A titanium tetrachloride-based effective methodology for the synthesis of dipeptides

A series of dipeptide systems have been easily achieved through a TiCl₄-assisted condensation reaction. The reaction of N-protected amino acids with amino acid methyl esters in pyridine and in the presence of TiCl₄ furnished the corresponding dipeptides with high yields and diastereoselectivity. The reaction was successfully applied to amino acids protected on the α-amino function with different protecting groups. The adopted experimental conditions allowed preserving both the protecting groups on the α-amino function and on the side chain functionalities. Furthermore, the preservation of the stereochemical integrity at the amino acid chiral centres has been verified.