To a solution of 1-(phenylsulfonyl)-2,3-dihydro-1H-pyrido[2,3-b][1,4]oxazine-7-carbonyl chloride (40 mg, 0.118 mmol; Example 1, Step 1) in DCM (2 mL) was added N-hydroxypropionimidamide (20.81 mg, 0.236 mmol) and DIPEA (50 μL, 0.286 mmol). The reaction was stirred at room temperature for 16 hours. LCMS analysis of the reaction mixture indicated consumption of starting material. The reaction mixture was treated with saturated aqueous NaHCO3 (10 mL) and extracted with EtOAc (3×10 mL). The combined organics were dried over anhydrous Na2SO4 and concentrated in vacuo. The resulting solid was diluted with THF (5 mL) and TBAF in THF (118 μL, 0.118 mmol) was added. The reaction was then stirred overnight. The reaction mixture was concentrated in vacuo and the resulting paste was purified by flash column chromatography using a gradient elution of hexanes with 30-100% EtOAc to provide 7-(3-ethyl-1,2,4-oxadiazol-5-yl)-1-(phenylsulfonyl)-2,3-dihydro-1H-pyrido[2,3-b][1,4]oxazine (29.7 mg, 0.076 mmol, 64.2% yield) as a white solid. LCMS (+ESI) m/z=373.0 [M+H]+; 1H-NMR (CDCl3) δ 8.87 (d, 1H), 8.77 (d, 1H), 7.71 (m, 2H), 7.63 (tt, 1H) 7.51 (m, 2H), 4.01 (m, 2H), 3.92 (m, 2H), 2.84 (q, 2H), 1.39 (t, 3H).
