The obtained phthaloyl group of 22 was removed by ethylenediamine and converted to compound 23, which was protected by the Boc group. There are two remaining amino acid residues necessary for the Larock macrocyclization key reaction. Carboxylic acid 23 was coupled with L-proline derivative 12 to induce the formation of amide 24. After the hydrolysis of its Me ester, amide coupling with alkyne fragment 7 mediated by HATU led to the synthesis of compound 25, the precursor for Larock macrocyclization.