Design and diversity-oriented synthesis of novel 1,4-thiazepan-3-ones fused with bioactive heterocyclic skeletons and evaluation of their antioxidant and cytotoxic activities

Article abstract of DOI:10.1016/j.bmcl.2011.09.081

This study has achieved the design and diversity-oriented synthesis of novel 1,4-thiazepine derivatives embedded with carbazole, pyrazole or isoxazole motif via microwave-assisted multicomponent reactions under solvent-free condition, thus providing a gre

Full text of DOI:10.1016/j.bmcl.2011.09.081

Bioorganic & Medicinal Chemistry Letters 22 (2012) 743–746
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design and diversity-oriented synthesis of novel 1,4-thiazepan-3-ones
fused with bioactive heterocyclic skeletons and evaluation of their
antioxidant and cytotoxic activities
Feng Shi a, , Xiao-Ning Zeng b, , Xu-Dong Cao a, Shu Zhang b, Bo Jiang a, Wei-Fa Zheng a, , Shu-Jiang Tu a,
⇑
⇑
a School of Chemistry and Chemical Engineering, Xuzhou Normal University, Xuzhou 221116, PR China
b Clinical Research Center, The First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
This study has achieved the design and diversity-oriented synthesis of novel 1,4-thiazepine derivatives
embedded with carbazole, pyrazole or isoxazole motif via microwave-assisted multicomponent reactions
under solvent-free condition, thus providing a green and facile access to 1,4-thiazepine derivatives with
prominent features of high structural diversity, short reaction time, high yields and environmental
friendliness. More importantly, these novel compounds have been subjected to the test of in vitro anti-
oxidant and cytotoxic activities, resulting in the finding that these 1,4-thiazepine derivatives not only
have significant antioxidant activity, but also exhibit remarkably selective cytotoxicity to carcinoma cell
line HCT 116.
Received 12 August 2011
Revised 18 September 2011
Accepted 20 September 2011
Available online 10 October 2011
Keywords:
1,4-Thiazepine
Multicomponent reactions
Antioxidant activity
Cytotoxicity
Ó 2011 Elsevier Ltd. All rights reserved.
The 1,4-thiazepine ring is one of important moieties in nitro-
gen- and sulfur-containing heterocycles and has been widely used
as key building block for pharmaceutical agents as well as biolog-
ically active compounds.1 Besides, carbazole, pyrazole and isoxaz-
ole skeletons constitute the core structural element of many
natural and synthesized products, which exhibit diverse pharma-
cological properties as exemplified by antitumor,2 antimicrobial,3
insecticidal,3 and anti-inflammatory activitites.4
economy and selectivity, time and energy savings, target product
specificity and minimal environmental impact.7,8
In view of the significance of 1,4-thiazepines fused with bioac-
tive heterocyclic skeletons and as our continuous efforts on syn-
thesizing heterocycles with potential bioactivities,9 herein, we
report the design and diversity-oriented synthesis of novel 1,4-
thiazepine derivatives 4 embedded with carbazole, pyrazole or
isoxazole motif via microwave-assisted multicomponent reactions
of aldehydes 1, mercaptoacetic acid 3 and various heteroaromatic
amines 2 (Scheme 1). Furthermore, we also report the evaluation
of the antioxidant and cytotoxic activities of the synthesized 1,4-
thiazepine compounds 4.
Initially, the reaction of p-methoxybenzaldehyde 1b, 3-amino-
9-ethylcarbazole 2a and mercaptoacetic acid 3 under microwave
irradiation (MW) was employed to optimize the reaction condi-
tions (Table 1). The screen of solvent (entries 1–7) revealed that
solvent-free condition was the best suitable condition for this reac-
tion (entry 7). Then, under solvent-free condition, the optimal reac-
tion temperature was further investigated (entries 7–12), and
120 °C with the highest yield of 92% (entry 11) was chosen as
the best suitable condition for all further microwave-assisted
reactions.
Based on the versatile bioactivities of the above mentioned
structures, it is promising that the integration of carbazole, pyra-
zole or isoxazole scaffold with 1,4-thiazepine segment might result
in the discovery of new drug candidates with unknown or en-
hanced bioactivities. However, the design of 1,4-thiazepine com-
pounds implanted with carbazole, pyrazole and isoxazole
frameworks for medicinal purpose has been less recognized and
only very few reports describe the synthesis of related com-
pounds.5 Therefore, the development of facile approaches to access
these novel targets with structural diversity is highly desirable and
valuable for medicinal chemistry and drug discovery.
Diversity-oriented synthesis (DOS)6,7 via multicomponent reac-
tions (MCRs)8 has become a powerful protocol to access pharma-
ceutically relevant heterocycles because of their combined
prominent features such as high reaction rate and efficiency, atom
With optimal conditions in hand, we then carried out the design
and diversity-oriented synthesis of novel 1,4-thiazepine deriva-
tives 4 embedded with carbazole, pyrazole and isoxazole motifs
(Table 2). Different heteroaromatic amines 2a–2d containing car-
bazole, pyrazole and isoxazole skeletons were utilized to the
⇑
Corresponding authors. Tel./fax: +86 516 83500065.
E-mail address: laotu2001@263.net (S.-J. Tu).
These authors contributed equally to this work.
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.09.081

744
F. Shi et al. / Bioorg. Med. Chem. Lett. 22 (2012) 743–746
R'
Table 2
Design and synthesis of 1,4-thiazepine derivatives 4a
N
S
HN
N
O
R'
H
4g-4l
HS
HO
MW, 120 oC
solvent-free
S
R'
+
+
CHO
NH2
O
NH2
N
N
H
O
N
1
2
3
4
H
2b
Et
N
R'
R'
R' CHO
N
Et
S
S
1
NH2
HS
2a
R
+
N
Entry
4
2
R0
Time
(min)
Yieldb
(%)
N
NH2
N
N
O
NH2
N
H
O
H
O
HO
2
4a-4f
3
1
2
4a
4b
p-Tolyl (1a)
4-Methoxyphenyl
(1b)
Benzo[d][1,3]dioxol-
6-yl (1c)
3,4-
Dimethoxyphenyl
(1d)
Thiophen-2-yl (1e)
4-Bromophenyl (1f)
9
9
92
93
N
2c
4m-4s
Et
N
N
3
4
4c
8
9
91
90
NH2
O
2d
R'
O
NH2
4d
S
2a
N
N
O
5
6
4e
4f
9
10
91
76
H
4t-4z
N
4-Methoxyphenyl
(1b)
Scheme 1. Synthesis of 4-aza-podophyllotoxin analogs.
7
4g
9
93
HN
8
9
4h
4i
p-Tolyl (1a)
Benzo[d][1,3]dioxol-
6-yl (1c)
9
8
92
91
NH2
Table 1
Reaction conditions optimization for the synthesis of 4ba
2b
10
4j
3,4,5-
9
92
Trimethoxyphenyl
(1g)
4-Bromophenyl (1f)
4-Chlorophenyl (1h)
OCH3
11
12
4k
4l
10
10
88
89
OCH3
4-Methoxyphenyl
(1b)
p-Tolyl (1a)
Benzo[d][1,3]dioxol-
6-yl (1c)
4-Chlorophenyl (1h)
2-Chlorophenyl (1i)
2,4-dichlorophenyl
(1j)
HS
13
4m
9
92
MW
+
Et
N
N
+
Et
N
S
NH2
14
15
4n
4o
9
8
91
90
conditions
N
O
HO
CHO
NH2
N
H
1b
2a
O
3
16
17
18
4p
4q
4r
9
9
10
93
92
90
4b
2c
19
4s
3-Nitrophenyl (1k)
10
90
Entry
Solvent
T (°C)
Time (min)
Yieldb (%)
4-Methoxyphenyl
(1b)
p-Tolyl (1a)
Benzo[d][1,3]dioxol-
6-yl (1c)
20
4t
9
93
1
2
3
4
5
6
7
8
9
THF
100
100
100
100
100
100
100
105
110
115
120
125
14
14
14
14
14
14
14
12
11
10
9
Trace
10
N
Ethanol
Glycol
DMF
21
22
4u
4v
NH2
9
9
92
91
O
15
27
39
48
57
66
75
80
2d
HOAc
H2O
23
4w
3,4-
9
94
Dimethoxyphenyl
(1d)
Thiophen-2-yl (1e)
2-Chlorophenyl (1i)
4-Bromophenyl (1f)
c
—
—
—
—
—
—
24
25
26
4x
4y
4z
9
10
10
94
90
91
10
11
12
92
89
a
Unless otherwise indicated, all the reactions were carried out in 1 mmol scale in
9
the absence of solvent at 120 °C under MW with the initial power of 200 W and the
maximum power of 350 W, and the ratio of 1/2/3 was 1:1:1.
a
Unless otherwise indicated, all the reactions were carried out in 1 mmol scale in
b
2 mL of solvent under MW with the initial power of 200 W and the maximum
Isolated yield.
power of 350 W, and the ratio of 1b/2a/3 was 1:1:1.
b
Isolated yield.
Solvent-free condition.
c
plausible mechanism for the reaction is similar to what has been
reported in the literaute.5
In order to survey the possible biological activities of this class
of novel compounds, 1,4-thiazepine derivatives 4 were subject to
the test of antioxidant activity and cytotoxicity to carcinoma cell
line HCT 116 (ATTC CCL 247) and mice lymphocytes.
three-component reactions in order to obtain target molecules
incorporated with bioactive units of 1,4-thiazepine and carbazole,
pyrazole or isoxazole. On the other hand, various aldehydes 1
including electronically poor or rich aromatic aldehydes and het-
eroaromatic aldehyde were applied to this reaction for the aim to
access target molecules with structural diversity. As shown in
Table 2, the protocol is amenable to a wide scope of aldehydes 1
and heteroaromatic amines 2a–2d, affording a library of novel
1,4-thiazepine derivatives 4 with high yields in short reaction time.
The structures of 1,4-thiazepine derivatives 4 were unambigu-
The antioxidant activity is represented by their capacities for
scavenging 1,1-diphenyl-2-picrylhydrazyl free radical (DPPH),
superoxide anion (O2ꢀ) and hydroxyl free radical (OH),10 and the
results are summarized in Table 3. Nearly all the tested compounds
ꢀ
showed strong capacities for scavenging DPPH, O2 and OH com-
ously characterized by IR, 1H NMR, 13C NMR and HRMS (ESI).10
A
pared with those of the positive control L-ascorbic acid. The top

F. Shi et al. / Bioorg. Med. Chem. Lett. 22 (2012) 743–746
745
Table 3
Table 4
Free radicals scavenging capacities of compounds 4a
Cytotoxicity of compounds 4a
ꢀ
Entry
4
DPPH (%/mg)
O2 (%/mg)
OH (%/mg)
Entry 4b
Inhibition rate on HCT-116
(%)
Viability rate of lymphocytes
(%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
4a
1038.46 8.81
528.84 18.71
235.57 11.24
261.21 7.28
519.23 12.57
291.66 5.36
394.23 8.54
381.41 11.39
201.92 5.84
195.51 6.12
238.78 6.12
193.91 5.57
161.85 5.36
176.28 3.27
209.93 6.56
346.15 12.27
225.96 11.56
179.48 5.57
384.61 7.63
448.71 14.78
375.00 14.35
674.67 8.06
195.51 7.45
352.56 10.93
173.07 5.84
1794.87 68.38
182.82 0.98
2395.11 72.79
1210.84 34.48
578.39 29.62
552.40 27.35
1018.47 22.27
559.40 40.55
1204.01 19.83
1211.93 25.82
610.65 9.00
994.21 31.88
476.77 10.99
348.06 5.64
370.89 2.36
770.48 7.48
271.38 5.22
393.92 3.73
368.45 6.65
187.37 4.25
247.07 3.90
200.05 4.59
195.16 1.89
477.55 28.92
676.76 10.27
643.89 9.10
1103.30 59.24
640.16 25.2
767.33 6.87
994.46 61.51
407.17 21.73
331.01 11.55
248.93 21.99
191.49 3.04
929.75 9.46
221.15 7.47
4189.50 66.65
97.25 0.83
1
2
4a 53.42 1.59
4b 58.88 2.91
93.21 2.51
51.42 5.23
157.59 3.33
101.15 4.41
44.99 5.43
136.07 4.44
44.81 0.74
20.46 0.82
154.81 5.18
166.22 2.04
42.60 2.36
67.90 3.82
78.81 2.97
25.67 3.808
66.94 4.96
82.30 4.51
68.66 5.665
156.06 6.03
154.00 3.25
164.84 3.26
102.59 4.57
87.25 2.81
165.37 5.08
159.91 3.25
170.13 0.79
156.87 3.09
4b
4c
4d
4e
4f
4g
4h
4i
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
4c 51.57 1.84
4d 56.16 1.93
4e 60.33 2.04
4f 62.00 0.98
4g 61.84 1.40
4h 66.82 0.42
4i 55.90 4.33
4j 58.23 0.09
4k 63.35 1.21
4l 60.93 1.62
4m 57.75 2.34
4n 58.44 3.71
4o 51.34 3.80
4p 50.18 2.22
4q 55.29 0.44
4r 53.27 4.42
4s 54.26 4.09
4t 60.34 2.85
4u 64.68 1.10
4v 50.43 6.72
4w 54.58 3.04
4x 62.59 4.14
4y 54.58 1.72
4z 63.05 3.48
4j
590.22 8.87
609.00 10.73
600.80 4.90
4k
4l
4m
4n
4o
4p
4q
4r
644.75 16.47
600.33 33.52
604.97 18.15
1248.83 10.96
589.07 12.96
592.46 10.08
1247.46 12.48
1231.44 20.69
1295.39 28.77
626.11 8.93
613.31 13.67
1264.57 27.94
621.91 10.04
6181.25 25.47
104.17 1.10
4s
4t
4u
4v
4w
4x
4y
4z
PCb
a
a
The cytotoxicity was represented as percentage inhibition (mean SD, n = 3) of
The scavenging capacities were represented as percentage inhibition
(mean SD, n = 3) of the free radicals by 1 mg tested compound.
HCT-116 cells and percentage viability (mean SD, n = 3) of lymphocytes.
b
b
The concentration of the tested compounds is 1 mg/mL.
L
-Ascorbic acid was used as a positive control (PC).
three for scavenging DPPH radical are 1,4-thiazepines 4z, 4a and 4v
containing carbazole and isoxazole skeletons with 4-bromophenyl,
p-tolyl and benzo[d][1,3]dioxol-6-yl as R0 group, respectively. And
natural products are believed to be the pharmaceuticals able to
treat or prevent oxidative stress-induced cancers.12 The results of
our study also demonstrate the correlations between the antioxi-
dant activity and cytotoxicity.
ꢀ
the top three for scavenging O2 radical are 1,4-thiazepines 4z, 4u
and 4a containing carbazole and isoxazole skeletons with 4-
bromophenyl and p-tolyl as R0 group. While the top three for scav-
enging OH are compounds 4z, 4p, 4s and 4a (4s and 4a almost have
the same capacity of scavenging OH) imbedded with carbazole,
pyrazole and isoxazole units with 4-bromophenyl, 4-chlorophenyl,
3-nitrophenyl and p-tolyl as R0 group, separately. It is worth-noting
that compound 4z has the most extraordinary capacities for scav-
enging all the three radicals, which are dozens of times higher than
those of the positive control. Although there is no regular relation-
ship between the structure and the antioxidant activity of the
tested compounds, it is obvious that these 1,4-thiazepine deriva-
tives 4 fused with carbazole, pyrazole and isoxazole skeletons have
remarkable antioxidant activity.
In summary, this study has achieved the diversity-oriented syn-
thesis of novel 1,4-thiazepine derivatives 4 embedded with carba-
zole, pyrazole or isoxazole motif via microwave-assisted
multicomponent reactions under solvent-free condition, thus pro-
viding a green and facile access to 1,4-thiazepine derivatives with
prominent features of high structural diversity, short reaction time,
high yields and environmental friendliness. More importantly,
these novel compounds have been subjected to the test of
in vitro antioxidant and cytotoxic activities, resulting in the finding
that these 1,4-thiazepine derivatives not only have significant anti-
oxidant activity, but also exhibit remarkably selective cytotoxicity
to carcinoma cell line HCT 116. Therefore, these novel 1,4-thiaze-
pine derivatives fused with bioactive heterocyclic skeletons may
find their pharmaceutical applications after further investigations.
The cytotoxic assay10 (Table 4) showed that all the tested com-
pounds inhibited the proliferation of HCT 116 cells with inhibition
rate ranging from 50.18% to 64.68%. However, most of the tested
compounds did not inhibit the proliferation of mice lymphocytes,
and on the contrary, some of the compounds promoted the growth
of lymphocytes with viability rate up to 166.22%. In general, most
of compounds inhibited the growth of HCT-116 cells in a rate high-
er than they did to mice lymphocytes. Therefore, these 1,4-thiaze-
pine derivatives 4 exhibited high selective cytotoxicity to HCT 116
cells. The top three for selectively inhibiting the proliferation of
HCT 116 cells but promoting the growth of mice lymphocytes
are 1,4-thiazepines 4u, 4z and 4x containing isoxazole skeleton
with p-tolyl, 4-bromophenyl and thiophen-2-yl as R0 group,
respectively.
Acknowledgments
We are grateful for financial support by Natural Science Foun-
dation of China (Nos. 21002083 and 21072163), the Natural Sci-
ence Foundation (09KJB150011) and Qing Lan Project (08QL001)
of Jiangsu Education Committee.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2011.09.081.
These results suggest that the 1,4-thiazepine derivatives 4 not
only have significant antioxidant activity, but also exhibit remark-
ably selective cytotoxicity to carcinoma cell line HCT 116. It has
been reported that most natural products inhibiting the growth
of tumor cells also possess antioxidant activity,11 and antioxidant
References and notes
1. (a) Zaleska, B.; Ciez, D.; Grochowski, J.; Serda, P.; Winnik, W. Liebigs Ann. 1996,
2, 211; (b) Sammers, P. G. Chem. Rev. 1976, 76, 113; (c) Matlin, S. A.; Chan, L.

746
F. Shi et al. / Bioorg. Med. Chem. Lett. 22 (2012) 743–746
Chem. Commun. 1980, 798; (d) Levai, A.; Ott, J.; Snatzke, G. Monatsh. Chem.
8. (a) Ramon, D. J.; Miguel, Y. Angew. Chem., Int. Ed. 2005, 44, 1602; (b) Weber, L.;
Illgen, K.; Almstetter, M. Synlett 1999, 366; (c) Li, G.; Wei, H. X.; Kim, S. H.;
Carducci, M. D. Angew. Chem., Int. Ed. 2001, 40, 4277; (d) Ramachary, D. B.; Jain,
S. Org. Biomol. Chem. 2011, 9, 1277; e Yu, J.; Shi, F.; Gong, L.-Z. Acc. Chem. Res.
2011, in press. doi:10.1021/ar2000343 and references cited therein.
9. (a) Jiang, B.; Tu, S. J.; Kaur, P.; Wever, W.; Li, G. J. Am. Chem. Soc. 2009, 131,
11660; (b) Shi, F.; Li, C.; Xia, M.; Miao, K.; Zhao, Y.; Tu, S.; Zheng, W.; Zhang, G.;
Ning, M. Bioorg. Med. Chem. Lett. 2009, 19, 5565; (c) Wei, P.; Zhang, X.; Tu, S.;
Yan, S.; Ying, H.; Ouyang, P. Bioorg. Med. Chem. Lett. 2009, 19, 828; (d) Jiang, B.;
Li, C.; Shi, F.; Tu, S.-J.; Kaur, P.; Wever, W.; Li, G. J. Org. Chem. 2010, 75, 2962; (e)
Shi, F.; Dai, A.-X.; Zhang, S.; Zhang, X.-H.; Tu, S.-J. Eur. J. Med. Chem. 2011, 46,
953; (f) Shi, F.; Ding, J.; Zhang, S.; Hao, W.-J.; Cheng, C.; Tu, S. Bioorg. Med. Chem.
Lett. 2011, 21, 1554.
1992, 123, 919; (e) Bohrisch, J.; Faltz, H.; Patzel, M.; Liebscher, J. Tetrahedron
1994, 50, 10701.
2. (a) Monks, N. R.; Blankey, D. C.; East, S. J.; Dowell, R. I.; Caluete, J. A.; Curtin, N.
J.; Arris, C. E.; Newell, D. R. Eur. J. Cancer 2002, 11, 1543; (b) LePez, J. B.;
DzXuong, N.; Gosse, C.; Paolett, C. Proc. Natl. Acad. Sci. U.S.A. 1974, 71, 5078.
3. (a) El-Tamany, E. S.; El-Shahed, F. A.; Mohamed, B. H. J. Serb. Chem. Soc. 1999,
64, 9; (b) Ismail, Z. H.; Aly, G. M.; El-Degwi, M. S.; Heiba, H. I.; Ghorab, M. M.
Egypt. J. Biotechnol. 2003, 13, 73.
4. Zaki, M. E. A.; Soliman, H. A.; Hiekal, O. A.; Rashad, A. E. Z. Naturforsch., C 2006,
61, 1.
5. Tu, S.-J.; Cao, X.-D.; Hao, W.-J.; Zhang, X.-H.; Yan, S.; Wu, S.-S.; Han, Z.-G.; Shi, F.
Org. Biomol. Chem. 2009, 7, 557.
6. (a) Schreiber, S. L. Science 2000, 287, 1964; (b) Dandapani, S.; Marcaurelle, L. A.
Curr. Opin. Chem. Biol. 2010, 14, 362; (c) Oh, S.; Jang, H. J.; Ko, S. K.; Ko, Y.; Park,
S. B. J. Comb. Chem. 2010, 12, 548; (d) Sore, H. F.; Blackwell, D. T.; MacDonald, S.
J. F.; Spring, D. R. Org. Lett. 2010, 12, 2806; (e) Kumar, A.; Gupta, G.; Srivastava,
S. J. Comb. Chem. 2010, 12, 458; (f) Karapetyan, V.; Mkrtchyan, S.; Hefner, J.;
Fischer, C.; Langer, P. J. Org. Chem. 2010, 75, 809; (g) Chen, C.-H.; Chien, M.-H.;
Kuo, M.-L.; Chou, C.-T.; Lai, J.-J.; Lin, S.-F.; Thummanagoti, S.; Sun, C.-M. J. Comb.
Chem. 2009, 11, 1038.
10. The experimental procedures of synthesis and bioassay as well as the
spectroscopic data of the synthesized compounds are available in the
Supplementary data.
11. Anderson, R. A.; Broadhurst, C. L.; Polansky, M. M.; Schmidt, W. F.; Khan, A.;
Flanagan, V. P.; Schoene, N. W.; Graves, D. J. J. Agric. Food Chem. 2004, 52, 65.
12. Zheng, W.; Zhao, Y.; Zhang, M.; Wei, Z.; Miao, K.; Sun, W. Med. Mycol. 2009, 47,
814.
7. (a) Jiang, B.; Hao, W.-J.; Wang, X.; Shi, F.; Tu, S.-J. J. Comb. Chem. 2009, 11, 846;
(b) Shi, F.; Dai, A.-X.; Zhang, X.-H.; Jiang, B.; Tu, S.-J. ACS Comb. Sci. 2011, 13,
147; (c) Shi, F.; Zhang, S.; Wu, S.-S.; Gao, Y.; Tu, S.-J. Mol. Divers. 2011, 15, 497.