A series of six double-functionalised nucleosides, in which aromatic moieties were inserted into the 5'-(S)-C-position, were synthesised and incorporated into DNA duplexes. The aromatic moieties were thymine-1-yl, phenyl, 1,2,3-triazol-1-yl, 1,2,3-triazol-4-yl, 4-(uracil-5-yl)-1,2,3-triazol-1-yl and 4-phenyl-1,2,3-triazol-1-yl. The DNA duplexes were studied with UV melting curves, CD spectroscopy and molecular modelling. The results showed that the aromatic moieties in some cases interact in the minor groove forming DNA zipper structures. The strongest specific interaction was found between two thymines or between a thymine and a phenyl group in a crossed (-3)-zipper motif (i.e., with two base pairs interspacing the modifications). Modelling revealed that the interaction is aromatic stacking across the minor groove. Also, the extended uracil-triazole moiety demonstrated zipper contacts in the minor groove as well as binding to the floor of the groove.

Herein we describe fluorescent oligonucleotides prepared by click chemistry between novel alkyne-modified locked nucleic acid (LNA) strands and a series of fluorescent azides for homogeneous (all-in-solution) detection of nucleic acids and autoimmune antibodies.

Four double-headed nucleosides were prepared by the CuAAC reaction. Hereby, a triazole-containing linker connects an additional thymine or adenine to the 2'-position of 2'-deoxyuridine, a thymine to the 5'-position of thymidine and a thymine to the 6'-position of an LNA-thymidine monomer. Whereas no conclusive recognition effects of the additional thymines were found when introduced in LNA or at the 5'-position, both thymine and adenine in the 2'-position were found to stabilise three-way junctions in both dsDNA and DNA : RNA contexts and to give cross-strand interactions in a DNA-duplex, when specifically introduced in a so-called (+1)-zipper motif.

Thymine intermediate 17 has been synthesized on a multigram scale (50 g, 70 mmol) from starting sugar 1 in 15 steps in an overall yield of 73%, with only 5 purification steps. The key thymine intermediate 18 was obtained from 17 in a single step in 96% yield, whereas the key 5-methylcytosine intermediate 20 was obtained from 17 in 2 steps in 58% yield. This highly efficient large scale route necessitates only 2 and 3 novel steps to obtain N2'-functionalized thymine and 5-methylcytosine amino-LNA phosphoramidites from these key intermediates, respectively.

Huntington's disease (HD) is a fatal, neurodegenerative disorder in which patients suffer from mobility, psychological and cognitive impairments. Existing therapeutics are only symptomatic and do not significantly alter the disease progression or increase life expectancy. HD is caused by expansion of the CAG trinucleotide repeat region in exon 1 of the Huntingtin gene (HTT), leading to the formation of mutant HTT transcripts (muHTT). The toxic gain-of-function of muHTT protein is a major cause of the disease. In addition, it has been suggested that the muHTT transcript contributes to the toxicity. Thus, reduction of both muHTT mRNA and protein levels would ideally be the most useful therapeutic option. We herein present a novel strategy for HD treatment using oligonucleotides (ONs) directly targeting the HTT trinucleotide repeat DNA. A partial, but significant and potentially long-term, HTT knock-down of both mRNA and protein was successfully achieved. Diminished phosphorylation of HTT gene-associated RNA-polymerase II is demonstrated, suggestive of reduced transcription downstream the ON-targeted repeat. Different backbone chemistries were found to have a strong impact on the ON efficiency. We also successfully use different delivery vehicles as well as naked uptake of the ONs, demonstrating versatility and possibly providing insights for in vivo applications.

Synthesis of three pyrene-modified nucleosides was accomplished using the CuAAC reaction. Hereby, pyrene is attached either to the 5'-position of thymidine or to the 2'-position of 2'-deoxyuridine through triazolemethylene linkers, or to the 2'-position of 2'-deoxyuridine through a more rigid triazole linker. The three nucleosides were incorporated into oligonucleotides, and these were combined in different duplexes and other secondary structures, which were analyzed by thermal stability and fluorescence studies. The three monomers were found to have different impacts on the nucleic acid complexes. Hence, pyrene attached to the 5'-position shows a tendency for intercalation into the duplex as indicated by a general decrease in fluorescence intensity followed by an increase in duplex thermal stability. Pyrene attached to the 2'-position through a rigid triazole linker also shows a tendency for intercalation but with decrease in duplex stability, whereas the pyrene attached to the 2'-position through a triazolemethylene linker is primarily situated in the minor groove as indicated by an increase in fluorescence but here in most cases leading to increase in duplex stability. All three pyrene nucleotides lead to thermal stabilization of bulged duplexes and three-way junctions. In some cases when two pyrenes were introduced into the core of these complexes, the formation or disappearance of a fluorescence excimer band can be used to indicate the hybridization process. Hereby these oligonucleotides can act as specific recognition probes.

No abstract

Sandwich assays are among the most powerful tools in molecular detection. These assays use "pairs" of affinity reagents so that the detection signal is generated only when both reagents bind simultaneously to different sites on the target molecule, enabling highly sensitive and specific measurements in complex samples. Thus, the capability to efficiently screen affinity reagent pairs at a high throughput is critical. In this work, we describe an experimental strategy for screening "aptamer pairs" at a throughput of 10 aptamer pairs per hour-which is many orders of magnitude higher than the current state of the art. The key step in our process is the conversion of solution-phase aptamers into "aptamer particles" such that we can directly measure the simultaneous binding of multiple aptamers to a target protein based on fluorescence signals and sort individual particles harboring aptamer pairs via the fluorescence-activated cell-sorter instrument. As proof of principle, we successfully isolated a high-quality DNA aptamer pair for plasminogen activator inhibitor 1 (PAI-1). Within only two rounds of screening, we discovered DNA aptamer pairs with low-nanomolar sensitivity in dilute serum and excellent specificity with minimal off-target binding even to closely related proteins such as PAI-2.