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Article

Jugiones A–D: Antibacterial Xanthone–Anthraquinone Heterodimers from Australian Soil-Derived Penicillium shearii CMB-STF067

by
Thulasi Sritharan
,
Angela A. Salim
,
Zeinab G. Khalil
and
Robert J. Capon
*
Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD 4072, Australia
*
Author to whom correspondence should be addressed.
Antibiotics 2024, 13(1), 97; https://doi.org/10.3390/antibiotics13010097
Submission received: 23 December 2023 / Revised: 17 January 2024 / Accepted: 17 January 2024 / Published: 18 January 2024
(This article belongs to the Special Issue Discovery and Development of the Novel Antimicrobial Agent)
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Abstract

:
The Australian roadside soil-derived fungus Penicillium shearii CMB-STF067 was prioritized for chemical investigation based on an SDA cultivation extract exhibiting both antibacterial properties and natural products with unprecedented molecular formulae (GNPS). Subsequent miniaturized 24-well plate cultivation profiling (MATRIX) identified red rice as optimal for the production of the target chemistry, with scaled-up cultivation, extraction and fractionation yielding four new xanthone–anthraquinone heterodimers, jugiones A–D (1–4), whose structures were assigned by detailed spectroscopic analysis and biosynthetic considerations. Of note, where 1–2 and 4 were active against the Gram-positive bacteria vancomycin-resistant Enterococcus faecalis (IC50 2.6–3.9 μM) and multiple-drug-resistant clinical isolates of Staphylococcus aureus (IC50 1.8–6.4 μM), and inactive against the Gram-negative bacteria Escherichia coli (IC50 > 30 μM), the closely related analog 3 exhibited no antibacterial properties (IC50 > 30 μM). Furthermore, where 1 was cytotoxic to human carcinoma (IC50 9.0–9.8 μM) and fungal (IC50 4.1 μM) cells, 2 and 4 displayed no such cytotoxicity (IC50 > 30 μM), revealing an informative structure activity relationship (SAR). We also extended the SAR study to other known compounds of this heterodimer class, which showed that the modification of ring G can reduce or eliminate the cytotoxicity while retaining the antibacterial activity.

1. Introduction

Soil microbes have been the source of many modern antibiotics in clinical use, including β-lactams, streptomycins, aminoglycosides and tetracyclines. With a global increase in multidrug-resistant pathogens challenging healthcare across the world, the need for new and more effective antibiotics is both urgent and compelling. As part of our ongoing search for new microbial natural products with antibiotic properties, we screened extracts obtained from agar plate cultivations of ×139 bacterial (on ISP2 medium) and ×254 fungal (on SDA or PDA media) isolates obtained from roadside soils collected in New South Wales (NSW), Australia, against Gram-positive and Gram-negative bacterial pathogens. This survey drew our attention to the extract prepared from an SDA cultivation of Penicillium shearii CMB-STF067, which exhibited promising Gram-positive antibacterial properties. Importantly, a Global Natural Products Social (GNPS) [1] molecular network comparison of this extract against an in-house library of ~2000 microbial extracts confirmed that CMB-STF067 was unique in producing a suite of metabolites with unprecedented molecular formulae (i.e., not attributable to any reported microbial natural product).
Capitalizing on the knowledge that the transcriptional status of natural-product biosynthetic gene clusters can be influenced by culture conditions (i.e., media composition, temperature, aeration…) [2,3,4], we employed a miniaturized 24-well plate approach to cultivation profiling known in lab as the MATRIX [5]. When integrated with UPLC-DAD and GNPS molecular networking, MATRIX analyses can be particularly effective and have proved pivotal to our prior discovery and reporting of many new natural-product structure classes (e.g., noonindoles [6], chrysosporazines [7], talarolides [8] and terreusides [9]). In this study, we employed both the standard MATRIX [5] and newly developed grain/pulse and cereal MATRIX [9] variations to probe the metabolite production capabilities of CMB-STF067.
This report provides an account of an optimized, scaled-up fermentation and chemical fractionation of CMB-STF067 to yield four new xanthone–anthraquinone heterodimers, jugiones A–D (1–4). The jugiones belong to a class of rare fungal metabolites and are the first examples of xanthone–anthraquinone heterodimers to be reported from the genus Penicillium. In addition to structure elucidation by detailed spectroscopic analysis, we carried out a structure activity relationship (SAR) assessment of the jugiones against vancomycin-resistant Enterococcus faecalis and multiple-drug-resistant isolates of Staphylococcus aureus, and against human colon and lung carcinoma and fungal cells. What follows is an account of these investigations.

2. Results and Discussion

MATRIX methodology comparing CMB-STF067 metabolite production in ×11 standard media compositions (Table S1) under solid phase (2.0 mL agar) as well as shaken and static broth (1.5 mL) conditions was further extended to include ×23 grain/pulse (Table S2) (grain MATRIX) and ×11 cereal (Table S3) (cereal MATRIX)-based solid media compositions, inclusive of uninoculated media controls. Subsequent in situ solvent (EtOAc) extraction followed by UPLC-DAD (Figures S5, S7 and S9) and UPLC-QTOF-MS/MS (GNPS) (Figures S6, S8 and S10) chemical profiling identified red rice as the preferred production media, with scale-up cultivation followed by solvent extraction and trituration, and gel and reversed-phase chromatography (Scheme S1) yielding the target chemistry, jugiones A–D (1–4) (Figure 1).
HRESI(+)MS measurement established a molecular formula for 1 (C39H34O13, ∆mmu +2.7) requiring ×23 double bond equivalents (DBEs), while analysis of the 1D and 2D NMR (CDCl3) (Table 1, Table 2 and Table S4, Figures S11–S16) data allowed assembly of four sub-structures A to D (Figure 2) accounting for ×21 DBE and necessitating two additional ring systems. Sub-structure A was identified as a conjugated triene octanoate with an all E configuration evident from diagnostic J values, while sub-structure B was attributed to a disubstituted phenol. An HMBC correlation from H-10 to C-1’, and from H-2 to C-7, allowed assembly of the consolidated sub-structure A–B. By contrast, sub-structures C and D featured more complex carbocycles, with an HMBC correlation from H-15 to C-10, and a ROESY correlation between H-15 and H-10, establishing a C-9 to C-10 linkage supportive of the consolidated sub-structure A–B–C. With the full suite of sub-structures A to D accounting for an oxygen atom in excess of the molecular formula necessitating a C-18 to C-24 ether bridge, the remaining disconnections and requirement for two additional rings required C-7 and C-22 ketone bridges to form rings B and F, to arrive at the complete planar structure for 1 as indicated (Figure 1).
In this regard, 1 shares a planar carbo/heterocyclic core framework (rings A to G) in common with JBIR-99 (5) first reported in 2010 [10] from an Okinawan marine sponge-derived fungus, Tritirachium sp. SpB081112MEf2, and subsequently re-isolated in 2021 [11] from the Indian Ocean marine seawater-derived fungus, Meyerozyma guilliermondii Y39, and assigned a relative configuration based on X-ray crystallographic analysis. Interestingly, a 2016 [12] re-isolation of 5 together with its isomer engyodontochone B (6) from a Croatian marine sponge-derived fungus, Engyodontium album LF069, employed ROESY and ECD correlations to assign absolute configurations to both 5 and 6 (Figure 3). Also noteworthy are the biosynthetically related xanthoquinodins B10 (7) and B11 (8), first reported in 2020 [13] from a Nepalese soil-derived fungus, Jugulospora vestita CBS 135.91, and assigned structures and absolute configurations based on spectroscopic and ECD analysis (Figure 3). Careful consideration of the spectroscopic data for 5–7, which collectively encompass the full array of C-24/C-25 stereoisomers, reveals useful empirical rules. For example, 5 (24R,25R) and 7 (24S,25S), which feature α and β facial cis disposed 24-CO2Me and 25-OH moieties, respectively, are characterized by comparable NMR (CDCl3) chemical shifts for C-25 (δC 72.0 and 71.7, respectively), which differ from those of the alternate trans disposed isomers 6 (24S,25R) and 8 (24R,25S) (δC 66.9 and 66.9, respectively). Furthermore, the 24R isomers 5 and 8 possess comparable experimental ECD spectra (Figure S18), which differ from the equally comparable experimental ECD spectra reported for the 24S isomers 6 and 7 (Figure S19). Drawing on these NMR and ECD observations, as 1 possesses a 13C NMR (CDCl3) chemical shift for C-25 (δC 68.9) in common with 6 and 8, and an ECD spectra (Figure S20) in common with 5 and 8, we propose that 1 shares a 10S,9R,12S,24R,25S configuration in common with 8. Finally, a ROESY correlation between 24-CO2CH3 and Hb-26 in 1, together with a J26b,27 of 10.2 Hz, is consistent with a large Hb-26/H-27 dihedral angle and 27S configuration. This hypothesis was further validated by the consideration of predicted dihedral angles and J values about ring G in energy-minimized models of 1 and its unnatural 27R epimer (Figure S21). Based on all of the above, the structure inclusive of absolute configurations for jugione A (1) was assigned as shown.
HRESI(+)MS measurement established a molecular formula for 2 (C39H34O13, ∆mmu +1.4) isomeric with 1. Comparison of the 1D and 2D NMR (CDCl3) data for 2 (Table 1, Table 2 and Table S6, Figure 4 and Figures S22–S27) with 1 allowed the key differences to be attributed to a reverse Claisen condensation-like opening of ring G (Figure 5) with concomitant replacement of the sp2 quaternary C-23 in 1 (δC 99.8) with a diastereotopic H2-23/C-23 methylene in 2 (δH 3.18/3.02, ABq, J 17.0 Hz; δC 38.2) and associated formation of a sidechain butyrolactone moiety, as evident from deshielding of H-25 in 2 compared to 1 (∆δH +0.37). On the basis of the spectroscopic similarities between 1 and 2 including near-identical ECD spectra (Figure S44) and biogenetic considerations, the structure inclusive of absolute configuration for jugione B (2) was assigned as shown.
HRESI(+)MS measurements established a molecular formula for 3 (C39H36O14, ∆mmu +1.6) and its homolog (+CH2) 4 (C40H38O14, ∆mmu –0.5), with a comparison of the NMR (methanol-d4) data for 3 and 4 (Table 1, Table 2, Tables S9 and S10, Figure 4 and Figures S31–S36, S38–S42) with that for 2 (Table S7, Figures S29 and S30) allowing key differences to be attributed to the hydrolysis and methanolysis of the butyrolactone moiety, respectively. More specifically, the chemical shifts for the H-25 methine in 3 (δH 4.31, br d, J 10.9 Hz) and 4 (δH 4.33, br d, J 10.8 Hz) were shielded and consistent with a hydroxy methine, relative to the lactone methine in 2 (δH 5.00, dd, J 10.1 and 6.2 Hz). These observations, taken together with 3 and 4 possessing comparable ECD spectra to 1 and 2 (Figure S44) and biosynthetic considerations, supported the assignment of structures for jugiones C–D (3–4) as shown.
Alert to the possibility that chemically reactive natural products can form artifacts during handling and storage [14], careful analysis of fresh CMB-STF067 extracts prior to chemical fractionation detected 1–4 and confirmed their status as natural products. Supportive of this, no chemical stability issues were observed during the handling and storage of pure samples of 1–4.
Jugiones belong to a rare class of xanthone–anthraquinone heterodimers whose biosynthesis has been proposed to originate from two C16 polyketide units [15]. Known fungal metabolites belonging to this family, including beticolins [16], cebetins [17], xanthoquinodins [13,15,18,19,20,21,22,23], JBIRs [10,11,12], engyodontochones [12], acremoxanthones [24,25,26,27] and acremonidins [28], can be grouped into four scaffolds (i–iv, Figure S46) based on the mode of dimerization between xanthone and anthraquinone monomers. Beticolins [16] (scaffold i) and cebetins [17] (scaffold ii) (Figure S47) produced by the fungal plant pathogen Cercospora beticola are the only examples with a chlorinated xanthone moiety and a C-13 to C-14 epoxide. Excluding beticolins and cebetins, all known compounds belonging to scaffolds (i) (e.g., JBIR-97/98 and engyodonthochone A) and (ii) (e.g., JBIR-99 and engyodonthochone B) have been isolated from marine-derived fungi [10,11,12], while those featuring scaffolds (iii) (e.g., xanthoquinodin A series and acremoxanthones A–B) and (iv) (e.g., xanthoquinodin B series and acremoxanthones C–E) have been isolated from soil-, insect- and plant-associated fungi [13,15,18,19,20,21,22,23,24,25,26,27,28]. The jugiones belonging to scaffold ii are the first xanthone–anthraquinone heterodimers to be reported from the Eurotiomycetes class—the soil-associated fungus P. shearii CMB-STF067 (family Aspergillaceae, order Eurotiales, class Eurotiomycetes). All reported heterodimers, with the exception of beticolins and cebetins produced by C. beticola (family Mycospharerellaceae, order Capnodiales, class Dothideomycetes), were produced by fungi from the Sordariomycetes class (albeit from various orders, families and genera).
The antibacterial activity against drug-sensitive Staphylococcus aureus ATCC 25923 that prompted our initial interest in CMB-STF067 was shown to be due to 1–2 and 4 (IC50 1.8 to 6.6 μM), with the closely related carboxylic acid 3 being inactive (IC50 >30 μM) (Table 3 and Figure S45). Of note, this antibacterial activity extended to both drug-sensitive and resistant Enterococcus faecalis strains (IC50 0.5 to 1.8 μM and 2.6 to 3.9 μM, respectively) and multiple-drug-resistant strains of S. aureus (IC50 1.8 to 6.4 μM) (Table 3). Notwithstanding, one of the challenges associated with discovering new natural product antibiotics is the need for selectivity, particularly in favor of pathogens over host (human) cells. To address this challenge, we assessed the ability of 1–4 to inhibit the growth of eukaryote cells, namely human colon and lung carcinoma and fungal cells. Significantly, while 1 was cytotoxic to carcinoma (IC50 9–10 μM) and fungal (IC50 4.1 μM) cells, the γ-lactone- and seco-ring G analogs 2 and 4, respectively, displayed no such cytotoxicity (IC50 >30 mM) and were selectively effective against Gram-positive bacteria (Table 3 and Figure S45).
Similar SARs have been observed for JBIR-97/98 and engyodontochones A and C (heterodimer scaffold i) and JBIR-99 and engyodontochones B, E and F (heterodimer scaffold ii) (Figure S48), where metabolites inclusive of ring G exhibit antibacterial, antifungal and cytotoxic properties, while those featuring a seco-ring G (including the γ-lactone) are antibacterial against Gram-positive bacteria but do not exhibit cytotoxicity towards eukaryote cells [12]. It has also been reported that xanthoquinodins A6-A8 (heterodimer scaffold iii) and xanthoquinodins B11, B14 and B15 (heterodimer scaffold iv) (Figure S48) with an intact ring G are antibacterial and cytotoxic to eukaryotic cells (fungi and human), while seco-ring G analogs (included the γ-lactone) are antibacterial but with reduced cytotoxicity to eukaryotic cells [13,21].

3. Materials and Methods

3.1. Collection and Isolation of CMB-STF067

The fungus CMB-STF067 was isolated from roadside soil collected in 2019 near Jugiong, NSW, Australia. The soil sample was transported to the laboratory in a sealed container at room temperature, after which, a portion (1 g) in sterile water (10 mL) was heated for 30 min at 55°C, with an aliquot (100 μL) serially diluted and applied to SDA and ISP-2 agar plates supplemented with both cycloheximide (100 μg/mL) and rifampicin (5 μg/mL). The plates were sealed with parafilm and incubated at 29 °C with periodic inspection over 4 weeks. The fungus CMB-STF067 (Figure S1) was manually recovered by colony picking from the SDA plate, and after recultivation on SDA medium, the pure isolate was cryopreserved at –80 °C in 15% aqueous glycerol.

3.2. Taxonomic Identification of CMB-STF067

Genomic DNA was extracted from the mycelia of an SD static broth culture of CMB-STF067 using the DNeasy Plant Mini Kit (QIAGEN) as per the manufacturer’s protocol. The 18S rRNA genes were amplified by PCR using the universal primers ITS 1 (5′-TCCGTAGGTGAACCTGCGG-3′) and ITS 4 (5ʹ TCCTCCGCTTATTGATATGC-3ʹ) purchased from Sigma-Aldrich (Merck, Darmstadt, Germany). The PCR mixture (50 μL) contained genomic DNA (2 μL, 20–40 ng), EmeraldAmpn GT PCR Master Mix (2× Premix, 25 μL), primer (0.2 μM, each) and H2O (up to 50 μL). PCR was performed using the following conditions: initial denaturation at 95 °C for 2 min, 40 cycles in series of 95 °C for 20 s (denaturation), 56 °C for 20 s (annealing) and 72 °C for 30 s (extension), followed by one cycle at 72 °C for 5 min. The PCR products were purified with a PCR purification kit (QIAGEN). Amplification products were examined by agarose gel electrophoresis. The DNA sequencing was performed by the Australian Genome Research Facility (AGRF) at The University of Queensland. A GenBank BLAST analysis (NCBI database) (Figure S2) on the resulting ITS gene sequence (accession number OR730993) and following a phylogenetic analysis revealed 100.0% identity with the fungal strain Penicillium shearii (Figure S3).

3.3. UPLC-DAD Profiling of MATRIX Extracts

Aliquots (1 μL, 5 mg/mL MeOH) of all MATRIX extracts prepared as noted above were analyzed by UPLC-DAD using the method outlined in the general experimental procedure (Figures S5, S7 and S9).

3.4. GNPS Molecular Network Profiling of MATRIX Extracts

Aliquots (1 μL, 0.05 mg/mL MeOH) of MATRIX extracts prepared as noted above were subjected to UPLC-QTOF analysis using the method outlined in the general experimental procedure. The resulting MS/MS Mass Hunter data files (.d) were converted to .mzXML file format using MS convert software version 3.0 [29] prior to being uploaded to the GNPS platform (gnps.ucsd.edu, accessed on 24 October 2023) [1] through FTP approaches (FileZilla). A molecular network analysis was performed using an online workflow at GNPS, setting the minimum cluster size at 2, cosine score 0.5 and the minimum number of fragments at 6. The spectral networks were imported into Cytoscape (version 3.9.1) [30] and visualized using a ball–stick layout where nodes represented parent masses and edge thickness corresponded to cosine score (Figures S4, S6, S8 and S10).

3.5. Scaled-Up Cultivation and Chemical Fractionation of CMB-STF067

The UPLC and GNPS profiling as outlined above prompted the optimized scaled-up cultivation of CMB-STF067 on red rice. To this end, cells recovered from a 7-day inhibitory mold agar (IMA, Table S1) cultivation of CMB-STF067 were used to inoculate flasks (2 × 2 L) containing red rice media (140 g, 200 mL distilled water), which were subsequently incubated at 27 °C for 21 days. After incubation, the red rice cultures were extracted with EtOAc (4 × 500 mL), and the organic phase was concentrated in vacuo at 40 °C to yield an extract (2.37 g) which was subjected to sequential trituration followed by concentration under N2 at 40 °C to yield an n-hexane (201 mg) and a combined CH2Cl2 and MeOH (1.80 g) soluble extract. The latter was subjected to gel chromatography (Sephadex LH-20, 2.5 × 85 cm, gravity isocratic elution with 50% CH2Cl2/MeOH) to yield fractions which were combined based on analytical HPLC-DAD-MS analysis. Fractions 24–25 (39.6 mg) were subjected to semi preparative HPLC (Agilent Zorbax SB-Phenyl 5 μm, 9.4 × 250 mm column, with a 3 mL/min gradient elution over 26 min from 50% H2O/MeCN to 30% H2O/MeCN inclusive of an isocratic 0.01% TFA/MeCN modifier) to afford jugione A (1) (tR 22.8 min, 6.0 mg, 0.33%), jugione B (2) (tR 23.6 min, 6.1 mg, 0.34%), jugione C (3) (tR 17.6 min, 2.1 mg, 0.12%) and jugione D (4) (tR 22.3 min, 1.5 mg, 0.08%), as summarized in Scheme S1. (Note: % yields determined on a mass-to-mass basis against the weight of the EtOAc extract.)
jugione A (1). Pale yellow powder; [α]D26 + 359.4 (c 0.05, MeOH); UV-vis (UPLC-DAD, MeCN/H2O) λmax 308, 358 nm; 1D and 2D NMR (600 MHz, CDCl3); see Table 1, Table 2 & Table S4 and Figures S11–S16; HRESI(+)MS m/z 733.1924 [M + Na] + (calcd for C39H34O13Na, 733.1897).
jugione B (2). Pale yellow powder; [α]D26 +269.8 (c 0.05, MeOH); UV-vis (UPLC-DAD, MeCN/H2O) λmax 308, 358 nm; 1D and 2D NMR (600 MHz, CDCl3); see Table 1, Table 2 & Table S6 and Figures S22–S27; 1D and 2D NMR (600 MHz, methanol-d4); see Table S7, Figures S29 and S30; HRESI(+)MS m/z 733.1911 [M + Na]+ (calcd for C39H34O13Na, 733.1897).
jugione C (3). Pale yellow powder; [α]D24 +350.8 (c 0.05, MeOH); UV-vis (UPLC-DAD, MeCN/H2O) λmax 308, 358 nm; NMR (600 MHz, methanol-d4); see Table 1, Table 2 & Table S9 and Figures S31–S36; HRESI(+)MS m/z 751.2019 [M + Na]+ (calcd for C39H36O14Na, 751.2003).
jugione D (4). Pale yellow powder; [α]D24 + 355.9 (c 0.05, MeOH); UV-vis (UPLC-DAD, MeCN/H2O) λmax 308, 358 nm; NMR (600 MHz, methanol-d4); see Table 1, Table 2 & Table S10 and Figures S38–S42; HRESI(+)MS m/z 765.2154 [M + Na]+ (calcd for C40H38O14Na, 765.2159).

3.6. Antibacterial Assay

LB agar plates inoculated with the bacterial isolate to be tested were incubated at 37 °C for 24 h, after which, several colonies were transferred to fresh sterile LB broth which was incubated at 37 °C for 24 h, and following the measurement of optical density, the cell density was adjusted to 5 × 105 CFU/mL. Analytes (1–4 and controls) were dissolved in DMSO and diluted with H2O to afford stock solutions (600 µM, 20% DMSO) which were serially diluted with 20% DMSO to yield analyte concentrations ranging from 600 to 0.2 µM. An aliquot (10 µL) of each analyte dilution was transferred to a 96-well microtiter plate along with freshly prepared bacterium broth (190 µL) to final concentrations of 30–0.01 µM in 1% DMSO. The resulting assay plates were incubated at 37 °C for 18 h and the optical density of each well was measured spectrophotometrically at 600 nm using the POLARstar Omega plate reader (BMG LABTECH, Offenburg, Germany). Antibacterial screening was carried out against Gram-positive Staphylococcus aureus ATCC 25923, clinical isolates of daptomycin-resistant Staphylococcus aureus 587701692:1, methicillin-resistant Staphylococcus aureus AUS-RBWH-MRSA-01/02, vancomycin-resistant Enterococcus AUS-RBWH-VRE-01, Enterococcus faecalis ACM 5184 and Gram-negative Escherichia coli ATCC11775. The positive control was rifampicin (10 µM in 1% DMSO) and the negative control was 1% DMSO in culture broth, together with extracts prepared from LB broth medium without bacterial inoculation. Each analysis was repeated two times and the data represented graphically, and IC50 and MIC values were calculated using GraphPad Prism version 10.0.1 (Figure S45).

3.7. Antifungal Assay

SD agar plates inoculated with Candida albicans ATCC 10231 were incubated at 27 °C for 48 h, after which, several colonies were transferred to fresh sterile SD broth (4 mL) which was incubated at 27 °C for 48 and, following the measurement of optical density, the cell density was adjusted to 5 × 105 CFU/mL. An aliquot (10 µL) of analytes as prepared above for antibacterial assays was transferred to a 96-well microtiter plate and freshly prepared fungal broth (190 µL) was added to each well to give final concentrations of 30–0.01 µM in 1% DMSO. The resulting assay plates were incubated at 27 °C for 48 h and the optical density of each well was measured spectrophotometrically at 600 nm using the POLARstar Omega plate reader (BMG LABTECH, Offenburg, Germany). The positive control was amphotericin (10 µM in 1% DMSO) and the negative control was 1% DMSO, together with extracts prepared from SD broth without fungal inoculation. Each analysis was repeated two times and the data represented graphically, and IC50 and MIC values were calculated using GraphPad Prism version 10.0.1 (Figure S45).

3.8. Cytotoxic Assay

Aliquots (3000 cells/well in 190 µL of Roswell Park Memorial Institute medium supplemented with 10% fetal bovine serum) of human colorectal (SW620) and lung (NCI-H460) carcinoma cells were transferred to 96-well plates and incubated at 37 °C in 5% CO2 for 3 days. An aliquot (10 µL) of analytes as prepared above for antibacterial assays was transferred to a 96-well microtiter plate and incubated again for 24 h, after which, an aliquot (10 µL) of a solution of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) in phosphate-buffered saline (5 mg/mL) was added to each well which were again incubated for 4 h. The media were then carefully removed (pipette) and the residue dissolved in DMSO (100 µL) by shaking at 50 rpm for 2 min. Finally, the absorbance of each well was measured spectrophotometrically at 600 nm using the POLARstar Omega plate reader (BMG LABTECH, Offenburg, Germany). The positive control was sodium dodecyl sulfate (SDS) and the negative control was 1% DMSO. Each analysis was repeated two times and the data represented graphically, and IC50 and MIC values were calculated using GraphPad Prism version 10.0.1 (Figure S45).

4. Conclusions

The jugiones are rare xanthone–anthraquinone heterodimers, which were only produced by one Penicillium strain (class Eurotiomycetes) in our in-house soil-derived microbe collection (~2000 isolates). Such heterodimers have only previously been reported from fungi belonging to the Sordariomycetes class isolated from various substrates (marine sponges, soil, insects and plants). An SAR assessment of jugiones A-D determined that 1 was antibacterial against vancomycin-resistant Enterococcus faecalis and multiple-drug-resistant isolates of Staphylococcus aureus and was cytotoxic to human carcinoma cells, while 2 and 4 retained antibacterial properties but were not cytotoxic, and 3 was neither antibacterial nor cytotoxic.
While most xanthone–anthraquinone heterodimers are cytotoxic towards eukaryotic cells, our investigations into the jugiones reveal that ring G modification can reduce cytotoxicity while retaining the antibacterial activity—as evidenced by jugiones B and D which exhibit antibacterial activity against both drug-susceptible and resistant Gram-positive bacteria but display no cytotoxicity against eukaryotic cells. Given the increase in multidrug-resistant bacteria in the community, jugiones and other related heterodimers could be viewed as antibacterial scaffolds with potential.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/antibiotics13010097/s1, general experimental procedures; MATRIX methodology; GNPS analysis; MATRIX study of CMB-STF067; NMR spectroscopic data (tabulated data and spectra of 1–4); ECD spectra; biological assay graphs; structures of known xanthone-anthroquinone dimers.

Author Contributions

R.J.C. conceptualized the research; T.S. performed GNPS study, carried out the MATRIX study, compound isolation and structural elucidation, and prepared Supplementary Materials; R.J.C. analyzed NMR data and assigned the structures, A.A.S. revised the NMR data; Z.G.K. performed antibacterial assays on MDR strains; R.J.C., writing—original draft, R.J.C., T.S. and A.A.S., writing—review and editing. All authors have read and agreed to the published version of the manuscript.

Funding

T.S. thanks the University of Queensland (UQ) for an International Postgraduate Scholarship. We also thank the UQ Institute for Molecular Bioscience and Australian Research Council (LE210100148) for supporting this research.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Raw NMR data for 1–4 have been deposited in the Natural Product Magnetic Resonance Database Project (NP-MRD). The MS/MS data (.mzXML) for 1–4 can be accessed from https://massive.ucsd.edu/ProteoSAFe/dataset.jsp?task=a8234245cf1f4e8a82be997c44676646, accessed on 6 December 2023.

Acknowledgments

We thank David Paterson and Patrick Harris (UQCCR) for providing MDR bacterial strains.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Aron, A.T.; Gentry, E.C.; McPhail, K.L.; Nothias, L.-F.; Nothias-Esposito, M.; Bouslimani, A.; Petras, D.; Gauglitz, J.M.; Sikora, N.; Vargas, F.; et al. Reproducible Molecular Networking of Untargeted Mass Spectrometry Data Using GNPS. Nat. Protoc. 2020, 15, 1954–1991. [Google Scholar] [CrossRef] [PubMed]
  2. Romano, S.; Jackson, S.A.; Patry, S.; Dobson, A.D.W. Extending the “One Strain Many Compounds” (OSMAC) Principle to Marine Microorganisms. Mar. Drugs 2018, 16, 244. [Google Scholar] [CrossRef] [PubMed]
  3. Pinedo-Rivilla, C.; Aleu, J.; Durán-Patrón, R. Cryptic Metabolites from Marine-Derived Microorganisms Using OSMAC and Epigenetic Approaches. Mar. Drugs 2022, 20, 84. [Google Scholar] [CrossRef]
  4. Tomm, H.A.; Ucciferri, L.; Ross, A.C. Advances in Microbial Culturing Conditions to Activate Silent Biosynthetic Gene Clusters for Novel Metabolite Production. J. Ind. Microbiol. Biotechnol. 2019, 46, 1381–1400. [Google Scholar] [CrossRef] [PubMed]
  5. Salim, A.A.; Khalil, Z.G.; Elbanna, A.H.; Wu, T.; Capon, R.J. Methods in Microbial Biodiscovery. Mar. Drugs 2021, 19, 503. [Google Scholar] [CrossRef]
  6. Kankanamge, S.; Khalil, Z.G.; Sritharan, T.; Capon, R.J. Noonindoles G–L: Indole Diterpene Glycosides from the Australian Marine-Derived Fungus Aspergillus noonimiae CMB-M0339. J. Nat. Prod. 2023, 86, 508–516. [Google Scholar] [CrossRef]
  7. Agampodi Dewa, A.; Khalil, Z.G.; Elbanna, A.H.; Capon, R.J. Chrysosporazines Revisited: Regioisomeric Phenylpropanoid Piperazine P-Glycoprotein Inhibitors from Australian Marine Fish-Derived Fungi. Molecules 2022, 27, 3172. [Google Scholar] [CrossRef]
  8. Salim, A.A.; Hussein, W.M.; Dewapriya, P.; Hoang, H.N.; Zhou, Y.; Samarasekera, K.; Khalil, Z.G.; Fairlie, D.P.; Capon, R.J. Talarolides Revisited: Cyclic Heptapeptides from an Australian Marine Tunicate-Associated Fungus, Talaromyces sp. CMB-TU011. Mar. Drugs 2023, 21, 487. [Google Scholar] [CrossRef]
  9. Sritharan, T.; Salim, A.A.; Capon, R.J. Miniaturized Cultivation Profiling Returns Indole-Sesquiterpene Michael Adducts from an Australian Soil-Derived Aspergillus terreus CMB-SWF012. J. Nat. Prod. 2023, 86, 2703–2709. [Google Scholar] [CrossRef]
  10. Ueda, J.-Y.; Takagi, M.; Shin-Ya, K. New Xanthoquinodin-Like Compounds, JBIR-97,-98 and-99, Obtained from Marine Sponge-Derived Fungus Tritirachium sp. SpB081112MEf2. J. Antibiot. 2010, 63, 615–618. [Google Scholar] [CrossRef]
  11. Wu, H.; Liu, J.; Duan, N.; Han, R.; Zhang, X.; Leng, X.; Liu, W.; Han, L.; Li, X.; Xing, S. Isolation and Purification of an Antibiotic Polyketide JBIR-99 from the Marine Fungus Meyerozyma Guilliermondii by High-Speed Counter-Current Chromatography. Int. J. Pharm. Chem. 2021, 7, 52–57. [Google Scholar] [CrossRef]
  12. Wu, B.; Wiese, J.; Wenzel-Storjohann, A.; Malien, S.; Schmaljohann, R.; Imhoff, J.F. Engyodontochones, Antibiotic Polyketides from the Marine Fungus Engyodontium album Strain LF069. Chem. Eur. J. 2016, 22, 7452–7462. [Google Scholar] [CrossRef] [PubMed]
  13. Shao, L.; Marin-Felix, Y.; Surup, F.; Stchigel, A.M.; Stadler, M. Seven New Cytotoxic and Antimicrobial Xanthoquinodins from Jugulospora vestita. J. Fungi 2020, 6, 188. [Google Scholar] [CrossRef] [PubMed]
  14. Capon, R.J. Extracting Value: Mechanistic Insights into the Formation of Natural Product Artifacts—Case Studies in Marine Natural Products. Nat. Prod. Rep. 2020, 37, 55–79. [Google Scholar] [CrossRef] [PubMed]
  15. Tabata, N.; Tomoda, H.; Matsuzaki, K.; Omura, S. Structure and Biosynthesis of Xanthoquinodins, Anticoccidial Antibiotics. J. Am. Chem. Soc. 1993, 115, 8558–8564. [Google Scholar] [CrossRef]
  16. Milat, M.; Prangé, T.; Ducrot, P.H.; Tabet, J.; Einhorn, J.; Blein, J.; Lallemand, J. Structures of the Beticolins, the Yellow Toxins Produced by Cercospora beticola. J. Am. Chem Soc. 1992, 114, 1478–1479. [Google Scholar] [CrossRef]
  17. Jalal, M.A.; Hossain, M.B.; Robeson, D.J.; Van der Helm, D. Cercospora Beticola Phytotoxins: Cebetins That Are Photoactive, Magnesium Ion-Binding, Chlorinated Anthraquinone-Xanthone Conjugates. J. Am. Chem. Soc. 1992, 114, 5967–5971. [Google Scholar] [CrossRef]
  18. Matsuzaki, K.; Tabata, N.; Tomoda, H.; Iwai, Y.; Tanaka, H.; Ōmura, S. The Structure of Xanthoquinodin A1, a Novel Anticoccidial Antibiotic Having a New Xanthone-Anthraquinone Conjugate System. Tetrahedron Lett. 1993, 34, 8251–8254. [Google Scholar] [CrossRef]
  19. Tabata, N.; Tomoda, H.; Iwai, Y.; Omura, S. Xanthoquinodin B3, a New Anticoccidial Agent Produced by Humicola sp. FO-888. J. Antibiot. 1996, 49, 267–271. [Google Scholar] [CrossRef]
  20. Chen, G.-D.; Chen, Y.; Gao, H.; Shen, L.-Q.; Wu, Y.; Li, X.-X.; Li, Y.; Guo, L.-D.; Cen, Y.-Z.; Yao, X.-S. Xanthoquinodins from the Endolichenic Fungal Strain Chaetomium elatum. J. Nat. Prod. 2013, 76, 702–709. [Google Scholar] [CrossRef]
  21. Sadorn, K.; Saepua, S.; Boonyuen, N.; Boonruangprapa, T.; Rachtawee, P.; Pittayakhajonwut, P. Antimicrobial Activity and Cytotoxicity of Xanthoquinodin Analogs from the Fungus Cytospora eugeniae BCC42696. Phytochemistry 2018, 151, 99–109. [Google Scholar] [CrossRef] [PubMed]
  22. Tantapakul, C.; Promgool, T.; Kanokmedhakul, K.; Soytong, K.; Song, J.; Hadsadee, S.; Jungsuttiwong, S.; Kanokmedhakul, S. Bioactive Xanthoquinodins and Epipolythiodioxopiperazines from Chaetomium globosum 7s-1, an Endophytic Fungus Isolated from Rhapis cochinchinensis (Lour.) Mart. Nat. Prod. Res. 2020, 34, 494–502. [Google Scholar] [CrossRef] [PubMed]
  23. Lee, J.W.; Collins, J.E.; Hulverson, M.A.; Aguila, L.K.T.; Kim, C.M.; Wendt, K.L.; Chakrabarti, D.; Ojo, K.K.; Wood, G.E.; Van Voorhis, W.C.; et al. Appraisal of Fungus-Derived Xanthoquinodins as Broad-Spectrum Anti-Infectives Targeting Phylogenetically Diverse Human Pathogens. J. Nat. Prod. 2023, 86, 1596–1605. [Google Scholar] [CrossRef] [PubMed]
  24. Isaka, M.; Palasarn, S.; Auncharoen, P.; Komwijit, S.; Gareth Jones, E.B. Acremoxanthones a and B, Novel Antibiotic Polyketides from the Fungus Acremonium sp. Bcc 31806. Tetrahedron Lett. 2009, 50, 284–287. [Google Scholar] [CrossRef]
  25. Ayers, S.; Graf, T.N.; Adcock, A.F.; Kroll, D.J.; Shen, Q.; Swanson, S.M.; Matthew, S.; Carcache de Blanco, E.J.; Wani, M.C.; Darveaux, B.A.; et al. Cytotoxic Xanthone–Anthraquinone Heterodimers from an Unidentified Fungus of the Order Hypocreales (MSX 17022). J. Antibiot. 2012, 65, 3–8. [Google Scholar] [CrossRef]
  26. Meléndez-González, C.; Murià-González, M.J.; Anaya, A.L.; Hernández-Bautista, B.E.; Hernández-Ortega, S.; González, M.C.; Glenn, A.E.; Hanlin, R.T.; Macías-Rubalcava, M.L. Acremoxanthone E, a Novel Member of Heterodimeric Polyketides with a Bicyclo[3.2.2]Nonene Ring, Produced by Acremonium camptosporum W. Gams (Clavicipitaceae) Endophytic Fungus. Chem. Biodivers. 2015, 12, 133–147. [Google Scholar] [CrossRef] [PubMed]
  27. Intaraudom, C.; Bunbamrung, N.; Dramae, A.; Boonyuen, N.; Komwijit, S.; Rachtawee, P.; Pittayakhajonwut, P. Acremonidins F–H and Acremoxanthones F–G, Antimicrobial Substances from the Insect Fungus Verticillium sp. BCC33181. Tetrahedron 2016, 72, 1415–1421. [Google Scholar] [CrossRef]
  28. He, H.; Bigelis, R.; Solum, E.H.; Greenstein, M.; Carter, G.T. Acremonidins, New Polyketide-Derived Antibiotics Produced by Acremonium sp., LL-Cyan 416. J. Antibiot. 2003, 56, 923–930. [Google Scholar] [CrossRef]
  29. Adusumilli, R.; Mallick, P. Data Conversion with Proteowizard Msconvert. In Proteomics: Methods and Protocols; Comai, L., Katz, J.E., Mallick, P., Eds.; Springer: New York, NY, USA, 2017; pp. 339–368. [Google Scholar] [CrossRef]
  30. Shannon, P.; Markiel, A.; Ozier, O.; Baliga, N.S.; Wang, J.T.; Ramage, D.; Amin, N.; Schwikowski, B.; Ideker, T. Cytoscape: A Software Environment for Integrated Models of Biomolecular Interaction Networks. Genome Res. 2003, 13, 2498–2504. [Google Scholar] [CrossRef]
Antibiotics 13 00097 g001
Figure 1. Jugiones A–D (1–4) from Penicillium shearii CMB-STF067.
Figure 1. Jugiones A–D (1–4) from Penicillium shearii CMB-STF067.
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Antibiotics 13 00097 g002
Figure 2. Selected NMR (CDCl3) correlations and J values for jugione A (1), with individual sub-structures A to D highlighted.
Figure 2. Selected NMR (CDCl3) correlations and J values for jugione A (1), with individual sub-structures A to D highlighted.
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Antibiotics 13 00097 g003
Figure 3. Known fungal natural products: JBIR-99 (5), engyodontochone B (6), and xanthoquinodins B10 (7) and B11 (8). Highlights (yellow and green) indicate relative configurational relationships.
Figure 3. Known fungal natural products: JBIR-99 (5), engyodontochone B (6), and xanthoquinodins B10 (7) and B11 (8). Highlights (yellow and green) indicate relative configurational relationships.
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Antibiotics 13 00097 g004
Figure 4. Selected 2D NMR correlations for jugione B (2) (CDCl3) and jugiones C–D (3–4) (methanol-d4).
Figure 4. Selected 2D NMR correlations for jugione B (2) (CDCl3) and jugiones C–D (3–4) (methanol-d4).
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Antibiotics 13 00097 g005
Figure 5. Plausible biomimetic relationship between jugiones A–D (1–4). Highlights (blue) indicate key functional groups and points of differentiation.
Figure 5. Plausible biomimetic relationship between jugiones A–D (1–4). Highlights (blue) indicate key functional groups and points of differentiation.
Antibiotics 13 00097 g005
Table 1. 1H NMR data for jugiones A–B (1–2) in CDCl3 and jugiones C–D (3–4) in methanol-d4.
Table 1. 1H NMR data for jugiones A–B (1–2) in CDCl3 and jugiones C–D (3–4) in methanol-d4.
(1) δH, Mult (J in Hz) (2) δH, Mult (J in Hz)(3) δH, Mult (J in Hz)(4) δH, Mult (J in Hz)
26.97, dd (8.6, 0.9)6.97, dd (8.4, 0.7)6.94, d (8.4)6.95, d (8.3)
37.45, dd (7.5, 8.6)7.44, dd (8.4, 7.3)7.48, dd (8.4, 7.3)7.49, dd (8.3, 7.2)
47.09, dd (7.5, 0.9)7.09, dd (7.3, 0.7)7.09, d (7.3)7.09, d (7.2)
106.05, s6.05, s6.07, br s6.08, s
124.52, d (1.5)4.48, d (1.4)4.74, s4.71, s
145.68, dq (1.5, 1.5)5.68, dq (1.4, 1.4)5.68, dq (1.4, 1.4)5.70, s
15a2.77, d (17.8)2.77, d (17.8)2.83, d (17.8)2.84, d (17.8)
15b2.68, d (17.8)2.67, d (17.8)2.60, d (17.8)2.61, d (17.8)
216.17, s6.16, s6.11, s6.12, s
23a-3.18, d (17.0) 3.22, d (17.3)a. 3.21, d (17.3)
23b-3.02, d (17.0)3.10, d (17.3)b. 3.08, d (17.3)
254.59, dd (4.4, 1.8)4.96, dd (9.8, 6.2)4.31, br d (10.9)4.33, d (10.8)
26a2.62, ddd (14.1, 6.7, 4.4)2.74, ddd (13.0, 8.9, 6.2)2.04, ddd (14.3, 10.9, 3.0)1.99, dd (13.2, 10.8)
26b1.98, ddd (14.1, 10.2, 1.8)2.34, ddd (13.0, 9.8, 9.8)1.85, dd (14.3, 9.8)1.87, dd (13.2, 10.8)
274.81, dd (10.2, 6.7)4.70, dd (9.8, 8.9)4.25, dd (9.8, 3.0)4.45, dd (10.8, 2.4)
291.86, d (1.5)1.88, dd (1.4, 1.4)1.91, br s 1.91, br s
2′5.75, d (13.9)5.74, d (15.2)5.76, d (15.2)5.75, d (15.2)
3′7.24, dd (13.9, 11.2)7.23, dd (15.2, 11.2)7.22, dd (15.2, 11.3)7.22, dd (15.2, 11.3)
4′6.12, dd (14.8, 11.2)6.12, dd (14.8, 11.2)6.21, dd (14.9, 11.3)6.21, dd (14.8, 11.3)
5′6.52, dd (14.8, 10.8)6.52, dd (14.8, 10.8)6.58, dd (14.9, 10.7)6.58, dd (14.8, 11.0)
6′6.12, dd (15.0, 10.8)6.13, dd (14.8, 10.8)6.16, dd (14.9, 10.7)6.16, dd (15.0, 11.0)
7′5.95, dq (15.0, 6.8)5.95, dq (14.8, 6.9)5.98, dq (14.9, 6.8)5.98, dq (15.0, 6.8)
8′1.82, d (6.8)1.82, d (6.9)1.79, d (6.8)1.79, d (6.8)
30-OMe3.75, s3.76, s3.67, s3.66, s
28-OMe---3.75, s
1-OH11.58, s11.65, s
11-OH14.21 A, br s14.11, s
20-OH11.05, s11.31, s
28-OH14.06 A, br s -
A assignments are interchangeable.
Table 2. 13C NMR data for jugiones A–D (1–4).
Table 2. 13C NMR data for jugiones A–D (1–4).
(1) δC, Mult
(CDCl3)		(2) δC, Mult
(CDCl3)		(2) δC, Mult
(methanol-d4)		(3) δC, Mult
(methanol-d4)		(4) δC, Mult
(methanol-d4)
1161.9, C161.9, C162.9, C162.8, C163.1, C
2119.5, CH119.5, CH120.1, CH120.0, CH120.1, CH
3136.3, CH136.2, CH137.2, CH137.0, CH137.1, CH
4122.2, CH122.2, CH123.1, CH123.0, CH123.1, CH
5137.2, C137.2, C138.7, C138.7, C138.7, C
6115.2, C115.2, C116.1, C116.2, C116.2, C
7186.7, C186.9, C188.3, CNDND
8106.6, C106.4, C107.6, C107.5 B, C107.5 B, C
941.5, C41.5, C42.7, C42.8, C42.7, C
1072.8, CH72.8, CH74.3, CH74.5, CH74.4, CH
11185.8, C185.8, C186.4, C187.4 B, C187.3 B, C
1243.4, CH43.3, CH44.3, CH44.4, CH44.4, CH
13141.4, C141.6, C142.9, C143.2, C143.0, C
14125.9, CH125.8, CH126.8, CH126.6, CH126.8, CH
1535.9, CH236.0, CH236.4, CH236.6, CH236.5, CH2
16148.7, C149.6, C150.4, C150.0, C150.1, C
17115.3 A, C115.0, C116.2, C116.2 B, C116.1, C
18154.1, C155.2, C156.9, C157.6, C157.4, C
19105.4, C105.9, C106.8, C106.9, C106.9, C
20160.4, C160.2, C161.1, C161.0, C161.1, C
21115.2 A, CH114.4, CH114.6, CH114.1, CH114.2, CH
22188.0, C193.9, C196.1, C198.1, C197.9, C
2399.8, C38.2, C39.6, CH240.6, CH240.3, CH2
2484.3, C84.2, C85.4, C89.2, C89.2, C
2568.9, CH77.7, CH78.8, CH72.8, CH71.7, CH
2632.4, CH231.5, CH232.4, CH237.7, CH236.9, CH2
2764.1, CH67.7, CH68.4, CH69.5, CH68.3, CH
28176.8, C175.4, C177.6, C180.3, C176.6, C
2921.0, CH321.0, CH320.8, CH320.7, CH320.7, CH3
30170.5, C168.8, C170.6, C171.9, C171.8, C
1′166.7, C166.7, C167.8, C167.8, C167.8, C
2′119.2, CH119.3, CH119.9, CH120.0, CH120.0, CH
3′146.5, CH146.4, CH147.6, CH147.6, CH147.6, CH
4′127.5, CH127.5, CH128.6, CH128.6, CH128.6, CH
5′142.2, CH142.2, CH143.4, CH143.4, CH143.4, CH
6′131.4, CH131.4, CH132.5, CH132.5, CH132.5, CH
7′136.1, CH136.0, CH136.7, CH136.6, CH136.7, CH
8′18.8, CH318.8, CH318.6, CH318.6, CH318.6, CH3
30-OMe54.0, CH354.2, CH354.0, CH353.4, CH353.5, CH3
28-OMe 52.6, CH3
A resonances with the same superscript within a column are interchangeable, B detected by HMBC. ND: resonance is not detected.
Table 3. Biological properties (IC50 μM) of jugiones A–D (1–4).
Table 3. Biological properties (IC50 μM) of jugiones A–D (1–4).
Assay Type(1)(2)(3)(4)
Antibacterial–Gram-positive
Staphylococcus aureus (ATCC 25923)1.86.6>303.7
Staphylococcus aureus A (581101692:1) 1.85.8>304.3
Staphylococcus aureus B (AUS-RBWH-MRSA-01)2.46.4>303.7
Enterococcus faecalis C (AUS-RBWH-VRE-01)2.63.9>303.7
Enterococcus faecalis D (ACM 5184)1.31.8>300.5
Antibacterial–Gram-negative
Escherichia coli (ATCC 11775)>30>30>30>30
Antifungal
Candida albicans (ATCC 10231)4.1>30>30>30
Anticancer–cell cytotoxicity
Human colon carcinoma (SW620)9.8>30>30>30
Human lung carcinoma (NCI-H460) 9.0>30>30>30
Clinical isolates resistant to A daptomycin, B methicillin and C vancomycin. D Vancomycin-susceptible clinical isolate.
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Sritharan, T.; Salim, A.A.; Khalil, Z.G.; Capon, R.J. Jugiones A–D: Antibacterial Xanthone–Anthraquinone Heterodimers from Australian Soil-Derived Penicillium shearii CMB-STF067. Antibiotics 2024, 13, 97. https://doi.org/10.3390/antibiotics13010097

AMA Style

Sritharan T, Salim AA, Khalil ZG, Capon RJ. Jugiones A–D: Antibacterial Xanthone–Anthraquinone Heterodimers from Australian Soil-Derived Penicillium shearii CMB-STF067. Antibiotics. 2024; 13(1):97. https://doi.org/10.3390/antibiotics13010097

Chicago/Turabian Style

Sritharan, Thulasi, Angela A. Salim, Zeinab G. Khalil, and Robert J. Capon. 2024. "Jugiones A–D: Antibacterial Xanthone–Anthraquinone Heterodimers from Australian Soil-Derived Penicillium shearii CMB-STF067" Antibiotics 13, no. 1: 97. https://doi.org/10.3390/antibiotics13010097

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