Synthesis of 2,3-disubstituted 1,4-naphthoquinones as antiplatelet agents

Article abstract of DOI:10.1002/ardp.200800024

In continuing search for novel antiplatelet agents, the highly potent agent 2-chloro-3-methoxycarbonylethylcarboxamido-1,4-naphthoquinone 2 was selected as lead compound. Structureactivity relationships in this series were examined. Some of these compound

Full text of DOI:10.1002/ardp.200800024

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Arch. Pharm. Chem. Life Sci. 2008, 341, 639–644
J.-C. Lien et al.
639
Full Paper
Synthesis of 2,3-Disubstituted 1,4-Naphthoquinones as
Antiplatelet Agents
Jin-Cherng Lien1, Chi-Rei Wu2, Mann-Jen Hour3, Li-Jiau Huang1, Tur-Fu Huang4,
and Sheng-Chu Kuo1
1 Graduate Institute of Pharmaceutical Chemistry, China Medical University, Taichung, Taiwan, R.O.C.
2 Graduate Institute of Chinese Pharmaceutical Sciences, Taichung, Taiwan, R.O.C.
3 School of Pharmacy, China Medical University, Taichung, Taiwan, R.O.C.
4 Pharmacological Institute, College of Medicine, National Taiwan University, Taiwan, R.O.C.
In continuing search for novel antiplatelet agents, the highly potent agent 2-chloro-3-methoxy-
carbonylethylcarboxamido-1,4-naphthoquinone 2 was selected as lead compound. Structure-
activity relationships in this series were examined. Some of these compounds showed significant
antiplatelet activities. Further studies on the action mechanism showed that 2-acetamido-3-
chloro-1,4-naphthoquinone 4 has a direct inhibitory action on cytosolic phospholipase A2 (cPLA2)
activity in platelets.
Keywords: Antiplatelet activity / cPLA2 / Naphthoquinones /
Received: January 24, 2008; accepted: May 15, 2008
DOI 10.1002/ardp.200800024
thylcarboxamido-1,4-naphthoquinone 2 was the most
promising agent and showed potent activity in concen-
tration-dependently inhibited thrombin (0.1 unit/mL),
arachidonic acid (100 lM), collagen (10 lg/mL), and plate-
let-activating factor (2 ng/mL) induced aggregation in
human platelet suspension. The IC50 values of compound
2 for inhibiting aggregation induced by the above men-
tioned inducers are 24.0, 2.6, 2.7, and 4.4 lM, respec-
tively. Further studies indicate that compound 2 exerts
antiplatelet effects by inhibiting phosphoinositide turn-
over [6]. In the present work, compound 2 was selected as
the lead compound and the 3-chloro group was replaced
by various 3-arylamino groups and tested for antiplatelet
activity. Our findings are summarized in this report.
Introduction
Myocardial infarction and ischemic stroke are the lead-
ing causes of morbidity and mortality in developed coun-
tries. These result from the formation of an occluding
vascular thrombus caused by rupture or erosion of unsta-
ble plaque. Blood platelets play a crucial role in the devel-
opment of a thrombus, a sequential event involving pla-
telet adhesion, activation, and subsequent aggregation.
Thus, many categories of antiplatelet agents have been
extensively researched and developed as potential thera-
pies for both, the treatment and prevention of cardiovas-
cular disease [1–3].
In the course of our search for new antiplatelet agents
[4, 5], a series of 2-alkylcarboxamido-3-chloro-1,4-naph-
thoquinones were synthesized and tested for their inhib-
itory activities on human platelet aggregation. Among
these active compounds, 2-chloro-3-methoxycarbonyle-
Results and discussion
2-Alkylcarboxamido-3-chloro-1,4-naphthoquinones 2–4
were synthesized using previously described methods [5].
As shown in Scheme 1, when 2-amino-3-chloro-1,4-naph-
thoquinone 1 was reacted with substituted acyl chlorides
or acetic anhydride, in the presence of dry hydrogen
chloride or concentrated sulfuric acid, the correspond-
ing compounds 2–4 were obtained. As illustrated in
Correspondence: Jin-Cherng Lien, Graduate Institute of Pharmaceutical
Chemistry, China Medical University, 91 Hsueh-Shih Road, Taichung,
Taiwan, R.O.C.
E-mail: jclien@mail.cmu.edu.tw
Fax: 886-4-22078083
Abbreviations: cytosolic phospholipase A2 (cPLA2)
i 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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J.-C. Lien et al.
Arch. Pharm. Chem. Life Sci. 2008, 341, 639–644
Table 1. Inhibitory Effect of 2,3-Disubstituted 1,4-Naphthoqui-
nones on Platelet Aggregation Induced by Thrombin, Arachi-
donic Acid (AA), Collagen, and Platelet-activating Factor (PAF)a).
Table 1. Continued.
No. conc.
Percentage aggregation
(lg/mL)
Thrombin
AA
Collagen
PAF
No. conc.
(lg/mL)
Percentage aggregation
19
100
20
10
5
IC50 (lM)
100
IC50 (lM)
100
50
20
10
5
2
1
0.5
0.2
87.7 l 0.8***
0.0 l 0.0*** 39.8 l 0.9*** 88.6 l 1.9
Thrombin
AA
Collagen
PAF
0.0 l 0.0***
0.0 l 0.0***
77.8 l 1.4***
85.4 l 1.3
2
100
0.0 l 0.0***
0.0 l 0.0***
25.2 l 2.3***
60.7 l 3.3***
83.8 l 2.5***
0.0 l 0.0***
0.0 l 0.0***
31.7 l 13.7*** 24.1 l 12.3*** 56.0 l 6.5***
71.0 l 4.5*** 74.9 l 2.1*** 74.7 l 5.2**
2.6
0.0 l 0.0***
20
10
5
2
1
0.5
ND
89.1 l 2.0
ND
36.7
82.7 l 1.3*
ND
ND
66.3 l 1.3*** 87.0 l 2.4
ND ND
0.0 l 0.0*** 0.0 l 0.0***
ND
20
21
0.0 l 0.0***
0.0 l 0.0*** 12.2 l 5.1***
0.0 l 0.0***
0.0 l 0.0***
0.0 l 0.0***
21.3 l 1.3***
42.2 l 1.3***
81.2 l 0.9***
IC50 (lM)
100
20
10
5
24.0
2.7
0.0 l 0.0***
4.4
0.0 l 0.0***
41.7 l 0.9***
61.5 l 1.1***
72.6 l 0.9***
77.3 l 1.0***
82.4 l 2.0**
11.3
3
4
5
0.0 l 0.0***
0.0 l 0.0***
57.9 l 3.9***
80.6 l 5.0***
0.0 l 0.0***
0.0 l 0.0***
0.0 l 0.0***
38.3 l 2.8***
56.7 l 3.1***
0.0 l 0.0***
16.7 l 10.2*** 0.0 l 0.0*** 59.8 l 2.3***
88.0 l 1.2
6.3
0.0 l 0.0***
2
1
83.1 l 1.4*
4.2
0.0 l 0.0***
10.4 l 9.0*** 0.0 l 0.0***
39.3 l 21.3** 54.9 l 13.3**
88.9 l 3.1
21.8
0.0 l 0.0***
IC50 (lM)
100
50
ND
90.2 l 1.0
ND
41.8
IC50 (lM)
100
5
2
1
0.5
0.2
IC50 (lM)
100
32.7
22
0.0 l 0.0*** 86.1 l 1.1
75.3 l 1.6***
87.9 l 1.1*
0.0 l 0.0***
43.3 l 5.6***
76.2 l 11.5
20
83.5 l 1.1**
10
IC50 (lM)
ASA IC50 (lM)
86.7 l 1.2***
173.7
20.0
0.0 l 0.0*** 86.6 l 3.0
7.7 l 6.3***
71.0 l 4.5***
90.4 l 1.6
ND
A100
ND
ND
A100
A100
88.8
66.2 l 0.9**
1.4
59.3
10.4
0.0 l 0.0***
57.4 l 2.2***
83.0 l 0.7*
88.5 l 1.4*
138.0
0.0 l 0.0*** 33.8 l 7.4***
0.0 l 0.0***
88.4 l 2.5
a) Platelets were incubated with test compounds at 378C for 1 min. Then,
thrombin (0.1 unit/mL), arachidonic acid (AA, 100 lM), collagen (10 lg/
mL), or platelet-activating factor (PAF, 2 ng/mL) was added to trigger
the aggregation. IC50 values are expressed as the concentration (lM) at
which 50% inhibition of platelet aggregation occurred. ASA (acetyl sali-
cylic acid) was used as a positive control.
50
20
10
IC50 (lM)
100
IC50 (lM)
100
IC50 (lM)
100
IC50 (lM)
100
ND
91.6 l 1.2
ND
87.4
ND
6
7
8
9
86.6 l 2.7
ND
84.1 l 2.4** 90.2 l 1.6
ND
ND
91.2 l 1.3
ND
89.2 l 2.0
ND
88.0 l 1.4
ND
90.3 l 1.7
ND
91.6 l 0.5
ND
33.3 l 1.7***
81.6 l 3.8** 82.5 l 1.0*** 90.3 l 1.4
ND ND ND
0.0 l 0.0*** 0.0 l 0.0*** 0.0 l 0.0***
0.0 l 0.0*** 0.0 l 0.0*** 24.9 l 10.2***
70.6 l 1.6*** 74.8 l 2.9*** 83.7 l 1.6***
50
20
10
5
IC50 (lM)
100
IC50 (lM)
100
IC50 (lM)
100
IC50 (lM)
100
IC50 (lM)
100
IC50 (lM)
100
79.9 l 2.4*** 87.9 l 2.6
86.4 l 1.0***
85.6 l 3.0**
90.9 l 1.5
105.2
90.1 l 1.8
ND
ND
91.5 l 1.8
ND
92.0 l 1.5
ND
90.4 l 0.5
ND
91.1 l 0.4
ND
93.3 l 1.7
ND
62.7
69.2
10
11
12
13
14
15
88.6 l 2.4
ND
88.7 l 1.3
ND
82.4 l 3.1
ND
75.2 l 7.9
ND
79.6 l 3.8**
ND
74.1 l 8.5*
ND
83.2 l 4.3*
ND
82.8 l 6.2
ND
76.9 l 2.3*** 24.4 l 9.8***
ND ND
84.0 l 0.9*** 84.6 l 2.3
ND ND
81.0 l 2.9** 57.7 l 7.7***
ND ND
Scheme 1. Synthesis of 2-alkylcarboxamido-3-chloro-1,4-naph-
thoquinones 2–4.
85.4 l 0.5***
0.0 l 0.0*** 15.4 l 7.7*** 0.0 l 0.0***
Scheme 2, reaction of compounds 2–4 with a variety of
substituted anilines or benzylamines afforded the target
compounds, 2-alkylcarboxamido-3-arylamino-1,4-naph-
thoquinone 5–22.
The antiplatelet activities of 2,3-disubstituted 1,4-
naphthoquinones 2–22 are summarized in Table 1. At a
concentration of 10–20 lg/mL, compounds 3 and 4, with
the 2-position side chain longer and shorter, respectively,
than in compound 2, completely inhibited the platelet
50
20
IC50 (lM)
100
IC50 (lM)
100
IC50 (lM)
100
IC50 (lM)
37.8 l 16.1**
85.6 l 2.7
113.8 ND
31.2 l 9.3***
82.7 l 3.4
106.7
ND
94.3 l 1.3
ND
89.4 l 2.4
ND
16
17
18
85.6 l 0.5
ND
50.2 l 13.6** 81.5 l 4.5**
ND
ND
87.7 l 2.7
ND
87.2 l 2.6
ND
86.1 l 1.5
ND
83.8 l 2.7
ND
88.1 l 0.8*** 65.6 l 1.6*** 0.0 l 0.0***
ND ND ND
i 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Arch. Pharm. Chem. Life Sci. 2008, 341, 639–644
Naphthoquinones as Antiplatelet Agents
641
Table 2. Physical and spectral data of 2,3-disubstituted 1,4-naphthoquinones.
No.
Yield
(%)
Mp. (8C)
MS (M+)
(m/z)
IR
(cm– 1
1H-NMR (ppm)
)
2
3
81
83
174–175
127–128
321
335
1740
1730
2.74–2.82 (m, 4H, -CH2CH2-); 3.70 (s, 3H, -OCH3); 7.69–7.77 (m, 2H, H-6,7); 8.07 –8.10
(m, 1H, H-5); 8.14–8.17 (m, 1H, H-8)
2.00–2.10 (m, 2H, -CH2CH2CH2-); 2.45 (t, J = 7.5 Hz, 2H, -CH2CH2CH2-); 2.57 (t, J = 7.5 Hz,
2H, -CH2CH2CH2-); 3.67 (s, 3H, -OCH3); 7.71–7.75 (m, 2H, H-6,7) ; 8.04–8.07 (m, 1H, H-
5); 8.12–8.15 (m, 1H, H-8)
4
5
98
84
219–220
182–184
249
378
1700
1710
2.31 (s, 3H, -COCH3); 7.71 (br, 1H, -NH-); 7.73 –7.82 (m, 2H, H-6,7) ; 8.10 –8.13 (m, 1H, H-
5); 8.18–8.20 (m, 1H, H-8)
1.91–2.03 (m, 4H, -CH2CH2-); 3.51 (s, 3H, -OCH3); 6.94 (d, J = 8.8 Hz, 2H, H-29,69); 7.06 –
7.10 (m, 1H, H-49); 7.16–7.24 (m, 2H, H-39,59); 7.77–7.84 (m, 2H, H-6,7); 7.98–8.04 (m,
2H, H-5,8); 8.90 (s, 1H, -NHCO-), 9.22 (s,1H, -NH-)
6
7
88
86
188–190
172–173
392
408
1710
1710
2.16 (s, 4H, -CH2CH2-); 2.30 (s, 3H, 49-CH3); 3.62 (s, 3H, -OCH3); 6.80 (d, J = 8.3 Hz, 2H, H-
39,59); 7.05 (d, J = 8.3 Hz, 2H, H-29,69); 7.62–7.70 (m, 2H, H-6,7); 7.67 (s, 1H, -NHCO-), 7.76
(s, 1H, -NH-); 8.05–8.09 (m, 2H, H-5,8)
1.93 (t, J = 7.2 Hz, 2H, -CH2CH2-); 2.05 (t, J = 7.2 Hz, 2H, -CH2CH2-); 3.52 (s, 3H, -OCH3);
3.72 (s, 3H, 49-OCH3); 6.79 (d, J = 8.3 Hz, 2H, H-39,59); 6.90 (d, J = 8.3 Hz, 2H, H-29,69);
7.75–7.83 (m, 2H, H-6,7); 7.96–8.03 (m, 2H, H-5,8); 8.89 (s, 1H, -NHCO-), 9.03 (s, 1H, -
NH-)
8
9
83
84
188–190
182–184
396
412
1730
1730
1.98–2.10 (m, 4H, -CH2CH2-); 3.52 (s, 3H, -OCH3); 6.95–7.03 (m, 4H, H-29,39,59,69); 7.75 –
7.83 (m, 2H, H-6,7) ; 7.97–8.03 (m, 2H, H-5,8); 8.90 (s, 1H, -NHCO-), 9.19 (s, 1H, -NH-)
1.99–2.07 (m, 4H, -CH2CH2-); 3.52 (s, 3H, -OCH3); 6.93 (d, J = 8.8 Hz, 2H, H-29,69); 7.23 (d,
J = 8.8 Hz, 2H, H-39,59); 7.77 –7.84 (m, 2H, H-6,7) ; 7.98 –8.03 (m, 2H, H-5,8); 8.99 (s, 1H, -
NHCO-), 9.31 (s, 1H, -NH-)
10
11
89
85
151–152
182–184
392
392
1730
1740
2.48–2.54 (m, 4H, -CH2CH2-); 3.56 (s, 3H, -OCH3); 4.59 (d, J = 5.8 Hz, 2H, -NHCH2-); 7.22–
7.33 (m, 5H, H-29,39,49,5‘,69); 7.72–7.81 (m, 2H, H-6,7); 7.92–7.98 (m, 2H, H-5,8); 8.97 (s,
1H, -NHCO-)
1.47–1.53 (m, 2H, -CH2CH2CH2-); 1.87 (t, J = 7.2 Hz, 2H, -CH2CH2CH2-); 2.20 (t, J = 7.2 Hz,
2H, -CH2CH2CH2-); 3.43 (s, 3H, -OCH3); 7.09–7.19 (m, 1H, H-29,49,69); 7.32–7.37 (m, 2H,
H-39,59); 7.91 –8.12 (m, 2H, H-6,7) ; 8.13 –8.18 (m, 2H, H-5,8); 9.04 (s, 1H, -NHCO-), 9.19
(1H, s, -NH-)
12
13
87
86
138–139
117–118
406
422
1730
1730
1.49–1.54 (m, 2H, -CH2CH2CH2-); 1.94 (t, J = 7.2 Hz, 2H, -CH2CH2CH2-); 2.05 (t, J = 7.2 Hz,
2H, -CH2CH2CH2-); 2.29 (s, 3H, 49-CH3); 3.62 (s, 3H, -OCH3); 6.80 (d, J = 8.3 Hz, 2H, H-39,59); 7.04
(d, J = 8.3 Hz, 2H, H-29,69); 7.57 (s, 1H, -NHCO-), 7.61-7.69 (m, 2H, H-6,7) ; 7.79 (s, 1H, -NH-);
8.04 – 8.07 (m, 2H, H-5,8)
1.35–1.40 (m, 2H, -CH2CH2CH2-); 1.72 (t, J = 7.2 Hz, 2H, -CH2CH2CH2-); 2.07 (t, J = 7.2 Hz,
2H, -CH2CH2CH2-); 3.56 (s, 3H, -OCH3); 3.72 (s, 3H, 49-OCH3); 6.77 (d, J = 8.3 Hz, 2H, H-
39,59); 6.91 (d, J = 8.3 Hz, 2H, H-29,69); 7.74–7.85 (m, 2H, H-6,7); 7.96–8.02 (m, 2H, H-
5,8); 8.81 (s, 1H, -NHCO-), 8.86 (s, 1H, -NH-)
14
15
86
86
158–159
143–144
410
426
1720
1730
1.33–1.42 (m, 2H, -CH2CH2CH2-); 1.75 (t, J = 7.2 Hz, 2H, -CH2CH2CH2-); 2.09 (t, J = 7.2 Hz,
2H, -CH2CH2CH2-); 3.56 (s, 3H, -OCH3); 6.96–7.04 (m, 4H, H-29,39,59,69); 7.76–7.85 (m,
2H, H-6,7) ; 7.97 –8.03 (m, 2H, H-5,8); 8.92 (s, 1H, -NHCO-), 9.02 (s, 1H, -NH-)
1.34–1.39 (m, 2H, -CH2CH2CH2-); 1.80 (t, J = 7.2 Hz, 2H, -CH2CH2CH2-); 2.01 (t, J = 7.2 Hz,
2H, -CH2CH2CH2-); 3.53 (s, 3H, -OCH3); 6.94 (d, J = 8.8 Hz, 2H, H-29,69); 7.21 (d, J = 8.8 Hz,
2H, H-39,59); 7.76 –7.84 (m, 2H, H-6,7) ; 7.97 –8.03 (m, 2H, H-5,8); 8.99 (s, 1H, -NHCO-),
9.14 (s, 1H, -NH-)
16
87
151–152
406
1730
1.71–1.75 (m, 2H, -CH2CH2CH2-); 2.23 (t, J = 7.2 Hz, 2H, -CH2CH2CH2-); 2.34 (t, J = 7.2 Hz,
2H, -CH2CH2CH2-); 3.58 (s, 3H, -OCH3); 4.63 (d, J = 5.8 Hz, 2H, -NHCH2-); 7.20–7.30 (m,
5H, H-29,39,49,59,69); 7.70–7.80 (m, 2H, H-6,7); 7.92–7.98 (m, 2H, H-5,8); 8.85 (s, 1H, -
NHCO-)
17
18
19
20
21
22
80
89
88
83
85
83
207–208
192–193
199–202
169–170
184–185
207–209
306
320
336
324
340
320
1655
1670
1660
1670
1660
1665
1.59 (s, 3H, -COCH3); 6.89–7.37 (m, 5H, H-29,39,49,59,69); 7.64–7.92 (m, 2H, H-6,7); 7.98-
8.04 (m, 2H, H-5,8)
1.59 (s, 3H, -COCH3); 2.33 (s, 3H, 49-CH3); 6.84 (d, J = 8.3 Hz, 2H, H-39,59); 7.08 (d, J =
8.3 Hz, 2H, H-29,69); 7.61–7.84 (m, 2H, H-6,7); 8.03–8.14 (m, 2H, H-5,8)
1.61 (s, 3H, -COCH3); 2.79 (s, 3H, 49-OCH3); 6.74-6.99 (m, 4H, H-29,39,59,69); 7.58 –7.76 (m,
2H, H-6,7); 8.02–8.13 (m, 2H, H-5,8)
1.65 (s, 3H, -COCH3); 6.85–6.99 (m, 4H, H-29,39,59,69); 7.60–7.73 (m, 2H, H-6,7); 7.91-
8.07 (m, 2H, H-5,8)
1.72 (s, 3H, -COCH3); 6.86 (d, J = 8.8 Hz, 2H, H-29,69); 7.08 (d, J = 8.8 Hz, 2H, H-39,59);
7.62–7.87 (m, 2H, H-6,7); 8.02–8.09 (m, 2H, H-5,8)
2.19 (s, 3H, -COCH3); 4.63 (d, J = 5.8 Hz, 2H, -NHCH2-); 7.26 –7.31 (m, 5H, H-29,39,49,59,69);
7.58–7.72 (m, 2H, H-6,7); 7.98-8.09 (2H, m, H-5,8)
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J.-C. Lien et al.
Arch. Pharm. Chem. Life Sci. 2008, 341, 639–644
After the treatment of enzyme preparation with compound 4, AACOCF3, or DMSO
(vehicle control) in the standard assay system at room temperature for 60 min, DTNB
/ EGTA reagent was added to the reaction mixture for 5 min to stop the enzyme catal-
ysis and develop color formation. Data were calculated relative to the maximal activity
from assay buffer-treated cPLA2, which was taken as 100%, and are presented as the
mean l SEM (n =3). * P a 0.05 and **P a 0.01 as compared with the vehicle control.
Figure 1. Effects of compound 4 on cPLA2 activity in human pla-
telets.
pounds 2–4 play an important role in the antiplatelet
activity, and the length of the amide chain did not affect
the potency.
Compound 4 was selected for further studies of mecha-
nism of action. The present study has shown that pre-
treatment of cPLA2 (cytosolic phospholipase A2) with com-
pound 4 resulted in the concentration-dependent inhibi-
tion of cPLA2 activity by 22.1 l 0.6, 53.6 l 0.3, 68.4 l 0.1,
and 72.2 l 0.4% at concentrations of 1, 2, 4, and 20 mM,
respectively, suggesting that compound 4 has a direct
inhibitory action on cPLA2 activity in platelets with an
IC50 value of 1.8 l 0.1 mM (Fig. 1). The physical and spec-
tral data of 2,3-disubstituted 1,4-naphthoquinones are
presented in Table 2.
Scheme 2. Synthesis of 2-alkylcarboxamido-3-arylamino-1,4-
naphthoquinones 5–22.
aggregation induced by thrombin, arachidonic acid (AA),
collagen, and platelet-activating factor (PAF) as effectively
as compound 2.
Furthermore, compound 4 was about two times more
potent than compound 2 in the inhibitory activity
against platelet aggregation induced by AA. The antipla-
telet activity of compound 2 decreased remarkably when
the chloro group was replaced by substituted arylamino
groups 5–10. Compounds 11–16 and 17–22 derivatives
of compound 3 and 4, respectively, in which the chloro
group was replaced by arylamino groups showed a poor
inhibitory effect compared to the lead compound 2.
Among these compounds 11–22, the IC50 value for com-
pound 21 on platelet aggregation induced by AA was
found to be 11.3 lM, which is about one-fourth less active
than the lead compound 2 but more active than the posi-
tive control (acetyl salicylic acid, IC50 = 20.0 lM).
These investigations were supported by grant CMU95-100,
CMU95-112, CMU96-230 from China Medical University, Tai-
chung, and by grant 96-2815-C-039-049-B from the National
Science Council of Taiwan, Taiwan, R.O.C.
The authors have declared no conflict of interest.
Experimental
To sum up, the inhibitory activities of these synthetic
2,3-disubstituted 1,4-naphthoquinones proved to be Chemistry
IR spectra were recorded on a Nicolet Impact 400 FT-IR spectro-
more potent in the AA-induced platelet aggregation assay
than other inducers. Furthermore, the antiplatelet activ-
ities of compounds 2–4 decreased extremely when the
chloro groups were replaced by arylamino groups 5–22.
These results suggest that the chloro groups of com-
photometer as KBr pellets (Nicolet, Madison, WI, USA). NMR spec-
tra were obtained on a Bruker Avance DPX-200 FT-NMR (Bruker
Bioscience, Billerica, MA, USA). MS were measured with HP 5995
GC-MS (Hewlett-Packard, USA) and VG PLATFORM II GC-MS (Var-
ian, USA) instruments. Elemental analyses of C, H, and N were
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