Reaction Steps
Cyclic peptide ester 13 (190 mg, 0.45 mmol) was dissolved in warm THF/MeOH (40 mL) and cooled to rt. NaOH (1 N, 0.5 mL) was slowly added with stirring. After 1 h, the completed reaction (TLC-disappearance of 13, 120:2:1 CHCl3 /MeOH/AcOH, ninhydrin stain) was concentrated and the residue was dissolved in water. Dropwise addition of 2 N HCl induced precipitation of the product which was collected on a filter and dried under vacuum in a dessicator to give a white solid (140 mg, 74%). mp >250° C; 1H NMR (CDCl3 /DMSO-d6): δ 8.30 (br s, 1 H), 7.98 (t, 1 H, J=6.3 Hz), 7.23 (d, 1 H, J=9.4 Hz), 7.14 (t, 1 H, J=7.0 Hz), 6.96 (d, 1 H, J=7.0 Hz), 6.66 (s, 1 H), 6.37 (d, 1 H, J=7.8 Hz), 4.39 (m, 1 H), 4.05 (m, 1 H), 3.85 (dd, 1 H, J=8.8, 14.0 Hz), 3.27 (1 H, obscured by H2O peak), 3.02-2.78 (m, 3 H), 2.67 (dd, 1 H, 8.2 Hz, J=12.9 Hz), 1.34 (s, 9 H); 13C NMR (DMSO-d6 ; CD3OD): δ 173.27, 173.05, 169.97, 156.14, 137.34, 136.43, 133.51, 129.55, 128.80, 128.18, 80.24, 56.76, 52.70, 49.45, 44.16, 37.58, 28.73. Anal. Calcd for C19H25N3O6H2O: C, 55.74; H, 6.65; N, 10.26. Found: C, 55.16; H, 6.59; N, 9.90.
