Synthesis and in vitro cytotoxic activity of pyrrolo[2,3-e]indole derivatives and a dihydro benzoindole analogue

Article abstract of DOI:10.1016/S0223-5234(01)01328-9

The synthesis of pyrrolo[2,3-e]indole derivatives with the structural characteristics of DNA bis- and mono-intercalators are described. A dihydro benzoindol analogue was also synthesised to elucidate the major structural requirements for cytotoxic activity. A biological evaluation of the test compounds was carried out in six different tumoral cell lines. The factors that affect the cytotoxic activity appear to be the substituents on the phenyl group, the presence of an amide group capable of strong interactions such as hydrogen bonding and solubility.

Full text of DOI:10.1016/S0223-5234(01)01328-9

European Journal of Medicinal Chemistry 37 (2002) 261–266
www.elsevier.com/locate/ejmech
Short communication
Synthesis and in vitro cytotoxic activity of pyrrolo[2,3-e]indole
derivatives and a dihydro benzoindole analogue
Luis Chaco´n-Garc´ıa, Roberto Mart´ınez *
Instituto de Qu´ımica, Uni6ersidad Nacional Auto´noma de Me´xico, Circuito Exterior, Ciudad Uni6ersitaria, Coyoaca´n 04510, Mexico, D.F.
Received 17 August 2001; received in revised form 22 November 2001; accepted 22 November 2001
Abstract
The synthesis of pyrrolo[2,3-e]indole derivatives with the structural characteristics of DNA bis- and mono-intercalators are
described. A dihydro benzoindol analogue was also synthesised to elucidate the major structural requirements for cytotoxic
activity. A biological evaluation of the test compounds was carried out in six different tumoral cell lines. The factors that affect
the cytotoxic activity appear to be the substituents on the phenyl group, the presence of an amide group capable of strong
´
interactions such as hydrogen bonding and solubility. © 2002 Editions scientifiques et me´dicales Elsevier SAS. All rights reserved.
Keywords: Pyrrolo[2,3-e]indole; Synthesis; Cytotoxic activity
1. Introduction
as a consequence of the preceding events that cause
DNA damage [15,16].
DNA intercalators are molecules that insert between
the base pairs of the DNA without denaturalizing it [1].
This insertion causes conformational changes in the
double helix such as increase in the phosphate-sugar
angles and the distance between base pairs [2,3]. DNA
intercalators have common structural characteristics
such as planarity and aromaticity. DNA bis-intercala-
tors are the respective homo- or hetero-dimers bridged
by a linker [4,5].
Once the DNA-intercalator complex forms, it is pri-
marily stabilized by hydrogen bonds, van der Waals
forces, hydrophobic effects and/or molecular orbital
interactions [6–12]. The cytotoxic effect of DNA inter-
calators is a consequence of the inhibition of topoiso-
merase I or II through the stabilization of the
DNA-intercalator–topo complex [13], as has been for
suggested for camptothecin [14]. The stabilization of
the DNA-intercalator–topo complex occurs as a result
of hydrogen bonding between the intercalator and the
amino acids of the enzyme. Finally, cell death takes
place, probably due to the intervention of protein p53
With these considerations in mind, we designed
molecules with the structural characteristics of DNA
intercalating and bis-intercalating compounds using
pyrrolo[2,3-e]indole as the aromatic portion. Com-
pounds of this type were chosen so as to investigate
angular chromophores, which have received little atten-
tion in the literature. In addition, compounds contai-
ning this structure have not been explored in this field,
although some studies have been made of compounds
of the type of pirroloindole [17].
As mentioned above, it is important that a part of
the molecule can form hydrogen bonds in order to
achieve enzymatic inhibition. In the present work an
amide group was chosen to fulfil this need, because of
its additional polar nature. It is important to note that
in some acridine derivatives with high cytotoxicity, such
as AMSA [18], the phenyl ring plays an essential role in
the antitumoral activity. Hence, we decided to incorpo-
rate p-acetanilide moiety into the structure. A sche-
matic of the homo-dimer resulting from the design
process is shown in Fig. 1.
The decision to place eight methylenes in the bis
derivative was made taking into consideration the
neighbor-exclusion principle, which states that the
length of the chain should sufficient to accommodate
the torsion necessary for bis-intercalation [19,20]. The
* Corresponding author. Tel.: +52-56-224441; fax: +52-56-
162217/03.
E-mail address: robmar@servidor.unam.mx (R. Mart´ınez).
´
0223-5234/02/$ - see front matter © 2002 Editions scientifiques et me´dicales Elsevier SAS. All rights reserved.
PII: S0223-5234(01)01328-9

262
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4-bromophenyl group was incorporated into the struc-
ture because it has shown cytotoxic activity in ana-
logues synthesised by our group, and the same
observation has been made in some other reported
work [21]. Taking into account the factors outlined
above, structures 1 and 2 were designed.
To test the importance of the 4%-acetamide portion
we designed a structure that replaced the acetanilide in
2 by a phenyl (structure 3), while to test the importance
of one of the p-Br-phenylpyrrole segments we replaced
the 4-Br-phenylpyrrole by a benzene (structure 5).
In addition, the previously reported compound 4 [22]
was incorporated in the cytotoxic evaluation, because it
is known that thiophene is a bioisosteric group of
benzene, pyrrole and furane [23]. Compound 4 is con-
sidered because its activity reflects the necessity of
having a pyrrole substituent instead of another aro-
matic portion in that region.
Fig. 3. Synthesis of compounds 1–3.
Structure 6 was designed to test the behaviour of a
homo-dimer bridged by only a phenyl group (Fig. 2).
While it was expected that bis-intercalation would not
occur for this structure, mono intercalation and DNA
groove recognition are still possible.
2. Chemistry
Fig. 1. Schematic representation of the homo-dimer.
Homo-dimer 1 was obtained from 1,3-cyclohexane-
dione [22] via the steps shown in Fig. 3. In this synthe-
sis pathway, the two pyrrole moieties were constructed
in different steps. Although there are two other
methodologies described for the synthesis of this skele-
ton, the method used here is more convenient. One of
these methods consists of the cyclization of m-
phenylenedihydrazones by Fisher’s indole synthesis
[24], and the other method requires the bis-annulations
of arylacetylenes [25]. In both of these reports,
pyrroloindoles with the same substitution in both nitro-
gen atoms are described.
Using our method, the anion of the 1,3-cyclohexane-
dione (7) formed with EtONa in ethanol was reacted
with chloroacetone to give the 1,4-dicarbonyl deriva-
tives. This derivative was reacted with 4-bromopheny-
laniline by a Paal–Knorr reaction to obtain 8 in
moderate yield (50%). Reaction of the tetrahydroin-
dolone 8 with LDA, generated in situ, and subsequent
addition of an excess of allyl bromide gave 9 with yields
corresponding to 80%. Oxidation of 9 with PdCl2 gave
10, which is the intermediate from which the rest of the
Fig. 2. Structures 1–6.

L. Chaco´n-Garc´ıa, R. Mart´ınez / European Journal of Medicinal Chemistry 37 (2002) 261–266
263
sponding to the ‘endo’ pyrrole hydrogen and its respec-
tive neighbour methyl groups. Variation of the
temperature confirmed the presence of both isomers,
which have a diastereoisomeric relationship (Fig. 4).
Benzoindole 5 was tried to be synthesised using the
same strategy as that described above for the pyrroloin-
doles, but with a-tetralone 14 as the starting material.
In this synthetic pathway the anion, formed from the
reaction of a-tetralone and LDA, reacted with allyl
bromide to give the allyl derivative 15 which, under the
same conditions used in the oxidation of 9, results in
the 1,4-dicarbonyl derivative 16. Reaction of 16 with
4-aminoacetanilide, under the conditions described ear-
lier, did not give the expected product 5, but afforded
instead the non-aromatized 17 (Fig. 5). It is interesting
that, whereas pyrroloindoles 1, 2, 3 and 6 tend to
aromatize in the same reaction conditions, 17 did not
show any tendency toward aromatisation, even after
hours at reflux in acetic acid.
Fig. 4. Synthesis of 6a and 6b.
Fig. 5. Synthesis of 17.
As expected for dihydro benzene derivatives, 17 is
not a flat molecule, unlike the other compounds in the
series.
Although compound 17 is not absolutely flat, and is
not aromatized, it still maintains a structural analogy
with the desired adduct. We therefore included it in the
panel of compounds to be investigated.
pyrroloindole compounds can be obtained. In another
Paal–Knorr reaction, 10 was reacted with decanodioic
acid bis-[(4-amino-phenyl)-amide] 11 to give 1. Diamide
11 was obtained by condensation of 4-nitroaniline with
sebacoyl chloride in acetone to give 13, followed by
reduction with NH2NH2 and Pd/C in ethanol. The
condensation of 10 with 4-aminoacetanilide and aniline
yielded compounds 2 and 3, respectively (Fig. 2).
An alternative synthetic pathway explored for 1 was
the reaction of 10 with 1,4-diaminobenzene to give 12,
followed by reaction with sebacoyl chloride in pyridine,
as shown in Fig. 3. The primary problem of this
synthetic route was the poor yield due to the instability
of 12, which was difficult to separate because of its
decomposition in silica and alumina.
3. Biological results and discussion
The first cytotoxic evaluation was made with 4. This
compound showed inactivity in NCI-H460 (Lung),
MCF7 (Breast) or SF-268 (CNS) cell line. Because of
its inactivity, no further evaluation was necessary.
Compounds 1, 2, 3, 6 and 17 were evaluated for
cytotoxic activity in cultures of PC-3 (prostate), U251
(CNS), K562 (leukemia), Hep-2 (Liver), HeLa (cervix),
and HCT-15 (colon) cells. The results are given in
Table 1.
To last of the pyrroloindole group of molecules,
dimeric compound 6, was obtained by reaction of 2
equivalents of 10 with 1 equivalents of 1,4-diaminoben-
zene in acetic acid, as shown in Fig. 4. Two conformers
6a and 6b were identified from the duplicity of the
1H-NMR signals detected at 5.92 and 5.62 ppm, corre-
The most active compound is 2, which showed poor
activity in all the cell lines probed with the best result in
Table 1
Cytotoxic evaluation of compounds 1, 2, 3, 6 and 17
Compound MW
IG50 [mM (9S.D.)]
PC3 (prostate)
U251 (CNS)
K562 (leukemia)
Hep-2 (liver)
HCT-15 (colon)
HeLa (cervix)
1
1026.90
\100
N.A.a
N.A.
N.A.
N.A.
N.A.
2
3
6
472.38
415.33
752.54
316.40
527
17.7 (2.5)
\100
\100
33.5 (2.4)
N.A.
N.A.
17.9 (7.9)
N.A.
N.A.
45.1 (4.6)
N.A.
N.A.
36.2 (1.6)
N.A.
\100
N.A.
36.3 (5.2)
N.A.
N.A.
17
25.3
\100
\100
N.A.
\100
Ad b
5×10−5
1.8×10−4
1.8×10−2
1.5×10−2
5×10−5
a N.A., not active.
b Ad, adriamycin.

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L. Chaco´n-Garc´ıa, R. Mart´ınez / European Journal of Medicinal Chemistry 37 (2002) 261–266
PC-3. All of the compounds listed in Table 1 showed
some degree of activity in the PC-3 cell line.
As mentioned above, compound 3 was not expected
to show significant activity because it lacks groups
capable of interacting strongly with an enzyme. The
results are in agreement with this hypothesis.
An unexpected result of the cytotoxicity tests, how-
ever, is the remarkable loss of cytotoxicity of dimer 1.
The fact that monomer 2 has a greater activity than its
bis analogue could be due to an increase in the molecu-
lar weight or moreover to the difference in solubility
(dimer 1 was the only compound which showed some
problems of insolubility).
M.p. 188–190 °C; IR w 3436, 3003, 1695, 1517;
1H-NMR l 1.63 (m, 4 H), 1.77 (m, 2H), 2.12 (s, 3H),
2.24 (s, 3H), 2.43 (t, J=7.5 Hz, 2H), 5.56 (s, 1H), 6.4
(s, 1H), 6.83 (s, J=8.4 Hz, 2H), 7.19 (d, J=8.7 Hz,
2H), 7.25 (d, J=8.4 Hz, 2H), 7.39 (d, J=8.7 Hz, 2H),
7.52 (s, 1H), 7.62 (d, J=8.4 Hz, 2H), 7.74 (d, J=8.4
Hz, 2H); 13C-NMR l 13.12, 13.21, 28.96, 29.08, 29.69,
37.73, 98.33, 101.78, 104.08, 113.27, 113.95, 120.1,
121.26, 128.3, 129.29, 129.43, 129.75, 130.04, 132.56,
133.66, 133.91, 135.17, 137.62, 137.83, 171.7; HRMS
Calc. for C58H54Br2N6O2 (FAB+): 1026.8966. Found:
1026.8962.
Comparison of the results for 2 and 3 makes it clear
that the acetamide group is necessary for cytotoxic
activity, and moreover comparison of 2 with 4 indicates
that the 4-acetanilide portion is also important for
activity. In addition, the N-(4%-bromophenyl)-pyrryl
portion appears to increase activity, as shown by the
difference in behaviour between 2 and 17, which
showed only a small amount of activity. In this last
instance, however, aromaticity may also play an impor-
tant role in determining the relative activities. To test
this, compound 5 will be synthesised and evaluated.
4.1.1.2.
N-{4-[6-(4-Bromo-phenyl)-2,7-dimethyl-6H-
1,6-diaza-as-indacen-1-yl]-phenyl}-acetamide (2). M.p.
130–132 °C (63% yield); IR w 3437, 2927, 1693, 1516;
1H-NMR l 2.14 (s, 3H), 2.26 (s, 3H), 2.26 (d, J=0.92
Hz, 3H), 5.54 (s, 1H), 6.41 (q, J=0.92 Hz, 1H), 6.83
(dd, J=8.56, 0.64 Hz, 2H), 7.21 (d, J=8.66 Hz, 2H),
7.26 (d, J=8.62 Hz, 2H), 7.39 (dd, J=8.6, 0.64 Hz,
2H), 7.43 (s, 1H), 7.63 (d, J=8.64 Hz, 2H), 7.72 (d,
J=8.58 Hz, 2H); 13C-NMR l 13.12, 13.21, 24.66,
98.33, 101.78, 104.08, 113.27, 113.95, 120.1, 121.26,
128.3, 129.29, 129.43, 129.75, 130.04, 132.56, 133.66,
133.91, 135.17, 137.62, 137.83, 168; HRMS Calc. for
C26H22BrN3O (FAB+): 472.3765. Found: 472.3767.
4. Experimental protocols
4.1.1.3. 6-(4-Bromo-phenyl)-2,7-dimethyl-1-phenyl-1,6-
dihydro-1,6-diaza-as-indacene (3). M.p. 105–107 °C;
(70% yield); IR w 2924, 1595, 1495; H-NMR l 2.13 (s,
4.1. Chemistry
1
Melting points are uncorrected. The IR spectra were
recorded on a Nicolet FT-55X spectrophotometer. The
1H-NMR spectra were determined on a Varian FT-200
and Varian FT-300 instrument in CDCl3 unless other
solvent specified. Chemical shift are expressed in l
(ppm) relative to TMS as internal standard and cou-
pling constants (J) in Hz. High resolution mass spectra
were recorded using a JEOL SX-102 mass spectrometer
using the direct inlet system with an ionization energy
of 70 eV, an emission current of 100 mA and ion source
temperature of 150 °C.
3H), 2.28 (s, 3H), 5.48 (s, 1H), 6.43 (s, 1H), 6.84 (dd,
J=8.52, 0.81 Hz, 2H), 7.21 (d, J=8.5 Hz, 2H), 7.28
(d, J=8.52 Hz, 2H), 7.46 (dd, J=7.95, 1.78 Hz, 2H),
7.56 (dd, J=7.9, 7.2 Hz, 2H), 7.57 (d, J=7.14 Hz,
1H), 7.63 (d, J=8.79 Hz, 2H); 13C-NMR l 13.15,
13.24, 98.23, 101.68, 104.03, 112.5, 113.89, 121.22,
128.06, 128.9, 129.18, 129.73, 132.54, 133.61, 133.84,
135.11, 137.59, 139.57; HRMS Calc. for C24H19N2Br
(FAB+): 414.0732. Found: 414.0734.
4.1.1.4. 1,4-bis-[6-(4-Bromo-phenyl)-2,7-dimethyl-1,6-
dihydro-1,6-diaza-as-indacene]-benzene (6). M.p. 97 °C
dec.; (45% yield); IR w 2927, 1515,1493, 1H-NMR l
2.18 (s, 3H), 2.4 and 2.5 (s, 3H), 5.62 and 5.92 (s br,
1H), 6.5 (s, 1H), 6.89 (d, J=8.6 Hz, 1H), 7.23 (d,
J=8.52 Hz, 2H), 7.32 (d, J=8.7 Hz, 1H), 7.65 (d,
J=8.52 Hz, 2H), 7.68 (s, 2H); 13C-NMR l 13.36,
29.69, 98.41, 102.37, 104.3, 113.21, 114, 121.41, 121.44,
129.75, 132.57, 132.64, 133.77, 135.29, 137.5; MS
(FAB+) m/z 752.
4.1.1. General procedure for the synthesis of 1–3, 6
and 17
4.1.1.1. Decanodioic acid bis-({4-[6-(4-bromo-phenyl)-
2,7-dimethyl-6H-1,6-diaza-as-andacen-1-yl]-phenyl}-
amide) (1). To a stirred solution of (0.1 g, 0.28 mmol) of
10 in 5 ml of acetic acid at 80 °C, diamine 11 (0.057 g,
0.15 mmol) was added. After 1 h of reflux and magnetic
stirring, acetic acid is neutralized with a solution of 5%
NaHCO3 in water in a separation funnel with CH2Cl2.
After reduction of the solvent, previously dried with
Na2SO4, under reduced pressure, 1 was obtained, by
recrystallisation (0.14 g, 50%) or by chromatographic
purification in silica gel 1:1 hexane–AcOEt (0.05 g,
17.5%) from the obtained mixture, as a green solid.
4.1.1.5.
N-[4-(2-Methyl-4,5-dihydro-benzo[g]indol-1-
yl)-phenyl]acetamide (17). M.p. 195–197 °C; (81%
1
yield); IR w 3437, 2935, 1695, 1516; H-NMR l 2.08 (s,
3H), 2.23 (s, 3H), 2.69 (t, J=8 Hz, 2H), 2.91 (t, J=8
Hz, 2H), 5.94 (s, 1H), 6.29 (dd, J=7.46, 1.56 Hz, 1H),

L. Chaco´n-Garc´ıa, R. Mart´ınez / European Journal of Medicinal Chemistry 37 (2002) 261–266
265
6.79 (td, J=7.42, 1.56 Hz, 1H), 6.89 (td, J=7.42, 1.5
Hz, 1H), 7.14 (dd, J=7 Hz, 1.56 1H), 7.26 (d, J=8.8
Hz, 2H), 7.35 (s, 1H), 7.63 (d, J=8.8 Hz, 2H); 13C-
NMR l 12.89, 22.46, 24.67, 30.88, 106.4, 120.05,
120.29, 122.48, 123.93, 125.92, 128.06, 128.77, 129.77,
132.06, 135.54, 135.88, 137.49, 168.36; HRMS Calc. for
C21H20ON2 (EI+): 316.1576. Found: 316.1570.
(dd, J=7.5, 0.6 Hz, 1H), 7.29 (td, J=7.2, 0.6 Hz, 1H),
7.45 (td, J=7.2, 1.5 Hz, 1H), 8.03 (dd, J=7.6, 1.5 Hz,
1H), 13C-NMR l 27.96, 28.61, 34.04, 47.19, 116.79,
126.57, 127.45, 128.69, 132.53, 133.17, 136.21, 144.04,
119.40; HRMS Calc. for C13H14O (FAB+): 186.1045.
Found: 186.1052.
4.1.5. 2-(2-Oxo-propyl)-3,4-dihydro-2H-naphthalen-
1-one (16)
4.1.2. Synthesis of decanodioic acid
bis-[(4-amino-phenyl)-amide] (11)
PdCl2 (0.246 g, 1.38 mM) was added to a magneti-
cally stirred solution of 10 mL of DMF and 1 mL of
distilled water. After 5 min, 15 (0.5 g, 1.38 mM)
dissolved in 2 mL of DMF was added dropwise. The
stirring was maintained for 12 h; the mixture was then
percolated in a column packed with cotton using
CH2Cl2 as solvent. Then DMF was eliminated with
consecutive washes with water. Solvent was reduced
and purification in column chromatography gave 16 as
a green solid.
M.p. 90 °C; (65% yield) IR w 2933, 1715, 1682;
1H-NMR l 1.92 (ddd, J=25.8, 12.9, 4.41 Hz, 1H), 2.19
(m, 1H), 2.27 (s, 3H), 2.45 (m, 1H), 2.95 (dt, J=16.8,
2.76 Hz, 1H), 3.11 (m, 1H), 3.15 (m, 1H), 3.18 (dd,
J=19.5, 6 Hz, 1H), 7.25 (t, J=7.68 Hz, 1H), 7.29 (t,
J=7.71 Hz, 1H), 7.47 (dd, J=7.68, 1.38 Hz, 1H), 8.0
(dd, J=7.68, 1.35 Hz, 1H); 13C-NMR l 29.35, 29.45,
30.47, 43.82, 44.18, 126.58, 127.36, 128.72, 132.17,
133.35, 144.07, 199, 207.14; MS (EI+), m/z 202 ([M+]
19).
Ethanol (10 ml), Pd/C 5% (0.046 g), hydrazine (0.818
ml, 25.9 mmol), water (0.93 ml) and 13 (2.59 mmol)
were mixed in a bottom flask. The mixture was refluxed
for 2 h. The resulting solid was dissolved in methanol in
heat and filtered at vacuum. Methanol was eliminated
up precipitation of a solid that was filtered and crystal-
lized from methanol to afford 11.
M.p. 199–201 °C, (90% yield); IR w 3379, 1699;
1H-NMR (dmso-d6) l 1.25 (s br, 4H), 1.55 (m, 2H),
2.33 (t, J=11.13 Hz, 2H), 4.79 (s br, 2H), 7.77 (d,
J=13.8 Hz, 2H), 8.14 (d, J=13.86 Hz, 2H), 10.47 (s,
1H).
4.1.3. Decanodioic acid bis-[(4-nitro-phenyl)-amide (13)
Sebacoyl chloride (0.172 g, 0.72 mmol) was added to
a solution of 4-nitroaniline (0.198 g, 1.44 mmol) in 15
ml of acetone at 5 °C. After 2 h stirring, the mixture
was filtered and washed with acetone to afford 13.
M.p. 193–195 °C; (55% yield); IR w 3398, 3286,
3307, 2929, 1650; 1H-NMR l (dmso-d6) 1.27 (s br, 4H),
1.54 (m, 2H), 2.19 (t, J=11.3 Hz, 2H), 7.77 (d, J=
13.5Hz, 2H), 8.14 (d, J=13.6 Hz, 2H), 10.47 (s, 1H).
4.2. Cytotoxic acti6ity
The IG50 for compound 2 was obtained from three
different experiments performed in duplicate, whereas
for all other compounds it was obtained from one
experiment performed in duplicate.
All of the experiments were carried out at four
different concentrations (3.1, 10, 31 and 100 mM).
The National Cancer Institute supplied the tumoral
cell lines PC-3, U251 and K562. Cytotoxicity assays
were carried out at 5000–7500 cells mL−1, as reported
by Skehan et al. and Monks et al., who used the
sulforhodamine B (SRB) protein assay to estimate cell
growth [26,27]. The percentage growth was evaluated
4.1.4. 2-Allyl-3,4-dihydro-2H-naphthalen-1-one (15)
To a solution of diisopropylamine (0.96 mL, 6.8
mM) in 20 mL of THF anhydrous, under nitrogen
atmosphere at −78 °C, n-butillithium 1.6 M (4.27 mL,
6.84 mM) were added with continues magnetic stirring.
After 1 h, a-tetralone (1g, 6.84 mM) was added, and the
reaction was maintained at the same temperature with
stirring for 2 h more. After this time, allyl bromide
(2.35 mL, 27.4 mM) was added and the reaction mix-
ture was raised at room temperature. After 12 h of
stirring, reaction flask was putted in a dry ice bath and
ammonium chloride was added. Then, excess of THF
was evaporated and extractions with water and methyl-
ene chloride were performed. The organic phase was
dried with anhydrous sodium sulfate and filtered. Sol-
vent reduction gave a viscose material containing 15.
Purification in column chromatography 9:1 hexane–
AcOEt, gave 15 as colorless oil, which solidify at low
temperature.
spectrophotometrically in
spectrophotometer.
a
Bio kinetics reader
The National Cancer Institute measured cytotoxic
activity of 4, with the same procedure mentioned
above.
M.p. B25 °C; (80% yield) IR 3072, 2930, 1683;
1H-NMR l 1.87 (m, 1H), 2.26 (m, 2H), 2.55 (m, 1H),
2.76 (m, 1H), 2.99 (dd, J=7.5, 4.5 Hz, 2H), 5.06 (m,
1H), 5.11 (dq, J=15, 2.1 Hz, 1H) 5.85 (m, 1H), 7.23
Acknowledgements
We thank CONACYT (32633-E) and DGAPA-
UNAM (IN206598) for financial support. L.C.-G.

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L. Chaco´n-Garc´ıa, R. Mart´ınez / European Journal of Medicinal Chemistry 37 (2002) 261–266
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