To a solution of 4 (0.5 g, 1.5 mmol) and FeSO4‚7H2O (3.4 g, 12 mmol) in 80 mL of 1 N H2SO4 was added an aqueous solution (50 mL) containing 1.3 mL of 70% tert-butyl hydroperoxide (9.5 mmol) dropwise over a period of 5 min. After being stirred at 0 °C for 60 min, the reaction mixture was neutralized with saturated KOH solution. The supernatant obtained by centrifugation resulting in a brownish solid was triturated three times with 100 mL of methanol. The combined methanol solution was concentrated, and the residue was subjected to silica gel column chromatography. Elution with CH2Cl2/methanol (9:1) afforded 8-meth- yl-N-isobutyryl-2′-deoxycarbaguanosine (5) as a white powder, yield