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Synthesis, Pairing, and Cellular Uptake Properties of C(6′)-Functionalized Tricyclo-DNA

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Publication date 2012
Author Lietard Jory, Leumann Christian J.,
Project Chemically modified Oligonucleotides for Biotechnology and Material Sciences
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Original article (peer-reviewed)

Journal Journal of Organic Chemistry
Volume (Issue) 77
Page(s) 4566 - 4577
Title of proceedings Journal of Organic Chemistry

Abstract

Tricyclo-DNA (tc-DNA) is a promising candidate for oligonucleotide-based therapeutic applications exhibiting increased affinity to RNA and increased resistance to nucleases. However, as many other oligonucleotide analogs, tc-DNA does not readily cross cell membranes. We wished to address this issue by preparing a prodrug of tc-DNA containing a metabolically labile group at C(6?) that promotes cellular uptake. Two monomeric nucleoside building blocks bearing an ester function at C(6?) (tcee-T and tchd-T) were synthesized starting from a known C(6?) functionalized bicyclic sugar unit to which the cyclopropane ring was introduced via carbene addition. NIS-mediated nucleosidation of the corresponding glycal with in situ persilylated thymine afforded the ?-iodonucleoside exclusively that was dehalogenated via radical reduction. Diversity in the ester function was obtained by hydrolysis and reesterification. The two nucleosides were subsequently incorporated into DNA or tc-DNA by standard phosphoramidite chemistry. The reactivity of the ester function during oligonucleotide deprotection was explored and the corresponding C(6?) amide, carboxylic acid, or unchanged ester functions were obtained, depending on the deprotection conditions. Compared to unmodified DNA, these tc-DNA derivatives increased the stability of duplexes investigated with ?Tm/mod of +0.4 to +2.0 °C. The only destabilizing residue was tchd-T, most likely due to self-aggregation of the lipophilic side chains in the single stranded oligonucleotide. A decamer containing five tchd-T residues was readily taken up by HeLa and HEK 293T cells without the use of a transfection agent.
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