Sodium Hydroxide → 9-(2,3,5-Tri-O-benzyl-beta-D-arabinofuranosyl)-2-fluoroadenine

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Reaction Steps

To a solution of 9-(2,3,5-tri-O-benzyl-β-D-arabinofuranosyl)adenine (5, 15.0 g., 27.1 mmoles) in a mixture of 500 ml. tetrahydrofuran and 1 l. of 48% fluoboric acid at -10° in a 4-l. beaker equipped with a mechanical stirrer was added dropwise in 20 minutes a saturated aqueous solution of sodium nitrite (7.5 g., 108 mmoles). The addition of sodium nitrite was repeated three times after which none of the 2-aminoadenine remained (tlc). The fluorboric acid was neutralized to pH 6 with 505% sodium hydroxide keeping the temperature between -40° and 0°. The solution was extracted four times with chloroform (300 ml., 250 ml., and two 200-ml. portions). The chloroform extract was washed with saturated sodium chloride solution and then dried over magnesium sulfate before it was evaporated to dryness in vacuo. The residual oil was dissolved in a liter of ethanolic ammonia (saturated at 0°), and the solution was allowed to stand for 4 days at 4° before it was evaporated to dryness. The residue was recrystallized from ethanol; yield 5.5 g. Additional material was recovered from the filtrate by recrystallization and the final filtrate was evaporated to dryness, diluted with 50 ml. of 1 N hydrochloric acid, stirred on a steam bath for 30 minutes, cooled, and the aqueous portion decanted. A chloroform solution of the residue was washed with saturated sodium bicarbonate, then water, and dried over magnesium sulfate before evaporation in vacuo. The residue was recrystallized from ethanol; total yield of 6, 7.2 g. (48%); m.p. 155°-157°. This material was essentially homogeneous according to tlc (19:1) and hplc [2 aqueous pentanesulfonic acid (0.005 M):3 acetonitrile-3% acetic acid].

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