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

Abstract

N-Nosyl-alpha-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 (1)H NMR and HPLC.