Oligonucleotides bearing a terminal lipophilic group attached through a biodegradable ester bond should be useful as antisense pro-drugs with improved cellular uptake. The synthesis of 5'-ester oligonucleotides is, however, problematic due to lability of the ester bond during aqueous ammonia treatment that is commonly used for the deprotection of synthetic oligonucleotides. The synthesis of 5'-palmitoyl oligodeoxynucleotides was accomplished in good yield by the use of a combination of base-labile tert-butylphenoxyacetyl amino protecting groups (t-BPA), the oxalyl-CPG anchor group, and ethanolamine (EA) as a deprotecting reagent.