Chromatographic approaches for the isolation and detection of a new antifungal phenolic compound from lichen Heterodermia leucomelos (L.) Poelt

Context: Chemical exploration from naturally grown lichens provides the basis for identifying novel compounds that can act as a new bio-based product. Aims: To evaluate antifungal metabolites from Heterodermia leucomelos through chromatographic approaches. Methods: Lichen H. leucomelos was collected from Kodagu district, Karnataka, India, and extracted using ethyl acetate, methanol, and acetone solvents. The obtained crude extracts were tested against the pathogenic fungi Fusarium oxysporum and Fusarium solani. Results: Well diffusion assay showed the highest zone of inhibition with 19.6 ± 0.5 mm in the methanol extract against F. oxysporum and 17.0 ± 0.5 mm against F. solani. A minimum inhibitory concentration of 0.0975 mg/mL was observed in the methanol extract, and TLC-bioautography showed an active band at Rf 0.74 in methanol against F. oxysporum. The active compound was isolated and purified using silica gel column chromatography. It was found that Fraction 5 was effective against F. oxysporum and F. solani. Gas chromatography-mass spectroscopic analysis detected the most predominant compound as methyl 2,4-dihydroxy-3,6-dimethylbenzoate (syn. atraric acid). This is the first report where atraric acid has been isolated from the lichen H. leucomelos. Conclusions: The results obtained from this study justify the fact that atraric acid, a phenolic compound, can be a promising source as a natural fungicide that could be exploited for industrial purposes.