Lipase-catalyzed resolution of 4-aryl-substituted β-lactams: Effect of substitution on the 4-aryl ring

Article abstract of DOI:10.1016/j.tet.2003.09.057

Pseudomonas cepacia lipase (PS-30) was used in hydrolytic resolution of 3-acetoxy-4-aryl-substituted azetidin-2-ones (>97% ee). Twenty-three β-lactam substrates with varied substituents at the C-4 center of the ring were synthesized and subjected to lipas

Full text of DOI:10.1016/j.tet.2003.09.057

Tetrahedron 59 (2003) 9147–9160
Lipase-catalyzed resolution of 4-aryl-substituted b-lactams:
effect of substitution on the 4-aryl ring
Jason A. Carr, Talal F. Al-Azemi, Timothy E. Long, Jeung-Yeop Shim, Cristina M. Coates,
*
Edward Turos and Kirpal S. Bisht
Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, FL 33620, USA
Received 7 February 2003; revised 17 September 2003; accepted 17 September 2003
This paper is dedicated to Professor David Crout to mark the occasion of his retirement
Abstract—Pseudomonas cepacia lipase (PS-30) was used in hydrolytic resolution of 3-acetoxy-4-aryl-substituted azetidin-2-ones (.97%
ee). Twenty-three b-lactam substrates with varied substituents at the C-4 center of the ring were synthesized and subjected to lipase-PS
catalyzed hydrolysis in phosphate buffer (pH 7.2, 0.2 M) at 258C. The reactions occurred with high enantioselectivity and substrate
conversion. The effect of substitution on the C-4 aryl ring on lipase hydrolytic activity was dependent upon the steric and electronic nature of
the substituent and its position on the aryl ring. The stereopreference of the lipase PS-30 for the (3S,4R) enantiomer was rationalized using a
known active site model. Absolute stereochemistry of the enantiomers was established using single crystal X-ray crystallographic
techniques.
q 2003 Elsevier Ltd. All rights reserved.
1. Introduction
1-caprolactones,10 versatile building blocks in organic
synthesis, through lipase-catalyzed kinetic resolution in
absence of added solvent. In another report,11 we have
described solventless stereoselective polymerizations of
racemic substituted caprolactones catalyzed by Candida
antarctica lipase.
The use of lipolytic enzymes, such as lipases, provides one
of the most useful and versatile biocatalytic methods in
asymmetric synthesis and resolution of organic substrates
with high efficiency and selectivity.1–4 Lipases, in this
regard, are excellent biocatalysts since they have the
remarkable ability of assuming a variety of conformations
to accommodate substrates of varying sizes and complex-
ities.5–9 Above all lipases do not require the use of co-
factors, can be recycled, and are effective under mild,
environmentally benign conditions. As a result of this broad
substrate specificity and their distinctive stereopreferences,
lipases have been used in numerous applications ranging
from enantioselective syntheses to the resolution of racemic
mixtures.5–9
The b-lactam (azetidin-2-one) is an interesting ring system
found in penicillins, one of the most utilized antibacterials
in clinical medicine.12,13 Moreover, b-lactams can be
readily synthesized via the Staudinger reaction starting
from an amine and an aldehyde (Scheme 1) and serve as
chiral synthons in organic synthesis.13 For example,
b-lactam have been used for assembly of the C-13 side
chain in the anti-tumor drug paclitaxel,14 in the asymmetric
synthesis of human leukocyte elastase inhibitors,15 and as
key intermediates for penems and carbepenems.16 Recently,
the stereocontrolled synthesis of monocyclic b-lactams has
been an active area of chemical research owing to their
utility as synthons for a variety of natural products14 and
activity against MRSA bacterial strains.13 Since these
compounds are interesting from chemical and pharmaco-
logical aspects, our goal was to study lipase catalyzed
resolution of monocyclic b-lactams in order to obtain them
in optically pure form. The previous results on enzymatic
resolution of racemic b-lactams have largely concentrated
on resolution of N-hydroxymethylated derivatives17–22 via
lipase catalyzed asymmetric acylation of the primary
hydroxyl on the N-hydroxymethyl group or by the
Stereoselective synthesis of enantiomerically pure com-
pounds is required not only for clinical compounds but also
for fine chemical industries and agrochemicals. It is possible
that an enantiomer in a racemic mixture may have
detrimental side effects. Syntheses of such homochiral
compounds, however, are often too difficult to obtain via
conventional chemical synthetic methods. Recently, we
have reported the preparation of optically active substituted
Keywords: lipase; kinetic resolution; lactam; enatioselectivity.
*
Corresponding author. Tel.: þ1-813-974-0350; fax: þ1-813-974-3203;
e-mail: kbisht@cas.usf.edu
0040–4020/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2003.09.057

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J. A. Carr et al. / Tetrahedron 59 (2003) 9147–9160
Scheme 1. General synthesis of 4-aryl-substituted b-lactams. 1 R¼H; 2 C4¼(–CHvCH–Ph); 3 C4¼(–CuC–Ph); 4 C4¼(–C4H3S); 5 R¼4-OCH3; 6 R¼4-
C(O)OCH3; 7 R¼4-NO2; 8 R¼3-NO2; 9 R¼4-CN; 10 R¼4-(CH3)2N; 11 R¼3-F; 12 R¼4-F; 13 R¼4-Cl; 14 R¼3-Cl; 15 R¼2-Cl; 16 R¼2,4-di-Cl; 17 R¼2-
Br; 18 R¼3-Br; 19 R¼2-I; 20 R¼4-Br; 21 R¼4-CF3; 22 R¼4-C(CH3)3; 23 R¼4-CH(CH3)2.
hydrolysis of their corresponding ester derivatives.17–22 In
a different approach, the b-lactam ring has been enantio-
specifically hydrolyzed via enzymatic catalysis to the
corresponding b-amino acid.23,24 This approach, however,
results in loss of the b-lactam ring in the hydrolyzed
enantiomer and would not be synthetically appealing
especially if the hydrolyzed enantiomer is needed for
subsequent synthetic transformations. In their quest to
prepare the C-13 side-chain of paclitaxel, Brieva et al.14
obtained enantiomerically enriched 3-hydroxy-4-phenyl-b-
lactams derivatives via lipase-catalyzed hydrolysis and
transesterification of racemic ester and alcohols, respect-
ively. These authors14 subjected three b-lactams with
different substituents (H–, PhCO–, and 4-CH3OPh–) on
the ring nitrogen and observed that lipase-catalyzed
resolutions were influenced by the nature of the substituents
on the lactam nitrogen.14 For example, introduction of the
N-benzoyl substituent, an electron withdrawing group
(EWG), caused the cleavage of the b-lactam ring in tert-
butyl methyl ether in the presence of CH3OH as a
nucleophile.14
Schiff base was then reacted with acetoxyacetyl chloride
and triethylamine in dichloromethane to yield the b-lactam
via a [2þ2]-cycloaddition reaction (Scheme 1). In all
reactions, only one diastereoisomer possessing the C-3
acetoxy and C-4 aryl groups in the cis configuration was
produced resulting in formation of (^)-racemates.
2.2. Lipase-catalyzed asymmetric deacetylation of
61–623
Our experiences with lipase catalyzed resolution of esters
and lactones6 in anhydrous organic solvents prompted
investigation of the deacetylation of the b-lactams in
anhydrous solvents. Pseudomonas fluorescens (AK), Por-
cine pancreatic lipase (PPL) and C. antarctica (Novozym-
435) lipases did not catalyze the transesterification reaction
between the n-butanol and b-lactam acetoxy group in
anhydrous tetrahydrofuran (THF), which we have pre-
viously found to be a solvent of choice for lipase catalyzed
transesterifications.26 Pseudomonas cepacia (PS-30) lipase
did catalyze the transesterification in anhydrous THF,
however, deacetylation proceeded at an exceedingly slow
rate and prolonged reaction times (.6 days) were required
for any reasonable substrate conversion. For example,
hydrolysis of compound 7 in buffer (pH 7.2, 0.2 M) led to
50% conversion within 48 h, while deacetylation in dry
THF/n-butanol gave only 35% substrate conversion after 6
days.
Our goal in this study was to develop an enzyme system that
invokes a resolution of the monocyclic b-lactams upon
hydrolysis of its 3-acetoxy derivatives and to probe the
effects of the nature of the lactam ring C-4 substituents on
enzyme selectivity. In this report, kinetic enzymatic
resolution of the 3-acetoxy derivatives was investigated as
an attractive alternative to the classical salt resolution or the
resolution of the N-hydroxymethyl derivatives.25 The
kinetic resolution led to quantitative yields and enantio-
merically enriched (.97% ee) b-lactams were thus
prepared. Importantly, the nature of the substituent on the
C-4 position affected the enzymatic resolution to a great
extent. Our efforts to understand the effect of the C-4
substituent on the selectivity of the lipase catalyst are
reported herein.
The synthesis of the stereochemically pure b-lactam,
therefore, was conceived via hydrolysis (Scheme 2) of the
racemic acetates (^)1–(^)23, which were exposed to a
series of lipases from different sources (PS-30, Novozym-
435, AK, PPL) in aqueous buffer. Generally, microbial
lipases exhibit pH optima ranging from 5.6 to 8.5 and at
temperature between 30 and 408C; we found that highest
conversions were obtained in pH 7.2 (0.2 M) phosphate
buffer at 258C. Of the enzymes screened, lipases Novozym-
435, AK and PPL did catalyze the hydrolysis of the
b-lactam acetates in buffer solution, however, long reaction
times (.10 days) were required. With P. cepacia lipase
(PS-30) reactions proceeded with moderate to excellent
substrates conversion and hence it was identified as the most
suitable biocatalyst for hydrolysis. Brieva14 et al. also had
previously described the lipase PS-30 as a suitable catalyst
for enantioselective hydrolysis of the racemic 3-acetoxy-1-
(4-methoxyphenyl)-4-phenylazetidin-2-one (1) in sodium
phosphate buffer (pH 7.5, 0.2 M). For optimal production of
the alcohols (2)1a–(2)23a (Scheme 2), water insoluble
2. Results and discussion
2.1. Synthesis of 4-aryl-substituted beta-lactams
(61–623)
The
racemic
3-acetoxy-1,4-diaryl-azetidin-2-ones
(^1–^23) were synthesized in a three-step reaction
scheme as described previously13 starting with the acid-
catalyzed Schiff base formation from the corresponding
substituted benzaldehyde and para-methoxyaniline. The

J. A. Carr et al. / Tetrahedron 59 (2003) 9147–9160
9149
Scheme 2. Lipase catalyzed asymmetric deacetylation of 4-aryl-substituted b-lactams. 1 R¼H; 2 C4¼(–CHvCH–Ph); 3 C4¼(–CuC–Ph); 4
C4¼(–C4H3S); 5 R¼4-OCH3; 6 R¼4-C(O)OCH3; 7 R¼4-NO2; 8 R¼3-NO2; 9 R¼4-CN; 10 R¼4-(CH3)2N; 11 R¼3-F; 12 R¼4-F; 13 R¼4-Cl; 14 R¼3-
Cl; 15 R¼2-Cl; 16 R¼2,4-di-Cl; 17 R¼2-Br; 18 R¼3-Br; 19 R¼2-I; 20 R¼4-Br; 21 R¼4-CF3; 22 R¼4-C(CH3)3; 23 R¼4-CH(CH3)2.
racemic acetates (^)1–(^)23 were dissolved in a minimal
amount of acetone and dispersed in an aqueous phosphate
medium (pH 7.2, 0.2 M) at 258C. The reaction was initiated
by addition of predetermined amounts of lipase PS-30. The
product alcohol and the unreacted acetate were extracted
with ethyl acetate and separated readily by silica-gel column
chromatography (Table 1). Using a stepwise elution of ethyl
acetate/petroleum ether (15:85) followed by ethyl acetate/
petroleum ether (30:70), unreacted acetate and the alcohol
were isolated in successive order.
of equal intensity for the two enantiomers in the presence of
(þ)-Eu(hfc)3. The product alcohol was acetylated and
enantiomeric purity was determined using (þ)-Eu(hfc)3 in
1H NMR experiments.
The activity of different lipases was greatly dependent upon
its source i.e. while lipases CALB (Novozym-435, immo-
bilized form from C. antarctica), AK (from Pseudomonas
fluorescens) and (PPL) showed little activity, the lipase PS-
30 (from P. cepacia) was highly efficient in buffer solution.
The effect of the enzyme concentration on the substrate
conversion was studied using a 1:1 (w/w) and 2:1 (w/w)
lactam 1 to lipase PS-30 ratio (Fig. 2). The rate of acetate
hydrolysis, as expected, was higher using more lipase in the
reaction, for example, 50% conversion was achieved after
11 h using 1:1 while more than 18 h were required using 2:1
The enantiopurity of the unreacted acetates were calculated
1
from their H NMR spectra acquired in presence of (þ)-
Eu(hfc)3, a chiral shift reagent (Fig. 1). The resonance signal
of the acetoxy protons in the racemic mixture, a singlet in
absence of the chiral shift reagent, was split into two signals
Table 1. Lipase PS-30 catalyzed hydrolysis of substituted b-lactams (^)1–(^)23
Substratea
Convb (%)
(3R,4S)-acetoxy-
E
(3S,4R)-hydroxy-
c
eep
eesc
% Yieldd
[a]2D5e
% Yieldd
[a]2D5e
–4-Phenyl (1)
–4-(2-Phenylethyenyl) (2)
–4-Phenylethynyl (3)
50
48
48
49
50
50
50
48
29
39
50
50
50
49
35
28
36
19
21
50
50
17
27
.97
91
71
99
99
88
87
98
98
84
66g
80
97
93
88
92
90
57g
85
68f
68g
98
99
80
75
þ11.6
þ59.6
þ149
þ19.2
þ16.7
þ43.3
þ56
277
209
277
277
277
277
277
277
97
140
277
277
277
277
115
87
.97
.97
.97
.97
.97
.97
–
.97
.97
.97
.97
.97
.97
.97
.97
.97
.97
.97
.97
.97
.97
.97
.97
98
96
96
98
95
95
99
96
60
69
98
99
66
96
72
48
56
46
10
99
98
15
25
2184.6
2348.0
2353.0
2115.0
2216.3
2404.4
0
2194.2
2203.6
2175.4
2328.0h
2203.9
2208.2
2338.0
2284.7
2238.4
2187.0
2138.6
2153.1
2174.4
2150.0h
2183.5
2187.2
.97
.97
.97
.97
.97
.97
40
–4-Thiophen-2-yl (4)f
–4-(4-Methoxyphenyl) (5)
–4-(4-Methoxycarbonylphenyl) (6)
–4-(4-Nitrophenyl) (7)
–4-(3-Nitrophenyl) (8)
þ37.7
þ15.1
þ29.5
þ13.3
þ2.2
–4-(4-Cyanophenyl) (9)
–4-(4-Dimethylaminophenyl) (10)
–4-(3-Fluorophenyl) (11)
–4-(4-Fluorophenyl) (12)
–4-(4-Chlorophenyl) (13)
–4-(3-Chlorophenyl) (14)
–4-(2-Chlorophenyl) (15)
–4-(2,4-Dichlorophenyl) (16)
–4-(2-Bromophenyl) (17)
–4-(3-Bromophenyl) (18)
–4-(2-Iodophenyl) (19)
71
.97
.97
.97
.97
56
29
64
34
15
þ21.5
þ12.5
þ62.4
þ20.1
þ229.0
þ4.7
127
91
76
277
277
72
þ6.5
–4-(4-Bromophenyl) (20)
–4-(4-Trifluoromethylphenyl) (21)
–4-(4-Tertbutylphenyl) (22)
–4-(4-Isopropylphenyl) (23)
.97
.97
10
þ265
þ196.5
þ90.5
þ194.5
68
134
a
Represents the aryl substituents on the b-lactam ring.
Determined from 1H NMR of crude product mixture after 48 h.
b
c
d
e
f
Determined from 1H NMR spectra in the presence of Eu(hfc)3, by integration of CH3CvO.
Yield 100% at 50% conversion.
c¼0.01 (g/mL), CHCl3
Configuration of unreacted substrate (3R,4R) and that of reacted substrate (3S,4S).
Yield 100% at 0% conversion.
g
h
c¼0.01 (g/mL), CH3OH.

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J. A. Carr et al. / Tetrahedron 59 (2003) 9147–9160
Figure 1. (a) 1H NMR of racemic 3-acetoxy-1-(4-methoxyphenyl)-4-phenyl-b-lactam with Eu(hfc)3. (b) 1H NMR of unreacted (þ) (3R,4S)-3-acetoxy-1-(4-
methoxyphenyl)-4-phenyl-b-lactam with Eu(hfc)3. (c) 1H NMR of acetylated (2) (3R,4S)-3-hydroxy-1-(4-methoxyphenyl)-4-phenyl-b-lactam with Eu(hfc)3.
substrate to lipase ratios. For subsequent studies 1:1 (w/w)
substrate to lipase ratio was used (Table 1).
hydrolysis proceeded with high enantioselectivity towards
the 3S enantiomer. For example, in compound 1, prolonged
reaction time (.72 h, not shown) beyond 50% conversion
did not result in hydrolysis of the 3R enantiomer (Fig. 2)
indicating that the enzymatic reaction proceeded with great
efficiency as measured by enantioselectivity (E¼277) and
substrate conversion (,50%). The lipase enantioselectivity
(E) values were determined from the following equation:
To understand the effect of b-lactam ring substitution on
hydrolytic activity of lipase PS-30, 23 b-lactam substrates
with different substituents on C-4 were synthesized and
subjected to lipase-catalyzed hydrolysis in phosphate buffer
(pH 7.2, 0.2 M). The results of the P. cepacia lipase-
catalyzed hydrolysis after 48 h are shown in Table 1. Even
though lipase PS-30 accepted substituted b-lactam rings
with phenyl (1), thiophen-2-yl (4), phenylethenyl (2), and
phenylethynyl (3) at the C-4 position as substrates, the C-4
substituent on the b-lactam ring influenced the hydrolysis to
a great extent and substrate conversions were greatly
affected (Table 1). For all substrates, the lipase-catalyzed
E¼ln[(12c)(12ees)]/ln[(12c)(1þees)]
where
the
ee¼[(S)2(R)]/[(S)þ(R)]£100%. The enantiomeric excesses
were determined from 1H NMR spectra recorded in
presence of the (þ)-[Eu(hfc)3] (Fig. 1).
To understand how the C-4 substituent affected lipase PS-
30’s ability to hydrolyze the acetoxy group, a number of

J. A. Carr et al. / Tetrahedron 59 (2003) 9147–9160
9151
Figure 2. Variation in substrate conversion with time using lactam 1 to PS-30 ratio (w/w) of 1:1 (O) and 2:1 (B).
substrates that differ in the position, size and electronic
nature of substituent(s) on the C-4 phenyl ring were
subjected to hydrolysis and substrate conversions were
carefully monitored as a function of reaction time by
1H NMR (Fig. 3). From Figure 3, it is important to note that:
and more than 48 h were needed to achieve reasonable
conversion (Fig. 3 and Table 1).
† Among the EWGs screened, the position of the
substituent(s) on the phenyl ring was of importance in
realizing high conversion. In general, a group at the C-40
position i.e. further away form the lactam ring, on the
phenyl moiety gave higher conversion. For example,
with C-40 chloro (in 13) or bromo (in 20) substituents
quantitative conversions were achieved but the C-20
chloro (in 15) and bromo (in 17) analogs gave only 32
and 27% substrate conversions, respectively, in 13 h
(Fig. 3). In the case of compound 16 having two chloro
groups at C-40 and C-20, the substrate conversion were
† The hydrolytic ability of the lipase PS-30, as illustrated
by substrate conversion, was greatly affected by the
substituent(s) on the C-4 aryl ring.
† Substrates 6, 14, 13, 20 and 21 with EWG on the aryl ring
typically had quantitative conversions (,50%) within
48 h, while compounds 5, 10, 22 and 23 with electron
donating groups (EDG) had lower substrate conversions
Figure 3. Effect of C-4 substitution on substrate conversion in PS-30 catalyzed hydrolysis.

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J. A. Carr et al. / Tetrahedron 59 (2003) 9147–9160
Scheme 3. Schematic representation of different chemical and enzymatic processes leading to the double epimerization of 3-hydroxy-4-(4-
nitrophenyl)azetidin-2-one.
about 32% i.e. much lower than that in compound 13
with a C-40 chloro substituent.
of the substituent (15,17,19). For example, only 21%
substrate conversion in 48 h was achieved for compound
19, with a large iodo group at C-20, while 35% substrate
conversion was observed for compound 15 with chloro, a
relatively smaller group, at C-20. Compounds 15, 17, and
19 with chloro, bromo and iodo groups have decreased
substrate conversion, which follow the order of their size
† The size of a substituent on the C-4 phenyl ring was
another important factor that affected substrate conver-
sion. For an EWG at C-40 the conversion increased with
increasing size (12,7,21,13,20), while for group at
C20 or C-30 the conversion decreased with increasing size
Figure 4. 1H NMR spectrum of the crude product mixture form lipase-catalyzed hydrolysis of 3-acetoxy-1-(4-methoxyphenyl)-4-(4-nitrophenyl)azetidin-2-
one (^)-7.

J. A. Carr et al. / Tetrahedron 59 (2003) 9147–9160
9153
(Cl,Br,I, Fig. 3). For compounds with EDGs on the
C-4 phenyl ring the substrate conversion decreased as the
size of the substituent increased i.e. 4-tert-butyl,4-
isopropyl,4-N,N-dimethylamino,4-methoxy,phenyl.
The lower substrate conversion in these substrates may
be attributed to their steric bulkiness, which could result
in van der Waals repulsive interactions in the enzyme
active site.
7.2, 0.2 M) in the absence of the lipase, indicating that the
hydrolysis observed in the presence of lipase indeed was an
enzymatic process. Several attempts to obtain the cis-
hydroxy compound upon chemical hydrolysis of racemic
cis-7 (Scheme 3) using K2CO3/acetone and K2CO3/CH3OH
at room temperature or 08C led to the formation of the
diastereomeric racemic cis- and trans-alcohols, suggesting
that the epimerization of the hydroxy lactam (under basic
conditions) was a chemical process. Further, when the cis-3-
hydroxy-4-(4-nitrophenyl)-1-(4-methoxyphenyl)azetidin-2-
one, isolated upon column chromatography from the cis-/
trans-mixture, was stirred in phosphate buffer (pH 7.2,
0.2 M without lipase) it rapidly led to an equilibrium
mixture of the cis-/trans-hydroxy products. To elucidate the
role of buffer in this racemization reaction, we removed the
buffer from the enzymatic reaction and instead the lipase
catalyzed deacetylation of 7 was carried out in dry THF/n-
butanol. Though deacetylation in THF/n-butanol was slow,
optically pure cis-hydroxy compound ([a]2D5¼271.28) and
unreacted optically enriched (þ)-cis-acetate were isolated
after 6 days. The positive and negative sign of the optical
rotation for the recovered acetate and the hydroxy product,
respectively, established that the enantiopreference of the
lipase PS remained unchanged between the buffer and the
THF reaction media. The optically pure (2)-cis-hydroxy
compound was subsequently stirred in phosphate buffer (pH
7.2, 0.2 M) in absence of lipase. The isolated compound was
found to be racemic mixture of the cis- and trans-hydroxyl
compounds. The formation of the trans- isomer from the
cis-isomer in absence of the lipase confirmed that the double
epimerization was a result of a non-enzymatic reaction and
that a free hydroxyl group was required for the double
epimerization. In light of these observations, it was
concluded that (1) racemization of the product alcohol
was an artifact and not a result of the enzymatic
catalysis and (2) a non-enzymatic cleavage of the C3–C4
bond followed by ring closure involving double epimeriza-
tion, it is believed, resulted in formation of a racemic,
diastereomeric mixture of the hydroxyl products
(Scheme 3).
† The dependence of the substrate conversion on the
size and electronic nature of the C-4 substituent
suggested that steric as well as electronic character-
istic of the substrates drive the lipase PS-30 catalyzed
hydrolysis.
In compound 7, analysis of the 1H NMR spectra (Fig. 4) of
the reaction mixture at 50% conversion revealed that the
product alcohol was a 1:1 racemic mixture of the cis and
trans alcohols. The reaction mixture was subjected to flash
column chromatography to obtain the recovered (3R,4S)-
acetate (50%, [a]2D5¼þ568, %ee¼.97), racemic-cis-alcohol
(25%, [a]2D5¼08, %ee¼0), and racemic-trans-alcohol (25%,
[a]2D5¼08, %ee¼0) (Fig. 2). The formation of the cis- and
trans-alcohols from a cis-acetate can only be explained via
an unusual ring opening across the lactam C3–C4 bond to a
benzylic carbanion (stabilized by the 40-nitro group) that
regenerates the lactam ring by attack on the planar carbonyl
group resulting in formation of the racemic cis- and trans-3-
hydroxy-b-lactam derivatives upon double epimerization
(Scheme 3).27 The observation that the recovered b-lactam
derivative i.e. (3R)-acetoxy-(4S)-(4-nitrophenyl) was opti-
cally active ([a]2D5¼þ1128) but the hydroxy compounds
were not only racemic but a mixture of cis- and trans-
stereoisomers suggested that the ring opening across the
C3–C4 bond in the hydroxyl compound might involve a
non-enzymatic process. However, it was not obvious if the
double epimerization involved an enzymatic process or was
just a reaction artifact. To uncover the role of enzyme in the
epimerization process, 3-hydroxy-4-(4-nitrophenyl)-1-(4-
methoxyphenyl)azetidin-2-one was sought. The compound
7, however, was stable to hydrolysis in phosphate buffer (pH
Figure 5. Ortep plot for the X-ray structures (a) of (þ)-(3R,4S)-3-acetoxy-1-(4-methoxyphenyl)-4-phenylazetidin-2-one (1) and (b) (þ)-(3R,4R)-3-acetoxy-1-
(4-methoxyphenyl)-4-thiophen-2-ylazetidin-2-one (4).

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J. A. Carr et al. / Tetrahedron 59 (2003) 9147–9160
Figure 6. Schematic representations of the orientation of favored (3S,4R) and disfavored (3R,4S) enantiomer in active site of the lipase PS-30. M, medium, L,
large.
2.3. Determination of absolute configuration
cis-(3R,4S) configuration of the unreacted substrate, (þ)-
(3R,4S)-3-acetoxy-1-(4-methoxyphenyl)-4-phenylazetidin-2-
one (Fig. 5). In the crystal of (þ)-(3R,4R)-3-acetoxy-1-(4-
methoxyphenyl)-4-thiophen-2-ylazetidin-2-one, two mol-
eculeswerefoundineachunitcell. Thecompoundcrystallized
in a monoclinic space group P2 (1), with cell dimensions
a¼5.3082 (10) A, b¼8.4869 (16) A, c¼17.005 (3) A. A total
of 4638 unique reflection data were obtained to give a final R
index [I.2s(I)] of 0.0618 and flack parameter of 0.19 (16).
The results of the structure determination study confirmed the
cis-(3R,4R) configuration (Fig. 5).
The absolute configuration of the two enantiomers was
determined by X-ray crystallography. Single crystals
suitable for X-ray crystallographic analysis were selected
following examination under a microscope. Single-crystal
X-ray diffraction data for the compound were collected on a
Bruker-AXS SMART APEX/CCD diffractometer. Dif-
fracted data were corrected for absorption using the
SADABS program. Direct methods and the structure
solution solved the structures and refinement was based on
F2. All non-hydrogen atoms were refined with anisotropic
displacement parameters whereas hydrogen atoms were
placed in calculated positions and given isotropic U values
based on the atom to which they are bonded. All crystal-
lographic calculations were conducted with the SHELXTL
6.1 program package.
˚
˚
˚
2.4. Stereopreference of the lipase PS-30
X-Ray crystallographic data (Fig. 5) collected using a single
crystal of the unreacted enantiomer of the 4-phenyl (1) and
4-thiophen-2-yl (4) b-lactam supported the (S)-enantiopre-
ference of the P. cepacia lipase. The data confirmed (3R,4S)
and (3R,4R) as the absolute configurations for the unreacted
enantiomer of 1 and 4, respectively. Hence the reacted
enantiomers must possess the (3S) absolute configurations.
For the crystal of (þ)-(3R,4S)-3-acetoxy-1-(4-methoxyphe-
nyl)-4-phenylazetidin-2-one, two molecules were found in
each unit cell. The compound crystallizes in a monoclinic
˚
space group P2 (1), with cell dimensions a¼5.7617 (8) A,
b¼8.1159 (11) A, c¼16.889 (2) A. A total of 4910 unique
reflection data were obtained to give a final R index
[I.2s(I)] of 0.0466 and a flack parameter of 0.0 (9). The
results of the structure determination study confirmed the
Modeling experiments28–30 have indicated that P. cepacia
has a stereochemical preference for the (R)-substrate over
the (S)-substrate but its stereoselectivity seems to be
dependent on the chemical nature and/or physical state of
˚
˚

J. A. Carr et al. / Tetrahedron 59 (2003) 9147–9160
9155
the substrate, as has been observed for other lipases.31 The
stereopreference of the lipase PS-30 for the (3S,4R)
enantiomer was rationalized using a known active site
model (Fig. 6) for the lipase as described by Zuegg et al.28
While the hydrogen at the asymmetric center of both
enantiomers is directed towards the same site (referred to as
H-alignment), the medium sized group (the carbonyl
function) and the large group (the phenyl attached to the
C-4 stereogenic center) trade places. This allows the
medium-sized group to fit into the smaller hydrophobic
pocket in the favored enantiomer whereas the larger-sized
group is made to accommodate the smaller hydrophobic
pocket in the disfavored enantiomer.
above 1 was prepared as a white solid, mp 163–1658C (lit.32
158–1608C). H NMR (250 MHz, CDCl3) d (ppm): 1.67
(3H, s, CH3CvO), 3.75 (3H, s, CH3O), 5.34 (1H, d,
J¼4.9 Hz, 4-H), 5.94 (1H, d, J¼4.9 Hz, 3-H), 6.78–7.34
(9H, m, Ph). 13C NMR (62.5 MHz, CDCl3): 19.8, 55.5,
61.4, 77.3, 114.1, 114.4, 118.8, 127.9, 128.5, 128.8, 130.3,
132.2, 156.6, 161.3, 169.3.
1
3.3.2. Racemic 3-acetoxy-1-(4-methoxyphenyl)-4-(2-phe-
nylethyenyl)azetidin-2-one (6)-2.33 With the procedure
described above 2 was prepared as a yellow solid, mp 138–
1
1408C. H NMR (250 MHz, CDCl3) d (ppm): 2.07 (3H, s,
CH3CvO), 3.77 (3H, s, CH3O), 4.94 (1H, dd, J¼4.9,
8.0 Hz, 4-H), 5.90 (1H, d, J¼4.9 Hz, 3-H), 6.16 (1H, dd,
J¼8.0, 16.1 Hz, 5-H), 6.80 (1H, d, J¼16.1 Hz, 6-H), 6.83–
7.43 (9H, m, Ph). 13C NMR (62.5 MHz, CDCl3): 20.3, 55.4,
60.1, 76.3, 114.1, 114.4, 118.7, 121.4, 126.7, 128.7, 130.6,
135.5, 137.1, 156.6, 161.1, 169.5.
3. Experimental
3.1. Materials and methods
3.3.3. Racemic 3-acetoxy-1-(4-methoxyphenyl)-4-(phe-
nylethynyl)azetidin-2-one (6)-3. With the procedure
described above 3 was prepared as a white solid, mp 94–
Lipases were obtained from Amano Enzymes (Elgin, IL,
1
USA) and Novozymes (Franklinton, NC, USA). H NMR
spectra were recorded on a Bruker 250 MHz spectrometer
and a Bruker 360 MHz spectrometer in CDCl3 with TMS or
CD3OD as the internal standard. Optical rotations were
measured with an AutoPol-IV (Rudolph research analytical)
automatic polarimeter. Elemental analysis was performed
using a NC-2100 Soil Analyzer, CE Elantech, Inc. Thin-
layer chromatography (TLC) was performed on glass plates
coated with 0.25 mm thickness of silica-gel. All solvents
were distilled prior to use and organic solvent extracts dried
over Na2SO4.
1
968C. H NMR (250 MHz, CDCl3) d (ppm): 2.21 (3H, s,
CH3CvO), 3.80 (3H, s, CH3O), 5.12 (1H, d, J¼4.7 Hz, 4-
H), 5.88 (1H, d, J¼4.7 Hz, 3-H), 6.90–7.54 (9H, m, Ph).
13C NMR (62.5 MHz, CDCl3): 20.3, 51.7, 55.3, 76.7, 81.0,
114.2, 118.7, 121.5, 128.3, 129.1, 130.0, 132.0, 156.6,
161.1, 169.5. Anal. calcd for C20H17NO4·0.22H20: C, 70.78;
H, 5.05; N, 4.13. Found: C, 70.92; H, 5.06; N, 3.95.
3.3.4. Racemic 3-acetoxy-1-(4-methoxyphenyl)-4-thio-
phen-2-ylazetidin-2-one (6)-4.34 With the procedure
described above 4 was prepared as a white solid, mp
3.2. X-Ray crystallography
1
148–1498C. H NMR (250 MHz, CDCl3) d (ppm): 1.87
(3H, s, CH3CvO), 3.76 (3H, s, CH3O), 5.62 (1H, d,
J¼4.7 Hz, 4-H), 5.96 (1H, d, J¼4.7 Hz, 3-H), 6.80–7.38
(7H, m, Ph). 13C NMR (62.5 MHz, CDCl3): 20.0, 55.4,
57.6, 114.4, 118.8, 126.8, 127.4, 128.4, 130.0, 135.6, 156.7,
161.0, 169.3.
Single-crystal X-ray diffraction data for the compounds 1
and 4 were collected on a Bruker-AXS SMART APEX/
CCD diffractometer using a Mo radiation source. Diffracted
data were corrected for absorption using the SADABS
program. Crystallographic data (excluding structure factors)
for the structures in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication numbers CCDC 191837 and 191838. Copies of
the data can be obtained, free of charge, on application to
CCDC, 12 Union road, Cambridge CB2 1Ez, UK (Fax:
þ44-1223-336033 or e-mail: deposit@ccdc.cam.ac.uk).
3.3.5. Racemic 3-acetoxy-1, 4-bis-(4-methoxyphenyl)aze-
tidin-2-one (6)-5.33 With the procedure described above 5
1
was prepared as a white solid, mp 144–1458C. H NMR
(250 MHz, CDCl3) d (ppm): 1.66 (3H, s, CH3CvO), 3.68
(3H, s, CH3O), 3.73 (3H, s, CH3O), 5.22 (1H, d, J¼4.8 Hz, 4-
H), 5.82 (1H, d, J¼4.8 Hz, 3-H), 6.71–7.22 (8H, m, Ph). 13C
NMR (62.5 MHz, CDCl3): 19.9, 55.4, 61.1, 113.6, 113.9,
114.3, 118.8, 124.0, 129.2, 130.3, 156.5, 159.9, 161.4, 169.3.
3.3. General procedure for synthesis of racemic
3-acetoxy-4-arylazetidin-2-ones 1–2332
3.3.6. Racemic 3-acetoxy-4-(4-methoxycarbonylphenyl)-
1-(4-methoxyphenyl)azetidin-2-one (6)-6. With the pro-
cedure described above 6 was prepared as a white solid, mp
A solution of acetoxyacetyl chloride (7.30 mmol) in dry
dichloromethane (12 mL) was added drop wise over 1 h at
room temperature to a mixture of the appropriately
substituted Schiff base (8.76 mmol) and triethylamine
(17.52 mmol) in dry dichloromethane (18 mL). The reaction
mixture was stirred for an additional hour at room
temperature and was then washed with water (2£50 mL).
The organic layer was separated and dried over sodium
sulfate. Evaporation of the solvent followed by purification
by column chromatography (dichloromethane/ether, 9:1)
afforded the desired product.
1
151–1528C. H NMR (250 MHz, CDCl3) d (ppm): 1.62
(3H, s, CH3CvO), 3.68 (3H, s, CH3O), 3.85 (3H, s, CH3O),
5.32 (1H, d, J¼4.9 Hz, 4-H), 5.89 (1H, d, J¼4.9 Hz, 3-H),
6.72–7.97 (8H, m, Ph). 13C NMR (62.5 MHz, CDCl3):
19.8, 52.3, 55.5, 61.1, 76.3, 114.5, 118.7, 127.9, 129.7,
130.0, 130.6, 137.6, 156.7, 160.9, 166.5, 169.2. Anal. calcd
for C20H19NO6·0.82H2O: C, 62.52; H, 4.98; N, 3.64. Found:
C, 62.64; H, 4.99; N, 3.48.
3.3.7. Racemic 3-acetoxy-1-(4-methoxyphenyl)-4-(4-
nitrophenyl)azetidin-2-one (6)-7.27 With the procedure
3.3.1. Racemic 3-acetoxy-1-(4-methoxyphenyl)-4-phenyl-
azetidin-2-one (6)-1.14,32 With the procedure described

9156
J. A. Carr et al. / Tetrahedron 59 (2003) 9147–9160
described above 7 was prepared as a yellow solid, mp 162–
1648C (lit.27 1658C). 1H NMR (250 MHz, CDCl3) d (ppm):
1.74 (3H, s, CH3CvO), 3.76 (3H, s, CH3O), 5.45 (1H, d,
J¼4.9 Hz, 4-H), 5.99 (1H, d, J¼4.9 Hz, 3-H), 6.80–8.24
(8H, m, Ph). 13C NMR (62.5 MHz, CDCl3): 19.9, 55.5,
60.6, 114.6, 118.6, 123.7, 128.9, 129.6, 140.0, 148.2, 156.9,
160.6, 169.1.
3.3.13. Racemic 3-acetoxy-4-(4-chlorophenyl)-1-(4-
methoxyphenyl)azetidin-2-one (6)-13. With the pro-
cedure described above 13 was prepared as a white solid,
mp 172–1738C. 1H NMR (250 MHz, CDCl3) d (ppm): 1.67
(3H, s, CH3CvO), 3.68 (3H, s, CH3O), 5.25 (1H, d,
J¼4.8 Hz, 4-H), 5.85 (1H, d, J¼4.8 Hz, 3-H), 6.72–7.28
(8H, m, Ph). 13C NMR (62.5 MHz, CDCl3) d (ppm): 55.4,
58.8, 84.9, 114.4, 118.6, 127.0, 128.9, 129.5, 130.3, 131.1,
133.2, 156.4, 163.6. Anal. calcd for C18H16ClNO4·1.25H20:
C, 58.71; H, 4.38; N, 3.80. Found: C, 57.50; H, 4.29; N, 3.35.
3.3.8. Racemic 3-acetoxy-1-(4-methoxyphenyl)-4-(3-
nitrophenyl)azetidin-2-one (6)-8. With the procedure
described above 8 was prepared as a brown solid, mp 89–
1
918C. H NMR (250 MHz, CDCl3) d (ppm): 1.73 (3H, s,
3.3.14. Racemic 3-acetoxy-4-(3-chlorophenyl)-1-(4-
methoxyphenyl)azetidin-2-one (6)-14. With the pro-
cedure described above 14 was prepared as a yellow solid,
mp 132–1348C. 1H NMR (250 MHz, CDCl3) d (ppm): 1.68
(3H, s, CH3CvO), 3.69 (3H, s, CH3O), 5.23 (1H, d,
J¼4.9 Hz, 4-H), 5.87 (1H, d, J¼4.9 Hz, 3-H), 6.73–7.25
(8H, m, Ph). 13C NMR (62.5 MHz, CDCl3): 19.8, 55.4,
60.8, 76.2, 114.2, 114.5, 118.7, 126.1, 127.9, 129.1, 130.0,
134.6, 156.7, 161.0, 169.2. Anal. calcd for C18H16ClNO4: C,
62.52; H, 4.66; N, 4.05. Found: C, 61.23; H, 4.56; N, 3.91.
CH3CvO), 3.76 (3H, s, CH3O), 5.45 (1H, d, J¼4.9 Hz, 4-
H), 5.99 (1H, d, J¼4.9 Hz, 3-H), 6.80–8.24 (8H, m, Ph).
13C NMR (62.5 MHz, CDCl3): 19.8, 55.3, 60.2, 76.3, 113.2,
114.3, 118.6, 122.9, 123.5, 129.6, 133.8, 135.00, 148.3,
156.8, 160.6, 169.0. Anal. calcd for C18H16N2O6·0.75H2O:
C, 58.46; H, 4.36; N, 7.57. Found: C, 58.79; H, 4.39; N, 7.00.
3.3.9. Racemic 3-acetoxy-4-(4-cyanophenyl)-1-(4-
methoxyphenyl)azetidin-2-one (6)-9. With the procedure
described above 9 was prepared as a yellow solid, mp 178–
1
1808C. H NMR (250 MHz, CDCl3) d (ppm): 1.66 (3H, s,
3.3.15. Racemic 3-acetoxy-4-(2-chlorophenyl)-1-(4-
methoxyphenyl)azetidin-2-one (6)-15. With the pro-
cedure described above 15 was prepared as a yellow solid,
CH3CvO), 3.69 (3H, s, CH3O), 5.32 (1H, d, J¼4.9 Hz, 4-H),
5.90 (1H, d, J¼4.9 Hz, 3-H), 6.73–7.61 (8H, m, Ph). 13C
NMR(62.5 MHz,CDCl3):19.8, 55.5, 60.8, 76.4, 112.8,114.6,
118.2, 118.6, 128.6, 129.7, 132.3, 138.0, 156.9, 160.6, 169.1.
Anal. calcd for C19H16N2O4·1.6H2O: C, 62.26; H, 4.39; N,
7.64. Found: C, 62.83; H, 4.44; N, 6.87.
1
mp 95–978C. H NMR (250 MHz, CDCl3) d (ppm): 1.69
(3H, s, CH3CvO), 3.69 (3H, s, CH3O), 5.71 (1H, d,
J¼5.0 Hz, 4-H), 6.09 (1H, d, J¼5.0 Hz, 3-H), 6.74–7.38
(8H, m, Ph). 13C NMR (62.5 MHz, CDCl3) d (ppm): 19.9,
55.4, 58.2, 75.4, 114.5, 118.6, 126.8, 128.7, 129.8, 130.0,
130.2, 133.8, 156.7, 161.4, 168.7. Anal. calcd for C18H16-
ClNO4·2.45H2O: C, 55.45; H, 4.13; N, 3.59. Found: C,
51.82; H, 4.56; N, 3.56.
3.3.10. Racemic 3-acetoxy-4-(4-dimethylaminophenyl)-
1-(4-methoxyphenyl)azetidin-2-one (6)-10. With the
procedure described above 10 was prepared as a white
solid, mp 198–1998C. 1H NMR (250 MHz, CDCl3) d
(ppm): 1.67 (3H, s, CH3CvO), 2.88 (6H, s, N(CH3)2), 3.67
(3H, s, CH3O), 5.18 (1H, d, J¼5.1 Hz, 4-H), 5.81 (1H, d,
J¼5.1 Hz, 3-H), 6.61–7.24 (8H, m, Ph). 13C NMR
(62.5 MHz, CDCl3) d (ppm): 20.0, 40.6, 55.4, 61.4, 112.9,
114.3, 118.9, 129.0, 130.5, 156.4, 161.6, 169.4. Anal. calcd
for C20H22N2O4·2.75H20: C, 59.45; H, 5.49; N, 6.93. Found:
C, 60.35; H, 5.57; N, 5.71.
3.3.16. Racemic 3-acetoxy-4-(2,4-dichlorophenyl)-1-(4-
methoxyphenyl)azetidin-2-one (6)-16. With the pro-
cedure described above 16 was prepared as a white solid,
mp 116–1188C. 1H NMR (250 MHz, CDCl3) d (ppm): 1.86
(3H, s, CH3CvO), 3.75 (3H, s, CH3O), 6.07 (1H, d,
J¼5.0 Hz, 4-H), 6.21 (1H, d, J¼5.0 Hz, 3-H), 6.80–7.43
(7H, m, Ph). 13C NMR (62.5 MHz, CDCl3) d (ppm): 20.0,
55.4, 57.8, 75.4, 114.5, 118.6, 127.2, 128.9, 129.7, 134.6,
135.2, 156.8, 161.2, 168.7. Anal. calcd for C18H15Cl2NO4:
C, 56.86; H, 3.98; N, 3.68. Found: C, 56.51; H, 3.96; N, 3.57.
3.3.11. Racemic 3-acetoxy-4-(3-fluorophenyl)-1-(4-meth-
oxyphenyl)azetidin-2-one (6)-11. With the procedure
described above 11 was prepared as a white solid, mp
1
166–1678C. H NMR (250 MHz, CDCl3) d (ppm): 1.67
3.3.17. Racemic 3-acetoxy-4-(2-bromophenyl)-1-(4-
methoxyphenyl)azetidin-2-one (6)-17.35 With the pro-
cedure described above 17 was prepared as a white solid,
(3H, s, CH3CvO), 3.69 (3H, s, CH3O), 5.26 (1H, d,
J¼4.9 Hz, 4-H), 5.88 (1H, d, J¼4.9 Hz, 3-H), 6.73–7.22
(8H, m, Ph). 13C NMR (62.5 MHz, CDCl3): 19.8, 55.4,
60.8, 76.2, 114.5, 114.7, 115.6, 116.0, 118.7, 123.6, 130.0,
135.0, 135.2, 156.7, 160.7, 161.0, 164.7, 169.2. Anal. calcd
for C18H16FNO4·0.7H2O: C, 63.12; H, 4.71; N, 4.09. Found:
C, 63.29; H, 4.39; N, 3.98.
1
mp 79–808C. H NMR (250 MHz, CDCl3) d (ppm): 1.77
(3H, s, CH3CvO), 3.77 (3H, s, CH3O), 5.76 (1H, d,
J¼5.0 Hz, 4-H), 6.19 (1H, d, J¼5.0 Hz, 3-H), 6.81–7.64
(8H, m, Ph). 13C NMR: 114.2, 114.8, 118.7, 123.7, 127.3,
128.9, 130.0, 131.7, 133.1, 156.7, 161.4, 168.7.
3.3.12. Racemic 3-acetoxy-4-(4-fluorophenyl)-1-(4-meth-
oxyphenyl)azetidin-2-one (6)-12.32 With the procedure
described above 12 was prepared as a yellow solid, mp
3.3.18. Racemic 3-acetoxy-4-(3-bromophenyl)-1-(4-
methoxyphenyl)azetidin-2-one (6)-18.36 With the pro-
cedure described above 18 was prepared as a yellow solid,
mp 150–1528C. 1H NMR (250 MHz, CDCl3) d (ppm): 1.75
(3H, s, CH3CvO), 3.76 (3H, s, CH3O), 5.29 (1H, d,
J¼4.9 Hz, 4-H), 5.94 (1H, d, J¼4.9 Hz, 3-H), 6.80–7.46
(8H, m, Ph). 13C NMR (62.5 MHz, CDCl3): 19.8, 55.4,
60.8, 76.2, 114.5, 118.7, 122.6, 126.6, 130.0, 130.8, 132.1,
134.8, 156.7, 161.0, 169.1.
1
1368C (lit.32 136–1378C). H NMR (250 MHz, CD3OD) d
(ppm): 1.60 (3H, s, CH3CvO), 3.62 (3H, s, CH3O), 5.39
(1H, d, J¼4.8 Hz, 4-H), 5.84 (1H, d, J¼4.8 Hz, 3-H), 6.73–
7.24 (8H, m, Ph). 13C NMR (62.5 MHz, CD3OD): 19.7,
55.9, 62.0, 77.7, 115.2, 115.5, 116.2, 116.5, 120.1, 130.2,
131.4, 158.3, 163.3, 170.5.

J. A. Carr et al. / Tetrahedron 59 (2003) 9147–9160
9157
3.3.19. Racemic 3-acetoxy-4-(2-iodophenyl)-1-(4-meth-
oxyphenyl)azetidin-2-one (6)-19. With the procedure
described above 19 was prepared as a white solid, mp
buffer (25 mL, pH 7.2, 0.2 M) in a 50 mL round bottom
flask. To this reaction mixture was added the enzyme
catalyst (lipase PS-30, 100 mg) and reaction flask was
capped to prevent loss of co-solvent due to evaporation. The
reaction mixture was stirred at 258C and progress of the
reaction was monitored via TLC until no further change was
detected. The products were isolated by extraction of the
reaction mixture with ethyl acetate. The crude product
mixture was analyzed by 1H NMR to determine the percent
conversion. The hydrolyzed product (the secondary alcohol)
and the unreacted O-acetate were separated by column
chromatography using a stepwise elution of ethyl acetate/
petroleum ether (15:85) followed by ethyl acetate/pet-
roleum ether (30:70).
1
139–1428C. H NMR (250 MHz, CDCl3) d (ppm): 1.76
(3H, s, CH3CvO), 3.77 (3H, s, CH3O), 5.63 (1H, d,
J¼5.0 Hz, 4-H), 6.18 (1H, d, J¼5.0 Hz 3-H), 6.82–7.91
(8H, m, Ph). 13C NMR (62.5 MHz, CDCl3): 20.0, 55.5,
65.4, 75.4, 98.8, 114.5, 118.7, 128.2, 128.6, 130.0, 130.3,
134.5, 139.8, 156.7, 161.3, 168.7. Anal. calcd for
C18H16INO4: C, 49.45; H, 3.69; N, 3.20. Found: C, 49.37;
H, 3.68; N, 3.04.
3.3.20. Racemic 3-acetoxy-4-(4-bromophenyl)-1-(4-
methoxyphenyl)azetidin-2-one (6)-20. With the pro-
cedure described above 20 was prepared as a white solid,
mp 178–1808C. 1H NMR (360 MHz, CDCl3) d (ppm): 1.76
(3H, s, CH3CvO), 3.78 (3H, s, CH3O), 5.30 (1H, d,
J¼5.0 Hz, 4-H), 5.92 (1H, d, J¼5.0 Hz, 3-H), 6.80–7.51
(8H, m, Ph). 13C NMR (125 MHz, CDCl3): 19.9, 55.4, 60.9,
76.2, 114.5, 118.7, 122.9, 129.6, 130.0, 131.5, 131.7, 156.7,
161.0, 169.2. Anal. calcd for C18H16BrNO4: C, 55.40; H,
4.13; N, 3.59. Found: C, 55.35; H, 4.07; N, 3.55.
For monitoring substrate conversion with time, reactions
were done in 20 mL scintillation vials using 1:1 ratio (w/w)
of substrate to the lipase PS-30. After predetermined times,
aliquot were withdrawn from the reaction, extracted with
ethyl acetate, and the crude reaction product after
evaporation of the solvent was analyzed by 1H NMR
spectroscopy to determine the substrate conversion.
3.3.21. Racemic 3-acetoxy-4-(4-trifluoromethylphenyl)-
1-(4-methoxyphenyl)azetidin-2-one (6)-21. With the
procedure described above 21 was prepared as a white
solid, mp 154–1568C. 1H NMR (250 MHz, CDCl3) d
(ppm): 1.70 (3H, s, CH3CvO), 3.76 (3H, s, CH3O), 5.40
(1H, d, J¼5.0 Hz, 4-H), 5.97 (1H, d, J¼5.0 Hz, 3-H), 6.80–
7.66 (8H, m, Ph). 13C NMR (62.5 MHz, CDCl3): 19.7, 55.4,
60.8, 76.3, 114.5, 118.6, 125.4, 128.3, 129.8, 130.7, 136.6,
156.7, 160.8, 169.1. Anal. calcd for C19H16F3NO4: C, 60.16;
H, 4.25; N, 3.69. Found: C, 60.14; H, 4.25; N, 3.74.
3.5. Non-enzymatic hydrolysis of racemic cis-7
In a 50 mL round bottom flask, 200 mg of the racemic cis-7
was added to a suspension of potassium carbonate (100 mg)
in 25 mL of methanol. The reaction mixture was stirred for
15 min at 08C. The potassium carbonate was filtered off and
the crude reaction mixture was isolated upon removal of
methanol under reduced pressure. The crude mixture was
1
analyzed from its H NMR spectrum, which confirmed the
formation of the diastereomeric racemic cis- and trans-
alcohols 7a and 7b.
3.3.22. Racemic 3-acetoxy-1-(4-methoxyphenyl)-4-(4-
tert-butyl phenyl)azetidin-2-one (6)-22. With the pro-
cedure described above 22 was prepared as a white solid,
mp 175–1778C. 1H NMR (250 MHz, CDCl3) d (ppm): 1.22
(9H, s, C(CH3)3), 1.56 (3H, s, CH3CvO), 3.68 (3H, s,
CH3O), 5.24 (1H, d, J¼4.8 Hz, 4-H), 5.84 (1H, d, J¼4.8 Hz,
3-H), 6.72–7.29 (8H, m, Ph). 13C NMR (62.5 MHz,
CDCl3): 19.7, 31.2, 34.6, 55.4, 61.2, 114.3, 118.8, 125.3,
127.6, 129.1, 130.3, 151.9, 156.5, 161.3, 169.3. Anal. calcd
for C22H25NO4: C, 71.91; H, 6.86; N, 3.81. Found: C, 71.85;
H, 6.72; N, 3.74.
3.6. Enzymatic transesterification of racemic cis-7
In a 50 mL round bottom flask, 100 mg of the racemic cis-7
was dissolved in dry THF (10 mL) to which 40 mL of n-
butanol was added. To this reaction mixture, 100 mg PS-30
was added and the reaction was stirred at 408C for 6 days. The
reaction mixture was filtered through a bed of celite and the
crude reaction mixture was analyzed by1H NMR to determine
its percent conversion. The hydrolyzed product (the secondary
alcohol, ee.97%, [a]2D5¼271.28) and the enantioenriched
O-acetate were separated by column chromatography using a
stepwise elution of ethyl acetate/petroleum ether (20:80)
followed by ethyl acetate/petroleum ether (50:50).
3.3.23. Racemic 3-acetoxy-1-(4-methoxyphenyl)-4-(4-iso-
propylphenyl)azetidin-2-one (6)-23. With the procedure
described above 23 was prepared as a white solid, mp 131–
1
1338C. H NMR (250 MHz, CDCl3) d (ppm): 1.15 (6H, d,
3.7. Determination of the enantiomeric excess
J¼7.0 Hz, CH(CH3)2), 1.58 (3H, s, CH3CvO), 2.82 (1H,
sep., J¼7.0 Hz, CH(CH3)3), 3.68 (3H, s, CH3O), 5.24 (1H,
d, J¼4.8 Hz, 4-H), 5.84 (1H, d, J¼4.8 Hz, 3-H), 6.72–7.24
(8H, m, Ph). 13C NMR (62.5 MHz, CDCl3): 19.7, 23.9,
33.8, 55.4, 61.3, 114.3, 118.8, 126.5, 127.9, 129.4, 130.3,
149.6, 156.5, 161.4, 169.2. Anal. calcd for C21H23NO4: C,
71.37; H, 6.56; N, 3.96. Found: C, 71.30; H, 6.44; N, 3.85.
The enantiopurity (the ee values) was determined from the
1H NMR spectrum acquired on a Bruker 250-MHz NMR
spectrometer in presence of (þ)-[Eu(hfc)3, a chiral shift
reagent. The resonance signal of the acetoxy protons, a
singlet in absence of the chiral shift reagent, was split into
two signals of equal intensity for the two enantiomers in the
racemic mixture. The ratio of the intensity of the CH3CvO
signal in the 1H NMR spectra for the respective enantiomer
was used to calculate the % enantiomeric excess. The %ee
values for the hydrolyzed alcohols were also obtained using
(þ)-[Eu(hfc)3 as a chiral shift reagent after their acetylation
with Ac2O/DMAP in dry THF.
3.4. General procedure for lipase catalyzed hydrolysis of
the acetoxy b-lactam
The racemic 3-acetoxy b-lactam (1–23, 200 mg) was
dissolved in acetone (5 mL) and then added to phosphate

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J. A. Carr et al. / Tetrahedron 59 (2003) 9147–9160
3.7.1. 3-Hydroxy-1-(4-methoxyphenyl)-4-phenylazeti-
din-2-one (2)-1a.14 With the enzymatic hydrolysis pro-
cedure described above, the reaction of racemic 1 afforded
for C18H17NO5·0.96H2O: C, 62.75; H, 4.97; N, 4.07. Found:
C, 62.03; H, 4.91; N, 3.62.
1
1a as a white solid, mp 190–1928C (lit.32 210–2128C). H
3.7.7. cis-3-Hydroxy-1-(4-methoxyphenyl)-4-(4-nitro-
phenyl)azetidin-2-one (6)-7a.27 With the enzymatic
hydrolysis procedure described above, the reaction of
racemic 7 afforded 7a as a yellow solid, mp 182–1838C,
([a]2D5¼08). 1H NMR (250 MHz, CDCl3) d (ppm): 3.65 (3H,
s, CH3O), 5.22 (1H, d, J¼5.2 Hz, 4-H), 5.26 (1H, d,
J¼5.2 Hz, 3-H), 6.64–8.16 (8H, m, Ph). 13C NMR
(62.5 MHz, CDCl3): 55.9, 63.4, 78.6, 115.2, 115.8, 119.9,
124.5, 130.0, 131.7, 143.7, 149.2, 158.1, 167.7.
NMR (250 MHz, CDCl3) d (ppm): 3.76 (3H, s, CH3O), 5.16
(1H, d, J¼5.0 Hz, 4-H), 5.27 (1H, d, J¼5.0 Hz, 3-H), 6.79–
7.45 (9H, m, Ph). 13C NMR (62.5 MHz, CDCl3): 55.4, 62.2,
77.2, 114.1, 114.4, 118.8, 127.4, 129.0, 129.2, 130.4, 133.1,
156.4, 165.3.
3.7.2. 3-Hydroxy-1-(4-methoxyphenyl)-4-(2-phenyl-
ethyenyl)azetidin-2-one (2)-2a.37 With the enzymatic
hydrolysis procedure described above, the reaction of
racemic 2 afforded 2a as a white solid, mp 166–1678C
3.7.8. trans-3-Hydroxy-1-(4-methoxyphenyl)-4-(4-nitro-
phenyl)azetidin-2-one (6)-7b.27 With the enzymatic
hydrolysis procedure described above, the reaction of
racemic 7 afforded 7b as a yellow solid, mp 98–998C,
1
(lit.37 157–1608C). H NMR (250 MHz, CDCl3) d (ppm):
3.74 (3H, s, CH3O), 4.38 (1H, bs, OH), 4.80 (1H, dd, J¼5.0,
8.0 Hz, 4-H), 5.13 (1H, d, J¼5.0 Hz, 3-H), 6.41 (1H, dd,
J¼8.0, 16.0 Hz, 5-H), 6.81–6.84 (1H, d, J¼16.0 Hz, 6-H),
6.76–7.44 (9H, m, Ph). 13C NMR (62.5 MHz, CDCl3):
55.4, 61.6, 77.2, 113.6, 114.0, 114.3, 114.6, 118.8, 123.0,
126.8, 128.6, 130.8, 135.8, 136.5, 156.4, 166.3.
1
([a]2D5¼08). H NMR (250 MHz, CD3OD) d (ppm): 3.60
(3H, s, CH3O), 4.52 (1H, d, J¼1.4 Hz, 4-H), 4.91 (1H, d,
J¼1.4 Hz, 3-H), 6.69–8.13 (8H, m, Ph). 13C NMR
(62.5 MHz, CDCl3): 55.9, 66.4, 85.2, 115.2, 115.5, 120.3,
125.2, 128.4, 131.3, 145.6, 149.3, 158.2, 167.5.
3.7.3. 3-Hydroxy-1-(4-methoxyphenyl)-4-(phenylethy-
nyl)azetidin-2-one (2)-3a. With the enzymatic hydrolysis
procedure described above, the reaction of racemic 3
3.7.9. 3-Hydroxy-1-(4-methoxyphenyl)-4-(3-nitrophenyl)
azetidin-2-one (2)-8a. With the enzymatic hydrolysis
procedure described above, the reaction of racemic 8
1
afforded 3a as a yellow solid, mp 170–1718C. H NMR
1
(250 MHz, CDCl3) d (ppm): 3.66 (3H, s, CH3O), 4.20 (1H,
d, J¼5.0 Hz, 4-H), 4.93 (1H, d, J¼5.0 Hz, 3-H), 5.04 (1H,
bs, OH), 6.66–7.42 (9H, m, Ph). 13C NMR (62.5 MHz,
CDCl3): 51.7, 55.3, 76.7, 81.0, 114.2, 118.7, 121.5, 128.3,
129.1, 130.0, 132.0, 156.6, 165.1. Anal. calcd for
C18H15NO3·0.47H2O: C, 71.64; H, 5.01; N, 4.65. Found:
C, 71.39; H, 4.99; N, 4.46.
afforded 8a as a brown solid, mp 151–1528C. H NMR
(250 MHz, CDCl3) d (ppm): 3.65 (3H, s, CH3O), 4.70
(1H, bs, OH), 5.22 (2H, d, J¼5.1 Hz, 3-H, 4-H), 6.69–
8.15 (8H, m, Ph). 13C NMR (62.5 MHz, CDCl3): 55.4,
61.9, 144.5, 118.8, 122.9, 123.5, 129.7, 133.9, 136.0,
148.3,
156.7,
166.2.
Anal.
calcd
for
C16H14N2O5·0.37H2O: C, 59.88; H, 4.40; N, 8.73.
Found: C, 59.99; H, 4.41; N, 8.09.
3.7.4. 3-Hydroxy-1-(4-methoxyphenyl)-4-thiophen-2-
ylazetidin-2-one (2)-4a.34 With the enzymatic hydrolysis
procedure described above, the reaction of racemic 4
3.7.10. 4-(4-Cyanophenyl)-3-hydroxy-1-(4-methoxyphe-
nyl)azetidin-2-one (2)-9a. With the enzymatic hydrolysis
procedure described above, the reaction of racemic 9
afforded 9a as a white solid, mp 85–88 8C. 1H NMR
(250 MHz, CDCl3) d (ppm): 3.69 (3H, s, CH3O), 4.17 (1H,
bs, OH), 5.20 (2H, s, 3-H, 4-H), 6.72–7.61 (8H, m, Ph). 13C
NMR (62.5 MHz, CDCl3): 55.5, 60.8, 77.2, 112.4, 114.5,
118.4, 118.7, 128.4, 129.8, 132.5, 139.2, 156.8, 165.8. Anal.
calcd for C17H14N2O3: C, 69.38; H, 4.79; N, 9.52. Found: C,
69.25; H, 4.55; N, 9.32.
1
afforded 4a as a white solid, mp 189–1918C. H NMR
(250 MHz, CDCl3) d (ppm): 3.76 (3H, s, CH3O), 5.18 (1H,
dd, J¼5.1 Hz, 4-H), 5.51 (1H, d, J¼5.1 Hz, 3-H), 6.80–7.38
(7H, m, Ph). 13C NMR (62.5 MHz, CDCl3): 55.4, 58.7,
114.4, 118.9, 126.6, 127.3, 127.6, 130.2, 136.5, 156.5,
165.5.
3.7.5. 3-Hydroxy-1,4-bis-(4-methoxyphenyl)-azetidin-2-
one (2)5a.38 With the enzymatic hydrolysis procedure
described above, the reaction of racemic 5 afforded 5a as a
white solid, mp 158–1598C. 1H NMR (250 MHz, CDCl3) d
(ppm): 3.67 (3H, s, CH3O), 3.72 (3H, s, CH3O), 5.07 (1H, d,
J¼5.2 Hz, 4-H), 5.13 (1H, d, J¼5.2 Hz, 3-H), 6.69–7.22
(8H, m, Ph). 13C NMR (62.5 MHz, CDCl3): 55.3, 61.9,
114.3, 114.4, 114.6, 118.9, 124.8, 128.8, 130.5, 156.3,
159.9, 166.0.
3.7.11. 3-Hydroxy-4-(4-dimethylaminophenyl)-1-(4-
methoxyphenyl)azetidin-2-one (2)-10a. With the enzy-
matic hydrolysis procedure described above, the reaction of
racemic 10 afforded 10a as a brown solid, mp 187–1908C.
1H NMR (250 MHz, CDCl3) d (ppm): 2.88 (6H, s,
N(CH3)2), 3.67 (3H, s, CH3O), 5.02 (1H, d, J¼5.0 Hz, 4-
H), 5.11 (1H, d, J¼5.0 Hz, 3-H), 6.67–7.25 (8H, m, Ph).
13C NMR (62.5 MHz, CDCl3) d (ppm): 40.5, 55.4, 62.0,
112.9, 114.3, 118.9, 128.4, 130.7, 150.4, 156.2, 165.9. Anal.
calcd for C18H20N2O3: C, 69.21; H, 6.45; N, 8.97. Found: C,
68.98; H, 6.43; N, 8.80.
3.7.6. 3-Hydroxy-4-(4-methoxycarbonylphenyl)-1-(4-
methoxyphenyl)azetidin-2-one (2)-6a. With the enzy-
matic hydrolysis procedure described above, the reaction of
racemic 6 afforded 6a as a white solid, mp 180–1828C. 1H
NMR (250 MHz, CDCl3) d (ppm): 3.67 (3H, s, CH3O), 3.82
(3H, s, CH3O), 5.12 (1H, d, J¼4.9 Hz, 4-H), 5.18 (1H, d,
J¼4.9 Hz, 3-H), 6.71–7.97 (8H, m, Ph). 13C NMR
(62.5 MHz, CDCl3): 52.1, 55.3, 62.3, 114.3, 118.7, 127.6,
129.7, 129.9, 130.2, 139.1, 156.4, 166.3, 166.9. Anal. calcd
3.7.12. 4-(3-Fluorophenyl)-3-hydroxy-1-(4-methoxyphe-
nyl)azetidin-2-one (2)-11a. With the enzymatic hydrolysis
procedure described above, the reaction of racemic 11
1
afforded 11a as a white solid, mp 217–2188C. H NMR
(250 MHz, CDCl3/CD3OD) d (ppm): 3.67 (3H, s, CH3O),

J. A. Carr et al. / Tetrahedron 59 (2003) 9147–9160
9159
5.08 (1H, d, J¼5.1 Hz, 4-H), 5.12 (1H, d, J¼5.1 Hz, 3-H),
6.71–7.21 (8H, m, Ph). 13C NMR (62.5 MHz, CDCl3/
CD3OD): 55.3, 61.1, 76.8, 114.3, 114.7, 115.1, 115.4, 118.7,
123.2, 130.2, 136.3, 136.4, 156.3, 166.4. Anal. calcd for
C19H16FNO3: C, 66.89; H, 4.91; N, 4.88. Found: C, 66.43;
H, 4.88; N, 4.58.
3.7.18. 4-(2-Bromophenyl)-3-hydroxy-1-(4-methoxyphe-
nyl)azetidin-2-one (2)-17a. With the enzymatic hydrolysis
procedure described above, the reaction of racemic 17
1
afforded 17a as a white solid, mp 205–2068C. H NMR
(250 MHz, CDCl3) d (ppm): 3.69 (3H, s, CH3O), 5.32 (1H,
d, J¼5.1 Hz, 4-H), 5.56 (1H, d, J¼5.1 Hz, 3-H), 6.74–7.53
(8H, m, Ph). 13C NMR (62.5 MHz, CDCl3): 29.3, 55.1,
62.4, 114.1, 118.5, 127.1, 128.4, 129.3, 130.2, 132.5, 132.8,
156.2, 166.3. Anal. calcd for C16H14BrNO3·0.23H2O: C,
54.54; H, 4.00; N, 3.97. Found: C, 54.71; H, 4.01; N, 3.37.
3.7.13. 4-(4-Fluorophenyl)-3-hydroxy-1-(4-methoxyphe-
nyl)azetidin-2-one (2)-12a. With the enzymatic hydrolysis
procedure described above, the reaction of racemic 12
1
afforded 12a as a yellow solid, mp 163–1668C. H NMR
(250 MHz, CDCl3/CD3OD) d (ppm): 3.69 (3H, s, CH3O),
6.16 (1H, d, J¼5.1 Hz, 4-H), 6.23 (1H, d, J¼5.1 Hz, 3-H),
7.82–8.36 (8H, m, Ph). 13C NMR (62.5 MHz, CDCl3/
CD3OD): 55.3, 62.0, 76.6, 114.6, 115.3, 118.7, 129.3, 130.2,
156.3, 160.7, 164.6, 166.5. Anal. calcd for C19H16-
FNO3·5.84H2O: C, 48.96; H, 3.59; N, 3.57. Found: C,
43.65; H, 3.20; N, 3.02.
3.7.19. 4-(3-Bromophenyl)-3-hydroxy-1-(4-methoxyphe-
nyl)azetidin-2-one (2)-18a. With the enzymatic hydrolysis
procedure described above, the reaction of racemic 18
1
afforded 18a as a yellow solid, mp 182–1838C. H NMR
(250 MHz, CDCl3) d (ppm): 3.68 (3H, s, CH3O), 5.11 (2H,
s, 3-H, 4-H), 6.71–7.44 (8H, m, Ph). 13C NMR (62.5 MHz,
CDCl3): 55.4, 62.0, 77.2, 114.2, 114.5, 118.7, 118.9, 123.0,
126.2, 127.7, 130.1, 130.6, 130.7, 131.9, 135.9, 156.6,
165.9. Anal. calcd for C16H14BrNO3: C, 55.15; H, 4.05; N,
4.02. Found: C, 55.10; H, 4.00; N, 4.05.
3.7.14. 4-(4-Chlorophenyl)-3-hydroxy-1-(4-methoxyphe-
nyl)azetidin-2-one (2)-13a.39 With the enzymatic hydroly-
sis procedure described above, the reaction of racemic 13
1
afforded 13a as a white solid, mp 180–1818C. H NMR
3.7.20. 3-Hydroxy-4-(2-iodophenyl)-1-(4-methoxypheny-
l)azetidin-2-one (2)-19a. With the enzymatic hydrolysis
procedure described above, the reaction of racemic 19
(250 MHz, CDCl3) d (ppm): 3.68 (3H, s, CH3O), 5.13 (1H,
d, J¼5.1 Hz, 4-H), 5.16 (1H, d, J¼5.1 Hz, 3-H), 6.71–7.31
(8H, m, Ph). 13C NMR (62.5 MHz, CDCl3) d (ppm):
55.4, 61.9, 114.4, 118.8, 129.0, 129.1, 130.1, 131.8, 134.7,
156.6.
1
afforded 19a as a yellow solid, mp 78–808C. H NMR
(250 MHz, CDCl3) d (ppm): 3.69 (3H, s, CH3O), 5.27 (1H,
d, J¼5.0 Hz, 4H), 5.36 (1H, d, J¼5.0 Hz, 3H), 6.73–7.86
(8H, m, Ph). 13C NMR (62.5 MHz, CDCl3): 55.4, 66.5,
76.9, 98.2, 114.2, 114.5, 118.8, 128.4, 130.1, 130.3, 135.5,
139.7, 156.5, 165.4. Anal. calcd for C16H14INO3: C, 48.63;
H, 3.57; N, 3.54. Found: C, 43.65; H, 3.45; N, 3.50.
3.7.15. 4-(3-Chlorophenyl)-3-hydroxy-1-(4-methoxyphe-
nyl)azetidin-2-one (2)-14a. With the enzymatic hydrolysis
procedure described above, the reaction of racemic 14
1
afforded 14a as a white solid, mp 197–1988C. H NMR
(250 MHz, CDCl3) d (ppm): 3.68 (3H, s, CH3O), 5.12 (2H,
s, 3-H, 4-H), 6.71–7.28 (8H, m, Ph). 13C NMR (62.5 MHz,
CDCl3): 55.4, 62.0, 77.2, 114.2, 114.4, 118.8, 125.8, 127.7,
129.0, 130.1, 134.9, 135.6, 156.6, 165.8. Anal. calcd for
C16H14ClNO3·0.75H2O: C, 60.56; H, 4.45; N, 4.41. Found:
C, 60.96; H, 4.48; N, 4.09.
3.7.21. 4-(4-Bromophenyl)-3-hydroxy-1-(4-methoxyphe-
nyl)azetidin-2-one (2)-20a. With the enzymatic hydrolysis
procedure described above, the reaction of racemic 20
1
afforded 20a as a pale yellow solid, mp 193–1948C. H
NMR (360 MHz, CDCl3) d (ppm): 3.68 (3H, s, CH3O), 5.05
(2H, s, 3-H,4-H), 6.62–7.46 (8H, dd, J¼5.9, 5.5 Hz, Ph).
13C NMR (62.5 MHz, CDCl3): 55.4, 61.9, 114.5, 118.8,
122.9, 129.3, 130.2, 132.1, 132.4, 156.6, 165.6. Anal. calcd
for C16H14BrNO3: C, 55.19; H, 4.05; N, 4.02. Found: C,
55.02; H, 3.97; N, 3.99.
3.7.16. 4-(2-Chlorophenyl)-3-hydroxy-1-(4-methoxyphe-
nyl)azetidin-2-one (2)-15a. With the enzymatic hydrolysis
procedure described above, the reaction of racemic 15
1
afforded 15a as a brown solid, mp 214–2178C. H NMR
(250 MHz, CDCl3/CD3OD) d (ppm): 3.69 (3H, s, CH3O),
5.19 (1H, d, J¼5.0 Hz, 4-H), 5.53 (1H, d, J¼5.0 Hz, 3-H),
6.75–7.38 (8H, m, Ph). 13C NMR (62.5 MHz, CDCl3/
CD3OD) d (ppm): 55.1, 60.2, 114.2, 118.5, 126.6, 128.2,
129.0, 129.3, 130.2, 131.3, 133.1, 156.2, 166.3. Anal. calcd
for C16H14ClNO3·1.13H2O: C, 59.30; H, 4.36; N, 3.35.
Found: C, 58.30; H, 4.28; N, 3.69.
3.7.22. 4-(4-Trifluoromethylphenyl)-3-hydroxy-1-(4-
methoxyphenyl)azetidin-2-one (2)-21a. With the enzy-
matic hydrolysis procedure described above, the reaction of
racemic 21 afforded 21a as a white solid, mp 220–2238C.
1H NMR (250 MHz, CDCl3/CH3OH) d (ppm): 3.66 (3H, s,
CH3O), 5.10 (1H, d, J¼5.0 Hz, 4-H), 5.17 (1H, d, J¼5.0 Hz,
3-H), 6.70–7.55 (8H, m, Ph). 13C NMR (62.5 MHz,
CDCl3): 55.2, 62.1, 76.8, 114.3, 118.6, 125.3, 128.0,
130.1, 138.0, 156.4, 166.3. Anal. calcd for C17H14F3NO3:
C, 60.54; H, 4.18; N, 4.15. Found: C, 60.32; H, 4.25; N,
4.10.
3.7.17. 4-(2,4-Dichlorophenyl)-3-hydroxy-1-(4-methoxy-
phenyl)azetidin-2-one (2)-16a. With the enzymatic
hydrolysis procedure described above, the reaction of
racemic 16 afforded 16a as a brown solid, mp 181–
1838C. 1H NMR (250 MHz, CDCl3/CD3OD) d (ppm): 3.70
(3H, s, CH3O), 5.19 (1H, d, J¼4.6 Hz, 4-H), 5.49 (1H, d,
J¼4.6 Hz, 3-H), 6.75–7.41 (7H, m, Ph). 13C NMR
(62.5 MHz, CDCl3/CD3OD) d (ppm): 55.3, 59.8, 114.4,
118.5, 127.1, 129.4, 130.1, 130.2, 134.0, 156.5. Anal. calcd
for C16H13Cl2NO3: C, 56.82; H, 3.87; N, 4.14. Found: C,
56.75; H, 3.90; N, 4.05.
3.7.23. 3-Hydroxy-4-(4-tert-butylphenyl)-1-(4-methoxy-
phenyl)azetidin-2-one (2)-22a. With the enzymatic
hydrolysis procedure described above, the reaction of
racemic 22 afforded 22a as a white solid, mp 180–1828C.
1H NMR (250 MHz, CDCl3) d (ppm): 1.30 (9H, s,
C(CH3)3), 3.76 (3H, s, CH3O), 5.14 (1H, d, J¼5.0 Hz, 4-
H), 5.21 (1H, d, J¼5.0 Hz, 3-H), 6.79–7.41 (8H, m, Ph).

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J. A. Carr et al. / Tetrahedron 59 (2003) 9147–9160
13C NMR (62.5 MHz, CDCl3): 30.8, 34.2, 55.0, 62.4, 114.0,
118.6, 125.2, 127.1, 130.1, 130.3, 151.0, 156.1. Anal. calcd
for C20H23NO3: C, 73.82; H, 7.12; N, 4.30. Found: C, 73.74;
H, 7.05; N, 4.19.
Dickey, S.; Lim, D. V.; Cannons, A. Bioorg. Med. Chem. Lett.
2002, 12, 2229–2231. Coates, C.;Long, T. E.;Turos,E.;Dickey,
S.;Lim, D.V.Bioorg. Med.Chem.2003, 11, 193–196. Turos, E.;
Konaklieva, M. I.; Ren, R. X.-F.; Shi, H.; Gonzalez, J.; Dickey,
S.; Lim, D. V. Tetrahedron 2000, 56, 5571–5578. Ren, X.-F.;
Konaklieva, M. I.; Shi, H.; Dickey, S.; Lim, D. V.; Gonzalez, J.;
Turos, E. J. Org. Chem. 1998, 63, 8898–8917. Long, T. E.;
Turos,E.;Konaklieva,M.I.;Blum,A.L.;Amry,A.;Baker,E.A.;
Suwandi, L. S.; McCain, M. D.; Rahman, M. F.; Dickey, S.; Lim,
D. V. Bioorg. Med. Chem. 2003, 11, 1859. Long, T. E.; Turos, E.
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3.7.24. 3-Hydroxy-4-(4-isopropylphenyl)-1-(4-methoxy-
phenyl)azetidin-2-one (2)-23a. With the enzymatic
hydrolysis procedure described above, the reaction of
racemic 23 afforded 23a as a white solid, mp 238–2408C.
1H NMR (250 MHz, CDCl3) d (ppm): 1.17 (6H, d,
J¼6.9 Hz, CH(CH3)2), 2.50 (1H, bs, OH), 2.83 (1H, sep.,
J¼6.9 Hz, CH(CH3)3), 3.68 (3H, s, CH3O), 5.07 (1H, bs, 4-
H), 5.17 (1H, d, J¼5.0 Hz, 3-H), 6.71–7.24 (8H, m, Ph).
13C NMR (62.5 MHz, CDCl3/CH3OH): 23.3, 33.5, 54.9,
62.5, 114.0, 118.6, 126.3, 127.3, 130.3, 130.5, 148.7, 156.0,
166.5. Anal. calcd for C19H21NO3: C, 73.29; H, 6.80; N,
4.50. Found: C, 73.15; H, 6.55; N, 4.40.
15. Cvetovich, R. J.; Chartrain, M.; Hartner, Jr. F. W. H.; Roberge,
C.; Amato, J. S.; Grabowski, E. J. J. J. Org. Chem. 1996, 61,
6575.
16. Seki, M.; Furutani, T.; Miyake, T.; Yamanaka, T.; Ohmizu, H.
Tetrahedron: Asymmetry 1996, 7, 1241.
Acknowledgements
17. Nagai, H.; Shiozawa, T.; Achiwa, K.; Terao, Y. Chem. Pharm.
Bull. Jpn 1992, 40, 2227.
Financial support from the American Lung Association, the
American Cancer Society, and the National Institute of
Health (ET) is greatly appreciated. We thank Dr Rosa Walsh
and Professor Mike Zaworotko for acquisition of the X-ray
crystallographic data. We also extend our thanks to
Professor Bill Baker for access to the optical polarimeter.
The gift of lipases from Novozymes North America Inc. and
Amano Enzymes is greatly appreciated.
18. Jouglet, B.; Rousseau, G. Tetrahedron Lett. 1993, 34, 2307.
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