To a solution of 2-amino-9-(2,3,5-tri-O-benzyl-β-D-arabinofuranosyl)adenine (14.5 g, 26.2 mmol) in a mixture of 500 ml tetrahydrofuran and 1 l. of 48% fluoboric acid at -15° in a 4-l. beaker equipped with a mechanical stirrer was added dropwise in 20 min a saturated aqueous solution of NaNO2 (7.2 g, 105 mmol). The addition of NaNO2 (5.4 g, 78.6 mmol) was repeated three times after which none of the 2-aminoadenine remained (TLC). The fluoroboric acid was neutralized with 50% NaOH keeping the temperature between -40 and 0°. The solution was extracted four times with CHCl3 (300 ml, 250 ml, and two 200-ml portions). The CHCl3 extract was washed with saturated NaCl solution and then dried over MgSO4 before it was evaporated to dryness in vacuo. The residual oil was dissolved in a liter of ethanolic NH3 (saturated at 0° ), and the solution was allowed to stand for three days at 0° before it was evaporated to dryness. The residue was recrystallized from 100 ml EtOH; yield 4.7 g. Additional material was recovered from the filtrate by recrystallization and preparative TLC. The total yield was 5.8 g (40%).
