An approach to the synthesis of 5,5-trans-fused lactam analogues of β-lactam antibiotics

Article abstract of DOI:10.1039/b007286i

A racemic synthesis of two diastereoisomeric α-benzyloxycarbonylamino substituted trans-fused bicyclic lactams (4 and 5), was achieved from cyclopentene oxide. These lactams are useful intermediates to investigate the possibility of using a trans-lactam t

Full text of DOI:10.1039/b007286i

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An approach to the synthesis of 5,5-trans-fused lactam analogues
of ꢀ-lactam antibiotics
Paul W. Smith,* Andrew R. Whittington, Kevin N. Cobley, Albert Jaxa-Chamiec and
Harry Finch
1
Department of Medicinal Chemistry, Glaxo Wellcome Limited, Gunnels Wood Road,
Stevenage, UK SG1 2NY
Received (in Cambridge, UK) 8th September 2000, Accepted 27th October 2000
First published as an Advance Article on the web 5th December 2000
A racemic synthesis of two diastereoisomeric α-benzyloxycarbonylamino substituted trans-fused bicyclic lactams
4 and 5), was achieved from cyclopentene oxide. These lactams are useful intermediates to investigate the possibility
(
of using a trans-lactam template as a replacement for the β-lactam ring found in conventional antibacterial agents.
One of the intermediates (4) was further elaborated to an analogue of the antibacterial agent ceftazidime.
Introduction
Over recent years the continuing problem of emerging resis-
tance to chemotherapeutic agents has intensified the search for
new and novel antibacterial drugs. In particular, the emergence
of broad spectrum β-lactamases has reduced the effectiveness
of many of the older β-lactam antibiotics and indeed rendered
some of them obsolete. The situation can be retrieved by the co-
1
administration of β-lactamase inhibitors e.g. Augmentin, but
there are already reports of β-lactamases resistant to clavulanic
2
3
acid. The new carbapenems such as imipenem are potent
antibacterials and useful inhibitors of β-lactamases which sug-
gests that it is possible to combine these two properties in a
single molecule. The ideal drug, however, would be a powerful
inhibitor of the bacterial transpeptidases whilst displaying
no affinity for β-lactamases. Towards this goal, in addition
to synthesising β-lactam antibiotics with improved stability to
β-lactamases, many groups have attempted to replace the β-
lactam nucleus with appropriately substituted novel ring
systems capable of selectively acylating the bacterial serine
transpeptidases. Notable successes have been few, but the
4
appreciable activity of the acyl hydrazides 1 and Lactivicin
5,6
2
(Fig. 1) suggests that other compounds of this type with
useful antibacterial properties will be found.
The highly strained trans-fused 5,5 lactam and lactone ring
systems 3a and b recently reported by co-workers at Glaxo-
Wellcome represent novel templates for the design of com-
pounds which can potentially acylate a wide range of serine
proteases. Selective inhibitors of both thrombin and elastase
7–12
have already been designed based on these templates.
The
Fig. 1
current manuscript describes a useful racemic synthesis of
the diastereoisomeric Cbz (CO CH C H ) protected trans-
2
2
6
5
cyclopentane ring trans to each other. Synthesis of 8 and 9 was
accomplished in 8 stages from the azido alcohol 10, which was
obtained from cyclopentene oxide by ring opening with sodium
lactams 4 and 5 which are suitable starting materials to investi-
gate the potential of the 5,5-trans-lactam template to mimic the
penicillin and cephalosporin β-lactam antibiotics. Transform-
ation of compound 4 to the aminothiazolyl derivative 6, struc-
turally related to the antibiotic ceftazidime 7, is also described.
13
azide (Scheme 1). Triphenylphosphine reduction of 10 and
treatment with di-tert-butyl dicarbonate afforded the protected
aminol 11 (41% yield) as a crystalline solid. Under Mitsunobu
conditions 11 was cleanly converted to the Boc protected
aziridine 12 in high yield (79%). The aziridine ring was then
opened by heating 12 with the sodium salt of dimethyl
malonate in DMF at 155 ЊC. This afforded 13 as a crystalline
solid after flash chromatography in good yield (73%). On a
larger scale 13 was isolated directly by crystallisation. By ring
opening the aziridine in this fashion the required ring junction
trans-stereochemistry has been fixed. The initial stages outlined
Results and discussion
Synthesis of the lactams 4 and 5
For the synthesis of derivatives 4 and 5 we required a reliable
method for the stereoselective formation of the protected
amino acids 8 and 9 (see Scheme 2) which fixed the relative
stereochemistry of the two adjacent chiral centres on the
DOI: 10.1039/b007286i
J. Chem. Soc., Perkin Trans. 1, 2001, 21–25
This journal is © The Royal Society of Chemistry 2001
21

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above were readily carried out on 50 g scale affording 13 in 24%
overall yield from 10 (Scheme 1).
Fig. 2 NOE’s observed in isomers 4 and 5.
5
was deduced from their proton NMR spectra by examining
the coupling constants and NOE’s between the H-3 proton
adjacent to the amide carbonyl group and the ring junction
protons H-3a and H-6a (Fig. 2). There is an NOE observed
in 4 between H-3 and H-3a, but not between H-3 and H-6a,
whereas in 5 there is an NOE between H-3 and H-6a but
not between H-3 and H-3a. The relative stereochemistry of the
earlier intermediates 14, 15, 8 and 9 was also inferred from this
experiment.
Scheme 1 Reagents: i) NaN , NH Cl, aq. EtOH; ii) Ph P; iii) Boc O;
3
4
3
2
iv) Ph P–diisopropylazodicarboxylate; v) CH (CO Me) , NaH, DMF.
3
2
2
2
Selective hydrolysis of 13 with aqueous KOH afforded a
diastereomeric mixture of monoacid esters in quantitative yield
(
Scheme 2). The isomers were not separated at this stage,
but the mixture subjected to a Curtius rearrangement with
diphenylphosphoryl azide (PhO) P(O)N3 (DPPA) and then
adding benzyl alcohol to trap the intermediate isocyanate
affording a mixture of the Cbz protected diastereomers 14
and 15 (1:1 ratio, 37% combined yield) (Scheme 2) which were
Design and synthesis of compound 6
2
14
In order to display antibacterial properties the β-lactam anti-
biotics require a suitably positioned acid moiety and an appro-
15
priately activated β-lactam nucleus. Once these features are in
place, then the choice of the appropriate sidechain is critical in
order to optimise binding affinity and specificity for the target
16–18
penicillin binding proteins.
Activation of the β-lactam is
achieved by creating strain in the amide bond either through
fusion to another ring (penicillins and cephalosporins etc.)
or by introducing electron withdrawing substituents onto
the amide nitrogen (monobactams such as aztreonam). An
indication of ring strain can often be inferred from the
19,20
IR stretching frequency of the amide carbonyl group.
The
carboxylic acid of the antibiotic forms a salt bridge with the
lysine residue of the highly conserved Lys-X-X-Ser motif found
21,22
in the penicillin binding proteins.
In the initial trans-lactam
target compound 6, the acetic acid extension from the amide
nitrogen was chosen to allow 6 the possibility of forming this
key interaction. Simple molecular modelling overlays (not
shown) indicated that similar positions of the amide carbonyl
groups and carboxylic acids of the trans-lactam 6 and
cephalosporin nucleus of ceftazidime 7 were likely. The amino-
thiazolyl derived amide sidechain was chosen since this group
has proved highly successful in the cephalosporin and mono-
23,24
bactam series of antibiotics.
N-Alkylation of the amide in 4 was achieved with tert-butyl
25
bromoacetate in acetonitrile with caesium carbonate pro-
ducing 16 (79%) (Scheme 3). The Cbz group was next removed
by hydrogenolysis liberating the amine 17 (94%). Conventional
26
coupling of 17 with the acid 18 afforded the fully protected
intermediate 19 (60%). Finally, TFA deprotection of 19 gave
the required target 6 (78%).
Scheme 2 Reagents: i) KOH; ii) DPPA, PhCH OH, heat; iii) NaOH;
2
iv) CF CO H; v) DPPA, DMF.
3
2
Disappointingly compound 6 showed no whole cell anti-
bacterial activity when evaluated in vitro against a screen of com-
monly encountered bacteria comprising both Gram positive
separable by flash chromatography. Products 14 and 15 now
contain both the nitrogens required for the final trans-lactam
products in a differentially protected form.
3
27
and Gram negative organisms (MIC’s all > 128 µg cm ).
Neither did it demonstrate any significant in vitro inhibition
Hydrolysis of the remaining methyl ester in 14 was achieved
by treatment with aqueous sodium hydroxide and the Boc
group subsequently removed with trifluoroacetic acid to afford
the required amino acid 8 (91%). A similar sequence of
reactions starting with 15 produced 9 also in high overall yield
of penicillin G binding to penicillin binding proteins, or any
28
inhibition of TEM-1 β-lactamase. Thus it appears likely that
the trans-lactam ring in compound 6 is not sufficiently activated
to acylate the bacterial enzymes. (The observed IR spectra
may provide some evidence for this. Whilst the highly strained
penicillins and cephalosporins typically show carbonyl
(
91%). Finally 8 and 9 were cyclised to the required trans-
Ϫ1
lactams 4 and 5 respectively using DPPA in DMF (69% yield
stretches between 1780 and 1790 cm the trans-lactam amide
6
Ϫ1
8
→4, 76% yield 9→5). In this reaction the initial acyl azide
carbonyl group in compound 6 stretches only at 1718 cm .)
formed by the DPPA is trapped by the nucleophilic amine in an
In conclusion, synthesis of further trans-lactams with
intramolecular reaction. The relative stereochemistry of 4 and
increased activation would be of interest in order to determine
2
2
J. Chem. Soc., Perkin Trans. 1, 2001, 21–25

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title compound 11 (21.4 g, 41%) as a white crystalline solid.
Mp 106 ЊC (Found C: 59.5; H, 9.25; N, 6.8. C H NO
10
Ϫ1
19
3
Requires C, 59.7; H, 9.5; N, 7.0%). νmax (CHBr )/cm 3437,
3
2
972, 1690, 1498 and 1366; δH (CDCl ): 4.7 (1H, br s, NH),
3
4
.0 (2H, m, OH, H-1), 3.6 (1H, m, H-2), 2.2–1.3 (6H, m,
H-3,4,5), 1.4 (9H, s, tBu).
cis-6-Azabicyclo[3.1.0]hexane-6-carboxylic acid tert-butyl
ester 12
To a stirred solution of triphenylphosphine (114.0 g, 0.435 mol,
3
1
.5 eq.) in THF (800 cm ) at Ϫ78 ЊC under nitrogen was added
3
diisopropyl azodicarboxylate (85.6 cm , 0.435 mol, 1.5 eq.)
dropwise over 30 min. The reaction mixture was stirred for
3
0 min until a pale yellow suspension was formed. A solution
3
of the alcohol 11 (58.3 g, 0.290 mol) in THF (200 cm ) was
added dropwise and the reaction stirred for 60 min at Ϫ78 ЊC
then allowed to warm to RT. After a further 21 h at RT the
solvent was evaporated and the residue treated with ether.
The precipitated triphenylphosphine oxide was removed by fil-
tration and the filtrate evaporated to a pale yellow residue
which was purified by flash chromatography (eluting with
petroleum ether–ether, 4:1) to give the title compound 12
Scheme 3 Reagents: i) BrCH CO tBu, Cs CO , MeCN; ii) H , Pd; iii)
2
2
2
3
2
Acid 18 ϩ (COCl) ; iv) CF COOH.
2
3
(
41.9 g, 79%) as a clear oil (Found C: 65.5; H, 9.35; N, 7.6.
C H NO Requires C, 65.1; H, 9.2; N, 7.6%); ν (CHBr )/
1
0
17
2
max
3
Ϫ1
cm 2973, 1699 and 1367; δ (CDCl ): 2.9 (2H, s, H-1,5), 2.05
whether a useful trans-lactam antibacterial agent can be
achieved. Compounds 4 and 5 will be ideal starting materials to
pursue this investigation.
H
3
(
(
2H, dd, H-2,4), 1.6 (3H, m, H-2,3,4), 1.4 (9H, s, tBu), 1.2
ϩ
1H, m, H-3). m/z C H NO M 183.26.
10 17
2
trans-2-(2-tert-Butoxycarbonylaminocyclopentyl)malonic acid
dimethyl ester 13
Experimental
General methods
Dimethyl malonate (90.3 g, 0.684 mol, 3 eq.) in DMF (1.5 l)
was treated with sodium hydride (60% dispersion in oil, 9.3 g,
0.232 mol, 1.02 eq.) at RT under nitrogen. After effervescence
had stopped and the solution had cleared a solution of the
FTIR spectra were recorded using a Nicolet 20SXB or a Bio-
1
Rad FTS-7. H NMR spectra were recorded either at 250 MHz
using a Bruker AC or AM 250 or at 400 MHz with a Varian
VXR 400. Mass spectra were measured on a HP Engine
3
aziridine 12 (41.8 g, 0.228 mol, 1 eq.) in DMF (25 cm )
(
thermospray positive) or VG Autospec Q (LSIMS). Routine
was added. The solution was stirred with heating (155 ЊC) for
18 h then cooled, filtered and evaporated to a solid. The
crude product was partitioned between ether (1.5 l) and water
(1.5 l). The organic layer was separated and the aqueous layer
further extracted with ether (1.5 l) and the combined organic
microanalyses were performed on a Leco CHNS-932 or Carlo-
Erba instrument. Fluorine analyses were carried out with a
Phillips PW 9415 ion selective meter and water analyses using
a Mitsubishi CA-05. Flash chromatography was performed
with Merck Kieselgel 9385.
extracts washed with brine (2 × 1 l) and then dried (MgSO
Evaporation gave a solid which was triturated with petrol 40–
0ЊC then filtered and dried in vacuo to give a white solid 13
52.5 g, 0.167 mol, 73%). Mp 104–105 ЊC (Found C, 57.05;
H, 8.1; N, 4.6. C H NO Requires C, 57.1; H, 8.0; N, 4.4);
).
4
6
(
trans-N-(2-Hydroxycyclopentyl)carbamic acid tert-butyl
ester 11
1
5
25
6
Cyclopentene oxide (50.0 g, 0.595 mol) was dissolved in 50%
aqueous ethanol (800 cm ) and ammonium chloride (31.9 g,
0
resulting mixture was refluxed for 48 h then concentrated to
a small volume and partitioned between water (200 cm ) and
ethyl acetate (200 cm ). The organic layer was dried (anhydrous
Ϫ1
νmax (CHBr )/cm : 3429, 2950, 1750, 1729, 1705 and 1503;
3
3
δ (CDCl ): 4.5 (1H, br s, NH), 3.75 (6H, s, MeO), 3.7 (1H, m,
H
3
.595 mol) and sodium azide (38.7 g, 0.595 mol) added. The
H-2Ј), 3.45 (1H, d, H-2, J2,1Ј 7.5 Hz), 2.3 (1H, m, H-1Ј), 2.15–1.2
ϩ
4
(
(
6H, m, H-3Ј,4Ј,5Ј), 1.4 (9H, s, tBu); m/z 333 (MNH ), 316
MH ), 216.
3
ϩ
3
MgSO ) and evaporated to a yellow oil (64.4 g, 85%) which was
4
Racemic [(1R,2S)-2-tert-butoxycarbonylaminocyclopentyl]-
(S)-benzyloxycarbonylamino]acetic acid methyl ester 14 and
Racemic [(1R,2S)-2-tert-butoxycarbonylaminocyclopentyl]-
(R)-benzyloxycarbonylamino]acetic acid methyl ester 15
used directly without further purification. (Crude azide νmax
[
Ϫ1
(
CHBr )/cm 3430 and 2105; δH (CDCl ): 4.2 (1H, m, H-1),
3
3
3
.7 (1H, m, H-2), 2.2–2.0 (2H, m), 1.9–1.5 (5H, m).)
[
The crude azido alcohol (33.4 g, 0.263 mol) was dissolved
3
in toluene (500 cm ) and refluxed with triphenylphosphine
To a solution of the malonate 13 (10.0 g, 31.7 mmol) in
3
(
103.2 g, 0.394 mol, 1.5 eq.) for 1.5 h. The solution was cooled
methanol (150 cm ) was added potassium hydroxide (8.6 g,
3
3
to 0 ЊC and diluted with ethyl acetate (50 cm ) and saturated
sodium bicarbonate solution (50 cm ). The resulting biphasic
153.6 mmol, 4.8 eq.) in water (60 cm ). The reaction mixture
3
3
was stirred for 20 min then partitioned between ether (750 cm )
3
mixture was then stirred rapidly as di-tert-butyl dicarbonate
and water (750 cm ). The aqueous phase was acidified with
3
(
57.3 g, 0.263 mol) in ethyl acetate (500 cm ) was added over
solid potassium hydrogen sulfate and extracted with ether (2 ×
3
several minutes. The mixture was allowed to warm to room
temperature and stirred for 12 h. The organic phase was then
750 cm ). The combined organic extracts were dried (anhydrous
MgSO ) and evaporated to an off-white foam containing
4
separated, dried (anhydrous MgSO ) and evaporated to a
yellow oil. This was treated with ether (500 cm ) to precipitate
a mixture of the mono-acid mono-esters (9.6 g, 100%).
4
3
δ (CDCl ): 5.1, 4.7 (1H, br d, NH), 3.75 (3H, s, MeO), 3.6–3.8
H
3
Ph PO which was removed by filtration. The filtrate was con-
centrated to an oil which was purified by flash chromatography
(2H, m, H-2,2Ј), 2.4–1.4 (7H, m, H-1Ј,3Ј4Ј5Ј), 1.4, 1.45 (9H, s,
tBu). This material was used in the next stage without further
purification.
3
(
eluted with ethyl acetate–petroleum ether 1:1) to afford the
J. Chem. Soc., Perkin Trans. 1, 2001, 21–25
23

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A mixture of acids prepared as above (17.9 g, 59.5 mmol) was
dissolved in dioxane (300 cm ) and treated with triethylamine
3.13 mmol) was treated with TFA to give the title compound 9
(1.00 g, 3.04 mmol, 97%) as an off-white solid. ν (Nujol)/
3
max
3
3
Ϫ1
(
1
8.3 cm , 59.5 mmol) and diphenylphosphoryl azide (14.1 cm ,
1.8 mmol). The solution was refluxed for 4 h under nitrogen
cm 2923, 1700, 1521, 1455 and 1376; δH (DMSO): 8.1 (3H,
ϩ
br s, NH ), 7.6 (1H, d, NH, J 8.5 Hz), 7.4–7.3 (5H, m, Ph),
3
3
when benzyl alcohol (25 cm ) was added and refluxing con-
tinued for a further 18 h. The reaction mixture was cooled and
poured into water (2 l). The aqueous solution was extracted
with ether (3 × 500 cm ) then treated with brine and further
extracted with ether (450 cm ). The combined organic extracts
5.05 (2H, s, PhCH ), 4.4 (1H, dd, H-2, J 5, 8.5 Hz), 3.3 (1H,
2
ϩ
m, H-2Ј), 2.4–1.5 (7H, m, H-1Ј,3Ј,4Ј,5Ј); m/z 293.1502. MH
C H N O requires 293.1501.
15
20
2
4
3
3
Racemic [(3S,3aS,6aS)-2-oxooctahydrocyclopenta[b]pyrrol-3-
yl]carbamic acid benzyl ester 4
3
were washed with brine (500 cm ) then dried (anhydrous
MgSO ) and the solvent evaporated finally in vacuo (water bath
4
The amino acid hydrochloride salt 8 (0.86 g, 2.6 mmol) was
at 90 ЊC) to remove the benzyl alcohol. The resulting brown
residue was purified by flash chromatography (eluting first with
petroleum ether–ether 2:1, then petroleum ether–ether, 1:1) to
obtain racemic 14 as a white crystalline solid (1.6 g, 3.9 mmol,
3
dissolved in DMF (10 cm ) and added via a syringe pump to a
3
solution of diphenylphosphoryl azide (1.12 cm , 5.20 mmol)
3
3
and triethylamine (1.26 cm , 9.09 mmol) in DMF (200 cm ).
The total addition time was 28 h. The solution was then
concentrated to an oily solid and partitioned between water
7
%) eluting first, and racemic isomer 15 eluting second as an
off-white gum (2.0 g, 5.0 mmol, 8%). Further 14 and 15 was
obtained as a mixed fraction (5.3 g, 13.1 mmol, 22%). Thus the
combined overall yield of 14 and 15 was 37%. Compound 14.
3
3
(
300 cm ) and ether (300 cm ). The aqueous layer was further
3
washed with ether (300 cm ) and the combined organic layers
washed with brine (2 × 300 cm ). The extracts were dried
3
(
Found C, 61.8; H, 7.35; N, 7.2. C H N O Requires C, 62.1;
21 30 2 6
Ϫ1
(anhydrous MgSO ) and then evaporated to an oil which was
H, 7.4; N, 6.9%); νmax (CHBr )/cm 3349 (br), 1728, 1714,
4
3
triturated, filtered and dried in vacuo to give the title compound
1
(
694, 1682 and 1519; δH (CDCl ): 7.4–7.3 (5H, m, Ph), 6.4
3
4
as a white solid (0.49 g, 1.80 mmol, 69%) (Found C, 65.4;
1H, br d, Cbz-NH), 5.1 (2H, s, PhCH ), 4.4 (2H, m, Boc-NH,
2
H, 6.6; N, 10.3. C H N O Requires C, 65.7; H, 6.6; N, 10.2%);
νmax (CHBr )/cm 3418, 2974, 1712, 1506; δ (CDCl ): 7.4–7.3
H-2), 3.72 (1H, m, H-2Ј), 3.7 (3H, s, MeO), 2.3–1.3 (7H, m,
H-1Ј,3Ј,4Ј,5Ј), 1.4 (9H, s, tBu). Compound 15. ν (CHBr )/
15 18
Ϫ1
2
3
3
H
3
max
3
Ϫ1
(5H, m, Ph), 6.26 (1H, br s, amide NH), 5.28 (1H, br d,
cm 3300 (br), 1721, 1712 and 1693; δ (CDCl ): 7.4–7.3 (5H,
H
3
Cbz-NH), 5.11 (2H, ABq, PhCH ), 4.24 (1H, t, H-3), 3.21 (1H,
m, Ph), 6.1 (1H, br s, Cbz-NH), 5.1 (2H, ABq, PhCH ), 4.55
2
2
dt, H-6a), 2.1–1.3 (7H, m, H-3a,4,5,6).
(
(
1H, br s, Boc-NH), 4.4 (1H, br t, H-2), 3.8 (1H, m, H-2Ј), 3.7
3H, s, MeO), 2.2–1.1 (7H, m, H-1Ј,3Ј,4Ј,5Ј), 1.45 (9H, s, tBu);
ϩ
m/z 407.2182. MH C H N O requires 407.2182.
Racemic [(3R,3aS,6aS )-2-oxooctahydrocyclopenta[b]pyrrol-3-
yl]carbamic acid benzyl ester 5
21
30
2
6
Racemic [(1S,2S)-2-aminocyclopentyl][(S)-benzyloxycarbonyl-
amino]acetic acid hydrochloride 8
Using the same procedure described for preparation of 4,
the amino acid hydrochloride salt 9 (0.90 g, 2.74 mmol) in
3
The ester 14 (0.57 g, 1.4 mmol) was dissolved in methanol
DMF (10 cm ) was added via a syringe pump to a solution of
3
3
(
10 cm ) and treated with 1 M potassium hydroxide (aq.) solu-
diphenylphosphoryl azide (1.35 cm , 6.26 mmol) and triethyl-
3
3
3
tion (4.2 cm , 3 eq.). The mixture was stirred for 3 h at room
temperature then partitioned between ether (150 cm ) and
water (100 cm ). The aqueous layer was further washed with
ether (150 cm ), then acidified to pH = 3 with cooling in an ice
amine (1.52 cm , 10.96 mmol) in DMF (200 cm ) to afford 5 as
a white solid (0.57 g, 76%) (Found C, 65.4; H, 6.5; N, 10.2.
C H N O Requires C, 65.7; H, 6.6; N, 10.2%); ν (CHBr )/
3
3
1
5
18
2
3
max
3
3
Ϫ1
cm 3419, 1707 and 1506; δH (CDCl ): 7.4–7.3 (5H, m, Ph),
3
bath. The resulting solution was extracted with ether (2 ×
6.2 (1H, br s, NH amide), 5.4 (1H, br s, Cbz-NH), 5.1 (2H,
3
1
00 cm ) and the combined organic extracts washed with brine
ABq, PhCH ), 3.97 (1H, dd, H-3), 3.09 (1H, m, H-6a), 2.1–1.3
2
3
(
100 cm ) and dried (anhydrous MgSO ). Evaporation of the
(7H, m, H-3a,4,5,6).
4
solvent gave a white foam containing the intermediate N-Boc
protected acid (0.50 g, 1.3 mmol, 91.0%). This material was
used in the next reaction without further purification (Found
C, 60.6; H, 7.1; N, 7.2. C H N O Requires C, 61.2; H, 7.1;
Racemic [(3S,3aR,6aS)-2-oxo-3-benzyloxycarbonylamino-
octahydrocyclopenta[b]pyrrol-1-yl]acetic acid tert-butyl ester 16
2
0
28
2
6
Ϫ1
Cbz protected trans-lactam 4 (0.15 g, 0.58 mmol) was dissolved
N, 7.1%); νmax (KBr)/cm 3322 (br), 1712, 1650 and 1518;
3
in acetonitrile (10 cm ) and caesium carbonate (0.47 g,
δH (CDCl ): 7.4–7.3 (5H, m, Ph), 6.85, 6.05 (1H, 2 × br d,
3
1
.45 mmol) added. The resulting suspension was treated with
NHCbz, rotamers), 5.1 (2H, m, PhCH ), 5.4, 4.9 (1H, 2 × br d,
2
3
tert-butyl bromoacetate (0.19 cm , 1.16 mmol) and the reaction
heated at 50 ЊC for 4 h. After cooling, filtration and evaporation
of solvent a residual gum was obtained which was purified by
flash chromatography (eluant ethyl acetate–cyclohexane, 1:3)
NHBoc, rotamers), 4.5 (1H, m, H-2), 3.75 (1H, m, H-2Ј),
2
.25–1.5 (7H, m, H-1Ј,3Ј,4Ј,5Ј), 1.4 (9H, s, tBu).
N-Boc protected acid (1.20 g, 2.9 mmol) prepared as above
3
was dissolved in TFA (40 cm ). After 10 min the solvent was
3
affording the title compound 16 (0.17 g, 79%) as a colourless
evaporated and the residue redissolved in ethyl acetate (50 cm )
Ϫ1
gum. νmax (CHBr )/cm 1738, 1729, 1712 (trans-lactam), 1694;
then treated with a solution of HCl in ether (1.5 M, excess).
Evaporation of the solvent gave a gum which crystallized
on trituration with ether. This material was dried in vacuo
affording the title compound 8 (0.97 g, 2.9 mmol, 100%) as a
3
δH (CDCl ): 7.4–7.3 (5H, m, Ph), 5.1 (3H, m, PhCH , NH),
3
2
4
.35 (1H, br t, H-3), 3.9 (2H, ABq, CH CO ), 3.35 (1H, dt,
2 2
H-6a), 2.1–1.3 (7H, m, H-3a,4,5,6), 1.4 (9H, s, tBu).
Ϫ1
white solid. νmax (film)/cm : 3487, 2960, 1715, 1669 and 1538;
ϩ
δH (DMSO): 8.1 (3H, br s, NH ), 7.7 (1H, d, NH, J 7.5 Hz),
Racemic [(3S,3aR,6aS)-2-oxo-3-aminohexahydrocyclopenta-
[b]pyrrol-1-yl]acetic acid tert-butyl ester acetate salt 17
3
7
.4–7.25 (5H, m, Ph), 5.05 (2H, s, PhCH ), 4.1 (1H, t, H-2,
2
J 7.5 Hz), 3.4 (1H, m, H-2Ј), 2.25–1.3 (7H, m, H-1Ј, 3Ј, 4Ј, 5Ј);
Cbz trans-lactam 16 (0.17 g, 0.44 mmol) was dissolved in acetic
acid (20 cm ) and hydrogenated with 10% palladium on carbon
ϩ
m/z 293.1500. MH C H N O requires 293.1501.
15
21
2
4
3
(
50 mg) at room temperature for 18 h. The solution was filtered
Racemic [(1S,2S)-2-aminocyclopentyl][(R)-benzyloxycarbonyl-
amino]acetic acid hydrochloride 9
and evaporation afforded the title compound 17 (0.13 g, 94%)
as a crystalline solid. νmax (KBr)/cm 1745, 1710 and 1554;
δH (DMSO): 4.35 (3H, br s, NH ), 3.95 (2H, ABq, CH CO ),
3.5 (2H, m, H-3,6a), 2.1–1.3 (7H, m, H-3a,4,5,6), 1.4 (9H, s,
Ϫ1
ϩ
The methyl ester 15 (1.47 g, 3.62 mmol) was treated similarly
to 14 to give the intermediate N-Boc protected acid (1.34 g,
3
2
2
ϩ
ϩ
3
.41 mmol, 94%) as a white foam. This crude material (1.23 g,
tBu); m/z 509 (2M ϩ H ), 254 (MH ).
2
4
J. Chem. Soc., Perkin Trans. 1, 2001, 21–25

View Article Online
Racemic 2-[(2-Aminothiazol-4-yl)-2-[(3S,3aR,6aS)-1-carboxy-
methyl-2-oxooctahydrocyclopenta[b]pyrrol-3-ylcarbamoyl]-
methyleneaminooxy]-2-methylpropionic acid trifluoroacetate 6
C. J. Mooney, C.-M. Tang, P. J. Thomas, S. Parry and C. Patel,
Bioorg. Med. Chem. Lett., 1999, 9, 1657.
8
9
M. Pass, R. E. Bolton, S. J. Coote, H. Finch, S. Hindley,
A. Lowdon, E. McDonald, J. McLaren, M. Owen, N. A. Pegg,
V. J. Mooney, C.-M. Tang, S. Parry and C. Patel, Bioorg. Med.
Chem. Lett., 1999, 9, 431.
H. Finch, N. A. Pegg, J. McLaren, A. Lowdon, R. Bolton,
S. J. Coote, U. Dyer, J. G. Montana, M. R. Owen, M. Dowle,
D. Buckley, B. C. Ross, C. Campbell, C. Dix, C. Mooney,
C.-M. Tang and C. Patel, Bioorg. Med. Chem. Lett., 1998, 8,
2955.
3
Oxalyl choride (0.050 cm , 0.57 mmol) was added to a solution
3
3
of DMF (0.066 cm , 0.85 mmol) in dichloromethane (5 cm )
at Ϫ20 ЊC under nitrogen. Upon completion of the addition, the
solution was warmed to ice bath temperature and the acid 18
1
8
(
0.416 g, 0.73 mmol) added as a solid. After 10 min a solution
of the acetate salt of the amine 17 (0.120 g, 0.38 mmol)
3
10 S. J. F. Macdonald, D. J. Belton, D. M. Buckley, J. E. Spooner,
M. S. Anson, L. A. Harrison, K. Mills, R. J. Upton, M. D. Dowle,
R. A. Smith, C. R. Molloy and C. Risley, J. Med. Chem., 1998,
in dichloromethane (2 cm ) was added with diisopropylethyl-
3
amine (0.4 cm , 2.29 mmol). After 24 h, the mixture was diluted
with ethyl acetate and water, and the organic layer washed
further with 10% aqueous citric acid solution, then saturated
aqueous sodium bicarbonate and finally brine. After drying
4
1, 3919.
1
1 H. A. Kelly, R. Bolton, S. A. Brown, S. J. Coote, M. Dowle,
U. Dyer, H. Finch, D. Golding, A. Lowdon, J. McLaren, J. G.
Montana, M. R. Owen, N. A. Pegg, B. C. Ross, R. Thomas and
D. A. Walker, Tetrahedron Lett., 1998, 39, 6979.
(
anhydrous MgSO ) and evaporation the residue was purified
4
by flash chromatography (eluant ethyl acetate–cyclohexane,
:3) affording the fully protected 19 (0.183 g, 60%) as a white
1
2 S. J. F. Macdonald, G. D. E. Clarke, M. D. Dowle, L. A. Harrison,
S. T. Hodgson, G. G. A. Inglis, M. R. Johnson, P. Shah, R. J. Upton
and S. B. Walls, J. Org. Chem., 1999, 64, 5166.
13 J. R. McCarthy, P. E. Wiedeman, A. J. Schuster, J. Whitten,
R. J. Barbuch and J. C. Huffman, J. Org. Chem., 1985, 50, 3095.
14 T. Shioiri, K. Ninomiya and S. Yamada, J. Am. Chem. Soc., 1972,
1
Ϫ1
solid. Compound 19: mp 103 ЊC; νmax (CHBr )/cm 3298 (br),
3
1
737, 1731, 1714, 1681 and 1519; δH (CDCl ): 7.4 (1H, d, NH
3
amide), 7.35–7.25 (15H, m, 3 × Ph), 6.8 (1H, s, trityl NH), 6.75
(
1H, s, thiazole H), 4.7 (1H, dd, H-3), 3.95 (2H, ABq, CH CO ),
2 2
9
4, 6203.
3
2
.4 (1H, dt, H-6a), 1.65, 1.60 (6H, 2s, CMe ), 1.4 (18H, s,
× tBu), 2.1–1.3 (7H, m, H-3a,4,5,6); m/z 808 (MH ), 243.
2
ϩ
15 For a review see F. C. Neuhaus and N. Georgopapakadou,
in Emerging Targets in Antibacterial and Antifungal Chemotherapy,
ch. 9, eds. J. Sutcliffe and N. H. Georgopapadakou, Chapman
and Hall, New York, London, 1992.
Compound 19 (0.122 g, 0.031 mmol) was dissolved in tri-
3
fluoroacetic acid (2 cm ) containing a trace of anisole. After
2
.5 h, the solution was diluted with ether which precipitated
16 M. P. Singh, Y. I. Lee, R. Singh, R. G. Micetich and B. J. Wilkinson,
J. Antimicrob. Chemother., 1991, 27, 459.
17 M. Nishida and Y. Shigi, The Role of Permeability and Affinity
for Penicillin-binding Proteins in the Antibacterial Activity of the
Third-generation Cephalosporins, in Symp. Front. Pharmacol., 1982,
vol. 1 (New β-Lactam Antibiotics), pp. 65–81.
the title compound 6 (0.067 g, 78%) as a white solid which
Ϫ1
was collected by filtration. Mp 141 ЊC; νmax (Nujol)/cm 1718
and 1674; δH (DMSO): 8.7 (1H, d, thiazole H), 4.45 (1H, dd,
H-3), 3.9 (2H, ABq, CH CO H), 3.35 (1H, m, H-6a), 1.45, 1.4
2
2
(
6H, 2s, CMe ), 2.0–1.3 (7H, m, H-3a,4,5,6); HPLC 95%;
2
ϩ
18 N. A. C. Curtis, D. Orr, G. W. Ross and M. G. Boulton, Antimicrob.
Agents Chemother., 1979, 16, 533.
m/z 454.1397. C H N O S requires MH 454.1396.
18
23
5
7
1
2
2
2
9 M. Narisada, Pure Appl. Chem., 1987, 59, 459.
0 M. Takasuka, J. Nishikawa and K. Tori, J. Antibiot., 1982, 35, 1729.
1 J. M. Ghuysen, Annu. Rev. Microbiol., 1991, 45, 37.
2 M. Leyh-Bouille, J. Van Beeumen, S. Renier-Pirlot, B. Joris,
M. Nguyen-Disteche and J. M. Ghuysen, Biochem. J., 1989, 260,
601.
Acknowledgements
The authors wish to express their thanks to Gavin Chung for
performing the biological evaluation of compound 6.
2
2
2
3 R. N. Brogden and R. C. Heel, Drugs, 1986, 31, 96.
4 C. E. Newall, Chem. Br., 1987, 23, 976.
5 D. Gala, M. Steinman and R. S. Jaret, J. Org. Chem., 1986, 51,
References
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1
2
3
D. Jackson and D. H. Staniforth, Acta Ther., 1982, 8, 367.
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S. P. Clissold, P. A. Todd and D. M. Campoli-Richards, Drugs, 1987,
26 C. H. O’Callaghan, B. E. Ayres and D. G. H. Livermore, Br. Pat.
Appl., 2 040 921, Oct 26, 1979.
27 Agar MIC’s were determined by a two-fold agar dilution method
using Mueller–Hinton media (Becton Dickinson Ltd, USA).
Exponentially growing cultures were inoculated onto the surface of
agar plates using a multipoint inoculator (Denley, UK) to produce
3
3, 183.
4
L. N. Jungheim, D. B. Boyd, J. M. Indelicato, C. E. Pasini,
D. A. Preston and W. E. Alborn, Jr. J. Med. Chem., 1991, 34, 1732
and references cited therein.
5
3
an inoculum of approximately 10 cfu per cm (cfu = colony forming
units). The plates were incubated at 37 ЊC for 18 hours and the
minimum inhibitory concentration (MIC) value interpreted as the
lowest antibiotic concentration which completely inhibited bacterial
growth.
5
6
Y. Nozaki, N. Katayama, H. Ono, S. Tsubotani, S. Harada,
H. Okazaki and Y. Nakao, Nature, 1987, 325, 179.
Y. Nakao, in Recent Advances in the Chemistry of β-Lactam
Antibiotics, eds. P. H. Bentley and R. Southgate, Special Publication
No. 70, RSC, London, 1989, ch. 8.
M. Pass, S. Abu-Rabie, A. Baxter, R. Conroy, S. J. Coote, A. P.
Craven, H. Finch, S. Hindley, H. A. Kelly, A. W. Lowdon,
E. McDonald, W. L. Mitchell, N. A. Pegg, P. A. Procopiou,
N. G. Ramsden, R. Thomas, D. A. Walker, N. S. Watson, H. Jhoti,
28 TEM-1 β-lactamase was pre-incubated with compound 6 before
Ϫ3
7
the chromogenic substrate nitrocefin (50 µg cm ) was added.
The enzymatic hydrolysis of nitrocefin was followed at 495 nm.
Compound 6 failed to inhibit the activity of TEM-1 at the highest
concentration used (1 mM).
J. Chem. Soc., Perkin Trans. 1, 2001, 21–25
25