In order to obtain new compounds with antibacterial activity, the derivatives 2,4-dihydroxy-6-methylbenzoic acid (orsellinic acid) and 2,4-dihydroxy-6-methylbenzoates (orsellinates) were obtained through alcoholyses of lecanoric acid. All these substances were tested against Gram-positive and Gram-negative bacteria by a microdilution method. Staphylococcus aureus, Xanthomonas campestris var. vesicatoria and Ralstonia solanacearum were most sensitive to n-propyl 2,4-dihydroxy-6-methylbenzoate, n-pentyl 2,4-dihydroxy-6-methylbenzoate and n-hexyl 2,4-dihydroxy-6-methylbenzoate with MIC (Minimal Inhibitory Concentration) values ranging from 62.5 to 7.8 µg⋅mL -1 . These results showed that homologation in carbon chain may lead to compounds with more pronunced activities.

The series of 2,4-dihydroxy-6-methylbenzoates 2-10 (methyl to hexyl orsellinates) prepared by alcoholysis of lecanoric acid (1) - a natural product from the lichen Parmotrema tinctorum (Nyl.) Hale - was submitted to the brine shrimp lethality test (BST), which was also performed for 2,4-dihydroxy-6-methylbenzoic acid (11) (orsellinic acid) and the derivative ethyl-2-hydroxy-4-methoxy-6-methylbenzoate (12) (4-methoxy-ethyl orsellinate), in order to detect new substances with probable antineoplasic activity. Results showed that chain elongation - increase in lipophilicity (log P) - causes a rise in the cytotoxic activity of orsellinates. Hexyl orsellinate (7) showed the highest cytotoxic activity (LC50 = 31 μм). A correlation between lipophilicity (log P) and cytotoxic activity (log 1/LC50) is presented. Compounds with ramified chains - iso-propyl, sec-butyl and tert-butyl orsellinates (8-10) - were less active than those with the correspondent linear chain. The activities presented by 4-methoxy-ethyl orsellinate (12) and ethyl orsellinate (3) suggest that the hydroxy group at the C-4 position causes effect in the cytotoxic activity of orsellinates against Artemia salina.

de peróxido de hidrogênio e óxido nítrico". Os efeitos dos compostos isolados de líquens brasileiros e seus derivados na produção de NO e H 2 O 2 foram estudados utilizando macrófagos murinos na tentativa de desvendar suas possíveis propriedades imunomodulatórias. A citotoxicidade dos compostos foi estudada utilizando o ensaio de MTT. A estimulação dos macrófagos foi avaliada através da determinação de NO (metodologia de Griess) e H 2 O 2 (peroxidase de raíz forte/vermelho de fenol) no sobrenadante de culturas de macrófagos peritoneais de camundongos Swiss. Este estudo demonstrou atividade estimulante de alguns compostos fenólicos e seus derivados na produção de NO e H 2 O 2 . A relação estrutura atividade sugere inúmeras direções sintéticas para futuros melhoramentos da atividade imunológica.Unitermos: líquens, peróxido de hidrogênio, óxido nítrico, macrófagos, compostos fenólicos. ABSTRACT:The effects of isolated compounds from Brazilian lichens and their derivatives on H 2 O 2 and NO production were studied using murine macrophages as a part of an attempt to understand their possible immunomodulatory properties. The compound cytotoxicity was studied using MTT assay. Macrophage stimulation was evaluated by the determination of NO (Griess assay) and H 2 O 2 (horseradish peroxidase/phenol red) in supernatants of peritoneal macrophage cultures of Swiss mice. This research demonstrated stimulatory activities of some phenolic compounds isolated from lichens and their derivatives on H 2 O 2 and NO production. Structure-activity relationships suggest several synthetic directions for further improvement of immunological activity.

With the aim of obtaining new compounds with potential antifungal activity, lecanoric acid, a chemical constituent of the lichen Parmotrema tinctorum and its derivatives prepared from structural modification were tested against the fungus Cladosporium sphaerospermum, by employing the bioautographic method. Activity of the derivatives ranged from 10- to 1-μg concentrations. Results demonstrated this series of compounds to have potent fungitoxic activity