S.Y. Chan, et al.
BioorganicChemistry104(2020)104239
153.14, 150.64, 130.61, 128.75, 127.99, 127.80, 121.31, 114.64,
114.01, 113.97, 112.13, 65.02, 64.01, 63.50, 15.10, 15.04, 14.88.ESI-
MS: 312.40 ([M+H]+).
white solid. SB 4b, SB 6b, SB 8e were synthesized from SB 4a, SB 6a,
SB 8a according to the describe method.
4.1.6.1. (E)-3-(4-Hydroxystyryl)benzene-1,2-diol
(trans-2,3,4′-trih-
4.1.5.7. (E)-1,3-Diethoxy-5-(4-ethoxystyryl)benzene (trans-3,5,4′-trieth-
oxystilbene) (SB 7a). White solid, yield: 58%, m.p. 70–72 °C (lit.
70–72 °C [33]). IR (cm−1): 3024 (Csp2-H stretching), 2981, 2933 and
2875 (Csp3-H stretching), 1588 and 1507(aromatic C]C stretching),
1243 (aromatic CeO stretching), 1052 (saturated CeO stretching), 954
(Csp2-Htrans bending);1H NMR (500 MHz, CDCl3) δ, ppm: 7.45 (d,
J = 8.5 Hz, 2H), 7.05 (d, Jtrans = 16.0 Hz, 1H), 6.91 (m, 3H), 6.66 (d,
J = 2.5 Hz, 2H), 6.39 (t, J = 2.0 Hz, 1H), 4.10–4.06 (m, 6H), 1.46–1.44
(m, 9H);13C NMR (125 MHz, CDCl3) δ, ppm: 160.27, 158.75, 139.62,
129.85, 128.63, 127.77, 126.57, 114.69, 104.9, 100.51, 62.5, 14.89,
14.85.ESI-MS: 312.40 ([M+H]+).
ydoxystilbene) (SB 4b). Off-white solid, yield: 65%, m.p.
216–218 °C.IR (cm−1): 3265 (OeH stretching), 1595 and 1506
(aromatic C]C stretching), 1224 (aromatic CeO stretching), 965
(Csp2-Htrans bending); 1H NMR (500 MHz, DMSO‑d6) δ, ppm: 7.36 (d,
J = 8.0 Hz, 2H), 7.20 (d, Jtrans = 16.5 Hz, 1H), 7.05–6.99 (m, 2H), 6.76
(d, J = 8.0 Hz, 2H), 6.67–6.60 (m, 2H); 13C NMR (125 MHz,
DMSO‑d6) δ, ppm: 157.37, 145.86, 143.33, 129.27, 128.13, 127.98,
125.35, 121.01, 119.5, 116.85, 116.03, 114.22.ESI-MS: 228.24 ([M
+H]+).
4.1.6.2. (E)-2-(4-Hydroxystyryl)benzene-1,4-diol
(trans-2,5,4′-trihyd-
oxystilbene) (SB 6b). Off-white solid, yield: 56%, m.p. 215–216 °C.IR
(cm−1): 3280 (OeH stretching), 1599 and 1509 (aromatic C]C
stretching), 1222 (aromatic CeO stretching), 964 (Csp2-Htrans
bending); 1H NMR (500 MHz, DMSO‑d6) δ, ppm: 9.55 (s, 1H), 8.95
(s, 1H), 8.72 (s, 1H), 7.36 (d, J = 8.5 Hz, 2H), 7.13 (d, Jtrans = 16.5 Hz,
1H), 6.96 (d, Jtrans = 16.0 Hz, 1H), 6.90 (d, J = 3.0 Hz, 1H), 6.76 (d,
J = 8.5 Hz, 2H), 6.65 (d, J = 8.5 Hz, 1H), 6.49 (dd, J = 8.5, 2.5 Hz,
1H); 13C NMR (125 MHz, DMSO‑d6) δ, ppm: 157.42, 150.41, 147.89,
129.21, 128.02, 127.89, 125.10, 120.99, 116.91, 116.02, 115.54,
111.94. ESI-MS: 228.24 ([M+H]+).
4.1.5.8. (E)-1,2-Diethoxy-4-(4-ethoxystyryl)benzene (trans-3,4,4′-trieth-
oxystilbene) (SB 8a). Pale yellow solid, yield: 90%, m.p. 150–152 °C
(lit. 150–152 °C [30]). IR (cm−1): 3051 (Csp2-H stretching), 2983, 2931
and 2840 (Csp3-H stretching), 1598 and 1510 (aromatic C]C
stretching), 1235 (aromatic CeO stretching), 1020 (saturated CeO
stretching), 967 (Csp2-Htrans bending); 1H NMR (500 MHz, CDCl3) δ,
ppm: 7.44 (d, J = 9.0 Hz, 2H), 7.08 (d, J = 2.0 Hz, 1H), 7.02 (dd,
J = 8.5, 2.0 Hz, 1H), 6.93 (s, 2H), 6.91–6.87 (m, 3H), 4.20–4.06 (m,
6H), 1.52–1.43 (m, 9H);13C NMR (125 MHz, CDCl3) δ, ppm: 158.42,
148.85, 148.40, 130.90, 130.28, 127.43, 126.41, 126.35, 119.61,
114.67, 113.47, 111.04, 64.61, 63.49, 14.91, 14.87.ESI-MS: 312.40
([M+H]+).
4.1.6.3. (E)-4-(4-Hydroxystyryl)benzene-1,2-diol
(trans-3,4,4′-trihyd-
oxystilbene) (SB 8b). Off-white solid, yield: 67%, m.p. 241–243 °C
(lit. 242–243 °C [34]). IR (cm−1): 3338 (OeH stretching), 1596 and
1519 (aromatic C]C stretching), 1228 (aromatic CeO stretching), 961
4.1.5.9. (E)-1,2-Dimethoxy-4-(4-methoxystyryl)benzene
(trans-3,4,4′-
1
trimethoxystilbene) (SB 8c). White solid, yield: 87%, m.p. 136–138 °C
(lit. 136–138 °C [32]).IR (cm−1): 3043 (Csp2-H stretching), 2973, 2931
and 2838 (Csp3-H stretching), 1602 and 1509 (aromatic C]C
stretching), 1237 (aromatic CeO stretching), 1023 (saturated CeO
stretching), 969 (Csp2-Htrans bending); 1H NMR (500 MHz, CDCl3) δ,
ppm: 7.36 (d, J = 8.0 Hz, 2H), 6.98–6.95 (m, 2H), 6.86 (s, 2H), 6.82 (d,
J = 8.5 Hz, 2H), 6.78 (d, J = 8.0 Hz, 1H), 3.87 (s, 3H), 3.83 (s, 3H),
3.76 (s, 3H);13C NMR (125 MHz, CDCl3) δ, ppm: 159.08, 149.12,
148.64, 130.83, 130.35, 127.46, 126.42, 119.52, 114.14, 111.26,
108.59, 55.97, 55.88, 55.34.ESI-MS: 284.35 ([M+H]+).
(Csp2-Htrans bending); H NMR (500 MHz, DMSO‑d6) δ, ppm: 9.49 (s,
1H), 9.01 (s, 1H), 8.91 (s, 1H), 7.35 (d, J = 8.5 Hz, 2H), 6.93 (d,
J = 2.0 Hz, 1H), 6.80 (m, 3H), 6.74 (d, J = 8.5 Hz, 2H), 6.70 (d,
J = 8.0 Hz, 1H);13C NMR (125 MHz, DMSO‑d6) δ, ppm: 157.18,
145.82, 145.47, 129.64, 129.06, 127.80, 126.04, 125.55, 118.5,
116.17, 115.94, 113.41. ESI-MS: 228.24 ([M+H]+).
4.1.6.4. (E)-4,4′-(Ethene-1,2-diyl)benzene-1,2-diol)
(trans-3,4,3′,4′-
tetrahydoxystilbene) (SB 8e). Purple solid, yield: 70%, m.p.
208–210 °C (lit. 211–212 °C [35]). IR (cm−1): 3309 (OeH
stretching), 1603 and 1513 (aromatic C]C stretching), 1273
(aromatic CeO stretching), 958 (Csp2-Htrans bending); 1H NMR
(500 MHz, DMSO‑d6) δ, ppm: 9.00 (s, 1H), 8.88 (s, 1H), 6.92 (s,
2H), 6.79 (d, J = 8.0 Hz, 2H), 6.80 (m, 4H);13C NMR (125 MHz,
DMSO‑d6) δ, ppm: 145.82, 145.44, 129.61, 125.9, 118.49, 116.14,
113.39. ESI-MS: 244.24 ([M+H]+).
4.1.5.10. (E)-4-(4-Ethoxystyryl)-1,2-dimethoxybenzene
(trans-3,4-
diethoxy-4′-methoxystilbene) (SB 8d). White solid, yield: 92%, m.p.
142–144 °C.IR (cm−1): 3051 (Csp2-H stretching), 2983, 2933 and
2840 (Csp3-H stretching), 1600 and 1510 (aromatic C]C stretching),
1235 (aromatic CeO stretching), 1041 (saturated CeO stretching), 964
(Csp2-Htrans bending); 1H NMR (500 MHz, CDCl3) δ, ppm: 7.44 (d,
J = 9.0 Hz, 2H), 7.07 (d, J = 2.0 Hz, 1H), 7.05 (dd, J = 8.5, 2.0 Hz,
1H), 6.95 (s, 2H), 6.91 (d, J = 9.0 Hz, 2H), 6.87 (d, J = 8.5 Hz, 1H),
4.08 (q, J = 7.0 Hz, 2H), 3.97 (s, 3H), 3.92 (s, 3H), 1.45 (t, J = 7.0 Hz,
3H);13C NMR (125 MHz, CDCl3) δ, ppm: 158.46, 149.10, 148.60,
130.86, 130.19, 127.46, 126.48, 126.30, 119.50, 114.69, 113.47,
111.26, 108.57, 63.50, 55.96, 55.87, 14.87.ESI-MS: 270.32 ([M
+H]+).
4.2. In vitro aortic rings assay
4.2.1. Materials
Acetylcholine (Ach) and phenylephrine (PE) were acquired from
Acros Organics (Belgium). Both the Ach and PE were diluted with
distilled water into 0.1 mM as stock solutions. The synthesized stibe-
noid derivatives, SB 1-8e were dissolved in 1% of Tween 80 and no
precipitation was observed. All the chemicals were stored in freezer
(Pensonic, PFZ-230) at −20 °C for future use.
4.1.6. General procedure for synthesis of compounds, SB 4b, SB 6b, SB
8b, SB 8e
Compound SB 8b was synthesized from SB 8a via poly O-deal-
kylation. SB 8a (1.50 g, 4.8 mmol) and N,N-dimethylaniline (30 mL)
were stirred at 100 °C. Anhydrous AlCl3 (3.0 equiv.) was slowly added
into the mixture and heated at 180 °C for 5 h. Then, the resultant
mixture was quenched with ice water followed by the step-wise addi-
tion of 37% HCl until the colour of the mixture turned to brownish-
orange colour. The mixture was then extracted by using ethyl acetate
and then the excess solvent was evaporated off. The crude product was
washed with chloroform to yield the desired compound SB 8b as off-
4.2.2. Animals
Sprague Dawley (SD) rats of 8–12 weeks old (around 180–240 g)
were acclimated in the animal transit house for 12-h light-dark cycles
with the access to water and food pellet. Animals were cared according
to the laid down rules by Animal Research and Service Centre (ARASC),
Universiti Sains Malaysia. The experiments were conducted based on
the Guideline of Universiti Sains Malaysia Institutional Animal Care and
Use Committee (USM IACUC) with animal ethics approval: USM/
IACUC/2019/(120)(1026).
7