Substituent activity relationship studies on new azolo benzoxazepinyl oxazolidinones

Article abstract of DOI:10.1016/j.bmc.2006.07.040

In an effort to discover potent antibacterials based on the entropically favored 'bioactive conformation' approach, a series of novel tricyclic molecules mimicking the conformationally constrained structure of Linezolid is reported. Based on the initial tricyclic molecule 1, the benzazepine derivative 2 was designed where the tricyclic structure had more flexibility around C-N bond compared to 1. While, the molecule 2 was less active, the molecule 3 showed promising antibacterial activity presumably after having obtained rigidity due to pyrrole ring. The syntheses, SAR studies, and evaluation of 3 as a lead compound are reported.

Full text of DOI:10.1016/j.bmc.2006.07.040

Bioorganic & Medicinal Chemistry 14 (2006) 8032–8042
Substituent activity relationship studies on new azolo
benzoxazepinyl oxazolidinonesq
Jagattaran Das, M. Sitaram Kumar, D. Subrahmanyam, T. V. R. S. Sastry,
C. Prasad Narasimhulu, C. V. Laxman Rao, M. Kannan, M. Roshaiah, Riti Awasthi,
Santosh N. Patil, H. M. Sarnaik, N. V. S. Rao Mamidi, N. Selvakumar* and Javed Iqbal*
Anti-infective Group, Discovery Research, Drtsaven "5128BMC.3d". Reddy’s Laboratories Ltd., Miyapur, Hyderabad 500 049, India
Received 1 July 2006; revised 20 July 2006; accepted 21 July 2006
Available online 10 August 2006
Abstract—In an effort to discover potent antibacterials based on the entropically favored ‘bioactive conformation’ approach, a series
of novel tricyclic molecules mimicking the conformationally constrained structure of Linezolid is reported. Based on the initial
tricyclic molecule 1, the benzazepine derivative 2 was designed where the tricyclic structure had more flexibility around C–N bond
compared to 1. While, the molecule 2 was less active, the molecule 3 showed promising antibacterial activity presumably after having
obtained rigidity due to pyrrole ring. The syntheses, SAR studies, and evaluation of 3 as a lead compound are reported.
ꢀ 2006 Elsevier Ltd. All rights reserved.
1. Introduction
an early stage.1 Linezolid, the first drug from this class
of compounds, was launched by Pharmacia in 2000. In
spite of its high potential as an antibiotic and unique
mode of action no molecule from oxazolidinone class,
except for Linezolid, could make it to the market. More-
over, development of resistance to an antibiotic is inev-
itable, and Linezolid has been no exception to this rule.2
Further, due to myelosuppression, Linezolid is not suit-
able for long-duration therapy, although there are cases
where patients receiving Linezolid for more than 2 years
are without serious side effects.3 Therefore, there is a
need to pursue development of potent and safer oxazo-
lidinone compounds.
The increasing reports of resistance to antibiotics
among bacteria, especially Gram-positive bacteria,
have compromised the current antibiotic therapies.
Methicillin-resistant Staphylococcus aureus (MRSA),
vancomycin-resistant enterococci (VRE), and glycopep-
tide-resistant S. aureus (GISA) are no longer objects of
scientific curiosity but a life-threatening proposition that
is confronting physicians all over the world. The ‘super
bugs’ are here to stay and in addition to the several mea-
sures to control spread of drug resistance, a concerted
effort is urgently needed to develop new antibiotics with
novel mechanism of action.
In our earlier communication,4 we discussed the role of
bioactive conformation in a drug molecule, which assists
the molecule to bind to a target favorably providing
entropic advantage. Every molecule and hence a drug
too is expected to have free rotation along the bonds.
A drug remains in innumerable energy states (conforma-
tions) and out of these innumerable conformations only
one, that is, the bioactive form binds to the receptor. In
other words, a flexible drug molecule has to limit its
rotation along bonds and freeze to the bioactive form
in order to bind to the receptor, which is entropically
disfavored process. One of the ways to restrict rotation
along the bonds is to constrain the drug molecule and
by this process if one comes across the bioactive confor-
Discovery of oxazolidinones, a new class of synthetic
antibacterials, opened up an exciting avenue of antibiot-
ic research because of its activity against resistant Gram-
positive organisms such as MRSA, VRE, and GISA.
Oxazolidinones bind selectively to 50S ribosomal sub-
unit thereby inhibiting bacterial protein biosynthesis at
Keywords: Oxazolidinones; Antibacterial; Tricyclic; Linezolid.
q
A part of this work was presented in 41st Interscience Conference on
Antimicrobial Agents and Chemotherapy, December 16–19, 2001,
Chicago, USA.
*
Corresponding authors. Tel.: +91 040 23045439; fax: +91 040
23045438; e-mail: selvakumarn@drreddys.com
0968-0896/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2006.07.040

J. Das et al. / Bioorg. Med. Chem. 14 (2006) 8032–8042
8033
acid produced the acetamide 3, which upon hydrogena-
tion yielded the pyrrolidine derivative 2. The thioaceta-
mide 27 was prepared by treating the amine 14 with
ethyldithioacetate and TEA. The carbamate derivatives
have been prepared from the amine 14 by treatment with
alkylchloroformates and TEA. The isothiocyanate 15
was obtained from the amine 14 by treatment with
carbon disulfide, TEA, and ethylchloroformate, which
upon refluxing with appropriate alcohols gave the
thiocarbamate derivatives (Table 1).
O
O
H
N
N
N
N
1
O
O
O
O
H
N
N
2
O
O
All the compounds synthesized above were screened for
in vitro antibacterial activity against a panel of Gram-
positive organisms. The compound 2 having more flexi-
bility around C–N bond compared to compound 1 lost
its antibacterial activity. However, the compound 3 pre-
sumably after having gained rigidity due to the pyrrole
ring instead of pyrrolidine exhibited activity similar to
Linezolid. Thus, in an attempt to further improve the
antibacterial activity, SAR studies on the amine 14 were
carried out (Table 2). Increasing the chain length or
bulkiness on the acetamide 3 resulted in molecules with
inferior activity (e.g., 3 vs 16–20). However, the chloro
acetamide compound 21 retained the activity. It is inter-
esting to note that the corresponding bromo derivative
22 was less active. The carbamates 24–26 were found to
be less active than the corresponding acetamides. But,
the thioamide 27 and the thiocarbamate 28 exhibited bet-
ter activity than the acetamide 3. However, the homolo-
gous thiocarbamate derivative 29 was less active than 28.
O
O
N
H
N
N
3
O
O
Figure 1.
mation, a potent drug can be delivered. In line with this
concept we designed structurally constrained tricyclic
molecule 1,4 wherein rotation around C–N bond was
restricted (Fig. 1). Further, to enumerate more on our
concept of bioactive conformation, we designed ben-
zazepine derivative 2, where the tricyclic structure had
more flexibility around C–N bond compared to 1. How-
ever, the molecule was inactive having obtained more
freedom of rotation. On the other hand molecule 3, an
intermediate toward 2, showed promising antibacterial
activity having obtained rigidity due to pyrrole ring.5
Thus, we have carried out SAR study on the right side
of the molecule to improve upon the activity. Herein
we report the synthesis of molecules 2 and 3, SAR stud-
ies carried out on 3, and evaluation of 3 as a lead
compound.
After having completed the SAR studies, the
compounds possessing in vitro activity comparable to
Linezolid (3, 19, 21, 27, and 28) were taken up for
pharmacokinetic and in vivo studies in mice. The mean
plasma concentration and ED50 values of these
compounds and Linezolid are presented in Table 3.
Upon oral administration, the absorption from mouse
gastrointestinal tract was rapid and the maximum
plasma concentration (Tmax), reached at 0.5 h in all the
compounds except for the compound 27 (Tmax ꢀ 1 h).
The data revealed the compound 3 to be superior to other
1.1. Synthesis of azide 13
The nitration of isatoic anhydride 4 to obtain nitro isatoic
anhydride 5 (Scheme 1). Methanolysis of the anhydride 5
resulted in the amino-ester 6. Amino functionality of the
compound 6 was then converted to pyrrole ring (7) by
refluxing in acetic acid with 2,5-dimethoxy tetrahydrofu-
ran. Vilsmeyer–Hack formylation of the compound 7 led
to the aldehyde 8, which on reduction with sodium
borohydride followed by acidification of the resulting diol
resulted in benz-azulene compound 9. Usual transforma-
tion of nitro to amine and subsequent protection of amine
with CBzCl produced compound 11, which on treatment
with (R)-glycidyl butyrate in presence of BuLi gave
alcohol 12. Alcohol functionality of 12 was further
converted to azide 13 by mesylation followed by displace-
ment with sodium azide.
compounds with mean plasma concentration (Cmax
)
11.7 lg/mL and an AUC(0–1) of 21.09 lg h/mL. All other
compounds exhibited poor pharmacokinetics and this
was clearly reflected in the pharmacodynamic study in
mice. The ED50 in the mouse systemic infection model
of compound 3 administered subcutaneously (sc) was
10.10 mg/kg and the ED50 by per os (po) administration
was 12.5 mg/kg as compared to 2.18 mg/kg (sc) and
5.38 mg/kg (po) for Linezolid. All the other compounds
failed to protect mice with ED50 > 30 mg/kg dose, which
correlated well with the poor pharmacokinetics exhibited
by these compounds.
1.2. Synthesis of the derivatives
The oral pharmacokinetic profile of compound 3 was
further evaluated in Wistar rats. The mean plasma
concentration versus time profiles of compound 3 and
Linezolid, and the pharmacokinetic parameters are
presented in Figure 2 and Table 4. After oral adminis-
tration, the compound 3 reached a maximum level
(Tmax) at 1.5 h, whereas Linezolid was rapidly absorbed
and reached Tmax at 0.5 h, the elimination rate (Kel) and
The amine 14 was obtained by reduction of azide 13 in
presence of triphenylphosphine and water (Scheme 2),
which was then converted to the derivatives using either
corresponding acid chlorides in presence of triethyl-
amine or corresponding acid in presence of DCC and
DMAP. The azide 13 upon treatment with thioacetic

8034
J. Das et al. / Bioorg. Med. Chem. 14 (2006) 8032–8042
H
H
N
H2N
N
O
O
N
O
b
a
c
MeO
MeO
O
O
NO2
NO2
NO2
O
O
O
5
7
4
6
CHO
e
N
O
g
N
O
f
d
NH2
NO2
N
O
MeO
NO2
10
8
9
O
O
O
N
O
N
O
N
O
i
h
N
O
NH OBn
N
O
N3
OH
13
12
11
Scheme 1. Reagents and conditions: (a) KNO3, H2SO4, 0–5 ꢁC, 86%; (b) MeOH, NaOH, 90%; (c) 2,5-dimethoxytetrahydrofuran, CH3COOH, 85%;
(d) DMF, POCl3, 86%; (e) NaBH4, MeOH, HCl, 60%; (f) ammonium formate, 10% Pd–C, THF–MeOH, 66%; (g) CBzCl, NaHCO3, 96%; (h) n-BuLi,
(R)-glycidyl butyrate, 85%; (i) MsCl/TEA and NaN3/DMF, 92%.
O
O
N
O
N
N
H
N
O
N
H
N
OR
O
3
O
O
c
e
O
Z = N3
Z = NH2
g
O
N
O
2
N
O
Z
f
d
Z = NH2
Z = NCS
O
O
13, Z = N3
14, Z = NH2
15. Z = NCS
N
O
a
b
N
O
O
N
O
N
H
H
N
N
OR
27
S
S
Scheme 2. Reagents: (a) Ph3P/H2O, 80%; (b) CS2, TEA, ethylchloroformate; (c) CH3COSH; (d) ethyldithioacetate, TEA; (e) ROCOCl, TEA;
(f) ROH; (g) Pd on charcoal, H2.
terminal half-life (t1/2) were comparable to Linezolid.
However, the Cmax of 12.9 lg/mL and AUC(0–1) of
52.90 lg h/mL were inferior to those of Linezolid, which
showed a Cmax of 27.09 lg/mL and AUC(0–1) of
83.45 lg h/mL.
pharmacokinetic profiles. Complementing the pharma-
cokinetic profile, the compound 3 showed good in vivo
efficacy. It is also interesting to note that the systemic
exposure and elimination half-life of 3 was superior in
rats compared to that of mice.
In conclusion, the SAR studies on azolo benzoxazepinyl
oxazolidinone resulted in acetamide derivative 3 as a
lead compound. The replacement of acetamide of 3 with
thioamide and thiocarbamate exhibited better in vitro
potency. However, minor changes at the acetamide po-
sition of 3, like replacement of acetamide group with
either lengthier or bulkier group, had adverse effect on
the in vitro activity. Although the thiocompounds 27
and 28 exhibited good in vitro potency, this was not
translated into in vivo efficacy possibly due to poor
2. Experimental
2.1. General
Melting points were recorded on capillary melting point
apparatus and are uncorrected. 1H NMR and 13C
NMR were recorded at 200 and 50 MHz, respectively.
Chemical shifts are reported in d (delta) units with respect
to tetramethylsilane (TMS) as internal standard. Mass

J. Das et al. / Bioorg. Med. Chem. 14 (2006) 8032–8042
8035
Table 1. SAR studies on the amine 14
O
N
N
O
R
O
Compound
R
Conditions
Yield (%)
H
N
16
Propionyl chloride TEA, DCM, 0 ꢁC, 0.5 h
34
41
41
30
66
75
43
49
23
29
14
21
40
38
O
O
O
O
O
O
O
O
O
O
O
S
H
N
17
18
19
20
21
22
23
24
25
26
27
28
29
Isovaleryl chloride TEA, DCM, 0 ꢁC, 0.5 h
H
N
Cyclopropyl carboxylic acid DCC, DMAP, CHCl3, 0 ꢁC, rt, 1 h
Acryloyl chloride TEA, DCM, 0 ꢁC, 0.5 h
H
N
H
N
Ph
Benzoyl chloride TEA, DCM, 0 ꢁC, 0.5 h
H
N
2-Chloroacetyl chloride TEA, DCM, 0 ꢁC, 0.5 h
2-Bromoacetyl chloride TEA, DCM, 0 ꢁC, 0.5 h
3,3,3-Trifluoropropionic acid DCC, DMAP, CHCl3, 0 ꢁC, rt, 1 h
Methylchloroformate TEA, DCM, 0 ꢁC, 0.5 h
Ethylchloroformate TEA, DCM, 0 ꢁC, 0.5 h
Benzylchloroformate TEA, DCM, 0 ꢁC, 0.5 h
Ethyldithioacetate TEA, THF, rt, 6 h
Cl
H
N
Br
H
N
CF3
H
N
O
O
O
H
N
H
N
Ph
H
N
H
N
O
O
CS2, NEt3, THF methylchloroformate, methanol, reflux
CS2, NEt3, THF methylchloroformate, ethanol, reflux
S
H
N
S
spectra were recorded on a HP-5989A spectrometer.
Combustion analysis was obtained using a Perkin-Elmer
2400 analyzer. All analytical works were carried out at the
Analytical Research Department of Discovery Research.
ice flakes and the precipitate formed was filtered. The
solid obtained was washed with water and dried under
vacuum to afford the nitro compound 5 as a pale brown
solid (24 g, 94%). IR (KBr): 3199, 1779, 1758, 1354,
1336, 1034 cmꢁ1 1H NMR (DMSO-d6): d 12.31 (s,
.
2.2. 6-Nitro-1H-benzo[d][1,3]oxazine-2,4-dione (5)
1H), 8.53 (m, 2H), 7.31 (d, J = 10.0 Hz, 1H). MS: 209
(M++1), 191, 182, 164, 134, 106, 90.
To a solution of isatoic anhydride 4 (20 g, 122.7 mmol)
in con. H2SO4 (30 mL) at 0 ꢁC was added potassium
nitrate (12.40 g, 122.7 mmol) in small batches over a
period of 30 min and the stirring was continued for an
additional 15 min. The reaction mixture was poured into
2.3. Methyl 2-amino-5-nitro-benzoate (6)
A solution of 6-nitro-1H-benzo[d][1,3]oxazine-2,4-dione
5 (25 g, 120.2 mmol) and NaOH (480 mg, 12.0 mmol) in

8036
J. Das et al. / Bioorg. Med. Chem. 14 (2006) 8032–8042
Table 2. In vitro potency of azolo benzoxazepinyl oxazolidinones
O
N
O
N
O
NHR
Compounda
R
SA 33591
4
SA 49951
8
SA 29213
16
EF 29212
16
EF 12201
16
EFe 12202
16
1
2
32
2
32
2
32
2
>32
2
>32
2
>32
2
O
3
O
O
16
4
4
4
8
8
8
17
4
8
8
8
8
8
O
18
16
4
16
2
32
2
32
4
32
4
32
4
O
O
19
20
>32
1
>32
2
>32
2
>32
2
>32
2
>32
2
Ph
O
O
21
Cl
22
4
4
4
4
4
4
Br
O
O
23
8
8
8
8
8
8
CF3
24
4
4
4
8
8
8
O
O
O
O
O
25
16
>32
0.5
0.5
4
16
>32
1
16
>32
1
16
>32
1
16
>32
0.5
2
16
>32
1
26
Ph
S
S
27
28
0.5
4
0.5
4
2
2
O
O
S
29
8
8
8
Linezolid
2
2
2
2
2
4
a Compounds 3, 19, 21, 27 and 28 were selected for in vivo studies.

J. Das et al. / Bioorg. Med. Chem. 14 (2006) 8032–8042
8037
Table 3. Pharmacokinetic and pharmacodynamic parameters of selected compounds in Swiss albino micea
Parameters
3
19
21
27
28
Linezolid
AUC(0–1) (lg h/mL)
21.09
0.5
3.83
0.5
0.55
0.5
1.04
1.0
6.72
0.5
3.2
0.8
71.03
0.5
Tmax (h)
Cmax (lg/mL)
t1/2 (h)
11.7
0.8
2.18
0.6
0.47
0.6
0.18
0.9
28.13
1.0
ED50 (mg/kg)
sc
po
10.10
12.50
>30
>30
>30
>30
>30
>30
>30
>30
2.18
5.38
a Pharmacokinetic experiments were performed by single dose using oral route of administration and the pharmacodynamic results were derived
upon doing b.i.d.
Table 4. Single dose oral pharmacokinetic parameters of compound 3
and Linezolid in Wistar rats
solution of 2,5-dimethoxy tetrahydrofuran (14.16 g,
107.1 mmol) in acetic acid (500 mL) and the resulting
mixture was heated at reflux under N2 for 2 h. The reac-
tion mixture was allowed to cool to rt, poured into water
(500 mL), and extracted with ethylacetate (500 mL 3·).
The combined organic layer was washed with saturated
NaHCO3 solution, water, and brine successively. It was
then dried over anhydrous Na2SO4 and concentrated to
afford the compound 7 as a viscous liquid (28 g, 85%).
Parameters
Compound 3
Linezolid
Data derived from (n)
AUC(0–1) (lg h/mL)
Cmax (lg/mL)
6
4
52.90 19.53
12.9 4.07
1.50 0.58
0.58 0.21
1.31 0.40
84.66 12.17
27.09 2.12
0.50 0.00
0.61 0.06
1.15 0.12
Tmax (h)
Kel (hꢁ1
t1/2 (h)
)
IR (Neat): 1741, 1502, 1335, 738 cmꢁ1 1H NMR
.
(CDCl3): d 8.60 (s, 1H), 8.41 (d, J = 8.0 Hz, 1H), 7.45
(d, J = 8.0 Hz, 1H), 6.85 (s, 2H) 6.18 (s, 2H), 3.80 (s,
3H). MS: 246 (M+), 188.
30
25
20
15
10
5
Compound 3
Linezolid
2.5. Methyl 2-(2-formyl-pyrrol-1-yl)-5-nitro-benzoate (8)
Phosphorus oxychloride (17 g, 110.9 mmol) was added
dropwise to DMF (250 mL) under N2 at 0 ꢁC to form
a viscous yellow complex. To this reaction mixture
was added a solution of methyl 5-nitro-2-pyrrol-1-yl-
benzoate (26 g, 105.7 mmol) in DMF at the same tem-
perature over a period of 0.5 h. The reaction mixture
was allowed to attain rt and stirred for additional 2 h.
It was then poured into water which was basified with
Na2CO3. The precipitate formed was filtered, washed
with water, and dried under vacuum to afford the
compound 8 as a white solid (21.6 g, 80%). IR
1
(KBr): 1720, 1661, 1344, 767 cmꢁ1. H NMR (CDCl3):
d 9.45 (s, 1H), 8.85 (s, 1H), 8.40 (d, J = 7.0 Hz, 1H),
7.35 (d, J = 7.0 Hz, 1H), 7.11 (s, 1H), 6.95 (s, 1H),
6.45 (m, 1H), 3.75 (s, 3H). MS: 274 (M+), 246, 215,
169, 140.
0
0
2
4
6
8
10
Time (h)
Figure 2. Single dose oral pharmacokinetic parameters of compound 3
and Linezolid in Wistar rats.
2.6. 8-Nitro-4H,6H-5-oxa-10b-aza-benzo[e]azulene (9)
To a solution of methyl 2-(2-formyl-pyrrol-1-yl)-5-nitro-
benzoate 8 (5.00 g, 18.3 mmol) in MeOH (40 mL) was
added sodium borohydride (690 mg, 18.3 mmol) in
small portions at rt. After stirring the reaction mixture
for an additional 1 h, con. HCl (10 mL) was added
and was diluted with water (100 mL). After stirring for
a further 10 min, the reaction mixture was extracted
with ethylacetate (100 mL 3·). The combined organic
layer was washed with water, brine, dried over anhy-
drous Na2SO4, and concentrated to afford the nitro
compound 9 as a yellow solid (2.50 g, 60%). IR (KBr):
methanol was refluxed under N2 for 15 min. The
reaction mixture was allowed to cool to rt, diluted with
ethylacetate (750 mL), washed with water, dried over
anhydrous Na2SO4, and concentrated to obtain 6 as a
yellow solid (21 g, 89%). IR (KBr): 3473, 3361, 1707,
1631, 1319 cmꢁ1 1H NMR (CDCl3): d 8.62 (s, 1H);
.
8.14 (d, J = 10.0 Hz, 1H), 7.83 (br s, 1H), 6.89 (br s,
2H), 3.85 (s, 3H). MS: 196 (M+), 180, 164, 134, 119,
106, 91.
1522, 1499, 1336, 1087 cmꢁ1 1H NMR (CDCl3): d
.
2.4. Methyl 5-nitro-2-pyrrol-1-yl-benzoate (7)
8.18 (d, J = 10.0 Hz, 2H), 7.58 (d, J = 5.0 Hz, 1H),
7.11 (s, 1H), 6.40 (s, 2H), 4.58 (d, J = 10.0 Hz, 4H).
MS: 230 (M+), 201, 183, 154, 127.
To a solution of methyl 2-amino-5-nitro-benzoate 6
(21 g, 107.1 mmol) in acetic acid (200 mL) was added a

8038
J. Das et al. / Bioorg. Med. Chem. 14 (2006) 8032–8042
2.7. 4H,6H-5-Oxa-10b-aza-benzo[e]azulen-8-ylamine
(10)
2.10. (R)-5-Azidomethyl-3-(4H,6H-5-oxa-10b-aza-
benzo[e]azulen-8-yl)-oxazolidin-2-one (13)
To an ice-cold solution of 8-nitro-4H,6H-5-oxa-10b-
aza-benzo[e]azulene 9 (1.00 g, 4.4 mmol) and ammo-
nium formate (1.09 g, 17.4 mmol) in THF–MeOH
(1:4, 15 mL) was added 10% Pd–C (500 mg) and
stirred at rt under N2 for 1 h. The reaction mixture
was filtered over a pad of Celite and filtrate was
concentrated. The residue was diluted with ethylace-
tate (100 mL), washed with water and brine succes-
sively. It was then dried over anhydrous Na2SO4
and concentrated to afford the amine 10 as a pale
brown solid (580 mg, 66%). IR (KBr): 3356, 2855,
To a cooled (0 ꢁC) solution of the alcohol 12 (6.10 g,
20.3 mmol) in CH2Cl2 (100 mL) was added triethyl-
amine (4.11 g, 41.0 mmol) followed by dropwise addi-
tion of methanesulfonylchloride (3.49 g, 30.5 mmol)
over a period of 30 min. The reaction mixture was dilut-
ed with CH2Cl2 (100 mL) and the organic layer was
washed with water, brine and dried (Na2SO4). Upon
concentration the mesylate (7.07 g) was obtained as an
off-white solid. To a solution of the mesylate (7.00 g,
18.5 mmol) in DMF (50 mL) was added sodium azide
(3.61 g, 55.6 mmol) and heated to 80 ꢁC for 1 h. The
reaction mixture was then poured into water (250 mL),
extracted with ethylacetate (200 mL 3·), and the com-
bined organic layer was washed with water (200 mL
2·), brine and dried (anhydrous Na2SO4). The title
compound was obtained as an off-white solid
(5.7 g, 95%) after evaporation of the volatiles. IR (KBr):
1668, 1625, 1512, 1310, 1268, 1064, 720 cmꢁ1 1H
.
NMR (CDCl3): d 7.20 (d, J = 1.6 Hz, 1H), 7.01 (s,
1H), 6.64–6.68 (m, 3H), 6.24 (s, 2H), 4.45 (s, 2H),
4.25 (s, 2H). MS: 200 (M+), 171, 154, 144, 130,
115, 106, 91.
1
2.8. Benzyl (4H,6H-5-oxa-10b-aza-benzo[e]azulen-8-yl)-
carbamate (11)
2104, 1745 cmꢁ1. H NMR (CDCl3): d 7.71–7.74 (m,
1H), 7.57 (s,1H), 7.43 (d, J = 8.6 Hz, 1H), 7.01 (s, 1H),
6.32 (s, 2H), 4.79–4.85 (m, 1H), 4.47 (d, J = 9.4 Hz,
4H), 4.14 (t, J = 8.9 Hz, 1H), 3.90–3.94 (m, 1H), 3.59–
3.76 (m, 2H). MS: 326 (M++1), 300, 298, 201.
To a solution of amine 10 (4 g, 20.0 mmol) in acetone
(20 mL) was added a solution of NaHCO3 (1.69 g,
40.0 mmol) in water (10 mL). Benzylchloroformate
(50%, 3.75 g, 22.0 mmol) was added dropwise to the
reaction mixture, cooled to 0 ꢁC, over a period of
0.5 h under N2. The reaction mixture was allowed to
attain rt and then poured into water (30 mL). The
precipitate formed was filtered and dried under vacu-
um to afford the compound 11 as an off-white solid
(6.00 g, 90%). IR (KBr): 3250, 1728, 1565, 1513,
2.11. (S)-N-[3-(4H,6H-5-Oxa-10b-aza-benzo[e]azulen-8-
yl)-2-oxo-oxazolidin-5-ylmethyl]-acetamide (3)
(R)-5-Azidomethyl-3-(4H,6H-5-oxa-10b-aza-benzo[e]azu-
len-8-yl)-oxazolidin-2-one 13 (1.2 g, 3.7 mmol) was treat-
ed with thiolacetic acid (8 mL) under nitrogen
atmosphere. The excess thiolacetic acid was evaporated
after 16 h and the residue obtained was purified on silica
gel (100–200 mesh) using a mixture of methanol–chloro-
form (1:9) as eluent to obtain the product 3 as a white sol-
id (700 mg, 58%): mp 256–258 ꢁC. IR (KBr): 3298, 1737,
1
1317, 1236 cmꢁ1. H NMR (CDCl3): d 7.28 (m, 8H),
7.01 (s, 1H), 6.78 (br s, 1H), 6.25 (s. 2H), 5.20 (s,
2H), 4.42 (d, J = 10.0 Hz, 4H). MS: 334 (M+), 199,
169, 91.
1
1679, 1512, 1321, 1059, 736 cmꢁ1. H NMR (CDCl3): d
2.9. (R)-5-Hydroxymethyl-3-(4H,6H-5-oxa-10b-aza-
benzo[e]azulen-8-yl)-oxazolidin-2-one (12)
7.72–7.43 (m, 3H), 7.06 (s, 1H), 6.36 (s, 2H), 6.17 (m,
1H), 4.48 (m, 1H), 4.51–4.49 (m, 4H), 3.66–4.18 (m,
4H), 2.06 (s, 3H). 13C NMR (DMSO-d6): 170.0, 154.1,
136.6, 135.5, 129.7, 129.5, 121.5, 120.9, 120.0, 119.5,
109.3, 109.2, 71.6, 66.1, 59.6, 47.3, 41.4, 22.4. MS: 341
(M+), 312, 297, 254, 209, 154, 127, 105, 91.
To
a
solution of benzyl (4H,6H-5-oxa-10b-aza-
benzo[e]azulen-8-yl)-carbamate 11 (8.00 g, 24.0 mmol)
in dry THF (100 mL) was added n-BuLi (15% solution
in hexane, 15.33 mL, 36.0 mmol) at ꢁ78 ꢁC over a peri-
od of 0.5 h and allowed to stir at the same temperature
for another 0.5 h. R-(ꢁ)-Glycidyl butyrate (3.45 g,
26.3 mmol) was added to the reaction mixture and then
allowed to come to rt and stirred for additional 4 h. The
reaction mixture was then diluted with ethylacetate
(300 mL) and water after quenching with saturated
NH4Cl solution. The organic layer was separated and
aqueous layer was extracted with ethylacetate (300 mL
2·). The combined organic layer was washed with brine
and dried over anhydrous Na2SO4. The residue obtained
upon concentration was crystallized from ethylacetate–
petroleum ether to afford the alcohol 12 as an off-white
solid (6.10 g, 85%). IR (KBr): 3398, 1726, 1511,
2.12. N-[2-Oxo-3-(2,3,3a,4-tetrahydro-1H,6H-5-oxa-
10b-aza-benzo[e]azulen-8-yl)-oxazolidin-5-ylmethyl]-acet-
amide (2)
A solution of the amide 3 (100 mg, 0.3 mmol) and 10%
Pd–C (31 mg, 10 mol%) in ethylacetate was hydrogenat-
ed over 16 h at 50 psi. The catalyst was filtered off over a
pad of Celite and the filtrate obtained was concentrated
to obtain the title compound 2 (82 mg, 82%) as a color-
less solid. Mp 262–264 ꢁC. IR (KBr): 3315, 1746, 1510,
752 cmꢁ1 1H NMR (CDCl3): d 8.21 (t, J = 5.8 Hz,
.
1H), 7.38–7.31 (m, 2H), 6.89 (d, J = 8.9 Hz, 1H), 4.72–
4.64 (m, 2H), 4.28 (d, J = 13.2 Hz, 1H), 4.09–4.03 (m,
1H), 3.88 (dd, J = 2.4 and 11.6 Hz, 1H), 3.72–3.67 (m,
1H), 3.39 (t, J = 5.5 Hz, 2H), 3.32–3.18 (m, 3H), 2.97–
2.80 (m, 1H), 2.12–2.04 (m, 1H), 1.91–1.78 (m, 5H),
1.52–1.45 (m, 1H). 13C NMR: 169.9, 154.2, 145.4,
130.6, 130.3, 120.0, 118.7, 115.4, 75.2, 73.4, 71.3, 62.6,
1062 cmꢁ1 1H NMR (CDCl3): d 7.71–7.74 (m, 1H),
.
7.59 (s, 1H), 7.43 (d, J = 8.9 Hz, 1H), 7.04 (s, 1H),
6.32 (s, 2H), 4.75–4.80 (m, 1H), 4.48 (d, J = 9.4 Hz,
4H), 4.01–4.12 (m, 3H), 3.76–3.82 (m, 1H). MS: 301
(M++1), 257, 176.

J. Das et al. / Bioorg. Med. Chem. 14 (2006) 8032–8042
8039
51.4, 47.6, 41.4, 27.6, 23.1, 22.4. MS: 346 (M++1), 296.
Anal. Calcd for C18H23N3O4: C: 62.59; H, 6.71; N,
12.17. Found: C, 63.11; H, 6.63; N, 12.03.
121.5, 120.4, 119.6, 109.6, 72.1, 66.9, 60.4, 47.6, 41.7,
29.6, 26.0, 22.3. MS: 383 (M+), 339, 213, 127, 91. Anal.
Calcd for C21H25N3O4: C, 65.78; H, 6.57; N, 10.96.
Found: C, 65.05; H, 6.56, N, 10.36.
2.13. (R)-5-Aminomethyl-3-(4H,6H-5-oxa-10b-aza-
benzo[e]azulen-8-yl)-oxazolidin-2-one (14)
2.16. (S)-[3-(4H,6H-5-oxa-10b-aza-benzo[e]azulen-8-yl)-
2-oxo-oxazolidin-5-ylmethyl]-cyclopropanamide (18)
To a solution of the azide 13 (7.0 g, 21.5 mmol) in THF
(60 mL) was added triphenylphosphine (6.22 g,
23.7 mmol). After stirring for 2 h, water (1 mL) was
added and the reaction mixture was heated to 40–
50 ꢁC for 16 h. The solvent was evaporated and the
water was removed azeotropically with benzene. The
residue obtained was purified on silica gel (100–200
mesh) column using acetone–chloroform (2:3) system
to obtain the amine 14 as a sticky material (5.5 g,
77.62%). IR (KBr): 3386, 1748 cmꢁ1. 1H NMR (CDCl3):
d 7.72–7.75 (m, 1H), 7.58 (s, 1H), 7.42 (d, J = 8.86 Hz,
1H), 7.04 (s, 1H), 6.32 (s, 1H), 4.68–4.74 (m, 1H), 4.47
(d, J = 9.1 Hz, 4H), 4.09 (t, J = 8.7 Hz, 1H), 3.90–3.94
(m, 1H), 2.98–3.17 (m, 2H). MS: 300 (M++1), 279, 270.
A solution of the amine 14, cyclopropane carboxylic
acid (0.03 mL, 0.3 mmol), DCC (67 mg, 0.3 mmol),
and DMAP (41 mg, 0.3 mmol) in chloroform was stirred
for 1 h at rt. The residue obtained upon concentration
was purified on silica gel (100–200 mesh) column using
acetone–chloroform (2:3) as eluent to obtain the title
compound 18 (50 mg, 41%) as a white solid. Mp
240 ꢁC. IR (KBr): 3298, 1736, 1670, 1555, 1513, 1320,
1237, 1062 cmꢁ1
.
1H NMR (CDCl3 + DMSO-d6,
200 MHz): d 8.37 (br s, 1H), 7.67 (d, J = 11.2 Hz, 2H),
7.45 (d, J = 8.3 Hz, 1H), 7.09 (s, 1H), 6.26 (s, 2H),
4.79 (br s, 1H), 4.40 (s, 4H), 4.13 (t, J = 9.0 Hz, 1H),
3.88–3.81 (m, 1H), 3.55 (d, J = 4.4 Hz, 2H), 1.61 (br s,
1H), 0.79–0.63 (m, 4H). 13C NMR (50 MHz, DMSO):
d 173.6, 154.2, 136.7, 135.6, 129.8, 129.6, 121.6, 121.0,
120.2, 120.0, 109.4, 109.3, 72.0, 66.1, 59.6, 47.4, 40.3,
13.5, 6.5. MS: 367 (M+), 323,119, 92. Anal. Calcd for
C20H21N3O4: C, 65.38; H, 5.76; N, 11.44. Found: C,
64.79; H, 5.41; N, 11.19.
2.14. (S)-N-[3-(4H,6H-5-Oxa-10b-aza-benzo[e]azulen-8-
yl)-2-oxo-oxazolidin-5-ylmethyl]-propionamide (16)
To a solution of the amine 14 (100 mg, 0.3 mmol) in
chloroform (10 mL) was added triethylamine (93 lL,
0.7 mmol) at 0 ꢁC followed by the addition of propionyl
chloride (70.52 mg, 0.5 mmol) and stirred at same
temperature for 30 min. The reaction mixture was dilut-
ed with chloroform and washed with water and brine
successively. It was then dried over anhydrous sodium
sulfate and concentrated. The residue obtained was
purified on silica gel (100–200 mesh) column using ace-
tone–chloroform (2:3) as eluent to afford the title com-
pound 16 (80 mg, 34%) as a white solid. Mp 256–
258 ꢁC. IR (KBr): 3441, 3295, 2924, 1737, 1678, 1513,
2.17. (S)-N-[3-(4H,6H-5-Oxa-10b-aza-benzo[e]azulen-8-
yl)-2-oxo-oxazolidin-5-ylmethyl]-acrylamide (19)
The title compound 19 was obtained following the pro-
cedure reported for the amide 16 using acryloyl chloride
instead of propionyl chloride in 60% yield. Mp 220–
221 ꢁC. IR (KBr): 3287, 1737, 1677, 1513, 1321, 1062,
1
735 cmꢁ1. H NMR (CDCl3 + DMSO-d6, 200 MHz): d
8.27 (br s, 1H), 7.64 (t, J = 9.5 Hz, 2H), 7.43 (d,
J = 8.3 Hz, 1H), 7.06 (s, 1H), 6.28 (d, J = 6.3 Hz, 3H),
5.62 (t, J = 5.9 Hz, 1H), 4.94–4.71 (m, 1H), 4.45 (d,
J = 3.9 Hz, 3H), 4.14 (t, J = 8.8 Hz, 1H), 3.92 (t,
J = 7.8 Hz, 1H), 3.70 (br s, 2H), 2.95 (s, 2H). 13C
NMR: (50 MHz, DMSO): d 165.4, 154.0, 136.5, 135.6,
131.2, 129.7, 129.5, 125.6, 123.6, 121.3, 120.7, 120.1,
119.4, 109.2, 71.5, 66.1, 59.6, 47.4, 41.5, 40.8, 40.3.
MS: 353 (M+), 309, 213, 154, 97. Anal. Calcd for
C19H19N3O4: C, 64.56; H, 5.42; N, 11.89. Found: C,
64.88; H, 5.69; N, 11.42.
732 cmꢁ1 1H NMR (CDCl3, 200 MHz): d 7.70–7.64
.
(m, 2H), 7.42 (d, J = 8.5 Hz, 1H), 7.04 (m, 1H), 6.33
(d, J = 2.0 Hz, 2H), 6.17 (br s, 1H), 4.82 (br s, 1H),
4.47 (d, J = 4.4 Hz, 1H), 4.12 (t, J = 8.9 Hz, 1H), 3.91–
3.83 (m, 1H), 3.71–3.67 (m, 2H), 2.32–2.27 (m, 2H),
1.14 (t, J = 7.6 Hz, 3H). 13C NMR (50 MHz, CDCl3):
d 174.2, 153.9, 136.3, 135.5, 129.6, 129.4, 121.0, 120.2,
119.8, 119.1, 109.0, 71.4, 66.2, 60.0, 47.2, 39.5, 28.4,
9.6. MS: 356 (M+), 312. Anal. Calcd for C19H21N3O4:
C, 64.21; H, 5.96; N, 11.82. Found: C, 64.77; H, 5.77;
N, 12.07.
2.18. (S)-N-[3-(4H,6H-5-Oxa-10b-aza-benzo[e]azulen-8-
yl)-2-oxo-oxazolidin-5-ylmethyl]-benzamide (20)
2.15. (S)-N-[3-(4H,6H-5-Oxa-10b-aza-benzo[e]azulen-8-
yl)-2-oxo-oxazolidin-5-ylmethyl]-isovalerylamide (17)
The title compound 20 was obtained following the pro-
cedure reported for the amide 16 using benzoyl chloride
instead of propionyl chloride in 49% yield. Mp 234–
236 ꢁC (colorless solid). IR (KBr): 3336, 1738, 1663,
The title compound was prepared following the proce-
dure reported for the amide 16 using isovaleryl chloride
instead of propionyl chloride in 41% yield: mp 206 ꢁC.
IR (KBr): 3423, 3305, 2959, 2924, 1736, 1671, 1513,
1540, 1515, 1319, 1233, 1054, 734 cmꢁ1 1H NMR
.
736 cmꢁ1
.
1H NMR (CDCl3, 200 MHz): d 7.69–7.65
(CDCl3, 200 MHz): d 7.70–7.64 (m, 2H), 7.42 (d,
J = 8.5 Hz, 1H), 7.04 (m, 1H), 6.33 (d, J = 2.0 Hz,
2H), 6.17 (br s, 1H), 4.82 (br s, 1H), 4.47 (d,
J = 4.4 Hz, 1H), 4.12 (t, J = 8.9 Hz, 1H), 3.91–3.83 (m,
1H), 3.71–3.67 (m, 2H), 2.32–2.27 (m, 2H), 1.14 (t,
J = 7.6 Hz, 3H). 13C NMR (50 MHz, CDCl3): d 167.1,
154.2, 136.6, 135.5, 134.0, 131.4, 129.7, 129.5, 128.3,
(m, 1H), 7.62 (d, J = 2.4 Hz, 1H), 7.45 (d, J = 8.3 Hz,
1H), 7.05 (s, 1H), 6.34 (s, 2H), 6.03 (m, 1H), 4.83 (m,
1H), 4.49 (d, J = 3.9 Hz, 4H), 4.12 (t, J = 9.0 Hz, 1H),
3.87 (dd, J = 6.8 and 8.8 Hz, 1H), 3.73–3.71 (m, 2H),
2.10 (s, 3H), 0.94–0.87 (m, 6H). 13C NMR (50 MHz,
CDCl3): d 173.7, 154.5, 136.7, 136.1, 130.5, 130.1,

8040
J. Das et al. / Bioorg. Med. Chem. 14 (2006) 8032–8042
127.3, 121.5, 120.9, 120.7, 119.4, 109.4, 109.3, 71.4, 66.1,
59.6, 47.6, 42.3. MS: 403 (M+), 359, 213, 147, 105, 91.
Anal. Calcd for C23H21N3O4: C, 68.47; H, 5.25; N,
10.42. Found: C, 69.01; H, 5.05; N, 10.17.
d 7.66 (d, J = 8.8 Hz, 2H), 7.47 (t, J = 4.2 Hz, 1H),
7.09 (s, 1H), 6.34 (s, 2H), 4.85 (br s, 1H), 4.49 (d,
J = 3.9 Hz, 4H), 4.18 (t, J = 9.0 Hz, 1H), 3.89 (t,
J = 8.0 Hz, 1H), 3.67 (d, J = 4.4 Hz, 2H), 3.36 (s,
1H), 3.15 (q, J = 7.1 and 20.5 Hz, 2H). 13C NMR
2.19. (S)-2-Chloro-N-[3-(4H,6H-5-oxa-10b-aza-
benzo[e]azulen-8-yl)-2-oxo-oxazolidin-5-ylmethyl]-acet-
amide (21)
(50 MHz, CDCl3): d 163.6, 163.5, 154.1, 136.6,
135.6, 129.8, 129.6, 121.5, 120.9, 120.1, 119.5, 109.4,
109.3, 71.5, 66.1, 50.6, 47.2. MS: 409 (M+), 380,
213, 154, 91. Anal. Calcd for C19H18F3N3O4: C,
55.75; H, 4.43; N, 10.26; Found: C, 56.23; H, 4.36;
N, 9.98.
The title compound was obtained following the proce-
dure reported for the amide 16 using chloroacetyl chlo-
ride instead of propionyl chloride in 75% yield. Mp 160–
162 ꢁC (pale brown solid). IR (KBr): 3293, 1736, 1661,
2.22. Methyl (S)-[3-(4H,6H-5-oxa-10b-aza-benzo[e]azu-
len-8-yl)-2-oxo-oxazolidin-5-ylmethyl]-carbamate (24)
1511, 1409, 1224, 716 cmꢁ1
.
1H NMR (CDCl3,
200 MHz): d 7.71 (dd, J = 2.4 and 8.8 Hz, 1H), 7.58
(d, J = 2.4 Hz, 1H), 7.46 (d, J = 8.8 Hz, 1H), 7.08–7.06
(m, 2H), 6.35 (d, J = 2.0 Hz, 2H), 4.90–4.84 (m, 1H),
4.50 (d, J = 4.9 Hz, 4H), 4.18 (t, J = 9.3 Hz, 1H), 4.11
(s, 2H), 3.90–3.65 (m, 3H). 13C NMR (50 MHz, CDCl3):
d 167.2, 154.3, 136.8, 135.8, 129.9, 129.7, 121.7, 121.2,
120.4, 119.8, 109.6, 109.5, 71.6, 66.3, 59.8, 47.5, 42.7,
42.0. MS: 376 (M+), 342, 298. Anal. Calcd for
C18H18N3O4Cl: C, 57.58; H, 4.83; N, 11.20. Found: C,
57.87; H, 4.46; N, 10.89.
To a solution of the amine 14 (250 mg, 0.8 mmol) in
DCM was added triethylamine (127 mg, 0.18 mmol)
at 0 ꢁC followed by methylchloroformate (95.3 mg,
0.07 mmol). Stirring was continued for an additional
0.5 h and then the reaction mixture was diluted with
water and extracted with chloroform (100 mL 3·).
The organic layer was washed with brine, dried over
sodium sulfate, and concentrated. The residue was
purified on silica gel column (60–120 mesh) using ace-
tone–methanol (93:7 to 85:15) mixture to obtain a
sticky compound, which was further washed with
diethyl ether and ethylacetate to get the title com-
pound 24 as a colorless solid (70 mg, 23.4%). Mp
187–191 ꢁC. IR (KBr): 3254, 1737, 1718, 1514, 890,
2.20. (S)-2-Bromo-N-[3-(4H,6H-5-oxa-10b-aza-
benzo[e]azulen-8-yl)-2-oxo-oxazolidin-5-ylmethyl]-acet-
amide (22)
To a solution of the amine 14 (300 mg, 1.0 mmol) in
chloroform (3 mL) were added DCC (248 mg,
1.2 mmol) and DMAP (61.3 mg, 1.2 mmol), and the
reaction mixture was stirred at 0 ꢁC for 30 min.
Bromoacetic acid (167 mg, 1.2 mmol) was added at
the same temperature and the stirring was continued
at rt for 1 h. The reaction mixture was diluted with
water and extracted with chloroform (100 mL 2·).
The combined organic layer was washed with brine
and dried over anhydrous sodium sulfate. The solvent
was evaporated and the residue was purified on silica
gel column (100–200 mesh) using acetone–chloroform
(2:3) system to obtain the compound 22 (60 mg,
43%). IR (KBr): 3254, 1737, 1718, 1514, 890,
732 cmꢁ1 1H NMR (CDCl3, 200 MHz): d 7.76 (d,
.
J = 8.5 Hz, 1H), 7.68 (s, 1H), 7.59 (d, J = 8.8 Hz,
1H), 7.28 (br s, 1H), 6.31 (s, 2H), 6.28–6.25 (m,
2H), 4.79–4.72 (m, 1H), 4.39 (d, J = 2.7 Hz, 4H),
4.18 (t, J = 9.1 Hz, 1H), 3.84 (t, J = 7.7 Hz, 1H),
3.41–3.30 (m, 4H). 13C NMR (50 MHz, CDCl3): d
157.2, 154.1, 136.6, 135.5, 129.7, 129.5, 121.5, 120.9,
120.1, 119.5, 109.4, 109.3, 71.4, 66.1, 59.6, 51.5,
47.2, 43.3. MS: 358 (M++1), 326. Anal. Calcd for
C18H19N3O5: C, 60.48; H, 5.36; N, 11.76. Found: C,
59.95; H, 5.29; N, 11.90.
2.23. Ethyl (S)-[3-(4H,6H-5-oxa-10b-aza-benzo[e]azulen-
8-yl)-2-oxo-oxazolidin-5-ylmethyl]-carbamate (25)
732 cmꢁ1 1H NMR (CDCl3, 200 MHz): d 7.66 (dd,
.
J = 6.4 and 8.8 Hz, 1H), 7.58 (d, J = 5.9 Hz, 1H),
7.43 (d, J = 8.3 Hz, 1H), 7.04 (br s, 2H), 6.33 (s, 2H),
4.82 (m, 1H), 4.47 (d, J = 4.4 Hz, 4H), 4.14 (t,
J = 9.1 Hz, 1H), 3.89–3.68 (m, 5H). 13C NMR
(50 MHz, CDCl3): d 136.0, 135.6, 129.6, 129.3, 120.9,
120.0, 119.2, 109.0, 78.4, 77.8, 77.1, 71.0, 66.2, 59.6,
47.0, 41.6, 28.1. MS: 421 (M++1), 392, 341, 237, 209.
154. Anal. Calcd for C18H18BrN3O4: C, 51.44; H,
4.32; N, 10.00. Found: C, 50.91; H, 4.44; N, 10.19.
The title compound was obtained following the proce-
dure reported for the derivative 24 using ethyl chlorofor-
mate instead of methyl chloroformate. It was purified on
silica gel column (60–120 mesh) using acetone–chloro-
form (1:4 to 1:3) to get a sticky compound, which was
washed with diethyl ether and ethylacetate to get a col-
orless powder in 29% yield. Mp 195 ꢁC. IR (KBr): 3259,
3129, 2924, 1738, 1715, 1513, 1321 cmꢁ1 1H NMR
.
(CDCl3, 200 MHz): d 7.72 (d, J = 6.8 Hz, 1H), 7.60 (s,
1H), 7.45 (d, J = 8.8 Hz, 1H), 7.07 (s, 1H), 6.36 (s,
2H), 5.18 (br s, 1H), 4.83 (br s, 1H), 4.50 (d,
J = 3.9 Hz, 4H), 4.10–4.17 (m, 3H), 3.92 (t, J = 7.8 Hz,
1H), 3.63 (d, J = 5.4 Hz, 2H), 1.22–1.29 (m, 3H). 13C
NMR (50 MHz, DMSO-d6): d 156.7, 154.1, 136.7,
135.5, 129.8, 129.5, 121.5, 120.9, 120.1, 119.5, 109.4,
109.3, 71.5, 66.1, 59.9, 59.6, 47.2, 43.2, 14.6. MS: 371
(M+), 342, 296, 154, 91. Anal. Calcd for C19H21N3O5:
C, 61.43; H, 5.70; N, 11.31; Found: C, 60.99; H, 5.33;
N, 10.96.
2.21. (S)-3,3,3-Trifluoro-N-[3-(4H,6H-5-oxa-10b-aza-
benzo[e]azulen-8-yl)-2-oxo-oxazolidin-5-ylmethyl]-propi-
onamide (23)
The compound was obtained following the procedure
reported for 22 using trifluoro propionic acid instead
of bromoacetic acid in 49% yield. Mp 203–205 ꢁC.
IR (KBr): 3271, 1738, 1695, 1513, 1321, 1238, 1128,
749 cmꢁ1 1H NMR (CDCl3 + DMSO-d6, 200 MHz):
.

J. Das et al. / Bioorg. Med. Chem. 14 (2006) 8032–8042
8041
2.24. Benzyl (S)-[3-(4H,6H-5-Oxa-10b-aza-benzo[e]azu-
len-8-yl)-2-oxo-oxazolidin-5-ylmethyl]-carbamate (26)
(s, 2H), 4.95 (br s, 1H), 4.48 (d, J = 4.4 Hz, 4H), 3.90–
4.19 (m, 3H), 4.01 (s, 3H). 13C NMR (50 MHz, CDCl3):
d 192.8, 154.3, 136.7, 136.1, 130.5, 130.1, 121.6, 120.5,
120.4, 119.8, 109.7, 71.4, 66.9, 60.4, 58.6, 57.7, 47.5.
MS: 373 (M+), 341, 312, 213, 117. Anal. Calcd for
C19H21N3O4S: C, 57.90; H, 5.13; N, 11.25. Found: C,
57.49; H, 5.07; N, 11.11.
The title compound was obtained following the proce-
dure reported for the derivative 24 using benzylchloro-
formate instead of methylchloroformate. It was
purified on silica gel column (60–120 mesh) using ace-
tone–chloroform (1:4 to 3:7) to get a cream color pow-
der in 14% yield. Mp 198 ꢁC. IR (KBr): 3266, 3066,
2.27. O-Ethyl (S)-[3-(4H,6H-5-oxa-10b-aza-benzo[e]azu-
len-8-yl)-2-oxo-oxazolidin-5-ylmethyl]-thiocarbamate
(29)
2961, 2864, 1735, 1718, 1517, 1449, 1264 cmꢁ1 1H
.
NMR (CDCl3, 200 MHz): d 7.68 (d, J = 8.8 Hz, 1H),
7.55 (s, 1H), 7.32–7.45 (m, 6H), 7.05 (s, 1H), 6.34 (s,
2H), 5.25 (br s, 1H), 5.12 (s, 1H), 4.78–4.90 (m, 3H),
4.48 (d, J = 5.9 Hz, 3H), 4.10 (t, J = 9.0 Hz, 1H), 3.87
(t, J = 7.6 Hz, 1H), 3.59–3.65 (m, 2H). 13C NMR
(50 MHz, DMSO-d6): d 156.7, 154.1, 136.9, 136.5,
135.5, 129.7, 129.5, 128.3, 127.8, 127.6, 121.5, 120.9,
120.1, 119.4, 109.4, 109.3, 71.5, 66.1, 65.5, 59.6, 47.1,
43.3, 40.7. MS: 433 (M+), 325, 296, 154, 108, 91.
The title compound was prepared following the proce-
dure as reported for the compound 28 using ethanol
instead of methanol in 38% yield. Mp 200 ꢁC (colorless
powder). IR (KBr): 3423, 2924, 1636, 1541, 1509, 1197,
714 cmꢁ1 1H NMR (CDCl3, 200 MHz): d 7.68 (d,
.
J = 8.8 Hz, 1H), 7.59 (s, 1H), 7.44 (d, J = 8.3 Hz, 1H),
7.05 (s, 1H), 6.70 (br s, 1H), 6.34 (s, 2H), 4.93 (br s, 1H),
4.51–4.55 (m, 2H), 4.48 (d, J = 3.9 Hz, 4H), 3.96–4.19
(m, 4H), 1.26–1.36 (m, 3H). 13C NMR (50 MHz, CDCl3):
d 192, 154.2, 136.7, 136.1, 130.5, 130.1, 121.6, 120.5, 120.4,
119.8, 109.7, 71.4, 70.7, 68.2, 67.1, 66.9, 60.4, 47.5, 14.1.
MS: 387 (M+), 343, 341, 213, 131, 102. Anal. Calcd for
C19H21N3O4S: C, 58.90; H, 5.46; N, 10.84. Found: C,
58.69; H, 5.71; N, 10.98.
2.25. (S)-N-[3-(4H,6H-5-Oxa-10b-aza-benzo[e]azulen-8-
yl)-2-oxo-oxazolidin-5-ylmethyl]-thioacetamide (27)
To a solution of the amine 14 (200 mg, 0.67 mmol) in
THF (2 mL) was added triethylamine followed by the
addition of ethyldithioacetate (43 lL) and stirred for 5–
6 h. The residue obtained after evaporation of volatiles
was purified on silica gel column (60–120 mesh) using
ethylacetate–petroleum ether (3:2) system to obtain the
title compound 27 as a white solid (50 mg, 21%). Mp
196–198 ꢁC. IR (KBr): 3251, 2919, 2851, 1749, 1619,
2.28. Biology: Materials and methods
2.28.1. Organisms. The panel of organisms consisted of
six reference Gram-positive bacteria including both sen-
sitive and resistant strains: S. aureus ATCC 29213
(MSSA), S. aureus ATCC 49951 (Smith), S. aureus
ATCC 33591 (MRSA), Enterococcus faecalis ATCC
29212, E. faecalis NCTC 12201 (VRE), and Enterococ-
cus faecium NCTC 12202 (VREf).
1589, 1511, 1321, 1066 cmꢁ1
.
1H NMR (CDCl3,
200 MHz): d 8.03 (br s, 1H), 7.63 (t, J = 8.3 Hz, 2H),
7.43 (d, J = 8.3 Hz, 1H), 7.04 (s, 1H), 6.34 (s, 2H), 5.02
(d, J = 6.8 Hz, 1H), 4.48 (d, J = 4.4 Hz, 4H), 4.05- 4.37
(m, 3H), 3.92 (t, J = 8.0 Hz, 1H), 2.62 (s, 3H). 13C
NMR (50 MHz, CDCl3 + DMSO-d6): d 201.3, 153.0,
135.3, 135.0, 129.0, 128.6, 120.2, 119.2, 118.4, 108.3,
108.2, 69.4, 65.5, 59.0, 46.9, 46.5, 31.9. MS: 357 (M+),
314, 313, 213, 154, 101.
2.28.2. Susceptibility tests. MIC was determined by agar
dilution on Mueller Hinton agar (MHM-Difco) as per
the guidelines prescribed by NCCLS.6 Using a multi-
point-inoculating device, 104–105 bacteria were trans-
ferred onto the surface of MHM agar. Plates were
incubated for 16–18 h at 35 ꢁC. MIC was defined as
the lowest concentration of antibiotic at which no visible
growth could be detected on the agar plate.
2.26. O-Methyl (S)-[3-(4H,6H-5-oxa-10b-aza-
benzo[e]azulen-8-yl)-2-oxo-oxazolidin-5-ylmethyl]-
thiocarbamate (28)
To a solution of the amine 14 (250 mg, 0.84 mmol) in
THF was added carbon disulfide (127.3 mg, 1.67 mmol)
in the presence of triethylamine (0.23 mL, 1.7 mmol)
and stirred for 6 h at rt. Methylchloroformate was then
added to the reaction mixture and stirred for 30–45 min.
It was then diluted with water (200 mL) and aqueous
layer was extracted with ethylacetate (300 mL 2·). The
organic layer was washed with brine, dried, and concen-
trated. The residue obtained was dissolved in methanol
and refluxed for 16 h. The compound obtained after
evaporation of volatiles was purified on silica gel (60–
120 mesh) column using methanol–chloroform (1:9) as
eluent to obtain the title compound 28 (135 mg, 40%).
Mp 186–188 ꢁC (colorless powder). IR (KBr): 3222,
3044, 2944, 1738, 1513, 1447, 1319, 1200, 1068,
2.28.3. Pharmacokinetics. Single dose oral pharmacoki-
netics experiment was carried out for selected com-
pounds (MIC < 4 lg/mL) and Linezolid in Swiss
albino mice. All the animal experiments were approved
by DRF Institutional Animal Ethics Committee. Single
dose oral pharmacokinetics experiment was also carried
out for compound 3 and Linezolid in Wistar rats.
Studies were conducted under overnight fasted condi-
tions and test compound was administered orally at
30 mg/kg dose in 0.25% carboxy methyl cellulose. Blood
samples were collected from orbital plexus at 0.5, 1, 2, 4,
6, and 8 h, and plasma was separated for bio-analysis.
Plasma concentration was determined by liquid–liquid
extraction followed by HPLC–UV detection with limit
of quantitation of 100 ng/mL. Pharmacokinetic parame-
ters were calculated from the mean plasma concentra-
tion by non-compartmental analysis.
723 cmꢁ1 1H NMR (CDCl3, 200 MHz): d 7.70 (dd,
.
J = 2.4 and 6.3 Hz, 1H), 7.58 (d, J = 2.4 Hz, 1H), 7.43
(d, J = 8.3 Hz, 1H), 7.05 (s, 1H), 6.89 (br s, 1H), 6.34

8042
J. Das et al. / Bioorg. Med. Chem. 14 (2006) 8032–8042
2131; (b) Shinabarger, D. L.; Marotti, K. R.; Murray,
R. W.; Lin, A. H.; Melchior, E. P.; Swaney, S. M.;
Dunyak, D. S.; Demyan, W. F.; Buysee, J. M.
Antimicrob. Agents Chemother. 1997, 41, 2132–2136;
(c) Swaney, S. M.; Aoki, H.; Ganoza, M. C.; Shina-
barger, D. L. Antimicrob. Agents Chemother. 1998, 42,
3251–3255.
2.28.4. Systemic infection. Selected compounds were
evaluated by mouse systemic infection model using Lin-
ezolid as positive control. Overnight growth of S. aureus
ATCC 29213 was inoculated to fresh BHIB and incubat-
ed on a rotary shaker for 2 h at 150 rpm at 35 ꢁC. Inoc-
ulum was adjusted to 100 · LD50 dose in 5% Hog Gastric
Mucin (Difco) and 0.5 mL was injected intraperitoneally
to Swiss albino mice weighing 19–21 g (n = 6). The test
compound suspended in 0.25% sterile CMC was admin-
istered orally or subcutaneously 1 and 6 h postinfection.
ED50 was calculated by linear regression analysis.
2. Mutnick, A. H.; Enne, V.; Jones, R. N. Ann. Pharmacother.
2003, 37, 769–774.
3. Hutchinson, D. K. Expert Opin. Ther. Patents 2004, 14,
1309–1328.
4. Selvakumar, N.; Srinivas, D.; Khera, M. K.; Sitaram
Kumar, M.; Rao Mamidi, N. V. S.; Sarnaik, H.;
Chandrasekhar, C.; Rao, B. S.; Raheem, M. A.; Das,
J.; Iqbal, J.; Rajagopalan, R. J. Med. Chem. 2002, 45,
3953–3962.
Acknowledgment
5. While this manuscript preparation was in progress, the
following letter appeared. Griera, R.; Cantos-Llopart, C.;
Amat, M.; Bosch, J.; Castillo, J. C. D.; Huguet, J. Bioorg.
Med. Chem. Lett. 2005, 15, 2515–2517.
We are thankful to the analytical department of Discov-
ery Research for their support.
6. National Committee for Clinical Laboratory Standards.
Methods for Antimicrobial susceptibility tests for bacteria
that grow aerobically: Approved Standards. M7-A5.
National Committee for Clinical Laboratory Standards:
Wayne, PA, 2000.
References and notes
1. (a) Lin, A. H.; Murray, R. W.; Vidmar, T. J.; Marotti,
K. R. Antimicrob. Agents Chemother. 1997, 41, 2127–