Synthesis and antipicornavirus activity of (R)- and (S)-1-[5-(4′- chlorobiphenyl-4-yloxy)-3-methylpentyl]-3-pyridin-4-yl-imidazolidin-2-one

Article abstract of DOI:10.1016/j.bmcl.2005.06.069

The new pyridyl imidazolidinone derivative, 1-[5-(4′-chlorobiphenyl- 4-yloxy)-3-methylpentyl]-3-pyridin-4-yl-imidazolidin-2-one (±)-1a, was synthesized and found to have an excellent antiviral activity against EV71 (IC₅₀ = 0.009 μM). Therefore, both the enantiomers, (S)-(+)-1a and (R)-(-)-1a, have been prepared starting from readily available monomethyl (R)-3-methylglutarate (7) as a useful chiral building block and their antiviral activity was evaluated in a plaque reduction assay. Interestingly, we observed that the enantiomer (S)-(+)-1a was 10-fold more active against enterovirus71 (EV71) (IC₅₀ = 0.003 μM) than the corresponding enantiomer (R)-(-)-1a (IC₅₀ = 0.033 μM). Similar results were found against all five strains (1743, 2086, 2231, 4643, and BrCr) of EV71 tested. This demonstrated that the absolute configuration of the chiral carbon atom at the 3-position of the alkyl linker considerably influenced the anti-EV71 activity of these pyridyl imidazolidinones.

Full text of DOI:10.1016/j.bmcl.2005.06.069

Bioorganic & Medicinal Chemistry Letters 15 (2005) 4206–4211
Synthesis and antipicornavirus activity of (R)- and
(S)-1-[5-(40-chlorobiphenyl-4-yloxy)-3-methylpentyl]-3-
pyridin-4-yl-imidazolidin-2-one
Jyh-Haur Chern,a,* Chih-Shiang Chang,a Chia-Liang Tai,a Yen-Chun Lee,a
Chung-Chi Lee,a Iou-Jiun Kang,a Ching-Yin Leeb and Shin-Ru Shihb,*
aDivision of Biotechnology and Pharmaceutical Research, National Health Research Institutes, 35 Keyan Road,
Zhunan Town, Miaoli County 350, Taiwan, ROC
bSchool of Medical Technology, Chang Gung University, Taoyuan 333, Taiwan, ROC
Received 31 March 2005; revised 24 June 2005; accepted 27 June 2005
Available online 27 July 2005
Abstract—The new pyridyl imidazolidinone derivative, 1-[5-(40-chlorobiphenyl-4-yloxy)-3-methylpentyl]-3-pyridin-4-yl-imidazoli-
din-2-one ( )-1a, was synthesized and found to have an excellent antiviral activity against EV71 (IC50 = 0.009 lM). Therefore, both
the enantiomers, (S)-(+)-1a and (R)-(ꢀ)-1a, have been prepared starting from readily available monomethyl (R)-3-methylglutarate
(7) as a useful chiral building block and their antiviral activity was evaluated in a plaque reduction assay. Interestingly, we observed
that the enantiomer (S)-(+)-1a was 10-fold more active against enterovirus71 (EV71) (IC50 = 0.003 lM) than the corresponding
enantiomer (R)-(ꢀ)-1a (IC50 = 0.033 lM). Similar results were found against all five strains (1743, 2086, 2231, 4643, and BrCr)
of EV71 tested. This demonstrated that the absolute configuration of the chiral carbon atom at the 3-position of the alkyl linker
considerably influenced the anti-EV71 activity of these pyridyl imidazolidinones.
Ó 2005 Elsevier Ltd. All rights reserved.
1. Introduction
can be lethal and life-threatening, with high risk for
morbidity and mortality. Many epidemic outbreaks
have been reported from Asian countries.5 A major out-
break of EV71 infection in Taiwan in 1998 caused many
severe by infected cases and 78 deaths.6 Currently, there
is no specific antiviral therapy to treat or prevent entero-
virus disease.
Enterovirus 71 (EV71) was first recognized in 1969 in
California, USA, when it was isolated from the feces
of an infant suffering from encephalitis.1 EV71 belongs
to the human Enterovirus A species of the Enterovirus
genus within the family of Picornaviridae.2 Virions con-
sist of a non-enveloped capsid surrounding a core of
single-stranded, positive-polarity RNA approximately
7.5 kb in size. The viral capsid is icosahedral in symme-
try and is composed of 60 identical units each consisting
of the four structural proteins VP1–VP4. The complete
nucleotide sequence of the EV71 prototype strain BrCr
has been determined.3 Symptoms for EV71 infections
range from non-specific upper respiratory infection
and mild fever to central nervous system infections
particularly viral meningitis, encephalitis, and severe
myocarditis.4 Children are considered to be relatively
immunodeficient, therefore EV71 infections of neonates
Pleconaril7 is a typical and systemically acting small-
molecule inhibitor of enteroviruses and rhinoviruses,
but this compound exhibited no activity against
EV71. In our laboratory, many structurally related
pyridyl imidazolidinones were recently found to have
strong activity against EV71.8 Among this series of
compounds synthesized, the pyridyl imidazolidinone
with a tether chain length of five carbons, DBPR103
(Fig. 1), was identified as the most potent enterovirus
71 inhibitor (IC50 = 0.054 lM) with no apparent cyto-
toxic effect toward RD (rhabdomyosarcoma) cell lines
(CC50 > 25 lM).8 Although DBPR103 is a new agent
with potent antiviral activity against EV71, the mech-
anism of action is still unclear. As part of our contin-
uous efforts toward the identification of more potent
anti-EV71 agents, we made a drastic change at the
Keyword: Antipicornavirus.
*
Corresponding authors. Tel.: +886 37 246 166x35716; fax: +886 37
586 456; e-mail: jhchen@nhri.org.tw
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.06.069

J.-H. Chern et al. / Bioorg. Med. Chem. Lett. 15 (2005) 4206–4211
4207
Figure 1. Structures of DBPR103, ( )-1a,b, (S)-(+)-1a, and (R)-(ꢀ)-1a.
3-position of the alkyl linker of DBPR103. However,
the racemic 3-methyl analogue ( )-1a, its correspond-
ing enantiomers, (S)-(+)-1a and (R)-(ꢀ)-1a, and the
3,3-dimethyl analogue 1b (Fig. 1) were successfully
synthesized and assayed for antiviral activity in a
plaque reduction assay.9 It is noteworthy to mention
that the chiral 3-methyl analogue (S)-(+)-1a has
shown significant improvement in potency relative to
the reference compound DBPR103 as well as broad-
spectrum activity against a variety of enterovirus
serotypes. Details of this investigation will be de-
scribed herein.
1-(4-pyridyl)-2-imidazolidinone 2 in the presence of
sodium hydride in DMF to give the target compounds
( )-1a and b (65% and 58% for two steps).
On the other hand, both the enantiomers of pyridyl imi-
dazolidinone, (S)-(+)-1a and (R)-(ꢀ)-1a, have been pre-
pared starting from enantiomerically pure monomethyl
(R)-3-methylglutarate 710 (Schemes 2 and 3). It has been
reported that (R)-7 is a useful chiral building block for
the synthesis of many biologically active compounds.11
In this paper, compound (S)-(+)-1a was prepared stereo-
specifically as shown in Scheme 2. Selective reduction of
monomethyl (R)-3-methylglutarate 7 with borane–disul-
fide followed by tosylation of the resulting hydroxyester
afforded the tosylate 8 (54% for two steps). Subsequent
nucleophilic substitution of 4-chloro-40-hydroxybiphe-
nyl with tosylate 8 in the presence of potassium carbon-
ate in acetonitrile gave compound 9, which was further
reduced with borane–tetrahydrofuran to give the alco-
hol 10 (65% for two steps). Tosylation of the alcohol
10 with p-toluenesulfonyl chloride in pyridine gave the
corresponding tosylate 11 (93%), which was then cou-
pled with 1-(4-pyridyl)-2-imidazolidinone 2 in the pres-
ence of sodium hydride in DMF to give the desired
compound (S)-(+)-1a ([a]D +11.1 (c 0.5, CHCl3)) in
80% yield.
2. Chemistry
Three different routes were employed to prepare the pyr-
idyl imidazolidinones ( )-1a,b, (S)-(+)-1a, and (R)-(ꢀ)-
1a. Compounds ( )-1a and b were synthesized by the
method summarized in Scheme 1. For the preparation
of 1-(4-pyridyl)-2-imidazolidinone 2 (Scheme 1), 4-
aminopyridine was first coupled with 2-chloroethyliso-
cyanate to give the corresponding urea intermediate in
80% yield. Subsequent intramolecular cyclization of
the intermediate by treatment with sodium hydride in
the THF/DMF (1:1) cosolvent system at room tempera-
ture resulted in the formation of cyclic urea 2 in 92%
yield. Reduction of the glutaric acids 3a and b with lith-
ium aluminum hydride in dry THF gave the diols 4a and
b, which were then reacted with p-toluenesulfonyl chlo-
ride in pyridine to give the corresponding ditosylates
5aand b (74 and 71% for two steps). Subsequent nucle-
ophilic substitution of 4-chloro-40-hydroxybiphenyl with
2 equiv of the ditosylates 5a and b using potassium
carbonate as a base at refluxing acetonitrile gave
compounds 6a and b, which were coupled with
For the preparation of the other enantiomer (R)-(ꢀ)-1a, a
different synthetic approach was followed (Scheme 3).
The tosylate 8 was first coupled with 1-(4-pyridyl)-
2-imidazolidinone 2 to give the corresponding pyridyl
imidazolidinone 12 (89%). Subsequent reduction of 12
with borane–tetrahydrofuran in dry ether afforded alco-
hol 13 (73%). Tosylation of 13 with p-toluenesulfonyl
chloride followed by the nucleophilic substitution of the
resulting tosylate 14 with 4-chloro-40-hydroxybiphenyl

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J.-H. Chern et al. / Bioorg. Med. Chem. Lett. 15 (2005) 4206–4211
Scheme 1. Synthesis of pyridyl imidazolidinones ( )-1a and b.
Scheme 2. Synthesis of pyridyl imidazolidinone (S)-(+)-1a.
afforded the desired compound (R)-(ꢀ)-1a ([a]D ꢀ10.6 (c
0.5, CHCl3)) in 56% yield. All the new pyridyl imidazolid-
inones gave satisfactory spectral data consistent with
their proposed structures.12
3. Results and discussion
The pyridyl imidazolidinones described herein were
tested in a plaque reduction assay9 under a standard

J.-H. Chern et al. / Bioorg. Med. Chem. Lett. 15 (2005) 4206–4211
4209
Scheme 3. Synthesis of pyridyl imidazolidinone (R)-(ꢀ)-1a.
procedure. Compounds ( )-1a,b, (S)-(+)-1a, and (R)-
(ꢀ)-1a were submitted for anti-EV71 testing as well as
cytotoxicity evaluation in the RD cell lines. The results
are shown in Table 1 and are compared to the reference
compound DBPR103. In this study, DBPR103 showed
inhibitory activity against EV71 with IC50 value of
0.054 lM. We first examined the skeleton of DBPR103
(Table 1). Introduction of a methyl group at the 3-posi-
tion of the alkyl linker (( )-1a vs DBPR103) resulted in
a 6-fold increase in inhibitory activity against EV71
(IC50 = 0.009 lM) with very low cytotoxicity toward
RD cell lines (CC50 > 25 lM). However, when two meth-
yl groups were introduced at the 3-position of the alkyl
linker (1b vs DBPR103), compound 1b showed similar
antiviral activity (IC50 = 0.040 lM) as the unsubstituted
lead compound. This effect might be due to their drasti-
cally conformational change and steric requirement of
the alkyl linker of these pyridyl imidazolidinones. On
the other hand, both the enantiomers of pyridyl imidazo-
lidinone, (S)-(+)-1a and (R)-(ꢀ)-1a, were synthesized and
their anti-EV71 activities were measured (Table 1). Inter-
estingly, we have found that the enantiomer (S)-(+)-1a
was 3-fold more potent (IC50 = 0.003 lM) against EV71
than the racemic compound ( )-1a (IC50 = 0.009 lM).
In contrast, the corresponding enantiomer (R)-(ꢀ)-1a
was considerably less active (IC50 = 0.033 lM). These
significant results demonstrated that the absolute config-
uration of the chiral carbon atom at the 3-position of the
alkyl linker considerably influenced the anti-EV71 activ-
ity of this series of compounds. It was therefore of interest
to explore this potential enantiomerically pure anti-EV71
compound (S)-(+)-1a.
Table 1. Anti-EV71 activity and cytotoxicity for DBPR103, ( )-1a,b, (S)-(+)-1a, and (R)-(ꢀ)-1a
IC50 (lM)a
CC50 (lM)b
e
Compound
R1
R2
Melting point (°C)
[a]D
EV71c
RDd
DBPR103
( )-1a
1b
H
H
167–169
166–167
150–152
166–167
166–167
—
—
0.054 0.010
0.009 0.001
0.040 0.003
0.003 0.001
0.033 0.001
>25
>25
>25
>25
>25
H
CH3
CH3
CH3
H
CH3
H
—
(S)-(+)-1a
(R)-(ꢀ)-1a
+11.1
ꢀ10.6
CH3
a Mean of triplicate well values. All experiments were performed at least twice. Plaque reduction assay was employed.
b Mean of triplicate well values. All experiments were performed at least twice.
c EV71: human enterovirus 71 strain 4643.
d RD: human rhabdomyosarcoma cells.
e (c 0.5, CHCl3).

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J.-H. Chern et al. / Bioorg. Med. Chem. Lett. 15 (2005) 4206–4211
Table 2. Comparative evaluation of DBPR103, (S)-(+)-1a, and (R)-(ꢀ)-1a against various viruses
IC50 (lM)a
DBPR103
(S)-(+)-1a
(R)-(ꢀ)-1a
Enterovirus 71 (1743) B
Enterovirus 71 (2086) C
Enterovirus 71 (2231) C
Enterovirus 71 (4643) C
Enterovirus 71 (BrCr) A
Enterovirus 68
0.092 0.010
0.043 0.013
0.092 0.010
0.054 0.010
0.13 0.01
>25
0.026 0.003
0.008 0.001
0.024 0.002
0.003 0.001
0.033 0.001
>25
0.17 0.01
0.049 0.003
0.16 0.02
0.033 0.001
0.32 0.14
>25
Coxsackievirus A9
Coxsackievirus A10
Coxsackievirus A16
Coxsackievirus A24
Coxsackievirus B1
Coxsackievirus B2
Coxsackievirus B3
Coxsackievirus B4
Coxsackievirus B5
Coxsackievirus B6
Echovirus 9
0.071 0.004
>25
>25
0.019 0.001
1.32 0.03
6.92 6.17
>25
0.15 0.01
>25
>25
1.30 0.94
>25
>25
>25
>25
>25
>25
>25
>25
>25
>25
1.30 0.79
1.14 0.56
>25
1.25 0.03
4.85
2.05 0.12
2.08 0.19
>25
>25
>25
1.31 0.13
0.39 0.06
>25
>25
Echovirus 29
Human rhinovirus 2
Human rhinovirus 14
1.30 0.02
>25
>25
1.47 0.13
>25
>25
>25
a Mean of triplicate well values. All experiments were performed at least twice. Plaque reduction assay was employed.
In addition to screening pyridyl imidazolidinones
against EV71, we examined the broad-spectrum nature
of this chemical platform. Both the enantiomers, (S)-
(+)-1a and (R)-(ꢀ)-1a, were selected for further screen-
ing against a panel of 15 additional viruses that was cho-
sen as representative of the large number of human
enteroviruses and human rhinoviruses. A comparison
of the activity of DBPR103, (S)-(+)-1a, and (R)-(ꢀ)-1a
against 16 serotypes is illustrated in Table 2. These com-
pounds were individually subjected to evaluation against
a variety of viruses, including coxsackieviruses (10 sero-
types), echoviruses (2 serotypes), and human enterovi-
ruses 68 and 71, and human rhinoviruses 2 and 14. As
shown, (S)-(+)-1a was found, in addition to strongly
inhibiting all the genotypes (A, B, and C) of EV71, to
possess antiviral activity against coxsackieviruses A9,
A10, A16, B4, B5, and echovirus 29. However, com-
pound (S)-(+)-1a showed no activity against human rhi-
noviruses 2 and 14 up to the concentration of 25 lM. On
the basis of these significant results, we observed that the
enantiomer (S)-(+)-1a was considerably more active
against the majority of human enterovirus serotypes
tested, in particular, enterovirus 71. We were pleased
to find that compound (S)-(+)-1a exhibited potency
and broad-spectrum activity against most of these virus-
es. Therefore, for our purpose, (S)-(+)-1a is well quali-
fied to serve as a lead compound for the further
development of anti-EV71 agent.
sponding 3,3-dimethyl analogue 1b was less active
(IC50 = 0.040 lM) than ( )-1a. These significant results
demonstrated that the methyl group at the 3-position
of the alkyl linker of pyridyl imidazolidinones seems to
play a very important role in influencing anti-EV71 activ-
ity. However, this unexpected biological result is not ful-
ly understood and is worthy of further study. On the
other hand, both the enantiomers, (S)-(+)-1a and (R)-
(ꢀ)-1a, have been synthesized and then submitted for
anti-EV71 testing as well as cytotoxicity evaluation in
the RD cell lines. In this study, we observed that the
enantiomer (S)-(+)-1a was 10-fold more active against
EV71 (IC50 = 0.003 lM) than the corresponding enan-
tiomer (R)-(ꢀ)-1a (IC50 = 0.033 lM). Similar results
were found against all five strains (1743, 2086, 2231,
4643, and BrCr) of EV71 tested. This demonstrated that
the absolute configuration of the chiral carbon atom at
the 3-position of the alkyl linker considerably influenced
the anti-EV71 activity of these pyridyl imidazolidinones.
Further SAR studies and mechanistic studies on these
new antiviral compounds are currently under active
investigation and will be reported in due course.
Acknowledgment
We are grateful to the National Health Research Insti-
tutes of the Republic of China for their financial
support.
4. Conclusion
References and notes
In summary, the new pyridyl imidazolidinones ( )-1a
andb were first synthesized and their anti-EV71 activity
was evaluated in a plaque reduction assay. It is very
interesting to note that the 3-methyl analogue ( )-1a of
DBPR103 was found to have excellent antiviral activity
against EV71 (IC50 = 0.009 lM). In contrast, the corre-
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12. All the new compounds gave satisfactory spectral data
consistent with their proposed structures. Selected spec-
tral data for compounds 1a and b. Compounds ( )-1a,
(S)-(+)-1a, and (R)-(ꢀ)-1a: white solid; mp 166–167 °C;
IR (CHCl3) mmax 1704, 1591, 1507, 1481, 1423, 830, 815,
746 cmꢀ1
; d 8.41 (d,
1H NMR (300 MHz, CDCl3)
J = 5.7 Hz, 2H), 7.46–7.42 (m, 6H), 7.35 (d, J = 8.4 Hz,
2H), 6.92 (d, J = 8.4 Hz, 2H), 4.06–4.01 (m, 2H), 3.80–
3.75 (m, 2H), 3.54–3.45 (m, 2H), 3.42–3.33 (m, 2H),
1.90–1.60 (m, 4H), 1.48–1.43 (m, 1H), 1.04 (d, J = 6.6 Hz,
3H); ESMS 450.5 (M+1). Anal. Calcd for
C26H28ClN3O2: C, 69.40; H, 6.27; N, 9.34. Found: C,
69.35; H, 6.21; N, 9.30. Compound 1b: white solid; mp
150–152 °C; IR (CHCl3) mmax 1703, 1606, 1594, 1482,
1428, 1392, 1377, 1285, 1252, 817, 747 cmꢀ1 1H NMR
;
(300 MHz, CDCl3) d 8.42 (brs, 2H), 7.46–7.43 (m, 6H),
7.35 (d, J = 8.7 Hz, 2H), 6.94 (d, J = 8.7 Hz, 2H), 4.07 (t,
J = 6.9 Hz, 2H), 3.82–3.76 (m, 2H), 3.56–3.50 (m, 2H),
3.41–3.35 (m, 2H), 1.81 (t, J = 6.9 Hz, 2H), 1.58 (t,
J = 6.9 Hz, 2H), 1.06 (s, 6H); ESMS 464.1 (M+1). Anal.
Calcd for C27H30ClN3O2: C, 69.89; H, 6.52; N, 9.06.
Found: C, 69.81; H, 6.47; N, 8.99.
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