Synthesis and hydrolytic stability of novel 3-[18F]fluoroethoxybis(1-methylethyl)silyl]propanamine-based prosthetic groups

Two new silicon-based prosthetic groups, derived from 3-[ethoxybis(1-methylethyl)silyl]propanamine, have been prepared in good yields. These silicon groups bearing an acid or an azide group were coupled to a model tripeptide (Leu-Gly-Gly) either through a classical amide bond formation or through “click chemistry” via the Huisgen cycloaddition. The radiolabelling with fluorine-18 by substitution of the ethoxy group at silicon has been carried out with success in 51–54% decay corrected radiochemical yields. Radiolabelled peptides were easily prepared by direct 18F-fluorination of the silicon-bearing tripeptide or by coupling the peptide with a radiolabelled silicon-based prosthetic group. Their stabilities in physiological medium were studied and proved poor.