“One-Pot” Methylation of N-Nosyl-α-amino Acid Methyl Esters with Diazomethane and Their Coupling To Prepare N-Methyl Dipeptides

Abstract
N-Nosyl-α-amino acid methyl esters are methylated quantitatively with diazomethane. After proper deprotection of the amino function by treatment with the reagent system mercaptoacetic acid/sodium methoxide, the obtained N-methyl amino acid methyl esters are coupled with N-Fmoc amino acid chlorides to afford the corresponding dipeptides. The obtained products do not show any detectable extent of racemization by 1H NMR and HPLC.