ACS Chemical Neuroscience
Research Article
determined by HPLC (Shimadzu Products), containing a DGU-
20A3R degassing unit, an LC20AB liquid chromatograph, and an
SPD-20A UV/vis detector. UV detection was measured at 254 nm.
Mass spectra were obtained by an LCMS 2020 (Shimadzu Products).
As a stationary phase, a Synergi 4U fusion-RP (150 mm × 4.6 mm)
column was used, and as a mobile phase, a gradient of methanol/
water with 0.1% formic acid was used. Parameters: A = water, B =
methanol, V(B)/(V(A) + V(B)) = from 5 to 90% over 10 min, V(B)/
(V(A) + V(B)) = 90% for 5 min, V(B)/(V(A) + V(B)) = from 90 to
5% over 3 min. The method was performed with a flow rate of 1.0
mL/min. Compounds were only used for biological evaluation if the
purity was ≥95%. Melting points were determined using an OptiMelt
automated melting point system (Scientific Instruments GmbH,
Gilching, Germany).
General Procedure A: Protection. Acid (1.0 equiv) was
dissolved in ethanol, and H2SO4 was added. The solution was
refluxed until TLC showed full conversion. The reaction mixture was
concentrated in vacuo and dissolved in ethyl acetate to be washed with
5% sodium hydrogen carbonate in water. The organic layers were
combined, and the solvent was evaporated.
General Procedure B: Substitution. K2CO3 (1.5 equiv) was
dissolved in dry acetone under argon and cooled to 0 °C in an ice
bath when the protected acid (1.0 equiv) was added. The mixture was
stirred at 0 °C for 15 min, and the respective iodine (2.0 equiv) was
added. The reaction was heated to reflux for 6 h, diluted with water
and 1 M HCl, extracted with ethyl acetate (3 × 30 mL), washed with
brine, and dried over Na2SO4. The solvent was removed, and the
compound was purified by silica column chromatography using 20%
ethyl acetate in petroleum ether to give the compound as an oil.
General Procedure C: Deprotection. The compound was
dissolved in ethanol, and 0.52 M NaOH was added. The mixture was
stirred at room temperature for 5 h. The reaction was diluted with 5
mL of water and extracted with ethyl acetate twice. The aqueous
layers were combined and acidified to pH 1 with 1 M HCl to be again
extracted with ethyl acetate. The organic layers were combined,
washed with brine, and dried over Na2SO4.
General Procedure D: Esterification. Acid (1.1 equiv) was
dissolved in 5 mL of dry THF, and oxalyl chloride (2.0 equiv)
together with catalytic amounts of DMF (4 μL) were added. The
reaction was stirred at room temperature until TLC showed complete
conversion of the acid to the acid chloride. The acid chloride was then
added dropwise to a solution of taxifolin (1.0 equiv) and triethylamine
(4.5 equiv) in dry THF and stirred at room temperature for 2 h. The
reaction was quenched with water and 1 M HCl and extracted with
ethyl acetate. The organic layer was combined, washed with brine, and
dried over Na2SO4. The mixture was purified by flash column
chromatography using a gradient of 4−15% acetone in dichloro-
methane to give the pure compound.15,17
13C NMR (101 MHz, acetone-d6): δ 167.0, 158.7, 145.2, 136.8,
130.9, 120.5, 119.10, 118.3, 115.4, 60.8, 14.6 ppm.
Ethyl (E)-3-(3-(Pent-4-yn-1-yloxy)phenyl)acrylate (6). Following
general procedure B, 5 (300 mg, 1.5 mmol, 1.0 equiv) was reacted
with 3 (605 mg, 3.12 mmol, 2.0 equiv) and K2CO3(311 mg, 2.25
mmol, 1.5 equiv). Compound 6 was obtained as a yellow oil (352 mg,
1.36 mmol, 91% yield).
1H NMR (400 MHz, CDCl3): δ 7.64 (d, J = 16.0 Hz, 1H, HC
CHCO), 7.27 (t, 1H, arom), 7.11 (m, 1H, arom), 7.05 (m, 1H,
arom), 6.93−6.91 (m, 1H, arom), 6.41 (d, J = 16.0 Hz, 1H, HC
CHCO), 4.26 (quart, 2H, OCH2CH3), 4.08 (t, 2H, H
CCH2CH2CH2O), 2.40 (dt, 2H, HCCH2CH2CH2O), 2.03−1.97
(m, 3H, HCCH2CH2CH2O), 1.33 (t, 3H, OCH2CH3) ppm.
13C NMR (101 MHz, CDCl3): δ 167.0, 159.3, 144.6, 135.9, 130.0,
120.9, 118.7, 116.8, 113.6, 83.4, 69.1, 66.3, 60.6, 28.2, 15.2, 14.4 ppm.
(E)-3-(3-(Pent-4-yn-1-yloxy)phenyl)acrylic Acid (7). Following
general procedure C, 290 mg 6 was dissolved in 3 mL of ethanol,
and 5 mL of 0.52 M NaOH was added. The compound was obtained
as a white solid (191 mg, 0.82 mmol, 73% yield).
1H NMR (400 MHz, CDCl3): δ 7.74 (d, J = 16.0 Hz, 1H, HC
CHCO), 7.31 (t, 1H, arom), 7.15 (d, J = 8.0 Hz 1H, arom), 7.08 (m,
1H, arom), 6.97 (dd, J = 8.0 and 2.3 Hz, 1H, arom), 6.46 (d, J = 16.0
Hz, 1H, HCCHCO), 4.11 (t, 2H, HCCH2CH2CH2O), 2.42 (td,
2H, HCCH2 CH2 CH2 O), 2.06−1.98 (m, 3H, H
CCH2CH2CH2O) ppm.
13C NMR (101 MHz, CDCl3): δ 172.0, 159.3, 147.0, 135.4, 130.0,
121.2, 117.5, 117.2, 113.8, 83.3, 69.0, 66.3, 28.1, 15.2 ppm.
7-O-Cinnamoyltaxifolin-pentyne (1). Following general procedure
D, 7 (120 mg, 0.52 mmol, 1.1 equiv) was dissolved in 5 mL of dry
THF, and 85 μL of oxalyl chloride (127 mg, 1.00 mmol, 2 equiv) and
catalytic amounts of DMF were added. Taxifolin (150 mg, 0.52 mmol,
1 equiv) and triethylamine (228 mg, 2.25 mmol, 4.5 equiv) were
dissolved in dry THF, and the acid chloride was added dropwise.
Target compound 1 was obtained as a white foam (137 mg, 0.26
mmol, 53% yield).
1H NMR (400 MHz, DMSO-d6): δ 11.73 (s, 1H, 5-OH), 9.03 (s,
2H, 3′ and 4′-OH), 7.80 (d, J = 16.0 Hz, 1H, ArCHCH−CO), 7.40
(s, 1H, arom CA), 7.35 (d, J = 5.1 Hz, 2H, arom CA), 7.05−7.02 (m,
1H, arom CA), 6.93 (m, 1H, arom B-ring), 6.88 (d, J = 16.0 Hz, 1H,
ArCHCH−CO), 6.79−6.76 (m, 2H, arom B-ring), 6.45 (d, J = 2.0
Hz, 1H, 8-H), 6.42 (d, J = 2.0 Hz, 1H, 6-H), 5.92 (d, J = 6.2 Hz, 1H,
3-OH), 5.15 (d, J = 11.6 Hz, 1H, 2-H), 4.70 (dd, J = 11.5, 6.3 Hz, 1H,
3-H), 4.09 (t, 2H, HCC−CH2−CH2−CH2), 2.80 (t, 1H, HCC−
CH2−CH2−CH2), 2.34 (td, J = 2.6 Hz, 2H, HCC−CH2−CH2−
CH2), 1.90 (tt, J = J′ = 6.5 Hz, 2H, HCC−CH2−CH2−CH2) ppm.
13C NMR (101 MHz, DMSO-d6): δ 199.6, 164.0, 162.0, 161.9,
158.9, 158.1, 147.2, 146.0, 145.0, 135.2, 130.1, 127.7, 121.5, 119.6,
117.7, 117.1, 115.5, 115.2, 113.8, 104.9, 102.8, 101.7, 83.7, 83.3, 71.9,
71.6, 66.2, 27.7, 14.5 ppm.
5-Iodo Pentyne (3). 5-Chloro pentyne (1.0 g, 9.76 mmol, 1.0
equiv) was dissolved in dry acetone, and sodium iodine (7.3 g, 48.8
mmol, 5.0 equiv) was added; the mixture was heated to reflux
overnight. The reaction was diluted with water and extracted with
dichloromethane (3 × 40 mL). The organic layer was combined,
washed with brine, and dried over Na2SO4, and the solvent was
evaporated. The compound was obtained as a yellow oil (1.8 g,
quantitative (quant)).
ESI: m/z calculated for C29H24O9 [M + H]+ 517.14, found 517.13;
HPLC purity = 99%.
Ethyl (E)-3-(3-(Pentyloxy)phenyl)acrylate (8). Following general
procedure B, 5 (500 mg, 2.6 mmol, 1.0 equiv) was reacted with 1-
iodopentane (1.03 g, 5.2 mmol, 2.0 equiv) and K2CO3(539 mg, 3.9
mmol, 1.5 equiv). Compound 8 was obtained as an off-white oil (330
mg, 1.26 mmol, 48% yield).
1H NMR (400 MHz, CDCl3): δ 3.28 (td, J = 6.7, 1.3 Hz, 2H),
2.34−2.26 (m, 2H), 2.01−1.92 (m, 3H) ppm.
1H NMR (400 MHz, CDCl3): δ 7.87 (d, J = 16.0 Hz, 1H), 7.49 (t,
1H), 7.30 (d, J = 7.9 Hz, 1H), 7.13 (dd, J = 7.9, 2.4 Hz, 1H), 6.64 (d,
J = 16.0 Hz, 1H), 4.48 (q, J = 7.1 Hz, 2H), 4.18 (t, 2H), 2.01 (quint,
2H), 1.72−1.59 (m, 4H), 1.56 (t, J = 7.1 Hz, 3H), 1.21−1.11 (m,
3H) ppm.
13C NMR (101 MHz, CDCl3): δ 82.4 (s), 69.6 (s), 32.0 (s), 19.6
(s), 5.2 (s) ppm.
Ethyl (E)-3-(3-Hydroxyphenyl)acrylate (5). Following general
procedure A, 500 mg of trans-3-hydroxycinnamic acid was dissolved
in 15 mL of ethanol, and 5 drops of sulfuric acid were added. After 6
h, TLC showed total consumption of the educt. Compound 5 was
obtained as an off-white solid (584 mg, quant).
13C NMR (101 MHz, CDCl3): δ 167.0, 159.5, 144.6, 135.8, 129.8,
120.6, 118.4, 116.7, 113.5, 68.1, 60.5, 28.9, 28.2, 22.5, 14.3, 14.0 ppm.
(E)-3-(3-(Pentyloxy)phenyl)acrylic Acid (9). Following general
procedure C, 250 mg of 8 was dissolved in 5 mL of ethanol, and 5
mL of 0.52 M NaOH was added. The compound was obtained as a
white solid (173 mg, 1.35 mmol, quant).
1H NMR (400 MHz, acetone-d6): δ 8.54 (s, 1H, −OH), 7.60 (d, J
= 16.0 Hz, 1H, HCCHCO), 7.26 (t, 1H, aromatic (arom)), 7.15−
7.11 (m, 2H, arom), 6.93−6.90 (m, 1H, arom), 6.43 (d, J = 16.0 Hz,
1H, HCCHCO), 4.20 (quart, 2H, OCH2CH3), 1.28 (t, 3H,
OCH2CH3) ppm.
1H NMR (400 MHz, CDCl3): δ 7.76 (d, J = 15.9 Hz, 1H), 7.31 (t,
J = 7.9 Hz, 1H), 7.13 (d, J = 7.7 Hz, 1H), 7.07 (s, 1H), 6.96 (dd, J =
8.2, 2.4 Hz, 1H), 6.44 (d, J = 15.9 Hz, 1H), 3.98 (t, J = 6.6 Hz, 2H),
J
ACS Chem. Neurosci. XXXX, XXX, XXX−XXX