Antibacterial Secondary Metabolites from the Marine-Derived Fungus Penicillium janthinellum
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ANTIBACTERIAL SECONDARY METABOLITES FROM THE MARINE-DERIVED FUNGUS Penicillium janthinellum
Tian-Tian Sun,1 Jian-Kun Yang,1 Hua-Jie Zhu,1 Li Pan,2* and Fei Cao1*
Exploration of microbial resources from special environments can contribute to the production of unique secondary metabolites with potential activities [1]. In particular, the bioactive natural products from marine-derived fungi have been considered to be a hot area of research in the field of pharmaceutical chemistry [2]. Many of these compounds have proved to have antifungal, anti-algal, anti-HIV, antihelminthic, antiprotozoan, antitumor, and anti-allergic properties [3]. Thus, the purpose of this research was to isolate and characterize bioactive secondary metabolites with diverse structures from the marinederived fungal strain Penicillium janthinellum JK07-5. Briefly, compounds 1–7 were isolated and identified from the fungus P. janthinellum, of which compounds 1–3 were alkaloids, 4 was a citrinin derivative, 5 was a chlorine-containing derivative, 6 was a meroterpenoid, and 7 was a sesquiterpenoid. Among 1–7, compound 4 showed significant antibacterial activity, stronger than the positive control ciprofloxacin. On the basis of 1H NMR, 13C NMR, and ESI-MS spectroscopic data and by comparison with related literature, the structures of 1–7 were identified as notoamide C (1) [4], cyclotryprostatin E (2) [5], verruculogen TR-2 (3) [6], citrinin F (4) [7], isochromophilone V (5) [8], dehydroaustin (6) [9], and sesquicaranoic acid B (7) [10], respectively. Antibacterial activity was evaluated by the conventional broth dilution assay [11]. Gram-positive bacteria (Micrococcus lysodeikticus, Bacillus subtilis) and Gram-negative bacteria (Salmonella typhi, Vibrio parahemolyticus) were used, and ciprofloxacin was used as a positive control. The MIC values of ciprofloxacin were 3.1 μM against M. lysodeikticus, 0.3 μM against B. subtilis, 5.0 μM against S. typhi, and 1.3 μM against V. parahemolyticus. Fungus Material. The fungal strain Penicillium janthinellum (JK07-5) was collected from the Bohai Sea in June 2016. The strain was deposited at the College of Pharmaceutical Sciences, Hebei University, China. Culture Conditions. Starter cultures were maintained on PDA medium. Plugs of agar supporting mycelia growth were cut and transferred aseptically to a 500 mL Erlenmeyer flask containing 100 mL of liquid medium (2.0 g glucose, 1.0 g yeast extract, 1.0 g peptone, 3.3 g sea salt, and 100 mL distilled water). The flask was incubated at 28°C on a rotary shaker for 72 h. The mycelium was aseptically transferred to 1000 mL Erlenmeyer flasks containing rice culture (100 mL water, 3.3 g sea salt, and 100 g rice), 5.0 mL each. Fifty flasks were then incubated at room temperature statically for 60 days. Extraction and Isolation. The solid culture of the fermentation was extracted six times with MeOH to give the crude extract (40.2 g). This extract was then chromatographed on a silica gel column using a stepwise gradient of petroleum ether– EtOAc (10:1–1:10) to afford three
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