Secondary metabolites from lichen Usnea longissima and its pharmacological relevance

Abstract

The objective of the study was to isolate chemical compounds from lichen Usnea longissima (UL) and to use lichen metabolites as antibiotics, antifungal, anti-HIV, anticancer, antiprotozoan, and antibacterial agents. Preparation of the lichen extracts: Fine powder of UL lichen was extracted using acetone, methanol, and water in a Soxhlet extractor. In a rotary evaporator, the extracts were filtered and then concentrated under reduced pressure. The dry extracts were stored at 18°C until they were used in the tests. The extracts were used for various assays. Sixteen compounds were isolated from lichen UL using various chromatographic techniques, including silica gel, Sephadex LH-20, operational data store, and semipreparative high-performance liquid chromatography. By spectroscopic data analyses, their structures were identified as (1) useanol, (2) lecanorin, (3) 3-hydroxy-5-methylphenyl 2-hydroxy-4-methoxy-6-methylbenzoate, (4) lecanorin E, (5) 3'-methylevernic acid, (6) evernic acid, (7) barbatinic acid, (8) 3,7-dihydroxy-1,9-dimethyldibenzofuran, (9) orcinol, (10) O-methyl orcinol, (11) methyl orsellinate, (12) methyl everninate, (13) 2,5-dimethyl-1,3-benzenediol, (14) 2-hydroxy-4-methoxy-3,6-dimethyl benzoic acid, (15) ethyl everninate, and (16) ethyl 2,4-dihydroxy-6-methylbenzoate. UL lichen is a great source of secondary metabolites, which can be used as antimicrobial, antiproliferative, and anticancer agents. This lichen can be used as a natural antioxidant or antitumor agent in clinical practice; commercially, it can be used as an anticancer drug.