Journal
AMINO ACIDS
Volume 45, Issue 5, Pages 1097-1108Publisher
SPRINGER WIEN
DOI: 10.1007/s00726-013-1562-5
Keywords
Solid-phase peptide synthesis; Tyr(3)-octreotate; Positron emission tomography; Carbon-11; [C-11]methyl triflate; Radiochemistry
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Funding
- Canada Foundation for Innovation (CFI) [203639]
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Radiolabeled peptides have emerged as an attractive platform for the diagnostic and therapeutic oncology. However, the C-11-radiolabeling of peptides for positron emission tomography (PET) has been poorly explored, owing to the relatively short half-life of carbon-11 (t (1/2) = 20.3 min) and time-consuming multi-step radiochemical reactions. Existing methods have found limited use and are not routinely encountered in the production of radiotracers. Herein, we propose a facile one-step direct C-11-methylation of cysteine residues in peptides using [C-11]methyl triflate under ambient temperatures (20 A degrees C) and short reaction times, on the order of seconds. Good regioselectivity of this method was demonstrated by HPLC in a simple peptide (glutathione, GSH) and a more complex test decapeptide (Trp-Tyr-Trp-Ser-Arg-Cys-Lys-Trp-Thr-Gly) bearing multiple nucleophilic sites. In addition, we extend this method towards the synthesis of [C-11]Cys(Me)-[Tyr(3)-octreotate] as a demonstration of applicability for peptides of biological interest. This octreotate derivative was obtained in non-decay-corrected radiochemical yields of 11 +/- A 2 % (n = 3) with a synthesis time of approx. 30 min.
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