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One new aromatic polyketide, prealnumycin B ( 1 ), and four known aromatic polyketides, K1115A ( 2 ), 1,6-dihydroxy-8-propylanthraquinone (DHPA, 3 ), phaeochromycin B ( 4 ), and ( R )-7-acetyl-3,6-dihydroxy-8-propyl-3,4dihydronaphthalen-1(2 H )-one ( 5 ), were isolated from the marine-derived Streptomyces sundarbansensis SCSIO NS01; these compounds represent four sets of aromatic polyketides differing in size and shape. A type II polyketide synthase (PKS) cluster, als , was identified by complete genome sequencing and was shown, by in vivo gene inactivation experiments in the wild-type (WT) NS01 strain and heterologous expression experiments, to encode the biosynthesis of compounds 1 - 5 . Moreover, heterologous expression of the als cluster afforded three additional aromatic polyketides representing two different carbon skeletons, the new phaeochromycin L ( 6 ) and two known aromatic polyketides, phaeochromycins D ( 7 ) and E ( 8 ). These findings expand our knowledge of type II PKS machineries and their versatility in generating structurally diverse aromatic polyketides and highlight the power of type II PKSs in accessing new polyketides via ectopic expression in heterologous hosts.

Three diphenyl ethers ( 1 - 3 ) and a cyclopentenone ( 4 ), together with seven known compounds ( 5 - 11 ), were isolated from the fermentation broth of the marine sediment-derived fungus Spiromastix sp. SCSIO F190. Compounds 3 and 4 were found to exist as a pair of atropisomers ( 3a , 3b ) and racemates ( 4a , 4b ), respectively. The planar structures of compounds 1 - 4 were elucidated on the basis of NMR and HRESIMS data sets. The absolute configurations of 2 and 3 were determined by spectroscopic and single-crystal X-ray diffraction analyses, whereas the configuration of 4 was determined by spectroscopic and chiral analyses. All compounds, except for 4 and 11 , displayed activities against various pathogenic bacteria. Notably, compounds 1 - 4 , especially 1 , exhibited strong activity against Gram-positive bacteria, including methicillin-resistant bacterial strains of Staphylococcus aureus (MRSA), Enterococcus faecalis ATCC 29212, and Bacillus subtilis BS01, with MIC values ranging from 0.5 to 4 μg/mL. Moreover, the structure-activity relationship analyses of the active compounds and their analogues revealed the critical structural features correlating to the observed antimicrobial activities, herein providing insights for antimicrobial drug development.

Three new actinopyrone derivatives, actinopyrones E-G ( 1 , 3 , and 4 ), together with three known analogues, PM050463 ( 2 ), actinopyrone D ( 5 ), and PM050511 ( 6 ), were isolated from Streptomyces sp. SCSIO ZS0520 derived from a deep-sea hydrothermal vent. Their structures, complete with absolute configurations, were elucidated using extensive spectroscopic analyses combined with Mosher's method, ECD calculations, and bioinformatics analyses. These findings corrected the absolute configurations of previously reported actinopyrone analogues 2 , 5 , and 6 at C-3, C-9, and C-10. Notably, compound 6 displayed notable cytotoxicity against six human cell lines with IC 50 values of 0.26-2.22 μM. A likely biosynthetic pathway and annotations of protein function are proposed on the basis of bioinformatics analyses. Genes coding for methyltransferase and glycosyltransferase tailoring chemistries needed to generate final structures were notably absent from the biosynthetic gene cluster. Taken together, these results enable further bioengineering of the actinopyrones and related congeners as potential antitumor agents.

Vicenistatin ( 1 ) is a potent polyketide antitumor antibiotic composed of a 20-membered macrolactam core appended to a unique aminosugar, vicenisamine. In this study, vicenistatin was isolated and its biosynthetic gene cluster identified from Monodonata labio -associated Streptomyces parvus SCSIO Mla-L010. A set of five genes, vicC , vicD , vicE , vicF , and vicG , was confirmed to be involved in the biosynthesis of the aminosugar by gene inactivations. VicG was characterized as an N -methyltransferase that catalyzes the methylation of the 4'-amino group in the last step of the aminosugar biosynthetic pathway; the N -demethyl intermediate 4'- N -demethylvicenistatin ( 2 ) was isolated from the Δ vicG mutant strain. In addition, vicR1 was characterized as a positive pathway-specific regulatory gene. Notably, N -demethyl compound 2 was found to exert impressive antibacterial activities, with MIC values spanning 0.06-4 μg/mL, against a panel of Gram-positive bacteria including methicillin-resistant Staphylococcus aureus , Gram-negative Helicobacter pylori , and mycobacterium Mycobacterium smegmatis and the fungal pathogen Candida albicans . Compound 2 was also found to display reduced cytotoxicities relative to vicenistatin, especially against noncancerous human cell lines.

Through precursor-directed biosynthesis, feeding halogenated (F-, Cl-, Br-, I-) or methoxy-substituted 4-methyl-3-hydroxyanthranilic acid (4-MHA) analogues to the acnGHLM -deleted mutant strain of Streptomyces costaricanus SCSIO ZS0073 led to the production of ten new actinomycin analogues ( 4 - 13 ). Several of the actinomycin congeners displayed impressive antimicrobial activities, with MIC values spanning 0.06-64 μg/mL to clinically derived antibiotic resistant pathogens, including Staphylococcus aureus , Enterococcus faecium , and Candida albicans , with low cytotoxicity.

Two new cyclodecapeptides, atratumycins B ( 1 ) and C ( 2 ), containing substituted cinnamoyl side chains were generated by converging elements of the atratumycin ( 3 ) and atrovimycin ( 4 ) biosynthetic pathways. The structures of 1 and 2 were determined on the basis of HRESIMS, 1D and 2D NMR data, and X-ray single-crystal diffraction studies. Atratumycin B ( 1 ) is active against autoluminescent Mycobacterium tuberculosis H37Rv, displaying a minimum inhibitory concentration of 3.1 μg/mL (2.3 μM).

Tuberculosis (TB) ranks as the leading cause of death from a single infectious agent (ranking more lethal than HIV/AIDS) over the course of the past decade. More concerning is that reports of multi-drug-resistant (MDR) and extensively drug-resistant (XDR) strains of TB have been dramatically increasing. It continues to become ever more clear that novel anti-TB drugs with improved efficacies and reduced toxicities are urgently needed. We report here the discovery of 12 new ilamycin analogues, ilamycins G-R ( 1 - 12 ), bearing various nonproteinogenic amino acids, along with ilamycins E 1 ( 13 ) and F ( 14 ), from a 200 L scale culture of the marine-derived mutant actinomycete Streptomyces atratus SCSIO ZH16 Δ ilaR . Importantly, bioassays against Mycobacterium tuberculosis H37Rv revealed that all 12 new agents displayed antitubercular activities with MIC values ranging from 0.0096 to 10 μM. The structures of 1 - 12 were elucidated on the basis of HRESIMS, 1D and 2D NMR, and X-ray single-crystal diffraction studies. In addition, compound 10 was found to be moderately cytotoxic against a panel of tumor human cell lines. From these data we can formulate tentative structure-activity relationships for the antitubercular and antitumor activities of the ilamycins.

Dithiolopyrrolones are microbial natural products containing a disulfide or thiosulfonate bridge embedded in a unique bicyclic structure. By interfering with zinc ion homeostasis in living cells, they show strong antibacterial activity against a variety of bacterial pathogens, as well as potent cytotoxicity against human cancer cells. In the current study, two new dithiolopyrrolones, pyrroloformamide C ( 3 ) and pyrroloformamide D ( 4 ), were isolated from Streptomyces sp. CB02980, together with the known pyrroloformamides 1 and 2 . The biosynthetic gene cluster for pyrroloformamides was identified from Streptomyces sp. CB02980, which shared high sequence similarity with those of dithiolopyrrolones, including holomycin and thiolutin. Gene replacement of pyfE , which encodes a nonribosomal peptide synthetase (NRPS), abolished the production of 1 - 4 . Overexpression of pyfN , a type II thioesterase gene, increased the production of 1 and 2 . Genome neighborhood network analysis of the characterized and orphan gene clusters of dithiolopyrrolones revealed a unified mechanism for their biosynthesis, involving an iterative-acting NRPS and a set of conserved tailoring enzymes for the bicyclic core formation.

Three new kendomycin analogues, kendomycins B-D ( 1 - 3 ), were discovered from the marine-derived actinomycete Verrucosispora sp. SCSIO 07399. The structures of 1 - 3 were elucidated using diverse spectroscopic data analyses, X-ray crystallography, and semisynthetic derivatization. In vitro antimicrobial assays revealed that 1 - 3 all display good antibacterial activities against six Gram-positive bacteria with MIC values ranging from 0.5 to 8.0 μg/mL. Additionally, 1 - 3 were found to be moderately cytotoxic against MGC803, A549, HeLa, HepG2, MCF-7, and RKO human tumor cell lines; IC 50 values ranged from 2.2 to 44 μM.

Four new hydroxamate-containing natural product cyclopeptides designated acremonpeptides A-D ( 1 - 4 ), together with Al(III)-acremonpeptide D ( 5 ) were obtained from the marine fungus Acremonium persicinum SCSIO 115. The planar structures of 1 - 5 were established on the basis of HRMS as well as 1D and 2D NMR data sets. Moreover, the amino acid absolute configurations were determined using Marfey's method. Compounds 1 - 5 all feature three 2-amino-5-( N -hydroxyacetamido)pentanoic acid ( N 5 -hydroxy- N 5 -acetyl-l-ornithine) metal ion chelating moieties. Beyond their discovery and structure elucidation, in vitro bioassays revealed acremonpeptides A ( 1 ), B ( 2 ), and Al(III)-acremonpeptide D ( 5 ) as moderate antiviral agents for herpes simplex virus 1 with EC 50 values of 16, 8.7, and 14 μM, respectively.

Three new abyssomicin monomers designated neoabyssomicins D (1), E (2), and A2 (3) and the two dimeric neoabyssomicins F (4) and G (5) were discovered from the marine-derived Streptomyces koyangensis SCSIO 5802, and their structures rigorously elucidated. Neoabyssomicin D (1) possesses an unprecedented 8/5/5/7 ring skeleton, the biosynthesis of which (as well as 2) is proposed herein. Additionally, dimeric agents 4 and 5 were found to be active against methicillin-resistant Staphylococcus aureus and vesicular stomatitis virus, respectively.

Four known compounds, rishirilide B (1), rishirilide C (2), lupinacidin A (3), and galvaquinone B (4), representing two anthracene scaffolds typical of aromatic polyketides, were isolated from a culture of the deep-sea-derived Streptomyces olivaceus SCSIO T05. From the S. olivaceus producer was cloned and sequenced the rsd biosynthetic gene cluster (BGC) that drives rishirilide biosynthesis. The structural gene rsdK 2 inactivation and heterologous expression of the rsd BGC confirmed the single rsd BGC encodes construction of 1-4 and, thus, accounts for two anthracene scaffolds. Precursor incubation experiments with 13 C-labeled acetate revealed that a Baeyer-Villiger-type rearrangement plays a central role in construction of 1-4. Two luciferase monooxygenase components, along with a reductase component, are presumably involved in the Baeyer-Villiger-type rearrangement reaction enabling access to the two anthracene scaffold variants. Engineering of the rsd BGC unveiled three SARP family transcriptional regulators, enhancing anthracene production. Inactivation of rsdR 4 , a MarR family transcriptional regulator, failed to impact production of 1-4, although production of 3 was slightly improved; most importantly rsdR 4 inactivation led to the new adduct 6 in high titer. Notably, inactivation of rsdH, a putative amidohydrolase, substantially improved the overall titers of 1-4 by more than 4-fold.

The C7 (C9 or C10)- O-l-rhodosamine-bearing anthracycline antibiotic cytorhodins and their biosynthetic intermediates were recently isolated from Streptomyces sp. SCSIO 1666. Cosmid p17C4 from the Streptomyces lydicus genomic library, which harbors both the biosynthetic genes for l-rhodinose (or 2-deoxy-l-fucose) and its glycosyltransferase (encoded by slgG), was introduced into SCSIO 1666 to yield the recombinant strain Streptomyces sp. SCSIO 1666/17C4. Chemical investigations of this strain's secondary metabolic potential revealed the production of different anthracyclines featuring C7- O-l-rhodinose (or 2-deoxy-l-fucose) instead of the typically observed l-rhodosamine. Purification of the fermentation broth yielded 12 new anthracycline antibiotics including three new ε-rhodomycinone derivatives, 1, 4, and 8, nine new β-rhodomycinone derivatives, 2, 3, 5-7, and 9-12, and three known compounds, l-rhodinose-l-rhodinose-l-rhodinoserhodomycinone (13), ε-rhodomycinone (14), and γ-rhodomycinone (15). All compounds were characterized on the basis of detailed spectroscopic analyses and comparisons with previously reported data. These compounds exhibited cytotoxicity against a panel of human cancer cell lines. Significantly, compounds 4 and 13 displayed pronounced activity against HCT-116 as characterized by IC 50 values of 0.3 and 0.2 μM, respectively; these IC 50 values are comparable to that of the positive control epirubicin.

Two new spirotetronate aglycones, 22-dehydroxymethyl-kijanolide (1) and 8-hydroxy-22-dehydroxymethyl-kijanolide (2), along with seven new spirotetronate glycosides, microsporanates A-F (3-8) and tetrocarcin P (9), together with three known tetrocarcins [tetrocarcins A (10), B (11), and AC6H (12)], were isolated from fermentation broths of the marine-derived Micromonospora harpali SCSIO GJ089. The structures of 1-9 were elucidated on the basis of 1D and 2D NMR and MS spectroscopic data. Compounds 3-8 feature an α,β-unsaturated carbonyl moiety within their spirotetronate skeletons. Moreover, compounds 3-12 displayed strong to moderate antibacterial activities against Gram positive bacteria Bacillus thuringiensis BT01 and B. subtilis BS01 with MIC values ranging from 0.016 to 8.0 μg/mL.

Emodacidamides A-H (1-8), natural products featuring anthraquinone-amino acid conjugates, have been isolated from a marine-derived fungus, Penicillium sp. SCSIO sof101, together with known anthraquinones 9 and 10. The planar structures of 1-8 were elucidated using a combination of NMR spectroscopy and mass spectrometry. The absolute configurations of the amino acid residues were confirmed using Marfey's method and chiral-phase HPLC analyses. Additionally, isolates were evaluated for possible immunomodulatory and cytotoxic activities. Emodacidamides A (1), C (3), D (4), and E (5) inhibited interleukin-2 secretion from Jurkat cells with IC 50 values of 4.1, 5.1, 12, and 5.4 μM, respectively.

The desotamides (DSAs) are potent antibacterial cyclohexapeptides produced by Streptomyces scopuliridis SCSIO ZJ46. We have identified the 39-kb dsa biosynthetic gene cluster by whole-genome scanning. Composed of 17 open reading frames, the cluster codes for four nonribosomal peptide synthetases and associated resistance, transport, regulatory, and precursor biosynthesis proteins. Heterologous expression of the dsa gene cluster in S. coelicolor M1152 afforded desotamides A and B and the new desotamide G. Cluster identification and its demonstrated amenability to heterologous expression provide the foundation for future mechanistic studies as well as the generation of new and potentially clinically significant DSA analogues.

Three new cyclohexapeptides, desotamides B-D (2-4), and the known desotamide (1) were isolated from marine microbe Streptomyces scopuliridis SCSIO ZJ46. The sequences and absolute configurations of 2-4 were elucidated on the basis of high-resolution spectroscopic data, Marfey's method, and chiral-phase HPLC data. Desotamide C (3) contains a unique N-formyl-kynurenine residue, whereas 4 lacks formylation at the same site. Compounds 1 and 2 displayed notable antibacterial activities against strains of Streptococcus pnuemoniae, Staphylococcus aureus, and methicillin-resistant Staphylococcus epidermidis (MRSE), and structure activity relationship studies revealed the indispensability of the Trp component for antibacterial activity within this new scaffold.

Four new sesquiterpenoid naphthoquinones, marfuraquinocins A-D (1-4), and two new geranylated phenazines, phenaziterpenes A (5) and B (6), were isolated from the fermentation broth of Streptomyces niveus SCSIO 3406, which originated from a South China Sea sediment sample obtained from a depth of 3536 m. The structures of 1-6 were elucidated on the basis of extensive MS and one-dimensional and two-dimensional NMR spectroscopic analyses. In a panel of cytotoxicity and antibacterial assays, 1 and 3 were found to inhibit a NCI-H460 cancer cell line with IC50 values of 3.7 and 4.4 μM, respectively. Compounds 1, 3, and 4 exhibited antibacterial activities against Staphylococcus aureus ATCC 29213 with equivalent MIC values of 8.0 μg/mL; compounds 3 and 4 each showed antibacterial activity against methicillin-resistant Staphylococcus epidermidis (MRSE) shhs-E1 with MIC values of 8.0 μg/mL.

A new sequential tristhiazole-thiazoline-containing cyclic peptide, marthiapeptide A (1), was isolated from a 60 L scale culture of the deep South China Sea-derived strain Marinactinospora thermotolerans SCSIO 00652. The planar structure and absolute configuration of 1 were elucidated by application of spectroscopic techniques, as well as by single-crystal X-ray diffraction and chiral-phase HPLC analysis of the acid hydrolysates. Marthiapeptide A (1) exhibited antibacterial activity against a panel of Gram-positive bacteria, with MIC values ranging from 2.0 to 8.0 μg/mL, and displayed strong cytotoxic activity against a panel of human cancer cell lines with IC(50) values ranging from 0.38 to 0.52 μM.

Metabolomic investigations focusing on the marine-derived fungus Aspergillus sp. SCSIO F063 have unveiled seven new chlorinated anthraquinones (1-7) related to averantin, together with five known analogues (11-15) when the fungus was fermented using sea salt-containing potato dextrose broth. Through the addition of sodium bromide to the broth, two new brominated anthraquinones (8, 9) and one new nonhalogenated anthraquinone (10) were obtained from the fungal mycelia. Their structures were elucidated by extensive spectroscopic analyses including MS and 1D and 2D NMR data. One metabolite, 6-O-methyl-7-chloroaveratin (2), displayed inhibition activity against three human tumor cell lines, SF-268, MCF-7, and NCI-H460, with IC(50) values of 7.11, 6.64, and 7.42 μM, respectively.

Three new cycloheptapeptides, cordyheptapeptides C-E (1-3), were isolated from the fermentation extract of the marine-derived fungus Acremonium persicinum SCSIO 115. Their planar structures were elucidated on the basis of extensive MS, as well as 1D and 2D (COSY, HMQC, and HMBC) NMR spectroscopic data analyses. The absolute configurations of the amino acid residues were determined by single-crystal X-ray diffraction, Marfey's method, and chiral-phase HPLC analysis. Compounds 1 and 3 displayed cytotoxicity against SF-268, MCF-7, and NCI-H460 tumor cell lines with IC(50) values ranging from 2.5 to 12.1 μM.

Five new C-glycoside angucyclines, named grincamycins B-F (1-5), and a known angucycline antibiotic, grincamycin (6), were isolated from Streptomyces lusitanus SCSIO LR32, an actinomycete of deep sea origin. The structures of these compounds were elucidated on the basis of extensive spectroscopic analyses, including MS and 1D and 2D NMR experiments. All compounds except grincamycin F (5) exhibited in vitro cytotoxicities against the human cancer cell lines HepG2, SW-1990, HeLa, NCI-H460, and MCF-7 and the mouse melanoma cell line B16, with IC₅₀ values ranging from 1.1 to 31 μM.

Four new β-carboline alkaloids, designated marinacarbolines A-D (1-4), two new indolactam alkaloids, 13-N-demethyl-methylpendolmycin (5) and methylpendolmycin-14-O-α-glucoside (6), and the three known compounds 1-acetyl-β-carboline (7), methylpendolmycin (8), and pendolmycin (9) were obtained from the fermentation broth of Marinactinospora thermotolerans SCSIO 00652, a new actinomycete belonging to the family Nocardiopsaceae. Their structures were elucidated by extensive MS and 1D and 2D NMR spectroscopic data analyses. The structure of compound 1 was further confirmed by single-crystal X-ray crystallography. The new compounds 1-6 were inactive against a panel of eight tumor cell lines (IC50>50 μM) but exhibited antiplasmodial activities against Plasmodium falciparum lines 3D7 and Dd2, with IC50 values ranging from 1.92 to 36.03 μM.

Eight secondary metabolites, including three new azaphilones (chermesinones A-C, 1-3), three new p-terphenyls (6'-O-desmethylterphenyllin, 4; 3-hydroxy-6'-O-desmethylterphenyllin, 5; 3''-deoxy-6'-O-desmethylcandidusin B, 7), and two known p-terphenyls (6, 8), were isolated from the culture of the mangrove endophytic fungus Penicillium chermesinum (ZH4-E2). Their structures were established by spectroscopic analysis. The absolute configuration of 1 was determined by X-ray crystallography. Terphenyls 4, 5, and 6 exhibited strong inhibitory effects against α-glucosidase with IC50 values of 0.9, 4.9, and 2.5 μM, respectively. Terphenyls 7 and 8 showed inhibitory activity toward acetylcholinesterase with IC50 values of 7.8 and 5.2 μM.

Tautomycetin (TTN) is a highly potent and specific protein phosphatase inhibitor isolated from Streptomyces griseochromogenes. The biological activity of TTN makes it an important lead for drug discovery, whereas its rare dialkylmaleic anhydride moiety and structural similarity to tautomycin (TTM), another potent phosphatase inhibitor with tremendous medicinal potential, draws attention to novel biosynthetic chemistries responsible for its production. To elucidate the biosynthetic machinery associated with TTN production, the ttn biosynthetic gene cluster from S. griseochromogenes was isolated and characterized, and its involvement in TTN biosynthesis confirmed by gene inactivation and complementation experiments. The ttn cluster was localized to a 79 kb DNA region, consisting of 19 open reading frames that encode two modular type I polyketide synthases (TtnAB), one type II thioesterase (TtnH), eight proteins for dialkylmaleic anhydride biosynthesis (TtnKLMNOPRS), four tailoring enzymes (TtnCDFI), two regulatory proteins (TtnGQ), and one resistance protein (TtnJ). A model for TTN biosynthesis is proposed on the basis of functional assignments from sequence analysis, which agrees well with previous feeding experiments, has been supported by in vivo gene inactivation experiments, and is supported by analogy to the recently reported ttm cluster. These findings set the stage to fully investigate TTN biosynthesis and to biosynthetically engineer new TTN analogues.

Fredericamycin (FDM) A ( 1), a pentadecaketide featuring two sets of peri-hydroxy tricyclic aromatic moieties connected through a unique asymmetric carbaspiro center, exhibits potent cytotoxicity and represents a novel anticancer drug lead. We have localized previously the fdm gene cluster to a 33 kb DNA segment of Streptomyces griseus ATCC49344, the involvement of which in the biosynthesis of 1 was confirmed by gene inactivation, complementation, and heterologous expression experiments. We now report the isolation and characterization of FDM E ( 5), a heretofore undetected intermediate for 1 biosynthesis from S. griseus, shedding new insight into the mechanism of carbaspirocycle formation. The structure of 5 was elucidated through the combination of spectroscopic methods and isotope-labeling experiments. The core spiro[4.5]decane scaffold of 5 is characterized by a unique cyclohexa-1,2,4-triketone moiety. Transformation of the spiro[4.5]decane 5 into the spiro[4.4]nonane 1 can be rationalized by a biosynthetic benzilic acid-like rearrangement. This unusual rearrangement can be mimicked in vitro by proceeding under aerobic conditions in the absence of enzyme. FDM E displays cytotoxic activity on par with 1 against a selected set of cancer cells, a finding that further supports the unique molecular topology, resulting from the unprecedented carbaspirocycle as exemplified by 1 and 5, as a novel pharmacophore for this family of anticancer agents.