The synthesis intermediate was treated at room temperature with TFA in water (8/2, conc. 0.14 M). After stirring for 3–6 h until completion of reaction (TLC DCM/MeOH), solvents were removed and the residue was coevaporated three times with 7 M NH3 in MeOH. The residue was purified by flash column chromatography on a reversed-phase silica gel column C18 (4 g, 40 μm) with a linear gradient of acetonitrile in TEAAc buffer 50 mM, pH 7. The fractions containing the pure compound were pooled, concentrated and lyophilized with water/dioxane to give desired compound as a powder.