Induced biosyntheses of a novel butyrophenone and two aromatic polyketides in the plant pathogen Stagonospora nodorum

Fungal aromatic compounds comprise an important and structurally diverse group of secondary metabolites.Several genome sequencing projects revealed many putative biosynthetic gene clusters of fungal aromatic compounds,but many of these genes seem to be silent under typical laboratory culture conditions.To gain access to this untapped reservoir of natural products,we utilized chemical epigenetic modifiers to induce the expression of dormant biosynthetic genes.As a result,the concomitant supplementation of the histone deacetylase inhibitors suberoylanilide hydroxamic acid(500mM)and nicotinamide(50mM)to the culture medium of a fungal pathogen,Stagonospora nodorum,resulted in the isolation of three aromatic compounds(1-3),including a novel natural butyrophenone,(+)-4'-methoxy-(2S)-methylbutyrophenone(1),and two known polyketides,alternariol(2)and(-)-(3R)-mellein methyl ether(3).

Furan Derivatives and Polyketides from the Fungus Irpex lacteus

Eight new furan derivatives,irpexins A‒H(1‒8),two new polyketides,irpexins I and J(9 and 10),together with nine known compounds were isolated from the fermentation of Irpex lacteus.The structures and absolute configurations were elucidated on the basis of extensive spectroscopic methods and Mosher ester reaction.All compounds shows no cytotoxicity to human MCF-7 and Hela cancer cell lines at the concentration of 10μM.

Five new polyketides from the basidiomycete Craterellus odoratus

Five new polyketides,craterellones A-E(1-5),were isolated from cultures of basidiomycete Craterellus odoratus,together with five known compounds(6-10).Structures of 1-5 were elucidated on the basis of extensive spectroscopic analysis.All compounds were evaluated for their inhibitory activities against one isozyme of 11β-hydroxysteroid dehydrogenase(11β-HSD1)and cytotoxic activities on five tumor cell lines.Compound 10 exhibited significant cytotoxicity against HL-60,SMMC-7721,A-549,MCF-7,and SW-480,with IC50 values of 0.50,0.69,0.64,1.10,0.54μM,respectively.

Koninginins N-Q, Polyketides from the Endophytic Fungus Trichoderma koningiopsis Harbored in Panax notoginseng

Four new fungal polyketides named koninginins N-Q(1–4),together with four known analogues(5–8),were isolated from the endophytic fungus Trichoderma koningiopsis YIM PH30002 harbored in Panax notoginseng.Their structures were determined on the basis of spectral data interpretation.These compounds were evaluated for their antifungal activity,nitric oxide inhibition,and anticoagulant activity.

Diversified Polyketides and Nitrogenous Compounds from the Mangrove Endophytic Fungus Penicillium steckii SCSIO 41025

Four new polyketide decalin derivatives,penicisteck acids A-D(1-4),and three new nitrogenous compounds(7-9)z together with eight previously reported compounds,were isolated from the mangrove endophytic fungus Penicillium steckii SCSIO 41025.

Peptides and polyketides isolated from the marine sponge-derived fungus Aspergillus terreus SCSIO 41008

Two new isomeric modified tripeptides,aspergillamides C and D(compounds 1 and 2),together with fifteen known compounds(compounds 3-17),were obtained from the marine sponge-derived fungus Aspergillus terreus SCSIO 41008.The structures of the new compounds,including absolute configurations,were determined by extensive analyses of spectroscopic data(NMR,MS,UV,and IR)and comparisons between the calculated and experimental electronic circular dichroism(ECD)spectra.Butyrolactone I(compound 11)exhibited strong inhibitory effects against Mycobacterium tuberculosis protein tyrosine phosphatase B(MptpB)with the IC_(50) being 5.11±0.53μmol·L^(–1),and acted as a noncompetitive inhibitor based on kinetic analysis.

Tripodalsporormielones A-C,unprecedented cage-like polyketides with complex polyvdent bridged and fused ring systems

A chemical investigation on Sporormiella sp.led to the isolation and structural elucidation of tripodalsporormielones Ae C(1-3),a new class of polyketide possessing unprecedented cage-like skeletons with polyvdent bridged and fused ring systems.These polyketides with cage-like skeletons were characterized as a high non-protonated carbon-containing system,which resulted in few HMBC correlations observed and made the accurate structures hard to be obtained by NMR.Especially,some signals of non-protonated sp;carbons are weak and even unobservable in compound 1.In order to establish the structure of 1,the calculated NMR with DP4 evaluation was applied to determine the structure from the plausible structure candidates obtained from the detailed NMR analysis.Based on NMR experiments and calculated NMR,the structures of isolated compounds were established and confirmed by X-ray technology.Through chiral isolation,the optically pure enantiomers of 1 and 3 were obtained,and their absolute configurations were determined based on ECD quantum chemical calculation.Based on the isolated compounds and our previous work,1-3 would be derived from 3-methylorcinaldehyde,and their plausible biosynthetic mechanism was proposed.Furthermore,1 exhibited obvious short-term memory improvement activity on an Alzheimer’s disease fly model.

Linear polyketides produced by co-culture of Penicillium crustosum and Penicillium fellutanum

Two new polyketides, penifellutins A (1) and B (2), possessing a 22 carbon linear skeleton, were isolated from a co-culture of the deep-sea-derived fungi Penicillium crustosum PRB-2 and Penicillium fellutanum HDN14-323. Meanwhile, two esterification products of 1, penifellutins C (3) and D (4), were obtained because compound 1 could be esterified spontaneously when stored in methanol. Their configurations were difficult to determine because of chiral central crowdedness, structural flexibility and instability. As such, we solved this issue by comprehensively using Mo2(OAc)4-based CD experiments, density functional theory calculation of 13C NMR, DP4 + probability analysis and many chemical reactions, including making acetonide derivative, Mosher’s method, PGME method, etc. Compounds 1 and 2 show obvious inhibitory activity on the liver hyperplasia of zebrafish larvae at a concentration of 10 μmol/L, while 3 and 4 show no activity, indicating that two carboxyls in the structure are important active sites.

Antimicrobial Aromatic Polyketides from Gorgonian- Associated Fungus, Penicillium commune 518

Seven new aromatic polyketides, communols A-G （1-7）, were isolated and identified from the fermentation broth of Penicillium commune 518, a marine-derived fungus associated with the Gorgonian, Muricella abnormalis. The new structures of 1-7 were determined by spectroscopic analysis and X-ray single crystal diffraction. Among them, communol D （4） was the first example of a naturally occurring aromatic polyketide with a sulfoxide group from marine thngi. Compounds 1, 6, and 7 all showed moderate antimicrobial activities against Escherichia coli and Enterobacter aerogenes with MIC values of 4.1/16.4, 6.4/25.8, and 23.8/23.8μmoloL^-1, respectively.

Engineered polyketides:Synergy between protein and host level engineering

Metabolic engineering efforts toward rewiring metabolism of cells to produce new compounds often require the utilization of non-native enzymatic machinery that is capable of producing a broad range of chemical functionalities.Polyketides encompass one of the largest classes of chemically diverse natural products.With thousands of known polyketides,modular polyketide synthases(PKSs)share a particularly attractive biosynthetic logic for generating chemical diversity.The engineering of modular PKSs could open access to the deliberate production of both existing and novel compounds.In this review,we discuss PKS engineering efforts applied at both the protein and cellular level for the generation of a diverse range of chemical structures,and we examine future applications of PKSs in the production of medicines,fuels and other industrially relevant chemicals.

Three New Compounds from the Actinomycete Actinocorallia aurantiaca

Aurantiadioic acids A(1)and B(2),two new furan-containing polyketides,and aurantoic acid A(3),a new natural product,were isolated from the liquid fermentation of the sika deer dung-derived actinomycete Actinocorallia aurantiaca.The structures of the new compounds were established by extensive spectroscopic methods,including 1D&2D NMR,HRESIMS spectroscopic analysis.The absolute configuration of 3 was assigned by comparison of the specific optical rotations with the reported derivatives.Biological activity evaluations suggested that compounds 1-3 showed weak inhibition on NO production in the murine monocytic RAW 264.7 macrophages with IC_(50)values of 35.8,41.8,45.2μM,respectively.Compound 3 showed weak inhibition on influenza A virus(A/PuertoRico/8/1934,H1N1)with an EC_(50)value of 35.9μM,and a selective index higher than 13.3.

Phylogenetic diversity of TypeⅠpolyketide synthase genes from sediments of Ardley Island in Antarctica

The diversity of modular polyketide synthase （PKS） genes in sediments of Ardley Island in Antarctica, was studied by restriction fragment length polymorphism （RFLP） analysis. Phylogenetic analysis of 14 amino acid （AA） sequences indicates that the identified ketosynthase （KS） domains were clustered with those from diverse bacterial groups, including Cyanobacteria, γ-Proteobacteria, Actinobacteria, Firmicutes, and some unidentified microorganisms from marine sponge, bryozoan and other environmental samples. The obtained KS domains showed 43%–81% similarity at the AA level to reference sequences in GenBank. Six identified KS domains showed diverse sequences of the motif （VQTACSTS） that was used to identify the hybrid PKS/nonribosomal peptide synthetase （NRPS） enzyme complex, and formed a new branch. These results reveal a high diversity and novelty of PKS genes in antarctic sediments.

SQUAMOSTATIN-B, A NEW POLYKETIDE FROM ANNONA SQUAMOSA (ANNONACEAE)

Squamostatin-B (1), a new polyketide or acetogenin, has been isolated from Annona squamosa L. (Annonaceae). Its structure and relative atereochemistry were elucidated on the basis of the spectral analyses of 1 and its derivatives, the acetate (2) and mesitoate (3).

Rufoolivacin B,a novel polyketide pigment from the fruiting bodies of the fungus Cortinarius rufo-olivaceus(basidiomycetes)

A novel polyketide pigment （1） with the 4＇,10-coupled linkage between 1-naphthalenol and 1,4-anthraquinone, named rufoolivacin B together with the known analog rufoolivacin （2）, has been isolated from the fruiting bodies of the Chinese toadstool Cortinarius rufo-olivaceus （basidiomycetes）. Their structures were characterized by means of analysis of spectroscopic methods, including 2D-NMR experiments and HR-ESI-MS.

Rational Engineering of Secondary Metabolic Pathways in a Heterologous Host to Enable the Biosynthesis of Hibarimicin Derivatives with Enhanced Anti-Melanomic Activity

A 61-kb biosynthetic gene cluster(BGC),which is accountable for the biosynthesis of hibarimicin(HBM)B from Microbispora rosea subsp.hibaria TP-A0121,was heterologously expressed in Streptomyces coelicolor M1154,which generated a trace of the target products but accumulated a large amount of shunt products.Based on rational analysis of the relevant secondary metabolism,directed engineering of the biosynthetic pathways resulted in the high production of HBM B,as well as new HBM derivates with improved antitumor activity.These results not only establish a biosynthetic system to effectively synthesize HBMs-a class of the largest and most complex Type-Ⅱpolyketides,with a unique pseudo-dimeric structure-but also set the stage for further engineering and deep investigation of this complex biosynthetic pathway toward potent anticancer drugs.

Three previously undescribed metabolites from Cordyceps cicadae JXCH-1,an entomopathogenic fungus

Three previously undescribed compounds,cordycicadione(1),cordycicadin F(2),and 7-hydroxybassiatin(3),were isolated from the cultures of Cordyceps cicadae JXCH1,an entomopathogenic fungus.Their structures and relative configurations were elucidated primarily by NMR spectroscopic analysis.The absolute configurations of 1 and 2 were determined by ECD calculations.Single-crystal X-ray diffraction method was adopted to determine the absolute configuration of 3.Compound 2 is a polycyclic polyketide with an unusual enol ether moiety and a spiro ring.The compounds obtained in this study were subjected to screening their inhibition against the proliferation of the human lung cancer cell line A549 and the production of nitric oxide in murine macrophages RAW264.7.

Gaining access to acetyl-CoA by peroxisomal surface display

Synthetic biology is constantly making progress for producing compounds on demand.Recently,Yocum and collaborators have developed an outstanding approach based on the anchoring of biosynthetic enzymes to the peroxisomal membrane.This allowed access to an untapped resource of acetyl-CoA and stimulated the synthesis of a valuable polyketide.

Global-scale analysis reveals distinct patterns of non-ribosomal peptide and polyketide synthase encoding genes in root and soil bacterial communities

Secondary metabolites(SMs)produced by soil bacteria,for instance antimicrobials and siderophores,play a vital role in bacterial adaptation to soil and root ecosystems and can contribute to plant health.Many SMs are non-ribosomal peptides and polyketides,assembled by non-ribosomal peptides synthetase(NRPS)and polyketide synthase(PKS)and encoded by biosynthetic gene clusters(BGCs).Despite their ecological importance,little is known about the occurrence and diversity of NRPs and PKs in soil.We extracted NRPS-and PKS-encodiing BGCs from 20 publicly available soil and root-associated metagenomes and annotated them using antiSMASH-DB.We found that the overall abundance of NRPSs and PKSs is similar in both environments,however NRPSs and PKSs were significantly clustered between soil and root samples.Moreover,the majority of identified sequences were unique to either soil-or root-associated datasets and had low identity to known BGCs,suggesting their novelty.Overall,this study illuminates the huge untapped diversity of predicted SMs in soil and root microbiomes,and indicates presence of specific SMs,which may play a role in inter-and intra-bacteriial interactions in root ecosystems.

Protein engineering for natural product biosynthesis:expanding diversity for therapeutic applications

In this dispensation of the fourth industrial revolution,protein engineering has become a popular approach for increasing enzymatic activity,stability,and titer in the biosynthesis of natural products.This is attributed to its numerous advantages(over direct isolation from plants or via chemical synthesis),including decreasing or eliminating reaction byproducts,high precision,moderate handling of intricate and chemically unstable chemicals,overall reusability,and cost efficiency.Recently,protein engineering tools have advanced to redesign and enhance natural product biosynthesis.These methods include direct evolution,substrate engineering,medium engineering,enzyme engineering and immobilization,structure-assisted protein engineering,and advanced computational.Recent successes in implementing these emerging protein engineering technologies were critically discussed in this article.Also,the advantages,limitations,and applications in industrial and medical biotechnology were discussed.Last,future research directions and potential were also highlighted.

Biosynthesis of trialkyl-substituted aromatic polyketide NFAT-133 involves unusual P450 monooxygenase-mediating aromatization and a putative metallo-beta-lactamase fold hydrolase

The bacterial trialkyl-substituted aromatic polyketides are structurally featured with the unusual aromatic core in the middle of polyketide chain such as TM-123(1),veramycin A(2),NFAT-133(3)and benwamycin I(4),which were discovered from Streptomyces species and demonstrated with antidiabetic and immunosuppressant activities.Though the biosynthetic pathway of 1-3 was reported as a type I polyketide synthase(PKS),the PKS assembly line was interpreted inconsistently,and it remains a mystery how the compound 3 was generated.Herein,the PKS assembly logic of 1-4 was revised by site-mutagenetic analysis of the PKS dehydratase domains.Based on gene deletion and complementation,the putative P450 monooxygenase nftE1 and metallo-beta-lactamase(MBL)fold hydrolase nftF1 were verified as essential genes for the biosynthesis of 1-4.The absence of nftE1 led to abolishment of 1-4 and accumulation of new products(5-8).Structural elucidation reveals 5-8 as the non-aromatic analogs of 1,suggesting the NftE1-catalyzed aromatic core formation.Deletion of nftF1 resulted in disappearance of 3 and 4 with the compounds 1 and 2 unaffected.As a rare MBL-fold hydrolase from type I PKSs,NftF1 potentially generates the compound 3 through two strategies:catalyze premature chain-offloading as a trans-acting thioesterase or hydrolyze the lactone-bond of compound 1 as an esterase.