New geiparvarin analogues from 7-(2-oxoethoxy)coumarins as efficient in vitro antitumoral agents

Article abstract of DOI:10.1016/S0040-4039(02)01798-7

A new class of compounds analogues of geiparvarin is described: aldolic condensation of 3(2H)-furanones and 7-(2-oxoethoxy)coumarins followed by a very efficient dehydration protocol led to the title compounds which show good antitumoral activity against several human cell lines.

Full text of DOI:10.1016/S0040-4039(02)01798-7

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 7473–7476
New geiparvarin analogues from 7-(2-oxoethoxy)coumarins as
efficient in vitro antitumoral agents
a,
a
b
c
c
Stefano Chimichi, * Marco Boccalini, Barbara Cosimelli, Giampietro Viola, Daniela Vedaldi and
c
Francesco Dall’Acqua
a
Dipartimento di Chimica Organica ‘U. Schiff’, via della Lastruccia 13, I-50019 Sesto F.no, Florence, Italy
b
Dipartimento di Chimica Organica ‘A. Mangini’, via S. Donato 15, I-40127 Bologna, Italy
c
Dipartimento di Scienze Farmaceutiche, Via Marzolo 5, I-35131 Padua, Italy
Received 17 July 2002; accepted 27 August 2002
Abstract—A new class of compounds analogues of geiparvarin is described: aldolic condensation of 3(2H)-furanones and
7
-(2-oxoethoxy)coumarins followed by a very efficient dehydration protocol led to the title compounds which show good
antitumoral activity against several human cell lines. © 2002 Elsevier Science Ltd. All rights reserved.
1
,2
4
In our previous papers, we reported the synthesis of
-(2-oxoethoxy)coumarins, key intermediates for the
cinoma of the nasopharinx. These results strongly
7
suggested the need for more in-depth evaluation of the
potentiality of geiparvarin in medicinal chemistry
research. Thus, the relative importance of moieties
appearing in the geiparvarin structure as the 3(2H)-
furanone ring, the coumarin group and the allyloxy
bridge have been extensively studied but conclusive
results have not been reached yet. In this regard, it
might be interesting to point out that, by preparing all
preparation of natural products and discussed the
chemistry of their transformation into psoralens. We
wish to report here a convenient and general procedure
leading to new geiparvarin analogues as well as to
geiparvarin itself (1).
5
possible geiparvarin regioisomers, the natural 7 posi-
tion has been confirmed to be the best one. Several
modifications have been applied on the chain between
the 3(2H)-furanone and the coumarin moiety. In partic-
ular, the allyloxy bridge of geiparvarin has been
6
changed in a 1,3-butadiene or has been spaced from
7
the furanone ring by a terpenoidal unit but none of
these modifications gave rise to compounds as active as
geiparvarin.
Thus, in order to study the structure–activity relation-
ships of analogues of geiparvarin, we have undertaken
a study aimed at synthesizing new geiparvarin ana-
logues modified on the unsaturated alkenyloxy bridge
where an hydrogen atom is replaced by a 3%-methyl
group in view of the development of efficient antitu-
moral drugs.
Geiparvarin (1), a natural compound isolated from the
leaves of Geijera parviflora, exhibits significant
inhibitory activity against a variety of cell lines includ-
3
ing P 388 lymphocytic leukemia, and human car-
Compounds 1–4 have been obtained by condensation
of the requisite aldehyde with the 3(2H)-furanone moi-
ety 8a,b which can be prepared through the synthesis of
the isoxazole scaffolds 7a,b, as depicted in Scheme 1.
Keywords: hydroxycoumarins; coumarinyloxyaldehydes; geiparvarin
analogues; antitumoral compounds.
*
Corresponding author. Tel.: +39 055 457 3537; fax: +39 055 457
568; e-mail: stefano.chimichi@unifi.it
3
0
040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)01798-7

7
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S. Chimichi et al. / Tetrahedron Letters 43 (2002) 7473–7476
1
available 7-(2-oxoethoxy)coumarins 9–11 and the
lithium enolate of 3(2H)-furanones followed by a dehy-
dration procedure. The first step of the synthesis gave
rise to the hydroxy derivatives 12–15 in quite good
yields (70% for each compound) according to the pro-
3
cedure reported by Smith et al. for 12. As for the
dehydration step, after different experiments (NaOH,
Me SiCl and MeSO Cl), we found that the Stork–
3
2
11
Kraus dehydration protocol (MeSO Cl/Et N/THF,
2
3
0
°C) can be successfully employed to obtain com-
pounds 1 and 16 in 95% overall yield with a
diastereomeric ratio E:Z of ca. 80:20 (Scheme 2). More-
over, we note that the reaction becomes completely
diastereoselective if carried out at room temperature,
the E stereoisomer 1 being the only isolated compound
in nearly quantitative yield (>95%). We wish to point
3
out that the previously reported method (DCC-CuCl-
catalyzed dehydration in refluxing benzene) gave an
isomeric mixture (1:1) of compounds 1 and 16 in poor
yield (30%).
Scheme 1. Reagents and conditions: (i) NaClO, Et N, CHCl ,
3
3
0
°C; (ii) POCl , Et N, CHCl , 10°C; (iii) H , Pd/C, 24 h and
3 3 3 2
+
then H /H O.
2
On the basis of this result, we applied the same proce-
dure to compounds 13–15 to obtain the new analogues
2
–4 in nearly quantitative yields (]95%). Once again
For example, the synthesis of 2,2-dimethyl-5-ethyl-
3
(2H)-furanone (8a) was easily achieved by [3+2]
this procedure was found to be remarkably efficient on
the stereoselectivity: the E stereoisomers of compounds
2–4 now being the unique products. Stereochemical
assignments were achieved on the basis of H2%–H3%
cycloaddition of 2-methyl-3-butyn-2-ol with the nitrile
oxide obtained from 5a or 6a under Lee or
Mukaiyama conditions, respectively, followed by
8
9
1
hydrogenation of the new isoxazole 7a in the presence
of 10% palladium on charcoal and acidification with
aqueous hydrochloric acid (pH<1) to give the desired
vicinal coupling constant values (15.8 Hz) from the H
NMR spectra.
12
10
furanone by cyclization with ammonia expulsion.
The antitumor activity of analogues 2–4 was evaluated
against leukemia-, carcinoma-, neuroblastoma-, and
sarcoma-derived human cell lines in comparison with
Next, we examined the possibility of obtaining com-
pounds 1–4 by aldolic condensation between the easily
13
the natural compound geiparvarin (1). It can be noted
Scheme 2.

S. Chimichi et al. / Tetrahedron Letters 43 (2002) 7473–7476
Table 1. Antitumoral activity of compounds 1–4
8. Lee, G. A. Synthesis 1982, 508–509.
7475
9
. Mukaiyama, T.; Hoshino, T. J. Am. Chem. Soc. 1960, 82,
Cell linesa
IC50 (mM)
b
5339–5342.
1
0. 2,2-Dimethyl-5-ethyl-3(2H)-furanone (8a): A solution of
1
2
3
4
POCl (27 mmol) in CHCl (10 mL) was added dropwise
3
3
under stirring to a cooled (10°C) solution of 2-methyl-3-
butyn-2-ol (40 mmol), nitropropane (6a) (28 mmol) and
HL-60
LoVo
SH-SY5Y
HT-1080
5.390.8
9.291.3
7.090.9
9.890.9
2.590.2
2.090.1
1.990.6
4.391.3
1.390.4
3.390.4
1.590.4
2.390.1
0.390.1
2.190.6
1.690.8
1.790.4
triethylamine (62 mmol) in CHCl (25 mL). The resulting
3
solution was allowed to reach room temperature, stirred
for 15 h and then washed with water (2×15 mL) and
saturated aqueous NaHCO3 (2×15 mL). After drying
over sodium sulfate and filtering, the solvent was
removed under reduced pressure and the dark residual oil
distilled (65–68°C, 0.05 mmHg) to give 2-(3-ethyl-5-isoxa-
zolyl)-2-propanol (7a) as a light yellow oil (55%): IR
a
HL-60 human promyelocytic leukemia; LoVo human colon adeno-
carcinoma; SH-SY5Y human neuroblastoma; HT-1080 human
fibrosarcoma.
Compound concentration required to reduce cell growth by 50%
after 72 h of incubation. Values are expressed as mean±SEM of at
least three independent experiments.
b
−
1
1
(
neat) 3700–3000 (br, OH), 1598, 1416 cm ; H NMR
(
Table 1) that the geiparvarin analogues 2–4 (R =H)
(200 MHz, CDCl ) l 5.99 (s, 1H, H-4%), 2.65 (q, 2H,
3
3
3
show an increased activity towards the lead compound
J=7.6 Hz, CH CH ), 1.59 (s, 6H, 2×2-Me), 1.24 (t, 3H,
2
3
3
+
1
. In particular, compound 4 was found to be the most
J=7.6 Hz, CH CH ); MS (EI) m/z (%): 155 (4, M ), 140
2 3
potent geiparvarin analogue, showing a 10-fold higher
activity than 1 on the leukemia cell line, followed in
order of decreasing potency by 3 and 2. These results
suggest that the antitumor activity could be related to
the replacement of the 3%-methyl group with a hydrogen
atom and to the introduction of a methyl group on the
coumarinic ring.
(79), 138 (6), 112 (39), 85 (42), 68 (70), 59 (64), 43 (100).
Anal. calcd for C H NO : C, 61.91; H, 8.44; N, 9.03.
8
13
2
Found: C, 61.82; H, 8.48; N, 9.00. A solution of isoxazole
7a (14 mmol) in methanol (5 mL) was added under
nitrogen to a suspension of 10% palladium on charcoal
(0.94 g) in methanol (10 mL). The reaction mixture was
then hydrogenated at 30 psi in a Parr hydrogenation
apparatus for 16 h. The catalyst was filtered off and
washed with methanol (2×5 mL). Removal of the solvent
under vacuum left a white solid that was treated under
stirring with water (10 mL) containing 1 M aqueous
hydrochloric acid (20 mL) for 2 h. The mixture was then
In summary, a convenient route to geiparvarin ana-
logues is described through the aldol condensation of
3
lowed by Stork–Kraus dehydration protocol. On the
basis of the biological evaluation, experiments aimed at
defining the targets and the mechanism of the antipro-
liferative effect against tumor cells are in progress.
(2H)-furanones and 7-(2-oxoethoxy)coumarins fol-
neutralized with solid NaHCO and saturated with NaCl.
3
Extraction with diethyl ether (5×10 mL) and removal of
the solvent left yellow oil identified as 8a (72%). An
1
analytical sample, identical ( H NMR and IR spectra) to
3
the product described by Smith, was obtained by distilla-
13
Acknowledgements
tion (bp 48–50°C, 0.07 mmHg); C NMR (75.43 MHz,
CDCl ) l 207.5 (C-3), 193.0 (C-5), 100.1 (C-4), 88.5
3
The authors thank Mrs. Brunella Innocenti for the
analytical data and Mr. Sandro Papaleo for the EI
mass spectra.
(C-2), 24.2 (CH CH ), 22.8 (2×2-Me), 10.2 (CH CH ).
11. Stork, J.; Kraus, A. J. Am. Chem. Soc. 1976, 98, 2351–
2
3
2
3
2352.
1
2. 7-{[(E)-3-(5,5-Dimethyl-4-oxo-4,5-dihydro-2-furanyl)-2-
propenyl]oxy}-4-methyl-2H-chromen-2-one (4): A 2 M
lithium diisopropylamide (LDA) solution in heptane/tet-
rahydrofuran/ethylbenzene (0.5 mL) was added under
nitrogen to a solution of the furanone 8b (1 mmol) in dry
tetrahydrofuran (10 mL) at −78°C. The solution was
stirred for 30 min, and a solution of the aldehyde 11 (1
mmol) in dry tetrahydrofuran (8 mL) was added drop-
wise; after 3 h the temperature was slowly allowed to rise
until 10°C. The mixture was poured onto ethyl acetate
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containing NH Cl (0.11 g) and filtered. The organic layer
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was separated and dried over Na SO . Removal of the
2
4
solvent under vacuum left a yellow oil that was purified
by flash-chromatography (ethyl acetate/diethyl ether=
1.5:1, v/v as eluant, yield 70%) and identified as the
corresponding alcohol 15. To a solution of the alcohol
(0.2 mmol) in dry tetrahydrofuran (8 mL) was added
triethylamine (2 mmol); the mixture was refrigerated to
6
7
. Baraldi, P. G.; Manfredini, S.; Simoni, D.; Tabrizi, M.
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mmol) in dry tetrahydrofuran (3 mL) was added. The
resulting suspension was stirred at 0°C for 90 min and
1
877–1882.

7
476
S. Chimichi et al. / Tetrahedron Letters 43 (2002) 7473–7476
then filtered through a pad of silica treated with diethyl
ether. Removal of the solvent under vacuum gave com-
pound 4 as an yellowish solid (95%); mp 184–185°C
for C H O : C, 69.93; H, 5.56. Found: C, 69.88; H,
19 18 5
5.62.
13. Antitumor assay. Exponentially growing HL-60 leukemia
5
(
from methanol); IR (KBr) 3074, 1738, 1709, 1659 and
cells were resuspended at a density of 1×10 cells/mL in a
−
1 1
1
614 cm ; H NMR (300 MHz, CDCl ) l 7.53 (d, 1H,
complete medium (RPMI 1640 containing 10% fetal
bovine serum, 100 UI/mL penicillin G and 100 mg/mL
streptomycin). Cell viability was determined after 72 h at
3
3
3
4
J=8.8 Hz, H-5), 6.91 (dd, 1H, J=8.8 and J=2.5 Hz,
3
3
H-6), 6.87 (dt, 1H, J=15.8 and J=4.3 Hz, H-2%), 6.83
4
3
14
(
d, 1H, J=2.5 Hz, H-8), 6.60 (dt, 1H, J=15.8 and
37°C by the MTT method. Activity against cell lines
4
4
J=1.8 Hz, H-3%), 6.15 (q, 1H, J=1.3 Hz, H-3), 5.51 (s,
H, H-3%%), 4.81 (dd, 2H, J=4.3 and J=1.8 Hz, H-1%),
.40 (d, 3H, J=1.3 Hz, 4-Me), 1.41 (s, 6H, 2×5%%-Me);
C NMR (75.43 MHz, CDCl ) l 206.8 (C-4%%), 179.8
derived from solid tumors was evaluated in exponentially
3
4
4
1
2
growing cultures seeded at 5×10 cells/mL which were
4
allowed to adhere for18 h to culture plates before addi-
tion of the drugs. Cell viability was determined after 72 h
as described above. Cell growth at each drug concentra-
tion was expressed as percentage of untreated controls
and the concentration resulting in 50% (IC ) growth
1
3
3
(
1
(
6
C-2%%), 160.9 (C-2), 160.8 (C-7), 155.1 (C-8a), 152.2 (C-4),
34.8 (C-2%), 125.7 (C-5), 120.6 (C-3%), 114.2 (C-4a), 112.5
C-6), 112.4 (C-3), 102.3 (C-3%%), 101.7 (C-8), 88.5 (C-5%%),
7.2 (C-1%), 23.1 (5%%-Me), 16.7 (4-Me); MS (EI) m/z
50
inhibition was determined by linear regression analysis.
+
(%): 326 (8, M ), 123 (32), 69 (74), 65 (100). Anal. calcd
14. Mosmann, T. J. Immunol. Methods 1983, 65, 55–63.