Synthesis and antibacterial activity of novel 4″-O-(1-aralkyl-1,2,3-triazol-4-methyl-carbamoyl) azithromycin analogs

Article abstract of DOI:10.1016/j.bmcl.2017.06.044

Three novel structural series of 4″-O-(1-aralkyl-1,2,3-triazol-4-methyl-carbamoyl) azithromycin analogs were designed, synthesized and evaluated for their in vitro antibacterial activity. All the target compounds exhibited excellent activity against erythromycin-susceptible Streptococcus pyogenes, and significantly improved activity against three phenotypes of erythromycin-resistant Streptococcus pneumoniae compared with clarithromycin and azithromycin. Among the three series of azithromycin analogs, the novel series of 11,4″-disubstituted azithromycin analogs 9a–k exhibited the most effective and balanced activity against susceptible and resistant bacteria. Among them, compound 9j showed the most potent activity against Staphylococcus aureus ATCC25923 (0.008?μg/mL) and Streptococcus pyogenes R2 (1?μg/mL). Besides, all the 11,4″-disubstituted azithromycin analogs 9a–k except 9f shared the identical activity with the MIC value <0.002?μg/mL against Streptococcus pyogenes S2. Furthermore, compounds 9g, 9h, 9j and 9k displayed significantly improved activity compared with the references against all the three phenotypes of resistant S. pneumoniae. Particularly, compound 9k was the most effective (0.06, 0.03 and 0.125?μg/mL) against all the erythromycin-resistant S. pneumoniae expressing the erm gene, the mef gene and the erm and mef genes, exhibiting 2133, 133 and 2048-fold more potent activity than azithromycin, respectively.

Full text of DOI:10.1016/j.bmcl.2017.06.044

Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and antibacterial activity of novel 400-O-(1-aralkyl-1,2,3-
triazol-4-methyl-carbamoyl) azithromycin analogs
Yinhu Wang a, Chao Cong a, Wern Chern Chai b, Ruiqian Dong c, Li Jia a, Di Song a, Ziteng Zhou a, Shutao Ma a,
⇑
a Department of Medicinal Chemistry, Key Laboratory of Chemical Biology (Ministry of Education), School of Pharmaceutical Sciences, Shandong University, 44 West Culture Road,
Jinan 250012, China
b School of Pharmacy & Medical Sciences, Sansom Institute for Health Research, University of South Australia, GPO Box 2471, Adelaide 5001, Australia
c Maternity and Child Care Centre of Jinan, Jinan 250001, China
a r t i c l e i n f o
a b s t r a c t
Three novel structural series of 400-O-(1-aralkyl-1,2,3-triazol-4-methyl-carbamoyl) azithromycin analogs
were designed, synthesized and evaluated for their in vitro antibacterial activity. All the target com-
pounds exhibited excellent activity against erythromycin-susceptible Streptococcus pyogenes, and signif-
icantly improved activity against three phenotypes of erythromycin-resistant Streptococcus pneumoniae
compared with clarithromycin and azithromycin. Among the three series of azithromycin analogs, the
novel series of 11,400-disubstituted azithromycin analogs 9a–k exhibited the most effective and balanced
activity against susceptible and resistant bacteria. Among them, compound 9j showed the most potent
activity against Staphylococcus aureus ATCC25923 (0.008 mg/mL) and Streptococcus pyogenes R2 (1 mg/
mL). Besides, all the 11,400-disubstituted azithromycin analogs 9a–k except 9f shared the identical activity
with the MIC value <0.002 mg/mL against Streptococcus pyogenes S2. Furthermore, compounds 9g, 9h, 9j
and 9k displayed significantly improved activity compared with the references against all the three phe-
notypes of resistant S. pneumoniae. Particularly, compound 9k was the most effective (0.06, 0.03 and
0.125 mg/mL) against all the erythromycin-resistant S. pneumoniae expressing the erm gene, the mef gene
and the erm and mef genes, exhibiting 2133, 133 and 2048-fold more potent activity than azithromycin,
respectively.
Article history:
Received 6 April 2017
Revised 16 June 2017
Accepted 18 June 2017
Available online xxxx
Keywords:
Bacterial resistance
Erythromycin-resistant bacteria
1,2,3-Triazol azithromycin analogs
Synthesis
Antibacterial activity
Ó 2017 Elsevier Ltd. All rights reserved.
Macrolide antibiotics as a safe and effective agents have been
widely used for the treatment of upper and lower respiratory tract
infections in the early 1950s.1,2 Erythromycin A (EMA), the first
generation macrolide, has been used clinically for more than
60 years, but it readily loses its antibacterial activity due to acid-
mediated decomposition, resulting in poor bioavailability and
undesirable gastrointestinal (GI) side effects.3 Second generation
macrolides exemplified by clarithromycin (CAM) and azithromycin
(AZM) (Fig. 1) have been developed to overcome the acid instabil-
ity of erythromycin A in late 1980s, which not only prevented the
formation of degradation products, but also exhibited more favor-
able pharmacokinetic profiles and better GI tolerability than first
generation macrolides.4,5
diverse, but two major mechanisms of resistance are ribosome
methylation resistance encoded by the erm gene and drug efflux
pump encoded by the mef gene.7 Expression of an erm-resistant
determinant in bacteria leads to production of a methyltransferase
which modifies the key nucleotide A2058 in the macrolide–lin-
cosamide–streptogramin B (MLSB) binding site, thereby conferring
resistance to macrolides, while efflux pump encoded by the mef
gene results in pumping macrolides out of cell, thus preventing
them from reaching the binding sites.8,9 Consequently, it’s urgent
to develop newer generation macrolides that exhibit significant
activity against resistant pathogens to control the infectious dis-
ease. The third generation macrolides known as ketolides such as
telithromycin and cethromycin were introduced in 1990s. They
exhibit excellent antibacterial activity against several macrolide-
resistant strains and may offer alternative therapy for Gram-posi-
tive infections attributable to resistant pathogens.10 The C-11,12
carbamate side chain or the C-6 side chain in the ketolides may
interact with secondary ribosomal binding site A752 directly in
domain II of the 23S rRNA in addition to the main interaction with
the nucleotide A2058 in domain V in bacterial ribosomes. This
With the widespread use of the antibiotics, especially misuse,
the increasing incidence of bacterial resistance to macrolides is
becoming a major threat to successful treatment of infectious dis-
eases.6 The molecular mechanisms of macrolide resistance are
⇑
Corresponding author.
E-mail address: mashutao@sdu.edu.cn (S. Ma).
http://dx.doi.org/10.1016/j.bmcl.2017.06.044
0960-894X/Ó 2017 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Wang Y., et al. Bioorg. Med. Chem. Lett. (2017), http://dx.doi.org/10.1016/j.bmcl.2017.06.044

2
Y. Wang et al. / Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
NMe2
NMe2
9
HO
O
H2N
HO
N
8
HO
N9a
10
7
NMe2
O
4'
3'
O
OH
O
2'
OH
HO
OMe
HO
HO
N
5'
6'
6
O
11
12
5
4
O
'
O
O
O
13
14
O6"
HO
3
O
2
O
O
HO
5"
1
O
O
O
4"
2"
O
3"
N
O
OH
O
N
H
O
O
OMe
OMe
CP-544372
Fig. 1. Structures of azithromycin, CP-544372 and EP-1553.
OH
OMe
O
OMe
Azithromycin
EP-1553
interaction results in tighter binding to the bacterial ribosomes and
imparts some activity against methylated ribosomes in some spe-
cies.11–13
roadblock, respectively. Based on this, we have reported a series
of novel 11, 12-cyclic carbonate-400-carbamate and 11,400-di-O-aryl-
carbamoyl azithromycin derivatives.9,16,18 Among them, Com-
pounds 7k, 28 and 30 (Fig. 2), as a representative of the above
respective series, exhibited remarkably improved activity against
erythromycin-resistant S. pneumoniae expressing the erm gene,
the mef gene, and the erm and mef gene compared to EMA, CAM
or AZM. Here we described a derivatization stream followed in
order to investigate the influence of linker features on biological
properties. Therefore, we introduced novel 400-O-carbamoyl side
chains containing 1,2,3-triazol group connecting 400-oxygen atom
and terminal groups together to probe the effect of the different
400-O-carbamoyl side chains on antibacterial activity. On the basis
of the considerations detailed above, we designed, synthesized
three novel structural series of 400-O-(1-aralkyl-1,2,3-triazol-4-
methyl-carbamoyl)azithromycin analogs to address macrolide
resistance caused by efflux and methylation of the ribosome. The
terminal groups employed to the C-11 and C-400 side chains were
a variety of substituted aromatic groups, which could be beneficial
for gaining a favorable binding affinity for the bacterial ribosome
Owing to the successful development of ketolide antibiotics,
especially telithromycin and cethromycin, numerous chemical
modifications of macrolides have been carried out to discover more
potent antimicrobial agents. CP-544372 (Fig. 1) containing a long
C-400 anchor group with six atoms from 400-oxygen atom to the ter-
minal benzene ring as a representative of C-400 modified carbamate
macrolides shows good in vitro and in vivo activity against MLSB-
resistant strains with competitive binding to chloramphenicol,
suggesting that the anchor group reaches the peptidyl transferase
center (PTC) region, the chloramphenicol-binding site.14,15 Besides,
EP-1553 (Fig. 1), as a representative of another structural series of
11-carbamate macrolides was reported, which exhibited excellent
activity against macrolide-resistant bacteria.9,14
Structure–activity relationships (SARs) of these mentioned
macrolide derivatives have provided us with the information
toward an understanding of the essential structural features
needed for antibacterial activity. Specifically, it has been recog-
nized that arylalkyl groups attached to the C-400 position of the
cladinose sugar in the structure are essential for overcoming MLSB
resistance, and their lengths are important for conferring potent
activity against resistant bacteria, whereas the introduction of
11,12-cyclic carbonate ring or 11-O-arylalkylcarbamoyl side chains
could strengthen the interaction with A752.16,17 Consequently, an
optimized strategy to overcome macrolide-resistant bacteria
would be the design of macrolide analogs with two side chains
which would interact with A752 in domain II of the 23S rRNA
and nucleotide binding sites between the PTC and the macrolide
through hydrogen bonding,
interaction.
p-stacking or van der Waals (VDW)
All the side chains (aminomethyl triazoles A1-A15) were pre-
pared according to methods outlined in Scheme 1. The reaction
of corresponding halide with NaN3 gave aromatic azides in the
presence of ethanol-water. Then aromatic azides were coupled
with propargyl amine to give corresponding aminomethyl triazoles
(A1-A15).
The synthetic method for 400-O-(1-aralkyl-1,2,3-triazol-4-
methyl-carbamoyl) azithromycin analogs (4a–j) is shown in
NMe2
NMe2
O
O
HO
HO
H
H
N
N
N
N
OH
OH
O
O
O
O
O
O
NO2
Cl
HO
HO
O
O
HO
O
O
O
O
O
O
H
N
O
N
H
O
N
H
NO2
O
O
OMe
OMe
Cl
O
7K
28
NMe2
O
O
O
HO
O
H
O
N
O
N
OH
HO
O
Br
O
O
O
N
H
O
OMe
30
Fig. 2. Structures of 7k, 28 and 30.
Please cite this article in press as: Wang Y., et al. Bioorg. Med. Chem. Lett. (2017), http://dx.doi.org/10.1016/j.bmcl.2017.06.044

Y. Wang et al. / Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
3
NH2
inhibitory concentrations (MICs). The sensitive and resistant
Gram-positive bacterial strains contain: S. aureus ATCC25923
(erythromycin-susceptible strain), S. pneumoniae ATCC49619
(erythromycin-susceptible strain), S. pyogenes S2 (erythromycin-
susceptible strain isolated clinically), S. aureus ATCC29213
(methicillin-resistant strain), S. pneumoniae B1 (erythromycin-
resistant strain encoded by the erm gene), S. pneumoniae A22072
(erythromycin-resistant strain encoded by the mef gene),
S. pneumoniae AB11 (erythromycin-resistant strain encoded by
the erm and mef genes), S. pyogenes R2 (erythromycin-resistant
strain isolated clinically). Two phenotypes of Gram-negative
strains are E. coli ATCC25922, P. aeruginosa ATCC27853.
R1
NH2
N
N
a
R1 N3
R1 Cl
N
b
A11 R1= 2,4-dichlorobenzyl
A6 R1= 4-bromobenzyl
A7 R1= 2-fluorobenzyl
A8 R1= 3-fluorobenzyl
A1 R1= 2-methylbenzyl
R1= 2-chlorobenzyl
R1= 3-methylbenzyl
A12
A2
A13 R1= 3-chlorobenzyl
A14 R1= 4-chlorobenzyl
A15 R1= cyclohexyl
A3 R1= 4-methylbenzyl
A4 R1= 4-nitrobenzyl
A5 R1= benzyl
R1= 4-fluorobenzyl
A9
A10 R1= 2,6-dichlorobenzyl
Scheme 1. Synthesis of aminomethyl triazoles. Reagents and conditions: a) NaN3,
EtOH, H20, reflux, 75–89%; b) Propargyl amine, CuSO4, Sodium ascorbate, tBuOH,
H2O, rt, 46–63%.
MIC values for 400-O-(1-aralkyl-1,2,3-triazol-4-methyl-car-
bamoyl) azithromycin analogs (4a–j) are presented in Table 1.
Most of the above analogs retained comparable activity compared
with AZM and CAM against erythromycin-susceptible S. pyogenes
S2, and all of them showed improved activity against ery-
thromycin-resistant S. pyogenes R2 and the three phenotypes of
resistant S. pneumoniae. In particular, compound 4g displayed the
most potent activity against not only erythromycin-resistant S.
Scheme 2. AZM was used as the starting material for the synthesis
of the target compounds. It was first coupled with acetic anhydride
catalyzed by triethylamine at room temperature for 24 h to gener-
ate the compound 2, which was treated with 1,1-carbonyldiimida-
zole (CDI) in toluene at 55 °C to give the important intermediate 3.
Finally, 400-carbamate azithromycin analogs (4a–j) were prepared
by coupling 3 with corresponding aminomethyl triazoles in the
presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), followed
by methanolysis.
pyogenes S2 (0.016
thromycin-resistant S. pneumoniae B1, S. pneumoniae A22072 and
S. pneumoniae AB11 (0.5, 0.25 and 0.25 g/mL), showing 12.5,
lg/mL) but also three phenotypes of ery-
The desired target compounds, 11,12-cyclic carbonate-400-O-(1-
aralkyl-1,2,3-triazol-4-methyl-carbamoyl) azithromycin analogs
(8a–o) and 11,400-di-O-arylalkylcarbamoyl azithromycin analogs
(9a–k), were synthesized as shown in Scheme 3. Compound 2
was treated with 1,1-carbonyldiimidazole (CDI) in toluene at
55 °C to generate the important intermediate 1400-O-acylimida-
zolyl-11,12-cyclic carbonate 5. Then compound 6 was obtained
by coupling the intermediate 5 with propargyl amine catalyzed
by 1,8-Diazabicyclo [5,4,0]-undec-7-ene (DBU), followed by depro-
tection of the acetyl group in methanol. Subsequently, compound 7
were reacted with the corresponding aromatic azides to give the
desired target compounds 8a–o. Then corresponding 11,12-cyclic
carbonate-400-O-(1-aralkyl-1,2,3-triazol-4-methyl-carbamoyl) azi-
thromycin analogs was readily converted to novel 11,400-di-O-ary-
lalkylcarbamoyl azithromycin analogs (9a–k) by coupling with the
corresponding amines in the presence of pyridine hydrochloride at
room temperature in yields ranging from 68% to 86%.
l
256, 16 and 1024-fold enhanced activity than AZM, respectively,
which suggested that introduction of the 1-aralkyl-1,2,3-triazol-
4-methyl-carbamoyl side chain into the C-400 position of AZM could
enhance antibacterial activity against erythromycin-resistant
bacteria.
Compared with their precursors 400-O-(1-aralkyl-1,2,3-triazol-4-
methyl-carbamoyl) azithromycin analogs, almost all of the 11,12-
cyclic
carbonate-400-O-(1-aralkyl-1,2,3-triazol-4-methyl-car-
bamoyl) azithromycin analogs (8a–o) showed compromised or
similar activity against all the tested strains, which suggested that
the introduction of 11,12-cyclic carbonate moiety failed to confer
lower MIC values against erythromycin-susceptible or ery-
thromycin-resistant strains. However, the compounds in this series
still showed potent activity against erythromycin-susceptible S.
pneumoniae ATCC49619 (0.5–1
lg/mL) and S. pyogenes S2 (0.008–
0.25 g/mL), and showed improved activity against all the three
l
All the target compounds, as well as CAM and AZM as refer-
ences, were tested for in vitro antibacterial activity against eight
phenotypes of Gram-positive strains and two phenotypes of
Gram-negative strains. Their activities are reported as minimum
phenotypes of resistant S. pneumoniae compared with AZM and
CAM. Among them, compounds 8a, 8e and 8g displayed the most
potent activity against S. pneumoniae ATCC49619 (0.5
l
g/mL),
and compound 8d (0.008
lg/mL) exhibited better activity against
NMe2
HO
NMe2
NMe2
O
AcO
OH
AcO
OH
O
N
O
N
O
N
OH
HO
HO
HO
HO
HO
HO
O
a
O
O
b
O
O
O
O
O
O
O
O
O
OH
OMe
N
O
N
O
OH
OMe
O
O
OMe
3
2
AZM
R1= 3-methylbenzyl
R1= 2-methylbenzyl
NMe2
4a
4b
HO
OH
N
O
4c R1= 4-methylbenzyl
4d R1= 4-nitrobenzyl
4e R1= benzyl
c,d
N
HO
HO
O
O
O
R1
N
N
NH2
4f R1= 2,6-dichlorobenzyl
4g R1= 2,4-dichlorobenzyl
4h R1= 4-chlorobenzyl
4i R1= 3-chlorobenzyl
4j R1= 2-chlorobenzyl
O
O
R1
N
N
O
OMe
O
N
H
N
4
Scheme 2. Synthesis of 400-O-(1-aralkyl-1,2,3-triazol-4-methyl-carbamoyl) azithromycin analogs (4a–j). Reagents and conditions: a) Ac2O, DCM, Et3N, rt, 24 h, 92%; b) CDI,
Et3N, toluene, 55 °C, 40 h, 95%; c) DMF, DBU, rt, 12 h, 82–93%; d) CH3OH, 55 °C, 12 h, 90–96%.
Please cite this article in press as: Wang Y., et al. Bioorg. Med. Chem. Lett. (2017), http://dx.doi.org/10.1016/j.bmcl.2017.06.044

4
Y. Wang et al. / Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
NMe2
O
NMe2
O
NMe2
AcO
OH
AcO
N
O
AcO
OH
O
N
O
N
O
OH
O
O
O
HO
HO
O
O
O
c
b
O
a
O
O
O
O
O
O
O
O
O
O
O
N
H
OH
N
O
N
O
OMe
O
OMe
O
OMe
N
5
6
2
NMe2
O
NMe2
O
HO
N
R2 NH
O
HO
OH
O
N
O
HO
OH
O
N
OH
O
O
e
O
O
d
O
O
O
O
O
HO
O
O
O
O
O
O
O
O
O
O
O
O
R1
O
N
H
N
H
N
O
OMe
N
H
R1
O
O
OMe
OMe
N
O
N
N
N
9
N
8
7
9a R1= 4-methylbenzyl
9b R1= benzyl
R2= benzyl
R2= benzyl
8a R1= 2-methylbenzyl
8b R1= 3-methylbenzyl
8c R1= 4-methylbenzyl
8d R1= 4-nitrobenzyl
8e R1= benzyl
8i R1= 4-fluorobenzyl
8j R1= 2,6-dichlorobenzyl
8k R1= 2,4-dichlorobenzyl
8l R1= 2-chlorobenzyl
8m R1= 3-chlorobenzyl
8n R1= 4-chlorobenzyl
8o R1= cyclohexyl
9c R1= 2,6-dichlorobenzyl R2= benzyl
R1= 4-chlorobenzyl
R1=benzyl
R2= benzyl
9d
9e
9f
9g
9h
R2= phenethyl
R1=benzyl
R2= pyridine-4-methyl
R2= 4-methoxybenzyl
8f R1= 4-bromobenzyl
8g R1= 2-fluorobenzyl
8h R1= 3-fluorobenzyl
R1= 4-methylbenzyl
R1= 2,6-dichlorobenzyl R2= 4-methoxybenzyl
9i R1= 2,4-dichlorobenzyl R2= 4-methoxybenzyl
9j R1= 4-chlorobenzyl
9k R1= 2-chlorobenzyl
R2= 4-methoxybenzyl
R2= 4-methoxybenzyl
Scheme 3. Synthesis of 11,12-cyclic carbonate-400-O-(1-aralkyl-1,2,3-triazol-4-methyl-carbamoyl) azithromycin analogs (8a–o) and 11,400-di-O-arylalkylcarbamoyl
azithromycin analogs (9a–k). Reagents and conditions: a) CDI, Et3N, toluene, 55 °C, 40 h, 93%; b) propargylamine, DMF, DBU, rt, 20 h, 96%; c) CH3OH, 55 °C, 12 h, 70%; d)
R1N3, CuSO4, sodium ascorbate, tBuOH, H2O, 8 h, 77–89%; e) pyridine hydrochloride, R2NH2, rt, 2–5 days, 68–86%.
Table 1
400-O-(1-Aralkyl-1,2,3-triazol-4-methyl-carbamoyl) azithromycin analogs with their in vitro antibacterial activity against susceptible and resistant strains (
lg/mL).
Compounds S. aureus
ATCC25923a
S. pneumoniae
S. aureus
S.
S.
S.
S. pneumoniae S.
E. coli
P. aeruginosa
ATCC49619b
ATCC29213c
pyogenes
pyogenes
pneumoniae
A22072g
pneumoniae
ATCC25922 ATCC27853
S2d
R2e
B1f
AB11h
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
CAM
AZM
1
1
1
1
1
1
1
1
1
1
0.12
0.25
0.5
0.25
0.5
1
0.5
0.5
0.25
0.5
0. 25
0.25
0.125
0.125
16
16
16
16
8
16
16
16
8
0.03
0.03
0.03
0.03
0.06
0.03
0.016
0.03
0.06
0.03
0.03
0.03
32
64
64
64
32
32
64
64
64
64
128
128
1
1
1
0.5
1
1
4
0.5
0.25
0.5
1
0.5
128
256
32
16
32
32
32
32
64
64
16
128
64
16
32
64
64
32
32
32
32
32
32
32
32
8
0.5
0.5
1
0.5
0.5
2
2
1
0.5
0.5
2
0.5
1
0.5
0.25
1
0.25
0.25
4
8
0.25
1
128
128
4
a
b
c
S. aureus ATCC25923: erythromycin-susceptible strain.
S. pneumoniae ATCC49619: erythromycin-susceptible strain.
S. aureus ATCC29213: methicillin-resistant strain.
S. pyogenes S2: erythromycin-susceptible strain isolated clinically.
S. pyogenes R2: erythromycin-resistant strain isolated clinically.
S. pneumoniae B1: erythromycin-resistant strain encoded by the ermB gene.
d
e
f
g
h
S. pneumoniae A22072: erythromycin-resistant strain encoded by the mefA gene.
S. pneumoniae AB11: erythromycin-resistant strain encoded by the ermB and mefA genes.
erythromycin-susceptible S. pyogenes S2 than the references. Par-
ticularly, compound 8j possessed the most potent activity against
three phenotypes of erythromycin-resistant S. pneumoniae B1, S.
pneumoniae A22072 and S. pneumoniae AB11 (1, 0.25 and
MIC values for 11,400-di-O-arylalkylcarbamoyl azithromycin
analogs (9a–k) are shown in Table 2. Compared with their precur-
sors
11,12-cyclic
carbonate-400-O-(1-aralkyl-1,2,3-triazol-4-
methyl-carbamoyl) azithromycin analogs (8a–o), almost all of
the 11,400-di-O-arylalkylcarbamoyl azithromycin analogs (9a–k)
showed improved activity against all the tested strains. Moreover,
all the analogs 9a–k showed remarkablely improved activity com-
pared with AZM and CAM against erythromycin-susceptible S. pyo-
genes S2 and all the three phenotypes of resistant S. pneumoniae.
Especially, for erythromycin-susceptible S. pyogenes S2, all the
0.25 lg/mL), showing 128, 16 and 1024-fold enhanced activity
than AZM, respectively (Table 2). As for Gram-negative organisms,
all of the target compounds displayed weaker activity against
E. coli ATCC25922 and P. aeruginosa ATCC27853 than the references
and a few of the target compounds such as compounds 8d and 8n
maintained the activity of CAM against E. coli ATCC25922.
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Y. Wang et al. / Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
5
Table 2
11,12-Cyclic carbonate-400-O-(1-aralkyl-1,2,3-triazol-4-methyl-carbamoyl) azithromycin analogs and 11,400-di-O-arylalkylcarbamoyl azithromycin analogs with their in vitro
antibacterial activity against susceptible and resistant strains (
l
g/mL).
Compounds S. aureus
ATCC25923a
S. pneumoniae
S. aureus
S.
S.
S.
S. pneumoniae S.
E. coli
P. aeruginosa
ATCC49619b
ATCC29213c
pyogenes
pyogenes
pneumoniae
A22072g
pneumoniae
ATCC25922 ATCC27853
S2d
R2e
B1f
AB11h
8a
8b
8c
8d
8e
8f
8g
8h
8i
4
2
4
4
4
2
4
4
4
4
4
4
4
4
0.5
1
1
1
0.5
1
0.5
1
1
1
1
32
32
64
32
32
32
32
32
32
32
32
32
32
32
64
16
16
16
16
16
32
32
16
16
16
16
0.25
1
0.06
0.25
0.25
0.008
0.06
64
64
64
128
128
32
128
128
32
16
32
16
16
64
32
32
32
64
32
32
32
8
4
4
2
4
8
4
2
4
8
1
4
8
4
8
8
2
2
1
4
8
1
1
4
1
0.25
1
2
0.5
1
2
2
1
0.5
4
128
128
128
64
64
64
64
64
64
64
64
64
64
64
64
64
64
64
64
32
32
32
32
8
128
128
128
128
128
128
128
128
128
64
128
32
16
32
32
16
32
16
16
16
16
32
64
0.06
1
0.125
0.125
0.125
0.125
0.125
0.06
0.06
0.125
0.25
<0.002
<0.002
<0.002
<0.002
<0.002
0.03
<0.002
<0.002
<0.002
<0.002
<0.002
0.03
0.25
0.5
4
0.25
2
4
1
4
4
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.125
0.125
128
256
8j
8k
8l
1
1
1
1
8m
8n
8o
9a
9b
9c
9d
9e
9f
16
0.5
0.016
0.25
0.25
0.25
1
0.06
0.25
0.25
0.008
0.03
0.12
0.25
1
0.125
0.125
0.125
0.25
0.125
0.5
0.125
0.06
0.06
0.125
0.125
0.125
0.125
0.25
0.25
0.25
0.25
0.25
0.125
0.125
0.125
0.125
0.125
0.06
128
128
0.125
0.25
0.25
0.125
0.125
0.06
0.03
0.03
0.125
0.06
0.03
4
64
64
16
16
8
8
32
8
9g
9h
9i
1
8
1
8
128
128
9j
9k
CAM
AZM
0.03
4
16
a
b
c
S. aureus ATCC25923: erythromycin-susceptible strain.
S. pneumoniae ATCC49619: erythromycin-susceptible strain.
S. aureus ATCC29213: methicillin-resistant strain.
S. pyogenes S2: erythromycin-susceptible strain isolated clinically.
S. pyogenes R2: erythromycin-resistant strain isolated clinically.
S. pneumoniae B1: erythromycin-resistant strain encoded by the ermB gene.
d
e
f
g
h
S. pneumoniae A22072: erythromycin-resistant strain encoded by the mefA gene.
S. pneumoniae AB11: erythromycin-resistant strain encoded by the ermB and mefA genes.
target compounds except compound 9f exhibited the MIC values of
<0.002 mg/mL. Besides, compounds 9g–k exhibited not only 16–
500-fold, 8–16-fold, >30-fold better activity than their precursors
8c, 8j–k, 8h and 8l against S. aureus ATCC25923, S. pneumoniae
ATCC49619 and S. pyogenes S2, but also presented 1024–2133-fold,
32–133-fold and 1024–2048-fold improved activity compared
with the references against erythromycin-resistant S. pneumoniae
expressing the erm gene, the mef gene, and the erm and mef genes.
Among them, compounds 9j (0.008 mg/mL) and 9b (0.016 mg/mL)
exhibited the most potent activity better than other 11,400-di-O-
arylalkylcarbamoyl azithromycin analogs in this series against ery-
thromycin-susceptible S. aureus ATCC25923, and compounds 9h
and 9i were the most effective (0.06 mg/mL) against ery-
thromycin-susceptible S. pneumoniae ATCC49619. Besides, com-
pound 9j displayed greatly improved activity against
erythromycin-resistant S. pyogenes R2 with the MIC value of
1 mg/mL, showing 128-fold improved activity better than CAM or
AZM. In addition, almost all of the target compounds 9a–k showed
improved activity against erythromycin-resistant S. pneumoniae
encoded by the erm gene, the mef gene, and the erm and mef genes
in comparison with their precursors 8c, 8e, 8h, 8l and 8j–k. These
results clearly indicated that introduction of an arylalkyl group
into the C-11 position of the 400-O-(1-aralkyl-1,2,3-triazol-4-
methyl-carbamoyl) azithromycin analogs dramatically enhanced
their antibacterial activity against erythromycin-resistant bacteria.
Among them, compounds 9g, 9h, 9j and 9k displayed favorable
activity against all the three phenotypes of resistant S. pneumoniae.
Particularly, compound 9k with the terminal 4-methoxybenzyl
group on its C-11 side chain was the most effective (0.06, 0.03
and 0.125 mg/mL) against erythromycin-resistant S. pneumoniae
B1, S. pneumoniae A22072 and S. pneumoniae AB11, exhibiting
2133, 133 and 2048-fold enhanced activity better than AZM,
respectively. Moreover, 11,400-di-O-arylalkylcarbamoyl azithromy-
cin analogs (9a–k) exhibited better activity against E. coli
ATCC25922 and P. aeruginosa ATCC27853 than their precursors,
which suggested that introduction of an arylalkyl group into the
11-position of 400-O-arylalkylcarbamoyl azithromycin analogs
might enhance their antibacterial activity against Gram-negative
organisms.
From the data mentioned above we can summarized their SARs
as follows. Introduction of the novel arylalkylcarbamoyl side
chains containing 1,2,3-triazol group into the C-400 position of
AZM could greatly improve activity against erythromycin-resistant
S. pneumoniae compared with AZM, which suggested that pro-
longed anchor group at the C-400 position might increase the affin-
ity for the new binding sites of the nucleotides in the peptide
tunnel, further enhancing antibacterial activity against resistant
strains. However, introduction of 11,12-cyclic carbonate ring into
the C-400 modified azithromycin analogs (4a–j) was not beneficial
for retaining or enhancing antibacterial activity, which might be
related to the absence of the 11-hydroxyl group as a hydrogen
bond donor. In remarkable contrast, introduction of the arylalkyl-
carbamoyl side chains into the C-11 position of the C-400 modified
azithromycin analogs (4a–j) showed significantly improved activ-
ity against erythromycin-resistant S. pneumoniae in comparison
with the C-400 modified azithromycin analogs (4a–j). This led us
Please cite this article in press as: Wang Y., et al. Bioorg. Med. Chem. Lett. (2017), http://dx.doi.org/10.1016/j.bmcl.2017.06.044

6
Y. Wang et al. / Bioorganic & Medicinal Chemistry Letters xxx (2017) xxx–xxx
to presume that the C-11 arylalkyl side chains could interact with a
new binding site of nucleotide in domain II of the 23S rRNA, result-
ing in tighter binding to the ribosomes in macrolide-resistant bac-
teria. Additionally, in the series of the 11,400-disubstituted
azithromycin analogs (9a–k) with the most effective and balanced
activity against susceptible and resistant bacteria, the compounds
bearing the same C-400 side chain showed significantly different
antibacterial activity, for example, 11-O-4-methoxybenzyl analogs
(9g, 9h and 9j) had much better activity than 11-O-benzyl analogs
(9a, 9c and 9d), which indicated that the terminal 11-O-4-
methoxybenzyl group might easily interact with the secondary
exhibited significantly improved activity compared with the refer-
ences against the three phenotypes of resistant S. pneumoniae.
Among three series of azithromycin analogs, the novel series of
11,400-di-O-arylalkylcarbamoyl azithromycin analogs 9a–k exhib-
ited the most effective and balanced activity against susceptible
and resistant bacteria. Among them, compound 9j exhibited the
most significantly enhanced activity against S. aureus ATCC25923
(0.008 mg/mL), S. pyogenes R2 (1 mg/mL), showing 31-fold and
128-fold better activity than AZM, respectively. Moreover, all the
azithromycin analogs 9g–k except 9f shared the identical activity
with the MIC value <0.002 mg/mL against S. pyogenes S2. In addi-
tion, compounds 9g, 9h, 9j and 9k displayed significantly improved
activity compared with the references against all the three pheno-
types of resistant S. pneumoniae. Particularly, compound 9k was
the most effective (0.06, 0.03 and 0.125 mg/mL) against ery-
thromycin-resistant S. pneumoniae B1, S. pneumoniae A22072 and
S. pneumoniae AB11, exhibiting 2133, 133 and 2048-fold more
potent activity than AZM, respectively. More importantly, the
results suggested that the modification of both C-11 and 400-O posi-
tions of azithromycin could dramatically enhance the antibacterial
activity.
ribosomal binding site A752 through hydrogen bonding,
p-stack-
ing or van der Waals (VDW) interaction, thereby further enhancing
affinity for the ribosomes.
On the whole, although three novel series of azithromycin ana-
logs had different modification sites, almost all of the compounds
displayed excellent activity against the susceptible S. pyogenes
and improved activity compared with AZM and CAM against all
the three phenotypes of resistant S. pneumoniae. In the series of
400-O-(1-aralkyl-1,2,3-triazol-4-methyl-carbamoyl) azithromycin
analogs (4a–j), almost all of the target compounds retained excel-
lent activity against erythromycin-susceptible S. pyogenes S2 and
showed improved activity against erythromycin-resistant S. pyoge-
nes and S. pneumoniae. These results suggested that introduction of
the 1-aralkyl-1,2,3-triazol-4-methyl-carbamoyl group into the 400-
position of 15-membered macrolides was beneficial for retaining
or enhancing activity of compounds against some erythromycin-
susceptible and erythromycin-resistant strains. Compared with
the parent 400-O-(1-aralkyl-1,2,3-triazol-4-methyl-carbamoyl) azi-
thromycin analogs, most of the 11,12-cyclic carbonate-400-O-(1-
aralkyl-1,2,3-triazol-4-methyl-carbamoyl) azithromycin analogs
(8a–o) showed compromised activity against all the tested strains.
Furthermore, 11,400-di-O-arylalkylcarbamoyl azithromycin analogs
(9a–k) showed greatly improved activity against all the tested
strains in comparison with their precursors 11,12-cyclic carbon-
ate-400-O-(1-aralkyl-1,2,3-triazol-4-methyl-carbamoyl) azithromy-
cin analogs. This suggested that introduction of an arylalkyl
group into the C-11 position of the 400-O-(1-aralkyl-1,2,3-triazol-
4-methyl-carbamoyl) azithromycin analogs dramatically enhanced
their antibacterial activity against some susceptible or resistant
strains. Among three series of azithromycin analogs, the novel ser-
ies of 11,400-di-O-arylalkylcarbamoyl azithromycin analogs 9a–k
exhibited potent and balanced activity against susceptible and
resistant bacteria. In particular, compounds 9g, 9h, 9j and 9k
showed favorable activity against susceptible bacteria and resis-
tant bacteria.
Acknowledgments
This research was supported financially by the National Natural
Science Foundation of China (81673284), the Natural Science
Foundation of Shandong (ZR2015BM019), Major Project of
Research
and
development
of
Shandong
Province
(2016GSF201202) and Major Project of Science and Technology
of Shandong Province (2015ZDJS04001).
A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2017.06.
044.
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