Natural products from plant-associated microorganisms: distribution, structural diversity, bioactivity, and implications of their occurrence

A growing body of evidence suggests that plant-associated microorganisms, especially endophytic and rhizosphere bacteria and fungi, represent a huge and largely untapped resource of natural products with chemical structures that have been optimized by evolution for biological and ecological relevance. A diverse array of bioactive small molecule natural products has been encountered in these microorganisms. The structures of over 230 metabolites isolated and characterized from over 70 plant-associated microbial strains during the past four years are presented with information on their hosts, culture conditions, and biological activities. Some significant biological and ecological implications of their occurrence are also reviewed.     

Biosynthesis of unusual aminocyclitol-containing natural products

The aminocyclitol family of natural products is a class of sugar-derived microbial secondary metabolites that demonstrate significant biological activities. Within this class of natural products are the C7N-aminocyclitol-containing compounds, which were originally associated with potent sugar-hydrolase inhibition. However, recent discoveries indicate a broader array of chemical structures and biological activities of this class of compounds. Using both conventional feeding experiments and contemporary molecular genetic approaches, some progress has been made in understanding the biosynthesis of this class of natural products. Results of in silico investigation also suggest a wide distribution of this class of natural products or closely related compounds across different classes of microorganisms, including cyanobacteria and fungi. This review describes our recent progress in the biosynthetic studies of a number of C7N-aminocyclitol-containing compounds and the potential use of bioinformatic approaches to search for novel aminocyclitol-containing natural products.     

Bioactive rearranged and halogenated semisynthetic derivatives of the marine natural product sarcophine

Cembranoids are natural diterpenes with 14-membered macrocyclic rings. The simplest natural cembranoid, (+)-cembrene, was isolated from pine oleoresin. Sarcophytols A and B are known cembranoids that inhibit tumor promotion. Sarcophine is a related cembranoid isolated from the Red Sea soft coral Sarcophyton glaucum. Sarcophine and its bioconversion products and semisynthetic derivatives are reported to possess cancer chemopreventive activity. Oxymercuration-demercuration of sarcophine using Hg(OAc)2 and NaBH4 afforded four new rearranged and hydroxylated products. Bromination of sarcophine with N-bromosuccinimide (NBS) furnished two new brominated and rearranged products. Reaction with iodine gave the known iso-sarcophinone and (+)-sarcophytoxin B. Structure elucidation was based on a combination of transition state modeling, molecular dynamics, mechanistic considerations, and 2D NMR data. The antiproliferative activity of the new products is also reported.     

Biologically active sesquiterpene coumarins from Ferula species

Extracts from different species of the genus Ferula (Apiaceae) have had various biomedical applications for many centuries. Many biological features of this genus such as cytotoxicity, antibacterial, antiviral, P-glycoprotein (P-gp) inhibitory and antiinflammatory activity have been attributed to sesquiterpene coumarins; structures containing a common coumarin group and a sesquiterpene moiety. This both highlights the importance of sesquiterpene coumarins as biologically active natural products and necessitates further studies on these compounds. Taking into account the versatile biological properties of compounds isolated from Ferula and the unprecedented interest in the application of natural products as a new generation of therapeutics, the present review will discuss reports on biological activities of sesquiterpene coumarins of the genus Ferula, from 1990 onwards.     

Fungal origins of the bicyclo[2.2.2]diazaoctane ring system of prenylated indole alkaloids

Over eight different families of natural products consisting of nearly 70 secondary metabolites that contain the bicyclo[2.2.2]diazaoctane ring system have been isolated from various Aspergillus, Penicillium, and Malbranchea species. Since 1968, these secondary metabolites have been the focus of numerous biogenetic, synthetic, taxonomic, and biological studies and, as such, have made a lasting impact across multiple scientific disciplines. This review covers the isolation, biosynthesis, and biological activity of these unique secondary metabolites containing the bridging bicyclo[2.2.2]diazaoctane ring system. Furthermore, the diverse fungal origin of these natural products is closely examined and, in many cases, updated to reflect the currently accepted fungal taxonomy.     

海洋天然产物研究进展

2007年我国科学家在海洋天然产物领域进行了大量研究,发现了倍半萜、二萜、三萜、甾体、舍卤素的杂环化合物、含卤素的酚类化合物、环肽、生物碱等类型的化合物,并且对其抗菌、抗炎、细胞毒、清除自由基等生物活性进行了研究。本文按照海洋生物的种类和研究的侧重点,综述2007年我国在海洋天然产物领域内所取得的研究成果。     

Natural antagonists of platelet-activating factor

Several groups of antagonists of platelet-activating factor (PAF) are reviewed. The characteristics of PAF binding sites on mammalian cell membranes are described together with the activities of non-specific and synthetic PAF-antagonists. The specificity of the ginkgolides to bind to PAF-receptors is discussed and the effects of these natural products in a range of biological systems is emphasized. Other groups of natural PAF-antagonists described are the lignans and gliotoxin related compounds. The structural chemistry, structure-activity relationships and pharmacological properties of these drugs are compared to the ginkgolides.     

Anti-inflammatory cembranoids from the soft corals Sinularia querciformis and Sinularia granosa

Four new cembranoids, querciformolides A-D (1-4), along with two known cembranoids, 7 and 8, have been isolated from the soft coral Sinularia querciformis. Furthermore, chemical investigation of Sinularia granosa has afforded three new cembranoids, querciformolide B (2) and granosolides A (5) and B (6). The structures of the new metabolites were elucidated on the basis of extensive spectroscopic methods, and that of 2 was further confirmed by X-ray diffraction analysis. The absolute configurations of 1 and 2 were determined by a modified Mosher's method. Among these metabolites, 2-6 are rarely found cembranoids possessing a tetrahydrofuran moiety with a 4,7-ether linkage; in addition, 1 is the first epsilon-lactone cembrane found that possesses a tetrahydropyran moiety with a 4,8-ether linkage. None of these compounds were found to be cytotoxic toward a limited panel of cancer cell lines. However, compounds 3, 7, and 8 significantly inhibited the accumulation of the pro-inflammatory iNOS and COX-2 proteins in LPS-stimulated RAW264.7 macrophage cells.     

海洋天然产物研究概述

近年来海洋天然产物越来越引起科学家们的注意,在浩瀚的海洋中存在着大量令人激动、活性独特、结构新颖的次生代谢产物。海洋天然产物已成为发现重要先导药物和新的生物作用机制的主要源泉。对目前海洋天然产物研究概况进行综述,其中重点介绍大环内酯类和聚醚类等化合物。     

海洋微生物次生代谢产物的结构特征和生物活性的研究进展

本文归纳了21世纪以来海洋微生物产生的次生代谢产物的结构类型及其抗菌、抗肿瘤、抗心脑血管疾病、抗炎症和酶抑制等生物活性,并展望了今后海洋微生物和海洋天然产物的发展方向。     

Biologically active compounds from Aphyllophorales (polypore) fungi

This review describes biologically active natural products isolated from Aphyllophorales, many of which are known as polypores. Polypores are a large group of terrestrial fungi of the phylum Basdiomycota (basidiomycetes), and they along with certain Ascomycota are a major source of pharmacologically active substances. There are about 25 000 species of basidiomycetes, of which about 500 are members of the Aphyllophorales, a polyphyletic group that contains the polypores. Many of these fungi have circumboreal distributions in North America, Europe, and Asia and broad distributions on all inhabited continents and Africa; only a small number of the most common species with the most obvious fruiting bodies (basidiocarps) have been evaluated for biological activity. An estimated 75% of polypore fungi that have been tested show strong antimicrobial activity, and these may constitute a good source for developing new antibiotics. Numerous compounds from these fungi also display antiviral, cytotoxic, and/or antineoplastic activities. Additional important components of this vast arsenal of compounds are polysaccharides derived from the fungal cell walls. These compounds have attracted significant attention in recent years because of their immunomodulatory activities, resulting in antitumor effects. These high molecular weight compounds, often called biological response modifiers (BRM), or immunopotentiators, prevent carcinogenesis, show direct anticancer effects, and prevent tumor metastasis. Some of the protein-bound polysaccharides from polypores and other basidiomycetes have found their way to the market in Japan as anticancer drugs. Finally, numerous compounds with cardiovascular, phytotoxic, immunomodulatory, analgesic, antidiabetic, antioxidant, insecticidal, and nematocidal activities, isolated from polypores, are also presented. In fact many of the fungi mentioned in this paper have long been used in herbal medicine, including polypores such as Ganoderma lucidum (Reishi or Ling Zhi), Laetiporus sulphureus (Chicken-of-the-Woods), Trametes versicolor (Yun Zhi), Grifola umbellata (Zhu Lin), Inonotus obliquus (Chaga), and Wolfiporia cocos (Hoelen).     

海绵药物的研究进展:化学和生物活性

近年来国际上对海洋天然产物的研究日益深入，依托现代大规模药理筛选，目前已有多种结构新颖、药理活性显著且作用机制特殊的海洋天然产物进入临床试验阶段或正在进行临床前研究。海绵种类繁多，代谢途径独特，生存环境多样，共生现象复杂而普遍，多年来一直是海洋天然产物领域最富成果的研究领域之一。本文简要介绍近几年海绵化学成份及其药理活性的研究进展，以供国内同行参考。     

Natural products chemistry and taxonomy of the marine cyanobacterium Blennothrix cantharidosmum

A Papua New Guinea field collection of the marine cyanobacterium Blennothrix cantharidosmum was investigated for its cytotoxic constituents. Bioassay-guided isolation defined the cytotoxic components as the known compounds lyngbyastatins 1 and 3. However, six new acyl proline derivatives, tumonoic acids D-I, plus the known tumonoic acid A were also isolated. Their planar structures were defined from NMR and MS data, while their stereostructures followed from a series of chiral chromatographies, degradation sequences, and synthetic approaches. The new compounds were tested in an array of assays, but showed only modest antimalarial and inhibition of quorum sensing activities. Nevertheless, these are the first natural products to be reported from this genus, and this inspired a detailed morphologic and 16S rDNA-based phylogenetic analysis of the producing organism.     

Overview of biological effects of Quercetin on ovary

Over the last few decades, using natural products has been increased to treat different diseases. Today, great attention has been pointed toward the usage of natural products such as flavonoids, especially Quercetin (QUR), in the treatment of diseases. QUR as a natural antioxidant has been traditionally used to prevent or treat a variety of diseases such as cancer, cardiovascular disease, polycystic ovary syndrome (PCOS), obesity, chronic inflammation, and reproductive system dysfunction. Several studies demonstrated that QUR acts as an anti‐inflammatory, anti‐apoptotic, antioxidant, and anticancer agent. With this in view, in this study, we intended to describe an overview of the biological effects of QUR on the ovary. QUR improves the quality of oocytes and embryos. It affects the proliferation and apoptosis and decreases the oxidative stress in granulosa cells (GCs). Furthermore, QUR can be used as a complementary and alternative therapy in ovarian cancer and it has beneficial effects in the treatment of PCOS patients. It seems that QUR as a supplementary factor has different activities for the treatment of different disorders and it also has bidirectional activities. However, further investigations are needed for understanding the efficacy of QUR in the treatment and improvement of gynecological patients.     

Isolation of the cembranolide diterpenes dihydrosinularin and 11-epi-sinulariolide from the marine mollusk Planaxis sulcatus

Marine mollusks have been identified as a rich source of novel compounds. The diversity of the chemical nature of these compounds can be partially attributed to the dietary sources inasmuch as mollusks are known to concentrate selectively compounds present in their diet. Although cembranolide diterpenses have been isolated in ever-growing numbers from a variety of marine as well as terrestrial sources, there is only one report about their presence in a marine mollusk. In this communication, we report the isolation of dihydrosinularin and 11-epi-sinulariolide from the mollusk Planaxis sulcatus Born. Dihydrosinularin and 11-epi-sinulariolide acetate have been isolated previously from soft corals which, together with gorgonians, are the richest sources of marine cembranoids. It should be pointed out that this is the first report on the occurrence of the parent 11-epi-sinulariolide in a marine invertebrate. It is expected these diterpenes are of dietary origin although the possibility of biotransformation of a precusor by the mollusk cannot be ruled out at this time. Both dihydrosinularin and 11-epi-sinulariolide have been reported to have marginal antineoplastic activity against P-388 lymphocytic leukemia.     

Effect of propolis, some isolated compounds and its source plant on antibody production

Propolis is a beehive product with a very complex chemical composition, widely used in folk medicine because of its several therapeutic activities. Its biological properties and chemical composition may vary according to the geographic location and to the different plant sources. The possible mechanism of action of propolis as well as of its active compounds has been the subject of researchers in recent years. In this work, first we reported the results of our study on the seasonal effect of the immunomodulatory action of propolis on antibody production in bovine serum albumin (BSA)-immunized rats. Then, we compared the effect of Brazilian and Bulgarian propolis, some isolated compounds and Baccharis extract on anti-BSA antibody levels. Based on the results, we conclude that propolis stimulates antibody production, independently of the season and geographic origin. Caffeic acid, quercetin and Baccharis extract had no effect on antibody production, although the importance of isolated compounds is well reported in other biological assays. Propolis action is a consequence of plant-derived products with synergic effects, while isolated compounds or extracts from its plant sources had no effect in this assay.     

Natural products for the prevention and treatment of cholestasis: A review

Cholestasis is a common manifestation of decreased bile flow in various liver diseases. It results in fibrosis and even cirrhosis without proper treatment. It is believed that a wide range of factors, including transporter dysfunction, oxidative stress, inflammatory damage, and immune disruption, can cause cholestasis. In recent years, natural products have drawn much attention for specific multiple‐target activities in diseases. Many attempts have been made to investigate the anticholestatic effects of natural products with advanced technology. This review summarizes recent studies on the biological activities and mechanisms of recognized compounds for cholestasis treatment. Natural products, including various flavonoids, phenols, acids, quinones, saponins, alkaloids, glycosides, and so on, function as comprehensive regulators via ameliorating oxidative stress, inflammation, and apoptosis, restoring bile acid balance with hepatic transporters, and adjusting immune disruption. Moreover, in this progress, nuclear factor erythroid 2‐related factor 2, reactive oxygen species production, heme oxygenase‐1, NF‐κB, cholesterol 7 alpha‐hydroxylase, and farnesoid X receptors are thought as main targets for the activity of natural products. Therefore, this review presents the detailed mechanisms that include multiple targets and diverse signalling pathways. Natural products are the valuable when seeking novel therapeutic agents to treat cholestatic liver diseases.     

Bioactive marine natural products, with emphasis on handling of water-soluble compounds

Recent progress in separation techniques has enabled us to work with water-soluble components which, more often than not, are responsible for biological activities found in marine organisms. Isolation techniques and chemical and biological aspects of water-soluble marine natural products will be discussed with some representative examples.     

黄酮类化合物合成途径及合成生物学研究进展

黄酮类化合物是来源于植物的一类重要的次生代谢产物,具有抗癌、抗氧化、抗炎、降低血管脆性等多种药理作用。黄酮类化合物的主要合成途径已经研究得比较清晰,即首先合成二氢黄酮类的柚皮素或松属素,然后进一步通过分支途径合成黄酮、异黄酮、黄酮醇、黄烷醇和花色素等。黄酮生物合成途径的解析为其合成生物学研究奠定了基础。利用合成生物学技术已成功在大肠杆菌或酵母中合成了黄酮类化合物,如柚皮素、松属素和非瑟酮等。合成生物学研究为黄酮类化合物提供了新的来源,将进一步推动黄酮类药物和保健品的研发,使其在人类饮食和健康等领域发挥更大的作用。     

Metabolites of Microcystis aeruginosa bloom material from Lake Kinneret, Israel

Six new metabolites, micropeptin KT1042, microguanidine KT636, aeruginosins KT608A, KT608B, and KT650, and pseudoaeruginosin KT554, were isolated along with the known micropeptins SF909 and HM978, cyanopeptolin S, anabaenopeptin F, and the two isomers of planktocyclin-S-oxide from a bloom material collected from Lake Kinneret, Israel, in March 2005. The structure elucidation and biological activity of the six new natural products isolated from this bloom material and the related aeruginosin GH553 are described.