Published on Sept. 29, 1988 in Tetrahedron Letters volume Volume 30, Issue 1, 1989.
The use of phenoxyacetyl group for the protection of the exocyclic amino function of purine bases and acetyl group for cytosine in oligonucleotide synthesis by the cyanoethylphosphoramidite approach is described. A side reaction - i.e. partial replacement of phenoxyacetyl group of protected guanines by acetyl group - was observed during the capping step. It can be avoided by the use of phenoxyacetic anhydride in place of acetic anhydride.