Novel clarithromycin analogs with C-4′′ 2-arylbenzimidazolyl bishydrazide side chain: Synthesis and antibacterial evaluation

Article abstract of DOI:10.2174/157018011797655269

A series of novel 4′′-O-2-arylbenzimidazolyl derivatives of clarithromycin were synthesized and evaluated. These 4′′-O-2- arylbenzimidazolyl derivatives demonstrated excellent activity against erythromycin-susceptible strains and showed remarkably improved activity against erythromycin-resistant strains compared with the references. In particular, compound 7c, which possesses the terminal 2-(2-methoxyphenyl)benzimidazolyl group on the C-4′′ bishydrazide side chain, not only presented the most potent activity against erythromycin-susceptible Streptococcus pneumoniae ATCC49619 and Staphylococcus aureus ATCC25923, exhibiting 4-fold and 4-fold higher efficacy than the parent clarithromycin, but also displayed the highest activity against erythromycin-resistant Streptococcus pneumoniae expressing the mef gene and the erm gene, which was 133-fold and 32-fold better than clarithromycin or azithromycin, respectively.

Full text of DOI:10.2174/157018011797655269

966
Letters in Drug Design & Discovery, 2011, 8, 966-971
Novel Clarithromycin Analogs with C-4ꢀ 2-arylbenzimidazolyl Bishy-
drazide Side Chain: Synthesis and Antibacterial Evaluation
Yunkun Qi1, Ruixin Ma2, Xin Li1, Yue Hu3, Siti Ma1, Chao Cong1, Xiaodong Ma1, Wenping Cui1
and Shutao Ma*,1
1Department of Medicinal Chemistry, School of Pharmaceutical Sciences, Shandong University, 44 West Culture Road,
Jinan 250012, P. R. China
2Affiliated Hospital of Medical College, Qingdao University, Qingdao 266003, P. R. China
3Marine College, Shandong University at Weihai, 180 West Culture Road, Weihai Shandon 264209, P. R. China
Received April 28, 2011: Revised September 05, 2011: Accepted September 05, 2011
Abstract: A series of novel 4ꢀ-O-2-arylbenzimidazolyl derivatives of clarithromycin were synthesized and evaluated.
These 4ꢀ-O-2-arylbenzimidazolyl derivatives demonstrated excellent activity against erythromycin-susceptible strains and
showed remarkably improved activity against erythromycin-resistant strains compared with the references. In particular,
compound 7c, which possesses the terminal 2-(2-methoxyphenyl)benzimidazolyl group on the C-4ꢀ bishydrazide side
chain, not only presented the most potent activity against erythromycin-susceptible Streptococcus pneumoniae
ATCC49619 and Staphylococcus aureus ATCC25923, exhibiting 4-fold and 4-fold higher efficacy than the parent
clarithromycin, but also displayed the highest activity against erythromycin-resistant Streptococcus pneumoniae
expressing the mef gene and the erm gene, which was 133-fold and 32-fold better than clarithromycin or azithromycin,
respectively.
Keywords: Antibacterial activity, Benzimidazolyl derivatives, Carbamates, Clarithromycin, Resistance, Synthesis.
INTRODUCTION
transporting them out of bacterial cytoplasm, conferring M
resistance [7, 8].
Erythromycin A (EMA) was well known for its broad-
spectrum antimicrobial activity and widely prescribed for the
patients intolerable of ꢀ-lactam antibiotics. However, EMA
readily loses its activity in acid condition in stomach for
degradation, which hampers its therapeutic effectiveness
greatly [1]. Structural modifications aimed to overcome the
defects of the first-generation macrolides gave rise to the
second-generation macrolides, such as clarithromycin
(CAM) [2] (Fig. 1) and azithromycin (AZM) [3]. CAM and
AZM were used widely for the treatment of upper and lower
respiratory tract infections and genital infections owing to
their good stability, superior antibacterial activity, improved
Significant efforts have been made to combat with the
bacterial resistance by the structural modification of the
existing macrolides, which has resulted in the discovery of
the third-generation macrolides (e.g. telithromycin) with
significantly improved activity against the resistant strains
[9]. The study of high-resolution X-ray co-crystal structures
has revealed that telithromycin can interact with a secondary
binding site A752 in domain II of the 23S rRNA by its C-
11,12-cyclic carbamate side chain in addition to the main
interaction with A2058 [10]. Other new generation
macrolides, especially, C-4ꢀ modified macrolides such as
CP-544372 (Fig. 1), demonstrate improved activity against
resistant bacteria as well [11]. The C-4" elongated side chain
of CP-544372, the distance of which is six atoms from the
4ꢀ-oxygen atom to the terminal benzene ring, can reach the
binding site of chloramphenicol, leading to an additionally
affinity for bacterial ribosome [12]. In addition, several
series of novel 4"-carbamates of AZM and CAM with
greatly improved activity against resistant bacteria were
synthesized in our previous work, the length of their C-4ꢀ
side chains having a distance of three to four atoms from the
4ꢀ-oxygen atom to the terminal benzene ring [13–16].
Therefore, the C-4ꢀ side chains with three to six atoms from
the 4ꢀ-oxygen atom to the terminal aromatic ring could play
an important role in overcoming bacterial mechanisms of
resistance.
pharmacokinetics
and
established
safety
profiles.
Unfortunately, the therapeutic effects of these macrolides
have been severely threatened by increasing bacterial
resistance [4–6]. Two of the commonest mechanisms of
macrolide resistance are erm-encoded methylation of 23S
rRNA in the ribosomal 50S subunit and mef-encoded active
efflux. The methyltransferase encoded by the erm gene can
modify the key nucleotide A2058 in domain V of the 23S
rRNA through mono- or di-methylation, which can weaken
the affinity of macrolides for the resistant ribosomes, leading
to the MLSB (macrolide-lincosamide-streptogramin B)
resistance. In contrast, the efflux pump encoded by mef gene
can limit the steady-state accumulation of macrolides by
On the basis of the consideration detailed above, we
designed and synthesized a series of novel 4ꢀ-O-2-
arylbenzimidazolyl derivatives of CAM with four atoms
from the 4ꢀ-oxygen atom to the terminal aromatic ring,
*Address correspondence to this author at the Department of Medicinal
Chemistry, School of Pharmaceutical Sciences, Shandong University, 44
West Culture Road, Jinan 250012, P. R. China; Tel: +86 531 88382009;
Fax: +86 531 88382548; E-mail: mashutao@sdu.edu.cn
1570-1808/11 $58.00+.00
© 2011 Bentham Science Publishers

C-4ꢀ Benzimidazolyl Derivatives
Letters in Drug Design & Discovery, 2011, Vol. 8, No. 10 967
N
N
O
H2N
HO
HO
OH
HO
OMe
O
O
O
HO
O
HO
12
HO
O
O
O
O
O
O
O
N
O
O
N
O
Clarithromycin (CAM)
H
OH
OMe
OMe
OCH3
CP-544372
Fig. (1). Structures of clarithromycin and CP-544372.
which are characterized by the C-4ꢀ bishydrazide linker and
the terminal benzimidazolyl groups. The benzimidazolyl
groups are chosen as the terminal groups in anticipation of
inheriting their beneficial antibacterial profiles mainly due to
the benzimidazole derivatives having a variety of biological
activities such as antibacterial and antiviral activity [17, 18].
arylbenzimidazolyl derivatives 7a–g were obtained by
coupling of the hydrazide 6 with the corresponding 2-
arylbenzimidazole-5-formyl chlorides 4a–g, and the
subsequent deprotection of 2ꢀ-O-acetyl group at 55°C in
methanol in 63–70% yields. The structures of these desired
compounds were confirmed by MS, IR and 1H NMR.
Antibacterial Activity
RESULTS AND DISCUSSION
Chemistry
The in vitro antibacterial activity (MICs) of the 4ꢀ-O-2-
arylbenzimidazolyl derivatives of CAM 7a–g, as well as the
references EMA, CAM and AZM, against five phenotypes of
Gram-positive strains were evaluated using broth micro-
dilution method. Streptococcus pneumoniae ATCC49619
and Staphylococcus aureus ATCC25923 are two
erythromycin-susceptible strains. S. pneumoniae B1, S.
pneumoniae A22072 and S. pneumoniae AB11 are three
erythromycin-resistant strains, whose resistance was encoded
by the erm gene, the mef gene, and both the erm and mef
genes, respectively.
The 2-arylbenzimidazole-5-formyl chlorides (4) were
synthesized as outlined in Scheme 1. The addition reaction
of 2-arylbenzaldehyde with sodium pyrosulfite provided the
addition product (2) in 72–83% yields. The condensation of
2 with 3,4-diaminobenzoic acid in DMF at 130 °C gave 2-
arylbenzimidazole-5-carboxylic acid (3) in yields ranging
from 68–75%, which was subsequently converted to 2-
arylbenzimidazole-5-formyl chlorides (4a–g) in the presence
of thionyl chloride.
The novel 4ꢀ-O-2-arylbenzimidazolyl derivatives of
CAM (7a–g) were synthesized from CAM as the starting
material (Scheme 2). 2ꢀ-O-Acetylation of CAM with acetic
anhydride in the presence of triethylamine (Et3N) was
followed by introduction of C-4ꢀ acylimidazole group
utilizing 1,1ꢀ-carbonyldiimidazole (CDI) in toluene at 65°C
for 12 h to generate 4ꢀ-O-acylimidazolide (5) in 84% yield.
And then, 4ꢀ-O-acylimidazolide 5 was subjected to the
reaction with hydrazine hydrate in the presence of 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU), affording clarithro-
mycin hydrazide (6) in 86% yield. The desired 4ꢀ-O-2-
As shown in Table 1, all of the 4ꢀ-O-2-arylbenz-
imidazolyl derivatives exhibited good activity against
erythromycin-susceptible S. pneumoniae ATCC49619 and S.
aureus ATCC25923, and some of them showed excellent
MIC values in the range of 0.03–0.12 μg/mL better than or
comparable to EMA, CAM and AZM. Among them,
compounds 7a, 7c and 7e displayed the most potent activity
(0.03 μg/mL) against erythromycin-susceptible S.
pneumoniae ATCC49619 better than the references, and
compound 7c displayed the highest activity (0.03 μg/mL)
against erythromycin-susceptible S. aureus ATCC25923
O
HOOC
NH2
HOOC
N
b
c
N
Cl
N
SO3Na
CHOH
NH2
R1
R1
N
H
H
R1
3,4-diaminobenzoic acid
3
4
4a R1 = hydrogen
4b R1 = 4-methyl
4c R1 = 2-methoxyl
4d R1 = 4-methoxyl
4e R1 = 4-chloro
4f R1 = 4-trifluoromethyl
4g R1 = 4-nitro
a
R1
2
CHO
2-arylbenzaldehyde
Scheme 1. Reagents and conditions: (a) C2H5OH, Na2S2O5, H2O, rt, 1–1.5 h, 72–83%; (b) DMF, 130°C, 6 h, 68–75%; (c) SOCl2, reflux, 8 h.

968 Letters in Drug Design & Discovery, 2011, Vol. 8, No. 10
Qi et al.
N
O
N
AcO
OMe
HO
OMe
O
O
HO
HO
HO
HO
O
O
O
a, b
c
O
O
O
O
O
O
O
O
O
OH
OMe
O
N
N
OMe
CAM
5
N
N
O
7a R2 = phenyl
AcO
OMe
7b R2 = 4-methylphenyl
7c R2 = 2-methoxyphenyl
7d R2 = 4-methoxyphenyl
7e R2 = 4-chlorophenyl
O
HO
OMe
O
HO
HO
HO
O
O
O
d
7f R2 = 4-trifluoromethylphenyl
7g R2 = 4-nitrophenyl
HO
O
O
O
O
O
O
O
O
O
N
O
O
NHNH2
O
NHNH
O
R2
OMe
6
OMe
7
N
H
Scheme 2. Reagents and conditions: (a) Ac2O, Et3N, CH2Cl2, rt, 24 h; (b) CDI, toluene, 65°C, 12 h, 84% for two steps; (c) 80% hydrazine
hydrate, DBU, DMF, rt, 24 h, 86%; (d) 2-arylbenzimidazole-5-formyl chlorides 4a–4g, THF, rt 4–6h; CH3OH, reflux, 8 h, 64–70% for two
steps.
Table 1. In Vitro Antibacterial Activity of 4ꢀ-O-2-arylbenzimidazolyl Derivatives of CAM
MICs (μg/mL)
Compounds/Strains
S. pneumoniae
S. pneumoniae
S. pneumoniae
S. pneumoniae
S. aureus
ATCC49619a
B1b
A22072c
AB11d
ATCC25923e
EMA
CAM
AZM
7a
0.12
0.12
0.12
0.03
0.12
0.03
0.12
0.03
0.25
0.25
128
128
128
8
8
256
128
256
16
0.12
0.12
0.12
0.25
0.25
0.03
0.25
0.5
4
4
0.03
0.03
0.03
0.03
0.03
0.06
0.03
7b
2
16
7c
2
16
7d
4
16
7e
8
16
7f
8
8
0.5
7g
16
16
1
aS. pneumoniae ATCC49619 : erythromycin-susceptible strain.
bS. pneumoniae B1: erythromycin-resistant strain encoded by the erm gene.
cS. pneumoniae A22072: erythromycin-resistant strain encoded by the mef gene.
dS. pneumoniae AB11: erythromycin-resistant strain encoded by the erm and mef genes.
eS. aureus ATCC25923: erythromycin-susceptible strain.
higher than the references. The most active compound 7c
with the terminal 2-(2-methoxyphenyl)benzimidazolyl group
on the C-4ꢀ bishydrazide side chain against the tested
erythromycin-susceptible S. pneumoniae ATCC49619 and S.
aureus ATCC25923 showed 4-fold and 4-fold higher
activity than the parent CAM, respectively. On the other
hand, all of the 4ꢀ-O-benzimidazolyl clarithromycin
derivatives
exhibited
improved
activity
against
erythromycin-resistant S. pneumonia compared with the
references. Among them, compounds 7a–e and 7g had the
most potent activity (0.03 μg/mL) against S. pneumoniae
A22072 expressing the mef gene, showing 133-fold and 267-
fold higher activity than CAM and ERM, and compounds 7b
and 7c showed the most improved activity (2 μg/mL) against

C-4ꢀ Benzimidazolyl Derivatives
Letters in Drug Design & Discovery, 2011, Vol. 8, No. 10 969
erythromycin-resistant S. pneumoniae B1 expressing the erm
gene, showing 64-fold better activity than the references
(128 μg/mL). Above all, compound 7c was the most
effective against the erythromycin-resistant strains
expressing both the erm gene and the mef gene. These results
suggest that the introduction of the bishydrazide side chains
with the terminal benzimidazolyl groups into the C-4ꢀ
position of CAM can retain or increase the activity against
erythromycin-susceptible strains and improve remarkably
activity against erythromycin-resistant strains in comparison
with the references.
resulting solution was allowed to stir for 1–3 h at room
temperature and then for 3–4 h at 0 °C. The precipitate was
collected and washed with EtOH to provide the addition
products (2) as solids in yields ranging from 72% to 83%.
A solution of 3,4-diaminobenzoic acid (0.62g, 4.00
mmol) and the addition products 2 (2.00 mmol) in DMF (5
mL) was stirred at 130 °C for 6–12 h. After the completion
of the reaction, the reaction solution was cooled to room
temperature and added water (15 mL). The precipitate was
collected and washed to give 2-arylbenzimidazole-5-
carboxylic acids (3a–g). The yields were within the range of
68–75%. Some of the 2-substituted benzimidazole-5-
carboxylic acids are as followed.
In
conclusion,
novel
4ꢀ-O-2-arylbenzimidazolyl
derivatives of CAM were synthesized and evaluated for their
in vitro antibacterial activities. These 4ꢀ-O-2-arylbenzimida-
zolyl derivatives showed high activity against the
erythromycin-susceptible strains better than EMA, CAM and
AZM, and greatly improved activity against the erythromycin-
resistant strains compared with the references. In particular,
compound 7c with the terminal 2-(2-methoxyphenyl)
benzimidazolyl group on the C-4ꢀ bishydrazide side chains
displayed the most potent activity against not only
erythromycin-susceptible S. pneumoniae ATCC49619 and S.
aureus ATCC25923, but also erythromycin-resistant S.
pneumoniae expressing the erm gene and the mef gene. It is
notable that the terminal benzimidazolyl groups on the C-4ꢀ
bishydrazide side chains are important in increasing the
activity against erythromycin-susceptible strains, especially
erythromycin-resistant strains.
2-Phenyl-1H-benzimidazole-5-carbohydrazide (3a)
Yellow powder, yield 74.5%, mp 240–244 °C, TLC Rf =
0.12 (methanol/dichlormethane, 1:10); IR (KBr): 3064,
2928, 1899, 1663, 1626, 1541, 1482, 1464, 1385, 1316,
1
1294, 1214, 1103, 1028 cmꢁ ; 1H NMR (400 MHz, DMSO):
ꢀ 13.26 (s, 1H), 12.74 (s, 1H), 8.24–8.21 (m, 3H), 7.89–7.86
(m, 1H), 7.70–7.67 (m, 1H), 7.62–7.57 (m, 3H); MS (ESI)
m/z calcd. for C14H10N2O2 238.1, found [M+H]+ 239.3.
2-(4-Methoxyphenyl)-1H-benzimidazole-5-carboxylic acid
(3d)
Yellow powder, yield 71.8%, mp 142–144 °C, TLC Rf =
0.10 (methanol/dichlormethane, 1:10); IR (KBr): 3370,
3070, 2993, 2932, 2839, 2560, 1903, 1667, 1611, 1582,
1499, 1466, 1442, 1422, 1383, 1298, 1260, 1183, 1115,
1
1
1100, 1029 cmꢁ ; H NMR (400 MHz, DMSO): ꢀ 13.03 (s,
1H), 12.69 (s, 1H), 8.17–8.14 (m, 3H), 7.85–7.82 (m, 1H),
7.62 (s, 1H), 7.16–7.13 (m, 2H), 3.86 (s, 3H); MS (ESI) m/z
calcd. for C15H12N2O3 268.1, found [M+H]+ 269.4.
EXPERIMENTAL
All necessary solvents were purified prior to use, unless
noted otherwise. Reactions were monitored by thin-layer
chromatography (TLC) using 0.25-mm pre-coated silica gel
plates (Qingdao Yumingyuan silica gel reagent factory,
Shandong, China, YUYUAN). Flash chromatography was
performed with the indicated solvents using silica gel 60
(particle size 0.040–0.063 mm, Qingdao Yumingyuan silica
gel reagent factory, Shandong, China, YUYUAN). Infrared
spectra were recorded on KBr pellets using Nicolet Nexus
2-(4-Chlorophenyl)-1H-benzimidazole-5-carboxylic
(3e)
acid
Light yellow powder, yield 68.3%, mp 192–194 °C, TLC
Rf = 0.10 (methanol/dichlormethane, 1:10); IR (KBr): 3185,
3076, 2928, 2871, 2806, 2498, 1908, 1663, 1625, 1597,
1484, 1438, 1417, 1386, 1321, 1300, 1237, 1201, 1217,
1
1190, 1102, 1090, 1012 cmꢁ ; 1H NMR (400 MHz, DMSO):
1
470FT-IR spectrometer (Wisconsin, USA). H NMR spectra
ꢀ 13.14 (m, 2H), 8.23–8.19 (m, 3H), 7.88–7.85 (m, 1H),
7.68–7.63 (m, 3H); MS (ESI) m/z calcd. for C14H9ClN2O2
272.0, found [M+H]+ 273.3.
were recorded on Bruker Avance DRX 400 or 600
spectrometers (Bruker, Switzerlands) at ambient temperature
(TMS as internal standard of chemical shifts). Mass spectra
were recorded on API 4000 instrument (Applied Biosystems,
Connecticut, USA). Melting points are uncorrected and were
determined on an X-6 melting point apparatus (Beijing
Tianchengwode Biotech Co. Ltd, Beijing, China). CAM was
used as starting material from Nexchem Pharmaceutical Co.,
Ltd. All final compounds were >95% analytical purity by
HPLC using phosphate buffer (1000 mL of 0.067 M KH2PO4
was added 2 mL Et3N and adjusted to pH 5.5 using
phosphonic acid)–CH3CN (6:4) as eluant at the flow rate of 1
mL/min.
2-(4-Trifluormethyl)-1H-benzimidazole-5-carboxylic acid
(3f)
Light yellow powder, yield 73.2%, mp 162–164 °C, TLC
Rf = 0.10 (methanol/dichlormethane, 1:10); IR (KBr): 3165,
2976, 1926, 1668, 1621, 1585, 1552, 1491, 1451,1424, 1378,
1
1327, 1294, 1226, 1170, 1121, 1086, 1068, 1048, 1016 cmꢁ ;
1H NMR (400 MHz, DMSO): ꢀ13.47 (m, 1H), 12.78 (m,
1H), 8.43–8.40 (m, 2H), 8.31–8.16 (m, 1H), 7.98–7.89 (m,
2H), 7.77–7.66 (m, 2H); MS (ESI) m/z calcd. for
C15H9F3N2O2 306.1, found [M+H]+ 307.3.
General Procedure for the Preparation of 2-
Arylbenzimidazole-5-Carboxylic Acids 3a–g
General Procedure for the Preparation of 2-
Arylbenzimidazole-5-Formyl Chlorides 4a–4g
To a solution of substituted benzaldehyde (1.50 mmol) in
absolute EtOH (50 mL) was added dropwise sodium
pyrosulfite (1.60 g, 8.00 mmol) in water (3 mL). The
A mixture of 2-arylbenzimidazole-5-carboxylic acids 3a–
g (1.2mml) and SOCl2 (4 ml) was refluxed for 8 h. After the
completion of the reaction, the reaction mixture was

970 Letters in Drug Design & Discovery, 2011, Vol. 8, No. 10
Qi et al.
concentrated in vacuo to afford the corresponding acyl
chlorides of 2-arylbenzimidazole-5-formyl chlorides 4a–4g
as solids in quantitative yields.
2.37 (m, 7H), 2.17–2.16 (m, 3H), 1.87–1.86 (m, 2H), 1.63–
1.60 (m, 2H), 1.42–1.41 (m, 4H), 1.19–1.17 (m, 12H), 1.11–
1.08 (m, 14H), 0.89–0.88 (m, 3H); MS (ESI) m/z calcd. for
C54H81N5O15 1039.6, found [M+H]+ 1041.0.
4ꢀ-O-(2-(2-Methoxyphenyl)-1H-benzimidazole-5-
carbonyl)hydrazinecarbonylclarithromycin (7c)
General Procedure for the Preparation of 4ꢀ-O-2-
Aylbenzimidazolyl Derivatives of CAM (7a–g)
White solid, yield 63.2%, mp 188–192 °C, TLC Rf = 0.08
(methanol/dichlormethane, 1:10); IR (KBr): 3435, 2973,
2939, 2834, 2786, 1734, 1689, 1624, 1605, 1584, 1530,
1472, 1379, 1316, 1276, 1244, 1212, 1171, 1110, 1072,
To a solution of 5 (1.00 g, 1.12 mmol) in DMF (15 mL)
was added DBU (0.50 mL, 3.41 mmol) and 80% hydrazine
hydrate (1.00 mL, 19.18 mmol). The resulting solution was
stirred for 7 h at room temperature. The reaction was
quenched with water (30 mL) and the aqueous layer was
extracted with ethyl acetate (3 ꢀ 20 mL). The combined
organic layers were washed with brine, and were dried over
anhydrous Na2SO4 and, filtered. The filtrate was
concentrated in vacuo to afford 0.82g (85.5%) of hydrazide 6
as white foam.
1
1
1050, 1015 cmꢁ ; H NMR (600 MHz, CDCl3): ꢁ 8.13–8.11
(m, 1H), 7.99–7.97 (m, 1H), 7.78–7.74 (m, 2H), 7.67–7.65
(m, 1H), 7.49–7.45 (m, 1H), 7.07–7.04 (m, 2H), 5.07–5.06
(m, 1H), 4.97–4.96 (m, 1H), 4.80–4.78 (m, 2H), 4.61–4.58
(m, 1H), 4.40–4.39 (m, 1H), 4.01–4.00 (m, 2H), 3.78–3.77
(m, 2H), 3.31–3.28 (m, 3H), 3.21–3.19 (m, 2H), 3.04–3.02
(m, 3H), 3.01–3.00 (m, 1H), 2.91–2.90 (m, 1H), 2.43–2.41
(m, 1H), 2.30–2.28 (m, 6H), 2.17 (m, 6H), 1.72–1.70 (m,
2H), 1.63–1.62 (m, 2H), 1.46–1.45 (m, 4H), 1.23–1.20 (m,
15H), 1.13–1.12 (m, 12H), 0.86–0.84 (m, 3H); MS (ESI) m/z
calcd. for C54H81N5O16 1055.6, found [M+H]+ 1056.8.
To a solution of 6 (0.81 g, 1.00 mmol) in THF (15 mL)
was added corresponding 2-arylbenzimidazole-5-formyl
chlorides 4a–4g (1.20 mmol). The resulting solution was
stirred for 4–6 h at room temperature. After concentrating
the reaction solution in vacuo, the residue was dissolved in
ethyl acetate (20 mL) and the organic layer was washed with
saturated sodium bicarbonate (2 ꢀ 10 mL). The organic layer
was dried over anhydrous Na2SO4 and, filtered. The filtrate
was concentrated in vacuo to afford white foam. The crude
product in methanol (30 mL) was heated to 75 °C and stirred
for 8 h at the same temperature. After concentrating the
reaction solution in vacuo, the residue was purified by flash
chromatography (dichloromethane/methanol, 40:1) to give
4ꢀ-O-2-arylbenzimidazolyl derivatives of CAM 7a–g in
yields ranging from 64% to 70%.
4ꢀ-O-(2-(4-Methoxyphenyl)-1H-benzimidazole-5-
carbonyl)hydrazinecarbonylclarithromycin (7d)
White solid, yield 68.1%, mp 186–191 °C, TLC Rf = 0.08
(methanol/dichlormethane, 1:10); IR (KBr): 3338, 2973,
2938, 2835, 2787, 1735, 1690, 1613, 1580, 1493, 1457,
1379, 1349, 1281, 1254, 1220, 1174, 1110, 1072, 1051,
1
1
1033, 1014 cmꢁ ; H NMR (600 MHz, CDCl3): ꢁ 8.13–8.11
(m, 1H), 7.93–7.92 (m, 4H), 7.64–7.62 (m, 1H), 6.89–6.88
(m, 2H), 5.07–5.05 (m, 1H), 4.96–4.95 (m, 1H), 4.81–4.79
(m, 1H), 4.60–4.58 (m, 1H), 4.53–4.52 (m, 1H), 4.37–4.36
(m, 1H), 4.00–3.99 (m, 1H), 3.88–3.85 (m, 5H), 3.34–3.31
(m, 3H), 3.20–3.18 (m, 2H), 2.96–2.95 (m, 6H), 2.34–2.31
(m, 3H), 2.18–2.17 (m, 6H), 1.85–1.83 (m, 3H), 1.41–1.40
(m, 2H), 1.39–1.38 (m, 4H), 1.20–1.19 (m, 12H), 1.13–1.12
(m, 12H), 0.91–0.89 (m, 6H); MS (ESI) m/z calcd. for
C54H81N5O16 1055.6, found [M+H]+ 1057.0.
4ꢀ-O-(2-Phenyl-1H-benzimidazole-5-
carbonyl)hydrazinecarbonylclarithromycin (7a)
White solid, yield 65.8%, mp 190–195 °C, TLC Rf = 0.08
(methanol/dichlormethane, 1:10); IR (KBr): 3447, 2974,
2939, 2881, 2833, 2788, 1734, 1689, 1627, 1541, 1459,
1
1379, 1348, 1280, 1220, 1171, 1110, 1072, 1051, 1014 cmꢁ ;
1H NMR (600 MHz, CDCl3): ꢁ 8.29–8.26 (m, 2H), 8.11 (s,
1H), 7.94–7.93 (m, 2H), 7.72–7.71 (m, 1H), 7.63–7.61 (m,
2H), 7.32–7.30 (m, 1H), 5.06–5.05 (m, 1H), 4.95–4.93 (m,
1H), 4.60–4.59 (m, 1H), 4.51–4.50 (m, 1H), 4.37–4.35 (m,
1H), 4.01 –3.99 (m, 1H), 3.76–3.74 (m, 2H), 3.67–3.66 (m,
2H), 3.30–3.29 (m, 3H), 3.18–3.16 (m, 2H), 3.03–3.00 (m,
6H), 2.28–2.26 (m, 6H), 2.20–2.17 (m, 4H), 1.93–1.91 (m,
2H), 1.37–1.36 (m, 4H), 1.19–1.18 (m, 14H), 1.13–1.12 (m,
14H), 0.84–0.83 (m, 3H); MS (ESI) m/z calcd. for
C53H79N5O15 1025.6, found [M+H]+ 1026.9.
4ꢀ-O-(2-(4-Chlorophenyl)-1H-benzimidazole-5-
carbonyl)hydrazinecarbonylclarithromycin (7e)
White solid, yield 69.5%, mp 178–183 °C, TLC Rf = 0.08
(methanol/dichlormethane, 1:10); IR (KBr): 3296, 2974,
2939, 2833, 2788, 1734, 1691, 1626, 1604, 1458, 1417,
1
1379, 1331, 1285, 1218, 1171, 1109, 1071, 1052, 1014 cmꢁ ;
1H NMR (600 MHz, CDCl3): ꢁ 8.13–8.11 (m, 3H), 8.00–7.99
(m, 1H), 7.96–7.95 (m, 1H), 7.72–7.70 (m, 1H), 7.55–7.53
(m, 2H), 5.06–5.05 (m, 1H), 4.62–4.61 (m, 1H), 4.51–4.50
(m, 1H), 4.39–4.38 (m, 1H), 4.01–4.00 (m, 1H), 3.77–3.76
(m, 2H), 3.64–3.63 (m, 2H), 3.33–3.31 (m, 3H), 3.18–3.17
(m, 2H), 3.04–3.03 (m, 6H), 2.89–2.87 (m, 1H), 2.57–2.56
(m, 2H), 2.30–2.28 (m, 6H), 2.17–2.15 (m, 1H), 1.85–1.84
(m, 2H), 1.71–1.69 (m, 2H), 1.48–1.47 (m, 2H), 1.38–1.36
(m, 2H), 1.19–1.12 (m, 27H), 0.89–0.88 (m, 3H); MS (ESI)
m/z calcd. for C53H78ClN5O15 1059.5, found [M+H]+ 1060.8.
4ꢀ-O-(2-(4-Methylphenyl)-1H-benzimidazole-5-
carbonyl)hydrazinecarbonylclarithromycin (7b)
White solid, yield 64.5%, mp 188–194 °C, TLC Rf = 0.08
(methanol/dichlormethane, 1:10); IR (KBr): 3292, 2972,
2936, 1733, 1625, 1457, 1379, 1348, 1262, 1220, 1171,
1
1109, 1072, 1052, 1014 cmꢁ ; 1H NMR (600 MHz, CDCl3): ꢁ
4ꢀ-O-(2-(4-Trifluormethylphenyl)-1H-benzimidazole-5-
carbonyl)hydrazinecarbonylclarithromycin (7f)
8.11 (s, 1H), 7.95–7.91 (m, 4H), 7.67–7.65 (m, 1H), 7.07–
7.05 (m, 2H), 5.07–5.05 (m, 1H), 4.96–4.94 (m, 1H), 4.76–
4.74 (m, 1H), 4.58–4.56 (m, 2H), 4.32–4.30 (m, 1H), 3.98–
3.96 (m, 1H), 3.77–3.75 (m, 3H), 3.67–3.66 (m, 3H), 3.36–
3.34 (m, 6H), 3.03–3.07 (m, 3H), 2.57–2.56 (m, 2H), 2.40–
White solid, yield 67.0%, mp 194–196 °C, TLC Rf = 0.08
(methanol/dichlormethane, 1:10); IR (KBr): 3450, 2974,
2940, 2834, 1734, 1621, 1551, 1456, 1379, 1325, 1281,

C-4ꢀ Benzimidazolyl Derivatives
Letters in Drug Design & Discovery, 2011, Vol. 8, No. 10 971
1
1
1222, 1170, 1127, 1113, 1066, 1051, 1016 cmꢀ ; H NMR
(600 MHz, CDCl3): ꢀ 8.19–8.17 (m, 2H), 8.04–8.03 (m, 1H),
7.98–7.97 (m, 1H), 7.75–7.72 (m, 1H), 7.55–7.54 (m, 1H),
7.27–7.26 (m, 2H), 5.07–5.05 (m, 1H), 4.96–4.95 (m, 1H),
4.61–4.60 (m, 1H), 4.52–4.51 (m, 1H), 4.39–4.38 (m, 1H),
4.01–3.99 (m, 1H), 3.78–3.76 (m, 1H), 3.67–3.65 (m, 2H),
3.32–3.30 (m, 3H), 3.22–3.20 (m, 2H), 3.03–3.00 (m, 6H),
2.89–2.88 (m, 1H), 2.58–2.57 (m, 2H), 2.29–2.28 (m, 6H),
2.18–2.17 (m, 1H), 1.91–1.89 (m, 2H), 1.72–1.70 (m, 2H),
1.48–1.47 (m, 2H), 1.39–1.37 (m, 2H), 1.22–1.19 (m, 12H),
1.13–1.12 (m, 15H), 0.85–0.84 (m, 3H); MS (ESI) m/z calcd.
for C54H78F3N5O15 1093.5, found [M+H]+ 1094.8.
[2]
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4ꢀ-O-(2-(4-Nitrophenyl)-1H-benzimidazole-5-
carbonyl)hydrazinecarbonylclarithromycin (7g)
White solid, yield 66.8%, mp 180–184 °C, TLC Rf = 0.08
(methanol/dichlormethane, 1:10); IR (KBr): 3447, 2974,
2938, 1733, 1605, 1524, 1457, 1379, 1348, 1222, 1171,
[7]
[8]
1
1
1109, 1073, 1014 cmꢀ ; H NMR (600 MHz, CDCl3) ꢀ
(ppm): 8.30–8.29 (m, 2H), 8.20–8.18 (m, 3H), 7.99–7.97 (m,
2H), 7.72–7.70 (m, 1H), 5.07–5.05 (m, 1H), 5.01–4.99 (m,
1H), 4.60–4.59 (m, 1H), 4.45–4.44 (m, 1H), 4.38–4.37 (m,
1H), 4.07–4.06 (m, 1H), 3.76–3.74 (m, 2H), 3.69–3.36 (m,
2H), 3.30–3.28 (m, 2H), 3.21–3.18 (m, 2H), 3.02–2.98 (m,
6H), 2.91–2.89 (m, 1H), 2.67–2.64 (m, 2H), 2.18–2.17 (m,
6H), 2.13–2.12 (m, 1H), 1.93–1.91 (m, 2H), 1.79–1.75 (m,
2H), 1.38–1.37 (m, 2H), 1.34–1.32 (m, 2H), 1.22–1.20 (m,
12H), 1.10–1.05(m, 15H), 0.89–0.87 (m, 3H); MS (ESI) m/z
calcd. for C53H78N6O17 1070.5, found [M+H]+ 1071.7.
[9]
Agouridas, C.; Denis, A.; Auger, J.M.; Benedetti, Y.; Bonnefoy,
A.; Bretin, F.; Chantot, J.F.; Dussarat, A.; Fromentin, C.;
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Ma, S.; Jiao, B.; Liu, Z.; Wang, H.; Xian, R.; Zheng, M.; Lou, H.
ACKNOWLEDGEMENTS
This research was financially supported by National
Natural Science Foundation of China (20872081and
21072114), Major R&D Program of New Drugs–National
S&T Key Special Subject of China (2009ZX09103-115),
Natural Science Foundation of Shandong (ZR2010HM092)
and the Project-sponsored by SRF for ROCS, SEM.
[13]
[14]
Synthesis
and
antibacterial
activity
of
4ꢁ,11-di-O-
arylalkylcarbamoyl azithromycin derivatives. Bioorg. Med. Chem.
Lett., 2009, 19(6), 1698–1701.
Ju, Y.; Xian, R.; Zhang, L.; Ma, R.; Cao, J.; Ma, S. Synthesis and
[15]
[16]
antibacterial activity of novel 4ꢁ-O-arylalkylcarbamoyl and 4ꢁ-O-
((arylalkylamino)-4-oxo-butyl)carbamoyl
clarithromycin
CONFLICT OF INTEREST
derivatives. Bioorg. Med. Chem. Lett., 2010, 20(11), 3272–3274.
Ma, S.; Ma, R.; Liu, Z.; Ma, C.; Shen, X. Synthesis and
antibacterial activity of novel 15-membered macrolide derivatives:
4"-carbamate, 11,12-cyclic carbonate-4ꢁ-carbamate and 11,4ꢁ-di-
O-arylcarbamoyl analogs of azithromycin. Eur. J. Med. Chem.,
2009, 44(10), 4010–4020.
The authors declare that this study was carried out only
with public funding. There is no funding or no agreement
with commercial for profit firms.
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[18]
Porcari, A.R.; Devivar, R.V.; Kucera, L.S.; Drach, J.C.; Townsend,
L.B. Design, synthesis, and antiviral evaluations of 1-
SUPPLEMENTARY MATERIAL
(substitutedbenzyl)-2-substituted-5,6-dichlorobenzimidazoles
as
Supplementary material is available on the publishers
Web site along with the published article.
nonnucleoside analogues of 2,5,6-trichloro-1-(beta-D-
ribofuranosyl)benzimidazole. J. Med. Chem., 1998, 41(8), 1252–
1262.
Kumar, K.; Awasthi, D.; Lee, S-Y.; Zanardi, I.; Ruzsicska, B.;
Knudson, S.; Tonge, P.J.; Slayden, R.A.; Ojima, I. Novel
trisubstituted benzimidazoles, targeting Mtb FtsZ, as a new class of
antitubercular agents. J. Med. Chem., 2011, 54(1), 374–381.
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