Syntheses of new isodethiaazacephems as potent antibacterial agents

Article abstract of DOI:10.1021/jm980476h

New isodethiaazacephems (±)-3, (±)-4, and (±)-10 as well as the 4- sulfonylated isodethiaazacepham (±)-5 were synthesized by chemical methods and found to possess biological activity against five pathogenic microorganisms in vitro. The mesylate and the tr

Full text of DOI:10.1021/jm980476h

J . Med. Chem. 1998, 41, 4681-4685
4681
Expedited Articles
Syn th eses of New Isod eth ia a za cep h em s a s P oten t An tiba cter ia l Agen ts
J ih Ru Hwu,*,
†,‡,∇
Shwu-Chen Tsay, and Shahram Hakimelahi
†
†,§
Organosilicon and Synthesis Laboratory, Institute of Chemistry, Academia Sinica, Nankang, Taipei, Taiwan 11529, Republic
of China, and Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 30043, Republic of China
Received August 14, 1998
New isodethiaazacephems (()-3, (()-4, and (()-10 as well as the 4-sulfonylated isodethiaaza-
cepham (()-5 were synthesized by chemical methods and found to possess biological activity
against five pathogenic microorganisms in vitro. The mesylate and the triflate functionalities
in (()-3 and (()-4, acting as effective leaving groups, enhanced remarkably the biological activity
in comparison with the parent 3-hydroxyisodethiaazacephem (()-10. The mode of action related
to (()-3 and (()-4 can be explained by a [1,4]-elimination process.
In tr od u ction
Sch em e 1. Mode of Action of Cephalosporins with
Transpeptidases
â-Lactam antibiotics exert certain biological activity
by acylating serine residues of transpeptidases so that
the cross-linking of peptidoglycans does not take place.
1
1
,2
As shown in Scheme 1, ring opening of the â-lactam
nucleus would occur when cephalosporins (1) react with
enzymes responsible for the cell wall synthesis of
bacteria. Consequently, the substituent at the C-3′
position is liberated.3
-7
When the eliminated species
possesses excellent leaving ability, cephalosporins (1)
may exhibit profound antibacterial activity. Accord-
ingly, we designed and synthesized unprecedented
isodethiaazacephems (()-3 and (()-4 (see Scheme 1).
We believe that the sulfone moiety at the O-3′ position
of (()-3 and (()-4 could act as a leaving group and thus
enhance the antibacterial activity in comparison with
that of the parent 3-hydroxyisodethiaazacephem (()-
1
0.
Recognizing the feasibility of 1,4-elimination in â-lac-
Sch em e 2. Proposed Mechanism for Reaction between
tam antibiotics as shown in Scheme 1, we also consid-
ered the possibility of 1,2-elimination occurring in
cepham sulfone (()-5 (see Scheme 2). The newly
designed compound (()-5 bears a leaving group at the
C-4 position; the elimination process could also be
initiated by bacterial enzymes. Results from our anti-
bacterial tests suggest that the mode of action resulting
from novel cephem sulfonates (()-3 and (()-4 as well
as sulfone (()-5 can come from the leaving ability of
their sulfone moieties.
a Cepham Sulfone and Transpeptidases
â-lactam 7 in 90% yield (Scheme 3). Catalytic hydro-
genation of 7 by use of Pd/C and H2 (30-35 psi) in
EtOAc at room temperature resulted in the reduction
of the azide moiety and spontaneous formation of
isodethiaazacephem 9 in 94% yield. Debenzylation of
Resu lts
Syn th esis of â-La cta m s (()-3, (()-4, (()-5, a n d
9
by use of PdCl2 and H2 (60 psi) in EtOH produced the
(
()-10. For the synthesis of isodethiaazacephems (()-3
target isodethiaazacephem (()-10 in 50% yield.
8
and (()-10, we treated racemic â-lactam mesylate 6
An alternative way to obtain 9 from azido â-lactam 7
involved two steps. Chlorination of 7 with CF3SO2Cl
in Et3N and CH2Cl2 produced chloride 8 in 90% yield.9
Consequent reduction of 8 by use of Pd/C and H2 (30-
with NaN3 in DMF at room temperature to give azido
†
Academia Sinica.
National Tsing Hua University.
Present address: Faculty of Pharmacy & Pharmaceutical Sciences,
‡
§
3
5 psi) in EtOAc gave the desired compound 9 in 87%
University of Alberta, Edmonton, Alberta T6G 2E1, Canada.
∇
yield (Scheme 3). On the other hand, reaction of 8 with
Recipient of the 1997 Third World Academy of Sciences Award in
Chemistry.
H2S in Et3N and CH2Cl2 produced a mixture of isode-
1
0.1021/jm980476h CCC: $15.00 © 1998 American Chemical Society
Published on Web 11/19/1998

4
682 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24
Hwu et al.
Sch em e 5. Synthesis of Isodethiaazacepham 5a
Sch em e 3. Synthesis of Isodethiaazacephems 3 and 4a
a
Reagents: (a) MeSO2Cl, Et3N, CH2Cl2, 0 °C (85%); (b) Pd/C,
H2, EtOAc, rt (90%); (c) PdCl2, H2, EtOH, rt; 16 f 5 (20%) + 17
50%).
(
Sch em e 6. Decarboxylation and Destruction of
â-Lactam 5 at Physiological or Acidic pH
a
Reagents: (a) NaN3, DMF, rt (90%); (b) CF3SO2Cl, Et3N,
CH2Cl2, 0 °C f rt (90%); (c) Pd/C, H2, EtOAc, rt; 7 f 9 (94%); (d)
Pd/C, H2, EtOAc, rt; 8 f 9 (87%); (e) PdCl2, H2, EtOH, rt (50%);
(f) MeSO2Cl, pyridine, CH2Cl2, 15 °C; 9 f 11 (45%); (g) CF3SO2Cl,
pyridine, CH2Cl2, 15 °C; 9 f 12 (30%) + 13 (10%); (h) PdCl2, H2,
EtOH, rt; 11 f 3 (35%), 12 f 4 (30%).
Sch em e 4. Alternative Way To Synthesize
Isodethiaazacephem 9a
a
Reagents: (a) H2S, Et3N, CH2Cl2, rt (55%); 8 f 9 (15%) + 14
12, they were destructed within 5-10 min. On the other
hand, 3-hydroxyisodethiaazacephem (()-10 was highly
soluble (35 mg/mL) in a phosphate buffer (0.10 M, pH
6.8) and was stable at least for 2 months.
Isodethiaazacepham (()-5, highly soluble (32 mg/mL)
in a phosphate buffer (0.10 M, pH 6.8), underwent
decarboxylation gradually to give (()-17 at room tem-
perature within 6 days (Scheme 6). In a basic solution
with pH 12, the decarboxylation also occurred to (()-5
within 20 min; in an acidic solution with pH 1.0, the
â-lactam ring in (()-5 was destructed within 3 h. The
â-lactam ring in (()-17, however, was destructed at pH
1.0 within 2 days.
(
40%).
thiaazacephem 9 (15%) and isodethiaazapenam 14
40%) as shown in Scheme 4.
We attached a sulfonyl group onto the cephem nucleus
of 9 by mesylation with MeSO2Cl in pyridine and CH2-
Cl2 to give the 3-mesyloxy â-lactam 11 in 45% yield
(
(
Scheme 3). It was then hydrogenated with PdCl2 in
EtOH at 60 psi of H2 to produce the desired isode-
thiaazacephem (()-3 in 35% yield. Moreover, we treated
â-lactam 9 with CF3SO2Cl in pyridine and CH2Cl2 to
afford a 3:1 mixture of trifluoromethanesulfonates 12
and 13 in 40% overall yield. Catalytic reduction of 12
with PdCl2 in EtOH at 60 psi of H2 gave the target
isodethiaazacephem (()-4 in 30% yield.
For the synthesis of isodethiaazacepham (()-5 bear-
ing a methylsulfonyl group at the C-4 position, we
treated racemic azido â-lactam 7 with MeSO2Cl in Et3N
and CH2Cl2 (Scheme 5). Sulfone 15, generated in 85%
yield, was treated with H2 (30-35 psi) and Pd/C in
EtOAc to give bicyclic â-lactam 16 in 90% yield through
sequential reduction and lactamization. Upon further
reduction with H2 at 60 psi in the presence of PdCl2 and
EtOH, compound 16 was converted to a mixture of the
desired 4-substituted isodethiaazacepham (()-5 in 20%
yield and the decarboxylated product (()-17 in 50%
yield.
In another series of assays, we dissolved isode-
thiaazacephems (()-3 and (()-4 as well as isodethiaaza-
cepham (()-5 in distilled water (5.0 mg/mL). The pH
value of the aqueous solutions was kept initially at
about 4.0 for (()-3 and (()-4 and at about 2.0 for (()-5.
The pH values of the aqueous solutions of (()-3 and
(()-4 changed to ∼1 within 3 and 2 days, respectively.
We found that the change in pH was accompanied by
the destruction of the â-lactam rings in (()-3 and (()-
4, as detected by IR spectroscopy, as well as the
liberation of MeSO H and CF SO H, respectively. On
2
3
2
the other hand, the pH value of an aqueous solution of
(()-5 changed from 2.0 to ∼6.0 within 5-6 days. This
change was accompanied by the gradual production of
(()-17 through a decarboxylation process (see Scheme
6).
Solu bility a n d Sta bility of â-La cta m s (()-3, (()-
, (()-5, (()-10, a n d (()-17 in Wa ter . We found that
the solubility in water was 21 and 27 mg/mL for
isodethiaazacephems (()-3 and (()-4, respectively; they
were stable at physiological pH for 6 and 4 days,
respectively. At pH 1.0, the â-lactam rings in (()-3 and
4
Biologica l Activity. We tested the antibacterial
activity of the synthesized â-lactams (()-3, (()-4, (()-
5, (()-10, (()-11, (()-12, and (()-17 as well as the
1
0,11
12
reference compounds cefotaxime,
penicillin G, and
7-(â-phenylacetamido)-3′-desacetoxycephalosporanic acid
6
(
()-4 survived for ∼4 and ∼2 h, respectively; yet at pH
((+)-2) in vitro against five pathogenic microorganisms.

New Isodethiaazacephems as Antibacterial Agents
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24 4683
Ta ble 1. Minimal Inhibitory Concentrationsa (µg/mL) of Synthetic â-Lactams as Well as the Reference Compounds Cefotaxime,
Penicillin G, and Cephalosporin (+)-2
S. aureus
E. coli
S. typhi
Ps. aeruginosa
K. pneumoniae
compound
FDA 209P
ATCC 39188
O-901
1101-75
NCTC 418
cefotaxime
penicillin G
0.080
0.40
0.64
0.25
2.30
13.13
0.95
20.30
>128
24.50
1.20
62.35
>128
100.0
4.38
10.25
>128
2.98
(
(
(
(
(
(
(
(
+)-2
()-3
0.070
0.010
48.50
29.50
>128
>128
>128
0.68
0.24
()-4
()-5
()-10
()-11
()-12
()-17
0.090
97.17
94.68
>128
>128
>128
0.68
1.15
65.30
>128
>128
>128
>128
120.0
>128
>128
>128
>128
51.02
>128
>128
>128
>128
a
Obtained by the serial broth dilution method. The values represent the average of triplicate determinations.
The doses used were as high as 128 µg/mL. The results
the apparatus was evacuated and filled with dry nitrogen at
least three times.
are summarized in Table 1.13
Melting points were obtained with a B u¨ chi 510 melting point
apparatus. Infrared (IR) spectra were recorded on a Beckman
IR-8 spectrophotometer. The wavenumbers reported are
referenced to the 1601 cm absorption of polystyrene. Proton
NMR spectra were obtained on a Varian XL-300 (300-MHz)
Discu ssion
-1
By following the newly proposed enzyme-initiated 1,2-
elimination as shown in Scheme 2, we found that
mesylated â-lactam (()-5 indeed exhibited some anti-
bacterial activity (Table 1). The lack of significant
activity is due to its instability in the testing media:
spectrometer. Chloroform-d and D
2
O were used as solvents;
Me Si (δ 0.00 ppm) was used as an internal standard. All
4
NMR chemical shifts are reported as δ values in parts per
million (ppm), and coupling constants (J ) are given in hertz
(Hz). The splitting pattern abbreviations are as follows: s,
singlet; d, doublet; t, triplet; q, quartet; br, broad; m, unre-
solved multiplet due to the field strength of the instrument;
and dd, doublet of doublets. Microanalyses were performed
on a Perkin-Elmer 240-B microanalyzer. Purification on silica
gel refers to gravity column chromatography on Merck silica
gel 60 (particle size 230-400 mesh), packed in glass column
(35 g of silica gel/gram of crude material). Analytical TLC was
performed on precoated plates purchased from Merck (silica
gel 60 F254). Compounds were visualized by use of UV light,
(
()-5 was gradually degraded to the biologically inactive
compound (()-17. A carboxyl group at the C-4 position
of cephalosporins (1) is essential for recognition by the
target enzymes,14 such as penicillin-binding proteins
(PBPs). Compound 17 cannot interact with the target
enzymes because it lacks such a functionality.
Results from biological tests reveal promising anti-
microbial activities for the enol sulfonate â-lactams
(()-3 and (()-4. In contrast, enol â-lactam (()-10
I
2
vapor, or 2.5% phosphomolybdic acid in ethanol with
exhibited much lower activity. Nevertheless, all of these
three â-lactams must be substrates of PBPs.1 Thus,
our results indicate the importance of mesylate and
triflate functionalities at the C-3 position on the biologi-
cal activity of cephalosporins. On the other hand, their
benzyl ester derivatives (()-11 and (()-12 did not
exhibit antibacterial activity (Table 1) although they
both possess an excellent SO2R leaving group. Thus,
both the chemical reactivity and the recognition capa-
bility of a substrate by the target enzymes are essential
for its biological activity, as expected.
heating.
4
(
()-Dib en zyl 2-[cis-4-(Azid om et h yl)-2-oxo-3-(p h en yl-
a ceta m id o)-1-a zetid in yl]m a lon a te (7). To a solution con-
taining (()-6 (2.97 g, 4.99 mmol) in DMF (40 mL) was added
NaN3 (1.30 g, 20.0 mmol). The solution was stirred at room
temperature for 48 h and then partitioned between Et
mL) and water (100 mL). The organic layer was washed with
water (4 × 80 mL), dried over MgSO (s), filtered, and
concentrated under reduced pressure. The crude product was
purified by use of column chromatography (CHCl as eluant)
to give (()-7 (2.43 g, 4.49 mmol) as a foam in 90% yield:
NMR (CDCl ) δ 3.59 (s, 2H), 3.68-3.88 (m, 2H), 4.10-4.28 (m,
1H), 5.27 (s, 4H), 5.32 (s, 1H), 5.34 (dd, J ) 8.5, 5.0, 1H), 6.99
d, J ) 8.5, 1H), 7.15-7.45 (m, 15H); IR (CH Cl ) 3405, 2100,
) C, H, N.
()-Dib en zyl 2-[cis-4-(Azid om et h yl)-2-oxo-3-(p h en yl-
a ceta m id o)-1-a zetid in yl]-2-ch lor om a lon a te (8). To a solu-
tion of (()-7 (2.70 g, 4.99 mmol) in CH Cl (50 mL) was added
Et N (0.61 g, 6.0 mmol). Trifluoromethanesulfonyl chloride
(0.86 g, 5.1 mmol) in CH Cl (5.0 mL) was added dropwise to
2
O (100
4
3
1
H
3
In conclusion, the antibacterial activity of cepha-
losporins is enhanced substantially by possessing a
(
2
2
-
1
3
,4,15-19
27 5 6
1768, 1740, 1680 cm . Anal. (C29H N O
potential leaving group at the C-3′ position.
The
(
trifluoromethane sulfone unit in (()-4 is a better leaving
group than the methane sulfone unit in (()-3. Thus,
antibacterial activity is more potent for (()-4 than (()-
2
2
3
3
, as observed. This is in agreement with our hy-
2
2
pothesis regarding their mode of action in biological
systems (Scheme 1).
the reaction mixture at 0 °C over 5.0 min. After the mixture
was warmed to room temperature, it was concentrated to
dryness, and then Et
washed with water (2 × 50 mL), dried over MgSO
treated with charcoal. After filtration, evaporation, and
purification by use of column chromatography (CHCl as
2
O was added. The ethereal layer was
4
(s), and
Exp er im en ta l Section
Gen er a l Meth od s. For anhydrous reactions, glassware
was dried overnight in an oven at 120 °C and cooled in a
desiccator over anhydrous CaSO or silica gel. Reagents were
4
purchased from Fluka Chemical Co. Solvents, including
chloroform, dichloromethane, dimethylformamide, ethyl ace-
3
eluant), â-lactam (()-8 (2.59 g, 4.49 mmol) was obtained in
1
9
3
(
0% yield as a foam: H NMR (CDCl
3
) δ 3.58 (s, 2H), 3.70-
.91 (m, 2H), 4.15-4.30 (m, 1H), 5.21 (s, 2H), 5.32 (s, 2H), 5.36
dd, J ) 8.0, 5.0, 1H), 7.00 (d, J ) 8.0, 1H), 7.20-7.38 (m,
-
1
1
5H); IR (CH
Cl) C, H, N, Cl.
Ben zyl (6RS,7SR)-3-Hyd r oxy-8-oxo-7-(p h en yla ceta m i-
2 2
Cl ) 3410, 2110, 1790, 1750, 1682 cm . Anal.
tate, hexanes, and pyridine, were distilled over CaH
nitrogen. Absolute ethanol was purchased from Merck and
used as received. Solid magnesium sulfate (i.e., MgSO (s))
2
under
29 26 5 6
(C H N O
4
from Aldrich was used for drying reaction products after
workup. Reactions were carried out in nitrogen atmosphere;
d o)-1,4-d ia za bicyclo[4.2.0]oct-2-en e-2-ca r boxyla te ((()-9).
Meth od A: â-Lactam (()-7 (2.70 g, 4.99 mmol) in EtOAc (80

4
684 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24
Hwu et al.
mL) was hydrogenated under 30-35 psi of H
of Pd/C (10%, 40.0 mg, 0.0400 mmol) at room temperature for
0 min. After filtration and evaporation, the crude foam was
chromatographed (EtOAc as eluant) to give (()-9 (1.91 g, 4.69
2
in the presence
en e-2-ca r b oxyla t e ((()-12) a n d Ben zyl (6SR,7SR)-3-
[[(Tr iflu or om et h yl)su lfon yl]oxy]-8-oxo-7-(p h en yla cet a -
am ido)-4-[(tr iflu or om eth yl)su lfon aza]-1-azabicyclo[4.2.0]-
oct-2-en e-2-ca r boxyla te ((()-13). To a solution containing
(()-9 (4.07 g, 9.99 mmol) and pyridine (2.80 g, 35.4 mmol)
3
1
mmol) as a foam in 94% yield: H NMR (CDCl
3
) δ 2.50-2.68
(br, 1H), 2.85-3.02 (br, 1H), 3.21-3.45 (m, 2H), 3.55 (s, 2H),
in CH
in CH
°C for 5.0 h, it was washed with water (100 mL), dried
over MgSO (s), and concentrated under reduced pressure.
2
Cl
2
(80 mL) was added CF
3 2
SO Cl (1.69 g, 10.0 mmol)
4
6
3
.18-4.43 (m, 1H), 5.09 (dd, J ) 8.0, 4.5, 1H), 5.15 (s, 2H),
.38 (d, J ) 8.0, 1H), 7.31-7.42 (m, 10H); IR (CH Cl ) 3500-
200, 1787, 1740, 1725, 1680 cm-1. Anal. (C22
) C, H,
2
Cl
2
(5.0 mL). After the solution was stirred at 15
2
2
H
21
N
3
O
5
4
N.
Purification of the residue by use of column chromatography
(EtOAc as eluant) gave (()-12 (1.62 g, 3.00 mmol) as a
foam in 30% yield. Further elution of the column with
Meth od B: â-Lactam (()-8 (575 mg, 0.998 mmol) in EtOAc
50 mL) was hydrogenated under 30-35 psi of H in the
(
2
presence of Pd/C (10%, 20.0 mg, 0.020 mmol) at room temper-
ature for 30 min. After filtration and evaporation, the crude
foam was chromatographed (EtOAc as eluant) to give (()-9
EtOAc afforded (()-13 (0.67 g, 1.0 mmol) as an oil in 10%
1
yield. For (()-12: H NMR (CDCl
3
) δ 2.96-3.10 (br, 1H),
3.24-3.48 (m, 2H), 3.54 (s, 2H), 4.21-4.49 (m, 1H), 5.04
(dd, J ) 9.0, 5.0, 1H), 5.25 (s, 2H), 6.48 (d, J ) 9.5,
(354 mg, 0.868 mmol) as a foam in 87% yield.
1
1
H), 7.25-7.48 (m, 10H); IR (CH
2
Cl
Anal. (C23
) δ 3.45-3.78 (m, 2H),
.58 (s, 2H), 4.26-4.51 (m, 1H), 5.06 (dd, J ) 8.0, 4.5,
H), 5.36 (s, 2H), 6.60 (d, J ) 8.0, 1H), 7.30-7.50 (m,
2
) 3455-3250, 1792,
20 3 3 7
(
6RS,7SR)-3-Hyd r oxy-8-oxo-7-(p h en yla ceta m id o)-1,4-
-
1
752, 1735, 1680 cm
.
H F N O S) C, H, F,
d ia za bicyclo[4.2.0]oct-2-en e-2-ca r boxylic Acid ((()-10). A
1
N, S. For (()-13: H NMR (CDCl
3
solution of (()-9 (0.41 g, 1.0 mmol) in EtOH (35 mL) was
3
1
1
2 2
hydrogenated on PdCl (150 mg, 0.846 mmol) at 60 psi of H
at room temperature for 3.0 h. It was then filtered and
concentrated under reduced pressure. The crude product was
recrystallized from EtOAc to afford pure (()-10 (0.16 g, 0.50
mmol) in 50% yield: mp 140-142 °C; H NMR (CDCl
-
1
0H); IR (CH
2 2
Cl ) 3350-3300, 1798, 1754, 1739, 1678 cm .
(6RS,7SR)-3-[[(Tr iflu or om eth yl)su lfon yl]oxy]-8-oxo-7-
(ph en ylacetam ido)-1,4-diazabicyclo[4.2.0]oct-2-en e-2-car -
boxylic Acid ((()-4). A solution of (()-12 (0.54 g, 1.0 mmol)
2 2
in EtOH (50 mL) was hydrogenated with H at 60 psi on PdCl
(150 mg, 0.846 mmol) at room temperature for 3.0 h. The
solution was then filtered and concentrated under reduced
pressure. Purification of the residue by use of column chro-
1
3
/DMSO-
d
5
3
6
/D
.05 (d, J ) 5.0, 1H), 7.30-7.58 (m, 5H); IR (Nujol) 3650-
155, 1781, 1725, 1680 cm-1. Anal. (C15
) C, H, N.
Dib en zyl (5RS,6SR)-7-Oxo-6-(p h en yla cet a m id o)-1,3-
2
O) δ 3.20-3.41 (m, 2H), 3.50 (s, 2H), 4.20-4.40 (m, 1H),
15 3 5
H N O
diazabicyclo[3.2.0]h eptan e-2,2-dicar boxylate ((()-14). Tri-
matography (EtOAc/EtOH (9:1)) gave (()-4 (135 mg, 0.300
ethylamine (0.12 g, 1.2 mmol) was added to a solution of (()-8
1
mmol) in 30% yield: mp 100-102 °C; H NMR (CDCl
3
/D
2
O) δ
2 2 2
(0.58 g, 1.0 mmol) in CH Cl (50 mL) at 0 °C, and then H S
3
.21-3.43 (m, 2H), 3.55 (s, 2H), 4.13-4.44 (m, 1H), 5.02 (d, J
was bubbled into the solution for 15 min. The solution was
allowed to stand at room temperature for 2.0 h while evolution
of N
for 30 min, which was then washed with water (4 × 50 mL),
dried over MgSO (s), and concentrated under reduced pres-
)
5.0, 1H), 7.30-7.50 (m, 5H); IR (CH
2
Cl
2
) 3465-3100, 1790,
S) C, H, F, N, S.
-
1
1
720, 1710, 1680 cm . Anal. (C16
H
14
F
3
N
3 7
O
2 2
gas was observed. The solution was purged with N gas
(()-Dib en zyl 2-[cis-4-(Azid om et h yl)-2-oxo-3-(p h en yl-
a ceta m id o)-1-a zetid in yl]-2-m esylm a lon a te (15). To a so-
lution containing (()-7 (5.41 g, 9.99 mmol) and Et N (1.05 g,
10.4 mmol) in CH Cl (80 mL) was added dropwise MeSO Cl
(1.15 g, 10.0 mmol) in CH Cl (10 mL). After the solution was
stirred at 0 °C for 1.0 h, it was washed with water (100 mL),
dried over MgSO (s), and concentrated under reduced pres-
sure. Purification of the residue by use of column chromatog-
raphy (CHCl as eluant) afforded (()-15 (5.26 g, 8.49 mmol)
in 85% yield: mp 114-115 °C; H NMR (CDCl
4
sure. The crude product was purified by use of column
3
chromatography (EtOAc as eluant) to afford (()-14 (0.21 g,
2
2
2
0
.40 mmol) as a foam in 40% yield. Further elution of the
2
2
column with EtOAc gave (()-9 (61 mg, 0.15 mmol) as a foam
1
in 15% yield. For (()-14: H NMR (CDCl
3
) δ 2.85-3.29 (m,
H), 3.31-3.46 (br, 1H), 3.53 (s, 2H), 4.29-4.52 (m, 1H), 5.31
dd, J ) 8.0, 4.5, 1H), 5.20 (s, 2H), 5.21 (s, 2H), 7.16-7.46 (m,
4
2
(
1
3
-
1
1
6H); IR (CH
) C, H, N.
Ben zyl(6RS,7SR)-3-[(Meth ylsu lfon yl)oxy]-8-oxo-7-(ph en -
ylacetamido)-1,4-diazabicyclo[4.2.0]oct-2-ene-2-carboxylate
(()-11). To a solution containing (()-9 (4.07 g, 9.99 mmol)
and pyridine (2.80 g, 35.4 mmol) in CH Cl (86 mL) was added
MeSO Cl (1.15 g, 10.0 mmol). After the solution was stirred
at 15 °C for 5.0 h, it was washed with water (100 mL), dried
over MgSO (s), and concentrated under reduced pressure.
Purification of the residue by use of column chromatography
EtOAc as eluant) gave (()-11 (2.18 g, 4.50 mmol) as a foam
2
Cl
2
) 3450-3300, 1786, 1749, 1682 cm . Anal.
3
) δ 3.39 (s, 3H),
(C
29
H
27
N
3
O
6
3.61 (s, 2H), 3.69-3.95 (m, 2H), 4.15-4.30 (m, 1H), 5.12 (s,
2H), 5.13 (s, 2H), 5.35 (dd, J ) 8.0, 5.0, 1H), 6.98 (d, J ) 8.0,
1H), 7.40-7.70 (m, 15H); IR (CH
2
Cl
2
) 3410, 2100, 1790, 1751,
-
1
(
1680 cm . Anal. (C30H N O S) C, H, N, S.
29 5 8
2
2
Ben zyl (2RS,6RS,7SR)- a n d (2SR,6RS,7SR)-2-(Meth yl-
su lfon yl)-3,8-dioxo-7-(ph en ylacetam ido)-1,4-diazabicyclo-
[4.2.0]octa n e-2-ca r boxyla te (Dia ster eoisom er ic Mixtu r e,
(()-16). A solution of (()-15 (3.10 g, 5.00 mmol) in EtOAc
(200 mL) was hydrogenated on 10% Pd/C (40 mg, 0.041 mmol)
at 30-35 psi of H2 at room temperature for 1.5 h. After
filtration and condensation, the crude foam was crystallized
2
2
4
(
1
in 45% yield: H NMR (CDCl
H), 3.22-3.45 (m, 2H), 3.55 (s, 2H), 4.10-4.41 (m, 1H), 5.05
dd, J ) 9.0, 5.0, 1H), 5.23 (s, 2H), 6.40 (d, J ) 9.0, 1H), 7.30-
.50 (m, 10H); IR (CH Cl ) 3450-3250, 1788, 1750, 1730, 1680
S) C, H, N, S.
6RS,7SR)-3-[(Met h ylsu lfon yl)oxy]-8-oxo-7-(p h en yl-
3
) δ 2.66-2.80 (br, 1H), 2.99 (s,
3
(
7
from Et O to give (()-16 (2.19 g, 4.50 mmol) in 90% yield: mp
1
135-137 °C; H NMR (CDCl ) δ 3.41 (s, 3H), 3.35-3.61 (m,
3
2
2
2H), 3.58 (s, 2H), 4.20-4.45 (m, 1H), 4.96 (dd, J ) 8.0, 4.5,
1H), 5.14 (s, 2H), 6.40-7.10 (br, 2H), 7.35-7.63 (m, 10H); IR
-
1
cm . Anal. (C23
23 3 7
H N O
-
1
(
(CH
2
Cl
2
) 3415-3405, 1791, 1745, 1682, 1668 cm
H N O S) C, H, N, S.
. Anal.
a ceta m id o)-1,4-d ia za bicyclo[4.2.0]oct-2-en e-2-ca r boxyl-
(C23
23 3 7
ic Acid ((()-3). A solution of (()-11 (0.500 g, 1.03 mmol) in
(2RS,6RS,7SR)- a n d (2SR,6RS,7SR)-2-(Meth ylsu lfon yl)-
3,8-d ioxo-7-(p h en yla cet a m id o)-1,4-d ia za b icyclo[4.2.0]-
octa n e-2-ca r boxylic Acid (Dia ster eoisom er ic Mixtu r e,
(()-5) a n d (6RS,7SR)-3-Hyd r oxy-8-oxo-7-(p h en yla ceta -
m id o)-1,4-d ia za bicyclo[4.2.0]oct-2-en e-2-m eth yl Su lfon e
((()-17). A solution of (()-16 (0.49 g, 1.0 mmol) in EtOH (40
2 2
EtOH (50 mL) was hydrogenated with H at 60 psi on PdCl
(150 mg, 0.846 mmol) at room temperature for 3.0 h. The
solution was then filtered and concentrated under reduced
pressure. Purification of the residue by use of column chro-
matography (EtOAc/EtOH (9:1)) gave (()-3 (0.14 g, 0.36 mmol)
1
in 35% yield: mp 115-117 °C; H NMR (CDCl
3
/D
2
O) δ 2.98
mL) was hydrogenated with H2 at 60 psi on PdCl (150 mg,
2
(
s, 3H), 3.20-3.43 (m, 2H), 3.52 (s, 2H), 4.12-4.42 (m, 1H),
.10 (d, J ) 5.0, 1H), 7.25-7.48 (m, 6H); IR (CH ) 3460-
100, 1787, 1710, 1700, 1680 cm-1. Anal. (C16
H N O S) C,
17 3 7
0.846 mmol) at room temperature for 4.0 h. The solution was
then filtered and concentrated under reduced pressure. Pu-
rification of the residue by use of column chromatography
(EtOAc as eluant) gave (()-17 (0.18 g, 0.50 mmol) as a foam
in 50% yield. Further elution of the column with a mixture
of EtOAc and EtOH (4:1) afforded (()-5 (80 mg, 0.20 mmol)
5
3
2
Cl
2
H, N, S.
Ben zyl (6RS,7SR)-3-[[(Tr iflu or om eth yl)su lfon yl]oxy]-
8
-oxo-7-(p h en yla ceta m id o)-1,4-d ia za bicyclo[4.2.0]oct-2-

New Isodethiaazacephems as Antibacterial Agents
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24 4685
1
in 20% yield. For (()-5: mp 160-166 °C; H NMR (CDCl
2
3
/
(7) Grabowski, E. J . J .; Douglas, A. W.; Smith, G. B. Ammonolysis
1
3
of Cephalosporins: C NMR Characterization of the Intermedi-
ates from â-Lactam Ring Cleavage Prior to Loss of the 3′-Group.
J . Am. Chem. Soc. 1985, 107, 267-268.
D
O) δ 3.20-3.42 (m, 2H), 3.19 (s, 3H), 3.55 (s, 2H), 4.15-
4
3
.40 (m, 1H), 5.13 (d, J ) 5.0, 1H), 7.23 (br s, 5H); IR (CH
2
Cl
400-3120, 1780, 1700, 1680, 1670 cm . For (()-17: 1H NMR
) δ 2.60-2.90 (br, 2H), 3.22-3.48 (m, 2H), 3.50 (s, 3H),
.59 (s, 2H), 4.17-4.42 (m, 1H), 5.13 (dd, J ) 8.0, 4.5, 1H),
.95 (d, J ) 8.0, 1H), 7.30 (br s, 5H); IR (CH Cl ) 3500-3200,
789, 1727, 1680 cm-1. Anal. (C15
S) C, H, N, S.
An tiba cter ia l Activity Tests. The serial broth dilution
2
)
-1
(8) Hakimelahi, G. H.; J ust, G.; Ugolini, A. The Synthesis of an O-2-
(CDCl
3
Isooxacephem. Helv. Chim. Acta 1982, 65, 1368-1373.
3
6
1
(9) Hakimelahi, G. H.; Tsay, S.-C.; Ramezani, Z.; Hwu, J . R.
Syntheses of New Isocephems and Isodethiaoxacephems as
Antimicrobial Agents. Helv. Chim. Acta 1996, 79, 813-819.
10) Muhtadi, F. J .; Hassan, M. M. A. In Analytical Profiles of Drug
Substances; Florey, K., Ed.; Academic: New York, 1982; Vol. 11,
pp 139-168.
2
2
17 3 5
H N O
(
1
3
method was used to study the antibiotic activity. The inocula
were prepared by use of the heart infusion broth (Difco
(11) Wise, R.; Rollason, T.; Logan, M.; Andrews, J . M.; Bedford, K.
A. HR 756, A Highly Active Cephalosporin: Comparison with
Cefazolin and Carbenicillin. Antimicrob. Agents Chemother.
-4
Laboratories) to make 10 dilutions of the overnight cultures.
Tubes of the seeded antibiotic-containing media were incu-
bated at 37 °C for 20 h. The lowest concentration of antibiotic
that prevented visible growth of microorganisms was then
determined.
1
978, 14, 807-811.
(
12) Morris, J . J .; Page, M. I. Intra- and Intermolecular Catalysis in
the Aminolysis of Benzylpenicillin. J . Chem. Soc., Perkin Trans.
2
1980, 212-219.
(
13) Pursiano, T. A.; Misiek, M.; Leitner, F.; Price, K. E. Effect of
Assay Medium on the Antibacterial Activity of Certain Penicil-
lins and Cephalosporins. Antimicrob. Agents Chemother. 1973,
Ack n ow led gm en t. We thank the National Science
Council of the Republic of China and Academia Sinica
for financial support of this work. We are also grateful
to Prof. Sunney I. Chan for helpful discussions.
3
, 33-39.
(
14) Neu, H. C. Structure-Activity Relationships: Biological. In The
Chemistry of â-Lactams; Page, M. I., Ed.; Blackie Academic &
Professional: New York, 1992; pp 101-128.
(
15) Boyd, D. B.; Hermann, R. B.; Presti, D. E.; Marsh, M. M.
Electronic Structures of Cephalosporins and Penicillins. 4.
Modeling Acylation by the â-Lactam Ring. J . Med. Chem. 1975,
18, 408-417.
(16) Boyd, D. B.; Herron, D. K.; Lunn, W. H. W.; Spitzer, W. A.
Parabolic Relationships Between Antibacterial Activity of Ceph-
alosporins and â-Lactam Reactivity Predicted from Molecular
Orbital Calculations. J . Am. Chem. Soc. 1980, 102, 1812-1814.
(17) Boyd, D. B. In Chemistry and Biology of â-Lactam Antibiotics;
Morin, R. B., Gorman, M., Eds.; Academic Press: New York,
1982; Vol. 1, pp 437-545.
(18) Boyd, D. B. Electronic Structures of Cephalosporins and Penicil-
lins. 15. Inductive Effect of the 3-Position Side Chain in
Cephalosporins. J . Med. Chem. 1984, 27, 63-66.
(19) Nishikawa, J .; Tori, K. 3-Substituent Effect and 3-Methylene
Substituent Effect on the Structure-Reactivity Relationship of
7â-(Acylamino)-3-cephem-4-carboxylic Acid Derivatives Studied
by Carbon-13 and IR Spectroscopies. J . Med. Chem. 1984, 27,
1657-1663.
Refer en ces
(
1) Waxman, D. J .; Strominger, J . L. Sequence of Active Site
Peptides from the Penicillin-sensitive D-Alanine Carboxypepti-
dase of Bacillus Subtilis. J . Biol. Chem. 1980, 255, 3964-3976.
2) Fr e` re, J . M.; Nguyen-Dist e` che, M.; Coyette, J .; J oris, B. Mode
of Action: Interaction with the Penicillin Binding Proteins. In
The Chemistry of â-Lactams; Page, M. I., Ed.; Blackie Academic
(
&
Professional: New York, 1992; pp 148-197.
(
(
(
3) Boyd, D. B. Elucidating the Leaving Group Effect in the
â-Lactam Ring Opening Mechanism of Cephalosporins. J . Org.
Chem. 1985, 50, 886-888.
4) Boyd, D. B.; Lunn, W. H. W. Electronic Structures of Cepha-
losporins and Penicillins. 9. Departure of a Leaving Group in
Cephalosporins. J . Med. Chem. 1979, 22, 778-784.
5) Faraci, W. S.; Pratt, R. F. Elimination of a Good Leaving Group
from the 3′-Position of a Cephalosporin Need Not Be Concerted
with â-Lactam Ring Opening. J . Am. Chem. Soc. 1984, 106,
1
489-1490.
(
6) Page, M. L.; Proctor, P. Mechanism of â-Lactam Opening in
Cephalosporins. J . Am. Chem. Soc. 1984, 106, 3820-3825.
J M980476H