Discovery of torezolid as a novel 5-hydroxymethyl-oxazolidinone antibacterial agent

Article abstract of DOI:10.1016/j.ejmech.2011.01.014

A series of novel substituted pyridyl phenyl oxazolidinone analogues were synthesized and their structure-activity relationship (SAR) was investigated based on in vitro and in vivo antibacterial activities. The minimum inhibitory concentrations (MICs) of the synthesized compounds against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) ranged from 0.12 to 2.0 μg/mL, and against Haemophilus influenzae (Hi) from 2.0 to 8.0 μg/mL. Compared to linezolid, only four compounds (11, 12, 21 and 29) showed higher in vitro antibacterial activities and better in vivo protective effects in mice. To improve the aqueous solubility, various prodrugs of compound 11 (DA-7157), which exerted a potency that was enhanced by 2-8-fold compared to that of linezolid, were synthesized. Among the prodrugs, the phosphate compound 42 exhibited excellent aqueous solubility (>50 mg/mL in DW) and good pharmacokinetic profiles, along with better in vivo efficacy than linezolid. This compound 42 is currently undergoing clinical trials with the brand name Torezolid.

Full text of DOI:10.1016/j.ejmech.2011.01.014

European Journal of Medicinal Chemistry 46 (2011) 1027e1039
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Discovery of torezolid as a novel 5-hydroxymethyl-oxazolidinone
antibacterial agent
,
,
*
Weon Bin Im a b, Sun Ho Choi b, Ju-Young Park a, Sung Hak Choi b, John Finn c, Sung-Hwa Yoon a
a Department of Molecular Science and Technology, Ajou University, San 5, Woncheon, Yeongtong, Suwon 443-749, Republic of Korea
b Dong-A Pharmaceutical Co., Ltd., Research Laboratories, Yongin 449-905, Republic of Korea
c Trius Therapeutics, 6310 Nancy Ridge Drive Suite 101, San Diego, CA 92121, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel substituted pyridyl phenyl oxazolidinone analogues were synthesized and their
structureeactivity relationship (SAR) was investigated based on in vitro and in vivo antibacterial activi-
ties. The minimum inhibitory concentrations (MICs) of the synthesized compounds against methicillin-
resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) ranged from 0.12 to
Received 31 August 2010
Received in revised form
31 December 2010
Accepted 11 January 2011
Available online 18 January 2011
2.0 mg/mL, and against Haemophilus influenzae (Hi) from 2.0 to 8.0 mg/mL. Compared to linezolid, only
four compounds (11, 12, 21 and 29) showed higher in vitro antibacterial activities and better in vivo
protective effects in mice. To improve the aqueous solubility, various prodrugs of compound 11 (DA-
7157), which exerted a potency that was enhanced by 2e8-fold compared to that of linezolid, were
synthesized. Among the prodrugs, the phosphate compound 42 exhibited excellent aqueous solubility
(>50 mg/mL in DW) and good pharmacokinetic profiles, along with better in vivo efficacy than linezolid.
This compound 42 is currently undergoing clinical trials with the brand name Torezolid.
Ó 2011 Elsevier Masson SAS. All rights reserved.
Keywords:
Oxazolidinone
Pyridine
Antibiotics
Prodrug
Antibacterial activity
DA-7867
1. Introduction
intravenously, has proven to be efficacious in several serious indi-
cations, including complicated skin soft structure infections and
Infections caused by bacteria resistant to multiple antibacterial
drug classes represent a serious world-wide health problem [1]. Of
the different resistant strains, methicillin-resistant Staphylococcus
aureus (MRSA) has become particularly troublesome, and is now
responsible for the majority of staphylococcal infections in hospi-
tals, as well as a leading cause of serious infections in the
community [2]. Other problematic resistant Gram-positive bacteria
include vancomycin-resistant enterococci (VRE) and penicillin-
resistant Streptococcus pneumoniae (PRSP).
Although infections due to resistant bacteria were responsible
for over 90,000 deaths in the US in 2001 [3], few drugs are currently
available for the treatment of these infections. The efficacy of
vancomycin, the drug most commonly used in hospitals to treat
infections caused by resistant Gram-positive bacteria, is decreasing
significantly due to a loss of potency over time, resulting in “MIC
creep” [4]. Thus, clinicians are increasingly treating these serious
infections with combinations of two novel antibacterial drugs such
as daptomycin and linezolid. Linezolid (Fig. 1), a member of the
oxazolidinone drug class which is administered both orally and
hospital-acquired pneumonia [5,6]. The success of linezolid in
treating bacterial infections has spurred significant interest in the
development of a new oxazolidinone drug class. In our previous
developmental efforts in the oxazolidinone area, we reported
a highly potent 4-((2-hetero)-pyridin-5-yl)-phenyl-oxazolidinone
series as typified by the lead compound DA-7867 (Fig. 1) [7].
Compared to linezolid, DA-7867, which is structurally similar to
other oxazolidinone series that contain biaryl ring systems [9e14],
exhibited increased antibacterial potency on Gram-positive
bacteria, including MRSA, VRE and PRSP, and is efficacious at
significantly lower doses than linezolid [8].
We attributed this increased antibacterial potency of DA-7867 to
additional interactions at the ribosomal peptidyl transferase center
in the 9-carbon of the 3-fluorophenyl-oxazolidinone (the B-A ring
system). Consequently, we evaluated the substituent effects at the
5-carbon of the oxazolidinone ring with compounds containing
favorable hetero-pyridine D-C rings. These compounds could take
advantage of the potency gained by incorporating a favorable D-C
ring system and expand the choices of substituents in the oxazo-
lidinone ring compatible with good antibacterial activity, despite
the possibility that these larger, more hydrophobic series encoun-
tered key problematic issues such as increased serum binding,
reduced solubility and lower oral bioavailability in comparison with
* Corresponding author. Tel.: þ82 31 219 2515; fax: þ82 31 219 1592.
E-mail address: shyoon@ajou.ac.kr (S.-H. Yoon).
0223-5234/$ e see front matter Ó 2011 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2011.01.014

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W.B. Im et al. / European Journal of Medicinal Chemistry 46 (2011) 1027e1039
was synthesized by rearrangement reaction of 8 with acetic
anhydride under DMF in reflux condition. Finally, Stille coupling
reaction of 5 with 9 and 10 provided the desired tetrazolyl 5-
hydroxymethyl oxazolidinone 11 and oxadiazolyl 5-hydroxymethyl
oxazolidinone 12, respectively.
The preparation of various heterocyclic analogues from 11 is
illustrated in Scheme 4. First, Mitsunobu reaction of 11 was per-
formed with isoxazol-3-ol, triphenylphosphine and diethyl azodi-
carboxylate (DEAD) to give isoxazol-3-yloxy methyl oxazolidinone
13. Fluoromethyl oxazolidinone 14 was prepared from the reaction
of 11 with diethylaminosulphurtrifluoride (DAST) as fluorinating
agent. After the hydroxyl group in 11 was converted into the cor-
responding mesylate group with mesyl chloride, the resulting
compound 15 was reacted with a wide variety of nucleophiles to
prepare the 5-substituted oxazolidinone analogues. Methoxy
methyl oxazolidinone 16 was prepared from the reaction of 15 with
sodium methoxide in methanol at room temperature while alky-
lamino-substituted methyl oxazolidinones (17 and 18) were
obtained from the reaction of 15 with the corresponding amines
(monomethylamine and dimethylamine hydrochloride as nucleo-
philes) under K2CO3 and DMF condition. To prepare the five-
membered heterocyclic compounds containing 1,2,4-triazole and
1,2,3-triazole moieties, compound 19, in which the mesyl group
was substituted with 1,2,4-triazole, was easily prepared from the
reaction of 15 with 1,2,4-triazole using NaH as a strong base under
DMF condition. However, substitution of the mesyl group in 15
with 1,2,3-triazole gave a mixture of 1,2,3-triazol-1-ylmethyl oxa-
zolidinone 21 and 1,2,3-triazol-2-ylmethyl oxazolidinone 20, which
were separated by silica-gel column chromatography. Several C-5-
substituted amide compounds (24e28) were prepared from azide
22, which was obtained from reacting 15 with sodium azide in DMF.
Thus, reduction of 22 in Pd/C under H2 gas at room temperature in
MeOH provided 23, which was then converted to compounds
24e27 by reaction with the corresponding acid chlorides in the
presence of triethylamine. Compound 28 was prepared by deben-
zylation of 27 under hydrogenation condition.
Fig. 1. Structure of linezolid and antibacterial potency of lead compound (DA-7867).
linezolid. To address the issue of solubility and oral activity, we
targeted
1-(4-((2-hetero)-pyridin-5-yl)-phenyl)-oxazolidinones,
with variations at the 5-carbon of the oxazolidinone, offering
a synthetic handle for highly soluble prodrug analogues. The
synthesis and antibacterial activities of these compounds are
reported herein.
2. Chemistry
Two heterocycles in the D ring were used in this study: 2-
methyl-tetrazol-5-yl and 2-methyl-oxadiazol-5-yl. The synthesis of
the 5-hydroxymethyl oxazolidinones containing these ring systems
is depicted in Schemes 1e3. The synthetic strategy utilized
a convergent approach where an organo-tin phenyl oxazolidinone
(A-B ring system) was coupled to a heterocyclic-bromopyridine (C-
D ring system) using the Stille reaction. For the synthesis of an
organo-tin phenyl oxazolidinone (A-B ring system), the phenyl-
oxazolidinone 3 was synthesized using a one-step process to
convert the carbobenzyloxy (Cbz)-protected fluoroaniline 2 directly
into a 5-hydroxymethyl oxazolidinone 3 [15]. Halogenation fol-
lowed by the palladium-catalyzed exchange reaction provided the
tributyltin compound 5 (Scheme 1). The corresponding heterocy-
clic-bromopyridine (C-D ring system) was synthesized from a 2,5-
dibromopyridine as depicted in Scheme 2. The 2-bromo atom was
substituted by cyanide ion using copper cyanide and sodium
cyanide as co-reagent under dimethylformamide (DMF) reflux
condition for 7 h. The tetrazole ring of 2-(tetrazol-5-yl)-5-bromo-
pyridine 8 was made with sodium azide under high temperature
reaction condition. Unfortunately, the addition of iodomethane to
the solution of 8 in DMF produced a mixture of 1-methyltetrazolyl
pyridine and 2-methyltetrazolyl pyridine at room temperature,
which was separated by silica-gel column chromatography to give
the desired 2-methyltetrazyl pyridine 9. Oxadiazolyl pyridine 10
The preparation of various heterocyclic analogues (29 and 31)
from 12 is illustrated in Scheme 5. 29 was obtained by Mitsunobu
reaction of 12 with isoxazol-3-ol under triphenylphosphine and
DEAD while 31 was prepared by mesylation of the hydroxyl group
in 12 followed by displacement of the resulting mesyl group with
1,2,3-triazole.
To improve water solubility, prodrugs of 11 were synthesized as
shown in Scheme 6. 11 was reacted with various Boc-protected
amino acids (L-proline, L-alanine, b-alanine, glycine, and L-valine)
Scheme 1. Reagents and conditions: a: NaHCO3, Cbz-Cl, THF, 0 ꢀC, 2 h; b: n-BuLi, (R)-(ꢁ)-glycidyl butylate, THF, ꢁ78 ꢀC to rt, 26 h; c: CF3COOAg, I2, ACN, rt, 24 h; d: (Bu)3SneSn(Bu)3,
Pd(PPh3)2Cl2, 1,4-dioxane, 100 ꢀC, 2 h.
Scheme 2. Reagents and conditions: a: CuCN, NaCN, DMF, 150 ꢀC, 7 h; b: NaN3, NH4Cl, DMF, 110 ꢀC, 3 h; c: CH3I, NaOH, DMF, 0 ꢀC to rt, 6 h; d: acetic anhydride, pyridine, 150 ꢀC, 3 h.

W.B. Im et al. / European Journal of Medicinal Chemistry 46 (2011) 1027e1039
1029
Scheme 3. Reagents and conditions: a: Pd(PPh3)2Cl2, LiCl, NMP, 120 ꢀC, 4 h.
using conventional coupling method (DCC/DMAP) in DMF at room
temperature. The crude products were purified by column chro-
matography to give the Boc-protected amino acid derivatives,
which were then reacted with trifluoroacetic acid (TFA) to produce
TFA salts of amino acid derivatives (32, 33, 35, 37 and 39). The HCl
salt derivatives (34, 36, 38 and 40) were obtained by replacing TFA
with HCl using a two-step method in which the compounds were
basified with NaHCO3 solution and then acidified with 2 N HCl in
diethyl ether solution. To synthesize the phosphate prodrug of 11,
the hydroxyl group in 11 was first converted to a phosphate ester
group using POCl3 in triethyl phosphate at room temperature, and
then the resulting compound 41 was reacted with sodium meth-
oxide in MeOH to give disodium phosphate salt 42.
Scheme 5. Reagents and conditions: a: isoxazol-3-ol, PPh3, DEAD, THF, rt, 12 h; b:
Et3N, MsCl, CH2Cl2, 0 ꢀC to rt, 0.5 h; c: NaH, DMF, rt, 48 h.
summarized in Table 1, the 17 tested compounds, except 17, 18 and
20, containing a variety of 5-substituents in both D ring systems,
exhibited in vitro antibacterial activities against four strains that
were enhanced by 2e8-fold compared to that of linezolid. This
result was not surprising since previous reports demonstrated that
the replacement of the acetamide group in linezolid with hetero-
aryl ethers, amides and triazoles groups improved the antibacterial
activity [16,17]. Although the good antibacterial activities of
compounds such as heteroaryl ethers (13 and 29), amides (24e28)
and triazole (21 and 31) were unsurprising, the strong antibacterial
activities of 11 and 12 were unexpected. This result was in sharp
contrast with the structureeactivity relationship (SAR) of linezolid
analogues containing the 1-(3-fluoro-4-morpholine-phenyl)-oxa-
zolidinone system where the corresponding hydroxymethyl lacked
antibacterial activity [18]. The compound 11 was one of most potent
3. Antibacterial evaluation
3.1. In vitro and in vivo antibacterial activity
The synthesized compounds were evaluated for in vitro anti-
bacterial activity against methicillin-susceptible S. aureus (MSSA),
MRSA, VRE and Hi, and for in vivo efficacy using the staphylococcal
systemic infection model in mice. Minimum inhibitory concentra-
tion (MIC) values were determined for the in vitro antibacterial
activity using standard agar dilution method while the in vivo
efficacy was evaluated by measuring the effective dose that pro-
tected 50% of the infected mice from death (ED50). In the results of
in vitro antibacterial activity against various bacterial strains,
compounds with MICs of 0.5, 0.5, 0.125 and 4 mg/mL against MSSA,
MRSA, VRE and Hi, respectively. Compounds possessing potent in
vitro antibacterial activity were tested in an in vivo study with
a staphylococcal systemic infection model in mice and compared
with linezolid. The ED50 values of these compounds and linezolid
are presented in Table 1. As expected, 11 and 12 showed higher in
vivo efficacy than linezolid. The ED50 values of 11 and 12 adminis-
tered orally were 8.8 mg/kg and 4.2 mg/kg, compared to 10.8 mg/kg
Scheme 4. Reagents and conditions: a: isoxazol-3-ol, PPh3, DEAD, THF, rt, 12 h; b: DAST, Et3N, CH2Cl2, rt, 24 h; c: Et3N, MsCl, CH2Cl2, 0 ꢀC to rt, 0.5 h; d: NaOMe, MeOH, rt, 24 h; e:
K2CO3, RH hydrochloride, DMF, 60 ꢀC or 80 ꢀC, 30 h; f: NaH, DMF, rt, 48 h; g: NaN3, DMF, 90 ꢀC, 3 h; h: Pd/C, H2, MeOH, rt, 2 h; i: R2COCl, Et3N, CH2Cl2, 0 ꢀC to rt, 0.5 h; and j: Pd/C, H2,
MeOH, rt, 48 h.

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W.B. Im et al. / European Journal of Medicinal Chemistry 46 (2011) 1027e1039
Scheme 6. Reagents and conditions: a: Boc-NH-R1COOH, DCC, DMAP, DMF, rt, 10 h; b: TFA, CH2Cl2, rt, 2 h; c: NaHCO3, H2O and then 2 N HCl in diethyl ether, rt; d: triethyl
phosphate, POCl3, rt, 2 h; e: NaOMe, MeOH, rt, 2 h.
and 9.4 mg/kg for linezolid, respectively. The triazole compound 21
and heteroaryl ether compound 29 also showed better in vivo
efficacies with ED50 values of 5.7 mg/kg and 6.5 mg/kg, compared
to 12.1 mg/kg and 19.1 mg/kg for linezolid, respectively. However,
all other compounds failed to protect mice from the infection with
ED50 > 30 mg/kg dosage.
either by intravenous injection or orally, it was rapidly converted
into 11 and eventually completely consumed. After oral adminis-
tration, the time to reach a maximum plasma concentration (Tmax
was 0.5 h for 42 compared to 2 h for 11. The maximum plasma
concentration (Cmax) of 42 was 8.37 g/mL, compared to 4.62 g/mL
)
m
m
for 11. Compared to 11, the oral bioavailability was significantly
improved from 48.5% to 92.8% with 42. The area under the curve
(AUC) and half-life (T1/2) of 42 were comparable to 11 by oral
administration. However, the AUC of 42 was only about half that of
11 after intravenous injection. The clearance (CL) of 3.11 mL/min/kg
and the volume of distribution (Vdss) of 0.918 L/kg for 42 were
superior to values of 1.61 mL/min/kg and 0.512 L/kg for 11,
respectively (Table 3).
3.2. Solubility of prodrugs of 11
Since 11 revealed an excellent potency in both in vitro and in vivo
antibacterial activities, its prodrugs were synthesized in order to
dramatically improve the solubility for intravenous administration
and oral bioavailability. The amino acid-conjugated ester salt
compounds (32e40), where the selected amino acids were proline
(32), alanine (33 and 34),
b
-alanine (35 and 36), glycine (37 and 38)
3.4. In vivo efficacy of 42
and valine (39 and 40), and the phosphate disodium salt (42) were
synthesized and evaluated for solubility in deionized water (DW)
and chemical stability in various pH solutions. The solubilities of
32e40 and 42 are shown in Table 2. Among the compounds, 33, 34
and 42 showed high water solubility over 50 mg/mL, and all
compounds except 32, 35, 39 and 40 had good solubility over 5 mg/
mL. However, the amino acid-conjugated ester salt compounds
(32e40) showed poor chemical stability in pH 7 solution, whereas
42 had the attractive features of staying unchanged in solution over
prolonged times at a variety of pHs and bringing the solution dis-
solved in DW to an almost neutral pH solution (pH ¼ 6.47).
Therefore, 42 was subjected to pharmacokinetic and in vivo efficacy
studies (Scheme 3).
The compound 42 was tested in comparison to linezolid in
a staphylococcal systemic infection model using both MRSA and
MSSA strains in mice. Whether administered orally or intravenously,
significantly lower dosages of 42 were required to cure both
the MSSA and MRSA infections compared to linezolid. In the MRSA
and MSSA infection models, the ED50 values for 42 were 2.8 and
3.3 mg/kg for intravenous administration and 3.7 and 5.0 mg/kg for
oral administration, compared to 12.9 and 29.1 mg/kg (iv) and 15.6
and 21.4 mg/kg (orally) for linezolid, respectively. These results
clearly demonstrated the superiority of 42 to linezolid in terms of
both antibacterial activity and pharmacokinetic profile. Therefore,
42 can be developed as an attractive new antibacterial drug (Table 4).
3.3. Pharmacokinetic properties of 11 and 42
4. Discussion
The pharmacokinetic properties of the prodrug compound 42
and the parent compound 11 were measured in mice by intrave-
nous injection and oral administration. When 42 was administered
For over a decade, the oxazolidinone class of antibacterial agents
has been the focus of intensive research. While many groups have
successfully increased the antibacterial potency within this class,

Table 1
Antibacterial activity and in vivo efficacy of oxazolidinones.
a
#
R
X
MIC (
m
g/mL)
ED50 MSSA mg/kg
(linezolid)
MSSA
2
MRSA
2
VRE
1
Hi
Linezolid
8
4
e
11
2-Methyl-2H-tetrazol-5-yl
0.5
0.5
0.5
0.5
0.125
8.8 (10.8)
4.2 (9.4)
12
13
5-Methyl-1,3,4-oxadiazol-2-yl
0.5
4
2-Methyl-2H-tetrazol-5-yl
0.5
0.5
0.25
ND
>30 (11.8)
14
16
2-Methyl-2H-tetrazol-5-yl
2-Methyl-2H-tetrazol-5-yl
1
2
1
2
1
2
64
ND
ND
ND
17
18
2-Methyl-2H-tetrazol-5-yl
2-Methyl-2H-tetrazol-5-yl
4
4
4
8
4
ND
ND
ND
ND
ND
19
2-Methyl-2H-tetrazol-5-yl
2
2
1
ND
ND
>30 (12.1)
20
21
2-Methyl-2H-tetrazol-5-yl
2-Methyl-2H-tetrazol-5-yl
16
16
16
ND
0.25
0.25
0.125
2
5.74 (17.3)
24
25
2-Methyl-2H-tetrazol-5-yl
2-Methyl-2H-tetrazol-5-yl
1
1
1
1
0.5
0.5
16
16
20.5 (11.2)
>30 (11.2)
26
28
2-Methyl-2H-tetrazol-5-yl
2-Methyl-2H-tetrazol-5-yl
0.5
1
0.5
1
0.5
ND
>30 (11.2)
>30 (11.7)
0.25
ND
29
31
5-Methyl-1,3,4-oxadiazol-2-yl
5-Methyl-1,3,4-oxadiazol-2-yl
1
1
0.5
>16
6.5 (19.1)
0.25
0.25
0.125
2
>30 (14.9)
ND: not determined.
a
In vivo efficacy was tested with a mouse systemic infection model. ED50 of Linezolid was slightly different with different batches due to the influence by biological
circumstances.

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W.B. Im et al. / European Journal of Medicinal Chemistry 46 (2011) 1027e1039
Table 2
Solubility and properties of prodrugs.
#
R
Solubility
(mg/mL)
% Remaining in D.W. (100
m
g/mL) after 8 h
pH 5
pH in D.W.
(100
mL)
mg/
D.W.
pH 3
pH 7
0.2
32
<1.6
76.4
81.9
65.2
6.49
33
34
>50
>50
90.7
92.3
97.0
98.0
87.8
88.1
6.3
7.5
4.64
3.93
35
36
2.6
96.9
99.6
99.5
94.9
94.9
50.5
6.71
4.40
20.4
99.9a
99.9a
37
38
28.0
12.0
79.5
85.7
86.6
95.1
92.7
93.3
8.10
11.6
4.23
3.77
39
4.7
99.4
99.9a
97.3
51.2
5.33
40
42
4.2
99.9a
99.9a
99.9a
99.9a
97.7
60.9
3.83
6.47
>50
99.9a
99.9a
D.W. means Distilled Water.
a
99.9 means that these compounds were not changed at all for 8 h.
the resulting compounds typically suffered from reduced drug
properties, notably aqueous solubility and oral bioavailability,
partly due to the increased molecular size and partly to the high
standard set by linezolid in aqueous solubility (3 mg/mL) and oral
bioavailability (100%). Our original work in the oxazolidinone area
generated highly potent compounds such as DA-7867, but this
compound had lower aqueous solubility and oral bioavailability
(F ¼ 70% in rats) than linezolid [19]. By exploring the SAR at the
5-position of the oxazolidinone with compounds containing
favorable C-D rings, we were able to retain the superior antibac-
terial activity while maintaining a modest molecular size. The
resulting molecular weight of compound 11, at 370, is only 10%
higher than that of linezolid (337). In addition, other substitutions
at the 5-position of the oxazolidinone ring that were typically
considered detrimental to antibacterial activity, such as 14, 17 and
18, retain good antibacterial potency. These results confirm the
original hypothesis that the incorporation of a favorable D-C ring
can lead to a wider series of 5-substituted oxazolidinones with
good antibacterial potency.
The SAR trends shown here are noteworthy in that they differ
significantly from those of the original oxazolidinone series pub-
lished by the Dupont group [20]. The 5-hydroxymethyl analogues
they prepared were significantly weaker in antibacterial activity
than those analogues containing the acetamide group [21].
Consequently, the SAR of the 5-substituents on the oxazolidinone
ring differs according to the various substituents to the phenyl ring.

W.B. Im et al. / European Journal of Medicinal Chemistry 46 (2011) 1027e1039
1033
Table 3
oxazolidinone revealed several highly potent antibacterial
compounds. Several prodrugs of the highly active compound 11
exhibited promising results, especially 42. This compound is very
active in vivo for treating Gram-positive infections and has a half-life
consistent with once daily dosing. Combined with its favorable drug
properties, including aqueous solubility and high oral bioavailability,
these attributes led to the promotion of 42 as a clinical candidate. The
compound demonstrated a very attractive preclinical profile and is
now the subject of clinical testing where it is currently in clinical trials
sponsored by Trius Therapeutics under the brand name Torezolid.
Comparison of the pharmacokinetic properties of oxazolidinone 11 and its prodrug
42 in mice.
Parameters
11
42
Route
Dose (mg/kg)
T1/2
iv
po
10
3.12
49.8
2
4.62
iv
po
10
3.49
103
10a
10a
3.42
53.6
3.82
49.8
0.5
AUC (
Tmax (h)
Cmax g/mL)
m
g h/mL)
(
m
8.81
3.11
0.918
8.37
CL (mL/min/kg)
Vdss (L/kg)
% F
1.61
0.512
48.5
92.8
6. Experimental
a
A dose of 10 mg/kg of 42 is equivalent to 7.46 mg/kg of 11. All values were
measured based on the amount of the active antibacterial agent 11 detected.
6.1. Chemistry
An examination of the recent publication of models and struc-
tures of linezolid bound to the ribosome target provides some
insights on the structural basis behind the SAR [22e24]. Our
colleagues at Trius Therapeutics recently published an initial model
of 11 bound to the ribosome (shown in Fig. 2) generated by docking
[25]. This structure suggests that the pyridine and tetrazole rings
form additional interactions with a binding pocket. This explains
the increased potency of both DA-7867 and many of the new
analogues prepared in this study. The oxazolidinone ring of both
linezolid and 11 bind in near identical orientation with the acet-
amide group of linezolid and the hydroxylmethyl group of 11 to
form hydrogen bonds to a backbone phosphate. The comparison of
11 to DA-7867 suggests minimal, if any, energetic loss of potency at
the target level from exchanging amide to alcohol. The previous
observation of weak antibacterial activity for multiple 5-hydrox-
ymethyl oxazolidinones is likely due to bacterial penetration/efflux
issues. From a resistance standpoint, the smaller footprint of
a hydroxyl group (MW ¼ 17) versus an acetamide group (MW ¼ 58)
impacts the antibacterial activity of 11 on linezolid-resistant
6.1.1. General information
Reagents and solvents were purchased from commercial
suppliers (Acros and SigmaeAldrich) and used as provided, unless
indicated otherwise. All other solvents used for reactions were
analytical grade and used as provided. Column chromatography
was carried out using Merck silica gel 60 (230e400 mesh). Reac-
tions were carried out in oven-dried glassware under a nitrogen
atmosphere and stirred at room temperature, unless indicated
otherwise. The melting points were determined on Mettler Toledo
FP62 apparatus. 1H NMR and 13C NMR spectra were recorded on
Varian 400 MHz spectrophotometer by CDCl3 or DMSO-d6 and TMS
as an internal standard (chemical shift in
d ppm). IR spectra were
measured on Nicolet Magna 550 series II IR spectrophotometer.
Mass spectra were obtained with Agilent 1100 series LC/MSD
system and MDS-SCIEX API 3000 system.
6.1.2. N-Carbobenzyloxy-3-fluoroaniline (2)
To a solution of 3-fluoroaniline (100 g, 900 mmol) and NaHCO3
(150 g, 1.80 mol) in THF (1 L) was slowly added N-carbobenzyloxy
chloride (154 mL, 1.08 mol). After being stirred for 2 h at 0 ꢀC, the
reaction mixture was poured into water and extracted with EtOAc.
The organic layer was washed with brine, dried over anhydrous
MgSO4, filtered and concentrated in vacuo. The residue was washed
with n-hexane to obtain the title compound (132 g, 60%). 1H NMR
strains. For example, 11 has MIC values between 0.5 and 1
the potentially problematic, plasmid-borne, cfr S. aureus strains but
linezolid has MICs ranging between 8 and 32 g/mL [25]. Overall,
mg/mL on
m
the structural features of 11 impart a positive impact in potency, the
ability to treat infections caused by linezolid resistant strains and
a reduced emergence of resistance going forward.
Of the several attractive prodrugs with increased solubility
and high oral bioavailability produced by the conversion of 11,
compound 42 has high aqueous solubility (>50 mg/mL) and
stability, an attractive pharmacokinetic profile that demonstrates
rapid conversion to the active antibacterial compound, a long
half-life and an oral bioavailability greater than 90%. Consequently,
the prodrug approach brings benefits to both intravenous and oral
routes of administration. While the hydroxymethyl group might
be expected to be a site of rapid metabolism, the long half-life of
11 in humans of 11 h clearly demonstrates the in vivo robustness
of this group and its suitability for once daily dosing [26].
(CDCl3):
2H), 5.18 (s, 2H).
d
7.35 (m, 6H), 7.21 (m, 1H), 6.99 (d, J ¼ 8.4 Hz, 1H), 6.74 (m,
6.1.3. (R)-3-(3-Fluorophenyl)-2-oxo-5-oxazolidinylmethanol (3)
To a solution of N-carbobenzyloxy-3-fluoroaniline 2 (132 g,
538 mmol) in THF (1.3 L) at ꢁ78 ꢀC added slowly n-butyllithium
1.6 M in n-hexane (370 mL, 600 mmol) under nitrogen condition.
After the solution was stirred at ꢁ78 ꢀC for 10 min, (R)-(ꢁ)-glycidyl
butylate (84.0 mL, 600 mmol) was slowly added. The mixture was
stirred at ꢁ78 ꢀC for 2 h and stirred at room temperature for 24 h.
After completion of the reaction, an aqueous saturated ammonium
chloride (NH4Cl) solution was added and the mixture was extracted
with EtOAc. The organic layer was washed with brine, dried over
anhydrous MgSO4 and concentrated in vacuo. The crude product
was recrystallized from EtOAc and n-hexane to give the title
5. Conclusion
An examination of the SAR for 1-(4-((2-hetero)-pyridin-5-yl)-
phenyl)-oxazolidinones with variations at the 5-position of the
compound (80 g, 70%). 1H NMR (DMSO-d6):
1H), 7.40 (m, 1H), 7.34 (m, 1H), 6.93 (t, J ¼ 6.8 Hz, 1H), 5.21 (t,
J ¼ 5.6 Hz,1H), 4.70 (m,1H), 4.07 (t, J ¼ 9.2 Hz,1H), 3.83 (m,1H), 3.68
(m, 1H), 3.55 (m, 1H).
d
7.51 (d, J ¼ 12.0 Hz,
Table 4
Efficacy of 42 compared to linezolid in a S. aureus lethal septicemia infection model
in mice.
6.1.4. (R)-3-(4-Iodo-3-fluorophenyl)-2-oxo-5-oxazolidinylmethanol (4)
ED50 MRSA (mg/kg)
ED50 MSSA (mg/kg)
To
a solution of (R)-3-(3-fluorophenyl)-2-oxo-5-oxazolidi-
42
Linezolid
42
Linezolid
nylmethanol 3 (30.0 g, 140 mmol) in acetonitrile (300 mL) was
added trifluoroacetic acid silver salt (CF3COOAg) (46.0 g, 210 mmol)
and iodine (43.0 g, 170 mmol). After being stirred for 24 h at room
iv
2.8
po
3.7
iv
12.9
po
15.6
iv
3.3
po
5.0
iv
29.1
po
21.4

1034
W.B. Im et al. / European Journal of Medicinal Chemistry 46 (2011) 1027e1039
Fig. 2. Models of 11 (blue) and linezolid (yellow) binding to the Escherichia coli ribosome.
temperature, the reaction mixture was poured into water and
extracted with EtOAc. The organic layer was washed with brine,
dried over anhydrous MgSO4, filtered and concentrated in vacuo to
6.1.8. 2-(2-Methyltetrazol-5-yl)-5-bromo pyridine (9)
To a solution of 2-(tetrazol-5-yl)-5-bromopyridine 8 (10.5 g,
46.5 mmol) in DMF (100 mL) at 0 ꢀC was slowly added NaOH
(6.50 g, 162 mmol) and iodomethane (4.08 mL, 65.5 mmol). After
being stirred at room temperature for 6 h, the reaction mixture was
poured into water and extracted with EtOAc. The organic layer was
washed with brine, dried over anhydrous MgSO4, filtered and
concentrated in vacuo. The crude product was purified by column
chromatography to obtain the title compound (5 g, 45%). 1H NMR
obtain the title compound (44 g, 93%). 1H NMR (DMSO-d6):
d 7.77 (t,
J ¼ 8.0 Hz, 1H), 7.56 (dd, J ¼ 12.0 Hz, 2.4 Hz, 1H), 7.20 (dd, J ¼ 8.8 Hz,
2.4 Hz, 1H), 5.20 (m, 1H), 4.70 (m, 1H), 4.07 (t, J ¼ 9.2 Hz, 1H), 3.80
(m, 1H), 3.67 (m, 1H), 3.56 (m, 1H).
6.1.5. (R)-3-(4-Tributylstannyl-3-fluorophenyl)-2-oxo-5-oxazolidinyl
methanol (5)
(CDCl3):
d
8.80 (d, J ¼ 2.0 Hz, 1H), 8.13 (d, J ¼ 8.4 Hz, 1H), 7.98 (dd,
J ¼ 8.4 Hz, 2.4 Hz, 1H), 4.42 (s, 3H).
To a solution of (R)-3-(4-iodo-3-fluorophenyl)-2-oxo-5-oxazo-
lidinylmethanol 4 (50.0 g, 148 mmol) in 1,4-dioxane (660 mL) was
added hexabutylditin (45.3 mL, 89.6 mmol) and Pd(PPh3)2Cl2
(9.30 g, 13.3 mmol). The reaction mixture was stirred for 2 h at
100 ꢀC. The solution was filtered through celite and the filtrate was
concentrated on a rotary evaporator. The residue was purified by
column chromatography to obtain the title compound (45 g, 61%).
6.1.9. 2-(2-Methyl-[1,3,4]oxadiazol-5-yl)-5-bromopyridine (10)
To a solution of 2-(tetrazol-5-yl)-5-bromopyridine 8 (8.60 g,
38.1 mmol) in acetic anhydride (130 mL) was added pyridine
(15.0 mL,185 mmol) and stirred for 3 h at 150 ꢀC. After being cooled
to room temperature, the reaction mixture was poured into water
and extracted with EtOAc. The organic layer was washed with
brine, dried over anhydrous MgSO4, filtered and concentrated in
vacuo to obtain the title compound (7.3 g, 80%). 1H NMR (CDCl3):
1H NMR (DMSO-d6):
d
7.44 (d, J ¼ 9.2 Hz, 1H), 7.33 (m, 2H), 5.22 (t,
J ¼ 5.6 Hz, 1H), 4.69 (m, 1H), 4.05 (t, J ¼ 9.2 Hz, 1H), 3.81 (m, 1H),
3.67 (m, 1H), 3.55 (m, 1H), 1.50 (m, 6H), 1.26 (m, 6H), 1.07 (m, 6H),
0.82 (t, J ¼ 7.2 Hz, 9H).
d
8.77 (d, J ¼ 2.4 Hz, 1H), 8.10 (d, J ¼ 8.4 Hz, 1H), 7.99 (dd, J ¼ 8.4 Hz,
2.4 Hz, 1H), 2.61 (s, 3H).
6.1.6. 2-Cyano-5-bromopyridine (7)
6.1.10. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-hydroxy methyl oxazolidin-2-one (11)
To a solution of 2,5-dibromopyridine 6 (100 g, 420 mmol) in
DMF (1 L) was added copper cyanide (32.0 g, 360 mmol) and
sodium cyanide (17.8 g, 360 mmol). The reaction mixture was
stirred for 7 h at 150 ꢀC. After being cooled to room tempera-
ture, the reaction mixture was poured into water and extracted
with EtOAc. The organic layer was washed with brine, dried
over anhydrous MgSO4, filtered and concentrated in vacuo to
To
a
solution of (R)-3-(4-tributhylstannyl-3-fluorophenyl)-
(37.0 g, 74.0 mmol) in NMP
2-oxo-5-oxazolidinylmethanol
5
(150 mL) was added 2-(2-methyltetrazol-5-yl)-5-bromopyridine 9
(19.7 g, 81.9 mmol), LiCl (10.4 g, 245 mmol) and Pd(PPh3)2Cl2
(2.90 g, 4.13 mmol). The reaction mixture was stirred for 4 h at
120 ꢀC. After being cooled to room temperature, the reaction
mixture was poured into water and extracted with EtOAc. The
organic layer was washed with brine, dried over anhydrous
MgSO4, filtered and concentrated in vacuo. The residue was further
purified by column chromatography to obtain the title compound
obtain the title compound (54 g, 70%). 1H NMR (CDCl3):
d 8.76
(s, 1H), 7.98 (dd, J ¼ 8.4 Hz, 2.4 Hz, 1H), 7.58 (dd, J ¼ 8.4 Hz,
1.2 Hz, 1H).
6.1.7. 2-(Tetrazol-5-yl)-5-bromopyridine (8)
(8 g, 26%). Mp: 201 ꢀC. 1H NMR (DMSO-d6):
d 8.90 (s, 1H), 8.18 (m,
To a solution of 2-cyano-5-bromopyridine 7 (10 g, 54.6 mmol) in
DMF (100 mL) was added sodium azide (5.33 g, 82.0 mmol) and
ammonium chloride (4.38 g, 82.0 mmol). The reaction mixture was
stirred for 3 h at 110 ꢀC. After being cooled to room temperature,
the reaction mixture was poured into water and extracted with
EtOAc. The organic layer was washed with brine, dried over anhy-
drous MgSO4, filtered and concentrated in vacuo to obtain the title
2H), 7.70 (m, 2H), 7.49 (dd, J ¼ 8.8 Hz, 2.4 Hz, 1H), 5.25 (t, J ¼ 5.6 Hz,
1H), 4.74 (m, 1H), 4.46 (s, 3H), 4.14 (t, J ¼ 8.8 Hz, 1H), 3.88 (m, 1H),
3.68 (m, 1H), 3.58 (m, 1H). 13C NMR (DMSO-d6):
d 163.56, 159.03,
154.06, 149.18, 144.78, 140.30, 136.96, 131.42, 130.73, 121.89, 118.36,
113.81, 105.18, 73.39, 61.52, 45.96, 39.63. IR (neat, cmꢁ1): 3251.40,
1746.23, 1619.91, 1473.35, 1406.82. [M þ H]þ: 371.02. HRMS [EI-
MS]: m/z, calculated for [C17H15FN6O3] 370.1190, found, 370.1100
[C17H15FN6O3].
compound (10.5 g, 85%). 1H NMR (DMSO-d6):
J ¼ 8.4 Hz, 1H), 8.03 (d, J ¼ 8.4 Hz, 1H).
d 8.75 (s, 1H), 8.14 (d,

W.B. Im et al. / European Journal of Medicinal Chemistry 46 (2011) 1027e1039
1035
6.1.11. (R)-3-(4-(2-(2-Methyl-[1,3,4]oxadiazol-5-yl)pyridin-5-yl)-3-
fluorophenyl)-5-hydroxymethyl oxazolidin-2-one (12)
anhydrous MgSO4, filtered and concentrated in vacuo to obtain the
title compound (1 g, 82%). 1H NMR (DMSO-d6):
8.93 (s, 1H), 8.20
d
2-(2-Methyl-[1,3,4]oxadiazol-5-yl)-5-bromopyridine 10 (14.3 g,
59.6 mmol) was subjected to the same reaction described for the
synthesisof thecompound 11 togivethe titlecompound (6.6 g, 22%).
(m, 2H), 7.76 (t, J ¼ 8.8 Hz, 1H), 7.69 (dd, J ¼ 13.6 Hz, 2.0 Hz, 1H), 7.51
(dd, J ¼ 8.4 Hz, 2.0 Hz, 1H), 5.07 (m, 1H), 4.54 (m, 2H), 4.70 (s, 3H),
4.26 (t, J ¼ 9.6 Hz, 1H), 3.91 (m, 1H), 3.27 (s, 3H).
Mp: >230 ꢀC.1H NMR (DMSO-d6):
d 8.93 (s,1H), 8.21 (s, 2H), 7.71 (m,
2H), 7.50 (dd, J ¼ 8.8 Hz, 2.4 Hz, 1H), 5.25 (t, J ¼ 5.6 Hz, 1H), 4.74 (m,
6.1.15. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-methoxy methyl oxazolidin-2-one (16)
1H), 4.14 (t, J ¼ 9.2 Hz, 1H), 3.89 (m, 1H), 3.68 (m, 1H), 3.59 (m, 1H),
2.64 (s, 3H). 13C NMR (DMSO-d6):
d 164.62, 163.13, 160.31, 157.86,
To a solution of (R)-3-(4-(2-(2-methyltetrazol-5-yl)pyridin-5-yl)-
3-fluorophenyl)-5-methanesulfonyloxy methyl oxazolidin-2-one 15
(400 mg, 0.890 mmol) in MeOH (10 mL) was added NaOMe (90.0 mg,
1.67 mmol). After being stirred for 24 h at room temperature, the
mixturewaspoured intowater and extracted withEtOAc. The organic
layer was washed with brine, dried over anhydrous MgSO4, filtered
and concentrated in vacuo. The residue was further purified by
column chromatography to obtain the title compound (200 mg, 58%).
154.09, 149.20, 141.36, 137.09, 132.36, 130.79, 122.29, 118.03, 113.82,
105.17, 73.45, 61.55, 45.98, 10.84. IR (neat, cmꢁ1): 3276.47, 1742.37,
1625.70, 1470.46, 1415.49. [M þ H]þ: 371.01.
6.1.12. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-(isoxazol-3-yl-oxy)methyl oxazolidin-2-one (13)
To a solution of EtOH (200 mL), 10% NaOH solution (250 mL) and
ethyl acetylenecarboxylate (20.7 mL, 204 mmol) was added
hydroxylamine hydrochloride (17.0 g, 245 mmol). The reaction
mixture was stirred at 30 ꢀC for 12 h. After the solution was cooled
to room temperature, the pH was adjusted to 2 by addition of
concentrated HCl solution. The mixture was extracted with EtOAc
and the organic layer was washed with brine, dried over anhydrous
MgSO4, filtered and concentrated in vacuo to obtain isoxazol-3-ol
(14.2 g, 82%). The crude product was used in the following step
without further purification. To a solution of (R)-3-(4-(2-(2-meth-
1H NMR (CDCl3):
d
8.88 (s, 1H), 8.25 (d, J ¼ 8.0 Hz, 1H), 8.00 (m, 1H),
7.44 (t, J ¼ 8.8 Hz, 1H), 7.22 (m, 2H), 4.24 (s, 3H), 4.11 (dd, J ¼ 15.2 Hz,
3.2 Hz,1H), 3.74 (s, 3H), 3.49 (dd, J ¼ 14.8 Hz, 6.4 Hz,1H), 3.28 (m,1H),
2.82(t, J ¼ 4.4 Hz,1H), 2.55(dd, J ¼ 4.8 Hz, 2.4 Hz,1H). IR(neat, cmꢁ1):
1734.66, 1620.88, 1511.92, 1458.89, 1404.89. [M þ H]þ: 385.03.
6.1.16. (S)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-N-methyl aminomethyloxazolidin-2-one (17)
To a solution of (R)-3-(4-(2-(2-methyltetrazol-5-yl)pyridin-5-
yl)-3-fluorophenyl)-5-methanesulfonyloxy methyl oxazolidin-2-
one 15 (200 mg, 0.44 mmol) in DMF (5 mL) was added K2CO3
(240 mg, 1.74 mmol) and methylamine hydrochloride (100 mg,
3.21 mmol). The solution was stirred for 30 h at 80 ꢀC. When the
reaction was complete, the solution was extracted with EtOAc. The
organic layer was washed with brine, dried over anhydrous MgSO4,
filtered and concentrated in vacuo. The residue was purified by
column chromatography to obtain the title compound (80 mg,
yltetrazol-5-yl)pyridin-5-yl)-3-fluorophenyl)-5-hydroxy
methyl
oxazolidin-2-one 11 (100 mg, 0.270 mmol) in THF (10 mL) was
added isoxazol-3-ol (32.0 mg, 0.380 mmol) and triphenylphos-
phine (113 mg, 0.430 mmol). To the solution was added dropwise
diethyl azodicarboxylate (640 mL, 0.410 mmol). After being stirred
for 12 h, the reaction mixture was poured into water and extracted
with EtOAc. The organic layer was washed with brine, dried over
anhydrous MgSO4, filtered and concentrated in vacuo. The residue
was further purified by column chromatography to obtain the title
45%). 1H NMR (DMSO-d6):
d 8.95 (s, 1H), 8.23 (s, 2H), 7.77 (t,
compound (60 mg, 51%). 1H NMR (DMSO-d6):
d 8.92 (s, 1H), 8.69 (s,
J ¼ 8.8 Hz, 1H), 7.70 (dd, J ¼ 13.6 Hz, 1.6 Hz, 1H), 7.52 (dd, J ¼ 8.8 Hz,
1.6 Hz, 1H), 5.09 (m, 1H), 4.61 (m, 2H), 4.26 (t, J ¼ 9.2 Hz, 1H), 3.91
(m, 1H), 3.26 (s, 3H), 2.63 (s, 3H). [M þ H]þ: 384.13.
1H), 8.20 (m, 2H), 7.75 (t, J ¼ 8.8 Hz, 1H), 7.68 (d, J ¼ 13.2 Hz, 1H),
7.45 (d, J ¼ 8.8 Hz, 1H), 6.39 (s, 1H), 5.13 (m, 1H), 4.50 (m, 2H), 4.47
(s, 3H), 4.27 (t, J ¼ 9.6 Hz, 1H), 3.98 (m, 1H). [M þ H]þ: 438.12.
6.1.17. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-(N,N-dimethyl aminomethyl)oxazolidin-2-one (18)
6.1.13. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-fluoromethyl oxazolidin-2-one (14)
To a solution of (R)-3-(4-(2-(2-methyltetrazol-5-yl)pyridin-5-yl)-
3-fluorophenyl)-5-methanesulfonyloxy methyl oxazolidin-2-one 15
(100 mg, 0.220 mmol) in DMF (5 mL) was added K2CO3 (93.0 mg,
0.670 mmol) and dimethylamine hydrochloride (30.0 mg,
0.670 mmol). After the solution was stirred at 60 ꢀC for 30 h, the
reaction mixture was poured into water and extracted with EtOAc.
The organic layer was washed with brine, dried over anhydrous
MgSO4, filtered and concentrated in vacuo. The residue was purified
by column chromatography to obtain the title compound (70 mg,
To a solution of (R)-3-(4-(2-(2-methyltetrazol-5-yl)pyridin-5-
yl)-3-fluorophenyl)-5-hydroxy methyl oxazolidin-2-one 11
(100 mg, 0.270 mmol) in CH2Cl2 (10 mL) was added dieth-
ylaminosulfur trifluoride (43.0 mg, 0.270 mmol) and triethylamine
(780 mL, 0.560 mmol). After the solution was stirred at room
temperature for 24 h, the reaction mixture was poured into water
and extracted with CH2Cl2. The organic layer was washed with brine,
dried over anhydrous MgSO4, filtered and concentrated invacuo. The
residue was further purified by column chromatography to obtain
76%).1HNMR(DMSO-d6):
d
8.91 (s,1H), 8.19 (m, 2H), 7.76 (t, J ¼ 8.4 Hz,
the title compound (75 mg, 75%). 1H NMR (DMSO-d6):
d 8.91 (s, 1H),
1H),7.65(d, J ¼ 13.6 Hz,1H),7.49(d,1H), 4.98(m,1H),4.47(s, 3H),4.27
(m,3H), 3.94(m,1H),2.79(s, 3H),2.74(s, 3H).IR(neat, cmꢁ1):1753.94,
1706.69, 1621.84, 1505.17, 1451.17, 1406.82. [M þ H]þ: 398.07.
8.19 (m, 2H), 7.74 (t, J ¼ 8.8 Hz, 1H), 7.66 (dd, J ¼ 13.6 Hz, 1.6 Hz, 1H),
7.49 (dd, J ¼ 8.8 Hz, 1.6 Hz, 1H), 5.06 (m, 1H), 4.89 (m, 2H), 4.46 (s,
3H), 4.23 (t, J ¼ 9.2 Hz, 1H), 3.95 (m, 1H). IR (neat, cmꢁ1): 3409.53,
1747.19, 1624.73, 1448.28, 1412.60. [M þ H]þ: 373.01.
6.1.18. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-([1,2,4]triazol-1-yl)methyl oxazolidin-2-one (19)
6.1.14. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-methanesulfonyloxy methyl oxazolidin-2-one (15)
To a solution of (R)-3-(4-(2-(2-methyltetrazol-5-yl)pyridin-5-
yl)-3-fluorophenyl)-5-hydroxy methyl oxazolidin-2-one 11 (1.00 g,
To a solution of (R)-3-(4-(2-(2-methyltetrazol-5-yl)pyridin-5-
yl)-3-fluorophenyl)-5-methanesulfonyloxy methyl oxazolidin-2-
one 15 (1.00 g, 2.23 mmol) in DMF (15 mL) was added NaH 60%
mineral oil (100 mg) and 1,2,4-triazole (300 mg, 4.34 mmol). After
being stirred at room temperature for 48 h, the reaction mixture
was poured into water and extracted with EtOAc. The organic layer
was washed with brine, dried over anhydrous MgSO4, filtered and
concentrated in vacuo. The residue was purified by column
2.70 mmol) and triethylamine (760
(50 mL) at 0 ꢀC was added dropwise methanesulfonyl chloride
(310 L, 4.05 mmol). After being stirred at room temperature for
mL, 5.40 mmol) in CH2Cl2
m
30 min, the reaction mixture was poured into water and extracted
with CH2Cl2. The organic layer was washed with brine, dried over

1036
W.B. Im et al. / European Journal of Medicinal Chemistry 46 (2011) 1027e1039
chromatography to obtain the title compound (400 mg, 43%). 1H
NMR (DMSO-d6): 8.91 (s, 1H), 8.57 (s, 1H), 8.19 (m, 2H), 8.00 (s,
1H), 7.74 (t, J ¼ 8.8 Hz,1H), 7.58 (dd, J ¼ 13.4 Hz,1.6 Hz,1H), 7.42 (dd,
J ¼ 8.0 Hz, 2.4 Hz, 1H), 5.13 (m, 1H), 4.64 (m, 2H), 4.46 (s, 3H), 4.28
(t, J ¼ 9.2 Hz, 1H), 3.99 (m, 1H). [M þ H]þ: 422.04.
with CH2Cl2. The organic layer was washed with brine, dried over
anhydrous MgSO4, filtered and concentrated in vacuo. The residue
was further purified by column chromatography to obtain the title
d
compound (85 mg, 71%). 1H NMR (DMSO-d6):
d 8.93 (s,1H), 8.20 (m,
3H), 7.74 (t, J ¼ 8.8 Hz, 1H), 7.66 (d, J ¼ 14.0 Hz, 1H), 7.48 (d,
J ¼ 8.4 Hz, 1H), 4.81 (m, 1H), 4.47 (s, 3H), 4.19 (t, J ¼ 9.2 Hz, 1H), 3.88
(m, 1H), 3.83 (s, 2H), 3.49 (m, 2H), 3.28 (s, 3H). IR (neat, cmꢁ1):
3298.64, 1736.58, 1654.62, 1625.70, 1510.95, 1440.56, 1410.67.
[M þ H]þ: 442.06.
6.1.19. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-([1,2,3]triazol-2-yl)methyl oxazolidin-2-one (20) and
(R)-3-(4-(2-(2-methyltetrazol-5-yl)pyridin-5-yl)-3-fluorophenyl)-
5-([1,2,3]-triazol-1-yl)methyl oxazolidin-2-one (21)
(R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluorophenyl)-
5-methanesulfonyloxy methyl oxazolidin-2-one 15 (200 mg,
0.450 mmol) and 1,2,3-triazole (46.0 mg, 0.670 mmol) was subjected
to the same reaction described for the synthesis of the compound 19.
The mixtures of compound 20 and compound 21 were separated by
column chromatography. Compound 20 (40 mg, 21%) and compound
21 (80 mg, 42%) was obtained. Compound 20: 1H NMR (DMSO-d6):
6.1.23. (S)-N-((3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-
fluorophenyl)-2-oxo-oxazo lidin-5-yl)methyl)furan-2-carboxamide
(25)
(S)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluorophenyl)-
5-aminomethyloxazolidin-2-one 23 (100 mg, 0.27 mmol) and 2-
furoyl chloride (320
reaction described for the synthesis of the compound 24 to give
the title compound (100 mg, 15%). 1H NMR (DMSO-d6):
8.93 (s,
mL, 0.320 mmol) was subjected to the same
d
d
8.90 (s,1H), 8.19 (m, 2H), 7.82 (s, 2H), 7.71 (t, J ¼ 8.8 Hz, 1H), 7.59 (dd,
1H), 8.73 (m, 1H), 8.21 (m, 2H), 7.85 (s, 1H), 7.74 (t, J ¼ 8.8 Hz,
1H), 7.66 (d, J ¼ 13.6 Hz, 1H), 7.49 (d, J ¼ 8.8 Hz, 1H), 7.15 (d,
J ¼ 3.6 Hz, 1H), 6.63 (m, 1H), 4.88 (m, 1H), 4.47 (s, 3H), 4.24 (t,
J ¼ 9.2 Hz, 1H), 3.93 (m, 1H), 3.60 (m, 2H). IR (neat, cmꢁ1):
3309.25, 1732.73, 1651.73, 1626.66, 1528.31, 1514.81, 1416.46.
[M þ H]þ: 463.94.
J ¼ 13.6 Hz, 2.0 Hz, 1H) 7.41 (dd, J ¼ 8.4 Hz, 2.0 Hz, 1H), 5.22 (m, 1H),
4.86 (m, 2H), 4.46 (s, 3H), 4.30 (t, J ¼ 9.6 Hz, 1H), 3.98 (m, 1H). IR (neat,
cmꢁ1): 1741.41, 1627.63, 1511.92, 1459.85, 1415.49. [M þ H]þ: 422.04.
Compound 21: 1H NMR (DMSO-d6):
d 8.90 (s, 1H), 8.18 (m, 3H), 7.75
(s, 1H), 7.72 (t, J ¼ 8.8 Hz, 1H), 7.59 (dd, J ¼ 13.6 Hz, 2.0 Hz, 1H), 7.42
(dd, J ¼ 8.8 Hz,1.6 Hz,1H), 5.22 (m,1H), 4.86 (m, 2H), 4.46 (s, 3H), 4.30
(t, J ¼ 9.2 Hz, 1H), 3.98 (m, 1H). IR (neat, cmꢁ1): 1752.01, 1624.73,
1511.92, 1457.92, 1408.75. [M þ H]þ: 422.04.
6.1.24. (S)-N-((3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-
fluorophenyl)-2-oxo-oxazolidin-5-yl)methyl)thiophene-2-carbox-
amide (26)
(S)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluorophenyl)-
5-aminomethyloxazolidin-2-one 23 (100 mg, 0.270 mmol) and 2-
6.1.20. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-azidomethyl oxazolidin-2-one (22)
To a solution of (R)-3-(4-(2-(2-methyltetrazol-5-yl)pyridin-5-
yl)-3-fluorophenyl)-5-methanesulfonyloxy methyl oxazolidin-2-
one 15 (1.00 g, 2.23 mmol) in DMF (20 mL) was added NaN3
(435 mg, 6.69 mmol). After being stirred at 90 ꢀC for 3 h, the reac-
tion mixture was poured into water and extracted with EtOAc. The
organic layer was washed with brine, dried over anhydrous MgSO4,
filtered and concentrated in vacuo. The residue was further purified
by column chromatography to obtain the title compound (830 mg,
thiophenecarbonyl chloride (34.0 mL, 0.320 mmol) was subjected to
the same reaction described for the synthesis of the compound 24
to give the title compound (100 mg, 77%). 1H NMR (DMSO-d6):
d
8.92 (s, 1H), 8.88 (m, 1H), 8.20 (m, 2H), 7.76 (m, 3H), 7.67 (d,
J ¼ 13.6 Hz, 1H), 7.49 (d, J ¼ 8.4 Hz, 1H), 7.15 (t, J ¼ 4.4 Hz, 1H), 4.90
(m, 1H), 4.47 (s, 3H), 4.25 (t, J ¼ 9.2 Hz, 1H), 3.92 (m, 1H), 3.63 (m,
2H). IR (neat, cmꢁ1): 3316.96, 1752.01, 1637.27, 1547.59, 1510.95,
1446.35, 1409.71. [M þ H]þ: 479.92.
94%). 1H NMR (DMSO-d6):
d 8.92 (s, 1H), 8.20 (m, 2H), 7.74 (t,
J ¼ 8.8 Hz, 1H), 7.69 (dd, J ¼ 13.6 Hz, 2.0 Hz, 1H), 7.51 (dd, J ¼ 8.4 Hz,
2.0 Hz, 1H), 5.06 (m, 1H), 4.47 (s, 3H), 4.26 (t, J ¼ 9.2 Hz, 1H), 4.00
(m, 2H), 3.90 (m, 1H).
6.1.25. (S)-2-(Benzyloxy)-N-((3-(3-fluoro-4-(6-(2-methyl-2H-
tetrazol-5-yl)pyridin-3-yl)phenyl)-2-oxooxazolidin-5-yl)methyl)
acetamide (27)
(S)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluorophenyl)-
5-aminomethyloxazolidin-2-one 23 (143 mg, 0.390 mmol) and
benzyloxyacetyl chloride (74.0 mL, 0.470 mmol) was subjected to
the same reaction described for the synthesis of the compound 24
to give the title compound (150 mg, 75%), which was used without
further purification.
6.1.21. (S)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-
fluorophenyl)-5-aminomethyloxazolidin-2-one (23)
The
(R)-3-(4-(2-(2-methyltetrazol-5-yl)pyridin-5-yl)-3-fluo-
rophenyl)-5-azidomethyl oxazolidin-2-one 22 (830 mg, 2.10 mmol)
was dissolved in MeOH (20 mL) and treated with Pd/C (83.0 mg)
under hydrogen. The reaction mixture was stirred for 2 h at room
temperature. The precipitate was filtered off and the filtrate was
evaporated in vacuo to obtain the title compound (590 mg, 76%). 1H
6.1.26. (S)-N-((3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-
fluorophenyl)-2-oxo-oxazolidin-5-yl)methyl)-2-hydroxy acetamide
(28)
NMR (DMSO-d6)
d
8.91 (s, 1H), 8.20 (m, 2H), 7.74 (t, J ¼ 8.8 Hz, 1H),
7.67 (dd, J ¼ 13.6 Hz, 1.6 Hz, 1H), 7.48 (dd, J ¼ 8.8 Hz, 1,6 Hz, 1H), 5.00
(bs, 2H), 4.79 (m,1H), 4.46 (s, 3H), 4.17 (t, J ¼ 8.8 Hz,1H), 3.93 (m,1H),
3.00 (m, 2H).
To
a
solution of (S)-2-(benzyloxy)-N-((3-(3-fluoro-4-(6-(2-
methyl-2H-tetrazol-5-yl)pyridin-3-yl)phenyl)-2-oxooxazolidin-5-yl)-
methyl)acetamide 27 (150 mg, 0.290 mmol) in MeOH (10 mL) was
added Pd/C (15.0 mg) under hydrogen. The reaction mixture was
stirred for 48 h at room temperature. The precipitate was filtered off
and the filtrate was evaporated in vacuo. The residue was further
purified by column chromatography to obtain the title compound
6.1.22. (S)-N-((3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-
3-fluorophenyl)-2-oxo-oxazol idin-5-yl)methyl)-2-methoxy
acetamide (24)
To a solution of (S)-3-(4-(2-(2-methyltetrazol-5-yl)pyridin-5-
yl)-3-fluorophenyl)-5-aminomethyloxazolidin-2-one 23 (100 mg,
(90 mg, 54%). 1H NMR (DMSO-d6):
d 8.93 (s, 1H), 8.21 (m, 2H), 8.10
(m, 1H), 7.75 (t, J ¼ 9.2 Hz, 1H), 7.67 (d, J ¼ 13.6 Hz, 1H), 7.49 (d,
J ¼ 9.2 Hz, 1H), 5.58 (m, 1H), 4.81 (m, 1H), 4.47 (s, 3H), 4.19 (t,
J ¼ 9.2 Hz, 1H), 3.89 (m, 1H), 3.84 (d, J ¼ 5.6 Hz, 2H), 3.49 (m, 2H). IR
(neat, cmꢁ1): 3368.07, 1741.41, 1646.91, 1625.70, 1532.17, 1408.75.
[M þ H]þ: 427.94.
0.270 mmol) and triethylamine (76.0
mL, 0.540 mmol) in CH2Cl2
(10 mL) was added dropwise methoxyacetyl chloride (30.0
mL,
0.320 mmol) at 0 ꢀC. After being stirred for 30 min at room
temperature, the solution was poured into water and extracted

W.B. Im et al. / European Journal of Medicinal Chemistry 46 (2011) 1027e1039
1037
6.1.27. (R)-3-(4-(2-(2-Methyl-[1,3,4]oxadiazol-5-yl)pyridin-5-yl)-
6.1.31. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
3-fluorophenyl)-5-(isoxazol-3-yl-oxy)methyl oxazolidin-2-one (29)
(R)-3-(4-(2-(2-Methyl-[1,3,4]oxadiazol-5-yl)pyridin-5-yl)-3-
fluorophenyl)-5-hydroxymethyl oxazolidin-2-one 12 (100 mg,
0.270 mmol) was subjected to the same reaction described for
the synthesis of the compound 13 to give the title compound
phenyl)-5-((S)-alanyloxy)methyl oxazolidin-2-one trifluoroacetic
acid (33)
(R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluorophenyl)-
5-hydroxy methyl oxazolidin-2-one 11 (2.00 g, 5.40 mmol) and Boc-
L
-alanine (1.28 g, 6.75 mmol) was subjected to the same reaction
described for the synthesis of the compound 32 to give the title
compound (2.07 g, 69%). Mp: 200 ꢀC. 1H NMR (DMSO-d6):
8.91 (s,
(53 mg, 45%). 1H NMR (CDCl3):
d 8.93 (s, 1H), 8.67 (s, 1H), 8.21
(s, 2H), 7.75 (t, J ¼ 8.8 Hz, 1H), 7.69 (dd, J ¼ 14.0 Hz, 1.6 Hz, 1H),
7.51 (dd, J ¼ 8.4 Hz, 2.0 Hz, 1H), 6.38 (s, 1H), 5.12 (m, 1H), 4.50
(m, 2H), 4.27 (t, J ¼ 9.6 Hz, 1H), 4.00 (m, 1H), 2.62 (s, 3H).
[M þ H]þ: 438.11.
d
1H), 8.42 (s, 3H), 8.20 (m, 2H), 7.75 (t, J ¼ 8.8 Hz, 1H), 7.67 (dd,
J ¼ 13.6 Hz, 1.6 Hz, 1H), 7.48 (dd, J ¼ 8.4 Hz, 2.0 Hz, 1H), 5.05 (m,
1H), 4.61 (dd, J ¼ 12.0 Hz, 2.0 Hz, 1H), 4.46 (s, 3H), 4.41 (dd,
J ¼ 12.4 Hz, 5.2 Hz, 1H), 4.26 (t, J ¼ 9.2 Hz, 1H), 4.18 (m, 1H), 3.96 (m,
1H), 1.36 (d, J ¼ 7.2 Hz, 3H). 13C NMR (DMSO-d6):
d 171.62, 163.88,
6.1.28. (R)-3-(4-(2-(2-Methyl-[1,3,4]oxadiazol-5-yl)pyridin-5-yl)-
3-fluorophenyl)-5-methanesulfonyl oxymethyl oxazolidin-2-one (30)
(R)-3-(4-(2-(2-Methyl-[1,3,4]oxadiazol-5-yl)pyridin-5-yl)-3-fluo-
rophenyl)-5-hydroxymethyl oxazolidin-2-one 12 (1.00 g, 2.70 mmol)
was subjected to the same reaction described for the synthesis of the
compound 15 to give the title compound (800 mg, 66%). 1H NMR
159.34, 154.37, 149.57, 145.10, 140.57, 137.23, 131.67, 130.98, 122.12,
118.59, 114.03, 105.51, 70.34, 65.43, 47.85, 45.99, 39.83, 15.69. IR
(neat, cmꢁ1): 2941.88, 1763.58, 1670.05, 1620.88, 1408.75.
[M þ H]þ: 441.96.
6.1.32. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-((S)-alanyloxy)methyl oxazolidin-2-one hydrochloride (34)
(R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluorophenyl)-
5-((S)-alanyloxy)methyl oxazolidin-2-one trifluoroacetic acid 33
(500 mg, 0.920 mmol) was dissolved in water (20 mL) and the pH
was adjusted to pH 5 with addition of saturated NaHCO3 solution.
The aqueous layer was extracted with EtOAc (30 mL) and the
organic layer was washed with brine, dried over anhydrous MgSO4,
filtered, concentrated in vacuo. The residue was dissolve in diethyl
ether and 2 N HCl in diethyl ether solution (1.38 mL, 2.76 mmol)
was added slowly. The formed precipitate was filtered off to obtain
the title compound (265 mg, 62%). Mp: 170 ꢀC. 1H NMR (DMSO-d6):
(DMSO-d6):
d
8.95 (s,1H), 8.23 (s, 2H), 7.77 (t, J ¼ 8.8 Hz,1H), 7.70 (dd,
J ¼ 13.6 Hz, 1.6 Hz, 1H), 7.52 (dd, J ¼ 8.8 Hz, 1.6 Hz, 1H), 5.09 (m, 1H),
4.61 (m, 2H), 4.26 (t, J ¼ 9.2 Hz, 1H), 3.91 (m, 1H), 3.26 (s, 3H), 2.63
(s, 3H).
6.1.29. (R)-3-(4-(2-(2-Methyl-[1,3,4]oxadiazol-5-yl)pyridin-5-yl)-
3-fluorophenyl)-5-([1,2,3]triazol-1-yl)methyl oxazolidin-2-one (31)
(R)-3-(4-(2-(2-Methyl-[1,3,4]oxadiazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-methanesulfonyl oxymethyl oxazolidin-2-one 30 (100 mg,
0.220 mmol) and 1,2,3-triazole (23.0 mg, 0.330 mmol) was subjected
to the same reaction described for the synthesis of the compound 19 to
give the title compound (46 mg, 49%). 1H NMR (DMSO-d6):
d 8.92 (s,
d
8.92 (s, 1H), 8.52 (bs, 3H), 8.20 (m, 2H), 7.75 (t, J ¼ 8.8 Hz, 1H), 7.66
1H), 8.20 (s, 2H), 8.17 (s, 1H), 7.75 (s, 1H), 7.73 (t, J ¼ 9.2 Hz, 1H), 7.61
(dd, J ¼ 13.6 Hz, 2.4 Hz, 1H), 7.43 (dd, J ¼ 8.4 Hz, 2.4 Hz, 1H), 5.18 (m,
1H), 4.85 (m, 2H), 4.29 (t, J ¼ 9.2 Hz, 1H), 3.96 (m, 1H), 2.62 (s, 3H). IR
(neat, cmꢁ1): 1745.26, 1623.77, 1518.67, 1469.49, 1412.60. [M þ H]þ:
422.03.
(dd, J ¼ 13.6 Hz, 2.0 Hz,1H), 7.49 (dd, J ¼ 8.8 Hz, 2.4 Hz,1H), 5.05 (m,
1H), 4.60 (dd, J ¼ 12.8 Hz, 2.4 Hz, 1H), 4.46 (s, 3H), 4.41 (dd,
J ¼ 12.0 Hz, 4.8 Hz, 1H), 4.26 (t, J ¼ 9.2 Hz, 1H), 4.18 (m, 1H), 4.00 (m,
1H), 1.37 (d, J ¼ 6.8 Hz, 3H). 13C NMR (DMSO-d6):
d 169.80, 163.85,
159.30, 153.81, 149.47, 145.11, 140.23, 137.29, 131.58, 131.04, 122.14,
118.91, 114.29, 105.65, 70.34, 65.33, 47.78, 46.04, 39.65, 15.58. IR
(neat, cmꢁ1): 2858.95, 1764.55, 1749.12, 1626.66, 1405.85. [M þ H]þ:
441.96.
6.1.30. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-((S)-prolinyl oxy)methyl oxazolidin-2-one trifluoroacetic
acid (32)
To a solution of (R)-3-(4-(2-(2-methyltetrazol-5-yl)pyridin-5-
yl)-3-fluorophenyl)-5-hydroxy methyl oxazolidin-2-one 11 (1.00 g,
6.1.33. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-(b-alanyloxy)methyl oxazolidin-2-one trifluoroacetic
2.70 mmol) in DMF (25 mL) was added Boc-L-proline (727 mg,
acid (35)
3.38 mmol), 1,3-dicyclohexylcarbodiimide (836 mg, 4.05 mmol)
and 4-dimethylaminopyridine (50.0 mg, 0.409 mmol) at room
temperature. After being stirred for 10 h at room temperature, the
solution was poured into water and extracted with EtOAc. The
organic layer was washed with brine, dried over anhydrous
MgSO4, filtered, concentrated in vacuo and purified by column
chromatography. The obtained compound was dissolved in CH2Cl2
(70 mL) and treated with trifluoroacetic acid (30 mL). The reaction
mixture was stirred for 2 h at room temperature. The residue was
washed with EtOH and diethyl ether and concentrated in vacuo to
give the title compound (960 mg, 61%). Mp: 174 ꢀC. 1H NMR
(R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluorophenyl)-
5-hydroxy methyl oxazolidin-2-one 11 (1.50 g, 4.05 mmol) and Boc-
b
-alanine (960 mg, 5.06 mmol) was subjected to the same reaction
described for the synthesis of the compound 32 to give the title
compound (970 mg, 43%). Mp: 173 ꢀC. 1H NMR (DMSO-d6):
8.91 (s,
d
1H), 8.20 (m, 2H), 7.75 (t, J ¼ 8.8 Hz, 1H), 7.73 (bs, 3H), 7.68 (dd,
J ¼ 13.2 Hz, 2.4 Hz,1H), 7.48 (dd, J ¼ 8.8 Hz, 2.4 Hz,1H), 5.02 (m,1H),
4.46 (s, 3H), 4.36 (m, 2H), 4.26 (t, J ¼ 9.6 Hz, 1H), 3.93 (m, 1H), 3.02
(m, 2H), 2.70 (t, J ¼ 7.2 Hz, 2H). 13C NMR (DMSO-d6):
d 169.82,
163.60, 159.05, 153.63, 149.22, 144.86, 140.01, 136.99, 131.38, 130.74,
121.95,118.72,114.09,105.51, 70.47, 64.69, 46.19, 39.89, 34.62, 31.43.
IR (neat, cmꢁ1): 2962.13, 1747.19, 1669.09, 1623.77, 1408.75.
[M þ H]þ: 442.06.
(DMSO-d6):
d 9.25 (bs, 2H), 8.91 (s, 1H), 8.20 (m, 2H), 7.76 (t,
J ¼ 8.8 Hz, 1H), 7.65 (dd, J ¼ 13.6 Hz, 2.4 Hz, 1H), 7.48 (dd,
J ¼ 8.4 Hz, 2.4 Hz, 1H), 5.05 (m, 1H), 4.57 (dd, J ¼ 12.0 Hz, 2.4 Hz,
1H), 4.45 (s, 3H), 4.41 (dd, J ¼ 12.0 Hz, 5.2 Hz, 1H), 4.26 (t,
J ¼ 9.2 Hz, 1H), 3.96 (m, 1H), 3.23 (m, 2H), 2.21 (m, 2H), 1.92 (m,
6.1.34. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-(
(R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluorophenyl)-
-alanyloxy)methyl oxazolidin-2-one trifluoroacetic acid 35
b-alanyloxy) methyl oxazolidin-2-one hydrochloride (36)
3H). 13C NMR (DMSO-d6):
d 168.41, 163.57, 159.02, 153.54, 149.18,
144.86, 139.97, 136.99, 131.34, 130.77, 121.92, 118.72, 114.07, 105.49,
70.31, 65.68, 58.56, 46.02, 45.45, 38.87, 27.78, 23.06. IR (KBr,
cmꢁ1): 3447.23, 1746.89, 1655.80. [M þ H]þ: 468.07. HRMS [EI-MS]:
m/z, calculated for [C24H23F4N7O6eTFA: C22H22FN7O4] 467.4530,
found, 467.1862 [C22H22FN7O4].
5-(b
(1.39 g, 2.50 mmol) was subjected to the same reaction described
for the synthesis of the compound 34 to give the title compound
(656 mg, 55%). Mp: 197 ꢀC. 1H NMR (DMSO-d6):
d
8.91 (s, 1H), 8.22
(m, 2H), 8.01 (bs, 3H), 7.76 (t, J ¼ 8.8 Hz, 1H), 7.65 (dd, J ¼ 13.6 Hz,

1038
W.B. Im et al. / European Journal of Medicinal Chemistry 46 (2011) 1027e1039
2.4 Hz, 1H), 7.48 (dd, J ¼ 8.8 Hz, 2.4 Hz, 1H), 5.02 (m, 1H), 4.46 (s,
3H), 4.36 (m, 2H), 4.23 (t, J ¼ 9.2 Hz, 1H), 3.95 (m, 1H), 3.00 (m,
(500 mg, 0.860 mmol) was subjected to the same reaction described
for the synthesis of the compound 34 to give the title compound
2H), 2.74 (t, J ¼ 7.2 Hz, 2H). 13C NMR (DMSO-d6):
d
169.79, 163.57,
(200 mg, 46%). Mp: 196 ꢀC. 1H NMR (DMSO-d6):
d 8.92 (s, 1H), 8.54
159.01, 153.60, 149.15, 144.80, 139.97, 136.94, 131.34, 130.72,
121.90, 118.67, 114.05, 105.49, 70.45, 64.66, 46.23, 39.61, 34.51,
31.37. IR (neat, cmꢁ1): 2897.52, 1741.41, 1624.73, 1407.78.
[M þ H]þ: 442.06.
(bs, 3H), 8.20 (m, 2H), 7.76 (t, J ¼ 8.8 Hz, 1H), 7.65 (dd, J ¼ 13.2 Hz,
2.4 Hz, 1H), 7.49 (dd, J ¼ 8.8 Hz, 2.4 Hz, 1H), 5.04 (m, 1H), 4.58 (dd,
J ¼ 12.4 Hz, 2.8 Hz,1H), 4.46 (s, 3H), 4.41 (dd, J ¼ 12.4 Hz, 5.2 Hz,1H),
4.26 (t, J ¼ 9.6 Hz, 1H), 3.95 (m, 2H), 2.17 (m, 1H), 0.97 (d, J ¼ 7.2 Hz,
3H), 0.94 (d, J ¼ 7.2 Hz, 3H). 13C NMR (DMSO-d6):
d 168.78, 163.84,
6.1.35. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-glycyloxy methyl oxazolidin-2-one trifluoroacetic acid (37)
(R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluorophenyl)-
5-hydroxy methyl oxazolidin-2-one 11 (1.50 g, 4.05 mmol) and Boc-
glycine (2.36 g, 13.5 mmol) was subjected to the same reaction
described for the synthesis of the compound 32 to give the title
159.28, 153.73, 149.45, 145.11, 140.21, 137.22, 131.56, 130.98, 122.11,
118.91,114.28,105.66, 70.30, 65.29, 57.23, 45.99, 29.31,18.34,17.40. IR
(neat, cmꢁ1): 2876.31, 1750.08, 1627.63, 1509.99, 1409.71. [M þ H]þ:
470.09. HRMS [EI-MS]: m/z, calculated for [C22H25ClFN7O4eHCl:
C22H24FN7O4] 469.1874, found, 469.7425 [C22H24FN7O4].
compound (4.47 g, 76%). Mp: 199 ꢀC. 1H NMR (DMSO-d6):
d
8.92 (s,
6.1.39. (R)-[3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-2-oxo-5-oxazolidinyl]methyl phosphate (41)
To a solution of (R)-3-(4-(2-(2-methyltetrazol-5-yl)pyridin-5-
yl)-3-fluorophenyl)-5-hydroxy methyl oxazolidin-2-one 11 (1.00 g,
2.70 mmol) in triethyl phosphate (14.8 mL) was added phospho-
1H), 8.19 (s, 3H), 8.17 (m, 2H), 7.77 (t, J ¼ 8.8 Hz, 1H), 7.69 (dd,
J ¼ 13.2 Hz, 2.4 Hz, 1H), 7.49 (dd, J ¼ 8.8 Hz, 2.4 Hz, 1H), 5.00 (m,
1H), 4.46 (m, 2H), 4.47 (s, 3H), 4.24 (t, J ¼ 9.6 Hz, 1H), 3.92 (m, 1H),
3.90 (s, 2H). 13C NMR (DMSO-d6):
d 167.36, 163.42, 159.05, 153.53,
148.91, 144.63, 140.21, 137.35, 131.53, 130.76, 122.13, 118.56, 114.18,
105.63, 70.48, 65.16, 46.17, 40.13, 40.05. IR (neat, cmꢁ1): 2875.34,
1740.44, 1675.84, 1621.84, 1407.78. [M þ H]þ: 427.94. HRMS [EI-
MS]: m/z, calculated for [C21H19F4N7O6eTFA: C19H18FN7O4]
427.1404, found, 427.1482 [C19H18FN7O4].
rous oxychloride (740 mL, 7.94 mmol). The solution was stirred for
2 h at room temperature. The reaction mixture was extracted with
ethyl acetate and stirred for 30 min. And the solution was then
poured into water and stirred for 2 h at 0 ꢀC. The product is isolated
by filtration and washed with acetone to obtain the title compound
(815 mg, 67%). 1H NMR (DMSO-d6):
d 8.92 (s, 1H), 8.20 (m, 2H), 7.74
6.1.36. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-glycyloxy methyl oxazolidin-2-one hydrochloride (38)
(R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluo-
(t, J ¼ 8.8 Hz, 1H), 7.66 (dd, J ¼ 13.6 Hz, 2.0 Hz, 1H), 7.50 (dd,
J ¼ 8.8 Hz, 2.0 Hz, 1H), 4.95 (m, 1H), 4.46 (s, 3H), 4.21 (t, J ¼ 9.6 Hz,
1H), 4.05 (m, 2H), 3.91 (m, 1H).
rophenyl)-5-glycyloxy methyl oxazolidin-2-one trifluoroacetic acid
37 (1.39 g, 2.50 mmol) was subjected to the same reaction described
for the synthesis of the compound 34 to give the title compound
6.1.40. (R)-[3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-2-oxo-5-oxazolidinyl] methyl disodium phosphate (42)
To a solution of (R)-[3-(4-(2-(2-methyltetrazol-5-yl)pyridin-5-
yl)-3-fluorophenyl)-2-oxo-5-oxazolidinyl]methyl phosphate 41
(400 mg, 0.890 mmol) in methanol (20 mL) was added NaOMe
0.5 M solution in MeOH (3.92 mL, 1.96 mmol). The reaction mixture
was stirred for 2 h at room temperature. The precipitate was
filtered off to obtain the title compound (300 mg, 68%). Mp:
(265 mg, 62%). Mp: 178 ꢀC. 1H NMR (DMSO-d6):
d 8.91 (s, 1H), 8.48
(bs, 3H), 8.18 (m, 2H), 7.75 (t, J ¼ 8.8 Hz, 1H), 7.65 (dd, J ¼ 13.6 Hz,
2.0 Hz,1H), 7.49 (dd, J ¼ 8.4 Hz, 2.0 Hz,1H), 5.03 (m,1H), 4.48 (m, 2H),
4.46(s, 3H), 4.24(t, J ¼ 9.6 Hz,1H), 3.99(m,1H), 3.86(m, 2H).13C NMR
(DMSO-d6):
d 167.26, 163.41, 159.05, 153.59, 148.94, 144.60, 140.11,
137.33,131.51,130.74,122.09,118.58,114.17,105.61, 70.47, 65.13, 46.14,
40.16, 40.05. IR (KBr, cmꢁ1): 3440.23, 1753.89, 1622.32. [M þ H]þ:
427.94. HRMS [EI-MS]: m/z, calculated for [C19H19ClFN7O4eHCl:
C19H18FN7O4] 427.1404, found, 427.1482 [C19H18FN7O4].
decomposed (>200 ꢀC). 1H NMR (D2O):
d 8.34 (s, 1H), 7.71 (d,
J ¼ 8.0 Hz, 1H), 7.63 (d, J ¼ 8.4 Hz, 1H), 7.06 (m, 2H), 6.90 (d,
J ¼ 8.8 Hz, 1H), 4.79 (m, 1H), 4.63 (s, 3H), 3.92 (t, J ¼ 9.2 Hz, 1H), 3.79
(m, 3H). 13C NMR (D2O):
d 163.16, 159.14, 155.63, 148.28, 142.64,
6.1.37. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-((S)-valyloxy)methyl oxazolidin-2-one trifluoroacetic
acid (39)
139.22, 137.10, 131.81, 130.02, 121.97, 118.17, 113.98, 105.92, 73.65,
64.48, 46.92, 40.14. IR (neat, cmꢁ1): 3317.93, 1753.94, 1622.80,
1512.88, 1455.99, 1410.67. [M þ H]þ: 494.85.
(R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluorophenyl)-
5-hydroxy methyl oxazolidin-2-one 11 (2.07 g, 5.58 mmol) and Boc-
L-
6.2. Biological evaluation
valine (1.52 g, 6.99 mmol) was subjected to the same reaction
described for the synthesis of the compound 32 to give the title
6.2.1. Assay for in vitro antibacterial activity
compound (2.28 g, 70%). Mp: 168 ꢀC. 1H NMR (DMSO-d6):
d
8.92 (s,
In vitro antimicrobial activity was tested by the CLSI agar dilu-
tion method [27]. Media used were Mueller-Hinton agar (Becton
Dickinson, Sparks, MD, USA) for testing S. aureus and Enterococcus
faecium, and Haemophilus test medium for Hi. All tested strains
were clinical isolates from patients at a Korean tertiary-care
hospital. The MIC was defined as the lowest drug concentration
that completely inhibited bacterial growth. Linezolid obtained from
a commercial source was used as a comparator agent.
1H), 8.40 (s, 3H), 8.21 (m, 2H), 7.76 (t, J ¼ 8.8 Hz, 1H), 7.65 (dd,
J ¼ 13.2 Hz, 2.0 Hz, 1H), 7.48 (dd, J ¼ 8.4 Hz, 2.4 Hz, 1H), 5.05 (m, 1H),
4.63 (dd, J ¼ 12.4 Hz, 2.4 Hz, 1H), 4.47 (s, 3H), 4.43 (dd, J ¼ 12.4 Hz,
5.6 Hz, 1H), 4.28 (t, J ¼ 9.6 Hz, 1H), 4.01 (d, J ¼ 4.4 Hz, 1H), 3.93 (m,
1H), 2.14 (m, 1H), 0.98 (d, J ¼ 7.2 Hz, 3H), 0.95 (d, J ¼ 7.2 Hz, 3H). 13C
NMR (DMSO-d6):
d 168.61, 163.62, 159.05, 153.53, 149.20, 144.86,
140.00, 136.97, 131.38, 130.75, 121.93, 118.72, 114.05, 105.48, 70.32,
65.36, 57.34, 46.12, 29.49, 18.39, 17.48. IR (KBr, cmꢁ1): 3437.11, 1771.02,
1743.77, 1683.04. [M þ H]þ: 470.09. HRMS [EI-MS]: m/z, calculated
for [C24H25F4N7O6eTFA: C22H24FN7O4] 469.1874, found, 469.7425
[C22H24FN7O4].
6.2.2. Assay for solubility
To test aqueous solubility, 2 mg of test compound was added to
0.2 mL distilled water. After vortex-mixing for 2 min, its turbidity
was observed with the naked eye. If compound is completely dis-
solved, another 2 mg of test compound was added to the solution
up to five times (final solubility was noted as >50 mg/mL). If the
solution was not clear when 2 mg of test compound was added to
0.2 mL distilled water at first, other 0.05 mL aliquots of distilled
6.1.38. (R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluoro-
phenyl)-5-((S)-valyloxy) methyl oxazolidin-2-one hydrochloride (40)
(R)-3-(4-(2-(2-Methyltetrazol-5-yl)pyridin-5-yl)-3-fluorophenyl)-
5-((S)-valyloxy)methyl oxazolidin-2-one trifluoroacetic acid 39

W.B. Im et al. / European Journal of Medicinal Chemistry 46 (2011) 1027e1039
1039
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