[CH3:1][S:2]([N:5]1[CH2:10][CH2:9][CH:8]([C:11]2[O:12][CH:13]=[C:14]([C:16]([O:18]CC)=[O:17])[N:15]=2)[CH2:7][CH2:6]1)(=[O:4])=[O:3].[OH-].[Li+]>C1COCC1.CO.O>[CH3:1][S:2]([N:5]1[CH2:6][CH2:7][CH:8]([C:11]2[O:12][CH:13]=[C:14]([C:16]([OH:18])=[O:17])[N:15]=2)[CH2:9][CH2:10]1)(=[O:3])=[O:4]Ethyl 2-(1-(methylsulfonyl)piperidin-4-yl)oxazole-4-carboxylate (590 mg, 1.951 mmol) was dissolved in THF/methanol mixture (9:1) and 1M lithium hydroxide (3.90 ml, 3.90 mmol) was added slowly. The reaction mixture was stirred at RT for 1 h, diluted with water and pH was adjusted to 1.5. The mixture was extracted three times with ethyl acetate. Ethyl acetate phases were combined and evaporated to yield the title compound (74.7%). 1H-NMR (400 MHz; DMSO): δ 1.68-1.81 (m, 2H), 2.06-2.15 (m, 2H), 2.85-2.96 (m, 5H), 2.99-3.10 (m, 1H), 3.51-3.59 (m, 2H), 8.67 (s, 1H), 13.02 (bs, 1H).
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