Dimeric Pyranonaphthoquinone Glycosides with Anti-HIV and Cytotoxic Activities from a Soil-Derived Streptomyces

Intramolecular 1,2-Aroyl Migration in Spiro Donor-Acceptor Cyclopropanes: Formation of 1,4-Naphthoquinones and 1-Naphthols as Ring-Expansion Products

Most of the known rearrangement reactions of donor-acceptor cyclopropanes (DACs) involve the migration of cationic carbon atom to anionic carbon or heteroatoms in 1,3- or 1,4-positions. In the present work, we observed that spiro DACs based on 1,3-indanedione or 1-indanone moiety undergo intramolecular 1,2-aroyl migration when treated with titanium(IV) chloride to afford 1,4-naphthoquinones and α-naphthols readily. The reactions take place through the formation of putative 1,3-dipolar intermediates, followed by cleavage and migration of the aroyl group to the adjacent carbon to afford the ring-expansion products.

Discovery of pyranonaphthoquinones and an eighteen-membered ring macrolide from the rhizospheric soil-derived fungus Phialocephala sp. YUD18001 by OSMAC strategy

Two new pyranonaphthoquinones, phialoyxinones A (1) and B (2), a new eighteen-membered ring lactone, phialoyxtone (3), and five known pyranonaphthoquinone derivatives were identified from the fungus Phialocephala sp. YUD18001, which was isolated from the rhizospheric soil associated with Gastrodia elata. Their structures were unequivocally established by a comprehensive interpretation of the spectroscopic data, with the stereochemistry for 1-3 was defined by a combination of TDDFT calculations, and the DP4+ probability analysis based on NMR chemical shift calculations. All of the new compounds 1-3 were evaluated for cytotoxicity and acetylcholinesterase inhibitory, compound 2 exhibited in vitro cytotoxic activities against five human cancer cell lines (HL-60, SMMC-7721, A549, MCF-7 and SW480) with IC50 values ranging from 11.80 to 19.32 μM. Compounds 2 and 3 exhibited moderate AChE inhibitory activities. A putative biosynthetic pathway for the pyranonaphthoquinones was proposed.

Natural epoxyquinoids: isolation, biological activity and synthesis. An update

Epoxyquinoids are of continuing interest due to their wide natural distribution and diverse biological activities, including, but not limited to, antibacterial, antifungal, anticancer, enzyme inhibitory, and others. The last review on their total synthesis was published in 2017. Since then, almost 100 articles have been published on their isolation from nature and their biological profile. In addition, the review specifically considers synthesis, including total and enantioselective, as well as the development of shorter approaches for the construction of epoxyquinoids with complex chemical architecture. Thus, this review focuses on progress in this area in order to stimulate further research.

Pyranonaphthoquinones and Naphthoquinones from the Stem Bark of Ventilago harmandiana and Their Anti-HIV-1 Activity

Seven previously undescribed compounds, including five pyranonaphthoquinones (ventilanones L-P) and two naphthoquinones (ventilanones Q and R), along with 15 known compounds were isolated from the stem bark of Ventilago harmandiana (Rhamnaceae). The structures were established by extensive analysis of their spectroscopic data. The absolute configuration of ventilanone L was established from single crystal X-ray crystallographic analysis using Cu Kα radiation and from its electronic circular dichroism data. Anti-HIV-1 activity using a syncytium inhibition assay and the cytotoxic activities of some isolated compounds were evaluated. Compounds 12, 13, 15, and 16 showed activity against syncytium formation with half maximal effective concentration (EC₅₀) values ranging from 9.9 to 47 μM (selectivity index (SI) 2.4-4.5).

Streptomyces: Still the Biggest Producer of New Natural Secondary Metabolites, a Current Perspective

There is a real consensus that new antibiotics are urgently needed and are the best chance for combating antibiotic resistance. The phylum Actinobacteria is one of the main producers of new antibiotics, with a recent paradigm shift whereby rare actinomycetes have been increasingly targeted as a source of new secondary metabolites for the discovery of new antibiotics. However, this review shows that the genus Streptomyces is still the largest current producer of new and innovative secondary metabolites. Between January 2015 and December 2020, a significantly high number of novel Streptomyces spp. have been isolated from different environments, including extreme environments, symbionts, terrestrial soils, sediments and also from marine environments, mainly from marine invertebrates and marine sediments. This review highlights 135 new species of Streptomyces during this 6-year period with 108 new species of Streptomyces from the terrestrial environment and 27 new species from marine sources. A brief summary of the different pre-treatment methods used for the successful isolation of some of the new species of Streptomyces is also discussed, as well as the biological activities of the isolated secondary metabolites. A total of 279 new secondary metabolites have been recorded from 121 species of Streptomyces which exhibit diverse biological activity. The greatest number of new secondary metabolites originated from the terrestrial-sourced Streptomyces spp.

Anti-inflammatory Dimeric Benzophenones from an Endophytic Pleosporales Species

Eight new polyketides, including three dimeric benzophenones, named dipleosporones A-C (1-3), three benzophenones (4-6), one xanthone (7), and one phenylbenzoate (8), along with seven known polyketides (9-15) were isolated from the fungus Pleosporales sp. YY-4. The structures of the new compounds were established on the basis of spectroscopic methods, including high-resolution electrospray ionization mass spectrometry and one- and two-dimensional nuclear magnetic resonance. This is the first report of a benzophenone dimer connection via a C bridge from natural sources. An anti-inflammatory assay indicated that the dimeric benzophenones (1-3) inhibited lipopolysaccharide-induced NO production in RAW 264.7 cells, with half-maximal inhibitory concentration (IC₅₀) values ranging from 8.8 to 18.1 μM, being more potent than the positive control, dexamethasone (IC₅₀ = 22.2 μM).

Discovery of Mycothiogranaticins from Streptomyces vietnamensis GIMV4.0001 and the Regulatory Effect of Mycothiol on the Granaticin Biosynthesis

Granaticins are benzoisochromanequinone polyketides with remarkable antibacterial and anticancer activities. Three sulfur-containing granaticin congeners, mycothiogranaticins A (1), B (2) and granaticin MA (3) were discovered from a granaticin-producing strain of Streptomyces vietnamensis GIMV4.0001. Two of them were structurally determined with mycothiol or N-acetylcysteine moieties and found to be bio-actively reluctant. Disruption of the mshA gene (SVTN_RS20640) that encodes the D-inositol-3-phosphate glycosyltransferase crucial for mycothiol biosynthesis, fully abolished the production of mycothiogranaticins. The result substantiated that the newly discovered mycothiogranaticins are consequences of the combination of the granaticin and mycothiol biosynthetic pathways. The overall granaticin production of the ΔmshA mutant strain was unexpectedly decreased by at least more than 50%, while similar production level of granaticins to that of the wild type strain was observed in an mycothiol-S transferase gene (SVTN_RS22215) disruptant Δmst. These results indicated that the mycothiol deficiency was responsible for the decreased production of granaticins. Mycothiol may positively regulate the biosynthesis of granaticin possibly by maintaining the cellular redox balance. To the best of our knowledge, this is the first report that mycothiol can not only be a direct building block of polyketides but also play a regulatory role in the polyketide biosynthesis.

Photocatalytic Homocoupling Transformations

Homocoupling reactions promoted by photocatalysts are not very abundant in the literature. However, the products generated from such processes are very interesting. In this review, we highlight the most relevant reports concerning photocatalyzed dimerizations covering the literature until the middle of 2020. Reactions will be classified according to the type of starting material employed, with an emphasis being placed on the corresponding mechanism.

1 Introduction

2 Arenes and Heteroarenes

3 Alkenes

4 Alkanes

5 Alkynes

6 Aldehydes, Ketones, Alcohols, Amines and Imines

7 Carboxylic Acids

8 Nitro Compounds

9 Conclusions

Pleiotropic effects of ActVI-ORFA as an unusual regulatory factor identified in the biosynthetic pathway of actinorhodin in Streptomyces coelicolor

Regulatory networks play critical roles in controlling the the biosynthesis of natural products in Streptomyces. ActVI-ORFA, a regulatory factor encoded by the actinorhodin biosynthetic gene cluster (act cluster), positively controls the production of actinorhodin (ACT) in Streptomyces coelicolor, although its regulatory mechanism remains obscure. This study aimed to identify the regulatory targets of ActVI-ORFA. Deletion of ActVI-ORFA caused the differential expression of hundreds of proteins, as determined by two-dimensional electrophoresis and peptide mass fingerprinting analysis. qRT-PCR analysis of some genes encoding these differentially expressed proteins, including act genes and non-act genes, confirmed that ActVI-ORFA could control their transcriptional levels. In an electrophoretic mobility shift assay with a promoter region of a target gene located in the act cluster, no binding was detected, consistent with the lack of a recognizable DNA-binding domain in ActVI-ORFA. Overall, our findings suggest that ActVI-ORFA is a pleiotropic regulatory factor that controls multiple physiological pathways, including secondary metabolite production, probably via an indirect mode.

Synthesis and Bioactivities of Novel 1,3,4-Thiadiazole Derivatives of Glucosides

A series of novel 1,3,4-thiadiazole derivatives of glucosides were synthesized by the starting materials d-glucose and 5-amino-1,3,4-thiadiazole-2-thiol in good yields with employing a convergent synthetic route. The results of bioactivities showed that some of the target compounds exhibited good antifungal activities. Especially, compounds 4i showed higher bioactivities against Phytophthora infestans (P. infestans), with the EC₅₀ values of 3.43, than that of Dimethomorph (5.52 μg/ml). In addition, the target compounds exhibited moderate to poor antibacterial activities against Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas campestris pv. citri (Xcc).

Small double-stranded RNA with anti-HIV activity abundantly produced by Bacillus subtilis MTCC5480 isolated from fermented soybean

Anti-viral RNA therapy is on high demand nowadays due to the emergence of several new viral infections. The small non-coding regulatory RNAs (dsRNA) from the microbial sources are not yet explored for anti-viral activity. In this study, we assessed the anti-HIV activity of the small dsRNA produced by 12 different microbial species isolated from naturally fermented foods of North-East India. For this, we selectively extracted the dsRNA from the microbial culture, confirmed its double-stranded nature by immunoblotting, and deep sequenced the cDNA library using Illumina platform. Further, we used conventional algorithms to predict the potential targets of the dsRNA sequences within the 3'-UTR region of HIV-1. A small dsRNA fragment with 34 bases in size with a sequence of 3'-UUGGUACACGAGAUGGUUCGACUCGAUGAAGGGC-5' produced abundantly (9.17% of the total dsRNA fraction) by Bacillus subtilis MTCC5480 showed a much higher base complementarity values than previously reported miRNAs analysed against HIV-1. We separated the dsRNA fraction and validated the anti-HIV activity against human peripheral blood mononuclear cells (PBMC) infected with JRCSF strain of HIV-1 virus and the EC50 value ranges from 0.2-0.3 μM. This small dsRNA abundantly produced by B. subtilis could be studied further for its application as an anti-viral therapeutic agent.

Antibacterial Pentacyclic Polyketides from a Soil-Derived Streptomyces

Nine new pentacyclic polyketides, fasamycins G-K (1-5) and formicamycins N-Q (6-9), along with 10 known analogues (10-19), were isolated from a rhizospheric soil-derived Streptomyces sp. KIB-1414. Their structures and absolute configurations were elucidated by interpretation of NMR and HRMS data and comparisons of CD data. The compounds were active against methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus aureus, Bacillus subtilis, and Escherichia coli strains, with MIC values ranging from 0.20 to 50.00 μg/mL.

Dimeric Pimprinine Alkaloids From Soil-Derived Streptomyces sp. NEAU-C99

Six new pimprinine alkaloids (1–6), including four dimers, dipimprinines A–D (1–4), and two monomers, (±)-Pimprinol D (5), and pimprinone A (6), along with six known congeners (7–12), were isolated from a soil-derived actinomycete Streptomyces sp. NEAU-C99. Structures of the new compounds were elucidated by extensive spectroscopic analyses, single-crystal X-ray diffractions, and ECD calculations. Dipimprinines A–D (1–4) showed weak cytotoxic activities against five tumor cell lines, including HL-60, SMMC-7721, A-549, MCF-7, and SW-480, with IC₅₀ values ranging from 12.7 to 30.7 μM.