New synthesis of 8-alkoxycarbonylangelicins

Article abstract of DOI:10.1023/A:1012434702051

A new procedure was developed for the synthesis of 8-alkoxycarbonylangelicins by base-catalyzed cyclization of ortho-acyl(hydroxy)coumarins with haloacetic acid esters. The procedure was successfully applied to prepare a series of new 8-alkoxycarbonyl-and 8-acylangelicins.

Full text of DOI:10.1023/A:1012434702051

Russian Journal of Organic Chemistry, Vol. 37, No. 7, 2001, pp. 1008 1012. Translated from Zhurnal Organicheskoi Khimii, Vol. 37, No. 7, 2001,
pp. 1058 1062.
Original Russian Text Copyright
2001 by Tolmachev, Podkhalyuzina, Kuznetsova, Traven’.
New Synthesis of 8-Alkoxycarbonylangelicins
A. Yu. Tolmachev, N. Ya. Podkhalyuzina, N. A. Kuznetsova, and V. F. Traven’
Mendeleev Russian University of Chemical Technology, Miusskaya pl. 9, Moscow, 125047 Russia
e-mail: alext@muctr.edu.ru
Received July 5, 1999
Abstract A new procedure was developed for the synthesis of 8-alkoxycarbonylangelicins by base-catalyzed
cyclization of ortho-acyl(hydroxy)coumarins with haloacetic acid esters. The procedure was successfully
applied to prepare a series of new 8-alkoxycarbonyl- and 8-acylangelicins.
Furocoumarin derivatives are well known as
compounds exhibiting phototherapic activity in the
treatment of a series of skin diseases. There are also
data on their bactericide and fungicide activity [1].
In addition, numerous publications appeared in the
recent years on the use of furocoumarins and their
analogs for blood disinfection [2, 3]. Especially strong
activity was demonstrated by psoralene derivatives.
The known method of synthesis of 8-alkoxycar-
bonylangelicins and 2-alkoxycarbonylpsoralenes is
based on the condensation of ortho-acyl(hydroxy)-
coumarins with diethyl bromomalonate by the action
of potassium carbonate in a polar aprotic solvent
(e.g., acetone, 2-butanone, or ethyl acetate) [12].
The reaction is carried out in one step, for inter-
mediate ester readily undergoes intramolecular
cyclization followed by aromatization to give the
corresponding furocoumarin. The condensation with
diethyl bromomalonate is accompanied by decar-
boxylation of one ester group. This scheme is applied
to the synthesis of only lower (mainly ethyl) esters
of angelicin-8-carboxylic and psoralene-2-carboxylic
acids. Various alkyl furocoumarincarboxylates could
be prepared by the condensation scheme given below
from the corresponding haloacetic acid esters. How-
ever, we have found no information on such reactions
in the literature.
However, the presence in the psoralene molecule
of two double bonds (C2 C3 and C5 C6) capable of
forming [2 + 2]-cycloaddition products with DNA
pyrimidine bases makes its derivatives difunctional
reagents [4, 5]; as a result, they can exhibit geno-
toxicity and increase the risk of cancer [1, 6]. There-
fore, numerous studies in the field of photochemo-
therapic drugs are concerned with search for new
compounds capable of forming monoadducts with
DNA bases. Much attention is given to angelicin
derivatives which are polyfunctional reagents [7]. In
particular, a large number of methylangelicins were
synthesized and tested. They showed a considerable
activity and a lower genotoxicity, as compared to
psoralenes [8 10]. Furocoumarins having electron-
acceptor substituents, including carbonyl-containing
groups, in the furan or pyran ring also attract interest.
These compounds are characterized by low geno- and
phototoxicity and are also promising for photochemo-
therapy [11].
While studying new schemes for preparation of
furocoumarins and their heteroanalogs [13], we
obtained new data on the synthesis of angelicins con-
taining an ester group in position 8. As starting com-
pounds we used 8-acyl-7-hydroxycoumarins I III.
The condensation of coumarins I III with haloacetic
acid esters in the presence of potassium carbonate was
found to be a convenient route to angelicines having
an ester substituent. With the use of ethyl bromo-
acetate we succeeded in obtaining 8-ethoxycarbonyl-
furocoumarins in one step with a yield of 40 50%.
In the synthesis of compounds XXI and XXII we
also isolated 25 30% of ethoxycarbonylmethoxy
derivatives X and XI (Scheme 1).
The general character of the proposed procedure
was demonstrated with the synthesis of cholesteryl
1070-4280/01/3707-1008$25.00 2001 MAIK Nauka/Interperiodica

NEW SYNTHESIS OF 8-ALKOXYCARBONYLANGELICINS
1009
Scheme.
I, II, X, XII XX, R1 = Me; III, XI, R1 = H; I, XII, XIII, XV, XVII, R2 = Me; II, XIV, XVIII XX, R2 = Et; III, XI, R2 = Ph;
IV, V, X, XI, XIII, XIV, R3 = OEt; VI, XII, R3 = C27H45O; VII, XV, XVIII, R3 = Me; VIII, XVI, XIX, R3 = Ph; IX, XVII,
XX, R3 = 4-CH3C6H4; IV, VI XII, XV XX, R4 = H; V, XIII, XIV, R4 = CO2Et; IV, V, VII IX, Hlg = Br; VI, Hlg = Cl.
XXI, XXIII XXX, R1 = Me; XXII, R1 = H; XXI, XXIII, XXV XXVII, R2 = Me; XXII, R2 = Ph; XXIV, XXVIII XXX,
R2 = Et; XXI, XXII, XXIV, R3 = OEt; XXIII, R3 = C27H45O; XXV, XXVIII, R3 = Me; XXVI, XXIX, R3 = Ph;
XXII, XXX, R3 = 4-CH3C6H4.
angelicin-8-carboxylate (XXIII) as an example.
Cholesteryl esters of 7-alkoxycoumarin-3-carboxylic
acids were previously synthesized as potential meso-
morphic compounds [14]. In addition, cholesteryl
esters derived from coumarin- and furocoumarincar-
boxylic acids are of interest for preparation of photo-
sensitive monomolecular Langmuir Blodgett films.
ketones VII IX and diethyl bromomalonate (V).
The products were furocoumarins XXI and XXIV
XXX which are promising as phototherapic agents.
The condensation in the system potassium carbonate
acetonitrile takes a considerably shorter time and
provides greater yield of the target products. For
example, the yield of compound XXI from diethyl
bromomalonate was 83% in 1 h against 43% in 6 h
under the conditions described in [12]. The yields
of acylangelicins XXV XXX from bromo ketones
were 65 85%, and the reaction time was 3 4 h
(cf. 12 18 h [15]).
It seems hardly promising to involve in the above
condensation dicholesteryl bromomalonate or mixed
chlolesteryl ethyl bromomalonate, for these reagents
are difficultly accessible. Moreover, in the reaction
with chlolesteryl ethyl bromomalonate it is impossible
to predict which of the ester groups will undergo
decarboxylation. Our attempts to obtain ester XXIII
by acylation of cholesterol with the corresponding
carboxylic acid or carbonyl chloride were unsuccess-
ful. Also, the alkylation of furocoumarincarboxylic
acid potassium salt with cholesteryl p-toluenesulfonate
gave no desired product. We succeeded in preparing
cholesteryl 4,9-dimethylangelicin-8-carboxylate
(XXIII) only by condensation of coumarin I with
cholesteryl chloroacetate according to the general
procedure described above. The isolated and purified
product showed a strong ability to form monomole-
cular Langmuir Blodgett films with high performance.
EXPERIMENTAL
1
The H NMR spectra were recorded on a Bruker
AC-200 spectrometer (200 MHz) in CDCl3 using
TMS as internal reference. The mass spectra (70 eV)
were obtained on a Finnigan-MAT SSQ-710 instru-
ment. The progress of reactions was monitored by
TLC on Silufol UV-254 plates using chloroform as
eluent. Preparative chromatographic separations were
performed on silica gel with chloroform as eluent.
Ethyl 2-(8-acetyl-4-methyl-2-oxo-2H-chromen-
7-yloxy)acetate (X) and ethyl 4,9-dimethyl-2-oxo-
2H-furo[2,3-h]chromene-8-carboxylate (XXI).
To a solution of 0.5 g (2.3 mmol) of 8-acetyl-7-hy-
The proposed conditions ensured smooth condensa-
tion of acyl(hydroxy)coumarins I III with -halo-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 7 2001

1010
TOLMACHEV et al.
droxy-4-methylcoumarin (I) and 1.58 g (0.01 mmol)
of potassium carbonate in 40 ml of anhydrous aceto-
nitrile, heated to the boiling point, we added drop-
wise under vigorous stirring a solution of 0.39 g
(2.3 mmol) of ethyl bromoacetate (IV) in 15 ml of
anhydrous acetonitrile. The mixture was stirred for
21 24 h under reflux, cooled to room temperature,
and evaporated under reduced pressure. Potassium
carbonate in the residue was neutralized by adding
10% hydrochloric acid to pH 2 3. The precipitate
was filtered off, washed with water, dried in air, and
subjected to column chromatography on silica gel
using chloroform as eluent. We isolated 0.26 g (40%)
of compound XXI and 0.17 g (25%) of compound X.
9.64 Hz), 7.75 d (1H, 4-H, J = 9.64 Hz), 7.46 7.56 m
(7H, Harom, 5-H, 6-H). Mass spectrum, m/z (Irel, %):
334 (100) [M]+ . Found, %: C 71.83; H 4.21.
C20H14O5. Calculated, %: C 71.85; H 4.22.
Cholesteryl 4,9-dimethyl-2-oxo-2H-furo[2,3-h]-
chromene-8-carboxylate (XXIII) was synthesized
from coumarin I and cholesteryl chloroacetate. Yield
0.38 g (25%), Rf 0.43 (chloroform), mp 229 230 C
1
(from EtOH). H NMR spectrum, , ppm: 0.70 s (3H,
18-CH3), 0.87 d [6H, CH(CH3)2, J = 6.40 Hz], 0.93 d
(3H, 21-CH3, J = 6.00 Hz), 1.09 s (3H, 19-CH3),
2.50 d (3H, 4-CH3, J = 1.06 Hz), 2.90 s (3H, 9-CH3),
4.93 m (1H, 3-H, cholesteryl), 5.44 d (1H, 6-H,
cholesteryl, J = 4.14 Hz), 6.29 d (1H, 3-H, J =
1.06 Hz), 7.45 d (1H, 6-H, J = 8.82 Hz), 7.63 d (1H,
5-H, J = 8.82 Hz). Mass spectrum, m/z (Irel, %): 627
(40) [M + 1]+ , 369 (60) [C27H46]+, 259 (100)
[C14H11O5]+. Found, %: C 78.43; H 8.69. C41H54O5.
Calculated, %: C 78.56; H 8.68.
Compound X. Rf 0.10 (chloroform), mp 114 115 C
1
(from EtOH) [10]. H NMR spectrum, , ppm: 1.30 t
(3H, CH2CH3, J = 7.02 Hz), 2.40 d (3H, 4-CH3,
J = 1.22 Hz), 2.66 s (3H, COCH3), 4.26 q (2H,
OCH2CH3, J = 7.02 Hz), 4.75 s (2H, OCH2), 6.18 d
(1H, 3-H, J = 1.22 Hz), 6.75 d (1H, 6-H, J = 8.84 Hz),
7.55 d (1H, 5-H, J = 9.14 Hz). Mass spectrum, m/z
(Irel, %): 304 (55) [M]+ , 203 (100) [M CO2Et CO]+.
C16H16O6.
Ethyl 9-ethyl-4-methyl-2-oxo-2H-furo[2,3-h]-
chromene-8-carboxylate (XXIV) was synthesized
from coumarin II and diethyl bromomalonate. Yield
1
0.52 g (81%), mp 174 175 C (EtOH). H NMR spec-
trum, , ppm: 1.38 t (3H, CH2CH3, J = 7.48 Hz),
1.45 t (3H, OCH2CH3, J = 7.12 Hz), 2.50 d (3H,
4-CH3, J = 0.92 Hz), 3.38 q (2H, CH2, J = 7.46 Hz),
4.47 q (2H, OCH2, J = 7.14 Hz), 6.29 d (1H, 3-H,
J = 0.94 Hz), 7.46 d (1H, 6-H, J = 8.84 Hz), 7.64 d
(1H, 5-H J = 8.84 Hz). Mass spectrum, m/z (Irel, %):
300 (100) [M]+ . Found, %: C 67.91; H 5.36.
C17H16O5. Calculated, %: C 67.99; H 5.37.
Compound XXI. Rf 0.30 (chloroform), mp 191
192 C (from EtOH) [12]. H NMR spectrum, , ppm:
1
1.46 t (3H, CH2CH3, J = 7.04 Hz), 2.50 d (3H,
4-CH3, J = 0.92 Hz), 2.90 s (3H, 9-CH3), 4.47 q (2H,
CH2, J = 7.04 Hz), 6.29 d (1H, 3-H, J = 0.92 Hz),
7.46 d (1H, 6-H, J = 8.84 Hz), 7.64 d (1H, 5-H, J =
8.86 Hz). Mass spectrum, m/z (Irel, %): 286 (100)
[M]+ . C16H14O5. Compound XXI was also obtained
from coumarin I and diethyl bromomalonate, yield
0.54 g (83%).
Ethyl 2-(8-benzoyl-2-oxo-2H-chromen-7-yloxy)-
acetate (XI) and ethyl 2-oxo-9-phenyl-2H-furo-
[2,3-h]chromene-8-carboxylate (XXII) were syn-
thesized in a similar way from coumarin III and ethyl
bromoacetate.
8-Acetyl-4,9-dimethyl-2H-furo[2,3-h]chromen-2-
one (XXV) was synthesized from coumarin I and
bromoacetone. Yield 0.38 g (65%), mp 231 232 C
1
(from EtOH). H NMR spectrum, , ppm: 2.51 d
(3H, 4-CH3, J = 1.14 Hz), 2.92 s (3H, 9-CH3), 2.63 s
(3H, COCH3), 6.30 d (1H, 3-H, J = 1.14 Hz), 7.43 d
(1H, 6-H, J = 8.84 Hz), 7.67 d (1H, 5-H, J = 8.86 Hz).
Mass spectrum, m/z (Irel, %): 256 (100) [M]+ . Found,
%: C 70.26; H 4.68. C15H12O4. Calculated, %:
C 70.31; H 4.72.
Compound XI. Yield 0.16 g (29%), Rf 0.11
1
(chloroform), mp 121 123 C (from EtOH). H NMR
spectrum, , ppm: 1.22 t (3H, CH3, J = 7.14 Hz),
4.19 q (2H, OCH2CH3, J = 7.14 Hz), 4.65 s (2H,
OCH2), 6.27 d (1H, 3-H, J = 9.58 Hz), 6.78 d (1H,
6-H, J = 8.68 Hz), 7.65 d (1H, 4-H, J 9.58 Hz),
7.91 d.d (2H, o-H, J = 7.02, J = 1.20 Hz), 7.59
7.35 m (4H, 5-H, m-H, p-H). Mass spectrum, m/z
(Irel, %): 352 (26) [M]+ . Found, %: C 68.06; H 4.56.
C20H16O6. Calculated, %: C 68.18; H 4.58.
8-Benzoyl-4,9-dimethyl-2H-furo[2,3-h]chromen-
2-one (XXVI) was synthesized as described above
for compound XXI from coumarin I and phenacyl
bromide. Yield 0.58 g (79%), mp 208 209 C (from
EtOH). 1H NMR spectrum, , ppm: 2.52 d (3H,
4-CH3, J = 1.08 Hz), 2.93 s (3H, 9-CH3), 6.31 d (1H,
3-H, J = 1.08 Hz), 7.46 d (1H, 6-H, J = 8.84 Hz),
7.49 7.64 m (3H, m-H, p-H), 7.68 d (1H, 5-H, J =
8.86 Hz), 8.05 d.d (2H, o-H, J = 8.20, J = 1.70 Hz).
Mass spectrum, m/z (Irel, %): 318 (95) [M]+ , 317
(100) [M H]+. Found, %: C 75.43; H 4.41. C20H14O4.
Calculated, %: C 75.46; H 4.43.
3
4
3
4
Compound XXII. Yield 0.34 g (54%), Rf 0.28
1
(chloroform), mp 168 170 C (from EtOH). H NMR
spectrum, , ppm: 1.22 t (3H, CH3, J = 7.12 Hz),
4.30 q (2H, CH2, J = 7.14 Hz), 6.34 d (1H, 3-H, J =
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 7 2001

NEW SYNTHESIS OF 8-ALKOXYCARBONYLANGELICINS
4,9-Dimethyl-8-(4-toluoyl)-2H-furo[2,3-h]chrom- REFERENCES
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(from EtOH). H NMR spectrum, , ppm: 1.36 t (3H,
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1
mp 206 207 C (from EtOH). H NMR spectrum, ,
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C 76.29; H 5.24.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 7 2001

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