Syntheses and antimicrobial activities of ogipeptin derivatives.

Novel cyclic peptide derivatives based on ogipeptins A, B, C, and D were synthesized. Starting with a mixture of ogipeptins A-D, a practical four-step synthetic procedure was followed to prepare novel derivatives with various kinds of acyl side chains. Among the 45 new synthetic derivatives identified, the antibacterial activities of compounds 8-3 and 8-38 were comparable with those of ogipeptin A. In in vitro nephrotoxicity screening using LLC-PK1 cells, compounds 8-3 and 8-38 showed significantly lower cytotoxicity (LD20 > 480 µM) than colistin (LD20 = 44.2 µM).

A Novel Natural Product-Derived Compound, Vestaine A1, Exerts both Pro-Angiogenic and Anti-Permeability Activity via a Different Pathway from VEGF.

BACKGROUND/AIMS: Vascular endothelial growth factor (VEGF) is a key molecule in the regulation of both angiogenesis and vascular permeability. However, it is known that overproduction of VEGF induces abnormal blood vessel formation and these vessels cause several disease pathologies, such as diabetic retinopathy. The purpose of this study was to find novel vasoactive compounds which have different properties from VEGF. METHODS/RESULTS: We screened a natural product library using a co-culture angiogenic assay of endothelial cells and fibroblasts. By focusing on morphological changes of endothelial cells, we isolated the novel compounds vestaine A1 and vestaine B1 from the cultured broth of an actinomycete strain, Streptomyces sp. SANK 63697. Vestaine A1 enhanced tube formation of endothelial cells in Matrigel and suppressed cell death induced by serum deprivation. Vestaine A1 activated both MEK1/2 and PI-3 kinase pathways independently of the VEGF pathway in a dose- and time-dependent fashion. Finally, vestaine A1 potently suppressed VEGF-induced vascular permeability both in vitro and in vivo. CONCLUSION: Vestaine A1 has the potential to exhibit both pro-angiogenic and anti-permeability properties, and would therefore be useful for therapeutic treatment for abnormal vascular permeability-related diseases.

Total Synthesis and Structural Elucidation of Ogipeptins.

The first total synthesis of ogipeptin A was achieved. Recently, using the advanced Marfey's method, we determined the absolute configuration patterns of three ß-hydroxy-α,γ-diaminobutyric acids (ß-OH Dabs) composing ogipeptins. On the basis of this result, we conducted solid-phase total synthesis of three diastereomers of ogipeptin A. The analytical data of one diastereomer exactly corresponded with those of natural ogipeptin A. Therefore, the absolute configurations of ogipeptins have been elucidated.

F-19848 A, a novel inhibitor of hyaluronic acid binding to cellular receptor CD44.

In the course of our screening for inhibitors of hyaluronic acid (HA) binding to cellular receptor CD44, a novel inhibitor, F-19848 A, was isolated from the cultured broth of the fungus strain Dacrymyces sp. SANK 20204. This compound inhibited the binding of CD44 and HA with an IC50 value of 23.5 microM and CD44-dependent HA degradation was inhibited with an IC50 value of 98.6 microM in a cell-based assay. The structure was elucidated by physico-chemical properties, analysis of spectral data, and decomposition experiments.

Ogipeptins, novel inhibitors of LPS: physicochemical properties and structural elucidation.

In the course of our screening program for inhibitors of lipopolysaccharide binding to cellular receptor CD14, a potent inhibitory activity was detected in the cultured broth of Pseudoalteromonas sp. SANK 71903. Four active compounds, ogipeptins A, B, C and D, were isolated from the cultured broth. The structures of these compounds were elucidated by physicochemical data and spectral analyses, and they were determined to be new cyclic lipopeptides.

Identification and biological activity of ogipeptins, novel LPS inhibitors produced by marine bacterium.

A library of secondary metabolites from microorganisms was screened to identify novel inhibitors against lipopolysaccharide (LPS), a strong stimulant of innate immunity. Novel cyclic peptides, ogipeptin A, B, C and D, were identified in the culture broth of the marine bacterium Pseudoalteromonas sp. SANK 71903. These compounds blocked LPS binding to the cluster of differentiation 14 (CD14) in vitro with IC50 values of 4.8, 6.0, 4.1 and 5.6 nm, respectively, and attenuated tumor necrosis factor-α secretion from LPS-stimulated macrophage-like cells. These compounds also displayed antimicrobial activity against Escherichia coli with minimum inhibitory concentrations ranging from 0.25 µg ml-1 to 1 µg ml-1. Thus, novel antibiotics that inhibited LPS-induced innate immune reactions were identified in this study.

F-36316 A and B, novel vasoactive compounds, isolated from Incrucipulum sp. SANK 10414.

In the course of our screening program for vasoactive compounds using co-culture assay of endothelial cells and fibroblast cells, potent activity was detected in the cultured broth of Incrucipulum sp. SANK 10414. Two active compounds, F-36316 A and B, and a non-active homolog, F-36316 C, were isolated from the broth. The structures of F-36316 A, B and C were elucidated by physicochemical data and spectral analyses, and found to be new 3-acylated tetronic acid homologs. F-36316 A and B induced morphological changes of endothelial cells different from vascular endothelial growth factor (VEGF) or vestaines in the assay with EC50 values of 1.8 and 11.7 µM, respectively. Furthermore, F-36316 A and B suppressed VEGF-induced vascular permeability induction in mice.

Vestaines, novel vasoactive compounds, isolated from Streptomyces sp. SANK 63697.

We conducted a screening program for vasoactive compounds and detected a potent activity in the cultured broth of Streptomyces sp. SANK 63697. From the cultured broth, two active compounds, vestaine A1 and B1, were isolated. The structures of these compounds were elucidated by physicochemical data and spectral analyses, and found to be new compounds.

F-16438s, novel binding inhibitors of CD44 and hyaluronic acid. I. Establishment of an assay method and biological activity.

In an attempt to obtain inhibitors of hyaluronic acid (HA) binding to its receptor, CD44, we established an efficient assay method to detect and quantify binding using fluorescein-labeled HA and HEK293 cells stably expressing CD44. As a result of the screening of culture broths of microorganisms, we found fungus strain Gloeoporus dichrous SANK 30502 produced inhibitory activity in this new assay. Five compounds, F-16438 A, B, E, F and G, were isolated from the fermentation broths, and their IC50 values were determined to be 10.3, 13.5, 27.3, 12.0 and 13.0 microM, respectively. F-16438 A, B, E, F and G are the first reported inhibitors of binding HA to CD44. F-16438 A, B, E and F have novel structures.

F-16438s, novel binding inhibitors of CD44 and hyaluronic acid. II. Producing organism, fermentation, isolation, physico-chemical properties and structural elucidation.

In the course of our screening for binding inhibitors of CD44 and hyaluronic acid, five active compounds, F-16438 A, B, E, F and G were found and isolated from the cultured broth of a fungal strain, Gloeoporus dichrous SANK 30502. The structures of these compounds except for F-16438 G were elucidated by physico-chemical and spectral data to be new compounds related to caloporoside; F-16438 G was identified to be the 6'-malonylated derivative of caloporoside.

Studies on novel HIF activators, A-503451sII: biological activities of A-503451A.

In the course of our screening, we discovered a novel compound, A-503451A, as a potent hypoxia-inducible factor (HIF) activator. In human hepatocarcinoma HepG2 cells, A-503451A induced HIF-mediated luciferase reporter gene expression and stabilized HIF-1α protein. A-503451A increased the mRNA expression levels and the protein secretion of HIF-dependent genes, vascular endothelial growth factor and erythropoietin. Addition of excess ferric chloride to the culture medium suppressed the HIF-induction activity of A-503451A. A-503451A did not have iron-chelating activity in vitro, but decreased the intracellular labile iron pool concentration. These data indicate that A-503451A is a unique HIF activator.

Studies on novel HIF activators, A-503451s.I. Producing organism, fermentation, isolation and structural elucidation.

In the course of our screening for activators of hypoxia-inducible factor (HIF), A-503451 A and virantmycin were isolated from the cultured broth of an actinomycete strain, Streptomyces sp. SANK 60101. From the same culture, the non-active homologs A-503451 B and D were also isolated. A-503451 A and virantmycin activated HIF-dependent reporter gene expression with EC50 values of 8 and 17 ng ml-1, respectively. They are highly potent activators of HIF and thus may be therapeutically useful for erythropoiesis and neural cell protection.

Pedopeptins, novel inhibitors of LPS: taxonomy of producing organism, fermentation, isolation, physicochemical properties and structural elucidation.

In the course of our screening for inhibitors of lipopolysaccharide (LPS) binding to cellular receptor CD14, potent inhibitory activity was detected in the cultured broth of Pedobacter sp. SANK 72003. Three active compounds, pedopeptin A, B and C, were isolated from the broth and their structures were elucidated by physicochemical and spectral data to be new cyclic depsipeptides.

Screening and biological activities of pedopeptins, novel inhibitors of LPS produced by soil bacteria.

Lipopolysaccharide (LPS) is a strong endotoxin and is delivered to the cell surface signaling receptor, Toll-like receptor 4 and MD-2 complex, via soluble cluster of differentiation (CD) 14 or membranous CD14, resulting in the induction of the inflammatory response. To obtain new compounds that block LPS binding to CD14, we designed a high-throughput screening based on time-resolved intermolecular fluorescence resonance energy transfer. This cell-free screening system successfully led to the discovery of novel inhibitors of LPS-CD14 interaction from the library of the secondary metabolites of microorganisms. We identified the novel compounds pedopeptin A, B and C from a culture broth of Pedobacter sp. SANK 72003. Pedopeptins blocked LPS binding to CD14 in vitro with IC50 values of 20, 11 and 47 nM, respectively, and also inhibited LPS binding to the cells expressing CD14, leading to the suppression of cytokine production. Moreover, they showed antimicrobial activities against Escherichia coli with minimum inhibitory concentration ranging from 2 to 4 µg ml(-1).