[NH:1]([C:15]([O:17][C:18]([CH3:21])([CH3:20])[CH3:19])=[O:16])[C@H:2]([C:4]([NH:6][C@H:7]([C:11]([O:13]C)=[O:12])[CH:8]([CH3:10])[CH3:9])=[O:5])[CH3:3].[OH-].[Na+]>CC(C)=O>[NH:1]([C:15]([O:17][C:18]([CH3:21])([CH3:20])[CH3:19])=[O:16])[C@H:2]([C:4]([NH:6][C@H:7]([C:11]([OH:13])=[O:12])[CH:8]([CH3:10])[CH3:9])=[O:5])[CH3:3]Boc-Ala-Val-OMe 53 (1.750 g, 5.79 mmol) was stirred in 40 mL acetone. NaOH solution (8.7 mL of 2.0 M aqueous solution) was added and stirred 2 h at 23° C. Acetone was removed under reduced pressure and the resulting solution was diluted with EtOAc (20 mL). The organic fraction was washed with water (2×20 mL), dried over sodium sulfate, and concentrated in vacuo to yield 1.561 g (99%) product. 1H NMR (CDCl3, 300 MHz) δ 12.28 (br s, 1H), 7.69 (d, J=8.7 Hz, 1H), 6.98 (d, J=7.5 Hz, 1H), 4.15 (dd, J=5.4, 8.4 Hz, 1H), 4.04 (quintet, J=7.2 Hz, 1H), 3.35 (br s, 2H), 2.04 (octet, J=6.6 Hz, 1H), 1.37 (s, 9H), 1.16 (d, J=7.2 Hz, 3H), 0.87 (d, J=7.2 Hz, 3H); 13C NMR (CDCl3, 75 MHz) δ 172.9, 155.1, 78.1, 56.8, 30.2, 28.2, 19.0, 18.0, 17.8.
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