Stereocontrolled [¹¹C]Alkylation of N-Terminal Glycine Schiff Bases To Obtain Dipeptides

The use of various quaternary ammonium salts as chiral phase-transfer catalysts allowed effective and stereoselective radiochemical [¹¹C]alkylation to obtain functionalized dipeptides. We herein report a broadly applicable procedure for the asymmetric [¹¹C]alkylation of dipeptides to give labeled N-terminal peptides by using different [¹¹C]alkyl halides. Contended stereoselectivities of the reactions were observed by using ¹¹C-labeled alkyl halides, [¹¹C]methyl iodide and [¹¹C]benzyl iodide, and diastereomeric ratios with different specialized catalysts of 95:5 and 90:10 were achieved, respectively. Accordingly, the straightforward synthesis of enantioenriched compounds should play a vital role in peptide-based radiopharmaceutical development and positron emission tomography imaging.