[CH2:1]([O:8][C:9]([NH:11][C@@H:12]([CH3:16])[C:13]([OH:15])=[O:14])=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[H-].[Na+].CS(O[CH2:24][CH2:25][S:26]([CH3:29])(=[O:28])=[O:27])(=O)=O>C1COCC1>[CH2:1]([O:8][C:9]([N:11]([CH2:24][CH2:25][S:26]([CH3:29])(=[O:28])=[O:27])[C@@H:12]([CH3:16])[C:13]([OH:15])=[O:14])=[O:10])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1In a 100 mL round-bottomed flask, (S)-2-(benzyloxycarbonylamino)propanoic acid (331 mg, 1.48 mmol, Eq: 1.00) was combined with THF (9 mL) to give a colorless solution. Sodium hydride (131 mg, 3.26 mmol, Eq: 2.2) was added. The reaction was stirred at rt for 30 min, then 2-(methylsulfonyl)ethyl methanesulfonate (300 mg, 1.48 mmol, Eq: 1.00) was added and the reaction was stirred at rt overnight. The reaction was quenched with saturated aqueous NH4Cl and extracted with EtOAc. The combined organic layers were washed with water and brine then dried over Na2SO4 and concentrated in vacuo. The crude material was purified by flash chromatography (silica gel, 40 g, 10% to 60% EtOAc in hexanes) to give (S)-2-[benzyloxycarbonyl-(2-methanesulfonyl-ethyl)-amino]-propionic acid (201 mg).
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