Design, synthesis and antibacterial activity of novel 1-oxacephem analogs

Article abstract of DOI:10.1016/j.cclet.2012.01.014

A series of 1-oxacephem analogs were synthesized and their antibacterial properties against five strains of Gram-positive and Gram-negative bacteria were evaluated in vitro while ceftazidine was selected as control. Some of the tested compounds, compound 12c in particular, showed more active against three selected strains than the standard.

Full text of DOI:10.1016/j.cclet.2012.01.014

Available online at www.sciencedirect.com
Chinese Chemical Letters 23 (2012) 407–410
www.elsevier.com/locate/cclet
Design, synthesis and antibacterial activity
of novel 1-oxacephem analogs
*
Yi He, Jian Bo Wu, Fan Lei, Pei Chen, Li Hai, Yong Wu
Key Laboratory of Drug Targeting and Drug Delivery System of the Education Ministry, Department of Medicinal Chemistry,
West China School of Pharmacy, Sichuan University, Chengdu 610041, China
Received 28 October 2011
Available online 3 March 2012
Abstract
A series of 1-oxacephem analogs were synthesized and their antibacterial properties against five strains of Gram-positive and
Gram-negative bacteria were evaluated in vitro while ceftazidine was selected as control. Some of the tested compounds, compound
12c in particular, showed more active against three selected strains than the standard.
# 2012 Yong Wu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: 1-Oxacephem; Synthesis; Antibacterial activity; Ceftazidine
1-Oxacephem is a special group among cephalosporin antibiotics family and a class of new compounds obtained by
substituting sulfur atom in the cephalosporin with oxygen according to principles of bioisostere. In the 1970s and
1980s, Narisada et al. published the synthesis of several l-oxacephalosporins. The antibacterial potency against
sensitive bacterial strains of l-oxa congeners, including l-oxacephalothin and l-oxacefamandole exhibited four to eight
more times than the corresponding cephalosporins [1,2]. Nagata et al. established a well sophisticated and industrially
feasible synthetic route to the nucleus of the 1-oxacephems and achieved in finding latamoxef and flomoxef [3–5]
(Fig. 1).
In recent years, a lot of new side chains of cephalosporin are developed and have made significant contribution in
promoting the antibacterial activity and spectrum of the cephalosporin, such as the use of the quaternary ammonium
group in the 3 position of the cephalosporin. This was demonstrated to be a good strategy to enhance its permeability to
the outer membrane of Gram-negative bacteria and results in improved antibacterial activity [6–9]. Oxacephem with
substituted thioacetamide at position 7 shows good antibacterial activity against Gram-positive and Gram-negative
bacteria, being especially highly active against clinical isolates of Staphylococcus aureus resistant to either ampicillin
or methicillin [4]. Cephalosporins with the similar group also displayed the similar efficacy [10]. Based on the
structure–activity relationships above, a series of new 1-oxacephems were designed, synthesized, and their
preliminary efficacy was also evaluated, expecting to get promoted antibacterial activity when the latest side chains of
cephalosporins were introduced to the nucleus of 1-oxacephems.
* Corresponding author.
E-mail address: wyong@scu.edu.cn (Y. Wu).
1001-8417/$ – see front matter # 2012 Yong Wu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2012.01.014

408
Y. He et al. / Chinese Chemical Letters 23 (2012) 407–410
Fig. 1. Structures of flomoxef, ceftazidine and the target compounds 12a–12i.
The synthetic route of the key intermediate 7 was illustrated in Scheme 1. The commercially available 6-APA 1 was
protected by p-methylbenzoyl group to get 2. Compounds 2–4 showed highly crystalline property, which benefits the
purification. Furthermore, we can prepare 4 starting from 1 in 3 steps with a higher yield [11]. The epimerization of 4
was achieved by treatment of trimethylchlorosilane and triethylamine in dichloromethane to afford 5 [12]. Thus,
epipenicillin sulfoxide 5 was treated with triphenylphosphine to give epioxazoline 6 [13]. Finally, the key intermediate
7 was obtained from 6 according to the known method in 8 steps [14].
With compound 7 in hand, we carried out to synthesize the 1-oxacephem derivatives. The acid 8a used for 7b side
chains was prepared in the reported method [4]. 8b and 8c were prepared by coupling of ethyl chloroacetate and
substituted thiophenol followed by hydrolysis with sodium hydroxide. Subsequent acylation of 7 with 8a–8c in the
presence of phosphorus oxychloride and pyridine to afford 9a–9c, followed by introduction of the heterocycles 10a–
10c to the allylic position using sodium iodide as a catalyst in acetone gave 10a–10i. Removal of the protective group
m-cresol furnished the target compounds 11a–11i. The chemical structures of target compounds were confirmed by 1H
NMR, MS spectra and elemental analyses (Scheme 2) [15].
All the new oxacephem derivatives were tested in vitro against several strains of Gram-positive and Gram-negative
bacteria, and the MIC values are shown in comparison with that of Ceftazidine in Table 1.
As shown in Table 1, some compounds displayed enhanced antibacterial potency over ceftazidine against different
strains. However, all compounds are less active than the standard against Escherichia coli and Pseudomonas
aeruginosa. The most promising compound 12c exhibited antibacterial activity against S. aureus, S. epidermidis and
Klebsiella pneumoniae strains with the MIC value of 4, 16, 16 mg/L, respectively.
The reported SARs of cephalosporins showed that the side chain at position 7 had great influence to the
antibacterial spectrum while the side chain at position 3 contributed less to its activity and only affected the
pharmacokinetics. In order to eliminate the influence of side chain at different position, orthogonal strategy was
adopted to synthesis of the target 1-oxacephems. Among 12a–12c which contain a difluoromethylthioacetamido
substituent at C-7, 12b was more active than 12a, but less than 12c. The result indicated that a substituent at pyridine
ring would increase its activity and a heterocycle was better than an alicycle. In the case of compounds having the same
O
S
H
H
H
H
H N
MBzHN
2
MBzHN
S
MBzHN
S
S
a
c
b
d
N
N
N
N
O
O
O
O
COOH
COOH
COOCHPh
COOCHPh
2
2
3
4
1
2
MPh
MBz
MBz
OCH
O
S
3
NH
N
O
NH
H N
O
2
H
O
j-m
H
e
f-i
N
Cl
COOCHPh
N
N
N
O
O
O
O
2
COOCHPh
COOCHPh
COOCHPh
2
2
2
6a
7
6
5
MBz = p-methylbenzoyl
MPh = p-methylphenyl
Scheme 1. Synthesis of 7. Reagents and conditions: (a) p-toluene sulfonyl chloride, NaHCO3, 0 8C. (b) benzhydrol, CH3SO2Cl, Py, À5 to 10 8C (c),
H2O2, Na2WO4, 0 8C, 80.4% yield over three steps. (d) Et3N, (CH3)3SiCl, 10 8C, 77%. (e) Ph3P, EA, 78 8C, 80.2%. (f) Cl2, EA, 20–25 8C, aqueous
NaHCO3. (g) NaI, THF, 25 8C. (h) Cu2O, DMSO, H2O, 55 8C. (i) BF3ÁEt2O, EA, 25 8C, 38.2% yield over four steps. (j) Cl2, Py, CH2Cl2. (k)
diethylamine, À20 8C. (l) t-BuOCl, CH3OLi, CH3OH, CH2Cl2, À45 8C. (m) PCl5, Py, CH3OH, CH2Cl2, À40 8C, 42.6 yield over four steps.

Y. He et al. / Chinese Chemical Letters 23 (2012) 407–410
409
OCH
OCH
3
H
N
3
H N
O
R
O
2
1
S
b
S
COOH
a
N
Cl
R
O
N
Cl
COOCHPh
+
1
O
O
8a R =difluoromethyl
1
COOCHPh
2
2
a =
10
N
8b R =2-chlorophenyl
1
7
9a-c
8c R =2,5-dichlorophenyl
1
H
N
OCH
3
OCH
H
3
b =
10
R
O
R
1
N
O
1
S
S
N
c
O
N
R
2
N
O
N
R
2
N
O
c =
O
10
COOCHPh
COOH
N
2
11a-i
12a-i
Scheme 2. Synthesis of compounds 12a–12i. Reagents and conditions: (a) POCl3, Py, CH3OH, CH2Cl2, À40–0 8C, 61–67.8%. (b) NaI, acetone,
CH2Cl2, 0 8C, 61–69%. (c) m-cresol, 40 8C, 81–88%.
Table 1
Structures and antibacterial activity to E. coli, S. aureus, P. aeruginosa, S. epidermidis, K. pneumoniae strains of target compounds.
Compd.
R1
R2
MIC (mg/L)
E. coli
32
S. aureus
P. aeruginosa
S. epidermidis
K. pneumoniae
12a
12b
32
>64
64
64
8
4
8
4
>64
32
16
32
16
12c
>64
12d
12e
64
32
128
64
>64
>64
>64
>64
>64
>64
12f
12g
12h
32
64
64
>128
>128
>64
>64
>64
>64
>64
>64
>64
>64
>64
128
12i
64
>128
>64
64
64
>64
Ceftazidine
<0.5
4
4
64
side chain at C-3, a difluoromethylthioacetamido substituent at C-7 had more advantages than the others. Compared
with 2-chlorophenylthioacetamido, additional substituent at phenyl may cause reduce of its activity.
As the preliminary result shown above, the activities of the target compounds did not seem as a simple combination
of each of the three moieties, C-7 side chain, 1-oxacephem nucleus and C-3 side chain. Nonetheless, this unexpected
result provides us new guidance for further study.
Acknowledgments
Financial support from the National Natural Sciences Foundation of China (No. 81072532) is gratefully
acknowledged.
References
[1] M. Narisada, H. Onoue, W. Nagata, Heterocycles 7 (1977) 839.

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Y. He et al. / Chinese Chemical Letters 23 (2012) 407–410
[2] M. Narisada, T. Yoshida, H. Onoue, et al. J. Med. Chem. 22 (1979) 757.
[3] H. Otsuka, W. Nagata, M. Yoshioka, et al. Med. Res. Rev. 1 (1981) 217.
[4] T. Tsuji, H. Satoh, M. Narisada, et al. J. Antibiot. 38 (1985) 446.
[5] W. Nagata, Pure Appl. Chem. 61 (1989) 325.
[6] H.A. Albrecht, G. Beskid, J.G. Christenson, et al. J. Med. Chem. 34 (1991) 669.
[7] R.F. Brown, M.D. Kinnick, J.M. Morin Jr., et al. J. Med. Chem. 33 (1990) 2114.
[8] M. Tsushima, Y. Kano, E. Umemura, et al. Bioorg. Med. Chem. 6 (1998) 1641.
[9] H. Ohki, K. Kawabata, Y. Inamoto, et al. Bioorg. Med. Chem. 5 (1997) 557.
[10] G.T. Kim, E.J. Ryu, Y.J. Jang, et al. J. Antibiot. 57 (2004) 468.
[11] Y. Yoshitsuru, T. Mamoru, Preparation of sulfoside. J.P. Patent 61-050986, August 15, 1986.
[12] L.C. Blaszczak, Process for penicillin epimerization, Indianapolis, IN, U.S. Patent 4320055, March 16, 1982.
[13] Y. Hamashima, S. Yamamoto, S. Uyeo, et al. Tetrahedron Lett. 20 (1979) 2595.
[14] M. Yoshioka, T. Tsuji, S. Uyeo, et al. Tetrahedron Lett. 21 (1980) 351.
[15] Physical and spectral data of some target compounds. All the target compounds are amorphous powder. 12a: 1H NMR (400 MHz, CDC13): d
3.40 (s, 3H), 3.55–3.69 (m, 2H), 4.43 (s, 1H), 5.17 (s, 1H), 5.42 (d, 1H, J = 14.4 Hz), 5.63 (d, 1H, J = 14.4 Hz), 7.31 (t, 1H, JHF = 56 Hz), 8.17
(t, 2H, J = 6.8 Hz), 8.63 (t, 1H, J = 7.6 Hz), 9.07 (t, 2H, J = 5.6 Hz), 9.33 (s, 1H); ESI-MS m/z: 558 (M+H)+; Anal. Calcd. for C17H18F2IN3O6S:
C, 36.64; H, 3.26; F, 6.82; I, 22.77; N, 7.54; S, 5.75. Found: C, 36.61; H, 3.29; F, 6.80; I, 22.75; N, 7.52; S, 5.71. 12b: 1H NMR (400 MHz,
CDC13): d 2.19–2.27 (m, 2H), 3.11–3.14 (m, 2H), 3.28–3.32 (m, 2H), 3.41 (s, 3H), 3.49–3.70 (m, 2H), 4.20–4.39 (m, 2H), 5.14 (s, 1H), 5.50 (s,
2H), 7.31 (t, 1H, JHF = 56 Hz), 7.89 (t, 1H, J = 6.8 Hz), 8.39 (d, 1H, J = 7.6 Hz), 8.76 (d, 1H, J = 6 Hz), 9.33 (s, 1H); ESI-MS m/z: 598 (M+H)+;
Anal. Calcd. for C20H22F2IN3O6S: C, 40.21; H, 3.71; F, 6.36; I, 21.24; N, 7.03; S, 5.37. Found: C, 40.18; H, 3.75; F, 6.35; I, 21.20; N, 7.01; S,
5.32. 12c: 1H NMR (400 MHz, CDC13): d 3.39 (s, 3H), 3.50–3.68 (m, 2H), 4.29–4.39 (m, 2H), 5.11 (s, 1H), 5.37 (d, 1H, J = 14.4 Hz), 5.61 (d,
1H, J = 14.4 Hz), 7.30 (t, 1H, JHF = 56 Hz), 8.00–8.03 (m, 1H), 8.49 (s, 1H), 8.83 (s, 1H), 8.92 (d, 1H, J = 9.6 Hz), 9.09 (d, 1H, J = 4.4 Hz),
9.32 (s, 1H); ESI-MS m/z: 598 (M+H)+; Anal. Calcd. for C18H18F2IN5O6S: C, 36.19; H, 3.04; F, 6.36; I, 21.25; N, 11.72; S, 5.37. Found: C,
36.15; H, 3.10; F, 6.34; I, 21.22; N, 11.68; S, 5.36. 12d: 1H NMR (400 MHz, CDC13): d 3.38 (s, 3H), 3.77–3.89 (m, 2H), 4.23–4.38 (m, 2H),
5.15 (s, 1H), 5.37 (d, 1H, J = 14.4 Hz), 5.73 (d, 1H, J = 14.4 Hz), 7.12–7.43 (m, 4H), 8.17 (t, 2H, J = 6.8 Hz), 8.63 (t, 1H, J = 7.6 Hz), 9.07 (t,
2H, J = 5.6 Hz), 9.33 (s, 1H); ESI-MS m/z: 618 (M+H)+; Anal. Calcd. for C22H21ClIN3O6S: C, 42.77; H, 3.43; Cl, 5.74; I, 20.54; N, 6.80; S,
5.19. Found: C, 42.73; H, 3.49; Cl, 5.71; I, 20.53; N, 6.76; S, 5.17. 12e: 1H NMR (400 MHz, CDC13): d 2.19–2.27 (m, 2H), 3.11–3.14 (m, 2H),
3.29–3.31 (m, 2H), 3.39 (s, 3H), 3.80–3.90 (m, 2H), 4.18–4.33 (m, 2H), 5.16 (s, 1H), 5.51 (s, 2H), 7.14–7.45 (m, 4H), 7.87 (t, 1H, J = 6.8 Hz),
8.40 (d, 1H, J = 7.6 Hz), 8.68 (d, 1H, J = 6 Hz), 9.44 (s, 1H); ESI-MS m/z: 658 (M+H)+; Anal. Calcd. for C25H25ClIN3O6S: C, 45.64; H, 3.83;
Cl, 5.39; I, 19.29; N, 6.39; S, 4.87. Found: C, 45.61; H, 3.87; Cl, 5.36; I, 19.27; N, 6.39; S, 4.88. 12f: 1H NMR (400 MHz, CDC13): d 3.33 (s,
3H), 3.81 (d, 1H, J = 15.6 Hz), 3.82 (d, 1H, J = 15.6 Hz), 3.98 (d, 1H, J = 16.8 Hz), 4.38 (m, 1H, J = 16.8 Hz), 4.94 (s, 1H), 5.17 (d, 1H,
J = 14.4 Hz), 5.75 (d, 1H, J = 14.4 Hz), 7.11–7.41 (m, 4H), 7.94–7.98 (m, 1H), 8.72 (s, 1H), 8.75 (s, 1H), 9.00 (d, 1H, J = 4.4 Hz), 9.19 (s, 1H),
9.41 (d, 1H, J = 9.6 Hz); ESI-MS m/z: 658 (M+H)+; Anal. Calcd. for C23H21ClIN5O6S: C, 41.99; H, 3.22; Cl, 5.39; I, 19.29; N, 10.65; S, 4.87;
Found: C, 41.92; H, 3.31; Cl, 5.36; I, 19.28; N, 10.67; S, 4.85. 12g: 1H NMR (400 MHz, CDC13): d 3.39 (s, 3H), 3.86–3.97 (m, 2H), 4.09(d, 1H,
J = 18.8 Hz), 4.34 (d, 1H, J = 18.8 Hz), 5.13 (1H, s), 5.23 (1d, H, J = 14.4 Hz), 5.73 (d, 1H, J = 14.4 Hz), 7.15–7.45 (m, 3H), 8.18 (t, 2H,
J = 6.8 Hz), 8.63 (t, 1H, J = 7.6 Hz), 9.07 (t, 2H, J = 5.6 Hz), 9.33 (s, 1H); ESI-MS m/z: 652 (M+H)+; Anal. Calcd. for C22H20Cl2IN3O6S: C,
40.51; H, 3.09; Cl, 10.87; I, 19.46; N, 6.44; S, 4.92. Found: C, 40.48; H, 3.12; Cl, 10.86; I, 19.45; N, 6.41; S, 4.88. 12h: 1H NMR (400 MHz,
CDC13): d 2.18–2.26 (m, 2H), 3.11–3.15 (m, 2H), 3.30 (m, 2H), 3.41 (s, 3H), 3.89–3.98 (m, 2H), 4.24 (s, 2H), 5.17 (s, 1H), 5.47–5.57 (m, 2H),
7.20–7.48 (m, 3H), 7.88 (t, 1H, J = 6.8 Hz), 8.41 (d, 1H, J = 7.6 Hz), 8.71 (d, 1H, J = 6 Hz), 9.44 (s, 1H); ESI-MS m/z: 692 (M+H)+; Anal.
Calcd. for C25H24Cl2IN3O6S: C, 43.37; H, 3.49; Cl, 10.24; I, 18.33; N, 6.07; S, 4.63. Found: C, 43.35; H, 3.52; Cl, 10.21; I, 18.32; N, 6.00; S,
4.58. 12i: 1H NMR (400 MHz, CDC13): d 3.38 (s, 3H), 3.81–3.95 (m, 2H), 4.15–4.38 (m, 2H), 5.12 (s, 1H), 5.35 (d, 1H, J = 14.4 Hz), 5.57 (d,
1H, J = 14.4 Hz), 7.15–7.45 (m, 3H), 8.01–8.04 (m, 1H), 8.53 (s, 1H), 8.84 (s, 1H), 9.00 (d, 1H, J = 9.6 Hz), 9.10 (d, 1H, J = 4.4 Hz), 9.41 (s,
1H); ESI-MS m/z: 692 (M+H)+; Anal. Calcd. for C23H20Cl2IN5O6S: C, 39.90; H, 2.91; Cl, 10.24; I, 18.33; N, 10.12; S, 4.63. Found: C, 39.87;
H, 2.95; Cl, 10.21; I, 18.32; N, 10.14; S, 4.60.