Background: In recent years

a new amyloid-?-peptide (A?) protein imaging agent 18F-AV-45 which can be used to diagnose Alzheimer’s disease (AD)

was developed. Whereas single-photon emission computed tomography (SPECT) was widely applied in medical clinic in China

a two function compound BAT was connected to the end of AV-45 to successfully synthesize a new compound BAT-AV-45

and its chemical kinetics of labeling reaction with 99mTc was studied. Purpose: 99mTc-BAT-AV-45 was synthesized via direct reaction and ligand exchange for obtaining high labeling yield. Methods: The labeling reactions were performed with three modes: (1) adding BAT-AV-45

GH and 99mTc; (2) adding BAT-AV-45 and 99mTc but non GH; (3) adding GH and 99mTc but non BAT-AV-45. Reactants were incubated at 4°C

25°C and 100°C

respectively. Samples were taken with capillary from vials at 2 min

5 min

10 min

20 min and 30 min

respectively. Labeling yields were determined by thin layer chromatography (TLC). Order of reaction n

rate constant k

average activation energy Ea and reaction half life t1/2 of labeling reaction were calculated with chemical kinetics software compiled by ourselves. Results: The results expressed that the labeling yields of 99mTc-BAT-AV-45 with direct reaction and ligand exchange were proportional to reaction temperature and reaction time. The highest labeling yields with direct reaction and ligand exchange were 3.45%±0.05% and 93.81%±0.91%

respectively. The parameters of chemical kinetics were calculated. n was 1. k were 2.00×10?4 min?1

3.00×10?4 min?1

1.40×10?3 min?1 with direct reaction and 0.108 min?1

0.115 min?1

0.265 min?1 with ligand exchange at 4°C

25°C and 100°C

respectively. Ea were 17.11 kJ?mol?1 with direct reaction and 6.84 kJ?mol?1 with ligand exchange

respectively. t1/2 were 3 890.60 min

2779.51 min

481.39 min with direct reaction and 6.43 min

6.00 min

2.62 min with ligand exchange at 4 °C

25 °C and 100°C

respectively. Conclusion: The results indicated that the high labeling yield of 99mTc-BAT-AV-45 could be obtained by using ligand exchange to reduce activation energy Ea of labeling reaction so as to accelerate the reaction. Abstract