Synthesis and biological evaluation of benzazepine oxazolidinone antibacterials

Article abstract of DOI:10.1016/j.bmcl.2003.07.017

Novel benzazepine oxazolidinone antibacterials were synthesized and evaluated against clinically relevant susceptible and resistant organisms. The effect of ring nitrogen position and N-substitution on antibacterial activity is examined.

Full text of DOI:10.1016/j.bmcl.2003.07.017

Bioorganic & Medicinal Chemistry Letters 13 (2003) 4197–4200
Synthesis and Biological Evaluation of Benzazepine
Oxazolidinone Antibacterials
Paul D. Johnson,a,* Paul A. Aristoff,a Gary E. Zurenko,b
Ronda D. Schaadt,b Betty H. Yagi,b Charles W. Ford,b
Judith C. Hamel,b Douglas Stapertb and Judy K. Moermanb
aDiscovery-Chemistry, Pharmacia Corporation, 7000 Portage Road, Kalamazoo, MI 49001, USA
bDiscovery-Infectious Diseases, Pharmacia Corporation, 7000 Portage Road, Kalamazoo, MI 49001, USA
Received 5 May 2003; accepted 30 July 2003
Abstract—Novel benzazepine oxazolidinone antibacterials were synthesized and evaluated against clinically relevant susceptible
and resistant organisms. The effect of ring nitrogen position and N-substitution on antibacterial activity is examined.
# 2003 Elsevier Ltd. All rights reserved.
The oxazolidinones are a totally synthetic class of anti-
biotics with a novel mechanism of action being investi-
gated for the treatment of bacterial infections. As the
first member of a new class of antibacterials in three
decades, ZYVOX1 (linezolid injection, tablets and oral
suspension) is approved in the United States for the
treatment of nosocomial pneumonia, community-
acquired pneumonia, uncomplicated and complicated
skin and soft tissue infections caused by Gram-positive
bacteria.1À4 Importantly, linezolid’s spectrum of activity
includes the methicillin-resistant Staphylococcus aureus
(MRSA) and Staphylococcus epidermidis (MRSE), and
vancomycin-resistant enterococci (VRE). The oxazoli-
dinones have been shown to selectively bind to the 50S
ribosomal subunit and inhibit bacterial protein synth-
esis prior to chain initiation.5,6
analogues with a variety of substituents including
nitrogen and carbon-linked heterocycles with five-, six-,
and seven-membered ring systems attached to the
4-position of the phenyl ring demonstrate antibacterial
activity.9,10 Thus, a high tolerance for structural diver-
sity in this region of the pharmacophore is tolerated. In
addition, free rotation about the bond between the
substituents and the phenyl core provide for multiple
possible conformations of the drug molecule in the
active site. Limiting the degrees of freedom by con-
formationally constraining the molecule could provide
an entropically advantageous situation in the active site.
Some fused-bicyclic oxazolidinones, including indolines
and tetrahydroquinolines have been reported.11,12 In
addition, tricyclic oxazolidinones have also been syn-
thesized.13 We report herein the synthesis and anti-
bacterial activity of novel benzazepine oxazolidinones.14
Benzazepines are available via a variety of routes
(Scheme 1). Ring expansion of a-tetralone 2 with
hydrazoic acid gives the lactam 3.15,16 Nitration with
fuming nitric acid in sulfuric acid at 0–5 ꢀC gave pri-
marily the 7-nitro benzazepinone 4 with minor amounts
of the 9-nitro and 7,9-dinitro benzazepines. The lactam
4 was reduced with borane to give 5 followed by
hydrogenation and Cbz-protection with benzyl chloro-
formate under Schotten–Bauman conditions to give 9.
If the lactam 3 is reduced with lithium aluminum
hydride and then nitrated, one obtains the 8-nitro-
benzazepine 7. Hydrogenation and Cbz-protection gave
A number of SAR studies of the oxazolidinones have
demonstrated that the phenyl oxazolidinone core struc-
ture is important for antibacterial activity.2,7,8 However,
*Corresponding author. Tel.: +1-269-833-2372; fax: +1-269-833-
2232; e-mail: paul.d.johnson@pharmacia.com
0960-894X/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2003.07.017

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P. D. Johnson et al. / Bioorg. Med. Chem. Lett. 13 (2003) 4197–4200
Scheme 1. Synthesis of Cbz-protected benzazepines.
8. The N-2-benzazepines are obtained by Beckmann
ring expansion of 6-amino-a-tetralone 10 with hydroxyl-
amine and sodium acetate17 followed by rearrangement
of the resulting oxime with polyphosphoric acid (PPA)
to give 11. Treatment of 11 with 2,5-hexanedione and
catalytic p-toluenesulfonic acid in refluxing toluene18,19
followed by reduction of the lactam with LAH pro-
ceeded smoothly to give 12. Removal of the unusual
amine protecting group with hydroxylamine20,21 and
Cbz-protection gave 13. N-3-benzazepine 14 is avail-
able by the method of Pecherer and Brossi.20 Protec-
tion of 14 with methylchloroformate followed by
nitration gives primarily 15. Hydrogenation, removal
of the methyl carbamate group with potassium
hydroxide in refluxing methanol, and Cbz-protection
gives 16.
lithium bis-(trimethylsilyl)amide followed by (R)-(À)-
glycidylbutyrate gave the hydroxymethyl oxazolidi-
nones 19 in good yields. Nosylation of 19 with 3-nitro-
benzenesulfonyl
displacement of the nosyl group with ammonia, and
acetylation gave the acetamide oxazolidinones 21.7,8
chloride
and
triethylamine,
A
variant of this procedure first forms the lithium amide
of the Cbz (or isobutyl carbamate) from 17 and
lithium t-amylate which is then treated with the epox-
ide derived in situ from (S)-(À)-3-chloro-1,2-propane-
diol (18) and potassium t-butoxide.21 Generally better
yields are obtained by this route and it is more
amenable to scale-up. During the course of this work
a one-step convergent oxazolidinone synthesis was
developed by Pearlman.22 Thus, treatment of 17 with
2 equivalents of 20 and 3 equivalents of lithium
t-amylate in DMF with 2 equivalents of methanol at
room temperature gave excellent yields of the desired
21. Finally, the Cbz-protecting group was removed by
catalytic hydrogenation.
The Cbz-protected benzazepines were converted to the
benzazepine oxazolidinones via previously described
methods (Scheme 2). Thus, treatment of a Cbz-pro-
tected aminobenzazepine (17) with n-butyl lithium or
Based on extensive previous SAR experience with
oxazolidinones1À8,11,14 we proceeded to synthesize some
selected analogues as illustrated for N-3-benzazepine
oxazolidinone in Scheme 3. N-Formamides were pre-
pared by treating the free amine with the reagent pre-
pared from formic acid and acetic anhydride (e.g., 36–
37).23 Hydroxyacetamides of the benzazepine oxazoli-
dinones were synthesized by acetylation with triethyl-
amine and acetoxyacetylchloride followed by
deacetylation with potassium carbonate in methanol. In
addition, selected amides, carbamates and ureas of the
benzazepines were prepared by standard methods.
The oxazolidinone analogues were tested in vitro versus
a panel of Gram-positive and Gram-negative bacterial
isolates (Table 1).1 Minimum inhibitory concentration
Scheme 2. Synthesis of benzazepine oxazolidinones.

P. D. Johnson et al. / Bioorg. Med. Chem. Lett. 13 (2003) 4197–4200
4199
(MIC) values were determined using standard agar
dilution methods.1 The unfunctionalized benzazepine
oxazolidonones (22, 26, 36, 46) were only weakly active,
if at all when tested in the panel of bacterial isolates.
The N-1- and N-5-benzazepine oxazolidinones (22–25
and 46–47, respectively) were at best only weakly active
as antibacterials as measured by the MIC’s. The only
exception was compound 23.
The N-2-benzazepine oxazolidinones (26–35) tolerated
small functional groups and displayed some activity, but
larger substituents caused a diminution in antibacterial
activity. Compound 27 exhibited MIC’s that were gen-
erally better than linezolid and 29 was equipotent to
linezolid, except against Haemophilus influenzae.
The N-3 benzazepine oxazolidinones (36–45) displayed
linezolid-like antibacterial activity with a broad range of
nitrogen substituents. The formamide 37, hydroxy-
Scheme 3. Synthesis of analogues of benzazepine oxazolidinones.
Table 1. MIC (mg/mL) for benzazepine oxazolidinones
S. a.a
S. a.b
S. e.c
S. p.d
E. f.e
H. inf.f
M. cat.g
ED50
h
Compd
R
1
Linezolid
H
CHO
COCH2OH
Cbz
H
CHO
COCH3
COCH2OH
C(O)OCH3
Cbz
4
64
2
64
>64
>64
1
8
4
8
16
32
16
64
64
32
4
2
32
2
32
>64
>64
1
1
16
<0.05
8
>64
32
2
4
1
2
16
8
4
32
32
8
<0.05
1
1
1
1
2
1
16
<0.05
8
>64
4
64
2
64
>64
>64
2
8
4
4
32
16
4
32
32
32
4
16
>64
16
>64
>64
>64
32
>64
64
>64
>64
>64
64
8
>64
4
>64
>64
>64
4
5.6 (2.9–8.5)i
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39COCH
40
41
42
43
44
45
46
47
8
1
2
1
2
8
4
1
8.1 (6.0–12.5)
4
16
COCH2Ph
CONHPh
CONHCH2CH2Ph
CONHCH(CH3)2
H
8
8
>64
>64
>64
>64
64
64
2
8
<0.05
1
<0.05
<0.05
1
2
1
1
8
>64
8
CHO
COCH3
2OH
Cbz
C(O)OCH3
C(O)OPh
COCH2Ph
COPh
SO2Me
H
CHO
4
2
4
4
4
4
8
2
4
4
2
4
2
2
2
2
32
8
16
8.5 (5.0–11.0)
>64
>64
>64
>64
>64
>64
>64
>64
1
1
16
8
>64
16
32
>64
32
32
>64
16
>64
8
>64
>64
>64
Minimum inhibitory concentration (MIC): lowest concentration of drug (mg/mL) that inhibits visible growth of the organism.
aMethicillin-suceptible S. aureus UC9218.
bMethicillin-resistant S. aureus UC6685.
cMethicillin-resistant S. epidermidis UC12084.
dStreptococcus pneumoniae UC9912.
eEnterococcus faecalis UC9217.
fHaemophilus influenzae UC30063.
gMoraxella catarrhalis UC30610.
hED50 is the amount of drug required after oral administration (mg/kg/day) to cure 50% of infected mice subjected to a lethal systemic infection of
S. aureus.
iNumbers in parentheses are 95% confidence ranges.

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P. D. Johnson et al. / Bioorg. Med. Chem. Lett. 13 (2003) 4197–4200
acetamide 39, and benzylcarbamate 40 all exhibited
comparable or slightly better Gram-positive anti-
bacterial activity compared to linezolid. The methylcar-
bamate 41, phenylcarbamate 42, and benzylamide 43
analogues had respectable in vitro activity against the
Gram-positive strains, but were also less active against
H. influenzae. Compounds 27 and 39 were selected for
testing in vivo in a lethal systemic S. aureus infection in
mice.1 Oral antibacterial activity (ED50) in this model
was comparable to linezolid.
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In conclusion, a number of novel benzazepine oxazoli-
dinones have been prepared. Compounds 23, 27, and 39
displayed in vitro Gram-positive antibacterial activity
better than linezolid against clinically relevant organ-
isms. Initial in vivo efficacy results are also encouraging.
Diverse functional groups are tolerated on N-3-benza-
zepine oxazolidinones with comparable Gram-positive
activity to linezolid, but generally they were less active
versus the Gram-negative species.
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