Abstract: The purpose of the present invention is to provide a stable composition comprising a nucleic acid oligomer having a phosphorothioate bond, and a process for preparing the same composition, and a process for preparing the nucleic acid oligomer efficiently from the composition. The present invention provides a composition comprising a nucleic acid oligomer having a phosphorothioate bond represented by formula (1) (wherein the symbols are defined in the specification), an alkylammonium salt, a water-soluble organic solvent, water, and an additive including at least one compound described in the specification. The present invention provides also a modified nucleic acid oligomer.

Abstract: The purpose of the present invention is to provide a stable composition comprising a nucleic acid oligomer having a phosphorothioate bond, and a process for preparing the same composition, and a process for preparing the nucleic acid oligomer efficiently from the composition. The present invention provides a composition comprising a nucleic acid oligomer having a phosphorothioate bond represented by formula (1) (wherein the symbols are defined in the specification), an alkylammonium salt, a water-soluble organic solvent, water, and an additive including at least one compound described in the specification.

Abstract: An object of the present invention is to provide a method for stabilizing a nucleic acid oligomer solution having a phosphorothioate bond, and a method for producing a purified nucleic acid oligomer. The present invention provides a method for stabilizing a nucleic acid oligomer, wherein an atmosphere in contact with an eluted fraction obtained by subjecting a crude nucleic acid oligomer containing a nucleic acid oligomer represented by Formula (1) (wherein symbols are as described in the specification) to a reverse-phase column chromatography treatment is set to an inert gas atmosphere having an oxygen concentration of 10% or less, and a method for producing a purified nucleic acid oligomer from the eluted fraction.