Epidithiodioxopiperazines. occurrence, synthesis and biogenesis

Disulfide Cleavage in a Dimeric Epipolythiodioxopiperazine Natural Product Diminishes Its Apoptosis-Inducing Effect but Enhances Autophagy in Tumor Cells

Gliocladicillin C (3) is a cytotoxic epipolythiodioxopiperazine (ETP) isolated from the Ophiocordyceps-associated fungus Clonostachys rogersoniana. Although the disulfides/polysulfides in ETPs are believed to account for their cytotoxicity, and 11'-deoxyverticillin A was demonstrated to induce apoptosis and autophagy, how they mediate apoptosis and autophagy remained unknown. Here, we revealed that 3 activated caspase-dependent apoptosis and autophagy in human tumor cells, while the prepared disulfide-cleavage product failed to induce reactive oxygen species production and PARP cleavage, but further enhanced the autophagic flux compared to 3. Gliocladicillin C and its derivative also increased the phosphorylation of AMP-activated protein kinase and stimulated autophagy by affecting the glycolytic pathway. These results demonstrated that the disulfides played an essential role in inducing apoptosis, but not autophagy.

Synthetic Studies toward Dimeric Indole Alkaloids Based on Convergent Synthetic Strategy

The total syntheses of dimeric indole alkaloids, haplophytine, and T988s are described. These dimeric compounds comprising two structurally different indole units are ubiquitous in nature, and many possess pharmaceutically important activities. To realize an efficient chemical synthesis of these dimeric indole alkaloids, the establishment of convergent synthetic strategies and development of new coupling methods are indispensable. The linkage of two highly functionalized units at a late stage of the synthesis frequently induces synthetic problems such as chemoselectivity and steric repulsion. Moreover, although transition metal-catalyzed reactions are usually an effective method for the cross-coupling of two units, the application of these cross-coupling reactions to bond formation involving a sterically hindered C(sp³) is often difficult. Thus, even with precise modern synthetic methods, it is currently difficult to realize convergent syntheses of dimeric indole alkaloids possessing a quaternary carbon linking two units. To combat these synthetic problems, we developed a synthetic method to link two indole units using an Ag-mediated nucleophilic substitution reaction. In this review, we provide a detailed discussion of convergent synthetic strategies and coupling methods for dimeric indole alkaloids.

Amphiepicoccins A-J: Epipolythiodioxopiperazines from the Fish-Gill-Derived Fungus Epicoccum nigrum HDN17-88

Ten new epipolythiodioxopiperazines (ETPs), namely, amphiepicoccins A-J (1-10), were isolated from the fish-gill-derived fungus Epicoccum nigrum HDN17-88. Their structures were deduced from extensive spectroscopic data and electronic circular dichroism (ECD) calculations. Amphiepicoccin A (1) which contains an aromatic indole motif is unprecedented among the epicoccin type of ETPs. Compounds 1, 3, and 6 displayed anti-HSV-2 activities, with IC₅₀ values of 70, 64, and 29 μM, respectively (acyclovir as positive control with an IC₅₀ value of 31 μM), while 5 and 6 also revealed inhibitory activity against Bacillus subtilis with minimum inhibitory concentration (MIC) values of 13 and 25 μM, respectively.

New Thiodiketopiperazine and 3,4-Dihydroisocoumarin Derivatives from the Marine-Derived Fungus Aspergillus terreus

Aspergillus terreus has been reported to produce many secondary metabolites that exhibit potential bioactivities, such as antibiotic, hypoglycemic, and lipid-lowering activities. In the present study, two new thiodiketopiperazines, emestrins L (1) and M (2), together with five known analogues (3–7), and five known dihydroisocoumarins (8–12), were obtained from the marine-derived fungus Aspergillus terreus RA2905. The structures of the new compounds were elucidated by analysis of the comprehensive spectroscopic data, including high-resolution electrospray ionization mass spectrometry (HRESIMS), one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR), and electronic circular dichroism (ECD) data. This is the first time that the spectroscopic data of compounds 3, 8, and 9 have been reported. Compound 3 displayed antibacterial activity against Pseudomonas aeruginosa (minimum inhibitory concentration (MIC) = 32 μg/mL) and antifungal activity against Candida albicans (MIC = 32 μg/mL). In addition, compound 3 exhibited an inhibitory effect on protein tyrosine phosphatase 1 B (PTP1B), an important hypoglycemic target, with an inhibitory concentration (IC)₅₀ value of 12.25 μM.

Nidulantes of Aspergillus (Formerly Emericella): A Treasure Trove of Chemical Diversity and Biological Activities

The genus Emericella (Ascomycota) includes more than thirty species with worldwide distribution across many ecosystems. It is considered a rich source of diverse metabolites. The published classes of natural compounds that are discussed here are organized according to the following biosynthetic pathways: polyketides (azaphilones, cyclopentenone pigments, dicyanides, furan derivatives, phenolic ethers, and xanthones and anthraquinones); shikimate derivatives (bicoumarins); mevalonate derivatives (meroterpenes, sesquiterpenes, sesterterpenes and steroids) and amino acids derivatives (alkaloids (indole-derivatives, isoindolones, and piperazine) and peptides (depsipeptides)). These metabolites produce the wide array of biological effects associated with Emericella, including antioxidant, antiproliferative, antimalarial, antiviral, antibacterial, antioxidant, antihypertensive, anti-inflammatory, antifungal and kinase inhibitors. Careful and extensive study of the diversity and distribution of metabolites produced by the genus Emericella (either marine or terrestrial) revealed that, no matter the source of the fungus, the composition of the culture medium effectively controls the metabolites produced. The topic of this review is the diversity of metabolites that have been identified from Emericella, along with the contextual information on either their biological or geographic sources. This review presents 236 natural compounds, which were reported from marine and terrestrial Emericella. Amongst the reported compounds, only 70.2% were biologically assayed for their effects, including antimicrobial or cytotoxicity. This implies the need for substantial investigation of alternative activities. This review includes a full discussion of compound structures and disease management, based on materials published from 1982 through December 2019.

Construction of sulfur-containing moieties in the total synthesis of natural products

This review surveys the total syntheses of sulfur-containing natural products where sulfur atoms are introduced with different sulfurization agents to construct related sulfur-containing moieties.

Occurrence and Properties of Thiosilvatins

The spread of studies on biodiversity in different environmental contexts is particularly fruitful for natural product discovery, with the finding of novel secondary metabolites and structural models, which are sometimes specific to certain organisms. Within the large class of the epipolythiodioxopiperazines, which are typical of fungi, thiosilvatins represent a homogeneous family that, so far, has been reported in low frequency in both marine and terrestrial contexts. However, recent observations indicate that these compounds have been possibly neglected in the metabolomic characterization of fungi, particularly from marine sources. Aspects concerning occurrence, bioactivities, structural, and biosynthetic properties of thiosilvatins are reviewed in this paper.

Double the Chemistry, Double the Fun: Structural Diversity and Biological Activity of Marine-Derived Diketopiperazine Dimers

While several marine natural products bearing the 2,5-diketopiperazine ring have been reported to date, the unique chemistry of dimeric frameworks appears to remain neglected. Frequently reported from marine-derived strains of fungi, many naturally occurring diketopiperazine dimers have been shown to display a wide spectrum of pharmacological properties, particularly within the field of cancer and antimicrobial therapy. While their structures illustrate the unmatched power of marine biosynthetic machinery, often exhibiting unsymmetrical connections with rare linkage frameworks, enhanced binding ability to a variety of pharmacologically relevant receptors has been also witnessed. The existence of a bifunctional linker to anchor two substrates, resulting in a higher concentration of pharmacophores in proximity to recognition sites of several receptors involved in human diseases, portrays this group of metabolites as privileged lead structures for advanced pre-clinical and clinical studies. Despite the structural novelty of various marine diketopiperazine dimers and their relevant bioactive properties in several models of disease, to our knowledge, this attractive subclass of compounds is reviewed here for the first time.

A Modular Construction of Epidithiodiketopiperazines

Epidithiodiketopiperazines (ETPs) possess remarkably diverse biological activities and have attracted significant synthetic attention. The preparation of analogues is actively pursued; however, they are structurally challenging, and more direct and modular methods for their synthesis are desirable. To this end, the utility of a bifunctional triketopiperazine building block for the straightforward synthesis of ETPs is reported. A modular strategy consisting of enolate alkylation followed by site-selective nucleophile addition enables the concise synthesis of (±)-hyalodendrin and a range of analogues.

[Search for Protein Tyrosine Phosphatase 1B Inhibitors from Marine Organisms and Induced Production of New Fungal Metabolites by Modulating Culture Methods]

Marine environments offer a rich source of natural products with potential therapeutic applications because the ocean covers 70% of the earth's surface and approximately 80% of all living organisms live in the sea. Therefore we have investigated bioactive compounds from marine organisms such as marine sponges, ascidians, and marine-derived microorganisms. This review consists of two topics based on marine natural product chemistry. (1) Protein tyrosine phosphatase (PTP) 1B plays a key role as a negative regulator in the insulin and leptin signaling pathways. Accordingly, the development of PTP1B inhibitors is expected to provide new drugs for type 2 diabetes and obesity. We have been searching for new types of PTP1B inhibitors among marine organisms and identified various PTP1B inhibitors from marine sponges and fungi. This review presents their structural diversities and unique biological properties. (2) In the course of our studies on the induced production of new fungal metabolites, the Palauan marine-derived fungus, Trichoderma cf. brevicompactum TPU199, was found to produce the unusual epipolythiodiketopiperazines, gliovirin and pretrichodermamide A. Long-term static fermentation of the strain induced production of a new dipeptide, dithioaspergillazine A, whereas fermentation of the strain with NaCl, NaBr, and NaI produced the Cl and Br derivatives of pretrichodermamide A and a new iodinated derivative, iododithiobrevamide, respectively. Moreover, DMSO-added seawater medium induced the production of diketopiperazine with the unprecedented trithio-bridge, chlorotrithiobrevamide. This fermentation study on the strain as well as the structures of the metabolites obtained are described in this review.

Toward the Total Synthesis of Scabrosins: Synthesis of a Desulfur-scabrosin Skeleton and Its Stereoisomers

The enantioselective synthesis of a desulfur-scabrosin skeleton was reported. The synthesis began from 3-(hydroxymethyl)phenol, and key steps include asymmetric nucleophilic epoxidation, a Mitsunobu reaction using a sulfonamide as the nucleophile, the construction of a pyrrolidine ring by intramolecular nucleophilic substitution, and inversion of configuration through base-induced keto-enol isomerization. Additionally, two isomers of the carbon skeleton were also obtained via an alternative ring-closing strategy.

Rogersonins A and B, Imidazolone N-Oxide-Incorporating Indole Alkaloids from a verG Disruption Mutant of Clonostachys rogersoniana

Rogersonins A (1) and B (2), two new indole alkaloid-polyketide hybrids, have been isolated from cultures of a verG disruption mutant of the Cordyceps-colonizing fungus Clonostachys rogersoniana; their structures were elucidated primarily by NMR experiments. The absolute configurations of 1 and 2 were assigned using the modified Mosher method and via electronic circular dichroism and NMR calculations. Compounds 1 and 2 incorporate an imidazolone N-oxide moiety that has not been reported in any natural products.

Thiodiketopiperazines with two spirocyclic centers extracted from Botryosphaeria mamane, an endophytic fungus isolated from Bixa orellana L

Three thiodiketopiperazines, botryosulfuranols A-C (1-3) were isolated from the endophytic fungus Botryosphaeria mamane. The three compounds present sulfur atoms on α- and β-positions of phenylalanine derived residues and unprecedented two spirocyclic centers at C-4 and C-2'. Their planar structures were determined by spectroscopic analysis and absolute configurations were achieved by X-ray diffraction analysis and ECD and NMR chemical shifts calculations. Botryosulfuranol A (1) was the most cytotoxic compound against four cancer cell lines (HT-29, HepG2, Caco-2, HeLa) and two healthy cell lines (IEC6, Vero) highlighting the importance of an electrophilic center for cell growth inhibition.

Antidiabeticin vitroandin vivoevaluation of cyclodipeptides isolated fromPseudomonas fluorescensIB-MR-66e

Cyclodipeptides cyclo(l-Pro-l-Leu),1; cyclo(l-Pro-l-Val),2; and cyclo (l-Pro-l-Phe),3fromPseudomonas fluorescensIB-MR-66e showed α-glucosidase inhibitory activity.

Reconstitution of Enzymatic Carbon-Sulfur Bond Formation Reveals Detoxification-Like Strategy in Fungal Toxin Biosynthesis

Gliotoxin is a virulence factor of the human pathogen Aspergillus fumigatus, the leading cause of invasive aspergillosis. The activity of this metabolite is mediated by a transannular disulfide bond, a hallmark of the epipolythiodiketopiperazine (ETP) family. Through the creation of fungal gene deletion mutants and heterologous protein expression, we unveiled the critical role of the cytochrome P450 monooxygenase (CYP450) GliC for the stepwise bishydroxylation of the diketopiperazine (DKP) core. We show for the first time the formation of the C-S bond from the DKP in a combined assay of GliC and the glutathione- S-transferase (GST) GliG in vitro. Furthermore, we present experimental evidence for an intermediary imine species. The flexible substrate scope of GliC and GliG in combination parallels P450/GST pairs used in eukaryotic phase I/II detoxification pathways.

Genome-based deletion analysis in Aspergillus terreus reveals the acetylaranotin bis-thiomethyltransferase gene

Acetylaranotin is an epipolythiodiketopiperazine (ETP) secondary metabolite with a broad range of bioactivities. We demonstrated that ATEG_01465.1 located outside of acetylaranotin gene cluster is responsible for catalyzing the S-methylation of its biosynthetic pathway. Combining the previous characterization of acetylaranotin biosynthetic gene cluster together with the identification of its S-methyltransferase provides a means to obtain second-generation acetylaranotin derivatives previously inaccessible. By permutations of targeted deletions of ATEG_01465.1, acetyltransferase (AtaH), and benzoate hydroxylase (AtaY), three novel acetylaranotin derivatives were produced by Aspergillus terreus.

Mini-Review: Ergothioneine and Ovothiol Biosyntheses, an Unprecedented Trans-Sulfur Strategy in Natural Product Biosynthesis

As one of the most abundant elements on earth, sulfur is part of many small molecular metabolites and is key to their biological activities. Over the past few decades, some general strategies have been discovered for the incorporation of sulfur into natural products. In this review, we summarize recent efforts in elucidating the biosynthetic details for two sulfur-containing metabolites, ergothioneine and ovothiol. Their biosyntheses involve an unprecedented trans-sulfur strategy, a combination of a mononuclear non-heme iron enzyme-catalyzed oxidative C-S bond formation reaction and a PLP enzyme-mediated C-S lyase reaction.

Highly Photosensitive Poly-Sulfur-Bridged Chetomin Analogues from Chaetomium cochliodes

The highly photosensitive characteristic of poly-sulfide chetomins was first unveiled, and four new unstable analogues, chetomins A-D (1-4), with significant cytotoxicity were successfully purified in darkness. The visible-light-induced desulfurization and intermolecular disproportionation were revealed to initiate the interconversion of chetomin analogues, which explained the long-recognized puzzle of rarity and instability of chetomin analogues.

Thermal conversion of primary alcohols to disulfidesviaxanthate intermediates: an extension to the Chugaev elimination

Heating primaryO-alkylS-difluoro(ethoxycarbonyl)methyl xanthates yields disulfides. This extends to the Chugaev elimination.

Structural Diversity and Biological Activities of the Cyclodipeptides from Fungi

Cyclodipeptides, called 2,5-diketopiperazines (2,5-DKPs), are obtained by the condensation of two amino acids. Fungi have been considered to be a rich source of novel and bioactive cyclodipeptides. This review highlights the occurrence, structures and biological activities of the fungal cyclodipeptides with the literature covered up to July 2017. A total of 635 fungal cyclodipeptides belonging to the groups of tryptophan-proline, tryptophan-tryptophan, tryptophan-Xaa, proline-Xaa, non-tryptophan-non-proline, and thio-analogs have been discussed and reviewed. They were mainly isolated from the genera of Aspergillus and Penicillium. More and more cyclodipeptides have been isolated from marine-derived and plant endophytic fungi. Some of them were screened to have cytotoxic, phytotoxic, antimicrobial, insecticidal, vasodilator, radical scavenging, antioxidant, brine shrimp lethal, antiviral, nematicidal, antituberculosis, and enzyme-inhibitory activities to show their potential applications in agriculture, medicinal, and food industry.

The Oxepane Motif in Marine Drugs

Oceans have shown to be a remarkable source of natural products. The biological properties of many of these compounds have helped to produce great advances in medicinal chemistry. Within them, marine natural products containing an oxepanyl ring are present in a great variety of algae, sponges, fungus and corals and show very important biological activities, many of them possessing remarkable cytotoxic properties against a wide range of cancer cell lines. Their rich chemical structures have attracted the attention of many researchers who have reported interesting synthetic approaches to these targets. This review covers the most prominent examples of these types of compounds, focusing the discussion on the isolation, structure determination, medicinal properties and total synthesis of these products.

Enzymatic Carbon-Sulfur Bond Formation in Natural Product Biosynthesis

Sulfur plays a critical role for the development and maintenance of life on earth, which is reflected by the wealth of primary metabolites, macromolecules, and cofactors bearing this element. Whereas a large body of knowledge has existed for sulfur trafficking in primary metabolism, the secondary metabolism involving sulfur has long been neglected. Yet, diverse sulfur functionalities have a major impact on the biological activities of natural products. Recent research at the genetic, biochemical, and chemical levels has unearthed a broad range of enzymes, sulfur shuttles, and chemical mechanisms for generating carbon-sulfur bonds. This Review will give the first systematic overview on enzymes catalyzing the formation of organosulfur natural products.

Enantioselective Synthesis of (-)-Acetylapoaranotin

The first enantioselective total synthesis of the epipolythiodiketopiperazine (ETP) natural product (-)-acetylapoaranotin (3) is reported. The concise synthesis was enabled by an eight-step synthesis of a key cyclohexadienol-containing amino ester building block. The absolute stereochemistry of both amino ester building blocks used in the synthesis is set through catalytic asymmetric (1,3)-dipolar cycloaddition reactions. The formal syntheses of (-)-emethallicin E and (-)-haemotocin are also achieved through the preparation of a symmetric cyclohexadienol-containing diketopiperazine.

Penicisulfuranols A-F, Alkaloids from the Mangrove Endophytic Fungus Penicillium janthinellum HDN13-309

Six new epipolythiodioxopiperazine (ETP) alkaloids, penicisulfuranols A-F (1-6), were isolated from the mangrove endophytic fungus Penicillium janthinellum HDN13-309. All structures including absolute configurations were elucidated on the basis of comprehensive spectroscopic data and ECD calculations. They belong to the unusual family of ETPs containing sulfur atoms on both α- and β-positions of amino acid residues and a rare 1,2-oxazadecaline core moiety. In addition, compounds 1-6 also possess a rare spiro-furan ring and 1-3 showed cytotoxicity with IC₅₀ values ranging from 0.1 to 3.9 μM.

Eutypellazines A–M, thiodiketopiperazine-type alkaloids from deep sea derived fungus Eutypella sp. MCCC 3A00281

Bioassay and NMR/MS guided fractionation resulted in the isolation of 13 new alkaloids from marine fungus Eutypella sp.

The Epipolythiodiketopiperazine Gene Cluster in Claviceps purpurea: Dysfunctional Cytochrome P450 Enzyme Prevents Formation of the Previously Unknown Clapurines

Claviceps purpurea is an important food contaminant and well known for the production of the toxic ergot alkaloids. Apart from that, little is known about its secondary metabolism and not all toxic substances going along with the food contamination with Claviceps are known yet. We explored the metabolite profile of a gene cluster in C. purpurea with a high homology to gene clusters, which are responsible for the formation of epipolythiodiketopiperazine (ETP) toxins in other fungi. By overexpressing the transcription factor, we were able to activate the cluster in the standard C. purpurea strain 20.1. Although all necessary genes for the formation of the characteristic disulfide bridge were expressed in the overexpression mutants, the fungus did not produce any ETPs. Isolation of pathway intermediates showed that the common biosynthetic pathway stops after the first steps. Our results demonstrate that hydroxylation of the diketopiperazine backbone is the critical step during the ETP biosynthesis. Due to a dysfunctional enzyme, the fungus is not able to produce toxic ETPs. Instead, the pathway end-products are new unusual metabolites with a unique nitrogen-sulfur bond. By heterologous expression of the Leptosphaeria maculans cytochrome P450 encoding gene sirC, we were able to identify the end-products of the ETP cluster in C. purpurea. The thioclapurines are so far unknown ETPs, which might contribute to the toxicity of other C. purpurea strains with a potentially intact ETP cluster.

Sequential Inactivation of Gliotoxin by the S-Methyltransferase TmtA

The epipolythiodioxopiperazine (ETP) gliotoxin mediates toxicity via its reactive thiol groups and thereby contributes to virulence of the human pathogenic fungus Aspergillus fumigatus. Self-intoxication of the mold is prevented either by reversible oxidation of reduced gliotoxin or by irreversible conversion to bis(methylthio)gliotoxin. The latter is produced by the S-methyltransferase TmtA and attenuates ETP biosynthesis. Here, we report the crystal structure of TmtA in complex with S-(5'-adenosyl)-l-homocysteine. TmtA features one substrate and one cofactor binding pocket per protein, and thus, bis-thiomethylation of gliotoxin occurs sequentially. Molecular docking of substrates and products into the active site of TmtA reveals that gliotoxin forms specific interactions with the protein surroundings, and free energy calculations indicate that methylation of the C10a-SH group precedes alkylation of the C3-SH site. Altogether, TmtA is well suited to selectively convert gliotoxin and to control its biosynthesis, suggesting that homologous enzymes serve to regulate the production of their toxic natural sulfur compounds in a similar manner.

The versatile low-molecular-weight thiols: Beyond cell protection

Low-molecular-weight (LMW) thiols are extensively involved in the maintenance of cellular redox potentials and the protection of cells from a variety of reactive chemical and electrophilic species. However, we recently found that the metabolic coupling of two LMW thiols - mycothiol (MSH) and ergothioneine (EGT) - programs the biosynthesis of the anti-infective agent lincomycin A. Remarkably, such a constructive role of the thiols in the biosynthesis of natural products has so far received relatively little attention. We speculate that the unusual thiol EGT might function as a chiral thiolation carrier (for modification) and a novel activator (for glycosylation) of sugar. Additionally, we examine recent evidence for LMW thiols (MSH and others) as sulfur donors of sulfur-containing natural products. Clearly, the LMW thiols have more diverse activities beyond cell protection, and more attention should be paid to the correlation of their functions with thiol-dependent enzymes.

Induced Production of Halogenated Epidithiodiketopiperazines by a Marine-Derived Trichoderma cf. brevicompactum with Sodium Halides

Marine-derived Trichoderma sp. TPU199 (cf. T. brevicompactum) produced gliovirin (1), pretrichodermamide A (2), and trichodermamide A (3) in a freshwater medium. Compounds 1 and 2 are rare epidithiodiketopiperazines possessing an unusual disulfide linkage. In the seawater medium, the strain biosynthesized the 5-chloro-5-deoxy derivatives (4 and 5) of 3 and 2. The production of 5 was proportional to the concentration of seawater (NaCl). Therefore, 5-bromo-5-deoxy (6) and 5-deoxy-5-iodo (7) derivatives were biosynthesized in the freshwater media supplemented with NaBr and NaI, respectively. The structure of a new iodo derivative (7) was elucidated on the basis of its spectroscopic data.

A Unified Strategy to 6-5-6-5-6-Membered Epipolythiodiketopiperazines: Studies towards the Total Synthesis of Scabrosin Diacetate and Haematocin

The family of epipolythiodiketopiperazine (ETP) natural products consists of over 200 members possessing a wide diversity of structures and biological activity. Recently, the subgroup of 6-5-6-5-6-membered ETPs has gained substantial attention, which has resulted in several total syntheses. Despite all the efforts that have been invested into accessing these complex structures, no synthesis of scabrosin diacetate (1 a) and its related esters has been reported. Herein, our attempts towards scabrosin diacetate (1 a) and haematocin (3) starting from diketopiperazine 12 a as a late-stage intermediate are presented. Diketopiperazine 12 a can be conveniently accessed in multigram quantities from aldehyde 18 and diketopiperazine 21 and was envisioned to serve as a general platform for the synthesis of 6-5-6-5-6-membered ETPs.

Interplay between Gliotoxin Resistance, Secretion, and the Methyl/Methionine Cycle in Aspergillus fumigatus

Mechanistic studies on gliotoxin biosynthesis and self-protection in Aspergillus fumigatus, both of which require the gliotoxin oxidoreductase GliT, have revealed a rich landscape of highly novel biochemistries, yet key aspects of this complex molecular architecture remain obscure. Here we show that an A. fumigatus ΔgliA strain is completely deficient in gliotoxin secretion but still retains the ability to efflux bisdethiobis(methylthio)gliotoxin (BmGT). This correlates with a significant increase in sensitivity to exogenous gliotoxin because gliotoxin trapped inside the cell leads to (i) activation of the gli cluster, as disabling gli cluster activation, via gliZ deletion, attenuates the sensitivity of an A. fumigatus ΔgliT strain to gliotoxin, thus implicating cluster activation as a factor in gliotoxin sensitivity, and (ii) increased methylation activity due to excess substrate (dithiol gliotoxin) for the gliotoxin bis-thiomethyltransferase GtmA. Intracellular dithiol gliotoxin is oxidized by GliT and subsequently effluxed by GliA. In the absence of GliA, gliotoxin persists in the cell and is converted to BmGT, with levels significantly higher than those in the wild type. Similarly, in the ΔgliT strain, gliotoxin oxidation is impeded, and methylation occurs unchecked, leading to significant S-adenosylmethionine (SAM) depletion and S-adenosylhomocysteine (SAH) overproduction. This in turn significantly contributes to the observed hypersensitivity of gliT-deficient A. fumigatus to gliotoxin. Our observations reveal a key role for GliT in preventing dysregulation of the methyl/methionine cycle to control intracellular SAM and SAH homeostasis during gliotoxin biosynthesis and exposure. Moreover, we reveal attenuated GliT abundance in the A. fumigatus ΔgliK strain, but not the ΔgliG strain, following exposure to gliotoxin, correlating with relative sensitivities. Overall, we illuminate new systems interactions that have evolved in gliotoxin-producing, compared to gliotoxin-naive, fungi to facilitate their cellular presence.