Heonjoong Kang

β-Carboline Alkaloids from a Korean Tunicate Eudistoma sp.

Seven new beta-carboline-based metabolites, designated as eudistomins Y1-Y7 ( 1- 7), were isolated from a tunicate of the genus Eudistoma collected near Tong-Yeong City, South Sea, Korea. These new metabolites differ from previously isolated marine metabolites due to the presence of a benzoyl group attached to the beta-carboline nucleus at C-1. Eudistomins Y 1-Y 7 were evaluated for their antibacterial activity, and eudistomin Y6 exhibited moderate antibacterial activity against Gram-positive bacteria Staphylococcus epidermis and Bacillus subtilis without cytotoxicity in the MTT assay at 100 microM.

Antibacterial Butenolides from the Korean Tunicate Pseudodistoma antinboja

Six new (1, 2, and 5-8) and three known (3, 4, and 9) butenolide metabolites were isolated from the tunicate Pseudodistoma antinboja by activity-guided fractionations. The structures were elucidated by combined NMR and MS spectroscopic methods. These compounds were evaluated for their antibacterial activity, and most of them exhibited moderate to significant activity that selectively targeted Gram-positive strains and did not exhibit cytotoxicity in the MTT assay at 100 μM. Cadiolides 5-9 in particular exhibited significant antibacterial activity that was comparable to or even better than those of marketed drugs such as vancomycin and linezolid against all of the drug-resistant strains tested.

Tuberatolides, Potent FXR Antagonists from the Korean Marine Tunicate Botryllus tuberatus

One isoprenoid, tuberatolide A (1), meroterpenoids tuberatolide B (2) and 2-epi-tuberatolide B (3), and the known meroterpenoids yezoquinolide (4), (R)-sargachromenol (5), and (S)-sargachromenol (6) were isolated from the Korean marine tunicate Botryllus tuberatus. The structures of these compounds were elucidated by NMR, MS, and CD spectroscopic analyses. These terpenoids antagonized the chenodeoxycholic acid (CDCA)-activated human farnesoid X receptor (hFXR) in a cell-based co-transfection assay with IC(50) values as low as 1.5 μM without significant effect on steroid receptors. Furthermore, they released the co-activator peptide from the CDCA-bound hFXR ligand binding domain in cell-free surface plasmon resonance experiments.

Gukulenins A and B, Cytotoxic Tetraterpenoids from the Marine Sponge Phorbas gukulensis

Gukulenins A (1) and B (2), both having an unprecedented skeleton with a bis-tropolone moiety, were isolated from the Korean marine sponge Phorbas gukulensis. They exhibited significant cytotoxicity against human pharynx, stomach, colon, and renal cancer cell lines in the range 0.05-0.80 microM.

Phosphoiodyns A and B, Unique Phosphorus-Containing Iodinated Polyacetylenes from a Korean Sponge Placospongia sp.

Two unprecedented phosphorus-containing iodinated polyacetylenes, phosphoiodyns A and B (1-2), were isolated from a Korean marine sponge Placospongia sp. Their structures were elucidated by spectroscopic data analysis. Phosphoiodyn A exhibited potent agonistic activity on human peroxisome proliferator-activated receptor delta (hPPARδ) with an EC(50) of 23.7 nM.

Phorone A and Isophorbasone A, Sesterterpenoids Isolated from the Marine Sponge Phorbas sp.

A chemical investigation of a Korean marine sponge, Phorbas sp., yielded unprecedented sesterterpenoids phorone A (1) and isophorbasone A (2) along with ansellone B (3) and phorbasone A acetate (4). Their complete structures were elucidated by the combination of spectroscopic data and chemical manipulation. Phorone A (1) and isophorbasone A (2) have the new phorane(5) and isophorbasane(6) sesterterpenoid carbon skeletons, respectively. Ansellone B (3) and phorbasone A acetate (4) exhibited potent inhibitory activity on nitric oxide production in RAW 264.7 LPS-activated mouse macrophage cells with IC(50) values of 4.5 and 2.8 μM, respectively.

Anmindenols A and B, Inducible Nitric Oxide Synthase Inhibitors from a Marine-Derived Streptomyces sp.

Anmindenols A (1) and B (2), inhibitors of inducible nitric oxide synthase (iNOS), were isolated from a marine-derived bacterium Streptomyces sp. Their chemical structures were elucidated by interpreting various spectroscopic data, including IR, MS, and NMR. Anmindenols A and B are sesquiterpenoids possessing an indene moiety with five- and six-membered rings derived from isoprenyl units. The absolute configuration of C-4 in anmindenol B was determined by electronic circular dichroism (ECD) of a dimolybdenum complex. Anmindenols A (1) and B (2) inhibited nitric oxide production in stimulated RAW 264.7 macrophage cells with IC50 values of 23 and 19 μM, respectively.

Bioactive sesterterpenoids from a Korean sponge Monanchora sp.

Chemical investigation of a Korean marine sponge, Monanchora sp., yielded nine new sesterterpenoids (1-9) along with phorbaketals A-C (10-12). The planar structures were established on the basis of NMR and MS analysis, and the absolute configurations of 1-9 were defined using the modified Moshers method and CD spectroscopic data analysis. Compounds 1-8, designated as phorbaketals D-K, possess a spiroketal-modified benzopyran moiety such as phorbaketal A, and their structural variations are due to oxidation and/or reduction of the tricyclic core or the side chain. Compound 9, designated as phorbin A, has a monocyclic structure and is proposed to be a possible biogenetic precursor of the phorbaketals. Compounds 1-9 were evaluated for cytotoxicity against four human cancer cell lines (A498, ACHN, MIA-paca, and PANC-1), and a few of them were found to exhibit cytotoxic activity.

Acredinones A and B, Voltage-Dependent Potassium Channel Inhibitors from the Sponge-Derived Fungus Acremonium sp. F9A015

Two new benzophenones, acredinones A (1) and B (2), were isolated from a marine-sponge-associated Acremonium sp. fungus. Their chemical structures were elucidated on the interpretation of spectroscopic data. The structure of 1 was confirmed by palladium-catalyzed hydrogenation, followed by spectroscopic data analysis. Acredinones A (1) and B (2) inhibited the outward K(+) currents of the insulin secreting cell line INS-1 with IC50 values of 0.59 and 1.0 μM, respectively.

A Facile One-Pot Preparation of Organoselanyltrifluoroborates from Dihalobenzenes and Their Cross-Coupling Reaction

Potassium organoselanyltrifluoroborates have been prepared from the corresponding dihalobenzene compounds in 56-92% yields through a facile one-pot, multicomponent reaction. The microwave-promoted Suzuki-Miyaura cross-coupling reaction of these substrates with various aryl and alkenyl bromides in the presence of 3.0 mol % of Pd(PPh(3))(4) and 3.0 equiv of K(2)CO(3) in aqueous 1,4-dioxane at 130 degrees C provided the desired compounds in 54-91% yields.