Structure, solubility, and permeability relationships in a diverse middle molecule library.

To develop methodology to predict the potential druggability of middle molecules, we examined the structure, solubility, and permeability relationships of a diverse library (HKDL ver.1) consisting of 510 molecules (359 natural product derivatives, 76 non-natural products, 46 natural products, and 29 non-natural product derivatives). The library included peptides, depsipeptides, macrolides, and lignans, and 476 of the 510 compounds had a molecular weight in the range of 500-2000 Da. The solubility and passive diffusion velocity of the middle molecules were assessed using the parallel artificial membrane permeability assay (PAMPA). Quantitative values of solubility of 471 molecules and passive diffusion velocity of 287 molecules were obtained, and their correlations with the structural features of the molecules were examined. Based on the results, we propose a method to predict the passive diffusion characteristics of middle molecules from their three-dimensional structural features.

Stalobacin: Discovery of Novel Lipopeptide Antibiotics with Potent Antibacterial Activity against Multidrug-Resistant Bacteria.

A novel lipopeptide antibiotic, stalobacin I (1), was discovered from a culture broth of an unidentified Gram-negative bacterium. Stalobacin I (1) had a unique chemical architecture composed of an upper and a lower half peptide sequence, which were linked via a hemiaminal methylene moiety. The sequence of 1 contained an unusual amino acid, carnosadine, 3,4-dihydroxyariginine, 3-hydroxyisoleucine, and 3-hydroxyaspartic acid, and a novel cyclopropyl fatty acid. The antibacterial activity of 1 against a broad range of drug-resistant Gram-positive bacteria was much stronger than those of "last resort" antibiotics such as vancomycin, linezolid, and telavancin (MIC 0.004-0.016 µg/mL). Furthermore, compound 1 induced a characteristic morphological change in Gram-positive and Gram-negative strains by inflating the bacterial cell body. The absolute configuration of a cyclopropyl amino acid, carnosadine, was determined by the synthetic study of its stereoisomers, which was an essential component for the strong activity of 1.

From Peptides to Peptidomimetics: A Strategy Based on the Structural Features of Cyclopropane.

Peptidomimetics, non-natural mimicries of bioactive peptides, comprise an important class of drug molecules. The essence of the peptidomimetic design is to mimic the key conformation assumed by the bioactive peptides upon binding to their targets. Regulation of the conformation of peptidomimetics is important not only to enhance target binding affinity and selectivity, but also to confer cell-membrane permeability for targeting protein-protein interactions in cells. The rational design of peptidomimetics with suitable three-dimensional structures is challenging, however, due to the inherent flexibility of peptides and their dynamic conformational changes upon binding to the target biomolecules. In this Minireview, a three-dimensional structural diversity-oriented strategy based on the characteristic structural features of cyclopropane to address this challenging issue in peptidomimetic chemistry is described.

Discovery of novel cyclic peptide inhibitors of dengue virus NS2B-NS3 protease with antiviral activity.

NS2B-NS3 protease is an essential enzyme for the replication of dengue virus (DENV), which continues to be a serious threat to worldwide public health. We designed and synthesized a series of cyclic peptides mimicking the substrates of this enzyme, and assayed their activity against the DENV-2 NS2B-NS3 protease. The introduction of aromatic residues at the appropriate positions and conformational restriction generated the most promising cyclic peptide with an IC50 of 0.95µM against NS2B-NS3 protease. Cyclic peptides with proper positioning of additional arginines and aromatic residues exhibited antiviral activity against DENV. Furthermore, replacing the C-terminal amide bond of the polybasic amino acid sequence with an amino methylene moiety stabilized the cyclic peptides against hydrolysis by NS2B-NS3 protease, while maintaining their enzyme inhibitory activity and antiviral activity.

Highly Conformationally Restricted Cyclopropane Tethers with Three-Dimensional Structural Diversity Drastically Enhance the Cell Permeability of Cyclic Peptides.

The conformation of cyclic peptides is closely related to their physicochemical and biological properties, but their rational design to obtain a conformation with the desired properties is difficult. Herein, we present a new strategy by using conformationally restricted cyclopropane tethers (CPTs) to control the conformation and improve the cell permeability of cyclic peptides regardless of the amino acid sequence. Newly designed cis- or trans-CPTs with three-dimensional structural diversity were introduced into a model cyclic peptide, and the relationship between the conformation of the cyclic peptides and their cell permeability was analyzed. Peptides containing a CPT exhibited conformational diversity due to the characteristic steric feature of cyclopropane, among which peptides containing a CPT, cis-NfCf had remarkably higher cell permeability than peptides containing other CPTs-even superior to that of cyclosporine A, a known permeable cyclic peptide.

Characterization of a Phytophthora mating hormone.

Water molds of the genus Phytophthora include many plant pathogens responsible for epidemics such as potato blight and sudden oak death, causing global economic damages. Sexual reproduction is of biological importance in Phytophthora and has been believed to be stimulated by unknown endogenous factors named a hormones. We describe here the chemical characterization of a Phytophthora mating hormone, a1, which was obtained from approximately 2 tons of culture fluid of one mating type of a species and which induced sexual spores on the counter-mating type at a nanogram level.

Erythroid differentiation in K562 chronic myelogenous cells induced by crambescidin 800, a pentacyclic guanidine alkaloid.

The differentiation induction of K562 chronic myelogenous leukemia (CML) cells by crambescidin 800, a pentacyclic guanidine alkaloid isolated from a marine sponge, was examined. Crambescidin 800 increased hemoglobin production in K562 cells at concentrations of 0.15-1 microM and arrested the cell cycle of K562 cells at the S-phase. The expression of p21 was detected after 24-h treatment with crambescidin 800, and an increase of the expression was observed after 48-h treatment, but there was no remarkable change in the expression level of p27. This evidence indicates that crambescidin 800 induced the differentiation of K562 cells into erythroblasts accompanied by cell cycle arrest at the S-phase. Furthermore, crambescidin 800 induced a morphological change with neurite outgrowth in Neuro 2A cells at a 0.03-0.1 microM concentration.

Sesquiterpene aminoquinones, from a marine sponge, induce erythroid differentiation in human chronic myelogenous leukemia, K562 cells.

A new sesquiterpene aminoquinone, 5-epi-smenospongorine, together with nine known sesquiterpene quinone/phenols, was isolated as differentiation-inducing substances to K562 cells into erythroblast from the marine sponge Dactylospongia elegans. The structure-activity relationship study of these compounds clarified that the quinone skeleton is indispensable and the amino group plays an important role for their differentiation-inducing activity to K562 cells into erythroblast.

Smenospongine, a spongean sesquiterpene aminoquinone, induces erythroid differentiation in K562 cells.

The differentiation of K562 chronic myelogenous leukemia (CML) cells by smenospongine, which is a sesquiterpene aminoquinone isolated from a marine sponge, was examined. Smenospongine increased hemoglobin production in K562 cells at concentrations of 3-15 microM. In addition, flow cytometric analysis of smenospongine-treated K562 cells with FITC-labeled glycophorin A antibody showed an increase of glycophorin A expression, a marker for erythroid differentiation. Cell-cycle analysis showed G1 arrest in K562 cells after treatment with smenospongine for 24 h. The effect on expression of CIP/KIP family cyclin-dependent kinase inhibitors was investigated by Western blotting analysis and the result showed increased expression of p21, which is known to play an important role in differentiation. Furthermore, smenospongine was also found to inhibit the phosphorylation of Crkl, a substrate of Bcr-Abl tyrosine kinase, which is known as a causative protein of CML. In conclusion, our investigation indicated that smenospongine induced the differentiation of K562 cells into erythroblasts along with cell-cycle arrest at G1 phase and the mechanism might be attributed to the increased expression of p21.

In situ photoaffinity labeling of the target protein for lembehyne A, a neuronal differentiation inducer.

A C(36) linear acetylene alcohol, lembehyne A (LB-A), induces neuronal differentiation against neuroblastoma cells morphologically and also functionally. The differentiation and cytostatic effect induced by LB-A was specific to neuroblastoma, Neuro 2A cells. To identify the target protein for LB-A, a radioactive photoaffinity probe, [(125)I]18-(2'-azido-5'-iodo-benzoyloxy)-LB-18 ([(125)I]azido-LB-18), was synthesized. As a result of in situ labeling experiments against Neuro 2A cells, a protein of M(r) 30 kDa was photolabeled specifically. This labeling was inhibited in the presence of LB-A or the active analogs of LB-A, whereas the inactive analogs showed no inhibitory effect on this labeling. These results suggest that this protein of M(r) 30 kDa is the target protein for LB-A and may play an important role for the neuronal differentiation in neuroblastoma, Neuro 2A cells.

Pyridoacridine alkaloids inducing neuronal differentiation in a neuroblastoma cell line, from marine sponge Biemna fortis.

A new and three known pyridoacridine alkaloids were isolated from the Indonesian marine sponge Biemna fortis as neuronal differentiation inducers against a murine neuroblastoma cell line, Neuro 2A. The chemical structure of the new compound, labuanine A (1), was determined by spectroscopic study and chemical conversion. These pyridoacridine alkaloids induced multipolar neuritogenesis in more than 50% of cells at 0.03-3 micro M concentration. Compound 3, which showed the strongest neuritogenic activity among them, also induced increase of acetylcholinesterase, a neuronal marker in Neuro 2A and arrested cell cycle at the G2/M phase.