Résumé
The non natural oligoribonucleotide α-[r(UCUUAACCC-ACA)] consisting exclusively of α-anomeric ribonucleoside units was synthesized according to the phosphoramidite methodology and the solid support technology. For this purpose, the base-protected α-rlbonucleosides were synthesized and converted into their O-methylphosphoramidites. Assembling was carried out on a DNA synthesizer with an average efficiency of 97% per step. Base composition of this nuclease-resistant α-RNA strand was ascertained after chemical and enzymatic hydrolysis and HPLC analysis of the hydrolysate. Whereas no spectroscopic evidence of base pairing was found above 0°C between α-[r(UCUUAACCCACA)] and ,β-[d(TGTGGGTTAAGA)], a clear UV absorbance transition (Tm 25.5°C) was observed during the hybridization of the same α-RNA strand with β-[d(AGAATTGGGTGT)]. In this latter case, the mixing curve titration suggests formation at low temperature of a triplex involving two α-RNA and one β-DNA strands. Moreover, this α-decaribonucleotide complementary in parallel orientation of the splice receptor of HIV-1 tat mRNA was found to inhibit (10 µW