[C:1]([O:5][C:6]([NH:8][C@H:9]([C:17]([O:19]C)=[O:18])[CH2:10][O:11][CH2:12][CH2:13][CH2:14][CH:15]=[CH2:16])=[O:7])([CH3:4])([CH3:3])[CH3:2].O.[OH-].[Li+].Cl>O1CCCC1.O.C(OCC)(=O)C>[C:1]([O:5][C:6]([NH:8][C@H:9]([C:17]([OH:19])=[O:18])[CH2:10][O:11][CH2:12][CH2:13][CH2:14][CH:15]=[CH2:16])=[O:7])([CH3:4])([CH3:2])[CH3:3]To a solution of 6.65 g (23 mmol) of N-tert-butoxycarbonyl-O-(4-pentenyl)-L-serine, methyl ester in 500 mL of tetrahydrofuran at room temperature was added a solution of 1.95 g (46 mmol) of lithium hydroxide monohydrate in 100 mL of water. The resulting mixture was stirred at room temperature for 40 hours. To the reaction mixture then was added 46 mL of 1.00N hydrochloric acid. The mixture was diluted with ethyl acetate, washed with water (3×) and brine, dried over anhydrous sodium sulfate, filtered, and concentrated under vacuum to afford 6.30 g of N-tert-butoxycarbonyl-O-(4-pentenyl)-L-serine as a colorless oil. NMR (300 MHz, CDCl3): δ 5.77 (d of d of t, 1H, J=17.2, 10.2, 6.6 Hz), 5.37 (br d, 1H, J=8.0 Hz), 5.03-4.92 (m, 2H), 4.42 (m, 1H), 3.87 (d of d, 1H, J=9.5, 2.6 Hz), 3.63 (d of d, 1H, J=9.5, 4.0 Hz), 3.45 (t, 2H, J=6.6 Hz), 2.07 (quart., 2H, J=7.3 Hz), 1.64 (quint., 2H, J=7.3 Hz), 1.44 (s, 9H).
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