For this work, a hydroalcoholic extract was prepared from the aerial parts of the Malvaviscus arboreus (Malvaceae) species, popularly known as hibisco-colibri in Brazil; and then, investigated by infrared and NMR spectroscopy. A class of special metabolites containing a porphyrin skeleton and pyrrole units was determined by typical absorption spectra, mainly 1H and 13C NMR, thus indicating the capability of showing anti-corrosion effect. Therefore, the M. arboreus extract was examined as a corrosion inhibitor for AISI 1020 carbon steel in H2SO4 1 mol L-1, using a mass loss (gravimetric) technique. Results showed good corrosion inhibition efficiency, at both time and temperature variation. The maximum efficiency observed at 500 ppm was 97.5%, at 3 h, 24 h and 48 h. The surface morphology was analyzed by scanning electron microscopy (SEM), through which a higher homogeneity was observed in the presence of the M. arboreus extract. The hydroalcoholic extract of hibisco-colibri can be considered an efficient green agent for preventing corrosion.

Dezenove dialquilfosforilidrazonas com diferentes substituintes no anel aromático foram avaliadas como inibidores potenciais de tirosinase, que poderiam ser usadas como agentes eficientes no controle de desordens de pigmentação. A atividade inibitória foi medida através de uma modificação do método de UV-Vis de Patil e Zucker. Os ensaios foram realizados com soluções contendo tampão fosfato, L-3,4-diidroxifenilalanina (L-DOPA), EDTA, tirosinase e diferentes concentrações de compostos organofosforados e a formação de dopacromona foi determinada através do monitoramento da absorvância a 475 nm. Três compostos foram os mais ativos da série (CI50 = 105 ± 20 µmol L-1), (CI50 = 127 ± 16 µmol L-1) e (CI50 = 188 ± 27 µmol L-1), sendo de 3 a 7 vezes mais ativos do que o ácido ascórbico (CI50 = 730 µmol L-1), utilizado como controle. O composto mais ativo é apenas 1,5 vezes menos ativo do que o ácido kójico (IC50 = 69,4 µmol L-1), que é utilizado comercialmente. Esta investigação pode levar à descoberta de agentes potentes contra importantes desordens de pigmentação inclusive a hiperpigmentação.

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.

The phytochemical investigation of the roots of Piptadenia rigida Benth., Fabaceae, known as "angico", afforded sitosterol, lupeol, betuline, the chalcone isoliquiritigenin, the flavonoids, 7,4'-dihydroxyflavone, 7,3',4'-trihydroxyflavone, 7,8,3',4'-tetrahydroxyflavanone, 4-hydroxy-3,5-dimethoxybenzaldehyde and methyl-3,4-dihydroxy-benzoate. Both flavones were also isolated from the branches of this plant. Five derivatives of the aldehyde were obtained by diazomethane treatment. The structures of compounds were identified by IR, NMR and mass spectral data analysis of natural compounds and some derivatives, and by comparison with literature data.

O fracionamento cromatográfico dos extratos orgânicos das folhas e galhos de Luxemburgia nobilis (Ochnaceae) forneceu o sitosterol, sitosterol-3-O-betaD-glicopiranosil, friedelina, friedelinol, a mistura dos triterpenos lupeol, alfa-amirina e beta-amirina, rutina, epicatequina, uma mistura de duas chalconas, isoliquiritigenina e 3'-hidróxiisoliquiritigenina, duas biflavonas conhecidas, amentoflavona e robustaflavona além de uma biflavona nova, 5,7,4'-triidróxiflavona-(3'-O-4"')-5",7" -diidróxiflavanona. As estruturas foram definidas através dos dados espectrométricos 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-betaD-glucopyranoside, friedelin, friedelinol, a mixture of triterpenes lupeol, alpha-amyrin and beta-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'-O-4'")-5",7"-dihydroxyflavanone. The structures were established from spectral data, including 2D-NMR experiments of the natural substances and of the acetyl and methyl ether derivatives of the new biflavone.

O fracionamento cromatográfico do extrato hexânico dos galhos de Luxemburgia nobilis (Ochnaceae) forneceu beta-sitosterol, estigmasterol, ácido betulínico, os ácidos graxos hexadecanóico, tetraeicosanóico, hexaeicosanóico e linoleico, 14-metilpentadecanoato de metila, óxido de 13-epimanoíla, o depsídeo atranorina (1), e dois triglicerídeos novos (2 e 3). As estruturas das substâncias isoladas foram determinadas através da análise dos dados espectroscópicos de I.V., massas e RMN de ¹H e de 13C incluindo comparação com dados da literatura. A análise do espectro de massas (FAB-MS) dos éteres tiometílicos (4 e 5) foi usada para definir as estruturas dos triglicerídeos.

Chromatographic fractionation of the hexane extract from the branches of Luxemburgia nobilis (Ochnaceae) afforded beta-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.