Synthesis and antibacterial activity of 4″-O-carbamoyl analogs of clarithromycin

Article abstract of DOI:10.1016/j.cclet.2009.11.023

A series of novel 4″-O-carbamoyl analogs of clarithromycin were synthesized and evaluated for their in vitro antibacterial activity. All of the desired compounds showed excellent activity against erythromycin-susceptible S. pneumoniae. Particularly, 4-fluorobenzyl carbamate 7a demonstrated potent activity against erythromycin-resistant S. pneumoniae encoded by the mef gene, and remarkably improved activity against erythromycin-resistant S. pneumoniae encoded by the erm gene, and the erm and mef genes.

Full text of DOI:10.1016/j.cclet.2009.11.023

Available online at www.sciencedirect.com
Chinese Chemical Letters 21 (2010) 257–260
www.elsevier.com/locate/cclet
Synthesis and antibacterial activity of 400-O-carbamoyl
analogs of clarithromycin
*
Xue Cui Shen, Bo Jiao, Shu Tao Ma
School of Pharmaceutical Sciences, Shandong University, Jinan 250012, China
Received 26 August 2009
Abstract
A series of novel 400-O-carbamoyl analogs of clarithromycin were synthesized and evaluated for their in vitro antibacterial activity.
All of the desired compounds showed excellent activity against erythromycin-susceptible S. pneumoniae. Particularly, 4-fluorobenzyl
carbamate 7a demonstrated potent activity against erythromycin-resistant S. pneumoniae encoded by the mef gene, and remarkably
improved activity against erythromycin-resistant S. pneumoniae encoded by the erm gene, and the erm and mef genes.
# 2009 Shu Tao Ma. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Clarithromycin analogs; 400-O-carbamate; Synthesis; Antibacterial activity; Resistant bacteria
First generation macrolides as exemplified by erythromycin A (EMA) demonstrated broad-spectrum antimicrobial
activity and were primarily prescribed for respiratory, skin and soft tissue infections, but they lose readily their
antibacterial activity attributing to degradation under acidic conditions [1,2]. Second generation macrolides such as
clarithromycin (CAM) (Fig. 1) and azithromycin (AZM) were developed to overcome the shortcomings of EMA [3].
However, the therapeutic utility of these macrolides has led to rapid increases in the resistance rates of bacteria isolated
clinically. Unfortunately, all of the macrolides belonging to the second generation exhibited less improvement in the
activity against erythromycin-resistant strains [4].
A significant amount of work has been carried out to discover new macrolides against resistant strains. It has been
reported that CP-544372 (Fig. 1) showed potent activity against both susceptible and resistant bacteria [5]. CP-544372
contains a prolonged aromatic side chain attached to the 400-position of the cladinose sugar, reaching to the binding site
of chloramphenicol [6,7]. Otherwise, our studies also confirmed that the 400-O-carbamoyl groups play an important
role in overcoming MLSB (macrolide–lincosamide–streptogramin B) resistance [8,9].
In order to probe the effect of a long 400-O-carbamoyl side chain in the antibacterial activity, five amines 4a–e were
obtained from 6-aminohexanonic acid by protection of (BOC)2O, condensation reaction with corresponding amines
catalized by DCC and HOBt, and finally, deprotection of the BOC groups in HCl as shown in Scheme 1.
CAM has been widely used in the treatment of respiratory tract infections owing to its high efficacy, ideal
pharmacokinetic property and safety [10,11]. In anticipation of inheriting these beneficial profiles of CAM, a series of
novel 400-O-cabamate analogs of CAM 7a–e were prepared by condensation with the amines synthesized above as
* Corresponding author.
E-mail address: mashutao@sdu.edu.cn (S.T. Ma).
1001-8417/$ – see front matter # 2009 Shu Tao Ma. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2009.11.023

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X.C. Shen et al. / Chinese Chemical Letters 21 (2010) 257–260
Fig. 1. Structures of clarithromycin and CP-544372.
outlined in Scheme 2. CAM was subjected to acetylation reaction with acetic anhydride to give 20-O-acetate 5. The 20-
O-acetate 6 was obtained by reaction of 5 with CDI (N,N-carbonyldiimidazole) in toluene in the presence of Et3N
(triethylamine) in good yield. Reaction of 6 with the corresponding amines 4 in DMF in the presence of DBU (1,8-
diazabicyclo[5.4.0]undec-7-ene) followed by methanolysis at 55 8C gave the desired compounds 7a–e (Table 1). Their
1
structures were confirmed by MS, IR, H NMR and elemental analysis [12].
The activity of 7a–e against four phenotypes of Gram-positive strains was evaluated using broth microdilution
method as shown in Table 2. All of the compounds tested retained excellent activity against erythromycin-susceptible
Scheme 1. Reagents and conditions: (a) (BOC)2O, 1 mol/L NaOH, THF, rt, 24 h, 76.0%; (b) DCC, HOBt, THF, 0 8C, 8 h, R1NH2, rt, 2 h; (c) HCl,
AcOEt, rt, 2 h 78.1–85.4% for 2 steps.
Scheme 2. Reagents and conditions: (a) Ac2O, Et3N, CH2Cl2, rt, 24 h, 85.4%; (b) CDI, toluene, rt, 48 h, 92.9%; (c) R1NH2ꢀHCl, DBU, DMF, rt,
24 h; (d) CH3OH, 55 8C, 24 h, 73.2–77.7% for 2 steps.

X.C. Shen et al. / Chinese Chemical Letters 21 (2010) 257–260
259
Table 1
Data of the target compounds 7a–e.
Compounds
R1
Molecular formula
Molecular weight
Mp (8C)
Overall yield (%)
7a
7b
7c
7d
7e
4-Fluorobenzyl-
Benzyl-
C52H86FN3O15
C52H87N3O15
C48H87N3O15
1011.6
994.3
946.2
944.2
974.3
110–112
115–118
112–115
119–122
104–107
59.7
58.0
61.6
58.8
58.9
Propyl-
Propenyl-
Pentyl-
C48H85N3O15
C50H91N3O15
Table 2
In vitro antibacterial activity of the target compounds 7a–e.
Compounds
Strain/MIC (mg/mL)
S. pneumoniae
S. pneumoniae B1
(ermB)
S. pneumoniae A22072
S. pneumoniae AB11
(ermB + mefA)
ATCC49619
(mefA)
EAM
CAM
AZM
7a
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
128
64
8
256
128
256
4
4
128
2
4
0.5
2
7b
7c
64
64
128
128
128
4
128
128
128
7d
7e
2
4
S. pneumoniae comparable to the references (MIC 0.03 mg/mL), and some of them showed improved activity against
erythromycin-resistant S. pneumoniae. Among them, 4-fluorobenzyl carbamate 7a showed greatly improved activity
against both S. pneumoniae B1 strain encoded by the erm B gene and pneumonia AB11 strain encoded by the erm B
and mef A genes, exhibiting 64-fold, 32-fold and 64-fold better activity than EMA, CAM and AZM, respectively.
Similarly, 4-fluorobenzyl carbamate 7a also had potent activity against S. pneumoniae A22072 encoded by the mef A
gene, demonstrating 16-fold, 8-fold and 8-fold greater than EMA, CAM and AZM, respectively. In contrast,
alkylcarbamates 7c–e possessed slightly improved activity against erythromycin-resistant strains compared with the
references. These results suggested that the prolonged arylalkylcarbamoyl group may enhance activity against
erythromycin-resistant strains. Besides, 4-fluorobenzyl carbamate 7a was 32-fold, 4-fold and 16-fold more potent
activity against erythromycin-resistant strains tested than benzyl carbamate 7b, indicating that the electron-
withdrawing group may further increase activity against erythromycin-resistant strains.
In conclusion, a series of novel 400-O-carbamate analogs of CAM were synthesized and evaluated. All of these
analogs tested, without exception, exhibited excellent activity against erythromycin-susceptible S. pneumoniae, and
some of them showed improved activity against erythromycin-resistant S. pneumoniae. Particularly, 4-fluorobenzyl
carbamate 7a demonstrated potent activity against erythromycin-resistant S. pneumoniae encoded by the mef gene,
and remarkably improved activity against erythromycin-resistant S. pneumoniae encoded by the erm gene, and the erm
and mef genes.
Acknowledgments
This research was supported by Major R&D Program of New Drugs—National S&T Key Special Subject of China
(No. 2009ZX09103-115), National Natural Science Foundation of China (No. 20872081) and Natural Science
Foundation of Shandong (No. Y2006C31).
References
[1] S. Omura (Ed.), Macrolide Antibiotics: Chemistry, Biology, and Practice, Second ed., Academic Press, London, 2002.
[2] W. Schoenfeld, H.A. Kirst (Eds.), Macrolide Antibiotics, Birkhaeuser, Basel, 2002.
[3] G.G. Zhanel, M. Dueck, D.J. Hoban, et al. Drugs 61 (2001) 443.

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X.C. Shen et al. / Chinese Chemical Letters 21 (2010) 257–260
[4] Y.J. Wu, W.G. Su, Curr. Med. Chem. 8 (2001) 1727.
[5] H. Masamune, W.G. Su, B.V. Yang, et al., US6025350 [P].
[6] H. Takashima, Curr. Top. Med. Chem. 3 (2003) 99.
[7] N. Ban, P. Nissen, J. Hansen, et al. Science 289 (2000) 905.
[8] R. Xian, S. Ma, B. Jiao, Chin. Chem. Lett. 19 (2008) 409.
[9] S. Ma, B. Jiao, Z. Liu, et al. Bioorg. Med. Chem. Lett. 19 (2009) 1698.
[10] J.L. Hansen, J.A. Ippolito, N. Ban, et al. Mol. Cell 10 (2002) 117.
[11] R.P. Bax, R. Anderson, J. Crew, et al. Nat. Med. 4 (1998) 545.
[12] Spectral data of the compounds 7a–e: 7a: White solid, yield 83.6%, mp 110–112 8C, TLC Rf = 0.36 (dichloromethane/methanol, 10:1); IR
(KBr): 3381, 2974, 2938, 1730, 1658, 1605, 1511, 1459, 1378, 1345, 1266, 1171, 1110, 1072, 1051, 1013 cmꢁ1; 1H NMR (600 MHz, CDCl3):d
(7.26–7.24 (m, 2H), 7.04–7.01 (m, 2H), 5.07 (dd, 1H, J = 11.4 Hz, J = 1.8 Hz), 4.98 (m, 1H), 4.41–4.40 (m, 2H), 4.30–4.26 (m, 2H), 4.10–1.09
(m, 1H), 3.82–3.76 (m, 2H), 3.69–3.59 (m, 2H), 3.23–3.17 (m, 8H), 3.05–3.03 (m, 1H), 2.94–2.87 (m, 2H), 2.65–2.55 (m, 2H), 2.43–2.41 (m,
2H), 2.33 (m, 6H), 2.22–2.20 (m, 3H), 1.94–1.92 (m, 1H), 1.72–1.63 (m, 3H), 1.55–1.48 (m, 8H), 1.38–1.35 (m, 9H), 1.26–1.15 (m, 9H), 1.14–
1.12 (m, 9H), 0.84 (t, 3H); MS (ESI) m/z calcd. for C52H86FN3O15 1011.6; found (M+H)+ 1012.8; Anal. Calcd. for C52H86FN3O15 (1012.25)
(%): C 61.70, H 8.56, F 1.88, N 4.15, Found (%): C 61.66, H 8.54, F 1.86, N 4.17. 7b: White solid, yield 81.3%, mp 115–118 8C, TLC Rf = 0.35
(dichloromethane/methanol, 10:1); IR (KBr): 3454, 2974, 2938, 1731, 1514, 1456, 1378, 1346, 1247, 1171, 1110, 1072, 1051, 1013 cmꢁ1; 1H
NMR (600 MHz, CDCl3): d 7.35–7.26 (m, 5H), 5.06 (d, 1H, J = 10.8 Hz), 4.58–4.50 (m, 2H), 4.44–4.43 (m, 2H), 4.30–4.27 (m, 2H), 3.98 (m,
1H), 3.81–3.76 (m, 2H), 3.67–3.63 (m, 2H), 3.35–3.27 (m, 3H), 3.21–3.17 (m, 4H), 3.00–2.98 (m, 2H), 2.90–2.89 (m, 2H), 2.58–2.56 (m, 2H),
2.30–2.29 (m, 7H), 2.22 (t, 2H), 1.94–1.84 (m, 1H), 1.72–1.62 (m, 2H), 1.54–1.46 (m, 8H), 1.39–1.35 (m, 11H), 1.25–1.23 (m, 9H), 1.12–1.10
(m, 9H), 0.84 (t, 3H), MS (ESI) m/z, calcd. for C52H87N3O15 993.6; found (M+H)+ 995.1; Anal. Calcd. for C52H87N3O15 (994.3) (%): C 62.82,
H 8.82, N 4.23, Found (%): C 62.78, H 8.84, N 4.24. 7c: White solid, yield 86.3%, mp 112–115 8C, TLC Rf = 0.36 (dichloromethane/methanol,
1
10:1); IR (KBr): 3452, 2972, 2937, 1731, 1655, 1537, 1459, 1378, 1337, 1266, 1171, 1110, 1072, 1050, 1012 cmꢁ1; H NMR (600 MHz,
CDCl3): d 5.07 (d, 1H, J = 10.2 Hz), 4.97–4.96 (m, 1H), 4.57–4.50 (m, 2H), 3.99 (s, 1H), 3.82–3.76 (m, 2H), 3.68–3.59 (m, 2H), 3.36–3.31 (m,
2H), 3.23–3.18 (m, 6H), 3.15–3.09 (m, 1H), 3.05–3.00 (m, 2H), 2.89 (m, 2H), 2.59–2.57 (m, 2H), 2.44–2.41 (m, 1H), 2.31–2.29 (m, 6H), 2.16
(t, 2H), 1.94–1.87 (m, 1H), 1.73–1.63 (m, 3H), 1.54–1.48 (m, 3H), 1.40–1.34 (m, 4H), 1.27–1.24 (m, 2H), 1.24–1.18 (m, 14H), 1.17–1.11 (m,
16H), 0.93 (t, 3H), 0.85 (t, 3H); MS (ESI) m/z calcd. for C48H87N3O15 945.6; found (M+H)+ 947.1; Anal. Calcd. for C48H87N3O15 (946.2) (%):
C 60.93, H 9.27, N 4.44, Found (%): C 60.89, H 9.30, N 4.41. 7d: White solid, yield 82.3%, mp 119–122 8C, TLC Rf = 0.38 (dichloromethane/
methanol, 10:1); IR (KBr): 3454, 2974, 2939, 1731, 1664, 1514, 1458, 1378, 1339, 1266, 1171, 1110, 1072, 1051, 1013, 986, 934 cmꢁ1; 1H
NMR (600 MHz, CDCl3): d 5.87–5.82 (m, 1H), 5.20–5.13 (m, 2H), 5.08–5.07 (m, 1H), 4.98–4.97 (m, 1H), 4.56–4.52 (m, 2H), 4.27 (m, 1H),
3.98 (s, 2H), 3.89 (t, 2H), 3.68–3.67 (m, 2H), 3.32 (m, 3H), 3.23–3.18 (m, 3H), 3.05 (m, 1H), 3.01 (m, 2H), 2.89 (m, 2H), 2.59 (m, 2H), 2.43–
2.41 (m, 7H), 2.22–2.19 (m, 2H), 1.96–1.85 (m, 2H), 1.70–1.63 (m, 4H), 1.55–1.49 (m, 6H), 1.39–1.35 (m, 9H), 1.27–1.24 (m, 2H), 1.22–1.14
(m, 9H), 1.13–1.10 (m, 9H), 0.85 (t, 3H,); MS (ESI) m/z, calcd. for C48H85N3O15 943.6; found (M+H)+ 945.0; Anal. Calcd. for C48H85N3O15
(944.2) (%): C 61.06, H 9.07, N 4.45, Found (%): C 61.10, H 9.04, N 4.48. 7e: White solid, yield 82.5%, mp 104–107 8C, TLC Rf = 0.34
(dichloromethane/methanol, 10:1); IR (KBr): 3391, 2936, 1731, 1656, 1536, 1459, 1378, 1343, 1247, 1171, 1111, 1072, 1051, 1013 cmꢁ1; 1H
NMR (600 MHz, CDCl3): d 5.08–5.06 (m, 1H), 4.98–4.96 (m, 1H), 4.74 (m, 1H), 4.54–4.51 (m, 2H), 4.31–4.28 (m, 2H), 4.10–4.09 (m, 1H),
3.99–3.97 (m, 2H), 3.79–3.74 (m, 1H), 3.69–3.64 (m, 2H), 3.33–3.31 (m, 2H), 3.26–3.17 (m, 6H), 3.05–2.97 (m, 3H), 2.92–2.88 (m, 2H), 2.60–
2.57 (m, 2H), 2.44–2.41 (m, 1H), 2.31–2.92 (m, 6H), 2.17–2.14 (m, 2H), 1.73–1.63 (m, 7H), 1.54–1.47 (m, 6H), 1.40–1.26 (m, 10H), 1.24–1.16
(m, 9H), 1.15–1.12 (m, 9H), 1.11–0.90 (t, 3H), 0.85 (t, 3H); MS (ESI) m/z calcd. for C50H91N3O15 973.7; found (M+H)+ 975.0; Anal. Calcd. for
C50H91N3O15 (974.3) (%): C 61.64, H 9.41, N 4.31, Found (%): C 61.60, H 9.44, N 4.29.