selectivity (Ki (σ2 ) = 830-1710 nM; Ki (σ2 )/Ki (σ1 ) = 680-887). [(18) F]9 was prepared in 42-46% isolated radiochemical yield, with a radiochemical purity of >99% by HPLC analysis after purification, via nucleophilic (18) F(-) substitution of the corresponding tosylate precursor. Biodistribution studies in mice demonstrated high initial brain uptakes and high brain-to-blood ratios. Administration of SA4503