Synthesis and antibacterial evaluation of oxazolidin-2-ones structurally related to linezolid

Article abstract of DOI:10.1016/j.farmac.2004.05.002

Compounds structurally related to the known antimicrobial drug linezolid were selected in order to evaluate the influence of electron-withdrawing properties and altered geometric features as a result of the N-substituent modification. After a preliminary

Full text of DOI:10.1016/j.farmac.2004.05.002

IL FARMACO 59 (2004) 685–690
www.elsevier.com/locate/farmac
Synthesis and antibacterial evaluation of oxazolidin-2-ones
structurally related to linezolid
Alessandra Ammazzalorso, Rosa Amoroso, Giancarlo Bettoni *, Marialuigia Fantacuzzi,
Barbara De Filippis, Letizia Giampietro, Cristina Maccallini, Domenico Paludi, Maria L. Tricca
Department of Drug Sciences, University of Chieti, via dei Vestini, 66100 Chieti, Italy
Received 9 April 2004; accepted 7 May 2004
Abstract
Compounds structurally related to the known antimicrobial drug linezolid were selected in order to evaluate the influence of electron-
withdrawing properties and altered geometric features as a result of the N-substituent modification. After a preliminary study of molecular
modeling, cinnamoyl-, pyridin- and pyrimidinoxazolidin-2-ones were synthesized. None of the new compounds showed antibacterial activity.
©
2004 Elsevier SAS. All rights reserved.
Keywords: Oxazolidin-2-ones; Antibacterial activity; Linezolid
1
. Introduction
on the heterocycle [7–9]. Very little is known about the
replacement of the above phenyl with other electron-rich
groups. In literature are described only some attempts to
space out the aromatic system to the oxazolidinone ring by
small groups, like carbonyl or methylene; the result is a total
loss of activity [10].
In this article we describe the synthesis of novel
oxazolidin-2-ones structurally related to linezolid, obtained
by replacement of phenyl with a cinnamoyl group and some
heteroaromatic rings (Fig. 1).
®
Linezolid (ZYVOX ) is the first member of a new class of
totally synthetic antimicrobial agents, the oxazolidinones
1–3]; it has been recently marketed in the USA and it is
[
available in oral and i.v. formulations. The oxazolidinones
are particularly efficacious in treating skin and soft tissues
infections, nosocomial and community-acquired pneumonia
and bacteremia caused by methicillin-resistant Staphylococ-
cus aureus (MRSA), vancomycin-resistant Enterococcus
faecium (VREF) and penicillin-resistant Streptococcus
pneumoniae (PRSP).
Oxazolidinones act by inhibiting the protein synthesis at
very early stage; they bind the 50S subunit, so preventing the
bacterial translation [4,5]. This represents a unique mecha-
nism of action, and cross-resistance with other protein syn-
thesis inhibitors has not been reported. Some rare cases of
oxazolidinone resistance have been described, but only after
a long treatment with linezolid [6].
Several SAR studies have been carried out on antibacterial
oxazolidinones, focused primarly on substituents at carbon
position 5 and at phenyl bound to the nitrogen in position 3
2. Experimental
2.1. Chemistry
Melting points were determined on an Electrothermal IA
9100 apparatus and are uncorrected. Optical rotations were
measured on a Perkin Elmer model 241 polarimeter. The
infrared spectra were recorded on an FT-IR 1600 Perkin
Elmer spectrometer. The NMR spectra were run at 300 MHz
on a Varian spectrometer; chemical shifts (d) are reported in
ppm. Microanalyses were carried out with an Eurovector
Euro EA 3000 model analyzer and the analytical results are
within 0.4% of the theoretical values. GC analyses were run
on an autosystem GC Perkin Elmer apparatus using a fused
*
Corresponding author.
E-mail address: bettoni@unich.it (G. Bettoni).
©
2004 Elsevier SAS. All rights reserved.
doi:10.1016/j.farmac.2004.05.002

686
A. Ammazzalorso et al. / IL FARMACO 59 (2004) 685–690
Fig. 1. Chemical structures of linezolid and new oxazolidin-2-ones.
silica capillary column (30 m, 0.53 mm ID), SPB-5 Supelco.
Commercial reagents were used as received from Aldrich.
THF was distilled from sodium/benzophenone.
chloride (4.22 g, 25.34 mmol) in THF (20 ml), were added to
a stirred solution of rac-2 (4.92 g, 18.1 mmol) in dry THF
(60 ml), at –78 °C under nitrogen atmosphere. After 5 h at
–
78 °C, the mixture was allowed to warm to room tempera-
2
.2. Synthesis of compound rac-6
ture and stirred for further 20 h. The solvent was evaporated
under reduced pressure to lead a crude product, which was
dissolved in CH Cl (60 ml). The organic phase was washed
2.2.1. Racemic 5-(hydroxymethyl)-1,3-oxazolidin-2-one
2
2
(rac-1)
with H O, dried over Na SO and concentrated at reduced
2 2 4
A
solution of 3-amino-1,2-propandiole (5.08 g,
pressure. The resulting oily product was purified by column
chromatography on silica gel (eluent CH Cl /acetone, 98:2)
5
5.8 mmol) and sodium carbonate (20.70 g, 195.3 mmol) in
2
2
water (60 ml) was stirred at room temperature whilst triph-
osgene (4.70 g, 16.74 mmol) was carefully added. After 4 h,
the mixture was extracted with CH Cl . The aqueous phase
to give the rac-3 (white solid, 65% yield, m.p. 169–171 °C).
–
1 1
IR (KBr) 1767, 1680, cm ; H NMR (CDCl ) d 2.43 (s, 3H,
3
ArCH ), 4.13–4.29 (m, 4H, NCH e CH OSO ), 4.78–4.81
2
2
3
2
2
2
was neutralized with HCl and then evaporated under reduced
pressure. The solid residue was suspended in absolute etha-
nol and the inorganic salts were filtered off. The filtrate was
evaporated to give an oil, purified by chromatography on
silica gel (eluent CH Cl /CH OH/NH OH, 10:4:0.5) to give
(m, 1H, OCHCH ), 7.35–7.89 (m, 11H, aromatic and
2
1
3
CH=CH); C NMR (CDCl ) d 21.9 (CH ), 44.5 (CH N ox),
3
3
2
68.2 (CH OS), 70.4 (CH), 116.5 (CHCO), 128.3 (CH aro-
2
matic), 128.9 (CH aromatic), 129.2 (CH aromatic), 130.4
(CH aromatic), 131.1 (C aromatic), 132.1 (C aromatic),
134.6 (C aromatic), 145.9 (C aromatic), 147.0 (CHPh), 152.4
(CO ox), 165.2 (COCHCH).
2
2
3
4
the oxazolidinone rac-1 (colourless oil, 50% yield). IR (KBr)
–
1 1
3
324, 1736 cm ; H NMR (DMSO) d 3.17–3.54 (m, 4H,
NHCH and CH OH), 4.46–4.54 (m, 1H, OCHCH ), 5.05 (t,
2
2
2
13
1
H, OH), 7.38 (s, 1H, NH); C NMR (DMSO) d 41.9 (CH2
2.2.4. Racemic 5-(azidomethyl)-3-cinnamoyl-1,3-oxazoli-
din-2-one (rac-4)
ox), 62.5 (CH OH), 76.6 (CH), 159.6 (C=O).
2
Sodium azide (0.81 g, 12.41 mmol) was added to a solu-
tion of rac-3 (4.53 g, 11.28 mmol) in dry DMSO (40 ml), at
60 °C under nitrogen atmosphere. After 2 h the mixture was
2
.2.2. Racemic (2-oxo-1,3-oxazolidin-5-yl)methyl 4-methyl-
benzenesulfonate (rac-2)
A mixture of alcohol rac-1 (3.15 g, 26.9 mmol), toluene-
p-sulfonyl chloride (6.15 g, 32.28 mmol) and triethylamine
diluted with H O and extracted with ethyl acetate. The or-
2
ganic phase was washed with a saturated aqueous solution of
NaCl, dried over Na SO and concentrated at reduced pres-
(
4.88 ml, 34.97 mmol) in CH Cl (30 ml) was stirred at room
2 2
2
4
temperature for 21 h. The solution was diluted with CH Cl ,
sure. The crude product rac-4 (white solid, 90% yield) was
2
2
washed with H O and a saturated aqueous solution of
used in the following reaction without purification.
2
NaHCO , dried on Na SO and evaporated under reduced
3
2
4
pressure. The crude material was purified by chromatogra-
phy on silica gel (eluent CH Cl /CH OH 95:5) to give the
2.2.5. Racemic 5-(aminomethyl)-3-cinnamoyl-1,3-oxazoli-
din-2-one (rac-5)
2
2
3
tosylate rac-2 (white solid, 69% yield, m.p. 99 °C). IR (KBr)
A mixture of rac-4 (2.61 g, 9.59 mmol), triphenylphos-
–1; 1
3289, 1754, 1703 cm
H NMR (CDCl ) d 2.45 (s, 3H,
phine (2.77 g, 10.55 mmol) and H O (1.72 ml, 95.5 mmol) in
3
2
CH ), 3.60 (dd, 1H, NHCHH), 3.69 (t, 1H, NHCHH), 4.15
THF (40 ml) was heated at 40 °C for 23 h. After cooling, the
reaction mixture was diluted with HCl 2 N and extracted with
ethyl acetate. Aqueous NaOH was added to the aqueous
phase and the resulting basic solution extracted with ethyl
3
(
1
d, 2H, CH OSO ), 4.76–4.84 (m, 1H, OCHCH ), 5.27 (s,
H, NH), 7.37 (d, 2H, aromatic), 7.79 (d, 2H, aromatic); C
2 2 2
1
3
NMR (CDCl ) d 21.9 (CH ), 42.2 (CH ox), 68.8 (CH OS),
3
3
2
2
73.1 (CH), 128.2 (CH aromatic), 130.3 (CH aromatic), 132.2
acetate. The organic phase was washed with H O, dried and
2
(C–S aromatic), 145.8 (C–C aromatic), 159.0 (C=O).
concentrated under reduced pressure to give the compound
rac-5 (white solid, 72% yield). H NMR (DMSO) d 2.19
1
2.2.3. Racemic (3-cinnamoyl-2-oxo-1,3-oxazolidin-5-yl)
(broad s, 2H, NH ), 3.06–3.11 (m, 2H,CH NH ), 4.25–4.33
2
2
2
methyl 4-methylbenzenesulfonate (rac-3)
(m, 2H, CH ox), 4.44–4.49 (m, 1H, CH), 7.14 (d, 1H,
2
Buthyllithium (11.3 ml, 18.1 mmol, 1.6 M solution in
hexane) in dry THF (20 ml) and after 15 min, cinnamoyl
CH=CH–CO), 7.44–7.80 (m, 6H, CH aromatic and
1
3
CH=CHPh); C NMR (DMSO) d 43.4 (CH NH ), 47.4
2
2

A. Ammazzalorso et al. / IL FARMACO 59 (2004) 685–690
687
(
CH ox), 76.8 (CH), 119.2 (CHCO), 128.1 (CH aromatic),
2.3.3. Oxiran-2-ylmethyl-4-methylbenzensulfonate (rac-8)
2
1
1
28.9 (CH aromatic), 136.2 (C aromatic), 145.0 (CHPh),
50.4 (CO ox), 166.2 (COCHCH).
Triethylamine (13.66 ml, 98.02 mmol) and toluene-p-
sulfonyl chloride (17.25 g, 90.48 mmol) were added to a
solution of glicidol (5.0 ml, 75.4 mmol) in CH Cl (40 ml), at
2
2
2
.2.6. Racemic N-[(3-cinnamoyl-2-oxo-1,3-oxazolidin-5-yl)
0 °C. The mixture was allowed to warm to room temperature
and after 2 h was washed with brine and a saturated aqueous
methyl]acetamide (rac-6)
Pyridine (1.01 ml, 12.50 mmol) and acetic anhydride
solution of NaHCO . The organic phase was dried over
3
(0.83 ml, 8.75 mmol) were added to rac-5 (1.54 g,
Na SO and concentrated under reduced pressure. The resi-
2
4
6
.25 mmol) under ice cooling, and the mixture was stirred at
due was purified on silica gel (eluent ciclohexane/ethyl ac-
room temperature for 2 h. Diluted HCl was added and the
solution extracted with ethyl acetate. The organic phase was
washed with brine, dried over Na SO and concentrated
etate, 8:2) to give the oxirane rac-8 (colourless oil, 67%
–1 1
yield, b.p. 285 °C). IR (KBr) 1596 cm ; H NMR (CDCl ) d
3
2
4
2.43 (s, 3H, CH ), 2.56–2.58 (dd, 1H, CHH oxirane), 2.79 (t,
3
under reduced pressure. The resulting oily product was puri-
fied on silica gel (eluent ethyl acetate) to give the acetamide
1
1
H, CHH oxirane), 3.16–3.21 (m, 1H, CH), 3.91–3.96 (dd,
H, CHHOS), 4.22–4.28 (dd, 1H, CHHOS), 7.35 (d, 2H,
–
1
rac-7 (white solid, 40% yield). IR (KBr) 1784, 1691 cm ;
13
aromatic), 7.80 (d, 2H, aromatic); C NMR (CDCl ) d 21.9
1
3
H NMR (CDCl ) d 2.42 (s, 3H, CH ), 3.42 (dd,
3
3
(
(
CH ), 44.8 (CH oxirane), 49.1 (CH), 70.7 (CH OS), 128.2
CH aromatic), 130.2 (CH aromatic), 132.8 (C–S aromatic),
3 2 2
1
4
H,CHHNH), 3.66 (t, 1H, CHHNH), 4.12 (d, 2H, CH CH),
.72–4.81 (m, 1H, CH), 6.42 (s, 1H, NH), 6.47 (d, 1H,
2
1
45.4 (C–C aromatic).
CHCHCO), 7.34 (d, 2H, aromatic), 7.57 (d, 1H, CHCHCO),
13
7
.76 (d, 2H aromatic); C NMR (CDCl ) d 21.9 (CH ), 42.3
3 3
2
4
.3.4.
(2-Oxo-3-pyridin-2-yl-1,3-oxazolidin-5-yl)methyl
(
CH NH), 69.0 (CH ox), 73.2 (CH), 120.1 (CHCHCO),
2 2
-methylbenzensulfonate (rac-9a)
128.2 (CH aromatic), 129.1 (1 CH aromatic), 130.2 (CH
A mixture of 7a (9.20 g, 47.4 mmol), rac-8 (10.81 g,
7.4 mmol) and triethylamine (0.06 ml, 0.47 mmol) was
aromatic), 141.7 (CHCHCO), 146.0 (CO ox), 159.8
CHCHCO), 168.2 (CONH).
4
(
heated to 150 °C for 3 h. After cooling, the resulting oil was
dissolved in CH Cl , washed with H O and brine, dried over
2
2
2
2.3. Synthesis of compounds rac-12a–b
Na SO and concentrated under reduced pressure. The crude
2
4
product was purified by chromatography on silica gel (eluent
ciclohexane/ethyl acetate, 8:2) to give rac-9a (white solid,
The compounds 9–12b were obtained following the same
synthetic procedures described for the corresponding 9–12a.
The starting material is the commercial 2-aminopyrimidine.
1
1
6% yield, m.p. 149–151 °C). IR (KBr) 1748, 1363,
–
1 1
195 cm ; H NMR (CDCl ) d 2.43 (s, 3H, CH ), 4.02–4.35
3
3
(
1
7
m, 4H, CH ox e CH OS), 4.79–4.85 (m, 1H, CH), 7.04 (dt,
2
.3.1. Isobutyl pyridin-2-yl carbamate (7a)
To a solution of 2-aminopyridine (10 g, 106.2 mmol) in
2 2
H, CH pyr), 7.34 (d, 2H, aromatic), 7.66 (dt, 1H, CH pyr),
.78 (d, 2H, aromatic), 8.14 (d, 1H, CH pyr), 8.29 (dd, 1H,
dry THF (80 ml), triethylamine (14.80 ml, 106.2 mmol) and
isobutyl chloroformate (13.89 ml, 106.2 mmol) were added
under nitrogen atmosphere. After stirring at room tempera-
ture for 22 h, the THF was evaporated under reduced pres-
sure; the resulting crude material was dissolved in CH Cl ,
1
3
CH pyr); C NMR (CDCl ) d 21.9 (CH ), 45.7 (CH ox.),
6
1
matic), 138.1 (CH pyr), 145.7 (C–C aromatic), 147.8 (CH
pyr), 150.5 (C pyr), 153.7 (C=O).
3
3
2
8.7 (CH OS), 70.2 (CH), 113.1 (CH pyr), 119.6 (CH pyr),
2
28.2 (CH aromatic), 130.3 (CH aromatic), 132.3 (C–S aro-
2
2
washed with brine, dried over Na SO and concentrated
2
4
under reduced pressure. After purification by chromatogra-
phy on silica gel (eluent ciclohexane/ethyl acetate, 8:2) was
obtained the carbamate 7a (white solid, 46% yield, m.p.
2
4
.3.5. (2-Oxo-3-pyrimidin-2-yl-1,3-oxazolidin-5-yl)methyl
-methylbenzensulfonate (rac-9b)
–1 1
White solid, 13% yield, m.p. 131–134 °C. IR (KBr)
7
0
2–75 °C). IR (KBr) 1731, 1536, cm ; H NMR (CDCl ) d
3
–1; 1
.97 (d, 6H, CH ), 2.00–2.09 (m, 1H, CH), 3.98 (d, 2H,
1758 cm H NMR (CDCl
(m, 4H, CH ox e CH OS), 4.78–4.86 (m, 1H, CH), 7.06 (t,
1H, CH pyr), 7.34 (d, 2H, CH aromatic), 7.76 (d, 2H, CH
3 3
) d 2.43 (s, 3H, CH ), 4.08–4.34
3
CH ), 6.95–6.99 (dd, 1H, CH pyr), 7.7 (dt, 1H, CH pyr), 8.00
2
2
2
(
d, 1H, CH pyr), 8.30 (dd, 1H, CH pyr), 8.92 (s broad, 1H,
1
3
13
NH); C NMR (CDCl ) d 19.3 (CH ), 28.2 (CH), 71.6
aromatic), 8.65 (d, 2H, CH pyr); C NMR (CDCl
3
) d 21.9
3
3
(
CH ), 112.8 (CH pyr), 118.6 (CH pyr), 138.7 (CH pyr),
(CH ), 46.3 (CH ox), 68.6 (CH OS), 69.6 (CH), 116.9 (CH
3
2
2
2
1
2
1
47.8 (CH pyr), 152.7 (C pyr), 154.1 (C=O).
pyr), 128.2 (CH aromatic), 130.4 (CH aromatic), 132.1 (C–S
aromatic), 145.8 (C–C aromatic), 151.8 (C pyr), 156.7
(C=O), 158.5 (CH pyr).
.3.2. Isobutyl pyrimidin-2-yl carbamate (7b)
White solid, 40% yield, m.p. 94–95 °C. IR (KBr) 3429,
-1 1
749 cm ; H NMR (CDCl ) d 0.96 (d, 6H, CH ), 1.96–2.05
2.3.6. 5-(Azidomethyl)-3-pyridin-2-yl-1,3-oxazolidin-2-one
(rac-10a)
Sodium azide (0.51 g, 7.89 mmol) was added to a solution
of rac-9a (2.50 g, 7.18 mmol) in dry DMSO (70 ml), at 60 °C
under nitrogen atmosphere. After 8 h the mixture was diluted
3
3
(m, 1H, CH), 4.02 (d, 2H, CH ), 6.99 (t, 1H, CH pyr), 8.63 (d,
2
13
2
1
H, CH pyr), 9.09 (s broad, 1H, NH); C NMR (CDCl ) d
9.3 (CH ), 28.1 (CH), 71.9 (CH ), 116.1 (CH pyr), 152.1 (C
3
3
2
pyr), 158.0 (C=O), 158.7 (CH pyr).

688
A. Ammazzalorso et al. / IL FARMACO 59 (2004) 685–690
–
1 1
with H O and extracted with ethyl acetate. The organic phase
1775, 1648 cm ; H NMR (CDCl ) d 2.02 (s, 3H, CH ),
3 3
2
was washed with brine, dried over Na SO and concentrated
3.40–3.49 (m, 1H, CHHNH), 3.79–3.87 (m, 1H, CHHNH),
3.91–3.97 (dd, 1H, CHH ox), 4.32–4.35 (dd, 1H, CHH ox),
4.74–4.83 (m, 1H, CH), 6.04 (s broad, 1H, NH), 7.02–7.06
(dd, 1H, CH pyr), 7.67–7.73 (dt, 1H, CH pyr), 8.16 (d, 1H
2
4
under reduced pressure. The crude product rac-10a (yellow
oil, 99% yield) was used in the following reaction without
purification.
1
3
CH pyr), 8.30–8.32 (dd, 1H CH pyr); C NMR (CDCl ) d
3
2.3.7. 5-(Azidomethyl)-3-pyrimidin-2-yl-1,3-oxazolidin-2-
23.4 (CH ), 42.6 (CH NH), 46.7 (CH ox.), 72.7 (CH), 113.1
3
2
2
one (rac-10b)
(CH pyr), 119.6 (CH pyr), 138.1 (CH pyr), 147.8 (CH pyr),
150.7 (C=O ox), 153.3 (C pyr), 170.8 (CONH).
-1 1
Yellow oil, 69% yield. IR (KBr) 2104, 1766 cm ; H
NMR (CDCl ) d 3.57–3.69 (dq, 2H, CH N ), 4.01–4.35 (m,
3
2 3
2
8
5
1
H, CH ox), 4.75–4.81 (m, 1H, CH), 7.07 (t, 1H, CH pyr),
2.3.11. N-[(2-oxo-3-pyrimidin-2-yl-1,3-oxazolidin-5-yl)me-
2
13
.68 (d, 2H, 2 CH pyr); C NMR (CDCl ) d 47.2 (CH ox),
thyl]acetamide (rac-12b)
3
2
1
3.3 (CH N ), 71.0 (CH), 116.8 (CH pyr), 151.8 (C pyr),
White solid, 35% yield. H NMR (CDCl
3
) d 2.05 (s, 3H,
ox), 4.98–5.00 (m,
H, CH), 6.02 (t, 1H, NH), 6.55 (t, 1H, CH pyr), 8.65 (d, 2H,
2
3
56.7 (C=O), 158.5 (CH pyr).
CH ), 3.41–3.98 (m, 4H, CH NH e CH
3 2 2
1
1
3
2.3.8. 5-(Aminomethyl)-3-pyridin-2-yl-1,3-oxazolidin-2-one
CH pyr); C NMR (CDCl ) d 23.5 (CH ), 40.0 (CH NH),
3 3 2
4
1
1.7 (CH ox), 71.9 (CH), 111.2 (CH pyr), 157.4 (C pyr),
58.2 (CH pyr), 158.5 (C=O ox), 170.9 (CONH).
(
rac-11a)
2
A solution of rac-10a (1.42 g, 6.48 mmol), triphenylphos-
phine (1.87 g, 7.13 mmol) and H O (1.17 ml, 64.8 mmol) in
2
2
.4. Biological evaluation
THF (20 ml) was heated at 40 °C for 24 h. After cooling, the
mixture was diluted with HCl 2 N and extracted with ethyl
acetate. Aqueous NaOH was added and the resulting basic
solution was extracted with ethyl acetate. The organic phase
was washed with H O, dried over Na SO and concentrated
The minimum inhibitory concentration (MIC) values of
the synthesized compounds were determined by agar dilution
or microtiter broth dilution methods, corresponding to the
National Committee for Clinical Laboratory Standards. The
bacterial strains used were clinically isolated and from the
American Type Culture Collection. Cultures were main-
tained on Mueller-Hinton agar (BBL Microbiology Systems,
Cockeysville, Md.) or grown at 37 °C in Mueller-Hinton
broth (GIBCO Laboratories, Grand Island, NY).
2
2
4
under reduced pressure to give the desired rac-11a (yellow
oil, 46% yield).
–1 1
IR (KBr) 3378, 1749 cm ; H NMR (CDCl ) d 1.44 (s
3
broad, 2H, NH ), 2.93–3.00 (dq, 2H, CH NH ), 3.98–4.04
2
2
2
(
(
dd, 1H, CHH ox), 4.25–4.31 (dd, 1H, CHH ox), 4.62–4.69
m, 1H, CH), 6.99–7.03 (dt, 1H, CH pyr), 7.65–7.71 (dt, 1H,
The compounds were dissolved in DMSO and the solu-
tions were diluted with distilled water. To ensure that DMSO
had no effect on bacterial growth, a control test was per-
formed with test medium supplemented with solvent at the
same dilutions as used in the experiments. Vancomycin was
used as reference drug. All tested compounds exhibited MIC
values >128 µg/ml against a number of Gram-positive micro-
organisms selected for this study (Staphylococcus aureus,
Staphylococcus haemolyticus, Streptococcus pyogenes,
Streptococcus agalactiae, Enterococcus faecalis, Entero-
coccus faecium, Staphylococcus epidermidis).
CH pyr), 8.18–8.22 (d, 1H, CH pyr), 8.29–8.31 (dd, 1H, CH
1
3
pyr); C NMR (CDCl ) d 45.5 (CH NH ), 46.8 (CH ox.),
3
2
2
2
7
1
5.0 (CH), 113.2 (CH pyr), 119.3 (CH pyr), 138.0 (CH pyr),
47.7 (CH pyr), 151.1(C=O), 154.7 (C pyr).
2.3.9. 5-(Aminomethyl)-3-pyrimidin-2-yl-1,3-oxazolidin-2-
one (rac-11b)
–
1
Yellow oil, 45% yield. IR (KBr) 3421, 2104, 1754 cm ;
1
H NMR (CDCl ) d 2.00 (s broad, 2H, NH ), 2.93–2.99 (dq,
3
2
2
1
8
4
1
H, CH NH ), 3.94–4.00 (dd, 1H, CHH ox), 4.27–4.31 (dd,
2 2
H, CHH ox), 4.62–4.71 (m, 1H, CH), 7.07 (t, 1H, CH pyr),
13
.66 (d, 2H, CH pyr); C NMR (CDCl ) d 45.3 (CH ox),
3
2
5.8 (CH NH ), 72.5 (CH), 111.1 (CH pyr), 157.4 (C pyr),
3. Results and discussion
2
2
58.4 (CH pyr), 158.5 (C=O).
Compounds rac-6, (R)-6, (S)-6, rac-12a and rac-12b were
selected after a preliminary study of molecular modeling.
The molecular electrostatic potentials (MEPs) were calcu-
lated by using the Grid 17 software [11]; we chose an hydro-
phobic probe (DRY) and water to explore MEPs distribution
in a number of designed compounds and some active oxazo-
lidinones. This approach allowed us to select compounds
with enhanced electron-withdrawing properties and altered
geometric features, as a result of the N-substituent modifica-
tions. We performed these structural changes by keeping the
acetylaminomethylic group at carbon in position 5, resulted
one of the best substituents.
2
.3.10. N-[(2-oxo-3-pyridin-2-yl-1,3-oxazolidin-5-yl)me-
thyl]acetamide (rac-12a)
Pyridine (0.39 ml, 4.86 mmol) and acetic anhydride
(0.32 ml, 3.40 mmol) were added to rac-11a (0.47 g,
2
.43 mmol) under ice cooling. After stirring at room tem-
perature for 1 h, the mixture was treated with HCl 2 N and
extracted with ethyl acetate. The organic phase was washed
with brine, dried over Na SO and concentrated under re-
2
4
duced pressure. The crude product was purified on silica gel
eluent ethyl acetate) to give the acetamide rac-12a (white
solid, 35% yield, m.p. 101.5–102.5 °C). IR (KBr) 3311,
(

A. Ammazzalorso et al. / IL FARMACO 59 (2004) 685–690
689
Scheme 1. Reagents and conditions: (a) POCl , Na CO , H O, r.t.; (b) TsCl, NEt , CH Cl , r.t.; (c) cinnamoyl chloride, BuLi, THF, –78 °C; (d) NaN , DMSO,
3
2
3
2
3
2
2
3
6
0 °C; (e) PPh , THF, 40 °C; (f) Ac O, Pyr, r.t.
3
2
The synthesis of cinnamoyl oxazolidinone rac-6 is shown
This reaction was carried out by mixing the carbamate and
the oxirane without solvent, using triethylamine as catalyst
and heating the mixture until 150 °C [13]. The mechanism of
this reaction proceeds via the initial formation of an aminoal-
cohol intermediate, which undergoes an intramolecular ex-
change of alcohols, to give the desired oxazolidinone.
Nucleophilic substitution with sodium azide gave rac-
10a, which was reduced with triphenylphosphine; the result-
ing amine rac-11a was acylated with acetic anhydride to
obtain the oxazolidinone rac-12a.
in Scheme 1. The hydroxymethyloxazolidinone rac-1 was
prepared by reaction of commercially available 3-amino-1,2-
propandiole with triphosgene, in the presence of Na CO ;
2
3
afterwards it was treated with tosyl chloride (TsCl) and NEt3
to give the tosylate rac-2. The reaction of rac-2 with BuLi
and cinnamoyl chloride, in freshly distilled THF at –78 °C,
afforded the intermediate rac-3, that was reacted with so-
dium azide to obtain the azido-derivative rac-4. Reduction of
rac-4 with triphenylphosphine, followed by acylation with
acetic anhydride and pyridine, led to the desired compound
rac-6.
The compound rac-12b was synthesized in a similar man-
ner, starting from commercial 2-aminopyrimidine.
The same synthetic route was followed in order to obtain
the chiral derivatives (R)-6 and (S)-6, starting from commer-
cially available (R)- and (S)-3-amino-1,2-propandiole.
The pyridin- and pyrimidinoxazolidinones rac-12a and
rac-12b were synthesized as depicted in Scheme 2, follow-
ing the same synthetic route described for linezolid [12].
Reaction of 2-aminopyridine with isobutyl chloroformate, in
the presence of triethylamine in dry THF, afforded the car-
bamate 7a. Treatment of 7a with glicidyl tosylate rac-8,
previously obtained from glicidol and TsCl, gave rac-9a.
All the intermediates and the final compounds were ana-
lytically characterized by means of TLC, GC, NMR, MS and
IR techniques.
The synthesized oxazolidinones were tested for antibacte-
rial activity against both standard and clinically isolated
strains of important Gram-positive pathogens. Compounds
were dissolved in DMSO and vancomycin was used as con-
trol. The antibacterial activity was completely lost
(MIC > 128) for all derivatives tested.
Scheme 2. Reagents and conditions: (a) CICOOi-Bu, NEt , THF, r.t.; (b) TsCl, NEt , CH Cl , 0 °C; (c) NEt , 150 °C; (d) NaN , DMSO, 60 °C; (e) PPh , THF,
3
3
2
2
3
3
3
4
0 °C; (f) Ac O, Pyr, r.t.
2

690
A. Ammazzalorso et al. / IL FARMACO 59 (2004) 685–690
Referring to linezolid structure and SAR studies we have
[2] D.J. Diekema, R.N. Jones, Oxazolidinones, Drugs 59 (2000) 7–16.
[
[
3] D. Clemett, A. Markham, Linezolid, Drugs 59 (2000) 815–827.
4] D.L. Shinabarger, K.R. Marotti, R.W. Murray, A.H. Lin, E.P. Mel-
chior, S.M. Swaney, et al., Mechanism of action of oxazolidinones:
effects of linezolid and eperezolid on translation reactions, Antimi-
crob Agents Chemother. 41 (1997) 2132–2136.
designed and synthesized novel compounds of oxazolidin-2-
one class, in order to investigate the relationships between
antimicrobial activity and increased electron-withdrawing
features. The total loss of activity of compound 6 is not so
surprising: the literature describes other oxazolidinones, in
which the aromatic ring is not directly linked to heterocyclic
nitrogen, resulted totally inactive. Regarding pyridine- and
pyrimidine-derivatives 12a–b, we have synthesized, at
present, only the racemic forms: this could have halved the
biological activity, because only (S)-oxazolidinones show
antibacterial properties, while (R)-forms are completely in-
active. Nevertheless, only this consideration does not explain
the total loss of biological activity.
[5] A.H. Lin, R.W. Murray, T.J. Vidmar, K.R. Marotti, The oxazolidinone
eperezolid binds to the 50S ribosomal subunit and competes with
binding of chloramphenicol and lincomycin, Antimicrob Agents
Chemother. 41 (1997) 2127–2131.
[
6] S. Tsiodras, H.S. Gold, G. Sakoulas, G.M. Eliopoulos, C. Wennersten,
L. Venkataraman, et al., Linezolid resistance in a clinical isolate of
Staphylococcus aureus, Lancet 358 (2001) 207–208.
[7] S.J. Brickner, Oxazolidinone antibacterial agents, Curr. Pharm.
Design 2 (1996) 175–194.
[
[
[
8] W.A. Gregory, D.R. Brittelli, C.J. Wang, M.A. Wuonola, R.J. McRi-
pley, D.C. Eustice, et al., Antibacterials. Synthesis and structure–
activity studies of 3-aryl-2-oxazolidinones. 1. The “B” group, J. Med.
Chem. 32 (1989) 1673–1681.
9] W.A. Gregory, D.R. Brittelli, C.J. Wang, H.S. Kezar, R.K. Carlson,
C. Park, et al., Antibacterials. Synthesis and structure–activity studies
of 3-aryl-2-oxazolidinones. 2. The “A” group, J. Med. Chem. 33
Further work is in progress in our laboratory in order to
evaluate the effect of substitution on heteroaromatic ring
with electron-withdrawing groups, in the attempt for the
discovery and development of new active agents.
(
1990) 2569–2578.
10] P. Seneci, M. Caspani, F. Ripamonti, R. Ciabatti, Synthesis and
antimicrobial activity of oxazolidin-2-ones and related heterocycles,
J. Chem. Soc. Perkin Trans. 1 (1994) 2345–2351.
Acknowledgements
We gratefully acknowledge financial support from the
Italian MIUR.
[
[
11] Grid 17, Molecular Discovery Inc., Oxford, UK, 1999.
12] S.J. Brickner, D.K. Hutchinson, M.R. Barbachyn, P.R. Manninen,
D.A. Ulanowicz, S.A. Garmon, et al., Synthesis and antibacterial
activity of U-100592 and U-100766, two oxazolidinone antibacterial
agents for the potential treatment of multidrug-resistant Gram-
positive bacterial infections, J. Med. Chem. 39 (1996) 673–679.
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