Eun La Kim

Antibacterial polyketides from the jellyfish-derived fungus Paecilomyces variotii.

Four new polyketides (1-4) were isolated from the fungus Paecilomyces variotii, which was derived from the jellyfish Nemopilema nomurai. The planar structures and relative configurations of these polyketides were elucidated on the basis of spectroscopic analyses, including 2D NMR experiments. The compounds showed inhibitory activity against pathogenic bacteria including methicillin-resistant Staphylococcus aureus 3089 and multi-drug-resistant Vibrio parahemolyticus 7001 with MIC values in the range 5-40 μg/mL.

Cytotoxic cytochalasins from the endozoic fungus Phoma sp. of the giant jellyfish Nemopilema nomurai

Four new cytochalasin derivatives (1-4), together with cytochalasin B (5), were isolated from the fungus Phoma sp. obtained from the giant jellyfish Nemopilema nomurai. The planar structure and relative stereochemistry were established by analysis of 1D and 2D NMR data. The absolute configuration was defined by the modified Moshers method. The compounds showed significant cytotoxicity against a small panel of human solid tumor cell lines (A549, SK-OV-3, SK-MEL-2, XF 498, and HCT15) with IC(50) values in the range of 0.5-30 μM. The cytochalasin B (5) showed obvious cytotoxicity with IC(50) of 7.9 μM against HeLa human cervical carcinoma cells.

Design and synthesis of marine fungal phthalide derivatives as PPAR-γ agonists

On the basis of a marine fungal phthalide (paecilocin A) skeleton, we synthesized 20 analogs and evaluated them for peroxisome proliferator-activated receptor gamma (PPAR-γ) binding and activation. Among these analogs, 6 and 7 had significant PPAR-γ binding activity, and 7 showed further PPAR-γ activation in rat liver Ac2F cells. In docking simulation, 7 formed H bonds with key amino acid residues of the PPAR-γ binding domain, and the overall positioning was similar to rosiglitazone. This new phthalide derivative is considered an interesting new molecular class of PPAR-γ ligands.

Epimeric methylsulfinyladenosine derivatives from the marine ascidian Herdmania momus.

Abstract Investigation of the secondary metabolites of the ascidian Herdmania momus led to the isolation and characterization of four new nucleoside derivatives (1–4). Structural studies showed that these derivatives represent a series of rare methylsulfinyladenosine derivatives of interconvertible transesterification isomers and/or sulfinyl epimers. The antiviral activities of these rare nucleosides were evaluated against a series of human pathogenic viruses.

Synthesis of PPAR-γ Activators Inspired by the Marine Natural Product, Paecilocin A

A series of N-substituted phthalimide derivatives were synthesized based on a pharmacophore study of paecilocin A (a natural PPAR-γ agonist) and synthetic leads. The introduction of hydrophilic and hydrophobic groups to the phthalimide skeleton yielded compounds 3–14. Compound 7 showed significant PPAR-γ activation in a luciferase assay using rat liver Ac2F cells. Docking simulations showed that a free hydroxyl group on the phthalimide head and a suitable hydrophilic tail, including a phenyl linker, were beneficial for PPAR-γ activation. Compound 7 and rosiglitazone concentration-dependently activated PPAR-γ with EC50 values of 0.67 μM and 0.028 μM, respectively. These phthalimide derivatives could be further investigated as a new class of PPAR-γ ligands.

Cytochalasin Derivatives from a Jellyfish-Derived Fungus Phoma sp.

Four new cytochalasin derivatives (1-4), together with proxiphomin (5), were isolated from a jellyfish-derived fungus Phoma sp. The planar structures and relative stereochemistry were established by analysis of 1D and 2D NMR data. The absolute configuration was defined by the modified Moshers method. The compounds showed moderate cytotoxicity against a small panel of human solid tumor cell lines (A549, KB, and HCT116).

Stable and biocompatible cystine knot peptides from the marine sponge Asteropus sp.

Two new cystine knot peptides, asteropsins F (ASPF) and G (ASPG), were isolated from the marine sponge Asteropus sp. ASPF and ASPG are composed of 33 and 32 amino acids, respectively, and contain six cysteines which are involved in three disulfide bonds. They shared the characteristic features of the asteropsin family, such as, N-terminal pyroglutamate modification, incorporation of cis prolines, and the unique anionic profile, which distinguish them from other knottin families. Tertiary structures of the peptides were determined by high resolution NMR. ASPF and ASPG were found to be remarkably resistant not only to digestive enzymes (chymotrypsin, pepsin, elastase, and trypsin) but also to thermal degradation. In addition, these peptides were pharmacologically inert; non-hemolytic to human and fish red blood cells, non-stimulatory to murine macrophage cells, and nontoxic in vitro or in vivo. These observations support their stability and biocompatibility as suitable carrier scaffolds for the design of oral peptide drug.

Design of PPAR-γ agonist based on algal metabolites and the endogenous ligand 15-deoxy-Δ12, 14-prostaglandin J2

In a previous study, we synthesized endocyclic enone jasmonate derivatives that function as anti-inflammatory and PPAR-γ-activating entities by using key functional moieties of anti-inflammatory algal metabolites. Herein, we designed additional derivatives containing an exocyclic enone moiety that resembles the key structure of the natural PPAR-γ ligand, 15-deoxy-Δ12, 14-prostaglandin J2 (15 d-PGJ2). The exocyclic enone moiety of 15 d-PGJ2 is essential for covalent bonding with the Cys285 residue in the PPAR-γ ligand-binding domain (LBD). In silico analysis of the designed compounds indicated that they may form hydrogen bonds with key amino acid residues in the PPAR-γ LBD, and thus, secure a position in the bioactive cavity in a similar fashion as does rosiglitazone and 15 d-PGJ2. By a luciferase reporter assay on rat liver Ac2F cells, the synthesized compounds were evaluated for PPAR-γ transcriptional activity. The differential PPAR-γ transcriptional activities of the geometric and enantiomeric isomers of the selected analog were also evaluated; based on our results, the enantiopure compound (+)-(R,E)-6a1 was suggested as a potential PPAR-γ ligand.