Synthesis and biological evaluation of novel 1β-methylcarbapenems with isothiazoloethenyl side chains

Article abstract of DOI:10.1016/S0960-894X(02)00948-4

The synthesis of novel 1β-methylcarbapenems 1a,b bearing isothiazoloethenyl moieties at C-5 position of pyrrolidine ring and their biological evaluation are described. Both compounds showed potent and well-balanced antibacterial activity as well as high stability to DHP-I. Especially, 5-isothiazole derivative 1a exhibited excellent DHP-I stability and advanced pharmacokinetics profiles, compared to 5-isoxazole derivative 2, imipenem, and meropenem.

Full text of DOI:10.1016/S0960-894X(02)00948-4

Bioorganic & Medicinal Chemistry Letters 13 (2003) 463–466
Synthesis and Biological Evaluation of Novel
1ꢀ-Methylcarbapenems with Isothiazoloethenyl Side Chains
Yong Koo Kang,a Kyung Seok Lee,a Kyung Ho Yoo,a Kye Jung Shin,a
Dong Chan Kim,a Chang-Seok Lee,b Jae Yang Kongc and Dong Jin Kima,*
aMedicinal Chemistry Research Center, Korea Institute of Science and Technology, PO Box 131, Cheongryang,
Seoul 130-650, South Korea
bLG Life Sciences Ltd., R&D Park, PO Box 61, Yusung, Daejeon 305-380, South Korea
cMedicinal Science Division, Korea Research Institute of Chemical Technology, PO Box 107, Yusung,
Daejeon 305-606, South Korea
Received 18 September2002; accepted 23 October2002
Abstract—The synthesis of novel 1b-methylcarbapenems 1a,b bearing isothiazoloethenyl moieties at C-5 position of pyrrolidine
ring and their biological evaluation are described. Both compounds showed potent and well-balanced antibacterial activity as well
as high stability to DHP-I. Especially, 5-isothiazole derivative 1a exhibited excellent DHP-I stability and advanced pharmaco-
kinetics profiles, compared to 5-isoxazole derivative 2, imipenem, and meropenem.
# 2002 Elsevier Science Ltd. All rights reserved.
1b-Methylcarbapenems such as meropenem1 and erta-
penem2,3 have been extensively studied recently because
of theirchemical and metabolic stabilities as well as
potent antimicrobial activities.4
stability and advanced pharmacokinetic profiles than
those of 2, imipenem, and meropenem.
Herein, we wish to describe the synthesis of novel 1b-
methylcarbapenems 1a,b with isothiazoloethenyl side
chains and biological evaluation including pharmacoki-
netics and in vivo efficacy forthe selected 1a.
In the preceding paper,5 we reported that a series of
novel
1b-methylcarbapenems
containing
isox-
azoloethenyl substituents at C-5 position of pyrrolidine
ring showed excellent antibacterial activity and high
DHP-I stability. In this series, 5-isoxazole derivative 2
exhibited the best combination of antibacterial activity
and stability to DHP-I (Fig. 1).
Chemistry
5-Substituted isothiazole 10a, Wittig agent forthe
synthesis of isothiazoloethenyl moiety, was prepared by
linearroute as shown in Scheme 1.
As a continuation of these studies, we carried out
introduction of isothiazole instead of isoxazole into the
pyrrolidine ring in order to improve the activity against
Propagyl alcohol (3) was oxidized with CrO3 under
reduced pressure to give propynal (4),8 which was trea-
ted with sodium thiosulfate to afford aldehyde dithio-
nite 5.9 Cyclization of 5 in liquid NH3 followed by
formylation of the resulting isothiazole (6)10 in the pre-
sence of n-BuLi provided 5-formylisothiazole (7).11
Subsequent reduction of 7 with NaBH4 in THF gave the
alcohol 8, which was brominated with N-bromosuccini-
mide in the presence of AIBN to give 5-bromomethyl-
isothiazole (9). Triphenylphosphonium bromide 10a
was obtained by treatment of 9 with triphenylphosphine
in CH3CN.
Gram-positive strains by the greater lipophilicity of
6,7
sulfurerlative to oxygen.
As expected, 5-isothiazole
derivative 1a, which is an isostere of our earlier 5-iso-
xazole derivative 2, showed slightly improved activity
against Gram-positive bacteria without the severe loss
of activity against Gram-negative bacteria compared to
2. In particular, 1a exhibited markedly enhanced DHP-I
*Corresponding author. Tel.: +82-2-958-5142; fax: +82-2-958-5189;
e-mail: djk2991@kist.re.kr
0960-894X/03/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00948-4

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Y. K. Kang et al. / Bioorg. Med. Chem. Lett. 13 (2003) 463–466
Figure 1.
Scheme 1. Reagents and reaction conditions: (i) CrO3, H2SO4–H2O, 30 mmHg, 2–10 ꢀC, 3 h (35%); (ii) Na2S2O3, AcOH, acetone–H2O, À5 ꢀC,
30 mim (65%); (iii) liquid NH3, À60 ꢀC to rt, 2 h (60%); (iv) n-BuLi, DMF, THF, À78 ꢀC, 1 h (73%); (v) NaBH4, THF (83%); (vi) PPh3, CBr4,
CH2Cl2, À20 ꢀC, 30 mim (80%); (vii) PPh3, CH3CN, reflux, 3 h (63%).
3-Substituted isothiazole 10b was prepared by using pro-
cedures analogous to those described above (Scheme 2).
thiols 18a,b. Treatment of enolphosphate 194 with
freshly prepared the thiols 18a,b in the presence of dii-
sopropyl-ethylamine afforded the protected 1b-methyl-
carbapenems 20a,b. Deprotection of 20a,b with Bu3SnH
in the presence of catalytic amount of Pd(PPh3)4 pro-
vided the corresponding 1b-methylcarbapenems 1a,b13
as an amorphous solid by lyophilization, after purifica-
tion by column chromatography on Diaion HP-20,
respectively.
3-Methylisothiazole (14) was successfully synthesized
from 3-butyn-2-ol (1) as a starting material via oxida-
tion of alcohol with CrO3, addition of sodium thio-
sulfate, and construction of isothiazole ring in liquid
NH3. Monobromination of 14 with N-bromosucci-
nimde in the presence of AIBN gave 3-bromomethyli-
sothiazole (15) and subsequent treatment of 15 with
triphenylphosphine in CH3CN afforded the desired
phosphonium salt 10b.
Biological Properties
Introduction of ethenylpyrrolidine group was achieved
by Wittig methodology of formylpyrrolidine 16 with
phosphonium salts 10a,b in THF in the presence of
sodium bis(trimethylsilyl)amide as a base to give the
mesyl protected isothiazoloethenylpyrrolidines 17a,b
(Scheme 3). The formylpyrrolidine 16 was prepared
from hydroxymethylpyrrolidine by the known
method.12 In this reaction, the E-isomers were obtained
exclusively whereas the Z-isomers did not detect as
meaningful amounts.
The in vitro antibacterial activity and stability to por-
cine renal DHP-I of novel 1b-methylcarbapenems pre-
pared above are listed in Table 1, togetherwith those of
2, imipenem, and meropenem as reference compounds.
With the exception of slightly reduced antipseudomonal
activities, both compounds 1a,b exhibited potent anti-
bacterial activities against a wide range of Gram-posi-
tive and Gram-negative organisms and high stability to
DHP-I superior to those of imipenem and meropenem.
In this class of analogues, 5-isothiazole derivative 1a
showed more potent antibacterial activity and higher
DHP-I stability than 3-isothiazole derivative 1b. Car-
bapenem 1a exhibited potent and well-balanced anti-
After the conversion of mesyl group of 17a,b with
potassium thioacetate, the resulting thioacetates with
inverted configuration were hydrolyzed to afford the
Scheme 2. Reagents and reaction conditions: (i) CrO3, H2SO4–H2O, 30 mmHg, 2–10 ꢀC, 3 h (38%); (ii) Na2S2O3, AcOH, acetone–H2O, À5 ꢀC,
30 mim (60%); (iii) liquid NH3, À60 ꢀC to rt, 2 h (52%); (iv) NBS, AIBN, CCI4, reflux, 15 h (45%); (v) PPh3, CH3CN, reflux, 3 h (63%).

Y. K. Kang et al. / Bioorg. Med. Chem. Lett. 13 (2003) 463–466
465
Scheme 3. Reagents and reaction conditions: (i) (2S,4R)-4-Methanesulfonyloxy-2-formyl-1-allyloxy-carbonylpyrrolidine (16), NaHMDS, THF,
À78 ꢀC to rt, 1.5 h; (ii) AcSK, CH3CN, reflux, 5 h; (iii) 2 N NaOH, MeOH, 0 ꢀC to rt, 30 min; (iv) Alloc (1R,5S,6S)-2-(diphenylphosphoryloxy)-6-
[(1R)-1-hydroxyethyl]-1-methylcarbapen-2-em-3-carboxylate (19), DIEA, CH3CN, 0 ꢀC, 1.5 h; (v) Pd(PPh3)4, Bu3SnH, CH2Cl2, 0 ꢀC, 1 h.
Table 1. In vitro antibacterial activity and DHP-I stability of 1a,b
Table 2. Pharmacokinetic parametersa of 1a
Organism
MIC (mg/mL)a
1b
IPMb MPMc
1a
2
IPM
MPM
1a
2
T1/2 (min)
23.5Æ6.8
16.3Æ1.5 3.46Æ0.1 3.99Æ4.1
330Æ23 383Æ36
17.8Æ1.5 61.5Æ3.7 54.2Æ3.7
AUC (mg/min/mL) 1801Æ486 1132Æ93
Streptococcus pyogenes 308A
Staphylococcus aureus SG 511
Staphylococcus aureus 285
Staphylococcus aureus 503
Escherichia coli 078
0.004 0.007 0.004 0.007 0.013
0.013 0.025 0.025 0.025 0.195
0.025 0.025 0.049 0.025 0.195
0.013 0.013 0.013 0.013 0.098
0.025 0.049 0.025 0.098 0.025
0.025 0.049 0.025 0.195 0.025
0.391 1.563 0.195 0.781 0.195
CL (mL/mim/kg)
11.6Æ2.7
aAt a single intravenous administration of 20 mg/kg in rat.
Escherichia coli 1507E
Psuedomonas aeruginosa 9027
Psuedomonas aeruginosa 1592E 0.391 1.563 0.195 1.563 0.195
Psuedomonas aeruginosa 1771M 0.195 0.391 0.098 0.195 0.049
Table 3. In vitro protective effectsa,b of 1a and Meropenem
Salmonella typhimurium
Klebsiella aerogenes 1522E
Enterobacter cloacae 1321E
DHP-I stabilityd
0.049 0.049 0.049 0.781 0.049
0.049 0.098 0.049 0.391 0.049
0.049 0.025 0.025 0.195 0.025
1a
MPM
3.36 1.42 1.95 0.19
1.00
S. pyogens 77A
S. aureus Y-80-1953
E. coli 078
0.32 (0.16–0.64)
1.27 (0.6–2.54)
0.32 (0.16–0.61)
6.17 (3.39–11.24)
4.72 (2.59–8.61)
4.49 (2.74–8.02)
1.11 (0.65–1.90)
5.43 (3.02–9.75)
aMIC was determined by agar dilution method using Mueller–Hinton.
bIPM=imipenem.
cMPM=meropenem.
P. aeruginosa 1771M
dRelative t1/2 of hydrolysis to meropenem by partially purified porcine
renal DHP-I.
aAt a single subcutaneous administration in mice.
bPD50 (mg/kg), parenthesis: 95% confidence limits.
bacterial activity against both Gram-positive and
Gram-negative bacteria including P. aeruginosa isolates.
Especially, 1a displayed excellent DHP-I stability com-
pared to 5-isoxazole derivative 2, imipenem, and mer-
openem. And also, 1a possessed highly effective in vitro
potency against respiratory tract pathogens, especially
such as S. pyogens, S. aureus, S. pneumoniae, K. pneu-
moniae, and Morxella catarrhalis.14 Based on a favor-
able combination of in vitro antibacterial activity and
DHP-I stability, 5-isothiazole derivative 1a was selected
forfurtherevaluation.
In vivo activities of 1a togetherwith the data of me-r
openem as a reference were shown in Table 3. As a
result, 1a showed excellent in vivo therapeutic efficacy
in systemic infections caused by S. pyogenes 77A, S.
aureus Y-80-1953, and E coli 078 in mice. 1a displayed
similarvalue to meorpenem against
1771M.
P. aeruginosa
In summary, the title 1b-methylcarbapenems exhibited
potent antibacterial activity against the target organ-
isms, including P. aeruginosa isolates. Introduction of
isothiazole instead of isoxazole into the pyrrolidine ring
resulted in slightly improved activity against Gram-
positive bacteria, especially remarkably enhanced DHP-
I stability and pharmacokinetics. Taking the overall
biological and physical properties into account, 1a was
selected as a good candidate.
The selected carbapenem 1a was evaluated forpharma-
cokinetics and in vivo therapeutic efficacy in systematic
infections in mice. 1a possessed excellent pharmacoki-
netics profiles in rat compared to those of 2, imipenem,
and meropenem, and the results were listed in Table 2.
It showed that the half-life of 1a was 6–7-fold longer
than those of imipenem and meropenem. Furthermore,
1a displayed 4–6 times highervalue in AUC and
approximately 5 times lower value in clearance than
imipenem and meropenem.
Acknowledgements
We are grateful to the Ministry of Science and Tech-
nology (MOST) of Korea for financial support.

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12. Shin, K. J.; Koo, K. D.; Yoo, K. H.; Kim, D. C.; Kim,
References and Notes
D. J.; Park, S. W. Bioorg. Med. Chem. Lett. 2000, 10,
1421.
1. Sunagawa, M.; Matsumura, H.; Inoue, T.; Fukasawa, M.;
Kato, M. J. Antibiot. 1990, 43, 519.
13. Spectral data: 1a: 1H NMR (300 MHz, CDCl3) d 1.07
(d, 3H, J=7.2 Hz), 1.16 (d, 3H, J=6.0 Hz), 1.57 (m, 1H),
2.65 (m, 1H), 3.05 (dd, 1H, J=3.8, 3.8 Hz), 3.28–3.36 (m,
3H), 3.78 (m, 1H), 3.95 (m, 1H), 4.05–4.12 (m, 2H), 6.32
(dd, 1H, J=7.7, 7.7 Hz), 6.77 (d, 1H, J=18.5 Hz), 7.19 (s,
1H), 8.27 (s, 1H); FABHRMS m/z calcd for
C19H23N3O4S2Na (M+Na)+ 444.1028, found 444.1029. 1b:
1H NMR (300 MHz, CDCl3) d 1.14 (d, 3H, J=7.3 Hz),
1.20 (d, 3H, J=6.3 Hz), 1.86 (m, 1H), 2.76 (m, 1H), 3.25–
3.40 (m, 3H), 3.68 (m, 1H), 3.82–4.07 (m, 1H), 4.16 (m,
2H), 4.37 (m, 1H), 6.55 (dd, 1H, J=8.2, 8.2 Hz), 6.88 (d,
1H, J=15.8 Hz), 7.49 (d, 1H, J=4.8 Hz), 8.80 (d, 1H,
J=4.1 Hz); FABHRMS m/z calcd forC 19H23N3O4S2Na
(M+Na)+ 444.1028, found 444.1014.
2. Betts, M. J.; Davies G. M.; Swain, M. L. US 5478820.
3. Hilliard, N. J.; Johnson, C. N.; Armstrong, S. H.; Quarles,
S.; Waites, K. B. Int. J. Antimicrob. Agents 2002, 20, 136.
4. Shih, D. H.; Baker, F.; Cama, L.; Christensen, B. G. Het-
erocycles 1984, 21, 29.
5. Kim, D. J.; Seo, K. J.; Lee, K. S.; Shin, K. J.; Yoo, K. H.;
Kim, D. C.; Park, S. W. Bioorg. Med. Chem. Lett. 2000, 10, 2799.
6. Imamura, H.; Ohtake, N.; Shimizu, A.; Sato, H.;
Sugimoto, Y.; Sakuraba, S.; Kiyonaga, H.; Suzuki-Sato, C.;
Nakano, M.; Nagano, R.; Yamada, K.; Hashizume, T.;
Morishima, H. Bioorg. Med. Chem. Lett. 2000, 10, 115.
7. Sato, H.; Sakoh, H.; Hashihayata, T.; Imamura, H.;
Ohtake, N.; Shimizu, A.; Sugimoto, Y.; Sakuraba, S.; Bamba-
Nagano, R.; Yamada, K.; Hashizume, T.; Morishima, H.
Bioorg. Med. Chem. 2002, 10, 1595.
14. MIC (mg/mL) data. S. pyogens 308A: 0.04 (1a), 0.007
(IPM), 0.013 (MPM); S. pyogens 77A: 0.002 (1a), 0.004 (IPM),
0.002 (MPM); S. aureus 6538P: 0.031 (1a), 0.016 (IPM), 0.13
(MPM); S. aureus giogio: 0.016 (1a), 0.008 (IPM), 0.13
(MPM); S. aureus 77: 0.25 (1a), 0.13 (IPM), 2 (MPM); S.
aureus 241: 8 (1a), 8 (IPM), 32 (MPM); S. pneumoniae PG-R
PN01: 0.25 (1a), 0.25 (IPM), 0.25 (MPM); K. pneumoniae
2011E: 0.063 (1a), 0.13 (IPM), 0.031 (MPM); M. catarrhalis
25240: ꢁ0.008 (1a), ꢁ0.008 (IPM), ꢁ0.008 (MPM).
8. Bowden, K.; Heilbron, I. M.; Jones, E. R. H.; Weedon,
B. C. L. J. Chem. Soc. 1946, 39.
9. Adams, A.; Slack, R. Chem. Ind. 1956, 1232.
10. Wille, F.; Capeller, L.; Steiner, A. Angew. Chem., Int. Ed.
1962, 1, 335.
11. Buttimore, D.; Jones, D. H.; Slack, R.; Wooldridge,
K. R. H. J. Chem. Soc. 1963, 2032.