A New Metabolite with a Unique 4-Pyranone-γ-Lactam-1,4-Thiazine Moiety from a Hawaiian-Plant Associated Fungus

Organocatalyzed Enantio- and Diastereoselective Formal Domino 1,3-Dipolar Cycloaddition/Rearrangement: Synthesis of Chiral Pyrrolo-thiazine-2-carbaldehydes

An efficient approach for the synthesis of chiral pyrrolo[1,2-d][1,4]thiazine-2-carbaldehydes is achieved via formal 1,3-dipolar cycloaddition/rearrangement reactions of benzothiazolium salt and α,β-unsaturated aldehydes, utilizing an asymmetric organocatalyst. This process results in the formation of fluorescent, highly enantioenriched chiral molecules with three contiguous stereogenic centers, one of which is a chiral quaternary center, with excellent yields and enantio- and diastereoselectivity. A computational study demonstrated the understanding of the reaction mechanism. The synthetic utility of this protocol was successfully employed for gram scale synthesis. Fluorescent and in silico studies showed the application of the present methodology.

Pseudo-Enantiomeric Paraphaeolactones and Their Biosynthetic Derivatives from Paraphaeosphaeria sp. KT4192: A Proposition of a Favorskii Rearrangement for Their Biosynthesis

Paraphaeolactones A1, A2, B1, and B2 (1-4, respectively), known arthropsadiol D (5), massariphenone (6) and its positional isomer 7, and massarilactones E (8) and G (9) were isolated from the culture broth of Paraphaeosphaeria sp. KT4192. Although the structural resemblance between 1 and 2 implies that these comprised a diastereomeric pair at the C-2 stereogenic center, electronic circular dichroism (ECD) spectral analyses revealed that they were pseudo-enantiomers possessing the common (2R)-configuration. Paraphaeolactones B1 and B2 (3 and 4) were the derivatives of 2, which equipped the 3-(1-hydroxy-2-oxopropyl)-4-methylcatechol moiety via an acetal bond at C-10. The relative configurations of their acetal carbons were elucidated by NOE experiments, and those of C-8' were deduced independently by ECD spectral analysis. The present study disclosed that 1-5, 8, and 9 contain a methylcyclohexene substructure with the same absolute configuration. This prompted us to reinvestigate the absolute configurations of known structurally related fungal metabolites, allowing us to conclude that the methylcyclohexene moieties of these natural products have the same absolute configuration despite the variety of configurations of other stereogenic centers. The plausible biosynthetic routes for 1-9 are discussed on the basis of the above conclusion. We propose a Favorskii rearrangement as the key transformation for biosyntheses of 1-4.

Sulfur-Containing Compounds from Endophytic Fungi: Sources, Structures and Bioactivities

Endophytic fungi have attracted increasing attention as an under-explored source for the discovery and development of structurally and functionally diverse secondary metabolites. These microorganisms colonize their hosts, primarily plants, and demonstrate diverse ecological distribution. Among endophytic fungal natural products, sulfur-containing compounds feature one or more sulfur atoms and possess a range of bioactivities, e.g., cytotoxicity and antimicrobial activities. These natural products mainly belong to the classes of polyketides, nonribosomal peptides, terpenoids, and hybrids. Here, we reviewed the fungal producers, plant sources, chemical structures, and bioactivities of 143 new sulfur-containing compounds that were reported from 1985 to March 2022.

Polyketides, diketopiperazines and an isochromanone from the marine-derived fungal strain Fusarium graminearum FM1010 from Hawaii

The fungal strain Fusarium graminearum FM1010 was isolated from a shallow-water volcanic rock known as "live rock" at the Richardson's Beach, Hilo, Hawaii. Eleven specialised metabolites, including two undescribed diketopiperazines, three undescribed polyketides, and one undescribed isochromanone, along with five known fusarielin derivatives were obtained from F. graminearum FM1010. The structures of the six undescribed compounds were elucidated by extensive analysis of NMR spectroscopy, HRESIMS, chemical reactions, and electronic circular dichroism (ECD) data. Kaneoheoic acids G-I showed mild inhibitory activity against S. aureus with the MIC values in the range of 20-40 μg/mL when assayed in combination with chloramphenicol (half of the MIC, 1 μg/mL), an FDA approved antibiotic. Kaneoheoic acid I exhibited both anti-proliferative activity against ovarian cancer cell line A2780 and TNF-α induced NF-κB inhibitory activity with the IC₅₀ values of 18.52 and 15.86 μM, respectively.

New Alkaloids From a Hawaiian Fungal Strain Aspergillus felis FM324

Two new alkaloids tryptoquivaline Y (1) and pseurotin I (2), together with eight known compounds (3-10), were purified from a fungal strain Aspergillus felis FM324, which was isolated from a Hawaiian beach soil sample. The absolute configuration and physicochemical data of tryptoquivaline Z (3) were reported for the first time here in this paper. Compound 1 is an uncommon tryptoquivaline analog containing a 3-O-isobutanoyl group. The structures of the new compounds 1-2 and known compound 3 were elucidated through HRESIMS, NMR spectroscopy and ECD analysis. All the compounds were evaluated for their antiproliferative, antibacterial and NF-κB inhibitory activities. Compound 4 showed weak antibacterial activity against Staphylococcus aureus, methicillin resistant Staphylococcus aureus and Bacillus subtilis with the same MIC value of 59.2 µM. Compounds 3 and 2 inhibited NF-κB with IC50 values of 26.7 and 30.9 μM, respectively.

NF-κB inhibitory, antimicrobial and antiproliferative potentials of compounds from Hawaiian fungus Aspergillus polyporicola FS910

Bioassay-guided experimental design and chromatographic analysis led to the isolation and identification of ten compounds (1-10) including two unusual sulfur-containing curvularin macrolides (1 and 2) from a Hawaiian fungal strain Aspergillus polyporicola FS910. Compounds 1 and 2 are rare curvularin macrolides each with a five-membered cyclic sulfur-containing moiety. The structures of the compounds were identified by HRESIMS, NMR spectroscopy, X-ray crystallography, ECD and DFT energy calculation, as well as comparing with previous literatures. Compounds 4, 6 and 8 were active against TNF-α-induced NF-κB inhibitory activity with IC₅₀ values of 26.45, 5.41 and 15.8 µM, respectively. Compounds 3 and 5-8 exhibited anti-proliferative activity against HT1080, T46D, and A2780S cell lines, with IC₅₀ values ranging from 2.48 to 29.17 μM. Additionally, Compound 3 showed promising antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA), Bacillus subtilis, Escherichia coli and Candida albicans. Moreover, when tested in combination with antibiotic adjuvant disulfiram [4 µg/mL], compounds 4, 5 and 10 also displayed significant antibacterial activity against S. aureus.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02877-7.

Z, Cubilla-Rios L. Structurally Uncommon Secondary Metabolites Derived from Endophytic Fungi

Among microorganisms, endophytic fungi are the least studied, but they have attracted attention due to their high biological diversity and ability to produce novel and bioactive secondary metabolites to protect their host plant against biotic and abiotic stress. These compounds belong to different structural classes, such as alkaloids, peptides, terpenoids, polyketides, and steroids, which could present significant biological activities that are useful for pharmacological or medical applications. Recent reviews on endophytic fungi have mainly focused on the production of novel bioactive compounds. Here, we focus on compounds produced by endophytic fungi, reported with uncommon bioactive structures, establishing the neighbor net and diversity of endophytic fungi. The review includes compounds published from January 2015 to December 2020 that were catalogued as unprecedented, rare, uncommon, or possessing novel structural skeletons from more than 39 different genera, with Aspergillus and Penicillium being the most mentioned. They were reported as displaying cytotoxic, antitumor, antimicrobial, antiviral, or anti-inflammatory activity. The solid culture, using rice as a carbon source, was the most common medium utilized in the fermentation process when this type of compound was isolated.

Aspochalasin H1: A New Cyclic Aspochalasin from Hawaiian Plant-Associated Endophytic Fungus Aspergillus sp. FT1307

Aspergillus is one of the most diverse genera, and it is chemically profound and known to produce many biologically active secondary metabolites. In the present study, a new aspochalasin H1 (1), together with nine known compounds (2-10), were isolated from a Hawaiian plant-associated endophytic fungus Aspergillus sp. FT1307. The structures were elucidated using nuclear magnetic resonance (NMR) (1H, 1H-1H COSY, HSQC, HMBC, ROESY and 1D NOE), high-resolution electrospray ionization mass spectroscopy (HRESIMS), and comparisons with the reported literature. The absolute configuration of the new compound was established by electronic circular dichroism (ECD) in combination with NMR calculations. The new compound contains an epoxide moiety and an adjacent trans-diol, which has not been reported before in the aspochalasin family. The antibacterial screening of the isolated compounds was carried out against pathogenic bacteria (Staphylococcus aureus, Methicillin-resistant S. aureus and Bacillus subtilis). The antiproliferative activity of compounds 1-10 was evaluated against human breast cancer cell lines (MCF-7 and T46D) and ovarian cancer cell lines (A2780).

Antibacterial and NF-κB Inhibitory Lumazine Peptides, Aspochalasin, γ-Butyrolactone Derivatives, and Cyclic Peptides from a Hawaiian Aspergillus flavipes

Five new lumazine peptides (1-5), a new aspochalasin derivative (6), and a new γ-butyrolactone derivative (7), together with seven known compounds (8-14), were isolated from a Hawaiian fungal strain, Aspergillus flavipes FS888. Compound 1 is an uncommon natural product containing an isocyano group. The structures of the new compounds 1-7 were elucidated by NMR spectroscopy, HRESIMS, chemical derivatization, and ECD analysis. Compounds 12-14 showed significant antibacterial activity against S. aureus when in combination with disulfiram. Additionally, compounds 9 and 13 showed NF-κB inhibitory activity with IC₅₀ values of 3.1 ± 1.0 and 10.3 ± 2.0 μM, respectively.

Tryptoquivalines W and X, two new compounds from a Hawaiian fungal strain and their biological activities

Two new compounds tryptoquivalines W (1) and X (2) were isolated from a Hawaiian soil fungal strain Aspergillus terreus FS107. The soil sample was collected on the top of Mauna Kea, the tallest mountain in Hawaii. The structures of compounds 1 and 2 were determined on the basis of MS spectroscopic and NMR analysis, and NMR calculation. The absolute configuration (AC) was determined by ECD calculations. Compounds 4 and 5 showed inhibition against NF-κB with IC50 values of 3.45 and 6.76 μM, respectively.

NF-κB Inhibitory and Antibacterial Helvolic and Fumagillin Derivatives from Aspergillus terreus

Two new helvolic acid analogues (1 and 2) and one new fumagillin derivative containing an octahydroisobenzofuran moiety (3), together with four known compounds (4-7), were isolated from an Aspergillus terreus, isolated from soil collected from Mauna Kea, the highest mountain in Hawaii. Compound 4 was recorded in SciFinder with a CAS Registry Number of 1379525-35-5, but it was not documented in the cited reference (ACS Chem. Biol. 2012, 7, 137). The structures of compounds 1-4 were elucidated by NMR spectroscopy and HRMS and ECD analysis. Compounds 5 and 6 showed significant inhibitory activity against NF-κB with IC₅₀ values of 2.7 ± 2.6 and 6.5 ± 0.8 μM, respectively. Compounds 1 and 2 were active against S. aureus with MICs of 6.25 and 6.25 μg/mL, respectively, while compound 5 inhibited E. coli with an MIC of 3.12 μg/mL.

Wheldone: Characterization of a Unique Scaffold from the Coculture of Aspergillus fischeri and Xylaria flabelliformis

Wheldone (1) was isolated and elucidated from a coculture of Aspergillus fischeri (NRRL 181) and Xylaria flabelliformis (G536), where secondary metabolite biosynthesis was stimulated by antagonism between these fungi. First observed via in situ analysis between these competing fungal cultures, the conditions were scaled to reproducibly generate 1, whose novel structure was elucidated by one- and two-dimensional NMR and mass spectrometry. Compound 1 displayed cytotoxic activity against breast, ovarian, and melanoma cancer cell lines.

Fungi: outstanding source of novel chemical scaffolds

A large number of remarkable studies on the secondary metabolites of fungi have been conducted in recent years. This review gives an overview of one hundred and sixty-seven molecules with novel skeletons and their bioactivities that have been reported in seventy-nine articles published from 2013 to 2017. Our statistical data showed that endophytic fungi and marine-derived fungi are the major sources of novel bioactive secondary metabolites.

Total Synthesis of the Proposed Structure of Paraphaeosphaeride C

Paraphaeosphaeride C is a demethoxy derivative of phaeosphaeride A and exhibits STAT3 inhibitory activity. Our previous papers reported the total synthesis of phaeosphaeride A using a diastereoselective vinyl anion aldol reaction as the key step to construct the dihydropyran ring. In this work, the first total synthesis of the proposed structure of paraphaeosphaeride C was achieved via a similar synthetic strategy. The synthetic compound was characterized through extensive nuclear magnetic resonance (NMR) analysis but the ¹H and ¹³C-NMR data for this compound did not correspond to those reported in the literature for paraphaeosphaeride C.

Phenyliodine(III) Diacetate/I2 -Mediated Domino Approach for Pyrrolo[1,4]Thiazines and 1,4-Thiazines by a One-Pot Morin Rearrangement of N,S-Acetals

An efficient domino transformation using a phenyliodine(III) diacetate (PIDA)/I₂ combination towards Morin 1,4-thiazine compounds has been developed starting from N,S-acetals. The latter leads to "one-step" regioselective methylene insertion without the need for traditional sulfoxide intermediates in good yields. The reaction involves easily accessible N,S-acetals obtained from cost-effective basic ketones and cysteamine as starting materials. This process ultimately leads to 1,4-thiazines related to natural product and fused derivatives necessary for further QSAR study.

Recent trends in the structural revision of natural products

Covering: 2012 to 2017 This article reviews recent reports on the structural revision of natural products. Through a critical assessment of the original and revised published structures, the article addresses why each structure was targeted for revision, discusses the techniques and key discrepancies that led to the proposal of the revised structure, and offers measures that may have been taken during the original structure determination to prevent error. With the revised structures in hand, weaknesses of original proposals are assessed, providing a better understanding on the logic behind structure determination.

An Unusual Benzoisoquinoline-9-one Derivative and Other Related Compounds with Antiproliferative Activity from Hawaiian Endophytic Fungus Peyronellaea sp. FT431

A new polyketide containing the benzoisoquinoline-9-one moiety, peyronetide A (1), and three other new derivatives peyronetides B–D (2–4), as well as one known compound (5) were purified from the cultured broth of the endophytic fungus Peyronellaea sp. FT431, which was isolated from the Hawaiian indigenous plant, Verbena sp. The structures of the new compounds were determined through the analysis of HRMS and NMR spectroscopic data. Compounds 1, 2, and 5 showed cytotoxic activities against TK-10 (human kidney adenocarcinoma cells), cisplatin sensitive A2780S (human ovarian carcinoma cells), and cisplatin resistant A2780CisR cell lines, with IC₅₀ values between 6.7 to 29.2 μM.

Unstable Tetramic Acid Derivatives from the Deep-Sea-Derived Fungus Cladosporium sphaerospermum EIODSF 008

Seven new unstable tetramic acid derivatives, cladosporiumins I-O (1–7), together with the known analogue cladodionen (8) were isolated from the extract of the deep-sea-derived fungus Cladosporium sphaerospermum EIODSF 008. Their structures were elucidated by spectroscopic analysis, quantum chemical calculations and ECD spectra. Compound 4 was a Mg complex of tetramic acid derivative. In acidic solvent, 4 could change to 1 and 6, and 7 could change to 5. In addition, 1, 5 and 8 existed as two exchangeable isomers, respectively. The structures of cladosporiumins E-H were reassigned as their Na complexes. The antibacterial and cytotoxic activities of 1–8 were also evaluated. However, because of their instability, all of the isolated compounds did not show significant antibacterial activity as the preliminary EtOAc extracts of the fungal strain.

Curvulin and Phaeosphaeride A from Paraphoma sp. VIZR 1.46 Isolated from Cirsium arvense as Potential Herbicides

Phoma-like fungi are known as producers of diverse spectrum of secondary metabolites, including phytotoxins. Our bioassays had shown that extracts of Paraphoma sp. VIZR 1.46, a pathogen of Cirsium arvense, are phytotoxic. In this study, two phytotoxically active metabolites were isolated from Paraphoma sp. VIZR 1.46 liquid and solid cultures and identified as curvulin and phaeosphaeride A, respectively. The latter is reported also for the first time as a fungal phytotoxic product with potential herbicidal activity. Both metabolites were assayed for phytotoxic, antimicrobial and zootoxic activities. Curvulin and phaeosphaeride A were tested on weedy and agrarian plants, fungi, Gram-positive and Gram-negative bacteria, and on paramecia. Curvulin was shown to be weakly phytotoxic, while phaeosphaeride A caused severe necrotic lesions on all the tested plants. To evaluate phaeosphaeride A's herbicidal efficacy, the phytotoxic activity of this compound in combination with five different adjuvants was studied. Hasten at 0.1% (v/v) was found to be the most potent and compatible adjuvant, and its combination with 0.5% (v/v) semi-purified extract of Paraphoma sp. VIZR 1.46 solid culture exhibited maximum damage to C. arvense plants. These findings may offer significant importance for further investigation of herbicidal potential of phaeosphaeride A and possibly in devising new herbicide of natural origin.

Banksialactones and Banksiamarins: Isochromanones and Isocoumarins from an Australian Fungus, Aspergillus banksianus

Chemical investigation of an Australian fungus, Aspergillus banksianus, led to the isolation of the major metabolite banksialactone A (1), eight new isochromanones, banksialactones B-I (2-9), two new isocoumarins, banksiamarins A and B (10 and 11), and the reported compounds, clearanol I (12), dothideomynone A (13), questin (14), and endocrocin (15). The structures of 1-11 were established by NMR spectroscopic data analysis, and the absolute configurations were determined from optical rotations and ECD spectra in conjunction with TD-DFT calculations. The secondary metabolite profile of A. banksianus is unusual, with the 11 most abundant metabolites belonging to a single isochromanone class. Conjugation of 1 with endocrocin, 5-methylorsellinic acid, 3,5-dimethylorsellinic acid, mercaptolactic acid, and an unknown methylthio source gave rise to five unprecedented biosynthetic hybrids, 5-9. The isolated compounds were tested for cytotoxicity, antibacterial, and antifungal activities, with hybrid metabolites 7-9 displaying weak cytotoxic and antibiotic activities.

Total Synthesis and Biological Evaluation of Phaeosphaerides

This article reviews studies regarding the total synthesis of phaeosphaerides A and B, nitrogen-containing bicyclic natural products isolated from an endophytic fungus. Numerous synthetic efforts and an X-ray crystal structure analysis of phaeosphaeride A have enabled revision of its originally proposed structure. In addition, a successful protic acid-mediated transformation of phaeosphaeride A to phaeosphaeride B revealed the hypothetical biosynthesis of phaeosphaeride B from phaeosphaeride A. Structure–activity relationship studies of phaeosphaeride derivatives are also discussed.

Structural Diversity and Biological Activities of Novel Secondary Metabolites from Endophytes

Exploration of structurally novel natural products greatly facilitates the discovery of biologically active pharmacophores that are biologically validated starting points for the development of new drugs. Endophytes that colonize the internal tissues of plant species, have been proven to produce a large number of structurally diverse secondary metabolites. These molecules exhibit remarkable biological activities, including antimicrobial, anticancer, anti-inflammatory and antiviral properties, to name but a few. This review surveys the structurally diverse natural products with new carbon skeletons, unusual ring systems, or rare structural moieties that have been isolated from endophytes between 1996 and 2016. It covers their structures and bioactivities. Biosynthesis and/or total syntheses of some important compounds are also highlighted. Some novel secondary metabolites with marked biological activities might deserve more attention from chemists and biologists in further studies.

NF-κB inhibitors, unique γ-pyranol-γ-lactams with sulfide and sulfoxide moieties from Hawaiian plant Lycopodiella cernua derived fungus Paraphaeosphaeria neglecta FT462

LC-UV/MS-based metabolomic analysis of the Hawaiian endophytic fungus Paraphaeosphaeria neglecta FT462 led to the identification of four unique mercaptolactated γ-pyranol-γ-lactams, paraphaeosphaerides E-H (1-4) together with one γ-lactone (5) and the methyl ester of compound 2 (11). The structures of the new compounds (1-5 and 11) were elucidated through the analysis of HRMS and NMR spectroscopic data. The absolute configuration was determined by chemical reactions with sodium borohydride, hydrogen peroxide, α-methoxy-α-(trifluoromethyl)phenylacetyl chlorides (Mosher reagents), and DP4 + NMR calculations. All the compounds were tested against STAT3, A2780 and A2780cisR cancer cell lines, E. coli JW2496, and NF-κB. Compounds 1 and 3 strongly inhibited NF-κB with IC50 values of 7.1 and 1.5 μM, respectively.

Anti-proliferative ambuic acid derivatives from Hawaiian endophytic fungus Pestalotiopsis sp. FT172

Five previously undescribed ambuic acid derivatives, pestallic acids A-E and three known analogs were isolated from the cultured broth of Pestalotiopsis sp. FT172. The structures of the pestallic acids A-E were determined through the analysis of HRMS and NMR spectroscopic data. The absolute configurations (ACs) of pestallic acids B-E were assigned by comparison of the experimental electric circular dichroism (ECD) spectra or the optical rotations with those in the literature. All compounds were tested against A2780 and cisplatin resistant A2780 (A2780CisR) cell lines. Pestallic acid E and (+)-ambuic acid showed potent activities with IC₅₀ values from 3.3 to 17.0 μM.

A New N-methoxypyridone from the Co-Cultivation of Hawaiian Endophytic Fungi Camporesia sambuci FT1061 and Epicoccum sorghinum FT1062

A new N-methoxypyridone analog (1), together with four known compounds, was isolated from the co-culture of Hawaiian endophytic fungi Camporesia sambuci FT1061 and Epicoccum sorghinum FT1062. The structure of the new compound was elucidated as 11S-hydroxy-1-methoxyfusaricide (1) by extensive spectroscopic analysis and comparison with the literature. The absolute configuration of 1 was determined by comparison with the experimental and calculated ECD spectra. The absolute configuration of compound 3 was investigated and renamed as (+)-epipyridone by comparison of the optical rotation and CD spectrum with those of 1. The other known compounds were identified as epicoccarine B (2), D8646-2-6 (4), and iso-D8646-2-6 (5). Compounds 4 and 5 showed modest inhibitory activity towards pathogenic fungi. Epicoccarine B (2) inhibited A2780 and TK-10 with an IC₅₀ value of 22 μM.

Verbenanone, an octahydro-5H-chromen-5-one from a Hawaiian-Plant Associated Fungus FT431

A new secondary metabolite verbenanone (1) with a unique (4aS,8aS)-octahydro-5H-chromen-5-one moiety has been obtained from the endophytic fungus FT431, which was isolated from the native Hawaiian plant Verbena sp. The structure of compound 1 was characterized based on NMR and MS spectroscopic analysis. The absolute configuration (AC) of compound 1 was determined by Mosher acids. Compound 1 was tested against A2780 and A2780cisR, but it was inactive.

Structural Revision and Biosynthesis of the Fungal Phytotoxins Phyllostictines A and B

The structure of the fungal phytotoxins known as the phyllostictines has been revised to a series of bicyclic 3-methylene tetramic acids. Genome sequencing of the producing organism Phyllostica cirsii has revealed a biosynthetic gene cluster responsible for the biosynthesis of the phyllostictines, and targeted knockout experiments have proven the link and produced an intermediate.

Condensation of Macrocyclic Polyketides Produced by Penicillium sp. DRF2 with Mercaptopyruvate Represents a New Fungal Detoxification Pathway

Application of a refined procedure of experimental design and chemometric analysis to improve the production of curvularin-related polyketides by a marine-derived Penicillium sp. DRF2 resulted in the isolation and identification of cyclothiocurvularins 6-8 and cyclosulfoxicurvularins 10 and 11, novel curvularins condensed with a mercaptolactate residue. Two additional new curvularins, 3 and 4, are also reported. The structures of the sulfur-bearing curvularins were unambiguously established by analysis of spectroscopic data and by X-ray diffraction analysis. Analysis of stable isotope feeding experiments with [U-(13)C3(15)N]-l-cysteine confirmed the presence of the 2-hydroxy-3-mercaptopropanoic acid residue in 6-8 and the oxidized sulfoxide in 10 and 11. Cyclothiocurvularins A (6) and B (7) are formed by spontaneous reaction between 10,11-dehydrocurvularin (2) and mercaptopyruvate (12) obtained by transamination of cysteine. High ratios of [U-(13)C3(15)N]-l-cysteine incorporation into cyclothiocurvularin B (7), the isolation of two diastereomers of cyclothiocurvularins, the lack of cytotoxicity of cyclothiocurvularin B (7) and its methyl ester (8), and the spontaneous formation of cyclothiocurvularins from 10,11-dehydrocurvularin and mercaptopyruvate provide evidence that the formation of cyclothiocurvularins may well correspond to a 10,11-dehydrocurvularin detoxification process by Penicillium sp. DRF2.

Eremophilane sesquiterpenes from Hawaiian endophytic fungus Chaetoconis sp. FT087

Seven sesquiterpene derivatives, including chaetopenoids A-F and dendryphiellin A1, and 6-methyl-(2E, 4E, 6S) octadienoic acid were isolated from the culture broth of Chaetoconis sp. FT087. Their structures were determined through the analysis of HRMS and NMR spectroscopic data. The absolute configurations of chaetopenoids A-D were elucidated by comparison of their CD and optical rotation data with those in the literature. Chaetopenoids A-C and E belong to the eremophilane type of sesquiterpenoids, while chaetopenoids D and F and dendryphiellin A1 have a trinor-eremophilane skeleton. All compounds were tested against A2780 and cisplatin resistant A2780CisR cell lines, and dendryphiellin A1 was moderately active with IC50 values of 6.6 and 9.1 μg/mL, respectively.

Hawaii natural compounds are promising to reduce ovarian cancer deaths

The low survival rate of patients with ovarian cancer largely results from the advanced ovarian tumors as well as tumor resistance to chemotherapy, leading to metastasis and recurrence. However, it is missing as to an effective therapeutic approach that focuses on these aspects to prolong progression-free survival and to decrease mortality in ovarian cancer patients. Here, based on our cancer drug discovery studies, we provide prospective insights into the development of a future line of drugs to effectively reduce ovarian cancer deaths. Pathways that increase the probability of cancer, such as the defective Fanconi anemia (FA) pathway, may render cancer cells more sensitive to new drug targeting.

Meroterpenoids with Antiproliferative Activity from a Hawaiian-Plant Associated Fungus Peyronellaea coffeae-arabicae FT238

Three unusual polyketide-sesquiterpene metabolites peyronellins A-C (1-3), along with the new epoxyphomalin analog 11-dehydroxy epoxyphomalin A (4), have been isolated from the endophytic fungus Peyronellaea coffeae-arabicae FT238, which was isolated from the native Hawaiian plant Pritchardia lowreyana. The structures of compounds 1-4 were characterized based on NMR and MS spectroscopic analysis. The absolute configuration (AC) of the compounds was determined by electronic circular dichroism (ECD). Compound 4 showed antiproliferative activity with an IC50 of 0.5 μM against OVCAR3, and it also strongly inhibited Stat3 at 5 μM.

Accessing Nature's diversity through metabolic engineering and synthetic biology

In this perspective, we highlight recent examples and trends in metabolic engineering and synthetic biology that demonstrate the synthetic potential of enzyme and pathway engineering for natural product discovery. In doing so, we introduce natural paradigms of secondary metabolism whereby simple carbon substrates are combined into complex molecules through “scaffold diversification”, and subsequent “derivatization” of these scaffolds is used to synthesize distinct complex natural products. We provide examples in which modern pathway engineering efforts including combinatorial biosynthesis and biological retrosynthesis can be coupled to directed enzyme evolution and rational enzyme engineering to allow access to the “privileged” chemical space of natural products in industry-proven microbes. Finally, we forecast the potential to produce natural product-like discovery platforms in biological systems that are amenable to single-step discovery, validation, and synthesis for streamlined discovery and production of biologically active agents.