3-(N-tert-butylcarboxamido)-1-propyl and 4-oxopentyl groups for phosphate/thiophosphate protection in oligodeoxyribonucleotide synthesis.

This unit provides procedures for the preparation of deoxyribonucleoside phosphoramidites and appropriate phosphordiamidite precursors with P(III) protecting groups different than the standard 2-cyanoethyl group. Specifically, these phosphoramidites are functionalized with the 3-(N-tert-butylcarboxamido)-1-propyl or 4-oxopentyl groups. The usefulness of these novel deoxyribonucleoside phosphoramidites in the solid-phase synthesis of a 20-mer DNA oligonucleotide and its phosphorothioated analog is demonstrated. It is also shown that removal of the 3-(N-tert-butylcarboxamido)-1-propyl phosphate/thiophosphate-protecting group from these oligonucleotides is rapidly effected under thermolytic conditions at neutral pH, whereas the 4-oxopentyl group is preferably removed by treatment with pressurized ammonia gas or concentrated ammonium hydroxide at ambient temperature. These detailed methods constitute an economical and alkylation-free approach to large-scale preparations of therapeutic oligonucleotides.