Alkaloids and Sesquiterpenoids from the Marine-Derived Fungus Aspergillus versicolor
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ALKALOIDS AND SESQUITERPENOIDS FROM THE MARINE-DERIVED FUNGUS Aspergillus versicolor
Ya-Hui Zhang,1,2 Yan Xu,1 Chang-Yun Wang,2 and Fei Cao1*
Marine-derived fungi, which have great structural diversity and activity and are unique secondary metabolites, have attracted much attention in the study of marine microorganisms [1, 2]. In particular, the marine-derived fungus Aspergillus sp. has become a research hot spot, together with Penicillium sp., in recent years [1, 2]. A lot of bioactive compounds have been isolated from the marine-derived fungi of Aspergillus species [3]. On the basis of our previous work on marine-derived Aspergillus sp. [4–8], we continue our investigation of the Bohai Sea-derived fungus Aspergillus versicolor CF-09-9. Chemical investigation of the extract led to the isolation of six compounds, including two alkaloids, paraherquamide (1) [9] and cottoquinazoline A (2) [10], and four sesquiterpenoids, expansol G (3) [11], (7S,11S)-(+)-12-hydroxysydonic acid (4) [12], (7S)-(–)-10-hydroxysydonic acid (5) [13], and (S)-(+)-11-dehydrosydonic acid (6) [14]. In the bioassay, compound 2 showed antibacterial activity against Escherichia coli with an MIC value of 5.0 μM. Herein, we report the isolation, structure elucidation, and biological activities of these compounds. The structures of compounds 1–6 were determined on the basis of detailed analysis of their 1D NMR and ESI-MS spectroscopic data and values of specific rotation with those in the literature [9–14]. The absolute configuration of C-7 in 5 was assigned by comparison of its experimental ECD spectrum with that of the reported compound in the literature [13], and their spectra matched very well. Thus, the absolute configuration at C-7 in 5 was assigned as S. General. 1H and 13C NMR spectroscopic data (TMS as internal standard) were acquired using a 600 MHz Agilent DD2 NMR spectrometer. The other instruments used in the experiments were the same as in our previous paper [8]. Fungal Material. The fungus strain Aspergillus versicolor CF-09-9 was collected from the Bohai Sea (Huanghua, Hebei Province, China, June 2016) and deposited in 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 into small pieces and transferred aseptically to 80 Erlenmeyer flasks of 1000 mL capacity containing rice culture (80 mL purified water, 100 g rice, 0.05 g NaCl, pH 7.0). The flasks were then incubated at room temperature statically for 30 days. Extraction and Isolation. The fermented solid medium (80 flasks) was extracted three times with MeOH–CHCl3 (1:1) and shaken for 30 min using an ultrasound system with a frequency of 100 Hz each time. All the organic extracts were combined and concentrated in vacuo to afford the wet extract. The extract was extracted five times with an equal volume of EtOAc and water; then the EtOAc extract was collected and concentrated in vacuo to give the dry crude extract (58.0 g). The crude extract was fractio
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