A mixture of 2-phenyl-1-(pyridin-2-yl)ethanone (Intermediate 27) (200 mg, 1.01 mmol), 3-ethoxy-4-hydroxy-5-nitrobenzaldehyde (214.1 mg, 1.01 mmol), urea (182.5 mg, 3.04 mmol), and concentrated hydrochloric acid solution (0.3 mL) in ethanol (1 mL) was refluxed for 60 h. After being cooled down to room temperature, the mixture was evaporated, and purified by preparative HPLC to give Compound 59 (132.5 mg, yield 30.2%). 1H NMR (DMSO-d6 400 MHz): δ 10.26 (brs, 1H), 8.59 (d, J=4.4 Hz, 1H), 8.37 (s, 1H), 7.62-7.54 (m, 2H), 7.42 (s, 1H), 7.30-7.27 (m, 1H), 7.14 (d, J=6.4 Hz, 4H), 6.93-6.90 (m, 3H), 5.25 (s, 1H), 4.03-3.99 (m, 2H), 1.33-1.29 (m, 3H); MS (ESI): m/z 433.0 [M+H]+.
