Pentane-2,4-dione complexes of technetium99

Complexes of Technetium(V) and Rhenium(V) with β-Diketonates

Reactions of (NBu₄)[MOCl₄] complexes (M = Tc or Re) with an excess of hexafluoroacetylacetone (Hhfac) give products with a composition of (NBu₄)[MOCl₃(hfac)] as bright yellow (Tc) or red (Re) solids. The products are stable as solids but rapidly decompose in solution. A number of related phenylimidorhenium(V) complexes were synthesized starting from [Re(NPhF)Cl₃(PPh₃)₂], where (NPhF)^2- is a para-fluorinated phenylimido ligand. Products with compositions of [Re(NPhF)Cl₂(PPh₃)(acac)], [Re(NPhF)Cl₂(PPh₃)(hfac)], [Re(NPhF)Cl₂(PPh₃)(tfac)], [Re(NPhF)Cl₂(PPh₃)(naphtfac)], and [Re(NPhF)Cl₂(PPh₃)(^tbutfac)] (Hacac = acetylacetone, Htfac = trifluoroacetylacetone, Hnaphtfac = naphthoyltrifluoroacetylmethane, and H^tbutfac = tert-butyroyltrifluoroacetylmethane) were isolated from reactions of the quite soluble [Re(NPhF)Cl₃(PPh₃)₂] with the corresponding β-diketones and studied spectroscopically and by X-ray diffraction. The β-diketonates are coordinated in a meridional arrangement with the phenylimide. The formation of two isomers was detected for nonsymmetric β-diketones with a preference for the "equatorial" position for the more bulky substituents. Products with more than one chelating ligand were not obtained. The technetium complexes [Tc(NPhX)Cl₃(PPh₃)₂] (X = p-F or p-CF₃) were prepared from reactions of pertechnetate, PPh₃, HCl, and substituted arylacetylhydrazines and isolated as green solids. They are sufficiently stable as solid but rapidly decompose in moist solvents upon hydrolysis of the Tc-N bonds. From reactions of [Tc(NPh)Cl₃(PPh₃)₂] or [Tc(NPhF)Cl₃(PPh₃)₂] in dry solvents, the complexes [Tc(NPh)Cl₂(PPh₃)(hfac)] and [Tc(NPhF)Cl₂(PPh₃)(hfac)] were prepared and isolated in crystalline form. An X-ray diffraction study shows that fluorination of the para position of the phenylimido ligand results in a slight lengthening of all bonds in the coordination sphere of technetium.

Synthesis, characterization and biodistribution of tris(beta-diketonato)technetium(III) complexes

New tris(beta-diketonato) complexes of trivalent 99Tc/99mTc with the ligands hexane-2,4-dione, heptane-2,4-dione, heptane-3,5-dione, and octane-3,5-dione were synthesized by reduction of pertechnetate with dithionite in the presence of excess beta-diketone. The complexes were purified by HPLC, identified by elemental analysis and FAB mass spectrometry, and characterized by vis./u.v./i.r. spectrophotometry. The hexane-2,4-dionato complex crystallizes in the monoclinic space group P21/c, isostructurally with pentane-2,4-dionatotechnetium(III). Biodistribution measurements in mice showed the neutral and lipophilic 99mTc-diketonato complexes to penetrate the blood-brain barrier. However, increasing lipophilicity decreased the brain uptake except for the heptane-2,4-dionato complex, which displayed the highest uptake of 0.82% injected dose/g.

Functionalization of hydroxy compounds with nitrilotriacetic acid for technetium-99m chelation: excretory properties of the radiolabelled chelates

Substituted monoanilides of nitrilotriacetic acid (NTA) have gained much popularity in recent years as an important class of ligands for technetium-99m (99mTc) radiopharmaceutical preparations used in liver imaging and function studies. We were interested in investigating the properties of the corresponding ester analogues of this important class of ligands and for this study cyclohexanol was selected as a hydroxy component, which on condensation with nitrilotriacetic acid in the presence of acetic anhydride, furnished the monoester, N-cyclohexyloxycarbonylmethyl iminodiacetic acid 4 and the corresponding diester 5. Phenol on similar condensation produced mainly the diester, N,N-di(phenyloxycarbonylmethyl) aminoacetic acid 2, with traces of the corresponding monoester 7. A reinvestigation of the well known condensation reaction of aniline with nitrilotriacetic acid revealed that in addition to the reported monoanilide, N-phenylcarbamoylmethyl imino diacetic acid 3, the corresponding dianilide 6 was also produced in appreciable amount. The ester ligands 2, 4, 5 after 99mTc chelation exhibited good in vitro and in vivo stabilities. The biodistribution characteristics of these radiolabelled esters and amides were very similar showing thereby that esterification with NTA could be an effective method for converting alcohols to 99mTc-radiopharmaceuticals without generating any unusual properties because of the ester linkage. Residual radiopharmaceutical concentration after i.v. administration of these amide and ester 99mTc chelates at 30 min in blood, urine, liver, kidney and intestine were correlated with their lipophilicities and during this correlation it was observed that in addition to lipophilicity the anionic strength of these chelates is also an important determinant in governing their biodistribution. The ester ligand 4 after 99mTc chelation showed ultrafast hepatobiliary kinetics and was therefore compared in a rabbit model with a standard hepatobiliary radiopharmaceutical 99mTc-N-(p-butylphenylcarbamoyl methyl) iminodiacetic acid (99mTc-BIDA) by gamma-camera scintigraphy to investigate the potential of the former for clinical studies.

Synthesis and biological properties of the lipophilic technetium-99m complex 99mTc(acac)3

In the development of technetium-99m radiopharmaceuticals for the evaluation of regional cerebral perfusion, one series of complexes that has remained unexplored is the neutral lipophilic tris complexes formed with beta-diketonato ligands. The prototype complex of this series, tris(2,4-pentanedionato) technetium(III), has been prepared via a new synthetic route and chemically characterized using 99Tc and the biodistribution of the no-carrier-added 99mTc complex has been determined. The 99mTc complex was found to be distributed throughout the body with persistent high blood levels indicative of a high degree of protein binding. The primary route of excretion was the hepatobiliary system as indicated by the appearance of 99mTc in the gut and feces at longer sample times post-injection. Although this complex was not retained by the brain, it does provide a starting point from which a more effective agent might be developed.