Abstract
Two new polyketides, cytospyrone (1), cytospomarin (2), together with three known metabolites dimethoxyphtalide (3), integracin A (4) and integracin B (5), were isolated from the culture of Cytospora sp. from the Chinese mangrove Ceriops tagal. Their structures were elucidated by extensive spectroscopic analyses and time dependent density functional theory (TDDFT), calculation of electronic circular dichroism (ECD) and optical rotation (OR) data. Compound 2 displayed weak inhibitory activity against Escherichia coli GIM1.201 (minimum inhibitory concentration (MIC) value of 0.35 mM). Compounds 4 and 5 displayed significant cytotoxicity against human cancer cell line HepG2 (IC50 values of 5.98 ± 0.12 µM and 9.97 ± 0.06 µM, respectively), more potent than the positive control 5-fluorouracil (IC50 value of 43.50 ± 3.69 µM).
Highlights
Mangrove endophytic fungi are attracting considerable attention from natural product chemists and biologists alike and a great deal of structurally diverse natural products with unusual biological activity have been discovered recently [1,2,3]
During our ongoing screening for biologically active secondary metabolites from mangrove endophytic fungi [7,8,9,10], we recently investigated Cytospora sp., an endophytic fungus derived from the hypocotyls of Chinese mangrove Ceriops tagal, resulting in the isolation of a new antimicrobial biscyclic sesquiterpene, seiricardine D, together with eight known metabolites [11]
13C nuclear magnetic resonance (NMR) data of 1 in association with distortionless enhancement by by polarization transfer (DEPT) and heteronuclear single quantum coherence (HSQC) spectrum polarization transfer (DEPT) and heteronuclear single quantum coherence (HSQC) spectrum suggested the presence of six upfield methyls [δH 1.03, (d, J = 6.7), δC 21.7, q, 50 -CH3 ; 1.07, (d, J = 7.0), suggested the presence of six upfield methyls
Summary
Mangrove endophytic fungi are attracting considerable attention from natural product chemists and biologists alike and a great deal of structurally diverse natural products with unusual biological activity have been discovered recently [1,2,3]. Fungal genera Alternaria, Aspergillus, Cladosporium, Colletotrichum, Fusarium, Paecilomyces, Penicillium, Pestalotiopsis, Phoma, Phomopsis, Phyllosticta, and Trichoderma are considered as the predominant producer of the most notable bioactive secondary metabolites [4,5,6]. Due to the high rediscovery of previously known compounds and scaffolds from these well-investigated organisms, neglected fungal species that are poorly studied might be an alternative source for the discovery of new bioactive compounds. During our ongoing screening for biologically active secondary metabolites from mangrove endophytic fungi [7,8,9,10], we recently investigated Cytospora sp., an endophytic fungus derived from the hypocotyls of Chinese mangrove Ceriops tagal, resulting in the isolation of a new antimicrobial biscyclic sesquiterpene, seiricardine D, together with eight known metabolites [11].
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