Assessment of labelled products with different radioanalytical methods: study on 18F-fluorination reaction of 4-[18F]fluoro-N-[2-[1-(2-methoxyphenyl)-1-piperazinyl]ethyl-N-2-pyridinyl-benzamide (p-[18F]MPPF)

The serotonin receptor 5-HT1A ligand 4-( 18 F) fluoro-N-(2-(1-(2-methoxyphenyl)-1-piperazinyl)ethyl-N- 2-pyridinyl-benzamide (p-( 18 F)MPPF) was produced by a simplified method of Le Bars et al. Traditional oil bath heating was compared to microwave heating. Various radioanalytical methods, radio-Thin Layer Chromatogra- phy (TLC), High Pressure Liquid Chromatography (HPLC) and Mass Spectrometry (MS), were compared in the evaluation of the labelled product(s). The crude reaction mixture consisted of p-( 18 F)MPPF and 2-4 radioactive by-products eluting after the product fraction, and the reverse-phase HPLC method failed occasionally to sepa- rate p-( 18 F)MPPF from the radioactive by-product with close retention time. The heating method had no significant effect on the composition of labelled by-products. In LC-(ESI)-MS analysis of p-( 18 F)MPPF the labelled product was identified with m/z ratio of 435 ((M ? H ? )). The other