Novel 4-N-substituted aryl but-3-ene-1,2-dione derivatives of piperazinyloxazolidinones as antibacterial agents

Article abstract of DOI:10.1016/j.bmcl.2009.07.106

Novel (5S)-N-[3-(3-fluoro-4-{4-[2-oxo-4-(substituted aryl)-but-3-enoyl]-piperazin-1-yl}-phenyl)-2-oxo-oxazolidin-5-ylmethyl]-acetamide 3a-j analogues were synthesized and their in vitro antibacterial activity was evaluated. Most of the compounds of series showed superior in vitro activity against Gram-positive resistant strains than linezolid. Compound 3f is the most potent compound in the series with 0.04-0.39 μg/mL MIC.

Full text of DOI:10.1016/j.bmcl.2009.07.106

Bioorganic & Medicinal Chemistry Letters 19 (2009) 6810–6812
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Novel 4-N-substituted aryl but-3-ene-1,2-dione derivatives
of piperazinyloxazolidinones as antibacterial agents q
Vandana Varshney a, Nripendra N. Mishra b, Praveen K. Shukla b, Devi P. Sahu a,
*
a Medicinal and Process Chemistry Division, Central Drug Research Institute, Lucknow 226 001, India
b Fermentation Technology Division, Central Drug Research Institute, Lucknow 226 001, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel (5S)-N-[3-(3-fluoro-4-{4-[2-oxo-4-(substituted aryl)-but-3-enoyl]-piperazin-1-yl}-phenyl)-2-oxo-
oxazolidin-5-ylmethyl]-acetamide 3a–j analogues were synthesized and their in vitro antibacterial activity
was evaluated. Most of the compounds of series showed superior in vitro activity against Gram-positive
resistant strains than linezolid. Compound 3f is the most potent compound in the series with 0.04–
Received 11 February 2009
Revised 18 July 2009
Accepted 23 July 2009
Available online 26 July 2009
0.39 lg/mL MIC.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Oxazolidinone
Antibacterial
Eperazolid
2-Oxo-4-aryl-3-butenoic acid
Drug development in the area of the infectious diseases has
been ever challenging due to the continuous development of resis-
tance to the antibiotics few years after their introduction. The sit-
uation is getting particularly critical in hospital settings where
Gram-positive pathogens like Staphylococci are becoming resistant
to b-lactam,1 vancomycin2 and other antibiotics.
However, several research groups9 have attempted modification of
eperezolid to get superior analogs devoid of side effects.
Derivatives of 4-piperazinoaryl oxazolidinones have higher stabil-
ity and low toxicity hence several libraries containing this motif have
been synthesized and their antibacterial activities were evaluated in
the past.10 Lohray9 et al. have been attempted to synergize the anti-
bacterial activities by incorporating unsaturated carbonyl scaffold
on the piperazinyl aryl oxazolidinone derivatives 1 (Fig. 2). They also
have investigated the antimicrobial activity of aryl-pent-2-ene-1,4-
dione derivative 2 (Fig. 2). Similar glyoxamide analog11a of eperazolid
and alkylated derivatives11b of 4 have recently been reported. We
herein report the synthesis of N-[3-(3-fluoro-4-{4-[2-oxo-4-(substi-
tuted aryl)-but-3-enoyl]-piperazin-1-yl}-phenyl)-2-oxo-oxazolidin-
5-ylmethyl]-acetamide 3a–j (Fig. 2) and their in vitro antibacterial
activity against Gram-positive and Gram-negative resistant strains.
Key intermediate 4 was synthesized from 3,4-difluoro nitroben-
zene by the reported protocol12a (Scheme 1).
Oxazolidinones, a new class of antimicrobial agents were first
introduced by chemists3 at E. I. DuPont Nemours and Co. (DUP-
721, Fig. 1) and finds no congeners amongst the natural products.
Linezolid (ZyvoxÒ,4 Fig. 1), discovered by Pharmacia and Upjohn,
is the first member of oxazolidinone family approved by FDA in
2000 which shows anti-bacterial activity against a wide spectrum
of Gram-positive bacteria including multi drug resistant strains.5 It
was presumed that oxazolidinones were not prone to resistance
development due to their unique mode of action.6,7 However resis-
tance to all antimicrobial agents is predictable and hence resis-
tance to linezolid has also been observed in clinical isolates of
Staphylococcus aureus and Enterococcus sp.8 The frequency of emer-
gence of resistant strains against linezolid is increasing rapidly.
Thus there is urgent need to initiate program in development of
new member of this class to be ready, if resistance becomes more
of an issue.
Compounds 5a–j, the potassium salts of 2-oxo-4-aryl-but-3-
enoic acid were prepared by Knoevenagel reaction of pyruvic acid
O
O
O
O
O
O
N
N
N
NHCOCH3
Eperezolid(Fig. 1), anotherlead moleculeof oxazolidinonefamily
is not approved for treating bacterial infection due to its side effects.
NHCOCH3
F
F
DUP-721
LINEZOLID
O
O
O
N
N
N
HO
NHCOCH3
F
q
EPEREZOLID
CDRI Communication 7702.
* Corresponding author. Tel.: +91 522 2612415x4378; fax: +91 522 2623405.
E-mail addresses: dpsahuin@yahoo.com, dp_sahu@cdri.res.in (D.P. Sahu).
Figure 1.
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.07.106

V. Varshney et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6810–6812
6811
O
N
O
O
O
O
R1
N
N
F
R1
N
N
F
N
O
NHCOCH3
NHCOCH3
O
2
1
O
N
O
O
R1
N
N
F
NHCOCH3
O
3a-j
Figure 2.
Table 1
O
O
MIC values (lg/mL) for oxazolidinones 3a–j
F
NO2
H N
N
N
NHCOCH3
O
F
F
O
4
O
N
N
N
NHCOCH3
O
F
Scheme 1.
R1
3a-j
O
O
(i)
(ii)
O- K +
Compounds
R1
C log P
S.a.a
S.ab
S.a.c
0.78
B.c.d
0.39
E.f.e
S.p.f
0.39
R1
OH
R1
O
R1
O
O
5a-j
6a-j
3a
0.925
0.78
0.78
0.78
0.78
>50
0.39
0.78
Scheme 2. Reagents and conditions: (i) pyruvic acid, methanolic KOH, 0 °C; (iii) 5 %
aqueous HCl.
3b
3c
3d
3e
3f
1.086
1.638
1.141
2.824
1.420
1.808
0.101
0.571
0.571
0.78
0.78
1.56
>50
1.56
0.78
3.12
>50
0.39
0.39
0.39
>50
0.78
0.78
0.78
>50
0.39
0.39
0.78
>50
F
with different substituted aromatic aldehydes in presence of meth-
anolic KOH.12b Treatment of 5a–j with aqueous HCl afforded 2-
oxo-4-aryl-3-butenoic acid 6a–j (Scheme 2).
Compounds 6a–j were coupled with intermediate 5 using EDC
and HOBt in presence of triethylamine at 0 °C afforded novel oxa-
zolidinone analogues 3a–j in good yields (Scheme 3).
Cl
F
All compounds 3a–j were well characterized13 and were sub-
mitted for the assessment of in vitro antibacterial activity against
a panel of susceptible and resistant Gram-positive and Gram-neg-
ative bacteria. None of these compounds exhibited any activity
against Gram-negative bacteria such as Escherichia coli, Klebsiella
pneumoniae and Pseudomonas aeruginosa. The data for selected
Gram-positive organisms have been reported as minimum inhibi-
tory concentration (MIC) expressed in lg/mL (Table 1).
MICs were determined by agar dilution method using doubling
dilutions in cation adjusted Mueller Hinton agar over a concentra-
F
Cl
Cl Cl
0.19
0.78
0.39
0.39
0.78
0.19
0.78
1.56
0.78
0.78
0.39
1.56
3.12
1.56
1.56
0.19
1.56
0.78
0.39
0.78
0.04
0.19
0.78
0.78
0.78
0.09
0.19
0.78
0.39
0.39
tion range of 50–0.019 lg/mL and incubation in air at 35 °C for
3g
3h
3i
F3C
24 h. The bacterial strains were grown on nutrient agar at 37 °C.
After 24 h of incubation, bacterial cells were suspended in normal
saline containing Tween 20 at 0.05% at a concentration of approx-
imately 1.0–2.0 Â 107 cells/mL by matching with 0.5 McFarland
standards. The activity of compounds was determined as per
NCCLS protocol using Mueller Hinton broth (Becton Dickinson,
USA) in 96-well tissue culture plates. Proper growth control, drug
control and the negative control were adjusted on to the plates.
Compounds were dissolved in DMSO at a concentration of 1 mg/
O
S
mL and 20
ture plate having 180
tion was serially diluted resulting in twofold dilution of the test
compounds in subsequent wells. 100 L of Mc Farland matched
bacterial suspension was diluted in 10 ml of media and then
100 L of it was added in each well and kept for incubation. The
maximum concentration of compounds tested was 50 g/mL. The
l
L of this was added to each well of 96-well tissue cul-
l
L Mueller Hinton broth. From here the solu-
3j
S
l
Linezolid
Vancomycin
1.56
0.39
1.56
6.25
3.12
1.56
0.78
0.19
3.12
0.78
1.56
0.39
l
a
Staphylococcus aureus ATCC 25923 (floxacin and methicillin resistant).
Staphylococcus aureus ATCC 70069 (methicillin resistant).
Staphylococcus aureus ATCC 29213 (methicillin and vancomycin resistant).
Bacillus cereus MTCC 430.
Enterococcus faecalis MTCC 439.
Streptococcus pyogens.
l
b
c
d
e
f
O
O
(i)
O
O
O
H N
N
N
N
N
N
NHCOCH3
NHCOCH3
O
F
F
R1
micro-titer plates were incubated at 35 °C in a moist, dark chamber
and MICs were recorded spectrophotometrically after 24 h using
SOFTmaxPro 4.3 Software (Molecular Devices, Sunnyvale, USA).
4
3a-j
Scheme 3. Reagents and conditions :(i) compounds 6a–j, EDCÁHCl, HOBt, Et3N, 0 °C.

6812
V. Varshney et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6810–6812
Most of the compounds of this series exhibited a range of MIC
0.04–1.56 g/mL some of which are superior as compared to that
of linezolid against Gram-positive bacterial strains. The most po-
also acknowledge the SAIF division, CDRI for providing spectro-
scopic data and thankful to Dr. Brijesh K. Srivastava of Zydus Cadil-
a, Ahmedabad, India for the gift sample of linezolid.
l
tent compound of the series was 3f , displaying MIC range between
0.04 and 0.39
(0.78–3.12 g/mL) and vancomycin (0.19–6.25
pound 3f was found to have better activity against Enterococcus
faecalis (MIC value: 0.04 g /mL) than against Streptococcus pyoge-
nes (MIC value 0.09 g/mL).
l
g/mL which was lower than MIC value of linezolid
Supplementary data
l
lg/mL). The com-
l
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2009.07.106.
l
Compound 3a was found either equipotent or more potent than
compound 3b against all strains examined in this study. It is obvi-
ous from this data that electronegative substitution at para posi-
tion decreased activity against S. aureus (ATCC 70069 and ATCC
29213). This observation was confirmed by the similar trend ob-
served in the MIC values of compound 3f and 3g. Compound 3f
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15. C log P values were computed by using CS ChemDraw Ultra ver. 7.0 by
Cambridge Soft. Com, MA, USA.
Earlier several groups attempted14 to correlate biological activ-
ities with C log P. We also attempted for the same but failed to
establish any significant correlation. The C log P value15 of the com-
pounds in this series was in the range 0.10–2.824 showing variable
MIC values against strains evaluated. Instead of having same
C log P value at 0.571, the compounds 3i and 3j exhibited different
MIC values against bacterial strains screened. Thus no correlation
of computed C log P of the compounds with their respective MIC
values could be established. This clearly indicates that lipophilicity
of compounds is not critical factor responsible for their antibacte-
rial activity. Other factors like steric and electronic might be
responsible for the variation in antibacterial activity.
In conclusion, a novel series of oxazolidinone analogues were
synthesized exhibiting excellent in vitro activity against several
Gram–positive resistant strains. The best compound of the series
is 3f more potent than linezolid as well as vancomycin against
all bacterial strains evaluated. Further lead optimisation in the ser-
ies is in progress.
Acknowledgements
We are thankful to the Director, CDRI, Lucknow, India for con-
stant encouragement of the drug development programme. We