A nucleic acid synthesis method at present mainly employs a solid-phase synthesis method according to a phosphoramidite method (Non Patent Literatures 1 to 3). In the phosphoramidite method, a 5′-hydroxyl group, an amino group of a base, and an amidite monomer having a protected 2′-hydroxyl group, if in RNA, are coupled with a promoter (activator) such as tetrazole compounds and imidazole compounds, and the resulting product is oxidized to form a phosphodiester bond (see the following formula):
where the protecting group represents DMTr, MMTr or the like; the protected base represents Bz-adenine, Bz-cytosine, iBu-guanine, thymine, uracil, Pac-adenine, Ac-cytosine, iPr-Pac-guanine, dmf-guanine, another protected modified base, or the like; X represents H, O-TBDMS, O-Tom, O-Cpep, an O-cyanoethyl group, O—F, or the like; and Y represents a hydrogen atom, an ethylthio group, a benzylmercapto group, or the like.
In the solid-phase synthesis method, molecules are sequentially connected to a solid component such as controlled pore glass (CPG) or a cross-linked polystyrene resin through a linker. In this method, products are readily separated and refined for every reaction, and its procedure can be easily mechanized. For this reason, the solid-phase synthesis method can synthesize a small amount and a variety of products, such as a primer used in a PCR method in a short time, which is one of strong scientific techniques supporting the current biotechniques.
The synthetic nucleic acid has been extensively used not only in basic research in molecular biology, but also in medical applications such as nucleic acid medicines using antisense techniques in an RNAi method or in applications to electronic devices in engineering.
Especially applications to medicines require continuous supply of a large amount of high-quality synthetic nucleic acid.
Unfortunately, the solid-phase synthesis method using a solid-phase column fixes the production capacity to lose scalability in the reaction, which causes new problems in steps of the production process to give significant load on persons who develop the process. In particular, synthesis of RNA needs an expensive amidite reagent as a raw material, resulting in huge cost even in a demonstration test using a few grams of the reagent. Another problem is that the reaction yield is usually lower than that in a liquid-phase method. The solid-phase synthesis method is still unsatisfactory.
Under such circumstances, the present inventors developed a nucleoside derivative (hydrophobic group-bonded nucleoside) to which a highly dispersible liquid-phase support (HDLS) enabling control of high dispersion and aggregation due to the polarity of a solvent is bonded, found that the nucleoside derivative used as a starting raw material for synthesis of oligonucleotide can significantly reduce the amount of a reagent to be added and can significantly reduce complexities in separation and recovery operations typically found in the liquid-phase synthesis, and filed a patent application (Patent Literature 1).