Isolation, Synthesis, and Biological Activity of Chlorinated Alkylresorcinols from Dictyostelium Cellular Slime Molds

Isolation and Structure Determination of New Pyrones from Dictyostelium spp. Cellular Slime Molds Coincubated with Pseudomonas spp

Cellular slime molds are excellent model organisms in the field of cell and developmental biology because of their simple developmental patterns. During our studies on the identification of bioactive molecules from secondary metabolites of cellular slime molds toward the development of novel pharmaceuticals, we revealed the structural diversity of secondary metabolites. Cellular slime molds grow by feeding on bacteria, such as Klebsiella aerogenes and Escherichia coli, without using medium components. Although changing the feeding bacteria is expected to affect dramatically the secondary metabolite production, the effect of the feeding bacteria on the production of secondary metabolites is not known. Herein, we report the isolation and structure elucidation of clavapyrone (1) from Dictyostelium clavatum, intermedipyrone (2) from D. magnum, and magnumiol (3) from D. intermedium. These compounds are not obtained from usual cultural conditions with Klebsiella aerogenes but obtained from coincubated conditions with Pseudomonas spp. The results demonstrate the diversity of the secondary metabolites of cellular slime molds and suggest that widening the range of feeding bacteria for cellular slime molds would increase their application potential in drug discovery.

Alkyl aromatic derivatives from the endophytic fungus Cytospora rhizophorae

Two new alkylresorcinols named herein 5'-methoxy-integracins A-B (1-2), two new monomeric alkyl aromatic derivatives 3-(7-hydroxyheptyl)-5-methoxyphenol (5) and 7-(3,5-dihydroxyphenyl) heptyl acetate (6), along with four known compounds including integracins A-B (3-4), 2,4-dihydroxy-6-(8-hydroxyoctyl) benzene (7), and cytosporone B (8) were isolated from the endophytic fungus Cytospora rhizophorae A761. The structures of the four new compounds were elucidated by NMR, HRESIMS data, and electronic circular dichroism (ECD) calculations, whereas the compounds 1 and 2 were disclosed as a class of the natural rare-occurring dimeric alkylresorcinol derivatives. Moreover, the bioassays of the new compounds clarified that compound 1 was a potent inhibitor for the α-glucosidase, and compound 2 showed relatively good activity against the tumor cell lines. It is worth mentioning that the known compound integracin B (4) was first reported to display significant antibacterial activity against Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) with MIC values of 6.25 μg ml^-1.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Diversity of Bacterial Secondary Metabolite Biosynthetic Gene Clusters in Three Vietnamese Sponges

Recent reviews have reinforced sponge-associated bacteria as a valuable source of structurally diverse secondary metabolites with potent biological properties, which makes these microbial communities promising sources of new drug candidates. However, the overall diversity of secondary metabolite biosynthetic potential present in bacteria is difficult to access due to the fact that the majority of bacteria are not readily cultured in the laboratory. Thus, use of cultivation-independent approaches may allow accessing "silent" and "cryptic" secondary metabolite biosynthetic gene clusters present in bacteria that cannot yet be cultured. In the present study, we investigated the diversity of secondary metabolite biosynthetic gene clusters (BGCs) in metagenomes of bacterial communities associated with three sponge species: Clathria reinwardti, Rhabdastrella globostellata, and Spheciospongia sp. The results reveal that the three metagenomes contain a high number of predicted BGCs, ranging from 282 to 463 BGCs per metagenome. The types of BGCs were diverse and represented 12 different cluster types. Clusters predicted to encode fatty acid synthases and polyketide synthases (PKS) were the most dominant BGC types, followed by clusters encoding synthesis of terpenes and bacteriocins. Based on BGC sequence similarity analysis, 363 gene cluster families (GCFs) were identified. Interestingly, no GCFs were assigned to pathways responsible for the production of known compounds, implying that the clusters detected might be responsible for production of several novel compounds. The KS gene sequences from PKS clusters were used to predict the taxonomic origin of the clusters involved. The KS sequences were related to 12 bacterial phyla with Actinobacteria, Proteobacteria, and Firmicutes as the most predominant. At the genus level, the KSs were most related to those found in the genera Mycolicibacterium, Mycobacterium, Burkholderia, and Streptomyces. Phylogenetic analysis of KS sequences resulted in detection of two known 'sponge-specific' BGCs, i.e., SupA and SwfA, as well as a new 'sponge-specific' cluster related to fatty acid synthesis in the phylum Candidatus Poribacteria and composed only by KS sequences of the three sponge-associated bacterial communities assessed here.

Design, synthesis, and structure-activity relationship studies of the anaephene antibiotics

The natural products, anaephenes A (1) and B (2), were found to have antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA). In this report, we expanded on our previous synthetic efforts by preparing a library of eighteen analogues in order to understand the structure-activity relationships (SAR) of this interesting class of natural products. These analogues were selected to explore the biological impact of structural variations in the alkyl chain and on the phenol moiety. Last, we further assessed the biological activity of anaephene B (2) and two additional analogues against other clinically relevant bacterial strains and the hemolytic activity of each and determined that these compounds act via a bactericidal mechanism. These studies led to the identification of compound 7, which was 4-fold more potent than the natural product (2) against MRSA (2 vs. 8 μg/ml) and a 2-hydroxypyridine analogue (18) which demonstrated equal potency compared with the natural product (2), albeit with a significant reduction in hemolytic activity (<1% vs. 80% at 100 μM).

Bioactive sesquiterpene coumarins from the resin of Ferula sinkiangensis targeted on over-activation of microglia

Nine undescribed (1-4, 6-10) sesquiterpene coumarins, together with a new natural one (5) and ten known ones (11-20), were isolated from the low polarity fraction of the 95% ethanol extract of the resin of Ferula sinkiangensis. Their structures were elucidated based on the comprehensive analysis of HRESIMS, 1D and 2D NMR data. The absolute configurations were determined by comparison of experimental and calculated ECD spectra. All the identified SCs were evaluated for their anti-neuroinflammatory activities in LPS-induced BV-2 cells. Ferusingensine G (8) displayed a significant inhibitory effect on nitric oxide (NO) production with an IC₅₀ value of 1.2 μM. The results suggested that natural SCs might be served as potential neuroinflammatory inhibitors.

Synthesis of the Cyanobacterial Antibiotics Anaephenes A and B

The first syntheses of the antibacterial natural products anaephenes A (1) and B (2) are reported. Both natural products were synthesized in five linear steps from commercially available tert-butyl(3-iodophenoxy)dimethylsilane. Key steps for the synthesis included a Sonogashira cross-coupling and a Julia-Kocienski olefination to selectively construct the E-alkene present in the natural products. This synthetic route allowed the identities and antimicrobial activities of anaephenes A (1) and B (2) to be confirmed. Additionally, these compounds displayed antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) with MIC values of 16 and 8 μg/mL, respectively.

Two New Terpenes Isolated from Dictyostelium Cellular Slime Molds

We report a protoilludane-type sesquiterpene, mucoroidiol, and a geranylated bicyclogermacranol, firmibasiol, isolated from Dictyostelium cellular slime molds. The methanol extracts of the fruiting bodies of cellular slime molds were separated by chromatographic methods to give these compounds. Their structures have been established by several spectral means. Mucoroidiol and firmibasiol are the first examples of more modified and oxidized terpenoids isolated from cellular slime molds. Mucoroidiol showed moderate osteoclast-differentiation inhibitory activity despite demonstrating very weak cell-proliferation inhibitory activity. Therefore, cellular slime molds produce considerably diverse secondary metabolites, and they are promising sources of new natural product chemistry.

Chemistry, bioactivity and biosynthesis of cyanobacterial alkylresorcinols

Covering: up to 2019 Alkylresorcinols are amphiphilic metabolites, well-known for their diverse biological activities, produced by both prokaryotes and eukaryotes. A few classes of alkylresorcinol scaffolds have been reported from the photoautotrophic cyanobacteria, ranging from the relatively simple hierridins to the more intricate cylindrocyclophanes. Recently, it has emerged that cyanobacteria employ two different biosynthetic pathways to produce unique alkylresorcinol scaffolds. However, these convergent pathways intersect by sharing biosynthetic elements which lead to common structural motifs. To obtain a broader view of the biochemical diversity of these compounds in cyanobacteria, we comprehensively cover the isolation, structure, biological activity and biosynthesis of their mono- and dialkylresorcinols. Moreover, we provide an overview of the diversity and distribution of alkylresorcinol-generating biosynthetic gene clusters in this phylum and highlight opportunities for discovery of novel alkylresorcinol scaffolds. Because some of these molecules have inspired notable syntheses, different approaches used to build these molecules in the laboratory are showcased.

Structure of Hierridin C, Synthesis of Hierridins B and C, and Evidence for Prevalent Alkylresorcinol Biosynthesis in Picocyanobacteria

Small, single-celled planktonic cyanobacteria are ubiquitous in the world's oceans yet tend not to be perceived as secondary metabolite-rich organisms. Here we report the isolation and structure elucidation of hierridin C, a minor metabolite obtained from the cultured picocyanobacterium Cyanobium sp. LEGE 06113. We describe a simple, straightforward synthetic route to the scarcely produced hierridins that relies on a key regioselective halogenation step. In addition, we show that these compounds originate from a type III PKS pathway and that similar biosynthetic gene clusters are found in a variety of bacterial genomes, most notably those of the globally distributed picocyanobacteria genera Prochlorococcus, Cyanobium and Synechococcus.

Dictyostelium: An Important Source of Structural and Functional Diversity in Drug Discovery

The cellular slime mold Dictyostelium discoideum is an excellent model organism for the study of cell and developmental biology because of its simple life cycle and ease of use. Recent findings suggest that Dictyostelium and possibly other genera of cellular slime molds, are potential sources of novel lead compounds for pharmacological and medical research. In this review, we present supporting evidence that cellular slime molds are an untapped source of lead compounds by examining the discovery and functions of polyketide differentiation-inducing factor-1, a compound that was originally isolated as an inducer of stalk-cell differentiation in D. discoideum and, together with its derivatives, is now a promising lead compound for drug discovery in several areas. We also review other novel compounds, including secondary metabolites, that have been isolated from cellular slime molds.

5-Alkylresorcinol Derivatives from the Bryozoan Schizomavella mamillata: Isolation, Synthesis, and Antioxidant Activity

The chemical study of the bryozoan Schizomavella mamillata has led to the isolation of six new 5-alkylresorcinol derivatives, schizols A–F (1–6), whose structures were established by spectrocospic means. Schizol A (1) exhibits a (E)-6-phenylnon-5-enyl moiety linked to the C-5 of a resorcinol ring, while in schizol B (2) the substituent at C-5 contains an unusual 1,2-dihydrocyclobutabenzene moiety. Schizols C (3) and D (4) have been characterized as the 1-sulfate derivatives of 1 and 2, respectively, and schizols E (5) and F (6) are the corresponding 1,3-disulfates. Schizol A (1) has been synthetized from 3,5-dimethoxybenzaldehyde through a sequence involving a Wittig reaction for the construction of the C-1′,C-2′ bond and a Julia–Kocienski olefination for the synthesis of the C-5′,C-6′ double bond. In the ABTS (2,2′-azinobis(3-ethylbenzothiazoline-6-sulphonic acid)) antioxidant assay, the natural compounds schizol A (1) and schizol B (2) showed higher radical scavenging activity than the Trolox standard.