Márcia C.C. de Oliveira

New Biflavonoid and Other Constituents from Luxemburgia nobilis (EICHL)

O fracionamento cromatografico dos extratos orgânicos das folhas e galhos de Luxemburgia nobilis (Ochnaceae) forneceu o sitosterol, sitosterol-3-O- βD-glicopiranosil, friedelina, friedelinol, a mistura dos triterpenos lupeol, α-amirina e β-amirina, rutina, epicatequina, uma mistura de duas chalconas, isoliquiritigenina e 3’-hidroxiisoliquiritigenina, duas biflavonas conhecidas, amentoflavona e robustaflavona alem de uma biflavona nova, 5,7,4’-triidroxiflavona-(3’-O-4”’)-5”,7”diidroxiflavanona. As estruturas foram definidas atraves dos dados espectrometricos incluindo experimentos bidimensionais de RMN das substâncias naturais e dos derivados metilados e acetilados da biflavona nova. Chromatographic fractionation of the organic extracts from the leaves and branches of Luxemburgia nobilis (Ochnaceae) afforded sitosterol, sitosterol-3-O- βD-glucopyranoside, friedelin, friedelinol, a mixture of triterpenes lupeol, α-amyrin and β-amyrin, rutin, epicatechin, a mixture of two chalcones, 2,4,3’,4’-tetrahydroxychalcone and 2,4,4’-trihydroxychalcone, two known biflavones, amentoflavone and robustaflavone along with a new biflavonoid, 5,7,4’-trihydroxyflavone-(3’-O4’”)-5”,7”-dihydroxyflavanone. The structures were established from spectral data, including 2DNMR experiments of the natural substances and of the acetyl and methyl ether derivatives of the new biflavone.

Síntese de 1,3,5-triazinas substituídas e avaliação da toxicidade frente a Artemia Salina leach

The synthesis of ten symmetrically and unsymmetrically substituted 1,3,5-triazines by Phase Transfer Catalysis (PTC) method is described. Their toxicities were determined against Artemia salina Leach. The LD50 values have also been obtained for these compounds.

SYNTHESIS, CHARACTERIZATION, MOLECULAR MODELING AND BIOLOGICAL ACTIVITY AGAINST ARTEMIA SALINA OF NEW SYMMETRICAL BISPHOSPHORAMIDATES

A series of N,N′-bis(dialkylphosphoryl)diamines were prepared by Todd-Atherton reaction of dialkylphosphites with symmetrical diamines in a biphasic system. They were characterized by IR, 1 H-NMR, 13C-NMR and mass spectroscopy. Compounds with butoxy groups, isobutoxy groups and isopropoxy groups on the phosphorus atoms showed the lowest LD50 values when tested against Artemia salina. All other compounds that showed LD50 values higher than 363 ppm are considered non toxic. The results of a molecular modeling study suggest that the biological activity of the compounds may be related to AChE inhibition. Contrary to classical organophophorus AChE inhibitors, the compounds synthestized in this study do not possess a good leaving group, which suggests that they may act only as reversible inhibitors.

Antioxidant, Iron Chelating and Tyrosinase Inhibitory Activities of Extracts from Talinum triangulare Leach Stem

The aim of this work is to evaluate the antioxidant activity against the radical species DPPH, the reducing capacity against Fe II ions, and the inhibitory activity on the tyrosinase enzyme of the T. triangulare. Hydromethanolic crude extract provided two fractions after the liquid/liquid partition with chloroform. The Folin-Ciocalteu method determined the total phenolic content of the crude extract (CE) and the hydromethanolic fraction (Fraction 1), resulting in a concentration of 0.5853 g/100 g for Fraction 1, and 0.1400 g/100 g for the CE. Taking into account the results of the DPPH, the free radical scavenging capacity was confirmed. The formation of complexes with Fe II ions was evaluated by UV/visible spectrometry; results showed that CE has complexing power similar to the positive control (Gingko biloba extract).The inhibitory capacity of samples against the tyrosinase enzyme was determined by the oxidation of L-DOPA, providing IC50 values of 13.3 μg·mL−1 (CE) and 6.6 μg·mL−1 (Fraction 1). The values indicate that Fraction 1 was more active and showed a higher inhibitory power on the tyrosinase enzyme than the ascorbic acid, used as positive control. The hydromethanolic extract of T. triangulare proved to have powerful antioxidant activity and to inhibit the tyrosinase enzyme; its potential is increased after the partition with chloroform.

Chemical constituents from Luxemburgia nobilis (EICHL)

Chromatographic fractionation of the hexane extract from the branches of Luxemburgia nobilis (Ochnaceae) afforded b-sitosterol, stigmasterol, betulinic acid, linoleic acid, methyl-14-methylpentadecanoate, 13-epimanoyl oxide, hexadecanoic acid, tetraeicosanoic acid, hexaeicosanoic acid, the depside atranorin (1) and two new triglycerides (2 and 3). The structures were defined by IR, MS and 1H- and 13C-NMR spectral analysis involving comparison with literature data. The FAB-MS spectra analysis of the thiomethyl ethers (4 and 5) were used to define the structures of the triglycerides.

Flavonóides das flores de Stiffitia chrysantha Mikan

The flowers of Stiffitia chrysantha Mikam(Asteraceae) contain eriodictiol, quercetin, luteolin and b-D-glycopyranosil-sitosterol. These compounds and its derivatives were identified by their 1H and 13C NMR, infra-red and mass spectra data. The heteronuclear 2D NMR were used to confirm the assignments of the proton and carbon chemical shifts, it was used to eliminate definitively the ambiguous correlation reported in the literature for C-5 and C-9 of quercetin and C-23 and C-25 of b-D-glycopyranosil-sitosterol.

Thiosemicarbazones as inhibitors of tyrosinase enzyme

In the search for compounds which may inhibit the development of melanomas, a series of thiosemicarbazones has been investigated as possible inhibitors of the tyrosinase enzyme. The results showed that all the thiosemicarbazones tested exhibited significant inhibitory effects on the enzyme. Thiosemicarbazones Thio-1, Thio-2, Thio-3 and Thio-4 substituted with oxygenate moieties, were better inhibitors (IC50 0.42, 0.35, 0.36 and 0.44mM, respectively) than Thio-5, Thio-6, Thio-7 and Thio-8. For the better inhibitors, molecular docking results suggested that the oxygen present in the para position of the aromatic ring is essential for the tyrosinase inhibition, due its high ability for complexation with Cu2+ ions. Inside the active protein pocket, Thio-2 - the best studied inhibitor - is able to interact with the amino acid residues His-155, Gly-170 and Val-172 via hydrogen bonding and hydrophobic force. Thio-2, containing a substituent on the aromatic ring similar to the substrate l-DOPA, showed a competitive inhibition mechanism as viewed in a Lineweaver-Burk plot. The same results were observed in the UV-Vis curves.

Dialkylphosphorylhydrazones as potent tyrosinase inhibitors

Nineteen dialkylphosphorylhydrazones with different substituents at the aromatic ring were evaluated as potential tyrosinase inhibitors, which could then be used as efficient agents in the control of pigmentation disorders. The inhibition activity was measured by a modified Patil and Zucker UV-Vis method. Briefly, the assays were carried out with solutions containing phosphate buffer, L-3,4-dihidroxyphenylalanine (L-DOPA), (EDTA), tyrosinase and varying concentrations of organophosphorus compounds. The formation of dopachromone was determined by monitoring the absorbance at 475 nm. Three compounds were found to be the most active compounds of the series (IC50 = 105 ± 20 µmol L-1), (IC50 = 127 ± 16 µmol L-1) and (IC50 = 188 ± 27 µmol L-1), being three to seven times more active than ascorbic acid (IC50 = 730 µmol L-1), used as a standard. The most active compound is only 1.5 times less potent than the commercial kojic acid (IC50 = 69.4 µmol L-1). This study may lead to the discovery of potent agents against very important pigmentation disorders including hyperpigmentation.

Novel piperonal 1,3,4-thiadiazolium-2-phenylamines mesoionic derivatives: Synthesis, tyrosinase inhibition evaluation and HSA binding study

A novel series of piperonal mesoionic derivatives (PMI 1-6) was synthesized. Tyrosinase inhibition in the presence of PMI-1, -2, -3, -4, -5 and -6 as well as human serum albumin (HSA) binding studies with PMI-5 and PMI-6 were done by spectroscopic and theoretical methods. The mesoionic compound PMI-5 is the most promising tyrosinase inhibitor with a noncompetitive inhibitory mechanism and an IC50=124μmolL-1. In accordance with the kinetic profile, molecular docking results show that PMI-5 is able to interact favorably with the tyrosinase active site containing the substrate molecule, L-DOPA, interacting with Val-247, Phe-263 and Val-282 residues. The spectroscopic results for the interaction HSA:PMI-5 and HSA:PMI-6 indicated that these mesoionic compounds can associate with HSA in the ground state and energy transfer can occur with high probability. The binding was moderate, spontaneous and can perturb significantly the secondary structure of the albumin. The molecular docking results suggest that PMI-5 and PMI-6 are able to be accommodated inside the Sudlows site I in HSA, interacting with hydrophobic and hydrophilic amino acid residues.

Synthesis and biological evaluation of N-aryl-2-phenyl-hydrazinecarbothioamides: Experimental and theoretical analysis on tyrosinase inhibition and interaction with HSA

A series of N-aryl-2-phenyl-hydrazinecarbothioamides have been investigated as possible inhibitors of tyrosinase, an enzyme involved in the development of melanomas. The hydrazinecarbothioamides 1-6 were synthesized from the reaction between phenylhydrazine and isothiocyanates, for which three different methods have been employed, namely stirring at room temperature, by microwave irradiation or by mechanochemical grinding. Quantitative yields were obtained for the later technique. Compound 4 showed the best value for tyrosinase inhibition (IC50 = 22.6 µM), which occurs through an uncompetitive mechanism. Molecular docking results suggested that 4 can interact via T-stacking with the substrate L-DOPA and via hydrogen bonding and hydrophobic forces with the amino acid residues Ala-79, His-243, Val-247, Phe-263, Val-282, and Glu-321. The interaction between human serum albumin (HSA) and compound 4 occurs through a ground state association and does not perturb the secondary structure of the albumin as well as the microenvironment around Tyr and Trp residues. The binding is spontaneous, moderate and occurs mainly in the Sudlows site I. Molecular docking results suggested hydrogen bonding, hydrophobic and electrostatic interactions as the main binding forces between the compound 4 and the amino acid residues Lys-198, Trp-214, Glu-449, Leu-452, and Leu-480.