Lichens produce phenolic compounds, such as depsides, depsidones, dibenzofuranes, usnic acids, depsones and others. Many of them are exclusive of lichens.1) These substances, as well as their derivatives obtained by structural modification, have shown an ample variety of pharmacological activities: antibiotic, antimycobacterial, antiviral, antitumour, analgesic, antipyretic and enzyme inhibitory.2-5) Although these activities continue to be investigated, both in lichen extracts and with pure substances, a number of others have been attributed to the compounds produced by lichens, such as anti-human immunodeficiency virus (anti-HIV) 6) and anti-herpes simplex virus 1 (anti-HSV-1).
7)Numerous studies on the biological activities of phenols have indicated that these substances are also potent antioxidants and free radical scavengers. 8) Although the free radicals perform an important role in the organism, their cumulative effects can promote the initiation and/or progression of several diseases, including atherosclerosis, inflammation, cancer, cardiovascular diseases, ischaemia, aging and other degenerative diseases. [9][10][11] The antioxidants are of interest in the treatment of several cellular degenerations, and they inhibit or delay the oxidation process by blocking the initiation or propagation of oxidizing chain reactions. 12) They are also used to preserve food by retarding rancidity, discoloration, or deterioration due to autoxidation.13) Due to the importance of antioxidants, many researches have been carried out with plants of several families and with simple phenolic substances, like those of the hydroxycinnamates group and the gallic acid derivatives. [14][15][16][17] Although the lichens are an important source of phenolic substances, studies of antioxidant activity with this group are more recent, and they have been performed mainly with extracts of some species. 12,[18][19][20][21] We have investigated lichens from the "cerrado" of the Mato Grosso do Sul State, in Brazil, through the isolation, structural elucidation, structural modifications and evaluation of biological activities of phenolic substances. The lecanoric acid isolated from the lichen Parmotrema tinctorum, and the orsellinates obtained through reactions of this acid with alcohols were evaluated against Artemia salina and microorganisms. [22][23][24] In continuing our investigations, we are relating here the results of the antioxidant activity of the lecanoric acid (1), orsellinic acid (2) and the methyl (3), ethyl (4), n-propyl (5), n-butyl (6), iso-propyl (7), sec-butyl (8) and tert-butyl (9) orsellinates. With the aim of establishing a qualitative correlation structure-activity we have also included the antioxidant activity of orcinol (10), resorcinol (11) and gallic acid (12).
Results and Discussion2,2-Diphenyl-1-picrylhydrazyl (DPPH) Radical-Scavenging Activity Antioxidants are closely related to their biofunctionalities, such as the reduction of chronic diseases like DNA damage, mutagenesis, carcinogenesis and inhibition of pathog...
