[CH3:1][N:2]1[N:6]=[N:5][C:4]([CH:7]2[CH2:12][CH:11]([C:13]([O:15]CC)=[O:14])[CH2:10][CH2:9][N:8]2[C:18]([O:20][CH2:21][C:22]2[CH:27]=[CH:26][CH:25]=[CH:24][CH:23]=2)=[O:19])=[N:3]1.[Li+].[OH-].Cl>C1COCC1.O>[CH2:21]([O:20][C:18]([N:8]1[CH2:9][CH2:10][CH:11]([C:13]([OH:15])=[O:14])[CH2:12][CH:7]1[C:4]1[N:5]=[N:6][N:2]([CH3:1])[N:3]=1)=[O:19])[C:22]1[CH:27]=[CH:26][CH:25]=[CH:24][CH:23]=11-Benzyl 4-ethyl 2-(2-methyl-2H-tetrazol-5-yl)piperidine-1,4-dicarboxylate (0.92 g, 2.36 mmol) was dissolved in THF (10 mL) and water (10 mL) and LiOH (0.239 g, 9.98 mmol) was added. The mixture was stirred at room temperature for 1 h 10 min and then diluted with water and acidified with 2 M HCl. The aqueous phase was extracted 3 times with EtOAc, the combined organic phase dried over Na2SO4 and evaporated to yield 1-(benzyloxycarbonyl)-2-(2-methyl-2H-tetrazol-5-yl)piperidine-4-carboxylic acid (828 mg, quant.). 1H NMR (400 MHz, cdcl3) δ 1.80-1.91 (m, 1H), 2.01-2.11 (m, 1H), 2.34 (dt, 1H), 2.63-2.79 (m, 2H), 3.55-3.65 (m, 1H), 4.01-4.09 (m, 1H), 4.24 (s, 3H), 5.13 (d, 2H), 5.60 (dd, 1H), 7.27-7.39 (m, 5H). MS m/z 346 (M+H)+
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