Phytochemistry Reviews (v.12, #4)

Preface: special issue Biocom12 by Francisco A. Macías; José M. G. Molinillo (579-580).

Aloe barbadensis: how a miraculous plant becomes reality by Nuria Chinchilla; Ceferino Carrera; Alexandra G. Durán; Mariola Macías; Ascensión Torres; Francisco A. Macías (581-602).
Aloe barbadensis Miller is a plant that is native to North and East Africa and has accompanied man for over 5,000 years. The aloe vera plant has been endowed with digestive, dermatological, culinary and cosmetic virtues. On this basis, aloe provides a range of possibilities for fascinating studies from several points of view, including the analysis of chemical composition, the biochemistry involved in various activities and its application in pharmacology, as well as from horticultural and economic standpoints. The use of aloe vera as a medicinal plant is mentioned in numerous ancient texts such as the Bible. This multitude of medicinal uses has been described and discussed for centuries, thus transforming this miracle plant into reality. A summary of the historical uses, chemical composition and biological activities of this species is presented in this review. The latest clinical studies involved in vivo and in vitro assays conducted with aloe vera gel or its metabolites and the results of these studies are reviewed.
Keywords: Aloe vera ; Phytochemistry; Acemannan; Bioactivity

Semiochemicals are natural products occurring in plants, bacteria or animals which function as carriers of a special message. Depending on the mode of function of the semiochemicals, they are divided into pheromones that trigger a response in members of the same species and allelochemicals (kairomones, allomones) that act between individuals of different species. Semiochemicals are very important compounds that influence the behavior of plants and animals and their adaption to a changing environment. As their importance for plants, animals and the ecological system itself is huge, the synthetic access to these chemicals, their precursors and derivatives is of high interest. Beyond novel strategies for the construction of semiochemical skeletons, combinatorial methods have been implemented to synthesize medium-sized and large-sized libraries that enable diverse modifications of the active compounds. These combinatorial approaches allow the screening for more active compounds and they elucidate the mode of action of the semiochemical or of the biological target. This review summarizes the state of the art procedures for the synthesis of important skeletons appearing in semiochemicals and gives special synthetic procedures for selected examples if the procedure is suitable for a general transfer to the synthesis of derivatives. The synthetic examples are given in the context of known active phytochemicals and their function that allows an evaluation of the given procedures with respect to the fulfillment of the common structural requirements (the structural diversity and flexibility) and the importance for the regulation of biological systems. Parts of this review were given in a lecture at the BioCom 12 in Cadiz, 2012.
Keywords: Combinatorial synthesis; Indole alkaloids; Natural products; Oxygen heterocycles; Solid-phase synthesis

Polyphenols as fungal phytotoxins, seed germination stimulants and phytoalexins by Alessio Cimmino; Anna Andolfi; Mohamed Abouzeid; Antonio Evidente (653-672).
This review deals with the sources and chemical and biological characterization of phytotoxic polyphenols produced essentially by pathogenic fungi of forest and crop plants and of weeds. Their potential use as natural herbicides and fungicides is discussed. The use of some polyphenols which could be applied as an alternative method to control parasitic weeds, the so called “suicidal germination”, will be covered. The sources and the isolation and identification of polyphenols produced by some crop plants in consequence of the attack of pathogenic fungi as plant defence compounds (phytoalexins), are also described.
Keywords: Polyphenols; Phytotoxins; Seed germination stimulants; Phytoalexins

Phytochemistry and pharmacognosy of the genus Psorospermum by Francesco Epifano; Serena Fiorito; Salvatore Genovese (673-684).
The genus Psorospermum Baker (tribe Vismieae, family Guttiferae, subfamily Hypericoideae) comprises 55 species, mainly of which are represented by shrubs or small trees typically growing in tropical regions of South America, Africa, and Madasgascar. Most of the species of the title genus have been used for centuries in the ethnomedical traditions of indigenous African populations as febrifugal, antidote against poisons, purgative, stomachic, and as a remedy for the treatment of leprosy, skin diseases (like dermatitis, scabies and eczemas), and subcutaneous wounds. Phytochemicals isolated from Psorospermum spp. comprise alkaloids, simple and prenylated anthraquinones, flavonoids, long chain alcohols and hydrocarbons, steroids, tannins, terpenes, and simple and prenylated xanthones. The reported biological activities of the above mentioned natural compounds refer to anti-bacterial, anti-protozoal, anti-fungal, anti-viral, anti-cancer, anti-oxidant, and neuroprotective effects. The aim of this review is to examine in detail from a phytochemical and pharmacologically points of view what is reported in the current literature about the properties of phytopreparations or individual active principles obtained from plants belonging to Psorospermum genus.
Keywords: Anthraquinones; Flavonoids; Oxyprenylated secondary metabolites; Psorospermin; Xanthones

Comparative genome analysis of Bacillus spp. and its relationship with bioactive nonribosomal peptide production by A. Hamdache; R. Azarken; A. Lamarti; J. Aleu; I. G. Collado (685-716).
Bacillus genus comprises an important number of species which produce a wide range of secondary metabolites displaying a broad spectrum of activity and great structural diversity. The genome sequences of an important number of species have been published and a large number of orphan genes reported. This review, covering all the literature in this field up to end of 2011, summarizes and compares the genetic potential of these organisms from the point of view of bioactive nonribosomal peptide production and their application as antibiotics, plant pathogen biocontrol, promotion of plant growth, etc. The biological and structural studies of the peptides isolated from Bacillus species are revised and some aspects of the biosynthesis of these metabolites and related compounds are discussed.
Keywords: Bacillus genome; Nonribosomal; Ribosomal; Peptide; Antibiotic; Lipopeptide; Siderophore

Lignans and lignins are among the main metabolic products of phenylpropanoid metabolism in vascular plants. They are compounds representing the building blocks of plant cell walls. Moreover they have a broad range of biological activities such as antitumoral, antimitotic, antiviral and cytotoxic and are thought to be involved in the plant defense against pathogens and pests. In this paper we report a survey of the past and current literature about lignans and neolignans and their germination inhibitory activity on cultivated and wild species from plants of the Mediterranean area. Some examples of synthetic methodologies of these molecules have also been reported.
Keywords: Lignan; Neolignan; Phytotoxicity; Mediterranean plants

Chemistry and biological activities of Calceolaria spp. (Calceolariaceae: scrophulariaceae) by Carlos L. Céspedes; Juan R. Salazar; Julio Alarcon (733-749).
Calceolaria spp. is regarded both as a notorious weed and a popular ornamental garden plant and have medicinal application. Some taxa of the America distributed Calceolaria genus are toxic to insects and its effect has been associated with the presence of diterpenes, triterpenes and naphthoquinones. However, Calceolaria spp. also produces a number of flavonoids and phenylpropanoids that have been shown to possess interesting biological activities. All these aspects are considered in this review to allow an evaluation of the potential for utilization of the large biodiversity of Calceolaria available. The phytochemistry of many members of the Calceolaria genus is included.
Keywords: Calceolariaceae; Diterpenes; Pimaradiene; Abietatriene; Biological activity

What makes Allium species effective against pathogenic microbes? by Virginia Lanzotti; Giuliano Bonanomi; Felice Scala (751-772).
The antimicrobial activity of garlic (Allium sativum L.) has been known since ancient times. The first citation dates back to the Egyptian period of fifteenth century BC when garlic was reported to be used in folk medicine as a remedy for microbial infections. Scientific investigations on garlic started in 1858 with the work of Pasteur who first noted antibacterial properties of garlic extracts. From that date to the discovery of antibiotics, garlic has been used against amoebic dysentery and epidemic diseases such as typhus, cholera, diphtheria, and tuberculosis. But what makes garlic and Allium species effective against pathogenic microbes? The volatile allicin and other thiosulfinates, giving pungency to Allium plants, are well-studied antimicrobial agents. The thiosulfinates can decompose to form additional sulfur constituents, including diallyl, methyl allyl, and dipropyl mono-, di-, tri- e tetra-sulfides, and (E)- and (Z)-ajoene without losing antimicrobial activity. Besides these compounds, onion and garlic are characterized by polar compounds of steroidal and phenolic origin, often glycosilated, not pungent and more stable during cooking, showing also antimicrobial activity. Recently, there has been increasing scientific attention given to such compounds. Nitrogen organic compounds, like alkaloids and polypeptides, have also been isolated from these plants and have shown antimicrobial activity. In this paper, the literature about the major volatile and non-volatile organic compounds of garlic and other Allium plants has been reviewed. Particular attention is given to the compounds possessing antimicrobial activity and to the correlation between the observed activity and the chemical structure of the tested compounds.
Keywords: Garlic; Onion; Thiosulfinates; Saponins; Phenolics; Antimicrobial activity

Classical and epigenetic approaches to metabolite diversification in filamentous fungi by Jacqueline Aparecida Takahashi; Ana Paula Campos Teles; Adriana de Almeida Pinto Bracarense; Dhionne Corrêia Gomes (773-789).
Studies on fungal metabolites have produced an overwhelming expectation concerning the production of novel bioactive compounds for pharmaceutical applications. The adding of various biosynthetic precursors and the changing of nutritional components in the fermentation medium can change biosynthesis pathways, also leading to the production of novel metabolites. In addition, several growing conditions can be classically manipulated to modify fungal metabolite profiles. Recently, modern genome sequence tools have shown that not all gene clusters are regularly expressed in conventional growing conditions, thus expanding the possibilities of modulating the chemical metabolite profiles produced by filamentous fungi. This review discusses and exemplifies classical and epigenetic tools successfully applied to diversify metabolite production and to produce fungal metabolites from silent metabolic pathways.
Keywords: Aspergillus ; Culture media; Epigenetic modifiers; Fungal metabolites; OSMAC; Penicillium

Nematicidal potential of Brassicaceae by P. Avato; T. D’Addabbo; P. Leonetti; M. P. Argentieri (791-802).
Brassicaceae Burnett (syn. Cruciferae A. L. de Jussieu) include many important economic plants used as edibile or ornamental. They are commonly known as the “mustard” plant family due to the sharp, potent flavour of their main metabolites, the glucosinolates (GLSs) which contain sulfur. Glucosinolates coexist in vivo with glycosylated thioglucosidases, myrosinase(s), responsible of their hydrolysis with the production of bioactive cognate isothiocyanates (ITC). GLSs and ITCs function as defence bioactive metabolites against plant pathogens, insects and herbivores. The present review paper focus on GLSs role as bionematicides. The current knowledge on the efficacy of these phytochemicals against the most common phytoparasitic nematodes affecting crops of agriculture importance such as tomato, potato and grapevine is reported. Data from our ongoing research on the in vitro biocidal activity of glucosinolate extracts, and their main components, against the virus-vector nematode Xiphinema index Thorne & Allen and the carrot cyst nematode Heterodera carotae Jones are also described.
Keywords: Brassicaceae; Glucosinolates; Isothiocyanates; Nematodes; Globodera rostochiensis ; Meloidogyne incognita ; Xiphinema index ; Heterodera carotae ; Pratylenchus penetrans

Plant growth inhibitors: allelopathic role or phytotoxic effects? Focus on Mediterranean biomes by Monica Scognamiglio; Brigida D’Abrosca; Assunta Esposito; Severina Pacifico; Pietro Monaco; Antonio Fiorentino (803-830).
Allelopathy (the chemical based communication among plants) is gaining more and more attention thanks to its likely outcomes in several fields, but it is, in the meantime, a questionable topic, due to a difficult determination. Despite the broad literature, allelopathic interactions are far from being clarified. Conclusive evidence in this field is not a simple find, as this biological activity is governed by a number of different factors. Such an issue can be solved only provided that suitable methods are used. Understanding allelopathy in natural ecosystems may be crucial in order to think about the exploitation of this resource. Mediterranean plants, in particular, have been proven to be a source of natural active compounds. This paper reviews the most outstanding methods used for plant extract or pure metabolite phytotoxic or allelopathic properties determination. Furthermore, it points out the bioactive metabolites reported from plants characteristics of Mediterranean ecosystems.
Keywords: Plant growth inhibitors; Mediterrantean plants; Allelopathy; Phytotoxicity; Bioassays

Geographically distinct populations of Paterson’s curse (Echium plantagineum L., Boragineacea), found near roadsides across New South Wales and Victoria, Australia were surveyed along 3 distinct longitudinal transects in spring of 2011 for presence of pyrrolizidine alkaloids and naphthoquinones in sampled plants. Composite samples of shoots and roots were collected from each of 45 sites; shoot extracts were subjected to solid phase extraction and LC-ESI/MS for determination of pyrrolizidine alkaloids (PAs) and related N-oxides (PANOs), while root periderm extracts were analysed for naphthoquinone content spectrophotometrically and by LC-ESI/MS. Metabolic profiling of 12 possible PAs and PANOs showed their consistent appearance in all shoot extracts, with lepthamine N-oxide, echimidine-N oxide and echumine N-oxide predominant. The three major PANOs were significantly higher in northern sampling locations than those further south. Root extracts contained shikonin and several related naphthoquinones, as well as two of the major PANOs found in the leaves. Naphthoquinones were highest in the northwest corner of the sampled region. The patterns of abundance of secondary metabolites in E. plantagienum suggest that climate change might result in greater production of defensive compounds by E. plantagineum, making this weed increasingly toxic to livestock.
Keywords: Echimidine; Echiumine; Leptanthine; Plant defence; Shikonin

Ecological phytochemistry of Cerrado (Brazilian savanna) plants by Paula Novaes; José M. G. Molinillo; Rosa M. Varela; Francisco A. Macías (839-855).
The Cerrado (the Brazilian savanna) is one of the vegetation formations of great biodiversity in Brazil and it has experienced strong deforestation and fragmentation. The Cerrado must contain at least 12,000 higher plant species. We discuss the ecological relevance of phytochemical studies carried out on plants from the Cerrado, including examples of phytotoxicity, antifungal, insecticidal and antibacterial activities. The results have been classified according to activity and plant family. The most active compounds have been highlighted and other activities are discussed. A large number of complex biochemical interactions occur in this system. However, only a small fraction of the species has been studied from the phytochemical viewpoint to identify the metabolites responsible for these interactions.
Keywords: Ecological phytochemistry; Semiochemical; Biocommunication

Terpenoid biotransformations by Mucor species by Eliane de Oliveira Silva; Niege Araçari Jacometti Cardoso Furtado; Josefina Aleu; Isidro González Collado (857-876).
Terpenoids are natural products of great interest due to their widespread use in agrochemicals, drugs, fragrances, flavouring and pigments. Biocatalysts are increasingly being used in the search for new derivatives with improved properties especially to obtain structurally novel leads for new drugs which are difficult to obtain using conventional organic chemical methods. This review, covering up to the end of 2012, reports on the application of Mucor species as catalysts in terpenoid biotransformation to obtain new drug targets, enhance pharmacological activity or decrease the unwanted effects of starting material.
Keywords: Biotransformation; Fungus; Mucor sp.; Terpenoids

Saponins and their role in biological processes in plants by Ahmad Faizal; Danny Geelen (877-893).
Saponins are steroid and triterpenoid glycosides that display diverse biological activities. The wide-spread occurrence in plants as well as the potential for pharmaceutical application has led to saponin extraction and identification in numerous species. Although these efforts are important to extend our knowledge of naturally occurring saponin structures, recent attention has been given to the biosynthesis and distribution in plants. In this review, we present recent advances on saponin production and distribution and highlight studies showing effects on the growth and development.
Keywords: Plant defense; Plant development; Saponin biosynthesis; Steroidal saponin; Triterpenoid saponin

Chemical genetics strategies for identification of molecular targets by José Manuel Botubol Ares; Mª Jesús Durán-Peña; Rosario Hernández-Galán; Isidro G. Collado (895-914).
Chemical genetics is an emerging field that can be used to study the interactions of chemical compounds, including natural products, with proteins. Usually, the identification of molecular targets is the starting point for studying a drug’s mechanism of action and this has been a crucial step in understanding many biological processes. While a great variety of target identification methods have been developed over the last several years, there are still many bioactive compounds whose target proteins have not yet been revealed because no routine protocols can be adopted. This review contains information concerning the most relevant principles of chemical genetics with special emphasis on the different genomic and proteomic approaches used in forward chemical genetics to identify the molecular targets of the bioactive compounds, the advantages and disadvantages of each and a detailed list of successful examples of molecular targets identified with these approaches.
Keywords: Chemical biology; Forward chemical genetics; Small molecules; Target proteins

Constituents from Aphanamixis species and their biological activities by Guo-Wei Wang; Hui-Zi Jin; Wei-Dong Zhang (915-942).
Members of the Meliaceae family have been studied extensively because they contain a series of interesting, structurally diverse and biologically important triterpenoids. Plants from the genus Aphanamixis of Meliaceae have a long history of medicinal use. Substantial investigations into their chemical and pharmacological properties have been performed. Recently, interest in this genus has been centred on their production of complex, highly oxidised tetranortriterpenoids (also known as limonoids or meliacins), which exhibit potent cytotoxic and antitumour activities against various human cancer cell lines and in preclinical animal models. This review summarises triterpenoids isolated from Aphanamixis plants and those triterpenoids’ bioactivities, structure–activity relationships and biosyntheses.
Keywords: Aphanamixis ; Biological activities; Limonoids; Meliaceae

Traditional Mongolian Medicine: history and status quo by A. Pitschmann; S. Purevsuren; A. Obmann; D. Natsagdorj; D. Gunbilig; S. Narantuya; Ch. Kletter; S. Glasl (943-959).
Traditional Mongolian Medicine (TMM) plays an important role within the medical system of Mongolia nowadays. This medical system is rather unknown in the Western world, and detailed information can hardly be found in literature. In this article various aspects of TMM are highlighted. The eventful history of TMM is presented, and the centres which offer today’s traditional medical care are introduced. Institutions which provide education in TMM are outlined, and the latest developments in the national standard are highlighted, according to which the different institutions have to develop their curricula. Furthermore, an overview is given about herbal medicines in Mongolia and the health situation in this country. Finally, the international and Mongolian literature of Achillea asiatica, Dianthus versicolor, Euphorbia pallasii, Lilium pumilum, and Saussurea amara, which are all used in TMM to cure liver diseases, is reviewed.
Keywords: Traditional Mongolian Medicine; Education; Herbal drugs; Liver diseases; Achillea asiatica ; Dianthus versicolor ; Euphorbia pallasii ; Lilium pumilum ; Saussurea amara

Primary aliphatic alkanols from C6 to C13 were tested for their antifungal activity against Saccharomyces cerevisiae using a broth dilution method. Undecanol (C11) was found to be the most potent fungicide against this yeast with the minimum fungicidal concentration (MFC) of 25 μg/ml (0.14 mM), followed by decanol (C10) with the minimum inhibitory concentration (MIC) of 50 μg/ml (0.31 mM). The time-kill curve study showed that undecanol was fungicidal against S. cerevisiae at any growth stages. This fungicidal activity was not influenced by pH values. Dodecanol (C12) was the most effective fungistatic but did not show any fungicidal activity up to 1600 μg/mL. Fungistatic dodecanol quickly reduced cell viability, but the cell viability recovered shortly after and then finally became no longer different from the control indicating that the effect of dodecanol on S. cerevisiae was classified as a sublethal damage. However, fungistatic dodecanol combined with sublethal amount of anethole showed a fungicidal activity against this yeast. Anethole completely restricted the recovery of cell viability. Therefore expression of the synergistic effect was probably due to the blockade of the recovering process from dodecanol induced-stress. The alkanols tested inhibited glucose-induced acidification by inhibiting the plasma membrane H+-ATPase. Octanol (C8) increased plasma membrane fluidity in the spheroplast cells of S. cerevisiae. The same series of aliphatic primary alkanols was also tested against a food spoilage fungus Zygosaccharomyces bailii and compared with their effects against S. cerevisiae. Decanol was found to be the most potent fungicide against Z. bailii with an MFC of 50 μg/ml (0.31 mM), whereas undecanol was found to be the most potent fungistatic with an MIC of 25 μg/ml (0.14 mM). The time-kill curve study showed that decanol was fungicidal against Z. bailii at any growth stage. This antifungal activity was slightly enhanced in combination with anethole. The primary antifungal action of medium-chain (C9–C12) alkanols comes from their ability as nonionic surfactants to disrupt the native membrane-associated function of the integral proteins. Hence, the antifungal activity of alkanols is mediated by biophysical process, and the maximum activity can be obtained when balance between hydrophilic and hydrophobic portions becomes the most appropriate.
Keywords: Antifungal activity; Aliphatic primary alkanols; Saccharomyces cerevisiae ; Zygosaccharomyces bailii ; Structure–activity relationship; Surfactants; Lipid-protein interface

Soy isoflavones and their relationship with microflora: beneficial effects on human health in equol producers by Juan Manuel Sánchez-Calvo; Manuel Antonio Rodríguez-Iglesias; José M. G. Molinillo; Francisco A. Macías (979-1000).
The bioavailability of soy isoflavones depends on the composition of the microflora for each subject. Bacteria act on different isoflavones with increased or reduced absorption and cause biotransformation of these compounds into metabolites with higher biological activity. S-equol is the most important metabolite and only 25–65 % of the population have the microflora that produces this compound. The presence of equol-producing bacteria in soy product consumers means that the consumption of such products for prolonged periods leads to lower cardiovascular risk, reduced incidence of prostate and breast cancer, and greater relief from symptoms related to the menopause such as hot flushes and osteoporosis.
Keywords: Aglycones; Glucosides; Daidzein; Equol-producer; Microflora