Synthesis and anticonvulsant activity of some 7-alkoxy-2H-1,4-benzothiazin- 3(4H)-ones and 7-alkoxy-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazines

Article abstract of DOI:10.1248/cpb.58.326

A series of 7-alkoxy-2H-1,4-benzothiazin-3(4H)-ones and a new series of 7-alkoxy-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine derivatives were synthesized using 5-methoxybenzo[d]thiazol-2-amine as starting material. The structures of the compounds were

Full text of DOI:10.1248/cpb.58.326

326
Chem. Pharm. Bull. 58(3) 326—331 (2010)
Vol. 58, No. 3
Synthesis and Anticonvulsant Activity of Some 7-Alkoxy-2H-1,4-
benzothiazin-3(4H)-ones and 7-Alkoxy-4H-[1,2,4]triazolo[4,3-
d]benzo[b][1,4]thiazines
b
a
b
b
,b
*
Li-Qiu ZHANG, Li-Ping GUAN, Cheng-Xi WEI, Xian-Qing DENG, and Zhe-Shan QUAN
a Food and Pharmacy College, Zhejiang Ocean University; Zhoushan 316004, P. R. China: and b College of Pharmacy,
Yanbian University; No. 1829, JuZi Street, Yanji, Jilin 133000, P. R. China.
Received September 10, 2009; accepted October 15, 2009; published online December 4, 2009
A series of 7-alkoxy-2H-1,4-benzothiazin-3(4H)-ones and a new series of 7-alkoxy-4H-[1,2,4]triazolo[4,3-
d]benzo[b][1,4]thiazine derivatives were synthesized using 5-methoxybenzo[d]thiazol-2-amine as starting mate-
1
rial. The structures of the compounds were elucidated by IR, H-NMR spectroscopic data and microanalyses.
The anticonvulsant activity of these compounds was evaluated by maximal electroshock (MES) test and rotarod
test following intraperitoneal injection in KunMing mice. Among the synthesized compounds 3a—v, 7-(hexyl-
oxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3f) could be considered potentially the most useful and safe therapeutic
compound. Among the synthesized compounds 4a—u, compound 7-(2-fluorobenzyloxy)-4H-[1,2,4]triazolo[4,3-
d]benzo[b][1,4]thiazine (4k) was the most active compound with an ED50 of 17.0 mg/kg, TD50 of 243.9 mg/kg and
protective index (PI) of 14.3. Its neurotoxicity was lower than all the other synthesized compounds and also
markedly lower than that of the reference drug carbamazepine.
Key words anticonvulsant; triazole; thiamine; maximal electroshock
Epilepsy, a common disease characterized by recurrent mers of 7-alkoxyl-4,5-dihydro-[1,2,4]triazolo[4,3-a]quino-
seizures, afflicts ꢀ50 million people worldwide according to lines. The structures of the compounds were elucidated
1
epidemiological studies.1) For epilepsy treatment, nearly 95% by IR, H-NMR spectroscopic data and microanalyses. The
of today’s clinically available drugs were approved before anticonvulsant activity was evaluated by maximal electro-
1985 and provide satisfactory seizure control for only 60— shock (MES) test; neurotoxicity was evaluated by rotarod
70% of patients. These drugs, however, also cause notable test. Among compounds 3a—v and 4a—u, compound 4k
adverse side effects such as drowsiness, ataxia, gastrointesti- was the most active with an ED50 of 17.0 mg/kg, TD50 of
nal disturbance, hepatotoxicity and megaloblastic anemia2—4) 243.9 mg/kg and protective index (PI; TD50/ED50) of 14.3.
and even life threatening conditions.5) Research to find more
Experimental
effective and safer antiepileptic drugs is, therefore, impera-
Chemistry Melting points were determined in open capillary tubes and
were uncorrected. 1H-NMR spectra were measured by AV-300 (Bruker,
Switzerland); all chemical shifts are given in parts per million relative to
tetramethylsilane. Mass spectra were measured by HP1100LC (Agilent
Technologies, U.S.A.). Elemental analyses were performed on a 204Q CHN
(PerkineElmer, U.S.A.). Microanalyses of C, N, and H were performed by
Heraeus CHN Rapid Analyzer. The major chemicals were purchased from
Aldrich Chemical Corp. All other chemicals were of analytical grade.
Synthesis of 2-Amino-5-methoxy-thiophenol (1) 2-Amino-6-methoxy-
benzothiazole (30.0 g; 172 mmol) was suspended in 50% KOH (180 g KOH
dissolved in 180 ml water) and ethylene glycol (40 ml). The suspension was
heated to reflux for 48 h. Upon cooling to room temperature, toluene
(300 ml) was added and the reaction mixture neutralized, and the aqueous
layer extracted with another 200 ml of toluene. The toluene layers were com-
bined and washed with water and dried over MgSO4. Evaporation of the sol-
vent gave 15.3 g of 2-amino-5-methoxy-thiophenol as yellow solid.
tive and challenging in medicinal chemistry.
In the previous study, we reported the synthesis and
anticonvulsant activities of 7-alkoxyl-3,4-dihydro-quino-
lin-2(1H)-ones (pre. 1),6) 7-alkoxyl-4,5-dihydro[1,2,4]tria-
zolo[4,3-a]quinolines (pre. 2).7) In our search for new com-
pounds with anticonvulsant activity, we changed the 4-posi-
tion CH2 of the compounds (pre. 1) into sulfur. 7-Alkoxyl-
2H-benzo[b] [1,4]thiazin-3(4H)-ones (3a—v) were designed
and synthesized as the bioisosterism of 7-alkoxyl-3,4-dihy-
dro-quinolin-2(1H)-ones.
From compounds pre. 1 to compounds pre. 2, we in-
corporated triazole with 7-alkoxyl-2H-benzo[b][1,4]thiazin-
3(4H)-ones at the third and fourth position of the latter
and obtained 7-alkoxyl-4H-[1,2,4]triazolo[4,3-d]benzo[b]-
[1,4]thiazines (4a—u). Additionally, 7-alkoxyl-4H-[1,2,4]-
triazolo[4,3-d]benzo[b][1,4]thiazines were the bioisostereo-
1
mp 74—76 °C; yield 85%; H-NMR (CDCl3, 300 MHz) d: 3.77 (s, 3 H),
6.43 (dd, 1H, Jꢁ2.6, 8.5 Hz), 6.57 (d, 1H, Jꢁ8.5 Hz), 6.66 (d, 1H, Jꢁ
2.6 Hz).
Synthesis of 7-Methoxy-2H-benzo[b][1,4]thiazin-3(4H)-one (3a)
Compound 1 (24.54 g; 158 mmol), sodium bicarbonate (53.20 g; 633 mol)
and benzyltriethylammonium chloride (TEBA) (25.18 g; 110 mmol) were
placed into a round-bottomed flask containing 500 ml of acetonitrile, and the
mixtune was put in an ice-salt bath to keep the temperature 0—5 °C, there-
after, 2-chloroacetyl-chloride (23.26 g; 21 mmol) was added at moderate
speed and reacted for 40 min. Replacing the ice-salt bath with an oil bath,
the mixture was heated to reflux for 2 h, then the solvent removed under re-
duced pressure. The resultant product was purified by recrystallization with
ethanol–water (1 : 1).
mp 169—171 °C; yield 92%; 1H-NMR (DMSO, 300 MHz) d: 3.47 (s, 2H,
–S–CH2–), 4.12 (s, 3H, –OCH3), 6.78—6.89 (m, 3H, Ar-H), 10.38 (s, 1H,
–CONH); IR (KBr) cmꢂ1: 3422 (NH), 1686 (CꢁO), 1490 (C–O–C), 1068
Fig. 1. Previous Work 1, 2 and Present Work
© 2010 Pharmaceutical Society of Japan
∗ To whom correspondence should be addressed. e-mail: zsquan@ybu.edu.cn; glp730@yahoo.com.cn

March 2010
327
Chart 1. The Synthesis Route of Target Compounds 3a—v
(C–O–C); MS m/z: 196 (Mꢃ1); Anal. Calcd for C9H9NO2S: C, 55.37; H, (NH), 1709 (CꢁO), 1495 (C–O–C), 1108 (C–O–C); MS m/z: 280 (Mꢃ1);
4.65; N, 7.17. Found: C, 55.18; H, 4.83; N, 7.31.
Anal. Calcd for C15H21NO2S: C, 64.48; H, 7.58; N, 5.01. Found: C, 64.68;
H, 7.39; N, 5.30.
7-Hydroxy-2H-benzo[b][1,4]thiazin-3(4H)-one (2) To a stirred solu-
tion of boron tribromide (9 mmol) in anhydrous CH2Cl2, a CH2Cl2 solution
of compound 3a (0.6 g; 3 mmol) was added drop-wise and the reaction con-
7-(Octyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3h) mp 109—
1
111 °C; yield 46%; H-NMR (CDCl3, 300 MHz) d: 0.90 (t, 3H, Jꢁ6.7 Hz,
tinued for 1 h at 0 °C and an additional 2 h at 20 °C. Following the addition –CH3), 1.30—1.59 (m, 8H, (–CH2)4), 1.72—1.74 (m, 2H, –CH2–), 1.77—
of ice cold water, the organic layer was separated and the aqueous layer ex- 1.79 (m, 2H, –CH2–), 3.42 (s, 2H, –S–CH2–), 3.92 (t, 2H, Jꢁ6.7 Hz,
tracted with ethyl acetate. The combined organic layers were dried over with –OCH2–), 6.75—6.86 (m, 3H, Ar-H), 8.04 (s, 1H, –CONH); IR (KBr) cmꢂ1
:
anhydrous magnesium sulfate and evaporated under reduced pressure. A 3509 (NH), 1727 (CꢁO), 1438 (C–O–C), 1129 (C–O–C); MS m/z: 294
brown solid was obtained. (Mꢃ1); Anal. Calcd for C16H23NO2S: C, 65.49; H, 7.90; N, 4.77. Found: C,
mp 235—237 °C; yield 95%; 1H-NMR (CDCl3, 300 MHz) d: 3.42 (s, 2H, 65.71; H, 7.76; N, 4.59.
–S–CH2–), 6.69—6.97 (m, 3H, Ar-H), 7.55 (s, 1H, –OH), 7.70 (s, 1H,
7-(Dodecyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3i) mp 108—
110 °C; yield 43%; H-NMR (CDCl3, 300 MHz) d: 0.89 (t, 3H, Jꢁ6.8 Hz,
1
–CONH); IR (KBr) cmꢂ1: 3417 (NH), 1645 (CꢁO).
General Procedure for the Synthesis of 7-Alkoxy-2H-benzo[b][1,4]thi- –CH3), 1.27—1.56 (m, 8H, (–CH2)4), 1.60—1.70 (m, 8H, (–CH2)4), 1.71—
azin-3(4H)-ones (3b—v) K2CO3 (0.42 g; 3 mmol), absolute ethanol
(40 ml) and 7-hydroxy-2H-benzo[b][1,4] thiazin-3(4H)-one (2) (0.53 g;
3 mmol) were added in a 100 ml round-bottomed flask equipped with reflux
1.73 (m, 2H, –CH2–), 1.74—1.76 (m, 2H, –CH2–), 3.42 (s, 2H, –S–CH2–),
3.91 (t, 2H, Jꢁ6.3 Hz, –OCH2–), 6.73—6.86 (m, 3H, Ar-H), 7.67 (s, 1H,
–CONH); IR (KBr) cmꢂ1: 3491 (NH), 1737 (CꢁO), 1525 (C–O–C), 1039
condenser. After refluxing the mixture 30 min, alkyl bromide or benzyl chlo- (C–O–C); MS m/z: 350 (Mꢃ1); Anal. Calcd for C20H31NO2S: C, 68.72; H,
ride derivative (4 mmol) was added drop-wise into the mixture. The reaction 8.94; N, 4.01. Found: C, 68.92; H, 8.76; N, 4.22.
mixture was heated at reflux for 4—24 h, then poured into 100 ml of water.
The aqueous layer was extracted with dichloromethane (30 mlꢄ3). The
combined layers of dichloromethane were dried by anhydrous MgSO4.
7-(Benzyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3j) mp 172—
174 °C; yield 50%; H-NMR (CDCl3, 300 MHz) d: 3.42 (s, 2H, –S–CH2–),
5.11 (s, 2H, –OCH2–), 6.80—6.95 (m, 3H, Ar-H), 7.35 (d, 2H, Jꢁ5.8 Hz,
1
Evaporation of the solvents gave a crude product, which was purified by sil- Ar-H), 7.37 (m, 1H, Ar-H), 7.41 (d, 2H, Jꢁ5.2 Hz, Ar-H), 8.53 (s, 1H,
ica gel column chromatography with petroleum ether : ethyl acetate (3 : 2) to
a light-yellow solid.
–CONH); IR (KBr) cmꢂ1: 3537 (NH), 1674 (CꢁO), 1496 (C–O–C), 1064
(C–O–C); MS m/z: 272 (Mꢃ1); Anal. Calcd for C15H13NO2S: C, 66.40; H,
7-Ethoxy-2H-benzo[b][1,4]thiazin-3(4H)-one (3b) mp 154—156 °C; 4.83; N, 5.16. Found: C, 66.50; H, 4.74; N, 5.27.
1
yield 43%; H-NMR (CDCl3, 300 MHz) d: 1.26 (t, 3H, Jꢁ7.0 Hz, –CH3),
7-(2-Fluoro-benzyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3k) mp
3.43 (s, 2H, –S–CH2–), 4.01 (q, 2H, Jꢁ7.0 Hz, –OCH2–), 6.74—6.85 (m, 181—183 °C; yield 44%; 1H-NMR (CDCl3, 300 MHz) d: 3.42 (s, 2H,
3H, Ar-H), 8.60 (s, 1H, –CONH); IR (KBr) cmꢂ1: 3432 (NH), 1679 (CꢁO),
–S–CH2–), 5.10 (s, 2H, –OCH2–), 6.77—6.97 (m, 3H, Ar-H), 7.07—7.51
1503 (C–O–C), 1059 (C–O–C); MS m/z: 210 (Mꢃ1); Anal. Calcd for (m, 4H, H-3, H-4, H-5, H-6), 8.21 (s, 1H, –CONH); IR (KBr) cmꢂ1: 3482
C10H11NO2S: C, 55.39; H, 5.30; N, 6.69. Found: C, 55.43; H, 5.45; N, 6.52. (NH), 1698 (CꢁO), 1654 (C–O–C), 1062 (C–O–C); MS m/z: 290 (Mꢃ1);
7-Propoxy-2H-benzo[b][1,4]thiazin-3(4H)-one (3c) mp 122—124 °C; Anal. Calcd for C15H12FNO2S: C, 62.27; H, 4.18; N, 4.84. Found: C, 62.36;
1
yield 40%; H-NMR (CDCl3, 300 MHz) d: 1.01 (t, 3H, Jꢁ7.4 Hz, –CH3), H, 4.01; N, 4.96.
1.82 (q, 2H, Jꢁ7.1 Hz, –CH2–), 3.43 (s, 2H, –S–CH2–), 3.89 (t, 2H,
Jꢁ6.5 Hz, –OCH2–), 6.75—6.87 (m, 3H, Ar-H), 7.94 (s, 1H, –CONH); IR
(KBr) cmꢂ1: 3410 (NH), 1706 (CꢁO), 1520 (C–O–C), 1123 (C–O–C); MS
7-(3-Fluoro-benzyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3l) mp
157—159 °C; yield 43%; 1H-NMR (CDCl3, 300 MHz) d: 3.42 (s, 2H,
–S–CH2–), 5.00 (s, 2H, –OCH2–), 6.75—6.93 (m, 3H, Ar-H), 7.27—7.36
m/z: 224 (Mꢃ1); Anal. Calcd for C11H13NO2S: C, 59.17; H, 5.87; N, 6.27. (m, 4H, H-2, H-4, H-5, H-6), 7.70 (s, 1H, –CONH); IR (KBr) cmꢂ1: 3501
Found: C, 59.36; H, 5.61; N, 6.44.
(NH), 1699 (CꢁO), 1423 (C–O–C), 1078 (C–O–C); MS m/z: 290 (Mꢃ1);
7-Butoxy-2H-benzo[b][1,4]thiazin-3(4H)-one (3d) mp 119—121 °C; Anal. Calcd for C15H12FNO2S: C, 62.27; H, 4.18; N, 4.84. Found: C, 62.43;
1
yield 45%; H-NMR (CDCl3, 300 MHz) d: 1.01 (t, 3H, Jꢁ7.5 Hz, –CH3), H, 4.04; N, 4.79.
1.26—1.78 (m, 4H, –CH2–CH2–), 3.42 (s, 2H, –S–CH2–), 3.93 (t, 2H,
Jꢁ6.5 Hz, –OCH2–), 6.74—6.87 (m, 3H, Ar-H), 7.73 (s, 1H, –CONH); IR
(KBr) cmꢂ1: 3409 (NH), 1686 (CꢁO), 1496 (C–O–C), 1074 (C–O–C); MS
7-(4-Fluoro-benzyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3m) mp
163—165 °C; yield 45%; 1H-NMR (CDCl3, 300 MHz) d: 3.43 (s, 2H,
–S–CH2–), 5.04 (s, 2H, –OCH2–), 6.75—6.94 (m, 3H, Ar-H), 7.01—7.40
m/z: 238 (Mꢃ1); Anal. Calcd for C12H15NO2S: C, 60.73; H, 6.37; N, 5.90. (m, 4H, H-2, H-3, H-5, H-6), 7.99 (s, 1H, –CONH); IR (KBr) cmꢂ1: 3489
Found: C, 60.82; H, 6.53; N, 6.01.
(NH), 1674 (CꢁO), 1491 (C–O–C), 1065 (C–O–C); MS m/z: 290 (Mꢃ1);
7-(Pentyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3e) mp 118— Anal. Calcd for C15H12FNO2S: C, 62.27; H, 4.18; N, 4.84. Found: C, 62.35;
1
120 °C; yield 41%; H-NMR (CDCl3, 300 MHz) d: 0.94 (t, 3H, Jꢁ7.1 Hz,
H, 4.00; N, 4.94.
–CH3), 1.27—1.60 (m, 4H, –CH2–CH2–), 1.76—1.80 (m, 2H, –CH2–), 3.42
7-(2-Chloro-benzyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3n) mp
(s, 2H, –S–CH2–), 3.92 (t, 2H, Jꢁ6.6 Hz, –OCH2–), 6.74—6.86 (m, 3H, Ar- 216—218 °C; yield 30%; 1H-NMR (CDCl3, 300 MHz) d: 3.43 (s, 2H,
H), 8.01 (s, 1H, –CONH); IR (KBr) cmꢂ1: 3410 (NH), 1692 (CꢁO), 1493 –S–CH2–), 5.14 (s, 2H, –OCH2–), 6.74—6.98 (m, 3H, Ar-H), 7.30—7.60
(C–O–C), 1069 (C–O–C); MS m/z: 252 (Mꢃ1); Anal. Calcd for
C13H17NO2S: C, 63.21; H, 6.82; N, 5.57. Found: C, 63.36; H, 6.65; N, 5.47.
7-(Hexyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3f) mp 112—
(m, 4H, H-3, H-4, H-5, H-6), 7.70 (s, 1H, –CONH); IR (KBr) cmꢂ1: 3476
(NH), 1635 (CꢁO), 1428 (C–O–C), 1106 (C–O–C); MS m/z: 306 (Mꢃ1);
Anal. Calcd for C15H12ClNO2S: C, 58.92; H, 3.96; N, 4.58. Found: C, 58.76;
H, 3.83; N, 4.78.
7-(3-Chloro-benzyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3o) mp
176—178 °C; yield 32%; 1H-NMR (CDCl3, 300 MHz) d: 3.43 (s, 2H,
–S–CH2–), 5.08 (s, 2H, –OCH2–), 6.76—6.94 (m, 3H, Ar-H), 7.27—7.43
1
114 °C; yield 45%; H-NMR (CDCl3, 300 MHz) d: 0.92 (t, 3H, Jꢁ6.4 Hz,
–CH3), 1.34—1.58 (m, 4H, (–CH2)2), 1.72—1.74 (m, 2H, –CH2–), 1.77—
1.79 (m, 2H, –CH2–), 3.42 (s, 2H, –S–CH2–), 3.92 (t, 2H, Jꢁ6.5 Hz,
–OCH2–), 6.71—6.86 (m, 3H, Ar-H), 8.19 (s, 1H, –CONH); IR (KBr) cmꢂ1
:
3521 (NH), 1703 (CꢁO), 1504 (C–O–C), 1071 (C–O–C); MS m/z: 266 (m, 4H, H-2, H-4, H-5, H-6), 7.56 (s, 1H, –CONH); IR (KBr) cmꢂ1: 3497
(Mꢃ1); Anal. Calcd for C14H19NO2S: C, 63.36; H, 7.22; N, 5.28. Found: C, (NH), 1638 (CꢁO), 1443 (C–O–C), 1097 (C–O–C); MS m/z: 306 (Mꢃ1);
63.65; H, 7.45; N, 5.39.
Anal. Calcd for C15H12ClNO2S: C, 58.92; H, 3.96; N, 4.58. Found: C, 58.78;
H, 3.81; N, 4.74.
7-(Heptyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3g) mp 110—
1
112 °C; yield 48%; H-NMR (CDCl3, 300 MHz) d: 0.90 (t, 3H, Jꢁ6.6 Hz,
7-(4-Chloro-benzyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3p) mp
–CH3), 1.26—1.38 (m, 6H, (–CH2)3), 1.45—1.62 (m, 2H, –CH2–), 1.72 (m,
189—191 °C; yield 41%; 1H-NMR (CDCl3, 300 MHz) d: 3.43 (s, 2H,
2H, –CH2–), 3.42 (s, 2H, –S–CH2–), 3.91 (t, 2H, Jꢁ6.9 Hz, –OCH2–), –S–CH2–), 5.02 (s, 2H, –OCH2–), 6.76—6.94 (m, 3H, Ar-H), 7.06—7.42
6.74—6.84 (m, 3H, Ar-H), 9.17 (s, 1H, –CONH); IR (KBr) cmꢂ1: 3492 (m, 4H, H-2, H-3, H-5, H-6), 8.11 (s, 1H, –CONH); IR (KBr) cmꢂ1: 3503

328
Vol. 58, No. 3
pound 5 with halogenated hydrocarbon in ethanol with K2CO3.
(NH), 1667 (CꢁO), 1462 (C–O–C), 1069 (C–O–C); MS m/z: 306 (Mꢃ1);
Anal. Calcd for C15H12ClNO2S: C, 58.92; H, 3.96; N, 4.58. Found: C, 58.68;
H, 3.79; N, 4.76.
7-Methoxy-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine (4a) mp
203—205 °C; yield 96%; 1H-NMR (CDCl3, 300 MHz) d: 3.85 (s, 3H,
–OCH3), 4.19 (s, 2H, –S–CH2–), 6.88 (dd, 1H, J1ꢁ 2.6 Hz, J2ꢁ6.7 Hz, Ar-
H), 7.02 (d, 1H, Jꢁ2.6 Hz, Ar-H), 7.37 (s, 1H, Ar-H), 8.56 (s, 1H,
N–CHꢁN–); IR (KBr) cmꢂ1: 1596 (CꢁN), 1301 (C–N), 1245, 1216
(C–O–C), 1032 (N–N). MS m/z: 220 (Mꢃ1); Anal. Calcd for C10H9N3OS:
C, 54.78; H, 4.14; N, 19.16. Found: C, 54.80; H, 4.17; N, 19.13.
7-Ethoxy-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine (4b) mp
157—159 °C; yield 68%; 1H-NMR (CDCl3, 300 MHz) d: 1.45 (t, 3H,
Jꢁ7.0 Hz, –CH3), 4.06 (t, 2H, Jꢁ7.1 Hz, –O–CH2–), 4.19 (s, 2H, –S–CH2–),
6.88 (dd, 1H, J1ꢁ2.6 Hz, J2ꢁ7.0 Hz, Ar-H), 7.02 (s, 1H, Ar-H), 7.37 (d, 1H,
Jꢁ8.9 Hz, Ar-H), 8.56 (s, 1H, N–CHꢁN–); IR (KBr) cmꢂ1: 1595 (CꢁN),
1305 (C–N), 1243, 1212 (C–O–C), 1030 (N–N). MS m/z: 234 (Mꢃ1); Anal.
Calcd for C11H11N3OS: C, 56.63; H, 4.75; N, 18.01. Found: C, 56.82; H,
4.64; N, 18.23.
7-Propoxy-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine (4c) mp
116—118 °C; yield 70%; 1H-NMR (CDCl3, 300 MHz) d: 1.05 (t, 3H,
Jꢁ7.4 Hz, –CH3), 1.82 (m, 2H, –CH2–), 3.94 (t, 2H, Jꢁ6.5 Hz, –OCH2–),
4.06 (s, 2H, –S–CH2–), 6.86 (dd, 1H, J1ꢁ 2.7 Hz, J2ꢁ 8.8 Hz, Ar-H), 7.01
(s, 1H, Ar-H), 7.34 (d, 1H, Jꢁ8.8 Hz, Ar-H), 8.54 (s, 1H, N–CHꢁN–); IR
(KBr) cmꢂ1: 1594 (CꢁN), 1306 (C–N), 1241, 1209 (C–O–C), 1039 (N–N).
MS m/z: 248 (Mꢃ1); Anal. Calcd for C12H13N3OS: C, 58.28; H, 5.30; N,
16.99. Found: C, 58.48; H, 5.19; N, 16.85.
7-(2,6-Dichloro-benzyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3q)
1
mp 184—186 °C; yield 31%; H-NMR (CDCl3, 300 MHz) d: 3.44 (s, 2H,
–S–CH2–), 5.13 (s, 2H, –OCH2–), 6.77—6.89 (m, 3H, Ar-H), 7.02—7.40
(m, 3H, H-3, H-4, H-5), 7.83 (s, 1H, –CONH); IR (KBr) cmꢂ1: 3457 (NH),
1648 (CꢁO), 1430 (C–O–C), 1054 (C–O–C); MS m/z: 340 (Mꢃ1); Anal.
Calcd for C15H11Cl2NO2S: C, 52.95; H, 3.26; N, 4.12. Found: C, 52.83; H,
3.44; N, 4.09.
7-(2-Bromo-benzyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3r) mp
226—228 °C; yield 32%; 1H-NMR (CDCl3, 300 MHz) d: 3.43 (s, 2H,
–S–CH2–), 5.11 (s, 2H, –OCH2–), 6.74—6.83 (m, 3H, Ar-H), 7.32—7.58
(m, 4H, H-2, H-3, H-4, H-5), 8.39 (s, 1H, –CONH); IR (KBr) cmꢂ1: 3479
(NH), 1659 (CꢁO), 1427 (C–O–C), 1048 (C–O–C); MS m/z: 350 (Mꢃ1);
Anal. Calcd for C15H12BrNO2S: C,51.44; H, 3.45; N, 4.00. Found: C, 51.56;
H, 3.26; N, 4.18.
7-(4-Bromo-benzyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3s) mp
211—213 °C; yield 31%; 1H-NMR (CDCl3, 300 MHz) d: 3.43 (s, 2H,
–S–CH2–), 4.99 (s, 2H, –OCH2–), 6.74—6.93 (m, 3H, Ar-H), 7.30—7.54
(m, 4H, H-2, H-3, H-5, H-6), 7.94 (s, 1H, –CONH); IR (KBr) cmꢂ1: 3424
(NH), 1690 (CꢁO), 1458 (C–O–C), 1017 (C–O–C); MS m/z: 350 (Mꢃ1);
Anal. Calcd for C15H12BrNO2S: C,51.44; H, 3.45; N, 4.00. Found: C, 51.65;
H, 3.38; N, 4.22.
7-Butoxy-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine (4d) mp
113—115 °C; yield 62%; 1H-NMR (CDCl3, 300 MHz) d: 0.98 (t, 3H,
Jꢁ7.4 Hz, –CH3), 1.50 (m, 2H, –CH2–), 1.78 (m, 2H, –CH2–), 3.97 (t, 2H,
Jꢁ6.4 Hz, –OCH2–), 4.17 (s, 2H, –S–CH2–), 6.86 (dd, 1H, J1ꢁ2.6 Hz,
J2ꢁ8.8 Hz, Ar-H), 7.01 (s, 1H, Ar-H), 7.35 (d, 1H, Jꢁ8.9 Hz, Ar-H), 8.54 (s,
1H, N–CHꢁN–); IR (KBr) cmꢂ1: 1597 (CꢁN), 1309 (C–N), 1246, 1215
(C–O–C), 1033 (N–N). MS m/z: 262(Mꢃ1); Anal. Calcd for C13H15N3OS:
C, 59.74; H, 5.79; N, 16.08. Found: C, 59.89; H, 5.56; N, 16.19.
7-(Pentyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine (4e) mp
107—109 °C; yield 63%; 1H-NMR (CDCl3, 300 MHz) d: 0.94 (t, 3H,
Jꢁ6.9 Hz, –CH3), 1.41 (m, 4H, –CH2–CH2–), 1.80 (m, 2H, –CH2–), 3.97 (t,
2H, Jꢁ6.5 Hz, –OCH2–), 4.18 (s, 2H, –S–CH2–), 6.86 (dd, 1H, J1ꢁ2.7 Hz,
J2ꢁ8.9 Hz, Ar-H), 7.01 (s, 1H, Ar-H), 7.35 (d, 1H, Jꢁ8.9 Hz, Ar-H), 8.54 (s,
1H, N–CHꢁN–); IR (KBr) cmꢂ1: 1596 (CꢁN), 1304 (C–N), 1247, 1211
(C–O–C), 1033 (N–N). MS m/z: 276 (Mꢃ1); Anal. Calcd for C14H17N3OS:
C, 61.06; H, 6.22; N, 15.26. Found: C, 61.23; H, 6.19; N, 15.33.
7-(4-Methyl-benzyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3t) mp
179—181 °C; yield 38%; 1H-NMR (CDCl3, 300 MHz) d: 2.38 (s, 3H,
–CH3), 3.42 (s, 2H, –S–CH2–), 5.00 (s, 2H, –OCH2–), 6.77—6.95 (m, 3H,
Ar-H), 7.21 (d, 2H, Jꢁ8.0 Hz, Ar-H), 7.31 (d, 2H, Jꢁ8.0 Hz, Ar-H), 7.88 (s,
1H, –CONH); IR (KBr) cmꢂ1: 3409 (NH), 1668 (CꢁO), 1430 (C–O–C),
1036 (C–O–C); MS m/z: 286 (Mꢃ1); Anal. Calcd for C16H15NO2S: C,67.34;
H, 5.30; N, 4.91. Found: C, 67.46; H, 5.21; N, 4.86.
7-(4-Methoxy-benzyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3u)
1
mp 165—167 °C; yield 34%; H-NMR (CDCl3, 300 MHz) d: 3.42 (s, 2H,
–S–CH2–), 4.23 (s, 3H, –OCH3), 4.96 (s, 2H, –OCH2–), 6.74—6.95 (m, 3H,
Ar-H), 6.93 (d, 2H, Jꢁ8.7 Hz, Ar-H), 7.34 (d, 2H, Jꢁ8.7 Hz, Ar-H), 7.90 (s,
1H, –CONH); IR (KBr) cmꢂ1: 3445 (NH), 1696 (CꢁO), 1437 (C–O–C),
1030 (C–O–C); MS m/z: 302 (Mꢃ1); Anal. Calcd for C16H15NO3S: C,63.77;
H, 5.02; N, 4.65. Found: C, 63.57; H, 5.26; N, 4.74.
7-(3,4-Dimethoxy-benzyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3v)
1
mp 179—181 °C; yield 29%; H-NMR (CDCl3, 300 MHz) d: 3.43 (s, 2H,
7-(Hexyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine (4f) mp
86—88 °C; yield 79%; 1H-NMR (CDCl3, 300 MHz) d: 0.92 (t, 3H,
Jꢁ6.6 Hz, –CH3), 1.35 (m, 4H, –CH2-CH2–), 1.46—1.63 (m, 2H, –CH2–),
1.80 (m, 2H, –CH2–), 3.97 (t, 2H, Jꢁ6.5 Hz, –OCH2–), 4.18 (s, 2H,
–S–CH2–), 6.86 (dd, 1H, J1ꢁ2.6 Hz, J2ꢁ8.8 Hz, Ar-H), 7.01 (s, 1H, Ar-H),
–S–CH2–), 3.82 (s, 3H, –OCH3), 4.28 (s, 3H, –OCH3), 4.96 (s, 2H,
–OCH2–), 6.66—6.79 (m, 3H, Ar-H), 6.80—6.95 (m, 3H, H-2, H-5, H-6),
7.91 (s, 1H, –CONH); IR (KBr) cmꢂ1: 3450 (NH), 1618 (CꢁO), 1420
(C–O–C), 1073 (C–O–C); MS m/z: 332 (Mꢃ1); Anal. Calcd for
C17H17NO4S: C,62.41; H, 5.82; N, 4.04. Found: C, 62.66; H, 5.73; N, 4.28.
Target compounds 4a—u were synthesized according to Chart 2.
7.35 (d, 1H, Jꢁ8.8 Hz, Ar-H), 8.54 (s, 1H, N–CHꢁN–); IR (KBr) cmꢂ1
:
1595 (CꢁN), 1306 (C–N), 1239, 1220 (C–O–C), 1039 (N–N). MS m/z: 290
(Mꢃ1); Anal. Calcd for C15H19N3OS: C, 62.25; H, 6.62; N, 14.52. Found: C,
62.47; H, 6.54; N, 14.61.
To a stirring mixture of acetonitrile and triethylamine in a three-necked
round-bottomed flask in an ice bath, P2S5 (1.2 eq) was divided into multiple
portions and added one portion at a time after the previous portion had com-
pletely dissolved. Then, 3a was added, and the solution was refluxed for 3 h
under nitrogen. After removing the solvent under reduced pressure, the
residue was dissolved in dichloromethane (30 ml), washed with water
(30 mlꢄ3) and dried over anhydrous MgSO4. Evaporation of the solvents
gave a crude product, which was purified by silica gel column chromatogra-
phy with dichloromethane to a light yellow solid. (compound 6). The result-
ing compound 6 reacted further with formohydrazide in cyclohexanol to
produce compound 4a. 7-Hydroxy-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]
thiazine (5) was yielded by compound 4a by demethylation. Demethylation
was accomplished by treatment of the dichloromethane with boron tribro-
mide. Then compounds 4b—u were synthesized through reaction of com-
7-(Heptyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine (4g) mp
97—99 °C; yield 77%; 1H-NMR (CDCl3, 300 MHz) d: 0.89 (t, 3H,
Jꢁ6.7 Hz, –CH3), 1.36 (m, 6H, –CH2–CH2–CH2–), 1.58—1.61 (m, 2H,
–CH2–), 1.81 (m, 2H, –CH2–), 3.97 (t, 2H, Jꢁ6.5 Hz, –OCH2–), 4.18 (s, 2H,
–S–CH2–), 6.86 (dd, 1H, J1ꢁ2.6 Hz, J2ꢁ8.8 Hz, Ar-H), 7.01 (s, 1H, Ar-H),
7.35 (d, 1H, Jꢁ8.8 Hz, Ar-H), 8.54 (s, 1H, N–CHꢁN–); IR (KBr) cmꢂ1
:
1591 (CꢁN), 1308 (C–N), 1241, 1219 (C–O–C), 1035 (N–N). MS m/z: 304
(Mꢃ1); Anal. Calcd for C16H21N3OS: C, 63.33; H, 6.98; N, 13.85. Found: C,
63.46; H, 6.82; N,13.64.
7-(Octyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine (4h) mp
96—98 °C; yield 79%; 1H-NMR (CDCl3, 300 MHz) d: 0.88 (t, 3H,
Jꢁ6.8 Hz, –CH3), 1.30 (m, 8H, (–CH2)4), 1.46—1.67 (m, 2H, –CH2–), 1.78
(m, 2H, –CH2–), 3.97 (t, 2H, Jꢁ6.5 Hz, –OCH2–), 4.18 (s, 2H, –S–CH2–),
6.86 (dd, 1H, J1ꢁ2.6 Hz, J2ꢁ8.8 Hz, Ar-H), 7.01 (s, 1H, Ar-H), 7.35 (d, 1H,
Jꢁ8.8 Hz, Ar-H), 8.54 (s, 1H, N–CHꢁN–); IR (KBr) cmꢂ1: 1599 (CꢁN),
1304 (C–N), 1247, 1212 (C–O–C), 1037 (N–N). MS m/z: 318 (Mꢃ1); Anal.
Calcd for C17H23N3OS: C, 64.32; H, 7.30; N, 13.24. Found: C, 64.54; H,
7.16; N,13.50.
7-(Dodecyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine (4i)
mp 95—97 °C; yield 72%; 1H-NMR (CDCl3, 300 MHz) d: 0.87 (t, 3H,
Jꢁ6.8 Hz, –CH3), 1.27—1.46 (m, 16H, (–CH2–)8), 1.57 (m, 2H, –CH2–),
1.78 (m, 2H, –CH2–), 3.97 (t, 2H, Jꢁ6.4 Hz, –OCH2–), 4.18 (s, 2H,
–S–CH2–), 6.86 (dd, 1H, J1ꢁ2.6 Hz, J2ꢁ8.8 Hz, Ar-H), 7.01 (s, 1H, Ar-H),
7.35 (d, 1H, Jꢁ8.8 Hz, Ar-H), 8.54 (s, 1H, N–CHꢁN–); IR (KBr) cmꢂ1
:
Chart 2. The Synthesis Route of Target Compounds 4a—u
1600 (CꢁN), 1301 (C–N), 1251, 1219 (C–O–C), 1029 (N–N). MS m/z: 374

March 2010
329
(Mꢃ1); Anal. Calcd for C21H31N3OS: C, 67.52; H, 8.36; N, 11.25. Found: C, Ar-H), 7.09 (d, 1H, Jꢁ2.6 Hz, Ar-H), 7.29—7.55 (m, 5H, Ar-H), 8.54 (s,
67.73; H, 8.13; N, 11.40.
1H, N–CHꢁN–); IR (KBr) cmꢂ1: 1590 (CꢁN), 1368 (C–N), 1255, 1284
(C–O–C), 1035 (N–N). MS m/z: 374 (Mꢃ1); Anal. Calcd for
7-(Benzyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine (4j) mp
135—137 °C; yield 57%; 1H-NMR (CDCl3, 300 MHz) d: 4.18 (s, 2H, C16H12BrN3OS: C, 51.35; H, 3.23; N, 11.23. Found: C, 51.54; H, 3.06; N,
–S–CH2–), 5.09 (s, 2H, –OCH2–), 6.94 (dd, 1H, J1ꢁ2.6 Hz, J2ꢁ8.8 Hz, Ar- 11.43.
H), 7.10 (s, 1H, Ar-H), 7.36 (d, 1H, Jꢁ8.6 Hz, Ar-H), 7.34—7.43 (m, 6H,
7-(4-Methylbenzyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine
(4t) mp 126—128 °C; yield 49%; H-NMR (CDCl3, 300 MHz) d: 2.38 (s,
1
Ar-H), 8.54 (s, 1H, N–CHꢁN–); IR (KBr) cmꢂ1: 1595 (CꢁN), 1384 (C–N),
1255, 1294 (C–O–C), 1018 (N–N). MS m/z: 296 (Mꢃ1); Anal. Calcd for 3H, Ar-CH3), 4.18 (s, 2H, –S–CH2–), 5.05 (s, 2H, –OCH2–), 6.93 (dd, 1H,
C16H13N3OS: C, 65.06; H, 4.44; N, 14.23. Found: C, 65.28; H, 4.50; N, J1ꢁ2.6 Hz, J2ꢁ8.8 Hz, Ar-H), 7.10 (d, 1H, Jꢁ2.9 Hz, Ar-H), 7.20—7.36 (m,
14.06.
5H, Ar-H), 8.54 (s, 1H, N–CHꢁN–); IR (KBr) cmꢂ1: 1597 (CꢁN), 1381
7-(2-Fluorobenzyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine (C–N), 1255, 1286 (C–O–C), 1035 (N–N). MS m/z: 310 (Mꢃ1); Anal.
(4k) mp 149—151 °C; yield 62%; 1H-NMR (CDCl3, 300 MHz) d: 4.19 (s,
2H, –S–CH2–), 5.16 (s, 2H, –OCH2–), 6.97 (dd, 1H, J1ꢁ2.6 Hz, J2ꢁ8.8 Hz,
Calcd for C17H15N3OS: C, 66.00; H, 4.89; N, 13.58. Found: C, 66.18; H,
4.67; N, 13.42.
Ar-H), 7.12—7.48 (m, 6H, Ar-H), 8.54 (s, 1H, N–CHꢁN–); IR (KBr) cmꢂ1
:
7-(4-Methoxybenzyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thi-
1
1598 (CꢁN), 1382 (C–N), 1255, 1296 (C–O–C), 1039 (N–N). MS m/z: 314 azine (4u) mp 137—139 °C; yield 52%; H-NMR (CDCl3, 300 MHz) d:
(Mꢃ1); Anal. Calcd for C16H12FN3OS: C, 61.33; H, 3.86; N, 13.41. Found: 3.92 (s, 3H, Ar-O–CH3), 4.13 (s, 2H, –S–CH2–), 5.05 (s, 2H, –OCH2–), 6.93
C, 61.48; H, 3.66; N, 13.50.
(d, 3H, Jꢁ8.4 Hz, Ar-H), 7.08 (d, 1H, Jꢁ2.9 Hz, Ar-H), 7.33—7.36 (m, 3H,
7-(3-Fluorobenzyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thi- Ar-H), 8.54 (s, 1H, N–CHꢁN–); IR (KBr) cmꢂ1: 1590 (CꢁN), 1377 (C–N),
azine(4l) mp 121—123 °C; yield 62%; 1H-NMR (CDCl3, 300 MHz) d: 1260, 1276 (C–O–C), 1036 (N–N). MS m/z: 326 (Mꢃ1); Anal. Calcd for
4.19 (s, 2H, –S–CH2–), 5.09 (s, 2H, –OCH2–), 6.93 (dd, 1H, J1ꢁ2.6 Hz,
C17H15N3O2S: C, 62.75; H, 4.65; N, 12.91. Found: C, 62.94; H, 4.53; N,
J2ꢁ8.8 Hz, Ar-H), 7.05—7.38 (m, 6H, Ar-H), 8.54 (s, 1H, N–CHꢁN–); IR 12.88.
(KBr) cmꢂ1: 1598 (CꢁN), 1381 (C–N), 1256, 1296 (C–O–C), 1039 (N–N).
Pharmacology The MES test and rotarod test were carried out accord-
MS m/z: 314 (Mꢃ1); Anal. Calcd for C16H12FN3OS: C, 61.33; H, 3.86; N, ing to procedures described in the Antiepileptic Drug Development Program
13.41. Found: C, 61.48; H, 3.66; N, 13.50.
(ADD) of the National Institutes of Health (U.S.A.).11,12) All compounds,
7-(4-Fluorobenzyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine which were dissolved in polyethyleneglycol-400, were evaluated for anticon-
(4m) mp 151—153 °C; yield 63%; 1H-NMR (CDCl3, 300 MHz) d: 4.23 (s,
2H, –S–CH2–), 5.05 (s, 2H, –OCH2–), 6.93 (dd, 1H, J1ꢁ2.7 Hz, J2ꢁ7.5 Hz,
vulsant activities in KunMing mice in the 18—25 g weight range. Groups of
10 mice were given a range of intraperitoneal doses of the test drug until at
Ar-H), 7.07—7.13 (m, 3H, Ar-H), 7.35—7.43 (m, 3H, Ar-H), 8.54 (s, 1H, least three points were established in the range of 10—90% seizure protec-
N–CHꢁN–); IR (KBr) cmꢂ1: 1599 (CꢁN), 1384 (C–N), 1254, 1296 tion or minimal observed neurotoxicity. From the plots of these data, the re-
(C–O–C), 1039 (N–N). MS m/z: 314 (Mꢃ1); Anal. Calcd for C16H12FN3OS:
C, 61.33; H, 3.86; N, 13.41. Found: C, 61.48; H, 3.66; N, 13.50.
spective ED50 and TD50 values, 95% confidence intervals, slopes of the re-
gression line and the standard error of the slopes were calculated by com-
puter program written by the National Institute of Neurological Disorders
and Stroke.
MES Test Seizures were elicited with a 60 Hz alternating current of
50 mA intensity in mice. The current was applied via corneal electrodes for
7-(2-Chlorobenzyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine
(4n) mp 148—150 °C; yield 52%; 1H-NMR (CDCl3, 300 MHz) d: 4.23 (s,
2H, –S–CH2–), 5.19 (s, 2H, –OCH2–), 6.96 (dd, 1H, J1ꢁ2.6 Hz, J2ꢁ7.5 Hz,
Ar-H), 7.13 (d, 1H, Jꢁ2.6 Hz, Ar-H), 7.30—7.51 (m, 5H, Ar-H), 8.54 (s,
1H, N–CHꢁN–); IR (KBr) cmꢂ1: 1597 (CꢁN), 1385 (C–N), 1255, 1297 0.2 s. Protection against the spread of MES-induced seizures was defined as
(C–O–C), 1034 (N–N). MS m/z: 330 (Mꢃ1); Anal. Calcd for
the abolition of the hind leg and tonic maximal extension component of the
C16H12ClN3OS: C, 58.27; H, 3.67; N, 12.74. Found: C, 58.51; H, 3.59; N, seizure. The derivatives in MES test were evaluated 15 min after administra-
12.60.
7-(3-Chlorobenzyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine
tion of the compounds.
Rotarod Test10) Fifteen minutes after administration of the compounds
(with different doses), the animals were tested on a 2.5-cm diameter knurled
plastic rod rotating at 6 rpm for 1 min. Neurotoxicity was indicated by the
inability of an animal to maintain equilibrium in each of three trials.
(4o) mp 123—125 °C; yield 51%; 1H-NMR (CDCl3, 300 MHz) d: 4.23 (s,
2H, –S–CH2–), 5.10 (s, 2H, –OCH2–), 6.93 (dd, 1H, J1ꢁ2.6 Hz, J2ꢁ6.2 Hz,
Ar-H), 7.10 (d, 1H, Jꢁ2.6 Hz, Ar-H), 7.31—7.43 (m, 5H, Ar-H), 8.54 (s,
1H, N–CHꢁN–); IR (KBr) cmꢂ1: 1598 (CꢁN), 1379 (C–N), 1255, 1296
(C–O–C), 1036 (N–N). MS m/z: 330 (Mꢃ1); Anal. Calcd for
C16H12ClN3OS: C, 58.27; H, 3.67; N, 12.74. Found: C, 58.51; H, 3.59; N,
12.60.
Results and Discussion
Chemistry Target compounds 3a—v were synthesized
according to Chart 1. Compound 1 was prepared by 2-amino-
6-methoxy-benzothiazole reacting with KOH solution for
7-(4-Chlorobenzyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine
(4p) mp 142—144 °C; yield 50%; 1H-NMR (CDCl3, 300 MHz) d: 4.18 (s,
2H, –S–CH2–), 5.06 (s, 2H, –OCH2–), 6.92 (dd, 1H, J1ꢁ2.6 Hz, J2ꢁ8.8 Hz,
Ar-H), 7.09 (d, 1H, Jꢁ2.6 Hz, Ar-H), 7.35—7.40 (m, 5H, Ar-H), 8.54 (s, 48 h according to the reference method,11) compound 3a was
1H, N–CHꢁN–); IR (KBr) cmꢂ1: 1596 (CꢁN), 1378 (C–N), 1254, 1294
prepared according to the reference method,12) 7-hydroxy-
2H-benzo[b][1,4] thiazin-3(4H)-one (2) was achieved by
compound 3a by demethylation. Demethylation was accom-
(C–O–C), 1033 (N–N). MS m/z: 330 (Mꢃ1); Anal. Calcd for
C16H12ClN3OS: C, 58.27; H, 3.67; N, 12.74. Found: C, 58.51; H, 3.59; N,
12.60.
plished by treatment of the dichloromethane with boron tri-
bromide as described by Bauer et al.13) Then compounds
3b—v were synthesized through the reaction of compound 2
with halogenated hydrocarbon in ethanol with K2CO3.
7-(2,4-Dichlorobenzyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thi-
azine (4q) mp 172—174 °C; yield 54%; H-NMR (CDCl3, 300 MHz) d:
1
4.24 (s, 2H, –S–CH2–), 5.14 (s, 2H, –OCH2–), 6.94 (dd, 1H, J1ꢁ2.7 Hz,
J2ꢁ8.8 Hz, Ar-H), 7.11 (d, 1H, Jꢁ2.7 Hz, Ar-H), 7.29—7.48 (m, 4H, Ar-H),
8.54 (s, 1H, N–CHꢁN–); IR (KBr) cmꢂ1: 1595 (CꢁN), 1380 (C–N), 1255,
1286 (C–O–C), 1029 (N–N). MS m/z: 364 (Mꢃ1); Anal. Calcd for
C16H11Cl2N3OS: C, 52.76; H, 3.04; N, 11.54. Found: C, 52.88; H, 3.13; N,
11.27.
Target compounds 4a—u were synthesized according to
Chart 2. Compound 6 was achieved by compound 3a reacted
further with P2S5 according to the reference method,10) and
compound 6 reacted further with formohydrazide in cyclo-
hexanol to produce compound 4a according to a previous-
ly reported method.7) 7-Hydroxy-4H-[1,2,4]triazolo[4,3-d]-
benzo[b] [1,4]thiazine (5) was achieved by compound 4a by
demethylation. Demethylation was accomplished by treat-
ment of the dichloromethane with boron tribromide as de-
scribed by Bauer et al.13) Then compounds 4b—u were syn-
thesized through the reaction of compound 5 with halo-
7-(2-Bromobenzyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine
1
(4r) mp 186—188 °C; yield 55%; H-NMR (CDCl3, 300 MHz) d: 3.84 (s,
2H, –S–CH2–), 5.15 (s, 2H, –OCH2–), 6.95 (dd, 1H, J1ꢁ2.6 Hz, J2ꢁ8.7 Hz,
Ar-H), 7.12 (d, 1H, Jꢁ2.5 Hz, Ar-H), 7.21—7.70 (m, 5H, Ar-H), 8.54 (s,
1H, N–CHꢁN–); IR (KBr) cmꢂ1: 1591 (CꢁN), 1380 (C–N), 1249, 1296
(C–O–C), 1040 (N–N). MS m/z: 374 (Mꢃ1); Anal. Calcd for
C16H12BrN3OS: C, 51.35; H, 3.23; N, 11.23. Found: C, 51.54; H, 3.06; N,
11.43.
7-(4-Bromobenzyloxy)-4H-[1,2,4]triazolo[4,3-d]benzo[b][1,4]thiazine
1
(4s) mp 151—153 °C; yield 58%; H-NMR (CDCl3, 300 MHz) d: 4.18 (s,
2H, –S–CH2–), 5.05 (s, 2H, –OCH2–), 6.93 (dd, 1H, J1ꢁ2.8 Hz, J2ꢁ7.5 Hz, genated hydrocarbon in ethanol with K2CO3.

330
Vol. 58, No. 3
Pharmacology All compounds, which were dissolved in provides an evaluation of the median effective dose and me-
polyethylene glycol-400, were evaluated for anticonvulsant dian neuotoxic dose. The slope of the regression line and SE
activities with KunMing mice in the 18—22 g weight range. of the alope were then calculated. These data are shown in
In the MES test, seizures were elicited with a 60-Hz alternat- Table 3. Compound 3e was the most active compound with
ing current of 50 mA intensity in mice. The current was ap- an ED50 of 34.1 mg/kg, TD50 of 305.5 mg/kg and PI of 8.9.
plied via corneal electrodes for 0.2 s. Protection against the So, among the seven compounds, 3f could be considered po-
spread of MES-induced seizures was defined as the abolition tentially the most useful and safe therapeutic compound with
of the hind leg and tonic maximal extension component of ED50ꢁ52.8 mg/kg, TD50ꢀ600 mg/kg and PIꢀ11.4. Com-
the seizure.
pound 4k was the most active compound with an ED50 of
The activity profile for the tested compounds is summa- 17.0 mg/kg, TD50 of 243.9 mg/kg and PI of 14.3. The neuro-
rized in Table 1 and Table 2 along with the literature data for toxicity of both 3f and 4k was markedly lower than that of
a standard drug. All the compounds were active in the MES the reference drug carbamazepine.
test, indicative of their ability to prevent seizure spread. All
Analyzing the activities of the synthesized compounds
synthesized compounds 3a—v exhibited weak anticonvulsant 3a—v and 4a—u, the following structure–activity relation-
activity; among the 22 compounds 3a—v: 3n, 3q, 3t and 3v ship (SAR) was gained. Among 3a—v, the three F-substi-
hardly exhibited anticonvulsant activity at the dose of tuted phenyl derivatives, the potency order was o-Fꢀp-Fꢀm-
200 mg/kg; 3a, 3i, 3o, 3p, 3r, 3s and 3u exhibited weak anti- F. Among the four Cl-substituted phenyl derivatives, the po-
convulsant activity at the dose of 200 mg/kg; 3h, 3j, 3l and tency order was m-Clꢁp-Clꢀo-Cl2ꢀ2,6-Cl2. Between the
3m exhibited median anticonvulsant activity; other com- two Br-substituted phenyl derivatives, the potency order was
pounds exhibited stronger anticonvulsant activity at a dose of p-Brꢀo-Br. Among the three electron-donor phenyl deriva-
100 mg/kg.
tives, the potency order was p-OCH3ꢀp-CH3ꢁ3,4-(OCH3)2.
Compared with compounds 3a—v, compounds 4a—u Among the six p-substituted phenyl derivatives, the potency
were more active. The results suggest that the incorporated order was HꢁFꢀBrꢁCH3OꢀClꢀCH3. Compound 3e was
triazole with 7-alkoxyl-2H-benzo[b][1,4]thiazin-3(4H)-ones the most active compound with an ED50 of 34.1 mg/kg, TD50
at the third and fourth position could improve the anticonvul- of 305.5 mg/kg and PI of 8.9. So, among the 22 compounds,
sant activity of the derivatives.
3f could be considered potentially the most useful and safe
All synthesized compounds 4a—u exhibited stronger anti- therapeutic compound with an ED50ꢁ52.79 mg/kg, TD50ꢀ
convulsant activity, among the 21 compounds. 4a, 4b, 4i and 600 mg/kg and PIꢀ11.4. Its neurotoxicity was the lowest
4n exhibited lower anticonvulsant activity; 4d, 4e, 4f, 4k, 4l among all the synthesized compounds. The SAR of com-
and 4o exhibited stronger anticonvulsant activity.
pounds 4a—u was similar to that of 3a—v. Among 4a—u,
As a result of preliminary screening, compounds 3b—g the length of the alkoxyl chain appeared to have an impact on
and 3k among 3a—v and compounds 4d, 4e, 4f, 4k, 4l and anticonvulsant activity of the derivatives. From 4a to 4e, as
4o among 4a—u were considered for the phase II trials. This the alkoxyl chain length increased, anticonvulsant activity
Table 1. Anticonvulsant Data in Mice (Test Drug Administered i.p.)a)
(Phase I)
Table 2. Anticonvulsant Data in Mice (Test Drug Administered i.p.)a)
(Phase I)
MESc)
MESc)
Compound
R
Compound
R
0.5 h
4 h
0.5 h
4 h
d)
200 (3/5)b)
100 (5/5)
100 (5/5)
100 (5/5)
100 (4/5)
100 (4/5)
100 (3/5)
200 (5/5)
200 (3/5)
200 (5/5)
100 (3/5)
200 (4/5)
200 (5/5)
200 (1/5)
200 (2/5)
200 (2/5)
200 (0/5)
200 (2/5)
200 (3/5)
200 (1/5)
200 (3/5)
200 (1/5)
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
d)
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
4s
–CH3
–C2H5
200 (5/5)b)
200 (5/5)
100 (4/5)
100 (5/5)
100 (5/5)
100 (5/5)
100 (4/5)
100 (3/5)
200 (5/5)
100 (5/5)e)
100 (5/5)
100 (5/5)
100 (4/5)
200 (5/5)
100 (5/5)
200 (4/5)
200 (2/5)
200 (4/5)
200 (2/5)
100 (5/5)e)
100 (1/5)
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
3s
–CH3
–C2H5
n-C3H7
n-C4H9
n-C5H11
n-C6H13
n-C7H15
n-C8H17
n-C12H25
–CH2C6H5
n-C3H7
n-C4H9
n-C5H11
n-C6H13
n-C7H15
n-C8H17
n-C12H25
–CH2C6H5
–CH2C6H4 (o-F)
–CH2C6H4 (m-F)
–CH2C6H4 (p-F)
–CH2C6H4 (o-F)
–CH2C6H4 (m-F)
–CH2C6H4 (p-F)
–CH2C6H4 (o-Cl)
–CH2C6H4 (m-Cl)
–CH2C6H4 (p-Cl)
–CH2C6H3 (2,4-Cl2)
–CH2C6H4 (o-Br)
–CH2C6H4 (p-Br)
–CH2C6H4 (p-CH3)
–CH2C6H4 (p-OCH3)
–CH2C6H4 (o-Cl)
–CH2C6H4 (m-Cl)
–CH2C6H4 (p-Cl)
–CH2C6H3 (2,6-Cl2)
–CH2C6H4 (o-Br)
–CH2C6H4 (p-Br)
–CH2C6H4 (p-CH3)
–CH2C6H4 (p-OCH3)
–CH2C6H3 (3,4-(OCH3)2)
3t
3u
3v
4t
4u
a) All of the tested compounds were dissolved in polyethylene glycol-400; b) the
maximal electroshock test was conducted 30 min after administration of the test com-
pounds; c) doses are in mg/kg; d) —ꢁno activity at 300 mg/kg; e) too much neurotoxi-
city.
a) All of the tested compounds were dissolved in polyethylene glycol-400; b) the
maximal electroshock test was conducted 30 min after administration of the test com-
pounds; c) doses are in mg/kg; d) —ꢁno activity at 300 mg/kg.

March 2010
331
Table 3. Quantitative Anticonvulsant Data in Mice (Test Drug Administered i.p.) (Phase II)
a)
c)
Compound
R
MES; ED50
Rotarod toxicity TD50
MES; PIb)
3b
3c
3d
3e
3f
3g
3k
4d
4e
4f
–C2H5
n-C3H7
n-C4H9
n-C5H11
n-C6H13
n-C7H15
–CH2C6H4 (o-F)
n-C4H9
n-C5H11
n-C6H13
76.18 (53.4—108.7)d)
68.14 (47.7—97.4)
52.79 (37.2—74.9)
34.08 (23.9—48.6)
52.79 (37.2—74.9)
91.23 (64.9—128.3)
81.77 (57.2—116.9)
20.45 (12.19—34.28)
18.34 (11.34—29.65)
24.54 (16.23—37.11)
17.04 (10.98—26.43)
18.33 (12.41—27.07)
20.45 (13.29—31.45)
11.80 (8.5—16.4)
353.5 (249.1—501.7)
254.6 (181.1—358.0)
366.6 (260.7—515.5)
305.5 (217.3—429.6)
ꢀ600
4.6
3.7
7.0
8.9
ꢀ11.4
ꢀ6.5
ꢀ7.3
3.2
3.9
4.5
14.3
12.4
12.4
6.4
ꢀ600
ꢀ600
65.40 (41.49—103.06)
72.98 (49.42—107.77)
110.0 (71.53—169.15)
243.9 (148.32—401.36)
227.2 (147.76—349.40)
253.5 (177.33—362.38)
76.1 (55.8—103.7)
4k
4l
4o
CPZ
–CH2C6H4 (o-F)
–CH2C6H4 (m-F)
–CH2C6H4 (m-Cl)
—
a) Doses are in mg/kg; b) PIꢁTD50/ED50; c) minimal neurotoxicity was determined by therotarod test 30 min after administration of the test compounds; d) the 95% confi-
dence limits.
gradually increased with compound 4e (with the 7-pentyloxy benzo[b][1,4]thiazine 4k was the most active compound with
group) being the most active compound. From 4e to 4i, as the ED50 of 17.0 mg/kg, TD50 of 243.9 mg/kg and PI of 14.3. Its
alkoxyl chain length increased, anticonvulsant activity gradu- neurotoxicity was lower than all other synthesized com-
ally decreased. Among the substituted benzyloxyl, the three pounds and also markedly lower than that of the reference
F-substituted phenyl derivatives, the potency order was o- drug carbamazepine.
Fꢁm-Fꢀp-F. Among the four Cl-substituted phenyl deriva-
tives, the potency order was m-Clꢀo-Clꢀp-Clꢀ2,4-Cl2. Be-
tween the two Br-substituted phenyl derivatives, the potency
Acknowledgment This work was supported by the National Natural
Science Foundation of China (No. 30760290 and No. 30860340) and Im-
portant Item Foundation of Ministry of Education P. R. China (No.
order was o-Brꢀp-Br. Among the three electron-donor
phenyl derivatives, the potency order was p-CH3ꢀp-OCH3.
Among the six p-substituted phenyl derivatives, the potency
order was HꢁCH3ꢀFꢀCH3OꢀClꢀBr. Compound 4k was
the most active compound with an ED50 of 17.0 mg/kg, TD50
value of 243.9 mg/kg and PI value of 14.3. Its neurotoxicity
was lower than all the other synthesized compounds and
also markedly lower than that of the reference drug car-
bamazepine.
20070422029).
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Conclusion
A series of 7-alkoxy-2H-1,4-benzothiazin-3(4H)-ones and
a new series of 7-alkoxy-4H-[1,2,4]triazolo[4,3-d]benzo[b]-
[1,4]thiazine derivatives were synthesized. The anticonvul-
sant activity of these compounds was evaluated with MES
test and rotarod test with intraperitoneal injection in Kun-
Ming mice. Among the synthesized compounds 3a—v, 7-
(hexyloxy)-2H-benzo[b][1,4]thiazin-3(4H)-one (3f) could
be considered potentially the most useful and safe therapeu-
tic compound. Among the synthesized compounds 4a—u,
compound 7-(2-fluorobenzyloxy)-4H-[1,2,4]triazolo[4,3-d]-
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