In vitro susceptibility of Helicobacter pylori to protolichesterinic acid from the lichen Cetraria islandica.

With reference to the traditional use of Cetraria islandica (Iceland moss) for relief of gastric and duodenal ulcer, plant extracts were screened for in vitro activity against Helicobacter pylori. (+)-Protolichesterinic acid, an aliphatic alpha-methylene-gamma-lactone, was identified as an active component. The MIC range of protolichesterinic acid, in free as well as salt form, was 16 to 64 micrograms/ml.

In vitro inhibition of 5-lipoxygenase by protolichesterinic acid from Cetraria islandica.

The aliphatic α-methylene-γ-lactone (+)-protolichesterinic acid (1), isolated from Cetraria islandica, has been shown to exhibit inhibitory effects on the enzyme 5-lipoxygenase in an in vitro assay in which porcine leucocytes are used as a source of the enzyme system. The isomeric compounds (+)-lichesterinic acid (2) and (-)-lichesterinic acid (4), prepared from (+)-protolichesterinic- and (-)-allo-protolichesterinic acids, respectively, exhibited anti-5-lipoxygenase activity of the same order of magnitude. (+)-Methyl lichesterinate (3) was, however, inactive. It was shown that despite its lipophilic nature, protolichesterinic acid is extractable into an aqueous medium, the concentration being dependent on the length of extraction.