Novel piperidinyloxy oxazolidinone antimicrobial agents

Article abstract of DOI:10.1016/S0960-894X(01)00305-5

Oxazolidinone antibacterial agents, where the N-substituted piperazinyl group of eperezolid was replaced with a N-substituted piperidinyloxy moiety, were synthesized and shown to be active against a variety of resistant and susceptible Gram-positive organ

Full text of DOI:10.1016/S0960-894X(01)00305-5

Bioorganic & Medicinal Chemistry Letters 11 (2001) 1829–1832
Novel Piperidinyloxy Oxazolidinone Antimicrobial Agents
Michele A. Weidner-Wells,* Christine M. Boggs, Barbara D. Foleno, Ellyn Wira,
Karen Bush, Raul M. Goldschmidt and Dennis J. Hlasta
Drug Discovery, The R. W. Johnson Pharmaceutical Research Institute, 1000 Route 202, Raritan, NJ 08869, USA
Received 29 March 2001; accepted 26 April 2001
Abstract—Oxazolidinone antibacterial agents, where the N-substituted piperazinyl group of eperezolid was replaced with a N-sub-
stituted piperidinyloxy moiety, were synthesized and shown to be active against a variety of resistant and susceptible Gram-positive
organisms. The effect of ring size, positional isomerism, and fluorine substitution on antibacterial activity was examined. # 2001
Elsevier Science Ltd. All rights reserved.
The rising prevalence of multidrug resistant Gram-
positive bacteria requires the discovery of novel agents
active against these pathogens. Recent reports indicate
that in 1998, at least 21% of all nosocomial
enterococcal infections in US hospitals were due to
vancomycin-resistant enterococci (VRE).1 The oxazoli-
dinones, a new class of synthetic antibacterial agents,
are active against a variety of clinically important sus-
ceptible and resistant Gram-positive organisms such as
methicillin-resistant Staphylococcus aureus (MRSA),
VRE, and penicillin-resistant Streptococcus pneumoniae
(PRSP). Scientists fromPharmacia identified two clin-
ical candidates fromthis class, eperezolid ( 1) and line-
zolid (2).2 Linezolid (ZyvoxR) is currently marketed for
the treatment of multidrug resistant Gram-positive
infections such as nosocomial and community-acquired
pneumonia and skin infections.
Previous investigations of the SAR of eperezolid and
linezolid have demonstrated a high tolerance for sub-
stitution at the 4-position of the phenyl ring, while the
oxazolidinone ring as well as the S-configuration at C-5
of this ring are essential for activity.5 Several moieties
(such as a methyl carbamate and small heterocycles) can
replace the acetamide without a significant loss of
activity, however, the acetamide functionality is usually
optimal.5,6 Based on these considerations, we have
developed a novel series of oxazolidinone antibacterial
agents I in which the piperazinyl group of eperezolid is
replaced with a 4-piperidinyloxy moiety (m=n=2).7,8
In addition, the regioisomeric 3-piperidinyloxy analo-
gues were synthesized. The pyrrolidinyloxy and azetidi-
nyloxy analogues were prepared in order to investigate
the importance of ring size on antibacterial activity. The
role of the aromatic fluorine substituent was examined
in the 4-piperidinyloxy series. The in vitro antibacterial
activity of these compounds is reported in this paper.
The oxazolidinone class of antibacterial agents selectively
binds to the 23S RNA component of the 50S ribosomal
subunit, inhibiting protein synthesis at an early phase of
translation.3 Due to its unique mechanism of action, it is
believed that there will be a lack of cross-resistance with
other classes of protein synthesis inhibitors.4
The target 4-piperidinyloxy oxazolidinones 9 and 10
were synthesized as shown in Scheme 1. N-t-Butoxy-
carbonylpiperidin-4-ol (3), prepared from4-hydroxy-
piperidinol, was reacted with potassium t-butoxide and
3,4-difluoronitrobenzene to afford nitro compound 4.
*Corresponding author. Fax: +1-908-203-8109; e-mail: mwells@prius.
jnj.com
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(01)00305-5

1830
M. A. Weidner-Wells et al. / Bioorg. Med. Chem. Lett. 11 (2001) 1829–1832
Scheme 1. Synthesis of 4-piperidinyloxy oxazolidinones 9 and 10.
Reduction to the aniline followed by protection as the
Cbz derivative gave intermediate 5. The oxazolidinone
ring was formed by reaction of the anion of Cbz deri-
vative 5 with (R)-glycidyl butyrate to afford alcohol 6.
Functional group manipulation of alcohol 6 yielded
acetamide 7 in several steps in good overall yield. The
Boc moiety was readily removed by treatment with tri-
fluoroacetic acid in methylene chloride. The TFA salt of
amine 8 was acylated with a-benzyloxyacetyl chloride.
Removal of the benzyl protecting group from 9 under
hydrogen transfer conditions led to desired a-hydroxy-
acetamide 10.
ethylchloroformate.9 The resulting HCl salt of the
amine was functionalized as in Scheme 1.
Utilization of 4-fluoronitrobenzene in place of 3,4-
difluoronitrobenzene in the displacement reaction
followed by formation of the oxazolidinone ring
afforded the des-fluoro 4-piperidinyloxy analogues 21
and 22.
Oxazolidinones 9–14 and 19–22 were tested for in vitro
antibacterial activity against a panel of important
Gram-positive pathogens. The minimum inhibitory
concentration (MIC) for these compounds against a
representative methicillin-susceptible S. aureus strain is
reported in Table 1. Compounds were tested in broth as
well as in the presence of 50% mouse serum in order to
give an indication of serumprotein binding. At least a
4-fold increase in the MIC in the presence of serum
suggests that the compound binds to serum proteins or
is inactivated by components of the serum. As a result,
there may no longer be a sufficient concentration of free
drug in the serumto inhibit the growth of bacteria
effectively in vivo.
The 3-piperidinyloxy analogues 11 and 12 were pre-
pared in a similar manner starting with N-t-butoxy-
carbonylpiperidin-3-ol.
Pyrrolidinyloxy analogues 13 and 14 were prepared in a
similar fashion utilizing N-(a-benzyloxyacetyl)pyrrolidin-
3-ol in the nucleophilic aromatic substitution reaction
(Scheme 2). However, in this series, the azide intermediate
was reduced to the amine with 1,3-propanedithiol and
triethylamine. The target compounds were submitted
for biological testing as a mixture of diastereomers.
Within the series of a-benzyloxyacetamides, the 4-sub-
stituted piperidinyloxy derivative 9 was the most potent
and was only 2-fold less potent than linezolid. The
regioisomeric 3-piperidinyloxy derivative 11 was less
potent than 9. In addition, contraction of the six-mem-
bered ring to a five-membered ring resulted in a decrease
Azetidinyloxy analogues 19 and 20 were synthesized
from commercially available N-(diphenylmethyl)-azeti-
din-3-ol. Removal of the benzhydryl protecting group
was accomplished on the fully elaborated oxazolidinone
acetamide utilizing standard conditions with a-chloro-

M. A. Weidner-Wells et al. / Bioorg. Med. Chem. Lett. 11 (2001) 1829–1832
1831
Scheme 2. Synthesis of the pyrrolidinyloxy oxazolidinones 13 and 14.
Table 1. MIC (mg/mL) for oxazolidinones 9–14 and 19–22a
In agreement with the literature SAR for the oxazolidi-
nones, removal of the fluorine atom from the phenyl
ring decreases in vitro potency several fold compared to
the fluoro analogues.2 The des-fluoro compounds 21 and
22 were 4-fold less potent than the parent compounds 9
and 10. Linezolid was more potent than compounds 9–
14 and 19–22 by at least 2-fold against this S. aureus
strain.
S. aureus OC 4172
Several of the a-benzyloxyacetamides bound to or were
inactivated by serumproteins, since these compounds
tended to exhibit an increase in the MIC in the presence
of mouse serum, whereas only one of the a-hydroxy-
acetamides did. This is most likely due to the increased
lipophilicity of the a-benzyloxyacetamides relative to
the a-hydroxyacetamides.
Compd
R
m
n
X
Without serumWith serum
9
11
13
19
21
10
12
14
PhCH2
PhCH2
PhCH2
PhCH2
PhCH2
H
2
1
1
1
2
2
1
1
2
3
2
1
2
2
3
2
F
F
F
F
H
F
4
32
16
8
16
4
16
32
16
16
64
4
H
H
F
F
8
8
4
4
This series of oxazolidinone antimicrobial agents was
active against a variety of susceptible as well as resistant
Gram-positive organisms (Table 2). In contrast to line-
zolid, none of these compounds exhibited significant
activity against Gram-negative organisms such as
Escherichia coli. As is evident fromthe data in Table 2,
none of the oxazolidinones 9–14 nor 19–22 was active
against either an E. coli wild type strain (OC 2605) or
against a mutant strain (OC 2530) that is hypersensitive
to antimicrobial agents due to a defective outer mem-
brane. Lack of Gram-negative activity may be attrib-
uted to several factors. Either the compounds did not
penetrate the outer membrane of the bacteria or the
compounds entered the organism but were actively
effluxed as described for linezolid.10 Alternatively, the
compounds may have entered the organism, but were
not active at the biological target.
20
22
Linezolid
H
H
—
1
2
—
1
2
—
F
H
—
8
16
2
8
32
2
aThe variance in the determination of MIC values is 2-fold such that
an MIC difference of at least 4-fold is significant.
in activity (13 vs 9). Interestingly, further contraction of
the ring leading to the azetidinyloxy derivative 19
restores some of the in vitro activity. This may be due to
the altered disposition of the nitrogen substituent in the
symmetrical four- and six-membered ring systems (9
and 19) versus the unsymmetical five- and six-membered
ring systems (11 and 13).
However, this trend was not observed in the a-hyd-
roxyacetamide series. Except for the des-fluoro analo-
gue 22, the compounds were either equipotent or were
2-fold less potent than 9 in vitro.
In conclusion, we have discovered a novel series of
oxazolidinone antibacterial agents. These compounds
are active against a variety of susceptible, as well as

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M. A. Weidner-Wells et al. / Bioorg. Med. Chem. Lett. 11 (2001) 1829–1832
Table 2. Spectrumof activity against susceptible and resistant Gram-
positive and Gram-negative organisms (MIC (mg/mL))
for his suggestions and critical reading of the manu-
script.
Compd S. aureus MRSA E. faecalis E. faecium E. coli E. coli
OC 4172 OC2878 ATTC
29212
OC 3312 OC 2605 OC 2530
(VRE)
References and Notes
(HS)
9
11
13
19
21
10
12
14
4
32
16
8
16
4
8
4
8
16
2
2
32
16
8
8
4
8
8
8
16
2
4
64
16
16
16
8
16
16
16
32
2
4
64
16
16
16
8
16
16
16
32
2
>128
>128
>128
>128
128
128
>128
128
>32
>64
128
64
128
128
128
128
>128
>128
8
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20
22
Linezolid
>128
>128
32
E. faecalis: Enterococcus faecalis; E. faecium: Enterococcus faecium.
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resistant, Gram-positive organisms. Modifications to
improve the potency of this series by diversification of
the piperidinyl nitrogen are currently being explored.
These results will be reported in the future.
Minimum Inhibitory Concentration (MIC)
Determinations
10. Buysse, J. M.; Demyan, W. F.; Dunyak, D. S.; Stapert,
D.; Hamel, J. C.; Ford, C. W. 36th Interscience Conference on
Antimicrobial Agents and Chemotherapy (ICAAC), New
Orleans, LA, 1996; C-42.
Antibacterial susceptibility testing was performed fol-
lowing the broth microdilution method of the National
Committee for Clinical Laboratory Standards.11
11. National Committee for Clinical Laboratory Standards,
1997. Methods for Dilution Antimicrobial Susceptibility Tests
for Bacteria that Grow Aerobically, 4th ed. Approved stan-
dard. NCCLS Document M7-A4. National Committee for
Clinical Laboratory Standards: Villanova, PA.
Acknowledgements
The authors wish to thank Dr. Mark J. Macielag