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C. Hubschwerlen et al. / Bioorg. Med. Chem. Lett. 13 (2003) 4229–4233
In the absence of structural information on the com-
plexes of quinolones with DNA gyrase and oxazolidi-
nones with the bacterial ribosome it is difficult to
rationalise these results at the molecular level. However,
some observations can be made. The general shape of
the molecule, though very important (e.g., 3g), is not the
only determinant factor for the mode of action since
compounds 3b and 3d behave very differently. The weak
oxazolidinone activity in 3b can be best explained by the
presence of a free NH in the spacer that abolishes the
antibacterial activity [all the intermediates in the synth-
esis containingthe oxazolidinone linked to the spacers
were devoid of antibacterial activity (data not shown)].
Although quinolones bearing some of the spacers
described above as substituents at position 7 are known
to be active, oxazolidinones beingsubstituted at posi-
tion 4 of the fluorophenyl ringthrough an oxygen atom
are weaker than LZD.22 This might suggest an addi-
tional contribution of the quinolone in the bindingto
the ribosome. In addition to the target enzymes other
factors such as bacterial penetration and efflux systems
may play an important role in definingthe SAR, espe-
cially for Gram-negative bacteria such as E. coli.
Although some oxazolidinone-quinolone hybrids were
reasonably active against wild type E. coli, they were
much more active against an outer membrane perme-
able mutant. This indicates a restricted penetration and/or
an active efflux as is observed for LZD.
2. Tsiodras, S.; Gold, H. S.; Sakoulas, G.; Eliopoulos, G. M.;
Wennersten, C.; Venkataraman, L.; Moellering, R. C. Lancet
2001, 358, 207.
3. Bassetti, M.; Farrel, P. A.; Allan, D. A.; Dembry, L. M.;
Opal, J. E. Abstracts of Papers, 41st Interscience Conference
on Antimicrobial Agents and Chemotherapy, Chicago, IL,
USA, Sept. 22–25, 2001; American Society for Microbiology:
Washington, DC, 2001; Poster K-1193.
4. Hubschwerlen, C.; Specklin, J.-L.; Sigwalt, C.; Schroeder,
S.; Locher, H. Bioorg. Med. Chem. 2003, 11, 2310.
5. Brickner, S. J.; Hutchinson, D. K.; Barbachyn, M. R.;
Manninen, P. R.; Ulanowicz, D. A.; Garmon, S. A.; Grega,
K. C.; Hendges, S. K.; Toops, D. S.; Ford, C. W.; Zurenko,
G. E. J. Med. Chem. 1996, 39, 673.
6. Preparation of (S)-3-amino-1-pyrrolidinecarboxylic acid
phenylmethyl ester and (S and R)-3-hydroxy-1-pyrrolidine-
carboxylic acid phenylmethyl ester Sanchez, Joseph P.;
Domagala, J. M.; Heifetz, C. L.; Priebe, S. R.; Sesnie, J. A.;
Trehan, A. K. J. Med. Chem. 1992, 35, 1764.
7. Preparation of 3-hydroxy-1-azetidinecarboxylic acid phe-
nylmethyl ester: Rosenberg, S. H.; Spina, K. P.; Condon, S. L.;
Polakowski, J.; Yao, Z. J. Med. Chem. 1993, 36, 460.
8. Preparation of 4-hydroxy-1-piperidinecarboxylic acid phe-
nylmethyl ester: Cooper, C. S.; Klock, P. L.; Chu, D. T. W.;
Hardy, D. J.; Swanson, R. N.; Plattner, J. J. J. Med. Chem.
1992, 35, 8 1393.
9. Preparation of 3-hydroxy-1-piperidinecarboxylic acid phe-
nylmethyl ester: Apostolopoulos, C. D.; Haroutounian, S. A.
J. Heterocycl. Chem. 1995, 32, 1843.
10. Preparation of 4-hydroxymethyl-1-piperidinecarboxylic
acid phenylmethyl ester: Yoneda, Y.; Kawajiri, S.; Sugimura,
M.; Osanai, K.; Kito, F.; Ota, E.; Mimura, T. Bioorg. Med.
Chem. Lett. 2001, 11, 2663.
In summary, a new class of oxazolidinone-quinolone
hybrids with potent antibacterial activity has been
identified. The antibacterial spectrum and mode of
action is highly dependent on the nature of the spacer.
Overall the most active derivative was 3k (and its pure
diastereoisomers 3l and 3m) which contains a 3-
hydroxyzmethyl-pyrrolidinyl spacer. These compounds
were approximately 4-fold more active than CIP, and 8-
to 16-fold more active than LZD against Gram-positive
bacteria. Furthermore, due to the balanced dual mode
of action the best representatives overcome all types of
resistance in clinically important Gram-positive patho-
gens, including resistance to quinolones and LZD. In
addition, compared to LZD, the antibacterial spectrum
is extended to Gram-negatives. Hence, this new series,
which also exhibits a strongbactericidal effect and a low
propensity to resistance development (data not shown),
has the potential for a promisingalternative treatment
of severe nosocomial Gram-positive infections.
11. Preparation of 4-hydroxyethyl-1-piperidinecarboxylic acid
phenylmethyl ester: Mazzini, C.; Lebreton, J.; Alphand, V.;
Furstoss, R. J. Org. Chem. 1997, 62, 5215.
12. Preparation of 4-hydroxypropyl-1-piperidinecarboxylic
acid phenylmethyl ester: Grumel, V.; Merour, J.-Y.; Lesur, B.;
Giboulot, T.; Frydman, A.; Guillaumet, G. Eur. J. Med.
Chem. Chim. Ther. 2002, 37, 45.
13. 4-Hydroxy-1-azepinecarboxylic acid phenylmethyl ester
was prepared from 4-perhydroazepinone by treatment with
benzylchloroformate and subsequent NaBH4 reduction
Roglans, A.; Marquet, J.; Moreno-Manas, M. Synth. Com
1992, 22, 1249.
14. Minimal inhibitory concentrations (MICs) were deter-
mined in cation-adjusted Mueller–Hinton Broth (BBL) by a
microdilution method followingNCCLS guidelines. 15 The pH
of the test medium was 7.2–7.3. The bacterial strains used were
from the Morphochem collection. Clinical isolates were ori-
ginally obtained from the Kantonspital Basel, Switzerland,
and from other European and US hospitals.
15. National Committee for Clinical Laboratory Standards.
Methods for Dilution Antimicrobial Susceptibility Tests for
Bacteria that Grow Aerobically, 4th ed.; Approved standard:
NCCLS Document M7-A4; National Committee for Clinical
Laboratory Standards: Villanova, PA, USA, 1997.
Acknowledgements
16. Zorzopoulos, J.; de Long, S.; Chapman, V.; Kozloff, L. M.
FEMS Microbiol. Lett. 1989, 52, 23.
Inhibition studies on DNA gyrase and topoisomerase
IV were kindly performed by A. Maxwell and A.
Howells, John Innes Enterprises, Ltd, Norwich, UK.
17. Inhibition of cell free protein synthesis was determined
with a coupled transcription/translation assay (E. coli S30
Extract System, Promega, Madison, WI, USA) using the
plasmid pBestLuc as DNA template.18 After pre-incubation
for 10 min, the reactions were initiated by adding0. 1 mgof
plasmid DNA and incubated at 37 ꢁC for 35 min. Then, the
reaction was stopped by coolingin ice, 15 mL was added to 15
mL luciferase substrate (Bright Glo, Promega, Madison, WI,
USA), and luminescence was quantified in a Tecan Spectra-
fluor Plus plate reader.
References and Notes
1. Fridkin, S. K.; Hill, H. A.; Volkova, N. V.; Edwards, J. R.;
Lawton, R. M.; Gaynes, R. P.; McGowan, J. E., Jr. Emerg.
Infect. Dis. 2002, 8, 697.