Synthesis and in vitro antitumor activity of 1,3,4-oxadiazole derivatives based on benzisoselenazolone

Article abstract of DOI:10.1248/cpb.c12-00250

A series of novel 1,3,4-oxadiazole derivatives based on benzisoselenazolone has been prepared and tested for antiproliferative activity in vitro against the cells of human cancer cell lines: SSMC-7721 (human liver cancer cell), MCF-7 (human breast cancer cell) and A549 (human lung cancer cell). All the compounds obtained exhibited antiproliferative activity and showed selective cytotoxicity against different cancer cells. Compounds 7d and 7i showed significant antiproliferative activities against MCF-7 cells, with IC₅₀ values of 1.07 and 1.76/μM respectively. Compound 7d were found to be the most potent compound against SSMC-7721 cells, with IC₅₀ values 4.46/μM.

Full text of DOI:10.1248/cpb.c12-00250

July 2012
Regular Article
Chem. Pharm. Bull. 60(7) 887–891 (2012)
887
Synthesis and in Vitro Antitumor Activity of 1,3,4-Oxadiazole
Derivatives Based on Benzisoselenazolone
Zhen-Hua Luo, Shuang-Yan He, Bao-Quan Chen,* Yan-Ping Shi, Yu-Ming Liu, Cai-Wen Li, and
Qiu-Sheng Wang
School of Chemistry and Chemical Engineering, Tianjin University of Technology; Binshui West Road 391, Tianjin
300384, P.R. China. Received March 14, 2012; accepted April 9, 2012
A series of novel 1,3,4-oxadiazole derivatives based on benzisoselenazolone has been prepared and
tested for antiproliferative activity in vitro against the cells of human cancer cell lines: SSMC-7721 (human
liver cancer cell), MCF-7 (human breast cancer cell) and A549 (human lung cancer cell). All the compounds
obtained exhibited antiproliferative activity and showed selective cytotoxicity against different cancer cells.
Compounds 7d and 7i showed significant antiproliferative activities against MCF-7 cells, with IC50 values of
1.07 and 1.76µM respectively. Compound 7d were found to be the most potent compound against SSMC-7721
cells, with IC50 values 4.46µM.
Key words 1,3,4-oxadiazole; benzisoselenazolone; synthesis; antitumor activity
Selenium is closely related with human health as a trace el- Finnigan-MAT4510 (electrospray ionization (ESI)) mass spec-
ement.1,2) For many years the organoselenium compounds were trometer. Elemental analyses (CHN) were performed on an
synthesized as potential pharmaceuticals, and have become Elementar Vario EL.
hot spots in the studies of tumor prevention and therapy.3,4)
Unless otherwise noted, all solvents and reagents were ob-
Among them, ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)- tained from commercial suppliers and used without further
one, Fig. 1) is one of the most well-known mimic of gluta- purification.
thione peroxidase (GSH-Px), which has been investigated as
The synthesis of target compounds 7a–j was achieved start-
good anti-inflammatory effects5) and anticancer activity.6) ing with 2-chloroselenobenzoyl chloride 4 and 2-amino-5-sub-
Moreover, the selenium in ebselen is not bioavailable. This stituted-1,3,4-oxadiazole 6a–j in Chart 1 with 85.3–91.2%
is probably the reason for its low toxicity (LD50: 6180mg/ yield.
kg,rats). Study has demonstrated that the biological activity
Compound 4 was prepared according to our previously re-
and low toxicity of ebselen may be related to cyclic selen- ported method as showed in Chart 1.12,13) Potassium diselenide
enamide structure, but selenium is still the central element of 1 was derived from selenium by potassium borohydride reduc-
biological activity.7) This conclusion has a great guiding sig- tion. The diazonium salt of anthranilic acid 2 was treated with
nificance for finding better selenium anticancer agents through compound 1 to yield 2,2′-diselenodibenzoic acid 3, which was
structural transformation.
treated with thionyl chloride to furnish compound 4 under
It has been shown that 1,3,4-oxadiazole derivatives possess refluxing condition for 3h in good yield. The reaction of vari-
interesting biological properties such as anticancer,8) anti- ous substituted aromatic aldehyde with semicarbazide hydro-
bacterial,9) anti-inflammatory10) and anticonvulsant activity.11) chloride yielded the desired semicarbazones 5a–j, which were
Moreover, the introduction of different heterocyclic backbone treated with bromine in glacial acetic acid containing sodium
to the oxadiazole nucleus will affect its biological activity, acetate to give 2-amino-5-substituted-1,3,4-oxadiazole 6a–j.
which has drawn widespread attention.8,11) In view of observa- Finally, the condensation of compounds 4 and 6a–j yielded
tions, we report herein on the synthesis of 1,3,4-oxadiazole the corresponding target compounds 7a–j in the presence of
derivatives based on benzisoselenazolone with ebselen as a n-butyllithium. All the synthesized compounds 7a–j were
lead compound. Meanwhile, their in vitro antitumor activities purified by recrystalization using various solvents and struc-
1
were evaluated against SSMC-7721, MCF-7 and A549 cells turally characterized by IR, H-NMR, ESI-MS techniques and
with the aim of obtaining more information about the influ- elemental analysis.
ence of substituents on antiproliferative activities in this class
of compounds.
Synthesis of 2,2′-Diselenodibenzoic Acid (3) 3 was pre-
pared from diazonium salt of anthranilic acid and potassium
diselenide according to the procedure reported previously in
83% yield,12) mp 294.0–295.0 C.
°
Experimental
Chemistry All melting points were determined by a X-6
Synthesis of 2-Chloroselenobenzoyl Chloride (4) 4 was
microscope melting point apparatus and are uncorrected. prepared from 2,2′-diselenodibenzoic acid and thionyl chlo-
Infrared spectra were recorded in KBr pellets on a Nicolet ride according to the procedure reported previously in 73%
5DXB spectrometer. 1H-NMR spectra were recorded on a yield,13) mp 62.0–63.0 C.
°
JNM-GX400 spectrometer using DMSO-d6 as solvent and
tetramethylsilane as internal standard; Chemical shifts are
showed in δ values (ppm) and the coupling constants are
expressed in J values (Hz). Mass spectra were taken with a
The authors declare no conflict of interest.
Fig. 1. Structure of Ebselen
© 2012 The Pharmaceutical Society of Japan
*To whom correspondence should be addressed. e-mail: chenbaoquan6@yahoo.com.cn

888
Vol. 60, No. 7
Chart 1. The Synthesis Route Target Compounds 7a–j
General Procedure for the Synthesis of 2-Amino-5-sub-
2-Amino-5-(4-chlorophenyl)-1,3,4-oxadiazole (6d): Yield
°
stituted-1,3,4-oxadiazole (6a–j) Semicarbazide hydrochlo- 68.2.%; pale yellow solid; mp 271.2–273.0 C (lit. mp
15)
°
ride (12mmol) was dissolved in water (10mL). The mixture 272–274 C ).
was adjusted pH=7 with 40% aqueous sodium hydroxide and 2-Amino-5-(4-bromophenyl)-1,3,4-oxadiazole (6e): Yield
°
°
slowly heated to 65 C. Aromatic aldehyde (10mmol) in 5mL 66.8%; pale yellow solid; mp 274.2–276.0 C (lit. mp
15)
°
ethanol was added dropwise to the solution of semicarbazide 275–276 C ).
hydrochloride and stirred for 1.5h. After cooling the result- 2-Amino-5-(4-methylphenyl)-1,3,4-oxadiazole (6f): Yield
ing precipitate was collected by filtration, washed with water 75.4%; pale yellow solid; mp 264.5–266.5 C (lit. mp
°
15)
°
(3×30mL) and of ethanol (2×10mL) to give crude semicarba- 265–267 C ).
zone 5. Bromine (12mmol) in glacial acetic acid (2mL) was 2-Amino-5-(4-isopropylphenyl)-1,3,4-oxadiazole (6g): Yield
added dropwise to a solution of semicarbazone 5 and sodium 70.5%; pale yellow solid; mp 216.7–218.1 C; IR (KBr) cm :
acetate (10mmol) in glacial acetic acid (12mL). The mixture 3311 (N–H), 3122 (C–H), 1444 (C=N), 748 (Ar-H), 690 (C–
−1
°
1
was stirred for 12 to 16h at room temperature (the end of O–C); H-NMR (DMSO-d6, 400MHz) δ: 7.72 (d, J=8.0Hz,
reaction was monitored by TLC). After completion of reac- 2H, ph-H), 7.40 (d, J=8.0Hz, 2H, ph-H), 7.22 (s, 2H, NH2),
tion the mixture was poured into crushed ice. The resulting 2.90–2.98 (m, 1H, CH), 1.23 (d, J=4.0Hz, 6H, CH3); ESI-MS
precipitate was collected by filtration, washed well with water m/z: 204 [M+H]+.
and further purified by recrystallization from ethanol to give
2-Amino-5-(4-methoxyphenyl)-1,3,4-oxadiazole (6h): Yield
°
68.5%; pale yellow solid; mp 249.2–251.0 C (lit. mp
the corresponding 2-amino-5-substituted-1,3,4-oxadiazole.
15)
°
2-Amino-5-phenyl-1,3,4-oxadiazole (6a): Yield 75.5%; pale 250–251 C ).
14)
°
°
yellow solid; mp 240.5–242.5 C(lit. mp 241–243 C ).
2-Amino-5-(3,4,5-trimethoxyphenyl)-1,3,4-oxadiazole (6i)
°
2-Amino-5-(2-fluorophenyl)-1,3,4-oxadiazole (6b): Yield Yield 76.9%; pale yellow solid; mp 204.5–206.1 C; IR (KBr)
−1
71.8%; pale yellow solid; mp 191.5–192.6 C; IR (KBr) cm : cm−1: 3148 (N–H), 2937 (C–H), 1425 (C=N), 1238 (C–O), 742
°
1
3304 (N–H), 3117 (C–H), 1443 (C=N), 1310 (C–F), 747 (Ar- (Ar-H), 683 (C–O–C); H-NMR (DMSO-d6, 400MHz) δ: 7.45
1
H), 684 (C–O–C); H-NMR (DMSO-d6, 400MHz) δ: 7.85 (t, (s, 1H, ph-H), 7.43 (s, 1H, ph-H), 7.34 (s, 2H, NH2), 3.89 (s,
J=8.0Hz, 1H, ph-H), 7.55–7.60 (m, 1H, ph-H), 7.37–7.44 (m, 6H, OCH3), 3.72 (s, 3H, OCH3); ESI-MS m/z: 252 [M+H]+.
2H, ph-H), 7.36 (s, 2H, NH2); ESI-MS m/z: 180 [M+H]+.
2-Amino-5-(4-nitrophenyl)-1,3,4-oxadiazole (6j): Yield
°
2-Amino-5-(4-fluorophenyl)-1,3,4-oxadiazole (6c): Yield 73.2%; pale yellow solid; mp 260.2–262.1 C (lit. mp
−1
16)
°
°
69.2%; pale yellow solid; mp 184.5–185.8 C; IR (KBr) cm : 260–262 C ).
3305 (N–H), 3085 (C–H), 1445 (C=N), 1309 (C–F), 745
General Procedure for the Synthesis of 2-(2-Substituted-
(Ar–H), 688 (C–O–C); H-NMR (DMSO-d6, 400MHz) δ: 7.73 1,3,4-thiadiazol-5-yl)benzisoselenazol-3(2H)-one (7a–j) n-
1
(s, 4H, ph-H), 7.31 (s, 2H, NH2); ESI-MS m/z: 180 [M+H]+.
Butyllithium (10mmol) in hexane (1.6M, 6.3mL) was injected

July 2012
889
into a solution of 2-amino-5-substituted-1,3,4-oxadiazole 6
2-[2-(4-Methylphenyl)-1,3,4-thiadiazol-5-yl]benzisosel-
(10mmol) in dry tetranydrofuran (THF) (60mL) under nitro- enazol-3(2H)-one (7f): Yield 91.2%; recrystallized from
°
°
gen atmosphere at −72 C and stirred for 1h. 2-Chloroseleno- ethanol; pale yellow solid; mp 266.2–268.2 C. IR (KBr)
benzoyl chloride 4 (10mmol) in dry THF (4mL) was added cm−1: 1614 (C=O), 1498 (C=N), 1315 (C–N), 1019 (Ar-Se),
1
dropwise to above solution and stirred for 6h at room tem- 734 (Ar-H), 669 (C–O–C); H-NMR (DMSO-d6, 400MHz) δ:
perature. After completion of reaction the mixture was poured 8.08 (d, J=8.0Hz, 1H, ph-H), 7.97 (d, J=7.2Hz, 1H, ph-H),
into water (150mL). The resulting precipitate was collected 7.88 (d, J=8.0Hz, 2H, ph-H), 7.78 (t, J=7.6Hz, 1H, ph-H),
by filtration, washed well with water and further purified by 7.53 (t, J=7.6Hz, 1H, ph-H), 7.43 (d, J=7.6Hz, 2H, ph-H),
recrystallization to give the corresponding title compounds 2.40(s, 3H, CH3); ESI-MS m/z: 357 [M+H]+. Anal. Calcd for
7a–j in good yields. The physical and analytical data are given C16H11N3O2Se: C, 53.94; H, 3.11; N, 11.80. Found: C, 53.81; H,
as follows.
3.15; N, 11.91.
2-(2-Phenyl-1,3,4-thiadiazol-5-yl)benzisoselenazol-3(2H)-
2-[2-(4-Isopropylphenyl)-1,3,4-thiadiazol-5-yl]benzisosel-
one (7a): Yield 89.8%; recrystallized from N,N-dimethylfor- enazol-3(2H)-one (7g): Yield 90.8%; recrystallized from
−1
°
°
mamide (DMF)–water; pale yellow solid; mp 218.0–220.0 C; ethanol; pale yellow solid; mp 231.6–233.2 C; IR (KBr) cm :
IR (KBr) cm−1: 1635 (C=O), 1479 (C=N), 1324 (C–N), 1018 1613 (C=O), 1439 (C=N), 1311 (C–N), 1018 (Ar-Se), 732 (Ar-
(Ar-Se), 734 (Ar-H), 669 (C–O–C); 1H-NMR (DMSO-d6, H), 670 (C–O–C); H-NMR (DMSO-d6, 400MHz) δ: 8.12 (d,
1
400MHz) δ: 8.10 (d, J=8.0Hz, 1H, ph-H), 7.98–8.01 (m, 3H, J=8.0Hz, 1H, ph-H), 7.98 (d, J=8.0Hz, 1H, ph-H), 7.91 (d,
ph-H), 7.78 (t, J=7.8Hz, 1H, ph-H), 7.63–7.65 (m, 3H, ph-H), J=8.0Hz, 2H, ph-H), 7.78 (t, J=7.6Hz, 1H, ph-H), 7.50–7.55
7.54 (t, J=7.6Hz, 1H, ph-H); ESI-MS m/z: 343 [M+H]+; Anal. (m, 3H, ph-H), 2.97–3.04 (m,1H, CH), 1.25 (d, J=6.8Hz,
Calcd for C15H9N3O2Se: C, 52.64; H, 2.65; N, 12.28. Found: C, 6H, CH3); ESI-MS m/z: 385 [M+H]+. Anal. Calcd for
52.50; H, 2.61; N, 12.37.
2-[2-(2-Fluorophenyl)-1,3,4-thiadiazol-5-yl]benzisosel- 3.89; N, 10.98.
enazol-3(2H)-one (7b): Yield 87.8%; recrystallized from 2-[2-(4-Methoxyphenyl)-1,3,4-thiadiazol-5-yl]benziso-
C18H15N3O2Se: C, 56.26; H, 3.93; N, 10.93. Found: C, 56.16; H,
°
DMF–water; pale yellow solid; mp 258.8–259.3 C; IR (KBr) selenazol-3(2H)-one (7h): Yield 90.3%; recrystallized from
−1
cm−1: 1657 (C=O), 1442 (C=N), 1347 (C–N), 1300 (C–F), ethanol; pale yellow solid; mp 261.7–263.7 C; IR (KBr) cm :
°
1
1029 (Ar-Se), 758 (Ar-H), 669 (C–O–C); H-NMR (DMSO-d6, 1634 (C=0), 1445 (C=N), 1319 (C–N), 1047 (C–O), 1032
400MHz) δ: 8.10 (d, J=8.0Hz, 1H, ph-H), 7.99–8.03 (m, 2H, (Ar-Se), 734 (Ar-H), 669 (C–O–C); 1H-NMR (DMSO-d6,
ph-H), 7.78 (t, J=7.6Hz, 1H, ph-H), 7.68–7.73 (m, 1H, ph-H), 400MHz) δ: 8.09 (d, J=8.4Hz, 1H, ph-H), 7.98 (d, J=7.6Hz,
7.45–7.55 (m, 3H, ph-H); ESI-MS m/z: 361 [M+H]+. Anal. 1H, ph-H), 7.93 (d, J=8.4Hz, 2H, ph-H), 7.77 (t, J=7.6Hz, 1H,
Calcd for C15H8N3FO2Se: C, 50.02; H, 2.24; N, 11.67. Found: ph-H), 7.57 (t, J=7.6Hz, 1H, ph-H), 7.18 (d, J=8.4Hz, 2H,
C, 50.13; H, 2.20; N, 11.73.
ph-H), 3.87 (s, 3H, OCH3); ESI-MS m/z: 373 [M+H]+. Anal.
2-[2-(4-Fluorophenyl)-1,3,4-thiadiazol-5-yl]benzisosel- Calcd for C16H11N3O3Se: C, 51.63; H, 2.98; N, 11.29. Found: C,
enazol-3(2H)-one (7c): Yield 86.6%; recrystallized from 51.50; H, 3.02; N, 11.35.
°
DMF–water; pale yellow solid; mp 274.9–276.1 C; IR (KBr)
2-[2-(3,4,5-Trimethoxyphenyl)-1,3,4-thiadiazol-5-yl]-
cm−1: 1614 (C=O), 1440 (C=N), 1315 (C–N), 1309 (C–F), benzisoselenazol-3(2H)-one (7i): Yield 87.9%; recrystallized
1
°
1019 (Ar-Se), 729 (Ar-H), 669 (C–O–C); H-NMR (DMSO-d6, from ethanol; pale yellow solid; mp 241.8–243.1 C. IR (KBr)
400MHz) δ: 8.15 (d, J=8.0Hz, 1H, ph-H), 8.04 (t, J=9.0Hz, cm−1: 1625 (C=O), 1443 (C=N), 1323 (C–N), 1021 (Ar-Se),
1
3H, ph-H), 7.79 (t, J=7.2Hz, 1H, ph-H), 7.54 (t, J=7.4Hz, 1238 (C–O), 734 (Ar-H), 669 (C–O–C); H-NMR (DMSO-d6,
1H, ph-H), 7.41 (t, J=8.8Hz, 2H, ph-H); ESI-MS m/z: 361 400MHz) δ: 8.08 (d, J=8.0Hz, 1H, ph-H), 7.93 (d, J=7.2Hz,
[M+H]+. Anal. Calcd for C15H8N3FO2Se: C, 50.02; H, 2.24; N, 1H, ph-H), 7.92–7.89 (m, 1H, ph-H), 7.66 (t, J=7.2Hz, 1H, ph-
11.67. Found: C, 50.15; H, 2.28; N, 11.58.
H), 7.37 (s, 2H, ph-H), 3.88 (s, 6H, OCH3), 3.75 (s, 3H, OCH3);
2-[2-(4-Chlorophenyl)-1,3,4-thiadiazol-5-yl]benziso- ESI-MS m/z: 433 [M+H]+. Anal. Calcd for C18H15N3O5Se: C,
selenazol-3(2H)-one (7d): Yield 88.6%; recrystallized from 50.01; H, 3.50; N, 9.72. Found: C, 49.89; H, 3.46; N, 9.80
°
DMF–water; pale yellow solid; mp 225.0–226.8 C; IR
2-[2-(4-Nitrophenyl)-1,3,4-thiadiazol-5-yl]benziso-
(KBr) cm−1: 1639 (C=O), 1446 (C=N), 1309 (C–N), 1309 selenazol-3(2H)-one (7j): Yield 85.3%; recrystallized from
(C–Cl), 1013 (Ar-Se), 725 (Ar-H), 669 (C–O–C); 1H-NMR DMF–water; pale yellow solid; mp 281.2–282.7 C. IR (KBr)
°
(DMSO-d6, 400MHz) δ: 8.10 (d, J=8.4Hz, 1H, ph-H), 7.98 cm−1: 1664 (C=0), 1446 (C=N), 1381 (C–N), 1022 (Ar-Se),
1
(t, J=6.8Hz,3H, ph-H), 7.78 (d, J=7.6Hz, 1H, ph-H), 7.71 (d, 1340 (C–N), 741 (Ar-H), 671 (C–O–C); H-NMR (DMSO-d6,
J=8.0Hz, 2H, ph-H), 7.52 (d, J=8.0Hz, 1H, ph-H); ESI-MS 400MHz) δ: 8.13 (t, J=8.0Hz, 2H, ph-H), 8.05 (d, J=7.6Hz,
m/z: 378 [M+H]+. Anal. Calcd for C15H8N3ClO2Se: C, 47.83; 1H, ph-H), 7.95 (d, J=7.6Hz, 1H, ph-H), 7.89 (d, J=6.4Hz,
H, 2.14; N, 11.16. Found: C, 47.73; H, 2.16; N, 11.21.
1H, ph-H), 7.79–7.87 (m, 1H, ph-H), 7.42 (t, J=6.4Hz, 1H, ph-
2-[2-(4-Bromophenyl)-1,3,4-thiadiazol-5-yl]benziso- H); ESI-MS m/z: 388 [M+H]+. Anal. Calcd for C15H8N4O4Se:
selenazol-3(2H)-one (7e): Yield 88.2%; recrystallized from C, 46.53; H, 2.08; N, 14.47. Found: C, 46.41; H, 2.04; N, 14.54.
−1
°
DMSO–water; yellow solid; mp >300 C; IR (KBr) cm : 1633
Bioassays The following established in vitro human
(C=O), 1458 (C=N), 1337 (C–N), 1311 (C–Br), 1026 (Ar-Se), cancer cell lines were used: SSMC-7721 (human liver cancer
1
751 (Ar-H), 678 (C–O–C); H-NMR (DMSO-d6, 400MHz) δ: cell), MCF-7 (human breast cancer cell) and A549 (human
8.27 (d, J=8.4Hz, 1H, ph-H), 8.01 (d, J=6.8Hz, 1H, ph-H), lung cancer cell) which were purchased from Tumor Cell Re-
7.86 (d, J=8.0Hz, 2H, ph-H), 7.52 (t, J=7.6Hz, 1H, ph-H), sources Bank, Chininese Academy of Medical Sciences. Cell
7.36 (d, 2H, ph-H); ESI-MS m/z: 422 [M+H]+. Anal. Calcd for counting kit-8 [2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-
C15H8N3BrO2Se: C, 42.78; H, 1.91; N, 9.98. Found: C, 42.88; 5-(2,4-disulfophenyl)-2H-tetrazolium monosodium salt] was
H, 1.90; N, 9.93.
from Dojindo (Japan).

890
Vol. 60, No. 7
Dissolve compounds 7a–j and ebselen in dimethyl sulfox- antitumor activity (IC50=5.24µM). Compounds 7f, 7i and 7j
ide (DMSO) to make stock solution at the concentration of showed similar activity, but these compounds all lowered the
1.0×10−2 mol·L−1. During the experiment, using cell culture activity compared with 7a and ebselen. Therefore, in SSMC-
medium RPMI-1640 to dilute to the desired concentration. 7721cells, the influence of substituent group on antitumor
Cells in the exponential phase were seeded in 96-well cul- activity did not show apparent regularity.
4
°
ture plates at the confluence of 10 cells/well, kept in 37 C,
Most of the compounds 7a–j showed higher antiprolifera-
5% CO2 incubator for 24h. Replaced the medium contain- tive activity than that ebselen did against MCF-7 cells. Espe-
ing different concentrations of compounds in fresh medium, cially noteworthy is compound 7d, which exhibited significant
°
at 37 C, 5% CO2 incubator for 48h. Added 90µL of fresh antiproliferative activity against MCF-7 cells (IC50=1.07µM).
°
medium and 10µL CCK-8, kept a 37 C and 5% CO2 for 1h. In addition, multi-electron-donating substitution of phenyl
The sample cell was added into 96-well microplate reader and ring displays higher antiproliferative activity than single-
read the plate at 450nm, recorded the absorbance value opti- electron-donating substitution of phenyl ring at C-2 position.
cal density(OD). The inhibition rate, half the concentration of For instance, compound 7i showed the best antiproliferative
IC50, of different compounds were calculated using SPSS soft- activity (IC50=1.76µM), that is much more effective than sin-
ware according to the following formula:
gle-electron-donating substituents 7f–h. The antiproliferative
activity (IC50=4.02µM) of phenyl substituent C-2 position 7a
is better than ebselen. But the activity was highly decreased
while the introduction of bromophenyl or nitrophenyl group
at C-2 position against MCF-7 cells, with IC50 values of 20.01
and 18.41µM, respectively. Whereas the 2-fluorophenyl sub-
relative cell viability
OD value for the test group  blank OD
control OD value  blank OD value
=
×100%
Results and Discussion
The antiproliferative activities of the newly synthesized stituents 7b at C-2 position significantly improved anticancer
compounds were tested against SSMC-7721 (human liver activity (IC50=3.55µM).
cancer cell), MCF-7 (human breast cancer cell) and A549 (hu-
All the compounds 7a–j showed lower antiproliferative
man lung cancer cell) cell lines using CCK-8 assay, which was activity than that ebselen did against A549 cells. But com-
used as a substitute for 3-(4,5-dimethylthiazol-2-yl)-2,5-di- pound 7i remained high activity (IC50=9.60µM). Moreover, the
phenyltetrazolium bromide (MTT) assay. The results of cyto- results obtained from the observation showed that the intro-
toxic activity in vitro were expressed as the IC50 (µM). Ebselen duction of electron-donating groups was effective to enhance
was used as a reference cytotoxic agent (positive test control). the anticancer activity. Apparently, this class of compounds
The results of the cytotoxicity studies are summarized in showed selective cytotoxicity against different human cancer
Table and compared with the activity of ebselen.
All these compounds possess a common 2-(1,3,4-oxadiazol-
cells.
Another noteworthy feature of the compounds that bromo-
5-yl)-benzisoselenazolone nucleus in which substituent group phenyl and nitrophenyl substituents at C-5 position, 7e and 7j
of phenyl ring at C-2 position on the 1,3,4-oxadiazole plays all showed weak antiproliferative activities against three hu-
important roles in the potency of biologically active com- man cancer cell lines.
pounds.
As shown in Table 1, most of the compounds 7a–j showed
Conclusion
moderate activity aganinst SSMC-7721 cells, while com-
In summary, we have synthesized a series of novel
pounds 7a, 7c and 7g having IC50 values ranging from 15.90 1,3,4-oxadiazole derivatives based on benzisoselenazolone and
to 19.63µmol/L exhibited similar activity to that of ebselen evaluated their in vitro antiproliferative activities against three
(IC50=18.33µM). but compound 7b showed better activity different human cancer cell lines. Some of the compounds
than ebselen did (IC50=12.87µM). Especially, 4-chlorophe- inhibited the proliferation better than lead compound ebselen
nyl substituent 7d showed the best antiproliferative activity did, and the performance of which has certain selectivity. In
(IC50=4.46µM), that was much more effective than ebselen. partticular, compounds 7d and 7i showed significant antipro-
Similarly, 4-methoxy-phenyl substituent 7h also showed good liferative activities against MCF-7 cells, with IC50 values of
Table 1. Antiproliferative Activity of Compounds 7a–j and Referential Ebselen against the Cells of Human Cancer Lines
Calculated IC50 value (µM)
Compd.
R
SSMC-7721
MCF-7
A549
7a
7b
Ph
2-F-Ph
19.63 1.4
12.87 0.9
15.90 1.0
4.46 0.1
7.23 0.04
3.55 0.2
8.15 0.1
1.07 0.05
20.01 1.1
18.73 0.7
8.81 0.08
9.09 0.7
1.76 0.1
18.41 0.9
15.02 0.5
25.65 0.7
27.54 3.1
48.87 4.9
15.48 1.1
41.46 2.8
20.38 0.4
20.84 1.2
23.06 1.9
9.60 0.4
7c
4-F-Ph
7d
4-Cl-Ph
7e
4-Br-Ph
35.80 3.7
27.09 2.1
16.36 0.8
5.24 0.1
7f
4-CH3-Ph
4-(i-C3H7)-Ph
4-OCH3-Ph
3,4,5-(OCH3)3-Ph
4-NO2-Ph
—
7g
7h
7i
24.31 1.1
25.29 1.6
18.33 0.4
7j
28.73 1.4
3.75 0.06
Ebselen

July 2012
891
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1.07 and 1.76µM respectively. Similarly, compound 7b also
showed highly effective antiproliferative activities against
MCF-7 cells, with IC50 values of 3.55µM. Compound 7d was
found to be the most potent compound against SSMC-7721
cells, with IC50 values 4.46µM. Therefore, the results laid a
foundation for further improving the potency and the selectiv-
ity of this series of compounds.
Acknowledgment We are grateful to the National Natural
Science Foundation of China (20971097) for financial support.
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