Nitronium tetrafluoroborate → 1-(7-Hydroxy-6-nitro-2-benzothiazolyl)-3-ethyl-urea

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To a solution of 2-methylpyridone (0.020 mL, 0.20 mmol, 1.2 eq) in anhydrous acetonitrile (0.5 mL), nitronium tetrafluoroborate (0.045 g, 0.32 mmol, 1.9 eq) was added. The suspension was stirred at about 20° C. for about 5 minutes to get an orange solution. The solution was then transferred to a suspension of 1-(7-hydroxy-2-benzothiazolyl)-3-ethyl-urea 8 (0.040 g, 0.17 mmol) in acetonitrile (0.5 mL). The reaction mixture was stirred at about 20° C. for about 15 minutes, then taken up in diethyl ether (8 mL), and neutralized by washing with saturated sodium bicarbonate solution (1.5 mL). The organic extract was concentrated and dissolved in methanol (2 mL). LC/MS purification was followed by flash chromatography purification on silica (methylene chloride/methanol=40/1) to afford 0.005 g (10%) of the desired compound 17. 1H NMR (DMSO) δ 11.20 (br s, 1H, NH), 8.02 (d, 1H, J=9.0 Hz, ArH), 7.23 (d, 1H, J=7.5 Hz, ArH), 6.78 (br s, 1H, NH), 3.20 (m, 2H, CH2), 1.10 (t, 3H, J=7.2 Hz, CH3). LC/MS 283 (MH+); RP-HPLC RT 2.74 minutes.

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