Bioactive Steroids from the Marine-Derived Fungus Aspergillus flavus JK07-1
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BIOACTIVE STEROIDS FROM THE MARINE-DERIVED FUNGUS Aspergillus flavus JK07-1
Jin-Meng Ren, Jian-Kun Yang, Hua-Jie Zhu, and Fei Cao*
Marine-derived fungi have been widely recognized as promising sources of secondary metabolites with unique structures and biological activities [1–5]. More and more bioactive compounds have been reported from the metabolites in research on marine-derived fungi [6]. In the course of our ongoing investigation on bioactive secondary metabolites from the marine-derived fungi, the fungus Aspergillus flavus JK07-1 collected from the Bohai Sea attracted our attention because the EtOAc extract of the fungal culture showed inhibitory activity against various pathogenic bacteria. The new steroids exhibited antibacterial activities, and cytotoxicities have been found from this fungus strain in previous studies [7]. From our ongoing studies on the active extracts from the refermentation of this fungus, six steroids (1–6) were discovered, including fusidic acid 1, four ring-expanding steroids 2–5, and an ergot derivative 6. Herein we described the isolation, structure elucidation, and biological activities of these compounds. The structures of 1–6 were determined by 1H NMR, 13C NMR, and ESI-MS spectroscopic data and by comparison with the related literature. They were assigned as fusidic acid (1) [8], neocyclocitrinols A–D (2–5) [9], and sitoindoside I (6) [10]. The spectral data of compounds 2–5 are similar; the main difference is the hydrogen signal at positions 23 and 24. Combined with the literature, compounds 3–5 are identified as isomers of compound 2. In order to determine the absolute their configurations, the dimolybdenum tetraacetate [Mo2(AcO)4] induced circular dichroism (ICD) method was used, which is a classical method to test the absolute configuration of vic-diol [11]. Compounds 2 and 3 showed a negative Cotton effect at 310 nm and a positive Cotton effect at 400 nm, while compounds 4 and 5 showed a positive Cotton effect at 310 nm and a positive Cotton effect at 400 nm. The activity of compounds 1–5 towards pathogenic bacteria showed that compound 1 exhibited significant inhibitory activities against Micrococcus lysodeikticus, Bacillus cereus, Bacillus megaterium, Bacillus anthracis, and Salmonella typhi, with MIC values of 0.07, 0.07, 0.07, 0.30, and 0.60 μM, respectively. Compound 5 exhibited effective inhibitory activities against Micrococcus lysodeikticus with MIC value of 1.30 μM. Other compounds displayed no obvious antibacterial activity at a concentration of 20.0 μM. 26
27 25
HO
HO 1
11
O 30
4
15 7
18
H 28
COOH
13
9
1
31
19
25
1
H H
H3C(CH2) 14OCO
15
7 3
3'
HO HO
1'
O 5'
9
H
3
O
H
29
24
12
24
17
H
O HO
1
23
18
17 29
H HO
21 20 21
11
19
28
18
23
H
21
OH
17
H
26 25 27
H
5
OH
5
O
2-5
6
2: 23R,24R; 3: 23R,24S; 4: 23S,24S; 5: 23S,24R
College of Pharmaceutical Sciences, Institute of Life Science and Green Development, Hebei University, 071002, Baoding, R. R. China, e-mail: [email protected]. Published in Khimiya
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