Asymmetric synthesis ofL-[3-11C]alanine andL-[3-11C]phenylalanine by a phase-transfer alkylation reaction

Abstract
The asymmetric syntheses of enantiomerically enriched L-[3-11C]alanine and L-[3-11C]phenylalanine (t½ 20.4 min for 11C) by phase-transfer alkylation of (–)-8-phenylmenthan-3-yl N-(diphenylmethylene) glycenate with [11C]methyl and [α-11C]benzyl iodides, respectively, are presented. The total synthesis times were 35–55 min, from the start of synthesis of the [11C]methyl and [α-11C]benzyl iodides. The products were obtained in 15–40%(decay corrected) radiochemical yields and higher than 98% radiochemical purities. The enantiomeric purities of the amino acids were determined to be 52–55% enantiomeric excess (e.e.). In a typical run 600 MBq of L-[11C]alanine was obtained, starting with 5.2 GBq of [11C]carbon dioxide.

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