Abstract: A method for preparing a phosphorothioate RNA based on the oxazaphospholidine method, wherein cyanoethoxymethyl group is used instead of tert-butyldimethylsilyl group as a protective group of 2?-hydroxyl group of RNA.

Abstract: A 2?-modified ribonucleoside having an alkoxymethyl protective group can be imparted with a high duplex-forming ability by introducing, as a substituent, a halogen atom into the protective group moiety. A modified form of RNA having a halogen-substituted alkoxymethyl protective group exhibits a high duplex-forming ability that is comparable to the duplex-forming ability of a 2?-O-methyl modified nucleic acid.

Abstract: [Problem] To provide a 2?-modified ribonucleoside or the like which has a high duplex-forming ability. [Solution] The present invention is generally based on the finding in embodiments that a modified form of a ribonucleoside or the like having an alkoxymethyl protective group can be imparted with a high duplex-forming ability by introducing, as a substituent, a halogen atom into the protective group moiety. As explained before, a modified form of RNA having an alkoxymethyl protective group has a low duplex-forming ability. A modified form of RNA having a halogen-substituted alkoxymethyl protective group, however, exhibits a high duplex-forming ability that is comparable to the duplex-forming ability of a 2?-O-methyl modified nucleic acid.

Abstract: Chiral auxiliaries useful for efficiently producing a phosphorus atom-modified nucleic acid derivative with high stereoregularity, and compounds represented by the following the general formula (I) or the general formula (XI) for introducing the chiral auxiliaries.

Abstract: A protective group represented by the following general formula (I) (the oxygen atom attached with * represents oxygen atom of 2?-hydroxyl group of a ribonucleoside, a ribonucleotide or a derivative thereof; R1 and R2 both represent hydrogen atom, or represent a halogen atom, a C1-6 alkyl group, or a C1-6 halo-substituted alkyl group; R3 and R4 represent hydrogen atom, a halogen atom, a C1-6 alkyl group, or a C1-6 halo-substituted alkyl group; and R5 and R6 represent a halogen atom, a C1-6 halo-substituted alkyl group, cyano group, nitro group, or the like), which is stable under the reaction conditions of the nucleic acid synthetic cycles and has little steric hindrance, and can be removed under mild conditions using fluoride ions as a base.

Abstract: A protective group represented by the following general formula (I) (the oxygen atom attached with * represents oxygen atom of 2?-hydroxyl group of a ribonucleoside, a ribonucleotide or a derivative thereof; R1 and R2 both represent hydrogen atom, or represent a halogen atom, a C1-6 alkyl group, or a C1-6 halo-substituted alkyl group; R3 and R4 represent hydrogen atom, a halogen atom, a C1-6 alkyl group, or a C1-6 halo-substituted alkyl group; and R5 and R6 represent a halogen atom, a C1-6 halo-substituted alkyl group, cyano group, nitro group, or the like), which is stable under the reaction conditions of the nucleic acid synthetic cycles and has little steric hindrance, and can be removed under mild conditions using fluoride ions as a base.