Synthesis and antibacterial activity of 4″,11-di-O-arylalkylcarbamoyl azithromycin derivatives

Article abstract of DOI:10.1016/j.bmcl.2009.01.092

A series of new 4″,11-di-O-arylalkylcarbamoyl azithromycin derivatives were designed, synthesized and evaluated for their in vitro antibacterial activities. Some derivatives exhibited greatly improved activity against erythromycin-resistant bacteria. Amon

Full text of DOI:10.1016/j.bmcl.2009.01.092

Bioorganic & Medicinal Chemistry Letters 19 (2009) 1698–1701
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and antibacterial activity of 400,11-di-O-arylalkylcarbamoyl
azithromycin derivatives
a
a
b
a
a
a,
*
Shutao Ma a, , Bo Jiao , Zhaopeng Liu , Hui Wang , Ruiqing Xian , Manjie Zheng , Hongxiang Lou
*
a Department of Medicinal Chemistry, School of Pharmaceutical Sciences, Shandong University, 44, West Culture Road, Jinan 250012, PR China
b Department of Clinical Laboratory, Peking Union Medical College Hospital, Beijing 100730, PR China
a r t i c l e i n f o
a b s t r a c t
A series of new 400,11-di-O-arylalkylcarbamoyl azithromycin derivatives were designed, synthesized and
evaluated for their in vitro antibacterial activities. Some derivatives exhibited greatly improved activity
against erythromycin-resistant bacteria. Among them, compounds 5f and 5k were found to have potent
activity against erythromycin-resistant Streptococcus pneumoniae whose resistance was encoded by the
erm or mef gene.
Article history:
Received 23 December 2008
Revised 24 January 2009
Accepted 28 January 2009
Available online 31 January 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
400,11-Disubstituted azithromycin
Synthesis
Antibacterial activity
Macrolide resistance
The first macrolide, erythromycin A, demonstrated a broad-
spectrum of antimicrobial activity and was used primarily for
respiratory, skin and soft tissue infections. Newer 14-and 15-mem-
bered macrolides such as clarithromycin (CLA) and azithromycin
(AZI) (Fig. 1), have been developed to address the limitations of
erythromycin.1 Unfortunately, like erythromycin A, both AZI and
CLA show poor activity against macrolide-resistant bacteria.2 The
most common mechanisms of resistance are mediated by erm-en-
coded methylation of 23S rRNA or mef-encoded efflux. Expression
of an erm resistance determinant in bacteria leads to the produc-
tion of a methyltransferase which modifies the key nucleotide,
A2058, in the MLSB (macrolide-lincosamide-streptogramin B)
binding site and thereby confers resistance to these macrolides.3
The ketolides, as exemplified by telithromycin and cethromycin,
may offer alternative therapy for Gram-positive infections attribut-
able to resistant pathogens.4 Their mechanism of action is that the
C-11, 12 carbamate side chain or C-6 side chain in the ketolides
interacts with nucleotide A752 directly in domain II of the 23S
rRNA and inhibits protein synthesis by blocking elongation.5
While significant efforts have gone into the discovery of
increasingly potent ketolides, a substantial amount work has also
been carried out on novel macrolides. These investigations have
lead to the discovery of 11-modified and 400-carbamate macro-
lides.2 11-O-substituented clarithromycin derivatives such as
EP-1553 (Fig. 1), exhibited excellent activity against macrolide-
resistantStaphylococcus aureus, Streptococcus pneumoniae andStrep-
tococcus pyogenes.6 Especially, one of the leading 400-carbamate
macrolides, CP-544372 (Fig. 1), demonstrated good in vitro and
in vivo activity against macrolide-susceptible and macrolide-resis-
tant organisms.
AZI, the first 15-membered macrolide, has been widely pre-
scribed for the treatment of respiratory tract infections owing to
its high efficacy and ideal pharmacokinetic property, but it is inac-
tive against resistant bacteria. The skeleton of AZI is also very sim-
ilar to that of CLA, except that the lactone ring is expanded around
the 9-position.7 However, there have been few modifications of 15-
membered macrolides. To obtain more potent macrolides against
resistant strains, a series of new 15-membered macrolide ana-
logues of AZI, including modified products to the hydroxyl group
at C-400 and the diol at C-11 and C-12, were designed and synthe-
sized in this paper.
By substitution of the 400-position with various arylalkyl side
chains, novel 400-substituted azithromycin derivatives were ob-
tained. The modification at the 11-position was carried out by
introducing an arylalkyl or alkyl chain. The combined modification
at the 400-O-arylalkylcarbamoyl group and the 11-O-arylalkylcarba-
moyl moiety was also performed to obtain new derivatives. On the
basis of report8 that 11,12-cyclic carbonate azithromycin was trea-
ted with corresponding amine in the presence of pyridine hydro-
chloride or 1-methyl-1H-imidazole to provide 11-carbamate of
azithromycin, novel 400,11-di-O-arylcarbamoyl azithromycin deriv-
atives were prepared from 11,12-cyclic carbonate azithromycin 400-
carbamates.
* Corresponding authors. Tel.: +86 531 88382009; fax: +86 531 88911612 (S.M.);
tel.: +86 531 88382012; fax: +86 531 88382731 (H.L.).
E-mail addresses: mashutao@sdu.edu.cn (S. Ma), louhongxiang@sdu.edu.cn (H.
Lou).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.01.092

S. Ma et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1698–1701
1699
N
N
N
9
HO
H2N
HO
HO
HO
HO
OMe
O
N
O
N9a
2′
2′
9
2′
9
OH
OH
N
O
HO
HO
O
6
6
O
6
O
O
O
11
12
11
12
11
12
HO
O
4″
O
4″
O
4″
O
O
O
O
O
O
O
N
OH
OMe
O
O
O
OH
O
N
H
OMe
OMe
OCH3
Azithromycin (AZI)
CP-544372
EP-1553
Figure 1. Structures of azithromycin, CP-544372 and EP-1553.
N
N
O
AcO
HO
OH
N
O
N
O
OH
a
HO
HO
HO
HO
O
O
O
O
O
O
b
O
O
O
OH
OMe
OH
OMe
AZI
2
N
N
AcO
OH
HO
OH
N
O
N
c, d
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
R
O
O
O
N
N
N
H
O
OMe
OMe
3
4
Scheme 1. Synthesis of 4 as precursors of the 400,11-di-O-arylcarbamoyl azithromycin derivatives. Reagents and conditions: (a) acetic anhydride, CH2Cl2, Et3N, rt, 12 h, 92%;
(b) CDI, Et3N, toluene, 75 °C, 24 h, 96%; (c) RNH2, DMF, DBU, rt,10 h; (d) CH3OH, 55 °C, 24 h, 73–80% for 2 steps.
A series of 11,12-cyclic carbonate azithromycin 400-carbamate
derivatives (4) were designed as precursors of the 400,11-di-O-arylc-
arbamoyl azithromycin derivatives. Synthesis of 4 is outlined in
Table 1
Scheme 1. Protection of the 20-hydroxyl group of AZI with acetic
Minimum inhibitory concentrations (MICs) value of 4a–d
anhydride provided 20-acetyl azithromycin (2) in 92% yield.
Compound R
MICs (
l
g/mL)
11,12-Carbonate 400-O-acylimidazolide 3 was obtained in 96% yield
in toluene at 75 °C by treatment of 2 with 1,10-carbonyldiimidazole
(CDI). In contrast, the reaction of 2 with CDI in toluene at room
temperature afforded a 400-O-acylimidazolide product.9 Finally,
compounds (4a–d) were prepared by coupling 3 with correspond-
ing amines in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU), followed by methanolysis. The yields were within the range
of 73–80%.
S. pneumoniae S.
S.
S.
ATCC49619a pneumoniae pneumoniae pneumoniae
B1b
A22072c
AB11d
OH
4a
4b
4c
<0.03
<0.03
<0.03
8
1
4
The activity of 4a–d against four phenotypes of Gram-positive
strains were evaluated using the broth microdilution method
(Table 1). The strains are S. pneumoniae ATCC49619 (erythromy-
cin-susceptible strain), S. pneumoniae B1 (erythromycin-resistant
strain encoded by the erm gene), S. pneumoniae A22072 (erythro-
mycin-resistant strain encoded by the mef gene) and S. pneumoniae
AB11 (erythromycin-resistant strain encoded by the erm and mef
genes). All the 400-carbamate derivatives (4a–d) retained excellent
activity against erythromycin-susceptible S. pneumoniae and
showed greatly improved activity against erythromycin-resistant
S. pneumoniae, compared with AZI and CLA. Among these com-
pounds, the most active compound was 4c, whose activity against
erythromycin-resistant S. pneumoniae encoded by the mef gene
exhibited 16-fold, 4-fold and 4-fold greater than 4a, 4b and 4d,
respectively. Compound 4d possessed the most activity against
8
8
0.25
0.06
16
4
OCH3
F
Cl
4d
AZI
CLA
<0.03
<0.03
<0.03
8
128
64
0.25
4
4
2
256
128
a
S. pneumoniae ATCC49619: erythromycin-susceptible strain.
b
c
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
d
genes.

1700
S. Ma et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1698–1701
Table 2
400,11-Di-O-arylcarbamoyl azithromycin derivatives
N
R1
O
N
O
NH
R1-NH2
pyridine hydrochloride
or 1-methyl-1H-imidazole
HO
OH
HO
OH
N
O
N
O
O
O
O
O
O
O
O
HO
rt, 2-5 days
O
O
O
O
O
O
R
R
O
O
N
H
N
H
O
O
OMe
OMe
4
5a-k
Compound
R
R1
Yielda (%)
mp (°C)
Rfb
OH
OH
OH
5a
79
76
78
69
64
65
67
67
66
79
65
104–107
0.44
CH3
Cl
5b
5c
5d
5e
5f
110–113
118–120
115–117
106–109
105–108
104–106
98–101
0.45
0.41
0.50
0.50
0.50
0.50
0.53
0.48
0.43
0.49
CH3
OCH3
OCH3
F
CH3
Cl
5g
5h
5i
F
Cl
CH3
Cl
Cl
Cl
115–117
119–121
121–124
5j
F
OH
5k
a
Isolated yield.
TLC solvent system: dichloromethane–methanol, 1:5.
b
erythromycin-resistant S. pneumoniae encoded by the erm and mef
genes, as well showing 2-fold, 8-fold and 2-fold better activity than
4a, 4b and 4c, respectively. These results confirm that the 400-O-
arylalkylcarbamoyl group can enhance the activity against erythro-
mycin-resistant S. pneumoniae.
79% (Table 2). The structures of 5a–k were identified by IR, 1H NMR
and MS spectra.10,11
As a consequence, 11 kinds of 400,11-di-O-arylalkylcarbamoyl
derivatives were efficiently prepared for in vitro antibacterial test-
ing, using the broth microdilution method (Table 3). All the com-
Compound 4 was readily converted to 400,11-di-O-arylalkylcar-
bamoyl derivatives (5a–k) by coupling with the related amines
in the presence of pyridine hydrochloride or 1-methyl-1H-imidaz-
ole at room temperature for 2–5 days in yields ranging from 64% to
pounds (5a–k) showed greatly improved activity (0.25–0.5
against erythromycin-resistant S. pneumoniae encoded by the erm
gene, exhibiting 16–32-fold greater activity than 4 (8 g/mL). Com-
pared to their precursors (4), most of the tested compounds still re-
lg/mL)
l

S. Ma et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1698–1701
1701
Table 3
Minimum inhibitory concentrations (MICs) value of 5a–k
Strain/compound
MICs (
lg/mL)
AZI
<0.03
128
4
CLA
<0.03
64
4
5a
<0.03
0.25
1
5b
5c
<0.03
0.25
0.12
5d
0.06
0.5
1
5e
5f
5g
5h
5i
5j
5k
S. pneumoniae ATCC49619a
S. pneumoniae B1b
<0.03
0.25
0.25
16
0.06
0.5
1
<0.03
0.25
0.06
32
<0.03
0.25
0.12
2
<0.03
0.5
0.5
<0.03
0.25
0.25
4
0.06
0.25
0.25
4
<0.03
0.25
0.06
16
S. pneumoniae A22072c
S. pneumoniae AB11d
256
128
128
128
32
128
16
a
S. pneumoniae ATCC49619: erythromycin-susceptible 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.
b
c
d
3. Zhanel, G. G.; Walters, M.; Noreddin, A.; Vercaigne, L. M.; Wierzbowski, A.;
Embil, J. M.; Gin, A. S.; Douthwaite, S.; Hobanl, D. J. Drugs 2002, 62, 1771.
4. Bryskier, A. Clin. Infect. Dis. 1998, 27, 865.
5. Weisblum, B. Antimicrob. Agents Chemother. 1995, 39, 577.
6. Niu, D. 42nd Interscience Conference on Antimicrobial Agents and
Chemotherapy, San Diego, Sept 27–30, 2002, Abst F 1666.
7. Takashima, H. Curr. Top. Med. Chem. 2003, 3, 991.
tained potent activity against erythromycin-resistant S. pneumoniae
encoded by the mef gene. In contrast, the tested compounds did not
show improved activity against erythromycin-resistant S. pneumo-
niae encoded by the erm and mef genes. These results suggest that
introduction of 11-O-arylalkylcarbamoyl or 11-O-alkylcarbamoyl
group to its precursor 4 can further enhance the activity against
erythromycin-resistant S. pneumoniae encoded by the erm gene,
but do not increase the activity against erythromycin-resistant S.
pneumoniae encoded by the mef gene or erm and mef genes.
In conclusion, a series of new 400,11-di-O-arylalkylcarbamoyl
azithromycin derivatives were designed and synthesized. They
possessed greatly improved activity against erythromycin-resis-
tant bacteria. Among them, compounds 5f and 5k were found to
have potent activity against erythromycin-resistant S. pneumoniae
encoded by the erm or mef gene. These results suggest that intro-
duction of 11-O-arylalkylcarbamoyl or 11-O-alkylcarbamoyl group
to its precursor 4 which has 400-O-arylalkylcarbamoyl group can
further enhance the activity against erythromycin-resistant S.
pneumoniae encoded by the erm gene.
8. Cheng, H.; Letavic, M. A.; Ziegler, C. B.; Dutra, J. K.; Bertinato, P.; Bronk, B. S. U.S.
Patent 6,043,227, 2000.
9. Xian, R.; Ma, S.; Jiao, B. Chin. Chem. Lett. 2008, 19, 409.
10. Typical
experimental
procedure;
11-O-butylcarbamoyl-400-O-(4-
hydroxylphenethyl-carbamoyl)-azithromycin (5a). To a solution of 4a (1.40 g,
1.50 mmol) in n-butylamine (5 mL) at room temperature was added pyridine
hydrochloride (0.34 g, 3.00 mmol). The resulting solution was allowed to stir
for 2–5 days at the same temperature. The reaction was quenched with water
(30 mL) and the aqueous layer was extracted with dichloromethane
(3 ꢀ 15 mL). The combined organic layers were washed with brine and dried
over anhydrous Na2SO4, filtered, and concentrated in vacuo. The residue
was purified by flash chromatography (dichloromethane–methanol, 10:1) to
afford 1.21 g (79%) of 5a as
(dichloromethane–methanol, 5:1); IR (KBr): 3419, 2974, 2934, 2874, 1724,
1615, 1516, 1459, 1382, 1301, 1251, 1170, 1118, 1072, 1049, 1034, 1016 cmꢁ1
a white solid: mp: 104–107 °C; Rf = 0.44
;
1H NMR (600 MHz, CDCl3) d (ppm) 7.02–7.01 (m, 4H), 5.05 (m, 1H), 4.98 (d,
J = 9.8 Hz, 1H), 4.50–4.46 (m, 3H), 4.36 (m, 1H), 4.26 (m, 2H), 3.57–3.50 (m,
3H), 3.48 (m, 2H), 3.32 (m, 2H), 3.29 (s, 3H), 3.15–3.13 (m, 3H), 2.97 (m, 1H),
2.74 (m, 7H), 2.22 (s, 3H), 2.10 (m, 1H), 2.01 (m, 2H), 1.90 (m, 1H), 1.74 (m, 2H),
1.65 (m, 1H), 1.36 (m, 6H), 1.26 (s, 3H), 1.22 (m, 2H), 1.20–1.17 (m, 6H), 1.14 (d,
J = 6.1 Hz, 3H), 0.99–0.95 (m, 12H), 0.92–0.89 (m, 9H); MS (ESI) m/z, 1012.0
[M+H]+, calcd for C52H90N4O15, 1012.3 [M+H].
Acknowledgments
11. 11-O-(4-hydroxyphenethyl-carbamoyl)-400-O-(2-chlorophen-ethyl-carbamo-
yl)-azithromycin (5k). To a solution of 4d (1.43 g, 1.50 mmol) in 1-methyl-1H-
imidazole (15 mL) at room temperature was added tyramine (0.41 g,
3.00 mmol). The resulting solution was allowed to stir for 2–5 days at the
same temperature. The reaction was quenched with water (30 mL) and the
aqueous layer was extracted with dichloromethane (3 ꢀ 15 mL). The combined
organic layers were washed with brine and dried over anhydrous Na2SO4,
filtered, and concentrated in vacuo. The residue was purified by flash
chromatography (dichloromethane–methanol, 20:1) to afford 1.06 g (65%) of
5k as a white solid: mp: 121–124 °C; Rf = 0.49 (dichloromethane–methanol,
5:1); IR (KBr): 3429, 2974, 2936, 2854, 1728, 1614, 1594, 1515, 1457, 1376,
This research was supported by the National Natural Science
Foundation of China (20872081), Natural Science Foundation of
Shandong (Y2006C31) and Shandong Science and Technology Pro-
motion Project (2005GG3202098).
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2009.01.092.
1344, 1245, 1170, 1111, 1093, 1073, 1050, 1036, 1015 cmꢁ1
;
1H NMR
(600 MHz, CDCl3) d (ppm) 7.28 (m, 1H), 7.21 (m, 3H), 7.09 (m, 2H), 6.84 (m,
2H), 5.00–4.95 (m, 2H), 4.56 (m, 2H), 4.40 (m, 1H), 4.42 (m, 1H), 4.29–4.26 (m,
3H), 3.59–3.56 (m, 4H), 3.55 (m, 4H), 3.30 (s, 3H), 3.00 (m, 3H), 2.74 (m, 6H),
2.60 (m, 1H), 2.37 (d, J = 14.8 Hz, 1H), 2.23 (s, 3H), 2.10 (m, 1H), 2.01 (m, 2H),
1.90 (m, 2H), 1.70–1.62 (m, 3H), 1.47 (m, 2H), 1.26 (s, 3H), 1.20 (m, 2H), 1.25–
1.13 (m, 18H), 1.02 (m, 6H), 0.89 (m, 3H); MS (ESI) m/z, 1094.0 [M+H]+, calcd
for C56H89ClN4O15, 1094.7 [M+H].
References and notes
1. Zhanel, G. G.; Dueck, M.; Hoban, D. J.; Vercaigne, L. M.; Embil, J. M.; Gin, A. S.;
Karlowsky, J. A. Drugs 2001, 61, 443.
2. Wu, Y. J.; Su, W. G. Curr. Med. Chem. 2001, 8, 1727.