Design, synthesis and antibacterial activity of novel actinonin derivatives containing benzimidazole heterocycles

Article abstract of DOI:10.1016/j.ejmech.2008.05.009

A series of novel actinonin derivatives containing a benzimidazole heterocycle linked as amide isostere have been designed and synthesized. The structures of all the synthesized compounds were confirmed by analytical and spectroscopic methods. All the com

Full text of DOI:10.1016/j.ejmech.2008.05.009

Available online at www.sciencedirect.com
European Journal of Medicinal Chemistry 44 (2009) 2202e2210
http://www.elsevier.com/locate/ejmech
Short communication
Design, synthesis and antibacterial activity of novel actinonin
derivatives containing benzimidazole heterocycles
Datong Zhang a, Zongheng Wang b, Weiren Xu c,
Fanggang Sun a, Lida Tang c, Jianwu Wang a,
*
a School of Chemistry and Chemical Engineering, Shandong University, 27 Shanda Nanlu, Jinan, Shandong 250100, PR China
b School of Life Science, Shandong University, Jinan, Shandong 250100, PR China
c Tianjin Institute of Pharmaceutical Research, Tianjin 300193, PR China
Received 14 March 2008; received in revised form 13 May 2008; accepted 16 May 2008
Available online 23 May 2008
Abstract
A series of novel actinonin derivatives containing a benzimidazole heterocycle linked as amide isostere have been designed and synthesized.
The structures of all the synthesized compounds were confirmed by analytical and spectroscopic methods. All the compounds were evaluated in
vitro against Staphylococcus aureus, Klebsiella pneumoniae, and Sarcina lutea. Among them, compound 1a with unsubstituted benzimidazole
ring exhibited potent antibacterial activities.
Ó 2008 Elsevier Masson SAS. All rights reserved.
Keywords: Actinonin derivatives; Benzimidazole; Synthesis; Antibacterial activity
1. Introduction
bioactivities [9,10], and the general structure of these com-
pounds consists of a metal-chelating group and various amida-
tion fragments. Given the apparent hydrolyzable amide bonds,
we decided to investigate a series of compounds bearing a het-
erocyclic moiety in place of amide fragment of actinonin mol-
ecule to work as an amide isostere. Several benzimidazole
heterocycles were chosen to be incorporated into our designed
new compounds in view of their ability to act as both hydrogen
bond acceptor and donor while maintaining the proper orien-
tation of the side chain (Fig. 1). Such a peptidomimetic mod-
ification has led to the discovery of potent, competitive, and
reversible inhibitors of tyrosine phosphatase 1B (PTP1B)
with improved caco-2 permeability [11]. In this paper, we
describe the synthesis of the title compounds with seven differ-
ent substituents on the benzimidazole ring. The antibacterial
activities were also evaluated.
The increase in bacterial resistance has attracted consider-
able interest in the discovery and development of new classes
of antibacterial agents [1]. The new agents should preferably
consist of chemical characteristics that clearly differ from
those of existing agents. Actinonin was first isolated from
a Malayan strain of Actinomyces and found to show a weak in-
hibitory activity against Gram-positive and Gram-negative
bacteria [2,3]. However, recently actinonin has been proven
to have antiproliferative effects on human tumor cells [4].
The action mechanism of actinonin is believed to be the inhi-
bition of the peptide deformylase that is a new class of metal-
loenzyme which is essential for bacterial survival [5,6]. The
hydroxamate group of actinonin, which can complex with
the metal ion in the active pocket of the peptide deformylase,
is necessary for its activity [7]. Nevertheless, actinonin lacks
in vivo efficacy, due to the poor bioavailability [7,8]. A lot
of actinonin analogues have been developed to test their
2. Chemistry
The general strategy for the synthesis of 1 is illustrated in
Scheme 1. The chiral intermediate (R)-2-butylbutanedioic
acid-4-tert-butyl ester was prepared in high ee value according
* Corresponding author. Tel.: þ86 531 883 62708; fax: þ86 531 885 64464.
E-mail address: jwwang@sdu.edu.cn (J. Wang).
0223-5234/$ - see front matter Ó 2008 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2008.05.009

D. Zhang et al. / European Journal of Medicinal Chemistry 44 (2009) 2202e2210
2203
O
O
1) LDA,THF/-78oC
O
LiOH
O
Ot-Bu
OH
MeOH/H2O
O
O
O
2) ICH2COOt-Bu
H
O
HN
H
HO
N
HO
N
N
N
R
N
H
N
O
O
O
O
H
1) L-(-)-α-methylbenzylamine
O
OH
OtBu
OH
OtBu
1
Actinonin
2) 1N HCl
Fig. 1. Peptidomimetic modification of actinonin.
O
Scheme 2. Synthesis of (R)-2-butylbutanedioic acid-4-tert-butyl ester.
to an alkylation procedure on methyl hexanoate followed by
resolution of the racemic 2-n-butylbutanedioic acid-4-tert-bu-
tyl monoester (Scheme 2) [12]. Benzimidazole intermediates 2
were deprotected with hydrogen catalyzed by Pd/C and then
coupled with the chiral succinate with the acceleration of 1-
chloro-3,5-dimethoxy-2,4,6-triazine (CDMT) and N-methyl
morpholine [13]. After removal of the tert-butyl group and for-
mation of new methyl ester 4, the hydroxamates were obtained
through a cyanide-catalyzed hydroxylamination of the esters
[14]. Actually, the cyanide-catalyzed hydroxylamination pro-
cedure with aqueous hydroxylamine solution simplified the
operation and gave consistently modest to good yield.
Preparation of benzimidazole intermediates 2ae2c was
achieved using a procedure similar to that described by
Chen et al. [15]. Coupling of 5 with Cbz-protected L-valine,
followed by the intramolecular cyclization in acetic acid
yielded benzimidazole intermediates 2ae2c. Amidation of 6
with appropriate amines and then condensing with Cbz-L-va-
line afforded the precursor amides 7. Heating the amides in
acetic acid gave the desired cyclization compounds 2de2g
(Scheme 3).
microorganism strains were Staphylococcus aureus
(CMCC26112), Klebsiella pneumoniae (CMCC46117), and
Sarcina lutea (CMCC28001). Cefoperazone was used as the
standard drug. The results of the antimicrobial studies of the
compounds and standard drug are given in Table 2.
4. Results and discussion
A series of seven new compounds were synthesized. We
obtained benzimidazole intermediates (2ae2g) through an in-
tramolecular cyclization after the coupling of Cbz-L-valine
with two kinds of substituted o-phenylenediamines. The con-
densation of the chiral succinate with the benzimidazole moi-
ety was accelerated by 1-chloro-3,5-dimethoxy-2,4,6-triazine
(CDMT) and N-methyl morpholine. With the combination of
the two reagents, high-yield target compounds were obtained
and the work-up procedures were simplified compared with
the conventional DCC/HOBt method. The deprotection proce-
dure of the tert-butyl group with trifluoroacetic acid in di-
chloromethane described by Chen et al. [15] gave a sticky
liquid difficult to deal with. Then 98% formic acid was em-
ployed and the free acid obtained could be used without fur-
ther purification. The methods of one-step condensation of
free carboxylic acid with hydroxylamine hydrochloride have
been reported [18,19]. However, all the attempts with our
benzimidazole-containing succinic acid derivatives failed to
afford the desired hydroxamic acids. The reaction of hydrox-
ylamine with ester (4ae4g) which was carried out in the pres-
ence of large amount of KOH [20] led to complex products
Some characteristics of the synthesized target compounds
are outlined in Table 1. Analytical and spectral data (1H
NMR, 13C NMR, ESI-MS, IR, and elemental analysis) con-
firmed the structures of the new compounds.
3. Biological activity
Antimicrobial activities of synthesized compounds were
tested using microbroth dilution method [16,17]. Tested
O
R
N
1) H2,Pd/C
R
N
O
ZNH
2) (R)-2-butyl butanedioic
acid 4-tert-butyl ester,
CDMT/NMM
N
H
N
H
N
H
O
3a-g
2a-g
O
R
N
NH2OH/NaCN
MeOH/THF
1) HCOOH
O
N
H
O
N
H
2) CH3OH/DCC/DMAP
4a-g
O
R
H
N
N
HO
N
O
H
O
H
N
a: H
N
f:
O
H
N
d:
e:
O
b: CH
3
O
O
H
N
1a-g
g:
N
OCH3
c: OCH
3
Scheme 1. Synthetic route to the title compounds.

2204
D. Zhang et al. / European Journal of Medicinal Chemistry 44 (2009) 2202e2210
R1
R1
N
H2N
H2N
1) ZValine/DCC/HOBt
2) HOAc,70oC
ZNH
N
H
5
2a,2 b, 2c
O
O
1) NH2R2/DCC/HOBt
2) ZValine/DCC/HOBt
HN
H2N
H2N
NHR2
ZNH
HOAc
70oC
OH
O
H2N
6
7
O
R1
R2
NHR2
N
2a: H
O
ZNH
2d:
2f:
N
H
2b: CH3
OCH3 2g:
2e:
2c: OCH3
2d,2 e, 2f,2 g
Scheme 3. Synthesis of benzimidazole intermediates 2ae2g.
and tedious purification steps. The cyanide-catalyzed hydrox-
ylamination procedures of ester (4ae4g) with 50% aqueous
hydroxylamine solution were proven to be simple and efficient
among these reported methods.
isopropyl, resonated as multiplets at d 2.21e2.30. The appear-
ance of a double doublet at d 2.06 clearly reveals the magnetic
nonequivalence of the two protons of CH2 group adjacent to
a chiral center. The chiral proton of succinate was observed
as multiplet between d 2.70 and 2.75. A triplet at d 4.87
(J ¼ 8.4 Hz) integrating for one proton was attributable to
the chiral proton adjacent to the benzimidazole ring. All the
other aromatic and active hydrogen were observed at expected
regions. 13C NMR chemical shift values of the carbon atoms at
d 35.10e35.31 (C3), 41.60e41.84 (C2), 167.50e167.79
(CONHOH) and 173.93e174.28 (CONH) corroborated the
succinamide character of these compounds deduced from the
1H NMR. 2-Methylpropyl moiety was confirmed by the car-
bon atoms observed at d 18.77e18.89 (CH3), 19.31e19.51
(CH3), 31.65e32.03 (eCH(CH3)2) and 53.07e53.22 (NHe
CHeAr).
In the IR spectrum of these compounds, a broad absorption
band around 3250 cmꢀ1 indicates the presence of active
hydrogen group in the compounds. The amide carbonyl
stretching frequency was observed at about 1646 cmꢀ1. The
other prominent absorption bands observed in the IR spectrum
are 3035 (AreH), 2924 (CeH) and 1540 (C]N) cmꢀ1
.
1H NMR spectrum of 1a showed a triplet at d 0.65 due to
the CH3 protons at the terminal of the butyl group. The two
CH3 protons of the isopropyl appeared as two doublets cen-
tered at d 0.80 and d 0.94 with a vicinal coupling constant
J ¼ 6.7 Hz. The six methylene protons of the butyl group res-
onated as complex multiplets at d 1.01e1.42. One of the meth-
ylene protons of the succinate moiety appeared as a double
doublet centered at d 2.06 (J ¼ 7.4, 14.5 Hz). The other meth-
ylene protons, mixed with the tertiary hydrogen signal of the
Further evidence for the formation of hydroxamates 1ae1g
was obtained by recording the mass spectra. The mass spectra
showed the molecular ion peak corresponding to its molecular
Table 1
Physical data for compounds 1ae1g
Compound
R ¼
eH
Mol. formula
M. wt
m.p. (ꢁC)
Yield (%)
1a
1b
1c
C19H28N4O3
C20H30N4O3
C20H30N4O4
360.45
374.48
390.48
132e134
134e135
123e125
76
65
75
eCH3
eOCH3
O
1d
1e
1f
C24H35N5O5
C27H35N5O5
C26H39N5O4
473.57
509.6
142e144
201e203
220e222
80
70
73
C
N
H
O
O
C N
OCH3
O
H
485.62
C N
O
1g
C25H37N5O4
471.59
138e140
77
N
C

D. Zhang et al. / European Journal of Medicinal Chemistry 44 (2009) 2202e2210
2205
Table 2
Antibacterial activities of 1ae1g (MIC, mg/mL)
determined by using an XT-4 microscopic apparatus and are
uncorrected. Thin-layer chromatography (TLC) was per-
formed on Silica Gel F254 plates with visualization by UV or
iodine vapor. 1H NMR and 13C NMR spectra of CDCl3/
DMSO-d6 solutions (TMS as an internal standard) were re-
corded on Bruker DPX300 and DPX400 spectrometers, re-
spectively. The IR spectra were measured on a Bruker
Vector FT-IR spectrophotometer as KBr pellets or film. Mass
spectra were obtained with an API4000 spectrometer. Elemen-
tal analyses were performed on a PerkineElmer 2400
analyzer. Optical rotations were measured with a WZZ-2
polarimeter.
Compound
Staphylococcus
aureus
Klebsiella
pneumoniae
Sarcina
lutea
1a
1b
2
8
0.5
4
4
8
1c
1d
8
16
8
8
16
8
1e
32
64
16
32
8
16
64
1f
1g
>64
0.25
>64
0.25
Standard
0.25
Standard: cefoperazone.
weight. The elemental analyses showed that all the newly syn-
thesized compounds were having proper purity.
6.1. General procedure for the synthesis of compounds
2ae2c
All target compounds 1ae1g were evaluated for their anti-
bacterial activities against S. aureus, K. pneumoniae and S. lu-
tea. MICs were recorded as the minimum concentration of
a compound that inhibits the growth of tested microorganisms.
The MIC values of all the new compounds are generally
within the range of 0.5e64 mg/mL against all evaluated
strains.
On comparing their MIC values with the standard, com-
pounds 1ae1c were effective against all evaluated strains.
Compound 1a exhibited a good inhibitory effect on these bac-
teria. Compound 1a especially showed high activity against K.
pneumoniae. Compounds 1de1g showed moderate activity.
The investigation on the structureeactivity relationship re-
vealed that the compounds with aliphatic substituents on the
benzene ring of the benzimidazole gave better result than
those with the amidation groups. Introduction of the amidation
groups into the 5-position of the benzimidazole led to the re-
duced inhibitory activity. Compounds 1f and 1g with saturated
cyclic hydrocarbon substituents at the amidation group
showed less activity when compared with compounds 1d
and 1e.
To a solution of Z-valine (5.5 mmol) in anhydrous tetrahy-
drofuran (10 mL) 1-hydroxybenzotriazole (6.05 mmol) was
added. After cooling to 0 ꢁC, dicyclohexylcarbodiimide
(5.8 mmol) was added in portions to the reaction mixture
and the resulting solution was stirred for 3 h with gradual
warming to room temperature. The precipitate obtained was
removed by suction filtration and compound 5 (5 mmol) was
introduced to the filtrate. The stirring was continued for 7 h.
After filtration, the filtrate was concentrated in an evaporator
and the residue was purified on a silica gel column with meth-
ylene dichloride/methanol (20:1).
The solution of the intermediates above in acetic acid
(8 mL) was heated at 70e75
ꢁC for 7 h. After removal of
the solvent under vacuum, the crude product was purified on
silica gel with petroleum ether/EtOAc (1:1).
6.1.1. N-Benzyloxycarbonyl-(1S )-(1-benzimidazol-2-yl)-
2-methylpropylamine (2a)
Slightly yellow solid, yield: 71%; m.p. 182e184 ꢁC;
[a]2D5 ¼ ꢀ58.5 (c 1, MeOH). H NMR (CDCl3, 400 MHz) d:
1
0.93 (d, J ¼ 6.7 Hz, 3H), 1.05 (d, J ¼ 6.5 Hz, 3H), 2.45e
2.55 (m, 1H), 4.66 (t, J ¼ 8 Hz, 1H), 4.98 (d, J ¼ 12 Hz,
1H), 5.10 (d, J ¼ 12 Hz, 1H), 6.09 (d, J ¼ 7.8 Hz, 1H),
5. Conclusion
Based on structureeactivity relationship and the peptidomi-
metic idea, the benzimidazole ring was incorporated into the
actinonin molecule as an amide isostere and the hydroxamate
group was retained. A series of seven new hydroxamates bear-
ing benzimidazole ring have been synthesized. The investiga-
tion on antibacterial screening data reveals that compound 1a
showed good bacterial inhibition. Varying the substituents on
the 5-position of the benzimidazole with different groups sig-
nificantly influenced the antibacterial activity. The compound
with unsubstituted benzimidazole exhibited potent inhibitory
activity. In conclusion, these preliminary results are promising
and are beneficial for further studies in developing new lead
compounds.
7.19e7.28 (m, 7H), 7.45e7.53 (m, 2H). IR (KBr) n/cmꢀ1
:
3375, 3309, 1690, 1540, 1257.
6.1.2. N-Benzyloxycarbonyl-(1S )-[1-(5-methylbenzimidazol-
2-yl)]-2-methylpropylamine (2b)
White-off solid, yield: 80%; m.p. 139e141 ꢁC;
[a]2D5 ¼ ꢀ63.0 (c 1, MeOH). H NMR (CDCl3, 400 MHz) d:
1
0.91 (d, J ¼ 6.7 Hz, 3H), 1.03 (d, J ¼ 6.5 Hz, 3H), 2.42 (s,
3H), 2.43e2.55 (m, 1H), 4.63 (t, J ¼ 8 Hz, 1H), 4.98 (d,
J ¼ 12.2 Hz, 1H), 5.10 (d, J ¼ 12.2 Hz, 1H), 6.09 (d,
J ¼ 7.8 Hz, 1H), 7.03 (d, J ¼ 8 Hz, 1H), 7.19e7.28 (m, 6H),
7.41e7.50 (m, 1H). IR (KBr) n/cmꢀ1: 3335, 3030, 1686,
1524, 1234.
6. Experimental
6.1.3. N-Benzyloxycarbonyl-(1S )-[1-(5-methoxyl
benzimidazol-2-yl)]-2-methylpropylamine (2c)
All reagents were used as purchased from commercial sup-
pliers without further purification. Melting points were
Slightly yellow solid, yield: 58%; m.p. 60e61 ꢁC;
[a]2D5 ¼ ꢀ52.5 (c 1, MeOH). H NMR (CDCl3, 400 MHz) d:
1

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D. Zhang et al. / European Journal of Medicinal Chemistry 44 (2009) 2202e2210
0.92 (d, J ¼ 6.7 Hz, 3H), 1.03 (d, J ¼ 6.6 Hz, 3H), 2.43e2.54
(m, 1H), 3.79 (s, 3H), 4.62 (t, J ¼ 8 Hz, 1H), 4.98 (d,
J ¼ 12.2 Hz, 1H), 5.10 (d, J ¼ 12.2 Hz, 1H), 6.06 (d,
J ¼ 7.8 Hz, 1H), 6.85 (dd, J ¼ 2.4, 8.8 Hz, 1H), 6.90e6.98
(m, 1H), 7.25e7.32 (m, 5H), 7.38e7.45 (m, 1H). IR (KBr)
n/cmꢀ1: 3288, 3032, 1695, 1538, 1267.
6.2.3. N-[2-Amino-5-(cyclohexylamino)carbonyl]phenyl-3-
methyl-2-(S )-benzyloxycarbonylaminobutamide (2f)
White foam, yield: 60%; [a]2D5 ¼ ꢀ34.0 (c 1, MeOH). H
NMR (DMSO-d6, 300 MHz) d: 0.83 (d, J ¼ 6.9 Hz, 3H),
0.94 (d, J ¼ 6.9 Hz, 3H), 1.14e1.35 (m, 6H), 1.59e1.82 (m,
4H), 2.22e2.28 (m, 1H), 3.73e3.78 (m, 1H), 4.62 (dd,
J ¼ 7.8 Hz, 1H), 4.97 (d, J ¼ 8.7 Hz, 1H), 5.04 (d,
J ¼ 8.7 Hz, 1H), 7.31e7.36 (m, 5H), 7.48e7.82 (m, 3H),
8.08e8.15 (m, 2H), 12.47 (s, 1H). IR (KBr) n/cmꢀ1: 3324,
3219, 3033, 1686, 1620, 1551, 1287.
1
6.2. General procedure for the synthesis of compounds 7
and 2de2g
1-Hydroxybenzotriazole (12 mmol) was added under N2 to
a solution of 3,4-diaminobenzoic acid (10 mmol) and triethyl-
amine (11 mmol) in dry dimethylformamide/methylene
dichloride (14 mL, 1:1). After cooling to 0 ꢁC, dicyclohexyl-
carbodiimide (1.1 mmol) was added in portions to the reaction
mixture followed by various amines (15 mmol) and the result-
ing solution was stirred for 12 h with gradual warming to room
temperature. The solution was filtered and evaporated under
vacuum. The residue was purified on a short silica gel
column with methylene dichloride/methanol (20:1). The
solid obtained above was dissolved in dry tetrahydrofuran
(50 mL) and Z-L-valine (5.5 mmol) and 1-hydroxybenzotria-
zole (6.05 mmol) were added under N2. After cooling to
0 ꢁC, dicyclohexylcarbodiimide (5.8 mmol) was added in
portions to the reaction mixture and the resulting solution
was stirred for 12 h with gradual warming to room temper-
ature. The solution was filtered and evaporated under vac-
uum. The residue was purified on a short silica gel column
with methylene dichloride/methanol (20:1) to afford com-
pound 7.
6.2.4. N-[2-Amino-5-(piperidino)carbonyl]phenyl-3-methyl-
2-(S )-benzyloxycarbonylaminobutamide (2g)
White-off solid, yield: 55%; m.p. 95e100 ꢁC;
[a]2D5 ¼ ꢀ36.5 (c 1, MeOH). H NMR (DMSO-d6, 300 MHz)
1
d: 0.83 (d, J ¼ 6.9 Hz, 3H), 0.95 (d, J ¼ 6.9 Hz, 3H), 1.43e
1.62 (m, 6H), 2.22e2.32 (m, 1H), 3.35e3.48 (m, 4H), 4.62
(t, J ¼ 7.8 Hz, 1H), 5.02 (d, J ¼ 12.6 Hz, 1H), 5.08 (d,
J ¼ 12.6 Hz, 1H), 7.14e7.61 (m, 8H), 7.79 (d, J ¼ 8.4 Hz,
6H), 12.43 (s, 1H). IR (KBr) n/cmꢀ1: 3303, 3029, 1717,
1603, 1524, 1233.
6.3. General procedure for the synthesis of compounds
3ae3g
A solution of compound 2 (1.65 mmol) in 15 mL of meth-
anol was hydrogenated over 5% Pd/C (145 mg) using an H2
balloon. After 3 h, the reaction mixture was filtered and evap-
orated to give a white solid which was used without further
purification.
The solution of compound 7 in acetic acid (10 mL) was
heated at 70e75 ꢁC for 7 h. After removal of the solvent under
vacuum, the crude product was purified on silica gel with
methylene dichloride/methanol (20:1) to produce 2de2g.
4,6-Dimethoxy-2-chloro-1,3,5-triazine (CDMT) (1.82 mmol)
and (R)-(þ)-2-butylbutanedioic acid-4-tert-butyl monoester
(1.65 mmol) were dissolved in dry methylene dichloride
(10 mL). N-Methyl morpholine (1.98 mmol) was added at
ꢀ5 to 0 ꢁC. After 4 h, the white solid obtained above was
added to the reaction mixture. The mixture was stirred at the
same temperature for 2 h, then overnight at room temperature.
The precipitate produced was removed by suction filtration
and washed with a small amount of methylene dichloride.
The combined filtrate was washed with water, 0.5 N HCl, sat-
urated NaHCO3, saturated saline successively and dried with
sodium sulfate. The solvent was concentrated, and the
residue was purified on silica gel with methylene dichloride/
methanol (30:1).
6.2.1. 2-[1-(S )-Benzyloxycarbonylamino-2-methyl]propyl-
5-(1-morpholin)carbonylbenzimidazole (2d)
White-off solid, yield: 70%; m.p. 95e97 ꢁC; [a]D25 ¼ ꢀ37.5
(c 1, MeOH). 1H NMR (DMSO-d6, 300 MHz) d: 0.84 (d,
J ¼ 6.6 Hz, 3H), 0.96 (d, J ¼ 6.6 Hz, 3H), 2.23e2.34 (m,
1H), 3.31e3.60 (m, 8H), 4.64 (t, J ¼ 7.8 Hz, 1H), 5.01 (d,
J ¼ 12.6 Hz, 1H), 5.08 (d, J ¼ 12.6 Hz, 1H), 7.19e7.63 (m,
8H), 7.81 (d, J ¼ 8.4 Hz, 1H), 12.47 (s, 1H). IR (KBr) n/
cmꢀ1: 3310, 3193, 3032, 1718, 1612, 1526, 1239.
6.3.1. N-[1-(S )-(Benzimidazol-2-yl)-2-methyl]propyl-(R)-
2-tert-butoxycarbonylmethylhexanamide(3a)
6.2.2. 2-[1-(S )-Benzyloxycarbonylamino-2-methyl]propyl-5-
(4-methoxyanilino)carbonylbenzimidazole (2e)
White solid, yield: 90%; m.p. 70e72 ꢁC; [a]D25 ¼ ꢀ85.5 (c
1, MeOH). 1H NMR (DMSO-d6, 400 MHz) d: 0.65 (t,
J ¼ 6.8 Hz, 3H), 0.80 (d, J ¼ 6.7 Hz, 3H), 0.96 (d,
J ¼ 6.6 Hz, 3H), 1.00e1.30 (m, 6H), 1.37 (s, 9H), 2.18e
2.25 (m, 2H), 2.42 (dd, J ¼ 9, 16 Hz, 1H), 2.71e2.76 (m,
1H), 4.87 (t, J ¼ 8.5 Hz, 1H), 7.11e7.18 (m, 2H), 7.44 (d,
J ¼ 6.8 Hz, 1H), 7.55 (d, J ¼ 6.8 Hz, 1H), 8.30 (d,
J ¼ 8.8 Hz, 1H), 12.19 (s, 1H). IR (KBr) n/cmꢀ1: 3288,
3035, 1732, 1644, 1565, 1116. ESI-MS m/z: 402 [M þ H]þ.
White solid, yield: 65%; m.p. 100e103 ꢁC; [a]D25 ¼ ꢀ34.5
(c 1, MeOH). 1H NMR (DMSO-d6, 300 MHz) d: 0.83 (d,
J ¼ 6.6 Hz, 3H), 0.96 (d, J ¼ 6.6 Hz, 3H), 2.25e2.34 (m,
1H), 3.75 (s, 3H), 4.64 (t, J ¼ 8.1 Hz, 1H), 5.02 (d,
J ¼ 12.6 Hz, 1H), 5.08 (d, J ¼ 12.6 Hz, 1H), 6.93 (d,
J ¼ 8.4 Hz, 2H), 7.23e7.42 (m, 5H), 7.53e7.84 (m, 5H),
10.09 (s, 1H), 12.57 (s, 1H). IR (KBr) n/cmꢀ1: 3288, 3032,
1703, 1645, 1511, 1244.

D. Zhang et al. / European Journal of Medicinal Chemistry 44 (2009) 2202e2210
2207
6.3.2. N-[1-(S )-(5-Methylbenzimidazol-2-yl)-2-methyl]
J ¼ 6.7 Hz, 3H), 0.80 (d, J ¼ 6.6 Hz, 3H), 0.96 (d,
J ¼ 6.6 Hz, 3H), 1.00e1.42 (m, 21H), 1.70e1.83 (m, 4H),
2.25e2.35 (m, 2H), 2.54 (dd, J ¼ 9, 16 Hz, 1H), 2.71e2.76
(m, 1H), 3.73e3.78 (m, 1H), 4.87 (t, J ¼ 8.4 Hz, 1H), 7.45e
7.55 (m, 1H), 7.67 (d, J ¼ 8 Hz, 1H), 7.92e8.13 (m, 2H),
propyl-(R)-2-tert-butoxycarbonylmethylhexanamide (3b)
White solid, yield: 91%; m.p. 193e194 ꢁC; [a]D25 ¼ ꢀ104.5
(c 1, MeOH). 1H NMR (DMSO-d6, 400 MHz) d: 0.65 (t,
J ¼ 6.8 Hz, 3H), 0.80 (d, J ¼ 6.7 Hz, 3H), 0.96 (d,
J ¼ 6.6 Hz, 3H), 1.02e1.20 (m, 4H), 1.25e1.39 (m, 11H),
2.18e2.25 (m, 1H), 2.32e2.38 (m, 4H), 2.54 (dd, J ¼ 9.2,
16 Hz, 1H), 2.73e2.78 (m, 1H), 4.86 (t, J ¼ 8.5 Hz, 1H),
6.95 (d, J ¼ 8 Hz, 1H), 7.24e7.39 (m, 2H), 8.31 (d,
J ¼ 9 Hz, 1H), 12.15 (s, 1H). IR (KBr) n/cmꢀ1: 3269, 3035,
1733, 1638, 1549, 1155. ESI-MS m/z: 416 [M þ H]þ.
8.31 (d, J ¼ 8 Hz, 1H), 12.41 (s, 1H). IR (KBr) n/cmꢀ1
:
3335, 3271, 3035, 1732, 1645, 1547, 1152. ESI-MS m/z:
527 [M þ H]þ.
6.3.7. N-[1-(S )-[5-(Piperidinocarbonyl)
benzimidazol-2-yl]-2-methyl]propyl-(R)-2-tert-
butoxycarbonylmethylhexanamide (3g)
6.3.3. N-[1-(S )-(5-Methoxybenzimidazol-2-yl)-2-methyl]
propyl-(R)-2-tert-butoxycarbonylmethylhexanamide (3c)
White solid, yield: 90%; m.p. 68.5e70.5 ꢁC; [a]D25 ¼ ꢀ80.5
(c 1, MeOH). 1H NMR (DMSO-d6, 400 MHz) d: 0.67 (t,
J ¼ 6.7 Hz, 3H), 0.78 (d, J ¼ 6.7 Hz, 3H), 0.93 (d,
J ¼ 6.6 Hz, 3H), 1.02e1.20 (m, 4H), 1.25e1.52 (m, 11H),
2.18e2.25 (m, 2H), 2.44 (dd, J ¼ 9, 16 Hz, 1H), 2.69e2.73
(m, 1H), 3.73 (s, 3H), 4.82 (t, J ¼ 8.3 Hz, 1H), 6.73e6.78
(m, 1H), 6.94 (d, J ¼ 1.7 Hz, 1H), 7.41 (d, J ¼ 8.7 Hz, 1H),
White solid, yield: 85%; m.p. 70e72 ꢁC; [a]D25 ¼ ꢀ72.0 (c
1, MeOH). 1H NMR (DMSO-d6, 400 MHz) d: 0.63 (t,
J ¼ 6.4 Hz, 3H), 0.80 (d, J ¼ 6.6 Hz, 3H), 0.96 (d,
J ¼ 6.6 Hz, 3H), 1.00e1.35 (m, 6H), 1.37 (s, 9H), 1.45e
1.63 (m, 6H), 2.25e2.35 (m, 2H), 2.42 (dd, J ¼ 9, 16 Hz,
1H), 2.71e2.76 (m, 1H), 3.35e3.46 (m, 4H), 4.85 (t,
J ¼ 8.4 Hz, 1H), 7.12e7.18 (m, 1H), 7.45e7.58 (m, 2H),
8.33 (d, J ¼ 8.4 Hz, 1H), 12.41 (s, 1H). IR (KBr) n/cmꢀ1
:
3275, 3035, 1731, 1643, 1539, 1153. ESI-MS m/z: 513
[M þ H]þ.
8.26 (d, J ¼ 9 Hz, 1H), 12.00 (s, 1H). IR (KBr) n/cmꢀ1
:
3270, 3068, 1733, 1642, 1558, 1157. ESI-MS m/z: 390
[M þ H]þ.
6.4. General procedure for the synthesis of compounds
4ae4g
6.3.4. N-[1-(S )-[5-(Morpholinocarbonyl)
benzimidazol-2-yl]-2-methyl]propyl-(R)-2-tert-
butoxycarbonylmethylhexanamide (3d)
A solution of compound 3 in formic acid (98%, 10 mL) was
stirred at room temperature for 10 h. Removal of the solvent
under vacuum gave a white solid. The white solid was added
to CH2Cl2 (10 mL), followed by methanol (1.5 mL) and 4-di-
methylaminopyridine (0.155 mmol). After cooling to 0 ꢁC,
DCC (1.63 mmol) was added and the solution was stirred at
the same temperature for 0.5 h. Then the reaction was contin-
ued at room temperature for 12 h. The precipitate produced
was removed by suction filtration. The solvent was concen-
trated, and the residue was purified on silica gel with petro-
leum ether/EtOAC (1:1).
White solid, yield: 95%; m.p. 178e180 ꢁC; [a]D25 ¼ ꢀ68.5
(c 1, MeOH). 1H NMR (DMSO-d6, 300 MHz) d: 0.74 (t,
J ¼ 6.4 Hz, 3H), 0.92 (d, J ¼ 6.3 Hz, 3H), 1.05 (d,
J ¼ 6.4 Hz, 3H), 1.04e1.30 (m, 6H), 1.37 (s, 9H), 2.25e
2.27 (m, 2H), 2.44 (dd, J ¼ 9, 16 Hz, 1H), 2.69e2.73 (m,
1H), 3.45e3.65 (m, 8H), 4.96 (t, J ¼ 8.1 Hz, 1H), 7.27e7.33
(m, 1H), 7.58e7.70 (m, 2H), 8.44 (d, J ¼ 8.7 Hz, 1H), 12.52
(s, 1H). IR (KBr) n/cmꢀ1: 3278, 3035, 1732, 1643, 1543,
1154. ESI-MS m/z: 515 [M þ H]þ, 537 [M þ Na]þ.
6.3.5. N-[1-(S )-[[5-(4-Methoxyanilino)carbonyl]
benzimidazol-2-yl]-2-methyl]propyl-(R)-2-tert-
butoxycarbonylmethylhexanamide (3e)
6.4.1. N-[1-(S )-(Benzimidazol-2-yl)-2-methyl]propyl-(R)-2-
methoxycarbonylmethylhexanamide (4a)
White solid, yield: 70%; m.p. 165e168 ꢁC; [a]D25 ¼ ꢀ92.0
1
White solid, yield: 90%; m.p. 168e169.5 ꢁC;
(c 0.5, MeOH). H NMR (DMSO-d6, 400 MHz) d: 0.64 (t,
1
[a]2D5 ¼ ꢀ74.0 (c 1, MeOH). H NMR (DMSO-d6, 400 MHz)
J ¼ 6.8 Hz, 3H), 0.80 (d, J ¼ 6.7 Hz, 3H), 0.94 (d,
J ¼ 6.7 Hz, 3H), 1.00e1.42 (m, 6H), 2.19e2.28 (m, 1H),
2.36 (dd, J ¼ 5.2, 16 Hz, 1H), 2.54 (dd, J ¼ 9.3, 16 Hz, 1H),
2.72e2.80 (m, 1H), 3.55 (s, 3H), 4.86 (t, J ¼ 8.5 Hz, 1H),
7.10e7.16 (m, 2H), 7.44 (dd, J ¼ 2.1, 6.4 Hz, 1H), 7.55 (dd,
J ¼ 1.7, 6.8 Hz, 1H), 8.34 (d, J ¼ 9.2 Hz, 1H), 12.20 (s, 1H).
IR (KBr) n/cmꢀ1: 3327, 3024, 1626, 1575. ESI-MS m/z: 360
[M þ H]þ.
d: 0.66 (t, J ¼ 6.8 Hz, 3H), 0.81 (d, J ¼ 6.5 Hz, 3H), 0.96 (d,
J ¼ 6.7 Hz, 3H), 1.04e1.21 (m, 4H), 1.29e1.37 (m, 11H),
2.21e2.27 (m, 2H), 2.45 (dd, J ¼ 9, 16 Hz, 1H), 2.68e2.76
(m, 1H), 3.75 (s, 3H), 4.89 (t, J ¼ 8.4 Hz, 1H), 6.92 (d,
J ¼ 9 Hz, 2H), 7.54e7.63 (m, 1H), 7.69 (d, J ¼ 9 Hz, 2H),
7.76e7.81 (m, 1H), 8.19e8.33 (m, 2H), 10.05 (s, 1H), 12.52
(s, 1H). IR (KBr) n/cmꢀ1: 3301, 3035, 1730, 1645, 1512,
1154. ESI-MS m/z: 551 [M þ H]þ.
6.4.2. N-[1-(S )-(5-Methylbenzimidazol-2-yl)-2-methyl]
propyl-(R)-2-methoxycarbonylmethylhexanamide (4b)
White solid, yield: 85%; m.p. 162e165 ꢁC; [a]D25 ¼ ꢀ110.0
6.3.6. N-[1-(S )-[5-(Cyclohexylaminocarbonyl)
benzimidazol-2-yl]-2-methyl]propyl-(R)-2-tert-
butoxycarbonylmethylhexanamide (3f)
1
(c 0.5, MeOH). H NMR (DMSO-d6, 400 MHz) d: 0.66 (t,
White solid, yield: 90%; m.p. 156e158 ꢁC; [a]D25 ¼ ꢀ67.0
J ¼ 6.8 Hz, 3H), 0.78 (d, J ¼ 6.7 Hz, 3H), 0.92 (d,
(c 1, MeOH). 1H NMR (DMSO-d6, 300 MHz) d: 0.63 (t,
J ¼ 6.7 Hz, 3H), 1.02e1.39 (m, 6H), 2.18e2.24 (m, 1H),

2208
D. Zhang et al. / European Journal of Medicinal Chemistry 44 (2009) 2202e2210
2.32e2.39 (m, 1H), 2.54 (dd, J ¼ 9.3, 16 Hz, 1H), 2.73e2.78
(m, 1H), 3.55 (s, 3H), 4.85 (t, J ¼ 8.5 Hz, 1H), 6.95 (d,
J ¼ 8 Hz, 1H), 7.24e7.39 (m, 2H), 8.31 (d, J ¼ 9 Hz, 1H),
12.05 (s, 1H). IR (KBr) n/cmꢀ1: 3271, 3035, 1744, 1642,
1550, 1168. ESI-MS m/z: 374 [M þ H]þ.
7.68 (d, J ¼ 8 Hz, 1H), 7.92e8.10 (m, 2H), 8.35 (d,
J ¼ 8.6 Hz, 1H), 12.41 (s, 1H). IR (KBr) n/cmꢀ1: 3290,
3035, 1741, 1644, 1542, 1170. ESI-MS m/z: 485 [M þ H]þ.
6.4.7. N-[1-(S )-[5-(Piperidinocarbonyl)benzimidazol-2-yl]
-2-methyl]propyl-(R)-2-methoxycarbonylmethylhexanamide
(4g)
6.4.3. N-[1-(S )-(5-Methoxybenzimidazol-2-yl)-2-methyl]
propyl-(R)-2-methoxycarbonylmethylhexanamide (4c)
White solid, yield: 70%; m.p. 151e153 ꢁC; [a]D25 ¼ ꢀ94.0
White solid, yield: 65%; m.p. 75e77 ꢁC; [a]D25 ¼ ꢀ74.0 (c
0.5, MeOH). 1H NMR (DMSO-d6, 400 MHz) d: 0.62 (t,
J ¼ 6.9 Hz, 3H), 0.81 (d, J ¼ 6.6 Hz, 3H), 0.96 (d,
J ¼ 6.6 Hz, 3H), 1.03e1.38 (m, 6H), 1.45e1.63 (m, 6H),
2.23e2.28 (m, 1H), 2.35 (dd, J ¼ 5.2, 16 Hz, 1H), 2.55 (dd,
J ¼ 9.3, 16 Hz, 1H), 2.71e2.76 (m, 1H), 3.33e3.60 (m, 7H),
4.87 (t, J ¼ 8.5 Hz, 1H), 7.16 (m, 1H), 7.50 (br s, 2H), 8.34
(d, J ¼ 8.8 Hz, 1H), 12.38 (s, 1H). IR (KBr) n/cmꢀ1: 3326,
3136, 3035, 1734, 1625, 1573, 1176. ESI-MS m/z: 471
[M þ H]þ.
1
(c 0.5, MeOH). H NMR (DMSO-d6, 400 MHz) d: 0.66 (t,
J ¼ 6.7 Hz, 3H), 0.79 (d, J ¼ 6.7 Hz, 3H), 0.93 (d,
J ¼ 6.6 Hz, 3H), 1.02e1.39 (m, 6H), 2.18e2.25 (m, 1H),
2.35 (dd, J ¼ 5.2, 16 Hz, 1H), 2.54 (dd, J ¼ 9.3, 16 Hz, 1H),
2.73e2.77 (m, 1H), 3.55 (s, 1H), 3.76 (s, 3H), 4.82 (t,
J ¼ 8.5 Hz, 1H), 6.74e6.76 (m, 1H), 6.94 (d, J ¼ 1.7 Hz,
1H), 7.42 (d, J ¼ 8.5 Hz, 1H), 8.29 (d, J ¼ 9 Hz, 1H), 12.00
(s, 1H). IR (KBr) n/cmꢀ1: 3325, 3272, 3068, 1740, 1642,
1541, 1158. ESI-MS m/z: 390 [M þ H]þ.
6.5. General procedure for the synthesis of compounds
1ae1g
6.4.4. N-[1-(S )-[5-(Morpholinocarbonyl)benzimidazol-2-yl]-
2-methyl]propyl-(R)-2-methoxycarbonylmethylhexanamide
(4d)
To a methanol/tetrahydrofuran (6 mL, 1:1) solution of com-
pound 4 (1 mmol) was added 50% aqueous hydroxylamine
(10 mmol), followed by NaCN (50 mg). After 5 h, several
drops of acetic acid were added to adjust the pH of the reaction
mixture to 6. The solution was concentrated and the residue
was purified on silica gel with methylene dichloride/methanol
(20:1).
White solid, yield: 75%; m.p. 74e76 ꢁC, [a]D25 ¼ ꢀ77.0 (c
0.5, MeOH). 1H NMR (DMSO-d6, 400 MHz) d: 0.63 (t,
J ¼ 6.4 Hz, 3H), 0.82 (d, J ¼ 6.6 Hz, 3H), 0.95 (d,
J ¼ 6.7 Hz, 3H), 1.03e1.40 (m, 6H), 2.20e2.31 (m, 1H),
2.36 (dd, J ¼ 9, 16 Hz, 1H), 2.55e2.65 (m, 1H), 2.75e2.85
(m, 1H), 3.41e3.65 (m, 11H), 4.86 (t, J ¼ 8.4 Hz, 1H),
7.17e7.23 (m, 1H), 7.48e7.59 (m, 2H), 8.38 (d, J ¼ 8.8 Hz,
1H), 12.42 (s, 1H). IR (KBr) n/cmꢀ1: 3275, 3035, 1738,
1644, 1541, 1115. ESI-MS m/z: 473 [M þ H]þ.
6.5.1. (R)-2-Butyl-N4-hydroxy-N1-[1-(S )-(benzimidazol-2-yl)-
2-methyl]propylsuccinamide (1a)
White solid, yield: 76%; m.p. 132e134 ꢁC, [a]D25 ¼ ꢀ86.7
1
6.4.5. N-[1-(S )-[[5-(4-Methoxyanilino)carbonyl]
(c 0.3, MeOH). H NMR (DMSO-d6, 400 MHz) d: 0.65 (t,
benzimidazol-2-yl]-2-methyl]propyl-(R)-2-
methoxycarbonylmethylhexanamide (4e)
J ¼ 6.9 Hz, 3H), 0.80 (d, J ¼ 6.7 Hz, 3H), 0.94 (d,
J ¼ 6.7 Hz, 3H), 1.01e1.42 (m, 6H), 2.06 (dd, J ¼ 7.4,
14.5 Hz, 1H), 2.21e2.30 (m, 2H), 2.70e2.75 (m, 1H), 4.87
(t, J ¼ 8.4 Hz, 1H), 7.12e7.14 (m, 2H), 7.50 (br s, 2H). 13C
NMR (DMSO-d6, 100 MHz) d: 13.71, 18.78, 19.31, 22.10,
28.65, 31.80, 31.94, 35.15, 41.68, 53.07, 111.10, 121.61,
134.15, 154.83, 167.64, 173.93. IR (KBr) n/cmꢀ1: 3243,
3057, 2924, 1649, 1539. ESI-MS m/z (%): 384 ([M þ Na]þ,
20), 361 ([M þ H]þ, 100%), 328 (28). Anal. Calcd for
C19H28N4O3: C, 63.30; H, 7.83; N, 15.54. Found: C, 63.41;
H, 7.79; N, 15.37.
White solid, yield: 70%; m.p. 95e96 ꢁC; [a]D25 ¼ ꢀ71.0 (c
0.5, MeOH). 1H NMR (DMSO-d6, 400 MHz) d: 0.66 (t,
J ¼ 6.8 Hz, 3H), 0.81 (d, J ¼ 6.6 Hz, 3H), 0.96 (d,
J ¼ 6.7 Hz, 3H), 1.01e1.21 (m, 4H), 1.29e1.42 (m, 2H),
2.24e2.28 (m, 1H), 2.36 (dd, J ¼ 5.2, 16 Hz, 1H), 2.55 (dd,
J ¼ 9.3, 16 Hz, 1H), 2.75e2.79 (m, 1H), 3.56 (s, 3H), 3.75
(s, 3H), 4.90 (t, J ¼ 8.5 Hz, 1H), 6.92 (d, J ¼ 9 Hz, 2H),
7.54e7.63 (m, 1H), 7.70 (d, J ¼ 9 Hz, 2H), 7.78e7.81 (m,
1H), 8.07e8.21 (m, 1H), 8.37 (d, J ¼ 8.8 Hz), 10.05 (s, 1H),
12.46 (s, 1H). IR (KBr) n/cmꢀ1: 3324, 3035, 1739, 1643,
1511, 1171. ESI-MS m/z: 509 [M þ H]þ.
6.5.2. (R)-2-Butyl-N4-hydroxy-N1-[1-(S )-(5-methyl
benzimidazol-2-yl)-2-methyl]propylsuccinamide (1b)
White solid, yield: 65%; m.p. 134e135 ꢁC; [a]D20 ¼ ꢀ101.7
6.4.6. N-[1-(S )-[5-(Cyclohexylaminocarbonyl)
benzimidazol-2-yl]-2-methyl]propyl-(R)-2-
1
(c 0.3, MeOH). H NMR (DMSO-d6, 400 MHz) d: 0.66 (t,
methoxycarbonylmethylhexanamide (4f)
J ¼ 6.8 Hz, 3H), 0.80 (d, J ¼ 6.7 Hz, 3H), 0.93 (d,
J ¼ 6.7 Hz, 3H), 1.05e1.40 (m, 6H), 2.06 (dd, J ¼ 7.2,
14.4 Hz, 1H), 2.19e2.27 (m, 2H), 2.39 (s, 3H), 2.72e2.75
(m, 1H), 4.85 (t, J ¼ 8.4 Hz, 1H), 6.95 (d, J ¼ 7.8 Hz, 1H),
7.24e7.38 (m, 2H). 13C NMR (DMSO-d6, 100 MHz) d:
13.83, 18.89, 19.51, 21.32, 22.20, 28.77, 31.66, 32.03,
35.31, 41.84, 53.15, 111.35, 118.25, 123.15, 131.07, 134.05,
141.23, 154.53, 167.79, 174.00. IR (KBr) n/cmꢀ1: 3229,
White solid, yield: 70%; m.p. 92e94 ꢁC; [a]D25 ¼ ꢀ76.0 (c
0.5, MeOH). 1H NMR (DMSO-d6, 400 MHz) d: 0.65 (t,
J ¼ 7.0 Hz, 3H), 0.79 (d, J ¼ 6.6 Hz, 3H), 0.95 (d,
J ¼ 6.6 Hz, 3H), 1.01e1.42 (m, 12H), 1.70e1.83 (m, 4H),
2.22e2.27 (m, 1H), 2.36 (dd, J ¼ 5.2, 16 Hz, 1H), 2.54 (dd,
J ¼ 9.3, 16 Hz, 1H), 2.73e2.78 (m, 1H), 3.55 (s, 3H), 3.73e
3.84 (m, 1H), 4.88 (t, J ¼ 8.4 Hz, 1H), 7.48e7.54 (m, 1H),

D. Zhang et al. / European Journal of Medicinal Chemistry 44 (2009) 2202e2210
2209
3051, 2925, 1648, 1538. ESI-MS m/z (%): 375 ([M þ H]þ,
6.5.6. (R)-2-Butyl-N4-hydroxy-N1-[1-(S )-[[5-
(cyclohexylamino)carbonyl]benzimidazol-2-yl]-2-
methyl]propylsuccinamide (1f)
100%), 342 (40). Anal. Calcd for C20H30N4O3: C, 64.15; H,
8.07; N, 14.96. Found: C, 64.01; H, 7.98; N, 15.11.
White solid, yield: 73%; m.p. 220e222 ꢁC; [a]D20 ¼ ꢀ80.0
1
6.5.3. (R)-2-Butyl-N4-hydroxy-N1-[1-(S )-(5-methoxy
benzimidazol-2-yl)-2-methyl]propylsuccinamide (1c)
White solid, yield: 75%; m.p. 123e125 ꢁC; [a]D25 ¼ ꢀ85.0
(c 0.3, MeOH). H NMR (DMSO-d6, 400 MHz) d: 0.65 (t,
J ¼ 6.6 Hz, 3H), 0.80 (d, J ¼ 6.5 Hz, 3H), 0.95 (d,
J ¼ 6.6 Hz, 3H), 1.03e1.34 (m, 12H), 1.74e1.89 (m, 4H),
2.05 (dd, J ¼ 7.3, 14.6 Hz, 1H), 2.22e2.32 (m, 2H), 2.72e
2.75 (m, 1H), 3.73e3.80 (m, 1H), 4.87 (t, J ¼ 8.2 Hz, 1H),
7.47e7.55 (m, 1H), 7.68 (s, 1H), 7.90e8.12 (m, 2H). 13C
NMR (DMSO-d6, 100 MHz) d: 137.72, 18.77, 19.36, 22.04,
24.97, 25.28, 28.61, 31.51, 31.65, 32.49, 35.11, 41.70,
48.31, 53.14, 110.09, 118.08, 121.15, 128.83, 135.30,
1
(c 0.3, MeOH). H NMR (DMSO-d6, 400 MHz) d: 0.66 (t,
J ¼ 6.9 Hz, 3H), 0.79 (d, J ¼ 6.7 Hz, 3H), 0.93 (d,
J ¼ 6.6 Hz, 3H), 1.04e1.38 (m, 6H), 2.05 (dd, J ¼ 7.4,
14.5 Hz, 1H), 2.19e2.26 (m, 2H), 2.71e2.74 (m, 1H), 3.76
(s, 3H), 4.83 (t, J ¼ 8.4 Hz, 1H), 6.77 (s, 1H), 6.94 (br s,
1H), 7.40 (br s, 1H). 13C NMR (DMSO-d6, 100 MHz) d:
13.67, 18.77, 19.36, 22.06, 28.67, 31.86, 31.94, 35.19,
41.79, 53.10, 55.40, 110.70, 126.37, 126.56, 127.97, 142.44,
154.40, 155.32, 167.77, 173.95. IR (KBr) n/cmꢀ1: 3242,
3068, 2925, 1646, 1540. ESI-MS m/z (%): 391 ([M þ H]þ,
100%), 358 (2). Anal. Calcd for C20H30N4O4: C, 61.52; H,
7.74; N, 14.35. Found: C, 61.65; H, 7.79; N, 14.24.
142.25, 156.50, 165.87, 167.63, 174.00. IR (KBr) n/cmꢀ1
:
3336, 3280, 3035, 2920, 1644, 1617, 1543. ESI-MS m/z
(%): 486 ([M þ H]þ, 100%), 453 (32). Anal. Calcd for
C26H39N5O4: C, 64.31; H, 8.09; N, 14.42. Found: C, 64.22;
H, 7.85; N, 14.66.
6.5.7. (R)-2-Butyl-N4-hydroxy-N1-[1-(S )-[(5-
piperidinocarbonyl)benzimidazol-2-yl]-2-
methyl]propylsuccinamide (1g)
6.5.4. (R)-2-Butyl-N4-hydroxy-N1-[1-(S )-[5-
(morpholinocarbonyl)benzimidazol-2-yl]-2-
methyl]propylsuccinamide (1d)
White solid, yield: 77%; m.p. 138e140 ꢁC; [a]D20 ¼ ꢀ78.3
1
White solid, yield: 80%; m.p. 142e144 ꢁC; [a]D20 ¼ ꢀ70.0
(c 0.3, MeOH). H NMR (DMSO-d6, 400 MHz) d: 0.62 (t,
1
J ¼ 6.7 Hz, 3H), 0.81 (d, J ¼ 6.6 Hz, 3H), 0.96 (d,
J ¼ 6.6 Hz, 3H), 1.03e1.38 (m, 6H), 1.50e1.61 (m, 6H),
2.05 (dd, J ¼ 7.4, 14.5 Hz, 1H), 2.19e2.32 (m, 2H), 2.70e
2.77 (m, 1H), 3.33e3.60 (m, 4H), 4.87 (t, J ¼ 8.4 Hz, 1H),
7.15 (br s, 1H), 7.46e7.56 (m, 2H). 13C NMR (DMSO-d6,
100 MHz) d: 13.66, 18.80, 19.37, 22.06, 24.06, 25.63, 28.63,
31.58, 31.78, 35.10, 41.69, 53.22, 62.87, 112.25, 126.36,
126.56, 127.96, 129.08, 142.41, 156.39, 167.72, 169.71,
174.07. IR (KBr) n/cmꢀ1: 3201, 3035, 2921, 1646, 1607,
1540. ESI-MS m/z (%): 472 ([M þ H]þ, 100%), 439 (71),
411 (1). Anal. Calcd for C25H37N5O4: C, 63.67; H, 7.91; N,
14.85. Found: C, 63.58; H, 7.79; N, 14.98.
(c 0.3, MeOH). H NMR (DMSO-d6, 400 MHz) d: 0.63 (t,
J ¼ 6.5 Hz, 3H), 0.81 (d, J ¼ 6.6 Hz, 3H), 0.95 (d,
J ¼ 6.6 Hz, 3H), 1.00e1.40 (m, 6H), 2.05 (dd, J ¼ 7.4,
14 Hz, 1H), 2.20e2.31 (m, 2H), 2.72e2.75 (m, 1H), 3.51e
3.60 (m, 8H), 4.86 (t, J ¼ 8.3 Hz, 1H), 7.20 (d, J ¼ 7.8 Hz,
1H), 7.55 (br s, 2H), 8.34 (d, J ¼ 8.7 Hz, 1H). 13C NMR
(DMSO-d6, 100 MHz) d: 13 .75, 18.86, 19.43, 22.11, 28.66,
31.60, 31.65, 35.11, 41.60, 53.18, 62.85, 66.12, 110.11,
121.27, 126.38, 126.59, 128, 142.37, 156.70, 167.63, 169.92,
174.04. IR (KBr) n/cmꢀ1: 3243, 3035, 2920, 1646, 1540.
ESI-MS m/z (%): 474 ([M þ H]þ, 100%), 441 (58), 413(12).
Anal. Calcd for C24H35N5O5: C, 60.87; H, 7.45; N, 14.79.
Found: C, 60.97; H, 7.56; N, 14.57.
6.6. In vitro antibacterial activity evaluation
6.5.5. (R)-2-Butyl-N4-hydroxy-N1-[1-(S )-[[5-
(4-methoxyanilino)carbonyl]benzimidazol-2-yl]-2-
methyl]propylsuccinamide (1e)
The newly synthesized compounds were screened for their
antibacterial activity against S. aureus (CMCC26112), K.
pneumoniae (CMCC46117), and S. lutea (CMCC28001) using
broth microdilution method [16,17]. Each compound was
tested over a range of doubling dilution concentrations. The
MIC of a compound was determined according to the lowest
concentration that prevented visible growth of bacteria after
incubation at 37 ꢁC for 24 h. MullereHinton broth was used
as the test medium. Cefoperazone was used as a standard
drug (positive control). Bacterial strains and broth were bought
from National Institute for the Control of Pharmaceutical and
Biological Products.
White solid, yield: 70%; m.p. 201e203 ꢁC; [a]D20 ¼ ꢀ78.3
1
(c 0.3, MeOH). H NMR (DMSO-d6, 400 MHz) d: 0.65 (t,
J ¼ 6.4 Hz, 3H), 0.82 (d, J ¼ 6.0 Hz, 3H), 0.96 (d,
J ¼ 6.5 Hz, 3H), 1.04e1.37 (m, 6H), 2.06 (dd, J ¼ 6.8,
14.4 Hz, 1H), 2.21e2.41 (m, 2H), 2.73e2.76 (m, 1H), 3.75
(s, 3H), 4.89 (t, J ¼ 8.2 Hz, 1H), 6.93 (d, J ¼ 8.8 Hz, 2H),
7.54 (d, J ¼ 8 Hz, 1H), 7.70 (d, J ¼ 8 Hz, 2H), 7.78e7.80
(m, 1H), 8.23 (s, 1H). 13C NMR (DMSO-d6, 100 MHz) d:
13.74, 18.80, 19.38, 22.06, 28.63, 31.52, 31.75, 35.10,
41.68, 53.18, 55.15, 110.08, 113.66, 117.80, 120.80, 121.86,
127.86, 132.56, 135.78, 142.80, 155.33, 157.15, 165.60,
167.61, 174.04. IR (KBr) n/cmꢀ1: 3299, 3035, 2918, 1641,
1621, 1530. ESI-MS m/z (%): 510 ([M þ H]þ, 100%), 477
(39), 449 (1). Anal. Calcd for C27H35N5O5: C, 63.64; H,
6.92; N, 13.74. Found: C, 63.75; H, 7.02; N, 13.51.
Acknowledgements
This research was supported by National Key Research Pri-
ority Program of Science and Technology Ministry, PR China

2210
D. Zhang et al. / European Journal of Medicinal Chemistry 44 (2009) 2202e2210
[9] R. Jain, A. Sundram, S. Lopez, G. Neckermann, C. Wu, C. Hackbarth,
D. Chen, W. Wang, N.S. Ryder, B. Weidmann, D. Patel, J. Trias,
R. White, Z. Yuan, Bioorg. Med. Chem. Lett. 13 (2003) 4223e4228.
[10] C.J. Hackbarth, D.Z. Chen, J.G. Lewis, K. Clark, J.B. Mangold,
J.A. Cramer, P.S. Margolis, W. Wang, J. Koehn, C. Wu, S. Lopez,
G. Withers III, H. Gu, E. Dunn, R. Kulathila, S. Pan, W.L. Porter,
J. Jacobs, J. Trias, D.V. Patel, B. Weidmann, R.J. White, Z. Yuan, Anti-
microb. Agents Chemother. 46 (2002) 2752e2764.
(2003CCA027) and the Special Project of Science and Tech-
nology of Shandong Province, PR China (032090104).
References
[1] S.J. Aarons, I.W. Sutherland, A.M. Chakrabarty, M.P. Gallagher, Micro-
biology 143 (1997) 641e652.
[2] J.J. Gordon, B.K. Kelly, G.A. Miller, Nature 195 (1962) 701e702.
[3] D.Z. Chen, D.V. Patel, C.J. Hackbarth, W. Wang, G. Dreyer, D.C. Young,
P.S. Margolis, C. Wu, Z. Ni, J. Trias, R.J. White, Z. Yuan, Biochemistry
39 (2000) 1256e1262.
[11] R.B. Sparks, P. Polam, W. Zhu, M.L. Crawley, A. Takvorian, E. McLaughlin,
M. Wei, P.J. Ala, L. Gonneville, N. Taylor, Y. Li, R. Wynn, T.C. Burn,
P.C. Liu, A.P. Combs, Bioorg. Med. Chem. Lett. 17 (2007) 736e740.
[12] D.T. Zhang, L.D. Tang, G.Y. Duan, G.L. Zhao, W.R. Xu, L.J. Meng,
J.W. Wang, Chem. Res. Chinese U 22 (2006) 584e588.
[4] M.D. Lee, Y. She, M.J. Soskis, C.P. Borella, J.R. Gardner, P.A. Hayes,
B.M. Dy, M.L. Heaney, M.R. Philips, W.G. Bornmann, F.M. Sirotnak,
D.A. Scheinberg, J. Clin. Invest. 114 (2004) 1107e1116.
[5] M.K. Chan, W.M. Gong, P.T.R. Rajagopalan, Biochemistry 36 (1997)
13904e13909.
[13] Z.J. Kamiski, Synthesis (1987) 917e920.
[14] C.Y. Ho, E. Strobel, J. Ralbovsky, R.A. Galemmo, J. Org. Chem. 70
(2005) 4873e4875.
[15] J.J. Chen, Y. Zhang, S.Hammond, N.Dewdney, T. Ho,X. Lin, M.F. Browner,
A.L. Castelhano, Bioorg. Med. Chem. Lett. 13 (1996) 1601e1606.
[16] K.G. Desai, K.R. Desai, J. Saudi Chem. Soc. 3 (2006) 631e640.
[17] K.G. Desai, K.R. Desai, J. Sulfur Chem. 4 (2006) 315e328.
[18] G. Giacomelli, A. Porcheddu, M. Salaris, Org. Lett. 15 (2003) 2715e2717.
[19] A.S. Reddy, M.S. Kumar, G.R. Reddy, Tetrahedron Lett. 33 (2000)
6285e6288.
[6] G. Giglone, A. Serero, M. Pierre, EMBO J. 19 (2000) 5916e5929.
[7] J.M. Clements, P. Beckett, A. Brown, G. Catlin, M. Lobell, S. Palan,
W. Thomas, M. Whittaker, P.J. Baker, F. Rodgers, V. Barynin,
D.W. Rice, M.G. Hunter, Antimicrob. Agents Chemother. 45 (2001)
563e570.
[8] B.J. Broughton, P. Chaplen, W.A. Freeman, P.J. Warren,
K.R.H. Wooldridge, D.E. Wright, Studies concerning the antibiotic acti-
nonin. Part VIII. Structureeactivity relationships in the actinonin series,
J. Chem. Soc., Perkin Trans. 1 (1975) 857e860.
[20] D.E. Levy, F. Lapierre, W. Liang, W. Ye, C.W. Lange, X. Li,
D. Grobelny, M. Terrell, K. Holme, A. Nadzan, R.E. Galardy, J. Med.
Chem. 2 (1998) 199e223.