Synthesis and characterization of neutral technetium(III)-99 and -99m complexes with O,P-bidentate phosphino-carboxylate ligands. Crystal structure of mer-[Tc(O2CCH2CH2PPh2) 3]·2Me2SO

Reduction-substitution reactions of pertechnetate with a class of O,P-bidentate phosphinocarboxylic acid ligands HLn [n = 1,2-(diphenylphosphino)benzoic acid; n = 2, 3-(diphenylphosphino)propionic acid; n = 3, (diphenylphosphino)acetic acid; n = 4, 3-(diethylphosphino)propionic acid] afforded a series of neutral and paramagnetic [TcLn 3] complexes. The products have been characterized by means of elemental analysis, IR, 1H NMR, UV/VIS and FAB mass spectroscopy, and X-ray crystallography for [TcL2 3]. The latter crystallizes in the monoclinic space group P21/n with Z = 4, a = 21.718(10), b = 12.954(6), c = 18.038(9) Å and ? = 106.59(4)°. The final R value was 0.061. Three deprotonated chelates surround the metal in a distorted-octahedral environment adopting a meridional configuration, and consequently there are two pairs of like donor atoms trans to one another with the remaining phosphorus atom trans to an oxygen atom. Similar reduction-substitution reactions have been performed utilizing the short-lived isotope 99mTc. The physicochemical properties of the resulting 99mTc-labelled species match very well those exhibited by the analogues prepared with the long-lived isotope 99Tc. Thus the chemical structures of [99mTcLn 3] and [99TcLn 3] analogues are identical. Female Sprague-Dawley rats were injected with pre-purified [99mTcLn 3] (n = 1, 2 or 4) and the resulting biodistributions evaluated at different times post injection. All the complexes undergo very low, but significant, brain uptake which decreases with time.