Substituted adenine quartets: interplay between substituent effect, hydrogen bonding, and aromaticity.

Adenine, one of the components of DNA/RNA helices, has the ability to form self-organizing structures with cyclic hydrogen bonds (A4), similar to guanine quartets. Here, we report a computational investigation of the effect of substituents (X = NO2, Cl, F, H, Me, and NH2) on the electronic structure of 9H-adenine and its quartets (A4-N1, A4-N3, and A4-N7). DFT calculations were used to show the relationships between the electronic nature of the substituents, strength of H-bonds in the quartets, and aromaticity of five- and six-membered rings of adenine. We demonstrated how the remote substituent X modifies the proton-donating properties of the NH2 group involved in the H-bonds within quartets and how the position of the substituent and its electronic nature affect the stability of the quartets. We also showed the possible changes in electronic properties of the substituent and aromaticity of adenine rings caused by tetramer formation. The results indicate that the observed relationships depend on the A4 type. Moreover, the same substituent can both strengthen and weaken intermolecular interactions, depending on the substitution position.

Substituent effects on the stability of the four most stable tautomers of adenine and purine.

Substituent effects at the C2-, C8- and N-positions of adenine and purine in their four the most stable tautomers are studied by means of B97D3/aug-cc-pvdz computation applying substituents of varying electronic properties: NO2, CN, CHO, Cl, F, H, Me, OMe, OH and NH2. The substituent effect is characterized by the substituent effect stabilization energy (SESE) and substituent Hammett constant σ. For adenine, SESE is obtained with purine as the reference system. Additionally, for both adenine and purine, SESE characteristics are estimated with benzene, imidazole and amino-pyrimidine as reference systems, when possible, taking into account substitution in topologically equivalent positions. The role of a C6-NH2 group in adenine in modifying the substitution effect is observed and discussed. Additionally, the proximity effect for some asymmetric substituents (e.g. CHO, OMe) is recognized and meticulously analyzed.

Copper-catalyzed direct C-H arylselenation of 4-nitro-pyrazoles and other heterocycles with selenium powder and aryl iodides. Access to unsymmetrical heteroaryl selenides.

A one-pot, Cu-catalyzed direct C-H arylselenation protocol using elemental Se and aryl iodides was developed for nitro-substituted, N-alkylated pyrazoles, imidazoles and other heterocycles including 4H-chromen-4-one. This general and concise method allows one to obtain a large number of unsymmetrical heteroaryl selenides bearing a variety of substituents. The presence of the nitro group was confirmed to be essential for the C-H activation and can also be used for further functionalisation and manipulation. Several examples of heteroannulated benzoselenazines were also synthesized using the developed synthetic protocol.

Structural Characterization and Pharmaceutical Properties of Three Novel Cocrystals of Ethenzamide With Aliphatic Dicarboxylic Acids.

Ethenzamide (ET) was screened in cocrystallization experiments with pharmaceutically acceptable coformer molecules to discover materials of improved physicochemical properties, that is, higher solubility and better stability. Three novel cocrystals of ET with glutaric, malonic, and maleic acids were obtained by neat grinding and slow evaporation from solution. The purpose of the study was to notice the changes in the geometry and interactions of ET molecule in crystalline phase introduced by different acid and relate them to physicochemical properties of pure ET. Therefore, the crystal structure of the cocrystals was determined by single crystal X-ray diffraction analysis. The powder samples were characterized by differential scanning calorimetry, Fourier-transform infrared spectroscopy, and 13C and 15N solid-state nuclear magnetic resonance spectroscopy. Spectroscopic studies were supported by gauge including projector augmented wave calculations of chemical shielding constants. The high stability of cocrystals during direct compression was proved. The solubility in simulated gastric fluids for studied cocrystals appeared to be approximately 1.6 times-fold higher than ET. The dissolution rates of all ET cocrystals were not faster than the pure drug, but after 240 min, more drugs were released.

The study of interactions with a halogen atom: influence of NH2 group insertion on the crystal structures of meta-bromonitrobenzene derivatives.

Halogen atoms in molecular crystals may be involved in various interactions, often playing a very important role in structure stabilization. By introducing electron-donating groups, such as NH2, the electron density of the molecule is changed and thus interactions with the bromine substituent may alter. Herein, the crystal structures of meta-bromonitrobenzene and its NH2-substituted derivatives are analyzed. In all four described structures, namely m-bromonitrobenzene [Charlton & Trotter (1963). Acta Cryst. 16, 313], 4-bromo-2-nitroaniline (C6H5BrN2O2, 1), 2-bromo-6-nitroaniline (2) and 2-bromo-4-nitroaniline [Arshad et al. (2009). Acta Cryst. E65, o480], the Br atom is engaged in different interactions (Br...π, Br...O, Br...Br and C-H...Br, respectively). The Hirshfeld surface analysis (HS) and Reduced Density Gradient NonCovalent Interaction (RDG NCI) plots are used to prove the relevance, directionality and stabilizing nature of these interactions. Their modifications have been associated with the position of the amino group in the molecular structure and its influence on charge distribution analyzed with electrostatic potential surfaces (EPS). The diversification of the interactions has been correlated with a σ-hole potential value that enables a switching of the Br-atom character from electrophilic to nucleophilic.

Synthon preference in the cocrystal of 3,4,5-trifluorophenylboronic acid with urea.

The comprehensive description of the crystal structure of a novel 1:1 cocrystal of 3,4,5-trifluorophenylboronic acid with urea, C6H4BF3O2·CH4N2O, is presented. Both components are good candidates for crystal engineering as they can create a variety of supramolecular synthons. The preference for the formation of different hetrosynthons is verified based on theoretical calculations. The syn-anti conformation of boronic acid has been found to be the most favourable in the formation of intermolecular interactions with urea. Moreover, the distortions present in the boron coordination sphere have been described quantitatively based on experimental data according to bond-valence vector model calculations. The results revealed that the deformation of the sphere is typical for a syn-anti conformation of boronic acids. The supramolecular structure of the cocrystal is composed of large synthons in the form of layers made up of O-H...O and N-H...O hydrogen bonds. The layers are joined via N-H...F hydrogen bonds which are unusual for urea cocrystal structures.

DRD1 and DRD4 dopamine receptors in the etiology of preeclampsia.

INTRODUCTION: Recent reports have suggested an association between genetic polymorphisms of dopamine receptors and the development of an increased risk of chronic hypertension, as well as preeclampsia (PE). OBJECTIVES: The aim of the study was to evaluate the impact of the -48A>G DRD1 and -521C>T DRD4 polymorphisms in the etiology of PE among Polish women. MATERIAL AND METHODS: Ninety-eight preeclamptic women and 120 healthy pregnant controls were enrolled in the study The investigated polymorphisms of the DRD 1 and DRD4 genes were identified using PCR/RFLP methods. RESULTS: As far as the -48A>G DRD 1 polymorphism is concerned, the mutated -48GG genotype was more often found in controls (14.2%) than in the PE group (10.2%, ns), and the subgroup with severe PE (8.2%). Also, the frequency of the mutated -48G allele was higher in controls (39.6%) than in the PE group (33.2%, ns), and in the subgroup with severe PE (31.6%, ns). As for the -521C>TDRD4 polymorphism, a similar occurrence of the mutated -521 TTgenotype and the -521T allele in all of the investigate groups was observed. Lower serum concentrations of total protein (5.59 g/L and 5.57 g/L vs. 6.17 g/L in carriers of the -52100 genotype, p=0.02) were noted in patients with the mutated homozygous -521 TT genotype and heterozygous -521CT genotype of DRD4. CONCLUSIONS: The obtained results suggest a possible protective role of the mutated -48G DRD1 allele in the etiology of preeclampsia, especially its severe form. The presence of the mutated -521 T DRD4 allele could influence the decrease of total blood protein in preeclamptic patients. The observed frequency of dopamine DRD1 and DRD4 polymorphisms is similar to the distribution of these variants in other Caucasian populations.

Comparative analysis of pharmaceuticals and dietary supplements containing extracts from the leaves of Ginkgo biloba L.

Abstract: Chromatography (TLC and HPLC) tests were performed of 11 preparations containing dry extract of Ginkgo biloba leaves: three pharmaceuticals (preparations 1, 3 and 5) and eight dietary supplements (preparations 2, 4, 6-11), and dry extract of Ginkgo biloba leaves (preparation 12) as a standard certified for compliance with Eur. Ph. 6.1. and FP VIII (1, 2). Preparations registered in Poland as pharmaceuticals contained the major active ingredients (flavonoids and terpene lactones) in amount declared by their producers (and consistent with pharmacopoeial requirements) and acceptable level of potentially toxic ginkgolic acids (below 5 ppm). The concentration of active compounds in dietary supplements was varied. Some of them satisfied applicable quality criteria (mainly preparation 8), however, the majority had reduced levels of therapeutic compounds (4, 6, 7, 11) and increased concentration of ginkgolic acids (4, 9, 10, 11).