Preparation of 18F-labeled 6- and 2-fluoro-9-benzylpurine as a potential brain-scanning agent

The preparations of [18F]-6-fluoro-9-benzylpurine(I) and [18F]-2-fluoro-9-benzylpurine(II) are described. (I) was prepared by two methods: (i) halogen exchange of 6-chloro-9-benzylpurine with Ag 18F; and (ii) displacement of trimethylpurin-6-ylammonium chloride with K 18F, followed by 9N benzylation. The latter labeling method was far superior to the former, both in radiochemical yield and in specific activity. (I) was relatively stable in a Tris-HCl buffer (0.4 M, pH 7.6) at 37 degrees C, but was easily hydrolyzed in 1 N HCl. Biodistribution of (I) in mice demonstrated high uptake in the brain. (I) can be expected to be a potential brain-scanning radiopharmaceutical for positron computed tomography.