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. 2024 Nov 20;49(4):262–270. doi: 10.1584/jpestics.D24-038

Discovery of anti-phytopathogenic fungal activity of a new type of (S)-coumarin bearing a phenylpropanoid unit at the 3-position

Hazna Sartiva 1, Hisashi Nishiwaki 1, Koichi Akiyama 2, Satoshi Yamauchi 1,*
PMCID: PMC11770133  PMID: 39877882

Abstract

The enantiospecific anti-phytopathogenic fungal activity of a new type of coumarin bearing a phenylpropanoid unit at the 3-position was found. (S)-3-[1-Methoxy-3-(4-methoxyphenyl)prop-2-yl]coumarin ((S)-5: EC50=16.5 µM) was 30 times more effective than the (R)-form against the Alternaria alternata Japanese pear pathotype. Derivatives bearing different substituents on the 7′-aromatic ring and the coumarin ring were synthesized to discover the more potent compounds. The 3′-CF3 and 4′-CF3 derivatives, 39 and 40, respectively, had the lowest EC50 values (1–2 µM) in this project, suggesting that the size of the electron-withdrawing and hydrophobic substituents at these positions gave an advantage. On the coumarin ring, the presence of the OCH3 or CH3 group at the 5-position accelerated the activity, as the (4′-OCH3, 5-OCH3) derivative 41 and (4′-OCH3, 5-CH3) derivative 45 were, respectively, 4–5 times more potent than the 4′-OCH3 derivative (S)-5.

Keywords: lignan; benzylidene lactone; antifungal activity; coumarin; lignano-9,9′-lactone

Introduction

The development of novel pesticides based on dietary components is one of the important strategies in green chemistry. We have developed a stereoselective synthetic method to provide phytotoxic (R)-3-(1-aryl-3-hydroxyprop-2-yl)coumarin.1) As we found the nonenzymatic trans–cis isomerization of o-hydroxycinnamic acid in the biosynthesis of coumarin (Fig. 1),2,3) E-β-benzyl-α-(2-hydroxybenzylidene)-γ-butyrolactone 1a (R3=H) could be isomerized to 3-(1-aryl-3-hydroxyprop-2-yl)coumarin 2a (R3=OH) via Z-β-benzyl-α-(2-hydroxybenzylidene)-γ-butyrolactone in the plant body. In previous work, we carried out an antifungal study on (R)-E-β-benzyl-α-(2-methoxybenzylidene)-γ-butyrolactone 1b (R3=CH3).4) Antifungal research on the (R/S)-3-(1-arylprop-2-yl)coumarin derivative 2a (R3=OH), 2b (R3=H), and 2c (R3=OCH3) and the structural isomer of 2a (1a: R3=H) bearing phenolic benzylidene structure is a new project. The anti-phytopathogenic fungal activities and structure-function analyses of butane,5) tetrahydrofuran,6) benzylidene lactone type lignans,7) and neolignan8) have been reported. Research on coumarins as anti-phytopathogenic fungal reagents has also been continuing. Thus, the extraction,9–13) syntheses,14–26) identification of the mode of action as a DNA gyrase inhibitor,27) and the effect on peroxisomes28) have been reported. In this new study, we report on the antifungal evaluation of (R/S)-3-(1-arylprop-2-yl)coumarin, which has both lignan and coumarin structures. In the preliminary examination, the effect of the stereochemistry of phenolic benzylidene and the 9′-structurally arranged coumarin on the activity was evaluated. After screening to determine the stereochemistry of phenolic benzylidene and 9′-derivatives of coumarin showing higher activity, synthesized analogues bearing different substituents on the aromatic rings were applied to antifungal tests to clarify the effect of the substituent and position on the growth of fungi. The utilities of natural benzylidene and new type of coumarin lignans for pesticides would be shown in this research.

Fig. 1. Biosynthesis of coumarin and structures of E-2-hydroxybenzylidene lactone and coumarin bearing phenylpropanoid at 3-position.

Fig. 1. Biosynthesis of coumarin and structures of E-2-hydroxybenzylidene lactone and coumarin bearing phenylpropanoid at 3-position

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Materials and methods

Melting points (mp) data are uncorrected. The silica gel used was Wako gel C-300, FUJIFILM Co., INC. (Tokyo, Japan). Optical rotations were measured on a JASCO P-2100 instrument (JASCO Corporation, Japan). 1H and 13C NMR data were recorded on a JNM ECS400 spectrometer (JEOL, Tokyo, Japan). EIMS data were measured with ESI-JMS-MS700V (JEOL, Tokyo, Japan). Compounds (S)-3, (R)-3, (S)-4, (R)-4, (R)-5, and (R)-6 have been synthesized in our previous experiment.1,4) The compounds (S)-5, (S)-6, and 7–28 and 9′-hydroxychoumarin intermediates (I-2), which are enantiomers of previously synthesized compounds, were synthesized in this research (supporting information). The general synthetic methods of (S)-5 and 29–50, which were also synthesized in this project, from intermediate (I-2) and their chemical data are described in this section.

1. General procedure for the syntheses of 9′-methoxycoumarins 29–50 from 9′-hydroxycoumarin intermediates (I-2)

A reaction mixture of 9′-hydroxycoumarin intermediate I-2s (1.0 eq.), Ag2O (2.5 eq.), and CH3I (10 eq.) in DMF (substrate 0.8 mmol/1 mL) was stirred at room temperature for 16 hr before filtration with EtOAc. The filtrate was washed with brine. The organic solution was separated and dried (Na2SO4). Concentration followed by silica gel column chromatography (EtOAc/hexane=1/3 or 5% ether/hexane) gave 9′-OCH3 compounds.

1.1. (S)-3-[1-Methoxy-3-phenylprop-2-yl]-2H-chromen-2-one (29)

14% yield, colorless oil; [α]25D+39 (c 0.4, CHCl3); 1H NMR (400 MHz, CDCl3) δ 3.03 (2H, d, J=7.4 Hz), 3.30 (3H, s), 3.38 (1H, m), 3.54 (1H, dd, J=9.4, 4.4 Hz), 3.59 (1H, dd, J=9.4, 6.3 Hz), 7.14–7.25 (6H, m), 7.29 (1H, d, J=8.3 Hz), 7.40 (1H, d, J=7.7 Hz), 7.45 (1H, dd, J=7.9, 7.7 Hz), 7.50 (1H, s); 13C NMR (100 MHz, CDCl3) δ 36.2, 42.6, 59.0, 72.7, 116.4, 119.5, 124.3, 126.3, 127.7, 2×128.5, 2×129.2, 129.6, 130.9, 139.5, 140.0, 153.1, 161.4; MS (EI) m/z 294 (M+, 24), 262 (100), 249 (58), 203 (97), 171 (49); HRMS (EI) m/z calcd for C19H18O3 294.1256, found 294.1264.

1.2. (S)-3-[1-Methoxy-3-(2-methoxyphenyl)prop-2-yl]-2H-chromen-2-one (30)

12% yield, colorless oil; [α]25D+76 (c 0.4, CHCl3); 1H NMR (400 MHz, CDCl3) δ 3.05 (2H, d, J=7.2 Hz), 3.32 (3H, s), 3.45 (1H, m), 3.58 (1H, dd, J=9.4, 5.0 Hz), 3.68 (1H, dd, J=9.4, 7.1 Hz), 3.71 (3H, s), 6.76 (1H, d, J=8.2 Hz), 6.84 (1H, dd, J=7.4, 7.4 Hz), 7.13 (1H, dd, J=8.7, 8.1 Hz), 7.20 (1H, dd, J=8.1, 7.5 Hz), 7.26–7.30 (2H, m), 7.36 (1H, d, J=8.7 Hz), 7.38 (1H, s), 7.44 (1H, dd, J=8.2, 7.4 Hz); 13C NMR (100 MHz, CDCl3) δ 30.5, 41.6, 55.1, 58.8, 73.1, 110.1, 116.2, 119.5, 120.3, 124.1, 127.4, 2×127.6, 129.7, 130.5, 130.9, 139.2, 153.0, 157.5, 161.3; MS (EI) m/z 324 (M+, 41), 292 (68), 121 (100); HRMS (EI) m/z calcd for C20H20O4 324.1362, found 324.1370.

1.3. (S)-3-[1-Methoxy-3-(3-methoxyphenyl)prop-2-yl]-2H-chromen-2-one (31)

27% yield, colorless oil; [α]25D+56 (c 0.4, CHCl3); 1H NMR (400 MHz, CDCl3) δ 3.02 (2H, d, J=6.8 Hz), 3.32 (3H, s), 3.40 (1H, m), 3.55 (1H, dd, J=9.4, 4.4 Hz), 3.61 (1H, dd, J=9.4, 6.4 Hz), 3.76 (3H, s), 6.71–6.80 (3H, m), 7.17 (1H, dd, J=7.8, 7.8 Hz), 7.23 (1H, dd, J=7.6, 7.5 Hz), 7.30 (1H, d, J=8.2 Hz), 7.43 (1H, d, J=7.8 Hz), 7.46 (1H, dd, J=8.2, 7.8 Hz), 7.53 (1H, s); 13C NMR (100 MHz, CDCl3) δ 36.1, 42.4, 55.1, 58.9, 72.6, 111.7, 114.6, 116.3, 119.4, 121.5, 124.2, 127.6, 129.3, 129.5, 130.8, 139.9, 141.0, 153.0, 159.5, 161.3; MS (EI) m/z 324 (M+, 74), 292 (100), 279 (55), 203 (93); HRMS (EI) m/z calcd for C20H20O4 324.1362, found 324.1365.

1.4. (S)-3-[1-Methoxy-3-(4-methoxyphenyl)prop-2-yl]-2H-chromen-2-one [(S)-5]

31% yield, colorless crystals, mp 95–96°C; [α]25D+51(c 0.2, CHCl3). NMR data agreed with previously synthesized (R)-form.

1.5. (S)-3-[1-Methoxy-3-(2-methylphenyl)prop-2-yl]-2H-chromen-2-one (32)

19% yield, colorless oil; [α]25D+37 (c 1.0, CHCl3); 1H NMR (400 MHz, CDCl3) δ 2.36 (3H, s), 2.98–3.08 (2H, m), 3.31 (3H, s), 3.36 (1H, m), 3.54 (1H, dd, J=9.3, 4.2 Hz), 3.62 (1H, dd, J=9.3, 6.3 Hz), 7.07–7.12 (4H, m), 7.23 (1H, dd, J=7.5, 7.5 Hz), 7.30 (1H, d, J=8.2 Hz), 7.42 (1H, d, J=8.3 Hz), 7.45 (1H, dd, J=7.5, 7.5 Hz), 7.57 (1H, s); 13C NMR (100 MHz, CDCl3) δ 19.5, 33.7, 41.6, 58.9, 72.7, 116.4, 119.5, 124.3, 125.9, 126.5, 127.7, 130.0, 130.1, 130.5, 130.9, 136.6, 137.7, 139.9, 153.2, 161.4; MS (EI) m/z 308 (M+, 36), 276 (73), 203 (100), 171 (39), 105 (55); HRMS (EI) m/z calcd for C20H20O3 308.1412, found 308.1416.

1.6. (S)-3-[1-Methoxy-3-(3-methylphenyl)prop-2-yl]-2H-chromen-2-one (33)

17% yield, colorless oil; [α]25D+35 (c 0.6, CHCl3); 1H NMR (400 MHz, CDCl3) δ 2.29 (3H, s), 2.98 (2H, d, J=7.4 Hz), 3.30 (3H, s), 3.38 (1H, m), 3.53 (1H, dd, J=9.3, 4.3 Hz), 3.59 (1H, dd, J=9.3, 6.5 Hz), 6.97–7.02 (3H, m), 7.13 (1H, dd, J=7.4, 7.4 Hz), 7.22 (1H, dd, J=8.5, 7.5 Hz), 7.29 (1H, d, J=8.2 Hz), 7.40–7.46 (2H, m), 7.52 (1H, s); 13C NMR (100 MHz, CDCl3) δ 21.5, 36.2, 42.5, 59.0, 72.7, 116.4, 119.5, 124.3, 126.3, 127.1, 127.7, 128.3, 129.8, 130.0, 130.8, 138.0, 139.4, 139.9, 153.1, 161.4; MS (EI) m/z 308 (M+, 47), 276 (97), 263 (52), 203 (100), 171 (57); HRMS (EI) m/z calcd for C20H20O3 308.1412, found 308.1417.

1.7. (S)-3-[1-Methoxy-3-(4-methylphenyl)prop-2-yl]-2H-chromen-2-one (34)

24% yield, colorless crystals, mp 91–92°C (hexane); [α]25D+46 (c 0.2, CHCl3); 1H NMR (400 MHz, CDCl3) δ 2.28 (3H, s), 2.98 (2H, d, J=7.4 Hz), 3.30 (3H, s), 3.36 (1H, m), 3.52 (1H, dd, J=9.5, 4.5 Hz), 3.59 (1H, dd, J=9.5, 6.4 Hz), 7.04 (2H, d, J=8.3 Hz), 7.07 (2H, d, J=8.3 Hz), 7.22 (1H, dd, J=7.7, 7.3 Hz), 7.29 (1H, d, J=8.2 Hz), 7.40 (1H, d, J=7.7 Hz), 7.44 (1H, dd, J=8.2, 7.3 Hz), 7.50 (1H, s); 13C NMR (100 MHz, CDCl3) δ 21.2, 35.8, 42.6, 59.0, 72.7, 116.4, 119.5, 124.3, 127.7, 2×129.1, 2×129.2, 129.8, 130.8, 135.8, 136.3, 139.9, 153.1, 161.4; MS (EI) m/z 308 (M+, 41), 276 (100), 263 (52), 203 (68), 171 (52), 105 (83); HRMS (EI) m/z calcd for C20H20O3 308.1412, found 308.1419.

1.8. (S)-3-[1-(2-Fluorophenyl)-3-methoxyprop-2-yl]-2H-chromen-2-one (35)

29% yield, colorless oil; [α]25D+75 (c 0.3, CHCl3); 1H NMR (400 MHz, CDCl3) δ 3.10 (2H, d, J=7.1 Hz), 3.32 (3H, s), 3.44 (1H, m), 3.58 (1H, dd, J=9.3, 4.9 Hz), 3.67 (1H, dd, J=9.3, 6.7 Hz), 6.95 (1H, d, J=9.0 Hz), 7.01 (1H, dd, J=9.1, 7.4 Hz), 7.12–7.26 (3H, m), 7.29 (1H, d, J=8.3 Hz), 7.40 (1H, d, J=7.7 Hz), 7.46 (1H, dd, J=8.1, 7.7 Hz), 7.50 (1H, s); 13C NMR (100 MHz, CDCl3) δ 29.3, 41.8, 58.9, 72.9, 115.3 (d, J=22.2 Hz), 116.3, 119.3, 124.0, 124.2, 126.2 (d, J=15.8 Hz), 127.6, 128.1 (d, J=8.0 Hz), 129.0, 130.8, 131.4 (d, J=4.7 Hz), 139.9, 153.1, 161.16, 161.18 (d, J=244.7 Hz); MS (EI) m/z 312 (M+, 28), 280 (69), 267 (77), 203 (100), 171 (49); HRMS (EI) m/z calcd for C19H17FO3 312.1162, found 312.1168.

1.9. (S)-3-[1-(3-Fluorophenyl)-3-methoxyprop-2-yl]-2H-chromen-2-one (36)

30% yield, colorless oil; [α]25D+50 (c 0.7, CHCl3); 1H NMR (400 MHz, CDCl3) δ 3.04 (2H, d, J=7.3 Hz), 3.32 (3H, s), 3.35 (1H, m), 3.54 (1H, dd, J=9.3, 4.3 Hz), 3.59 (1H, dd, J=9.3, 6.4 Hz), 6.85–6.93 (2H, m), 6.98 (1H, d, J=7.5 Hz), 7.18–7.26 (2H, m), 7.31 (1H, d, J=8.1 Hz), 7.42 (1H, d, J=7.6 Hz), 7.47 (1H, dd, J=8.1, 7.7 Hz), 7.53 (1H, s); 13C NMR (100 MHz, CDCl3) δ 35.8, 42.4, 58.9, 72.4, 113.2, 115.9, 116.3, 119.3, 124.2, 124.7, 127.6, 129.2, 129.8 (d, J=8.3 Hz), 130.9, 139.9, 142.0 (d, J=7.2 Hz), 153.0, 161.2, 162.8 (d, J=245.7 Hz); MS (EI) m/z 312 (M+, 37), 280 (67), 267 (61), 203 (100), 171 (44); HRMS (EI) m/z calcd for C19H17FO3 312.1162, found 312.1170.

1.10. (S)-3-[1-(4-Fluorophenyl)-3-methoxyprop-2-yl]-2H-chromen-2-one (37)

21% yield, colorless crystals, mp 65–67°C; [α]25D+46 (c 0.4, CHCl3); 1H NMR (400 MHz, CDCl3) δ 3.01 (2H, d, J=7.5 Hz), 3.32 (3H, s), 3.34 (1H, m), 3.54 (1H, dd, J=9.5, 4.2 Hz), 3.58 (1H, dd, J=9.5, 6.2 Hz), 6.94 (2H, m), 7.15 (2H, m), 7.24 (1H, dd, J=7.7, 7.6 Hz), 7.30 (1H, d, J=8.3 Hz), 7.42 (1H, d, J=7.6 Hz), 7.47 (1H, dd, J=8.3, 7.7 Hz), 7.50 (1H, s); 13C NMR (100 MHz, CDCl3) δ 35.3, 42.7, 58.9, 72.5, 2×115.2 (d, J=21.2 Hz), 116.4, 119.3, 124.2, 127.6, 129.4, 2×130.5 (d, J=8.0 Hz), 130.9, 135.1, 139.9, 153.0, 161.3, 161.4 (d, J=244.2 Hz); MS (EI) m/z 312 (M+, 36), 280 (75), 267 (45), 203 (100), 171 (49); HRMS (EI) m/z calcd for C19H17FO3 312.1162, found 312.1167.

1.11. (S)-3-[1-Methoxy-3-(2-trifluoromethylphenyl)prop-2-yl]-2H-chromen-2-one (38)

18% yield, colorless oil; [α]25D+78 (c 0.7, CHCl3); 1H NMR (400 MHz, CDCl3) δ 3.24 (2H, d, J=7.4 Hz), 3.31 (3H, s), 3.50 (1H, m), 3.56 (1H, dd, J=9.0, 4.5 Hz), 3.74 (1H, dd, J=9.0, 7.2 Hz), 7.21–7.31 (3H, m), 7.35–7.42 (3H, m), 7.46 (1H, dd, J=8.2, 7.5 Hz), 7.51 (1H, s), 7.62 (1H, d, J=7.8 Hz); 13C NMR (100 MHz, CDCl3) δ 32.6, 42.3, 58.9, 72.9, 116.3, 119.3, 124.3, 124.6 (q, J=273.8 Hz), 126.2 (q, J=5.7 Hz), 126.4, 127.6, 128.8 (q, J=29.5 Hz), 129.0, 130.9, 131.4, 131.7, 138.1, 140.3, 153.1, 161.2; MS (EI) m/z 362 (M+, 8), 330 (58), 277 (80), 203 (100); HRMS (EI) m/z calcd for C20H17F3O3 362.1130, found 362.1125.

1.12. (S)-3-[1-Methoxy-3-(3-trifluoromethylphenyl)prop-2-yl]-2H-chromen-2-one (39)

23% yield, colorless crystals, mp 108–111°C; [α]25D+25 (c 1.2, CHCl3); 1H NMR (400 MHz, CDCl3) δ 3.10 (2H, d, J=7.5 Hz), 3.32 (3H, s), 3.38 (1H, m), 3.54 (2H, d, J=5.0 Hz), 7.25 (1H, dd, J=7.4, 6.3 Hz), 7.31 (1H, d, J=8.8 Hz), 7.36–7.50 (6H, m), 7.56 (1H, s); 13C NMR (100 MHz, CDCl3) δ 35.9, 42.2, 58.9, 72.2, 116.4, 119.3, 123.2 (q, J=3.8 Hz), 124.1 (q, J=272.2 Hz), 124.3, 125.9 (q, J=3.6 Hz), 127.6, 128.9, 129.2, 130.7 (q, J=32.0 Hz), 131.0, 132.5, 140.1, 140.4, 153.0, 161.3; MS (EI) m/z 362 (M+, 16), 330 (63), 203 (100); HRMS (EI) m/z calcd for C20H17F3O3 362.1130, found 362.1120.

1.13. (S)-3-[1-Methoxy-3-(4-trifluoromethylphenyl)prop-2-yl]-2H-chromen-2-one (40)

13% yield, colorless crystals, mp 84–86°C (hexane); [α]25D+42 (c 0.4, CHCl3); 1H NMR (400 MHz, CDCl3) δ 3.09 (1H, dd, J=14.1, 8.5 Hz), 3.12 (1H, dd, J=14.1, 7.3 Hz), 3.33 (3H, s), 3.39 (1H, m), 3.54 (1H, dd, J=9.4, 4.6 Hz), 3.58 (1H, dd, J=9.4, 5.7 Hz), 7.23–7.26 (2H, m), 7.31–7.33 (3H, m), 7.43 (1H, d, J=7.6 Hz), 7.46–7.54 (3H, m); 13C NMR (100 MHz, CDCl3) δ 35.9, 42.4, 58.9, 72.4, 116.4, 119.3, 124.2 (q, J=271.5 Hz), 124.3, 2×125.3 (q, J=3.6 Hz), 127.6, 128.6 (q, J=32.5 Hz), 129.1, 2×129.4, 131.0, 140.1, 143.7, 153.1, 161.2; MS (EI) m/z 362 (M+, 26), 330 (59), 317 (26), 297 (31), 203 (100), 171 (31); HRMS (EI) m/z calcd for C20H17F3O3 362.1130, found 362.1123.

1.14. (S)-5-Methoxy-3-[1-methoxy-3-(4-methoxyphenyl)prop-2-yl]-2H-chromen-2-one (41)

42% yield, colorless oil, [α]25D+55 (c 0.4, CHCl3); 1H NMR (400 MHz, CDCl3) δ 2.97 (2H, d, J=7.6 Hz), 3.31 (3H, s), 3.36 (1H, m), 3.52 (1H, dd, J=9.5, 4.7 Hz), 3.59 (1H, dd, J=9.5, 6.5 Hz), 3.77 (3H, s), 3.91 (3H, s), 6.67 (1H, d, J=8.2 Hz), 6.80 (2H, d, J=8.5 Hz), 6.89 (1H, d, J=8.3 Hz), 7.12 (2H, d, J=8.5 Hz), 7.37 (1H, dd, J=8.3, 8.2 Hz), 7.89 (1H, s); 13C NMR (100 MHz, CDCl3) δ 35.3, 42.7, 55.2, 55.9, 58.8, 72.8, 104.8, 108.7, 110.0, 2×113.7, 127.5, 2×130.0, 131.2, 131.5, 134.7, 154.0, 155.7, 157.8, 161.4; MS (EI) m/z 354 (M+, 19), 322 (22), 233 (15), 121 (100); HRMS (EI) m/z calcd for C21H22O5 354.1467, found 354.1472.

1.15. (S)-6-Methoxy-3-[1-methoxy-3-(4-methoxyphenyl)prop-2-yl]-2H-chromen-2-one (42)

82% yield, colorless crystals, mp 88–90°C (iso-Pr2O-hexane), [α]25D+27 (c 0.4, CHCl3); 1H NMR (400 MHz, CDCl3) δ 2.95 (1H, dd, J=13.9, 8.0 Hz), 2.99 (1H, dd, J=13.9, 6.9 Hz), 3.31 (3H, s), 3.34 (1H, m), 3.53 (1H, dd, J=9.4, 4.5 Hz), 3.59 (1H, dd, J=9.4, 6.3 Hz), 3.77 (3H, s), 3.83 (3H, s), 6.80 (2H, d, J=8.6 Hz), 6.85 (1H, d, J=2.8 Hz), 7.04 (1H, dd, J=9.0, 2.8 Hz), 7.10 (2H, d, J=8.6 Hz), 7.23 (1H, d, J=9.0 Hz), 7.45 (1H, s); 13C NMR (100 MHz, CDCl3) δ 35.2, 42.7, 55.2, 55.8, 58.9, 72.5, 109.6, 2×113.7, 117.3, 118.5, 119.7, 129.9, 2×130.1, 131.4, 139.7, 147.4, 155.9, 157.9, 161.5; MS (EI) m/z 354 (M+, 64), 322 (58), 233 (18), 202 (22), 121 (100); HRMS (EI) m/z calcd for C21H22O5 354.1467, found 354.1475.

1.16. (S)-7-Methoxy-3-[1-methoxy-3-(4-methoxyphenyl)prop-2-yl]-2H-chromen-2-one (43)

41% yield, colorless crystals, mp 83–84°C, [α]25D+60 (c 0.4, CHCl3); 1H NMR (400 MHz, CDCl3) δ 2.69 (2H, d, J=7.3 Hz), 3.31 (3H, s), 3.52 (1H, dd, J=9.3, 4.6 Hz), 3.59 (1H, dd, J=9.3, 6.4 Hz), 3.76 (3H, s), 3.85 (3H, s), 6.78–6.81 (4H, m), 7.10 (2H, d, J=8.2 Hz), 7.30 (1H, d, J=8.3 Hz), 7.43 (1H, s); 13C NMR (100 MHz, CDCl3) δ 35.2, 42.5, 55.2, 55.7, 58.8, 72.7, 100.3, 112.3, 113.0, 2×113.7, 125.9, 128.4, 2×130.0, 131.5, 139.9, 154.7, 157.9, 161.6, 162.0; MS (EI) m/z 354 (M+, 26), 322 (24), 233 (90), 202 (13), 121 (100); HRMS (EI) m/z calcd for C21H22O5 354.1467, found 354.1470.

1.17. (S)-8-Methoxy-3-[1-methoxy-3-(4-methoxyphenyl)prop-2-yl]-2H-chromen-2-one (44)

23% yield, colorless oil, [α]25D+51 (c 0.6, CHCl3); 1H NMR (400 MHz, CDCl3) δ 2.95 (1H, dd, J=13.9, 7.4 Hz), 2.99 (1H, dd, J=13.9, 7.2 Hz), 3.30 (3H, s), 3.34 (1H, m), 3.53 (1H, dd, J=9.3, 4.5 Hz), 3.60 (1H, dd, J=9.3, 6.7 Hz), 3.76 (3H, s), 3.95 (3H, s), 6.78 (2H, d, J=8.3 Hz), 6.97–7.02 (2H, m), 7.09 (2H, d, J=8.3 Hz), 7.15 (1H, dd, J=8.0, 8.0 Hz), 7.46 (1H, s); 13C NMR (100 MHz, CDCl3) δ 35.1, 42.8, 55.2, 56.2, 58.8, 72.5, 112.6, 2×113.7, 119.0, 120.0, 124.0, 129.8, 2×130.0, 131.3, 139.9, 142.6, 146.9, 157.9, 160.6; MS (EI) m/z 354 (M+, 30), 322 (29), 121 (100); HRMS (EI) m/z calcd for C21H22O5 354.1467, found 354.1471.

1.18. (S)-3-[1-Methoxy-3-(4-methoxyphenyl)prop-2-yl]-5-methyl-2H-chromen-2-one (45)

70% yield, colorless oil, [α]25D+51 (c 0.6, CHCl3); 1H NMR (400 MHz, CDCl3) δ 2.47 (3H, s), 2.99 (2H, d, J=7.5 Hz), 3.32 (3H, s), 3.36 (1H, m), 3.55 (1H, dd, J=9.4, 4.6 Hz), 3.63 (1H, dd, J=9.4, 6.4 Hz), 3.77 (3H, s), 6.80 (2H, d, J=8.6 Hz), 7.05 (1H, d, J=7.4 Hz), 7.11 (2H, d, J=8.6 Hz), 7.14 (1H, d, J=8.5 Hz), 7.33 (1H, dd, J=8.5, 7.4 Hz), 7.65 (1H, s); 13C NMR (100 MHz, CDCl3) δ 18.4, 35.3, 43.0, 55.2, 58.9, 72.7, 2×113.7, 114.3, 118.1, 125.4, 128.7, 2×130.1, 130.5, 131.4, 135.6, 136.9, 153.4, 157.9, 161.3; MS (EI) m/z 338 (M+, 68), 306 (66), 127 (20), 185 (20), 121 (100); HRMS (EI) m/z calcd for C21H22O4 338.1518, found 338.1508.

1.19. (S)-3-[1-Methoxy-3-(4-methoxyphenyl)prop-2-yl]-6-methyl-2H-chromen-2-one (46)

25% yield, colorless crystals, mp 38–39°C (EtOH), [α]25D+51 (c 0.1, CHCl3); 1H NMR (400 MHz, CDCl3) δ 2.37 (3H, s), 2.97 (2H, d, J=6.8 Hz), 3.31 (3H, s), 3.34 (1H, m), 3.53 (1H, dd, J=9.3, 4.5 Hz), 3.59 (1H, dd, J=9.3, 6.4 Hz), 3.76 (3H, s), 6.79 (2H, d, J=8.5 Hz), 7.10 (2H, d, J=8.6 Hz), 7.18 (1H, d, J=8.4 Hz), 7.19 (1H, s), 7.25 (1H, d, J=8.4 Hz), 7.44 (1H, s); 13C NMR (100 MHz, CDCl3) δ 20.7, 35.1, 42.6, 55.1, 58.8, 72.6, 2×113.6, 115.9, 119.1, 127.4, 129.3, 2×130.0, 131.4, 131.7, 133.7, 139.8, 151.0, 157.9, 161.5; MS (EI) m/z 338 (M+, 73), 306 (80), 127 (21), 185 (21), 121 (100); HRMS (EI) m/z calcd for C21H22O4 338.1518, found 338.1511.

1.20. (S)-3-[1-Methoxy-3-(4-methoxyphenyl)prop-2-yl]-7-methyl-2H-chromen-2-one (47)

27% yield, colorless crystals, mp 127–128°C (EtOH), [α]25D+55 (c 0.5, CHCl3); 1H NMR (400 MHz, CDCl3) δ 2.43 (3H, s), 2.96 (2H, d, J=6.6 Hz), 3.31 (3H, s), 3.34 (1H, m), 3.53 (1H, dd, J=9.4, 4.6 Hz), 3.59 (1H, dd, J=9.4, 6.3 Hz), 3.76 (3H, s), 6.79 (2H, d, J=8.4 Hz), 7.04 (1H, d, J=7.9 Hz), 7.099 (2H, d, J=8.4 Hz), 7.103 (1H, s), 7.29 (1H, d, J=7.9 Hz), 7.46 (1H, s); 13C NMR (100 MHz, CDCl3) δ 21.7, 35.2, 42.6, 55.2, 58.8, 72.6, 2×113.7, 116.4, 116.9, 125.3, 127.2, 128.2, 2×130.0, 131.4, 139.8, 141.8, 153.1, 157.9, 161.6; MS (EI) m/z 338 (M+, 52), 306 (61), 217 (28), 152 (17), 121 (100); HRMS (EI) m/z calcd for C21H22O4 338.1518, found 338.1513.

1.21. (S)-3-[1-Methoxy-3-(4-methoxyphenyl)prop-2-yl]-8-methyl-2H-chromen-2-one (48)

47% yield, colorless oil, [α]25D+42 (c 0.9, CHCl3); 1H NMR (400 MHz, CDCl3) δ 2.45 (3H, s), 2.98 (2H, d, J=7.0 Hz), 3.31 (3H, s), 3.36 (1H, m), 3.54 (1H, dd, J=9.4, 4.5 Hz), 3.60 (1H, dd, J=9.4, 6.4 Hz), 3.76 (3H, s), 6.79 (2H, d, J=8.6 Hz), 7.11 (2H, d, J=8.6 Hz), 7.12 (1H, dd, J=8.0, 7.3 Hz), 7.25 (1H, d, J=8.0 Hz), 7.30 (1H, d, J=7.3 Hz), 7.48 (1H, s); 13C NMR (100 MHz, CDCl3) δ 15.4, 35.1, 42.5, 55.1, 58.8, 72.6, 2×113.7, 119.0, 123.7, 125.2, 125.7, 129.1, 2×130.0, 131.4, 132.0, 140.2, 151.3, 157.9, 161.5; MS (EI) m/z 338 (M+, 14), 306 (15), 121 (100); HRMS (EI) m/z calcd for C21H22O4 338.1518, found 338.1514.

1.22. (S)-6-Fluoro-3-[1-methoxy-3-(4-methoxyphenyl)prop-2-yl]-2H-chromen-2-one (49)

43% yield, colorless oil, [α]25D+14 (c 0.5, CHCl3); 1H NMR (400 MHz, CDCl3) δ 2.96 (2H, d, J=6.7 Hz), 3.31 (3H, s), 3.32 (1H, m), 3.53 (1H, dd, J=9.2, 4.2 Hz), 3.60 (1H, dd, J=9.2, 6.4 Hz), 3.77 (3H, s), 6.80 (2H, d, J=8.3 Hz), 7.10 (2H, d, J=8.3 Hz), 7.16–7.19 (2H, m), 7.29 (1H, m), 7.45 (1H, s); 13C NMR (100 MHz, CDCl3) δ 35.1, 42.7, 55.2, 58.9, 72.3, 112.8 (d, J=23.8 Hz), 2×113.7, 117.8 (d, J=8.5 Hz), 118.1 (d, J=24.8 Hz), 120.1 (d, J=9.2 Hz), 2×130.0, 130.9, 131.1, 138.9, 149.1, 158.0, 158.6 (d, J=243.5 Hz), 160.9; MS (EI) m/z 342 (M+, 47), 310 (30), 206 (42), 137 (68), 121 (100); HRMS (EI) m/z calcd for C20H19FO4 342.1268, found 342.1276.

1.23. (S)-7-Fluoro-3-[1-methoxy-3-(4-methoxyphenyl)prop-2-yl]-2H-chromen-2-one (50)

12% yield, colorless crystals, mp 117–119°C (EtOH), [α]25D+37 (c 0.1, CHCl3); 1H NMR (400 MHz, CDCl3) δ 2.96 (2H, d, J=6.9 Hz), 3.29–3.33 (1H, overlapped), 3.31 (3H, s), 3.53 (1H, dd, J=9.4, 4.4 Hz), 3.59 (1H, dd, J=9.4, 6.4 Hz), 3.77 (3H, s), 6.80 (2H, d, J=8.5 Hz), 6.95–7.04 (2H, m), 7.10 (2H, d, J=8.5 Hz), 7.39 (1H, dd, J=8.6, 6.0 Hz), 7.47 (1H, s); 13C NMR (100 MHz, CDCl3) δ 35.2, 42.7, 55.2, 58.9, 72.4, 103.9 (d, J=25.6 Hz), 112.3 (d, J=22.9 Hz), 2×113.7, 116.1, 128.3, 129.0 (d, J=10.1 Hz), 2×130.0, 131.2, 139.3, 154.0 (d, J=12.7 Hz), 158.0, 160.9, 163.8 (d, J=252.1 Hz); MS (EI) m/z 342 (M+, 70), 310 (47), 189 (15), 133 (18), 121 (100); HRMS (EI) m/z calcd for C20H19FO4 342.1268, found 342.1272.

2. Evaluation of antifungal activity

2.1. Fungal strains

The Alternaria alternata Japanese pear pathotype and Colletotrichum lagenarium employed were stored at Ehime University. Each fungal strain was cultured on potato dextrose agar (PDA, Sigma-Aldrich, Canada).

2.2. Antifungal assay

Thirty microliters 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 for 3 days for A. alternata and for 5 days for C. lagenarium, respectively, the diameter of the mycelial colony was measured with a caliper. All assays were performed in triplicate.

2.3. Calculation of the EC50 values

The EC50 values were calculated using a standard dose–response curve by non-linear regression analysis fitting by employing PRISM software ver. 5.0 (GraphPad software Inc., San Diego, CA, U.S.A.). The antifungal activity data at six different concentrations of each compound were analyzed by this method. These analyses were performed in triplicate to obtain EC50 value of each compound.

Results and discussion

We commenced with tests for the ability of coumarins bearing phenylpropanoids at the 3-position ((S)- and (R)-4, (S)- and (R)-5, (S)- and (R)-6) to inhibit the growth of phytopathogenic fungi. The results were compared with 2-hydroxybenzylidene-γ-butyrolactone ((S)- and (R)-3) (Table 1). In our previous study,4) (S)-E-phenolic benzylidene lactone (S)-3 was more susceptible than (R)-3 against A. alternata. In this research, the antifungal activities of both coumarin enantiomer structures bearing the phenylpropanoid moiety 4–6 were estimated for the first time. In the case of coumarin compounds, which are assumed to be structures transformed from benzylidene lactone compounds (Fig. 1), (R)- and (S)-9′-OH, (R)- and (S)-9′-reductive coumarins 4, 6, and (R)-9′-OCH3 derivative 5 showed lower activities than the (S)-9′-OCH3 derivative 5 against A. alternata. The phytotoxic (S)- and (R)-9′-hydroxycoumarin 41) were 17 to 22 times less potent than (S)-5, suggesting the disadvantage of the hydrophilic group at the 9′-position. Even though they have hydrophobic features, the (S)- and (R)-9′-reductive compounds 6 were 3 to 4 times less potent than (S)-9′-OCH3 5. A greater difference was observed between (S)- and (R)-9′-OCH3 5. Thus, the (S)-form was ca. 30 times more effective than the (R)-form. These results forced us to pursue our research further using the derivative 5 bearing the (S)-form and the 9′-OCH3 group. A smaller difference between (S)- and (R)-form of 4 and 6 would be due to a different mode of action from 5. Against C. lagenarium, only the (R)-9′-OH compound 4 showed lower activity (EC50=426 µM).

Table 1. Comparison of Antifungal Activities between Enantiomers of E-2-hydroxybenzylidene lactone and coumarin compounds (EC50±SD).

graphic file with name jps-49-4-D24-038-table01a.jpg
Compounds Alternaria alternata Japanese pear pathotype Colletotricum lagenarium
(S)-3 28.8±2.19 µM 77% growth at 500 µM
(R)-3 65% growth at 500 µM 72% growth at 500 µM
(S)-4 285±10.2 µM 51% growth at 500 µM
(R)-4 370±24.5 µM 426±29.5 µM
(S)-5 16.5±1.57 µM 86% growth at 500 µM
(R)-5 65% growth at 500 µM 90% growth at 500 µM
(S)-6 48.9±6.79 µM 77% growth at 500 µM
(R)-6 68.8±3.57 µM 72% growth at 500 µM
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To allow comparison of the effect of substituents on the 7′-aromatic ring, derivatives 29–50 were synthesized (Tables 2, 3). E-2-Hydroxybenzylidene lactone derivatives 7–28 and 9′-hydroxycoumarin intermediates (I-2) were prepared from the benzyl intermediate (I-1) obtained by stereoselective benzylation employing Evans’ auxiliary (Table 2). The chiral centers of our desired derivatives were constructed by this stereoselective benzylation. The final 9′-OCH3 derivatives 29–50 were prepared from 9′-hydroxycoumarin intermediates (I-2) by methylation employing Ag2O and CH3I (Table 3). Mild reaction conditions were required for this methylation because of the production of Z-benzylidene lactone.

Table 2. Syntheses of (S)-E-2-Hydroxybenzylidene lactone derivatives 7–28 and Their Antifungal Activities (EC50±SD).

graphic file with name jps-49-4-D24-038-table02a.jpg
Compounds R1, R2 Alternaria alternata Japanese pear pathotype Colletotrichum lagenarium
7: R1=H, R2=H 101±1.67 µM 55% growth at 500 µM
8: R1=2′-OCH3, R2=H 122±21.0 µM 49% growth at 500 µM
9: R1=3′-OCH3, R2=H 181±29.0 µM 65% growth at 500 µM
(S)-3: 4′-OCH3, R2=H (Table 1) 28.8±2.19 µM 77% growth at 500 µM
10: R1=2′-CH3, R2=H 56.9±1.06 µM 60% growth at 500 µM
11: R1=3′-CH3, R2=H 89.1±7.86 µM 173±0.97 µM
12: R1=4′-CH3, R2=H 65.5±8.61 µM 76% growth at 500 µM
13: R1=2′-F, R2=H 99.2±6.60 µM 258±28.0 µM
14: R1=3′-F, R2=H 205±7.41 µM 372±72.9 µM
15: R1=4′-F, R2=H 218±37.3 µM 335±37.6 µM
16: R1=2′-CF3, R2=H 52% growth at 500 µM 61% growth at 500 µM
17: R1=3′-CF3, R2=H 97.1±11.5 µM 209±16.5 µM
18: R1=4′-CF3, R2=H 141±7.84 µM 72% growth at 500 µM
19: R1=4′-OCH3, R2=3-OCH3 173±15.6 µM 50% growth at 500 µM
20: R1=4′-OCH3, R2=4-OCH3 235±9.73 µM 69% growth at 500 µM
21: R1=4′-OCH3, R2=5-OCH3 158±15.6 µM 62% growth at 500 µM
22: R1=4′-OCH3, R2=6-OCH3 56% growth at 500 µM 77% growth at 500 µM
23: R1=4′-OCH3, R2=3-CH3 55% growth at 500 µM 82% growth at 500 µM
24: R1=4′-OCH3, R2=4-CH3 88.1±17.0 µM 71% growth at 500 µM
25: R1=4′-OCH3, R2=5-CH3 53.6±12.4 µM 79% growth at 500 µM
26: R1=4′-OCH3, R2=6-CH3 95% growth at 500 µM 78% growth at 500 µM
27: R1=4′-OCH3, R2=4-F 86.2±12.4 µM 326±31.8 µM
28: R1=4′-OCH3, R2=5-F 126±9.44 µM 79% growth at 500 µM
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Table 3. Syntheses of coumarin derivatives bearing phenylpropanoid unit at 3-position 29–50 and Their Antifungal Activities (EC50±SD).

graphic file with name jps-49-4-D24-038-table03a.jpg
Compounds R1, R2 Alternaria alternata Japanese pear pathotype Colletotrichum lagenarium
29: R1=H, R2=H 5.37±0.39 µM 51% growth at 500 µM
30: R1=2′-OCH3, R2=H 392±63.4 µM 66% growth at 500 µM
31: R1=3′-OCH3, R2=H 11.1±0.94 µM 55% growth at 500 µM
(S)-5: 4′-OCH3, R2=H (Table 1) 16.5±1.57 µM 86% growth at 500 µM
32: R1=2′-CH3, R2=H 88.1±2.54 µM 55% growth at 500 µM
33: R1=3′-CH3, R2=H 4.75±1.08 µM 59% growth at 500 µM
34: R1=4′-CH3, R2=H 8.96±0.25 µM 87% growth at 500 µM
35: R1=2′-F, R2=H 94.6±15.2 µM 48% growth at 500 µM
36: R1=3′-F, R2=H 4.16±0.85 µM 345±47.6 µM
37: R1=4′-F, R2=H 3.44±0.45 µM 50% growth at 500 µM
38: R1=2′-CF3, R2=H 193±7.28 µM 67% growth at 500 µM
39: R1=3′-CF3, R2=H 1.41±0.06 µM 74% growth at 500 µM
40: R1=4′-CF3, R2=H 1.71±0.26 µM 88% growth at 500 µM
41: R1=4′-OCH3, R2=5-OCH3 3.92±0.88 µM 56% growth at 500 µM
42: R1=4′-OCH3, R2=6-OCH3 75% growth at 500 µM 86% growth at 500 µM
43: R1=4′-OCH3, R2=7-OCH3 150±20.7 µM 60% growth at 500 µM
44: R1=4′-OCH3, R2=8-OCH3 129±15.9 µM 75% growth at 500 µM
45: R1=4′-OCH3, R2=5-CH3 2.92±0.35 µM 63% growth at 500 µM
46: R1=4′-OCH3, R2=6-CH3 29.3±0.73 µM 79% growth at 500 µM
47: R1=4′-OCH3, R2=7-CH3 89% growth at 500 µM 83% growth at 500 µM
48: R1=4′-OCH3, R2=8-CH3 27.7±2.17 µM 54% growth at 500 µM
49: R1=4′-OCH3, R2=6-F 56% growth at 500 µM 90% growth at 500 µM
50: R1=4′-OCH3, R2=7-F 74% growth at 500 µM 85% growth at 500 µM
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The activities of (S)-E-2-hydroxybenzylidene lactone derivatives 7–28 are illustrated in Table 2. Against A. alternata, the 4′-OCH3 compound (S)-3 showed the lowest EC50 value (29 µM). The activity of the non-substituted derivative 7 was 3.5 times less than that of the 4′-OCH3 compound (S)-3. The 2′-, 3′-OCH3 derivatives 8, 9 were 4–6 times less potent than the 4′-OCH3 compound ((S)-3). The 2′-, 3′-, and 4′-CH3 derivatives 10–12 showed 2–3 times weaker activities. The derivatives bearing electron-withdrawing substituents, the F derivatives 13–15 and CF3 derivatives 16–18, exhibited 3–17 times less potent activities. Especially, the introduction of the CF3 group to the 2′-position (derivative 16) resulted in a strong drop in activity. The 4′-OCH3 group, which is a higher electron-donating group, is indispensable for increasing the activity of (S)-2-hydroxybenzylidene lactone. The effects of substituents at the 3–6 positions were also checked by employing derivatives 19–28. All the derivatives 19–28 were less active than the 4′-OCH3 compound ((S)-3) against A. alternata, confirming the disadvantage of the presence of substituents at the 3–6 positions. Especially, a significant loss of activity in 6-OCH3, 3-CH3, and 6-CH3 derivatives 22, 23, 26 was observed. The 2 to 8 times less potent activities of 3-OCH3, 4-OCH3, 5-OCH3, 4-CH3, 5-CH3, 4-F, and 5-F derivatives 19–21, 24, 25, 27, 28 were shown. After screening the derivatives against C. lagenarium, we identified that the introduction of a small fluorine atom at each position from the 2′- to 4′-positions accelerated the activities, the derivatives 13–15 showing EC50 values of 258–372 µM. Although the 3′-OCH3 derivative 9 was inactive, the presence of the larger hydrophobic substituent, CH3 or CF3 group, at the 3′-position was also advantageous. Thus, the EC50 values of the 3′-CH3 derivative 11 and the 3′-CF3 derivative 17 were 173 µM and 372 µM, respectively. Of the derivatives 19–28 bearing substituents at the 3–6-positions, only the (4′-OCH3, 4-F) derivative 27 showed weak activity (EC50=326 µM). We designed more potent phenolic benzylidene lactone compounds 11, 13–15, 17, and 27 against C. lagenarium than the lead compound, phenolic 4′-OCH3 ((S)-3); however, their activities were weak.

The 22 analogues 29–50, whose structural hallmarks are coumarin, were screened for antifungal activity (Table 3). Against A. alternata, significant losses of activity were observed in all the 2′-derivatives 30, 32, 35, 38, whose activities were 18–78 times less potent than the non-substituted derivative 29, which had an EC50 value of 5 µM. Both electron-donating and electron-withdrawing substituents at the 2′-position reduced the activity. The activities of the 3′-substituted derivatives 31, 33, 36, 39 were equipotent with the corresponding 4′-substituted derivatives (S)-5, 34, 37, 40. Among them, the 3′-CF3 and 4′-CF3 derivatives 39, 40 showed the lowest EC50 values (1.41 µM and 1.71 µM), which were 3 times more effective than the non-substituted derivative 29. Although the activities of the 3′-CH3, 4′-CH3, 3′-F, and 4′-F derivatives 33, 34, 36, 37 (EC50=3.4–9.0 µM) were similar to the non-substituted derivative 29, the 3′-OCH3 and 4′-OCH3 derivatives 31, (S)-5 were 2–3 times less effective than these compounds (33, 34, 36, 37). A sizeable electron-withdrawing substituent at the 3′- or 4′-position would be necessary for higher activity. Substituents were introduced at the 5-position to the 8-position of the 4′-OCH3 derivative (S)-5, to determine their influence on activity. Electron-donating OCH3 and CH3 groups at the 5-position accelerated the activity, the (4′-OCH3, 5-OCH3) derivative 41 and the (4′-OCH3, 5-CH3) derivative 45 being 4.2 and 5.6 times more potent, respectively, than (S)-5. Although the activities of the (4′-OCH3, 6-CH3) derivative 46 and the (4′-OCH3, 8-CH3) derivative 48 were almost equipotent with (S)-5, 8–9 times lower activities were observed in the (4′-OCH3, 7-OCH3) derivative 43 and the (4′-OCH3, 8-OCH3) derivative 44. On the other hand, the (4′-OCH3, 6-OCH3) derivative 42 and the (4′-OCH3, 7-CH3) derivative 47 were inactive. The small electron-withdrawing fluorine derivatives, (4′-OCH3, 6-F) derivative 49 and (4′-OCH3, 7-F) derivative 50, were also inactive. Against C. lagenarium, only the 3′-F derivative 36 was active, showing a high EC50 value (345 µM). Finally, we confirmed that coumarin without a phenylpropanoid unit at the 3-position did not show any antifungal activity.

Conclusion

In summary, access to coumarin derivatives bearing phenylpropanoid through syntheses enabled us to demonstrate the structure-function relationship of this new type of coumarin against A. alternata. It was shown that the (S)-configuration and the 9′-OCH3 group are necessary for higher activity. As for the aromatic ring of the phenylpropanoid portion, the 3′-CF3 derivative 39 and the 4′-CF3 derivative 40 showed the highest activities, suggesting the importance of a higher electron-withdrawing group. In the coumarin ring, the electron donating group at the 5-position seemed to be effective, the (4′-OCH3, 5-OCH3) derivative 41 and (4′-OCH3, 5-CH3) derivative 45 showing the higher activities. Compared with E-benzylidene lactones bearing a phenolic 2-OH group, which is a precursor of the coumarin structures with the same stereochemistry, the coumarin derivatives bearing phenylpropanoid had higher activity against A. alternata. Although the mode of action was not studied, the results of the higher effect than C. lagenarium is also found in our previous lignan research.1,4–6) The coumarin type lignan bearing phenylpropanoid at 3-position also showed species specific activity such as previously described antifungal lignans. Because of new coumarin compound bearing lignan structure, it is impossible to compare the mode of action with known coumarin compounds. Some E-benzylidene lactones bearing a phenolic 2-OH group were effective against C. lagenarium. These results will make an novel contribution to the development of novel agrochemicals based on both lignan and coumarin structures.

Acknowledgements

Part of this study was performed at Division of Material Science Research Support and Genetic Research Support in Advanced Research Support Center (ADRES), Ehime University.

Declarations of interest

None

Electronic supplementary materials

The online version of this article contains supplementary material, which is available at https://www.jstage.jst.go.jp/browse/jpestics/.

Supplementary Data

Supplementary Data

References

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Supplementary Materials

Supplementary Data
jps-49-4-D24-038-s001.pdf (3.1MB, pdf)

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