Process for the deprotection of oligonucleotides

A method for purifying oligonucleotides comprising removing an acid labile 5′hydroxy protecting group at the 5′-O-oligonucleotide terminus of the oligonucleotide by way of an on-column de-protection with acetic acid, comprising the steps:

• a. passing a buffer solution comprising a phosphate salt and a polar aprotic solvent to an anion-exchange column as a first equilibration step;
• b. charging a diluted aqueous ammonia solution of a crude oligonucleotide onto the column;
• c. passing a buffer solution comprising a phosphate salt and a polar aprotic solvent to the column as a second equilibration step;
• d. washing the column with a buffer solution comprising a phosphate salt, a polar aprotic solvent and an alkali halide;
• e. passing a buffer solution comprising a phosphate salt and a polar aprotic solvent to the column as a third equilibration step;
• f. passing an acid solution to the column to remove an acid labile 5′hydroxy protecting group at the 5′-O-oligonucleotide terminus of the oligonucleotide;
• g. passing a buffer solution comprising a phosphate salt and a polar aprotic solvent to the column as a fourth equilibration step;
• h. eluting the de-protected oligonucleotide with a buffer solution comprising a phosphate salt, a polar aprotic solvent and an alkali halide.