Facile radiosynthesis of fluorine-18 labeled β-blockers.: Synthesis, radiolabeling, and ex vivo biodistribution of [18F]-(2S and 2R)-1-(1-fluoropropan-2-ylamino)-3-(m-tolyloxy)propan-2-ol

An efficient and genral method has been developed for fluorine-18 labeling of beta-blockers that possess the propanolamine moiety. A new synthetically versatile intermediate, 3-(1-(benzyloxy)propan-2-yl)-2-oxoox-azolidin-5-yl)methyl 4-methylbenzenesulfonate (13), was prepared and can be conjugated to any phenoxy core. To demonstrate the synthetic methodology, fluorinated derivatives of toliprolol were prepared, namely, [(18)F]-(2S and 2R)-]-(1-fluoropropan-2-ylamino)-3-(m-tolyloxy)propan-2-ol ((2S and 2R)-[(18)F]1). The radiosyntheses were accomplished in < 1 h, with 20-24% (uncorrected for decay, n = 7) radiochemical yields, > 96% radiochemical and > 99% enantiomeric purities, with specific activities of 0.9-1.1 Ci/mu mol(EOS). Ex vivo biodistribution studies with the radiotracers demonstrated excessively rapid washout that May limit their use for cerebral PET imaging.