Ursolic acid, an important bioactive compound, was isolated from ethanol extract of aerial parts of Sambucus australis. In order to develop bioactive ursolic acid derivatives, two semi-synthetic compounds were obtained through modification at C-3. The antibacterial activity of the ursolic acid and its derivatives was investigated. The microdilution method was used for determination of the minimal inhibitory concentration (MIC), against twelve bacterial strains. The influence of ursolic acid and its derivatives on the susceptibility of some bacterial pathogens to the aminoglycosides antibiotics neomycin, amikacin, kanamycin and gentamicin was evaluated. The most representative synergistic effect was observed by 3β-formyloxy-urs-12-en-28-oic acid at the concentration of 64 μg/mL in combination with kanamycin against Escherichia coli (27), a multidrugresistant clinical isolate from sputum, with reduction of MIC value from 128 μg/mL to OPEN ACCESSMolecules 2014, 19 1318 8 μg/mL. Ursolic acid and its derivatives were examined for their radical scavenger activity using the DPPH assay, and showed significant activity.

Eugenol is the major component of clove essential oil and has demonstrated relevant biological potential with well-known antimicrobial and antioxidant action. Therefore, this work carried out the synthesis, purification, characterization, and evaluation of the antioxidant and antibacterial potential of 19 eugenol derivatives. The derivatives were produced by esterification reactions in the hydroxyl group (−OH) of eugenol with different carboxylic acids and also by addition reactions in the double bond of the allyl group. The derivatives had a promising antibacterial potential, including a lower minimum inhibitory concentration of 500 μg/mL than eugenol (1000 μg/mL). In addition, the derivatives were active against bacterial strains (Escherichia coli, Staphylococcus aureus) that eugenol itself showed no activity, thus increasing the spectrum of antibacterial action. As for the antioxidant activity, it was observed that the derivatives that involved esterification reactions in the hydroxyl group (−OH) of the eugenol molecule’s phenol resulted in a significant reduction of the antioxidant action (IC50 > 100 μg/mL) when compared with the eugenol precursor molecule (IC50 = 4.38 μg/mL). On the other hand, the structural changes located in the double bond affected much more smoothly the capacity of capturing radicals than the starting molecule, also being obtained derivatives with proximal antioxidant capacity (IC50 = 19.30 μg/mL) to commercial standards such as Trolox (IC50 = 16.00 μg/mL).Electronic supplementary materialThe online version of this article (10.1186/s13065-018-0407-4) contains supplementary material, which is available to authorized users.

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In order to produce bioactive derivatives of carvacrol and thymol, nine derivatives of each compound were prepared through modifications the phenolic hydroxyl group. The structures of compounds were confirmed by spectral data from MS, IR and NMR. Carvacrol, thymol and derivatives were submitted to the evaluation of the inhibition of the enzyme acetylcholinesterase, using a colorimetric method in which the inhibition of the enzyme is measured by coloration, and larvicidal activity against Aedes aegypti. Derivatives carvacryl acetate-1b and thymyl hexanoate-2b showed the best results for the inhibition of the acetylcholinesterase enzyme, and for the larvicidal activity the derivatives 1a, 1b, 1c, 3h, 2a, 2b, 2c and 4h showed positive results, emphasizing compound thymyl 4-methoxybenzoate-4h which showed LC 50 values of 23.60 ppm, considered a very good result.

Chemical investigation of the ethanol extract of propolis allowed the isolation of 2'-hydroxy-4',7-dimethoxyisoflavan (1) 2',7-dihydroxy-4'-methoxyisoflavan (2) 2',4'-dihydroxy-7-methoxyisoflavan (3), 4',7-dihydroxy-2'-methoxyisoflavan (4) 2',4',4-trihydroxychalcone (5) and lup-20(29)-en-3-ol (6). The structures of compounds were identified based on their spectral data and by comparison with the literature. It was performed test to evaluate antioxidant activity by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method of the ethanol extract and its fractions obtaining significant results similar to Vitamin C. It was also evaluated anticholinesterase activity, observing promising results with the extract and fractions. Being the red propolis of these activities, it can be used in the treatment of degenerative diseases such as Alzheimer. There are already records of propolis as an antioxidant, however, the activity of anticholinesterase is being cited for the first time.