Ivo Vencato

Study of N -benzoyl-activation in the HgCl 2 -promoted guanylation reaction of thioureas. Synthesis and structural analysis of N -benzoyl-guanidines

Abstract In this work, it is demonstrated that the benzoyl group is an activating group for thioureas in the HgCl2-guanylation reaction. Thus N-benzoyl-thioureas containing electronically neutral and even electron-withdrawing or electron-releasing substituents are converted into guanidines with reasonable yields. In addition, NMR and X-ray structural analyses were performed to understand the intra- and intermolecular features of the synthesized guanidines.

Resonance Raman and crystallographic studies on the complex [Fe2(bbpnol)2]·2DMF (bbpnol=N,N′-bis(2-hydroxybenzyl)-2-ol-1,3-propanediamine)

Abstract The ligand N,N′-bis(2-hydroxybenzyl)-2-ol-1,3-propanediamine (H3bbpnol) reacts with iron(III) perchlorate forming two dinuclear bis-μ-alkoxo complexes, a ‘cis–trans’ isomer (complex 1) previously reported and a ‘cis–cis’ isomer (complex 2) characterized in this work. The main differences found in complex 2 structure are, (a) the four phenolic oxygens are trans to the alkoxo bridges; (b) each ligand is shared by the two Fe(III) ions occupying two coordination positions at each center. The Fe(III) centers in the resulting centrosymmetric structure in complex 2 have a distorted-octahedral geometry with the equatorial plane occupied by the phenolic and alcoholic oxygen atoms and the apical positions are filled by the aminic nitrogen atoms. The resonance Raman (RR) spectra of these two isomeric complexes are somewhat different with the intensity of some low-frequency modes increasing in the less symmetric core. The electronic spectra of both complexes are similar, but the molar absorptivities are substantially increased in complex 2, indicating the presence of an electronic coupling between the phenolate moieties trans in relation to the alkoxo bridge, and that phenolates coordinated cis to the alkoxo bridge do not seem to contribute to LMCT oscillator strength. This is directly reflected in the Raman excitation profiles (REP) of the chromophore modes, with the vibrational modes of the ‘cis–cis’ isomer showing a greater intensification compared with the ‘cis–trans’ isomer.

Biological and structure-activity evaluation of chalcone derivatives against bacteria and fungi

O presente trabalho descreve as atividades antibacterianas e antifungicas de diversas chalconas obtidas diretamente atraves da condensacao aldolica tipo Claisen-Schmidt das quais se determinou a concentracao inibitoria minima frente a diferentes microrganismos (bacterias Gram-positivas e Gram-negativas e fungos). Estruturas no estado solido cristalino de sete chalconas foram determinadas por analise de difracao de raios X (XRD). Estudos quimiometricos foram realizados com intuito de identificar uma potencial relacao entre estrutura e atividade.

Jatrowediol, a lathyrane diterpene from Jatropha weddelliana

A partir das raizes de Jatropha weddelliana foram isolados os diterpenoides jatrogrossidiona, 4Z-jatrogrossidentadiona, 15-epi-4Z-jatrogrossidentadiona, 4E-jatrogrossidentadiona,15-epi-4E-jatrogrossidentadiona, 2-hidroxiisojatrogrossidiona, 2-epi-hidroxiisojatrogrossidiona e jatrowediol. A elucidacao da estrutura do jatrowediol, um novo diterpenoide latirânico, foi realizada por meio de analises por tecnicas de RMN e de difracao de raios-X.

Synthesis, molecular structure and spectroscopic, electrochemical and magnetic properties of a new dinuclear iron complex containing µ-sulfate-di-µ-alkoxo bridges: evaluating the influence of the sulfate bridge on the physicochemical properties of the di-µ-alkoxo-diiron unit

Complex [Fe2III(BPClNOL)2(SO4)] 3 was synthesized through the reaction of the pro-ligand N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)[(3-chloro)(2-hydroxy)]propylamine (H2BPClNOL) and FeSO4.7H2O. The maximum absorption for the oxidized compound was at 519 nm (e = 1.40X103 dm3 mol-1 cm-1) while that of the mixed-valence compound was at 439 nm (e = 9.8X102 dm3 mol-1 cm-1). The redox process to transform the oxidized compound to the mixed-valence form occurs at E1/2 = -0.843 V vs. Fc/Fc+. The Mossbauer spectrum confirms the presence of FeIII high spin ions and the magnetic studies reveal a weak antiferromagnetically coupled dimer, J/kB = - 15 K ( J = -10.4 cm-1). Complex 3 is the third of a family of dinuclear iron compounds synthesized with the H2BPClNOL ligand ([Fe2III(BPClNOL)2 (OAc)]+ 1, [Fe2III(BPClNOL)2(H2O) 2]2+ 2). Analysis of the physicochemical properties of these complexes allowed us to infer that the number and kind of bridging groups have a significant influence on their electrochemical and UV-Vis properties.

Guanylation of thiosemicarbazones: a new synthetic route to polysubstituted guanylhydrazones with antimicrobial activity

Guanil-hidrazonas poli-substituidas foram sintetizadas atraves da reacao de guanilacao de tiossemicarbazonas com aminas aromaticas e alifaticas, promovida HgCl 2 . Este metodo representa o primeiro emprego de tiossemicarbazonas como componente eletrofilico em reacoes de sintese de guanidinas mediadas por tiofilo, onde a introducao de cada substituinte dos nitrogenios das guanil-hidrazonas ocorreu de forma regiosseletiva. As atividades antibacteriana e antifungica foram avaliadas e alguns derivados mostraram atividade em valores pequenos de concentracao inibitoria minima e com amplo espectro de atividade. Estudou-se a estrutura cristalina de duas guanil-hidrazonas, determinando-se suas configuracoes e, as unicas interacoes relevantes observadas foram intermoleculares do tipo N–H...N e C–H...N. Thiosemicarbazones were employed for the first time as electrophiles in the guanylation reaction promoted by HgCl 2 , affording polysubstituted guanylhydrazones, with regioselective introduction of each nitrogen substituent. The antibacterial and antifungal activities of guanylhydrazones were evaluated by determination of minimal inhibitory concentrations. Some of them exhibited very low minimal inhibitory concentrations (MIC) and broad-spectrum activities. The configurations of two guanylhydrazones were assigned by X-ray analysis that also revealed intramolecular interactions of the type N–H...N and C–H...N.

Structural and reactivity analyses of 2-benzylamino-1,4-naphthoquinone by X-ray characterization, electrochemical measurements, and dft single-molecule calculations

This study represents an integrated approach towards understanding the electronic and structural aspects of 2-benzylamino-1,4-naphthalenedione, a representative 2-amino-napfthoquinone. To this end, theoretical calculations performed at the B3PW91/6-31+G(d) level of density functional theory, electrochemical and X-ray structural investigation were employed. Two intramolecular H-bonds and other two intermolecular H-bonds were observed, including non-classical interactions. Cyclic voltammogram (CV) and differential pulse voltammetry (DPV) show two pairs of peaks, being each one a monoelectronic process.

Synthesis, characterization, absolute structural determination and antifungal activity of a new chlorinated aromatic avenaciolide analogue

BACKGROUND Avenaciolide, a natural product isolated from Aspergillus avenaceus H. Smith, possesses several interesting biological properties, such as antifungal and antibacterial activities and inhibition of glutamate transport in mitochondria. In a study aiming to discover new compounds with antifungal activity, a bis-gamma-lactone analogous to avenaciolide was prepared and characterized by elemental analysis, mass spectrometry, and infrared and NMR spectroscopy. RESULTS The absolute structures of this compound and of the synthetic precursor (also a bis-gamma-lactone) were determined by X-ray diffraction analysis. The bis-gamma-lactones synthesized crystallize in the orthorhombic space group P2(1)2(1)2(1), and the crystal packings are supported by C--H...O hydrogen bonds. The compound showed antifungal activity against Colletotrichum gloeosporioides (Penz.) Penz. & Sacc., while the synthetic precursor was inactive under the in vitro test conditions employed. CONCLUSION The results indicate that it is not only the bis-gamma-lactone skeleton that is important to antifungal activity. The latter also depends on the presence of the exocyclic double bond possibly due to a Michael addition type reaction with the fungal enzymes.