Mercaptoacetyltriglycine forms complexes with R186/188e and T99mc radionuclides that are useful
in nuclear medicine because they are substrates of the renal anion transport system. However,
the renal clearance of [MO(MAG3)]2- (MAG3 = penta-anionic form of mercaptoacetyltriglycine, M =
Re, Tc) complexes are less than ideal. Organic sulphonates are also transported by the renal
anion transport system and phosphonates are similar to sulphonates in size and shape. In an
effort to develop new ligands that form Re and Tc complexes and have improved renal clearances
compared to [MO(MAG3)]2- complexes, the sulphonate and phosphonate derivatives of
mercaptoacetyltriglycine were synthesized. The dianion [ReO(MAG2-AMS)]2- (MAG2-AMS =
penta-anionic form of mercaptoacetylglycylglycylaminomethanesulphonic acid) was prepared for
characterization by exchange reaction of ReOCl3(Me2S)(OPPh3) and isolated as the disodium
salt. The structure of Na2[ReO(MAG2-AMS)]·3H2O (6) was determined by X-ray diffraction. The
coordination geometry is pseudo square pyramidal, with the nitrogen and sulfur donor atoms
forming a square base and the oxo ligand at the apex. The deprotonated sulphonate group has a
syn conformation with respect to the oxo ligand. The renal clearances of [T99mcO(MAG2-AMS)]2-
and [T99mcO(MAG2-AMP)]3- were similar in rats and suggest that the difference in total charge
between the SO3- and PO32- groups is not important to renal clearance. However, their renal
clearances were 40-50% less than that of [T99mcO(MAG3)]2- suggesting that the size and shape
of the large tetrahedral SO3- and PO32- groups of [T99mcO(MAG2-AMS)]2- and [T99mcO(MAG2-AMP)]3- inhibit recognition by the renal transport system compared to the small planar CO2- group
of [T99mcO(MAG3)]2-.
