Strained Ammonium Precursors for Radiofluorinations

The increasing application of positron emission tomography (PET) in nuclear medicine has stimulated the extensive development of a multitude of novel and versatile techniques to introduce fluorine-18, especially for the radiolabelling of biologically or pharmacologically active molecules. Taking into consideration that the introduction of fluorine-18 (t(1/2)=109.8 min) mostly proceeds under harsh conditions, radiolabelling of such molecules represents a challenge and is of enormous interest. Ideally, it should proceed in a regioselective manner under mild physiological conditions, in an acceptable time span, with high yields and high specific activities. Special attention has been drawn to 2-fluoroethyl and 3-fluoropropyl groups, which are often the active sites of radiofluorinated compounds. Precursors containing an ammonium leaving group - such as a strained azetidinium or aziridinium moiety - can help to overcome these obstacles leading to a convenient and mild introduction of [F-18]fluoride with high radiochemical yields.

Automated summary

The increasing use of PET in nuclear medicine has led to the development of various techniques for introducing fluorine-18 into biologically or pharmacologically active molecules. Special attention has been focused on 2-fluoroethyl and 3-fluoropropyl groups, which are commonly found in radiofluorinated compounds.