Synthesis, molecular docking and biological evaluation of Schiff base transition metal complexes as potential urease inhibitors

Article abstract of DOI:10.1016/j.ejmech.2010.07.007

Six transition metal compounds of Schiff base ligands were evaluated for the inhibitory activity on jack bean urease, of which compounds 2-6 were determined by single crystal X-ray analysis. It was found that copper(II) complexes 1 and 4 showed strong inhibitory activity against jack bean urease (IC₅₀ = 0.52 and 0.46 μM), compared with acetohydroxamic acid (IC₅₀ = 42.12 μM) as a positive reference. Cobalt(II), nickel(II) and zinc(II) compounds also exhibited potent inhibitory activity (IC ₅₀ = 3.88-25.20 μM). A docking analysis using the AUTODOCK 4.0 program could explain the inhibitory activities of 1 and 4 against urease.

Full text of DOI:10.1016/j.ejmech.2010.07.007

European Journal of Medicinal Chemistry 45 (2010) 4473e4478
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis, molecular docking and biological evaluation of Schiff base
transition metal complexes as potential urease inhibitors
1
1
*
*
Wu Chen , Yuguang Li , Yongming Cui, Xian Zhang, Hai-Liang Zhu , Qingfu Zeng
Engineering Research Center for Clean Production of Textile Printing, Ministry of Education, Wuhan Textile University, Wuhan 430073, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
Six transition metal compounds of Schiff base ligands were evaluated for the inhibitory activity on jack
bean urease, of which compounds 2e6 were determined by single crystal X-ray analysis. It was found
that copper(II) complexes 1 and 4 showed strong inhibitory activity against jack bean urease (IC50 ¼ 0.52
Received 16 March 2010
Received in revised form
12 June 2010
Accepted 5 July 2010
Available online 14 July 2010
and 0.46
m
M), compared with acetohydroxamic acid (IC50 ¼ 42.12
m
M) as a positive reference. Cobalt(II),
M). A
nickel(II) and zinc(II) compounds also exhibited potent inhibitory activity (IC50 ¼ 3.88e25.20
m
docking analysis using the AUTODOCK 4.0 program could explain the inhibitory activities of 1 and 4
against urease.
Keywords:
Ó 2010 Elsevier Masson SAS. All rights reserved.
Schiff base ligands
Transition metal complexes
Crystal structures
Urease inhibitors
1. Introduction
Urease could affect not only human health, for example,
causing peptic ulcers, stomach cancer, etc [15], but also the effi-
Transition metal complexes of Schiff base ligands have been
extensively investigated for many years due to their novel structures
and potential applications in many fields [1]. Among them, salen-
type Schiff base complexes have been becoming the hot topics of
contemporary research [2]. Schiff base ligands, derived from the
condensation of salicylaldehyde and its derivatives with various
primary amines, may act as the bidentate N,O- [3] and tridentate
N,O,O-donor ligands [4], and so on [5], to construct mono-, di-mer,
and one-dimensional (1D), two-dimensional (2D), three-dimen-
sional (3D) complexes [6]. Currently, the use foreground of such
metal complexes is promising such as acting as single-molecule
magnets (SMMs) [7], as luminescent probes [8], as catalysts for
specific DNA [9] and RNA [10] cleavage reactions. In addition, Schiff
base complexes as the inhibitor were also investigated in prostate
cancer cells [11] and tumor cells [12]. Recently, some salen-type
Schiff base complexes possessing potent inhibitory activities against
xanthine oxidase and excellent antibacterial activities have been
reported by our group [13]. And some transition metal complexes
(M ¼ Cu, Co, Ni, etc.,) of Schiff base ligands with the potent inhibitory
activities against urease have also been reported by us [14].
ciency of soil nitrogen fertilization, and ammonia volatilization
and root damage [16]. It’s interesting to find the excellent urease
inhibitors [17]. As a follow-up to our previous characterization of
Schiff base transition metal complexes as the urease inhibitor,
urease inhibitory activities of compounds 1e6 were investigated
and reported in this paper. A docking analysis using the AUTO-
DOCK 4.0 program could explain the inhibitory activities of
complexes 1 and 4 against urease and the structure activity rela-
tionship was also discussed.
2. Results and discussion
2.1. Synthesis
Schiff base ligands HL1e4 were prepared by reaction of 3,5-dibro-
mosalicylaldehyde with 2-chlorobenzylamine (L1, C14H9NOBr2Cl),
benzylamine (L2, C14H10NOBr2), cyclohexylamine (L3, C13H14NOBr2)
and N,N0-dimethylethylenediamine (L4, C11H13N2OBr2), in nearly
80e90% yield in MeOH, respectively. Complex 1 was obtained from
reaction of HL1 with Cu(NO3)2$3H2O in MeOH. Unfortunately,
attempts to grow suitable single crystals for its structural determi-
nation failed. However, spectroscopic data support the proposed
structure as shown in Scheme 1. Similar to analogous copper(II)
complexes [14a,18], the central Cu(II) atom of complexes 1 and 4 is
four-coordinated by the oxygen and nitrogen donor atoms of two
* Corresponding authors. Tel./fax: þ86 27 8761 1776.
E-mail address: hlzhu@wtu.edu.cn (H.-L. Zhu).
1
These authors contributed equally to this work.
0223-5234/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2010.07.007

4474
W. Chen et al. / European Journal of Medicinal Chemistry 45 (2010) 4473e4478
Cl
Br
Br
N
O
Cu
N
O
Br
Br
Cl
Fig. 2. An ORTEP diagram showing the structure of compound 3 with selected atom-
labeling. The thermal ellipsoids plotted at 30% probability and H atoms omitted for the
plot clarity. Symmetry codes A: 1 ꢀ x, 1 ꢀ y, ꢀz.
Scheme 1. Proposed structure of Schiff base compound 1.
Schiff base ligands. The elemental analysis is in good agreement with
the chemical formula proposed for compounds 1e6.
asymmetric unit. As shown in Fig.1, cobalt(II) atom is in a distorted-
tetrahedral geometry and is four-coordinated by two N atoms and
two O atoms from two Schiff base ligands (L1). The average bond
2.2. IR and UV analysis
ꢀ
distances of Co1eO and Co1eN are 1.903(8) and 1.991(8) A,
The IR spectra of compounds 1e6 exhibit strong absorption at
1609e1649 cmꢀ1, assignable to the v(C]N) absorption [19,22a].
Due to the impact of metal atoms, the amino-absorption peaks of
the Schiff base ligands shift to lower wave number. The strong
absorption at 1642, 1633, 1632, 1618, 1612 cmꢀ1 are attributed to
the stretching vibration of C]N group of compounds 1e6,
respectively. For compounds 1e6, the appearances of the broad
strong absorption at about 1600, 1585, 1500 and 1450 cmꢀ1 could
be reasonably attributed to the presence of the benzene ring C]C
backbone stretching vibration absorption peak.
respectively, while the average bond distances of Co2eO and
ꢀ
Co2eN are 1.901(8) and 2.010(8) A, respectively. The angles sub-
tended at the Co(II) ion of the distorted-tetrahedral geometry
(CoN2O2) is in the range 95.5(4)e118.9(4)ꢁ. The angle between two
six-membered chelate planes was 89.1(2)ꢁ. In contrast to complex
2, the Ni(II) atom of complex 3 lies on a crystallographic inversion
center (symmetry codes: 1 ꢀ x, 1 ꢀ y, ꢀz). Nickel atom is four-
coordinated by two N atoms and two O atoms from two Schiff base
ligands (L2), which affords a square planar trans-[NiN2O2] coordi-
nation geometry. The bond distances of Ni1eO1 and Ni1eN1 are
The UVeVis spectra for the compounds 1e6 were obtained in
assay condition (DMSO:H2O, 1:1 v/v). The weak but characteristic
absorption bands in the 370e396 nm regions are attributed to the
L / M charge transfer (CT) in the UVeVis spectra of 1e6 [8b,20].
The middle absorption at around 270 nm may also be associated
with charge transfer and/or n / p* transitions [21]. The strong
absorption bands at about 250 nm could be attributed to intra-
ꢀ
1.847(3) and 1.944(4) A, respectively, which are comparable with
the corresponding values reported for analogous square planar Ni
(II) species [14a,22].
The molecular structures of 4 and 5 were determined by single
crystal X-ray analysis. Their structures are very much alike. Crystal
structure of complex 4 is shown in Fig. 3. The copper(II) atom is
four-coordinated by two N atoms and two O atoms from two Schiff
base ligands (L3) in the usual trans arrangement. Cu(II) atom is in
a slightly distorted-tetrahedral geometry, which is intermediate
between square planar and tetrahedral. Analogous tetrahedral Cu
(II) species were previously reported in the literatures [18,23]. The
average bond distances of CueO and CueN are 1.890(3) and 1.970
ligand
p /
p* transitions.
2.3. Crystal structure description
Crystal structures of compounds 2e6 are shown in Figs. 1e5,
respectively. Single crystal X-ray diffraction reveals that these
compounds are the mononuclear structures. The Schiff base ligands
(HL1, HL2, HL3, HL4) derived from 3,5-dibromosalicylaldehyde act as
a bidentate N,O-donor ligand. Crystal structure of complex 2
contains two independent mononuclear cobalt(II) molecules in
ꢀ
(4) A, respectively. The angles subtended at the Cu(II) ion in the
distorted-tetrahedral geometry (CuN2O2) is in the range 91.28(13)e
Fig. 1. An ORTEP diagram showing the structure of compound 2 with selected atom-
labeling. The thermal ellipsoids plotted at 30% probability and H atoms omitted for the
plot clarity.
Fig. 3. An ORTEP diagram showing the structure of compound 4 with selected atom-
labeling. The thermal ellipsoids plotted at 30% probability and H atoms omitted for the
plot clarity.

W. Chen et al. / European Journal of Medicinal Chemistry 45 (2010) 4473e4478
4475
Table 1
Inhibition of jack bean urease by compounds 1e6, Schiff base
ligands and metal ions.
Tested materials
IC50
>100
0.37
2.87
>100
(
m
M)
HL1e4
Cu2þ
Ni2þ
M2þ (Co2þ, Zn2þ
)
1
2
3
4
5
6
0.52
25.20
3.88
0.46
19.18
9.27
Acetohydroxamic acid
42.12
Fig. 4. An ORTEP diagram showing the structure of compound 5 with selected atom-
labeling. The thermal ellipsoids plotted at 30% probability and H atoms omitted for the
plot clarity.
the activity of jack bean urease. Under the same condition, Schiff base
Cu(II) complexes 1 and 4 showed better inhibitory activity with IC50
154.81(15)ꢁ. The angle between two six-membered chelate planes
was 39.4(2)ꢁ. In contrast, Zn(II) atom of complex 5 has a distorted-
tetrahedral coordination, which is essentially similar to that of
complexes 2 and 4. The zinc(II) atom is four-coordinated by two N
atoms and two O atoms from two Schiff base ligands (L3), as shown
in Fig. 4. Analogous tetrahedral Zn(II) species were previously
reported in the literatures [13b,24]. The average bond distances of
values of 0.52 and 0.46
(II) complexes as the potent urease inhibitor with IC50 values of
0.43 M [14a]. It should be noted that Co(II) complex 2 and Zn(II)
mM, respectively. This is near to Schiff base Cu
m
complexes 5, 6 possess the inhibitory activities although the corre-
sponding metal ions had no inhibitory activities against urease. In
contrast, both Ni(II) ion and its Schiff base complex 3 showed potent
urease inhibitory activities. This indicates that inhibitory activities of
Schiff base metal complexes as the urease inhibitor depend on not
only the central ions but also the organic ligand.
ꢀ
ZneO and ZneN are 1.908(3) and 1.999(3) A, respectively. The
angles subtended at the Zn(II) ion in the distorted-tetrahedral
geometry (ZnN2O2) is in the range 96.31(11)e126.45(13)ꢁ. The
angle between two six-membered chelate planes was 100.5(2)ꢁ.
Single crystal X-ray diffraction reveals that compound 6 crystal-
lizes in monoclinic space group P21/c. Crystal structure of the
mononuclear unit [Zn(HL4)2]2þ is shown in Fig. 5. Compound 6
consists of the mononuclear unit [Zn(HL4)2]2þ, two nitrate counter
ions and two lattice acetonitrile molecules. There are two indepen-
dent mononuclear zinc(II) cations [Zn(HL4)2]2þ in asymmetric unit.
Each zinc(II) atom of compound 6, lying on an inversion center
(symmetry codes: 1 ꢀ x, 2 ꢀ y, ꢀz), is six-coordinated by two N atoms
and four O atoms from two Schiff base ligands (L4) and two water
molecules. The bond distances of Zn1eO1, Zn1eO2 and Zn1eN1 are
2.5. Molecular docking study
The binding models of Schiff base copper(II) complexes 1 and 4
in the enzyme active site of urease were depicted in Figs. 6 and 7,
respectively [27]. It’s interesting that there is one kind of hydrogen
ꢀ
2.014(3), 2.261(3), 2.124(3)A. ThebonddistancesofZn2eO3, Zn2eO4
ꢀ
and Zn2eN3 are 1.995(3), 2.296(3), and 2.119(3) A, respectively.
2.4. Inhibitory activity against jack bean urease
As shown in Table 1, transition metal ions as enzyme inhibitors
exhibit different ability to inhibit urease, which follows the order:
Cu2þ > Ni2þ > Co2þ z Zn2þ. This is in accords with inhibitory effi-
ciency of metal ions toward urease following the order:
Cu2þ > Ni2þ > Co2þ > Zn2þ, which has been reported in the literature
[25,26]. Compared with the standard inhibitor acetohydroxamic acid
(IC50 ¼ 42.12
m
M), the Schiff base ligands (HL1e4) have no influence on
Fig. 6. Compound 1 (colored by atom: carbonsegray; nitrogenseblue; oxygensered;
bromineegreen) is bound into urease (entry 1E9Z in the Protein Data Bank). The
dotted lines show the hydrogen bond. (For interpretation of the references to colour in
this figure legend, the reader is referred to the web version of this article.)
Fig. 5. An ORTEP diagram showing the structure of the cation [Zn(HL4)2$2H2O]2þ in
compound 6 with selected atom-labeling (symmetry codes: 1 ꢀ x, 2 ꢀ y, ꢀz). The
thermal ellipsoids plotted at 30% probability and H atoms omitted for the plot clarity.

4476
W. Chen et al. / European Journal of Medicinal Chemistry 45 (2010) 4473e4478
ꢀ
THR171OeH/Ncomplex-4 ¼ 1.753 A；angle of hydrogen bond:
THR171OeH/Ncomplex-4 ¼ 141.5ꢁ). And the other was composed of
amino hydrogen of ILE220 and the nitrogen atom of complex 4
ꢀ
(length of hydrogen bond: ILE220NeH/Ocomplex-4 ¼ 2.159 A；
angle of the hydrogen bond: ILE220NeH/Ocomplex-4 ¼ 147.7ꢁ). In
addition, complex 1 may form hydrophobic interactions with
Ala197, Leu196 and Phe273 of urease. In comparison to 1eurease
interactions, complex 4 may also form hydrophobic interactions
with Ile172, Leu196, Ala197, Ile220 and Ile247. The result of
molecular docking study could explain the better inhibitory activity
of 1 and 4 against jack bean urease.
3. Experimental section
3.1. Materials and measurements
3,5-Dibromosalicyladehyde, cyclohexylamine, 2-chlorobenzyl-
amine, benzylamine, were purchased from Aldrich and used
without further purification. Elemental analyses for C, H and N
were carried out on a PerkineElmer 2400 analyzer. IR spectra were
recorded using KBr pellets (4000e400 cmꢀ1) on a Nexus 870 FT-IR
spectrophotometer. Electronic spectra in the 200e800 nm range
were measured using DMSOeH2O (1:1 v/v) solution on a Shimadzu
UV-160 Aspectrophotometer.
3.2. Compounds synthesis
General procedure for the synthesis of compounds 1e6: Primary
amine (0.2 mmol) was added to the solution of 3,5-dibromosali-
cyladehyde (56 mg, 0.2 mmol) in an aqueous acetonitrile solution
(5 mL). The mixture was stirred for 5 min to give an orange solution,
which was added to a methanol solution (1 mL) of M(NO3)2 ꢂ H2O
(0.1 mmol) (M ¼ Cu, x ¼ 3; M ¼ Co, Ni, Zn, x ¼ 6). The mixture was
stirred for another 5 min at room temperature to give a clear
solution and then filtered. The filtrate was kept in air for about
a week, forming block crystals. The crystals were isolated, washed
three times with distilled water and dried in a vacuum desiccator
containing anhydrous CaCl2.
Fig. 7. Compound 4 (colored by atom: carbonsegray; nitrogenseblue; oxygensered;
bromineegreen) is bound into urease (entry 1E9Z in the Protein Data Bank). The
dotted lines show the hydrogen bond. (For interpretation of the references to colour in
this figure legend, the reader is referred to the web version of this article.)
bond that is formed by the phenolic oxygen atom of complex 1 and
3.2.1. [Cu(L1)2] (1)
the amino hydrogen of Ile220 (length of hydrogen bond:
ꢀ
Black solid, yield: 40.8 mg (47%). IR (KBr, cmꢀ1): 3020, 2966,
2947, 1612, 1514, 1450, 1163, 864, 756, 717, 592, 522, 476. UVeVis
(DMSOeH2O, k/nm): 243, 257, 378. Anal. Calcd. for
C28H18Br4Cl2CuN2O2: C, 38.72; H, 2.09; N, 3.23. Found: C, 38.56; H,
2.25; N, 3.11%.
Ile220 NeH/Ocomplex-1 ¼ 1.908 A；angle of hydrogen bond:
Ile220 NeH/Ocomplex-1 ¼ 152.941ꢁ). In contrast, there are two
kinds of hydrogen bonds in the binding model of complex 4 (Fig. 7).
One kind was formed by the phenolic oxygen atom of complex 4
and hydroxy of THR171 (length of hydrogen bond:
Table 2
Crystal data for compounds 2e6.
Compounds
2
3
4
5$CH3CN
6$2CH3CN
Empirical formula
C28H18Br4Cl2CoN2O2
C28H20Br4NiN2O2
C26H27Br4CuN2O2
C28H31Br4ZnN3O2
C26H38Br4ZnN8O10
Molecular weight
Crystal system
Space group
863.92
Monoclinic
P21/c
16.4449(7)
12.5497(5)
31.6709(12)
90
116.179(2)
90
291(2)
5865.7(4)
4
1.957
3336
794.81
Monoclinic
P21/c
10.6062(6)
6.1056(4)
20.7125(15)
90
102.431(3)
90
291(2)
1309.84(15)
2
2.015
772
782.68
Monoclinic
P21/c
15.309(3)
12.858(3)
14.161(3)
90.00
93.24(3)
90.00
293(2)
2783.0(10)
4
1.868
1528
826.57
Monoclinic
P21/n
9.4743(3)
16.3900(5)
20.4619(6)
90
91.8410(10)
90
291(2)
3175.76(17)
4
1.729
1624
1007.66
Triclinic
P-1
7.5691(3)
14.8691(5)
17.6475(6)
78.688(2)
84.203(2)
80.706(2)
291(2)
1917.06(12)
1
1.746
1000
4.868
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
T (K)
3
ꢀ
V (A )
Z
rcalc. (g cmꢀ3
F(000)
)
m(Mo-K
a
) (mmꢀ1
)
6.247
6.872
6.554
5.835
Data/restraint/parameters
11565/31/703
1.445
2712/0/169
1.049
6906/0/316
1.010
6556/0/350
1.021
7409/0/452
1.007
Goodness-of-fit on F2
Final R1, wR2 [I > 2
s(I)]
0.0689, 0.1322
0.0432, 0.1081
0.0467, 0.0909
0.0402, 0.1049
0.0436, 0.1020

W. Chen et al. / European Journal of Medicinal Chemistry 45 (2010) 4473e4478
4477
Table 3
(DMSOeH2O, k/nm): 243, 276, 384. Anal. Calcd. for
C26H28Br4CuN2O2: C, 39.85; H, 3.60; N, 3.57. Found: C, 39.70; H,
4.21; N, 3.65%.
ꢁ
ꢀ
Selected bond lengths [A] and angles [ ] in compounds 2e6.
2
Co(1)eO(1)
Co(1)eO(2)
Co(1)eN(2)
Co(1)eN(1)
O(1)eCo(1)eO(2)
O(1)eCo(1)eN(2)
O(2)eCo(1)eN(2)
O(1)eCo(1)eN(1)
O(2)eCo(1)eN(1)
N(2)eCo(1)eN(1)
1.897(8)
1.908(8)
1.976(11)
2.005(10)
118.9(4)
115.5(4)
95.8(4)
95.5(4)
118.2(4)
114.4(4)
Co(2)eO(4)
Co(2)eO(3)
Co(2)eN(4)
Co(2)eN(3)
O(4)eCo(2)eO(3)
O(4)eCo(2)eN(4)
O(3)eCo(2)eN(4)
O(4)eCo(2)eN(3)
O(3)eCo(2)eN(3)
N(4)eCo(2)eN(3)
1.899(8)
1.903(9)
2.002(11)
2.018(10)
124.4(4)
93.6(4)
108.7(4)
119.9(4)
95.0(4)
3.2.5. [Zn(L3)2] (5)
Yellow solid, yield: 23.5 mg (30%). IR (KBr, cmꢀ1): 3064, 3030,
2927, 2873, 1635, 1633, 1508, 1446, 1398, 1020, 1153, 866, 597, 547,
501. UVeVis (DMSOeH2O, k/nm): 243, 274, 382. Anal. Calcd. for
5$CH3CN, C28H31Br4ZnN3O2: C, 40.69; H, 3.78; N, 5.08. Found: C,
40.23; H, 3.99; N, 5.00%.
116.3(4)
3.2.6. [Zn(HL4)2$2H2O]$2NO3 (6)
3 (a: 1 ꢀ x, 1 ꢀ y, ꢀz)
Ni(1)eO(1)
Yellow solid, yield: 63.8 mg (69%). IR (KBr, cmꢀ1): 3456, 3062,
2960, 2789, 1633, 1456, 1219, 1143, 875, 704, 567, 460. UVeVis
(DMSOeH2O, k/nm): 251, 284, 386. Anal. Calcd. for 6$2CH3CN,
C26H38Br4ZnN8O10: C, 30.99; H, 3.80; N, 11.12. Found: C, 30.55; H,
3.52; N, 11.00%.
1.847(3)
1.944(4)
180.00(18)
91.97(15)
88.03(15)
Ni(1)eO(1)a
1.847(3)
1.944(4)
88.03(15)
91.97(15)
180.0(2)
Ni(1)eN(1)
Ni(1)eN(1)a
O(1)eNi(1)eO(1)a
O(1)eNi(1)eN(1)
O(1)aeNi(1)eN(1)
O(1)eNi(1)eN(1)a
O(1)aeNi(1)eN(1)a
N(1)eNi(1)eN(1)a
4
Cu(1)eO(1)
Cu(1)eO(2)
1.898(3)
1.882(3)
Cu(1)eN(1)
Cu(1)eN(2)
1.975(4)
1.964(4)
3.3. Measurement of inhibitory activity against jack bean urease
O(1)eCu(1)eO(2)
O(1)eCu(1)eN(2)
O(2)eCu(1)eN(2)
151.85(14)
93.30(13)
94.62(13)
O(1)eCu(1)eN(1)
O(2)eCu(1)eN(1)
N(2)eCu(1)eN(1)
92.94(13)
91.28(13)
154.81(15)
Jack bean urease was purchased from SigmaeAldrich Co. (St.
Louis, Mo, USA). The measurement of urease was carried out
according to the literature reported by Tanaka et al. [28]. Generally,
5
the assay mixture, containing 25
mL of jack bean urease (10 kU/L)
Zn(1)eO(1)
Zn(1)eO(2)
O(1)eZn(1)eO(2)
O(1)eZn(1)eN(2)
O(2)eZn(1)eN(2)
1.905(3)
1.911(3)
115.97(12)
111.50(12)
96.63(11)
Zn(1)eN(1)
Zn(1)eN(2)
O(1)eZn(1)eN(1)
O(2)eZn(1)eN(1)
N(2)eZn(1)eN(1)
1.999(3)
1.998(3)
96.31(11)
111.31(12)
126.45(13)
and 25 L of the tested complexes of various concentrations (dis-
m
solved in the solution of DMSO:H2O ¼ 1:1 (v/v)), was preincubated
for 1 h at 37 ꢁC in a 96-well assay plate. After preincubation, 0.2 mL
of 100 mM HEPES (N-[2-hydroxy-ethyl] piperazine-N0-[2-ethane-
sulfonic acid]) buffer [29] pH ¼ 6.8 containing 500 mM urea and
0.002% phenol red were added and incubated at 37 ꢁC. The reaction
time was measured by micro plate reader (570 nm), which was
required to produce enough ammonium carbonate to raise the pH
of a HEPES buffer from 6.8 to 7.7, the end-point being determined
by the color of phenol red indicator [30].
6 (a: 1 ꢀ x, 2 ꢀ y, ꢀz; b: 2 ꢀ x, 1 ꢀ y, 1 ꢀ z)
Zn(1)eO(1)a
2.014(3)
2.014(3)
2.124(3)
2.124(3)
2.261(3)
Zn(2)eO(3)
1.995(3)
1.995(3)
2.119(3)
2.119(3)
2.296(3)
Zn(1)eO(1)
Zn(2)eO(3)b
Zn(1)eN(1)a
Zn(2)eN(3)
Zn(1)eN(1)
Zn(1)eO(2)
Zn(1)eO(2)
Zn(2)eN(3)b
Zn(2)eO(4b)
Zn(2)eO(4)
2.261(3)
2.296(3)
O(1)aeZn(1)eO(1)
O(1)aeZn(1)eN(1)a
O(1)eZn(1)eN(1)a
O(1)aeZn(1)eN(1)
O(1)eZn(1)eN(1)
N(1)aeZn(1)eN(1)
O(1)aeZn(1)eO(2)a
O(1)eZn(1)eO(2)a
N(1)aeZn(1)eO(2)a
N(1)eZn(1)eO(2)a
O(1)aeZn(1)eO(2)
O(1)eZn(1)eO(2)
N(1)aeZn(1)eO(2)
N(1)eZn(1)eO(2)
O(2)aeZn(1)eO(2)
180.00(1)
88.37(11)
91.63(11)
91.63(11)
88.37(11)
180.00(19)
90.77(12)
89.23(12)
89.65(11)
90.35(11)
89.23(12)
90.77(12)
90.35(11)
89.65(11)
180.00(13)
O(3)eZn(2)eO(3)b
O(3)eZn(2)eN(3)
O(3)beZn(2)eN(3)
O(3)eZn(2)eN(3)b
O(3)beZn(2)eN(3)b
N(3)eZn(2)eN(3)b
O(3)eZn(2)eO(4)b
O(3)beZn(2)eO(4)b
N(3)eZn(2)eO(4)b
N(3)beZn(2)eO(4)b
O(3)eZn(2)eO(4)
O(3)beZn(2)eO(4)
N(3)eZn(2)eO(4)
N(3)beZn(2)eO(4)
O(4b)eZn(2)eO(4)
180.00(1)
88.92(11)
91.08(11)
91.08(11)
88.92(11)
180.00(1)
89.11(12)
90.89(12)
92.58(11)
87.42(11)
90.89(12)
89.11(12)
87.42(11)
92.58(11)
180.00(13)
The abilities of the Schiff base ligands HL1e4, metal ions
(M ¼ Cu2þ, Ni2þ, Co2þ, Zn2þ) and compounds 1e6 as the inhibitors
were studied by the IC50 values of the material (25
mL, 100
mg)
tested against jack bean urease (25
mL, 10 kU/L) using urea
(500 mM) in HEPES buffer (0.2 mL, 100 mM; pH ¼ 6.8) (Table 1).
3.4. Crystal structure determinations
Diffraction intensities for compounds 2e6 were collected at 291
(2) and 293(2) K using a Bruker SMART CCD area detector with Mo-
ꢀ
Ka
radiation (
l
¼ 0.71073 A). The collected data were reduced using
the SAINT program [31], and empirical absorption corrections were
performed using the SADABS program [32]. The structures were
solved by direct methods and refined against F2 by full-matrix least-
squares methods using the SHELXTL version 5.1 [33]. All of the non-
hydrogen atoms were refined anisotropically. All other hydrogen
atoms were placed in geometrically ideal positions and constrained
to ride on their parent atoms. The crystallographic data for
compounds 2e6 are summarized in Table 2. Selected bond lengths
and angles are given in Table 3.
a and b are for the symmetry related position.
3.2.2. [Co(L1)2] (2)
Red solid, yield: 60.4 mg (70%). IR (KBr, cmꢀ1): 3065, 2960, 2779,
1642, 1620, 1580, 1450, 1222, 1153, 865, 710, 580, 561, 450. UVeVis
(DMSOeH2O, k/nm): 246, 272, 370. Anal. Calcd. for
C28H18Br4Cl2CoN2O2: C, 38.93; H, 2.10; N, 3.24. Found: C, 39.82; H,
2.30; N, 3.41%.
3.2.3. [Ni(L2)2] (3)
4. Conclusions
Brown solid, yield: 23.8 mg (30%). IR (KBr, cmꢀ1): 3028, 2926,
2868, 1618, 1517, 1496, 1444, 1168, 871, 746, 717, 607, 555, 457.
UVeVis (DMSOeH2O, k/nm): 256, 267, 396. Anal. Calcd. for
C28H20Br4N2NiO2: C, 42.31; H, 2.54; N, 3.52. Found: C, 42.20; H,
2.99; N, 3.41%.
Six transition metal compounds of Schiff base ligands were
evaluated for the inhibitory activity on jack bean urease. It was found
that most of them have inhibitory activity against jack bean urease. It
is noteworthy that copper(II) complexes 1 and 4 exhibit stronger
activity to inhibit jack bean urease (IC50 ¼ 0.52 and 0.46
those of the nickel(II), cobalt(II) and zinc(II) compounds
(IC50 ¼ 3.88e25.20 M). A docking analysis using the AUTODOCK 4.0
program could explain the inhibitory activities of compounds 1 and
mM) than
3.2.4. [Cu(L3)2] (4)
Black solid, yield: 41.5 mg (53%). IR (KBr, cmꢀ1): 2939, 2858,
1642, 1624, 1514, 1448, 1210, 1155, 864, 559, 561, 478. UVeVis
m

4478
W. Chen et al. / European Journal of Medicinal Chemistry 45 (2010) 4473e4478
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Acknowledgements
This work was supported by the National Natural Science Foun-
dation of China (50978208) the Hubei National Science Foundation
(2009CDA022), and the Education Office of Hubei Province
(D20091704 & Q20101610).
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