Novel large-ring 1,3-bridged 2-azetidinones as potential inhibitors of penicillin-binding proteins

Article abstract of DOI:10.1002/ejoc.200801193

Novel bicyclic 2-azetidinones, in which the β-laclam moiety is embedded in a 1,3-bridging large ring, have been studied experimentally and theoretically. The compounds were prepared from (3S,4R)-3-[(1R)-1-(tert- butyldimethylsilyloxy)- ethyl]-4-propyl-2-a

Full text of DOI:10.1002/ejoc.200801193

FULL PAPER
DOI: 10.1002/ejoc.200801193
Novel Large-Ring 1,3-Bridged 2-Azetidinones as Potential Inhibitors of
Penicillin-Binding Proteins
Allan Urbach,[a] Georges Dive,[b] and Jacqueline Marchand-Brynaert*[a]
Dedicated to Professor Alain Krief
Keywords: Lactams / Macrocycles / Ring-closing metathesis / Ab initio calculations / Enzymes / Inhibitors
Novel bicyclic 2-azetidinones, in which the β-lactam moiety
is embedded in a 1,3-bridging large ring, have been studied
experimentally and theoretically. The compounds were pre-
pared from (3S,4R)-3-[(1R)-1-(tert-butyldimethylsilyloxy)-
ethyl]-4-propyl-2-azetidinone (3) by sequential N1 and O5
functionalization with ω-alkenyl chains by acylation and/or
alkylation reactions. Cyclization by ring-closing metathesis
(RCM) gave a series of 12- and 13-membered-ring com-
pounds 7, 12b,c, 17b,c and 24 featuring the internal HC=CH
double bond with a preferential (E) configuration, and then
the corresponding saturated 1,3-bridged bicycles 8, 13b,c,
18b,c and 25 after hydrogenation. Bridges of 9–11 atoms
were inaccessible and bridges of 12 atoms appeared fav-
oured over those with 13 atoms according to ab initio quan-
tum chemistry calculations. This was confirmed experimen-
tally because ω-alkenyl double-bond migration occurred in
competition with the RCM reaction in the case of 13-atom
precursors, leading to a mixture of 12- and 13-membered
rings. Modelling of the reactivity of our 1,3-bridged 2-azetid-
inones, towards hydrolysis and processing by serine en-
zymes, highlighted the important roles of geometrical and
conformational factors and predicted a modest “acylating
power” in comparison with classical penam compounds (an-
tibiotics). Biochemical evaluation against the R39 bacterial
enzyme (D,D-peptidase) revealed a weak inhibition effect of
the 13-membered-ring 1,3-bridged O,N-bis(acylated) azetid-
inones 7 and 8.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
ases.[4] ,-Transpeptidases and most of the β-lactamases
are serine proteases. Their mechanism of action for pro-
cessing 2-azetidinone is well established:[5] an acyl-enzyme
intermediate is formed by nucleophilic attack of the Oγ
atom of the active serine on the azetidinone carbonyl group
followed by N–C(O) bond cleavage assisted by acidic and
basic residues of the catalytic pocket involved in the proton
transfer. Acyl-enzymes are stable entities in the case of the
inhibition of ,-transpeptidases. These esters can also be
rapidly hydrolysed in the β-lactamases with regeneration of
the active enzymes enabling the antibiotics to reach their
targets.
Introduction
β-Lactam (i.e., 2-azetidinones) antibiotics are still the
main drugs given, in the form of penicillins and cephalo-
sporins, to treat infections caused by bacteria. These mole-
cules disturb the final step of bacterial cell wall biosynthesis
by inhibiting the ,-transpeptidase enzymes involved in
the cross-linking of peptidoglycan strands.[1] β-Lactamases
are bacterial defence enzymes that very efficiently hydrolyse
the β-lactam moiety in practically all classes of β-lactam
antibiotics.[2] The production of these enzymes is the most
common resistance mechanism of bacteria and nowadays
represents a major challenge in human health.[3]
Traditionally, the search for novel β-lactam drugs has
been based on strained bicyclic 1,4-fused structures with a
view to increasing the so-called “acylating power” of the
twisted amide motif of the 2-azetidinone ring.[6] This could
be illustrated by the recent development of carbapenem an-
tibiotics (Figure 1), often considered as “last-resort” drugs
To overcome the action of the β-lactamases, the struc-
tures of the existing β-lactam drugs have to be altered. This
has stimulated a lot of work devoted to novel 2-azetidinone
derivatives that act as antibiotics or inhibitors of β-lactam-
[a] Unité de Chimie Organique et Médicinale, Université catho- in the treatment of infections due to resistant bacteria.[7]
lique de Louvain, Bâtiment Lavoisier,
Another strategy involves the discovery of non-β-lactam
Place Louis Pasteur no. 1, 1348 Louvain-la-Neuve, Belgium
active compounds, either by diversity-oriented synthesis[8]
Fax: +32-10-474168
or by the rational design of penicillin mimics.[9]
E-mail: jacqueline.marchand@uclouvain.be
[b] Centre d’Ingénierie des Proteines, Université de Liège, Bâtiment
Recently, we indicated that we would investigate a new
family of bicyclic 2-azetidinones, in which the β-lactam mo-
B6a,
Allée du 6 Août, 4000 Sart-Tilman-Liège, Belgium
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A. Urbach, G. Dive, J. Marchand-Brynaert
FULL PAPER
against representative isolated bacterial enzymes. We can
show that modest inhibitors featuring non-traditional β-lac-
tam bicyclic cores have been developed.
Results and Discussion
Synthesis
The synthesis of 1,4-fused bicyclic β-lactams is well
documented, because such structures constitute the pharm-
acophores of penicillin- and cephalosporin-like compounds.
Novel structures that include small, medium or large fused
rings are continually prepared by making use of various
cyclization methods.[11] On the other hand, 1,3-bridged bi-
cyclic β-lactams have scarcely been reported. A few strained
derivatives have been obtained by carbenoid insertion reac-
tions into the N–H lactam bond,[12] but large-ring 1,3-
bridged structures require further exploration.[13]
Figure 1. Chemical structures of the carbapenems in clinical use.
We decided to use the ring-closing metathesis (RCM) re-
action to achieve the synthesis of bridged 2-azetidinones
with the general structure A (Figure 2). This strategy has
already proven to be very efficient in the synthesis of vari-
ous nitrogen-containing polycyclic systems[14] and was suc-
cessfully used in our preliminary work dealing with 1,3-
bridged 4-acetoxy-2-azetidinones.[10] Accordingly, the key
intermediates are the monocyclic 2-azetidinones B equipped
with two ω-alkenyl chains (Figure 2). The commercially
available acetoxyazetidinone 1 is the starting material that
provides the required C3 substitution and the configura-
tions of the three chiral centres of the penem.
tif is embedded in a 1,3-bridging large ring.[10] Our idea was
to decrease the activation barrier of the 2-azetidinone N–
C(O) bond cleavage by increasing the conformational
adaptability of the macrocyclic structure that would be in-
volved in the reorganization of the atoms.
Our target molecules A are depicted in Figure 2. They
are related to the carbapenem family by virtue of the C3
side-chain and the C3–C4 stereochemistry. However, the
1,4-fused cyclopentenyl ring, decorated with the bulky sub-
stituent SR2, has been replaced by a large 1,3-bridging ring
fixed on the N1 and O5 heteroatoms through alkyl and/or
acyl functions. The C4 substitution of the carbapenems is
simply mimicked with an n-propyl chain.
4-Allyl-2-azetidinone
2 was prepared according to
Kang’s protocol[15] and transformed into precursor 3 by
catalytic hydrogenation (90% overall yield) with retention
of configuration. N-Acylation with 4-pentenoyl chloride
and pyridine was performed in dichloromethane (DCM) at
reflux. Treatment of 4 with a cold mixture of acids (HCl/
AcOH) in acetonitrile deprotected the silyl ether without
touching the β-lactam function.[10] The alcohol 5 could be
acylated as previously to furnish the cyclization precursor
6 in 86% yield after chromatography (Scheme 1). Treatment
of 6 with the Grubbs catalyst (second generation)[16] under
the usual conditions (5 mol-% of catalyst and substrate di-
lution of 5 m) led readily to the 1,3-bridged azetidinone
7; a high yield (95%) was obtained in DCM at room tem-
perature, and the use of Ti(OiPr)4 as additive was not re-
quired.[17] From 1H NMR analysis of the crude product
we concluded that a single stereoisomer was obtained, the
HC=CH bond in the bridge having an (E) configuration
(3JH,H = 15.5 Hz, as determined by selective decoupling).
Finally, catalytic hydrogenation quantitatively furnished the
N,O-bis(acylated) azetidinone 8 (member of the first family
of 1,3-bridged 2-azetidinones.[10]).
Figure 2. Bicyclic target molecules.
N-Alkylation of precursor 3 was realized under phase-
In this article we describe the synthesis of four families transfer conditions inspired by Genêt et al.:[14c] a mixture of
of compounds A and support our experimental results by powdered KOH, KI, ω-alkenyl bromides, azetidinone and
ab initio quantum chemistry calculations. The reactivities catalyst in dry tetrahydrofuran (THF) was stirred overnight
of selected azetidinones versus penicillin binding proteins to produce N-propenyl- (9a), N-butenyl- (9b) and N-penten-
(PBPs) have been evaluated theoretically and in vitro ylazetidinones (9c) in good yields after chromatography
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Potential Inhibitors of Penicillin-Binding Proteins
20 h], migration of the N-pentenyl double bond partially
occurred before cyclization,[18,19] thus leading to the formal
extrusion of one CH2 motif in the bridge. Treatment of pre-
cursor 11b under the previous RCM conditions (but with
2.5 mol-% of catalyst) gave the cyclized compound 12b as
an (E)/(Z) mixture [(E)/(Z) ratio = 70:30] in 74% yield after
purification. Besides NMR spectroscopy, gas chromatog-
raphy (GC) was also used to analyse the crude cyclization
mixtures: RCM of 11c gave two major products with reten-
tion times (tr) of 37.0 (12c) and 35.4 min (12b), and RCM
of 11b led to one major product with tr = 35.4 min (12b).
Whatever the RCM conditions applied, we never succeeded
in cyclizing the precursor 11a: thus, the 11-membered-ring
bridged azetidinones (namely 12a and 13a, with n = 1) are
not accessible in this second family of target compounds
(N-alkyl,O-acyl derivatives, Scheme 2).
Scheme 1. Synthesis of the N,O-bis(acyl) derivatives (Family 1).
Reagents and conditions: (a) In (2 equiv.), KI (3 equiv.), allyl bro-
mide (3 equiv.), DMF, room temp.; (b) H2, Pd/C (5 mol-%), EtOAc,
room temp.; (c) 4-pentenoyl chloride, pyridine, CH2Cl2, reflux; (d)
HCl/AcOH (5:7), CH3CN, 0 °C; (e) 4-pentenoyl chloride, pyridine,
CH2Cl2, room temp.; (f) 5 mol-% Grubbs cat. (2nd generation),
CH2Cl2, room temp.; (g) H2 (1 atm), Pd/C (5 mol-%), EtOAc, room
temp.
(Scheme 2). Alcohol deprotection and acylation with 4-pen-
tenoyl chloride, as described above, led to the key interme-
diates 11a–c. Purified compound 11c was submitted to the
RCM conditions used for the preparation of 7 (DCM,
20 °C). The cyclized azetidinone 12c was formed in moder-
ate yield as a mixture of (E)/(Z) stereoisomers. In compari-
son with precursor 6, in which N1 forms part of an imide
function, N1 of precursor 11c, forming part of an amide
function, should be able to form a complex with the metal
centre of the Grubbs catalyst and so contribute to its deacti-
vation. Indeed, by adding Ti(OiPr)4 (20 mol-%) to the reac-
tion mixture,[17] we improved the yield of 12c. Finally, the
best conditions were obtained in toluene at 80 °C, which
gave 100% conversion, as determined by 1H NMR analysis.
The NMR spectrum showed the presence of (E)/(Z) stereo-
Scheme 2. Synthesis of N-alkyl,O-acyl derivatives (Family 2). Rea-
gents and conditions: (a) KOH (1.5 equiv.), KI (2 equiv.),
Bu4NHSO4 (0.04 equiv.), alkenyl bromide (3 equiv.), THF, room
temp.; (b) HCl/AcOH (5:7), CH3CN, 0 °C; (c) 4-pentenoyl chloride,
pyridine, CH2Cl2, room temp.; (d) 2.5–5 mol-% Grubbs cat. (2nd
generation), Ti(OiPr)4 (20 mol-%), toluene, 80 °C; (e) H2 (1 atm),
Pd/C (5 mol-%), EtOAc, room temp.
Starting from alcohol 10, we performed etherification re-
isomers of 12c and byproducts still containing the azetid- actions under the usual Williamson’s conditions
inone motif (ratio of main products/byproducts ≈ 75:25). (Scheme 3). The alcohol was deprotonated with NaH in di-
Column chromatography allowed the recovery of pure 12c methylformamide at 0 °C and then treated with 2-propenyl,
in 62% yield [(E)/(Z) ratio = 60:40] and unidentified bicy- 3-butenyl or 4-pentenyl bromide (3 equiv.) in the presence
clic azetidinones in 19% yield. Catalytic hydrogenation of KI except for the synthesis of 16b (20 °C, 6–8 h). Yields
solved this problem: reduction of 12c quantitatively af- of purified (column chromatography) azetidinones 14, 15
forded the 13-membered-ring bridged azetidinone 13c, and 16 were moderate to good when the C5 chains were the
whereas reduction of the unknown mixture yielded the 12- 2-propenyloxy (m = 1) and 4-pentenyloxy (m = 3) groups.
membered-ring bridged azetidinone 13b. We concluded that Products bearing the 3-butenyloxy (m = 2) chain at C5 were
under our RCM conditions [5 mol-% Grubbs catalyst, never obtained: elimination reaction occurred with 3-
20 mol-% Ti(OiPr)4, 5 m dilution of 11c, toluene, 80 °C, butenyl bromide instead of nucleophilic substitution. The
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A. Urbach, G. Dive, J. Marchand-Brynaert
FULL PAPER
cyclization of the key intermediates 14–16 could be realized DMF, 0 °C). The resulting ester 19 (Scheme 4) was treated
only with the 4-pentenyloxy (m = 3) precursors 15b and at low temperatures in THF with lithium hexamethyldisil-
16b, leading to the 12- and 13-membered-ring bridged azeti- azide (LiHMDS) and trimethylsilyl chloride (TMSCl) to
dinones 17b and 17c in 83 and 72% yields, respectively, af- produce an O-silyl enolate intermediate that suffers a
ter purification by column chromatography. Here again, Claisen–Ireland sigmatropic rearrangement when the tem-
Ti(OiPr)4 was required as additive to the Grubbs catalyst perature was increased from –78 to 80 °C (Scheme 5). In
to complete the RCM reaction. Compounds 17b and 17c situ hydrolysis of the silyl ester intermediate by methanol
were obtained as (E)/(Z) mixtures of stereoisomers [(E)/(Z) gave the acid 20 as a 66:33 mixture of diastereoisomers.
ratio = 73:27 and 25:75, respectively, by 1H NMR analysis], This crude product was directly converted into the p-ni-
and 17c was accompanied by the formation of 17b as the trobenzyl (PNB) ester 21 under solid/liquid phase-transfer
byproduct[18,19] (8% isolated yield after chromatography). conditions. Chromatographic purification afforded 21 in
The formation of the (Z) configuration of the HC=CH 86% yield from 19. Subsequently O-deprotection, O-acyl-
double bond in the major stereoisomer of 17c was assigned ation with 4-pentenoyl chloride and cyclization by RCM
3
on the basis of the JH,H coupling constant of 10.9 Hz (de- [2.5 mol-% catalyst, 20 mol-% Ti(OiPr)4, toluene, 20 °C,
termined by selective decoupling). As above, 17b was iden- 24 h] were performed; this last reaction was carried out at
tified as a side-product of 17c by NMR analysis of the sepa- room temperature to avoid degradation of the PNB ester.
rated compounds (comparison with an authentic sample af- After chromatography, 24 was isolated in 67% yield as a
ter hydrogenation) and by GC analysis of RCM crude mix- mixture of diastereoisomers at C6 (ratio of 66:33) and (E)/
tures. Starting from 16b, we observed two products with tr (Z) stereoisomers of the HC=CH double bond [(E)/(Z) ra-
= 33.5 (17c) and 31.2 min (17b), whereas 15b gave one prod- tio = 75:25]. Finally, catalytic hydrogenation was performed
uct with tr = 31.2 min (17b). Finally, catalytic hydrogenation to reduce the double bond and simultaneously deprotect
led to the N,O-bis(alkylated) compounds 18b and 18c the carboxy function to furnish the 12-membered-ring
(members of the third family of 1,3-bridged 2-azetidinones, bridged azetidinone 25 belonging to the fourth family
Scheme 3). As previously (see 11a), the 11-membered-ring (penem-like structures, Scheme 4). Unfortunately, this com-
compounds were not accessible from 14b (n = 1, m = 3) or pound could not be purified by chromatography.
16a (n = 3, m = 1), nor the nine-membered-ring compound
from 14a (n = m = 1). The failure of the RCM process in
these cases may result not only from conformational and
steric drawbacks, but also from the rapid isomerization of
the N/O-allyl chains catalysed by Ru complexes, leading fi-
nally to an N/O-deprotection-like reaction.[20]
Scheme 3. Synthesis of N,O-bis(alkyl) derivatives (Family 3). Rea-
gents and conditions: (a) NaH (1.1 equiv.), alkenyl bromide
(3 equiv.), KI (3 equiv.), DMF, 0 °C to room temp.; (b) 2.5–5 mol-
% Grubbs cat. (2nd generation), Ti(OiPr)4 (20 mol-%), toluene,
80 °C; (c) H2 (1 atm), Pd/C (5 mol-%), EtOAc, room temp.
Scheme 4. Synthesis of penem-like large-ring derivatives (Family 4).
Reagents and conditions: (a) NaH (1.2 equiv.), allyl bromoacetate
(2 equiv.), DMF, 0 °C to room temp.; (b) see Scheme 5; (c) K2CO3
(1.5 equiv.), Bu4NHSO4 (0.1 equiv.), p-nitrobenzyl bromide
(2 equiv.), DMF, room temp.; (d) HCl/AcOH (5:7), CH3CN, 0 °C;
(e) 4-pentenoyl chloride, pyridine, CH2Cl2, room temp.; (f) 2.5–
5 mol-% Grubbs cat. (2nd generation), Ti(OiPr)4 (20 mol-%), tolu-
ene, room temp.; (g) H2 (1 atm), Pd/C (5 mol-%), EtOAc, room
Functionalization of the N1-alkenyl chain with a car-
boxy group (penem mimic) was successfully achieved by
using the strategy of Barrett and co-workers.[21] Azetidinone
3 was first N-alkylated with allyl bromoacetate (NaH, temp.
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Potential Inhibitors of Penicillin-Binding Proteins
the more stable conformer II. After cyclization, conformer
II of the O,N-bis(acylated) product 7 is more stable for the
(E) stereoisomer, whereas conformers II of the series 12 (O-
acyl,N-alkyl) and 17 [O,N-bis(alkyl)] are almost equally sta-
bilized for both stereoisomers. This is consistent with our
experimental data: 7 was recovered as a single (E) stereoiso-
mer and 12b,c and 17b,c were mixtures of (E)/(Z) stereoiso-
mers, with the (Z) isomer being the major compound for
17c only.
Table 1. Energy differences between conformers I and II, given as
a function of the HC=CH double bond configuration.
Scheme 5. Sigmatropic rearrangement.
Compound
Energy [kcalmol–1]
(E) isomer
(Z) isomer
Theoretical Study[22]
7
5.30
11.99
9.48
9.73
4.48
9.19
12.00
9.19
11.68
3.64
12b
12c
17b
17c
A number of stable conformers were found for the mono-
cyclic precursors 6, 11, 15, 16 and the corresponding
bridged bicyclic products 7, 12 and 17. This was examined
by ab initio quantum chemistry calculations in vacuo at the
B3LYP level of theory with the double basis set 6-31G(d).
For at least two conformers of the starting azetidinones, the
related conformers of the bicyclic azetidinones were com-
puted with the HC=CH double bond in the (E) or (Z) con-
figuration. Two representative conformers I and II of pre-
cursor 11c are shown in Figure 3. The relative energy differ-
ences between conformers I and II of the RCM products
are collected in Table 1 and were calculated with respect to
The heats of formation of the bicyclic compounds by
RCM reaction were calculated by reference to the open pre-
cursors minus ethylene (Table 2). All reactions are slightly
endothermic. The (E) isomer has, in general, a smaller heat
of formation than the (Z) isomer. Moreover, the heat of
formation of the (E) or (Z) conformer I is higher than that
of the more stable conformer II. Finally, when comparing
the esters 12b and 12c and the ethers 17b and 17c, the for-
mation of the 12-membered rings 12b and 17b appears to
be easier than the closure of the 13-membered rings 12c and
17c. Experimentally, we found that the cyclization of 11c
was quite sluggish and led to both 13- and 12-membered
rings by double-bond migration in the open precursor. A
similar trend was observed during the RCM cyclization of
16b. The co-existence of conformers could be proved experi-
mentally in one case. Fortunately, after HC=CH double-
bond hydrogenation, the 12-membered-ring 1,3-bridged
azetidinone 12b [mixture of (E)/(Z) isomers] gave a single
compound 13b, which crystallizes slowly in an acetone/di-
ethyl ether mixture (1:2, v/v). X-ray diffraction analysis of
a single crystal revealed two conformers in the same unit
cell: they differ by the orientation of the n-propyl chain and
the spatial arrangement of the bridging cycle, as shown in
Figure 4.[23]
Table 2. Heats of formation [kcalmol–1] for conformers II and I,
given as a function of the HC=CH double-bond configuration.
Compound
(E) isomer
(Z) isomer
∆E (II)
∆E (I)
∆E (II)
∆E (I)
7
4.91
3.51
6.00
4.80
6.58
9.02
8.94
8.39
14.25
8.18
12.05
4.93
7.80
4.79
7.01
12.28
10.35
10.77
12.28
9.46
12b
12c
17b
17c
Two reactivity models were considered to mimic the pro-
cessing of monocyclic and bridged bicyclic azetidinones by
serine enzymes. Both are concerted mechanisms involving
Figure 3. Two representative conformers of 11c. Conformer II is
more stable than I.
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A. Urbach, G. Dive, J. Marchand-Brynaert
FULL PAPER
enzyme family. For Model A, both approaches to the azeti-
dinone ring can be considered, that is, from either the α or
β face of the small cycle,[24] whereas for Model B, only the
attack from the α face is the relevant one.[10] Owing to the
size of the analysed systems, the activation energies (EA)
have been computed at the RHF level with the minimal
Figure 4. X-ray structure of 13b showing two conformers in the
unit cell.
nucleophilic attack on the β-lactam carbonyl group ac-
companied by N–C(O) bond cleavage and proton shuttle,
as described previously.[10] Briefly, Model A considers the
duplex H2O/H2O as a nucleophile, whereas Model B con-
siders the triplex 2-(formylamino)-1-ethanol/H2O/imidazole
as a mimic of the active site catalytic triad of the trypsin
Table 3. Activation energies EA for concerted nucleophilic attack
on azetidinones. Calculations for conformers I.
Entry Compound
EA [kcalmol–1]
Model A Model A Model B Family/bridge
(β face)
(α face)
(α face)
size
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
6
29.54
23.13
20.24
38.34
36.61
34.98
27.16
25.40
30.63
25.87
30.25
30.43
26.08
25.88
26.66
26.80
32.53
34.26
27.15
30.32
35.19
14.62
(E)-7
8
11b
1/13
1/13
(E)-12b
(Z)-12b
11c
(E)-12c
(Z)-12c
15b
(E)-17b
(Z)-17b
16b
(E)-17c
(Z)-17c
penam
2/12
2/12
29.08
32.49
36.58
2/13
2/13
3/12
3/12
43.21
26.56
3/13
3/13
reference
Figure 5. Structures of the transition states of azetidinone 7 pro-
cessed by using Model A (attack on the α and β face) and Model B
(attack on the α face).
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Potential Inhibitors of Penicillin-Binding Proteins
basis set MINI-1Ј. The results are collected in Table 3.[25] (100 µ) were incubated (16 h, 30 °C), and then fluorescent
The chemical hydrolysis model (Model A) clearly shows ampicillin (25 µ) was added. After 45 min, the peptidase
that nucleophilic attack by water on the β face is favoured was denatured and the fluorescence intensity measured.
over the α face. Indeed, this corresponds to HO–C(O) bond Thus, in this protocol, the azetidinones 6–8 are supposed
formation from the less hindered face, because the large to be capable of acylating R39 (giving stable acyl-enzyme
bridging ring unfolds over the azetidinone α face in all com- intermediates), and the residual activity of R39 is deter-
pounds. The O,N-bis(acylated) bicyclic compounds 7 and 8 mined by the amount of covalent R39–ampicillin complexes
(Entries 2 and 3) appeared to be more reactive than the O- formed, as measured by fluorescence spectroscopy. The re-
acyl,N-alkyl and O,N-bis(alkyl) derivatives 12c and 17c sults are presented in Table 4 as percentages of the R39 ini-
(Entries 8 and 14) featuring the same bridge size (13-mem- tial activity, low values indicating active compounds. In
bered ring). Also, the bicyclic compounds were predicted to such a test, the limiting value for a “hit” is 80%. Interest-
be more reactive than the monocyclic precursor (compare ingly, the large-ring 1,3-bridged β-lactams 7 and 8 were
7 and 8 to 6). Computation of Model B revealed a different found to be active R39 inhibitors, whereas the monocyclic
behaviour. On the basis of nucleophilic attack on the α face, precursor 6 was inactive. We similarly evaluated 6–8 against
as should occur in the serine enzyme active site, the mono- a set of high-molecular-weight ,-peptidases responsible
cyclic precursors 11b, 15b and 16b (Entries 4, 10 and 13) for bacterial resistance to β-lactam antibiotics,[29] namely
were found to be more reactive than the corresponding bi- PBP2a from S. aureus, PBP5fm from E. faecium and PBP2x
cyclic azetidinones 12b, 17b and 17c (Entries 5, 6, 11, 12 from S. pneumoniae. β-Lactam 7 was weakly active com-
and 14, 15), and in the bicyclic series, the (E) isomers were pared with PBP2a, whereas 8 was modestly active com-
favoured over the (Z) isomers. Bicycle 7 (Entry 2) was pre- pared with PBP2x (Table 4). As a control experiment, the
dicted to be more reactive than its precursor 6 (Entry 1), activities of β-lactams 6–8 against a mammalian serine en-
but less reactive after reduction of the HC=CH bond giving zyme, PPE (Porcin Pancreatic Elastase), were assayed in a
compound 8 (Entry 3). Very similar reactivities were calcu- competition experiment with a chromogenic substrate (N-
lated for 11c (open precursor, Entry 7) and the correspond- succinyl--alanyl--alanyl--alanyl-p-nitroanilide);[30] all of
ing (E) and (Z) isomers of 12c (Entries 8 and 9). Interest- the compounds were inactive at a concentration of 100 µ.
ingly, the EA values of all the monocyclic azetidinones, 6,
Table 4. Inhibition of PBPs.[a]
11b, 11c, 15b and 16b, are in the range between 25.9 and
27.1 kcalmol–1, showing no particular influence of the O,N-
Compound
R39
PBP2a
(2.5 µ)
PBP5fm
(2.5 µ)
PBP2x
(0.8 µ)
(0.8 µ)
acyl motifs and/or chain lengths on reactivity. For the bicy-
clic azetidinones, the EA values covered a larger range, from
25.4 to 35.2 kcalmol–1; no correlation with the bridge size
(12- or 13-membered ring) could be found. The ease of
atom reorganization during the azetidinone N–C(O) bond
cleavage depends mainly on torsion (or eclipse) strains and
transannular interactions, hardly predictable when sp2 car-
bon atoms of the bridge are replaced with sp3 ones (C=O
replaced with CH2; CH=CH reduced to CH2–CH2). Fig-
ure 5 shows the structures of the transition states (TS) of
the 1,3-bridged azetidinone (E)-7 processed by Models A
and B.
6
7 (E)
110Ϯ11
80Ϯ10
77Ϯ12
n.d.
107Ϯ14
92Ϯ5
95Ϯ7
13Ϯ3
107Ϯ2
100Ϯ11
98Ϯ4
101Ϯ3
103Ϯ5
91Ϯ6
Ͻ 5
8
Penicillin G
10Ϯ3
[a] Results are expressed as percentages of the initial activity. Me-
ans of at least three independent experiments.
Conclusions
RCM is a well-established strategy for achieving small-,
medium- or large-ring bicyclic systems. We have documen-
ted a novel application of RCM for achieving bridged azeti-
dinones designed as potential inhibitors of PBPs. The scope
and limitations of the cyclization of precursors B into target
Biochemical Evaluation[26]
The β-lactams 6–8 were evaluated for their potential inhi- molecules A (Figure 2), depending on the nature of the X
bition effect on bacterial serine enzymes. Both theoretical and Y functions and the ring size, were determined. Bridges
Models A and B predicted that the 13-membered-ring of 9–11 atoms are inaccessible for at least two reasons other
bridged compound (E)-7 should be our best acylating rea- than simply angular strain: (i) O-alkylation with 3-butenyl
gent, but quite modest in relation to the penam reference bromide (m = 2) failed and (ii) cleavage of the O,N-allyl
(Table 3, Entry 16).
motifs occurred under RCM conditions (n = 1; m = 1).
The activities of compounds 6–8 against the β-lactamase The accessibility of 13-membered bridges depends on the
TEM-1 from E. coli (Class A enzyme)[27] was assayed in a azetidinone N-functionalization: the N-acyl derivative 6 re-
competition experiment with a chromogenic substrate (ni- acted rapidly and quantitatively (DCM, 20 °C), whereas the
trocefine); none of the compounds was found to be active N-alkyl derivatives 11c and 16b required the presence of
at a concentration of 100 µ. R39 from Actinomadura is a Ti(OiPr)4 as an additive to avoid deactivation of the ruthe-
low-molecular-weight ,-carboxypeptidase-transpeptidase nium intermediate species; the cyclization process required
enzyme usually used for a preliminary screening of penicil- thermal activation (toluene, 80 °C) and competition with
lin-like compounds.[28] R39 and the tested azetidinones double-bond migration occurred. For electronic and con-
Eur. J. Org. Chem. 2009, 1757–1770
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1763

A. Urbach, G. Dive, J. Marchand-Brynaert
FULL PAPER
MN OPTIMAS capillary column (30 mϫ0.25 mm; 0.25 µm) by
using a temperature program of 5 °C/min from 50 to 290 °C. NMR
spectra were recorded with a Varian Gemini 200 spectrometer at
200 (1H) and 50 MHz (13C) or with a Bruker Avance 500 spectrom-
eter at 500 (1H) and 125 MHz (13C) in CDCl3 with TMS as the
internal standard. IR spectra were recorded with a Shimadzu
FTIR-8400S spectrometer; compounds were deposited on NaCl
plates as a thin film by evaporation of CH2Cl2 from solution. High-
resolution mass spectra were recorded at the Mass Spectrometry
Service of the University of Mons-Hainaut, Belgium.
formational reasons, illustrated in Figure 6, Ru–azetidinone
complexes should be formed more easily in the case of N-
alkyl derivatives (a) than with N-acyl (b) derivatives.
Twelve-membered bridges formed readily from precursors
11c, 15b and 23 under modified RCM conditions (Ru cata-
lyst + Lewis acid). GC analysis showed that the cyclized
products 12b and 17b are identical to the side-products re-
covered during the synthesis of 13-membered bridged com-
pounds. Accordingly, olefin migration occurs mainly in the
N-alkenyl rather than in the O-alkenyl chain.
(3S,4R)-3-[(1R)-1-(tert-Butyldimethylsilyloxy)ethyl]-4-(prop-2-enyl)-
2-azetidinone (2):[15] KI (1.733 g, 10.44 mmol, 3 equiv.) and allyl
bromide (0.90 mL, 10.44 mmol, 3 equiv.) were added to a stirred
suspension of indium powder (800 mg, 6.96 mmol, 2 equiv.) in dry
DMF at room temp. The mixture was stirred under argon for 1 h
before the addition of acetoxyazetidinone 1 (1 g, 3.48 mmol). After
4 h, the solution was diluted with diethyl ether (50 mL), washed
with a saturated NH4Cl solution (50 mL) and brine (2ϫ50 mL),
dried with MgSO4, and the solvent was removed under reduced
pressure to provide a white solid (930 mg). Purification by flash
chromatography (CyHex/AcOEt, 5:2) furnished pure compound 2
(850 mg, 91%). TLC (CyHex/AcOEt, 5:3): Rf = 0.54. M.p. 81.5–
Figure 6. Possible ways of sequestrating Ru intermediates.
Our theoretical studies supported well the experimental
data of the compounds synthesized (ring size and HC=CH
stereochemistry). Modelling of the reactivity of the 1,3-
bridged azetidinones in the active site of the serine enzymes
illustrated the important role of geometrical factors (attack
of the α or β face), probably as crucial as the conforma-
tional factors. Despite the great complexity of our systems,
we could predict that large-ring 1,3-bridged 2-azetidinones
should be endowed with acceptable “acylating power” (EA
values of around 30 kcalmol–1). Fortunately, the prelimi-
nary biochemical evaluations confirmed the bicyclic com-
pounds 7 and 8 as modest inhibitors of the R39 enzyme
and very weak inhibitors of two resistant PBPs, whereas the
open precursor 6 was not active at all. These results remain,
however, questionable because a related series of com-
pounds previously reported,[10] featuring an acyloxy chain
(OAc) at C4 instead of the nPr chain, showed contrasting
behaviour: the open precursor was a good inhibitor of R39
and the cyclized derivatives (unsaturated and saturated)
were inactive towards the same enzyme, but all members of
this C4–OAc series weakly inhibited PBP2a.
1
82.6 °C. H NMR (200 MHz, CDCl3, 25 °C): δ = 6.80 (br. s, 1 H,
NH), 5.74–5.86 (ddt, 1 H), 5.09–5.14 (m, 4 H), 4.17 (qt, 1 H), 3.68
(dt, 2 H), 2.77 (dd, 2 H), 2.3–2.5 (m, 2 H), 1.20 (d, 2 H), 0.86 (s, 9
H), 0.05–0.06 (2 s, 6 H) ppm. 13C NMR (50 MHz, CDCl3, 25 °C):
δ = 169.1, 133.4, 117.8, 65.4, 63.5, 50.4, 39.2, 25.6, 22.6, 17.8, –3.0,
–3.7 ppm.
(3S,4R)-3-[(1R)-1-(tert-Butyldimethylsilyloxy)ethyl]-4-propyl-2-
azetidinone (3): Precursor 2 (1.33 g, 4.94 mmol) dissolved in AcOEt
(15 mL) was placed under H2 (1 atm) at room temp. in the presence
of Pd catalyst (26 mg, 0.25 mmol, 0.05 equiv.) for 5 h. Then Pd/C
was removed by filtration and the solution concentrated under vac-
uum to provide pure product 3 as a white solid (1.31 g, 98%). TLC
1
(CyHex/AcOEt, 5:3): Rf = 0.59. M.p. 73 °C. H NMR (200 MHz,
CDCl3, 25 °C): δ = 6.16 (br. s, 1 H, NH), 4.14 (qd, JH,H = 6.2, JH,H
= 5.1 Hz, 1 H), 3.61 (dt, JH,H = 1.9, JH,H = 6.6 Hz, 1 H), 2.69 (dd,
JH,H = 1.8, JH,H = 5.1 Hz, 1 H), 1.56 (m, 2 H), 1.35 (m, 2 H), 1.19
(d, JH,H = 6.2 Hz, 3 H), 0.94 (t, JH,H = 7.2 Hz, 3 H), 0.95 (s, 9 H),
0.0 (2 s, 6 H) ppm. 13C NMR (50 MHz, CDCl3, 25 °C): δ = 169.2,
65.7, 64.3, 51.2, 37.2, 25.7, 22.6, 19.8, 17.9, 13.9, –4.4, –5.0 ppm.
HRMS (TOF MS ES+): calcd. for C14H29NO2Si 272.2046 [M +
H]+; found 272.2036.
Definitively, the search for PBP inhibitors remains a
challenging task. Nevertheless, we have prepared non-tradi-
tional bicyclic β-lactams and in doing so developed novel
biochemically active compounds showing that high angular
strain (cf. penems) is not the only valuable strategy that can
be applied to reach our goal.
(3S,4R)-3-[(1R)-1-(tert-Butyldimethylsilyloxy)ethyl]-1-(pent-4-
enoyl)-4-propyl-2-azetidinone (4): Pyridine (0.36 mL, 4.42 mmol,
2 equiv.) and 4-pentenoyl chloride (0.48 mL, 4.42 mmol, 2 equiv.)
were added to a stirred solution of β-lactam 3 (600 mg, 2.21 mmol)
in dry CH2Cl2 (15 mL). The solution was warmed to 35 °C under
argon for 24 h. Then the reaction medium was diluted with CH2Cl2
(50 mL) and sequentially washed with a 3.3  HCl solution
(50 mL), a saturated NaHCO3 solution (50 mL), and brine
(50 mL). After drying with MgSO4 and concentration under vac-
uum, the residue was purified by flash chromatography (CyHex/
AcOEt, 5:1) to provide 4 as a colourless oil (780 mg, 89%). TLC
(CyHex/AcOEt, 5:1): Rf = 0.79. 1H NMR (500 MHz, CDCl3,
25 °C): δ = 5.81 (ddt, JH,H = 6.6, JH,H = 10.2, JH,H = 16.9 Hz, 1
Experimental Section
General: Manipulations were performed under argon in flame-
dried glassware. Reagents were used as received, and anhydrous
solvents (CH2Cl2, DMF, THF and toluene) were purchased from
commercial suppliers. TLC analyses were performed on aluminium
plates coated with silica gel 60F254 (Merck) and visualized with a
KMnO4 solution and UV (254 nm) detection. Melting points were
measured with an Electrothermal apparatus calibrated with ben-
zoic acid (melting points are uncorrected). Column chromatog-
raphy was performed on silica gel Merck 60 (40–60 µm). GC analy-
ses were performed with a CE Instruments GC-8000 Top with an
H), 5.06 (dd, JH,H = 1.6, JH,H = 17.1 Hz, 1 H), 4.98 (dd, JH,H
=
1.6, JH,H = 10.2 Hz, 1 H), 4.24 (qd, JH,H = 3.4, JH,H = 6.0 Hz, 1
H), 4.10 (ddd, JH,H = 3.4, JH,H = 3.4, J = 8.9 Hz, 1 H), 2.79 (m, 1
H), 2.78 (dd, JH,H = 3.4, JH,H = 3.4 Hz, 1 H), 2.72 (m, 1 H), 2.38
(m, 2 H), 2.11 (m, 1 H), 1.49 (m, 1 H), 1.34 (m, 2 H), 1.20 (d, JH,H
= 6.0 Hz, 3 H), 0.96 (t, JH,H = 7.2 Hz, 3 H), 0.82 (s, 9 H), 0.02 (s,
1764
www.eurjoc.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 1757–1770

Potential Inhibitors of Penicillin-Binding Proteins
3 H), 0.05 (s, 3 H) ppm. 13C NMR (125 MHz, CDCl3, 25 °C): δ = 9.1 Hz, 1 H), 3.27 (m, 1 H), 2.85 (dd, JH,H = 1.9, JH,H = 3.0 Hz, 1
170.4, 166.7, 136.6, 115.5, 64.8, 62.3, 52.6, 35.8, 34.3, 27.9, 25.5,
22.3, 18.8, 17.7, 14.0, –4.4, –5.3 ppm. HRMS (TOF MS ES+):
calcd. for C19H35NO3Si 376.2284 [M + Na]+; found 376.2296. IR
H), 2.32 (m, 2 H), 2.25–2.39 (m, 3 H), 2.23 (m, 2 H), 2.11 (m, 1
H), 1.45 (m, 1 H), 1.31 (m, 2 H), 1.21 (d, JH,H = 6.6 Hz, 3 H), 0.94
(t, JH,H = 7.3 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3, 25 °C):
δ = 171.6, 171.4, 165.2, 129.8, 128.3, 65.0, 59.7, 52.1, 34.7, 34.3,
33.6, 30.2, 27.9, 18.8, 18.7, 13.8 ppm. HRMS (TOF MS ES+):
calcd. for C16H23NO4 316.1525 [M + Na]+; found 316.1531. IR
(NaCl): ν
= 1786, 1702, 1638, 1310 cm–1.
˜
max
(3S,4R)-3-[(1R)-1-Hydroxyethyl]-1-(pent-4-enoyl)-4-propyl-2-azetid-
inone (5): β-Lactam 4 (1.22 g, 3.46 mmol) was dissolved in CH3CN
(100 mL) with AcOH (17 , 1.42 mL, 24.2 mmol, 7 equiv.) and
HCl (12 , 1.44 mL, 17.3 mmol, 5 equiv.) at 0 °C and stirred for
3 h. The solvent was removed and the residue diluted with AcOEt
(50 mL). Then the organic phase was washed with a 10% Na2CO3
solution and brine (2ϫ50 mL), dried with MgSO4 and concen-
trated. The crude product was purified by flash chromatography
(CyHex/AcOEt, 5:2) to yield 5 as a white paste (700 mg, 85%); 5
can also be used without purification in the next step. TLC
(CyHex/AcOEt, 5:2): Rf = 0.45. 1H NMR (500 MHz, CDCl3,
25 °C): δ = 5.71 (ddt, JH,H = 6.4, JH,H = 10.3, JH,H = 16.6 Hz, 1
(NaCl): ν
= 2874–2959), 1792, 1736, 1697 cm–1.
˜
max
(11R,12S,14R)-11-Methyl-2,9,13-trioxo-14-propyl-10-oxa-1-aza-
bicyclo[10.1.1]tetradecane (8): β-Lactam 8 was obtained from pre-
cursor 7 (260 mg, 0.91 mmol) by the procedure used for the synthe-
sis of 3. Filtration and concentration under vacuum furnished the
reduced compound as a white solid (268 mg, 100%). TLC (CyHex/
1
AcOEt, 5:2): Rf = 0.52. M.p. 67 °C. H NMR (500 MHz, CDCl3,
25 °C): δ = 5.52 (qd, JH,H = 2.2, JH,H = 6.6 Hz, 1 H), 4.09 (dt, JH,H
= 3.2, JH,H = 9.0 Hz, 1 H), 3.26 (dt, JH,H = 3.4, JH,H = 13.7 Hz, 1
H), 2.88 (dd, JH,H = 2.2, JH,H = 3.2 Hz, 1 H), 2.22–2.28 (m, 3 H),
2.12 (m, 1 H), 1.98 (m, 1 H), 1.75 (m, 1 H), 1.41–1.59 (m, 3 H),
H), 4.96 (dd, JH,H = 1.5, JH,H = 17.1 Hz, 1 H), 4.89 (dd, JH,H
=
1.22 (d, JH,H = 6.6 Hz, 3 H), 1.12–1.39 (m, 6 H), 0.94 (t, JH,H
=
1.5, JH,H = 10.3 Hz, 1 H), 4.06 (qd, JH,H = 5.9, J = 6.4 Hz, 1 H),
3.96 (m, 1 H), 3.32 (br. s, 1 H), 2.76 (dd, JH,H = 2.9, JH,H = 5.4 Hz,
7.3 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3, 25 °C): δ = 172.2,
166.1, 65.6, 59.6, 52.9, 34.7, 32.9, 32.7, 25.6, 25.4, 25.3, 25.2, 19.0,
18.5, 13.9 ppm. HRMS (TOF MS ES+): calcd. for C16H25NO4
1 H), 2.68 (t, JH,H = 7.3 Hz, 2 H), 2.27 (td, JH,H = 6.8, JH,H
=
7.3 Hz, 2 H), 2.01 (m, 1 H), 1.40 (m, 1 H), 1.27 (m, 2 H), 1.18 (d,
JH,H = 6.4 Hz, 3 H), 0.86 (t, JH,H = 7.3 Hz, 3 H) ppm. 13C NMR
(125 MHz, CDCl3, 25 °C): δ = 170.6, 166.5, 136.1, 115.3, 64.2, 61.6,
53.2, 35.6, 33.9, 27.7, 21.4, 18.3, 13.7 ppm. HRMS (TOF MS ES+):
calcd. for C13H21NO3 240.1600 [M + H]+; found 240.1592. IR
318.1681 [M + Na]+; found 318.1693. IR (NaCl): ν
= 2866–
˜
max
2930, 1796, 1726, 1701 cm–1.
(3S,4R)-3-[(1R)-1-(tert-Butyldimethylsilyloxy)ethyl]-1-(prop-2-enyl)-
4-propyl-2-azetidinone (9a): KOH (155 mg, 2.77 mmol, 1.5 equiv.),
KI (613 mg, 3.70 mmol, 2 equiv.), Bu4NHSO4 (25 mg, 0.074 mmol,
0.04 equiv.) and allyl bromide (0.48 mL, 5.53 mmol, 3 equiv.) were
added to a stirred solution of β-lactam 3 (500 mg, 1.85 mmol) in
anhydrous THF (10 mL). The reaction was performed at room
temp. under argon for 15 h. Then the reaction medium was filtered
and the solvent removed under reduced pressure. The crude prod-
uct was directly purified by flash chromatography (CyHex/AcOEt,
5:2) to provide 9a as a yellow oil (535 mg, 93%). TLC (CyHex/
(NaCl): ν = 3470, 1784, 1701, 1641, 1321 cm–1.
˜
(3S,4R)-1-(Pent-4-enoyl)-3-[(1R)-1-(pent-4-enoyloxy)ethyl]-4-
propyl-2-azetidinone (6): Pyridine (0.17 mL, 2.10 mmol, 2 equiv.)
and 4-pentenoyl chloride (0.23 mL, 2.10 mmol, 2 equiv.) were
added to a stirred solution of β-lactam 5 (250 mg, 1.05 mmol) in
dry CH2Cl2 (5 mL). The reaction was performed at room temp.
under argon for 3 h. Then the reaction medium was diluted with
CH2Cl2 (15 mL) and sequentially washed with a 3.3  HCl solution
(15 mL), a saturated NaHCO3 solution (15 mL), and brine
(15 mL). The organic layer was dried with MgSO4 and concen-
trated. The crude product was purified by flash chromatography
(CyHex/AcOEt, 10:1) to provide 6 as a pale-yellow oil (291 mg,
1
AcOEt, 5:2): Rf = 0.59. H NMR (200 MHz, CDCl3, 25 °C): δ =
5.58–5.79 (ddt, JH,H = 6.1, JH,H = 10.2, JH,H = 16.8 Hz, 1 H), 5.20
(dd, JH,H = 1.5, JH,H = 16.8 Hz, 1 H), 5.05 (dd, JH,H = 1.5, JH,H
= 10.0 Hz, 1 H), 4.09 (qd, JH,H = 4.6, JH,H = 6.2 Hz, 1 H), 3.85–
3.96 (ddd, JH,H = 1.5, JH,H = 5.4, JH,H = 15.7 Hz, 1 H), 3.60 (m,
2 H), 2.62 (dd, JH,H = 1.8, JH,H = 4.5 Hz, 1 H), 1.65 (m, 1 H), 1.40
(m, 3 H), 1.12 (d, JH,H = 6.2 Hz, 3 H), 0.88 (t, JH,H = 6.8 Hz, 3
H), 0.80 (s, 9 H), 0.00 (2 s, 6 H) ppm. 13C NMR (50 MHz, CDCl3,
25 °C): δ = 167.8, 132.7, 117.9, 65.4, 63.2, 54.1, 43.0, 35.0, 25.8,
22.8, 19.3, 17.9, 14.2, –4.5, –4.8 ppm. HRMS (TOF MS ES+):
calcd. for C17H33NO2Si 334.2178 [M + Na]+; found 334.2188. IR
1
86%). TLC (CyHex/AcOEt, 5:1): Rf = 0.52. H NMR (500 MHz,
CDCl3, 25 °C): δ = 5.81 (ddt, JH,H = 6.5, JH,H = 10.2, JH,H
16.8 Hz, 1 H), 5.77 (ddt, JH,H = 5.9, JH,H = 10.7, JH,H = 16.8 Hz,
1 H), 5.21 (qd, JH,H = 6.4, JH,H = 6.6 Hz, 1 H), 5.05 (dd, JH,H
=
=
1.6, JH,H = 10.2 Hz, 1 H), 5.03 (m, 1 H), 4.99 (m, 2 H), 3.92 (m, 1
H), 2.95 (dd, JH,H = 3.2, JH,H = 6.7 Hz, 1 H), 2.78 (t, JH,H = 7.4 Hz,
2 H), 2.38 (m, 2 H), 2.34 (m, 4 H), 2.15 (m, 1 H), 1.46 (m, 1 H),
1.34 (m, 2 H), 1.34 (d, JH,H = 6.7 Hz, 3 H), 0.95 (t, JH,H = 7.4 Hz,
3 H) ppm. 13C NMR (125 MHz, CDCl3, 25 °C): δ = 171.7, 170.5,
164.5, 136.3, 136.1, 115.6, 67.4, 59.5, 54.5, 35.9, 34.2, 33.4, 28.6,
27.8, 18.44, 18.41, 13.8 ppm. HRMS (TOF MS ES+): calcd. for
(NaCl): ν
= 2856–2958, 1756, 1645, 1320, 836 cm–1.
˜
max
(3S,4R)-1-(But-3-enyl)-3-[(1R)-1-(tert-butyldimethylsilyloxy)ethyl]-
4-propyl-2-azetidinone (9b): The N-(but-3-enyl) derivative was ob-
tained according to the procedure described above for the synthesis
of compound 9a from β-lactam 3 (1 g, 3.69 mmol). Flash
chromatography (CyHex/AcOEt, 5:2) provided 9b as a yellow oil
(828 mg, 69%). TLC (CyHex/AcOEt, 5:2): Rf = 0.60. 1H NMR
C H NO 344.1838 [M + Na]+; found 344.1847. IR (NaCl): ν
˜
18 27
4
max
= 1786, 1739, 1704, 1321 cm–1.
(5E,11R,12S,14R)-11-Methyl-2,9,13-trioxo-14-pRopyl-10-oxa-1-az-
abicyclo[10.1.1]tetradec-5-ene (7). Method A: Grubbs catalyst
(39.7 mg, 0.047 mmol, 0.05 equiv.) was added to a stirred solution
(200 MHz, CDCl3, 25 °C): δ = 5.66–5.84 (ddt, JH,H = 6.8, JH,H =
10.1, JH,H = 17.0 Hz, 1 H), 5.0–5.2 (m, 2 H), 4.09 (qd, JH,H = 5.4,
JH,H = 6.1 Hz, 1 H), 3.55 (m, 1 H), 3.3–3.5 (m, 1 H), 2.9–3.1 (m,
of β-lactam 6 (300 mg, 0.934 mmol) in dry CH2Cl2 (200 mL, 5 m). 1 H), 2.64 (dd, JH,H = 1.8, JH,H = 5.4 Hz, 1 H), 2.28 (td, JH,H
=
The reaction was performed at room temp. under argon for 5 h.
Then the solvent was removed and the crude product purified by
flash chromatography (CyHex/AcOEt, 5:2) to provide 7 as a white
6.6, JH,H = 7.3 Hz, 2 H), 1.65 (m, 1 H), 1.40 (m, 3 H), 1.19 (d,
JH,H = 6.2 Hz, 3 H), 0.96 (t, JH,H = 6.8 Hz, 3 H), 0.86 (s, 9 H),
0.04 and 0.06 (2 s, 6 H) ppm. 13C NMR (50 MHz, CDCl3, 25 °C):
solid (260 mg, 95%). TLC (CyHex/AcOEt, 5:2): Rf = 0.56. M.p. δ = 168.0, 135.2, 116.9, 65.9, 63.0, 54.6, 39.5, 35.0, 32.8, 25.7, 22.9,
1
57.4 °C. H NMR (500 MHz, CDCl3, 25 °C): δ = 5.55 (qd, JH,H
1.9, JH,H = 6.5 Hz, 1 H), 5.40 (m, JH,H = 15.5 Hz, 1 H), 5.33 (m,
JH,H = 15.5 Hz, 1 H), 4.06 (ddd, JH,H = 3.0, JH,H = 3.6, JH,H
=
19.3, 17.9, 14.3, –4.5, –4.7 ppm. HRMS (TOF MS ES+): calcd. for
C18H35NO2Si 348.2335 [M + Na]+; found 348.2321. IR (NaCl):
=
ν
= 2853–2958, 1750, 1640, 833 cm–1.
max
˜
Eur. J. Org. Chem. 2009, 1757–1770
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1765

A. Urbach, G. Dive, J. Marchand-Brynaert
FULL PAPER
(3S,4R)-3-[(1R)-1-(tert-Butyldimethylsilyloxy)ethyl]-1-(pent-4-enyl)-
(3S,4R)-3-[(1R)-1-(Pent-4-enoyloxy)ethyl]-1-(prop-2-enyl)-4-
4-propyl-2-azetidinone (9c): The N-(pent-4-enyl) derivative was ob- propyl-2-azetidinone (11a): The O-acylated β-lactam 11a was ob-
tained according to the procedure described above for the synthesis
of compound 9a from β-lactam 3 (400 mg, 1.75 mmol). Flash
chromatography (CyHex/AcOEt, 5:2) provided 9c as a yellow oil
(384 mg, 74%). TLC (CyHex/AcOEt, 5:2): Rf = 0.65. 1H NMR
tained according to the procedure described above for the synthesis
of compound 6 from β-lactam 10a (900 mg, 4.57 mmol). Flash
chromatography (CyHex/AcOEt, 5:2) provided the desired com-
pound as a yellow oil (1.065 g, 83%). TLC (CyHex/AcOEt, 5:2):
Rf = 0.58. 1H NMR (500 MHz, CDCl3, 25 °C): δ = 5.79 (ddt, JH,H
(200 MHz, CDCl3, 25 °C): δ = 5.65–5.85 (ddt, JH,H = 6.5, JH,H
=
10.1, JH,H = 16.8 Hz, 1 H), 5.02 (m, 1 H), 4.94 (m, 1 H), 4.10 (qd, = 5.1, JH,H = 10.4, JH,H = 17.3 Hz, 1 H), 5.73 (m, 1 H), 5.22 (dddd,
JH,H = 5.1, JH,H = 6.1 Hz, 1 H), 3.51 (m, 1 H), 3.29 (m, 1 H), 2.93 JH,H = 1.5, JH,H = 1.5, JH,H = 1.5, JH,H = 17.2 Hz, 1 H), 5.18 (m,
(m, 1 H), 2.62 (dd, JH,H = 1.8, JH,H = 5.1 Hz, 1 H), 2.0 (m, 2 H), 1 H), 5.17 (m, 1 H), 5.04 (ddt, JH,H = 1.5, JH,H = 1.5, JH,H
1.28–1.60 (m, 6 H), 1.16 (d, JH,H = 6.2 Hz, 3 H), 0.93 (t, JH,H 17.3 Hz, 1 H), 4.99 (ddt, JH,H = 1.5, JH,H = 1.5, JH,H = 10.4 Hz, 1
H), 4.02 (dddd, JH,H = 1.5, JH,H = 1.5, JH,H = 5.1, JH,H = 15.8 Hz,
1 H), 3.55 (dddd, JH,H = 1.5, JH,H = 1.5, JH,H = 6.9, JH,H
=
=
6.8 Hz, 3 H), 0.83 (s, 9 H), 0.02 and 0.03 (2 s, 6 H) ppm. 13C NMR
(50 MHz, CDCl3, 25 °C): δ = 167.9, 137.4, 115.2, 65.5, 62.8, 54.2,
39.6, 34.9, 31.1, 27.4, 25.7, 22.8, 19.3, 17.8, 14.2, –4.6, –4.8 ppm.
HRMS (TOF MS ES+): calcd. C19H37NO2Si 362.2491 [M + Na]+;
=
15.8 Hz, 1 H), 3.45 (ddd, JH,H = 1.8, JH,H = 4.3, JH,H = 8.4 Hz, 1
H), 2.85 (dd, JH,H = 1.8, JH,H = 8.0 Hz, 1 H), 2.35 (m, 4 H), 1.73
(m, 1 H), 1.38 (m, 3 H), 1.34 (d, JH,H = 6.2 Hz, 3 H), 0.93 (t, JH,H
= 7.3 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3, 25 °C): δ =
172.0, 165.9, 136.4, 132.0, 118.1, 115.4, 68.5, 60.3, 55.6, 42.7, 34.6,
33.6, 28.6, 18.8, 18.6, 14.0 ppm. HRMS (TOF MS ES+): calcd. for
found 362.2477. IR (NaCl): ν
= 2856–2956, 1753, 1641,
˜
max
836 cm–1.
(3S,4R)-3-[(1R)-1-Hydroxyethyl]-1-(prop-2-enyl)-4-propyl-2-azetid-
inone (10a): The O-deprotected β-lactam 10a was obtained accord-
ing to the procedure described above for the synthesis of compound
5 from β-lactam 9a (1.48 g, 4.76 mmol) in 96% yield (900 mg) as a
pale-yellow oil and was used in the next step without purification.
TLC (CyHex/AcOEt, 5:4): Rf = 0.20. 1H NMR (200 MHz, CDCl3,
25 °C): δ = 5.70 (ddt, JH,H = 6.6, JH,H = 10.2, JH,H = 17.5 Hz, 1
C H NO 280.1913 [M + H]+; found 280.1925. IR (NaCl): ν
˜
16 25
3
max
= 3080, 2874–2958, 1755, 1740, 1642 cm–1.
(3S,4R)-1-(But-3-enyl)-3-[(1R)-1-(pent-4-enoyloxy)ethyl]-4-propyl-2-
azetidinone (11b): The O-acylated β-lactam 11b was obtained ac-
cording to the procedure described above for the synthesis of com-
pound 6 from β-lactam 10b (350 mg, 1.66 mmol). Flash chromatog-
raphy (CyHex/AcOEt, 5:1) provided the desired compound as a
pale-yellow oil (440 mg, 90 %). TLC (CyHex/AcOEt, 5:2): Rf =
H), 5.22 (dd, JH,H = 1.4, JH,H = 17.5 Hz, 1 H), 5.08 (dd, JH,H
=
1.3, JH,H = 10.2 Hz, 1 H), 4.07 (qd, JH,H = 5.4, JH,H = 6.3 Hz, 1
H), 3.95 (dd, JH,H = 6.6, JH,H = 15.9 Hz, 1 H), 3.53 (m, 3 H), 2.70
(dd, JH,H = 1.9, JH,H = 5.1 Hz, 1 H), 1.65 (m, 1 H), 1.20–1.40 (m,
3 H), 1.20 (d, JH,H = 6.3 Hz, 3 H), 0.89 (t, JH,H = 6.7 Hz, 3 H)
ppm. 13C NMR (50 MHz, CDCl3, 25 °C): δ = 168.0, 132.1, 117.8,
64.6, 62.6, 54.3, 42.9, 34.8, 21.6, 19.2, 14.2 ppm. MS (CI, CH4/
1
0.48. H NMR (500 MHz, CDCl3, 25 °C): δ = 5.76 (m, 1 H), 5.72
(ddt, JH,H = 6.7, JH,H = 10.2, JH,H = 17.1 Hz, 1 H), 5.11 (m, 1 H),
5.08 (m, 1 H), 5.04 (m, 1 H), 5.01 (m, 1 H), 4.97 (dd, JH,H = 1.6,
JH,H = 10.1 Hz, 1 H), 3.43 (m, 1 H), 3.40 (m, 1 H), 2.97 (m, 1 H),
2.78 (dd, JH,H = 1.5, JH,H = 8.1 Hz, 1 H), 2.32 (m, 4 H), 2.24 (m,
2 H), 1.71 (m, 1 H), 1.35 (m, 2 H), 1.30 (d, JH,H = 6.4 Hz, 3 H),
1.27 (m, 1 H), 0.93 (t, JH,H = 7.3 Hz, 3 H) ppm. 13C NMR
(125 MHz, CDCl3, 25 °C): δ = 171.9, 165.8, 136.3, 134.6, 117.0,
115.3, 68.7, 60.1, 55.6, 39.2, 34.5, 33.5, 32.2, 28.6, 18.7, 18.5,
13.9 ppm. HRMS (TOF MS ES+): calcd. for C17H27NO3 294.2069
+
NO2): m/z = 198.1 [M H]+ for C11H19NO2.
(3S,4R)-1-(But-3-enyl)-3-[(1R)-1-hydroxyethyl]-4-propyl-2-azetid-
inone (10b): The O-deprotected β-lactam 10b was obtained accord-
ing to the procedure described above for the synthesis of compound
5 from β-lactam 9b (1.15 g, 3.54 mmol) in 82% yield (613 mg) as a
yellow oil and was used in the next step without purification. TLC
(CyHex/AcOEt, 5:4): Rf = 0.21. 1H NMR (200 MHz, CDCl3,
25 °C): δ = 5.72 (ddt, JH,H = 6.7, JH,H = 10.3, JH,H = 17.0 Hz, 1
[M + H]+; found 294.2064. IR (NaCl): ν
= 3077, 2873–2958,
˜
max
1752, 1740, 1641 cm–1.
H), 5.09 (dd, JH,H = 1.6, JH,H = 17.0 Hz, 1 H), 4.98 (dd, JH,H
=
(3S,4R)-3-[(1R)-1-(Pent-4-enoyloxy)ethyl]-1-(pent-4-enyl)-4-propyl-
2-azetidinone (11c): The O-acylated β-lactam 11c was obtained ac-
cording to the procedure described above for the synthesis of com-
pound 6 from β-lactam 10c (300 mg, 1.33 mmol). Flash chromatog-
raphy (CyHex/AcOEt, 5:2) provided the desired compound as a
pale-yellow oil (375 mg, 92 %). TLC (CyHex/AcOEt, 1:1): Rf =
1.6, JH,H = 10.3 Hz, 1 H), 4.05 (qd, JH,H = 5.4, JH,H = 6.4 Hz, 1
H), 3.55 (m, 1 H), 3.40 (m, 1 H), 2.90 (m, 1 H), 2.70 (br. s, 1 H),
2.68 (dd, JH,H = 2.0, JH,H = 5.2 Hz, 1 H), 2.24 (m, 2 H), 1.70 (m,
1 H), 1.40 (m, 3 H), 1.20 (d, JH,H = 6.7 Hz, 3 H), 0.92 (t, JH,H
=
7.1 Hz, 3 H) ppm. 13C NMR (50 MHz, CDCl3, 25 °C): δ = 167.9,
134.8, 116.8, 64.8, 62.4, 54.4, 39.5, 34.7, 32.4, 21.5, 19.1, 14.2 ppm.
MS (CI, CH4/NO2): m/z = 212.2 [M + H]+ for C12H21NO2.
1
0.76. H NMR (500 MHz, CDCl3, 25 °C): δ = 5.78 (m, 2 H), 5.16
(qd, JH,H = 6.3, JH,H = 8.0 Hz, 1 H), 5.04 (ddd, JH,H = 1.5, JH,H
= 1.5, JH,H = 17.3 Hz, 1 H), 5.03 (ddd, JH,H = 1.5, JH,H = 1.5, JH,H
= 17.3 Hz, 1 H), 5.00 (ddd, JH,H = 1.5, JH,H = 1.5, JH,H = 10.4 Hz,
1 H), 4.99 (ddd, JH,H = 1.5, JH,H = 1.5, JH,H = 10.4 Hz, 1 H), 3.42
(3S,4R)-3-[(1R)-1-Hydroxyethyl]-1-(pent-4-enyl)-4-propyl-2-azetid-
inone (10c): The O-deprotected β-lactam 10c was obtained accord-
ing to the procedure described above for the synthesis of compound
5 from β-lactam 9c (2.09 g, 6.16 mmol) in 100% yield (1.39 g) as a
yellow oil and was used in the next step without purification. TLC
(CyHex/AcOEt, 5:4): Rf = 0.22. 1H NMR (200 MHz, CDCl3,
25 °C): δ = 5.76 (ddt, JH,H = 6.6, JH,H = 10.2, JH,H = 16.8 Hz, 1
H), 5.05 (dd, JH,H = 1.7, JH,H = 16.8 Hz, 1 H), 4.94 (dd, JH,H
1.7, JH,H = 10.2 Hz, 1 H), 4.12 (qd, JH,H = 5.5, JH,H = 6.3 Hz, 1
H), 3.55 (m, 1 H), 3.35 (m, 1 H), 2.95 (m, 1 H), 2.72 (dd, JH,H
1.8, JH,H = 5.1 Hz, 1 H), 2.44 (br. s, 1 H), 2.08 (td, JH,H = 6.6,
JH,H = 7.0 Hz, 2 H), 1.30–1.80 (2 m, 6 H), 1.24 (d, JH,H = 6.4 Hz,
3 H), 0.95 (t, JH,H = 7.3 Hz, 3 H) ppm. 13C NMR (50 MHz,
CDCl3, 25 °C): δ = 168.0, 137.2, 115.2, 64.6, 62.3, 54.2, 39.6, 34.8,
31.0, 27.2, 21.6, 19.2, 14.2 ppm. MS (CI, CH4/NO2): m/z = 226.2
[M + H]+ for C13H23NO2.
(ddd, JH,H = 1.8, JH,H = 4.3, JH,H = 8.3 Hz, 1 H), 3.37 (dt, JH,H
=
7.6, JH,H = 14.3 Hz, 1 H), 2.94 (dt, JH,H = 7.6, JH,H = 14.3 Hz, 1
H), 2.82 (dd, JH,H = 1.8, JH,H = 8.0 Hz, 1 H), 2.35 (m, 4 H), 2.07
(m, 2 H), 1.75 (m, 1 H), 1.62 (m, 2 H), 1.38 (m, 2 H), 1.34 (d, JH,H
= 6.3 Hz, 3 H), 1.29 (m, 1 H), 0.95 (t, JH,H = 7.3 Hz, 3 H) ppm.
13C NMR (125 MHz, CDCl3, 25 °C): δ = 172.0, 166.0, 137.1, 136.4,
115.4, 115.3, 68.6, 60.1, 55.5, 39.5, 34.6, 33.6, 30.9, 28.7, 27.1, 18.8,
18.6, 14.0 ppm. HRMS (TOF MS ES+): calcd. for C18H29NO3
=
=
330.2045 [M + Na]+; found 330.2056. IR (NaCl): ν
= 3078,
˜
max
2874–2958, 1754, 1745, 1641 cm–1.
(10R,11S,13R)-10-Methyl-8,12-dioxo-13-propyl-9-oxa-1-azabicyclo-
[9.1.1]tridec-4-ene (12b). Method B: Ti(OiPr)4 (20 mol-%) was in-
1766
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 1757–1770

Potential Inhibitors of Penicillin-Binding Proteins
jected into a stirred solution of precursor 11b (415 mg, 1.42 mmol)
in anhydrous toluene (5 m) under argon. The temperature was
raised to 80 °C and Grubbs catalyst (2.5 mol-%) was added. The
reaction was performed at this temperature for 24 h. Then the reac-
tion medium was filtered through Celite and the solvent removed
under reduced pressure. The dark residue was purified by flash
chromatography (CyHex/AcOEt, 5:3) to provide the cyclized com-
pound 12b as a white solid (280 mg, 74%) in a stereoisomeric ratio
of 75:25. TLC (CyHex/AcOEt, 5:3): Rf = 0.18. GC: tr = 35.4 min.
(3S,4R)-1-(Prop-2-enyl)-3-[(1R)-1-(prop-2-enyloxy)ethyl]-4-propyl-
2-azetidinone (14a): NaH (60% dispersion in oil, 83 mg, 1.72 mmol,
1.1 equiv.) was added to a stirred solution of β-lactam 10a (306 mg,
1.56 mmol) in dry DMF (10 mL) at 0 °C under argon. After
20 min, KI (702 mg, 4.68 mmol, 3 equiv.) and allyl bromide
(0.40 mL, 4.68 mmol, 3 equiv.) were added, and the temperature of
the reaction medium was allowed to slowly rise to room temp. After
6 h, a saturated solution of NH4Cl was injected dropwise and the
medium diluted with diethyl ether (50 mL). The organic layer was
1H NMR (500 MHz, CDCl3, 25 °C, major isomer): δ = 5.48 (m, 1 washed three times with brine, dried with MgSO4, filtered and the
H), 5.46 (m, 1 H), 5.33 (m, 1 H), 3.75 (m, 1 H), 3.68 (m, 1 H), 2.88
(m, 1 H), 2.80 (br. s, 1 H), 2.47 (m, 1 H), 2.36 (m, 3 H), 2.22 (m,
2 H), 1.77 (m, 1 H), 1.43 (m, 3 H), 1.24 (d, JH,H = 6.9 Hz, 3 H),
1.02 (t, JH,H = 7.3 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3,
25 °C): δ = 171.4, 167.0, 132.7, 128.2, 64.3, 60.1, 51.8, 38.6, 35.2,
34.7, 31.3, 29.0, 19.7, 19.6, 14.3 ppm. HRMS (TOF MS ES+):
solvent removed under reduced pressure. The crude product was
purified by flash chromatography (CyHex/AcOEt, 5:2) to provide
14a as a pale-yellow oil (254 mg, 69%). TLC (CyHex/AcOEt, 5:2):
Rf = 0.45. 1H NMR (500 MHz, CDCl3, 25 °C): δ = 5.84 (dddd,
JH,H = 5.4, JH,H = 5.4, JH,H = 10.4, JH,H = 17.3 Hz, 1 H), 5.71
(dddd, JH,H = 5.1, JH,H = 6.9, JH,H = 10.4, JH,H = 17.3 Hz, 1 H),
calcd. for C15H23NO3 266.1756 [M + H]+; found 266.1747. IR 5.22 (m, 2 H), 5.14 (ddd, JH,H = 1.5, JH,H = 1.8, JH,H = 10.4 Hz,
(NaCl): ν 1 H), 5.10 (dddd, JH,H = 1.5, JH,H = 1.5, JH,H = 1.5, JH,H
= 2858–2959, 1763, 1728 cm–1.
=
˜
max
10.4 Hz, 1 H), 4.06 (dddd, JH,H = 1.5, JH,H = 1.5, JH,H = 5.4, JH,H
= 12.7 Hz, 1 H), 4.02 (dddd, JH,H = 1.8, JH,H = 1.8, JH,H = 5.1,
(11R,12S,14R)-11-Methyl-9,13-dioxo-14-propyl-10-oxa-1-azabi-
cyclo[10.1.1]tetradec-5-ene (12c): The cyclized compound 12c was
obtained from precursor 11c by using Method B (395 mg,
1.29 mmol) with 5 mol-% of Grubbs catalyst. After 19.5 h and the
usual workup, flash chromatography (CyHex/AcOEt, 5:3) provided
the desired β-lactam (220 mg, 62%) as a mixture of 12c and 12b in
a 75:25 ratio. TLC (CyHex/AcOEt, 5:3): Rf = 0.16. GC: tr =
JH,H = 15.8 Hz, 1 H), 3.92 (dddd, JH,H = 1.5, JH,H = 1.5, JH,H
=
5.4, JH,H = 12.7 Hz, 1 H), 3.76 (qd, JH,H = 5.8, JH,H = 6.3 Hz, 1
H), 3.57 (ddd, JH,H = 1.8, JH,H = 4.3, JH,H = 8.3 Hz, 1 H), 3.52
(dd, JH,H = 6.9, JH,H = 15.8 Hz, 1 H), 2.72 (dd, JH,H = 1.8, JH,H
= 5.8 Hz, 1 H), 1.70 (m, 1 H), 1.35 (m, 3 H), 1.21 (d, JH,H = 6.3 Hz,
3 H), 0.91 (t, JH,H = 7.3 Hz, 3 H) ppm. 13C NMR (125 MHz,
25 °C): δ = 167.6, 134.9, 132.1, 117.6, 116.3, 71.9, 69.8, 61.5, 54.7,
42.6, 34.7, 18.9, 18.4, 14.0 ppm. HRMS (TOF MS ES+): calcd. for
1
37.0 min. H NMR (500 MHz, CDCl3, 25 °C, major isomer): δ =
5.43 (m, 3 H), 3.67 (m, 1 H), 3.55 (m, 1 H), 2.88 (m, 1 H), 2.72
(br. s, 1 H), 2.47 (m, 2 H), 1.5–2.4 (5 m, 7 H), 1.36 (m, 3 H), 1.20
(d, JH,H = 6.4 Hz, 3 H), 0.97 (t, JH,H = 7.3 Hz, 3 H) ppm. 13C
NMR (125 MHz, CDCl3, 25 °C): δ = 171.7, 165.9, 129.5, 128.4,
65.1, 59.9, 52.4, 40.2, 33.8, 32.9, 32.4, 26.9, 25.5, 19.2, 19.0,
14.2 ppm. HRMS (TOF MS ES+): calcd. for C16H25NO3 280.1913
C H NO 238.1807 [M + H]+; found 238.1809. IR (NaCl): ν
˜
14 23
2
max
= 2931–2961, 1750, 1641 cm–1.
(3S,4R)-3-[(1R)-1-(Pent-4-enyloxy)ethyl]-1-(prop-2-enyl)-4-propyl-2-
azetidinone (14b): The O-(pent-4-enyl) derivative was obtained ac-
cording to the procedure described above for the synthesis of com-
pound 14a from β-lactam 10a (779 mg, 3.95 mmol) and 4-pentenyl
bromide. Flash chromatography (CyHex/AcOEt, 5:2) provided 14b
[M + H]+; found 280.1901. IR (NaCl): ν
= 2858–2957,
˜
max
1751 cm–1.
(10R,11S,13R)-10-Methyl-8,12-dioxo-13-propyl-9-oxa-1-azabicyclo-
[9.1.1]tridecane (13b): Compound 13b was quantitatively obtained
as a white solid from the cyclized β-lactam 12b (400 mg,
1.51 mmol) by using the procedure described above for the synthe-
as a pale-yellow oil (394 mg, 38%). TLC (CyHex/AcOEt, 5:2): Rf
1
= 0.50. H NMR (500 MHz, CDCl3, 25 °C): δ = 5.73 (ddt, JH,H
=
6.7, JH,H = 10.2, JH,H = 17.0 Hz, 1 H), 5.66 (ddt, JH,H = 6.7, JH,H
= 10.2, JH,H = 17.0 Hz, 1 H), 5.19 (dd, JH,H = 1.2, JH,H = 17.0 Hz,
sis of compound 3. TLC (CyHex/AcOEt, 5:4): Rf = 0.33. M.p.
1 H), 5.10 (dd, JH,H = 1.2, JH,H = 10.2 Hz, 1 H), 4.94 (dd, JH,H
1.0, JH,H = 17.0 Hz, 1 H), 4.88 (dd, JH,H = 1.0, JH,H = 10.2 Hz, 1
H), 3.98 (dd, JH,H = 6.7, JH,H = 15.9 Hz, 1 H), 3.64 (qd, JH,H
=
1
70.4 °C. H NMR (500 MHz, CDCl3, 25 °C): δ = 5.38 (qd, JH,H
=
0.9, JH,H = 6.4 Hz, 1 H), 3.67 (m, 1 H), 3.44 (m, 1 H), 2.79 (m, 1
H), 2.65 (br. s, 1 H), 2.40 (m, 1 H), 2.12 (m, 1 H), 1.69 (m, 1 H),
1.37 (m, 3 H), 1.18–1.75 (m, 8 H), 1.14 (d, JH,H = 6.4 Hz, 3 H),
0.88 (t, JH,H = 7.3 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3,
25 °C): δ = 171.0, 166.1, 64.6, 60.0, 52.4, 38.5, 34.3, 34.0, 26.3, 24.5,
22.8, 22.5, 19.2, 19.0, 14.0 ppm. HRMS (TOF MS ES+): calcd. for
=
5.8, JH,H = 6.2 Hz, 1 H), 3.50 (m, 3 H), 3.28 (m, 3 H), 2.67 (dd,
JH,H = 1.8, JH,H = 5.8 Hz, 1 H), 2.03 (td, JH,H = 6.7, JH,H = 7.3 Hz,
2 H), 1.67 (m, 1 H), 1.55 (quint, JH,H = 7.3 Hz, 3 H), 1.31 (m, 3
H), 1.16 (d, JH,H = 6.2 Hz, 3 H), 0.88 (t, JH,H = 7.3 Hz, 3 H) ppm.
13C NMR (125 MHz, 25 °C): δ = 167.7, 138.0, 132.1, 117.5, 114.4,
72.3, 68.0, 61.5, 54.6, 42.4, 34.6, 30.0, 29.0, 18.9, 18.2, 13.9 ppm.
HRMS (TOF MS ES+): calcd. for C16H27NO2 288.1939 [M +
C H NO 268.1913 [M + H]+; found 268.1914. IR (NaCl): ν
˜
15 25
3
max
= 2858–2959, 1755, 1736 cm–1.
Na]+; found 288.1942. IR (NaCl): ν
= 3077, 2871–2931, 1750,
˜
max
(11R,12S,14R)-11-Methyl-9,13-dioxo-14-propyl-10-oxa-1-azabi-
cyclo[10.1.1]tetradecane (13c): Compound 13c was quantitatively
obtained as a white gum from the cyclized β-lactam 12c (70 mg,
1637 cm–1.
(3S,4R)-1-(But-3-enyl)-3-[(1R)-1-(pent-4-enyloxy)ethyl]-4-propyl-2-
0.26 mmol) by using the procedure described above for the synthe- azetidinone (15b): The O-(pent-4-enyl) derivative was synthesized
sis of compound 3. TLC (CyHex/AcOEt, 5:3): Rf = 0.30. 1H NMR
(500 MHz, CDCl3, 25 °C): δ = 5.36 (qd, JH,H = 2.0, JH,H = 6.6 Hz,
according to the procedure described above for the synthesis of
compound 14a from β-lactam 10b (260 mg, 1.23 mmol), with NaH
added in portions (3ϫ1.1 equiv.), pent-4-enyl bromide and no KI.
1 H), 3.74 (m, 1 H), 3.54 (m, 1 H), 2.80 (dd, JH,H = 1.9, JH,H
=
2.0 Hz, 1 H), 2.76 (m, 1 H), 2.31 (t, JH,H = 5.9 Hz, 2 H), 1.26–1.83 Flash chromatography (CyHex/AcOEt, 5:1) provided 15b as a pale-
(m, 14 H), 1.24 (d, JH,H = 6.6 Hz, 3 H), 0.98 (t, JH,H = 7.3 Hz, 3
yellow oil (240 mg, 70%). TLC (CyHex/AcOEt, 5:2): Rf = 0.56. 1H
H) ppm. 13C NMR (125 MHz, 25 °C): δ = 172.5, 166.7, 65.6, 60.0, NMR (500 MHz, CDCl3, 25 °C): δ = 5.77 (ddt, JH,H = 6.6, JH,H
53.5, 40.2, 34.4, 33.6, 26.8, 26.4, 25.8, 25.4, 23.6, 19.2, 19.1, 10.2, JH,H = 16.9 Hz, 1 H), 5.73 (ddt, JH,H = 6.7, JH,H = 10.2, JH,H
=
14.2 ppm. HRMS (TOF MS ES+): calcd. for C16H27NO3 304.1889 = 17.1 Hz, 1 H), 5.06 (dd, JH,H = 1.7, JH,H = 17.1 Hz, 1 H), 5.01
[M + Na]+; found 304.1889. IR (NaCl): ν
= 2860–2930,
(dd, JH,H = 1.7, JH,H = 10.2 Hz, 1 H), 4.96 (dd, JH,H = 2.0, JH,H
= 16.9 Hz, 1 H), 4.91 (dd, JH,H = 2.0, JH,H = 10.2 Hz, 1 H), 3.61
˜
max
1751 cm–1.
Eur. J. Org. Chem. 2009, 1757–1770
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1767

A. Urbach, G. Dive, J. Marchand-Brynaert
(qd, JH,H = 6.3, JH,H = 6.4 Hz, 1 H), 3.52 (m, 1 H), 3.50 (m, 1 H), 25 °C): δ = 168.9, 135.6, 124.6, 70.6, 69.6, 60.5, 50.6, 38.6, 34.4,
FULL PAPER
3.45 (m, 1 H), 3.30 (m, 1 H), 2.95 (m, 1 H), 2.65 (dd, JH,H = 1.8,
JH,H = 6.4 Hz, 1 H), 2.25 (m, 2 H), 2.05 (m, 2 H), 1.71 (m, 1 H),
32.2, 31.1, 28.9, 19.2, 19.1, 14.0 ppm. HRMS (TOF MS ES+):
calcd. for C15H25NO2 252.1964 [M + H]+; found 252.1960. IR
1.57 (quint, JH,H = 7.3 Hz, 2 H), 1.35 (m, 3 H), 1.18 (d, JH,H
=
(NaCl): ν
= 2872–2959, 1751 cm–1.
max
˜
6.2 Hz, 3 H), 0.93 (t, JH,H = 7.3 Hz, 3 H) ppm. 13C NMR
(125 MHz, 25 °C): δ = 167.8, 138.2, 135.0, 116.8, 114.6, 72.9, 68.0,
61.4, 55.0, 39.3, 34.7, 32.4, 30.2, 29.1, 19.0, 18.4, 14.1 ppm. HRMS
(TOF MS ES+): calcd. for C17H29NO2 280.2276 [M + Na]+; found
280.2273.
(11R,12S,14R)-11-Methyl-13-oxo-14-propyl-10-oxa-1-azabicyclo-
[10.1.1]tetradec-5-ene (17c): Cyclized compound 17c was obtained
from precursor 16b (293 mg, 1 mmol) by using Method B with
5 mol-% of Grubbs catalyst. After 24 h and the usual workup, flash
chromatography (CyHex/AcOEt, 5:2) provided the desired β-lac-
tam (190 mg, 72%, white gum) as a mixture of stereoisomers in a
ration of 25:75. (Z) isomer: TLC (CyHex/AcOEt, 5:4): Rf = 0.45.
(3S,4R)-1-(Pent-4-enyl)-3-[(1R)-1-(prop-2-enyloxy)ethyl]-4-propyl-2-
azetidinone (16a): The O-(prop-2-enyl) derivative was obtained ac-
cording to the procedure described above for the synthesis of com-
pound 14a from β-lactam 10c (405 mg, 1.8 mmol) and allyl bro-
mide. Flash chromatography (CyHex/AcOEt, 5:3) provided 16a as
a pale-yellow oil (408 mg, 85%). TLC (CyHex/AcOEt, 5:2): Rf =
1
GC: tr = 33.5 min. H NMR (500 MHz, CDCl3, 25 °C): δ = 5.33
(m, JH,H = 10.9 Hz, 2 H), 3.85 (qd, JH,H = 1.3, JH,H = 6.6 Hz, 1
H), 3.68 (m, 1 H), 3.60 (m, 1 H), 3.50 (m, 1 H), 3.38 (m, 1 H), 2.75
(m, 1 H), 2.59 (dd, JH,H = 1.3, JH,H = 1.8 Hz, 1 H), 2.37 (m, 2 H),
2.06 (m, 1 H), 1.90 (m, 1 H), 1.67 (m, 1 H), 1.63 (m, 3 H), 1.45
(m, 1 H), 1.36 (m, 1 H), 1.30 (m, 2 H), 1.10 (d, JH,H = 6.6 Hz, 3
H), 0.91 (t, JH,H = 7.1 Hz, 3 H) ppm. 13C NMR (125 MHz, 25 °C):
δ = 168.7, 130.1, 128.8, 71.3, 68.5, 61.00, 53.2, 38.1, 34.8, 29.9, 25.9,
23.5, 23.0, 19.7, 19.2, 14.1 ppm. HRMS (EI): calcd. for C16H27NO2
0.43. 1H NMR (500 MHz, CDCl3, 25 °C): δ = 5.80 (ddt, JH,H
=
5.4, JH,H = 10.4, JH,H = 17.3 Hz, 1 H), 5.72 (ddt, JH,H = 6.5, JH,H
= 10.4, JH,H = 17.3 Hz, 1 H), 5.18 (ddt, JH,H = 1.5, JH,H = 1.5,
JH,H = 17.3 Hz, 1 H), 5.06 (ddt, JH,H = 1.5, JH,H = 1.5, JH,H
=
10.4 Hz, 1 H), 4.96 (ddt, JH,H = 1.5, JH,H = 1.5, JH,H = 17.3 Hz, 1
H), 4.91 (ddt, JH,H = 1.5, JH,H = 1.5, JH,H = 10.4 Hz, 1 H), 4.02
(dddd, JH,H = 1.5, JH,H = 1.5, JH,H = 5.4, JH,H = 12.7 Hz, 1 H),
3.88 (dddd, JH,H = 1.5, JH,H = 1.5, JH,H = 5.4, JH,H = 12.7 Hz, 1
H), 3.71 (qd, JH,H = 5.8, JH,H = 6.3 Hz, 1 H), 3.49 (m, 1 H), 3.33
265.2041; found 265.2039. IR (NaCl): ν
= 2869–2929,
˜
max
1747 cm–1. (E) isomer: TLC (CyHex/AcOEt, 5:4): Rf = 0.36. 1H
NMR (500 MHz, CDCl3, 25 °C): δ = 5.48 (m, 1 H), 5.38 (m, 1 H),
3.83 (qd, JH,H = 1.5, JH,H = 6.4 Hz, 1 H), 3.73 (m, 1 H), 3.57 (m,
1 H), 3.52 (m, 1 H), 3.47 (m, 1 H), 2.92 (dd, JH,H = 5.9, JH,H
=
(td, JH,H = 7.9, JH,H = 14.3 Hz, 1 H), 2.88 (td, JH,H = 7.6, JH,H
14.3 Hz, 1 H), 2.65 (dd, JH,H = 1.8, JH,H = 5.8 Hz, 1 H), 2.02 (m,
2 H), 1.69 (m, 1 H), 1.56 (m, 2 H), 1.33 (m, 3 H), 1.17 (d, JH,H
=
14.2 Hz, 1 H), 2.56 (d, JH,H = 1.5 Hz, 1 H), 2.05–2.18 (m, 4 H),
1.48–1.75 (m, 5 H), 1.34 (m, 3 H), 1.09 (d, JH,H = 6.4 Hz, 3 H),
0.95 (t, JH,H = 7.4 Hz, 3 H) ppm. 13C NMR (125 MHz, 25 °C): δ
= 168.5, 130.1, 129.5, 71.1, 69.4, 60.9, 52.1, 40.1, 34.0, 32.3, 29.8,
27.7, 25.6, 19.7, 19.3, 14.3 ppm.
=
6.3 Hz, 3 H), 0.90 (t, JH,H = 7.1 Hz, 3 H) ppm. 13C NMR
(125 MHz, 25 °C): δ = 167.5, 137.2, 134.8, 116.2, 115.0, 71.8, 69.7,
61.1, 54.4, 39.1, 34.6, 30.7, 26.9, 18.9, 18.3, 13.9 ppm. HRMS (TOF
MS ES+): calcd. for C16H27NO2 288.1939 [M + Na]+; found
(10R,11S,13R)-10-Methyl-12-oxo-13-propyl-9-oxa-1-azabicyclo-
[9.1.1]tridecane (18b): Compound 18b was quantitatively obtained
as a pale-yellow oil from the cyclized β-lactam 17b (530 mg,
2.11 mmol) by using the procedure described above for the synthe-
sis of compound 3. TLC (CyHex/AcOEt, 5:4): Rf = 0.60. 1H NMR
(500 MHz, CDCl3, 25 °C): δ = 3.77 (m, 1 H), 3.73 (m, 1 H), 3.40–
3.54 (m, 3 H), 2.80 (m, 1 H), 2.51 (br. s, 1 H), 1.65 (m, 1 H), 1.27
(m, 3 H), 1.00–1.75 (several m, 10 H), 1.04 (d, JH,H = 6.9 Hz, 3 H),
0.87 (t, JH,H = 7.3 Hz, 3 H) ppm. 13C NMR (125 MHz, 25 °C): δ
= 168.0, 69.8, 67.5, 60.4, 51.8, 38.9, 33.9, 28.4, 27.2, 23.5, 22.4,
20.0, 19.2, 14.0 ppm. HRMS (TOF MS ES+): calcd. for
288.1928. IR (NaCl): ν
= 2872–2959, 1749, 1641 cm–1.
˜
max
(3S,4R)-1-(Pent-4-enyl)-3-[(1R)-1-(pent-4-enyloxy)ethyl]-4-propyl-2-
azetidinone (16b): The O-(pent-4-enyl) derivative was obtained ac-
cording to the procedure described above for the synthesis of com-
pound 14a from β-lactam 10c (300 mg, 1.34 mmol), with NaH
added in portions (3ϫ1.1 equiv.), 4-pentenyl bromide and no KI.
Flash chromatography (CyHex/AcOEt, 5:2) provided 16b as a pale-
yellow oil (269 mg, 68%). TLC (CyHex/AcOEt, 5:2): Rf = 0.50. 1H
NMR (500 MHz, CDCl3, 25 °C): δ = 5.77 (m, 2 H), 5.01 (m, 1 H),
4.98 (m, 1 H), 4.96 (m, 1 H), 4.92 (m, 1 H), 3.67 (qd, JH,H = 5.7,
JH,H = 6.2 Hz, 1 H), 3.54 (m, 1 H), 3.52 (m, 1 H), 3.37 (m, 1 H),
3.32 (m, 1 H), 2.91 (m, 1 H), 2.67 (dd, JH,H = 1.8, JH,H = 5.7 Hz,
1 H), 2.07 (m, 4 H), 1.72 (m, 1 H), 1.59 (m, 4 H), 1.37 (m, 3 H),
C H NO 254.2120 [M + H]+; found 254.2120. IR (NaCl): ν
˜
15 27
2
max
= 2860–2926, 1751 cm–1.
(11R,12S,14R)-11-Methyl-13-oxo-14-propyl-10-oxa-1-azabicyclo-
[10.1.1]tetradecane (18c): Compound 18c was quantitatively ob-
tained as a yellow gum from the cyclized β-lactam 17c (120 mg,
0.45 mmol) by using the procedure described above for the synthe-
sis of compound 3. TLC (CyHex/AcOEt, 5:4): Rf = 0.51. 1H NMR
(500 MHz, CDCl3, 25 °C): δ = 3.79 (qd, JH,H = 2.2, JH,H = 6.4 Hz,
1 H), 3.69 (m, 1 H), 3.61 (m, 1 H), 3.50 (m, 1 H), 3.22 (m, 1 H),
2.72 (m, 1 H), 2.62 (br. s, 1 H), 1.68 (m, 1 H), 1.24–1.61 (m, 13 H),
1.20 (m, 2 H), 1.08 (d, JH,H = 6.4 Hz, 3 H), 0.91 (t, JH,H = 7.3 Hz,
3 H) ppm. 13C NMR (125 MHz, 25 °C): δ = 168.7, 70.8, 69.6, 61.0,
52.2, 39.3, 34.4, 27.5, 26.3, 25.8, 25.7, 24.1, 19.1, 18.1, 14.0 ppm.
HRMS (TOF MS ES+): calcd. for C16H29NO2 290.2096 [M +
1.19 (d, JH,H = 6.2 Hz, 3 H), 0.94 (t, JH,H = 7.3 Hz, 3 H) ppm. 13
C
NMR (125 MHz, 25 °C): δ = 167.8, 138.2, 137.3, 115.1, 114.5, 72.5,
68.1, 61.3, 54.5, 39.3, 34.7, 30.8, 30.1, 29.1, 27.1, 19.0, 18.3,
14.1 ppm. HRMS (TOF MS ES+): calcd. C18H31NO2 316.2252 [M
+ Na]+; found 316.2250. IR (NaCl): νmax = 3077, 2872–2958, 1749,
˜
1641 cm–1.
(10R,11S,13R)-10-Methyl-12-oxo-13-propyl-9-oxa-1-azabicyclo-
[9.1.1]tridec-4-ene (17b): The cyclized compound 17b was obtained
from the corresponding precursor 15b (530 mg, 1.9 mmol) by using
Method B with 5 mol-% of Grubbs catalyst. After 24 h and the
usual workup, flash chromatography (CyHex/AcOEt, 5:1) provided
the desired β-lactam (395 mg, 83%) as a mixture of stereoisomers
in a 73:27 ratio. TLC (CyHex/AcOEt, 5:4): Rf = 0.37. GC: tr =
Na]+; found 290.2097. IR (NaCl): ν
= 2858–2955, 1747 cm–1.
˜
max
Prop-2-enyl 2-{(3S,4R)-3-[(1R)-1-(tert-Butyldimethylsilyloxy)ethyl]-
2-oxo-4-propyl-1-azetidinyl}acetate (19): NaH (60% dispersion in
1
31.2 min. H NMR (500 MHz, CDCl3, 25 °C; major isomer): δ =
5.03–5.37 (m, 2 H), 3.47–3.60 (m, 4 H), 3.32 (m, 1 H), 2.71 (m, 1 oil, 85 mg, 2.12 mmol, 1.2 equiv.) was added to a stirred solution
H), 2.49 (br. s, 1 H), 2.13 (m, 1 H), 2.00 (m, 1 H), 1.88 (m, 1 H),
of β-lactam 3 (480 mg, 1.77 mmol) in anhydrous DMF (15 mL) at
0 °C under argon. After 15 min, allyl bromoacetate (633 mg,
1.57 (m, 1 H), 1.50 (m, 2 H), 1.24 (m, 3 H), 0.95 (d, JH,H = 6.4 Hz,
3 H), 0.83 (t, JH,H = 7.3 Hz, 3 H) ppm. 13C NMR (125 MHz, 3.54 mmol, 2 equiv.) was injected and the mixture stirred for 1 h.
1768
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Eur. J. Org. Chem. 2009, 1757–1770

Potential Inhibitors of Penicillin-Binding Proteins
The reaction medium was then diluted with diethyl ether (50 mL)
and washed three times with brine. The organic layer was collected,
dried with MgSO4, and the solvent removed under reduced pres-
sure. The residue was purified by flash chromatography (CyHex/
cedure described above for the synthesis of compound 6. Flash
chromatography (CyHex/AcOEt, 5:2) provided the β-lactam 23 as
a yellow oil (545 mg, 77%). TLC (CyHex/AcOEt, 5:2): Rf = 0.45.
1H NMR (500 MHz, CDCl3, 25 °C): δ = 8.22 (d, JH,H = 8.4 Hz, 2
AcOEt, 5:1) to provide compound 19 as a yellow oil (380 mg, H), 7.53 (d, JH,H = 8.4 Hz, 2 H), 5.75 (ddt, JH,H = 6.4, JH,H = 10.3,
1
58%). TLC (CyHex/AcOEt, 5:2): Rf = 0.55. H NMR (500 MHz, JH,H = 17.1 Hz, 2 H), 5.26 (sharp AB q, 2 H), 5.15 (m, 1 H), 5.12
CDCl3, 25 °C): δ = 5.84 (ddt, JH,H = 5.9, JH,H = 10.3, JH,H
17.1 Hz, 1 H), 5.27 (dd, JH,H = 1.5, JH,H = 17.1 Hz, 1 H), 5.20 (dd,
JH,H = 1.5, JH,H = 10.3 Hz, 1 H), 4.56 (m, 2 H), 4.09 (qd, JH,H
=
(m, 1 H), 5.10 (m, 1 H), 5.01 (dd, JH,H = 1.5, JH,H = 17.1 Hz, 1
H), 4.99 (dd, JH,H = 1.5, JH,H = 10.3 Hz, 1 H), 4.35 (m, 1 H), 3.61
(m, 1 H), 2.86 (dd, JH,H = 2.0, JH,H = 8.8 Hz, 1 H), 2.66 (m, 2 H),
=
6.4, JH,H = 6.4 Hz, 1 H), 4.04 (d, JH,H = 17.9 Hz, 1 H), 3.79 (d, 2.34 (sharp m, 4 H), 1.79 (m, 1 H), 1.23 and 1.40 (2 m, 3 H), 1.32
JH,H = 17.9 Hz, 1 H), 3.68 (m, 1 H), 2.70 (dd, JH,H = 2.0, JH,H
=
(d, JH,H = 5.9 Hz, 3 H), 0.91 (t, JH,H = 7.3 Hz, 3 H) ppm. 13C
6.4 Hz, 1 H), 1.68 (m, 1 H), 1.42 (m, 1 H), 1.30 (m, 2 H), 1.18 (d, NMR (125 MHz, 25 °C): δ = 171.9, 169.2, 166.3, 147.7, 142.2,
JH,H = 6.4 Hz, 3 H), 0.89 (t, JH,H = 7.3 Hz, 3 H), 0.81 (s, 9 H), 136.4, 132.7, 128.6, 123.8, 118.7, 115.5, 68.6, 65.6, 60.4, 57.8, 54.5,
0.00 and 0.01 (2 s, 6 H) ppm. 13C NMR (125 MHz, 25 °C): δ =
168.0, 167.8, 131.3, 118.9, 66.0, 65.8, 63.8, 56.2, 41.6, 34.7, 25.6,
22.7, 19.4, 17.7, 14.1, –4.5, –4.9 ppm. HRMS (TOF MS ES+):
calcd. C19H35NO4Si 370.2414 [M + H]+; found 370.2398.
35.6, 34.9, 33.5, 28.6, 18.9, 18.6, 14.0 ppm. HRMS (TOF MS ES+):
calcd. for C25H32N2O7 495.2107 [M + Na]+; found 495.2115. IR
(NaCl): ν
= 3081, 2867–2961, 1737, 1638, 1601, 1523,
˜
max
1343 cm–1.
4-Nitrobenzyl 2-{(3S,4R)-3-[(1R)-1-(tert-Butyldimethylsilyloxy)-
ethyl]-2-oxo-4-propyl-1-azetidinyl}pent-4-enoate (21): A freshly pre-
pared solution of LiHMDS (3.52 mmol, 1.2 equiv.) in THF
(20 mL) was added to a stirred solution of β-lactam 19 (1.08 g,
2.93 mmol) in THF (9 mL) at –78 °C under argon over 30 min.
The solution was stirred for 15 min before the addition of TMSCl
(0.38 mL, 2.93 mmol, 1 equiv.). After a further 15 min at this tem-
perature, the reaction medium was heated at reflux for 4 h. The
solution was then cooled to 0 °C, and MeOH (5 mL) was added
dropwise. After a further 15 min of stirring, the solvents were re-
moved under reduced pressure, and the white paste obtained was
dissolved in a 1:1 mixture (100 mL) of diethyl ether/aq. HCl (3.3 ).
The organic layer was collected, washed three times with brine,
dried with MgSO4, filtered, and the solvent removed to provide a
yellow oil (1.15 g). The crude acid 20 (1.08 g, 2.93 mmol) was then
stirred in a solution of anhydrous DMF (25 mL) containing K2CO3
(606 mg, 4.39 mmol, 1.5 equiv.), Bu4NHSO4 (99 mg, 0.293 mmol,
0.1 equiv.) and p-nitrobenzyl bromide (1.265 g, 5.86 mmol, 2 equiv.)
at room temp. under argon for 21 h. The reaction medium was
then diluted with a 1:1 mixture (100 mL) of a diethyl ether/NH4Cl
solution. The organic layer was collected, washed three times with
brine (50 mL), dried with MgSO4, filtered, and the solvent re-
moved. The crude product was purified by flash chromatography
(CyHex/AcOEt, 5:1) to provide the ester 21 (1.264 g, 86%, yellow
oil) as a diastereoisomeric mixture (66:33). A sample of the major
diastereoisomer could be isolated for analyses. TLC (CyHex/Ac-
OEt, 5:2): Rf = 0.70. 1H NMR (500 MHz, CDCl3, 25 °C): δ = 8.25
(d, JH,H = 8.5 Hz, 2 H), 7.55 (d, JH,H = 8.5 Hz, 2 H), 5.80 (ddt,
4-Nitrobenzyl (10R,11S,13R)-10-Methyl-8,12-dioxo-13-propyl-9-
oxa-1-azabicyclo[9.1.1]tridec-4-ene-2-carboxylate (24): The cyclized
compound 24 was obtained from the corresponding precursor 23
(550 mg, 1.17 mmol) by using Method B with 2.5 mol-% of Grubbs
catalyst at room temp. After 24 h and the usual workup, flash
chromatography (CyHex/AcOEt, 1:1) provided the desired β-lac-
tam (350 mg, 67%, yellow oil) as a mixture of stereoisomers. TLC
(CyHex/AcOEt, 1:1): Rf = 0.67. 1H NMR (500 MHz, CDCl3,
25 °C; major isomer): δ = 8.16 (d, JH,H = 8.2 Hz, 2 H), 7.50 (d,
JH,H = 8.2 Hz, 2 H), 5.32–5.54 (m, 2 H), 5.35 (m, 1 H), 5.24 (sharp
AB q, 2 H), 3.75 (dd, JH,H = 4.9, JH,H = 10.3 Hz, 1 H), 3.58 (m, 1
H), 2.99 (m, 1 H), 2.77 (dd, JH,H = 1.8, JH,H = 2.0 Hz, 1 H), 2.50
(m, 1 H), 2.43 (m, 2 H), 2.29 (m, 2 H), 1.70 (m, 1 H), 1.44 (m, 1
H), 1.31 (m, 2 H), 1.19 (d, JH,H = 6.4 Hz, 3 H), 0.89 (t, JH,H
=
7.3 Hz, 3 H) ppm. 13C NMR (125 MHz, 25 °C): δ = 171.1, 169.3,
165.8, 147.6, 142.5, 134.0, 128.3, 125.8, 123.6, 65.6, 64.9, 59.7, 57.1,
55.3, 35.0, 34.4, 32.9, 27.0, 19.1, 19.0, 14.0 ppm. HRMS (TOF MS
ES+): calcd. for C23H28N2O7 467.1794 [M + Na]+; found 467.1807.
IR (NaCl): ν
= 2872–2959, 1751, 1736, 1606, 1522, 1346 cm–1.
˜
max
(10R,11S,13R)-10-Methyl-8,12-dioxo-13-propyl-9-oxa-1-azabicyclo-
[9.1.1]tridecane-2-carboxylic Acid (25): Crude compound 25 was
quantitatively obtained as a yellow gum from the cyclized β-lactam
24 (80 mg, 0.18 mmol) by using the procedure described above for
the synthesis of compound 3. TLC (CyHex/AcOEt, 1:1): Rf = 0.65.
1H NMR (500 MHz, CDCl3, 25 °C; major stereoisomer): δ = 9.46
(br. s, 1 H), 5.41 (qd, JH,H = 1.7, JH,H = 6.6 Hz, 1 H), 3.70 (ddd,
JH,H = 1.7, JH,H = 4.4, JH,H = 9.6 Hz, 1 H), 3.61 (dd, JH,H = 3.2,
JH,H = 10.8 Hz, 1 H), 2.83 (dd, JH,H = 1.7, JH,H = 1.7 Hz, 1 H),
2.32 (m, 2 H), 2.27 (m, 1 H), 2.03 (m, 1 H), 1.79 (m, 1 H), 1.35
(m, 2 H), 1.26 (d, JH,H = 6.6 Hz, 3 H), 1.21–1.75 (4 m, 7 H), 0.98
(t, JH,H = 7.3 Hz, 3 H) ppm. 13C NMR (125 MHz, 25 °C): δ =
173.1, 172.1, 167.9, 65.5, 59.5, 59.3, 56.6, 34.4, 33.8, 27.4, 27.2,
24.6, 23.4, 19.4, 19.0, 14.1 ppm. HRMS (TOF MS ES+): calcd. for
JH,H = 6.8, JH,H = 10.3, JH,H = 17.1 Hz, 1 H), 5.26 (ABq, JH,H
=
13.2 Hz, 2 H), 5.20 (dd, JH,H = 1.0, JH,H = 17.1 Hz, 1 H), 5.15 (d,
JH,H = 10.3 Hz, 1 H), 4.41 (dd, JH,H = 6.4, JH,H = 6.8 Hz, 1 H),
4.06 (qd, JH,H = 6.4, JH,H = 6.4 Hz, 1 H), 3.60 (m, 1 H), 2.72 (m,
1 H), 2.68 (dd, JH,H = 2.0, JH,H = 6.4 Hz, 1 H), 2.64 (m, 1 H), 1.68
(m, 1 H), 1.34 (m, 3 H), 1.24 (d, 3 H), 0.88 (m, 12 H), 0.04 and
0.07 (2 s, 6 H) ppm. 13C NMR (125 MHz, 25 °C): δ = 169.3, 167.7,
147.4, 142.3, 132.9, 128.5, 123.7, 118.5, 65.9, 65.3, 63.1, 56.8, 54.4,
35.8, 35.6, 25.6, 22.7, 19.3, 17.7, 14.1, –4.6, –4.8 ppm. HRMS (TOF
MS ES+): calcd. for C26H40N2O6 505.2734 [M + H]+; found
C H NO 334.1630 [M + Na]+; found 334.1618. IR (NaCl): ν
˜
16 25
5
max
= 2869–2932, 1747 (br.) cm–1.
Acknowledgments
505.2733. IR (NaCl): ν
= 3080, 2856–2957, 1747, 1643, 1606,
˜
max
1526, 1348 cm–1. Minor stereoisomer: TLC (CyHex/AcOEt, 5:2):
This work was supported by the PAI (Pôle d’Attraction Interuni-
versitaire, Belgium) with contracts P5/33 and P6/19, and the FRS-
Rf = 0.62.
4-Nitrobenzyl 2-{(3S,4R)-3-[(1R)-1-(Pent-4-enoyloxy)ethyl]-2-oxo-4- FNRS (Fonds de la Recherche Scientifique, Belgium) for the high-
propyl-1-azetidinyl}pent-4-enoate (23): After the usual deprotection
of the silyl group of β-lactam 21 (745 mg, 1.48 mmol), the free
alcohol 22 quantitatively obtained (580 mg, 1.48 mmol) was used
without purification in the O-acylation step according to the pro-
performance computing systems installed at Liège and Louvain-la-
Neuve. Biochemical evaluations on bacterial enzymes were per-
formed by Dr. Valérie Duval and Ir. Stana Grusbisic at the CIP
(Centre d’Ingénierie des Protéines) of the Université de Liège. The
Eur. J. Org. Chem. 2009, 1757–1770
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1769

A. Urbach, G. Dive, J. Marchand-Brynaert
FULL PAPER
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Received: December 1, 2008
Published Online: February 5, 2009
1770
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 1757–1770