Chemical Constituents and Biological Activities of Bruguiera Genus and Its Endophytes: A Review

The genus Bruguiera, a member of the Rhizophoraceae family, is predominantly found in coastal areas as a mangrove plant, boasting a rich and diverse community of endophytes. This review systematically compiled approximately 496 compounds derived from both the Bruguiera genus and its associated endophytes, including 152 terpenoids, 17 steroids, 16 sulfides, 44 alkaloids and peptides, 66 quinones, 68 polyketides, 19 flavonoids, 38 phenylpropanoids, 54 aromatic compounds, and 22 other compounds. Among these, 201 compounds exhibited a spectrum of activities, including cytotoxicity, antimicrobial, antioxidant, anti-inflammatory, antiviral, antidiabetic, insecticidal and mosquito repellent, and enzyme inhibitory properties, etc. These findings provided promising lead compounds for drug discovery. Certain similar or identical compounds were found to be simultaneously present in both Bruguiera plants and their endophytes, and the phenomenon of their interaction relationship was discussed.

Fungal Endophytes: Microfactories of Novel Bioactive Compounds with Therapeutic Interventions; A Comprehensive Review on the Biotechnological Developments in the Field of Fungal Endophytic Biology over the Last Decade

The seminal discovery of paclitaxel from endophytic fungus Taxomyces andreanae was a milestone in recognizing the immense potential of endophytic fungi as prolific producers of bioactive secondary metabolites of use in medicine, agriculture, and food industries. Following the discovery of paclitaxel, the research community has intensified efforts to harness endophytic fungi as putative producers of lead molecules with anticancer, anti-inflammatory, antimicrobial, antioxidant, cardio-protective, and immunomodulatory properties. Endophytic fungi have been a valuable source of bioactive compounds over the last three decades. Compounds such as taxol, podophyllotoxin, huperzine, camptothecin, and resveratrol have been effectively isolated and characterized after extraction from endophytic fungi. These findings have expanded the applications of endophytic fungi in medicine and related fields. In the present review, we systematically compile and analyze several important compounds derived from endophytic fungi, encompassing the period from 2011 to 2022. Our systematic approach focuses on elucidating the origins of endophytic fungi, exploring the structural diversity and biological activities exhibited by these compounds, and giving special emphasis to the pharmacological activities and mechanism of action of certain compounds. We highlight the tremendous potential of endophytic fungi as alternate sources of bioactive metabolites, with implications for combating major global diseases. This underscores the significant role that fungi can play in the discovery and development of novel therapeutic agents that address the challenges posed by prevalent diseases worldwide.

Metabolic profiling for the discovery of two rare fusidane-type heterodimers from the fungal endophyte Acremonium pilosum F47

In our process of studying fusidane-type antibiotics, metabolomics-guided chemical investigation on the endophytic Acremonium pilosum F47 led to the isolation of two unique heterodimers, acremonidiols B and C (1 and 2) consisting of a fusidane-type triterpenoid motif and a steroid unit. Four biosynthetically related known natural products including fusidic acid (FA, 3), as well as ergosterol derivatives (4-6) were also obtained. Their structures were determined by the analyses of ESI-HRMS and NMR data. Compounds 1 and 2, as hybrid molecules comprising the fusidane triterpenoid and steroid, are rare in nature. Compared with the clinically used antibiotic FA (3), new compounds 1 and 2 showed no obvious antibiotic activity, indicating the importance of free C-21 carboxyl group for antibacterial activity.

Unusual Secondary Metabolites from the Mangrove Ecosystems: Structures, Bioactivities, Chemical, and Bio-Syntheses

Mangrove ecosystems are widely distributed in the intertidal zone of tropical and subtropical estuaries or coasts, containing abundant biological communities, for example, mangrove plants and diverse groups of microorganisms, featuring various bioactive secondary metabolites. We surveyed the literature from 2010 to 2022, resulting in a collection of 134 secondary metabolites, and classified them into two major families in terms of the biological sources and 15 subfamilies according to the chemical structures. To highlight the structural diversity and bioactivities of the mangrove ecosystem-associated secondary metabolites, we presented the chemical structures, bioactivities, biosynthesis, and chemical syntheses.

Secondary metabolites from mangrove-associated fungi: source, chemistry and bioactivities

Covering 1989 to 2020The mangrove forests are a complex ecosystem occurring at tropical and subtropical intertidal estuarine zones and nourish a diverse group of microorganisms including fungi, actinomycetes, bacteria, cyanobacteria, algae, and protozoa. Among the mangrove microbial community, mangrove associated fungi, as the second-largest ecological group of the marine fungi, not only play an essential role in creating and maintaining this biosphere but also represent a rich source of structurally unique and diverse bioactive secondary metabolites, attracting significant attention of organic chemists and pharmacologists. This review summarizes the discovery relating to the source and characteristics of metabolic products isolated from mangrove-associated fungi over the past thirty years (1989-2020). Its emphasis included 1387 new metabolites from 451 papers, focusing on bioactivity and the unique chemical diversity of these natural products.

Structure and absolute configuration assignments of ochracines F-L, chamigrane and cadinane sesquiterpenes from the basidiomycete Steccherinum ochraceum HFG119

Ochracines F-L (1-7), seven previously undescribed chamigrane and cadinane sesquiterpenoids, together with four known chamigranes were isolated from cultures of the wood-decaying fungus Steccherinum ochraceum HFG119. Ochracines F-L were structurally characterized by extensive analysis of HRMS and NMR spectroscopic data. The relative configurations were assigned through a combination of NOE correlations and J-based configuration analysis (JBCA), while the absolute configurations were determined by X-ray single-crystal diffraction, and calculated methods (ECD, [α], 13C NMR). All the new isolates were evaluated for their cytotoxicity against five human cancer cell lines HL-60, SMMC-7721, A549, MCF-7, and SW-480, and inhibitory activity on NO production in RAW 264.7 macrophages.

Assessment of alpha glucosidase inhibitors produced from endophytic fungus Alternaria destruens as antimicrobial and antibiofilm agents

Diabetes is considered as a major health concern worldwide and patients with diabetes are at high risk for infectious diseases. Therefore, α-glucosidase inhibitors possessing antibacterial activity along with the ability to inhibit biofilms would be better therapeutic agents for diabetic patients. In the present study, two fractions (AF1 and AF2) possessing α-glucosidase inhibitory activity were purified from an endophytic fungus Alternaria destruens (AKL-3) isolated from Calotropis gigantea. These were evaluated for their antimicrobial and antibiofilm potential against human pathogens. AF1 exhibited broad spectrum antimicrobial activity against all the tested pathogens. It also significantly inhibited biofilm formation and dispersed the preformed biofilm at sub-optimal concentrations. AF2 possessed lesser activity as compared to AF1. The active compounds were purified using semi preparative HPLC. Some of the active compounds were identified to be phenolic in nature. The active fractions were also determined to be non-mutagenic and non-cytotoxic in safety analysis. The study highlights the role of endophytic fungi as sources of α-glucosidase inhibitors with antimicrobial potential which can have application in management of diabetes.

Ochracines A-E, chamigrane-related norsesquiterpene derivatives from the basidiomycete Steccherinum ochraceum HFG119

Ochracines A-E, five previously undescribed norsesquiterpenes featured by unusual scaffolds biogenetically related to chamigrane, were isolated from the cultures of Steccherinum ochraceum. Ochracines A (1) and B (2) represent the first examples of norsesquiterpenes with an unprecedented 1,2-6,7-diseco-1,8-cyclochamigrane scaffold. Ochracines C-D (3-5) possess an unusual 1,2-6,7-diseco-chamigrane skeleton. Their structures were elucidated by analysis of spectroscopic data. The absolute configuration of ochracine A (1), and the relative configuration of ochracine B (2) were determined by ECD and/or NMR calculations. The biosynthetic pathways for the norsesquiterpenes were proposed. All isolates were evaluated for their cytotoxicity against the five human cancer cell lines HL-60, SMMC-7721, A549, MCF-7, and SW-480.

New secondary metabolites from the endophytic fungus Fusarium sp. HP-2 isolated from "Qi-Nan" agarwood

A novel pyrone derivative (1) bearing two fused five-member rings, together with two new naphthalenone derivatives (2, 3), as well as two known compounds (4, 5) were obtained from the endophytic fungus Fusarium sp. HP-2, which was isolated from "Qi-Nan" agarwood. The structures of the new compounds were elucidated by analysis of 1D and 2D NMR, and by HRESIMS spectra, as well as by comparison with the literature. Bioactivity results indicated that compound 3 showed weak acetylcholinesterase inhibitory activity.

Novel natural compounds from endophytic fungi with anticancer activity

Plant endophytes are microorganisms that live in healthy plant tissues in part or all of their life history without causing obvious symptoms of infection in the host plants. Endophytes, a new type of microbial resource that can produce a variety of biological constituents, have great values for research and broad prospects for development. This article reviewed the research and development progress of endophytic fungi with cytotoxic activity between 2014 and 2017, including endophytic fungi sources, microbial taxonomy, compound classification and cytotoxic activity. The results showed that the 109 strains of endophytic fungi belong to 3 phyla, 7 classes and 50 genera. The secondary metabolites mainly contained alkaloids, terpenes, steroids, polyketides, quinones, isocoumarins, esters etc. The results of this study provide references for the development of new antitumor drugs and endophytes resources.

New cytochalasin from Rosellinia sanctae-cruciana, an endophytic fungus of Albizia lebbeck

AIM

To explore the potential of Rosellinia sanctae-cruciana an endophytic fungus associated with Albizia lebbeck for pharmaceutically important cytotoxic compounds.

METHODS AND RESULTS

One novel cytochalasin, named jammosporin A (1) and four known analogues (2-5) were isolated from the culture of the endophytic fungus R. sanctae-cruciana, harboured from the leaves of the medicinal plant A. lebbeck. Their structures were elucidated by extensive spectroscopic analyses including one-dimensional and two-dimensional nuclear magnetic resonance data along with MS data and by comparison with literature reports. In preliminary screening the ethyl acetate extract of the fungal culture was tested for cytotoxic activity against a panel of four cancer cell lines (MOLT-4, A549, MIA PaCa-2 and MDA-MB-231), and found to be active against MOLT-4 with an IC₅₀ value of 10 μg ml^-1 . Owing to the remarkable cytotoxic activity of the extract the isolated compounds (1-5) were evaluated for their cytototoxicity against the MOLT-4 cell line by MTT assay. Interestingly, compounds 1-2, 4 and 5 showed considerable cytotoxic potential against the human leukaemia cancer cell line (MOLT-4) with IC₅₀ values of 20·0, 10·0, 8·0 and 6·0 μmol l^-1 , respectively, while compound 3 showed an IC₅₀ value of 25 μmol l^-1 . This is the first report of the existence of this class of secondary metabolites in R. sanctae-cruciana fungus.

CONCLUSION

This study discovered a novel compound, named jammosporin A, isolated for the first time from R. sanctae-cruciana, an endophytic fungus of A. lebbeck with anticancer activity against the MOLT-4 cell line.

SIGNIFICANCE AND IMPACT OF THE STUDY

Rosellinia sanctae-cruciana represents an interesting source of a new compound with bioactive potential as a therapeutic agent against a human leukaemia cancer cell line (MOLT-4).

Antibacterial potential of secondary metabolites produced by Aspergillus sp., an endophyte of Mitrephora wangii

Mitrephora wangii, an ethnomedicinal plant, has been used as a natural antibiotic and immunity booster in Thailand. A total of 22 fungi were isolated from M. wangii flowers. The fungal isolates were categorized into six genera including Agrocybe, Aspergillus, Colletotrichum, Nigrospora, Puccinia and Ustilago. Most extracts exhibited antibacterial activity against at least one of the test bacteria. Aspergillus sp. MFLUCC16-0845 was identified as the most bioactive fungus. Chemical composition of Aspergillus sp. MFLUCC16-0845 investigated using gas chromatography-mass spectrometry indicated that the major antibacterial compound was β-thujaplicin. Moreover, the newly isolated Aspergillus sp. MFLUCC16-0845 could be exploited as a potential source of bioactive compounds and plant defense activators. In addition, it is the first time that strain of Aspergillus sp. isolated and cultured from M. wangii flowers could produce β-thujaplicin at high yield with strong antimicrobial spectrum, which may lead to wide utilization in producing cosmetics and clinical products.

Indole diterpenoids from the endophytic fungus Drechmeria sp. as natural antimicrobial agents

A fungal strain, Drechmeria sp., was isolated from the root of Panax notoginseng. Totally, seven new indole diterpenoids, drechmerins A-G (1-7), were isolated from the fermentation broth of Drechmeria sp. together with four known analogues (8-11). Their structures were determined on the basis of 1D and 2D NMR and electronic circular dichroism (ECD) spectroscopic analyses as well as theoretical calculations. All the isolated compounds were evaluated for their antimicrobial activities against Candida albicans, Staphylococcus aureus, Bacillus cereus, B. subtillis, Pseudomonas aeruginosa, and Klebsiella pneumonia, respectively. Drechmerin B (2) displayed antimicrobial activity against C. albicans with an MIC value of 12.5 μg/mL. Molecular docking was used to investigate interactions of peptide deformylase with compounds 1-3, 5-7, 9, and 10.

Intramolecular Morita-Baylis-Hillman reaction as a strategy for the construction of tricyclic sesquiterpene cores

Starting from a common polyfunctionalized bicyclo[3.2.1]octane-6,8-dione intermediate, a concise synthetic route to tricyclic cores found in quadrane, suberosane, cedrane and related sesquiterpenes was developed using a Morita-Baylis-Hillman intramolecular reaction as a key step.

Diversity Modification and Structure-Activity Relationships of Two Natural Products 1β-hydroxy Alantolactone and Ivangustin as Potent Cytotoxic Agents

Sesquiterpene lactones (STLs) are a class of plant secondary metabolites widely found in nature with potent antitumor activities. In this work, two isolated STLs 1β-hydroxy alantolactone (1) and ivangustin (2) were derivatized through diversity-oriented strategy, and in vitro cytotoxic activity assessments were conducted against six cell lines including HeLa, PC-3, HEp-2, HepG2, CHO and HUVEC. The cytotoxic structure-activity relationship showed that the double bond between C5 and C6 was beneficial to improve activity; C1-OH oxidized derivatives showed a slight stronger activity, comparable to the positive drug etoposide (VP-16). Yet, C1-OH esterified derivatives decreased the potency which were different from those of 1-O-acetylbritannilactone (ABL) reported previously by us, and C13-methylene reductive and spiro derivatives resulted in almost complete ablation of cytotoxic activity. Mechanistic basis of cytotoxicity of the representative compound 1i was assayed to relate with apoptosis and cell cycle arrest. Furthermore, 1i inhibited TNF-α-induced canonical NF-κB signaling in PC-3 cells. Molecular modeling studies exhibited additional hydrogen bond interaction between 1i and the residue Lys37 of p65, indicating that 1i could form covalent protein adducts with Cys38 on p65.

Antibacterial and Antioxidant Metabolites of Diaporthe spp. Isolated from Flowers of Melodorum fruticosum

Fifty-two strains of endophytic fungi were isolated from flowers of the medicinal plant Melodorum fruticosum. Seven genera were identified including Alternaria, Aspergillus, Colletotrichum, Diaporthe, Fusarium, Greeneria and Nigrospora. All strains were cultured for 30 days and further macerated in ethyl acetate solvent for 3 days. The obtained fungal extracts were examined for antibacterial activity using agar disc diffusion against nine pathogenic bacteria: Staphylococcus aureus, Bacillus subtilis, B. cereus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli, Shigella flexneri, Vibrio cholerae and V. parahaemolyticus. Forty-three fungal extracts exhibited antibacterial activity against at least one tested pathogen. The antioxidant properties of all extracts were also investigated by DPPH scavenging assay. Sixteen extracts displayed high antioxidant capacity (IC₅₀ ranging from 10 to 50 µg/mL) when compared to the gallic acid and trolox standards (IC₅₀ of 12.46 and 2.55 µg/mL, respectively). The crude extracts of Diaporthe sp. MFLUCC16-0682 and Diaporthe sp. MFLUCC16-0693 exhibited notable antibacterial and antioxidant activities. Analysis of chemical composition using gas chromatography-mass spectrometry suggested that the observed antibacterial activity of the two Diaporthe spp. was possibly due to the presence of abienol, 4-methoxy stilbene, phenethyl cinnamate and 2Z,6Z-farnesal, while their potential antioxidant activity could be attributed to phenolic compounds, such as benzene acetaldehyde, benzyl benzoate, salicylaldehyde, benzoin and benzyl cinnamate. The results suggest that the genus Diaporthe is a potential source of metabolites that can be used in a variety of applications.

Semisynthesis, an Anti-Inflammatory Effect of Derivatives of 1β-Hydroxy Alantolactone from Inula britannica

1β-hydroxy alantolactone, a sesquiterpene lactone mainly isolated from Inula genus plants, exhibits potent anti-inflammatory and anticancer activities. In this work, 1β-hydroxy alantolactone was isolated and five derivatives were prepared through different reactions at the C1-OH and C13-methylene motifs. The structure-activity relationships (SAR) of anti-inflammatory effects against NO production in RAW264.7 cells showed that the α-methylene-γ-butyrolactone motif was essential for NO production suppression and that retaining the C1-OH group can remarkably improve this effect. The NF-κB signaling pathway plays a pivotal role in the regulation of NO expression. Moreover, the levels of p65 and p50 phosphorylation were investigated and active compound 1 inhibited phosphorylation of p65 and p50 in TNF-α-induced NF-κB signaling. Further molecular docking suggested that 1 may target the p65 of NF-κB.

Fungal endophytes associated with Viola odorata Linn. as bioresource for pancreatic lipase inhibitors

Background

As per the recent statistical reports of World Health Organisation (WHO), 13% of total global population is obese. Orlistat remains to be the only drug approved for the long term treatment of obesity. Recent findings highlighted severe adverse effects of orlistat that included hepatotoxicity, gall stones, kidney stones and acute pancreatitis. Therefore, search for new drug is required. The investigations based on endophytic natural products would prove pivotal in the global fight against this health issue.

Methods

Obesity is associated with lipid metabolism involving pancreatic lipase enzyme. The inhibition of pancreatic lipase is demonstrated by using the extracts of endophytes isolated from Viola odorata Linn. In addition, endophytes were identified using ITS based rDNA sequencing.

Results

Present study involves the isolation and identification of 27 endophytes from V. odorata. All the endophytes were evaluated for lipase inhibitory activities. The extracts of seven endophytes exhibited lipase inhibitory activity with IC₅₀ < 10 μg/mL. The extract of VOLF4 (Aspergillus sp.) displayed promising lipase inhibitory activity (IC₅₀ 3.8 μg/mL).

Conclusion

The present study demonstrates that V. odorata harbors endophytic community with potent lipase inhibitory activity. VOLF4 is the potential endophyte. The extract of VOLF4 can be used to develop the potential drug to treat obesity.

Fungal Endophytes: an Alternative Source for Production of Volatile Compounds from Agarwood Oil of Aquilaria subintegra

Fungal endophytes are microorganisms that are well-known for producing a diverse array of secondary metabolites. Recent studies have uncovered the bioprospecting potential of several plant endophytic fungi. Here, we demonstrate the presence of highly bioactive fungal endophytic species in Aquilaria subintegra, a fragrant wood plant collected from Thailand. Thirty-three fungal endophytic strains were isolated and further identified to genus level based on morphological characteristics. These genera included Colletotrichum, Pestalotiopsis, Fusarium, Russula, Arthrinium, Diaporthe and Cladosporium. All strains were cultured on potato dextrose broth for 30 days prior to partitioning with ethyl acetate. The volatile compounds of all extracts were investigated by gas chromatography-mass spectrometry (GC-MS). Four strains-Arthrinium sp. MFLUCC16-0042, Colletotrichum sp. MFLUCC16-0047, Colletotrichum sp. MFLUCC16-0048 and Diaporthe sp. MFLUCC16-0051-produced a broad spectrum of volatile compounds, including β-agarofuran, α-agarofuran, δ-eudesmol, oxo-agarospirol, and β-dihydro agarofuran. These compounds are especially important, because they greatly resemble those originating from the host-produced agarwood oil. Our findings demonstrate the potential of endophytic fungi to produce bioactive compounds with applications in perfumery and cosmetic industries. Antioxidant activity of all extracts was also evaluated by using 2,2-diphenyl-2-picrylhydrazyl radical scavenging assays. The ethyl acetate extract of Diaporthe sp. MFLUCC16-0051 demonstrated superior antioxidant capacity, which was comparable to that of the gallic acid standard. Our results indicate that the MFLUCC16-0051 strain is a resource of natural antioxidant with potential medicinal applications.

Cytotoxic and antibacterial naphthoquinones from an endophytic fungus, Cladosporium sp

Objective

Endophytes have the potential to synthesize various bioactive secondary metabolites. The aim of the study was to find new cytotoxic and antibacterial metabolites from endophytic fungus, Cladosporium sp. isolated from the leaves of Rauwolfia serpentina (L.) Benth. ex Kurz. (Fam: Apocyanaceae).

Materials and methods

The endophytic fungus was grown on potato dextrose agar medium and extracted using ethyl acetate. Secondary metabolites were isolated by chromatographic separation and re-crystallization, and structures were confirmed by ¹H NMR, ¹³C NMR and mass spectroscopic data. The cytotoxicity was determined by WST-1 assay and brine shrimp lethality bioassay, while antibacterial activity was assessed by disc diffusion method.

Results

Two naphthoquinones, namely anhydrofusarubin (1) and methyl ether of fusarubin (2), were isolated from Cladosporium sp. The isolated compounds 1 and 2, by WST-1 assay against human leukemia cells (K-562) showed potential cytotoxicity with IC₅₀ values of 3.97 μg/mL and 3.58 μg/mL, respectively. Initial screening of crude ethyl acetate extract and column fractions F-8 and F-10 exhibited noticeable cytotoxicity to brine shimp nauplii with LC₅₀ values of 42.8, 1.2 and 2.1 μg/mL, respectively. Moreover, the isolated compound 2 (40 μg/disc) showed prominent activities against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Bacillus megaterium with an average zone of inhibition of 27 mm, 25 mm, 24 mm and 22 mm, respectively and the activities were compared with kanamycin (30 μg/disc).

Conclusion

Our findings indicate that anhydrofusarubin (1) and methyl ether of fusarubin (2) might be useful lead compounds to develop potential cytotoxic and antimicrobial drugs.

Marine natural products

This review covers the literature published in 2014 for marine natural products (MNPs), with 1116 citations (753 for the period January to December 2014) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1378 in 456 papers for 2014), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Cytotoxic sesquiterpenes from the endophytic fungus Pseudolagarobasidium acaciicola

Twenty previously unknown compounds and two known metabolites, merulin A and merulin D, were isolated from the endophytic fungus Pseudolagarobasidium acaciicola, which was isolated from a mangrove tree, Bruguiera gymnorrhiza. Structures of the 20 compounds were elucidated by analysis of spectroscopic data. The absolute configuration of seven of these compounds was addressed by a single crystal X-ray analysis using CuKα radiation and an estimate of the Flack parameter. Three compounds also possessed a tricyclic ring system. Terpene endoperoxides isolated exhibited cytotoxic activity, while those without an endoperoxide moiety did not show activity. The endoperoxide moiety of sesquiterpenes has significant impact on cytotoxic activity, and thus is an important functionality for cytotoxicity. One terpene endoperoxide displayed potent cytotoxic activity (IC50 0.28μM), and selectively exhibited activity against the HL-60 cell line.

Expeditious entry to the chamigrane endoperoxide family of natural products

Several members of the recently reported peroxy chamigrane family of natural products were synthesized via a distereoselective route with a novel facial-selective epoxidation of a spiroundecadiene, a facile epoxide rearrangement, and a Co(II)-mediated silylperoxidation as the key steps. Adaptation of the diastereoselective route to an enantioselective one is also illustrated.