Design, synthesis, and structure-activity relationships of pyrazolo[3,4-d]pyrimidines: A novel class of potent enterovirus inhibitors

Article abstract of DOI:10.1016/j.bmcl.2004.02.092

A series of pyrazolo[3,4-d]pyrimidines were synthesized and their antiviral activity was evaluated in a plaque reduction assay. It is very interesting that this class of compounds provide remarkable evidence that they are very specific for human enteroviruses, in particular, coxsackieviruses. Some derivatives proved to be highly effective in inhibiting enterovirus replication at nanomolar concentrations. SAR studies revealed that the phenyl group at the N-1 position and the hydrophobic diarylmethyl group at the piperazine largely influenced the in vitro antienteroviral activity of this new class of potent antiviral agents. It was found that the pyrazolo[3,4-d]pyrimidines with a thiophene substituent, such as compounds 20-24, in general exhibited high activity against coxsackievirus B3 (IC₅₀=0.063-0.089μM) and moderate activity against enterovirus 71 (IC₅₀=0.32-0.65μM) with no apparent cytotoxic effect toward RD (rhabdomyosarcoma) cell lines (CC₅₀25μ M).

Full text of DOI:10.1016/j.bmcl.2004.02.092

Bioorganic & Medicinal Chemistry Letters 14 (2004) 2519–2525
Design, synthesis, and structure–activity relationships
of pyrazolo[3,4-d]pyrimidines: a novel class of potent
enterovirus inhibitors
Jyh-Haur Chern,a,* Kak-Shan Shia,a Tsu-An Hsu,a Chia-Liang Tai,a Chung-Chi Lee,a
Yen-Chun Lee,a Chih-Shiang Chang,a Sung-Nien Tsengb and Shin-Ru Shihb,*
aDivision of Biotechnology and Pharmaceutical Research, National Health Research Institutes, Taipei 114, Taiwan, ROC
bSchool of Medical Technology, Chang Gung University, Taoyuan 333, Taiwan, ROC
Received 10 February 2004; revised 26 February 2004; accepted 28 February 2004
Abstract—A series of pyrazolo[3,4-d]pyrimidines were synthesized and their antiviral activity was evaluated in a plaque reduction
assay. It is very interesting that this class of compounds provide remarkable evidence that they are very specific for human ente-
roviruses, in particular, coxsackieviruses. Some derivatives proved to be highly effective in inhibiting enterovirus replication at
nanomolar concentrations. SAR studies revealed that the phenyl group at the N-1 position and the hydrophobic diarylmethyl group
at the piperazine largely influenced the in vitro antienteroviral activity of this new class of potent antiviral agents. It was found that
the pyrazolo[3,4-d]pyrimidines with a thiophene substituent, such as compounds 20–24, in general exhibited high activity against
coxsackievirus B3 (IC50 ¼ 0.063–0.089 lM) and moderate activity against enterovirus 71 (IC50 ¼ 0.32–0.65 lM) with no apparent
cytotoxic effect toward RD (rhabdomyosarcoma) cell lines (CC50>25 lM).
Ó 2004 Elsevier Ltd. All rights reserved.
1. Introduction
have been reported from Asian countries.2 In 1998, the
epidemic outbreak of enterovirus 71 infection in Taiwan
resulted in almost 80 fatalities and 405 severe cases.3
Unfortunately, there is no effective antiviral drug for
treatment of enteroviral disease. This highlights the
urgency and significance for developing antienteroviral
agents.
Enteroviruses comprise more than 60 distinct serotypes
within the family of picornaviridae. The enteroviruses
are frequently classified by their sub-genus names: polio-
viruses, coxsackieviruses A and B, echoviruses, and
the newer numbered enteroviruses.1 Human entero-
viruses are the most common cause for viral infections in
humans along with rhinoviruses. Symptoms for entero-
viral infections range from nonspecific upper respiratory
infection and mild fever to central nervous system
infections particularly viral meningitis, encephalitis, and
severe myocarditis.1 Children are considered to be rel-
atively immunodeficient, therefore enteroviral infections
of neonates can be lethal and life threatening, with high
risk for morbidity, and mortality.
In 1966, a novel antienteroviral agent, pleconaril A (Fig.
1), was made available for treatment of life threatening
enteroviral infections, such as meningitis, encephalitis,
myocarditis.4 It is under development by Viropharma,
Inc. for the treatment of severe enteroviral infection in
phase 2 clinical trials. But it is worth to mention that
pleconaril exhibited no activity against enterovirus 71.
In our previous study, we reported the synthesis,
antiviral and cytotoxic properties of imidazolidinones B
(Fig. 1).5 This is a novel class of potent and selective
human enterovirus 71 inhibitors. Further SAR studies
of this class of compounds are currently under active
investigation. Recently, an antiviral screening program
was initiated to search for new enterovirus inhibitors via
plaque reduction assay6 in our laboratory. Interestingly,
a novel pyrazolo[3,4-d]pyrimidine, compound 1, was
identified as a potential antienteroviral agent, the
Enteroviral infection is a worldwide distribution. It is
estimated that worldwide they cause over 5 billion
enteroviral infections annually, and many outbreaks
Keywords: Enterovirus inhibitor.
* Corresponding authors. Tel.: +886-2-2653-4401x6573; fax: +886-2-
2792-9703; e-mail: jhchen@nhri.org.tw
0960-894X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.02.092

2520
J.-H. Chern et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2519–2525
H3C
N
CH3
R1
O
O
O
N
(CH2)n
R
O
N
N
N
R2
H3C
CF3
n = 5-7
N
O
Pleconaril A
Imidazolidinones B
2
1
N
N
3
7
N
N
N
6
4 N
5
Compound 1
Figure 1. Structures of pleconaril A, imidazolidinones B, and compound 1.
structure of which is illustrated in Figure 1. This com-
pound was found to possess antiviral activity against
three genotypes (A, B, and C) of enterovirus 71, cox-
sackieviruses A9, A10, A16, A24, B1–B6, echovirus 9,
and enterovirus 68. Therefore many structurally related
pyrazolo[3,4-d]pyrimidines were synthesized and evalu-
ated against enterovirus 71 (EV71) and coxsackievirus
B3 (CVB3). Details of this investigation will be
described herein.
in acetonitrile to give compound 30. The treatment of
compound 30 with compound 26 and triethylamine in
refluxing ethanol gave the target compounds 1–8 and
14–20.
In similar fashion, the thiophene-containing compounds
21–24 were synthesized in a short convergent synthetic
route as shown in Scheme 2. Reaction of 2-bromo-3-
methylthiophene 31 with turning magnesium in dry
THF followed by nucleophilic addition with the alde-
hyde gave compound 32. Compound 32 was subse-
quently treated with thionyl chloride to give the
corresponding chloro compound 33, which was directly
treated with piperazine in acetonitrile to give compound
34. The treatment of compound 34 with compound 26
and triethylamine in refluxing ethanol gave the target
compounds 21–24.
2. Results and discussion
A variety of synthetic procedures for pyrazolopyrim-
idine derivatives have been reported in the literature.7 To
the best of our knowledge, there is no report concerning
the synthesis of these interesting piperazine-containing
pyrazolo[3,4-d]pyrimidines. We report here an efficient
synthesis of the novel antiviral pyrazolo[3,4-d]pyrim-
idines 1–24 via the key nucleophilic substitution8 of
compound 269 or 3610 with various diarylmethylpiper-
azines 3011 and 3411 (Schemes 1–3). The parental com-
pound 1 was subjected to evaluation against a variety of
viruses. The results of this biological evaluation are
illustrated in Table 1. Preliminary structure–activity
relationship against EV71 and CVB3 are also reported
(Tables 2–4).
Other pyrazolo[3,4-d]pyrimidines 9–13 were prepared by
the reported method summarized in Scheme 3.10 Com-
pound 36, 4-chloro-1H-pyrazolo[3,4-d]pyrimidine, is
commercially available or conveniently prepared by
chlorination of allopurinol 35 with phosphoryl chloride
in N,N-dimethylaniline at refluxing temperature.
Nucleophilic substitution of compound 36 with 1-benz-
hydrylpiperazine gave compound 9. Compound 9 was
subsequently treated with alkyl iodide and cesium car-
bonate to give target compounds 10–13. The new pyr-
1
azolo[3,4-d]pyrimidines 1–24 were characterized by H
NMR, ESMS, and FT-IR.12;13
3. Chemistry
4. Bioactivity
Pyrazolo[3,4-d]pyrimidines 1–8 and 14–20 were pre-
pared by the method summarized in Scheme 1. The key
intermediate 26, 4-chloro-1-phenyl-1H-pyrazolo[3,4-d]-
pyrimidine, was obtained in 90% yield by treating
phosphoryl chloride with compound 25 in dichloroeth-
ane at refluxing temperature. Reaction between com-
pound 27 and phenylmagnesium bromide gave
compound 28. Compound 28 was subsequently treated
with thionyl chloride to give the corresponding chloro
compound 29 which was directly treated with piperazine
Pyrazolo[3,4-d]pyrimidines described herein were tested
in a plaque reduction assay6 under a standard proce-
dure. The parental compound 1 was subjected to eval-
uation against
a
variety of viruses, including
coxsackieviruses (10 serotypes), echoviruses (2 sero-
types), human enteroviruses 68 and 71, influenza A and
B viruses, herpes simplex virus 1 (HSV-1), human rhi-
novirus 2 (HRV 2), and 14 (HRV 14). As shown in
Table 1, this compound exhibited significant activities

J.-H. Chern et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2519–2525
2521
Cl
OH
N
POCl3
N
N
N
N
N
N
N
ClCH2CH2Cl
90 oC, 12 h
25
26
O
SOCl2
MgBr
Ar
Ar
H
+
Ar
OH
CH2Cl2
0 oC, 1 h
Cl
dry THF
27
r.t., 1h
28
29
N
N
N
Ar
26
HN
NH
N
N
N
N
NH
Ar
Et3N, EtOH
90 oC, 4 h
CH3CN, reflux
overnight
30
14. Ar = 3-pyridyl
15. Ar = 4-pyridyl
16. Ar = 2-pyridyl
17. Ar = 2-thiazole
18. Ar = 3-furanyl
1. Ar = Ph
2. Ar = 4-ClPh
3. Ar = 4-BrPh
4. Ar = 4-CF3Ph
5. Ar = 4-PhPh
6. Ar = 4-CNPh
7. Ar = 3-CNPh
8. Ar = 2-CH3Ph
19. Ar = 2,5-dimethyl-3-isoxazolyl
20. Ar = 5-methyl-2-thienyl
Scheme 1. General synthetic route to pyrazolo[3,4-d]pyrimidines 1–8 and 14–20.
O
viruses tested in the submicromolar range and also
possess a very low cytotoxic effect on the uninfected
rhabdomyosarcoma (RD) host cells (IC50>25 lM). It
was therefore of interest to explore the SAR of pyraz-
olo[3,4-d]pyrimidines.
CH3
MgBr
S
OH
32
CH3
Br
Ar
H
Mg
Ar
CH
3
dry THF
r.t., 1h
S
THF
S
31
S
HN
NH
CH
In preliminary SAR studies, a series of pyrazolo[3,4-
d]pyrimidines 1–13 were synthesized according to
Schemes 1 and 3 then submitted for anti-EV71 and anti-
CVB3 testing as well as cytotoxicity evaluation in RD
cell lines. These significant biological results were sum-
marized in Table 2. As shown in Table 2, compared to
the parental compound 1, when a substituent (Br, Cl,
CF3, CN, Me, Ph) was introduced on one of the phenyl
rings of the diphenylmethyl group, compounds 2–8
showed a slight decrease in activity against EV71,
retained activity against CVB3, and showed no cyto-
toxicity against RD cell lines. This effect might be due to
their distinct differences of hydrophobic properties. On
the other hand, replacement of the phenyl group at the
N-1 position with either a hydrogen or alkyl substituent
(Me, Et, n-Pr, benzyl), such as compounds 9–13,
resulted in a complete loss of antiviral activity against
both EV71 and CVB3. However, this unexpected bio-
logical result is not fully understood and is worthy of
further study.
3
Ar
SOCl2
S
Ar
34
CH
3
N
NH
Cl
CH3CN, reflux
overnight
CH2Cl2
0 oC, 1 h
33
N
N
CH
N
3
S
26
N
N
21. Ar = 2-CH3Ph
22. Ar = 2-BrPh
23. Ar = 2-pyridyl
24. Ar = 2,5-dimethyl-3-isoxazolyl
N
Ar
Et3N, EtOH
90 oC, 4 h
21-24
Scheme 2. General synthetic route to pyrazolo[3,4-d]pyrimidines 21–
24.
against human enterovirus 68 (IC50 ¼ 0.18 lM), human
enterovirus 71 (IC50 ¼ 0.35–0.52 lM), echovirus
9
B
(IC50 ¼ 0.30 lM), and coxsackieviruses
A
and
(IC50 ¼ 0.05–0.94 lM). However, it showed no activity
against influenza A and B viruses, HSV-1, HRV 2, HRV
14, and echovirus 29 up to the concentration tested
(25 lM). We observed that the parental compound 1 is
highly active against most of the serotypes of entero-
According to Scheme 1, a variety of heteroaryl-con-
taining pyrazolo[3,4-d]pyrimidines 14–20 were synthe-
sized. The results are shown in Table 3 and are

2522
J.-H. Chern et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2519–2525
N
NH
Cl
N
OH
N
POCl3
N
N
N
N
H
N
N
H
N,N-dimethylaniline
Et3N, EtOH
90 oC, 4 h
90 oC, 2 h
35
36
N
N
N
R-I
NH
10. R = CH3
11. R = Et
12. R = n-Pr
13. R = Benzyl
R
N
N
N
N
Cs2CO3
N
N
N
N
DMF
0 oC, 6 h
9
Scheme 3. General synthetic route to pyrazolo[3,4-d]pyrimidines 9–13.
Table 1. Antiviral activity of compound 1 and imidazolidinone B (R ¼ R1 ¼ H, R2 ¼ 4-Br, n ¼ 6) against various viruses
IC50 (lM)a
Imidazolidinone B
Compound 1
(R ¼ R1 ¼ H, R2 ¼ 4-Br, n ¼ 6)
Enterovirus 68
2.13 ꢀ 0.19
0.60 ꢀ 0.02
1.15 ꢀ 0.05
1.26 ꢀ 0.05
0.77 ꢀ 0.05
5.88 ꢀ 0.34
>25
0.18 ꢀ 0.08
0.47 ꢀ 0.17
0.52 ꢀ 0.17
0.35 ꢀ 0.02
0.26 ꢀ 0.02
0.39 ꢀ 0.01
0.23 ꢀ 0.06
0.05 ꢀ 0.01
0.69 ꢀ 0.02
0.08 ꢀ 0.01
0.15 ꢀ 0.01
0.16 ꢀ 0.01
0.44 ꢀ 0.04
0.94 ꢀ 0.34
0.30 ꢀ 0.04
>25
Enterovirus 71 (1743) genotype B
Enterovirus 71 (2231) genotype C
Enterovirus 71 (BrCr) genotype A
Coxsackievirus A9
Coxsackievirus A10
Coxsackievirus A16
Coxsackievirus A24
Coxsackievirus B1
0.55 ꢀ 0.06
5.10 ꢀ 0.05
>25
Coxsackievirus B2
Coxsackievirus B3
>25
>25
Coxsackievirus B4
Coxsackievirus B5
>25
>25
Coxsackievirus B6
Echovirus 9
Echovirus 29
2.82 ꢀ 0.01
>25
>25
Influenza A virus (WSN)
Influenza B virus (HK)
Herpes simplex virus 1
Human rhinovirus 2
Human rhinovirus 14
>25
>25
>25
>25
>25
>25
>25
11.60 ꢀ 0.12
>25
a Mean of triplicate well values. All experiments were performed at least twice. Plaque reduction assay was employed.
compared to the parental compound 1. Replacement of
one of the phenyl rings of the diphenylmethyl group
with either a 3-pyridine ring (14), 4-pyridine ring (15), or
3-furan ring (18) slightly lowered activity against both
EV71 and CVB3; but replacing the phenyl ring with
a 2-pyridine ring (16) retained activity. However,
replacement of the phenyl ring of diphenylmethyl group
with either a 2-thiazole ring (17), 2,5-dimethyl-3-isox-
azole ring (19), or 5-methyl-2-thiophene ring (20)
resulted in a significant improvement in activity against
CVB3, but retained activity against EV71. These
encouraging results prompt us to further investigate this
new class of pyrazolo[3,4-d]pyrimidines.
didate for further development as an antienteroviral
agent. On the basis of the skeleton of compound 20,
several 5-methyl-2-thiophene derivatives 21–24 were
thus synthesized (Scheme 2). The results are shown in
Table 4 and are compared to the compound 20.
Replacement of one of the phenyl rings of the di-
arylmethyl group with either a 2-methylphenyl ring (21),
2-bromophenyl ring (22), 2-pyridine ring (23), or 2,5-
dimethyl-3-isoxazole ring (24) provide
a
slight
improvement in activity against both EV71 and CVB3.
It is very interesting to note that this series of com-
pounds exhibited very high activity against CVB3
(IC50 ¼ 0.063–0.089 lM) and moderate activity against
EV71 (IC50 ¼ 0.32–0.65 lM) with no cytotoxicity up to
the concentration of 25 lM. These significant results
demonstrated that the substituted thiophene moiety of
the pyrazolo[3,4-d]pyrimidines seem to play a very
In this study, we observed that the substituted thio-
phene-containing compound 20, in terms of potency and
selectivity index, appear to be the most promising can-

J.-H. Chern et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2519–2525
Table 2. Antienteroviral activity and cytotoxicity for compounds 1–13
R2
2523
N
R3
N
N
N N
N
R
1
Compound
R1
R2
R3
IC50 (lM)a
IC50 (lM)a
CC50 (lM)b
EV71
CVB3
RD
1
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
H
0.41 ꢀ 0.08
1.97 ꢀ 0.012
0.91 ꢀ 0.28
1.65 ꢀ 0.26
1.90 ꢀ 0.96
0.94 ꢀ 0.42
0.78 ꢀ 0.08
1.98 ꢀ 1.56
>25
0.15 ꢀ 0.01
0.26 ꢀ 0.07
0.49 ꢀ 0.04
0.30 ꢀ 0.05
0.31 ꢀ 0.01
0.18 ꢀ 0.02
0.11 ꢀ 0.05
0.13 ꢀ 0.01
>25
>25
>25
>25
>25
>25
>25
>25
>25
>25
>25
>25
>25
>25
2
4-Cl
4-Br
4-CF3
4-Ph
4-CN
3-CN
2-CH3
H
3
4
5
6
7
8
9
10
11
12
13
H
CH3
Et
>25
>25
>25
>25
H
H
n-Pr
Benzyl
>25
>25
>25
>25
H
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.
Table 3. Antienteroviral activity and cytotoxicity for compounds 14–20
N
N
Ar
N
N
N
N
Compound
Ar
IC50 (lM)a
IC50 (lM)a
CC50 (lM)b
EV71
CVB3
RD
1
0.41 ꢀ 0.08
4.60 ꢀ 0.23
0.15 ꢀ 0.01
0.53 ꢀ 0.02
>25
N
14
>25
>25
>25
>25
>25
15
16
17
18
0.78 ꢀ 0.02
0.37 ꢀ 0.02
0.34 ꢀ 0.06
1.25 ꢀ 0.06
0.30 ꢀ 0.003
0.17 ꢀ 0.002
0.11 ꢀ 0.05
0.27 ꢀ 0.11
N
N
N
S
O
H C
3
O
N
19
0.58 ꢀ 0.27
0.095 ꢀ 0.008
>25
>25
H C
3
H C
3
20
0.46 ꢀ 0.14
0.089 ꢀ 0.033
S
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.
important role in enhancing the anti-CVB3 activity.
This effect might be due to their drastically conforma-
tional change and steric requirement between the two
adjacent aromatic rings of diarylmethyl group.
5. Conclusion
In summary, a novel pyrazolo[3,4-d]pyrimidine, com-
pound 1, was found to possess significant antiviral

2524
J.-H. Chern et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2519–2525
Table 4. Antienteroviral activity and cytotoxicity for compounds 21–24
N
N
Ar
N
S
N
N
N
CH
3
Compound
Ar
IC50 (lM)a
IC50 (lM)a
CC50 (lM)b
EV71
CVB3
RD
20
21
22
23
0.46 ꢀ 0.14
0.41 ꢀ 0.17
0.32 ꢀ 0.26
0.36 ꢀ 0.09
0.089 ꢀ 0.033
0.084 ꢀ 0.041
0.072 ꢀ 0.005
0.063 ꢀ 0.013
>25
>25
>25
>25
H C
3
Br
N
H C
3
O
N
24
0.65 ꢀ 0.35
0.081 ꢀ 0.002
>25
H C
3
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.
B., Straus, S. E., Eds.; Lippincott–Raven: Philadelphia,
PA, 1996; pp 655–712.
activity against human enteroviruses in our screening
program. Preliminary studies revealed that this com-
pound is very specific for human enteroviruses, in par-
ticular, coxsackieviruses. We have developed an efficient
synthesis of these new pyrazolo[3,4-d]pyrimidines in an
attempt to evaluate their antienteroviral activity in a
plaque reduction assay. Compound 1–24 were synthe-
sized and evaluated against EV71 and CVB3. According
to our SAR investigation, the phenyl group at the N-1
position and the hydrophobic diarylmethyl group at
the piperazine largely influenced the in vitro antiente-
roviral activity of this new class of potent antiviral
agents. On the basis of these biological results, a series
of thiophene-containing compounds 20–24 were found
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to exhibit high antiviral activity against CVB3 (IC50
¼
0.063–0.089 lM) and moderate antiviral activity against
EV71 (IC50 ¼ 0.32–0.65 lM) with very low cytotoxic
effect toward RD cell lines. Further SAR studies and
mechanistic studies on this new class of antiviral com-
pounds are currently under active investigation and will
be reported in due course.
Acknowledgements
7. (a) Dhainaut, A.; Regnier, G.; Tizot, A.; Pierre, A.;
Leonce, S.; Guilbaud, N.; Kraus-Berthier, L.; Atassi, G.
J. Med. Chem. 1996, 39, 4099–4108; (b) Gilligan, P. J.;
Baldauf, C.; Cocuzza, A.; Chidester, D.; Zaczek, R.;
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L.; Saye, J. A.; Christ, D.; Trainor, G.; Robertson, D. W.;
Hartig, P. Bioorg. Med. Chem. 2000, 8, 181–189; (c) He,
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We are grateful to the National Health Research Insti-
tutes of the Republic of China for Financial support.
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H, 5.63; N, 21.91. Found: C, 72.41; H, 5.56; N, 21.85.
Compound 23: mp 330 °C (decomposed); IR (CHCl3) mmax
2913, 2811, 1571, 1547, 1501 cmꢁ1 1H NMR (300 MHz,
;
CDCl3) d 8.55 (d, 1H, J ¼ 0:6 Hz), 8.40 (d, 1H, J ¼ 1:8 Hz),
8.08 (d, 2H, J ¼ 8:1 Hz), 8.01 (s, 1H), 7.64–7.55 (m, 2H),
7.49 (t, 2H, J ¼ 7:2 Hz), 7.30–7.12 (m, 3H), 6.71 (dd, 1H,
J ¼ 4:2 Hz, J ¼ 1:2 Hz), 4.83 (s, 1H), 4.00 (br s, 4H), 2.73–
2.53 (m, 4H), 2.27 (s, 3H); ESMS 468.4 [Mþ1], 490.4
[Mþ23]. Anal. Calcd for C26H25N7S: C, 66.78; H, 5.39; N,
20.97. Found: C, 66.86; H, 5.48; N, 20.95.
12. All the new compounds gave satisfactory spectral data
consistent with their proposed structures. Selected spectral
data for compounds 1, 16, and 23. Compound 1: mp 215–
13. Selected spectral data for compounds 9 and 11. Com-
pound 9: mp 216–217 °C; IR (KBr) mmax 3425, 3200, 3111,
2995, 2820, 1597, 1563, 1521, 1490 cmꢁ1
;
1H NMR
1
216 °C; IR (CHCl3) mmax 2810, 1573, 1547, 1501 cmꢁ1; H
(300 MHz, CD3OD) d 8.20 (s, 1H), 7.96 (s, 1H), 7.44–
7.42 (m, 5H), 7.30–7.18 (m, 5H), 4.28 (s, 1H), 3.99 (br s,
4H), 2.57 (br s, 4H); ESMS 371.2 [Mþ1], 393.2 [Mþ23].
Anal. Calcd for C22H22N6: C, 71.33; H, 5.99; N, 22.69.
Found: C, 71.30; H, 5.91; N, 22.66. Compound 11: mp
169–170 °C; IR (KBr) mmax 2974, 2852, 2816, 2766, 1547,
1499, 1478, 1450 cmꢁ1; 1H NMR (300 MHz, CDCl3) d 8.34
(s, 1H), 7.87 (s, 1H), 7.45 (dd, 4H, J ¼ 7:2 Hz, J ¼ 1:2 Hz),
7.32–7.19 (m, 6H), 4.43 (q, 2H, J ¼ 7:2 Hz), 4.29 (s, 1H),
4.00 (q, 4H, J ¼ 4:8 Hz), 2.57 (t, 4H, J ¼ 4:8 Hz), 1.49 (t,
3H, J ¼ 7:2 Hz); ESMS 399.2 [Mþ1]. Anal. Calcd for
C24H26N6: C, 72.33; H, 6.58; N, 21.09. Found: C, 72.25; H,
6.53; N, 21.07.
NMR (300 MHz, CDCl3) d 8.41 (s, 1H), 8.07 (dd, 2H,
J ¼ 6:3 Hz, J ¼ 0:9 Hz), 8.04 (s, 1H), 7.52–7.44 (m, 6H),
7.33–7.21 (m, 7H), 4.29 (s, 1H), 4.04 (br s, 4H), 2.57 (br s,
4H); ESMS 447.3 [Mþ1]. Anal. Calcd for C28H26N6: C,
75.31; H, 5.87; N, 18.82. Found: C, 75.33; H, 5.80; N, 18.85.
Compound 16: mp 185–186 °C; IR (CHCl3) mmax 2958,
2817, 1571, 1547, 1501 cmꢁ1; 1H NMR (300 MHz, CDCl3)
d 8.54 (d, 1H, J ¼ 4:5 Hz), 8.41 (s, 1H), 8.08 (dd, 2H,
J ¼ 8:1 Hz, J ¼ 1:2 Hz), 8.04 (s, 1H), 7.66–7.46 (m, 6H),
7.34–7.23 (m, 4H), 7.15 (t, 1H, J ¼ 0:9 Hz), 4.49 (s, 1H),
4.04 (t, 4H, J ¼ 5:1 Hz), 2.68–2.56 (m, 4H); ESMS 448.2
[Mþ1], 470.2 [Mþ23]. Anal. Calcd for C27H25N7: C, 72.46;