Novel artificial nucleic acid, method for producing same, and use thereof

Provided is an artificial nucleic acid having a unit derived from a compound represented by formula (1) or a salt thereof: wherein Base represents an optionally substituted aromatic heterocyclic group or an optionally substituted aromatic hydrocarbon cyclic group; x1 is a hydrogen atom, an optionally substituted alkyl group, an optionally substituted alkenyl group, an optionally substituted alkynyl group, an optionally substituted cycloalkyl group, or an optionally substituted aryl group, X2 is a hydrogen atom or-OR7, R1, R2, and R7 are the same or different, and X is a hydrogen atom or-OR7. A hydrogen atom, an optionally substituted alkyl group, an optionally substituted alkenyl group, an optionally substituted alkynyl group, an optionally substituted cycloalkyl group, an optionally substituted cycloalkenyl group, an optionally substituted aryl group, a hydroxy protecting group, or a substituted phosphino group; (In formula (1), R1, R2, R3, R4, R5, and R6 may be the same or different and are each a hydrogen