Design, synthesis characterization and in vitro biological activity of a series of 3-aryl-6-(bromoarylmethyl)-7H-thiazolo[3,2-b]-1, 2, 4-triazin-7-one derivatives as the novel acetylcholinesterase inhibitors

Article abstract of DOI:10.1016/j.cclet.2012.04.022

Bromination is used as a strategy to improve biological activity in medicinal chemistry. In order to study on the structure-activity relationships of the novel acetylcholinesterase inhibitors with 7H-thiazolo[3,2-b]-1, 2, 4-triazin-7-one scaffold, based o

Full text of DOI:10.1016/j.cclet.2012.04.022

Available online at www.sciencedirect.com
Chinese Chemical Letters 23 (2012) 765–768
www.elsevier.com/locate/cclet
Design, synthesis characterization and in vitro biological
activity of a series of 3-aryl-6-(bromoarylmethyl)-7H-
thiazolo[3,2-b]-1, 2, 4-triazin-7-one derivatives as the
novel acetylcholinesterase inhibitors
c
He Nan Xu a,b, Zhe Jin b, Si Jie Liu b, Hong Min Liu a, , Shuo Li ,
*
Huang Quan Lin c, David Chicheong Wan c, Chun Hu a,b
a New Drug Research & Development Center, Zhengzhou University, Zhengzhou 450052, China
b Key Laboratory of Structure-Based Drug Design Discovery, Ministry of Education, Shenyang Pharmaceutical
University, Shenyang 110016, China
c Department of Biochemistry, The Chinese University of Hong Kong, Hong Kong SAR, China
Received 16 February 2012
Available online 9 June 2012
Abstract
Bromination is used as a strategy to improve biological activity in medicinal chemistry. In order to study on the structure–activity
relationships of the novel acetylcholinesterase inhibitors with 7H-thiazolo[3,2-b]-1, 2, 4-triazin-7-one scaffold, based on our
previous work and molecular modeling, a series of novel 3-aryl-6-(bromoarylmethyl)-7H-thiazolo[3,2-b]-1, 2, 4-triazin-7-one
derivatives were designed by molecular docking, synthesized and characterized by mass spectra, infrared spectra, proton NMR and
elemental analyses. The study of AChE inhibitory activity was carried out using the Ellman colorimetric assay with huperzine-A as
the positive control. Most of all target compounds exhibited more than 45% inhibition at 10 mmol/L. The preliminary structure–
activity relationship was the bromine atoms and the hydroxyl group at the phenyl ring at the C6 position of the parent nucleus played
significant roles in the AChE inhibitory activity of the target compounds.
# 2012 Hong Min Liu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Acetylcholinesterase inhibitor; Bromination; Heterocycle; Synthesis; 7H-Thiazolo[3,2-b]-1, 2, 4-triazin-7-one derivatives
The global population has reached seven billion on Monday, October 31, 2011, accompanied by an aging society
[1]. What will life in an aging society be maybe dramatically increased the age-related diseases. Alzheimer’s disease
(AD) is the most common single cause of dementia in the aging society, and can be diagnosed in people over 65 years
of age, although the less-prevalent early-onset Alzheimer’s can occur much earlier. In 2006, there were 26.6 million
sufferers worldwide. Alzheimer’s is predicted to affect 1 in 85 people globally by 2050 [2].
AD is a degenerative brain syndrome characterized by a progressive decline in memory, thinking, comprehension,
calculation, language, learning capacity and judgment sufficient to impair personal activities of daily living [3].
* Corresponding author.
1001-8417/$ – see front matter # 2012 Hong Min Liu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2012.04.022

766
H.N. Xu et al. / Chinese Chemical Letters 23 (2012) 765–768
Reduction in the activity of the cholinergic neurons is a well-known feature of Alzheimer’s disease.
Acetylcholinesterase (AChE) inhibitors are employed to reduce the rate at which acetylcholine (ACh) is broken down,
thereby increasing the concentration of ACh in the brain and combating the loss of ACh caused by the death of
cholinergic neurons. Now, three acetylcholinesterase inhibitors, donepezil, galantamine and rivastigmine are currently
approved by regulatory agencies such as the U.S. Food and Drug Administration (FDA) and the European Medicines
Agency (EMA) to treat the cognitive manifestations of AD [4]. Many of the side effects of the AChE inhibitors are
attributable to peripheral cholinergic effects, and nausea, vomiting and diarrhea were the most frequently reported [5].
Lack and side effects of the AChE inhibitors driven us to discover some new acetylcholinesterase inhibitors.
In our previous work, 3-aryl-6-arylmethyl-7H-thiazolo[3,2-b]-1, 2, 4-triazin-7-one derivatives were designed and
synthesized, which exhibited inhibitory activity against AChE, and the molecular docking exhibited 6-arylmethyl-3-
phenyl-7H-thiazolo[3,2-b]-1, 2, 4-triazin-7-one derivatives interacted with the PAS and the CAS of AChE [6]. And 3,
6-diaryl-7H-thiazolo[3,2-b]-1, 2, 4-triazin-7-ones were also exhibited inhibitory activity against AChE, the structure
activity relationship showed the inhibitory activity could be enhanced with the presence of the halogen atoms [7,8].
Bromination is a frequent modification in medicinal chemistry and can play a significant improvement on the
biological activity [9].
In order to rationalize the presence of the bromine atoms influences on the inhibitory activity against AChE, and
reveal the interactions between the target molecules and AChE at the molecular level and examine the structure–
activity relationship for the 7H-thiazolo[3,2-b]-1, 2, 4-triazin-7-one derivatives, a series of 3-aryl-6-
(bromoarylmethyl)-7H-thiazolo[3,2-b]-1, 2, 4-triazin-7-one derivatives were designed and synthesized, and the
inhibitory activity against AChE was evaluated.
For this study, the model was obtained from 3D structural information, of which the human AChE (hAChE)
complex with the inhibitor (fasciculin-2), i.e. hAChE–fasciculin-2 complex (1B41), was available in the RSCB Protein
Data Bank [10]. Molecular docking was carried out using Molegro Virtual Docker (MVD) [11]. Based on the Molegro
Virtual Docker docking, the schematic diagrams of the interactions between hAChE (1B41) after eliminating the
inhibitor (fasciculin-2) and 6-(3, 5-dibromo-4-hydroxybenzyl)-3-(2-hydroxy-4-methylphenyl)-7H-thiazolo[3,2-b]-1,
2, 4-triazin-7-one (5h) were shown in Fig. 1, where the hydrogen bonds are indicated with green dotted lines. There
were some hydrogen bonds between compound 5h and His447, Tyr337, and Tyr124 of hAChE. The protein residue
His447 was located at the CAS, the protein residue Tyr337 was located at the anionic binding site, and Tyr124 was
located at the PAS. Therefore, the CAS, the anionic binding site and the PAS of hAChE were action sites of 5h. The
similar binding actions between the other target compounds and hAChE were identified by molecular docking.
In general, the target compounds (5a–5h) were obtained in satisfactory yields, and the synthetic pathways are
described in Scheme 1. According to our developed procedure [6], the general synthetic procedures for the target
Fig. 1. Docking model of compound 5h at the active sites of hAChE.

H.N. Xu et al. / Chinese Chemical Letters 23 (2012) 765–768
767
CHO
OH
O
CH COOH
2
O
X
X
NHCOCH
3
HCl
OH
O
N
O
AcONa, Ac O
2
HO
HO
X
Br
Br
Br
2a: X = H
2b: X = Br
3a: X = H
3b: X = Br
1a: X = H
1b: X = Br
5a: X = H, Ar = phenyl
5b: X = Br, Ar = phenyl
5c: X = H, Ar = 4-methylphenyl
5d: X = Br, Ar = 4-methylphenyl
5e: X = H, Ar = 4-methoxyphenyl
5f: X = Br, Ar = 4-methoxyphenyl
5g: X = H, Ar = 2-hydroxy-4-methylphenyl
5h: X = Br,Ar = 2-hydroxy-4-methylphenyl
Ar
N
N
X
X
NH
S
H NCSNHNH
ArCOCH Cl
2
2
2
N
AcOH, AcONa
K CO
HO
O
S
2
3
N
H
HO
O
N
Br
Br
4a: X = H
4b: X = Br
Scheme 1. The synthetic route of 3-aryl-6-(bromoarylmethyl)-7H-thiazolo[3,2-b]-1,2,4-triazin-7-one derivatives.
Table 1
Inhibition of AChE activities by the targets at 10 mmol/L (n = 3).
No.
Inhibition (%)
No.
Inhibition (%)
No.
Inhibition (%)
No.
Inhibition (%)
5a
5b
5c
57.66
66.33
46.94
5d
5e
5f
62.13
48.09
55.88
5g
5h
27.56
55.31
L1
47.62
49.04
L2
Huperzine-A
100.00
compounds were described as follows. The raw material 4-hydroxybenzaldehyde was converted to 3-bromo-4-
hydroxybenzaldehyde or 3, 5-dibromo-4-hydroxybenzaldehyde (1) by bromination. 1 reacted with N-acetylglycine, to
obtain 4-(bromoarylmethylene)-2-methyl-5(4H)-oxazolones (2) in good yield. 2 were then converted into the
corresponding arylpyruvic acids (3) by treatment with 3 mol/L hydrochloric acid. 6-(Bromoarylmethyl)-3, 4-dihydro-3-
thioxo-1, 2, 4-triazin-5(2H)-ones(4) werepreparedbyreactionof3withthiosemicarbazideinthepresenceofalcoholand
water. And 3-aryl-6-(bromoarylmethyl)-7H-thiazolo[3,2-b]-1, 2, 4-triazin-7-ones (5) were obtained by reaction of 4 with
substituted phenacyl chlorides in the presence of acetic acid. The structures of the target compounds synthesized herein
were fully confirmed by mass analysis, infrared spectra, elemental analyses and proton NMR spectroscopic data [12].
The target compounds 5a–5h were initially assessed for the biological activity against hAChE, and the positive
control drug was huperzine-A by the Ellman assay [13]. The biological activity is summarized in Table 1.
In our previous work, 6-benzyl-3-phenyl-7H-thiazolo[3,2-b]-1, 2, 4-triazin-7-one (L1) and 6-benzyl-3-(4-methyl-
phenyl)-7H-thiazolo[3,2-b]-1, 2, 4-triazin-7-one (L2) exhibited inhibitory activity against AChE [6]. Compared with
L1 and L2, the bromine atoms and hydroxyl group were introduced into the aromatic nucleus at the C6 position of the
target compounds (5a–5d). The inhibitory activities of 5a, 5b and 5d were stronger than L1 and L2, which may be due
to the hydrogen bonds of the halogen atom and hydroxyl group.
Compared with 5e and 5g, the bromine atom was introduced into the aromatic nucleus at the C6 position of
compounds 5f and 5h. The inhibitory activities of 5f and 5h were stronger than corresponding 5e and 5g, which were
due to the hydrogen bonds of the hydroxyl group, showed in Fig. 1.
These phenomena showed that the CAS, the PAS and the anionic binding site were the main active sides of 3-aryl-6-
(bromoarylmethyl)-7H-thiazolo[3,2-b]-1, 2, 4-triazin-7-one derivatives. The hydroxyl group and the halogen atoms at
the aromatic ring at the C6 position played significant roles in the AChE inhibitory activities of the target compounds.
In summary, 3-aryl-6-(bromoarylmethyl)-7H-thiazolo[3,2-b]-1, 2, 4-triazin-7-one derivatives would be a kind of
highly active AChE inhibitors. The inhibitory activity could be enhanced with the presence of the hydroxyl groups, the
bromine atoms.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (No. 21072130). The authors thank
Molegro ApS for kindly providing a free evaluation copy of their software package.

768
H.N. Xu et al. / Chinese Chemical Letters 23 (2012) 765–768
References
[1] H.E. Nasser, http://www.usatoday.com/news/world/story/2011-10-30/world-population-hits-seven-billion/51007670/1 (30.10.11).
[2] R. Brookmeyer, E. Johnson, K. Ziegler-Graham, et al. Alzheimer’s Dementia 3 (2007) 186.
[3] A. Kumar, S. Dogra, Drugs Future 33 (2008) 433.
[4] C. Geula, M.M. Mesulam, Alzheimer Dis. Assoc. Disord. 2 (Suppl. 9) (2012) 23.
[5] S.J. Liu, L. Yang, X.G. Liu, et al. Lett. Drug Des. Dis. 7 (2010) 5.
[6] S.J. Liu, L. Yang, Z. Jin, et al. ARKIVOC (2009) 333.
[7] Z. Jin, L. Yang, S.J. Liu, et al. Arch. Pharm. Res. 33 (2010) 1641.
[8] Z. Jin, L. Yang, H.N. Xu, et al. Sci. China Chem. 53 (2010) 2297.
[9] C.S. Neumann, D.G. Fujimori, C.T. Walsh, Chem. Biol. 15 (2008) 99.
[10] G. Kryger, M. Harel, K. Giles, et al. Acta Crystallogr. Sect. D 56 (2000) 1385.
[11] R. Thomsen, M.H. Christensen, J. Med. Chem. 49 (2006) 3315.
[12] The characteristic data for the target compounds. 5a: white solid, 56.4% yield, mp: 244–245 8C. ESI–MS (m/z): 411.8 (MÀH)À, 413.8
(M+2ÀH)À. 1H NMR (300 MHz, DMSO-d6): d 3.87 (s, 2H), 6.86 (d, 1H, J = 8.1 Hz), 7.07 (dd, 1H, J1 = 2.1 Hz, J2 = 8.4 Hz), 7.40–7.48 (m,
4H), 7.52 (s, 1H), 7.62–7.65 (m, 2H), 10.07 (s, 1H). Anal. Calcd. for C18H12O2N3SBr (%): C, 52.19; H, 2.92; N, 10.14. Found: C, 52.10; H,
2.87; N, 10.22. IR (KBr): y 3150, 1602, 1508, 1473, 1417, 1355, 1287, 1265, 1236, 1214, 1132, 1047, 899, 824, 793, 765, 733, 687 cmÀ1. 5b:
white solid, 62.0% yield, mp: 236–237 8C. ESI–MS (m/z): 489.8 (MÀH)À, 491.8 (M+2ÀH)À, 493.7 (M+4ÀH)À. 1H NMR (300 MHz, DMSO-
d6): d 3.92 (s, 2H), 7.39–7.48 (m, 5H), 7.52 (s, 1H), 7.60–7.63 (m, 2H), 9.78 (s, 1H). Anal. Calcd. for C18H11O2N3SBr2 (%): C, 43.84; H, 2.25;
N, 8.52. Found: C, 43.75; H, 2.21; N, 8.45. IR (KBr): d 3122, 1635, 1577, 1556, 1480, 1409, 1385, 1278, 1241, 1168, 1148, 1120, 750, 735,
691 cmÀ1. 5c: white solid, 67.2% yield, mp: 246–247 8C. ESI–MS (m/z): 425.8 (MÀH)À, 427.8 (M+2ÀH)À. 1H NMR (300 MHz, DMSO-d6):
d 2.35 (s, 3H), 3.86 (s, 2H), 6.86 (d, 1H, J = 8.4 Hz), 7.06 (dd, 1H, J1 = 2.1 Hz, J2 = 8.4 Hz), 7.25 (d, 2H, J = 8.4 Hz), 7.42 (d, 1H, J = 2.1 Hz),
7.46 (s, 1H), 7.51–7.54 (m, 2H), 10.08 (s, 1H). Anal. Calcd. for C19H14O2N3SBr (%): C, 53.28; H, 3.29; N, 9.81. Found: C, 53.21; H, 3.32; N,
9.75. IR (KBr): d 3044, 2769, 2712, 2640, 2575, 1613, 1505, 1468, 1423, 1299, 1254, 1222, 1186, 1118, 1043, 876, 809, 784, 746, 715,
667 cmÀ1. 5d: yellowish solid, 48.5% yield, mp: 255–256 8C. ESI–MS (m/z): 503.8 (MÀH)À, 505.8 (M+2ÀH)À, 507.8 (M+4ÀH)À. 1H NMR
(300 MHz, DMSO-d6): d 2.35 (s, 3H), 3.90 (s, 2H), 7.23 (d, 2H, J = 7.8 Hz), 7.46–7.50 (m, 5H), 9.78 (s, 1H). Anal. Calcd. for
C19H13O2N3SBr2 (%): C, 44.99; H, 2.58; N, 8.28. Found: C, 44.91; H, 2.62; N, 8.33. IR (KBr): d 3106, 1651, 1573, 1549, 1480,
1403, 1381, 1353, 1306, 1282, 1235, 1147, 1112, 819, 769, 734, 695 cmÀ1. 5e: white solid, 56.6% yield, mp: 248–250 8C. ESI–MS (m/z): 441.7
(MÀH)À, 443.7 (M+2ÀH)À. 1H NMR (300 MHz, DMSO-d6): d 10.09 (s, 1H), 7.53–7.58 (m, 2H), 7.40 (s, 1H), 7.07 (d, 2H), 6.98 (d, 1H), 6.95
(d, 1H), 6.87 (d, 1H), 3.87 (s, 2H), 3.81 (3H, s). Anal. Calcd. for C19H14O3N3SBr (%): C, 51.36; H, 3.18; N, 9.46. Found: C, 51.29; H, 3.21; N,
9.41. IR (KBr): d 3115, 2768, 2640, 2570, 1615, 1561, 1505, 1475, 1421, 1391, 1302, 1264, 1250, 1224, 1177, 1117, 1028, 875, 834, 808, 744,
716, 683 cmÀ1. 5f: greenish solid, 51.6% yield, mp: 247–248 8C. ESI–MS (m/z): 519.8 (MÀH)À, 521.8 (M+2ÀH)À, 523.7 (M+4ÀH)À. 1H
NMR (300 MHz, DMSO-d6): d 3.81 (s, 3H), 3.92 (s, 2H), 6.92–6.97 (m, 2H), 7.40 (s, 1H), 7.48 (s, 2H), 7.50–7.55 (m, 2H), 9.81 (1H, s). Anal.
Calcd. for C19H13O3N3SBr2 (%): C, 43.62; H, 2.50; N, 8.03. Found: C, 43.70; H, 2.45; N, 8.07. IR (KBr): d 3118, 1644, 1605, 1574, 1551, 1507,
1478, 1419, 1354, 1262, 1237, 1181, 1146, 1027, 836, 769, 735, 694 cmÀ1. 5g: white solid, 56.9% yield, mp: 246–247 8C. ESI–MS (m/z): 444.5
(M+H)+, 446.5 (M+2+H)+, 468.5 (M+Na)+. 1H NMR (600 MHz, DMSO-d6): d 2.28 (s, 3H), 3.78 (s, 2H), 6.70 (d, 1H, J = 7.8 Hz), 6.79 (s, 1H),
6.83 (d, 1H, J = 8.4 Hz), 7.04 (dd, 1H, J1 = 2.4 Hz, J2 = 8.4 Hz), 7.22 (d, 1H, J = 7.8 Hz), 7.32 (s, 1H), 7.36 (d, 1H, J = 2.4 Hz), 9.82 (s, 1H),
10.07 (s, 1H). Anal. Calcd. for C19H14O3 N3SBr (%): C, 51.36; H, 3.18; N, 9.46. Found: C, 51.43; H, 3.21; N, 9.40. IR (KBr): d 3361, 1609,
1498, 1463, 1417, 1296, 1255, 1121, 1044, 964, 810, 767, 720, 675 cmÀ1. 5h: white solid, 28.6% yield, mp: 261–262 8C. ESI–MS (m/z): 520.0
(MÀH)À, 521.9 (M+2ÀH)À, 523.8 (M+4ÀH)À. 1H NMR (300 MHz, DMSO-d6): d 2.28 (s, 3H), 3.82 (s, 2H), 6.66–6.78 (m, 2H), 7.19 (d, 1H,
J = 7.8 Hz), 7.33 (s, 1H), 7.40 (s, 2H), 9.74 (s, 1H), 9.75 (s, 1H). Anal. Calcd. for C19H13O3N3SBr2 (%): C, 43.62; H, 2.50; N, 8.03. Found: C,
43.53; H, 2.45; N, 8.07. IR (KBr): d 3497, 3318, 1611, 1580, 1416, 1247, 1158, 1128, 1047, 872, 808, 770, 733, 713, 682 cmÀ1
.
[13] P. Elsinghorst, C. Tanarro, M. Gutschow, J. Med. Chem. 49 (2006) 7540.