L. Hansen, R. Cini, Andrew T. Taylor
Jun 1, 1992
Citations
1
Influential Citations
33
Citations
Journal
Inorganic Chemistry
Abstract
The synthesis and characterization of three rhenium(V) oxo complexes derived from isomers of mercaptoacetylglycylglycylaminobenzoic acid (MAG[sub 2]-ABAH[sub 5]) are reported. The isomers were synthesized from o-, m- and p-aminobenzoic acid and differed in the position of the terminal carboxyl group. The anions of 8-10, [ReO(MAG[sub 2]-*ABAH)][sup [minus]] (* = para (8), meta (9), ortho (10)), contained the tetraanionic form of the ligands with the carboxyl group protonated. Compounds 8,9, and 10 were synthesized by exchange reactions of ReOCl[sub 3](Me[sub 2]SO)(Ph[sub 3]P) under moderate conditions and were isolated as [Ph[sub 4]P][sup +], [Bu[sub 4]N][sup +], and [Ph[sub 4]P][sup +] salts, respectively. The structures of 8 and 10 were determined by X-ray diffraction methods; except for the location of the carboxyl group, the structures are similar. The coordination geometry is pseudo square pyramidal, with nitrogen and sulfur donor atoms forming a square base and the oxo ligand at the apex. The orientation of the carboxyl group in 10 is anti to the Re[double bond]O group. Since the carboxyl groups are protonated in 8 and 10 and in other relevant structures from this class of radiopharmaceuticals including [Ph[sub 4]As][TcO(MAG[sub 3]H)] (MAG[sub 3]H = tetraanionic form of mercaptoacetyltriglycine), the authors developed molecular mechanics parametersmore » that allowed them to calculate the structures of 8, 10, and [TcO(MAG[sub 3]H)][sup [minus]]. They then extended the calculations to all three isomeric complexes in their deprotonated forms and to [TcO(MAG[sub 3])][sup 2[minus]] in order to approximate their solution phase structures. They conclude that the [TcO(MAG[sub 3])][sup 2[minus]] species is conformationally flexible, and they have made an initial assessment of structures vs renal clearance.« less