Semisynthesis of linarin, acacetin, and 6-iodoapigenin derivatives from diosmin

Article abstract of DOI:10.1021/np040079b

Semisynthesis of linarin and acacetin from the Citrus flavonoid diosmin was performed via, as first intermediate, the 3′-O-phenyltetrazolyl ether of diosmin. This paper relates also a semisynthetic access to 6-iodoapigenin derivatives, which are key compounds in the synthesis of some biflavonoids such as robustaflavone.

Full text of DOI:10.1021/np040079b

1624
J . Nat. Prod. 2004, 67, 1624-1627
Sem isyn th esis of Lin a r in , Aca cetin , a n d 6-Iod oa p igen in Der iva tives fr om
Diosm in
J e´roˆme Quintin and Guy Lewin*
Laboratoire de Pharmacognosie (BioCIS, UMR 8076 CNRS), Centre d’Etudes Pharmaceutiques, 5 Rue J .-B. Cle´ment,
92296 Chaˆtenay-Malabry Cedex, France
Received March 26, 2004
Semisynthesis of linarin and acacetin from the Citrus flavonoid diosmin was performed via, as first
intermediate, the 3′-O-phenyltetrazolyl ether of diosmin. This paper relates also a semisynthetic access
to 6-iodoapigenin derivatives, which are key compounds in the synthesis of some biflavonoids such as
robustaflavone.
Diosmin (diosmetin 7-O-rutinoside) (1) is a natural
flavone glycoside therapeutically used to improve the
symptoms of venous and lymphatic vessel insufficiency.
Diosmin is readily obtained by dehydrogenation of the
corresponding flavanone glycoside, hesperidin, that is
abundant in the pericarp of various Citrus.1 The readily
availability of 1 or its aglycone diosmetin (2) from the low-
priced hesperidin makes these flavones excellent starting
materials for semisynthetic modifications. In previous
papers, we described the preparation of original flavones
endowed with new biological activities compared with 1 and
2 (modulation of multidrug resistance, inhibition of phos-
phodiesterases IV).2,3 The purpose of this present study is
twofold and consists of the semisynthetic access to linarin
(3) on one hand and to 6-iodoapigenin derivatives on the
other hand. Linarin is the main active compound of some
medicinal plants such as Buddleia cordata from Mexico4
and Chrysanthemum zawadskii var. latilobum from Ko-
rea.5 This flavonoid was shown to possess antipyretic,
analgesic, and anti-inflammatory activities, which could
account for some indications of these plants in folk medi-
cine.4,5 More recently, linarin was identified in the well-
known species in herbal medicine Valeriana officinalis, and
its sedative and sleep-enhancing properties were described
for the first time.6 6-Iodoapigenin derivatives are known
to be key intermediates for access to some biflavonoids with
apparatus, transfer hydrogenation with hydrazine, formic
two apigenin (4) units connected via at least one 6-position
acid, or ammonium formate).9,10 The best results were
such as robustaflavone (5), an inhibitor of hepatitis B virus
observed with 10% Pd-C and ammonium formate in
(HBV).7
refluxing methanol, which cleaved the C3′-O bond within
Synthesis of linarin (3) or 6-iodoapigenin derivatives
4.5 h. Workup of the reaction allowed isolation of pure
from diosmin (1) requires removal of the 3′-hydroxyl group
linarin (3); however, the majority of this compound re-
in a two-step deoxygenation sequence. Two distinct meth-
mained either adsorbed on or crystallized within the
ods were conceivable through reduction of either a sul-
charcoal after filtration, which was then selectively eluted
fonate ester8 or an electron-withdrawing ether such as
with DMF. The identification of 3 was done by comparison
phenyltetrazolyl ether.9 The unlikely regiospecific sulfona-
(physical and spectroscopic data) with an authentic sample.
tion of the 3′-hydroxy group in the presence of the rutinosyl
The overall yield of the conversion of diosmin to linarin
moiety prompted consideration of 3′-OH ether formation
without isolation of the intermediate tetrazolyl ether was
(Scheme 1). Treatment of diosmin (1) with 5-chloro-1-
53%.
phenyl-1H-tetrazole (DMF, KHCO3, 80 °C, 2 h) gave the
With access to linarin, the second aim of this study was
tetrazolyl ether (6) as the main compound. 6 could be
the synthesis of 6-iodoapigenin derivatives. The regiose-
isolated and identified as a pure compound after crystal-
lective 6-iodination was accomplished with benzyltri-
lization from methanol (ESIMS m/z 775 [M + Na]+; mp
methylammonium dichloroiodate (BTMA‚ICl2)11 according
175-177 °C; 40% yield). However, according to TLC (silica
to a method recently developed in our laboratory.12 Linarin
gel, CH2Cl2-MeOH, 85:15), the crude, dried residue of 6
was first converted to 5-hydroxyhexaacetyllinarin (7) in two
could be submitted to the next step without further
steps: (a) Ac2O-pyridine, rt, 48 h; (b) TFA, rt, 6 h;13 88%).
purification. Hydrogenolysis of the tetrazolyl ether (6) was
Reaction of 7 with 1 equiv of BTMA‚ICl2 (CH2Cl2-MeOH,
investigated under various conditions (H2/Pd-C in a Parr
CaCO3, rt, 24 h) led to formation of the amorphous
compound 8 in 98% yield. 8 was homogeneous on TLC
(silica gel, CH2Cl2-MeOH, 98:2), but its H NMR spectrum
* To whom correspondence should be addressed. Tel: 33 1 46 83 55 93.
Fax: 33 1 46 83 53 99. E-mail: guy.lewin@cep.u-psud.fr.
1
10.1021/np040079b CCC: $27.50
© 2004 American Chemical Society and American Society of Pharmacognosy
Published on Web 08/18/2004

Notes
J ournal of Natural Products, 2004, Vol. 67, No. 9 1625
Sch em e 2a
Sch em e 1a
a
a
Reagents: (a) KHCO3, 5-chloro-1-phenyl-1H-tetrazole in DMF; (b) Pd-
Reagents: (a) KHCO3, benzyl chloride in DMF; (b) KHCO3, 5-chloro-
C, HCOONH4 in MeOH; (c) Ac3O in pyridine; TFA; (d) BTMA‚ICl2, CaCO3
in CH2Cl2-MeOH; (e) NaOH-THF; HCl until pH 4; removal of THF;
naringinase; (e) HCl 11 N.
1-phenyl-1H-tetrazole in DMF; (c) Pd-C, HCOONH4 in MeOH; (c) K2CO3
MeI in DMF; (e) BTMA,ICl2, CacO3 in CH2Cl2-MeOH.
(95%), which was iodinated to 7,3′-dimethyl-6-iodoapigenin
(15) (73%).12
To the best of our knowledge, this work describes the
first semisynthesis of linarin and acacetin from an easily
available citroflavonoid and allows access to key intermedi-
ates in the synthesis of some biflavonoids.
displayed a mixture of two compounds in a 92:8 ratio [easily
inferred from the H NMR spectrum by comparing integra-
1
tion of signals of the hydrogen-bonded phenolic proton at
13.90 (major) and 14.05 ppm (minor)]. The iodo substitution
at C-6 for the major compound was proven by comparison
of HMQC and HMBC NMR experiments on 7 and 8, which
indicated a strong shielding by the iodine of C-6 at δ 71.0
ppm for 8 (99.5 ppm for 7), Finally, the observation in the
ESI mass spectrum of 8 of a single peak at m/z 993 [M +
Na]+ confirmed 8 to be a mixture of two derivatives,
monoiodinated at C-6 for the major product and, by analogy
with our previous results,12 at C-8 for the minor component.
The last step of the sequence was the hydrolysis of the
glycosidic bond, which was not expected to pose problems.
However, the various acid hydrolytic conditions mainly
gave rise to acacetin (9), resulting from a protodehaloge-
nation mechanism.14 This unwanted result prompted us
to turn to enzymatic hydrolysis. Compound 8 was submit-
ted sequentially in a one-pot procedure to saponification
(THF-1 N NaOH, rt, 3 h), then, after removal of THF and
adjustment of the medium to pH 4, to the action of
naringinase for 120 h at 40 °C. Successive extractions of
the reaction with CH2Cl2 and EtOAc afforded 6-iodoacace-
tin (10) (EIMS m/z 410 M+; mp 254-256 °C; 52% yield)
and 6-iodoacacetin 7-O-glucoside (11) (ESIMS m/z 595 (M
+ Na)+; mp 239-240 °C; 6% yield) resulting from a partial
hydrolysis. A detailed NMR study (HMQC, HMBC, NOE-
SY) of 10 unambiguously confirmed the 6-iodo substitution.
The protodehalogenation encountered during the acid
hydrolysis indicated that it is more judicious to carry out
the 6-iodination step with an aglycone rather than a
glycoside. Therefore, acacetin (9) was easily prepared by
acid hydrolysis of linarin (HCl 11 N, 50 °C, 1.5 h, 70%).
An alternative pathway to acacetin (9) from the readily
available diosmetin (2) was also performed via the isolated
intermediate compounds 7-benzyldiosmetin (12) and 7-ben-
zyl-3′-phenyltetrazolyldiosmetin (13) in 30% overall yield
(Scheme 2). Last, methylation of 9 at the 7-position (K2-
CO3, MeI, DMF, rt) afforded 7,4′-dimethylapigenin (14)
Exp er im en ta l Section
Gen er a l Exp er im en ta l P r oced u r es. Melting points were
determined with a micro-Koffler and are uncorrected. 1H NMR
spectra, NOESY experiments, and 1H-1H (COSY) and 1H-
13C (HMQC and HMBC) were performed with a Bruker AM-
400. EIMS were registered on an Automass Thermoquest with
EI source (70 eV) and ESIMS on a Navigator Aqa thermoquest
with an ES source (MeOH, flow rate 5 µL/min) (70 eV). TLC
data were obtained with Merck 60 F 254 silica precoated on
aluminum sheets. Samples of linarin and acacetin were from
Extrasynthese.
Lin a r in (3) fr om Diosm in (1). To a suspension of 1 (4.864
g, 8 mmol) and KHCO3 (1.6 g, 16 mmol) in DMF (100 mL)
was added 5-chloro-1-phenyl-1H-tetrazole (2.98 g, 16 mmol)
and the mixture stirred under nitrogen for 2 h at 80 °C. The
reaction mixture was cooled, filtered, and evaporated to
dryness. One-hundredth of the dried residue (78 mg) was
crystallized from MeOH and provided 6 (24 mg, 40%).
3′-O-(1-P h en yltetr a zol-5-yl)d iosm in (6): pale-yellow crys-
tals; mp 175-177 °C; 1H NMR (DMSO-d6) δ [aglycone moiety]
3.88 (3H, s, OCH3-4′), 6.47 (1H, d, J ) 2 Hz, H-6), 6.81 (1H, d,
J ) 2 Hz, H-8), 7.00 (1H, s, H-3), 7.48 (1H, d, J ) 8.8 Hz,
H-5′), 7.62 (1H, t, J ) 8.8 Hz, H-4 phenyltetrazole), 7.70 (2H,
t, J ) 8.8 Hz, H-3 and H-5 phenyltetrazole), 7.87 (2H, d, J )
8.8 Hz, H-2 and H-6 phenyltetrazole), 8.12 (1H, dd, J ) 8.8
and 2 Hz, H-6′), 8.34 (1H, d, J ) 2 Hz, H-2′), 12.8 (1H, s, OH-
5); [sugar moiety] inner glucose 3.18 (1H, H-4′′), 3.29 (2H, H-2′′
and H-3′′), 3.47 (1H, H-6′′), 3.58 (1H, H-5′′), 3.86 (1H, H-6′′),
5.06 (1H, d, J ) 7.2 Hz, H-1′′); terminal rhamnose 1.07 (3H,
d, J ) 6.4 Hz, H-6′′′), 3.18 (1H, H-4′′′), 3.40 (1H, H-5′′′), 3.47
(1H, H-3′′′), 3.68 (H-2′′′), 4.55 (1H, s, H-1′′′); 4.44, 4.59, 4.68,
5.18, 5.20, 5.43 (6H, sugar hydroxyls); 13C NMR (DMSO-d6) δ
[aglycone moiety] 56.0 (CH3, OCH3-4′), 94.5 (CH, C-8), 99.2
(CH, C-6), 104.4 (CH, C-3), 105.4 (C, C-10), 113.8 (CH, C-5′),
120.0 (CH, C-2′), 122.8 (CH, C-2 and C-6 phenyltetrazole),

1626 J ournal of Natural Products, 2004, Vol. 67, No. 9
Notes
122.9 (C, C-1′), 126.2 (CH, C-6′), 129.9 (CH, C-4 phenyltetra-
zole), 130.1 (CH, C-3 and C-5 phenyltetrazole), 142.0 (C, C-3′),
153.1 (C, C-4′), 156.8 (C, C-9), 162.4 (C, C-2), 163.0 (C, C-7),
181.8 (C, C-4); [sugar moiety] inner glucose 66.1 (CH2, C-6′′),
69.5a (CH, C-4′′), 72.8 (CH, C-2′′), 75.6 (CH, C-5′′), 76.1 (CH,
C-3′′), 99.8 (CH, C-1′′); terminal rhamnose 17.6 (CH3, C-6′′′),
68.1 (CH, C-5′′′), 70.1a (CH, C-2′′′), 70.2a (CH, C-3′′′), 72.1 (CH,
C-4′′′), 100.5 (CH, C-1′′′), ainterchangeable; ESIMS m/z 775 [M
+ Na]+; HRESIMS m/z 775.2120 (calcd for C35H36N4O15Na,
775.2075).
A solution of the remaining dried residue in MeOH (500 mL)
was added to ammonium formate (2.52 g, 40 mmol) and 10%
Pd-C (1.75 g) and the mixture stirred at reflux under nitrogen
for 5 h. The reaction mixture was cooled, and the catalyst was
separated and washed with MeOH (twice 50 mL) then DMF
until the filtrate was colorless. Evaporation to dryness of DMF
afforded pure linarin (3) (2.485 g, 53%) as an off-white powder.
residue of compound 8 [TLC on silica gel (CH2Cl2-MeOH, 98:
2): homogeneous blue spot with FeCl3] (0.719 g, 99%).
5-Hyd r oxy-6-iod oh exa a cetyllin a r in (8): yellowish amor-
phous powder; 1H NMR (CDCl3) δ [aglycone moiety] 3.90 (3H,
s, OCH3-4′), 6.66 (2H, s, H-3 and H-8), 7.04 (2H, d, J ) 8.8
Hz, H-3′ and H-5′), 7.86 (major) and 8.01 (minor) (2H, d, J )
8.8 Hz, H-2′ and H-6′), 13.90 (major) and 14.05 (minor) (1H,
s, OH-5); [sugar moiety] 1.15 (3H, d, J ) 6.4 Hz, H-6′′′), 3.7-
5.4 (12 sugar protons); 1.84-2.10 (18H, 6s, 6 sugar acetyles);
13C NMR (CDCl3) δ [aglycone moiety] 55.5 (CH3, OCH3-4′), 71.0
(C, C-6), 93.9 (CH, C-8), 104.4 (CH, C-3), 106.2 (C, C-10), 114.2
(CH, C-3′ and C-5′), 123.1 (CH, C-2′), 128.0 (CH, C-2′ and C-6′),
157.4 (C, C-9), 161.0 (C, C-5), 162.5 (C, C-4′), 164.5 (C, C-2),
181.5 (C, C-4); [sugar moiety] inner glucose 65.9 (CH2, C-6′′),
69.0 (CH, C-4′′), 70.6 (CH, C-3′′), 72.5 (CH, C-2′′), 73.1 (CH,
C-5′′), 98.9 (CH, C-1′′); terminal rhamnose 17.0 (CH3, C-6′′′),
66.1 (CH, C-5′′′), 67.3a (CH, C-2′′′), 68.8a (CH, C-3′′′), 70.4 (CH,
C-4′′′), 97.7 (CH, C-1′′′); 20-22 and 167-172 (6 sugar acetyl
Lin a r in (3): mp 260-262 °C; 1H NMR (DMSO-d6) δ
[aglycone moiety] 3.86 (3H, s, OCH3-4′), 6.49 (1H, d, J ) 2
Hz, H-6), 6.78 (1H, d, J ) 2 Hz, H-8), 6.92 (1H, s, H-3), 7.14
(2H, d, J ) 8.5 Hz, H-3′ and H-5′), 8.04 (2H, d, J ) 8.5 Hz,
H-2′ and H-6′), 12.9 (1H, s, OH-5); [sugar moiety] 1.10 (3H, d,
J ) 6.4 Hz, H-6′′′), 3.1-3.9 (10 sugar protons) 4.52 (1H, s,
H-1′′′), 5.04 (1H, d, J ) 7.2 Hz, H-1′′), 4.40, 4.52, 4.64, 5.12,
5.17, 5.40 (6H, sugar hydroxyls); 13C NMR (DMSO-d6) δ
[aglycone moiety] 55.7 (CH3, OCH3-4′), 95.0 (CH, C-8), 99.9
(CH, C-6), 104.0 (CH, C-3), 105.7 (C, C-10), 114.9 (CH, C-3′
and C-5′), 122.8 (C, C-1′), 128.6 (CH, C-2′ and C-6′), 157.1 (C,
C-9), 161.3 (C, C-5), 162.6 (C, C-4′), 163.1 (C, C-7), 164.1 (C,
C-2), 182.2 (C, C-4); [sugar moiety] inner glucose 66.3 (CH2,
C-6′′), 69.8a (CH, C-4′′), 73.3 (CH, C-2′′), 75.9 (CH, C-5′′), 76.5
(CH, C-3′′), 100.2 (CH, C-1′′); terminal rhamnose 18.0 (CH3,
C-6′′′), 68.5 (CH, C-5′′′), 70.6a (CH, C-2′′′), 71.2a (CH, C-3′′′),
a
groups), interchangeable; ESIMS m/z 993 [M + Na]+.
A solution of 8 (0.194 g, 0.2 mmol) in a mixture of THF-
0.1 N aqueous NaOH (1:2) (15 mL) was stirred at room
temperature for 3 h. THF was removed under vacuum, then
the medium was adjusted to pH 4 with 1 N aqueous HCl. To
the reaction mixture was then added naringinase (Sigma no.
1385) (45 mg) and stirred at 40 °C for 5 days. The resulting
suspension was centrifuged, then the supernatant extracted
by EtOAc. The centrifugate and the organic phase were
evaporated under vacuum to dryness (96 mg). A solution of
this dried residue in THF (5 mL) was diluted with H2O (100
mL) and then extracted with CH2Cl2 (5 × 30 mL) and then
EtOAc (3 × 30 mL). The separate standard workup of both
organic phases and crystallization of each residue from EtOH
provided 10 (43 mg, 52%) and 11 (7 mg, 6%) as pale yellow
crystals from the CH2Cl2 and EtOAc extracts, respectively.
6-Iod oa ca cetin (10): mp 254-256 °C; 1H NMR (DMSO-
d6) δ 3.85 (3H, s, OCH3-4′), 6.68 (1H, s, H-8), 6.94 (1H, s, H-3),
7.10 (2H, d, J ) 8.5 Hz, H-3′ and H-5′), 8.04 (2H, d, J ) 8.5
Hz, H-2′ and H-6′), 14.0 (1H, s, OH-5); 13C NMR (DMSO-d6) δ
55.0 (CH3, OCH3-4′), 69.3 (C, C-6), 92.7 (CH, C-8), 102.5 (CH,
C-3), 103.0 (C, C-10), 113.9 (CH, C-3′ and C-5′), 121.9 (C, C-1′),
127.7 (CH, C-2′ and C-6′), 156.8 (C, C-9), 160.6 (C, C-5), 161.8
(C, C-4′), 162.1 (C, C-7), 162.8 (C, C-2), 181.0 (C, C-4); EIMS
m/z (%) 410 (M+) (100).
a
72.3 (CH, C-4′′′), 100.7 (CH, C-1′′′), interchangeable; ESIMS
m/z 615 [M + Na]+.
6-Iod oa ca cetin (10) fr om Lin a r in (3). A suspension of
linarin (3) (0.850 g, 1.44 mmol) in a mixture of pyridine-Ac2O
(6:4) (10 mL) was stirred at 80 °C until dissolution. The
reaction was left for 48 h at room temperature. A standard
workup of the mixture provided a dry residue of pure linarin
heptaacetate [TLC on silica gel (CH2Cl2-MeOH, 98:2): homo-
geneous colorless spot with FeCl3] (1.193 g, 94%). The residue
was dissolved in TFA (10 mL), and the mixture was left at
room temperature for 6 h. The medium was diluted with iced
water and carefully adjusted to pH 6 with 30% aqueous NaOH.
Extraction with CH2Cl2 afforded 5-hydroxyhexaacetyllinarin
(7) [TLC on silica gel (CH2Cl2-MeOH, 98:2): homogeneous blue
spot with FeCl3] (1.068 g, 94%).
5-Hyd r oxyh exa a cetyllin a r in (7): yellowish amorphous
powder; 1H NMR (CDCl3) δ [aglycone moiety] 3.90 (3H, s,
OCH3-4′), 6.42 (1H, d, J ) 2 Hz, H-6), 6.56 (1H, d, J ) 2 Hz,
H-8), 6.59 (1H, s, H-3), 7.03 (2H, d, J ) 8.8 Hz, H-3′ and H-5′),
7.84 (2H, d, J ) 8.8 Hz, H-2′ and H-6′), 12.85 (1H, s, OH-5);
[sugar moiety] inner glucose 3.67 (1H, H-6′′), 3.82 (1H, H-6′′),
3.92 (1H, H-5′′), 5.18 (1H, H-4′′), 5.23 (1H, H-1′′), 5.25a (1H,
H-2′′), 5.35 (1H, H-3′′); terminal rhamnose 1.15 (3H, d, J )
6.4 Hz, H-6′′′), 3.88 (1H, H-5′′′), 4.73 (1H, s, H-1′′′), 5.02 (1H,
H-4′′′), 5.23a (1H, H-2′′′), 5.26a (H-3′′′); 1.93-2.12 (18H, 6s, 6
sugar acetyles), ainterchangeable; 13C NMR (CDCl3) δ [aglycone
moiety] 55.0 (CH3, OCH3-4′), 95.0 (CH, C-8), 99.5 (CH, C-6),
104.1 (CH, C-3), 106.6 (C, C-10), 114.2 (CH, C-3′ and C-5′),
123.0 (CH, C-2′), 128.0 (CH, C-2′ and C-6′), 157.0 (C, C-9),
162.0 (C, C-7), 162.0 (C, C-5), 162.4 (C, C-4′), 164.6 (C, C-2),
182.1 (C, C-4); [sugar moiety] inner glucose 66.4 (CH2, C-6′′),
68.3 (CH, C-4′′), 70.0 (CH, C-3′′), 71.5a (CH, C-2′′), 73.1 (CH,
C-5′′), 97.8 (CH, C-1′′); terminal rhamnose 17.1 (CH3, C-6′′′),
66.2 (CH, C-5′′′), 68.4a (CH, C-2′′′), 70.6 (CH, C-4′′′), 72.3a (CH,
C-3′′′), 97.8 (CH, C-1′′′); 19-21 and 168-171 (6 sugar acetyl
groups), ainterchangeable.
1
6-Iod oa ca cetin 7-O-glu cosid e (11): mp 239-240 °C; H
NMR (DMSO-d6) δ 3.1-3.7 (6 sugar protons), 3.84 (3H, s,
OCH3-4′), 4.5-5.3 (4 sugar hydroxyls), 5.02 (1H, d, J ) 7 Hz,
H-1′′), 6.99 and 7.04 (2H, 2s, H-3 and H-8), 7.10 (2H, d, J )
8.5 Hz, H-3′ and H-5′), 8.04 (2H, d, J ) 8.5 Hz, H-2′ and H-6′),
13.9 (1H, s, OH-5); ESIMS m/z 595 [M + Na]+; HRESIMS m/z
595.0068 (calcd for C22H21N4O10NaI, 595.0077).
Aca cetin (9) fr om Lin a r in (3). Linarin (118 mg, 0.2 mmol)
in aqueous 11 N HCl (10 mL) was stirred between 50 and 55
°C for 1.5 h and left for 2 h at room temperature. The resulting
suspension was filtered, washed several times with water, and
dried with P2O5 under vacuum to yield a crude residue of
acacetin, which was crystallized from MeOH (40 mg, 70%).
Aca cet in (9) fr om Diosm et in (2). To a mixture of di-
osmetin (3 g, 10 mmol) and KHCO3 (1.1 g, 11 mmol) in DMF
(40 mL) was added benzyl chloride (1.38 mL, 12 mmol) and
the mixture stirred under nitrogen for 2.5 h at 120 °C. The
reaction mixture was cooled, filtered, and evaporated to
dryness. The dried residue was purified by flash chromatog-
raphy (silica gel, CH2CH2-MeOH, 99:1) to provide pure
7-benzyldiosmetin (12) (2.58 g, 66%) as yellow crystals and
7,3′-dibenzyldiosmetin (0.575 g, 12%).
7-Ben zyldiosm etin (12): mp 213-215 °C; 1H NMR (DMSO-
d6) δ 3.86 (3H, s, OCH3-4′), 5.23 (2H, s, CH2 of the benzyl
group), 6.45 (1H, s, H-6), 6.79 (1H, s, H-3), 6.82 (1H, s, H-8),
7.08 (1H, d, J ) 8.5 Hz, H-5′), 7.33-7.48 (6H, m, 5H of the
benzyl group and H-2′), 7.55 (1H, d, J ) 8.5 Hz, H-6′), 9.43
(1H, s, OH-3′), 12.9 (1H, s, OH-5); 13C NMR (DMSO-d6) δ 55.9
(CH3, OCH3-4′), 70.1 (CH2, benzylic carbon), 93.5 (CH, C-8),
98.7 (CH, C-6), 103.8 (CH, C-3), 105.0 (C, C-10), 112.2 (CH,
C-5′), 113.2 (CH, C-2′), 118.9 (CH, C-6′), 123.1 (C, C-1′), 127.9-
128.2-128.6 (CH, 5C of the benzyl group), 136.3 (C, 1C of the
A mixture of 7 (0.633 g, 0.75 mmol), BTMA.ICl2 (0.263 g,
0.75 mmol), and CaCO3 (0.54 g) in CH2Cl2-MeOH, 5:2 (35 mL),
was stirred at room temperature for 24 h. The reaction mixture
was taken up in water and extracted at pH 6 with CH2Cl2.
Standard workup of the organic layer provided an amorphous

Notes
J ournal of Natural Products, 2004, Vol. 67, No. 9 1627
(2) Ferte´, J .; Ku¨hnel, J .-M.; Chapuis, G.; Rolland, Y.; Lewin, G.;
Schwaller, M. J . Med. Chem. 1999, 42, 478-489.
(3) Adir et Cie EP Patent 832 886, 1997.
(4) (a) Martinez-Vazquez, M.; Ramirez Apan, T. O.; Hidemi Aguilar, M.;
Bye, R. Planta Med. 1996, 62, 137-140. (b) Martinez-Vazquez, M.;
Ramirez Apan, T. O.; Lastra A. L.; Bye, R. Planta Med. 1998, 64,
134-138.
benzyl group), 146.9 (C, C-3′), 151.4 (C, C-4′), 157.3 (C, C-9),
161.4 (C, C-5), 164.0 (C, C-2), 164.2 (C, C-7), 181.9 (C, C-4).
To a mixture of 12 (2.340 g, 6 mmol) and KHCO3 (0.6 g, 6
mmol) in DMF (25 mL) was added 5-chloro-1-phenyl-1H-
tetrazole (1.134 g, 6.3 mmol), and the mixture was stirred
under nitrogen for 1 h at 120 °C. The reaction mixture was
cooled, filtered, and evaporated to dryness. Flash chromatog-
raphy (silica gel, CH2CH2-MeOH, 98:2) of the dried residue
followed by crystallization from MeOH afforded pure 7-benzyl-
3′-phenyltetrazolyldiosmetin (13) (2.14 g, 67%) as yellow
crystals.
7-Ben zyl-3′-p h en yltetr a zolyld iosm etin (13): mp 210-
214 °C; 1H NMR (CDCl3) δ 3.89 (3H, s, OCH3-4′), 5.12 (2H, s,
CH2 of benzyl), 6.45 (1H, s, H-6), 6.53 (1H, s, H-3), 6.58 (1H,
s, H-8), 7.14 (1H, d, J ) 8.5 Hz, H-5′), 7.36-7.88 (12H, m, 5H
of benzyl, 5H of phenyltetrazole, H-2′ and H-6′), 12.66 (1H, s,
OH-5).
A suspension of 13 (2.100 g, 3.94 mmol) in MeOH (100 mL)
was added to ammonium formate (1.5 g, 24 mmol) and 10%
Pd-C (0.5 g) and the mixture stirred at reflux under nitrogen
for 2.5 h. The mixture was cooled, and the catalyst was filtered
off and washed with MeOH, then THF (150 mL), until the
filtrate was colorless. Evaporation to dryness of the mixed
filtrates followed by crystallization from MeOH gave pure
acacetin (9) (mp 267-269 °C) (0.762 g, 68%) as pale yellow
crystals. 1H and 13C NMR spectra of 9 were in accordance with
the literature.15
7,3′-Dim eth yl-6-iod oa p igen in (15) fr om Aca cetin (9).
Methylation of 9 into 7,4′-di-O-methylapigenin (14) (95%) was
performed according to a classical procedure (K2CO3, MeI,
DMF, rt),16 then iodination to 7,3′-dimethyl-6-iodoapigenin (15)
(73%) as previously described.12
(5) Han, S.; Sung, K.-H.; Yim, D.; Lee, S.; Lee, C.-K.; Ha, N.-J .; Kim, K.
Arch. Pharm. Res. 2002, 25, 170-177.
(6) Fernandez, S.; Wasowski, C.; Paladini, A. C.; Marder, M. Pharmacol.
Biochem. Behav. 2004, 77, 399-404.
(7) (a) Zembower, D. E.; Zhang, H. J . Org. Chem, 1998, 63, 9300-9305.
(b) Lin, Y.-M.; Zembower, D. E.; Flavin, M. T.; Schure, R.; Zhao, G.-
X. US Patent 6 399 654.
(8) (a) Cacchi, S.; Ciattini, P. S.; Morera, E.; Ortar, G. Tetrahedron Lett.
1986, 27, 5541-5544. (b) Wang, F.; Chiba, K.; Tada, M. J . Chem.
Soc., Perkin Trans. 1 1992, 1897-1900. (c) Ritter, K. Synthesis 1993,
735-762. (d) Kotsuki, H.; Datta, P. K.; Hayakawa, H.; Suenaga, H.
Synthesis 1995, 1348-1350. (e) Lipshutz, B. H.; Buzard, D. J .; Vivian,
R. W. Tetrahedron Lett. 1999, 40, 6871-6874.
(9) Musliner, W. J .; Gates, J . W., J r. J . Am. Chem. Soc. 1966, 88, 4271-
4273.
(10) (a) Musliner, W. J .; Gates, J . W., J r. J . Org. Synth. Coll. 1988, 6,
150-152. (b) Entwistle, I. D.; Hussey, B. J .; J ohnstone, R. A. W.
Tetrahedron Lett. 1980, 21, 4747-4748. (b) Lowe, J . A.; Ewing, F.
E.; Drozda, S. E. Synth. Commun. 1989, 19, 3027-3035. (c) De Meyer,
N.; Haemers, A.; Mishra, L.; Pandey, H.-K.; Pieters, L. A. C.; Vanden
Berghe, D. A.; Vlietinck, A. J . J . Med. Chem. 1991, 34, 736-746.
(11) Kajigaeshi, S.; Kakinami, T.; Yamasaki, H.; Fujisaki, S.; Kondo, M.;
Okamoto, T. Chem. Lett. 1987, 2109-2112.
(12) Quintin, J .; Lewin, G. Tetrahedron Lett. 2004, 45, 3635-3638.
(13) Lewin, G.; Bert, M.; Dauguet, J .-C.; Schaeffer, C.; Guinamant, J .-L.;
Volland, J .-P. Tetrahedron Lett. 1989, 30, 7049-7052.
(14) de la Mare, P. B. D.; Swedlund, B. E. In The Chemistry of the Carbon-
Halogen Chain; Patai, S., Ed.; J ohn Wiley & Sons: New York, 1973;
Chapter 7, pp 522-526.
(15) (a) Itokawa, H.; Suto, K.; Takeya, K. Chem. Pharm. Bull. 1981, 29,
1777-1779. (b) Matsuda, H.; Cai, H.; Kubo, M.; Tosa, H.; Iinuma,
M. Biol. Pharm. Bull. 1995, 18, 463-466.
Ack n ow led gm en t. The authors are grateful to J .-C.
J ullian for NMR measurements.
(16) Bouktaib, M.; Lebrun, S.; Atmani, A.; Rolando, C. Tetrahedron 2002,
58, 10001-10009.
Refer en ces a n d Notes
(1) Innokem FR Patent 2 782 518, 1998, and references within.
NP040079B