New 7,8-benzoflavanones as potent aromatase inhibitors: Synthesis and biological evaluation

Article abstract of DOI:10.1016/j.bmc.2007.10.057

Some natural compounds such as flavonoids are known to possess a moderate inhibitory activity against aromatase, this enzyme being an interesting target for hormone-dependent breast cancer treatment. It has been demonstrated that the modulation of flavonoid skeleton could increase anti-aromatase effect. Therefore, new 7,8-benzoflavanones were synthesized and tested for their activity toward aromatase inhibition. It was observed that the introduction of a benzo ring at position C-7 and C-8 on flavanone skeleton led to new potent aromatase inhibitors, the resulting 7,8-benzoflavanones being until nine times more potent than aminogluthetimide (the first aromatase inhibitor used clinically).

Full text of DOI:10.1016/j.bmc.2007.10.057

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry 16 (2008) 1474–1480
New 7,8-benzoflavanones as potent aromatase inhibitors:
Synthesis and biological evaluation
Samir Yahiaoui, Catherine Fagnere, Christelle Pouget,
*
´
Jacques Buxeraud and Albert-Jose Chulia
UPRES EA 4021 ‘‘Biomole´cules et The´rapies anti-tumorales’’, Faculte´ de Pharmacie, 2 rue du Docteur Marcland,
87025 Limoges cedex, France
Received 19 April 2007; revised 28 September 2007; accepted 17 October 2007
Available online 22 October 2007
Abstract—Some natural compounds such as flavonoids are known to possess a moderate inhibitory activity against aromatase, this
enzyme being an interesting target for hormone-dependent breast cancer treatment. It has been demonstrated that the modulation of
flavonoid skeleton could increase anti-aromatase effect. Therefore, new 7,8-benzoflavanones were synthesized and tested for their
activity toward aromatase inhibition. It was observed that the introduction of a benzo ring at position C-7 and C-8 on flavanone
skeleton led to new potent aromatase inhibitors, the resulting 7,8-benzoflavanones being until nine times more potent than amino-
gluthetimide (the first aromatase inhibitor used clinically).
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
tive to anti-estrogen drugs, this superiority being dem-
onstrated by several studies.4,5
Flavonoids are a group of polyphenolic phytochemical
compounds that occur ubiquitously in foods of plant
origin. Over 4000 different naturally occurring flavo-
noids have been described.1 Several studies have
addressed the ability of flavonoids to interfere with the
catalytic activity or expression of aromatase which is a
cytochrome P-450 enzyme,2 this enzyme being responsi-
ble for the final step of the estrogen biosynthesis (i.e. the
conversion of androgens to estrogens). Estrogens are
known to be important in the development of breast
cancer in both pre- and postmenauposal women.
Besides the large number of synthetic aromatase inhibi-
tors, a significant number of natural products such as
flavonoids have been identified to possess also anti-aro-
matase effect with about the same activity as aminoglu-
thetimide (AG), the first non-steroidal inhibitor used
clinically. Among flavonoids, flavones and flavanones
generally have a higher inhibitory effect than isoflavones
and isoflavanones.6
Flavanones which possess a chiral center at C-2 are usu-
ally tested as racemic mixture; however, Kao et al. dem-
onstrated that only the S-configuration isomer can bind
to the active site of aromatase, which could explain the
lower activity of flavanones relative to flavones.7
With reference to the mechanisms by which estrogens
may increase the risk of breast cancer,3–5 two general
strategies have been developed to reduce the action of
these hormones. The first strategy is to block estrogen
receptors by anti-estrogens such as tamoxifen; the sec-
ond pharmacological approach is to block estrogen syn-
thesis through aromatase inhibition. The action level of
aromatase inhibitors can explain their superiority rela-
Several works have tried to establish the nature of flavo-
noid-aromatase interactions; we noticed that flavones
bind to the active site of aromatase with an orientation
in which A and C rings mimic rings D and C of andro-
gen substrate, respectively.7 Moreover, the presence of
the C4-keto group on flavanone and flavone structures
seems to be crucial for aromatase inhibition since its
reduction to hydroxyl group causes complete loss of bio-
logical activity.8 It appears that the keto group makes an
interaction with the iron heme of aromatase.7
Keywords: 7,8-Benzoflavanones; Flavonoids; Aromatase inhibitors;
Breast cancer.
*
Corresponding author. Tel.: +33 (0) 555 435 834; fax: +33 (0) 555 435
910; e-mail: jose.chulia@unilim.fr
0968-0896/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2007.10.057

S. Yahiaoui et al. / Bioorg. Med. Chem. 16 (2008) 1474–1480
1475
HO
O
O
O
O
7,8-benzoflavone (ANF)
C4-keto group activation
Scheme 3. Structure of 7,8-benzoflavone (ANF).
Scheme 1.
introduction of a benzo cycle at C7 and C8 leading to
new 7,8-benzoflavanones. Indeed, the presence of such
a substitution moiety on flavone skeleton was found to
be essential for inhibitory effectiveness.
Other studies showed that the modulation of A, B, and
C rings of flavan skeleton can increase significantly the
inhibitory activity and many elements came out from
these investigations. First, the A ring modulation of fla-
vanone and flavone skeleton by hydroxylation at posi-
tion 7 enhances the biological activity8–10; this effect
could be explained by the activation of C4-keto group
by the n–p–p–p conjugation caused by the hydroxyl
group (Scheme 1). This activation seems to increase
the connection between the C4 group and the heme iron
of aromatase. Thus, 7-hydroxyflavone is 20 times more
potent than flavone,8 while the 7-hydroxyflavanone is
six times more active than flavanone.10 It appears also
that hydroxylation at position 5 decreases the inhibitory
activity; thus, 5-hydroxyflavone and 5,7-dihydroxyflav-
one (chrysin) are less active than flavone8 and 7-hydrox-
yflavone,7,9 respectively. The possible intra-molecular
hydrogen bond between 5-OH group and C-4 keto
may decrease the connecting potential of C4-keto with
the heme iron of aromatase (Scheme 2).
Thus, the 7,8-benzoflavone or a-naphthoflavone (ANF)
(Scheme 3) has been extensively studied with regard to
its inhibition of chemical carcinogenesis and of certain
cytochrome P-450 mixed-function oxidase.12 ANF,
which is a synthetic flavonoid, has a similar affinity with
aromatase to that of the natural substrates (androstene-
dione and testosterone); the study of its inhibition mech-
anism demonstrated that ANF is
a competitive
aromatase inhibitor.13 Several comparative studies
about flavonoid inhibitory effect against aromatase
showed that ANF is the most potent inhibitor among
the whole compounds tested.13–15 We can notice that
ANF is 15 and 136 times more potent than aminoglu-
thetimide and flavone, respectively14; the 7-hydroxyflav-
one is also five times less potent than ANF.15
In the following, the preparation and the biological eval-
uation of new 7,8-benzoflavanones are described.
It was demonstrated that a 7-methoxy group is also
favorable for activity; however, the 7-methoxyflavanone
remains less active than the 7-hydroxyflavanone.9,10
N
Concerning the B ring modulation of 7-methoxyflava-
none skeleton, we demonstrated that additional hydro-
xyl groups led to an increase in aromatase inhibition,
the 30,40-dihydroxy-7-methoxyflavanone being the most
active molecule. Thus, this latter compound was found
to be twice more active than AG.11
N
N
In the search of a new substitution pattern which could
reinforce the interaction of flavanone skeleton with aro-
matase enzyme, we report in the course of the present
study, the modulation of A ring of flavanone by the
NC
CN
Scheme 4. Structure of anastrozole.
N
O
N
N
O
O
H
NC
intra-molecular hydrogen bond
CN
Scheme 2.
Scheme 5. Structure of letrozole.

1476
S. Yahiaoui et al. / Bioorg. Med. Chem. 16 (2008) 1474–1480
2. Chemistry
In order to determin the impact of this group on
flavanone skeleton, we decided to synthesize two cya-
nobenzoflavanone derivatives. Additionally, two
hydroxyl derivatives were also prepared with regard to
the importance of hydroxyl groups for the flavonoid-
enzyme interactions. Totally, five benzoflavanone deriv-
atives were synthesized (Scheme 6): the non-substituted
benzoflavanone (F1), two cyanobenzoflavanones (F2
and F3), and two hydroxybenzoflavanones (F4 and F5).
2.1. General procedure of synthesis
Third generation aromatase inhibitors such as anas-
trozole (Scheme 4) and letrozole (Scheme 5) were
shown to be useful in the second-line therapy of estro-
gen-dependent breast cancer and have recently been
approved as first-line therapy in several countries.16
Letrozole and anastrozole structure contains a cyano
group, which is probably important for the biological
activity.
The 7,8-benzoflavanones (F1–F5) were obtained
through the same synthesis pathway (Scheme 7) as de-
scribed by Pouget et al.11 and which is based on the
cyclization of corresponding 20-hydroxychalcones.
2.2. Synthesis and characterization
R1
2.2.1. 30,40-Benzo-20-hydroxychalcones
5"
3'
2.2.1.1. Synthesis. 30,40-Benzo-20-hydroxychalcones
were obtained by the Claisen–Schmidt condensation be-
tween 1-hydroxy-5,6-benzo-1-acetophenone (1) and
appropriatly substituted benzaldehydes (Scheme 8).
The preparation of 30,40-benzo-20,4-dihydroxychalcone
(C5) necessitated a protection step of 4-hydroxybenzal-
dehyde by 3,4-dihydro-a-pyrane (3,4-DHP), then the
deprotection was carried out using APTS (Scheme 9).
R2
4'
6"
8
2'
1'
4"
3"
1
2
O
5'
7
6'
3
F1 : R1 = H , R2 = H
F2 : R1 = CN, R2 = H
F3 : R1 = H , R2 = CN
F4 : R1 = OH, R2 = H
F5 : R1 = H , R2 = OH
6
4
5
O
7,8-benzoflavanones
Benzochalcones were obtained with variable yields rang-
ing from 35% to 85%. The synthesis of the non-substi-
Scheme 6. Structure of 7,8-benzoflavanones.
R'
OH
R'
O
OH
R'
R
R
Ba(OH)2
EtOH
H
H2SO4 / MeOH
CH3
+
R
O
O
O
O
Scheme 7. General synthesis of chalcones and flavanones.
R1
3
5''
2''
R2
4
4''
3''
6''
2
R1
1''
1
R2
3'
OH
+
OH
O
5
C1 : R1 = H , R2 = H
2'
1'
C2 : R1 = CN, R2 = H
C3 : R1 = H , R2 = CN
C4 : R1 = OH, R2 = H
Ba(OH)2
4'
6
H
CH3
5'
6'
O
O
(1)
Scheme 8. Synthesis of benzochalcones C1–C4.
OH
CH3
O
OH
HO
O
O
O
3,4-DHP
CH2Cl2
O
OH
H
OH
O
APTS
MeOH
H
O
Ba(OH)2
EtOH
O
O
C5
Scheme 9. Synthesis of 30,40-benzo-20,4-dihydroxychalcone C5.

S. Yahiaoui et al. / Bioorg. Med. Chem. 16 (2008) 1474–1480
Table 1. Characteristics of benzochalcone synthesis
1477
Hax
Compound
Ratio (acetophenone/
benzaldehyde)
Reaction’s
time (h)
Yield
(%)
1
2
O
Pheq
C1
C2
C3
C4
C5
1/1.2
1/1.5
1/1.5
1/2
1.5
4
85
35
56
45
72
3
Heq
4
20
29
48
Hax
O
1/2
Scheme 11. Conformation of the heterocyclic ring of flavanones.
tuted benzochalcone was carried out with 1.2 equivalent
of benzaldehyde, this ratio being used for the synthesis
of previous chalcones.11 However, the quantity of benz-
aldehyde was increased for the other benzochalcones
(Table 1).
Table 2. Aromatase inhibitory activity of tested compounds
Compound
IC50 (lM)
RP/AG
Flavanone
28
0.2
0.7
1.4
1.3
2.9
7-Methoxyflavanone
7-Hydroxyflavanone
7,8-Benzoflavanone
7,8-Benzoflavone
8.0
3.8
4.3
2.0
2.2.1.2. Structural analysis. Some characteristic 1H
NMR data are common between the five benzochalcone
compounds. First, all proton signals are between 6.8 and
8.5 ppm, corresponding to aromatic and ethylenic pro-
tons. Then, all benzochalcones have two protons with
a coupling constant of 15.5 Hz corresponding to a
trans-ethylenic coupling.
3. Biology
Inhibitory activity of compounds on aromatase was
evaluated in vitro using human placental microsomes
and [1,2,6,7-3H] androstenedione as substrate. Aroma-
tase inhibitory activity of compounds at five appropriate
concentrations was expressed as percent inhibition of
the aromatization of androstenedione which had an ini-
tial concentration of 40 nM. All experiments were per-
formed in duplicate in order to determine the IC50
value. The pharmacological data for compounds F1–
F5 are summarized in Tables 2 and 3.
2.2.2. 7,8-Benzoflavanones
2.2.2.1. Synthesis. The synthesis method for the 7,8-
benzoflavanones is characterized by a chemical balance
with corresponding chalcones, catalyzed by sulfuric acid
(Scheme 10). 7,8-Benzoflavanones were obtained with
satisfying yields (more than 59%) except for F3
(yield = 25%). The presence of a cyano group at para
position of B ring seems to be responsible for the lower
yield. Indeed, the cyano group exerts a –M electronic ef-
fect which can decrease the Cb affinity, to the detriment
of the nucleophilic attack provoked by the oxygen of hy-
droxyl group at 20 position.
4. Results and discussion
First, our results (Table 2) confirm the relation between
flavanones and flavones previously cited in this paper.
Indeed, 7,8-benzoflavanone appears to be twice less po-
tent than ANF; however, it possesses a similar activity
to that of aminogluthetimide (5.8 lM). Then, we ob-
served that the extension of A ring of flavanone by a
benzo ring at positions 7 and 8 increases significantly
the inhibitory activity. Thus, 7,8-benzoflavanone is se-
ven times more potent than flavanone. Moreover, 7,8-
benzoflavanone is twice more active than 7-methoxyf-
lavanone; nevertheless, it possesses the same activity as
7-hydroxyflavanone.
2.2.2.2. Structural analysis. These compounds are
characterized by three proton signals in the aliphatic
zone corresponding to the heterocyclic ring protons,
H-2, H-3eq, and H-3ax.
The H-3ax and H-3eq are coupled approximately with a
constant of 17 Hz corresponding to a geminal coupling.
Then, the value of the J2,3ax is so large (13 Hz) that it can
only arise from a trans-diaxial coupling, thus H-2 is ax-
ial and the 2-phenyl group is equatorial. Finally, the
coupling constant between H-2 and H-3eq which is close
to 3.5 Hz confirms also the conformation of the hetero-
cycle (Scheme 11).
The inhibitory activities of the whole 7,8-benzoflavanon-
es and their 7-methoxy and 7-hydroxy analogs are listed
R1
R1
5"
3'
R2
R
4'
6"
8
2'
1'
4"
3"
2
1
OH
2
O
5'
7
H2SO4 / MeOH
6'
3
6
4
5
O
O
Scheme 10. Cyclization of 30,40-benzochalcones into corresponding 7,8-benzoflavanones.

1478
S. Yahiaoui et al. / Bioorg. Med. Chem. 16 (2008) 1474–1480
Table 3. Anti-aromatase activity of 7,8-benzoflavanones compared to 7-hydroxy and 7-methoxyflavanones
Substitutents
7-Methoxyflavanones
IC50 RP/AG
7-Hydroxyflavanones
IC50 RP/AG
7,8-Benzoflavanones
IC50 RP/AG
Non-substituted
30-CN
8.0
/
0.7
/
3.8
/
1.4
/
4.3
1.3
4.2
3.7
9.3
9.0
1.37
1.54
0.61
0.63
40-CN
/
/
/
/
30-OH
40-OH
3.5
3.7
1.5
1.4
3.4
2.1
1.5
2.5
in Table 3. The modulation of the B ring of the 7,8-ben-
zoflavanone has highly increased the biological effect
since 7,8-benzoflavanones are until nine times more po-
tent than AG.
of the C4-keto group by an imidazolyl moiety, led to
highly potent aromatase inhibitors.17 The resulting com-
pounds (4-imidazolylflavans) demonstrated a high po-
tential against aromatase; they proved to be more
potent than AG, exhibiting relative potencies ranging
from 40 to 130.17 Further modulation of the C ring of
the present 7,8-benzoflavanones could increase the
inhibitory effect and lead to compounds as active as
the third-generation aromatase inhibitors.
Introduction of an electron-withdrawing substituent
such as the cyano group or electron-donating group
such as the hydroxyl group on the B ring of 7,8-benzof-
lavanone increases the aromatase inhibitory effect. First,
the presence of an hydroxyl group at 30 or 40 position is
essential for high potency, the hydroxyl derivatives
being seven times more potent than 7,8-benzoflavanone.
We observed that hydroxyl groups on B ring exert a bet-
ter effect on activity when they are associated to a 7,8-
benzo ring rather than to a 7-methoxy or a 7-hydroxy
group; indeed, the hydroxyl derivatives of both 7-meth-
oxyflavanone and 7-hydroxyflavanone are at the most
two times more potent than the corresponding
flavanone.
As a conclusion, the modulation of flavonoids provides
new leads for aromatase inhibition such as 7,8-benzof-
lavanones. Our results should contribute substantially
to establish a structure–activity relationship between
aromatase and their inhibitors which is important in
the drug design strategy.
6. Characterization
Additionally, we observed that the cyano substituent
plays also an important role for activity. The introduc-
tion of this latter group on B ring at position 30 or 40
of 7,8-benzoflavanone increases the inhibitory effect
since cyano derivatives (F2 and F3) are three times more
potent than 7,8-benzoflavanone. However, we observed
that hydroxyl compounds are two times more potent
than their cyano analogs; so, the substituent nature
influences the structure–activity relationship of 7,8-
benzoflavanones.
The identification of benzochalcones and benzoflava-
nones was carried out by NMR spectroscopy and
electrospray mass spectrometric (ESI-TOF) analysis.
NMR spectra were recorded on Bruker DPX
Avance spectrometer using tetramethylsilane as inter-
nal standard. Mass spectrometry was carried out on
a Waters Alliance system equipped with electrospray
interface.
6.1. Characterization of 30,40-benzo-20-hydroxychalcones
On the contrary, there is no significant difference of
activity between 30-CN and 40-CN analogs or between
30-OH and 40-OH derivatives; therefore, the position
of these substituents does not influence the inhibitory
activity on 7,8-benzoflavanone skeleton.
30,40-Benzo-20-hydroxychalcone (C1) was obtained in
85% yield as a red solid, mp: 112 °C. Rf 0.83 (toluene
100%). 1H NMR (400 MHz; CDCl3): d 7.30 (1H, d,
J = 8.2 Hz, H-50), d 7.44 (3H, m, H-3, H-4 and H-5), d
7.53 (1H, m, H-500 ), d 7.63 (1H, m, H-400), d 7.69 (2H,
m, H-2 and H-6), d 7.74 (1H, d, J = 15.4 Hz, H-a), d
7.77 (1H, br d, J = 7.8 Hz, H-300), d 7.84 (1H, d,
J = 8,9 Hz, H-60), d 7.98 (1H, d, J = 15.5 Hz, H-b), d
8.50 (1H, br d, J = 8.2 Hz, H-600). 13C NMR
(100 MHz; CDCl3): d 113.6 (C-10), d 118.3 (C-50), d
120.7 (C-a), d 124.0 (C-60), d 124.6 (C-600), d 125.6 (C-
30), d 126.0 (C-500), d 127.4 (C-300), d 128.7 (C-2/C-6), d
129.1 (C-3 and C-5), d 130.2 (C-400), d 130.8 (C-4), d
134.9 (C-1), d 137.5 (C-40), d 145.1 (C-b), d 164.5 (C-
20), d 193.3 (C@O). HR-MS (ESI) measured for
C19H15O2 (M+H)+: 275.1075.
5. Conclusion
In conclusion, the introduction of a benzo ring at C7
and C8 positions of flavanone skeleton led to a new class
of synthetic flavanones (i.e. 7,8-benzoflavanones) which
are potent aromatase inhibitors since they are up to nine
times more active than AG. Moreover, the B ring mod-
ulation of the new 7,8-benzoflavanone skeleton through
the introduction of hydroxyl or cyano group at position
30 or 40 increases significantly the biological effect; there-
fore, further investigations will concern other substitu-
ent groups on different positions of the B ring.
30,40-Benzo-3-cyano-20-hydroxychalcone (C2) was ob-
tained in 35% yield as a red solid, mp: 200 °C. Rf 0.44
1
(toluene 100%). H NMR (400 MHz; CDCl3): d 7.32
Our recent studies showed that the C ring modulation of
7-OMe and 7-OH flavanones, through the replacement
(1H, d, J = 8.9 Hz, H-50), d 7.55 (1H, m, H-500), d 7.57
(1H, t, J = 7.8 Hz, H-5), d 7.66 (1H, m, H-400), d 7.70

S. Yahiaoui et al. / Bioorg. Med. Chem. 16 (2008) 1474–1480
1479
(1H, dt, J = 1.2 and 7.8 Hz, H-4), d 7.76 (1H, d,
J = 15.5 Hz, H-a), d 7.78 (1H, br d, J = 7.8 Hz, H-300),
d 7.81 (1H, d, J = 9.0 Hz, H-60), d 7.88 (1H, br dt,
J = 7.8 Hz, H-6), d 7.90 (1H, d, J = 15.4 Hz, H-b), d
7.96 (1H, br t, H-2), d 8.50 (1H, br d, J = 8.3 Hz, H-
(C-2 and C-6), d 138.8 (C-40), d 147.0 (C-b), d 162.0
(C-4), d 164.6 (C-20), d 195.1 (C@O). HR-MS (ESI)
measured for C19H15O3 (M+H)+: 291.1020.
6.2. Characterization of 7,8-benzoflavanones
3
600). C NMR (100 MHz; CDCl3): d 113.3 (C-10), d
113.5 (C-3), d 118.1 (CN), d 118.5 (C-50), d 123.0 (C-
a), d 123.7 (C-60), d 124.6 (C-600), d 125.4 (C-30), d
126.1 (C-500), d 127.5 (C-300), d 129.9 (C-5), d 130.6 (C-
400), d 131.5 (C-2), d 133.5 (C-4), d 132.6 (C-6), d 137.5
(C-40), d 136.1 (C-1), d 141.9 (C-b), d 164.7 (C-20), d
192.5 (C@O). HR-MS (ESI) measured for C20H14O2N
(M+H)+: 300.1037.
7,8-Benzoflavanone (F1) was obtained in 59% yield as a
colorless oil. Rf 0.28 (toluene 100%). 1H NMR
(400 MHz; CDCl3): d 2.99 (1H, dd, J = 3.2 and
16.8 Hz, H-3eq), d 3.18 (1H, dd, J = 13.5 and 16.8 Hz,
H-3ax), d 5.69 (1H, dd, J = 3.1 and 13.5 Hz, H-2), d
7.40–7.48 (4H, m, H-6, H-30, H-40 and H-50), d 7.52
(1H, m, H-500), d 7.58 (2H, br d, J = 8.0 Hz, H-20 and
H-60), d 7.62 (1H, m, H-400), d 7.81 (1H, br d,
J = 8.2 Hz, H-300), d 7.91 (1H, d, J = 8.7 Hz, H-5), d
8.34 (1H, br d, J = 8.4 Hz, H-600). 13C NMR
(100 MHz; CDCl3): d 44.1 (C-3), d 80.2 (C-2), d 115.5
(C-4a), d 121.3 (C-6), d 121.7 (C-5), d 123.7 (C-600), d
124.9 (C-8), d 126.1 (C-2 and C-6), d 126.3 (C-500), d
127.9 (C-300), d 128.8 (C-40), d 128.9 (C-30 and C-50), d
129.7 (C-400), d 137.6 (C-7), d 138.8 (C-10), d 159.8 (C-
8a), d 191.6 (C-4). HR-MS (ESI) measured for
C19H15O2 (M+H)+: 275.1072.
30,40-Benzo-4-cyano-20-hydroxychalcone (C3) was ob-
tained in 56% yield as a red solid, mp: 218 °C. Rf 0.57
(toluene 100%). 1H NMR (400 MHz; DMSO-d6): d
7.47 (1H, d, J = 8.9 Hz, H-50), d 7.61 (1H, m, H-500), d
7.74 (1H, m, H-400), d 7.94 (1H, br d, J = 8.0 Hz, H-
300), d 7.95 (2H, d, J = 8.3 Hz, H-3 and H-5), d 7.96
(1H, d, J = 15.3 Hz, H-b), d 8.17 (2H, d, J = 8.2 Hz,
H-2 and H-6), d 8.31 (1H, d, J = 9.1 Hz, H-60), d 8.32
(1H, d, J = 15.4 Hz, H-a), d 8.36 (1H, br d, J = 8.3 Hz,
3
H-600). C NMR (100 MHz; DMSO-d6): d 112.6 (C-4),
d 113.4 (C-10), d 118.4 (C-50), d 118.6 (CN), d 123.7
(C-600), d 124.3 (C-30), d 124.4 (C-a), d 125.1 (C-60), d
126.3 (C-500), d 127.7 (C-300), d 129.8 (C-2 and C-6), d
130.7 (C-400), d 132.7 (C-3 and C-5), d 137.2 (C-40), d
138.9 (C-1), d 142.9 (C-b), d 163.4 (C-20), d 193.3
(C@O). HR-MS (ESI) measured for C20H14O2N
(M+H)+: 300.1025.
30-Cyano-7,8-benzoflavanone (F2) was obtained in 59%
yield as a colorless oil. Rf 0.22 (toluene 100%). 1H
NMR (400 MHz; CDCl3): d 3.01 (1H, dd, J = 3.4 and
16.8 Hz, H-3eq), d 3.12 (1H, dd, J = 13.1 and 16.8 Hz,
H-3ax), d 5.72 (1H, dd, J = 3.4 and 13.1 Hz, H-2), d
7.48 (1H, d, J = 8.6 Hz, H-6 ), d 7.56 (1H, m, H-500), d
7.61 (1H, t, J = 7.8 Hz, H-50), d 7.66 (1H, m, H-400), d
7.72 (1H, dt, J = 1.3 and 7.8 Hz, H-40), d 7.79 (1H, br
dt, J = 7.8 Hz, H-60), d 7.83 (1H, br d, J = 8.1 Hz, H-
300), d 7.90 (1H, d, J = 8.7 Hz, H-5), d 7.93 (1H, br t,
J = 1.6 Hz, H-20), d 8.33 (1H, br d, J = 8.3 Hz, H-600).
13C NMR (100 MHz; CDCl3): d 43.9 (C-3), d 79.1 (C-
2), d 113.3 (C-30), d 115.6 (C-4a), d 118.4 (CN), d
121.6 (C-5), d 121.8 (C-6), d 123.4 (C-600), d 124.6 (C-
8), d 126.6 (C-500), d 128.0 (C-300), d 129.7 (C-20), d
129.8 (C-50), d 130.0 (C-400), d 130.3 (C-60), d 132.4 (C-
40), d 137.7 (C-7), d 140.5 (C-10), d 159.2 (C-8a), d
190.4 (C@O). HR-MS (ESI) measured for C20H14O2N
(M+H)+: 300.1035.
30,40-Benzo-20,3-dihydroxychalcone (C4) was obtained
in 45% yield as a red solid, mp: 163 °C. Rf 0.59
CH2Cl2–EtOAc 9.75:0.25. 1H NMR (400 MHz;
CD3OD): d 6.89 (1H, dt, J = 2.6 and 6.4 Hz, H-4), d
7.18 (1H, m, H-2), d 7.27 (1H, m, H-6), d 7.28 (1H,
m, H-5), d 7.37 (1H, d, J = 8.9 Hz, H-50), d 7.53 (1H,
m, H-500), d 7.65 (1H, m, H-400), d 7.81 (1H, br d,
J = 8.2 Hz, H-300), d 7.88 (2H, br s, H-b and H-a), d
8.02 (1H, br d, J= 9.0 Hz, H-60), d 8.43 (1H, br d,
J = 8.2 Hz, H-600). 3C NMR (100 MHz; CD3OD): d
114.8 (C-10), d 116.1 (C-2), d 119.2 (C-4), d 119.6 (C-
50), d 121.5 (C-6), d 121.7 (C-a), d 125.1 (C-600), d
125.5 (C-60), d 126.5 (C-30), d 127.0 (C-500), d 128.6
(C-300), d 131.2 (C-400), d 131.3 (C-5), d 137.6 (C-1), d
139.0 (C-40), d 146.6 (C-b), d 159.2 (C-3), d 164.9 (C-
20), d 195.2 (C@O). HR-MS (ESI) measured for
C19H15O3 (M+H)+: 291.1021.
7,8-Benzo-40-cyanoflavanone (F3) was obtained in 25%
yield as a colorless oil. Rf 0.18 (toluene–EtOAc
1
9.75:0.25). H NMR (400 MHz; CDCl3): d 3.02 (1H,
dd, J = 3.6 and 16.8 Hz, H-3eq), d 3.12 (1H, dd,
J = 12.9 and 16.8 Hz, H-3ax), d 5.76 (1H, dd, J = 3.6
and 12.9 Hz, H-2), d 7.48 (1H, d, J = 8.7 Hz, H-6), d
7.56 (1H, m, H-500), d 7.66 (1H, m, H-400), d 7.71
(2H, d, J = 8.2 Hz, H-20 and H-60), d 7.79 (2H, d,
30,40-Benzo-20,4-dihydroxychalcone (C5) was obtained in
72% yield as a red solid, mp: 183 °C. Rf 0.21 (toluene–
1
EtOAc 9.5:0.5). H NMR (400 MHz; CD3OD): d 6.87
J = 8.4 Hz, H-30 and H-50),
d 7.83 (1H, br d,
(2H, d, J = 8.6 Hz, H-3 and H-5), d 7.35 (1H, d,
J = 8.8 Hz, H-50), d 7.52 (1H, m, H-500), d 7.63 (1H, m,
H-400), d 7.67 (2H, d, J = 8.6 Hz, H-2 and H-6), d 7.77
(1H, d, J = 15.4 Hz, H-a), d 7.80 (1H, br d, J = 8.2 Hz,
H-300), d 7.92 (1H, d, J = 15.3 Hz, H-b), d 8.02 (1H, d,
J = 9.0 Hz, H-60), d 8.41 (1H, br d, J= 8.4 Hz, H-600).
3C NMR (100 MHz; CD3OD): d 114.8 (C-10), d 117.0
(C-3 and C-5), d 118.3 (C-a), d 119.4 (C-50), d 125.1
(C-600), d 125.5 (C-60), d 126.6 (C-30), d 126.8 (C-500), d
127.8 (C-1), d 128.6 (C-300), d 131.1 (C-400), d 132.2
J = 8.1 Hz, H-300), d 7.90 (1H, d, J = 8.7 Hz, H-5), d
8.33 (1H, br d, J = 8.4 Hz, H-600). 13C NMR
(100 MHz; CDCl3): d 43.9 (C-3), d 79.3 (C-2), d
112.7 (C-40), d 115.6 (C-4a), d 118.4 (CN), d 121.6
(C-5), d 121.8 (C-6), d 123.4 (C-600), d 124.6 (C-8), d
126.6 (C-500), d 126.7 (C-20 and C-60), d 128.0 (C-300),
d 129.9 (C-400), d 132.8 (C-30 and C-50), d 137.7 (C-
7), d 140.5 (C-10), d 159.2 (C-8a), d 190.4 (C@O).
HR-MS (ESI) measured for C20H14O2N (M+H)+:
300.1029.

1480
S. Yahiaoui et al. / Bioorg. Med. Chem. 16 (2008) 1474–1480
7,8-Benzo-30-hydroxyflavanone (F4) was obtained in
86% yield as a colorless oil. Rf 0.37 (CH2Cl2–EtOAc
9.75:0.25). 1H NMR (400 MHz; DMSO-d6): d 2.97
(1H, dd, J = 3.3 and 16.8 Hz, H-3eq), d 3.26 (1H,
dd, J = 12.6 and 16.7 Hz, H-3ax), d 5.84 (1H, dd,
J = 3.3 and 12.5 Hz, H-2), d 6.80 (1H, dt, J = 1.6
and 7.9 Hz, H-40), d 7.03 (1H, br d, J = 7.4 Hz, H-
Acknowledgment
The authors are grateful to the CNRS central service of
analyses, Vernaison, France, for recording the high res-
olution mass spectrometry.
60),
d
7.04 (1H, br s, H-20),
d
7.26 (1H, t,
References and notes
J = 7.9 Hz, H-50), d 7.55 (1H, d, J = 8.6 Hz, H-6),
d 7.62 (1H, m, H-500), d 7.72 (1H, m, H-400), d
7.78 (1H, d, J = 8,6 Hz, H-5), d 7.95 (1H, br d,
J = 8.1 Hz, H-300), d 8.27 (1H, br d, J = 8.2 Hz, H-
600), d 9.51 (1H, s, 30-OH). 13C NMR (100 MHz;
DMSO-d6): d 42.7 (C-3), d 79.3 (C-2), d 113.1 (C-
20), d 115.1 (C-4a), d 115.3 (C-40), d 116.7 (C-60),
d 120.7 (C-6), d 121.1 (C-5), d 122.9 (C-600), d
124.2 (C-8), d 126.5 (C-500), d 127.9 (C-300), d 129.5
(C-50), d 129.7 (C-400), d 136.8 (C-7), d 140.2 (C-
10), d 157.5 (C-30), d 158.8 (C-8a), d 190.9 (C@O).
HR-MS (ESI) measured for C19H15O3 (M+H)+:
291.1018.
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