Min Ah Lee

Ieodomycins A-D, antimicrobial fatty acids from a marine Bacillus sp.

Bioassay-guided isolation of the EtOAc extract of a marine Bacillus sp., cultured in modified Bennetts broth medium, yielded four new antimicrobial fatty acids, named ieodomycins A-D. The planar structures of these new compounds were determined by extensive 1D and 2D NMR and HRESIMS spectroscopic data analysis. Their absolute configurations were elucidated by modified Moshers method and literature data review. All four new compounds demonstrated antimicrobial activities in vitro.

Gageotetrins A-C, noncytotoxic antimicrobial linear lipopeptides from a marine bacterium Bacillus subtilis.

Gageotetrins A-C (1-3), a unique class of linear lipopeptides, consisting of di- and tetrapeptides and a new fatty acid were isolated from a Marine Bacillus subtilis. The structures of 1-3 were assigned by spectroscopic data and their absolute stereochemistries were ascertained by chemical derivatization. Compounds 1-3 displayed good antimicrobial activities with MIC values of 0.01-0.06 μM. However, these compounds failed to register any cytotoxicity (GI50 > 30 μg/ml) against human cancer cell lines.

Cyclic Ether-Containing Macrolactins, Antimicrobial 24-Membered Isomeric Macrolactones from a Marine Bacillus sp.

Bioassay-guided isolation of bioactive metabolites from the ethyl acetate extract of a marine Bacillus sp. fermentation broth has led to the discovery of three new 24-membered macrolactones, macrolactins 1-3, which contain an oxetane, an epoxide, and a tetrahydropyran ring, respectively. The configurations of 1-3 were assigned by a combination of coupling constants, ROESY data analysis, and application of the modified Moshers method. Compounds 1-3 showed in vitro antimicrobial activity.

Ieodoglucomides A and B from a marine-derived bacterium Bacillus licheniformis.

Ieodoglucomides A (1) and B (2), unique glycolipopeptides consisting of an amino acid, a new fatty acid, a succinic acid, and a sugar, were isolated from a Marine-derived bacterium Bacillus licheniformis. The absolute stereochemistry of 1 and 2 was determined by deploying coupling constants, Marfeys and Moshers methods, and literature reviews. Compounds 1 and 2 displayed moderate in vitro antimicrobial activity. Furthermore, ieodoglucomide B (2) exhibited cytotoxic activity against lung cancer and stomach cancer cell lines with GI(50) values of 25.18 and 17.78 μg/mL, respectively.

Violapyrones H and I, New Cytotoxic Compounds Isolated from Streptomyces sp. Associated with the Marine Starfish Acanthaster planci

Two new α-pyrone derivatives, violapyrones H (1) and I (2), along with known violapyrones B (3) and C (4) were isolated from the fermentation broth of a marine actinomycete Streptomyces sp. The strain was derived from a crown-of-thorns starfish, Acanthaster planci, collected from Chuuk, Federated States of Micronesia. The structures of violapyrones were elucidated by the analysis of 1D and 2D NMR and HR-ESIMS data. Violapyrones (1–4) exhibited cytotoxicity against 10 human cancer cell lines with GI50 values of 1.10–26.12 μg/mL when tested using sulforhodamine B (SRB) assay. This is the first report on the cytotoxicity of violapyrones against cancer cell lines and the absolute configuration of violapyrone C.

Gageostatins A-C, Antimicrobial Linear Lipopeptides from a Marine Bacillus subtilis

Concerning the requirements of effective drug candidates to combat against high rising multidrug resistant pathogens, we isolated three new linear lipopeptides, gageostatins A–C (1–3), consisting of hepta-peptides and new 3-β-hydroxy fatty acids from the fermentation broth of a marine-derived bacterium Bacillus subtilis. Their structures were elucidated by analyzing a combination of extensive 1D, 2D NMR spectroscopic data and high resolution ESIMS data. Fatty acids, namely 3-β-hydroxy-11-methyltridecanoic and 3-β-hydroxy-9,11-dimethyltridecanoic acids were characterized in lipopeptides 1 and 2, respectively, whereas an unsaturated fatty acid (E)-7,9-dimethylundec-2-enoic acid was assigned in 3. The 3R configuration of the stereocenter of 3-β-hydroxy fatty acids in 1 and 2 was established by Mosher’s MTPA method. The absolute stereochemistry of amino acid residues in 1–3 was ascertained by acid hydrolysis followed by Marfey’s derivatization studies. Gageostatins 1–3 exhibited good antifungal activities with MICs values of 4–32 µg/mL when tested against pathogenic fungi (R. solani, B. cinerea and C. acutatum) and moderate antibacterial activity against bacteria (B. subtilis, S. aeureus, S. typhi and P. aeruginosa) with MICs values of 8–64 µg/mL. Futhermore, gageostatins 1–3 displayed cytotoxicity against six human cancer cell lines with GI50 values of 4.6–19.6 µg/mL. It is also noteworthy that mixed compounds 1+2 displayed better antifungal and cytotoxic activities than individuals.

Non-cytotoxic Antifungal Agents: Isolation and Structures of Gageopeptides A–D from a Bacillus Strain 109GGC020

Antifungal resistance and toxicity problems of conventional fungicides highlighted the requirement of search for new safe antifungal agents. To comply with the requirement, we discovered four new non-cytotoxic lipopeptides, gageopeptides A-D, 1-4, from a marine-derived bacterium Bacillus subtilis. The structures and stereochemistry of gageopeptides were determined by NMR data analysis and chemical means. Gageopeptides exhibited significant antifungal activities against pathogenic fungi Rhizoctonia solani, Botrytis cinerea, and Colletotrichum acutatum with minimum inhibitory concentration (MIC) values of 0.02-0.06 μM. In addition, these lipopeptides showed significant motility inhibition and lytic activities against zoospores of the late blight pathogen Phytophthora capsici. These compounds also showed potent antimicrobial activity against Gram positive and Gram negative bacteria with MIC values of 0.04-0.08 μM. However, gageopeptides A-D did not exhibit any cytotoxicity (GI50 > 25 μM) against cancer cell lines in sulforhodamine B (SRB), 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT), and WST-1 ((4-[3-4-iodophenyl]-2-(4-nitrophenyl)-2H-5-tetrazolio)-1,3-benzene disulfonate)) assays, demonstrating that these compounds could be promising candidates for the development of non-cytotoxic antifungal agents.

New antimicrobial compounds from a marine-derived Bacillus sp.

In the course of our ongoing research for antimicrobial agents, we isolated five new compounds, three 24-membered macrolactones, macrolactins X–Z (1–3) and two hydroxy unsaturated fatty acids, linieodolides A (5) and B (6), together with a known metabolite, macrolactinic acid (4), from the culture broth of a marine Bacillus sp. The structures of these metabolites were determined on the basis of their spectroscopic data interpretation. Their absolute configurations were addressed by modified Mosher’s method and literature data review. Compounds 1–6 showed moderate to potent inhibitory activities (8∼128 μg ml−1) against selected pathogenic microorganisms.

Antimicrobial gageomacrolactins characterized from the fermentation of the marine-derived bacterium Bacillus subtilis under optimum growth conditions.

Marine bacteria are a potential source of structurally diversified bioactive secondary metabolites that are not found in terrestrial sources. In our continuous effort to search for new antimicrobial agents from marine-derived bacteria, we isolated bacterial strain 109GGC020 from a marine sediment sample collected from Gageocho, Republic of Korea. The strain was identified as Bacillus subtilis based on a 16s rRNA sequence analysis. After a 7-day fermentation of the B. subtilis strain under optimum growth conditions three new and four known secondary metabolites were discovered using chromatographic procedures, and their biological activities were evaluated against both bacteria and crop-devastating fungi. The discovered metabolites were confirmed by extensive 2D NMR and high-resolution ESI-MS data analyses to have the structures of new macrolactin derivatives gageomacrolactins 1-3 and known macrolactins A (4), B (5), F (6), and W (7). The stereoconfigurations of 1-3 were assigned based on coupling constant values, chemical derivatization studies, and a literature review. The coupling constants were very crucial to determine the relative geometries of olefins in 1-3 because of overlap of the ¹H NMR signals. The NMR data of these compounds were recorded in different solvents to overcome this problem and obtain accurate coupling constant values. The new macrolactin derivatives 1-3 displayed good antibiotic properties against both Gram-positive (S. aureus, B. subtilis, and B. cereus) and Gram-negative (E. coli, S. typhi, and P. aeruginosa) bacteria with minimum inhibitory concentration (MIC) values of 0.02-0.05 μM. Additionally, the antifungal activities of 1-7 were evaluated against pathogenic fungi and found to inhibit mycelial growth of A. niger, B. cinerea, C. acutatum, C. albicans, and R. solani with MIC values of 0.04-0.3 μM, demonstrating that these compounds were good fungicides.

GLYCOSYLATED METHOXY-MACROLACTINS FROM A MARINE SEDIMENT BACTERIUM BACILLUS SUBTILIS

Fermentation of a bacterium Bacillus subtilis isolated from the marine sediment sample collected at Gageocho, Republic of Korea in sea water based modified Bennett’s medium followed by double ethyl acetate (EA) extraction of the supernatant, sequential fractionations and purifications afforded three new glycosylated methoxymacrolactins (13). The characterization of these compounds was achieved by various spectroscopic techniques including HRESIMS and extensive 1D and 2D NMR data analyses. The stereoconfiguration was assigned based on the chemical derivatization studies and literature data reviews. Methoxymacrolactins were found to exhibit good antimicrobial properties when tested against bacteria and fungi. But, these compounds did not display any antiplasmodial activity against Plasmodium falciparum (D10). INTRODUCTION To date, a number of pharmaceutically active compounds have been isolated from marine organisms and associated microorganisms with varying degrees of action, such as antibacterial, antifungal, anti-tumor, anti-cancer, anti-viral, cytotoxic, and immunosuppressive. Drug discovery research from marine organisms adjacent to terrestrial sources is increasing day by day and involves interdisciplinary research including biochemistry, biology, ecology, organic chemistry and pharmacology. Moreover, as the emergence of drug resistant pathogens is increasing enormously, there is a continuing interest on the microbial products by the pharmaceutical as well as agrochemical industries in the development of new therapeutic agents. Macrolactins are a group of 24-membered macrolides possessing potent antibacterial, antifungal and antiviral activities. Most of these macrolactins were derived as secondary metabolites from the marine microorganisms, while several of them were produced by some soil microorganisms as well. We have focused our attention on the isolation and biological activity investigation of secondary metabolites from the strain 109GGC020 that revealed 100% 16S rRNA sequencing similarity to B. subtilis. This bacterium was found to produce antibacterial, antifungal and antiviral compounds like peptides, macrolides, and unsaturated fatty acids. We found from these reviews that varieties of bioactive compounds have been isolated from the culture of the species B. subtilis at variable conditions and collected from different origins, which inspired us to advance further study on this species. And, in the course of our study three new glycosylated methoxymacrolactins (13) were isolated and revealed as good antimicrobial agents.