Into a solution of NaN3 (65 mg) in CHCl3 (2 ml) was added H2SO4 (0.5 ml). The resulting solution was cooled to 0° C. 8-(2-Oxo-bicyclo[2.2.1]hept-7-yl)-1,3-dipropyl-3,7-dihydro-purine-2,6-dione (173 mg) in CHCl3 (3 ml) was added. The resulting solution was stirred at room temperature for 3 hrs. The reaction mixture was poured over ice and neutralized with NaHCO3, extracted with ethyl acetate (3×25 ml). The combined extract was dried over MgSO4, filtered, and concentrated. The crude product was purified by recrystallization from MeOH. Yield 155 mg. Mass (ES+ 360).
