrate the location and density of Abeta plaques in the brain. The aim of this study was to develop potential technetium 99m (99mTc)-labeled diagnostic imaging agents specific for the detection of Abeta plaques. Based on previously obtained Abeta plaque-specific biphenyls containing a p-N, N-dimethylaminophenyl group, a series of 99mTc and Re-N2S2-biphenyl derivatives was prepared. The stable neutral and lipophilic 99mTc complexes, [99mTc]19 and [99mTc]23, A+B, were successfully obtained. As surrogates for the 99mTc complexes, the corresponding surrogates, Re complexes of 23, were also prepared. Surprisingly, it was found that the Re complexes showed distinctively different retention profiles as compared with the corresponding 99mTc complexes. Biodistribution studies indicated that [99mTc]23A readily passed through the blood-brain barrier (1.18% dose/brain at 2 min) in contrast to the low brain penetration of [99mTc]19 (0.29% dose/brain at 2 min). Initial results suggested that [99mTc]23A showed selective binding to the Abeta plaque-like structures in the brain sections from transgenic mice but not in the postmortem human brain tissue of patients with confirmed AD. The results provide encouraging evidence that development of a 99mTc-labeled agent for imaging Abeta plaques in the brain may be feasible. Caution should be taken when comparing these 99mTc complexes with the corresponding surrogates--the Re complexes.

A potential melanoma tracer: synthesis, radiolabeling, and biodistribution in mice of a new nitridotechnetium bis(aminothiol) derivative pharmacomodulated by a N-(diethylaminoethyl)benzamide

Radioiodobenzamides are the best-known agents under study for the diagnosis of cutaneous melanoma and its metastases. We report the synthesis of a new BAT derivative radiopharmaceutical in which radioiodine is replaced by 99m-technetium. The cyclic intermediary methyl 4-[3-(4,4,7,7-tetramethyl-5,6-dithia-2, 9-diazacyclodecyl)-2-oxapropyl]benzoate (5) occurred in two different conformations identified by spectroscopic analysis. The final BAT ligand was radiolabeled using the nitridotechnetium core by a ligand-exchange reaction. Two different complexes were purified. After macroscopic 99-technetium synthesis, syn and anti isomers were identified. The global radiochemical yield was over 80%. The biodistribution of these two complexes was evaluated in mice bearing murine B16 melanoma. Extensive liver and kidney uptake was observed, but the benzamide tropism for the tumor was partially preserved.

A technetium-99m SPECT imaging agent which targets the dopamine transporter in primate brain

The dopamine transporter (DAT), located presynaptically on dopamine neurons, provides a marker for certain neurological diseases. In particular, the DAT is depleted in Parkinson's disease, and the extent of depletion correlates with the loss of dopamine. Herein we describe the design, synthesis, and biological evaluation of technepine, the first 99mTc-labeled SPECT imaging agent which targets the dopamine transporter in striatum. We have demonstrated that the DAT can accommodate a chelating unit attached to the 8-amine function of a tropane skeleton. Further, we have demonstrated for the first time that a molecule can be designed to carry the radionuclide 99mTc across the blood-brain barrier in sufficient quantity to obtain in vivo images of the striatum in monkeys. This advance will undoubtedly lead to the design of new receptor and transporter-mediated 99mTc agents which can label specific transporter and receptor targets in the central nervous system.

Novel TcVO(III) N2S2 complexes: interconversion by redox reaction

To improve the versatility of ligands suitable for complexing a TcVO center core, a new bisaminoethanethiol (BAT) ligand, 7, was synthesized. A neutral and stable complex, [99mTc]7 (reduced), was initially formed. The reduced form of the Tc-99m complex can be converted to the oxidized form, and vice versa. Both Tc-99m complexes showed moderate uptakes in rat brain (0.17% and 0.1% dose/organ at 30 min for the reduced and oxidized forms, respectively). It may be possible to use the same reaction schemes to prepare various derivatives for further studies of these neutral and stable Tc-99m complexes.

Synthesis and characterization of novel N3O3-Schiff base complexes of 99gTc, and in vivo imaging studies with analogous 99mTc complexes

Sixteen novel derivatives of 1,1,1-tris (salicylaldiminomethyl)ethane have been synthesized for the purpose of encapsulating 99mTc(IV) ions and generating new 99mTc radiopharmaceuticals. Two methods for the preparation of the 99gTc(IV) analog complexes are presented; one utilizes SnCl2 reduction on 99gTcO4- and the other a direct substitution route starting with [99gTcCl6]2-. Free ligands (H3L) are characterized by melting points, 1H NMR, 13C NMR, mass spectroscopy, TLC, and/or elemental analyses. [99gTcL]+ complexes are characterized by FAB-ms, UV-VIS, IR and/or CV. An X-ray structural analysis was performed on a crystal of [M(6,6'-[[2-[[((4-Methoxy-2-hydroxyphenyl) methylene)-amino]methyl]-2-methyl- 1,3-propanediyl]bis(nitrilomethylidyne)]-bis-3-methoxyphenol )] tetraphenylborate, where M represents a 1/3 isomorphous mixture of 99gTc/Sn as determined by SEM. The metal coordination site is 6-coordinate, composed of N3O3 donor atoms, and intermediate between octahedral and trigonal prismatic geometry. The [99mTcL]+ complexes were prepared in a stannous environment; equivalence of the 99mTc and 99gTc complexes is demonstrated by HPLC techniques. The [SnL]+ complex was prepared for comparison purposes. An unusual ligand oxidation occurs for one series of ligands in which in situ amine-->imine conversion is observed during the complexation reaction in reducing media. Guinea pig, rat, dog, and human metabolism studies are reported for selected [99mTcL]+ complexes, the myocardial uptake of which approaches 2% of the injected dose.

Heterodimeric Bis(amino thiol) Complexes of Oxorhenium(V) That Mimic the Structure of Steroid Hormones. Synthesis and Stereochemical Issues

We have prepared a series of bis-bidentate complexes of rhenium that mimic the size, shape, and peripheral functionality of steroidal androgens. In a model system, we used 2D NMR and X-ray crystallographic analysis to show that adjacent N-methyl and oxo substitutents adopt an anti configuration during the coordination reaction. We have synthesized a bis-bidentate oxorhenium(V) complex whose structure and peripheral functionality mimic 5alpha-dihydrotestosterone. 2D-NMR analysis indicates that the N-methyl and oxo substituents are driven into the steroidal anti configuration (beta-N-methyl, alpha-oxo) by the beta-orientation of the methyl group equivalent to C-18. Thus, this metal complex provides a remarkable structural and stereochemical mimic of a steroid. Its in vivo stability, however, appears to be limited.

New bisaminoethanethiol (BAT) ligands which form two interconvertible Tc-99m complexes

Most commonly used radiopharmaceuticals in diagnostic nuclear medicine are labeled with Tc-99m. This is due to its superior physical characteristics (T1/2 = 6 h and gamma energy 140 KeV) and convenient availability from the 99Mo/99mTc generator. In an attempt to fine tune the properties of Tc-99m complexes, the synthesis and radiolabeling of two novel N2S2 ligands, N,-2-mercaptobenzyl-N'-(1-oxo-2-mercapto-2-methyl)propyl ethylene-diamine, 8, and N,-2-methylthiobenzyl-N'-(1-oxo-2-mercapto-2-methyl)propyl ethylenediamine, 11, with an ionizable SH or unionizable SMe group, respectively, for the formation of complexes with TcvO center cores, have been examined. Both ligands initially formed one apparently stable, lipophilic and neutral complex (HPLC, Rt = 7 min, reverse-phase column, acetonitrile: buffer, pH 7.0; 55/45; V/V; partition coefficient between 1-octanol and buffer of 410 and 335, respectively) with [99mTc]pertechnetate in the presence of stannous chloride. After treatment with a reducing agent, NaCNBH3, the initial [99mTc]8 and 11 complexes were reduced; the reduced complexes were less lipophilic (shorter retention time, Rt = 5 min, on the same reversed phase HPLC). However, only the oxidized form showed sufficient stability. The reduced forms of both [99mTc]8 and 11 were readily and completely converted back to the oxidized forms by a stream of air. Biodistribution studies in rats demonstrated that the [99mTc]8 (oxidized form) penetrated the blood-brain barrier (0.67% dose/organ at 2 min postinjection), but washed out from the brain quickly (0.29% dose/organ at 30 min postinjection).(ABSTRACT TRUNCATED AT 250 WORDS)