The Chemistry and Allelopathic Effects of Phenolic Compounds from the Lichen Evernia prunastri (L.) Ach.

Abstract

Fifteen biogenetically-related phenolic substances were obtained from the lichen Evernia prunastri: orsellinic acid, everninic acid, methyl everninate, ethyl everninate, methyl di-O-methylorsellinate, evernic acid, methyl 2’-O-methyl lecanorate, methyl β-orsellinate, methyl hematomate, ethyl hematomate, evernin, atranorin, 2,2’-di-O-methylgyrophoric acid, prunastrin, and (+)-usnic acid. Seven were found for the first time in this species and three (methyl 2’-O-methyl lecanorate, 2,2’-di-O-methylgyrophoric acid and prunastrin) have never been reported before. New physicochemical data were recorded for all compounds. Chemical/HPLC chromatographic correlation detected the two monocyclic fragments of evemic acid, the unstable orsellinic and everninic acids in the acetone extract of the lichen. A mixture of all the phenolic substances from E. Prunastri,known as “Evemal”, was applied to cabbage, green pepper and tomato seedlings, at both steady and alternant (night/day) temperatures and it was observed that although some seeds were more resistant than others, a 2.0% concentration of the phenolic fraction totally inhibited seed germination at 20 °C, while germination with less than 2% concentrations produced a sickly crop which withered after a few days. LD50 (in % w/w evernal) were 0.31 for cabbage, 0.37 for tomato and 1.80 for peppers. Sharp, regular drops in temperature increased the allelopathic activity by 61–65%, so that the LD50 (in % w/w evernal) fell to 0.22 for cabbage and 0.66 for peppers.