Synthesis and antibacterial activity of novel 3-O-carbamoyl derivatives of clarithromycin and 11,12-cyclic carbonate azithromycin

Article abstract of DOI:10.1016/j.ejmech.2009.11.032

Two series of novel 3-O-carbamoyl derivatives of clarithromycin and 11,12-cyclic carbonate azithromycin were designed, synthesized and evaluated for their in vitro antibacterial activities. Compounds 4j and 4k were the most potent activity against erythro

Full text of DOI:10.1016/j.ejmech.2009.11.032

European Journal of Medicinal Chemistry 45 (2010) 915–922
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and antibacterial activity of novel 3-O-carbamoyl derivatives
of clarithromycin and 11,12-cyclic carbonate azithromycin
*
Ling Zhang, Linchen Song, Zhaopeng Liu, Hui Li, Yingdong Lu, Zerong Li, Shutao Ma
Department of Medicinal Chemistry, School of Pharmaceutical Sciences, Shandong University, 44, West Culture Road, Jinan 250012, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two series of novel 3-O-carbamoyl derivatives of clarithromycin and 11,12-cyclic carbonate azithromycin
were designed, synthesized and evaluated for their in vitro antibacterial activities. Compounds 4j and 4k
were the most potent activity against erythromycin-susceptible Staphylococcus aureus, Streptococcus
pyogenes and Streptococcus pneumoniae, which were comparable to those of clarithromycin and azi-
thromycin. Compounds 4d, 4h and 4i showed potent activity against erythromycin-resistant S. pneu-
moniae encoded by the mef gene and compounds 4h and 4i displayed greatly improved activity against
erythromycin-resistant S. pneumoniae encoded by the erm gene. Compound 7c exhibited improved
activity against erythromycin-resistant S. pneumoniae encoded by the erm and mef genes.
Ó 2009 Elsevier Masson SAS. All rights reserved.
Received 24 September 2009
Received in revised form
11 November 2009
Accepted 13 November 2009
Available online 28 November 2009
Keywords:
3-O-descladinosylclarithromycin derivative
3-O-Descladinosylazithromycin derivative
Synthesis
Antibacterial activity
Bacterial resistance
1. Introduction
modifies the key nucleotide, A2058, in the macrolide–lincosamide–
streptogramin B (MLSB) binding site, thereby conferring resistance
Macrolides belong to one of the most commonly used families of
clinically important antibiotics, which are applied primarily for the
infections caused by Gram-positive bacteria such as Staphylococcus
aureus, Streptococcus pneumoniae and Streptococcus pyogenes. They
are usually safe and effective for the treatment of upper and lower
respiratory tract infections, as well as genital infections [1,2]. First-
generation macrolides (e.g. erythromycin A (Fig. 1)) readily lose
their antibacterial activity under acidic conditions due to degra-
dation [3]. These degraded products are known to be responsible
for undesirable gastrointestinal side effects [4,5]. Second-generation
macrolides such as clarithromycin (CAM) and azithromycin (AZM)
(Fig. 1) have been developed to address the limitations of eryth-
romycin A, and are widely prescribed owing to their efficacy and
safety [6]. However, the therapeutic utility of these macrolides has
been severely compromised by the emergence of resistant patho-
gens [7]. Particularly, the increasing resistance of community-
acquired respiratory tract infections to various antimicrobials is
a pandemic phenomenon [8]. The commonest mechanism of
resistance is mediated by erm-encoded methylation of 23S rRNA or
mef-encoded efflux. Expression of an erm resistant determinant in
to macrolides [9–11]. Ketolides such as telithromycin can effectively
address bacterial resistance and other issues associated with
current macrolide regimens [12,13]. The C-11,12 carbamate side
chain or the C-6 side chain in the ketolides may interact with
nucleotide A752 directly in domain II of the 23S rRNA in addition to
the main interaction of the drugs in domain V. This leads to tighter
binding to ribosomes and imparts some activity against methylated
ribosomes in some species [14,15].
Emergence of bacterial resistance has also prompted further
research directed toward the discovery of new generation macro-
lides that exhibit greater efficacy and safety, has a broader spec-
trum of activity, and is particularly effective against resistant
pathogens. The study of high-resolution X-ray cocrystal structures
have revealed that macrolides bind at the entrance to the peptide
tunnel in the 23S rRNA, and the cladinose group in their structures
is located at and fits with the cavity formed by G2505, C2610 and
C2611 in domain V [16]. On the basis of the results of the X-ray
cocrystal structure study, many new derivatives of macrolides for
the effective management of erythromycin resistance have been
investigated by different research groups [17]. These investigations
have led to the discovery of a promising class of macrolide antibi-
otics, named as acylides [18–21]. TEA0777 [18] and TEA0929 [17]
(Fig. 2), for example, showed significantly potent activity against
not only erythromycin-susceptible Gram-positive pathogens but
also MLSB-resistant S. aureus and efflux-resistant S. pneumoniae.
bacteria results in production of
a methyltransferase which
* Corresponding author. Tel.: þ86 531 88382009; fax: þ86 531 88911612.
E-mail address: mashutao@sdu.edu.cn (S. Ma).
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.11.032

916
L. Zhang et al. / European Journal of Medicinal Chemistry 45 (2010) 915–922
N
N
N
HO
OH
HO
OH
HO
OMe
O
O
N
9a
2
′
2
′
2′
9
9
HO
HO
HO
HO
HO
HO
O
O
O
6
3
6
3
O
O
O
6
11
12
11
12
11
12
3
O
O
O
O
O
O
O
O
O
4
″
4″
4
″
O
OH
OMe
O
OH
OMe
O
OH
OMe
Erythromycin
Clarithromycin
Azithromycin
Fig. 1. Structures of erythromycin, clarithromycin and azithromycin.
Acylides therefore are innovative semisynthetic macrolides that
have potential as new generation macrolide antibiotics.
11,12-cyclic carbonate AZM comprising the essential features for
addressing bacterial resistance due to efflux and methylation of the
ribosome.
The acylides possess a 3-O-acyl group, the length of which is two
atoms distance from 3-oxygen atom to aromatic ring as well as
a five-membered cyclic carbamate attached to the 11,12-position
that was crucial to rigidify the conformation of the mother ring
[21]. In particular, 3-O-arylacetyl group were mostly active in the
acylides and display a higher affinity for forming interactions with
bacterial ribosomes [19]. However, the 3-O-acyl side chains in the
acylides are unstable and are easily subjected to hydrolysis under
physiological condition. Besides, the acylides have poor activity
against erythromycin-resistant S. pneumoniae encoded by the
erm gene. These encouraged us to explore the synthesis of new
3-O-modified macrolide derivatives bearing other stable side
chains for example 3-O-carbamoyl side chain at the 3-O-position in
place of the 3-O-acyl side chain. On the other hand, the cavity
formed by G2505, C2610 and C2611 in domain V [16] is very
informative for the development of new 3-O-modified macrolide
derivatives with the activity against erythromycin-resistant strains.
Particularly, the high nucleotide content in the cavity gives rise to
2. Chemistry
2.1. Synthesis of 3-O-carbamoyl derivatives of CAM
By substituting L-cladinose at the 3-O-position with various
carbamoyl groups, novel 3-O-carbamoyl derivatives of CAM (4a–k)
were prepared in 30–36% yields as shown in Scheme 1. Selective
cleavage of the 3-O-sugar moiety from CAM with 1 M aqueous
hydrochloric acid (HCl) and subsequent protection of the 20-
hydroxyl group with acetic anhydride (Ac2O) in the presence of
triethylamine (Et3N) gave 20-acetate (2). Treatment of 2 with 1,10-
carbonyldiimidazole (CDI) in the presence of 4-(dimethylamino)-
pyridine (DMAP) provided the 3-O-acylimidazolide (3) as
a common intermediate to introduce various functional groups at
the 3-O-position.
3-O-Arylcarbamoyl derivatives of CAM (4a–g) were obtained in
56–69% yields by condensation of 3 with the corresponding aryl-
amines in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU) in dimethylformamide (DMF), followed by selective removal
of the 20-O-acetyl group by heating with methanol. In contrast, 3-O-
alkylcarbamoyl derivatives of CAM (4h–k) were prepared by
coupling 3 with the corresponding alkylamines in methyl cyanide
(CH3CN) and water at 65 ꢀC, followed by methanolysis. The yields
were within the range of 56%–63%.
a number of possible interactions such as hydrogen bonding,
p-
stacking as well as electrostatic interactions. Therefore, a prolonged
anchor groups at the 3-O-position may be helpful for the interac-
tion with the binding sites of the nucleotides in the cavity.
On the basis of the consideration detailed above, we designed
novel 3-O-carbamoyl derivatives of CAM with prolonged 3-O-car-
bamoyl side chains, the length of which is three or four atom
distance from 3-oxygen atom to aromatic ring in order to probe the
effect of different lengths of 3-O-carbamoyl side chains in anti-
bacterial activity. Since hydrogen bonding and
p-stacking may
2.2. Synthesis of 3-O-carbamoyl derivatives of 11,12-cyclic
carbonate AZM
increase binding affinity, the substituted aromatic moieties in the
structures have different bulk of molecule and different distribu-
tion of heteroatoms. In addition, AZM is first 15-membered azalide
antibiotic and has beneficial antibacterial and excellent pharma-
cokinetic profiles. Its skeleton is very similar to that of CAM except
that the lactone ring is expanded around the 9-position [17]. In
order to investigate the effect of the azalide skeleton in antibacte-
rial activity, we also designed novel 3-O-carbamoyl derivatives of
Novel 3-O-carbamoyl derivatives of 11,12-cyclic carbonate AZM
(7a–g) were obtained in 47–55% yields by substituting L-cladinose
at the 3-O-position with various carbamoyl groups. The synthetic
route is outlined in Scheme 2. Selective removal of the 3-O-sugar
moiety with 1 M HCl afforded 3-O-descladinosyl AZM. Treatment of
the 3-O-descladinosyl AZM with Ac2O in the presence of Et3N in
dichloromethane (CH2Cl2) gave the 20-acetate AZM (5). Treatment
of 5 with CDI in toluene provided the 11,12-cyclic carbonate
3-O-acylimidazolide (6). Finally, the desired compounds were
synthesized by condensation of 6 with the corresponding amines in
the presence of DBU in DMF, followed by selective deprotection of
the 20-O-acetyl group by heating with methanol.
N
O
N
HO
OMe
HO
O
O
9
9
2
′
H
N
OMe
O
HO
HO
6
3
6
3
O
O
11
11
12
O
12
O
O
O
O
O
3. Antibacterial activity
O
O
O
O
NO2
N
The antibacterial screening of 3-O-carbamoyl derivatives of
CAM and 11,12-cyclic carbonate AZM prepared above was per-
formed by a standard dilution assay for the determination of
TEA0929
Fig. 2. Structures of TEA0777 and TEA0929.
TEA0777

L. Zhang et al. / European Journal of Medicinal Chemistry 45 (2010) 915–922
917
N
O
N
N
HO
OMe
AcO
O
AcO
O
O
OMe
OMe
O
HO
HO
HO
HO
HO
HO
O
O
a, b
c
O
O
N
O
O
O
OH
O
O
O
O
N
O
O
O
OH
OMe
2
3
CAM
R
1 = 4-hydroxyphenethyl
R1 = 4-methoxybenzyl
1 = 4-fluorobenzyl
4a
4b
4c
N
O
HO
OMe
O
R
d, e
4d R1 = 2-chlorophenethyl
HO
HO
O
4e
R
R
1 = benzyl
1 = phenethyl
R1 = 3,4-methlenedioxyphenethyl
O
4f
R1
4g
O
N
H
4h R1 = propyl
O
4i
R
R
R
1 = propenyl
1 = butyl
O
4j
4k
1 = pentyl
4
Scheme 1. Reagents and conditions: (a) HCl, EtOH/H2O, rt, 20 h, 85%; (b) Ac2O, Et3N, CH2Cl2, rt, 48 h, 90%; (c) CDI, DMAP, CH2Cl2, rt, 24 h, 69%; (d) R1NH2 (arylamines), DBU, DMF,
55 ꢀC, 12 h or R1NH2 (alkylamines), CH3CN/H2O, 65 ꢀC, 12 h; (e) CH3OH, 50 ꢀC, 12 h, 56–69% for 2 steps.
minimal inhibitory concentrations (MICs). MIC values for all
compounds were determined in comparison with CAM and AZM on
six phenotypes of sensitive and resistant Gram-positive bacterial
strains. S. aureus ATCC25923, S. pyogenes and S. pneumoniae
ATCC49619 are three erythromycin-susceptible strains. S. pneu-
moniae B1, S. pneumoniae A22072 and S. pneumoniae AB11 are three
erythromycin-resistant strains whose resistance were encoded by
the erm gene, the mef gene, and the erm and mef genes, respectively.
excellent activity against erythromycin-susceptible strains and
some of them exhibited improved activity against erythromycin-
resistant S. pneumoniae, compared with CAM, AZM. In marked
contrast, compound 2 as precursor of 3-O-carbamoyl derivatives of
CAM did not show any antibacterial activity. Among the target
compounds, compounds 4j and 4k were found to be the most potent
activity (MIC 0.03 and 0.03 mg/mL) against the erythromycin-
susceptible strains tested, which were comparable to those of CAM
and AZM. Compounds 4d, 4h and 4i had significant activity (MIC
0.25, 0.25 and 0.25 mg/mL) against erythromycin-resistant S. pneu-
4. Results and discussion
moniae encoded by the mef gene, showing 512-fold, 512-fold and
512-fold greater activity than the precursor 2, respectively.
Compounds 4h and 4i showed greatly improved activity against
MIC values for 3-O-carbamoyl derivatives of CAM are shown in
Table 1. Almost all of the 3-O-carbamoyl derivatives of CAM showed
N
N
O
N
HO
AcO
AcO
OH
N
O
N
O
N
O
OH
O
OH
HO
HO
HO
HO
O
O
O
O
O
N
c
a, b
O
O
O
O
O
OH
O
N
O
O
O
OH
OMe
AZM
5
6
N
O
R1 = 4-methoxybenzyl
HO
OH
7a
N
O
7b R1 =4-fluorobenzyl
7c R1 = 2-chlorophenethyl
7d R1 = benzyll
O
O
d, e
O
O
R1
R1 = phenethyl
7f
O
7e
N
O
R1 = butyl
H
7g R1 = pentyl
O
7
Scheme 2. Reagents and conditions: (a) HCl, MeOH/H2O, rt, 24 h, 92%; (b) Ac2O, Et3N, CH2Cl2, rt, 24 h, 90%; (c) CDI, Et3N, toluene, rt, 48 h, 90%; (d) R1NH2, DBU, DMF, rt, 10 h;
(e) CH3OH, 55 ꢀC, 24 h, 63–74% for 2 steps.

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L. Zhang et al. / European Journal of Medicinal Chemistry 45 (2010) 915–922
Table 1
In vitro antibacterial activity of 3-O-carbamoyl-3-O-descladinosylclarithromycin derivatives.
Strain/compound
MICs (
m
g/mL)
4a
4b
4c
4d
0.25
0.25
0.12
32
0.25
64
4e
4f
4g
4h
4i
4j
0.12
0.12
0.03
32
0.5
64
4k
0.12
0.12
0.03
32
0. 5
32
2
CAM
0.12
0.12
0.03
64
4
AZM
0.25
0.12
0.03
128
4
S. aureus ATCC25923a
S. pyogenesb
0.12
0.25
0.25
0.25
0.5
0.12
256
4
0.25
0.25
0.06
0. 5
0. 5
0.25
0.25
0.25
0.5
0.25
0.5
0.25
0.25
0.25
0.25
2
0.25
4
0.25
0.25
0.12
2
0.25
4
128
128
128
128
128
256
S. pneumoniae ATCC49619c
S. pneumoniae B1d
64
0.5
128
256
4
256
256
8
256
128
2
128
64
S. pneumoniae A22072e
S. pneumoniae AB11f
1
256
128
128
256
a
S. aureus ATCC25923: erythromycin-susceptible strain.
S. pyogenes: erythromycin-susceptible strain.
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
e
f
erythromycin-resistant S. pneumoniae encoded by the erm gene or
the erm and mef genes, showing 64-fold and 64-fold better activity
than AZM or precursor 2, respectively. The results described above
exhibited significantly improved activity against erythromycin-
resistant S. pneumoniae encoded by the erm and mef genes, showing
32-fold and 32-fold higher activity than AZM and precursor 5,
respectively. These suggested that removal of the L-cladinosyl
moiety of AZM results in a complete loss of antibacterial
activity and introduction of the 3-O-carbamoyl side chains at
the 3-O-position does not completely restores the activity against
the erythromycin-susceptible strains, but it shows improved
activity against erythromycin-resistant S. pneumoniae encoded by
the erm and mef genes.
suggested that removal of the L-cladinosyl sugar of CAM leads to
a complete loss of antibacterial activity, and introduction of the 3-O-
carbamoyl side chains at the 3-O-position completely restores the
activity against erythromycin-susceptible strains and shows greatly
improved activity against erythromycin-resistant S. pneumoniae
encoded by the mef gene. These results are consistent with the
results with 3-O-acylerythromycin A derivatives reported by Tani-
kawa T. et al. [18,19] In addition, compounds 4h and 4i increased
significantly the activity against erythromycin-resistant S. pneu-
moniae encoded by the erm gene, showing 50-fold and 50-fold
Two series of 3-O-carbamoyl macrolide derivatives described
above displayed different antibacterial activities owing to differ-
ences in their skeleton structures. The 3-O-carbamoyl derivatives of
CAM are 14-membered macrolide derivatives with the 3-O-carba-
better activity than TEA0777 (MIC > 100
mg/mL) [18] or TEA0929
(MIC > 100 g/mL) [19], respectively. This suggested that introduc-
m
moyl side chain in place of
L-cladinose at the 3-O-position. They
tion of the 3-O-carbamoyl side chain at the 3-O-position in place of
the 3-O-acyl side chain in acylides may increase the activity against
erythromycin-resistant S. pneumoniae encoded by the erm gene.
For comparison with the 3-O-carbamoyl derivatives of CAM, the
3-O-carbamoyl derivatives of 11,12-cyclic carbonate AZM (7a–g)
were tested for in vitro antibacterial activity against the Gram-
positive strains described above. Their activities are summarized in
Table 2. The 3-O-carbamoyl derivatives of 11,12-cyclic carbonate
AZM did not show the activity against erythromycin-susceptible
strains. Similarly, Compound 5 as precursor of the 3-O-carbamoyl
derivatives of 11,12-cyclic carbonate AZM did not show the activity
against erythromycin-susceptible strains as well. In contrast, some
of the target compounds showed slightly improved activity against
erythromycin-resistant S. pneumoniae. Especially, compound 7c
exhibited not only excellent activity against erythromycin-suscep-
tible strains such as S. aureus, S. pneumoniae and S. pyogenes, but
also significant activity against erythromycin-resistant S. pneumo-
niae encoded by the mef gene. The results suggested that the 3-O-
carbamoyl side chain in their structures could interact with the
binding sites in the cavity formed by G2505, C2610 and C2611 in
domain V, resulting in a higher affinity to bacterial ribosomes. The
3-O-carbamoyl derivatives of 11,12-cyclic carbonate AZM are 15-
membered azalide derivatives with the 3-O-carbamoyl side chain
and 11,12-cyclic carbonate group. The 11,12-cylic carbonate group
introduced into the azalide derivatives is to overcome efflux resis-
tance on the basis of previous reports [22,23] that the introduction of
a cyclic carbonate to the 11,12-position of CAM derivatives enhanced
activity against resistant bacteria mediated by mef-encoded efflux.
However, the 3-O-carbamoyl derivatives of 11,12-cyclic carbonate
AZM did not show activity against both erythromycin-susceptible
strains and erythromycin-resistant S. pneumoniae encoded by the
mef gene. These results led us to presume that the expansion of
lactone ring around the C-9a position might change the stereo-
chemistry of the azalide derivatives compared with 3-O-carbamoyl
derivatives CAM so that their 3-O-carbamoyl side chain could not
interact with the binding sites in the cavity in domain V and the
11,12-cylic carbonate group could not impart its activity against the
mef-encoded efflux. Finally, these alterations affect the antibacterial
activity of the 3-O-carbamoyl derivatives of 11,12-cyclic carbonate
AZM.
Table 2
In vitro antibacterial activity of 3-O-carbamoyl-3-O-descladinosylazithromycin
11,12-cyclic carbonate derivatives.
Strain/compound
MICs (
7a 7b 7c 7d 7e 7f 7g
128 64 32 64 64 64 64 128
mg/mL)
5
CAM
0.12
0.12
0.03
AZM
0.12
0.12
0.03
128
4
S. aureus ATCC25923a
S. pyogenesb
16 16
8
4
32
16
8
4
8
8
16 128
128
S. pneumoniae ATCC49619c
S. pneumoniae B1d
8
4
4
64 64 32 64 64 64 32 128 64
128 32 16 128 64 128 64 128
64 64 64 32 32 32 256 128
S. pneumoniae A22072e
S. pneumoniae AB11f
4
8
256
a
5. Conclusion
S. aureus ATCC25923: erythromycin-susceptible strain.
S. pyogenes: erythromycin-susceptible strain.
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
b
c
d
e
f
Two series of novel 3-O-carbamoyl derivatives of CAM and
11,12-cyclic carbonate AZM were designed, synthesized by intro-
ducing the 3-O-carbamoyl group instead of
L-cladinose at the 3-O-
genes.
position. Almost all of the 3-O-carbamoyl derivatives of CAM

L. Zhang et al. / European Journal of Medicinal Chemistry 45 (2010) 915–922
919
showed excellent activity against erythromycin-susceptible
6.2. 20-O-Acetyl-3-O-acylimidazolyl-3-O-
descladinosylclarithromycin (3)
bacteria. Among them, compounds 4j and 4k were the most potent
activity against erythromycin-susceptible S. aureus, S. pyogenes and
S. pneumoniae, which were comparable to those of CAM and AZM.
In marked contrast, 3-O-carbamoyl derivatives of 11,12-cyclic
carbonate AZM did not exhibit the activity against the erythro-
mycin-susceptible strains. As for the activity against erythromycin-
resistant strains, compounds 4d, 4h and 4i showed potent activity
against erythromycin-resistant S. pneumoniae encoded by the mef
gene and displayed greatly improved activity against erythro-
mycin-resistant S. pneumoniae encoded by the erm gene.
Compound 7c exhibited improved activity against erythromycin-
resistant S. pneumoniae encoded by the erm and mef genes. The
results suggested that introduction of the 3-O-carbamoyl side
chains at the 3-O-position shows greatly improved activity against
erythromycin-resistant S. pneumoniae encoded by the mef gene and
the erm gene, and introduction of the 3-O-carbamoyl side chain at
the 3-O-position in place of the 3-O-acyl side chain in acylides may
increase the activity against erythromycin-resistant S. pneumoniae
encoded by the erm gene.
To a solution of 2 (4.1 g, 6.49 mmol) in CH2Cl2 (40 mL) at room
temperature was added DMAP (1.58 g, 12.98 mmol) and CDI (3.16 g,
19.47 mmol). The resulting solution was allowed to stir for 24 h at
the same temperature. The reaction was quenched with 5% aqueous
NaHCO3 (40 mL) and the aqueous layer was extracted with CH2Cl2
(2 ꢁ 20 mL) saturated brine (2 ꢁ 20 mL). The organic layer were
washed with brine (2 ꢁ 20 mL), dried over anhydrous Na2SO4,
filtered, and concentrated in vacuo to afford 3.26 g (69.1%) of 3 as
a white solid: mp 124–128 ꢀC, Rf ¼ 0.60 (dichloromethane/meth-
anol 10:1, v/v).
6.3. General methods for the preparation of 3-O-arylalkylcarbamoyl-
3-O-descladinosylclarithromycin derivatives (4a–k)
Method I To a solution of 3 (1.6 g, 2.2 mmol) in DMF (25 mL) was
added DBU (0.48 mL, 3.3 mmol) and corresponding arylamine
(11.0 mmol). The resulting solution was stirred for 12 h at 55 ꢀC. The
reaction was quenched with water (40 mL) and the aqueous layer
was extracted with ethyl acetate (2 ꢁ 20 mL). The combined
organic layers were washed with 5% aqueous NaHCO3 and brine,
and dried over anhydrous Na2SO4, filtered. The filtrate was
concentrated in vacuo to afford a crude product.
A solution of the above crude product in methanol (15 mL) was
heated to 50 ꢀC and stirred for 12 h at the same temperature. After
concentrating the reaction solution in vacuo, the residue was
purified by flash chromatography (dichloromethane/methanol 7:1,
v/v) to afford the desired products 4a–g.
Method II To a solution of 3 (1.6 g, 2.2 mmol) in CH3CN (20 mL)
and water (2 mL) was added the corresponding alkylamine
(11.0 mmol). The resulting solution was stirred for 12 h at 65 ꢀC. The
reaction was quenched with 0.5 M NaH2PO4 (20 mL) and the
aqueous layer was extracted with ethyl acetate (3 ꢁ 20 mL). The
combined organic layers were washed with brine, and dried over
anhydrous Na2SO4, filtered. The filtrate was concentrated in vacuo
to afford a crude product.
A solution of the above crude product in methanol (15 mL) was
heated to 50 ꢀC and stirred for 12 h at the same temperature. After
concentrating the reaction solution in vacuo, the residue was
purified by flash chromatography (dichloromethane/methanol 7:1,
v/v) to afford the desired products 4h–k.
6. Experimental
All necessary solvents were purified prior to use. Dichloro-
methane, toluene and N, N-dimethylformamide were distilled from
calcium hydride and stored over 4 Å molecular sieves. Triethyl-
amine were distilled from calcium hydride and stored over sodium
hydroxide. Reactions were monitored by thin-layer chromatog-
raphy (TLC) using 0.25-mm pre-coated silica gel plates. Visualiza-
tion was accomplished with UV light and aqueous potassium
permanganate stain followed by charring on a hot-plate. Flash
chromatography was performed with the indicated solvents using
silica gel 60 (particle size 0.040–0.063 mm). Yields refer to chro-
matographically and spectroscopically pure compounds unless
otherwise stated. 1H NMR spectra were recorded on Bruker Avance
DRX 600 spectrometer at ambient temperature. Infrared spectra
were recorded on KBr pellets using Nicolet Nexus 470FT-IR spec-
trometer. Mass spectra were recorded on API 4000 instrument. The
C, H, N analyses were carried out on PE-2400 II elemental analyser.
Melting points are uncorrected and were determined on an X-6
melting point apparatus.
6.1. 20-O-Acetyl-3-O-descladinosylclarithromycin (2)
To a solution of clarithromycin (9.0 g, 12.0 mmol) in absolute
ethanol (39 mL) and water (108 mL) at room temperature was
added dropwise 1 M HCl (21.6 mL). The resulting solution was
allowed to stir for 20 h at the same temperature. And then, the
reaction solution was neutralized to pH ¼ 10.5–11.0 with 1 M
sodium hydroxide and stirred for 2 h at the room temperature.
The resulting precipitate was filtered, washed with cool water,
dried to afford 6.01 g (84.8%) of 3-O-descladinosylclarithromycin
as a white solid: mp 158–160 ꢀC, Rf ¼ 0.53 (dichloromethane/
methanol 10:1, v/v).
To a solution of 3-O-descladinosylclarithromycin (5.6 g, 9.49
mmol) prepared above in CH2Cl2 (40 mL) at room temperature was
added Ac2O (1.8 mL,18.9 mmol) and Et3N (5.5 mL, 37.96 mmol). The
resulting solution was allowed to stir for 24 h at the same
temperature. The reaction was quenched with 5% aqueous NaHCO3
(50 mL) and the aqueous layer was extracted with CH2Cl2
(2 ꢁ 30 mL). The combined organic layers were washed with brine,
dried over anhydrous Na2SO4, filtered, and concentrated in vacuo.
The residue was crystallized from ethyl acetate-n-hexane (1:20) to
afford 5.37 g (89.5%) of 2 as a white solid: mp 132–136 ꢀC, Rf ¼ 0.56
(dichloromethane/methanol 10:1, v/v).
6.3.1. 3-O-((4-Hydroxyphenethyl)carbamoyl)-3-O-descladino-
sylclarithromycin (4a)
White crystals, yield 56.4%, mp 159–162 ꢀC, TLC Rf ¼ 0.31
(dichloromethane/methanol 7:1, v/v); IR (KBr): 3453, 2973, 2938,
2878, 2835, 2785, 1735, 1612, 1586, 1513, 1457, 1404, 1377, 1330,
1246, 1172, 1109, 1074, 1050,1033 cmꢂ1; 1H NMR (600 MHz, CDCl3):
d
7.28 (m, 2H), 6.86 (m, 2H), 5.18 (dd, J ¼ 11.1 Hz, J ¼ 1.78 Hz, 1H),
4.92 (d, J ¼ 11.0 Hz, 1H), 4.31–4.29 (m, 2H), 3.96–3.95 (m, 2H), 3.82
(m, 2H), 3.79 (s, 3H), 3.25 (m, 1H), 3.05 (s, 3H), 3.02–2.99 (m, 2H),
2.36 (s, 6H), 1.83–1.79 (m, 2H), 1.60–1.51 (m, 9H), 1.28–1.22 (m, 5H),
1.17–1.10 (m, 18H), 0.83 (t, 3H); MS (ESI) m/z calcd. for C39H64N2O12
752.5, found [M þ H]þ 753.8; Analysis calculated for C39H64N2O12
:
C 62.21, H 8.57, N 3.72. Found: C 62.13, H 8.53, N 3.76.
6.3.2. 3-O-((4-Methoxybenzyl)carbamoyl)-3-O-
descladinosylclarithromycin (4b)
White crystals, yield 55.8%, mp 108–110 ꢀC, TLC Rf ¼ 0.47
(dichloromethane/methanol 7:1, v/v); IR(KBr): 3475, 2973, 2939,
2879, 2835, 2785,1735,1659,1612,1586,1513,1458,1404,1378,1344,
1330, 1246, 1172, 1139, 1109, 1074, 1050, 1033 cmꢂ1 1H NMR
;
(600 MHz, CDCl3):
d 7.28–7.26 (m, 2H), 6.86 (m, 2H), 5.46 (m, 1H),

920
L. Zhang et al. / European Journal of Medicinal Chemistry 45 (2010) 915–922
5.18 (dd, J ¼ 11.1 Hz, J ¼ 2.2 Hz,1H), 4.91 (d, J ¼ 11.0 Hz 1H), 4.31–4.29
(m, 2H), 4.00–3.96 (m, 2H), 3.84–3.81 (m, 1H), 3.81–3.78 (m, 3H),
3.75 (m, 1H), 3.25–3.23 (m, 1H), 3.18–3.16 (m, 1H), 3.05 (s, 3H), 2.98
(m, 2H), 2.84–2.80 (m,1H), 2.42–2.36 (m, 7H), 2.18 (m,1H),1.96–1.92
(m, 2H), 1.83–1.79 (m, 2H), 1.53–1.47 (m, 3H), 1.28–1.25 (m, 4H),
1.26–1.23 (m, 9H), 1.18–1.10 (m, 9H), 0.83 (t, 3H); MS (ESI) m/z calcd.
for C39H64N2O12 752.4, found [M þ H]þ 753.7; Analysis calculated for
C39H64N2O12: C 62.21, H 8.57, N 3.72. Found: C 62.30, H 8.54, N 3.70.
(m, 1H), 3.41–3.38 (m, 1H), 3.30–3.25 (m, 2H), 3.24 (m, 1H), 3.06 (s,
3H), 2.83–2.80 (m, 1H), 2.56 (m, 1H), 2.37 (m, 1H), 2.32 (m, 6H),
2.14–2.13 (m, 1H), 1.93 (m, 1H), 1.83–1.79 (m, 2H), 1.57–1.53 (m, 2H),
1.53–1.49 (m, 1H), 1.29–1.28 (m, 4H), 1.25–1.20 (m, 6H), 1.16–1.08
(m, 15H), 0.83 (t, 3H); MS (ESI) m/z calcd. for C39H64N2O11 736.5,
found [M þ H]þ 738.1; Analysis calculated for C39H64N2O11: C 63.56,
H 8.75, N 3.80. Found: C 63.49, H 8.70, N 3.83.
6.3.7. 3-O-((3,4-Methylenedioxyphenethy)carbamoyl)-3-O-
descladinosylclarithromycin (4g)
6.3.3. 3-O-((4-Fluorobenzyl)carbamoyl)-3-O-descladinosyl-
clarithromycin (4c)
Slightly yellow crystals, yield 64.8%, mp 110–113 ꢀC, TLC
Rf ¼ 0.54 (dichloromethane/methanol 7:1, v/v); IR(KBr): 3446,
2973, 2938, 2879, 2785, 1735, 1504, 1490, 1456, 1378, 1331, 1247,
White crystals, yield 59.4%, mp 115–117 ꢀC, TLC Rf ¼ 0.50
(dichloromethane/methanol 7:1, v/v); IR(KBr): 3458, 2974, 2940,
2879, 2834, 2786, 1736, 1606, 1510, 1458, 1404, 1378, 1345, 1330,
1109, 1075, 1050 cmꢂ1 1H NMR (600 MHz, CDCl3):
; d 6.75 (m, 1H),
1260, 1225, 1171, 1109, 1074, 1051, 1033 cmꢂ1
;
1H NMR (600 MHz,
6.67 (m, 1H), 6.63 (m, 1H), 5.94 (s, 2H), 5.18 (dd, J ¼ 11.1, J ¼ 1.8, 1H),
4.91–4.89 (m, 2H), 4.13–4.10 (m, 1H), 4.03 (m, 1H), 3.96 (m, 1H),
3.81–3.77 (m, 2H), 3.62–3.59 (m, 1H), 3.24–3.21 (m, 1H), 3.19–3.17
(m, 2H), 3.06 (s, 3H), 3.00 (m, 1H), 2.82–2.80 (m, 1H), 2.76–2.71 (m,
2H), 2.57–2.54 (m, 1H), 2.31 (s, 6H), 1.94–1.92 (m, 2H), 1.84–1.79 (m,
2H), 1.70–1.65 (m, 3H), 1.52–1.47 (m, 2H), 1.29 (m, 9H), 1.18–1.10 (m,
12H), 0.83 (t, 3H); MS (ESI) m/z calcd. for C40H64N2O13 780.4, found
[M þ H]þ 781.9; Analysis calculated for C40H64N2O13: C 61.52, H
8.26, N 3.59. Found: C 61.55, H 8.21, N 3.62.
CDCl3):
d 7.32–7.30 (m, 2H), 7.02–7.00 (m, 2H), 5.45 (m, 1H), 5.18
(dd, J ¼ 11.0 Hz, J ¼ 1.95, 1H), 4.92–4.90 (d, J ¼ 11.0 Hz, 1H),
4.39–4.34 (m, 2H), 3.97–3.95 (m, 2H), 3.83–3.78 (m, 2H), 3.25 (m,
1H), 3.17–3.14 (m, 1H), 3.05 (s, 3H), 3.01–2.99 (m, 2H), 2.85–2.83
(m, 1H), 2.57–2.54 (m, 1H), 2.19 (s, 6H), 2.19–2.17 (m, 1H), 1.95–1.92
(m, 2H), 1.83–1.79 (m, 3H), 1.54–1.48 (m, 3H), 1.29–1.25 (m, 3H),
1.20–1.09 (m, 18H), 0.83 (t, 3H); MS (ESI) m/z calcd. for
C38H61FN2O11 740.4, found [M þ H]þ 741.8; Analysis calculated for
C38H61FN2O11: C 61.60, H 8.30, N 3.78. Found: C 61.52, H 8.32, N 3.74.
6.3.8. 3-O-((Propyl)carbamoyl)-3-O-descladinosylclarithromycin (4h)
White crystals, yield 58.8%, mp 217–220 ꢀC, TLC Rf ¼ 0.49
(dichloromethane/methanol 7:1, v/v); IR(KBr): 3446, 2972, 2938,
2877, 2786, 1735, 1633, 1521, 1459, 1405, 1378, 1344, 1263, 1171,
6.3.4. 3-O-((2-Chlorophenethyl)carbamoyl)-3-O-descladinosyl-
clarithromycin (4d)
White crystals, yield 58.2%, mp 118–121 ꢀC, TLC Rf ¼ 0.47
(dichloromethane/methanol 7:1, v/v); IR(KBr): 3447, 2974, 2939,
2879, 2834, 2786, 1816, 1736, 1511, 1457, 1404, 1378, 1330, 1245,
1109, 1077, 1052, 1034, 1008 cmꢂ1 1H NMR (600 MHz, CDCl3):
;
d
5.25–5.20 (m, 1H), 5.19 (dd, J ¼ 11.1, J ¼ 2.1, 1H), 4.91 (m, 1H), 4.12
1170, 1109, 1074, 1051, 1033 cmꢂ1; 1H NMR (600 MHz, CDCl3):
d
7.36
(d, J ¼ 20.0, 1H), 3.84 (m, 1H), 3.79 (m, 1H), 3.37 (m, 1H), 3.27–3.25
(m, 1H), 3.24–3.22 (m, 2H), 3.05 (s, 3H), 3.02 (m, 2H), 2.83 (m, 1H),
2.68 (m, 1H), 2.57–2.54 (m, 2H), 2.41 (s, 6H), 2.34 (m, 1H), 2.18 (m,
1H), 1.94 (m, 1H), 1.82 (m, 1H), 1.72 (m, 1H), 1.56–1.51 (m, 4H), 1.28
(s, 4H), 1.27–1.23 (m, 3H), 1.16 (s, 3H), 1.14–1.10 (m, 12H), 0.94 (t,
(d, J ¼ 2.0 Hz, 1H), 7.26–7.19 (m, 3H), 5.18 (dd, J ¼ 11.1 Hz, J ¼ 1.98,
1H), 5.02–4.99 (m, 1H), 4.90 (d, J ¼ 11.1 Hz, 1H), 4.13 (m, 1H), 4.03–
3.97 (m, 1H), 3.82–3.79 (m, 2H), 3.64–3.60 (m, 1H), 3.35–3.30 (m,
3H), 3.25 (m, 1H), 3.20–3.17 (m, 1H), 3.06 (s, 3H), 3.01–2.98 (m, 3H),
2.83–2.80 (m, 1H), 2.58–2.55 (m, 1H), 2.43–2.41 (m, 1H), 2.31 (s,
6H), 2.18–2.14 (m, 1H), 1.94–1.92 (m, 1H), 1.84–1.80 (m, 2H), 1.65–
1.63 (m, 1H), 1.56–1.47 (m, 2H), 1.29 (s, 3H), 1.26–1.23 (m, 3H),
1.18–1.10 (m, 15H), 0.83 (t, 3H); MS (ESI) m/z calcd. for
C39H63ClN2O11 771.3, found [M þ H]þ 771.9; Analysis calculated for
C39H63ClN2O11: C 60.72, H 8.23, N 3.63. Found: C 60.79, H 8.19, N 3.67.
3H), 0.83 (t, 3H); 13C NMR (600 MHz, CDCl3):
d 220.7, 173.9, 156.6,
103.0, 81.7, 78.3, 77.8, 77.0, 74.2, 70.5, 69.5, 65.7, 50.1, 45.5, 43.2,
42.9, 40.2, 38.7, 37.3, 35.6, 29.2, 23.3, 21.2, 19.3, 18.0, 16.1, 14.9, 12.6,
11.3, 10.5, 9.1; MS (ESI) m/z calcd. for C34H62N2O11 674.4, found
[M þ H]þ 675.9; Analysis calculated for C34H62N2O11: C 60.51, H
9.26, N 4.15. Found: C 60.58, H 9.22, N 4.12.
6.3.5. 3-O-((Benzyl)carbamoyl)-3-O-descladinosylclarithromycin (4e)
Slightly yellow crystals, yield 69.0%, mp 100–103 ꢀC, TLC
Rf ¼ 0.58 (dichloromethane/methanol 7:1, v/v); IR(KBr): 3462, 2975,
2940, 2880, 2834, 2786, 1817, 1743, 1693, 1458, 1378, 1330, 1264,
1233, 1171, 1109, 1077, 1050, 1033 cmꢂ1; 1H NMR (600 MHz, CDCl3):
6.3.9. 3-O-((Propenyl)carbamoyl)-3-O-descladinosylclarithromycin (4i)
White crystals, yield 61.8%, mp 219–223 ꢀC, TLC Rf ¼ 0.52
(dichloromethane/methanol 7:1, v/v); IR(KBr): 3458, 2974, 2940,
2879, 2834, 2786, 1737, 1645, 1515, 1458, 1405, 1378, 1238, 1171,
1109, 1075, 1051, 1033 cmꢂ1 1H NMR (600 MHz, CDCl3):
; d 5.89–
d
7.33–7.31 (m, 2H), 7.29 (m, 1H), 7.28 (m, 2H), 5.37 (m, 1H), 5.21–
5.83 (m, 1H), 5.23–5.14 (m, 2H), 5.08–5.04 (m, 1H), 4.92–4.90 (m,
1H), 4.06 (d, J ¼ 7.3, 1H), 4.00–3.96 (m, 1H), 3.91–3.89 (m, 1H), 3.82–
3.80 (m, 2H), 3.72 (m, 1H), 3.39–3.37 (m, 2H), 3.25 (m, 1H), 3.22–
3.19 (m, 1H), 3.05 (s, 3H), 3.02–2.99 (m, 1H), 2.86–2.82 (m, 1H),
2.58–2.55 (m, 1H), 2.14 (s, 1H), 2.32 (s, 6H), 2.20–2.18 (m, 1H), 1.96–
1.92 (m, 1H), 1.84–1.80 (m, 2H) 1.69–1.67 (m, 2H), 1.56–1.53 (m, 1H),
1.50–1.47 (m, 1H), 1.29 (s, 3H), 1.23 (m, 3H), 1.16–1.07 (m, 15H), 0.83
(t, 3H); MS (ESI) m/z calcd. for C34H60N2O11 672.4, found [M þ H]þ
673.8; Analysis calculated for C34H60N2O11: C 60.69, H 8.99, N 4.16.
Found: C 60.64, H 9.02, N 4.13.
5.16 (m, 3H), 5.07 (m, 1H), 4.93 (m, 1H), 4.84 (m, 1H), 4.39–4.27 (m,
2H), 3.99–3.94 (m, 2H), 3.85–3.81 (m, 1H), 3.78–3.75 (m, 1H), 3.25–
3.23 (m, 1H), 3.06 (m, 3H), 3.02–2.99 (m, 1H), 2.56 (m, 1H), 2.31–
2.28 (s, 6H), 2.17 (m, 1H), 2.13 (m, 1H), 1.95–1.93 (m, 1H), 1.83–1.79
(m, 2H), 1.57–1.55 (m, 1H), 1.52–1.49 (m, 2H), 1.29–1.25 (m, 3H),
1.23–1.08 (m, 18H), 0.85–0.83 (m, 3H); MS (ESI) m/z calcd. for
C38H62N2O11 722.4, found [M þ H]þ 723.9; Analysis calculated for
C38H62N2O11: C 63.14, H 8.64, N 3.88. Found: C 63.17, H 8.60, N 3.89.
6.3.6. 3-O-((Phenethyl)carbamoyl)-3-O-descladinosyl-
clarithromycin (4f)
Slightly yellow crystals, yield 60.6%, mp 107–109 ꢀC, TLC
Rf ¼ 0.51 (dichloromethane/methanol 7:1, v/v); IR(KBr): 3453, 2974,
2939, 2879, 2834, 2786, 1737, 1604, 1498, 1456, 1405, 1378, 1330,
1246, 1171, 1109, 1075, 1051, 1033 cmꢂ1; 1H NMR (600 MHz, CDCl3):
6.3.10. 3-O-((Butyl)carbamoyl)-3-O-descladinosylclarithromycin (4j)
White crystals, yield 56.4%, mp 107–110 ꢀC, TLC Rf ¼ 0.48
(dichloromethane/methanol 7:1, v/v); IR(KBr): 3460, 2973, 2939,
2877, 2834, 2786, 1737, 1695, 1515, 1458, 1405, 1378, 1345, 1330,
1245, 1171, 1109, 1075, 1052, 1032 cmꢂ1; 1H NMR (600 MHz, CDCl3):
d
7.33–7.30 (m, 2H), 7.27 (m,1H), 7.20 (m, 2H), 5.07 (m, 1H), 4.93 (m,
d
5.19–5.17 (dd, J ¼ 11.1, J ¼ 2.2, 1H), 4.90 (m, 2H), 4.07–4.05 (m, 1H),
1H), 4.03–4.01 (d, J ¼ 14.5,1H), 3.97 (m,1H), 3.82 (m, 2H), 3.69–3.63
3.99–3.96 (m, 1H), 3.84–3.81 (m, 2H), 3.37–3.35 (m, 2H), 3.29–3.20

L. Zhang et al. / European Journal of Medicinal Chemistry 45 (2010) 915–922
921
(m, 2H), 3.09 (m, 1H), 3.05 (s, 3H), 3.01–2.99 (m, 1H), 2.83 (m, 1H),
6.6. General methods for the preparation of 3-O-arylalkylcar-
bamoyl-3-O-descladinosylazithromycin 11,12-cyclic carbonate
derivatives (7a–g)
2.39–2.31 (m, 6H), 2.19–2.17 (m, 2H), 1.95–1.92 (m, 1H), 1.84–1.80
(m, 2H),1.70–1.68 (m, 3H),1.56–1.47 (m, 4H),1.38–1.34 (m, 2H),1.29
(s, 3H), 1.23 (m, 3H), 1.16–1.08 (m, 15H), 0.93 (t, 3H), 0.83 (t, 3H); MS
(ESI) m/z calcd. for C35H64N2O11 688.5, found [M þ H]þ 689.7;
Analysis calculated for C35H64N2O11: C 61.02, H 9.36, N 4.07. Found:
C 60.97, H 9.33, N 4.10.
To a solution of 6 (1.6 g, 2.13 mmol) in DMF (15 mL) was
added DBU (0.33 mL, 2.25 mmol, 1.0 equiv) and corresponding
amine (2.25 mmol, 1.0 equiv). The resulting solution was stirred
for 10 h at the room temperature. The reaction was quenched
with water (30 mL) and the aqueous layer was extracted with
ethyl acetate (3 ꢁ 15 mL). The combined organic layers were
washed with brine (3 ꢁ 15 mL), and dried over anhydrous
Na2SO4, filtered. The filtrate was concentrated in vacuo to afford
a crude product.
6.3.11. 3-O-((Pentyl)carbamoyl)-3-O-descladinosylclarithromycin (4k)
White crystals, yield 63.0%, mp 105–107 ꢀC, TLC Rf ¼ 0.48
(dichloromethane/methanol 7:1, v/v); IR(KBr): 3457, 2972, 2938,
2876, 2786, 1737, 1517, 1458, 1405, 1379, 1331, 1250, 1171, 1110,
1075, 1051, 1033 cmꢂ1 1H NMR (600 MHz, CDCl3):
; d 5.18 (dd,
J ¼ 11.1, J ¼ 2.0, 1H), 4.90–4.87 (m, 2H), 4.05 (d, J ¼ 7.3, 1H), 3.96 (s,
1H), 3.82–3.80 (m, 2H), 3.37 (m, 1H), 3.31–3.30 (m, 1H), 3.28–3.25
(m, 1H), 3.20–3.17 (m, 1H), 3.08 (s, 3H), 3.01–2.99 (m, 1H), 2.85–
2.80 (m, 1H), 2.57–2.55 (m, 1H), 2.43–2.41 (m, 1H), 2.29 (s, 6H),
2.18–2.16 (m, 1H), 1.95–1.90 (m, 3H), 1.68–1.64 (m, 2H), 1.54–1.50
(m, 4H), 1.38–1.32 (s, 4H), 1.32–1.29 (m, 3H), 1.22 (m, 4H), 1.15–
1.09 (m, 15H), 0.90 (t, 3H), 0.83 (t, 3H); 13C NMR (600 MHz, CDCl3)
A solution of the above crude product in methanol (15 mL) was
heated to 55 ꢀC and stirred for 20 h at the same temperature. After
concentrating the reaction solution in vacuo, the residue was
purified by flash chromatography (dichlormethane/methanol, 10:1,
v/v) to afford products 7a–g.
6.6.1. 3-O-((4-Methoxybenzyl)carbamoyl)-3-O-descladinosyl-
azithromycin 11,12-cyclic carbonate (7a)
d
220.8, 173.9, 156.5, 103.1, 81.2, 78.3, 77.9, 77.0, 74.2, 70.5, 69.5,
66.1, 50.1, 45.5, 43.2, 41.2, 40.4, 38.7, 37.3, 35.6, 29.8, 29.0, 28.7,
22.4, 21.2, 19.4, 18.0, 16.1, 15.0, 14.0, 12.6, 10.5, 9.1; MS (ESI) m/z
calcd. for C36H66N2O11 702.5, found [M þ H]þ 703.9; Analysis
calculated for C36H66N2O11: C 61.51, H 9.46, N 3.99. Found: C 61.57,
H 9.42, N 4.01.
White solids, yield 64.9%, mp 113–116 ꢀC; TLC Rf ¼ 0.634
(dichlormethane/methanol 10:1, v/v); IR (KBr): 3430, 2972,
2938, 2878, 2835, 1812, 1726, 1612, 1586, 1513, 1459, 1378, 1349,
1378, 1349, 1241, 1213, 1164, 1112, 1071, 1052 cmꢂ1 1H NMR
;
(600 MHz, CDCl3)
d 7.27–7.24 (m, 2H), 6.87–6.84 (m, 2H), 5.05–
5.04 (m, 1H), 4.54 (m, 2H), 4.38–4.36 (m, 1H), 4.26–4.19 (m, 2H),
3.99–3.97 (m, 1H), 3.80 (s, 3H), 3.72–3.70 (m, 1H), 3.64–3.61 (m,
1H), 3.57–3.55 (m, 2H), 3.27–3.23 (m, 1H), 2.96 (m, 1H), 2.88–
2.82 (m, 2H), 2.67–2.62 (m, 1H), 2.52–2.49 (m, 2H), 2.25 (m, 9H),
1.98 (m, 3H), 1.92–1.86 (m, 6H), 1.31–1.26 (m, 5H), 1.25–1.23 (m,
7H), 0.94–0.90 (m, 9H); MS (ESI) m/z calcd. for C40H65N3O12
779.5, found [M þ H]þ 780.9; Analysis calculated for
C40H65N3O12: C 61.60, H 8.40, N 5.39. Found: C 61.55, H 8.39, N
5.35.
6.4. 20-O-Acetyl-3-O-descladinosylazithromycin (5)
To a solution of azithromycin (2.0 g, 2.67 mmol) in anhydrous
methanol (20 mL) at room temperature was added dropwise 1 M
HCl until the reaction mixture was adjusted to pH ¼ 1.0–1.5. The
resulting solution was allowed to stir for 24 h at the same
temperature. And then the reaction solution was neutralized to
pH ¼ 10.5–11.0 with 1 M sodium hydroxide and was stirred for 24 h
at the room temperature. The reaction was quenched with 5%
NaHCO3 (20 mL) and the aqueous layer was extracted with CH2Cl2
(2 ꢁ 10 mL). The combined organic layers were dried over anhy-
drous Na2SO4, filtered, and concentrated in vacuo to afford 1.50 g
(92.1%) of 3-O-descladinosylazithromycin as a white foam: mp 137–
140 ꢀC, Rf ¼ 0.522 (dichlormethane/methanol, 10:1, v/v).
6.6.2. 3-O-((4-Fluorobenzyl)carbamoyl)-3-O-descladinosyl-
azithromycin 11,12-cyclic carbonate (7b)
White solids, yield 57.5%, mp 106–110 ꢀC; TLC Rf ¼ 0.612
(dichlormethane/methanol 10:1, v/v); IR (KBr): 3435, 2973, 2939,
2879, 2790, 1813, 1729, 1606, 1510, 1458, 1378, 1350, 1336, 1240,
To a solution of 3-O-descladinosylazithromycin (1.5 g, 2.67
mmol) prepared above in CH2Cl2 (20 mL) at room temperature was
added Ac2O (0.5 mL, 5.34 mmol) and Et3N (1.48 mL, 10.68 mmol).
The resulting solution was allowed to stir for 24 h at the same
temperature. The reaction was quenched with 5% aqueous NaHCO3
(20 mL) and the aqueous layer was extracted with CH2Cl2
(2 ꢁ 10 mL). The combined organic layers were dried over anhy-
drous Na2SO4, filtered, and concentrated in vacuo. The residue was
crystallized from acetone–water (2:1) to afford 1.34 g (89.7%) of 5 as
a white solid: mp 141–143 ꢀC, Rf ¼ 0.554 (dichlormethane/meth-
anol, 10:1, v/v).
1164, 1112, 1051 cmꢂ1 1H NMR (600 MHz, CDCl3)
; d 7.30–7.26 (m,
2H), 7.02–6.98 (m, 2H), 5.11 (m, 1H), 4.50–4.39 (m, 2H), 4.34–4.21
(m, 2H), 4.33–4.21 (m, 2H), 3.68–3.54 (m, 2H), 3.27–3.22 (m, 1H),
2.88–2.82 (m, 1H), 2.69–2.60 (m, 2H), 2.53–2.43 (m, 1H), 2.37 (m,
2H), 2.25 (m, 9H), 2.19 (m, 1H), 1.91–1.85 (m, 2H), 1.68–1.63 (m, 4H),
1.45 (m, 3H), 1.31–1.23 (m, 4H), 1.06–1.01 (m, 9H), 0.94–0.90 (m,
9H); MS (ESI) m/z calcd. for C39H62FN3O11 767.4, found [M þ H]þ
768.7; Analysis calculated for C39H62FN3O11: C 61.00, H 8.14, N 5.47.
Found: C 60.95, H 8.10, N 5.54.
6.6.3. 3-O-((2-Chlorophenethyl)carbamoyl)-3-O-
descladinosylazithromycin 11,12-cyclic carbonate (7c)
6.5. 20-O-Acetyl-3-O-acylimidazolyl-3-O-descladinosyla-
zithromycin 11,12-cyclic carbonate (6)
White solids, yield 55.3%, mp 117–111 ꢀC; TLC Rf ¼ 0.582
(dichlormethane/methanol 10:1, v/v); IR (KBr): 3435, 2972, 2934,
2877, 1812, 1737, 1637, 1509, 1457, 1379, 1351, 1327, 1239, 1166, 1113,
To a solution of 5 (1.5 g, 2.37 mmol) in toluene (20 mL) was
added Et3N (0.60 mL, 4.33 mmol) and CDI (1.02 g, 5.80 mmol).
The resulting solution was stirred for 48 h at the room temperature.
The reaction was quenched with saturated NaHCO3 (20 mL) and the
aqueous layer was extracted with toluene (2 ꢁ 6 mL). The
combined organic layers were dried over anhydrous Na2SO4,
filtered, and concentrated in vacuo to afford 1.60 g (89.8%) of 6 as
a white foam: mp 147–150 ꢀC; Rf ¼ 0.592 (dichlormethane/meth-
anol, 10:1, v/v).
1048 cmꢂ1; 1H NMR (600 MHz, CDCl3)
d 7.26–7.19 (m, 3H), 5.04 (m,
1H), 4.60 (s, 1H), 4.55 (m, 1H), 4.40 (d, J ¼ 4.2 Hz, 1H), 3.95 (m, 1H),
3.82–3.80 (m, 1H), 3.66 (m, 2H), 3.56 (m, 1H), 3.36–3.35 (m, 2H),
3.00–2.95 (m, 3H), 2.83 (m, 4H), 2.68–2.60 (m, 1H), 2.50–2.47 (m,
1H), 2.25 (m, 6H), 2.19 (m, 2H), 1.89 (m, 2H), 1.66 (m, 2H), 1.45–1.42
(m, 5H), 1.23 (m, 1H), 1.07–1.00 (m, 12H), 0.94–0.89 (m, 9H); MS
(ESI) m/z calcd. for C40H64ClN3O11 797.4, found [M þ H]þ 798.7;
Analysis calculated for C40H64ClN3O11: C 61.17, H 8.08, N 5.26.
Found: C 61.13, H 8.09, N 5.22.

922
L. Zhang et al. / European Journal of Medicinal Chemistry 45 (2010) 915–922
6.6.4. 3-O-((Benzyl)carbamoyl)-3-O-descladinosylazithromycin
11,12-cyclic carbonate (7d)
1164, 1113, 1051 cmꢂ1 1H NMR (600 MHz, CDCl3)
; d 4.93–4.90
(m, 1H), 4.48–4.46 (m, 2H), 4.31–4.27 (m, 1H), 3.68–3.65 (m,2H),
3.54–3.51 (m, 2H), 3.27–3.23 (m, 1H), 3.19–3.14 (m, 2H), 3.08–
3.02 (m, 2H), 2.86–2.83 (m, 2H), 2.67–2.63 (m, 1H), 2.53–2.49
(m, 1H), 2.26 (m, 9H), 2.19–2.17 (m, 1H), 1.96–1.90 (m, 1H), 1.71
(m, 1H), 1.53–1.50 (m, 6H), 1.46 (m, 3H), 1.32–1.28 (m, 2H),
1.25–1.20 (m, 5H), 1.09–1.01 (m, 9H), 0.95–0.88 (m, 12H); MS
(ESI) m/z calcd. for C37H67N3O11 729.5, found [M þ H]þ 730.8;
Analysis calculated for C37H67N3O11: C 60.88, H 9.25, N 5.76
Found: C 60.85, H 9.22, N 5.80.
White solids, yield 55.3%, mp 126–130 ꢀC; TLC Rf ¼ 0.605
(dichlormethane/methanol 10:1, v/v); IR (KBr): 3430, 2972, 2936,
2878, 2789, 1812, 1714, 1636, 1497, 1456, 1380, 1350, 1238, 1213,
1165, 1113, 1051 cmꢂ1 1H NMR (600 MHz, CDCl3)
; d 7.33–7.24 (m,
5H), 5.13 (m, 1H), 4.53 (m, 1H), 4.47–4.45 (m, 1H), 4.38 (m, 1H),
4.34–4.28 (m, 2H), 3.71 (d, J ¼ 10.4 Hz, 2H), 3.51–3.47 (m, 2H),
3.27–3.22 (m, 2H), 2.84–2.82 (m, 1H), 2.67–2.63 (m, 1H), 2.50–2.45
(m, 1H), 2.28–2.20 (m, 7H), 2.25–2.23 (m, 6H), 2.01 (m, 1H), 1.89 (m,
1H), 1.75 (m, 1H), 1.67–1.63 (m, 2H), 1.46 (m, 2H), 1.25–1.23 (m, 4H),
1.05–1.01 (m, 9H), 0.94–0.88 (m, 9H); MS (ESI) m/z calcd. for
C39H63N3O11 749.5, found [M þ H]þ 750.5; Analysis calculated for
C39H63N3O11: C 62.46, H 8.47, N 5.60. Found: C 62.40, H 8.49, N 5.57.
Acknowledgments
This research was supported by Major R&D Program of New
DrugsdNational S&T Key Special Subject of China (2009ZX09103-115)
and National Natural Science Foundation of China (20872081).
6.6.5. 3-O-((Phenethyl)carbamoyl)-3-O-descladinosylazithromycin
11,12-cyclic carbonate (7e)
White solids, yield 59.0%, mp 106–108 ꢀC; TLC Rf ¼ 0.605
(dichlormethane/methanol, 10:1, v/v); IR (KBr): 3415, 2972, 2934,
2878, 1810, 1734, 1632, 1497, 1457, 1378, 1328, 1241, 1166, 1110,
Appendix. Supplemental data
Supplemental data associated with this article can be found in
online version at doi:10.1016/j.ejmech.2009.11.032.
1050 cmꢂ1
; d 7.31–7.29 (m, 2H),
1H NMR (600 MHz, CDCl3)
7.26–7.21 (m, 3H), 5.03 (m, 1H), 4.62–4.60 (m, 2H), 4.44 (m, 1H),
3.65–3.55 (m, 2H), 3.52–3.44 (m, 2H), 3.33 (m,1H), 3.28–3.25 (m,
3H), 2.84 (m, 4H), 2.49 (m, 1H), 2.39–2.37 (m, 1H), 2.32–2.20 (m,
10H), 1.91–1.86 (m, 1H), 1.77–1.67 (m, 4H), 1.48–1.43 (m, 4H), 1.30–
1.24 (m, 4H), 1.04–1.00 (m, 9H), 0.96–0.89 (m, 9H); MS (ESI) m/z
calcd. for C40H65N3O11 763.5, found [M þ H]þ 764.8; Analysis
calculated for C40H65N3O11: C 62.89, H 8.38, N 5.50. Found: C 62.80,
H 8.42, N 5.55.
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White solids, yield 64.8%, mp 121–124 ꢀC; TLC Rf ¼ 0.634
(dichlormethane/methanol, 10:1, v/v); IR (KBr): 3414, 2971, 2937,
2874, 2790, 1813, 1714, 1639, 1508, 1458, 1380, 1350, 1335, 1239,
1213, 1164, 1113, 1051 cmꢂ1 1H NMR (600 MHz, CDCl3)
; d 4.92 (dd,
J ¼ 9.2 Hz, J ¼ 3.2 Hz, 1H), 4.49 (m, 2H), 4.43 (m, 1H), 3.69–3.65 (m,
2H), 3.56–3.47 (m, 2H), 3.29–3.24 (m, 1H), 3.20–3.13 (m, 2H),
3.10–3.03 (m, 1H), 2.88–2.81 (m, 2H), 2.55–2.49 (m, 2H), 2.28 (m,
9H), 2.17 (s, 1H), 1.90 (m, 1H), 1.70–1.68 (m, 1H), 1.50 (m, 3H), 1.46
(m, 6H), 1.30 (m, 3H), 1.24(m, 1H), 1.06–1.01 (m, 12H), 0.95–0.90 (m,
12H); MS (ESI) m/z calcd. for C36H65N3O11 715.5, found [M þ H]þ
716.5; Analysis calculated for C36H65N3O11: C 60.40, H 9.15, N 5.87.
Found: C 60.35, H 9.12, N 5.84.
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6.6.7. 3-O-((Pentyl)carbamoyl)-3-O-descladinosylazithromycin
11,12-cyclic carbonate (7g)
White solids, yield 59.0%, mp 111–115 ꢀC; TLC Rf ¼ 0.634
(dichlormethane/methanol, 10:1, v/v); IR (KBr): 3415, 2935,
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