A mixture of commercially available 8-(2-methoxyphenyl)-1-methyl-7-phenyl-1H-imidazo[2,1-f]purine-2,4(3H,8H)-dione (5, 100 mg, 0.258 mmol) in acetic acid (0.387 mL) and formalin (36%, 1.1 mL) was refluxed for 15 h. The solution was then was cooled to room temperature and neutralized with sat. Na2CO3, and the resulting precipitate was filtered off. Cristallization in methanol afforded the desired product as a white solid (6 mg, 5% yield). 1H NMR (500 MHz, DMSO-d6): δ=11.27 (s, 1H), 7.49 (d, J=7.8 Hz, 1H), 7.45 (t, J=7.8 Hz, 1H), 7.32-7.37 (m, 3H), 7.23-7.24 (m, 2H), 7.12 (d, J=7.8 Hz, 1H), 7.05 (t, J=7.8 Hz, 1H), 5.90-5.93 (m, 1H), 4.69-4.72 (m, 2H), 3.55 (s, 3H), 3.32 (s, 3H); 13C NMR (125 MHz, DMSO-d6): δ=154.7, 154.5, 153.6, 150.6, 147.1, 131.1, 129.7, 129.4, 129.2, 128.7, 128.2, 127.0, 122.1, 120.7, 119.4, 112.7, 99.4, 55.5, 52.9, 28.9; IR (film): ν=3134, 2995, 2806, 1668, 1496, 1024, 749, 596 cm−1; HRMS (ESI): m/z: calcd for C22H19N5O4Na+: 440, 1335, found: 440, 1336.
