Methanol (25 mL) and aqueous 2M sodium hydroxide solution (25.4 mmol, 12.7 mL, 10 equiv) were added to 8-methyl-6-(methyloxy)-4-[4-(2-oxo-2,3-dihydro-1H-benzimidazol-1-yl)piperidin-1-yl]pteridin-7(8H)-one (1.00 g, 2.54 mmol, 1 equiv) in a 100 mL single-necked round bottomed flask fitted with a Teflon stirrer. The resulting stirred slurry was then heated to 80° C. and the reaction was monitored by LC/MS. The reaction mixture gradually became clear and homogenous. LC/MS indicated that the reaction was complete after 12 hours. The new product peak was characterized by a 394 (MH+) molecular ion and a 350 (MH+−44 (—CO2) decarboxylation fragmentation peak. The reaction mixture was then allowed to cool to room temperature. The stirred reaction mixture was then acidified to pH 2 by the gradual addition of aqueous 3M hydrochloric acid, resulting in the precipitation of a white solid. The resulting slurry was then stirred for 30 minutes and then filtered off. The solid was washed with cold water (2×10 mL) and dried at reduced pressure to give 5.89 g (82% yield) of the title compound as a white solid. 1H NMR (400 MHz, DMSO-d6): δ 10.89 (broad s, 1H), 8.33 (s, 1H), 7.17 (dd, 1H), 6.91 (m, 3H), 5.40 (v broad s, 2H), 4.56 (t, 1H), 3.22 (broad s, 2H), 2.33 (d, 2H), 1.85 (d, 2H). MS (EI) for C18H17N7O3: 394 (MH+), 350 (MH+−44 (—CO2).
