C5-alkynyl-functionalized α-L-LNA: synthesis, thermal denaturation experiments and enzymatic stability

Recent Advances in Nucleic Acid Targeting Probes and Supramolecular Constructs Based on Pyrene-Modified Oligonucleotides

In this review, we summarize the recent advances in the use of pyrene-modified oligonucleotides as a platform for functional nucleic acid-based constructs. Pyrene is of special interest for the development of nucleic acid-based tools due to its unique fluorescent properties (sensitivity of fluorescence to the microenvironment, ability to form excimers and exciplexes, long fluorescence lifetime, high quantum yield), ability to intercalate into the nucleic acid duplex, to act as a π-π-stacking (including anchoring) moiety, and others. These properties of pyrene have been used to construct novel sensitive fluorescent probes for the sequence-specific detection of nucleic acids and the discrimination of single nucleotide polymorphisms (SNPs), aptamer-based biosensors, agents for binding of double-stranded DNAs, and building blocks for supramolecular complexes. Special attention is paid to the influence of the design of pyrene-modified oligonucleotides on their properties, i.e., the structure-function relationships. The perspectives for the applications of pyrene-modified oligonucleotides in biomolecular studies, diagnostics, and nanotechnology are discussed.

Synthesis of 3′-azido/-amino-xylobicyclonucleosides

Lipozyme® TL IM mediated the selective deacetylation of one of the two acetoxy groups in 4-C-acetoxymethyl-5-O-acetyl-3-azido-3-deoxy-1,2-O-isopropylidene-α-d-xylofuranose, leading to the first efficient syntheses of 3′-azido/3′-amino-xylobicyclonucleosides T, U, C and A.

Oligonucleotides containing a piperazino-modified 2'-amino-LNA monomer exhibit very high duplex stability and remarkable nuclease resistance

Incorporation of a piperazino-modified 2'-amino-LNA monomer (PipLNA-T) into oligonucleotides conferred very high affinity and base-pairing selectivity towards complementary DNA and RNA strands. Furthermore, one PipLNA-T modification provided a robust nuclease resistance that safeguarded three neighbouring natural nucleosides from 3'-exonucleolytic degradation. These favourable properties render PipLNA-T a promising oligonucleotide modification for various biological applications.

Allele-Selective Inhibition of Mutant Huntingtin with 2-Thio- and C5- Triazolylphenyl-Deoxythymidine-Modified Antisense Oligonucleotides

We report the effect of introducing a single incorporation of 2-thio-deoxythymidine (2S-dT) or C5-Triazolylphenyl-deoxythymidine (5-TrPh-dT) at four positions within the gap region of RNase H gapmer antisense oligonucleotides (ASOs) for reducing wild-type and mutant huntingtin mRNA in human patient fibroblasts. We show that these modifications can modulate processing of the ASO/RNA heteroduplexes by recombinant human RNase H1 in a position-dependent manner. We also created a structural model of the catalytic domain of human RNase H bound to ASO/RNA heteroduplexes to rationalize the activity and selectivity observations in cells and in the biochemical assays. Our results highlight the ability of chemical modifications in the gap region to produce profound changes in ASO behavior.

Conjugation and Evaluation of Small Hydrophobic Molecules to Triazole-Linked siRNAs

Short interfering RNAs (siRNAs) have tremendous potential as a new class of next-generation therapeutics; however, their progress is lagging due to issues related to stability, biodistribution, and cell-membrane permeability. To overcome these issues, there is widespread interest in chemically modifying siRNAs. In this study, siRNAs that contain a triazole-backbone unit with pyrimidine-modified hydrophobic substituents were synthesized and examined for their gene-silencing activity. In our study, we generated a library of siRNAs that target both a plasmid reporter system and an endogenous gene target, bcl-2. Our results indicate that these unique modifications are well tolerated within the RNA interference pathway. In addition, a cholesterol-modified triazole-linked siRNA targeting the exogenous target firefly luciferase was capable of gene-silencing at levels greater than 80% in the absence of a carrier complex.

Synthesis, hybridization characteristics, and fluorescence properties of oligonucleotides modified with nucleobase-functionalized locked nucleic acid adenosine and cytidine monomers

Conformationally restricted nucleotides such as locked nucleic acid (LNA) are very popular as affinity-, specificity-, and stability-enhancing modifications in oligonucleotide chemistry to produce probes for nucleic acid targeting applications in molecular biology, biotechnology, and medicinal chemistry. Considerable efforts have been devoted in recent years to optimize the biophysical properties of LNA through additional modification of the sugar skeleton. We recently introduced C5-functionalization of LNA uridines as an alternative and synthetically more straightforward approach to improve the biophysical properties of LNA. In the present work, we set out to test the generality of this concept by studying the characteristics of oligonucleotides modified with four different C5-functionalized LNA cytidine and C8-functionalized LNA adenosine monomers. The results strongly suggest that C5-functionalization of LNA pyrimidines is indeed a viable approach for improving the binding affinity, target specificity, and/or enzymatic stability of LNA-modified ONs, whereas C8-functionalization of LNA adenosines is detrimental to binding affinity and specificity. These insights will impact the future design of conformationally restricted nucleotides for nucleic acid targeting applications.

Synthesis and biophysical properties of C5-functionalized LNA (locked nucleic acid)

Oligonucleotides modified with conformationally restricted nucleotides such as locked nucleic acid (LNA) monomers are used extensively in molecular biology and medicinal chemistry to modulate gene expression at the RNA level. Major efforts have been devoted to the design of LNA derivatives that induce even higher binding affinity and specificity, greater enzymatic stability, and more desirable pharmacokinetic profiles. Most of this work has focused on modifications of LNA's oxymethylene bridge. Here, we describe an alternative approach for modulation of the properties of LNA: i.e., through functionalization of LNA nucleobases. Twelve structurally diverse C5-functionalized LNA uridine (U) phosphoramidites were synthesized and incorporated into oligodeoxyribonucleotides (ONs), which were then characterized with respect to thermal denaturation, enzymatic stability, and fluorescence properties. ONs modified with monomers that are conjugated to small alkynes display significantly improved target affinity, binding specificity, and protection against 3'-exonucleases relative to regular LNA. In contrast, ONs modified with monomers that are conjugated to bulky hydrophobic alkynes display lower target affinity yet much greater 3'-exonuclease resistance. ONs modified with C5-fluorophore-functionalized LNA-U monomers enable fluorescent discrimination of targets with single nucleotide polymorphisms (SNPs). In concert, these properties render C5-functionalized LNA as a promising class of building blocks for RNA-targeting applications and nucleic acid diagnostics.