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A versatile strategy for the enantioselective synthesis of a benzo[c]oxepine structural core containing natural secondary metabolites was developed. The key steps of the synthetic approach include ring-closing alkene metathesis for seven-member ring construction, the Suzuki–Miyaura cross-coupling reaction for the installation of the double bond and Katsuki–Sharpless asymmetric epoxidation for the introduction of chiral centers. The first total synthesis and absolute configuration assignment of heterocornol D (3a) were achieved. Four stereoisomers, 3a, ent-3a, 3b and ent-3b, of this natural polyketide were prepared, starting with 2,6-dihydroxy benzoic acid and divinyl carbinol. The absolute and relative configuration of heterocornol D was assigned via single-crystal X-ray analysis. The extension of the described synthetic approach is further presented with the synthesis of heterocornol C by applying the ether group reduction method to the lactone.

Streptomyces sp. N11-50 was isolated from deep-sea water and found to produce diketopiperazine (DKP) compounds such as albonoursin and cyclo(Phe-Leu). This study aimed to reveal the potential to synthesize diverse nonribosomal peptide and polyketide compounds as the other secondary metabolites different from DKP after clarifying the taxonomic position. Strain N11-50 was identified as Streptomyces albus, as it showed 100% 16S rRNA gene sequence similarities and 95.5% DNA–DNA relatedness to S. albus NBRC 13014T. We annotated the nonribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) gene clusters in the genome. Consequently, five NRPS, one hybrid PKS/NRPS, five type-I PKS and one type-II PKS gene clusters were observed, of which we predicted the products through bioinformatic analysis. These gene clusters were well conserved in already whole-genome sequence (WGS)-published strains belonging to S. albus. On the other hand, our taxonogenomic analysis revealed that three WGS-published S. albus strains were not S. albus. Two of the three should be classified as Streptomyces albidoflavus, and the remaining one was likely a new genomospecies. After reclassifying these appropriately, we demonstrated species-specific profiles of the NRPS and PKS gene clusters with little strain-level diversities.

Natural products have high structural diversity with various pharmacological or biological activities, which are of great significance to our life and drug research. Millions of natural products with versatile structural diversity have been found in nature. In recent years, a large number of microbial genome sequences have been released in public databases and revealed many silent or cryptic secondary metabolite gene clusters hidden in their genomes. This shows the great potential for discovering new metabolites. Advances in sequencing technology and bioinformatics analysis also provide great advantages for studying the biosynthesis and structural diversity of these metabolites. Structural differentiation of natural products begins with the formation of basic scaffolds using basic building blocks derived from primary metabolism catalyzed by different backbone enzymes. The structural complexity of natural products mainly arises from tailoring enzymes to highly functionalize the skeletons with a set of chemical transformations. The well-studied modification enzymes range from different types of oxidoreductases, cytochrome P450 enzymes, to various prenyltransferases (PTs) and methyltransferases (MTs). In addition, nonenzymatic events have also contributed to the formation of final products with vast diversity and complexity. Therefore, fully exploring these unexplored gene clusters and the substrate promiscuity of enzymatic and non-enzymatic reactions for the natural product formation may be a promising way and a new strategy to explore the metabolite diversity. In a cooperation study with Dr. Liujuan Zheng, the biosynthesis of a highly oxygenated phenethyl derivative ustethylin A, isolated from Aspergillus ustus, was elucidated. Due to the instability of ustethylin A, it was acetylated before isolation and structure elucidation. Gene deletion and heterologous expression proved that the phenethyl core structure is assembled by a polyketide synthase (UttA) harboring a methyltransferase domain. Isotopic labelling experiments proved that the backbone of ustethylin A is derived from malonyl-CoA and the methyl groups, also in the phenethyl residue, are from L-methionine. Modifications on the core structure by an aryl acid reductase (UttJ), a putative nonheme FeII/2-oxoglutarate dependent oxygenase (UttH), a cytochrome P450 enzyme (UttC) and a O-methyltransferase (UttF) led to the final product ustethylin A. This study is the first report on the biosynthetic pathway of a phenethyl-containing natural product. In cooperation with Dr. Jing Liu, the biosynthesis of streptoazine C and guanitrypmycin D1 was elucidated. Firstly, a three-gene cluster coding for a cyclodipeptide synthase, a prenyltransferase, and a methyltransferase was identified in Streptomyces aurantiacus by genome mining. Heterologous expression and precursor incubation experiments led to the elucidation of the biosynthetic steps of streptoazine C. In vivo biotransformation experiments proved the high flexibility of the prenyltransferase SasB toward tryptophan-containing cyclodipeptides and their dehydroderivatives for regular C-3-prenylation. This study provides an enzyme with a high substrate promiscuity from the less explored prenyltransferase group in cyclodipeptide synthase-related pathways. Afterwards, a two-gene cluster coding for a CDPS and a cytochrome P450 was identified in Streptomyces sp. NRRL S-1521 by phylogenetic analysis. Heterologous expression and structural elucidation of the isolated products proved that the cytochrome P450 GutD1521 catalyzes the regiospecific transfer of guanine to C-2 of the indole ring of cyclo-(L-Trp-L-Tyr) via a C−C linkage, which represents a new chemical transformation within this enzyme class. Precursor incubation experiments revealed that GutD1521 efficiently accepts several other tryptophan-containing cyclodipeptides or derivatives for regiospecific coupling with guanine, thus generating different guanitrypmycin analogs. This study provides a biocatalyst for a new linkage pattern between a indole ring and a guanine moiety and expands the functional spectrum of P450s as tailoring enzymes.

Microfluidics-based sorting of cells after encapsulation in water-in-oil or water/oil/water droplet emulsions has great potential to significantly accelerate the design-build-test cycle for production strain engineering. This is especially true for non-conventional hosts and products that are secreted, as screening can be performed with minimal prior biological knowledge (relative to rational engineering) and entrapment of secreted product with the responsible producer cell can enable high throughput screening directly for extracellular product concentration. Microfluidic technology for droplet sorting has advanced and become more available in recent years, but gaps remain, including the limited number of droplet-compatible methods for transducing extracellular product titers into sortable fluorescence signals, and a lack of direct, matched comparisons to more established techniques such as fluorescence activated cell sorting (FACS). This research used yeast-based systems (Saccharomyces cerevisiae and Yarrowia lipolytica) as test beds for focusing on and addressing three areas that are related to these limitations. In the first focus area, we develop RNA aptamers in droplets (RAPID) screening, a method that expands the generality of high throughput microfluidic droplet screening. Using RNA aptamers, we transduce extracellular titer into fluorescence, enabling the screening of millions of yeast variants and ultimately enhancing secretion of a recombinant protein (streptavidin) from yeast. For the second focus area, we undertook a comparative analysis of traditional single cell fluorescence activated cell sorting (single cell FACS) and microdroplet-enabled FACS (droplet FACS) using water/oil/water (w/o/w) emulsions. To do so, we engineered and evolved the non-conventional yeast Y. lipolytica for high extracellular production of riboflavin (vitamin B2), an innately fluorescent product. In a parity-matched comparison of single cell FACS and droplet FACS, both techniques led to significant increases in total riboflavin. However, single cell FACS favored intracellular accumulation, while droplet FACS favored extracellular product accumulation and yielded higher total riboflavin production. In the third focus area, a droplet-based bacterial-fungal consortium/co-culture approach was applied, wherein Escherichia coli biosensors were used to screen for improved extracellular polyketide production from Y. lipolytica. This droplet sorting strategy was used to screen genome-wide piggyBac transposon libraries, leading to the identification of several alleles for enhancing triacetic acid lactone (TAL) production.

Building strains of filamentous fungi for stable long-term heterologous expression of large biosynthetic pathways is limited by the low transformation efficiency or genetic stability of current methods. Here, we developed a system for targeted chromosomal integration of large biosynthetic gene clusters in Aspergillus nidulans based on site-specific recombinase-mediated cassette exchange. We built A. nidulans strains harboring a chromosomal landing pad for Cre/lox-mediated recombination and demonstrated efficient targeted integration of a 21 kb DNA fragment in a single step. We further evaluated the integration at two loci by analyzing the expression of a fluorescent reporter and the production of a heterologous polyketide metabolite. We compared chromosomal expression at those landing loci to episomal AMA1-based expression, which also shed light on uncharacterized aspects of episomal expression in filamentous fungi. This is the first demonstration of site-specific recombinase-mediated integration in filamentous fungi, setting the foundations for the further development of this tool.

A new, highly modified fatty acid ester, funitatin A (1), was isolated from the Yellow River wetland-derived fungus Talaromyces funiculosus HPU-Y01 cultivated with the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA). The structure of 1 was established by analysis of NMR and HRESIMS data. Compound 1 featured a rare dimeric cyclopaldic acid structure and showed promising antimicrobial activity against both Proteus species and Escherichia coli with MIC values of 3.13 μM.

Covering: 1999 up to 2021Fungal polyketides encompass a range of structurally diverse molecules with a wide variety of biological activities. The giant multifunctional enzymes that synthesize polyketide backbones remain enigmatic, as do many of the tailoring enzymes involved in functional modifications. Recent advances in elucidating biosynthetic gene clusters (BGCs) have revealed numerous examples of fungal polyketide synthases that require the action of collaborating enzymes to synthesize the carbon backbone. This review will discuss collaborating and trans-acting enzymes involved in loading, extending, and releasing polyketide intermediates from fungal polyketide synthases, and additional modifications introduced by trans-acting enzymes demonstrating the complexity encountered when investigating natural product biosynthesis in fungi.

The genus Amphidinium has been the subject of recent attention due to the production of polyketide metabolites. Some of these compounds have shown significant bioactivities and could be related to species interactions in the natural benthic microenvironment. Among these compounds, amphidinols (AMs) are suspected to be related to fish kills and probably implicated in ciguatera symptoms associated with the occurrence of benthic harmful algal blooms (bHABs). Here, we present the first report of a variety of AMs produced by cultured strains from several species from the Mexican Pacific, the Gulf of California, and the Gulf of Mexico. Through ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS), ten previously known AMs (AM02, -04, -05, -06, -07, -09, -11, -14, -15, and -17), four recently reported AMs (N7, N8/N9, N12, and N13), and three new variants (U1, U2, and U3) were identified. Of the twelve analyzed Amphidinium cultures, five were not AM producers, and the cell quotas of the remaining seven strains ranged from close to nondetectable to a maximum of 1694 fg cell−1, with many intermediate levels in between. The cultures from the Mexican North Pacific coast produced AMs in a higher quantity and variety than those from worldwide locations. This is the first study of AMs from Mexican Amphidinium strains, and our results confirm the relevance of continuing the investigation of the genus bioactive metabolites.

Micromonospora sp. AKA109 is a producer of akazaoxime and A-76356, whereas Micromonospora sp. AKA38 is that of levantilide C. We aimed to clarify their taxonomic positions and identify biosynthetic gene clusters (BGCs) of these compounds. In 16S rRNA gene and DNA gyrase subunit B gene (gyrB) sequence analyses, strains AKA109 and AKA38 were the most closely related to Micromonosporahumidisoli MMS20-R2-29T and Micromonospora schwarzwaldensis HKI0641T, respectively. Although Micromonospora sp. AKA109 was identified as M.humidisoli by the gyrB sequence similarity and DNA–DNA relatedness based on whole genome sequences, Micromonospora sp. AKA38 was classified to a new genomospecies. M. humidisoli AKA109 harbored six type-I polyketide synthase (PKS), one type-II PKS, one type-III PKS, three non-ribosomal peptide synthetase (NRPS) and three hybrid PKS/NRPS gene clusters, among which the BGC of akazaoxime and A-76356 was identified. These gene clusters are conserved in M.humidisoli MMS20-R2-29T. Micromonospora sp. AKA38 harbored two type-I PKS, one of which was responsible for levantilide C, one type-II PKS, one type-III PKS, two NRPS and five hybrid PKS/NRPS gene clusters. We predicted products derived from these gene clusters through bioinformatic analyses. Consequently, these two strains are revealed to be promising sources for diverse non-ribosomal peptide and polyketide compounds.

phlD is a novel kind of polyketide synthase involved in the biosynthesis of non-volatile metabolite phloroglucinol by iteratively condensing and cyclizing three molecules of malonyl-CoA as substrate. Phloroglucinol or 2,4-diacetylphloroglucinol (DAPG) is an ecologically important rhizospheric antibiotic produced by pseudomonads; it exhibits broad spectrum anti-bacterial and anti-fungal properties, leading to disease suppression in the rhizosphere. Additionally, DAPG triggers systemic resistance in plants, stimulates root exudation, as well as induces phyto-enhancing activities in other rhizobacteria. Here, we report the cloning and analysis of the phlD gene from soil-borne gram-negative bacteria—Pseudomonas. The full-length phlD gene (from 1078 nucleotides) was successfully cloned and the structural details of the PHLD protein were analyzed in-depth via a three-dimensional topology and a refined three-dimensional model for the PHLD protein was predicted. Additionally, the stereochemical properties of the PHLD protein were analyzed by the Ramachandran plot, based on which, 94.3% of residues fell in the favored region and 5.7% in the allowed region. The generated model was validated by secondary structure prediction using PDBsum. The present study aimed to clone and characterize the DAPG-producing phlD gene to be deployed in the development of broad-spectrum biopesticides for the biocontrol of rhizospheric pathogens.

Die vorliegende Arbeit befasst sich mit der Aufklärung der Ambruticin-Biosynthese. Die Ambruticine sind Polyketidnaturstoffe aus dem Myxobakterium Sorangium cellulosum So ce10, welche über einen sehr selektiven Mechanismus fungizid wirken. Dies macht sie als neuartige Antimykotika interessant. Ein Umstand, der dem kommerziellen Nutzen aber im Wege steht, ist die hohe strukturelle Komplexität. Diese Komplexität wird durch eine außerge-wöhnliche Biosynthese erreicht. Aktuell stützen sich die Annahmen zu deren Ablauf v.a. auf die Genclusteranalyse und die Isolierung von Intermediaten aus knockout-Experimenten durch Reeves et al. und die Studien von Hahn et al. Der Ablauf der Biosynthese des mittleren Divinylcyclopropyl-Fragments ist allerdings noch unklar. Nur die Eckpunkte davon, ein ACP-gebundenes Intermediat aus Modul 5 (AmbD) und das bereits abgespaltene Ambruticin J, sind bisher bekannt. Die Hypothese von Hahn et al. ist, dass AmbF die Bildung des Cyclopropans katalysiert, gefolgt von AmbG welches die Entfernung einer Kohlenstoffeinheit durch AmbI ermöglicht. Die vorliegende Arbeit ist der Versuch Licht in das Dunkel der Bildung des Divinylcyclopropyl-Mittelfragments durch AmbF zu bringen. Dieses Ziel sollte durch einen interdisziplinären Ansatz aus Strukturbiologie, Molekularbiologie und Enzymologie mit hochrealistischen Substraten erreicht werden. Es wurde eine neue Hypothese zu den AmbF-katalysierten Reaktionen aufgestellt, welche auf den chemischen Eigenschaften der Substrate, dem Vergleich mit anderen Biosynthesen und den strukturellen Besonderheiten von AmbF beruht. Nach der Bildung eines mehrfach ungesättigten β-Ketopolyens in einer Verlängerungsreaktion mit einer noch unbekannten trans-AT erfolgt die Bildung eines Imins mit dem Cofaktor Pyridoxaminphosphat. Dieser erleichtert als electron sink factor die nachfolgenden Reaktionen. In einem Additions-Eliminierungs-Mechanismus findet dann der Ringschluss zum Cyclopropan durch einen Elektronenshift entlang des konjugierten π-Systems statt. Das dabei simultan gebildete Cyclopropanon wird dann durch die Hydrolase-Domäne in einer Favorskii-artigen Umlagerung zur verzweigten Carbonsäure geöffnet. Zur Überprüfung der postulierten Biosynthese wurden möglichst realistische Surrogate vom postuliertem ACP-gebundenen Substrat synthetisiert. Dafür wurde nach ausgiebigen Optimierungsarbeiten ein Protokoll für die Synthese von mehrfach ungesättigten β-Ketothioaten entwickelt. Mit diesem können diese schnell, flexibel und mit guten Ausbeuten sowie hervorragenden Selektivitäten dargestellt werden. In einer ausgegliederten Untersuchung zur Stereoselektivität der Ketoreduktasedomäne MycKRB aus der Mycotoxin-Biosynthese wurde der große Praxisnutzen der Synthese und der damit hergestellten Substrate unter Beweis gestellt. Hier wurde gezeigt, dass in vitro-Experimente präziser die natürliche Selektivität abbilden, wenn charakteristische Strukturelemente in den Surrogaten vorhanden sind. Das bekräftigt wiederum den Ansatz dieses Projekts in den in vitro-Versuchen zu den AmbF-Domänen möglichst realistische Substrate einzusetzen. Durch bioinformatische Untersuchungen, insbesondere durch Strukturhomologiemodelle, wurden die Domänengrenzen der an der Zyklisierung beteiligten Domänen aus AmbF neu bestimmt. Auch wurde gezeigt, dass die Px-Domäne aus einer kleinen (PxN) und einer großen Subdomäne (PxC) besteht, während in der Literatur nur ein C-terminaler Teil der großen Subdomäne angegeben wird. Diese neuen Sequenzen wurden erfolgreich in pET28a(+)-Expressionvektoren kloniert. Während die heterologe Proteinproduktion der Px-Domäne in den von Reeves et al. gesetzten Grenzen scheiterte, konnte sowohl die HPx-Didomäne, als auch die neu eingegrenzte PxNC-Domäne in E. coli löslich hergestellt werden. In den Aktivitätstests zu den AmbF-Domänen H und Px konnte keine enzymatische Aktivität mit dem Substratsurrogat nachgewiesen werden. In künftigen Experimenten sollten allerdings beispielsweise noch weitere Reaktionsbedingungen oder ein erweitertes Substratsspektrum getestet werden. Mit dieser Arbeit wurde das Fundament gelegt, auf dem weitere Versuche zur Aufklärung der Biosynthese des Ambruticin-Mittelfragments aufgebaut werden können. Für die Charakterisierung von AmbG wurden verschiedene Carbonsäuren synthetisiert. Aus der Substratselektivität und bioinformatischen Analyse lässt sich schließen, dass AmbG eine FAAL-ACP-Didomäne mit einer außergewöhnlich breiten Substrattoleranz ist. Damit konnte die Hypothese, dass die Ambruticin-Biosynthese über die Aktivierung der verzweigten Thioestercarbonsäure abläuft, gestützt werden.

Pseudomonas species are prominent producers of lipopeptides that support proliferation in a multitude of environments and foster varied lifestyles. By genome mining of biosynthetic gene clusters (BGCs) with lipopeptide-specific organization, we mapped the global Pseudomonas lipopeptidome and linked its staggering diversity to taxonomy of the producers, belonging to different groups within the major Pseudomonas fluorescens lineage.

p53 is frequently mutated in tumor cells. Mutant p53 (mut p53) accumulates in cells to promote cancer progression, invasion, and metastasis, and it is attracting attention as a target for cancer therapies. In this study, we used immunofluorescence staining of Saos-2 cells harboring doxycycline-inducible p53R175H [Saos-2 (p53R175H) cells] to search for compounds from natural sources that can target mut p53 and found an extract of Colletotrichum sp. (13S020) that was active. Bioassay-guided fractionation of the extract afforded a known polyketide, colletofragarone A2 (1), and three new analogues, colletoins A-C (2-4). The relative and absolute configurations of 1 were determined by the spectroscopic method and DFT calculation. Compounds 1 and 2 inhibited the growth of Saos-2 (p53R175H) cells and decreased mut p53 in the cells.

A new pluramycin-class polyketide, rausuquinone (1), and its known congener hydramycin (2) were isolated from the culture extract of the deep-sea water-derived Rhodococcus sp. RD015140. Compound 1 possesses a γ-pyrone-fused anthraquinone core with a 3-butene-1,2-diol side chain. Structures of 1 was determined by extensive analysis of 1D and 2D NMR spectroscopic data. Compound 1 showed antimicrobial activity against Gram-positive bacteria. This is the first discovery of aromatic polyketides from the genus Rhodococcus.

The semipinacol rearrangement (SPR) is highly useful in the asymmetric synthesis of complex compounds. In biological systems, only a few semi-pinacolases belonging to a few families have been ident...

Mupirocin, a polyketide antibiotic produced by Pseudomonas fluorescens, is used as a topical antimicrobial treatment to cure various skin infections. Quorum sensing system plays an important role in regulation of mupirocin biosynthesis in P. fluorescens NCIMB 10586. In Pseudomonas, the RpeA/RpeB two-component signal transduction (TCST) system regulates quorum sensing system. However, the influences of the RpeA/RpeB TCST system on mupirocin production or other cell activities have not been studied. In this work, the homologous genes of rpeA and rpeB in P. fluorescens NCIMB 10586 were identified and inactivated in the chromosome, respectively. The deletion of rpeA reduced the mupirocin production from 160 in the wild-type to 21.3 mg/L along with slightly decreased cell growth, while no significant effected on mupirocin production in the rpeB mutant. Next, it was found that the RpeA/RpeB TCST system regulated the biosynthesis of mupirocin by modulating the quorum sensing system. Furthermore, untargeted metabolomics analysis was employed to detect the influences of RpeA on other cell activities modulated by quorum sensing system. Combined with quantitative real-time PCR, the results demonstrated that RpeA also regulated other cell activities including central carbon, amino acids, fatty acids, and purine metabolism. Overall, this study expands the current understanding of the RpeA/RpeB TCST system and provides several targets for increasing yields of mupirocin. • In P. fluorescens, the RpeA/RpeB TCST system regulates the biosynthesis of mupirocin. • RpeA modulates the cell activities through effecting the central carbon metabolism.

Streptomyces coelicolor A3(2) is used worldwide for genetic studies, and its complete genome sequence was published in 2002. However, as the whole genome of the type strain of S. coelicolor has not been analyzed, the relationship between S. coelicolor A3(2) and the type strain is not yet well known. To clarify differences in their biosynthetic potential, as well as their taxonomic positions, we sequenced whole genomes of S. coelicolor NBRC 12854T and type strains of its closely related species—such as Streptomyces daghestanicus, Streptomyces hydrogenans, and Streptomyces violascens—via PacBio. Biosynthetic gene clusters for polyketides and non-ribosomal peptides were surveyed by antiSMASH, followed by bioinformatic analyses. Type strains of Streptomyces albidoflavus, S. coelicolor, S. daghestanicus, S. hydrogenans, and S. violascens shared the same 16S rDNA sequence, but S. coelicolor A3(2) did not. S. coelicolor A3(2) and S. coelicolor NBRC 12854T can be classified as Streptomycesanthocyanicus and S. albidoflavus, respectively. In contrast, S. daghestanicus, S. hydrogenans, and S. violascens are independent species, despite their identical 16S rDNA sequences. S. coelicolor A3(2), S. coelicolor NBRC 12854T, S. daghestanicus NBRC 12762T, S. hydrogenans NBRC 13475T, and S. violascens NBRC 12920T each harbor specific polyketide synthase (PKS) and non-ribosomal peptide synthetase (NRPS) gene clusters in their genomes, whereas PKS and NRPS gene clusters are well conserved between S. coelicolor A3(2) and S. anthocyanicus JCM 5058T, and between S. coelicolor NBRC 12854T and S. albidoflavus DSM 40455T, belonging to the same species. These results support our hypothesis that the repertoires of PKS and NRPS gene clusters are different between different species.

The medically important bacterial aromatic polyketide natural products typically feature a planar, polycyclic core structure. An exception is found for the rubromycins, whose backbones are disrupted by a bisbenzannulated [5,6]-spiroketal pharmacophore that was recently shown to be assembled by flavin-dependent enzymes. In particular, a flavoprotein monooxygenase proved critical for the drastic oxidative rearrangement of a pentangular precursor and the installment of an intermediate [6,6]-spiroketal moiety. Here we provide structural and mechanistic insights into the control of catalysis by this spiroketal synthase, which fulfills several important functions as reductase, monooxygenase, and presumably oxidase. The enzyme hereby tightly controls the redox state of the substrate to counteract shunt product formation, while also steering the cleavage of three carbon-carbon bonds. Our work illustrates an exceptional strategy for the biosynthesis of stable chroman spiroketals., Angewandte Chemie. International Edition, 60 (52), ISSN:1433-7851, ISSN:1521-3773, ISSN:0570-0833

Activation of a cryptic polyketide synthase gene cluster hkn from Aspergillus hancockii via overexpression of the gene-cluster-specific transcription factor HknR led to the discovery of a novel polycyclic metabolite, which we named hancockinone A. The compound features an unprecedented prenylated 6/6/6/5 tetracarbocyclic skeleton and shows moderate antibacterial activity. Heterologous expression, substrate feeding, and in vitro assays confirmed the role of cytochrome P450 HknE in constructing the five-membered ring in hancockinone A from the precursor neosartoricin B.

Redox tailoring enzymes play key roles in generating structural complexity and diversity in type II polyketides. In chartreusin biosynthesis, the early 13 C-labeling experiments and bioinformatic analysis suggest the unusual aglycone is originated from a tetracyclic anthracyclic polyketide. Here, we demonstrated that the carbon skeleton rearrangement from a linear anthracyclic polyketide to an angular pentacyclic biosynthetic intermediate requires two redox enzymes. The flavin-dependent monooxygenase ChaZ catalyses a Baeyer-Villiger oxidation on resomycin C to form a seven-membered lactone. Subsequently, a ketoreductase ChaE rearranges the carbon skeleton and affords the α-pyrone containing pentacyclic intermediate in an NADPH-dependent manner via tandem reactions including the reduction of the lactone carbonyl group, Aldol-type reaction, followed by a spontaneous γ-lactone ring formation, oxidation and aromatization. Our work reveals an unprecedented function of a ketoreductase that contributes to generate structural complexity of aromatic polyketide.

A metabolome-guided screening approach in the novel myxobacterium Corallococcus sp. MCy9072 resulted in the isolation of the unprecedented natural product myxofacycline A, which features a rare isoxazole substructure. Identification and genomic investigation of additional producers alongside targeted gene inactivation experiments and heterologous expression of the corresponding biosynthetic gene cluster in the host Myxococcus xanthus DK1622 confirmed a noncanonical megaenzyme complex as the biosynthetic origin of myxofacycline A. Induced expression of the respective genes led to significantly increased production titers enabling the identification of six further members of the myxofacycline natural product family. Whereas myxofacyclines A-D display an isoxazole substructure, intriguingly myxofacyclines E and F were found to contain 4-pyrimidinole, a heterocycle unprecedented in natural products. Lastly, myxofacycline G features another rare 1,2-dihydropyrol-3-one moiety. In addition to a full structure elucidation, we report the underlying biosynthetic machinery and present a rationale for the formation of all myxofacyclines. Unexpectedly, an extraordinary polyketide synthase-nonribosomal peptide synthetase hybrid was found to produce all three types of heterocycle in these natural products.

Filamentous soil bacteria are known to produce diverse specialized metabolites. Despite having enormous potential as a source of pharmaceuticals, they often produce bioactive metabolites at low titers. Here, we show that inactivation of the pactamycin, NFAT-133, and conglobatin biosynthetic pathways in Streptomyces pactum ATCC 27456 significantly increases the production of the mitochondrial electron transport inhibitors piericidins. Similarly, inactivation of the pactamycin, NFAT-133, and piericidin pathways significantly increases the production of the heat-shock protein (Hsp) 90 inhibitor conglobatin. In addition, four new conglobatin analogues (B2, B3, F1, and F2) with altered polyketide backbones, together with the known analogue conglobatin B1, were identified in this mutant, indicating that the conglobatin biosynthetic machinery is promiscuous toward different substrates. Among the new conglobatin analogues, conglobatin F2 showed enhanced antitumor activity against HeLa and NCI-H460 cancer cell lines compared to conglobatin. Conglobatin F2 also inhibits colony formation of HeLa cells in a dose-dependent manner. Molecular modeling studies suggest that the new conglobatins bind to human Hsp90 and disrupt Hsp90/Cdc37 chaperone/co-chaperone interactions in the same manner as conglobatin. The study also showed that genes that are involved in piericidin biosynthesis are clustered in two different loci located distantly in the S. pactum genome.

Anthraquinones (AQs) are found in a variety of consumer products, including foods, nutritional supplements, drugs, and traditional medicines, and have a wide range of pharmacological actions. Rubiadin, a 1,3-dihydroxy-2-methyl anthraquinone, primarily originates from Rubia cordifolia Linn (Rubiaceae). It was first discovered in 1981 and has been reported for many biological activities. However, no review has been reported so far to create awareness about this molecule and its role in future drug discovery. Therefore, the present review aimed to provide comprehensive evidence of Rubiadin’s phytochemistry, biosynthesis, physicochemical properties, biological properties and therapeutic potential. Relevant literature was gathered from numerous scientific databases including PubMed, ScienceDirect, Scopus and Google Scholar between 1981 and up-to-date. The distribution of Rubiadin in numerous medicinal plants, as well as its method of isolation, synthesis, characterisation, physiochemical properties and possible biosynthesis pathways, was extensively covered in this review. Following a rigorous screening and tabulating, a thorough description of Rubiadin’s biological properties was gathered, which were based on scientific evidences. Rubiadin fits all five of Lipinski’s rule for drug-likeness properties. Then, the in depth physiochemical characteristics of Rubiadin were investigated. The simple technique for Rubiadin’s isolation from R. cordifolia and the procedure of synthesis was described. Rubiadin is also biosynthesized via the polyketide and chorismate/o-succinylbenzoic acid pathways. Rubiadin is a powerful molecule with anticancer, antiosteoporotic, hepatoprotective, neuroprotective, anti-inflammatory, antidiabetic, antioxidant, antibacterial, antimalarial, antifungal, and antiviral properties. The mechanism of action for the majority of the pharmacological actions reported, however, is unknown. In addition to this review, an in silico molecular docking study was performed against proteins with PDB IDs: 3AOX, 6OLX, 6OSP, and 6SDC to support the anticancer properties of Rubiadin. The toxicity profile, pharmacokinetics and possible structural modifications were also described. Rubiadin was also proven to have the highest binding affinity to the targeted proteins in an in silico study; thus, we believe it may be a potential anticancer molecule. In order to present Rubiadin as a novel candidate for future therapeutic development, advanced studies on preclinical, clinical trials, bioavailability, permeability and administration of safe doses are necessary., Graphical Abstract

Actinobacteria embroil Gram-positive microbes with high guanine and cytosine contents in their DNA. They are the source of most antimicrobials of bacterial origin utilized in medicine today. Their genomes are among the richest in novel secondary metabolites with high biotechnological potential. Actinobacteria reveal complex patterns of evolution, responses, and adaptations to their environment, which are not yet well understood. We analyzed three novel plant isolates and explored their habitat adaptation, evolutionary patterns, and potential secondary metabolite production. The phylogenomically characterized isolates belonged to Actinoplanes sp. TFC3, Streptomyces sp. L06, and Embleya sp. NF3. Positively selected genes, relevant in strain evolution, encoded enzymes for stress resistance in all strains, including porphyrin, chlorophyll, and ubiquinone biosynthesis in Embleya sp. NF3. Streptomyces sp. L06 encoded for pantothenate and proteins for CoA biosynthesis with evidence of positive selection; furthermore, Actinoplanes sp. TFC3 encoded for a c-di-GMP synthetase, with adaptive mutations. Notably, the genomes harbored many genes involved in the biosynthesis of at least ten novel secondary metabolites, with many avenues for future new bioactive compound characterization-specifically, Streptomyces sp. L06 could make new ribosomally synthesized and post-translationally modified peptides, while Embleya sp. NF3 could produce new non-ribosomal peptide synthetases and ribosomally synthesized and post-translationally modified peptides. At the same time, TFC3 has particularly enriched in terpene and polyketide synthases. All the strains harbored conserved genes in response to diverse environmental stresses, plant growth promotion factors, and degradation of various carbohydrates, which supported their endophytic lifestyle and showed their capacity to colonize other niches. This study aims to provide a comprehensive estimation of the genomic features of novel Actinobacteria. It sets the groundwork for future research into experimental tests with new bioactive metabolites with potential application in medicine, biofertilizers, and plant biomass residue utilization, with potential application in medicine, as biofertilizers and in plant biomass residues utilization. KEY POINTS: • Potential of novel environmental bacteria for secondary metabolites production • Exploring the genomes of three novel endophytes isolated from a medicinal tree • Pan-genome analysis of Actinobacteria genera.

Background: The proposed central role of cancer stem cells (CSCs) in tumor development has been extended to explain the diverse oncologic phenomena such as multidrug resistance, metastasis and tumor recurrence in clinics. Due to the enhanced expression of ATP-binding cassette transporters and anti-apoptotic factors, stagnation on G0 phase and the strong ability of self-renewal, the CSCs were highly resistant to clinical anticancer drugs. Therefore, the discovery of new drug candidates that could effectively eradicate cancer stem cells afforded promising outcomes in cancer therapy. Objective: Natural products and their synthetic analogues are a rich source of biologically active compounds and several of them have already been recognized as potent CSCs killers. We aim to provide a collection of recently identified natural products that suppressed the survival of the small invasive CSC populations and combated the drug resistance of these cells in chemotherapy. Results: These anti-CSCs natural products included flavonoids, stilbenes, quinones, terpenoids, polyketide antibiotics, steroids and alkaloids. In the present review, we highlighted the therapeutic potential of natural products and their derivatives against the proliferation and drug resistance of CSCs, their working mechanisms and related structure- activity relationships. Conclusion: Meanwhile, in this survey, several natural products with diverse cellular targets such as the naphthoquinone shikonin and the stilbene resveratrol were characterized as promising lead compounds for future development.

An efficient synthetic route to citreochlorol analogues, halogenated polyketide secondary metabolites, is described. The key features are Krische’s enantioselective carbonyl allylation, IBr-promoted cyclization, and regioselective epoxide opening. The importance of the route lies in accessing a versatile epoxy ether that enables the formation of citreochlorol monochloro derivatives.

Fluorinated compounds are widely used in the fields of molecular imaging, pharmaceuticals, and materials. Fluorinated natural products in nature are rare, and the introduction of fluorine atoms into organic compound molecules can give these compounds new functions and make them have better performance. Therefore, the synthesis of fluorides has attracted more and more attention from biologists and chemists. Even so, achieving selective fluorination is still a huge challenge under mild conditions. In this review, the research progress of enzymatic synthesis of fluorinated compounds is summarized since 2015, including cytochrome P450 enzymes, aldolases, fluoroacetyl coenzyme A thioesterases, lipases, transaminases, reductive aminases, purine nucleoside phosphorylases, polyketide synthases, fluoroacetate dehalogenases, tyrosine phenol-lyases, glycosidases, fluorinases, and multienzyme system. Of all enzyme-catalyzed synthesis methods, the direct formation of the C-F bond by fluorinase is the most effective and promising method. The structure and catalytic mechanism of fluorinase are introduced to understand fluorobiochemistry. Furthermore, the distribution, applications, and future development trends of fluorinated compounds are also outlined. Hopefully, this review will help researchers to understand the significance of enzymatic methods for the synthesis of fluorinated compounds and find or create excellent fluoride synthase in future research. Key points • Fluorinated compounds are distributed in plants and microorganisms, and are used in imaging, medicine, materials science. • Enzyme catalysis is essential for the synthesis of fluorinated compounds. • The loop structure of fluorinase is the key to forming the C-F bond. Supplementary Information The online version contains supplementary material available at 10.1007/s00253-021-11608-0.

Reduction and optimization of the microbial genome is an important strategy for constructing synthetic biological chassis cells and overcoming obstacles in natural product discovery and production. However, it is of great challenge to discover target genes that can be deleted and optimized due to the complicated genome of actinomycetes. Saccharopolyspora pogona can produce butenyl-spinosyn during aerobic fermentation, and its genome contains 32 different gene clusters. This suggests that there is a large amount of potential competitive metabolism in S. pogona, which affects the biosynthesis of butenyl-spinosyn. By analyzing the genome of S. pogona, six polyketide gene clusters were identified. From those, the complete deletion of clu13, a flaviolin-like gene cluster, generated a high butenyl-spinosyn-producing strain. Production of this strain was 4.06-fold higher than that of the wildtype strain. Transcriptome profiling revealed that butenyl-spinosyn biosynthesis was not primarily induced by the polyketide synthase RppA-like but was related to hypothetical protein Sp1764. However, the repression of sp1764 was not enough to explain the enormous enhancement of butenyl-spinosyn yields in S. pogona-Δclu13. After the comparative proteomic analysis of S. pogona-Δclu13 and S. pogona, two proteins, biotin carboxyl carrier protein (BccA) and response regulator (Reg), were investigated, whose overexpression led to great advantages of butenyl-spinosyn biosynthesis. In this way, we successfully discovered three key genes that obviously optimize the biosynthesis of butenyl-spinosyn. Gene cluster simplification performed in conjunction with multiomics analysis is of great practical significance for screening dominant chassis strains and optimizing secondary metabolism. This work provided an idea about screening key factors and efficient construction of production strains.

Background Rubiginones belong to the angucycline family of aromatic polyketides, and they have been shown to potentiate the vincristine (VCR)-induced cytotoxicity against VCR-resistant cancer cell lines. However, the biosynthetic gene clusters (BGCs) and biosynthetic pathways for rubiginones have not been reported yet. Results In this study, based on bioinformatics analysis of the genome of Streptomyces sp. CB02414, we predicted the functions of the two type II polyketide synthases (PKSs) BGCs. The rub gene cluster was predicted to encode metabolites of the angucycline family. Scale-up fermentation of the CB02414 wild-type strain led to the discovery of eight rubiginones, including five new ones (rubiginones J, K, L, M, and N). Rubiginone J was proposed to be the final product of the rub gene cluster, which features extensive oxidation on the A-ring of the angucycline skeleton. Based on the production profiles of the CB02414 wild-type and the mutant strains, we proposed a biosynthetic pathway for the rubiginones in CB02414. Conclusions A genome mining strategy enabled the efficient discovery of new rubiginones from Streptomyces sp. CB02414. Based on the isolated biosynthetic intermediates, a plausible biosynthetic pathway for the rubiginones was proposed. Our research lays the foundation for further studies on the mechanism of the cytochrome P450-catalyzed oxidation of angucyclines and for the generation of novel angucyclines using combinatorial biosynthesis strategies.

Drimane‐type sesquiterpenes exhibit various biological activities and are widely present in eukaryotes. Here, we completely elucidated the biosynthetic pathway of the drimane‐type sesquiterpene esters isolated from Aspergillus calidoustus and we discovered that it involves a drimenol cyclase having the same catalytic function previously only reported in plants. Moreover, since many fungal drimenol derivatives possess a γ‐butyrolactone ring, we clarified the functions of the cluster‐associated cytochrome P450 and FAD‐binding oxidoreductase discovering that these two enzymes are solely responsible for the formation of those structures. Furthermore, swapping of the enoyl reductase domain in the identified polyketide synthase led to the production of metabolites containing various polyketide chains with different levels of saturation. These findings have deepened our understanding of how fungi synthesize drimane‐type sesquiterpenes and the corresponding esters., Reported here is the complete elucidation of the biosynthetic pathway of drimane‐type sesquiterpene esters from Aspergillus calidoustus, including the first identified fungal drimenol cyclase. The cluster‐associated acyltransferase is then employed to transfer different lengths of ACP‐activated polyketides, but also very diverse CoA‐esters.

Three new polyketide derivatives, 2-ethoxycarbonyl-endocrocin (1), 6-methoxy-2-ethoxycarbonyl-endocrocin (2) and pannorin C (3), along with sixteen known compounds (4-19) were isolated from a plant endophytic fungus Aspergillus cristatus 2H1. Their structures were elucidated by 1D/2D NMR and HR-ESI-MS data analysis. Compound 3 showed weak antibacterial activity against Staphylococcus aureus (MIC 20 μg/ml). Compounds 14 and 15 showed effective cytotoxicity on human melanoma A375 cells (IC50 4.13 μM for 14, 3.39 μM for 15).

Clarithromycin is an improved semi-synthetic analogue of the naturally occurring macrolide, erythromycin. The subtle modification of a methyl group on the C-6 hydroxyl group endows the molecule with improved acid stability and results in a clinically useful antibiotic. Here we show that the effector specificity of the biosensor protein, MphR, can be evolved to selectively recognize clarithromycin, and therefore report on the production of this molecule in vivo. In addition, a crystal structure of the evolved variant illustrates the molecular basis for selectivity and provides a guide for the evolution of new metabolic function using this biosensor.

Goniodomin A (GDA, 1) is a phycotoxin produced by at least four species of Alexandrium dinoflagellates that are found globally in brackish estuaries and lagoons. It is a linear polyketide with six oxygen heterocyclic rings that is cyclized into a macrocyclic structure via lactone formation. Two of the oxygen heterocycles in 1 comprise a spiro-bis-pyran, whereas goniodomin B (GDB) contains a 2,7-dioxabicyclo[3.3.1]nonane ring system fused to a pyran. When H2O is present, 1 undergoes facile conversion to isomer GDB and to an α,β-unsaturated ketone, goniodomin C (GDC, 7). GDB and GDC can be formed from GDA by cleavage of the spiro-bis-pyran ring system. GDA, but not GDB or GDC, forms a crown ether-type complex with K+. Equilibration of GDA with GDB and GDC is observed in the presence of H+ and of Na+, but the equilibrated mixtures revert to GDA upon addition of K+. Structural differences have been found between the K+ and Na+ complexes. The association of GDA with K+ is strong, while that with Na+ is weak. The K+ complex has a compact, well-defined structure, whereas Na+ complexes are an ill-defined mixture of species. Analyses of in vitro A. monilatum and A. hiranoi cultures indicate that only GDA is present in the cells; GDB and GDC appear to be postharvest transformation products.

During the previous decade, genome-built researches on marine heterotrophic microorganisms displayed the chemical heterogeneity of natural product resources coupled with the efficacies of harnessing the genetic divergence in various strains. Herein, we describe the whole genome data of heterotrophic Bacillus amyloliquefaciens MB6 (MTCC 12,716), isolated from a marine macroalga Hypnea valentiae, a 4,107,511-bp circular chromosome comprising 186 contigs, with 4154 protein-coding DNA sequences and a coding ratio of 86%. Simultaneously, bioactivity-guided purification of the bacterial extract resulted in six polyketide classes of compounds with promising antibacterial activity. Draft genome sequence of B. amyloliquefaciens MB6 unveiled biosynthetic gene clusters (BGCs) engaged in the biosynthesis of polyketide-originated macrolactones with prospective antagonistic activity (MIC ≤ 5 µg/mL) against nosocomial pathogens. Genome analysis manifested 34 putative BGCs necessitated to synthesize biologically active polyketide-originated frameworks or their derivatives. These results provide insights into the genetic basis of heterotrophic B. amyloliquefaciens MTCC 12,716 as a prospective lead for biotechnological and pharmaceutical applications.

Highly reducing polyketide synthases (HR-PKSs) produce structurally diverse polyketides (PKs). The PK diversity is constructed by a variety of factors, including the β-keto processing, chain length, methylation pattern, and relative and absolute configurations of the substituents. We examined the stereochemical course of the PK processing for the synthesis of polyhydroxy PKs such as phialotides, phomenoic acid, and ACR-toxin. Heterologous expression of a HR-PKS gene, a trans-acting enoylreductase gene, and a truncated non-ribosomal peptide synthetase gene resulted in the formation of a linear PK with multiple stereogenic centers. The absolute configurations of the stereogenic centers were determined by chemical degradation followed by comparison of the degradation products with synthetic standards. A stereochemical rule was proposed to explain the absolute configurations of other reduced PKs and highlights an error in the absolute configurations of a reported structure. The present work demonstrates that focused functional analysis of functionally related HR-PKSs leads to a better understanding of the stereochemical course.

Polyketide synthases (PKS) produce polyketides, a large group of secondary metabolites produced in bacteria, fungi, plants and certain animal families. PKSs have a huge potential to biosynthesize high-value active pharmaceuticals, agrochemicals, biofuels and industrial chemicals, among others. Additionally, they present ideal opportunities to engineer new polyketides, and the latter chemical novelty can result in even better, or at least alternative, active molecules to the existing ones. We present the structure, catalysis and altogether machinery of the PKS, as well as their enzyme engineering and applications in biotechnology. We also briefly discuss the current progress on the study of PKSs by computational chemists, and the fact that PKS reactivity and catalysis remain, presently, almost open fields for the computational chemist to explore.

Four polyketide-amino acid derivatives, pardinumones A-D (1-4), were isolated from the wild mushroom Tricholoma pardinum. Their structures together with absolute configurations were characterized by means of spectroscopic data analyses, as well as calculated electronic circular dichroism (ECD) and NMR with sorted training set (STS) protocol analysis. Compounds 1-4 exhibited antibacterial activity against Staphylococcus aureus, Staphylococcus epidermidis, and Escherichia coli with MIC values in the range of 6.25-50 μg/mL.

The environment of Lake Baikal is a well-known source of microbial diversity. The strain Streptomyces sp. IB2014/011-12, isolated from samples collected at Lake Baikal, was found to exhibit potent activity against Gram-positive bacteria. Here, we report isolation and characterization of linear polyketide alpiniamide A (1) and its new derivatives B-D (2-5). The structures of alpiniamides A-D were established and their relative configuration was determined by combination of partial Murata's method and ROESY experiment. The absolute configuration of alpiniamide A was established through Mosher's method. The gene cluster, responsible for the biosynthesis of alpiniamides (alp) has been identified by genome mining and gene deletion experiments. The successful expression of the cloned alp gene cluster in a heterologous host supports these findings. Analysis of the architecture of the alp gene cluster and the feeding of labeled precursors elucidated the alpiniamide biosynthetic pathway. The biosynthesis of alpiniamides is an example of a rather simple polyketide assembly line generating unusual chemical diversity through the combination of domain/module skipping and double bond migration events.

Three new tetronate-class polyketides, nomimicins B, C, and D, along with nomimicin, hereafter named nomimicin A, were isolated from the culture extract of Actinomadura sp. AKA43 collected from floating particles in the deep-sea water of Sagami Bay, Japan. The structures of nomimicins B, C, and D were elucidated through the interpretation of NMR and MS analytical data, and the absolute configuration was determined by combination of NOESY/ROESY and ECD analyses. Nomimicins B, C, and D showed antimicrobial activity against Gram-positive bacteria, Kocuria rhizophila and Bacillus subtilis, with MIC values in the range of 6.5 to 12.5 μg/mL. Nomimicins B and C also displayed cytotoxicity against P388 murine leukemia cells with IC50 values of 33 and 89 μM, respectively.

Acyltransferases are responsible for the selection and loading of acyl units onto carrier proteins in polyketide and fatty-acid biosynthesis. Despite the importance of protein–protein interactions between the acyltransferase and the carrier protein, structural information on acyltransferase–carrier protein interactions is limited because of the transient interactions between them. In the biosynthesis of the polyketide vicenistatin, the acyltransferase VinK recognizes the carrier protein VinL for the transfer of a dipeptidyl unit. The crystal structure of a VinK–VinL covalent complex formed with a 1,2-bismaleimidoethane cross-linking reagent has been determined previously. Here, the crystal structure of a VinK–VinL covalent complex formed with a pantetheine cross-linking probe is reported at 1.95 Å resolution. In the structure of the VinK–VinL–probe complex, the pantetheine probe that is attached to VinL is covalently connected to the side chain of the mutated Cys106 of VinK. The interaction interface between VinK and VinL is essentially the same in the two VinK–VinL complex structures, although the position of the pantetheine linker slightly differs. This structural observation suggests that interface interactions are not affected by the cross-linking strategy used.

The hunt for microbially-synthesized secondary metabolites have long generate exceptional interest due to their unique functionalities. In this study, shotgun metagenomic was used to decipher the array of secondary metabolites present in a contaminated agricultural soil (AB1) via detection of their biosynthetic genes. Functional annotation of AB1 metagenome’s putative open reading frames (ORFs) for polyketide synthases (PKSs) and non-ribosomal peptide synthetases (NRPSs) revealed that majority of the detected biosynthetic genes belong to type I polyketides and non-ribosomal peptides. Biosynthetic genes for type I polyketides such as macrolides, polyene macrolides, rapamycin-related compounds (FK506, FKF20), myxobacterial compounds (epothilone A, soraphen A), lovastatin, enediynes, among others were detected. Similarly, biosynthetic genes for non-ribosomal peptides such as surfactin, fengycin, iturin, lichenysin, arthrofactin, vibriobactin, mycobactin, bacitracin, gramicidin S, viomycin, bleomycin, vancomycin, pristinamycin, tyrocidine, fumiquinazoline and several others were also detected. Taxonomic characterization of the detected biosynthetic genes revealed microorganisms that are not known to be natural producers of the secondary metabolites, thus pointing to the possibility of horizontal gene transfer. The huge repository of these genes in the soil environment is a clear reminder of the pivotal role the soil as a natural resource can play as a source of exciting natural products that can be deployed as viable alternatives to solve myriad of challenges facing the medical, industrial, and environmental settings.

The first chemical total synthesis of the highly oxygenated polyketide enterocin has been accomplished. The key step of the synthesis was a late‐stage biomimetic reaction cascade involving two intramolecular aldol reactions in which each step proceeded in 52 % yield (averaged) and which established four of the seven stereogenic centers. The pivotal precursor for the cascade reaction was assembled from three readily available building blocks. A chiral dithioacetal with two stereogenic centers originating from L‐arabinose represented the core fragment to both ends of which the other building blocks were attached by aldol reactions. The remaining stereogenic center was installed by Davis oxygenation immediately prior to the key step., Entering Nature's Design Office: The highly oxygenated natural product enterocin, which has so far resisted total synthetic attempts, was obtained in a biomimetic key step from triketone 1, which in turn was assembled from an L‐arabinose‐derived core fragment with a defined absolute configuration.

Dysoxylactam A is a 17-membered macrocyclic lipid which has been found to dramatically reverse multidrug resistance in cancer cells. Three previous syntheses have been reported in 15-17 steps. Using iterative lithiation-borylation reactions as the key C−C bond forming and stereocontrolling steps, we now describe an 11-step synthesis of dysoxylactam A. The complete sequence only required a total of five chromatographic purifications and used minimal protecting groups making it both rapid and efficient.

A heterotrophoic Bacillus amyloliquefaciens MTCC12713 isolated from an intertidal macroalga Kappaphycus alverezii displayed promising antibacterial activities against multidrug-resistant bacteria. Genome mining of the bacterium predicted biosynthetic gene clusters coding for antibacterial secondary metabolites. Twenty-one membered macrocyclic lactones, identified as difficidin analogues bearing 6-hydroxy-8-propyl carboxylate, 9-methyl-19-propyl dicarboxylate, 6-methyl-9-propyl dicarboxylate-19-propanone, and (20-acetyl)-6-methyl-9-isopentyl dicarboxylate (compounds 1 through 4) functionalities were purified through bioassay-guided fractionation. The difficidin analogues exhibited bactericidal activities against vancomycin-resistant Enterococcus faecalis, methicillin-resistant Staphylococcus aureus, and other drug-resistant strains, such of Klebsiella pneumonia and Pseudomonas aeruginosa with the minimum inhibitory concentration of about 2–9 × 10−3 μM. A plausible enzyme-catalyzed biosynthetic pathway that is generated through addition of acrylyl initiator unit by repetitive decarboxylative Claisen condensation modules with malonate units was recognized, and their structures were corroborated with gene organization of the dif operon, which could comprehend dif A-O (~ 70 kb). Drug-likeness score for 5-ethoxy-28-methyl-(9-methyl-19-propyl dicarboxylate) difficidin (compound 2, 0.35) was greater than those of other difficidin analogues, which corroborated the potential in vitro antibacterial properties of the former. The present study demonstrated the potential of difficidin analogues for pharmaceutical and biotechnological uses against the bottleneck of emergent drug-resistant pathogens. • Difficidins were isolated from marine alga associated Bacillus amyloliquefaciens. • Whole-genome mining of bacterial genome predicted biosynthetic gene clusters. • Greater drug-likeness for difficidin 2 confirmed its potent antibacterial activity.

Full details on the design, development, and successful implementation of suitable synthetic strategies directed toward the total synthesis of iso-archazolids and archazologs are reported. Both a biomimetic and a multistep total synthesis of iso-archazolid B, the most potent and least abundant archazolid, are described. The bioinspired conversion from archazolid B was realized by a high-yielding 1,8-Diazabicyclo[5.4.0]undec-7-ene catalyzed one-step double-bond shift. A highly stereoselective total synthesis was accomplished in 25 steps, involving a sequence of highly stereoselective aldol reactions, an efficient aldol condensation to forge two elaborate fragments, and a challenging ring-closing metathesis macrocyclization with an unusual Stewart-Grubbs catalyst. These strategies proved to be generally useful and could be successfully implemented for the preparation of three novel iso-archazolids as well as five novel archazologs, lacking the thiazole side chain. A wide variety of further archazolids and archazologs may now be targeted for exploration of the promising anticancer potential of these polyketide macrolides.

A convergent route for the asymmetric total synthesis of potent anticancer polyketide natural product amphirionin-2 has been developed. Our initial synthetic trials revealed that the proposed structures of amphirionin-2 need to be revised consistent with a recent report of Fuwa et al., where the actual structure of amphirionin-2 was established. The key features of our synthesis comprised Sharpless asymmetric dihydroxylation, followed by cycloetherification, Wittig olefination, Julia-Kocienski olefination, and Crimmins propionate aldol reaction.

Polyketide cyclase from Mycobacterium tuberculosis (MtPC) is related to the formation of sterol derivatives, which may play a role in immune escape in the initial stage of macrophage infection by Mycobacterium tuberculosis. However, the structure and specific functions of MtPC are still unknown. Here we report the backbone and side-chain NMR resonance assignments for the MtPC. Most resonances were assigned and the secondary structure was predicted according to the assigned backbone resonances by TALOS-N and PECAN. These NMR assignments represent a first step towards researching the structure and function of MtPC.

Peridecalins C and D (1 and 2), one decalin and one oxygen-decalin containing polyketide-amino acid hybrids with 5/6/6 ring system, was isolated from a genetic mutant of Periconia sp. F-31. Their structures were elucidated through extensive spectroscopic data analysis, including 1 D/2D NMR and HR-MS spectra. Biosynthetically, two proposed Diels-Alder reactions are supposed to be involved in the skeleton construction of 1 and 2.