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Semisynthetic phenol derivatives were obtained from the natural phenols: thymol, carvacrol, eugenol, and guaiacol through catalytic oxychlorination, Williamson synthesis, and aromatic Claisen rearrangement. The compounds characterization was carried out by H NMR,C NMR, and mass spectrometry. The natural phenols and their semisynthetic derivatives were tested for their antimicrobial activity against the bacteria: Staphylococcus aureus, Escherichia coli, Listeria innocua, Pseudomonas aeruginosa, Salmonella enterica Typhimurium, Salmonella enterica ssp. enterica, and Bacillus cereus. Minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values were determined using concentrations from 220 to 3.44 μg mL. Most of the tested compounds presented MIC values ≤220 μg mL for all the bacteria used in the assays. The molecular properties of the compounds were computed with the PM6 method. Through principle components analysis, the natural phenols and their semisynthetic derivatives with higher antimicrobial potential were grouped.

Six nostoclide analogues were synthesised from 3-benzyl-2(5H)-furanone in one step, with yields ranging from 10 to 71%, and subjected to several biological assays. The two most active of these, 5d and 5e, were shown to be phytogrowth inhibitors of the radicle of Lolium multiflorum Lam, while enhancing the root growth of Physalis ixocarpa Brot. Both compounds inhibited electron flow (basal, phosphorylating and uncoupled) from water to methylviologen (MV); both acted as Hill reaction inhibitors, since the synthesis of ATP was prevented. The uncoupled electron transport from photosystem II (PSII) (water to 2,6-dichlorophenol-indophenol (DPIP)) and photosystem I (PSI) (2,6-dichlorophenol-indophenol reduced (DPIPred) to MV) was inhibited with 500 microM of 5d by 22 and 14% respectively. In addition, 400 microM of 5d inhibited PSI (from tetramethyl-p-benzohydroquinone (TMQH(2)) to MV) by 40%. Thus 5d inhibited electron transport at the b(6)f complex. Finally, 500 microM of 5e inhibited electron flow (basal and phosphorylating) by 25%, and 300 microM of 5e enhanced light-activated membrane-bound Mg(2+)-ATPase by 66%. Thus 5e behaved as a weak Hill reaction inhibitor and an uncoupler. In general, the phytotoxicity of the synthetic lactones was only weakly related to inhibition of photosynthesis.

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