This compound can be obtained by two different ways: 1) The cyclization of 2,4,5,6-tetraaminopyrimidine (I) with refluxing formamide (II) gives 2-aminoadenine (III), which is acetylated by treatment with acetic anhydride in refluxing pyridine to yield 2,6-diacetamidopurine (IV). The condensation of (IV) with 2,3,5-tri-O-benzyl-1-O-p-nitrobenzoyl-D-arabinofuranose (V) by treatment with HCl in CH2Cl2 affords 2-amino-9-(2,3,5-tri-O-benzyl-beta-D-arabinofuranosyl)adenine (VI) which is fluorinated by reaction with HBF4 in THF giving 9-(2,3,5-tri-O-benzyl-beta-D-arabinofuranosyl)-2-fluoroadenine (VII). Finally this compound is debenzylated by treatment with BCl3 in CH2Cl2 or with Na in liquid NH3.
2) The condensation of 2,6-dichloropurine (VIII) with 2,3,5-tri-O-benzyl-D-arabinofuranosyl chloride (IX) by means of Hg(CN)2 in CH2Cl2 gives 9-(2,3,5-tri-O-benzyl-D-arabinofuranosyl)-2,6-dichloropurine (X), which is treated with NaN3 in refluxing ethanol - water to yield 2,6-diazido-9-(2,3,6-tri-O-benzyl-D-arabinofuranosyl)purine (XI). Finally this compound is reduced with H2 over Pd/C in ethanol to afford adenine (VI).