Synthesis and antimicrobial activity of new bromine-rich pyrrole derivatives related to monodeoxypyoluteorin

Article abstract of DOI:10.1016/j.ejmech.2006.07.009

The synthesis and antimicrobial activity of new pyrrole derivatives structurally related to monodeoxypyoluteorin are described. The insertion of a keto or methylene spacer between the phenol group and the pyrroloyl moiety of brominated 2-(2′-hydroxybenzoy

Full text of DOI:10.1016/j.ejmech.2006.07.009

European Journal of Medicinal Chemistry 41 (2006) 1439e1445
http://www.elsevier.com/locate/ejmech
Original article
Synthesis and antimicrobial activity of new bromine-rich pyrrole
derivatives related to monodeoxypyoluteorin
*
Maria Valeria Raimondi , Stella Cascioferro, Domenico Schillaci, Salvatore Petruso
Dipartimento di Chimica e Tecnologie Farmaceutiche, Universita` degli Studi di Palermo, via Archirafi 32, 90123 Palermo, PA, Italy
Received 8 March 2006; received in revised form 4 July 2006; accepted 11 July 2006
Available online 25 September 2006
Abstract
The synthesis and antimicrobial activity of new pyrrole derivatives structurally related to monodeoxypyoluteorin are described. The insertion
of a keto or methylene spacer between the phenol group and the pyrroloyl moiety of brominated 2-(20-hydroxybenzoyl)pyrroles leads to a de-
crease of the antibacterial activity.
Ó 2006 Elsevier Masson SAS. All rights reserved.
Keywords: Antimicrobics; Bromopyrroles; Pyoluteorin analogs
1. Introduction
improvement of the antibacterial activity. Laatsch et al. [4]
suggest that separation of the phenol and pyrrole systems, in-
creasing the coplanarity of the two rings, enhances the forma-
tion of an intermolecular hydrogen bond with the hypothetical
receptor. The strength of this hydrogen bond is indicative of
antibacterial activity.
On the basis of such considerations, we have investigated
the antibacterial activity of 2-(20-hydroxybenzoyl)pyrrole bro-
mine derivatives with a keto or methylene spacer used to sep-
arate the phenol and pyrroloyl moiety of the original
compound.
In a previous paper [1] the results of the bromination of
2-(20-hydroxybenzoyl)pyrrole were reported giving a series of
derivatives, related to monodeoxypyoluteorin 1 (Fig. 1), whose
antimicrobial activity against Staphylococcus aureus increased
with the degree of halogenation. The most active member of
this series, the pentabromo compound 2, exhibited an MIC
(minimum inhibitory concentration) against S. aureus ATCC
25923 of 0.005 mg/ml and promising activity against pre-
formed Staphylococcus epidermidis and S. aureus biofilms [2].
Compound 2 presents particular structural analogies with
halogenated pyrroles from natural sources, such as pentabro-
mopseudilin 3. This compound, produced by marine bacterium
Pseudoalteromonas luteoviolaceus, shows a good antibacterial
effect against Bacillus subtilis and Escherichia coli and an in-
teresting antifungal activity against Candida albicans and Mu-
cor miehei [3].
In this paper the synthesis of the most halogenated deriva-
tives 4a,b and 5a,b (Fig. 2) is described.
2. Chemistry
Our synthetic strategy for the preparation of compounds
4a,b is outlined in Scheme 1. The starting material, (3,5-di-
bromo-2-hydroxyphenyl)acetic acid 6, can be obtained from
commercially available (2-hydroxyphenyl)acetic acid and
N-bromosuccinimide, using the methodology previously de-
scribed in Carren˜o et al. in the nuclear bromination of methox-
ybenzene [5]. The alkylation of 6 with an excess of dimethyl
sulfate in the presence of anhydrous potassium carbonate [6],
followed by hydrolysis with aqueous sodium hydroxide of
Comparison of the antimicrobial activity of 2 with that of
pentabromopseudilin 3, implies that the insertion of a carbon
atom between the aromatic rings, yielding benzoylpyrrole 2,
leads to a decrease in the antifungal activity but an
* Corresponding author. Tel.: þ390916236115; fax: þ390916236119.
E-mail address: mvraimondi@unipa.it (M.V. Raimondi).
0223-5234/$ - see front matter Ó 2006 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2006.07.009

1440
M.V. Raimondi et al. / European Journal of Medicinal Chemistry 41 (2006) 1439e1445
Br
Br
Br
Br
Cl
Br
Br
N
H
Br
Cl
N
H
Br
Br
N
H
O
H
O
O
OH
OH
Br
1
2
3
Fig. 1. Monodeoxypyoluteorin 1, 3,4,5,30,50-pentabromo-2-(20-hydroxybenzoyl)pyrrole 2, pentabromopseudilin 3 molecular structures.
methyl ester so obtained, provided the (3,5-dibromo-2-me-
thoxyphenyl)acetic acid 7. Compound 7 was reacted with
thionyl chloride to give the (3,5-dibromo-2-methoxyphenyl)-
acetyl chloride which, by reaction with pyrrylmagnesium bro-
mide in anhydrous diethyl ether (see our preceding syntheses
of pyrrylketones [1,7]), furnished the 2-(3,5-dibromo-2-me-
thoxyphenyl)-1-(1H-pyrrol-2-yl)ethanone 8 in moderate yield
(side products of the reaction were 3-isomer and variable
amounts of oxidation products from unreacted pyrrole).
When 8 was allowed to react with 2 molar equivalents of
NBS, for 6 h at room temperature, the tetrabromoderivative
9 was obtained in excellent yield.
The further halogenation of 9 at 60 ꢀC with 1 molar equiv-
alent of NBS gave the pentabromo derivative 10. The subse-
quent demethylation of compounds 9 and 10, using boron
tribromide in dichloromethane [8], afforded the desired
2-(3,5-dibromo-2-hydroxyphenyl)-1-(4,5-dibromo-1H-pyrrol-
2-yl)ethanone 4a and 2-(3,5-dibromo-2-hydroxyphenyl)-1-
(3,4,5-tribromo-1H-pyrrol-2-yl)ethanone 4b. Aluminium
chloride was found not suitable for this demethylation.
Another pathway for the preparation of compounds 4a and
4b employed the methodology shown below (see Scheme 2).
The reaction of the unstable 5,7-dibromo-1-benzofuran-
2(3H )-one 11, obtained according to the lactonization method
of Johnson [9], with pyrrylmagnesium bromide in anhydrous
diethyl ether, led to the formation of 2-(3,5-dibromo-2-
hydroxyphenyl)-1-(1H-pyrrol-2-yl)ethanone 12 in moderate
yield. Following the same procedure used for the bromination
of 8, compounds 4a and 4b were easily obtained.
Compounds 5a and 5b were synthesized adopting a protect-
ing/deprotecting strategy slightly different from the one illus-
trated in the preceding Scheme 1 for the preparation of 4a,b.
The oxidation of 9 and 10 with selenium dioxide [10], fol-
lowed by demethylation of the resulting 13 and 14 derivatives
with aluminium chloride in dichloromethane, gave rise to
1-(3,5-dibromo-2-hydroxyphenyl)-2-(4,5-dibromo-1H-pyrrol-
2-yl)ethane-1,2-dione 5a and 1-(3,5-dibromo-2-hydroxy-
phenyl)-2-(3,4,5-tribromo-1H-pyrrol-2-yl)ethane-1,2-dione
5b, respectively (see Scheme 3).
The structures of all the newly prepared compounds were
assigned according to reaction mechanisms and were con-
firmed by analytical and spectroscopic data.
3. Biological results and discussion
Our compounds were screened for their in vitro antimicro-
bial activity against two representative Gram-positive and
Gram-negative bacterial strains and against a human pathogen
fungal strain. The results expressed in MIC values (minimum
inhibitory concentration) are reported in Table 1 along with
the activity of Amikacin and Amphotericin B for comparison.
Compounds 4a,b and 5a,b were found to be active against
S. aureus. In particular, ethanones 4a and 4b resulted the most
active compounds with MIC values equal to 0.75 and
0.093 mg/ml, respectively. Ethanediones 5a and 5b possessed
a weaker activity against S. aureus with MIC values of 1.5
and 0.37 mg/ml, respectively. In both cases the activity is
linked to the degree of halogenation. Weak (MIC equal to
Br
X
Br
X
O
Br
Br
Br
N
H
Br
N
H
O
O
HO
HO
Br
Br
4a,b
5a,b
a: X = H
b: X = Br
Fig. 2. 2-(3,5-Dibromo-2-hydroxyphenyl)-1-(4,5-dibromo-1H-pyrrol-2-yl)ethanone 4a, 2-(3,5-dibromo-2-hydroxyphenyl)-1-(3,4,5-tribromo-1H-pyrrol-2-yl)etha-
none 4b, 1-(3,5-dibromo-2-hydroxyphenyl)-2-(4,5-dibromo-1H-pyrrol-2-yl)ethane-1,2-dione 5a and 1-(3,5-dibromo-2-hydroxyphenyl)-2-(3,4,5-tribromo-1H-pyr-
rol-2-yl)ethane-1,2-dione 5b molecular structures.

M.V. Raimondi et al. / European Journal of Medicinal Chemistry 41 (2006) 1439e1445
1441
OH
Br
OH
Br
Cl
Br
(ii)
(i)
O
OMe
O
O
OMe
OH
Br
Br
Br
7
6
(iii)
Br
Br
Br
Br
Br
Br
N
H
(iv)
Br
N
H
Br
(v)
O
MeO
N
H
O
MeO
O
MeO
Br
Br
10
Br
9
8
(vi)
(vi)
4b
4a
Scheme 1. Synthesis of compounds 4a,b. Reagents: (i) (CH3)2SO4eK2CO3 in acetone reflux, 24 h, then NaOH 10% at 60 ꢀC, 12 h; (ii) SOCl2 reflux, 8 h; (iii)
pyrrylmagnesium bromide in anhydrous diethyl ether; (iv) N-bromosuccinimide (2 equiv) in acetonitrile at room temperature; (v) N-bromosuccinimide (1 equiv)
in acetonitrile at 60 ꢀC; (vi) BBr3 99% in anhydrous dichloromethane.
6.25 mg/ml) anti-Gram-negative activity was only shown by
4b. The other substances resulted inactive at the maximum
tested concentration of 12.5 mg/ml. The synthesized
compounds were shown to be inactive against C. albicans at
the maximum screening concentration of 12.5 mg/ml.
From the obtained results we can conclude that further sep-
aration of the pyrrolyl moiety from the phenol group in com-
pound 2 leads to decreased anti-Gram-positive activity.
Moreover, introduction of a methylene spacer moderates the
anti-Gram-positive activity to a lesser degree than the intro-
duction of a keto spacer (compounds 4b and 5b are about
18 times and 74 times less active, respectively, than benzoyl-
pyrrole 2).
At present, our group is concerned with molecular model-
ling studies aimed at the synthesis of new derivatives of lead
compound 2 with improved antibacterial and anti-biofilm ac-
tivity. In particular our aim is the discovery of new agents
with activity against bacteria in a protective physiological
form such as biofilms, which are intrinsically refractory to
conventional antibiotics [11].
4. Experimental protocols
4.1. General methods
Melting points were determined on a BuchieTottoli micro
¨
Such a decrease leads us to believe that reference com-
pound 2 fits better with the hypothetical target than the newly
synthesized compounds.
melting point apparatus in open capillary tubes and are uncor-
rected. The IR spectra were recorded at room temperature in
Nujol mulls with a Perkin Elmer Spectrum RXI FT-IR System
OH
Br
Br
(ii)
(i)
Br
N
O
OH
O
O
O
H
HO
Br
Br
6
Br
11
12
(iii)
(iv)
4a
4b
Scheme 2. Alternative synthesis of compounds 4a,b. Reagents: (i) p-toluenesulfonic acid monohydrate in toluene reflux, 12 h; (ii) pyrrylmagnesium bromide in
anhydrous diethyl ether; (iii) N-bromosuccinimide (2 equiv) in acetonitrile; (iv) N-bromosuccinimide (1 equiv) in acetonitrile.

1442
M.V. Raimondi et al. / European Journal of Medicinal Chemistry 41 (2006) 1439e1445
Br
X
Br
X
O
Br
Br
Br
N
H
(i)
Br
N
H
O
MeO
O
MeO
Br
Br
9: X = H
10: X = Br
13: X = H
14: X = Br
(ii)
5a,b
Scheme 3. Synthesis of compounds 5a,b. Reagents: (i) selenium dioxide in 1,4-dioxane reflux; (ii) anhydrous aluminium chloride in dry dichloromethane.
1
spectrometer. The H NMR spectra were recorded at room
temperature on a Bruker SF 250 spectrometer in DMSO-d6,
unless otherwise specified, using tetramethylsilane as the in-
ternal standard. Microanalyses (C, H, N) were carried out
with Elemental Vario EL III apparatus and were in agreement
with theoretical values ꢁ0.4%. Chromatographic separations
were carried out on columns packed with Macherey Nagel
Kiesel gel 60 (70e230 mesh ASTM). All reactions were mon-
itored by TLC on precoated aluminium sheets 20 ꢂ 20 of sil-
ica gel (0.2 mm Kiesel gel 60 G F254, Merck, Germany) and
C-18 reverse phase (RP-18 F254 S, Merck, Germany) using
UV light at 254 nm for visualization.
reaction mixture was evaporated under vacuum. The solid res-
idue was triturated with water, filtered, dried, then crystallized
from toluene to give 6 (11.40 g, 92% yield) as white needles,
m.p. 145 ꢀC, lit. 155 ꢀC [13]. 1H NMR (d): 3.61 (s, 2H, CH2),
7.37 (d, 1H, J ¼ 2.4 Hz, H-6), 7.61 (d, 1H, J ¼ 2.4 Hz, H-4),
9.54 (br s, 1H, exchangeable with D2O, OH); IR (n): 3466
(OH), 1703 (CO) cmꢃ1. Anal. Calc. (Found) for C8H6Br2O3:
C, 31.00% (31.13%); H, 1.95% (2.01%).
4.1.2. (3,5-Dibromo-2-methoxyphenyl)acetic acid 7
A mixture of 12.40 g (40 mmol) of 6, 22 g (160 mmol) of
anhydrous potassium carbonate and 25.20 g (200 mmol) of di-
methyl sulfate was refluxed in 140 ml of acetone for 24 h. Af-
ter cooling the solid was filtered out and the solution was
rotavaped to dryness. The oil residue was heated at 60 ꢀC
for 12 h with 100 ml of 10% sodium hydroxide. The cold clear
solution was acidified with 10% sulfuric acid. The obtained
crude acid was filtered, washed with water until neutrality,
dried and crystallized from ethanol to give 7 (11.27 g, 87%
The compounds 4a,b and 5a,b were tested for their in vitro
growth inhibitory activity against the following bacteria and
yeasts: S. aureus ATCC 25923, E. coli ATCC 25922, C. albi-
cans ATCC 10231. Amikacin and Amphotericin B (Sigma)
were used for comparative purposes and quality control of
the methods. MICs against bacterial strains were determined
using the broth dilution micro-method as described in
Ref. [2]. Antifungal activity was carried out using the broth di-
lution macro-method as described [12].
1
yield) as white crystals, m.p. 146 ꢀC. H NMR (d): 3.63 (s,
2H, CH2), 3.71 (s, 3H, OCH3), 7.52 (d, 1H, J ¼ 2.3 Hz, H-6)
7.76 (d, 1H, J ¼ 2.3 Hz, H-4); IR (n): 1706 (CO) cmꢃ1
.
Anal. Calc. (Found) for C9H8Br2O3: C, 33.37% (33.52%);
H, 2.49% (2.55%).
4.1.1. (3,5-Dibromo-2-hydroxyphenyl)acetic acid 6
To a stirred solution of 6.08 g (40 mmol) of 2-hydroxyphe-
nylacetic acid in 100 ml of acetonitrile 14.24 g (80 mmol) of
N-bromosuccinimide was added slowly. After 24 h the
4.1.3. 2-(3,5-Dibromo-2-methoxyphenyl)-1-(1H-pyrrol-2-
yl)ethanone 8
6.48 g (20 mmol) of 7 and 15 ml (24.50 g, 200 mmol) of
thionyl chloride were refluxed until the generation of hydro-
chloric acid ceased (approximately 8 h). The excess thionyl
chloride was removed under vacuum and the crude (3,5-di-
bromo-2-methoxyphenyl)acetyl chloride, dissolved in 100 ml
of anhydrous diethyl ether, was added, dropwise under nitro-
gen atmosphere, to a stirred suspension of pyrrylmagnesium
bromide (20 mmol in 150 ml of anhydrous diethyl ether) [1].
The reaction mixture was heated at reflux for 0.5 h, cooled
to room temperature, then quenched with 5% sulfuric acid
(50 ml). After stirring for 1 h, the ethereal solution was sepa-
rated and the aqueous layer was extracted with diethyl ether
Table 1
Antimicrobial activity in vitro, MIC values expressed in mg/ml for all strains
tested
S. aureus
ATCC 25923
E. coli
ATCC 25922
C. albicans
ATCC 10231
2
4a
0.005
0.75
0.093
1.5
6.2
>12.5
6.2
>12.5
>12.5
>12.5
>12.5
>12.5
e
4b
5a
>12.5
>12.5
10
5b
Amikacin
Amphotericin B
0.37
1
e
e
0.15

M.V. Raimondi et al. / European Journal of Medicinal Chemistry 41 (2006) 1439e1445
1443
(3 ꢂ 50 ml). The combined organic phases were washed with
4.1.6. General procedure for the demethylation of com-
pounds 9 and 10
water, dried over anhydrous sodium sulfate and evaporated
to dryness. The crude product was purified by chromatogra-
phy, eluted with 9/1 (v/v) cyclohexaneeethyl acetate mixture,
to provide 8 (3.51 g, 47% yield) as white needles from ethanol,
In a typical experiment, to a solution of 1 mmol of 9 or 10
in 20 ml of anhydrous dichloromethane in an iceesalt bath,
1 ml of BBr3 99% (10 mmol) was added. After 2 h, the solu-
tion was cautiously decomposed with iceesulfuric acid 5%
(30 ml), then 50 ml of diethyl ether was added. The mixture
was stirred vigorously for 10 min, the organic layer was sepa-
rated and the aqueous phase extracted with diethyl ether
(2 ꢂ 30 ml). The combined extracts were washed with water
until neutrality, dried over anhydrous sodium sulfate, and
evaporated. The crude product was crystallized to give,
respectively,
1
m.p. 134 ꢀC. H NMR (d): 3.71 (s, 3H, CH3), 4.18 (s, 2H,
CH2), 6.28 (m, 1H, H-40), 7.17 (m, 2H, H-30 and H-50), 7.51
(d, 1H, J ¼ 2.4 Hz, H-600), 7.77 (d, 1H, J ¼ 2.4 Hz, H-400),
11.89 (s, 1H, exchangeable with D2O, NH). IR (n): 3289
(NH), 1642 (CO) cmꢃ1
.
Anal. Calc. (Found) for
C13H11Br2NO2: C, 41.86% (41.68%); H, 2.97% (2.80%); N,
3.75% (3.61%).
4.1.4. 2-(3,5-Dibromo-2-methoxyphenyl)-1-(4,5-dibromo-
1H-pyrrol-2-yl)ethanone 9
(a) 2-(3,5-Dibromo-2-hydroxyphenyl)-1-(4,5-dibromo-1H-pyr-
rol-2-yl)ethanone 4a (0.44 g, 85% yield) as white crystals
from ethanol, m.p. 178 ꢀC. 1H NMR (d): 4.15 (s, 2H,
CH2), 7.32 (d, 1H, J ¼ 2.4 Hz, s after exchange with
D2O, H-30), 7.35 (d, 1H, J ¼ 2.3 Hz, H-600), 7.61 (d, 1H,
J ¼ 2.3 Hz, H-400), 9.50 (s, 1H, exchangeable with D2O,
OH), 13.06 (s, 1H, exchangeable with D2O, NH); IR (n):
3495 (OH), 3229 (NH), 1640 (CO) cmꢃ1. Anal. Calc.
(Found) for C12H7Br4NO2: C, 27.89% (27.59%); H,
1.37% (1.22%); N, 2.71% (2.50%).
A solution of 3.56 g (20 mmol) of N-bromosuccinimide in
20 ml of acetonitrile was added dropwise to a stirred solution
of 3.73 g (10 mmol) of 8 in 150 ml of acetonitrile. After 6 h,
the reaction mixture was evaporated under reduced pressure.
The residue was partitioned between water (100 ml) and di-
ethyl ether (150 ml) and, subsequently, extracted twice with
diethyl ether (100 ml). The combined extracts were washed
with water, dried over anhydrous sodium sulfate and evapo-
rated to dryness. The crude product was crystallized from ace-
tonitrile to afford 9 (4.67 g, 88% yield) as white needles, m.p.
(b) 2-(3,5-Dibromo-2-hydroxyphenyl)-1-(3,4,5-tribromo-1H-
pyrrol-2-yl)ethanone 4b (0.43 g, 72% yield) as white crys-
1
1
168 ꢀC. H NMR (d): 3.66 (s, 3H, CH3), 4.19 (s, 2H, CH2),
tals from ethanol, m.p. 198 ꢀC. H NMR (d): 4.27 (s, 2H,
7.40 (d, 1H, J ¼ 1.8 Hz, s after exchange with D2O, H-30),
7.51 (d, 1H, J ¼ 2.5 Hz, H-600), 7.78 (d, 1H, J ¼ 2.5 Hz, H-
400), 13.12 (br s, 1H, exchangeable with D2O, NH); IR (n):
3220 (NH), 1635 (CO) cmꢃ1. Anal. Calc. (Found) for
C13H9Br4NO2: C, 29.41% (29.65%); H, 1.71% (1.82%); N,
2.64% (2.60%).
CH2), 7.35 (d, 1H, J ¼ 2.3 Hz, H-600), 7.62 (d, 1H,
J ¼ 2.3 Hz, H-400), 9.50 (s, 1H, exchangeable with D2O,
OH), 13.43 (s, 1H, exchangeable with D2O, NH); IR (n):
3486 (OH), 3202 (NH), 1648 (CO) cmꢃ1. Anal. Calc.
(Found) for C12H6Br5NO2: C, 24.19% (23.93%); H,
1.02% (0.96%); N, 2.35% (2.15%).
4.1.7. 5,7-Dibromo-1-benzofuran-2(3H )-one 11
A mixture of 6.20 g (20 mmol) of (3,5-dibromo-2-hydrox-
yphenyl)acetic acid 6 and 0.38 g (2 mmol) of p-toluenesul-
fonic acid monohydrate in 100 ml of toluene was refluxed
under a Dean-Stark trap until the evolution of water ceased
(12 h). The cooled solution was chromatographed over silica
gel (100 g) and activated at 200 ꢀC for 24 h eluting with anhy-
drous toluene (200 ml).
4.1.5. 2-(3,5-Dibromo-2-methoxyphenyl)-1-(3,4,5-tribromo-
1H-pyrrol-2-yl)ethanone 10
To a solution of 9 (1.06 g, 2 mmol, in 150 ml of acetoni-
trile) heated at 60 ꢀC, a solution of N-bromosuccinimide
(0.36 g, 2 mmol) in 10 ml of acetonitrile was added dropwise
under stirring.
After addition was complete the reaction mixture was
stirred at 60 ꢀC for an additional 2 h, then left at room temper-
ature overnight. The white needles of 10 (0.83 g, 68% yield)
so obtained were filtered out and the solution was concentrated
under reduced pressure. The residue was partitioned between
water (100 ml) and diethyl ether (100 ml) and extracted twice
with diethyl ether (50 ml). The combined extracts were
washed with water, dried over anhydrous sodium sulfate and
evaporated to dryness. The crude product was crystallized
from acetone to give a further 0.18 g of 10 (overall yield
The solution of unstable compound 11 so obtained was
used directly for the next reaction as described below.
4.1.8. 2-(3,5-Dibromo-2-hydroxyphenyl)-1-(1H-pyrrol-2-
yl)ethanone 12
To a stirred suspension of pyrrylmagnesium bromide
(20 mmol in 100 ml of anhydrous diethyl ether freshly dis-
tilled) the previously obtained toluenic solution of 11 was
added, slowly under nitrogen atmosphere. The reaction mix-
ture was heated at reflux for 0.5 h then quenched with sulfuric
acid 5% (50 ml). After stirring for 1 h, the organic solution
was separated and the aqueous layer was extracted with di-
ethyl ether (2 ꢂ 50 ml). The combined extracts were washed
with water, dried over anhydrous sodium sulfate and evapo-
rated to dryness. The crude product, purified by
1
83%) as white needles, m.p. 216 ꢀC. H NMR (d): 3.65 (s,
3H, CH3), 4.33 (s, 2H, CH2), 7.53 (d, 1H, J ¼ 2.4 Hz, H-600),
7.79 (d, 1H, J ¼ 2.4 Hz, H-400), 13.51 (s, 1H, exchangeable
with D2O, NH); IR (n): 3200 (NH), 1649 (CO) cmꢃ1. Anal.
Calc. (Found) for C13H8Br5NO2: C, 25.61% (25.80%); H,
1.32% (1.38%); N, 2.30% (2.45%).

1444
M.V. Raimondi et al. / European Journal of Medicinal Chemistry 41 (2006) 1439e1445
chromatography, gave 12 (2.0 g, 28% yield) as white needles
from acetonitrile, m.p. 160 ꢀC. 1H NMR (d): 4.17 (s, 2H,
CH2), 6.22 (m, 1H, H-40), 7.13 (m, 2H, H-30 and H-50), 7.92
(d, 1H, J ¼ 2.4 Hz, H-400), 8.30 (d, 1H, J ¼ 2.4 Hz, H-600),
9.56 (s, 1H, exchangeable with D2O, OH), 11.67 (s, 1H, ex-
changeable with D2O, NH); IR (n): 3314 (NH), 1622 (CO)
cmꢃ1. Anal. Calc. (Found) for C12H9Br2NO2: C, 40.15%
(40.35%); H, 2.53% (2.60%); N, 3.90% (3.71%).
acetonitrile, m.p. 180 ꢀC. 1H NMR (d): 3.66 (s, 3H,
CH3), 8.04 (d, 1H, J ¼ 2.4 Hz, H-600), 8.35 (d, 1H,
J ¼ 2.4 Hz, H-400), 14.20 (s, 1H, exchangeable with D2O,
NH); IR (n): 3208 (NH), 1680 and 1624 (CO) cmꢃ1
.
Anal. Calc. (Found) for C13H6Br5NO3: C, 25.03%
(25.32%), H, 0.97% (1.09%), N, 2.25% (2.11%).
4.1.12. 1-(3,5-Dibromo-2-hydroxyphenyl)-2-(4,5-dibromo-
1H-pyrrol-2-yl)ethane-1,2-dione 5a and 1-(3,5-dibromo-2-
hydroxyphenyl)-2-(3,4,5-tribromo-1H-pyrrol-2-yl)ethane-
1,2-dione 5b
4.1.9. 2-(3,5-Dibromo-2-hydroxyphenyl)-1-(4,5-dibromo-
1H-pyrrol-2-yl)ethanone 4a from 12
A solution of 0.71 g (4 mmol) of N-bromosuccinimide in
10 ml of acetonitrile was added dropwise to a stirred solu-
tion of 0.72 g (2 mmol) of 12 in 20 ml of acetonitrile. After
12 h, the reaction mixture was evaporated. The residue was
added to 20 ml of water, then extracted with diethyl ether
(3 ꢂ 30 ml). The combined extracts were washed with water,
dried over anhydrous sodium sulfate, evaporated to dryness
and then crystallized to give 4a (0.38 g, 75% yield).
To a solution of 0.27 g (0.5 mmol) of 13 or 0.31 g
(0.5 mmol) of 14 in 10 ml of dry dichloromethane 0.65 g
(5 mmol) of anhydrous aluminium chloride was added under
stirring. After 24 h the mixture was cautiously decomposed
with iceesulfuric acid 5% (30 ml), then 50 ml of diethyl ether
was added. The mixture was vigorously stirred until the solid
residue was entirely dissolved. The organic layer was sepa-
rated and the aqueous phase extracted with diethyl ether
(2 ꢂ 30 ml). The combined extracts were washed with water
until neutrality, dried over anhydrous sodium sulfate and evap-
orated to give
4.1.10.
2-(3,5-Dibromo-2-hydroxyphenyl)-1-(3,4,5-tri-
bromo-1H-pyrrol-2-yl)ethanone 4b from 4a
0.089 g (0.5 mmol) of solid N-bromosuccinimide was
added to a stirred solution of 0.26 g (0.5 mmol) of 4a in
10 ml of acetonitrile. After 48 h, the mixture was evaporated.
The residue was partitioned between water (20 ml) and diethyl
ether (20 ml) and, subsequently, extracted twice with diethyl
ether (30 ml). The combined extracts were washed with water,
dried over anhydrous sodium sulfate, and evaporated to dry-
ness. The crude product was chromatographed over silica
gel, using an 8/2 (v/v) mixture of cyclohexaneeethyl acetate
as the eluent to give 4b (0.14 g, 46% yield).
(a) 5a (0.23 g, 85% yield) as yellow needles from ethanol,
m.p. 211 ꢀC. 1H NMR (CDCl3) (d): 7.03 (d, 1H,
J ¼ 2.5 Hz, H-40, s after exchange with D2O), 7.88 (d,
1H, J ¼ 2.4 Hz, H-600), 7.95 (d, 1H, J ¼ 2.4 Hz, H-400),
9.80 (br s, 1H, exchangeable with D2O, OH), 11.92 (s,
1H, exchangeable with D2O, NH) [14]; IR (n): 3232
(NH), 1621 (CO) cmꢃ1. Anal. Calc. (Found) for
C12H5Br4NO3: C, 27.15% (27.12%); H, 0.95% (1.06%);
N, 2.64% (2.77%).
(b) 5b (0.28 g, 92% yield) as yellow crystals from acetonee
petroleum ether, m.p. 176 ꢀC. 1H NMR (CDCl3) (d):
7.58 (d, 1H, J ¼ 2.4 Hz, H-600), 7.96 (d, 1H, J ¼ 2.4 Hz,
H-400), 10.43 (br s, 1H, exchangeable with D2O, OH),
14.66 (s, 1H, exchangeable with D2O, NH) [15]; IR (n):
3208 (NH), 1625 (CO) cmꢃ1. Anal. Calc. (Found) for
C12H4Br5NO3: C, 23.64% (23.92%); H, 0.66% (0.81%);
N, 2.30% (2.59%).
4.1.11. General procedure for the oxidation of 9 and 10
with selenium dioxide
A mixture of 9 (0.32 g, 0.6 mmol) or 10 (0.37 g, 0.6 mmol)
in 30 ml of 1,4-dioxane and selenium dioxide (1.0 g, 9 mmol)
in 20 ml of water was refluxed for 96 h. The resulting solid
was filtered out and the solution, diluted with 200 ml of water
and saturated with sodium chloride, was extracted with diethyl
ether (3 ꢂ 50 ml). The combined organic extracts were washed
with water, dried with sodium sulfate, and evaporated. The re-
mainder was chromatographed over silica gel using as eluents
the following, respectively,
Acknowledgements
`
Financial support from Fondi di Ateneo Universita degli
Studi di Palermo, Italy, is gratefully acknowledged.
(a) 85/15 cyclohexaneeethyl acetate to give 1-(3,5-dibromo-
2-methoxyphenyl)-2-(4,5-dibromo-1H-pyrrol-2-yl)ethane-
1,2-dione 13 (0.14 g, 43% yield) as pale yellow crystals
from ethanol, m.p. 124 ꢀC. 1H NMR (d): 3.64 (s, 3H,
CH3), 7.16 (s, 1H, H-30), 7.92 (d, 1H, J ¼ 2.2 Hz, H-600),
8.30 (d, 1H, J ¼ 2.2 Hz, H-400), 13.71 (s, 1H, exchangeable
with D2O, NH); IR (n): 3244 (NH), 1688 and 1619 (CO)
cmꢃ1. Anal. Calc. (Found) for C13H7Br4NO3: C, 28.66%
(28.71%); H, 1.30% (1.21%); N, 2.57% (2.44%).
References
[1] S. Petruso, S. Bonanno, S. Caronna, M. Ciofalo, B. Maggio, D. Schillaci,
J. Heterocycl. Chem. 31 (1994) 941.
[2] D. Schillaci, S. Petruso, V. Sciortino, Int. J. Antimicrob. Agents 25
(2005) 338e340.
[3] R.J. Andersen, M.S. Wolfe, D.J. Faulkner, Mar. Biol. 27 (1974) 281.
[4] H. Laatsch, B. Rennemberg, U. Hanefeld, M. Kellner, H. Pudleiner,
G. Hamprecht, H.P. Kraemer, H. Anke, Chem. Pharm. Bull. 43 (4)
(1995) 537e546.
(b) 8/2 cyclohexaneeethyl acetate to give 1-(3,5-dibromo-2-
methoxyphenyl)-2-(3,4,5-tribromo-1H-pyrrol-2-yl)ethane-
1,2-dione 14 (0.27 g, 73% yield) as white crystals from

M.V. Raimondi et al. / European Journal of Medicinal Chemistry 41 (2006) 1439e1445
1445
´
[5] M.C. Carren˜o, J.L. Garcıa Ruano, G. Sanz, M.A. Toledo, A. Urbano,
J. Org. Chem. 60 (1995) 5328e5331.
[11] S.J. Projan, P.J. Youngman, Curr. Opin. Microbiol. 5 (2002) 463e465.
[12] L.H. Lennette, E.H. Spaulding, P. Truant, Manual of Clinical Microbiology,
American Society for Microbiology, Washington DC, 1974 (Chapter 42).
[13] H. Kindl, Eur. J. Biochem. 7 (1969) 340e347.
[6] J.A. Findlay, D. Kwan, Can. J. Chem. 51 (1973) 3299.
[7] S. Petruso, S. Caronna, V. Sprio, J. Heterocycl. Chem. 27 (1990) 1209.
[8] Y. Lambert, J.P. Daris, I. Monkovic, Can. J. Chem. 55 (1977) 2523.
[9] W.S. Johnson, V.J. Bauer, J.L. Margrave, M.A. Frisch, L.H. Dreger,
W.N. Hubbard, J. Am. Chem. Soc. 83 (1961) 606e614.
[14] Only very broad signals for the different protons have been shown in
DMSO-d6.
[15] The 1H NMR spectrum in DMSO-d6 seems to suggest the co-existence,
in this solvent, of two potential tautomeric forms of comparable stability.
[10] T. Ajello, V. Sprio, Gazz. Chim. Ital. 89 (1959) 2526.