Depsides and depsidones, metabolites commonly isolated from lichens, are biosynthesized through esterification of two or more units of orsellinic
or [beta]-methyl orsellinic
Lichen phenolics are mainly monocyclic phenols, depsides, depsidones, dibenzofurans, derived through the acetyl-polymalonly pathway, with mainly orsellinic acid as the basic unit in the biosynthesis.
Of the 17 known secondary metabolites which have shown antidiabetic activity, namely, zeorin, methylorsellinate, methyl-[beta]-orcinol carboxylate, methyl haematommate, orsellinic acid, lecanoric acid, atranorin, sekikaic acid, salazinic acid, gyrophoric acid, usnic acid, lobaric acid, divaricatic acid, gyrophoric acid, ethyl haematomate, ethyl orsellinate, Brialmontin 1 (Table 1), 13 are already reported for their antioxidant potentials (Table 2).
The other compounds such as salazinic acid, gyrophoric acid, sekikaic acid, usnic acid, methyl haematommate, orsellinic acid, lobaric acid, and divaricatic acid have also been reported for both antidiabetic and antioxidant potentials.
 have isolated five 3-alkyl-34- dihydroisocoumarins and one derivative of orsellinic
The depsides (atranorin, diffractaic and lecanoric acids), depsidones (protocetraric, salazinic, hypostictic and norstictic acids), xanthones (lichexanthone and secalonic acid), and usnic acid, as well seven orsellinic acid esters, five salazinic acid 8',9'-0-alkyl derivatives and four lichexanthone derivatives, were evaluated for their activity against Mycobacterium tuberculosis.
In all reactions, orsellinic acid and the corresponding esters 2,4-dihydroxy-6-methylbenzoates (orsellinates), (11-17), were obtained.
The compounds in study, namely: depsides (atranorin (1), diffractaic (3) and lecanoric (6) acids), depsidones (protocetraric (7), salazinic (8), hypostictic (9) and norstictic (10) acids), xanthones (lichexanthone (4) and secalonic acid (5) ) and usnic acid (2), as well the orsellinic acid esters (11-17), salazinic acid derivatives (18-22) and lichexanthone derivatives (23-26), were evaluated against M.
[sup.13]C and DEPT-135 spectra show signals of chemical shift corresponding to alkyl groups ([delta] 13.3-42.8 ppm) and methine carbons at [delta] 105.4, 107.4, 111.8, and 113.2 ppm, indicative of a structure derived from orsellinic
and p-methyl orsellinic
acids and 4-O-methyl derivatives have been shown to inhibit growth in L.
The compounds isolated are derived from orsellinic or [beta]-methyl orsellinic acids.
 employed a [beta]-carotene linoleate model system to demonstrate the moderate antioxidant activity of methyl orsellinate, orsellinic acid, atranorin, and lecanoric acid isolated from Parmotrema stuppeum (Nyl.) Hale.