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Issue 3, 2017
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A rapid and highly enantioselective C–11C bond formation of L-[11C]phenylalanine via chiral phase-transfer catalysis

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Abstract

A rapid method for the synthesis of carbon-11 radiolabeled phenylalanine was developed using a chiral phase-transfer catalyst and a sub-nanomolar quantity of [11C]benzyl iodide as a radio-precursor. Based on a reported synthesis of [11C]benzyl iodide, a Schiff base precursor was evaluated for stereoselective [11C]benzylation. Extensive and interactive screening of the precursor, catalyst, base, stirring and temperature was required to achieve high stereoinduction. The result is an efficient 5-step radiolabeling method to reliably synthesize L- or D-[11C]phenylalanine with an excellent enantiomeric excess of >90% and almost quantitative radiochemical conversion of >95% (n > 5). Additionally, a phase-transfer catalyzed alkylation was utilized on the preparative scale using automated platform. The application resulted in high specific activity ranging from 85–135 GBq μmol−1 of the enantiomerically pure [11C]phenylalanine, showing that the process is robust and amenable to broad use in PET.

Graphical abstract: A rapid and highly enantioselective C–11C bond formation of l-[11C]phenylalanine via chiral phase-transfer catalysis

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Publication details

The article was received on 01 Dec 2016, accepted on 13 Dec 2016 and first published on 13 Dec 2016


Article type: Communication
DOI: 10.1039/C6OB02633H
Citation: Org. Biomol. Chem., 2017,15, 570-575
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    A rapid and highly enantioselective C–11C bond formation of L-[11C]phenylalanine via chiral phase-transfer catalysis

    A. Pekošak, U. Filp, J. Škrinjar, A. J. Poot and A. D. Windhorst, Org. Biomol. Chem., 2017, 15, 570
    DOI: 10.1039/C6OB02633H

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