Synthesis and evaluation of dihydroimidazolo and dihydrooxazolo ring-fused 2-pyridones-targeting pilus biogenesis in uropathogenic bacteria

Article abstract of DOI:10.1016/j.tet.2008.07.015

Dihydrothiazolo ring-fused 2-pyridones have previously been shown to inhibit pilus assembly in uropathogenic Escherichia coli. Methods have now been developed to synthesize both dihydroimidazolo and dihydrooxazolo ring-fused 2-pyridones. To obtain the nitrogen analogs, Cbz-protected imidazolines were reacted with an acyl-Meldrum's acid derivative under acidic conditions. To prepare the oxygen analogs, a one-pot procedure was developed that allowed synthesis of dihydrooxazolo ring-fused 2-pyridones starting from acylated serine derivatives. After hydrolysis to their corresponding carboxylic acids and lithium carboxylates, biological evaluation revealed that the sulfur could be replaced by an oxygen atom and still maintains the ability to inhibit pilus assembly in uropathogenic E. coli. However, introducing a secondary amine instead of oxygen resulted in a substantial decrease in biological activity.

Full text of DOI:10.1016/j.tet.2008.07.015

Tetrahedron 64 (2008) 9368–9376
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and evaluation of dihydroimidazolo and dihydrooxazolo ring-fused
2-pyridonesdtargeting pilus biogenesis in uropathogenic bacteria
,
Nils Pemberton a, Jerome S. Pinkner b, Sofie Edvinsson a, Scott J. Hultgren b, Fredrik Almqvist a
*
a Department of Chemistry, Umeå University, SE-90187 Umeå, Sweden
b Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Dihydrothiazolo ring-fused 2-pyridones have previously been shown to inhibit pilus assembly in ur-
opathogenic Escherichia coli. Methods have now been developed to synthesize both dihydroimidazolo
and dihydrooxazolo ring-fused 2-pyridones. To obtain the nitrogen analogs, Cbz-protected imidazolines
were reacted with an acyl-Meldrum’s acid derivative under acidic conditions. To prepare the oxygen
analogs, a one-pot procedure was developed that allowed synthesis of dihydrooxazolo ring-fused 2-
pyridones starting from acylated serine derivatives. After hydrolysis to their corresponding carboxylic
acids and lithium carboxylates, biological evaluation revealed that the sulfur could be replaced by an
oxygen atom and still maintains the ability to inhibit pilus assembly in uropathogenic E. coli. However,
introducing a secondary amine instead of oxygen resulted in a substantial decrease in biological activity.
Ó 2008 Elsevier Ltd. All rights reserved.
Received 15 April 2008
Received in revised form 17 June 2008
Accepted 3 July 2008
Available online 8 July 2008
1. Introduction
the periplasmic chaperone to block the formation of pili.16 Impor-
tantly, this key protein has a high level of structural preservation
Bacterial resistance is recognized as one of the major health
threats in modern times.1,2 Dealing with the rapidly increasing
number of resistant pathogens necessitates not only the de-
velopment of new antibacterial agents but also finding new targets
and strategies to battle bacterial infections. One such strategy is the
development of so-called virulence inhibitors.3–8 These make the
bacteria non-pathogenic without affecting survival. This approach
is believed to reduce the evolutionary pressure on the bacteria, as
compared to traditional antibacterial agents, and thereby, delay
development of resistance.
Bicyclic sulfur containing 2-pyridones 1 and 2 are virulence
inhibitors that belong to a class of compounds known as pilicides
(Fig. 1), which prevent the assembly of pili in uropathogenic
Escherichia coli (UPEC).6,9 These compounds have also been used as
chemical tools to regulate pili expression in order to investigate the
functional properties of the pilus rod.10,11 Pili/fimbriae are multi-
protein fibers present on the surface of bacteria and are crucial for
adhesion and invasion of the host,12,13 and have also been shown to
play an important role in evading host defenses.14 In brief, pili are
assembled via a highly conserved mechanism called the chaper-
one-usher pathway, where an escort protein, chaperone, folds and
transports pili subunits to an outer membrane assembly site, where
they are incorporated into the growing pilus rod.13,15 Pilicides target
among pathogens utilizing the chaperone-usher pathway.12,17
Previous pilicides contain a rigid bicyclic 2-pyridone framework,
constructed by reacting D
2-thiazolines with acylketenes generated
from acyl-Meldrum’s acid derivatives (Fig. 1).18 This reaction has
been performed using both solid-phase techniques and microwave
irradiation (MWI),19,20 allowing the preparation of small libraries of
substituted ring-fused 2-pyridones in a fast and parallel manner.
Initial evaluations indicated that compounds 1 and 2 were the most
promising.20,21 Further functionalization at the readily available C-6
has resulted in a new set of substituted pilicides (class A, Fig. 1),22,23
of which several had maintained or even improved activity as
pilicides.16,23 Based on an amino-functionalized 2-pyridone, N-
terminal extended peptide mimetics have also been designed and
synthesized (class B, Fig. 1).24 Several of these showed enhanced
affinities for the chaperone as measured by relaxation edited 1H
NMR spectroscopy, however, the ability to prevent pilus assembly
in vivo was significantly decreased when compared to the parent
compounds 1 and 2.
By transforming the carboxylic acid at C-3 to other functional-
ities (class C, Fig. 1) we have been able to show that this function-
ality is vital to maintain the ability to prevent pilus assembly.25 The
use, however, of carboxylic acid isosteres such as tetrazoles or acyl
sulfonamides can improve the potency.26 Interestingly, de-
sulfurization with Raney nickel to the monocyclic 2-pyridone D
(Fig.1) resulted in a compound with a considerable loss of biological
activity when compared to the bicyclic parent compound, clearly
indicating the importance of the bicyclic 2-pyridone system.26
* Corresponding author. Tel.: þ46 90 786 6925; fax: þ46 90 13 88 85.
E-mail address: fredrik.almqvist@chem.umu.se (F. Almqvist).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.07.015

N. Pemberton et al. / Tetrahedron 64 (2008) 9368–9376
9369
R1
O
C
S
N
O
CO2Me
R1
R1
R1
O
S
S
N
N
N
6
R2
3
CO2H
CO2H
CO2Li
O
O
R2= -CH2NH2,-CH2NHR,-CH2NR2,
1 R1=Ph
D
A
B
2 R1=cyclopropyl
-CHO,-CO2H,-CH2OH,-CONHR
R2= -NO2,-NH2,-NHCOR,-NHSO2R,
-NH-amino acid,
R1
O
S
N
R2
R2= -CH2OH,-CH2OMe,-CHO,-CO2Me
-CN,-CH3,CH2I,-CH2CO2H,-CH2NH2
C
Figure 1. Based on the first two lead compounds 1 and 2, further functionalization has resulted in new compounds, here divided into four different classes A–D. These have been
evaluated as so-called pilicides, compounds that prevent the formation of adhesive protein organelles called pili.
Earlier we have shown that the imine component in the acyl-
ketene imine condensation can be exchanged from thiazolines to
3,4-dihydroisoquinolines or b-carbolines, thus resulting in multi-
imine condensation on a cheaper and more readily available
starting material. Thus, commercially available tolazoline was
chosen as the starting material. Both the N-Boc 4a and the N-Cbz 4b
protected derivatives were prepared.32 These protecting groups
were chosen to complement each other. The N-Boc could be too
labile due to the acidic conditions used in the 2-pyridone forming
step, but there was still a possibility that the conditions would al-
low both the 2-pyridone formation and a subsequent deprotection
in one pot. The N-Cbz alternative on the other hand would be
ring-fused systems.27 To further investigate the scope and limita-
tion of this reaction, and at the same time generate compounds that
would allow us to study the importance of the heteroatom in the
fused 2-pyridone scaffold from a pilicide point of view, we draw our
attention to imidazolines and oxazolines and their reactivity with
acylketenes generated in situ from acyl-Meldrum’s acid derivatives.
In this paper we describe the synthesis of dihydroimidazolo and
dihydrooxazolo ring-fused 2-pyridones. In addition, their ability to
inhibit pilus assembly in uropathogenic E. coli and thus acting as
pilicides is also reported.
Table 1
Synthesis of dihydroimidazolo[2,3-a]pyridin-5-ones 9a–c
MeO2C
NH
R
N
2. Results
O
10
2.1. Synthesis of analogs
R
To our knowledge no reports of dihydroimidazolo[2,3-a]pyr-
idin-5-ones (Table 1) or dihydrooxazolo[2,3-a]pyridin-5-ones (Ta-
ble 2) with a carboxylic acid functionality at C-3 have been
described in the literature. Nevertheless, reports of the preparation
of compounds without the carboxylic acid functionality have been
published; Jones et al. prepared imidazolo[2,3-a]pyridin-5-ones by
OH
H
N
R
Cbz
N
O
O
N
O
O
N
CO2Me
O
CO2Me
7b-d
8
9a-c
annulations of imidazolines with
have also been synthesized by using a similar method based on
reacting heterocyclic ketene aminals with -unsaturated
b
-ketoesters.28,29 These systems
Entry
R
Method
Product
Yield 9 (%)
Yield 10 (%)
1
2
3
4
5
6
Ph
Ph
Aa
Bb
Aa
Bb
Aa
Bb
9a
9a
9b
9b
9c
9c
53c
70d
42e
38e
61e
17e
13
a,b
df
df
df
df
df
esters.30,31 However, since our previously developed acylketene
imine condensation has proven to be mild and effective allowing
synthesis of bicyclic thiazolo ring-fused 2-pyridones in a parallel
manner,18–20 we wished to explore the possibilities of expanding
this method to also allow the preparation of nitrogen and oxygen
analogs.
Cyclopropyl
Cyclopropyl
H
H
a
b
c
Method A: (i) MW, 120 ꢀC, 5 min, TFA, DCE; (ii) Pd/C, H2 (atm), MeOH.
Method B: (i) 64 ꢀC, 14 h, 1
satd HCl$DCE; (ii) Pd/C, H2 (atm), MeOH.
Enantiomeric excess: 63% as determined by chiral HPLC see Supplementary data
⁄
2
To synthesize the imidazolo[2,3-a]pyridin-5-ones a suitably
protected imidazololine was required as a building block, and in
contrast to the thiazoline and oxazoline derivatives this structure is
not based on a natural amino acid. We therefore decided to first test
the conditions and the protective group strategy for the acylketene
for more details.
d
Enantiomeric excess: 61% as determined by chiral HPLC see Supplementary data
for more details.
e
Enantiomeric excess not determined.
f
Not formed.

9370
N. Pemberton et al. / Tetrahedron 64 (2008) 9368–9376
Table 2
R1
One-pot synthesis of dihydrooxazolo[2,3-a]pyridin-5-ones 12a–c from N-acylated
serine derivatives 11a–c
R
N
RHN
HN
RHN
H2N
b
a
R
N
CO2Me
CO2Me
(NH4)2MoO4,toluene,
3Åmol sieves,soxhlet,
then TFA and 8
O
CO2Me
HO
HN
O
R1
N
7a: R=Boc,R1=Ph 37%
CO2Me
6a: R=Boc and HCl salt
CO2Me
7b: R=Cbz,R1=Ph 88% 78%ee
7c: R=Cbz,R1=cyclopropyl 84%
7d: R=Cbz,R1=H 95%
O
6b: R=Cbz
O
R
11a-c
12a-c
Scheme 2. Reagents and conditions: (a) for 7a: BnCOCl, TEA, CH2Cl2, rt; compound 7a
was synthesized from the commercially available HCl salt; for 7b: BnCOCl, TEA, CH2Cl2,
0 ꢀC; for 7c: DCC, HOAt, cyclopropylacetic acid, CH2Cl2, rt; for 7d: Ac2O, TEA, CH2Cl2,
0 ꢀC; (b) for 7a and 7b: Tf2O, Ph3PO, CH2Cl2, 0 ꢀC; for 7c and 7d: Tf2O, polymer sup-
ported Ph3PO, CH2Cl2, 0 ꢀC.
Entry Compound
R
TFA (equiv) Time (h) Product Yield (%) ee (%)
1
2
3
4
5
11a
11b
11c
11a
11a
Ph
5
8
9
7
5
5
12a
12b
12c
12a
12a
78
32
16
62
28
2a
db
db
16a
91a
Cyclopropyl
H
Ph
Ph
5
5
1
0.1
heating) and using a half saturated HCl (g) solution of 1,2-di-
chloroethane, prevented the formation of this by-product and 9a
was isolated in 70% yield. These two sets of conditions were then
used to prepare the cyclopropyl substituted 2-pyridone 9b and the
hydrogen substituted 2-pyridone 9c, which were included to fur-
ther evaluate the synthetic method (entries 3–6, Table 1). Both the
alkyl substituted 2-pyridone 9b and the hydrogen substituted 2-
pyridone 9c were isolated in lower yields than the aryl substituted
2-pyridone 9a but for these two, no formation of the isomeric
4-pyridones were observed under the microwave irradiation
conditions (Table 1). The enantiomeric purity was measured for
compound 9a using chiral HPLC and a drop in enantiomeric excess
from the starting imidazoline 7b was observed (78% ee to 63% and
61% ee, respectively, for both methods, entries 1 and 2, Table 1).
To prepare the corresponding oxygen analogs a recently de-
veloped dehydrative cyclization using molybdenum oxide as cata-
lyst was employed to obtain the desired oxazolines.34 Thus, serine
derivative 11a was cyclized to the corresponding oxazoline using
10 mol % of (NH4)2MoO4 in toluene at reflux with removal of water
(Table 2). However, previous efforts to convert oxazolines to 2-pyr-
idones by reacting themwith acyl-Meldrum’s acid derivatives in HCl
(g) saturated or partly saturated 1,2-dichloroethane solutions had
been sluggish, resulting in very poor yields or more commonly in no
formation of the desired 2-pyridones. Therefore, we were seeking
a one-pot procedure thus avoiding the isolation of the oxazoline.
Hence, after 6 h at reflux the formation of the oxazoline was com-
plete (monitored by 1H NMR spectroscopy) and to this reaction
mixture acyl-Meldrum’s acid derivative 8 and trifluoroacetic acid
were added. To our delight, afteradditional 2 h at reflux this resulted
in the formation of 2-pyridone 12a, which was isolated in 78% yield
(entry 1, Table 2). This one-pot procedure was then used to prepare
2-pyridones 12b and 12c from the acylated serine derivatives 11b
and 11c. These 2-pyridones had not been obtainable via the old
procedure and although the yield dropped to a modest level (32%
and 16% yields for 12b and 12c, respectively), we were delighted to
finally isolate enough material for biological evaluation.
Unfortunately, although this method was practical and resulted
in fair yields of isolated substituted dihydrooxazolo fused 2-pyr-
idones, it appeared as the sterocentre at C-3 almost epimerized
completely for 2-pyridones 12a–c, since they displayed low optical
rotation. This was further confirmed by chiral HPLC, which showed
that the enantiomeric excess was as low as 2% for compound 12a
(entry 1, Table 2). Fortunately, by reducing the amount of acid the
enantiomeric excess could be improved to 91%, but this also
resulted in a considerable drop in yield (entry 5, Table 2).
At this point we had established synthetic protocols that, be-
sides the synthesis of thiazolo ring-fused 2-pyridones, also allowed
synthesis of both the nitrogen and the oxygen analogs. To be able to
test these compounds as pilicides the only transformation that
remained was to hydrolyze the methyl esters to the corresponding
lithium carboxylates or carboxylic acids. For the nitrogen analogs
a
Enantiomeric excess determined by chiral HPLC see Supplementary data for
more details.
b
Enantiomeric excess not determined.
a more robust alternative that would withstand the acidic condi-
tions in the acylketene imine condensation but would then need
a subsequent deprotection step. With the N-Boc-protected imida-
zoline 4a and the N-Cbz-protected imidazoline 4b in hand we
allowed them to react with acyl-Meldrum’s acid derivative 3 under
microwave irradiation at 120 ꢀC for 5 min using trifluoroacetic acid
as the acid component (Scheme 1). To our delight, both imidazo-
lines reacted well and gave the desired 2-pyridone 5 in good to
excellent yields after standard deprotection conditions (Scheme 1).
Especially the N-Boc strategy appeared ideal at this point, since the
deprotection could simply be conducted in the same pot by just
adding more trifluoroacetic acid and allow the mixture to stand in
room temperature for 30 min.
Me
OH
R
N
O
O
H
N
Me
i or ii
O
O
N
N
O
3
4a R=-Boc
4b R=-Cbz
5 From 4a (92%)
From 4b (78%)
Scheme 1. Reagents and conditions: (i) TFA (0.75%), DCE, MW 120 ꢀC, 5 min, then
more TFA, rt, 30 min; (ii) (a) TFA (1.5%), DCE, MW 120 ꢀC, 5 min; (b) Pd/C, H2 (atm),
MeOH.
Based upon the results from the model system we decided to
continue our study with the N-Boc-protected imidazoline 7a
(Scheme 2). This imidazoline was prepared starting from N-Boc-
protected diaminopropionic acid methyl ester 6a, which was
acylated and then ring-closed using triflic anhydride and triphe-
nylphosphine oxide.33 Unfortunately, we experienced some
deprotection of the N-Boc group in the latter step. In addition, ef-
forts to react the N-Boc-protected imidazoline 7a with acyl-Mel-
drum’s acid derivative 8 (Table 1) resulted in a very poor yield of the
desired 2-pyridone, which further confirmed that this was not the
appropriate protecting group for our purposes. Consequently, we
decided to instead use the more acid stable Cbz protective group,
and starting from diaminopropionic acid 6b the N-Cbz-protected
imidazolines 7b–d were prepared in excellent yields (Scheme 2).
Starting with the previously developed method (TFA and MW at
120 ꢀC for 5 min followed by deprotection of the Cbz group by
hydrogenation) the desired 2-pyridone 9a was obtained in 53%
yield (Table 1). This time, however, the 2-pyridone 9a was also
accompanied by the isomeric 4-pyridone 10 in a 5:1 ratio (Table 1).
However, lowering the temperature to 64 ꢀC (conventional

N. Pemberton et al. / Tetrahedron 64 (2008) 9368–9376
9371
9a–c we applied the saponification conditions that we had pre-
viously used for the main part of our studied thiazolo ring-fused
pilicides.16 Hence, 9a–c were hydrolyzed (0.1 M LiOH (aq) in THF) to
the corresponding lithium carboxylates 13a–c in good yields
(Scheme 3). The hydrolysis of the oxygen analogs 12a–c was not as
straightforward, and the standard saponification (LiOH in THF)
resulted in very slow conversion in combination with the formation
of several unidentified by-products. It has been shown that addi-
tion of hydrogen peroxide to lithium hydroxide may effect reaction
rate and selectivity.35 However, also this experiment resulted in
decomposition of the starting material. Fortunately, using a re-
cently published method that takes use of lithium bromide, trie-
thylamine and water in acetonitrile the esters were smoothly
converted to the desired carboxylic acids 13d–f in moderate to good
yields (57–83%) (Scheme 3).36
R
O
R
O
0.1 M LiOH (aq.)
THF
H
N
H
N
N
N
CO2Me
CO2Li
13a: R1 = Ph 93%
9a-c
13b: R1 = cyclopropyl 97%
13c: R1 = H 85%
R
O
R
LiBr,TEA,MeCN
cont.2v/v % H2O
O
O
N
N
CO2Me
CO2H
O
13d:R1 = Ph 57%
12a-c
13e:R1 = cyclopropyl 73%
13f :R1 = H 83%
Scheme 3. Hydrolysis of dihydroimidazolo[2,3-a]pyridine-5-ones 9a–c and dihy-
drooxazolo[2,3-a]pyridine-5-ones 12a–c.
2.2. Biological evaluation
Figure 2. (A) The heteroatom analogs 13a–f and the parent sulfide containing com-
pounds 1 and 2 were screened in a biofilm assay. All compounds were tested at 400 mM
Pili are important for the formation of biofilms,37 the binding and
invasion of host tissues,38 and the formation of biofilm-like in-
tracellular bacterial communities (IBC’s),39,40 thereby allowing the
bacteria to persist in the host and evade host defenses.14 Effective
pilicides have previously been shown to be capable of reducing the
formation of biofilms dependent on type 1 pilus formation in an in
vitro biofilm assay.16 This assay can be performed in 96 well plates
with small volumes and does not consume too much of the precious
potential inhibitors. Although biofilm inhibition can occur by other
mechanisms than blocking pili assembly, this assay will still always
identify a pilicide. Therefore, this assay is an ideal initial screen.
However, to verify that the biofilm inhibition is correlated to de-
creased piliation, a hemagglutination assay (HA titer) can be per-
formed to evaluate and compare potential pilicides.16
The new derivatives 13a–f and the parent compounds 1 and 2
were initially screened at 400 mM in a biofilm assay (A, Fig. 2). Ni-
trogen analogs 13a and 13c had some effect on the formation of
biofilms, but were considerably less effective than the correspond-
ing oxygen analogs 13d and 13f. These two oxygen analogs and the
parent thiazolo fused compound 1 reduced biofilm formation by
and inhibition of biofilm formation is shown as percent when compound is present
relative to an untreated control. Error bars represent the standard deviation of the
mean where shown. (B) The three best compounds from the initial screen were titrated
down at lower concentrations to confirm that they have a dose-dependant effect on
the formation of biofilms. (C) To confirm that the effect seen in the biofilm formation
was due to low pili abundance. Uropathogenic E. coli (UTI89) was grown in the pres-
ence of compound and HA titers were determined. A low HA titer indicates that less
pili are formed, and is thus a verification of an efficient pilicide.
Finally 13d, 13f, and 1 were also tested in a HA-assay to verify
that the results seen in the biofilm assay were a consequence of low
abundance of pili (C, Fig. 2). Indeed all three compounds had an
effect on pili formation in E. coli (clinical isolate UTI89) as shown by
HA titers, and the oxygen analog 13d was as potent as the corre-
sponding sulfur containing compound 1. Further confirming that
the sulfur atom in thiazolo fused pilicides can be exchanged to
oxygen, and still maintain the ability to prevent pilus assembly in
uropathogenic E. coli.
3. Conclusion
over 90% at 400
m
M and were further evaluated at lower concen-
A previously developed method to prepare thiazolo fused 2-
pyridones have been further developed to give both oxygen and
nitrogen analogs. Both systems were constructed by reacting either
trations (B, Fig. 2), confirmingthat they behavedin a dose dependent
manner.

9372
N. Pemberton et al. / Tetrahedron 64 (2008) 9368–9376
protected imidazolines or oxazolines with an acylketene generated
from an acyl-Meldrum’s acid derivative. The imidazolo fused 2-
pyridones 9a–c could be synthesized from Cbz-protected imidazo-
lines, by using either trifluoroacetic acid and microwave irradiation,
or by performing the reaction at 64 ꢀC with a partly HCl (g) saturated
1,2-dichloroethane solution. The corresponding oxazolo fused 2-
pyridones 12a–c were prepared in a one-pot procedure starting
from acylated serine derivatives, which were first ring-closed to the
oxazoline using a molybdenum oxide catalyst. This was followed by
addition of trifluoroacetic acid and acyl-Meldrum’s acid derivative 8,
which gave the desired oxazolo fused 2-pyridones 12a–c. All com-
pounds were hydrolyzed and evaluated for their ability to prevent
pili formation. From these data it could be concluded that ex-
changing the sulfur toward a secondaryamine gave a distinct drop in
activity. However, these compounds are still interesting in the future
development of pilicides, as this functionality provides a chemical
diversification point, which can be used to further substitute and
thereby fine-tune the chemical properties to increase affinity and
bioavailability. In contrast to the nitrogen analogs the oxazolo fused
2-pyridones had activities comparable to the parent sulfur con-
taining pilicides. The oxygen analog 13d was as potent as the cor-
responding sulfur containing compound 1 in a HA-assay. These
insights concerning the importance of the sulfur atom will be im-
portant for future design and development of pilicides.
allowed to attain room temperature and was diluted with DCE
(3.6 mL) and TFA (4 mL) was added. The solution was allowed to stir
for 30 min at room temperature and was then diluted with CH2Cl2,
washed with saturated aqueous NaHCO3 and brine. The aqueous
layers were extracted with CH2Cl2, and the combined organic layers
were concentrated and further purified by column chromatography
to yield 5 (100 mg, 92%) as a white solid.
From Cbz-protected tolazoline 4b: Meldrum’s acid derivative 3
(285 mg, 1.53 mmol) was added to a stirred solution of 4b (150 mg,
0.51 mmol) in DCE (2.6 mL) at room temperature. This was fol-
lowed by addition of TFA (39 mL, 0.51 mmol) and the solution was
then irradiated at 120 ꢀC for 300 s (fixed hold time, normal ab-
sorption) using a microwave apparatus. The solution was allowed
to attain room temperature and was then diluted with CH2Cl2 and
washed with saturated aqueous NaHCO3 and brine. The aqueous
layers were extracted with CH2Cl2 and the combined organic layers
were concentrated. The resulting crude mixture was dissolved in
MeOH (20 mL) and a catalytic amount of Pd/C was added and hy-
drogenation was carried out at atmospheric pressure for 1 h. The
catalyst was removed by filtration through Celite and the solid
phase was rinsed with MeOH. The filtrate was concentrated and
further purified by column chromatography to yield 5 (90 mg, 78%)
as a white solid. Mp 162–164 ꢀC (lit.28 161–162 ꢀC); IR
1209, 1114, 1060; 1H NMR (400 MHz, CDCl3)
1.93 (s, 3H), 3.65 (t,
l 1745, 1369,
d
J¼8.4 Hz, 2H), 4.23 (t, J¼8.4 Hz, 2H), 4.38 (br s, 1H), 5.82 (s, 1H),
4. Experimental
4.1. General
7.20–7.23 (m, 2H), 7.28–7.34 (m, 1H), 7.36–7.43 (m, 2H); 13C NMR
(100 MHz, CDCl3)
d 20.5, 42.7, 44.8, 99.8, 106.9, 127.4, 129.0, 130.5,
135.2, 150.1, 152.4, 160.5. HRMS (FAB) calcd for [MþH]þ C14H15N2O
227.1184, obsd 227.1171.
All reactions were carried out under an inert atmosphere with
dry solvents under anhydrous conditions, unless otherwise stated.
CH2Cl2 and 1,2-dichlorethane (DCE) were distilled from calcium
hydride. Dimethylformamide (DMF) and acetonitrile (MeCN) were
freshly distilled and stored over 3 Å molecular sieves. Trifluoroacetic
acid (TFA) and triflic anhydride (Tf2O) were freshly distilled before
use. HCl (g) was passed through concentrated H2SO4 prior to use. All
microwave reactions were carried out in a monomode reactor (Ini-
tiatior, Biotage AB) using process vials sealed with Teflon septa and
an aluminum crimp top. Reaction times refer to irradiation time at
the target temperature, not the total irradiation time. The temper-
ature was measured with an IR sensor. TLC was performed on Silica
Gel 60 F254 using UV light detection. Flash column chromatography
4.3. Preparation of N-b-Z-L-diaminopropionic acid methyl
ester 6b
N,N0-Carbonyldiimidazole (2.5 g, 15.4 mmol) was added to
a stirred solution of commercially available N- -Fmoc-N- -Z-
a
b
L-
diaminopropionic acid (2.5 g, 5.43 mmol) in CH2Cl2 (40 mL) at
room temperature. After 90 min, dry MeOH was added. The solu-
tion was allowed to stir for an additional 10 min and was then di-
luted with CH2Cl2 and washed with 10% aqueous citric acid. The
organic layer was dried over anhydrous Na2SO4, filtered, and con-
centrated to yield the crude product, which was used in the next
step without further purification.
employed normal phase silica gel (Matrex, 60 Å, 35–70
Amicon). The 1H and 13C NMR spectra were recorded at 298 K with
aBruker DRX-400spectrometerexcept compound 13c wherethe 13
m
m, Grace
Diethylamine (25 mL) was added to a solution of the crude
methyl ester in MeCN (25 mL) at 0 ꢀC, which was allowed to stir for
1 h at 0 ꢀC. The solution was then concentrated and purified by
column chromatography to yield 6b (1.25 g, 91%) as a colorless oil.
C
NMR spectra were recorded on a Bruker Avance DRX-360 spec-
trometer. The 1H and 13C NMR spectra were recorded in CDCl3 [re-
[a
]
23 14 (c 0.5, MeCN); IR
l
3320, 1729, 1691, 1531, 1253; 1H NMR
1.82 (br s, 2H), 3.27–3.37 (m, 1H), 3.49–3.62 (m,
2H), 3.71 (s, 3H), 5.08 (s, 2H), 5.42 (br s, 1H), 7.27–7.38 (m, 5H); 13
D
sidual CHCl3
standard], or MeOD-d4 [residual CD2HOD (dH 3.30 ppm) or CD3OD
dC 49.0 ppm) as internal standard], or DMSO-d6 [residual DMSO (dH
(dH 7.26 ppm) or CDCl3
(
dC 77.0 ppm) as internal
(400 MHz, CDCl3) d
C
(
NMR (100 MHz, CDCl3) d 44.4, 52.3, 54.2, 66.8, 128.1 (split), 128.5,
2.50 ppm) or DMSO (dC 40.0 ppm) as internal standard]. IR spectra
were recorded on an FTIR spectrometer. Enantiomeric purity for
selected compounds was determined by chiral HPLC, see Supple-
mentary data for further details. For experimental procedures re-
garding preparation of serine derivatives 11a–c and tolazoline
derivatives 4a and 4b see Supplementary data.
136.4, 156.5, 174.2. HRMS (FAB) calcd for [MþH]þ C12H17N2O4
253.1188, obsd 253.1180.
4.4. Preparation of 4-(S)-1-tert-butoxycarbonyl-2-benzyl-4,5-
dihydro-imidazole-4-carboxylic acid methyl ester 7a
The commercially available HCl salt of diaminopropionic acid
4.2. Preparation of 7-methyl-5-oxo-8-phenyl-2,3-dihydro-5H-
imidazolo[3,2-a]pyridine 5
methyl ester 6a (300 mg, 1.12 mmol) was dissolved in CH2Cl2
(100 mL). Then phenylacetyl chloride (175
mL, 1.32 mmol) followed
by triethylamine (330
m
L, 2.38 mmol) were added dropwise at 0 ꢀC
From Boc-protected tolazoline 4a: Meldrum’s acid derivative 3
(268 mg, 1.44 mmol) was added to a stirred solution of 4a (125 mg,
0.48 mmol) in DCE (2.4 mL) at room temperature. This was fol-
lowed by addition of TFA (18 mL, 0.24 mmol) and the solution was
then irradiated at 120 ꢀC for 300 s (fixed hold time, normal ab-
sorption) using a microwave apparatus. The solution was then
and the solution was stirred for 1 h and then diluted with CH2Cl2
and washed with 10% aqueous NaHCO3, the aqueous layers were
extracted with CH2Cl2. The combined organic layers were dried
over anhydrous Na2SO4, filtered, concentrated, and further purified
by column chromatography to yield the acylated product (334 mg,
85%) as a colorless oil.

N. Pemberton et al. / Tetrahedron 64 (2008) 9368–9376
9373
Tf2O (252
m
L, 1.34 mmol) was added to a stirred solution of
then filtered off and washed with CH2Cl2. The filtrate was washed
with 10% aqueous NaHCO3 and brine and the aqueous layers were
extracted with CH2Cl2. The combined organic layers were concen-
Ph3PO (746 mg, 2.68 mmol) in CH2Cl2 (8 mL) at 0 ꢀC. The solution
was stirred at 0 ꢀC for 10 min and then the acylated product
(300 mg, 0.86 mmol) dissolved in CH2Cl2 (4 mL) was added. The
solution was stirred at 0 ꢀC for 1 h and was then diluted with CH2Cl2
and washed with 10% aqueous NaHCO3, and the aqueous layers
were extracted with CH2Cl2. The combined organic layers were
dried over anhydrous Na2SO4, filtered, concentrated, and purified
trated to yield 7c (151 mg, 97%) as a colorless oil. [
CHCl3); IR
1722, 1633, 1392, 1301, 1157; 1H NMR (400 MHz, CDCl3)
0.13–0.25 (m, 2H), 0.42–0.54 (m, 2H), 1.08–1.20 (m, 1H), 2.59 (dd,
a]
23 102 (c 1.0,
D
l
d
J1¼7.1 Hz, J2¼15.6 Hz, 1H), 2.74 (dd, J1¼6.7 Hz, J2¼15.6 Hz, 1H), 3.76
(s, 3H), 3.95–4.02 (m, 1H), 4.10 (dd, J1¼7.5 Hz, J2¼11.0 Hz, 1H), 4.61–
4.69 (m, 1H), 5.17 (s, 2H), 7.29–7.39 (m, 5H); 13C NMR (100 MHz,
by column chromatography to yield 7a (119 mg, 43%) as a colorless
oil. [
a]
142 (c 1.0, CHCl3); IR
l
2977, 1720, 1369, 1141; 1H NMR
CDCl3) d 4.3, 4.5, 8.0, 35.2, 48.6, 52.6, 65.5, 67.8, 128.2, 128.5, 128.6,
23
D
(400 MHz, CDCl3)
d
1.41 (s, 9H), 3.80 (s, 3H), 3.95 (t, J¼11.2 Hz, 1H),
135.3, 151.0, 162.9, 171.5. HRMS (FAB) calcd for [MþH]þ C17H21N2O4
4.06 (dd, J1¼7.6 Hz, J2¼11.2 Hz, 1H), 4.11 (d, J¼14.8 Hz, 1H), 4.20 (d,
317.1501, obsd 317.1495.
J¼14.8 Hz, 1H), 4.66 (dd, J1¼7.6 Hz, J2¼11.2 Hz, 1H), 7.19–7.43 (m,
5H); 13C NMR (100 MHz, CDCl3)
d
28.0, 35.0, 49.2, 52.6, 65.0, 82.5,
4.7. Preparation of 4-(S)-1-benzyloxycarbonyl-2-methyl-4,5-
126.6, 128.3, 128.9, 135.8, 149.8, 162.0, 171.7. HRMS (FAB) calcd for
dihydro-imidazole-4-carboxylic acid methyl ester 7d
[MþH]þ C17H23N2O4 319.1658, obsd 319.1662.
Compound 6b (230 mg, 0.91 mmol) was dissolved in CH2Cl2
4.5. Preparation of 4-(S)-1-benzyloxycarbonyl-2-benzyl-4,5-
dihydro-imidazole-4-carboxylic acid methyl ester 7b
(40 mL). Then acetic anhydride (95
mL, 1.0 mmol) followed by trie-
thylamine (126
m
L, 0.91 mmol) were added dropwise at 0 ꢀC. The
solution was stirred at 0 ꢀC for 1 h and was then diluted with CH2Cl2
and washed with 10% aqueous NaHCO3 and brine. The aqueous
layers were extracted with CH2Cl2, and the combined organic layers
were concentrated and further purified by filtering through a short
silica plug to yield the acetylated product, which was used in the
next step without further purification.
Compound 6b (135 mg, 0.54 mmol) was dissolved in CH2Cl2
(50 mL). Then phenylacetyl chloride (110
mL, 0.59 mmol) followed
by triethylamine (74
m
L, 0.54 mmol) were added dropwise at 0 ꢀC.
The solution was stirred at room temperature for 1 h and then di-
luted with CH2Cl2 and washed with saturated aqueous NaHCO3 and
brine. The aqueous layers were extracted with CH2Cl2. The com-
bined organic layers were dried over anhydrous Na2SO4, filtered,
and concentrated to yield the acylated product, which was used in
the next step without further purification.
Tf2O (225 mL, 1.34 mmol) was added to a stirred solution of
polymer supported Ph3PO (986 mg, 2.74 mmol) in CH2Cl2 (8 mL) at
0 ꢀC. The mixture was stirred at 0 ꢀC for 10 min and then the
acetylated product dissolved in CH2Cl2 (8 mL) was added. The so-
lution was stirred at 0 ꢀC for 1 h and then filtered and the beads
were washed with CH2Cl2. The filtrate was washed with 10%
aqueous NaHCO3 and brine. The aqueous layers were extracted
with CH2Cl2. The combined organic layers were concentrated to
Tf2O (135 mL, 0.54 mmol) was added to a stirred solution of
Ph3PO (448 mg, 1.61 mmol) in CH2Cl2 (6 mL) at 0 ꢀC. The solution
was stirred at 0 ꢀC for 10 min and then the acylated product (from
above) dissolved in CH2Cl2 (4 mL) was added. The solution was
stirred at 0 ꢀC for 1 h and was then diluted with CH2Cl2 and washed
with 10% aqueous NaHCO3 and the aqueous layer was extracted
with CH2Cl2. The combined organic layers were dried over anhy-
yield 7d (239 mg, 95%) as a colorless oil. [
l
a]
23 110 (c 1.0, CHCl3); IR
D
1773, 1637, 1398, 1315; 1H NMR (400 MHz, CDCl3)
d 2.37 (d,
J¼1.4 Hz, 3H), 3.79 (s, 3H), 3.96–4.03 (m, 1H), 4.12 (dd, J1¼7.7 Hz,
drous Na2SO4, filtered, concentrated, and purified by column
J2¼11.1 Hz, 1H), 4.59–4.66 (m, 1H), 5.19 (s, 2H), 7.32–7.41 (m, 5H);
23
chromatography to yield 7b (165 mg, 88%) as a colorless oil. [
89 (c 1.0, CHCl3); IR
CDCl3)
a]
13C NMR (100 MHz, CDCl3)
d 17.8, 48.6, 52.8, 65.6, 68.0, 128.4, 128.7,
D
l
1727, 1396, 1301, 1201; 1H NMR (400 MHz,
128.8, 135.4, 151.4, 160.2, 171.5. HRMS (FAB) calcd for [MþH]þ
d
3.80 (s, 3H), 3.96–4.03 (m, 1H), 4.09–4.23 (m, 3H), 4.70 (dd,
C14H17N2O4 277.1188, obsd 277.1183.
J1¼7.6 Hz, J2¼11.1 Hz, 1H), 5.12 (s, 2H), 7.20–7.39 (m, 10H); 13C NMR
(100 MHz, CDCl3)
d
36.0, 48.9, 52.7, 65.6, 67.9, 126.7, 128.2, 128.4,
4.8. General procedure for the preparation of imidazolo[2,3-
128.5, 128.6, 128.9, 135.2, 135.5, 150.8, 161.5, 171.4. HRMS (FAB)
a]pyridin-5-ones 9a–c
calcd for [MþH]þ C20H21N2O4 353.1501, obsd 353.1504.
Method A: Meldrum’s acid derivative 8 (3 equiv) was added to
a stirred solution of imidazolines (7a–c) in DCE (0.2 mmol/mL) at
room temperature. This was followed by addition of TFA (1 equiv)
and the solution was then heated to 120 ꢀC and irradiated at the
target temperature for 300 s (fixed hold time, normal absorption)
using a microwave apparatus. The solution was allowed to attain
room temperature and was then diluted with CH2Cl2 and washed
with saturated aqueous NaHCO3 and brine. The aqueous layers
were extracted with CH2Cl2, and the combined organic layers were
concentrated. The resulting crude mixture was dissolved in MeOH
and a catalytic amount of Pd/C was added and hydrogenation was
carried out at atmospheric pressure for 2 h. The catalyst was re-
moved by filtration through Celite and the solid phase was rinsed
with MeOH. The filtrate was concentrated and further purified by
column chromatography to yield 9a–c in 42–61% yield.
Method B: Meldrum’s acid derivative 8 (1.5 equiv) was added to
a stirred solution of imidazolines (7a–c) in DCE (0.1 mmol/mL) at
room temperature. This was followed by addition of HCl (g) satu-
rated DCE (0.1 mmol/mL) and the solution was heated to 64 ꢀC and
allowed to stir for 12 h and then more Meldrum’s acid derivative 8
(0.5 equiv) was added. Stirring was maintained for an additional 3 h
and then cooled to room temperature, diluted with CH2Cl2, and
4.6. Preparation of 4-(S)-1-benzyloxycarbonyl-2-
cyclopropylmethyl-4,5-dihydro-imidazole-4-carboxylic acid
methyl ester 7c
A flask was charged with HOAt (126 mg, 0.93 mmol), DCC
(191 mg, 0.93 mmol), and CH2Cl2 (15 mL). This was followed by
addition of cyclopropylacetic acid (93 mg, 0.93 mmol) and the
mixture was allowed to stir at room temperature for 5 min before
6b in CH2Cl2 (5 mL) was added. The mixture was stirred for 1 h at
room temperature and was then diluted with CH2Cl2 and washed
with ice-cold 1 M HCl and brine. The aqueous layers were extracted
with CH2Cl2. The combined organic layers were dried over anhy-
drous Na2SO4, filtered, and concentrated. EtOAc was added to the
crude mixture, which was cooled to ꢁ78 ꢀC and then filtered. The
filtrate was concentrated and purified by column chromatography
to yield the acylated product (207 mg, 87%).
Tf2O (125 mL, 0.74 mmol) was added to a stirred solution of
polymer supported Ph3PO (530 mg, 1.48 mmol) in CH2Cl2 (5 mL) at
0 ꢀC. The mixture was stirred at 0 ꢀC for 10 min and then the ac-
ylated product (165 mg, 0.49 mmol) dissolved in CH2Cl2 (5 mL) was
added. The solution was stirred at 0 ꢀC for 1 h and the beads were

9374
N. Pemberton et al. / Tetrahedron 64 (2008) 9368–9376
washed with saturated aqueous NaHCO3 and brine. The aqueous
layers were extracted with CH2Cl2, and the combined organic layers
were concentrated. The resulting crude mixture was dissolved in
MeOH and a catalytic amount of Pd/C was added and hydrogena-
tion was carried out at atmospheric pressure for 2 h. The catalyst
was removed by filtration through Celite and the solid phase was
rinsed with MeOH. The filtrate was concentrated and further pu-
rified by column chromatography to yield 9a–c in 17–70% yield.
using a Soxhlet apparatus containing activated 3 Å molecular
sieves. After 6 h at reflux, the reaction mixture was cooled to room
temperature for 5 min and Meldrum’s acid derivative 8 (527 mg,
1.69 mmol) followed by TFA (325 ml, 4.22 mmol) were added. The
solution was heated to reflux for 2 h and then allowed to attain
room temperature, filtered through Celite, and concentrated under
reduced pressure. Purification by column chromatography yielded
23
pyridone 12a (268 mg, 78% yield) as a colorless foam. [
1.1, CHCl3); IR
a]
ꢁ6 (c
D
l
1752, 1666, 1508, 1207; 1H NMR (400 MHz, CDCl3)
4.8.1. (3S)-7-(Naphthalen-1-ylmethyl)-5-oxo-8-phenyl-2,3-
dihydro-5H-imidazolo[3,2-a]pyridine-3-carboxylic acid methyl
d
3.83 (s, 3H), 4.03 (d, J¼17.0 Hz, 1H), 4.10 (d, J¼17.0 Hz, 1H), 4.65
(dd, J1¼4.6 Hz, J2¼9.4 Hz, 1H), 4.80 (t, J1¼9.3 Hz, 1H), 5.22 (dd,
J1¼4.6 Hz, J2¼9.4 Hz, 1H), 5.71 (s, 1H), 7.24 (d, J¼7.2 Hz, 1H), 7.33–
7.46 (m, 8H), 7.62 (m, 1H), 7.74 (d, J¼8.3 Hz, 1H), 7.83 (m, 1H); 13C
ester 9a
23
[a]
ꢁ44 (c 1.0, CHCl3); IR
3.70–3.75 (m,1H), 3.81 (s, 3H), 3.91–4.06 (m, 3H),
l
1749, 1646, 1521, 1209; 1H NMR
D
(400 MHz, CDCl3)
d
NMR (100 MHz, CDCl3) d 37.0, 53.4, 57.1, 71.4, 99.9, 111.3, 123.8,
4.27(brs,1H), 5.19(dd,J1¼4.5 Hz,J2¼10.0 Hz,1H), 5.53(s,1H), 7.23(d,
125.4, 125.6, 126.1, 127.7, 127.9 (split), 128.7 (split), 130.8, 131.8,
132.5, 133.9, 134.1, 153.6, 157.1, 159.1, 168.2. HRMS (FAB) calcd for
[MþH]þ C26H22NO4 412.1549, obsd 412.1550.
J¼7.0 Hz,1H), 7.27–7.48 (m, 8H), 7.64–7.68 (m,1H), 7.72 (d, J¼8.4 Hz,
1H), 7.78–7.83 (m, 1H); 13C NMR (100 MHz, CDCl3)
d 36.9, 47.0, 53.1,
57.8, 99.3, 107.5, 124.0, 125.5, 125.6, 126.0, 127.5, 127.8, 127.9, 128.7,
129.3,130.8,132.0,133.9,134.7 (split),150.0,155.9,160.1,169.4. HRMS
(FAB) calcd for [MþH]þ C26H23N2O3 411.1709, obsd 411.1704.
When 12a was prepared using 0.1 equiv of TFA, which resulted
23
in 91% ee the optical rotation was [
a]
ꢁ63 (c 1.0, CHCl3).
D
4.10. Preparation of (3S)-7-(naphthalen-1-ylmethyl)-5-oxo-8-
cyclopropyl-2,3-dihydro-5H-oxazolo[3,2-a]pyridine-3-
carboxylic acid methyl ester 12b
4.8.2. (3S)-5-(Naphthalen-1-ylmethyl)-7-oxo-8-phenyl-2,3-
dihydro-7H-imidazolo[3,2-a]pyridine-3-carboxylic acid methyl
ester 10
23
[a
]
ꢁ39 (c 0.7, CHCl3); IR
l
2919, 1633, 1536, 1508, 1434; 1H
(NH4)2MoO4 (19 mg, 0.01 mmol) was added to a stirred solution
of serine derivative 11b (190 mg, 0.94 mmol) in toluene (95 mL).
The solution was heated to reflux with removal of water using
a Soxhlet apparatus containing activated 3 Å molecular sieves. After
5 h at reflux, the reaction mixture was cooled in room temperature
for 5 min and Meldrum’s acid derivative 8 (590 mg, 1.89 mmol)
D
NMR (400 MHz, CDCl3)
d
3.74–3.82 (m, 2H), 3.83 (s, 3H), 4.19 (br s,
2H), 4.64 (br s, 1H), 4.90 (dd, J1¼2.5 Hz, J2¼8.3 Hz, 1H), 5.85 (s, 1H),
7.20–7.26 (m, 1H), 7.30–7.39 (m, 3H), 7.41–7.47 (m, 3H), 7.48–4.57
(m, 2H), 7.83 (d, J¼8.3 Hz, 1H), 7.87–7.95 (m, 2H); 13C NMR
(100 MHz, CDCl3)
d 35.1, 47.8, 53.5, 59.6, 106.0, 116.2, 123.3, 125.6,
126.1,126.7,127.0,127.3,128.5,128.7,128.9,130.0,130.8,131.9,133.6,
134.0, 143.4, 153.1, 169.5, 177.7. HRMS (FAB) calcd for [MþH]þ
C26H23N2O3 411.1709, obsd 411.1712.
followed by TFA (360 mL, 4.67 mmol) were added. The solution was
heated to reflux for 2 h and then allowed to attain room temper-
ature for 40 min. Then more Meldrum’s acid derivative 11 (295 mg,
0.94 mmol) was added and the reaction mixture was heated to
reflux for an additional 90 min. The solution was allowed to attain
room temperature, filtered through Celite, and concentrated. Pu-
4.8.3. (3S)-7-(Naphthalen-1-ylmethyl)-5-oxo-8-cyclopropyl-2,3-
dihydro-5H-imidazolo[3,2-a]pyridine-3-carboxylic acid methyl
ester 9b
rification by column chromatography gave 2-pyridone 12b as
23
23
[a
]
ꢁ134 (c 1.0, CHCl3); IR
l
1749, 1643, 1521, 1207; 1H NMR
a brown oil (114 mg, 32% yield). [
a
]
D
ꢁ18 (c 1.0, CHCl3); IR
l 1752,
D
(400 MHz, CDCl3)
d
0.48–0.61 (m, 2H), 0.77–0.94 (m, 2H), 1.37–1.46
1671, 1594, 1509, 1211; 1H NMR (400 MHz, CDCl3)
d 0.68–0.76 (m,
(m, 1H), 3.70–3.85 (m, 4H), 3.95–4.01 (m, 1H), 4.31 (d, J¼16.9 Hz,
1H), 4.45 (d, J¼16.9 Hz, 1H), 4.75 (br s, 1H), 5.12 (dd, J1¼4.3 Hz,
J2¼9.9 Hz, 1H), 5.46 (s, 1H), 7.26–7.30 (m, 1H), 7.37–7.42 (m, 1H),
7.43–7.49 (m, 2H), 7.75 (d, J¼8.3 Hz, 1H), 7.83–7.89 (m, 2H); 13C
2H), 0.80–0.93 (m, 2H), 1.40–1.47 (m, 1H), 3.78 (s, 3H), 4.37 (d,
J¼17.2 Hz, 1H), 4.50 (d, J¼17.2 Hz, 1H), 4.66 (dd, J1¼4.5 Hz,
J2¼9.5 Hz, 1H), 4.75 (t, J¼9.5 Hz, 1H), 5.12 (dd, J1¼4.5 Hz, J2¼9.5 Hz,
1H), 5.61 (s, 1H), 7.28 (d, J¼7.3 Hz, 1H), 7.37–7.52 (m, 3H), 7.74–7.87
NMR (100 MHz, CDCl3)
d
6.5, 7.0, 7.1, 36.4, 47.2, 53.0, 57.3, 96.1,108.1,
(m, 3H); 13C NMR (100 MHz, CDCl3)
d 6.3, 6.6, 6.6, 36.4, 53.1, 56.6,
123.9, 125.5, 125.6, 126.0, 127.3 (split), 128.7, 132.1, 133.9, 134.7,
151.0, 158.4, 159.9, 169.5. HRMS (FAB) calcd for [MþH]þ C23H23N2O3
375.1709, obsd 375.1701.
71.0, 97.9, 111.1, 123.7, 125.4, 125.5, 126.0, 127.3, 127.4, 128.7, 131.9,
133.8, 134.0, 154.3, 158.9, 159.6, 168.3. HRMS (FAB) calcd for
[MþH]þ C23H22NO4 376.1549, obsd 376.1550.
4.8.4. (3S)-7-(Naphthalen-1-ylmethyl)-5-oxo-2,3-dihydro-5H-
4.11. Preparation of (3S)-7-(naphthalen-1-ylmethyl)-5-oxo-
2,3-dihydro-5H-oxazolo[3,2-a]pyridine-3-carboxylic acid
methyl ester 12c
imidazo[3,2-a]pyridine-3-carboxylic acid methyl ester 9c
23
[a
]
ꢁ69 (c 1.0, CHCl3); IR
l
1741, 1654, 1535, 1209; 1H NMR
3.63–3.69 (m, 1H), 3.76 (s, 3H), 3.80–3.87 (m,
D
(400 MHz, CDCl3)
d
1H), 4.15 (s, 2H), 4.58 (br s, 1H), 5.05 (dd, J1¼4.1 Hz, J2¼9.9 Hz, 1H),
5.20 (s, 1H), 5.81 (s, 1H), 7.30–7.54 (m, 4H), 7.77 (d, J¼8.2 Hz, 1H),
7.80–7.87 (m, 1H), 7.88–7.95 (m, 1H); 13C NMR (100 MHz, CDCl3)
(NH4)2MoO4 (25 mg, 0.13 mmol) was added to a stirred solution
of serine derivative 11c (210 mg, 1.30 mmol) in toluene (140 mL).
The solution was heated to reflux with azeotropic removal of water
using a Soxhlet apparatus containing activated 3 Å molecular
sieves. After 4 h at reflux, the reaction mixture was cooled at room
temperature for 5 min and Meldrum’s acid derivative 8 (893 mg,
d
39.4, 47.0, 53.0, 57.0, 84.9, 106.4, 124.1, 125.4, 125.7, 126.2, 127.6,
127.8,128.6,132.1,133.9,134.4,151.9,157.7,160.8,169.3. HRMS (FAB)
calcd for [MþH]þ C20H19N2O3 335.1396, obsd 335.1386.
2.86 mmol) followed by TFA (100 mL, 1.30 mmol) were added. The
4.9. Preparation of (3S)-7-(naphthalen-1-ylmethyl)-5-oxo-8-
phenyl-2,3-dihydro-5H-oxazolo[3,2-a]pyridine-3-carboxylic
acid methyl ester 12a
solution was then heated to reflux for 1 h and then allowed to at-
tain room temperature, filtered through Celite, and concentrated.
Purification by column chromatography yielded 2-pyridone 12c as
23
a yellow oil (74 mg, 17% yield). [
a
]
D
ꢁ37 (c 0.5, CHCl3); IR
l 1751,
d 3.81 (s, 3H),
(NH4)2MoO4 (16 mg, 0.08 mmol) was added to a stirred solution
of serine derivative 11a (200 mg, 0.84 mmol) in toluene (84 mL).
The solution was heated to reflux with azeotropic removal of water
1673, 1596, 1529, 1218; 1H NMR (400 MHz, CDCl3)
4.23 (s, 2H), 4.63 (dd, J1¼4.5 Hz, J2¼9.3 Hz, 1H), 4.74 (t, J1¼9.3 Hz,
1H), 5.14 (dd, J1¼4.5 Hz, J2¼9.3 Hz, 1H), 5.50 (d, J¼1.1 Hz, 1H), 6.00

N. Pemberton et al. / Tetrahedron 64 (2008) 9368–9376
9375
(s, 1H), 7.35 (d, J¼6.7 Hz, 1H), 7.40–7.51 (m, 3H), 7.79 (d, J¼8.3 Hz,
1H), 7.83–7.92 (m, 2H); 13C NMR (100 MHz, CDCl3)
39.4, 53.3, 56.5,
71.3, 84.9, 109.8, 123.8, 125.4, 125.7, 126.2, 127.8 (split), 128.7, 131.9,
133.7, 133.9, 156.5, 158.2, 160.0, 168.1. HRMS (FAB) calcd for [MþH]þ
C20H18NO4 336.1236, obsd 336.1233.
further purified by centrifugal chromatography. This product was
lyophilized from H2O to yield carboxylic acid 13d (50 mg, 57%).
d
23
[a
]
ꢁ2 (c 0.5, CHCl3); IR
l
1652, 1575, 1511, 1396; 1H NMR
4.04 (d, J¼17.0 Hz, 1H), 4.11 (d, J¼17.0 Hz,
D
(400 MHz, DMSO-d6)
d
1H), 4.68 (dd, J1¼3.6 Hz, J2¼8.8 Hz, 1H), 4.82–4.90 (m, 1H), 5.04 (dd,
J1¼3.6 Hz, J2¼9.3 Hz, 1H), 5.29 (s, 1H), 7.29–7.36 (m, 2H), 7.38–7.51
(m, 7H), 7.65–7.70 (m, 1H), 7.83 (d, J¼8.2 Hz, 1H), 7.89–7.94 (m, 1H);
4.12. Preparation of (3S)-7-(naphthalen-1-ylmethyl)-5-oxo-8-
phenyl-2,3-dihydro-5H-imidazo[3,2-a]pyridine-3-lithium
carboxylate 13a
13C NMR (100 MHz, MeOD-d4)
d 36.4, 57.9, 72.7, 98.8, 109.7, 124.2,
126.0, 126.2, 126.7, 127.7, 127.8, 128.0, 128.9, 129.0, 131.3, 131.8,
133.3, 133.8, 135.1, 154.9, 156.0, 158.4, 169.8.
LiOH (0.1 M, 1.58 mL, 0.158 mmol) was added dropwise to
a stirred solution of 9a (65 mg, 0.158 mmol) in THF (5.0 mL) at 0 ꢀC.
The solution was allowed to attain room temperature while stirring
4.16. Preparation of (3S)-7-(naphthalen-1-ylmethyl)-5-oxo-8-
cyclopropyl-2,3-dihydro-5H-oxazolo[3,2-a]pyridine-3-lithium
carboxylate 13e
for 2 h and was then concentrated and lyophilized from H2O to
23
yield lithium carboxylate 13a (59 mg, 93%). [
MeOH); IR
DMSO-d6)
a]
ꢁ44 (c 0.5,
D
l
3270, 1639, 1527, 1396, 1295; 1H NMR (400 MHz,
LiBr (69 mg, 0.79 mmol) and TEA (33 mL, 0.24 mmol) were
d
3.55 (dd, J1¼3.6 Hz, J2¼9.2 Hz, 1H), 3.62–3.70 (m, 1H),
added to a stirred solution of 12b (30 mg, 0.08 mmol) in MeCN
(0.4 mL) containing 2 v/v % H2O. The reaction mixture was allowed
to stir for 2 h at room temperature and was then diluted with EtOAc
and washed with 2 M HCl. The aqueous layer was extracted with
EtOAc. The combined organic layers were dried, concentrated, and
further purified by centrifugal chromatography. This product was
3.90 (s, 2H), 4.56 (dd, J1¼3.6 Hz, J2¼10.1 Hz, 1H), 4.91 (br s, 1H), 6.31
(s, 1H), 7.26–7.52 (m, 9H), 7.66–7.72 (m, 1H), 7.80 (d, J¼8.2 Hz, 1H),
7.87–7.92 (m, 1H); 13C NMR (100 MHz, DMSO-d6)
d 36.3, 48.2, 61.0,
97.9, 104.7, 124.4, 126.0, 126.1, 126.5, 127.4, 127.9, 128.9, 129.2, 131.4,
132.0, 133.8, 135.9 (split), 151.9, 153.4, 160.2, 171.0.
lyophilized from H2O to yield carboxylic acid 13e (21 mg, 73%).
23
l
1656, 1513, 1209, 1174; 1H NMR
4.13. Preparation of (3S)-7-(naphthalen-1-ylmethyl)-5-oxo-8-
cyclopropyl-2,3-dihydro-5H-imidazolo[3,2-a]pyridine-3-
lithium carboxylate 13b
[
a
]
34 (c 0.1, CHCl3); IR
0.57–0.73 (m, 2H), 0.78–0.87 (m, 2H), 1.46–
D
(400 MHz, DMSO-d6)
d
1.55 (m, 1H), 4.39 (d, J¼17.3 Hz, 1H), 4.48 (d, J¼17.3 Hz, 1H), 4.72
(dd, J1¼3.6 Hz, J2¼8.8 Hz, 1H), 4.80–4.86 (m, 1H), 4.92 (dd,
J1¼3.6 Hz, J2¼9.1 Hz, 1H), 5.13 (s, 1H), 7.36 (d, J¼6.9 Hz, 1H), 7.47–
LiOH(0.1 M, 0.51 mL, 0.05 mmol) was added dropwise to a stirred
solution of 9b (19 mg, 0.05 mmol) in THF (3.0 mL) at 0 ꢀC. The solu-
tion was allowed to attain room temperature while stirring for 2 h
7.57 (m, 3H), 7.84–7.99 (m, 3H); 13C NMR (100 MHz, DMSO-d6)
d 6.7,
7.0, 7.2, 36.1, 57.6, 72.5, 96.8, 109.6, 124.5, 126.1, 126.3, 126.8, 127.7,
127.9, 129.1, 132.1, 133.9, 135.2, 155.5, 158.5, 159.1, 170.1.
and was thenconcentrated and lyophilized from H2O toyieldlithium
23
carboxylate 13b (18 mg. 97%). [
a
]
D
ꢁ53 (c 0.5, MeOH); IR
l 3274,
0.44–0.56
1644, 1525, 1396, 1294; 1H NMR (400 MHz, DMSO-d6)
d
4.17. Preparation of (3S)-7-(naphthalen-1-ylmethyl)-5-oxo-
2,3-dihydro-5H-oxazolo[3,2-a]pyridine-3-lithium
carboxylate 13f
(m, 2H), 0.77–0.89 (m, 2H),1.36–1.47 (m,1H), 3.63–3.72 (m, 2H), 4.27
(d, J¼7.0 Hz,1H), 4.37 (d, J¼7.0 Hz,1H), 4.47 (dd, J1¼3.9 Hz, J2¼9.4 Hz,
1H), 4.77 (s,1H), 6.50 (s,1H), 7.33 (d, J¼6.8 Hz,1H), 7.44–7.54 (m, 3H),
7.33 (d, J¼8.1 Hz, 1H), 7.87–7.97 (m 2H); 13C NMR (100 MHz, CDCl3)
LiBr (142 mg,1.64 mmol) and TEA (68 mL, 0.49 mmol) were added
d
7.2, 7.6, 8.1, 36.1, 48.5, 60.8, 95.0, 104.8, 124.7, 126.1, 126.2, 126.6,
to a stirred solution of 12c (55 mg, 0.16 mmol) in MeCN (1 mL) con-
taining 2 v/v % H2O. The reaction mixture was allowed to stir for 5 h at
room temperature and wasthendilutedwith EtOAc and washed with
2 M HCl. The aqueous layer was extracted with EtOAc. The combined
organic layers were dried, concentrated, and further purified by
127.4, 127.8, 129.0, 132.3, 133.9, 136.2, 153.3, 156.3, 160.2, 170.8.
4.14. Preparation of (3S)-7-(naphthalen-1-ylmethyl)-5-oxo-
2,3-dihydro-5H-imidazolo[3,2-a]pyridine-3-lithium
carboxylate 13c
chromatography and then lyophilized from H2O to yield carboxylic
23
acid 13f (44 mg, 83%). [
a
]
ꢁ4 (c 0.5, CHCl3); IR
l 1660, 1525, 1396,
4.24 (s, 2H), 4.68 (dd, J1¼3.6 Hz,
D
1220; 1HNMR (400 MHz, DMSO-d6)
d
LiOH (0.1 M, 0.90 mL, 0.09 mmol) was added dropwise to a stir-
red solution of 9c (30 mg, 0.09 mmol) in THF (4.0 mL) at 0 ꢀC. The
solution was allowed to attain room temperature while stirring for
J2¼8.8 Hz,1H), 4.77–4.84 (m,1H), 4.95 (dd, J1¼3.6 Hz, J2¼9.3 Hz,1H),
5.58(s,1H), 5.68(s,1H), 7.43–7.63(m, 4H), 7.81–8.10(m, 3H);13CNMR
4 h and was then concentrated and lyophilized from H2O to yield
(100 MHz, CDCl3)
d 39.4, 58.8, 70.4, 88.8, 108.6, 123.7, 125.5, 125.9,
23
lithium carboxylate 13c (25 mg, 85%). [
a
]
D
ꢁ69 (c 0.4, MeOH); IR
l
126.5, 128.0, 128.2, 128.9, 131.8, 133.0, 134.0, 156.9, 161.2, 162.1, 167.3.
2915, 1660, 1527, 1425, 1301; 1H NMR (400 MHz, DMSO-d6)
d
3.54–
3.68 (m, 2H), 4.10 (s, 2H), 4.49 (dd, J1¼3.5 Hz, J2¼9.3 Hz,1H), 5.09 (s,
Acknowledgements
1H), 5.30 (s, 1H), 6.94 (br s, 1H), 7.36–7.57 (m, 4H), 7.82 (d, J¼7.6 Hz,
1H), 7.88–8.06 (m, 2H); 13C NMR (100 MHz, DMSO-d6)
d 38.3, 47.5,
We thank the Swedish Natural Science Research Council and the
JC Kempe foundation for financial support.
60.1, 83.2, 103.0, 124.3, 125.6, 125.7, 126.1, 127.1, 127.6, 128.5, 131.8,
133.5, 135.5, 153.7, 155.4, 160.7, 170.7.
Supplementary data
4.15. Preparation of (3S)-7-(naphthalen-1-ylmethyl)-5-oxo-8-
phenyl-2,3-dihydro-5H-oxazolo[3,2-a]pyridine-3-lithium
carboxylate 13d
Electronic Supplementary Information (ESI) available: 13C NMR
spectra of compounds. Supplementary data associated with this
article can be found in the online version, at doi:10.1016/
j.tet.2008.07.015.
LiBr (190 mg, 2.19 mmol) and TEA (90 mL, 0.65 mmol) were
added to a stirred solution of 12a (90 mg, 0.22 mmol) in MeCN
(1 mL) containing 2 v/v % H2O. The reaction mixture was allowed to
stir for 3 h at room temperature and was then diluted with EtOAc
and washed with 2 M HCl. The aqueous layer was extracted with
EtOAc. The combined organic layers were dried, concentrated, and
References and notes
1. Report from Infectious Disease Society of America (IDSA); www.idsociety.org,
2004.

9376
N. Pemberton et al. / Tetrahedron 64 (2008) 9368–9376
2. Report from European Academies Science Advisory Council (EASAC); www.
easac.eu, 2007.
22. Pemberton, N.; Åberg, V.; Almstedt, T.; Westermark, A.; Almqvist, F. J. Org.
Chem. 2004, 69, 7830–7835.
3. Alekshun, M. N.; Levy, S. B. Drug Discov. Today 2004, 1, 483–489.
4. Alksne, L. E.; Projan, S. J. Curr. Opin. Biotechnol. 2000, 11, 625–636.
5. Marra, A. Drugs R D 2006, 7, 1–16.
6. Lee, Y. M.; Almqvist, F.; Hultgren, S. J. Curr. Opin. Pharmacol. 2003, 3, 513–519.
7. Clatworthy, A. E.; Pierson, E.; Hung, D. T. Nat. Chem. Biol. 2007, 3, 541–548.
8. Cegelski, L.; Marshall, G. R.; Eldridge, G. R.; Hultgren, S. J. Nat. Rev. Microbiol.
2008, 6, 17–27.
9. Åberg, V.; Almqvist, F. Org. Biomol. Chem. 2007, 5, 1827–1834.
10. Åberg, V.; Fa¨llman, E.; Axner, O.; Uhlin, B. E.; Hultgren, S. J.; Almqvist, F. Mol.
Biosyst. 2007, 3, 214–218.
11. Andersson, M.; Axner, O.; Uhlin, B. E.; Almqvist, F.; Fa¨llman, E. ChemPhysChem
2008, 9, 221–235.
12. Hung, D. L.; Knight, S. D.; Woods, R. M.; Pinkner, J. S.; Hultgren, S. J. EMBO J.
1996, 15, 3792–3805.
13. Sauer, F. G.; Remaut, H.; Hultgren, S. J.; Waksman, G. Biochim. Biophys. Acta
2004, 1694, 259–267.
14. Mulvey, M. A.; Lopez-Boado, Y. S.; Wilson, C. L.; Roth, R.; Parks, W. C.; Heuser, J.;
Hultgren, S. J. Science 1998, 282, 1494–1497.
15. Thanassi, D. G.; Saulino, E. T.; Hultgren, S. J. Curr. Opin. Microbiol. 1998, 1, 223–
231.
23. Pemberton, N.; Pinkner, J. S.; Jones, J. M.; Jakobsson, L.; Hultgren, S. J.; Almqvist,
F. Tetrahedron Lett. 2007, 48, 4543–4546.
24. Åberg, V.; Sellstedt, M.; Hedenstro¨m, M.; Pinkner, J. S.; Hultgren, S. J.; Almqvist,
F. Bioorg. Med. Chem. 2006, 14, 7563–7581.
25. Åberg, V.; Hedenstro¨m, M.; Pinkner, J. S.; Hultgren, S. J.; Almqvist, F. Org. Biomol.
Chem. 2005, 3, 3886–3892.
26. Åberg, V.; Das, P.; Chorell, E.; Hedenstro¨m, M.; Pinkner, J. S.; Hultgren, S. J.;
Almqvist, F. Bioorg. Med. Chem. Lett., 2008 18, 3536–3540.
27. Pemberton, N.; Jakobsson, L.; Almqvist, F. Org. Lett. 2006, 8, 935–938.
28. Jones, R. C. F.; Dimopoulos, P.; Coles, S. C.; Light, M. E.; Hursthouse, M. B. J.
Chem. Soc., Perkin Trans. 1 2000, 2331–2342.
29. Jones, R. C. F.; Patel, P.; Hirst, S. C.; Smallridge, M. J. Tetrahedron 1998, 54, 6191–
6200.
30. Zhitang, H.; Pingcheng, Z. Chem. Ber. 1989, 122, 2011–2016.
31. Zhao, M. X.; Wang, M. X.; Huang, Z. T. Tetrahedron 2002, 58, 1309–1316.
32. Compounds 4a and 4b were prepared by standard protection procedures see
Supplementary data for further details.
33. You, S. L.; Kelly, J. W. Org. Lett. 2004, 6, 1681–1683.
34. Sakakura, A.; Kondo, R.; Ishihara, K. Org. Lett. 2005, 7, 1971–1974.
35. Boger, D. L.; Yohannes, D.; Zhou, J. C.; Patane, M. A. J. Am. Chem. Soc. 1993, 115,
3420–3430.
36. Mattsson, S.; Dahlstro¨m, M.; Karlsson, S. Tetrahedron Lett. 2007, 48, 2497–
2499.
16. Pinkner, J. S.; Remaut, H.; Buelens, F.; Miller, E.; Aberg, V.; Pemberton, N.; He-
denstrom, M.; Larsson, A.; Seed, P.; Waksman, G.; Hultgren, S. J.; Almqvist, F.
Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 17897–17902.
17. Kuehn, M. J.; Ogg, D. J.; Kihlberg, J.; Slonim, L. N.; Flemmer, K.; Bergfors, T.;
Hultgren, S. J. Science 1993, 262, 1234–1241.
18. Emtena¨s, H.; Alderin, L.; Almqvist, F. J. Org. Chem. 2001, 66, 6756–6761.
19. Emtena¨s, H.; Taflin, C.; Almqvist, F. Mol. Divers. 2003, 7, 165–169.
20. Emtena¨s, H.; Åhlin, K.; Pinkner, J. S.; Hultgren, S. J.; Almqvist, F. J. Comb. Chem.
2002, 4, 630–639.
37. O’Toole, G. A.; Kolter, R. Mol. Microbiol. 1998, 28, 449–461.
38. Roberts, J. A.; Marklund, B. I.; Ilver, D.; Haslam, D.; Kaack, M. B.; Baskin, G.;
Louis, M.; Mollby, R.; Winberg, J.; Normark, S. Proc. Natl. Acad. Sci. U.S.A. 1994,
91, 11889–11893.
39. Anderson, G. G.; Palermo, J. J.; Schilling, J. D.; Roth, R.; Heuser, J.; Hultgren, S. J.
Science 2003, 301, 105–107.
21. Svensson, A.; Larsson, A.; Emtenas, H.; Hedenstrom, M.; Fex, T.; Hultgren, S. J.;
Pinkner, J. S.; Almqvist, F.; Kihlberg, J. ChemBioChem 2001, 2, 915–918.
40. Justice, S. S.; Hung, C.; Theriot, J. A.; Fletcher, D. A.; Anderson, G. G.; Footer, M. J.;
Hultgren, S. J. Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 1333–1338.