Paulo Marcos Donate

EFFECTS OF SUBSTITUTION FOR HYDROXYL IN THE B-RING OF THE FLAVYLIUM CATION

Abstract The electronic structure of mono, bis and trihydroxylated derivatives in the B-ring of the flavylium cation was studied. The AM1 semiempirical method of molecular orbital calculations was used. Data showed that substitution in the B-ring causes resonance increase between this ring and the C-ring, except for substitution on C(3′). Bond orders were interpreted through the variation in the contribution of resonance structures and they helped to explain the relative stability of the several dissubstituted isomers. Another factor that contributes to this stability is the formation of a hydrogen bond in the B-ring and between the B-and C-rings. The rotation enthalpies in the B-ring were calculated and they confirm that the rotation on the C(2)-C(1′) bond is free in the compounds with substitution on position 3′. The molecule planarity can be attributed to the interaction between the oxygen atom in the C-ring and the hydrogen atoms in the B-ring, or between the hydrogen atoms in these rings. The charge variations are in agreement with the proposed resonance structures. Substitution in the B-ring does not affect the sites of basic and nucleophilic attack.

Ethanol Electro‐oxidation in Ruthenium‐Oxide‐Coated Titanium Electrodes

A systematic investigation of ethanol oxidation on Ti/RuO 2 electrodes has been carried out in 1.0 mol dm -3 HClO 4 acid solution. The experimental results show high selectivity toward acetaldehyde formation. One of the secondary oxidation products of ethanol forms a blocking film at the electrode surface which can be removed during electrosynthesis using pulse control of the working potential. The influence of the electrolysis conditions, the electrode mechanism of ethanol oxidation, and R Ω values measured under pseudo-Tafel plots are discussed.

Gas‐phase fragmentation of γ‐lactone derivatives by electrospray ionization tandem mass spectrometry

Fragmentation reactions of beta-hydroxymethyl-, beta-acetoxymethyl- and beta-benzyloxymethyl-butenolides and the corresponding gamma-butyrolactones were investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS) using collision-induced dissociation (CID). This study revealed that loss of H(2)O [M+H-8](+) is the main fragmentation process for beta-hydroxymethylbutenolide (1) and beta-hydroxymethyl-gamma-butyrolactone (2). Loss of ketene ([M+H-42](+)) is the major fragmentation process for protonated beta-acetoxymethyl-gamma-butyrolactone (4), but not for beta-acetoxymethylbutenolide (3). The benzyl cation (m/z 91) is the major ion in the ESI-MS/MS spectra of beta-benzyloxymethylbutenolide (5) and beta-benzyloxymethyl-gamma-butyrolactone (6). The different side chain at the beta-position and the double bond presence afforded some product ions that can be important for the structural identification of each compound. The energetic aspects involved in the protonation and gas-phase fragmentation processes were interpreted on the basis of thermochemical data obtained by computational quantum chemistry.

Electronic structure of hydroxylated derivatives of the flavylium cation

Abstract The electronic structure of the flavylium cation (1) and those of some of its hydroxylated derivatives were studied by semiempirical and ab initio molecular orbital methods. This ion presents a small resonance in the pyrylium group (Cring), which is not conjugated to the phenyl group (B-ring). The planarity of the molecule is due to a hydrogen bond between the oxygen atom in C-ring and some hydrogen atoms in B-ring. There is also a repulsive interaction between hydrogen atoms of these rings. The theoretical locations of the sites of nucleophilic and electrophilic attack corresponds to those experimentally observed. Monohydroxylation does not cause important alterations in the electronic structure of the cation (1) except for the substitution on C(4′), which causes the appearance of resonance between B- and C-rings.

Electronic structure of chromone and its hydroxylated derivatives on positions 2 and 3

Abstract The electronic structure of chromone ( 1 ) and those of its 2-hydroxy ( 2 ) and 3-hydroxy ( 3 ) derivatives were studied by semiempirical and ab initio molecular orbital methods. Several electronic parameters show that the A-ring is an aromatic system, whereas the C-ring does not present conjugation. In the C-ring, the double bonds are located in the carbonyl group and between C(2)–C(3). These results were confirmed by comparison with geometries of chromone derivatives which were determined by X-ray diffraction data. The relative stability of compounds ( 2 ) and ( 3 ) was explained and the sites of acid, basic, nucleophilic and electrophilic attack were also determined.

Trypanocidal structure–activity relationship for cis- and trans-methylpluviatolide

The trypanocidal activity of racemic mixtures of cis- and trans-methylpluviatolides was evaluated in vitro against trypomastigote forms of two strains of Trypanosoma cruzi, and in the enzymatic assay of T. cruzi gGAPDH. The cytotoxicity of the compounds was assessed by the MTT method using LLC-MK2 cells. The effect of the compounds on peroxide and NO production were also investigated. The mixture of the trans stereoisomers displayed trypanocidal activity (IC50 approximately 89.3 microM). Therefore, it was separated by chiral HPLC, furnishing the (+) and (-)-enantiomers. Only the (-)-enantiomer was active against the parasite (IC50 approximately 18.7 microM). Despite being inactive, the (+)-enantiomer acted as an antagonistic competitor. Trans-methylpluviatolide displayed low toxicity for LLC-MK2 cells, with an IC50 of 6.53 mM. Furthermore, methylpluviatolide neither inhibited gGAPDH activity nor hindered peroxide and NO production at the evaluated concentrations.

Green synthesis from biomass

This review describes how to apply green chemistry principles to transform biomass into several types of molecules. On the basis of selected papers published over the last three to four years, it includes the main reactions used to convert renewable feedstocks into chemical products that are potentially applicable as raw materials or synthetic intermediates in fine chemical industries with emphasis on preparative organic synthesis.

Upgrading of sugar cane bagasse by thermal processes. 9: Catalytic liquefaction in ethanol

This article presents the results of a study on the process of direct catalytic liquefaction of sugar cane bagasse, using ethanol as solvent. A systematic study with 12 different types of commercially available catalysts was accomplished. For each catalyst, the conversion yield of sugar cane bagasse into liquefied products, which are useful as liquid fuels and chemical feedstocks, was determined. The highest conver sion yield was observed when a nickel catalyst on SiO2-Al2 O3 was used. The liquefied products were fractionated into oils, asphaltenes, and asphaltols. The oil samples were separated and then fractionated into eight different chemical classes by preparative liquid chromatography. The highest proportion of light-oils (F1 to F5) was obtained with the potassium fluoride catalyst on silica gel. High proportions of resins (F6) were obtained with three types of catalysts: nickel on SiO2-Al2 O3 , ruthenium, or platinum on activated carbon powder. The highest proportion of asphaltenes (F7) and of asph...

Complete assignments of 1H and 13C NMR spectral data for arylnaphthalene lignan lactones

In this work we describe the complete 1H and 13C NMR analyses of three arylnaphtalene lignan lactones (taiwanin C, 4‐methyl dehydroretrodendrin and justicidin B) using modern NMR techniques such as gCOSY, nonedited gHSQC, gHMBC and NOE experiments. Complete assignment and homonuclear hydrogen coupling constant measurements were performed. Copyright

SYNTHESIS OF BENZOFURANOFURAN DERIVATIVES: MODEL OF NATURAL PRODUCTS

Several benzofuranofuran derivatives were synthesized employing intramolecular cycloaddition reactions of ketenes with alkenes. (Alkenyloxy)ketenes, prepared from the tosylate by treatment with triethylamine, easily undergo intramolecular [2 + 2] cycloaddition to give tricyclic benzocyclobutafuranones. Baeyer-Villiger oxidation of the cycloadducts gives benzofurano-furanones, which are closely related to natural products with anticoagulant and antimalarial properties.