Hypoprotocetraric acid

A chemical study of the lichen Ramalina siliquosa complex found in Brittany was conducted. Eight chemotypes were considered and their chemical composition was elucidated for the first time by LC-MS analysis. Ten main compounds were identified: conhypoprotocetraric acid (1), salazinic acid (2), peristictic acid (3), cryptostictic acid (4), protocetraric acid (5), stictic acid (6), norstictic acid (7), hypoprotocetraric acid (8), 4-O-demethylbarbatic acid (9), (+)-usnic acid (10) and 22 minor compounds were reported. The MS/MS fragmentation patterns of each compound of R. siliquosa complex were determined and proposed.

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.