An efficient synthesis of enantiomeric ribonucleic acids from D-glucose

Enantiomeric oligoribonucleotides (ent-RNA) up to a sequence length of 35, consisting of the (L-configurated) nucleosides ent-adenosine, ent-guanosine, ent-cytidine, ent-uridine, and 1-(b-L-ribofuranosyl)thymine were prepd. by automated synthesis from appropriate building blocks, carrying a known photo-labile 2'-O-protecting group. A simple large-scale synthesis of 1,2,3-tri-O-benzoyl-5-O-(triisopropylsilyl)-L-ribose from L-glucose and its straightforward conversion into phosphoramidites and solid supports, resp., were elaborated. Within this project, a novel, superior strategy for the synthesis of 2'-O-{[(2-nitrobenzyl)oxy]methyl} nucleosides as key intermediates by regioselective alkylation of their 5'-O-dimethoxytritylated precursors was developed. Furthermore, an improved set-up for the final light-induced cleavage of the 2'-O-protecting groups from the oligonucleotide sequences was designed. The correct compn. of all ent-oligoribonucleotides prepd. was established by their MALDI-TOF mass spectra. The 1H NMR of a dodecameric ent-RNA sequence was in excellent agreement with the published data of its natural counterpart, synthesized by conventional methods. The known specific cleavage of a tetradecamer sequence by a 35mer ribozyme structure could be reproduced by ent-oligoribonucleotides, synthesized by the presented methods. [on SciFinder (R)]

3'-Deoxyribopyranose (4' -> 2')-oligonucleotide duplexes (=p-DNA duplexes) as substitutes of RNA hairpin structures

Damian Ackermann

By automated synthesis, we prepd. hybrid oligonucleotides consisting of covalently linked RNA and p-DNA sequences (p-DNA = 3'-deoxyribopyranose (4'->2')-oligonucleotides). The pairing properties of corresponding hybrid duplexes formed from fully complementary single strands were investigated. An uninterrupted p-p-stacking at the p-DNA/RNA interface and cooperative pairing between the two systems was achieved by connecting them via a 4'-p-DNA-2'->5'-RNA-3' and 5'-RNA-2'->4'-p-DNA-2' phosphodiester linkage, resp. The RNA 2'-phosphoramidites required for the formation of the RNA-2'->4'-p-DNA phosphodiester linkage were synthesized from the corresponding, 3'-O-tom-protected ribonucleosides (tom = [(triisopropylsilyl)oxy]methyl). Analogs of the FMN binding aptamer and the hammerhead ribozyme were prepd. Each of these analogs consisted of two p-DNA/RNA hybrid single strands with complementary p-DNA sequences, designed to substitute stem/loop and stem motifs within the parent compds. By comparative binding and cleavage studies, it was found that mixing of the two complementary p-DNA/RNA hybrid sequences resulted in the formation of the fully functional analogs of the FMN-binding aptamer and of the hammerhead ribozyme, resp. [on SciFinder (R)]

2002

Synthesis of 2'-O-[(triisopropylsilyl)oxy]methyl(=tom)-protected ribonucleoside phosphoramidites containing various nucleobase analogs

Sébastien Porcher

The first results of a study aiming at an efficient prepn. of a large variety of 2'-O-[(triisopropylsilyl)oxy]methyl(=tom)-protected ribonucleoside phosphoramidite building blocks contg. modified nucleobases are reported. All of the here presented nucleosides have already been incorporated into RNA sequences by several other groups, employing 2'-O-tbdms- or 2'-O-tom-protected phosphoramidite building blocks (tbdms=(tert-butyl)dimethyl-silyl). We now optimized existing reactions, developed some new and shorter synthetic strategies, and sometimes introduced other nucleobase-protecting groups. The 2'-O-tom, 5'-O-(dimethoxytrityl)-protected ribonucleosides N2-acetyl-iso-cytidine, O2-(diphenyl-carbamoyl)-N6-isobutyryl-isoguanosine, N6-isobutyryl-N2-(methoxy-acetyl)purine-2,6-diamine ribonucleoside (=N8-isobutyryl-2-[(methoxyacetyl)amino]adenosine), 5-methyluridine, and 5,6-dihydro-uridine were prepd. by first introducing the nucleobase protecting groups and the dimethoxytrityl group, resp., followed by the 2'-O-tom group. The other presented 2'-O-tom, 5'-O-(dimethoxytrityl)-protected ribonucleosides inosine, 1-methyl-inosine 18, N6-iso-pent-2-enyl-adenosine, N6-methyl-adenosine, N6,N6-dimethyl-adenosine, 1-methyl-guanosine, N2-methylguanosine, N2,N2-dimethyl-guanosine, N6-(chloroacetyl)-1-methyladenosine, N6-(1S,2R)-2-[(tert-butyl)dimethyl-silyl]oxy-1-[2-(4-nitrophenyl)ethoxy]carbonylpropylamino carbonyl-adenosine (derived from L-threonine) and N4-acetyl-5-methyl-cytidine were prepd. by nucleobase transformation reactions from std., already 2'-O-tom-protected. Finally, all these nucleosides were transformed into the corresponding phosphoramidites, which are fully compatible with the assembly and deprotection conditions for std. RNA synthesis based on 2'-O-tom-protected monomeric building blocks. [on SciFinder (R)]

2005

Synthesis of modified nucleosides for the incorporation into tRNAs

Sébastien Porcher

More than 100 modified nucleosides have been found in naturally occurring RNA sequences. These modifications are involved in the correct folding, in the maintenance of the reading frame during translation and in the proper interaction with enzymes and protein complexes. For an exhaustive study of their function it would be necessary to incorporate by chemical synthesis such modifications at selected positions of RNA sequences. Here we present optimized protocols for the preparation of a large variety of 2'-O-TOM protected ribonucleoside phosphoramidite building blocks containing the most frequently encountered modified nucleobases m2G, m22G, m1A, m5U, D, m5C, ψ, m1I, i6A, m62A, m6A, m1G, t6A, I and imG. In addition, the non-natural ribonucleoside phosphoramidites containing isoG, isoC and 4-desmethyl-5-methylwyosine have been prepared (Chapters I, II and III). For the introduction of base-labile modifications into RNA sequences, modified deprotection conditions in combination with the new N2-methoxyacetyl protected guanosine phosphoramidite have been developed (Chapter V). For the first time, the sensitive modified nucleoside wyosine was incorporated into a 18mer RNA sequence and into the anticodon loop of a truncated tRNA. For this purpose, enzymatic ligation strategies, based on T4 RNA and T4 DNA ligase, were evaluated and optimized (Chapters III and V). The decoding properties of modified anticodons have been reviewed and new models, based on the formation of secondary hydrogen bonds have been proposed (Chapter IV). For the efficient preparation of tRNA analogues esterified with unnatural amino acids, a synthesis of modified RNA sequences containing a 3'-terminal 2'-deoxy-2'-thioadenosine was developed. In analogy to the "native chemical ligation" of oligopeptides, its spontaneous and site-specific aminoacylation with weakly activated amino acid thioesters occurred efficiently in buffered aqueous solutions and under a wide range of conditions. This concept could be employed for a straightforward aminoacylation of analogously modified tRNAs (Chapter VI).

EPFL2006

Synthesis of modified nucleosides for the incorporation into tRNAs

Sébastien Porcher

EPFL2006