5'-O-(3,4-dibenzyloxybenzyl)thymidine (I) was converted to the corresponding phosphoramidite (III) upon treatment with 2-cyanoethyl-N,N-diisopropylchlorophosphoramidite (II) in the presence of diisopropylethylamine. This was applied to an automatic DNA synthesizer and coupled to the polymer support-linked pentadeoxyribonucleotide sequence GGGAG. The resulting oligonucleotide was liberated from the solid support using aqueous ammonia, and then purified by reverse phase-HPLC in the presence of a triethylammonium acetate buffer to furnish the title compound as the triethylammonium salt.