Synthesis and characterization of oligonucleotides containing 2 '-deoxyxanthosine using phosphoramidite chemistry

Oligodeoxynucleotides containing 2'-deoxyxanthosine (X-d) were synthesized in good yield from a O-2,O-6-bis[2-(4-nitrophenyl)ethyl](NPE)-protected pho sphoramidite of X-d. Attempts to synthesize a O-6-monoNPE-protected phospho ramidite resulted in formation of a major by-product. The NPE protecting gr oups were removed by treatment with oximate ion after other protecting grou ps were removed with aqueous NH,OH solution. The composition of the synthet ic oligonucleotides was verified by enzymatic degradation and MALDI-TOF mas s spectrometry. The efficacy of this procedure allowed isolation of oligode oxynucleotides containing multiple X-d residues.