1-Alkoxycarbonyl-3-halogenoazetidin-2-ones as elastase (PPE) inhibitors

Article abstract of DOI:10.1016/S0968-0896(02)00304-8

A series of 1-alkoxycarbonyl-3-halogenoazetidin-2-ones, designed as potential suicide inhibitors of serine proteases, has been synthesized and evaluated against porcine pancreatic elastase (PPE). All the compounds were transient inhibitors, their activity depending mainly on the nature of the halogen substituent: bromo- and iodo- derivatives are more active (K_i ～2-22 μM) than 3-chloroazetidinones (K_i ～20-150 μM). The lipophilicity of the N-1 substituent appeared to exert a slightly positive effect.

Full text of DOI:10.1016/S0968-0896(02)00304-8

Bioorganic & Medicinal Chemistry 10 (2002) 3955–3964
1-Alkoxycarbonyl-3-halogenoazetidin-2-ones as
Elastase (PPE) Inhibitors
Stephane Gerard, Gaetan Nollet, Jennifer Vande Put and
Jacqueline Marchand-Brynaert*
´ ´ ´
Unite de Chimie Organique et Medicinale, Universite catholique de Louvain, Batiment Lavoisier,
Place Louis Pasteur 1, B-1348Louvain-la-Neuve, Belgium
ˆ
Received 25 February 2002; accepted 10 July 2002
Abstract—A series of 1-alkoxycarbonyl-3-halogenoazetidin-2-ones, designed as potential suicide inhibitors of serine proteases, has
been synthesized and evaluated against porcine pancreatic elastase (PPE). All the compounds were transient inhibitors, their
activity depending mainly on the nature of the halogen substituent: bromo- and iodo- derivatives are more active (Ki ꢀ2–22 mM)
than 3-chloroazetidinones (Ki ꢀ20–150 mM). The lipophilicity of the N-1 substituent appeared to exert a slightly positive effect.
# 2002 Elsevier Science Ltd. All rights reserved.
Introduction
residue of the N-alkoxycarbonyl substituent was chosen
as a small electron-withdrawing group (R1=CH2CX3)
susceptible to improve the nucleofugal ability of OR1.
Experimentally, enzyme-catalyzed cleavage of the N1–
C2azetidinone bond could be observed, but not the
departure of the potential leaving group; molecules A
(R2=Br; R1=CH2Ph, CH2CCl3, CH2CF3) are transient
inhibitors of PPE (slowly deacylating substrates).11
Inhibition of serine proteases by bicyclic azetidinones
has been widely documented, since the discovery of the
naturally-occurring penam and cephem antibiotics till
the development of synthetic penem, carbapenem and
cephemsulfone derivatives as inactivators of bacterial
D,D-peptidases and b-lactamases1,2 on the one hand, and
mammalian elastases3 on the other hand. Adequately
substituted monocyclic azetidinones have been further
considered as lead-structures for the inhibition of the
previous enzymes4,5 and other serine enzymes such as
prostate specific antigen (PSA),6 thrombin,7 human
cytomegalovirus protease (HCMV),8 and human chy-
mase.9 The design of potentially active structures relies
upon the combination of chemical reactivity (activation
towards nucleophilic attack by a serine residue) and
enzymic recognition (selective fit into the target-enzyme
active site).10
In the continuation of this preliminary study, we have
now examined a series of azetidinones A (Fig. 1) equip-
ped with a lipophilic R1 substituent in order to improve
the interaction of the potential leaving group with the
enzyme subsite S20.12À15 We have also considered the
role of the R2 substituent, fitting in the subsite S1, by
the replacement of bromine with chlorine and iodine.
Surprisingly, C3 monohalogenated and C4 unsub-
stituted azetidinones have been scarcely described in the
field of organic synthesis,16À19 as well as in the partic-
ular domain of serine proteases inhibition.20,21
A few years ago, we disclosed the activity of three
representatives of 1-alkoxycarbonyl-3-bromoazetidin-2-
ones towards porcine pancreatic elastase (PPE).11 Our
molecules were constructed in order to behave as suicide
inhibitors by unmasking an isocyanate function under
processing by the enzyme (Fig. 1). For that, the R1
Results
Synthesis
(3S)-(tert-Butyloxycarbonyl)aminoazetidin-2-one
1,
obtained in five steps from (L)-serine,22 was chosen as
the starting material for introducing the alkoxycarbonyl
group at position N1. Treatment of 1 with lithium
*Corresponding author. Tel.:+32-10-472740; fax:+32-10-474168;
e-mail: marchand@chim.ucl.ac.be
0968-0896/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0968-0896(02)00304-8

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3956
Figure 1. Expected mechanism of suicide-inhibition of elastase.
hexamethyldisilazide (LiHMDS) at low temperature
followed by the addition of chloroformates 2 gave the
N-1 substituted azetidinones 3, contaminated with the
bis-acylated compounds 4 (Scheme 1). Reagents 2,
offering the various lipophilic chains R1, were prepared
by reaction of the corresponding alcohols with tri-
phosgene and pyridine.23,24 Substitution products 3 and
4 have been isolated by column-chromatography on
silica gel and characterized as usual (see Experimental,
and Table 1, entries 1–7 and 8–14).
with N-ethyl morpholine. 3-Chloroazetidinones 8a–c
and 8f were similarly prepared (Scheme 3) and purified
(Table 1, entries 25–28). However, in the crude mix-
tures, the presence of the corresponding 3-hydroxyl
derivatives 10 was visible in the 1H NMR spectra (H3 at
4.92 d), resulting from a competition between chloride
and water as nucleophiles. Such side-products 10 could
not be detected during the synthesis of 3-bromoazetidi-
nones 7a–g, nor in the case of 3-iodoazetidinones 9a–b
(Table 1, entries 29–30), due to the good nucleophilicity
of bromide and iodide.
Since azetidinones 3 were not stable in neat tri-
fluoroacetic acid (TFA), we examined other methods of
Boc deprotection under neutral conditions. By using
ammonium cerium(IV) nitrate (CAN) in refluxing ace-
tonitrile,25 we could easily cleave the Boc group on bis-
acylated derivatives 4 (Scheme 2; Table 1, entries 15–
17); however, the same method failed with precursors 3,
giving degradation products only. In this case, the best
way to remove Boc group remained the acidic treat-
ment, but under smooth conditions such as TFA in di-
chloromethane (1:10, v/v) or 3 N HCl in ethyl acetate
(1:10, v/v).26 The free amines 6 were not isolated, and
directly transformed into the corresponding diazonium
salts which were substituted in situ by a nucleophile
(potassium bromide, chloride or iodide), according to a
procedure27 initially developed in the cephem series
(Scheme 3). Applied to C4-unsubstituted monocyclic
azetidinones, this reaction led to racemization.11
All the 3-substituted azetidinones were characterized by
1
a typical ABX pattern in H NMR for protons H3, H4
and H40: they appeared, respectively, at d 4.8–4.9
(Jcisꢀ5.8 Hz and Jtransꢀ2.9 Hz), d 3.6–3.8 and 3.9–4.2
(JABꢀ7.8 Hz). In 13C NMR, the b-lactam and urethane
carbonyls gave signals at d 160–165 and 148–150,
respectively. Carbon C3 was found at d 55–58 for the
NHBoc series, at d 40 for the bromo series, at d 49 for
the chloro derivatives and at d 10 for the iodo deriva-
tives. In IR, the b-lactam and urethane carbonyls
showed bands at 1820–1825 and 1725–1735 cmÀ1
respectively.
,
Biochemical Evaluation
Suicide inhibition of serine enzymes by synthetic inhibi-
tors possessing a masked isocyanate function is scarcely
described in the literature; such an electrophilic function
usually results from Lossen and related rearrange-
ments.28À30 The mechanism we are interested in relies
upon a simple elimination reaction initiated by the b-
lactam ring opening. Some precedents exist about the
We first synthesized 3-bromoazetidinones 7a–g (Table 1,
entries 18–24). Purification of these compounds was a
difficult task due to their instability on normal silica gel.
Thus, preparative thin layer chromatographies were
performed on silica gel plates previously neutralized
Scheme 1. Synthesis of compounds 3–4.

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S. Gerard et al. / Bioorg. Med. Chem. 10 (2002) 3955–3964
3957
Table 1. Yield of compounds 3–9
Entry
R1
C3 substituent
Compd
Rf (solvent)a
Yield (%)b
1
2PhCH
PhCH2
t-BuOCONH
t-BuOCONH
t-BuOCONH
t-BuOCONH
t-BuOCONH
t-BuOCONH
t-BuOCONH
3a
3b
3c
3d
3e
3f
0.4 (A)
0.3 (A)
0.3 (A)
0.4 (A)
0.4 (A)
0.3 (A)
0.4 (A)
77
53
34
70
37
55
33
2CH2
3
4
5
6
7
PhCH2CH2CH2
pMeO-Ph-CH2CH2
pF-Ph-CH2CH2
Fluorenyl-CH2
2-Indanyl
3g
8
9
PhCH2
PhCH2CH2
PhCH2OCON(Boc)
PhCH2CH2OCON(Boc)
4a
4b
4c
4d
4e
4f
0.9 (A)
0.9 (A)
0.9 (A)
0.8 (A)
0.9 (A)
0.8 (A)
0.9 (A)
12
15
20
11
3
10
11
12
13
14
PhCH2CH2CH2
pMeO-Ph-CH2CH2
pF-Ph-CH2CH2
Fluorenyl-CH2
2-Indanyl
PhCH2CH2CH2OCON(Boc)
pMeO-PhCH2CH2OCON(Boc)
pF-PhCH2CH2OCON(Boc)
Fluorenyl-CH2OCON(Boc)
2-Indanyl-OCON(Boc)
12
21
4g
15
16
17
PhCH2
PhCH2CH2
Fluorenyl-CH2
PhCH2OCONH
PhCH2CH2OCONH
Fluorenyl-CH2OCONH
5a
5b
5f
0.4 (A)
0.4 (A)
0.6 (A)
57
48
63
18
19
20
21
22
23
24
PhCH2
PhCH2CH2
Br
Br
Br
Br
Br
Br
Br
7a
7b
7c
7d
7e
7f
0.4 (B)
0.4 (B)
0.5 (B)
0.3 (B)
0.4 (B)
0.3 (B)
0.4 (B)
71
69
40
47
39
39
50
PhCH2CH2CH2
pMeO-Ph-CH2CH2
pF-Ph-CH2CH2
Fluorenyl-CH2
2-Indanyl
7g
25
26
27
28
PhCH2
PhCH2CH2
PhCH2CH2CH2
Fluorenyl-CH2
Cl
Cl
Cl
Cl
8a
8b
8c
8f
0.4 (B)
0.4 (B)
0.4 (B)
0.3 (B)
31
34
63
47
29
30
PhCH2
PhCH2CH2
I
I
9a
9b
0.4 (B)
0.4 (B)
67
65
aA=CH2Cl2–AcOEt, 95:5 B=CH2Cl2..
bIsolated by column chromatography (entries 1–17) or preparative TLC (entries 18–30).
Scheme 3. Synthesis of compounds 7–10.
Scheme 2. Deprotection of compounds 3–4.
possible formation of isocyanate intermediates by
chemical hydrolysis of activated (N-acyl or N-sulfonyl)
carbamates; this has been discussed previously.24
We designed compounds 7–9 (see Table 1) as b-lactamic
inhibitors of elastases based on our preliminary results11
and the following considerations: (a) the C3 sub-
stituents, fitting the S1 pocket, are halogens21 and gem-
dihalogens31 in the N-aryl-azetidin-2-ones developed by
Wakselman et al.; the order of activity (ClꢀF>Br)
does not strictly reflect the electron-withdrawing effects
of these substituents; (b) the C4 substituents of the
Merck’s inhibitors, such as L-694.458, act as leaving
groups and do not strictly interact with the enzyme;32
(c) The N1 substituents of the previous Merck’s azeti-
dinones, fitting the S0 pockets of elastase, are bulky and
lipophilic urethane groups derived from substituted
benzylamines33 (Scheme 4). Accordingly, we selected as
C3 and N1 substituents of the general structure A (Fig. 1)
a series of halogen and arylalkyloxycarbonyl groups,
Scheme 4. Reference compounds.
respectively; the C4 substituent was suppressed, since the
potential leaving group is now part of the N1 substituent.
Azetidinones 7–9 were evaluated for their inhibitory
effect on porcine pancreatic elastase (PPE). The rates of
enzyme-catalyzed hydrolysis of N-succinyl-Ala-Ala-Ala-
p-nitroanilide (substrate) were measured in the presence
of different concentrations of inhibitors. The variation

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S. Gerard et al. / Bioorg. Med. Chem. 10 (2002) 3955–3964
3958
Table 2. Inhibitory activity
Entry Compd Ki (mM) Compd Ki (mM) Compd Ki (mM)
1
2
3
4
5
6
7
7a
7b
7c
7d
7e
7f
2–5
18–20
20–22
7–11
13–15
5–7
8a
8b
8c
45–47
159–161
65–70
9a
9b
6–8
9–11
8f
19–21
7g
5–10
compounds are inactive or slightly active (Ki>103
mM).24 Synthetic intermediates 3 and 5 bearing (3S)-
(alkoxycarbonyl)amino substituents were also tested
against PPE and found to be inactive.34
Figure 2. Inhibition of PPE.
Discussion
of the absorbance at 410 nm was recorded as a function
of time:24 Figure 2shows typical curves with the ‘S’
shape observed at the begining of the reaction (illustra-
tion with compound 7a). Plots of V/Vi, corresponding
to the ratios of initial rates of hydrolysis in the absence
and the presence of inhibitors, versus the concentration
of inhibitor gave a straight line which slope corresponds
to 1/Ki. The measured inhibition constants (Ki) are col-
lected in Table 2.
1-Alkoxycarbonyl-3-halogenoazetidin-2-ones constitute a
class of serine protease inhibitors illustrated by their activ-
ity against porcine pancreatic elastase. This enzyme could
be considered as a good model of human leukocyte elas-
tase (HLE) in view of the great similarity of the respective
active sites.35 Compounds 7–9 transitorily block PPE with
apparent inhibition constants in the micromolar range.
Their mechanism most probably occurs via an acyl-
enzyme intermediate which slowly deacylates.11
All 3-bromoazetidinones 7 (Table 2, first column)
exhibited quite similar activities with Ki values com-
prised between 2and 22 mM; the best inhibitors corre-
sponding to R1 residues as benzyl (7a) or less flexible
fluorenylmethyl (7f) and 2-indanyl (7g) groups. 3-
Chloroazetidinones 8 (second column) appeared sys-
tematically about 5- to 10-fold less potent than the cor-
responding bromo derivatives. This result in opposite to
the halogen effect reported by Wakselman et al.31 sti-
mulated our interest in the preparation and evaluation
of some iodo compounds. Unfortunately, we found that
3-iodoazetidinones 9 (third column) are not better, but
equally potent as the corresponding 3-bromoazetidi-
nones 7. The lipophilicity of the R1 substituent
appeared to exert a slightly positive effect since chloro-
azetidinone 8f (R1=fluorenyl) was also equally potent
as compounds 7b and 7c. All tested azetidinones
behaved as transient inhibitors of PPE: complete
enzyme activity was restored after about 3 h (see
Experimental). Thus, the expected suicide mechanism of
Figure 1 did not occur.
The C3 halogen substituent certainly increases the azeti-
dinone chemical reactivity towards nucleophilic attack by
Ser-195. This effect has been evaluated by theoretical
methods.36,37 The cleavage of the N1–C2azetidinone
bond is mimicked by a catalytic environment made of an
imidazole as model of His-57, a water molecule as a tran-
sient vehicle of the proton, and the side chain of Ser-195
including the amide bond of the backbone which is
involved in the stabilization of the oxyanion hole (Fig. 3).
Such a model of concerted mechanism has been pre-
viously validated on class-A b-lactamases and enzymes of
the trypsin family.38 The ꢀG values have been computed,
at the ab initio level with a minimal basis set, by reference
to the isolated partners.24 The bromine electronic effect is
expressed by the decrease of the energy barrier of about 3.2
kcal/mol. Inductive effects of bromine (Taft sI para-
meter=0.44) and chlorine (Taft sI parameter=0.46) are
slightly different; however the biological activities of 7a
(X=Br) and 8a (X=Cl) are significantly different (one
order of magnitude), and in favour of the azetidinone
bearing the less electronegative bromine substituent. This
1
We have previously demonstrated, by H NMR analy-
sis, that the product of enzymic hydrolysis of 7a is the
N-(benzyloxycarbonyl)-b-aminoacid resulting from aze-
tidinone ring opening.11 Moreover, the enantio-
selectivity of this PPE-catalyzed reaction in favour of
the (R)-enantiomer has been established by GC mon-
itoring on a chiral phase.11 Presently, compounds 7–9
were evaluated as racemic mixtures, and their selectivity
of recognition was no more tested.
We have controlled that C3-halogen substituent is neces-
sary for biological activity: related C3-unsubstituted a–g
Figure 3. Theoretical evaluation of nucleophilic attack in a model of
elastase active site.

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S. Gerard et al. / Bioorg. Med. Chem. 10 (2002) 3955–3964
3959
effect is not still further enhanced with the iodo com-
pound 9a (Taft sI parameter=0.39). The experimental
order of activity (Br ꢀI>Cl ꢁ H) could indeed reflect
the best fit of the C3 substituent into the enzyme pocket
S1, rather than the activating electronic effect only.
Molecular volumes given by molar refractivity (MR)
parameters are 13.9, 8.9 and 6.0 for I, Br and Cl,
respectively.39 In the seminal work of the Merck’s
group40 concerning cephem derivatives as elastase inhi-
bitors, the selected b-lactam substituent was OCH3 (MR
parameter=7.9 and Taft sI parameter=0.27).
mg in 200 mL of N-methyl pyrrolidone (NMP) diluted
with Tris buffer (20 mL at 100 mM, pH 7.5 solution)]
were added 20 mL of the solution of the tested
compound (10À2–10À4 M in NMP) and 67 mL of the
solution of elastase [6Â10À6 M in acetate buffer (50
mM, pH 5)]. The appearance of the substrate hydrolysis
product (p-nitroaniline) was measured (with a Cary 210)
at 410 nm as a function of time. Plots of V/Vi versus [I]
(ratios of initial rates of hydrolysis in the absence and in
the presence of inhibitors) gave the inhibition constants
indicated in the Table 2. All experiments were per-
formed two or three times.
By varying the nature of the R1 group making part of
the N1 alkyloxycarbonyl substituent, we could not
improve the activity of the azetidinones 7–9. The factors
considered were: the length of the spacer connecting the
aromatic residue to the carbamate function, the steric
nature and substitution of the aromatic residue, and the
flexibility of the N1 side chain. Our preliminary results11
were confirmed: the suicide mechanism (irreversible
inhibition) does not operate, compounds 7–9 behave as
transient inhibitors (or slow substrates). We are cur-
rently examining the possibility to replace the alkyloxy
residue (OR1) with an alkylthioxy residue (SR1) acting
as a better potential leaving group.
The reversibility of the inhibition was controlled by the
incubation/dilution method. The incubation solution
consisted of 5 mL of inhibitor solution (10À3 M in
DMSO), 34 mL of elastase solution (2.5Â10À4 M in ace-
tate buffer, 50 mM, pH 5) and 161 mL of Tris buffer (100
mM, pH 7.5). At various times (0, 5, 10, 15, 20, 30 min),
10 mL of the incubation solution were dissolved in 2mL
of the substrate solution (10À4 M in Tris buffer), and the
enzyme activity was measured as before. No decrease of
activity was recorded as a function of incubation time.
General procedure for the preparation of chloroformates
(2)
Pyridine (1.01 mL, 12.5 mmol) was added dropwise (over
2h) to an ice-cold solution of triphosgene (1.19 g, 4 mmol)
in dry toluene (10 mL). After 1 h stirring at 0 ꢂC, alcohol
(10 mmol) was added dropwise (over 30 min). The mixture
was allowed to reach room temperature and stirred over-
night, then filtered. The precipitate was rinsed twice with
toluene (2Â20 mL). Concentration of the filtrates under
vacuum gave crude 2 (75–85% yield) which was directly
used in the acylation reaction of azetidinone 1.
Experimental
General
Reagents and solvents were purchased from Acros
chimica, Aldrich or Fluka. Porcine pancreatic elastase
(type 1) and N-succinyl-l-alanyl-l-alanyl-l-alanyl-p-
nitroanilide were obtained from Sigma Chemical Co.
Tetrahydrofuran was dried with sodium/benzophenone,
then distilled. Column chromatographies were carried
out with silica gel 60 (70–230 mesh ASTM) supplied by
Merck. Preparative chromatographies were performed
on silica gel plates 60F254 (Merck) of 2mm thichness
previously neutralised with N-ethyl morpholine. The IR
spectra were recorded with a Perkin-Elmer 1710 instru-
ment, only the most significant absorption bands being
reported. The mass spectra were obtained with a Finni-
gan MAT TSQ-70 instrument. The microanalyses were
performed at the Christopher Ingold Laboratories of
the University College, London (Dr. A. Stones). The
melting points were determined with an Electrothermal
microscope and are uncorrected. The 1H and 13C NMR
spectra were recorded on Varian Gemini 300 (at
300 MHz for proton and 75 MHz for carbon) or Brucker
AM-500 spectrometers (at 500 MHz for proton and
125 MHz for carbon); the chemical shifts are reported in
ppm (d) downfield from tetramethylsilane (internal stan-
dard). The high resolution mass spectra were obtained at
the University of Mons, Belgium (Prof. R. Flammang).
The optical rotations (Æ0.1ꢂ) were determined with a
Perkin-Elmer 241 MC polarimeter.
Chloroformates 2a and 2f are commercially available.
Chloroformates 2b, 2c, and 2g have been described
elsewhere.24
p-Methoxyphenethyl chloroformate (2d). 1H NMR
(CDCl3, 300 MHz) d 3.06 (t, J=6.9 Hz, 2H, CH2Ar),
3.89 (s, 3H, OCH3), 4.55 (t, J=6.9 Hz, 2H, OCH2), 6.95
(d, J=8.8 Hz, 2H, Ar), 7.22 (d, J=8.8 Hz, 2H, Ar). 13C
NMR (CDCl3, 75 MHz) d 33.3 (CH2), 54.8 (OCH3),
72.2 (OCH2), 113.7 (CHAr), 129.5 (CHAr), 140.6 (CAr),
145.8 (CAr), 150.0 (CO).
p-Fluorophenethyl chloroformate (2e). 1H NMR (CDCl3,
300 MHz) d 3.01 (t, J=6.7 Hz, 2H, CH2Ar), 4.48 (t,
J=6.7 Hz, 2H, OCH2), 6.99–7.05 (m, 2H, Ar), 7.16–
7.21 (m, 2H, Ar). 13C NMR (CDCl3, 75 MHz) d 34.1
(CH2), 72.2 (OCH2), 115.8 (CHAr), 130.5 (CHAr), 132.1
(CAr), 150.9 (CO), 163.8 (CF).
General procedure for the preparation of 1-
alkoxycarbonyl-(3S)-(t-butoxycarbonyl) aminoazetidin-
2-ones (3) and 1-alkoxycarbonyl-(3S)-(t-butoxycarbonyl)
(alkoxycarbonyl) aminoazetidin-2-ones (4)
Assay of PPE (porcine pancreatic elastase)
To 2mL of the solution of substrate (solution of N-
succinyl-l-alanyl-l-alanyl-l-alanyl-p-nitroanilide
To a solution of azetidinone 1 (1 equiv) in dry THF (1
mmol/10 mL), was added, at À78 ꢂC under argon
[2.7

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S. Gerard et al. / Bioorg. Med. Chem. 10 (2002) 3955–3964
3960
atmosphere, a solution of LiHMDS (1 equiv) in THF
(1 mmol/5 mL), dropwise over 15 min. After a further
15 min of stirring at À78 ꢂC, a solution of crude
chloroformate 2 (1 equiv) in THF (1 mmol/mL) was
added. The mixture was stirred for 1 h at À78 ꢂC and 1
h at room temperature, then poured into water.
Extraction with CH2Cl2 (three times), washing with
brine, drying over MgSO4 and concentration under
vacuum gave crude 3 and 4. Column chromatography
on silica gel (elution with CH2Cl2–EtOAc, 95:5; then
90:10) furnished 4 (minor product, eluting first) and 3
(major product).
1-(40 -Methoxy-phenethyloxycarbonyl)-3S-(t-butoxycar-
bonyl) aminoazetidin-2-one (3d). Yield from 1 mmol of
1: 254 mg (70%) as a colorless oil; IR (film) 3436, 2985,
1820, 1720 cmÀ1 1H NMR (acetone-d6, 300 MHz) d
;
1.40 (s, 9H, tBu), 2.87 (t, J=6.8 Hz, 2H, CH2Ar), 3.66
(dd, J=6.2and 3.8 Hz, 1H, H-4), 3.76 (s, 3H, OCH ),
3
0
3.83 (dd, J=6.8 and 6.2Hz, 1H, H-4 ), 4.30 (t, J=6.8
Hz, 2H, OCH2), 4.83 (ddd, J=8.1 Hz, 6.8 Hz and 3.8
Hz, 1H, H-3), 6.87 (d, J=8.1 Hz, 1H, NH), 6.95 (d,
J=8.8 Hz, 2H, Ar), 7.22 (d, J=8.8 Hz, 2H, Ar); 13C
NMR (acetone-d6, 75 MHz)
d 28.7 (CH3), 35.3
(CH2Ar), 46.8 (C-4), 55.6 (OCH3), 58.3 (C-3), 67.8
(OCH2), 80.1 (C–O), 114.8 (CHAr), 130.9 (CHAr), 131.2
(CAr), 150.0 (C¼O carbamate), 155.6 (C¼O Boc), 159.6
(CAr), 165.7 (C-2); MS (CI) m/z 363 (M-1). Anal. calcd
for C18H24N2O6: C, 59.33; H, 6.64. Found:C, 59.18; H,
6.76%.
1-Benzyloxycarbonyl-3S-(t-butoxycarbonyl) aminoazeti-
din-2-one (3a). Yield from 1 mmol of 1: 247 mg (77%)
20
D
as a white solid; mp 147.5–148.5 ꢂC; ½aŠ À1.9 (c 0.1,
1
CH2Cl2); IR (KBr) 3366, 2977, 1816, 1713 cmÀ1; H
NMR (acetone-d6, 300 MHz) d 1.41 (s, 9H, tBu), 3.71
(dd, J=6.4 Hz and 3.7 Hz, 1H, H-4), 3.91 (dd, J=6.4
Hz and 5.8 Hz, 1H, H-40), 4.85 (ddd, J=7.9 Hz, 5.8 Hz
and 3.7 Hz, 1H, H-3), 5.25 (s, 2H, OCH2), 6.88 (d,
J=7.9 Hz, 1H, NH), 7.25–7.50 (m, 5H, Ph); 13C NMR
(acetone-d6, 75 MHz) d 28.4 (CH3), 46.8 (C-4), 58.1 (C-
3), 68.1 (OCH2), 80.2 (C–O), 128.9, 129.1 and 129.3
(CHAr), 136.7 (CAr), 149.9 (C¼O carbamate), 155.8
(C¼O Boc), 165.8 (C-2); MS (FAB+) m/z 321 (MH+).
Anal. calcd for C16H20N2O5. H2O: C, 56.80; H, 5.92; N,
8.28. Found: C, 56.94; H, 5.96; N, 7.96%.
1-(40 -Fluoro-phenethyloxycarbonyl)-3S-(t-butoxycarbo-
nyl) aminoazetidin-2-one (3e). Yield from 1 mmol of 1:
131 mg (37%) as a white solid; mp 121.5–122.5 ꢂC;
½aŠ20+8.1 (c 1.2, CHCl3); IR (KBr) 3443, 2984, 1821,
D
1
1721 cmÀ1; H NMR (acetone-d6, 300 MHz) d 1.41 (s,
9H, tBu), 2.98 (t, J=6.6 Hz, 2H, CH2Ar), 3.66 (dd,
J=6.3 and 3.8 Hz, 1H, H-4), 3.85 (t, J=6.3 and 6.3 Hz,
1H, H-40), 4.34 (t, J=6.6 Hz, 2H, OCH2), 4.83 (ddd,
J=8.4 Hz, 6.3 and 3.8 Hz, 1H, H-3), 6.85 (d, J=8.4 Hz,
1H, NH), 7.05 (t, J=8.5 Hz, 2H, Ar), 7.35 (dd, J=8.5
and 5.1 Hz, 2H, Ar); 13C NMR (acetone-d6, 75 MHz) d
28.8 (CH3), 34.9 (CH2Ar), 46.9 (C-4), 58.3 (C-3), 67.5
(OCH2), 80.2(C–O), 116.0 (CH Ar), 131.8 (CHAr), 135.0
(CAr), 150.0 (C¼O carbamate), 155.8 (C¼O Boc), 160.3
(C–F), 165.8 (C-2); MS (CI) m/z 351 (C17H21N2O5F,
MÀ1), 123, 109, 96.
1-Phenethyloxycarbonyl-3S-(t-butoxycarbonyl) amino-
azetidin-2-one (3b). Yield from 1 mmol of 1: 176 mg
20
D
(53%) as a colorless oil; ½aŠ À5.6 (c 5.35, CH3OH);
1
IR (film) 3369, 2977, 1819, 1712 cmÀ1; H NMR (ace-
tone-d6, 300 MHz) d 1.41 (s, 9H, tBu), 2.90 (t, J=7.0
Hz, 2H, CH2Ph), 3.67 (dd, J=6.3 and 3.8 Hz, 1H,
H-4), 3.86 (dd, J=6.6 and 6.3, 1H, H-40), 4.23 (t,
J=7.0 Hz, OCH2), 4.84 (ddd, J=8.0, 6.6 and 3.8 Hz,
H-3), 6.85 (d, J=8.0 Hz, 1H, NH), 7.20–7.36 (m, 5H,
Ph); 13C NMR (acetone-d6, 75 MHz) d 28.4 (CH3), 35.9
(CH2Ph), 47.0 (C-4), 58.4 (C-3), 67.5 (OCH2), 80.5
(C–O), 127.5, 129.4 and 129.9 (CHAr), 130.1 (CAr),
150.0 (C¼O carbamate), 155.8 (C¼O Boc), 165.8 (C-2);
MS (CI) m/z 333 (MÀ1). Anal. calcd for C17H22N2O5:
C, 61.07; H, 6.63; N, 8.37. Found: C, 61.31; H, 6.75;
N, 8.19%.
1-(90 -Fluorenylmethoxycarbonyl)-3S-(t-butoxycarbonyl)
aminoazetidin-2-one (3f). Yield from 1 mmol of 1: 2 2 6
mg (55%) as a white solid; mp 129.5–130.5 ꢂC;
½aŠ20+12.3 (c 2.8, CHCl3); IR (KBr) 3374, 2977, 1817,
D
1
1716 cmÀ1; H NMR (CDCl3, 500 MHz) d 1.41 (s, 9H,
tBu), 3.76 (dd, J=6.6 Hz and 3.7 Hz, 1H, H-4), 3.88
(dd, J=6.6 and 6.6 Hz, 1H, H-40), 4.30 (dd, J=13.1 and
7.4 Hz, 1H, OCHA), 4.32(dd, J=13.1 and 7.4 Hz, 1H,
OCHB), 4.43 (t, J=7.4 Hz, CH fluorenyl), 4.78 (ddd,
J=8.0, 6.6 and 3.7 Hz, 1H, H-3), 5.32(d, J=8.0 Hz,
1H, NH), 7.26–7.44 (m, 4H, Ar), 7.68–7.80 (m, 4H, Ar);
13C NMR (CDCl3, 125 MHz) d 28.2 (CH3), 46.5 (C-4),
46.7 (CH fluorenyl), 57.5 (C-3), 68.7 (OCH2), 80.5 (C–
O), 120.0, 125.4, 127.2 and 127.9 (CHAr), 141.3 (CAr),
143.2(C Ar), 149.2(C ¼O carbamate), 154.6 (C¼O Boc),
164.6 (C-2). Anal. calcd for C23H24N2O5: C, 67.63; H,
5.92; N, 6.85. Found: C, 67.95; H, 6.16; N, 6.53%.
1-(30 -Phenylpropyloxycarbonyl)-3S-(t-butoxycarbonyl)
aminoazetidin-2-one (3c). Yield from 1 mmol of 1: 118
20
D
mg (34%) as a colourless oil; ½aŠ +6.0 (c 5.4, CHCl3);
1
IR (film) 3055, 2984, 1820, 1720 cmÀ1; H NMR (ace-
tone-d6, 300 MHz) d 1.40 (s, 9H, tBu), 2.07 (quint,
J=6.7 Hz, 2H, CH2CH2CH2), 2.71 (t, J=6.7 Hz, 2H,
CH2Ph), 3.69 (dd, J=6.9 and 3.9 Hz, 1H, H-4), 4.00
(dd, J=6.9 and 4.0 Hz, 1H, H-40), 4.18 (t, J=6.7 Hz,
2H, OCH2), 4.83 (ddd, J=8.2, 4.0 and 3.9 Hz, 1H, H-
3), 6.84 (d, J=8.2Hz, 1H, NH), 7.15–7.36 (m, 5H, Ph);
13C NMR (acetone-d6, 75 MHz) d 28.4 (CH3), 31.8
(CH2), 32.6 (CH2Ph), 46.9 (C-4), 55.0 (C-3), 66.1
(OCH2), 80.7 (C–O), 126.7, 126.9 and 129.4 (CHAr),
142.3 (CAr), 150.2(C ¼O carbamate), 156.2(C ¼O Boc),
165.9 (C-2); MS (CI) m/z 347 (MÀ1). Anal. calcd for
C18H24N2O5: C, 62.07; H, 6.90; N, 8.04. Found: C,
62.60; H, 7.21; N, 7.69%.
1-(20-Indanyloxycarbonyl)-3S-(t-butoxycarbonyl) amino-
azetidin-2-one (3g). Yield from 1 mmol of 1: 115 mg
(33%) as a white solid; mp 114.5–115.5 ꢂC; IR (KBr)
3055, 2986, 1819, 1718 cmÀ1 1H NMR (acetone-d6,
;
300 MHz) d 1.45 (s, 9H, tBu), 3.15 (dd, J=17.2and 2.3
Hz, 2H, ArCHA), 3.46 (dd, J=17.2and 6.4 Hz, 2H,
ArCHB), 3.74 (dd, J=6.7 and 3.0 Hz, 1H, H-4), 4.15
(dd, J=13.8 and 6.7 Hz, 1H, H-40), 4.89 (ddd, J=13.8,
8.2and 3.0 Hz, 1H, H-3), 5.62(m, 1H, CH indanyl),
6.88 (d, J=8.2Hz, NH), 7.20–7.40 (m, 4H, Ar); 13C

´
S. Gerard et al. / Bioorg. Med. Chem. 10 (2002) 3955–3964
3961
NMR (acetone-d6, 75 MHz) d 28.5 (CH3), 40.1 and 40.2
(CH2Ar), 40.3 (C-4), 46.9 (C-3), 75.8 (CH indanyl), 78.4
(C–O), 125.4 and 127.7 (CHAr), 141.1 (CAr), 141.8
(C¼O Boc), 149.9 (C¼O carbamate), 165.7 (C-2); MS
(CI) m/z 347 (C18H22N2O5, M+1), 117, 75.
(CDCl3, 75 MHz) d 27.8 (CH3), 34.2and 34.5 (CH Ar),
2
45.3 (C-4), 55.3 and 55.4 (OCH3), 59.7 (C-3), 67.6 and
68.6 (OCH2), 85.3 (O–C), 114.2, 114.3, 129.3 and 130.0
(CHAr), 149.5 and 150.2(C Ar), 152.9 and 155.2 (C¼O
carbamate), 158.6 (C¼O Boc), 158.7 and 158.8 (CAr),
163.1 (C-2).
1-Benzyloxycarbonyl-3S-(t-butoxycarbonyl) (benzyloxy-
carbonyl) aminoazetidin-2-one (4a). Yield from 1 mmol
of 1: 53 mg (12%) as a white solid; mp 100–101 ꢂC; IR
1-(40 -Fluoro-phenethyloxycarbonyl)-3S-(t-butoxycarbo-
nyl) (40-fluoro-phenethyloxycarbonyl) aminoazeti din-2-
one (4e). Yield from 1 mmol of 1: 16 mg (3%) as a
1
(KBr) 3040, 2980, 1817, 1749 cmÀ1; H NMR (CDCl3,
1
300 MHz) d 1.41 (s, 9H, tBu), 3.72(dd, J=6.6 Hz and
4.1 Hz, 1H, H-4), 3.91 (dd, J=6.6 Hz and 6.6 Hz, 1H,
H-40), 5.23 (s, 2H, CH2O), 5.24 (s, 2H, CH2O), 5.59 (dd,
J=6.6 and 4.1 Hz, 1H, H-3), 7.30–7.45 (m, 10H, Ph);
13C NMR (CDCl3, 75 MHz) d 27.6 (CH3), 45.1 (C-4),
59.4 (C-3), 68.1 (OCH2), 69.5 (OCH2), 85.2(O–C),
128.3, 128.4, 128.5, 128.6, 128.7 and 128.9 (CHAr), 134.4
and 134.8 (CAr), 149.1 and 150.0 (C¼O carbamate),
152.6 (C¼O Boc), 162.9 (C-2); MS (FABÀ) m/z 453
(MÀ1).
white solid; H NMR (CDCl3, 300 MHz) d 1.43 (s, 9H,
tBu), 2.98 and 3.00 (t, J=7.0 Hz, 2H, CH2Ar), 3.68
(dd, J=6.6 and 4.1 Hz, 1H, H-4), 3.82(dd, J=6.6 and
6.6 Hz, 1H, H-40), 4.36 and 4.41 (t, J=7.0 Hz, 2H,
OCH2), 5.55 (dd, J=6.6 Hz and 4.1 Hz, 1H, H-3),
6.93–7.07 (m, 4H, Ar), 7.17–7.31 (m, 4H, Ar); 13C
NMR (CDCl3, 75 MHz) d 27.9 (CH3), 34.3 and 34.5
(CH2Ar), 45.1 (C-4), 59.8 (C-3), 68.4 and 68.5 (OCH2),
85.5 (O–C), 115.4, 115.8, 130.5 and 130.6 (CHAr), 147.1
(CAr), 153.2(C ¼O carbamate), 158.4 (C¼O Boc, CAr),
163.1 (C-2).
1-Phenethyloxycarbonyl-3S-(t-butoxycarbonyl) (phene-
thyloxycarbonyl) aminoazetidin-2-one (4b). Yield from 1
mmol of 1: 70 mg (15%) as a colorless oil; IR (film)
1-(90 -Fluorenylmethoxycarbonyl)-3S-(t-butoxycarbonyl)
(90-fluorenylmethoxycarbonyl) aminoazetidin-2-one (4f).
Yield from 1 mmol of 1: 75 mg (12%) as a white solid;
3062, 2977, 1824, 1732 cmÀ1
;
1H NMR (CDCl3,
300 MHz) d 1.41 (s, 9H, tBu), 3.02(t, J=7.3 Hz, 2H,
CH2Ph), 3.03 (t, J=7.2Hz, H2 , CH 2Ph), 3.68 (dd,
J=6.5 and 4.1 Hz, 1H, H-4), 3.81 (dd, J=6.6 and 6.5
Hz, 1H, H-40), 4.43 (t, J=7.3 Hz, 2H, OCH2), 4.45 (t,
J=7.2Hz, 2H, OCH 2), 5.55 (dd, J=6.6 Hz and 4.1 Hz,
1H, H-3), 7.17–7.35 (m, 10H, Ph); 13C NMR (CDCl3,
75 MHz) d 27.7 (CH3), 34.8 and 35.1 (CH2Ph), 45.1 (C-
IR (KBr) 3073, 2977, 1817, 1733 cmÀ1 1H NMR
;
(CDCl3, 300 MHz) d 1.41 (s, 9H, tBu), 3.72(dd, J=6.6
and 4.2Hz, 1H, H-4), 3.88 (dd, J=6.6 and 6.6 Hz, 1H,
H-40), 4.30 (t, J=6.6 Hz, 2H, 2ÂCH fluorenyl), 4.52(m,
4H, 2ÂOCH2), 5.56 (dd, J=6.6 and 4.2Hz, 1H, H-3),
7.29–7.45 (m, 8H, Ar), 7.60–7.78 (m, 8H, Ar); 13C NMR
(CDCl3, 75 MHz) d 27.7 (CH3), 45.1 (C-4), 46.5 (CH
fluorenyl), 59.6 (C-3), 68.7 and 69.7 (OCH2), 85.5 (O–
C), 120.0, 120.1, 125.1, 125.4, 127.2, 127.3 and 128.0
(CHAr), 141.3 and 143.2(C Ar), 149.2and 150.0 (C ¼O
carbamate), 153.1 (C¼O Boc), 162.9 (C-2).
4), 59.4 (C-3), 67.3 and 68.2(OCH ), 85.3 (O–C), 126.7,
2
126.8, 128.5, 128.6, 128.9 and 129.1 (CHAr), 136.9 and
137.1 (CAr), 149.3 and 150.0 (C¼O carbamate), 152.8
(C¼O Boc), 163.1 (C-2).
1-(30 -Phenylpropyloxycarbonyl)-3S-(t-butoxycarbonyl)
(30-phenylpropyloxycarbonyl) aminoazetidin-2-one (4c).
Yield from 1 mmol of 1: 102mg (02%) as a white
1-(20-Indanyloxycarbonyl)-3S-(t-butoxycarbonyl) (20-in-
danyloxycarbonyl) aminoazetidin-2-one (4g). Yield from
1 mmol of 1: 109 mg (21%) as a white solid; H NMR
1
1
solid; H NMR (CDCl3, 300 MHz) d 1.51 (s, 9H, tBu),
(CDCl3, 300 MHz) d 1.35 (s, 9H, tBu), 3.05 and 3.15
(dd, J=6.8 and 2.6 Hz, 2H, ArCHA), 3.31 and 3.39 (dd,
J=6.8 and 6.8 Hz, 2H, ArCHB), 3.65 (dd, J=6.6 and
4.0 Hz, 1H, H-4), 3.78 (dd, J=6.6 and 6.6 Hz, 1H, H-
40), 5.50 (dd, J=6.6 and 4.0 Hz, 1H, H-3), 5.56 (m, 2H,
2ÂCH indanyl), 7.12–7.27 (m, 8H, Ar); 13C NMR
(CDCl3, 75 MHz) d 27.6 (CH3), 39.3 (CH2Ar), 45.2(C-
4), 59.4 (C-3), 79.3 (CH indanyl), 84.9 (O–C), 124.6 and
126.8 (CHAr), 139.8 (CAr), 149.0 and 150.5 (C¼O car-
bamate), 152.4 (C¼O Boc), 163.0 (C-2).
2.02 and 2.03 (quint, J=7.0 Hz, 2H, CH2CH2CH2),
2.72 (t, J=7.0 Hz, 4H, 2ÂCH2Ph), 3.73 (dd, J=6.5 Hz
and 4.1ꢂHz, 1H, H-4), 3.84 (dd, J=6.5 Hz and 6.5 Hz,
1H, H-40), 4.25 and 4.26 (t, J=7.0 Hz, 2H, OCH2), 5.55
(dd, J=6.5 and 4.1 Hz, 1H, H-3), 7.15–7.37 (m, 10H,
Ar); 13C NMR (CDCl3, 75 MHz) d 28.0 (CH3), 30.1 and
30.2(CH CH2CH2), 32.1 and 32.2 (CH2Ar), 45.3 (C-4),
2
59.7 (C-3), 66.3 and 67.6 (OCH2), 85.3 (O–C), 126.3,
128.2, 128.3, 128.6, 128.8 and 128.9 (CHAr), 140.9 and
141.0 (CAr), 149.7 and 150.3 (C¼O carbamate), 153.1
(C¼O Boc), 163.2(C-2).
General procedure of Boc deprotection with CAN (5)
1-(40 -Methoxy-phenethyloxycarbonyl)-3S-(t-butoxycar-
bonyl) (40-methoxy-phenethyloxycarbonyl) amino azeti-
din-2-one (4d). Yield from 1 mmol of 1: 59 mg (11%)
A solution of 4 (0.2mmol) and CAN (0.04 mmol) in
CH3CN (5 mL) was refluxed for 10 min, then poured
into water and extracted twice with CH2Cl2. The
organic layers were washed with aqueous NH4Cl,
dried over MgSO4, concentrated and purified by col-
umn-chromatography on silica gel (CH2Cl2–EtOAC,
95:5).
1
as a white solid; H NMR (CDCl3, 300 MHz) d 1.43 (s,
9H, tBu), 2.84 (t, J=7.1 Hz, 2H, CH2Ar), 2.92 (t, J=7.4
Hz, 2H, CH2Ar), 3.69 (dd, J=6.2and 4.0 Hz, 1H, H-4),
3.76 (s, 6H, 2ÂOCH3), 3.87 (dd, J=6.8 and 6.2Hz, 1H,
H-40), 4.24 (t, J=7.1 Hz, 2H, OCH2), 4.35 (t, J=7.4 Hz,
2H, OCH2), 5.66 (dd, J=6.8 and 4.0 Hz, 1H, H-3),
6.82–6.92 (m, 4H, Ar), 7.17–7.30 (m, 4H, Ar); 13C NMR
1-Benzyloxycarbonyl-3S-(benzyloxycarbonyl) aminoaze-
tidin-2-one (5a). Yield 57% (white solid); mp

´
S. Gerard et al. / Bioorg. Med. Chem. 10 (2002) 3955–3964
3962
108–109 ꢂC; IR (KBr) 3380, 3031, 2971, 1808, 1711
cmÀ1 1H NMR (acetone-d6, 300 MHz) d 3.72(dd,
1-Phenethyloxycarbonyl-3-bromoazetidin-2-one
(7b).
;
Yield from 0.15 mmol of 3b: 31 mg (69%) as a color-
less oil; IR (film) 3055, 2986, 1824, 1733 cmÀ1; 1H NMR
(CDCl3, 500 MHz) d 3.03 (t, J=7.3 Hz, 2H, CH2Ph),
3.73 (dd, J=7.8 and 2.9 Hz, 1H, H-4), 4.14 (dd, J=7.8
and 5.8 Hz, 1H, H-40), 4.44 (t, J=7.3 Hz, 2H, OCH2),
4.82(dd, J=5.8 and 2.9 Hz, 1H, H-3), 7.25–7.31 (m,
5H, Ph); 13C NMR (CDCl3, 125 MHz) d 34.9 (CH2Ph),
40.3 (C-3), 48.8 (C-4), 67.6 (OCH2), 126.8, 128.5 and
129.0 (CHAr), 136.7 (CAr), 148.6 (C¼O carbamate),
160.2(C-)2; HRMS (CI) calcd for C 12H1179BrNO3
(MÀ1): 295.9922. Found: 295.9911.
J=6.6 and 6.6 Hz, 1H, H-4), 3.85 (dd, J=6.6 and 4.0
Hz, 1H, H-40), 4.95 (ddd, J=8.3, 6.6 and 4.0 Hz, 1H, H-
3), 5.10 (s, 2H, OCH2), 5.23 (s, 2H, OCH2), 7.20 (d,
J=8.3 Hz, 1H, NH), 7.30–7.50 (m, 10H, Ph); 13C NMR
(acetone–d6, 75 MHz) d 46.9 (C-4), 58.5 (C-3), 67.4 and
68.2(OCH 2), 129.0, 129.1, 129.2, 129.3, 129.4 and 129.5
(CHAr), 136.8 and 137.8 (CAr), 149.0 and 149.9 (C¼O
carbamate), 165.4 (C-2); MS (CI) m/z 353 (MÀ1).
1-Phenethyloxycarbonyl-3S-(phenethyloxycarbonyl) ami-
noazetidin-2-one (5b). Yield 48% (pale yellow oil); IR
(film) 3363, 3062, 2965, 1822, 1724 cm À1
;
1H NMR
1-(30 -Phenylpropyloxycarbonyl)-3-bromoazetidin-2-one
(7c). Yield from 0.17 mmol of 3c: 21 mg (40%) as a
yellow oil; IR (film) 3055, 2986, 1826, 1734 cmÀ1; H
(CDCl3, 300MHz) d 2.94 (t, J=7.0 Hz, 2H, CH2Ph), 3.03
(t, J=7.2Hz, 2H, CH 2Ph), 3.70 (dd, J=6.6 and 3.7 Hz,
1H, H-4), 3.87 (dd, J=6.6 and 6.6 Hz, 1H, H-40), 4.33 (t,
J=7.0 Hz, 2H, OCH2), 4.43 (t, J=7.2Hz, 2H, OCH 2),
4.73 (ddd, J=8.0, 6.6 and 3.7 Hz, 1H, H-3), 5.32(d, J=8.0
Hz, 1H, NH), 7.15–7.40 (m, 10H, Ph); 13C NMR (CDCl3,
75 MHz) d 35.0 and 35.2(CH 2Ph), 46.5 (C-4), 57.2(C-3),
66.2and 67.3 (OCH 2), 126.6, 126.8, 128.5, 128.6, 128.9 and
129.1 (CHAr), 137.0 and 137.5 (CAr), 149.1 and 155.4
(C¼O carbamate), 164.0 (C-2); MS (CI) m/z 381 (MÀ1).
1
NMR (CDCl3, 500 MHz) d 2.07 (quint, J=7.6 Hz, 2H,
CH2CH2CH2), 2.74 (t, J=7.6 Hz, 2H, CH2Ph), 3.73
(dd, J=7.8 and 2.6 Hz, 1H, H-4), 4.14 (dd, J=7.8 and
5.8 Hz, 1H, H-40), 4.28 (t, J=7.6 Hz, 2H, OCH2), 4.82
(dd, J=5.8 and 2.6 Hz, 1H, H-3), 7.20–7.30 (m, 5H,
Ph); 13C NMR (CDCl3, 125 MHz) d 29.6 (CH2), 31.8
(CH2Ph), 40.3 (C-3), 48.7 (C-4), 66.5 (OCH2), 126.0,
128.3 and 128.4 (CHAr), 140.6 (CAr), 148.7 (C¼O car-
bamate), 160.2(C);-2 HRMS (CI) calcd for
C13H1581BrNO3 (M+1): 314.0214. Found: 314.0207.
1-(90 -Fluorenylmethoxycarbonyl)-3S-(90 -fluorenylmeth-
oxycarbonyl) aminoazetidin-2-one (5f). Yield: 63%
(white solid); mp 189–190 ꢂC; IR (KBr) 3342, 3056,
1-(40 -Methoxy-phenethyloxycarbonyl)-3-bromoazetidin-
2-one (7d). Yield from 0.16 mmol of 3d: 26 mg (47%)
as a yellow oil; IR (film) 3055, 2987, 1823, 1735 cmÀ1
;
1
2929, 1817, 1720 cmÀ1; H NMR (CDCl3, 300 MHz) d
3.73 (dd, J=6.6 and 3.9 Hz, 1H, H-4), 3.94 (dd, J=6.6
Hz and 6.6 Hz, 1H, H-40), 4.23 (t, J=6.6 Hz, 2H, 2ÂCH
fluorenyl), 4.38 (m, 4H, 2ÂOCH2), 4.79 (ddd, J=7.6,
6.6 and 3.9 Hz, 1H, H-3), 7.25–7.48 (m, 8H, Ar), 7.68–
7.80 (m, 8H, Ar); 13C NMR (CDCl3, 75 MHz) d 46.7
(C-4), 47.4 (CH fluorenyl), 57.5 (C-3), 67.8 and 69.1
(OCH2), 120.0, 120.3, 125.1, 125.5, 127.3, 127.4, 128.1
and 128.2 (CHAr), 141.4 and 143.3 (CAr), 149.4 and
155.5 (C¼O carbamate), 163.7 (C-2).
1H NMR (CDCl3, 500 MHz) d 2.96 (t, J=7.3 Hz, 2H,
CH2Ar), 3.73 (dd, J=7.8 and 2.9 Hz, 1H, H-4), 3.80 (s,
3H, OCH3), 4.15 (dd, J=7.8 and 5.8 Hz, 1H, H-40), 4.40
(t, J=7.3 Hz, 2H, OCH2), 4.83 (dd, J=5.8 and 2.9 Hz,
1H, H-3), 6.86 (d, J=8.7 Hz, 2H, Ar), 7.29 (d, J=8.7
Hz, 2H, Ar); 13C NMR (CDCl3, 125 MHz) d 34.0
(CH2Ar), 40.3 (C-3), 48.8 (C-4), 55.1 (OCH3), 67.8
(OCH2), 113.9 (CHAr), 128.7 (CAr), 130.0 (CHAr), 148.7
(C¼O carbamate), 158.4 (CAr), 160.2(C-2); MS (CI)
m/z 329 and 327 (C13H14BrNO4, M), 135, 119, 91.
General procedure for the preparation of 1-
alkoxycarbonyl-3-bromoazetidin-2-ones (7)
1-(40 -Fluoro-phenethyloxycarbonyl)-3-bromoazetidin-2-
one (7e). Yield from 0.08 mmol of 3e: 12mg (39%) as
a colorless oil; IR (film) 3055, 2987, 1822, 1734 cmÀ1
Precursor 3 (1 equiv) was dissolved in an ice-cold solu-
tion of TFA (10%) in CH2Cl2 (1 mL/0.1 mmol). The
solution was stirred for 3–4 h at 20 ꢂC, then con-
centrated under vacuum. The residue was washed twice
with cold ether and dried under vacuum to furnish
quantitatively crude amine 6 as the trifluoroacetate salt.
To this amine was added 2.5 N H2SO4 (1 mL/0.1 mmol)
at 10 ꢂC, KBr (5 equiv), ethanol (0.15 mL/0.1 mmol),
and at least, an ice-cold solution of NaNO2 (1.5 equiv)
in water (0.25 mL/0.1 mmol) (dropwise addition). The
mixture was stirred for 3 h 30 min at 6 ꢂC, then extrac-
ted three times with CHCl3. The organic phases were
washed with cold brine, dried over MgSO4, and con-
centrated under vacuum. Crude 7 was purified by
preparative TLC on silica gel plates neutralised with 1%
N-ethylmorpholine in CH2Cl2.
;
1H NMR (CDCl3, 500 MHz) d 3.00 (t, J=7.1 Hz, 2H,
CH2Ar), 3.73 (dd, J=7.7 and 2.9 Hz, 1H, H-4), 4.15
(dd, J=7.7 and 5.8 Hz, 1H, H-40), 4.41 (t, J=7.1 Hz,
2H, OCH2), 4.83 (dd, J=5.8 and 2.9 Hz, 1H, H-3), 7.00
(t, J=8.7, 2H, Ar), 7.22 (dd, J=8.7 Hz and 5.3 Hz, 2H,
Ar); 13C NMR (CDCl3, 125 MHz) d 34.1 (CH2Ar), 40.3
(C-3), 48.7 (C-4), 67.5 (OCH2), 115.3 (CHAr), 128.7
(CAr), 130.6 (CHAr), C¼O carbamate and C–F not visi-
ble, 162.7 (C-2); MS (CI) m/z 316 and 318
(C12H11BrFNO3, M+1), 123, 81.
1-(90-Fluorenylmethoxycarbonyl)-3-bromoazetidin-2-one
(7f). Yield from 0.3 mmol of 3f: 41 mg (39%) as a yel-
low oil; IR (film) 3056, 2919, 1817, 1732 cmÀ1; 1H NMR
(CDCl3, 500 MHz) d 3.79 (dd, J=7.8 and 2.9 Hz, 1H,
H-4), 4.21 (dd, J=7.8 and 5.8 Hz, 1H, H-40), 4.30 (t,
J=7.3 Hz, 1H, CH fluorenyl), 4.46 (dd, J=10.8 and 7.3
Hz, 1H, OCHA), 4.50 (dd, J=10.8 and 7.3 Hz, 1H,
OCHB), 4.89 (dd, J=5.8 and 2.9 Hz, 1H, H-3), 7.33–7.43
1-Benzyloxycarbonyl-3-bromoazetidin-2-one (7a). Yield
from 0.71 mmol of 3a: 142mg (71%) as a pale yellow
solid; HRMS (EI) calcd for C11H1079BrNO3: 282.9844.
Found: 282.9841; other characterizations: see ref 11.

´
S. Gerard et al. / Bioorg. Med. Chem. 10 (2002) 3955–3964
3963
(m, 4H, Ar), 7.71–7.78 (m, 4H, Ar); 13C NMR (CDCl3,
125 MHz) d 40.3 (C-3), 46.4 (CH fluorenyl), 48.7 (C-4),
69.1 (OCH2), 120.0, 125.2, 127.2 and 127.9 (CHAr),
141.2and 142.9 (C Ar), 148.7 (C¼O carbamate), 160.2
(C-2); HRMS (EI) calcd for C18H1479BrNO3: 371.0157.
Found: 371.0147.
128.3 and 128.4 (CHAr), 140.6 (CAr), 148.8 (C¼O car-
bamate), 160.2(C-)2; MS (CI)
(C13H14ClNO3, M), 119, 105, 91.
m/z 267 and 269
1-(90-Fluorenylmethoxycarbonyl)-3-chloroazetidin-2-one
(8f). Yield from 0.33 mmol of 3f: 51 mg (47%) as a yel-
low oil; IR (film) 3052, 2987, 1819, 1732 cmÀ1; 1H NMR
(CDCl3, 500 MHz) d 3.71 (dd, J=7.8 Hz and 2.9 Hz,
1H, H-4), 4.14 (dd, J=7.8 and 5.8 Hz, 1H, H-40), 4.30
(t, J=7.3 Hz, 1H, CH fluorenyl), 4.46 (dd, J=10.8 and
7.3 Hz, 1H, OCHA), 4.50 (dd, J=10.8 and 7.3 Hz, 1H,
OCHB), 4.90 (dd, J=5.8 Hz and 2.9 Hz, 1H, H-3), 7.33–
7.43 (m, 4H, Ar), 7.71–7.78 (m, 4H, Ar); 13C NMR
(CDCl3, 125 MHz) d 46.4 (CH fluorenyl), 49.0 (C-3),
1-(20-Indanyloxycarbonyl)-3-bromoazetidin-2-one (7g).
Yield from 0.33 mmol of 3g: 51 mg (50%) as a yellow
1
oil; IR (film) 3055, 2987, 1824, 1730 cmÀ1; H NMR
(CDCl3, 500 MHz) d 3.15 (dd, J=17.0 Hz and 3.6 Hz,
1H, ArCHA), 3.16 (dd, J=17.0 and 3.6 Hz, 1H,
0
ArCHA ), 3.39 (dd, J=17.0 and 6.6 Hz, 2H, ArCHB and
0
ArCHB ), 3.73 (dd, J=7.7 and 2.6 Hz, 1H, H-4), 4.14
(dd, J=7.7 and 5.8 Hz, 1H, H-40), 4.80 (dd, J=5.8 Hz
and 2.6 Hz, 1H, H-3), 5.58 (m, 1H, CH indanyl), 7.16–
7.28 (m, 4H, Ar); 13C NMR (CDCl3, 125 MHz) d 39.2
and 39.3 (CH2Ar), 40.4 (C-3), 48.9 (C-4), 78.5 (CH
indanyl), 124.5, 126.7 and 126.9 (CHAr), 139.5 (CAr),
148.4 (C¼O carbamate), 160.3 (C-2); MS (CI) m/z 310
and 312(C 13H12BrNO3, M+1), 117, 91.
54.4 (C-4), 69.2(OCH ), 120.0, 125.2, 127.2 and 127.9
2
(CHAr), 141.2and 142.9 (C Ar), 148.8 (C¼O carbamate),
160.2(C-)2; HRMS (EI) calcd for C 18H1435ClNO3:
327.0662. Found: 327.0664.
General procedure for the preparation of 1-alkoxycarbonyl-
3-iodoazetidin-2-ones (9)
The procedure described for 7 was applied by replacing
KBr with KI.
General procedure for the preparation of 1-alkoxycarbonyl-
3-chloroazetidin-2-ones (8)
The procedure described for 7 was applied by replacing
KBr with KCl.
1-Benzyloxycarbonyl-3-iodoazetidin-2-one (9a). Yield
from 0.3 mmol of 3a: 66 mg (67%) as a yellow oil; IR
1
(film) 3054, 2987, 1819, 1733 cmÀ1; H NMR (CDCl3,
1-Benzyloxycarbonyl-3-chloroazetidin-2-one (8a). Yield
from 0.45 mmol of 3a: 33 mg (31%) as a colorless oil;
300 MHz) d 3.81 (dd, J=7.7 and 3.0 Hz, 1H, H-4), 4.27
(dd, J=7.7 and 5.9 Hz, 1H, H-40), 4.95 (dd, J=5.9 and
3.0 Hz, 1H, H-3), 5.28 (s, 2H, OCH2), 7.34–7.48 (m, 5H,
Ph); 13C NMR (CDCl3, 75 MHz) d 10.8 (C-3), 50.2(C-
4), 68.9 (OCH2), 128.7, 128.9 and 129.1 (CHAr), 134.9
(CAr), 148.6 (C¼O carbamate), 161.5 (C-2); MS (EI)
m/z 331 (C11H10INO3, M), 204, 107, 91.
IR (film) 3058, 2977, 1824, 1734 cmÀ1 1H NMR
;
(CDCl3, 300 MHz) d 3.69 (dd, J=7.7 and 3.2Hz, 1H,
H-4), 4.11 (dd, J=7.7 and 5.9 Hz, 1H, H-40), 4.84 (dd,
J=5.9 and 3.2Hz, 1H, H-3), 5.29 (s, 2H, OCH 2), 7.30–
7.48 (m, 5H, Ph); 13C NMR (CDCl3, 75 MHz) d 49.1
(C-3), 54.2(C-4), 68.4 (OCH ), 128.5, 128.6 and 128.7
2
(CHAr), 136.1 (CAr), 148.2(C ¼O carbamate), 160.1 (C-
2); HRMS (EI) calcd for C11H1035ClNO3: 239.0358.
Found: 239.0349.
1-Phenethyloxycarbonyl-3-iodoazetidin-2-one (9b). Yield
from 0.26 mmol of 3b: 58 mg (65%) as a yellow oil; IR
1
(film) 3055, 2987, 1818, 1734 cmÀ1; H NMR (CDCl3,
500 MHz) d 3.03 (t, J=7.2Hz, 2H, CH 2Ph), 3.78 (dd,
J=7.8 and 3.2Hz, 1H, H-4), 4.23 (dd, J=7.8 Hz and
5.9 Hz, 1H, H-40), 4.44 (t, J=7.2Hz, 2H, OCH 2), 4.94
(dd, J=5.9 Hz and 3.2 Hz, 1H, H-3), 7.22–7.35 (m, 5H,
Ph); 13C NMR (CDCl3, 125 MHz) d 10.5 (C-3), 34.9
(CH2Ph), 49.3 (C-4), 67.5 (OCH2), 126.8, 128.5 and
129.0 (CHAr), 136.8 (CAr), 148.6 (C¼O carbamate),
161.8 (C-2); HRMS (CI) calcd for C12H12INO3:
345.9940. Found: 345.9935.
1 - Phenethyloxycarbonyl - 3 - chloroazetidin - 2 - one (8b).
Yield from 0.53 mmol of 3b: 45 mg (34%) as a yellow
1
oil; IR (film) 3054, 2987, 1824, 1734 cmÀ1; H NMR
(CDCl3, 500 MHz) d 3.03 (t, J=7.1 Hz, 2H, CH2Ph),
3.65 (dd, J=7.7 Hz and 3.0 Hz, 1H, H-4), 4.07 (dd,
J=7.7 and 5.9 Hz, 1H, H-40), 4.45 (t, J=7.1 Hz, 2H,
OCH2), 4.83 (dd, J=5.9 and 3.0 Hz, 1H, H-3), 7.25–
7.32(m, 5H, Ph); 13C NMR (CDCl3, 125 MHz) d 34.9
(CH2Ph), 49.0 (C-3), 54.3 (C-4), 67.6 (OCH2), 126.7,
128.5 and 129.0 (CHAr), 136.7 (CAr), 148.6 (C¼O car-
bamate), 160.2(C-)2; MS (EI)
(C12H12ClNO3, M), 105, 77.
m/z 253 and 255
References and Notes
1-(30 -Phenylpropyloxycarbonyl)-3-chloroazetidin-2-one
(8c). Yield from 0.11 mmol of 3c: 22 mg (63%) as a
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