Novel prodrugs of meropenem with two lipophilic promoieties: Synthesis and pharmacokinetics

Article abstract of DOI:10.1038/ja.2010.164

To improve the oral absorption of meropenem (MEPM), we synthesized and evaluated a series of its double-promoiety prodrugs, in which lipophilic promoieties were introduced into carboxyl and pyrrolidinyl groups. Among these prodrugs, pivaloyloxymethyl (1R,5S,6S)-2-[(3S,5S)-5-(N,N-dimethylcarbamoyl)-1- (isobutyryloxymethyloxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydroxyethyl] -1-methylcarbapen-2-em-3-carboxylate (4) and 1-ethylpropyloxycarbonyloxymethyl (1R,5S,6S)-2-[(3S,5S)-5-(N,N-dimethylcarbamoyl)-1- (isobutyryloxymethyloxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydroxyethyl] -1-methylcarbapen-2-em-3-carboxylate (8) were chosen for further evaluation. Compounds 4 and 8 were well absorbed after oral administration to rats and beagles (bioavailability 18.2-38.4%), and expected to show potent therapeutic efficacy in patients infected with various pathogens, such as penicillin-resistant S. pneumoniae and β-lactamase-negative ampicillin-resistant H. influenzae.

Full text of DOI:10.1038/ja.2010.164

The Journal of Antibiotics (2011) 64, 233–242
2011 Japan Antibiotics Research Association All rights reserved 0021-8820/11 $32.00
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&
ORIGINAL ARTICLE
Novel prodrugs of meropenem with two lipophilic
promoieties: synthesis and pharmacokinetics
Shunkichi Tanaka, Hiroshi Matsui, Masayasu Kasai, Kazuyoshi Kunishiro, Nobuharu Kakeya and
Hiroaki Shirahase
To improve the oral absorption of meropenem (MEPM), we synthesized and evaluated a series of its double-promoiety prodrugs,
in which lipophilic promoieties were introduced into carboxyl and pyrrolidinyl groups. Among these prodrugs, pivaloyloxymethyl
(1R,5S,6S)-2-[(3S,5S)-5-(N,N-dimethylcarbamoyl)-1-(isobutyryloxymethyloxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydroxyethyl]-
1-methylcarbapen-2-em-3-carboxylate (4) and 1-ethylpropyloxycarbonyloxymethyl (1R,5S,6S)-2-[(3S,5S)-5-(N,N-dimethylcarbamoyl)-
1-(isobutyryloxymethyloxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydroxyethyl]-1-methylcarbapen-2-em-3-carboxylate (8)
were chosen for further evaluation. Compounds 4 and 8 were well absorbed after oral administration to rats and beagles
(bioavailability 18.2–38.4%), and expected to show potent therapeutic efficacy in patients infected with various pathogens,
such as penicillin-resistant S. pneumoniae and b-lactamase-negative ampicillin-resistant H. influenzae.
The Journal of Antibiotics (2011) 64, 233–242; doi:10.1038/ja.2010.164; published online 12 January 2011
Keywords: carbapenem; double-promoiety prodrug; meropenem; single-promoiety prodrug
INTRODUCTION
P. aeruginosa. Recently, tebipenem was developed in Japan and
Carbapenems are the most potent class of b-lactam antibiotics, which approved as a new orally active carbapenem (Figure 1). Tebipenem
have a broad spectrum of potent antibacterial activities against Gram- showed potent activity against penicillin-resistant S. pneumoniae,
positive and Gram-negative organisms, including P. aeruginosa.1,2 b-lactamase-negative ampicillin-resistant H. influenzae, H. influenzae
Carbapenems are stable to hydrolysis by various b-lactamase, and and E. coli;13–15 however, unlike MEPM, tebipenem has no activity
thus, effective against most cephalosporin-resistant microorganisms.3–5 against b-lactamase-producing P. aeruginosa2 and its therapeutic use is
Imipenem, panipenem and meropenem (MEPM) have long been used still limited to pediatric otitis media, rhinitis and pneumonia. In the
for serious infectious diseases, including complicated urinary tract present study, we attempted to increase the oral bioavailability of
infection and complicated respiratory tract infection (Figure 1).1 MEPM by chemical modification to a double-promoiety prodrug,
Recently, doripenem has been launched as a new potent carbapenem because MEPM is chemically and biologically more stable than
(Figure 1).6 However, these are all for parenteral use only. Imipenem imipenem and panipenem, and has a lower molecular weight than
and panipenem are unstable chemically and to renal dehydropepti- doripenem. Furthermore, its efficacy in infection therapy and safety
dase-I, and are thus used in combination with cilastatin and betami- have been established.16
pron, respectively. MEPM and doripenem have a 1b-methyl group,
We have reported the successful modification of ceftizoxime,
and are stable against chemical degradation and hydrolysis by a parenteral cephalosporin, to a double-promoiety prodrug with
dehydropeptidase-I,7–9 and are thus used without cilastatin or lipophilic and hydrophilic promoieties.17,18 Here, double-promoiety
betamipron.
prodrugs of MEPM, in which two kinds of lipophilic promoieties
All these parenteral carbapenems have a carboxyl group at the were introduced at the carbapene C-3 and pyrrolidine N-1 position
carbapene C-3 position, which is essential for interaction with a target of MEPM to increase oral bioavailability, were synthesized and bio-
protein, penicillin-binding protein,1 and a basic group at the pyrro- logically evaluated.
lidine N-1 position, which promote their invasion through D2 porin
into P. aeruginosa,10 resulting in little oral absorption because of the Drug design
two ionizable groups. Many attempts to find new orally active First, single-promoiety prodrugs of MEPM were designed using
carbapenems have been reported,11,12 in which the basic group at pivaloyloxymethyl (POM) and 1-ethylpropyloxycarbonyloxymethyl
the pyrrolidine N-1 position was eliminated and the carboxyl group (EPC), as shown in Figure 2. b-Lactam antibiotics, such as penicillins,
was esterified by easily hydrolizable promoiety to increase oral cephalosporins and carbapenems, have a carboxyl group that decreases
absorption, but most showed very weak antibacterial activity against their membrane permeability, resulting in low oral absorption. In many
Research Laboratories, Kyoto Pharmaceutical Industries, Nakagyo-ku, Kyoto, Japan
Correspondence: Dr H Shirahase, Research Laboratories, Kyoto Pharmaceutical Industries, Ltd., 38, Nishinokyo Tsukinowa-cho, Nakagyo-ku, Kyoto 604-8444, Japan.
E-mail: shirahase@kyoto-pharm.co.jp
Received 9 August 2010; revised 27 October 2010; accepted 11 November 2010; published online 12 January 2011

Prodrug of meropenem
S Tanaka et al
234
HO
HO
HO
H
H
H
H
N
H
H
1
3
CON(CH3)2
NH
5
6
2
S
S
S
7
N
N
N
4
O
O
O
HN
CO2H
CO2H
CO2H
HN
NH
Meropenem (MEPM)
Imipenem
Panipenem
HO
HO
O
O
H
H
N
H
H
N
S
S
N
H
NH2
S
S
N
NH
N
O
O
CO2H
CO2H
Tebipenem
Doripenem
Figure 1 Chemical structures of carbapemems.
HO
HO
HO
H H
H H
H H
N
CON(CH3)2
CON(CH3)2
NH
CON(CH3)2
S
S
S
N
NH
N
N
O
O
O
B
B
CO2H
MEPM
A
A
CO2
CO2
Double-promoiety prodrugs
Single-promoiety prodrugs
A
B
A
-CH2OCOC(CH3)3 (POM)
-CO2CH2OCOCH(CH3)2
-CO2CH2OCOC2H5
-CO2CH2OCOC3H7
-CO2CH2OCOC4H9
-CH2OCO2CH(C2H5)2 (EPC)
-CH2OCOC(CH3)3 (POM)
-CH2OCO2CH(C2H5)2 (EPC)
-CO2CH2OCOCH(CH3)2
Figure 2 Drug design.
orally used penicillins and cephalosporins, their carboxyl group is were prepared by N-alkylation and esterification in one pot, as
esterified with a lipophilic and hydrolyzable promoiety: these pro- described above.
drugs are efficiently absorbed and then rapidly hydrolyzed to an active
Other synthetic routes of compounds 4 and 8 are shown in Scheme
form. As such a promoiety, POM is used in pivmecillinam, cefteram, 2–4. In Scheme 2, introduction of 1-isobutyryloxymethyl (2S,4S)-2-N,
cefetamet, cefditoren and cefcapene; however, a POM promoiety in N-dimethylcarbamoyl-4-mercaptopyrrolidine-1-carboxylate (BMP)21
cephalosporins has been reported to decrease plasma carnitine levels to p-nitrobenzyl (1R,5S,6S)-2-diphenylphosphoryl-6-[(1R)-1-hydro-
in children.19 As a non-POM promoiety, carbonate-type promoieties xyethyl]-1-methylcarbapen-2-em-3-carboxylate (MAP) at the carba-
have been used: 1-(cyclohexyloxycarbonyloxy)ethyl and 1-(isopropy- pene C-2 position was achieved to give 11 in accordance with
loxycarbonyloxy)ethyl in cefotiam and cefpodoxime, respectively, both the literature.22 p-Nitrobenzyl moiety of 11 was removed by Pd-C
racemic promoieties. Here, we chose EPC without an asymmetric catalyzed hydrogenation to yield a carboxylic acid derivative, which
carbon as a non-POM promoiety for a prodrug. was esterified with POM-I and EPC-I in the presence of benzyl
Second, double-promoiety prodrugs of MEPM were designed by triethylammonium chloride (BTEAC) to give compounds 4 and 8,
introduction of the second lipophilic promoiety to the pyrrolidine respectively.
N-1 position of MEPM (Figure 2) because no single-promoiety In Scheme 3, compound 4 was prepared from (3S,4S)-3-[(1R)-
prodrugs of parenteral carbapenems have been successfully developed, (t-butyldimethyl-silyloxy)ethyl]-4-[(1R)-1-carboxyethyl]-2-azetidinone
probably due to their basic side chain, which is also considered to (b-MAC). The b-MAC was esterified with a magnesium salt of POM-
decrease their membrane permeability. As the second lipophilic esterified malonate using 1,1¢-carbonyldiimidazole (CDI) as
promoiety, carbonate promoieties (isobutyryloxymethyloxycarbonyl, condensing reagent to give 12. Compound 12 was treated with
a
propionyloxymethyloxycarbonyl, butyryloxymethyloxycarbonyl and p-dodecylbenzenesulfonyl azide to give a-diazoester 13, which was
valeryloxymethyloxycarbonyl) were used.
then cyclized with rhodium catalyst, and the product was phosphory-
lated to give 14.22 Compound 14 was treated with BMP to give 15,
from which the tert-butyldimethylsilyl (TBS) group was removed by
Chemistry
The general synthetic routes of prodrugs of MEPM are shown Et3Nꢀ3HF to give 4.
in Scheme 1. All prodrugs were prepared from MEPM. Single-
In Scheme 4, the carboxyl moiety of b-MAC was converted
promoiety prodrugs 1 and 2 were prepared by esterification to thioester of BMP using 1-ethyl-3-(dimethylaminopropyl)carbodiimide
with the corresponding alkyl iodides, and 3 was afforded by N- hydrochloride (EDC) and N-methylmorpholine to give 16. Acylation
alkylation of pyrrolidine moiety.20 Double-promoiety prodrugs 4–10 of 16 with EPC ester of oxalic acid afforded 17, which was reacted with
The Journal of Antibiotics

Prodrug of meropenem
S Tanaka et al
235
HO
O
HO
H H
N
H H
a
CON(CH3)2
NH
CON(CH3)2
NH
S
S
N
O
CO2H
CO2R1
HCl
.
MEPM
1: R1; -CH2OCOC(CH3)3
b
c
2: R1; -CH2OCO2CH(C2H5)2
d
HO
O
HO
H H
N
H H
N
CON(CH3)2
NCO2CH2OCOR2
CON(CH3)2
S
S
NCO2CH2OCOCH(CH3)2
O
CO2R1
CO2Na
3
R1
R2
4
5
6
7
8
9
-CH2OCOC(CH3)3
-CH2OCOC(CH3)3
-CH2OCOC(CH3)3
-CH2OCOC(CH3)3
CH(CH3)2 Reagents, conditions and yields:
-C2H5
(a) POM-I or EPC-I, K2CO3, DMF, 5 to 10 or -20 to -15°C,
23 or 16%;
-C3H7
(b) p-NO2-C6H4-OCO2CH2OCOCH(CH3)2, DMF, rt, 42%;
(c) p-NO2-C6H4-OCO2CH2OCOR2, DMF, rt;
-C4H9
-CH2OCO2CH(C2H5)2
-CH(CH3)OCO2-C6H11
-CH(CH3)2
-CH(CH3)2
-CH(CH3)2
(d) R1-I, K2CO3, DMF, 0°C, 28-70%.
10 -CH(CH3)OCO2CH(CH3)2
Scheme 1 Synthesis of prodrugs of MEPM.
HO
HO
H H
N
H H
CON(CH3)2
a
OPO(OPh)2
S
N
NCO2CH2OCOCH(CH3)2
O
O
CO2PNB
MAP
CO2PNB
11
HO
H H
CON(CH3)2
b
c
S
N
NCO2CH2OCOCH(CH3)2
O
CO2R1
4: R1; -CH2OCOC(CH3)3
8: R1; -CH2OCO2CH(C2H5)2
PNB:p-nitrobenzyl
Reagents, conditions and yields: (a) BMP, i-Pr2NEt, CH3CN, 5°C, 92%;
(b) H2, Pd-C, THF-0.1M MOPS Buffer (pH 7.0), 35°C;
(c) POM-I or EPC-I, BTEAC, CH2Cl2-MOPS Buffer (pH 7.0), rt, 82 or 83%, 2 steps.
Scheme 2 Synthesis of 4 and 8 from MAP.
diethoxymethyl phosphine in toluene, and cyclized by heat to give 18. after oral administration of MEPM or prodrugs in male rats. Bioavail-
Finally, the TBS group of 18 was removed to give 8, as described in abilities were calculated by comparing AUC values of MEPM after
Scheme 3.
intravenous administration of MEPM and oral administration of
MEPM or prodrugs. In comparison with MEPM, single-promoiety
prodrugs with POM (1) or EPC (2) at the carbapene C-3 position
showed moderately higher logD values and comparable high water
solubility. The Cmax and bioavailability were increased moderately in 1
RESULTS
Physicochemical properties and oral absorption of single- and
double-promoiety prodrugs of MEPM
LogD (pH 7.0), water solubility (pH 7.0) and oral absorption of MEPM and slightly in 2. A single-promoiety prodrug 3 with isobutyryloxy-
and its single- and double-promoiety prodrugs are shown in Table 1. methyloxycarbonyl at the pyrrolidine N-1 position was also synthesized;
Plasma concentrations of MEPM were determined 30, 60 and 180 min however, there was little effect on the LogD, Cmax and bioavailability.
The Journal of Antibiotics

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236
TBSO
TBSO
H H
NH
H H
NH
CO2H
CO2CH2OCOC(CH3)3
a
O
O
O
12
beta-MAC
TBSO
H H
O
c
d
b
NH
N2
O
CO2CH2OCOC(CH3)3
TBSO
13
TBSO
H H
N
H H
N
CON(CH3)2
e
OPO(OPh)2
S
NCO2CH2OCOCH(CH3)2
O
O
CO2CH2OCOC(CH3)3
14
HO
CO2CH2OCOC(CH3)3
15
H H
f
CON(CH3)2
S
N
NCO2CH2OCOCH(CH3)2
O
CO2CH2OCOC(CH3)3
TBS: tert-butyldimethylsilyl
4
Reagents, conditions and yields:
(a) CDI, Mg[OCOCH2CO2CH2OCOC(CH3)3]2, CH3CN, rt to 40°C, 12%;
(b) p-dodecylbenzenesulfonyl azide, Et3N, CH3CN, 0°C, 85%;
(c) [(AcO)2Rh]2·2H2O, AcOEt, 50°C;
(d) (PhO)2P(O)Cl, i-Pr2NEt, CH3CN, 0°C, 77%, 2 steps;
(e) BMP, i-Pr2NEt, CH3CN, 0°C, 43%; (f) Et3N·3HF, DMF, rt, 17%.
Scheme 3 Synthesis of 4 from b-MAC.
Introduction of a second lipophilic promoiety to the pyrrolidine double-promoiety prodrugs in comparison with the corresponding
N-1 position increased logD to 1.53–2.68 and decreased water single-promoiety prodrugs (4 vs 1 and 8 vs 2).
solubility to 51.8–846.5mg mlꢁ1 (4–8). Double-promoiety prodrugs
In male beagles, the pharmacokinetics of compounds 4 and 8
with POM (4–7) showed similar Cmax and bioavailability. Com- were evaluated (Figure 4, Table 3). The Cmax was similar between
pound 4 was chosen for further evaluation among compounds compounds 4 and 8, and AUC and bioavailability were higher and
4–7 as it was most stable in the preliminary stability test, in which T1/2 was longer in compound 4 than 8.
the solid compounds were kept at 401C in a tightly capped glass
bottle with silica gel for 2 weeks followed by determination of DISCUSSION
their purity. A double-promoiety prodrug with EPC (8) showed MEPM has potent and broad antibacterial activities, and has long
slightly lower Cmax and bioavailability than those of POM-type been used clinically. Its efficacy and safety have been established, and
double-promoiety prodrugs. To further increase its Cmax and bioa- thus, it is still a useful parenteral antibiotic.16 Development of orally
vailability, racemic promoieties 1-(cyclohexyloxycarbonyloxy)ethyl active carbapenems has been desired because of the increase of
and 1-(isopropyloxycarbonyloxy)ethyl were introduced (9 and 10); microorganisms resistant to oral antibacterial agents, such as cepha-
however, little changed in 9 and rather decreased in 10. Compound 9, losporin and fluoroquinolone; however, it is difficult to improve the
but not 8 was unstable in the preliminary stability test. Compound 8 oral absorption of parenteral carbapenems by conventional prodrug
was also chosen for further evaluation as a non-POM double- methods used in cephalosporin, such as cefuroxime,23 in which a
promoiety prodrug.
carboxyl group was esterified, because carbapenems are chemically
and biologically less stable than cephalosporins. Furthermore, their
basic group, which is essential for anti-bacterial activities against
Pharmacokinetics of compounds 4 and 8 in rats and beagles
In male rats, the pharmacokinetics of MEPM after oral administration P. aeruginosa,10 is also considered to limit their oral absorption.
of compounds 4 and 8 was reevaluated to more precisely determine Although some newly synthesized chemically and biologically
the parameters: blood was taken at 10, 20, 30, 45, 60, 90 and 120 min stable carbapenems lacking a basic group were reported,11,12 no
after administration. The Cmax was similar between compounds 4 compounds have been successfully developed. Recently, tebipenem,
and 8, and AUC and bioavailability were slightly higher and T1/2 showing high bioavailability and high activity against penicillin-
was longer in compound 4 than 8 (Figure 3, Table 2). It was con- resistant S. pneumoniae and b-lactamase-negative ampicillin-resistant
firmed that oral absorption of MEPM was effectively increased in the H. influenzae, was approved in Japan for pediatric otitis media, rhinitis
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Prodrug of meropenem
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237
TBSO
CON(CH3)2
NCO2CH2OCOCH(CH3)2
TBSO
H H
NH
H H
NH
S
CO2H
a
O
O
O
16
CON(CH3)2
NCO2CH2OCOCH(CH3)2
beta-MAC
b
TBSO
H H
N
S
O
O
COCO2CH2OCO2CH(C2H5)2
17
TBSO
H H
CON(CH3)2
c
d
S
N
NCO2CH2OCOCH(CH3)2
O
CO2CH2OCO2CH(C2H5)2
18
HO
H H
N
e
CON(CH3)2
S
NCO2CH2OCOCH(CH3)2
CO2CH2OCO2CH(C2H5)2
O
8
Reagents, conditions and yields:
(a) BMP, EDC, N-methylmorpholine, DMF, rt, 71%;
(b) 1-ethylpropyloxycarbonyloxymethyloxyoxalyl chloride, Et3N, CH2Cl2, 0°C, 60%;
(c) MeP(OEt)2, toluene, rt; (d) xylene, 140 to 150°C, 53%, 2 steps;
(e) Et3N·3HF, DMF, rt, 72%.
Scheme 4 Synthesis of 8 from b-MAC.
Table 1 Physicochemical properties and pharmacokinetics in rats of single- and double-promoiety prodrugs of MEPM
Compound
R1
R2
Cmax (mg mlꢁ1
)
BA (%)
Water solubility (mg mlꢁ1
)
LogD
MEPM
H
H
H1)
H1)
0.24 0.13
0.74 0.32
0.29 0.10
0.14 0.10
3.9
19.8
6.3
41000
41000
41000
41000
oꢁ2.5
ꢁ0.52
ꢁ0.37
oꢁ1
1
2
3
CH2OCOC(CH3)3 (POM)
CH2OCO2CH(C2H5)2 (EPC)
Na
CO2CH2OCOCH(CH3)2
3.4
4
5
6
7
CH2OCOC(CH3)3 (POM)
CO2CH2OCOCH(CH3)2
CO2CH2OCOC2H5
CO2CH2OCOC3H7
CO2CH2OCOC4H9
1.16 0.22
1.05 0.21
1.11 0.14
0.94 0.14
27.5
29.5
29.5
27.0
130
2.00
1.53
2.13
2.68
846.5
143.8
154.9
8
CH2OCO2CH(C2H5)2 (EPC)
CH(CH3)OCO2-C6H11
CO2CH2OCOCH(CH3)2
0.89 0.33
1.00 0.51
0.65 0.12
18.8
16.9
15.4
51.8
121.9
772.5
2.51
2.86
1.81
9
10
CH(CH3)OCO2CH(CH3)2
Abbreviations: BA, bioavailability; EPC, 1-ethylpropyloxycarbonyloxymethyl; MEPM, meropenem; POM, pivaloyloxymethyl.
aHCl salt, Cmax; Mean s.d. (n¼3), Water solubility (pH 7.0) and LogD (pH 7.0); Mean (n¼2).
and pneumonia.13–15 In the present study, we attempted to apply our because of the presence of a basic group. Indeed, compound 1 with
double-promoiety prodrug method to MEPM to increase its bioavail- POM and compound 2 with EPC at the carbapene C-3 position still
ability. We succeeded in modifying ceftizoxime, a parenteral cepha- had low lipophilicity and were highly water soluble, and thus their oral
losporin, to orally bioavailable double-promoiety prodrugs, in which absorption was little or only slightly increased. However, in addition,
the appropriate balance of lipophilicity and hydrophilicity was introduction of a second lipophilic group, which is known to be
achieved by the introduction of both lipophilic promoiety and hydrolyzable and useful in promoieties, at the pyrrolidine N-1 posi-
hydrophilic promoiety.17,18 In MEPM, conventional esterification of tion increased lipophilicity and decreased water solubility, and mark-
the carboxyl group is not enough to achieve appropriate lipophilicity edly enhanced Cmax and AUC compared with the corresponding
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Prodrug of meropenem
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238
Table 3 Pharmacokinetic profile of MEPM after oral administration
of compounds 4 and 8 at a dose of 10 mg potency per kg and
intravenous administration of MEPM at a dose of 1 mg potency
per kg to male beagles
10
1
Compound
Cmax (mg mlꢁ1
)
T1/2 (h)
AUC (mg h mlꢁ1
)
BA (%)
4
2.86 1.02
2.92 0.39
—
2.30 0.53
1.04 0.17
0.70 0.07
11.8 0.22
7.50 1.17
3.08 0.26
38.4
24.4
—
8
MEPM
Abbreviations: BA, bioavailability; MEPM, meropenem.
Mean s.d. (n¼4).
0.1
used cephalosporins; however, double-promoiety prodrugs including
ceftizoxime alapivoxil, showed higher urinary recovery in humans
than rats or beagles (more than twofold).17,24 Compounds 4 and 8 are
also expected to show higher bioavailability in humans than animals,
and to show potent anti-infection effects in patients. Indeed, the
dosage regimen of compound 8 in mice for the simulation of the
predicted human pharmacokinetics significantly reduced viable cell
counts in the lungs of mice intranasally infected with three strains
of drug-resistant S. pneumoniae.25 Whereas compound 4 showed
longer T1/2 than 8, the POM moiety of 4 might decrease plasma
carnitine levels in children, as reported previously for cephalo-
sporins.19 To select a candidate for clinical study, further study
is needed to precisely determine their pharmacokinetic properties,
safety and therapeutic efficacy in various infectious models, includ-
ing respiratory tract infection and urinary tract infection models.
Compounds 4 and 8 would be the first orally active carbapenems
effective against P. aeruginosa, derived from a parenteral antibiotic,
which could be also useful in switch therapy from injection of MEPM
to oral administration.
30
60
90
120
Time (minute)
Figure 3 Plasma concentrations of MEPM after oral administration of
compounds 4 and 8 at a dose of 20 mg potency per kg and intravenous
administration of MEPM at a dose of 2 mg potency per kg to male SD rats.
Mean s.d. (n¼4); J, compound 4 p.o.; n, compound 8 p.o.; &, MEPM i.v.
Table 2 Pharmacokinetic profile of MEPM after oral administration
of compounds 4 and 8 at a dose of 20mg potency per kg and
intravenous administration of MEPM at a dose of 2 mg potency
per kg to male SD rats
Compound
Cmax (mg mlꢁ1
)
T1/2 (min)
AUC (mg min mlꢁ1
)
BA (%)
4
0.96 0.18
1.05 0.26
—
47.8 24.3
24.8 4.40
4.53 0.46
82.1 21.5
63.9 7.04
35.1 1.88
23.4
18.2
—
8
MEPM
Abbreviations: BA, bioavailability; MEPM, meropenem.
In conclusion, MEPM was successfully modified to double-promoiety
prodrugs with excellent oral absorption by the introduction of two
lipophilic promoieties on two sides. This method is thought to be
applicable to other small parenteral drugs with low oral absorption
because of two or more ionizable promoieties.
Mean s.d. (n¼4).
10
EXPERIMENTAL PROCEDURE
General procedure
Chemicals were obtained from commercial sources and used without purifica-
tion. Reactions were monitored by TLC on Merck precoated silica gel 60 F254
(0.25 mm, Merck, Darmstadt, Germany) plates. The spots on TLC were
visualized by UV light (254nm), iodine and ninhydrin. Column chromato-
graphy was performed on silica gel (Daisogel NO.1001W; Daiso, Osaka, Japan)
or HP-21 (Diaion; Mitsubishi Chemical, Tokyo, Japan). Melting points were
measured on a melting point apparatus (MP-21; Yamato Scientific, Tokyo,
Japan) and are uncorrected. IR spectra were obtained with an infrared
spectrometer (FT-720; HORIBA, Kyoto, Japan or FT-IR8200PC; Shimadzu,
Kyoto, Japan). 1H-NMR spectra were recorded at 400 MHz (JNM-AL400;
JEOL, Tokyo, Japan) or 90MHz (Hitachi FT-NMR R-1900; Hitachi High-
Technologies, Tokyo, Japan) on a nuclear magnetic resonance spectrometer
using tetramethylsilane as an internal standard. Mass spectra (MS) were
obtained on a QTRAP LC/MS/MS system (API2000; Applied Biosystems,
Foster City, CA, USA).
1
0.1
1
2
3
5
8
Time (hour)
Figure 4 Plasma concentrations of MEPM after oral administration of
compounds 4 and 8 at a dose of 10 mg potency per kg and intravenous
administration of MEPM at a dose of 1 mg potency per kg to male beagles.
Mean s.d. (n¼4); J, compound 4 p.o.; n, compound 8 p.o.; &, MEPM i.v.
Synthetic procedures in Scheme 1
Pivaloyloxymethyl
single-promoiety prodrugs. Among them, compounds 4 and 8 showed
similar Cmax in rats and beagles (0.96–2.92 mg mlꢁ1), which were
higher than the minimum inhibitory concentration of MEPM against
penicillin-resistant S. pneumoniae, H. influenzae and E. coli. Their
(1R,5S,6S)-2-[(3S,5S)-5-(N,N-Dimethylcarbamoyl)pyrrolidin-
3-ylthio]-6-[(1R)-1-hydroxyethyl]-1-methylcarbapen-2-em-3-carboxylate Hydrochloride
(1). To a suspension of MEPM (5.98 g, 15.6 mmol) in N,N-dimethylforma-
mide (DMF) (27 ml) at 5 1C were added pivaloyloxymethyl iodide (8.4g,
bioavailabilities in animals are relatively low compared with clinically 31mmol) and K2CO3 (2.59 g, 18.7mmol), and the mixture was stirred at
The Journal of Antibiotics

Prodrug of meropenem
S Tanaka et al
239
5–10 1C for 0.5 h, followed by the addition of pivaloyloxymethyl iodide (2.5g, cmꢁ1 3436, 1759, 1724, 1649. 1H NMR (CDCl3) d 1.14 (3H, t, J¼7.7 Hz), 1.22
9.4mmol), and stirring at the same temperature for 0.5 h. The mixture was (9H, s), 1.26 (3H, d, J¼7.1 Hz), 1.32 (3H, d, J¼6.1 Hz), 1.7–2.1, 2.4–2.8 (total
poured into Et2O-i-Pr2O (1:2) (300ml), and supernatant was removed by 2H, m), 2.38 (2H, q, J¼7.7 Hz), 2.95, 2.98 (total 3H, each s), 3.07, 3.11 (total
decanting. A solution of the residue in ethyl acetate (EtOAc) was washed with 3H, each s), 3.1–3.8 (4H, m), 3.9–4.3 (3H, m), 4.73 (1H, m), 5.6–5.8 (2H, m),
5% NaCl aq., and extracted with 0.5 M HCl aq. The aqueous layer was purified 5.88 (2H, ABq, J¼6.1Hz). MS m/z 643 (M+H)+. Anal. Calc for
by column chromatography (HP-21, CH3CN-H2O), and lyophilized. The C28H41N3O11SꢀH2O: C 52.08, H 6.71, N 6.51. Found: C 51.83, H 6.32, N 6.36.
residue was solidified from EtOAc to give crude 1 (1.91 g, 23% yield).
Compound 1 was obtained as a white solid by recrystallization of crude 1
from a mixture of MeOH and EtOAc. M.p. 183–1851C (dec). IR nmax (Nujol)
Pivaloyloxymethyl (1R,5S,6S)-2-[(3S,5S)-1-(Butyryloxymethyloxycarbonyl)-5-(N,
N-dimethylcarbamoyl)-pyrrolidin-3-ylthio]-6-[(1R)-1-hydroxyethyl]-1-methylcar-
cmꢁ1 3358, 2758, 1773, 1753, 1720, 1663. 1H NMR (DMSO-d6) d 1.15 (9H, s),
1.0-1.3 (6H, m), 1.4–2.0 (1H, m), 2.91 (3H, s), 3.02 (3H, s), 4.5–4.8 (1H, br t),
bapen-2-em-3-carboxylate (6). Yield 51%. M.p. 134–136 1C. IR nmax (Nujol)
cmꢁ1 3395, 1794, 1753, 1728, 1636. 1H NMR (CDCl3) d 0.94 (3H, t, J¼7.2 Hz),
4.8–5.4 (1H, br), 5.6–6.1 (2H, ABq, J¼5.7Hz), 9.2–10.6 (2H, br).
1.22 (9H, s), 1.26 (3H, d, J¼7.3 Hz), 1.33 (3H, d, J¼6.1 Hz), 1.65 (2H, m), 2.34
(2H, t, J¼7.2Hz), 1.70–2.80 (3H, m), 2.90–3.20 (6H, m), 3.10–3.90 (4H, m),
1-Ethylpropyloxycarbonyloxymethyl (1R,5S,6S)-2-[(3S,5S)-5-(N,N-Dimethylcar-
3.90–4.40 (3H, m), 4.71 (1H, m), 5.60–5.80 (2H, m), 5.89 (2H, q, J¼6.4 Hz).
bamoyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydroxyethyl]-1-methylcarbapen-2-em-3-
carboxylate Hydrochloride (2). To a suspension of MEPM (2.99 g, 7.80 mmol)
MS m/z 643 (M+H)+. Anal Calc for C29H43N3O11S: C 54.28, H 6.75, N 6.55.
Found: C 54.33, H 6.79, N 6.53.
in DMF (12 ml) at ꢁ20 to ꢁ15 1C were added dropwise a solution of
1-ethylpropyl iodomethyl carbonate (2.12 g, 7.79mmol) in DMF (3.0ml)
and K2CO3 (1.29 g, 9.36 mmol), and the mixture was stirred at the same
Pivaloyloxymethyl (1R,5S,6S)-2-[(3S,5S)-5-(N,N-Dimethylcarbamoyl)-1-(valery-
temperature for 0.5 h. Compound 2 was obtained as a white solid (700 mg,
loxymethyloxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydroxyethyl]-1-methylcar-
16% yield) by a similar procedure to that described in the synthesis of 1. IR
bapen-2-em-3-carboxylate (7). Yield 37%. M.p. 90–92 1C. IR nmax (Nujol)
nmax (Nujol) cmꢁ1 3362, 1765, 1720, 1657. 1H NMR (CDCl3) d 0.91, 0.92
cmꢁ1 3395, 1755, 1709, 1647. 1H NMR (CDCl3) d 0.91 (3H, t, J¼7.3 Hz), 1.22
(total 6H, each t, J¼7.3 Hz), 1.25 (3H, d, J¼7.1 Hz), 1.32 (3H, d, J¼6.1 Hz),
(9H, s), 1.26, 1.27 (total 3H, each d, J¼7.1 Hz), 1.34, 1.35 (total 3H, each d,
1.58–1.70 (4H, m), 1.60–1.70 (1H, br), 1.75–1.86 (1H, m), 2.97–3.10 (1H, m),
J¼5.8 Hz), 1.20–1.40 (2H, m), 1.55–1.70 (2H, m), 1.88–1.99 (1H, m), 2.33–
3.00 (3H, s), 3.09 (3H, s), 3.26 (1H, dd, J¼5.6, 2.4 Hz),
2.40 (2H, m), 2.63–2.73 (1H, m), 2.95, 2.98 (total 3H, each s), 3.07, 3.11 (total
3.35–3.47 (1H, m), 3.60–3.70 (1H, m), 4.08–4.25 (2H, m), 4.25–4.34 (1H,
3H, each s), 3.22, 3.24 (total 1H, each dd, J¼7.1, 2.7Hz), 3.32–3.42
m), 4.50 (1H, dd, J¼9.5, 2.4 Hz), 4.64 (1H, quintet, J¼6.1 Hz), 5.03 (1H, t,
(1H, m), 3.43, 3.45 (total 1H, each dd, J¼10.5, 1.4 Hz), 3.55–3.68 (1H, m),
J¼8.6Hz), 5.79 (2H, q, J¼5.8 Hz).
4.04, 4.13 (total 1H, each dd, J¼10.5, 7.3 Hz), 4.22, 4.26 (total 1H, each dd,
J¼9.5, 2.7 Hz), 4.20–4.28 (1H, m), 4.69, 4.75 (total 1H, each t, J¼8.2, 8.1 Hz),
Sodium (1R,5S,6S)-2-[(3S,5S)-5-(N,N-Dimethylcarbamoyl)-1-(isobutyryloxymethyl-
oxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydroxyethyl]-1-methylcarbapen-2-em-3-
5.64, 5.68 (total 1H, each ABq, J¼5.8 Hz), 5.68, 5.79 (total 1H, each ABq,
J¼5.6 Hz), 5.83, 5.94 (total 2H, each ABq, J¼5.4 Hz). MS m/z 657 (M+H)+.
carboxylate (3). To a solution of isobutyryloxymethyl p-nitrophenyl carbonate
Anal Calc for C30H45N3O11Sꢀ0.5H2O: C 54.20, H 6.97, N 6.32. Found: C 54.08,
(405 mg, 1.43 mmol) in DMF (2 ml) at 0 1C was added MEPM (500 mg,
H 6.81, N 6.24.
1.30 mmol), and the mixture was stirred at room temperature for 1 h. The
reaction mixture was poured into EtOAc-i-Pr2O (1:1) (70ml), and left to stand at
01C for 10 min. The formed precipitate was collected by filtration and washed
with EtOAc-i-Pr2O (1:1). To a solution of the obtained compound in H2O
(40 ml) was added NaHCO3 (164mg, 1.95mmol) for salting, and the mixture was
purified by column chromatography (HP-21, CH3CN-H2O), and lyophilized to
give 3 (300mg, 42% yield) as a solid. IR nmax (Nujol) cmꢁ1 3400, 1728. 1H NMR
(D2O) d 1.14 (6H, d, J¼6.8 Hz), 1.21 (3H, d, J¼6.1Hz), 1.28 (3H, d, J¼7.7 Hz),
1.60–2.87 (3H, m), 2.93–3.11 (6H, m), 3.23–4.36 (7H, m),
4.80–5.01 (1H, m), 5.66–5.73 (2H, m).
1-Ethylpropyloxycarbonyloxymethyl (1R,5S,6S)-2-[(3S,5S)-5-(N,N-Dimethylcarba-
moyl)-1-(isobutyryloxymethyloxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydro-
xyethyl]-1-methylcarbapen-2-em-3-carboxylate (8). Yield 70%. M.p. 108–
110 1C. IR nmax (Nujol) cmꢁ1 3395, 1759, 1724, 1651. 1H NMR (CDCl3) d
0.91 (6H, t, J¼7.3Hz), 1.17 (6H, d, J¼7.0 Hz), 1.25 (3H, d, J¼7.3 Hz), 1.33
(3H, d, J¼6.1Hz), 1.50–2.80 (8H, m), 2.95, 2.97 (total 3H, each s), 3.07, 3.11
(total 3H, each s), 3.10–3.90 (4H, m), 3.90–4.40 (3H, m), 4.50–4.80 (2H, m),
5.60–6.00 (4H, m). MS m/z 673 (M+H)+. Anal Calc for C30H45N3O12S: C
53.64, H 6.75, N 6.26. Found: C 53.57, H 6.72, N 6.22.
Pivaloyloxymethyl (1R,5S,6S)-2-[(3S,5S)-5-(N,N-Dimethylcarbamoyl)-1-(isobu-
tyryloxymethyloxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydroxyethyl]-1-methyl-
carbapen-2-em-3-carboxylate (4). To
a suspension of MEPM (17.4 g,
1-(Cyclohexyloxycarbonyloxy)ethyl (1R,5S,6S)-2-[(3S,5S)-5-(N,N-Dimethylcar-
bamoyl)-1-(isobutyryloxymethyloxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydr-
oxyethyl]-1-methylcarbapen-2-em-3-carboxylate (9). Yield 39%. M.p. 85–86 1C.
IR nmax (Nujol) cmꢁ1 3395, 1749, 1717, 1653. 1H NMR (CDCl3) d 1.18 (6H, d,
J¼7.0 Hz), 1.26 (3H, d, J¼7.0Hz), 1.33 (3H, d, J¼6.4 Hz), 1.10–2.40 (12H, m),
1.58, 1.60 (total 3H, each d, J¼5.5 Hz), 2.40–2.90 (2H, m), 2.95, 2.97 (total 3H,
each s), 3.06, 3.10 (total 3H, each s), 3.10–3.90 (4H, m), 3.90–4.40 (3H, m),
4.60–5.10 (2H, m), 5.60–5.80 (2H, m), 6.87 (1H, q, J¼5.5 Hz). MS m/z 699
(M+H)+. Anal Calc for C32H47N3O12SꢀH2O: C 53.69, H 6.90, N 5.87. Found:
C 53.63, H 6.70, N 5.79.
45.5 mmol) in DMF (70 ml) at 0 1C was added isobutyryloxymethyl p-nitro-
phenyl carbonate (15.0 g, 50.1mmol), and the mixture was stirred at room
temperature for 1 h, followed by the addition of pivaloyloxymethyl iodide
(30.6g, 114 mmol) at 0 1C, and stirring at room temperature for 2 h. After the
addition of 5% NaHCO3 aq. (150ml), the mixture was extracted with EtOAc
(200 ml), and then the organic layer was washed with 5% NaHCO3 aq. and
brine, dried over Na2SO4, and evaporated under reduced pressure. The residue
was purified by column chromatography (silica gel, n-hexane-EtOAc) to give a
solid (16.5g). The solid was recrystallized from EtOAc-i-Pr2O (2:3) (200ml) to
give 4 (12.0 g, 41% yield) as a white solid. M.p. 139–141 1C. IR nmax (Nujol)
cmꢁ1 3385, 1796, 1755, 1728, 1636. 1H NMR (CDCl3) d 1.18 (6H, d,
J¼7.5Hz), 1.22 (9H, s), 1.26 (3H, d, J¼7.3 Hz), 1.34 (3H, d, J¼6.4Hz), 1.7–
2.8 (4H, m), 2.95, 2.97 (total 3H, each s), 3.07, 3.11 (total 3H, each s), 3.1–3.9
(4H, m), 3.9–4.4 (3H, m), 4.71 (1H, m), 5.6–5.8 (2H, m), 5.88 (2H, ABq,
J¼6.1 Hz). MS m/z 643 (M+H)+. Anal Calc for C29H43N3O11S: C 54.28, H
6.75, N 6.55. Found: C 54.27, H 6.48, N 6.55.
1-(Isopropyloxycarbonyloxy)ethyl (1R,5S,6S)-2-[(3S,5S)-5-(N,N-Dimethylcarbamoyl)-
1-(isobutyryloxymethyloxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydroxyethyl]-1-
methylcarbapen-2-em-3-carboxylate (10). Yield 48%. M.p. 76–781C. IR nmax
(Nujol) cmꢁ1 3234, 1749, 1716, 1645. 1H NMR (CDCl3) d 1.14–1.22 (6H, m),
1.23–1.38 (12H, m), 1.56–1.62 (3H, m), 1.88–2.10 (2H, m), 2.54–2.73 (2H, m),
2.95, 2.98 (total 3H, each s), 3.07, 3.11 (total 3H, each s), 3.30–3.49 (2H, m),
3.54–3.70 (1H, m), 4.00–4.15 (1H, m), 4.17–4.27 (2H, m), 4.69, 4.74 (total 1H,
Compounds 5–10 were prepared according to the procedure for 4.
Pivaloyloxymethyl (1R,5S,6S)-2-[(3S,5S)-5-(N,N-Dimethylcarbamoyl)-1-(propio- each t, J¼8.0 Hz), 4.85–4.95 (1H, m), 5.63–5.82 (2H, m), 6.83–6.90 (1H, m).
nyloxymethyloxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydroxyethyl]-1-methylcar- MS m/z 659 (M+H)+. Anal Calc for C29H43N3O12Sꢀ1.5H2O: C 50.87, H 6.77, N
bapen-2-em-3-carboxylate (5). Yield 28%. M.p. 75–77 1C. IR nmax (Nujol) 6.14. Found: C 50.90, H 6.52, N 6.08.
The Journal of Antibiotics

Prodrug of meropenem
S Tanaka et al
240
Synthetic procedures in Scheme 2
Pivaloyloxymethyl (4R)-4{(2R,3S)-3-[(1R)-1-(tert-Butyldimethylsilyloxy)ethyl]-4-
oxoazetidin-2-y}-2-diaza-3-oxo-pentanoate (13). To a solution of 12 (500 mg,
1.09 mmol) in CH3CN (10 ml) at 0 1C were added p-dodecylbenzenesulfonyl
azide (461 mg, 1.31 mmol) and Et3N (0.18 ml, 1.29 mmol), and the mixture was
stirred at the same temperature for 30 min. The mixture was evaporated under
reduced pressure, and the residue was purified by column chromatography (silica
gel, n-hexane-EtOAc) to give 13 (450 mg, 85% yield) as an oil. 1H NMR (CDCl3)
d 0.06, 0.07 (total 6H, each s), 0.86 (9H, s), 1.18 (3H, d, J¼6.8 Hz), 1.19 (3H, d,
J¼6.4 Hz), 1.23 (9H, s), 2.96 (1H, dd, J¼4.4, 1.4 Hz), 3.85–3.92 (2H, m),
4.14–4.22 (1H, m), 5.87 (2H, s), 5.90 (1H, br s).
p-Nitrobenzyl (1R,5S,6S)-2-[(3S,5S)-5-(N,N-Dimethylcarbamoyl)-1-(isobutyry-
loxymethyloxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydroxyethyl]-1-methylcar-
bapen-2-em-3-carboxylate (11). To a solution of BMP (9.64 g, 30.3mmol) in
CH3CN (150ml) at 5 1C were added MAP (15.0g, 25.2mmol) and i-Pr2NEt
(6.0ml, 35mmol), and the mixture was stirred at the same temperature for 2 h
under Ar atmosphere. After evaporation of the mixture under reduced
pressure, a solution of the residue in EtOAc was washed with 10% citric acid
aq., 5% NaHCO3 aq. and 5% NaCl aq., dried over Na2SO4, and evaporated
under reduced pressure. A solution of the residue in a mixture of EtOAc-i-Pr2O
(1:1) (150ml) was stirred at room temperature overnight, and the resulting
precipitate was collected by filtration to give 11 (15.4 g, 92% yield) as a solid. IR
nmax (ATR) cmꢁ1 3430, 1766, 1732, 1705, 1655. 1H NMR (CDCl3) d 1.15–1.20
(6H, m), 1.27, 1.29 (total 3H, each d, J¼6.1Hz, 7.1 Hz), 1.37, 1.38 (total 3H,
each d, J¼5.6, 6.1 Hz), 1.88–2.00 (1H, m), 2.53–2.65 (1H, m), 2.63–2.73 (1H,
m), 2.95, 2.98 (total 3H, each s), 3.06, 3.11 (total 1H, each s), 3.26, 3.28 (total
1H, each dd, J¼7.1, 2.5 Hz), 3.32–3.43 (1H, m), 3.45, 3.48 (total 1H, each d,
J¼10.5Hz), 3.57–3.68 (1H, m), 4.05, 4.14 (total 1H, each dd, J¼10.5, 7.1 Hz),
4.25, 4.28 (total 1H, each dd, J¼9.5, 2.5Hz), 4.25–4.32 (1H, m), 4.69, 4.74
(total 1H, each t, J¼8.1 Hz), 5.24, 5.25 (total 1H, each d, J¼13.7 Hz), 5.49 (1H,
d, J¼13.7 Hz), 5.65, 5.68 (total 1H, each d, J¼5.6Hz), 5.69, 5.80 (total 1H, each
d, J¼5.6 Hz), 7.60–7.70 (2H, m), 8.15–8.25 (2H, m).
Pivaloyloxymethyl (1R,5R,6S)-6-[(1R)-1-(tert-Butyldimethylsilyloxy)ethyl]-2-
(diphenylphosphoryloxy)-1-methylcarbapen-2-em-3-carboxylate (14). To a
solution of 13 (440mg, 0.91mmol) in EtOAc (3.5ml) at 501C was added
[(AcO)2Rh]2ꢀ2H2O (22 mg, 0.05mmol), and the mixture was stirred for
20min, and then evaporated under reduced pressure. To a solution of the
residue in CH3CN (4ml) at 0 1C were added diphenyl chlorophosphate
(0.21 ml, 1.0mmol) and i-Pr2NEt (0.17 ml, 0.98 mmol), and then the mixture
was stirred at the same temperature for 40min. After the addition of EtOAc,
the mixture was washed with water and brine, dried over Na2SO4, and
evaporated under reduced pressure. The residue was purified by column
chromatography (silica gel, n-hexane-EtOAc) to give 14 (480mg, 77% yield)
1
as an oil. H NMR (CDCl3) d 0.06, 0.07 (total 6H, each s), 0.86 (9H, s), 1.18
(3H, d, J¼5.8 Hz), 1.19 (9H, s), 1.22 (3H, d, J¼8.0 Hz), 3.23 (1H, dd, J¼6.1,
2.9 Hz), 3.38–3.49 (1H, m), 4.13 (1H, dd, J¼10.2, 2.9Hz), 4.15–4.23 (1H, m),
5.78, 5.80 (total 2H, each ABq, J¼5.4 Hz), 7.19–7.43 (10H, m).
Pivaloyloxymethyl (1R,5S,6S)-2-[(3S,5S)-5-(N,N-Dimethylcarbamoyl)-1-(isobu-
tyryloxymethyloxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydroxyethyl]-1-methyl-
carbapen-2-em-3-carboxylate (4). A solution of 11 (1.00 g, 1.51 mmol) in
THF-0.1M MOPS buffer (pH 7.0) (1:1) (100 ml) was hydrogenated at
3 kgcmꢁ2 in the presence of 10% Pd-C (250 mg) at 35 1C for 1 h. After
removal of the catalyst by filtration, the filtrate was extracted with 0.1M MOPS
buffer (pH 7.0) (30 ml), and then, THF was evaporated under reduced
pressure. The aqueous residue was washed with EtOAc, and evaporated under
reduced pressure. To a solution of the residue in CH2Cl2 (10 ml) were added
BTEAC (100mg, 0.44mmol) and pivaloyloxymethyl iodide (548mg,
2.26 mmol), and the mixture was stirred at room temperature overnight. After
evaporation of the mixture under reduced pressure, the solution of the residue
in EtOAc (100ml) was washed with water (50 ml) and 5% NaCl aq., dried over
Na2SO4, and evaporated under reduced pressure. The residue was purified by
column chromatography (silica gel, EtOAc-acetone) to give an oil (1.1g). To
the solution of the oil in EtOAc (2.2ml) was added i-Pr2O (5.0ml), and the
Pivaloyloxymethyl (1R,5S,6S)-6-[(1R)-1-(tert-Butyldimethylsilyloxy)ethyl]-2-[(3S,
5S)-5-(N,N-dimethylcarbamoyl)-1-(isobutyryloxymethyloxycarbonyl)pyrrolidin-3-
ylthio]-1-methylcarbapen-2-em-3-carboxylate (15). Compound 15 was obtained
as an oil (230 mg, 43% yield) from 14 (480 mg, 0.70 mmol) in a similar manner
as described in the synthesis of 11 in Scheme 2. 1H NMR (CDCl3) d 0.08 (6H, s),
0.89 (9H, s), 1.14–1.29 (12H, m), 1.22 (9H, s), 1.86–1.99 (1H, m), 2.53–2.63
(1H, m), 2.63–2.73 (1H, m), 2.95, 2.98 (total 3H, each s), 3.06, 3.11 (total 3H,
each s), 3.19, 3.21 (total 1H, each dd, J¼6.1, 2.7 Hz), 3.24–3.34 (1H, m), 3.44,
3.46 (total 1H, each dd, J¼11.0, 3.4 Hz), 3.55–3.69 (1H, m), 3.99–4.15 (1H, m),
4.18–4.27 (2H, m), 4.68, 4.74 (total 1H, each t, J¼8.1, 8.1 Hz), 5.66, 5.69 (total
1H, each ABq, J¼5.8 Hz), 5.68, 5.81 (total 1H, each ABq, J¼5.6 Hz), 5.83, 5.92
(total 2H, each ABq, J¼5.4 Hz).
mixture was stirred at room temperature overnight. The resulting precipitate Pivaloyloxymethyl (1R,5S,6S)-2-[(3S,5S)-5-(N,N-Dimethylcarbamoyl)-1-(isobu-
was collected by filtration to give 4 (803 mg, 83% yield) as a white solid.
tyryloxymethyloxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydroxyethyl]-1-methyl-
carbapen-2-em-3-carboxylate (4). To a solution of 15 (70 mg, 0.093 mmol) in
DMF (0.7ml) was added Et3Nꢀ3HF (30 mg, 0.9 mmol), and the mixture was
stirred at room temperature for 23 h. After the addition of EtOAc, the mixture
was washed with 5% NaCl aq. and brine, dried over Na2SO4, and evaporated
under reduced pressure. To a solution of the residue in EtOAc (0.5ml) at 01C
was added i-Pr2O (1.0ml), and the mixture was stirred for 2 h. The resulting
precipitate was collected by filtration to give 4 (10 mg, 17% yield) as a white
solid.
1-Ethylpropyloxycarbonyloxymethyl (1R,5S,6S)-2-[(3S,5S)-5-(N,N-Dimethylcarba-
moyl)-1-(isobutyryloxymethyloxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydro-
xyethyl]-1-methylcarbapen-2-em-3-carboxylate (8). Compound 8 was obtained
as a white solid (833mg, 82% yield) from 11 (1.00 g, 1.51 mmol) in a similar
manner to that described in the synthesis of 4.
Synthetic procedures in Scheme 3
Pivaloyloxymethyl (4R)-4{(2R,3S)-3-[(1R)-1-(tert-Butyldimethylsilyloxy)ethyl]-
Synthetic Procedures in Scheme 4
4-oxoazetidin-2-y}-3-oxopentanoate (12). To a suspension of b-MAC (5.70 g, (3S,4S)-3-[(R)-1-(tert-Butyldimethylsilyloxy)ethyl]-4-[(1R)-1{[(3S,5S)-5-(N,N-
18.9 mmol) in CH3CN (57 ml) was added CDI (3.37 g, 20.8mmol), and the dimethylcarbamoyl)-1-(isobutyryloxymethyloxycarbonyl)pyrrolidin-3-ylthio]car-
mixture was stirred at room temperature for 1.5h. The mixture was poured bony}ethyl]-2-azetidinone (16). To a solution of b-MAC (5.03 g, 16.7mmol)
into magnesium bis(pivaloyloxymethyloxycarbonylacetate) (15.8 g, 34.4mmol), and BMP (6.38 g, 20.0mmol) in DMF (25 ml) at 0 1C were added EDC (6.40 g,
and the mixture was stirred at room temperature for 1.5 h, at 30–401C for 33.4mmol) and N-methylmorpholine (3.67 ml, 33.4mmol) at 0 1C, and the
1.5h, and then evaporated under reduced pressure. A solution of the residue in mixture was stirred at room temperature for 1 h. After the addition of EtOAc,
EtOAc was washed with water and brine, dried over Na2SO4, and evaporated the mixture was washed with water and brine, dried over Na2SO4, and
under reduced pressure. The residue was purified by column chromatography evaporated under reduced pressure. The residue was purified by column
1
(silica gel, n-hexane-EtOAc) to give 12 (1.02 g, 12% yield) as an oil. H NMR chromatography (silica gel, n-hexane-EtOAc) to give 16 (7.18 g, 71% yield)
d
0.06, 0.07 (total 6H, s), 0.87 (9H, s), 1.13, 1.15 (total as an oil. 1H NMR (CDCl3) d 0.06, 0.07 (total 6H, each s), 0.87 (9H, s), 1.15,
(CDCl3)
3H, each t, J¼6.3 Hz), 1.18–1.25 (3H, m), 1.22 (9H, s), 2.38–2.47, 2.88–2.98 1.17 (total 3H, each d, J¼6.3, 7.1 Hz), 1.18 (6H, d, J¼7.1 Hz), 1.24 (3H, d,
(total 1H, each m), 2.87–2.95 (1H, m), 3.57 (1.2H, s), 3.82 (0.4H, dd, J¼6.6, J¼7.1 Hz), 1.91 (1H, ddd, J¼13.2, 9.5, 7.1 Hz), 2.53–2.65 (1H, m), 2.84–2.91
2.2 Hz), 3.95 (0.6H, dd, J¼4.4, 2.2 Hz), 4.15–4.22 (1H, m), 5.09 (0.4H, s), 5.76, (1H, m), 2.95, 2.98 (total 3H, each s), 3.06, 3.11 (total 3H, each s), 3.42, 3.46
5.78 (total 1.2H, each q, J¼5.6 Hz), 5.81 (0.8H, s), 5.90, 5.91 (total 1H, each br (total 1H, each dd, J¼10.7, 9.0 Hz), 3.81–3.86 (1H, m), 3.88–4.02 (1H, m), 4.07
s), 11.84 (0.4H, s).
(0.5H, dd, J¼10.7, 7.8 Hz), 4.10 (0.5H, dd, J¼10.7, 7.6 Hz), 4.13–4.22 (1H, m),
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Prodrug of meropenem
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241
4.68, 4.75 (total 1H, each dd, J¼8.0, 7.1 Hz), 5.66, 5.69 (total 1H, each ABq, then centrifuged at 3000 r.p.m. for 10min. Concentrations in the octanol
J¼5.6Hz), 5.68, 5.80 (total 1H, each ABq, J¼5.6 Hz), 5.91 (1H, s).
fraction and buffer fraction were determined using the HPLC described above.
(3S,4S)-3-[(R)-1-(tert-Butyldimethylsilyloxy)ethyl]-4-[(1R)-1{[(3S,5S)-5-(N,N-
dimethylcarbamoyl)-1-(isobutyryloxymethyloxycarbonyl)pyrrolidin-3-ylthio]-
carbony}ethyl]-1-(1-ethylpropyloxycarbonyloxymethyloxyoxalyl)-2-azetidinone
(17). To a solution of 16 (1.50 g, 2.49mmol) in CH2Cl2 (15 ml) at ꢁ101C
were added Et3N (0.95 ml, 6.8 mmol) and 1-ethylpropyloxycarbonyloxymethy-
loxyoxalyl chloride (1.57 g, 6.23mmol) in CH2Cl2 (15 ml), and the mixture was
stirred at 0 1C for 1 h. After the addition of EtOAc, the mixture was washed
with satd NH4Cl aq., satd NaHCO3 aq. and brine, dried over Na2SO4, and
evaporated under reduced pressure. The residue was purified by column
chromatography (silica gel, n-hexane-EtOAc) to give 17 (1.22 g, 60% yield)
Oral absorption in rats
Male SD rats (217–238 g) were used to determine plasma concentrations of
MEPM after oral administration of MEPM, and its single- and double-
promoiety prodrugs. The animals were starved overnight before dosing, but
were allowed to drink water. Test compounds were dissolved in 1.5% SDS, and
administered orally at 20mg potency per kg. Blood was collected from the
jugular vein at 30, 60 and 180min after oral dosing, and the blood was
centrifuged at 3000 r.p.m. for 10min at 4 1C. Concentrations of MEPM in the
plasma were determined using the HPLC as described above.
1
as an oil. H NMR (CDCl3) d 0.01, 0.06 (total 6H, each s), 0.83 (9H, s), 0.92
(6H, t, J¼6.6 Hz), 1.17, 1.18 (total 3H, each d, J¼6.8 Hz), 1.19 (6H, d, Pharmacokinetic evaluation in rats and beagles
J¼7.1Hz), 1.26 (3H, d, J¼7.1 Hz), 1.62–1.70 (4H, m), 1.85–1.96 (1H, m),
Pharmacokinetic evaluations were performed in male SD rats (192–211g) and
2.52–2.65 (1H, m), 2.66–2.78 (1H, m), 2.94, 2.97 (total 3H, each s), 3.05 (3H,
s), 3.10 (3H, s), 3.38, 3.42 (total 1H, each dd, J¼10.8, 9.3Hz), 3.49–3.58 (1H,
m), 3.56–3.60 (1H, m), 3.88–4.02 (1H, m), 4.07 (0.5H, dd, J¼10.8, 7.6 Hz),
4.10 (0.5H, dd, J¼10.8, 7.3 Hz), 4.23–4.33 (1H, m), 4.35–4.43 (1H, br),
4.58–4.68 (1H, m), 4.66, 4.74 (total 1H, each t, J¼7.5 Hz), 5.66, 5.69 (total
1H, each ABq, J¼5.8Hz), 5.68, 5.80 (total 1H, each ABq, J¼5.6 Hz), 5.84, 5.92
(total 1H, each ABq, J¼5.6Hz), 5.85, 5.92 (total 1H, each ABq, J¼5.8Hz).
beagles (9.0–11.0kg). The animals were starved overnight before dosing, but
were allowed to drink water. Test compounds were dissolved in 1.5% SDS and
administered orally to rats at a dose of 20 mg potency per kg, and to beagles at
a dose of 10 mg potency per kg, respectively. Blood was collected from the
jugular vein at 10, 20, 30, 45, 60, 90 and 120 min in rats, and at 0.25, 0.5, 1, 3, 5,
8 and 12h in beagles after dosing, respectively. MEPM was dissolved in saline,
and administered intravenously to rats at a dose of 2 mg potency per kg, and to
beagles at a dose of 1 mgkgꢁ1, respectively. Blood was collected from the
jugular vein at 5, 10, 15, 20 and 30 min in rats and at 0.25, 0.5, 1, 3, 5, 8 h in
beagles, respectively. Blood was centrifuged at 3000r.p.m. for 10 min at 41C.
Concentrations of MEPM in the plasma were determined by HPLC as
described above.
1-Ethylpropyloxycarbonyloxymethyl (1R,5S,6S)-6-[(1R)-1-(tert-Butyldimethylsi-
lyloxy)ethyl]-2-[(3S,5S)-5-(N,N-dimethylcarbamoyl)-1-(isobutyryloxymethyloxycarbonyl)
pyrrolidin-3-ylthio]-1-methylcarbapen-2-em-3carboxylate (18). To a solution
of 17 (720mg, 0.880 mmol) in toluene (8ml) was added MeP(OEt)2 (1.00 g,
7.35 mmol), and the mixture was stirred in a sealed tube at room temperature
for 2 h under an Ar atmosphere. The mixture was evaporated under reduced
pressure. A solution of the residue in xylene (50 ml) was stirred in a sealed
tube at 140–1501C for 3 h under an Ar atmosphere. The mixture
was evaporated under reduced pressure. The residue was purified by column
chromatography (silica gel, n-hexane-EtOAc) to give an oil, which was
solidified from n-hexane-EtOAc to give 18 (366mg, 53% yield) as a solid.
1H NMR (CDCl3) d 0.08, 0.09 (total 6H, each s), 0.89 (9H, s), 0.92 (6H, t,
J¼7.3Hz), 1.17, 1.18, 1.19 (total 6H, each d, J¼7.1 Hz), 1.23, 1.24 (total 6H,
each d, J¼5.8Hz), 1.58–1.70 (4H, m), 1.88–2.00 (1H, m), 2.59, 2.60 (total 1H,
each q, J¼7.1Hz), 2.63–2.73 (1H, m), 2.95, 2.98 (total 3H, each s), 3.06 (3H, s),
3.10 (3H, s), 3.19, 3.20 (total 1H, each dd, J¼6.1, 2.7 Hz), 3.23–3.34 (1H, m),
3.43, 3.46 (total 1H, each dd, J¼10.7, 3.9Hz), 3.56–3.71 (1H, m), 4.02 (0.5H,
dd, J¼10.7, 7.6Hz), 4.12 (0.5H, dd, J¼10.8, 6.8 Hz), 4.19, 4.22 (total 1H, each
dd, J¼9.8, 1.9Hz), 4.17–4.28 (1H, m), 4.62 (1H, quintet, J¼6.1 Hz), 4.68, 4.74
(total 1H, each t, J¼8.0 Hz), 5.66, 5.69 (total 1H, each ABq, J¼5.6 Hz), 5.68,
5.81 (total 1H, each ABq, J¼5.6 Hz), 5.87, 5.89 (total 1H, each ABq, J¼5.6 Hz).
1
2
3
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obtained as a white solid (208mg, 72% yield) from 18 (337mg, 0.429 mmol)
in a similar manner to that described in the synthesis of 4 in Scheme 3.
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for 10 min and filtration using DISMIC-13HP (0.45 mm, Toyo Roshi Kaisha,
Tokyo, Japan), concentrations of the compounds in the filtrate were determined
using HPLC, consisting of a pump (PU-980; JASCO, Tokyo, Japan), a UV-
detector (UV-970; JASCO), an autosampler (AS-950; JASCO) and Develosil-
ODS-UG-5 (5mm, 4.6ꢂ150 mm; Nomura Chemical, Seto, Japan).
Determination of LogD
Octanol-water partition coefficients were determined and logD values were
calculated as an index of lipophilicity. Test compounds (1mg) were dissolved in
1 ml octanol and mixed with 1 ml Britton-Robinson buffer (pH 7.0). The
mixed solution was vigorously shaken at room temperature for 30 min and
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The Journal of Antibiotics