A theoretical and experimental NMR study of the prototropic tautomerism of tris(tetrabutylammonium) hydrogen pyrophosphate salt in solution and in the solid-state

The structure of tris(tetrabutylammonium)hydrogen pyrophosphate(HPP) has been studied in solution and in the solid-state by 31P NMR. GIAO/DFT calculations of the isolated molecule in its open and closed conformations, of their water complexes and the solvent effects (continuum model) have been useful to discuss the experimental NMR data. Contrary to literature reports, the 31P NMR spectra of HPP in solution have a single band, that broadenedconsiderably when the temperature is lowered till 193 K without reaching the coalescence. In the solid-state, two very close signals are observed that the calculations do not reproduce adequately

The Structure of N-Benzylazoles from Pyrrole to Carbazole: Geometries and Energies

International audienceThe complete series of 18 parents N-benzylazoles (10 azoles and 8 benzazoles) have been calculated at the B3LYP/6-311++G(d,p) level. The geometries have been compared with the X-ray structures reported in the literature for six derivatives (1H-imidazole, 1H-1,2,3-triazole, 1H-1,2,3,4-tetrazole, 1H-benzimidazole, 1H-benzotriazole, and 9H-carbazole). Only one minimum has been found for the 18 molecules, but several transition states connecting them have been located. The calculated geometries agree well with those reported by X-ray crystallography

Fluorination Effects on NOS Inhibitory Activity of Pyrazoles Related to Curcumin

A series of new (E)-3(5)-[β-(aryl)-ethenyl]-5(3)-phenyl-1H-pyrazoles bearing fluorine atoms at different positions of the aryl group have been synthesized starting from the corresponding β-diketones. All compounds have been characterized by elemental analysis, DSC as well as NMR (1H, 13C, 19F and 15N) spectroscopy in solution and in solid state. Three structures have been solved by X-ray diffraction analysis, confirming the tautomeric forms detected by solid state NMR. The in vitro study of their inhibitory potency and selectivity on the activity of nNOS and eNOS (calcium-calmodulin dependent) as well as iNOS (calcium-calmodulin independent) isoenzymes is presented. A qualitative structure–activity analysis allowed the establishment of a correlation between the presence/ absence of different substituents with the inhibition data proving that fluorine groups enhance the biological activity. (E)-3(5)-[β-(3-Fluoro-4-hydroxyphenyl)-ethenyl]-5(3)-phenyl-1H-pyrazole (13), is the best inhibitor of iNOS, being also more selective towards the other two isoforms.This work has been financed by Ministerio de Ciencia e Innovación (CTQ2010-16122) and Ministerio de Economía y Competitividad of Spain (CTQ2014-56833-R, RD12/0043/0005, and PI13-00981) and Comunidad Autónoma de Madrid (Project MADRISOLAR2, ref. S2009/PPQ-1533). One of us (C. I. Nieto) is indebted to UNED for a predoctoral fellowship (FPI “Grupos de Investigación” UNED)

Evaluation of the Antioxidant and Neuroprotectant Activities of New Asymmetrical 1,3-Diketones

A series of fourteen new asymmetrical 1,3-diketone derivatives have been synthesized and evaluated in the ABTS, FRAP and DPPH assays as a new chemotype with antioxidant and drug-like properties. All the compounds displayed low cytotoxicity in comparison to curcumin against the human neuroblastoma SH-SY5Y cell line. Among them, (3Z,5E)-6-(2,5-difluoro-4-hydroxy-phenyl)-1,1,1-trifluoro-4-hydroxyhexa-3,5-dien-2-one (6b) and (3Z,5E)-6-(2,3-difluoro-4-hydroxy-phenyl)-1,1,1-trifluoro-4-hydroxyhexa-3,5-dien-2-one (7b) with excellent solubility and chemical stability in biorelevant media, have also shown a similar Fe+2 chelation behavior to that of curcumin. Additionally, both derivatives 6b and 7b have afforded good neuroprotection activity against H2O2 induced oxidative stress in the same neuronal cell line, with a significant reduction of intracellular ROS levels, in parallel with a good recovery of the Mitochondrial Membrane Potential (ΔΨm). Compounds 6b and 7b with a promising antioxidant and drug-like profile, with low cytotoxic and good neuroprotectant activity, constitute a new interesting chemical class with high potential as new therapeutic agents against neurodegenerative diseases

Syntheses and Structural Studies of Schiff Bases Involving Hydrogen Bonds

Abstract: New Schiff bases have been prepared by reacting 3-hydroxy-4-pyridinecarboxaldehyde with various amines. NMR spectroscopic methods provided clear evidence that the Schiff bases exist in the solid state and in solution as hydroxyimino tautomers with the E-configuration. A study of the stabilities of the tautomeric forms and the different conformers has been carried out using density functional calculations at the B3LYP/6-31G* * level

Mechano heterocyclic chemistry: Grinding and Ball Mills

This review covers till 2013 the main publications dealing with the use of mechanochemistry in heterocyclic chemistry. Physical aspects, like polymorphism and cocrystals, physicochemical problems, like tautomerism and desmotropy, and pure chemical ones, like synthesis and reactivity, are discussed. The review puts special emphasis on active pharmaceutical ingredients and, in general, on biological aspects. It will become clear that the technique has the advantages of time, simplicity, cost, and lower waste. Moreover, some complex structures that are difficult to prepare in solution, can be easily obtained by using simple, solventless grinding. The conclusion of this survey is that mechanochemistry will become another green method as important as microwave ovens in chemistry, although much exciting work remains to be done, both experimental and theoretically.Peer Reviewe

The structures of two scorpionates: Thallium tetrakis(3-phenyl-1H-pyrazol-1-yl)borate and potassium tetrakis(3-cyclopropyl-1H-pyrazol-1-yl)borate

The introduction of poly(1H-pyrazolyl)borate anions, better known as scorpionates, as negatively charged ligands for a great diversity of metal cations has had a tremendous influence in coordination chemistry. The structures of two salts of tetrakispyrazolylborate, namely [tetrakis(3-phenyl-1H-pyrazol-1-yl)borato]thallium(I), [Tl(C36H28BN8)], and catena-poly[potassium-[μ2-tetrakis(3-cyclopropyl-1H-pyrazol-1-yl)borato]], [K(C24H28BN8)] n , have been determined at 296-K in the monoclinic P21/c and C2/c space groups, respectively. In their crystal structures, the thallium salt presents discrete molecular motifs, while the potassium salt shows infinite polymeric chains. The C and N CPMAS (cross polarization magic angle spinning) NMR spectra of these compounds were recorded and the chemical shifts compared with theoretically calculated ones at the GIAO/B3LYP/6-311++G(d,p) level. Both techniques are complementary and mutually consistent.Peer Reviewe

The Structure of N-Benzylazoles from Pyrrole to Carbazole: Geometries and Energies

International audienceThe complete series of 18 parents N-benzylazoles (10 azoles and 8 benzazoles) have been calculated at the B3LYP/6-311++G(d,p) level. The geometries have been compared with the X-ray structures reported in the literature for six derivatives (1H-imidazole, 1H-1,2,3-triazole, 1H-1,2,3,4-tetrazole, 1H-benzimidazole, 1H-benzotriazole, and 9H-carbazole). Only one minimum has been found for the 18 molecules, but several transition states connecting them have been located. The calculated geometries agree well with those reported by X-ray crystallography