Chemical constituents of lichen usnea baileyi (Stirt.) Zahlbr. From Vietnam and biological activities

Abstract

Lichens, symbiotic association of fungal and photosynthetic partners, have been well known used as folk and traditional medicine. In this study, lichen Usnea baileyi (Stirt.) Zahlbr., collected from Tam Bo mountain, Di Linh, Lam Dong, Vietnam was investigated. Twenty four constituents were isolated and identified based on spectroscopic evidence and compared the data with those reported in literatures as stictic acid (1), constictic acid (2), babartic acid (3), diffactaic acid (4), cryptostictic acid (5), hypoconstictic acid (6), menegazziaic acid (7), virensic acid (8), methylstictic acid (9), methyl 4-O-methyl haematomate (10), 8´-O-methylconstictic acid (11), 8´-O-methylmenegazziaic acid (12), 9´-O-methylprotocetraric acid (13), protocetraric acid (14), atranorin (15), methyl b-orsinol carboxylate (16), atranol (17), usnic acid (18), (20R,24R)-ocotillone (19), (20S,24R)-ocotillone (20), betulonic acid (21), dasypogalactone (22), 4-O-demethylbabartic acid (23), and 7-hydroxy-5-methoxy-6-methylphthalide (24). The antibacterial activities of nineteen compounds (1, 2, 4-9, 13-22, 24) were investigated against Propionibacterium acnes KCCM41747, Staphylococcus aureus ATCC25923, Streptococcus sobrinus KCCM11898, Streptococcus mutans ATCC25175 and Salmonella typhi ATCC442. Usnic acid (18) of 1 mM exhibited the highest activity against all bacteria with inhibition zone average in a range of 21-28 mm. Moreover, the antioxidant activity of thirteen compounds (1, 4, 5, 7-11, 14, 17, 19, 20, 22, 24) were investigated using DPPH radical scavenging assay. The scavenging effects of all compounds were in the range of 20-86 %. Among tested compounds, virensic acid (8) exhibited the highest DPPH radical scavenging activity with IC50 0.41 mM.