Journal of Agricultural and Food Chemistry
Article
with water (2 × 100 mL) and the crude product was eluted with
acetone (3 × 50 mL). The filtrate was evaporated under vacuum (no
heat) and compound 15 was afforded as a light brown solid.
hexane/EtOAc/MeOH (4:1:0.1, 3:1:0.1, 2:1:0.1)] to give 0.94 g
(84%) of a yellow solid: mp 202−204 °C. 1H NMR 500 MHz,
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DMSO-d6): δ (ppm) 12.73 (1H, s, OH-5); 7.55 (1H, d, J = 2.2 Hz,
H2′); 7.47−7.30 (11H, m, Ph, H6′); 6.87 (1H, d, 3J = 8.5 Hz, H5′);
Synthesis of (2S,3S,4S,5R,6R)-6-((5,7-Dihydroxy-2-(4-hydroxy-3-
methoxyphenyl)-4-oxo-4H-chromen-3-yl)oxy)-3,4,5-trihydroxyte-
trahydro-2H-pyran-2-carboxylic acid (3).30 Compound 15 was
debenzylated without further purification, the acetyl and methyl
ester groups were hydrolyzed, and the crude product was purified as
described for compound 5, to give compound 3 (85.3 mg, 43% overall
yield of three last steps) as a yellow solid. 1H NMR (500 MHz,
CD3OD): δ (ppm) 7.99 (1H, d, 4J = 1.7 Hz, H2′), 7.52 (1H, dd, 3J =
8.4 Hz, 4J = 1.7 Hz, H6′), 6.87 (1H, d, 3J = 8.4 Hz, H5′), 6.36 (1H, d,
4J = 1.6 Hz, H8), 6.17 (1H, d, 4J = 1.6 Hz, H6), 5.46 (1H, d, 3J = 6.8
4
4
6.76 (1H, d, J = 2.1 Hz, H8); 6.44 (1H, d, J = 2.1 Hz, H6); 5.22
(2H, s, CH2); 5.01 (2H, s, CH2). 13C{1H} NMR (125 MHz, DMSO-
d6): δ (ppm) 178.2 (CO−C4), 164.3 (C7), 161.2 (C5), 157.0
(C2), 156.4 (C9), 149.0 (C4′), 145.4 (C3′), 136.8 (C3), 136.6 (Ph),
136.3 (Ph), 128.7 (Ph), 128.6 (Ph), 128.4 (Ph), 128.3 (Ph), 128.3
(Ph), 128.0 (Ph), 121.1 (C6′), 120.9 (C1′), 115.9 (C2′), 115.7
(C5′), 105.5 (C10), 98.6 (C8), 93.2 (C6), 73.5 (CH2), 70.2 (CH2).
MS m/z: [M − H]− calcd for C29H21O7, 481.1; found, 481.0.
Synthesis of 3,7-Bis(benzyloxy)-5-hydroxy-2-(3-hydroxy-4-me-
thoxyphenyl)-4H-chromen-4-one (19).39 Dimethyl sulfate (0.4 mL,
4.66 mmol), benzyl triethyl ammonium chloride (0.21 g, 0.93 mmol),
sodium hydrogen carbonate (0.63 g, 7.46 mmol), and water (8 mL)
were added to a solution of compound 18 (0.90 g, 1.86 mmol) in
acetone (60 mL). The mixture was stirred at 45 °C for 6 h, cooled to
room temperature, and water (50 mL) was added. The resulting
mixture was extracted with ethyl acetate (3 × 50 mL) and the organic
layers were dried over anhydrous sodium sulfate and evaporated
under vacuum. The crude product was purified by column
chromatograph [silica gel, hexane/EtOAc/CHCl3 (9:2:0.5, 8:2:0.5,
7:2:0.5)] to give 0.66 g (71%) of a light yellow solid (19): mp 160−
162 °C. 1H NMR (400 MHz, CDCl3): δ (ppm) 12.68 (1H, s, OH-5),
7.63 (1H, d, 3J = 7.8, Hz 2J = 2.4 Hz, H6′), 7.58 (1H, d, 2J = 2.4 Hz,
Hz, H1″), 3.93 (3H, s, OCH3), 3.65 (1H, d, 3J = 8.9 Hz, H5″), 3.58−
3.48 (3H, m, H2″, H3″, H4″). 13C{1H} NMR (125 MHz, CD3OD):
δ (ppm) 179.3 (CO−C4), 178.0 (COOH), 165.9 (C7), 163.0
(C5), 158.8 (C2), 158.4 (C9), 150.7 (C4′), 148.4 (C3′), 135.3 (C3),
123.6 (C6′), 123.0 (C1′), 115.9 (C5′), 114.5 (C2′), 105.7 (C10),
103.7 (C1″), 99.8 (C6), 94.7 (C8), 76.2 (C5″), 77.7, 75.7, 73.3 (C2″,
C3″, C4″), 56.8 (OCH3). ESI-MS m/z: [M − H]− calcd for
C22H19O13, 491.1; found, 491.2.
Synthesis of 2-(3,4-Dihydroxyphenyl)-5,7-dihydroxy-3-methoxy-
4H-chromen-4-one (16).41 To a suspension of compound 11 (0.3 g,
0.60 mmol) in a mixture of ethanol (120 mL) and cyclohexene (30
mL) was added 20% palladium hydroxide on charcoal (0.52 g). The
reaction mixture was refluxed under argon for 60 min, cooled at room
temperature, and filtered through a pad of Celite to remove the
catalyst. The Celite pad was rinsed with methanol (2 × 20 mL). The
combined filtrate was concentrated to dryness under air and the
residue was purified by preparative HPLC in four injections (4 × 0.5
mL). The purity of the fractions was checked by LC−MS. Fractions
with purity ≥98% were combined and partially evaporated under
nitrogen. The aqueous remainder was lyophilized for 72 h to furnish
compound 16 as a yellow solid (177.76 mg, 93%): mp 271−273 °C.
1H NMR (500 MHz, DMSO-d6): δ (ppm) 12.72 (1H, s, OH-5), 7.56
3
H2′), 7.40−7.25 (10H, m, Ph), 6.85 (1H, d, J = 7.8 Hz, H5′), 6.47
(1H, d, 2J = 2.2 Hz, H8), 6.41 (1H, d, 2J = 2.2 Hz, H6), 5.74 (1H, s,
OH-3′), 5.10 (2H, s, CH2), 5.04 (2H, s, CH2), 3.93 (3H, s, OCH3).
13C{1H} NMR (100 MHz, CDCl3): δ (ppm) 178.9 (CO−C4),
164.5 (C7), 162.1 (C5), 156.8 (C9), 156.5 (C2), 148.8 (C4′), 145.4
(C3′), 137.6 (C3), 136.5 (Ph), 135.9 (Ph), 128.9 (Ph), 128.8 (Ph),
128.4 (Ph), 128.4 (Ph), 128.3 (Ph), 127.6 (Ph), 123.7 (C1′), 122.0
(C6′), 114.7 (C2′), 110.2 (C5′), 106.3 (C10), 98.7 (C6), 93.1 (C8),
74.3 (CH2), 70.5 (CH2), 56.1 (OCH3). MS m/z: [M − H]− calcd for
C30H23O7, 495.1; found, 495.1.
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3
4
(1H, d, J = 2.2 Hz, H2′), 7.46 (1H, dd, J = 8.5 Hz, J = 2.2 Hz,
3
4
H6′), 6.91 (1H, d, J = 8.5 Hz, H5′), 6.41 (1H, d, J = 2.1 Hz, H8),
6.19 (1H, d, 4J = 2.1 Hz, H6), 3.79 (3H, s, OCH3), 3.38 (1H, s, OH).
13C{1H} NMR (125 MHz, DMSO-d6): δ (ppm) 177.9 (CO−C4),
Synthesis of (2R,3R,4S,5S,6S)-2-(5-(3,7-Bis(benzyloxy)-5-hydroxy-
4 - o x o - 4 H - c h r o m e n - 2 - y l ) - 2 - m e t h o x y p h e n o x y ) - 6 -
(methoxycarbonyl)tetrahydro-2H-pyran-3,4,5-triyl triacetate (20).
Acid glucuronidation of compound 19 (0.20 g, 0.40 mmol) was
carried out following the same procedure as for compound 14 to
furnish a light orange solid (20), which was directly subjected to
debenzylation.
164.1 (C7), 161.3 (C5), 156.3 (C9), 155.6 (C2), 148.7 (C4′), 145.2
(C3′), 137.7 (C3), 120.8 (C1′), 120.6 (C6′), 115.8 (C5′), 115.4
(C2′), 104.2 (C10), 98.5 (C6), 93.6 (C8), 59.7 (OCH3). MS m/z:
[M − H]− calcd for C16H11O7, 315.1; found, 315.0.
Synthesis of 3,5,7-Trihydroxy-2-(4-hydroxy-3-methoxyphenyl)-
4H-chromen-4-one (17).39 The benzyl groups of compound 12
(0.25 g, 0.50 mmol) were removed following the same procedure of
obtaining and purifying compound 16 to afford 146.5 mg of 17
Synthesis of (2R,3R,4S,5S,6S)-2-(2-Methoxy-5-(3,5,7-trihydroxy-
4-oxo-4H-chromen-2-yl)phenoxy)-6-(methoxycarbonyl)-
tetrahydro-2H-pyran-3,4,5-triyl triacetate (21). The removal of the
benzyl groups of the above quercetin moiety (20) was accomplished
following the procedure for generation of compound 16 to obtain an
orange solid (21), which directly underwent deacetylation.
1
(92%): mp 305−307 °C. H NMR (500 MHz, DMSO-d6): δ (ppm)
12.45 (1H, s, OH-5), 7.76 (1H, d, 4J = 2.0 Hz, H2′), 7.69 (1H, dd, 3J
= 8.5 Hz, 4J = 2.0 Hz, H6′), 6.94 (1H, d, 3J = 8.5 Hz, H5′), 6.47 (1H,
Synthesis of (2S,3S,4S,5R,6R)-3,4,5-Trihydroxy-6-(2-methoxy-5-
(3,5,7-trihydroxy-4-oxo-4H-chromen-2-yl)phenoxy)tetrahydro-2H-
pyran-2-carboxylic acid (6)..34,35 Compound 21 was dissolved in 10
mL of dry methanol, zinc acetate (0.37 g, 2.01 mmol) was added, and
the solution was stirred at 75 °C for 24 h. Then, the solvent was
removed under air, and the crude residue was dissolved in dimethyl
sulfoxide (2.5 mL) and 35 mL of 20 mM of phosphate buffer
(NaH2PO4/Na2HPO4pH 7.2) was added. The mixture was heated
in a water bath at 37 °C for 5 min, and then 140 mg of pig-liver
esterase (PLE) was added. The solution was stirred at 37 °C for 8 h.
Solvent was removed under nitrogen and the residue was purified by
preparative HPLC in 10 injections (10 × 0.5 mL). The purity of the
fractions was checked by LC−MS. Fractions with purity ≥98% were
combined and partially evaporated under nitrogen. The aqueous
remainder was lyophilized for 72 h to obtain compound 6 as a yellow
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d, J = 1.9 Hz, H8), 6.20 (1H, s, H6), 3.84 (3H, s, OCH3). 13C{1H}
NMR (125 MHz, DMSO-d6): δ (ppm) 175.9 (CO−C4), 164.0
(C7), 160.7 (C5), 156.2 (C9), 148.8 (C2), 147.4 (C3′), 146.5 (C4′),
135.8 (C3), 122.0 (C1′), 121.7 (C6′), 115.6 (C5′), 111.7 (C2′),
102.9 (C10), 98.3 (C6), 93.7 (C8), 55.8 (OCH3). MS m/z: [M −
H]− calcd for C16H11O7, 315.1; found, 315.0.
Synthesis of 3,7-Bis(benzyloxy)-2-(3,4-dihydroxyphenyl)-5-hy-
droxy-4H-chromen-4-one (18).43 A mixture of quercetin (1) (0.70
g, 2.32 mmol), borax (2.67 g, 6.95 mmol), benzyl triethyl ammonium
chloride (0.08 g, 0.35 mmol), and anhydrous dimethylformamide (20
mL) was stirred at room temperature for 1 h to obtain the boron
complex of quercetin. Benzyl chloride (1.1 mL, 9.26 mmol) and
potassium carbonate (0.96 g, 6.95 mmol) were then added and the
mixture was stirred for 24 h. A second batch of benzyl chloride (0.7
mL, 6.24 mmol) was added and the stirring continued for 24 h. Water
(80 mL) was added to quench the reaction and the mixture was
extracted with ethyl acetate (6 × 150 mL). The organic extracts were
combined and washed with water (1 × 200 mL), dried over
anhydrous magnesium sulfate, and concentrated under vacuum. The
residue was purified by flash column chromatography [silica gel,
1
solid (90 mg, 45% overall yield of four last steps). H NMR (600
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MHz, DMSO-d6): δ (ppm) 7.94/7.98 (1H, dd, J = 8.7/8.7 Hz, J =
1.9/2.1 Hz, H6′), 7.81/7.91 (1H, d, 4J = 1.9/2.1 Hz, H2′), 7.18/7.18
(1H, d, 3J = 8.7/8.7 Hz, H5′), 6.52/6.52 (1H, d, 4J = 2.0/2.0 Hz, H8),
6.20/6.20 (1H, d, 4J = 2.0/2.0 Hz, H6), 5.13/5.16 (1H, d, 3J = 7.3/7.7
Hz, H1″), 3.86/3.87 (3H, s, OCH3), 3.83/3.78 (1H, ds, 3J = 9.5/10.2
D
J. Agric. Food Chem. XXXX, XXX, XXX−XXX