Chun-Shun Li

Cytoglobosins A-G, cytochalasans from a marine-derived endophytic fungus, Chaetomium globosum QEN-14.

Cytoglobosins A-G (1-7), seven new cytochalasan derivatives, along with two structurally related known compounds, isochaetoglobosin D (8) and chaetoglobosin F(ex) (9), were isolated and identified from the cultures of Chaetomium globosum QEN-14, an endophytic fungus derived from the marine green alga Ulva pertusa. The structures of the new natural products as well as their relative configurations were elucidated on the basis of 1D and 2D NMR spectra (COSY, HSQC, HMBC, and NOESY) and HRESIMS data. Cytoglobosins C and D (3 and 4) displayed cytotoxic activity against the A-549 tumor cell line.

Nigerapyrones A-H, α-pyrone derivatives from the marine mangrove-derived endophytic fungus Aspergillus niger MA-132.

Eight new α-pyrone derivatives, namely, nigerapyrones A-E (1-5) and nigerapyrones F-H (8-10), along with two known congeners, asnipyrones B (6) and A (7), were isolated from Aspergillus niger MA-132, an endophytic fungus obtained from the fresh tissue of the marine mangrove plant Avicennia marina. The structures of these compounds were elucidated on the basis of spectroscopic analysis. The undescribed geometries of the trisubstituted double bonds (C-9 and C-11) for asnipyrone B (6) have now been explicitly determined, while the incorrect placement of the methyl group at C-5 of asnipyrone A (7) has now been revised at C-3. The cytotoxic activities of the isolated α-pyrone derivatives against eight tumor cell lines as well as antimicrobial activities against two bacteria and four plant-pathogenic fungi of these compounds were evaluated. Compounds 2, 4, 5, and 7 showed weak cytotoxicity against some of the tested tumor cell lines.

Asperolides A-C, Tetranorlabdane Diterpenoids from the Marine Alga-Derived Endophytic Fungus Aspergillus wentii EN-48

Bioassay-guided fractionation of the culture extract of Aspergillus wentii EN-48, an endophytic fungus isolated from an unidentified marine brown algal species of the genus Sargassum, led to the isolation of three new tetranorlabdane diterpenoids, asperolides A-C (1-3), and five related derivatives (4-8). The structures of these compounds were established on the basis of spectroscopic interpretation, and compound 1 was confirmed by X-ray crystallographic analysis. The absolute configuration of 1 was determined by application of the modified Moshers method. An X-ray structure for wentilactone B (6) is also reported. Compounds 1-8 were evaluated for cytotoxic and antibacterial activities.

Secondary Metabolites from a Marine-Derived Endophytic Fungus Penicillium chrysogenum QEN-24S

Penicillium chrysogenum QEN-24S, an endophytic fungus isolated from an unidentified marine red algal species of the genus Laurencia, displayed inhibitory activity against the growth of pathogen Alternaria brassicae in dual culture test. Chemical investigation of this fungal strain resulted in the isolation of four new (1–3 and 5) and one known (4) secondary metabolites. Their structures were identified as two polyketide derivatives penicitides A and B (1 and 2), two glycerol derivatives 2-(2,4-dihydroxy-6-methylbenzoyl)-glycerol (3) and 1-(2,4-dihydroxy-6-methylbenzoyl)- glycerol (4), and one monoterpene derivative penicimonoterpene (5). Penicitides A and B (1 and 2) feature a unique 10-hydroxy- or 7,10-dihydroxy-5,7-dimethylundecyl moiety substituting at C-5 of the α-tetrahydropyrone ring, which is not reported previously among natural products. Compound 5 displayed potent activity against the pathogen A. brassicae, while compound 1 exhibited moderate cytotoxic activity against the human hepatocellular liver carcinoma cell line.

4-Phenyl-3,4-dihydroquinolone Derivatives from Aspergillus nidulans MA-143, an Endophytic Fungus Isolated from the Mangrove Plant Rhizophora stylosa

Six new 4-phenyl-3,4-dihydroquinolone derivatives (1-6) along with the related aflaquinolone A (7) were isolated and identified from the cultures of Aspergillus nidulans MA-143, an endophytic fungus obtained from the fresh leaves of the marine mangrove plant Rhizophora stylosa. Their structures including absolute configurations were determined by spectroscopic analysis and electronic circular dichroism experiments, and the structure of compound 1 was confirmed by single-crystal X-ray crystallographic analysis. In bioscreening experiments, none of the isolated compounds showed potent antibacterial or cytotoxic activity. However, compounds 2, 3, and 7 exhibited lethality against brine shrimp (Artemia salina), with LD50 values of 7.1, 4.5, and 5.5 μM, respectively.

Cristatumins A-D, new indole alkaloids from the marine-derived endophytic fungus Eurotium cristatum EN-220.

Four new indole alkaloids, namely, cristatumins A-D (1-4), along with six known congeners (5-10) were identified from the culture extract of Eurotium cristatum EN-220, an endophytic fungus isolated from the marine alga Sargassum thunbergii. The structures of these compounds were established on the basis of extensive spectroscopic analysis. Each of these compounds was evaluated for antimicrobial and insecticidal activity. Compounds 1 and 9 showed antibacterial activity against Escherichia coli and Staphyloccocus aureus, respectively, while compounds 2, 6, and 7 exhibited moderate lethal activity against brine shrimp. Preliminary structure-activity relationships were also discussed.

Triazole and dihydroimidazole alkaloids from the marine sediment-derived fungus Penicillium paneum SD-44.

A novel triazole carboxylic acid, penipanoid A (1), two new quinazolinone alkaloids, penipanoids B (2) and C (3), and a very recently reported quinazolinone derivative (4) were isolated from the marine sediment-derived fungus Penicillium paneum SD-44. Their structures were elucidated by spectroscopic analysis, and the structure for 1 was confirmed by X-ray crystallographic analysis. Compound 1 represents the first example of a triazole derivative from marine sediment-derived fungi, and compound 2 is a rare quinazolinone derivative having a dihydroimidazole ring system. The cytotoxicity of compounds 1 and 4 and the antimicrobial activity of 1-4 were evaluated.

Penicisteroids A and B, antifungal and cytotoxic polyoxygenated steroids from the marine alga-derived endophytic fungus Penicillium chrysogenum QEN-24S

Two new polyoxygenated steroids, namely, penicisteroids A and B (1 and 2), were obtained from the culture extract of Penicillium chrysogenum QEN-24S, an endophytic fungus isolated from an unidentified marine red algal species of the genus Laurencia. In addition, seven known steroids (3-9) were also isolated and identified. The structures of these compounds were established on the basis of extensive spectroscopic analysis. The absolute configuration for compound 1 was determined by application of the modified Moshers method. Penicisteroid A (1), which is a structurally unique steroid having tetrahydroxy and C-16-acetoxy groups, displayed potent antifungal and cytotoxic activity in the preliminary bioassays. Preliminary structure-activity relationships are discussed.

7-Nor-ergosterolide, a Pentalactone-Containing Norsteroid and Related Steroids from the Marine-Derived Endophytic Aspergillus ochraceus EN-31

7-Nor-ergosterolide (1), a rare 7-norsteroid with an unusual pentalactone B-ring system, and two new steroid derivatives, 3β,11α-dihydroxyergosta-8,24(28)-dien-7-one (2) and 3β-hydroxyergosta-8,24(28)-dien-7-one (3), were characterized from the culture extract of Aspergillus ochraceus EN-31, an endophytic fungus isolated from the marine brown alga Sargassum kjellmanianum. In addition, nine known related steroids were isolated and identified. The structures of these compounds were established on the basis of extensive spectroscopic analysis. The absolute configuration of the new steroids (1-3) was determined by application of the modified Moshers method. Compound 1, which represents the first example of a 7-nor-ergosteroid possessing a pentalactone B-ring system in a naturally occurring steroid, displayed cytotoxicity against NCI-H460, SMMC-7721, and SW1990 cell lines with IC(50) values of 5.0, 7.0, and 28.0 μg/mL, respectively. Compound 2 also displayed cytotoxicity against the SMMC-7721 cell line with an IC(50) value of 28.0 μg/mL.

Daphenylline, a New Alkaloid with an Unusual Skeleton, from Daphniphyllum longeracemosum

A new alkaloid, daphenylline (1), with an unprecedented rearranged 22-nor-calyciphylline skeleton, was isolated from the fruits of Daphniphyllum longeracemosum. Its structure and stereochemistry were elucidated on the basis of spectroscopic and computational approaches. A plausible biosynthetic pathway of 1 was also proposed.