Synthesis and antibacterial activity of isothiazolyl oxazolidinones and analogous 3(2H)-isothiazolones

Article abstract of DOI:10.1016/j.ejmech.2009.09.019

The synthesis and antibacterial activity of several new 5-((3-oxoisothiazol-2(3H)-yl)methyl)-3-phenyloxazolidin-2-ones 8 and analogous 2-(4-substituted phenyl)-3(2H)-isothiazolones 3 and 4 substituted at 4 and/or 3-positions of the phenyl moiety with different groups of which some have shown to increase the antibacterial activity of both 3-aryl-2-oxazolidinones and 3(2H)-isothiazolones is described. The most active compounds were isothiazolyl oxazolidinones 8a,j with unsubstituted and 8b with 4-F substituted phenyl rings which showed activities higher than analogous 3(2H)-isothiazolones and comparable or superior to linezolid, vancomycin, and ciprofloxacin against some tested microorganisms. The change in position of F and/or the use of larger substituents gave compounds with reduced or no activity. Evaluation of cytotoxicity to mouse fibroblast (NIH/3T3) cells indicated that these compounds exhibit antibacterial activity at non-cytotoxic concentrations.

Full text of DOI:10.1016/j.ejmech.2009.09.019

European Journal of Medicinal Chemistry 45 (2010) 19–24
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and antibacterial activity of isothiazolyl oxazolidinones
and analogous 3(2H)-isothiazolones
,
,
c
Neda Adibpour a 1, Ali Khalaj b , Saeed Rajabalian
*
a Department of Medicinal Chemistry, School of Pharmacy, Ahwaz Jundishapur University of Medical Sciences, Ahwaz, Iran
b Department of Medicinal Chemistry, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran
c Kerman Neuroscience Research Center, Kerman University of Medical Sciences, Kerman, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and antibacterial activity of several new 5-((3-oxoisothiazol-2(3H)-yl)methyl)-3-phenyl-
oxazolidin-2-ones 8 and analogous 2-(4-substituted phenyl)-3(2H)-isothiazolones 3 and 4 substituted at
4 and/or 3-positions of the phenyl moiety with different groups of which some have shown to increase
the antibacterial activity of both 3-aryl-2-oxazolidinones and 3(2H)-isothiazolones is described. The
most active compounds were isothiazolyl oxazolidinones 8a,j with unsubstituted and 8b with 4-F
substituted phenyl rings which showed activities higher than analogous 3(2H)-isothiazolones and
comparable or superior to linezolid, vancomycin, and ciprofloxacin against some tested microorganisms.
The change in position of F and/or the use of larger substituents gave compounds with reduced or no
activity. Evaluation of cytotoxicity to mouse fibroblast (NIH/3T3) cells indicated that these compounds
exhibit antibacterial activity at non-cytotoxic concentrations.
Received 7 January 2009
Received in revised form
25 July 2009
Accepted 10 September 2009
Available online 16 September 2009
Keywords:
2-Oxazolidinone
3(2H)-isothiazolone
Antibacterial activity
Ó 2009 Elsevier Masson SAS. All rights reserved.
1. Introduction
antibacterial activity and a good safety profile and their effects are
enhanced by one or two fluorine atoms flanking these substituents
In recent years 3-aryl-2-oxazolidinones have been subject of
many investigations since they are a class of totally synthetic
antimicrobial agents with a novel mechanism of action involving
inhibition of bacterial protein synthesis at a very early stage and are
active against Gram-positive bacteria resistant to methicillin (MRS)
and vancomycin (VRS) [1]. Originally these compounds were
developed from an extensive SAR studies on 5-(hydroxymethyl)-3-
aryl-2-oxazolidinone, S-6123 [2] which had weak in vitro activity
against certain human pathogens. Results showed that aceta-
midomethyl group is the best substituent for the 5-position of the
3-aryl-2-oxazolidinones, and the presence of strongly electron
withdrawing groups at the 4-position of the 3-aryl moiety, enhance
the antibacterial activity [3]. These findings resulted in introduction
of Dup 721 and Dup 105 [3] into phase 1 of the clinical studies
which were discontinued from further developments due to their
toxicity profiles [4]. Subsequent investigations showed that a suit-
able electron donating amino substitution like piperazine or mor-
pholine at the 4-position of the 3-aryl moiety can confer excellent
[4]. Linezolid and eperozolid [4] were emerged from the results of
these investigations of which latter was not advanced to phase 3
clinical trial due to its shorter half life [5]. Linezolid as the first drug
of this class of compounds has been approved for the treatment of
skin soft tissue infections and bacterimia [1]. Further structural
modifications mainly through replacement of 5-acetamido group
with heterocyclic rings has led to the development of PH-027 [6],
YX-10 [7], and AZD2563[8] which compared to linezolid have
shown similar or more activity against Gram-positive microor-
ganisms susceptible to this drug. Of these compounds PH-027 [6]
has also shown activity against Gram-positive strains resistant to
linezolid (Scheme 1).
On the basis of these reports and known antimicrobial activities
of 3(2H)-isothiazolones [9] it seemed that replacement of 5-
acetamidomethyl group of 3-aryl-2-oxazolidinones with 3(2H)-
isothiazolones enhance the antibacterial activities of both classes of
compounds. This paper describes the synthesis of 5-((3-oxoiso-
thiazol-2(3H)-yl)methyl)-3-phenyloxazolidin-2-ones 8 substituted
at the 4 and/or 3-positions of the phenyl moiety with groups of
which some have shown to potentiate antimicrobial activity of
3(2H)-isothiazolones [10,11] and 3-aryl-2-oxazolidinones [3,4] and
comparison of their antibacterial activities with analogous 3(2H)-
isothiazolones 3a-k, 4a,b,d-k (Scheme 2), and vancomycin, line-
zolid and ciprofloxacin as reference drugs.
* Corresponding author. Tel.: þ98 21 88962007; fax: þ98 21 66461178.
E-mail addresses: n.adibpour@ajums.ac.ir (N. Adibpour), khalaj@ams.ac.ir
(A. Khalaj).
1
Tel.: þ98 611 3738378; fax: þ98 611 3738381.
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.09.019

20
N. Adibpour et al. / European Journal of Medicinal Chemistry 45 (2010) 19–24
Scheme 1. Structures of S-6123, Dup-721, Dup-105, linezolid, eperezolid, PH-027, YX-10 and AZD2563.
2. Chemistry
3. Results and discussion
Isothiazolones 3 and 4 as outlined in Scheme 3 and described
previously [10,12] were prepared through the reaction of sulfuryl
chloride with dithiodipropionamides 2 which in turn were obtained
by the reaction of dithiodipropionyl chloride with amines 1
(Scheme 3).
Reviewing of the antibacterial activities of 3(2H)-isothiazolones
3a–k and 4a,b,d–k (Table 1) indicate that with exception of the
activities of 4f,g,h against Pseudomonas aeruginosa, and 4a against
Staphylococcus aureus, the activity of other compounds against Gram-
positivebacteriawerecomparableorhigherthanthoseagainstGram-
negative bacteria. Furthermore with exception of activities of 4a,b
against S. aureus, 4h against Staphylococcus epidermidis, 4j against
P. aeruginosa and 4k against Salmonella typhimurium, other
3(2H)-isothiazoleones substituted at the 5-position of the iso-
thiazolone ring with chloro in comparison with unsubstituted anal-
ogous compounds, showed higher or equal activity.
As it was anticipated introduction of 3(2H)-isothiazolone at the 5-
position of oxazolidin-2-ones resulted in compounds which in
general were more active than linezolid and vancomycin against
tested gram negative bacteria. The most active compounds of this
series were unsubstituted phenyl derivatives 8a,j and 4-fluorophenyl
derivative 8b which with exception of the lower activity of 8j against
Escherichia coli, showed higher activities than analogous 3(2H)-iso-
thiazolones against all tested microorganisms. These compounds also
in comparison to the reference drugs showed higher or comparable
5-((3-oxoisothiazol-2(3H)-yl)methyl)-3-phenyloxazolidin-2-ones
8 (Scheme 4) were obtained by nucleophilic displacement of the
hydroxylsulfonateestersof1,3-oxazolidin-2-onemethane-sulfonates
7 with 3(2H)-isothiazolone 3l. All 1,3-oxazolidin-2-one methanesul-
fonates 7 were prepared by the reaction of methansulfonyl chloride
with 5-hydroxymethyl-2-oxazolidinones 6 [4] which were prepared
byalkylation–cyclizationof carbamates 5 with glycidyl butyrate in the
presence of n-butyl lithium in THF at ꢀ78 ꢁC [4]. Carbamates 5a–k
were synthesized through the reaction of arylamines 1 with ethyl
chloroformate [13]. Except 1i, which wasprepared by the nucleophilic
displacement of 4-fluoro atom of 3,4-difluoronitrobenzene with
excess of morpholine followed by the reduction of the nitro group to
amine [4], other amines 1 which were used in this study, are
commercial (Merck Co).
Scheme 2. Structures of 2-oxazolidinones 8 and 3(2H)-isothiazolones 3a–k, 4a,b,d–k.

N. Adibpour et al. / European Journal of Medicinal Chemistry 45 (2010) 19–24
21
Scheme 3. (i): SOCl2, reflux, 1 h; (ii): NaOH 25%, 0–5 ꢁC, r. t. 18 h; (iii): SO2Cl2, 0–10 ꢁC, r. t. 18 h.
activities against some tested microorganisms. Particularly, the
activityof8athe mostpotent compound ofthisstudywashigher than
linezolidandcomparabletovancomycinagainst S.aureus, higherthan
ciprofloxacin against S. epidermidis and equal to ciprofloxacin against
all tested Gram-negative bacteria. The activity of 8j, another
compound with unsubstituted phenyl ring was higher than linezolid
and vancomycin and comparable to ciprofloxacin against S. aureus
and higher than vancomycin and ciprofloxacin against S. epidermidis.
Moreover the activity of the 4-fluorophenyl derivative 8b was higher
than linezolid and comparable to vancomycin against S. aureus.
While substitution of the 4-position of the phenyl ring of 3(2H)-
isothiazolones with chloro, methoxy, and methyl group increased
their antibacterial activities against all (3d and 4d) or some tested
bacteria like S. aureus (4f,g), P. aeruginosa (4f,g) and S. epidermidis
(3f,g and 4f) in comparison to their unsubstituted analogous 3a and
4a, replacement of 4-fluroro atom of the phenyl ring of isothiazolyl
oxazolidinone 8 with these groups (8d,f and g) diminished their
activities. Similarly substitution of the phenyl ring with tri-
fluoromethyl (8h) [14], acetyl (8k) [3], and 3-fluoro-4-(4-morpho-
linyl) (8i) [4], which have been reported to increase the potency of
3-aryl-2-oxazolidinones resulted in less active compounds. Also
changing the position of fluoro and chloro from 4 to 3 (8c,e),
reduced their antibacterial activities.
use of larger groups whether with electron-donating (CH3, OCH3) or
electron-withdrawing properties (Cl, CF3 and COCH3) and irre-
spective of differences in lipophilicity of substituents resulted in
compounds with reduced or no antibacterial activity.
4. Experimental
4.1. Chemistry
All common reagents and solvents were obtained from Merck Co.
Column chromatography was carried out using silica gel (Kieselgel
60, 230–400 mesh, Merck). Melting points were determined on
a MEL-270 Sibata melting point apparatus and are uncorrected. 1H
NMR spectra were recorded on a Bruker 500 MHz, a Varian Unity
Plus 400 (300.866 MHz) and a Bruker 80 MHz spectrometers using
DMSO-d6 and CDCl3 as solvent. Chemical shifts (d) are reported in
ppm relative to TMS as internal standard. Mass spectra were
obtained on a Finningan TSQ-70 instrument. Infrared spectra were
recorded on a Nicolet Magna IR 550 spectrometer. Elemental anal-
yses for C, H and N were performed using a Heracus CHN–O-rapid
elemental analyzer and the results are within ꢂ0.4% of the theo-
retical values. All compounds were characterized by the above
techniques. Analytical and spectroscopic data for the known
compoundswereconsistent with reported literaturevalues anddata
only for new compounds are presented. Ciprofloxacin, linezolid, and
vancomycin were commercial.
Antibacterial activity of compounds 8a,b,j which showed lower
MICs against tested gram-positive bacteria listed in Table 1 were
further evaluated against two clinical isolates of S. aureus resistant
to methicillin and results are presented in Table 2. All these
compounds were found inferior to linezolid with MIC > 4 which is
greater than susceptibility break point for this antibiotic.
The cytotoxic properties of compounds 8a,b,d,j were also inves-
tigated on normal mouse fibroblast (NIH/3T3) cell line using MTT
colorimetric assay [15] and the results are shown in Table 3.These
4.1.1. Synthesis of 3(2H)-isothiazolones 3,4 and
5-((3-oxoisothiazol-2(3H)-yl)methyl)-3-phenyloxazolidin-2-one 8
4.1.1.1. Preparation of 3(2H)-isothiazolones (3,4). Preparation of
compounds 3a,d,f–h,k,4a,d,f–h,k [10], 3e,j,l and 4j [12] by the
reaction of corresponding dithiodipropionamides 2 with sulfuryl
chloride have been described previously and physicochemical data
for those of 3b,c,i and 4b,c,e,i which were prepared by the same
method, are as follows.
compounds were not cytotoxic at concentration below 162
after 24 h incubation and compound 8j showed lower cytotoxicity at
162–273 g/mL range. A comparison between MIC and IC50 of the
mg/mL
m
tested compounds suggests that compounds 8a,b,d,j exhibit in vitro
antibacterial activity at non-cytotoxic concentrations.
4.1.1.1.1. 2-(4-fluorophenyl)isothiazol-3(2H)-one (3b). Yield 20.4%,
mp 97–100 ꢁC (toluene). 1H NMR (500 MHz, CDCl3)
d: 6.32(d, 1H,
The results of this study suggests that replacement of the 5-
acetamidomethyl of the 3-aryl-2-oxazolidinones with 3(2H)-iso-
thiazolones enhance the potency and antibacterial spectrum of both
classes of compounds only when the 4-position of the 3-aryl group is
unsubstituted or substituted with small size fluoro atomwhich might
be due to dual modes of action. The change in position of F and/or the
J ¼ 8.5 Hz), 7.12–7.15(m, 2H), 7.51–7.54(m, 2H), 8.16(d,1H, J ¼ 8.5 Hz).
MS (EI) m/z: 194.0(Mþ). Anal. Calcd. For C9H6FNOS: C, 55.37; H, 3.10;
N, 7.18. Found: C, 55.35; H, 3.11; N, 7.20.
4.1.1.1.2. 5-chloro-2-(4-fluorophenyl)isothiazol-3(2H)-one
(4b). Yield 70%, mp 119 ꢁC (ethyl acetate). 1H NMR (500 MHz,
CDCl3) d: 6.36(s, 1H), 7.12–7.15(m, 2H), 7.46–7.49(m, 2H). MS (EI) m/
Scheme 4. (i): Pyr., 0–5 ꢁC, r. t. 12 h; (ii): n-Buthyl lithium, Glycidyl butyrate, ꢀ78 ꢁC, r. t. 18 h; (iii): CH3SO2Cl, 0 ꢁC, r. t.; (iv): NaH, DMF, r. t. overnight.

22
N. Adibpour et al. / European Journal of Medicinal Chemistry 45 (2010) 19–24
Table 1
MIC (
mg/mL) values of compounds 3a–k,4a,b,d–k,8a–k and vancomycin and ciprofloxacin as reference drugs.
O
O
O
N
O
R
N
N
R
X
S
S
3: X=H
4: X=Cl
8
Compound
X
R
S. aa
S. eb
E. colic
S. typhd
Ps. ae
12.5
1.25
0.01
12.5
12.5
0.75
12.5
100
10
0.6
3a
4a
8a
3b
4b
8b
3c
8c
3d
4d
8d
3e
4e
8e
3f
4f
8f
3g
4g
8g
3h
4h
8h
3i
4i
8i
3j
4j
8j
3k
4k
8k
H
Cl
H
H
Cl
H
H
Cl
H
Cl
H
H
Cl
H
H
Cl
H
H
Cl
H
H
Cl
H
H
Cl
H
H
Cl
H
H
Cl
H
–
Phenyl
Phenyl
Phenyl
3.25
50
0.75
1.5
3
0.75
6
50
3
0.1
1.5
10
6
12.5
10
1.5
50
25
5
25
25
5
50
3.25
0.3
0.75
3
3
1.5
3.25
12.5
0.6
0.01
6
6
25
0.3
0.01
12.5
6
0.75
12.5
100
10
0.3
12.5
25
12.5
12.5
12.5
1.5
100
25
4-Fluorophenyl
4-Fluorophenyl
4-Fluorophenyl
3-Fluorophenyl
3-Fluorophenyl
4-Chlorophenyl
4-Chlorophenyl
4-Chlorophenyl
3-Chlorophenyl
3-Chlorophenyl
3-Chlorophenyl
4-Methoxyphenyl
4-Methoxyphenyl
4-Methoxyphenyl
4-Methylphenyl
4-Methylphenyl
4-Methylphenyl
4-Trifluoromethylphenyl
4-Trifluoromethylphenyl
4-Trifluoromethylphenyl
3-Fluoro-4-morpholinophenyl
3-Fluoro-4-morpholinophenyl
3-Fluoro-4-morpholinophenyl
Benzyl
Benzyl
Benzyl
0.75
12.5
100
10
0.3
12.5
25
12.5
12.5
25
1.5
100
25
5
25
25
25
100
25
25
25
100
1.5
0.1
1.5
12.5
10
12.5
3
0.25
50
2
0.5
25
0.25
5
100
10
10
12.5
6
0.5
0.5
12.5
12.5
25
25
25
12.5
12.5
25
0.01
100
25
0.01
25
25
0.1
100
25
12.5
12.5
12.5
25
12.5
12.5
12.5
5
25
25
12.5
100
25
12.5
10
6
12.5
0.5
0.5
12.5
12.5
12.5
25
12.5
12.5
12.5
12.5
12.5
25
12.5
0.5
12.5
12.5
12.5
50
>100
0.01
>100
4-Acetylphenyl
4-Acetylphenyl
4-Acetylphenyl
–
–
–
50
100
>100
0.01
>100
Vancomycin
Ciprofloxacin
Linezolid
0.75
0.5
2
0.75
1
0.03
>100
0.01
>100
–
–
a
S. a: Staphylococcus aureus ATCC 29737.
S. e: Staphylococcus epidermidis ATCC 12229.
E. coli: Escherichia coli ATCC 8739.
S.typh: Salmonella typhimurium ATCC 1639.
Ps. a: Pseudomonas aeruginosa ATCC 9027.
b
c
d
e
z: 229.1(Mþ), 194.1, 166.1. Anal. Calcd. For C9H5ClFNOS: C, 47.07; H,
2.19; N, 6.10. Found: C, 47.20; H, 2.12; N, 6.30.
4.1.1.1.4. 5-chloro-2-(3-fluorophenyl)isothiazol-3(2H)-one (4c).
Yield 49%, mp 115 ꢁC (n-hexane). 1H NMR (500 MHz, CDCl3)
d
:
4.1.1.1.3. 2-(3-fluorophenyl)isothiazol-3(2H)-one (3c). Yield 20%,
6.38(s, 1H), 7.02–7.07(m, 1H), 7.28–7.31(m, 1H), 7.39–7.44(m, 2H).
MS (EI) m/z: 228.4(Mþ). Anal. Calcd. For C9H5ClFNOS: C, 47.07; H,
2.19; N, 6.10. Found: C, 47.19; H, 2.10; N, 6.02.
mp 95–97 ꢁC (triturated with n-hexane). 1H NMR (500 MHz, CDCl3)
d
: 6.35(d, 1H, J ¼ 8.0 Hz), 7.0–7.05(m, 1H), 7.29–7.33(m, 1H), 7.39–
7.5(m, 2H), 8.25(d, 1H, J ¼ 8.0 Hz). MS (EI) m/z: 195.4(Mþ). Anal.
Calcd. For C9H6FNOS: C, 55.37; H, 3.10; N, 7.18. Found: C, 55.29; H,
3.05; N, 7.10.
4.1.1.1.5. 5-chloro-2-(3-chlorophenyl)isothiazol-3(2H)-one (4e).
Yield 57.3%, mp 118–120 ꢁC (triturated with petroleum ether). 1H
Table 3
Cytotoxic activity of compounds 8a,b,d,j in comparison with linezolid against mouse
Table 2
fibroblast (NIH/3T3) cell line.
MIC (
mg/mL) values of compounds 8a,b,d,j and linezolid as reference drug against
Compound
IC50 (m
g/mL)a
two clinical isolates of S. aureus resistant to methicillin (MRSA).
8a
8b
8d
8j
162 ꢂ 15.5
174 ꢂ 16
194 ꢂ 8.4
273 ꢂ 17.6
465
Compound
MRSA1
MRSA2
8a
8b
8d
8j
6
10
12.5
8
10
12.5
12.5
12.5
2.5
Linezolid
a
IC50 is the concentrations required to inhibit 50% of cell growth. The values
Linezolid
2
represent mean ꢂ SD

N. Adibpour et al. / European Journal of Medicinal Chemistry 45 (2010) 19–24
23
NMR (500 MHz, CDCl3)
d
: 6.35(s, 1H), 7.29–7.31(m, 1H), 7.37(t, 1H,
8.47(d, 1H, J ¼ 4.4 Hz). MS (EI) m/z: 293.9(Mþ), 194.1. Anal. Calcd.
For C13H11FN2O3S: C, 53.05; H, 3.77; N, 9.52. Found: C, 53.10; H,
3.79; N, 9.43.
J ¼ 8.0 Hz), 7.41–7.44(m, 1H), 7.60(t, 1H, J ¼ 2.0 Hz). MS (EI) m/z:
245.3(Mþ). Anal. Calcd. For C9H5Cl2NOS: C, 43.92; H, 2.05; N, 5.69.
Found: C, 43.99; H, 2.19; N, 5.72.
4.1.1.3.4. 3-(4-chlorophenyl)-5-((3-oxoisothiazol-2(3H)-yl)me-
thyl)oxazolidin-2-one (8d). Yield 45%, mp 97–100 ꢁC (triturated
4.1.1.1.6. 2-(3-fluoro-4-morpholinophenyl)isothiazol-3(2H)-one
(3i). Yield 15%, mp 128–130 ꢁC. 1H NMR (500 MHz, CDCl3)
d:
with petroleum ether). 1H NMR (80 MHz, CDCl3)
d: 3.9, 4.15(ddt, 2H,
3.05–3.12(m, 4H), 3.79–3.88(m, 4H), 6.33(d, 1H, J ¼ 8.0 Hz), 6.95
(d, 1H, J ¼ 9.0 Hz), 7.17–7.20(m, 1H), 7.26–7.28(m, 1H), 8.14(d, 1H,
J ¼ 8.0 Hz). MS (EI) m/z: 278.8(Mþ). Anal. Calcd. For C13H13 FN2O2S:
C, 55.70; H, 4.67; N, 9.99. Found: C, 55.78; H, 4.61; N, 9.74.
4.1.1.1.7. 5-chloro-2-(3-fluoro-4-morpholinophenyl)isothiazol-
3(2H)-one (4i). Yield 45%, mp 135–137 ꢁC (ethyl acetate-n-hexane).
J ¼ 12.0, 6.4, 8.8 Hz), 4.66(d, 2H, J ¼ 4.4 Hz), 4.9–5.2(m, 1H), 6.6(d,
1H, J ¼ 4.7 Hz), 7.35(d, 2H, J ¼ 10.4 Hz), 7.45(d, 2H, J ¼ 10.4 Hz),
8.45(d,1H, J ¼ 4.7 Hz). MS (EI) m/z: 312.1(M þ 2), 310.7(Mþ), 212.5,
167.4. Anal. Calcd. For C13H11ClN2O3S: C, 50.24; H, 3.57; N, 9.01.
Found: C, 50.20; H, 3.53; N, 9.14.
4.1.1.3.5. 3-(3-chlorophenyl)-5-((3-oxoisothiazol-2(3H)-yl)me-
1H NMR (500 MHz, CDCl3)
d: 3.08–3.10(m, 4H), 3.86–3.88(m, 4H),
thyl)oxazolidin-2-one (8e). Yield 45%, oil. 1H NMR (500 MHz, CDCl3)
6.34(s, 1H), 6.97(t, 1H, J ¼ 9.1 Hz), 7.15–7.19(m, 1H), 7.24–7.28(m,
1H). MS (EI) m/z: 314.8(Mþ). Anal. Calcd. For C13H12 ClFN2O2S: C,
49.61; H, 3.84; N, 8.90. Found: C, 49.75; H, 3.95; N, 8.82.
d
: 3.99(dd, 1H, J ¼ 9.0, 6.5 Hz), 4.16 (t, 1H, J ¼ 8.5 Hz), 4.66(dddd, 2H,
J ¼ 12.0, 4.5 Hz), 5.02–5.06(m, 1H), 6.63(d, 1H, J ¼ 4.5 Hz),
7.13(dddd, 1H, J ¼ 2.0, 1.0 Hz), 7.31(t, 1H, J ¼ 8.0 Hz), 7.48(dddd, 1H,
J ¼ 2.5, 1.0 Hz), 7.6(t, 1H, J ¼ 2.0 Hz), 8.47(d, 1H, J ¼ 4.5 Hz). Anal.
Calcd. For C13H11ClN2O3S: C, 50.24; H, 3.57; N, 9.01. Found: C, 50.20;
H, 3.51; N, 8.95.
4.1.1.2. Preparation of dithiodipropionamides (2). Physicochemical
data for the novel dithiodipropionamides 2b,c,i which were prepared
by the reported method for the preparation of known dithiodipro-
pionamides 2a,d,f–h,j,k [10] and 2e,l [12] through the reaction of the
dithiodipropionyl chloride with amines 1b,c,i are as follows:
4.1.1.2.1. 3,30-disulfanediylbis(N-(4-fluorophenyl)propanamide)
(2b). Yield 94.8%, mp 169–174 ꢁC. MS (EI) m/z: 198.1, 165.1, 136.1. IR
(KBr, cmꢀ1): 3282, 3068, 2914, 1651, 1610. Anal. Calcd. For
C18H18F2N2O2S2: C, 54.53; H, 4.58; N, 7.07. Found: C, 54.67; H, 4.66;
N, 6.98.
4.1.1.3.6. 3-(4-methoxyphenyl)-5-((3-oxoisothiazol-2(3H)-yl)me-
thyl)oxazolidin-2-one (8f). Yield 33%, mp 100–105 ꢁC (triturated
with n-hexane). 1H NMR (400 MHz, CDCl3)
d: 3.80(s, 3H), 3.95(dd,
1H, J ¼ 6.8, 4.8 Hz), 4.14(t, 1H, J ¼ 6.8 Hz), 4.64(dddd, 2H, J ¼ 9.2,
3.6 Hz), 4.98–5.01(m, 1H), 6.61(d, 1H, J ¼ 4.0 Hz), 6.92(d, 2H,
J ¼ 7.2 Hz), 7.45(d, 2H, J ¼ 7.2 Hz), 8.45(d, 1H, J ¼ 4.0 Hz). MS (EI)
m/z: 306.9(Mþ), 290.5, 275.5. Anal. Calcd. For C14H14N2O4S: C,
54.89; H, 4.61; N, 9.14. Found: C, 54.88; H, 4.64; N, 9.17.
4.1.1.2.2. 3,30-disulfanediylbis(N-(3-fluorophenyl)propanamide)
(2c). Yield96%,mp122–125 ꢁC. MS (EI) m/z: 197.1,166.2,137.2. IR (KBr,
cmꢀ1): 3372, 3106, 2940,1663,1596. Anal. Calcd. For C18H18F2N2O2S2:
C, 54.53; H, 4.58; N, 7.07. Found: C, 55.45; H, 4.63; N, 7.12.
4.1.1.2.3. 3,30-disulfanediylbis(N-(3-fluoro-4-morpholinophenyl)-
propanamide) (2i). Yield 56.3%, mp 158–162 ꢁC. MS (EI) m/z: 283.1,
249.9, 222.0. IR (KBr, cmꢀ1): 3294, 2912, 1664. Calcd. For
C26H32F2N4O4S2: C, 55.11; H, 5.69; N, 9.89. Found: C, 54.91; H, 5.48;
N, 9.95.
4.1.1.3.7. 5-((3-oxoisothiazol-2(3H)-yl)methyl)-3-p-tolylox-
azolidin-2-one (8g). Yield 39.3%, 76–80 ꢁC(ethyl acetate-n-hex-
ane).1H NMR (400 MHz, CDCl3)
d
: 2.33(s, 3H), 3.96(dd, 1H, J ¼ 7.2,
5.2 Hz), 4.15(t, 1H, J ¼ 7.2 Hz), 4.61, 4.67(dddd, 2H, J ¼ 9.6, 4.0 Hz),
4.98–5.02(m, 1H), 6.61(d, 1H, J ¼ 4.0 Hz), 7.19(d, 2H, J ¼ 6.8 Hz),
7.43(d, 2H, J ¼ 6.8 Hz), 8.45(d, 1H, J ¼ 4.0 Hz). MS (EI) m/z:
290.5(Mþ). Anal. Calcd. For C14H14N2O3S: C, 57.92; H, 4.86; N, 9.65.
Found: C, 57.96; H, 4.91; N, 9.63.
4.1.1.3.8. 5-((3-oxoisothiazol-2(3H)-yl)methyl)-3-(4-(tri-
fluoromethyl)phenyl)oxazolidin-2-one (8h). Yield 30%, mp 90–93 ꢁC
4.1.1.3. General procedure for preparation of 5-((3-oxoisothiazol-
2(3H)-yl)methyl)-3-phenyloxazolidin-2-one (8). A mixture of 3(2H)-
isothiazolone 3l (0.03 g, 0.0003 mol), NaH (0.01 g) and mesylates 7
(0.0003 mol) in DMF (2 mL) under N2 was stirred at room
temperature overnight. The solution was then poured to a mixture
of crushed ice-water and the solid was filtered. The solid was
purified by chromatography using chloroform–ethyl acetate (2:1)
to afford compounds 8a–k.
(triturated with petroleum ether).1H NMR (500 MHz, CDCl3)
d:
4.05(dd, 1H, J ¼ 9.2, 5.5 Hz), 4.23(t,1H, J ¼ 7.4 Hz), 4.69(dddd, 2H,
J ¼ 11.5, 4.5 Hz), 5.06–5.09(m,1H), 6.62(d,1H, J ¼ 5.0 Hz), 7.65(d, 2H,
J ¼ 9.0 Hz), 7.71(d, 2H, J ¼ 9.0 Hz), 8.48(d, 1H, J ¼ 5.0 Hz). MS (EI)
m/z: 343.9(Mþ). Anal. Calcd. For C14H11F3N2O3S: C, 48.84; H, 3.22;
N, 8.14. Found: C, 48.92; H, 3.21; N, 8.16.
4.1.1.3.9. 3-(3-fluoro-4-morpholinophenyl)-5-((3-oxoisothiazol-
2(3H)-yl)methyl)oxazolidin-2-one (8i). Yield 34%, mp 88–91 ꢁC
4.1.1.3.1. 5-((3-oxoisothiazol-2(3H)-yl)methyl)-3-phenyl-
(ethyl acetate-n-hexane). 1H NMR (400 MHz, CDCl3)
d: 3.1–3.25(m,
oxazolidin-2-one (8a). Yield 15%, mp 115–118 ꢁC (ethyl acetate-n-
4H), 3.74–4.03(m, 5H), 4.14(t, 1H, J ¼ 8.0 Hz), 4.61–4.69(m, 2H), 5.0–
5.07(m, 1H), 6.62(d, 1H, J ¼ 4.0 Hz), 7.0–7.1(m, 1H), 7.23–7.30(m,
1H), 7.53(d, 1H, J ¼ 14.0 Hz), 8.48(d, 1H, J ¼ 4.0 Hz). MS (EI) m/z:
378.9(Mþ), 377.5. Anal. Calcd. For C17H18FN3O4S: C, 53.82; H, 4.78;
N, 11.08. Found: C, 53.76; H, 4.72; N, 11.07.
hexane). 1H NMR (80 MHz, CDCl3)
d: 3.9–4.3(m, 2H,), 4.68(d, 2H,
J ¼ 4.5 Hz), 5.03(m, 1H), 6.56(d, 1H, J ¼ 4.6 Hz), 7.1–7.6(m, 5H),
8.5(d, 1H, J ¼ 4.6 Hz). MS (EI) m/z: 276.0 (Mþ), 174.9. Anal. Calcd. For
C13H12N2O3S: C, 56.51; H, 4.38; N, 10.14. Found: C, 56.62; H, 4.40; N,
10.05.
4.1.1.3.10. 3-benzyl-5-((3-oxoisothiazol-2(3H)-yl)methyl)ox-
4.1.1.3.2. 3-(4-fluorophenyl)-5-((3-oxoisothiazol-2(3H)-yl)methy-
azolidin-2-one (8j). Yield 31%, oil. 1H NMR (500 MHz, DMSO-d6)
d:
l)oxazolidin-2-one (8b). Yield 35%, mp 83–86 ꢁC (ethyl acetate). 1H
3.58(t, 2H, J ¼ 6.8 Hz), 4.3–4.5(m, 4H), 4.84–4.88(m, 1H), 6.75(d, 1H,
J ¼ 4.4 Hz), 7.28–7.40(m, 5H), 8.90(d, 1H, J ¼ 4.4 Hz). MS (EI) m/z:
289.7(Mþ). Anal. Calcd. For C14H14N2O3S: C, 57.92; H, 4.86; N, 9.65.
Found: C, 57.94; H, 4.88; N, 9.53.
NMR (500 MHz, CDCl3)
d
: 3.99(dd, 1H, J ¼ 8.5, 6.0 Hz), 4.16(t, 1H,
J ¼ 8.5 Hz), 4.66(dddd, 2H, J ¼ 11.5, 4.5 Hz), 5.02–5.05(m, 1H),
6.63(d, 1H, J ¼ 4.5 Hz), 7.10(dd, 2H, J ¼ 9.0, 8.5 Hz), 7.53 (dd, 2H,
J ¼ 9.0, 4.5 Hz), 8.47(d, 1H, J ¼ 4.5 Hz). MS (EI) m/z: 293.8(Mþ),
194.4, 150.4. Anal. Calcd. For C13H11FN2O3S: C, 53.05; H, 3.77; N,
9.52. Found: C, 53.09; H, 3.75; N, 9.56.
4.1.1.3.11. 3-(4-acetylphenyl)-5-((3-oxoisothiazol-2(3H)-yl)me-
thyl)oxazolidin-2-one (8k). Yield 47%, mp 98–103 ꢁC (triturated
with petroleum ether). 1H NMR (80 MHz, CDCl3)
d: 2.59(s, 3H), 3.9–
4.1.1.3.3. 3-(3-fluorophenyl)-5-((3-oxoisothiazol-2(3H)-yl)methy-
4.3(m, 2H), 4.7(d, 2H, J ¼ 8.0 Hz), 4.9–5.2(m, 1H), 6.60(d, 1H,
J ¼ 8.0 Hz), 7.68(d, 2H, J ¼ 16.0 Hz), 7.94(d, 2H, J ¼ 16.0 Hz), 8.45(d,
1H, J ¼ 8.0 Hz). MS (EI) m/z: 317.6(Mþ), 218.1. Anal. Calcd. For
C15H14N2O4S: C, 56.59; H, 4.43; N, 8.80. Found: C, 56.48; H, 4.36; N,
8.81.
l)oxazolidin-2-one (8c). Yield 10%, oil. 1H NMR (400 MHz, CDCl3)
d:
3.99(dd, 1H, J ¼ 8.8, 6.4 Hz), 4.10–4.27(m,1H), 4.62–4.71(m, 2H),
5.02–5.07(m,1H), 6.63(d,1H, J ¼ 4.4 Hz), 6.86–6.87(m, 1H),
7.25(dd,1H, J ¼ 7.0, 1.5 Hz), 7.32–7.38(m,1H), 7.48–7.71(m, 1H),

24
N. Adibpour et al. / European Journal of Medicinal Chemistry 45 (2010) 19–24
4.1.1.4. Preparation of mesylates (7). The synthesis of mesylates 7a
[16], 7b,d,f [17],7c [18],7g,h [19],7i [4] and 7k [3] by the reaction of
methanesulfonyl chloride with 5-hydroxymethyl oxazolidinones 6
and with exception that 7a their physical and analytical data have
been reported. Physicochemical data of 7a and the novel mesylates
7e,j which were prepared by a similar method, are as follows:
4.1.1.4.1. (2-oxo-3-phenyl-1,3-oxazolidin-5-yl)methyl methanesul
fonate (7a). Yield 56%, mp 116–119 ꢁC (n-hexane). 1H NMR
resistant to methicillin (MRSA), S. aureus ATCC 29737 and S. epi-
dermidis ATCC 12229.Gram-negative bacteria used in the study
were E. coli ATCC 8739, S. typhimurium ATCC 1639 and P. aeruginosa
ATCC 9027. The tested compounds, vancomycin and ciprofloxacin
were dissolved in DMSO while linezolid was dissolved in water.
Suspensions of each of bacteria were prepared to contain approx-
imately 106 colony forming units (CFU/mL) and applied to plates
with two fold serially diluted compounds to be tested in distilled
(80 MHz, CDCl3)
d
: 3.11(s, 3H), 3.8–4.1(m, 4H), 4.6–4.8 (m, 2H),
water in concentration ranging from 0.01 to 100 mg/mL and incu-
7.3–7.6(m, 5H). MS (EI) m/z: 271.1(Mþ), 162.3. Anal. Calcd. For
C11H13NO5S: C, 48.70; H, 4.83; N, 5.16. Found: C, 48.52; H, 4.66; N,
5.20.
bated at 37 ꢁC for 18 h. To ensure that the solvent had no effect on
bacterial growth, a control test was performed with test medium
supplemented with DMSO at the same dilution as used in the
experiments. The minimum inhibitory concentration (MICs) values
were the lowest concentration of compounds, which resulted in no
visible growth on the plate and are listed in Table 1.
4.1.1.4.2. [3-(3-chlorophenyl)-2-oxo-1,3-oxazolidin-5-yl]methyl
methanesulfonate (7e). Yield 50%, mp 78–80 ꢁC (triturated with
petroleum ether). 1H NMR (400 MHz, CDCl3)
d: 3.03(s, 3H), 3.9(dd,
1H, J ¼ 9.0, 6.4 Hz), 4.14 (t, 1H, J ¼ 8.2 Hz), 4.55(dddd, 2H, J ¼ 12.0,
4.2 Hz), 4.64–4.66(m,1H), 7.12(dddd,1H, J ¼ 2.0, 0.6 Hz), 7.29(t,1H,
J ¼ 6.2 Hz), 7.45(ddt,1H, J ¼ 2.0, 0.5,1.2 Hz), 7.57(t,1H, J ¼ 2.0 Hz).MS
(EI) m/z: 304.8(Mþ),195. Anal. Calcd. For C11H12ClNO5S: C, 43.21; H,
3.96; N, 4.58. Found: C, 43.01; H, 3.89; N, 4.61.
4.3. Cytotoxic activity
The in vitro cytotoxicity of compounds 8a,b,d,j against normal
mouse fibroblast (NIH/3T3) cell line was assessed using MTT
colorimetric assay [15] according to the previously described
method in literature and results are presented in Table 3.
4.1.1.4.3. (3-benzyl-2-oxo-1,3-oxazolidin-5-yl)methyl methanesul
fonate (7j). Yield 68%, oil. 1H NMR (400 MHz, CDCl3)
d: 3.03(s, 3H),
3.31(dd, 1H, J ¼ 9.2, 6.4 Hz), 3.51(t, 1H, J ¼ 5.6 Hz), 3.78(dd, 1H,
J ¼ 11.6, 4.8 Hz), 4.20(dd, 1H, J ¼ 11.6, 4.8 Hz), 4.41(s, 2H),
4.72–4.78(m,1H), 7.32–7.39(m, 5H). MS (EI) m/z: 285.1(Mþ), 190.7.
Anal. Calcd. For C12H15NO5S: C, 50.52; H, 5.30; N, 4.91. Found: C,
50.54; H, 5.28; N, 4.83.
Acknowledgments
The authors thank Tehran University of Medical Sciences for the
financial support of this investigation.
4.1.1.5. Preparation of 5-hydroxymethyl oxazolidin-2-ones (6). All 5-
hydroxymethyl oxazolidin-2-one 6 of this study were prepared by
the reaction of carbamates 5 with glycidyl butyrate in THF at ꢀ78 ꢁC
[4] in the presence of n-buthyl lithium. Physical and analytical data
of 6a [20], 6c [18], 6g,h [19], 6i [4], prepared by this method and
those of 6b,d,f [17], 6j [21] and 6k [3] prepared by the reaction of
arylamines with glycidol followed by dialkyl carbonate hetero-
cyclization, have been described previously and for the novel
compound 6e are as follows:
References
[1] B. Bozdogan, P.C. Appelbaum, Int. J. Antimicrob. Agents 23 (2004) 113–119.
[2] W.A. Gregory. US Patent 4461773(1984). Chem. Abst. 101 p211126n
[3] W.A. Gregory, D.R. Britelli, C.L.J. Wang, M.A. Wuonola, R.J. McRipley,
D.C. Eustice, V.S. Eberly, P.T. Bartholomew, A.M. Slee, M. Forbes, J. Med. Chem.
32 (1989) 1673–1681.
[4] S.J. Brickner, D.K. Hutchinson, M.R. Barbachyn, P.R. Manninen, D.A. Ulanowicz,
S.A. Garmon, K.C. Grega, S.K. Hendges, D.S. Toops, C.W. Ford, G.E. Zurenko, J.
Med. Chem. 39 (1996) 673–679.
[5] M.R. Barbachyn, C.W. Ford, Angew. Chem. Int. Ed. 42 (2003) 2010–2023.
[6] O.A. Philips, E.E.Udo,A.A.M. Ali, N. Al-Hassawi, Bioorg. Med. Chem.11(2003) 35–41.
[7] F. Houxing, X. Gang, C. Yilang, J. Zhiteng, Z. Shuhua, Y. Yushe, J. Ruyun. Eur. J.
Med. Chem. 42 (2007) 1137–1143.
[8] M.B. Gravestock, D.G. Acton, M.J. Betts, M. Dennis, G. Hatter, A. McGregor,
M.L. Swain, R.G. Wilson, L. Woods, A. Wookey, Bioorg. Med. Chem. Lett. 13
(2003) 4179–4186.
4.1.1.5.1. 3-(3-chlorophenyl)-5-(hydroxymethyl)oxazolidin-2-one
(6e). Yield 46%, mp 57–60 ꢁC (ethyl acetate-n-hexane). 1H NMR
(400 MHz, CDCl3)
d
: 3.76(d, 1H, J ¼ 10.0 Hz), 3.97–4.04(m, 4H),
4.74–4.76(m, 1H), 7.11(dddd, 1H, J ¼ 1.6, 0.8 Hz), 7.29(t,1H,
J ¼ 6.4 Hz), 7.44(ddt,1H, J ¼ 1.6, 0.4, 1.2 Hz), 7.59(t, 1H, J ¼ 2.0 Hz).
MS (EI) m/z: 226.8(Mþ), 152.8. Anal. Calcd. For C10H10ClNO3: C,
52.76; H, 4.43; N, 6.15. Found: C, 52.83; H, 4.49; N, 6.04.
[9] S.N. Lewis, G.A. Miller, A.B. Law. US Patent 3761488 (1973).
[10] A. Khalaj, N. Adibpour, A.R. Shahverdi, M. Daneshtalab, Eur. J. Med. Chem. 39
(2004) 699–705.
[11] N. Adibpour, A. Khalaj, S. Rezaee, M. Daneshtalab, Folia. Microbiol. 52 (2007)
573–576.
[12] S.N. Lewis, G.A. Miller, M. Hausman, E.C. Szamborski. J. Het. Chem. (1971),
571–580.
[13] G.C. Finger, D.R. Dickerson, D.E. Orlopp, J.W. Ehrmantraut, J. Med. Chem. 7
(1964) 572–573.
4.1.1.6. Preparation of ethyl carbamates (5). Carbamates 5a–k were
prepared by the reaction of ethyl chloroformate with arylamines.
Preparation of 5b,c [13], 5d–g [22], and 5j [23] under similar
conditions, and of 5a [24], 5h [25], and 5k [26] by the reaction of
aryl isocyanates with alcohols have been reported previously.
Physicochemical data for the novel carbamate 5i are as follows:
4.1.1.6.1. ethyl 3-fluoro-4-morpholinophenylcarbamate (5i).
Yield 94%, mp 150–152 ꢁC(triturated with warm n-hexane).1H NMR
[14] W.A. Gregory, D.R. Brittelli, C.L.J. Wang, H.S. Kezar III, R.K. Carlson, C.H. Park,
P.F. Corless, S.J. Miller, P.R. Rajagopalan, M.A. Wuonola, R.J. McRipley,
V.S. Eberly, A.M. Slee, M. Forbes, J. Med. Chem. 33 (1990) 2569–2578.
[15] T. Mosmann, J. Immunol. Methods 65 (1983) 55–63.
[16] H. Prucher, R. Gottschlich, A. Haase, M. Stohrer, C. Seyfried, Bioorg. Med. Chem.
Lett. 2 (1992) 165–170.
[17] H. Pruecher, H. Boettcher. DE 3723797 (1989), Chem. Abstr. 111 p7390w.
[18] L. Jae-Gul,L. Wou-Bin.PCTInt.Appl.World0194342(2001),Chem. Abs.13637590v.
[19] Y. Toshihiko, T. Tatsumitsu. Japanian Kokai Tokkyo Koho 11322729 (1999),
Chem. Abstr. 131 p351320r
[20] P.R. Manninen, S.J. Brickner, Org. Syn. 81 (2005) 112–117.
[21] Y. Osa, Y. Hikima, Y. Sato, K. Takino, Y. Ida, S. Hirono, H. Nagase, J. Org. Chem. 70
(2005) 5737–5740.
[22] M. Michman, S. Patai, Y. Wiesel, J. Chem. Soc. Perkin Trans. 1 (1977) 1705–1710.
[23] P.A. Argabright. US Patent 3526655(1970), Chem. Abstr. 73 p98584y.
[24] A.J. Bloodworth, A.G. Davies, J. Chem. Soc. B (1966) 125–127.
[25] H. Martin, A. Lukaszczyk dipl-ing, D. Duerr, G. Pissiotas, O. Rohr, A. Hubele, S.
Janiak. DE 1802739(1969), Chem. Abstr. 71 p91056c.
(400 MHz, CDCl3)
d
: 1.32(t, 3H, J ¼ 6.7 Hz), 4.25(q, 2H, J ¼ 6.7 Hz),
3.11(bs, 4H), 3.93(bs, 4H), 6.65(bs, 1H), 6.98–7.04(m, 2H), 7.35(d,1H,
J ¼ 13.2 Hz). MS (EI) m/z: 267.6 (Mþ), 222.1. Anal. Calcd. For C13H17
FN2O3: C, 58.20; H, 6.39; N, 10.44. Found: C, 58.05; H, 6.25; N, 10.36.
4.2. Antibacterial susceptibility testing
The in vitro antibacterial activities of the compounds 3a–
k,4a,b,d–k,8a–k and vancomycin, ciprofloxacin and linezolid as the
reference drugs was determined by the conventional agar dilution
method using Mueller Hinton agar medium [27].The tested Gram-
positive organisms included two clinical isolates of S. aureus
[26] S. Witek, J. Bielawski, A. Bielawska, J. Prakt. Chemie 321 (1979) 804–812.
[27] A. Barry, Antibiotics in Laboratory Medicine. Willams and Wilkins, Baltimore,
1991, pp. 1–16.