Nucleoside phosphoramidites are derivatives of natural or synthetic nucleosides. They are used to synthesizeoligonucleotides, relatively short fragments of nucleic acidand their analogs. Nucleoside phosphoramidites were first introduced in 1981 by Beaucage and Caruthers.[1] To avoid undesired side reactions, reactive hydroxy and exocyclic amino groups present in natural or synthetic nucleosides are appropriately protected. As long as a nucleoside analog contains at least one hydroxy group, the use of the appropriate protecting strategy allows one to convert that to the respective phosphoramidite and to incorporate the latter into synthetic nucleic acids. To be incorporated in the middle of an oligonucleotide chain using phosphoramidite strategy, the nucleoside analog must possess two hydroxy groups or, less often, a hydroxy group and another nucleophilic group (amino or mercapto). Examples include, but are not limited to, alternative nucleotides, LNA, morpholino, nucleosides modified at the 2'-position (OMe, protected NH2, F), nucleosides containing non-canonical bases (hypoxanthine and xanthine contained in natural nucleosides inosine and xanthosine, respectively, tricyclic bases such as G-clamp,[2] etc.) or bases derivatized with a fluorescent group or a linker arm.
https://en.wikipedia.org/wiki/Nucleoside_phosphoramidite
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