[C:1]([O:5][C:6](=[O:15])[NH:7][C:8]1[CH:13]=[CH:12][CH:11]=[C:10]([CH3:14])[N:9]=1)([CH3:4])([CH3:3])[CH3:2].C([N-]C(C)C)(C)C.[Li+].[C:24](=[O:26])=[O:25]>C1COCC1.C1COCC1.CCCCCCC.C(C1C=CC=CC=1)C>[C:1]([O:5][C:6]([NH:7][C:8]1[N:9]=[C:10]([CH2:14][C:24]([OH:26])=[O:25])[CH:11]=[CH:12][CH:13]=1)=[O:15])([CH3:4])([CH3:3])[CH3:2](6-Methyl-pyridin-2-yl)-carbamic acid tert-butyl ester (1.04 g, Pitts, J. Med. Chem., 43, 2000, 27) under an argon atmosphere in THF (40 mL) was cooled to −20° C. and treated dropwise at −20° C. with 5.5 mL of a 2 M solution of lithium diisopropylamide in THF/heptane/ethylbenzene (Fluka). The solution was stirred 1 h at −20° C., cooled to −70° C. and then treated with an access of dry ice. The mixture was allowed to warm to 10° C. and partitioned between aqueous 1N HCl and AcOEt, the layers were separated, the organic layer dried over Na2SO4, filtered, evaporated and the residue was purified by flash chromatography (MeOH/CH2Cl2 0-15%). The obtained material was triturated with ether, the crystalline solid obtained was filtered off by suction and dried in vacuo to give (6-tert-butoxycarbonylamino-pyridin-2-yl)-acetic acid as an off-white solid (0.3 g). MS (ESI−): 251.1 ([M−H]−).
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