Structures and Biosynthetic Pathway of Pulvomycins B–D: 22-Membered Macrolides from an Estuarine Streptomyces sp

Chemical constituents from the roots of Cynanchum wilfordii with PCSK9 secretion inhibitory activities

From the Cynanchum wilfordii roots, 32 compounds, including 5 previously undescribed (1, 4-6, 12) and 27 known (2, 3, 7-11, 13-32) compounds, were isolated, and their structures were elucidated using NMR spectroscopic data and MS data aided by ECD calculations or the modified Mosher's reaction. All isolates were tested for their inhibitory effects on proprotein convertase subtilisin/kexin type 9 (PCSK9) secretion. Among the isolates, compound 4, a methyl cholesterol analog, exhibited the most potent effect in reducing PCSK9 secretion, along with PCSK9 downregulation at the mRNA and protein levels via FOXO1/3 upregulation. Moreover, compound 4 attenuated statin-induced PCSK9 expression and enhanced the uptake of DiI-LDL low-density lipoprotein. Thus, compound 4 is suggested to be a potential candidate for controlling cholesterol levels.

Biocatalytic role of cytochrome P450s to produce antibiotics: A review

Cytochrome P450s belong to a family of heme-binding monooxygenases, which catalyze regio- and stereospecific functionalisation of C-H, C-C, and C-N bonds, including heteroatom oxidation, oxidative C-C bond cleavages, and nitrene transfer. P450s are considered useful biocatalysts for the production of pharmaceutical products, fine chemicals, and bioremediating agents. Despite having tremendous biotechnological potential, being heme-monooxygenases, P450s require either autologous or heterologous redox partner(s) to perform chemical transformations. Randomly distributed P450s throughout a bacterial genome and devoid of particular redox partners in natural products biosynthetic gene clusters (BGCs) showed an extra challenge to reveal their pharmaceutical potential. However, continuous efforts have been made to understand their involvement in antibiotic biosynthesis and their modification, and this review focused on such BGCs. Here, particularly, we have discussed the role of P450s involved in the production of macrolides and aminocoumarin antibiotics, nonribosomal peptide (NRPSs) antibiotics, ribosomally synthesized and post-translationally modified peptide (RiPPs) antibiotics, and others. Several reactions catalyzed by P450s, as well as the role of their redox partners involved in the BGCs of various antibiotics and their derivatives, have been primarily addressed in this review, which would be useful in further exploration of P450s for the biosynthesis of new therapeutics.

Glycosylated and Succinylated Macrocyclic Lactones with Amyloid-β-Aggregation-Regulating Activity from a Marine Bacillus sp

Two new glycosylated and succinylated macrocyclic lactones, succinyl glyco-oxydifficidin (1) and succinyl macrolactin O (2), were isolated from a Bacillus strain collected from an intertidal mudflat on Anmyeon Island in Korea. The planar structures of 1 and 2 were proposed using mass spectrometric analysis and NMR spectroscopic data. The absolute configurations of 1 and 2 were determined by optical rotation, J-based configuration analysis, chemical derivatizations, including the modified Mosher's method, and quantum-mechanics-based calculation. Biological evaluation of 1 and 2 revealed that succinyl glyco-oxydifficidin (1) inhibited/dissociated amyloid β (Aβ) aggregation, whereas succinyl macrolactin O (2) inhibited Aβ aggregation, indicating their therapeutic potential for disassembling and removing Aβ aggregation.

Phytohabitols A-C, δ-Lactone-Terminated Polyketides from an Actinomycete of the Genus Phytohabitans

Phytohabitols A-C (1-3), new terminally δ-lactonized linear polyketides, were isolated from the culture extract of a rare actinomycete of the genus Phytohabitans. The structures of 1-3, substituted with multiple methyl and hydroxy groups on a conjugated and a skipped diene-containing backbone, were elucidated by NMR and MS spectroscopic analyses. The absolute configuration of 1 was determined by chemical derivatization and chiral anisotropic analysis, coupled with ROESY and J-based configuration analysis. In addition, closely similar 1H and 13C NMR data and optical rotations among 1-3 supported the same stereochemistry of these polyketides. The related streptomycetes metabolites lagunapyrones B, C, and D have α-pyrone rings on the linear part in place of the δ-lactone, but their chirality at the C19-C21 stereocenters were opposite from those described here, posing a question on the previous assignment made solely by comparison of the optical rotations of four possible diastereomers. Compounds 1-3 inhibited migration of cancer cells with IC50 values of 15, 11, and 8.3 μM, respectively, at noncytotoxic concentrations. In addition, 1-3 displayed potent antitrypanosomal activity against Trypanosoma cruzi with IC50 values of 12, 6.4, and 18 μM, comparable to a commonly used therapeutic drug, benznidazole (IC50 16 μM).

Nyuzenamide C, an Antiangiogenic Epoxy Cinnamic Acid-Containing Bicyclic Peptide from a Riverine Streptomyces sp

A new nonribosomal peptide, nyuzenamide C (1), was discovered from riverine sediment-derived Streptomyces sp. DM14. Comprehensive analysis of the spectroscopic data of nyuzenamide C (1) revealed that 1 has a bicyclic backbone composed of six common amino acid residues (Asn, Leu, Pro, Gly, Val, and Thr) and four nonproteinogenic amino acid units, including hydroxyglycine, β-hydroxyphenylalanine, p-hydroxyphenylglycine, and 3,β-dihydroxytyrosine, along with 1,2-epoxypropyl cinnamic acid. The absolute configuration of 1 was proposed by J-based configuration analysis, the advanced Marfey's method, quantum mechanics-based DP4 calculations, and bioinformatic analysis of its nonribosomal peptide synthetase biosynthetic gene cluster. Nyuzenamide C (1) displayed antiangiogenic activity in human umbilical vein endothelial cells and induced quinone reductase in murine Hepa-1c1c7 cells.

Hamuramicin C, a Cytotoxic Bicyclic Macrolide Isolated from a Wasp Gut Bacterium

A new bicyclic macrolide, hamuramicin C (1), was isolated from Streptomyces sp. MBP16, a gut bacterial strain of the wasp Vespa crabro flavofasciata. Its 22-membered macrocyclic lactone structure was determined by NMR and mass spectrometry. The relative configurations of hamuramicin C (1) were assigned by J-based configuration analysis utilizing ¹H rotating frame Overhauser effect spectroscopy and heteronuclear long-range coupling NMR spectroscopy. Genomic and bioinformatic analyses of the bacterial strain enabled identification of the type-I polyketide synthase pathway, which employs a trans-acyltransferase system. The absolute configurations of 1 were proposed based on the analysis of the sequences of ketoreductases in the modular gene cluster. Moreover, hamuramicin C (1) demonstrated significant inhibitory activity against diverse human cancer cell lines (HCT116, A549, SNU-638, SK-HEP-1, and MDA-MB-231).

Marine natural products

Covering: 2020This review covers the literature published in 2020 for marine natural products (MNPs), with 757 citations (747 for the period January to December 2020) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1407 in 420 papers for 2020), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. A meta analysis of bioactivity data relating to new MNPs reported over the last five years is also presented.

Ligiamycins A and B, Decalin-Amino-Maleimides from the Co-Culture of Streptomyces sp. and Achromobacter sp. Isolated from the Marine Wharf Roach, Ligia exotica

Streptomyces sp. GET02.ST and Achromobacter sp. GET02.AC were isolated together from the gut of the wharf roach, Ligia exotica, inhabiting the intertidal zone of the west coast of Korea. The co-cultivation of these two strains significantly induced the production of two new metabolites, ligiamycins A (1) and B (2), which were barely detected in the single culture of Streptomyces sp. GET02.ST. The planar structures of ligiamycins A (1) and B (2) were elucidated as new decalins coupled with amino-maleimides by the analysis of various spectroscopic data, including nuclear magnetic resonance (NMR), ultraviolet (UV), and mass (MS) data. The assignment of two nitrogen atoms in amino-maleimide in 1 was accomplished based on 1H-15N heteroatom single quantum coherence spectroscopy (HSQC) NMR experiments. The relative configurations of the ligiamycins were determined using rotating frame Overhauser effect spectroscopy (ROESY) NMR data, and their absolute configurations were deduced by comparing their experimental and calculated optical rotations. Ligiamycin A (1) displayed antibacterial effects against Staphylococcus aureus and Salmonella enterica, while ligiamycin B (2) exhibited mild cell cytotoxicity against human colorectal cancer cells.

Cytotoxic compounds from marine actinomycetes: Sources, Structures and Bioactivity

Marine actinomycetes produce a substantial number of natural products with cytotoxic activity. The strains of actinomycetes were isolated from different sources like fishes, coral, sponges, seaweeds, mangroves, sediments etc. These cytotoxic compounds can be categorized briefly into four classes: polyketides, non-ribosomal peptides and hybrids, isoprenoids and hybrids, and others, among which majority are polyketides (146). Twenty two out of the 254 compounds showed potent cytotoxicity with IC₅₀ values at ng/mL or nM level. This review highlights the sources, structures and antitumor activity of 254 natural products isolated from marine actinomycetes, which were new when they were reported from 1989 to 2020.

Survey of natural products reported by Asian research groups in 2020

The new natural products reported in 2020 in peer-reviewed articles in journals with good reputations were reviewed and analyzed. The advances made by Asian research groups in the field of natural products chemistry in 2020 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on their structural classification.

Total Synthesis of Pulvomycin D

A synthetic route to the pulvomycin class of natural products is presented, which culminated in the first synthesis of a pulvomycin, pulvomycin D. Key elements of the strategy include a pivotal aldol reaction which led to bond formation between the C24‐C40 and the C8‐C23 fragment. The remaining C1‐C7 fragment was attached by a Yamaguchi esterification completing the assembly of the 40 carbon atoms within the main skeleton. Ring closure to the 22‐membered lactone ring was achieved in the final stages of the synthesis by a Heck reaction. The completion of the synthesis required the removal of six silyl protecting groups in combination with olefin formation at C26‐C27 by a Peterson elimination.

Antitumor Activity of Pulvomycin via Targeting Activated-STAT3 Signaling in Docetaxel-Resistant Triple-Negative Breast Cancer Cells

Although docetaxel-based regimens are common and effective for early-stage triple-negative breast cancer (TNBC) treatment, acquired drug resistance frequently occurs. Therefore, a novel therapeutic strategy for docetaxel-resistant TNBC is urgently required. Signal transducer and activator of transcription 3 (STAT3) plays a pivotal role in the tumorigenesis and metastasis of numerous cancers, and STAT3 signaling is aberrantly activated in TNBC cells. In this study, a docetaxel-resistant TNBC cell line (MDA-MB-231-DTR) was established, and mechanisms for the antitumor activity of pulvomycin, a novel STAT3 inhibitor isolated from marine-derived actinomycete, were investigated. Levels of activated STAT3 (p-STAT3 (Y705)) increased in docetaxel-resistant cells, and knockdown of STAT3 recovered the sensitivity to docetaxel in MDA-MB-231-DTR cells. Pulvomycin effectively inhibited the proliferation of both cell lines. In addition, pulvomycin suppressed the activation of STAT3 and subsequently induced G0/G1 cell cycle arrest and apoptosis. Pulvomycin also significantly inhibited the invasion and migration of MDA-MB-231-DTR cells through the modulation of epithelial-mesenchymal transition markers. In an MDA-MB-231-DTR-bearing xenograft mouse model, the combination of pulvomycin and docetaxel effectively inhibited tumor growth through STAT3 regulation. Thus, our findings demonstrate that the combination of docetaxel and STAT3 inhibitors is an effective strategy for overcoming docetaxel resistance in TNBC.

Polyketide β-branching: diversity, mechanism and selectivity

Covering: 2008 to August 2020 Polyketides are a family of natural products constructed from simple building blocks to generate a diverse range of often complex chemical structures with biological activities of both pharmaceutical and agrochemical importance. Their biosynthesis is controlled by polyketide synthases (PKSs) which catalyse the condensation of thioesters to assemble a functionalised linear carbon chain. Alkyl-branches may be installed at the nucleophilic α- or electrophilic β-carbon of the growing chain. Polyketide β-branching is a fascinating biosynthetic modification that allows for the conversion of a β-ketone into a β-alkyl group or functionalised side-chain. The overall transformation is catalysed by a multi-protein 3-hydroxy-3-methylglutaryl synthase (HMGS) cassette and is reminiscent of the mevalonate pathway in terpene biosynthesis. The first step most commonly involves the aldol addition of acetate to the electrophilic carbon of the β-ketothioester catalysed by a 3-hydroxy-3-methylglutaryl synthase (HMGS). Subsequent dehydration and decarboxylation selectively generates either α,β- or β,γ-unsaturated β-alkyl branches which may be further modified. This review covers 2008 to August 2020 and summarises the diversity of β-branch incorporation and the mechanistic details of each catalytic step. This is extended to discussion of polyketides containing multiple β-branches and the selectivity exerted by the PKS to ensure β-branching fidelity. Finally, the application of HMGS in data mining, additional β-branching mechanisms and current knowledge of the role of β-branches in this important class of biologically active natural products is discussed.

Formicolides A and B, Antioxidative and Antiangiogenic 20-Membered Macrolides from a Wood Ant Gut Bacterium

Two new macrolides, formicolides A (1) and B (2), were isolated from Streptomyces sp. BA01, a gut bacterial strain of the wood ant (Formica yessensis). Their 20-membered macrocyclic lactone structures were established using NMR and mass spectrometric data. The relative configurations of the formicolides were determined by J-based configuration analysis utilizing ROESY, HETLOC, and HECADE NMR spectroscopic data. Genomic and bioinformatics analysis of the bacterial strain enabled us to identify the type-I polyketide synthase pathway employing a trans-acyltransferase system. The absolute configurations of 1 and 2 are proposed based on detailed analysis of the sequences of the ketoreductases in the modular gene cluster and statistical comparative analysis of the experimental NMR chemical shifts and quantum mechanical calculations. Formicolides A and B (1 and 2) induced quinone reductase activity in murine Hepa-1c1c7 cells and antiangiogenic activity by suppression of tube formation in human umbilical vein endothelial cells.