Next Article in Journal
The Effect of Fe3O4 Nanoparticle Size on Electrical Properties of Nanofluid Impregnated Paper and Trapping Analysis
Previous Article in Journal
The Study of HEMs Based on the Mechanically Activated Intermetallic Al12Mg17 Powder
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Communication

Potent and Non-Cytotoxic Antibacterial Compounds Against Methicillin-Resistant Staphylococcus aureus Isolated from Psiloxylon mauritianum, A Medicinal Plant from Reunion Island

1
Association DESIBER, 98 rue Roger Payet, Rivière des Pluies, La Réunion, 97438 Sainte Marie, France
2
CNRS, Institute of Chemistry of Natural Substances UPR2301, University of Paris-Saclay, 91198 Gif-sur-Yvette, France
3
Laboratoire Shigeta, 62 boulevard Davout, 75020 Paris, France
4
Laboratory of Biodiversity and Microbial Biotechnologies (LBBM), Sorbonne University, CNRS, 75006 Paris, France, UPMC Univ Paris 06, Banyuls-sur-Mer oceanological observatory, 66650 Banyuls-sur-Mer, France
*
Authors to whom correspondence should be addressed.
Molecules 2020, 25(16), 3565; https://doi.org/10.3390/molecules25163565
Submission received: 22 July 2020 / Revised: 30 July 2020 / Accepted: 3 August 2020 / Published: 5 August 2020
(This article belongs to the Section Analytical Chemistry)

Abstract

:
With the occurrence of antibiotic-resistant Staphylococcus aureus strains, identification of new anti-staphylococcal drugs has become a necessity. It has long been demonstrated that plants are a large and diverse source of antibacterial compounds. Psiloxylon mauritianum, an endemic medicinal plant from Reunion Island, was chemically investigated for its reported biological activity against S. aureus. Aspidin VB, a phloroglucinol derivative never before described, together with Aspidin BB, were first isolated from the ethyl acetate extract of P. mauritianum leaves. Their structures were elucidated from spectroscopic data. Aspidin VB exhibited strong antibacterial activity against standard and methicillin-resistant S. aureus strains, with a minimal inhibition concentration (MIC) of 0.25 μg/mL, and no cytotoxicity was observed at 10−5 M in MRC5 cells. Due to its biological activities, Aspidin VB appears to be a good natural lead in the fight against S. aureus.

Graphical Abstract

1. Introduction

Staphylococcus aureus is a Gram-positive bacterium and the major cause of hospital-acquired infections, often resulting in longer stays and increases in patient mortality [1]. Such S. aureus infections, promoted by the use of ventilators or venous catheters, affect the bloodstream, lower respiratory tract, and the skin and soft tissues [2]. The microbial world is ruled by adaptation to environmental pressure, and S. aureus has developed very effective tools to resist antibiotics since the introduction of penicillin in the 1940s to cure infections. The selective pressure of antibiotics continually promotes the emergence of drug-resistant strains of S. aureus, which have dramatically increased and spread around the world [3].
Methicillin-resistant Staphylococcus aureus (MRSA) emerged quickly after introduction of the first semi-synthetic β-lactam in 1961 and has become a major worldwide health care problem [2]. Due to the rapidity and extent of its spread, as well as the high diversity among clones and strain virulence, the WHO has classified MRSA as a high priority target for new antibiotic development [4].
Even if pharmaceutical companies prefer combinatorial chemistry library strategies, the large diversity of natural products offers a wide range of antimicrobials [5]. Plant sources of anti-staphylococcal compounds should be highlighted due to reports in the literature of remarkable activities of acylphloroglucinols or terthiophenes, which have minimum inhibitory concentrations (MIC) of less than 1 μg/mL [5].
Psiloxylon mauritianum Baill. is a dioecious glabrous flowering plant classified as a member of the Myrtaceae family and is a unique species of the genus Psiloxylon [6]. P. mauritianum is endemic to Reunion Island and Mauritius and used there as a medicinal plant for the treatment of common infectious and inflammatory diseases, hypercholesterolemia, gout, dysentery and to alleviate symptoms of amenorrhea [7,8]. In 2013, the leaves of P. mauritianum were listed in the French pharmacopoeia and constitute one of the best-selling medicinal plants on Reunion Island. Aqueous extracts of P. mauritianum have also demonstrated antiviral activity against strains of Zika and Dengue viruses in vitro, without exhibiting genotoxic effects, in several mammalian cell types [9]. The crude acetone extract of P. mauritianum was found to harbor antioxidant activity and showed antimicrobial activity, with an MIC of 51 μg/mL recorded against S. aureus. Through bioassay guided fractionation, this anti-staphylococcal activity was linked to the presence of corosolic and asiatic acids [10]. Despite its promising biological activities and a large consumption of the leaf infusions by Reunionese people, very few phytochemical studies were found in the literature, and to date, only the two pentacyclic triterpenes mentioned above have been isolated from P. mauritianum [8,10].
In an effort to identify new natural antimicrobial compounds and to explore the chemical diversity of plants from Reunion Island, we found that the ethyl acetate extract (EtOAc) from P. mauritianum demonstrated strong antimicrobial activity against S. aureus (MIC of 8 μg/mL).

2. Results and Discussion

Bioassay guided fractionation of the antibacterial EtOAc extract of Psiloxylon mauritianum led to isolation of the known molecules Aspidin BB (1) [11,12], ursolic acid (3) and oleanic acid (4) [13], along with compound 2 that had not previously been isolated or described in the literature (Figure 1). The known compounds were identified by comparison of 1H and 13C data with values reported in the literature, together with crystallography data for 1. The common triterpenic acids 3 and 4 were isolated as a 6:4 ratio mixture, and the complete 1H and 13C-NMR assignments were deduced from NMR 1D and 2D experiments conducted on a 700 MHz NMR spectrometer.
Compound 2 was initially obtained as a white amorphous solid. HRESIMS analysis of 2 revealed a molecular formula of C27H36O8 (m/z 489.2490 for [M + H]+), implying 2 C and 4 H more than in Aspidin BB 1. The 1H-NMR spectrum displayed remarkably downfield-shifted singulet signals at δH 15.86, 11.41 and, 10.05, which are characteristic of the hydroxyl groups found in acylphloroglucinols Aspidin derivatives [14]. The 1H-NMR data of 2 were very similar to those for 1 except for the presence of a supplementary signal at δH 1.39 (m) integrating four protons (H11 and H12), and a two methyl triplet at δH 0.98 (J = 7.4 Hz) and δH 0.93 (J = 7.1 Hz), which are the common signals for methyl terminal groups (Table 1).
These findings suggest that 2 is an analogue of 1 with different structure of the side chains. Interpretation of COSY and HMBC experiments, especially HMBC correlations observed with the two ketonic carbons at δC 208.0 (C8′) and δC 207.5 (C8), easily revealed the presence of valeryl and butyryl chains. The connection of the valeryl side chain to the acylfilicinic acid moiety was determined with HMBC correlation between the protons of the methylene H9 at δH 3.19 with the quaternary carbon C3 at δC 108.9 ppm. The allocation of the butyryl chain was established with the ROESY experiment (Figure 2). In fact, the protons of the methylene H9′ at δH 3.15 displayed a ROE correlation with the protons of the methoxyl H7′ at δH 3.80, which exhibited a clear ROE correlation with the toluene methyl H12′ at δH 2.10.
The structure determined with the NMR data was confirmed by single-crystal X-ray diffraction analysis (See Tables S9–S16). Crystallographic data were recorded at 150 K to reduce agitation induced by the length of the valeryl side chain. Compound 2 was named Aspidin VB, and although its presence has already been mentioned in the literature [14,15], this is the first time that it has been isolated and characterized.
Next, the antimicrobial activity of the crude extract and isolated compounds 1 and 2 was evaluated. First, response against human Staphylococcus aureus and MRSA were examined, followed by Candida albicans and Trichophyton rubrum (Table 2).
Our plant extract exhibited antibacterial activity as well as anticandidal activity with an MIC of 8 µg/mL for S. aureus and C. albicans.
Compounds 1 and 2 exhibited antibacterial activity against S. aureus and MRSA higher than the positive control, with MICs of 0.25 μg/mL for 2 and 2 and 1 μg/mL for 1, respectively, against these two pathogens. Our results indicated that compound 2 has the same MIC as oxacillin against S. aureus and was 16-fold more potent than the standard antibiotic vancomycin against MRSA. Interestingly, Aspidin VB (2) showed higher activity than compound 1 against both bacteria. Furthermore, no cytotoxicity was observed for compound 2 at concentrations up to 10−5 M (Table 2). In our assays, Aspidin VB (2) was more active against MRSA and slightly less toxic than 1, which is known to exhibit no toxicity when S. aureus was killed [16].
In accordance with the literature [16], Aspidin BB (1) was strongly active against both S. aureus and MRSA but was inactive against the human pathogenic fungi. Aspidin BB (1) is known to exert strong antibacterial activity against Gram-positive bacteria, like S. aureus, S. epidermis or Propionibacterium acnes [16,17]. Li et al. identified the relationship between antibacterial activity and increase levels of reactive oxygen species in S. aureus cells. Moreover, the authors demonstrated that 1 induced peroxidation of membranes, DNA damage and protein degradation in S. aureus [16]. By comparing the effects of compounds 1 and 2 on S. aureus strains, our results demonstrated that a longer carbon chain (2 additional carbons) on the acylfilinic acid moiety is correlated with 4- to 8-fold stronger activity (Table 2). Compared to Aspidin BB (1), the antibacterial potency of Aspidin VB (2) may result from better cell wall penetration due to a longer alkyl chain inducing improved lipophilicity. Computed molecular properties of compounds 1 and 2 were obtained with the SwissADME web tool (http://www.swissadme.ch), and the results are detailed in Supplementary materials (Figures S14 and S15).

3. Materials and Methods

3.1. General Experimental Procedures

Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker 500 MHz spectrometer or on a Bruker 700 MHz spectrometer equipped with 5 mm inverse detection Bruker. Chemical shifts (δ) are reported in ppm based on the signal for TMS. Chemical shifts were referenced using the corresponding solvent signals (δH 2.05 and δC 29.92 for (CD3)2CO). HRESIMS measurements were performed using a Waters Acquity UHPLC system with a column bypass coupled to a Waters Micromass LCT Premier time-of-flight mass spectrometer equipped with an electrospray interface (ESI). X-ray diffraction data for compound 1 were collected on the PROXIMA 2A (PX2A) beamline at the SOLEIL Synchrotron, Gif-sur-Yvette, Paris, France. They were indexed, integrated with XDS [18] and scaled with AIMLESS [19], as implemented within the autoProc toolbox [20]. For compound 2, data were collected using redundant ω scans on a Rigaku XtaLabPro single-crystal diffractometer using microfocus Mo Kα radiation and a HPAD PILATUS3 R 200K detector. Its structure was readily solved by intrinsic phasing methods (SHELXT) [21] and by full-matrix least-squares methods on F2 using SHELX-L [22]. The non-hydrogen atoms were refined anisotropically, and hydrogen atoms, identified in difference maps, were positioned geometrically and treated as riding on their parent atoms. Molecular graphics were computed with Mercury 4.3.0. Flash chromatography was performed on a Grace Reveleris system with dual UV and ELSD detection equipped with a 40 g C18 column. Preparative HPLCs were conducted with a Gilson system equipped with a 322 pumping device, a GX-271 fraction collector, a 171 diode array detector, and a prepELSII detector electrospray nebulizer. The columns used for these experiments included a Phenomenex Kinetex C8 5 μm 4.6 × 250 mm analytical column and Phenomenex Kinetex C8 5 μm 21.2 × 250 mm preparative column. The flow rate was set to 1 or 21 mL/min, respectively, using a linear gradient of H2O mixed with an increasing proportion of CH3CN. Both solvents were of HPLC grade, modified with 0.1% formic acid.

3.2. Plant Material

Leaves of Psiloxylon mauritianum Baill. (Myrtaceae) were collected in Les Avirons, Reunion Island in 2016, identified by Raymond Lucas (Association APN, Réunion). A voucher specimen was deposited at ICSN-CNRS.

3.3. Extraction and Isolation

After collection, plant material was air dried in the shade at room temperature. Crushed dried leaves (135 g) were extracted by maceration with EtOAc (2 × 0.7 L, 2 × 24 h) on a rotary shaker (90 rpm). The organic solvent was collected by vacuum filtration and concentrated to dryness under reduced pressure to yield 10.6 g of extract. A portion of the extract (1.2 g) was subjected to reverse phase flash chromatography using a gradient of H2O mixed with an increasing proportion of CH3CN, both with 0.1% formic acid, to afford 14 fractions (A to N). A portion of fraction I (10 mg), eluted with 100% CH3CN, was subjected to preparative HPLC (isocratic elution at 20:80) to afford the mixture ursolic acid 3:oleanic acid 4 (6:4) (2.4 mg, RT = 6.0 min), and Aspidin BB 1 (4.3 mg, RT = 12.5 min). A portion of fraction J (40 mg) was washed with cold MeOH (0 °C) to afford Aspidin VB 2 (20 mg). After NMR experiments, small crystal needles were observed in samples tubes of Aspidin BB 1 and Aspidin VB 2. These crystals were carefully collected and analyzed by X ray crystallography.
Aspidin BB (1): White amorphous solid or colorless crystal needles; 1H-NMR (500 MHz, (CD3)2CO: δH 3.80 (3H, s, H7′), 3.57 (2H, s, H7), 3.18 (2H, dd, J = 7.3, 7.3 Hz, H9), 3.15 (2H, dd, J = 7.2, 7.2 Hz, 2H), 2.10 (3H, s, H12′), 1.70 (4H, m, H10, H10′), 1.49 (6H, s, H12, H13), 1.00 (3H, t, J = 7.4 Hz, H11), 0.98 (3H, t, J = 7.4 Hz, H11′); 13C-NMR (125 MHz, (CD3)2CO: δC 208.0 (C8′), 207.4 (C8), 199.8 (C4), 188.4 (C2), 172.7 (C6), 163.6 (C6′), 161.5 (C4′), 160.3 (C2′), 113.1 (C5′), 111.8 (C1), 110.2 (C1′), 109.0 (C3), 108.5 (C3′), 62.1 (C7′), 45.0 (C5), 44.4 (C9′), 43.5 (C9), 25.1 (C12), 25.1 (C13), 18.8 (C10), 18.2 (C10′), 17.7 (C7), 14.2 (C11), 14.1 (C11′), C12′ (9.5); HRESIMS [M + H]+ m/z 461.2173 (calc. for C25H33O8, 461.2175).
Aspidin VB (2): White amorphous solid or colorless crystal needles; 1H-NMR (500 MHz, (CD3)2CO and 13C-NMR (125 MHz, (CD3)2CO) see Table 1; HRESIMS [M + H]+ m/z 489.2490 (calculated for C27H37O8, 489.2488).
Ursolic acid (3): oleanic acid (4) (6:4 mixture): White amorphous; 1H-NMR (700 MHz, (CD3)2CO and 13C-NMR (175 MHz, (CD3)2CO) see Table 1; HRESIMS [M + H]+ m/z 457.3661 (calculated for C30H49O3, 457.3682).

3.4. Determination of Minimal Inhibitory Concentration

The crude extract and pure compounds isolated were tested against human pathogenic microorganisms, including the bacterium Staphylococcus aureus (ATCC 29213), MRSA (ATCC 33591), Candida albicans (ATCC 10213) and Trichophyton rubrum (SNB-TR1) to screen their antibacterial and antifungal activities. All ATCC strains were purchased from the Pasteur Institute. The clinical isolate was provided by Prof. Philippe Loiseau, Université Paris Sud. The ITS sequence was deposited in the NCBI GenBank database under the registry number KC692746 corresponding to SNB-TR1 strain. The tests were conducted in accordance to the reference protocols from the European Committee on Antimicrobial Susceptibility Testing [23,24,25,26]. The standard microdilutions, ranging from 256 to 0.25 μg/mL were made from stock solutions prepared in DMSO (Sigma-Aldrich, France). The microplates were incubated at 35 °C, and MIC values were obtained after 48 h for C. albicans, 24 h for S. aureus and 5 days for T. rubrum. The MIC values reported in Table 2 refer to the lowest concentration preventing visible growth in the wells. Vancomycin (Sigma-Aldrich, Saint-Quentin Fallavier, France) and oxacillin (Sigma-Aldrich, Saint-Quentin Fallavier, France) were used as positive controls for bacteria. Fluconazole (Sigma-Aldrich, Saint-Quentin Fallavier, France) and itraconazole (Sigma-Aldrich, Saint-Quentin Fallavier, France) were used as positive controls for fungi. All assays were conducted in duplicate.

3.5. Cytotoxicity Evaluation

Human lung fibroblast cells (MRC-5) were purchased from ATCC (Rockville, MD, USA) and cultured as recommended. Cell growth inhibition was determined by an MTS assay according to the manufacturer’s instructions (Promega, Madison, WI, USA). The cells were seeded in 96-well plates containing the growth medium. After 24 h of culture, samples were dissolved in DMSO (Sigma-Aldrich, France), and added to the cells (at 1 and 10 μM final concentrations). After 72 h of incubation, the reagent was added, and the absorbance at 490 nm was recorded using a plate reader. Cell viability was evaluated in comparison with untreated control cultures. Docetaxel (Taxotère) was used as positive control (IC50: 0.5 nM). All assays were conducted in triplicate.

4. Conclusions

Chemical investigation of the ethyl acetate extraction of P. mauritianum leaves led to the first report of the known compounds Aspidin BB (1), ursolic acid (3) and oleanic acid (4) in this plant. We also reported the presence of Aspidin VB (2), an acylphloroglucinol derivative never before described. The structure of compound 2 was determined by X-ray and NMR analyses. Aspidin VB (2) exhibited very strong activity against bacteria S. aureus and MRSA and showed no toxicity at 10−5 M in an MRC5 cell line. The two acylphloroglucinols compounds, 1 and 2, seem to be responsible for the antibacterial activity identified in the crude extract. Due to the biological activities of Aspidin VB, the antibacterial potency of 2 will be evaluated against different resistant S. aureus strains and additional pathogenic bacteria. This study further demonstrates the importance of phytochemical studies on medicinal plants from Reunion Island, which are largely unexplored.

Supplementary Materials

The following are available online, Crystallographic data have been deposited in the Cambridge Crystallographic Data Centre database (CCDC) (for compound 1, the deposition number CCDC is 2015192; for compound 2, the deposition number CCDC is 2015193). Copies of the data can be obtained free of charge from the CCDC at www.ccdc.cam.ac.uk.

Author Contributions

Conceptualization, J.S. and V.E.; methodology, J.S., D.S. and V.E.; validation, J.S., D.S. and V.E.; formal analysis, J.S., A.A., E.V.E., D.S. and V.E.; investigation, J.S., A.A. and E.V.E.; resources, D.S. and V.E.; data curation, J.S. and V.E.; writing—original draft preparation, J.S.; writing—review and editing, D.S. and V.E.; supervision, V.E. and J.S.; project administration, J.S. and V.E.; funding acquisition, J.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the European Commission and the Conseil Régional de la Réunion through European Regional Development Fund, Grant N° 2017-1600-0002373 (MEBIOPAM Project).

Acknowledgments

The authors thank the CCAS and the city of Sainte Marie for supporting this work. We are particularly grateful to R. Lucas and members of the APN Association for plant collection support and ethno-pharmacological discussions. We acknowledge the use of the synchrotron-radiation facility at the SOLEIL synchrotron, Gif-sur-Yvette, France. We also thank the staff of the PROXIMA 2A beamline at SOLEIL, and particularly Pierre Legrand, for assistance with data collection. This article is dedicated to the memory of Marc Rivière (1926–2017), a réunionese pioneer of scientific research on Medicinal Plants from Reunion Island.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Ridenour, G.A.; Wong, E.S.; Call, M.A.; Climo, M.W. Duration of colonization with methicillin-resistant Staphylococcus aureus among patients in the intensive care unit: Implications for intervention. Infect. Control Hosp. Epidemiol. 2006, 27, 271–278. [Google Scholar] [CrossRef]
  2. Schito, G.C. The importance of the development of antibiotic resistance in Staphylococcus aureus. Clin. Microbiol. Infect. 2006, 12, 3–8. [Google Scholar] [CrossRef] [Green Version]
  3. Chambers, H.F.; DeLeo, F.R. Waves of resistance: Staphylococcus aureus in the antibiotic era. Nat. Rev. Microbiol. 2009, 7, 629–641. [Google Scholar] [CrossRef]
  4. WHO: World Health Organization. Available online: https://www.who.int/en/news-room/detail/27-02-2017-who-publishes-list-of-bacteria-for-which-new-antibiotics-are-urgently-needed (accessed on 1 June 2020).
  5. Gibbons, S. Anti-staphylococcal plant natural products. Nat. Prod. Rep. 2004, 21, 263–277. [Google Scholar] [CrossRef]
  6. Wilson, P.G.; O’Brien, M.M.; Heslewood, M.M.; Quinn, C.J. Relationships within Myrtaceae sensu lato based on a matK phylogeny. Plant Syst. Evol. 2005, 251, 3–19. [Google Scholar] [CrossRef]
  7. Lavergne, R. Tisaneurs et Plantes Médicinales Indigenes de L’Ile de la Reunion, 3rd ed.; Orphie: Livry Gargan, France, 1990; pp. 160–161. [Google Scholar]
  8. Mahomoodally, F.M.; Korumtollee, H.N.K.; Khan Chady, Z.Z.B. Psiloxylon mauritianum (Bouton ex Hook.f.) Baillon (Myrtaceae): A promising traditional medicinal plant from the Mascarene Islands. J. Intercult. Ethnopharmacol. 2014, 3, 192–195. [Google Scholar] [CrossRef]
  9. Clain, E.; Haddad, J.G.; Koishi, A.C.; Sinigaglia, L.; Rachidi, W.; Desprès, P.; Duarte dos Santos, C.N.; Guiraud, P.; Jouvenet, N.; El Kalamouni, C. The Polyphenol-Rich Extract from Psiloxylon mauritianum, an Endemic Medicinal Plant from Reunion Island, Inhibits the Early Stages of Dengue and Zika Virus Infection. Int. J. Mol. Sci. 2019, 20, 1860. [Google Scholar] [CrossRef] [Green Version]
  10. Rangasamy, O.; Mahomoodally, F.M.; Gurib-Fakim, A.; Quetin-Leclercq, J. Two anti-staphylococcal triterpenoid acids isolated from Psiloxylon mauritianum (Bouton ex Hook.f.) Baillon, an endemic traditional medicinal plant of Mauritius. S. Afr. J. Bot. 2014, 93, 198–203. [Google Scholar] [CrossRef] [Green Version]
  11. Chen, N.-H.; Zhang, Y.-B.; Huang, X.-J.; Jiang, L.; Jiang, S.-Q.; Li, G.Q.; Yao-Lan Li, Y.-L.; Wang, G.-C. Drychampones A−C: Three Meroterpenoids from Dryopteris championii. J. Org. Chem. 2016, 81, 9443–9448. [Google Scholar] [CrossRef]
  12. Ito, H.; Muranaka, T.; Mori, K.; Jin, Z.-X.; Tokuda, H.; Nishino, H.; Yoshida, T. Ichthyotoxic Phloroglucinol Derivatives from Dryopteris fragrans and Their Anti-tumor Promoting Activity. Chem. Pharm. Bull. 2000, 48, 1190–1195. [Google Scholar] [CrossRef] [Green Version]
  13. Dais, P.; Plessel, R.; Williamson, K.; Hatzakis, E. Complete 1H and 13C NMR assignment and 31P NMR determination of pentacyclic triterpenic acids. Anal. Methods 2017, 9, 949–957. [Google Scholar] [CrossRef]
  14. Socolsky, C.; Hernández, M.A.; Bardón, A. Studies in Natural Products Chemistry, 1st ed.; Elsevier: Amsterdam, The Netherlands, 2012; Chapter 5; pp. 105–157. [Google Scholar]
  15. Widén, C.-J.; Lounasmaa, M.; Sarvela, J. Phloroglucinol Derivatives of eleven Dryopteris species from Japan. Planta Med. 1975, 28, 144–164. [Google Scholar] [CrossRef]
  16. Li, N.; Gao, C.; Peng, X.; Wang, W.; Luo, M.; Fu, Y.J.; Zu, Y.G. Aspidin BB, a phloroglucinol derivative, exerts its antibacterial activity against Staphylococcus aureus by inducing the generation of reactive oxygen species. Res. Microbiol. 2014, 165, 263–272. [Google Scholar] [CrossRef]
  17. Gao, C.; Guo, N.; Li, N.; Peng, X.; Wang, P.; Wang, W.; Luo, M.; Fu, Y.-J. Investigation of antibacterial activity of aspidin BB against Propionibacterium acnes. Arch. Dermatol. Res. 2016, 308, 79–86. [Google Scholar] [CrossRef]
  18. Kabsch, W. XDS. Acta Cryst. 2010, D66, 125–132. [Google Scholar] [CrossRef] [Green Version]
  19. Evans, P.R.; Murshudov, G.N. How good are my data and what is the resolution? Acta Cryst. 2013, D69, 1204–1214. [Google Scholar] [CrossRef]
  20. Vonrhein, C.; Flensburg, C.; Keller, P.; Sharff, A.; Smart, O.; Paciorek, W.; Womack, T.; Bricogne, G. Data processing and analysis with the autoPROC toolbox. Acta Crystallogr. D 2011, 67, 293–302. [Google Scholar] [CrossRef] [Green Version]
  21. Sheldrick, G.M. SHELXT- Integrated space-group and crystal-structure determination. Acta Crystalogr. A 2015, 71, 3–8. [Google Scholar]
  22. Sheldrick, G.M. Crystal structure refinement with SHELXL. Acta Crystallogr. C 2015, 71, 3–8. [Google Scholar] [CrossRef]
  23. European Committee on Antimicrobial Susceptibility Testing EUCAST. Available online: http://www.eucast.org (accessed on 11 April 2016).
  24. Sorres, J.; Sabri, A.; Brel, O.; Stien, D.; Eparvier, V. Ilicicolinic acids and ilicicolinal derivatives from the fungus Neonectria discophora SNB-CN63 isolated from the nest of the termite Nasutitermes corniger found in French Guiana show antimicrobial activity. Phytochemistry 2018, 151, 69–77. [Google Scholar] [CrossRef]
  25. EUCAST Definitive Document EDef 7.1: Method for the determination of broth dilution MICs of antifungal agents for fermentative yeasts. Clin. Microbiol. Infect. 2008, 15, 398–405.
  26. EUCAST Discussion Document, E.Dis 5.1: Determination of minimum inhibitory concentrations (MICs) of antibacterial agents by broth dilution. Clin. Microbiol. Infect. 2003, 9, 1–7.
Sample Availability: Samples of the compounds are available from the authors.
Figure 1. Structure of the compounds isolated from Psiloxylon mauritianum.
Figure 1. Structure of the compounds isolated from Psiloxylon mauritianum.
Molecules 25 03565 g001
Figure 2. Key ROESY correlations in Aspidin VB (2).
Figure 2. Key ROESY correlations in Aspidin VB (2).
Molecules 25 03565 g002
Table 1. The 1D and 2D NMR data for Aspidin VB (2) in acetone-d6.
Table 1. The 1D and 2D NMR data for Aspidin VB (2) in acetone-d6.
PositionAspidin VB
δC1δH(J in Hz) 2COSYHMBCROESY
1111.9
2188.4
3108.9
4199.9
545.1
6172.7
717.73.57, s C1, C2, C6, C1′, C2′, C6′
8207.5
941.63.19, dd (7.2, 7.2)H8C3, C8, C10, C11H11
1025.31.67, mH9, H11C8, C9, C11, C12
1132.51.39, mH10, H12C12H9
1223.21.38, mH11, H13C11
1314.30.93, t (7.1)H12C11, C12
1′110.2
2′160.6
3′108.5
4′161.5
5′113.2
6′163.6
7′62.13.80, s C4′H9′
8′208.0
9′44.83.15, dd (7.2, 7.2)H10′C8′, C10′, C11′H7′
10′18.81.72, sex (7.4)H9′, H11′C8′, C10′, C11′
11′14.20.98, t (7.4)H10′C9′, C10′H9′
12′9.52.10, s C4′, C5′, C6′H7′
6-OH 10.05, s C1, C5, C6H7, 2′-OH, 6′-OH
2′-OH 15.86, s C1′, C3′, C8′6-OH
6′-OH 11.41, s C1′, C5′, C6′H7, 6-OH
1 Recorded at 500 MHz. 2 Recorded at 125 MHz.
Table 2. Antimicrobial and cytotoxic results for EtOAc crude extract and isolated compounds.
Table 2. Antimicrobial and cytotoxic results for EtOAc crude extract and isolated compounds.
CompoundsMIC (µg/mL)MRC5 Cell Viability (%)
C. albicans
ATCC 10213
T. rubrum
SNB-TR1
S. aureus
ATCC 29213
MRSA
ATCC 33591
10−5 M10−6 M
1>256>2562186 ± 3104 ± 1
2>2562560.250.2599 ± 2105 ± 2
Crude extract82568nd96 ± 2100 ± 3
Fluconazole 114ndndndnd
Itraconazole 1<0.5<0.5ndndndnd
Oxacillin 1nd 2nd0.25ndndnd
Vancomycin 1ndndnd4ndnd
1 Positive control. 2 Not determined.

Share and Cite

MDPI and ACS Style

Sorres, J.; André, A.; Elslande, E.V.; Stien, D.; Eparvier, V. Potent and Non-Cytotoxic Antibacterial Compounds Against Methicillin-Resistant Staphylococcus aureus Isolated from Psiloxylon mauritianum, A Medicinal Plant from Reunion Island. Molecules 2020, 25, 3565. https://doi.org/10.3390/molecules25163565

AMA Style

Sorres J, André A, Elslande EV, Stien D, Eparvier V. Potent and Non-Cytotoxic Antibacterial Compounds Against Methicillin-Resistant Staphylococcus aureus Isolated from Psiloxylon mauritianum, A Medicinal Plant from Reunion Island. Molecules. 2020; 25(16):3565. https://doi.org/10.3390/molecules25163565

Chicago/Turabian Style

Sorres, Jonathan, Amandine André, Elsa Van Elslande, Didier Stien, and Véronique Eparvier. 2020. "Potent and Non-Cytotoxic Antibacterial Compounds Against Methicillin-Resistant Staphylococcus aureus Isolated from Psiloxylon mauritianum, A Medicinal Plant from Reunion Island" Molecules 25, no. 16: 3565. https://doi.org/10.3390/molecules25163565

Article Metrics

Back to TopTop