Synthesis, antibacterial activity and docking of 14-membered 9-O-(3-arylalkyl) oxime 11,12-cyclic carbonate ketolides

Article abstract of DOI:10.1016/j.ejmech.2012.10.054

A series of 9-O-(3-aryl-2-propargyl)oxime ketolides 8 was synthesized and evaluated for in vitro antibacterial activity. Among 8, 8b-8d, and 8h-8l displayed dramatically improved potency against inducibly MLS _B-resistant and efflux-resistant pathogens as compared to clarithromycin and azithromycin. Especially, 8i (Ar4-isoquinolyl) possessed an MIC of 0.064 μg/mL against constitutively MLS_B-resistant Streptococcus pneumoniae, and MICs of 0.032-0.064 μg/mL against methicillin-resistant Staphylococcus aureus and methicillin-resistant Staphylococcus hominis. The analog 10 with a propyl linker was less effective than both the corresponding 8 and 9 containing propynyl and propenyl linkers. A docking study was performed to gain insight into the binding mode of series 8 and 9 and to rationalize the disparity found in the SAR of 8 and 9.

Full text of DOI:10.1016/j.ejmech.2012.10.054

European Journal of Medicinal Chemistry 59 (2013) 54e63
Contents lists available at SciVerse ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis, antibacterial activity and docking of 14-membered 9-O-(3-arylalkyl)
oxime 11,12-cyclic carbonate ketolides
, ,
,
,
**
Jian-Hua Liang a 1, Kun An a, Wei Lv b, Mark Cushman b 2, He Wang c, Ying-Chun Xu c
*
a School of Life Science, Beijing Institute of Technology, Beijing 100081, China
b Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, and the Purdue Center for Cancer Research, Purdue University, 47907, USA
c Department of Clinical Laboratory, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences, Beijing 100730, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 9-O-(3-aryl-2-propargyl)oxime ketolides 8 was synthesized and evaluated for in vitro anti-
bacterial activity. Among 8, 8be8d, and 8he8l displayed dramatically improved potency against indu-
cibly MLSB-resistant and efflux-resistant pathogens as compared to clarithromycin and azithromycin.
Received 6 August 2012
Received in revised form
3 October 2012
Accepted 4 October 2012
Available online 8 November 2012
Especially, 8i (Ar]4-isoquinolyl) possessed an MIC of 0.064
mg/mL against constitutively MLSB-resistant
Streptococcus pneumoniae, and MICs of 0.032e0.064 g/mL against methicillin-resistant Staphylococcus
m
aureus and methicillin-resistant Staphylococcus hominis. The analog 10 with a propyl linker was less
effective than both the corresponding 8 and 9 containing propynyl and propenyl linkers. A docking study
was performed to gain insight into the binding mode of series 8 and 9 and to rationalize the disparity
found in the SAR of 8 and 9.
Keywords:
Erythromycin
Multi-drug resistance
Ketolide
Ó 2012 Elsevier Masson SAS. All rights reserved.
Antibacterial activity
Macrolide
Oxime
1. Introduction
counties: Vietnam (92.1%), Taiwan (86%), Korea (80.6%), Hong Kong
(76.8%), and China (73.9%) [2].
The development of bacterial resistance to currently available
antibiotics is a growing global health problem. Of particular
concern are respiratory tract infections caused by multi-drug
resistant Gram-positive pathogens. For Streptococcus pneumoniae,
penicillin susceptibility ranged from 41.5% (Asia) to 75.3% (Europe),
while susceptibility to erythromycin ranged from 23.7% (Asia) to
87.0% (Central and South America) [1]. Macrolide antibiotics have
been in successful clinical use against Gram-positive pathogens for
several decades. Clarithromycin, azithromycin and roxithromycin,
the second-generation macrolide antibiotics, possess improved
acid-stability and pharmacokinetics as compared to erythromycin
(Fig. 1). However, they do not show any significant activity against
bacterial isolates showing macrolide-lincosamide-streptogramin B
(designated MLSB) resistance. Recent research has revealed that the
prevalence of erythromycin resistance is extremely high in Asian
The resistant pathogens against MLSB are mainly found in two
genotypes: a base-specific mono- or dimethylation of 23S ribo-
somal RNA encoded by an erm gene, and acquisition of efflux pump
proteins that export the macrolides outside the cells encoded by an
mef gene [3]. In addition, MLSB resistance can express an inducible,
or a constitutive or an efflux phenotype. Ma’s research clearly
revealed that 3-O-cladinose is responsible for erm-mediated
inducible resistance [4]
Ketolides, 6-O-substituted-3-keto-erythromycin derivatives,
were developed to address MLSB resistance [5e7]. Acylides [8,9],
alkylides [10,11] and bicyclolides [12] are representative non-
ketolides that are active against resistant bacteria. Among keto-
lides, telithromycin (HMR-3647) [13] has been marketed in 2001,
cethromycin (ABT-773) [4] is suspended in phase-Ⅲ clinical trials,
solithromycin (CEM-101) [14] and modithromycin (EDP-420) [15]
have entered clinical phase-Ⅱ, while PF-04287881 [16] has step-
ped in clinical phase-Ⅰ(Fig. 2). Besides a 3-keto functional group,
the aforementioned compounds all possess a long chain anchored
by an aryl group, which is believed to be the key factor conferring
antibacterial activity by an additional secondary interaction with
resistant organisms [17,18]. It is noteworthy that the sidechains
of telithromycin, cethromycin, solithromycin, modithromycin and
* Corresponding author. Tel.: þ86 10 68912140.
** Corresponding author. Tel.: þ1 765 494 1465; fax: þ1 765 494 6790.
E-mail addresses: ljhbit@bit.edu.cn (J.-H. Liang), cushman@purdue.edu
(M. Cushman).
1
Design, SAR study and molecular modeling.
Molecular docking.
2
0223-5234/$ e see front matter Ó 2012 Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.ejmech.2012.10.054

J.-H. Liang et al. / European Journal of Medicinal Chemistry 59 (2013) 54e63
55
O
O
O
O
9
N
9
9
OR
11
OH
HO
11
12
HO
HO
11
12
OH
OH
N
OH
N
6
5
12
N
6
5
2'
2'
2'
3'
3'
5
3'
HO
HO
HO
O
O
O
O
O
O
O
O
O
3
1
3
3
1
O
O
O
O
OCH3
3"
O
OCH3
O
OCH3
3"
3"
4"
4"
OH
4"
OH
OH
O
R=H Erythromycin A
R=CH3 Clarithromycin
O
O
Roxithromycin
Azithromycin
Fig. 1. Structures of erythromycin A and the second-generation erythromycin derivatives (clarithromycin, azithromycin and roxithromycin).
PF-04287881 are positioned on C-11,12, C-6, C-11,12, C-6,11 and C-
11,12, respectively. Apart from these positions, 9-oxime ethers have
been a point of interest, including those carrying a 3-O-cladinose
[19e22] or carrying a 3-keto group [5,23e25]. Among them, rox-
ithromycin [19] (Fig. 1) has been successfully marketed. Never-
theless, roxithromycin is inefficient against erythromycin-resistant
pathogens. Thus, such impaired efficacy of available antibiotics
requires continuous efforts to search for clinical candidates against
MLSB-resistant pathogens.
compounds was comparable to azithromycin against Gram-
negative pathogens, such as Haemophilus influenzae, and Morax-
ella catarrhalis (unpublished MIC50 data). Triggered by this success,
we herein report recent progress on the SAR of other 14-membered
9-oxime ether ketolides against a variety of clinical isolates asso-
ciated with varying genotypes and phenotypes. Moreover,
a molecular modeling and docking study was performed in an
attempt to illustrate the potential binding site of the novel ketolides
with bacterial ribosomal RNA.
In addition to 14-membered ketolides, no promising 15-
membered ketolides derived from the skeleton of azithromycin
have arisen for clinical trials due to their lower activity than cor-
responding 14-membered analogs, although azithromycin
possesses good activity against some Gram-negative pathogens [26]
As a part of our ongoing efforts to develop novel macrolides
acting against erythromycin-resistant bacteria, we previously re-
ported a series of novel ketolides bearing a 3-aryl-E-prop-2-enyl
group attached to the 9-oxime, which resulted in a remarkable
improvement against key Gram-positive resistant pathogens [27].
Further extensive study indicated the in vitro activity of these
2. Chemistry
The synthesis of target compounds 8 was conducted from 1 in
seven steps, as shown in Scheme 1. Compound 1, 20, 400-O-bis(-
trimethylsilyl)-6-O-methylerythromycinA9-O-(1-ethoxycyclohexyl)
oxime, is the key intermediate for the scaleable synthesis of clari-
thromycin [28]. Treatment of 1 with dilute hydrochloric acid in
ethanol yielded 2. Next, acylation of 2 generated 3 with acetyl groups
atboth20-OHand the 9-oxime hydroxyl. Asdescribed previously [27],
the acetyl group at the 9-oxime is labile and removed selectively in
N
O
O
9
N
N
9
O
O
O
O
11
1
OCH3
O
11
1
6
N
N
2'
6
N
3'
N
H
2'
3'
HO
HO
O
O
O
O
O
O
3
3
O
O
O
O
Cethromycin (ABT-773)
Telithromycin (HMR-3647)
O
HO
N
N
9
O
O
N
N
N
N
9
9
O
O
O
HO
OCH3
11
1
OCH3
O
O
11
1
11
1
6
N
6
N
6
N
2'
3'
N
N
2'
2'
3'
3'
HO
HO
O
HO
O
O
O
O
O
O
O
O
3
3
3
O
O
O
O
O
O
F
Solithromycin (CEM-101)
Modithromycin (EDP-420)
PF-04287881
Fig. 2. Structures of the third-generation erythromycineketolide analogs (telithromycin, cethromycin, modithromycin, solithromycin and PF-04287881).

56
J.-H. Liang et al. / European Journal of Medicinal Chemistry 59 (2013) 54e63
O
O
OAc
OH
N
9
N
N
N
c
b
a
OMe
OMe
OMe
HO
OMe
HO
HO
HO
OH
OH
OH
OH
12
6
2'
N
N
N
N
Me3SiO
O
HO
O
AcO
O
AcO
O
O
O
O
O
O
O
O
O
3
OMe
O
O
O
O
O
OSiMe3
4"
O
1
4
3
2
N
O
N
N
N
O
g
f
d
OMe
e
O
O
OMe
OMe
O
OMe
O
O
O
N
O
O
N
O
O
O
N
AcO
O
O
N
AcO
O
HO
O
AcO
O
O
O
O
O
O
O
O
O
O
O
5
8
6
7
N
N
S
S
S
N
a
b
c
d
e
f
N
N
N
N
N
g
h
i
j
k
l
Scheme 1. Synthesis of the ketolides 8ae8l. (a) HCl, EtOH; (b) acetic anhydride, CH2Cl2; (c) KOtBu, propargyl bromide, DMF; (d) pyridine, bis(trichloromethyl)carbonate, CH2Cl2; (e)
NCS, DMS, Et3N, CH2Cl2; (f) ArBr, (PPh3)2PdCl2, CuI, Et3N, 80 ꢀC, 3 h, acetonitrile; (g) MeOH, 65 ꢀC, 3 h 8a:Ar]2-thienyl; 8b: Ar]2-pyridyl; 8c: Ar]3-pyridyl; 8d: Ar]5-pyrimidyl;
8e: Ar]2-[5-(2-pyridyl)]thienyl; 8f: Ar]2-(5-benzoyl)thienyl; 8g: Ar]5-indolyl; 8h: Ar]5-isoquinolyl; 8i: Ar]4-isoquinolyl; 8j: Ar]4-quinolyl; 8k: Ar]3-quinolyl; 8l: Ar]6-
quinolyl.
the presence of base. Thus, removal of the acetyl group at the 9-oxime
and subsequent introduction of a propargyl were accomplished in
a one-pot synthesis, which produced 9-O-propargyloxime 4. To reach
a better yield, the solvent DMF was substituted for the original THF in
the synthesis of 4.
hydrogenation of 8i using Lindlar catalysis, and only the starting
material 8i was recovered, as shown in Scheme 4.
3. Antibacterial activity
As a 11,12-cyclic carbonate would enhance antibacterial activity
[25,27], we prepared 5 by an optimized procedure for cyclic
carbonylation at 11,12-OH [29]. Based on a recent investigation [30]
of the stability of the Corey-Kim intermediate, we obtained 3-keto 6
in high yield and with minimal side reaction. Next, 7 was prepared
by Sonogashira coupling of 6 and the appropriate aryl bromide in
the presence of Pd(PPh3)2Cl2, CuI and Et3N in acetonitrile. Depro-
tection of the 20-acetate of 7 afforded the final compounds 8.
To probe the effects of side chain configuration on antibacterial
activity, we prepared compounds 10k, 10i from 9k, 8i, respectively
(see Schemes 2 and 3). Compound 9k was one of the most potent
ketolides bearing a 3-aryl-E-prop-2-enyl group at the 9-oxime
against resistant bacteria [27]. Hydrogenation of E-olefin 9k in
the presence of 10% PdeC and acidic medium yielded the saturated
side chain 10k. In a similar way, the hydrogenation product 10i was
obtained from 8i, one of most effective ketolides bearing a 3-aryl-2-
propargyl group discussed in this paper. Unfortunately, the desired
Z-olefin 11i was not produced at low temperature by attempted
The antibacterial activity of the samples was assessed against
a panel of erythromycin-susceptible and clinical erythromycin-
resistant isolates, including Staphylococcus aureus, Staphylococcus
Ar
Ar
O
O
N
O
N
a
OMe
OMe
O
O
O
N
N
O
O
O
O
HO
HO
O
O
O
O
O
O
O
O
9
10
Scheme 2. Synthesis of the ketolide 10k. (a) 10% PdeC, HCOOH, HCOONH4, H2, 65 ꢀC,
24 h, MeOH. 9k, 10k: Ar]3-quinolyl.

J.-H. Liang et al. / European Journal of Medicinal Chemistry 59 (2013) 54e63
57
Table 1
Ar
Ar
Selected organisms and their resistant determinants.
O
O
Strain
Phenotype
Genotype
None
N
O
N
O
Streptococcus
pneumoniae
Streptococcus
pneumoniae
Streptococcus
pneumoniae
Streptococcus
pneumoniae
Streptococcus
dysgalactiae
Streptococcus
pyogenes
Streptococcus
pyogenes
Staphylococcus
aureus
Staphylococcus
aureus
Staphylococcus
aureus
ATCC
49619
PU 11
Erythromycin-susceptible
a
O
OMe
O
OMe
MLS-resistant(constitutive),
PRSPa
erm þ mef
mef
N
O
O
N
Efflux, PSSPb
O
PU 09
PU 27
A 1
HO
HO
O
O
O
O
O
MLS-resistant(constitutive),
PSSP
erm
O
O
O
O
Efflux, erythromycin-resistant NTh
10
8
A 2
MLS-resistant(constitutive)
Erythromycin-susceptible
Erythromycin-susceptible
NT
Scheme 3. Synthesis of the ketolide 10i. (a) 10% PdeC, HCOOH, HCOONH4, H2, 65 ꢀC,
24 h, MeOH. 8i , 10i: Ar]4-isoquinolyl.
A 3
NT
ATCC
29213
PU 32
None
ermA
ermC
ermA
ermA
NT
haemolyticus, Staphylococcus epidermidis, Staphylococcus hominis,
S. pneumoniae, Streptococcus pyogenes, and Streptococcus dysga-
lactiae. All isolates tested were identified by 16S rDNA sequencing.
S. aureus ATCC 29213 and S. pneumoniae ATCC 49619 were used as
controls. All the strains, separately labeled by corresponding
genotypes and phenotypes, are listed in Table 1.
Azithromycin and clarithromycin were tested as the reference
compounds. Data are presented in Table 2 as the minimal inhibitory
concentration (MIC), which was determined by the broth micro-
dilution method as recommended by the Clinical and Laboratory
Standards Institute [31]
MLS-resistant(inducible),
MRSAc
MLS-resistant(constitutive),
MRSA
PU 20
PU 64
PU 19
E 1
Staphylococcus
aureus
MLS-resistant(inducible),
MSSAd
Staphylococcus
haemolyticus
Staphylococcus
epidermidis
Staphylococcus
epidermidis
Staphylococcus
hominis
MLS-resistant(constitutive),
MRSCone
MLS-resistant(inducible),
MSSEf
E 2
MLS-resistant(constitutive),
MRSEg
MLS-resistant(inducible),
MRSCon
NT
E 3
NT
4. Results and discussion
a
PRSP: penicillin-resistant Streptococcus pneumoniae.
PSSP: penicillin-susceptible Streptococcus pneumoniae.
MRSA: methicillin-resistant Staphylococcus aureus.
MSSA: methicillin-susceptible Staphylococcus aureus.
MRSCon: methicillin-resistant coagulase-negative Staphylococci.
MSSE: methicillin-susceptible Staphylococcus epidermidis.
MRSE: methicillin-resistant Staphylococcus epidermidis.
NT: not tested.
b
c
Compounds 8, bearing a 3-aryl-2-propargyl group at the 9-
oxime, were equally as active as clarithromycin and azithromycin
against erythromycin-susceptible strains, and showed significantly
improved antibacterial activity against erythromycin-resistant
bacteria as compared to the references. More importantly, some
compounds, exemplified by 8h and 8i, even exhibited higher
potency than previously reported 9k bearing a 3-aryl-E-prop-2-
enyl group at the 9-oxime [27]
The potency of series 8 was found to depend markedly on the
aryl groups attached to the end of the propargyl linker. Among
them, 8g (5-indolyl) showed the poorest activity and was the only
one that contained a potential hydrogen bond donor. Except for 8g,
the other sulfur-containing and nitrogen-containing compounds
(8ae8f, 8he8l) were potential hydrogen bond acceptors. Nam re-
ported the 2-thienyl group linked to a ketolide via a propenyl linker
conferred high potency [25], but the compounds with a 2-thienyl
group attached to the end of a propargyl group, such as 8a (2-
thienyl), 8e (2-[5-(2-pyridyl)]thienyl), and 8f (2-[5-(1-benzoyl)]
d
e
f
g
h
thienyl), were inferior to the other pyridine-containing and
quinoline-containing compounds, such as 8be8d, 8he8l. This point
strongly suggested nitrogen-containing heteroaryl groups are
favorable due to their hydrogen bonding with bacterial rRNA.
Within the fused bicyclic aryl groups, the point of attachment of the
quinoline ring had an impact on antibacterial activity. For instance,
8i (4-isoquinolyl) was significantly more potent than its analogs 8h
(5-isoquinolyl), whereas 8l (6-quinolyl) was slightly more effective
than its isomers 8k (3-quinolyl) and 8j (4-quinolyl). It is worth
noting that the shift of the nitrogen atom from the aryl position-1
(8j) to the position-2 (8i) resulted in a dramatic improvement in
antibacterial activity ranging from 4-fold to 32-fold against both
inducibly MLSB-resistant and efflux-resistant organisms, which
suggests the existence of a powerful interaction between the latter
and the bacterial rRNA. In contrast, within the monocyclic aryl
groups, a shift of the nitrogen atom (8b vs 8c) and incorporation of
an additional nitrogen atom in the aryl groups (8c vs 8d) led to less
profound change in antibacterial activity.
Apart from the aryl groups, the nature of the side chain deter-
mined the potency of the 9-oxime ether ketolides. The loss of
rigidity of the linker attenuated the activity (8k > 10k; 8i > 10i),
which revealed that greater flexibility might be unfavorable for
formation of the optimal pharmacophoric conformation. Different
linker chains resulted in different antibacterial profiles. For
instance, 8i was more effective than 9i and 10i (Ar]4-isoquinolyl),
whereas 9k was superior to 8k and 10k (Ar]3-quinolyl).
Ar
Ar
O
O
N
O
N
O
a or b
OMe
O
OMe
O
N
N
O
O
O
O
HO
HO
O
O
O
O
O
O
O
O
11
8
Scheme 4. Unsuccessful synthesis of the ketolide 11i; only the starting material 8i was
recovered in the presence of the conditions a or b. (a) Lindlar catalyst (5% Pd on
calcium carbonate poisoned with lead), H2, 30 ꢀC, 24 h, MeOH; (b) Lindlar catalyst,
HCOOH, HCOONH4, H2, 35 ꢀC, 24 h, MeOH. 8i , 11i: Ar]4-isoquinolyl.
To our surprise, the SAR of series 8 differed greatly from the
analogs 9 bearing 3-aryl-E-prop-2-enyl groups at the 9-oxime [27].
Isoquinolyl groups [8h (5-isoquinolyl) and 8i (4-isoquinolyl)]

58
J.-H. Liang et al. / European Journal of Medicinal Chemistry 59 (2013) 54e63
Table 2
In vitro antibacterial activity of ketolides against erythromycin-susceptible and-resistant pathogens.
Compd MIC( g/ml)
m
Streptococcus
S. pneumoniae
Staphylococcus
S. aureus
S. dysgalactiae S. pyogenes
S.haemolyticus S. epidermidis S.hominis
49619
eryS
PU 11
cMLS
PU 09
efflux
PU 27
cMLS
A 1
efflux
A 2
cMLS eryS
A 3
29213
eryS
PU 32
PU 20
cMLSc
PU 64
iMLS
PU 19
cMLS
E 1
E 2
E 3
a
iMLSb
iMLS cMLS iMLS
d
e
Cla
Azi
8a
8b
8c
8d
8e
8f
8g
8h
8i
8j
8k
8l
0.032
0.25
0.25
>256
>256
64
128
128
128
32
64
128
32
16
32
64
64
32
64
32
4
8
1
0.25
0.25
0.25
2
2
2
0.125
0.032
0.5
0.5
0.25
0.25
0.5
0.5
1
64
4
0.5
0.25
0.25
0.25
1
8
32
1
0.064
0.125
0.125
2
2
2
0.125
0.016
0.25
0.5
0.25
0.25
0.5
>256 0.032 0.25
1
8
1
>256
>256
NTf
NT
NT
256
NT
NT
NT
NT
2
8
NT
NT
NT
0.064
NT
NT
NT
NT
NT
NT
0.25
0.125
0.064
1
>256
>256
64
>256
>256
256
NT
128
NT
64
>256 >256 >256
>256 >256 >256
>256 0.125
1
1
32
128
64
128
32
32
128
32
0.25
1
64
0.125 >256 0.125
0.125 256 0.125
0.064 >256 0.064
1
ꢁ0.008
ꢁ0.008
0.032
ꢁ0.008
0.125
0.5
0.016
ꢁ0.008
0.016
ꢁ0.008
0.016
0.016
0.064
0.032
ꢁ0.008 0.064
ꢁ0.008 0.064
0.016 0.125
0.125
0.064
0.5
ꢁ0.008 0.064
ꢁ0.008 0.016
0.016 0.5
0.125
0.125
0.125
1
2
2
0.125
0.032
0.5
0.5
0.125
0.5
1
1
2
1
4
2
2
128
128
>256
8
2
8
4
0.125
0.064
1
0.5
0.25
0.125
1
0.064 64
0.016 32
0.125
0.064
0.25
16
32
NT
NT
32
64
0.25
0.25
64
64
64
32
32
ꢁ0.008 0.25
ꢁ0.008 0.125
ꢁ0.008 0.25
0.016 0.5
128
64
>256
>256
>256
128
64
>256
>256
>256
>256 0.25
0.032 >256 0.125
0.032 >256 0.064
9k
10k
10i
0.5
>256
2
1
0.25
64
0.016 0.125
0.5
0.25
0.25
>256 0.5
a
eryS: Erythromycin susceptible.
iMLS: Inducibly MLSB resistant.
cMLS: Constitutively MLSB resistant.
Cla: Clarithromycin.
Azi: Azithromycin.
NT: Not tested.
b
c
d
e
f
significantly enhanced potency compared to the corresponding
quinolyl groups [8j (4-quinolyl), 8k (3-quinolyl), and 8l (6-
quinolyl)], which is contrary to the previous conclusion drawn on
the 9 series. We previously disclosed that a bicyclic aryl group is
beneficial to antibacterial activity in contrast to a monocyclic aryl
group in the 9 series [27], however, no appreciable effect was
observed in the comparison of 8a (2-thienyl), 8e (2-[5-(2-pyridyl)]
thienyl), and 8f (2-[5-(1-benzoyl)]thienyl). Likewise, no improve-
ment was observed when comparing 8b (2-pyridyl), 8c (3-pyridyl)
and 8d (5-pyrimidyl) to 8j (4-quinolyl), 8k (3-quinolyl), and 8l (6-
quinolyl).
Compared to the second-generation erythromycins, 8i was
significantly more active against all of the pathogens tested, and
reached >4000-fold as active as the references against both
erythromycin-and methicillin-resistant S. homins E3, and even
>16000-fold against inducibly MLSB-resistant S. epidermis E1. It is
notable that ermA-mediated resistant S. aureus PU32 was
extracted from its crystal complex with the 50S ribosomal subunit
of Deinococcus radiodurans (PDB code: 1NWX).
It has been shown that the arylalkyl moiety of the ketolides
confers an additional and critical interaction with bacterial ribo-
somal RNA, particularly with mutation or methylation on A2058
(Escherichia coli numbering, equal to A2041 in D. radiodurans). The
extended heteroaryl groups of telithromycin and cethromycin are
considered to bind to domain Ⅱ of 23s rRNA [17,18,32]. The aryl
groups substituted at the 9-oxime via an appropriate linker (six-
atom length) reportedly extend to the same spatial position [23].
According to our docking results, the 9-O-(3-arylalkyl) oxime
sidechains of 8i and 9k may bind to a different pocket from the
arylalkyl group of cethromycin, as illustrated in Fig. 3 and Fig. 4. The
aryl groups of 9k and 8i approached domain Ⅴ of 23s rRNA.
On the other hand, the variation in the chemical structures in
series 8 and 9 produces an important difference in the binding
mode. Compound 9k could form a hydrogen bond with the
ꢀ
methicillin-resistant (MRSA); however, 8i had an MIC of 0.032
mg/
hydroxyl group of the pentose of G2044 (3.7 A, Fig. 3). Compound 8i
mL while azithromycin was inactive (MIC of 8 g/mL). As for efflux-
m
might hydrogen bond with the oxygen atom of the phosphate of
C2421 (3.1 A, Fig. 3). In addition to the hydrogen bonding, an extra
hydrophobic stacking effect was found between 8i and the adenine
group of A2045, which may account for the stronger potency of 8i
compared to that of 9k.
ꢀ
resistant strains, for instance S. pneumoniae PU09 encoding an mef
gene and S. dysgalactiae A1, 8i was 125-fold and 500-fold more
active than clarithromycin, respectively. Surprisingly, 8i was mark-
edly potent against constitutively MLSB-resistant S. pneumoniae
PU27 encoding an erm gene (MIC of 0.064
m
g/mL) as compared to
The aforementioned discrepancy of SAR found in the series 8
and 9 can be attributed to the structural variation of the sidechains
and the resulting change of orientation of the aryl groups. In other
words, the binding pocket located in the bacterial ribosome could
not accommodate the steric bulk of orientationally unsuitable
bicyclic aryl groups appended to the macrolide core via a propargyl
linker. When the orientation is suitable, such as in the most potent
candidate 8i, hydrogen bonding and hydrophobic interaction are
the most important attractive forces between the aryl group of the
drug and the rRNA of the bacteria, which is consistent with
the previous conclusion drawn on the X-ray crystal structure of the
complexity of ketolides and bacterial rRNA [17]. In addition, the
presence of the two kinds of interactions is implied by the
clarithromycin (MIC of 1 g/mL) and azithromycin (MIC of 64
m
mg/
mL). Regarding the other constitutively MLSB-resistant bacteria
PU11, A2, PU19, and E2, 8i showed >8-fold improvement over the
references, but unfortunately it was still only weakly active (MICs of
16e32 mg/mL).
5. Molecular docking and molecular modeling
To gain insight into the binding mode of the potent compounds
8i and 9k with the ribosome, we performed molecular docking and
energy minimization by using GOLD and AMBER, respectively. The
starting conformation was the crystal structure of cethromycin

J.-H. Liang et al. / European Journal of Medicinal Chemistry 59 (2013) 54e63
59
suggested the possibility of a novel binding mode that is different
from teltithromycin and cethromycin.
It is interesting to note that 8 displayed significant antibacterial
activity against inducibly MLSB-resistant and efflux-mediated
resistant pathogens, regardless of methicillin-susceptible or
methicillin-resistant phenotypes carried. Among the compounds in
the series 8, 8h (Ar]5-isoquinolyl) and 8i (Ar]4-isoquinolyl) were
the best candidates for further investigation.
7. Experimental
All solvents and reagents were obtained from commercial
sources (J & K Scientific) and used without further purification
unless otherwise noted. Flash column chromatography was per-
formed on silica gel (0.035e0.070 mm, Aldrich). 1H and 13C nuclear
magnetic resonance (NMR) spectra were recorded in CDCl3 on
Bruker ARX 400 MHz and 600 MHz spectrometers with tetrame-
thylsilane (TMS) as an internal standard. High resolution mass
spectra (HRMS) were obtained with a Bruker Apex IV FT mass
spectrometer.
Fig. 3. The docking poses of 8i (purple) and 9k (cyan) overlapped with the crystal
structure of cethromycin (green). (For interpretation of the references to color in this
figure legend, the reader is referred to the web version of this article.)
7.1. Docking calculations
The crystal structure of the 50S ribosomal subunit in complex
with cethromycin was retrieved from the RCSB Protein Data Bank
(PDB code: 1NWX). Only residues within 30 Å of cethromycin were
kept. The quinolinyl-propylene side chain in position 6 was
removed and replaced with a methoxyl group. The carbamate
nitrogen in position 11 was changed to oxygen. The carbonyl
oxygen in position 9 was mutated to nitrogen and it was used as the
anchor point for the oxime side chain. The docking calculation was
performed using the GOLD 3.0.1 program. The oxime side of 8i and
9k was docked to the binding site through a covalent attachment
with the oxime nitrogen. Each side chain was docked 10 times and
the best docking solution according to the GoldScore fitness func-
tion was chosen as the binding conformation. The binding confor-
mation was further optimized by energy minimization using Amber
9. The Parm99 force field was applied for the 50S ribosome, while
the ligand parameters were taken from the general Amber force
field (GAFF), and the atomic partial charges were calculated by the
bcc method. The energy minimization consisted of 3000 steps in
which the first 1000 were steepest descent (SD) and the last 2000
conjugate gradient (CG).
Fig. 4. The extended aryl groups of 8i (purple), 9k (cyan) and cethromycin (green)
interact with different rRNA pockets. The surface of rRNA is shown in solid. The
surfaces of 8i and 9k are shown in mesh. (For interpretation of the references to color
in this figure legend, the reader is referred to the web version of this article.)
7.2. 3-O-Descladinosyl-3-OH-6-O-methylerythromycin A E-9-
oxime (2)
Compound 1, 20,400-bis(trimethylsilyl)-6-O-methylerythromycin
A 9-O-(1-ethoxycyclohexyl)oxime, was prepared in three steps
following a published procedure [28] starting from commercially
available erythromycin A 9-oxime (20.00 g).
To a solution of resulting 1 in ethanol (30 mL) was added a dilute
HCl (8 mL of 36% aqueous HCl in 80 mL of water). The mixture was
stirred at 40 ꢀC for 1 h, and then was adjusted to pH 9 with 25%
aqueous NH3. The precipitate was collected by filtration and
washed with cold water. Recrystallization form ethanolewater
afforded 10.40 g of 2 [27]. MS (M þ Hþ) m/z: 605.5.
comparison of the potency of 8i (4-isoquinolyl) and 8h (5-
isoquinolyl), as well as 8i and 8c (3-pyridyl). In conclusion,
compound 8i is more potent than the other two compounds
because it can form both hydrogen bonds and hydrophobic inter-
actions with bacterial ribosomal RNA.
6. Conclusion
A series of 9-O-(3-arylalkyl)oxime ketolides 8 and 10 containing
a 11,12-cyclic carbonate was synthesized and evaluated. Ketolides 8
with
a
propargyl linker showed
a
very different profile of
7.3. 20-O-acetyl-3-O-descladinosyl-3-OH-6-O-methylerythromycin
structureeactivity relationships compared to previously reported
ketolides 9 with a propenyl linker [27]. Without a rigid linker, the 9-
O-(3-aryl-propgyl)oxime ketolides 10 were less potent than the
corresponding series 8 and series 9. Molecular docking studies
elucidated the disparity of SAR found in the series 8 and 9, and
A E-9-O-acetyloxime (3)
A solution of 2 (6.61 g, 10.93 mmol) in CH2Cl2 (50 mL) was
treated with acetic anhydride (3.2 mL, 32.60 mmol) at room
temperature for 1 h. The reaction mixture was washed with

60
J.-H. Liang et al. / European Journal of Medicinal Chemistry 59 (2013) 54e63
saturated NaHCO3, water and brine. The organic layer was
concentrated and dried to get 3 [27] (6.90 g, 91.7%).
(d, J ¼ 7.8 Hz, 3 H, 4-CH3), 0.99 (d, J ¼ 6.6 Hz, 3 H, 8-CH3), 0.89
(t, J ¼ 7.2 Hz, 3 H, 15-CH3).
7.4. 20-O-acetyl-3-O-descladinosyl-3-OH-6-O-methylerythromycin
A E-9-O-propargyloxime (4)
7.7. 3-O-Descladinosyl-3-keto-6-O-methylerythromycin A E-9-O-
[3-(40-isoquinolyl)-2-propargyl] oxime 11,12-cyclic carbonate (8i)
To a solution of 3 (0.50 g, 0.73 mmol) in DMF (15 mL) was added
KOtBu (0.12 g, 1.10 mmol). After stirring for 10 min, additional
KOtBu (0.81 g, 0.73 mmol) and propargyl bromide (0.07 mL,
0.80 mmol) were added. The reaction mixture was stirred for 1 h at
room temperature, then extracted with ethyl acetate, and washed
with water and brine. The organic layer was concentrated and dried
to yield 4 (0.47 g, 94.5%). 4: HRMS (ESI) (MHþ) m/z 685.42599, calcd
To a solution of 6 (1.000 g, 1.412 mmol), CuI (27 mg, 0.14 mmol)
and PdCl2(PPh3)2 (0.050 g, 0.05 mmol) in acetonitrile (12 mL) were
added 4-bromoisoquinoline (0.734 g, 3.35 mmol) and triethyl-
amine (0.29 mL, 2.12 mmol). The reaction mixture was flushed with
nitrogen and sealed in a pressure tube. The reaction mixture was
stirred at 80 ꢀC for 3 h. The mixture was extracted with ethyl
acetate and washed with water and brine. The organic phase was
concentrated in vacuo. The crude mixture was purified by column
chromatography on silica gel (15:0.4:0.1 CH2Cl2/C2H5OH/NH3$H2O)
for C35H61N2O11 685.42699. 1H NMR (400 MHz, CDCl3)
d: 5.25 (dd,
J ¼ 1.6 H, 11.0 Hz, 1 H, H-13), 4.76 (dd, J ¼ 7.7 Hz, 10.2 Hz, 1 H, H-20),
4.62 (d, J ¼ 7.6 Hz, 1 H, H-10), 4.57 (s, 2 H, CH2eC^CH), 4.48 (s, 1 H,
11-OH), 3.81 (s, 1 H, H-11), 3.71 (d, J ¼ 1.7 Hz, 1 H, H-5), 3.58e3.62
(m, 1 H, H-8), 3.47e3.51 (m, 1 H, H-50), 3.41 (d, J ¼ 10.5 Hz, 1 H, H-3),
3.33 (s, 1 H, 12-OH), 2.98 (s, 3 H, 6-OCH3), 2.57e2.73 (m, 3 H, H-10,
H-2, H-30), 2.49 (t, J ¼ 2.1 Hz, 1 H, CH2eC^CH), 2.26 (s, 6 H,e
N(CH3)2), 2.06e2.11 (m, 1 H, H-4), 1.94e1.96 (m, 1 H, H-14eq),
2.06 (s, 3 H, 20-OeAc), 1.71e1.75 (m, 1 H, H-40eq), 1.31e1.49 (m, 3 H,
H-7, H-14ax), 1.30 (s, 3 H, 6-CH3), 1.15e1.24 (m,13 H, H-40ax, 10-CH3,
12-CH3, 20-CH3, 50-CH3), 0.97 (d, J ¼ 7.0 Hz, 3 H, 4-CH3), 0.90 (d,
J ¼ 7.3 Hz, 3 H, 8-CH3), 0.83 (t, 3 H, 15-CH3); 13C NMR (100 MHz,
to yield 7i (0.278 g, 23.6%). 7i: 1H NMR (400 MHz, CDCl3)
d: [9.18 (s,
1 H), 8.65 (s, 1 H), 8.29 (d, J ¼ 7.6 Hz, 1 H), 7.97 (d, J ¼ 7.6 Hz, 1 H),
7.79 (t, J ¼ 6.4 Hz, 1 H), 7.65 (t, J ¼ 6.4 Hz, 1 H), 4-isoquinolyl], 4.97e
5.05 (m, 3 H, CH2eC^CeAr, H-13), 4.66e4.85 (m, 2 H, H-11, H-20),
4.38 (d, J ¼ 6.4 Hz, 1 H, H-10), 4.15 (d, J ¼ 6.8 Hz, 1 H, H-5), 3.55e3.78
(m, 3 H, H-8, H-2, H-50), 3.00e3.11 (m, 1 H, H-4), 2.67 (s, 3 H, 6-
OCH3), 2.50e2.55 (m, 2 H, H-10, H-30), 2.33 (s, 6H, eN(CH3)2),
2.09 (s, 3 H, 20-OCCH3), 1.80e1.92 (m, 2 H, H-40eq, H-14eq), 1.57 (s,
3 H, 12-CH3), 1.43 (s, 3 H, 6-CH3), 1.25e1.34 (m, 9 H, 10-CH3, 50-CH3,
2-CH3),1.11 (d, J ¼ 6.8 Hz, 3 H, 4-CH3),1.02 (d, J ¼ 5.6 Hz, 3 H, 8-CH3),
0.89 (t, 3 H, 15-CH3).
CDCl3) d: 174.6, 170.8, 169.8, 99.5, 80.3, 79.7, 78.0, 77.2, 74.2, 73.8,
71.2 70.2, 68.4, 62.9, 60.7, 49.9, 44.0, 36.8, 35.8, 32.9, 30.8, 26.2, 21.3,
21.2, 20.9, 19.1, 18.2, 16.1, 15.2, 15.0, 10.2, 7.6.
A solution of 7i (0.278 g, 0.333 mmol) in MeOH (25 mL) was
stirred at 65 ꢀC for 3 h and was then concentrated. The residue was
purified by column chromatography on silica gel (5:5:0.2 petro-
leum ether/acetone/triethylamine) to yield analytically pure
product 8i (0.126 g, 47.7%). 8i: HRMS (ESI) (MHþ) m/z 794.42221,
7.5. 20-O-acetyl-3-O-descladinosyl-3-OH-6-O-methylerythromycin
A E-9-O-propargyloxime 11,12-cyclic carbonate (5)
calcd for C43H60N3O11 794.42224. 1H NMR (400 MHz, CDCl3)
d: [9.18
To an ice-cold solution of 4 (1.77 g, 2.58 mmol) and pyridine
(2.29 mL, 28.49 mmol) in CH2Cl2 (70 mL) was added dropwise
a solution of bis(trichloromethyl)carbonate (1.54 g, 5.18 mmol) in
CH2Cl2 (30 mL). The reaction mixture was stirred at ꢂ5 ꢀC for 4 h
and then stirred at room temperature for 12 h. After the reaction
mixture was allowed to cool to 0 ꢀC, to the reaction mixture was
added dropwise brine (70 mL). The organic layer was washed with
saturated NaHCO3, water and brine, and was concentrated to afford
5 (1.49 g, 81.4%).
(s, 1 H), 8.65 (s, 1 H), 8.30 (d, J ¼ 8.4 Hz, 1 H), 7.97 (d, J ¼ 8.4 Hz, 1 H),
7.79 (td, 1 H), 7.64 (td, 1 H), 4-isoquinolyl], 4.97e5.06 (m, 3 H, CH2e
C^CeAr, H-13), 4.82 (s,1 H, H-11), 4.28 (d, J ¼ 7.3 Hz,1 H, H-10), 4.17
(d, J ¼ 8.5 Hz, 1 H, H-5), 3.78 (br, 1 H, H-8), 3.46e3.55 (m, 2 H, H-2,
H-50), 3.18 (dd, J ¼ 7.3 and 10.2 Hz, 1 H, H-20), 3.01e3.05 (m, 1 H, H-
4), 2.69 (s, 3 H, 6-OCH3), 2.63 (br, 1 H, H-10), 2.40e2.47 (m, 1 H, H-
30), 2.26 (s, 6 H, eN(CH3)2), 1.89e1.93 (m, 1 H, H-14eq), 1.64e1.75
(m, 3 H, H-7, H-40eq), 1.57 (s, 3 H, 12-CH3), 1.46 (s, 3 H, 6-CH3),
1.21e1.33 (m,12 H, 4-CH3,10-CH3, 50-CH3, 2-CH3),1.02 (d, J ¼ 6.8 Hz,
3 H, 8-CH3), 0.89 (t, J ¼ 7.2 Hz, 3 H, 15-CH3); 13C NMR (100 MHz,
7.6. 20-O-acetyl-3-O-descladinosyl-3-keto-6-O-methylerythromycin
CDCl3) d: 203.9, 169.0, 165.9, 154.4, 152.1, 146.6, 135.8, 131.2, 127.9,
A E-9-O-propargyloxime 11,12-cyclic carbonate (6)
127.7, 125.2, 115.5, 103.9, 93.2, 84.7, 82.7, 80.9, 79.4, 78.5, 77.2, 76.4,
70.4, 69.5, 65.9, 62.0, 51.1, 49.7, 47.8, 46.1, 40.2, 38.4, 28.2, 22.5, 21.2,
19.8, 18.9, 15.8, 15.5, 14.3, 13.2, 10.4.
A solution of N-chlorosuccinimide (NCS) (0.45 g, 3.35 mmol) in
CH2Cl2 (30 mL) was stirred at ꢂ15 ꢀC for 10 min and then dimethyl
sulfide (DMS) (0.29 mL, 3.98 mmol) was added slowly. After stirring
for 30 min, a solution of 5 (1.49 g, 2.10 mmol) in CH2Cl2 (20 mL) was
added to the reaction mixture. When TLC showed the reaction
reached completion, triethylamine (0.58 mL) was added dropwise
to the reaction mixture. The solution soon became clear and stirring
was continued at ꢂ5 ꢀC for 1 h. The organic layer was washed with
saturated NaHCO3, water and brine, and was concentrated to yield 6
(1.40 g, 94.3%). 6: HRMS(ESI) (MHþ) m/z 709.38920, calcd for
7.8. 3-O-Descladinosyl-3-keto-6-O-methylerythromycin A E-9-O-
[3-(20-thienyl)-2-propargyl] oxime 11,12-cyclic carbonate (8a)
Following the procedure for the synthesis 7i and 8i, 7a and 8a
were obtained from the coupling of 6 (0.700 g, 0.988 mmol) and 2-
bromothiophene (0.28 mL, 2.96 mmol) in yields of 15.0% and 64.2%,
respectively. 8a: HRMS(ESI) (MHþ) m/z: 749.36901, calcd for
C38H57N2O11S 749.36776; 1H NMR (400 MHz, CDCl3)
d: [7.22 (d,
C36H57N2O12 709.39060; 1H NMR (600 MHz, CDCl3)
d:, 5.04
J ¼ 4.4 Hz, 1 H), 7.18 (d, J ¼ 3.6 Hz, 1 H), 6.93e6.95 (m, 1 H), 2-
thienyl], 5.02 (dd, J ¼ 2.4 Hz, 10.0 Hz,1 H, H-13), 4.90 and 4.84 (d,
J ¼ 16.0 Hz, 2 H, CH2eC^CeAr), 4.77 (s,1 H, H-11), 4.30 (d, J ¼ 7.2 Hz,
1 H, H-10), 4.16 (d, J ¼ 8.4 Hz, 1 H, H-5), 3.51e3.80 (m, 3 H, H-8, H-50,
H-2), 3.25 (dd, J ¼ 7.2 Hz,10.0 Hz,1 H, H-20), 3.01e3.05 (m,1 H, H-4),
2.71 (s, 3 H, 6-OCH3), 2.49e2.64 (m, 2 H, H-30, H-10), 2.37 (s, 6 H, eN
(CH3)2), 1.87e1.91 (m, 1 H, H-14eq), 1.67e1.77 (m, 2 H, H-7, H-40eq),
1.56 (s, 3 H, 12-CH3), 1.41 (s, 3 H, 6-CH3), 1.33 (d, J ¼ 6.8 Hz, 3 H, 2-
CH3), 1.23e1.26 (m, 10 H, 4-CH3, 10-CH3, 50-CH3, H-40ax), 1.00 (d,
J ¼ 6.4 Hz, 3 H, 8-CH3), 0.88 (t, J ¼ 7.6 Hz, 3 H, 15-CH3); 13C NMR
(d, J ¼ 10.2 Hz, 1 H, H-13), 4.79 (s, 1 H, H-11), 4.74 (t, J ¼ 8.4 Hz, 1 H,
H-20), 4.65 and 4.61 (d, J ¼ 15.6 Hz, 2 H, CH2eC^CH), 4.37 (d,
J ¼ 7.2 Hz, 1 H, H-10), 4.17 (d, J ¼ 7.2 Hz, 1 H, H-5), 3.82 (q, J ¼ 6.0 Hz,
1 H, H-2), 3.62 (br,1 H, H-8), 3.52e3.55 (m,1 H, H-50), 2.99e3.02 (m,
1 H, H-4), 2.70 (s, 3 H, 6-OCH3), 2.65e2.70 (m, 1 H, H-30), 2.52e2.53
(m, 1 H, H-10), 2.40 (s, 1 H, CH2eC^CH), 2.25 (s, 6 H, eN (CH3)2),
2.04 (s, 3 H, 20-OAc),1.89e1.93 (m, 1 H, H-14eq), 1.74 (d, 1 H), 1.56 (s,
3 H, 12-CH3), 1.53e1.60 (m, 1 H, H-14ax), 1.38 (s, 3 H, 6-CH3), 1.36
(d, J ¼ 7.2 Hz, 3 H, 2-CH3), 1.24e1.26 (m, 6 H, 10-CH3, 50-CH3), 1.12

J.-H. Liang et al. / European Journal of Medicinal Chemistry 59 (2013) 54e63
61
(75 MHz, CDCl3)
d
: 204.2,169.2,165.9,154.5133.4,132.4,131.9,127.3,
3 H, 6-OCH3), 2.47e2.53 (m, 2 H, H-30, H-10), 2.29 (s, 6 H, eN
(CH3)2), 1.85e1.90 (m, 1 H, H-14eq), 1.66e1.69 (m, 2 H, H-7, H-40eq),
1.53(s, 3 H, 12-CH3), 1.40 (s, 3 H, 6-CH3), 1.33 (d, J ¼ 6.8 Hz, 3 H, 2-
CH3), 1.21e1.32 (m, 10 H, 4-CH3, 10-CH3, 50-CH3, H-40ax), 0.98 (d,
J ¼ 6.8 Hz, 3 H, 8-CH3), 0.87 (t, J ¼ 7.2 Hz, 3 H, 15-CH3); 13C NMR
127.0, 103.7, 89.9, 84.9, 82.8, 79.6, 79.3, 78.6, 70.4, 69.3, 66.3, 62.3,
51.3, 49.9, 48.0, 40.4, 38.6, 31.0, 29.1, 26.7, 22.7, 21.2, 19.9, 19.0, 16.0,
15.6, 14.5, 13.4, 10.5.
7.9. 3-O-Descladinosyl-3-keto-6-O-methylerythromycin A E-9-O-
[3-(20-pyridyl)-2-propargyl] oxime 11,12-cyclic carbonate (8b)
(75 MHz, CDCl3) d: 204.0, 169.2, 166.2, 158.9, 157.0, 154.5, 119.5,
103.8, 93.2, 84.8, 82.8, 79.4, 79.2, 78.5, 76.5, 70.4, 69.5, 66.2, 61.8,
51.2, 49.8, 47.8, 40.4, 38.4, 31.0, 28.7, 26.6, 22.6, 21.2, 19.9, 18.9, 15.8,
15.6, 14.4, 13.3, 10.4.
Following the procedure for the synthesis 7i and 8i, 7b and 8b
were obtained from the coupling of 6 (0.700 g, 0.988 mmol) and 2-
bromopyridine (0.29 mL, 2.96 mmol) in yields of 14.2% and 66.4%,
respectively. 8b: HRMS(ESI) (MHþ) m/z: 744.40835, calcd for
7.12. 3-O-Descladinosyl-3-keto-6-O-methylerythromycin A E-9-O-
[3-[20-(50-(2"-pyridyl))thienyl]-2-propargyl]oxime 11,12-cyclic
carbonate (8e)
C39H58N3O11 744.40659; 1H NMR (400 MHz, CDCl3)
d: [8.52 (d,
J ¼ 4.8 Hz, 1 H), 7.59e7.63 (m, 1 H), 7.39 (d, J ¼ 7.6 Hz, 1 H), 7.19 (dd,
J ¼ 6.8 Hz, 5.2 Hz, 1 H), 2-pyridyl], 5.00 (dd, J ¼ 10.0 Hz, 2.0 Hz,1 H,
H-13), 4.89 and 4.83 (d, J ¼ 16.0 Hz, 2 H, CH2eC^CeAr), 4.77 (s, 1 H,
H-11), 4.26 (d, J ¼ 7.2 Hz,1 H, H-10), 4.15 (d, J ¼ 8.4 Hz,1 H, H-5), 3.79
(q, J ¼ 6.8 Hz, 1 H, H-2), 3.64 (br, 1 H, H-8), 3.47e3.53 (m, 1 H, H-50),
3.17 (dd, J ¼ 10.0 Hz, 7.2 Hz, 1 H, H-20), 2.95e3.07 (m, 1 H, H-4),
2.68(s, 3 H, 6-OCH3), 2.41e2.52 (m, 2 H, H-10, H-30), 2.26 (s, 6 H, -N
(CH3)2), 1.85e1.91 (m, 1 H, H-14eq), 1.64e1.69 (m, 2 H, H-7, H-40eq),
1.53 (s, 3 H, 12-CH3), 1.40 (s, 3 H, 6-CH3), 1.35(d, J ¼ 6.8 Hz, 3 H, 2-
CH3), 1.20e1.24 (m, 10 H, 4-CH3, 10-CH3, 50-CH3, H-40ax), 0.97 (d,
J ¼ 6.8 Hz, 3 H, 8-CH3), 0.86 (t, 3 H, J ¼ 7.2 Hz, 15-CH3); 13C NMR
Following the procedure for the synthesis 7i and 8i, 7e and 8e
were obtained from the coupling of 6 (0.700 g, 0.988 mmol) and 2-
(5-bromo-2-thienyl)pyridine (0.505 g, 2.10 mmol) in yields of 6.9%
and 48.5%, respectively. 8e: HRMS(ESI)(MHþ) m/z: 826.39418, calcd
for C43H60N3O11S 826.39431; 1H NMR (600 MHz, CDCl3)
d: [8.54 (d,
J ¼ 4.2 Hz, 1 H), 7.65e7.69 (m, 1 H), 7.61(d, J ¼ 7.8 Hz, 1 H), 7.42 (d,
J ¼ 3.6 Hz,1 H), 7.15e7.20(m, 2 H), 2-(5-(2-pyridyl)thienyl)], 5.04 (d,
J ¼ 9.0 Hz, 1 H, H-13), 4.93 and 4.88 (d, J ¼ 15.6 Hz, 2 H, CH2eC^Ce
Ar), 4.79 (s, 1 H, H-11), 4.32 (d, J ¼ 7.2 Hz, 1 H, H-10), 4.17 (d,
J ¼ 6.6 Hz, 1 H, H-5), 3.54e3.82 (m, 3 H, H-8, H-50, H-2), 3.26 (dd,
J ¼ 7.8 Hz, 9.6 Hz, 1 H, H-20), 3.03e3.06 (m, 1 H, H-4), 2.73 (s, 3 H, 6-
OCH3), 2.61e2.70 (m, 2 H, H-30, H-10), 2.39 (s, 6 H, eN (CH3)2),
1.89e1.93 (m, 1 H, H-14eq), 1.76 (d, J ¼ 12.0 Hz, 1 H, H-7), 1.68e1.72
(m, 1 H, H-40eq), 1.57 (s, 3 H, 12-CH3), 1.42 (s, 3 H, 6-CH3), 1.33 (d,
J ¼ 4.8 Hz, 3 H, 2-CH3), 1.24e1.36 (m, 10 H, 4-CH3,10-CH3, 50-CH3, H-
40ax), 1.02 (d, J ¼ 3.6 Hz, 3 H, 8-CH3), 0.89 (t, J ¼ 7.2 Hz, 3 H, 15-CH3);
(100 MHz, CDCl3) d: 204.0, 169.2, 165.8, 154.5, 150.0, 143.1, 136.2,
132.1, 127.4, 123.0, 103.8, 85.8, 85.2, 84.8, 82.8, 79.6, 78.5, 76.4, 70.4,
69.5, 66.0, 61.9, 51.2, 49.8, 48.0, 40.3, 38.4, 28.5, 26.5, 22.5, 21.2, 19.9,
18.9, 16.0, 15.5, 14.4, 13.3, 10.5.
7.10. 3-O-Descladinosyl-3-keto-6-O-methylerythromycin A E-9-O-
[3-(30-pyridyl)-2-propargyl]oxime 11,12-cyclic carbonate (8c)
13C NMR (100 MHz, CDCl3)
d: 203.8, 168.6, 165.7, 154.2, 151.6, 149.4,
136.4, 133.2, 132.8, 124.2, 123.9, 122.0, 118.6, 69.9, 68.9, 65.9, 62.0,
50.9, 49.5, 47.6, 40.0, 20.9, 15.2, 14.1, 10.2.
Following the procedure for the synthesis 7i and 8i, 7c and 8c
were obtained from the coupling of 6 (1.000 g, 1.41 mmol) and 3-
bromopyridine (0.41 mL, 4.20 mmol) in yields of 10.1% and 46.9%,
respectively. 8c: HRMS(ESI) (MHþ) m/z 744.40750, calcd for
7.13. 3-O-Descladinosyl-3-keto-6-O-methylerythromycin A E-9-O-
[3-(20-(50-benzoyl)thienyl)-2-propargyl]oxime 11,12-cyclic
carbonate (8f)
C39H58N3O11 744.40659; 1H NMR (400 MHz, CDCl3)
d: [8.65 (s, 1 H),
8.53 (s, 1 H), 7.71 (d, J ¼ 8.0 Hz, 1 H),7.24e7.26 (m, 1 H), 3-pyridyl],
5.04 (dd, J ¼ 2.4 Hz, 10.4 Hz, 1 H, H-13), 4.91 and 4.85 (d, J ¼ 15.6 Hz,
2 H, CH2eC^CeAr), 4.80 (s, 1 H, H-11), 4.30 (d, J ¼ 7.2 Hz,1 H, H-10),
4.19 (d, J ¼ 8.4 Hz, 1 H, H-5), 3.81 (q, J ¼ 6.8 Hz, 1 H, H-2), 3.66 (br,
1 H, H-8), 3.53e3.57 (m, 1 H, H-50), 3.22 (t, J ¼ 7.6 Hz, 1 H, H-20),
3.02e3.06 (m, 1 H, H-4), 2.72 (s, 3 H, 6-OCH3), 2.47e2.56 (m, 2 H, H-
30, H-10), 2.30 (s, 6 H, -N (CH3)2), 1.89e1.94 (m, 1 H, H-14eq), 1.69e
1.72 (m, 2 H, H-7, H-40eq), 1.56 (s, 3 H, 12-CH3), 1.44 (s, 3 H, 6-CH3),
1.36 (d, J ¼ 6.8 Hz, 3 H, 2-CH3),1.20e1.31 (m,10 H, 4-CH3,10-CH3, 50-
CH3, H-40ax), 1.01 (d, J ¼ 6.8 Hz, 3 H, 8-CH3), 0.90 (t, 3 H, J ¼ 7.2 Hz,
Following the procedure for the synthesis 7i and 8i, 7f and 8f
were obtained from the coupling of 6 (0.600 g, 0.847 mmol) and 2-
bromo-5-benzoylthiophene (0.452 g, 1.69 mmol) in yields of 26.7%
and 23.9%, respectively. 8f: HRMS(ESI) (MHþ) m/z 853.39585, calcd
for C45H61N2O12S 853.39397; 1H NMR (600 MHz, CDCl3)
d: [7.83e
7.85 (m, 2 H), 7.58e7.61 (m, 1 H), 7.49e7.52 (m, 3 H), 7.19 (d,
J ¼ 3.6 Hz, 1 H), 2-(5-benzoyl)thienyl], 5.04 (dd, J ¼ 3.0 Hz,
7.2 Hz,1 H, H-13), 4.92 and 4.88 (d, J ¼ 16.2 Hz, 2 H, CH2eC^CeAr),
4.80 (s, 1 H, H-11), 4.30 (d, J ¼ 7.8 Hz, 1 H, H-10), 4.19 (d, J ¼ 9.0 Hz,
1 H, H-5), 3.81 (q,1 H, H-2), 3.65 (br,1 H, H-8), 3.53e3.56 (m, 1 H, H-
50), 3.20 (dd, J ¼ 7.8 Hz, 10.2 Hz, 1 H, H-20), 3.03e3.05 (m, 1 H, H-4),
2.72 (s, 3 H, 6-OCH3), 2.47e2.54 (m, 2 H, H-30, H-10), 2.29 (s, 6 H, eN
(CH3)2), 1.89e1.93 (m, 1 H, H-14eq), 1.68e1.72 (m, 2 H, H-7, H-40eq),
1.56 (s, 3 H, 12-CH3), 1.43 (s, 3 H, 6-CH3), 1.35 (d, J ¼ 7.2 Hz, 3 H, 2-
CH3), 1.23e1.27 (m, 10 H, 4-CH3, 10-CH3, 50-CH3, H-40ax), 1.02 (d,
J ¼ 6.6 Hz, 3 H, 8-CH3), 0.89 (t, J ¼ 7.2 Hz, 3 H, 15-CH3).
15-CH3); 13C NMR (75 MHz, CDCl3)
d: 204.1, 169.2, 165.9, 154.5,
152.5, 148.8, 138.8, 103.8, 89.3, 84.9, 82.8, 79.5, 78.6, 77.4, 76.6, 70.4,
69.4, 66.2, 62.0, 51.3, 49.8, 47.9, 40.4, 38.5, 28.8, 26.6, 22.6, 21.3, 19.9,
19.0, 15.9, 15.6, 14.4, 13.4, 10.5.
7.11. 3-O-Descladinosyl-3-keto-6-O-methylerythromycin A E-9-O-
[3-(50-pyrimidyl)-2-propargyl]oxime 11,12-cyclic carbonate (8d)
Following the procedure for the synthesis 7i and 8i, 7d and 8d
were obtained from the coupling of 6 (0.700 g, 0.988 mmol) and 5-
bromopyrimidine (0.471 g, 2.96 mmol) in yields of 37.3% and 14.6%,
respectively. 8d: HRMS (ESI) (MHþ) m/z 745.40115, calcd for
7.14. 3-O-Descladinosyl-3-keto-6-O-methylerythromycin A E-9-O-
[3-(50-indolyl)-2-propargyl]oxime 11,12-cyclic carbonate (8g)
Following the procedure for the synthesis 7i and 8i, 7g and 8g
were obtained from the coupling of 6 (0.600 g, 0.847 mmol) and 5-
bromoindole (0.415 g, 2.12 mmol) in yields of 7.9% and 40.3%,
respectively. 8g: HRMS(ESI) (MHþ) m/z: 782.42287, calcd for
C38H57N4O11 745.40184; 1H NMR (400 MHz, CDCl3)
d: [9.10 (s, 1 H),
8.73 (s, 2 H), 5-pyrimidyl], 5.01 (dd, J ¼ 2.4 Hz, 10.4 Hz,1 H, H-13),
4.88 and 4.83 (d, J ¼ 16.4 Hz, 2 H, CH2eC^CeAr), 4.76 (s, 1 H, H-11),
4.28 (d, J ¼ 7.6 Hz, 1 H, H-10), 4.17 (d, J ¼ 8.4 Hz, 1 H, H-5), 3.80
(q, J ¼ 6.8 Hz, 1 H, H-2), 3.50e3.64 (m, 2 H, H-50, H-8), 3.19
(dd, J ¼ 7.6 Hz, 10.0 Hz, 1 H, H-20), 2.98e3.02 (m, 1 H, H-4), 2.68 (s,
C42H60N3O11 782.42224; 1H NMR (600 MHz, CDCl3)
d: [8.33 (s, 1 H),
7.75 (s, 1 H), 7.31 (d, J ¼ 8.4 Hz, 1 H), 7.25 (d, 1 H), 7.22 (d, J ¼ 2.4 Hz,
1H), 6.51 (s, 1 H), 5-indolyl], 5.03 (dd, 1 H, H-13), 4.92 and 4.87

62
J.-H. Liang et al. / European Journal of Medicinal Chemistry 59 (2013) 54e63
(d, J ¼ 16.0 Hz, 2 H, CH2eC^CeAr), 4.78 (br, 1 H, H-11), 4.30 (d,
J ¼ 7.2 Hz,1 H, H-10), 4.15 (br,1 H, H-5), 3.52e3.84 (m, 3 H, H-8, H-50,
H-2), 3.26 (dd, J ¼ 7.2 Hz, 9.6 Hz, 1 H, H-20), 3.02e3.04 (m, 1 H, H-4),
2.73 (s, 3 H, 6-OCH3), 2.49e2.61 (m, 2 H, H-30, H-10), 2.35 (s, 6 H, eN
(CH3)2), 1.71e1.93 (m, 3 H, H-14eq, H-7, H-40eq), 1.59 (s, 3 H, 12-
CH3), 1.42 (s, 3 H, 6-CH3), 1.33 (d, J ¼ 6.8 Hz, 3 H, 2-CH3), 1.24e
1.36 (m, 10 H, 4-CH3, 10-CH3, 50-CH3, H-40ax), 1.03 (d, J ¼ 3.6 Hz,
3 H, 8-CH3), 0.89 (t, J ¼ 7.2 Hz, 3 H, 15-CH3).
7.78 (d, J ¼ 8.3 Hz, 1 H), 7.65e7.69 (m, 1 H), 7.51e7.55 (m, 1 H), 3-
quinolyl], 5.05 (dd, J ¼ 2.6, 10.0 Hz,1 H, H-13), 4.96 and 4.91 (d,
J ¼ 15.4 Hz, 2 H, CH2C^CeAr), 4.80 (s, 1 H, H-11), 4.29 (d, J ¼ 7.3 Hz,
1 H, H-10), 4.19 (d, J ¼ 8.4 Hz, 1 H, H-5), 3.51e3.84 (m, 3 H, H-2, H-8,
H-50), 3.20 (dd, J ¼ 7.3 Hz, 10.2 Hz, 1 H, H-20), 3.00e3.06 (m, 1 H, H-
4), 2.73 (s, 3 H, 6-OCH3), 2.44e2.57 (m, 2 H, H-30, H-10), 2.27 (s,
6 H, eN(CH3)2), 1.89e1.93 (m, 1 H, H-14eq), 1.66e1.74 (m, 2 H, H-7,
H-40eq), 1.57 (s, 3 H, 12-CH3), 1.46 (s, 3 H, 6-CH3), 1.22e1.34 (m,
13 H, 4-CH3, 10-CH3, 50-CH3, 2-CH3, H-40ax), 1.08 (d, J ¼ 6.8 Hz, 3 H,
7.15. 3-O-Descladinosyl-3-keto-6-O-methylerythromycin A E-9-O-
[3-(50-isoquinolyl)-2-propargyl]oxime 11,12-cyclic carbonate (8h)
8-CH3), 0.89 (t, J ¼ 7.4 Hz, 3 H,15-CH3). 13C NMR (CDCl3, 100 MHz)
d:
204.0, 169.1,165.9,159.5,154.4,152.1,146.9,138.8,130.1,129.4,127.7,
127.2, 117.0, 103.6, 76.4, 70.3, 69.3, 66.1, 62.0, 51.2, 49.7, 47.8, 40.3,
29.3, 22.5, 21.1, 19.8, 18.9, 15.8, 14.3, 13.2, 10.4.
Following the procedure for the synthesis 7i and 8i, 7h and 8h
were obtained from the coupling of 6 (0.700 g, 0.988 mmol) and 5-
bromoisoquinoline (0.514 g, 2.47 mmol) in yields of 13.5% and
28.6%, respectively. 8h: HRMS(ESI) (MHþ) m/z: 794.42208, calcd for
7.18. 3-O-Descladinosyl-3-keto-6-O-methylerythromycin A E-9-O-
[3-(60-quinolyl)-2-propargyl]oxime 11,12-cyclic carbonate (8l)
C43H60N3O11 794.42224; 1H NMR (400 MHz, CDCl3)
d: [9.25 (s, 1 H),
8.61 (s, 1 H), 8.11 (d, J ¼ 4.0 Hz, 1 H), 7.94 (d, J ¼ 8.0 Hz, 1 H), 7.83 (d,
J ¼ 8.0 Hz, 1 H), 7.55 (t, J ¼ 4.0 Hz,1 H), 5-isoquinolyl], 4.96e5.05 (m,
3 H, CH2eC^CeAr, H-13),, 4.82 (s,1 H, H-11), 4.29 (d, J ¼ 4.0 Hz,1 H,
H-10), 4.17 (d, J ¼ 8.0 Hz, 1 H, H-5), 3.54e3.80 (m, 3 H, H-2, H-50, H-
8), 3.23 (t, J ¼ 8.0 Hz,1 H, H-20), 3.02e3.04 (m, 1 H, H-4), 2.69 (s, 3 H,
6-OCH3), 2.55e2.57 (m, 2 H, H-30, H-10), 2.33 (s, 6 H, eN(CH3)2),
1.89e1.91 (m, 1 H, H-14eq), 1.69e1.72 (m, 2 H, H-7, H-40eq), 1.57 (s,
3 H, 12-CH3), 1.47 (s, 3 H, 6-CH3), 1.22e1.38 (m, 12 H, 4-CH3, 10-CH3,
50-CH3, 2-CH3),1.02 (d, J ¼ 4.0 Hz, 3 H, 8-CH3), 0.89 (t, J ¼ 8.0 Hz, 3 H,
Following the procedure for the synthesis 7i and 8i, 7l and 8l
were obtained from the coupling of 6 (0.700 g, 0.988 mmol) and 6-
bromoquinoline (0.330 mL, 2.43 mmol) in yields of 8.8% and 23.0%,
respectively. 8l: HRMS (ESI) (MHþ) m/z 794.42082, calcd for
C43H60N3O11 794.42224; 1H NMR (400 MHz, CDCl3)
d: [8.90 (dd,
J ¼ 1.6 Hz, 4.4 Hz, 1 H), 8.11 (d, J ¼ 8.0 Hz, 1 H), 8.02 (d, J ¼ 8.8 Hz,
1 H), 7.93 (s, 1 H), 7.69 (dd, J ¼ 1.6 Hz, 8.8 Hz, 1 H), 7.41 (q, J ¼ 4.4 Hz,
1 H), 6-quinolyl], 5.04 (dd, J ¼ 2.4 Hz, 10.0 Hz, 1 H, H-13), 4.94 and
4.89 (d, J ¼ 15.6 Hz, 2 H, CH2eC^CeAr), 4.81 (s, 1 H, H-11), 4.29 (d,
J ¼ 7.6 Hz, 1 H, H-10), 4.18 (d, J ¼ 8.4 Hz, 1 H, H-5), 3.77 (br, 1 H, H-2),
3.49e3.56 (m, 2 H, H-50, H-8), 3.21 (dd, J ¼ 7.6 Hz,10.0 Hz,1 H, H-20),
2.99e3.08 (m, 1 H, H-4), 2.73 (s, 3 H, 6-OCH3), 2.46e2.58 (m, 2 H, H-
30, H-10), 2.29 (s, 6 H, -N (CH3)2), 1.89e1.95 (m, 1 H, H-14eq), 1.72 (d,
1 H), 1.68 (d, 1 H), 1.57 (s, 3 H, 12-CH3), 1.46 (s, 3 H, 6-CH3), 1.23e1.32
(m, 13 H, 2-CH3, 4-CH3, 10-CH3, 50-CH3, H-40ax), 1.02 (d, J ¼ 6.4 Hz,
3 H, 8-CH3), 0.89 (t, J ¼ 7.2 Hz, 3 H, 15-CH3). 13C NMR (CDCl3,
15-CH3); 13C NMR (100 MHz, CDCl3)
d: 204.1, 169.1, 166.0, 154.6,
152.7, 144.1, 136.3, 134.4, 128.2, 126.8, 120.0, 119.0, 103.7, 92.0, 84.8,
82.9, 82.5, 79.5, 78.5, 76.5, 70.3, 69.3, 66.2, 62.2, 51.2, 49.8, 47.9,
40.4, 38.5, 28.9, 26.6, 22.6, 21.2, 19.9, 19.0, 16.0, 15.7, 14.4, 13.4, 10.5.
7.16. 3-O-Descladinosyl-3-keto-6-O-methylerythromycin A E-9-O-
[3-(40-quinolyl)-2-propargyl]oxime 11,12-cyclic carbonate (8j)
100 MHz) d: 204.0, 169.0, 165.7, 154.4, 150.9, 147.7, 135.8, 132.2,
Following the procedure for the synthesis 7i and 8i, 7j and 8j
were obtained from the coupling of 6 (0.600 g, 0.847 mmol) and 4-
bromoquinoline (0.400 g, 2.12 mmol) in yields of 15.0% and 33.1%,
respectively. 8j: HRMS(ESI) (MHþ) m/z 794.42359, calcd for
131.4, 129.5, 128.0, 121.7, 121.2, 103.8, 87.0, 85.5, 84.8, 82.8, 79.5,
78.5, 77.2, 76.4, 70.4, 69.5, 65.6, 62.1, 51.2, 49.7, 47.9, 40.4, 40.2, 38.4,
28.3, 26.5, 22.5, 21.2, 19.8, 18.9, 15.9, 15.5, 14.3, 13.3, 10.4.
C43H60N3O11 794.42224; 1H NMR (600 MHz, CDCl3)
d: [8.85 (d,
7.19. 3-O-Descladinosyl-3-keto-6-O-methylerythromycin A E-9-O-
[3-(30-quinolyl)-2-propyl]oxime 11,12-cyclic carbonate (10k)
J ¼ 4.2 Hz, 1 H), 8.30 (d, J ¼ 8.4 Hz, 1 H), 8.09 (d, J ¼ 9.0 Hz, 1 H), 7.73
(t, J ¼ 7.2 Hz, 1 H), 7.61 (t, J ¼ 7.2 Hz, 1 H), 7.46 (d, J ¼ 4.2 Hz, 1 H), 4-
quinolyl], 4.98e5.06 (m, 3 H, H-13, CH2eC^CeAr), 4.82 (s, 1 H, H-
11), 4.29 (d, J ¼ 7.2 Hz, 1 H, H-10), 4.19 (d, J ¼ 8.4 Hz, 1 H, H-5), 3.71e
3.81 (m, 2 H, H-8, H-2), 3.52e3.55 (m, 1 H, H-50), 3.19 (dd, J ¼ 7.8 Hz,
10.2 Hz, 1 H, H-20), 3.01e3.05 (m, 1 H, H-4), 2.71 (s, 3 H, 6-OCH3),
2.58 (br, 1 H, H-10), 2.43e2.49 (m, 1 H, H-30), 2.28 (s, 6 H, eN
(CH3)2), 1.89e1.94 (m, 1 H, H-14eq), 1.72 (d, J ¼ 13.8 Hz, 1 H, H-7),
1.67 (d, J ¼ 12.0 Hz, 1 H, H-40eq), 1.57 (s, 3 H, 12-CH3), 1.55e1.62 (m,
1 H, H-14ax), 1.47 (s, 3 H, 6-CH3), 1.34 (d, J ¼ 6.0 Hz, 3 H, 2-CH3),
1.22e1.30 (m, 10 H, 4-CH3, 10-CH3, 50-CH3, H-40ax), 1.03 (d,
J ¼ 6.6 Hz, 3 H, 8-CH3), 0.89 (t, J ¼ 7.2 Hz, 3 H, 15-CH3); 13C NMR
To a solution of 9k [27] (0.254 g, 0.319 mmol) in MeOH (10 mL)
were added HCOONH4 (0.200 g, 3.19 mmol), HCOOH (0.24 mL,
6.38 mmol), and 10% PdeC (0.13 g). The reaction mixture was
flushed with hydrogen and sealed in a pressure tube, and then was
stirred at 65 ꢀC for 24 h. 10% PdeC was removed by filtration before
the solvent was evaporated. The residue was dissolved in CH2Cl2,
and aqueous NaOH (2 mol/L) was added to adjust the pH to ꢃ9.
Additional water (20 mL) was added, and the mixture was stirred
for 20 min. The organic phase was washed with brine (20 mL) and
then concentrated in vacuo. The crude product was purified by
column chromatography on silica gel (5:5:0.2 petroleum ether/
acetone/triethylamine) to yield 10k (47 mg, 18.7%). 10k: HRMS (ESI)
(M þ H)þ m/z 798.45416, calcd for C43H64N3O11 798.45354.1H NMR
(75 MHz, CDCl3) d: 204.1, 169.2, 166.3, 154.5, 149.8, 148.2, 130.0,
129.9, 129.5, 128.0, 127.4, 126.2, 123.9, 103.9, 95.5, 84.8, 82.9, 81.8,
79.5, 78.6, 70.4, 69.5, 66.2, 62.1, 51.3, 49.9, 47.9, 40.4, 38.5, 29.8, 28.7,
26.7, 22.6, 21.3, 20.0, 19.0, 15.9, 15.7, 14.4, 13.4, 10.5.
(400 MHz, CDCl3)
d
: [8.78 (d, J ¼ 2.0 Hz,1 H), 8.07 (d, J ¼ 8.4 Hz,1 H),
7.98 (s, 1 H), 7.79 (d, J ¼ 8.4 Hz, 1 H), 7.63e7.67 (m, 1 H), 7.50e7.53
(m,1 H), 3-quinolyl], 5.05 (dd, J ¼ 2.4,10.0 Hz,1 H, H-13), 4.79 (s,1 H,
H-11), 4.30 (d, J ¼ 7.2 Hz, 1 H, H-10), 4.19 (d, J ¼ 8.4 Hz, 1 H, H-5),
4.03e4.15 (m, 2 H, eCH2eCH2eCH2eAr), 3.82 (q, J ¼ 6.8 Hz, 1 H, H-
2), 3.53e3.56 (m, 2 H, H-8, H-50), 3.20e3.25 (m, 1 H, H-20), 3.01e
3.09 (m, 1 H, H-4), 2.84e2.91 (m, 2 H, eCH2eCH2eCH2eAr), 2.70
(s, 3 H, 6-OCH3), 2.45e2.56 (m, 2 H, H-30, H-10), 2.30 (s, 6 H,
-N(CH3)2), 1.99e2.17 (m, 2 H, eCH2eCH2eCH2eAr), 1.86e1.94 (m,
1 H, H-14eq), 1.62e1.72 (m, 2 H, H-7, H-40eq), 1.56 (s, 3 H, 12-CH3),
1.42 (s, 3 H, 6-CH3), 1.37 (d, J ¼ 6.8 Hz, 3 H, 2-CH3), 1.20e1.28 (m,
7.17. 3-O-Descladinosyl-3-keto-6-O-methylerythromycin A E-9-O-
[3-(30-quinolyl)-2-propargyl]oxime 11,12-cyclic carbonate (8k)
Following the procedure for the synthesis 7i and 8i, 7k and 8k
were obtained from the coupling of 6 (0.700 g, 0.988 mmol) and 3-
bromoquinoline (0.342 mL, 2.51 mmol) in yields of 11.6% and 41.7%,
respectively. 8k: HRMS(ESI) (MHþ) m/z: 794.42311, calcd for
C43H60N3O11 794.42224; 1H NMR (400 MHz, CDCl3)
d
: [8.88
(d, J ¼ 2.0 Hz, 1 H), 8.24 (d, J ¼ 1.8 Hz, 1 H), 8.08 (d, J ¼ 8.4 Hz, 1 H),

J.-H. Liang et al. / European Journal of Medicinal Chemistry 59 (2013) 54e63
63
10 H, 4-CH3, 10-CH3, 50-CH3, H-40ax), 0.99 (d, J ¼ 6.8 Hz, 3 H, 8-CH3),
N. Parasakthi, P.H. Van, C. Carlos, T. So, T.K. Ng, A. Shibl, Antimicrob. Agents
Chemother. 48 (2004) 2101e2107.
[3] L. Katz, G.W. Ashley, Chem. Rev. 105 (2005) 499e527.
0.90 (t, J ¼ 7.6 Hz, 3 H, 15-CH3). 13C NMR (CDCl3, 100 MHz)
d: 203.9,
169.1, 164.1, 154.4, 152.0, 146.8, 134.6, 134.4, 129.0, 128.6, 128.2,
127.4, 126.6, 103.8, 84.8, 82.8, 79.4, 78.5, 76.4, 72.2, 70.3, 69.4, 65.9,
51.2, 49.7, 47.9, 40.3, 40.2, 38.4, 30.6, 29.6, 28.7, 26.3, 22.5, 21.2, 19.8,
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7.20. 3-O-Descladinosyl-3-keto-6-O-methylerythromycin A E-9-O-
[3-(40-isoquinolyl)-2-propyl]oxime 11,12-cyclic carbonate (10i)
To a solution of 8i (0.162 g, 0.204 mmol) in MeOH (10 mL) were
added HCOONH4 (0.130 g, 2.04 mmol), HCOOH (0.15 mL,
4.08 mmol), and 10% PdeC (81 mg). The reaction mixture was
flushed with hydrogen and sealed in a pressure tube, and then was
stirred at 65 ꢀC for 24 h. 10% PdeC was removed by filtration before
the solvent was evaporated. The residue was dissolved in CH2Cl2,
and aqueous NaOH (2 mol/L) was added to adjust the pH to ꢃ9.
Additional water (20 mL) was added, and the mixture was stirred
for 20 min. The organic phase was washed with brine (20 mL) and
then concentrated in vacuo. The crude product was purified by
column chromatography on silica gel (5:5:0.2 petroleum ether/
acetone/triethylamine) to yield 10i (57 mg, 0.07 mmol, 34.8%). 10i:
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7.92e7.98 (m, 2 H), 7.57e7.70 (m, 2 H), 4-isoquinolyl], 5.00 (dd,
J ¼ 2.8, 10.0 Hz, 1 H, H-13), 4.75 (s, 1 H, H-11), 4.25 (d, J ¼ 7.2 Hz, 1 H,
H-10), 4.05e4.16 (m, 3 H, H-5, eCH2eCH2eCH2eAr), 3.49e3.78 (m,
3 H, H-2, H-8, H-50), 2.91e3.22 (m, 4 H, H-20, H-4, eCH2eCH2eCH2e
Ar), 2.63 (s, 3 H, 6-OCH3), 2.39e2.53 (m, 2 H, H-30, H-10), 2.23 (s,
6 H, eN(CH3)2), 2.03e2.13 (m, 2 H, eCH2eCH2eCH2eAr), 1.61e1.86
(m, 3 H, H-14eq, H-7, H-40eq), 1.51 (s, 3 H, 12-CH3), 1.39 (s, 3 H, 6-
CH3), 1.15e1.33 (m, 13 H, 2-CH3, 4-CH3, 10-CH3, 50-CH3, H-40ax),
0.94 (m, 3 H, 8-CH3), 0.85 (t, J ¼ 7.2 Hz, 3 H, 15-CH3). 13C NMR
(CDCl3, 100 MHz) d: 203.9, 169.1, 164.2, 154.4, 151.2, 142.6, 134.7,
131.1, 130.2, 128.3, 127.3, 126.9, 123.0, 103.9, 84.8, 82.8, 79.4, 78.5,
76.4, 72.6, 70.4, 69.5, 65.8, 51.2, 49.7, 47.9, 46.0, 40.3, 38.4, 30.1, 28.5,
26.7, 22.5, 21.2, 19.8, 19.0, 15.9, 15.4, 14.3, 13.2, 10.4.
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Acknowledgments
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This research was supported by a grant from the National
Natural Science Foundation of China (20602002) and partially from
Basic Research Foundation of Beijing Institute of Technology.
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