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

The serotonin receptor 5-HT ligand 4-[F]fluoro-N-[2-[1-(2-methoxyphenyl)-1-piperazinyl]ethyl-N-2-pyridinyl-benzamide ( p-[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 Chromatography (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-[F]MPPF and 2-4 radioactive by-products eluting after the product fraction, and the reverse-phase HPLC method failed occasionally to separate p-[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-[F]MPPF the labelled product was identified with m/ z ratio of 435 ([M + H]). The other HPLC fractions were measured to have following m/ z ratios: (1) 327; 349; (675) (2) 402; 407/408; (791) and (3) 436, suggesting different kind of decomposition of the labelled product and/or the inactive precursor. The ion trap mass spectrometer was sufficient for the qualitative analysis of p-[F]MPPF. However, differentiation of by-products arising from the decomposition of p-[F]MPPF or from its precursor p-MPPNO proved to be challenging. [ABSTRACT FROM AUTHOR]