Chemistry and pharmacology of oxyprenylated secondary plant metabolites

Oxyprenylated natural products (isopentenyloxy-, geranyloxy- and the less spread farnesyloxy- compounds and their biosynthetic derivatives) represent a family of secondary metabolites that have been considered for years just as biosynthetic intermediates of C-prenylated derivatives. Only in the last decade these natural products have been recognized as interesting and valuable biologically active phytochemicals. Up to now about 300 molecules have been isolated from plants mainly belonging to the families of Rutaceae and Compositae, comprising common edible vegetables and fruits. A wide variety of compounds containing a prenyloxy side chain have been isolated and these comprise alkaloids, coumarins, flavonoids, cinnamic acids, benzoic acids, phenols, alcohols, aldehydes, anthraquinones, chalcones, lignans, xanthones, aceto- and benzophenones and other more uncommon skeletons. Many of the isolated oxyprenylated natural products and their semisynthetic derivatives were shown to exert in vitro and in vivo remarkable anti-cancer, anti-inflammatory, anti-microbial and anti-fungal effects. The aim of this review is to examine in detail the different types of oxyprenylated natural compounds from a phytochemical and pharmacological point of view.     

Biosynthesis pathways for deoxysugars in antibiotic-producing actinomycetes: isolation, characterization and generation of novel glycosylated derivatives

Many bioactive natural products synthesized by actinomycetes are glycosylated compounds in which the appended sugars contribute to specific interactions with their biological target. Most of these sugars are 6-deoxyhexoses, of which more than 70 different forms have been identified, and an increasing number of gene clusters involved in 6-deoxyhexoses biosynthesis are being characterized from antibiotic-producing actinomycetes. Novel glycosylated compounds have been generated by modifying natural deoxysugar biosynthesis pathways in the producer organisms, and/or the simultaneous expression in these strains of selected deoxysugar biosynthesis genes from other strains. Non-producing strains endowed with the capacity to synthesize novel deoxysugars through the expression of engineered deoxysugar biosynthesis clusters can also be used as alternative hosts. Transfer of these deoxysugars to a multiplicity of aglycones relies upon the existence of glycosyltransferases with an inherent degree of 'relaxed substrate specificity'. In this review, we analyze how the knowledge coming out from isolation and characterization of deoxysugar biosynthesis pathways from actinomycetes is being used to produce novel glycosylated derivatives of natural products.     

Sugar-mediated induction of Agrobacterium tumefaciens virulence genes: structural specificity and activities of monosaccharides.

The virulence genes of Agrobacterium tumefaciens are induced by specific plant phenolic metabolites and sugars (G. A. Cangelosi, R. G. Ankenbauer, and E. W. Nester, Proc. Natl. Acad. Sci. USA, in press). In this report, monosaccharides, derivatives, and analogs which induce the vir regulon have been identified and the structural requirements for monosaccharide-mediated induction have been determined. Pyranose sugars with equatorial hydroxyls at C-1, C-2, and C-3 displayed strong vir gene-inducing activity; the C-4 hydroxyl could be epimeric and a wide variety of substitutions at C-5 were permissible. The acidic monosaccharide derivatives D-galacturonic acid and D-glucuronic acid were the strongest inducers among the monosaccharides tested. Eight of the 11 inducing compounds are known plant metabolites, and 7 are monomers of major plant cell wall polysaccharides. A role for monosaccharides and plant phenolic compounds as wound-specific plant metabolites which signal the ChvE/VirA/VirG regulatory system is proposed.     

植物组织中糖与糖醇乙酰化及毛细管气相色谱分析

介绍了一种用1-甲基咪唑为溶剂和催化剂、盐酸羟胺和乙酸酐为肟化和乙酰化试剂,对植物样品中糖与糖醇进行乙酰化衍生化后的气相色谱分离和质谱鉴定的分析方法。并对糖与糖醇乙酰化影响较大的反应温度、反应时间、反应物组成和反应物浓度等条件进行了比较研究,确定了糖与糖醇乙酰化各步反应的最佳反应温度和反应时间,分析了各组分间相互作用及其用量对衍生化效率的影响。对多种糖与糖醇乙酰化产物进行毛细管气相色谱分离、FID检测及GC-MS结构鉴定。研究证明, 在合适条件下应用此方法对糖与糖醇进行乙酰化,反应完全,产物单一,能得到理想的分离、检测和定量分析效果。适用于微量植物组织中多种单糖、双糖及其糖醇的定量分析。     

Novel biologically active natural and unnatural products

Natural products have been used as medicinal agents for many years. In addition, these compounds have served as the starting points for semisynthetic analogs with improved properties. This review highlights work on several classes of natural products and their derivatives, including both well established and emerging structural classes that are in, or nearing, clinical use for a variety of important indications.     

植物组织中糖与糖醇乙酰化及毛细管气相色谱分析

介绍了一种用1-甲基咪唑为溶剂和催化剂、盐酸羟胺和乙酸酐为肟化和乙酰化试剂,对植物样品中糖与糖醇进行乙酰化衍生化后的气相色谱分离和质谱鉴定的分析方法.并对糖与糖醇乙酰化影响较大的反应温度、反应时间、反应物组成和反应物浓度等条件进行了比较研究,确定了糖与糖醇乙酰化各步反应的最佳反应温度和反应时间,分析了各组分间相互作用及其用量对衍生化效率的影响.对多种糖与糖醇乙酰化产物进行毛细管气相色谱分离、FID检测及GC-MS结构鉴定.研究证明,在合适条件下应用此方法对糖与糖醇进行乙酰化,反应完全,产物单一,能得到理想的分离、检测和定量分析效果.适用于微量植物组织中多种单糖、双糖及其糖醇的定量分析.     

Engineering the glycosylation of natural products in actinomycetes

Bioactive natural products are frequently glycosylated with saccharide chains of different length, in which the sugars contribute to specific interactions with the biological target. Combinatorial biosynthesis approaches are being used in antibiotic-producing actinomycetes to generate derivatives with novel sugars in their architecture. Recent advances in this area indicate that glycosyltransferases involved in the biosynthesis of natural products have substrate flexibility regarding the sugar donor but also, less frequently, with respect to the aglycon acceptor. Therefore, the possibility exists of altering the glycosylation pattern of natural products, thus enabling an increase in the structural diversity of natural products.     

Natural products with calmodulin inhibitor properties

This review summarizes properties of various naturally occurring compounds with reported calmodulin (CaM)-inhibitory properties which include about 159 natural products belonging to different structural classes. Most inhibitors are alkaloid and peptide type of compounds and have been isolated from a wide variety of natural sources, including many plant species. Among the most potent natural anti-CaM substances, however, are several animal venoms and the antibiotic polymixin. The largest number of compounds described were discovered by means of enzymatic functional assays.     

Small-molecule natural products: new structures, new activities

A wide variety of novel small-molecule natural products has recently been reported. These compounds were isolated from marine and terrestrial sources, and from a variety of animals, plants and microorganisms. With the breadth of diversity represented in these bioactive small molecules, the future of natural product drug discovery looks bright.     

New developments in the synthesis of phosphopolyprenols and their glycosyl esters.

Efficient methods were developed in our group in recent years for chemical synthesis of polyprenyl phosphates, polyprenyl monophosphate sugars, and polyprenyl diphosphate sugars, which were known to serve as important intermediates in biosynthesis of complex carbohydrates. A simple procedure was developed involving the phosphorylation of aliphatic alcohols with tetra-n-butylammonium dihydrogen phosphate and trichloroacetonitrile. Monophosphates of various natural and modified dolichols and polyprenols, as well as the derivatives of retinol, cholesterol, and nonacosanol, were prepared in high yields. First syntheses of dolichyl thiophosphate and dolichyl hydrogen phosphonate were developed, and these derivatives were of interest as analogs of dolichyl phosphate. Polyprenyl monophosphate sugars, including derivatives of alpha- and beta-anomers of D-glucopyranose, D-galactopyranose, D-mannopyranose, and 2-acetamido-2-deoxy-D-glucopyranose, were obtained smoothly from moraprenyl trichloroacetimidate and acylated glycosyl phosphates after deprotection. A method for the synthesis of polyprenyl diphosphate sugars from polyprenyl phosphoroimidazolidate and unprotected glycosyl phosphates was shown to be applicable for a wide range of the monosaccharide derivatives including hexoses, deoxyhexoses, 2-acetamido-2-deoxyhexoses, and uronic acids. A series of the oligosaccharide derivatives was also prepared by this method.     

1-N-glycyl beta-oligosaccharide derivatives as stable intermediates for the formation of glycoconjugate probes.

Incubation of reducing sugars in ammonium bicarbonate was found to be a simple procedure for the formation of beta-D-glycosylamines of purified complex oligosaccharides in 70-80% yield. These provide valuable intermediates for the synthesis of a wide range of oligosaccharide probes and derivatives by acylation of the 1-amino function. The 1-amino function showed different rates of reactivity with different reagents. In general, interactions with large ring systems such as the fluorophores dansyl chloride and carboxyfluorescein gave 10-20% yields of products, which consisted of mixtures of both anomeric forms, whereas smaller acylating reagents gave near-quantitative yields of the desired beta-D-derivatives. Steric effects may explain differences in reactivity. N-Chloroacetamido derivatives could be obtained in high yield with retention of the beta-anomeric configuration. Subsequent ammonolysis of the chloroacetamido function afforded the corresponding N-glycyl beta-derivatives. The linker thereby introduced retains the amino function, possesses the useful properties of fixed anomeric configuration, improved stability, and uniform reactivity with a variety of reagents, and is structurally analogous to an asparagine side chain. The potential therefore exists for the generation of oligosaccharide derivatives tailored for different applications.     

Potential antioxidant activity of Morita-Baylis-Hillman adducts

The wide variety of potent biological activities of Morita-Baylis-Hillman adducts (MBH) encouraged us to synthesize new series of products belonging to this class of compounds, possessing different functionalities and exhibiting potential antioxidant activity.As part of our on-going program on targeting molecules with antioxidant activity, we describe herein different DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging activities of MBH alcohols and their derivatives including acetates, phosphonates and hydrazonophosphonates. The obtained results showed that the strongest DPPH radical scavenging activity was observed in the case of hydrazonophosphonates in comparison to the other MBH derivatives.     

Marine pharmacology in 2007–8: Marine compounds with antibacterial,anticoagulant, antifungal,anti-inflammatory,antimalarial, antiprotozoal,antituberculosis, and antiviral activities; affecting the immune and nervous system,and other miscellaneous mechanisms of action

The peer-reviewed marine pharmacology literature in 2007–8 is covered in this review, which follows a similar format to the previous 1998–2006 reviews of this series. The preclinical pharmacology of structurally characterized marine compounds isolated from marine animals, algae, fungi and bacteria is discussed in a comprehensive manner. Antibacterial, anticoagulant, antifungal, antimalarial, antiprotozoal, antituberculosis and antiviral activities were reported for 74 marine natural products. Additionally, 59 marine compounds were reported to affect the cardiovascular, immune and nervous systems as well as to possess anti-inflammatory effects. Finally, 65 marine metabolites were shown to bind to a variety of receptors and miscellaneous molecular targets, and thus upon further completion of mechanism of action studies, will contribute to several pharmacological classes. Marine pharmacology research during 2007–8 remained a global enterprise, with researchers from 26 countries, and the United States, contributing to the preclinical pharmacology of 197 marine compounds which are part of the preclinical marine pharmaceuticals pipeline. Sustained preclinical research with marine natural products demonstrating novel pharmacological activities, will probably result in the expansion of the current marine pharmaceutical clinical pipeline, which currently consists of 13 marine natural products, analogs or derivatives targeting a limited number of disease categories.     

Evaluation of coumarin derivatives as anti-fungal agents against soil-borne fungal pathogens

Development of new and safer pesticides that are target-specific is backed by a strong Federal, public and commercial mandate. In order to generate a new generation of pesticides that are more ecologically friendly and safe, natural products are being evaluated for pesticidal activities. Many plant-derived chemicals have proven pesticidal properties, including compounds like sesamol (3,4-Methylenedioxyphenol), a lipid from sesame oil and coumarins (1,2-Benzopyrone) found in a variety of plants such as clover, sweet woodruff and grasses. Both of these plant-derived compounds have been shown to inhibit a range of fungi and bacteria and it is believed that these cyclic compounds behave as natural pesticidal defense molecules for plants. These compounds represent a starting point for the exploration of new derivative compounds possessing a range of antifungal activity and for use as seed protectants. Within this study, six derivatives of coumarin that resembled sesamol's structure were screened for their antifungal activity against a range of soil-bome plant pathogenic fungi. Fungi in this in vitro screen included Macrophomina phaseolina (causal agent of charcoal rot) and Pythium spp. (causal agent of seedling blight), two phylogenetically diverse and economically important plant pathogens. Preliminary studies indicate that many of these novel coumarin derivatives work very effectively in vitro to inhibit fungal growth and several coumarin derivatives have higher antifungal activity and stability as compared to either the original coumarin or sesamol compounds alone. Interestingly, several of these highly active coumarin derivatives are halogenated compounds with solubility in water, and they are relatively easy and inexpensive to synthesize. These halogenated coumarin derivatives remained active for extended periods of time displaying 100% inhibition of fungal growth for greater than 3 weeks in vitro. In addition to the in vitro fungal inhibition assays, preliminary phytotoxicity assays of these halogenated coumarin compounds show no obvious plant toxicity issues or interference in plant development. These results support additional research in this area of natural pesticide development.     

Construction of a microbial natural product library for chemical biology studies

The RIKEN Natural Products Depository (NPDepo) is a public depository of small molecules. Currently, the NPDepo chemical library contains 39,200 pure compounds, half of which are natural products and their derivatives. In order to reinforce the uniqueness of our chemical library, we have improved our strategies for the collection of microbial natural products. Firstly, a microbial metabolite fraction library coupled with an MP (microbial products) plot database provides a powerful resource for the efficient isolation of microbial metabolites. Secondly, biosynthetic studies of microbial metabolites have enabled us to not only access ingenious biosynthetic machineries, but also obtain a variety of biosynthetic intermediates. Our chemical library contributes to the discovery of molecular probes for increasing our understanding of complex biological processes and for eventually developing new drug leads.     

天然真菌与人工发酵制品对免疫系统的影响研究概况

整理分析有关真菌及其生物技术制品生物活性的研究文献,发现真菌类中药资源丰富、品种繁多、成分复杂、药理作用广泛。目前已被动物实验或临床研究证实具有显著生物活性的主要成分是多糖类、三萜类、核苷类以及多肽类等天然化合物。尤其是作为真菌细胞结构物质的高分子多糖体对机体免疫系统具有显著的影响。如在保护机体免疫器官、增加免疫器官重量,以及对单核吞噬细胞系统、T细胞、B细胞、红细胞、NK细胞、LAK细胞、补体系统、白细胞介素、干扰素、集落刺激因子、肿瘤坏死因子及一氧化碳等多项或单项免疫功能具有显著的增强或调节作用。在抗病毒与抗肿瘤免疫等方面显示出自身特点和优势。虽然也有一些真菌及其提取物被证明对机体免疫功能具有显著的、与药物剂量相关的抑制作用,但并未发现对机体免疫器官或免疫细胞有任何的毒副反应。作者拟将20年来有关真菌及其提取物对机体免疫系统的影响研究文献进行了整理,并按免疫功能分类进行了综述,对相关问题在文后还作了讨论,以期为真菌类药物在医学上进行深入的临床研究与应用提供思路。     

The impacts of pretreatment on the fermentability of pretreated lignocellulosic biomass: a comparative evaluation between ammonia fiber expansion and dilute acid pretreatment

The sustainable production of biofuels will require the efficient utilization of lignocellulosic biomass. A key barrier involves the creation of growth-inhibitory compounds by chemical pretreatment steps, which ultimately reduce the efficiency of fermentative microbial biocatalysts. The primary toxins include organic acids, furan derivatives, and phenolic compounds. Weak acids enter the cell and dissociate, resulting in a drop in intracellular pH as well as various anion-specific effects on metabolism. Furan derivatives, dehydration products of hexose and pentose sugars, have been shown to hinder fermentative enzyme function. Phenolic compounds, formed from lignin, can disrupt membranes and are hypothesized to interfere with the function of intracellular hydrophobic targets. This review covers mechanisms of toxicity and tolerance for these compounds with a specific focus on the important industrial organism Escherichia coli. Recent efforts to engineer E. coli for improved tolerance to these toxins are also discussed.     

Will natural products remain an important source of drug research for the future?

In the highly competitive environment of contemporary pharmaceutical research, natural products provide a unique element of molecular diversity and biological functionality which is indispensable for drug discovery. The emergence of strategies to deliver drug leads from natural products within the same time frame as synthetic chemical screening has eliminated a major limitation of the past. At a more functional level, the application of molecular genetics techniques has permitted the manipulation of biosynthetic pathways for the generation of novel chemical species as well as rendering hitherto uncultivatable microorganisms accessible for secondary metabolite generation. These developments augur well for an industry confronted with the challenge of finding lead compounds directed at the plethora of new targets arising from genomics projects. The exploitation of structural chemical databases comprising a wide variety of chemotypes, in conjunction with databases on target genes and proteins, will facilitate the creation of new chemical entities through computational molecular modelling for pharmacological evaluation.     

Biosynthesis and function of polyacetylenes and allied natural products

Polyacetylenic natural products are a substantial class of often unstable compounds containing a unique carbon–carbon triple bond functionality, that are intriguing for their wide variety of biochemical and ecological functions, economic potential, and surprising mode of biosynthesis. Isotopic tracer experiments between 1960 and 1990 demonstrated that the majority of these compounds are derived from fatty acid and polyketide precursors. During the past decade, research into the metabolism of polyacetylenes has swiftly advanced, driven by the cloning of the first genes responsible for polyacetylene biosynthesis in plants, moss, fungi, and actinomycetes and the initial characterization of the gene products.

The current state of knowledge of the biochemistry and molecular genetics of polyacetylenic secondary metabolic pathways will be presented together with an up-to-date survey of new terrestrial and marine natural products, their known biological activities, and a discussion of their likely metabolic origins.     

VO(acac)(2)/H(2)O(2)/NaI: a mild and efficient combination for the cleavage of dithioacetal derivatives of sugars

A wide variety of dithioacetal derivatives of sugars can be cleaved easily into the corresponding open-chain aldehydo sugars using an efficient combination of VO(acac)₂/H₂O₂/NaI at 0–5 °C. Some of the salient features of this protocol are mild reaction conditions, good yields, short reaction times, easy work-up procedures, and non-involvement of toxic chemicals.