New Furan Derivatives from a Mangrove-Derived Endophytic Fungus Coriolopsis sp. J5

Six new furan derivatives, named 5-(3-methoxy-3-oxopropyl)-furan-2-carboxylic acid (1), 1-(5-(2-hydroxypropanoyl)-furan-2-yl)-pentan-3-one (2), 2-hydroxy-1-(5-(1-hydroxypentyl)-furan-2-yl)-propan-1-one (3), 1-(5-(1,2-dihydroxypropyl)-furan-2-yl)-pentan-1-one (4), 5-(1-hydroxypent-4-en-1-yl)-furan-2-carboxylic acid (5) and 5-(3-hydroxypentyl)-furan-2-carboxylic acid (6), together with two new natural products, named 5-(1-hydroxypentyl)-furan-2-carboxylic acid (7) and (E)-5-(2-carboxyvinyl)-furan-2-carboxylic acid (8), were isolated from the solid rice fermentation of endophytic fungus Coriolopsis sp. J5, which was derived from mangrove plant Ceriops tagal. Their structures were unambiguously elucidated based on 1D and 2D NMR spectroscopy, and by HRESIMS measurements, as well as by comparison with the literature.

Compound 3 was obtained as a colorless oil. The molecular formula of 3 was deduced as C 12 H 18 O 4 by HRESIMS prominent ion peak at m/z 249.1096 [M + Na] + (calcd. for C 12 H 18 O 4 Na, 249.1097) and 13 C-NMR spectral data, requiring four degrees of unsaturation in the structure, which was one degree reduced than that of 2. By comparison, the 1 H-and 13 C-NMR data were similar to those of 2, only differing in the presence of a hydroxylated methine (C-1 , δ C/H 69.9/4.75) instead of the carbonyl carbon at δ C 209.1 (C-3 ) in 2. Detailed analysis of the 1D and 2D NMR data, the moiety of pentan-1-ol was induced by 1 H 0.88). The pentan-1-ol moiety could be located at C-5 based on HMBC correlations from H-1 to C-4 (δ C 108.7) and C-5 (δ C 163.2). Accordingly, compound 3 was determined as 2-hydroxy-1-(5-(1-hydroxy-pentyl)-furan-2-yl)-propan-1-one.
Compound 5 was obtained as a colorless oil. The molecular formula of 5 was deduced as C 10  Compound 7 was obtained as a colorless oil. The 1 H-and 13 C-NMR data ( Table 2) showed highly similarity to those of 6. Detailed analysis of 2D NMR, the minor difference between these two compounds was the position of the hydroxyl group at 5 -aliphatic chain. Instead of 3 -OH in 6, 7 possessed 1 -OH, which was induced by 1  Compound 8 was isolated as a pale yellow powder. The 1 H-and 13 C-NMR data ( Table 2) established a 2-furancarboxylic acid unit in the structure. Similarly, the remaining signals consisted of acrylic acid by the 1 H-1 H COSY cross-peak of H-1 (δ H 7.41)/H-2 (δ H 6.34) and key HMBC correlations from H-1 and H-2 to C-3 (δ C 167.1). The attachment to C-5 was inferred by HMBC correlations from H-1 and H-2 to C-5 (δ C 153.2). The large 3 J coupling constant between H-1 and H-2 (15.9 Hz) suggested the geometry of the double bond at C-1 /C-2 to be E [12]. Thus, compound 8 was determined as (E)-5-(2-carboxyvinyl)-furan-2-carboxylic acid, which was corresponding with the molecular weight observed in ESIMS spectrum with the positive ion peak at m/z 205.1 [M + Na] + . To the best of our knowledge, compounds 7 and 8 are commercially available, however, this was the first report of their isolation from Nature. Assessment of the absolute configurations of compounds 2-7 could not be performed due to the minute amounts of metabolites remaining after bioactivity assays.
Since an even number of carbon atoms was observed in the structural skeletons of the isolated substances, these furans most likely arise through the polyketide pathway [7].

General
The NMR spectra were recorded on an AV-500 spectrometer (500 MHz for 1 H-NMR and 125 MHz for 13 C-NMR; Bruker, Billerica, MA, USA), using the solvent residue signal as the internal standard. Optical rotations were recorded using a Rudolph Autopol III polarimeter (Rudolph Research Analytical, Hackettstown, NJ, USA). The UV spectra were obtained from a DU-800 spectrometer (Beckman, Brea, CA, USA). The IR spectra (KBr pellets) were run on a 380 FT-IR instrument from Nicolet (Thermo, Pittsburgh, PA, USA). Column chromatography was performed with ODS gel (20-45 mm, Fuji Silysia Chemical Co. Ltd., Durham, NC, USA), Sephadex LH-20 (Merck, Darmstadt, Germany) and silica gel (60-80, 200-300 mesh, Qingdao Haiyang Chemical Co. Ltd., Qingdao, China). TLC analyses were carried out on silica gel G precoated plates (Qingdao Haiyang Chemical Co. Ltd.), and spots were detected by spraying with 5% H 2 SO 4 in EtOH followed by heating.

Fungal Material
The mangrove endophytic fungus Coriolopsis sp. J5 used in this study was isolated from healthy branches of Ceriops tagal (Rhizophoraceae), which were collected in July 2011 from Dong Zhai Gang Mangrove National Nature Reserve in Hainan Island, China. The fungus was identified by sequence analysis of the ITS region of its 18 s rDNA. A BLAST search result indicated that the sequence was most similar (99%) to the sequence of Coriolopsis sp. (compared to AY336771.1). The reserved sample was stored at the Institute of Tropical Bioscience and Biotechnology, Chinese Academy of Tropical Agricultural Sciences (Haikou, China), and maintained on potato dextrose agar (PDA) slant at 4 • C.

Fermentation, Extraction and Isolation
The fungus stored on PDA medium was inoculated and cultured on PDA agar for 7 days. Seed medium (potato 200 g, dextrose 20 g, distilled water 1000 mL) in 500 mL × 10 Erlenmeyer flasks was inoculated with fungus and incubated at room temperature for 4 days on a rotating shaker (120 rpm). Production medium of solid rice in 1000 mL flasks (rice 80 g, distilled water 120 mL for each) was inoculated with seed solution 10 mL for each. Flask cultures were incubated at room temperature under static conditions and daylight for 60 days, and cultures from 200 flasks were harvested for the isolation of substances. Each fungal culture was diced and extracted with EtOH, followed by filter through cheesecloth. Subsequently, the filtrate was extracted three times with an equal volume of Petroleum ether, EtOAc and n-BuOH, successively.