New Metabolite from the Endophytic Fungus Corynespora smithii
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NEW METABOLITE FROM THE ENDOPHYTIC FUNGUS Corynespora smithii
Yung-Shun Su,1 Ming Jen Cheng,2* Ming Der Wu,2 Sung Yuan Hsieh,2 Chee-Yin Chai,1,3* and Aij-Li Kwan1,4*
A new isopimarane-type diterpene glycoside, named hypomonticuside (1), was isolated from the BuOH-soluble fraction of the liquid fermentation of an endophytic fungus Corynespora smithii, derived from the stems of Ardisia cornudentata Mez (Myrsinaceae). The structure of 1 was elucidated by spectroscopic methods, including UV, IR, HR-ESI-MS, and extensive 1D and 2D NMR techniques. Keywords: Hypoxylon monticulosum, Xylariaceae, diterpene, secondary metabolite. Plant endophytes are a group of microorganisms, including fungi and bacteria, which not only live within plants′ internal tissues or organs, without causing any apparent symptoms of disease in the host plant [1–3], but also serve as important sources of bioactive compounds, presumably owing to the symbiotic relationship with their hosts [1–3]. Research on endophytes from different plant sources has yielded many structurally diverse and pharmacologically active natural products [4–10]. During a program of investigation on potentially bioactive secondary metabolites from Formosan endemic plant endophytes, an endophytic fungal strain, Corynespora smithii (Corynesporascaceae), was isolated from the stems of Ardisia cornudentata Mez (Myrsinaceae). Previous chemical investigations of the fungus Corynespora smithii have received less attention, and only one article has been reported [11]. In the course of our search for potentially diverse secondary metabolites from natural fungal sources, and to further our understanding of the minor metabolites of the genus Hypoxylon, we examined the BuOH-soluble fraction of C. smithii. Investigation of the secondary metabolites of the BuOH extract from fungus C. smithii led to the isolation of one new isopimarane-type diterpene glycoside, named hypomonticuside (1). The structure of 1 was established by means of spectral experiments. The BuOH-soluble fraction of the MeOH extract of rice produced by the endophytic fungus C. smithii was fractionated by a combination of silica gel, RP-18 columns, Sephadex LH-20, and prep. TLC to furnish compound 1, the structure of which was elucidated by 1D and 2D NMR spectra and comparison with literature data. Compound 1 was obtained as an optically active syrup with [α]25 D +42.2° (c 0.25, MeOH) and assigned the molecular formula C26H44O7 , as deduced from ESI-MS m/z 491 [M + Na]+ and HR-ESI-MS data, which implies five degrees of unsaturation. The IR spectrum revealed the presence of an OH group (3445 cm–1) and a C=C bond (1642 cm–1). The 1H NMR and 13C NMR spectra (Table 1) of 1 closely resembled those of elaeicolaside B [12], except that 4-OMe of 1 is replaced 4-OH of elaeicolaside B [12], suggesting that the two compounds most likely have different substituent at C-4.
1) Graduate Institute of Medicine, College of Medicine, Kaohsiung Medical University, 807, Kaohsiung, Taiwan; 2) Bioresource Collection and Research Center (BCRC), F
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