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 99mTc at neutral pH, leading to a single species in high yield (>95%) in 30 min. RP-HPLC comparison with the analogue ReV-oxo complexes identified the labeled compounds as the anti isomers of pentacoordinated 99mTcO[PN2S]-OH and 99mTcO[PN2S]-OMe complexes. The compounds are stable from pH 7 to pH 9 when 99mTcO[PN2S]-OH interconverts to related syn isomer, while 99mTcO[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