Francisco J. Martínez-Martínez

Syntheses and Characterization by NMR Spectroscopy and X-ray Diffraction of Complexes Derived from Metals of Groups 2 and 13 and the Ligand Bis(3,5-di-tert-butyl-1-hydroxy-2-phenyl)amine

Reaction of 3,5-di-tert-butylcatechol and aqueous ammonia with boron, aluminum, gallium, or strontium chloride, or with calcium or barium acetate produce, under oxidizing conditions, neutral complexes of stoichiometric formulae ML (M = BCl), ML2, [M = Al (2), Ga (3), Ca (4), and Ba (5)], and ML3H [M = Sr (6)] [L = different oxidation states of bis(3,5-di-tert-butyl-1-hydroxy-2-phenyl)amine]. The structures of 1 and 4–6 were established by 1H- and 13C-NMR spectroscopy and of 2, 3, and 6 by X-ray diffraction. The coordination compound ClBL (1) was obtained by transmetallation of ZnL2 with BCl3. It is a tetracyclic compound with tetracoordinated boron and nitrogen atoms, the ligand being in the reduced form, bis(hydroxyphenyl)amine. The paramagnetic complexes 2 and 3 crystallized in the triclinic system and are hexacoordinated with two orthogonal planar ligands bonded to the metal atoms. The ligands appear in two different oxidation states: one as the monoanion and another as a radical dianion. Based on their X-ray diffraction molecular structures, it is deduced that both ligands have similar structures, confirming electronic delocalization and fast interconversion of their oxidation states. Ca and Ba complexes are diamagnetic and hexacoordinated, both ligands being monoanions The strontium complex crystallized in the monoclinic system, the metal atom is nonacoordinated, having two ligands as monoanions, and a third one is a neutral protonated diquinone. Its structure is a distorted helix with three paddles in a C3 geometry and its unexpected diamagnetic behaviour is due to the presence of a reduced protonated ligand.

1 H, 13C, 15N, 2D and variable temperature NMR study of the role of hydrogen bonding in the structure and conformation of oxamide derivatives

The structure and conformation of N,N′-bis[(2-hydroxy)phenyl]oxamide (1); N,N′-bis[(2-methoxy)-phenyl]oxamide (2); N,N′-bis(phenyl)oxamide (3); N,N′-bis[(1R,2S)-(–)-norephedrine]oxamide (4); N,N′-bis[(1R,2R)-(–)-norpseudoephedrine]oxamide (5); N-[(2-hydroxy)phenyl]methylamide (6); N-[(2-methoxy)phenyl]methylamide (7); N-phenylmethylamide (8); N-[(–)-norephedrine]-methylamide (9) and N-[(–)-norpseudoephedrine]methylamide (10) were unambiguously established by 1H, 13C, 15N, 2D and variable temperature NMR spectroscopy. A careful NMR investigation of the conformational behaviour in these systems was relevant. It has been found that the dicarbonylic group in compounds 1–5 has a trans geometry, stabilized by intramolecular hydrogen bonding and that they possess a C2 axis. Compounds 1 and 2 are planar and compounds 1, 2, 4 and 5 present the amidic proton coordinated by two oxygen atoms.

Antioxidant Activity of Butyl- and Phenylstannoxanes Derived from 2-, 3- and 4-Pyridinecarboxylic Acids

In vitro antioxidant activity for 12 stannoxanes derived from Ph3SnCl (compounds 1-3), Ph2SnCl2 (compounds 4-6), Bu3SnCl (compounds 7-9), and Bu2SnCl2 (compounds 10-12), was assayed qualitatively by the chromatographic profile with 1,1-diphenyl-2-picrylhydrazil (DPPH) method and by two quantitative methods: the DPPH radical scavenging activity and Ferric-Reducing Antioxidant Power (FRAP) assays. The results were compared with those obtained with the starting materials 2-pyridine- carboxylic acid (I), 3-pyridinecarboxylic acid (II) and 4-pyridinecarboxylic acid (III), as well as with standard compounds, such as vitamin C and vitamin E, respectively. The in vitro antiradical activity with DPPH of diphenyltin derivative 5 showed a very similar behavior to vitamin C at a 20 μg/mL concentration, whereas according to the FRAP method, compound 8 was better. This difference is due to the mechanism of the antioxidant process. The Structure-Activity Relationships (SAR) for both methods is also reported.

Dynamic NMR and X-ray diffraction study of (N-B) -diphenyl(2-aminoethoxy) borane derivatives of ephedrines', and pseudoephedrines

Abstract The preparation and characterization of various (N-B)-diphenyl-(2-aminoethoxy)boranes derived from ephedrine and pseudoephedrine derivatives ( 1b–6b ) are reported: (N-B)-diphenyl(1-( R )-phenyl-2-( S )-methyl-2-aminoethoxy)borane ( 1b ), (N-B)-diphenyl(1-( R )-phenyl-2-( R )-methyl-2-aminoethoxy)borane ( 2b ), (N-B)-diphenyl[ N -( R )-methyl-(1-( R )-phenyl-2-( S )-methyl-2-aminoethoxy)]borane ( 3b - trans ), (N-B)-diphenyl[ N -( S )-methyl-(1-( R )-phenyl-2-( S )-methyl-2-aminoethoxy)]borane ( 3b - cis ), (N-B)-diphenyl[ N -( S )-methyl-(1-( R )-phenyl-2-( R )-methyl-2-aminoethoxy)]borane ( 4b - trans ). (N-B)-diphenyl[ N,N -dimethyl-(1-( R )-phenyl-2-( S )-methyl-2-aminoethoxy)]borane ( 5b ) and (N-B)-diphenyl[ N,N -dimethyl-(1-( R )-phenyl-2-( R )-methyl-2-aminoethoxy)]borane ( 6b ). The five membered N → B cyclic structures 1b–6b were assigned based on 1 H-. 13 C-, 11 B- and 15 N-NMR data and all compounds except for 3b - trans were subjected to X-ray diffraction analysis showing N → B bond lengths of 1.66(2) and 1.64(2)A for 1b , 1.657(9) and 1.664(9))A for 2b , 1.68(2) A for 3b - cis , 1.66(1)A for 4b - trans , 1.744(8)A for 5b and 1.74(1)A for 6b . The study of the intramolecular N → B coordination by means of dynamic NMR spectroscopy afforded Δ G ‡ values of 67.9, 70.9, 64.8, 68.2, 49.7 and 52.7 kJ mol −1 for the dissociation of the N → B bond in compounds 1b–6b respectively. The results show that steric interactions between the substituents at the (2-aminoethoxy)borane ring determine the stability of the N → B bond as well as the nitrogen configuration. Theoretical calculations of the electrostatic charges for the boron and nitrogen atoms in 1b , 2b , 3b - cis , 3b - trans , 4b - cis , 5b and 6b show that the increase of positive charge on the nitrogen atom causes a shift to lower frequencies in the 15 N NMR spectra.

Carbon­yl–carbonyl, carbon­yl–π and carbon­yl–halogen dipolar inter­actions as the directing motifs of the supra­molecular structure of ethyl 6-chloro-2-oxo-2H-chromene-3-carboxyl­ate and ethyl 6-bromo-2-oxo-2H-chromene-3-carboxyl­ate

The title compounds, C(12)H(9)ClO(4), (I), and C(12)H(9)BrO(4), (II), are isomorphous and crystallize in the monoclinic space group P2(1)/c. Both compounds present an anti conformation between the 3-carboxy and the lactone carbonyl groups. Both carbonyl groups are out of the plane defined by the remaining chromene atoms, by 8.37 (6) and 17.57 (6) degrees for (I), and by 9.07 (8) and 18.96 (18) degrees for (II), owing to their involvement in intermolecular interactions. In both compounds, layers of centrosymmetric hydrogen-bonded dimers are developed in the [-5 -2 22] plane through C-H...O interactions, involving both carbonyl groups as acceptors. Two families of dimers stack through C=O...C=O, C=O...pi and C-X...C=O (X = Cl and Br) dipolar interactions, as well as a C-H...pi interaction, developing the three-dimensional structure along the c axis.

Synthesis and in Vitro Antioxidant Activity Evaluation of 3-Carboxycoumarin Derivatives and QSAR Study of Their DPPH• Radical Scavenging Activity

The in vitro antioxidant activities of eight 3-carboxycoumarin derivatives were assayed by the quantitative 1,1-diphenyl-2-picrylhydrazil (DPPH•) radical scavenging activity method. 3-Acetyl-6-hydroxy-2H-1-benzopyran-2-one (C1) and ethyl 6-hydroxy-2-oxo-2H-1-benzopyran-3-carboxylate (C2) presented the best radical-scavenging activity. A quantitative structure-activity relationship (QSAR) study was performed and correlated with the experimental DPPH• scavenging data. We used structural, geometrical, topological and quantum-chemical descriptors selected with Genetic Algorithms in order to determine which of these parameters are responsible of the observed DPPH• radical scavenging activity. We constructed a back propagation neural network with the hydrophilic factor (Hy) descriptor to generate an adequate architecture of neurons for the system description. The mathematical model showed a multiple determination coefficient of 0.9196 and a root mean squared error of 0.0851. Our results shows that the presence of hydroxyl groups on the ring structure of 3-carboxy-coumarins are correlated with the observed DPPH• radical scavenging activity effects.

Competition between OH⋯O and multiple halogen–dipole interactions on the formation of intramolecular three-centred hydrogen bond in 3-acyl coumarins

This paper describes the synthesis and structural study in solution, by NMR, and in the solid state, by X-ray analysis, of 6-substituted (H, NO2, OCH3, Cl, Br) 2-oxo-2H-chromene-3-carboxylic acid (2-hydroxy-ethyl) amides. The results were supported by ab initio calculations at RHF-631G** level of theory. The crystal structures of compounds 6-Cl and 6-Br show deviations from the predicted theoretical conformation and also from that observed in solution, pointing to the influence exerted by intermolecular interactions on the molecular structure and on intramolecular three-centred hydrogen bond formation (O2⋯H12⋯O1). The significance of the plethora of non-covalent interactions [C‒H⋯A (A = O, X, π), CO⋯CO, CO⋯π, C‒X⋯OC (X = halogen), Br⋯Br and π‒π stacking] is discussed.

Thermal [4 + 2] Cycloadditions of 3-Acetyl-, 3-Carbamoyl-, and 3-Ethoxycarbonyl-Coumarins with 2,3-Dimethyl-1,3-butadiene under Solventless Conditions: A Structural Study

The thermal [4+2] cycloadditions of 3-acetyl-, 3-carbamoyl, and 3-ethoxy-carbonylcoumarins with 2,3-dimethyl-1,3-butadiene under solvent free conditions are reported, as well as the epoxidation reactions of some adducts. Discussion is focused on the structural features of the Diels-Alder adducts and their epoxides, based upon NMR, X-ray, and mass spectral data, and supported by ab initio theoretical calculations.

QSAR study of the DPPH· radical scavenging activity of coumarin derivatives and xanthine oxidase inhibition by molecular docking

AbstractA Quantitative Structure-Activity Relationship (QSAR) of coumarins by genetic algorithms employing physicochemical, topological, lipophilic and electronic descriptors was performed. We have used experimental antioxidant activities of specific coumarin derivatives against the DPPH· radical molecule. Molecular descriptors such as Randic Path/Walk, hydrophilic factor and chemical hardness were selected to propose a mathematical model. We obtained a linear correlation with R2 = 96.65 and QLOO2 = 93.14 values. The evaluation of the predictive ability of the model was performed by applying the QASYM2,

Three-center intramolecular hydrogen bonding in oxamide derivatives. NMR and X-ray diffraction study

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