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Journal of the Chilean Chemical Society

versión On-line ISSN 0717-9707

J. Chil. Chem. Soc. v.54 n.4 Concepción dic. 2009

http://dx.doi.org/10.4067/S0717-97072009000400023 

J. Chil. Chem. Soc., 54, N° 4 (2009), págs. 428-431.

 

SYNTHESIS OF DIBENZYLBUTANEDIOL LIGNANS AND THEIR ANTI-HIV, ANTI-HSV, ANTI-TUMOR ACTIVITIES

 

YA-MU XIA,* WEN-HUI BI, YUAN-YUAN ZHANG

(College of Chemical Engineering, Qingdao University of Science and Technology, Shandong, Qingdao, 266042) e-mail: xiaym@qust.edu.cn


ABSTRACT

An effcient route to the synthesis of dibenzylbutanediol lignans and their analogues was reported. The syntheses were based on a strategy involving Stobbe condensation and alkylation reaction to give the skeleton of lignan, the resolution of (±)-diacid with quinine, the transformation of functional groups to obtain seven dibenzylbutanediol lignans and one analogue. Among the synthesized lignans, four compounds were natural products. All dibenzylbutanediol lignans and their analogue synthesized were evaluated on HIV Tat transactivation in human epithelial cells, HSV-1 gene and human leukemic, liver, prostate, stomach, and breast cancer cell in vitro, but some compounds displayed weak activity against HIV, HSV and MDA-MB-435 human breast cancer cell.

Key words: Dibenzylbutanediol lignan; Biological activity; Synthesis.


 

INTRODUCTION

Lignans are a class of secondary plant metabolites produced by oxidative dimerization of two phenylpropanoid units. They are widely distributed in the plant kingdom and have been found in species belonging to more than seventy families. Lignans are found in roots, rhizomes, stems, leaves, seeds and fruits1,2. Lignans probably participate in plant development, and may play an important role in plant defense against various biological pathogens and pests. In addition to their purpose in nature, lignans also possess signifcant pharmacological activities, including antitumor, anti-infammatory, immunosuppressive, cardiovascular, antioxidant and antiviral actions. From a chemical point of view, lignans show an enormous structural diversity, although their molecular backbone consists only of two phenylpropane units. Different families of lignans include the aryltetrahydronaphthalenes, typifed by podophyllotoxin, the diverse family of dibenzocyclooctadienes, the dibenzylbutanediol lignans and so on3-6.

Dibenzylbutanediol lignans and their analogues are a class of lignans that have received considerable interest because of their biological and medicinal properties. The dibenzylbutanediol lignans seco-isolariciresinol and its metabolits enterodiol induced a signifcant decrease in the invasion (MDAMB-231) through Matrigel7.Isotaxiresinol and its analogue (+)-taxiresinol from Taxus wallichiana were explored for anticancer properties. It was found that two lignans were active against colon adenocarcinoma cell lines in the MTT assay. However, isotaxiresinol was most active against the Caco-2 cell line in a clonogenic assay8. Kuepeli et al. investigated fve dibenzylbutanediol lignans and the analogues for their anti-infammatory activities, in which the lignans signifcantly inhibited carrageenan-induced hind paw edema in mice. The result showed that lariciresinol and isolariciresinol possess a potent in vitro inhibitory effect on the production of TNF-α, a pro-infammatory cytokine9. Other many dibenzylbutanediol lignans and their analogues have been shown to have a benefcial anti-virus effect10. These studies help to conclude that in future the dibenzylbutanediol lignans and their analogues may be an effective means of dealing with cancer, as well as providing antiviral and anti-infammatory benefts.

Several strategies for the synthesis of dibenzylbutanediol lignans and their analogues have been reported11-15.Among them, the alkylation of β-substituted γ-butyrolactone with an appropriate benzylic halide is the most widely used16. Herein, we report an effcient route to the synthesis of dibenzylbutanediol lignans and their analogues. The syntheses were based on a strategy involving Stobbe condensation and alkylation reaction to give the skeleton of lignan, the transformation of functional groups to obtain target compound. All lignans synthesized were evaluated on HIV Tat transactivation in human epithelial cells, HSV-1 gene and human leukemic, liver, prostate, stomach, and breast cancer cell in vitro. We would like to point out structure-activity relationship could be established, and the mechanism of action was determined.

EXPERIMENTAL

Melting points were taken on Gallenkamp melting point apparatus and are uncorrected. Optical rotations were determined on a Perkin-Elmer 341 polarimeter. Infrared spectra were recorded on a Nicolet NEXUS 670 FT-IR.

The 1HNMR and 13CNMR spectra were recorded on Mercury Plus-300 MHz and Avance-200 MHz spectrometers. Mass spectra were recorded on a ZAB-HS spectrometer. HRMS were obtained on a Bruker Daltonics APEXII47e spectrometer. Flash column chromatography was performed on silica gel (200–300 mesh) and TLC inspections on silica gel GF254 plates.

Diethyl 2-(3',4'-methylenedioxybenzylidene)succinate 2a. The piper-onal 1a (15.0 g, 100 mmol) and diethylsuccinate (17.4 g, 100 mmol) were added to a solution of NaOEt (13.6 g, 200 mmol) in EtOH (200 ml). After refuxing for 4 hrs, ethanol was removed. The residue was cooled and acidi-fed with HCl (5N). The mixture was extracted with EtOAc (3×80 ml). The EtOAc layer was then re-extracted with NaHCO3 saturated solution (100 ml). The NaHCO3 extract was acidifcated with HCl and the pH value was adjusted to 2. Then the obtained an oily layer was again extracted with EtOAc (3×100 ml). The combined organic layer was dried over MgSO4 and concentrated in vacuo. This residue was then added to the mixture of EtOH (250 ml), benzene (100 ml), and H2SO4 (2 ml), then refuxed in a Dean and Stark apparatus for 24 hrs so that water removed. The reaction mixture was concentrated in vacuo and extracted with EtOAc (200 ml), then washed with the NaHCO3 saturated solution (3×50 ml). The extract was dried over MgSO4 and concentrated in vacuo. Flash column chromatography of the residue afforded compound 2a as a yellow oil (28.2 g, 92%). 1H NMR (200 MHz, CDCl3): δ 1.22 (t, J = 7.3 Hz, 3H), 1.29 (t, J = 7.3 Hz, 3H), 3.51 (s, 2H), 4.16 (q, J = 7.3 Hz, 2H), 4.27 (q, J = 7.3 Hz, 2H), 5.96 (s, 2H), 6.76-6.87 (m, 3H), 7.76 (s, 1H); EI-MS (m/z, %): 306 (M+, 70), 261 (20), 232 (34), 203 (52), 175 (59), 159 (100). Anal. Calcd for C16H18O6: C, 62.88; H, 5.97. Found: C, 62.74; H, 5.92.

Diethyl 2-(3',4'-dimethoxybenzylidene)succinate 2b. Following the procedure described for the preparation of 2a, and starting with the veratralde-hyde 1b (16.6 g, 100 mmol), compound 2b was obtained as a yellow oil (29.6 g, 92%). 1H NMR (200 MHz, CDCl3): δ 1.33 (t, J = 7.3 Hz, 3H), 1.26 (t, J = 7.2 Hz, 3H), 3.58 (s, 2H), 3.87 (s, 3H), 3.90 (s, 3H), 4.21 (q, J = 7.3 Hz, 2H), 4.27 (q, J = 7.3 Hz, 2H), 6.86-7.00 (m , 3H), 7.84 (s, 1H); EI-MS (m/z, %): 322 (M+, 42), 276 (14), 249 (16), 175 (100). Anal. Calcd for C17H22O6: C, 63.34; H, 6.88. Found: C, 63.31; H, 6.83.

Diethyl 2-(3',4'-methylenedioxybenzylidene)-3-(3'',4'' methylene-dioxybenzyl) succinate 3a. To a well-stirred solution of compound 2a (24.5 g, 80 mmol) in THF (100 ml) was added dropwise a solution of LDA (80 mmol, 2 M in THF) in THF at –78°C under nitrogen atmosphere. The mixture was stirred at this temperature for 20 mins, then 3,4- methylenedioxybenzyl bromide (17.2 g, 80 mmol) in THF (50 ml) was added. The mixture was stirred at –78°C for 2 hrs. The mixture was quenched with NH4Cl saturated solution (100 ml). After warmed to room temperature, the mixture was extracted with CH2Cl2 (3 × 80 ml) and the organic layer was dried over MgSO4 and concentrated in vacuo. Flash chromatography of the residue over silica gel gave compound 3a as a white crystal (31.6 g, 90%). M.p. 58–59°C. IR (KBr/cm-1): 3410, 2981, 1736, 1490, 1246, 1039, 930, 809, 770. 1H NMR (200 MHz, CDCl3): δ 1.26 (t, J = 7.2 Hz, 3H, CH3), 1.34 (t, J = 7.2 Hz, 3H, CH3), 2.85 (dd, J = 10.0, 14.2 Hz, 1H, H-7''α), 3.34 (dd, J = 5.0, 14.2 Hz, 1H, H-7''β), 3.98 (dd, J = 5.0, 10.0 Hz, 1H, H-3), 4.15-4.32 (m, 4H, 2 × CH2CH3), 5.88 (s, 2H, OCH2O), 5.97 (s, 2H, OCH2O), 6.35-6.73 (m , 6H, ArH), 7.66 (s, 1H, H-7'). 13C NMR (50 MHz, CDCl3): δ 14.4 (2 × CH2CH3), 36.0 (C-3), 45.8 (C-7''), 61.2 (2 × OCH2CH3), 100.9 (OCH2O), 101.4 (OCH2O), 108.1 (C-5'), 108.4 (C-5''), 108.7 (C-2'), 109.7 (C-2"), 122.4 (C-6'), 122.7 (C-6"), 129.3 (C-l'), 130.1 (C-l"), 133.2 (C-2), 142.5 (C-7'), 146.1(C-4'), 147.5 (C-4"), 147.8 (C-3', C-3"), 166.9 (C=0), 172.9 (C=0). EI-MS (m/z, %): 440 (M+, 4), 395 (1), 306 (5), 231 (40), 137 (100). HRMS caled for C24H2JOs (M+H+): 441.1544. Found: 441.1538. Anal. Caled for C24H24Os: C, 65.45; H, 5.49. Found: C, 65.41; H, 5.45.

Diethyl 2-(3',4'-dimethoxybenzylidene)-3-(3",4"-methylenedioxy-benzyl)succinate 3b. Following the procedure described for the preparation of 3a, and starting with 2b (25.8 g, 80 mmol), compound 3b was obtained as a yellowish oil (31.7 g, 87%). IR (KBr/cm1): 2958, 2839, 1741, 1517, 918, 810, 760. 'H NMR (200 MHz, CDC13): 5 1.26 (t, J = 7.2 Hz, 3H, CH3), 1.35 (t, J = 7.2 Hz, 3H, CH3), 2.91 (dd, J = 9.8, 14.2 Hz, 1H, H-7"a), 3.34 (dd, J = 5.0, 14.2 Hz, 1H, H-7"p), 3.78 (s, 3H, OCH3), 3.88 (s, 3H, OCH3), 4.10 (dd, J = 5.0, 9.8 Hz, 1H, H-3), 4.18 (q, J = 7.2 Hz, 2H, CH2CH3), 4.30 (q, J = 7.2 Hz, 2H, CH2CH3), 5.85 (s, 2H, OCH20), 6.35-6.80 (m, 6H, ArH), 7.71 (s, 1H, H-7'); 13C NMR (50 MHz, CDC13): 5 14.1 (CH2CH3), 14.2 (CH2CH3), 35.7 (C-3), 45.5 (C-7"), 55.7 (OCH3), 55.8 (OCH3), 60.9 (2 x CH2CH3), 100.7 (OCH20), 107.7 (C-5'), 109.4 (C-5"), 110.7 (C-2'), 111.4 (C-2"), 121.1 (C-6'), 122.0 (C-6"), 127.9 (C-l'), 129.5 (C-l"), 132.9 (C-2), 142.3 (C-7'), 145.7 (C-4'), 147.2 (C-4"), 148.6 (C-3'), 149.1 (C-3"), 166.7 (C=0), 172.7 (C=0). EI-MS {m/z, %): 456 (M+, 3), 411 (1), 382 (1), 322 (4), 247 (51), 137 (100). HRMS caled for CH„0„ (M+H+): 457.1857. Found: 457.1856. Anal. Caled for CH O„: 25 29 8 25 28 8 C, 65.78; H, 6.18. Found: C, 65.72; H, 6.13.

(—)-2-(3 ',4' -methylenedioxybenzylidene)-3-(3 " ,4" -methylenedioxy-benzyl)succinic acid 4a.
Diester 3a (26.4 g, 60 mmol) was added to a solution of 20% aqueous NaOH (250 ml) and refuxed for 3 hrs. After cooled to room temperature, the mixture was washed with EtOAc (3x30 ml). After decolored with active carbon, the mixture was acidifcated with HC1 (2N), and obtained white solids. The crude product was crystallized from HOAc to give the (±)-di-acid 4a. The (±)-diacid 4a and (-)-quinine (38.9 g, 120 mmol) in ethanol (120 ml) was refuxed for 1 hrs. The reaction mixture was allowed to cool to room temperature slowly, fne white crystals were obtained. Two recrystallizations from ethanol was added to a solution of HC1 (2 N, 100 ml) and stirred for lhrs. The mixture was extracted with EtOAc (3 x 80 ml), and the extract was dried over MgS04 and evaporated. The white solids were recrystallized in EtOAc to yield the (-)-diacid 4a as a white crystal (10.1 g, 44%). M.p. 98-99°C. [a]D16 -95.3 (c 1.0, EtOH). IR (KBr/cm1): 3385, 2898, 1703, 1498, 1242, 1040, 928, 813, 620. 'H NMR (200 MHz, DMSO-d): 5 2.85 (dd, J = 10.2, 13.8 Hz, 1H H-7"a), 3.25 (dd, J = 4.4, 13.8 Hz, 1H, H-7"p), 3.93 (dd, J = 4.4, 10.2 Hz, 1H, H-3), 5.92 (d, J = 7.6 Hz, 2H, OCH20), 6.04 (s, 2H, OCH20), 6.37-6.90 (m , 6H, ArH), 7.53 (s, 1H, H-7'). EI-MS (m/z, %): 384 (M+, 1), 366 (1), 244 (1), 203 (3), 159 (2), 135 (100). Anal. Caled for C H O„: C, 62.50; H, 4.20.20 16 8 Found: C, 62.46; H, 4.17.

The white solids from concentrating the mother liquors were recrystallized twice in methanol and water to yield the (+)-diacid 4a' as a white crystal (9.0 g, 39%). M.p. 96-97°C. Tal 16 +94.8 (c 0.8, EtOH). 'H NMR, IR and MS of 4a' are in agreement with 4a.

(—)-2-(3',4'-Dimethoxybenzylidene)-3-(3",4"-methylenedioxybenzyl) succinic acid 4b. Following the procedure described for the preparation of 4a, and starting with the diester 3b (27.4 g, 60 mmol), (-)-diacid 4b was obtained as a white crystal (10.8 g, 45%). M.p. 159-160°C [a]D16 -143.2 (c 0.7, EtOH). IR (KBr/cm1): 3522, 2943, 1714, 1516, 1255, 1142, 925.'H NMR (200 MHz, DMSO-d6): 5 2.83 (dd, J = 10.2, 14.0 Hz, 1H, H-7"a), 3.18 (dd, J = 4.8, 14.0 Hz, 1H, H-7"p), 3.64 (s, 3H, OCH3), 3.73 (s, 3H, OCH3), 3.95 (dd, J = 4.8, 10.2 Hz, 1H, H-3), 5.87 (d, J = 8.2 Hz, 2H, OCH20), 6.35-6.89 (m, 6H, ArH), 7.52 (s, 1H, H-7'). EI-MS (m/z, %): 400 (M+, 1), 382 (17), 260 (5), 219 (12), 175 (26), 135 (100). HRMS caled for C21H21Os (M+H+): 401.1231. Found: 401.1239. Anal. Caled for CH O„: C, 63.00; H, 5.03. Found: C, 62.96; H, 21 20 8 5.01. (+)-diacid 4b' was obtained as a white crystal (9.2 g, 38%). M.p. 89-91°C [al„" +142.6 (c 0.6, EtOH). 'H NMR, IR and MS of 4b' are in agreement with L JD 4b.

(—)-Diethyl 2-(3',4'-methylenedioxybenzylidene)-3-(3",4"-methylene-dioxybenzyl)succinate 5a. To the 151 ml mixture of EtOH : benzene : H2S04 (100 : 50 : 1) was added 4a (7.7 g, 20 mmol), refuxed in a Dean and Stark apparatus for 36 hrs so that water removed. The reaction mixture was concentrated in vacuo and extracted with EtOAc (100 ml), and then neutralized with the NaHC03 saturated solution (3x30 ml). The extract was dried over MgS04 and concentrated in vacuo. Flash column chromatography of the residue gave (-)-diester 5a as a colorless oil (8.0 g, 91%). [a]D16 -68.4 (c 1.0, CHC13). 'H NMR, IR, MS and HRMS of 5a are in agreement with 3a.

(—)-Diethyl 2-(3',4'-Dimethoxybenzylidene)-3-(3",4"-methylene-dioxybenzyl)succinate 5b. Following the procedure described for the preparation of 5a, and starting with the diester 4b (8.0 g, 20 mmol), diacid 5b was obtained as a colorless oil (8.2 g, 90%).[α]D16 –170.1 (c 1.0, CHCl3). 1H NMR, IR, MS and HRMS of 5b are in agreement with 3b.

(–)-2-(3',4'-methylenedioxybenzylidene)-3-(3'',4''-methylenedioxy-benzyl)butane-1,4-diol 6a. AlCl3 (0.32 g, 2.4 mmol) added to a stirred suspension of LiAlH4 (0.32 g, 8 mmol). The mixture was stirred for 20 mins. Then (–)-diester 5a (3.72 g, 8 mmol) was added to the solution and the reaction mixture was stirred for 10 hrs. The reaction was quenched by ice water and fltered. The fltrate was dried over MgSO4 and concentrated in vacuo. Flash column chromatography of the residue gave (–)-6a (2.5 g°C87%).White crystals. M.p. 125–126°C. [α]D16 –27.6 (c 0.4, CHCl3). IR (KBr/cm-1): 3375, 1600, 1490, 920. 1H NMR (300 MHz, CDCl3): δ 2.46-2.82 (m, 2H, ArCH2), 3.38-3.63 (m, 1H, H-3), 4.02-4.48 (m, 4H, H-1, H-4), 5.90 (s, 2H, OCH2O), 5.97 (s, 2H, OCH2O), 6.54-6.82 (m, 6H, ArH), 7.61 (s, 1H, ArCH=C); 13C NMR (50 MHz, CDCl3): 35.8 (C-3), 45.6 (C-7''), 62.3 (C-4), 67.1 (C-1), 100.8 (OCH2O), 108.2 (C-5'), 109.1 (C-5''), 109.9 (C-2'), 110.4 (C-2''), 121.4 (C-6'), 122.3 (C-6''), 127.9 (C-1'), 130.6 (C-1''), 132.4 (C-2), 141.3 (C-7'), 145.7 (C-4'), 147.8 (C-4''), 149.1 (C-3''), 149.2 (C-3''); EI-MS (m/z, %): 356 (M+, 2), 338 (3), 221 (5), 203 (16), 135 (100). HRMS calcd for C20H24NO6 (M+NH4+): 374.1599. Found: 374.1592. Anal. Calcd for C20H20O6: C, 67.41; H, 5.66. Found: C, 67.38; H, 5.63.

(+)-2-(3',4'-Dimethoxybenzylidene)-3-(3'',4''-methylenedioxybenzyl) butane-1,4-diol 6b. Following the procedure described for the preparation of 6a, and starting with the (–)-diester 5b (3.7 g, 8 mmol), the 6b was obtained as a colorless oil (2.6 g, 85%).[α]D16 +14.0 (c 2.9, CH3COCH3). IR (KBr/cm-1):= 3382, 1600, 1493, 920. 1H NMR (300 MHz, CDCl3): δ 2.45-2.80 (m, 2H, ArCH2), 3.42-3.67 (m, 1H, H-3), 3.77 (s, 3H, OCH3), 3.89 (s, 3H, OCH3), 4.05-4.46 (m, 4H, H-1, H-4), 5.92 (s, 2H, OCH2O), 6.52-6.87 (m, 6H, ArH), 7.67 (s, 1H, ArCH=C); 13C NMR (50 MHz, CDCl3): 35.2 (C-3), 45.1 (C-7''), 55.6 (OCH3), 55.8 (OCH3), 62.0 (C-4), 66.8 (C-1), 100.8 (OCH2O), 107.2 (C-5'), 109.4 (C-5''), 109.8 (C-2'), 111.3 (C-2''), 120.9 (C-6'), 122.0 (C-6''), 128.2 (C-1'), 129.8 (C-1''), 133.8 (C-2), 142.1 (C-7'), 144.9 (C-4'), 147.2 (C-4''), 150.2 (C-3''), 150.6 (C-3''); EI-MS (m/z, %): 372 (M+, 12), 354 (8), 203 (7), 135 (100). HRMS calcd for C21H28NO6 (M+NH4+): 390.1912. Found: 390.1905. Anal. Calcd for C21H24O6: C, 67.73; H, 6.50. Found: C, 67.69; H, 6.47.

(–)-Dihydrocubebin 7a and meso-2,3-Bis(3',4'-methylenedioxybenzyl) butane-1,4-diol 8a. (–)-Diester 5a (3.6 g, 8 mmol) in ethyl acetate (100 ml) was stirred under hydrogen atmosphere for 12 hrs in the presence of 10% Pd/C (0.35 g). The reaction mixture was fltered through a pad of Celite, and the solvent was removed in vacuo to give a white solid. The solid was dissolved in dry THF (40 ml) and added to a stirred suspension of LiAlH4 (0.7 g, 18 mmol). The mixture was stirred for 10 hrs. Then the reaction was quenched by ice water and fltered. The fltrate was dried over MgSO4 and concentrated in vacuo. Flash column chromatography of the residue gave threo-(–)-7a (1.34 g) and erythro-8a (1.31 g) . (–)-Dihydrocubebin (7a). Yield 47%. White crystals. M.p. 112–113°C. [α]D16 –41.9 (c 0.8, CHCl3). IR (KBr/cm-1): 3382, 2921, 1514, 1242, 1032, 928, 809, 764. 1H NMR (200 MHz, CDCl3): δ 1.73-1.84 (m, 2H, H-2, H-3), 2.55-2.81 (m, 4H, 2 × ArCH2), 3.48 (d, J = 11.2 Hz, 2H, CH2OH), 3.72 (s, 2H, 2×OH), 3.74 (d, J = 11.2 Hz, 2H, CH2OH), 5.91 (s, 4H, 2 × OCH2O), 6.58-6.73 (m, 6H, ArH); 13C NMR (100 MHz, CDCl3): δ 35.8 (C-2, C-3), 44.2 (C-7', C-7''), 59.9 (C-1, C-4), 100.7 (2×OCH2O), 108.1 (C-5', C-5''), 109.2 (C-2', C-2''), 121.8 (C-6', C-6''), 134.3 (C-1', C-1''), 145.6 (C-4', C-4''), 147.5 (C-3', C-3''). EI-MS (m/z, %): 358 (M+,2), 340 (0.1), 204 (0.3), 161 (3), 135 (100). HRMS calcd for C20H26NO6 (M+NH4+): 376.1755. Found: 376.1760. Anal. Calcd for C20H22O6: C, 67.03; H, 6.19. Found: C, 66.98; H, 6.15. The spectral data were in agreement with the literature17. meso-2,3-Bis(3',4'-methylenedioxybenzyl)butane-1,4-diol (8a). Yield 46%. Colorless oil. IR (KBr/cm-1): 3293, 2920, 1488, 1246, 1037, 928, 811, 731. 1H NMR (200 MHz, CDCl3): δ 1.91-2.05 (m, 2H, H-2, H-3), 2.49-2.63 (m, 4H, 2 × ArCH2), 3.45-3.61 (m, 4H, 2 × CH2OH), 3.71 (s, 2H, 2 × OH), 5.92 (s, 4H, 2 × OCH2O), 6.61-6.76 (m, 6H, ArH). 13C NMR (50 MHz, CDCl3): δ 33.4 (C-2, C-3), 45.2 (C-7', C-7''), 62.9 (C-1, C-4), 100.8 (2 × OCH2O), 108.1 (C-5', C-5''), 109.2 (C-2', C-2''), 121.8 (C-6', C-6''), 134.1 (C-1', C-1''), 145.8 (C-4', C-4''), 147.6 (C-3', C-3''). EI-MS (m/z, %): 358 (M+, 3), 340 (0.3), 204 (0.8), 161 (4), 135 (100). HRMS calcd for C20H26NO6 (M+NH4+): 376.1755. Found: 376.1760. Anal. Calcd for C20H22O6: C, 67.03; H, 6.19. Found: C, 66.98; H, 6.15.

(–)-Dihydro-3', 4'-dimethoxy-3'', 4''-demethylenedioxycubebin 7b and (–)-2,3-Desmethoxy seco-isolintetralin 8b. Following the procedure described for the preparation of 7a and 8a, and starting with the diester 5b (3.6 g, 8 mmol), the 7b (1.3 g) and 8b (1.45 g) were obtained. (–)-Dihydro-3',4'-dimethoxy-3'',4''-demethylenedioxycubebin (7b). Yield 44%. Colorless oil. [α]D16 –36.8 (c 0.5, CHCl3). IR (KBr/cm-1): 3374, 1593, 1515, 1488, 1442, 928.

'H NMR (200 MHz, CDC13): 5 1.73-1.92 (m, 2H, H-2, H-3), 2.60-2.80 (m, 4H, 2 x H-7, 2 x H-7"), 3.50 (d, 2H, J = 11.6 Hz, CH2OH), 3.56 (s, 2H, 2 x OH), 3.80 (d, 2H, J = 11.6 Hz, CH2OH), 3.82 (s, 3H, OCH3), 3.84 (s, 3H, OCH3), 5.90 (s, 2H, OCHO), 6.57-6.80 (m, 6H, ArH). 13C NMR (100 MHz, CDCL):2 3 5 35.7 (C-2), 35.9 (C-3), 43.9 (C-7'), 44.1 (C-7"), 55.8 (OCH3), 55.9 (OCH3), 60.2 (C-l), 60.3 (C-4), 100.7 (OCH20), 108.0 (C-5'), 109.3 (C-5"), 111.2 (C-2'), 112.1 (C-2"), 121.0 (C-6'), 121.8 (C-6"), 133.1 (C-l'), 134.3 (C-l"), 145.7(C-4'), 147.3 (C-4"), 147.5 (C-3'), 148.8 (C-3"). EI-MS (m/z, %): 374 (M+, 4), 356 (0.4), 220 (3), 203 (3), 151 (100). HRMS caled for C21H30NO6 (M+NH +): 392.2068. Found: 392.2063. Anal. Caled for C H O : C, 67.36; 4 21 26 6 H, 7.00. Found: C, 67.31; H, 6.97. The spectral data were in agreement with the literature18. (—)-2,3-Desmethoxy seco-isolintetralin (8b). Yield 48%. Colorless oil. [a]D16 -1.7 (c 0.3, CHC13). IR (KBr/cm1): 3365, 2919, 1514, 1241, 1032, 727, 643. 'H NMR (200 MHz, CDC13): 5 1.71-1.93 (m, 2H, H-2, H-3), 2.56-2.82 (m, 4H, 2 x H-7, 2 x H-7"), 3.50 (d, 2H, J = 11.0 Hz, CH2OH), 3.75 (d, 2H, J = 11.0 Hz, CH2OH), 3.81 (s, 3H, OCH3), 3.83 (s, 3H, OCH3), 3.95 (s, 2H, 2 x OH), 5.89 (s, 2H, OCH20), 6.56-6.78 (m, 6H, ArH). 13C NMR (100 MHz, CDC13): 5 33.1 (C-2), 33.4 (C-3), 45.0 (C-7'), 45.2 (C-7"), 55.8 (OCH3), 55.9 (OCH3), 62.9 (C-l), 63.0 (C-4), 100.8 (OCH20), 108.1 (C-5'), 109.3 (C-5"), 111.2 (C-2'), 112.1 (C-2"), 121.0 (C-6'), 121.8 (C-6"), 133.0 (C-l'), 134.2 (C-l"), 145.8 (C-4'), 147.3 (C-4"), 147.6 (C-3'), 148.8 (C-3"). EI-MS {m/z, %): 374 (M+, 4.7), 356 (0.23), 220 (1.8), 203 (2.5), 151 (100). HRMS caled for C H NO .(M+NH +): 392.2068. Found: 392.2063. Anal. Caled for 21 30 6 4 C21H2606: C, 67.36; H, 7.00. Found: C, 67.31; H, 6.97. The spectral data were in agreement with the literature19.

(±)-Dihydrosesamin 9. DDQ (0.34 g, 1.5 mmol) added to a solution of dihydrocubebin 7a (0.36 g, 1 mmol) in glacial acetic acid. The mixture stirred for 5 hrs. The reaction mixture was poured onto crushed ice and extracted with EtOAc (80 ml). The organic layer was washed with the NaHS03 saturated solution (3x30 ml) and the NaHC03 saturated solution (3x30 ml). The extract was dried over MgS04 and concentrated in vacuo. Flash column chromatography of the residue gave (±)-dihydrosesamln 9 as a colorless oil (0.15 g, 42%). IR (KBr/cm1): 3431, 2934, 1592, 1514, 1466, 1230, 1022. :H NMR (300 MHz, CDCLJ: 5 1.67 (s, 1H, OH), 2.25-2.47 (m, 1H, H-3), 2.51 (dd, 1H, J = 10.3, 13.1 Hz, H-6a), 2.55-2.73 (m, 1H, H-4), 2.85 (dd, 1H, J = 4.9, 13.1 Hz, H-6p), 3.72 (dd, 1H, J = 6.3, 8.5 Hz, H-5a), 3.74 (dd, 1H, J = 6.6, 10.8 Hz, H-7a), 3.86 (dd, 1H, J = 6.9, 10.7 Hz, H-7p), 4.03 (dd, 1H, J = 6.5, 8.5 Hz, H-5p), 4.77 (d, 1H, J = 6.2 Hz, H-2), 5.92 (s, 2H, OCH20), 5.93 (s, 2H, OCH20), 6.60-6.82 (m, 6H, ArH). 13C NMR (75 MHz, CDCLJ: 5 33.4 (C-6), 42.7 (C-4), 52.9 (C-3), 60.7 (C-7), 73.3 (C-5), 82.7 (C-2), 101.0 (OCH20), 101.1 (OCH20), 106.6(C-5'), 108.2(C-5"), 108.7(C-2'), 109.3 (C-2"), 119.3 (C-6'), 121.4 (C-6"), 134.1 (C-l'), 137.4 (C-l"), 146.1 (C-4'), 147.2 (C-4"), 147.8(C-3'), 148.2 (C-3"). EI-MS {m/z, %): 356 (M+, 12), 217 (16), 192 (15), 149 (21), 135 (100). HRMS caled for C20H24NO6 (M+NH4+):374.1599. Found: 374.1603. Anal. Caled for C20H20O6: C, 67.41; H, 5.66. Found: C, 67.37; H, 5.63. The spectral data were in agreement with the literature20.

(±)-Dibenzocyclooctadiene diol 10. To a mixture dihydrocubebin 7a (0.53 g, 1.5 mmol) and DDQ (0.79 g, 3.5 mmol) was added freshly distilled TFA (12 ml). The mixture stirred for 2 hrs. The reaction mixture was poured onto crushed ice and extracted with EtOAc (60 ml). The organic layer was washed with the NaHS03 saturated solution (3x30 ml) and the NaHC03 saturated solution (3x30 ml). The extract was dried over MgSO, and concentrated in vacuo. Flash 4 column chromatography of the residue gave (±)-Dibenzocyclooctadiene diol 10 a white crystal (0.28 g, 52%). M.p. 270-272°C. IR (KBr/cm1): 3428, 2936, 1613, 1512, 1452, 1207. :H NMR (300 MHz, CDC13): 5 1.32-1.56 (m, 2H, H-2, H-3), 2.07 (dd, 2H, J = 10.2, 13.0 Hz, H-7'a, H-7"a), 2.73 (dd, 2H, J = 4.2, 13.0 Hz, H-7'p, H-7"p), 3.26 (dd, 1H, J = 6.0, 9.2 Hz, H-la), 3.68 (d, 1H, J = 5.4, 9.2 Hz, H-lp), 4.43 (s, 2H, OH), 5.94 (s, 2H, OCH20), 5.98 (s, 2H, OCH20), 6.64-6.78 (m, 6H, ArH). 13C NMR (75 MHz, CDCLJ: 5 34.8 (C-7', C-7"), 43.9 (C-2, C-3), 65.2 (C-l, C-4), 100.6 (2 x OCH20), 107.9 (C-5', C-5"), 108.9 (C-2', C-2"), 133.2 (C-6', C-6"), 135.0 (C-l', C-l"), 145.2 (C-4', C-4"), 146.7 (C-3', C-3"). EI-MS {m/z, %): 356 (M+, 40), 267 (23), 254 (11), 200 (16), 151 (100). HRMS caled for C20H24NO6 (M+NH4+):374.1599. Found: 374.1605. Anal. Caled for C24H3J06: C, 68.71; H, 8.41. Found: C, 68.65; H, 8.37. The spectral data were in agreement with the literature21.

RESULTS AND DISCUSSION

Synthesis of compounds

Piperonal 1a or veratraldehyde 1b was reacted with diethyl succinate in sodium ethoxide-ethanol solution to produce the benzylidene succinate half-ester, following by the esterifcation provided the diester 2a or 2b. Alkylation reaction of 2a or 2b to diester 3a or 3b was achieved by treatment with LDA and 3, 4-methylenedioxybenzyl bromide under –78°C. Hydrolysis of diester 3a or 3b under conventional conditions (NaOH, H2O) produced diacid, following by resolution via the quinine salt afforded diacid (–)-4a or (–)-4b, (+)-4a' or (+)-4b'. The diacid (–)-4a or (–)-4b was esterifed to produce unsaturated diester (–)-5a or (–)-5b (Scheme 1).


Reaction of (–)-5a or (–)-5b with LiAlH4/AlCl3 in THF afforded unsaturated diol lignans (–)-6a or (–)-6b (Scheme 2).


Treatment of (–)-5a or (–)-5b with Pd/C (10%) under hydrogen atmosphere gave saturated diester, following by reduction with LiAlH4 in THF to produce a readily separable mixture (approximate 1:1) of dibenzylbutanediol lignans threo-(–)-7a and erythro-8a or threo-(–)-7b and erythro-8b (Scheme 3). erythro-7a did not have optical rotation and was a meso-compound. The spectral data threo-(–)-7a, erythro-8a and threo-(–)-7b were in agreement with those found in the literatures.


When (–)-5a was treated with DDQ in acetic acid dehydrogenation occurred to give the compound 9. Treatment of (–)-5a with DDQ in trifuoroacetic acid dehydrogenation afforded the dibenzocyclooctadiene diol 10 (Scheme 4).


Bioactivity

Anti-virus activity

The synthesized compounds 6a, 6b, 7a, 7b, 8a, 8b, 9 and 10 were evaluated for their antiviral activities against HIV-1 and HSV in vitro. The anti-HIV assays of the synthesized lignans reported here were in agree with the methods previously reported22.

Among all the synthesized compounds, derivatives 7a, 7b, 8a, 8b with two free hydroxyl group were the most potent inhibitors of HIV replication, coupled with the highest selectivity index. In fact, compound erythro-8b showed the weak activities against HIV-1 (IC50=150 µg/ml), while the rest of the compounds did not exhibit any obvious activity.

The process of anti-HSV assay was previously described23. The results showed that 8b exhibited antiviral activity against herpes virus (77.04 µg/ml). The rest of the compounds did not exhibit any obvious activity. On the other hand, the results showed that SI of 8b was much lower (SI<1.0). Thus, we should enhance SI in the latter study in structure-function relationship in order to increase the selectivity of activity.

The biological data of the synthesized compounds led to some considerations that permitted a more regular pattern. Only compound 8b, bearing two free hydroxyl groups with erythro-structure, was characterized by modest antiviral activity against both HIV-1 and HSV. Thus, within the dibenzylbutanediol lignans, the best activity was provided by the two free hydroxyl groups and erythro-structure.

Anti-tumor activity

The synthesized dibenzylbutanediol lignans and their analogues were evaluated against HL-60 human leukemic cell, PC-3MIE8 human prostatic carcinoma cell, BGC-823 human stomach cancer cell, MDA-MB-435 human breast cancer cell in vitro, and the assays of the lignans have been previously published24.

We observed that all of the compounds at 10-5M, 10-6M and 10-7M inhibited HL-60 cell, PC-3MIE8 cell, BGC-823 cell, Bel-7402 cell and MDA-MB-435 cell. Most interesting activities, however, were showed against MDA-MB-435 human breast cancer cell. In a screen against MDA-MB-435 human breast cancer cell, we observed that the compound 10 possessed weak activity and showed inhibition ratio above 22.3% at 10-5M. The anti-tumor activities of the other compounds indicated the inhibitory rates of tumor cell were less than 20% or showed no obvious anti-tumor activity.

The biological activity of the synthesized compounds showed the dibenzylbutanediol lignans exhibited low inhibition ratio against tumor cell. Among these serial modifcations, only diol-10 with dibenzocyclooctadiene structure gave the weak activity against human breast cancer cell. Thus, dibenzocyclooctadiene structure seems to be benefcial to inhibit breast cancer cell and led to an increase in anti-tumor activity.

CONCLUSIONS

In the aspect of synthesis of compounds, we have developed an effcient chiral synthetic route to give eight dibenzylbutanediol lignans including four natural products. With cheap materials, short experimental procedures, mild conditions and simple operations, the route exhibited more potential value in the future. Within the dibenzylbutanediol lignans, lignan 8b with the two free hydroxyl groups and erythro-structure showed the best anti-virus activity. In the aspect of anti-tumor activity, lignan 10 with dibenzocyclooctadiene structure seem to be benefcial to inhibit breast cancer cell and dibenzocyclooctadiene ring led to an increase in anti-tumor activity.

ACKNOWLEDGEMENTS

This work was supported by Taishan Scholar Project of Shandong Province (No. 2006011036) and Open Foundation of Chemical Engineering Subject, Qingdao University of Science & Technology.

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(Received: March 31, 2009 - Accepted: August 5, 2009).