An alternate preparation of 5'-amino-2',5'-dideoxyguanosine is to treat the protected 2'-deoxyguanosine (protected at either the N-2-phenylacetyl or the N-2-FMOC derivative) (1 mmol) with tosyl chloride (1.3 mmol) in pyridine at 0° C. overnight. The solution is evaporated to dryness and the residue is dissolved in chloroform. The resulting solution is washed twice with aqueous sodium bicarbonate and dried over sodium sulfate. The solvent is evaporated and the residue chromatographed on silica gel eluting with methanol/chloroform mixtures. The resulting tosylate (1 mmol) is treated with sodium azide (6 mmol) in DMF at 80°-100° C. for a few h. The solvent is removed by rotovap and the residue is chromatographed on silica gel eluting with chloroform/ methanol solvent mixtures. The azide is reduced to the desired amine using the catalytic hydrogenation procedure above.
