Electron paramagnetic resonance (EPR) study of spin-labeled camptothecin derivatives: a different look of the ternary complex

Metal-Free Chemoselective Oxidation of 4-Methylquinolines into Quinoline-4-Carbaldehydes

A convenient protocol for the synthesis of quinoline-4-carbaldehydes via chemoselective oxidation of 4-methylquinolines using hypervalent iodine(III) reagents as oxidant is described. This method highlights metal-free and mild reaction conditions, nice yield, good functional group tolerance, and high chemoselectivity.

Gel actuators based on polymeric radicals

Low-voltage electrochemical actuation of radical polymer gels has been demonstrated in an organic electrolyte. Polymer gels were prepared by post-modification of active-ester precursor gels with an amine-functionalised radical. A combination of few-layer graphene and multiwall carbon nanotubes gave high conductivity and improved actuation in the gels, with 32% linear actuation. The actuator system showed good stability over at least 10 cycles, showing its promise. The cycle time was several hours due to mass-transport limited transport of ions and solvent into the device.

Photo-induced spin switching in a modified anthraquinone modulated by DNA binding

An anthraquinone modified with a nitroxide radical and able to intercalate into DNA has been synthesized to obtain a molecule the spin state of which can be manipulated by visible light and DNA binding. The doublet ground state of the molecule can be photo-switched to either a strongly coupled spin state (quartet + doublet), when isolated, or to an uncoupled spin state (triplet and doublet), when bound to DNA. The different spin state that is obtained upon photoexcitation depends on the intercalation of the quinonic core into double-stranded DNA which changes the conformation of the molecule, thereby altering the exchange interaction between the excited state localized on the quinonic core and the nitroxide radical. The spin state of the system has been investigated using both continuous-wave and time-resolved EPR spectroscopy.

DNA Topoisomerase 1 Structure-BASED Design, Synthesis, Activity Evaluation and Molecular Simulations Study of New 7-Amide Camptothecin Derivatives Against Spodoptera frugiperda

Camptothecin and its derivatives (CPTs) have strong toxicity to eukaryotic cells by targeting their DNA topoisomerase 1 (Top1) protein and have been increasingly explored as potential pesticides for plant protection. However, the detailed structure-binding mechanism of the interactions between CPTs and the insect Top1 protein remains unclear, which significantly hinders the development of novel CPTs as new insecticides. Herein, a series of 7-amide camptothecin analogs based on the binding mode of camptothecin in complex with Top1 (Sf Top1)-DNA from Spodoptera frugiperda cultured cell line Sf9 were designed and synthesized. Fifteen of these compounds exhibited excellent cytotoxic activity (values of IC₅₀ from 2.01 to 6.78 μM) compared with camptothecin (29.47 μM). The molecular simulations revealed the binding mechanism when the camptothecin parent rings were inserting parallel to DNA bases and stabling the ternary complex by π-π stacked and hydrogen-bond interactions, and further suggested that introduction of lipophilic and some electron-withdrawing groups on the amide linkage of camptothecin could be beneficial to its activity via some non-covalent interactions. Furthermore, almost all the synthesized compounds could inhibit the growth of Spodoptera litura larvae strongly (Inhibition rate from 50.20 to 79.05%), superior or comparable to camptothecin (55.69%) after 8 days of exposure. In particular, the compounds 4c, 4d, 4f, and 4j, which presented more than 70% inhibitory activities, were deserved to be developed as potential biorational pesticides. The information described here would be useful for the further design and development of potentially effective pesticides in the field of plant protection.

Glutaraldehyde-polymerized hemoglobin and tempol (PolyHb-tempol) has superoxide dismutase activity that can attenuate oxidative stress on endothelial cells induced by superoxide anion

A Tempol compound with an amine group (4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl, NH₂-Tempol) was cross-linked to hemoglobin in a one-step polymerization reaction to produce a novel hemoglobin-based oxygen carrier (HBOC) designated PolyHb-Tempol. The reaction parameters, including the reaction time, pH, temperature, and ratio of reactants, were optimized, and the physiochemical properties of the resulting product were characterized. PolyHb-Tempol didn't show any toxicity towards endothelial cells. Furthermore, from observations of cell morphology and viability, PolyHb-Tempol showed a significant ability to inhibit or eliminate oxidative stress induced by superoxide free radicals. These results suggest that PolyHb-Tempol may potentially be suitable as an HBOC.

Structure and packing of aminoxyl and piperidinyl acrylamide monomers

The closely related title compounds, 4-acrylamido-2,2,6,6-tetramethylpiperidine-1-oxyl, C12H21N2O2, (I), and N-(2,2,6,6-tetramethylpiperidin-4-yl)acrylamide monohydrate, C12H22N2O·H2O, (II), are important monomers in the preparation of redox-active polymers. They comprise an acrylamide group of the usual s-cis configuration appended to a 2,2,6,6-tetramethyl-substituted piperidine-1-oxyl radical or a piperidinyl chair, respectively. The adjacent amide and piperidinyl H atoms are approximately trans across the C-N bond. The packing in (I) is dominated by N-H...O hydrogen bonds; these are supported by C-H...O contacts to form an R2(1)(6) ring repeat, a motif which has been observed in other acrylamide structures. In (II), hydrogen bonds are again key to the packing arrangements. In this case, the incorporated solvent water molecule acts as an acceptor through its O atom and as a donor through both H atoms, binding three adjacent piperidinylacrylamide molecules into layers. In both structures, weak C-H...O contacts involving the piperidinyl methyl H atoms and a proximal acrylamide carbonyl O atom extend the structure in the third dimension.

TEMPO-derived spin labels linked to the nucleobases adenine and cytosine for probing local structural perturbations in DNA by EPR spectroscopy

Three 2´-deoxynucleosides containing semi-flexible spin labels, namely (T)A, (U)A and (U)C, were prepared and incorporated into deoxyoligonucleotides using the phosphoramidite method. All three nucleosides contain 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) connected to the exocyclic amino group; (T)A directly and (U)A as well as (U)C through a urea linkage. (T)A and (U)C showed a minor destabilization of a DNA duplex, as registered by a small decrease in the melting temperature, while (U)A destabilized the duplex by more than 10 °C. Circular dichroism (CD) measurements indicated that all three labels were accommodated in B-DNA duplex. The mobility of the spin label (T)A varied with different base-pairing partners in duplex DNA, with the (T)A•T pair being the least mobile. Furthermore, (T)A showed decreased mobility under acidic conditions for the sequences (T)A•C and (T)A•G, to the extent that the EPR spectrum of the latter became nearly superimposable to that of (T)A•T. The reduced mobility of the (T)A•C and (T)A•G mismatches at pH 5 is consistent with the formation of (T)AH(+)•C and (T)AH(+)•G, in which protonation of N1 of A allows the formation of an additional hydrogen bond to N3 of C and N7 of G, respectively, with G in a syn-conformation. The urea-based spin labels (U)A and (U)C were more mobile than (T)A, but still showed a minor variation in their EPR spectra when paired with A, G, C or T in a DNA duplex. (U)A and (U)C had similar mobility order for the different base pairs, with the lowest mobility when paired with C and the highest when paired with T.