Synthesis of three ¹⁸F-labelled cyclooxygenase-2 (COX-2) inhibitors based on a pyrimidine scaffold

Cyclooxygenase (COX) is the key enzyme within the complex conversion of arachidonic acid into prostaglandins (PGs). Inhibitors of this enzyme represent a particularly promising class of compounds for chemoprevention and cancer therapy. The experimental data on the involvement of COX isoform COX-2 in tumour development and progression, as well as the observed overexpression of COX-2 in a variety of human cancers provide the rationale for targeting COX-2 for molecular imaging and therapy of cancer. A series of trifluoromethyl-substituted pyrimidines was prepared as a novel class of selective COX-2 inhibitors, based on the lead structure 1a. All compounds were tested in cyclooxygenase (COX) assays in vitro to determine COX-1 and COX-2 inhibitory potency and selectivity. Molecular docking studies using the catalytic site of COX-1 and COX-2, respectively, provided complementary theoretical support for the obtained experimental biological structure-activity relationship data of three highly potent and selective fluorobenzyl-containing COX-2 inhibitors. Selected fluorobenzyl-substituted pyrimidine derivatives were further developed as ¹⁸F-labelled radiotracers ([¹⁸F]1a, [¹⁸F]2a, [¹⁸F]3a). Radiotracers [¹⁸F]1a and [¹⁸F]2a were radiolabelled using 4-[¹⁸F]fluorobenzylamine ([¹⁸F]FBA) as a building block. Radiotracer [¹⁸F]3a was radiofluorinated directly using a nucleophilic aromatic substitution reaction with no-carrier-added (n.c.a.) [¹⁸F]fluoride on an iodylaryl compound as a labelling precursor.