An efficient and highly selective deprotection of N-Fmoc-alpha-amino acid and lipophilic N-Fmoc-dipeptide methyl esters with aluminium trichloride and N,N-dimethylaniline.

A novel procedure for the deprotection of the carboxyl group of amino acid methyl esters is presented. The process is carried out by the reagent system aluminium trichloride/N,N-dimethylaniline that can successfully be applied to unblock the carboxyl moiety either of N-Fmoc-protected amino acid methyl esters and N-Fmoc-protected short dipeptide methyl esters. The chiralities of the optically pure amino acid or peptide precursors are maintained totally unchanged.