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Boc-Gly-Pro-Nleu-NH2 (3.5 g, 0.0089 mol.) was dissolved in a solution of 30% TFA in DCM (50 ml). The solution was stirred for 40 minutes. The DCM and TFA were removed under reduced pressure, and 3×50 ml benzene were added and distilled under reduced pressure to remove trace TFA. The resulting mixture was dissolved in 30 ml methanol and the solution was chilled to 0° C. HCl/dioxane (4N, 10 ml) was added to the solution to transfer the product from TFA salt to HCl salt. Ethyl ether (200 ml) was added to the solution and a precipitation formed. The ether was removed by filtration and a white solid product was obtained (2.9 g, 87%). Analytical RP-HPLC chromatogram, single peak, RT=15.7 min. (5-15% B in 30 min.). FAB-MS, observed (M+H)+=285. 1H-NMR (500 MHz, DMSO-d6, 25° C., assignment by TOCSY) δ8.03 (m, 3H, Gly-NH3), 7.65 (s, C-terminal NH2), 7.46 (s, C-terminal NH2), 7.34 (s, C-terminal NH2), 7.24 (d, C-terminal NH2), 7.08 (s, C-terminal NH2), 6.92 (s, C-terminal NH2), 4.94 (d, Pro-α), 4.76 (m, Pro-α), 4.59 (m, Pro-α), 4.25-3.52 (sets of bands, Nleu-α, Gly-α), 3.52-3.44 (m, Pro-δ), 3.42-2.70 (sets of bands, Gly-α, Nleu-β), 2.36-1.65 (sets of bands, Pro-β, Pro-γ, Nleu-γ), 0.90 (m, Nleu-δ), 0.79 (m, Nleu-δ).

1. customThe DCM and TFA were removed under reduced pressure, and 3×50 ml benzene
2. additionwere added
3. distillationdistilled under reduced pressure
4. customto remove trace TFA
5. dissolutionThe resulting mixture was dissolved in 30 ml methanol
6. additionHCl/dioxane (4N, 10 ml) was added to the solution
7. additionEthyl ether (200 ml) was added to the solution
8. customa precipitation
9. customformed
10. customThe ether was removed by filtration
11. customa white solid product was obtained (2.9 g, 87%)
12. customAnalytical RP-HPLC chromatogram, single peak, RT=15.7 min. (5-15% B in 30 min.)