3-(2-Carbamoylvinyl)-4,5-dimethylpyrrole-2-carboxylic acids as ligands at the NMDA glycine-binding site: A study on the 2-carbamoylvinyl chain modification

Article abstract of DOI:10.1016/S0014-827X(98)00110-4

Twenty 4,5-dimethylpyrrole-2-carboxylic acids (5a-t) with different 2-carbamoylvinyl chains in position 3 were prepared to further investigate the relationships between structure and in vitro affinity for the strychnine-insensitive glycine-binding site. N

Full text of DOI:10.1016/S0014-827X(98)00110-4

Il Farmaco 54 (1999) 101–111
3-(2-Carbamoylvinyl)-4,5-dimethylpyrrole-2-carboxylic acids as
ligands at the NMDA glycine-binding site: a study on the
2-carbamoylvinyl chain modification
Cesarino Balsamini a, Annalida Bedini a, Giuseppe Diamantini a, Gilberto Spadoni a,
Giorgio Tarzia a,*, Andrea Tontini a, Romano Di Fabio b, Daniele Donati b
a Istituto di Chimica Farmaceutica e Tossicologica, Uni6ersita` degli Studi di Urbino, Piazza Rinascimento 6, I-61029 Urbino, Italy
b GlaxoWellcome S.p.A., 6ia Fleming 4, I-37100 Verona, Italy
Received 29 July 1998; accepted 7 December 1998
Abstract
Twenty 4,5-dimethylpyrrole-2-carboxylic acids (5a–t) with different 2-carbamoylvinyl chains in position 3 were prepared to
further investigate the relationships between structure and in vitro affinity for the strychnine-insensitive glycine-binding site. None
of these compounds was superior to (E)-3-(N-phenyl-2-carbamoylvinyl)-4,5-dimethylpyrrole-2-carboxylic acid III (pKi=6.70),
which was taken as a reference standard, but overall the results obtained indicate that the N-phenyl-2-carbamoylvinyl substituent
of III may be replaced with the N-(1-adamantyl)-2-carbamoylvinyl group as in 5h (pKi=6.20) without considerable loss of
affinity. This finding adds to previous knowledge. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: 3-(2-Carbamoylvinyl)-4,5-dimethylpyrrole-2-carboxylic acid; Strychnine-insensitive glycine site; NMDA receptor
bond donor, (b) a Coulombic interaction of an ioniz-
able acidic group positioned in alpha to the NH, (c) a
size-limited hydrophobic pocket, and (d) a hydrogen
bond acceptor linked to a lipophilic chain. Several
compounds can be fitted into this model and among
them the glycine antagonist GV150526 [20] and a series
of 4,5-disubstituted-3-(2-carbamoylvinyl)pyrrole-2-car-
boxylic acids [21]. As to point (d), it is worth noticing
that compounds suitably modified in the lipophilic
chain led, in the case of GV150526, to products with
better affinity than the parent molecule [20].
We recently reported the synthesis and preliminary
biological evaluation of a series of (E)-3-(N-phenyl-2-
carbamoylvinyl)pyrrole-2-carboxylic acid derivatives,
bearing various substituents at the 4- and 5-positions
[21]. These compounds were studied in vitro as antago-
nists at the strychnine-insensitive glycine-binding site of
the NMDA receptor complex, showing good potency
and selectivity. The most active compounds of the
series i.e. (E)-4,5-dibromo-3-(N-phenyl-2-carbamoyl-
vinyl)pyrrole-2-carboxylic acid (I) (pKi=7.95) and
its 4-bromo-5-methyl (II) (pKi=7.24) and 4,5-di-
methyl (III) (pKi=6.70) analogs (Fig. 1), blocked
1. Introduction
Overstimulation
of
the N-methyl-D-aspartate
(NMDA) receptor by excessive release of endogenous
L
-glutamate causes abnormal influx of Ca2+ into the
post-synaptic neurons, ultimately leading to cell death
[1]. Excessive glutamatergic activity has been associated
with many ischemia- and hypoxia-related disorders
such as stroke, hypoglycemia and traumatic head and
spinal cord injuries [2–6] and may be involved in some
neurodegenerative diseases of the CNS, including Hunt-
ington’s chorea and Alzheimer’s dementia [7–10].
Among the several binding sites on the NMDA recep-
tor complex, the strychnine-insensitive glycine-binding
site plays a key role in the activation of the NMDA
receptor [11–14] and therefore, during the last decade,
many glycine antagonists have been prepared because
of their therapeutic potential [15–19]. These com-
pounds led to a model [15] of the glycine-binding site,
the essential features of which are: (a) a NH hydrogen-
* Corresponding author. Fax: +39-0722-2737.
E-mail address: gat@chim.uniurb.it (G. Tarzia)
0014-827X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0014-827X(98)00110-4

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C. Balsamini et al. / Il Farmaco 54 (1999) 101–111
investigation of the effects caused by aromatic sub-
stituents was carried out according to the Topliss deci-
sional scheme [22] (5b,c,e,f,o,p) and subsequently, after
ascertaining the ineffectiveness of the approach, by
selecting additional compounds (5a,d,g,j,k,l,n,q,r) so that
the resulting set (5a–g,j–l,n–r) would range over five out
of the eight octants of the 3D space spanned by the scaled
first three principal properties (*t1, *t2 and *t3)1 [23].
Non-aromatic substitution of the carbamoyl nitrogen was
also considered (5h,i,m) as well as major modifications
such as the retro compound 5s and the des-carbamoyl
derivative 5t.
Fig. 1. Structures of analogs I–III.
2. Chemistry
NMDA-induced convulsions in mice when tested in vivo
[21]. These results indicated that the 4,5-disubstituted
pyrrole-2-carboxylates represent novel templates for the
design of glycine antagonists.
The synthesis of intermediate methyl 4,5-dimethyl-
pyrrole-2-carboxylates (4a–q) was achieved as in Scheme
1. Wittig reaction of methyl 4,5-dimethyl-3-formyl-
pyrrole-2-carboxylate (1) [24] with (t-butoxycarbonyl-
methyl)-triphenylphosphonium bromide gave the t-butyl
ester derivative 2, which afforded the methyl (E)-3-(2-
carboxyethenyl)-4,5-dimethylpyrrole-2-carboxylate (3)
via selective HCOOH-mediated hydrolysis. Compounds
4a–q were obtained by reaction of 3 with 2,2%-dipyridyl
disulfide/triphenylphosphine and subsequent condensa-
tion with the suitable amine (N-Boc-1,4-diaminobenzene
and N-Boc-1,3-diaminobenzene [25] for 4p and 4q,
respectively). Hydrolysis of the intermediate esters 4a–n
carried out in basic media gave acids 5a–n.
We had not explored however, the effects of the
structural modification of the N-phenyl-2-carbamoyl-
vinyl side chain on the affinity of the compounds, and
to investigate this point we decided to synthesize a series
of 4,5-disubstituted pyrrole-2-carboxylic acids bearing
different chains in position 3. In the present study,
(E)-3-(N-phenyl-2-carbamoylvinyl)-4,5-dimethyl-pyr-
role-2-carboxylic acid (III) was chosen as a template,
instead of the more active 4,5-dibromo derivative (I),
because of its easier synthesis and of the putative
equivalence of the structural information obtainable by
modification of these two related compounds. Initially,
Product 5o was obtained as sodium salt after hydro-
lysis with NaOH in aqueous MeOH. The p- and m-
1 *t1 is mainly related to bulk and hydrophobicity; *t2 is related to
sm and sp; *t3 is related to hydrophobicity and shape.
Scheme 1.

C. Balsamini et al. / Il Farmaco 54 (1999) 101–111
103
Scheme 2.
Scheme 3.
Scheme 4.
Scheme 5.
aminophenyl-substituted compounds 5p,q were obtained
from 4p,q, which were first de-protected to 6,7 (trifl-
uoroacetic acid) and then hydrolyzed with NaOH to their
sodium salts (Scheme 2).
The ureido derivative 5r was prepared by reaction of
6 with potassium isocyanate and subsequent hydrolysis
of the ester 8 with LiOH (Scheme 3).
The methyl (E)-3-[(3-isoquinolyl)-2-vinyl)]-4,5-dime-
thylpyrrole-2-carboxylate (14) was prepared by Wittig
reaction between 1 and 3-isoquinolylmethyl-triphe-
nylphosphonium bromide (13) in the presence of DBU.
Hydrolysis of 14 afforded the lithium salt of the relative
acid 5t (Scheme 5).
(E)-3-(cinnamoylamino)-4,5-dimethylpyrrole-2-carbo-
xylic acid (5s) was prepared as shown in Scheme 4. The
unknown 3-aminopyrrole derivative 11 was prepared by
cyclization of the enamine 10 obtained by the condensa-
tion of glycine ethyl ester hydrochloride with 2-methyl-3-
oxobutyronitrile (9) [26]. The condensation of 3-amino-
pyrrole (11) with cinnamic acid in the presence of
2,2%-dipyridyl disulfide/triphenylphosphine gave 12
which afforded 5s upon basic hydrolysis.
3. Pharmacology
The affinity of 5a–t for the glycine-binding site asso-
ciated with the NMDA receptor channel complex was
determined by the inhibition they induced of the bin-
ding of [3H]glycine to crude synaptic membranes pre-
pared from adult rat cerebral cortex (Section 5 and Table
1).

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C. Balsamini et al. / Il Farmaco 54 (1999) 101–111
4. Results and discussion
analyses were performed on a Carlo Erba analyzer
and, when reported (C, H, N), were within 90.4
The several aromatic substituents that were used to
modify the 3-(N-phenyl-2-carbamoylvinyl) moiety of
the lead compound III (pKi=6.70) all failed to give
from the theoretical value.
5.1.1. Methyl (E)-3-[2-(t-butoxycarbonyl)6inyl]-4,5-
dimethylpyrrole-2-carboxylate (2)
compounds endowed with
a higher affinity, the
highest pKi values being those relative to 5r (pKi=
6.4), 5p (pKi=6.32), 5k (pKi=6.25) and 5g (pKi=
6.23). This is somewhat surprising in view of what
had been reported for the analogues of GV 150526
[20], for which an increase in pKi of 0.4 units is ob-
tained when the phenyl ring is substituted with a
para-amino group. The reversal of the order of the
structural elements in the chain (5s), or its lengthen-
ing (5n) resulted in reduction of affinity, whereas re-
moval of the carboxamido group and introduction of
a heterocyclic moiety (5t) yielded a compound retain-
ing a modest binding affinity. The affinity of the
adamantyl derivative 5h is essentially the same as
those of 5g,k, indicating that an N-aryl group is not
an absolute requirement for efficient binding and that
shape and bulk effects are probably as relevant as the
electronic ones, as is shown by the pKi of 5k versus
5l,j and of 5h versus 5i,m. This observation adds to
previous knowledge of the structure–activity relation-
ships in this class of compounds.
DBU (0.225 ml, 1.5 mmol) was added to a suspen-
sion of (t-butoxycarbonylmethyl)triphenylphosphon-
ium bromide (690 mg, 1.5 mmol) in 5 ml of CH3CN
and the resulting mixture stirred for 15 min at room
temperature (r.t.); after this time 181 mg (1 mmol) of
1 [24] were added and the resulting solution was
refluxed for 3 h. The solvent was evaporated to dry-
ness and the residue purified by flash chromatography
on silica gel (cyclohexane–EtOAc 7:3) and crystalliza-
tion. 78% yield; m.p. 171°C (MeOH). 1H NMR
(CDCl3) l: 8.85 (s, 1H), 8.23 (d, J=16.5 Hz, 1H),
6.24 (d, J=16.5 Hz, 1H), 3.88 (s, 3H), 2.21 (s, 3H),
2.13 (s, 3H), 1.53 (s, 9H). IR (CDCl3): 1688, 1632
cm−1. MS (FAB): m/z 280 (M+H)+.
5.1.2. (E)-3-[2-(Methoxycarbonyl)-4,5-dimethyl-1H-
pyrrol-3-yl]prop-2-enoic acid (3)
A 280 mg (1 mmol) sample of 2 was suspended in
12 ml of HCOOH and stirred at r.t. for 2 h.
Table 1
The results of this study confirm our previous re-
port that (E)-3-(N-phenyl-2-carbamoylvinyl)-4,5-disub-
stitu-
Affinities at the glycine-binding site of compounds 5a–ta
ted pyrrole-2-carboxylic acids are a class of ligands of
the glycine-binding site of the NMDA receptor, and
indicate that these compounds deviate, to some ex-
tent, from the structure–activity relationships estab-
lished in the indole series [20,27–30].
5. Experimental
5.1. Chemistry
Solvents and reagents were of the highest commer-
cial grade and were used without additional purifica-
tion. Melting points were determined on a Bu¨chi
SMP-510 capillary melting point apparatus, and are
uncorrected. 1H NMR spectra were recorded on
Varian Unity 400, Varian Unity plus 500, Varian
VXRS 5000 or Varian EM 60 spectrometer using
TMS as internal standard; chemical shifts are re-
ported in ppm (l scale). EI-MS spectra (70 eV) were
taken on
a Fisons-Trio 1000 spectrometer (only
molecular ions M+ are given); FAB-MS were ob-
tained on a VG-4 triple quadrupole on a 4-nitroben-
zoic acid matrix and only (M+H)+ are given. IR
spectra were recorded on a Bruker IFS 48 spectrome-
ter; absorbances are reported in w (cm−1). Elemental
a Inhibition of binding of [3H]Gly (Refs. [28,29]).

C. Balsamini et al. / Il Farmaco 54 (1999) 101–111
105
HCOOH was evaporated under reduced pressure and
the crude material purified by crystallization. 88%
yield; m.p. 260°C (dec.) (MeOH). H NMR (DMSO-
d6) l: 12.2 (br s, 1H), 11.8 (s, 1H), 8.21 (d, J=16.4
Hz, 1H), 6.13 (d, J=16.4 Hz, 1H), 3.76 (s, 3H), 2.13
(s, 3H), 2.04 (s, 3H). IR (Nujol): 3298, 1668, 1612
cm−1. MS (FAB): m/z 224 (M+H)+.
NMR (acetone-d6, 60 MHz) l: 11.6 (br s, 1H), 9.6
(br s, 1H), 8.6 (s, 1H), 8.3 (s, 1H), 7.9–7.3 (m, 4H),
6.6 (d, 1H), 3.8 (s, 3H), 2.2 (s, 3H), 2.1 (s, 3H). IR
(Nujol): 3302, 1672, 1664, 1612 cm−1. MS (EI): m/z
366 (M+).
1
5.1.3.5. Methyl (E)-3-[N-(4-chlorophenyl)-2-carbamoyl-
6inyl]-4,5-dimethylpyrrole-2-carboxylate (4e). 70% yield;
1
m.p. 275°C (MeOH). H NMR (DMSO-d6) l: 11.76
5.1.3. General procedure for the synthesis of methyl
(E)-3-(N-substituted-2-carbamoyl6inyl)-4,5-dimethyl-
pyrrole-2-carboxylates (4a–q)
(s, 1H), 10.21 (s, 1H), 8.24 (d, J=16.4 Hz, 1H), 7.71
(d, 2H), 7.36 (d, 2H), 6.59 (d, J=16.4 Hz, 1H), 3.78
(s, 3H), 2.15 (s, 3H), 2.12 (s, 3H). IR (Nujol): 3304,
1672, 1626 cm−1. MS (FAB): m/z 333 (M+H)+.
Triphenylphosphine (524 mg, 2 mmol) and 2,2%-
dipyridyldisulfide (440 mg, 2 mmol) were added to a
solution of 223 mg (1 mmol) of 3 dissolved in 20 ml
of anhydrous THF under N2. The resulting mixture
was stirred at r.t. for 2 h, after which 1.2–2.4 mmol
of the suitable amine were added and stirring contin-
ued under reflux (at r.t. for 4f–i and 4m–o) for 16–
60 h (4 days for 4c). In the case of the isopropyl
derivative a solution obtained from isopropylamine
hydrochloride in CH2Cl2 and a stoichiometric amount
of DBU, was added to the reaction mixture.
5.1.3.6. Methyl (E) - 3 - [N - (4-methoxyphenyl) - 2 - carba-
moyl6inyl]-4,5-dimethylpyrrole-2-carboxylate(4f). 77%
yield; m.p. 276°C (Et2O). 1H NMR (DMSO-d6) l:
11.71 (br s, 1H), 9.94 (s, 1H), 8.17 (d, J=16.2 Hz,
1H), 7.59 (d, 2H), 6.88 (d, 2H), 6.57 (d, J=16.2 Hz,
1H), 3.77 (s, 3H), 3.71 (s, 3H), 2.15 (s, 3H), 2.11 (s,
3H). IR (Nujol): 3302, 1674, 1651, 1616 cm−1. MS
(FAB): m/z 329 (M+H)+.
The solvent was evaporated to dryness and the
residue dissolved in diethyl ether. The desired product
crystallized spontaneously.
5.1.3.7. Methyl (E)-3-[N-(4-methylphenyl)-2-carbamoyl-
6inyl]-4,5-dimethylpyrrole-2-carboxylate (4g). 60% yield;
m.p. 268–70°C (Et2O). H NMR (DMSO-d6) l: 11.72
1
(s, 1H), 9.97 (s, 1H), 8.19 (d, J=16.4 Hz, 1H), 7.55
(d, 2H), 7.10 (d, 2H), 6.58 (d, J=16.4 Hz, 1H), 3.77
(s, 3H), 2.24 (s, 3H), 2.15 (s, 3H), 2.11 (s, 3H). IR
(Nujol): 3304, 1676, 1657, 1618 cm−1. MS (FAB):
m/z 313 (M+H)+.
5.1.3.1. Methyl (E)-3-[N-(4-fluorophenyl)-2-carbamoyl-
6inyl]-4,5-dimethylpyrrole-2-carboxylate (4a). 93% yield;
m.p. 267–8°C (MeOH). H NMR (DMSO-d6) l: 11.8
(br s, 1H), 10.2 (br s, 1H), 8.23 (d, J=16.1 Hz, 1H),
7.71 (dd, 2H), 7.17 (t, 2H), 6.59 (d, J=16.1 Hz, 1H),
3.8 (s, 3H), 2.15 (ds, 6H). IR (Nujol): 3294, 1672,
1661, 1622 cm−1. MS (EI): m/z 316 (M+).
1
5.1.3.8. Methyl (E)-3-[N-(1-adamantyl)-2-carbamoyl-
6inyl]-4,5-dimethylpyrrole-2-carboxylate (4h). 90% yield;
m.p. 218°C (CHCl3–hexane). 1H NMR (DMSO-d6)
l: 11.59 (s, 1H), 7.95 (d, J=15.9 Hz, 1H), 7.50 (s,
1H), 6.40 (d, J=15.9 Hz, 1H), 3.74 (s, 3H), 2.12 (s,
3H), 2.04 (s, 3H), 2.01–1.62 (m, 15H). IR (Nujol):
3306, 1672, 1655, 1616 cm−1. MS (EI): m/z 356
(M+).
5.1.3.2. Methyl (E)-3-[N-(3-methylphenyl)-2-carbamoyl-
6inyl]-4,5-dimethylpyrrole-2-carboxylate (4b). 77% yield;
1
m.p. 239°C (Et2O). H NMR (DMSO-d6) l: 11.7 (s,
1H), 10.0 (s, 1H), 8.2 (d, J=16.1 Hz, 1H), 7.5 (s,
1H), 7.45 (m, 1H), 7.2 (t, 1H), 6.75 (d, 1H), 6.6 (d,
J=16.1 Hz, 1H), 3.8 (s, 3H), 2.3 (s, 3H), 2.2 (s, 3H),
2.1 (s, 3H). IR (Nujol): 3292, 1672, 1655, 1616 cm−1
.
MS (EI): m/z 312 (M+).
5.1.3.9. Methyl (E)-3-(N-isopropyl-2-carbamoyl6inyl)-
4,5-dimethylpyrrole-2-carboxylate (4i). 83% yield; m.p.
249–50°C (dec.) (Et2O). 1H NMR (DMSO-d6) l:
11.62 (s, 1H), 8.01 (d, J=16 Hz, 1H), 7.86 (d, 1H),
6.36 (d, J=16 Hz, 1H), 3.92 (m, 1H), 3.75 (s, 3H),
2.13 (s, 3H), 2.05 (s, 3H), 1.08 (d, 6H). IR (Nujol):
3302, 1668, 1651 cm−1. MS (EI): m/z 264 (M+).
5.1.3.3. Methyl (E)-3-[N-(3-chlorophenyl)-2-carbamoyl-
6inyl]-4,5-dimethylpyrrole-2-carboxylate (4c). 79% yield;
1
m.p. 242°C (MeOH). H NMR (DMSO-d6) l: 11.76
(br s, 1H), 10.25 (s, 1H), 8.24 (d, J=16 Hz, 1H),
7.95 (t, 1H), 7.47 (dd, 1H), 7.33 (t, 1H), 7.08 (dd,
1H), 6.58 (d, J=16 Hz, 1H), 3.78 (s, 3H), 2.15 (s,
3H), 2.12 (s, 3H). IR (Nujol): 3304, 1680, 1622 cm−1
.
5.1.3.10. Methyl (E)-3-[N-(h-naphthyl)-2-carbamoyl-
6inyl]-4,5-dimethylpyrrole-2-carboxylate (4j). 69% yield;
MS (FAB): m/z 333 (M+H)+.
1
m.p. 275–6°C (Et2O). H NMR (DMSO-d6) l: 11.75
5.1.3.4. Methyl (E)-3-[N-(3-trifluoromethylphenyl)-2-
carbamoyl6inyl]-4,5-dimethylpyrrole-2-carboxylate (4d).
36% yield; m.p. 214°C (MeOH–Et2O–hexane). 1H
(s, 1H), 10.06 (s, 1H), 8.31 (d, J=16.5 Hz, 1H), 8.17
(d, 1H), 7.96–7.93 (dd, 2H), 7.76 (d, 1H), 7.61–7.51
(m, 3H), 6.93 (d, J=16.5 Hz, 1H), 3.81 (s,

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C. Balsamini et al. / Il Farmaco 54 (1999) 101–111
3H), 2.20 (s, 6H). IR (Nujol): 3314, 3271, 1676, 1651,
5.1.3.17. Methyl (E)-3-[N-(3-Boc-aminophenyl)-2-car-
bamoyl6inyl]-4,5-dimethylpyrrole-2-carboxylate (4q).
1616 cm−1. MS (FAB): m/z 349 (M+H)+.
1
94% yield; m.p. 130°C (Et2O). H NMR (DMSO-d6) l:
11.73 (s, 1H), 10.03 (s, 1H), 9.37 (s, 1H), 8.23 (d, J=16
Hz, 1H), 7.86 (m, 1H), 7.49 (m, 1H), 7.17 (t, 1H), 7.02
(m, 1H), 6.65 (d, J=16 Hz, 1H), 3.81 (s, 3H), 2.18 (s,
3H), 2.14 (s, 3H), 1.49 (s, 9H). IR (Nujol): 3296, 1717,
1678, 1610 cm−1. MS (FAB): m/z 414 (M+H)+.
5.1.3.11. Methyl (E)-3-[N-(i-naphthyl)-2-carbamoyl-
6inyl]-4,5-dimethylpyrrole-2-carboxylate (4k). 78% yield;
m.p. 262°C (Et2O). H NMR (DMSO-d6) l: 11.75 (bs,
1H), 10.28 (s, 1H), 8.43 (d, 1H), 8.28 (d, J=16.4 Hz,
1H), 7.86 (d, 1H), 7.81 (dd, 2H), 7.64 (dd, 1H), 7.48–
7.36 (m, 2H), 6.67 (d, J=16.4 Hz, 1H), 3.79 (s, 3H),
2.16 (s, 3H), 2.15 (s, 3H). IR (Nujol): 3312, 1676, 1655,
1616 cm−1. MS (EI): m/z 348 (M+).
1
5.1.4. Methyl (E)-3-[N-(4-aminophenyl)-2-carbamoyl-
6inyl]-4,5-dimethylpyrrole-2-carboxylate (6) and methyl
(E)-3-[N-(3-aminophenyl)-2-carbamoyl6inyl]-4,5-dime-
thylpyrrole-2-carboxylate (7)
5.1.3.12. Methyl (E)-3-[N-(3-phenoxyphenyl)-2-carba-
moyl6inyl]-4,5-dimethylpyrrole-2-carboxylate (4l). 84%
A total of 0.8 ml of CF3COOH was added to a
suspension of 413 mg (1 mmol) of 4p or 4q in 11 ml of
CH2Cl2. The mixture was stirred at r.t. for 24 h, after
which the solvent was evaporated and the residue
treated with EtOAc. The organic phase was washed
once with 2 N Na2CO3 solution, twice with water and
then dried (Na2SO4). The solvent was evaporated and
the crude material was purified by crystallization.
Compound 6: quantitative yield; m.p. 242°C (dec.)
1
yield; m.p. 194°C (MeOH). H NMR (acetone-d6, 60
MHz) l: 10.6 (br s, 1H), 9.3 (br s, 1H), 8.4 (d, J=16
Hz, 1H), 7.6–6.9 (m, 9H), 6.6 (d, J=16 Hz, 1H), 3.8 (s,
3H), 2.2 (s, 3H), 2.1 (s, 3H). IR (Nujol): 3297, 1669,
1590 cm−1. MS (EI): m/z 390 (M+).
5.1.3.13. Methyl(E)-3-(N-cyclohexyl-2-carbamoyl6inyl)-
4,5-dimethylpyrrole-2-carboxylate (4m). 86% yield; m.p.
1
(MeOH). H NMR (DMSO-d6) l: 11.7 (s, 1H), 9.7 (s,
1
1H), 8.1 (d, J=16 Hz, 1H), 7.3 (d, 2H), 6.6 (d, J=16
272°C (Et2O). H NMR (DMSO-d6) l: 11.61 (s, 1H),
Hz, 1H), 6.5 (d, 2H), 4.9 (s, 2H), 3.8 (s, 3H), 2.2 (s,
8.01 (d, J=16 Hz, 1H), 7.85 (d, 1H), 6.38 (d, J=16
Hz, 1H), 3.75 (s, 3H), 3.60 (m, 1H), 2.13 (s, 3H), 2.05
(s, 3H), 1.79–1.1 (m, 10H). IR (Nujol): 3312, 1672,
1651, 1616 cm−1. MS (FAB): m/z 305 (M+H)+.
3H), 2.1 (s, 3H). IR (Nujol): 3290, 1664, 1616 cm−1
.
MS (EI): m/z 313 (M+).
1
Compound 7: 93% yield; m.p. 238°C (MeOH). H
NMR (DMSO-d6) l: 11.71 (s, 1H), 9.75 (s, 1H), 8.20
(d, J=16 Hz, 1H), 7.03 (m, 1H), 6.93 (t, 1H), 6.79 (m,
1H), 6.62 (d, J=16 Hz, 1H), 6.25 (m, 1H), 5.06 (s, 2H),
3.80 (s, 3H), 2.18 (s, 3H), 2.14 (s, 3H). IR (Nujol): 3296,
1680, 1657, 1620 cm−1. MS (FAB): m/z 314 (M+
H)+.
5.1.3.14. Methyl (E)-3-(N-benzyl-2-carbamoyl6inyl)-4,5-
dimethylpyrrole-2-carboxylate (4n). 79% yield; m.p.
1
247°C (Et2O). H NMR (DMSO-d6) l: 11.65 (s, 1H),
8.49 (t, 1H), 8.08 (d, J=16 Hz, 1H), 7.35–7.21 (m,
5H), 6.46 (d, J=16 Hz, 1H), 4.39 (d, 2H), 3.75 (s, 3H),
2.13 (s, 3H), 2.05 (s, 3H). IR (Nujol): 3312, 3267, 1670,
1651, 1614 cm−1. MS (FAB): m/z 313 (M+H)+.
5.1.5. Methyl (E)-3-[N-(4-ureidophenyl)-2-carbamoyl-
6inyl]-4,5-dimethylpyrrole-2-carboxylate (8)
A 200 mg (2.4 mmol) sample of KCNO, dissolved in
1 ml of water, was added portion-wise to a solution of
312 mg (1 mmol) of 6 in 1 ml of water, 0.5 ml of glacial
CH3COOH and THF until complete solubilization. The
mixture was stirred for 4 h at r.t. and the desired
product separated as a white solid upon concentration
of the solvent at reduced pressure. 94% yield; m.p.
5.1.3.15. Methyl (E)-3-[N-(4-dimethylaminophenyl)-2-
carbamoyl6inyl]-4,5-dimethylpyrrole-2-carboxylate (4o).
73% yield; m.p. 270–3°C (Et2O). H NMR (DMSO-d6)
l: 11.69 (br s, 1H), 9.79 (br s, 1H), 8.14 (d, J=15.9 Hz,
1H), 7.50 (d, 2H), 6.69 (d, 2H), 6.56 (d, J=15.9 Hz,
1H), 3.77 (s, 3H), 2.83 (s, 6H), 2.15 (s, 3H), 2.11 (s,
3H). IR (Nujol): 3302, 1674, 1651,1616 cm−1. MS
(FAB): m/z 342 (M+H)+.
1
1
\300°C. H NMR (DMSO-d6) l: 11.72 (s, 1H), 9.93
(s, 1H), 8.43 (s, 1H), 8.19 (d, J=16 Hz, 1H), 7.56 (m,
2H), 7.33 (m, 2H), 6.61 (d, J=16 Hz, 1H), 5.78 (s, 2H),
3.80 (s, 3H), 2.18 (s, 3H), 2.14 (s, 3H). IR (Nujol): 3308,
1674, 1616 cm−1. MS (FAB): m/z 357 (M+H)+.
5.1.3.16. Methyl (E)-3-[N-(4-Boc-aminophenyl)-2-car-
bamoyl6inyl] - 4,5 - dimethylpyrrole - 2 - carboxylate (4p).
1
4% yield; m.p. 245°C (dec.) (Et2O). H NMR (DMSO-
5.1.6. General procedure for the synthesis of (E)-3-(N-
substituted-2-carbamoyl6inyl)-4,5-dimethylpyrrole-2-
carboxylic acids (5a–r)
A total of 1 mmol of the suitable ester was sus-
pended in 1 ml of MeOH–20% water (THF–20%
d6) l: 11.7 (s, 1H), 9.9 (s, 1H), 9.2 (s, 1H), 8.18 (d,
J=16 Hz, 1H), 7.50 (d, 2H), 7.36 (d, 2H), 6.58 (d,
J=16 Hz, 1H), 3.77 (s, 3H), 2.15 (s, 3H), 2.11 (s, 3H),
1.45 (s, 9H). IR (Nujol): 3342, 3302, 1693, 1678 cm−1
.
MS (EI): m/z 413 (M+).

C. Balsamini et al. / Il Farmaco 54 (1999) 101–111
107
Table 2
Elemental analyses of new target compounds
5a
5b
5c
5d
5e
5f
For C16H15FN2O3 · 1H2O
For C17H18N2O3
(MW 320.32)
(MW 298.34)
(MW 322.36)
(MW 370.33)
(MW 340.38)
(MW 346.38)
(MW 352.81)
(MW 364.06)
(MW 268.31)
(MW 352.39)
(MW 348.79)
(MW 380.01)
(MW 338.43)
(MW 336.79)
(MW 403.41)
(MW 384.36)
(MW 402.38)
(MW 360.37)
Calc.: C, 60.00; H, 5.35; N, 8.75
Found: C, 60.28; H, 5.37; N, 8.39
Calc.: C, 68.44; H, 6.08; N, 9.39
Found: C, 68.39; H, 6.24; N, 9.27
Calc.: C, 59.61; H, 4.82; N, 8.69
Found: C, 59.57; H, 4.81; N, 8.39
Calc.: C, 55.14; H, 4.63; N, 7.56
Found: C, 55.29; H, 4.73; N, 7.44
Calc.: C, 56.46; H, 5.15; N, 8.23
Found: C, 56.61; H, 5.22; N, 7.83
Calc.: C, 62.42; H, 6.40; N, 8.09
Found: C, 62.37; H, 6.00; N, 7.73
Calc.: C, 63.66; H, 7.09; N, 7.94
Found: C, 63.62; H, 6.73; N, 7.54
Calc.: C, 65.98; H, 7.86; N, 7.69
Found: C, 65.74; H, 7.90; N, 7.29
Calc.: C, 58.19; H, 7.51; N, 10.44
Found: C, 58.59; H, 7.52; N, 10.22
Calc.: C, 68.17; H, 5.72; N, 7.95
Found: C, 68.28; H, 5.97; N, 7.57
Calc.: C, 68.87; H, 5.66; N, 8.03
Found: C, 68.81; H, 5.42; N, 8.08
Calc.: C, 69.53; H, 5.41; N, 7.37
Found: C, 69.55; H, 5.56; N, 7.36
Calc.: C, 62.11; H, 8.34; N, 8.28
Found: C, 62.08; H, 7.96; N, 8.38
Calc.: C, 64.91; H, 6.82; N, 8.32
Found: C, 64.88; H, 6.46; N, 8.32
Calc.: C, 53.59; H, 6.50; N, 10.42
Found: C, 53.49; H, 6.22; N, 10.11
Calc.: C, 50.00; H, 6.03; N, 10.93
Found: C, 50.01; H, 5.71; N, 10.61
Calc.: C, 47.76; H, 6.26; N, 10.44
Found: C, 47.35; H, 6.06; N, 10.13
Calc.: C, 56.66; H, 5.59; N, 15.55
Found: C, 56.54; H, 5.68; N, 15.16
Calc.: C, 66.55; H, 6.36; N, 8.62
Found: C, 66.47; H, 6.23; N, 8.74
Calc.: C, 62.97; H, 5.87; N, 8.16.
Found: C, 63.29; H, 5.48; N, 7.94
For C16H15ClN2O3 · 0.2H2O
For C17H15F3N2O3 · 1H2O
For C16H15ClN2O3 · 1.2H2O
For C17H18N2O4 · 1CH3OH
For C17H18N2O3 · 1.7CH3OH
For C20H26N2O3 · 1.2H2O
For C13H18N2O3 · 1H2O
For C20H18N2O2 · 1H2O
For C20H18N2O2 · 0.8H2O
For C22H20N2O4 · 0.2H2O
For C16H22N2O3 · 1.5CH3OH
For C17H18N2O3 · 1.2CH3OH
For C18H20N3O3Na · 3H2O
For C16H16N3O3Na · 3.5H2O
For C16H16N3O3Na · 4.5H2O
For C17H18N4O4 · 1H2O
5g
5h
5i
5j
5k
5l
5m
5n
5o
5p
5q
5r
5s
5t
For C16H16N2O3 · 0.25H2O · 0.5THF
For C18H15LiN2O2 · 2.5H2O
(MW 360.37)
(MW 343.31)
water for 8); LiOH · H2O (NaOH for 4o, 6 and 7) (4
mmol) was added and the resulting mixture was
stirred under reflux for 2–24 h. The solvent was
evaporated to dryness to give a residue which was
treated with water and EtOAc; 2 N HCl was added
until acidic pH was reached. The organic phase was
washed three times with water and dried (Na2SO4);
the solvent was then evaporated to give a crude mate-
rial which was purified by crystallization. In the case
of 4o, 6 and 7, the residue obtained from the evapo-
ration of the solvent was purified by crystallization
from water and the products were obtained as
sodium salts. In the case of 5r the desired product
separated, upon acidification, as a highly insoluble
white solid, which was washed well with hot MeOH
and used without any further purification. Elemental
analysis results for compounds 5a–t are listed in
Table 2.
5.1.6.1. (E)-3-[N-(4-Fluorophenyl)-2-carbamoyl6inyl]-
4,5-dimethylpyrrole-2-carboxylic acid (5a). 73% yield;
1
m.p. 204°C (dec.) (MeOH). H NMR (DMSO-d6) l:
12.50 (s, 1H), 11.56 (s, 1H), 10.08 (s, 1H), 8.30 (d,
J=15.9 Hz, 1H), 7.69 (m, 2H), 7.14 (t, 2H), 6.53 (d,
J=15.9 Hz, 1H), 2.13 (s, 3H), 2.11 (s, 3H). IR (Nu-
jol): 3290, 3213, 1659, 1647 cm−1. MS (FAB): m/z
303 (M+H)+. Anal. (C16H15FN2O3 · 1H2O) C, H, N.

108
C. Balsamini et al. / Il Farmaco 54 (1999) 101–111
5.1.6.2. (E)-3-[N-(3-Methylphenyl)-2-carbamoyl6inyl]-
4,5-dimethylpyrrole-2-carboxylic acid (5b). 80% yield;
m.p. 208°C (dec.) (MeOH). H NMR (DMSO-d6) l:
12.48 (s, 1H), 11.55 (s, 1H), 9.95 (s, 1H), 8.28 (d,
J=15.9 Hz, 1H), 7.48 (m, 2H), 7.17 (t, 1H), 6.84 (d,
J=15.9 Hz, 1H), 6.55 (d, 1H), 2.27 (s, 3H), 2.14 (s, 3H),
2.11 (s, 3H). IR (Nujol): 3312, 1672, 1618 cm−1. MS
(FAB): m/z 299 (M+H)+. Anal. (C17H18N2O3) C, H,
N.
5.1.6.8. (E)-3-[N-(1-Adamantyl)-2-carbamoyl6inyl]-4,5-
dimethylpyrrole-2-carboxylic acid (5h). 80% yield; m.p.
150°C (dec.) (MeOH). 1H NMR (DMSO-d6) l: 12.3 (br
s, 1H), 11.41 (s, 1H), 8.03 (d, J=16.2 Hz, 1H), 7.45 (s,
1H), 6.35 (d, J=16.2 Hz, 1H), 2.10 (s, 3H), 2.03 (s, 3H),
1.98 (m, 9H), 1.62 (m, 6H). IR (Nujol): 3270, 3196, 1645
1
cm−1
(C20H26N2O3 · 1.2H2O) C, H, N.
.
MS
(EI):
m/z
342
(M+).
Anal.
5.1.6.9. (E)-3-(N-Isopropyl-2-carbamoyl6inyl)-4,5-
dimethylpyrrole-2-carboxylic acid (5i). 71% yield; m.p.
184°C (MeOH–i-Pr2O–hexane). H NMR (DMSO-d6)
5.1.6.3. (E)-3-[N-(3-Chlorophenyl)-2-carbamoyl6inyl]-
4,5-dimethylpyrrole-2-carboxylic acid (5c). 63% yield;
m.p. 209°C (dec.) (MeOH). H NMR (DMSO-d6) l:
1
l: 12.35 (br s, 1H), 11.46 (s, 1H), 8.06 (d, J=16 Hz,
1H), 7.82 (d, 1H), 6.31 (d, J=16 Hz, 1H), 3.90 (m, 1H),
2.11 (s, 3H), 2.04 (s, 3H), 1.07 (d, 6H). IR (Nujol): 3346,
3267, 1639, 1599 cm−1. MS (FAB): m/z 251 (M+H)+.
Anal. (C13H18N2O3 · 1H2O) C, H, N.
1
12.53 (br s, 1H), 11.61 (s, 1H), 10.22 (s, 1H), 8.31 (d,
J=16.2 Hz, 1H), 7.94 (t, 1H), 7.47 (dd, 1H), 7.33 (t,
1H), 7.07 (dd, 1H), 6.53 (d, J=16.2 Hz, 1H), 2.14 (s,
3H), 2.12 (s, 3H). IR (Nujol): 3300, 1668, 1612 cm−1
.
MS (FAB): m/z 319 (M+H)+. Anal. (C16H15ClN2O3 ·
5.1.6.10. (E)-3-[N-(h-Naphthyl)-2-carbamoyl6inyl]-4,5-
dimethylpyrrole-2-carboxylic acid (5j). 77% yield; m.p.
210°C (dec.) (EtOH). 1H NMR (DMSO-d6) l: 12.46 (br
s, 1H), 11.58 (s, 1H), 10.01 (s, 1H), 8.35 (d, J=16.4 Hz,
1H), 8.14 (dd, 1H), 7.93 (dd, 1H), 7.88 (d, 1H), 7.73 (d,
1H), 7.56 (m, 1H), 7.50 (m, 2H), 6.86 (d, J=16.4 Hz,
1H), 2.18 (s, 3H), 2.16 (s, 3H). IR (Nujol): 3242, 1651,
1618 cm−1. MS (FAB): m/z 335 (M+H)+. Anal.
(C20H18N2O2 · 1H2O) C, H, N.
0.2H2O) C, H, N.
5.1.6.4. (E)-3-[N-(3-Trifluoromethylphenyl)-2-carbamoyl-
6inyl]-4,5-dimethylpyrrole-2-carboxylic acid (5d). 72%
1
yield; m.p. 155–8°C (dec.) (MeOH–Et2O–hexane). H
NMR (DMSO-d6) l: 12.52 (br s, 1H), 11.64 (s, 1H),
10.39 (s, 1H), 8.37 (d, J=16 Hz, 1H), 8.23 (s, 1H), 7.85
(d, 1H), 7.57 (t, 1H), 7.40 (d, 1H), 6.58 (d, J=16 Hz,
1H), 2.17 (s, 3H), 2.16 (s, 3H). IR (Nujol): 3466, 1670,
1643 cm−1. MS (FAB): m/z 353 (M+H)+. Anal.
(C17H15F3N2O3 · 1H2O) C, H, N.
5.1.6.11. (E)-3-[N-(i-Naphthyl)-2-carbamoyl6inyl]-4,5-
dimethylpyrrole-2-carboxylic acid (5k). 42% yield; m.p.
1
191°C (dec.) (MeOH). H NMR (DMSO-d6) l: 12.49
(br s, 1H), 11.59 (s, 1H), 10.24 (s, 1H), 8.40 (d, 1H), 8.35
(d, J=16.4 Hz, 1H), 7.85 (d, 1H), 7.82 (d, 1H), 7.78 (d,
1H), 7.65 (dd, 1H), 7.45 (td, 1H), 7.38 (td, 1H), 6.63 (d,
J=16.4 Hz, 1H), 2.15 (s, 3H), 2.14 (s, 3H). IR (Nujol):
3265, 1651 cm−1. MS (FAB): m/z 335 (M+H)+. Anal.
(C20H18N2O2 · 0.8H2O) C, H, N.
5.1.6.5. (E)-3-[N-(4-Chlorophenyl)-2-carbamoyl6inyl]-
4,5-dimethylpyrrole-2-carboxylic acid (5e). 43% yield;
m.p. 175–8°C (EtOH). H NMR (DMSO-d6) l: 12.5
(br s, 1H), 11.59 (s, 1H), 10.17 (s, 1H), 8.30 (d, J=16
Hz, 1H), 7.70 (d, 2H), 7.36 (d, 2H), 6.54 (d, J=16 Hz,
1H), 2.14 (s, 3H), 2.12 (s, 3H). MS (FAB): m/z 319
(M+H)+. Anal. (C16H15ClN2O3 · 1.2H2O) C, H, N.
1
5.1.6.12. (E)-3-[N-(3-Phenoxyphenyl)-2-carbamoyl6inyl]
4,5-dimethylpyrrole-2-carboxylic acid (5l). 55% yield;
1
5.1.6.6. (E)-3-[N-(4-Methoxyphenyl)-2-carbamoyl6inyl]-
4,5-dimethylpyrrole-2-carboxylic acid (5f). 82% yield;
m.p. 208°C (dec.) (MeOH). H NMR (DMSO-d6) l:
12.48 (s, 1H), 11.59 (s, 1H), 10.09 (s, 1H), 8.27 (d, J=16
Hz, 1H), 7.44–7.38 (m, 4H), 7.30 (t, 1H), 7.15 (m, 1H),
7.04 m, 2H), 6.69 (m, 1H), 6.52 (d, J=16 Hz, 1H), 2.13
1
m.p. 199°C (dec.) (MeOH). H NMR (DMSO-d6) l:
12.44 (br s, 1H), 11.56 (s, 1H), 9.90 (s, 1H), 8.24 (d,
J=16.2 Hz, 1H), 7.59 (d, 2H), 6.87 (d, 2H), 6.53 (d,
J=16.2 Hz, 1H), 3.71 (s, 3H), 2.13 (s, 3H), 2.11 (s, 3H).
IR (Nujol): 3261, 1653, 1618 cm−1. MS (FAB): m/z 315
(M+H)+. Anal. (C17H18N2O4 · 1CH3OH) C, H, N.
(s, 3H), 2.10 (s, 3H). IR (Nujol): 3433, 1659, 1620 cm−1
.
MS (FAB): m/z 377 (M+H)+. Anal. (C22H20N2O4 ·
0.2H2O) C, H, N.
5.1.6.13. (E)-3-(N-Cyclohexyl-2-carbamoyl6inyl)-4,5-
dimethylpyrrole-2-carboxylic acid (5m). 82% yield; m.p.
179–80°C (dec.) (MeOH–i-Pr2O–hexane). 1H NMR
(DMSO-d6) l: 12.33 (br s, 1H), 11.46 (br s, 1H), 8.06 (d,
J=16.4 Hz, 1H), 7.81 (d, 1H), 6.33 (d, J=16.4 Hz,
1H), 3.60 (m, 1H), 2.11 (s, 3H), 2.04 (s, 3H), 1.78–1.06
(m, 10H). IR (Nujol): 3287, 1645, 1593 cm−1. MS
(FAB): m/z 291 (M+H)+. Anal. (C16H22N2O3 ·
1.5CH3OH) C, H, N.
5.1.6.7. (E)-3-[N-(4-Methylphenyl)-2-carbamoyl6inyl]-
4,5-dimethylpyrrole-2-carboxylic acid (5g). 75% yield;
m.p. 195–6°C (MeOH). H NMR (DMSO-d6) l: 12.46
(br s, 1H), 11.57 (s, 1H), 9.94 (s, 1H), 8.26 (d, J=16.2
Hz, 1H), 7.55 (d, 2H), 7.10 (d, 2H), 6.54 (d, J=16.2 Hz,
1H), 2.24 (s, 3H), 2.14 (s, 3H), 2.11 (s, 3H). IR (Nujol):
3279, 3190, 1653, 1616 cm−1. MS (FAB): m/z 299
(M+H)+. Anal. (C17H18N2O3 · 1.7CH3OH) C, H, N.
1

C. Balsamini et al. / Il Farmaco 54 (1999) 101–111
109
5.1.6.14. (E)-3-(N-Benzyl-2-carbamoyl6inyl)-4,5-dime-
thylpyrrole-2-carboxylic acid (5n). 71% yield: m.p. 195–
6°C (dec.) (MeOH–i-Pr2O–hexane). 1H NMR (DMSO-
d6) l: 12.37 (br s, 1H), 11.49 (br s, 1H), 8.45 (t, 1H), 8.14
(d, J=16 Hz, 1H), 7.33–7.2 (m, 5H), 6.41 (d, J=16 Hz,
1H), 4.35 (d, 2H), 2.11 (s, 3H), 2.04 (s, 3H). IR (Nujol):
3258, 1647, 1601 cm−1. MS (FAB): m/z 299 (M+H)+.
Anal. (C17H18N2O.3 1.2 CH3OH) C, H, N.
mg of a residue which was purified by crystallization.
71% yield; m.p. 101–2°C (CHCl3–light pet.). H NMR
(CDCl3, 60 MHz) l: 4.6 (br s, 1H), 4.23 (q, 2H), 3.90
(d, 2H), 2.06 (s, 3H), 1.69 (s, 3H), 1.25 (t, 3H). IR (Nujol):
3378, 2176, 1739, 1601 cm−1. MS (EI): m/z 182 (M+).
1
5.1.8. Ethyl 3-amino-4,5-dimethylpyrrole-2-carboxylate
(11)
A 364 mg sample of 10 (2 mmol) was added to a
solution of 2.4 mmol of EtONa in 5 ml of absolute EtOH.
The mixture was heated at 70°C for 6 h, then cooled to
r.t. The solvent was evaporated under reduced pressure
and the residue treated with water and EtOAc. The water
phase was extracted twice with EtOAc and the organic
phases were combined, washed with water, dried
(Na2SO4), and evaporated to dryness. The residue was
further purified by filtration on silica gel (cyclohexane–
EtOAc 1:1) and crystallization. 69% yield; m.p. 111–2°C
(i-Pr2O). 1H NMR (DMSO-d6) l: 10.10 (s, 1H), 4.75 (s,
2H), 4.12 (q, 2H), 2.00 (s, 3H), 1.72 (s, 3H), 1.22 (t, 3H).
IR (Nujol): 3449, 3285, 1659, 1605 cm−1. MS (EI): m/z
182 (M+).
5.1.6.15. (E)-3-[N-(4-Dimethylaminophenyl)-2-carbam-
oyl6inyl]-4,5-dimethylpyrrole-2-carboxylic acid sodium
salt (5o). 90% yield; m.p. 217°C (dec.) (H2O). H NMR
(DMSO-d6) l: 10.45 (s, 1H), 9.48 (s, 1H), 8.69 (d,
J=16.2 Hz, 1H), 7.49 (d, 2H), 6.68 (d, 2H), 6.27 (d,
J=16.2 Hz, 1H), 2.82 (s, 6H), 2.06 (s, 3H), 2.05 (s, 3H).
IR (Nujol): 3258, 1647, 1603 cm−1. MS (FAB): m/z 350
(M+H)+. Anal. (C18H20N3O3Na · 3H2O) C, H, N.
1
5.1.6.16. (E)-3-[N-(4-Aminophenyl)-2-carbamoyl6inyl]-
4,5-dimethylpyrrole-2-carboxylic acid sodium salt (5p).
60% yield; m.p. \300°C (dec.) (H2O). 1H NMR
(DMSO-d6) l: 10.44 (s, 1H), 9.36 (s, 1H), 8.66 (d,
J=16.5 Hz, 1H), 7.30 (m, 2H), 6.48 (m, 2H), 6.26 (d,
J=16.5 Hz, 1H), 4.77 (s, 2H), 2.06 (s, 3H), 2.04 (s, 3H).
IR (Nujol): 3288, 3190, 1670, 1612 cm−1. MS (FAB): m/z
322 (M+H)+. Anal. (C16H16N3O3Na · 3.5H2O) C, H, N.
5.1.9. Ethyl (E)-3-(cinnamoylamino)-4,5-dimethyl-
pyrrole-2-carboxylate (12)
A mixture of cinnamic acid (148 mg, 1 mmol), 2,2%-
dipyridyl disulfide (397 mg, 1.8 mmol) and (Ph)3P (472
mg, 1.8 mmol) were dissolved in 25 ml of anhydrous
THF. The solution was stirred under N2 at r.t. for 3 h.
Then 200 mg (1.1 mmol) of 11 were added and the stirring
continued for 14 h. The white solid which appeared was
filtered and washed with diethyl ether and further
purified by crystallization. 50% yield; m.p. 250–1°C
5.1.6.17. (E)-3-[N-(3-Aminophenyl)-2-carbamoyl6inyl]-
4,5-dimethylpyrrole-2-carboxylic acid sodium salt (5q).
82% yield; m.p. 215–20°C (dec.) (H2O). 1H NMR
(DMSO-d6) l: 10.48 (s, 1H), 9.44 (s, 1H), 8.70 (d,
J=16.4 Hz, 1H), 6.98 (t, 1H), 6.87 (t, 1H), 6.77 (m, 1H),
6.31 (d, J=16.4 Hz, 1H), 6.19 (m, 1H), 4.98 (s, 2H), 2.07
1
(s, 3H), 2.05 (s, 3H). IR (Nujol): 3335, 3196, 1618 cm−1
.
(THF–hexane). H NMR (DMSO-d6) l: 11.3 (s, 1H),
MS (FAB): m/z 322 (M+H)+. Anal. (C16H16N3O3Na ·
9.30 (s, 1H), 7.58–7.40 (m, 6H), 6.9 (d, 1H), 4.14 (q, 2H),
2.13 (s, 3H), 1.77 (s, 3H), 1.21 (t, 3H). IR (Nujol): 3290,
1674, 1659 cm−1. MS (EI): m/z 312 (M+).
4.5H2O) C, H, N.
5.1.6.18. (E)-3-[N-(4-Ureidophenyl)-2-carbamoyl6inyl]-
4,5-dimethylpyrrole-2-carboxylic acid (5r). 72% yield;
m.p. 174–8°C (dec.) (MeOH). H NMR (DMSO-d6) l:
5.1.10. (E)-3-(cinnamoylamino)-4,5-dimethylpyrrole-2-
carboxylic acid (5s)
1
12.43 (s, 1H), 11.54 (s, 1H), 9.88 (s, 1H), 8.41 (s, 1H),
8.23 (d, J=16.4 Hz, 1H), 7.52 (d, 2H), 7.30 (d, 2H), 6.53
(d, J=16.4 Hz, 1H), 5.76 (s, 2H), 2.14 (s, 3H), 2.11 (s,
3H). IR (Nujol): 3500, 3344, 3252, 1655, 1619 cm−1. MS
(FAB): m/z 343 (M+H)+. Anal. (C17H18N4O4 · 1H2O)
C, H, N.
Hydrolysis of ethyl (E)-3-(cinnamoylamino)-4,5-
dimethylpyrrole-2-carboxylate (12) was performed ac-
cording to the general procedure reported for 4a–o using
EtOH as solvent with a reaction time of 2 h. 84% yield;
m.p. 163–5°C (dec.) (THF–hexane). 1H NMR (DMSO-
d6) l: 12.0 (s, 1H), 11.2 (s, 1H), 9.27 (s, 1H), 7.60 (d, 2H),
7.48 (d, J=15.6 Hz, 1H), 7.42 (t, 2H), 7.38 (m, 1H), 6.93
(d, J=15.6 Hz, 1H), 2.11 (s, 3H), 1.76 (s, 3H). IR
(Nujol): 3277, 1654, 1628 cm−1. MS (FAB): m/z 285
(M+H)+. Anal. (C16H16N2O3 · 0.25H2O · 0.5THF) C,
H, N.
5.1.7. Ethyl N-(3-cyanobutyl)glycinate (10)
A total of 140 mg (1 mmol) of ethyl glycinate hy-
drochloride and 101 mg (1 mmol) of triethylamine were
added to a solution of 2-methyl-3-oxobutyronitrile (9)
[26] (97 mg, 1 mmol) in EtOH (2 ml). The mixture was
stirred at r.t. for 16 h. The solvent was evaporated to
dryness and the residue treated with water and Et2O. The
layers were separated and the organic phase was washed
with water, dried (Na2SO4) and evaporated to give 170
5.1.11. 3-Isoquinolylmethyl-triphenylphosphonium bro-
mide (13)
A total of 222 mg (1 mmol) of 3-(bromomethyl)-iso-
quinoline [31] was dissolved in 3 ml of anhydrous THF,

110
C. Balsamini et al. / Il Farmaco 54 (1999) 101–111
to which 262 mg (1 mmol) of triphenylphosphine were
added. The mixture was refluxed for 24 h. The solid
was filtered, washed well with THF and dried. 91%
yield; m.p. 205°C. 1H NMR (DMSO-d6) l: 9.10 (s,
1H), 8.04 (dd, 1H), 7.85–7.60 (m, 19H), 5.55 (d, 2H).
values were measured from at least six-point inhibition
curves and are the geometric mean of at least three
different experiments. The standard error associated
with the mean was B0.05.
IR (Nujol): 1626 cm−1
.
Acknowledgements
5.1.12. Methyl (E)-3-[(3-isoquinolyl)-2-6inyl]-4,5-
dimethylpyrrole-2-carboxylate (14)
The authors of the group of the University of Urbino
gratefully acknowledge financial support from Glaxo
Wellcome; they also wish to thank Francesco Palazzi
for technical assistance, Dr C. Marchioro and her
colleagues (GW, Verona) for providing part of spectro-
scopic characterization, Dr M. Mugnaini (GW,
Verona) for binding assays and Dr M. Hamdan for
providing part of spectrometric analysis.
A 181 mg (1 mmol) sample of 3-formylpyrrole 1 was
suspended in toluene (16 ml); DBU (0.22 ml, 1.48
mmol) and 726 mg (1.5 mmol) of the phosphonium
bromide 13 were added, after which the mixture was
stirred under reflux for 3 h. The solvent was evaporated
under reduced pressure and the residue was purified by
flash chromatography on silica gel (cyclohexane–
1
EtOAc 1:1). 70% yield; m.p. 246°C (MeOH). H NMR
(DMSO-d6) l: 11.51 (s, 1H), 9.28 (s, 1H), 8.40 (d,
J=16.4 Hz, 1H), 8.07 (d, 1H), 7.89 (d, 1H), 7.76 (s,
1H), 7.72 (dt, 1H), 7.58 (dt, 1H), 7.13 (d, J=16.4 Hz,
1H), 3.78 (s, 3H), 2.18 (s, 3H), 2.16 (s, 3H). IR (Nujol):
3288, 1674, 1666 cm−1. MS (FAB): m/z 307 (M+
H)+.
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