This thesis deals with the synthesis and development of ¹⁸F-labelled alkyl etomidate and vorozole analogues, and their use as positron emission tomography (PET) tracers for the imaging of the steroid enzymes 11β-hydroxylase and aromatase. Two synthetic ¹⁸F-labelling approaches to the etomidate and vorozole analogues were developed, and the analogues were evaluated in some biological assays.

The two-step labelling method was used to synthesise many compounds for biological evaluation. In the first step, a ¹⁸F-labelled intermediate based on a ditosylate or a halogenated diethyl ether was synthesised and used directly in the next alkylation step. The decay-corrected (d.c.) radiochemical yield was higher compared to other known two-step labelling methods.

Once an appropriate candidate has been chosen for clinical evaluation, a one-step labelling method will be more suitable. We therefore developed a method based on precursors that had leaving groups at the end of their alkyl chains, and used these directly in the ¹⁸F-labelling synthesis. The one-step ¹⁸F-labelling synthesis required less reaction time and produced higher specific radioactivity and d.c. radiochemical yield than our two-step synthesis. With microwave heating, the reaction time was reduced to seconds and the d.c. radiochemical yield was better than that obtained with conventional heating. The one-step synthesis simplified the technical handling by allowing the tracer syntheses to be automated on the TRACERLab FX_FN.