| 1. |
- Zhou, Chuanzheng, et al.
(författare)
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Fine Tuning of Electrostatics Around the Internucleotidic Phosphate through Incorporations of Functionalized 2', 4'-Carbocyclic-LNAs and –ENAs Lead to Significant Modulation of Antisense Properties
- 2009
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 74:1, s. 118-134
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Tidskriftsartikel (refereegranskat)abstract
- In the antisense (AS) and RNA interference (RNAi) technologies, the native single-stranded 2'-deoxyoligonucleotides (for AS) or double-stranded RNA (for RNAi) are chemically modified to bind to the target RNA in order to give improved downregulation of gene expression through inhibition of RNA translation. It is shown here how the fine adjustment of the electrostatic interaction by alteration of the substituents as well as their stereochemical environment around the intemucleotidic phosphodiester moiety near the edge of the minor grove of the antisense oligonucleotides (AON)-RNA heteroduplex can lead to the modulation of the antisense properties. This was demonstrated through the synthesis of various modified carbocyclic-locked nucleic acids (LNAs) and -ethylene-bridged nucleic acids (ENAs) with hydroxyl and/or methyl substituents attached at the carbocyclic pan and their integration into AONs by solid-phase DNA synthesis. The target affinity toward the complementary RNA and DNA, nuclease resistance, and RNase H elicitation by these modified AONs showed that both the nature of the modification (-OH versus -CH3) and their respective stereochemical orientations vis-a-vis vicinal phosphate play a very important role in modulating the AON properties. Whereas the affinity to the target RNA and the enzymatic stability of AONs were not favored by the hydrophobic and sterically bulky modifications in the center of the minor groove, their positioning at the edge of the minor groove near the phosphate linkage resulted in significantly improved nuclease resisitance without of target affinity. On the other hand, hydrophilic modification, such as a hydroxyl group, close to the phosphate linkage made the internucleotidic phosphodiester especially nucleolytically unstable, and hence was not recommended. The substitutions on the carbocyclic moiety of the carba-LNA and -ENA did not affect significantly the choice of the cleavage sites of RNase H mediated RNA cleavage in the AON/RNA hybrid duplex, but the cleavage rate depended on the modification site in the AON sequence. If the original preferred cleavage site by RNase H was included in the 4-5nt stretch from the 3'-end of the modification site in the AON, decreassed cleavage rate was observed. Upon screening of 52 modified AONs, containing 13 differently modified derivatives at C6' and C7' (or CS') of the carba-LNAs and -ENAs, two excellent modifications in the carba-LNA series were identified, which synergistically gave outstanding antisense properties such as the target RNA affinity, nuclease resistance, and RNase H activity and were deemed to be ideal candidates as potential antisense or siRNA therapeutic agents.
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| 2. |
- Zhou, Chuanzheng, et al.
(författare)
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Synthesis and Structure of New Methylene-bridged hexopyranosyl nucleoside (BHNA)
- 2009
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Ingår i: Heterocycles. - 0385-5414 .- 1881-0942. ; 78:7, s. 1715-1728
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Tidskriftsartikel (refereegranskat)abstract
- A new member of hexopyranosyl nucleoside family, methylene-bridged hexopyranosyl nucleoside (BHNA), has been synthesized through generation of carbon radical at C6' in [6'S-Me, 7'S-Me]-carba-LNA T nucleoside, followed by rearrangement to C4' radical which was quenched by hydrogen atom to give BHNA. The stereoelectronic requirement for this unusual radical rearrangement has been elucidated by chemical model building and ab intio calculations to show that the coplanarity of the single electron occupied p-orbital at C6' with sigma*(O4'-C4') plays an important role for the rearrangement reaction to take place. The solution structure of BHNA has also been studied using NMR as well as by ab initio calculations. The new six-membered pyranosyl ring in BHNA, unlike other known hexopyranosyl nucleosides, adopts a twist conformation, with base moiety occupying the axial position while 3'-hydroxymethyl and 4'-hydroxyl occupying the equatorial position.
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