Abstract: Disclosed is a compound represented by formula (1) or a salt thereof: (wherein: “Base” represents an aromatic heterocyclic group which may have a substituent or an aromatic hydrocarbon ring group which may have a substituent; A1 represents a linear alkylene group; A2 represents a single bond or an alkylene group; X represents an alkylene group, —O— or —S(?O)k—; R1 and R2 are the same as or different from each other and independently represent a hydrogen atom, etc.; and R3 represents an amino group which may have a substituent).

Abstract: The invention provides a method of selectively amplifying a detection target nucleic acid by inhibiting amplification of a detection non-target nucleic acid (e.g., wild-type gene) in a test sample by using, in a nucleic acid amplification reaction, an oligonucleotide analog containing one or more kinds of one or more unit structures of various nucleoside analogs represented by the following formula (I): wherein the symbols are as defined in the DESCRIPTION, and the like, or a salt thereof, as a clamp nucleic acid, and detecting the amplified nucleic acid.

Abstract: The invention provides a method of selectively amplifying a detection target nucleic acid by inhibiting amplification of a detection non-target nucleic acid (e.g., wild-type gene) in a test sample by using, in a nucleic acid amplification reaction, an oligonucleotide analog containing one or more kinds of one or more unit structures of various nucleoside analogs represented by the following formula (I): wherein the symbols are as defined in the DESCRIPTION, and the like, or a salt thereof, as a clamp nucleic acid, and detecting the amplified nucleic acid.