Phosphorothioate bonds
Non-bridging oxygen in phosphates can be substituted by a sulfur atom in oligonucleotides. Phosphorothioates increase oligonucleotide resistance to degradation by nucleases and improve PK/PD in vivo.
Note! Sometimes phosphorothioates might increase oligonucleotide toxicity, so accurate tox evaluation is always needed for in vitro and in vivo applications.
Available site for modification is internal.
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