To a solution of (R)-8-cyclopentyl-7-ethyl-2-(2-hydroxypyridin-4-yl)-5-methyl-7,8-dihydropteridin-6(5H)-one (Example 14, 200 mg, 0.6 mmol) in 5 mL of 1,4-dioxane, DBU (26 mg, 3 mmol) and PO(OMe)3 (42 mg, 3 mmol) were added, and the mixture was heated to reflux for 18 h, then concentrated under reduced pressure, and extracted with EtOAc. The combined organic phase was dried with Na2SO4, concentrated under reduced pressure and the residue was chromatographed (PE:EA=1:1) to give the title compound as a yellow solid (100 mg, 50% yield). 1H NMR (CDCl3) δ: 7.95 (s, 1H), 7.53 (s, 1H) 7.35 (d, 1H), 7.11 (m, 1H), 4.54 (m, 1H), 4.29 (m, 1H), 3.6 (s, 3H), 3.38 (s, 3H), 2.2-1.6 (m, 10H) and 0.87 ppm (t, 3H); LCMS: 368.2 m/z (M+H)+; ret. Time: 1.53 min (Analytical Method E).
