Synthesis and cytotoxicity of 3,4-diaryl-2(5H)-furanones

Article abstract of DOI:10.1016/S0960-894X(01)00831-9

A series of 3,4-diaryl-2(5H)-furanone derivatives were synthesized and evaluated for their cytotoxicity in a small panel of cancer cell lines. Four out of 10 compounds in this series, for example 3-(3,4,5-trimethoxyphenyl)-4-(4-methoxyphenyl)-, 3-(3,4,5-trimethoxyphenyl)-4-(3-hydroxy-4-methoxyphenyl)-, 3-(3,4,5-trimethoxyphenyl)-4-(3-amino-4-methoxyphenyl)-, and 3-(3,4,5-trimethoxyphenyl)-4-(2-naphthyl)-2(5H)-furanones, were found to have potent cytotoxic activities with ED₅₀values of less than 20 nM in most of the cell lines tested.

Full text of DOI:10.1016/S0960-894X(01)00831-9

Bioorganic & Medicinal Chemistry Letters 12 (2002) 719–722
Synthesis and Cytotoxicity of 3,4-Diaryl-2(5H)-furanones
Yong Kim, Nguyen-Hai Nam, Young-Jae You and Byung-Zun Ahn*
College of Pharmacy, Chungnam National University, Taejon 305-764, Republic of Korea
Received 20 October 2001; accepted 13 December 2001
Abstract—A series of 3,4-diaryl-2(5H)-furanone derivatives were synthesized and evaluated for their cytotoxicity in a small panel of
cancer cell lines. Four out of 10 compounds in this series, for example 3-(3,4,5-trimethoxyphenyl)-4-(4-methoxyphenyl)-, 3-(3,4,5-
trimethoxyphenyl)-4-(3-hydroxy-4-methoxyphenyl)-, 3-(3,4,5-trimethoxyphenyl)-4-(3-amino-4-methoxyphenyl)-, and 3-(3,4,5-trimeth-
oxyphenyl)-4-(2-naphthyl)-2(5H)-furanones, were found to have potent cytotoxic activities with ED50 values of less than 20 nM in
most of the cell lines tested. # 2002 Elsevier Science Ltd. All rights reserved.
Introduction
found in a number of drugs with diverse biological
activities, as mentioned above. Moreover, 3,4-diaryl-
2(5H)-furanone derivatives could be considered as cis-
restricted analogues of combretastatins (Fig. 1), the
potent antimitotic and cytotoxic agents isolated from
Combretum caffrum.9
2(5H)-Furanone is a common moiety incorporated in a
number of drugs with diverse biological activities such
as antifungal, antibacterial and antiinflammatory.1ꢀ4
A
number of 2(5H)-furanone derivatives have also been
reported from nature as cytotoxic and antitumor
agents.4ꢀ6 For example, gonbiobutenolide B6, isolated
from the ethanol extract of the stem bark of Goniotha-
lamus giganteus, exhibited significant cytotoxicity
against human lung carcinoma (A549, ED50, 0.9 mg/
mL).6 In a previous study, we reported the isolation of a
furanone containing principle, deoxypodophyllotoxin
(DPT, Fig. 1) from Pulsatilla koreana, one indigenous
plant in Korea. This compound showed potent cyto-
toxicity in a variety of tumor cell lines. Strikingly, it was
also shown to exhibit significant antiangiogenic activity
at non-cytotoxic concentrations. In vivo, DPT was
found to possess potent antitumor activity in several
solid tumor models.7
In this paper, we would like to describe the synthesis
and evaluation of the cytotoxicity of a series of such 3,4-
diaryl-2(5H)-furanone derivatives.
Recently, we reported a series of diaryloxazolone deri-
vatives with potent cytotoxicity and antitumor activity.8
The dihedral angles (52.6ꢁ) between 3,4-diaryl groups in
these 3,4-diaryloxazolones, especially that of compound
1 (Fig. 2) were found to be similar to that of DPT
(70.3ꢁ). These results prompted us to design and syn-
thesize compound 3-(3,4,5-trimethoxyphenyl)-4-(3,4-
methylendioxyphenyl)-2(5H)-furanone 2f and a series of
its analogues, in which the two aromatic rings are teth-
ered directly into the 2(5H)-furanone ring, a biomoiety
Figure 1. Deoxypodophyllotoxin (DPT), 3-(3,4,5-trimethoxy)-4-(3,4-
methylenedioxyphenyl)oxazolone (1, 3,4-diaryloxazolone), 3-(3,4,5-
trimethoxyphenyl)-4-(3,4-methylenedioxyphenyl)-2(5H)-furanone (2f,
3,4-diaryl-2(5H)-furanone), and combretastatin (CA-4).
*Corresponding author. Tel.:+82-42-821-5923; fax: +82-42-823-
6566; e-mail: ahnbj@cnu.ac.kr
0960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(01)00831-9

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Y. Kim et al. / Bioorg. Med. Chem. Lett. 12 (2002) 719–722
Results and Discussion
Chemistry
The general methods for the preparation of 3,4-diaryl-
2(5H)-furanone derivatives 2a–f and 2 h–k are outlined
in Scheme 1. The appropriate acetophenones 310,11 were
brominated at the a carbonyl position. Reaction of
3,4,5-trimethoxyphenylacetic acid with the resulting
a-bromo acetophenones 4 in the presence of triethylamine
gave phenacylacetates 5a–d, 5f, 5i, and 5k in 59–75%
yields. The aldol-type condensation and subsequent
dehydration of the resulting phenacylacetates with tri-
ethylamine and p-toluenesulfonic acid (p-TsOH) gave
the target compounds12 2a–d, 2f, and 2k in 56–73%
yields. Debenzylation of (3-benzyloxy-4-methoxy)phenacyl-
30,40,50-trimethoxyphenylacetate 5g by catalytic hydro-
genation with 10% Pd/C gave (3-hydroxy-4-methoxy)
Figure 2. Superimposition of the lowest energy conformations of DPT
(AC, 11.9 nM), diaryloxazolone (1, AC, 64.5 nM), and 3-(3,4,5-tri-
methoxyphenyl)-4-(3,4-methylenedioxyphenyl)-2(5H)-furanone (2f,
AC, 83.8 nM).
phenacyl-30,40,50-trimethoxyphenylacetate
phenacylacetate 5h was then treated with triethylamine
5h.
The
Scheme 1. (a) Br2, AcOH, HCl, rt; (b) 3,4,5-trimethoxyphenylacetic acid, NEt3, CH3CN, rt; (c) 10% Pd/C, THF, rt; (d) TEA, p-TsOH, 4 A molecular
sieve, CH3CN, reflux; (e) DBU, CH3CN, 0 ꢁC; (f) p-TsOH, benzene, reflux; (g) Zn, AcOH, rt.

Y. Kim et al. / Bioorg. Med. Chem. Lett. 12 (2002) 719–722
721
and p-TsOH to give 2h12 in 66% yield. Ring closure of
5i was satisfactorily accomplished in a high yield by an
aldol-type cyclization mediated by DBU to give 6i that
was dehydrated with p-TsOH in refluxing benzene to
afford the target compound 2i. The nitro groups on the
A-ring of 2d and 2i were reduced by Zn/AcOH to give
the corresponding aniline compounds12 2e and 2j in 81
and 83% yields, respectively.
compounds 2d and 2e. As shown in Table 1, compound
2d, possessing the electron-withdrawing nitro group
suffered a substantial loss of cytotoxicity in all three cell
lines (AC, 3767 nM), meanwhile compound 2e, bearing
the electron-donating amino group, showed much
stronger cytotoxicity (AC, 45.7 nM) compared to 2d.
These results indicated that the introduction of the
electron-withdrawing group in the A-ring strongly
reduced the activity of these types of compound.
Cytotoxic activity
Next, since the 4-methoxy group proved to be more
favorable for bioactivity, we maintained this substituent
at 4-position and introduced additional substituents at
position 3 in the A ring. In overall, the introduction of
electron-donating groups, as in compounds 2h, 2j, and
2k, improved the cytotoxicity of these compounds by
1.5-, 4-, and 2-fold, respectively, compared to that of 2c,
meanwhile the presence of the electron-withdrawing
NO2 group reduced the activity by more than 2-fold
compared to that of 2c (compound 2i, AC value of 42.2
nM versus compound 2c, AC value of 19.6 nM). These
results again indicated that the electron-withdrawing
group on the A-ring was not favorable for the cyto-
toxicity of this compound type.
Cytotoxic activities of the synthesized compounds were
tested13 against A549, SK-MEL-2, and MCF-7 cell
lines. The results are shown in Table 1. For comparison
purposes, the average cytotoxic activity (AC) of the
compounds (average of the ED50 values) in three cancer
cell lines was calculated and the results from this com-
putation are included in Table 1. Previously, it was
reported that the 3,4,5-trimethoxy group on the B-ring
was essential for strong cytotoxic activities of the di-
aryloxazolones.8 Taking into consideration these results
and structural features of DPT, in the present study we
fixed the B-ring as a trimethoxyphenyl group and mod-
ification was mainly focused on the variation of the
substituents on the A ring.
However, compound 2f (AC, 83.8 nM) possessing a 3,4-
methylendioxy group in the A-ring was found to be 4
times less potent than 2c (AC, 19.6 nM). Compared to
the bioactivity of DPT, it was found that 2f was nearly
8-fold less active than DPT, meanwhile the AC values
of 2h, 2j, and 2k were comparable to that of DPT. Fur-
thermore, 2f was found to be less potent than the 3,4-
diaryloxazolone 18 (AC, 83.8 and 64.5 nM, respec-
tively). To gain some insights into the causes of dimin-
ished activity observed with 2f, we performed molecular
modeling studies of these three compounds using
Hyperchem1 software and calculated the dihedral
Compound 2c (AC, 19.6 nM) possessing a 4-methoxy
group in the A ring showed potent cytotoxic activity,
meanwhile otherwise mono-substituted compounds
were found to be inactive (2a, AC >5000 nM; 2b,
AC=3200 nM). This result indicated that location of
the substituent at 4-position was important for cyto-
toxic activity.
In attempts to discern the electronic effects of the
substituent in the A ring, a nitro group and an amino
group were introduced into 4-position, resulting in
Table 1. Cytotoxic activities of 3,4-diaryl-2(5H)-furanone analogues against some cancer cell linesa
Compd
R1
R2
R3
ED50 (nM)b
SK-MEL-2
ACc
A549
MCF-7
2a
2b
2c
2d
2e
2f
2h
2i
OCH3
H
H
H
H
H
H
H
H
H
OCH3
H
H
H
H
H
OCH3
NO2
NH2
>5000
3200
19.1
4800
54.7
>5000
4200
17.5
3200
49.3
70.8
10.2
40.2
3.3
>5000
2500
22.2
3300
33.0
80.4
11.4
41.9
4.7
>5000
3300
19.6
3767
45.7
–OCH2–
100.2
16.3
44.6
5.3
83.8
12.6
42.2
4.4
OH
NO2
NH2
OCH3
OCH3
OCH3
2j
2k
DPTd
Naphthyl (A-ring)
9.8
15.5
8.19.91.0
8.4
11.7
11.9
aA549, human lung cancer; SK-MEL-2, human melanoma, MCF-7, human breast cancer.
bThe sample concentration produces a 50% reduction in cell growth.
cAverages of the ED50 values in three cancer cell lines.
dDeoxypodophyllotoxin.

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Y. Kim et al. / Bioorg. Med. Chem. Lett. 12 (2002) 719–722
References and Notes
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Figure 3. cis-Restricted five-membered heterocyclic combratastatins.9
7. Kim, Y.; You, Y. J.; Kim, S. B.; Ahn, B. Z. Planta Med. In
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8. Nguyen, H. N.; Kim, Y.; You, Y. J.; Hong, D. H.;
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angles between the two 3,4-aryl rings in each com-
pound. As shown in Figure 1, the dihedral angles
between the A and B rings in DPT, diaryloxazolone 1
and diarylfuranone 2f were 70.3, 52.6, and 15.4ꢁ. The
potencies of the three compounds were found to be in
the same order (AC values of 11.9, 64.5, and 83.8 nM,
respectively). Thus it seemed that the magnitude of the
dihedral angle between A and B rings positively influ-
enced the bioactivity of the compounds in this series.
9. Ohsumi, K.; Hatanaka, T.; Fujita, K.; Nahagawa, R.;
Fukuda, Y.; Nuhei, Y.; Suga, Y.; Morinaga, Y.; Akiyama, Y.;
Tsuji, T. Bioorg. Med. Chem. Lett. 1998, 8, 3153.
10. Starting material of 2h, 3-benzyloxy-4-methoxy-
acetophenone was synthesized as follows: commercially avail-
able 3-hydroxy-4-methoxybenzaldehyde was treated with
benzylbromide in the presence of anhydrous K2CO3 to give 3-
benzyloxy-4-methoxybenzaldehyde, which was then con-
densed with methylmagnesium bromide to give 1-(3-benzyl-
oxy-4-methoxy)-1-ethanol in 92% yield. Oxidation of the
alcohol group of 1-(3-benzyloxy-4-methoxy)-1-ethanol by
PDC gave a 3-benzyloxy-4-methoxy-acetophenone in 98%
yield.
Previously, Oshumi et al. reported a series of cis-
restricted 5-membered heterocyclic combratastatins,
and observed that substituents as small as –NH2,–CH3,
carbonyl group on position 1or 3 of the five-membered
heterocycles substantially decreased their bioactivity
(Fig. 3).9 In contrast, it was noteworthy that most
compounds in the present series of 3,4-diaryl-2(5H)-
furanones which possess a carbonyl group on position 1
showed very potent cytotoxic activity.
11. Starting material of 2i, 3-nitro-4-methoxyacetophenone
was synthesized as follows: commercially available 3-nitro-4-
hydroxyacetophenone was refluxed with dimethylformamide
(DMF) in the presence of anhydrous K2CO3 to give 3-nitro-4-
methoxyacetophenone in 92% yield.
In conclusion, we have synthesized a series of 3,4-diaryl-
2(5H)-furanone derivatives with potent cytotoxic activ-
ity in tumor cell lines. This is the first report revealing
compound of 3,4-diaryl-2(5H)-furanone type, a class of
compounds well known previously as selective COX-II
inhibitors, with potent cytotoxic activity in tumor cells.
Four compounds in this series including 2c, 2h, 2j and
2k were found to have ED50 value of less than 20 nM in
most of the cell lines assayed. Evaluation of a repre-
sentative compound from this series, compound 2j, in in
vivo model is underway in our laboratory and the
results will be disclosed in due course.
12. All newly synthesized compounds gave satisfactory ana-
lytical and spectroscopic data. 2j: 1H NMR (90 MHz, CDCl3):
d 6.71(dd, J=8.77, 2.15 Hz, 1H), 6.58 (d, J=8.77 Hz, 1H),
6.51(d, J=2.15 Hz, 1H), 6.49 (s, 2H), 5.25 (s, 2H), 3.99 (s,
3H), 3.89 (s, 3H), 3.78 (s, 6H). Anal. (C20H21NO6) calcd: C,
64.68; H, 5.70; N, 3.77; found: C, 64.42; H, 5.64; N, 3.71. 2k:
1H NMR (90 MHz, CDCl3): d 7.88–7.76 (m, 4H), 7.57–7.53
(m, 2H), 7.40 (dd, J=1.78, 8.60 Hz, 1H), 6.72 (s, 2H), 5.30 (s,
2H), 3.89 (s, 3H), 3.70 (s, 6H). Anal. (C23H20O5) calcd: C,
73.39; H, 5.36; found: C, 73.13; H, 5.31.
13. Skehan, P.; Storeng, R.; Scudiero, D.; Monks, A.;
McMahon, J.; Vistica, D.; Warren, J. T.; Bokesch, H.; Kenny,
S.; Boyd, M. R. J. Natl. Cancer Inst. 1990, 82, 1107.