Synthesis, Crystal Structure and Biological Activity of (2,4-Dihydroxy-3,6-dimethoxyphenyl)-((1R,2S,3S,4R,7R)-isopropyl-5-methyl-3-phenylbicyclo[2.2.2]-oct-5-en-2-yl)methanone①

SUN Zhen-Ling DU Peng YAN Xue-Bing LI Ho HUANG Lin-Sheng QU Xio KONG Cheng LV Zhi-Ling QIN Hung-Long

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Synthesis, Crystal Structure and Biological Activity of (2,4-Dihydroxy-3,6-dimethoxyphenyl)-((1,2,3,4,7)-isopropyl-5-methyl-3-phenylbicyclo[2.2.2]-oct-5-en-2-yl)methanone①

SUN Zhen-LiangaDU PengbYAN Xue-BingaLI HaoaHUANG Lin-ShengaQU XiaoaKONG ChengaLV Zhi-LiangbQIN Huang-Longa②

a(200092)b(201203)

The crystal structure of the natural terpene derivative (2,4-dihydroxy-3,6-dimethoxy-phenyl)((1,2,3,4,7)-7-isopropyl-5-methyl-3-phenylbicyclo[2.2.2]oct-5-en-2-yl)-methanone was determined by single-crystal X-ray diffraction method. The compound crystallizes in triclinic, space group21/with= 16.1444(9),= 16.5294(9),= 19.7875(11) ?,= 5280.4(5) ?3,= 4,D= 1.209 g/cm3,(000) = 2064,(Cu)= 0.675 mm-1,= 1.069,= 0.0520 and(> 2()) = 0.1392. The spiro structure constructed by Diels-Alder reaction was highly symmetric. In addition, the title compound showed inhibitory activities against cancer cell line with varied potencies.

monoterpene, total synthesis, crystal structure, biological activity;

1 INTRODUCTION

Celosia cristata, an edible and medicinal herb of the genus of, functioning as dysentery, coughs, spitting up blood, excessive menstruation, amenorrhea, intestinal bleeding, female disorders, hemorrhoids, urinary tract infections, is widely distributed in subtropical and temperate zones of Africa, South America, and South East Asia[1, 2]. In particular, its dry mature seeds are usually used in traditional Chinese medicine to treat diseases like blurred vision, eye inflammation, eyes bothered by bright light, headache, intestinal worms, painful urination, cough, dysentery, bleeding and diarrhea[3, 4]. In recent years,. has attracted great attention and bioactive compounds such as saponins were found in[5-8].

Natural terpenes play an important role in modern drug discovery[9-10]. However, little information of terpenes has been reported from the extraction of seeds of., especially regarding their mode of purification, chemical characteristics, and anticancer activities. In this study, a novel skeleton of monoterpenes chalcone was extracted and separated from the mature seeds of. The title compound (5) was synthesized, characterized and its potential biological activity against cancer was also investigated (Table 1).

Table 1. In vitro Binding Affinities of Compound 5

PCC:prostate cancer cell line, BCC: breast cancer cell line, HLC: human leukemia cell line, HCCC: human colon cancer cell, STSC: soft tissue sarcoma cell, SHEF-11 and BAL-17 are two new compounds separated from.

2 EXPERIMENTAL

2.1 Materials and apparatuses

1H NMR and13C NMR spectra were acquired on a Varian Mercury (400MHz) using TMS as the internal standard. Mass spectra were recorded on a VGZAB-HS (70 eV) spectrometer with ESI source as ionization. X-ray diffraction was performed using a Super Nova. (Dual. Cu at zero, Eos) diffractometer. All reagents and solvents for synthesis and analyses were of analytical grade and used without further purification.Eight human tumor cells (PC3, PU145, MCF7, MDA-MB-231, NB4, NB4-R1, HCT-116, STS) were purchased from Institute of Basic Medical Sciences (IBMS) of Chinese Academy of Medical Sciences (Beijing, China).

2.2 Synthesis

The general procedure for the synthesis of the title compound is shown in Scheme 1.

Scheme 1. Synthesis route of the title compound 5

2. 2. 1 Synthesis of (E)-1-(2,4-dihydroxy-3,6-dime thoxyphenyl)-3-phenylprop-2-en-1-one (3)

The intermediate (3) was synthesized by 2,5-dimethoxybenzene-1,3-diol (1) and cinnamoyl chlo- ride (2) in the presence of BF3-Et2O[11].

A mixture of 2,5-dimethoxybenzene-1,3-diol (2.0 g, 11.8 mmol) and cinnamoyl chloride (2.6 g, 17.7 mmol) in boron trifluoride diethyl etherate solution (20 mL) was stirred at 45oC for 1 h. The reaction was quenched with water (10 mL), and extracted with EA (3 * 50 mL). The organic layer was com- bined, dried with anhydrous sodium sulfate, con- centrated, and purified by reversed phase column chromatography on C18 silica gel (water:acetonitrile = 60%) to get the desired product as an orange solid (1.0 g, yield: 28.6%). EI-MS (m/z) = 301 (M+H)+,1H NMR (400Hz, DMSO)= 13.83 (s, 1H), 10.48 (s, 1H), 7.87～7.67 (m, 4H), 7.48～7.46 (m, 3H), 6.10 (s, 1H), 3.87 (s, 3H), 3.67 (s, 3H).

2. 2. 2 Synthesis of (2,4-dihydroxy-3,6-dime thoxyphenyl)((1,2,3,4,7)-7-isopropyl-5-methyl-3-phenyl-bicyclo[2.2.2]oct-5-en-2-yl)methanone (5)

The title compound (5) was constructed by Diels-Alder cycloaddition using in situ-generated active silica-supported AgNP (Silica-supported Silver Nanoparticles) as catalyst[12].

A mixture of (E)-1-(2,4-dihydroxy-3,6-dime-thoxyphenyl)-3-phenylprop-2-en-1-one (320 mg, 1.07 mmol), (-)-alpha-phellandrene (950 mg, 70.0 mmol), and silica-supported AgNP catalyst (1.0 g, containing 27 μg Ag, 0.25 mol%) in dichloroethane (15 mL) was stirred at 70oC for 16 h. Then the reaction was filtered, concentrated, and the residue was purified by reversed phase column chromatography on C18 silica gel (water: acetonitrile = 60%) to get the desired product as a light yellow solid (300 mg, yield: 64.4%). EI-MS (m/z) = 437 (M+H)+,1H NMR(400Hz, DMSO)= 13.61 (s, 1H), 10.35 (s, 1H), 7.33～7.14(m, 5H), 6.07 (s, 1H), 5.46 (d,= 6.28 Hz, 1H), 3.98 (d,= 6.92 Hz, 1H), 3.87 (s, 3H), 3.36 (s, 3H), 3.48 (d,= 6.84 Hz, 1H), 2.88 (d,= 6.36 Hz, 1H), 2.37 (s, 1H), 1.87 (s, 3H), 1.82～1.76 (m, 1H), 1.58～1.55 (m, 1H), 1.08～1.03 (m, 1H), 0.86 (d,= 6.48 Hz, 3H), 0.82 (d,= 6.48 Hz, 3H), 0.74 (d,= 13.04 Hz, 1H).13C NMR (400 MHz, CDCl3):19.9, 20.8, 21.3, 25.8, 33.3, 38.9, 42.5, 43.3, 49.0, 56.0, 56.1, 60.8, 89.3, 105.5, 120.0, 125.9, 128.1, 128.3, 128.6, 143.7, 145.8, 154.6, 158.5, 159.1, 206.2.

2.3 X-ray crystal structure determination

The crystal of the title compound (5) was cultivated from ethyl acetate and petroleum ether (V/V = 1:8), and the light yellow prism with dimensions of 0.20mm × 0.15mm × 0.10mm was selected for X-ray diffraction studies.The data were collected on a Bruker APEX-II CCD diffractometer equipped with Cu-radiation (1.54178 ?) at 173(2) K.= 16.1444(9),= 16.5294(9),= 19.7875(11) ?,= 4,D= 1.209 g/cm3,(000) = 2064,= 0.675 mm-1,= 1.069,= 0.0520 and= 0.1392. In the scan range of 3.5≤≤64.0o(–18≤≤19, –18≤≤19, –22≤≤23), a total of 28412 reflections were collected with 8460 unique ones (int= 0.035), of which 8074 were observed with> 2(). The structure was solved by direct methods with SHELXS-97 program[13]. Refinement was done by full-matrix least-squares on2with SHELXL-97[14].

2.4 Biological screening

Thecytotoxicities of compound 5 were evaluated in five human tumor cells by the SRB (sulforhodamine B) method and the results are summarized in Table 1. Active screening was per- formed towards five typical cancer cell lines, and it was surprise to find compound 5 showed inhibition to all these cell lines. The IC50values of compound 5 against PC3, PU145, MCF7, MDA-MB-231, NB4, NB4-R1, HCT-116 and STS were of the order of magnitude of 10 μM, which indicated compound 5 can be considered as a novel lead compound and structural modification would be put forward to increase its drug activities.

3 RESULTS AND DISCUSSION

The structure of the title compound 5 was characterized by1H NMR,13C NMR, and LCMS. These spectroscopic data are in good agreement with the assumed structure, and its structure was further determined by X-ray diffraction analysis. The selected bond distances, bond angles and torsion angles are listed in Table 2, and the molecular structure and packing diagram are shown in Figs. 1 and 2, respectively.

Table 2. Selected Bond Lengths (?) and Bond Angles (o)/Torsion Angles (o) of Compound 5

Fig. 1. X-ray structure of compound 5 showing atom-numbering scheme

Fig. 2. Perspective view of the molecular packing of compound 5

Geometric structure analysis showed that the single crystal exists in the form of double molecules with one ethylacetate included. The cyclohexane ring itself showed a boat conformation, and theconfiguration ethene bond (C(12)=C(13), 1.316(5) ?) was set behind the cyclohexane ring, with the angles C(12)–C(11)–C(10), C(13)–C(14)–C(9) of 116.9(3)oand 109.6(2)o, respectively. The bond lengths of O(1)–C(2) (1.380(4) ?), O(2)–C(3) (1.340(4) ?), O(4)–C(5) (1.365(3) ?) and O(5)–C(7) (1.350(4) ?) were slightly shorter than the typical C–O bond (1.43 ?)[15-17], indicating2hybridization of the corresponding O atom with the phenyl ring. All the C–C single bonds are in the normal range. However, the C(12)–C(13) (1.316(5) ?) double bond is slightly shorter than the typical C=C (1.35 ?)[18], which could be pressed by intermolecular interaction while the crystal was growing. The two substituted benzene rings are non-coplanar with the cyclo- hexane moiety with torsion angles C(26)–C(21)–C(10)–C(9) (20.1(5)o) and C(8)–C(9)–C(14)–C(13) (78.5(3)o), respectively.

4 CONCLUSION

The natural product compound 5was synthesized and characterized by1H NMR,13C NMR and MS. Its 3D structure was confirmed by single-crystal X-ray diffraction. Bioactive tests showed compound 5 has an obvious preventive and therapeutic effect in the treatment of various cancer cell lines. Up to now, the novel scaffold has not been studied in the anti-cancer field, and its structural modification will be carried out in future.

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30 November 2017;

28 June 2018 (CCDC 1488037)

① This work was financially sponsored by Municipal Human Resources Development Program for Outstanding Young Talents in Medical and Health Sciences in Shanghai (2017YQ048), China Postdoctoral Science Foundation (2017M610278), National Nature Science Foundation of China (No. 81730102), Shanghai Rising-Star Program (16QB1403800)

Qin Huang-Long. E-mail: huanlong_qing@live.cn; Lv Zhi-Liang. E-mail: lvzhiliang_1983@hotmail.com

10.14102/ j.cnki.0254-5861.2011-1905