Determination of usnic and perlatolic acids and identification of olivetoric acids in Northern reindeer lichen (Cladonia stellaris) extracts

摘要

The ecologically important lichen Cladonia stellaris forms thick carpets in boreal forest floors. In addition to affecting temperature and water conditions in the soil underneath, the secondary metabolites formed by the lichen layer are of ecological interest. In this paper, we investigated the distribution of lichen acids in C. stellaris collected at different latitudes in Finland and developed methods to quantify the two optical enantiomers of usnic acid separately. The lichen extracts were analysed by high-performance liquid chromatography (HPLC) with UV and mass spectrometric (MS) detection and by gas chromatography with flame ionization (GC-FID) and MS detection. Usnic acid and perlatolic acid were quantified using GC-FID. The concentration of usnic acid in the top 20 mm of the lichen thallus ranged from 0.48-3.08% of dry weight, and that of perlatolic acid from 0.08-0.54%. The enantiomeric composition of usnic acid was determined using a chiral HPLC column coupled to an electrospray ionization-tandem mass spectrometer. (-)-Usnic acid was found to be the predominating enantiomer in all extracts; the proportion of (+)-usnic acid ranged from 0.4%-10.0%. Olivetoric acid methyl ester, diphenylmethanol, and 5-pentylresorcinol were identified, and several other olivetoric acid-type compounds were tentatively identified in the extracts.