New pyranonaphthoquinones and a phenazine alkaloid isolated from Streptomyces sp. IFM 11307 with TRAIL resistance-overcoming activity

Benzochromenopyrimidines: Synthesis, Antiproliferative Activity against Colorectal Cancer and Physicochemical Properties

Ten new differently substituted 3-benzyl-5-aryl-3,5-dihydro-4H-benzo[6,7]chromeno[2,3-d]pyrimidin-4,6,11-triones 3 were synthesized by a simple and cost-efficient procedure in a one-pot, three-component reaction from readily available ethyl 2-amino-4-aryl-5,10-dioxo-5,10-dihydro-4H-benzo[g]chromene-3-carboxylates, benzylamine and triethyl orthoformate under solvent- and catalyst-free conditions. All the new compounds were screened for their antiproliferative activity against two colorectal-cancer-cell lines. The results showed that the compounds 3-benzyl-5-phenyl-3,5-dihydro-4H-benzo[6,7]chromeno[2,3-d]pyrimidine-4,6,11-trione (3a) and 3-benzyl-5-(3-hydroxyphenyl)-3,5-dihydro-4H-benzo[6,7]chromeno[2,3-d]pyrimidine-4,6,11-trione (3g) exhibited the most potent balanced inhibitory activity against human LoVo and HCT-116 cancer cells.

N-Acetyl-Cysteinylated Streptophenazines from Streptomyces

Here, we describe two N-acetyl-cysteinylated streptophenazines (1 and 2) produced by the soil-derived Streptomyces sp. ID63040 and identified through a metabolomic approach. These metabolites attracted our interest due to their low occurrence frequency in a large library of fermentation broth extracts and their consistent presence in biological replicates of the producer strain. The compounds were found to possess broad-spectrum antibacterial activity while exhibiting low cytotoxicity. The biosynthetic gene cluster from Streptomyces sp. ID63040 was found to be highly similar to the streptophenazine reference cluster in the MIBiG database, which originates from the marine Streptomyces sp. CNB-091. Compounds 1 and 2 were the main streptophenazine products from Streptomyces sp. ID63040 at all cultivation times but were not detected in Streptomyces sp. CNB-091. The lack of obvious candidates for cysteinylation in the Streptomyces sp. ID63040 biosynthetic gene cluster suggests that the N-acetyl-cysteine moiety derives from cellular functions, most likely from mycothiol. Overall, our data represent an interesting example of how to leverage metabolomics for the discovery of new natural products and point out the often-neglected contribution of house-keeping cellular functions to natural product diversification.

Total synthesis of griseusins and elucidation of the griseusin mechanism of action

An efficient divergent synthesis of griseusins enabled SAR studies, mechanistic elucidation and evaluation in an axolotl tail regeneration model.

A divergent modular strategy for the enantioselective total synthesis of 12 naturally-occurring griseusin type pyranonaphthoquinones and 8 structurally-similar analogues is described. Key synthetic highlights include Cu-catalyzed enantioselective boration–hydroxylation and hydroxyl-directed C–H olefination to afford the central pharmacophore followed by epoxidation–cyclization and maturation via diastereoselective reduction and regioselective acetylation. Structural revision of griseusin D and absolute structural assignment of 2a,8a-epoxy-epi-4′-deacetyl griseusin B are also reported. Subsequent mechanistic studies establish, for the first time, griseusins as potent inhibitors of peroxiredoxin 1 (Prx1) and glutaredoxin 3 (Grx3). Biological evaluation, including comparative cancer cell line cytotoxicity and axolotl embryo tail inhibition studies, highlights the potential of griseusins as potent molecular probes and/or early stage leads in cancer and regenerative biology.

Recent progress in the isolation, bioactivity, biosynthesis, and total synthesis of natural spiroketals

The isolation, bioactivity, biosynthesis, and total synthesis of natural spiroketals from 2011 to July 2017 have been summarized in this review.

Pyranonaphthoquinones - isolation, biology and synthesis: an update

Covering: 2008 to 2015. A review on the isolation, biological activity and synthesis of pyranonaphthoquinone natural products from 2008-2015 is providedThis review discusses the isolation, biological activity and synthesis of pyranonaphthoquinone natural products, covering the years 2008-2015. The pyranonaphthoquinones are a group of metabolites sharing a common naphtho[2,3-c]pyran-5,10-dione ring system that have been isolated from a wide range of microorganisms, plants and insects. In addition to their synthetically challenging molecular structures, pyranonaphthoquinones exhibit a wide array of biological activity, including anti-bacterial, anti-fungal and anti-cancer properties. The therapeutic potential of these compounds has led to a dynamic interplay between total synthesis and biological evaluation.

Recent developments in the isolation, biological function, biosynthesis, and synthesis of phenazine natural products

Phenazines are natural products which are produced by bacteria or by archaeal Methanosarcina species. The tricyclic ring system enables redox processes, which producing organisms use for oxidation of NADH or for the generation of reactive oxygen species (ROS), giving them advantages over other microorganisms. In this review we summarize the progress in the field since 2005 regarding the isolation of new phenazine natural products, new insights in their biological function, and particularly the now almost completely understood biosynthesis. The review is complemented by a description of new synthetic methods and total syntheses of phenazines.

Restoring TRAIL Induced Apoptosis Using Naturopathy. Hercules Joins Hand with Nature to Triumph Over Lernaean Hydra

Cancer is a multifaceted disease. Our deepened knowledge about genetic and biological mechanisms of cancer cells presents an opportunity to explore the inter-individual differences in the body’s ability to metabolize and respond to different nutrients. It is becoming progressively more understandable that the deregulation of several signaling pathways and the alterations in apoptotic response are some of the major determinants that underpin carcinogenesis. Tumor necrosis factor-Related Apoptosis-Inducing Ligand (TRAIL)-mediated signaling has gained a remarkable appreciation because of its ability to selectively induce apoptosis in cancer cells leaving normal cells intact. However, technological advances have started to shed light on underlying mechanisms of resistance against TRAIL-induced apoptosis in cancer cells. The impairment of TRAIL-mediated apoptosis includes various factors ranging from the loss or down regulation of TRAIL receptors or pro-apoptotic proteins to the up regulation of anti-apoptotic proteins. Intriguingly to mention that there is an ever-increasing number of natural herbal extracts (phytometabolites), which have been explored to date for their potential action in restoring apoptosis TRAIL-mediated in cancer cells. In this review, we will highlight the progress in understanding the mechanisms opted by phenolic compounds in overcoming TRAIL resistance.

A divergent enantioselective strategy for the synthesis of griseusins

The first enantioselective total synthesis of griseusin A, griseusin C, 4'-deacetyl-griseusin A, and two non-native counterparts in 11-14 steps is reported. This strategy highlights a key hydroxy-directed CH olefination of 1-methylene isochroman with an α,β-unsaturated ketone followed by subsequent stereoselective epoxidation and regioselective cyclization to afford the signature tetrahydro-spiropyran ring. Colorectal cancer cell cytotoxicities of the final products highlight the impact of the griseusin tetrahydro-spiropyran ring on bioactivity. As the first divergent enantioselective synthesis, the strategy put forth sets the stage for further griseusin mechanism-of-action and SAR studies.

Functional gene-based discovery of phenazines from the actinobacteria associated with marine sponges in the South China Sea

Phenazines represent a large group of nitrogen-containing heterocyclic compounds produced by the diverse group of bacteria including actinobacteria. In this study, a total of 197 actinobacterial strains were isolated from seven different marine sponge species in the South China Sea using five different culture media. Eighty-seven morphologically different actinobacterial strains were selected and grouped into 13 genera, including Actinoalloteichus, Kocuria, Micrococcus, Micromonospora, Mycobacterium, Nocardiopsis, Prauserella, Rhodococcus, Saccharopolyspora, Salinispora, Serinicoccus, and Streptomyces by the phylogenetic analysis of 16S rRNA gene. Based on the screening of phzE genes, ten strains, including five Streptomyces, two Nocardiopsis, one Salinispora, one Micrococcus, and one Serinicoccus were found to be potential for phenazine production. The level of phzE gene expression was highly expressed in Nocardiopsis sp. 13-33-15, 13-12-13, and Serinicoccus sp. 13-12-4 on the fifth day of fermentation. Finally, 1,6-dihydroxy phenazine (1) from Nocardiopsis sp. 13-33-15 and 13-12-13, and 1,6-dimethoxy phenazine (2) from Nocardiopsis sp. 13-33-15 were isolated and identified successfully based on ESI-MS and NMR analysis. The compounds 1 and 2 showed antibacterial activity against Bacillus mycoides SJ14, Staphylococcus aureus SJ51, Escherichia coli SJ42, and Micrococcus luteus SJ47. This study suggests that the integrated approach of gene screening and chemical analysis is an effective strategy to find the target compounds and lays the basis for the production of phenazine from the sponge-associated actinobacteria.

Isolation of β-Indomycinone Guided by Cytotoxicity Tests from Streptomyces sp. IFM11607 and Revision of its Double Bond Geometry

The antibiotic β-indomycinone was isolated from Streptomyces sp. IFM11607 by cytotoxicity-guided fractionation against human gastric adenocarcinoma AGS cells, and the geometry of its Δ17,18-double bond was revised from E to Z based on the coupling constant.

Chromomycins A2 and A3 from marine actinomycetes with TRAIL resistance-overcoming and Wnt signal inhibitory activities

A biological screening study of an actinomycetes strain assembly was conducted using a cell-based cytotoxicity assay. The CKK1019 strain was isolated from a sea sand sample. Cytotoxicity-guided fractionation of the CKK1019 strain culture broth, which exhibited cytotoxicity, led to the isolation of chromomycins A₂ (1) and A₃ (2). 1 and 2 showed potent cytotoxicity against the human gastric adenocarcinoma (AGS) cell line (IC₅₀1; 1.7 and 2; 22.1 nM), as well as strong inhibitory effects against TCF/β-catenin transcription (IC₅₀1; 1.8 and 2; 15.9 nM). 2 showed the ability to overcome tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) resistance. To the best of our knowledge, the effects of chromomycins A₂ (1) and A₃ (2) on TRAIL resistance-overcoming activity, and on the Wnt signaling pathway, have not been reported previously. Thus, 1 and 2 warrant potential drug lead studies in relation to TRAIL-resistant and Wnt signal-related diseases and offer potentially useful chemical probes for investigating TRAIL resistance and the Wnt signaling pathway.

Synthesis of the griseusin B framework via a one-pot annulation-methylation-double deprotection-spirocyclization sequence

A highly convergent synthesis of the griseusin B scaffold is described. The key step involves an efficient one-pot Hauser-Kraus annulation-methylation-double deprotection-spirocyclization sequence that directly affords the target parent tetracyclic ring system.

Griseusins F and G, spiro-naphthoquinones from a tin mine tailings-derived alkalophilic Nocardiopsis species

Griseusins F (1) and G (2), two 2a-hydro-8a-(2-oxopropyl)-substituted spiro-naphthoquinones with a previously undescribed C23 polyketide skeleton, were isolated from a Yunnan tin mine tailings-derived alkalophilic actinomycete, Nocardiopsis sp. YIM DT266. Their complete structure assignments with the absolute stereochemistry were elucidated by spectroscopic data, X-ray crystal diffraction, calculation of optical rotation, and CD spectroscopic analysis. Compounds 1 and 2 exhibited strong cytotoxicity (IC50 0.37-0.82 μM) and antibacterial activity (MIC 0.80-1.65 μg/mL) against Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA) in vitro.

A novel anticancer and antifungus phenazine derivative from a marine actinomycete BM-17

A marine actinomycete, designated strain BM-17, was isolated from a sediment sample collected in the Arctic Ocean. The strain was identified as Nocardia dassonvillei based on morphological, cultural, physiological, biochemical characteristics, along with the cell wall analysis and 16S rDNA gene sequence analysis. A new secondary metabolite (1), N-(2-hydroxyphenyl)-2-phenazinamine (NHP), and six known antibiotics (2-7) have been isolated from the saline culture broth of the stain by sequentially purification over macroporous resin D101, silica gel, Sephadex LH-20 column chromatography and preparative HPLC after the stain was incubated in soy bean media at 28°C for 7 days. The chemical structures of the compounds were elucidated on the basis of spectroscopic analysis, including two-dimensional (2D) NMR and HR-ESI-MS data. The new compound showed significant antifungal activity against Candida albicans, with a MIC of 64 μg/ml and high cancer cell cytotoxicity against HepG2, A549, HCT-116 and COC1 cells.