Microwave-assisted synthesis of new sulfonyl hydrazones, screening of biological activities and investigation of structure–activity relationship

Article abstract of DOI:10.1007/s00044-016-1592-0

Abstract: Sulfonyl hydrazone scaffold and the piperidine rings have important role in medicinal chemistry. This study shows the synthesis of two novel series of sulfonyl hydrazone having piperidine derivatives by condensing benzene sulfonyl hydrazides with ethyl 4-oxopiperidine-1-carboxylate and 2,6-diphenylpiperidin-4-one. Physical and chemical properties of compounds have been characterized and reported by utilizing their melting point, elemental analysis, IR, ¹H-NMR, ¹³C NMR, 2D NMR and mass spectra results. Synthesized compounds were evaluated for antioxidant capacity and anticholinesterase activity. The antioxidant capacity of the compounds were screened through four complementary test, i.e., β-carotene–linoleic acid for lipid peroxidation, DPPH free radical (DPPH^·), ABTS cation radical (ABTS^+·) and CUPRAC assays. Assay results showed that N′-(2,6-diphenylpiperidin-4-ylidene)-4-bromobenzenesulfonohydrazide (11) has the highest lipid peroxidation inhibitory activity. Within the assay series, N′-(2,6-diphenylpiperidin-4-ylidene)-4-bromobenzenesulfonohydrazide (11) exhibited better activity than standard BHT in DPPH^· scavenging, while N′-(2,6-diphenylpiperidin-4-ylidene)benzenesulfonohydrazide (10) showed the best ABTS^+· scavenging assay. The CUPRAC assay revealed that ethyl 4-(2-(4-methoxyphenylsulfonyl)hydrazono)piperidine-1-carboxylate (5) indicated the best activity with A_0.50 value among the tested compounds than the antioxidant standard α-tocopherol. According to AChE assay, N′-(2,6-diphenylpiperidin-4-ylidene)-4-chlorobenzenesulfonohydrazide (12) had the best activity, while in BChE assay the highest activity was found for compound N′-(2,6-diphenylpiperidin-4-ylidene)-4-methylbenzenesulfonohydrazide (16). Electronic and structural characteristics and density functional studies of the all newly synthesized compounds have been reported for better understanding in molecular-level. NMR, molecular electrostatic potential (MEP), ΔE_HOMO–LUMO band gap and the dipole moments of the molecules have been also analyzed and reported. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s00044-016-1592-0

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res
DOI 10.1007/s00044-016-1592-0
ORIGINAL RESEARCH
Microwave-assisted synthesis of new sulfonyl hydrazones,
screening of biological activities and investigation of structure–
activity relationship
Nurcan Karaman1 Emine Elc¸in Oruc¸-Emre1
Yusuf Sıcak2,4 Berna C¸ atıkkas¸3
•
•
•
•
1
4
¨
˙
•
˘
Ays¸egu¨l Karaku¨c¸u¨k-Iyidogan Mehmet Oztu¨rk
Received: 15 September 2015 / Accepted: 28 April 2016
Ó Springer Science+Business Media New York 2016
Abstract Sulfonyl hydrazone scaffold and the piperidine
rings have important role in medicinal chemistry. This study
shows the synthesis of two novel series of sulfonyl hydrazone
having piperidine derivatives by condensing benzene sulfonyl
hydrazides with ethyl 4-oxopiperidine-1-carboxylate and 2,6-
diphenylpiperidin-4-one. Physical and chemical properties of
compounds have been characterized and reported by utilizing
standard BHT in DPPHÁ scavenging, while N0-(2,6-diphe-
nylpiperidin-4-ylidene)benzenesulfonohydrazide(10)showed
the best ABTS?Á scavenging assay. The CUPRAC assay
revealed that ethyl 4-(2-(4-methoxyphenylsulfonyl)hydra-
zono)piperidine-1-carboxylate (5) indicated the best
activity with A0.50 value among the tested compounds than
the antioxidant standard a-tocopherol. According to AChE
assay, N0-(2,6-diphenylpiperidin-4-ylidene)-4-chloroben-
zenesulfonohydrazide (12) had the best activity, while in
BChE assay the highest activity was found for compound
N0-(2,6-diphenylpiperidin-4-ylidene)-4-methylbenzenesulfono-
hydrazide (16). Electronic and structural characteristics and
density functional studies of the all newly synthesized com-
pounds have been reported for better understanding in
molecular-level. NMR, molecular electrostatic potential
(MEP), DEHOMO–LUMO band gap and the dipole moments of
the molecules have been also analyzed and reported.
1
their melting point, elemental analysis, IR, H-NMR, 13C
NMR, 2D NMR and mass spectra results. Synthesized com-
pounds were evaluated for antioxidant capacity and anti-
cholinesterase activity. The antioxidant capacity of the
compounds were screened through four complementary test,
i.e., b-carotene–linoleic acid for lipid peroxidation, DPPH free
radical (DPPHÁ), ABTS cation radical (ABTS?Á) and
CUPRAC assays. Assay results showed that N0-(2,6-diphe-
nylpiperidin-4-ylidene)-4-bromobenzenesulfonohydrazide (11)
has the highest lipid peroxidation inhibitory activity. Within
the assay series, N0-(2,6-diphenylpiperidin-4-ylidene)-4-bro-
mobenzenesulfonohydrazide (11) exhibited better activity than
Graphical Abstract
Electronic supplementary material The online version of this
article (doi:10.1007/s00044-016-1592-0) contains supplementary
material, which is available to authorized users.
& Emine Elc¸in Oruc¸-Emre
oruc@gantep.edu.tr
1
Department of Chemistry, Faculty of Arts and Sciences,
Gaziantep University, Gaziantep, Turkey
2
˘
¨
Department of Herbal and Animal Production, Koycegiz
˘
˘
Vocational School, Mugla Sıtkı Koc¸man University, Mugla,
Turkey
3
4
Department of Physics, Faculty of Arts and Sciences,
Mustafa Kemal University, Hatay, Turkey
˘
Department of Chemistry, Faculty of Sciences, Mugla Sıtkı
˘
Koc¸man University, Mugla, Turkey
123

Med Chem Res
et al., 2007; Li et al., 2007; Pissarnitski et al., 2007; Gir-
isha et al., 2009; Prinz et al., 2013).
Keywords Piperidine Á Sulfonyl hydrazone Á Alzheimer’s Á
Antioxidant Á DFT calculations
Studies on the donepezil molecule and its applications
prompted us to design series of compounds consisting of
piperidine, sulfonyl and hydrazone groups. In addition to
these groups, halogen, methyl, trifluoromethyl, methoxy,
trifluoromethoxy and nitro-substituted phenyl groups were
used in order to determine the effects of the substituents on
activity. These types of molecules carrying piperidine ring
and hydrazone also have been shown to exhibit significant
antioxidant properties (Parthiban et al., 2011; Bala et al.,
2012). The proper use of antioxidants can reduce AD
progress, and accordingly, the neuronal degeneration can
be minimized. Thus, in this work the b-carotene–linoleic
acid for lipid peroxidation activity, DPPH free radical
scavenging, ABTS cation radical scavenging and cupric
reducing antioxidant capacity (CUPRAC) analysis of the
synthesized compounds were also screened in addition to
acetylcholinesterase (AChE) and butyrylcholinesterase
(BChE) inhibitory activities.
Introduction
Alzheimer disease (AD) has been known more than a
century, but there is still no medical treatment to retard or
stop this disease. In the ‘‘World Alzheimer Report 2013,’’
it is reported that over 35 million people worldwide suffer
from dementia including AD and this number is expected
to be 70 million in 2030 (Prince et al., 2013). Currently,
acetylcholinesterase inhibitors (AChEIs) such as donepezil
(Rao et al., 2007), rivastigmine (Jann and Pharm, 2000)
and galantamine (Michaelis, 2003) are used to decrease the
effects of the disease (Fig. 1) and beneficiary effects of
these drugs vary among patients. Therefore, new effective
anti-Alzheimer’s molecules are urgently needed.
The principal enzyme acetylcholinesterase (AChE)
hydrolyzes acetylcholine to choline and acetate at cholin-
ergic synapses. In the AD brain, the amount of acetyl-
choline is lower than the healthy brain as AChE is in
excess. One of the main approaches to treat AD is to
increase the concentration of acetylcholine. Accordingly,
developing AChE inhibitors can be potential strategy in
anti-Alzheimer’s drug research. It has been shown that not
only the inhibition of AChE but also the inhibition of
butyrylcholinesterase (BChE) is necessary to restore the
level of the acetylcholine and butyrylcholine to cure the
disease. In addition, amyloid beta (Ab) peptides, found in
the brain of the Alzheimer’s disease patients, are formed by
the cleavage of the amyloid precursor protein by c-secre-
tase. Thus, inhibiting c-secretase can be another approach
in AD treatment. AChE, BChE and c-secretase inhibitors
which are derivatives of piperidine ring, ester and sulfonyl
hydrazone groups were previously reported (Gundersen
et al., 2005; Viegas et al., 2005; Josien et al., 2007; Kwon
Theoretical studies on piperidine and sulfonyl hydra-
zone derivatives utilized B3LYP density functional method
with 6-31G(d) basis set (Vayner and Ball, 2000; Alver
et al., 2007; Parlak, 2010; Shalaby et al., 2014). In addi-
tion, GIAO/DFT (gauge-including atomic orbitals/density
functional theory) approach is mostly used for the calcu-
lations of chemical shifts for a variety of heterocyclic
compounds (Rauhut and Pulay, 1995). Studies related to
electronic structure of the title compounds have not been
previously reported and analyzed. In this study, investiga-
tion of molecular geometry optimization, 1H and 13C NMR
chemical shifts, molecular electrostatic potential surface,
frontier molecular orbital properties and dipole moment (l)
were determined with Gaussian 09 W software package
(Frisch et al., 2009).
Materials and methods
General
O
OH
H
H3CO
H3CO
All chemicals used in the synthesis of the compounds and
ethyl 4-oxo-piperidine-1-carboxylate were purchased from
Sigma-Aldrich (St. Louis, MO, USA). The reactions and
the purities of the compounds were monitored by thin-layer
chromatography (TLC) on silica gel 60 F254 aluminum
sheets purchased from Merck (Darmstadt, Germany).
Melting points were recorded by open capillaries on
EzMelt melting point apparatus and were uncorrected.
FTIR spectra were recorded on Perkin-Elmer Frontier
spectrometer by attenuated total reflectance (ATR) appa-
ratus (Waltham, Massachusetts, USA). C, H, N, S percent
of the compounds were detected by Thermo Scientific
O
H3CO
N
donepezil
N
galanthamine
O
N
N
O
rivastigmine
Fig. 1 Drugs as acetylcholinesterase inhibitors
123

Med Chem Res
(3H, t, J = 6.8 Hz, HG), 2.26 (2H, t, J = 5.6 Hz, HE), 2.41
(2H, t, J1 = 6.0 Hz, J2 = 6.8 Hz, HD), 4.05 (2H, q,
J = 6.8 Hz, HI), 8.01 (2H, d, J = 8.0 Hz, HC), 8.06 (2H, d,
J = 8.0 Hz, HB), 10.63 (1H, s, HA); 1H-NMR (CDCl3/
TMS, 400 MHz): d = 1.28 (3H, t, J1 = 6.8 Hz,
J2 = 7.2 Hz, HG), 2.37 (2H, t, J = 6.0 Hz, HE), 2.43 (2H,
t, J1 = 6.0 Hz, J2 = 6.4 Hz, HD), 3.57–3.60 (4H, m, HF),
4.16 (2H, q, J1 = 6.8 Hz, J2 = 7.2 Hz, HI), 7.69 (2H, d,
J = 6.8 Hz, HC), 7.83 (2H, d, J = 6.8 Hz, HB), 7.66 (1H,
s, HA); 13C-NMR (DMSO-d6/TMS, 100 MHz): d = 159.4
(C4), 155.0 (C7), 138.6 (C10), 132.6 (C12, C14), 130.0
(C11, C15), 127.2 (C13), 61.3 (C8), 43.6, 40.6 (C2, C6),
33.5, 28.1 (C3, C5), 15.0 (C9); MS m/z (%) 403.6 [M-H]–
(9.33); 221.2 (100); 219.2 (1.16); 201.2 (1.08); 173.2
(2.93); 156.8 (19.97); 155.4 (1.47); 99.4 (3.55); 81.4
(58.06); 79.4 (4.93); 64.2 (1.23); Anal. calcd. for C14H18
BrN3O4S: C, 41.59; H, 4.49; N, 10.39; S, 7.93 %. Found:
C, 41.60; H, 4.49; N, 10.18; S, 7.45 %.
Flash 2000 (Finnegan MAT, USA) elemental analyzer. By
direct injection in Ab-SciEx 3200 Q-Trap MSMS detector
with electrospray ionization probe (Framingham, MA,
USA), mass spectra were recorded. 1H-NMR and 13C-
NMR spectra were recorded on Bruker Avance -400 MHz
spectrometer (Billerica, MA, USA) by using DMSO-d6 or
CDCl3 as a solvent and TMS as an internal standard. The
peaks of the DMSO-d6 and CDCl3 were observed at 2.5
and 7.2 ppm, respectively. The water peaks of the solvents
were seen at 3.3 ppm with DMSO and 1.6 ppm with
chloroform. The activity tests were done by using Molec-
ular Devices Spectra Max PC340 microplate reader (Sun-
nyvale, CA, USA). The NMR spectra of the compounds
2–18 were given in the supporting information.
Synthesis of the compounds
Synthesis of 2,6-diphenylpiperidine-4-one
Ethyl 4-(2-(4-chlorophenylsulfonyl)hydrazono)piperidine-
1-carboxylate (3) White powder (the compound was
prepared by the reaction of 4-chlorophenylsulfonyl hydra-
zide with ethyl 4-oxo-piperidine-1-carboxylate. It was
obtained as white solid, yield 80 %); m.p. 160–162 °C; IR
Acetone, benzaldehyde and ammonium acetate in 1:2:1
ratio in ethanol were reacted at room temperature using
%30 L-proline as a catalyst according to the procedures
presented in Baliah (1983) and Hemalatha et al. (2008).
m
max 3113 (N–H), 3086, 3072 (aromatic C–H), 2989, 2972,
Synthesis of 4-substituted phenylsulfonyl hydrazides
2885, 2836 (aliphatic C–H), 1645 (C=O, C=N), 1345
1
(asym S=O), 1170 (sym S=O), 1112 (C–Cl) cm-1; H-
0.01 mol 4-substituted phenylsulfonyl chloride was added
into 0.04 mol hydrazine monohydrate in dichloromethane
dropwise, stirred at room temperature and monitored by
TLC after dichloromethane was distilled off and the crude
product was washed with water and hexane (Siemann
et al., 2002; Kummerle et al., 2012).
NMR (DMSO-d6/TMS, 400 MHz): d = 1.18 (3H, t,
J1 = 6.8 Hz, J2 = 7.2 Hz, HG), 2.25 (2H, t, J = 6.0 Hz,
HE), 2.39 (2H, t, J = 6.0 Hz, HD), 3.41–3.46 (4H, m, HF),
4.04 (2H, q, J1 = 6.8 Hz, J2 = 7.2 Hz, HI), 7.69 (2H, d,
J = 8.8 Hz, HC), 7.84 (2H, d, J = 8.4 Hz, HB), 10.45 (1H,
s, HA); 13C-NMR (DMSO-d6/TMS, 100 MHz): d = 159.4
(C4), 155.0 (C7), 138.4 (C10), 138.3 (C13), 129.9 (C11,
C15), 129.6 (C12, C14), 61.3 (C8), 43.6, 41.8 (C2, C6),
33.5, 28.1 (C3, C5), 15.0 (C9); MS m/z (%) 359.6 [M-H]-
(14.16); 177.2 (100); 113.4 (43.36); 111.4 (6.34); 64.4
(2.07); 37.4 (3.10); Anal. calcd. for C14H18ClN3O4S: C,
46.73; H, 5.04; N, 11.68; S, 8.91 %. Found: C, 47.11; H,
5.06; N, 11.51; S, 8.53 %.
Synthesis of 4-substituted phenyl sulfonyl hydrazones
(2218)
0.01 mol ketone, 0.01 mol 4-substituted phenylsulfonyl
hydrazide and 30 mL ethanol were heated inside a micro-
wave oven for 15 min at 400 W. After cooling to room
temperature, the crude products were obtained by filtration
and then dried. The crudes were purified by washing with
diethyl ether or petroleum ether (Siemann et al., 2002;
Kummerle et al., 2012).
Ethyl 4-(2-(4-fluorophenylsulfonyl)hydrazono)piperidine-
1-carboxylate (4) White powder (the compound was
prepared by the reaction of 4-fluorophenylsulfonyl hydra-
zide with ethyl 4-oxo-piperidine-1-carboxylate. It was
obtained as white solid, yield 87 %); m.p. 145–147 °C; IR
mmax 3187 (N–H), 3065, 3047 (aromatic C–H), 2976, 2326
(aliphatic C–H), 1658 (C=O, C=N), 1339 (asym S=O),
Ethyl 4-(2-(4-bromophenylsulfonyl)hydrazono)piperidine-
1-carboxylate (2) White powder (the compound was
prepared by the reaction of 4-bromophenylsulfonyl
hydrazide with ethyl 4-oxo-piperidine-1-carboxylate. It
was obtained as white solid, yield 85 %); m.p.
176–178 °C; IR mmax 3117 (N–H), 3090 (aromatic C–H),
2988, 2943, 2889, 2855 (aliphatic C–H), 1673 (C=O), 1643
(C=N), 1323 (asym S=O), 1171 (sym S=O), 1112 (C–Br)
1
1295 (C–F), 1156 (sym S=O) cm-1; H-NMR (DMSO-d6/
TMS, 400 MHz): d = 1.17 (3H, t, J1 = 6.8 Hz,
J2 = 7.2 Hz, HG), 2.25 (2H, t, J1 = 5.6 Hz, J2 = 6.0 Hz,
HE), 2.39 (2H, t, J = 6.0 Hz, HD), 3.41–3.47 (4H, m, HF),
4.04 (2H, q, J1 = 6.8 Hz, J2 = 7.2 Hz, HI), 7.42–7.47 (2H,
m, HC), 7.89–7.93 (2H, m, HB), 10,42 (1H, s, HA); 13C-
cm-1 1H-NMR (DMSO-d6/TMS, 400 MHz): d = 1.18
;
123

Med Chem Res
NMR (DMSO-d6/TMS, 100 MHz): d = 166.1, 163.6
(C13), 159.2 (C4), 155.0 (C7), 135.9, 135.9 (C10), 131.1,
130.9 (C11, C15), 116.8, 116.5 (C12, C14), 61.3 (C8),
43.7, 41.7 (C2, C6), 33.5, 28.1 (C3, C5), 15.0 (C9); MS m/z
(%) 341.7 [M-H]- (11.97); 159.6 (100); 139.4 (2.16);
111.4 (3.01); 95.4 (68.65); 79.4 (1.03); 75.4 (1.08); 64.4
(7.15); Anal. calcd. for C14H18FN3O4S: C, 48.97; H, 5.28;
N, 12.24; S, 9.34 %. Found: C, 48.55; H, 5.27; N, 12.09; S,
8.91 %.
Ethyl 4-(2-(4-methylphenylsulfonyl)hydrazono)piperidine-
1-carboxylate (7) (Imanishi et al., 1982) White powder
(the compound was prepared by the reaction of
4-methylphenylsulfonyl hydrazide with ethyl 4-oxo-piper-
idine-1-carboxylate. It was obtained as white solid, yield
76 %); m.p. 148–150 °C (lit 149–151 °C) (Imanishi et al.,
2006); IR mmax 3259 (N–H), 3051 (aromatic C–H), 2986,
2954, 2924, 2869 (aliphatic C–H), 1694 (C=O), 1641
(C=N), 1329 (asym S=O), 1168 (sym S=O) cm-1 1H-
;
NMR (DMSO-d6/TMS, 400 MHz): d = 1.18 (3H, t,
J1 = 6.8 Hz, J2 = 7.2 Hz, HG), 2.24 (2H, t, J = 6.0 Hz,
HE), 2.37–2.40 (5H, m, HD, J), 3.42–3.46 (4H, m, HF), 4.04
(2H, q, J = 7.2 Hz, HI), 7.39 (2H, d, J = 8.0 Hz, HC), 7.73
(2H, d, J = 8.4 Hz, HB), 10.28 (1H, s, HA); 13C-NMR
(DMSO-d6/TMS, 100 MHz): d = 158.5 (C4), 155.0 (C7),
143.6 (C10), 136.8 (C13), 129.8 (C11, C15), 128.0 (C12,
C14), 61.3 (C8), 43.7, 40.6 (C2, C6), 33.5, 28.0 (C3, C5),
21.5 (C16), 15.0 (C9); MS m/z (%) 337.7 [M-H]- (7.78);
155.41 (100); 107.6 (5.26); 91.4 (12.82); 64.4 (43.36);
Anal. calcd. for C15H21N3O4S: C, 53.08; H, 6.24; N, 12.38;
S, 9.45 %. Found: C, 53.41; H, 6.27; N, 12.04; S, 9.32 %.
Ethyl 4-(2-(4-methoxyphenylsulfonyl)hydrazono)piperidine-1-
carboxylate (5) White powder (the compound was prepared
by the reaction of 4-methoxyphenylsulfonyl hydrazide with
ethyl 4-oxo-piperidine-1-carboxylate. It was obtained as
white solid, yield 57 %); m.p. 132–134 °C; IR mmax 3121
(N–H), 3098 (aromatic C–H), 2969, 2935, 2883, 2842 (ali-
phatic C–H), 1669 (C=O), 1643 (C=N), 1336 (asym S=O),
1162 (sym S=O) cm-1
;
1H-NMR (DMSO-d6/TMS,
400 MHz): d = 1.18 (3H, t, J1 = 6.8 Hz, J2 = 7.2 Hz, HG),
2.24 (2H, t, J = 6.0 Hz, HE), 2.38 (2H, t, J1 = 5.6 Hz,
J2 = 6.4 Hz, HD), 3.41–3.46 (4H, m, HF), 3.84 (3H, s, HJ),
4.04 (2H, q, J = 7.2 Hz, HI), 7.11 (2H, d, J = 9.2 Hz,
HC), 7.77 (2H, d, J = 9.2 Hz, HB), 10.21 (1H, s, HA);
13C-NMR (DMSO-d6/TMS, 100 MHz): d = 162.2 (C4,
C13), 155.1 (C7), 130.0 (C10, C11, C15), 113.9 (C12,
C14), 61.3 (C8), 55.8 (C16), 44.0, 42.2, 40.6 (C2, C6),
34.1, 28.5 (C3, C5), 15.1 (C9); MS m/z (%) 353.7 [M-
H]- (19.69); 171.4 (100); 108.4 (5.97); 107.4 (22.57);
92.4 (4.2); 64.4 (31.42); Anal. calcd. for C15H21N3O5S: C,
50.69; H, 5.96; N, 11.82; S, 9.02 %. Found: C, 50.17; H,
5.86; N, 11.46; S, 8.41 %.
Ethyl 4-(2-(4-trifluoromethylphenylsulfonyl)hydrazono)-
piperidine-1-carboxylate (8) Pale yellow powder (the
compound was prepared by the reaction of 4-trifluo-
romethylphenylsulfonyl hydrazide with ethyl 4-oxo-piper-
idine-1-carboxylate. It was obtained as pale yellow solid,
yield 50 %); m.p. 121–123 °C; IR mmax 3155 (N–H), 2983
(aromatic C–H), 2930, 2867 (aliphatic C–H), 1669 (C=O),
1651 (C=N), 1320 (asym S=O), 1164 (sym S=O) cm-1
;
1H-NMR (DMSO-d6/TMS, 400 MHz): d = 1.18 (3H, t,
J = 7.2 Hz, HG), 2.25 (2H, t, J1 = 5. 6 Hz, J2 = 6.4 Hz,
HE), 2.39 (2H, t, J = 6.0 Hz, HD), 3.41–3.46 (4H, m, HF),
4.04 (2H, q, J1 = 6.8 Hz, J2 = 7.2 Hz, HI), 7.77 (2H, d,
J = 8.8 Hz, HC), 7.83 (2H, d, J = 8.8 Hz, HB), 10.46 (1H,
s, HA); 13C-NMR (DMSO-d6/TMS, 100 MHz): d = 163.0
(C4), 155.0 (C7), 129.0 (C13), 126.8 (C10, C16), 125.4,
125.3 (C12, C14), 123.2 (C11, C15), 46.6, 40.6 (C2, C6),
15.0 (C9); MS m/z (%) 391.8 [M-H]- (15.00); 209.4 (100);
189.4 (5.47); 161.4 (32.85); 145.4 (93.29); 141.4 (1.00);
121.4 (1.54); 85.4 (1.16); 64.4 (1.54); Anal. calcd. for
C15H18F3N3O4S: C, 45.80; H, 4.61; N, 10.68; S, 8.15 %.
Found: C, 45.02; H, 4.69; N, 10.34; S, 7.86 %.
Ethyl 4-(2-(4-trifluoromethoxyphenylsulfonyl)hydrazono)-
piperidine-1-carboxylate (6) White powder (the com-
pound was prepared by the reaction of 4-trifluo-
romethoxyphenylsulfonyl hydrazide with ethyl 4-oxo-
piperidine-1-carboxylate. It was obtained as white solid,
yield 75 %); m.p. 107–109 °C; IR mmax 3239 (N–H), 3104
(aromatic C–H), 2986, 2965, 2878 (aliphatic C–H), 1698
(C=O), 1650 (C=N), 1344 (asym S=O), 1163 (sym S=O)
cm-1 1H-NMR (DMSO-d6/TMS, 400 MHz): d = 1.16
;
(3H, t, J1 = 6.6 Hz, J2 = 7.2 Hz, HE), 2.24 (2H, t,
J = 6.0 Hz, HE), 2.38 (2H, t, J = 6.0 Hz, HD), 3.41–3.44
(4H, m, HF), 4.02 (2H, q, J1 = 6.6 Hz, J2 = 7.2 Hz, HI),
7.58 (2H, d, J = 8.4 Hz, HC), 7.95 (2H, d, J = 8.4 Hz,
HB), 10.46 (1H, s, HA); 13C-NMR (DMSO-d6/TMS,
100 MHz): d = 159.7 (C4), 155.0 (C7), 151.6 (C13), 138.4
(C10), 130.6 (C11, C15), 128.1 (C12, C14), 120.7 (C16),
61.4 (C8), 43.6, 41.7 (C2, C6), 33.5, 28.1 (C3, C5), 15.0
(C9); MS m/z (%) 407.8 [M-H]- (12.06) 225.6 (73.35);
205.4 (1.63); 177.4 (2.05); 161.4 (24.92); 85.6 (100); 64.4
(1.20); Anal. calcd. for C14H18BrN3O4S: C, 44.01; H, 4.43;
N, 10.26; S, 7.83 %. Found: C, 43.68; H, 4.88; N, 10.06; S,
7.63 %.
Ethyl 4-(2-(4-nitrophenylsulfonyl)hydrazono)piperidine-1-
carboxylate (9) Pale yellow powder (the compound was
prepared by the reaction of 4-nitrophenylsulfonyl hydra-
zide with ethyl 4-oxo-piperidine-1-carboxylate. It was
obtained as pale yellow solid, yield 97 %); m.p.
117–119 °C; IR mmax 3117 (N–H), 3106, 3042 (aromatic
C–H), 2985, 2910, 2874, 2834 (aliphatic C–H), 1652
(C=O, C=N), 1540, 1352 (NO2), 1338 (asym S=O), 1162
1
(sym S=O) cm-1; H-NMR (DMSO-d6/TMS, 400 MHz):
d = 1.17 (3H, t, J1 = 6.8 Hz, J2 = 7.2 Hz, HG), 2.25 (2H,
123

Med Chem Res
t, J1 = 5.6 Hz, J2 = 6.0 Hz, HE), 2.41 (2H, t, J = 6.0 Hz,
HD), 3.41–3.47 (4H, m, HF), 4.03 (2H, q, J1 = 6.8 Hz,
J2 = 7.2 Hz, HI), 8.10 (2H, d, HB), 8.42 (2H, d, HC), 10.74
(1H, s, HA); 13C-NMR (DMSO-d6/TMS, 100 MHz):
d = 160.2 (C4), 155.0 (C7), 150.3 (C13), 144.8 (C10),
129.6 (C12, C14), 124.8 (C11, C15), 61.3 (C8), 43.6, 41.8
(C2, C6), 33.5, 28.2 (C3, C5), 15.0 (C9); MS m/z (%) 370.9
[M ? H]? (25.00); 293.6 (100); 274.8 (5.00); 215.4 (7.5);
185.2 (7.5); 173.2 (5.00); 149.0 (6.25); 131.2 (6.25); 127.2
(5.0); 125.2 (5.00); 121.0 (5.00); 119.2 (6.25); 113.4 (15.0);
111.2 (7.5); 98.4 (11.25); 97.4 (8.75); 85.2 (7.5); 72.4
(61.25); 71.2 (11.25); 57.4 (27.5); 56.6 (10.00); Anal.
calcd. for C14H18N4O6S: C, 45.40; H, 4.90; N, 15.13; S,
8.66 %. Found: C, 44.87; H, 5.04; N, 14.99; S, 8.27 %.
d, J = 8.8 Hz, HC), 7.84 (2H, d, J = 8.8 Hz, HB), 10.46
(1H, s, HA); 13C-NMR (DMSO-d6/TMS, 100 MHz):
d = 160.2 (C4), 144.3 (C7, C70), 138.9 (C13), 132.6 (C15,
C17), 130.0 (C14, C18), 127.2 (C16), 128.7, 127.7, 127.6,
127.1, 127.1 (C8, C9, C10, C11, C12), 61.3, 60.0 (C2, C6),
?
43.2, 36.9 (C3, C5); MS m/z (%) 486.9 [M ? H] (6.74);
343.2 (10.11); 277.4 (6.74); 265.4 (33.71); 251.4 (8.99);
250.6 (5.62); 249.0 (7.86); 205.4 (14.61); 199.4 (16.85);
187.4 (87.64); 173.4 (39.33); 171.4 (15.73); 157.4 (37.08);
145.4 (26.97); 127.4 (100); 113.4 (67.42); 97.4 (60.67);
77.4 (3.37); Anal. calcd. for C23H22BrN3O2S: C, 57.03; H,
4.58; N, 8.67; S, 6.62 %. Found: C, 56.18; H, 4.37; N, 8.31;
S, 6.06 %.
N0-(2,6-diphenylpiperidin-4-ylidene)-4-chlorobenzenesulfono-
hydrazide (12) White powder (the compound was pre-
pared by the reaction of 4-chlorophenylsulfonyl hydrazide
with 2,6-diarylpiperidine-4-one. It was obtained as white
solid, yield 73 %); m.p. 158–160 °C; IR mmax 3320 (sec-
onder amine N–H), 3216 (sulfonyl hydrazone N–H), 3085,
3024 (aromatic C–H), 2974, 2918, 2836, 2792 (aliphatic
C–H), 1645 (C=N), 1347 (asym S=O), 1165 (sym S=O),
1112 (C–Cl) cm-1; 1H-NMR (DMSO-d6/TMS, 400 MHz):
d = 1.96 (1H, t, J1 = 12 Hz, J2 = 13.6 Hz, HE),
2.24–2.36 (2H, m, HD’, E’), 2.81 (1H, s, HG), 3.03 (1H, d,
J = 13.6 Hz, HD), 3.78 (2H, t, J = 12.8 Hz, HF),
7.23–7.28 (2H, m, HK, K’), 7.30–7.38 (4H, m, HI,I’), 7.46
(2H, d, J = 7.6 Hz, HJ’), 7.51 (2H, d, J = 7.6 Hz, HJ),
7.79 (2H, d, J = 8.0 Hz, HC), 7.88 (2H, d, J = 8.4 Hz,
HB), 10.50 (1H, s, HA); 13C-NMR (DMSO-d6/TMS,
100 MHz): d = 160.2 (C4), 144.3, 144.2 (C7, C70), 138.4
(C13), 138.2 (C16), 129.9 (C14, C18), 129.7 (C15, C17),
128.7, 127.7, 127.6, 127.1, 127.1 (C8, C9, C10, C11, C12),
61.3, 60.0 (C2, C6), 43.2, 36.9 (C3, C5); MS m/z (%) 439.6
[M-H]- (8.00); 177.4 (100); 175.4 (10.60); 157.2 (2.60);
155.0 (1.00); 129.4 (4.20); 113.4 (46.00); 112.0 (3.00);
111.4 (13.6); 64.2 (2.6); 37.4 (1.80); Anal. calcd. for C23
H22ClN3O2S: C, 62.79; H, 5.04; N, 9.55; S, 7.29 %. Found:
C, 62.59; H, 5.00; N, 9.67; S, 6.98 %.
N’-(2,6-diphenylpiperidin-4-ylidene)benzenesulfonohydrazide
(10) White powder (the compound was prepared by the
reaction of phenylsulfonyl hydrazide with 2,6-di-
arylpiperidine-4-one. It was obtained as white solid, yield
52 %); m.p. 160–162 °C; IR mmax 3290 (seconder amine N–
H), 3194 (sulfonyl hydrazone N–H), 3086, 3060 (aromatic
C-H), 2969, 2910, 2805, 2791 (aliphatic C–H), 1651 (C=N),
1340 (asym S=O), 1154 (sym S=O) cm-1; 1H-NMR (DMSO-
d6/TMS, 400 MHz): d = 1.95 (1H, t, J1 = 12.0 Hz,
J2 = 14.0 Hz, HE), 2.23–2.35 (2H, m, HD’, E’), 2.76 (1H, s,
HG), 3.05 (1H, d, J = 13.6 Hz, HD), 3.77 (2H, t,
J1 = 11.6 Hz, J2 = 12.0 Hz, HF), 7.23–7.28 (2H, m, HK, K’),
7.30–7.38 (4H, m, HI,I’), 7.45 (2H, d, HJ’), 7.50 (2H, d, HC),
7.59–7.69 (2H, m, HJ), 7.87 (2H, d, HB), 10.39 (1H, s, HA);
13C-NMR (DMSO-d6/TMS, 100 MHz): d = 159.6 (C4),
144.4, 144.2 (C7, C70), 139.7 (C13), 133.3 (C16), 129.5 (C14,
C18), 127.9(C15, C17),128.7,127.7,127.6,127.1,127.1(C8,
C9, C10, C11, C12), 61.3, 60.0 (C2, C6), 43.3, 36.9 (C3, C5);
MS m/z (%) 405.9 [M ? H]? (12.51); 301.6 (9.78); 249.8
(7.69); 247.6 (7.58); 194.8 (20.5); 160.6 (8.93); 159.6 (11.84);
144.6 (4.74); 128.6 (5.19); 115.6 (8.18); 106.8 (100); 103.6
(5.94); 91.6 (8.81); 83.6 (7.46); 79.8 (33.64); 77.6 (13.07);
65.6 (2.39); Anal. calcd. for C23H23N3O2S: C, 68.12; H, 5.72;
N, 10.36; S, 7.91 %. Found: C, 67.23; H, 5.33; N, 9.83; S,
7.63 %.
N0-(2,6-diphenylpiperidin-4-ylidene)-4-fluorobenzenesulfono-
hydrazide (13) Pale yellow powder (the compound was
prepared by the reaction of 4-fluorophenylsulfonyl hydra-
zide with 2,6-diarylpiperidine-4-one. It was obtained as
pale yellow solid, yield 63 %); m.p. 160–161 °C; IR mmax
3212 (seconder amine N–H), 3103 (sulfonyl hydrazone N–
H), 3073, 3044 (aromatic C–H), 2974, 2919, 2835, 2804
(aliphatic C–H), 1647 (C=N), 1333 (asym S=O), 1293
(aromatic C–F), 1154 (sym S=O) cm-1; 1H-NMR (DMSO-
d6/TMS, 400 MHz): d = 1.96 (1H, t, J1 = 12.4 Hz,
J2 = 13.6 Hz, HE), 2.24–2.36 (2H, m, HD’, E’), 2.76 (1H, s,
HG), 3.03 (1H, d, J = 13.6 Hz, HD), 3.77 (2H, t,
J1 = 12.4 Hz, J2 = 13.6 Hz, HF), 7.19–7.38 (6H, m,
N0-(2,6-diphenylpiperidin-4-ylidene)-4-bromobenzenesulfono-
hydrazide (11) White powder (the compound was pre-
pared by the reaction of 4-bromophenylsulfonyl hydrazide
with 2,6-diarylpiperidine-4-one. It was obtained as white
solid, yield 74 %); m.p. 162–164 °C; IR mmax 3231 (sul-
fonyl hydrazone N–H), 3084, 3058 (aromatic C–H), 2841,
2822, 2804 (aliphatic C–H), 1321 (asym S=O), 1179 (sym
S=O), 1106 (C–Br) cm-1 1H-NMR (DMSO-d6/TMS,
;
400 MHz): d = 1.97 (1H, t, J1 = 12 Hz, J2 = 13.6 Hz,
HE), 2.24–2.36 (2H, m, HD’, E’), 2.81 (1H, s, HG), 3.03 (1H,
d, J = 13.6 Hz, HD), 3.75–3.82 (2H, m, HF), 7.23–7.28
(2H, m, HK, K’), 7.30–7.38 (4H, m, HI,I’), 7.46 (2H, d,
J = 7.2 Hz, HJ’), 7.51 (2H, d, J = 7.2 Hz, HJ), 7.80 (2H,
H
I,I’,K,K’), 7.44–7.47 (4H, m, HC, J’), 7.50 (2H, d,
123

Med Chem Res
J = 7.2 Hz, HJ), 7.92–7.95 (2H, m, HB), 10.44 (1H, s, HA);
13C-NMR (DMSO-d6/TMS, 100 MHz): d = 166.1, 163.6
(C16), 160.1 (C4), 144.3, 144.2 (C7, C70), 135.9, 135.9
(C13), 131.1, 131.0 (C14, C18), 116.8, 116.6 (C15, C17),
128.7, 127.7, 127.6, 127.1, 127.1 (C8, C9, C10, C11, C12),
61.3, 60.0 (C2, C6), 43.2, 36.9 (C3, C5); MS m/z (%) 423.9
[M ? H]? (9.97); 319.6 (5.72); 249.8 (5.81); 247.6 (7.60);
194.6 (11.31); 160.6 (5.14); 159.6 (6.66); 115.6 (7.29);
106.6 (100); 103.6 (6.21); 91.8 (7.02); 83.6 (5.28); 79.8
(37.06); 77.6 (7.73); 65.6 (1.70); 53.6 (1.30); Anal. calcd.
for C23H22FN3O2S: C, 65.23; H, 5.24; N, 9.92; S, 7.57 %.
Found: C, 64.93; H, 5.21; N, 9.99; S, 6.98 %.
J = 8.4 Hz, HC), 7.99–8.02 (2H, m, HB), 10.56 (1H, s, HA);
13C-NMR (DMSO-d6/TMS, 100 MHz): d = 160.3 (C4),
151.6 (C16), 144.1 (C7, C70), 138.5 (C13), 130.6 (C14, C18),
128.7, 127.7, 127.6, 127.1, 127.1 (C8, C9, C10, C11, C12,
C19), 121.7 (C15, C17), 61.3, 60.0 (C2, C6), 40.6, 39.4 (C3,
C5); MS m/z (%) 487.7 [M-H]- (9.23); 225.4 (84.93); 205.4
(1.58); 177.4 (2.07); 161.4 (24.66); 85.04 (100); Anal. calcd.
for C14H18BrN3O4S: C, 58.89; H, 4.53; N, 8.58; S 6.55 %.
Found: C, 58.93; H, 4.78; N, 8.54; S, 6.96 %.
N0-(2,6-diphenylpiperidin-4-ylidene)-4-methylbenzenesulfono-
hydrazide (16) White powder (the compound was pre-
pared by the reaction of 4-methylphenylsulfonyl hydrazide
with 2,6-diarylpiperidine-4-one. It was obtained as white
solid, yield 67 %); m.p. 145–147 °C; IR mmax 3318 (sec-
onder amine N–H), 3215 (sulfonyl hydrazone N–H), 3063,
3031 (aromatic C–H), 2973, 2957, 2836, 2816 (aliphatic
C–H), 1644 (C=N), 1334 (asym S=O), 1155 (sym S=O)
N0-(2,6-diphenylpiperidin-4-ylidene)-4-methoxybenzenesulfono-
hydrazide (14) White powder (the compound was prepared
by the reaction of 4-methoxyphenylsulfonyl hydrazide with
2,6-diarylpiperidine-4-one. It was obtained as white solid,
yield 54 %); m.p. 146–148 °C; IR mmax 3317 (seconder amine
N–H), 3215 (sulfonyl hydrazone N–H), 3065, 3024 (aromatic
C–H), 2971, 2843 (aliphatic C–H), 1641 (C=N), 1343 (asym
cm-1
(1H, t, J1 = 12 Hz, J2 = 13.6 Hz, HE), 2.24–2.32 (2H, m,
D’, E’), 2.39 (3H, s, HL), 3.05 (1H, d, J = 13.6 Hz, HD),
;
1H-NMR (DMSO-d6/TMS, 400 MHz): d = 1.95
1
S=O), 1157 (sym S=O) cm-1; H-NMR (DMSO-d6/TMS,
H
400 MHz): d = 1.96 (1H, t, J1 = 12.4 Hz, J2 = 13.2 Hz,
HE), 2.28–2.32 (2H, m, HD’, E’), 2.83 (1H, s, HG), 3.03 (1H, d,
J = 13.2 Hz, HD), 3.75–3.80 (2H, m, HF, F’), 3.84 (3H, s,
HL), 7.13 (2H, d, J = 8.8 Hz, HC), 7.24–7.39 (6H, m,
3.75–3.82 (2H, m, HF), 7.23–7.39 (6H, m, HI, I’, K, K’), 7.41
(2H, d, J = 8.0 Hz, HC), 7.46 (2H, d, J = 7.2 Hz, HJ’),
7.51 (2H, d, J = 7.2 Hz, HJ), 7.76 (2H, d, J = 8.0 Hz,
HB), 10.37 (1H, s, HA); 13C-NMR (DMSO-d6/TMS,
100 MHz): d = 159.2 (C4), 144.1, 144.0 (C7, C70), 143.6
(C13), 136.8 (C16), 129.9 (C14, C18), 128.0 (C15, C17),
128.7, 127.7, 127.7, 127.2, 127.1 (C8, C9, C10, C11, C12),
61.3, 60.0 (C2, C6), 43.1, 36.7 (C3, C5), 21.5 (C19); MS
m/z (%) 419.9 [M ? H]? (12.27); 315.6 (8.94); 249.6
(5.61); 247.6 (5.76); 194.6 (45.61); 167.6 (5.91); 160.6
(13.18); 159.6 (19.09); 155.4 (1.36); 142.6 (5.30); 128.6
(5.00); 116.6 (8.49); 116.6 (9.55); 106.6 (100); 91.6
(17.58); 83.6 (11.82); 79.6 (36.67); 77.6 (11.50); 65.6
(8.33); Anal. calcd. for C24H25N3O2S: C, 68.71; H, 6.01;
N, 10.02; S, 7.64 %. Found: C, 67.76; H, 6.01; N, 9.99; S,
7.24 %.
HI,I’,K,K’), 7.46 (2H, d, J = 7.2 Hz, HJ’), 7.51 (2H, d,
J = 7.6 Hz, HJ), 7.80 (2H, d, J = 8.8 Hz, HB), 10.30 (1H, s,
HA); 13C-NMR (DMSO-d6/TMS, 100 MHz): d = 162.9
(C16), 159.0 (C4), 144.1 (C7, C70), 131.31, 130.3, 130.1
(C13, C14, C18), 128.7, 127.7, 127.7, 127.5, 127.2 (C8, C9,
C10, C11, C12), 114.6 (C15, C17), 61.3, 60.0 (C2, C6), 56.1
(C19), 43.1, 36.6 (C3, C5); MS m/z (%) 436 [M ? H]?
(11.64); 331.6 (7.86); 247.6 (5.17); 194.6 (55.42); 171.4
(12.54); 167.6 (8.56); 160.6 (7.16); 159.6 (19.10); 152.4
(5.27); 128.4 (5.08); 123.4 (6.37); 116.6 (9.06); 115.6 (10.35);
106.6 (100); 103.6 (5.97); 92.6 (6.17); 91.6 (13.13); 83.6
(9.06); 79.6 (37.71); 77.6 (15.82); 64.4 (1.59); Anal. calcd. for
C14H18BrN3O4S: C, 66.18; H, 5.79; N, 9.65; S, 7.36 %.
Found: C, 65.63; H, 5.76; N, 9.59; S, 7.65 %.
N0-(2,6-diphenylpiperidin-4-ylidene)-4-trifluoromethylben-
zenesulfonohydrazide (17) White powder (the compound
was prepared by the reaction of 4-trifluoromethylphenyl-
sulfonyl hydrazide with 2,6-diarylpiperidine-4-one. It was
obtained as white solid, yield 64 %); m.p. 137–138 °C; IR
mmax 3316 (seconder amine N–H), 3220 (sulfonyl hydra-
zone N–H), 3063, 3031 (aromatic C–H), 2968, 2899, 2813
(aliphatic C–H), 1640 (C=N), 1323 (asym S=O), 1160
N0-(2,6-diphenylpiperidin-4-ylidene)-4-trifluoromethoxyben-
zenesulfonohydrazide (15) White powder (the compound
was prepared by the reaction of 4-trifluoromethoxyphenyl-
sulfonyl hydrazide with 2,6-diarylpiperidine-4-one. It was
obtained as white solid, yield 50 %); m.p. 108–110 °C; IR
m
max 3317 (seconder amine N–H), 3210 (sulfonyl hydrazone
1
N–H), 3063, 3030 (aromatic C–H), 2969, 2899, 2834, 2814
(sym S=O) cm-1; H-NMR (DMSO-d6/TMS, 400 MHz):
(aliphatic C–H), 1636 (C=N), 1332 (asym S=O), 1156 (sym
S=O) cm-1
d = 1.98 (1H, t, J = 12.8 Hz, HE), 2.25–2.36 (2H, m,
HD’, E’), 2.84 (1H, s, HG), 3.03 (1H, d, J = 13.2 Hz, HD),
;
1H-NMR (DMSO-d6/TMS, 400 MHz):
d = 1.97 (1H, t, J = 12.8 Hz, HE), 2.25–2.37 (2H, m,
D’,E’), 2.82 (1H, s, HG), 3.03 (1H, d, J = 13.2 Hz, HD), 3.79
3.79 (2H, t, J1 = 9.6 Hz, J2 = 11.2 Hz, HF, F’), 7.23–7.39
(6H, m, H I, I’, K, K’), 7.45 (2H, d, J = 7.2 Hz, HJ’), 7.51
(2H, d, J = 7.2 Hz, HJ), 8.02 (2H, d, J = 8.4 Hz, HC),
8.09 (2H, d, J = 8.4 Hz, HB), 10.7 (1H, s, HA); 13C-NMR
H
(2H, t, HF,F’), 7.23–7.39 (6H, m, HI,I’,K,K’), 7.45 (2H, d,
J = 7.2 Hz, HJ’), 7.51 (2H, d, J = 7.2 Hz, HJ), 7.62 (2H, d,
123

Med Chem Res
(DMSO-d6/TMS, 100 MHz): d = 160.6 (C4), 144.1, 143.4
(C7, C70), 129.0 (C16), 128.7, 127.7, 127.6, 127.2, 127.1
(C8, C9, C10, C11, C12, C19), 126.8 (C13), 125.3 (C15,
C17), 122.6 (C14, C18), 61.2, 60.0 (C2, C6), 43.1, 36.9
(C3, C5); MS m/z (%) 473.9 [M ? H]? (6.76); 249.8
(7.41); 247.6 (7.53); 194.6 (6.61); 160.6 (3.95); 159.6
(5.18); 144.6 (5.13); 115.6 (6.88); 106.6 (100); 103.6
(5.03); 91.6 (6.73); 79.6 (31.38); 77.6 (6.61); Anal. calcd.
for C24H22FN3O2S: C, 60.88; H, 4.68; N, 8.87; S, 6.77 %.
Found: C, 60.37; H, 4.71; N, 8.70; S, 6.43 %.
DPPH free radical scavenging assay
The free radical scavenging activity was determined
¨
spectrophotometrically by the DPPH assay (Oztu¨rk et al.,
2007; Blois, 1958). Solutions of synthesized compounds
were prepared at concentrations of 400, 200, 100, 50, 25,
12.5 and 6.25 lM. DMSO was used as a control, while
BHT and a-tocopherol were used as reference standards.
The results were given as 50 % concentration (IC50).
ABTS cation radical scavenging assay
N0-(2,6-diphenylpiperidin-4-ylidene)-4-nitrobenzenesulfono-
hydrazide (18) White powder (the compound was prepared
by the reaction of 4-nitrophenylsulfonyl hydrazide with 2,6-
diarylpiperidine-4-one. It was obtained as white solid, yield
61 %); m.p. 172–173 °C; IR mmax 3322 (seconder amine N–
H), 3223 (sulfonyl hydrazone N–H), 3108, 3085, 3028
(aromatic C–H), 2986, 2960, 2818 (aliphatic C–H), 1637
(C=N), 1530, 1348 (NO2), 1341 (asym S=O), 1161 (sym
The spectrophotometric analysis of ABTS?Á scavenging
activity was determined according to the previously
described method (Re et al., 1999) with slight modifica-
¨
tions (Oztu¨rk et al., 2007). Solutions of synthesized com-
pounds were prepared at concentrations of 400, 200, 100,
50, 25, 12.5 and 6.25 lM. The ABTS?Á was produced by
the reaction between 7 mM ABTS in water and 2.45 mM
potassium persulfate, stored in the dark at room tempera-
ture for 12 h. Before usage, the ABTS?Á solution was
diluted to get an absorbance of 0.703, 0.025 at 734 nm with
DMSO. DMSO was used as a control, while BHT and a-
tocopherol were used as reference standards. The results
were given as 50 % inhibition concentration (IC50). The
sample concentration providing 50 % ABTS?Á scavenging
effect (IC50) was calculated from the graph of ABTS?Á
scavenging effect percentage against sample concentration.
S=O) cm-1
;
1H-NMR (DMSO-d6/TMS, 400 MHz):
d = 1.99 (1H, t, J1 = 12 Hz, J2 = 13.6 Hz, HE), 2.26–2.39
(2H, m, HD’,E’), 3.07 (1H, d, J = 13.6 Hz, HD), 3.79 (2H, t,
J1 = 13.6 Hz, J2 = 12.0 Hz, HF), 7.23–7.39 (6H, m,
H
I, I’, K’ K’), 7.45 (2H, d, J = 7.6 Hz, HJ’), 7.51 (2H, d,
J = 7.6 Hz, HJ), 8.13 (2H, d, J = 8.8 Hz, HB), 8.43 (2H, d,
J = 8.8 Hz, HC), 9.42 (1H, s, HA); 13C-NMR (DMSO-d6/
TMS, 100 MHz): d = 160.5 (C4), 150.3 (C16), 145.0 (C13),
144.0 (C7, C70), 129.6 (C15, C17), 128.8, 127.7, 127.7,
127.2, 127.1 (C8, C9, C10, C11, C12), 124.8 (C14, C18),
61.3, 60.0 (C2, C6), 43.1, 36.8 (C3, C5); MS m/z (%) 450.9
[M ? H]? (8.35); 295.8 (6.94); 249.8 (6.50); 247.6 (10.57);
144.6 (5.67); 128.6 (5.05); 115.6 (6.35); 106.6 (100); 91.6
(6.06); 79.8 (29.34); 77.6 (7.15); 65.4 (1.16); Anal. calcd. for
C23H22N4O4S: C, 61.32; H, 4.92; N, 12.44; S, 7.12 %.
Found: C, 60.83; H, 4.63; N, 12.01; S, 6.81 %.
Cupric reducing antioxidant capacity (CUPRAC)
The cupric reducing antioxidant capacity was determined
according to the previous method (Apak et al., 2004;
¨
Oztu¨rk et al., 2007). Solutions of synthesized compounds
were prepared at concentrations of 400, 200, 100, 50, 25,
12.5 and 6.25 lM. Results were given as absorbance
compared with the absorbances of BHT and a-tocopherol
used as antioxidant standards.
Biological studies
b-Carotene–linoleic acid assay
Determination of acetylcholinesterase (AChE)
The total antioxidant activity was evaluated using the b-
carotene–linoleic acid model test system (Marco, 1968;
and butyrylcholinesterase (BChE) inhibitory activity
¨
Oztu¨rk et al., 2011). Solutions of synthesized compounds
AChE and BChE inhibitory activities were measured by the
spectrophotometric method. AChE from electric eel and
BChE from horse serum were used, while acetylthiocholine
iodide and butyrylthiocholine chloride were employed as
substrates. DTNB (5,50-dithiobis(2-nitrobenzoic)acid was
used for the measurement of the anticholinesterase activity
(Ellman et al., 1961; Tel et al., 2013).
were prepared at concentrations of 400, 200, 100, 50, 25,
12.5 and 6.25 lM. DMSO was used as a control, while
BHT and a-tocopherol were used as reference standards.
The results were given as 50 % concentration (IC50). IC50
was determined from the graph of antioxidant activity
percentage against sample concentration.
123

Med Chem Res
ZA is the charge of nucleus A, located RA, and q(r0) is the
electronic density function for the molecule (Truhlar, 1981;
Politzer et al., 1985). In the map of total electron density,
surface with the electrostatic potential is defined by the neg-
ative and positive charge contribution. Different values of the
electrostatic potential are demonstrated the range values of
different color scales to figure out the negative (red) and the
positive (blue) potential region. Potential increase red\ or-
ange\ yellow\ green \ cyan\ blue, respectively. Hence,
while blue is showing the positive region, red side shows
negative region of the surface and green appears over zero. To
observe electrophilic or nucleophilic region of the molecule,
map of molecular electrostatic potential for the ground state
geometry has been obtained at cam-b3lyp/6-31G(d) level.
Calculations
The geometry optimization of the compounds (1–18) was
carried out by using DFT/cam-B3LYP/6-31G(d)(6D, 7F)
level; in addition, ultrafine and tight convergence criteria
(Lee et al., 1988; Becke, 1993) were performed. Calcula-
tion of chemical shift was performed gauge-independent
atomic orbital (GIAO) method, one of the most common
approaches for calculating nuclear magnetic shielding
tensor (Ditchfield, 1974). These calculations have been
carried out by using b3lyp/6-311??G (2d, 2p) level in the
DMSO solvent. Selected descriptors such as ionization
potential (I = -EHOMO), electron affinity (A = -ELUMO),
global
hardness
(g = I - A/2),
electronegativity
(v = I ? A/2) chemical potential (l = -v), softness
(S = 1/g) and global electrophilicity index (x = l2/2g)
were calculated with DFT/cam-b3lyp/6–31g(d) level from
HOMO and LUMO energies (Koopmans, 1934). In order
to understand and predict the reactive characteristic of
numerous of chemical systems, the map of molecular
electrostatic potential (MEP) surface was also visualized
reactive sites of the molecules in both electrophilic and
nucleophilic reactions (Truhlar, 1981). Molecular electro-
static potential V(r) is defined by;
Results and discussion
Chemistry
In this study, we synthesized seventeen sulfonyl hydra-
zones bearing piperidine ring and evaluated their anti-
cholinesterase and antioxidant activities. The general
schematic representation describing the synthesis of target
compounds is shown in Fig. 2. Previously, 2,6-diaryl
piperidine 4-one was shown to be obtained with 20 % yield
Z
X
ZA
qðr0Þ
VðrÞ ¼
À
dðr0Þ
ðRA À rÞ
ðr0 À rÞ
A
Fig. 2 Synthetic pathway of
4-substituted phenylsulfonyl
hydrazones (2–18). Reagents
and conditions: a DCM, rt.;
b EtOH, reflux; and c EtOH,
L-proline, rt
O
S
O
Cl
+
NH2NH2.H2O
R
a
O
S
O
H
N
R
O
N
N
N
O
S
O
NH2
MW
b
N
+
H
(2-9)
R
O
O
+
O
O
O
+
O
O
O
c
H
H
N
H
NH4OAc
b
MW
O
S
O
H
N
R
N
N
H
(10-18)
123

Med Chem Res
HI
HJ
HF'
O
O
S
HA
HA
N
HE'
HE
HK
N N S
O
R (HL)
N
R (HJ)
HF
HF'
O
HE
HE
HGN
O
N
HF
HD'
HD
HJ'
HD
HB
HC
HB
HC
HG
HG
HG
HD
O
Compound 10-18
Compound 2-9
HI
HI
HK'
HI'
15
14
18 17
O
O
9
H
H
8
19
R
N N S
N N S
O
R
10
11
16
6
13
14
16
15
13
10
11 12
6
5
2
5
7
4
4
O
HN
12'
O
8
N
1
2
1
3
3
12
7
7'
8'
9'
9
O
11'
Compound 10-18
Compound 2-9
10'
1
Fig. 3 Compound labeling for H NMR and 13C NMR
by the condensation of benzaldehyde, acetone and ammo-
nium acetate in the ratio of 2:1:1 (Baliah, 1983; Hemalatha
et al., 2008). Several initial quantities, reaction times and
temperatures were tested to increase the yield. When the
reaction time and temperature were increased, the yield
decreased due to the polymerization of intermediate imines
(Vatsadze et al., 2000); therefore, the reaction time and
temperature should not exceed 30 min and 60 °C, respec-
tively. It has been shown that the use of ketones in stoi-
chiometric ratio can improve the yield. In such cases, the
reaction requires 4 times more mole of acetone to obtain
35 % yield. After literature survey, we decided that L-
proline could be useful catalyst as it was used for similar
reactions (Aznar et al., 2006). We performed some tests
using 30 % L-proline as catalyst and improved the yield by
65 % (Supporting information—Table 1).
vibrations of sulfonyl hydrazones were observed at
3103–3259 cm-1; C=O stretching vibration bands at
1640–1698 cm-1; asymmetric S=O stretching vibrations at
1320–1347 cm-1; and symmetric S=O stretching vibra-
tions at 1155–1179 cm-1
.
Piperidine molecules generally prefer chair conforma-
tion (Jayabharathi et al., 2007; Aridoss et al., 2009). In
order to elicit the exact conformation, compounds 4 and 13
were chosen as a prototype and the spectra of other com-
pounds were interpreted according to theirs. For that pur-
pose COSY, HETCOR, NOESY and ROESY spectra were
1
acquired in addition to H and 13C NMR spectra. All dis-
cussions were carried out according to the labeling of the
compounds in Fig. 3.
1
In the H NMR spectra, HA protons of the compounds 4
and 13 had a chemical shift of 10.42 and 10.44 ppm,
respectively, as a singlet. NOESY and ROESY spectra
indicated far interactions between protons. In the NOESY
spectrum of compound 13 (Fig. 4), there is two far inter-
actions of HA, that is, with HG and HD, but HG interaction is
smaller. According to the COSY spectrum (Fig. 5), HD’ and
HE’ interacted with each other, where only the HE’ was
affected by HF’, so the multiplet at 2.24–2.36 ppm was
attributed to the HD’ and HE’ together. HE proton split into
triplet at 1.95 ppm by the HD and HF protons. HD resonated
as doublet at 3.01 ppm affected by only the HE proton. HF,F’
split into triplet at 3.76 ppm by HE and HE’. Because of the
conformation of the molecule, HJ and HJ’ were not identical;
the HJ shifted to the downfield where the HJ’ and HC res-
onated together. The chemical shift of the aromatic field
The sulfonyl hydrazides were obtained according to the
previously reported procedures (Siemann et al., 2002;
Kummerle et al., 2012) and then condensed with ethyl
4-oxo-piperidine-1-carboxylate and 2,6-diarylpiperidine-4-
one. To determine the appropriate method for synthesizing
the sulfonyl hydrazones, the conventional method was
compared with the MW-assisted method. When 4-chloro-
sulfonyl hydrazide was condensed with ethyl 4-ox-
opiperidine-1-carboxylate, using the conventional method
only the 35 % yield was reached, but with the MW-assisted
method 80 % yield was obtained. Similarly, the yield was
increased from 37 to 82 % by using the MW method for the
condensation of same hydrazide with 2,6-diarylpiperidine-
4-one. It was decided to use MW in the synthesis of all
derivatives after getting similar results for other sub-
0
0
0
protons aligned as following HB [ HJ [ HJ ?C[HI?I ?K?K
to the diamagnetic area (Muhlhausen et al., 2010). The
COSY spectrum results were supported by the HETCOR
spectrum (Fig. 5) that HD and HE belonged to C3 and HD’
and HE’ belonged to C5. Compound 4 had more far
1
stituents. The compounds were characterized by FTIR, H
NMR, 13C NMR, mass spectra and elemental analysis.
In the IR spectra, the C=N stretching vibration bands
were observed at 1640 and 1651 cm-1; N–H stretching
123

Med Chem Res
Fig. 4 NOESY and ROESY spectrum of compound 13
ppm
ppm
2
3
4
5
6
7
8
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9
155 150 145 140 135 130 125 120 115 110 105 100 95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
ppm
9.0 8.5 8.0
7.5 7.0 6.5
6.0 5.5 5.0 4.5
4.0 3.5 3.0 2.5
2.0 1.5
ppm
Fig. 5 COSY and HETCOR spectrum of compound 13
Fig. 6 NOESY and ROESY spectrum of compound 4
123

Med Chem Res
O
H
O
S
O
other aromatic carbons of benzene rings attached to the
piperidine ring were observed between 127.0 and
128.7 ppm. In the aliphatic range of compounds 2–9, at
40.6–44.0 ppm C2 and C6 and at 28.0–33.5 ppm C3 and
C5 were observed as two separate peaks. The peaks at
61.3–61.4 ppm were attributed to C8 and at 15.0–15.1 ppm
to C9. In the aliphatic range of compounds 10–18, at
60.0–61.3 ppm C2 and C6 and at 36.6–43.2 ppm C3 and
C5 were detected as two separate peaks. Because of the
high electronegativity of fluorine atoms, carbon of trifluo-
romethoxy appeared at 120.7 ppm (compound 6) and
119.0 ppm (compound 15) where the carbon of methoxy
was observed at 55.8 ppm (compound 5) and 56.1 ppm
(compound 14). Similarly, carbon of methyl group was
observed at 21.5 ppm (compound 7) and 21.49 ppm
(compound 16). As compounds 2–9 were considered, sul-
fonyl group withdraw the electrons so the peak of the C10
shifted to the downfield. According to the substituent,
occasionally the peak of ipso carbon C13 shifted more than
the ipso carbon C10 to the downfield. In the case of fluo-
rine, methoxy and trifluoromethoxy groups attached to the
benzene ring at para position, by the inductive effect of
oxygen and fluorine atoms C13 resonated at
151.5–166.0 ppm, but by the resonance effect of these
atoms C12 and C14 were shifted to the upfield. In this
study, all C11 and C15 resonated at 129.9–131.0 ppm,
H
N
N
S
R
R
N
N
N
O
N
H
O
O
Fig. 7 Mass fragmentation pattern of the compounds
interactions than compound 13 according to the NOESY and
ROESY spectra (Fig. 6) that HA was coupled with HD,
where HC correlates with the protons HI, HD, HE, HF and
HG. The HI split into quartet at 4.04 ppm by HG protons;
quartet at 3.44 ppm was the correlation peaks between HF
and HD?E. The HD and HE gave triplet by the interaction
between each other and HF at 2.39 and 2.25 ppm, respec-
tively. Finally, HG gives triplets at 1.18 ppm. In the aromatic
field of these compounds, HB and HC were expected to
resonate as doublets, but by the effect of the fluorine atom at
para position, protons split again and gave multiplets.
13C NMR spectra were analyzed, and C4 carbons were
observed at 159.2–163.0 ppm. In the spectra of compounds
2–9, the peak of 155.0 ppm was attributed to the C7.
Analyzing the HETCOR spectrum, C7 and C70 of com-
pounds 10–18 were observed at 143.4–144.4 ppm. The
Table 1 Antioxidant activity results of compounds (2–18), BHT and a-tocopherol by the b-carotene/linoleic acid, DPPHÁ, ABTS?Á and
CUPRAC assay
Compounds
R
b-carotene/linoleic acid assay DPPHÁ assay IC50 (lM)a ABTS?Á assay IC50 (lM)a CUPRAC A0.50 (lM)a
IC50 (lM)a
2
Br
–
75.76 0.34
57.88 0.81
57.20 0.37
52.23 0.39
63.92 0.44
78.99 0.33
69.30 1.60
35.17 0.30
73.56 0.65
30.56 0.03
92.00 0.49
38.38 0.88
70.19 0.61
34.99 0.61
37.56 0.39
31.35 1.07
52.45 0.33
54.97 0.99
12.26 0.07
104.37 0.97
55.31 1.17
93.66 1.72
55.19 1.90
70.40 2.46
59.41 1.42
71.59 1.22
36.88 0.61
7.26 0.47
24.64 1.18
11.06 0.86
39.86 0.79
75.40 2.58
45.66 1.10
35.23 1.84
40.92 1.24
10.91 0.68
2.91 0.55
4.87 0.45
36.01 0.03
30.93 0.03
23.49 0.01
17.72 0.03
83.11 0.02
19.95 0.05
87.82 0.01
34.63 0.02
29.95 0.02
41.93 0.02
22.46 0.01
30.11 0.01
52.41 0.01
37.12 0.01
17.89 0.03
44.82 0.02
57.42 0.05
3.80 0.02
40.48 1.87
3
Cl
–
4
F
–
5
OCH3
OCF3
CH3
CF3
NO2
H
62.71 0.70
6
85.62 1.80
7
–
8
89.55 0.57
9
79.10 0.70
10
–
11
Br
51.52 0.91
12
Cl
–
–
13
F
14
OCH3 94.60 0.12
15
OCF3
CH3
CF3
–
16
–
17
–
18
BHTb
a-Tocopherolb
NO2
93.81 1.15
2.34 0.09
4.50 0.09
a
Values expressed are mean SEM of three parallel measurements. p \ 0.05, significantly different with student’s t test
Reference compounds
b
123

Med Chem Res
Table 2 Acetyl- and butyrylcholinesterase inhibitory activities of compounds (2–18)
Compounds
Anticholinesterase assay
Compounds
Anticholinesterase assay
AChE assay IC50 (lM)a
BChE assay IC50 (lM)a
AChE assay IC50 (lM)a
BChE assay IC50 (lM)a
2
3
4
5
6
7
8
9
10
a
104.44 0.56
119.23 0.34
137.43 0.36
109.39 0.8
130.82 0.36
119.69 1.52
134.52 0.09
101.53 0.58
139.89 0.58
94.03 0.64
89.05 1.09
99.31 1.06
136.38 0.97
116.42 1.62
119.06 0.84
112.14 0.60
80.63 1.67
90.75 1.06
11
108.24 0.38
80.32 0.69
91.72 0.42
97.79 0.05
102.02 0.36
96.93 0.16
125.83 0.05
142.46 0.17
4.48 0.78
120.72 0.57
112.15 0.44
83.94 0.98
83.42 0.97
82.85 0.59
76.39 0.74
93.52 1.32
124.68 1.20
46.03 0.14
12
13
14
15
16
17
18
Galantamineb
Values expressed are mean SEM of three parallel measurements. p \ 0.05, significantly different with student’s t test
Reference compound
b
Fig. 8 Geometry-optimized molecular structures of the compounds 1–18 with the R substitutions
except the nitro and trifluoromethyl groups, which were
most electron-withdrawing groups (DeBergh et al., 2013;
Backes et al., 2014; Madabhushi et al., 2014).
compounds 5, 9, 6, 8, 18 and 14, respectively. In DPPH
assay, all the synthesized compounds were inhibited DPPH
radical very well. The IC50 values of all compounds were
calculated lower than 100 lM. Compounds 5, 9, 11, 13, 15,
16, 17 and 18 showed very good free radical scavenging
activity, indicating IC50 values between 30.56 0.03 and
52.23 0.39 lM. At the conditions, the BHT exhibited
less activity (IC50: 54.97 0.99 lM) than those of com-
pounds. In the ABTS assay, among the tested compounds,
10, 18 and 12 exhibited higher cation radical scavenging
activity. The lower activity was observed for 4 and 2. In the
CUPRAC assay, most of the synthesized sulfonyl hydra-
zones exhibited good reducing effect. The A0.50 values
It was also confirmed by the presence of molecular ion
peaks for the sulfonyl hydrazones in the mass spectra, the
cleavage of N–N bond and the R group at para position of
benzene, and benzene sulfonamide fragment was observed
in all mass spectra. The other observed peaks were
obtained by the fragmentation of piperidine ring according
to the fragmentation pattern shown in Fig. 7. This con-
firmed the spectral analysis of the structure.
Pharmacology
were
calculated
between
17.72 0.03
and
Antioxidant activity of synthesized compounds
37.12 0.01 lM. A0.50 value of a-tocopherol, however,
was 40.48 1.87 lM. The compounds 6, 8, 14 and 18 had
lesser reducing effect capacity which are higher than
50 lM (Table 1).
Compound 11 (IC50: 51.52 0.91 lM) exhibited the
highest lipid peroxidation inhibitory activity, followed by
123

Med Chem Res
Fig. 9 Molecular electrostatic potential of the compounds 1–18
123

Med Chem Res
Acetyl- and butyrylcholinesterase inhibitory activities
of synthesized compounds
Similarly, compounds 2–4, 9–10 and 13–17 have had good
potential against BChE (Table 2).
The synthesized seventeen compounds were tested
for their in vitro inhibitory activity against acetyl-
cholinesterase (AChE) and butyrylcholinesterase (BChE)
enzymes at five different concentrations (200–100–50–25–
12.5–6.25–3.125 lM) compared to that of galantamine.
Galantamine is used to treat Alzheimer’s disease and
demonstrates good inhibition against AChE and BChE
(IC50: 4.48 0.78 and 46.03 0.14 lM, respectively).
The synthesized compounds were unable to exhibit more
activity against both enzymes. Nevertheless, since the IC50
values of compounds 12, 13, 16 and 14 were lower than
100 lM, it can be said that they have had good activity
against AChE. Compounds 16 and 9 having methyl and
nitro group at para position of phenyl ring, among all
compounds against BChE, showed better IC50 values.
Structure activity relationship
In this study, the series of sulfonyl hydrazone were
designed in order to discuss the structure–activity rela-
tionship that two derivatives of piperidine ring and 4-sub-
stituted benzene rings with both electron-withdrawing and
electron-donating groups were preferred.
For the antioxidant activity, the DPPH assay results
revealed that molecules (10–18) including 2,6-diphenyl
substituted piperidine ring possessed better activity than
the molecules (2–9) bearing non-substituted piperidine
ring. In ABTS assay, non-substituted derivative (10) was
most potent that the activity was decreased for the com-
pounds having substituent at para position of the benzene
ring. For CUPRAC assay, in the presence of the electron-
Fig. 10 HOMO–LUMO molecular orbital plots of optimized compounds 1–18
123

Med Chem Res
Table 3 Calculated energy values of ELUMO (eV), EHOMO (eV),
DEHOMO–LUMO (eV), ionization potential (I, eV), electron affinity (A,
eV), chemical hardness (g, eV), electronegativity (v, eV), chemical
potential (l, eV), softness (S, 1/eV), electrophilicity index (x, eV)
and dipole moment (l, Debye) by DFT calculations
Compounds
ELUMO
EHOMO
DEHOMO–LUMO
I
A
g
v
l
S
x
l
1
-5.103
-5.078
-5.003
-5.020
-5.003
-5.136
-5.030
-5.136
-5.546
-5.116
-5.110
-5.106
-5.106
-5.105
-5.108
-5.106
-5.141
-5.548
-8.402
-8.396
-8.260
-8.385
-8.415
-8.399
-8.399
-8.399
-8.397
-8.478
-8.476
-8.316
-8.468
-8.454
-8.466
-8.474
-8.480
-8.482
-3.299
-3.318
-3.257
-3.365
-3.412
-3.263
-3.369
-3.263
-2.851
-3.362
-3.366
-3.210
-3.362
-3.349
-3.358
-3.368
-3.339
-2.933
8.402
8.396
8.260
8.385
8.415
8.399
8.399
8.399
8.397
8.478
8.476
8.316
8.468
8.454
8.466
8.474
8.480
8.482
5.103
5.078
5.003
5.020
5.003
5.136
5.030
5.136
5.546
5.116
5.110
5.106
5.106
5.105
5.108
5.106
5.141
5.548
1.649
1.659
1.629
1.682
1.706
1.631
1.684
1.631
1.425
1.681
1.683
1.605
1.681
1.674
1.679
1.684
1.670
1.467
6.753
6.737
6.631
6.702
6.709
6.768
6.715
6.768
6.972
6.797
6.793
6.711
6.787
6.779
6.787
6.790
6.811
7.015
-6.753
-6.737
-6.631
-6.702
-6.709
-6.768
-6.715
-6.768
-6.972
-6.797
-6.793
-6.711
-6.787
-6.779
-6.787
-6.790
-6.811
-7.015
0.303
0.301
0.307
0.297
0.293
0.306
0.297
0.306
0.351
0.297
0.297
0.312
0.297
0.299
0.298
0.297
0.299
0.341
13.824
13.680
13.501
13.349
13.189
14.038
13.384
14.038
17.050
13.742
13.709
14.033
13.703
13.725
13.715
13.691
13.891
16.777
6.199
5.211
5.129
5.357
5.792
3.907
6.532
3.907
4.752
4.238
4.451
4.492
4.283
4.734
4.388
4.357
4.759
6.242
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
donating groups attached to the benzene ring (especially
compounds having methyl group), activities were found
better among the other compounds.
observed as blue; oxygens of the sulfonyl and the ester
groups were observed as red, as expected. As compounds
1–9 compared to compounds 10–18, the electrophilicity of
the hydrazo moiety was decreased because the benzene
rings attached to the piperidine ring, donated electrons.
Methoxy-substituted benzene ring (compounds 5 and 14)
was observed less positive because of the resonance effect
of the oxygen, while the trifluoromethoxy-substituted
benzene (compounds 6 and 15) was more positive because
of the high electronegativity of the fluorine atoms. Similar
relationship was analyzed between the methyl- and triflu-
oromethyl-substituted derivatives (compounds 7, 8, 16 and
17). Benzene ring of the methyl-substituted compound was
less positive than the trifluoromethyl substituted. The sul-
fonyl group of compounds 11–13 was more negative than
the other compounds by the resonance effect of the
halogens.
For the anti-Alzheimer activity, by the presence of the
phenyl groups attached to the piperidine ring (10–18), the
activities of the compounds were increased. As the electron
donor groups, such as –F, –OCH3 and –CH3, were substi-
tuted at para position of the benzene ring, activities were
observed better than the non-substituted derivatives.
Among the all compounds, 4-methyl-substituted phenyl
ring derivative (16) was found to be more active.
Computational studies
DFT calculation studies were carried out to support the
chemical and pharmacological findings. The most
stable conformer found in the DFT studies coincided with
the conformer predicted by the NMR spectral studies. As
seen from the lowest-energy conformer, molecules pre-
ferred chair conformation (Fig. 8) (Kassaee et al., 2005).
And also the calculations of the 1H and 13C NMR data were
mostly correlated with the experimental values (Supporting
information—Table 2 and Table 3).
The HOMO and LUMO are shown in Fig. 10. The
HOMO showed that the charge density localized mainly on
piperidine and hydrazo moiety. The LUMO showed that
the charge density localized mainly on benzene groups.
The other calculated energy values including ionization
potential (I), electron affinity (A), electronegativity (v) and
frontier orbital energy (HOMO and LUMO) were useful in
predicting global chemical reactivity trends (Table 3).
The electron affinity (A) value of compound 18 was
5.548 eV which was the highest value among other
To screen the electrophilic and nucleophilic region of
the molecule, maps of MEP were prepared (Fig. 9).
According to the maps, nitrogens of hydrazone group were
123

Med Chem Res
compounds. Compound 18 was also found among most
active compounds according to the ABTS method. In
addition, for compound 18 high electronegativity energy
(v) value was observed as 7.015 eV. Accordingly, the low
electronegativity value of compound 4 as 6.702 eV
belonged to low activity value according to ABTS method.
Compound 18 having lowest ELUMO energy value exerted
activity value of 10.91 lM in ABTS and 52.45 lM in
DPPH method which were good values. Also lowest
DEHOMO–LUMO energy gap values of compounds 5, 7 and
16 showed best antioxidant activities in CUPRAC test.
These compounds have OCH3 and CH3 groups at 4-posi-
tion of benzene ring. High ionization potential values of
compounds 13–16 were concluded as good antiBChE
activity and good antioxidant activity according to
CUPRAC method. High dipole moment values of com-
pounds 2–5 and 7 at a range of 5.129–6.532 Debye con-
cluded good antioxidant effect according to the CUPRAC
method (17.72–36.01 lM). In the same manner, com-
pounds 6 and 8 show that lowest antioxidant values of
83.11 and 87.82 lM had a dipole moment value of 3.907
Debye.
benzoyl hydrazones will be synthesized and evaluated for
the changes of activity results.
Acknowledgments This study was supported by the Research
Foundation of Gaziantep University (Project No: FEF.11.03). We
would like to thanks the Gazi University for providing Gaussian 09 W
software. The numerical calculations reported in this paper were
performed at TUBITAK ULAKBIM, High Performance and Grid
Computing Center (TRUBA Resources).
Compliance with ethical standards
Conflict of interest The authors declare that they have no conflicts of
interest to disclose.
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