To a mixture of tert-butyl 3-(6-amino-8-oxo-7H-purin-9(8H)-yl)phenyl(methyl)carbamate (24) (600 mg, 1.68 mmol) and 4 A MS (800 mg) in dry DMF (10 mL) were added 4-phenoxyphenylboronic acid (1.08 g, 5.06 mmol), Cu(OAc)2 (307 mg, 1.68 mmol) and pyridine (1 mL). The reaction mixture was heated to 37° C. overnight under O2 atmosphere, and filtered through a Celite pad. The filtrate was diluted with water (30 mL), extracted with EtOAc (10 mL×3). The combined organic layer was washed with water and brine, dried over Na2SO4, and concentrated. The residue was purified by column chromatography (silica gel, 0 to 5% methanol in methylene chloride) to give tert-butyl 3-(6-amino-8-oxo-7-(4-phenoxyphenyl)-7H-purin-9(8H)-yl)phenyl(methyl)carbamate as a light yellow solid (31) (450 mg, 51%). LC-MS (ESI): m/z (M+1) 525.
