Compound 1B was prepared starting from compound 1A in three steps following an analogous method to that described in U.S. Pat. No. 6,358,971, which is incorporated by reference herein in its entirety. Specifically, a mixture of methyl 6-aminonicotinate (1A, 3 g, 19.7 mmol) and tosylchloride (4.5 g, 23.6 mmol) in pyridine (40 mL) was heated at 80° C. for 16 hrs. The reaction was cooled to room temperature and pyridine was removed in vacuo. The resulting residue was diluted with water and allowed to stir for 10 min. The resulting solid was filtered and dried under vacuum to provide methyl 6-(4-methylphenylsulfonamido)nicotinate which was used without further purification. To a suspension of methyl 6-(4-methylphenylsulfonamido)nicotinate (5.3 g, 17.3 mmol) in anhydrous DMF was sequentially added DIEA (3.31 mL, 19.03 mmol) and then 2-bromoacetamide (2.63 g, 19.03 mmol). The reaction was stirred at ambient temperature for 24 hrs and then poured into water. The resulting solid was filtered and dried under vacuum to provide methyl 1-(2-amino-2-oxoethyl)-6-(4-methylphenylsulfonamido)-1,6-dihydropyridine-3-carboxylate which was used without further purification. To a suspension of methyl 1-(2-amino-2-oxoethyl)-6-(4-methylphenylsulfonamido)-1,6-dihydropyridine-3-carboxylate (1.0 g, 2.8 mmol) in DCM (20 mL) was added TFAA (8.0 mL, 57.5 mmol) dropwise at ambient temperature. The reaction was refluxed for 2 hrs, cooled to ambient temperature, and then concentrated in vacuo. The resulting residue was suspended in saturated sodium bicarbonate and stirred for 15 min. The resulting solid was filtered and dried under vacuum to provide methyl 2-(2,2,2-trifluoroacetamido)imidazo[1,2-a]pyridine-6-carboxylate (1B) which was used without further purification.
