A New Chromene Derivative from Alternaria sp. ZG22
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A NEW CHROMENE DERIVATIVE FROM Alternaria sp. ZG22
Xin-Ming Song,1 Juan-Juan Luo,1 Ya-Ling Li,1 Li-Bing Huang,1 Cai-Cui Chen,1 Zi-Wei Ma,1 Bing Chen,1 Xue-Ming Zhou,1 Xiao-Ping Song,1* and Chang-Ri Han1,2*
A new chromene derivative, alternapyran (1), along with three known compounds (2–4), was isolated from the Alternaria sp. ZG22 obtained from a Dasymaschalon rostratum collected from the Hainan. The structure of the new compound 1 was elucidated by NMR and mass spectroscopic data. Compounds 2 and 3 showed broad spectrum antibacterial activity against four terrestrial pathogenic bacteria. Keywords: Alternaria sp., chromene, antibacterial activity. Endophytic fungi are well known to be rich sources of new natural products with promising biological and pharmacological activities [1–3]. Previous chemical studies on the genus Alternaria have led to the isolation of an array of compounds including altertoxins, curvularins, quinones, glycerides, steroids, pyranones, dibenzo-a-pyrones, nitrogen-containing compounds, perylenequinone, terpenoids, and phenolics. These compounds showed a range of biological activities such as antimalarial, BRD4 inhibitor, anti-HIV, antibacterial, antileishmanial, antioxidant, cytotoxic, etc. activities [4–8]. In our investigation of new antibacterial natural products, a new chromene derivative, alternapyran (1), along with three known naphthalene derivatives (Fig. 1) identified as 8-methoxynaphthalene-1,5-diol (2) [9], 8-methoxynaphthalene-1,7-diol (3) [10], and 8-methoxynaphthalen-1-ol (4) [11], were isolated from Alternaria sp. ZG22 obtained from a Dasymaschalon rostratum collected from Hainan. Compounds 1–4 were evaluated for their antibacterial activities. Compounds 2 and 3 showed broad spectrum antibacterial activity against four terrestrial pathogenic bacteria. Compound 1 was obtained as a colorless oil, with the molecular formula C10H10O2 from HR-ESI-MS data combined 1 with H and 13C NMR spectroscopic data. The 1H NMR data revealed five olefinic protons δ 6.90 (1H, dd, J = 8.4, 8.0 Hz, H-8), 6.72 (1H, dd, J = 10.0, 1.2 Hz, H-4), 6.40 (1H, dd, J = 8.4, 1.2 Hz, H-7), 6.26 (1H, d, J = 8.0 Hz, H-9), 5.66 (1H, dd, J = 10.0, 3.2 Hz, H-3), one oxygenated methine signal at δ 4.88 (1H, m, H-2) and one methyl signal at δ 1.37 (3H, d, J = 6.4 Hz, H-1). The 13C NMR spectrum showed 10 resonances, including eight olefinic carbons (δ 108.3–155.6), an oxygenated carbon (δ 71.6), and a methyl carbon (δ 21.3). These data indicated that compound 1 had a chromene skeleton. The COSY correlations of H-1 to H-2, H-2 to H-3, and H-3 to H-4 indicated the presence of a fragment from C-1 to C-4 (Fig. 1). The HMBC correlations from H-4 to C-5/C-6/C-10 indicated that C-4 was linked to C-5. Furthermore, the HMBC correlations from H-2 to C-6 indicated that C-2 was linked to C-6 (Fig. 1). Thus, the 2D structure of 1 was constructed as shown in Fig. 1. Compound 1 has the (2R)-form based on the negative optical rotation ([α]24 D –88.2°), and the reported similar compound 2,4-dimethyl2H-chromene ([α]24 –131.3°) in the
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