A New Synthetic Method for Oligoribonucleotides by the Phosphite Triester Approach

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1. Synthesis of ribooligonucleotides using the phosphoramidite derivativesRibooligonucleotide derivatives (1), which are protected with an o-nitrobenzyl group at the 2'-hydroxyl, a methoxytrityl group at the 5'-hydroxyl and an acyl group at the base amino group, were synthesized. Methyl or cyanoethylidiisopropylamidite derivatives(2) were synthesized by phosohitylation at the 3'-hydroxyl group. On the other hand, nucleoside resin derivatives (3) were synthesized by coupling 1 with the controlled pore glass support. The oligomers were synthesized by repeated coupling of 2 with 3. When 5-(P-nitrophenyl)tetrazole is used for activation of the amidite, the coupling reaction is usually completed within one miunte.2. Synthesis of ribooligonucleotides using the H-phosphonate derivativesH-Phosphonate derivatives (4) were synthesized from 1 by treatment with PC1_3. The oligomers were synthesized by repeated coupling of 4 with 3 using pivaloyl chloride as the condensing agent. tRNA fragments with chain lengths up to 34 were synthesized by using a mucleic acid synthesizer.3. Synthesis of ribooligonucleotides in quantityA method for synthesis of the oligomers with chain lengths 10-20 by solid-phase phosphoramidite approach was established. Thus the RNA oligamers of abaout 100 absorbance units (260 nm), which can be used for NMR measurement, are easily synthesized in a short time in 10-20%yields.4. Conformational studies on the ribooligonucleotides by NMR spectroscopyOligomer complexes having a catalytic activity or partial base sequence of an RNA enzyme and oligomers with extraordinary stable hairpin structures were synthesized by the above method and their conformation was examined by NMR.