Byeng Wha Son

Inhibitory phlorotannins from the edible brown algaecklonia stolonifera on total reactive oxygen species (ROS) generation

Reactive oxygen species (ROS) play an important role in the pathogenesis of many human degenerative diseases such as cancer, aging, arteriosclerosis, and rheumatism. Much attention has been focused on the development of safe and effective antioxidants. To discover sources of antioxidative activity in marine algae, extracts from 17 kinds of seaweed were screened for their inhibitory effect on total ROS generation in kidney homogenate using 2′,7′-dichlorofluorescein diacetate (DCFH-DA). ROS inhibition was seen in three species:Ulva pertusa, Symphyocladia latiuscula, andEcklonia stolonifera. At a final concentration of 25 μg/mL,U. pertusa inhibited 85.65±20.28% of total ROS generation,S. latiscula caused 50.63±0.09% inhibitory, and theEcklonia species was 44.30±7.33% inhibition.E. stolonifera Okamura (Laminariaceae), which belongs to the brown algae, has been further investigated because it is commonly used as a foodstuff in Korea. Five compounds, phloroglucinol (1), eckstolonol (2), eckol (3), phlorofucofuroeckol A (4), and dieckol (5), isolated from the ethyl acetate soluble fraction of the methanolic extract ofE. stolonifera inhibited total ROS generation.

Tyrosinase inhibitors isolated from the edible brown alga Ecklonia stolonifera.

Extracts from seventeen seaweeds were determined for tyrosinase inhibitory activity using mushroom tyrosinase with L-tyrosine as a substrate. Only one of them,Ecklonia stoloniferaOkamura (Laminariaceae) belonging to brown algae, showed high tyrosinase inhibitory activity. Bioassay-guided fractionation of the active ethyl acetate (EtOAc) soluble fraction from the methanolic extract ofE. stolonifera, led us to the isolation of phloroglucinol derivatives [phloroglucinol (1), eckstolonol (2), eckol (3), phlorofucofuroeckol A (4), and dieckol (5)]. Compounds1~5 were found to inhibit the oxidation of L-tyrosine catalyzed by mushroom tyrosinase with IC50 values of 92.8, 126, 33.2, 177, and 2.16 μg/mL, respectively. It was compared with those of kojic acid and arbutin, well-known tyrosinase inhibitors, with IC50 values of 6.32 and 112 μg/ mL, respectively. The inhibitory kinetics analyzed from Lineweaver-Burk plots, showed compounds1 and2 to be competitive inhibitors with Ki of 2.3×10-4 and 3.1×10-4 M, and compounds3×5 to be noncompetitive inhibitors with Ki of 1.9×10-5, 1.4×10-3 and 1.5×10-5 M, respectively. This work showed that phloroglucinol derivatives, natural compounds found in brown algae, could be involved in the control of pigmentation in plants and other organisms through inhibition of tyrosinase activity using L-tyrosine as a substrate.

A new antibacterial dioxopiperazine alkaloid related to gliotoxin from a marine isolate of the fungus Pseudallescheria

A new antibacterial dioxopiperazine, dehydroxybisdethiobis(methylthio)gliotoxin (1), and the previously described bisdethiobis(methylthio)gliotoxin (2) and gliotoxin (3), have been isolated from the broth of a marine-derived fungus of the genus Pseudallescheria. The structure and absolute stereochemistry of the new compound was assigned on the basis of NMR and CD experiments. Compounds 1~3 exhibit potent antibacterial activity against the methicillin-resistant and multidrug-resistant Staphylococcus aureus with MIC values of 31.2, 31.2, and 1.0 µg/ml, respectively. Compound 3 also exhibited a significant radical scavenging activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) with IC50 value of 5.2 µM.

Chlorohydroaspyrones A and B, antibacterial aspyrone derivatives from the marine-derived fungus Exophiala sp.

Chlorohydroaspyrones A (1) and B (2), antibacterial aspyrone derivatives, and the previously described aspyrone (3), asperlactone (4), and penicillic acid (5) have been isolated from the broth of a marine isolate of the fungus Exophiala. The structure and absolute stereochemistry of the compounds were determined on the basis of the physicochemical data analysis and chemical reactions. Compounds 1 and 2 exhibited a mild antibacterial activity against Staphylococcus aureus, methicillin-resistant S. aureus, and multidrug-resistant S. aureus. The MIC values of each strain are as follows: compound 1 showed 62.5 microg/mL for S. aureus and 125 microg/mL for methicillin-resistant S. aureus and multidrug-resistant S. aureus, and compound 2, 62.5 microg/mL for S. aureus and methicillin-resistant S. aureus and 125 microg/mL for multidrug-resistant S. aureus.

Circumdatin I, a New Ultraviolet-A Protecting Benzodiazepine Alkaloid from a Marine Isolate of the Fungus Exophiala

AbstractA new ultraviolet-A (UV-A) protecting benzodiazepine alkaloid, circumdatin I (1), along with the previously described circumdatin C (2) and circumdatin G (3), have been isolated from the mycelium of a marine-derived fungus of the genus Exophiala. The structures of the three circumdatins were assigned on the basis of physicochemical evidence. The absolute stereochemistry of 1 was determined by comparison of optical rotation and CD experiments with those of 2 and 3.

A Radical Scavenging Farnesylhydroquinone from a Marine-Derived Fungus Penicillium sp.

Farnesylhydroquinone (1) has been isolated from the mycelium of a marine-derived fungus of the genusPenicillium. The structure of the compound (1) has been elucidated by spectral method. The compound1 exhibits potent radical scavenging activity (IC5012.5 μM) against the DPPH.

Induced production of bromomethylchlamydosporols A and B from the marine-derived fungus Fusarium tricinctum.

The addition of CaBr(2) to the fermentation of a marine-derived Fusarium tricinctum resulted in production of halogenated chlamydosporol analogues. Two new antimicrobial halogenated pyranopyranones, bromomethylchlamydosporols A (1) and B (2), and two known compounds, chlamydosporol (an inseparable epimeric mixture of 7R:7S = 1:1 from (1)H NMR data) (3) and fusarielin A (4), were isolated from the culture. The structures of 1 and 2 were assigned through a combination of spectroscopic data analyses. Compounds 1-4 exhibited mild antibacterial activity against Staphylococcus aureus, methicillin-resistant S. aureus, and multidrug-resistant S. aureus. The MIC values of each strain were as follows: compounds 1 and 2 showed an MIC of 15.6 μg/mL against S. aureus, methicillin-resistant S. aureus, and multidrug-resistant S. aureus, and compounds 3 and 4 exhibited an MIC of 31.5 μg/mL against S. aureus and methicillin-resistant S. aureus and 62.5 μg/mL against multidrug-resistant S. aureus.

Indolyl alkaloid derivatives,Nb-acetyltryptamine and oxaline from a marine-derived fungus

Indolyl alkaloids,Nb-acetyltryptamine (1) and the known oxaline (2) have been isolated from the organic extract of the broth of an unidentified fungus collected from the surface of the marine red algaGracilaria verrucosa. The structure ofNb-acetyltryptamine (1) was assigned on the basis of comprehensive spectroscopic analyses.

Induced Production of Halogenated Diphenyl Ethers from the Marine-Derived Fungus Penicillium chrysogenum

Manipulation of the fermentation of the marine‐derived fungus Penicillium chrysogenum by addition of CaBr2 resulted in induced production of bromodiphenyl ether analogs. Two new free‐radical‐scavenging polybrominated diphenyl ethers, 1 and 2, and three known diphenyl ethers, 3,3′‐dihydroxy‐5,5′‐dimethyldiphenyl ether (3), and an inseparable mixture of violacerol‐I (4) and violacerol‐II (5) were isolated. The structures of the two new polybromodiphenyl ethers 1 and 2 were assigned by combined spectroscopic‐data analysis, including deuterium‐induced isotope effect. Compounds 1–3, and a mixture of 4 and 5 exhibited radical‐scavenging activities against 1,1‐diphenyl‐2‐picrylhydrazyl with IC50 values of 18, 15, 42, and 6 μM, respectively. With the exception of 3, the compounds were, therefore, more active than the positive control, ascorbic acid (IC50 20 μM).

γ-Pyrone derivatives, kojic acid methyl ethers from a marine-derived fungusaltenaria sp

Kojic acid dimethyl ether (1), and the known kojic acid monomethyl ether (2), kojic acid (3) and phomaligol A (4) have been isolated from the organic extract of the broth of the marine-derived fungusAltenaria sp. collected from the surface of the marine green algaUlva pertusa. The structures were assigned on the basis of comprehensive spectroscopic analyses. Each isolate was tested for its tyrosinase inhibitory activity. Kojic acid (3) was found to have significant tyrosinase inhibitory activity, but compounds1,2, and4 were found to be inactive.