Stereocontrolled [ 11 C]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 [ 11 C]alkylation to obtain functionalized dipeptides. We herein report a broadly applicable procedure for the asymmetric [ 11 C]alkylation of dipeptides to give labeled N‐terminal peptides by using different [ 11 C]alkyl halides. Contended stereoselectivities of the reactions were observed by using 11 C‐labeled alkyl halides, [ 11 C]methyl iodide and [ 11 C]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.