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Jul 6, 2017 - Advanced Research Support Center (ADRES), Ehime University, 3-5-7 ... South Ehime Fisheries Research Center, 1289-1 Funakoshi, Ainan, ...
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Structure-Antifungal Activity Relationship of Fluorinated Dihydroguaiaretic Acid Derivatives and Preventive Activity against Alternaria alternata Japanese Pear Pathotype Hisashi Nishiwaki,† Shoko Nakazaki,† Koichi Akiyama,‡ and Satoshi Yamauchi*,†,§ †

Graduate School of Agriculture, Ehime University, 3-5-7 Tarumi, Matsuyama, Ehime 790-8566, Japan Advanced Research Support Center (ADRES), Ehime University, 3-5-7 Tarumi, Matsuyama, Ehime 790-8566, Japan § South Ehime Fisheries Research Center, 1289-1 Funakoshi, Ainan, Ehime 798-4292, Japan ‡

S Supporting Information *

ABSTRACT: The structure−activity relationship of the antifungal fluorinated dihydroguaiaretic acid derivatives was evaluated. Some of the newly synthesized lignan compounds were found to show higher antifungal activity against phytopathogenic fungi such as Alternaria alternata (Japanese pear and apple pathotypes) and A. citri than the lead compound, 3-fluoro-3′methoxylignan-4′-ol (3). The broad antifungal spectrum of 3′-hydroxyphenyl derivative 16 was observed, and the 3′-fluoro-4′hydroxyphenyl derivative 38 was found to show the highest activity against the A. alternata Japanese pear pathotype, with an EC50 value of 11 μM. The preventive effect of the potent lignan on the infection of A. alternata in the Japanese pear’s leaves was also shown. KEYWORDS: lignan, antifungal activity, Alternaria alternata, Alternaria citri

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pathotype,7 demonstrating that the antifungal spectrum of compound 3 was not broad. The purpose of the present study was to clarify the SAR of the butane-type lignans based on the structure of the potent lead compound 3 to discover novel compounds exhibiting more potent activity and a wider antifungal spectrum. To achieve this purpose, the 7′-modified derivatives 11−42 and 7,8-dehydro, γ-butyrolactone, and tetrahydrofuran derivatives, whose main structures are biosynthesized in many types of plants,8 43−45 and the 9,9′-modified DGA derivatives 4−10 were synthesized (Figure 1) because the effect of the 7′aromatic ring and main butylene moiety as well as that of 9 and 9′ structures on the activity should be examined to elucidate their SAR systematically. In addition, an infection test using a Japanese pear leaf was performed to examine whether the potent lignan could prevent the plant leaves from being infected by A. alternata and be applied to a new agrochemical.

INTRODUCTION Lignans, which are important components in food plants,1 are composed of two C6−C3 units combined between the 8 and 8′ positions and classified into many types derived from the different oxidation and cyclization patterns. Among them, the butane-type lignans such as secoisolariciresinol 1 (Figure 1) and its 9,9′-reductive compound dihydroguaiaretic acid (DGA) 2 (Figure 1) have a simple structure to synthesize various derivatives for examining the biological activity, which suggests that their application to industry could be easily achieved. This advantage prompts us to clarify the relationship between structure and biological activity of the butane-type lignans. Our previous studies have shown the effect of substituents of their one aromatic ring and main butylene structure on antimicrobial and insecticidal activities,2−4 and cytotoxicity,5 suggesting that butane-type lignans should be expected as one of the key sources for the development of new pesticides. Regarding the effect of butane-type lignans on the fungi, the growth inhibitory activity of secoisolariciresinol 1 against toxigenic fungi Fusarium graminearum was reported,6 whereas the effect of 1 against the plant pathogenic fungi Alternaria alternate Japanese pear pathotype was not observed in our previous study.2 By contrast, DGA 2 showed antifungal activity against A. citri and A. alternata apple and Japanese pear pathotypes with EC50 values of approximately 60 μM,7 suggesting that the structure−activity relationship (SAR) of the butane-type lignans should be clarified in a more detailed and systematic manner. These results led us to investigate the SAR of 7-phenyl group of 2 to discover the fluorinated compound 3 (Figure 1) (bearing a small electron withdrawing group) with the EC50 value of 20 μM against A. alternata Japanese pear pathotype.7 However, compound 3 showed 2and 3-fold less potency against A. citri and the A. alternata apple © 2017 American Chemical Society

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MATERIALS AND METHODS

Chemicals. NMR data were acquired by a JEOL JNM-EX400 using TMS as a standard (0 ppm) and trifluoroacetic acid as a standard (0 ppm) for 1 H, 13C NMR and (−76.5 ppm) for 19F-NMR, respectively. MS data were acquired with a JEOL JMS-MS 700 V spectrometer, and optical rotation values were evaluated with a JASCO P-2100 instrument. We employed previously reported methods with modification for the syntheses of compounds 10−45,9−11 which are described in the Supporting Information. The numbering of the compounds follows the nomenclature of the lignans.12 9,9′-Modified derivatives 4−9 were synthesized from D-glutamic acid by employing a Received: Revised: Accepted: Published: 6701

April 25, 2017 July 3, 2017 July 6, 2017 July 6, 2017 DOI: 10.1021/acs.jafc.7b01896 J. Agric. Food Chem. 2017, 65, 6701−6707

Article

Journal of Agricultural and Food Chemistry

Figure 1. Structures of secoisolariciresinol (1), dihydroguaiaretic acid (2), antifungal fluorinated lead compound (3), 9,9′-modified derivatives (4− 10) and 3/3′-fluorophenyl derivatives (11−45). previously described method for enantiomers.5 The NMR data of compounds 4−9 agreed with those of their enantiomers in the literature. The compound characterization data except for 1H NMR data are noted in the Supporting Information. (8S,8′S)-4,4′-Dihydroxy-3,3′-dimethoxy-9a-homolignane9a-nitrile (10). 1H NMR (400 MHz, CDCl3) δ 0.94 (3H, d, J = 6.7 Hz), 1.90−2.00 (2H, m), 2.24 (1H, dd, J = 17.1, 6.3 Hz), 2.28 (1H, dd, J = 17.1, 6.2 Hz), 2.43 (1H, dd, J = 13.8, 7.8 Hz), 2.62 (1H, dd, J = 14.0, 7.8 Hz), 2.63 (1H, dd, J = 14.0, 6.5 Hz), 2.73 (1H, dd, J = 13.8, 7.0 Hz), 3.807 (3H, s), 3.814 (3H, s), 5.62 (2H, br. s), 6.53 (2H, d, J = 1.9 Hz), 6.58 (1H, dd, J = 8.0, 2.0 Hz), 6.60 (1H, dd, J = 8.0, 2.0 Hz), 6.81 (1H, d, J = 8.0 Hz), 6.82 (1H, d, J = 8.0 Hz). (8S,8′S)-3-Fluorolignane (11). 1H NMR (400 MHz, CDCl3) δ 0.84 (6H, d, J = 6.2 Hz), 1.80 (2H, m), 2.40−2.45 (2H, m), 2.64 (2H, dd, J = 13.3, 6.0 Hz), 6.78 (1H, m), 6.84−6.87 (2H, m), 7.07−7.09 (2H, m), 7.17−7.19 (2H, m), 7.24−7.27 (2H, m). (8S,8′S)-3-Fluoro-2′-methoxylignane (12). 1H NMR (400 MHz, CDCl3) δ 0.81 (3H, d, J = 6.6 Hz), 0.85 (3H, d, J = 6.6 Hz), 1.76−1.86 (2H, m), 2.40 (1H, dd, J = 13.6, 8.5 Hz), 2.43 (1H, dd, J = 13.6, 8.3 Hz), 2.63 (1H, dd, J = 13.0, 6.6 Hz), 2.67 (1H, dd, J = 13.0, 5.3 Hz), 3.71 (3H, s), 6.78−6.86 (5H, m), 7.03 (1H, d, J = 6.9 Hz), 7.14−7.20 (2H, m). (8S,8′S)-3-Fluoro-3′-methoxylignane (13). 1H NMR (400 MHz, CDCl3) δ 0.84 (6H, d, J = 5.2 Hz), 1.80 (2H, m), 2.41 (1H, dd, J = 13.3, 4.9 Hz), 2.43 (1H, dd, J = 13.3, 5.0 Hz), 2.62 (1H, dd, J = 13.3, 6.2 Hz), 2.63 (1H, dd, J = 13.3, 7.6 Hz), 3.77 (3H, s), 6.63 (1H, m), 6.67−6.74 (2H, m), 6.78 (1H, m), 6.83−6.88 (2H, m), 7.15−7.22 (2H, m). (8S,8′S)-3-Fluoro-4′-methoxylignane (14). 1H NMR (400 MHz, CDCl3) δ 0.82 (6H, d, J = 6.7 Hz), 1.73−1.80 (2H, m), 2.38 (1H, dd, J = 13.5, 8.4 Hz), 2.42 (1H, dd, J = 13.5, 8.5 Hz), 2.58 (1H, dd, J = 13.5, 6.4 Hz), 2.63 (1H, dd, J = 13.5, 6.4 Hz), 3.79 (3H, s), 6.76−6.83 (1H, overlapped), 6.80 (2H, m), 6.83−6.88 (2H, m), 7.00 (2H, m), 7.19 (1H, m). (8S,8′S)-3-Fluoro-2′-lignanol (15). 1H NMR (400 MHz, CDCl3) δ 0.85 (3H, d, J = 6.7 Hz), 0.86 (3H, d, J = 6.7 Hz), 1.78−1.92 (2H, m), 2.42 (1H, dd, J = 13.5, 8.5 Hz), 2.43 (1H, dd, J = 13.5, 8.2 Hz),

2.66 (1H, dd, J = 13.5, 5.8 Hz), 2.68 (1H, dd, J = 13.5, 5.6 Hz), 4.59 (1H, br s), 6.71 (1H, d, J = 8.0 Hz), 6.80 (1H, m), 6.82−6.87 (3H, m), 7.02 (1H, m), 7.06 (1H, m), 7.19 (1H, m). (8S,8′S)-3-Fluoro-3′-lignanol (16). 1H NMR (400 MHz, CDCl3) δ 0.825 (3H, d, J = 6.7 Hz), 0.828 (3H, d, J = 6.7 Hz), 1.73−1.83 (2H, m), 2.38 (1H, dd, J = 13.6, 8.3 Hz), 2.43 (1H, dd, J = 13.6, 8.3 Hz), 2.59 (1H, dd, J = 13.5, 6.2 Hz), 2.63 (1H, dd, J = 13.5, 6.3 Hz), 4.82 (1H, s), 6.55 (1H, m), 6.63−6.67 (2H, m), 6.79 (1H, m), 6.84−6.89 (2H, m), 7.12 (1H, dd, J = 7.8, 7.8 Hz), 7.20 (1H, m). (8S,8′S)-3-Fluoro-4′-lignanol (17). 1H NMR (400 MHz, CDCl3) δ 0.82 (6H, d, J = 6.8 Hz), 1.6−1.82 (2H, m), 2.36 (1H, dd, J = 13.6, 8.4 Hz), 2.42 (1H, dd, J = 13.5, 8.5 Hz), 2.56 (1H, dd, J = 13.6, 6.5 Hz), 2.63 (1H, dd, J = 13.5, 6.5 Hz), 4.69 (1H, br s), 6.73 (2H, d, J = 8.3 Hz), 6.78 (1H, m), 6.83−6.88 (2H, m), 6.94 (2H, d, J = 8.3 Hz), 7.19 (1H, m). (8S,8′S)-2′,3-Difluorolignane (18). 1H NMR (400 MHz, CDCl3) δ 0.85 (6H, d, J = 4.7 Hz), 1.81 (2H, m), 2.42 (1H, dd, J = 13.3, 8.7 Hz), 2.46 (1H, dd, J = 13.4, 8.5 Hz), 2.66 (1H, dd, J = 13.4, 5.9 Hz), 2.69 (1H, dd, J = 13.3, 6.0 Hz), 6.78 (1H, m), 6.82−6.88 (2H, m), 6.96−7.09 (3H, m), 7.12−7.23 (2H, m). (8S,8′S)-3,3′-Difluorolignane (19). 1H NMR (400 MHz, CDCl3) δ 0.83 (6H, d, J = 6.4 Hz), 1.78 (2H, m), 2.42 (2H, dd, J = 13.4, 8.3 Hz), 2.63 (2H, dd, J = 13.4, 6.1 Hz), 6.78 (2H, m), 6.84−6.89 (4H, m), 7.17−7.24 (2H, m). (8S,8′S)-3,4′-Difluorolignane (20). 1H NMR (400 MHz, CDCl3) δ 0.82 (3H, d, J = 6.6 Hz), 0.83 (3H, d, J = 6.6 Hz), 1.69−1.82 (2H, m), 2.40 (1H, dd, J = 13.5, 9.6 Hz), 2.42 (1H, dd, J = 13.3, 8.9 Hz), 2.61 (1H, dd, J = 13.3, 6.4 Hz), 2.62 (1H, dd, J = 13.5, 6.4 Hz), 6.78 (1H, m), 6.83−6.89 (2H, m), 6.91−6.95 (2H, m), 7.00−7.04 (2H, m), 7.19 (1H, m). (8S,8′S)-2′-Chloro-3-fluorolignane (21). 1H NMR (400 MHz, CDCl3) δ 0.84 (3H, d, J = 6.8 Hz), 0.88 (3H, d, J = 6.7 Hz), 1.78−1.95 (2H, m), 2.43 (1H, dd, J = 13.5, 8.6 Hz), 2.51 (1H, dd, J = 13.4, 8.8 Hz), 2.65 (1H, dd, J = 13.5, 6.5 Hz), 2.81 (1H, dd, J = 13.4, 5.7 Hz), 6.80 (1H, ddd, J = 10.1, 2.1, 2.1 Hz), 6.82−6.89 (2H, m), 7.09 (1H, ddd, J = 7.4, 2.4, 2.4 Hz), 7.12−7.23 (3H, m), 7.31 (1H, dd, J = 6.8, 2.1 Hz). 6702

DOI: 10.1021/acs.jafc.7b01896 J. Agric. Food Chem. 2017, 65, 6701−6707

Article

Journal of Agricultural and Food Chemistry (8S,8′S)-3′-Chloro-3-fluorolignane (22). 1H NMR (400 MHz, CDCl3) δ 0.83 (6H, d, J = 6.3 Hz), 1.72−1.83 (2H, m), 2.40 (1H, dd, J = 13.5, 8.5 Hz), 2.42 (1H, dd, J = 13.5, 8.5 Hz), 2.62 (1H, dd, J = 13.3, 7.1 Hz), 2.63 (1H, dd, J = 13.3, 6.5 Hz), 6.78 (1H, ddd, J = 10.0, 2.0, 2.0 Hz), 6.84−6.90 (2H, m), 6.95 (1H, ddd, J = 6.7, 1.7, 1.7 Hz), 7.07 (1H, m), 7.13−7.17 (2H, m), 7.21 (1H, m). (8S,8′S)-4′-Chloro-3-fluorolignane (23). 1H NMR (400 MHz, CDCl3) δ 0.82 (3H, d, J = 6.6 Hz), 0.83 (3H, d, J = 6.7 Hz), 1.71−1.80 (2H, m), 2.39 (1H, dd, J = 13.5, 8.5 Hz), 2.42 (1H, dd, J = 13.5, 8.5 Hz), 2.60 (1H, dd, J = 13.5, 6.3 Hz), 2.62 (1H, dd, J = 13.5, 6.3 Hz), 6.78 (1H, ddd, J = 10.0, 2.0. 2.0 Hz), 6.83−688 (2H, m), 7.00 (2H, d, J = 8.4 Hz), 7.17−7.23 (1H, overlapped), 7.21 (2H, d, J = 8.4 Hz). (8S,8′S)-3-Fluoro-2′a-homolignane (24). 1H NMR (400 MHz, CDCl3) δ 0.82 (3H, d, J = 6.9 Hz), 0.89 (3H, d, J = 6.8 Hz), 1.75 (1H, m), 1.84 (1H, m), 2.18 (3H, s), 2.40 (1H, dd, J = 13.6, 9.0 Hz), 2.45 (1H, dd, J = 13.6, 8.7 Hz), 2.63 (1H, dd, J = 13.6, 7.6 Hz), 2.64 (1H, dd, J = 13.6, 6.1 Hz), 6.79 (1H, m), 6.83−6.87 (2H, m), 7.02 (1H, m), 7.07−7.11 (3H, m), 7.19 (1H, m). (8S,8′S)-3-Fluoro-3′a-homolignane (25). 1H NMR (400 MHz, CDCl3) δ 0.83 (6H, d, J = 6.8 Hz), 1.74−1.84 (2H, m), 2.31 (3H, s), 2.39 (1H, dd, J = 13.4, 8.2 Hz), 2.42 (1H, dd, J = 13.6, 8.4 Hz), 2.60 (1H, dd, J = 13.4, 6.2 Hz), 2.64 (1H, dd, J = 13.6, 6.3 Hz), 6.78 (1H, m), 6.83−6.90 (4H, m), 6.99 (1H, m), 7.13 (1H, m), 7.19 (1H, m). (8S,8′S)-3-Fluoro-4′a-homolignane (26). 1H NMR (400 MHz, CDCl3) δ 0.82 (6H, d, J = 6.8 Hz), 1.73−1.83 (2H, m), 2.32 (3H, s), 2.39 (1H, dd, J = 13.4, 9.8 Hz), 2.41 (1H, dd, J = 13.4, 8.8 Hz), 2.60 (1H, dd, J = 13.4, 6.1 Hz), 2.64 (1H, dd, J = 13.4, 6.2 Hz), 6.78 (1H, m), 6.83−6.87 (2H, m), 6.97 (2H, d, J = 7.8 Hz), 7.06 (2H, d, J = 7.8 Hz), 7.19 (1H, m). (8S,8′S)-3-Fluoro-3′a-homolignan-3′a-ol (27). 1H NMR (400 MHz, CDCl3) δ 0.835 (3H, d, J = 6.5 Hz), 0.838 (3H, d, J = 6.6 Hz), 1.73 (1H, br s), 1.79 (2H, m), 2.42 (1H, dd, J = 13.8, 7.2 Hz), 2.44 (1H, dd, J = 13.8, 6.7 Hz), 2.636 (1H, dd, J = 13.4, 6.4 Hz), 2.642 (1H, dd, J = 13.4, 6.3 Hz), 4.64 (2H, s), 6.76 (1H, m), 6.83 (2H, m), 7.01 (1H, br d, J = 7.4 Hz), 7.07 (1H, br s), 7.15−7.21 (2H, m), 7.23 (1H, m). (8S,8′S)-3-Fluoro-3′a-homolignan-3′a-oic acid (28). 1H NMR (400 MHz, CDCl3) δ 0.85 (3H, d, J = 6.7 Hz), 0.86 (3H, d, J = 6.8 Hz), 1.75−1.88 (2H, m), 2.43 (1H, dd, J = 13.5, 8.5 Hz), 2.51 (1H, dd, J = 13.5, 8.4 Hz), 2.66 (1H, dd, J = 13.5, 6.3 Hz), 2.72 (1H, dd, J = 13.5, 6.4 Hz), 6.78 (1H, m), 6.84−6.89 (2H, m), 7.20 (1H, m), 7.32− 7.39 (2H, m), 7.87 (1H, br s), 7.95 (1H, m). (8S,8′S)-3-Fluoro-3′a-homolignane-3′a-nitrile (29). 1H NMR (400 MHz, CDCl3) δ 0.83 (3H, d, J = 7.0 Hz), 0.85 (3H, d, J = 7.1 Hz), 1.72−1.80 (2H, m), 2.44 (1H, dd, J = 13.6, 7.7 Hz), 2.46 (1H, dd, J = 13.7, 7.9 Hz), 2.62 (1H, dd, J = 13.6, 6.4 Hz), 2.66 (1H, dd, J = 13.7, 6.3 Hz), 6.77 (1H, ddd, J = 10.0, 1.9, 1.9 Hz), 6.84 (1H, br. d, J = 7.7 Hz), 6.88 (1H, ddd, J = 8.5, 8.5, 2.6 Hz), 7.21 (1H, ddd, J = 8.0, 8.0, 5.9 Hz), 7.30 (1H, ddd, J = 7.8, 1.5, 1.5 Hz), 7.33−7.37 (2H, m), 7.48 (1H, ddd, J = 7.5, 1.5, 1.5 Hz). (8S,8′S)-3′-Amino-3-fluorolignane (30). 1H NMR (400 MHz, CDCl3) δ 0.82 (3H, d, J = 6.7 Hz), 0.83 (3H, d, J = 6.8 Hz), 1.72−1.84 (2H, m), 2.34 (1H, dd, J = 13.4, 8.3 Hz), 2.42 (1H, dd, J = 13.5, 8.3 Hz), 2.55 (1H, dd, J = 13.4, 6.4 Hz), 2.63 (1H, dd, J = 13.5, 6.4 Hz), 3.57 (2H, br s), 6.40 (1H, m), 6.48−6.52 (2H, m), 6.80 (1H, m), 6.83−6.89 (2H, m), 7.04 (1H, dd, J = 7.7, 7.7 Hz), 7.20 (1H, m). (8S,8′S)-3-Fluoro-3′-(N-methylamino)lignane (31). 1H NMR (400 MHz, CDCl3) δ 0.82 (3H, d, J = 6.7 Hz), 0.83 (3H, d, J = 6.6 Hz), 1.80 (2H, m), 2.36 (1H, dd, J = 13.4, 8.6 Hz), 2.42 (1H, dd, J = 13.4, 8.2 Hz), 2.57 (1H, dd, J = 13.4, 6.2 Hz), 2.64 (1H, dd, J = 13.4, 6.3 Hz), 2.80 (3H, s), 3.20−3.70 (1H, br), 6.33 (1H, m), 6.42−6.47 (2H, m), 6.80 (1H, m), 6.82−6.88 (2H, m), 7.07 (1H, dd, J = 7.7, 7.7 Hz), 7.19 (1H, m). (8S,8′S)-3-Fluoro-3′,4′-lignanediol (32). 1H NMR (400 MHz, CDCl3) δ 0.80 (3H, d, J = 6.8 Hz), 0.81 (3H, d, J = 6.8 Hz), 1.70 (1H, m), 1.78 (1H, m), 2.31 (1H, dd, J = 13.5, 8.4 Hz), 2.41 (1H, dd, J = 13.5, 8.5 H), 2.51 (1H, dd, J = 13.5, 6.5 Hz), 2.61 (1H, dd, J = 13.5, 6.5 Hz), 5.39 (1H, s), 5.43 (1H, s), 6.52 (1H, dd, J = 8.1, 1.9 Hz), 6.59 (1H, d, J = 1.9 Hz), 6.75 (1H, d, J = 8.1 Hz), 6.78 (1H, m), 6.83−6.88 (2H, m), 7.21 (1H, m).

(8S,8′S)-3-Fluoro-3′,5′-lignanediol (33). 1H NMR (400 MHz, CDCl3) δ 0.79 (3H, d, J = 6.6 Hz), 0.80 (3H, d, J = 6.7 Hz), 1.69−1.80 (2H, m), 2.28 (1H, dd, J = 13.5, 8.3 Hz), 2.39 (1H, dd, J = 13.5, 8.4 Hz), 2.49 (1H, dd, J = 13.5, 6.2 Hz), 2.60 (1H, dd, J = 13.5, 6.5 Hz), 5.41 (1H, br s), 5.50 (1H, br s), 6.15 (2H, br s), 6.19 (1H, m), 6.79 (1H, m), 6.83−6.88 (2H, m), 7.19 (1H, m). (8S,8′S)-3-Fluoro-4′-methoxy-3′-lignanol (34). 1H NMR (400 MHz, CDCl3) δ 0.81 (3H, d, J = 6.8 Hz), 0.82 (3H, d, J = 6.7 Hz), 1.69−1.85 (2H, m), 2.33 (1H, dd, J = 13.5, 8.6 Hz), 2.41 (1H, dd, J = 13.5, 8.6 Hz), 2.55 (1H, dd, J = 13.5, 6.3 Hz), 2.63 (1H, dd, J = 13.5, 6.3 Hz), 3.85 (3H, s), 5.56 (1H, s), 6.55 (1H, dd, J = 8.1, 2.1 Hz), 6.68 (1H, d, J = 2.1 Hz), 6.74 (1H, d, J = 8.1 Hz), 6.78 (1H, m), 6.83−6.85 (1H, overlapped), 6.86 (1H, m), 7.19 (1H, m). (8S,8′S)-3′-Ethoxy-3-fluoro-4′-lignanol (35). 1H NMR (400 MHz, CDCl3) δ 0.821 (3H, d, J = 6.8 Hz), 0.825 (3H, d, J = 6.8 Hz), 1.42 (3H, t, J = 7.0 Hz), 1.69−1.82 (2H, m), 2.36 (1H, dd, J = 13.6, 8.0 Hz), 2.43 (1H, dd, J = 13.6, 8.1 Hz), 2.53 (1H, dd, J = 13.6, 6.8 Hz), 2.61 (1H, dd, J = 13.6, 6.8 Hz), 4.03 (2H, q, J = 7.0 Hz), 5.52 (1H, s), 6.53 (1H, d, J = 1.5 Hz), 6.57 (1H, dd, J = 7.9, 1.5 Hz), 6.78 (1H, m), 6.80 (1H, d, J = 7.9 Hz), 6.82−6.88 (2H, m), 7.19 (1H, m). (8S,8′S)-3′-Butoxy-3-fluoro-4′-lignanol (36). 1H NMR (400 MHz, CDCl3) δ 0.82 (3H, d, J = 6.7 Hz), 0.83 (3H, d, J = 6.8 Hz), 0.99 (3H, t, J = 7.4 Hz), 1.49 (2H, m), 1.70−1.82 (2H, overlapped), 1.78 (2H, m), 2.36 (1H, dd, J = 13.5, 8.1 Hz), 2.43 (1H, dd, J = 13.5, 8.2 Hz), 2.54 (1H, dd, J = 13.5, 6.8 Hz), 2.62 (1H, dd, J = 13.5, 6.8 Hz), 3.96 (2H, t, J = 7.4 Hz), 5.51 (1H, s), 6.53 (1H, d, J = 1.3 Hz), 6.57 (1H, dd, J = 8.1, 1.3 Hz), 6.78 (1H, m), 6.81 (1H, d, J = 8.1 Hz), 6.82−6.88 (2H, m), 7.18 (1H, m). (8S,8′S)-3-Fluoro-3′a-homolignan-4′-ol (37). 1H NMR (400 MHz, CDCl3) δ 0.82 (6H, d, J = 6.7 Hz), 1.68−1.82 (2H, m), 2.21 (3H, s), 2.33 (1H, dd, J = 13.5, 8.3 Hz), 2.41 (1H, dd, J = 13.5, 8.4 Hz), 2.53 (1H, dd, J = 13.5, 6.6 Hz), 2.63 (1H, dd, J = 13.5, 6.5 Hz), 4.61 (1H, s), 6.66 (1H, d, J = 8.1 Hz), 6.76−6.82 (3H, m), 6.83−6.89 (2H, m), 7.19 (1H, m). (8S,8′S)-3,3′-Difluoro-4′-lignanol (38). 1H NMR (400 MHz, CDCl3) δ 0.82 (6H, d, J = 6.8 Hz), 1.68−1.80 (2H, m), 2.35 (1H, dd, J = 13.7, 8.3 Hz), 2.42 (1H, dd, J = 13.5, 8.4 Hz), 2.55 (1H, dd, J = 13.7, 6.6 Hz), 2.62 (1H, dd, J = 13.5, 6.5 Hz), 5.01 (1H, s), 6.73 (1H, m), 6.76−6.80 (2H, m), 6.84−6.90 (3H, m), 7.20 (1H, m). (8S,8′S)-3′-Chloro-3-fluoro-4′-lignanol (39). 1H NMR (400 MHz, CDCl3) δ 0.82 (6H, d, J = 6.8 Hz), 1.68−1.82 (2H, m), 2.34 (1H, dd, J = 13.7, 8.3 Hz), 2.42 (1H, dd, J = 13.5, 8.4 Hz), 2.54 (1H, dd, J = 13.7, 6.6 Hz), 2.62 (1H, dd, J = 13.5, 6.5 Hz), 5.40 (1H, s), 6.78 (1H, m), 6.84−6.89 (3H, m), 6.91 (1H, d, J = 8.2 Hz), 7.03 (1H, d, J = 1.6 Hz), 7.20 (1H, m). (8S,8′S)-3-Fluoro-3′,4′-dimethoxylignane (40). 1H NMR (400 MHz, CDCl3) δ 0.83 (3H, d, J = 6.7 Hz), 0.84 (3H, d, J = 6.8 Hz), 1.73−1.82 (2H, m), 2.39 (1H, dd, J = 13.6, 8.0 Hz), 2.44 (1H, dd, J = 13.6, 8.1 Hz), 2.57 (1H, dd, J = 13.6, 6.7 Hz), 2.62 (1H, dd, J = 13.6, 6.7 Hz), 3.82 (3H, s), 3.86 (3H, s), 6.58 (1H, d, J = 1.8 Hz), 6.63 (1H, dd, J = 8.1, 1.8 Hz), 6.76 (1H, d, J = 8.1 Hz), 6.82 (1H, m), 6.83−6.88 (2H, m), 7.19 (1H, m). (8S,8′S)-3,3′,4′-Trifluorolignane (41). 1H NMR (400 MHz, CDCl3) δ 0.82 (3H, d, J = 6.8 Hz), 0.83 (3H, d, J = 6.7 Hz), 1.69−1.81 (2H, m), 2.38 (1H, dd, J = 13.6, 8.3 Hz), 2.43 (1H, dd, J = 13.6, 8.2 Hz), 2.58 (1H, dd, J = 14.0, 6.4 Hz), 2.62 (1H, dd, J = 14.0, 6.4 Hz), 6.75−6.80 (2H, m), 6.83−6.90 (3H, m), 7.02 (1H, ddd, J = 8.4, 8.3, 8.2 Hz), 7.21 (1H, ddd, J = 7.8, 7.7, 6.3 Hz). (8S,8′S)-3,3′-Difluoro-4′a-homolignane (42). 1H NMR (400 MHz, CDCl3) δ 0.818 (3H, d, J = 6.8 Hz), 0.821 (3H, d, J = 6.5 Hz), 1.70−1.83 (2H, m), 2.23 (3H, s), 2.38 (1H, dd, J = 13.6, 8.4 Hz), 2.41 (1H, dd, J = 13.6, 8.3 Hz), 2.58 (1H, dd, J = 13.6, 6.2 Hz), 2.62 (1H, dd, J = 13.6, 6.1 Hz), 6.71−6.80 (3H, m), 6.83−6.88 (2H, m), 7.03 (1H, dd, J = 8.2, 7.8 Hz), 7.19 (1H, ddd, J = 7.7, 7.6 5.9 Hz). (8S,7′E)-3,3′-Difluorolign-7′-en-4′-ol (43). 1H NMR (400 MHz, CDCl3) δ 1.09 (3H, d, J = 6.6 Hz), 1.80 (3H, d, J = 1.2 Hz), 2.02 (1H, m), 2.60 (1H, dd, J = 13.3, 7.5 Hz), 2.79 (1H, dd, J = 13.3, 7.1 Hz), 5.30 (1H, s), 6.05 (1H, s), 6.80 (1H, m), 6.85−6.93 (5H, m), 7.21 (1H, m). 6703

DOI: 10.1021/acs.jafc.7b01896 J. Agric. Food Chem. 2017, 65, 6701−6707

Article

Journal of Agricultural and Food Chemistry

groups such as fluoro and cyano groups were more potent than 4, 5, and 9 but were less potent than DGA 2. The butyl derivative 6 was equipotent to 2, suggesting that a liner and hydrophobic group at the 9 or 9′ position is tolerable for retaining the higher activity. The isopropyl derivative 7 showed approximately 2-fold less potency than 6 and DGA 2, thereby proving the disadvantage of the bulky substituent at this position. Taking all into consideration, the hydrophobicity of the substituents on these positions should be more important for high activity than their electrostatic features. Next, the antifungal activity of 7-(3-fluorophenyl)-7′-aryl derivatives 11−42 across the three strains of fungi was evaluated to clear the effect of the 7′-aryl-substituent on the activity (Table 2). Compound 11 bearing the unsubstituted phenyl group at the 7′ position as well as the methoxyphenyl derivatives 12−14, fluorophenyl derivatives 18−20, chlorophenyl derivatives 21−23, and methylphenyl derivatives 24−26 showed no activity even at 1000 μM. On the other hand, phenolic derivatives 15−17 exhibited EC50 values of 21−62 μM. In particular, 3′-hydroxyphenyl derivative 16 was found to be the most potent among the three phenolic derivatives 15− 17, with EC50 values of 21−29 μM against the three fungi strains, thereby demonstrating that the presence of the hydroxy group at the 3′ position would favor the higher activity in the monosubstituted 7′-aryl derivatives. As a further investigation of the 3′-substituted derivatives, the activity of 3′-hydroxymethyl (27), 3′-carboxylic acid (28), 3′-cyano (29), 3′-amino (30), and 3′-methylamino (31) derivatives were examined. Among them, 3′-cyano derivative 29 showed no activity at 1000 μM, suggesting that an electron withdrawing group should be unfavorable for the activity in the case of monosubstituted 7′aryl derivatives. Furthermore, compound 29 as well as the other compounds 27, 28, 30, and 31 were less potent than 3′hydroxyphenyl derivative 16, suggesting that the presence of a phenolic hydroxy group on the 7′-aryl group would be important for the higher activity. The 7′-disubstituted aryl derivatives 32−42 were also applied to the antifungal assay. The activities of dihydroxyphenyl derivatives 32 and 33 were almost similar to that of 3′hydroxyphenyl derivative 16 against the A. alternata Japanese pear pathotype and 2−3-fold less potent than that of 16 against the A. alternata apple pathotype and A. citri, demonstrating that the additional phenolic hydroxy group on the 7′-aryl group did not strengthen the activity of the monohydroxyphenyl derivatives. Compound 34, in which the positions of the hydroxy and methoxy group are exchanged compared with lead compound 3, was approximately 5-fold less potent than compound 3, demonstrating the importance of the positions of the phenolic hydroxy group on the 4′-position and methoxy groups at the 3′ position in the case of disubstituted phenyl compounds. We therefore decided to prepare the disubstituted derivatives 35−39 bearing the phenolic hydroxy group at the 4′ position. Comparing the activity of compound 3 with that of compounds 35 and 36, the presence of the longer alkoxy group at the 3′ position dramatically reduced the activity. The 3′methyl-4′-hydroxyphenyl derivative 37 against the A. alternata Japanese pear pathotype was 9-fold less potent than 3, whereas 37 was almost equipotent to 3 against the A. alternata apple pathotype and A. citri. Against the A. alternata Japanese pear pathotype, 3′-chloro-4′-hydroxyphenyl derivative 39 showed a similar activity to compound 3, but 3′-fluoro-4′-hydroxyphenyl derivative 38, the most potent compound in the present study, was 2-fold more potent than lead compound 3, suggesting that

(8S,8′S)-3,3′-Difluoro-4-hydroxylignano-9,9′-lactone (44). H NMR (400 MHz, CDCl3) δ 2.45−2.60 (3H, m), 2.68 (1H, dd, J = 13.5, 5.9 Hz), 2.88 (1H, dd, J = 14.3, 6.7 Hz), 2.96 (1H, dd, J = 14.3, 5.2 Hz), 3.87 (1H, dd, J = 8.9, 7.8 Hz), 4.14 (1H, dd, J = 8.9, 7.3 Hz), 5.56 (1H, br. s), 6.70 (1H, ddd, J = 9.6, 1.8, 1.8 Hz), 6.76−6.81 (2H, m), 6.85 (1H, dd, J = 11.4, 1.5 Hz), 6.90−6.95 (2H, m), 7.24 (1H, ddd, J = 7.8, 7.8, 6.3 Hz). (8S,8′S)-3,3′-Difluoro-4-hydroxy-9,9′-epoxylignane (45). 1H NMR (400 MHz, CDCl3) δ 2.12−2.24 (2H, m), 2.50 (1H, dd, J = 13.8, 8.1 Hz), 2.55−2.60 (2H, m), 2.66 (1H, dd, J = 13.7, 6.6 Hz), 3.51−3.55 (2H, m), 3.93 (2H, dd, J = 8.7, 6.8 Hz), 6.06 (1H, br. s), 6.71 (1H, m), 6.74−6.78 (2H, m), 6.84−6.90 (3H, m), 7.21 (1H, ddd, J = 7.9, 7.9, 7.9 Hz). Fungal Strains. A. alternata Japanese pear pathotype employed was stored at Ehime University. A. alternata apple pathotype MAFF305016 and A. citri MAFF242828 were purchased from the NIAS Genebank. Each fungal strain was cultured on potato dextrose agar (PDA, Sigma-Aldrich, Canada). Antifungal Assay. In total, 30 μL of dimethyl sulfoxide solution containing each test compound was added to 3 mL of PDA at 50 °C, followed by rapid mixing, and the resultant mixture was poured into a Petri dish (diameter 50 mm) to prepare the PDA agar plate containing the test compound. Dimethyl sulfoxide without any test compound served as the negative control. After inoculating each strain on the center of the PDA agar plate and incubation at 28 °C or 3 days, the diameter of the mycelial colony was measured with a caliper. All assays were performed in triplicate. Evaluation of the Suppressive Potency of a Synthesized Lignan against the Infection of A. alternata Inoculated on the Leaves of Japanese Pear. The leaf surface of the Japanese pear Nijisseiki (sensitive strain to the A. alternata Japanese pear pathotype) was scratched with a tiny pin and dipped into the PD broth containing compound 16 (3-OH) dissolved in DMSO. The final concentrations of compound 16 and DMSO were 125 μM and 1% (v/v), respectively. As a negative control, the PD broth containing DMSO (1%) was applied. The PD broth (30 μL) of the A. alternata Japanese pear pathotype (0.40, OD600) was then applied at the same prescratched position. The inoculated leaf was incubated on the prewetted paper in the Petri dish for 5−6 days, and it was observed whether black spots appeared on the leaf surface. The experiments were separately performed in triplicate. 1

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RESULTS AND DISCUSSION First, the effects of the 9 and 9′ positions of DGA 2 on the antifungal activity against the Alternaria alternata Japanese pear pathotype were examined (Table 1). The apparent activity of compounds 4, 5, and 9 bearing the methoxy, acetoxy, and dimethylamino groups was not detected even at 1000 μM, suggesting that the oxygen or nitrogen atoms attached at 9 and 9′ positions are disadvantageous for the higher activity. By contrast, compounds 8 and 10 bearing electron-withdrawing Table 1. Antifungal Activity of 9,9′-Modified Derivatives 4− 10 of Dihydroguaiaretic Acid 2 against the A. alternata Japanese Pear Pathotype

a

no.

compounds

EC50 (μM ± SD)

26 4 5 6 7 8 9 10

9-H, 9′-H ((+)-DGA) 9-OCH3, 9′-OCH3 9-OAc, 9′-OAc 9-(CH2)3CH3, 9′-H 9-CH(CH3)2, 9′-H 9-F, 9′-H 9-N(CH3)2, 9′-H 9-CN, 9′-H

71.8 ± 5.1 >1000 (62.4 ± 9.4%)a >1000 (55.6 ± 1.7%)a 89.0 ± 9.5 158 ± 28.5 178 ± 19.9 >1000 (64.7 ± 5.2%)a 306 ± 37.5

Growth ratio value with SEM (n = 3) at 1000 μM. 6704

DOI: 10.1021/acs.jafc.7b01896 J. Agric. Food Chem. 2017, 65, 6701−6707

Article

Journal of Agricultural and Food Chemistry Table 2. Antifungal Activity of 7-(3-Fluorophenyl)-7′-aryl Derivatives 11−42 EC50 (μM ± SD) no.: compounds

A. alternata Japanese pear pathotype

A. alternata apple pathotype

3 : 3′-OCH3, 4′-OH 11: H 12: 2′-OCH3 13: 3′-OCH3 14: 4′-OCH3 15: 2′-OH 16: 3′-OH 17: 4′-OH 18: 2′-F 19: 3′-F 20: 4′-F 21: 2′-Cl 22: 3′-Cl 23: 4′-Cl 24: 2′-CH3 25: 3′-CH3 26: 4′-CH3 27: 3′-CH2OH 28: 3′-CO2H 29: 3′-CN 30: 3′-NH2 31: 3′-NHCH3 32: 3′-OH, 4′-OH 33: 3′-OH, 5′-OH 34: 3′-OH, 4′-OCH3 35: 3′-OCH2CH3, 4′-OH 36: 3′-O(CH2)3CH3, 4′-OH 37: 3′-CH3, 4′-OH 38: 3′-F, 4′-OH 39: 3′-Cl, 4′-OH 40: 3′-OCH3, 4′-OCH3 41: 3′-F, 4′-F 42: 3′-F, 4′-CH3

20.4 ± 1.3 >1000 (64.4 ± 1.2%)a >1000 (85.2 ± 2.4%)a >1000 (65.6 ± 3.2%)a >1000 (81.3 ± 4.7%)a 55.3 ± 6.9 28.5 ± 2.5 49.3 ± 3.7 >1000 (76.2 ± 1.3%)a >1000 (70.5 ± 1.1%)a >1000 (69.8 ± 3.9%)a >1000 (85.2 ± 4.7%)a >1000 (85.8 ± 2.7%)a >1000 (89.9 ± 2.3%)a >1000 (88.7 ± 6.9%)a >1000 (86.8 ± 0.8%)a >1000 (86.1 ± 0.7%)a 405 ± 67.0 237 ± 57.4 >1 000 (64.1 ± 3.9%)a 285 ± 87.7 210 ± 10.4 32.3 ± 2.3 38.6 ± 2.7 104 ± 17.3 62.6 ± 8.6 >1000 (88.2 ± 4.8%)a 181 ± 15.6 11.2 ± 2.7 24.4 ± 2.5 74.3 ± 8.2 >1000 (79.0 ± 5.5%)a >1000 (96.3 ± 2.2%)a

47.3 ± 3.1 >1000 (80.5 ± 4.2%)a >1000 (81.9 ± 0.6%)a >1000 (80.4 ± 4.4%)a >1000 (81.9 ± 1.2%)a 33.0 ± 3.7 21.2 ± 1.7 42.4 ± 4.1 >1000 (86.1 ± 0.32%)a >1000 (89.4 ± 1.82%)a >1000 (88.7 ± 1.41%)a >1000 (108 ± 5.40%)a >1000 (115 ± 2.23%)a >1000 (106 ± 6.42%)a >1000 (83.1 ± 3.80%)a >1000 (88.2 ± 2.58%)a >1000 (86.6 ± 4.18%)a 154 ± 21.2 259 ± 42.2 >1000 (84.2 ± 5.9%)a 280 ± 26.6 153 ± 2.9 43.0 ± 5.4 57.0 ± 12.9 129 ± 33.0 >1000 (55.0 ± 1.2%)a >1000 (97.9 ± 6.7%)a 54.3 ± 7.3 55.7 ± 2.8 101 ± 29.3 >1000 (82.3 ± 2.7%)a >1000 (92.5 ± 5.1%)a >1000 (103 ± 5.4%)a

6

a

A. citri 64.9 ± 7.5 >1000 (89.4 >1000 (94.3 >1000 (69.8 >1000 (97.3 43.9 ± 8.0 24.9 ± 3.3 61.5 ± 7.4 >1000 (93.9 >1000 (88.6 >1000 (93.6 >1000 (93.5 >1000 (96.7 >1000 (97.1 >1000 (95.1 >1000 (90.2 >1000 (90.3 126 ± 16.7 126 ± 11.4 >1000 (75.0 390 ± 20.0 151 ± 11.4 84.7 ± 8.3 53.7 ± 3.6 123 ± 10.7 >1000 (53.1 >1000 (83.4 51.2 ± 2.3 54.2 ± 5.7 60.2 ± 4.4 >1000 (71.9 >1000 (89.7 >1000 (93.0

± ± ± ±

4.7%)a 2.1%)a 4.6%)a 12.9%)a

± ± ± ± ± ± ± ± ±

4.9%)a 3.4%)a 1.6%)a 1.0%)a 0.3%)a 0.4%)a 6.4%)a 0.8%)a 0.7%)a

± 0.8%)a

± 0.7%)a ± 0.7%)a

± 2.3%)a ± 3.0%)a ± 1.0%)a

Growth ratio value with SEM (n = 3) at 1000 μM.

the small electron-withdrawing group at the 3′ position is also important for a higher effect. Against the A. alternata apple pathotype and A. citri, the activities of derivatives 38 and 39 were similar to or 2-fold less than that of compound 3. To confirm the importance of the 4′-phenolic hydroxy group, the 3′,4′-dimethoxyphenyl derivative 40, 3′,4′-difluorophenyl derivative 41, and 3′-fluoro-4′-methylphenyl derivative 42 were subjected to the antifungal tests. Except for compound 40 against the A. alternata Japanese pear pathotype, which was 7fold less potent than that of 3′-fluoro-4′-hydroxyphenyl derivative 38, the EC50 values were more than 1000 μM, suggesting that the 4-hydroxy group of 38 plays an important role for the higher activity. In the course of the SAR research on 7-(3-fluorophenyl)-7′aryl derivative (Table 2), the 3′-fluoro-4′-hydroxyphenyl derivative 38 was found to be more potent against the A. alternata Japanese pear pathotype than lead compound 3. To evaluate the effect of the butylene moiety of 38 on the antifungal activity, the additional derivatives of 7,8-dehydro type 43, 9,9′-lactone structure 44, and 9,9′-epoxy structure 45 were prepared to examine their activity (Table 3). A 7- to 45fold lower activity than that of compound 38 was observed, suggesting that the hydrophobic butane lignan structure should be advantageous for antifungal activity against these fungi

Table 3. Antifungal Activities of (E)-7-ene 43, 9,9′-Lactone 44, and 9,9′-Epoxy 45 (EC50 μM ± SD) EC50 (μM ± SD) no.: compounds

A. alternata Japanese pear pathotype

A. alternata apple pathotype

A. citri

43: (E)-7-ene 44: 9,9′-lactone 45: 9,9′-epoxy

105 ± 33.5 497 ± 34.1 71.6 ± 1.11

140 ± 18.0 186 ± 12.2 131 ± 12.7

136 ± 4.02 235 ± 15.4 157 ± 10.5

strains and that the flexibility of the compound might play an important role in exerting the high activity. Since most of the compounds were more effective against the A. alternata Japanese pear pathotype than against the others (Tables 2 and 3), the preventive effect of compound 16 on the infection of the A. alternata Japanese pear pathotype was examined using the leaves of the A. alternata sensitive pear, Nijisseiki. The black spots caused by A. alternata appeared on the surface of the leaf to which the PD broth containing only DMSO was applied, whereas the area of the black spots was considerably suppressed when compound 16 was applied at the concentration of 125 μM before inoculation of the A. alternata Japanese pear pathotype (Figure 2). It was shown that the lignan derivative also acts on the plant body. We found 6705

DOI: 10.1021/acs.jafc.7b01896 J. Agric. Food Chem. 2017, 65, 6701−6707

Journal of Agricultural and Food Chemistry

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Article

AUTHOR INFORMATION

Corresponding Author

*Phone: +81-89-946-9846. Fax: +81-89-977-4364. E-mail: [email protected], [email protected]. ac.jp. ORCID

Satoshi Yamauchi: 0000-0002-7181-4568 Funding

We are grateful to Sumitomo Chemical Co., Ltd. for financial support. Notes

The authors declare no competing financial interest.

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Figure 2. Preventive effect of compound 16 at the concentration of 125 μM: (left) treatment with compound 16 solution in DMSO and (right) DMSO.

ACKNOWLEDGMENTS We are grateful to Inada pear farm (Uchiko, Ehime) for a kind gift of the leaves of the Japanese pear Nijisseiki. Part of this study was performed at the Advanced Research Support Center (ADRES) in Ehime University.

previous reports on the antifungal lignan,2,6,7,13−19 but the preventive effect of lignan structure was shown herein for the first time. In conclusion, we prepared 45 novel lignan derivatives to examine their antifungal activities. The broad antifungal spectrum of 3′-hydroxyphenyl derivative 16 was observed, and the 3′-fluoro-4′-hydroxyphenyl derivative 38 exhibited the highest activity against the A. alternata Japanese pear pathotype. The presence of the 3′-OH group was effective for exhibiting the broad effect. By contrast, the 4′-hydroxy group showed lower activity against A. alternate, and the spectrum was not broad. However, the combination of the 4′-hydroxy group and 3′-halogen atom yielded the specificity against A. alternata. It could be assumed that the presence of a small electronwithdrawing group at the 3′ position with the 4′-phenolic group would be important for the specificity. In addition, the preventive activity of compound 16 against plant pathogens was shown. Most of the lignan compounds synthesized in the present study were more effective against the A. alternata Japanese pear pathotype than against the other phenotypes, but three derivatives, 3′-hydroxymethylphenyl derivative 27, 3′methyl-4′-hydroxyphenyl derivative 37, and 9,9′-lactone derivative 44, showed a higher antifungal activity against the A. alternata apple pathotype and A. citri, suggesting that further research will lead us to other potent compounds showing different, specific fungicidal activities if we design potent compounds from compounds 27, 37, and 44. Finally, the main structures of the lignans in the present study are biosynthesized in many types of plants, including food plants,8 and this study could be an approach for developing a new agrochemical based on these simple and natural structures.

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jafc.7b01896. Synthesis details of nitrile 10, preparation of intermediate for the syntheses of derivatives, syntheses of derivatives 11−26, 32−42, syntheses of derivatives 27−29, syntheses of derivatives 30 and 31, syntheses of dehydro-derivative 43, and syntheses of 9,9'-lactone 44 and 9,9'-epoxy 45 (PDF) 6706

DOI: 10.1021/acs.jafc.7b01896 J. Agric. Food Chem. 2017, 65, 6701−6707

Article

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DOI: 10.1021/acs.jafc.7b01896 J. Agric. Food Chem. 2017, 65, 6701−6707