Polyalkoxybenzenes from plant sources 2. Synthesis of isoxazoline analogs of combretastatin from natural allyl(methylenedioxy)methoxybenzenes

Article abstract of DOI:10.1007/s11172-007-0391-7

A series of analogs of the natural mitostatic agent combretastatin were synthesized by the reaction of nitrile oxides with natural allylbenzenes, such as myristicin, apiol, and dillapiol. The 1,3-dipolar cycloaddition reactions in allylic systems proceed regiospecifically. The reactions with trans isomers of propenylbenzenes, viz., isomyristicin, isoapiol, and isodillapiol, as dipolarophiles produce regioisomers.

Full text of DOI:10.1007/s11172-007-0391-7

Russian Chemical Bulletin, International Edition, Vol. 56, No. 12, pp. 2460—2465, December, 2007
2460
Polyalkoxybenzenes from plant sources
2.* Synthesis of isoxazoline analogs of combretastatin
from natural allyl(methylenedioxy)methoxybenzenes

D. V. Tsyganov, A. P. Yakubov, L. D. Konyushkin, S. I. Firgang, and V. V. Semenov
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5328. Eꢀmail: tsyg@mail.ioc.ac.ru
A series of analogs of the natural mitostatic agent combretastatin were synthesized by the
reaction of nitrile oxides with natural allylbenzenes, such as myristicin, apiol, and dillapiol.
The 1,3ꢀdipolar cycloaddition reactions in allylic systems proceed regiospecifically. The reacꢀ
tions with trans isomers of propenylbenzenes, viz., isomyristicin, isoapiol, and isodillapiol, as
dipolarophiles produce regioisomers.
Key words: isoxazolines, nitrile oxides, 1,3ꢀdipolar cycloaddition, myristicin, apiol, dillapiol.
Combretastatins 1 (САꢀ1, CAꢀ2, and СAꢀ4), which
are natural antimitotic compounds isolated from the bark
To search for more effective combretastatin derivaꢀ
tives, a series of their analogs have been synthesized in
recent years, and compounds superior to natural combreꢀ
tastatins in activity were found.5
The affinity of combretastatin for tubulin is deterꢀ
mined by the presence of two polyoxybenzene rings
bridged by an appropriate linker, which provides the bioꢀ
logically active spatial configuration of the molecule and
forces the rings to be located at a strictly specified disꢀ
tance from each other necessary for the interaction with
the colchicine site of tubulin.5
of the South African bush willow tree (Combretum cafꢀ
frum),2 are potent tubulin polymerization inhibitors
,
bound to the colchicine site.3 The Оꢀphosphorylated deꢀ
rivative of combretastatin CAꢀ4 is currently under cliniꢀ
cal trials as an antitumor drug.4
To prevent isomerization of the active cis form of comꢀ
bretastatin to the inactive trans form taking place in living
organisms, i.e., to fix the relative arrangement of the rings,
many researchers used6—9 heterocycles (most often, fiveꢀ
membered heterocycles), in particular, isoxazolines (for
example, 2) and isoxazoles 3, as linkers. 3,5ꢀDiaryl derivꢀ
atives were found to be less active than the 4,5ꢀisomers.
The introduction of various substituents (OH, NH2,
or F) into the ring В was documented.5 However, studies
on modifcations of the ring A are lacking due, apparently,
to low accessibility of polyalkoxybenzenes containing
more than three alkoxy groups.
In the only study,6 the modification of the ring А by
introducing the 2ꢀNH2 group was demonstrated to give a
combretastatin analog with the same activity level. We
expected that the replacement of the NH2 group by the
bioisosteric methoxy group would lead to the formation
of highly active combretastatin analogs.
The aim of the present study was to synthesize new
combretastatin analogs containing a larger number of
methoxy groups in the ring А starting from natural alꢀ
lylpolyalkoxybenzenes 4—7 and to investigate their antiꢀ
R = OH, R´ = Me
R = H, R´R´ = —CH2— (CA-2)
R = H, R´ = Me (CA-4)
(CA-1)
* For Part 1, see Ref. 1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2375—2380, December, 2007.
1066ꢀ5285/07/5612ꢀ2460 © 2007 Springer Science+Business Media, Inc.

Synthesis of isoxazoline analogs of combretastatin Russ.Chem.Bull., Int.Ed., Vol. 56, No. 12, December, 2007 2461
Scheme 1
proliferative activity. The replacement of the double bond
by the isoxazoline or isoxazole fragments seemed to be
most reasonable, because these analogs were demonstratꢀ
ed to be most active among known azolocombretastꢀ
atins.6—9 According to our unpublished data, the starting
polymethoxybenzenes isoapiol and isodillapiol exhibit the
antiproliferative activity, i.e., arrest the cell division of sea
R
CH2
Cl
O
O
Et3N
HO
+
N
CO2Et
20 C
RT
8
OMe
urchin embryo at concentrations of 5—20 µmol L–1
.
R
4—6
O
CO2Et
O
N
O
RT
OMe
9—11
4, 9: R = R´ = H
5, 10: R = OMe, R´ = H
6, 11: R = H, R´ = OMe
R = R´ = H (4, myristicin)
R = OMe, R´ = H (5, apiol)
R = H, R´ = OMe (6, dillapiol)
Scheme 2
We found1 that allylpolymethoxybenzenes 4—7 are
present at high concentrations in commercial essence oils
from seeds of certain varieties of dill and parsley and
developed procedures for the isolation of these compounds
at the kilogram scale.
Results and Discussion
Isoxazolines were synthesized by the 1,3ꢀdipolar cyꢀ
cloaddition reaction of nitrile oxides with unsaturated
compounds10 (myristicin, apiol, dillapiol, and the trans
isomers of the corresponding isomeric propenylbenzenes)
in the temperature range of 0—20 °C. Unstable nitrile
oxides were generated from hydroximoyl chlorides using
triethylamine as a base. In addition to the target isoxazoꢀ
lines, the corresponding furoxans were obtained as byꢀ
products in moderate yields. The latter compounds were
removed by crystallization. To decrease the amount of
furoxans, a small excess of an unsaturated compound and
dilute solutions of the reagents were used.
Ethoxycarbonylformonitrile oxide (hydroximoyl chloꢀ
ride 8 10,11 is a precursor of this compound) served as the
model 1,3ꢀdipole (Scheme 1).
The yields of crystalline isoxazolines 9—11 were
60—70%; the purity was higher than 95%. In addition,
small amounts of the regioisomers were produces. The
latter were detected by NMR spectroscopy.
The reaction of compounds 4—6 with 4ꢀmethoxybenꢀ
zonitrile oxide (the corresponding hydroximoyl chloride
12 is a precursor of the latter compound) (Scheme 2) was
carried out at 0—5 °C. The yields of isoxazolines 13—15
were 65—80%.
Closer analogs of combretastatin in which the aromatꢀ
ic moiety of the fragment В is directly bound to isoxazoꢀ
line were synthesized from the readily available trans isoꢀ
mers isomyristicin 16, isoapiol 17, and isodillapiol 18
4, 13: R = R´ = H
5, 14: R = OMe, R´ = H
6, 15: R = H, R´ = OMe
(generated from compounds 4—6). The yields of the corꢀ
responding isoxazolines 19A, 20A, and 21A in the reacꢀ
tions with hydroximoyl chloride 8 are somewhat lower
due to the formation of regioisomeric products 19B, 20B,
and 21B in noticeable amounts (Scheme 3).
We failed to isolate the minor regioisomers of isoxazoꢀ
lines in the pure form, but the presence of these compounds
in the reaction mixture was unambiguously confirmed by
NMR spectroscopy based on the ratio of the signals for H(5)
of the isoxazoline ring. The formation of regioisomers is
associated with the less pronounced polarization of the douꢀ
ble bond in compounds 16—18 (compared to the allylic
system of myristicin, apiol, and dillapiol).
The cycloaddition of benzonitrile oxide to isoapiol (17)
has been studied earlier.12 The reaction gave the target
product in low yield. The formation of regioisomers was
not observed. However, we obtained compounds 22A+22B,
23A+23B, and 24A+24B in the reactions with 4ꢀmethoxyꢀ
benzonitrile oxide as the 1,3ꢀdipolarophile (Scheme 4).

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Russ.Chem.Bull., Int.Ed., Vol. 56, No. 12, December, 2007
Tsyganov et al.
Scheme 3
Only isoxazoline 23A was isolated in the individual
state. Isoxazolines 22A+22B and 24A+24B were obtained
as chromatographically inseparable mixtures. The ratios
of the regioisomers were determined by NMR spectrosꢀ
copy. The structures of compounds 24A and 24B were
confirmed by the NOESY spectrum of the mixture of
these compounds. The observed contacts are presented in
Scheme 5.
Scheme 5
16, 19A, 19B: R = R´ = H
17, 20A, 20B: R = OMe, R´ = H
18, 21A, 21B: R = H, R´ = OMe
Isoxazoline
Yield (%)
Ratio
A : B
19A
20A
21A
41.0
39.0
40.0
2.3 : 1.0
3.1 : 1.0
13.1 : 1.0
Evidently, sterically hindered nitrile oxides should beꢀ
have differently in this reaction. We chose stable nitrile
oxide of the aromatic series, viz., 2,4,6ꢀtrimethylbenzoniꢀ
trile oxide 25, as an example (Scheme 6).
Scheme 4
Scheme 6
16: R = R´ = H
16, 22A, 22B: R = R´ = H
17: R = OMe, R´ = H
18: R = H, R´ = OMe
17, 23A, 23B: R = OMe, R´ = H
18, 24A, 24B: R = H, R´ = OMe
Isoxazoline
Yield of regio-
isomers (%)
58.0
67.3 (47.5*)
68.5
Ratio
A : B
3.7 : 1.0
4.0 : 1.0
4.2 : 1.0
Isoxazoline
Yield of regio -
isomers (%)
81.2
76.0
83.4 (39.5*)
Ratio
A : B
1.0 : 1.9
1.0 : 1.8
1.0 : 1.4
22A+22B
23A+23B
24A+24B
26A+26B
27A+27B
28A+28B
* The yield of isoxazoline 23A after crystallization.
* The yield of isoxazoline 28B after crystallization.

Synthesis of isoxazoline analogs of combretastatin Russ.Chem.Bull., Int.Ed., Vol. 56, No. 12, December, 2007 2463
a rotary evaporator. The oily residue was crystallized from a 1 : 1
ethyl acetate—hexane mixture (200 mL), washed with hexane
(2×50 mL), and dried in air.
In this case, the inverse ratio of the regioisomers was
observed. 5ꢀMethylisoxazolines 26B, 27B, and 28B were
the major products. This is apparently associated with
considerable steric hindrance.13 We succeeded in isolatꢀ
ing isomer 28B in moderate yield by chromatography and
fractional crystallization in the reaction with isodillapiol
18. In other cases, the reactions gave chromatographicalꢀ
ly inseparable mixtures of regioisomers. The structure of
compound 28B was confirmed by the observed contacts
in the NOESY spectrum (Scheme 7).
Ethyl 5ꢀ(3ꢀmethoxyꢀ4,5ꢀmethylenedioxybenzyl)ꢀ4,5ꢀdihyꢀ
droisoxazoleꢀ3ꢀcarboxylate (9). The yield was 69%, m.p.
84—86 °C. Found (%): С, 58.24; Н, 5.37; N, 4.36. С15Н17NО6.
Calculated (%): С, 58.63; Н, 5.58; N, 4.56. 1Н NMR, δ: 1.25
(t, 3 H, MeCH2O, J = 7.0 Hz); 2.76 and 2.87 (both dd, 1 Н
each, CH2Ar, J = 7.9 Hz, J = 15.0 Hz); 2.91 (dd, 1 H, H(4), J =
8.0 Hz, J = 17.0 Hz); 3.17 (dd, 1 H, H(4), J = 10.0 Hz, J =
17.0 Hz); 3.80 (s, 3 H, OMe); 4.23 (q, 2 H, MeCH2O); 5.01 (dq,
1 H, H(5)); 5.95 (s, 2 H, OCH2O); 6.53 (s, 1 H, H(6´); 6.57 (s,
1 H, H(2´)).
Scheme 7
Ethyl 5ꢀ(2,5ꢀdimethoxyꢀ3,4ꢀmethylenedioxybenzyl)ꢀ4,5ꢀdihyꢀ
droisoxazoleꢀ3ꢀcarboxylate (10). The yield was 59%, m.p.
74—76 °C. Found (%): С, 57.12; Н, 5.36; N, 3.92. С16Н19NО7.
Calculated (%): С, 56.97; Н, 5.68; N, 4.15. 1Н NMR, δ: 1.26
(t, 3 H, MeCH2O, J = 7.0 Hz); 2.75 and 2.91 (both dd, 1 H each,
CH2Ar, J = 7.0 Hz, J = 15.0 Hz); 2.93 (dd, 1 H, H(4), J =
8.0 Hz, J = 17.0 Hz); 3.20 (dd, 1 H, H(4), J = 10.0 Hz, J =
17.0 Hz); 3.77 and 3.83 (both s, 3 H each, OMe); 4.25 (q, 2 H,
MeCH2O); 4.92 (dq, 1 H, H(5)); 6.00 (s, 2 H, OCH2O); 6.55
(s, 1 H, H(6´)).
Ethyl 5ꢀ(2,3ꢀdimethoxyꢀ4,5ꢀmethylenedioxybenzyl)ꢀ4,5ꢀdihyꢀ
droisoxazoleꢀ3ꢀcarboxylate (11). The yield was 62%, m.p.
79—81 °C. Found (%): С, 56.25; Н, 5.81; N, 4.01. С16Н19NО7.
Calculated (%): С, 56.97; Н, 5.68; N, 4.15. 1Н NMR, δ: 1.26
(t, 3 H, MeCH2O, J = 7.0 Hz); 2.73 and 2.89 (both dd, 1 H
each, CH2Ar, J = 7.9, J = 10.0 Hz); 2.93 (dd, 1 H, H(4), J =
8.0 Hz, J = 17.0 Hz); 3.32 (dd, 1 H, H(4), J = 10.0 Hz, J =
17.0 Hz); 3.69 and 3.93 (both s, 3 H each, OMe); 4.25 (q, 2 H,
MeCH2O); 4.96 (dq, 1 H, Н(5)); 5.97 (s, 2 H, OCH2O); 6.07
(s, 1 H, H(6´)).
Ethyl 5ꢀ(3ꢀmethoxyꢀ4,5ꢀmethylenedioxyphenyl)ꢀ4ꢀmethylꢀ
4,5ꢀdihydroisoxazoleꢀ3ꢀcarboxylate (19A). The yield was 41%,
m.p. 81—82 °C. Found (%): С, 58.94; Н, 5.79; N, 4.68.
С15Н17NО6. Calculated (%): С, 58.63; Н, 5.58; N, 4.56.
1Н NMR, δ: 1.27 (t, 3 H, MeCH2O, J = 7.0 Hz); 1.33 (d, 3 H,
MeCH, J = 7.0 Hz); 3.50 (m, 1 H, H(4)); 3.84 (s, 3 H, OMe);
4.27 (q, 2 H, MeCH2O); 5.25 (d, 1 H, H(5), J = 7.0 Hz); 6.00
(s, 2 H, OCH2O); 6.63 (s, 1 H, H(2´)); 6.70 (s, 1 H, H(6´)).
Ethyl 4ꢀ(3ꢀmethoxyꢀ4,5ꢀmethylenedioxyphenyl)ꢀ5ꢀmethylꢀ
4,5ꢀdihydroisoxazoleꢀ3ꢀcarboxylate (19B). 1Н NMR, δ: 1.17
(t, 3 H, MeCH2O, J = 7.0 Hz); 1.35 (d, 3 H, MeCH, J =
7.0 Hz); 4.10 (d, 1 H, H(4), J = 7.0 Hz); 4.17 (q, 2 H, MeCH2O);
4.71 (m, 1 H, H(5)); 5.99 (s, 2 H, OCH2O); 6.44 (s, 1 H,
H(2´)); 6.47 (s, 1 H, H(6´)).
To summarize, we demonstrated that the double bond
in biologically active natural compounds, such as myristiꢀ
cin, apiol, and dillapiol, as well as in their isomers, is
rather active in the 1,3ꢀdipolar cycloaddition reactions
with various nitrile oxides. According to the preliminary
data, compounds 9—11, 14, 15, and 21A exert an effect
on the cell division of sea urchin embryo.14
Experimental
1
Н NMR spectra were recorded on a Bruker DRXꢀ500
spectrometer (500 MHz) in DMSOꢀd6 with Me4Si as the interꢀ
nal standard. Mass spectra were obtained on a Finningan MAT
in INCOS 50 quadrupole mass spectrometer. TLC was carried
out on Merck 60F254 plates. Preparative chromatography was
performed on silica gel Аcros 0.035—0.070 mm, 60 А. Melting
points were determined on a Kofler hot stage. Elemental analyꢀ
sis was carried out on an automated Perkin—Elmer 2400 CHN
microanalyzer. Etoxycarbonylformohydroximoyl chloride,10
4ꢀmethoxybenzohydroximoyl chloride,15 2,4,6ꢀtrimethylbenꢀ
zonitrile oxide,16 isomyristicin,17 isoapiol,17 and isodillapiol17
were synthesized according to known procedures.
Cycloaddition of ethoxycarbonylformonitrile oxide to myristiꢀ
cin (4), apiol (5), dillapiol (6), and their isomers (16—18) (generꢀ
al procedure). A solution of triethylamine (17.3 g, 171 mmol) in
CH2Cl2 (200 mL) was added dropwise to a solution of comꢀ
pound 8 (24.8 g, 163 mmol) and the unsaturated compound
(180 mmol) in CH2Cl2 (600 mL) at 20 °C for 5 h. The reaction
mixture was stirred for 24 h, washed with water (2×150 mL),
and dried with anhydrous Na2SO4. The solvent was removed on
Ethyl 5ꢀ(2,5ꢀdimethoxyꢀ3,4ꢀmethylenedioxyphenyl)ꢀ4ꢀmethꢀ
ylꢀ4,5ꢀdihydroisoxazoleꢀ3ꢀcarboxylate (20A). The yield was 39%,
m.p. 97—98 °C. Found (%): С, 56.54; Н, 5.79; N, 4.01.
С16Н19NО7. Calculated (%): С, 56.97; Н, 5.68; N, 4.15.
1Н NMR, δ: 1.28 (t, 3 H, MeCH2O, J = 7.0 Hz); 1.34 (d, 3 H,
MeCH, J = 7.0 Hz); 3.47 (m, 1 H, H(4)); 3.78 and 3.80 (both s,
3 H each, OMe); 4.28 (q, 2 H, MeCH2O); 5.40 (d, 1 H, H(5),
J = 7.0 Hz); 6.05 (s, 2 H, OCH2O); 6.56 (s, 1 H, H(6´)).
Ethyl 4ꢀ(2,5ꢀdimethoxyꢀ3,4ꢀmethylenedioxyphenyl)ꢀ5ꢀmethꢀ
1
ylꢀ4,5ꢀdihydroisoxazoleꢀ3ꢀcarboxylate (20B). Н NMR, δ: 1.16
(t, 3 H, MeCH2O, J = 7.0 Hz); 1.47 (d, 3 H, MeCH, J =
7.0 Hz); 3.75 and 3.83 (both s, 3 H each, OMe); 4.08 (d, 1 H,
H(4), J = 7.0 Hz); 4.17 (q, 2 H, MeCH2O); 4.43 (m, 1 H,
H(5)); 6.04 (s, 2 H, OCH2O); 6.22 (s, 1 H, H(6´)).

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Russ.Chem.Bull., Int.Ed., Vol. 56, No. 12, December, 2007
Tsyganov et al.
Ethyl 5ꢀ(2,3ꢀdimethoxyꢀ4,5ꢀmethylenedioxyphenyl)ꢀ4ꢀmethylꢀ
4,5ꢀdihydroisoxazoleꢀ3ꢀcarboxylate (21A). The yield was 40%,
m.p. 92—94 °C. Found (%): С, 57.35; Н, 5.31; N, 4.02.
С16Н19NО7. Calculated (%): С, 56.97; Н, 5.68; N, 4.15.
1Н NMR, δ: 1.28 (t, 3 H, MeCH2O, J = 7.0 Hz); 1.33 (d, 3 H,
MeCH, J = 7.0 Hz); 3.43 (m, 1 H, H(4)); 3.71 and 3.94 (both s,
3 H each, OMe); 4.28 (q, 2 H, MeCH2O); 5.42 (d, 1 H, H(5),
J = 7.0 Hz); 6.00 and 6.01 (both s, 1 H each, OCH2O); 6.55 (s,
1 H, H(6´)).
(1.54 g, 8.28 mmol) and the unsaturated compound (7.52 mmol)
in CH2Cl2 (50 mL) at 0 °C for 2 h. The reaction mixture was
stirred for 24 h, washed with water (2×30 mL), and dried with
anhydrous Na2SO4. The solvent was removed on a rotary evapoꢀ
rator. The residue was subjected to column chromatography
(ethyl acetate—hexane, 1 : 4, as the eluent). The oily fraction
with Rf 0.58 was isolated (ethyl acetate—hexane, 1 : 2). Chroꢀ
matographically indistinguishable regiosiomers accounted for
97% of the total content of this fraction. The ratio between the
major and minor regioisomers was determined by 1Н NMR
spectroscopy. In the case of the addition to isodillapiol, the
major regioisomer (23A) was isolated by fractional crystallizaꢀ
tion from a 1 : 2 ethyl acetate—hexane mixture.
Ethyl 4ꢀ(2,3ꢀdimethoxyꢀ4,5ꢀmethylenedioxyphenyl)ꢀ5ꢀmethꢀ
1
ylꢀ4,5ꢀdihydroisoxazoleꢀ3ꢀcarboxylate (21B). Н NMR, δ: 1.17
(t, 3 H, MeCH2O, J = 7.0 Hz); 1.35 (d, 3 H, MeCH, J =
7.0 Hz); 3.65 and 3.90 (both s, 3 H each, OMe); 4.08 (d, 1 H,
H(4); J = 7.0 Hz); 4.17 (q, 2 H, MeCH2O); 4.59 (m, 1 H,
H(5)); 5.97 (s, 2 H, OCH2O); 6.18 (s, 1 H, H(6´)).
3ꢀ(4ꢀMethoxyphenyl)ꢀ5ꢀ(3ꢀmethoxyꢀ4,5ꢀmethylenedioxyꢀ
1
phenyl)ꢀ4ꢀmethylꢀ4,5ꢀdihydroisoxazole (22A). Н NMR, δ: 1.30
Cycloaddition of 4ꢀmethoxybenzonitrile oxide to myristicin
(4), apiol (5), and dillapiol (6) (general procedure). A solution of
triethylamine (24.10 g, 239 mmol) in CH2Cl2 (300 mL) was
added dropwise to a solution of hydroximoyl chloride 12 (42.10 g,
227 mmol) and the unsaturated compound (250 mmol) in
CH2Cl2 (700 mL) at 0 °C for 8 h. The reaction mixture was
stirred for 24 h, washed with water (2×150 mL), and dried with
anhydrous Na2SO4. The solvent was removed on a rotary evapoꢀ
rator. The oily residue was crystallized from a 1 : 2 ethyl aceꢀ
tate—hexane mixture (300 mL), washed with hexane (2×70 mL),
and dried in air.
3ꢀ(4ꢀMethoxyphenyl)ꢀ5ꢀ(3ꢀmethoxyꢀ4,5ꢀmethylenedioxyꢀ
benzyl)ꢀ4,5ꢀdihydroisoxazole (13). The yield was 67%, m.p. 103—
105 °C. Found (%): С, 66.62; Н, 5.43; N, 3.84. С19Н19NО5.
Calculated (%): С, 66.85; Н, 5.61; N, 4.10. 1Н NMR, δ: 2.77
and 2.91 (both dd, 1 H each, CH2Ar, J = 8.0 Hz, J = 15.0 Hz);
3.08 (dd, 1 H, H(4), J = 8.0 Hz, J = 17.0 Hz); 3.48 (dd, 1 H,
H(4), J = 10.0 Hz, J = 17.0 Hz); 4.87 (dq, 1 H, H(5)); 5.96 (s,
2 H, OCH2O); 6.58 (s, 1 H, H(2´)); 6.00 (s, 1 H, H(6´)); 7.00
(d, 2 H, H(2´), H(6´), J = 8.0 Hz); 7.60 (d, 2 H, H(3´), H(5´),
J = 8.0 Hz).
(d, 3 H, MeCH, J = 7.0 Hz); 3.79 (m, 1 H, H(4)); 3.80 and 3.83
(both s, 3 H each, OMe); 5.22 (d, 1 H, H(5), J = 7.0 Hz); 5.97
(s, 2 H, OCH2O); 6.17 (s, 1 H, H(6´)); 6.58 (s, 1 H, H(2´)); 7.02
(d, 2 H, H(3´), H(5´), J = 8.0 Hz); 7.65 (d, 2 H, H(2´), H(6´),
J = 8.0 Hz).
3ꢀ(4ꢀMethoxyphenyl)ꢀ4ꢀ(3ꢀmethoxyꢀ4,5ꢀmethylenedioxꢀ
yphenyl)ꢀ5ꢀmethylꢀ4,5ꢀdihydroisoxazole (22B). 1Н NMR, δ: 1.33
(d, 3 H, MeCH J = 7.0 Hz); 3.77 and 3.80 (both s, 3 H each,
OMe); 4.53 (q, 1 H, H(4), J = 7.0 Hz); 4.56 (m, 1 H, H(5));
5.89 and 5.91 (both s, 1 H each, OCH2O); 6.41 (s, 1 H, H(2´));
6.57 (s, 1 H, H(6´)); 6.92 (d, 2 H, H(3´), H(5´), J = 8.0 Hz);
7.55 (d, 2 H, H(2´), H(6´), J = 8.0 Hz).
3ꢀ(4ꢀMethoxyphenyl)ꢀ5ꢀ(2,5ꢀdimethoxyꢀ3,4ꢀmethylenedioxꢀ
yphenyl)ꢀ4ꢀmethylꢀ4,5ꢀdihydroisoxazole (23A). The yield was
48%, m.p. 91—93 °C. Found (%): С, 65.04; Н, 5.32; N, 3.51.
С20Н21NО6. Calculated (%): С, 64.68; Н, 5.70; N, 3.77. 1Н
NMR, δ: 1.31 (d, 3 H, MeCH, J = 7.0 Hz); 3.72 (m, 1 H, H(4));
3.73, 3.80, and 3.86 (all s, 3 H each, OMe); 5.31 (d, 1 H, H(5),
J = 7.0 Hz); 6.03 (d, 2 H, OCH2O, Jgem = 4.0 Hz); 6.49 (s, 1 H,
H(6´)); 7.00 (d, 2 H, H(3´), H(5´), J = 8.0 Hz); 7.65 (d, 2 H,
H(2´), H(6´), J = 8.0 Hz).
3ꢀ(4ꢀMethoxyphenyl)ꢀ5ꢀ(2,5ꢀdimethoxyꢀ3,4ꢀmethylenedioxꢀ
ybenzyl)ꢀ4,5ꢀdihydroisoxazole (14). The yield was 78%, m.p.
102—103 °C. Found (%): С, 64.21; Н, 5.31; N, 3.56.
С20Н21NО6. Calculated (%): С, 64.68; Н, 5.70; N, 3.77.
1Н NMR, δ: 2.72 and 2.89 (both dd, 1 H each, CH2Ar, J = 8.0
Hz, J = 15.0 Hz); 3.08 (dd, 1 H, H(4), J = 8.0 Hz, J = 17.0 Hz);
3.49 (dd, 1 H, H(4), J = 10.0 Hz, J = 17.0 Hz); 3.70 (s, 3 H,
OMe); 3.80 (s, 3 H, OMe(4´)); 3.93 (s, 3 H, OMe); 4.83 (dq, 1 H,
H(5)); 5.92 (s, 2 H, OCH2O); 6.60 (s, 1 H, H(6´)); 7.00 (d, 2 H,
H(3´), H(5´), J = 8.0 Hz); 7.60 (d, 2 H, H(2´), H(6´), J =
8.0 Hz).
3ꢀ(4ꢀMethoxyphenyl)ꢀ5ꢀ(2,3ꢀdimethoxyꢀ4,5ꢀmethylenedioxꢀ
ybenzyl)ꢀ4,5ꢀdihydroisoxazole (15). The yield was 67%, m.p. 98—
100 °C. Found (%): С, 64.32; Н, 5.45; N, 3.86. С20Н21NО6.
Calculated (%): С, 64.68; Н, 5.70; N, 3.77. 1Н NMR, δ: 2.73
and 2.90 (both dd, 1 H each, CH2Ar, J = 8.0 Hz, J = 15.0 Hz);
3.08 (dd, 1 H, H(4), J = 8.0 Hz, J = 17.0 Hz); 3.36 (dd, 1 H,
H(4), J = 10.0 Hz, J = 17.0 Hz); 3.77 (s, 3 H, OMe); 3.78 (s,
3 H, OMe(4´)); 3.81 (s, 3 H, OMe); 4.83 (dq, 1 H, H(5)); 5.98
(s, 2 H, OCH2O); 6.07 (s, 1 H, H(6´)); 6.99 (d, 2 H, H(2´),
H(6´), J = 8.0 Hz); 7.09 (s, 1 H, H(3´), H(5´), J = 8.0 Hz).
Cycloaddition of 4ꢀmethoxybenzonitrile oxide to isomyristicin
(16), isoapiol (17), and isodillapiol (18) (general procedure).
A solution of triethylamine (0.96 g, 9.52 mmol) in CH2Cl2
(30 mL) was added dropwise to a solution of compound 12
3ꢀ(4ꢀMethoxyphenyl)ꢀ4ꢀ(2,5ꢀdimethoxyꢀ3,4ꢀmethylenedioxꢀ
yphenyl)ꢀ5ꢀmethylꢀ4,5ꢀdihydroisoxazole (23B). 1Н NMR, δ: 1.36
(d, 3 H, MeCH, J = 7.0 Hz); 3.67, 3.74, and 3.81 (all s, 3 H
each, OMe); 4.52 (m, 1 H, H(5)); 4.66 (d, 1 H, H(4), J =
7.0 Hz); 6.02 (s, 2 H, OCH2O); 6.24 (s, 1 H, H(6´)); 6.93 (d,
2 H, H(3´), H(5´), J = 8.0 Hz); 7.46 (d, 2 H, H(2´), H(6´), J =
8.0 Hz).
3ꢀ(4ꢀMethoxyphenyl)ꢀ5ꢀ(2,3ꢀdimethoxyꢀ4,5ꢀmethylenedioxꢀ
yphenyl)ꢀ4ꢀmethylꢀ4,5ꢀdihydroisoxazole (24A). 1Н NMR, δ: 1.31
(d, 3 H, MeCH, J = 7.0 Hz); 3.41 (m, 1 H, H(4)); 3.77 (s, 3 H,
OMe(2´)); 3.80 (s, 3 H, OMe(4´)); 3.95 (s, 3 H, OMe(3´)); 5.39
(d, 1 H, H(5), J = 7.0 Hz); 5.95 and 5.99 (both s, 1 H each,
OCH2O); 6.42 (s, 1 H, H(6´)); 7.00 (d, 2 H, H(3´), H(5´), J =
8.0 Hz); 7.65 (d, 2 H, H(2´), H(6´), J = 8.0 Hz).
3ꢀ(4ꢀMethoxyphenyl)ꢀ4ꢀ(2,3ꢀdimethoxyꢀ4,5ꢀmethylenedioxꢀ
yphenyl)ꢀ5ꢀmethylꢀ4,5ꢀdihydroisoxazole (24B). 1Н NMR, δ: 1.34
(d, 3 H, MeCH, J = 7.0 Hz); 3.74 (s, 3 H, OMe(4´)); 3.76 (s,
3 H, OMe(2´)); 3.95 (s, 3 H, OMe(3´)); 4.50 (m, 1 H, H(5));
4.67 (d, 1 H, H(4), J = 7.0 Hz); 5.92 and 5.96 (both s, 1 H each,
OCH2O); 6.14 (s, 1 H, H(6´)); 6.92 (d, 2 H, H(3´), H(5´), J =
8.0 Hz).
Cycloaddition of 2,4,6ꢀtrimethylbenzonitrile oxide to isomyrisꢀ
ticin (16), isoapiol (17), and isodillapiol (18) (general procedure).
A solution of compound 25 (1.52 g, 9.44 mmol) and the unsatꢀ
urated compound (9.44 mmol) in CH2Cl2 (50 mL) was stirred at

Synthesis of isoxazoline analogs of combretastatin Russ.Chem.Bull., Int.Ed., Vol. 56, No. 12, December, 2007 2465
20 °C for 3 days. The solvent was removed on a rotary evaporaꢀ
tor. The ratio between the major (26B, 27B, and 28B) and
minor (26A, 27A, and 28a) regioisomers was determined by
1Н NMR spectroscopy. In the case of the addition to isodillapiꢀ
ol, the major regioisomer (28B) was isolated by fractional crysꢀ
tallization from a 1 : 2 ethyl acetate—hexane mixture.
5ꢀ(3ꢀMethoxyꢀ4,5ꢀmethylenedioxyphenyl)ꢀ4ꢀmethylꢀ3ꢀ
(2,4,6ꢀtrimethylphenyl)ꢀ4,5ꢀdihydroisoxazole (26A). 1Н NMR,
δ: 1.09 (d, 3 H, MeCH, J = 7.0 Hz); 2.16 (s, 6 H, Me(2´),
Me(6´)); 2.25 (s, 3 H, Me(4´)); 3.53 (m, 1 H, H(4)); 3.85 (s,
3 H, OMe); 5.20 (d, 1 H, H(5), J = 7.0 Hz); 6.02 (s, 2 H,
OCH2O); 6.70 (s, 1 H, H(6´)); 6.73 (s, 1 H, H(2´)); 6.94 (s, 2 H,
H(3´), H(5´)).
4ꢀ(3ꢀMethoxyꢀ4,5ꢀmethylenedioxyphenyl)ꢀ5ꢀmethylꢀ3ꢀ
(2,4,6ꢀtrimethylphenyl)ꢀ4,5ꢀdihydroisoxazole (26B). 1Н NMR,
δ: 1.42 (d, 3 H, MeCH, J = 7.0 Hz); 2.11 (s, 6 H, Me(2´),
Me(6´)); 2.19 (s, 3 H, Me(4´)); 3.71 (s, 3 H, OMe); 4.37 (d,
1 H, H(4), J = 7.0 Hz); 4.87 (m, 1 H, H(5)); 5.93 (s, 2 H,
OCH2O); 6.40 (s, 1 H, H(6´)); 6.42 (s, 1 H, H(2´)); 6.72 (s, 2 H,
H(3´), H(5´)).
5ꢀ(2,5ꢀDimethoxyꢀ3,4ꢀmethylenedioxyphenyl)ꢀ4ꢀmethylꢀ3ꢀ
(2,4,6ꢀtrimethylphenyl)ꢀ4,5ꢀdihydroisoxazole (27A). 1Н NMR,
δ: 1.23 (d, 3 H, MeCH, J = 7.0 Hz); 2.29 (s, 6 H, Me(2´),
Me(6´)); 2.25 (s, 3 H, Me(4´)); 3.53 (m, 1 H, H(4)); 3.79 and
3.86 (both s, 3 H each, OMe); 5.36 (d, 1 H, H(5); J = 7.0 Hz);
6.04 and 6.06 (both s, 1 H each, OCH2O); 6.61 (s, 1 H, H(6´));
6.94 (s, 2 H, H(3´), H(5´)).
4ꢀ(2,5ꢀDimethoxyꢀ3,4ꢀmethylenedioxyphenyl)ꢀ5ꢀmethylꢀ3ꢀ
(2,4,6ꢀtrimethylphenyl)ꢀ4,5ꢀdihydroisoxazole (27B). 1Н NMR,
δ: 1.43 (d, 3 H, MeCH, J = 7.0 Hz); 2.11 (s, 6 H, Me(2´),
Me(6´)); 3.37 (s, 3 H, OMe(2´)); 3.75 (s, 3 H, OMe(5´)); 4.67
(d, 1 H, H(4), J = 7.0 Hz); 4.87 (m, 1 H, H(5)); 5.95 and 5.96
(both s, 1 H each, OCH2O); 6.46 (s, 1 H, H(6´)); 6.85 (s, 2 H,
H(3´), H(5´)).
References
1. V. V. Semenov, V. V. Rusak, E. M. Chartov, M. I. Zaretskii,
L. D. Konyushkin, S. I. Firgang, A. O. Chizhov, V. V. Elkin,
N. N. Latin, V. M. Bonashek, and O. N. Stas´eva, Izv. Akad.
Nauk, Ser. Khim., 2007, 2364 [Russ. Chem. Bull., Int. Ed.,
2007, 56, 2364].
2. G. R. Pettit, S. B. Singh, E. Hamel, C. M. Lin, D. S.
Alberts, and D. CarciaꢀKendall, Experientia, 1989, 45, 209.
3. C. M. Lin, S. B. Singh, P. S. Chu, R. O. Dempcy, J. M.
Schmidt, G. R. Pettit, and E. Hamel, Mol. Pharmacol., 1988,
34, 200.
4. G. R. Pettit, C. Jr. Temple, V. L. Narayanan, R. Varma,
M. J. Simpson, M. R. Boyed, G. A. Rener, and N. Bansal,
Antiꢀcancer Drug Des., 1995, 10, 299.
5. G. C. Tron, T. Pyrali, G. Sorba, F. Pagliai, S. Busacca, and
A. A. Genazzani, J. Med. Chem., 2006, 49, 3033.
6. J. Kaffy, R. Pontikis, D. Carrez, A. Croisy, C. Monneret,
C. Mailliet, and JꢀC. Florent, Bioorg. Med. Chem., 2006,
14, 4067.
7. J. Kaffy, C. Monneret, C. Mailliet, A. Commercon, and R.
Pontikis, Tetrahedron Lett., 2004, 45, 3359.
8. D. Simoni, G. Grisolia, G. Giannini, M. Roberti, R. Ronꢀ
danin, L. Piccagli, R. Baruchello, M. Rossi, R. Romagnoli,
F. P. Invidiata, S. Grimaudo, M. K. Jung, E. Hamel, N.
Gebbia, L. Grosta, V. Abbadessa, A. D. Cristina, L. Dusoꢀ
nchet, M. Meli, and M. Tolomeo, J. Med. Chem., 2005,
48, 723.
9. ChangꢀMing Cun, LeeꢀGin Lin, HisꢀLung Yu, ChinꢀYu
Cheng, YaꢀChuan Tsai, ChiꢀWei Chu, YiꢀHui Din, Yatꢀ
Pang Chau, and MingꢀJaw Don, Bioorg. Med. Chem., 2007,
17, 1078.
10. A. P. Kozikowski and M. Adamczyk, J. Org. Chem., 1983,
48, 366.
11. L. Panizzi, Gazz. Chim. Ital., 1939, 69, 322.
12. G. Stagno d´Alcontres, Gazz. Chim. Ital., 1952, 82, 823.
13. C. Grundmann and P. Grunanger, The Nitrile Oxides, Springꢀ
erꢀVerlag, Berlin, 1971, 116.
5ꢀ(2,3ꢀDimethoxyꢀ4,5ꢀmethylenedioxyphenyl)ꢀ4ꢀmethylꢀ3ꢀ
(2,4,6ꢀtrimethylphenyl)ꢀ4,5ꢀdihydroisoxazole (28A). 1Н NMR,
δ: 1.00 (d, 3 H, MeCH, J = 7.0 Hz); 2.16 (s, 6 H, Me(2´),
Me(6´)); 2.25 (s, 3 H, Me(4´)); 3.54 (m, 1 H, H(4)); 3.77 and
3.97 (both s, 3 H each, OMe); 5.37 (d, 1 H, H(5), J = 7.0 Hz);
6.02 (s, 2 H, OCH2O); 6.61 (s, 1 H, H(6´)); 6.93 (s, 2 H, H(3´),
H(5´)).
14. M. N. Semenova, D. V. Tsyganov, A. P. Yakubov, A. S.
Kiselyov, and V. V. Semenov, ACS Chemical Biology, 2007,
2, No. 12.
4ꢀ(2,3ꢀDimethoxyꢀ4,5ꢀmethylenedioxyphenyl)ꢀ5ꢀmethylꢀ3ꢀ
(2,4,6ꢀtrimethylphenyl)ꢀ4,5ꢀdihydroisoxazole (28B). The yield
was 40%, m.p. 128—130 °C. Found (%): С, 64.29; Н, 5.81; N,
3.61. С20Н21NО6. Calculated (%): С, 64.68; Н, 5.70; N, 3.77.
1Н NMR, δ: 1.42 (d, 3 H, MeCH, J = 7.0 Hz); 2.10 (s, 6 H,
Me(2´), Me(6´)); 2.19 (s, 3 H, Me(4´)); 3.25 (s, 3 H, OMe(2´));
3.84 (s, 3 H, OMe(3´)); 4.63 (d, 1 H, H(4), J = 7.0 Hz); 4.79 (m,
1 H, H(5)); 5.95 and 5.97 (both s, 1 H each, OCH2O); 6.49 (s,
1 H, H(6´)); 6.84 (s, 2 H, H(3´), H(5´)).
15. H. Metzger, Herstellung von Oximen, Methoden der Organisꢀ
chen Chemie (HoubenꢀWeyl), 4. Aufl., Georg Thieme Verlag,
Stuttgart, 1968, 10/4, 98.
16. M. Desroses, F. Chery, A. Tatibouet, O. Lucchi, and
P. Rollin, Tetrahedron: Asymmetry, 2002, 13, 2535.
17. J. Ginsberg, Ber., 1888, 21, 1192.
Received July 6, 2007;
in revised form November 23, 2007