A mixture of 1-cyclopentyl-2-phenylethanone (Intermediate 91) (1.6 mmol, 300 mg), 3-ethoxy-4-hydroxy-5-nitrobenzaldehyde (1.91 mmol, 404 mg), and urea (4.8 mmol, 288 mg) in anhydrous ethanol (5 mL) was added concentrated HCl (0.2 mL), the above mixture was refluxed for 13 hours. The reaction mixture was concentrated and the residue was purified by column chromatography, followed by preparative HPLC to afford the product Compound 172 as yellow solid (20 mg, yield: 2.96%). 1H NMR (DMSO 400 MHz): δ 10.23 (s, 1H), 8.25 (s, 1H), 6.98-7.33 (m, 8H), 5.00 (d, J=2.4 Hz, 1H), 3.94-4.04 (m, 2H), 2.65-2.69 (t, J=9.2 Hz, 1H), 1.24-1.79 (m, 11H); MS (ESI): m/z 424.1 [M+1]+.
