[O:1]1[C:5]2=[N:6][CH:7]=[C:8]([C:10]([OH:12])=[O:11])[CH:9]=[C:4]2[CH:3]=[CH:2]1.C([NH:16]C(C)C)(C)C.C([Li])CCC.CCCCCC.C(O)(=O)C.O.O.O.C([O-])(=O)C.[Na+].N[O:44][S:45]([OH:48])(=O)=O>O1CCCC1.C(OCC)C>[S:45]([C:2]1[O:1][C:5]2=[N:6][CH:7]=[C:8]([C:10]([OH:12])=[O:11])[CH:9]=[C:4]2[CH:3]=1)(=[O:48])(=[O:44])[NH2:16]To a suspension of furo[2,3-b]pyridine-5-carboxylic acid (1.8 g, 11 mmol) in dry tetrahydrofuran (45 mL), under a nitrogen atmosphere and cooled to -70° C., was added diisopropylamine (1.54 mL, 11 mmol) to give a partial solution. Then 1.6M butyl lithium in hexane (19.7 mL, 31.5 mmol) was added dropwise to give a yellow precipitate. This suspension was stirred for 2.5 hours and then sulfur dioxide gas was bubbled over the reaction surface to give a very thick precipitate. After warming to room temperature, the reaction mixture was diluted with diethyl ether (50 mL) and glacial acetic acid (0.63 mL, 11 mmol) was added. This precipitate was collected by filtration and rinsed with diethyl ether. The hydroscopic sulfinate salt was dissolved in water (43 mL) and sodium acetate trihydrate (12.4 g, 92 mmol) and hydroxylamine-o-sulfonic acid (3.46 g, 30.6 mmol) were added. After stirring for 12-20 hours, the partial suspension was acidified with conc. hydrochloric and after stirring for several hours, the precipitated product was collected by filtration. This crude product (2.2 g) was recrystallized twice from ethanol/methanol (1:1) to give pure product (1.51 g, 57% yield), mp: 307°-308° (decomposition).
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