Synthesis of new (+)-usnic acid derivatives with the flavone structure

Article abstract of DOI:10.1007/s11172-013-0031-3

Reactions of a chalcone derivative (synthesized earlier from usnic acid) with various oxidants (hydrogen peroxide, tert-butyl hydroperoxide, and dichlorodicyanobenzoquinone) gave new flavonols, dihydroflavonols, and flavones. Treatment of the starting chalcone with a nucleophilic reagent (NH ₂NH₂·H₂O) afforded a dihydropyrazole-containing derivative.

Full text of DOI:10.1007/s11172-013-0031-3

Russian Chemical Bulletin, International Edition, Vol. 62, No. 1, pp. 212—216, January, 2013
212
Synthesis of new (+)ꢀusnic acid derivatives with the flavone structure
D. N. Sokolov,a M. E. Rakhmanova,b O. A. Luzina,a A. V. Shernyukov,a and N. F. Salakhutdinova
aN. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences,
9 prosp. Akad. Lavrent´eva, 630090 Novosibirsk, Russian Federation.
Eꢀmail: luzina@nioch.nsc.ru
bNovosibirsk National Research State University,
2 ul. Pirogova, 630090 Novosibirsk, Russian Federation
Reactions of a chalcone derivative (synthesized earlier from usnic acid) with various oxiꢀ
dants (hydrogen peroxide, tertꢀbutyl hydroperoxide, and dichlorodicyanobenzoquinone) gave
new flavonols, dihydroflavonols, and flavones. Treatment of the starting chalcone with a nucleoꢀ
philic reagent (NH2NH2•H2O) afforded a dihydropyrazoleꢀcontaining derivative.
Key words: (+)ꢀusnic acid, chalcones, flavonoids.
A constantly growing interest in natural and synthetic
acid (1), a unique and accessible plant metabolite, can
serve as an appropriate synthon because of its high optical
purity and various biological properties.2 However, the
polyvariant (and hence highly unpredictable) reactivity of
usnic acid deters researchers from its extensive use in synꢀ
thetic practice.
Earlier,3 we have proposed a fourꢀstep procedure for
the synthesis of chalcones from usnic acid (1) (Scheme 1).
This work was intended to study further transformaꢀ
tions of the chalcones obtained earlier and develop methꢀ
flavonoids (chalcones, flavones, and aurones) is largely
due to their antioxidant activity and the associated tenꢀ
dency of metabolites of this class to prevent or inhibit
tumor formation, strengthen blood vessels, and protect
liver and the gastrointestinal tract.1 Particular attention in
relevant investigations is given to a structure—activity reꢀ
lationship. In connection with this, it seems to be promisꢀ
ing to make a flavonoid structure biologically active via
introduction of a fragment possessing native activity. Usnic
Scheme 1
Reagents and conditions: i. PhNHNH2, EtOH, reflux; ii. NaBH4, THF, –20 C; iii. CH2N2, CHCl3, Et2O; iv. 4ꢀMeOC6H4CHO,
KOH, MeOH, H2O, 70 C.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 0211—0215, January, 2013.
1066ꢀ5285/13/6201ꢀ212 © 2013 Springer Science+Business Media, Inc.

Usnic acid derivatives with flavone structure
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 1, January, 2013
213
Scheme 2
ods for the synthesis of new flavonoids with the usnic acid
core as the main structural element.
Dichlorodicyanobenzoquinone (DDQ) employed for
cyclodehydration of 2´ꢀhydroxychalcones4 also oxidizes
the hydroxy group in the ring C of compound 2. However,
this is accompanied by intramolecular heterocyclization
leading to flavone 6 (Scheme 4). We found that a reaction
of chalcone 2 with DDQ under reflux for 10 h gives a 1 : 3
mixture of compounds 5 and 6 (1H NMR data). More
prolonged reflux (15 h) affords compound 6 in 75% yield.
2ꢀHydroxychalcones are known to undergo intraꢀ
molecular cyclization into flavanones in the presence of
an acid5 or ethylenediamine.6 However, no flavanone
products are formed from compound 2 under the reaction
conditions studied.
A reaction of chalcone 2 with a nucleophilic reagent
(NH2NH2•H2O) affords a 1 : 1 mixture of isomeric diꢀ
hydropyrazoles 7a,b in a total yield of 82% (Scheme 5).
The reaction occurs in boiling ethanol, and an equimolar
amount of NH2NH2•H2O should be used. A decrease in
the hydrazine amount results in a lower content of comꢀ
pounds 7a,b in the reaction mixture. The structures of
compounds 7a,b were determined by NMR spectroscopy
as well as by comparing the experimental chemical shifts
Treatment of chalcones with H2O2 in the presence of
alkali results in epoxidation at the exocyclic double bond.
Such epoxides derived from 2ꢀhydroxychalcones are unꢀ
stable and readily undergo intramolecular cyclization into
dihydroflavonols. For instance, a reaction of compound 2
with H2O2 in methanol in the presence of aqueous alkali
gave a mixture of compounds 3a,b and 4 in a total yield
of ~80%; the ratio of the products varies with the reꢀ
action conditions. Structurally, compounds 3a,b and 4
are classified among dihydroflavonols and flavonols,
respectively. Compound 3 was obtained as a 1 : 1 mixture
of transꢀdiastereomers. The arrangement of the substiꢀ
tuents was confirmed by 1H NMR data. Flavonol 4 seems
to be a product of further oxidation of compound 3
(Scheme 2).
When treated with another epoxidating oxidant
(ButOOH), compound 2 yields no cyclization products.
Instead, the hydroxy group in the ring C is oxidized only
(Scheme 3). Product 5 was isolated by column chromatoꢀ
graphy in 67% yield.

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Russ.Chem.Bull., Int.Ed., Vol. 62, No. 1, January, 2013
Sokolov et al.
Scheme 3
Scheme 4
Scheme 5
of the signals for the dihydropyrazole ring with the literaꢀ
ture data.7,8 Note that phenylhydrazine is inert under these
conditions.
To sum up, using methoxychalcone 2 derived from
usnic acid as a starting material, we obtained flavonols,
dihydroflavonols, and flavones. A reaction of compound 2
with hydrazine hydrate gives dihydropyrazoleꢀcontaining
products.
Experimental
Analytical and spectroscopic investigations were performed
at the Chemistry Service Joint Center of the Siberian Branch of
the Russian Academy of Sciences. NMR spectra were recorded
on Bruker AVꢀ400 (400.13 (1H) and 100.61 MHz (13C)), Bruker
DRXꢀ500 (500.13 (1H) and 125.76 MHz (13C)), and Bruker
AVꢀ600 spectrometers (600.3 (1H) and 150.95 MHz (13C)) in

Usnic acid derivatives with flavone structure
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 1, January, 2013
215
CDCl3 with the signals for chloroform (H 7.24, C 76.90) as the
internal standards. The products obtained were identified and
structurally characterized by NMR spectroscopy using 2D
techniques (1H—1H COSY, 13C—1H COSY, COLOC, HMBC,
and HSQC). The atomic numbering in the structural formulas of
the compounds refers to signal assignments in the NMR spectra
and may differ from the numbering implied by their IUPAC
names. The signal multiplicity in the 13C NMR spectra was deꢀ
termined using the JMOD mode. Mass spectra were recorded on
a DFS Thermo Scientific highꢀresolution mass spectrometer
(ionizing energy 70 eV). Melting points were measured on
a Kofler hot stage.
(+)ꢀUsnic acid (1) ([]D +478 (c 0.1, CHCl3)) was isolated
from a blend of lichens of the Usnea genus as described earlier.9
For column chromatography, silica gel (60—200 m, Merck)
was used.
Compound 2 was prepared as described earlier.3 The
13C NMR spectra of compounds 3—7 are given in Table 1.
Reaction of compound 2 with hydrogen peroxide. A 33% soluꢀ
tion of H2O2 (0.15 mL) and 6 M NaOH (0.025 mL) were added
to a solution of compound 2 (220 mg, 0.4 mmol) in methanol
(5 mL). The reaction mixture was stirred at 10—14 C for 4 h
until the substrate was consumed completely (monitoring by
TLC). Then the mixture was warmed to ~20 C, diluted with
water, and neutralized with dilute HCl. The precipitate that
formed was filtered off, dried in air, and chromatographed on
silica gel. Gradient elution with CH2Cl2—ethanol (020%) gave
a 1 : 1 : 1 mixture of compounds 3a,b and 4 in a total yield of
60—65%. Compound 4 was isolated in the individual state
(17% yield).
Compounds 3a,b are transꢀdiastereomers about the C(14)
and C(21) atoms. The signals in the NMR spectra were assigned
using a diastereomerically enriched sample.
(2S,3R,15R,16R)ꢀ3,15ꢀDihydroxyꢀ20ꢀmethoxyꢀ16ꢀ(4ꢀmethꢀ
oxyphenyl)ꢀ2,5,19ꢀtrimethylꢀ7ꢀphenylꢀ11,17ꢀdioxaꢀ6,7ꢀdiazaꢀ
pentacyclo[10.8.0.02,10.04,8.013,18]icosaꢀ1(12),4(8),5,9,13(18),
19ꢀhexaenꢀ14ꢀone (3a or 3b). 1H NMR (500 MHz, CDCl3),
: 1.51 (s, 3 H, H(15)); 2.13 (s, 3 H, H(10)); 2.45 (d, 3 H, H(12),
JH(12),H(1) = 0.3 Hz); 3.76 (ws, 1 H, OH(14)); 3.82 (d, 1 H,
OH(1), JOH,H(1) = 1.6 Hz); 3.83 (s, 3 H, H(26)); 3.95 (s, 3 H,
H(20)); 4.49 (d, 1 H, H(14), JH(14),H(21) = 12.2 Hz); 5.06 (d, 1 H,
H(21), JH(21),H(14) = 12.2 Hz); 5.42 (dd, 1 H, H(1), JH(1),OH
= 1.6 Hz, JH(1),H(12) = 0.3 Hz); 6.99 (d, 2 H, H(24), JH(24),H(23)
=
=
= 8.8 Hz); 7.48 (d, 2 H, H(23), JH(23),H(24) = 8.8 Hz); 7.46—7.51
(m, 2 H, H(17)); 7.41—7.46 (m, 2 H, H(18)); 7.28—7.32 (m, 1 H,
H(19)).
(2S,3R,15S,16S)ꢀ3,15ꢀDihydroxyꢀ20ꢀmethoxyꢀ16ꢀ(4ꢀmethꢀ
oxyphenyl)ꢀ2,5,19ꢀtrimethylꢀ7ꢀphenylꢀ11,17ꢀdioxaꢀ6,7ꢀdiazaꢀ
Table 1. 13C NMR spectra (CDCl3) of compounds 3—7a
Atom

3аa
3ba
4a
5a
6a
7ab
7bb
1
2
3
4
4а
5а
6
7
8
74.43 (d)
112.08 (s)
136.37 (s)
91.15 (d)
167.39 (s)
156.61 (s)
102.85 (s)
154.61 (s)
113.09 (s)
160.14 (s)
118.84 (s)
52.16 (s)
74.38 (d)
112.12 (s)
136.41 (s)
91.95 (d)
167.39 (s)
156.61 (s)
102.55 (s)
154.66 (s)
113.10 (s)
160.47 (s)
118.84 (s)
52.08 (s)
74.38 (d)
111.81 (s)
136.50 (s)
91.24 (d)
167.46 (s)
156.39 (s)
105.75 (s)
154.71 (s)
113.22 (s)
157.50 (s)
120.90 (s)
52.65 (s)
192.73 (s)
111.28 (s)
145.48 (s)
88.69 (d)
172.12 (s)
156.02 (s)
104.22 (s)
164.64 (s)
115.21 (s)
162.14 (s)
110.96 (s)
61.05 (s)
192.32 (s)
110.97 (s)
145.94 (s)
89.57 (d)
172.72 (s)
153.81 (s)
108.10 (s)
155.95 (s)
115.79 (s)
159.83 (s)
117.88 (s)
61.08 (c)
9.94 (q)
150.68 (s)
13.01 (q)
176.60 (s)
106.39 (d)
29.96 (q)
138.21 (c)
123.49 (d)
129.38 (d)
128.05 (d)
63.06 (q)
162.39 (s)
123.75 (s)
127.75 (d)
114.51 (d)
162.41 (s)
55.42 (q)
74.65 (d)
112.22 (s)
136.75 (s)
89.21 (d)
167.75 (s)
154.57 (s)
99.37 (s)
157.88 (s)
111.85 (s)
154.97 (s)
114.81 (s)
52.69 (s)
74.66 (d)
112.27 (s)
136.76 (s)
89.23 (d)
167.75 (s)
154.59 (s)
99.37 (s)
157.88 (s)
111.85 (s)
154.97 (s)
114.84 (s)
52.70 (s)
9
9a
9b
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
9.53 (q)
9.72 (q)
9.79 (q)
9.45 (q)
9.48 (q)
9.48 (q)
147.47 (s)
12.81 (q)
191.28 (s)
73.11 (d)
18.07 (q)
139.12 (s)
122.80 (d)
129.11 (d)
126.84 (d)
61.96 (q)
83.14 (d)
128.20 (s)
128.65 (d)
114.01 (d)
160.22 (s)
55.22 (q)
147.75 (s)
12.80 (q)
191.25 (s)
73.23 (d)
17.97 (q)
139.13 (s)
122.81 (d)
129.11 (d)
126.84 (d)
61.85 (q)
83.12 (d)
128.16 (s)
128.68 (d)
114.02 (d)
160.22 (s)
55.22 (q)
147.17 (s)
12.82 (q)
171.10 (s)
137.39 (d)
18.18 (q)
139.14 (s)
122.76 (d)
129.11 (d)
126.82 (d)
62.46 (q)
144.42 (s)
123.33 (s)
129.11 (d)
114.13 (d)
161.02 (s)
55.30 (q)
150.69 (s)
12.94 (q)
190.99 (s)
122.45 (d)
27.73 (q)
138.31 (s)
123.68 (d)
129.45 (d)
128.00 (d)
62.38 (q)
145.06 (s)
127.50 (s)
130.52 (d)
114.37 (d)
161.79 (c)
55.30 (q)
147.71 (s)
12.78 (q)
151.26 (s)
41.12 (t)
147.74 (s)
12.78 (q)
151.34 (s)
41.12 (t)
18.20 (q)
139.22 (s)
122.86 (d)
129.02 (d)
126.65 (d)
61.69 (q)
62.08 (d)
133.96 (s)
127.35 (d)
114.11 (d)
159.23 (s)
55.17(q)
18.25 (q)
139.23 (s)
122.92 (d)
129.02 (d)
126.69 (d)
61.69 (q)
62.20 (d)
134.08 (s)
127.38 (d)
114.11 (d)
159.23 (s)
55.20 (q)
a The operating frequency is 125 MHz.
b The operating frequency is 150 MHz.

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Sokolov et al.
pentacyclo[10.8.0.02,10.04,8.013,18]icosaꢀ1(12),4(8),5,9,13(18),
19ꢀhexaenꢀ14ꢀone (3a or 3b). 1H NMR (500 MHz, CDCl3),
: 1.49 (s, 3 H, H(15)); 2.13 (s, 3 H, H(10)); 2.45 (d, 3 H, H(12),
JH(12),H(1) = 0.3 Hz); 3.76 (ws, 1 H, OH(14)); 3.82 (d, 1 H,
OH(1), JOH,H(1) = 1.6 Hz); 3.83 (s, 3 H, H(26)); 3.96 (s, 3 H,
H(20)); 4.50 (d, 1 H, H(14), JH(14),H(21) = 12.2 Hz); 5.03 (d, 1 H,
Reaction of compound 2 with NH2NH2•H2O. Hydrazine hyꢀ
drate (0.5 mmol) and acetic acid (0.5 mmol) were added to a
solution of compound 2 (260 mg, 0.5 mmol) in ethanol (10 mL).
The reaction mixture was refluxed for 2 h, cooled to 20 C, and
diluted with water. The precipitate that formed was filtered off,
dried in air, and chromatographed on silica gel (gradient elution
with CHCl3—ethanol (020%)). Yield 82%, m.p. 117—119 C.
Found: m/z 564.2360 [M]+. C33H32O5N4. Calculated:
M = 564.2373. NMR spectra were recorded for a sample conꢀ
taining a 1 : 1 mixture of diastereomers.
(4R,4aS)ꢀ5ꢀMethoxyꢀ8ꢀ[(5R)ꢀ5ꢀ(4ꢀmethoxyphenyl)ꢀ4,5ꢀdiꢀ
hydroꢀ1Hꢀpyrazolꢀ3ꢀyl]ꢀ3,4a,6ꢀtrimethylꢀ1ꢀphenylbenzofuroꢀ
[3,2ꢀf]indazoleꢀ4,7ꢀdiol (7a) and (4R,4aS)ꢀ5ꢀmethoxyꢀ8ꢀ[(5S)ꢀ
5ꢀ(4ꢀmethoxyphenyl)ꢀ4,5ꢀdihydroꢀ1Hꢀpyrazolꢀ3ꢀyl]ꢀ3,4a,6ꢀtriꢀ
methylꢀ1ꢀphenylbenzofuro[3,2ꢀf]indazoleꢀ4,7ꢀdiol (7b). 1H NMR
(600 MHz, CDCl3), : 1.47 (s, 3 H, H(15)); 1.49 (s, 3 H, H(15));
2.19 (s, 3 H, H(10)); 2.19 (s, 3 H, H(10)); 2.44 (s, 3 H, H(12));
2.45 (s, 3 H, H(12)); 3.27 (dd, 1 H, H(14), 2J = 17.4 Hz,
JH(14),H(21) = 9.2 Hz); 3.28 (dd, 1 H, H(14), 2J = 17.4 Hz,
JH(14),H(21) = 9.2 Hz); 3.71 (dd, 1 H, H(14), 2J = 17.4 Hz,
JH(14),H(21) = 10.2 Hz); 3.71 (dd, 1 H, H(14), 2J = 17.4 Hz,
JH(14),H(21) = 10.2 Hz); 3.76 (s, 3 H, H(26)); 3.78 (s, 3 H, H(26));
3.90 (s, 3 H, H(20)); 3.91 (s, 3 H, H(20)); 4.11 (d, 1 H, OH(1),
JOH,H(1) = 1.4 Hz); 4.12 (d, 1 H, OH(1), JOH,H(1) = 1.4 Hz); 4.78
(dd, 1 H, H(21), JH(21),H(14) = 10.2 Hz, JH(21),H(14) = 9.2 Hz);
H(21), JH(21),H(14) = 12.2 Hz); 5.43 (dd, 1 H, H(1), JH(1),OH
= 1.6 Hz, JH(1),H(12) = 0.3 Hz); 6.99 (d, 2 H, H(24), JH(24),H(23)
=
=
= 8.8 Hz); 7.48 (d, 2 H, H(23), JH(23),H(24) = 8.8 Hz); 7.46—7.51
(m, 2 H, H(17)); 7.41—7.46 (m, 2 H, H(18)); 7.28—7.32
(m, 1 H, H(19)).
(2S,3R)ꢀ3,15ꢀDihydroxyꢀ20ꢀmethoxyꢀ16ꢀ(4ꢀmethoxypheꢀ
nyl)ꢀ2,5,19ꢀtrimethylꢀ7ꢀphenylꢀ11,17ꢀdioxaꢀ6,7ꢀdiazapentaꢀ
cyclo[10.8.0.02,10.04,8.013,18]icosaꢀ1(12),4(8),5,9,13(18),15,
19ꢀheptaenꢀ14ꢀone (4), m.p. 156—159 C. 1H NMR (500 MHz,
CDCl3), : 1.55 (s, 3 H, H(15)); 2.50 (s, 3 H, H(10)); 2.46 (d, 3 H,
H(12), JH(12),H(1) = 0.3 Hz); 3.89 (d, 1 H, OH(1), JOH,H(1)
=
= 1.6 Hz); 3.87 (s, 3 H, H(26)); 4.02 (s, 3 H, H(20)); 5.50 (dd, 1 H,
H(1), JH(1),OH = 1.6 Hz, JH(1),H(12) = 0.3 Hz); 7.03 (d, 2 H,
H(24), JH(24),H(23) = 9.1 Hz); 7.04 (ws, 1 H, OH(14)); 8.19
(d, 2 H, H(23), JH(23),H(24) = 9.1 Hz); 7.46—7.51 (m, 2 H,
H(17)); 7.41—7.46 (m, 2 H, H(18)); 7.28—7.32 (m, 1 H,
H(19)). Found: m/z 564.1887 [M]+. C33H28O7N2. Calculated:
M = 564.1891.
Reaction of compound 2 with tertꢀbutyl hydroperoxide. A 5.5 M
solution of ButOOH (0.3 mL) in hexane and seven crystalline
grains of VO(acac)2 were added to a solution of compound 2
(163 mg, 0.3 mmol) in dry toluene (10 mL). The reaction mixꢀ
ture was stirred at 55 C for 2 h, cooled to 20 C, and diluted with
water. The product was extracted with chloroform and the orꢀ
ganic extract was concentrated. The residue was chromatoꢀ
graphed on silica gel (gradient elution with CHCl3—ethanol
(020%)).
4.79 (dd, 1 H, H(21), JH(21),H(14) = 10.2 Hz, JH(21),H(14)
= 9.2 Hz); 5.39 (d, 1 H, H(1), JH(1),OH = 1.4 Hz); 5.39 (d, 1 H,
H(1), JH(1),OH = 1.4 Hz); 6.84 (d, 2 H, H(24), JH(24),H(23)
= 8.7 Hz); 6.86 (d, 2 H, H(24), JH(24),H(23) = 8.7 Hz); 7.25 (d, 2 H,
H(23), JH(23),H(24) = 8.7 Hz); 7.26 (d, 2 H, H(23), JH(23),H(24)
=
=
=
= 8.7 Hz); 7.44—7.56 (m, 2 H, H(17)); 7.44—7.56 (m, 2 H,
H(17)); 7.38—7.41 (m, 2 H, H(18)); 7.38—7.41 (m, 2 H, H(18));
7.24—7.28 (m, 1 H, H(19)); 7.24—7.28 (m, 1 H, H(19)).
(R,E)ꢀ7ꢀHydroxyꢀ5ꢀmethoxyꢀ8ꢀ[3ꢀ(4ꢀmethoxyphenyl)acꢀ
ryloyl]ꢀ3,4a,6ꢀtrimethylꢀ1ꢀphenylꢀ1Hꢀbenzofuro[3,2ꢀf]indazolꢀ
4(4aH)ꢀone (5). Yield 67%, m.p. 155—157 C. 1H NMR
(400 MHz, CDCl3), : 1.89 (s, 3 H, H(15)); 2.20 (s, 3 H, H(10));
2.55 (s, 3 H, H(12)); 3.83 (s, 3 H, H(26)); 4.10 (s, 3 H, H(20));
6.17 (s, 1 H, H(4)); 6.90 (d, 2 H, H(24), H(24´), J = 8.5 Hz);
7.35—7.60 (m, 7 H, Harom); 7.74 (d, 1 H, H(14), J = 15.5 Hz);
7.89 (d, 1 H, H(21), J = 15.5 Hz); 13.96 (s, 1 H, H(7)). Found:
m/z 548.1937 [M]+ C33H28O6N2. Calculated: M = 548.1942.
Reaction of compound 2 with DDQ. Dichlorodicyanobenzoꢀ
quinone (184 mg, 0.72 mmol) was added to a solution of comꢀ
pound 2 (200 mg, 0.36 mmol) in dioxane (10 mL). The reaction
mixture was refluxed for 15 h, cooled to 20 C, and diluted with
water. Then a saturated solution of NaHCO3 was added and the
product was extracted with chloroform. The organic extract was
concentrated. The residue was chromatographed on silica gel
(gradient elution with CH2Cl2—methanol (020%)).
(2R)ꢀ20ꢀMethoxyꢀ16ꢀ(4ꢀmethoxyphenyl)ꢀ2,5,19ꢀtrimethylꢀ7ꢀ
phenylꢀ11,17ꢀdioxaꢀ6,7ꢀdiazapentacyclo[10.8.0.02,10.04,8.013,18]ꢀ
icosaꢀ1(12),4(8),5,9,13(18),15,19ꢀheptaeneꢀ3,14ꢀdione (6).
Yield 75%, m.p. 140—142 C. 1H NMR (500 MHz, CDCl3),
: 1.89 (s, 3 H, H(15)); 2.51 (s, 3 H, H(10)); 2.56 (s, 3 H, H(12));
3.88 (s, 3 H, H(26)); 4.17 (s, 3 H, H(20)); 6.40 (s, 1 H, H(4));
6.65 (s, 1 H, H(14)); 7.02 (d, 2 H, H(24), JH(24),H(23) = 9.0 Hz);
7.38—7.42 (m, 1 H, H(19)); 7.47—7.52 (m, 2 H, H(18));
References
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7.53—7.57 (m, 2 H, H(17)); 7.84 (d, 2 H, H(23), JH(23),H(24)
=
= 9.0 Hz). Found: m/z 546.1788 [M]+ C33H26O6N2. Calculated:
Received October 30, 2012;
M = 546.1785.
in revised form December 21, 2012