Der 2-Trimethylsilyläthyl-Rest als selektiv abspaltbare Carboxy-Schutzgruppe

The 2-trimethylsilylethyl residue, a selectively cleavable carboxyl protecting group In a search for new carboxyl protecting groups suitable for use in peptide synthesis, 2-trimethylsilylethyl esters -COOCH₂CH₂Si(CH₃)₃] of several N-protected amino acids have been prepared. These esters can be synthesized in good yields from N^a-benzyloxycarbonyl-amino acids and 2-trimethylsilylethanol with dicyclohexylcarbodiimide in the presence of pyridine. They are stable under a wide variety of conditions used during coupling and work-up in peptide synthesis. For removal the 2-trimethylsilylethyl group is readily cleaved by fluoride ions, preverably using a quaternary ammonium fluoride in dimethylformamide. Some side reactions which occurred during the removal of the 2-trimethylsilylethyl group are discussed. Special attention has been paid to the question of racemization during the treatment with fluoride ions. No. evidence of racemization was found in any of the cases examined.