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A protocol exploiting isocyanides as carbamoylating agents for the α‐C(sp3)‐H functionalization of cyclic ethers has been optimized via a combined visible light‐driven hydrogen atom transfer/Lewis acid‐catalyzed approach. The isocyanide substrate scope revealed an exquisite functional group compatibility (18 examples, with yields up to 99 %). Both radical and polar trapping, kinetic isotopic effect and real‐time NMR studies support the mechanistic hypothesis and provide insightful details for the design of new chemical processes involving the generation of oxocarbenium ions. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of a small series of cyclic triimidazole derivatives functionalized with methylated pyridine or guanidine moieties is reported. These compounds were tested for their ability to bind to G‐quadruplexes from both telomeric and oncogene promoter sequences. Some of them exhibited high affinity and effective G‐quadruplex‐stabilizing properties. Overall, these compounds may represent useful leads for developing more potent and selective analogues. [ABSTRACT FROM AUTHOR]

NADH:ubiquinone oxidoreductase, respiratory complex I, plays a central role in cellular energy metabolism. As a major source of reactive oxygen species (ROS) it affects ageing and mitochondrial dysfunction. The novel inhibitor NADH‐OH specifically blocks NADH oxidation and ROS production by complex I in nanomolar concentrations. Attempts to elucidate its structure by NMR spectroscopy have failed. Here, by using X‐ray crystallographic analysis, we report the structure of NADH‐OH bound in the active site of a soluble fragment of complex I at 2.0 Å resolution. We have identified key amino acid residues that are specific and essential for binding NADH‐OH. Furthermore, the structure sheds light on the specificity of NADH‐OH towards the unique Rossmann‐fold of complex I and indicates a regulatory role in mitochondrial ROS generation. In addition, NADH‐OH acts as a lead‐structure for the synthesis of a novel class of ROS suppressors. [ABSTRACT FROM AUTHOR]

The i‐motif DNA, also known as i‐DNA, is a non‐canonical DNA secondary structure formed by cytosine‐rich sequences, consisting of two intercalated parallel‐stranded duplexes held together by hemi‐protonated cytosine–cytosine+ (C:C+) base pairs. The growing interest in the i‐DNA structure as a target in anticancer therapy increases the need for tools for a rapid and meaningful interpretation of the spectroscopic data of i‐DNA samples. Herein, we analyzed the circular dichroism (CD) and thermal difference UV‐absorbance spectra (TDS) of 255 DNA sequences by means of multivariate data analysis, aiming at unveiling peculiar spectral regions that could be used as diagnostic features during the analysis of i‐DNA‐forming sequences. [ABSTRACT FROM AUTHOR]

DNA-minor-groove-binding ligands are potent antineoplastic molecules. The antibiotic distamycin A is the prototype of one class of these DNA-interfering molecules that have been largely used in vitro. The affinity of distamycin A for DNA is well known, and the structural details of the complexes with some B-DNA and G-quadruplex-forming DNA sequences have been already elucidated. Here, we show that distamycin A binds S100β, a protein involved in the regulation of several cellular processes. The reported affinity of distamycin A for the calcium(II)-loaded S100β reinforces the idea that some biological activities of the DNA-minor-groove-binding ligands arise from the binding to cellular proteins. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Triplex with a twist: Through metadynamics calculations, the thrombin binding aptamer (TBA) has been shown to adopt a stable G‐triplex structural motif, in addition to the usual G‐quadruplex (see scheme). An 11‐mer oligonucleotide was also shown to form a stable G‐triplex, whose structural and thermodynamic properties have been characterized. [ABSTRACT FROM AUTHOR]

Abstract: Alkaline incubation of NADH results in the formation of a very potent inhibitor of lactate dehydrogenase. High resolution mass spectroscopy along with NMR characterization clearly showed that the inhibitor is derived from attachment of a glycolic acid moiety to the 4-position of the dihydronicotinamide ring of NADH. The very potent inhibitor is competitive with respect to NADH. The inhibitor added in submicromolar concentrations to cardiomyocytes protects them from damage caused by hypoxia/reoxygenation stress. In isolated mouse hearts, addition of the inhibitor results in a substantial reduction of myocardial infarct size caused by global ischemia/reperfusion injury. [Copyright &y& Elsevier]

The thrombin-binding aptamer (TBA) is a consensus DNA 15-mer that binds specifically to human α-thrombin at nanomolar concentrations and inhibits its procoagulant functions. Recently, a modified TBA (mTBA) containing a 5′-5′ inversion-of-polarity site has been shown to be more stable and to possess a higher thrombin affinity than its unmodified counterpart. The structure of the thrombin-TBA complex has previously been determined at low resolution, but did not provide a detailed picture of the aptamer conformation or of the protein-DNA assembly, while that of the complex with mTBA is unknown. Crystallographic analysis of the thrombin-mTBA complex has been attempted. The crystals diffracted to 2.15 Å resolution and belonged to space group I222. [ABSTRACT FROM AUTHOR]

Locked nucleic acids (LNAs) are formed by bicyclic ribonucleotides where the O2' and C4' atoms are linked through a methylene bridge and the sugar is blocked in a 3'-endo conformation. They represent a promising tool for therapeutic and diagnostic applications and are characterized by higher thermal stability and nuclease resistance with respect to their natural counterparts. However, structural descriptions of LNA-containing quadruplexes are rather limited, since few NMR models have been reported in the literature. Here, the first crystallographically derived model of an all-LNA-substituted quadruplex-forming sequence 5'-TGGGT-3' is presented refined at 1.7 Å resolution. This high-resolution crystallographic analysis reveals a regular parallel G-quadruplex arrangement terminating in a well defined thymine tetrad at the 3'-end. The detailed picture of the hydration pattern reveals LNA-specific features in the solvent distribution. Interestingly, two closely packed quadruplexes are present in the asymmetric unit. They face one another with their 3'-ends giving rise to a compact higher-order structure. This new assembly suggests a possible way in which sequential quadruplexes can be disposed in the crowded cell environment. Furthermore, as the formation of ordered structures by molecular self-assembly is an effective strategy to obtain nanostructures, this study could open the way to the design of a new class of LNA-based building blocks for nanotechnology.

The thrombin-binding aptamer (TBA) is a consensus DNA 15-mer that binds specifically to human alpha-thrombin at nanomolar concentrations and inhibits its procoagulant functions. Recently, a modified TBA (mTBA) containing a 5'-5' inversion-of-polarity site has been shown to be more stable and to possess a higher thrombin affinity than its unmodified counterpart. The structure of the thrombin-TBA complex has previously been determined at low resolution, but did not provide a detailed picture of the aptamer conformation or of the protein-DNA assembly, while that of the complex with mTBA is unknown. Crystallographic analysis of the thrombin-mTBA complex has been attempted. The crystals diffracted to 2.15 A resolution and belonged to space group I222.