[NH:1]([C:8]([O:10][C:11]([CH3:14])([CH3:13])[CH3:12])=[O:9])[C:2]([C:5]([OH:7])=O)([CH3:4])[CH3:3].[CH3:15][NH:16][O:17][CH3:18].Cl.CCN(C(C)C)C(C)C.C1CCC(N=C=NC2CCCCC2)CC1>CN(C1C=CN=CC=1)C.C(Cl)Cl>[C:11]([O:10][C:8](=[O:9])[NH:1][C:2]([C:5](=[O:7])[N:16]([O:17][CH3:18])[CH3:15])([CH3:3])[CH3:4])([CH3:14])([CH3:13])[CH3:12]
To a stirred mixture of Boc-Aib-OH (5 g, 24.61 mmol, 1 eq), MeNHOMe.HCl (2.88 g, 29.53 mmol, 1.2 eq), DMAP (3.61 g, 29.53 mmol, 1.2 eq), i-Pr2NEt (5.02 mL, 29.53 mmol, 1.2 eq) and CH2Cl2 (100 mL) was added DCC (6.09 g, 29.53 mmol, 1.2 eq). The mixture was stirred at room temperature for 5 days. The mixture was filtered to remove precipitated N,N′-dicyclohexylurea and the filtrate was evaporated under reduced pressure. The residue was dissolved in ethyl acetate (200 mL), washed with 10% aqueous citric acid (3×200 mL), 10% aqueous NaHCO3 (3×200 mL) and saturated aqueous sodium chloride (3×200 mL), and dried over MgSO4. Removal of the solvent yielded the crude product which was purified by column chromatography (hexane/ethyl acetate 60:40) to afford [1-(methoxy-methyl-carbamoyl)-1-methyl-ethyl]-carbamic acid tert-butyl ester (4.85 g, 80%) as a white solid. 1H NMR (200 MHz, CDCl3) δ (ppm): 1.43 (s, 6H), 1.58 (s, 9H), 3.22 (s, 3H), 3.69 (s, 3H), 6.95 (bs, 1H). MS (ESI, +ve ion): m/z 247.2 (M+1)+.
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