A Triterpene and a Depside from Parmotrema austrocetratum Elix and J. Johnst.

Ragasa, Tan, Linis, and Shen: A Triterpene and a Depside from Parmotrema austrocetratum Elix and J. Johnst.

Authors

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INTRODUCTION

Parmotrema austrocetratum Elix and J. Johnst. (syn. Rimelia austrocetrata Elix and J. Johnst.) belongs to a large genus of lichenized fungi under family Parmeliaceae.1 Thallus of P. austrocetratum are loosely adnate with broad, rotund lobe apices. The upper surface is reticulately cracked, maculae forming areoles, then eventually flaking off to expose the medulla. Erhizinate marginal in the lower cortex are either absent or very narrow. Lower cortex generally black with brown marginal area Soredia are absent. Marginal cilia frequent while rhizines are simple to squarrose and black in color.1 Its genus name Parmotrema refers to the perforate apothecia (Greek parmos = cup and trema = perforation).2 In the Philippines, P. austrocetratum is distributed in Northern Cordillera in Luzon island and Mount Apo in Mindanao island.3-4 The Philippine specimen chosen for our chemical investigation was gathered from the trunk of a Benguet pine (Pinus kesiya Royle ex Gordon) in Camp John Hay, Baguio City.

Parmotrema austrocetratum was reported to contain atranorin and salazinic acid.1 Of relevance to our present report are several studies on the genus Parmotrema which reported the presence of atranorin in P. arnoldii,5 P. crinitum,5 P. perlatum,5 P. stuppeum,5 P. crocoides,6 P. dilatatum,6 P. eciliatum,6 P. endosulphureum,6 P. erubescens,6 P. flavescens,6 P. flavomedullosum,6 P. gardneri,6 P. latissimum,6 P. eucosemothetum,6 P. masonii,6 P. mellissii,6 P. neotropicum,6 P. permutatum,6 P. robustum,6 P. rubifaciens,6 P. subarnoldii,6 P. subisidiosum,6 P. subsumptum,6 P. wrightii,6 P. sancti-angeli,6 P. simulans,6 P. sorediiferum,6 P. soredioaliphaticum,6 P. hydrium,7 P. praesorediosum,8 P. rampoddense,8 P. tinctorum,8-9 P. reticulatum,8 P. negrosorientalum,4 P. lichexanthonicum,10 P. cetratum,11 P. cristiferum,11 P. defectum,11 P. grayanum,11 P. margaritatum,11 P. perlatum,11 P. pseudocrinitum,11 P. reticulatum,11 P. subtinctorium.11

We report herein the isolation of zeorin (1) and atranorin (2) (Figure 1) from P. austrocetratum. To the best of our knowledge this is the first report on the isolation of 1 from P. austrocetratum and the genus Parmotrema.

Figure 1

Chemical structures of zeorin (1) and atranorin (2).

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MATERIALS AND METHODS

General Experimental Procedure

NMR spectra were recorded on a Varian VNMRS spectrometer in CDCl3 at 600 MHz for 1H NMR and 150 MHz for 13C NMR spectra. Column chromatography was performed with silica gel 60 (70-230 mesh). Thin layer chromatography was performed with plastic backed plates coated with silica gel F254 and the plates were visualized by spraying with vanillin/ H2SO4 solution followed by warming.

Sample Collection

The Philippine specimen chosen for our chemical investigation was gathered from the trunk of a Benguet pine (Pinus kesiya Royle ex Gordon) in Camp John Hay, Baguio City (date of collection: 14 October 2017).

Isolation of the Chemical Constituents of P. austrocetratum

The freeze-dried P. austrocetratum (17.52 g) was ground in a blender, soaked in CH2Cl2 for three days and then filtered. The filtrate was concentrated under vacuum to afford a crude extract (0.1578 g) which was chromatographed by gradient elution using petroleum ether, 2.5% EtOAc in petroleum ether, 5% EtOAc in petroleum ether, 7.5% EtOAc in petroleum ether, 10% EtOAc in petroleum ether, 12.5% EtOAc in petroleum ether, 15% EtOAc in petroleum ether, CH2Cl2, CH3CN:Et2O:CH2Cl2 (0.5:0.5:9, v/v), CH3CN:Et2O:CH2Cl2 (1:1:8, v/v), CH3CN:Et2O:CH2Cl2 (2:2:6, v/v). The CH3CN:Et2O:CH2Cl2 (0.5:0.5:9, v/v) fraction was rechromatographed using 15% EtOAc in petroleum ether, followed by CH3CN:Et2O:CH2Cl2 (0.5:0.5:9, v/v). The fractions eluted with 15% EtOAc in petroleum ether were combined and rechromatographed using the same solvent to afford 1 (4.3 mg) after washing with petroleum ether. The fractions eluted with CH3CN:Et2O:CH2Cl2 (0.5:0.5:9, v/v) were combined and rechromatographed using the same solvent to yield 2 (15.1 mg) after washing with petroleum ether.

Zeorin (1): 1H NMR (600 MHz, CDCl3): δ 0.74 (s, CH3-28), 0.85 (s, CH3-25), 0.96 (s, CH3-27), 1.00 (s, CH3-26), 1.02 (s, CH3-23), 1.13 (s, CH3-24), 1.16, 1.19 (s, CH3-29, CH3-30), 3.94 (dt, J = 4.2, 10.8 H-z); 13C NMR (150 MHz, CDCl3): δ 40.33 (C-1), 18.50 (C-2), 43.79 (C-3), 33.60 (C-4), 61.07 (C-5), 69.30 (C-6), 45.48 (C-7), 42.85 (C-8), 49.41 (C-9), 39.33 (C-10), 21.03 (C-11), 23.98 (C-12), 49.77 (C-13), 41.86 (C-14), 34.32 (C-15), 21.90 (C-16), 53.94 (C-17), 43.99 (C-18), 41.21 (C-19), 26.58 (C-20), 51.05 (C-21), 73.90 (C-22), 36.73 (C-23), 22.10 (C-24), 17.11 (C-25), 18.25 (C-26), 17.05 (C-27), 16.07 (C-28), 28.75 (C-29), 30.87 (C-30).

Atranorin (2): 1H NMR (600 MHz, CDCl3): δ 6.38 (s, H-5), 10.34 (s, H-8), 2.67 (s, CH3-9), 6.50 (s, H-6’), 2.07 (s, CH3-8’), 2.53 (s, CH3-9’), 3.97 (s, OCH3) 12.48 (s, 2-OH), 12.53 (s, 4-OH), 11.92 (s, 3’-OH); 13C NMR (150 MHz, CDCl3): δ 102.82 (C-1), 169.07 (C-2), 108.53 (C-3), 167.47 (C-4), 112.84 (C-5), 152.42 (C-6), 169.68 (C-7), 193.82 (C-8), 25.56 (C-9), 151.97 (C-1’), 116.77 (C-2’), 162.86 (C-3’), 110.24 (C-4’), 139.85 (C-5’), 116.00 (C-6’), 172.18 [C-7’), 9.35 (C-8’), 24.01 (C-9’), 52.32 (OCH3).

RESULTS AND DISCUSSION

Silica gel chromatography of the dichloromethane extract of P. austrocetratum has led to the isolation of zeorin (1) and atranorin (2). The structures of 1 and 2 were elucidated by extensive 1D and 2D NMR spectroscopy and confirmed by comparison of their NMR data with those reported in the literature for zeorin12-13 and atranorin,14 respectively.

Although there is no reported biological activity for P. austrocetratum, the compounds isolated from the plant were reported to possess diverse activities. Zeorin (1) and atranorin (2) have shown antidiabetic and antioxidant activities.15 Triterpene 1 also showed strong activity against bacteria and fungi.16 Depside 2 exhibited anti-proliferative action against malignant cell lines,17 antinociceptive effects18-19 and antibiotic action against M. aurum.20 It was found to inhibit leukotriene B4 synthesis in leukocytes, which might affect inflammatory processes21 and modulates the wound healing process.22

CONCLUSION

P. austrocetratum shares similar chemical characteristic with other Parmotrema species which yielded atranorin. This study highlights the first reported isolation of 1 from P. austrocetratum and the genus Parmotrema.

ACKNOWLEDGEMENT

A research grant from the De La Salle University Science Foundation through the URCO is gratefully acknowledged.

CONFLICT OF INTEREST

The authors declare no conflict of interest.

ABBREVIATIONS

CH2Cl2

Dichloromethane

CH3CN

Acetonitrile

EtOAc

Ethyl acetate

Et2O

Diethyl ether.

SUMMARY

Chemical investigation of the dichloromethane extract of Parmotrema austrocetratum Elix and J. Johnst. has led to the isolation of a triterpene, zeorin (1) and a depside, atranorin (2). The structures of 1 and 2 were elucidated by 1D and 2D NMR spectroscopy and confirmed by comparison of their NMR data with literature data.

REFERENCES

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Mahato SB, and Kundo AP , authors. 13C NMR spectra of pentacyclic triterpenoids - A compilation and some salient features. Phymchem. 1994; 37 (6): 1517 –75

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Ragasa CY, Tan MCS, Alba LDV, Shen CC , authors. A depside from Frullania trichodes Mitt. Der Pharmacia Lettre. 2016; 8 (5): 76 –8

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Thadhani VM, Karunaratne V , authors. Potential of lichen compounds as antidiabetic agents with antioxidative properties: A review. Oxidative Medicine and Cellular Longevity. 2017; 10: Article ID 2079697.

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GRAPHICAL ABSTRACT

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SUMMARY

  • Chemical investigation of the dichloromethane extract of P. austrocetratum has led to the isolation of zeorin (1) and atranorin (2). This is the first report on the isolation of 1 from P. austrocetratum and the genus Parmotema.

ABOUT AUTHORS

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Consolacion Y. Ragasa: Full Professor 10 of the Chemistry Department and a University Fellow of De La Salle University - Manila, Philippines.

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Maria Carmen S. Tan: Academic Service Faculty of De La Salle University - Manila, Philippines.

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Virgilio C. Linis: Assistant Professorial Lecturer 5 of the Biology Department, College of Science, De La Salle University - Manila, Philippines.

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Chien-Chang Shen: Associate Research Fellow in Division of Chinese Medicinal Chemistry, National Research Institute of Chinese Medicine, Ministry of Health and Welfare, Taiwan, ROC.