Positron labeled phorbol ester: Synthesis method for "non-carrier added" phorbol 13-[1-11C] butyrate using ketene reaction

A new method was developed to synthesize positron labeled phorbol esters for second messenger imaging based on a receptor binding to protein kinase C. [1‐11C]propyl ketene was produced by the pyrolytic decomposition of [1‐11C]butyric acid. This new method was made possible by the reaction of [1‐11C]propyl ketene to the hydroxyl group of phorbol under the non‐carrier added conditions. The precursor protected in the 20‐hydroxyl group of phorbol was acylated by [1‐11C]propyl ketene to the 13‐hydroxyl group producing phorbol 13‐[11C]butyrate ([11C]P13Bu). Total synthesis time was about 60 minutes and the specific activity was greater than 67 GBq/μmol (1800 mCi/μmol). [11C] P13Bu will prove to be useful ligand for PET studies due to the simple procedures required for synthesis.