Highly lipophilic trityloxyethylamine (TEAm) or trityloxyethylaniline (TEAn) were prepared and used for the protection of the 5'-terminal phosphate. We synthesized 5'-phosphorylated oligodeoxyribonucleotides by the solid phase synthesis. TEAm or TEAn groups enabled us to isolate the desired oligonucleotide easily by the reversed phase column due to their high lipophilicity and could be removed by the aq. AcOH treatment.