O1CCCC1.C[O:7][C:8]([C:10]1[CH:15]=[N:14][C:13]([N:16]2[CH2:21][CH2:20][CH2:19][CH2:18][CH2:17]2)=[C:12]([C:22]2[CH:27]=[CH:26][C:25]([F:28])=[CH:24][CH:23]=2)[N:11]=1)=[O:9].[OH-].[Li+].Cl>O>[F:28][C:25]1[CH:26]=[CH:27][C:22]([C:12]2[N:11]=[C:10]([C:8]([OH:9])=[O:7])[CH:15]=[N:14][C:13]=2[N:16]2[CH2:21][CH2:20][CH2:19][CH2:18][CH2:17]2)=[CH:23][CH:24]=1
To a tetrahydrofuran (5 ml) solution of 6-(4-fluoro-phenyl)-5-piperidin-1-yl-pyrazine-2-carboxylic acid methyl ester (0.48 g, 1.52 mmol, 1.0 eq) was added a solution of lithium hydroxide (1M, 1.52 ml, 1.52 mmol, 1.0 eq) in water. The mixture was stirred overnight at room temperature after which time the resulting solution was acidified with hydrochloric acid (pH˜5) and aqueous phase extracted with ethyl acetate (2×10 ml). The organic phase was dried over magnesium sulfate and concentrated in vacuo to afford 6-(4-fluoro-phenyl)-5-piperidin-1-yl-pyrazine-2-carboxylic acid as white crystals. Yield=0.42 g (91%). 1H NMR (400 MHz, DMSO): δ 1.46-1.53 (6H, m), 3.22-3.25 (4H, m), 7.32 (2H, t, J=8.87 Hz), 7.82-7.86 (2H, m), 8.62 (1H, s).
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