Inhibitory effects of the lichen metabolite lobaric acid on arachidonate metabolism in vitro.

An extract containing phenolic constituents of the lichen Stereocaulon alpinum was shown to exhibit potent in vitro inhibitory effects on arachidonate 5-lipoxygenase from porcine leucocytes. The active component has been identified as the orcinol depsidone lobaric acid (1), which shows dose-dependent inhibitory effects on the enzyme, with an IC(50) value of 7.3 μM. Lobaric acid exhibits approximately 4-fold in vitro selectivity for 5-lipoxygenase as compared to cyclooxygenase.