Letter Cite This: Org. Lett. 2018, 20, 1647−1650
pubs.acs.org/OrgLett
Anti-Inflammatory Isoquinoline with Bis-seco-aporphine Skeleton from Dactylicapnos scandens Bei Wang,†,§,∥ Zi-Feng Yang,‡,∥ Yun-Li Zhao,† Ya-Ping Liu,† Jun Deng,† Wan-Yi Huang,‡ Xiao-Nian Li,† Xin-Hua Wang,*,‡ and Xiao-Dong Luo*,†,‡ †
State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, People’s Republic of China ‡ Guangzhou Medical University, Guangzhou 511436, People’s Republic of China § University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China S Supporting Information *
ABSTRACT: Dactyllactone A (1), which was isolated from Dactylicapnos scandens, is an isoquinoline alkaloid with a rearranged and reconstructed D ring, making it the first of a new subtype of aporphines. Compound 1 might be derived from a common aporphine skeleton, which may have undergone biogenetic rearrangement and cleavage of the aromatic ring. Its structure was determined by extensive spectroscopic analysis and single-crystal X-ray diffraction. Compound 1 exhibited anti-inflammatory activity in vitro significantly by inhibiting the expression of IL-1β and PGE2 in a dose-dependent manner.
I
thenes,19 1-azaoxoaporphinoids,20 and azahomoaporphines;21 (4) heteroring B-seco phenanthrene derivatives, which possess a CH2CH2NR1R2 chain22 or have lost C-5 and generally contain a five-membered lactam ring;23,24 and (5) dimeric aporphinoid alkaloids, which are exemplified by the aporphine-benzylisoquinoline dimers.25 Inspired by the explorations of alkaloids with novel structures as potential drug leads,26−34 our phytochemical investigation of Dactylicapnos scandens (Papaveraceae)35 led to the isolation of an unprecedented alkaloid, dactyllactone A (1), which possesses a rearranged benzofuran lactone bearing a gemdimethoxycarbonyl unit (Figure 1) and is derived from a 8,9;11,11a-bis-seco-aporphine skeleton. Compound 1 was evaluated for anti-inflammatory effect in the lipopolysaccharide (LPS)-induced RAW264.7 cell line and showed significant
soquinoline alkaloids, which are an important class of Nheterocyclic bioactive natural products, are common throughout the plant kingdom.1 They are likely derived from tyrosine or phenylalanine building blocks, and they show a wide range of structural diversity.2 Since the first bioactive isoquinoline, morphine, was isolated from the opium plant in the early 19th century,3 these compounds have attracted considerable attention as lead compounds with high probabilities of success in the drug discovery and development process.4 Inspired by several revolutionary drugs, such as the antitussive codeine,5 the antibacterial berberine,6 the antirheumatic sinomenine,7 and the acetylcholinesterase inhibitor galanthamine,8 the search for novel isoquinolines as promising drug leads remains an active area of study in natural product chemistry. Aporphine alkaloids are a large group of isoquinolines that generally possess a characteristic tetracyclic ring system (rings A−D) with a nitrogen in ring B.9 The structures of the aporphine alkaloids can be classified into five subtypes:10,11 (1) simple aporphines and their dehydro derivatives, which generally have a double bond between C-6a and C-7 and are N-methylated; (2) oxoaporphines, which mostly have a hydroxyl or methoxyl group at C-712,13 or two such groups at C-4 and C-7 and have an aromatic isoquinoline ring and a carbonyl group at C-7;14 (3) miscellaneous aporphinoids, such as duguenaine-type aporphinoids,15 ring A quinonoid aporphinoids,16 oxoisoaporphines,17 azafluoranthenes,18 diazafluoran© 2018 American Chemical Society
Figure 1. Structure of dactyllactone A (1). Received: February 3, 2018 Published: March 6, 2018 1647
DOI: 10.1021/acs.orglett.8b00400 Org. Lett. 2018, 20, 1647−1650
Letter
Organic Letters activity by inhibiting the expression of IL-1β and PGE2 in a dose-dependent manner. Herein, the details of the structural elucidation, biogenetic pathway, and bioactivity of this novel aporphine alkaloid are described. The molecular formula of dactyllactone A (1)36 was determined to be C21H21NO8 by HRESIMS (m/z 416.1341 [M + H]+, calcd for 416.1340), implying 12 degrees of unsaturation. The UV spectrum showed strong bands at 209 nm (log ε = 4.15), 236 nm (log ε = 4.13), and 250 nm (log ε = 4.17), which indicated a π−π* transition (K-band) of the conjugated double bond, suggesting an extended conjugation system in the molecule.37 Moreover, other absorption bands at 301, 331, and 403 nm in the UV spectrum were typical of a highly unsaturated chromophore and auxochromes.38 The 13C NMR and DEPT spectra of 1 showed 21 carbon signals, including 4 methoxyl groups, 2 methylenes, 2 aromatic methines, 1 N-methyl, 9 downfield quaternary carbons, and 3 carbonyls. Methoxyl groups at δH 3.90 (s, H-12), 3.93 (s, H13), and 3.74 (s, H-15/16), 2 coupled methylenes at δH 3.22 (t, H-4) and 3.44 (t, H-5), 1 N-methyl at δH 3.08 (s, H-14), and 2 aromatic singlets at δH 7.05 (s, H-3) and 6.67 (s, H-7) were observed in its 1H NMR spectrum (Table 1), which is
Figure 2. Structural units and key HMBC correlations of dactyllactone A (1).
a typical isoquinoline ring B. Moreover, the correlations of δH 6.67 (s, H-7) with δC 129.7 (C-11a) and 120.6 (C-1b) suggested that the C ring was also a pentasubstituted aromatic ring. Then, based on detailed analysis of the HMBC correlations, the A/B/C ring system (unit A) of 1 was elucidated to be identical to that of isocorydione,41 which is a common aporphine alkaloid isolated from the same plant. The remaining signals, especially those of the three carbonyls at δC 165.3 (C-9/11) and 170.4 (C-8), in 1 were completely different from other aporphine alkaloids. In the HMBC spectrum of 1 (Figure 2), the correlation of δH 6.67 (s, H-7) with δC 170.4 allowed the tentative assignment of the carbonyl group at C-8. Moreover, the overlapping signals at δH 3.74 (6H, H-15/16) were correlated with the signal at δC 165.3 (C-9/11), which was indicative of two methyl ester fragments. The downfield signal at δC 110.0 (C-10) was assigned as an oxygenated sp3 quaternary carbon rather than an aromatic carbon. This assignment linked the two terminal methoxycarbonyls and the carbonyl group (C-8) (unit B) and accounted for the remaining oxygen in the molecular formula. However, the linkage could not be confirmed from the HMBC correlation data because the carbons involved are all quaternary. Since the preceding data accounted for 11 degrees of unsaturation, the presence of an additional five-membered lactone (ring D) was required to satisfy the molecular formula of 1 (Figure 2). Therefore, compound 1 was recrystallized from a mixture of n-hexane/isopropyl alcohol several times. Single-crystal X-ray diffraction analysis42 could then be used to confidently determine the linkage of ring D and the functional groups, and it unambiguously confirmed the final structure (Figure 3).
Table 1. 1H (600 MHz) and 13C (150 MHz) NMR Spectral Data of 1 in CDCl3 1 no.
δC
1 1a 1b 2 3 3a 4 5 6a 7 7a 8 9, 11 10 11a 12 13 14 15, 16
141.3 124.9 120.6 148.6 114.3 129.0 30.1 50.1 148.4 95.4 124.2 170.4 165.3 110.0 129.7 60.3 56.5 40.3 53.3
δH (J in Hz)
7.05, s 3.22, t (6.3) 3.44, t (6.3) 6.67, s
3.90, 3.93, 3.08, 3.74,
s s s s
consistent with the 13C NMR data. Notably, the overlapping signals at δH 3.74, δC 53.3 and 165.3 in the 1H and 13C NMR spectra of 1, were indicative of functional groups that were chemically equivalent.39,40 The above observations suggested that 1 might be an aporphine alkaloid with an unusual skeleton. In the HMBC spectrum of 1 (Figure 2), the correlations of δH 7.05 (s, H-3) with δC 148.6 (C-2), 141.3 (C-1), 120.6 (C1b), 129.0 (C-3a), 30.1 (C-4), and δH 3.90 (−OCH3, H-12) and those of 3.93 (−OCH3, H-13) with δC 141.3 (C-1) and 148.6 (C-2) suggested a pentasubstituted aromatic A ring. In addition, the correlations of δH 3.22 (H-4) with δC 129.0 (C3a), 120.6 (C-1b), 114.3 (C-3), and 50.1 (C-5) and those of δH 3.44 (H-5) with 129.0 (C-3a), 148.4 (C-6a), and 30.1 (C-4) combined with the correlations of δH 3.08 (−NCH3, H-14) with δC 50.1 (C-5) and 148.4 (C-6a) indicated the presence of
Figure 3. ORTEP drawing of dactyllactone A (1).
Structurally, the synthesis of the five-membered lactone with the gem-dimethoxycarbonyl moiety requires proceeding delicately. Thus, a plausible biogenetic pathway for dactyllactone A (1) was postulated, as shown in Scheme 1. Compound 1 could be traced back to the precursor, isocorydine,43 a major isoquinoline from D. scandens, which had been oxygenated to 1648
DOI: 10.1021/acs.orglett.8b00400 Org. Lett. 2018, 20, 1647−1650
Letter
Organic Letters
anti-inflammatory activity did not result from cytotoxicity. The research expands the aporphine-type scaffolding and might present promising anti-inflammatory natural product for further chemical and pharmacological investigation.
Scheme 1. Plausible Biosynthetic Pathway of 1
■
ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.8b00400. General experimental procedures, 1H and 13C NMR, HSQC, HMBC, UV, ESIMS and HRESIMS spectra of dactyllactone A (1) (PDF) Accession Codes
CCDC 1537088 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_
[email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, U.K.; fax: +44 1223 336033.
■
AUTHOR INFORMATION
Corresponding Authors
isocorydione.41 Further modification of ring D of isocorydione would afford key intermediate A, which could then undergo a benzilic acid-like rearrangement44−46 of an o-quinone by cleavage of C-11a/11 bond, followed by the formation of the new C-11a/10 bond (intermediate B). After that, intermediate B, which possesses a five-membered ring D, might be oxidized to the carboxylic acid anhydride by the insertion of an oxygen atom between C-8 and C-9.47−49 Finally, hydrolysis of ring D of intermediate C might produce the dicarboxylic acid form, which could further undergo lactonization and methylation to yield dactyllactone A (1). Following the procedures described,50,51 dactyllactone A (1) was evaluated for its ability to inhibit lipopolysaccharide (LPS)induced IL-1β and PGE2 production in RAW264.7 cells.52 As a result (Figure 4), dactyllactone A inhibited IL-1β and PGE2
*Tel./Fax: +86-871-65223177. E-mail:
[email protected] (X.-D. Luo). *E-mail:
[email protected] (X.-H. Wang). ORCID
Ya-Ping Liu: 0000-0002-2164-2489 Jun Deng: 0000-0002-7463-1329 Xiao-Dong Luo: 0000-0002-6768-5679 Author Contributions ∥
These authors contributed equally to this work.
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS The authors are grateful to the “Ten Thousand Plan”, a National High-level Talents Special Support Plan and the Natural Science Foundation of China (No. 81225024) for partial financial support.
■
REFERENCES
(1) Bhadra, K.; Kumar, G. S. Med. Res. Rev. 2011, 31, 821−862. (2) Koleva, I. I.; van Beek, T. A.; Soffers, A. E. M. F.; Dusemund, B.; Rietjens, I. M. C. M. Mol. Nutr. Food Res. 2012, 56, 30−52. (3) Santoro, D.; Bellinghieri, G.; Savica, V. J. Nephrol. 2011, 24 (Suppl. 17), 133−136. (4) Newman, D. J.; Cragg, G. M. J. Nat. Prod. 2016, 79, 629−661. (5) Freestone, C.; Eccles, R. J. Pharm. Pharmacol. 1997, 49, 1045− 1049. (6) Chu, M.; Xiao, R. X.; Yin, Y. N.; Wang, X.; Chu, Z. Y.; Zhang, M. B.; Ding, R.; Wang, Y. D. Clin. Microbiol.: Open Access 2014, 3, 1000150/1−1000150/4. (7) Xu, M.; Liu, L.; Qi, C.; Deng, B.; Cai, X. Planta Med. 2008, 74, 1423−1429. (8) Heinrich, M.; Teoh, H. L. J. Ethnopharmacol. 2004, 92, 147−162. (9) Perecim, G. P.; Rodrigues, A.; Raminelli, C. Tetrahedron Lett. 2015, 56, 6848−6851. (10) Guinaudeau, H.; Leboeuf, M.; Cave, A. J. Nat. Prod. 1994, 57, 1033−1135.
Figure 4. Effect of dactyllactone A (1) on IL-1β (A) and PGE2 (B) secretions in (LPS)-induced RAW264.7 cells. These data are expressed as the mean ± SEM. Statistics: (▲▲) p < 0.01 vs control; (*) p < 0.05, and (**) p < 0.01 vs LPS. DXM (dexamethasone) was used as a positive control.
production significantly in a dose-dependent manner, and its inhibitory effect (2.4−12 μM) was even superior to positive control (Dexamethasone at 20 μM). Furthermore, dactyllactone A did not show cytotoxic against RAW 264.7 cell line at test concentrations (see the Supporting Information, Figure S08) evaluated by the MTT method,51 which suggested that its 1649
DOI: 10.1021/acs.orglett.8b00400 Org. Lett. 2018, 20, 1647−1650
Letter
Organic Letters (11) Guinaudeau, H.; Leboeuf, M.; Cave, A. J. Nat. Prod. 1979, 42, 325−357. (12) Mathouet, H.; Elomri, A.; Lameiras, P.; Daich, A.; Verite, P. Phytochemistry 2007, 68, 1813−1818. (13) Guinaudeau, H.; Shamma, M.; Tantisewie, B.; Pharadai, K. J. Nat. Prod. 1982, 45, 355−357. (14) Del Rayo Camacho, M.; Kirby, G. C.; Warhurst, D. C.; Croft, S. L.; Phillipson, J. D. Planta Med. 2000, 66, 478−480. (15) Debourges, D.; Hocquemiller, R.; Cave, A.; Levy, J. J. Nat. Prod. 1985, 48, 310−312. (16) Alimova, M.; Israilov, I. A.; Yunusov, M. S.; Abdullaev, N. D.; Yunosov, S. Yu. Chem. Nat. Compd. 1982, 18, 689−692. (17) Kunitomo, J.; Satoh, M. Chem. Pharm. Bull. 1982, 30, 2659− 2660. (18) Cava, M. P.; Buck, K. T.; DaRocha, A. I. J. Am. Chem. Soc. 1972, 94, 5931. (19) Hufford, C. D.; Liu, S.; Clark, A. M.; Oguntimein, B. O. J. Nat. Prod. 1987, 50, 961−964. (20) Mahdi, F.; Morgan, J. B.; Liu, W.; Agarwal, A. K.; Jekabsons, M. B.; Liu, Y.; Zhou, Y. D.; Nagle, D. G. J. Nat. Prod. 2015, 78, 3018− 3023. (21) Rasamizafy, S.; Hocquemiller, R.; Cave, A.; Jacquemin, H. J. Nat. Prod. 1986, 49, 1078−1085. (22) Lin, H. F.; Huang, H. L.; Liao, J. F.; Shen, C. C.; Huang, R. L. Planta Med. 2015, 81, 830−837. (23) Ge, Y. W.; Zhu, S.; Shang, M. Y.; Zang, X. Y.; Wang, X.; Bai, Y. J.; Li, L.; Komatsu, K.; Cai, S. Q. Phytochemistry 2013, 86, 201−207. (24) Levrier, C.; Balastrier, M.; Beattie, K. D.; Carroll, A. R.; Martin, F.; Choomuenwai, V.; Davis, R. A. Phytochemistry 2013, 86, 121−126. (25) Guinaudeau, H.; Leboeuf, M.; Cave, A. J. Nat. Prod. 1979, 42, 133−149. (26) Cai, X. H.; Bao, M. F.; Zhang, Y.; Zeng, C. X.; Liu, Y. P.; Luo, X. D. Org. Lett. 2011, 13, 3568−3571. (27) Cai, X. H.; Du, Z. Z.; Luo, X. D. Org. Lett. 2007, 9, 1817−1820. (28) Cai, X. H.; Luo, X. D.; Zhou, J.; Hao, X. J. Org. Lett. 2005, 7, 2877−2879. (29) Cai, X. H.; Tan, Q. G.; Liu, Y. P.; Feng, T.; Du, Z. Z.; Li, W. Q.; Luo, X. D. Org. Lett. 2008, 10, 577−580. (30) Feng, T.; Cai, X. H.; Li, Y.; Wang, Y. Y.; Liu, Y. P.; Xie, M. J.; Luo, X. D. Org. Lett. 2009, 11, 4834−4837. (31) Feng, T.; Li, Y.; Liu, Y. P.; Cai, X. H.; Wang, Y. Y.; Luo, X. D. Org. Lett. 2010, 12, 968−971. (32) Li, X. N.; Zhang, Y.; Cai, X. H.; Feng, T.; Liu, Y. P.; Li, Y.; Ren, J.; Zhu, H. J.; Luo, X. D. Org. Lett. 2011, 13, 5896−5899. (33) Pan, Z. Q.; Qin, X. J.; Liu, Y. P.; Wu, T.; Luo, X. D.; Xia, C. F. Org. Lett. 2016, 18, 654−657. (34) Yang, X. W.; Yang, C. P.; Jiang, L. P.; Qin, X. J.; Liu, Y. P.; Shen, Q. S.; Chen, Y. B.; Luo, X. D. Org. Lett. 2014, 16, 5808−5811. (35) Air-dried roots of D. scandens (3.9 kg) were extracted with 80.0% CH3OH/H2O at reflux, and then the solvent was evaporated in vacuo. The residue was dissolved in 0.37% HCl (pH 2−3), and the solution was subsequently basified to pH 9−10 using aqueous ammonia. The basic solution was partitioned with EtOAc to afford a biphasic mixture. The EtOAc fraction (104 g) was divided into Frs. A−F by using silica gel chromatography (CHCl3/CH3OH, 1:0−2:8, v/ v). Fr. A (2.5 g) was separated on Sephadex LH-20 (CHCl3/CH3OH) to produce four fractions (Frs. A1−A6). Fr. A1 (0.4 g) was subjected to silica gel chromatography under isocratic conditions (petroleum ether/EtOAc, 20:1, v/v) to afford dactyllactone A (1) (2.0 mg). (36) Dactyllactone A (1): Light yellow needles (n-hexane: isopropanol = 1:1 (v/v), mp 142.7−143.5 °C; UV (MeOH) λmax (log ε): 209 nm (4.15), 236 nm (4.13), 250 nm (4.17), 301 nm (3.60), 331 nm (3.48), 403 nm (3.56); IR (KBr) νmax 2926, 1761, 1632, 1384, 1069 cm−1; 1H and 13C NMR spectroscopic data, see Table 1; ESIMS m/z 438 [M + Na]+; HRESIMS m/z 416.1341 [M + H]+ (calcd for 416.1340). (37) Grant, A. J.; Lerner, L. M. J. Med. Chem. 1980, 23, 795−798. (38) Chia, Y. C.; Chang, F. R.; Wu, Y. C. J. Nat. Prod. 1998, 61, 1430−1432.
(39) Wagner, R.; Berger, S. Magn. Reson. Chem. 1997, 35, 199−202. (40) Luy, B.; Hauser, G.; Kirschning, A.; Glaser, S. J. Angew. Chem., Int. Ed. 2003, 42, 1300−1302. (41) Lee, S. S.; Chen, C. K.; Chen, I. S.; Chen, C. H. J. Nat. Prod. 1996, 59, 55−58. (42) X-ray crystallographic analysis of dactyllactone A (1): C21H21NO8, M = 415.39, a = 14.0113(5) Å, b = 19.7144(7) Å, c = 14.2623(5) Å, α = 90°, β = 108.242(2)°, γ = 90°, V = 3741.6(2) Å3, T = 100(2) K, space group P21/c, Z = 8, μ(Cu Kα) = 0.964 mm−1, 22423 reflections measured, 6874 independent reflections (Rint = 0.0628). The final R1 values were 0.0686 (I > 2σ(I)). The final wR (F2) values were 0.1936 (I > 2σ(I)). The final R1 values were 0.0856 (all data). The final wR (F2) values were 0.2148 (all data). The goodness of fit on F2 was 1.061. (43) Zhong, M.; Jiang, Y.; Chen, Y.; Yan, Q.; Liu, J.; Di, D. Tetrahedron: Asymmetry 2015, 26, 1145−1149. (44) Otaka, J.; Hashizume, D.; Masumoto, Y.; Muranaka, A.; Uchiyama, M.; Koshino, H.; Futamura, Y.; Osada, H. Org. Lett. 2017, 19, 4030−4033. (45) Hine, J.; Haworth, H. W. J. Am. Chem. Soc. 1958, 80, 2274− 2275. (46) Eyong, K. O.; Puppala, M.; Kumar, P. S.; Lamshoeft, M.; Folefoc, G. N.; Spiteller, M.; Baskaran, S. Org. Biomol. Chem. 2013, 11, 459−468. (47) Mohebbi, A. R.; Munoz, C.; Wudl, F. Org. Lett. 2011, 13, 2560− 2563. (48) Yan, J.; Travis, B. R.; Borhan, B. J. Org. Chem. 2004, 69, 9299− 9302. (49) Zhang, D. L.; Zhou, L. Y.; Quan, J. M.; Zhang, W.; Gu, L. Q.; Huang, Z. S.; An, L. K. Org. Lett. 2013, 15, 1162−1165. (50) Li, K. K.; Zhou, X.; Wong, H. L.; Ng, C. F.; Fu, W. M.; Leung, P. C.; Peng, G.; Ko, C. H. J. Ethnopharmacol. 2016, 192, 192−200. (51) Chen, Q. Y.; Wang, C. Q.; Yang, Z. W.; Tang, Q.; Tan, H. R.; Wang, X.; Cai, S. Q. Chin. J. Nat. Med. 2017, 15, 515−524. (52) The macrophage RAW 264.7 cells were cultivated in DMEM in a humidified atmosphere with 5% CO2 at 37 °C and 2 × 104 cells/well grown in 96-well plates and incubated for 24 h. After that, the varying concentration of dexamethasone and compound 1 were added to each well for 2 h, and then stimulated with LPS (20 μM) for 24 h. Cell supernatants were collected and then assayed for IL-1β and PGE2 by ELISA assay. The production of prostaglandin E2 (PGE2) and interleukin (IL)-1β were measured using PGE2 and IL-1β Assay Kits (Wuhan Huamei Biotechnology, Wuhan, China) according to the manufacturers’ protocols. All experiments were performed within the concentration without cytotoxicity. Results are expressed as the mean ± SEM. Statistical significance was determined using the two tailed Student’s t-test, with (**) p < 0.01 or (*) p < 0.05 accepted as significant.
1650
DOI: 10.1021/acs.orglett.8b00400 Org. Lett. 2018, 20, 1647−1650
