Antibacterial Activities of Ramalin, Usnic Acid and Its Three
Total Page：16
File Type：pdf, Size：1020Kb
Antibacterial Activities of Ramalin, Usnic Acid and its Three Derivatives Isolated from the Antarctic Lichen Ramalina terebrata Babita Paudela,c, Hari Datta Bhattaraia, Hong Kum Leea, Hyuncheol Ohb, Hyun Woung Shinc, and Joung Han Yima,* a Polar BioCenter, Korea Polar Research Institute (KOPRI), Songdo Technopark, Songdo-dong 7-50, Yeonsu-gu, Incheon 406-840, South Korea. Fax: +82-32-260-6301. E-mail: [email protected] b College of Medical and Life Sciences, Silla University, Busan 617-736, South Korea c Department of Marine Biotechnology, Soonchunhyang University, Asan 336-745, South Korea * Author for correspondence and reprint requests Z. Naturforsch. 65 c, 34 – 38 (2010); received October 5, 2009 The development of new antibacterial compounds is an urgent issue to meet the evolution of resistivity of pathogenic bacteria against the available drugs. The objective of this study was to investigate the antibacterial compounds from the Antarctic lichen species Rama- lina terebrata. A total of fi ve compounds, usnic acid, usimine A, usimine B, usimine C, and ramalin, were isolated by bioactivity guided-fractionation of the methanol extract of R. ter- ebrata after several chromatographic procedures. The qualitative antibacterial activities of the crude extract and isolated compounds were determined by the disk diffusion method while the minimum inhibitory concentration (MIC) determination assay gave the quantita- tive strength of the test samples. All the test samples showed antibacterial activity against Bacillus subtilis. The crude extract and usnic acid showed antibacterial activity against Sta- phylococcus aureus. The MIC values of the isolated compounds against B. subtilis were in the range of 1 to 26 μg/mL. These observed experimental data showed the strong antibacte- rial potential of these compounds against B. subtilis. Key words: Antimicrobial, Antarctic Lichen, Ramalina terebrata, Usnic Acid Introduction anthraquinones, naphthoquinones, xanthones as well as epidithiopiperazinediones (Müller, 2001). Lichens are symbiotic associations of a fungus Several pathogenic microbes, especially Gram- (mycobiont) and one or more photosynthetic positive bacteria such as Staphylococcus aureus partners (photobiont). They are cosmopolitan and Bacillus subtilis, cause several human infec- in distribution from arctic to tropical regions tious diseases. Despite the reports on the de- and from plains to the highest mountains and, velopment of several new antibiotics each year, even, some survive in the extreme environment microbes with antibiotic resistance capacities are of deserts. Lichens are used for several purposes evolving day by day causing serious challenges since ancient times such as food, dyes, decoration, in health care settings all over the world. There- and several folk medicines. In addition, several fore, it is very urgent to explore novel antibiot- experiments have shown that lichens consist of ics against specifi c pathogenic bacteria to meet various secondary metabolites having antibiotic, the rate of evolution of a superpathogen. Sev- antimycobacterial, antiviral, anti-infl ammatory, eral lichen metabolites were found active against analgesic, antipyretic, antiproliferative, cytotoxic Gram-positive bacteria and mycobacteria. In this effects and antioxidant properties (Ingólfdóttir, report, we describe the quantitative antibacterial 2002; Kumar and Müller, 1999). More than 800 li- activities of recently reported ramalin and three chen metabolites are reported from several class- usnic acid derivatives, usimine A, usimine B, and es: aliphatic acids, pulvinic acid derivatives, dep- usimine C, isolated from the Antarctic lichen sides and depsidones, dibenzofurans, diterpenes, Ramalina terebrata for the fi rst time. 0939 – 5075/2010/0100 – 0034 $ 06.00 © 2010 Verlag der Zeitschrift für Naturforschung, Tübingen · http://www.znaturforsch.com · D B. Paudel et al. · Antibacterial Constituents from Ramalina terebrata 35 Material and Methods Purifi cation of the water-soluble fraction Collection and identifi cation of lichen species The water-soluble fraction (5 g) was subjected Ramalina terebrata was collected from the Ko- to automated mild pressure liquid chromato- rean Antarctic Research Station site (King Sejong graphy (MPLC) using a C18 ODS silica column Station) on King George Island (61°50’ to 62°15’ (150 cm × 3 cm). Ramalin was isolated using vari- S and 57°30’ to 59°01’ W), in early February 2006 ous chromatographic techniques as described pre- and in early January 2008. The species was identi- viously (Paudel, 2009). The identifi cation of the compound was performed by comparing HPLC fi ed morphologically as well as by analyzing the (retention time) and various spectroscopic data ribosomal DNA sequence of the total internal (HRESIMS, 1H NMR and 13C NMR) with those transcribed spacer (ITS) region as described pre- of an authentic probe as described previously viously (Paudel et al., 2008a). A voucher speci- (Paudel, 2009). men was deposited in the Polar Lichen Herbar- ium, Korea Polar Research Institute (KOPRI), Purifi cation of the chloroform-soluble fraction Incheon, South Korea. The chloroform-soluble fraction was subjected Extraction and isolation of the antibacterial to semi-preparative reversed-phase HPLC us- compounds ing a C18 ODS column (250 mm × 10 mm). The gradient HPLC solvent system was as follows: A completely freeze-dried and ground lichen 20 – 40% acetonitrile in water (0.1% formic acid) sample (672 g) was extracted in a mixture of over 20 min, followed by 60% acetonitrile over methanol and water (80:20 v/v). The extract was 30 min, and 100% acetonitrile over 31 min. The fi ltered and the solvent evaporated at 45 °C in total run time was 50 min. The fl ow rate was vacuo. This extraction procedure was repeated 2 mL/min. Three compounds usimine B, usimine three times to ensure the complete extraction of C and usimine A were isolated at 29.6, 32.7 and extractable compounds. Finally, 83 g of crude ex- 36.6 min, respectively. Similarly, yellow crystalline tract were obtained after freeze-drying, and the needles were also purifi ed from the chloroform- extract was stored at – 20 °C until further use. soluble fraction and further purifi ed by repeti- tive crystallization. The identifi cation of these Purifi cation and characterization of the active compounds was performed by comparing various secondary metabolites spectroscopic data such as HRESIMS, 1H NMR Initially, 83 g of crude extract were dissolved in and 13C NMR with those of authentic probes as 1 L of distilled water. Then, the hexane-soluble described previously (Rashid et al., 1999; Seo et extract was fi rst extracted with 1 L hexane three al., 2008). times to extract low polar compounds. The fi nal weight of the hexane extracts was 12.7 g after Antimicrobial assays freeze-drying. The remaining aqueous phase was Antimicrobial assays of the crude extract of R. extracted with 1 L chloroform three times to ex- terebrata and isolated compounds were performed tract low or moderately polar compounds. The against fi ve clinical microorganisms, including fi nal weight of the chloroform extract was 9.1 g two Gram-positive (Bacillus subtilis KCTC1022 after freeze-drying. Finally, the remaining extract and Staphylococcus aureus KCTC3881) and two was only the water-soluble one and the yield was Gram-negative (Escherichia coli KCTC1039 and 52 g after freeze-drying. Then, the antimicrobial Pseudomonas aeruginosa KCTC1636) bacteria activities of all three extracts were performed. and one fungus (Candida albicans KCTC 7965). Among them, the chloroform-soluble and water- All strains were purchased from Korean Collec- soluble extracts were active against the Gram- tion of Type Culture (KCTC), Deajeon, South Ko- positive bacteria B. subtilis and S. aureus. Thus, rea. Bacterial strains were grown on nutrient agar these two fractions were preceded for further (NA) at 30 – 37 °C and C. albicans was grown on purifi cation. yeast mannitol (YM) agar at 25 °C. The qualita- tive antibacterial assay was performed by the disk diffusion assay as described previously (Bhattarai 36 B. Paudel et al. · Antibacterial Constituents from Ramalina terebrata et al., 2006) to measure the zone of inhibition of Results and Discussion the target microorganism. The quantitative anti- Identifi cation of the antibacterial compounds bacterial assay was performed by determining the minimum inhibitory concentration (MIC) of the A total of fi ve compounds, ramalin, usnic acid, test sample against the target microorganism as and its three derivatives usimines A – C, were iso- described previously (Swenson et al., 1982). lated (Fig. 1). Ramalin was the major constitu- OH OH O H O H O O N O OH O N OCH3 OH OH OH OH HO O Usimine A HO O O Usimine B O O N O O OH R OH OH OH COOH O HO O HO R= C CH2CH2COOH (+)-Usnic acid Usimine C O O H O O OH H N HO N H NH2 Ramalin Fig. 1. Antibacterial compounds, ramalin, usimines A – C, and usnic acid, isolated from R. terebrata. B. Paudel et al. · Antibacterial Constituents from Ramalina terebrata 37 ent in the water-soluble fraction of the R. tere- against Gram-positive pathogenic bacteria. The brata extract. The molecular formula of ramalin further work of isolation of bioactive compounds was determined as C11H15N3O4 by analysis of its gave fi ve compounds as described above. The an- HRESIMS data (m/z = 254.1141 [M + H]+); its tibacterial activities of usnic acid, usimines A – 1 13 H and C NMR data (D2O + acetone d6) were C, and ramalin in terms of inhibition zones and comparable to previously reported data (Paudel, MIC values against two Gram-positive bacterial 2009). Usnic acid was the major constituent in strains, Bacillus subtilis and Staphylococcus au- the chloroform fraction of the R. terebrata ex- reus, are presented here (Table I). In this experi- tract. It was obtained as yellow needles when the ment, none of the isolated compounds was found saturated chloroform fraction was mixed with to be active against the Gram-negative strains E. coli and P. aeruginosa and the yeast C. albicans. methanol.