Gentil J. Vidotti

Reaction of Glycidyl Methacrylate at the Hydroxyl and Carboxylic Groups of Poly(vinyl alcohol) and Poly(acrylic acid): Is This Reaction Mechanism Still Unclear?

Transesterification and epoxide ring-opening reactions are two mechanism routes that explain chemical modifications of macromolecules by glycidyl methacrylate (GMA). Although the coupling reaction of the GMA with macromolecules has widely been investigated, there are still mechanisms that remain to be explained when GMA is processed in an aqueous solution at different pH conditions. To this end, reaction mechanisms of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAAc) by GMA in water in acidic and basic conditions were investigated thoroughly. The presence of hydroxyl groups in PVA and carboxyl groups in PAAc allowed for a better evaluation of the reaction mechanisms. The analysis of the (1)H and (13)C NMR spectra clearly demonstrated that the chemical reactions of GMA with carboxyl groups and alcohols of the macromolecules in an aqueous solution are dependent on pH conditions. At pH 3.5, the GMA reacts with both the carboxylic and the hydroxyl groups through an epoxide ring-opening mechanism. At pH 10.5, the GMA undergoes a hydrolysis process and reacts with hydroxyl groups by way of both the transesterification and the epoxide ring-opening mechanisms, whereas the ring-opening reaction is the preferential pathway.

Antitrypanosomal Activity of Novel Benzaldehyde- Thiosemicarbazone Derivatives from Kaurenoic Acid †

A series of new thiosemicarbazones derived from natural diterpene kaurenoic acid were synthesized and tested against the epimastigote forms of Trypanosoma cruzi to evaluate their antitrypanosomal potential. Seven of the synthesized thiosemicarbazones were more active than kaurenoic acid with IC50 values between 2-24.0 μM. The o-nitro-benzaldehyde-thiosemicarbazone derivative was the most active compound with IC50 of 2.0 μM. The results show that the structural modifications accomplished enhanced the antitrypanosomal activity of these compounds. Besides, the thiocyanate, thiosemicarbazide and the p- methyl, p-methoxy, p-dimethylamine, m-nitro and o-chlorobenzaldehyde-thiosemicarbazone derivatives displayed lower toxicity for LLMCK2 cells than kaurenoic acid, exhibing an IC50 of 59.5 μM.

Triterpenic acids from Eugenia moraviana

A novel triterpene, characterized as 6a-hydroxybetulinic acid, was isolated from the leaves and stems of Eugenia moraviana (Myrtaceae), known in Brazil as Cambui, together with three known compounds, platanic acid, betulinic acid and b-sitosterol. Unequivocal 1H and 13C assignments of 6a-hydroxybetulinic acid (3b,6a-dihydroxy-20(29)-lupen-28-oic acid) and platanic acid were undertaken by spectral analysis including NOE and 2 D NMR experiments.

Qualitative determination of indole alkaloids of Tabernaemontana fuchsiaefolia (Apocynaceae)

This paper describes a fast and efficient procedure to separate and identify indole alkaloids from the ethanolic extract of Tabernaemontana fuchsiaefolia (Apocynaceae). The alkaloidal fractions obtained from ethanolic extracts of leaves and stem barks and root barks were fractioned and analyzed by Thin-Layer Chromatography (TLC) and by Gas Chromatography coupled to Mass Spectrometry (GC-MS). The following indole alkaloids were identified: ibogamine, coronaridine, ibogaine pseudoindoxyl, voacangine hydroxyindolenine, voacangine pseudoindoxyl, tabernanthine, catharanthine, voacangine, 19-oxovoacangine, 10-hydroxycoronaridine, affinisine, 16-epi-affinine, voachalotine, ibogaline, and conopharyngine.

Estudo fitoquímico e avaliação da atividade moluscicida da Kielmeyera variabilis Mart (Clusiaceae)

Methanol extract obtained from Kielmeyera variabilis stems showed significant molluscicidal activity against Biomphalaria glabrata. The phytochemical studies of the plants stem to the isolation of three xanthones (assiguxanthone-B, kielcorin and 1,3,5,6-tetrahtydroxy-2-prenylxanthone) and a organic acid (2,5-dihydroxy benzoic acid). The structures of these compounds were identified by IR, MS, 1H and 13C NMR spectral analysis and comparison with literature data.

Anti-inflammatory and Antioxidant Activities of Randia Hebecarpa. and Major Constituents

Abstract The methanol extract of Randia hebecarpa. Benth. (Rubiaceae) leaves was evaluated for anti-inflammatory activity using carrageenan- and dextran-induced rat paw edema models. Antioxidant activities of the methanol extract and of the fractions resulting from its partition were also measured using the 1,1-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay and the linoleic acid peroxidation method. The methanol extract, ethyl acetate fraction, and hydromethanol fraction exhibited percent inhibition of lipid peroxidation comparable to that of commercial antioxidant butylated hydroxytoluene (BHT). Fractionation of the ethyl acetate and hydromethanol fractions through chromatographic methods yielded kaempferol-3, 7-O.-α.-L-dirhamnoside, kaempferol-3-O.-β.-D-galactoside, quercetin-3-O.-β.-D-galactoside, myricetin-3-O.-α.-L-rhamnoside, kaempferol-3-O.-α.-L-rhamnosyl-(1 → 6)-β.-D-galactosyl-7-O.-α.-L-rhamnoside, quinovic acid-3-O.-β.-D-quinovopyranosil-28-O.-β.-D-glucopyranoside, cincholic acid 3-O.-β.-D-quinovopyranosil-28-O.-β.-D-glucopyranoside, and the sugar D-mannitol.

Iridoid glucosides from Bouchea fluminensis

Abstract From the aerial parts of Bouchea fluminensis , a new iridoid glucoside, named boucheoside, along with four known iridoid glucosides, lamiide, lamiidoside, durantoside II, and duranterectoside C, were isolated. The structure of the new compound was elucidated based on the spectroscopic evidence.

Evaluation of the molluscicidal and Schistosoma mansoni cercariae activity of Croton floribundus extracts and kaurenoic acid.

Lethality of the extracts of Croton floribundus (Euphorbiaceae), a medicinal plant from south Brazil, and of the kaurenoic acid, an isolated compound, and two of its derivatives against adult Biomphalaria glabrata snails, Schistosoma mansoni cercariae and Artemia salina Leach. brine shrimp larvae are reported. Both extracts and the isolated compound showed significant molluscicidal and cercaricidal activities and reduced toxicity in brine shrimp assays.

Estudo fitoquímico e avaliação da toxicidade frente a Artemia salina e da atividade antimicrobiana de Calycorectes psidiiflorus (O. Berg) Sobral, Myrtaceae

The phytochemical study of Calycorectes psidiiflorus (O. Berg) Sobral leaves resulted in isolation and identification of the sesquiterpene 8-hydroxycalamenene (1), triterpenes α-amyrin (2a) and β-amyrin (2b), flavonoid 3-O-α-rhamnopyranosyl-7-O-β-glucopyranosyl kaempferol (3), and of the alkaloid 1,2,3,4-tetrahydro-1-methyl-β-carboline (4). The structures of the isolated compounds were elucidated based on their spectroscopic NMR data and comparison with those reported in literature. Substance 1 presented antibacterial (MIC = 7.8 µg/mL) and antifungal (MIC = 15.6 µg/ mL) activities.

Some kinetic parameters of the degradation of natural rubber induced by chloranil and iron (III) chloride, in solution

The degradation of natural rubber (NR) induced by chloranil and FeCl3, in solution, was investigated by efflux time measurements and by FTIR and 1H NMR spectroscopies. GC–MS was used to investigate the influence of chloranil on residues generated during thermal degradation of NR. 2-Methyl-2-butene (MB) was used as a model compound for the reactions. The results show that the reaction occurs by the scission of the double bond. The reactions were characterised by second-order kinetics, independent of the catalyst. The rate constants determined from efflux time data show a strong contribution of the physical entanglements: if the reactants are diluted 10-fold the value of the rate constant decreases significantly. Thus, the rate constants were more realistically calculated from the changes in the CC concentration measured by 1H NMR. The rate constants for the reaction of MB and chloranil (or FeCl3) are lower than for the corresponding NR degradation. The presence of chloranil does not alter the chromatogram profile obtained by GC–MS for the thermal degradation of NR. It is concluded that chloranil decreases the activation parameters for the degradation because the degradation products are the same as those obtained thermally in absence of chloranil. Activation parameters such as energy, enthalpy, entropy and Gibbs energy were determined. Activation energies (in kJ mol−1) for the degradation of NR are 60.1 for NR/chloranil and 41.9 for NR/FeCl3. From the values of activation parameters, it was suggested that the activation step of the reaction induced by chloranil is more thermally dependent than the reaction induced by FeCl3 that, otherwise, is more entropically dependent.