Synthesis of oligodeoxyribo- and oligoribonucleotides according to the H-phosphonate method

Oligonucleotides can be synthesized by condensing a protected nucleoside H-phosphonate monoester with a second nucleoside in the presence of a coupling agent to produce a dinucleoside H-phosphonate diester. This can then be converted to a dinucleoside phosphate or to a backbone-modified analog such as a phosphorothioate or phosphoramidite. This unit discusses four alternative methods for synthesizing nucleoside H-phosphonate monoesters. The methods are efficient and experimentally simple, and use readily available reagents. The unit describes the activation of the monoesters, as well as competing acylation and other potential side reactions.