10028 J. Agric. Food Chem., Vol. 58, No. 18, 2010
Lu et al.
these nine newly synthesized DOBs was >99%. The substitutions of
DOBs 1-25 are illustrated in Table 1. The substitution patterns presented
can be classified into 2,4-dioxygenated (1-7), 3,4-dioxygenated (8, 9), 2,5-
dioxygenated (10), 2,3,4-trioxygenated (11-16), 2,4,5-trioxygenated
(17-20), and 2,4,6-trioxygenated (21-25) series of DOBs with various
rings B. DOB 13 was found to be a new compound, and the NMR spectral
data of 24 (29) were the first presented. DOBs 1, 3, and 4 were synthesized
€ € €
by Wahala et al. (20), and the data of 5 and 18 were reported previously in
a NMR spectral study by Jha et al. (30). The structures of DOBs 11 and 23
were recently reported by Goto et al. (17) and Hastings et al. (31),
respectively.
2,4-Dihydroxydeoxybenzoin (1): 2.10 g, 92%; Rf = 0.50 (EtOAc/
acetone/n-hexane = 2:0.5:7.5); yellowish masses (MeOH þ H2O); mp
116 °C; 1H NMR (acetone-d6, 400 MHz, 25 °C) δ 4.29 (2H, s, CH2), 6.36
(1H, d, J = 2.4 Hz, H-3), 6.46 (1H, dd, J = 2.4, 8.8 Hz, H-5), 7.24 (1H, m,
H-40), 7.33 (4H, m, H-20,30,50,60), 7.96 (1H, d, J = 8.8 Hz, H-6), 9.54 (1H, s,
OH), 12.73 (1H, s, C-2 OH); 13C NMR (acetone-d6, 100 MHz, 25 °C)
δ 44.4 (CH2), 103.1 (C-3), 108.3 (C-5), 112.9 (C-1), 126.9 (C-40), 128.7
(C-30,50), 129.7 (C-20,60), 133.6 (C-6), 135.5 (C-10), 165.1 (C-2), 166.1 (C-4),
202.7 (CdO); EI-MS m/z 228 [M]þ, 137 (20).
2,4-Dihydroxy-30-methoxydeoxybenzoin (3): 1.91 g, 74%; Rf = 0.42
(EtOAc/acetone/n-hexane = 2:0.5:7.5); colorless plates (acetone þ n-hexane),
mp 128-129 °C; 1H NMR (CDCl3, 400 MHz, 25 °C) δ 3.77 (3H, s, OMe),
4.26 (2H, s, CH2), 6.33 (1H, d, J = 2.4 Hz, H-3), 6.45 (1H, dd, J = 2.4,
8.8 Hz, H-5), 6.81 (1H, dd, J = 2.4, 8.8 Hz, H-60), 6.91 (1H, dd, J = 1.6,
8.4 Hz, H-20), 6.94 (1H, t, J = 2.0 Hz, H-20), 7.23 (1H, t, J = 8.0 Hz, H-50),
7.97 (1H, d, J = 8.8 Hz, H-6), 9.49 (1H, s, OH), 12.70 (1H, s, C-2 OH); 13C
NMR (CDCl3, 100 MHz, 25 °C) δ 44.5 (CH2), 54.8 (OMe), 103.0 (C-3),
108.2 (C-5), 112.2 (C-40), 115.2 (C-1), 115.5 (C-20), 121.8 (C-60), 129.6
(C-50), 136.9 (C-10), 160.2 (C-30), 165.0 (C-2), 166.1 (C-4), 202.6 (CdO);
EI-MS m/z 258 [M]þ, 137 (20).
Figure 1. Proposed generation of DOBs found in natural sources.
2,4-Dihydroxy-20-methoxydeoxybenzoin (4): 2.24 g, 87%; Rf = 0.45
(EtOAc/acetone/n-hexane = 2:0.5:7.5); colorless powders (acetone þ
n-hexane), mp 193 °C; 1H NMR (acetone-d6, 400 MHz, 25 °C) δ 3.79
(3H, s, OMe), 4.26 (2H, s, CH2), 6.34 (1H, d, J = 2.4 Hz, H-3), 6.45 (1H,
dd, J = 2.4, 8.8 Hz, H-5), 6.90 (1H, td, J = 7.6, 1.2 Hz, H-50), 6.98 (1H, dd,
J = 0.8, 8.4 Hz, H-30), 7.21 (1H, dd, J = 2.0, 7.6 Hz, H-60), 7.25 (1H, td,
J = 8.0, 1.6 Hz, H-50), 7.95 (1H, d, J = 8.8 Hz, H-6), 9.50 (1H, s, OH),
12.70 (1H, s, C-2 OH); 13C NMR (acetone-d6, 100 MHz, 25 °C) δ 40.3
(CH2), 56.5 (OMe), 104.3 (C-3), 109.4 (C-5), 112.2 (C-30), 114.4 (C-1),
121.9 (C-50), 125.3 (C-10), 129.8 (C-40), 132.5 (C-60), 134.5 (C-6), 158.9
(C-20), 166.1 (C-2), 167.0 (C-4), 204.1 (CdO); EI-MS m/z 258 [M]þ, 137 (20).
2-Hydroxy-4,40-dimethoxydeoxybenzoin (5): 1.41 g, 52%; Rf = 0.40
(EtOAc/acetone/n-hexane = 2:0.5:7.5); colorless needles (MeOH), mp 110 °C;
1H NMR (CDCl3, 400 MHz, 25 °C) δ 3.79, 3.83 (each 3H, s, OMe), 4.15
(2H, s, CH2), 6.42 (1H, d, J = 2.4 Hz, H-3), 6.44 (1H, dd, J = 2.4, 8.8 Hz,
H-5), 6.88 (2H, d, J = 8.8 Hz, H-30,50), 7.19 (2H, d, J = 8.8 Hz, H-20,60),
7.75 (1H, d, J = 8.8 Hz, H-6), 12.74 (1H, s, C-2 OH); 13C NMR (CDCl3,
100 MHz, 25 °C) δ 43.9 (CH2), 55.3 (OMe), 55.5 (OMe), 101.0 (C-3), 107.8
(C-5), 113.1 (C-1), 114.2 (C-30,50), 126.3 (C-10), 130.3 (C-20,60), 132.0 (C-6),
158.7 (C-40), 165.8 (C-4), 166.1 (C-2), 202.3 (CdO); EI-MS m/z 272 [M]þ,
151 (30).
relaxing evaluation was continued by advanced synthesis of
DOBs with diverse substitution. In this study, 25 DOBs were
synthesized and evaluated for vascular relaxing potential. Be-
cause Kþ ion is an important vascular contracting factor, KCl-
induced porcine coronary arterial contracting model was selected
for the study. The hit skeleton and structure-activity relation-
ships (SARs) in the inhibition of contracted coronary artery were
also investigated. The results displayed that DOBs are powerful
inhibitors of arterial contraction and have shown their potential
for use in treating cardiovascular diseases.
MATERIALS AND METHODS
Chemistry. The synthetic materials, including resorcinol, 1,2,4-tri-
hydroxybenzene, phenyl acetonitriles, phenylacetic acids, and zinc chloride
(ZnCl2), were purchased from Tokyo Chemical Industry (Tokyo, Japan).
Boron trifluoride etherate (BF3-Et2O) and other phenols (phloroglucinol,
pyrogallol, etc.) were purchased from Lancaster Synthesis (Morecambe,
U.K.). Melting points (uncorrected) were determined by an Electro-
thermal 9100 melting point apparatus (Electrothermal Engineering Ltd.,
Landon, U.K.). Mass spectra were performed on a Shimadzu LCMS-IT-
TOF mass spectrometer (Japan) or a Fourier transform mass spectrom-
eter, Bruker APEX II (German). 1H (400 MHz) and 13C (100 MHz) NMR
spectra were obtained by a Varian Mercury-400 spectrometer (Varian Inc.,
Palo Alto, CA).
2,3,4-Trihydroxydeoxybenzoin (11): 1.93 g, 79%; Rf = 0.43 (EtOAc/
acetone/n-hexane = 3:0.5:6.5); colorless needles (acetone þ H2O), mp
163-165 °C; 1H NMR (acetone-d6, 400 MHz, 25 °C) δ 4.29 (CH2), 6.50
(1H, d, J = 8.8 Hz, H-5), 7.27 (1H, m, H-40), 7.33 (4H, m, H-20,30,50,60),
7.56 (1H, d, J = 8.8 Hz, H-6), 12.72 (1H, s, C-2 OH); 13C NMR (acetone-d6,
100 MHz, 25 °C) δ 44.4 (CH2), 107.8 (C-5), 113.2 (C-1), 123.5 (C-6), 126.9
(C-40), 128.7 (C-20, 60), 129.7 (C-30, 50), 132.5 (C-3), 135.6 (C-10), 152.1
(C-2), 152.8 (C-4), 203.4 (CdO); EI-MS m/z 244 [M]þ, 153 (17).
2,3,4-Trihydroxy-20-methoxydeoxybenzoin (13): 2.14 g, 78%; Rf =
0.35 (EtOAc/acetone/n-hexane = 3:0.5:6.5); colorless powders (acetone þ
n-hexane), mp 160 °C; 1H NMR (acetone-d6, 400 MHz, 25 °C) δ 3.78 (3H,
s, OMe), 4.27 (2H, s, CH2), 6.50 (1H, d, J = 8.8 Hz, H-5), 6.90 (1H, td, J =
8.4, 1.2 Hz, H-50), 6.97 (1H, dd, J = 1.2, 8.4 Hz, H-30), 7.21 (1H, dd, J =
1.6, 8.4 Hz, H-60), 7.25 (1H, td, J = 8.0, 1.6 Hz, H-50), 7.55 (1H, d, J =
8.8 Hz, H-6), 8.22 (2H, br, OH), 12.74 (1H, br, OH); 13C NMR (acetone-d6,
100 MHz, 25 °C) δ 40.3 (CH2), 56.4 (OMe), 109.0 (C-5), 112.1 (C-30), 114.7
(C-10), 121.9 (C-50), 124.3 (C-6), 125.3 (C-10), 132.6 (C-60), 133.7 (C-3),
153.2 (C-4), 153.7 (C-2), 159.0 (C-20), 204.7 (CdO); EI-MS m/z 274 [M]þ,
General Procedure for Synthesis of DOBs. The synthesis of DOBs 1-18
was performed by condensing respective phenols with equivalent quan-
tities (0.01 mol) of various phenylacetic acids in BF3-Et2O at 80-90 °C
under nitrogen atmosphere. DOBs 19-25 were prepared by condensing
1,2,4-trihydroxybenzene or phloroglucinol (0.02 mol each) and related
phenylacetonitriles (0.01 mol) by ZnCl2 (0.01 mol) and saturated HCl (gas,
caution!) at 0 °C (Table 1). The reaction and quenching details were
described in our previous paper (14). The DOBs were all purified by
column chromatography and recrystallized with proper solvents. Among
the DOBs, 1, 3-5, 11, 13, 18, 23, and 24 (Table 1) were newly synthesized;
others were previously reported (14). The syntheses was all achieved in
high yields at gram scale. On the basis of the LC-MS analysis, the purity of