Annularins I and J: New Metabolites Isolated from Endophytic FungusExserohilum rostratum

Abstract

The paper describes the isolation of ergosterol peroxide, monocerin, annularin I and annularin J compounds of Exserohilum rostratum biomass extracts. Compounds were isolated by silica gel column chromatography in polarity gradient and the structures were determined by nuclear magnetic resonance (NMR) and mass spectrometry (MS) methods. Monocerin, annularin I and annularin J compounds were tested against Escherichia coli, Pseudomonas aeruginosa and Bacillus subtilis bacteria and showed moderate activity. Annularin I and annularin J compounds are new natural products. Keywords: annularins, polyketides, E. rostratum, endophytic fungi IntroductionEndophytic microorganisms live in plants internal tissues without causing apparent disease to their hosts. 1 Endophyte microbial colonization can be demonstrated by isolating plant tissues disinfected through histological cut and by DNA amplification technique. 2 In tropical and temperate forests (which cover only 1.5% of the terrestrial surface), there are approximately 300,000 (three hundred thousand) plant species analyzed so far, homing more than 60% of the world's biodiversity. 3 Extreme diversity allows for the opportunity to discover new microorganisms that may be potential bioactive compounds producers for agriculture, industry and medicine. 4 There is a great interest in the study of endophytic microorganisms, including their application in pest biocontrol. Fungi are good secondary metabolite producers, and many have the same biological activity, 5-8 especially polyketides. For example, the polyketide citrinin isolated from Penicillium janthinellum completely inhibited the growth of Leishmania braziliensis.9 Some fungi species of Penicillium and Pestalotiopsis genera produce high diversity of polyketides with antimicrobial activity. 10,11In another study with a variety of endophytes isolated from Vigueira arenaria and Tithonia diversifolia fungal extracts, important antiparasitic and antimicrobial activities were observed in fungal extracts. 12 In the Nodulisporium sp. (Xylariaceae) fungus extract, which was isolated from the woody plant species Erica arborea (Ericaceae), nodulisporina D, E and F compounds were obtained, having antifungal, antibacterial and algaecide activity.13 From the endophytic fungus Ampelomyces sp., isolated from the medicinal plant Urospermum picroides (Asteraceae), 6-O-methylalaternina and altersolanol A compounds were isolated, which showed antimicrobial activity against Gram-positive pathogens Staphylococcus aureus, S. epidermidis and Enteorococcus faecalis.14 Brazil is estimated to be home of about 20% of the world's biodiversity and is considered the country in the world with the largest number of endemic species.15 About 270,000 plant species on this planet are estimated to harbor about 13.6 million unique endophytic fungal species, in addition to approximately 100,000 fungi species already known to date. Therefore, there are great chances of finding Pinheiro et al. 1433 Vol. 27, No. 8, 2016 new substances produced by endophytic fun...

Spiro-Phthalides and Isocoumarins Isolated from the Marine-Sponge-Derived Fungus Setosphaeria sp. SCSIO41009

“…Recently, because of the structurally unique as well as interesting biological and pharmacological properties, secondary metabolites obtained from marine-derived fungi have attracted considerable attention . The fungal genus Setosphaeria has been mainly isolated from terrestrial plants, with fewer strains isolated from marine sources. , Among this genus, S. rostrata and S. turcica are well known as plant pathogenic fungi and widely researched for their pathogenicity. − Nearly 30 bioactive secondary metabolites have been isolated from the fungal genus Setosphaeria together with the genus Exserohilum , which is an anamorph of Setosphaeria . − Those secondary metabolites showed phytotoxic, anticancer, , antiplasmodial, antifungal, antibacterial, α-glucosidase inhibitory, and porcine pancreatic alpha amylase inhibitory activities …”

Fungal Endophytes: A Potential Source of Antibacterial Compounds

“…Aspergillus sp. YXf3, an endophyte residing inside the leaves of Ginkgo biloba, yielded some novel p-terphenyls named prenylterphenyllin D (187), prenylterphenyllin E (188), and 2 -O-methylprenylterphenyllin (189), along with the known compounds prenylterphenyllin (190) and prenylterphenyllin B (191,Figure 11). Compounds 187-191 displayed antibacterial activity against X. oryzae pv.…”

“…Compound 442 exhibited antibacterial activity with MIC values of 62.50 and 31.25 µg/mL against E. coli and B. subtilis, respectively. Compound 443 displayed weak activity against E. coli and B. subtilis with MIC values of 62.50 µg/mL each [191].…”

Overview of Bioactive Fungal Secondary Metabolites: Cytotoxic and Antimicrobial Compounds

“…From the Brazilian biodiversity, the fungus Exserohilum rostratum ( Figure 6 ) was isolated from Bauhinia guianensis [ 209 ] and Phanera splendens [ 210 ], which are typical Amazonian plants used in popular medicine to combat infections. Among the SMs produced by this species are the polyketide monocerin, ergosterol peroxide, annularins, and ravenelin, which presented moderated antimicrobial activity on B. subtilis , S. aureus , E. coli , P. aeruginosa , and B. subtilis and Salmonella typhimurium [ 209 , 210 ].…”