Concept of counterattack reagents: Intramolecular counterattack strategy in the synthesis of biologically active isopenams

Article abstract of DOI:10.1002/(SICI)1521-3765(19990903)5:9<2705::AID-CHEM2705>3.0.CO;2-9

A novel strategy was developed for the synthesis of isopenams in high yields. The strategy involves use of the intramolecular counterattack process in the conversions of (±)-5 → (±)-11, (±)-6 → (±)-12, and (±)-19 → (±)-11. Catalytic hydrogenation of (±)-1

Full text of DOI:10.1002/(SICI)1521-3765(19990903)5:9<2705::AID-CHEM2705>3.0.CO;2-9

FULL PAPER
Concept of Counterattack Reagents: Intramolecular Counterattack Strategy
in the Synthesis of Biologically Active Isopenams
Jih Ru Hwu,*[a, b] Shahram Hakimelahi,[a]
Ali A. Moosavi-Movahedi,[c] and Shwu-Chen Tsay[a]
Abstract: A novel strategy was devel-
oped for the synthesis of isopenams in
high yields. The strategy involves use of
the intramolecular counterattack pro-
cess in the conversions of (Æ)-5 !(Æ)-
11, (Æ)-6 !(Æ)-12, and (Æ)-19 !(Æ)-11.
Catalytic hydrogenation of (Æ)-11 af-
forded isopenam (Æ)-13, which pos-
sessed notable antimicrobial activities.
Oxidation of (Æ)-13 with KMnO4 gave
sulfone (Æ)-15, which functioned as a
potent inhibitor of various bacterial b-
lactamases. Sulfone (Æ)-15 exerted a
great synergistic effect on antimicrobial
agent (Æ)-13. Results from the CVFF
calculations of the C-2 b-epimer of
isopenam 13 (i.e., 23) and the corre-
sponding sulfone derivative 24 indicate
the existence of a severe electronic
repulsion between the b-lactam carbon-
yl and the C-2 carboxyl groups. Steric
interaction also exists between the C-6
amide side chain and the C-2 carboxylic
acid moiety in 23 and 24. These inter-
actions, however, do not exist in the
corresponding a-epimers 13 and 15.
Keywords: antimicrobial agents
´
´
´
counterattack
isopenam
´
´
drug research
lactams
reaction mechanisms
Introduction
Results
Application of a counterattack reagent strategy in organic
synthesis allows two transformations or more to be accom-
plished in one flask.[1] In the first transformation, the reagent
is attacked by a reactant to give a stable intermediate. In the
second transformation, a moiety produced from this originally
consumed reagent counterattacks the intermediate to afford
the desired product. The concept of counterattack reagents
has been utilized in the performance of various chemical
transformations.[2±5] Use of this method can simplify chemical
conversions and minimize manipulations. With these advan-
tages in mind, we developed an intramolecular counterattack
process for efficient synthesis of isopenams (Æ)-13 and (Æ)-15.
These compounds were found to possess important biological
activities.
For the synthesis of isopenams (Æ)-13 and (Æ)-15, we treated
racemic monocyclic b-lactam 1[6] with KSCOMe in DMF to
produce the corresponding thioester 3 in 90% yield (Meth-
od A in Scheme 1). Chlorination of thioester
3 with
CF3SO2Cl[7] in Et3N generated chloride 5 in 90% yield.
Treatment of 5 with piperidine afforded isopenam 11 in 90%
yield (Method C). By the same procedures, we successfully
accomplished the transformations of diastereomeric mono-
cyclic b-lactam 2[8] !4 (95%) !6 (95%) !12 (95%) in an
excellent yield for each step.
Finally, we debenzylated 11 and 12 with H2 at 458C in the
presence of Pd/C and MeOH to give the corresponding
carboxylic acids (Æ)-13 and (Æ)-14, respectively, in 55% yield.
Oxidation of sulfides 13 and 14 with KMnO4 in aqueous acetic
acid solution gave the corresponding sulfones (Æ)-15 (40%)
and (Æ)-16 (50%), respectively. The low yields for the
formation of compounds 13 ± 16 could be attributed to the
susceptibility of their b-lactam rings toward nucleophilic
attack by methanol or water. This was confirmed by the lack
of the b-lactam ring in the corresponding residues, as
evidenced by IR spectroscopy.
To support the proposed mechanism for the transforma-
tions of 5 !11 and 6 !12, we performed the following control
experiments. Treatment of chloride 5 with nBuSH in a
mixture of CH2Cl2 and Et3N afforded sulfide 18 in 60% yield
(Method F in Scheme 2). Performance of the same reaction in
[a] Prof. J. R. Hwu, S. Hakimelahi, Dr. S.-C. Tsay
Organosilicon and Synthesis Laboratory, Institute of Chemistry
Academia Sinica, Nankang, Taipei
Taiwan 11529 (Republic of China)
Fax : (‡ 886)22-788-1337
E-mail: jrhwu@chem.sinica.edu.tw
[b] Prof. J. R. Hwu
Department of Chemistry, National Tsing Hua University
Hsinchu, Taiwan 30043 (Republic of China)
[c] Prof. A. A. Moosavi-Movahedi
Institute of Biochemistry-Biophysics
Tehran University, Tehran (Iran)
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J. R. Hwu et al.
FULL PAPER
the absence of Et3N gave dechlorinated product 3, isolated in
85% yield (Method B), and nBuSCl. Subsequent treatment of
this mixture with Et3N afforded 18 in 46% yield. Further-
more, reaction of pure 3 with nBuSCl and Et3N also generated
18 in 46% yield (Method G in Scheme 2).
To investigate the mechanism of an intramolecular cycliza-
tion process, we mesylated racemic malonate 3 with MeSO2Cl
in Et3N (Scheme 3). The corresponding sulfone thioester 19
was obtained in 98% yield. Deacetylation of sulfone thioester
19 in DMF with piperidine in the presence of 1,8-diazabicy-
clo[5.4.0]undec-7-ene (DBU) at 608C produced isopenam
(Æ)-11 in 80% yield (Method D). In the absence of DBU,
sulfone thioester 19 was deacetylated by piperidine at 258C to
give mercaptomesylate 22 (96% yield). This reaction involved
a protonation step of anion 21 by a 1-acyl piperidinium species
generated in situ. In a separate reaction, we cleaved the
S SO2Me bond in 22 through an intramolecular cyclization by
use of DBU in DMF at 608C (Method E). Accordingly,
isopenam (Æ)-11 was isolated in 78% yield.
With a Silicon Graphics workstation, we carried out the
CVFF calculations on the isopenam 13, its sulfone derivative
15, and their corresponding b-epimers 23 and 24. Our goal was
to justify the exclusive formation of the a-epimers 13 and 15.
The thermodynamically most stable forms for compounds 13,
15, 23, and 24 are shown in Figure 1. We found that the
distance between the lactam carbonyl oxygen and the
carboxyl oxygen atoms in the b-epimer 23 was 3.69 Š (see
Figure 1). It is significantly shorter than 4.09 Š in the a-
epimeric isopenam 13. The distances between the lactam
Scheme 1. Synthesis of isopenams 13 ± 16 involving an intramolecular
counterattack process.
Scheme 2. Counterattack strategy in the conversion of chloride 5 to sulfide
18.
carbonyl oxygen and the carboxyl oxygen atoms in the a-
epimer 15 and the b-epimer 24 were 4.34 Š and 3.78 Š,
respectively (see Figure 1). We obtained these values by the
same calculation method.
In the Figure 1, the blue ball on the top center side
represents the C-6 amide nitrogen atom; the two red balls
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Chem. Eur. J. 1999, 5, No. 9

Counterattack Reagents
2705±2711
attached to the same green (not yellow) atom on the right side
represent the C-2 carboxylate oxygen atoms. We observe
severe steric interaction between the C-6 amide side chain and
the C-2 carboxylic acid moiety in b-epimers 23 and 24. Such
interaction is absent in the a-epimeric isopenam 13 and
isopenam sulfone 15. On the basis of these two factors, 13 and
15 are thermodynamically more stable than 23 and 24 by 3.50
1
and 2.73 kcalmol , respectively.
Discussion
By examining the reaction conditions and products of the
control experiments shown in Scheme 2, we believe that
nBuS , generated from nBuSH and Et3N in the first reaction,
attacks chloride 5 to give nBuSCl and carbanion 17. Regarded
as a nucleophile, this carbanion then counterattacks nBuSCl,
generated in situ, to produce sulfide 18. A similar mechanism
can be applied to cyclizations of 5 !11 and 6 !12 (Scheme 1):
upon deacetylation with piperidine, thioesters 5 and 6 would
give the corresponding sulfide anions 7 and 8. The thiolate
moiety of each then attacks the corresponding chlorine atoms
in 7 and 8 intramolecularly to produce carbanions 9 and 10,
respectively. Subsequently, intramolecular cyclizations occur
in 9 and 10 by cleavage of the weak S Cl bond to afford the
corresponding thiazolidines 11 and 12, respectively.
Scheme 3. Intramolecular counterattack strategy in the transformation of
thioester 3 to isopenam 11.
Feasibility of the intramolecular counterattack process is
further confirmed in a related conversion (i.e., 19 !11) as
shown in Scheme 3. Upon reaction with piperidine, sulfone
thioester 19 affords sulfide 20. Intramolecular transfer of the
sulfone moiety then takes place in 20 to give the mercapto-
mesylate carbanion 21, which has an ideal geometry to allow
intramolecular cyclization to occur through the favorable
5-Exo-Tet mode.[9] Our experimental results about the suc-
cessful conversion of 22 to 11 by DBU provide more evidence
to support the mechanism.
In the transformation of 5 !18 in the presence of nBuSH
and Et3N as shown in Scheme 2, chloride 5 can be regarded as
a counterattack reagent. By analogy, the conversions of
5 !11, 6 !12 (Scheme 1), and 19 !11 (Scheme 3) under basic
conditions involve an intramolecular counterattack process.
The a-chloro ester moieties in 7 and 8 as well as the sulfone
malonate moiety in 20 are first attacked intramolecularly by
the sulfide moieties, which are generated by deacetylation of
the corresponding thioesters 5, 6, and 19. The resultant
carbanions 9, 10, and 21 then counterattack the S Cl or the
S SO2Me unit to form the thiazolidine ring in 11 and 12.
Biological activity: We carried out the screening experiments
for antimicrobial activities[10, 11] of b-lactams (Æ)-13 ± (Æ)-16, a
mixture of (Æ)-13 and (Æ)-15 (1:1 w/w), as well as the
reference compounds ampicillin (25), amoxicillin (26), peni-
cillin G (27), and clavulanic acid (28). The experiments were
performed in vitro against different strains of five pathogenic
Figure 1. The structures represented by ball-and-stick as well as CPK
space filling molecular models are those with the lowest energy obtained by
the CVFF calculations. The green balls represent carbon atoms, white for
hydrogen, red for oxygen, blue for nitrogen, and yellow for sulfur:
a) isopenam 13 with an a-carboxylic group at the C-2 position; b) isopenam
23 with a b-carboxylic group at the C-2 position; c) isopenam sulfone 15
with an a-carboxylic group at the C-2 position; and d) isopenam sulfone 24
with a b-carboxylic group at the C-2 position.
1
microorganisms up to 128 mgmL . The results are summar-
ized in Table 1. Furthermore, we tested the b-lactamase
inhibitory[12] properties of b-lactams (Æ)-13 ± (Æ)-16. Clavu-
lanic acid (28) was used in vitro as the reference compound.
The results are shown in Table 2.
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J. R. Hwu et al.
FULL PAPER
Table 1. Minimum inhibitory concentrations[a] of synthetic b-lactams (Æ)-13, (Æ)-14, (Æ)-15, a 1:1 (w/w) mixture of (Æ)-13 and (Æ)-15, and (Æ)-16 as well as
the reference compounds ampicillin (25), amoxicillin (26), penicillin G (27), and clavulanic acid (28).
Microorganism
(Æ)-13
(Æ)-14
(Æ)-15
12.5
(Æ)-13 ‡ (Æ)-15
(Æ)-16
25
26
27
28
S. a. FDA 209P
S. a. A9606[b]
S. a. A15091[b]
S. a. A20309[b]
S. a. 95[b,c]
E. c. ATCC 39188
E. c. A9675[b]
E. c. A21223[b]
S. t. O-901
P. a. 1101-75
P. a. 18S-H[b]
K. p. NCTC 418
K. p. A20634 TEM[b]
0.10
1.20
0.92
1.70
3.25
0.76
2.56
1.77
35.0
128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
0.060
0.20
0.47
0.70
0.98
0.17
1.20
0.89
15.0
45.0
37.0
35.0
23.5
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
0.33
0.78
0.40
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
16.7
8.85
15.3
16.6
8.93
7.85
8.72
62.9
65.8
85.0
> 128
> 128
100
> 128
> 128
112
> 128
120
> 128
> 128
> 128
> 128
2.50
70.3
3.60
57.1
80.5
> 128
> 128
> 128
> 128
> 128
2.30
100
128
125
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
100
98.4
68.0
> 128
100
[a] The values of minimum inhibitory concentrations (mgmL 1), obtained as the average of triplicate determinations, represent the lowest concentrations of
antibiotics required to prevent visible growth of Staphylococcus aureus (S. a.), Escherichia coli (E. c.), Salmonella typhi (S. t.), Pseudomonas aeruginosa
(P. a.), and Klebsiella pneumoniae (K. p.). These values were obtained by use of an agar dilution method whereby organisms were deposited onto medicated
agar plates by the replication device of Steers et al.[15] [b] b-Lactamase-producing organism. [c] Methicillin resistant organism.
Isopenam (Æ)-13, which has an identical skeleton to
penicillin antibiotics at the C-2 position, exhibited notable
antimicrobial activities but low b-lactamase inhibitory proper-
ties. Isopenam sulfone (Æ)-15, however, showed excellent
minimum protective concentration (MPC) values against the
b-lactamases of different bacterial species. It also exhibited
moderate minimum inhibitory concentration (MIC) against
some pathogenic microorganisms.
The b-lactamase inhibitory properties of (Æ)-15 allowed it
to exert a large synergistic effect on antimicrobial agent (Æ)-
13. Thus a 1:1 mixture of (Æ)-13 and (Æ)-15 exhibited notable
antimicrobial activity (Table 1). The oxidation of the sulfur
atom in isopenam (Æ)-13 to the corresponding sulfone
derivative (Æ)-15 led to significant changes in antimicrobial
as well as b-lactamase inhibitory properties.
In contrast to isopenam (Æ)-13 (see Table 1), isopenam 29
does not inhibit the growth of the bacteria S. aureus.[13]
Moreover, isopenam sulfone (Æ)-15 exhibited b-lactamase
Table 2. b-Lactamase inhibitory properties of synthetic b-lactams (Æ)-13 ±
(Æ)-16 as well as natural clavulanic acid (28) against bacterial b-lactamases.
1
Minimum protective concentrations[a] [mgmL
]
S. a.
E. c.
P. a.
K. p.
inhibitory properties (Table 2), yet isopenam sulfone 30 has
no effect upon the b-lactamase from P. aeruginosa. These
results indicate that the presence of a cis-oriented acylamino
group at the C-6 position is necessary for the biological
activity of isopenams[14] and isopenam sulfones. It should be
noted that our synthetic b-lactams were in a racemic form,
whereas natural b-lactam antibiotics are single stereoiso-
mers.[15] Thus, only one half of the minimum inhibitory or
protective concentrations would be necessary for each of the
desired single enantiomer of 13 ± 16.
b-Lactams (Æ)-14 and (Æ)-16 possess a phenyl functionality
at the C-2 position. The quaternary carbon center therein
makes these two b-lactams biologically inactive either as
antimicrobial agents (Table 1) or b-lactamase inhibitors
(Table 2).
(Æ)-13
(Æ)-14
(Æ)-15
(Æ)-16
28
74.1
60.6
58.9
68.5
> 128
0.88
126
0.56
> 128
3.15
114
5.12
> 128
2.74
128
3.00
> 128
0.98
> 128
0.17
[a] The values of minimum protective concentrations, obtained as the
average of triplicate determinations, represent the ability of compounds to
inhibit the hydrolysis of an indicator, 3-[E-(2,4-dinitro)styryl]-(6R,7R)-7-
(2-thienylacetamido)-3-cephem-4-carboxylic acid by b-lactamases from S.
aureus A9606 (S. a.), E. coli A9675 (E. c.), P. aeruginosa 18S-H (P. a.), and
K. pneumoniae A20634 TEM (K. p.). The values of minimum protective
concentrations, determined by the procedure of OꢁCallaghan et al.,[12]
represent the lowest concentrations of inhibitors required to protect the
indicator from hydrolysis by b-lactamases under standard test conditions
within 30 min. The hydrolysis of indicators was evidenced by the
appearance of a distinct red color.
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Counterattack Reagents
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(CH2Cl2): nÄ ˆ 3405 (NH), 1775 (b-lactam), 1740 (ester), 1732 (thioester),
1680 (amide) cm 1; C31H30N2O7S (574.7): calcd C 64.79, H 5.26, N 4.87, S
5.58; found C 64.70, H 5.13, N 4.72, S 5.60.
Conclusion
A new type of reaction mechanism was established for the
construction of a heterocyclic ring fused with a b-lactam
nucleus. In the formation of the thiazolidine ring in isopenams
11 and 12 from the corresponding thioesters 5 and 6 under
basic conditions, the sulfide unit in intermediates 7 and 8
attacked the corresponding chloromalonate and chlorophen-
ylacetate moieties, respectively. An intramolecular cyclization
occurred subsequently in the resultant intermediates 9 and 10
to form the corresponding isopenams 11 and 12. The entire
reaction thus went through an intramolecular counterattack
process. The thioesters 5 and 6 acted as counterattack
reagents. The same mechanism was responsible for the
transformation of sulfone thioester 19 to isopenam 11 via
sulfide 20 and malonate anion 21. Formation of isopenam 11
from 19 through intramolecular cyclization indicates that 19
functioned as an intramolecular counterattack reagent in the
presence of a base.
Our CVFF computational results indicate that a-epimers
isopenam 13 and isopenam sulfone 15 were thermodynami-
cally more stable than the corresponding b-epimers. They
possessed the same epimeric configuration as that of pen-
icillins at the C-2 position.
Isopenam (Æ)-13 showed notable antimicrobial activities
and its sulfone derivative (Æ)-15 exhibited potent b-lactamase
inhibitory properties. Moreover, a mixture of isopenam (Æ)-
13 and isopenam sulfone (Æ)-15 in a ratio of 1:1 (w/w) was
found to possess remarkable activities against different strains
of pathogenic microorganisms in vitro.
Method B: nBuSH (187 mg, 2.10 mmol) was added to a solution of (Æ)-5
(1.22 g, 2.01 mmol) in CH2Cl2 (10 mL) at room temperature. After 30 min,
the solution was concentrated and the residue was purified by column
chromatography (CHCl3 as eluant) to afford (Æ)-3 (980 mg, 1.70 mmol) in
85% yield.
Benzyl(3RS,4RS)-2-(4-acetylthiomethyl-2-oxo-3-phenylacetamido-1-aze-
tidinyl)-2-phenylacetates [(Æ)-4]: Compounds (Æ)-4 (4.90 g, 9.49 mmol)
were prepared in 95% yield from (Æ)-2[8] (5.36 g, 9.99 mmol) and
KSCOMe (2.28 g, 19.9 mmol) by the same procedure for the conversion
1
of 1 !3. H NMR (CDCl3): d ˆ 2.35 (s, 3H; CH3CO), 2.65 ± 2.90 (br, 2H;
CH2S), 3.60 (s, 2H; CH2CO), 3.99 ± 4.20 (m, 1H; HC(4)), 5.19 (s, 2H;
CH2O), 5.50 (dd, 3J(H,H) ˆ 9.0, 4.8 Hz, 1H; HC(3)), 5.70 (s, 1H; CH),
6.90 ± 7.59 (m, 16H; NH, 3  C6H5); IR (CH2Cl2): nÄ ˆ 3400 (NH), 1770 (b-
lactam), 1750 (ester), 1730 (thioester), 1680 (amide) cm 1; C29H28N2O5S
(516.6): calcd C 67.42, H 5.46, N 5.42, S 6.21; found C 67.30, H 5.45, N 5.51, S
6.11.
Dibenzyl(3RS,4RS)-2-(4-acetylthiomethyl-2-oxo-3-phenylacetamido-1-
azetidinyl)-2-chloromalonate (5): CF3SO2Cl (0.86 g, 5.1 mmol) in CH2Cl2
(5.0 mL) was added to a solution containing (Æ)-3 (2.87 g, 4.99 mmol) and
Et3N (0.61 g, 6.0 mmol) in CH2Cl2 (50 mL) at 08C over a period of 5.0 min.
The reaction mixture was stirred and allowed to warm to room temperature
within 1.0 h. The solvent was evaporated to dryness under reduced
pressure, and then Et2O (50 mL) was added. The ethereal solution was
washed with water (2 Â 50 mL), dried over MgSO4, and treated with
charcoal. After filtration, evaporation, and then purification by use of
column chromatography (CHCl3 as eluant), (Æ)-5 (2.74 g, 4.49 mmol) was
obtained as a foam in 90% yield. 1H NMR (CDCl3): d ˆ 2.35 (s, 3H;
CH3CO), 2.68 ± 2.92 (br, 2H; CH2S), 3.61 (s, 2H; CH2CO), 4.12 ± 4.29 (m,
1H; HC(4)), 5.16, 5.18 (2s, 4H; 2  CH2O), 5.30 (dd, 3J(H,H) ˆ 9.0, 5.0 Hz,
1H; HC(3)), 7.04 (d, 3J(H,H) ˆ 9.0 Hz, 1H; NH), 7.39 (brs, 15H; 3  C6H5);
IR (CH2Cl2): nÄ ˆ 3410 (NH), 1791 (b-lactam), 1750 (ester), 1730 (thioester),
1680 (amide) cm 1; C31H29N2O7SCl (609.1): calcd C 61.13, H 4.80, N 4.60, S
5.26, Cl 5.82; found C 61.12, H 4.81, N 4.71, S 5.30, Cl 5.89.
Benzyl(3RS,4RS)-2-(4-acetylthiomethyl-2-oxo-3-phenylacetamido-1-aze-
tidinyl)-2-chloro-2-phenylacetates [(Æ)-6]: Compounds (Æ)-6 (4.05 g,
7.34 mmol) were prepared in 95% yield from (Æ)-4 (4.00 g, 7.74 mmol),
Et3N (0.94 g, 9.3 mmol), and CF3SO2Cl (1.30 g, 7.90 mmol) by the same
Experimental Section
General: Chemicals were purchased from Fluka. Reagent-grade solvents
were distilled and then stored over molecular sieves 4Š. Products were
isolated by use of column chromatography (Merck silica gel 60, particle size
230 ± 400 mesh ASTM), packed in glass column (35 g of silica gel per gram
of crude material). Analytical thin-layer chromatography (TLC) analyses
were performed on precoated plates (silica gel 60F254), purchased from
Merck. Melting points were carried out with Büchi510 apparatus. Proton
NMR spectra were obtained on a Bruker-WH90 or a Varian-XL200
spectrometer, which was used to determine the ratios (1:1 to 1:1.2) of all
diasteromeric isomers. Infrared spectra were measured on a Beckman IR-8
spectrophotometer. Microanalysis data were obtained by use of a Perkin ±
Elmer 240B microanalyzer.
1
procedure for the conversion of 3 !5. H NMR (CDCl3): d ˆ 2.30 (s, 3H;
CH3CO), 2.61 ± 2.90 (brm, 2H; CH2S ), 3.60 (s, 2H; CH2CO), 4.12 ± 4.30
3
(m, 1H; HC(4)), 5.17 (s, 2H; CH2O), 5.31 (dd, J(H,H) ˆ 9.5, 5.0 Hz, 1H;
HC(3)), 6.80 (d, 3J(H,H) ˆ 9.5 Hz, 1H; NH), 7.10 ± 7.65 (m, 15H; 3  C6H5);
IR (CH2Cl2): nÄ ˆ 3405 (NH), 1790 (b-lactam), 1750 (ester), 1730 (thioester),
1680 (amide) cm 1; C29H27N2O5SCl (551.1): calcd C 63.21, H 4.94, N 5.08, S
5.82, Cl 6.43; found C 63.20, H 4.90, N 5.17, S 5.70, Cl 6.33.
Dibenzyl(5RS,6RS)-7-oxo-6-(phenylacetamido)-3-thia-1-azabicyclo-
[3.2.0]heptane-2,2-dicarboxylate (11): Method C: Piperidine (0.85 g,
1.0 mmol) was added to a solution containing (Æ)-5 (0.61 g, 1.0 mmol) in
CH2Cl2 (3.0 mL) at room temperature. The mixture was stirred for 1.5 h,
diluted with CH2Cl2 (20 mL) and washed with 2% aqueous HCl solution
(20 mL) and water (20 mL). The organic layer was dried over MgSO4,
concentrated under reduced pressure, and then purified by use of column
chromatography (CHCl3 as eluant) to give (Æ)-11 (0.48 g, 0.90 mmol) in
Computation was performed on a Silicon Graphics IRIS CRIMSON/Elan
workstation. The Builder and Discover modules of Insight II (Biosym
Technologies, versions 2.3.5 and 2.9.5) were used for model building and
energy minimization, respectively. The energies for all conformations were
minimized with the consistent valence forcefield (CVFF)[16] until the
1
90% yield. H NMR (CDCl3): d ˆ 2.71 ± 3.10 (m, 2H; CH2S), 3.52 (s, 2H;
CH2CO), 4.31 ± 4.57 (m, 1H; HC(5)), 5.08, 5.12 (2s, 4H; 2 Â CH2O), 5.22
(dd, 3J(H,H) ˆ 8.0, 4.5 Hz, 1H; HC(6)), 6.81 ± 7.01 (br, 1H; NH), 7.30 ± 7.51
(m, 15H; 3  C6H5); IR (CH2Cl2): nÄ ˆ 3410 (NH), 1785 (b-lactam), 1745
(ester), 1670 (amide) cm 1; C29H26N2O6S (530.6): calcd C 65.65, H 4.94, N
5.28, S 6.04; found C 65.59, H 4.88, N 5.30, S 6.14.
1
1
maximum derivative was less than 0.0004 kcalmol
Š .
Dibenzyl-(3RS,4RS)-2-(4-acetylthiomethyl-2-oxo-3-phenylacetamido-1-
azetidinyl) malonate (3)
Method A: KSCOMe (2.28 g, 19.9 mmol) was added to a solution of (Æ)-1[6]
(5.94 g, 9.99 mmol) in DMF (80 mL). The mixture was stirred at room
temperature under N2 for 15 h. Then EtOAc (100 mL) was added, and the
mixture was washed with water (5 Â 100 mL), dried over MgSO4, and
concentrated under reduced pressure. The crude product was purified by
column chromatography (CHCl3 as eluant) to give (Æ)-3 (5.17 g,
8.99 mmol) as a foam in 90% yield. 1H NMR (CDCl3): d ˆ 2.34 (s, 3H;
CH3CO), 2.67 ± 2.93 (br, 2H; CH2S), 3.62 (s, 2H; CH2CO), 4.11 ± 4.28 (m,
1H; HC(4)), 5.23 (s, 4H; 2  CH2O), 5.33 (s, 1H; CH), 5.39 (dd, 3J(H,H) ˆ
8.5, 5.0 Hz, 1H; HC(3)), 7.02 (brs, 1H; NH), 7.42 (brs, 15H; 3 Â C6H5); IR
Method D: Piperidine (0.85 g, 1.0 mmol) and DBU (0.15 g, 0.99 mmol) was
added to a solution containing (Æ)-19 (0.65 g, 1.0 mmol) in DMF (5.0 mL).
The mixture was stirred at 608C for 3.0 h. After cooling, Et2O (50 mL) was
added, and the mixture was washed with 2% aqueous HCl solution
(20 mL) and water (5 Â 40 mL). The organic layer was dried over MgSO4,
concentrated under reduced pressure, and then purified by use of column
chromatography (CHCl3 as eluant) to give (Æ)-11 (0.42 g, 0.80 mmol) in
80% yield.
Chem. Eur. J. 1999, 5, No. 9
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2709

J. R. Hwu et al.
FULL PAPER
Method E: DBU (0.15 g, 0.99 mmol) was added to a solution containing
(Æ)-22 (0.61 g, 1.0 mmol) in DMF (5.0 mL). The mixture was heated at
608C for 2.0 h. After cooling, Et2O (50 mL) was added, and the mixture was
washed with water (5 Â 40 mL). The organic layer was dried over MgSO4,
concentrated under reduced pressure, and then purified by use of column
chromatography (CHCl3 as eluant) to give (Æ)-11 (0.41 g, 0.78 mmol) in
78% yield.
Dibenzyl(3RS,4RS)-2-(4-acetylthiomethyl-2-oxo-3-phenylacetamido-1-
azetidinyl)-2-butylthiomalonate (18): Method F: A solution containing
(Æ)-5 (610 mg, 1.00 mmol), 1-butanethiol (92.0 mg, 1.02 mmol), and Et3N
(105 mg, 1.04 mmol) in CH2Cl2 (15 mL) was stirred at room temperature
under N2 for 1.0 h. The solution was then washed with water (2 Â 15 mL),
dried over MgSO4, and concentrated under reduced pressure. Purification
of the residue by use of column chromatography (CH2Cl2 followed by
CHCl3 as the eluant) gave (Æ)-18 (398 mg, 0.600 mmol) in 60% yield.
3
Benzyl(5RS,6RS)-7-oxo-6-(phenylacetamido)-3-thia-1-azabicyclo[3.2.0]-
heptane-2-phenyl-2-carboxylates [(Æ)-12]: Compounds (Æ)-12 (2.08 g,
4.40 mmol) were prepared in 95% yield from (Æ)-6 (2.55 g, 4.63 mmol)
and piperidine (0.394 g, 4.63 mmol) by the same procedure for the
conversion of 5 !11. 1H NMR (CDCl3): d ˆ 2.70 ± 3.10 (m, 2H; CH2S),
3.62 (brs, 2H; CH2CO), 3.91 ± 4.20 (m, 1H; HC(5)), 4.90, 5.00 (2s, 2H;
1H NMR (CDCl3): d ˆ 0.94 (t, J(H,H) ˆ 6.0 Hz, 3H; CH3), 1.39 ± 1.78 (m,
4H; CH2CH2), 2.35 (s, 3H; CH3CO), 2.49 ± 3.05 (m, 4H; CH2S ‡
CH2SCO), 3.59 (s, 2H; CH2CO), 4.08 ± 4.30 (m, 1H; HC(4)), 5.30, 5.34
(2s, 4H; 2  CH2O), 5.31 (dd, 3J(H,H) ˆ 8.0, 5.0 Hz, 1H; HC(3)), 7.08 (brs,
1H; NH), 7.45 (brs, 15H; 3  C6H5); IR (CH2Cl2): nÄ ˆ 3410 (NH), 1772 (b-
lactam), 1743 (ester), 1732 (thioester), 1679 (amide) cm 1; C35H38N2O7S2
(662.8): calcd C 63.42, H 5.78, N 4.23, S 9.67; found C 63.31, H 5.79, N 4.09, S
9.51.
3
CH2O), 5.20 (dd, J(H,H) ˆ 8.0, 4.5 Hz, 1H; HC(6)), 6.81 (brs, 1H; NH),
7.22 ± 7.45 (m, 15H; 3  C6H5); IR (CH2Cl2): nÄ ˆ 3405 (NH), 1781 (b-
lactam), 1740 (ester), 1685 (amide) cm 1; C27H24N2O4S (472.6): calcd C
68.63, H 5.12, N 5.93, S 6.78; found C 68.51, H 5.20, N 5.88, S 6.70.
Method G: nBuSCl (127 mg, 1.02 mmol) and Et3N (105 mg, 1.04 mmol) was
added to a solution containing (Æ)-3 (575 mg, 1.00 mmol) in CH2Cl2
(15 mL). After the solution was stirred at room temperature under N2
for 1.0 h, it was washed with water (2 Â 15 mL), dried over MgSO4,
concentrated under reduced pressure, and then purified by use of column
chromatography (CH2Cl2 followed by CHCl3 as the eluant) to afford (Æ)-
18 (305 mg, 0.46 mmol) in 46% yield.
(2RS,5SR,6SR)-7-Oxo-6-(phenylacetamido)-3-thia-1-azabicyclo[3.2.0]-
heptane-2-carboxylic acid (13): A solution of (Æ)-11 (2.65 g, 4.99 mmol) in
MeOH (100 mL) containing 1% aqueous NaHCO3 (15 mL) was hydro-
genated over Pd/C (10%, 1.50 g, 1.41 mmol) and 60 psi of H2 at 458C for
5.0 h. The mixture was filtered and then acetic acid (20 mL) was added to
the residue. The solvent was removed under reduced pressure, and then the
residue was purified by use of column chromatography (EtOAc as eluant)
to give (Æ)-13 (0.84 g, 2.7 mmol) in 55% yield. M.p. 141 ± 1438C; 1H NMR
([D6]DMSO): d ˆ 2.72 ± 3.12 (m, 2H; CH2S), 3.50 (s, 2H; CH2CO), 4.21 ±
4.28 (m, 1H; HC(5)), 4.88 (s, 1H; CH), 5.17 (dd, 3J(H,H) ˆ 9.0, 4.5 Hz, 1H;
HC(6)), 6.91 (brs, 1H; NH), 7.38 (s, 5H; C6H5), 7.80 ± 8.50 (br, 1H; CO2H);
IR (Nujol): nÄ ˆ 3500 ± 3300 (NH, CO2H), 1779 (b-lactam), 1705 (acid), 1669
(amide) cm 1; C14H14N2O4S (306.3): calcd C 54.89, H 4.61, N 9.14, S 10.47;
found C 54.81, H 4.50, N 9.20, S 10.39.
Dibenzyl(3RS,4RS)-2-(4-acetylthiomethyl-2-oxo-3-phenylacetamido-1-
azetidinyl)-2-methanesulfonylmalonate (19): MeSO2Cl (1.15 g, 10.0 mmol)
in CH2Cl2 (5.0 mL) was added dropwise to a solution of (Æ)-3 (5.74 g,
9.99 mmol) and Et3N (2.02 g, 20.0 mmol) in CH2Cl2 (80 mL). The solution
was stirred at 08C for 1.0 h and then washed with water (100 mL), dried
over MgSO4, and concentrated under reduced pressure. The crude product
was purified by use of column chromatography (CHCl3 as eluant) to give
(Æ)-19 (6.39 g, 9.79 mmol) in 98% yield. M.p. 112 ± 1148C; 1H NMR
(CDCl3): d ˆ 2.38 (s, 3H; CH3CO), 2.65 ± 2.83 (br, 2H; CH2S), 3.39 (s, 3H;
CH3SO2), 3.63 (s, 2H; CH2CO), 4.12 ± 4.30 (m, 1H; HC(4)), 5.11, 5.13 (2s,
4H; 2  CH2O), 5.31 (dd, 3J(H,H) ˆ 9.5, 5.0 Hz, 1H; HC(3)), 7.01 (brs, 1H;
NH), 7.32 ± 7.51 (m, 15H; 3  C6H5); IR (CH2Cl2): nÄ ˆ 3410 (NH), 1790 (b-
lactam), 1752 (ester), 1730 (thioester), 1679 (amide) cm 1; C32H32N2O9S2
(652.7): calcd for C 58.88, H 4.94, N 4.29, S 9.82; found C 58.90, H 5.01, N
4.39, S 9.78.
(5RS,6RS)-7-Oxo-6-(phenylacetamido)-3-thia-1-aza-bicyclo[3.2.0]hep-
tane-2-phenyl-2-carboxylic acids [(Æ)14]: Compounds (Æ)-14 (1.05 g,
2.75 mmol) were prepared in 55% yield from (Æ)-12 (2.36 g, 4.99 mmol)
and Pd/C (10%, 1.50 g, 1.41 mmol) by the same procedure for the
conversion of 11 !13. M.p. 149 ± 1518C; 1H NMR (CDCl3 ‡ D2O): d ˆ
2.83 ± 3.31 (m, 2H; CH2S), 3.51 (s, 2H; CH2CO), 3.89 ± 4.15 (m, 1H;
HC(5)), 5.14, 5.17 (2 d, 3J(H,H) ˆ 5.0 Hz, 1H; HC(6)), 7.31 (brs, 5H; C6H5),
7.44 (brs, 5H; C6H5); IR (CH2Cl2): nÄ ˆ 3650 ± 3150 (OH, NH), 1779 (b-
lactam), 1702 (acid), 1680 (amide) cm 1; C20H18N2O4S (382.4): calcd C
62.81, H 4.74, N 7.32, S 8.38; found C 62.79, H 4.60, N 7.22, S 8.40.
Dibenzyl(3RS,4RS)-2-(4-methanesulfonylthiomethyl-2-oxo-3-phenylacet-
amido-1-azetidinyl)malonate (22): A solution containing (Æ)-19 (3.26 g,
4.99 mmol) and piperidine (4.25 g, 49.9 mmol) in DMF (25 mL) was stirred
at room temperature under N2 for 10 h. After addition of EtOAc (100 mL)
to quench the reaction, the mixture was washed with water (5 Â 100 mL),
dried over MgSO4, and concentrated under reduced pressure. The crude
product was purified by use of column chromatography (CHCl3 as eluant)
to give (Æ)-22 (2.93 g, 4.79 mmol) in 96% yield. M.p. 118 ± 1208C; 1H NMR
(CDCl3): d ˆ 2.81 ± 3.20 (m, 2H; CH2S), 2.89 (s, 3H; CH3SO2), 3.61 (s, 2H;
CH2CO), 4.14 ± 4.31 (m, 1H; HC(4)), 5.22 (s, 4H; 2 Â CH2O), 5.27 (s, 1H;
CH), 5.40 (dd, 3J(H,H) ˆ 8.0, 5.0 Hz, 1H; HC(3)), 7.08 (d, 3J(H,H) ˆ
8.0 Hz, 1H, NH), 7.45 (brs, 15H; 3  C6H5); IR (CH2Cl2): nÄ ˆ 3400 (NH),
1778 (b-lactam), 1748 (ester), 1680 (amide) cm 1; C30H30N2O8S2 (610.7):
calcd C 59.00, H 4.95, N 4.59, S 10.50; found C 59.12, H 5.00, N 4.48, S 10.51.
(2RS,5SR,6SR)-7-Oxo-6-(phenylacetamido)-3-dioxothia-1-azabicyclo-
[3.2.0]heptane-2-carboxylic acids (15): A solution of KMnO4 (316 mg,
2.00 mmol) in H2O (2.0 mL) was added to a solution of (Æ)-13 (306 mg,
0.999 mmol) in glacial acetic acid (8.0 mL) at 258C. The reaction mixture
was treated dropwise with 30% H2O2 (3.0 mL) until the solution became
clear. The solution was poured into water (25 mL) and stored at 108C for
2.0 h. The crystalline sulfone was collected, washed with H2O (20 mL), and
dried under reduced pressure over P2O5 to give (Æ)-15 (135 mg,
1
0.400 mmol) in 40% yield. M.p. 145 ± 1478C; H NMR ([D6]DMSO): d ˆ
3.08 ± 3.42 (br, 2H; CH2SO2), 3.61 (s, 2H; CH2CO), 4.26 ± 4.31 (m, 1H;
HC(5)), 5.12 (s, 1H; CH), 5.26 (dd, 3J(H,H) ˆ 9.6, 5.0 Hz, 1H; HC(6)), 7.01
(brs, 1H; NH), 7.40 (s, 5H; C6H5), 7.61 ± 8.01 (br, 1H; CO2H); IR (Nujol):
nÄ ˆ 3350 ± 3000 (NH, CO2H), 1795 (b-lactam), 1700 (acid), 1675
(amide) cm 1; C14H14N2O6S (338.4): calcd C 49.70, H 4.17, N 8.28, S 9.48;
found C 49.55, H 4.20, N 8.30, S 9.52.
Acknowledgment
We thank the National Science Council of Republic of China and
Academia Sinica for financial support of this work. S.H. is a recipient of
European Council of International Schoolsꢁ Award for Outstanding
Achievements in Promotion of Cross Cultural Understanding, 1997; his
current address: Department of Cell Biology, Faculty of Medicine,
University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
(5RS,6RS)-7-Oxo-6-(phenylacetamido)-3-dioxothia-1-azabicyclo[3.2.0]-
heptane-2-phenyl-2-carboxylic acids [(Æ)16]: Compounds (Æ)-16 (207 mg,
0.499 mmol) were prepared in 50% yield from (Æ)-14 (382 mg,
0.999 mmol), glacial acetic acid (8.5 mL), and KMnO4 (316 mg, 2.00 mmol)
by the same procedure for the conversion of 13 !15. 1H NMR
([D6]DMSO): d ˆ 3.10 ± 3.41 (br, 2H; CH2SO2), 3.60 (brs, 2H; CH2CO),
4.21 ± 4.35 (m, 1H; HC(5)), 5.29 (dd, 3J(H,H) ˆ 9.0, 4.9 Hz, 1H; HC(6)),
6.90 (brs, 1H; NH), 7.30 (s, 5H; C6H5CCON), 7.41 ± 7.60 (m, 5H; C6H5),
7.62 ± 8.03 (br, 1H; CO2H)); IR (Nujol): nÄ ˆ 3350 ± 3010 (NH, CO2H), 1795
(b-lactam), 1705 (acid), 1672 (amide) cm 1; C20H18N2O6S (414.4): calcd C
57.96, H 4.38, N 6.76, S 7.74; found C 57.87, H 4.30, N 6.66, S 7.80.
[1] J. R. Hwu, B. A. Gibert, Tetrahedron 1989, 45, 1233.
[2] J. R. Hwu, L. C. Lin, B. R. Liaw, J. Am. Chem. Soc. 1988, 110, 7252.
[3] J. R. Hwu, S.-C. Tsay, J. Org. Chem. 1990, 55, 5987.
[4] J. R. Hwu, G. H. Hakimelahi, F. F. Wong, C. C. Lin, Angew. Chem.
1993, 105, 591; Angew. Chem. Int. Ed. Engl. 1993, 32, 608.
[5] J. R. Hwu, S.-C. Tsay, Chem. Commun. 1998, 161.
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Chem. Eur. J. 1999, 5, No. 9

Counterattack Reagents
2705±2711
[6] G. H. Hakimelahi, G. Just, A. Ugolini, Helv. Chim. Acta 1982, 65,
1368.
[13] P. H. Crackett, C. M. Pant, R. J. Stoodley, J. Chem. Soc. Perkin Trans. 1
1984, 2785.
[7] G. H. Hakimelahi, G. Just, Tetrahedron Lett. 1979, 3643.
[8] G. H. Hakimelahi, V. Naeemi, J. Sci. Tech. (Iran) 1986, 10, 175.
[9] J. E. Baldwin, J. Chem. Soc. Chem. Commun. 1976, 736.
[10] T. A. Pursiano, M. Misiek, F. Leitner, K. E. Price, Antimicrob. Agents
Chemother. 1973, 3, 33.
[11] F. Steers, F. L. Foltz, B. S. Graves, Antibiot. Chemother. 1959, 9, 307.
[12] C. H. OꢁCallaghan, A. Morris, S. M. Kirby, A. H. Shingler, Antimi-
crob. Agents Chemother. 1972, 1, 283.
[14] W. F. Huffman, R. F. Hall, J. A. Grant, K. G. Holden, J. Med. Chem.
1978, 21, 413.
[15] J. C. Sheehan, K. R. Henry-Logan, J. Am. Chem. Soc. 1959, 81, 3089.
[16] P. Dauber-Osguthorpe, V. A. Roberts, D. J. Osguthorpe, J. Wolff, M.
Genest, A. T. Hagler, Proteins: Structure, Function and Genetics 1988,
4, 31.
Received: August 21, 1998 [F1316]
Chem. Eur. J. 1999, 5, No. 9
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0947-6539/99/0509-2711 $ 17.50+.50/0
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