Technetium-99m Labeling of N-[N-(3-Diphenylphosphino Propionyl)Glycyl]Cysteine (PN2S-OH) and its Methyl Ester Derivative (PN2S-OME),

N-[N-(3-diphenylphosphinopropionyl)glycyl]cysteine and its methyl ester derivative were labeled with Tc-99m at neutral pH, leading to a single species in high yield (>95%) in 30 min. RP-HPLC comparison with the analogue Re-V-oxo complexes identified the labeled compounds as the anti isomers of pentacoordinated (TcO)-Tc-99m[PN2S]-OH and (TcO)-Tc-99m[PN2S]-OMe complexes. The compounds are stable from pH 7 to pH 9 when (TcO)-Tc-99m[PN2S]-OH interconverts to related syn isomer, while (TcO)-Tc-99m[PN2S]-OMe undergoes both saponification and interconversion. They exhibit high stability in human plasma and in vivo (mice), and a biodistribution characterized by hepatobiliary excretion.