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M. Curini et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2241–2243
X
In this paper we describe the synthesis of several cou-
marin analogues (3–7 and 9–12) structurally related to
auraptene and collinin and we evaluated their anti-
inflammatory activity. Indomethacin, a nonsteroidal
anti-inflammatory drug (NSAID) was used as a refer-
ence compound.
X
HO
O
O
GerO
O
O
HO
O
O
f
e
8
9-12
Scheme 3. Reagents and conditions: (f) X ¼ –I, I2/KI, NH4OH 20%
rt, 1 h; X ¼ –Br, Br2, t-BuNH2, toluene, reflux, 2 h; X ¼ –Cl, Chlor-
amine T, 1:1 dioxane/water, reflux, 1 h; X ¼ –F, Selectfluorâ, CH3CN,
reflux, 30 min; (e) geranyl bromide, DBU, acetone, rt, 3 h.
Ethers (4) and (5) were synthesised from 7-geranyloxy-8-
hydroxycoumarin4 (3) by alkylation with NaH and n-
pentyl iodide and geranyl bromide in DMF (62% and
55% yield, respectively). 8-Acetoxy-7-geranyloxycoum-
arin (6) was synthesised in 93% yield from (3) by reac-
tion with Ac2O and Et3N in dichloromethane catalysed
by 4-pyrrolidinopyridine (Scheme 1).
All these 8-halo derivatives were geranylated employing
the same experimental conditions described above giving
compounds 9–12 (9: X ¼ –I, 10: X ¼ –Br, 11: X ¼ –Cl,
12: X ¼ –F) in 55%, 51%, 60% and 52% yield, respec-
tively.12
The synthesis of 8-methyl derivative (7) was performed
starting from 2-methylresorcinol according to the
pathway shown in Scheme 2.
The anti-inflammatory activity of the tested coumarins
was evaluated as inhibition of the Croton oil ear oedema
in mice (10 mice per treatment group).10 Inflammation
was induced on the right ear (surface: about 1 cm2)
of male CD-1 mice (28–32 g, Harlan-Italy, Udine,
Italy) anaesthetised with ketamine hydrochloride
(145 mg kgÀ1, i.p., Virbac S.r.l., Milano, Italy) by
application of 80 lg of Croton oil (Sigma Chemical Co.,
St. Louis, USA) dissolved in acetone. Control mice
received only the irritant solution, whereas the others
received both the irritant and the substances under test
dissolved in acetone. Six hours later, mice were sacri-
ficed and a plug (6 mm£) was excised from both the
treated and untreated ears: oedema was quantified by
the difference in weight between the two plugs. The anti-
inflammatory activity was expressed as percent reduc-
tion of the control mice using as reference, the NSAID
indomethacin. Experiments complied with the Italian
D.L. n. 116 of January 1992 and associated guidelines in
the European Communities Council Directive of 24
November 1986. Oedema values, expressed as
mean standard deviation of the mean, were analysed
by one-way analysis of variance by DunnettÕs test for
multiple comparison of unpaired data. A probability
level lower than 0.05 was considered as statistically
significant.
Treatment of 2-methylresorcinol with propiolic acid in
concentrated H2SO4 at 120 °C led to 8-methylumbelli-
ferone in 37% yield involving a Pechmann condensation;
alkylation of the latter with geranyl bromide and DBU
in acetone gave (7) in 75% yield.
8-Halocoumarin derivatives were synthesised starting
from umbelliferone (Scheme 3): 8-iodoumbelliferone
(8a) was obtained in 42% yield by reaction with iodine
and KI in 20% NH4OH aqueous solution;9 8-bromo-
umbelliferone (8b) was synthesised in 35% yield by
reaction with bromine and t-butyl amine in refluxing
toluene;9 8-chloroumbelliferone (8c) was obtained in
32% yield by reaction with chloramine T in refluxing 1:1
water/dioxane mixture and finally 8-fluoroumbelliferone
(8d) was synthesised by reaction with Selectfluorâ in
refluxing acetonitrile.
O
OH
GerO
O
O
O
O
O
a
4
3
b
OGer
c
The anti-inflammatory effects of auraptene (1), collinin
(2) and compounds 3–7 and 9–12 (1 lmol/cm2), are
reported in Table 1.
GerO
O
O
OAc
GerO
O
O
5
At the tested doses auraptene, its 8-methoxy derivate
(collinin, 2) and its 8-acetoxy derivate (6) were the most
active compounds inhibiting the oedematous response
by about 50% (Table 1). The other compounds (3, 5, 7,
9–12) showed an oedema reduction ranging from 27% to
43%. As expected, the reference NSAID indomethacin
(0.25 lmol/cm2), provoked 47% oedema reduction.
6
Scheme 1. Reagents and conditions: (a) NaH, n-pentyl iodide, DMF,
rt, 2 h; (b) NaH, geranyl bromide, DMF, rt, 2 h; (c) Ac2O, Et3N,
4-pyrrolidinopyridine (cat.), CH2Cl2, rt, overnight.
CH3
CH3
CH3
In our test system, aurapetene showed in vivo anti-
inflammatory activity, while previously any effect was
observed after acute application.2 This apparent dis-
crepancy with literature data can be ascribed to the
severe dermatitis induced by Murakami et al.:2 the
oedematous response of controls was much more severe
(11.2 mg/cm2) than in the present study (7.0 mg/cm2).
GerO
HO
O
O
OH
HO
O
O
e
d
7
Scheme 2. Reagents and conditions: (d) propiolic acid, H2SO4 concd,
120 °C, 30 min; (e) geranyl bromide, DBU, acetone, rt, 3 h.