Vinitha M. Thadhani

Antioxidant activity of some lichen metabolites.

Antioxidant activity of several classes of lichen metabolites were assessed in the in vitro superoxide radical (SOR), nitric oxide radical and 2,2-diphenyl-1-picrylhydrazil radical scavenging assays. The despsides sekikaic acid and lecanoric acid showed promising antioxidant activity in SOR assay with IC50 values of 82.0 ± 0.3 µmol and 91.5 ± 2.1 µmol, respectively, while the depsidone lobaric acid exhibited an IC50 value of 97.9 ± 1.6 µmol, all relative to the standard, propyl gallate (IC50 = 106.0 ± 1.7 µmol). One of the most abundant mononuclear phenolic compounds, methyl-β-orcinol carboxylate was found to be a potent NO scavenger (IC50 = 84.7 ± 0.1 µmol), compared to the standard rutin (IC50 = 86.8 ± 1.9 µmol).

Rapid identification of lichen compounds based on the structure–fragmentation relationship using ESI-MS/MS analysis

Lichens are symbiotic composites of algae and fungi which produce characteristic secondary metabolites of interest. This study, based on negative mode electrospray quadrupole time-of-flight mass spectrometry (ESI-Qq-TOF-MS/MS), reveals the structure–fragmentation relationship of ten metabolites belonging to various chemical classes such as monocyclic phenols, depsides, depsidones and dibenzofurans. Low energy collision induced dissociation tandem mass spectrometric analysis of these deprotonated molecules yielded key fragments due to the loss of neutral components like CO, CO2, methanol, ethanol, and ethene. Interestingly, odd electron fragments were also observed in sekikaic acid, lobaric acid, and usnic acid as characteristic fragments. The fragmentation pattern of standard compounds, high resolution analysis and database were used for the rapid identification of compounds in lichen species, Parmotrema grayana and Heterodermia obscurata. Furthermore MS/MS spectra revealed different fragmentation pathways for different classes of secondary metabolites. In total fifteen compounds were identified from the methanolic and dichloromethane extracts of Parmotrema grayana and Heterodermia obscurata.

Novel entry into 5-decarboxydibenzofurans via Smiles rearrangement of the lichen para-depside, erythrin

Erythrin, isolated in 7.3% yield from the lichen Roccella montagnei, was converted via a Smiles rearrangement to a series of diphenyl ethers. Those with a free carboxylic acid at C-1 underwent a novel decarboxylative oxidative cyclisation in the presence of Pd(OAc)2 to produce 5-decarboxydibenzofurans. All compounds were assayed for their antioxidant and β-glucuronidase enzyme inhibitory activity.

Potential of Lichen Compounds as Antidiabetic Agents with Antioxidative Properties: A Review

The advancement in the knowledge of potent antioxidants has uncovered the way for greater insight in the treatment of diabetic complications. Lichens are a rich resource of novel bioactive compounds and their antioxidant potential is well documented. Herein we review the antidiabetic potential of lichens which have received considerable attention, in the recent past. We have correlated the antidiabetic and the antioxidant potential of lichen compounds. The study shows a good accordance between antioxidant and antidiabetic activity of lichens and points out the need to look into gathering the scarce and scattered data on biological activities for effective utilization. The review establishes that the lichen extracts, especially of Parmotrema sp. and Ramalina sp. have shown promising potential in both antidiabetic and antioxidant assays. Ubiquitous compounds, namely, zeorin, methylorsellinate, methyl-β-orcinol carboxylate, methyl haematommate, lecanoric acid, salazinic acid, sekikaic acid, usnic acid, gyrophoric acid, and lobaric acid have shown promising potential in both antidiabetic as well as antioxidant assays highlighting their potential for effective treatment of diabetic mellitus and its associated complications. The available compilation of this data provides the future perspectives and highlight the need for further studies of this potent herbal source to harvest more beneficial therapeutic antidiabetic drugs.

Sensitive analysis of bioactive secondary metabolites in lichen species using liquid chromatography–mass spectrometry

HIGHLIGHTSA Sensitive LC–MS method was developed based on MRM approach.Total 9 metabolites were quantified in eight lichen species.Metabolites 1 and 3 were present in highest concentration in analysed lichen species. ABSTRACT Lichens are a large group of valuable lower plants with unique features and diverse applications worldwide such as in medicine, cosmetics, food, and textile industries. They are also well known for their potential in observing climate and environmental monitoring. Their successful exploitations require reliable analytical methods to check and maintain quality and efficacy of the products based on them. This study focuses on the development of a sensitive and reliable quantification method for the analysis of important depsides, depsidones, dibenzofuran and monocyclic phenols inseven known and an unidentified lichen species. Multiple Reaction Monitoring (MRM) approach using UHPLC‐QqQ‐MS instrument was employed for the development of the quantitative method. Both LC and MS parameters were optimized to ensure maximum separation. High sensitivity, and selectivity. LODs and LOQs were found to be in the range of 2.1–71.5 ng/mL and 6.3–212.9 ng/mL, respectively. The accuracy (% bias) and precision (% RSD) were found to be <5% in most cases. Metabolites 1–9 were found in the range of 0.5–41429 &mgr;g/g in the analysed lichen extracts. The analysis revealed that metabolites 1, 2 and 3 are the predominant ones. This method can be used for the identification and absolute quantification of secondary metabolites in lichen extracts, and herbal or consumer products based upon them.