Synthesis and evaluation of novel chromone analogs for their inhibitory activity against interleukin-5

Article abstract of DOI:10.1016/j.ejmech.2010.02.041

A novel series of chromone analogs were synthesized and evaluated for their inhibitory activity against interleukin-5. Among them compounds 5-Cyclohexylmethoxy-3-(4-hydroxybenzyl)-4H-chromen-4-one (6a, 98% inhibition at 30?μM, IC₅₀?50?=?7.6?μM) showed most potent activity. The structural requirement of chromone analogs possessing the inhibitory activity against IL-5 could be summarized as: (i) importance of hydrophobic group such as cyclohexylmethoxy at 5th position of ring A, (ii) requirement of ring B with small size of hydrogen bonding group with electron donating property such as phenolic hydroxyl group at 4th position and (iii) planarity of the chromen-4-one ring.

Full text of DOI:10.1016/j.ejmech.2010.02.041

European Journal of Medicinal Chemistry 45 (2010) 2531e2536
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and evaluation of novel chromone analogs for their inhibitory activity
against interleukin-5
Pillaiyar Thanigaimalai a, Tuan Anh Le Hoang a, Ki-Cheul Lee a, Vinay K. Sharma a, Seong-Cheol Bang a,
,
Jun Ho Yun b, Eunmiri Roh b, Youngsoo Kim b, Sang-Hun Jung a
*
a College of Pharmacy and Institute of Drug Research and Development, Chungnam, National University, Daejeon 305-764, Republic of Korea
b College of Pharmacy, Chungbuk National University, Cheongju 361-763, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel series of chromone analogs were synthesized and evaluated for their inhibitory activity against
interleukin-5. Among them compounds 5-Cyclohexylmethoxy-3-(4-hydroxybenzyl)-4H-chromen-4-one
Received 12 December 2009
Received in revised form
12 February 2010
Accepted 15 February 2010
Available online 20 February 2010
(6a, 98% inhibition at 30
4-one (8a, 84% inhibition at 30
m
M, IC50 < 3.0
m
M) and 5-Cyclohyxylmethoxy-3-(hydroxymethyl)-4H-chromen-
M) showed most potent activity. The structural
m
M, IC50 ¼ 7.6
m
requirement of chromone analogs possessing the inhibitory activity against IL-5 could be summarized as:
(i) importance of hydrophobic group such as cyclohexylmethoxy at 5th position of ring A, (ii) require-
ment of ring B with small size of hydrogen bonding group with electron donating property such as
phenolic hydroxyl group at 4th position and (iii) planarity of the chromen-4-one ring.
Ó 2010 Elsevier Masson SAS. All rights reserved.
Keywords:
Chromone analogs
Inhibitor
Interleukin-5
Eosinophils
1. Introduction
related to severity of the disease [11,12]. In addition, inhalation of IL-5
has been shown to increase the percentage of eosinophils in induced
Eosinophilic inflammation in the airway, along with hyper-
responsiveness and tissue injury, is a characteristic feature in the
pathogenesis of bronchial asthma [1,2]. There is a strong evidence for
a major role of T helper type 2 (Th2) cytokines in diseases such as
asthma and, the therapeutic strategies that target Th2 cytokines are
of potential benefit in such allergic disease [3,4]. Several studies
indicate the role of eosinophil as a major effector cell in allergic
inflammation, capable of causing most of the morphological and
functional alterations observed in asthma. Several cytokines can
affect eosinophils but despite possible redundancy with IL-3 and
granulocyte-macrophage colony stimulating factors (GM-CSF), IL-5
seems to be the primary cytokine involved in the production,
differentiation, maturation and activations of the eosinophils under
in vivo conditions [5]. It was observed that IL-5 transgenic mice
developed lifelong eosinophilia, whereas GM-CSF transgenic showed
increased numbers of mononuclear cells and neutrophils, but only
a minimal increase in the number of eosinophils [6,7]. Similar find-
ings have emerged from knockout mice studies [8e10]. It has also
been shown that IL-5, is present in increased amounts in the mucosa
of asthmatic airways and the expression of IL-5 mRNA is directly
sputum and to augment airway hyper-responsiveness in asthmatics
[13]. These observations suggest that eosinophils are the major cell
type in allergic reactions and thus the action of IL-5 emerges as one of
the new immunomodulatory therapeutic strategy in the treatment of
allergic diseases like bronchial asthma. The major advantage of this
strategy is the specificity of reducing eosinophillic inflammation,
without any side effects.
Recently, some small organic compounds have been found to
inhibit the activity of IL-5. Isothiazolones synthesized by modifica-
tion of Cys 66 residue in IL-5, have been identified as IL-5 antago-
nists [14]. Naturally occurring sophoricoside (1a, 92.1% inhibition at
50
m
M, IC50 ¼ 1.4
mM) and its analogs have been isolated and
identified as inhibitors of IL-5 [15], besides acting as differential
inhibitors of IL-3 and GM-CSF [16]. Considering the activity of
budesonide (70.3% inhibition at 50
m
M, IC50 ¼ 26.8
mM), which is
used for the treatment of chronic asthma, the activity of sopho-
ricoside appears to be very potent. Isoflavonoid analogs of sopho-
ricoside [17,18] and chalcones [19,20] have been demonstrated to be
novel inhibitors of IL-5.
Structureeactivity relationship of sophoricoside analogs 1aed
[17] revealed the necessity for the planar chromen-4-one ring and
a phenolic hydroxyl group at 4th position of ring B. More potent
activity of sophoricoside (Chart 1) than its aglycon, genistein (79.1%
* Corresponding author. Tel.: þ82 42 821 5939; þ82 42 823 6566.
E-mail address: jungshh@cnu.ac.kr (S.-H. Jung).
inhibition at 50
mM, IC50 ¼ 10.6
mM) indicates the necessity for
0223-5234/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2010.02.041

2532
P. Thanigaimalai et al. / European Journal of Medicinal Chemistry 45 (2010) 2531e2536
R
R
O
O
R3
O
O
O
R1
O
O
R1
R1
O
R2
8, 9, 10, 11 and 12 (a-b)
6 (a-l)
1
1a: Sophoricoside R1,R2 = OH, R3 = OGlu
1b: R1 = benzyloxy, R2 = H, R3 = OH
1c: R1 = H, R2 = benzyloxy, R3 = OH
1d: R1 = cyclohexylmethoxy, R2 =H, R3 = OH
Chart 1. Interleukin-5 inhibitors 1 and chromone analogs.
a glucopyranosyl moiety. Introduction of benzyloxy, cylohexyl-
methoxy or isopentyloxy groups at 5th position of isoflavone
increased the activity and eliminated the necessity of glucopyranosyl
moiety of sophoricoside. However, the role of B ring of isoflavone
analogs for the inhibition of IL-5 has not been explored. For contin-
uation of our effort to find the more detail structureeactivity rela-
tionship of isoflavones as IL-5 inhibitor, we designed and prepared
the derivatives 6e12 shown in Chart 1 structurally varied around B
ring of isoflavones and evaluated them for their inhibitory activity
against interleukin-5.
was achieved by treating with N, N-dimethylformamide, meth-
anesulfonyl chloride and boron trifluoride diethyl etherate at reflux.
The substituents of 6ael are listed in Table 1.
The synthetic route used to synthesize aliphatic substituted
chromone analogs is outlined in Fig. 2. Preparation of 7 was accom-
plished by the cyclization of 2 using N, N-dimethylformamide and
phosphoryl chloride at ambient temperature [22,23]. Compound 7
was then oxidized to acid 10 by the treatment of Jones reagent [24].
Reduction of 7 using isopropanol and basic alumina under refluxing
condition gave alcohol 8 [23], which was then treated with thionyl
chloride to produce the corresponding halide 9 [25]. One pot reaction
of 7 and cyclic malonate in the presence of triethylamine and formic
acid (1:1) under reflux for 2 h [26] gave carboxylic acid 11. Oxime 12
was prepared by the treatment of 7 with hydroxylamine hydro-
chloride at ambient temperature for 1 h [27].
2. Chemistry
In continuation of our previous work [17,18] on the modification of
B ring of compound 1, we have synthesized a series of new chromone
analogs starting from commercially available 2, 6-dihydrox-
yacetophenone as shown in Fig.1. The preparation of chalcones 4 was
accomplished by the aldol condensation of substituted 2-hydrox-
yacetophenone and appropriate commercially available benzalde-
hyde 3 in the presence of potassium hydroxide in ethanol at 50 ꢀC for
12 h [17e20]. Trans-stereochemistry of propenone moiety of 4 was
confirmed by coupling constants of vinyl hydrogens (15e16 Hz).
Acetophenones 2 used in the preparation of 4 were prepared by the
partial alkylation of 2, 6-dihydroxyacetophenone [17]. Most benzal-
dehydes 3 used in the preparation of 4 are commercially available.
The 4-formyl benzenesulfonamide used for the preparation of 4b by
van Es's procedure [21]. The catalytic hydrogenation of 4 gave the
intermediates 5 [20]. The cyclization of 5 to the desired compound 6
3. Pharmacology
Inhibitory activity of the chromone analogs against IL-5 was
evaluated using the IL-5-dependent pro-B Y16 cell line according to
the known procedure [15]. The cells were incubated with 3 units/mL
mIL-5 for 48 h, in the presence or absence of sample, and then
measured cell metabolism as an index of proliferation, using
Table 1
Substituents and inhibitory activity of chromone analogs against interleukin-5.
Compd.
R
R1
Inhibition at IC50
30 M [%]
[m
M]b
m
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
8a
8b
9a
9b
Cyclohexylmethyl OH
Cyclohexylmethyl SO2NH2
Cyclohexylmethyl COOH
98
31
77
73
36
35
56
86
45
36
47
85
84
56
45
43
43
33
3.0
>30
12.3
11.4
>30
>30
22.9
14.8
>30
>30
>30
12.5
7.6
21.6
R
O
O
OH
O
O
Isobutyl
Isopentyl
COOH
OH
a
CH3
CH3
H
R-Br
R1
Isopentyl
Cyclohexylmethyl
CH3
H
OH
OH
3
2
Cyclohexylmethyl CH3
Cyclohexylmethyl C2H5
Cyclohexylmethyl Cl
Cyclohexylmethyl CF3
Cyclohexylmethyl 3,4,5-OCH3
Cyclohexylmethyl CH2OH
b
R
R
O
O
O
O
c
R1
R1
Isobutyl
Cyclohexylmethyl CH2Cl
Isobutyl CH2Cl
Cyclohexylmethyl COOH
Isobutyl COOH
CH2OH
OH
OH
>30
4
5
>30
>30
>30
>30
>30
>30
>30
d
10a
10b
11a
11b
12a
12b
Sophoricoside
(1a)
Budesonide
R
O
O
Cyclohexylmethyl CH2CH2COOH <10
Isobutyl CH2CH2COOH <10
Cyclohexylmethyl C(]N) OH
Isobutyl C(]N) OH
<10
<10
R1
O
93.8a
10.3
6
70.3a
26.2
Fig. 1. Synthesis of chromone analogs. (a) CH3CN, aqueous 95% KOH, reflux, overnight,
(b) KOH/90% ethanol, overnight reflux, (c) H2-Pd/methanol, 20e30 psi, h,
(d) BF3eEt2O, CH3SO2Cl, DMF, 2 h reflux. Note ¼ substitutions are located in Table 1.
a
2
Inhibition at 50
m
M.
b
IC50 is taken as a mean value from 3 independent experiments.

P. Thanigaimalai et al. / European Journal of Medicinal Chemistry 45 (2010) 2531e2536
2533
R
Compound 6h (86% inhibition at 30
m
M, IC50 ¼ 14.8
m
M) with
R
R
O
O
O
O
O
O
O
a cyclohexylmethoxy group on ring A and a methyl group on ring B
showed greater activity than 6g (56% inhibition at 30 M,
IC50 ¼ 22.9 M) without methyl group. Based on these finding, we
increased the hydrophobicity of this positionwith ethyl group shown
in 6i(45% inhibition at 30 M, IC50 > 30 M), chloro group shownin 6j
(36% inhibition at 30 M) and trifluoromethyl shown in
M, IC50 ¼ 48
6k (47% inhibition at 30 M) to get the more insight of
Cl
CH3
OH
m
OH
c
m
O
8
9
2
m
m
m
m
b
a
m
M, IC50 ¼ 36.2
m
structureeactivity relationship. However, these changes were not
R
R
O
O
O
much encouraging on activity.
O
O
O
O
Compound 6a and 6l (85% inhibition at 30
showed better activity than trifluoromethyl analog 6k (47% inhibi-
tion at 30 M) and 6b. Since the hydroxyl and
mM, IC50 ¼ 12.3
mM)
d
OH
H
O
10
mM, IC50 ¼ 36.2
m
methoxy groups are highly electron donating to phenyl ring as
compared to trifluoromethyl or sulfonamide groups, the high elec-
tron density at B ring would be important for binding to the
receptor.
7
O
O
e
O
O
R
f
O
O
O
O
R
O
O
To get more detail about the importance of ring B we have also
synthesized some chromone derivatives 8e12 without phenyl ring.
On introduction of hydroxylmethyl group at chromone ring with
cyclohexylmethoxy group at 5th position on ring A as shown in 8a
OH
N
OH
O
11
12
(85% inhibition at 30
moderate in comparison to 6a. Similarly the chloromethyl
substituted analog 9a (45% inhibition at 30 M, IC50 > 30 M), acid
derivatives 10a (43% inhibition at 30 M, IC50 > 30 M) and 11a
M) and oxime derivative 12a
M) did not contribute much
m
M, IC50 ¼ 7.6
mM) the activity becomes
Fig. 2. Preparation of aliphatic substituted chromone analogs. (a) POCl3, DMF,
overnight, rt; (b) Alumina (Basic), IPA, reflux, 4 h; (c) SO2Cl2, reflux, 2 h; (d) Jone's
reagent, 0 ꢀC, 1 h; (e) TEA: HCOOH 1/1 reflux, 2 h; (f) NH2OH, ethanol, rt 1 h.
Note ¼ substitutions are located in Table 1.
m
m
m
m
m
m
(<10% inhibition at 30
(<10% inhibition at 30
mM, IC50 > 30
mM, IC50 > 30
2-(4-iodophenyl)-3-(nitrophenyl)-5-(2,4-disulphophenyl)-2H tetra-
zolium sodium salt (WST-1). Effect on the IL-5 bioassay by each test
compound is represented as inhibition % at 30 mM samples and also
IC50 values (Table 1). Data were collected from three independent
experiments.
on enhancing the activity.
Further, on replacing cyclohexylmethyl group with isobutyl on
ring A, compound 8b (56% inhibition at 30 M) and
mM, IC50 ¼ 21.6
m
chloromethyl substituted analog 9b. The extended side chain of 11b
and the oxime derivatives 12b dose not turn up with any inhibition
against IL-5 activity. These findings further strengthen our view
point regarding the importance of ring B with an electron donating
group at 4th position is critical for the activity.
4. Results and discussion
As we have reported earlier [17] that the isoflavones (1c, 1d) with
4-hydroxyl on the ring B and benzyloxy (or cyclohexylmethoxy)
group on the ring A plays an important role in modulating inhibitory
activity of IL-5 [18]. To further confirm the role of ring B of isoflavone
for their inhibitory activity, we synthesized a series of chromone
analogs.
5. Conclusion
It can be concluded from the whole study that the structural
requirements of chromone analogs possessing their inhibitory
activity against IL-5 could be summarized as:
The analogs 6a (98% inhibition at 30
(84% inhibition at 30 M) had much better activity
M, IC50 ¼ 7.6
than others. The level of activity of 6a is comparable to that of 1d
(91.7% inhibition at 50 M) [18]. This indicate that
ring B of isoflavone analog [18] needs a strong electron donating
group with hydrogen acceptor property and is not necessary to
attach directly on chromone ring.
Since the hydroxyl group at 4th position of ring B showed good
activity as shown in 6a, the larger hydrogen bond acceptor such as
eSO2NH2 or carboxylic acid on ring B was introduced in 6b
mM, IC50 < 3.0 mM) and 8a
m
m
(1) Importance of hydrophobic group such as cyclohexylmethoxy
at 5th position of ring A,
m
M, IC50 ¼ 5.8
m
(2) Requirement of ring B with small size of hydrogen bonding
group such as phenolic hydroxyl group at 4th position,
(3) Planarity of the chromen-4-one ring. Further, the introduction
of a methylene unit between chromone ring and ring B did not
show much beneficial effect on activity. However, the intro-
duction of aliphatic groups on chromone ring in place of phenyl
ring (B ring) decreases the overall activity.
(31% inhibition at 30
m
M, IC50 > 30
m
M), 6c (77% inhibition at 30
M, IC50 ¼ 11.4
m
M,
IC50 ¼ 12.3 M) and 6d (73% inhibition at 30
m
m
mM).
Surprisingly, they showed the less activity compared to 6a. This
implies that the small size of hydrogen bonding group like hydroxyl
at this position might be important factor in the activity.
6. Materials and methods
6.1. Chemistry
In addition to that, the cyclohexylmethoxy group at 5th position
on ring A of 6a and 8a plays an important role to increase the
hydrophobicityand cell permeability for the enhancement of activity.
The smaller alkoxy group such as isopentyl decreases the activity as
Melting points (m.p.) were determined on Electro thermal 1A
9100 MK2 apparatus and are uncorrected. All commercial chemicals
were used as obtained and all solvents were purified by the standard
procedures prior to use [28]. Thin layer chromatography was per-
formed on E Merck silica gel GF-254 precoated plates and the iden-
tification was done with UV light and colorization with spray 10%
phosphomolybdic acid followed by heating. Flash column chroma-
tography was performed with E Merck silica gel (230e400 mesh).
shown in compounds 6e (36% inhibition at 30
m
M, IC50 ¼ 38
mM) and
6f (35%inhibition at 30 M, IC50 > 30 M) compared to 6a. Thus the
m
m
optimum alkoxy group at this position of 6 or 8 such as cyclo-
hexylmethoxy group should be important as was in isoflavone
analogs [18]

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P. Thanigaimalai et al. / European Journal of Medicinal Chemistry 45 (2010) 2531e2536
Infra red spectrum was recorded by using sample (neat sample
without solvent or KBr) as such on FT-IR spectrum with Nicolete380
models. NMR spectra were measured against the peak of tetrame-
thylsilane by JEOL JNM-EX90 NMR (89.45 MHz) and Varain Unity
Inova 400 NMR (400 MHz) spectrometers. Elemental analyses were
performed using an EA1110 elemental analyzer (CE Instrument).
(d, J ¼ 8.8 Hz, 2H), 7.43 (s, 1H), 7.49 (t, J ¼ 8.8 Hz, 1H). Anal. Calc. for
C21H22O4: C, 74.54; H, 6.55. Found: C, 74.49; H, 6.47.
6.1.2.6. 5-(Isopentyloxy)-3-(4-methylbenzyl)-4H-chromen-4-one (6f).
Yield 40%; Yellow solid; m.p. 65e67 ꢀC; Rf ¼ 0.45 (Ethyl acetate:
hexane ¼ 1:1); IR (cmꢁ1): 2848, 1647, 1620, 1464; 1H NMR (CDCl3)
d
0.99 (d, J ¼ 6.4 Hz, 6H), 1.86 (t, J ¼ 7.2 Hz, 2H), 1.92e1.97 (m, 1H),
6.1.1. Procedures for the preparation of compounds 2(aec), 4 (ael)
and 5 (ael)
The synthetic procedures for all compounds 2(aec), 4 (ael) and
5 (ael) are followed according to the same procedures as described
previously [17e20].
3.73 (s, 2H), 4.11 (t, J ¼ 7.2 Hz, 2H), 6.78 (d, J ¼ 8.4 Hz, 1H), 6.91
(d, J ¼ 8.0 Hz,1H), 7.11 (d, J ¼ 8.4 Hz, 2H), 7.16 (d, J ¼ 8.0 Hz, 2H), 7.31
(s, 1H), 7.47 (t, J ¼ 8.4 Hz, 1H). Anal. Calc. for C22H24O3: C, 78.54; H,
7.19. Found: C, 78.49; H, 7.12.
6.1.2.7. 3-Benzyl-5-(cyclohexylmethoxy)-4H-chromen-4-one (6g).
Yield 60%; Yellow solid; m.p. 93e95 ꢀC; Rf ¼ 0.42 (Ethyl acetate:
hexane ¼ 2:3); IR (cmꢁ1): 2910, 2848, 1655, 1628; 1H NMR
6.1.2. General synthetic procedure for the compounds 6 (ael)
Boron trifluoride etherate (4 equiv) was added drop wise to
a compound 5, 0.7 g (0.001 mol) in anhydrous DMF (20 mL) under
nitrogen at room temperature. The solution was stirred for 10 min
before the drop wise addition of CH3SO2Cl (3 equiv). The resulting
solution was warmed to 80 ꢀC and stirred for 2 h. The reaction was
cooled to room temperature before H2O (25 mL) was added. The
combined organic extracts were washed with saturated aqueous
NaCl, dried over Na2SO4, filtered, and evaporated under reduced
pressure. The residue was purified by column chromatography to
afford desired compounds.
(CDCl3)
d
1.09e2.05 (m, 11H), 3.79 (s, 1H), 3.87 (d, J ¼ 6.0 Hz, 2H),
6.76 (d, J ¼ 8.0 Hz, 1H), 6.91 (d, J ¼ 8.8 Hz, 1H), 7.20e7.33 (m, 6H),
7.46 (t, J ¼ 8.4 Hz, 1H). Anal. Calc. for C23H24O3: C, 79.28: H, 6.94.
Found: C, 79.19; H, 6.88.
6.1.2.8. 5-(Cyclohexylmethoxy)-3-(4-methylbenzyl)-4H-chromen-4-
one (6h). Yield 50%; Yellow solid; m.p. 80e82 ꢀC; Rf ¼ 0.48 (Ethyl
acetate:hexane ¼ 2:3); IR (cmꢁ1): 2912, 2854, 1658, 1615; 1H NMR
(CDCl3)
d 1.05e1.30 (m, 5H), 1,56 (s, 3H), 1.72e1.85 (m, 6H), 3.73
(s, 2H), 3.85 (d, J ¼ 5.6 Hz, 2H), 6.37 (d, J ¼ 8.4 Hz, 1H), 6.49
(d, J ¼ 8.8 Hz, 2H), 6.55 (d, J ¼ 8.4 Hz, 1H), 7.10 (s, 1H), 7.18
(t, J ¼ 8.4 Hz, 1H), 7.32 (d, J ¼ 8.4 Hz). Anal. Calc. for C24H26O3: C,
79.53; H, 7.23. Found: C, 79.44; H, 7.15.
6.1.2.1. 5-(Cyclohexylmethoxy)-3-(4-hydroxybenzyl)-4H-chromen-4-
one (6a). Yield 40%; Yellow solid; m.p. 88e90 ꢀC; Rf ¼ 0.39 (Ethyl
acetate:hexane ¼ 2:3); IR (cmꢁ1): 2905, 2848, 1655, 1628; 1H NMR
(CDCl3)
d
1.06e2.04 (m, 11H), 3.70 (s, 2H), 3.86 (d, J ¼ 6.0 Hz, 2H),
5.72 (s, 1H), 6.73 (d, J ¼ 8.4 Hz, 2H), 6.75 (d, J ¼ 8.4 Hz, 1H), 6.92 (d,
J ¼ 8.4 Hz, 1H), 7.08 (d, J ¼ 8.4 Hz, 2H), 7.36 (s, 1H), 7.47 (t, J ¼ 8.4 Hz,
1H). Anal. Calc. for C23H24O4: C, 75.80; H, 6.64. Found: C, 75.65; H,
6.58.
6.1.2.9. 5-(Cyclohexylmethoxy)-3-(4-ethylbenzyl)-4H-chromen-4-one
(6i). Yield 51%; Colorless solid; m.p. 88e89ꢀ C; Rf ¼ 0.55 (Ethyl
acetate:hexane ¼ 1:4); IR (cmꢁ1): 2920, 2852, 1747, 1645; 1H NMR
(CDCl3)
d
1.095 (t, J ¼ 3.4 Hz, 3H), 1.17e2.0 (m, 1H), 2.62
(q, J ¼ 7.6 Hz, 2H), 3.76 (s, 2H), 3.87 (d, J ¼ 6.4 Hz, 2H), 6.75
(d, J ¼ 8.0 Hz, 1H), 6.90 (d, J ¼ 8.8 Hz, 1H), 7.12e1.24 (m, 4H), 7.28
(d, J ¼ 8.0 Hz, 1H), 7.47 (t, J ¼ 8.4 Hz, 1H). Anal. Calc. for C25H28O3: C,
79.75; H, 7.50. Found: C, 79.60; H, 7.42.
6.1.2.2. 4-((5-(Cyclohexylmethoxy)-4-oxo-4H-chromen-3-yl)methyl)
benzene sulfonamide (6b). Yield 56%; Colorless solid; m.p.
190e191 ꢀC; Rf ¼ 0.10 (Ethyl acetate:hexane ¼ 1:1); IR (cmꢁ1):
2900, 2852, 1650, 1620; 1H NMR (CDCl3)
d 1.07e2.04 (m, 11H), 3.12
(s, 2H), 3.87 (d, J ¼ 6.0 Hz, 2H), 6.71 (d, J ¼ 8.0 Hz, 1H), 6.93 (d,
J ¼ 8.4 Hz,1H), 7.32 (d, J ¼ 8.4 Hz, 2H), 7.40 (s, 2H), 7.48 (t, J ¼ 8.4 Hz,
1H), 7.82 (d, J ¼ 6.8 Hz, 2H), 8.10 (s, 1H). Anal. Calc. for C23H25NO5S:
C, 64.62; H, 5.89. Found: C, 64.55; H, 5.81.
6.1.2.10. 3-(4-Chlorobenzyl)-5-(cyclohexylmethoxy)-4H-chromen-4-
one (6j). Yield 40%; Yellow solid; m.p. 70e72 ꢀC; Rf ¼ 0.29 (Ethyl
acetate:hexane ¼ 1:4); IR (cmꢁ1): 2895, 2832, 1630, 1610; 1H NMR
(CDCl3)
d
1.02e1.74 (m, 11H), 3.49 (s, 2H), 3.81 (d, J ¼ 5.6 Hz, 2H),
6.35 (d, J ¼ 8.4 Hz, 1H), 6.56 (d, J ¼ 8.4 Hz, 1H), 7.15 (d, J ¼ 8.4 Hz,
2H), 7.22 (s, 1H), 7.26 (d, J ¼ 8.4 Hz, 2H), 7.31 (t, J ¼ 8.4 Hz, 1H). Anal.
Calc. for C23H23ClO3: C, 72.15; H, 6.05. Found: C, 72.05; H, 5.94.
6.1.2.3. 4-((5-(Cyclohexylmethoxy)-4-oxo-4H-chromen-3-yl)methyl)
benzoic acid (6c). Yield 60%; Colorless solid; m.p. 149e151 ꢀC;
Rf ¼ 0.12 (Ethyl acetate:hexane ¼ 1:1); IR (cmꢁ1): 2921, 2848, 1647,
1620; 1H NMR (CDCl3)
d
1.07e1.89 (m, 11H), 3.66 (s, 2H), 3.82
6.1.2.11. 5-(Cyclohexylmethoxy)-3-(4-(trifluoromethyl)benzyl)-
4H-chromen-4-one (6k). Yield 55%; Yellow solid; m.p. 90e91 ꢀC;
Rf ¼ 0.42 (Ethyl acetate:hexane ¼ 1:4); IR (cmꢁ1): 2926, 2853,1650;
(d, J ¼ 6.0 Hz, 2H), 6.92 (d, J ¼ 8.4 Hz, 1H), 7.05 (d, J ¼ 8.4 Hz, 1H),
7.29 (s, 4H), 7.59 (t, J ¼ 8.4 Hz, 1H), 8.13 (s, 1H). Anal. Calc. for
C24H24O5: C, 73.45; H, 6.16. Found C, 73.38; H, 6.10.
1H NMR (CDCl3)
d
1.05e2.17 (m,11H), 3.84 (s,1H), 3.87 (d, J ¼ 6.4 Hz,
2H), 6.71 (d, J ¼ 8.0 Hz, 1H), 6.93 (d, J ¼ 8.4 Hz, 1H), 7.40
(d, J ¼ 8.0 Hz, 3H), 7.48 (t, J ¼ 8.0 Hz, 1H), 7.56 (d, J ¼ 8.4 Hz, 2H).
Anal. Calc. for C24H23F3O3: C, 69.22; H, 5.57. Found: C, 69.13; H, 5.48.
6.1.2.4. 4-((5-Isobutoxy-4-oxo-4H-chromen-3-yl)methyl)benzoic acid
(6d). Yield 60%; Colorless solid; m.p. 91e92 ꢀC; Rf ¼ 0.08 (Ethyl
acetate:hexane ¼ 1:1); IR (cmꢁ1): 2959, 2873, 1747, 1716, 1646,
1570; 1H NMR (CDCl3)
d
1.03 (d, 6H), 2.06 (m, 1H), 3.79 (s, 2H), 3.99
6.1.2.12. 5-(Cyclohexylmethoxy)-3-(3,4,5-trimethoxybenzyl)-4H-chro-
men-4-one (6l). Yield 55%; Yellow solid; m.p. 108e110 ꢀC; Rf ¼ 0.73
(Ethyl acetate:hexane ¼ 1:1); IR (cmꢁ1): 2920, 2850, 1645, 1602,
(d, J ¼ 5.6 Hz, 2H), 6.80 (d, J ¼ 8.4 Hz, 1H), 7.06 (d, J ¼ 7.6 Hz, 1H),
7.29 (m, 4H), 7.59 (t, J ¼ 8.4 Hz, 1H), 8.15 (s, 1H). Anal. Calc. for
C21H20O5: C, 71.58; H, 5.72. Found: C, 71.46; H, 5.65.
1505; 1H NMR (CDCl3):
d 1.08e2.04 (m, 11H), 3.72 (s, 2H), 3.85
(m, 9H), 3.81 (d, J ¼ 6.0 Hz, 2H), 6.52 (s, 2H), 6.71 (d, J ¼ 8.0 Hz, 1H),
6.95 (d, J ¼ 8.4 Hz,1H), 7.31 (s,1H), 7.50 (t, J ¼ 8.4 Hz,1H),13.0 (s,1H).
Anal. Calc. for C26H30O6: C, 71.21; H, 6.90. Found: C, 71.15; H, 6.81.
6.1.2.5. 3-(4-Hydroxybenzyl)-5-(isopentyloxy)-4H-chromen-4-one
(6e). Yield 30%; Yellow solid; m.p. 85e87 ꢀC; Rf ¼ 0.40 (Ethyl
acetate:hexane ¼ 1:1); IR (cmꢁ1): 2960, 2850, 1700, 1619, 1527; 1H
NMR (CDCl3)
d
0.94 (d, J ¼ 6.4 Hz, 6H), 1.82 (t, J ¼ 6.8 Hz, 2H),
6.1.3. General procedure for the preparation of 7(aeb)
1.85e1.90 (m, 1H), 3.66 (s, 2H), 4.11 (t, J ¼ 6.8 Hz), 6.73 (d, J ¼ 8.8 Hz,
To a mono-protected ketone 2a or 2b in 50 mL DMF (1 mol) was
2H), 6.81 (d, J ¼ 8.8 Hz, 1H), 6.94 (d, J ¼ 8.8 Hz, 1H), 7.09
added drop wise POCl3 (6 mol) for 15 min at 0 ꢀC. After addition was

P. Thanigaimalai et al. / European Journal of Medicinal Chemistry 45 (2010) 2531e2536
2535
completed, the reaction was allowed to stand at room temperature
for overnight. Reaction mixture was quenched with water and
extracted with ethyl acetate. The resulting organic layer was
washed with brine, dried over Na2SO4 and concentrated under
reduced pressure to give a pure compound.
hexane ¼ 1:1); IR (cmꢁ1): 3350, 2955, 2851, 1729, 1645; 1H NMR
(CDCl3)
d
1.11 (d, J ¼ 7.2 Hz, 6H), 2.21 (m,1H), 3.85 (d, J ¼ 6.4 Hz, 2H),
4.49 (d, J ¼ 6.8 Hz, 2H), 6.74 (d, J ¼ 8.4 Hz, 1H), 6.91 (d, J ¼ 8.4 Hz,
1H), 7.51 (t, J ¼ 8.0 Hz, 1H), 7.77 (s, 1H). Anal. Calc. for C14H15ClO3: C,
63.04; H, 5.67. Found: C, 62.91; H, 5.58.
6.1.3.1. 5-(Cyclohexylmethoxy)-4-oxo-4H-chromene-3-carbaldehyde
(7a). Yield 85%; Yellow solid; m.p. 133e134 ꢀC; Rf ¼ 0.54 (Ethyl
acetate:hexane ¼ 1:1); IR (cmꢁ1): 2923, 2853, 1696, 1653; 1H NMR
6.1.6. General procedure for the preparation of 10(aeb)
To the solution of 4-oxo-benzopyran-3-carboxaldehyde 7a or 7b
(0.1 mol) in methylenechloride was added jone's reagent at 0 ꢀC. After
addition was completed, the reaction mixture was allowed to stir at
room temperature for 2 h. It was poured in to water and extracted
with methylenechloride. The resulting mixture was washed with
brine, dried over Na2SO4 and concentrated to give an acid, which was
purified by column chromatography.
(CDCl3)
d
1.09e2.03 (m, 11H), 3.91 (d, J ¼ 6.4 Hz, 2H), 6.82
(d, J ¼ 8.4 Hz, 1H), 7.01 (d, J ¼ 7.6 Hz, 1H), 7.55 (t, J ¼ 8.0 Hz,1H), 8.37
(s, 1H), 10.36 (s, 1H). Anal. Calc. for C17H18O4: C, 71.31; H, 6.34.
Found: C, 71.26; H, 6.28.
6.1.3.2. 5-Isobutoxy-4-oxo-4H-chromene-3-carbaldehyde (7b). Yield
78%; Yellow solid; m.p. 97e98 ꢀC; Rf ¼ 0.14 (Ethyl acetate:
hexane ¼ 1:9); IR (cmꢁ1): 2954, 2864, 1696, 1662, 1566; 1H NMR
6.1.6.1. 5-(Cyclohexylmethoxy)-4-oxo-4H-chromene-3-carboxylic acid
(10a). Yield 80%; Yellow solid; m.p. 166e167 ꢀC; Rf
¼
0.5
(100% Ethyl acetate); IR (cmꢁ1): 3373, 2924, 2860, 1728, 1649; 1H
NMR (CDCl3)
(CDCl3)
d
1.13 (s, 6H), 2.23 (m, 1H), 3.85 (d, J ¼ 5.8 Hz, 2H), 6.87
(d, J ¼ 8.0 Hz, 1H), 7.04 (d, J ¼ 8.4 Hz, 1H), 7.57 (t, J ¼ 8.4 Hz, 1H), 8.37
(s, 1H), 10.3 (s, 1H). Anal. Calc. for C14H14O4: C, 68.28; H, 5.73. Found:
C, 68.21; H, 5.66.
d
1.13e2.17 (m, 11H), 3.92 (d, J ¼ 6.0 Hz, 2H), 6.91
(d, J ¼ 8.4 Hz, 1H), 7.12 (d, J ¼ 8.0 Hz, 1H), 7.66 (t, J ¼ 8.4 Hz, 1H).
Anal. Calc. for C17H18O5: C, 67.54; H, 6.00. Found: C, 67.40; H,
5.88.
6.1.4. General procedure for the preparation of 8 (aeb)
About 2 g of basic alumina and about 100 mg of the corre-
sponding formylchromone 7a or 7b (5% of alumina weight), dis-
solved in 50 mL of isopropanol were placed in a round-bottom flask
containing a magnetic bar, the mixture was stirred for 4 h at 75 ꢀC.
The mixture was filtered by vacuum filtration through celite, and
evaporation of solvent to give crude alcohol. This may be purified by
column chromatography using 15% ethyl acetate in hexane.
6.1.6.2. 5-Isobutoxy-4-oxo-4H-chromene-3-carboxylic acid (10b).
Yield: 81%; Colorless solid; m.p. 115e117 ꢀC; Rf ¼ 0.27 (100%
Ethylacete); IR (cmꢁ1): 2964, 2854, 1728, 1624; 1H NMR (CDCl3)
d
1.09 (d, 6H), 2.24 (m, 1H), 3.91 (d, J ¼ 6.4 Hz, 2H), 6.91
(d, J ¼ 8.4 Hz, 1H), 7.13 (d, J ¼ 7.6 Hz, 1H), 7.69 (t, J ¼ 8.4 Hz, 1H),
8.86 (s, 1H), 14.0 (s, 1H). Anal. Calc. for C14H14O5: C, 64.12; H, 5.38.
Found: C, 64.00; H, 5.27.
6.1.4.1. 5-(Cyclohexylmethoxy)-3-(hydroxymethyl)-4H-chromen-4-
one (8a). Yield 87%; Colorless solid; m.p. 84e86 ꢀC; Rf ¼ 0.55 (Ethyl
acetate:hexane ¼ 6:4); IR (cmꢁ1): 3402, 3363, 2924, 2859, 1726,
6.1.7. General procedure for the preparation of 11 (aeb)
A mixture of 4-oxo-benzopyran-3-carboxaldehyde 7a or 7a
(0.1 mol), meldrum's acid (0.1 mol) and triethylamine formic acid
(1:1) 50 mL was refluxed at 95e100 ꢀC for 2e3 h, until the disap-
pearance of starting material. It was cooled to room temperature
and poured into ice water. The mixture was acidified to pH 2 with
6 N HCl. The pale yellow solid was filtered washed with water and
purified by column chromatography.
1650; 1H NMR (CDCl3)
d
1.09e2.17 (m.11H), 3.87 (d, J ¼ 6.0 Hz, 2H),
4.51 (d, J ¼ 4.4 Hz, 2H), 6.80 (d, J ¼ 8.0 Hz, 1H), 6.98 (d, J ¼ 8.4 Hz,
1H), 7.51 (t, J ¼ 8.4 Hz, 1H), 7.76 (s, 1H). Anal. Calc. for C17H20O4: C,
70.81; H, 6.99. Found: C, 70.72; H, 6.85.
6.1.4.2. 3-(Hydroxymethyl)-5-isobutoxy-4H-chromen-4-one (8b).
>Yield 85%; Colorless solid; m.p. 99e101 ꢀC; Rf ¼ 0.52 (100% Ethyl
acetate); IR (cmꢁ1): 3354, 2953, 2861, 1726, 1649; 1H NMR
6.1.7.1. 3-(5-(Cyclohexylmethoxy)-4-oxo-4H-chromen-3-yl)propanoic
acid (11a). Yield 64%; Colorless solid; m.p. 155e157 ꢀC; Rf ¼ 0.26
(100% Ethyl acetate); IR(cmꢁ1): 3401, 2922, 2853, 1699, 1647; 1H
(CDCl3)
d
1.11 (d, J ¼ 7.2 Hz, 6H), 2.25 (m, 1H), 3.86 (d, J ¼ 6.0 Hz,
2H), 4.51 (d, J ¼ 6.8 Hz, 2H), 6.75 (d, J ¼ 8.4 Hz, 1H), 6.90
(d, J ¼ 8.4 Hz, 1H), 7.52 (t, J ¼ 8.4 Hz, 1H), 7.77 (s, 1H). Anal. Calc.
for C14H16O4: C, 67.73; H, 6.50. Found: C, 67.64; H, 6.41.
NMR (CDCl3)
d
1.05e2.04 (m, 11H), 2.78 (s, 4H), 3.87 (d, J ¼ 6.4 Hz,
2H), 6.76 (d, J ¼ 8.0 Hz,1H), 6.94 (d, J ¼ 8.0 Hz,1H), 7.48 (t, J ¼ 8.4 Hz,
1H), 7.73 (s, 1H). Anal. Calc. for C19H22O5: C, 69.07; H, 6.71. Found: C,
68.89; H, 6.58.
6.1.5. General procedure for the preparation of 9 (aeb)
Thionylchloride 2 mL was added drop wise to 3-hydroxy methyl
derivative 8a or 8b (100 mg) in methylenechloride solution. After the
solution was stirred at 35 ꢀC for 2 h, reaction mixture was quenched
by ice water and extracted with methylenechloride. A resulting
organic layer was dried over Na2SO4 and concentrated to give
a crude compound which was purified by column chromatography.
6.1.7.2. 3-(5-Isobutoxy-4-oxo-4H-chromen-3-yl)propanoic acid
(11b). Yield 65%; Colorless solid; m.p. 123e125 ꢀC; Rf ¼ 0.26
(100% Ethyl acetate); IR(cmꢁ1): 3401, 2954, 2855, 1707, 1642; 1H
NMR (CDCl3):
d
1.14 (d, J ¼ 7.2 Hz, 6H), 2.23 (m, 1H), 2.72 (s, 4H),
3.84 (d, J ¼ 5.8 Hz, 2H), 6.77 (d, J ¼ 8.4 Hz, 1H), 6.96
(d, J ¼ 8.4 Hz, 1H), 7.47 (t, J ¼ 8.4 Hz, 1H), 7.74 (s, 1H), 8.16
(s, 1H). Anal. Calc. for C16H18O5: C, 66.19; H, 6.25. Found: C,
66.08; H, 6.15.
6.1.5.1. 3-(Chloromethyl)-5-(cyclohexylmethoxy)-4H-chromen-4-one
(9a). Yield 60%; Colorless solid; m.p. 130e131 ꢀC; Rf ¼ 0.75 (Ethyl
acetate:hexane ¼ 1:1); IR (cmꢁ1): 3354, 2950, 2852, 1727, 1651; 1H
6.1.8. General procedure for the preparation of 12 (aeb)
NMR (CDCl3)
d
1.08e2.03 (m, 11H), 3.87 (d, J ¼ 6.0 Hz, 2H), 4.50
To a well stirred solution of 4-oxo-benzopyran-3-carbox-
(s, 2H), 6.78 (d, J ¼ 8.4 Hz, 1H), 6.98 (d, J ¼ 8.4 Hz, 1H), 7.51
(t, J ¼ 8.0 Hz), 7.9 (s,1H). Anal. Calc. for C17H19ClO3: C, 66.56; H, 6.24.
Found: C, 66.40; H, 6.15.
aldehyde 7a or 7b (0.1 mol) in ethanol (30 mL), hydroxylamine
hydrochloride (0.1 mol) was added. The solution was stirred
vigorously for 1 h. Mixture was concentrated, extracted with ethyl
acetate, washed with brine, dried, and evaporated the solvent to
give corresponding oxime derivatives. A pure compound was
obtained by flash column chromatography.
6.1.5.2. 3-(Chloromethyl)-5-isobutoxy-4H-chromen-4-one (9b). Yield
65%; Colorless solid; m.p. 139e141 ꢀC; Rf ¼ 0.55 (Ethyl acetate:

2536
P. Thanigaimalai et al. / European Journal of Medicinal Chemistry 45 (2010) 2531e2536
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6.1.8.1. (E)-5-(Cyclohexylmethoxy)-4-oxo-4H-chromene-3-carbalde-
hyde oxime (12a). Yield 73%; Yellow solid; m.p. 164e165 ꢀC;
Rf ¼ 0.59 (Ethyl acetate:hexane ¼ 1:1); IR (cmꢁ1): 2923, 2855, 1712,
1651; 1H NMR (CDCl3)
d
1.09e2.02 (m, 11H), 3.88 (d, J ¼ 5.6 Hz, 2H),
6.79 (d, J ¼ 8.0 Hz, 1H), 6.99 (d, J ¼ 8.4 Hz, 1H), 7.87 (s, 1H), 8.19
(s, 1H), 9.25 (s, 1H). Anal. Calc. for C17H19NO4: C, 67.76; H, 6.36.
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6.1.8.2. (E)-5-Isobutoxy-4-oxo-4H-chromene-3-carbaldehyde oxime
(12b). Yield 69%; Yellow solid; m.p. 139e140 ꢀC; Rf ¼ 0.76 (Ethyl
acetate:hexane ¼ 4:1); IR (cmꢁ1): 3293, 2926, 2876,1641, 1607; 1H
NMR (CDCl3)
d
1.13 (d, J ¼ 6.4 Hz, 6H), 2.26 (m, 1H), 3.84
(d, J ¼ 6.0 Hz, 2H), 6.81 (d, J ¼ 7.6 Hz, 1H), 6.99 (d, J ¼ 8.4 Hz, 1H),
7.52 (t, J ¼ 8.8 Hz, 1H), 7.85 (s, 1H), 8.15 (s, 1H), 9.21 (s, 1H). Anal.
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Acknowledgment
This work was supported by the Korea Research Foundation
funded by Korean Government (MOEHRD) (KRF-2007-313-
E00651).
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