no-carrier-added (n.c.a.) [18F]fluoride. A second synthesis route was based on the acylation reaction of 2-aminothiazole derivative with labeling agent [18F]SFB. Directradiofluorination afforded 18 F-labeled CDK-2 inhibitor in very low yields of 1%–3%, whereas acylation reaction with [18F]SFB gave 18 F-labeled CDK-2 inhibitor [18 F]2 in high yields of up to 85% based upon [18 F]SFB during the optimization