Syntheses and biological studies of novel spiropiperazinyl oxazolidinone antibacterial agents using a spirocyclic diene derived acylnitroso Diels-Alder reaction

Article abstract of DOI:10.1016/j.bmc.2012.04.026

Several novel oxazolidinone antibiotics with a spiropiperazinyl substituent at the 4′-position of the phenyl ring were synthesized through nitroso Diels-Alder chemistry and the in vitro antibacterial activities were evaluated against various Gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus, Enterococcus faecalis), Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa) and mycobacteria (Mycobacterium vaccae, Mycobacterium tuberculosis). Analogs (8a and 12) were active against selected drug resistant microbes, like methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) and had no mammalian toxicity in a Hep-2 cellular assay (CC₅₀ >100 μM).

Full text of DOI:10.1016/j.bmc.2012.04.026

Bioorganic & Medicinal Chemistry 20 (2012) 3422–3428
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Syntheses and biological studies of novel spiropiperazinyl oxazolidinone
antibacterial agents using a spirocyclic diene derived acylnitroso
DielsꢀAlder reaction
Cheng Ji a, Weimin Lin a, Garrett C. Moraski a, Jane A. Thanassi b, Michael J. Pucci b, Scott G. Franzblau c,
Ute Möllmann d, Marvin J. Miller a,
⇑
a Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA
b Achillion Pharmaceuticals, 300 George Street, New Haven, CT 06511, USA
c Institute for Tuberculosis Research, College of Pharmacy, University of Illinois at Chicago, Chicago, IL 60612, USA
d Leibniz Institute for Natural Product Research and Infection Biology, Hans Knoell Institute, Beutenbergstrasse 11a, 07745 Jena, Germany
a r t i c l e i n f o
a b s t r a c t
Several novel oxazolidinone antibiotics with a spiropiperazinyl substituent at the 40-position of the phe-
nyl ring were synthesized through nitroso Diels–Alder chemistry and the in vitro antibacterial activities
were evaluated against various Gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus, Enterococ-
cus faecalis), Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa) and mycobacteria
(Mycobacterium vaccae, Mycobacterium tuberculosis). Analogs (8a and 12) were active against selected
drug resistant microbes, like methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resis-
Article history:
Received 15 February 2012
Revised 3 April 2012
Accepted 9 April 2012
Available online 18 April 2012
Keywords:
Oxazolidinone
Antibiotics
tant enterococci (VRE) and had no mammalian toxicity in a Hep-2 cellular assay (CC50 >100 lM).
Ó 2012 Elsevier Ltd. All rights reserved.
Nitroso DielsꢀAlder reaction
Spirocyclic diene
MRSA
1. Introduction
linezolid was observed not long after it was put into use.14–17
The development of resistance encourages the design, syntheses,
studies and hopefully development of novel oxazolidinone
derivatives.
Extensive structure–activity relationships have been estab-
lished for oxazolidinone derivatives (Fig. 1).3 The S-configuration
at the C-5 position of the oxazolidinone ring is necessary and the
acetamide is good for antibacterial activity. Meanwhile, electron-
donating nitrogen substituents at the 40-position of the phenyl ring
are well tolerated and often improve the overall safety profile.4–6,18
For example, a number of linezolid derivatives with pyrroloaryl,19
azabicyclic20–23 and cyanomethylpiperidinyl24,25 N-substituents
have been reported and some display improved properties relative
to the parent drug.26
Nitroso Diels–Alder (NDA) chemistry has been used as a
remarkably efficient method for derivatization of complex diene-
containing natural products by direct incorporation of a 1,4-ami-
no-oxo group (Scheme 1).27–30 This provides opportunities for
Modular Enhancement of Nature’s Diversity (MEND).31,32 NDA
adducts derived from cyclopentadiene and other dienes are also
synthetically valuable precursors for many biologically interesting
molecules, such as carbocyclic nucleosides33–36 and natural prod-
uct analogs.37,38 Herein we report the synthesis and biological
activity evaluation of novel oxazolidinone derivatives with various
The rate of antimicrobial resistance has increased dramatically
in the past few decades due to the misuse and overuse of antibiot-
ics.1,2 Infections caused by resistant organisms such as methicillin-
resistant Staphylococcus aureus (MRSA), vancomycin-resistant
enterococci (VRE), and penicillin-resistant Streptococcus pneumo-
niae (PRSP) are often extremely difficult to treat. Therefore, efforts
towards the discovery of new antibiotics are of great significance.
The oxazolidinones are a class of wholly synthetic, orally active
antibiotics that has excellent activity against a variety of suscepti-
ble and resistant Gram-positive bacteria.3–6 Targeting bacterial
protein synthesis, this class of compounds possesses a unique
mode of action by preventing binding of the aminoacyl-tRNA to
the A site of the ribosome.7,8 This unique activity indicates the po-
tential for oxazolidinones to have low cross-resistance with exist-
ing protein synthesis inhibitors.9–11 To date, linezolid (ZyvoxTM
,
Fig. 1) is the only oxazolidinone that has been approved for clinical
use for the treatment of pneumonia and skin infections due to drug
resistant Gram-positive bacteria such as MRSA, VRE and PRSP.3,12,13
Unfortunately, though in only a few cases, resistance against
⇑
Corresponding author. Tel.: +1 574 631 7571; fax: +1 574 631 6652.
E-mail address: mmiller1@nd.edu (M.J. Miller).
0968-0896/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmc.2012.04.026

C. Ji et al. / Bioorg. Med. Chem. 20 (2012) 3422–3428
3423
Figure 1. Structure–activity relationships of linezolid and several examples of different N-substituents at the 40-position of the phenyl ring.
hydrogen gas (1 atm) to give amine 6 in 95% yield. The amine
was then protected with a Cbz group to generate intermediate 7
in 90% yield. The oxazolidinone ring was constructed according
to precedent by treatment of 7 with n-butyl lithium and R-glycidyl
butyrate sequentially at ꢀ78 °C, producing alcohol derivative 8a in
85% yield with defined stereochemistry at the C-5 position.40 An
ester derivative 8b was also formed in 5% yield in the same reac-
tion. It was easily and quantitatively converted to 8a by treatment
with sodium hydroxide. The hydroxyl group of 8a was converted to
mesylate 9 in 90% yield. Sodium azide displacement of the mesy-
late provided compound 10 in 74% yield (Scheme 3).
Scheme 1. Acyl-nitroso DielsꢀAlder (NDA) reaction.
spiropiperazinyl substituents using acyl-nitroso Diels–Alder (NDA)
reactions.
Exposure of 10 to hydrogen over palladium on carbon produced
the corresponding amine 11 in 95% yield. Acetylation then afforded
linezolid analog 12 in 70% yield. Compound 12 can serve as a com-
mon intermediate for various modifications on the spiropiperazine
moiety without cleaving the NꢀO bond, which retains the rigidity
of the molecule. For example, after removal of the N-Boc protecting
group of 12 with trifluoroacetic acid, reductive amination can be
done as shown by incorporation of a nitrofuranyl substituent in
moderate yield. Nitrofuranyl was chosen because of its structural
similarity of 14 to the dual action antimicrobial agent RBx-7644 re-
ported by the Ranbaxy Laboratories.41 Cleavage of the NꢀO bond in
the spiropiperazine moiety was anticipated to produce more flex-
ible derivatives as the restriction of ring conformation would be
eliminated. Indeed, molybdenum hexacarbonyl-mediated bond
cleavage42 of compounds 11 and 12 provided the ring opened
derivatives 15 and 16 in 64% and 80% yields, respectively
(Scheme 4).
2. Results and discussion
2.1. Chemistry
The spirocyclic diene 1 was prepared from cyclopentadienyl
anion and N-Cbz-bis-(2-chloro-ethyl) amine, as reported previ-
ously.34 Diene 1 was reacted with the nitroso species generated
from Boc-protected hydroxylamine by in situ oxidation with
sodium periodate, providing spirocycloadduct 2 in 61% yield.39 To
remove the Cbz protecting group, 2 was treated with a catalytic
amount of 10% palladium on carbon and hydrogen gas (1 atm).
However, a selective reduction of the alkene occurred to give com-
pound 3 in 93% yield while leaving the Cbz group intact. The reason
for the selectivity was proposed to be the steric effect of the bulky
Boc group during the hydrogenolysis process. Increasing hydrogen
gas to 50 psi and changing the catalyst to palladium hydroxide
(20% palladium on carbon) simultaneously reduced the alkene
and removed the Cbz protecting group, producing compound 4 in
91% yield for further reactions (Scheme 2).
3. Biological activity
Compound 5 was prepared in 85% yield by an SNAr reaction of 4
with 3,4-difluoronitrobenzene in the presence of Hünig’s base. The
nitro group was reduced with 10% palladium on carbon and
Compounds 8a, 11, 12 and 16 were initially screened for antibi-
otic activity against representative Gram-positive and Gram-nega-
tive bacteria as well as Mycobacterium vaccae using agar diffusion
assays (Table 1). Compounds 8a and 12 displayed in vitro antibac-
terial activities comparable to linezolid. Both showed good activity
against all Gram-positive organisms tested including drug-resis-
tant strains such as Staphylococcus aureus 134/93 (MRSA) and
Enterococcus faecalis 1528 (VRE) as indicated by the large zones
of inhibition they induced. Mycobacterium vaccae is a non-patho-
genic model organism for Mycobacterium tuberculosis, the causative
agent of tuberculosis. Although less active than linezolid, all
compounds showed moderate to good activities against Mycobac-
terium vaccae, suggesting their potential in anti-tuberculosis agent
development. Interestingly, compound 16 derived from reduction
of the N–O bond showed decreased activity compared to its parent
cycloadduct 12. Similar phenomena were observed in studies of
C-5 side chain modification of linezolid through nitroso Diels–Al-
der chemistry.43 None of the compounds tested in this study
Scheme 2. Reagents: (a) NaIO4, BocNHOH, H2O/MeOH, rt, 8 h, 61%; (b) H2 (1 atm),
10% Pd/C, MeOH, rt, 8 h, 93%; (c) H2 (50 psi), Pd(OH)2, MeOH, rt, 8 h, 91%.

3424
C. Ji et al. / Bioorg. Med. Chem. 20 (2012) 3422–3428
Scheme 3. Reagents: (a) 3,4-difluoronitrobenzene, DIPEA, CH3CN, rt, 8 h, 85%; (b) H2, 10% Pd/C, MeOH, rt, 1 h, 95%; (c) Cbz-Cl, NaHCO3, 0 °C to rt, 2 h, 90%; (d) (R)-(ꢀ)-glycidyl
butyrate, n-BuLi, THF, ꢀ78 °C to rt, 2 h, 85%; (e) NaOH, H2O/THF, rt, 100%; (f) MsCl, Et3N, CH2Cl2, 0 °C to rt, 90%; (g) NaN3, DMSO, 75 °C, 8 h, 74%.
Scheme 4. Reagents: (a) H2, 10% Pd/C, MeOH, rt, 8 h, 95%. (b) AcCl, pyridine, CH2Cl2, 0 °C to rt, 70%; (c) TFA, CH2Cl2, rt, 2 h, 95%; (d) 5-nitrofuraldehyde, NaBH(OAc)3,
ClCH2CH2Cl, HOAc, rt, 2 h, 53%; (e) Mo(CO)6, NaBH4, CH3CN/H2O, 60 °C, 6 h, 64% (for 15), 80% (for 16).
Table 1
Antimicrobial activity in the agar diffusion assay (diameter of inhibition zone, measured in mm)
Gram-positive bacteria
Gram-negative bacteria
Compds
Bacillus subtilis
Staphylococcus aureus
Enterococcus faecalis
Escherichia coli
Pseudomonas aeruginosa
Mycobacterium vaccae
ATCC 6633
SG 511
134/93 (MRSA)
1528 (VRE)
SG 458
SG 137
K799/61
IMET 10670
Linezolida
31/35P
23.5/28A/30p
12
25/27A
14/19A
27/36P
22
10/13A
18/22p
16p
NT
24
14A
25
14/18A
NT
22
14P
23
15/18p
NT
0
10
0
NT
0
0
0
0
10P
0
A
0
0
42
30p
18/25P
24/37p
13p
8a
11
12
16
0
p, partially clear inhibition zone/colonies in the inhibition zone; P, unclear inhibition zone/many colonies in the inhibition zone; A, indication of growth inhibition; NT, not
tested; Exactly 50 L of a 2.0 mM solution of each compound dissolved in 1:9 DMSO/MeOH was filled in 9 mm wells in agar media (Standard I Nutrient Agar, Serva or Mueller
l
Hinton II Agar, Becton, Dickinson and Company). Inhibition zones read after incubation at 37 °C for 24 h.
a
Linezolid data from Ref.43
displayed any noticeable significant activity against several Gram-
negative indicator strains including E. coli and P. aeruginosa.
Cycloadducts 8a and 12, the two most active compounds in the
agar diffusion assay, were subjected to further assays to determine
their minimum inhibitory concentrations (MIC). Although both
showed inferior antibacterial activity relative to linezolid,44
compound 12 has one dilution lower (better) MIC values against
MSSA and MRSA than did compound 8a (Table 2), consistent with
the expected advantage of having an acetamide on the C-5 side
chain. To further assess their potential, the effect of protein binding
on the activity was assessed by adding 50% mouse or human serum
to the MIC assays, and calculating the fold shift in MIC values.
Comparing to 8a which is relatively inactive in serum, compound
12 exhibited only 2 and 4-fold MIC shift in mouse and human
Table 2
MIC determination (
compounds
l lM) of spiropiperazinyl
g mLꢀ1) of methicillin-susceptible (MS) and resistant (MR) Staphylococcus aureus, assessment of protein binding, and toxicity (
Compds
Mol. Wt.
MSSA
MRSA
MRSA +50% mouse serum
Fold shift mouse
MRSA +50% human serum
Fold shift human
Hep2 toxicity (CC50 lM)
8a
12
477.53
518.58
>64
64
32
16
>64
32
>2ꢁ
2ꢁ
>64
64
>2ꢁ
4ꢁ
>100
>100
Abbreviations: ATCC, American Type Culture Collection; MSSA, methicillin-susceptible Staphylococcus aureus ATCC 29213; MRSA, methicillin-resistant Staphylococcus aureus
ATCC 700699; CC50 is defined as the concentration of drug that results in toxicity to 50% of the cells compared with untreated control cells.

C. Ji et al. / Bioorg. Med. Chem. 20 (2012) 3422–3428
3425
serum, respectively, demonstrating that the spiropiperazinyl sub-
stituent at 40-position of the phenyl ring of linezolid does not sig-
nificantly change its stability or protein binding property in
plasma. Potential mammalian toxicity was preliminarily assessed
by screening the compounds against the Hep2 cancer cell line. Both
compounds 8a and 12 did not show toxicity against the mamma-
lian cell line.
commercial sources and used without further purification unless
otherwise stated. Tetrahydrofuran (THF) was distilled from sodium
and benzophenone. Reactions were monitored by thin-layer
chromatography (TLC) on 0.25 mm silica gel plates visualized
under UV light, iodine or KMnO4 staining. Silica gel column
chromatography was performed using Sorbent Technologies silica
gel 60 (32–63 lm). NMR spectra were recorded on a Varian Unity-
Additionally, since linezolid and its thiomorpholine analog
(PNU-100480)45 are under consideration as potential antitubercu-
lar treatments, we decided to evaluate a set of compounds (5–9, 12
and 16) against replicating M. tuberculosis H37Rv in two different
media, GAS46 and GAST47 (Table 3). The analogs lacking the oxazo-
plus 300 MHz spectrometer, Varian Inova 500 MHz spectrometer,
or Varian 600 MHz spectrometer at ambient temperature. Benzyl
8-azaspiro[4.5]deca-1,3-diene-8-carboxylate (1) and 10-benzyl
3-tert-butyl 2-oxa-3-azaspiro[bicyclo[2.2.1]hept[5]ene-7,40-piperi-
dine]-10,3-dicarboxylate (2) were prepared according to published
procedures.39
lidinone core (5, 6, and 7) all were inactive (>128 lM). The incor-
poration of this moiety in compounds (8a, 8b, 9, 12, and 16)
produced a range of antitubercular activity (MICs of 97, 19, 118,
5.2. Synthesis
24, >128
compound 12, the one most similar to linezolid, had one of the
lowest MIC values at 24 M. Interestingly, compound 8b also had
potency similar to that of compound 12 at 19 M despite missing
lM, respectively in the GAS medium). As expected
5.2.1. 10-Benzyl 3-tert-butyl 2-oxa-3-azaspiro[bicyclo[2.2.1]
heptane-7,40-piperidine]-10,3-dicarboxylate (3)
l
l
Compound 2 (1.5 g, 3.7 mmol) was dissolved in 10 mL of meth-
anol in a 25-mL round-bottomed flask under argon. 10% Pd on car-
bon (0.2 g) was added and the flask was flushed with H2 gas and
left to stir under a hydrogen atmosphere (balloon) for 8 h. After
purging with argon, the mixture was filtered and concentrated in
vacuo to give compound 3 (1.4 g, 90%) as a light yellow oil: IR
(neat, cmꢀ1): 2927, 1698, 1432; 1H NMR (600 MHz, CDCl3) d
7.29–7.37 (m, 5H), 5.12 (s, 2H), 4.19–4.28 (m, 2H), 3.41–3.56 (m,
4H), 1.80–2.00 (m, 4H), 1.56–1.75 (m, 4H), 1.47 (s, 9H); 13C NMR
(150 MHz, CDCl3) d 155.1, 136.6, 128.4, 127.9, 127.8, 82.7, 81.8,
67.0, 63.4, 62.2, 41.9, 28.1, 27.6, 26.6; HRMS (FAB) calcd for
the N-acyl moiety thought to be essential for antibacterial activity.
Compound 16 derived from reduction of the N–O bond was
inactive (>128
lM), in sharp contrast to its parent cycloadduct 12
(24 M). This trend correlated to the observation in the agar
l
diffusion assay against M. vaccae in which compound 16 gave only
a small and unclear inhibition zone. Linezolid is reported to have
excellent antitubercular potency45 (MIC range of 0.125–1 g mLꢀ1
l )
which was substantiated by our Mtb assay where it showed an
MIC of 0.4 M (0.135
l
l
g mLꢀ1) in the GAST medium and superior
to our spiropiperazinyl analogs.
C
22H30N2O5 (M)+Å: 402.2155; found 402.2165.
4. Conclusion
5.2.2. tert-Butyl 2-oxa-3-azaspiro[bicyclo[2.2.1]heptane-7,40-
piperidine]-3-carboxylate (4)
In conclusion, novel oxazolidinone antibiotics with a spiropip-
erazinyl substituent at the 40-position of the phenyl ring were syn-
thesized through nitroso Diels–Alder chemistry. The Gram-positive
antibacterial activities of some of the compounds indicate that the
diverse functionalities were well tolerated at phenyl 40-position.
The syntheses further exemplify the practicability of nitroso
Diels–Alder chemistry as a powerful synthetic tool for the creation
of unique structural and functional diversity.
Compound 2 (1.0 g, 2.5 mmol) was dissolved in 15 mL of meth-
anol in a 250-mL Parr bottle under argon. Pd(OH)2 (20% Pd on car-
bon, 0.2 g) was added and the bottle was flushed with H2 gas. The
flask was shaken under 50 psi hydrogen using a Parr shaker at
room temperature for 8 h. After purging with argon, the mixture
was filtered and concentrated in vacuo to give compound 4
(0.61 g, 90%) as a light yellow oil: IR (neat, cmꢀ1): 3485, 2978,
1697, 1368; 1H NMR (500 MHz, CDCl3) d 4.12–4.45 (m, 2H),
3.20–3.35 (m, 4H), 1.86–2.10 (m, 8H), 1.48 (s, 9H); 13C NMR
(125 MHz, CDCl3) d 157.0, 82.4, 81.4, 63.6, 61.7, 42.4, 42.3, 28.2,
27.4, 26.3, 25.2, 23.8; HRMS (FAB) calcd for C14H25N2O3 (M+H)+:
269.1865; found, 269.1871.
5. Experimental
5.1. General
All reactions were carried out under argon by using standard
techniques. All solvents and reagents were obtained from
5.2.3. tert-Butyl 10-(2-fluoro-4-nitrophenyl)-2-oxa-3-azaspiro
[bicyclo[2.2.1]heptane-7,40-piperidine]-3-carboxylate (5)
Table 3
A
10-mL oven-dried, round-bottomed flask was charged
Activity of various compounds against replicating Mtb H37Rv in various media (lM)
with compound 4 (0.35 g, 1.3 mmol), 3,4-difluoronitrobenzene
(0.25 mL, 2.0 mmol) and DIPEA (0.45 mL, 2.6 mmol) in acetonitrile
(5 mL). The reaction mixture was stirred at room temperature for
18 h and quenched by adding 1 N HCl (4 mL). The solution was ex-
tracted with ethyl acetate (5 mL ꢁ 3) and the combined organic
layers were washed sequentially with sat. NaHCO3 (5 mL), brine
(5 mL), dried over Na2SO4, filtered, and evaporated under reduced
pressure. The residue was purified by chromatography on a silica
gel column (hexanes:ethyl acetate = 3:1) to give compound 5
(0.45 g, 85%) as a yellow oil: IR (neat, cmꢀ1): 2974, 1699, 1517;
1H NMR (500 MHz, CDCl3) d 7.97 (dd, J = 8.9, 2.6 Hz, 1H), 7.90
(dd, J = 13.1, 2.6 Hz, 1H), 6.92 (t, J = 8.8 Hz, 1H), 4.10–4.34 (m,
2H), 3.22–3.38 (m, 4H), 1.82–2.01 (m, 8H), 1.58 (s, 9H); 13C NMR
(125 MHz, CDCl3) d 153.9, 152.0, 145.6, 140.4, 121.0, 117.2,
112.6, 112.4, 83.2, 82.0, 64.0, 62.4, 48.5, 48.4, 28.3, 27.6, 26.6;
Compds
Mol. Wt.
MIC (
l
M) against Mtb H37Rv in medium:
GAS
GAST
5
6
7
8a
8b
9
12
16
407.44
377.45
511.59
477.53
561.64
555.62
518.58
520.59
337.35
>128
>128
>128
97
19.2
118
24.4
>128
NT
>128
>128
>128
>128
29.2
67.4
22
>128
0.40
Linezolid
MIC = Minimum Inhibitory Concentration required to inhibit the growth of 90% of
organisms; NT = Not tested; GAS = Glycerol-alanine-salts media; GAST = Iron defi-
cient glycerol-alanine-salts with Tween 80 media. Values reported are the average
of three individual measurements.

3426
C. Ji et al. / Bioorg. Med. Chem. 20 (2012) 3422–3428
HRMS (FAB) calcd for C20H25FN3O5 (M-H)+: 406.1778; found
406.1787.
154.6, 154.5, 136.6, 133.1, 119.3, 113.8, 107.4, 83.3, 81.9, 72.8,
64.3, 62.7, 49.4, 46.4, 28.8, 28.2, 28.0, 27.1; HRMS (FAB) calcd for
C
24H32FN3O6 (M)+Å: 477.2275; found 477.2293; 8b: IR (neat, cmꢀ1):
2966, 1715, 1517; 1H NMR (600 MHz, CDCl3) d 7.42 (dd, J = 14.0,
2.4 Hz, 1H), 7.10 (d, J = 7.6 Hz, 1H), 6.95 (t, J = 9.1 Hz, 1H), 4.85
(m, 1H), 4.38 (dd, J = 12.3, 3.8 Hz, 1H), 4.26–4.34 (m, 3H), 3.78
(dd, J = 8.8, 6.2 Hz, 1H), 3.00–3.12 (m, 4H), 2.32 (t, J = 7.6 Hz, 2H),
1.80–2.00 (m, 8H), 1.62–1.67 (m, 2H), 1.50 (s, 9H), 0.92 (t,
J = 7.3 Hz, 3H); 13C NMR (150 MHz, CDCl3) d 173.2, 156.4, 154.8,
154.0, 136.9, 136.8, 133.0, 119.4, 113.8, 107.5, 105.2, 81.7, 70.0.
63.8, 49.7, 47.2, 35.8, 28.3, 18.3, 13.6. Ester 8b can be converted
to 8a by the following procedure: A 10-mL oven-dried, round-bot-
tomed flask was charged with compound 8b (66 mg, 0.12 mmol)
and sodium hydroxide (40 mg, 1.0 mmol) in a mixture of THF-
H2O 1:1 (4 mL). After stirred at room temperature for 1 h, the solu-
tion was neutralized with 1 N HCl and extracted with ethyl acetate
(5 mL ꢁ 3). The combined organic layers were washed sequentially
with sat. NaHCO3 (5 mL), brine (5 mL), dried over Na2SO4, filtered,
and evaporated under reduced pressure to give 8a in quantitative
yield.
5.2.4. tert-Butyl 10-(4-amino-2-fluorophenyl)-2-oxa-3-aza spiro
[bicyclo[2.2.1]heptane-7,40-piperidine]-3-carboxylate (6)
Compound 5 (0.30 g, 0.74 mmol) was dissolved in 4 mL of
methanol in a 10-mL round-bottomed flask under argon. 10% Pd
on carbon (30 mg) was added and the flask was flushed with H2
gas and left to stir under a hydrogen atmosphere (balloon) for
4 h. After purging with argon, the mixture was filtered and concen-
trated in vacuo to give compound 6 (0.27 g, 95%) as a viscous oil: IR
(neat, cmꢀ1): 2924, 1701, 1513; 1H NMR (300 MHz, CDCl3) d 7.42–
7.54 (m, 1H), 6.58–6.72 (m, 2H), 4.10–4.42 (m, 2H), 3.20–3.40 (m,
4H), 1.82–2.20 (m, 8H), 1.44 (s, 9H); 13C NMR (150 MHz, CDCl3) d
156.7, 155.1, 135.9, 132.3, 122.8, 113.8, 105.9, 82.3, 54.7, 51.4,
50.3, 46.1, 45.1, 41.1, 34.6, 28.2; HRMS (FAB) calcd for C20H28FN3O3
(M)+Å: 377.2115; found 377.2118.
5.2.5. tert-Butyl 10-(4-(benzyloxycarbonylamino)-2-fluorophe
nyl)-2-oxa-3-azaspiro[bicyclo[2.2.1]heptane-7,40-piperidine]-3-
carboxylate (7)
5.2.7. tert-Butyl 10-(2-fluoro-4-((R)-5-((methylsulfonyloxy)
methyl)-2-oxooxazolidin-3-yl)phenyl)-2-oxa-3-azaspiro
A 10-mL oven-dried, round-bottomed flask was charged with
[bicyclo[2.2.1]heptane-7,40-piperidine]-3-carboxylate (9)
compound
6 (0.38 g, 1.0 mmol), sodium bicarbonate (92 mg,
Compound 8a (0.37 g, 0.78 mmol) was dissolved in 4 mL of
dichloromethane in a 10-mL round-bottomed flask. Methyl sulfo-
nyl chloride (0.10 mL, 1.2 mmol) and triethylamine (0.20 mL,
1.2 mmol) were added and the mixture was stirred at room tem-
perature for 18 h. The solution was neutralized with 1 N HCl and
extracted with ethyl acetate (5 mL ꢁ 3). The combined organic lay-
ers were washed sequentially with sat. NaHCO3 (5 mL), brine
(5 mL), dried over Na2SO4, filtered, and evaporated under reduced
pressure. The residue was purified by chromatography on a silica
gel column (hexanes:ethyl acetate = 1:1) to give 9 (0.39 g, 90%)
as a light yellow oil: IR (neat, cmꢀ1): 2975, 2360, 1752, 1517,
1356; 1H NMR (300 MHz, CDCl3) d 7.42 (dd, J = 14.0, 2.4 Hz, 1H),
7.07–7.13 (m, 1H), 6.95 (t, J = 9.0 Hz, 1H), 4.88–4.96 (m, 1H), 4.50
(dd, J = 11.7, 3.7 Hz, 1H), 4.41 (dd, J = 11.7, 4.2 Hz, 1H), 4.08–4.36
(m, 3H), 3.91 (dd, J = 9.1, 6.1 Hz, 1H), 3.00–3.12 (m, 7H), 1.76–
2.00 (m, 8H), 1.49 (s, 9H); 13C NMR (125 MHz, CDCl3) d 156.5,
154.5, 153.6, 137.0, 132.4, 119.4, 114.0, 107.6, 83.0, 81.8, 69.4,
68.1, 63.9, 62.3, 49.4, 46.6, 37.8, 28.7, 28.5, 27.9, 26.8; HRMS
(FAB) calcd for C25H34FN3O8S (M)+Å: 555.2051; found 555.2036.
1.1 mmol) in a mixture of THF–H2O 1:1 (4 mL). After the solution
was cooled to 0 °C, benzylchloroformate (0.18 mL, 1.1 mmol) was
added and the mixture was stirred at the same temperature for
1 h. The reaction was quenched by adding 1 N HCl (4 mL) and ex-
tracted with ethyl acetate (5 mL ꢁ 3). The combined organic layers
were washed sequentially with sat. NaHCO3 (5 mL), brine (5 mL),
dried over Na2SO4, filtered, and evaporated under reduced pres-
sure. The residue was purified by chromatography on a silica gel
column (hexanes:ethyl acetate = 3:1) to give 7 (0.46 g, 90%) as a
colorless oil: IR (neat, cmꢀ1): 2936, 1704, 1516; 1H NMR
(600 MHz, CDCl3) d 7.28–7.40 (m, 5H), 6.94–7.00 (m, 1H), 6.86–
6.89 (m, 1H), 6.72–6.76 (m, 1H), 5.19 (s, 2H), 4.08–4.33 (m, 2H),
2.88–3.08 (m, 4H), 1.76–1.98 (m, 8H), 1.49 (s, 9H); 13C NMR
(75 MHz, CDCl3) d 166.7, 157.1, 153.9, 153.3, 135.9, 133.4, 128.6,
128.4, 128.3, 119.2, 114.3, 107.5, 83.2, 81.6, 66.8, 64.1, 62.5, 49.4,
28.6, 28.0, 27.5, 26.8; HRMS (FAB) calcd for C28H34FN3O5 (M)+Å,
511.2482; found 511.2473.
5.2.6. 10-(2-Fluoro-4-((R)-5-(hydroxymethyl)-2-oxooxazolidin-
3-yl)phenyl)-2-oxa-3-azaspiro[bicyclo[2.2.1]heptane-7,40-pipe
ridine]-3-carboxylate (8a) and tert-butyl 10-(4-((R)-5-(butyrylo
xymethyl)-2-oxooxazolidin-3-yl)-2-fluorophenyl)-2-oxa-3-azas
piro[bicyclo[2.2.1]heptane-7,40-piperidine]-3-carboxylate (8b)
Compound 7 (0.41 g, 0.80 mmol) was dissolved in 4 mL of anhy-
drous tetrahydrofuran in a 10-mL oven-dried, round-bottomed
flask. The solution was cooled to ꢀ78 °C using dry ice-acetone bath
and n-butyl lithium (1.6 M in hexane, 1.0 mL, 1.6 mmol) was
added. After stirred at that temperature for 15 min, the solution
was treated with (R)-glycidyl butyrate (0.15 mL, 1.0 mmol) and
slowly warmed to 25 °C. After stirred for additional 2 h, the reac-
tion mixture was quenched with sat. NH4Cl (3 mL) and extracted
with ethyl acetate (5 mL ꢁ 3). The combined organic layers were
washed with brine (5 mL), dried over Na2SO4, filtered, and evapo-
rated under reduced pressure. The residue was purified by chroma-
tography on a silica gel column (hexanes:ethyl acetate = 1:1) to
give 8a (0.32 g, 85%) and 8b (22 mg, 5%) as light yellow oils. 8a:
IR (neat, cmꢀ1): 3421 (br), 2968, 2360, 1732, 1516; 1H NMR
(500 MHz, CDCl3) d 7.43 (d, J = 14.2 Hz, 1H), 7.09 (m, 1H), 6.94
(m, 1H), 4.70–4.78 (m, 1H), 4.10–4.32 (m, 2H), 4.08 (m, 2H),
3.93–4.01 (m, 3H), 3.72–3.80 (m, 1H), 2.92–3.14 (m, 4H), 1.74–
2.00 (m, 8H), 1.49 (s, 9H); 13C NMR (125 MHz, CDCl3) d 156.5,
5.2.8. tert-Butyl 10-(4-((R)-5-(azidomethyl)-2-oxooxazolidin-3-
yl)-2-fluorophenyl)-2-oxa-3-azaspiro[bicyclo[2.2.1]heptane-7,
40-piperidine]-3-carboxylate (10)
A 10-mL oven-dried, round-bottomed flask was charged with
compound
9 (0.28 g, 0.5 mmol) and sodium azide (65 mg,
1.0 mmol) in anhydrous dimethylsulfoxide (4 mL). The solution
was stirred at 80 °C for 8 h. After the reaction mixture was cooled
to room temperature, water (4 mL) was added. The mixture was
extracted with ethyl acetate (5 mL ꢁ 5). The combined organic
layers were washed with brine (5 mL), dried over Na2SO4, filtered,
and evaporated under reduced pressure. The residue was purified
by chromatography on
a silica gel column (hexanes:ethyl
acetate = 1:1) to give 10 (0.19 g, 74%) as a yellow oil: IR (neat,
cmꢀ1): 2921, 2105, 1717, 1514; 1H NMR (500 MHz, CDCl3) d 7.42
(dd, J = 14.2, 2.4 Hz, 1H), 7.10–7.14 (m, 1H), 6.95 (t, J = 9.0 Hz,
1H), 4.76–4.81 (m, 1H), 4.10–4.34 (m, 2H), 4.04 (dd, J = 8.8,
8.8 Hz, 1H), 3.82 (dd, J = 8.8, 6.2 Hz, 1H), 3.70 (dd, J = 13.2, 4.6 Hz,
1H), 3.58 (dd, J = 13.2, 4.6 Hz, 1H), 2.94–3.12 (m, 4H), 1.82–2.00
(m, 8H), 1.50 (s, 9H); 13C NMR (125 MHz, CDCl3) d 156.7, 154.8,
154.0, 137.1, 133.1, 119.6, 114.0, 107.7, 83.3, 82.0, 70.7, 64.2,
53.2, 49.6, 47.9, 28.8, 28.5, 27.9, 27.1.

C. Ji et al. / Bioorg. Med. Chem. 20 (2012) 3422–3428
3427
5.2.9. tert-Butyl 10-(4-((S)-5-(aminomethyl)-2-oxooxazolidin-3-
yl)-2-fluorophenyl)-2-oxa-3-azaspiro[bicyclo[2.2.1]heptane-7,
40-piperidine]-3-carboxylate (11)
with 5 mL of sat. NaHCO3 solution. The mixture was extracted with
ethyl acetate (5 mL ꢁ 3). The combined organic layers were
sequentially washed with sat. NaHCO3 (5 mL), brine (5 mL), dried
over Na2SO4, filtered, and evaporated under reduced pressure.
The residue was purified by chromatography on a silica gel column
(100% ethyl acetate) to give 14 (58 mg, 53%) as a colorless oil: IR
(neat, cmꢀ1): 2929, 1674, 1517; 1H NMR (600 MHz, CDCl3) d 7.43
(dd, J = 14.1, 2.6 Hz, 1H), 7.30 (d, J = 3.5 Hz, 1H), 7.07–7.10 (m,
1H), 6.95 (dd, J = 9.1, 9.1 Hz, 1H), 6.55 (d, 1H, J = 3.5 Hz), 5.9 (t,
J = 6.2 Hz, 1H), 4.75–4.79 (m, 1H), 4.22 (d, 1H, J = 15.6 Hz), 4.07
(s, 1H), 4.03 (t, J = 9.1 Hz, 1H), 3.99 (d, J = 15.6 Hz, 1H), 3.70–3.76
(m, 2H), 3.58–3.63 (m, 1H), 3.37 (s, 1H), 2.96–3.17 (m, 4H), 2.16–
2.27 (m, 4H), 2.03 (s, 3H), 1.85–1.99 (m, 4H); 13C NMR (150 MHz,
CDCl3) d 170.9, 156.5, 154.2, 112.9, 111.1, 88.9, 80.6, 71.8, 53.2,
49.6, 47.6, 42.0, 29.1, 28.9, 23.2; HRMS (FAB) calcd for C26H30FN5O7
(M)+Å: 543.2129; found 543.2115.
Compound 10 (0.14 g, 0.28 mmol) was dissolved in 4 mL of
methanol in a 10-mL round-bottomed flask under argon. 10% Pd
on carbon (15 mg) was added and the flask was flushed with H2
gas and left to stir under a hydrogen atmosphere (balloon) for
8 h. After purging with argon, the mixture was filtered and concen-
trated in vacuo to give compound 11 (0.13 g, 95%) as a viscous oil:
IR (neat, cmꢀ1): 2980, 1515; 1H NMR (500 MHz, CDCl3) d 7.45 (dd,
J = 14.2, 2.4 Hz, 1H), 7.10–7.16 (m, 1H), 6.95 (dd, J = 9.1, 9.0 Hz, 1H),
4.65–4.83 (m, 1H), 4.10–4.34 (m, 2H), 4.00–4.04 (m, 1H), 3.81–3.84
(m, 1H), 2.89–3.14 (m, 6H), 1.80–2.00 (m, 8H), 1.50 (s, 9H); 13C
NMR (125 MHz, CDCl3) d 156.6, 154.6, 136.6, 133.3, 119.3, 113.4,
107.4, 107.2, 83.3, 81.8, 73.7, 71.9, 64.2, 62.6, 54.5, 49.5, 47.8,
44.9, 36.4, 28.8, 28.5, 27.9, 27.1; HRMS (FAB) calcd for C24H33FN4O5
(M)+Å: 476.2435; found 476.2449.
5.2.13. tert-Butyl 8-(4-((S)-5-(aminomethyl)-2-oxooxazolidin-3-
yl)-2-fluorophenyl)-4-hydroxy-8-azaspiro[4.5]decan-1-ylcarba
mate (15)
5.2.10. tert-Butyl 10-(4-((S)-5-(acetamidomethyl)-2-oxooxazoli
din-3-yl)-2-fluorophenyl)-2-oxa-3-azaspiro[bicyclo[2.2.1]hep
tane-7,40-piperidine]-3-carboxylate (12)
Compound 11 (0.12 g, 0.25 mmol) was dissolved in a mixture of
3 mL of acetonitrile and 1 mL of water in a 10-mL oven-dried, round-
bottomed flask. Molybdenumhexacarbonyl (20 mg, 0.07 mmol) and
sodium borohydride (15 mg, 0.50 mmol) were added to the solution
in the indicated order. The mixture was stirred at 60 °C for 6 h. After
the reaction mixture cooled to room temperature, all the solvent
was removed under reduced pressure, and the residue was
purified by chromatography on a silica gel column (ethyl acetate:
MeOH = 10:1) to give compound 15 (76 mg, 64%) as a colorless oil:
IR (neat, cmꢀ1): 3487, 2927, 1747, 1616; 1H NMR (300 MHz, CDCl3)
d 7.40 (d, J = 14.1, 1.9 Hz, 1H), 6.98–7.06 (m, 1H), 6.86–6.96 (m, 1H),
5.46–5.54 (m, 1H), 4.58–4.76 (m, 1H), 3.92–4.06 (m, 3H), 3.73–3.79
(m, 1H), 2.84–3.12 (m, 6H), 2.14–2.32 (m, 4H), 1.66–2.00 (m, 6H),
1.40 (s, 9H). 13C NMR (75 MHz, CDCl3) d 157.0, 155.5, 154.5, 153.7,
137.0, 132.7, 119.1, 113.6, 107.2, 106.9, 80.0, 78.8, 77.4, 73.7, 55.3,
48.2, 47.6, 44.8, 33.2, 31.1, 30.5, 28.3, 27.2; HRMS (FAB) calcd for
Compound 11 (0.11 g, 0.23 mmol) was dissolved in 4 mL of
dichloromethane in
a 10-mL round-bottomed flask. Acetic
anhydride (0.08 mL, 0.80 mmol) and triethylamine (0.11 mL,
0.80 mmol) were added and the mixture was stirred at room tem-
perature for 2 h. After neutralized with 1 N HCl, the mixture was
extracted with ethyl acetate (5 mL ꢁ 3). The combined organic lay-
ers were washed sequentially with sat. NaHCO3 (5 mL), brine
(5 mL), dried over Na2SO4, filtered, and evaporated under reduced
pressure. The residue was purified by chromatography on a silica
gel column (100% ethyl acetate) to give 12 (84 mg, 70%) as a color-
less oil: IR (neat, cmꢀ1): 2922, 1749, 1516; 1H NMR (500 MHz,
CDCl3) d 7.42 (dd, J = 14.2, 2.4 Hz, 1H), 7.04–7.09 (m, 1H), 6.93
(dd, J = 9.1, 9.0 Hz, 1H), 6.30 (t, J = 6.0 Hz 1H), 4.75–4.80 (m, 1H),
4.10–4.32 (m, 2H), 4.02 (d, J = 9.0, 9.0 Hz, 1H), 3.74–3.77 (m, 1H),
3.67–3.72 (m, 1H), 3.58–3.64 (m, 1H), 2.93–3.11 (m, 4H), 2.02 (s,
3H), 1.79–1.99 (m, 8H), 1.50 (s, 9H); 13C NMR (125 MHz, CDCl3) d
171.1, 156.5, 154.5, 154.3, 136.8, 133.0, 119.3, 113.8, 107.4, 83.3,
81.8, 71.8, 64.2, 62.6, 49.4, 47.6, 41.9, 28.7, 28.5, 27.9, 27.1, 23.3;
C
24H35FN4O5 (M)+Å: 478.2591; found 478.2592.
5.2.14. tert-Butyl 8-(4-((S)-5-(acetamidomethyl)-2-oxooxazoli
din-3-yl)-2-fluorophenyl)-4-hydroxy-8-azaspiro[4.5]decan-1-
ylcarbamate (16)
HRMS (FAB) calcd for
518.2518.
C
26H35FN4O6 (M)+Å: 518.2541; found
Compound 12 (21 mg, 0.04 mmol) was dissolved in a mixture of
3 mL of acetonitrile and 1 mL of water in a 10-mL round-bottomed
flask. Molybdenumhexacarbonyl (5 mg, 0.02 mmol) and sodium
borohydride (5 mg, 0.16 mmol) were added to the solution in the
indicated order. The mixture was stirred at 60 °C for 6 h. After
the reaction mixture cooled to room temperature, all the solvent
was removed under reduced pressure, and the residue was purified
by chromatography on a silica gel column (hexanes:ethyl ace-
tate = 1:1) to give compound 16 (16 mg, 80%) as a colorless oil:
IR (neat, cmꢀ1): 3331 (br), 2962, 1686, 1518; 1H NMR (300 MHz,
CDCl3) d 7.39 (d, J = 14.2 Hz, 1H), 6.90–7.04 (m, 2H), 6.32–6.38
(m, 1H), 5.38–5.48 (m, 1H), 4.72–4.81 (m, 1H), 3.96–4.10 (m,
3H), 3.56–3.76 (m, 3H), 2.86–3.16 (m, 4H), 1.72–2.08 (m, 11H),
1.44 (s, 9H); 13C NMR (75 MHz, CDCl3) d 171.2, 157.0, 155.5,
154.4, 153.8, 149.9, 137.3, 132.4, 129.7, 128.7, 126.9, 126.2,
119.4, 113.8, 107.4, 80.2, 78.9, 77.4, 71.8, 55.6, 48.5, 47.9, 47.7,
42.2, 33.6, 31.4, 30.8, 30.1, 28.7, 27.4, 23.2; HRMS (FAB) calcd for
5.2.11. N-(((5S)-3-(3-fluoro-4-(3-((5-nitrofuran-2-yl)methyl)-2-
oxa-3-azaspiro[bicyclo[2.2.1]heptane-7,40-piperidine]-10-yl)
phenyl)-2-oxooxazolidin-5-yl)methyl)acetamide (13)
Compound 12 (20 mg, 0.04 mmol) was dissolved in 3 mL of
dichloromethane in a 10-mL round-bottomed flask. Trifluoroacetic
acid (0.5 mL) was added and the mixture was stirred at room tem-
perature for 1 h. The solution was concentrated under reduced
pressure to give the cyclic hydroxylamine which is used without
further purification: IR (neat, cmꢀ1): 2980, 1644, 1419; 1H NMR
(300 MHz, CD3OD) d 7.50 (dd, J = 14.6, 2.5 Hz, 1H), 7.08–7.21 (m,
2H), 4.74–4.83 (m, 2H), 4.24–4.27 (m, 1H), 4.12 (dd, J = 9.2,
9.1 Hz, 1H), 3.77–3.82 (m, 1H), 3.54–3.58 (m, 2H), 3.01–3.22 (m,
4H), 1.90–2.25 (m, 11H); HRMS (FAB) calcd for C21H28FN4O4
(M+H)+, 419.2095; found, 419.2086.
5.2.12. N-(((5S)-3-(3-fluoro-4-(3-((5-nitrofuran-2-yl)methyl)-2-
oxa-3-azaspiro[bicyclo[2.2.1]heptane-7,40-piperidine]-10-yl)phe
nyl)-2-oxooxazolidin-5-yl)methyl)acetamide (14)
C
26H37FN4O6 (M)+Å, 520.2697; found 520.2697.
Compound 13 (84 mg, 0.2 mmol) and 5-nitrofuraldehyde
(84 mg, 0.6 mmol) were dissolved in 4 mL of 1,2-dichloroethane
in a 10-mL round-bottomed flask. After stirred at room tempera-
ture for 15 min, the solution was treated with sodium triacetoxy-
borohydride (0.12 g, 0.6 mmol) and acetic acid (0.05 mL). The
reaction was stirred at room temperature for 2 h and quenched
Acknowledgments
This research was supported in part by grants GM 68012 and
GM 075885 from the National Institutes of Health (NIH) as well
as Eli Lilly and Company. We gratefully acknowledge the use of
the NMR facilities provided by the Lizzadro Magnetic Resonance

3428
C. Ji et al. / Bioorg. Med. Chem. 20 (2012) 3422–3428
21. Renslo, A. R.; Jaishankar, P.; Venkatachalam, R.; Hackbarth, C.; Lopez, S.; Patel,
D. V.; Gordeev, M. F. J. Med. Chem. 2005, 48, 5009.
Research Center at the University of Notre Dame (UND) under the
direction of Dr. Jaroslav Zajicek and the mass spectrometry services
provided by The UND Mass Spectrometry & Proteomics Facility
(Mrs. N. Sevova, Dr. W. Boggess, and Dr. M. V. Joyce; supported
by the National Science Foundation under CHE-0741793). We
thank Mrs. Patricia A. Miller (UND) for antibacterial susceptibility
testing.
22. Gordeev, M. F.; Renslo, A.; Patel, D. V. U. S. Patent 6,875,784, 2005.
23. Barbachyn, M. R.; Brickner, S. J.; Hutchinson, D. K. U. S. Patent 6,090,820, 2000.
24. Patel, M. V.; Deshpande, P. K.; Sindkhedkar, M. D.; Gupte, S. V.; Chugh, Y.;
Shetty, N.; Shukla, M. C.; Yeole, R. D.; De Souza, N. J. U. S. Patent Application
2004/0063954, 2004.
25. Chugh, Y.; Shetty, N.; Deshpande, P. K.; Sindkhedkar, M. D.; Jafri, M. D.; Yeole, R.
D.; Shukla, M. C.; Gupte, S. V.; Patel, M. V.; De Souza, N. J. U. S. Patent
Application 2004/0235900, 2004.
26. Prasad, J. V. Curr. Opin. Microbiol. 2007, 10, 454.
27. Tietze, L. F.; Kettschau, G. Top. Curr. Chem. 1997, 189,
Heterocyclic Synthesis I).
References and notes
1 (Stereoselective
1. Spellberg, B.; Guidos, R.; Gilbert, D.; Bradley, J.; Boucher, H. W.; Scheld, W. M.;
Bartlett, J. G.; Edwards, J., Jr. Clin. Infect. Dis. 2008, 46, 155.
2. Boucher, H. W.; Talbot, G. H.; Bradley, J. S.; Edwards, J. E.; Gilbert, D.; Rice, L. B.;
Scheld, M.; Spellberg, B.; Bartlett, J. Clin. Infect. Dis. 2009, 48, 1.
3. Barbachyn, M. R.; Ford, C. W. Angew. Chem., Int. Ed. 2003, 42, 2010.
4. Gravestock, M. B. Curr. Opin. Drug Discovery Dev. 2005, 8, 469.
5. Hutchinson, D. K. Expert Opin. Ther. Pat. 2004, 14, 1309.
6. Renslo, A. R.; Luehr, G. W.; Gordeev, M. F. Bioorg. Med. Chem. 2006, 14, 4227.
7. Ippolito, J. A.; Kanyo, Z. F.; Wang, D. P.; Franceschi, F. J.; Moore, P. B.; Steitz, T.
A.; Duffy, E. M. J. Med. Chem. 2008, 51, 3353.
28. Vogt, P. F.; Miller, M. J. Tetrahedron 1998, 54, 1317.
29. Yamamoto, H.; Momiyama, N. Chem. Commun. (Cambridge, U. K.) 2005, 3514.
30. Bodnar, B. S.; Miller, M. J. Angew. Chem., Int. Ed. 2011, 50, 5629.
31. Li, F. Z.; Yang, B. Y.; Miller, M. J.; Zajicek, J.; Noll, B. C.; Möllmann, U.; Dahse, H.
M.; Miller, P. A. Org. Lett. 2007, 9, 2923.
32. Krchnak, V.; Waring, K. R.; Noll, B. C.; Möllmann, U.; Dahse, H. M.; Miller, M. J. J.
Org. Chem. 2008, 73, 4559.
33. Ji, C.; Miller, M. J. Tetrahedron Lett. 2010, 51, 3789.
34. Lin, W. M.; Gupta, A.; Kirn, K. H.; Mendel, D.; Miller, M. J. Org. Lett. 2009, 11,
449.
8. Leach, K. L.; Swaney, S. M.; Colca, J. R.; McDonald, W. G.; Blinn, J. R.; Thomasco,
L. M.; Gadwood, R. C.; Shinabarger, D.; Xiong, L.; Mankin, A. S. Mol. Cell 2007, 26,
393.
9. Barry, A. L. Antimicrob. Agents Chemother. 1988, 32, 150.
10. Neu, H. C.; Novelli, A.; Saha, G.; Chin, N. X. Antimicrob. Agents Chemother. 1988,
32, 580.
11. Slee, A. M.; Wuonola, M. A.; McRipley, R. J.; Zajac, I.; Zawada, M. J.;
Bartholomew, P. T.; Gregory, W. A.; Forbes, M. Antimicrob. Agents Chemother.
1987, 31, 1791.
12. Brickner, S. J.; Hutchinson, D. K.; Barbachyn, M. R.; Manninen, P. R.; Ulanowicz,
D. A.; Garmon, S. A.; Grega, K. C.; Hendges, S. K.; Toops, D. S.; Ford, C. W.;
Zurenko, G. E. J. Med. Chem. 1996, 39, 673.
13. Brickner, S. J.; Barbachyn, M. R.; Hutchinson, D. K.; Manninen, P. R. J. Med. Chem.
1981, 2008, 51.
14. Tsiodras, S.; Gold, H. S.; Sakoulas, G.; Eliopoulos, G. M.; Wennersten, C.;
Venkataraman, L.; Moellering, R. C.; Ferraro, M. J. Lancet 2001, 358, 207.
15. Gonzales, R. D.; Schreckenberger, P. C.; Graham, M. B.; Kelkar, S.; DenBesten, K.;
Quinn, J. P. Lancet 2001, 357, 1179.
16. Auckland, C.; Teare, L.; Cooke, F.; Kaufmann, M. E.; Warner, M.; Jones, G.;
Bamford, K.; Ayles, H.; Johnson, A. P. J. Antimicrob. Chemother. 2002, 50, 743.
17. Seedat, J.; Zick, G.; Klare, I.; Konstabel, C.; Weiler, N.; Sahly, H. Antimicrob.
Agents Chemother. 2006, 50, 4217.
18. Hutchinson, D. K. Curr. Top. Med. Chem. 2003, 3, 1021.
19. Paget, S. D.; Foleno, B. D.; Boggs, C. M.; Goldschmidt, R. M.; Hlasta, D. J.;
Weidner-Wells, M. A.; Werblood, H. M.; Wira, E.; Bush, K.; Macielag, M. J.
Bioorg. Med. Chem. Lett. 2003, 13, 4173.
35. Li, F. Z.; Brogan, J. B.; Gage, J. L.; Zhang, D. Y.; Miller, M. J. J. Org. Chem. 2004, 69,
4538.
36. Kim, K. H.; Miller, M. J. Tetrahedron Lett. 2003, 44, 4571.
37. Li, F. Z.; Miller, M. J. J. Org. Chem. 2006, 71, 5221.
38. Li, F. Z.; Warshakoon, N. C.; Miller, M. J. J. Org. Chem. 2004, 69, 8836.
39. Lin, W. M.; Virga, K. G.; Kim, K. H.; Zajicek, J.; Mendel, D.; Miller, M. J. J. Org.
Chem. 2009, 74, 5941.
40. Tucker, J. A.; Allwine, D. A.; Grega, K. C.; Barbachyn, M. R.; Klock, J. L.; Adamski,
J. L.; Brickner, S. J.; Hutchinson, D. K.; Ford, C. W.; Zurenko, G. E.; Conradi, R. A.;
Burton, P. S.; Jensen, R. M. J. Med. Chem. 1998, 41, 3727.
41. Das, B.; Rudra, S.; Yadav, A.; Ray, A.; Rao, A.; Srinivas, A.; Soni, A.; Saini, S.;
Shukla, S.; Pandya, M.; Bhateja, P.; Malhotra, S.; Mathur, T.; Arora, S. K.; Rattan,
A.; Mehta, A. Bioorg. Med. Chem. Lett. 2005, 15, 4261.
42. Cicchi, S.; Goti, A.; Brandi, A.; Guarna, A.; Desarlo, F. Tetrahedron Lett. 1990, 31,
3351.
43. Yan, S. S.; Miller, M. J.; Wencewicz, T. A.; Möllmann, U. Bioorg. Med. Chem. Lett.
2010, 20, 1302.
44. Typical MIC values of linezolid against MSSA and MRSA are 1–2 and 0.5–2 mg
mL-1, respectively. See Phillips, O. A.; Udo, E. E.; Ali, A. A. M.; Samuel, S. M. Eur.
J. Med. Chem. 2007, 42, 214.
45. Williams, K. N.; Stover, C. K.; Zhu, T.; Tasneen, R.; Tyagi, S.; Grosset, J. H.;
Nuermberger, E. Antimicrob. Agents Chemother. 2009, 53, 1314.
46. Collins, L. A.; Franzblau, S. G. Antimicrob. Agents Chemother. 1997, 41, 1004.
47. Cho, S. H.; Warit, S.; Wan, B.; Hwang, C. H.; Pauli, G. F.; Franzblau, S. G.
Antimicrob. Agents Chemother. 2007, 51, 1380.
20. Fukuda, Y. H.; Hammond, M. L. U. S. Patent 6,897,230, 2005.