Synthesis and antibacterial activity of 5-substituted oxazolidinones

Article abstract of DOI:10.1016/S0968-0896(02)00423-6

A series of 5-substituted oxazolidinones with varying substitution at the 5-position of the oxazolidinone ring were synthesized and their in vitro antibacterial activity was evaluated. The compounds demonstrated potent to weak antibacterial activity. A novel compound (PH-027) demonstrated potent antibacterial activity, which is comparable to or better than those of linezolid and vancomycin against antibiotic-susceptible standard and clinically isolated resistant strains of gram-positive bacteria. Although the presence of the C-5-acetamidomethyl functionality at the C-5 position of the oxazolidinones has been widely claimed and reported as a structural requirement for optimal antimicrobial activity in the oxazolidinone class of compounds, our results from this work identified the C-5 triazole substitution as a new structural alternative for potent antibacterial activity in the oxazolidinone class.

Full text of DOI:10.1016/S0968-0896(02)00423-6

Bioorganic & Medicinal Chemistry 11 (2003) 35–41
Synthesis and Antibacterial Activity of
5-Substituted Oxazolidinones
O. A. Phillips,a,* E. E. Udo,b A. A. M. Alic and N. Al-Hassawia
aDepartment of Pharmaceutical Chemistry, Faculty of Pharmacy, Kuwait University, PO Box 24923, Safat 13110, Kuwait
bDepartment of Microbiology, Faculty of Medicine, Kuwait University, PO Box 24923, Safat 13110, Kuwait
cDepartment of Chemistry, Faculty of Science, Kuwait University, PO Box 5969, Safat 13060, Kuwait
Received 10 June 2002; accepted 20 August 2002
Abstract—A series of 5-substituted oxazolidinones with varying substitution at the 5-position of the oxazolidinone ring were syn-
thesized and their in vitro antibacterial activity was evaluated. The compounds demonstrated potent to weak antibacterial activity.
A novel compound (PH-027) demonstrated potent antibacterial activity, which is comparable to or better than those of linezolid
and vancomycin against antibiotic-susceptible standard and clinically isolated resistant strains of gram-positive bacteria. Although
the presence of the C-5-acetamidomethyl functionality at the C-5 position of the oxazolidinones has been widely claimed and reported
as a structural requirement for optimal antimicrobial activity in the oxazolidinone class of compounds, our results from this work
identified the C-5 triazole substitution as a new structural alternative for potent antibacterial activity in the oxazolidinone class.
# 2002 Elsevier Science Ltd. All rights reserved.
Introduction
Recent studies have indicated that the oxazolidinones
bind to 50S subunits, of the 70S ribosome, but not to
30S subunits; thus inhibiting bacterial translation at the
initiation phase of protein synthesis.4,5 Linezolid has
been shown to inhibit the binding of N-for-
mylmethionine-transfer-RNA (fMet-tRNA) to 70S
ribosomes.6 Since the oxazolidinones have a unique
mode of action,5 by inhibiting protein synthesis early in
translation, cross-resistance with other antimicrobial
agents is believed to be unlikely. However, the potential
for the development of resistance cannot be ignored.
Already resistance to linezolid has been reported in
clinical isolates of VREF7 and S. aureus8 in the USA.
The potential for resistance developments, warrants
investigation of newer and more effective antimicrobial
agents.
The rising prevalence of multi-drug resistant gram-
positive bacteria continues to provide impetus for the
search and discovery of novel antimicrobial agents
active against these pathogens. Oxazolidinones are a
novel class of totally synthetic antimicrobial agents
active against gram-positive pathogenic bacteria includ-
ing methicillin-resistant Staphylococcus aureus (MRSA),
penicillin-resistant Streptococcus pneumoniae (PRSP)
and
vancomycin-resistant
Enterococcus
faecium
(VREF).1,2 Linezolid (ZYVOX1, 1; Chart 1) is the first
member of this class recently licensed in the USA and
Europe, and available in both iv and oral formulations.
Linezolid is efficacious in treating skin and soft tissue
infections, pneumonia and bacteremia; and is particu-
larly effective against infections caused by MRSA,
PRSP and VREF.3
Concerning the C-5 substituent on the oxazolidinone
ring, Dupont9 and Pharmacia10 groups concluded that
the acetylaminomethyl moiety was the best substituent
at this position of the oxazolidinone for optimal anti-
bacterial activity. However, recent studies have reported
the introduction of substituents such as the 5-thiourea
2a and 5-thiocarbamate11 2b, 5-dithiocarbamate12 2c
and nitrogen substituted heterocyclic aryl moieties13,14
in 3 as potential replacements for the acetamidomethyl
side chain at the C-5 position (Chart 1).
Oxazolidinones are antibacterial agents that act pri-
marily against a wide spectrum of gram-positive and
anaerobic bacteria by inhibiting protein synthesis.1
*Corresponding author. Tel.: +965-531-2300x6048; fax: +965-534-
2807; e-mail: dphillips@hsc.kuniv.edu.kw
0968-0896/03/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0968-0896(02)00423-6

36
O. A. Phillips et al. / Bioorg. Med. Chem. 11 (2003) 35–41
Chart 1. Structures of oxazolidinone antibacterial agents.
In this paper, we describe the synthesis and antibacterial
activity of a series of oxazolidinone derivatives bearing
the five-membered ring nitrogen heterocycles (triazolyl
and imidazolyl moieties) and the hydroxamic acid
functionality at the C-5 position.
vice versa. This observed NOE indicated the closer
proximity of the triazole C-50 proton to the methylene
protons (4.88 ppm) in 8, compared to the lack of NOE
observed for 9 (ca. 5.10 ppm).
Antimicrobial activity
All newly synthesized oxazolidinone derivatives were
tested for antibacterial activity against both standard
and clinically isolated strains of gram-negative and
gram-positive pathogenic bacteria. Initially, suscept-
ibility testing was carried out by measuring the inhibi-
tory zone diameters on Mueller-Hinton (MH) agar,
with conventional paper disk containing 30 mg of each
compound; and the inhibitory zone diameters were read
and rounded up to the nearest whole numbers (mm) for
analysis. From the inhibition zone diameter data analy-
sis, the 5-triazole oxazolidinone compound PH-027 was
identified as the most active compound with an inhibi-
tory zone diameter of 39 mm for S. aureus ATCC 25923,
MRSA, and methicillin-sensitive Staphylococci epi-
dermidis ATCC 12228 (coagulase-negative staphylo-
cocci) strain. The 4-acetyltriazole derivative 8 and the
hydroxamic acid derivative 17 demonstrated moderate
activity with inhibition zone diameter of 19 mm for
antibiotic-susceptible strains of S. aureus ATCC 25923
and S. epidermidis ATCC 12228; and clinical isolates of
MRSA, methicillin-sensitive S. aureus (MSSA), methi-
cillin-resistance coagulase-negative staphylococci (MR-
CNS) and methicillin-sensitive coagulase-negative sta-
phylococci (MS-CNS). The other related compounds in
this study demonstrated only weak antibacterial activ-
ity. Furthermore, none of the compounds evaluated in
this class were active against gram-negative bacteria
strains including Escherichia coli (E. coli ATCC 25922),
Haemophilus influenzae (H. influenzae ATCC 49247)
and Pseudomonas aeruginosa (P. aeruginosa ATCC
27853), with inhibitory zone diameter of <17 mm. The
reported inhibitory zone diameters for linezolid 1 (Chart
1) of ꢀ21 mm for susceptible and ꢁ17 mm for resis-
tance16 were referred to as standard reference values in
this study.
Chemistry
The key intermediates, 5-methanesulfonate oxazolidi-
none 6 and 5-azide oxazolidinone 7 were prepared from
4 and 5 according to the usual method.10,15 Further
chemical transformation of the azide intermediate 7 by
condensation with 3-butyn-2-one in dimethoxyethane
(DME) gave 4-acetyltriazolyl and 5-acetyltriazolyl oxa-
zolidinones 8 and 9, respectively. Reaction of 8 with
methylhydroxylamine hydrochloride gave 10 as mixture
of the E and Z isomers. Treatment of 7 with acetylene
afforded the 5-triazole oxazolidinone PH-027 (Scheme
1). The disubstituted triazole derivative 11 was prepared
by treatment of 7 with dimethyl acetylenedicarboxylate,
while basic hydrolysis of the ester functionalities gave
the disodium salt 12. The reaction of intermediate 6
with sodium hydride treated imidazole in DMF affor-
ded the imidazole derivative 13. Treatment of 6 with tert-
butyl N-(tert-butoxycarbonyloxy)carbamate and sodium
hydride in DMF gave 14, which was deprotected with
trifluoroacetic acid in DCM to give the N-hydroxylamine
15. Diacetylation of the hydroxylamine 15 with acetic
anhydride in the presence of triethylamine to give 16,
which was followed by basic hydrolysis of the ester to
give the hydroxamic acid derivative 17 (Scheme 2).
Results and Discussion
Chemistry
The reaction of the 5-azide oxazolidinone 7 with 3-
butyn-2-one yielded the 4-acetyltriazolyl oxazolidinone
8 (R0=–CH3CO, R00=H) and 5-acetyltriazolyl oxazoli-
dinone 9 (R0=H, R00=–CH3CO; Scheme 1) respectively
in approximately 10:1 ratio as observed in the 1H NMR
spectrum. The structural assignment to these two posi-
tional isomers was accomplished by nuclear Overhauser
enhancement (NOE) studies. Irradiation of the triazole
C-50 proton signal (8.80 ppm) of 8 resulted in about
12% enhancement of the methylene protons signal
(–CH2–, 4.88 ppm) bonded to the C-5 position of the
oxazolidinone ring as observed in the NMR spectra and
The minimum inhibitory concentrations (MIC’s, mg/
mL) of compounds 8, 10, 15, 17 and PH-027 in com-
parison to those of linezolid and vancomycin against
antibiotic-susceptible standard and clinically isolated
resistant strains of gram-positive bacteria were deter-
mined. The results are presented in Tables 1 and 2.
Amongst all the compounds tested, the triazole oxazo-

O. A. Phillips et al. / Bioorg. Med. Chem. 11 (2003) 35–41
37
Scheme 1. Synthesis of 5-triazolyl and 5-imidazolyl oxazolidinone derivatives.
lidinone PH-027, demonstrated the most potent anti-
bacterial activity against both sensitive and resistant
gram-positive bacteria strains, including MRSA,
MSSA, MS-CNS, MR-CNS, PRSP and enterococci
(Enterococcus faecium and Enterococcus faecalis). None
of the compounds showed activity against gram-nega-
tive bacteria including E. coli, H. influenzae and P. aer-
uginosa with MIC’s of >32 mg/mL.
those of linezolid and vancomycin (Table 1). In parti-
cular, the MIC values of PH-027 against vancomycin-
susceptible E. faecium (VSE), vancomycin-intermediate
resistant E. faecalis (VIRE) and vancomycin-resistant E.
faecalis (VRE) were 0.5, 0.5 and 2 mg/mL, respectively,
compared to an MIC of 2 mg/mL demonstrated by line-
zolid against these strains. However, the MIC’s of van-
comycin against the same strains were 4, 8 and >32 mg/
mL, respectively.
Against some of the gram-positive bacteria strains tes-
ted, the triazole oxazolidinone PH-027 demonstrated
MIC values comparable to or 1- to 2-fold lower than
Attempts were made to correlate the antibacterial
activities of these compounds to the calculated log of
Scheme 2. Synthesis of hydroxamic acid oxazolidinone derivatives.

38
O. A. Phillips et al. / Bioorg. Med. Chem. 11 (2003) 35–41
Table 1. Spectrum of activity against susceptible and resistant gram-
positive clinical isolates
From our study, mono- and di-substitution on the tria-
zole C-4 and C-5 positions as found in 8, 9, 10, 11 and
12 resulted in complete loss of antibacterial activity
against both gram-negative and gram-positive bacteria
irrespective of their Clog P values. This observation
may suggest the negating effects of the bulky group(s)
on antibacterial activity, which may result from
increased steric effects at these positions, due to sub-
stitutions on the triazole moiety. Previous studies9,18
have suggested that the oxazolidinone-binding site is
very sensitive to steric environment about the 5-position
of the oxazolidinone. Furthermore, the replacement of
the triazole moiety in PH-027 with Clog P=0.89, for
imidazole as in 13 (Clog P=1.26) also resulted in com-
plete loss of antibacterial activity. The imidazole oxa-
zolidinone, compound 13 demonstrated an inhibitory
zone diameter of <17 mm and MIC of >32 mg/mL
against all the bacteria strains tested. The superior anti-
bacterial activity of PH-027 may be interpreted as an
indication of a stronger intrinsic ‘binding attraction’ for
the triazole-oxazolidinone at the site of action.
Organism
Strain no.
MIC (mg/mL) for
8
10 15 17 PH-027 Lin Van
S. aureus
S. aureus
MRSA
MRSA
MSSA
MSSA
S. epidermidis
S. epidermidisa
S. haemolyticus
S. pneumoniae
S. pneumoniaeb
E. faecalis
E. faecium (VSE)
E. faecalis (VIRE)
E. faecalis (VRE)
ATCC25923 >32 >32 >32 >321
ATCC25913 32 >32 >32 >321
2
1
2
2
2
2
1
1669
3014
249189
1191918
ATCC12228
1777365
8186366
32 >32 >3216
2
1
2
3216 32320.5 0.5
32 >32 >3216 0.5
16 >32 >32321
1
2
2
8
32 >32 >3216
32 >3216 0.5
1
2
1
2
2
32 >32 >32 >320.5 0.5
ATCC49619 >32 >32 >32 >322
99.388 >32 >32 >32 >320.5
ATCC29212 16 32 >32 >321
1
1
1
2
2
2
1
2
4
8
1
7
>32 >32 >32 >320.5
>32 >32 >32 >320.5
ENT 90 >32 >32 >32 >322
2
2
>32
>32
E. faecalis (VRE) ENT 11U >32 >32 >32 >322
aMethicillin resistant strain (MR-CNS).
bPenicillin resistant strain (PRSP).
The hydroxamic acid oxazolidinone derivative 17 with
Clog P value of 1.31 demonstrated only minimal anti-
bacterial activity with inhibition zone diameter of
18 mm against S. aureus, and coagulase-negative sta-
phylococci strains. Compound 17 demonstrated an
MIC range of 16–>32 mg/mL against all sensitive and
resistant clinically isolated bacteria strains tested in this
study. This further strengthened previously indicated
significance of the amide-hydrogen (N–H) present in
linezolid for antibacterial activity,18 compared to the
hydroxamic acid-hydrogen (N–OH) present in 17. The
replacement of the amide hydrogen (NH) by methyl
group (NCH3)19 and substitution of the amide func-
tionality for other groups, namely NH2, OH, and mor-
pholinyl18 resulted in compounds with weaker
antibacterial activity. However, other structural
requirements including the presence of the 3-fluoro and
4-morpholinyl groups on the phenyl ring, and the oxa-
zolidinone functionality are highly essential for anti-
bacterial activity of this class of compounds among
other factors.18 In addition, all the intermediates (14, 15,
and 16) leading to 17 were void of antibacterial activity;
this probably is expected for 16, with very high Clog P
value of 4.38.
partition coefficient (Clog P).17 However, no direct
correlation could be established between the Clog P and
antibacterial activity (Table 2). The Clog P values of
compounds 8 (0.78) and 9 (0.78) were identical and were
comparable to that of linezolid (Clog P=0.76). How-
ever, both of these compounds 8 and 9 demonstrated
only weak antibacterial activity with their MIC values
in the range 8–>32 mg/mL against both the sensitive
control and clinically resistant bacteria strains.
Although, studies from other laboratories have reported
that compounds in the 5-thiocarbonyl and 5-thiocarba-
mate oxazolidinone series with Clog P values within a
favorable range of ꢂ1 to +2show strong in vitro anti-
bacterial activity against gram-positive bacteria includ-
ing MRSA and VRE;11,12 a similar correlation could
not be established in this series of 5-heterocycle and
hydroxamic acid substituted oxazolidinones. It becomes
apparent that the criteria relating to favorable Clog P
value range may not be the sole predicting factor for
antibacterial activity; since most of the compounds
reported in the present study showed Clog P values (0.5-
1.31) within the reported optimal range.12
Table 2. Summary of activity against susceptible and resistant gram-positive and gram-negative clinical isolates
Compd Clog Pa
MIC’s (mg/mL) ranges against
MSSA (n=8) MRSA (n=20) MS-CNS (n=5) MR-CNS (n=5) H. influ. (n=7) S. pn. (n=8) VSE (n=11) VRE (n=6)
8
9
10
15
17
PH-027
Lin
Van
0.78
0.78
1.92
0.57
1.31
0.89
0.76
n.d.
>3216–32 8–32
>3232
>328–
32
>32
>32
>32
>32
>32
32
>3216–
>32
>3216–
>32
>32
>32
>32
>32
>32
>32
0.5–2
>32
>32
>32
>32
>32
0.5—2
>32
>32
>3216–
>3216–
>32
>32
>32
>32
0.5–1
>32
>32
16–3216–
0.5–1
>3216–
>3216–
0.5–2
1
0.5–1
20.5–02.5—1
1–20.5–2 1—2
0.5–1
8
0.5–1
11–—2 2
5–1>320.2 1–4
2
8–
>32
aref 17.

O. A. Phillips et al. / Bioorg. Med. Chem. 11 (2003) 35–41
39
Conclusion
(R)-5-{(5-Acetyl-[1,2,3]triazol-1-ylmethyl)-3-(3-fluoro-
4-morpholin-4-yl-phenyl)} oxazolidin-2-one (9). The con-
centrated filtrate (800 mg) from above, containing
approximately 1:1 ratio of two components, was sub-
jected to silica gel column chromatography eluting with
ethyl acetate–benzene 5:1, to give a less polar compound
as a foam 200 mg. The foam was digested with ether to
give a yellow solid, which was recrystallized from ethyl
acetate–hexane to afford 9 (127 mg, 5%) as a light yel-
low amorphous solid, mp 152–153 ꢄC. 1H NMR
(DMSO-d6, 400 MHz): d 8.62(s, 1H), 7.45 (dd, 1H,
J=2.4 Hz, J=14.9 Hz), 7.17 (dd, 1H, J=2.3 Hz,
J=9.1 Hz), 7.07 (t, 1H, J=9.1), 5.10 (m, 3H), 4.22 (t,
1H, J=9.0 Hz), 3.91 (dd, 1H, J=4.8 Hz, J=9.2Hz),
3.74 (t, 4H, J=4.5 Hz), 2.97 (t, 4H, J=4.5), 2.59 (s,
3H). IR (KBr pellet, cmꢂ1): n 3351, 1744, 1679, 1445,
1252. MS: m/z 389 (100, M+). Anal. CHN: calcd 55.52,
5.18, 17.99, found 55.78, 5.20, 17.79.
In conclusion, 5-triazole, 5-imidazole and 5-hydro-
xamate oxazolidinone derivatives were synthesized and
their antibacterial activities against the antibiotic sus-
ceptible standard and clinically isolated resistant gram-
positive bacteria including MRSA, MR-CNS, PRSP,
and VRE were evaluated. The 5-triazole oxazolidinone
PH-027 demonstrated strong in vitro activity, compar-
able to or better than those of linezolid and vancomy-
cin. No correlation between activity and lipophilicity
(Clog P values) could be established. The 5-imidazole
and 5-hydroxamate oxazolidinones were void of anti-
bacterial activity. We have identified the C-5 triazole
substitution as a new structural alternative for strong
antibacterial activity in the oxazolidinone class. Further
work in this area is on going in our laboratories.
(R)-3-{3-Fluoro-4-morpholin-4-yl-phenyl)-5-[4-(E/Z)(1-
methoxyiminoethyl)-[1,2,3]triazol-1-ylmethyl]}oxazolidin-
2-one (10). A mixture of 8 (300 mg, 0.78 mmol), meth-
oxylamine hydrochloride (85 mg, 1.0 mmol) and pyri-
dine (86 mL, 1.0 mmol) in dimethoxyethane-ethanol
(20:10 mL) was stirred at room temperature for 6 h. The
reaction mixture was concentrated to dryness, and the
residue treated with ethyl acetate and water, the organic
layer was separated, washed with water, brine, dried
(Na2SO4) and concentrated to afford a beige foam
(280 mg). Recrystallized from ethyl acetate–ether affor-
ded 10 as an off-white amorphous solid (215 mg, 67%),
mp 142–143 ꢄC. This compound was obtained as mix-
Experimental
Melting points were determined on a Gallenkamp melt-
ing point apparatus and are uncorrected. The Science
Analytical Facilities (SAF), Faculty of Science, Kuwait
University, performed all the analyses. Elemental ana-
lyses were determined on LECO elemental analyzer
CHNS 932apparatus, and were within ꢃ0.4% of the
1
calculated values. H NMR spectra were recorded on
Bruker DPX 400 NMR (400 MHz) spectrometer using
tetramethylsilane (TMS) as an internal standard. High-
resolution mass spectra were measured on a Finnigan
MAT INCOS XL mass spectrometer. Infrared (IR)
spectra were recorded on Perkin–Elmer System 2000
FT-IR spectrometer. Column chromatography was car-
ried out with silica gel [Kieselgel 60, 70–230 mesh
(Aldrich)]. TLC was conducted on 0.25 mm precoated
silica gel plates (60F254, Merck). All extracted solvents
were dried over Na2SO4, followed by evaporation in
vacuo. The calculated partition coefficient (Clog P)
values were determined by using the CS ChemDraw
Ultra version 6.01, computer software by Cam-
bridgeSoft.Com.17
1
ture of inseparable E/Z-isomer. H NMR (DMSO-d6,
400 MHz): d 8.72and 8.42(two sets of s, 1H), 7.43
(overlapping dd, 1H, J=2.4 Hz, J=14.9 Hz), 7.15
(overlapping dd, 1H, J=2.4 Hz, J=8.8 Hz), 7.06 (t, 1H,
J=9.4), 5.14 (m, 1H), 4.88 and 4.83 (two sets of d, 2H,
J=5.3 Hz), 4.21 (t, 1H, J=9.0 Hz), 3.92and 3.90 (two
sets of s, 3H), 3.89 (m, 1H), 3.74 (t, 4H, J=4.5 Hz), 2.96
(t, 4H, J=4.5 Hz) 2.27 and 2.22 (two sets of s, 3H). IR
(KBr pellet, cmꢂ1): n 1751, 1625, 1517, 1478, 1451,
1256. Anal. CHN: calcd 54.54, 5.54, 20.08, found 54.87,
5.50, 20.10.
Syntheses
(R)-3-(3-Fluoro-4-morpholin-4-yl-phenyl)-5-[1,2,3]triazol
-
(R)-5-{(4-Acetyl-[1,2,3]triazol-1-ylmethyl)-3-(3-fluoro-
4-morpholin-4-yl-phenyl)} oxazolidin-2-one (8). A solu-
tion of the 5-azidomethyl10 7 (2.0 g, 6.2 mmol) in dime-
thoxyethane (40 mL) was treated with 3-butyn-2-one
(0.64 g, 9.3 mmol) and heated at 90 ꢄC overnight for
24 h. The reaction mixture was cooled and concentrated
to give a foam 2.50 g. Recrystallization from a dime-
thoxyethane-ethyl acetate mixture gave the more polar
component 8 (1.5 g, 62%) as a light brown solid, mp
1-ylmethyl oxazolidin-2-one (PH-027). A solution of the
5-azidomethyl10 7 (1.01 g, 3.14 mmol) in dimethoxy-
ethane (30 mL) was placed in a steel bomb and cooled to
ꢂ78 ꢄC in a dry ice-acetone bath. A stream of excess
acetylene gas was passed into the bomb to condense
over a period of 4 min, the steel bomb was tightly closed
and the mixture was heated at 90 ꢄC for 12h. The bomb
was cooled to 0 ꢄC and excess acetylene was released
carefully and the mixture was concentrated to give a
yellow solid 1.1 gm, which was recrystallized from tet-
rahydrofuran–diethyl ether mixture to afford PH-027;
169–170 ꢄC. H NMR (DMSO-d6, 400 MHz): d 8.80 (s,
1
1H), 7.43 (dd, 1H, J=2.4 Hz, J=14.9 Hz), 7.15 (dd, 1H,
J=2.3 Hz, J=9.1 Hz), 7.06 (t, 1H, J=9.1), 5.17 (m,
1H), 4.88 (d, 2H, J=6.80 Hz), 4.22 (t, 1H, J=9.2Hz),
3.91 (dd, 1H, J=4.8 Hz, J=9.2Hz), 3.73 (t, 4H,
J=4.5 Hz), 2.96 (t, 4H, J=4.5 Hz), 2.55 (s, 3H). IR
(KBr pellet, cmꢂ1): n 3350, 1735, 1693, 1448, 1247. MS:
m/z 389 (100, M+). Anal. CHN: calcd 55.52, 5.18,
17.99, found 55.42, 5.06, 17.88.
809 mg, 74% as a crystalline solid, mp 169–170 ꢄC. H
1
NMR (DMSO-d6, 400 MHz): d 8.17 (s, 1H), 7.77 (s,
1H), 7.41 (dd, 1H, J=2.4 Hz, J=14.9 Hz), 7.13 (dd, 1H,
J=2.4, J=9.4 Hz), 7.05 (t, 1H, J=9.4 Hz), 5.13 (m,
1H), 4.83 (d, 2H, J=5.1 Hz), 4.20 (t, 1H, J=9.2Hz),
3.86 (dd, 1H, J=5.7 Hz, J=9.3 Hz), 3.73 (t, 4H,
J=4.6 Hz), 2.96 (t, 4H, J=4.6 Hz). IR (KBr pellet,

40
O. A. Phillips et al. / Bioorg. Med. Chem. 11 (2003) 35–41
cmꢂ1): n 1749, 1625, 1518, 1472, 1447, 1288. MS: m/z
347 (100, M+). Anal. CHN: calcd 55.33, 5.22, 20.16,
found 55.26, 5.20, 20.03.
4.98 (m, 1H), 4.37 (m, 2H), 4.14 (t, 1H, J=9.0 Hz)
3.77 (dd, 1H, J=5.7 Hz, J=9.3 Hz), 3.74 (t, 4H,
J=4.6 Hz), 2.96 (t, 4H, J=4.6 Hz). IR (KBr pellet,
cmꢂ1): n 1729, 1625, 1517, 1480, 1271. MS: m/z 346
(100, M+). Anal. CHN: calcd 58.95, 5.53, 16.18, found
58.55, 5.53, 15.99.
(R)-1-[3-(3-Fluoro-4-morpholin-4-yl-phenyl)-2-oxo-oxa-
zolidin-5-ylmethyl]-1H-[1,2,3]triazole-4,5-dicarboxylic
acid methyl ester (11). A mixture of 5-azidomethyl 710
(1.0 g, 3.1 mmol) and dimethyl acetylenedicarboxylate
(671 mg, 4.7 mmol) in dimethoxyethane (30 mL) was
heated at 90 ꢄC for 24 h. The mixture was concentrated
to give a yellow solid, which was recrystallized from
ethyl acetate to afford 11 (1.07 g, 73%) as a crystalline
(R)-[N-3-(3-Fluoro-4-morpholin-4-ylphenyl)-2-oxo-5-oxa-
zolidinyl] methyl N,O-bis-(tert-butoxycarbonyl)hydroxy-
lamine (14).
A
solution of tert-butyl N-(tert-
butoxycarbonyloxy)carbamate (3.14 g, 13.5 mmol) in
anhydrous DMF (50 mL) under an atmosphere of N2
gas, was treated with sodium hydride (584 mg of 60%
NaH in mineral oil, 14.59 mmol). The reaction was stir-
red for 30 min at room temp and treated with a solution
of the methanesulfonate 6 (4.2g, 11.2mmol) in DMF
(50 mL). The mixture was stirred at room temp for 48 h,
diluted with water and extracted with methylene chlo-
ride (3 ꢅ 80 mL). The methylene chloride extracts were
pooled, washed with water, brine, dried (Na2SO4), and
concentrated to give a brown oil 6.50 g. Purification by
silica gel column chromatography eluting with ethyl
acetate–hexane 1:1.5 afforded 14 (4.01 g, 70%) as a
ꢄ
1
solid, mp 144–145 C. H NMR (DMSO-d6, 400 MHz):
d 7.46 (dd, 1H, J=2.4 Hz, J=14.9 Hz), 7.17 (dd, 1H,
J=2.4 Hz, J=8.8 Hz), 7.07 (t, 1H, J=9.5), 5.14 (m,
1H), 5.03 (d, 2H, J=5.0 Hz), 4.23 (t, 1H, J=9.2Hz),
3.94 (s, 3H), 3.90 (dd, 1H, J=5.6 Hz, J=9.5 Hz), 3.89
(s, 3H), 3.74 (t, 4H, J=4.5 Hz), 2.97 (t, 4H, J=4.5 Hz).
IR (KBr pellet, cmꢂ1): n 1766, 1727, 1561, 1519, 1483,
1465, 1272. MS: m/z 463 (95%, M+). Anal. CHN: calcd
51.84, 4.79, 15.11, found 51.97, 4.66, 15.12.
(R)-1-[3-(3-Fluoro-4-morpholin-4-yl-phenyl)-2-oxo-oxa-
zolidin-5-ylmethyl]-1H-[1,2,3]triazole-4,5-dicarboxylic
acid, sodium salt (12). A solution of dimethyl ester 11
(700 mg, 1.5 mmol) in methanol–tetrahydrofuran
(15 mL:20 mL) was cooled to 0 ꢄC and treated with a
solution of sodium hydroxide (123 mg, 3.01 mmol) in
10 mL water, and stirred for 2h. The mixture was eva-
porated to remove methanol and tetrahydrofuran, and
the aqueous solution was freeze dried to give a solid,
which was recrystallized from methanol–ether to afford
12 (610 mg, 84%) as a white fluffy solid mp 270–272 ꢄC
1
brown viscous oil. H NMR (DMSO-d6, 400 MHz): d
7.49 (dd, 1H, J=2.45 Hz, J=14.9 Hz), 7.18 (dd, 1H,
J=2.6 Hz, J=8.8 Hz), 7.07 (t, 1H, J=9.4 Hz), 4.86 (m,
1H), 4.13 (t, 1H, J=6.9 Hz), 3.85 (dd, 1H, J=7.5 Hz,
J=14.9 Hz), 3.73 (m, 5H), 3.35 (m, 1H, overlaps with
D2O signal), 2.96 (t, 4H, J=4.6 Hz), 1.45 (s, 9H), 1.40
(s, 9H). MS: m/z 511.55 (M+).
(R) 3-(3-Fluoro-4-morpholin-4-yl-phenyl)-5-N-hydroxy-
aminomethyl-oxazolidin-2-one (15). A solution of 14
(3.41 g, 6.67 mmol) in anhydrous dichloromethane
(40 mL) at 0 ꢄC was treated with trifluoroacetic acid
(21 mL; 274 mmol), then stirred at 0 ꢄC for 2.5 h, and
concentrated to dryness. The crude was diluted with di-
chloromethane 100 mL and 10% potassium carbonate
solution. The DCM layer was separated and the aqu-
eous layer further extracted with additional DCM (3 ꢅ
60 mL). The organic layers were combined, dried
(Na2SO4), filtered and concentrated to give a white
solid. Recrystallization from dichloromethane-ether
afforded 15 (1.2g, 58%) as white crystalline solid, mp
148–149 ꢄC. 1H NMR (DMSO-d6, 400 MHz): d 7.50
(dd, 1H, J=2.5 Hz, J=15.1 Hz), 7.44 (s, 1H, NOH
exchangeable with D2O), 7.19 (t, 1H, J=2.1 Hz,
J=8.8 Hz), 7.06 (t, 1H, J=9.5 Hz), 6.03 (br. s, 1H,
NH exchangeable with D2O), 4.80 (m, 1H), 4.10 (t,
1H, J=8.9 Hz), 3.82(dd, 1H, J=6.8 Hz, J=8.9 Hz),
3.74 (t, 4H, J=4.5 Hz), 3.03 (ABq, 2H, J=6.19 Hz,
J=13.6 Hz) 2.96 (t, 4H, J=4.5 Hz). IR (KBr pellet,
cmꢂ1): n 3275, 3180, 1719, 1631, 1523, 1478, 1272.
Anal. CHN: calcd 54.01, 5.83, 13.50, found 54.05, 5.71,
13.50.
1
(dec). H NMR (DMSO-d6, 400 MHz): d 7.48 (dd, 1H,
J=2.5 Hz, J=14.6 Hz), 7.17 (dd, 1H, J=2.5 Hz,
J=8.8 Hz), 7.06 (t, 1H, J=9.3), 5.15 (s, 2H), 4.78 (m,
1H), 4.20 (t, 1H, J=9.2Hz), 3.97 (dd, 1H, J=5.6 Hz,
J=9.5 Hz), 3.72(t, 4H,
J=4.5 Hz), 2.96 (t, 4H,
J=4.5 Hz). IR (KBr pellet, cmꢂ1): n 3437, 1747, 1627,
1518, 1449, 1239. Anal. CHN: calcd 45.10, 3.36, 14.61
found 45.33, 3.46, 14.90
(S)-3-(3-Fluoro-4-morpholin-4-yl-phenyl)-5-imidazol-1-
ylmethyl-oxazolidin-2-one (13). A solution of imidazole
(183 mg, 2.68 mmol) in anhydrous DMF (25 mL) under
nitrogen, treated with 60% NaH in mineral oil (120 mg)
was stirred at room temp for 20 min, a solution of 6
(1.0 g, 2.68 mmol) in anhydrous DMF (10 mL) was
added in rapid drops and the mixture stirred at room
temp under nitrogen for 48 h. The reaction mixture
was diluted with water and ethyl acetate; and the
ethyl acetate layer separated. The aqueous layer was
further extracted with ethyl acetate and the combined
ethyl acetate extracts were washed with water, brine,
dried (Na2SO4), and concentrated to give a white solid
500 mg. Purification by silica gel column chromato-
graphy eluting with ethyl acetate–methanol gave a white
solid. Recrystallization from methanol/ethyl acetate
afforded 13 (200 mg, 22%) as a white amorphous
solid, mp 153–154 ꢄC. 1H NMR (DMSO-d6,
400 MHz): d 7.68 (s, 1H), 7.43 (dd, 1H, J=2.4 Hz,
J=14.9 Hz), 7.23 (s, 1H), 7.16 (dd, 1H, J=2.4,
J=8.9 Hz), 7.05 (t, 1H, J=9.42Hz), 6.91 (s, 1H),
(R)-N-[3-(3-Fluoro-4-morpholin-4-yl-phenyl)-2-oxo-
oxazolidin-5-ylmethyl]-N-hydroxyacetamide (17).
A
solution of 15 (1.1 g, 3.5 mmol) in anhydrous CH2Cl2
(30 mL) with stirring at room temp was treated with
triethylamine (3.0 mL; 21.1 mmol); then acetic anhy-
dride (833 mL; 8.83 mmol) was added and the mixture
stirred at room temp for 3 h. The reaction mixture was

O. A. Phillips et al. / Bioorg. Med. Chem. 11 (2003) 35–41
41
diluted with a solution of 10% potassium carbonate and
Acknowledgements
the dichloromethane layer was separated, washed with
brine, dried (Na2SO4), and concentrated to give N-acet-
oxy-N-[3-(3-fluoro-4-morpholin-4-yl-phenyl)-2-oxo-oxa-
zolidin-5-ylmethyl]acetamide 16 (1.50 g, quantitative
yield) as a viscous oil. A solution of 16 (1.30 g,
3.3 mmol) in methanol–THF (36 mL:9 mL) at 0 ꢄC was
treated with NaOH solution (132mg in 30 mL water)
and stirred for 1 h 10 min at this temp. The mixture was
acidified with dilute HCl solution adjusting the pH of
the solution to ꢆ7.0, and concentrated to remove THF
and methanol. The aqueous layer was extracted with
dichloromethane (2 ꢅ 30 mL), the organic layer was
separated, dried (Na2SO4), and concentrated to give a
crude. Purification by silica gel column chromatography
eluting with ethyl acetate-hexane afforded 17 (920 mg,
This project was supported by Kuwait University
Research Grant PC01/00, and the Science Analytical
Facilities (SAF) Project no. GS01/01.
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79%) as
a
brown foam. 1H NMR (DMSO-d6,
400 MHz): d 10.08 (s, 1H, –NOH exchangeable with
D2O), 7.49 (dd, 1H, J=2.4 Hz, J=15.0 Hz), 7.19 (dd,
1H, J=2.32 Hz, J=8.8 Hz), 7.07 (t, 1H, J=9.5 Hz),
4.84 (m, 1H), 4.13 (t, 1H, J=8.9 Hz), 4.03 (dd, 1H,
J=7.0 Hz, J=14.7 Hz), 3.73 (t, 4H, J=4.5 Hz), 3.70
(ABq, 2H, J=4.4 Hz, J=14.6 Hz) 2.96 (t, 4H,
J=4.5 Hz), 2.02 (s, 3H). IR (KBr pellet, cmꢂ1): n 3435,
1751, 1630, 1518, 1419, 1228. MS: m/z 353 (M+). Anal.
CHN: calcd 54.39, 5.71, 11.89, found 54.58, 5.96,
10.95.
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20. National Committee for Clinical Laboratory Standards.
Methods for Dilution Antimicrobial Susceptibility Tests for
Bacteria that Grow Aerobically, Approved Standard. NCCLS
Document M7-A4, 4th ed.; National Committee for Clinical
Laboratory Standards: Villanova, PA, 1997.
Microbiology
In vitro antibacterial tests. Antibacterial susceptibility
testing was performed by disk diffusion and the agar
dilution methods of the National Committee for
Clinical Laboratory Standards.20 Inhibitory zone
diameters were measured on Mueller-Hinton (MH)
agar, with conventional paper disk (Whatman, Grade
AA Discs, 6.00 mm in diameter) containing 30 mg of
each compound. The inhibitory zone diameters were
read with a caliper, and all results were rounded up to
the nearest whole numbers (mm) for analysis. The
Minimum Inhibitory Concentrations (MIC’s, mg/mL)
were determined on MH agar with medium containing
dilutions of antibacterial agents ranging from 0.25 to
32mg/L. The new compounds were dissolved in 20%
water in DMSO, while linezolid and vancomycin were
dissolved in 40% water in ethanol and water,
respectively.
The test compounds were diluted in MH broth for
all staphylococci and enterococci, and in MH broth
supplemented with 5% sheep blood to facilitate the
growth of S. pneumoniae and H. influenzae. The
Gram-positive organisms utilized in this study con-
sisted of MRSA, MSSA, MR-CNS, MS-CNS, S.
pneumoniae, PRSP, VSE, VIRE and VRE. The Gram-
negative species include E. coli, P. aeruginosa and H.
influenzae. The final bacterial concentration for inocula
was of 107 CFU/mL, and was incubated at 35 ꢄC for
18 h. The MIC was defined as the lowest drug con-
centration that completely inhibited growth of the
bacteria.