Discovery and evolution of [4 + 2] cyclases.

[4 + 2] Cyclases are potent biocatalysts that have been bestowed upon microorganisms and plants by nature, equipping them with the powerful tools to utilize and implement the [4 + 2] cycloaddition reaction for constructing the cyclohexene core in synthesizing valuable molecules. Over the past two years, eleven new enzymes have joined this pericyclase club and undergone extensive investigation. In this review, we present a comprehensive overview of recent advancements in characterizing [4 + 2] cyclases with regard to their catalytic mechanism and stereoselectivity.

Berkeleylactones S-T, novel 16-membered macrolides isolated from the endophytic fungus .

The fungus has been reported as a producer of the 16-membered macrolide antibiotic A26771B. In this study, two new berkeleylactone analogues, berkeleylactones S-T (-), were isolated from . Their structures were determined by the analyses of 1D- and 2D-NMR data, HRESIMS, and chemical derivatization.

Two pairs of 2-pyrone enantiomers and a benzophenone analogue from the endophytic fungus .

Four new 2-pyrone derivatives, two pairs of enantiomers, (±)-egypyrone A [(±)-] and (±)-egypyrone B [(±)-], together with a new benzophenone analogue, orbiophenone B (), were isolated from the endophytic fungus . The enantiomeric mixtures (±)- and (±)- were separated through chiral HPLC, respectively. Their structures were elucidated by extensive analysis of spectroscopic data and the absolute configuration was determined by comparing the optical rotation of structurally similar molecule.

Tandem intermolecular [4 + 2] cycloadditions are catalysed by glycosylated enzymes for natural product biosynthesis.

Tandem Diels-Alder reactions are frequently used in the construction of polycyclic ring systems in complex organic compounds. Unlike the many Diels-Alderases (DAases) that catalyse a single cycloaddition, enzymes for multiple Diels-Alder reactions are rare. Here we demonstrate that two calcium-ion-dependent glycosylated enzymes, EupfF and PycR1, independently catalyse sequential, intermolecular Diels-Alder reactions in the biosynthesis of bistropolone-sesquiterpenes.

Pretrichodermamide A Biosynthesis Reveals the Hidden Diversity of Epidithiodiketopiperazines.

Fungal epidithiodiketopiperazines (ETPs) possess large structural diversity and complexity due to modifications of the cyclodipeptide skeleton. Elucidation of the biosynthetic pathway of pretrichodermamide A (1) in Trichoderma hypoxylon revealed a flexible catalytic machinery of multiple enzymes for generating ETP diversity. Seven tailoring enzymes encoded by the tda cluster are involved in 1 biosynthesis, that is, four P450s TdaB and TdaQ for 1,2-oxazine formation, TdaI for C7'-hydroxylation, and TdaG for C4, C5-epoxidation, two methyltransferases TdaH for C6'- and TdaO for C7'-O-methylation, and a reductase TdaD for furan opening.

Biosynthesis of rumbrins and inspiration for discovery of HIV inhibitors.

Investigation on how nature produces natural compounds with chemical and biological diversity at the genetic level offers inspiration for the discovery of new natural products and even their biological targets. The polyketide rumbrin () is a lipid peroxide production and calcium accumulation inhibitor, which contains a chlorinated pyrrole moiety that is a rare chemical feature in fungal natural products. Here, we identify the biosynthetic gene cluster (BGC) of and its isomer 12-rumbrin () from DSM3193, and elucidate their biosynthetic pathway based on heterologous expression, chemical complementation, and isotopic labeling.

Investigation of citrinin and monacolin K gene clusters variation among pigment producer Monascus species.

The filamentous fungi Monascus spp. have been widely used in the production of food colorants. However, the presence of mycotoxin citrinin and the antihypercholestrolemia agent monacolin K in Monascus-fermented products (MFPs) has raised food safety concerns.

A concise synthesis of herbertenolide.

A concise synthesis of (±)-herbertenolide has been accomplished herein. The strategy relies on a HO-mediated oxidative ring contraction of all-substituted cyclic α-formyl ketones for the stereospecific construction of contiguous quaternary carbon centers (CQCCs). Furthermore, a Sc(OTf)/chiral ,'-dioxide catalyzed asymmetric Michael addition of benzofuranone to MVK has been optimized for forging a chiral aromatic quaternary carbon center, which enables the formal synthesis of (+)--herbertenolide.

Flavin-Dependent Monooxygenase-Mediated 1,2-Oxazine Construction Meisenheimer Rearrangement in the Biosynthesis of Paeciloxazine.

The [1,2]-Meisenheimer rearrangement is well known as the [1,2]-migration of an -substituted hydroxylamine from a tertiary amine N-oxide, and it is frequently employed in organic synthesis to enforce adjacent carbon oxidation or install a 1,2-oxazine core, which is a prevalent structural feature and pharmacophore of many bioactive natural products. Although the [1,2]-Meisenheimer rearrangement was proposed to occur in the biosynthesis of a number of 1,2-oxazine-containing natural products, it has never been proved biosynthetically. Here, we identified the biosynthetic gene cluster of an insecticidal natural product, paeciloxazine (), from and characterized a flavin-dependent monooxygenase, PaxA, as the first example that mediates the formation of a 1,2-oxazine moiety Meisenheimer rearrangement.

Genome mining combined metabolic shunting and OSMAC strategy of an endophytic fungus leads to the production of diverse natural products.

Endophytic fungi are promising producers of bioactive small molecules. Bioinformatic analysis of the genome of an endophytic fungus revealed 43 biosynthetic gene clusters, exhibited its strong ability to produce numbers of secondary metabolites. However, this strain mainly produce rubratoxins alone with high yield in varied culture conditions, suggested most gene clusters are silent.

Enzymatic dimerization in the biosynthetic pathway of microbial natural products.

Covering: up to August 2020The dramatic increase in the identification of dimeric natural products generated by microorganisms and plants has played a significant role in drug discovery. The biosynthetic pathways of these products feature inherent dimerization reactions, which are valuable for biosynthetic applications and chemical transformations. The extraordinary mechanisms of the dimerization of secondary metabolites should advance our understanding of the uncommon chemical rules for natural product biosynthesis, which will, in turn, accelerate the discovery of dimeric reactions and molecules in nature and provide promising strategies for the total synthesis of natural products through dimerization.

Self-Resistance in the Biosynthesis of Fungal Macrolides Involving Cycles of Extracellular Oxidative Activation and Intracellular Reductive Inactivation.

Self-resistance genes are employed by many microbial producers of bioactive natural products to avoid self-harm. Herein, we describe a unique strategy for self-resistance toward a macrolide antibiotic, A26771B (1), identified by elucidating its biosynthetic pathway in the fungus Penicillium egyptiacum. A highly reducing polyketide synthase and a trans-acting thioesterase generate the macrolide backbone, and a cytochrome P450 and an acyltransferase, respectively catalyze hydroxylation and succinylation to form the prodrug berkeleylactone E (2).

Highly Oxygenated Caryophyllene-Type Sesquiterpenes from a Plant-Associated Fungus, , and Their Biosynthetic Gene Cluster.

Seven new β-caryophyllene derivatives, pestalotiphains A-G (-), along with six known analogues (-), were isolated from the plant-associated . Compound represents the first example of a caryophyllene-adenine hybrid, and contains a novel oxatricyclo[4.3.

Reisolation and Configurational Reinvestigation of Cottoquinazolines E-G from an Arthropod-Derived Strain of the Fungus .

The reported fumiquinazoline-related alkaloids cottoquinazolines E-G (-) were reisolated from solid cultures of the fungus , which was isolated from the medicinal arthropod . The unresolved issues regarding the absolute configurations (for cottoquinazolines E and F) prompted a reinvestigation of the configurations for all three compounds, as enabled by extensive spectroscopic methods, comparisons of experimental electronic circular dichroism data, and X-ray crystallography. In addition, cottoquinazoline F () showed significant antibacterial activity against ESBL-producing , , , and with MIC values of 8, 32, 32, and 16 μg/mL, respectively.

Enzymatic Intermolecular Hetero-Diels-Alder Reaction in the Biosynthesis of Tropolonic Sesquiterpenes.

Diels-Alder reactions are among the most powerful synthetic transformations to construct complex natural products. Despite that increasing of enzymatic intramolecular Diels-Alder reactions have been discovered, natural intermolecular Diels-Alderases are rarely described. Here, we report an intermolecular hetero-Diels-Alder reaction in the biosynthesis of tropolonic sesquiterpenes and functionally characterize EupfF as the first fungal intermolecular hetero-Diels-Alderase.

Six new monacolin analogs from red yeast rice.

Six novel monacolin analogs, monacolins V-V (1-6), together with seven known ones (7-13), were isolated from the ethyl acetate extract of red yeast rice. Their structures and absolute configurations were determined by spectroscopic methods, especially 2D NMR (H-HCOSY, HSQC, HMBC, and NOESY/ROESY) and CD spectroscopic analyses as well as chemical derivation. Monacolins V (2) and V (3) represent the first examples of monacolins with 3-hydroxybutyrate substitute.

Unprecedented [5.5.5.6]Dioxafenestrane Ring Construction in Fungal Insecticidal Sesquiterpene Biosynthesis.

Fenestranes, a specific class of natural products, contain four fused rings that share a central quaternary carbon atom. The fungal natural product penifulvin A (1) is a potent insecticidal sesquiterpene that features the [5.5.

Complexity and Diversity Generation in the Biosynthesis of Fumiquinazoline-Related Peptidyl Alkaloids.

Fumiquinazolines are multicyclic peptidyl alkaloids where FAD-dependent oxidases are main tailing redox enzymes in their biosynthesis. Here, we characterized the use of an α-KG/Fe(II)-dependent dioxygenase (α-KGD) as a new strategy in Nature to increase structural complexity in fumiquinazolines biosynthesis by elucidating the concise three enzymes biosynthetic pathway of heptacyclical alanditrypinone (1). Further genome mining led to the discovery of additional gene cluster with α-KGD and trimodular NRPS as partner, which generates diverse fumiquinazolines.

Diphenyl Ethers from a Marine-Derived .

Six new diphenyl ethers (⁻) along with eleven known analogs were isolated from the ethyl acetate extract of a marine-derived guided by LC-UV-MS. Their structures were unambiguously characterized by HRESIMS, NMR, as well as chemical derivatization. Compounds and are rare diphenyl ether glycosides containing d-ribose.

Coordinated Biosynthesis of the Purine Nucleoside Antibiotics Aristeromycin and Coformycin in Actinomycetes.

Purine nucleoside antibiotic pairs, concomitantly produced by a single strain, are an important group of microbial natural products. Here, we report a target-directed genome mining approach to elucidate the biosynthesis of the purine nucleoside antibiotic pair aristeromycin (ARM) and coformycin (COF) in DSM 45626 (a new producer for ARM and COF) and NBRC 13005 (a new COF producer). We also provide biochemical data that MacI and MacT function as unusual phosphorylases, catalyzing an irreversible reaction for the tailoring assembly of neplanocin A (NEP-A) and ARM.

Epigenetic modification in histone deacetylase deletion strain of leads to diverse diterpenoids.

Epigenetic modifications have been proved to be a powerful way to activate silent gene clusters and lead to diverse secondary metabolites in fungi. Previously, inactivation of a histone H3 deacetylase in had led to pleiotropic activation and overexpression of more than 75% of the biosynthetic genes and isolation of ten compounds. Further investigation of the crude extract of strain resulted in the isolation of twelve new diterpenoids including three cassanes (-), one cleistanthane (), six pimaranes (-), and two isopimaranes ( and ) along with two know cleistanthane analogues.

Activation of an unconventional meroterpenoid gene cluster in leads to the production of new berkeleyacetals.

Fungal genomes carry many gene clusters seemingly capable of natural products biosynthesis, yet most clusters remain cryptic or down-regulated. Genome mining revealed an unconventional paraherquonin-like meroterpenoid biosynthetic gene cluster in the chromosome of . The cryptic or down-regulated pathway was activated by constitutive expression of pathway-specific regulator gene encoded within biosynthetic gene cluster.

Biosynthesis of Heptacyclic Duclauxins Requires Extensive Redox Modifications of the Phenalenone Aromatic Polyketide.

Duclauxins are dimeric and heptacyclic fungal polyketides with notable bioactivities. We characterized the cascade of redox transformations in the biosynthetic pathway of duclauxin from Talaromyces stipitatus. The redox reaction sequence is initiated by a cupin family dioxygenase DuxM that performs an oxidative cleavage of the peri-fused tricyclic phenalenone and affords a transient hemiketal-oxaphenalenone intermediate.