Cytotoxic Bromine- and Iodine-Containing Cytochalasins Produced by the Mangrove Endophytic Fungus Phomopsis sp. QYM-13 Using the OSMAC Approach

New Secondary Metabolites of Mangrove-Associated Strains

Positioned at the dynamic interface between terrestrial and marine realms, mangroves embody a vibrant tapestry of biodiversity, encompassing an array of plants, animals, and microorganisms. These microbial inhabitants of mangrove habitats have emerged as a pivotal resource for antimicrobials and a plethora of pharmaceutically valuable compounds, spanning enzymes, antineoplastic agents, pesticides, immunosuppressants, and immunomodulators. This review delves into the recent landscape (January 2021 to May 2024, according to the time of publication) of novel secondary metabolites isolated from mangrove-associated microorganisms, analyzing 41 microbial strains that collectively yielded 165 distinct compounds. Our objective is to assess the productivity and potential of natural products derived from microbial populations within mangrove ecosystems in recent times. Notably, fungi stand out as the preeminent contributors to the emergence of these novel natural products, underscoring their pivotal role in the bioprospecting endeavors within these unique environments.

Peniapyrones A-I, Cytotoxic Tricyclic-Fused α-Pyrone Derivatives from an Endophytic Penicillium brefeldianum F4a

Five cyclopenta[d]pyrano[4,3-b]pyran-1,7(6H)-dione 6/6/5-fused tricyclic ring system containing metabolites peniapyrones A-E (1-5), and four previously undescribed cyclopenta[4,5]furo[3,2-c]pyran-1-one 6/5/5-fused tricyclic ring system containing compounds peniapyrones F-I (6-9), were isolated from the endophytic Penicillium brefeldianum F4a. Their structures, including absolute configurations, were determined through spectroscopic analysis and quantum chemical calculations. Peniapyrones D (4) and E (5) were a pair of diastereoisomers. Compounds 1, 3, and 5-9 showed cytotoxic activity against AsPC-1, CRL-2234, and MCF-7 cancer cell lines. Compounds 1, 3, 6, 8, and 9 inhibited the Kirsten rat sarcoma viral oncogene homologue (KRAS) mutant AsPC-1 cell line.

Talaroacids A-D and Talaromarane A, Diterpenoids with Anti-Inflammatory Activities from Mangrove Endophytic Fungus Talaromyces sp. JNQQJ-4

Five new diterpenes including four diterpenes with 1,2,3,4,4a,5,6,8a-octalin skeleton talaroacids A-D (1-4) and an isopimarane diterpenoid talaromarane A (5) were isolated from the mangrove endophytic fungus Talaromyces sp. JNQQJ-4. Their structures and absolute configurations were determined by analysis of high-resolution electrospray ionization mass spectroscopy (HRESIMS), 1D/2D Nuclear Magnetic Resonance (NMR) spectra, single-crystal X-ray diffraction, quantum chemical calculation, and electronic circular dichroism (ECD). Talaromarane A (5) contains a rare 2-oxabicyclo [3.2.1] octan moiety in isopimarane diterpenoids. In bioassays, compounds 1, 2, 4, and 5 displayed significant anti-inflammatory activities with the IC50 value from 4.59 to 21.60 μM.

Combining the Elicitor Up-Regulated Production of Unusual Linear Diterpene-Derived Variants for an In-Depth Assessment of the Application Value and Risk of the Medicinal and Edible Basidiomycete Schizophyllum commune

To better assess the practical value and avoid potential risks of the traditionally medicinal and edible basidiomycete Schizophyllum commune, which may arise from undescribed metabolites, a combination of elicitors was introduced for the first time to discover products from cryptic and low-expressed gene clusters under laboratory cultivation. Treating S. commune NJFU21 with the combination of five elicitors led to the upregulated production of a class of unusual linear diterpene-derived variants, including eleven new ones (1-11), along with three known ones (12-14). The structures and stereochemistry were determined by 1D and 2D NMR, HRESIMS, ECD, OR and VCD calculations. Notably, the elongation terminus of all the diterpenes was decorated by an unusual butenedioic acid moiety. Compound 1 was a rare monocyclic diterpene, while 2-6 possessed a tetrahydrofuran moiety. The truncated metabolites 4, 5 and 13 belong to the trinorditerpenes. All the diterpenes displayed approximately 70% scavenging of hydroxyl radicals at 50 μM and null cytotoxic activity at 10 μM. In addition, compound 1 exhibited potent antifungal activity against the plant pathogenic fungi Colletotrichum camelliae, with MIC values of 8 μg/mL. Our findings indicated that this class of diterpenes could provide valuable protectants for cosmetic ingredients and the lead compounds for agricultural fungicide development.

A Survey of Recently Discovered Naturally Occurring Organohalogen Compounds

The discovery of naturally occurring organohalogen compounds has increased astronomically in the 55 years since they were first discovered─from fewer than 50 in 1968 to a combined 7,958 described examples in three comprehensive reviews. The present survey, which covers the period 2021-2023, brings the number of known natural organohalogens to approximately 8,400. The organization is according to species origin, and coverage includes marine and terrestrial plants, fungi, bacteria, marine sponges, corals, cyanobacteria, tunicates, and other marine organisms.

OSMAC Strategy: A promising way to explore microbial cyclic peptides

Microbial secondary metabolites are pivotal for the development of novel drugs. However, conventional culture techniques, have left a vast array of unexpressed biosynthetic gene clusters (BGCs) in microorganisms, hindering the discovery of metabolites with distinct structural features and diverse biological functions. To address this limitation, several innovative strategies have been emerged. The "One Strain Many Compounds" (OSMAC) strategy, which involves altering microbial culture conditions, has proven to be particularly effective in mining numerous novel secondary metabolites for the past few years. Among these, microbial cyclic peptides stand out. These peptides often comprise rare amino acids, unique chemical structures, and remarkable biological function. With the advancement of the OSMAC strategy, a plethora of new cyclic peptides have been identified from diverse microbial genera. This work reviews the progress in mining novel compounds using the OSMAC strategy and the applications of this strategy in discovering 284 microbial cyclic peptides from 63 endophytic strains, aiming to offer insights for the further explorations into novel active cyclic peptides.

Griseofulvin enantiomers and bromine-containing griseofulvin derivatives with antifungal activity produced by the mangrove endophytic fungus Nigrospora sp. QQYB1

Marine microorganisms have long been recognized as potential sources for drug discovery. Griseofulvin was one of the first antifungal natural products and has been used as an antifungal agent for decades. In this study, 12 new griseofulvin derivatives [(±)-1-2, (+)-3, (±)-4, 10-12, and 14-15] and two new griseofulvin natural products (9 and 16) together with six known analogues [(-)-3, 5-8, and 13] were isolated from the mangrove-derived fungus Nigrospora sp. QQYB1 treated with 0.3% NaCl or 2% NaBr in rice solid medium. Their 2D structures and absolute configurations were established by extensive spectroscopic analysis (1D and 2D NMR, HRESIMS), ECD spectra, computational calculation, DP4 + analysis, and X-ray single-crystal diffraction. Compounds 1-4 represent the first griseofulvin enantiomers with four absolute configurations (2S, 6'S; 2R, 6'R; 2S, 6'R; 2R, 6'S), and compounds 9-12 represent the first successful production of brominated griseofulvin derivatives from fungi via the addition of NaBr to the culture medium. In the antifungal assays, compounds 6 and 9 demonstrated significant inhibitory activities against the fungi Colletotrichum truncatum, Microsporum gypseum, and Trichophyton mentagrophyte with inhibition zones varying between 28 and 41 mm (10 μg/disc). The structure-activity relationship (SAR) was analyzed, which showed that substituents at C-6, C-7, C-6' and the positions of the carbonyl and double bond of griseofulvin derivatives significantly affected the antifungal activity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-023-00210-0.

OSMAC-Based Discovery and Biosynthetic Gene Clusters Analysis of Secondary Metabolites from Marine-Derived Streptomyces globisporus SCSIO LCY30

The one strain many compounds (OSMAC) strategy is an effective method for activating silent gene clusters by cultivating microorganisms under various conditions. The whole genome sequence of the marine-derived strain Streptomyces globisporus SCSIO LCY30 revealed that it contains 30 biosynthetic gene clusters (BGCs). By using the OSMAC strategy, three types of secondary metabolites were activated and identified, including three angucyclines, mayamycin A (1), mayamycin B (2), and rabolemycin (3); two streptophenazines (streptophenazin O (4) and M (5)); and a macrolide dimeric dinactin (6), respectively. The biosynthetic pathways of the secondary metabolites in these three families were proposed based on the gene function prediction and structural information. The bioactivity assays showed that angucycline compounds 1-3 exhibited potent antitumor activities against 11 human cancer cell lines and antibacterial activities against a series of Gram-positive bacteria. Mayamycin (1) selectively exhibited potent cytotoxicity activity against triple-negative breast cancer (TNBC) cell lines such as MDA-MB-231, MDA-MB-468, and Bt-549, with IC50 values of 0.60-2.22 μM.

Cytosporones with Anti-Inflammatory Activities from the Mangrove Endophytic Fungus Phomopsis sp. QYM-13

Six previously undescribed cytosporone derivatives (phomotones A-E (1-5) and phomotone F (13)), two new spiro-alkanol phombistenes A-B (14-15), and seven known analogs (6-12) were isolated from the mangrove endophytic fungus Phomopsis sp. QYM-13. The structures of these compounds were elucidated using spectroscopic data analysis, electronic circular dichroism (ECD), and 13C NMR calculations. Compound 14 features an unprecedented 1,6-dioxaspiro[4.5]decane ring system. All isolates were evaluated for their inhibitory effect on nitric oxide (NO) in LPS-induced RAW264.7 cells. The results showed that compounds 1, 6, 8, and 11 exhibited potent bioactivities by comparing with positive control. Then, compound 1 displayed the anti-inflammatory effect by inhibiting the MAPK/NF-κB signaling pathways. Molecular docking further revealed the possible mechanism of compound 1 interaction with ERK protein.

Metabolites isolated from the mangrove endophytic fungus Didymella sp. CYSK-4 and their cytotoxic activities

Two new 12- or 13- membered-ring macrocyclic alkaloids ascomylactam D and E (1 & 2), and a pair of new enantiomer (+)- and (-)- didymetone (3) were purified from the mangrove endophytic fungus Didymella sp. CYSK-4. Their structures and absolute configurations were determined by extensive spectroscopic analysis, single-crystal X-ray diffraction, ECD and 13C NMR calculations. Compound 2 exhibited significant cytotoxicity against human A549 and KYSE 150 cancer cell lines with IC50 values of 2.8 μM and 5.9 μM, respectively.

Cactus Endophytic Fungi and Bioprospecting for their Enzymes and Bioactive Molecules: A Systematic Review

Endophytic fungi are associated with plant health and represent a remarkable source of potential of enzymes and bioactive compounds, but the diversity of endophytes remains uncertain and poorly explored, especially in Cactaceae, one of the most species-rich families adapted to growing in arid and semi-arid regions. The aim of this study was to conduct a systematic review on the diversity and bioprospecting of endophytic fungi from Cactaceae. We analysed peer-reviewed articles from seven databases using PRISMA guidelines. The results showed that the Cactaceae family is a source of new taxa, but the diversity of endophytic fungi of Cactaceae is little explored, mainly the diversity among tissues and by metagenomics. Bioprospecting studies have shown that these microorganisms can be used in the production of enzymes and larvicidal and antifungal compounds. Our results are relevant as a starting point for researchers to develop studies that expand the knowledge of plant mycobiota in arid and semi-arid ecosystems, as well as comprising a remarkable source of fungal compounds with several biotechnological applications.

Cyclohexenoneterpenes A-J: Cytotoxic meroterpenoids from mangrove-associated fungus Penicillium sp. N-5

Ten previously undescribed meroterpenoids, cyclohexenoneterpenes A-J (1-7, 18-20), together with 10 known analogues (8-17) were isolated from the mangrove-associated fungus Penicillium sp. N-5. Their structures were elucidated on the basis of extensive spectroscopic and mass spectrometric data. The absolute configurations of the undescribed compounds were assigned by electronic circular dichroism calculations, the modified Mosher's method, NMR calculations and DP4+ analysis. In the bioassay, compounds 10, 11, 15, and 20 exhibited cytotoxicities against SNB-19, MDA-MB-231, MDA-MB-435 and HCT-116 cell lines with IC50 values ranging from 1.4 to 19.1 μM.

Boerelasins A-D, Four Unprecedented Cytochalasins from the Endophytic Fungus Boeremia Exigua

Four undescribed cytochalasins (1-4) were isolated from the endophytic fungus Boeremia exigua. Structurally, boerelasin A (1) represents the first example of a cytochalasin with a rare 5/5 bicyclic carbon core. Boerelasin B (2) possesses an unprecedented 5/6/5/6/8 pentacyclic ring system. Boerelasin C (3), a derivative from the common biosynthetic intermediate to 1, is a macrocyclic ring-opening cytochalasin, and boerelasin D (4) contains an uncommon six-carbon alkyl acid side chain. The structures were elucidated based on spectroscopic methods, electronic circular dichroism, spin-spin coupling constants, and calculated nuclear magnetic resonance with DP4+ analysis. These compounds exhibited significant cytotoxicity against the tumor cells.

Plasmodium-Resistant Indole Diterpenoid Biosynthesis Gene Cluster Derived from Aspergillus oryzae Was Activated by Exogenous P450 Gene Ast B

Synthetic biology is an effective way to activate silent biosynthetic gene clusters. Five new indole diterpenoids (1, 2, 5, 9, and 10), together with 10 known derivatives (3, 4, 6-8, and 11-15) were activated from Aspergillus oryzae transformants by an exogenous P450 gene Ast B and obtained under the guidance of molecular networking. Their planar structures were determined by NMR and HR-ESI-MS. The absolute configuration of compound 1 was determined by single crystal X-ray diffraction, and those of compounds 2, 5 , 9, and 10 were confirmed by comparing the observed ECD with the calculated ECD. HPLC analysis suggested that the BGCs of indole diterpenoids in A. oryzae were activated by exogenous P450 gene Ast B. Compounds 1-4, 7, 8, and 11 displayed strong activity against chloroquine-sensitive plasmodium strain P.f.3D7 with IC50 values ranging from 0.84 to 2.9 μM. It is the first report that indole diterpenoids have potential antimalarial activity. The structure-activity relationship study showed that the linear indole diterpenoids contribute significantly to the antiparasite activity. Molecular docking studies showed that 1 and positive control chloroquine were at the center of the active pocket of PfHsp90, while 11 was far from the active site.

Antioxidative Indenone and Benzophenone Derivatives from the Mangrove-Derived Fungus Cytospora heveae NSHSJ-2

Seven new polyketides, including four indenone derivatives, cytoindenones A–C (1, 3–4), 3′-methoxycytoindenone A (2), a benzophenone derivative, cytorhizophin J (6), and a pair of tetralone enantiomers, (±)-4,6-dihydroxy-5-methoxy-α-tetralone (7), together with a known compound (5) were obtained from the endophytic fungus Cytospora heveae NSHSJ-2 isolated from the fresh stem of the mangrove plant Sonneratia caseolaris. Compound 3 represented the first natural indenone monomer substituted by two benzene moieties at C-2 and C-3. Their structures were determined by the analysis of 1D and 2D NMR, as well as mass spectroscopic data, and the absolute configurations of (±)-7 were determined on the basis of the observed specific rotation value compared with those of the tetralone derivatives previously reported. In bioactivity assays, compounds 1, 4–6 showed potent DPPH· scavenging activities, with EC50 values ranging from 9.5 to 16.6 µM, better than the positive control ascorbic acid (21.9 µM); compounds 2–3 also exhibited DPPH· scavenging activities comparable to ascorbic acid.

Unreported cytochalasins from an acid-mediated transformation of cytochalasin J isolated from Diaporthe cf. ueckeri

Chemical investigation of an endophytic fungus herein identified as Diaporthe cf. ueckeri yielded four known compounds, named cytochalasins H and J and dicerandrols A and B. Reports of acid sensitivity within the cytochalasan family inspired an attempt of acid-mediated conversion of cytochalasins H and J, resulting in the acquisition of five polycyclic cytochalasins featuring 5/6/5/8-fused tetracyclic and 5/6/6/7/5-fused pentacyclic skeletons. Two of the obtained polycyclic cytochalasins constituted unprecedented analogues, for which the trivial names cytochalasins J₄ and J₅ were proposed, whereas the others were identified as the known phomopchalasin A, phomopchalasin D and 21-acetoxycytochalasin J₃. The structures of the compounds were determined by extensive spectral analysis, namely HR-ESIMS, ESIMS and 1D/2D NMR. The stereochemistry of cytochalasins J₄ and J₅ was proposed using their ROESY data, biosynthetic and mechanistic considerations and by comparison of their ECD spectra with those of related congeners. All compounds except for cytochalasins H and J were tested for antimicrobial and cytotoxic activity. Cytochalasins J₄ and J₅ showed neither antimicrobial nor cytotoxic activity in the tested concentrations, with only weak antiproliferative activity observable against KB3.1 cells. The actin disruptive properties of all cytochalasins obtained in this study and of the previously reported cytochalasins RKS-1778 and phomopchalasin N were examined, and monitored by fluorescence microscopy using human osteo-sarcoma (U2-OS) cells. Compared to their precursor molecules (cytochalasins H and J), phomopchalasins A and D, 21-acetoxycytochalasin J₃, cytochalasins J₄ and J₅ revealed a strongly reduced activity on the F-actin network, highlighting that the macrocyclic ring is crucial for bioactivity.

Anti-Tumor Secondary Metabolites Originating from Fungi in the South China Sea's Mangrove Ecosystem

A mangrove is a unique ecosystem with abundant resources, in which fungi are an indispensable microbial part. Numerous mangrove fungi-derived secondary metabolites are considerable sources of novel bioactive substances, such as polyketides, terpenoids, alkaloids, peptides, etc., which arouse people's interest in the search for potential natural anti-tumor drugs. This review includes a total of 44 research publications that described 110 secondary metabolites that were all shown to be anti-tumor from 39 mangrove fungal strains belonging to 18 genera that were acquired from the South China Sea between 2016 and 2022. To identify more potential medications for clinical tumor therapy, their sources, unique structures, and cytotoxicity qualities were compiled. This review could serve as a crucial resource for the research status of mangrove fungal-derived natural products deserving of further development.

A Pair of Chromone Epimers and an Acetophenone Glucoside from the Mangrove Endophytic Fungus Mycosphaerella sp. L3A1

Three new compounds, including a pair of chromone derivatives (1-2), and an acetophenone glucoside (3), together with three known compounds (4-6), were isolated from the mangrove endophytic fungus Mycosphaerella sp. L3A1. Their structures were elucidated by HR-ESI-MS analysis and extensive spectroscopic data. The absolute configurations of new compounds were determined using single-crystal X-ray diffraction analysis, electronic circular dichroism (ECD) calculations and chemical hydrolysis. In bioassays, compound 4 showed moderate cytotoxic activity against MDA-MB-435, HCT116, and SNB19 with IC₅₀ values in the range of 18.5-26.29 μM.

Halometabolites isolated from the marine-derived fungi with potent pharmacological activities

Halometabolites, usually produced in marine environment, are an important group of natural halogenated compounds with rich biological functionality and drugability and thus play a crucial role in pharmaceutical and/or agricultural applications. In the exploration of novel halometabolites from marine microorganisms, the growing number of halogenated compounds makes it necessary to fully present these metabolites with diverse structures and considerable bioactivities. This review particularly focuses on the chemodiversity and bioactivities of halometabolites from marine-derived fungi. As a result, a total of 145 naturally halogenated compounds, including 118 chlorinated, 23 brominated, and four iodinated compounds, were isolated from 17 genera of marine-derived fungi. Interestingly, many of halometabolites, especially for the brominated and iodinated compounds, are generated by the substitution of bromide and iodide ions for the chloride ion in cultivation process. In addition, these compounds possess diverse structural types, which are classified into polyketides (62.7%), phenols (16.6%), alkaloids (14.5%), and terpenoids (6.2%). Their cytotoxic, antibacterial, and anti-inflammatory activities indicate the high potential of these halogenated compounds as lead compounds for drug discovery.

Hemiacetalmeroterpenoids A-C and Astellolide Q with Antimicrobial Activity from the Marine-Derived Fungus Penicillium sp. N-5

Four new compounds including three andrastin-type meroterpenoids hemiacetalmeroterpenoids A-C (1–3), and a drimane sesquiterpenoid astellolide Q (15), together with eleven known compounds (4–14) were isolated from the cultures of the marine-derived fungus Penicillium sp. N-5, while compound 14 was first isolated from a natural source. The structures of the new compounds were determined by analysis of detailed spectroscopic data, and the absolute configurations were further decided by a comparison of the experimental and calculated ECD spectra. Hemiacetalmeroterpenoid A (1) possesses a unique and highly congested 6,6,6,6,5,5-hexa-cyclic skeleton. Moreover, the absolute configuration of compound 14 was also reported for the first time. Compounds 1, 5 and 10 exhibited significant antimicrobial activities against Penicillium italicum and Colletrichum gloeosporioides with MIC values ranging from 1.56 to 6.25 μg/mL.

Pyrone Derivatives from a Mangrove Endophytic Fungus Phomopsis asparagi LSLYZ-87

Chemical investigation of the endophytic fungus Phomopsis asparagi LSLYZ-87 cultured on PDB medium led to the isolation of two new pyrone derivatives, phomasparapyrone A (1), and phomasparapyrone B (2), together with the known kojic acid (3). Their planar structures were connected through 1D and 2D NMR spectroscopic data. And the stereo structures of 1 and 2 were defined by comparison of the experimental ECD spectra to calculated one. All isolates were evaluated for their anti-neuroinflammatory activities. Among them, compound 2 showed moderate inhibition on NO accumulation induced by LPS on BV-2 cells in a dose dependent manner at 30, 40 and 50 μM, and without cytotoxicity in a concentration of 50.0 μM.

New polyketides from the liquid culture of Diaporthebreyniae sp. nov. (Diaporthales, Diaporthaceae)

During the course of a study on the biodiversity of endophytes from Cameroon, a fungal strain was isolated. A multigene phylogenetic inference using five DNA loci revealed that this strain represents an undescribed species of Diaporthe, which is introduced here as D.breyniae. Investigation into the chemistry of this fungus led to the isolation of two previously undescribed secondary metabolites for which the trivial names fusaristatins G (7) and H (8) are proposed, together with eleven known compounds. The structures of all of the metabolites were established by using one-dimensional (1D) and two-dimensional (2D) Nuclear Magnetic Resonance (NMR) spectroscopic data in combination with High-Resolution ElectroSpray Ionization Mass Spectrometry (HR-ESIMS) data. The absolute configuration of phomopchalasin N (4), which was reported for the first time concurrently to the present publication, was determined by analysis of its Rotating frame Overhauser Effect SpectroscopY (ROESY) spectrum and by comparison of its Electronic Circular Dichroism (ECD) spectrum with that of related compounds. A selection of the isolated secondary metabolites were tested for antimicrobial and cytotoxic activities, and compounds 4 and 7 showed weak antifungal and antibacterial activity. On the other hand, compound 4 showed moderate cytotoxic activity against all tested cancer cell lines with IC50 values in the range of 5.8-45.9 µM. The latter was found to be less toxic than the other isolated cytochalasins (1-3) and gave hints in regards to the structure-activity relationship (SAR) of the studied cytochalasins. Fusaristatin H (8) also exhibited weak cytotoxicity against KB3.1 cell lines with an IC50 value of 30.3 µM. Graphical abstract.

Cytochalasans from the Endophytic Fungus Phomopsis sp. shj2 and Their Antimigratory Activities

Cytochalasans from the endophytic fungi featured structure diversity. Our previous study has disclosed that cytochalasans from the endophytic fungus Phomopsis sp. shj2 exhibited an antimigratory effect. Further chemical investigation on Phomopsis sp. shj2 has led to the discovery of seven new cytochalasans (1–7), together with four known ones. Their structures were elucidated through extensive spectroscopic data interpretation and single-crystal X-ray diffraction analysis. Compounds 1–3 and 8–11 exhibited antimigratory effects against MDA-MB-231 in vitro with IC₅₀ values in the range of 1.01−10.42 μM.