Structure-activity relationship (SAR) studies on oxazolidinone antibacterial agents. 1. Conversion of 5-substituent on oxazolidinone

Article abstract of DOI:10.1248/cpb.49.347

A structure-activity relationship (SAR) study on 5-substituted oxazolidinones as an antibacterial agent is described. The oxazolidinones, of which 5-acetylaminomethyl moiety was converted into other functions, were prepared and evaluated for antibacterial

Full text of DOI:10.1248/cpb.49.347

April 2001
Chem. Pharm. Bull. 49(4) 347—352 (2001)
347
Structure–Activity Relationship (SAR) Studies on Oxazolidinone
Antibacterial Agents. 1. Conversion of 5-Substituent on Oxazolidinone
Ryukou TOKUYAMA,* Yoshiei TAKAHASHI, Yayoi TOMITA, Tomio SUZUKI, Toshihiko YOSHIDA,
Nobuhiko IWASAKI, Noriyuki KADO, Eiichi OKEZAKI, and Osamu NAGATA
Research and Development Division, Hokuriku Seiyaku Co., Ltd., 37–1–1, Inokuchi, Katsuyama, Fukui, 911–8555, Japan.
Received July 21, 2000; accepted December 22, 2000
A structure–activity relationship (SAR) study on 5-substituted oxazolidinones as an antibacterial agent is
described. The oxazolidinones, of which 5-acetylaminomethyl moiety was converted into other functions, were
prepared and evaluated for antibacterial activity. Elongation of the methylene chain (8) and conversion of the ac-
etamido moiety into guanidino moiety (12) decreased the antibacterial activity. The replacement of carbonyl oxy-
gen (؍O) by thiocarbonyl sulfur (؍S) enhanced in vitro antibacterial activity. Especially, compound 16, which
had the 5-thiourea group, showed 4—8 stronger in vitro activity than linezolid. Our SAR study revealed that the
antibacterial activity was greatly affected by the conversion of 5-substituent.
Key words oxazolidinone; antibacterial activity; 5-substituted oxazolidinone; structure–activity relationship
Several antibiotics have been widely prescribed and found functionalized oxazolidinones exhibited excellent activities
to be greatly effective on various infectious disorders in at the same time that we synthesized a series of oxazolidi-
recent years. The emergence of multi-drug-resistant gram- nones with these functionalities.
positive bacteria, however, has become a significant prob-
In this paper, we describe our extensive SAR study on var-
lem. In particular, methicillin-resistant Staphylococcus au- ious 5-substituents of oxazolidinone for antibacterial activity.
reus (MRSA) and vancomycin-resistant enterococci (VRE)
are becoming imminent pathogens in clinical.
Chemistry Elongated compound 8 was synthesized as
shown in Chart 2. Conversion of compound 4 to oxazolidi-
The oxazolidinones, exemplified by Dup-721 (1),1) are an none 6 was accomplished by use of n-BuLi and (S)-3, 4-
exciting new class of synthetic antibacterial agents and are epoxybutenyl propionate (5). The alcohol 6 was reacted with
reported to be effective against staphylococci, streptococci methanesulfonyl chloride, followed by a treatment of sodium
and enterococci.2) Dup-721 has been found to effectively in- azide to yield compound 7. Hydrogenation of the azide 7 and
hibit the protein synthesis in the initial stage.3) Because of following acetylation gave the desired compound 8.
their unique mode of action, the oxazolidinones are thought
5-Guanidine 12 and 5-thiocarbonyl compounds (13—21)
to exhibit antibacterial activity without evidence of cross-re- were prepared as shown in Chart 3. The guanidine 12 was
sistance to any known antibiotics. However, Dupont’s group synthesized from 104) with 1H-pyrazole-1-carboxamidine.
was forced to discontinue the development of Dup-721 due Thioamide derivatives (13—15) were efficiently obtained by
to its severe toxicity. Pharmacia group then started a program treatment of the reference compounds (2, 22, 23) with
to ameliorate the properties of Dup-721 and were successful Lawesson’s reagent. Thiourea derivatives (16, 19) were ob-
in discovering PNU-100480 (2)4) and linezolid (3).5) Line- tained from isothiocyanate 11, which was easily derived from
zolid is effective against numerous serious Gram-positive key intermediate 10 with carbon disulfide and ethyl chloro-
human pathogens caused by MRSA and VRE without severe formate. The other thiourea derivatives (17, 18) were synthe-
toxicity. It has been shown to selectively bind to the 50S ri- sized by treatment of compound 10 with various alkylisothio-
bosomal subunit and to inhibit bacterial translation at the ini- cyanate reagents. Thiosemicarbazide derivative (20) was syn-
tial phase of protein synthesis.6)
Concerning the 5-substituent on the oxazolidinone ring,
Dupont’s group reported that the 5-hydroxymethyl or the 5-
halogenomethyl group had weak antibacterial activities
against gram-positive bacterial strains.7) Furthermore, Gre-
gory et al.1) concluded that the acetylaminomethyl moiety
was the best substituent at the 5-position on oxazolidinone,
in consequence of their SAR study. But their effort was
mainly limited to carbonyl functionalities. So we set about to
convert the 5-substituent on the oxazolidinone into other
functionalities such as thiocarbonyl groups, in order to deter-
mine the effect of the 5-substituent on antibacterial activity
and to find a promising oxazolidinone antibacterial agent
with excellent antibacterial activities against MRSA and
VRE.
The introduction of thiocarbonyl functionalities, however,
was reported by Bayer and Pharmacia groups simulta-
neously.8) The two groups revealed that some 5-thiocarbonyl-
Chart 1
To whom correspondence should be addressed. e-mail: organ-hs@mitene.or.jp
© 2001 Pharmaceutical Society of Japan

348
Vol. 49, No. 4
Chart 2
Chart 3
thesized from 10 with 4-methyl-4-phenyl-3-thiosemicar- able length for the activity would be nϭ1. We next replaced
bazide. Regarding N,NЈ-dimethylthiourea derivative (21), the the carbonyl oxygen (ϭO) by imino nitrogen (ϭNH) or thio-
substitution of methanesulfonyl group (9) with methylamine carbonyl sulfur (ϭS) and investigated their influence on the
followed by the reaction with methylisothiocyanate reagent antibacterial activity. The guanidine compound 12 was inac-
gave the desired compound. The physicochemical data of tive while the corresponding urea compound 24 showed
these compounds are listed in the experimental section.
moderate activity. The guanidino moiety exists in equilib-
rium with three conjugated bases since proton dissociation
can occur from each of the three nitrogen atoms; it is nor-
Results and Discussion
All of the oxazolidinone derivatives were tested for an- mally considered to exist as a charged monocationic species
tibacterial activity against both standard (Staphylococcus au- under any physiological conditions that might be envisaged.
reus SMITH) and clinically isolated strains [S. aureus We assumed that these characteristics of guanidino moiety
HPC1360 (MRSA), S. aureus HPC428 (MRSA), Enterococ- might reduce the activity. On the other hand, the replacement
cus faecium HPC1322 and E. casseliflavus HPC1310 of carbonyl oxygen (ϭO) by thiocarbonyl sulfur (ϭS) (13 vs.
(VRE)]. Their minimum inhibitory concentrations (MICs 22, 15 vs. 23, 16 vs. 24) enhanced antibacterial activity. Es-
mg/ml) are shown in Table 1. Linezolid (3) and vancomycin pecially, the activity of thiourea derivative 16 was 2—4 times
were used as reference compounds.
stronger than that of the corresponding urea compound 24.
The elongated compound 8 showed no antibacterial activ- Moreover, the activity of compound 16 was 4—8 times
ity. This result suggested that the length of methylene (n) at stronger than that of linezolid (3). The introduction of methyl
5-position would greatly influence the activity and that suit- (17), ethyl (18) and dimethyl (19) groups at the terminal ni-

April 2001
349
Table 1. In Vitro Antibacterial Activities and Hydrophobic Parameter of 5-Substituted Oxazolidinones
MICs (mg/ml)a)
Hydrophobic
parameter
Standard
strain
Clinical
isolates
S. aureus
SMITH
S. aureus
S. aureus
E. faecium
HPC1322
E. casseliflavus
No.
n
R1
X
R2
Me
NH2
H
Calculated log Pb)
HPC1360c)
HPC428c)
HPC1310d)
8
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
H
H
H
H
H
H
H
H
H
H
Me
H
H
H
H
O
NH
S
S
S
S
S
S
S
S
S
O
O
O
O
Ϫ0.14
Ϫ0.79
0.69
0.23
0.76
0.04
0.24
0.77
0.34
Ϫ0.14
0.34
0.09
0.17
Ϫ0.54
Ϫ0.37
Ͼ100
Ͼ50
3.13
1.56
3.13
0.78
6.25
12.5
12.5
6.25
Ͼ100
6.25
6.25
3.13
3.13
6.25
0.78
Ͼ100
Ͼ50
3.13
0.78
3.13
1.56
6.25
6.25
25
6.25
Ͼ100
12.5
6.25
6.25
3.13
6.25
0.78
Ͼ100
Ͼ50
3.13
1.56
3.13
0.78
6.25
6.25
25
6.25
Ͼ100
6.25
25
Ͼ100
Ͼ50
1.56
12.5
0.78
0.78
3.13
6.25
25
6.25
Ͼ100
6.25
6.25
1.56
3.13
3.13
0.78
Ͼ100
Ͼ50
3.13
6.25
3.13
0.78
3.13
6.25
25
6.25
Ͼ100
12.5
6.25
3.13
3.13
6.25
12.5
12
13e)
14e)
Me
Et
15
16
17
18
19
20
21
22
23
24
2
3
NH2
NHMe
NHEt
N(Me)2
NHNH2
NHMe
H
Et
NH2
Me
3.13
3.13
3.13
0.78
Vancomycin
a) Inoculum size, one loopful of 106 CFU/ml. b) Ref. 9). c) MRSA. d) VRE. e) Ref. 10).
trogen atom, however, led to remarkably decreased antibacte- moiety is probably essential as the binding site in 5-thiocar-
rial activities. Partition coefficient (log P), which is well used bonyl oxazolidinones.
as an index of lipophilicity, is one of the important physico-
In conclusion, we synthesized some oxazolidinones in
chemical parameters. We were interested in their lipophilici- order to investigate the effect of the 5-substituent for antibac-
ties since the introduction of alkyl groups induced the in- terial activity. It was proved that the antibacterial activity was
crease of lipophilicity. However, thiosemicarbazide com- greatly affected by conversion of the 5-substituent, as a con-
pound 20 also decreased antibacterial activity in spite of its sequence of our effort. Among them, 5-thiocarbonyl groups,
hydrophilicity (Ϫ0.14). Additionally, compound 20 had an- especially the 5-thiourea group, would take the place of 5-ac-
tibacterial activity similar to compounds 17 and 18, though etamide group for the activity. Compound 16, which has 5-
they had quite different calculated log P values. Thus, the va- thiourea moiety, was found to be one of the most potent can-
riety of antibacterial activity by introduction of the sub- didates for the activity.
stituent at the terminal nitrogen atom seems to be caused by
other factors, such as bulkiness of the substituent, rather than Experimental
Melting points were measured with a Yanagimoto melting point apparatus
and are uncorrected. Elemental analyses were measured with a Yanagimoto
by the variety of lipophilicity.
We next investigated the effect of hydrogen atom (R1) at
MT-5 elemental analysis apparatus, and were within Ϯ0.4% of calculated
the proximal nitrogen atom. Methylation at the proximal ni-
1
values. H-NMR spectra were measured with a JEOL A-500 (500 MHz) or
trogen atom, as demonstrated for compound 21, was inactive.
Therefore, the hydrogen atom at this position is essential for
antibacterial activity in 5-thiocarbonyl oxazolidinone. Denis
and Seneci11) reported that the oxygen atom at 1-position on
oxazolidinone ring was indispensable for the appearance of
antibacterial activity. And some reports referred to the pres-
ence of an internal hydrogen bond as an active conformation in
[2-(4-piperidinyl)ethyl]thiourea or phenethylthiazolethiourea
compounds.12) We therefore assumed that pseudo intramolec-
ular hydrogen bonding between NH moiety at the 5-position
and oxygen atom on the oxazolidinone ring could be formed
and be considered to act as an active conformation. However,
the existence of intramolecular hydrogen bonding was not
JEOL JNM-LA300 (300 MHz) spectrometer using tetramethylsilane as an
internal standard. Specific optical rotations were measured on a JASCO
DIP-370 polarimeter. Column chromatography was carried out with silica
gel [Kieselgel 60(Merck)]. TLC was conducted on 0.25 mm pre-coated sil-
ica gel plates (60F254, Merck). All extracted solvents were dried over Na2SO4
and the solvent was evaporated in vacuo.
(S)-3, 4-Epoxybutenyl Propionate (5) A suspension of (S)-(Ϫ)-4-iodo-
1, 2-epoxybutane13) (1.00 g, 5.05 mmol), propionic acid (0.37 ml, 5.05
mmol) and K2CO3 (0.90 g, 6.51 mmol) in methylethylketone (14 ml) was re-
fluxed at 18 h. The mixture was diluted with water and extracted with
AcOEt. The extract was washed with brine, dried and concentrated. The
residue was purified by column chromatography [SiO2, n-Hexane–AcOEt (7 :
1→4 : 1)] to afford 5 (0.21 g, 29%) as colorless oil. [a]2D0 Ϫ17.8° (cϭ0.5,
1
CH3Cl). H-NMR (CDCl3) d: 1.15 (3H, t, Jϭ7.5 Hz), 1.80—2.00 (2H, m),
2.35 (2H, q, Jϭ7.5 Hz), 2.52 (1H, dd, Jϭ5, 2.5 Hz), 2.79 (1H, t, Jϭ5 Hz),
3.00—3.05 (1H, m), 4.10—4.30 (2H, m).
1
observed in our H-NMR studies by comparison with corre-
(S)-3-[3-Fluoro-4-(4-thiomorpholinyl)phenyl]-5-hydroxyethyl oxazoli-
dine-2-one (6) To a solution of N-carbobenzoxy-3-fluoro-4-(4-thiomor-
sponding pyrrolidone derivatives that could not form the in-
ternal hydrogen bond with NH moiety at 5-position. The NH pholinyl)aniline4) (4) (20.0 g, 57.7 mmol) in tetrahydrofuran (THF) (200 ml)

350
Vol. 49, No. 4
Table 2. Physical and Analytical Data for 5-Substituted Oxazolidinones
under N2 at Ϫ70 °C, n-BuLi (37.2 ml of 1.63 M solution in hexane, 60.6
mmol) was added. After the solution was stirred at the same temperature for
1 h, 5 (8.74 g, 60.6 mmol) was added to the reaction mixture. The mixture
was then stirred at room temperature for 17 h, saturated aqueous NH4Cl was
added, and extracted with AcOEt. The extract was washed with brine, dried
and concentrated. The residue was purified by column chromatography
[SiO2, CH2Cl2–AcOEt (50 : 1→10 : 1→1 : 1)] to afford 6 (3.89 g, 21%) as
pale brown crystals. Recrystallization from MeOH gave pale brown crystals.
mp: 132.5—135 °C. [a]2D0 Ϫ34.9° (cϭ0.1, DMSO). 1H-NMR (CDCl3) d:
1.65 (1H, t, Jϭ5 Hz), 1.90—2.15 (2H, m), 2.80 (4H, t, Jϭ5 Hz), 3.29 (4H, t,
Jϭ5 Hz), 3.72 (1H, dd, Jϭ9, 7 Hz), 3.85—3.95 (2H, m), 4.10 (1H, t, Jϭ9
Hz), 4.80—4.90 (1H, m), 6.95 (1H, t, Jϭ8.5 Hz), 7.12 (1H, dd, Jϭ8.5, 2.5
Hz), 7.40 (1H, dd, Jϭ14, 2.5 Hz). Anal. Calcd for C15H19FN2O3S·1/8H2O:
C, 54.82; H, 5.90; N, 8.52. Found: C, 54.81; H, 5.89; N, 8.45.
(S)-5-Azidoethyl-3-[3-fluoro-4-(4-thiomorpholinyl)phenyl]oxazolidine-
2-one (7) To a mixture of 6 (3.50 g, 10.7 mmol) and Et3N (3.40 ml, 24.2
mmol) in CH2Cl2 (70 ml), methanesulfonyl chloride (1.00 ml, 13.1 mmol)
was added under ice cooling, followed by stirring at room temperature for 1
h. The reaction mixture was washed with water and brine, dried and concen-
trated to give methanesulfonate. A suspension of the methanesulfonate and
sodium azide (2.65 g, 40.7 mmol) in N,N-dimethylformamide (DMF) (93 ml)
was heated at 65 °C for 6 h. After cooling, the reaction mixture was poured
into water and extracted with AcOEt. The extract was washed with brine,
dried and concentrated to afford 7 (4.69 g, 100%) as pale brown crystals. Re-
crystallization from MeOH gave pale brown crystals. mp: 101.5—102 °C.
[a]2D0 Ϫ46.8° (cϭ0.1, DMSO). 1H-NMR (CDCl3) d: 1.95—2.10 (2H, m),
2.80 (4H, t, Jϭ5 Hz), 3.30 (4H, t, Jϭ5 Hz), 3.55—3.65 (2H, m), 3.65 (1H,
dd, Jϭ8.5, 6.5 Hz), 4.10 (1H, t, Jϭ8.5 Hz), 4.70—4.80 (1H, m), 6.95 (1H, t,
Jϭ8.5 Hz), 7.10 (1H, dd, Jϭ8.5, 2 Hz), 7.40 (1H, dd, Jϭ14, 2 Hz). Anal.
Calcd for C15H18FN5O2S: C, 51.27; H, 5.16; N, 19.93. Found: C, 51.15; H,
4.99; N, 19.63.
(S)-[[3-[3-Fluoro-4-(4-thiomorpholinyl)phenyl]-2-oxo-5-oxazolidinyl]
ethyl]acetamide (8) A mixture of 7 (4.09 g, 11.6 mmol) and triphen-
ylphosphine (3.36 g, 12.8 mmol) and H2O (4 ml, 116 mmol) in THF (60 ml)
was heated at 40 °C for 17 h. After cooling, the reaction mixture was diluted
with dilute hydrochloric acid and extracted with AcOEt. The aqueous layer
was made alkaline with aqueous NaOH and extracted with AcOEt. The ex-
tract was washed with water, dried and concentrated to afford pale yellow
crystals.
To a solution of the above crystals in pyridine (10 ml), acetic anhydride
(5.50 ml, 58.2 mmol) was added under ice cooling, followed by stirring at
room temperature for 1 h. The reaction mixture was evaporated, and then the
residue was diluted with dilute hydrochloric acid, and extracted with AcOEt.
The extract was washed with brine, dried and concentrated. The residue was
washed with AcOEt to afford 8 as pale yellow crystals. The physicochemical
data are listed in Tables 2 and 3.
Analysis (%)
Calcd (Found)
[a]D20
DMSO
Yield
mp (°C)
Formula
No.
(%) (Recryst. solv.)
(cϭ0.1)
C
H
N
8
12
13
14
15
16
17
18
19
20
21
22
23
24
40
31
44
53
30
42
58
32
41
38
50
81
85
37
169—169.5
(MeOH)
258—263
(MeOH)
127.5—128
(iso-PrOH)
160—161
(EtOH)
158—159
(CH3CN)
C17H22FN3O3S 55.57 6.03 11.44 Ϫ35.1
(55.44 6.09 11.42)
C15H20FN5O2S 46.05 5.42 18.21 Ϫ51.1
·HCl
(46.21 5.43 17.96)
C15H18FN3O2S2 50.69 5.10 11.82 ϩ18.9
(50.50 5.10 11.67)
C16H20FN3O2S2 52.01 5.46 11.37 ϩ6.0
(51.98 5.22 11.37)
C17H22FN3O2S2 53.24 5.78 10.96 ϩ8.0
(53.16 5.38 11.01)
189.5—190.5 C15H19FN4O2S2 48.63 5.17 15.12 Ϫ16.9
(CH3CN)
167.5—170
(CH3CN)
155—156
(CH3CN)
145—147
(EtOH)
(48.63 5.12 15.05)
C16H21FN4O2S2 49.98 5.51 14.57 Ϫ21.0
(49.74 5.32 14.47)
C17H23FN4O2S2 51.24 5.82 14.06 Ϫ17.0
(51.22 6.00 14.18)
C17H23FN4O2S2 51.24 5.82 14.06 Ϫ23.1
(51.12 5.67 13.89)
C15H20FN5O2S2 46.20 5.30 17.96 Ϫ27.0
191—192
(CH2Cl2–MeOH) ·1/4H2O
(46.33 5.17 17.71)
C17H23FN4O2S2 51.24 5.82 14.06 Ϫ12.0
149—150
(EtOH)
(51.28 5.89 13.90)
177.5—178.5 C15H18FN3O3S 53.08 5.35 12.38 Ϫ29.1
(CH3CN)
168—169
(AcOEt)
210—211
(53.26 5.12 12.41)
C17H22FN3O3S 55.57 6.03 11.44 Ϫ21.0
(55.70 5.78 11.35)
C15H19FN4O3S 50.84 5.40 15.81 Ϫ30.0
(50.99 5.38 15.67)
(CH2Cl2–MeOH)
and extracted with AcOEt. The extract was washed with brine, dried and
concentrated. The residue was purified by column chromatography [SiO2,
AcOEt–n-Heptane (1 : 1)] to afford 14 as colorless crystals. The physico-
chemical data are listed in Tables 2 and 3.
Compounds 13 and 15 were prepared in a similar manner, and their
physicochemical data are also listed in Tables 2 and 3.
(S)-N-[[3-[3-Fluoro-4-(4-thiomorpholinyl)phenyl]-2-oxo-5-oxazo-
lidinyl]methyl]thiourea (16) A mixture of 11 (0.50 g, 1.42 mmol) and
16% ammonia in methanol solution (10 ml) in MeOH (10 ml) was stirred at
room temperature for 2 h. The precipitates were collected by filtration and
washed with MeOH to afford 16 as colorless crystals. The physicochemical
data are listed in Tables 2 and 3.
(R)-[[3-[3-Fluoro-4-(4-thiomorpholinyl)phenyl]-2-oxo-5-oxazolidinyl]
methyl]isothiocyanate (11) A mixture of 104) (5.00 g, 16.1 mmol), carbon
disulfide (1.00 ml, 16.1 mmol) and Et3N (2.30 ml, 16.1 mmol) in THF (50
ml) was stirred at room temperature for 5 h. Then ethyl chloroformate (1.53
ml, 16.1 mmol) was added to the mixture and stirred at the same temperature
for 1 h. The mixture was quenched with water and extracted with AcOEt.
The extract was washed with brine, dried and concentrated. The residue was
purified by column chromatography [SiO2, CH2Cl2–MeOH (50 : 1)] to give
11 (3.53 g, 62%) as pale yellow crystals. Recrystallization from CH3CN
gave pale yellow columns. mp: 135.5—136.5 °C. [a]2D0 Ϫ151.9° (cϭ0.1,
Compound 19 was prepared in a similar manner. The physicochemical
data are also listed in Tables 2 and 3.
(S)-N؅-Methyl-N-[[3-[3-fluoro-4-(4-thiomorpholinyl)phenyl]-2-oxo-5-
oxazolidinyl]methyl]thiourea (17) A mixture of 10 (9.84 g, 16.0 mmol),
Et3N (5.00 ml, 35.9 mmol) and methyl isothiocyanate (2.30 ml, 32.0 mmol)
in CH2Cl2 (100 ml) was stirred at room temperature for 18 h. The mixture
was washed with water, dried and concentrated. The residue was purified by
column chromatography [SiO2, CH2Cl2–MeOH (30 : 1)] to give 17 as color-
less crystals. The physicochemical data are listed in Tables 2 and 3.
Compound 18 was prepared in a similar manner. The physicochemical
data are listed in Tables 2 and 3.
(S)-4-[[3-[3-Fluoro-4-(4-thiomorpholinyl)phenyl]-2-oxo-5-oxazo-
lidinyl]methyl]thiosemicarbazide (20) A mixture of 10 (0.30 g, 0.963
mmol) and 4-methyl-4-phenyl-3-thiosemicarbazide (0.26 g, 1.44 mmol) in
DMF (1 ml) was heated at 90 °C for 7 h. The reaction mixture was diluted
with water. The precipitates were collected by filtration, and purified by col-
umn chromatography [SiO2, CH2Cl2–MeOH (50 : 1)] to give 20 as brown
crystals. The physicochemical data are listed in Tables 2 and 3.
1
DMSO). H-NMR (DMSO-d6) d: 2.74 (4H, t, Jϭ5 Hz), 3.22 (4H, t, Jϭ5
Hz), 3.79 (1H, dd, Jϭ9, 5.5 Hz), 4.03 (1H, dd, Jϭ15.5, 5 Hz), 4.11 (1H, dd,
Jϭ15.5, 3.5 Hz), 4.18 (1H, t, Jϭ9 Hz), 4.90—4.97 (1H, m), 7.10 (1H, t,
Jϭ9.5 Hz), 7.20 (1H, dd, Jϭ9.5, 2.5 Hz), 7.46 (1H, dd, Jϭ14.5, 2.5 Hz).
Anal. Calcd for C15H16FN3O2S2: C, 50.97; H, 4.56; N, 11.89. Found: C,
51.01; H, 4.60; N, 11.85.
(S)-3-[3-Fluoro-4-(4-thiomorpholinyl)phenyl]-5-guanidinomethyl oxa-
zolidine-2-one Hydrochloride (12) A mixture of 10 (0.30 g, 0.963 mmol),
N,N-diisopropylethylamine (0.25 ml, 1.45 mmol) and 1H-pyrazole-1-carbox-
amidine hydrochloride (0.21 g, 1.45 mmol) in DMF (3 ml) was heated at 50
°C for 1.5 h. After cooling, the reaction mixture was diluted with CH2Cl2.
The precipitates were collected by filtration and washed with water to afford
12 as colorless crystals. The physicochemical data are listed in Tables 2 and
3.
(S)-N-[[3-[3-Fluoro-4-(4-thiomorpholinyl)phenyl]-2-oxo-5-oxazo-
lidinyl]methyl]thioacetamide (14) A mixture of 24) (1.58 g, 4.47 mmol)
and Lawesson’s reagent (1.80 g, 4.47 mmol) in toluene (20 ml) was heated at
90 °C for 7 h. After the cooling, the reaction mixture was diluted with water,
(S)-N,N؅-Dimethyl-N-[[3-[3-fluoro-4-(4-thiomorpholinyl)phenyl]-2-
oxo-5-oxazolidinyl]methyl]thiourea (21) A mixture of 94) (1.00 g, 2.67
mmol), MeOH (10 ml) and 40% methylamine in methanol solution (6ml)
was refluxed for 72 h. The mixture was concentrated, and then the residue
was treated with Et3N (0.80 ml, 5.63 mmol) and methyl isothiocyanate (0.70
ml, 7.47 mmol) in CH2Cl2 (16 ml) at room temperature and stirred for 2.5 h.

April 2001
351
Table 3. Spectral Data for 5-Substituted Oxazolidinones
No.
1H-NMR (in DMSO-d6) d (ppm)
8
1.81 (3H, s), 1.80—1.90 (2H, m), 2.74 (4H, t, Jϭ5 Hz), 3.10—3.25 (2H, m), 3.22 (4H, t, Jϭ5 Hz), 3.69 (1H, dd, Jϭ9, 8.5 Hz), 4.11
(1H, t, Jϭ9 Hz), 4.60—4.70 (1H, m), 7.09 (1H, t, Jϭ9 Hz), 7.19 (1H, dd, Jϭ9, 2.5 Hz), 7.46 (1H, dd, Jϭ14.5, 2.5 Hz), 7.83 (1H, brs)
2.65—2.80 (4H, m), 3.17—3.30 (4H, m), 3.53 (1H, dd, Jϭ15, 6.5 Hz), 3.62 (1H, dd, Jϭ15, 3.5 Hz), 3.73 (1H, dd, Jϭ9, 6 Hz), 4.12
(1H, t, Jϭ9 Hz), 4.75—4.83 (1H, m), 7.10 (1H, t, Jϭ8.5 Hz), 7.19 (1H, dd, Jϭ8.5, 2 Hz), 7.37 (3H, br s), 7.47 (1H, dd, Jϭ14.5, 2 Hz),
8.07 (1H, br s)
12
13
14
15
2.74 (4H, t, Jϭ5.5 Hz), 3.22 (4H, t, Jϭ5.5 Hz), 3.79 (1H, dd, Jϭ9, 6.5 Hz), 3.96 (2H, t, Jϭ5.5 Hz), 4.13 (1H, t, Jϭ9 Hz), 4.90—5.00
(1H, m), 7.09 (1H, t, Jϭ9 Hz), 7.17 (1H, dd, Jϭ9, 2.5 Hz), 7.45 (1H, dd, Jϭ14.5, 2.5 Hz), 9.36 (1H, d, Jϭ5.5 Hz), 10.5 (1H, brs)
2.44 (3H, s), 2.74 (4H, t, Jϭ4.5 Hz), 3.22 (4H, t, Jϭ4.5 Hz), 3.80 (1H, t, Jϭ8 Hz), 3.85—3.95 (2H, m), 4.12 (1H, t, Jϭ9 Hz), 4.90—
5.00 (1H, m), 7.09 (1H, t, Jϭ9 Hz), 7.19 (1H, dd, Jϭ9, 1 Hz), 7.45 (1H, dd, Jϭ14.5, 1 Hz), 10.2 (1H, brs)
1.15 (3H, t, Jϭ7.5 Hz), 2.59 (2H, q, Jϭ7.5 Hz), 2.74 (4H, t, Jϭ5 Hz), 3.20 (4H, t, Jϭ5 Hz), 3.80 (1H, dd, Jϭ9, 6 Hz), 3.85—4.00 (2H,
m), 4.12 (1H, t, Jϭ9 Hz), 4.90—5.00 (1H, m), 7.09 (1H, t, Jϭ9 Hz), 7.17 (1H, dd, Jϭ9, 2.5 Hz), 7.45 (1H, dd, Jϭ14.5, 2.5 Hz), 10.2
(1H, br s)
16
17
18
19
20
21
2.74 (4H, t, Jϭ5 Hz), 3.22 (4H, t, Jϭ5 Hz), 3.70—3.85 (3H, m), 4.08 (1H, t, Jϭ9 Hz), 4.78—4.84 (1H, m), 7.09 (1H, t, Jϭ9 Hz), 7.18
(1H, dd, Jϭ9, 2.5 Hz), 7.19 (2H, brs), 7.46 (1H, dd, Jϭ14.5, 2.5 Hz), 7.84 (1H, t, Jϭ6 Hz)
2.74 (4H, t, Jϭ5 Hz), 2.84 (3H, brs), 3.22 (4H, t, Jϭ5 Hz), 3.75—3.85 (3H, m), 4.08 (1H, t, Jϭ9 Hz), 4.81—4.90 (1H, m), 7.09 (1H, t,
Jϭ8.5 Hz), 7.17 (1H, dd, Jϭ8.5, 2.5 Hz), 7.45 (1H, dd, Jϭ14.5, 2.5 Hz), 7.52 (1H, brs), 7.65 (1H, t, Jϭ6 Hz)
1.05 (3H, t, Jϭ7 Hz), 2.73 (4H, t, Jϭ5 Hz), 3.22 (4H, t, Jϭ5 Hz), 3.38 (2H, brs), 3.80—3.85 (3H, m), 4.08 (1H, t, Jϭ9 Hz), 4.81—4.87
(1H, m), 7.09 (1H, t, Jϭ9 Hz), 7.18 (1H, dd, Jϭ9, 2 Hz), 7.45 (1H, dd, Jϭ14.5, 2 Hz), 7.52 (1H, brs), 7.56 (1H, t, Jϭ5.5 Hz)
2.74 (4H, t, Jϭ5 Hz), 3.16 (6H, s), 3.20 (4H, t, Jϭ5 Hz), 3.76—4.10 (3H, m), 4.20 (1H, t, Jϭ9 Hz), 4.85—4.95 (1H, m), 7.10 (1H, t,
Jϭ8.5 Hz), 7.20 (1H, dd, Jϭ8.5, 2.5 Hz), 7.45 (1H, dd, Jϭ14.5, 2.5 Hz), 7.57 (1H, t, Jϭ5.5 Hz)
2.65—2.80 (4H, m), 3.10—3.30 (4H, m), 3.86 (2H, brs), 3.90 (1H, dd, Jϭ9, 6 Hz), 4.07 (1H, t, Jϭ9 Hz), 4.48 (2H, brs), 4.80—4.90
(1H, m), 7.09 (1H, t, Jϭ9 Hz), 7.18 (1H, dd, Jϭ9, 2.5 Hz), 7.45 (1H, dd, Jϭ14.5, 2.5 Hz), 8.00 (1H, brs), 8.76 (1H, brs)
2.74 (4H, t, Jϭ5 Hz), 2.93 (3H, d, Jϭ4.5Hz), 3.13 (3H, s), 3.22 (4H, t, Jϭ5 Hz), 3.82 (1H, t, Jϭ9 Hz), 3.99 (1H, dd, Jϭ14.5, 9 Hz),
4.08 (1H, t, Jϭ9 Hz), 4.32 (1H, dd, Jϭ14.5, 3.5 Hz), 4.90—4.98 (1H, m), 7.09 (1H, t, Jϭ9 Hz), 7.19 (1H, dd, Jϭ9, 2.5 Hz), 7.45 (1H,
dd, Jϭ14.5, 2.5 Hz), 7.51 (1H, d, Jϭ4.5 Hz)
22
23
2.74 (4H, t, Jϭ5 Hz), 3.22 (4H, t Jϭ5 Hz), 3.47 (2H, t, Jϭ5.5 Hz), 3.72 (1H, dd, Jϭ9, 6 Hz), 4.09 (1H, t, Jϭ9 Hz), 4.70—4.80 (1H, m),
7.09 (1H, t, Jϭ9 Hz), 7.17 (1H, dd, Jϭ9, 2.5 Hz), 7.45 (1H, dd, Jϭ14.5, 2.5 Hz), 8.09 (1H, brs), 8.27 (1H, brs)
0.97 (3H, t, Jϭ7.5 Hz), 2.10 (2H, q, Jϭ7.5 Hz), 2.74 (4H, t, Jϭ5 Hz), 3.22 (4H, t, Jϭ5 Hz), 3.35—3.45 (2H, m), 3.71 (1H, dd, Jϭ9, 6
Hz), 4.07 (1H, t, Jϭ9 Hz), 4.65—4.75 (1H, m), 7.09 (1H, t, Jϭ9 Hz), 7.16 (1H, dd, Jϭ9, 2.5 Hz), 7.44 (1H, dd, Jϭ14.5, 2.5 Hz), 8.02
(1H, t, Jϭ5.5 Hz)
24
2.70—2.80 (4H, m), 3.20—3.30 (4H, m), 3.34 (2H, t, Jϭ5.5 Hz), 3.72 (1H, dd, Jϭ9, 6.5 Hz), 4.06 (1H, t, Jϭ9 Hz), 4.65—4.70 (1H,
m), 5.48 (2H, brs), 6.24 (1H, t, Jϭ6 Hz), 7.08 (1H, t, Jϭ9 Hz), 7.17 (1H, dd, Jϭ9, 2.5 Hz), 7.46 (1H, dd, Jϭ14.5, 2.5 Hz)
The reaction mixture was washed with water, dried and concentrated to af- References and Notes
ford 21 as pale yellow crystals. The physicochemical data are listed in Ta-
bles 2 and 3.
1) Gregory W. A., Brittelli D. R., Wang C.-L. J., Wuonola M. A., McRip-
ley R. J., Eustice D. C., Eberly V. S., Bartholomew P. T., Slee A. M.,
Forbes M., J. Med. Chem., 32, 1673—1681 (1989).
(S)-N-[[3-[3-Fluoro-4-(4-thiomorpholinyl)phenyl]-2-oxo-5-oxazo-
lidinyl]methyl]formamide (22) A mixture of 10 (1.00 g, 3.21 mmol) and
ethyl formate (3.00 ml, 38.5 mmol) in EtOH (10 ml) was refluxed for 17 h.
After cooling, the reaction mixture was concentrated. The residue was
washed with EtOH to afford 22 as colorless crystals. The physicochemical
data of compound 22 are listed in Tables 2 and 3.
2) Slee A. M., Wuonola M. A., McRipley R. J., Zajac I., Zawada M. J.,
Bartholomew P. T., Gregory W. A., Forbes M., Antimicrob. Agents
Chemother., 31, 1791—1797 (1987); Barry A. L., ibid., 32, 150—152
(1988); Neu H.C., Novelli A., Saha G., Chin N.-X., ibid., 32, 580—
583 (1988).
(S)-N-[[3-[3-Fluoro-4-(4-thiomorpholinyl)phenyl]-2-oxo-5-oxazo-
lidinyl]methyl]propionamide (23) To a mixture of 10 (1.00 g, 3.21 mmol)
and Et3N (0.49 ml, 3.53 mmol) in THF (10 ml), propionyl chloride (0.31 ml,
3.53 mmol) was added under ice cooling, followed by stirring at the same
temperature for 5 h. Then the reaction mixture was washed with water and
extracted with AcOEt. The extract was dried and concentrated to afford 23
as pale brown crystals. The physicochemical data are listed in Tables 2 and
3.
3) Eustice D. C., Feldman P.A., Zajac I., Slee A. M., Antimicrob. Agents.
Chemother., 32, 1218—1222 (1988).
4) Barbachyn M. R., Brickner S. J., Hutchinson D. K., World Intellectual
Property Organization 9507271 (1995) [Chem. Abstr., 123, 256742f
(1995)]; Barbachyn M. R., Hutchinson D. K., Brickner S. J., Cynamon
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(S)-N-[[3-[3-Fluoro-4-(4-thiomorpholinyl)phenyl]-2-oxo-5-oxazolidinyl]
methyl]urea (24) A mixture of 10 (0.30 g, 0.963 mmol) and sodium
cyanate (0.22 g, 2.89 mmol) in acetic acid-water 1 : 1 (2.4 ml) was stirred at
room temperature for 4 h. The reaction mixture was evaporated, and the
residue was washed with water to afford 24 as colorless crystals. The physic-
ochemical data of compound 24 are listed in Tables 2 and 3.
In Vitro Studies These studies were conducted according to the method
of the Japan Society of Chemotherapy.14) The minimum inhibitory concen-
trations (MICs, mg/ml) were determined by an agar dilution method with
Muller-Hinton agar (MHA, Difco Laboratories, Detroit, Mich). Bacterial
suspensions for inocula were prepared by diluting overnight cultures of or-
ganisms to give a final concentration of 106 CFU/ml, and one loopful (5 ml)
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on drug-containing agar plates. The plates were incubated for 18—24 h at 37
°C. The MIC was defined as the lowest drug concentration that prevented
visible growth of bacteria.
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Endermann R., Kroll H-P., Ger. Offen. Patent 19601264 (1997)

352
Vol. 49, No. 4
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