Synthesis and electrochemical studies of an anthraquinone-conjugated nucleoside and derived oligonucleotides

An electrochemical aptasensor for Δ9-tetrahydrocannabinol detection in saliva on a microfluidic platform

We present a novel "on-off", cost-effective, rapid electrochemical aptasensor combined with a microfluidics cartridge system for the detection of Δ⁹-THC (Δ⁹-tetrahydrocannabinol) in human saliva via differential pulse voltammetry. The assay relied on the competitive binding between the Δ⁹-THC and a soluble redox indicator methylene blue, using an aptamer selected via FRELEX. We found that the aptasensor can detected 1 nM of Δ⁹-THC in PBS in a three-electrode cell system, while the sensitivity and both the dissociation constant (K_d) and association constant (K_b) were dependent on the aptamer density. The aptamer also showed great affinity towards Δ⁹-THC when tested against cannabinol and cannabidiol. The same limit of detection of 1 nM in PBS was achieved in small volume samples (∼60 μL) using the aptamer-modified gold screen-printed electrodes combined with the microfluidic cartridge setup, however, the presence of 10% raw human saliva had a negative effect which manifested in a 10-fold increase in the LOD due to interfering elements. Filtering the saliva, improved the tested volume to 50% and the LOD to 5 nM of Δ⁹-THC which is lower than the concentrations associated with impairment (6.5-32 nM). The aptasensor showed a good storage capability up to 3 days, however, the reusability significantly dropped from 10 cycles (freshly prepared) to 5 cycles. The results clearly demonstrate the feasibility of the aptasensor platform with the microfluidics chamber towards a point-of-care testing application for the detection of Δ⁹-THC in saliva.

Novel Carbazole-Based N-Heterocyclic Carbene Ligands to Access Synthetically Relevant Stilbenes in Pd-Catalyzed Coupling Processes

A series of new carbazole-based N-heterocyclic carbene (NHC) ligands have been synthesized in a simple and facile synthetic route and subsequently used in a Pd/carbazole-based NHC catalytic system, which was found to be effective in catalyzing Heck reactions to provide substituted stilbene derivatives in good yields. Several bioactive stilbenes, including pterostilbene, pinosylvin, trimethoxy resveratrol, and resveratrol, were synthesized in good yields, and a 10 mmol scale-up was also performed for trimethoxy resveratrol. The synthetic application was also extended by performing a double-tandem chemoselective Heck reaction followed by Miyaura borylation in a one-pot procedure to give single-step access to synthetically useful stilbenyl boronate esters. Similarly, a unique triple-tandem protocol of a chemoselective Heck reaction/Miyaura borylation/Suzuki-Miyaura coupling reaction sequence was performed for the one-pot modification of biologically relevant molecules.

Electrochemical monitoring of ROS generation by anticancer agents: the case of chartreusin

Generation of ROS by anticancer agents is monitored using solid state electrochemical techniques.

Impedimetric monitoring of apoptosis using cytochrome-aptamer bioconjugated silver nanocluster

It is well known that cytochrome c (Cyt c) is a crucial death regulator that triggers programmed cell death, apoptosis. Here, we report on the successful application of an aptamer bioconjugated nanoclusters for the detection of apoptosis based on release of cytochrome c from mitochondria in lysates human embryonic kidney cells HEK293T. The aptamer-conjugated silver nanoclusters (Apt@AgNCs) were synthesized and immobilized on gold electrode for impedimetric detection of Cyt c over the range of 0.15-375nM. It was found that the presence of Ag(I) ions shell at the surface of prepared NCs could increase their affinity to the donor groups (COO^- and some amine groups in its deprotonated form, NH₂) of cysteine attached on the gold electrode surface. The use of NCs, which play the role of conductive holders, established a simple immobilization procedure based on a low cost non-functionalized DNA sequence. To diminish the probable nonspecific impedance changes and decrease time of measurement, a rapid single frequency measurements (SFM) was assessed based on recording total impedance |Z| in different individual frequencies.

Novel water-soluble phosphatriazenes: versatile ligands for Suzuki–Miyaura, Sonogashira and Heck reactions of nucleosides

Two new water-soluble phosphatriazene as versatile ligands for catalyzing Suzuki–Miyaura reactions of purines and pyrimidines in neat water with the possibility of recycling. Copper-free Sonogashira and Heck reaction were also made possible.

Palladium-catalyzed modification of unprotected nucleosides, nucleotides, and oligonucleotides

Synthetic modification of nucleoside structures provides access to molecules of interest as pharmaceuticals, biochemical probes, and models to study diseases. Covalent modification of the purine and pyrimidine bases is an important strategy for the synthesis of these adducts. Palladium-catalyzed cross-coupling is a powerful method to attach groups to the base heterocycles through the formation of new carbon-carbon and carbon-heteroatom bonds. In this review, approaches to palladium-catalyzed modification of unprotected nucleosides, nucleotides, and oligonucleotides are reviewed. Polar reaction media, such as water or polar aprotic solvents, allow reactions to be performed directly on the hydrophilic nucleosides and nucleotides without the need to use protecting groups. Homogeneous aqueous-phase coupling reactions catalyzed by palladium complexes of water-soluble ligands provide a general approach to the synthesis of modified nucleosides, nucleotides, and oligonucleotides.

High-affinity RNA targeting by oligonucleotides displaying aromatic stacking and amino groups in the major groove. Comparison of triazoles and phenyl substituents

Three 5-modified 2'-deoxyuridine nucleosides were synthesized and incorporated into oligonucleotides and compared with the previously published 5-(1-phenyl-1,2,3-triazol-4-yl)-2'-deoxyuridine monomer W. The introduction of an aminomethyl group on the phenyl group led to monomer X, which was found to thermally stabilize a 9-mer DNA:RNA duplex, presumably through the partial neutralization of the negative charge of the backbone. By also taking advantage of the stacking interactions in the major groove of two or more of the monomer X, an extremely high thermal stability was obtained. A regioisomer of the phenyltriazole substituent, that is the 5-(4-phenyl-1,2,3-triazol-1-yl)-2'-deoxyuridine monomer Y, was found to destabilize the DNA:RNA duplex significantly, but stacking in the major groove compensated for this when two to four monomers were incorporated consecutively. Finally, the 5-phenyl-2'-deoxyuridine monomer Z was incorporated for comparison, and it was found to give a more neutral influence on duplex stability indicating less efficient stacking interactions. The duplexes were investigated by CD spectroscopy and MD simulations.

Palladium-catalyzed Suzuki reaction in aqueous solvents applied to unprotected nucleosides and nucleotides

Nucleoside analogues have attracted much attention due to their potential biological activities.

Efficient synthesis of unprotected C-5-aryl/heteroaryl-2'-deoxyuridine via a Suzuki-Miyaura reaction in aqueous media

Following our previous results on an environmentally benign one-pot Sonogashira-cyclization protocol to obtain substituted furopyrimidine nucleosides under aqueous conditions, we investigate herein the Suzuki-Miyaura cross-coupling reactions of aryl and heteroaryl derivatives at the C5 position of unprotected 2'-deoxyuridine in the same media with a common catalyst system avoiding exotic ligands, since palladium acetate and triphenylphosphine afforded the expected products in moderate to good yields.

Anthraquinone as a redox label for DNA: synthesis, enzymatic incorporation, and electrochemistry of anthraquinone-modified nucleosides, nucleotides, and DNA

Modified 2'-deoxynucleosides and deoxynucleoside triphosphates (dNTPs) bearing anthraquinone (AQ) attached through an acetylene or propargylcarbamoyl linker at the 5-position of pyrimidine (C) or at the 7-position of 7-deazaadenine were prepared by Sonogashira cross-coupling of halogenated dNTPs with 2-ethynylanthraquinone or 2-(2-propynylcarbamoyl)anthraquinone. Polymerase incorporations of the AQ-labeled dNTPs into DNA by primer extension with KOD XL polymerase have been successfully developed. The electrochemical properties of the AQ-labeled nucleosides, nucleotides, and DNA were studied by cyclic and square-wave voltammetry, which show a distinct reversible couple of peaks around -0.4 V that make the AQ a suitable redox label for DNA.

"Off-on" electrochemical hairpin-DNA-based genosensor for cancer diagnostics

A simple and robust "off-on" signaling genosensor platform with improved selectivity for single-nucleotide polymorphism (SNP) detection based on the electronic DNA hairpin molecular beacons has been developed. The DNA beacons were immobilized onto gold electrodes in their folded states through the alkanethiol linker at the 3'-end, while the 5'-end was labeled with a methylene blue (MB) redox probe. A typical "on-off" change of the electrochemical signal was observed upon hybridization of the 27-33 nucleotide (nt) long hairpin DNA to the target DNA, in agreement with all the hitherto published data. Truncation of the DNA hairpin beacons down to 20 nts provided improved genosensor selectivity for SNP and allowed switching of the electrochemical genosensor response from the on-off to the off-on mode. Switching was consistent with the variation in the mechanism of the electron transfer reaction between the electrode and the MB redox label, for the folded beacon being characteristic of the electrochemistry of adsorbed species, while for the "open" duplex structure being formally controlled by the diffusion of the redox label within the adsorbate layer. The relative current intensities of both processes were governed by the length of the formed DNA duplex, potential scan rate, and apparent diffusion coefficient of the redox species. The off-on genosensor design used for detection of a cancer biomarker TP53 gene sequence favored discrimination between the healthy and SNP-containing DNA sequences, which was particularly pronounced at short hybridization times.