Biaryl isoxazolinone antibacterial agents

Article abstract of DOI:10.1016/j.bmcl.2005.04.003

In an era of increasing resistance to classical antibacterial agents, the synthetic oxazolidinone series of antibiotics has attracted much interest. Zyvox was the first oxazolidinone to be approved for clinical use against infections caused by multi-drug

Full text of DOI:10.1016/j.bmcl.2005.04.003

Bioorganic & Medicinal Chemistry Letters 15 (2005) 2728–2733
Biaryl isoxazolinone antibacterial agents
Claude A. Quesnelle,a,* Patrice Gill,a Stephan Roy,a Marco Dodier,a Anne Marinier,a
Alain Martel,a Lawrence B. Snyder,b Stanley V. DꢀAndrea,b Joanne J. Bronson,b
MaryBeth Frosco,b Danielle Beaulieu,b Glen A. Warr,b Ken L. DenBleyker,b
Terry M. Stickle,b Hyekyung Yang,b Susan E. Chaniewski,b Cheryl A. Ferraro,b
Dennis Taylor,b John W. Russell,b Kenneth S. Santone,b Junius Clarke,b
Rebecca L. Drain,b Jay O. Knipe,b Kathleen Mosureb and John F. Barrettb
aBristol-Myers Squibb Pharmaceutical Research Institute, Discovery Chemistry, 100, boul. de l’Industrie,
´
Candiac, Quebec, Canada J5R 1J1
bBristol-Myers Squibb Pharmaceutical Research Institute, 5 Research Parkway, Wallingford, CT 06492, USA
Received 18 February 2005; revised 31 March 2005; accepted 4 April 2005
Abstract—In an era of increasing resistance to classical antibacterial agents, the synthetic oxazolidinone series of antibiotics has
attracted much interest. ZyvoxTM was the first oxazolidinone to be approved for clinical use against infections caused by multi-drug
resistant Gram-positive bacteria. In the course of studies directed toward the discovery of novel antibacterial agents, a new series of
synthetic phenyl-isoxazolinone agents that displayed potent activity against Gram-positive bacterial strains was recently discovered
at Bristol-Myers Squibb. Extensive investigation of various substitutions on the phenyl ring was then undertaken. We report here,
the synthesis and antibacterial activity of a series of biaryl isoxazolinone compounds.
ꢀ 2005 Elsevier Ltd. All rights reserved.
The development of bacterial resistance to current ther-
apies is an important driving force behind the discovery
of new antibiotics that function through novel mecha-
nisms of action. The incidence of vancomycin-resistant
Enterococcus faecium (VRE) and methicillin-resistant
Staphylococcus aureus (MRSA) infections in intensive-
care units of hospitals has significantly increased be-
tween 1989 and 1997.1 A more troubling occurrence
was the first case of vancomycin-resistant S. aureus
(VRSA) infection.2 The oxazolidinones, a new class of
synthetic antibacterial agents, are active against a vari-
ety of clinically important susceptible and resistant
Gram-positive organisms. Although their mode of ac-
tion is not clearly understood, these compounds appear
to inhibit protein synthesis at the initiation of transla-
tion by binding directly to the 50S ribosomal subunit.3
and development was discontinued. This was followed
by the Pharmacia clinical candidates eperezolid (2) and
linezolid (3, now marketed as ZyvoxTM).3,5 ZyvoxTM is
currently being used for complicated and uncomplicated
skin and soft tissue infections, community- and hospital-
acquired pneumonia and drug-resistant Gram-positive
infections (MRSA and VRE). Several recent compounds
in preclinical development have been disclosed, includ-
ing AZD25636 from AstraZeneca and RBX 7644 (Ranbe-
zolid)7 from Ranbaxy.
Linezolid possesses many attributes which make it an
attractive starting point for the design of novel antibac-
terials with a similar mechanism of action. Our investi-
gation has resulted in the discovery of the 4-
arylisoxazolin-5-one (4)8 as an oxazolidinone isostere.
Consequently, this paper will outline the synthesis and
antibacterial activity of a series of aryl and heteroaryl
phenyl-isoxazolinones.
The first oxazolidinone was reported by Dupont (1,
Dup-721, Fig. 1)4 but was eventually shown to be toxic
The preparation of the various aryl or heteroaryl phenyl-
isoxazolinones is as follows. To facilitate analog pre-
paration, two common intermediates were prepared that
allowed for late stage derivatization. The diazonium
Keywords: Antibacterial; Oxazolidinone; Isoxazolinone.
*
Corresponding author. Tel.: +1 450 444 6121; fax: +1 450 444
4166; e-mail: claude.quesnelle@bms.com
0960-894X/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.04.003

C. A. Quesnelle et al. / Bioorg. Med. Chem. Lett. 15 (2005) 2728–2733
2729
Figure 1. Early clinical oxazolidinones and BMS isoxazolinone antibacterial core.
compound 7 and the iodo derivative 9, that were used in
a modified Suzuki reaction9 or a Stille coupling employ-
ing Farinaꢀs method.10 Briefly (Scheme 1), methyl-p-
nitrophenyl acetate (5) was reacted with DMF–DMA
and, subsequently, hydroxylamine to give the isoxazoli-
none core. After introduction of the acetamidomethyl
side chain (6), the nitro functionality was reduced to
the aniline which was then converted to the diazonium
compound (7). Preparation of analogs via cross-cou-
pling using a modified Suzuki reaction9 with boronic
acids were then carried out to introduce various substi-
tuents (Scheme 2). The preparation of the iodo deriva-
tive (9) started with ethyl-p-aminophenyl acetate (8).
After diazotization and reaction with potassium iodide,
the resulting acetate was treated with ethyl formate and
hydroxylamine to afford the iodophenyl-isoxazolinone.
Reaction with the acetamidoacetoxy-methyl electrophile
gave intermediate 9 which was submitted to Stille cou-
pling conditions employing Farinaꢀs method10 (Scheme
2) to introduce various substituents.
Scheme 2. Cross-coupling methodology for the preparation of isox-
azolinone analogs. Reagents and conditions: For 7: ArB(OH)2/
Pd(OAc)2/MeOH, 50 ꢁC; For 9: ArSnBu3/Pd2(dba)3/AsPh3/NMP/
70 ꢁC.
Reduced analogs, for example the dihydropyran, dihy-
drothiopyran, and dehydropiperidines, were prepared
starting with the corresponding vinyl stannanes (54a–c).
These were easily prepared (Scheme 3) via addition of
the tin anion onto ketones 53a–c followed by elimina-
tion.11 These stannanes were then used as the organome-
tallic counterparts in Stille reactions with the iodo
derivative 9, giving 55a–c. Functional group transform-
ations provided the sulfoxide (55d), sulfone (55e), the
deprotected dehydropiperidine (55f), as well as the acyl-
ated analogs (55g–i).
Scheme 3. Synthesis of reduced heterocyclic analogs. Reagents and
conditions: (a) 1. Bu3SnLi/THF/ꢀ78 ꢁC, 2. MsCl/Et3N/CH2Cl2: 36%
for 54a, 78% for 54b, 59% for 54c; (b) 9/Pd2(dba)3/AsPh3/NMP/70 ꢁC:
70% for 55a, 53% for 55b, 57% for 55c; (c) for X = S: 1 equiv
CH3CO3H/MeOH/CH2Cl2 gave 55d (73%); excess CH3CO3H gave 55e
(77%); (d) For X = NBoc: TFA/CH2Cl2: 93% for 55f; (e) For 55g:
Ac2O/Py/0 ꢁC (63%). For 55h: 1. TBSOCH2COCl/Et3N/DCM/DMF
(65%), 2. TFA/DCM/0 ꢁC (65%). For 55i: 1H-pyrrole-1-carboxami-
dine hydrochloride/i-Pr2NEt/DMF/rt (97%).
quently (Scheme 4), Suzuki cross-coupling12 of vinyl
triflates 57a,b with pinacol arylboronate 5613 provided
the desired analogs 58a,b. Reduction at this stage fol-
lowed by construction of the isoxazolinone was accom-
plished in standard fashion. Further elaboration
provided the desired analogs (60a–e).
The reduced (tetrahydropyran and piperidine) analogs
required the development of de novo syntheses as reduc-
tion of the vinyl-isoxazolinone derivatives failed. Conse-
Within these compounds, significant SAR can be ex-
tracted. Various substitutions on the phenyl ring are tol-
erated, as many potent compounds against S. aureus
(Table 1) and Gram-positive organisms were obtained.
Bulky substituents are detrimental (cf. 20), and mono-
and di-substituted analogs are preferred over tri-substi-
tuted derivatives. In general, introduction of heteroaryl
groups gave potent compounds against staphylococcal
strains. Only 38 and 51 were inactive.
Scheme 1. Preparation of the isoxazolinone cross-coupling precursors.
Reagents and conditions: (a) 1. DMF–DMA, 2. H2NOHÆH2O/EtOH/
NEt3, 3. H2SO4/AcOCH2NHAc (92%); (b) 1. H2/Pd–C/MeOH (85%),
2. NaNO2/HBF4/H2O/EtOH (72%); (c) 1. NaNO2/KI/HCl/THF/H2O
(89%), 2. (i) NaH/EtOCHO, (ii) H2NOH/MeOH (88%), 3. H2SO4/
AcOCH2NHAc (72%).
H. influenzae activity was obtained with a few aryl ana-
logs: 4-fluoro (11), 2,4-difluoro (12), 4-CO2H (27), 4-CN
(25), 4-COCH3 (31) and 3-NH2 (22), but combining

2730
C. A. Quesnelle et al. / Bioorg. Med. Chem. Lett. 15 (2005) 2728–2733
Table 1 (continued)
Compd
Structure
MICa
20
64 (>32)/>32
21
22
23
24
25
26
27
0.5 (16)/>32
0.125 (2)/2
0.03 (1)/>32
0.25 (8)/>32
0.06 (2)/4
Scheme 4. Alternate synthesis of fully reduced isoxazolinone analogs.
Reagents and conditions: (a) PdCl2(dppf)/K3PO4/dioxane/80 ꢁC: 71%
for 58a, 97% for 58b; (b) H2 (30 psi)/10% Pd–C/EtOH: 97% for 59a,
96% for 59b; (c) 1. NaH/EtOCHO, 2. NH2OH/MeOH/"#, 3.
AcOCH2NHAc/K2CO3/CH2Cl2: 31% for 60a, 38% for 60b; (d) TFA/
CH2Cl2 (89%); (e) For 60d: Ac2O/Py/0 ꢁC (48%). For 60e: 1.
TBSOCH2COCl/Et3N/DCM/DMF (79%), 2. TFA/DCM/0 ꢁC (78%).
Table 1. Minimum inhibitory concentration values for isoxazolinone
analogs
Compd
Structure
MICa
0.06 (0.5)/>32
1 (8)/2
10
1 (32)/>32
11
12
0.03 (4)/2
28
29
16 (16)/8
0.125 (4)/4
32(>64)/64
13
14
0.06 (8)/>32
1 (2)/8
30
31
4 (32)/32
0.06 (2)/4
15
16
0.5 (8)/32
32
33
34
0.125 (4)/4
0.5 (16)/>32
1 (2)/8
0.06 (1)/>64
17
18
2 (8)/>32
0.25 (1)/32
35
36
0.5 (4)/2
19
4 (16)/>32
0.06 (0.5)/2

C. A. Quesnelle et al. / Bioorg. Med. Chem. Lett. 15 (2005) 2728–2733
2731
Table 1 (continued)
Table 1 (continued)
Compd
Structure
MICa
Compd
Structure
MICa
37
0.25 (2)/8
55d
0.5(1)/2
55e
55c
0.5(1)/4
38
39
32 (>64)/64
0.25 (0.25)/4
8(32)/>64
40
8 (16)/>64
55f
8(8)/16
41
42
4 (8)/>64
2 (8)/>64
55g
0.25(0.5)/2
55h
55i
0.25(0.5)/2
8(16)/32
1(2)/32
43
44
0.5 (4)/4
1 (32)/16
60a
60b
60c
60d
45
0.125 (4)/4
8(16)/32
32(16)/32
1(1)/8
46
47
48
0.25 (8)/2-8
0.03 (0.03)/4
0.25 (4)/>64
60e
3
1(2)/16
1(2)/32
49
50
51
0.25 (4)/32
0.5 (1)/64
Linezolid
a MIC = Minimum inhibitory concentration for the strains and in the
format: S. aureus (+10% calf serum)/H. influenzae (lg/mL).
these substituents was detrimental (cf. 29 and 30). In
vivo efficacy was assessed for 11 and 27 (Table 2), but
only 11 was found to be as active as linezolid in vivo.
8 (>64)/>64
The pyridines (34–37) were found particularly active
against both S. aureus (and other Gram-positive, data
not shown) and H. influenzae strains. Some of them also
showed good in vivo efficacy (see 35 and 36, Table 2).
52
0.06 (8)/4
0.25(1)/4
55a
The pyrimidine 39 is also worthy of note for its antibac-
terial activity. It however showed borderline efficacy.
The thiazole, furan, and thiophene analogs (43, 45,
55b
1(4)/32

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C. A. Quesnelle et al. / Bioorg. Med. Chem. Lett. 15 (2005) 2728–2733
Table 2. Mouse in vivo efficacy (PD50) and pharmacokinetics (PK) for selected analogs
Compd
Structure
Miscellaneousa
Compd
Structure
Miscellaneousa
PD50 = 5.6 mg/kg/day
11
PD50 <5 mg/kg/day
55d
PK:
Cmax = 8.3 lg/mL
T1/2 = 22.2 min
AUC = 5.5 lgh/mL
PD50 >50 mg/kg/day
PK:
PD50 = 4 mg/kg/day
PK:
27
35
55e
55g
Cmax = 1.7 lg/mL
T1/2 = 8.5 min
Cmax = 17.7 lg/mL
T1/2 = 12.2 min
AUC = 19.4 lgh/mL
AUC = 0.56 lgh/mL
PD50 = 10 mg/kg/day
PK:
PD50 = 9 mg/kg/day
PK:
Cmax = 15.3 lg/mL
T1/2 = 86.7 min
AUC = 41.1 lgh/mL
Cmax = 2.6 lg/mL
T1/2 = 6.4 min
AUC = 1.5 lgh/mL
PD50 = 8.9 mg/kg/day
PK:
PD50 = 4 mg/kg/day
PK:
36
55h
Cmax = 17.7 lg/mL
T1/2 = 203 min
AUC = 56 lgh/mL
Cmax = 22.9 lg/mL
T1/2 = 23.5 min
AUC = 16.9 lgh/mL
PD50 = 14.1 mg/kg/day
PK:
39
45
60e
PD50 = 3.5 mg/kg/day
PD50 = 5–6 mg/kg/dayb
Cmax = 10.4 lg/mL
T1/2 = 103.2 min
AUC = 29.1 lgh/mL
PD50 >50 mg/kg/day
3
Linezolid
a PD50 = efficacy evaluation against S. aureus in an experimental systemic infection model in mice. Inoculum 1.05 · 107 cfu/mouse i.p. in 7% mucin.
Drugs dissolved in 10% DMSO, 5%Tw-80, and water, administered orally b.i.d., 1 and 5 h p.i. Death recorded for 8 days (10 mice per group).
b Vehicle = water.
and 47) also showed broad-spectrum antibacterial activ-
ity, but suffered from either CYP liabilities (data not
shown) or lack of efficacy (e.g., 45, Table 2).
In conclusion, the synthesis of C-linked derivatives was
shown to be straightforward from late stage intermedi-
ates through different cross-coupling approaches. Most
of the compounds were found to be potent against
Gram-positive strains. Some were also found to have
broad-spectrum antibacterial activity: 22 (3-NH2-phenyl),
27 (4-CO2H-phenyl), 39 (4-pyrimidinyl), 47 (3-thienyl),
55h (tetrahydropyridine), and 55d (dihydrothiopyran-
sulfoxide). The sulfoxide 55d was shown to be slightly
less toxic than linezolid in a 7-day rat toxicity assay.
In the reduced heterocycle series, the dihydropyran 55a
showed encouraging H. influenzae potency. Tetrahydro-
pyran 60a (the reduced analog of 55a) displayed slightly
reduced potency versus all strains, while the dihydrothio-
pyran 55b showed lower potency than dihydropyran
55a. Oxidation to the sulfoxide 55d and sulfone 55e
resulted in analogs displaying increased potency and
modest mouse PK. Moreover, 55d showed some
improvement from linezolid in a 7-day rat toxicity
assay.14
References and notes
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=
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However, the hydroxyacetamides 55h and 60e showed
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