Large-scale synthesis of "Cpep" RNA monomers and their application in automated RNA synthesis

[Protection of 2'-hydroxyls in the chemical synthesis of oligoribonucleotides]

The review is devoted to the chemical synthesis of oligoribonucleotides and the protecting groups used. In particular the existent methods of blocking 2'-OH function in nucleotide monomers for the RNA synthesis are discussed in detail.

Synthesis of 2'-O-[2-(N-methylcarbamoyl)ethyl]ribonucleosides using oxa-Michael reaction and chemical and biological properties of oligonucleotide derivatives incorporating these modified ribonucleosides

To develop oligonucleotides containing new 2'-O-modified ribonucleosides as nucleic acid drugs, we synthesized three types of ribonucleoside derivatives modified at the 2'-hydroxyl group with 2-(methoxycarbonyl)ethyl (MOCE), 2-(N-methylcarbamoyl)ethyl (MCE), and 2-(N,N-dimethylcarbamoyl)ethyl (DMCE) groups, as key intermediates, via the oxa-Michael reaction of the appropriately protected ribonucleoside (U, C, A, and G) derivatives. Among them, the 2'-O-MCE ribonucleosides were found to be the most stable under basic conditions. To study the effects of the 2'-O-modification on the nuclease resistance of oligonucleotides incorporating the 2'-O-modified ribonucleosides and their hybridization affinities for the complementary RNA and DNA strands, 2'-O-MCE-ribonucleoside phosphoramidite derivatives were successfully synthesized and subjected to the synthesis of 2'-O-MCE-oligonucleotides and 2'-O-methyl-oligonucleotides incorporating 2'-O-MCE-ribonucleosides. The 2'-O-MCE-oligonucleotides and chimeric oligomers with 2'-O-MCE and 2'-O-methyl groups thus obtained demonstrated complementary RNA strands and much higher nuclease resistances than the corresponding 2'-O-methylated species. Finally, we incorporated the 2'-O-MCE-ribonucleosides into antisense 2'-O-methyl-oligoribonucleotides to examine their exon-skipping activities in splicing reactions related to pre-mRNA of mouse dystrophin. The exon-skipping assay of these 2'-O-methyl-oligonucleotide incorporating 2'-O-MCE-uridines showed better efficacies than the corresponding 2'-O-methylated oligoribonucleotide phosphorothioate derivatives.

Recent advances in the chemical synthesis of RNA

As a consequence largely of recent developments in RNA interference (RNAi) research, the availability of rapid and efficient methods for the chemical synthesis of RNA sequences has become a matter of considerable urgency. This unit is concerned mainly with work that has been carried out, especially in the past decade, on the design of new and improved methods of RNA synthesis. The main criteria for the choice of protecting groups for the 2'-hydroxy functions of the ribonucleoside building blocks, which is arguably the most crucial strategic decision to be made, are discussed. A number of new ether-, acetal-, orthoester-, and ester-based 2'-protecting groups are described and their application, mainly in phosphoramidite-based solid-phase synthesis, is discussed in some detail. Brief consideration is also given to solution-phase RNA synthesis, which may well prove to be of great importance if a systemic drug is developed and multikilogram quantities of synthetic RNA sequences are required.