Three New Phenolic Compounds from the Lichen Thamnolia vermicularis and Their Antiproliferative Effects in Prostate Cancer Cells

• Abstract
• Materials and Methods
• Supporting information
• Acknowledgements
• References

Abstract

Three new phenolic compounds, thamnoliadepsides A (1), B (2), and thamnolic acid A (3), and seven known compounds, everninic acid (4), baeomycesic acid (5), β-orcinol (6), β-resorcylic acid (7), ethyl orsellinate (8), squamatic acid (9), and vermicularin (10), were isolated from the lichen Thamnolia vermicularis (Sw.) Ach. ex Schaerer. Their structures were determined based on spectroscopic analysis, including 2D-NMR experiments and HR-MS techniques. Compound 1 inhibited growth of prostate cancer cells and bonded to G-quadruplex DNA based on NMR determination.

Thamnolia vermicularis (Sw.) Ach. ex Schaerer. (Thamnoliaceae), a common lichen distributed in the high, frigid mountain region of Yunnan, Shanxi, and Sichuan Provinces of China, has been used as a folk medicine named “Baixuecha” for the treatment of hypertension, cough and neurasthenia. Several phenolic compounds, such as vermicularin [1], thamnolin, squamatic acid, barbatinic acid, and baeomycesic acid [2], have been isolated from this plant and baeomycesic acid was reported to possess antiproliferative effects against several human tumor cell lines [3]. In searching for the bioactive constituents of T. vermicularis, three new depsides (1–3), together with seven known phenolic acid derivatives including everninic acid (4) [4], baeomycesic acid (5) [2], β-orcinol (6) [5], β-resorcylic acid (7) [6], ethyl orsellinate (8) [7], squamatic acid (9) [2], and vermicularin (10) [1], were obtained from the CHCl₃ extract ([Fig. 1]). The structural elucidation of the three new compounds, and their antiproliferative effects on prostate cancer PC-3 cells are reported.

Compound 1 was obtained as a yellow needle and its molecular formula was determined as C₁₈H₁₈O₆ on the basis of its HR-ESI-MS ([M − H]⁻ m/z 329.1028). Its UV spectrum showed absorptions at 335 and 280 nm. The IR spectrum indicated the presence of a carbonyl (1724 cm⁻¹). The ¹H-NMR spectrum ([Table 1]) indicated the presence of the signals for three aromatic protons at δ _H 6.69 (1H, s), 6.56 (1H, brs), and 6.42 (1H, brs), three methyl groups at δ _H 2.44, 2.20, and 1.96, a methoxy group at δ _H 3.94, an aldehyde group at δ _H 10.20, and two phenolic hydroxy groups at δ _H 12.51 and 9.58. The ¹³C-NMR spectrum showed the presence of 4 sp³ carbons and 14 sp² carbons including an ester carbonyl carbon at δ _C 164.5 and an aldehyde carbon at δ _C 193.8. Based on the above data, compound 1 was determined as a depside derivative [2], [8], [9], [10]. Depsides exhibited two fragments (A and B) in the mass spectrum due to the cleavage of the depside ester bond [6]. The significant peaks at m/z 192.8 and 136.6 in the ESI-MS spectrum of compound 1 indicated the presence of two moieties (A and B). A careful comparison of the NMR spectral data of 1 with those of baeomycesic acid (5) [2] indicated that compound 1 had no carboxylic group in ring B. The substitution pattern of rings A and B were determined by the HMBC experiment ([Fig. 2]). The long-range correlations of the methyl signal at δ _H 2.44 (9-CH₃) with C-5 (δ _C 104.6), C-1 (δ _C 114.2), and C-6 (δ _C 148.7), the aromatic proton at δ _H 6.69 (H-5) with C-1 (δ _C 114.2), C-3 (δ _C 108.2), C-4 (δ _C 163.0), and C-9 (δ _C 21.0), the chelated hydroxy group at δ _H 12.51 (2-OH) with C-3 (δ _C 108.2), C-1 (δ _C 114.2), and C-2 (δ _C 160.6), and the methoxy group at δ _H 3.94 with C-4 (δ _C 163.0) confirmed the structure of ring A. Additionally, the HMBC correlations of the methyl signal (H-7′) at δ _H 1.96 (δ _C 9.1) with C-3′ (δ _C 113.9), C-4′ (δ _C 149.8), and C-2′ (δ _C 156.3), the methyl signal (H-8′) at δ _H 2.20 (δ _C 20.8) with C-1′ (δ _C 113.3) and C-6′ (δ _C 136.0), the aromatic proton at δ _H 6.42 (H-5′) with 8′-CH₃ (δ _C 20.8), C-1′ (δ _C 113.3), and C-3′ (δ _C 113.9), the aromatic proton at δ _H 6.56 (H-1′) with 8′-CH₃ (δ _C 20.8), C-3′ (δ _C 113.9), and C-2′ (δ _C 156.3) confirmed the structure of ring B. Thus, the structure of compound 1 was established as 3-formyl-2,2′-dihydroxy-4-methoxy-6,3′,6′-trimethyl-depside, and named thamnoliadepside A.

Compound 2 was obtained as a yellow needle and possessed a molecular formula of C₁₈H₁₈O₇, as revealed from its HR-ESI-MS ([M − H]⁻ m/z 345.0975). Its UV spectrum showed absorptions at 304 and 228 nm. The absorption peaks at 1717 (ester carbonyl) and 1668 cm⁻¹ (conjugated carboxylic) were observed in the IR spectrum. The ¹H-NMR spectrum ([Table 1]) indicated the presence of the signals for three aromatic protons at δ _H 6.60, 6.55, and 6.43, three methyl groups at δ _H 2.45, 2.18, and 1.93, a methoxy group at δ _H 3.84, and a phenolic hydroxy group at δ _H 9.55. The ¹³C-NMR spectrum revealed 18 carbon signals including a carboxylic carbon at δ _C 170.0 and an ester carbonyl carbon at δ _C 166.4. Detailed comparison of the NMR data of compounds 1 and 2 showed that they had the identical structure in ring B, whose significant peak is at m/z 136.7 in the ESI-MS spectrum, which was further supported by the HMBC correlations ([Fig. 2]) of the methyl signal of 3′-CH₃ at δ _H 1.93 (δc 9.1) with C-3′ (δ _C 113.9), C-4′ (δ _C 149.7), and C-2′ (δ _C 156.3), the methyl signal of 6′-CH₃ at δ _H 2.18 (δ _C 20.8) with C-1′ (δ _C 113.3), C-5′ (δ _C 113.1), and C-6′ (δ _C 135.9), the aromatic proton at δ _H 6.43 (H-5′) with 6′-CH₃ (δ _C 20.8), C-1′ (δ _C 113.3), C-3′ (δ _C 113.9), and C-4′ (δ _C 149.7), and the aromatic proton at δ _H 6.55 (H-1′) with 6′-CH₃ (δ _C 20.8), C-3′ (δ _C 113.9), and C-2′ (δ _C 156.3). The carboxylic carbon signal at δ _C 170.0 indicated a carboxylic group in 2 instead of an aldehyde in ring A, which was confirmed by the HMBC experiment. The methyl signal at δ _H 2.45 showed long-range correlations with C-5 (δ _C 105.4), C-1 (δ _C 112.2), and C-6 (δ _C 143.5), indicating that the methyl was located at C-6. The HMBC correlations of the aromatic proton at δ _H 6.60 (H-5) with C-1 (δ _C 112.2), C-3 (δ _C 104.9) and 6-CH₃ (δ _C 21.3), as well as the correlation between the methoxy group at δ _H 3.84 and C-4 (δ _C 160.6), confirmed that the carboxylic group was substituted at C-3. Consequently, the structure of compound 2 was deduced as 3-carboxyl-2,2′-dihydroxy-4-methoxy-6,3′,6′-trimethyl-depside, with the trivial name thamnoliadepside B.

Compound 3 was obtained as colorless needles and possessed the molecular formula C₁₂H₁₄O₆, as revealed from its HR-ESI-MS analysis ([M − H]⁻ at m/z 253.0716). Its IR spectrum indicated the presence of an ester carbonyl (1726 cm⁻¹) and a conjugated carboxylic group (1673 cm⁻¹). The UV spectrum showed absorption maxima at 306, 226 and 213.5 nm. The ¹H-NMR spectrum ([Table 1]) indicated the presence of an aromatic proton at δ _H 6.53 (1H, s), a methyl group at δ _H 2.36 (3H, s), an ethoxy group at δ _H 1.29 (3H, t, J = 7.1 Hz), and 4.28 (2H, q, J = 7.1 Hz), a methoxy group at δ _H 3.81, and a carboxylic group at δ _H 12.59. The ¹³C-NMR spectrum confirmed the presence of 4 sp³ carbons and 8 sp² carbons including one ester carbonyl carbon at δ _C 169.3 and a free carboxylic carbonyl at δ _C 169.7. According to the prominent HMBC correlation between the methylene at δ _H 4.28 and the ester carbonyl at δ _C 169.3, compound 3 was assumed to be an ethyl ester of a phenolic acid derivative. The substitution pattern in the benzene ring was established by the HMBC experiment. The position of the methyl at C-6 was deduced from the long-range correlation between the methyl signal at δ _H 2.36 and the carbons at δ _C 106.2 (C-5), 112.3 (C-1), and 143.9 (C-6). The aromatic proton was designated at C-5 by the HMBC correlations between the proton at δ _H 6.53 and the carbons at δ _C 107.4 (C-3), 112.3 (C-1), and 22.5 (C-9). The ³ J correlation of the methoxy proton at δ _H 3.81 with the carbon at δ _C 160.5 (C-2) established a methoxy group located at C-4. Based on the chemical shifts of C-2 (δ _C 160.0) and C-3 (δ _C 107.4), a hydroxy group was located at C-2, and a carboxylic group at C-3. Finally, compound 3 was elucidated as 3-carboxyl-2-hydroxy-4-methoxy-6-methyl benzoic acid ethyl ester, with the name of thamnolic acid A.

It has been discovered that depsides have antiproliferative effects on prostate cancer cells (PC-3), leukemia (K-562), gastric adenocarcinoma (AGS), mammary carcinoma (T47-D), pancreas cancer (Capan-2), and small cell lung cancer (NCI-H1417) [3], [11]. The antiproliferative effects of the isolated compounds were determined and compared in prostate cancer PC-3 cells. Compounds 1 and 2 exhibited a growth inhibitory effect in PC-3 cells with IG₅₀ values of 70.06 and 79.37 µM, respectively ([Table 2]). The IG₅₀ values of the other tested compounds were higher than 100 µM. The antiproliferative activities of compounds 1 and 2 are more potent than those of their corresponding 1′–COOH derivatives, baeomycesic acid (5) and squamatic acid (9), suggesting that the addition of a 1′–COOH group decreases the antiproliferative effects of compounds 1 and 2. Compounds that specifically bind G-quadruplex DNA may interact directly with telomeres, in addition to inhibiting telomerase, and produce more immediate antiproliferative effects [12]. A number of G-quadruplex ligands with the common feature of an extended aromatic ring system capable of interacting with G-tetrads [13], [14] have been reported. Because compounds 1, 2, 5, 9, and 10 have the approximative planar aromatic structures and ester carbonyl groups that can be protonated in line with the ligands' feature, G-quadruplex binding experiments via NMR were determined [15]. Compound 1 shifted the peak of the G5 position, indicating an interaction with G-quadruplex ([Fig. 3]). Compounds 2, 5, 9, and 10 did not change the peak positions of G3, G4 and G5. Agents stabilizing G-quadruplexes have the potential to interfere with telomere replication by blocking the elongation step catalyzed by telomerase and can therefore act as antitumor agents [16], [17], [18], [19], [20]. The antiproliferative activity of compound 1 may work through stabilizing the G-quadruplex structure [21], which needs to be further studied. Compound 2 cannot bind to G-quadruplex, which may be attributed to an additional 3–COOH group apt to ionize in the aqueous solution, which repels with the peripheral negative charges of DNA. Through computer-assisted docking experiments ([Fig. 4]), we found the reactive groups of compound 1 may be 2-OH, 2′-OH, and 7-C=O.

Materials and Methods

The UV spectrum was measured on a Shimadzu UV-1700 spectrometer. The FT-IR spectra were obtained on a Bruker IFS-55 spectrometer. ESI-MS was operated on an Agilent 1100 ion trap spectrometer and HR-ESI-MS was recorded on a Bruker microTOFQ-Q instrument. ¹H and ¹³C NMR data were obtained from a Bruker ARX-300 spectrometer using DMSO-d ₆ as the solvent with TMS as an internal standard. 2D NMR experiments were carried out on a Bruker AV-600 spectrometer. The silica gel for column chromatography (200–300 mesh) was purchased from Qingdao Haiyang Chemical Co. Ltd. ODS (50 µm) was produced by YMC Co. Ltd., and Sephadex LH-20 was produced by GE Healthcare. Primer d(TTGGGTT) was purchased from Tsingke Biotechnology Ltd., and purified by the C18 column. Doxorubicin hydrochloride, which was used as a positive control, was purchased from Hua Bo Technology Co. Ltd.

Thamnolia vermicularis was purchased from Yunnan province, China and identified by Prof. Qishi Sun of School of Traditional Chinese Materia Medica, Shenyang Pharmaceutical University. A voucher specimen (TV-090701) was deposited in the Department of Natural Products Chemistry, Shenyang Pharmaceutical University, Shenyang, People's Republic of China.

Thamnolia vermicularis (5.2 kg) was extracted with 70 % ethanol (3 × 40 L) to give an alcohol extract. The residue (314.6 g) after removing ethanol was suspended in water (2 L), and partitioned with CHCl₃ (3 × 2 L) and n-BuOH (3 × 2 L), successively. The CHCl₃ extract (15.4 g of 19.6 g) was fractionated by column chromatography (CC) on silica gel (4 × 28.5 cm, 120 g) with a gradient system of increasing polarity (CHCl₃-methanol; 100 : 0 to 100 : 70, 4 L each). The collected fractions were combined according to the TLC result to give 8 fractions (C1-C8). Fr. C1 (100 : 0, 2.4 L, 500 mg) was subjected to silica gel CC (1.5 × 22.0 cm, 10 g) eluted with petroleum ether (PE)-acetone (8 : 1) to yield compounds 4 (200 mL, 13.8 mg) and 3 (300 mL, 8.2 mg). Fr. C2 (100 : 0, 1.6 L, 2.0 g) was separated by open ODS CC (2.5 × 15.0 cm, 30 g) eluted with a gradient system of methanol-H₂O (10 : 90 to 35 : 65) to give compounds 6 (10 : 90, 120 mL, 39.1 mg), 8 (30 : 70, 200 mL, 7.9 mg), and 1 (35 : 65, 200 mL, 39.1 mg). Fr. C3 (100 : 1, 1.2 L, 2.0 g) was subjected to Sephadex LH-20 CC (2.5 × 30.0 cm, 25 g) eluted by methanol to give subfractions C-3-1 and C-3-2. The subfraction C-3-1 (250 mg) was purified by silica gel CC (1.5 × 22.0 cm, 10 g) eluted by PE-acetone (4 : 1) to afford compound 7 (160 mL, 14.2 mg). The subfraction C-3-2 (200 mg) was purified by silica gel CC (1.5 × 22.0 cm, 10 g) eluted by PE-ethyl acetate (2 : 1) to give compound 5 (10.0 mg). Fr. C4 (100 : 1, 2.8 L, 1.5 g), Fr. C-5 (100 : 2, 2.0 L, 0.8 g), and Fr. C6 (100 : 2, 2.0 L, 1.0 g) were purified by Sephadex LH-20 CC (2.5 × 30.0 cm, 25 g) and eluted by methanol to yield compounds 2 (7.6 mg), 9 (9.6 mg), and 10 (9.2 mg), respectively.

Thamnoliadepside A (1): yellow needle; m.p. 215–216 °C; UV (MeOH) λ _max (log ε) 335 (2.99), 280 (3.57) nm; FT-IR (KBr): ν _max = 3414, 2927, 1724, 1630, 1590, 1517, 1301, 1280, 1225, 1160, 1076 cm⁻¹. ¹H- (300 MHz, measured in DMSO-d ₆) and ¹³C-NMR (75 MHz, measured in DMSO-d ₆) data, see [Table 1]; (+) ESI-MS: m/z = 330.9 [M + H]⁺, 352.9 [M + Na]⁺, 192.8, 136.6; (−) ESI-MS: m/z = 328.7 [M − H]⁻; HR-ESI-MS: m/z = 329.1028 [M − H]⁻ (calcd. for C₁₈H₁₇O₆, 329.1025).

Thamnoliadepside B (2): yellow needle; m.p. 234–235 °C; UV (MeOH) λ _max (log ε) λ _max = 304 (3.03), 228 (3.43) nm; FT-IR (KBr): ν _max = 3422, 2926, 1718, 1669, 1636, 1403, 1278, 1208, 1189, 1120, 1071 cm⁻¹. ¹H-(300 MHz, measured in DMSO-d ₆) and ¹³C-NMR (75 MHz, measured in DMSO-d ₆) data, see [Table 1]; (−) ESI-MS: m/z = 344.9 [M − H]⁻, 206.7, 136.7; HR-ESI-MS: m/z = 345.0975 [M − H]⁻ (calcd. for C₁₈H₁₇O₇, 345.0974).

Thamnolic acid A (3): colorless needle; m.p. 179–180 °C; UV (MeOH) λ _max (log ε) λ _max = 306 (3.01), 226 (3.58), 213.5 (3.67) nm; FT-IR (KBr): ν _max = 3428, 3197, 2992, 1726, 1673, 1635, 1578, 1454, 1420, 1276, 1210, 1189, 1124, 1019; ¹H-(300 MHz, measured in DMSO-d ₆) and ¹³C-NMR (75 MHz, measured in DMSO-d ₆) data, see [Table 1]; (+) ESI-MS: m/z = 276.9 [M + Na]⁺; (−) ESI-MS: m/z = 252.7 [M − H]⁺; HR-ESI-MS: m/z = 253.0716 [M − H]⁻ (calcd. for C₁₂H₁₃O₆, 253.0712).

The antiproliferative assay was done as reported before [22]. PC-3 cells (2 × 10³) were plated in each well of a 96-well plate and allowed to adhere and spread for 24 h. Then various concentrations of those compounds were added. Cells were cultured for 4 days at 37 °C. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide solution (50 µL of 2 mg/mL) was added per well, and the cultures were continued for an additional 4 h. The medium was aspirated, the cells were dissolved in 200 µL DMSO, and the optical density (OD) at 570 nm was determined in each well with a 96-well plate reader. The cell growth inhibition rate was calculated as (ODc – ODt)/ODc × 100 %. ODc represents OD of the control group and ODt represents OD of the treated group. The concentration inhibiting 50 % of the cell proliferation (IG₅₀) was calculated.

The method of the preparation of G-quadruplex d(TTGGGTT)₄ was done as described in the literature [23]. G-quadruplex d(TTGGGTT)₄ was formed by dissolving primer d(TTGGGTT) in the buffer solution (10 mM K₂HPO₄/KH₂PO₄, 90 % H₂O/10 % DMSO, pH 7.0) and the formation of d(TTGGGTT)₄ was confirmed by NMR analyses. The solution was equilibrated at room temperature for 24 h before experiments. The tested compounds were added to the DNA solution, mixed, and incubated overnight at 25 °C. The NMRs of G-quadruplexes mixed with or without the tested compounds were recorded by the standard Bruker pulse program p3919gp that applies 3-9-19 pulses with gradients for water suppression. All experiments were carried out at 298.2 K.

Supporting information

¹H, ¹³C NMR, HMBC, HR-ESI-MS, UV, and IR spectra of compounds 1–3 are available as Supporting Information.

Acknowledgements

We are grateful to Prof. Ya-Lin Tang and Dr. Hong-Xia Sun of the Institute of Chemistry, Chinese Academy of Science for instructions for the G-quadruplex experiments. We appreciate Wen Li and Yi Sha for the NMR experiments. This work was partly supported by the National Science and Technology Key Specific Project for Significant Creation of New Drugs of China (2009ZX09301-012).

Conflict of Interest

There are no conflicts of interest for all authors.

References

• 1 Sun H D, Shen X Y. The structure of vermicularin.  Acta Bot Yunn. 1985;  7 109-113
  PubMedSearch in Google Scholar
• 2 Jiang B, Sun H D. Constituents from Thamnolia vermicularis.  Acta Bot Yunn. 2002;  24 525-530
  PubMedSearch in Google Scholar
• 3 Haraldsdottir S, Guolaugsdottir E, Ingolfsdottir K, Ogmundsdottir H M. Anti-proliferative effects of lichen-derived lipoxygenase inhibitors on twelve human cancer cell lines of different tissue origin in vitro.  Planta Med. 2004;  70 1098-1100
  Thieme ConnectPubMedSearch in Google Scholar
• 4 Li B, Sun H D. The chemical constituents of four lichens from China.  Acta Bot Yunn. 1991;  13 81-84
  PubMedSearch in Google Scholar
• 5 Cresp T M, Djura P, Sargent M V, Elix J A, Engkaninan U, Murphy D P H. The synthesis of notatic acid and 4-O-methylhypoprotocetraric acid.  Aust J Chem. 1975;  28 2417-2434
  CrossrefPubMedSearch in Google Scholar
• 6 Nishitoba Y, Nishimura H, Nishiyaya T, Mizutani J. Lichen acids, plant growth inhibitors from Usnea longissima.  Phytochemistry. 1987;  26 3181-3185
  CrossrefPubMedSearch in Google Scholar
• 7 Feng J, Yang X W, Su S D, He C. Studies on chemical constituents from herbs of Usnea longissima.  Chin J Chin Mater Med. 2009;  34 708-711
  PubMedSearch in Google Scholar
• 8 Sun H D, Shen X Y. Studies on ¹³C-NMR of depside.  Acta Bot Yunn. 1992;  14 445-452
  PubMedSearch in Google Scholar
• 9 Athukoralage P S, Herath H M, Deraniyagala S A, Wijesundera R L, Weerasinghe P A. Antifungal constituent from Gordonia dassanayakei.  Fitoterapia. 2001;  72 565-567
  CrossrefPubMedSearch in Google Scholar
• 10 Jiang B, Zhao Q S, Yang H, Hou A J, Lin Z W, Sun H D. Constituents from Lethariella cladonioides.  Fitoterapia. 2001;  72 832-833
  CrossrefPubMedSearch in Google Scholar
• 11 Bucar F, Schneider I, Gmundsdottir H O, Ingolfsdottir K. Anti-proliferative lichen compounds with inhibitory activity on 12(S)-HETE production in human platelets.  Phytomedicine. 2004;  11 602-606
  CrossrefPubMedSearch in Google Scholar
• 12 Kerwin S M. G-Quadruplex DNA as a target for drug design.  Curr Pharm Des. 2000;  6 441-471
  CrossrefPubMedSearch in Google Scholar
• 13 Cuesta J, Read M A, Neidle S. The design of G-quadruplex ligands as telomerase inhibitors.  Mini Rev Med Chem. 2003;  3 11-21
  PubMedSearch in Google Scholar
• 14 Monchaud D, Teulade-Fichou M P. A hitchhiker's guide to G-quadruplex ligands.  Org Biomol Chem. 2008;  6 627-636
  CrossrefPubMedSearch in Google Scholar
• 15 Sun H X, Tang Y L, Xiang J F, Xu G Z, Zhang Y Z, Zhang H, Xu L H. Spectroscopic studies of the interaction between quercetin and G-quadruplex DNA.  Bioorg Med Chem Lett. 2006;  16 3586-3589
  CrossrefPubMedSearch in Google Scholar
• 16 Han H Y, Hurley L H. G-quadruplex DNA: a potential target for anti-cancer drug design.  Trends Pharmacol Sci. 2000;  21 136-142
  CrossrefPubMedSearch in Google Scholar
• 17 Hurley L H, Wheelhouse R T, Sun D, Kerwin S M, Salazar M, Fedoroff O Y, Han F X, Han H Y, Izbicka E, Von Hoff D D. G-quadruplexes as targets for drug design.  Pharmacol Ther. 2000;  85 141-158
  CrossrefPubMedSearch in Google Scholar
• 18 Neidle S, Read M A. G-quadruplexes as therapeutic targets.  Biopolymers 2000 –. 2001;  56 195-208
  PubMedSearch in Google Scholar
• 19 Sun D, Thompson B, Cathers B E, Salazar M, Kerwin S M, Trent J O, Jenkins T C, Neidle S, Hurley L H. Inhibition of human telomerase by a G-quadruplex-interactive compound.  J Med Chem. 1997;  40 2113-2116
  CrossrefPubMedSearch in Google Scholar
• 20 Riou J F, Guittat L, Mailliet P, Laoui A, Renou E, Petitgenet O, Megnin-Chanet F, Helene C, Mergny J L. Cell senescence and telomere shortening induced by a new series of specific G-quadruplex DNA ligands.  PNAS. 2002;  99 2672-2677
  CrossrefPubMedSearch in Google Scholar
• 21 Zhou Q J, Li L, Xiang J F, Tang Y L, Zhang H, Yang S, Li Q, Yang Q F, Xu G Z. Screening potential antitumor agents from natural plant extracts by G-quadruplex recognition and NMR methods.  Angew Chem Int Ed. 2008;  47 5590-5592
  CrossrefPubMedSearch in Google Scholar
• 22 Yang X, Liu G, Li H, Zhang Y, Song D, Li C, Wang R, Liu B, Liang W, Jing Y K, Zhao G. Novel oxadiazole analogues derived from ethacrynic acid: design, synthesis, and structure-activity relationships in inhibiting the activity of glutathione S-transferase P1-1 and cancer cell proliferation.  J Med Chem. 2010;  53 1015-1022
  CrossrefPubMedSearch in Google Scholar
• 23 Sun H X, Tang Y L, Xiang J F, Xu G Z. Regulation and recognization of the extended G-quadruplex by rutin.  Biochem Biophys Res Commun. 2007;  352 942-946
  CrossrefPubMedSearch in Google Scholar

Prof. Dr. Hui-ming Hua

Key Laboratory of Structure-Based Drug Design & Discovery
Ministry of Education
School of Traditional Chinese Materia Medica
Shenyang Pharmaceutical University

Box 49

Shenyang 110016

People's Republic of China

Phone: +86 24 23 98 64 65

Fax: +86 24 23 98 64 65

Email: huimhua@163.com

References

• 1 Sun H D, Shen X Y. The structure of vermicularin.  Acta Bot Yunn. 1985;  7 109-113
  PubMedSearch in Google Scholar
• 2 Jiang B, Sun H D. Constituents from Thamnolia vermicularis.  Acta Bot Yunn. 2002;  24 525-530
  PubMedSearch in Google Scholar
• 3 Haraldsdottir S, Guolaugsdottir E, Ingolfsdottir K, Ogmundsdottir H M. Anti-proliferative effects of lichen-derived lipoxygenase inhibitors on twelve human cancer cell lines of different tissue origin in vitro.  Planta Med. 2004;  70 1098-1100
  Thieme ConnectPubMedSearch in Google Scholar
• 4 Li B, Sun H D. The chemical constituents of four lichens from China.  Acta Bot Yunn. 1991;  13 81-84
  PubMedSearch in Google Scholar
• 5 Cresp T M, Djura P, Sargent M V, Elix J A, Engkaninan U, Murphy D P H. The synthesis of notatic acid and 4-O-methylhypoprotocetraric acid.  Aust J Chem. 1975;  28 2417-2434
  CrossrefPubMedSearch in Google Scholar
• 6 Nishitoba Y, Nishimura H, Nishiyaya T, Mizutani J. Lichen acids, plant growth inhibitors from Usnea longissima.  Phytochemistry. 1987;  26 3181-3185
  CrossrefPubMedSearch in Google Scholar
• 7 Feng J, Yang X W, Su S D, He C. Studies on chemical constituents from herbs of Usnea longissima.  Chin J Chin Mater Med. 2009;  34 708-711
  PubMedSearch in Google Scholar
• 8 Sun H D, Shen X Y. Studies on ¹³C-NMR of depside.  Acta Bot Yunn. 1992;  14 445-452
  PubMedSearch in Google Scholar
• 9 Athukoralage P S, Herath H M, Deraniyagala S A, Wijesundera R L, Weerasinghe P A. Antifungal constituent from Gordonia dassanayakei.  Fitoterapia. 2001;  72 565-567
  CrossrefPubMedSearch in Google Scholar
• 10 Jiang B, Zhao Q S, Yang H, Hou A J, Lin Z W, Sun H D. Constituents from Lethariella cladonioides.  Fitoterapia. 2001;  72 832-833
  CrossrefPubMedSearch in Google Scholar
• 11 Bucar F, Schneider I, Gmundsdottir H O, Ingolfsdottir K. Anti-proliferative lichen compounds with inhibitory activity on 12(S)-HETE production in human platelets.  Phytomedicine. 2004;  11 602-606
  CrossrefPubMedSearch in Google Scholar
• 12 Kerwin S M. G-Quadruplex DNA as a target for drug design.  Curr Pharm Des. 2000;  6 441-471
  CrossrefPubMedSearch in Google Scholar
• 13 Cuesta J, Read M A, Neidle S. The design of G-quadruplex ligands as telomerase inhibitors.  Mini Rev Med Chem. 2003;  3 11-21
  PubMedSearch in Google Scholar
• 14 Monchaud D, Teulade-Fichou M P. A hitchhiker's guide to G-quadruplex ligands.  Org Biomol Chem. 2008;  6 627-636
  CrossrefPubMedSearch in Google Scholar
• 15 Sun H X, Tang Y L, Xiang J F, Xu G Z, Zhang Y Z, Zhang H, Xu L H. Spectroscopic studies of the interaction between quercetin and G-quadruplex DNA.  Bioorg Med Chem Lett. 2006;  16 3586-3589
  CrossrefPubMedSearch in Google Scholar
• 16 Han H Y, Hurley L H. G-quadruplex DNA: a potential target for anti-cancer drug design.  Trends Pharmacol Sci. 2000;  21 136-142
  CrossrefPubMedSearch in Google Scholar
• 17 Hurley L H, Wheelhouse R T, Sun D, Kerwin S M, Salazar M, Fedoroff O Y, Han F X, Han H Y, Izbicka E, Von Hoff D D. G-quadruplexes as targets for drug design.  Pharmacol Ther. 2000;  85 141-158
  CrossrefPubMedSearch in Google Scholar
• 18 Neidle S, Read M A. G-quadruplexes as therapeutic targets.  Biopolymers 2000 –. 2001;  56 195-208
  PubMedSearch in Google Scholar
• 19 Sun D, Thompson B, Cathers B E, Salazar M, Kerwin S M, Trent J O, Jenkins T C, Neidle S, Hurley L H. Inhibition of human telomerase by a G-quadruplex-interactive compound.  J Med Chem. 1997;  40 2113-2116
  CrossrefPubMedSearch in Google Scholar
• 20 Riou J F, Guittat L, Mailliet P, Laoui A, Renou E, Petitgenet O, Megnin-Chanet F, Helene C, Mergny J L. Cell senescence and telomere shortening induced by a new series of specific G-quadruplex DNA ligands.  PNAS. 2002;  99 2672-2677
  CrossrefPubMedSearch in Google Scholar
• 21 Zhou Q J, Li L, Xiang J F, Tang Y L, Zhang H, Yang S, Li Q, Yang Q F, Xu G Z. Screening potential antitumor agents from natural plant extracts by G-quadruplex recognition and NMR methods.  Angew Chem Int Ed. 2008;  47 5590-5592
  CrossrefPubMedSearch in Google Scholar
• 22 Yang X, Liu G, Li H, Zhang Y, Song D, Li C, Wang R, Liu B, Liang W, Jing Y K, Zhao G. Novel oxadiazole analogues derived from ethacrynic acid: design, synthesis, and structure-activity relationships in inhibiting the activity of glutathione S-transferase P1-1 and cancer cell proliferation.  J Med Chem. 2010;  53 1015-1022
  CrossrefPubMedSearch in Google Scholar
• 23 Sun H X, Tang Y L, Xiang J F, Xu G Z. Regulation and recognization of the extended G-quadruplex by rutin.  Biochem Biophys Res Commun. 2007;  352 942-946
  CrossrefPubMedSearch in Google Scholar

Prof. Dr. Hui-ming Hua

Key Laboratory of Structure-Based Drug Design & Discovery
Ministry of Education
School of Traditional Chinese Materia Medica
Shenyang Pharmaceutical University

Box 49

Shenyang 110016

People's Republic of China

Phone: +86 24 23 98 64 65

Fax: +86 24 23 98 64 65

Email: huimhua@163.com

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