Lycopodium alkaloids have been attracting many natural product chemists and synthetic organic chemists due to their important biological activities and unique skeletal characteristics. Our recent chemical investigation on Lycopodium plants, aiming to find novel seed– and lead–molecules for drug development, resulted in the isolation of a number of biologically active alkaloids. Among them, two Fawcettimine–type alkaloids, lycoposerramines–B and –C, four Phlegmarine–type alkaloids, lycoposerramines–V, –W, –X, and –Z, and five Quinolizidine–type alkaloids involving cernuine and cermizine–D, have been synthesized to determine the structures including their absolute configuration.
In search of new pharmaceutically valuable substances from marine organisms, we have been engaged in chemical studies 1] structural elucidation; 2] asymmetric total synthesis; 3] elucidation of pharmacophore by analysis of structure–activity relationship; 4] action mechanism and search for target protein on the bioactive substances, which were isolated from marine invertebrates and marine microorganisms at Japanese coasts and Indonesian coral reefs on the guidance of new practical bioassay. a) Anti–angiogenic substance: selective growth–inhibitor against human umbilical vein endothelial cells (HUVECs) (e.g. cortistatin A: 9(10–19)–abeo–androstane–type steroidal alkaloid having isoquinoline unit) b) Hypoxia–selective growth inhibitor: growth inhibitor against tumor cells under hypoxic environment selectively (e.g. furospinosulin–1: furanosesterterpene) c) Anti–mycobacterial substances, which are effective to both active and non–replicating persistent (NRP) states of tuberculosis (e.g. halicyclamine A: macrocyclic alkaloid)
The increasing incidence of vancomycin resistance in clinical settings has prompted research into new antibiotics against vancomycin–resistant strains. Recent efforts toward the development of novel glycopeptide antibiotics including our works are reviewed. Introduction of a carbon substituent at the amino acid residue 2 of vancomycin by Suzuki–Miyaura cross–coupling reaction led to an enhancement of antibacterial activity against vancomycin–resistant Staphylococcus aureus (VRSA). The potent activities of Van–M–02 against the Gram–positive bacteria including vancomycin–resistant enterococci (VRE) and VRSA are also described, and its mode of action was investigated with an assay system employing cell–membrane fraction of S.aureus as a crude enzyme mixture.
Exploitation of novel small molecules from natural sources such as microbial metabolites, medicinal plants, and marine invertebrates has contributed to the discovery of lead molecules for drugs as well as research tools on chemical biology. Chemical biology based on forward/reverse chemical genetics is a new paradigm that accelerates drug development and the functional analysis of genes and proteins. Moreover, novel natural products with unique structural or biological characteristics attract both chemists and biologists, thereby developing the field of chemical biology and medicinal chemistry. We have discovered several novel bioactive microbial metabolites by both in vivo cell–based phenotypic screenings and in vitro target–oriented screenings, and investigated their modes of action using a chemical genetics or a chemical genomics approach. In this review, we focus on the following topics; i) recent screening technology and the chemical library, ii) overview of bioactive natural products and semi–synthetic derivatives we have discovered, iii) chemical genetics approach for apoptosis signaling pathway, iv) chemical genomics approach for target identification of antifungal agent, and v) perspective.
Glycosphingolipids (GSLs) are glycoconjugates that consist of sphingosine base, fatty acid, and carbohydrate, and found in cell membranes of living world. Gangliosides are sialoglycolipids that present in the central nervous system, and play critical roles in the physiological properties as carbohydrate antigens, cellular recognition, cell–to–cell communication, receptors of cholera toxin B, differentiation inducer, and so on. Many studies of mammalian gangliosides regarding structures, biosynthesis, metabolism, and functions have been accumulated. On the other hand, in the invertebrates, most of the gangliosides could be found from echinoderms, such as sea urchin, starfish, and sea cucumber, and their chemical structures are quite different from mammalian gangliosides. For nearly 30 years, chemical studies on the GSLs of echinoderms have been carried out in our laboratory. In this paper, we will discuss about the chemical diversity of carbohydrate and ceramide in the GSLs of echinoderms.
There is an expression which states that “the plants act as producer, animals as consumer, and fungi as restorer and decomposer”. In other words, the plants create organic compounds by means of photosynthesis and animals consume such plants. Then fungi, including mushrooms, play an important role in restoring the plants and animals back to the land. There are some differences in the structures of metabolic products by mushrooms compared to those by plants and animals. These differences sometimes indicate biological activities indigenous to mushrooms. The review presents some of our studies on biologically functional molecules isolated from various mushrooms. The following compounds are introduced; 1) anti–dementia compounds, 2) anti–MRSA compounds, 3) osteoclast–forming suppressing compounds, 4) diarrhea–causing compounds, 5) acetaldehyde dehydrogenase inhibitors, 6) hyaluronan–degradation regulating compounds, and 7) glial–cell–toxic compounds.
Clarithromycin (CAM), a semi–synthetic 14–membered macrolide antibiotic, has a feature that the 6–hydroxy group of naturally occurring erythromycin A (EM–A) is methylated. Given its potent antibacterial activity against respiratory pathogens and the excellent pharmacokinetic properties by the chemical modification, CAM has been widely prescribed for the initial empirical treatment of respiratory infections. The most challenging task in the drug development was to establish the synthetic route, especially the selective 6–O–methylation against other four hydroxyl groups of EM–A. In this paper we report the synthetic study led to the establishment of chemical process route of CAM and successively our recent drug discovery research on the next generation macrolides exampled by Acylides (3–O–acyl–EM–A derivatives) and Ketolides (3–oxo–EM–A derivatives). Furthermore, as a promising novel series of the next generation macrolides, we refer to 11a–Azalides (11a–aza–11a–homo EM–A derivatives) based on an underexplored strategy consisting of cleavage and reconstruction of the macrolide aglycon.
Marine microbial resources have been considered as potent sources for new and potent medicines. We have constructed marine microbial library consists of 50,000 strains. Among them, 26,000 strains have phylogenetically analyzed based on SSU–rRNA sequences. Number of biologically active substances have been isolated from marine microbes in this library using the screening based on marine phenomena. One typical example is thallusin (2), isolated in 2005 after pursuing for more than 50 years, showed foliaceous morphology–inducing activity at the exceptionally low concentration. Antimicroalgal substances HML (6) and Kailuin B (9) have been isolated from marine bacteria belongs to Vibrio. These compounds showed selective toxicity only against dinofragellates. Useful microalgae such as diatom was unaffected by these substances. Interestingly, these substances also showed potent anti–malarial activity. It is not strange, because dinofragellete and malaria are phylogenetically related to each other. As shown in the isolation of above mentioned substances and unnermicins, the screening methods based on marine phenomena seemed to be useful for the efficient isolation of novel biologically active compounds.
At present, antibodies are indisputably the most successful reagents in molecular targeting therapy. However, use of antibodies has been limited due to the biophysical properties and the cost to manufacture. To enable new applications where antibodies show some limitations, we have developed an alternative–binding molecule with non–immunoglobulin domain. The molecule is a helix–loop–helix peptide, which is stable against natural enzymes in vivo and is small size to be non–immunogenic. We refer it as “MicroAntibody”. The peptide is composed of three structural regions, N–terminal α–helix, C–terminal α–helix, and flexible connecting loop. In both helical regions, uncharged leucine residues were incorporated into the heptad repeat positions to dimerize the α–helices by hydrophobic interactions. Since the peptide folds by virtue of the interactions between the amino acid residues positioned inside the helix–loop–helix, the solvent–exposed, outside residues were randomized to give a library of MicroAntibodies. Here, we report the construction of the phage–displayed library and the screening of MicroAntibodies binding to cytokine receptors. The obtained MicroAntibodies gave 3D structural information of the pharmacophores for the receptor binding. Therefore, using the structural information, we propose a strategy of molecular design of small ligands for the receptor.
Since higher plants are unable to move in their environment, interesting and mysterious developmental events (allelopathy, phototropism, apical dominance, nyctinasty, flowering, senescence, etc.) are observed in their life cycle. Chemical substances released from plant organs to the neighboring environment stimulate or suppress the development and/or growth of other plants; this chemical interaction is called “allelopathy”. The bending of the organs of a plant toward to the light is a well–known phenomenon called “phototropism”. The growth of lateral buds of some plants is normally repressed by a strongly growing main shoot apex, so–called “apical dominance”. Plants open their leaves during the day and close them at night as if sleeping is known as “nyctinasty”. Here I describe the review of the recent studies on isolation and structure elucidation of bioactive substances involved in their life cycle and determination of the molecular mechanisms for these developmental events.