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Article

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

by
Mallique Qader
1,†,
KH Ahammad Uz Zaman
1,†,
Zhenquan Hu
2,3,
Cong Wang
1,4,
Xiaohua Wu
1 and
Shugeng Cao
1,*
1
Department of Pharmaceutical Sciences, Daniel K. Inouye College of Pharmacy, University of Hawai’i at Hilo, Hilo, HI 96720, USA
2
Warshel Institute for Computational Biology, The Chinese University of Hong Kong, Shenzhen 518172, China
3
School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, China
4
Guangxi Key Laboratory of Chemistry and Chemical Engineering of Forest Products, School of Chemistry for Nationalities, Nanning 530006, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Molecules 2021, 26(14), 4239; https://doi.org/10.3390/molecules26144239
Submission received: 16 June 2021 / Revised: 7 July 2021 / Accepted: 9 July 2021 / Published: 12 July 2021
(This article belongs to the Special Issue Natural Products Discovery and Development: A Themed Issue Dedicated to Professor Leslie Gunatilaka)
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Abstract

:
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).

1. Introduction

Searching for antimicrobial agents has become one of the major research fields in natural products chemistry [1,2] because the development of pathogens resistant to the clinically used antimicrobials has been increasing alarmingly day by day [3,4]. Therefore, the usage of initially discovered antibiotics and antifungal drugs in treating human diseases has been greatly reduced [5]. Hence, there is an urgent need for new antibiotics in order to tackle, in particular, antimicrobial resistance. The accidental discovery of first broad spectrum antibiotic penicillin from the fungus Penicillium notatum has marked the starting point of the antibiotic’s era [6]. The diversity and the distribution of the fungi in a diverse array of habitats categorized them as an understudied group of organisms [7]. Fungi are considered remarkable and valuable organisms as they have provided the world with medicinally important drugs such as antibiotics, anticancer agents, cholesterol lowering statins, immunomodulators, and agriculturally important herbicides and weedicides, and they are environmentally important as decomposers and for the distribution of nutrients [8,9,10,11].
Fungi harbored in untapped and unique environments produce new compounds with greater biological activity. Endophytic fungi that inhabit plant tissues are a widely studied group of organisms as they live inside the plant tissues without having any adverse effect on the plants [8,9,10,11]. Additionally, they are capable of biosynthesizing similar chemicals which are produced by the plant or new compounds that plants could not synthesize by themselves [12]. Therefore, endophytic fungi have recently become popularized in the field of drug discovery following the discovery of the million-dollar anticancer drug Taxol from the fungal endophyte Taxomyces andreanae, which was isolated from the inner bark of the Pacific yew, Taxus brevifolia [13].
Aspergillus is one of the dominant and most studied fungal genera in endophytes [14]. The World Data Centre for Microorganisms (WDCM) has reported around 380 species in the Aspergillus genus [14]. More than 350 new fungal metabolites have been discovered during 2015–2019 [14]. Therefore, these filamentous fungi are described as one of the richest sources of bioactive fungal secondary metabolites with a great chemical and biological diversity [14,15].
Since the diversity and abundance of fungi are excessive, their presence in different ecosystems makes them an ideal source of drug discovery [7]. Hawai’i has 10 out of 14 world climatic zones. These diverse climatic, ecological and geographical features have made Hawai’i a home for organisms with a vast diversity. Our studies over the past few years disclosed that fungi isolated from different Hawaiian sources such as soil, plants and the marine environment showed a great chemical and biological diversity [16,17,18,19,20,21,22,23,24].
As part of our continuing search for new and biologically active compounds from Hawaiian fungi, six fungal endophytes were isolated from the leaves of Heliotropium sp. (family Boraginaceae) (http://theplantlist.org, accessed on 28 June 2021). The crude extracts obtained from a small-scale fermentation of these fungi were evaluated for their antibacterial activity, but only FT1307 showed inhibition against the methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (at 80 μg/mL). This observation led us to further study the fungal strain Aspergillus sp. FT1307 and to identify the antimicrobial compounds. A new cyclic aspochalasin (1) together with nine known fungal metabolites (2–10) (Figure 1) were isolated, and their structures were determined. Herein we report the large-scale fermentation, isolation and structure elucidation of the fungal metabolites and their antimicrobial activity against a panel of pathogenic microorganisms, together with their antiproliferative activity.

2. Results and Discussion

Compound 1 was obtained as oil. The molecular formula C24H35NO5 with eight degrees of unsaturation was established by the positive mode quasi-molecular ion peaks at m/z 418.2592 for [M + H]+ (calcd. 418.2593 for C24H36NO5) and m/z 440.2398 for [M + Na]+ (calcd. 440.2413 for C24H35NO5Na) in combination with its NMR data. The 1H NMR together with heteronuclear single quantum coherence (HSQC) spectra revealed the presence of five methyl groups [δH 0.90 (d, J = 2.5 Hz), 0.91 (d, J = 2.5 Hz), 1.21 (d, J = 7.0 Hz), 1.42 (s), 1.76 (s)], two olefinic protons [δH 5.39 (s), 6.04 (d, J = 11.0 Hz)], four oxygenated methine protons [δH 2.82 (s), 3.78 (m, overlapped), 3.80 (m, overlapped), 4.40 (d, J = 1.9 Hz)], three methylene protons including two diastereotopic methylenes [δH 1.29 (m), 2.29/2.10 (m), 1.76/1.63 (m)] and five aliphatic methine protons [δH 1.56 (m), 2.60 (m), 2.64 (m), 3.02 (d, J = 11.5 Hz), 3.10 (d, J = 10.0 Hz)]. In addition, five quaternary carbons were extracted from the heteronuclear multiple bond correlation (HMBC) spectrum, including one keto carbonyl (δC 208.0), one amide carbonyl (δC 174.6), two sp2-quaternary carbons (δC 135.6, 140.6) and one sp3-quaternary carbon at δC 68.4 (Table 1). These features supported the characteristic aspochalasin skeleton [25]. A detailed NMR data analysis and further literature search showed the close similarity of 1 to the previously isolated compound aspochalasin H [26] (Table 1). Due to the obvious 13C chemical shift difference in the stereocenters (C-17, C-18, C-19 and C-20) of 1 from the NMR data of aspochalasin H (δC aspochalasin H/compound 1: C-17, 72.9/70.8; C-18, 78.4/73.4; C-19, 61.7/60.5; C-20, 54.7/52.2), we concluded that 1 was a stereoisomer of aspochalasin H, probably with a different diol orientation. 2D ROESY provided important information on the proton signals arising from each proton through the space, even though they were not bonded to each other. The ROESY experiment showed correlations between H-4 and H-8, between H-4 and H-10, and between H-3 and H-11, which were identical to the isoindolone moiety of the reported cytochalasans, especially aspochalasin H [26], except H-17, H-18, H-19 and H-20. The small coupling constant (J = 1.9 Hz) between H-19 and H-20 indicated a trans epoxide, which was the same as that in aspochalasin H [26]. Moreover, the ROESY and NOE correlations between H-19 and H-17 and between H-13 and H-17 revealed an alpha (α) orientation of H-17 (Figure 2) and probably a beta (β) orientation of H-18. If H-17 were in a beta (β) orientation, it would be impossible to have a NOE correlation between H-13 and H-17.
To confirm the absolute configuration of compound 1, advanced computational quantum chemical calculations were carried out. The NMR of eight stereoisomers (Supplementary Information, Table S1) were calculated, among which the calculated NMR data of the 17R, 18S, 19S, 20R and 17R, 18S, 19R, 20R isomers matched those of the experimental data of 1 better than the other six isomers. Electronic Circular Dichroism (ECD) is a very sensitive and nondestructive experimental technique, which may provide a powerful approach to the determination of the absolute configurations of the molecule [27]. Both the experimental ECD of 1 and the calculated ECDs of the 17R, 18S, 19S and 20R isomer together with the 17R, 18S, 19R and 20R isomer showed a strong positive Cotton effect at 225 nm (Figure S9). We then carried out a conformation analysis (Figure S10). In all the main stable conformers of 17R, 18S, 19S, 20R and 17R, 18S, 19R, 20R isomers, H-19/H-17 were in the axial/equatorial orientations in the 11-member ring, respectively. H-18 was equatorial in the 17R, 18S, 19S, 20R isomer and axial in the 17R, 18S, 19R, 20R isomer. Since H-17 and H-18 were overlapped in CDCl3, we collected 1H NMR of 1 in DMSO-d6. The 1H NMR spectrum of 1 in DMSO-d6 showed that H-19 was still a singlet and H-18 was a doublet with a coupling constant of about 10 Hz. Only H-18 in equatorial form (17R, 18S, 19S, 20R) could meet the H-H coupling requirement of the experimental results. Hence, the absolute configuration of 1 was determined to be 17R, 18S, 19S, 20R.
The other isolated known metabolites from Aspergillus sp. FT1307 were structurally characterized by comparing their NMR and optical rotation data with the literature and were identified as aspochalasin P (2) [28], alatinone (3) [29], dimerumic acid (4) [30], NBRI-16716B (N,5-dihydroxy-N-(3-5-(3-(N-hydroxyacetamido)propyl)-3,6-dioxopiperazin-2-yl)propyl)-3-methylpent-2-enamide)) (5) [31], α-11-hydroxyurvularine (6) [32], β-11-hydroxycurvularine (7) [32], β-11-methoxy curvularine (8) [32], 12-keto-10,11-dehydrocurvularine (9) [33] and WIN66306 (10) [34].
All the isolated compounds were tested for their antibacterial activity against pathogenic Staphylococcus aureus ATCC12600 (Gram-positive), Bacillus subtilis ATCC6633 (Gram-negative) and methicillin-resistant S. aureus ATCC43300 (MRSA). Compounds 2, 3, 8 and 9 showed weak activity in the range of 40 to 80 μg/mL (Table 2). Further, structural features of aspochalasins and their contribution to the bioactivity have been previously studied [35]. Flashner and co. [35] showed that the α,β-ketounsaturation in the 11-membered macrolide ring was responsible for antibacterial inhibitory activity, specifically against Gram-positive pathogenic bacteria [35].
Compounds 1–10 were also evaluated for their antiproliferative activity against MCF-7 (Human breast cancer cell line), T46D (Human breast cancer cell line) and A2780 (Human ovarian cancer cell line). Only compounds 2 and 8 showed a mild antiproliferative activity against the A2780 ovarian cancer cell line with IC50 values of 17.29 µM and 11.76 µM, respectively. Compounds 1–10 were further tested against an immortalized human vascular endothelial cell (EA.hy926) for their cytotoxicity effect, and they did not show any significant inhibition against EA.hy926 at the tested concentrations (50 μM).

3. Materials and Methods

3.1. General Experimental Procedures

Optical rotations, CD and IR spectra were measured with a Rudolph Research analytical AutoPol automatic polarimeter (Rudolph Research Analytical, Hackettstown, NJ, USA), JASCO J-815 CD (Jasco Corporation, Tokyo, Japan) and Thermo Scientific Nicolet iS10 IR spectrometer (Thermo Fisher Scientific, Madison, WI, USA), respectively. The structure characterizations of all the compounds were based on 1D NMR (1H, 13C) and 2D NMR (COSY, HSQC, HMBC, 1D-NOE and ROESY) data, recorded on a Bruker AM-400 spectrometer (Bruker BioSpin AG, Faellanden, Switzerland). An Agilent 6530 Accurate-Mass Q-TOF LC-MS spectrometer (Agilent Technologies, Waldbronn, Germany) was used to record high-resolution mass spectra. Preparative RP-HPLC was carried out on an Ultimate 3000 chromatographic system (Agilent Technologies, Waldbronn, Germany) with a Phenomenex preparative column (Phenyl-hexyl, 5 μ, 100 × 21.2 mm) and semipreparative RP-HPLC on an Ultimate 3000 chromatographic system (Agilent Technologies, Waldbronn, Germany) with a Phenomenex semipreparative column (C18, 5 μ, 250 × 10 mm), connected to a Dionex Ultimate 3000 DAD detector (Agilent Technologies, Waldbronn, Germany) (detected at 210, 254, 320 and 365 nm) and a Dionex Ultimate 3000 automated fraction collector. All solvents were HPLC grade. Diaion HP-20 (Alfa Aesar, Japan) was used to run the open-column chromatography.

3.2. Sample Collection and Fungi Isolation

Healthy and disease-free leaves from a plant were collected from Big Island, Hawai’i (155°3′15.51″ W 19°43′53.63″ N) in February 2020, and they were morphologically identified as Heliotropium sp. (family Boraginaceae). The voucher specimen was deposited at Daniel K. Inouye College of Pharmacy, University of Hawai’i at Hilo, HI, USA (Code: MQ21-2020). Leaves were washed thoroughly with running tap water and surface-sterilized in 70% ethanol for 1 min, in sterile distilled water for 1 min, in 2.5% sodium hypochlorite (NaOCl) for 1 min and again in sterile distilled water. The procedure was repeated three times to ensure the removal of surface-dwelling microorganisms. The sterilized samples were left on sterile filter papers for drying, then cut into small segments, placed on potato dextrose agar (PDA) and incubated at room temperature for 7–14 days. The growing fungi were removed before seven days to ensure the isolation of endophytic fungi. After the incubation, six morphologically different fungi were isolated and serially sub-cultured to potato dextrose agar (PDA)-containing Petri dishes until pure colonies were formed. Pure strains were maintained at −80 °C in 50% glycerol and deposited at Daniel K. Inouye College of Pharmacy, University of Hawai’i at Hilo, HI, USA (Code: MQ-FT1307-2020).

3.3. Molecular Identification of the Endophytic Fungi

The strain FT1307 was grown on liquid potato dextrose broth (PDB) media for 28 days, and the mycelium was harvested under aseptic conditions. About 300 μg of the mycelium was crushed using liquid nitrogen into fine powder. Then, DNA extraction, amplification and sequencing of the Internal Transcribe Spacer regions using the primers ITS1 and ITS4 were carried out as described in our previously published articles [12,13,14,15,16,17,18,19,20]. The BLAST search indicated that the sequence of the ITS region had a 98% similarity score between two Aspergillus species. Hence, strain FT1307 was unable to be identified to the species level. Therefore, FT1307 was identified as the unknown Aspergillus sp., and the sequence was deposited in the NCBI Gene Bank under Accession No. MW774248.

3.4. Fermentation and Extraction

Equal size agar plugs with the mycelium of the pure FT1307 fungus grown on PDA media for five days was aseptically transferred to liquid broth media-containing 1-L conical flasks (350 mL × 65 for the large scale; 350 mL × 3 for the small scale). The liquid broth media consisted of mannitol 20 g, sucrose 10 g, monosodium glutamate 5 g, KH2PO4 0.5 g, MgSO4·7H2O 0.3 g and 3 g of yeast extract dissolved in 1 L of distilled water (pH of the liquid media adjusted to 6.5 before sterilization). Then, the media flasks were sterilized for 15 min at 121 °C. The inoculated flasks were fermented for 28 days at 24 °C under static conditions. After the completion of the fermentation period, extraction was carried out as described in our previous publications [18,19] with slight modifications. Aqueous mycelium and broth media treated with Diaion HP-20 resins were loaded into an open column and separated using different concentrations of MeOH/H2O systems (10, 50, 90 and 100% MeOH) as the eluent. The 90% and 100% fractions shared a similar RP-HPLC profile. Hence, both fractions were combined (3.5 g) and subjected to further purification.

3.5. Isolation of Fungal Secondary Metabolites

Combined fractions were initially purified by using preparative RP-HPLC (Phenyl-hexyl column, 100 × 21.20 mm, 5 μ, 8 mL/min) eluted with 40−100% MeOH/H2O in 20 min to yield 26 subfractions (SFr 1−26). SFr 4 and 5 were combined (170 mg) and purified using semipreparative RP-HPLC (30% isocratic MeOH/H2O, 1.0% formic acid, 3.0 mL/min for 20 min) over a C18 column to furnish compound 4 (tR 9.8 min, 2.5 mg). SFr 8 (150 mg) was purified using semipreparative RP-HPLC (40% isocratic MeOH/H2O, 1.0% formic acid, 3.0 mL/min for 20 min) over a C18 column to afford compounds 5 (tR 11.8 min, 2.0 mg) and 7 (tR 15.5 min, 2.0 mg). SFr 10 (170 mg) was purified using semipreparative RP-HPLC (50% isocratic MeOH/H2O, 1.0% formic acid, 3.0 mL/min for 20 min) over a C18 column to afford compounds 6 (tR 12.4 min, 2.0 mg) and 3 (tR 15.5 min, 2.0 mg). SFr 11–14 were combined due to a low yield (120 mg) and purified using semipreparative RP-HPLC (60% isocratic MeOH/H2O, 1.0% formic acid, 3.0 mL/min for 20 min) over a C18 column to afford compounds 8 (tR 8.8 min, 1.5 mg) and 9 (tR 18.2 min, 1.5 mg). SFr 16 was (100 mg) purified using semipreparative RP-HPLC (60% isocratic MeOH/H2O, 1.0% formic acid, 3.0 mL/min for 20 min) over a C18 column to afford compound 10 (tR 20.1 min, 5.0 mg). SFr 17 was (150 mg) purified using semipreparative RP-HPLC (70% isocratic MeOH/H2O, 1.0% formic acid, 3.0 mL/min for 20 min) over a C18 column to afford compounds 1 (tR 13.2 min, 2.0 mg) and 2 (tR 17.9 min, 5.0 mg).
Aspochalasin H1 (1): oil; [α]25 = 25 (c = 0.12, MeOH). UV (MeOH): λmax (log ε) = 208 (2.90) nm. IR (KBr): νmax = 3327, 2945, 2835, 1652, 1452, 1114, 1016 cm−1. 1H and 13C NMR: See Table 1. HR-ESI-MS m/z 418.2592 [M + H]+ (calc. 418.2593) 440.2398 [M + Na]+ (calc. 440.2413) for C24H35NO5.

3.6. Computational Methods

The ECD and NMR computational calculations were carried out as previously described in our publications [36,37].

3.7. Antibacterial Assay

The assay was carried out according to the EUCAST guidelines with modifications. Bacteria were grown on agar plates containing tryptic soy agar (TSA) or Brain Heart Infusion (BHI)] for 24 h at 37 °C and then added to the corresponding broth medium (TSB for S. aureus and methicillin-resistant S. aureus, and BHI for B. subtilis). After incubation at 37 °C overnight, cultures were diluted with TSB or BHI media to obtain an absorbance of 0.1 at OD600 (McFarland 0.5 and 5 × 105 CFU/mL). The bacteria-containing media (100 μL) were then added to each well of 96-well plates, containing each compound dissolved in 0.5% DMSO solution (100 μL) in TSB or BHI media. Then, the 96-well plates were incubated at 37 °C for 18 h. After 18 h, twenty microliters of resazurin dye (0.015%) were then added to each well and further incubated for 2–3 h at 37 °C. The color change (blue to pink) was visually observed. 1% DMSO was used as the negative control, whereas chloramphenicol was used as the positive control, which was active against S. aureus, multidrug-resistant S. aureus and B. subtilis with MIC values ranging from 5 µg/mL to 10 µg/mL. All experiments were performed in triplicate. The compounds were tested from a 0.625 to 80 µg/mL concentration range.
The Minimum Inhibitory Concentration (MIC) is defined as the lowest concentration of a drug or compound/s that inhibits the visible growth of a bacterial organism after a specific incubation time [38].

3.8. Cell Viability Assay

An MTT assay was performed to estimate the viability of two human breast cancer cell lines (MCF-7 and T46D), one human ovarian cancer cell line (A2780) and one healthy human cell line (immortalized human vascular endothelial cell/EA.hy926). Cells (1 × 104 per well) were seeded in 96-well plates, cultured at 37 °C in a 5% CO2 incubator for 24 h, and then incubated with or without the compounds for 24 h. The culture medium was carefully removed, and 200 μL of DMSO was added per well to dissolve the formed precipitate. Plates were shaken for 10 s, and the absorbance was measured at a wavelength of 570 nm on a microplate reader (BIO-TEK instruments, Inc., Winooski, VT, USA).

4. Conclusions

In conclusion, ten compounds (1–10) including a new cyclic aspochalasin H1 (1) were isolated from a Hawaiian plant-associated endophytic fungus, Aspergillus sp. FT1307. Compound 1 is a stereoisomer of aspochalasin H with an adjacent trans-diol configuration. Compounds 1–10 were evaluated for their antibacterial activity against Gram-positive and Gram-negative bacteria as well as for their antiproliferative activities against A2780, MCF-7 and T46D cell lines. Compounds 2, 3, 8 and 9 showed moderate antibacterial activity against gram-positive bacteria, and compounds 2 and 8 also showed antiproliferative activity against the A2780 ovarian cancer cell line. The finding of the current study indicates that the Hawaiian environment is an arsenal of fungi that can produce new and bioactive compounds.

Supplementary Materials

The following are available online. 1D and 2D NMR, CD spectra of compound 1.

Author Contributions

M.Q. and K.A.U.Z. performed the experiments; K.A.U.Z. and X.W. conducted the bioassays and identification of fungus; Z.H. conducted the computational work and analyzed the data; M.Q., K.A.U.Z., C.W., X.W. and S.C. analyzed the data; M.Q. wrote the paper; S.C. initiated the project, supervised the study and revised the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the Hawaii Community Foundation (20CON-102163) (to SC). Funding for this work was also supported by the Hawaii IDeA Network for Biomedical Research Excellence IV (INBRE-IV) project (NIGMS Grant 5P20GM103466).

Acknowledgments

The authors would like to express their gratitude to Justin Reinicke for his support in collecting NMR, UV and optical rotation data.

Conflicts of Interest

The authors declare no conflict of interest. The funding sponsors had no role in the design of the study; in collection, analysis, or interpretation of data; in writing the manuscript, and in the publishing the results.

Sample Availability

Samples of the compounds are not available.

References

  1. Rossiter, S.E.; Fletcher, M.H.; Wuest, W.M. Natural products as platforms to overcome antibiotic resistance. Chem. Rev. 2017, 117, 12415–12474. [Google Scholar] [CrossRef]
  2. Atanasov, A.G.; Zotchev, S.B.; Dirsch, V.M.; Supuran, C.T. Natural products in drug discovery: Advances and opportunities. Nat. Rev. Drug Discov. 2021, 20, 1–17. [Google Scholar] [CrossRef] [PubMed]
  3. Fair, R.J.; Tor, Y. Antibiotics and bacterial resistance in the 21st century. Perspect. Med. Chem. 2014, 6, PMC-S14459. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  4. Prestinaci, F.; Pezzotti, P.; Pantosti, A. Antimicrobial resistance: A global multifaceted phenomenon. Pathog. Glob. Health 2015, 109, 309–318. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  5. Aminov, R.I. A brief history of the antibiotic era: Lessons learned and challenges for the future. Front. Microbiol. 2010, 1, 134. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  6. Gaynes, R. The discovery of penicillin—New insights after more than 75 years of clinical use. Emerg. Infect. Dis. 2017, 23, 849. [Google Scholar] [CrossRef]
  7. Hyde, K.D.; Xu, J.; Rapior, S.; Jeewon, R.; Lumyong, S.; Niego, A.G.T.; Abeywickrama, P.D.; Aluthmuhandiram, J.V.; Brahamanage, R.S.; Brooks, S.; et al. The amazing potential of fungi: 50 ways we can exploit fungi industrially. Fungal Divers. 2019, 97, 1–136. [Google Scholar]
  8. Strobel, G.; Daisy, B.; Castillo, U.; Harper, J. Natural products from endophytic microorganisms. J. Nat. Prod. 2014, 67, 257–268. [Google Scholar] [CrossRef]
  9. Strobel, G. Harnessing endophytes for industrial microbiology. Curr. Opin. Microbiol. 2006, 9, 240–244. [Google Scholar] [CrossRef]
  10. Newman, D.J.; Cragg, G.M. Natural products as sources of new drugs over the last 25 years. J. Nat. Prod. 2007, 70, 461–477. [Google Scholar] [CrossRef] [Green Version]
  11. Gunatilaka, L. Natural products from plant-associated microorganisms: Distribution, structural diversity, bioactivity, and implications of their occurrence. J. Nat. Prod. 2006, 69, 509–526. [Google Scholar] [CrossRef] [Green Version]
  12. Nisa, H.; Kamili, A.N.; Nawchoo, I.A.; Shafi, S.; Shameem, N.; Bandh, S.A. Fungal endophytes as prolific source of phytochemicals and other bioactive natural products: A review. Microb. Pathog. 2015, 82, 50–59. [Google Scholar] [CrossRef] [PubMed]
  13. Strobel, G.A.; Hess, W.M.; Ford, E.; Sidhu, R.S.; Yang, X. Taxol from fungal endophytes and the issue of biodiversity. J. Ind. Microbiol. 1996, 17, 417–423. [Google Scholar] [CrossRef]
  14. Vadlapudi, V.; Borah, N.; Yellusani, K.R.; Gade, S.; Reddy, P.; Rajamanikyam, M.; Vempati, L.N.S.; Gubbala, S.P.; Chopra, P.; Upadhyayula, S.M.; et al. Aspergillus secondary metabolite database, a resource to understand the secondary metabolome of Aspergillus genus. Sci. Rep. 2017, 7, 7325. [Google Scholar]
  15. El-hawary, S.S.; Moawad, A.S.; Bahr, H.S.; Abdelmohsen, U.R.; Mohammed, R. Natural product diversity from the endophytic fungi of the genus Aspergillus. RSC Adv. 2020, 10, 22058–22079. [Google Scholar] [CrossRef]
  16. Li, C.; Yang, B.J.; Turkson, J.; Cao, S. Anti-proliferative ambuic acid derivatives from Hawaiian endophytic fungus Pestalotiopsis sp. FT172. Phytochemistry 2017, 140, 77–82. [Google Scholar] [CrossRef] [PubMed]
  17. Li, C.; Sarotti, A.M.; Turkson, J.; Cao, S. Verbenanone, an octahydro-5H-chromen-5-one from a Hawaiian-plant associated fungus FT431. Tetrahedron Lett. 2017, 58, 2290–2293. [Google Scholar] [CrossRef]
  18. Li, C.; Sarotti, A.M.; Huang, P.; Dang, U.T.; Hurdle, J.G.; Kondratyuk, T.P.; Pezzuto, J.M.; Turkson, J.; Cao, S. NF-κB inhibitors, unique γ-pyranol-γ-lactams with sulfide and sulfoxide moieties from Hawaiian plant Lycopodiella cernua derived fungus Paraphaeosphaeria neglecta FT462. Sci. Rep. 2017, 7, 10424. [Google Scholar]
  19. Li, C.; Sarotti, A.M.; Wu, X.; Yang, B.; Turkson, J.; Chen, Y.; Liu, Q.; Cao, S. An unusual benzoisoquinoline-9-one derivative and other related compounds with antiproliferative activity from Hawaiian endophytic fungus Peyronellaea sp. FT431. Molecules 2019, 24, 196. [Google Scholar] [CrossRef] [Green Version]
  20. Wang, F.; Hu, Z.; Li, C.; Wu, X.; Cao, S. Circumdatin M, a new benzodiazepine alkaloid with a unique pyrimidone-4-pyrone moiety from a Hawaiian marine fungus Aspergillus sp. FM242. Tetrahedron Lett. 2019, 60, 1724–1726. [Google Scholar] [CrossRef]
  21. Yu, J.S.; Li, C.; Kwon, M.; Oh, T.; Lee, T.H.; Kim, D.H.; Ahn, J.S.; Ko, S.K.; Kim, C.S.; Cao, S.; et al. Herqueilenone A, a unique rearranged benzoquinone-chromanone from the Hawaiian volcanic soil-associated fungal strain Penicillium herquei FT729. Bioorg. Chem. 2020, 105, 104397. [Google Scholar] [CrossRef] [PubMed]
  22. Zaman, K.A.U.; Wu, X.; Hu, Z.; Yoshida, W.; Hou, S.; Saito, J.; Avad, K.A.; Hevener, K.E.; Alumasa, J.N.; Cao, S. Antibacterial kaneoheoic acids A-F from a Hawaiian fungus Fusarium sp. FM701. Phytochemistry 2021, 181, 112545. [Google Scholar] [CrossRef] [PubMed]
  23. Wang, C.; Wu, X.; Bai, H.; Zaman, K.A.U.; Hou, S.; Saito, J.; Wongwiwatthananukit, S.; Kim, K.S.; Cao, S. Antibacterial and NF-κB inhibitory lumazine peptides, aspochalasin, γ-butyrolactone derivatives, and cyclic peptides from a Hawaiian Aspergillus flavipes. J. Nat. Prod. 2020, 83, 2233–2240. [Google Scholar] [CrossRef] [PubMed]
  24. Wang, F.; Sarotti, A.M.; Jiang, G.; Huguet-Tapia, J.C.; Zheng, L.; Wu, X.; Li, C.; Ding, Y.; Cao, S. Waikikiamides A–C: Complex diketopiperazine dimer and diketopiperazine–polyketide hybrids from a Hawaiian marine fungal strain Aspergillus sp. FM242. Org. Lett. 2020, 22, 4408–4412. [Google Scholar] [CrossRef] [PubMed]
  25. Keller-Schierlein, W.; Kupfer, E. Stoffwechselprodukte von mikroorganismen. 186. mitteilung. über die aspochalasine A, B, C and D. Helv. Chim. Acta 1979, 62, 1501–1524. [Google Scholar] [CrossRef]
  26. Tomikawa, T.; Shin-Ya, K.; Seto, H.; Okusa, N.; Kajiura, T.; Hayakawa, Y. Structure of aspochalasin H, a new member of the aspochalasin family. J. Antibiot. 2002, 55, 666–668. [Google Scholar] [CrossRef] [Green Version]
  27. Li, C.; Ferreira, D.; Ding, Y. Determination of absolute configuration of natural products: Theoretical calculation of electronic circular dichroism as a tool. Curr. Org. Chem. 2010, 14, 1678–1697. [Google Scholar] [CrossRef] [PubMed]
  28. Lin, Z.; Zhu, T.; Wei, H.; Zhang, G.; Wang, H.; Gu, Q. Spicochalasin A and new aspochalasins from the marine-derived fungus Spicaria elegans. Eur. J. Org. Chem. 2009, 3045–3051. [Google Scholar] [CrossRef]
  29. Sun, R.; Miao, F.P.; Zhang, J.; Wang, G.; Yin, X.L.; Ji, N.Y. Three new xanthone derivatives from an algicolous isolate of Aspergillus wentii. Magn. Reson. Chem. 2013, 51, 65–68. [Google Scholar] [CrossRef]
  30. Krasnoff, S.B.; Howe, K.J.; Heck, M.L.; Donzelli, G. Siderophores from the entomopathogenic fungus Beauveria bassiana. J. Nat. Prod. 2020, 83, 296–304. [Google Scholar] [CrossRef] [PubMed]
  31. Kawada, M.; Someno, T.; Inoue, H.; Ohba, I.; Masuda, T.; Kato, T.; Ikeda, D. NBRI16716A, a new antitumor compound against human prostate cancer cells, produced by Perisporiopsis melioloides Mer-f16716. J. Antibiot. 2010, 63, 319–323. [Google Scholar] [CrossRef]
  32. Lai, S.; Shizuri, Y.; Yamamura, S.; Kawai, K.; Furukawa, H. New curvularin-type metabolites from the hybrid strain ME 0005 derived from Penicillium citreo-viride B. IFO 4692 and 6200. Bull. Chem. Soc. Jpn. 1991, 64, 1048–1050. [Google Scholar] [CrossRef] [Green Version]
  33. de Castro, M.V.; Ióca, L.P.; Williams, D.E.; Costa, B.Z.; Mizuno, C.M.; Santos, F.; de Jesus, K.; Ferreira, L.; Seleghim, H.; Sette, L.D.; et al. Condensation of macrocyclic polyketides produced by Penicillium sp. DRF2 with mercaptopyruvate represents a new fungal detoxification pathway. J. Nat. Prod. 2016, 79, 1668–1678. [Google Scholar] [CrossRef]
  34. Barrow, C.J.; Doleman, M.S.; Bobko, M.A.; Cooper, R. Structure, determination, pharmacological evaluation, and structure-activity studies of a new cyclic peptide substance P antagonist containing the new amino acid 3-prenyl-β-hydroxytyrosine isolated from Aspergillus flavipes. J. Med. Chem. 1994, 37, 356–363. [Google Scholar] [CrossRef]
  35. Flashner, M.; Rasmussen, J.; Patwardhan, B.H.; Tanenbaum, S.W. Structural features of cytochalasins responsible for Gram-positive bacterial inhibitions. J. Antibiot. 1982, 35, 1345–1350. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  36. Li, C.S.; Ding, Y.; Yang, B.J.; Miklossy, G.; Yin, H.Q.; Walker, L.A.; Turkson, J.; Cao, S. A new metabolite with an unique 4-pyranone−γ-lactam–1,4-thiazine moiety from a Hawaiian-plant associated fungus. Org. Lett. 2015, 17, 3556–3559. [Google Scholar] [CrossRef] [PubMed]
  37. Wang, Q.; Hu, Z.; Li, X.; Wang, A.; Wu, H.; Liu, J.; Cao, S.; Liu, Q. Salviachinensines A–F, Antiproliferative phenolic derivatives from the Chinese medicinal plant Salvia chinensis. J. Nat. Prod. 2018, 81, 2531–2538. [Google Scholar] [CrossRef] [PubMed]
  38. Andrews, J.M. Determination of minimum inhibitory concentrations. J. Antimicrob. Chemother. 2001, 48, 48–71. [Google Scholar] [CrossRef] [Green Version]
Molecules 26 04239 g001 550
Figure 1. Structures of compounds 1–10.
Figure 1. Structures of compounds 1–10.
Molecules 26 04239 g001
Molecules 26 04239 g002 550
Figure 2. 1H-1H COSY, HMBC and ROESY correlations of 1.
Figure 2. 1H-1H COSY, HMBC and ROESY correlations of 1.
Molecules 26 04239 g002
Table
Table 1. 13C (100 MHz) and 1H (400 MHz) NMR assignments for compound 1 in CDCl3.
Table 1. 13C (100 MHz) and 1H (400 MHz) NMR assignments for compound 1 in CDCl3.
No.δCδH
(Multiplicity, J in Hz)		δC [a]δH
(Multiplicity, J in Hz) [a]
1174.6-174.6-
2-NH-6.32 (brs)-6.06 (brs)
351.63.10 (d,10.0)51.73.08 (dt, 10.0, 3.5)
452.92.64 (m)52.82.64 (d, 3.5)
535.42.60 (m)35.42.58 (m)
6140.6-140.7-
7125.65.39 (s)125.55.38 (m)
843.83.02 (d,11.5)44.13.02 (d, 11.0)
968.4-67.4-
1048.81.29 (m)48.61.29, 1.19 (m)
1113.71.21 (d, 7.0)13.71.19 (d, 7.0)
1220.11.76 (s)20.11.75 (s)
13125.26.04 (d, 11.0)124.65.98 (d, 11.0)
14135.6-136.0-
1538.82.29, 2.10 (m)38.92.25, 2.11 (m)
1631.01.76, 1.63 (m)29.32.12, 1.53 (m)
1770.83.78 (m, overlapped)72.94.04 (s)
1873.73.80 (m, overlapped)78.43.37 (d, 7.0)
1960.52.82 (s)61.72.62 (dd, 7.0, 1.5)
2052.24.40 (d, 1.9)54.74.19 (d, 1.5)
21208.0-205.6-
2225.21.56 (m)25.21.53 (m)
2323.70.91 (d, 2.5)23.60.90 (d, 6.0)
2421.40.90 (d, 2.5)21.20.88 (d, 6.0)
2515.51.42 (s)15.51.42 (s)
[a] Reference 13C (125 MHz) and 1H (500 MHz) NMR data for aspochalasin H in CDCl3 [26]. 13C NMR data of 1 was extracted from the HSQC and HMBC spectra.
Table
Table 2. MIC (μg/mL) of the tested compounds.
Table 2. MIC (μg/mL) of the tested compounds.
Compound No.Staphylococcus aureus ATCC12600Methicillin-Resistant S. aureus ATCC43300Bacillus subtilis ATCC6633
2**40
3404040
8**80
9404080
Chloramphenicol5510
1, 4–7 and 10 were not active at 80 μg/mL; * MIC ≥ 80 μg/mL.
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Qader, M.; Zaman, K.A.U.; Hu, Z.; Wang, C.; Wu, X.; Cao, S. Aspochalasin H1: A New Cyclic Aspochalasin from Hawaiian Plant-Associated Endophytic Fungus Aspergillus sp. FT1307. Molecules 2021, 26, 4239. https://doi.org/10.3390/molecules26144239

AMA Style

Qader M, Zaman KAU, Hu Z, Wang C, Wu X, Cao S. Aspochalasin H1: A New Cyclic Aspochalasin from Hawaiian Plant-Associated Endophytic Fungus Aspergillus sp. FT1307. Molecules. 2021; 26(14):4239. https://doi.org/10.3390/molecules26144239

Chicago/Turabian Style

Qader, Mallique, KH Ahammad Uz Zaman, Zhenquan Hu, Cong Wang, Xiaohua Wu, and Shugeng Cao. 2021. "Aspochalasin H1: A New Cyclic Aspochalasin from Hawaiian Plant-Associated Endophytic Fungus Aspergillus sp. FT1307" Molecules 26, no. 14: 4239. https://doi.org/10.3390/molecules26144239

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