Lepraric acid

Introduction: Lichens are self-sustaining partnerships comprising fungi as shape-forming partners for their enclosed symbiotic algae. They produce a tremendous diversity of metabolites (1050 metabolites described so far). Objectives: A comparison of metabolic profiles in nine lichen species belonging to three genera (Lichina, Collema and Roccella) by using an optimised extraction protocol, determination of the fragmentation pathway and the in situ localisation for major compounds in Roccella species. Methods: Chemical analysis was performed using a complementary study combining a Taguchi experimental design with qualitative analysis by high-performance liquid chromatography coupled with mass spectrometry techniques. Results: Optimal conditions to obtain the best total extraction yield were determined as follows: mortar grinding to a fine powder, two successive extractions, solid:liquid ratio (2:60) and 700 rpm stirring. Qualitative analysis of the metabolite profiling of these nine species extracted with the optimised method was corroborated using MS and MS/MS approaches. Nine main compounds were identified: 1 β-orcinol, 2 orsellinic acid, 3 putative choline sulphate, 4 roccellic acid, 5 montagnetol, 6 lecanoric acid, 7 erythrin, 8 lepraric acid and 9 acetylportentol, and several other compounds were reported. Identification was performed using the m/z ratio, fragmentation pathway and/or after isolation by NMR analysis. The variation of the metabolite profile in differently organised parts of two Roccella species suggests a specific role of major compounds in developmental stages of this symbiotic association. Conclusion: Metabolic profiles represent specific chemical species and depend on the extraction conditions, the kind of the photobiont partner and the in situ localisation of major compounds.

Hypoxylon aeruginosum (Xylariaceae), an infrequently encountered predominantly tropical pyrenomycete, of which two varieties are known to science, is characterised by having a cyan blue stromatal surface or subsurface. In the course of our ongoing chemotaxonomic evaluation of the Xylariaceae, specific profiles of H. aeruginosum were observed by high performance liquid chromatography, coupled with diode array detection and mass spectrometry (hplc-DAD/MS). By comparison with an authentic standard, lepraric acid and several yet unidentified metabolites with similar hplc-DAD/MS characteristics were detected in the stromata of the type material and other specimens of this species. Interestingly, lepraric acid was hitherto only known from lichenised ascomycetes. Hypoxylon aeruginosum, which is here reported first from Africa and Asia, contained none of the metabolites that were previously detected in other Xylariaceae, except for stromata growing hyperparasitically on other Hypoxylon species. A different lepraric acid derivative was also detected in the type specimen of Chlorostroma subcubisporum, which differs from H. aeruginosum by having a green stromatal surface, cuboid ascospores, and in lacking an amyloid ascal apical apparatus. A second species of Chlorostroma, which showed essentially the same metabolite profile as H. aeruginosum, is described from Thailand. We conclude that Chlorostroma and H. aeruginosum are closely related. However, no taxonomic conclusions are drawn from these findings because no cultures have so far become available to study their anamorphic morphology, their secondary metabolites in culture, and their molecular phylogeny. Taxonomic novelty: Chlorostroma cyaninum Læssøe, Srikitikulchai & J. Fournier, sp. nov.

The oral bacteria not only infect the mouth and reside there, but also travel through the blood and reach distant body organs. If left untreated, the dental biofilm that can cause destructive inflammation in the oral cavity may result in serious medical complications. In dental biofilm, Streptococcus gordonii, a primary oral colonizer, constitutes the platform on which late pathogenic colonizers like Porphyromonas gingivalis, the causative agent of periodontal diseases, will bind. The aim of this study was to determine the antibacterial activity of eleven natural lichen compounds belonging to different chemical families and spanning from linear into cyclic and aromatic structures to uncover new antibiotics which can fight against the oral bacteria. The compounds were screened by broth microdilution assay. Three compounds were shown to have promising antibacterial activities where the depsidone core with certain functional groups constituted the best compound, psoromic acid, with the lowest MICs=11.72 and 5.86μg/mL against S. gordonii and P. gingivalis, respectively. The compounds screened had promising antibacterial activity which might be attributed to some important functional groups as discussed in our study. The best compounds did not induce the death of gingival epithelial carcinoma cells (Ca9-22). These results introduce new compounds having potent antibacterial activities against oral pathogens causing serious medical complications.