Abstract
Carotane sesquiterpenes are commonly found in plants but are infrequently reported in the fungal kingdom. Chemical investigation of Trichoderma virens QA-8, an endophytic fungus associated with the inner root tissue of the grown medicinal herb Artemisia argyi H. Lév. and Vaniot, resulted in the isolation and characterization of five new carotane sesquiterpenes trichocarotins I–M (1–5), which have diverse substitution patterns, and seven known related analogues (6–12). The structures of these compounds were established on the basis of a detailed interpretation of their NMR and mass spectroscopic data, and the structures including the relative and absolute configurations of compounds 1–3, 5, 9, and 10 were confirmed by X-ray crystallographic analysis. In the antibacterial assays, all isolates exhibited potent activity against Escherichia coli EMBLC-1, with MIC values ranging from 0.5 to 32 µg/mL, while 7β-hydroxy CAF-603 (7) strongly inhibited Micrococcus luteus QDIO-3 (MIC = 0.5 µg/mL). Structure-activity relationships of these compounds were discussed. The results from this study demonstrate that the endophytic fungus T. virens QA-8 from the planted medicinal herb A. argyi is a rich source of antibacterial carotane sesquiterpenes, and some of them might be interesting for further study to be developed as novel antibacterial agents.
Highlights
The fungus T. virens QA-8 was isolated from the fresh inner root tissue of the Compositae medical plants A. argyi collected at Qichun, Hubei Province, in central China in July 2014 and was identified by analysis of its ITS region of the rDNA
Fr. 5.5 (436 mg) was purified by column chromatography (CC) on Si gel eluting with a CH2Cl2−acetone gradient and purified by CC on Sephadex LH-20 (MeOH) to give compounds 7 (3.6 mg), 8 (8.9 mg) and 12 (9.3 mg), respectively
Five new carotane sesquiterpenes trichocarotins I–M (1–5) and seven known analogues (6–12) were identified from the culture extract of endophytic fungus Trichoderma virens QA-8. Their structures were elucidated by a detailed interpretation of the spectroscopic data and the structures and absolute configurations of compounds 1–3, 5, 9, and 10 were confirmed by X-ray crystallographic analysis
Summary
A number of bioactive constituents such as flavonoids [4], polysaccharides [5], terpenes [6,7], and polyketides [8,9], have been reported from the plant A. argyi and its associated endophytic fungi Several of these components have been investigated to show anticoagulation, antioxidant, antimicrobial, and anticancer activities [4,5,6,7,8,9,10]. Upon slow evaporation of the solvent (MeOH : H2O = 15 : 1) by storage in a refrigerator, quality single crystals of compound 5 were obtained, and the relative and absolute configuration of 5 was established by a single-crystal X-ray diffraction experiment using Cu Kα radiation (Figure 5). SEiCm: iEla. crolyli,. tMhLe:8M,9.-leupteouxsy; –g: nroouapctiavtittyhe(MseICve>n6-4mμegm/Mble)r. ed ring increased the activity against E. coli and decreased the activity against M. luteus (12 vs. 6)
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