Synthesis and evaluation of 5-benzyl-1,3,4-thiadiazole derivatives as acetylcholinesterase inhibitors

Article abstract of DOI:10.3184/174751917X15094552081242

Three novel 5-benzyl-1,3,4-thiadiazole derivatives were synthesised starting from phenylacetic acid derivatives. These compounds were characterised by NMR, HRMS and single-crystal X-ray diffraction analysis. 2-Pyrrolidyl-5-[2-(4-bromophenyl)methyl]-1,3,4-

Full text of DOI:10.3184/174751917X15094552081242

6
64 RESEARCH PAPER
VOL. 41 NOVEMBER, 664–667
JOURNAL OF CHEMICAL RESEARCH 2017
Synthesis and evaluation of 5-benzyl-1,3,4-thiadiazole derivatives as
acetylcholinesterase inhibitors
a,b,c*
a,b
b
b
b
b
Da-Hua Shi
, Hui-Long Zhu , Yu-Wei Liu , Zong-Ming Tang , Chen Lu , Xiao-Dong Ma ,
b
b
b
b
Xiao-Kai Song , Wei-Wei Liu , Tong Dong and Meng-Qiu Song
a
Jiangsu Institute of Marine Resources, Huaihai Institute of Technology, Lianyungang 222005, P.R. China
Jiangsu Key Laboratory of Marine Pharmaceutical Compound Screening, Huaihai Institute of Technology, Lianyungang 222005, P.R. China
Co-Innovation Center of Jiangsu Marine Bio-industry Technology, Lianyungang 222005, P.R. China
b
c
Three novel 5-benzyl-1,3,4-thiadiazole derivatives were synthesised starting from phenylacetic acid derivatives. These compounds were
characterised by NMR, HRMS and single-crystal X-ray diffraction analysis. 2-Pyrrolidyl-5-[2-(4-bromophenyl)methyl]-1,3,4-thiadiazole
showed moderate acetylcholinesterase-inhibition activity with a 50% inhibitory concentration value of 33.16 µM. 2-Pyrrolidyl-5-[2-(4-
bromophenyl)methyl]-1,3,4-thiadiazole and acetylcholinesterase docking was demonstrated using the Molecular Operating Environment
program.
Keywords: 5-benzyl-1,3,4-thiadiazole derivatives, acetylcholinesterase, Alzheimer’s disease
Alzheimer’s disease (AD) is a multifaceted neurodegenerative
disorder characterised at the molecular level by protein
5-benzyl-1,3,4-thiadiazole derivatives derived from phenylacetic
acids. The AChE inhibition activity of these compounds was
tested to find inhibitors for the treatment of AD.
misfolding and aggregation, oxidative stress, mitochondrial
1
abnormalities
and
neuroinflammatory
processes.
Results and discussion
Acetylcholinesterase (AChE) inhibitors (e.g. tacrine, donepezil,
rivastigmine and galantamine), developed based on the
cholinergic hypothesis of memory dysfunction, the depletion of
neurotransmitter acetylcholine and loss of associated synapses
during the progression of AD, and N-methyl-d-aspartate
receptor antagonists (e.g. memantine) are used for the treatment
The synthetic route for the 5-benzyl-1,3,4-thiadiazole derivatives
is shown in Scheme 1. The commercially available starting
material 2-(4-bromophenyl)acetic acid (1) was subjected to
reaction with thiosemicarbazide to give the 5-(4-bromobenzyl)-
14
1,3,4-thiadiazol-2-amine (2). Compound 2 was reacted with
2
of AD. However, AChE inhibitors have some limitations in
CuBr and tert-butyl nitrite to give the compound 2-bromo-5-(4-
2
their use for the treatment of AD, such as non-selectivity, poor
bioavailability, adverse cholinergic side effects in the periphery,
bromobenzyl)-1,3,4-thiadiazole (3). The final compounds 4a–c
were obtained by reaction of intermediate 3 with cyclic secondary
amines. The structures of the compounds were confirmed by
NMR and MS. The detailed physical and analytical data are listed
in the Experimental section. Their analytical and spectroscopic
data were in accordance with the predicted structures.
3,4
15
narrow therapeutic ranges and hepatotoxicity. Therefore,
further studies of novel AChE inhibitors are necessary.
The 1,3,4-thiadiazole nucleus is a common and integral feature
5
of a variety of natural products and medicinal agents. Recently,
some 1,3,4-thiadiazole derivatives with AChE inhibition activity
The structure of compound 4a was demonstrated by
X-ray diffraction analysis. The crystal data are presented in
Table 1 and Fig. 1 and have been deposited at the Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC 1571930. The compound is monoclinic: space group
6
–8
were designed and synthesised. We have previously synthesised
a series of 1,3,4-thiadiazole derivatives and found that they
9,10
showed AChE inhibitory activity. Following our studies on
11–13
AChE inhibitors,
here we report the synthesis of a series of
Scheme 1 Synthesis of 5-benzyl-1,3,4-thiadiazole derivatives.
Correspondent. E-mail: shidahua@hhit.edu.cn
*

JOURNAL OF CHEMICAL RESEARCH 2017 665
Fig. 1 Molecular structure of compound 4a at 30% probability ellipsoids.
Table 1 Crystallographic data for the compound 4a
Formula
FW
C H BrN S
13 14 3
324.24
Crystal shape/colour
Crystal size (mm)
T (K)
Block/white
0.21 × 0.20 × 0.18
296(2)
λ (MoKα) (Å)
Crystal system
Space group
a (Å)
0.71073
Monoclinic
P2(1)/n
6.3086(7)
27.282(3)
8.7338(10)
90.00
b (Å)
c (Å)
α (°)
β (°)
109.0690(10)
90.00
γ (°)
3
V (Å )
1420.7(3)
4
Z
–1
µ(MoKα) (mm )
3.026
Tmin
0.5690
Tmax
0.6119
–
3
D (g cm )
1.516
c
Measured reflections
Unique reflections
11441
2742
0.0519
R
int
Observed reflections
1359
Data/restraints/parameters
2742/0/163
1.011
2
Goodness of fit on F
R1 [I ≥ 2σ(Iꢀ)]
0.0592
0.1412
0.1303
wR [I ≥ 2σ(Iꢀ)]
2
R1 (all data)
wR (all data)
0.1799
2
–
3
Large diff. peak and hole (e Å )
1.086 and −0.555
Fig. 2 The AChE active site cavity (A) and interaction map (B) displaying
the binding and interactions of compound 4a with AChE.
16
P2(1)/n, a = 6.3086(7), b = 27.282(3), c = 8.7338(10) Å, β =
Ellman et al. In this test, tacrine was used as the reference
drug and the AChE inhibition results are presented in Table 2.
Only compound 4a showed moderate AChE inhibitory activity
with a 50% inhibitory concentration (IC ) value of 33.16 µM.
3
1
09.0690(10)°, V = 1420.7(3) Å , Z = 4.
The target compounds 4a–c were tested for AChE (from
electric eel) inhibitory activity using the method published by
5
0

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66 JOURNAL OF CHEMICAL RESEARCH 2017
Table 2 In vitro inhibitory activities of compounds 4a–c against AChE
filtered and recrystallised from ethanol to obtain compound 3 a white
−1
a
solid; yield 96.4%; m.p. 84.2–86.3 °C; IR (KBr) (cm ): 3435, 3002,
Compound
IC (µM)
50
1
2
971, 2928, 1576, 1488, 1428, 1397; H NMR (400 MHz, CD OD):
3
4
4
4
a
b
c
33.16 ± 4.32
–
–
δ 4.43 (s, 2H, CH2), 7.29–7.22 (m, 2H, Ar–H), 7.53–7.47 (m, 2H,
13
Ar–H); C NMR (100 MHz, CD OD): δ 174.3, 139.9, 135.8, 131.8,
3
+
1
30.5, 121.2, 34.9. HRMS (ESI) m/z calcd for C H Br N S [M + H] :
9
7
2
2
Tacrine
0.25 ± 0.05
332.8691; found: 332.8691.
a
5
0% inhibitory concentration (mean ± SD of three experiments) of AChE from electric eel.
Synthesis
of
2-amino-5-(substituted-benzyl)-1,3,4-thiadiazoles
(4a–c); general procedure
A docking study of the most potent anti-AChE compound 4a
Triethylamine (2.4 mmol) was added to a mixture of 2-bromo-5-(4-
bromophenethyl)-1,3,4-thiadiazole (2 mmol) with amine (4 mmol)
in 1,4-dioxane at 70 °C with stirring. The reaction was monitored by
TLC. When the reaction was completed and the mixture had cooled to
room temperature, the organic layer was extracted with EtOAc, dried
was conducted to identify the possible interactions between the
compound and the enzyme active site. The docking study was
performed using the Molecular Operating Environment (MOE)
17
program. The molecular docking of compound 4a can interact
18
over MgSO , filtered and concentrated in vacuo to obtain the crude
with the catalytic active site (CAS) of AChE (Fig. 2). When
4
product. The precipitate was filtered and recrystallised from methanol
or purified by column chromatography using CH Cl and MeOH to
4
a is docked with AChE, one N atom of the 1,3,4-thiadiazole
group can interact with His440 via the hydrogen bond.
2
2
obtain compounds 4a–c.
-(4-Bromobenzyl)-5-(pyrrolidin-1-yl)-1,3,4-thiadiazole (4a): White
2
Conclusion
−1
solid; yield 80.8%; m.p. 98.7–99.2 °C; IR (KBr) (cm ): 3446, 2970, 2870,
637, 1524, 1415; H NMR (400 MHz, MEOD): δ 2.02–2.05 (m, 4H,
CH ), 3.41 (s, 4H, 2CH ), 4.18 (s, 2H, CH ), 7.20–7.23 (d, 2H, J = 8.4 Hz,
Ar–H), 7.46–7.48 (m, 2H, Ar–H); C NMR (100 MHz, DMSO): δ 169.2,
57.7, 136.8, 131.6, 130.3, 120.7, 50.3, 35.0, 25.3. HRMS (ESI) m/z calcd
for C H BrN S [M + H] : 324.0165; found: 324.0159.
In summary, three 5-benzyl-1,3,4-thiadiazole derivatives 4a–c
were synthesised and their AChE inhibition ability in vitro
was tested. The data showed that compound 4a was the most
potent anti-AChE derivative, and it could interact with CAS of
AChE. All these results suggest that compound 4a could be a
promising multi-target lead candidate against AD.
1
1
2
2
2
2
13
1
+
1
3
15
3
2
-(4-Bromobenzyl)-5-(piperazin-1-yl)-1,3,4-thiadiazole (4b): White
−1
solid; yield 81.7%; m.p. 76.3–79.2 °C; IR (KBr) (cm ): 3432, 3282, 2979,
846, 1546, 1487, 1446; H NMR (400 MHz, DMSO): δ 2.75–2.78 (m,
4H, 2CH ), 3.28–3.31 (m, 5H, 2CH , NH), 4.21 (s, 2H, CH ), 7.25–7.27
(d, 2H, J = 8.4 Hz, Ar–H), 7.52–7.54 (m, 2H, Ar–H); C NMR (100
MHz, DMSO) δ: 173.0, 158.3, 137.8, 132.1, 131.4, 120.6, 50.9, 45.1, 35.3.
HRMS (ESI) m/z calcd for C H BrN S [M + H] : 339.0274; found:
Experimental
Analytical reagent grade 2-(4-bromophenyl)acetic acid was purchased
from Aladdin Industrial Corporation. AChE from electric eel,
1
2
2
2
2
13
5
,5′-dithio-bis(2-nitrobenzoic acid) (DTNB) and acetylthiocholine
+
iodide (ATCI) were purchased from Sigma-Aldrich (St. Louis, MO,
USA). All other reagents and solvents were purchased from Sinopharm
Chemical Regent Co., Ltd. and were used as received. TLC was
performed on glass-backed silica gel sheets (Silica Gel 60 GF254).
Melting points were determined on a Yanaco melting point apparatus
and are uncorrected. Infrared (IR) spectra were recorded on a Thermo
13
16
4
339.0268.
2-(4-Bromobenzyl)-5-(4-methylpiperazin-1-yl)-1,3,4-thiadiazole
−1
(4c): White solid; yield 73.6%; m.p. 78.8–81.8 °C; IR (KBr) (cm ):
1
3434, 2937, 2848, 2803, 1640, 1536, 1497; H NMR (400 MHz,
DMSO): δ 2.20 (s, 3H, CH ), 2.37–2.39 (m, 4H, 2CH ), 3.35–3.38 (t,
3
2
1
13
Scientific Nicolet iS10 spectrometer in KBr. H NMR and C NMR
spectra were recorded on a Bruker Avance 400 MHz instrument or
4H, 2CH ), 4.22 (s, 2H, CH ), 7.25–7.27 (m, 2H, Ar–H), 7.52–7.54
2 2
13
(m, 2H, Ar–H); C NMR (100 MHz, DMSO) δ: 172.6, 158.7, 137.8,
132.1, 131.4, 120.6, 54.0, 49.7, 46.1, 35.2. HRMS (ESI) m/z calcd for
5
(
00 MHz instrument using MeOD or CDCl , with tetra methyl silane
3
+
TMS) as an internal standard. The MS (ESI) spectra were recorded
C H BrN S [M + H] : 353.0430; found: 353.0424.
14
18
4
using an Agilent Technologies 6224 TOF LC/MS.
X-ray crystallography
5
-(4-Bromobenzyl)-1,3,4-thiadiazol-2-amine (2)
POCl3 (0.28 mol) was added dropwise to
-(4-bromophenyl)acetic acid (1) (0.07 mol) and thiosemicarbazide
0.105 mol) in an ice bath. Then the reaction mixture was refluxed
Diffraction intensities for the complexes were collected at 296(2) K
using a Bruker SMART APEX-II CCD area-detector with MoKα
radiation (λ = 0.71073 Å). The collected data were reduced with the
a
mixture of
2
(
19,20
SAINT program,
and multi-scan absorption corrections were
21
over an oil bath for 6 h. The reaction was monitored by TLC. When
the reaction was complete and the mixture had cooled to room
temperature, water (100 mL) was added and the reaction mixture was
refluxed for 1 h. After cooling, the mixture was basified to pH 8–9
by the dropwise addition of 50% NaOH solution in an ice bath. The
precipitate was filtered and recrystallised from ethanol to obtain
compound 2 as white crystals; yield 85%; m.p. 203–205 °C; IR (KBr)
performed using the SADABS program. Both structures were solved
2
by direct methods. The complexes were refined against F by full-
2
2
matrix least-squares methods using the Olex2-1.2 package. All of
the non-hydrogen atoms were refined anisotropically. Hydrogen atoms
were placed in calculated positions and constrained to their parent
atoms. The crystallographic data for the complexes are summarised in
Table 1. Crystallographic data for the complexes have been deposited
with the Cambridge Crystallographic Data Center (CCDC 1571930).
−
1
1
(cm ): 3396, 3273, 3122, 1578, 1488, 1420; H NMR (400 MHz,
CD OD): δ 7.48 (d, J = 8.4 Hz, 2H), 7.21 (d, J = 8.4 Hz, 2H), 4.16 (s,
3
+
Biological tests
2
H). HRMS (ESI) m/z calcd for C H BrN S [M + H] : 269.9695;
9
9
3
The methods for biological tests are provided in the ESI.
found: 269.9700.
2
-Bromo-5-(4-bromobenzyl)-1,3,4-thiadiazole (3)
-(4-Bromobenzyl)-1,3,4-thiadiazol-2-amine (20 mol) was added
Acknowledgements
5
We acknowledge financial support from the Natural Science
Foundation of Jiangsu Province (BK20141246), a project
funded by Jiangsu Key Laboratory of Marine Pharmaceutical
Compound Screening (2015HYB07, HY201603), public
science and technology research funds projects of the ocean
slowly to a mixture of CuBr2 (24 mmol) and t-BuNO2 (30 mmol)
in MeCN (100 mL) and the reaction mixture was stirred at room
temperature overnight. The reaction was monitored by TLC. When
the reaction was completed, saturated NH Cl (120 mL) was added to
4
the reaction mixture and the organic layer was extracted with EtOAC,
(201505023) and a project funded by the priority academic
dried over MgSO , filtered and concentrated in vacuo to obtain the
4
program development of Jiangsu higher education institutions.
crude product, which was triturated in MeOH. The precipitate was

JOURNAL OF CHEMICAL RESEARCH 2017 667
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