Investigation of the potential anticancer and antifungal active secondary metabolites from marine natural products

The oceans are a unique resource that has contributed greatly to the field of natural products chemistry. Secondary metabolites from natural sources still play an important role in drug discovery and development by providing pharmaceutical candidates with novel structures that are valuable for synthetic modification. Of the marine organisms described to date, the vast majority of marine natural products derive from invertebrates such as sponges, ascidians, bryozoans, and tunicates. Recently, marine microbes have also come to the forefront of natural products research since they are now being recognized as a significant new source of diverse and unique chemical compounds. With the existence of various diseases which pose a dangerous threat to human health, many bioassays have been developed in an attempt to find suitable agents as cures to those symptoms. Among recognizable infectious diseases, fungal infection is one of the significant causes of mortality and morbidity. As there are only few numbers of antifungal drugs available for therapeutic treatment, searching for new classes of active compounds proves to be crucial. This thesis discusses different methods for screening extracts of marine organisms in search of novel antifungal agents that possess relevant clinical value, with emphasis on the isolation and characterization of these compounds. Chapter I introduces the concept of the main thesis research that is described in subsequent chapters. Chapter II provides details of the discovery of new secondary metabolites from marine invertebrates, including sponges and ascidians, through a bioassay-guided screening process. The new compounds that were isolated include the merotriterpenoid adociasulfate, steroidal sulfates, and a pyridoacridine alkaloid. This chapter also describes antifungal bioassays that were performed and the results of the screening. Chapter III describes the isolation of new secondary metabolites from marine actinomycete strains selected based upon the results of a liquid antifungal assay. In this latter chapter, the problem regarding the screening of marine microbes using the liquid antifungal assay, and the subsequent adjustment by assay modification are described. The isolation and identification of new quinoline alkaloids, a bacterial sesterterpenoid and a novel cytotoxic macrolide are also discussed in detail, with respect to structural elucidation and biological activit

Investigation of the potential anticancer and antifungal active secondary metabolites from marine natural products

The oceans are a unique resource that has contributed greatly to the field of natural products chemistry. Secondary metabolites from natural sources still play an important role in drug discovery and development by providing pharmaceutical candidates with novel structures that are valuable for synthetic modification. Of the marine organisms described to date, the vast majority of marine natural products derive from invertebrates such as sponges, ascidians, bryozoans, and tunicates. Recently, marine microbes have also come to the forefront of natural products research since they are now being recognized as a significant new source of diverse and unique chemical compounds. With the existence of various diseases which pose a dangerous threat to human health, many bioassays have been developed in an attempt to find suitable agents as cures to those symptoms. Among recognizable infectious diseases, fungal infection is one of the significant causes of mortality and morbidity. As there are only few numbers of antifungal drugs available for therapeutic treatment, searching for new classes of active compounds proves to be crucial. This thesis discusses different methods for screening extracts of marine organisms in search of novel antifungal agents that possess relevant clinical value, with emphasis on the isolation and characterization of these compounds. Chapter I introduces the concept of the main thesis research that is described in subsequent chapters. Chapter II provides details of the discovery of new secondary metabolites from marine invertebrates, including sponges and ascidians, through a bioassay-guided screening process. The new compounds that were isolated include the merotriterpenoid adociasulfate, steroidal sulfates, and a pyridoacridine alkaloid. This chapter also describes antifungal bioassays that were performed and the results of the screening. Chapter III describes the isolation of new secondary metabolites from marine actinomycete strains selected based upon the results of a liquid antifungal assay. In this latter chapter, the problem regarding the screening of marine microbes using the liquid antifungal assay, and the subsequent adjustment by assay modification are described. The isolation and identification of new quinoline alkaloids, a bacterial sesterterpenoid and a novel cytotoxic macrolide are also discussed in detail, with respect to structural elucidation and biological activit

Marinoterpins A-C: Rare Linear Merosesterterpenoids from Marine-Derived Actinomycete Bacteria of the Family Streptomycetaceae.

The chemical examination of two undescribed marine actinobacteria has yielded three rare merosesterterpenoids, marinoterpins A-C (1-3, respectively). These compounds were isolated from the culture broth extracts of two marine-derived actinomycetes associated with the family Streptomycetaceae, (our strains were CNQ-253 and AJS-327). The structures of the new compounds were determined by extensive interpretation of 1D and 2D NMR, MS, and combined spectroscopic data. These compounds represent new chemical motifs, combining quinoline-N-oxides with a linear sesterterpenoid side chain. Additionally, consistent in all three metabolites is the rare occurrence of two five-ring ethers, which were derived from an apparent cyclization of methyl group carbons to adjacent hydroxy-bearing methylene groups in the sesterterpenoid side chain. Genome scanning of AJS-327 allowed for the identification of the marinoterpin (mrt) biosynthetic cluster, which consists of 16 open-reading frames that code for a sesterterpene pyrophosphate synthase, prenyltransferase, type II polyketide synthase, anthranilate:CoA-ligase, and several tailoring enzymes apparently responsible for installing the N-oxide and bis-tetrahydrofuran ring motifs

Marinoterpins A-C: Rare Linear Merosesterterpenoids from Marine-Derived Actinomycete Bacteria of the Family Streptomycetaceae.

The chemical examination of two undescribed marine actinobacteria has yielded three rare merosesterterpenoids, marinoterpins A-C (1-3, respectively). These compounds were isolated from the culture broth extracts of two marine-derived actinomycetes associated with the family Streptomycetaceae, (our strains were CNQ-253 and AJS-327). The structures of the new compounds were determined by extensive interpretation of 1D and 2D NMR, MS, and combined spectroscopic data. These compounds represent new chemical motifs, combining quinoline-N-oxides with a linear sesterterpenoid side chain. Additionally, consistent in all three metabolites is the rare occurrence of two five-ring ethers, which were derived from an apparent cyclization of methyl group carbons to adjacent hydroxy-bearing methylene groups in the sesterterpenoid side chain. Genome scanning of AJS-327 allowed for the identification of the marinoterpin (mrt) biosynthetic cluster, which consists of 16 open-reading frames that code for a sesterterpene pyrophosphate synthase, prenyltransferase, type II polyketide synthase, anthranilate:CoA-ligase, and several tailoring enzymes apparently responsible for installing the N-oxide and bis-tetrahydrofuran ring motifs

Ophiocordyceps flavida sp. nov. (Ophiocordycipitaceae), a new species from Thailand associated with Pseudogibellula formicarum (Cordycipitaceae), and their bioactive secondary metabolites

During a diversity study of entomopathogenic fungi in an agricultural ecosystem, two fungi were collected, isolated, and identified based on molecular phylogenetic analyses of three nuclear loci (LSU, TEF1, and RPB1) combined with morphological data. In this study, one novel species is described, Ophiocordyceps flavida, and a new record of Pseudogibellula formicarum for Thailand. Ophiocordyceps flavida morphologically resembles the Hirsutella anamorph of Ophiocordyceps pruinosa by having a mononematous character of the conidiophores and the same insect host (Hemiptera: Cicadellidae). Pseudogibellula formicarum is found to occur simultaneously with O. flavida, producing white conidiophores on the host. Additionally, secondary metabolites of both fungi were investigated and the major compound in O. flavida was identified as 2-[2-(4-chlorophenyl)ethyl]-2-(1,1-dimethylethyl)-oxirane. Pseudogibellula formicarum from Ghana and Thailand produces 6-methoxy-1H-indole-3-carbonitrile as a main component. These compounds are known from chemical synthesis or as products of biotransformation, respectively. However, they were obtained in our study as genuine fungal metabolites for the first time and may even constitute chemotaxonomic markers for the respective speciesNational Center for Genetic Engineering and Biotechnolog

Cytochalasans Act as Inhibitors of Biofilm Formation of <i>Staphylococcus aureus</i>

During the course of our ongoing work to discover new inhibitors of biofilm formation of Staphylococcus aureus from fungal sources, we observed biofilm inhibition by cytochalasans isolated from cultures of the ascomycete Hypoxylon fragiforme for the first time. Two new compounds were purified by a bioassay-guided fractionation procedure; their structures were elucidated subsequently by nuclear magnetic resonance (NMR) spectroscopy and high-resolution mass spectrometry (HR-MS). This unexpected finding prompted us to test further cytochalasans from other fungi and from commercial sources for comparison. Out of 21 cytochalasans, 13 showed significant inhibition of Staphylococcus aureus biofilm formation at subtoxic levels. These findings indicate the potential of cytochalasans as biofilm inhibitors for the first time, also because the minimum inhibitory concentrations (MIC) are independent of the anti-biofilm activities. However, cytochalasans are known to be inhibitors of actin, making some of them very toxic for eukaryotic cells. Since the chemical structures of the tested compounds were rather diverse, the inclusion of additional derivatives, as well as the evaluation of their selectivity against mammalian cells vs. the bacterium, will be necessary as next step in order to develop structure-activity relationships and identify the optimal candidates for development of an anti-biofilm agent