| Summary: | The therapeutic efficacy of double-stranded short interfering RNAs (ds-siRNAs) is limited by the formation of the lipid complex to deliver them to cells. Whereas if effective single-stranded siRNAs (ss-siRNAs) could be developed, they would offer an easier way of delivery and they can be produced at half price. Chemical modifications to ss-siRNAs are required to improve gene-silencing efficacy in vivo and to enhance their nuclease stability. This study describes a synthetic route that can access all the possible combinations of the modified (E)-vinylphosphonate ((E)-VP) linked-dinucleotides. Additionally, it demonstrates a method to synthesise a ss-siRNA contain a single 5′-terminus (E)-vinyphosphonate (5′-(E)-VP) using the standard phosphoramidite method that does not require additional deprotection steps. The study shows that the vinylphosphonate is well tolerated in the 5′-terminus between nucleotide 1 and nucleotide 2 of the ss-siRNA, and that shown efficient in vitro and in vivo knockdown of luciferase in MDA-MB fluc cells in comparison to a negative control.
This study shows that (E)-VP linked-dinucleotides can also be incorporated in the 3′-terminus of the oligonucleotide, this can extend the study to investigate the effect of the presence of multiple vinylphosphonates on the overall stability and activity of the oligonucleotide. Furthermore, the study describes a synthetic method to synthesise dinucleotide and trinucleotide that have two and three consecutive 5′-(E)-VP but can only be used in the 5′-termius of the oligonucleotide. Finally, this thesis will suggest a synthetic route to synthesise consecutive vinylphosphonates that possibly can be used at any position of the oligonucleotide.
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