[NH2:1][CH2:2][CH2:3][C:4]([OH:6])=[O:5].[C:7](O)(=[C:12]1[C:20](=[O:21])[CH2:19][C:16]([CH3:18])([CH3:17])[CH2:15][C:13]1=[O:14])[CH2:8][CH:9]([CH3:11])[CH3:10]>CCO.C(O)(C(F)(F)F)=O>[NH:1]([C:7](=[C:12]1[C:13](=[O:14])[CH2:15][C:16]([CH3:17])([CH3:18])[CH2:19][C:20]1=[O:21])[CH2:8][CH:9]([CH3:11])[CH3:10])[CH2:2][CH2:3][C:4]([OH:6])=[O:5]To a stirred suspension of H-β-Ala-OH (1.02 g, 11.4 mmol) and ivDde-OH (5 ml, 22.9 mmol) in EtOH was added TFA (88 μL, 1 mmol) at room temperature.1 The mixture was then refluxed for 24 hours. After the solvent was evaporated in vacuo, a crude product was purified by column chromatography with CH3OH/CH2Cl2 (0.1% TFA) gradient to afford ivDde-β-Ala-OH (3.3 g, 97.6%). 1H NMR (CDCl3) δ 1.02 (m, 12H), 1.90-2.03 (m, 1H), 2.39 (s, 4H), 2.75 (t, J=6.0 Hz, 2H), 3.06 (br d, J=6.0 Hz, 2H), 3.78 (q, J=6.0 Hz, 2H); 13C NMR (CDCl3) δ 22.8, 28.4, 29.4, 30.2, 34.1, 37.4, 39.6, 52.9, 107.4, 173.0, 177.2; MS (MALDI): m/z: calcd for C16H26NO4 296.2; found 296.5 [M+H]+.
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