Syntheses and studies of quinolone-cephalosporins as potential anti-tuberculosis agents

Article abstract of DOI:10.1016/j.bmcl.2006.08.045

The syntheses and anti-tuberculosis activity of quinolone-cephalosporin conjugates (1 and 2) are described. Both showed broad-spectrum antibacterial activity and significant anti-TB activity. The carbamate-linked quinolone-cephem 2 showed better antimycobacterial activity, including anti-TB activity, than the direct amine-linked quinolone-cephem 1, while quinolone-cephem 1 was slightly more effective against some Gram-negative bacterial strains.

Full text of DOI:10.1016/j.bmcl.2006.08.045

Bioorganic & Medicinal Chemistry Letters 16 (2006) 5534–5537
Syntheses and studies of quinolone-cephalosporins as potential
anti-tuberculosis agents
Gaiying Zhao,a Marvin J. Miller,a,* Scott Franzblau,b Baojie Wanb and Ute Mo¨llmannc
aDepartment of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA
bInstitute for Tuberculosis Research, College of Pharmacy, M/C 964, Rm 412, University of Illinois at Chicago,
833 S. Wood St., Chicago, IL 60612-7231, USA
cLeibniz Institute for Natural Product Research and Infection Biology, Hans-Kno¨ll-Institute,
Beutenbergstrasse 11a, D-07745 Jena, Germany
Received 21 June 2006; revised 6 August 2006; accepted 8 August 2006
Available online 30 August 2006
Abstract—The syntheses and anti-tuberculosis activity of quinolone-cephalosporin conjugates (1 and 2) are described. Both showed
broad-spectrum antibacterial activity and significant anti-TB activity. The carbamate-linked quinolone-cephem 2 showed better
antimycobacterial activity, including anti-TB activity, than the direct amine-linked quinolone-cephem 1, while quinolone-cephem
1 was slightly more effective against some Gram-negative bacterial strains.
Ó 2006 Elsevier Ltd. All rights reserved.
Tuberculosis (TB) is one of the leading causes of death
and suffering worldwide. The increasing microbial resis-
tance, toxicity, and side effects of currently used anti-tu-
berculosis drugs also emphasize the urgent need for new,
safer, and more effective anti-tuberculosis agents.1–5
Quinolonyl-b-lactams are a class of multifunctional b-
lactams and some examples showed high potency and
broad antibacterial activity against a range of clinically
significant bacterial pathogens, especially against newly
emerging strains of quinolone- and b-lactam-resistant
bacteria, for example, methicillin-resistant ciprofloxa-
cin-resistant (MRCR) Staphylococcus aureus, penicil-
The synthesis of the direct amine-linked quinolone-
cephalosporin 1 is shown in Scheme 1. 3-Chlorometh-
yl-7-phenylacetylamino cephalosporanic acid p-meth-
oxybenzyl ester (GCLE) was converted to 3-iodo-
methyl cephalosporin 3 in 92% yield according to the
literature procedure.8 The key intermediate 4 was
obtained in 30% yield by coupling compound 3 with
ciprofloxacin that had been pretreated with N-methyl-
N-(trimethylsilyl) trifluoro acetamide (MSTFA).9 Subse-
quent deprotection with TFA in the presence of anisole
provided the desired product 1 in 70% yield.
lin-resistant
Streptococcus
pneumoniae,
and
The synthesis of carbamate-linked quinolone-cephalo-
sporin compound 2 is shown in Scheme 2. This synthesis
began with a controlled hydrolysis to remove the acetyl
group of commercially available 7-amino cephalospor-
anic acid (7-ACA). Reaction with phenylacetyl chloride
vancomycin-resistant Enterococcus faecium.6
However, no anti-TB activity data of quinolonyl-b-lac-
tams were reported. Based on our previous work on
the synthesis of a carbacephalosporin-quinolone con-
jugate,7 we describe here the syntheses and anti-TB
activity of direct amine-linked quinolonyl-cephem 1
O
and carbamate-linked quinolonyl-cephem
Fig. 1).
2
(see
F
COOH
H
N
R
S
N
N
O
N
N
X
O
Keywords: Anti-tuberculosis; Antibacterial agents; Quinolonyl-b-
lactams.
CO2H
1. X = CH2 2. X = CH2OCO
*
Corresponding author. Tel.: +1 574 631 7571; e-mail: mmiller1@
nd.edu
Figure 1. QLAs: quinolone-cephalosporin conjugates.
0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.08.045

G. Zhao et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5534–5537
5535
O
N
F
COOH
O
O
Ph
Ph
N
HN
O
HN
S
S
, MSTFA
30%
HN
NaI, acetone
N
Cl
CO2PMB
GCLE
N
I
92%
O
DMF/Dioxane (1/1)
CO2PMB
3
O
N
O
O
F
COOH
O
Ph
F
N
COOH
Ph
HN
S
HN
O
S
N
TFA / Anisole
70%
N
N
N
N
N
O
CO2PMB
CO2H
4
1
Scheme 1. Procedure for synthesis of amine-linked quinolone-cephalosporin conjugate.
H
H2N
O
1. 10M NaOH, MeOH, -20oC
2. BSA, PhCH2COCl, DMAC
N
S
S
Ph
ClCOOCHClCCl3
O
N
OAc
N
OH
CO2CHPh2
Py, CH2Cl2
81%
O
3. Diphenyldiazomethane
44% over three steps
CO2H
7-ACA
5
O
F
COOH
H
H
N
N
S
Cipro/MSTFA
S
Ph
N
N
Ph
O
N
O
N
O
80%
N
O
OCHClCCl3
O
O
COOR
O
CO2CHPh2O
7. R=benzhydryl
2. R=H
6
TFA, anisole
64%
Scheme 2. Procedure for synthesis of carbamate-linked quinolone-cephalosporin conjugate.
followed by treatment with diphenyldiazomethane pro-
vided 5 in 44% yield for three steps.10 Subsequent cou-
pling with tetrachloroethyl chloroformate gave
intermediate carbonate 6 in 81% yield. Direct reaction
with ciprofloxacin under basic aqueous conditions fol-
lowed by deprotection gave the desired product, 2, in
51% yield for two steps.11
toward M. luteus. For the Gram-negative bacteria and
for the enterococcus strain used here, ciprofloxacin
alone was still more active than the corresponding b-lac-
tam conjugates 1, 4, and 7. As noted, the hydrophobic
protecting group of 7 increased activity against staphy-
lococci and enterococci relative to compounds 1, 2,
and 4 that are more hydrophobic. Generally, com-
pounds 1 and 2 with hydrophilic properties (or without
hydrophobic protecting groups) were found to be more
active than conjugate 4 with a hydrophobic (PMB)
protecting group. Activity of all compounds against
Pseudomonas aeruginosa did not depend on outer mem-
brane permeability since essentially the same MIC val-
ues were obtained for the wild-type strain and for the
mutant strain with an impaired outer membrane barrier.
Activity of all compounds (except for the inactive pre-
cursor b-lactams 3 and 5) against E. coli was increased
for the permeability mutant DC2 in contrast to the
wild-type strain DC0.
Quinolone-cephalosporin compounds 1, 2, 4, 7, as well
as GCLE, ciprofloxacin, mixtures, and precursors 3
and 5, were tested for their antibacterial activities
against various strains of Gram-positive and Gram-neg-
ative bacteria, several strains of mycobacteria, as well as
against Mycobacterium tuberculosis (Table 1).12–17 Com-
pound 2 was found to be comparable to or by 1 to 2
dilution steps more active than compound 1 for all fast
growing mycobacteria, and also for M. tuberculosis
H37Rv. Interestingly, the very hydrophobic benzhydryl
ester, compound 7, was the most active compound
against enterobacteria (Escherichia coli and Enterobacter
cloacae), against staphylococci and enterococci as well
as fast growing mycobacteria. On the other hand, 7
and ciprofloxacin were less effective against Micrococcus
luteus, while conjugates 1, 2, and 4 were highly active
Compounds 1, 2, and 7 also showed good anti-TB activ-
ity, but starting GCLE, 4, and conjugate precursors 3
and 5 displayed weak to no activity. Carbamate-based
conjugate 2 was active against M. tuberculosis H37Rv

5536
G. Zhao et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5534–5537
Table 1. Antibacterial activity of quinolone-cephalosporin compounds
Species/strains
MIC (lM)
1
4
2
7
Ciproa/GCLE
tested separately
3
5
GCLE +
Cipro
Escherichia coli DC0 wild type
Escherichia coli DC2 permeability mutant
Enterobacter cloacae P99
3.12
0.8
25
3.12
0.8
1.56
0.2
0.4/200
<0.1/NTe
<0.1/NT
25/50
200
200
100
100
100
>200
200
200
25
3.12
NT
NT
50
6.25
0.4
0.1
0.4
0.2
0.2
<0.1
12.5
1.56
Micrococcus luteus ATCC 10240
Pseudomonas aeruginosa
3.12
12.5
1.56
3.12
0.8/100
100
3.12
KW 799/WT wild type
Pseudomonas aeruginosa
1.56
12.5
3.12
1.56
0.4/50
100
100
100
1.56
KW 799/61 permeability mutant
Mycobacterium vaccae IMET 10670
Mycobacterium smegmatis SG987
Mycobacterium aurum SB66
Mycobacterium aurum DSM 43436
Mycobacterium fortuitum B
Staphylococcus aureus SG 511
Staphylococcus aureus 134/93 MRSA
Enterococcus faecalis 1528 VRE
Mycobacterium tuberculosis
H37Rv MABAb/GASc
3.12
3.12
0.4
3.12
12.5
0.8
1.56
3.12
0.2
1.56
1.56
0.2
0.8/100
0.8/NT
0.1/NT
0.1/NT
0.2/100
0.8/1.56
50/NT
200
200
50
6.25
NT
NT
NT
1.56
1.56
NT
NT
1.8
>200
100
50
0.4
1.56
12.5
1.56
>200
50
0.2
0.8
0.2
0.8
25
200
3.12
1.56
200
12.5
3.8
200
0.4
0.2
6.25
3.12
200
6.25
1.6
100
3.12
8.0
>200
200
>128
>200
200
>128
1.56/NT
1.8/31.5
62.3
Vero cells IC50 (lM)d
>128
13.1
>128
>128
NT/NT
NT
NT
NT
a Ciprofloxacin from BioChemika.
b MABA, microplate alamar blue assay.15
c GAS, glycerol-alanine-salts.16
d Concentration resulting in 50% inhibition of the growth of VERO cells.17
e NT, not tested.
with an MIC of 1.6 lM. Interestingly, its benzhydryl
ester 7 also was active with an MIC of 8.0 lM. The
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Supplementary data
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NCCLS Document M7-A5, 5th ed.; National Commit-
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.bmcl.2006.08.045.

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