FIGURE 6.

(A) The first reported direct nucleophilic radiolabeling of a molecule with [¹⁸F]fluoride at silicon under aqueous conditions involved the fluorination of silyl chloride 46 with [¹⁸F]TBAF. (B) The biotin derivative 48 can be directly radiolabeled with [¹⁸F]fluoride at room temperature over a broad pH range and within an hour in almost quantitative yields. Carrier KHF₂ is added to obtain a Si:F ratio of 1:4. Theoretically, 49 could be radiolabeled with [¹⁸F]fluoride a total of four times which would increase the specific activity substantially.