More versatile synthesis of oligonucleotides

Abstract

Solid-phase phosphoramidite chemistry developed by Beaucage and Caruthers (1) couples appropriately protected nucleosides as 39-phosphoramidites to the 59-hydroxy group of an immobilized growing oligonucleotide. The phosphite triester intermediate is then either oxidized or sulfurized, the 59-protection of the connected nucleotide is removed, and the coupling cycle is repeated. The superior coupling efficiency, availability of the reagents, standardized coupling protocols, and established automated instrumentation of this method have limited the use of alternative technologies (such as H-phosphonate and phosphotriester coupling chemistry) (2–4) to small-molecule synthesis and applications that require a special chemical orthogonality. On page 1265 of this issue, Huang et al. (5) report on a phosphotriester-based technology, a “P(V) platform,” that has oligonucleotide-chain elongation efficiency competitive with the phosphoramidite coupling cycle. A unified coupling condition is used for native phosphodiester, either diastereomer of phosphorothioate, and phosphorodithioate linkages.