Synthesis and antimicrobial activity of new 7β-(benzo[a] dihydrocarbazolyloxyacetyl)-substituted cephalosporins

Article abstract of DOI:10.1016/j.farmac.2004.05.001

Selected 7β-(benzo[a]dihydrocarbazolyloxyacetyl)-substituted cephalosporins (1a-e) were synthesised and tested for their antimicrobial activity against Gram-positive and Gram-negative clinical pathogens. All compounds synthesised (1a-e) showed an in vitro antimicrobial activity similar to that of ceftriaxone and cefpirome against the Gram-positive bacteria, and superior to that of penicillin and cefaclor against pen-R Staphylococcus aureus species. Like all β-lactam agents, compounds 1a-e were in an inactive Minimum Inhibitory Concentration (MIC > 32 μg/ml) against methicillin-resistant S. aureus species. Furthermore, as expected, no cross-resistance was observed against the erythromycin-resistant Staphylococcus pyogenes strain. Finally, it is worth underlining that compounds 1a and 1e showed a similar activity to that of ceftriaxone and superior to cefaclor against penicillin-resistant Streptococcus pneumoniae isolates, a key respiratory tract infection (RTI) causing pathogen difficult to treat with currently marketed antibiotics.

Full text of DOI:10.1016/j.farmac.2004.05.001

IL FARMACO 59 (2004) 691–696
www.elsevier.com/locate/farmac
Synthesis and antimicrobial activity of new
7b-(benzo[a]dihydrocarbazolyloxyacetyl)-substituted cephalosporins
a,
a
a
a
Armando Rossello *, Elisabetta Orlandini , Elisa Nuti , Simona Rapposelli ,
a
b
a
Marco Macchia , Enza Di Modugno , Aldo Balsamo
a
Dipartimento di Scienze Farmaceutiche, Università degli Studi di Pisa, via Bonanno, 6, Pisa 56126, Italy
b
Microbiology Department, Drug Metabolism and Pharmacokinetic Department, GlaxoSmithKline Medicines Research, Verona 37135, Italy
Received 4 April 2004; accepted 8 May 2004
Abstract
Selected 7b-(benzo[a]dihydrocarbazolyloxyacetyl)-substituted cephalosporins (1a–e) were synthesised and tested for their antimicrobial
activity against Gram-positive and Gram-negative clinical pathogens. All compounds synthesised (1a–e) showed an in vitro antimicrobial
activity similar to that of ceftriaxone and cefpirome against the Gram-positive bacteria, and superior to that of penicillin and cefaclor against
pen-R Staphylococcus aureus species. Like all b-lactam agents, compounds 1a–e were in an inactive Minimum Inhibitory Concentration
(MIC > 32 µg/ml) against methicillin-resistant S. aureus species. Furthermore, as expected, no cross-resistance was observed against the
erythromycin-resistant Staphylococcus pyogenes strain. Finally, it is worth underlining that compounds 1a and 1e showed a similar activity to
that of ceftriaxone and superior to cefaclor against penicillin-resistant Streptococcus pneumoniae isolates, a key respiratory tract infection
(RTI) causing pathogen difficult to treat with currently marketed antibiotics.
©
2004 Elsevier SAS. All rights reserved.
Keywords: Cephalosporins; 7b-(benzo[a]dihydrocarbazolyloxyacetyl)-substituted; Antimicrobial activity
1
. Introduction
evident that there is a need for new antibiotics, in order to
overcome the multi-drug resistance shown by these infec-
tious agents. In the field of cephalosporin b-lactam antibiot-
ics of type A, the antimicrobial properties of the new com-
pounds essentially depend on their ability to interact more or
less strongly with the bacterial penicillin-binding proteins
(PBPs), which appear to be mutated in the resistant patho-
gens. These interactions are essentially linked to the nature of
the substituents bound to the C-3 and C-7 atoms of the
cephem nucleus. In particular, as regards the C-7 position,
there is good evidence that appropriate variations in the steric
hindrance and/or lipophilicity of the substituent X on the
amido side-chain can modify the affinity and the selectivity
of new cephalosporins against the mutated PBPs of the
Gram-positive pen-R and met-R strains [9–11]. In the more
recent cephalosporins which possess a good activity against
resistant Gram-positive cocci, the C-7 acylamido side-chain
is characterised by the presence of a bulky heteroaromatic
portion, in its structure which is probably able to give the
drugs better molecular characteristics for their interaction
with the PBPs [12]. Previous studies aiming to find new
Since modern antibiotic therapy was started, the abuse of
antibacterial agents in many fields of human medicine and of
zootechnic activities has promoted the progressive develop-
ment of bacterial resistance. In the case of Gram-positive
bacteria, for example, some cocci, such as Staphylococcus
aureus (S.a.) and Streptococcus pneumoniae (S.p.), once
very sensitive to the action of penicillins (S.a. pen-S or S.p.
pen-S), have become very resistant to these antibiotics (S.a.
pen-R or S.p. pen-R) or, in the case of some strains of S.a.
also to methicillin (S.a. met-R). Some of these cocci, once
sensitive to vancomicin or to its associations with rifampicin
or cephotaxime [1–5], are now resistant also to this antibiotic
[6–8].
In general, at present, bacterial infection caused by pen-R
Gram-positive cocci is treated with the more recent b-lactam
antibiotics and/or macrolides, but it is beginning to appear
*
Corresponding author.
E-mail address: aros@farm.unipi.it (A. Rossello).
©
2004 Elsevier SAS. All rights reserved.
doi:10.1016/j.farmac.2004.05.001

692
A. Rossello et al. / IL FARMACO 59 (2004) 691–696
nucleus are atoms or atomic groups able to exert different
electronic effects, such as chlorine or bromine atoms, or nitro
or methoxy groups [15].
2
. Chemistry
Scheme 1 shows the synthetic route to the new cepha-
losporins (1a–e) substituted on their C-7 amido side-chain
with the benzo[a]dihydrocarbazolyl group. Acidic cleavage
of 6-methoxy-1-tetralone 2 with 48% aqueous HBr in AcOH
gave 6-hydroxy-1-tetralone 3, which was alkylated with eth-
ylbromoacetate in anhydrous acetone in the presence of po-
tassium carbonate to give ether 4. Reaction of 4 with meta- or
para-substituted phenylhydrazine in refluxing AcOH gave
pure C-8- or C-9-substituted ethyl 2-[(6,11-dihydro-5H-
benzo[a]carbazol-3-yl)oxy]-acetates 5a–e. Basic hydrolysis
of ethyl esters 5a–e by KOH in ethanol gave acids 6a–e,
which were used as acylating agents of the tert-butyl ester of
.
Fig. 1
7
-ACA (in the presence of EDCI as the condensing agent in
anhydrous THF) to yield the corresponding tert-butyl esters
a–e. Acidic deprotection of 7a–e with trifluoroacetic acid in
pharmacologically active compounds indicated that some
benzo[a]dihydrocarbazole derivatives with a B structure may
possess different biopharmacological properties which may
also be of the antimicrobial type [13,14].
7
dichloromethane in the presence of anisole gave pure cepha-
losporins 1a–e.
On the basis of the hypothesis that the combination of the
cephalosporanic nucleus with a bulky amido side-chain of a
heteroaromatic type, including a molecular portion with hy-
pothetical pharmacophoric properties, might lead to new
biologically interesting cephalosporins, we planned the syn-
thesis of compounds of type 1, in which the 7-amino-
cephalosporanic portion (7-ACA) of the ‘‘classic’’ cepha-
losporins is acylated on the amino nitrogen with an oxyacetyl
group bearing a benzo[a]dihydrocarbazolic nucleus. There-
fore, a limited number of cephalosporins of type 1 were
3
. Results and conclusions
The in vitro antibacterial activity of the synthesised cepha-
losporins 1a–e against some common Gram-positive patho-
gens is summarised in Table 1.A comparison with marketed
1
1
The Gram-positive strains used in the present work were clinical
isolates and belonged to the Culture Collection of GlaxoWellcome S.p.A.
(Verona, Italy). Strain identification and pattern of antibiotic resistance were
carded out by using the Vitek apparatus (BioMerieux, Milan, Italy). Each
synthesised (Fig. 1), in which the R and R substituents on
1
the phenylindole portion of the benzo[a]dihydrocarbazolyl
.
Scheme 1

A. Rossello et al. / IL FARMACO 59 (2004) 691–696
693
Table 1
In vitro antibacterial activity of cephalosporins 1a–e and of the reference compounds penicillin G, cefaclor, ceftriaxone and cefpirome against some
Gram-positive pathogens
a
Compound
R
R
1
MIC (µg/ml)
b
S.a. 63E pen-S f S.a. 853E pen-Rg S. p. 3512 pen-S S. p. 3272 pen-S S. p. 4635 pen-R S. p. 4636 pen-R
c
S. py. eritro-Rh C. p. 615E
d
e
1
1
1
1
1
a
b
c
MeO
H
1
2
0.03
0.03
012
0.03
0.03
0.12
0.03
0.03
≤0.5
1
4
8
0.03
0.03
0.12
0.06
0.06
N.D.
0.5
0.5
0.5
1
NO
Cl
Br
H
2
H
0.5
2
1
8
8
H
4
16
8
32
16
4
d
e
H
1
2
0.06
0.06
≤0.5
0.5
0.25
0.5
N.D.
2
NO
2
0.5
≤0.5
2
≤0.5
64
>32
4
4
i
Penicillin G
Cefaclor
Ceftriaxone
Cefpirome
a
8
8
32
2
32
2
2
0.03
0.03
0.03
0.03
0.6
0.6
0.12
2
2
1
1
0.03
Minimum inhibitory concentration.
Staphylococcus aureus.
Streptococcus pneumoniae.
Streptococcus pyogenes.
Clostridium perfringens.
Penicillin sensitive.
Penicillin resistant.
Eritromicin resistant.
Not determined.
b
c
d
e
f
g
h
i
b-lactam antibiotics such as penicillin G, cefaclor, ceftriax-
activity of compounds 1a–e against penicillin-resistant S. au-
reus 853 was similar to that of cefpirome, and significantly
higher than that of penicillin G and cefaclor. As expected,
like other b-lactam agents, compounds 1a–e appeared to be
completely devoid of any activity (MIC > 32 µg/ml) towards
certain Methicillin-Resistant S. aureus (MRSA) strains (data
not shown). Against S. pneumoniae bacteria, all new com-
pounds 1a–e exhibited an activity similar to that of all the
reference compounds in the case of the penicillin-sensitive
strains (S.p. 3512 and S.p. 3272). They also showed an
antimicrobial activity similar to that of penicillin G and
cefaclor, or slightly lower than that of ceftriaxone and cef-
pirome, against the penicillin-resistant strains (S.p. 4635 and
S.p. 4636). Also in the case of the erythromycin-resistant
Streptococcus pyogenes and the Clostridium perfringens
615E strains, compounds 1a–e exhibited an activity similar
to that of ceftriaxone and cefpirome and slightly better than
cefaclor. No significant differences were observed in the
trend of the activity of the new compounds towards the
strains tested, as a function of the type or the position of the
2
one and cefpirome is also reported . Data are expressed as
3
Minimum Inhibitory Concentration (MIC) values (µg/ml) .
Compounds 1a–e were also tested against some Gram-
4
negative bacteria , but they were found inactive up to a
concentration of 32 µg/ml.
The activity of the tested compounds against penicillin-
sensitive S. aureus 663E was similar to that of penicillin G
and of the second-, third- and fourth-generation cephalospor-
ins, cefaclor, ceftriaxone, and cefpirome (see Fig. 2). The
strain was maintained as a lyophilised culture and was sub-cultured twice on
Blood Agar Base (BBL, Cockeysville, MD) just before use.
2
Penicillin G, cefuroxime, cefaclor, ceftriaxone, cefpirone and
amoxicillin/clavulanate combination were obtained from commercial sour-
ces.
3
All compounds tested were daily prepared in 0.1 mM sodium phos-
phate buffer, pH 7.4. The Minimal Inhibitory Concentration (MIC) was
determined in accordance with the technical procedure recommended by the
National Committee for Clinical Laboratory Standards (1997). Methods for
Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobi-
cally, fourth ed. Approved Standards M7-A4. (National Committee for
Clinical Laboratory Standards, Villanova, PA.) Serial doubling dilution, in
appropriate growth medium, was prepared from each antibiotic solution.
The bacterial inoculum was prepared by making a direct saline suspension
of isolated colonies from an overnight agar plate. The suspension was
adjusted to match the 0.5 McFarland turbidity standard and diluted in sterile
substituent R or R on the benzo[a]dihydrocarbazolic sys-
1
tem.
These data show that all the cephalosporins 1a–e, while
possessing antimicrobial properties similar to those of cepha-
losporins of the third and fourth generations, such as ceftri-
axone and cefpirome, towards the Gram-positive bacteria
tested, are, on the other hand, poorly active against selected
Gram-negative pathogens (MIC > 32 µg/ml).
5
broth to obtain a final inoculum of about 5 × 10 colony-forming units/ml in
the microtitre plate. The plates were inoculated using a replicating device
(Dynatech AM80, Molecular Devices, USA). In the case of S. pneumoniae
and S. pyogenes strains Tood Hewitt media (BBL, Cockeysville, MD) were
This result may indicate that the benzo[a]dihydrocarba-
zolyloxyacetic nucleus, chosen as the acyl substituent of the
amino nitrogen of 7-ACA, possesses molecular characteris-
tics suitable to interact with the Gram-positive PBPs,
whereas it does not allow an effective interaction with Gram-
negative b-lactam molecular targets, probably due to the
extra barrier, present only in the Gram-negatives, which may
used and the Minimum Inhibitory Concentration (MIC) value was recorded
after 24 h of incubation at 35 °C in 5% CO atmosphere. The MIC was
2
defined as the lowest concentration that resulted in no visible growth after
2
0 h of incubation at 35 °C.
4
Escherichia coli, Pseudomonas aeruginosa, Haemophylus influenzae
and Bacteroides fragilis, from the GlaxoWellcome S.p.A. (Verona, Italy)
bacterial culture collection were used as the Gram-negative reference
strains.

694
A. Rossello et al. / IL FARMACO 59 (2004) 691–696
.
Fig. 2
limit the penetration of the molecules tested. A possible
explanation of the narrow activity spectrum of compounds
4.2. Ethyl [(5-oxo-5,6,7,8-tetrahydronaphthalen-2-yl)oxy]
acetate 4
1a–e may be found in the lack of an additional substituent on
the carbon adjacent to the carbonyl of the acetamido side-
chain, which is usually present in the corresponding molecu-
lar portion of most of the commercially available broad-
spectrum cephalosporins (see for example ceftriaxone and
cefpirome of Fig. 1).
Potassium carbonate (32.7 mmol) and ethylbromoacetate
(49.0 mmol) were added sequentially to a stirred solution of
tetralone 3 (32.7 mmol) in anhydrous acetone (215 ml). The
stirred mixture was refluxed for 12 h and then filtered, and the
resulting solution was evaporated to give the pure ester 4. 4
1
(
68%): m.p. 115–118 °C; H NMR (CDCl ) d 1.23 (t, 3H,
3
J = 7.2 Hz), 2.12 (m, 2H), 2.60 (t, 2H, J = 5.6 Hz), 2.90 (t, 2H,
J = 6.4 Hz), 4.18 (q, 2H, J = 7.2 Hz), 4.72 (s, 2H), 6.70 (m,
4. Experimental section
2
H), and 7.90 m (m, 1H). Anal. C H O (C, H).
14 16 4
Melting points were determined on a Kofler hot-stage
1
apparatus and are uncorrected. H NMR spectra of all com-
pounds were obtained with a Varian Gemini 200 instrument
operating at 200 MHz, in a ca. 2% solution of deuterated
solvent (DMSO-d , CD OD, or CDCl ). Analytical TLCs
4
.3. General procedure for the synthesis of the 8-substi-
tuted ethyl[(6,11-dihydro-5H-benzo[a]carbazol-3-yl)oxy]
acetate 5a–d and ethyl[(9-nitro-6,11-dihydro-5H-benzo[a]
carbazol-3-yl)oxy]acetate 5e
6
3
3
were carried out on 0.25-mm layer silica gel plates contain-
ing a fluorescent indicator; spots were detected under UV
light (254 nm). Column chromatography was performed
using 70–230 mesh silica gel. Mass spectra were detected
with an HP-5988 A spectrometer (EI, 70 eV). Evaporation
was performed in vacuo (rotating evaporator). Commercial
A stirred mixture of tetralone 4 (8.1 mmol) and the appro-
priate 4- or 3-substituted phenylhydrazine (8.4 mmol) in
glacial AcOH (11.4 ml) was refluxed for 6 h. The resulting
solution was then cooled at room temperature and evaporated
to give a crude solid residue which, by crystallisation from
6
-methoxy-1-tetralone 2 was purchased from Aldrich.
EtOH/Et O, yielded pure carbazole derivatives 5a–e. 5a
Na SO was always used as the drying agent. Elemental
2
2
4
1
(69%): m.p. 167–170 °C; H NMR (DMSO-d ) d 1.25 (t, 3H,
analyses were performed in our analytical laboratory and
agreed with theoretical values to within ±0.4%.
6
J = 7.2 Hz), 2.91 (m, 4H), 3.78 (s, 3H), 4.20 (q, 2H,
J = 7.2 Hz), 4.78 (s, 2H), 6.68–7.65 (m, 6H) and 11.05 m (s,
1
1
H). Anal. C H NO (C, H, N). 5b (10%): m.p. 183–
4.1. 6-Hydroxy-3,4-dihydronaphthalen-1(2H)-one 3
21 21 4
1
84 °C; H NMR (DMSO-d ) d 1.25 (t, 3H, J = 7.2 Hz), 2.91
6
A solution of aqueous 48% HBr was added to a stirred
(m, 4H), 4.20 (q, 2H, J = 7.2 Hz), 4.77 (s, 2H), 6.70–7.66 (m,
6H) and 11.05 m (s, 1H). Anal. C20 (C, H, N). 5c
solution of 6-methoxy-3,4-dihydronaphthalen-1(2H)-one 2
56.7 mmol) in glacialAcOH and the mixture was refluxed at
20 °C for 12 h, and then cooled and evaporated to yield
H N O
18 2 5
1
(
1
(51%): m.p. 146–149 °C; H NMR (DMSO-d ) d 1.25 (t, 3H,
6
J = 7.2 Hz), 2.92 (m, 4H), 4.20 (q, 2H, J = 7.2 Hz), 4.79 (s,
crude 3 [16] as a semisolid residue, which was purified by
2H), 6.85–7.65 (m, 6H) and 11.45 m (s, 1H). Anal.
1
crystallisation from methanol/water. 3 (88%): m.p. 150–
C H ClNO (C, H, N). 5d (62%): m.p. 153–155 °C; H
2
0
18
3
1
1
2
1
52 °C; H NMR (DMSO-d ) d 1.98 (m, 2H), 2.55 (m, 2H),
NMR (DMSO-d ) d 1.25 (t, 3H, J = 7.2 Hz), 2.91 (m, 4H),
6
6
.80 (m, 2H), 5.10 (brs, 1H), 6.55 (m, 2H) and 7.68 m (m,
H). Anal. C H O (C, H).
4.20 (q, 2 H, J = 7.2 Hz), 4.79 (s, 2H), 6.81–7.68 (m, 6H) and
11.47 m (s, 1H). Anal. C H BrNO (C, H, N). 5e (65%):
1
0
10
2
20 18
3

A. Rossello et al. / IL FARMACO 59 (2004) 691–696
695
1
m.p. 182–184 °C; H NMR (DMSO-d ) d 1.22 (t, 3H,
J = 4.8 Hz ), 5.07 (d, 1H, , J = 12.8 Hz), 5.88 (dd, 1H,
J = 4.8 and 7.6 Hz), 6.70–8.19 (m, 7H) and 8.10 m (s, 1H).
Anal. C H N O S (C, H, N). 7c (87%): m.p. 110–113 °C;
6
J = 7.2 Hz), 3.00 (m, 4H), 4.20 (q, 2H, J = 7.2 Hz), 4.82 (s,
H), 6.89–8.20 (m, 6H) and 11.05 m (s, 1H). Anal.
C H N O (C, H, N).
2
3
2 32 4 9
1
H NMR (DMSO-d ) d 1.54 (s, 9H), 2.06 (s, 3H), 2.95 (m,
20
18
2
5
6
4
H), 3.22 and 3.60 (2d, 2H, J = 18 Hz), 4.55 (d, 1H,
4
.4. General procedure for the synthesis of the 8-substi-
J = 12.8 Hz), 4.99 (d, 1H, J = 4.8 Hz ), 5.02 (d, 1 H,
J = 12.8 Hz), 5.89 (dd, 1H, J = 4.8 and 7.2 Hz), 6.75–7.50 (m,
7H) and 8.23 m (s, 1H). Anal. C H ClN O S (C, H, N). 7d
tuted-[(6,11-dihydro-5H-benzo[a]carbazol-3-yl)oxy]acetic
acids 6a–d and [(9-nitro-6,11-dihydro-5H-benzo[a]car-
bazol-3-yl)oxy]acetic acid 6e
3
2
32
3 7
1
(89%): m.p. 107–110 °C; H NMR (DMSO-d ) d 1.54 (s,
6
9
H), 2.06 (s, 3H), 2.95 (m, 4H), 3.25 and 3.55 (2d, 2H,
A mixture of the appropriate carbazole 5a–e (1.1 mmol)
and KOH (1.2 mmol) in EtOH (37 ml) was stirred at room
temperature for 48 h, and then the solvent was evaporated
J = 18 Hz), 4.56 (s, 2H), 5.00 (d, 1H, J = 4.8 Hz ), 5.05 (d, 1H,
J = 12.8 Hz), 5.87 (dd, 1H, J = 4.8 and 7.2 Hz), 6.70–7.80 (m,
7H) and 8.18 m (s, 1H). Anal. C H BrN O S (C, H, N). 7e
3
2
32
3 7
1
and the resulting residue was dissolved in H O. The aqueous
(75%); H NMR (DMSO-d ) d 1.55 (s, 9H), 2.11 (s, 3H),
2
6
solution was washed twice with AcOEt, acidified at pH
2.94 (m, 4H), 4.65 (s, 2H), 5.08 (d, 1H, J = 4.4 Hz ), 5.87 (dd,
1H, J = 4.4 and 7.6 Hz), 6.75–8.35 (m, 7H) and 8.10 m (s,
1H). Anal. C H N O S (C, H, N).
3
with 10% aqueous HCl and extracted three times with
AcOEt. The organic extracts, washed twice with H O, were
2
32 32 4 9
dried and evaporated to give pure 6a–e as solids. 6a (68%):
1
m.p. 330–332 °C; H NMR (DMSO-d ) d 2.90 (m, 4H), 3.31
4.6. General procedure for the preparation of the 7-(((8-
or 9-substituted-((6,11-dihydro-5H-benzo[a]carbazol-3-yl)
oxy)acetyl)))-cephalosporanic acids 1a–e
6
(
s, 3H), 4.68 (s, 2H), 6.68–7.65 (m, 6H) and 11.05 m (s, 1H).
Anal. C H NO (C, H, N). 6b (45%): m.p. 290–292 °C; H
1
1
9
17
4
NMR (DMSO-d ) d 2.91 (m, 4H), 4.77 (s, 2H), 6.70–7.66
6
(
(
4
m, 6H) and 11.05 m (s, 1H).Anal. C H N O (C, H, N). 6c
Anisole (0.62 ml) and then TFA (8 mmol) were added to a
cooled (0 °C) and stirred solution of the appropriate tert-
butyl ester of 7-ACA 7a–e (1.0 mmol) in anhydrous CH Cl
18 14 2 5
1
81%): m.p. 222–225 °C; H NMR (CD OD) d 3.01 (m, 4H),
3
.77 (s, 2H), 6.85 (m, 2H), 7.57 (m, 1H) and 10.56 m (s, 1H).
2
2
Anal. C H ClNO (C, H, N). 6d (58%): m.p. 232–235 °C;
(5.0 ml). The reaction mixture was stirred continuously at
room temperature for 18–24 h until the disappearance of the
starting ester (TLC). The solvent was then evaporated at r.t.
and the resulting oily residue was purified by flash chroma-
1
8
14
3
1
H NMR (DMSO-d ) d 2.91 (m, 4H), 4.69 (s, 2H), 6.92–7.68
6
(
6
4
m, 6H) and 11.47 m (s, 1H). Anal. C H BrNO (C, H, N).
18 14 3
1
e (77%): m.p. 258–259 °C; H NMR (DMSO-d ) d 2.80 (m,
6
H), 4.72 (s, 2H), 6.99–8.20 (m, 6H) and 11.15 m (s, 1H).
tography eluting with CHCl /MeOH, 3:1, to yield pure
3
Anal. C H N O (C, H, N).
cephalosporin derivatives 1a–e as solid products. 1a (52%):
1
8 14 2 5
1
m.p. 105–107 °C; H NMR (DMSO-d ) d 2.05 (s, 3H), 2.90
6
4
.5. General procedure for the preparation of the tert-
butyl esters of the 7-, 8- or 9-substituted- [(6,11-dihydro-
-benzo[a]carbazol-3-yl)oxy]acetyl-cephalosporanic
acids 7a–e
(m, 4H), 3.74 (d, 1H, J = 18.2 Hz), 3.77 (s, 3H), 4.01 (d, 1H,
J = 18.2 Hz), 4.65 (s, 2H), 4.66 and 5.01 (2d, 2H,
J = 13.6 Hz ), 5.14 (d, 1H, J = 4.8 Hz ), 5.70 (dd, 1H,
J = 4.8 and 8.2 Hz), 6.65–7.76 (m, 6H), 9.04 (d, 1H,
J = 8.2 Hz) and 11.06 m (s, 1H). Anal. C H N O S (C, H,
5
H
2
9 27 3 8
1
EDCI (1-ethyl-3-[3-(dimethylamino)-propyl]carbodii-
N). 1b (42%): m.p. 108–111 °C; H NMR (DMSO-d ) d 2.04
6
mide hydrochloride) (1.2 mmol) was added to a cooled (0 °C)
and stirred mixture of the appropriate acid 6a–e (1.0 mmol)
and tert-butyl ester of 7-ACA (1.0 mmol) in anhydrous THF
(s, 3H), 2.75 (m, 4H), 4.68 (s, 2H), 5.06 (d, 1H, J = 4.8 Hz ),
5.70 (dd, 1H, J = 4.8 and 8.2 Hz), 6.75–8.50 (m, 6H), 9.15 (d,
1H, J = 8.2 Hz) and 10.96 m (s, 1H). Anal. C H N O S (C,
2
8 24 4 9
1
(
48.0 ml). The reaction was stirred continuously at room
temperature until the disappearance of the starting reagents
TLC) (reaction time 18–24 h). The solvent was evaporated
H, N). 1c (42%): m.p. 146–148 °C; H NMR (DMSO-d ) d
6
2.05 (s, 3H), 2.92 (m, 4H), 4.62 (s, 2H), 4.86 (d, 1H,
J = 13.6 Hz), 5.12 (d, 1H, J = 4.8 Hz ), 5.02 (d, 1H,
J = 13.6 Hz), 5.82 (dd, 1H, J = 4.8 and 8.2 Hz), 6.75–7.50 (m,
6H), 9.10 (d, 1H, J = 8.2 Hz) and 11.49 m (s, 1H). Anal.
(
at r.t. and the residue was dissolved in CHCl (25 ml),
3
washed three times with H O, dried and evaporated under a
2
1
vacuum to give the tert-butyl esters 7a–e as pure solids. 7a
C H ClN O S (C, H, N). 1d (54%): m.p. 134–136 °C; H
2
8
24
3 7
1
(
97%): m.p. 105–107 °C; H NMR (DMSO-d ) d 1.53 (s,
NMR (DMSO-d ) d 2.15 (s, 3H), 3.25 (m, 4H), 4.96 (s, 2H),
6
6
9
H), 2.06 (s, 3H), 2.96 (m, 4H), 3.25 and 3.55 (2d, 2H,
5.09 (d, 1H, J = 13.6 Hz), 5.39 (d, 1H, J = 4.2 Hz ), 5.44 (d,
1H, J = 4.2 Hz), 6.15 (dd, 1H, J = 4.2 and 8.2 Hz), 7.10–8.25
(m, 7H) 11.86 m (s, 1H).Anal. C H BrN O S (C, H, N). 1e
J = 18 Hz), 3.84 (s, 1H), 4.56 (s, 2H), 4.76 (d, 1H,
J = 12.8 Hz), 4.97 (d, 1H, J = 4,8 Hz ), 5.06 (d, 1H,
J = 12.8 Hz), 5.80 (dd, 1H, J = 4.8 and 7.6 Hz), 6.70–7.80 (m,
2
8
24
3 7
1
(40%): m.p. 190–191 °C; H NMR (DMSO-d ) d 2.02 (s,
6
7
H) and 8.18 m (s, 1H). Anal. C H N O S (C, H, N). 7b
3H), 2.70 (m, 4H), 4.70 (s, 2H), 5.01 (d, 1H, J = 4.4 Hz), 5.60
(dd, 1H, J = 4.4 and 9.6 Hz), 6.80–8.30 (m, 6H), 8.85 (d, 1H,
J = 9.6 Hz) and 11.96 m (s, 1H). Anal. C H N O S (C, H,
3
3 35 3 8
1
(92%): m.p. 94–97 °C; H NMR (DMSO-d ) d 1.54 (s, 9H),
6
2
4
.07 (s, 3H), 2.96 (m, 4H), 3.25 and 3.55 (2d, 2H, J = 18 Hz),
.57 (s, 2H), 4.73 (d, 1H, J = 12.8 Hz), 5.00 (d, 1H,
2
8 24 4 9
N).

696
A. Rossello et al. / IL FARMACO 59 (2004) 691–696
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