A solution of 3-[7-(3,5-Dimethylisoxazol-4-yl)-2-oxo-1,2,4,5-tetrahydroimidazo[1,5,4-de][1,4]benzoxazin-4-yl]pyridine-2-carboxylic acid (30.0 mg, 0.0764 mmol) (from step 2) in N,N-dimethylformamide (1.0 mL) was treated with ethylamine (10.8 μL, 0.191 mmol) followed by N,N-diisopropylethylamine (66.6 μL, 0.382 mmol) and stirred at room temperature for 5 min. The reaction mixture was subsequently treated with benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate [Aldrich #: 226084](50.7 mg, 0.115 mmol) and stirred at room temperature for 1 h. Purification by preparative LCMS (XBridge C18 column, eluting with a gradient of acetonitrile/water containing 0.1% ammonium hydroxide, at flow rate of 60 mL/min) gave the desired product (23 mg, 71%) as a single enantiomer. 1H NMR (400 MHz, DMSO-d6) δ 9.03 (t, J=5.9 Hz, 1H), 8.58 (dd, J=4.6, 1.4 Hz, 1H), 7.49 (dd, J=8.0, 4.6 Hz, 1H), 7.11 (dd, J=8.0, 1.2 Hz, 1H), 6.87 (d, J=8.0 Hz, 1H), 6.80 (d, J=8.0 Hz, 1H), 6.54-6.41 (m, 1H), 4.64-4.45 (m, 2H), 3.43-3.24 (m, 2H), 2.24 (s, 3H), 2.07 (s, 3H), 1.15 (t, J=7.2 Hz, 3H); LCMS calculated for C22H22N5O4 (M+H)+: m/z=420.2. found: 420.2.
