One aspect of the present invention relates to a double-stranded
oligonucleotide comprising at least one ligand tethered to an altered or non-natural
nucleobase. In certain embodiments, the non-natural
nucleobase is difluorotolyl, nitropyrrolyl, or nitroimidazolyl. In certain embodiments, the ligand is a
steroid or aromatic compound. In certain embodiments, only one of the two
oligonucleotide strands comprising the double-stranded
oligonucleotide contains a ligand tethered to an altered or non-natural
nucleobase. In certain embodiments, both of the oligonucleotide strands comprising the double-stranded oligonucleotide independently contain a ligand tethered to an altered or non-natural nucleobase. In certain embodiments, the oligonucleotide strands comprise at least one modified
sugar moiety. Another aspect of the present invention relates to a single-stranded oligonucleotide comprising at least one ligand tethered to an altered or non-natural nucleobase. In certain embodiments, the non-natural nucleobase is difluorotolyl, nitropyrrolyl, or nitroimidazolyl. In certain embodiments, the ligand is a
steroid or aromatic compound. In certain embodiments, the
ribose sugar moiety that occurs naturally in nucleosides is replaced with a
hexose sugar, polycyclic heteroalkyl ring, or cyclohexenyl group. In certain embodiments, at least one
phosphate linkage in the oligonucleotide has been replaced with a phosphorothioate linkage.