Résumé
A great renewal in the chemical synthesis of RNA has grown up since the advent of RNA interference (RNAi) with the crucial need of short RNA molecules for biological research and therapeutic applications. RNA synthesis requires a suitable protection for 2'-OH to ensure successful RNA assembly and to avoid RNA damage during the deprotection process. Of special interest is our all-base-labile strategy which provides highly pure RNA sequences efficiently and rapidly. This method consists in protecting 2'-OH with base-labile pivaloyloxymethyl (PivOM) protection compatible with standard protections for 5'-OH, phosphates and nucleobases. The main advantage of this RNA synthesis is a simple and straightforward two-step deprotection in mild basic conditions without any concomitant RNA degradation or 2'-O-migration. In this chapter this original method will be described. Besides development of innovative RNA synthesis, the chemical production of 5'-functionalized RNA with triphosphate (TP/ppp) or cap moieties is also attractive for biologists since these molecules are important substrates in many biological processes such as ligation of RNA molecules, detection of viral responses via activation of the RIG-1 protein, induction of antiviral immunity, enzymatic synthesis of 5'-capped ((7m)Gppp)-RNA, recognition signal for translation, RNA splicing, and nucleocytoplasmic exportation. To face the high demand of such molecules, we have developed a new synthetic approach on solid support using H-phosphonate intermediate for the large-scale synthesis of the 5'-triphosphate or 5'-GpppRNA where RNA assembly was performed with PivOM technology. We will report on the synthetic procedures which represent a highly efficient alternative to the methods described in the literature to date.