@article{oai:repo.qst.go.jp:00047116,
 author = {Suzuki, Chie and Kato, Koichi and B, Tsuji Atsushi and Zhang, Ming-Rong and Arano, Yasushi and Saga, Tsuneo and 鈴木 千恵 and 加藤 孝一 and 辻 厚至 and 張 明栄 and 荒野 泰 and 佐賀 恒夫},
 issue = {3},
 journal = {Journal of labelled compounds & radiopharmaceuticals},
 month = {Mar},
 note = {α-(11) C-Methyl amino acids are useful tools for biological imaging studies. However, a robust procedure for the labeling of amino acids has not yet been established. In this study, the (11) C-methylation of Schiff-base-activated α-amino acid derivatives has been optimized for the radiosynthesis of various α-(11) C-methyl amino acids. The benzophenone imine analog of methyl 2-amino butyrate was (11) C-methylated with [(11) C]methyl iodide following its initial deprotonation with potassium tert-butoxide (KOtBu). The use of an alternative base such as tetrabutylammonium fluoride, triethylamine, and 1,8-diazabicyclo[5.4.0]undec-7-ene did not result in the (11) C-methylated product. Furthermore, the KOtBu-promoted (11) C-methylation of the Schiff-base-activated amino acid analog was enhanced by the addition of 1,2,4,5-tetramethoxybenzene or 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and inhibited by the addition of 1,10-phenanthroline. These results suggest that inhibition of radical generation induced by KOtBu improves the α-(11) C-methylation of the Schiff-base-activated amino acids. The addition of a mixture of KOtBu and TEMPO to a solution of Schiff-base-activated amino acid ester and [(11) C]methyl iodide provided optimal results, and the tert-butyl ester and benzophenone imine groups could be readily hydrolyzed to give the desired α-(11) C-methyl amino acids with a high radiochemical conversion. This strategy could be readily applied to the synthesis of other α-(11) C-methyl amino acids.},
 pages = {127--132},
 title = {Inhibition of radical reactions for an improved potassium tert-butoxide-promoted (11) C-methylation strategy for the synthesis of α-(11) C-methyl amino acids.},
 volume = {58},
 year = {2015}
}