Efficient synthesis and biological evaluation of 4-arylcoumarin derivatives

Article abstract of DOI:10.1016/j.cclet.2010.12.017

Two bioactive natural 4-arylcoumarins, 5,7,4′-trimethoxy-4- phenylcoumarin (1a), 5,7-dimethoxy-4-phenylcoumarin (1b) and five closely related derivatives 1c-g were synthesized. In vitro evaluation with a catechol subunit for antioxidant and antimicrobial activity, these compounds using standard methods showed that compounds 1d, 1f displayed promise radical scavenging activity and 1f was found to be the most active one against Bacillus dysenteriae.

Full text of DOI:10.1016/j.cclet.2010.12.017

Available online at www.sciencedirect.com
Chinese Chemical Letters 22 (2011) 667–670
www.elsevier.com/locate/cclet
Efficient synthesis and biological evaluation
of 4-arylcoumarin derivatives
Jie Sun a,c, Wei Xian Ding b, Ke Yun Zhang b, Yong Zou a,
*
a Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China
b Department of Zoology, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
c Graduate School of the Chinese Academy of Sciences, Beijing 100039, China
Received 29 September 2010
Abstract
Two bioactive natural 4-arylcoumarins, 5,7,40-trimethoxy-4-phenylcoumarin (1a), 5,7-dimethoxy-4-phenylcoumarin (1b) and
five closely related derivatives 1c–g were synthesized. In vitro evaluation with a catechol subunit for antioxidant and antimicrobial
activity, these compounds using standard methods showed that compounds 1d, 1f displayed promise radical scavenging activity and
1f was found to be the most active one against Bacillus dysenteriae.
# 2010 Yong Zou. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: 4-Arylcoumarin; Synthesis; Antimicrobial; Antioxidant
4-Arylcoumarins (neoflavones) represent a minor class of natural compounds with C6–C3–C6 skeleton and a
characteristic 4-aryl group. These compounds have commonly been classified as the family members of flavonoids.
There are at least 131 4-arylcoumarins were isolated from 58 plants belonging to the families Clusiaceae, Fabaceae,
Rubiaceae, Thelypteridaceae, Passifloraceae, Asteraceae and Rutaceae [1]. 5,7,40-Trimethoxy-4-phenylcoumarin 1a
and 5,7-dimethoxy-4-phenylcoumarin 1b isolated as the major active ingredients from the culture filtrate of
Streptomyces aureofaciens CMUAc130 are proved to be the most outstanding compounds possessing antifungal [2],
anti-inflammatory [3,4], antiallergenic [5], antitumor activities [6], and closely related with antiprotozoal [7] and
antimalarial properties [8].
The scarcity in nature and the capability for extensive chemical modification of 4-arylcoumarins make this class of
compounds exceedingly attractive in organic synthesis. The synthetic methods represented by 5,7,40-trimethoxy-4-
phenylcoumarin (1a) and 5,7-dimethoxy-4-phenylcoumarin (1b) are mainly involved Pechmann reaction, Perkin
reaction, Ponndorf reaction, Houben–Hoesch reaction and Wittig reaction [9–16]. However, most of the reported
methods suffered from one or more drawbacks such as harsh reaction conditions, long reaction times, low yields, use
of toxic reagents and inconvenient workup procedures. Therefore, facile synthetic procedure for the preparation of 4-
arylcoumarin and derivatives is highly desirable. In continuation of our ongoing program to develop arylcoumarin
analogues with medical interest, we herein report a phenylpropiolic acid based condensation with corresponding
* Corresponding author.
E-mail address: zouyong@gic.ac.cn (Y. Zou).
1001-8417/$ – see front matter # 2010 Yong Zou. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2010.12.017

[()TD$FIG]
668
J. Sun et al. / Chinese Chemical Letters 22 (2011) 667–670
COOH
COOCH3
COOCH3
Br
CHO
Br
a
c
d
b
R
R
3a R=OCH3
3b R=H
R
R
5a R=OCH3
5b R=H
2a R=OCH3
2b R=H
4a R=OCH3
4b R=H
R
COOH
R
f
e
OCH3
OH
H3CO
R
O
O
HO
O
O
7a R=OCH3
7b R=H
1a R=OCH3
1b R=H
6a R=OCH3
6b R=H
OCH3
COOH
R1
g
OH
R3
R1
R2
O
O
OCH3
R2
R3
8a R2=OH, R3=H
8b R2=OCH3, R3=H
8c R2=R3=OH
6a R1=H
6c R1=OCH3
6d R1=OH
1c R1=OCH3, R2=OH, R3=H
1d R1=OCH3, R2=R3=OH
1e R1=R2=OCH3, R3=H
1f R1=OH, R2=R3=OH
1g R1=R3=H, R2=OCH3
Scheme 1. Reagents and conditions: (a) malonic acid, pyridine and piperidine 90 8C, 4 h 88.2% 3a and 83.0% 3b; (b) MeOH, SOCl2, reflux, 4 h,
97.8% 4a and 96.0% 4b; (c) Br2, CH2Cl2, 0 8C, 20 min, 91.3% for 5a and 92.9% for 5b; (d) KOH, EtOH, reflux, 6 h, 74.6% for 6a and 75.9% for 6b;
(e) phloroglucinol, CF3COOH, r.t., 4 h. for 7a, 91.1%; 60 8C, 12 h for 7b, 89.1%; (f) (CH3)2SO4, K2CO3, (Me)2CO, reflux, 4 h, 72.7% for 1a and
70.5% for 1b; (g) CF3COOH, r.t., 4–8 h, 56.4% for 1c, 58.0% for 1d, 53.8% for 1e, 53.7% for 1f, 60.1% for 1 g.
polyphenols which lead to 5,7,40-trimethoxy-4-phenylcoumarin (1a) and 5,7-dimethoxy-4-phenyl-coumarin (1b) as
well as their analogues 1c–1g under mild conditions with satisfactory yields.
As shown in Scheme 1, starting from the readily available benzaldehydes 2a, 2b, the cinnamic acids 3a, 3b can be
obtained through condensation reaction with malonic acid in the presence of pyridine and piperidine. Esterification of
3a, 3b with methanol in the presence of SOCl2 gave methyl cinnamates 4a, 4b which were readily brominated to give
the dibromides 5a, 5b in high yields. Treatment of the dibromides 5a, 5b with KOH in ethanol at 80 8C afforded the
key intermediate phenylpropiolic acid 6a, 6b. Then, a straightforward tandem reaction between 6a, 6b and
phloroglucinol in the presence of CF3COOH at room temperature was conducted, giving hydroxylated 4-
arylcoumarins 7a, 7b in approximately 90% yield. It is worth mentioning that, unlike the published procedure which
utilized the arylpropiolic acid chlorides or ethyl esters for coupling with phloroglucinol [13–16], our protocol showed
improvements both in simplicity and production yield. Finally, through methylation with dimethyl sulfate, the target
molecules 1a, 1b were obtained in 38.9% and 35.3% overall yield, respectively. Crude product of 1a, 1b can be
purified either by column chromatography on silica gel or by washing with water, dried and crystallized from ethyl

J. Sun et al. / Chinese Chemical Letters 22 (2011) 667–670
669
Table 1
In vitro antimicrobial activity and DPPH radical scavenging activity (EC50, mmol/L)a for compounds 1c–1g.
Compound
EC50 (mmol/L) for DPPH radical scavengingb
MIC (mg/mL)b
S. aureus
E. coli
B. dysenteriae
C. albicans
c
d
d
d
d
1c
1d
–
–
–
–
–
d
3.06 ꢀ 0.25
117
–
29.3
d
78
c
d
d
d
1e
–
–
–
–
–
1f
1g
2.85 ꢀ 0.38
156
156
4.9
d
–
58.5
d
–
c
d
d
–
–
–
Amoxicillin
Gentamicin
Ascorbic acid
BHTe
<1.95
<1.95
23
29
<1.95
2.9
<1.95
<1.95
4.42 ꢀ 0.33
142.4 ꢀ 0.8
a
The negative control DMSO showed no activity.
b
c
d
e
Average of three experiments.
Totally inactive (EC50 > 1250 mmol/mL).
Totally inactive (MIC > 1250 mg/mL).
BHT (2,6-di-tert-butyl-4-methylphenol).
acetate and petroleum ether for two or three times. The 1H NMR, 13C NMR, EI-MS data of the synthetic compounds
1a and 1b were identical with those of reported [20].
Based on the above-mentioned results, the scope of this protocol was further explored by reactions between
methoxy or hydroxy substituted phenylpropiolic acid 6a, 6c, 6d and corresponding polyphenols 8a–8c. As shown in
Scheme 1, all of the tested combinations successfully provided 4-arylcoumarins 1c–1g with 53–60% isolated yields in
presence of trifluoroacetic acid at room temperature. However, the attempt to produce these 4-arylcoumarins by means
of another catalyst POCl3/BF3-Et2O resulted low yields of desired compounds. The newly synthesized compounds
were characterized by 1H NMR, IR and MS analyses [21] and were screened for antioxidant and antimicrobial activity.
The radical scavenging activity of the synthesized compounds (1c–1g) was evaluated by 1,1-diphenyl-2-
picrylhydrazyl (DPPH) assay [17], the results are summarized in Table 1. The compound 1d and 1f which bear a
catechol moiety (7,8-dihydroxy group) showed strong scavenging activities against DPPH radical (ED50 = 3.06 mmol/
L, 2.85 mmol/L, respectively), whereas compounds 1c, 1e, 1g without such group were totally inactive in the same
experiments. These results were in good agreement with recent reports on the hydroxylated isoflavone derivatives [18].
The synthesized compounds (1c–1g) were also evaluated for their in vitro activity against four microorganisms,
including Staphylococcus aureus (ATCC2592) (Gram-positive), Escherichia coli (ATCC25922) (Gram-negative),
Bacillus dysenteriae (Bacillaceae) and Candida albicans (ATCC2002) (fungus) according to published techniques
[19]. Minimum inhibitory concentration (MIC) is defined as the concentration of the compound required to exert
complete inhibition of bacterial growth. Compounds 1d and 1f exhibited relatively high activity against B. dysenteriae
(MIC = 29.3, 4.9 mg/mL, respectively) and displayed weak to moderate inhibitory activity against S. aureus and C.
albicans (MIC = 58.5–156 mg/mL) (Table 1). The results also demonstrated that the catechol moiety in 4-
arylcoumarins played an essential role in antimicrobial activity.
In conclusion, an efficient and straightforward portocol for the synthesis of 4-arylcoumarins 1a, 1b and their closely
related derivatives 1c–1g was described. Compounds 1d, 1f with a catechol moiety exhibited remarkable in vitro
antioxidant and antimicrobial activity, suggesting that the catechol moiety may be a beneficial scaffold for therapeutic
purpose.
Acknowledgments
We thank the Science and Technology Program of Guangdong Province, Strategic Cooperation Program between
Guangdong Province and Chinese Academy of Sciences and National Key Technology R&D Program, China (Nos.
2003B31603, 2006B35604002, 2009B091300125 and 2007BAD82B02) for financial support.

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J. Sun et al. / Chinese Chemical Letters 22 (2011) 667–670
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[20] 1a: mp 151–152 8C; 1H NMR (400 MHz, CDCl3): d 3.46 (s, 3H, 5-OCH3), 3.83 (2 ꢁ s, 6H, 7-OCH3, 40-OCH3), 5.97 (s, 1H, 3-H), 6.22 (d, 1H,
J = 2.4 Hz, 6-H), 6.49(d, 1H, J = 2.5 Hz, 8-H), 6.87 (dd, 2H, J = 6.8 Hz and 2.0 Hz, 30-H, 50-H), 7.20 (dd, 2H, J = 6.8 Hz and 2.0 Hz, 20-H, 60-
H), IR(KBr): 1712, 1624, 1591, 1510, 1460, 1356, 1244, 1228, 1203, 1157, 1107 cmꢂ1; EI-MS: m/z: 312 [M]+, 284 [M-CO]+, 269 [M-CO-
Me]+, 226, 211, 167, 149. 1b: mp 213–215 8C; 1H NMR (400 MHz, CDCl3): d 3.40(s, 3H, 5-OCH3), 3.85(s, 3H, 7-OCH3), 5.99(s, 1H, 3-H),
6.21(d, 1H, J = 2.0 Hz, 6-H), 6.51(d, 1H, J = 2.0 Hz, 8-H), 7.23–7.25 (m, 2H, 30-H, 50-H), 7.34–7.36 (m, 3H, 20-H, 40-H, 60-H), IR(KBr): 1716,
1612, 1460, 1352, 1227, 1205, 1159, 1111 cmꢂ1; EI-MS: m/z: 282 [M]+, 254 [M-CO]+, 239[M-CO-Me]+, 211, 196, 168, 152, 139.
[21] 1c: mp 233–234 8C; 1H NMR (400 MHz, CD3COCD3):d 3.90 and 3.94(s, 6H, 3H and 3H, 2ꢁ OCH3), 6.20(s, 1H, 3-H), 6.74(s, 1H, J = 2.4 Hz
and 8.0 Hz, 60-H), 6.91(s, 1H, J = 2.4 Hz, 20-H), 6.97(d, 1H, J = 8.0 Hz, 50-H), 6.98(d, 1H, J = 2.0 Hz, 8-H), 7.02(dd, 1H, J = 2 Hz and 8.8 Hz,
6-H), 7.45(d, 1H, J = 8.8 Hz, 5-H); IR(KBr): 3194(OH), 1695(CO), 1624, 1599, 1518, 1263 and 1140 cmꢂ1; EI-MS m/z (%) 298[M]+,
283[MꢂCH3]+, 270, 255, 227, 199, 184, 113. 1d: mp 271–272 8C; 1H NMR (400 MHz, CD3COCD3): d 3.87 and 3.88(s, 6H, 3H and 3H, 2ꢁ
OCH3), 6.07(s, 1H, 3-H), 6.83 and 7.00 (2 ꢁ d, 2H, J = 8.8 Hz, 5-H and 6-H) 7.06(dd, 1H, J = 2.0 Hz and 8.4 Hz, 50-H), 7.10(d, 1H, J = 2.0 Hz,
20-H), 7.11(d, 1H, J = 8.4 Hz, 60-H); IR(KBr): 2987, 1726(CO), 1618, 1518, 1379, 1255, 1147 and 814 cmꢂ1; EI-MS m/z (%) 314[M]+,
286[MꢂCO]+, 271[MꢂCO–CH3]+, 161, 133, 115, 103. 1e: mp 148–149 8C; 1H NMR (400 MHz, CD3COCD3):d 3.88, 3.89 and 3.93(s, 9H,
3H, 3H and 3H, 3ꢁ OCH3), 6.14(s, 1H, 3-H), 6.90(dd, 1H, J = 8.4, 2.0 Hz, 60-H), 6.94(d, H, J = 2.0 Hz, 20-H), 7.08(dd, 1H, J = 8.8, 2.4 Hz, 6-
H), 7.12(d, H, J = 2.4 Hz, 8-H), 7.12(d, H, J = 8.4 Hz, 50-H), 7.55(d, H, 8.8 Hz, 5-H); IR(KBr): 3411(OH), 1695(CO), 1606, 1518, 1448, 1173
and 1140 cmꢂ1; EI-MS m/z (%) 312[M]+, 297[MꢂCH3]+, 284[MꢂCO–CH3]+, 269, 213, 183, 139. 1f: mp 176–177 8C; 1H NMR (400 MHz,
CD3COCD3): d 3.91(s, 3H, OCH3), 6.03(s, 1H, 3-H), 6.83(d, 1H, J = 8.8 Hz, 6-H), 6.95–6.99(m, 3H, 5-H, 20-H and 60-H), 7.10(d, 1H,
J = 8.0 Hz, 50-H); IR(KBr): 3371(OH), 1695(CO), 1653, 1599, 1448, 1240, 1178 and 1130 cmꢂ1; EI-MS m/z (%) 300[M]+, 272[MꢂCO]+,
1
257[MꢂCO–CH3]+, 229, 115. 1g: mp 155–157 8C; H NMR (400 MHz, CDCl3): d 3.86(s, 6H, 2ꢁ OCH3), 6.18(s, 1H, 3-H), 6.78(dd, 1H,
J = 8.8 Hz and 2.4 Hz, 6-H), 6.87(d, 1H, J = 2.4 Hz, 8-H), 7.01(dd, 2H, J = 8.4 Hz and 2 Hz, 30-H, 50-H) and 7.37(dd, 2H, J = 8.4 Hz and 2 Hz,
20-H, 60-H), 7.43(d, 1H, J = 8.8 Hz, 5-H); IR(KBr): 3440, 3064, 2993, 1738(CO), 1612, 1510, 1375, 1250, and 825 cmꢂ1; EI-MS m/z (%)
282[M]+, 254[MꢂCO]+, 239[MꢂCO–CH3]+, 211, 196, 168, 152, 140, 127.