Synthesis of (±)Abyssinone I and related compounds: Their anti-oxidant and cytotoxic activities

Article abstract of DOI:10.1016/j.ejmech.2008.05.032

An efficient and facile synthesis of naturally occurring prenylated flavonoids and their analogs have been described. Abyssinone I (9a) was prepared by condensing 2,2-dimethyl chrom-3-en-6-carboxaldehyde (5a) with protected resacetophenone under phase transfer conditions followed by deprotection and cyclization. The influence of prenyl group on anti-oxidant and cytotoxic activities was studied. The presence of 3′-prenyl group as in 8c enhanced radical scavenging activity but decreased reducing power activity when compared to non-prenylated analog 8f. In vitro testing in MCF-7 cell line revealed that prenylated chalcones and flavanones showed better inhibitory activity than their non-prenylated counterparts. Abyssinone I and its chalcone though exhibited negligible anti-oxidant activity their cytotoxic activities were comparable with other prenylated analogs.

Full text of DOI:10.1016/j.ejmech.2008.05.032

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European Journal of Medicinal Chemistry 44 (2009) 2239e2245
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Short communication
Synthesis of (ꢀ)Abyssinone I and related compounds: Their anti-oxidant
and cytotoxic activities
Gudapati Venkateswara Rao, Badrappa Narayana Swamy, Venkateshappa Chandregowda,
*
G. Chandrasekara Reddy
Vittal Mallya Scientific Research Foundation, P.B. No. 406, K.R. Road, Bangalore 560004, India
Received 15 October 2007; received in revised form 9 May 2008; accepted 23 May 2008
Available online 3 June 2008
Abstract
An efficient and facile synthesis of naturally occurring prenylated flavonoids and their analogs have been described. Abyssinone I (9a) was
prepared by condensing 2,2-dimethyl chrom-3-en-6-carboxaldehyde (5a) with protected resacetophenone under phase transfer conditions
followed by deprotection and cyclization. The influence of prenyl group on anti-oxidant and cytotoxic activities was studied. The presence
of 30-prenyl group as in 8c enhanced radical scavenging activity but decreased reducing power activity when compared to non-prenylated analog
8f. In vitro testing in MCF-7 cell line revealed that prenylated chalcones and flavanones showed better inhibitory activity than their non-
prenylated counterparts. Abyssinone I and its chalcone though exhibited negligible anti-oxidant activity their cytotoxic activities were compa-
rable with other prenylated analogs.
Ó 2008 Elsevier Masson SAS. All rights reserved.
Keywords: Abyssinone; Chalcone; Lipophilicity; Prenyl; Reducing power; Radical scavenging; MCF-7 cell line
1. Introduction
Abyssinones which are prenylated flavonoids/polyphenols
were isolated from East African medicinal plant Erythrina
abyssinica [16]. This plant has been widely used in folk medi-
cine for treating malaria and syphilis [17] and methanolic
extract of roots was found to possess anti-fungal and antibacte-
rial properties [18]. Further Kinghorn et al. [19,20] reported the
chemopreventive and aromatase inhibitory activity of preny-
lated flavanones. Because abyssinones exhibited the above
biological activities many chemists turned their attention
towards synthesis of these molecules. Recently, Moriarty
et al. [21] have reported the aromatase inhibitory activity of
Abyssinone II and its synthesis. Though Abyssinone I is iso-
lated from natural source [16], there is no report of its synthesis
or its biological activity and hence we have undertaken its
synthesis and studied anti-oxidant and cytotoxic activities.
Flavonoids represent an important class of naturally occur-
ring compounds and within the flavonoid class the prenylated
derivatives are quite rich in structural variety and pharmacolog-
ical activity. These compounds are known to exhibit a variety
of biological activities such as anti-oxidant [1,2], anti-cancer
[3], anti-viral [4,5], anti-inflammatory [6], anti-ulcer [7], anti-
fungal [8] and also act as potential modulators in multidrug re-
sistance [9e12]. Most of the above activities are influenced by
the number and position of prenyl and hydroxyl groups present
in the flavonoid ring [13]. Barron et al. [14] reported that
substitution of the flavonoid ring system with prenyl groups in-
creased the lipophilicity and conferred the molecule a strong
affinity to biological membranes [15].
2. Result and discussion
* Corresponding author. Tel.: þ91 80 26611664, 26620536; fax: þ91 80
26612806.
E-mail address: gcreddy@vmsrf.org (G.C. Reddy).
Key intermediates used in the synthesis of Abyssinone I are
3,3-dimethyl allyl bromide (2), 4-hydroxy-3-(3-methylbut-2-enyl)
0223-5234/$ - see front matter Ó 2008 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2008.05.032

2240
G.V. Rao et al. / European Journal of Medicinal Chemistry 44 (2009) 2239e2245
OH
OH
benzaldehyde (4), 2,2-dimethylchrom-3-enyl-6-carboxalde-
hyde (5a) and 2,4-bis (methoxymethoxy) acetophenone (7).
Compound 2 was prepared (Scheme 1) in high purity using
much cheaper 2-methyl-3-butene-2-ol instead of isoprene.
Earlier reports of C-alkylation of phenols to make compound
4 suffer from set backs such as poor yields [22], scalability
[23] and usage of alkyl lithium reagents [24]. Hence, we
have modified the method reported by Moriarty et al. to im-
prove the yield of compound 4 from 7.5 to 38% by simulta-
neous addition (portion wise) of alkali and 3,3-dimethyl
allyl bromide to 4-hydroxybenzaldehyde (3) at room tem-
perature (Scheme 2). Compound 4 on heating in toluene
with 2,3-dichloro-5,6-dicyanobenzoquinone(DDQ) afforded
5a (Scheme 3).
2,4-Dihydroxyacetophenone was efficiently protected with
methoxymethyl (MOM) chloride using sodium hydride
(NaH) in dimethylformamide (DMF) to get 2,4-bis (methoxy-
methoxy) acetophenone (7). Compound 8 was prepared
(Scheme 4) by condensing compound 7 with 5a in 50% aque-
ous potassium hydroxide (KOH) and methylene dichloride
(MDC) using phase transfer catalyst at room temperature,
which was then deprotected with 2 N HCl and cyclised using
sodium acetate to give Abyssinone I (9a) (Scheme 5).
+
2
+ Other products
CHO
CHO
3
4
Scheme 2.
show better anti-oxidant properties over their flavanone coun-
terparts, aromatase inhibitory activity and anti-oxidant activity
are not complimentary to each other.
Compounds 8ae8g and 9ae9d, 9f and 9g were subjected to
in vitro testing using breast carcinoma MCF-7 cell line for their
cytotoxic activity (Fig. 2). It is observed that flavonoids contain-
ing prenyl groups in its ring system showed higher inhibitory
activity than their non-prenylated analogs. This may be due to
lipophilicity conferred to the molecule by the prenyl group
and which may increase the affinity for the cell membrane.
In conclusion, we have synthesized Abyssinone I for the first
time, also made related compounds including Abyssinone II,
and studied their anti-oxidant and cytotoxic activities.
Chalcones were found to have better radical scavenging as
well as reducing power activity than their respective flavanones.
Further prenylated flavonoids showed better cytotoxic activity
than their non-prenylated analogs.
Apart from Abyssone I (9a), six different chalcones 8beg
and corresponding flavanones 9beg including Abyssinone II
(9c) were synthesized using different aldehydes 5beg.
Compound 9e was not taken up for further studies because
of stability problem. Radical scavenging and reducing power
assays for compounds 8aeg and 9aeg were measured using
2,2-diphenyl-1-picrylhydrazyl (DPPH) by Blois [25] method
and by Oyaizu [26] method, respectively. Chalcones 8aeg
were found to have better radical scavenging as well as reduc-
ing power activity than their respective flavanones 9aeg
(Fig. 1) which is in agreement with the general observation
made by Miranda et al. [27]. Further, it was noticed that the
40-hydroxy group of flavanone has exerted major influence
on these activities. When the 40-hydroxy group is free, the rad-
ical scavenging and reducing power activities are maximum
and when it is blocked with methyl (8d, 9d, 8g, 9g) or prenyl
(8e) or any other alkyl group (8a, 9a, 8b, 9b) these activities
are minimal. Moreover, the presence of 30-prenyl group as in
8c enhances radical scavenging activity but decreases reducing
power activity when compared to its non-prenylated analog 8f.
Anti-oxidant values of these compounds were measured at
200 mg concentrations and compared with trolox at concentra-
tions of 200 mg for reducing power and 50 mg for DPPH
assays. A study by Maiti et al. [24] revealed that flavones ex-
hibited enhanced aromatase inhibitory activity compared to
precursor chalcones, and also concluded that non-prenylated
flavanones showed higher aromatase inhibitory activity com-
pared to prenylated ones. Since it is known that chalcones
3. Experimental
3.1. General experimental procedures
Crystallizations were performed in chloroform and hexane
mixtures. Melting points were determined on Acro melting
point apparatus and are uncorrected. IR spectra were recorded
1
on Thermo Nicolet FT-IR Instrument in KBr discs. H NMR
and 13C NMR spectra were recorded on Bruker 200 MHz in-
strument in CDCl3 with tetramethylsilane as an internal stan-
dard. Mass spectra were recorded on Shimadzu-QP 2010 S
GCeMS instrument. All chemicals and solvents used in the
synthesis were of laboratory grade procured from local sources
except for 2-methyl-3-butene-2-ol and DPPH which were ob-
tained from Acros Organics (Belgium) and SigmaeAldrich
(USA), respectively.
3.1.1. 3,3-Dimethyl allyl bromide (2)
To a stirred solution of phosphorous tribromide (780 g,
2.88 mol) in n-hexane (3.4 L) a mixture of 2-methyl-3-butane-
2-ol (600 g, 6.98 mol) and pyridine (100 g, 1.27 mol) was
CHO
CHO
CHO
or
or
or
4
R1
3
O
O
R
PBr3
5a
5b
5c-5g
5c R = OMOM; R1 = Prenyl
5d R = OMe; R1 = Prenyl
Br
5e R = Oprenyl; R1 = H
5f R = OMOM; R1 = H
5g R = OMe; R1 = H
OH
1
2
Scheme 1.
Scheme 3.

G.V. Rao et al. / European Journal of Medicinal Chemistry 44 (2009) 2239e2245
2241
O
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
O
Reducing Power
DPPH
HO
OH
MOMO
OMOM
6
7
Scheme 4.
added drop wise over a period of 1e2 h by maintaining the
temperature between 0 and 5 ꢁC. Stirring was continued for
a further period of 1 h at room temperature. Quenched the
reaction mass in ice water (3.5 L), separated the hexane layer.
Hexane layer was washed with 10% sodium bicarbonate
solution, water and dried over anhydrous Na2SO4. Evaporated
hexane under reduced pressure and distilled the residue under
vacuum to get the product (450 g, 45%yield). GCeMS
showed Mþ peak at m/z 148 with a base peak at m/z 69.
8f
9f
8c
9c
8a
9a
8b
9b
8d
9d
8e
8g
9g
trolox
Compounds
Fig. 1. Absorbance values of reducing power and radical scavenging activity.
by maintaining temperature at 10 ꢁC. Stirred the reaction mass
for further 10 min and the respective alkyl halide (2.0 M
equiv.) was added drop wise over 10 min at ice cold and
then continued stirring at room temperature for further 1 h.
Solvent was evaporated under reduced pressure, quenched re-
action mass in cold water and extracted product into toluene.
Organic layer was dried over anhydrous Na2SO4 and evapo-
rated solvent under reduced pressure to get the product. The
crude product obtained was column chromatographed on silica
gel eluting with 6% ethyl acetate in hexane to afford the pure
product.
3.1.2. 4-Hydroxy-3-(3-methylbut-2-enyl) benzaldehyde (4)
4-Hydroxybenzaldehyde (200 g, 1.64 mol) was dissolved in
aqueous potassium hydroxide (108 g in 1080 mL water,
1.64 mol) solution at room temperature. To this solution,
3,3-dimethyl allyl bromide (340 g, 2.28 mol) and aqueous
potassium hydroxide (108 g in 1080 mL water, 1.64 mol)
were added parallely, in portions at 1 h intervals over 48 h un-
der vigorous stirring at around 30 ꢁC. After the complete addi-
tion, the reaction mass was basified further with potassium
hydroxide (1.64 mol, 108 g in 1080 mL water) extracted with
toluene (2 ꢂ 750 mL) to remove O-prenylated products. The
aqueous layer was then acidified with acetic acid at ice cold to
pH 5.0 and extracted product into ethyl acetate (3 ꢂ 500 mL).
Organic layer was dried over anhydrous Na2SO4 and evaporated
solvent under reduced pressure to get the product (150 g). The
crude product obtained was column chromatographed on silica
gel eluting with 9% ethyl acetate in hexane to afford the pure
product (120 g, 38% yield) mp 66e68 ꢁC; GCeMS showed
Mþ peak at m/z 190 with a base peak at m/z 135.
3.2.1. 2,2-Dimethylchrom-3-ene-6-carboxaldehyde (5a)
Compound 4 (5 g, 26.3 mmol) and DDQ (8 g, 35.2 mmol)
were taken in toluene heated at reflux for 2 h. Reaction mass
was cooled to room temperature, filtered insoluble solids and
washed solids thoroughly with toluene. The filtrate obtained
was washed with 2% NaOH solution (10 mL) and water.
The organic layer was dried over anhydrous Na2SO4 and evap-
orated solvent under reduced pressure to get the product
1
(3.5 g, 71%yield): H NMR (CDCl3, 200 MHz) d 1.46 (6H,
s), 5.68 (1H, d, J ¼ 10 Hz), 6.36 (1H, d, J ¼ 10 Hz), 6.85
(1H, d, J ¼ 8.4 Hz), 7.50 (1H, d, J ¼ 2.0 Hz), 7.63 (1H, dd,
J ¼ 8.4, 2.0 Hz), 9.82 (1H, s).
3.2. General procedure for the preparation of
compounds 5cef
3.2.2. 2,2-Dimethylchroman-6-carboxaldehyde (5b)
Compound 4 (5 g, 26.3 mmol) and p-toluene sulphonic acid
(0.2 g) were taken in toluene heated at reflux for 2 h. The re-
action mass was cooled to room temperature, washed with 2%
To a stirred solution of respective aldehyde (3 or 4) in DMF
(50 mL) sodium hydride (2.0 M equiv.) was added in portions
O
O
+
5
7
HO
O
Ar
HO
OH Ar
9
8
c
R = OH; R1 = Prenyl
R = OMe; R1 = Prenyl
R = Oprenyl; R1 = H
R = OH; R1 = H
d
Ar =
R1
e
O
O
R
f
c-g
a
b
g
R = OMe; R1 = H
Scheme 5.

2242
G.V. Rao et al. / European Journal of Medicinal Chemistry 44 (2009) 2239e2245
120
100
80
60
40
20
0
3.2.6. 4-Methoxymethoxybenzaldehyde (5f)
Compound 3 (5 g, 40.9 mmol), sodium hydride (3.9 g,
84.7 mmol), chloromethyl methyl ether (6.6 g, 80 mmol) and
product (6 g, 88% yield).
3.2.7. 2,4-bis (Methoxymethoxy) acetophenone (7)
To a stirred solution of 2,6-dihydroxy acetophenone (150 g,
0.99 mol) in DMF (1.2 L), sodium hydride (94.7 g, 2.05 mol)
was added in portions at around 10 ꢁC. Stirred the reaction
mass for further 10 min and chloromethyl methyl ether
(169 g, 2.1 mol) was added slowly over a period of 1 h at ice
cold and then continued stirring at room temperature for further
1 h. Distilled off DMF under reduced pressure, quenched the
reaction mass in cold water and extracted with toluene
(4 ꢂ 250 mL). Organic layer was dried over anhydrous
Na2SO4 and evaporated solvent under reduced pressure to get
the product. The crude product obtained was subjected to silica
gel column chromatography and on elution with 6% ethyl ace-
8a 9a 8b 9b 8c 9c 8d 9d 8e 8f 9f 8g 9g
Compounds
Fig. 2. Cytotoxic activity of compounds (8ae8g and 9ae9g) on MCF-7 (breast
adeno carcinoma) cell line. IC 50 (mM solutions); determined by MTT assay;
(values are average of at least two independent experiments ꢀ10% (SD) con-
ducted in triplicate for each concentration).
NaOH solution (10 mL) and water. The organic layer was
dried over anhydrous Na2SO4 and evaporated solvent under re-
1
1
duced pressure to get the product (4.5 g, 90%yield): H NMR
tate in hexane afforded pure product (201 g, 85% yield) H
NMR (CDCl3, 200 MHz), d 2.60 (3H, s), 3.48 (3H, s), 3.52
(3H, s), 5.20 (2H, s), 5.27 (2H, s), 6.72 (1H, dd, J ¼ 2.0,
8.6 Hz), 6.82 (1H, d, J ¼ 2.0 Hz), 7.78 (1H, d, J ¼ 8.6 Hz).
(CDCl3, 200 MHz) d 1.36 (6H, s), 1.83 (2H, t, J ¼ 6.8 Hz),
2.81 (2H, t, J ¼ 6.8 Hz), 6.86 (1H, d, J ¼ 8.8 Hz), 7.62 (2H,
m), 9.81 (1H, s).
3.3. General procedure for the preparation of
compounds 8aeg
3.2.3. 4-Methoxymethoxy-3-(3-methylbut-2-enyl)
benzaldehyde (5c)
To a stirred solution of compound 4 (90 g, 0.47 mol) in
DMF (500 mL), sodium hydride (45 g, 0.93 mol) was added
in portions at around 10 ꢁC. Stirred the reaction mass for fur-
ther 10 min and chloromethyl methyl ether (80 g, 1.0 mol) was
added slowly over a period of 1 h at ice cold and then contin-
ued stirring for further 1 h at room temperature. Distilled off
DMF under reduced pressure quenched the reaction mass in
cold water and extracted with toluene (4 ꢂ 250 mL). Organic
layer was dried over anhydrous Na2SO4 and evaporated sol-
vent under reduced pressure to get the product. The crude
product obtained was subjected to silica gel column chroma-
tography and on elution with 6% ethyl acetate in hexane
To hydroxy protected aldehydes (5ae5g) in MDC and 50%
aqueous potassium hydroxide solution (1:1) were added com-
pound 7 and tetra butyl ammonium sulphate (5 mol%). The re-
action mass was stirred at room temperature till starting
materials disappeared (24e72 h). MDC layer was separated,
washed with water (3 ꢂ 50 mL), dried over anhydrous
Na2SO4 and evaporated solvent under reduced pressure to
get thick mass. The material obtained was dissolved in a mix-
ture of methanol and MDC (40 mL:10 mL) and 2 N HCl
(5 mL) was added under stirring at room temperature. After
24 h stirring, evaporated solvent under reduced pressure and
quenched reaction mass in water. Extracted the mixture with
MDC and organic layer was dried over anhydrous Na2SO4
and evaporated solvent to get the product. The crude product
obtained was subjected to silica gel column chromatography
and on elution with 12e15% ethyl acetate in hexane afforded
the pure product.
1
afforded pure product (98 g, 89% yield). H NMR (CDCl3,
200 MHz), d 1.72 (3H, s), 1.75 (3H, s), 3.37 (2H, d,
J ¼ 7.5 Hz), 3.49 (3H, s), 5.29 (2H, s), 5.30 (1H, t,
J ¼ 7.5 Hz), 7.16 (1H, d, J ¼ 9.0 Hz), 7.68 (1H, dd, J ¼ 2.5,
9.0 Hz), 7.70 (1H, d, J ¼ 2.5 Hz), 9.87 (1H, s).
3.3.1. 1-(2,4-Dihydroxyphenyl)-3-(2,2-dimethylchrom-3-
ene-6yl)-prop-2-en-1-one (8a)
3.2.4. 4-Methoxy-3-(3-methylbut-2-enyl) benzaldehyde (5d)
Compound 4 (5 g, 26.3 mmol), sodium hydride (2.5 g,
52 mmol), iodomethane (3.7 g, 54 mmol) and product (5 g,
94% yield); 1H NMR (CDCl3, 200 MHz) d 1.70 (3H, s),
1.75 (3H, s), 3.34 (2H, d, J ¼ 7.4 Hz), 3.92 (3H, s), 5.30
(1H, t, J ¼ 7.4), 6.94 (1H, d, J ¼ 8.4 Hz), 7.68 (1H, d,
J ¼ 2.4 Hz), 7.71 (1H, dd, J ¼ 2.4, 8.4 Hz), 9.85 (1H, s).
To compound 5a (4 g, 21.2 mmol) in MDC and 50%KOH
(20 mL:20 mL) were added compound 7 (5 g, 20.8 mmol)
and 0.2 g of phase transfer catalyst. The reaction mass was
stirred for 48 h and separated layers. Organic layer was
washed with water (3 ꢂ 50 mL), dried under anhydrous
Na2SO4 and evaporated under reduced pressure to get thick
mass. The material obtained was dissolved in a mixture of
methanol and MDC (40 mL:10 mL) and 5 mL of 2 N HCl
was added at room temperature. The reaction mass was stirred
at room temperature for 24 h, evaporated solvent under re-
duced pressure and quenched in water (20 L). Extracted the
3.2.5. 4-(3-Methylbut-2-enyl)oxy phenyl benzaldehyde (5e)
Compound 3 (5 g, 40 mmol), sodium hydride (3.9 g,
84.7 mmol), prenyl bromide (12.2 g, 81.8 mmol) and product
(6.5 g, 84% yield).

G.V. Rao et al. / European Journal of Medicinal Chemistry 44 (2009) 2239e2245
2243
product with MDC (2 ꢂ 50 mL) and organic layer was dried
over anhydrous Na2SO4 and on evaporation of solvent ob-
tained the product. The crude product obtained was subjected
to silica gel column chromatography to get pure product (5 g,
75% yield); mp 180e183 ꢁC; IR (KBr) ymax 3193, 2931, 1631,
127.20, 128.44, 129.78, 130.97, 131.92, 133.09, 145.15,
159.81, 162.39, 166.41,192.14.
3.3.5. 1-(2,4-Dihydroxyphenyl)-3-[(4-(3-methylbut-2-
enyl)oxyphenyl)]-prop-2-en-1-one (8e)
1600, 1550, 1488, 1361, 1307, 1226, 1141, 1103, 1026 cmꢃ1
;
Compound 5e (4.5 g, 23.7 mmol), compound 7 (5 g,
20.8 mmol), PTC (0.2 g) and product (3 g, 44% yield): mp
155e158 ꢁC; IR (KBr) ymax 3163, 2920, 1627, 1604, 1546,
1H NMR (CDCl3, 200 MHz) d 1.47 (6H, s), 5.68 (1H, d,
J ¼ 8.8 Hz), 5.92 (1H, s), 6.36 (1H, d, J ¼ 8.8 Hz), 6.46 (m,
2H), 6.81 (1H, d, J ¼ 8.4 Hz), 7.28 (1H, d, J ¼ 2.0 Hz), 7.42
(1H, d, J ¼ 15.4 Hz), 7.44 (1H, dd, J ¼ 2.0, 8.4 Hz), 7.82
(1H, d, J ¼ 15.4 Hz), 7.83 (1H, d, J ¼ 8.4 Hz), 13.53 (1H, s);
13C NMR (CDCl3, 200 MHz) d 28.20, 77.20, 103.65,
107.55, 115.22, 116.85, 117.38, 121.32, 121.52, 126.61,
127.39, 130.04, 131.36, 131.78, 144.58, 156.52, 162.41,
166.24, 191.84.
1
1508, 1373, 1292, 1226, 1172, 1145, 1029 cmꢃ1; H NMR
(CDCl3, 200 MHz) d 1.76 (3H, s), 1.81 (3H, s), 4.57 (2H, d,
J ¼ 6.6 Hz), 5.49 (1H, t, J ¼ 6.6 Hz), 6.44 (2H, m), 6.95 (2H,
d, J ¼ 8.8 Hz), 7.44 (1H, d, J ¼ 15.44 Hz), 7.60 (2H, d, J ¼
8.6 Hz), 7.83 (1H, d, J ¼ 9.2 Hz), 7.86 (1H, d, J ¼ 15.4 Hz);
13C NMR (CDCl3, 50 MHz) d 18.13, 25.70, 64.90, 103.66,
107.46, 114.53, 115.08, 117.55, 119.02, 127.28, 130.27,
131.75, 138.70, 144.48, 161.12, 162.30, 166.29, 191.91.
3.3.2. 1-(2,4-Dihydroxyphenyl)-3-(2,2-dimethylchroman-
6yl)-prop-2-en-1-one (8b)
3.3.6. 1-(2,4-Dihydroxyphenyl)-3-(4-hydroxyphenyl)-
prop-2-en-1-one (8f)
Compound 5b (4 g, 21 mmol), compound
20.8 mmol), PTC (0.2 g) and product (5 g, 75% Yield); mp
7 (5 g,
Compound 5f (4 g, 24 mmol), compound 7 (5 g, 20.8 mmol),
PTC (0.2 g) and product (4 g, 75% yield): mp 190e195 ꢁC; IR
(KBr) ymax 3379, 3282, 1627, 1542, 1512, 1288, 1207, 1141,
1029 cmꢃ1; 1H NMR (CDCl3, 200 MHz) d 6.38 (2H, m), 6.83
(2H, d, J ¼ 8.4 Hz), 7.35 (1H, d, J ¼ 15.4 Hz), 7.46 (2H, d,
J ¼ 8.4 Hz), 7.72 (1H, d, J ¼ 9.4 Hz), 7.75 (1H, d,
J ¼ 15.4 Hz), 9.21 (1H, br s), 9.74 (1H, br s), 13.48 (1H, s);
13C NMR (DMSO-d6, 50 MHz) d 103.06, 108.56, 113.48,
116.32, 117.89, 126.24, 131.69, 133.32, 144.74, 160.74,
165.42, 166.26, 192.01.
188e189 ꢁC; IR (KBr) ymax 3209, 2931, 1631, 1600, 1546,
1
1488, 1372, 1307, 1230, 1145, 1118, 1026 cmꢃ1; H NMR
(CDCl3, 200 MHz) d 1.36 (3H, s), 1.84 (2H, t, J ¼ 6.6 Hz),
2.81 (2H, t, J ¼ 6.6 Hz), 5.99 (1H, br s), 6.43 (2H, m), 6.81
(1H, d, J ¼ 8.4 Hz), 7.41 (1H, d, J ¼ 15.0 Hz), 7.43 (2H, d,
J ¼ 9.6 Hz), 7.82 (1H, d, J ¼ 15.0 Hz), 7.83 (1H, d,
J ¼ 9.6 Hz); 13C NMR (CDCl3, 200 MHz) d 22.24, 26.82,
32.45, 75.28, 103.65, 107.55, 114.49, 116.91, 117.97, 121.37,
126.39, 127.88, 130.75, 131.79, 145.03, 156.83, 162.39,
166.21,191.99.
3.3.7. 1-(2,4-Dihydroxyphenyl)-3-(4-methoxyphenyl)-
prop-2-en-1-one (8g)
3.3.3. 1-(2,4-Dihydroxyphenyl)-3-[4-hydroxy-3-
(3-methylbut-2-enyl) phenyl]-prop-2-en-1-one (8c)
Compound 5c (5 g, 21.3 mmol), compound
Compound 5g (3.5 g, 25.7 mmol), compound 7 (5 g,
20.8 mmol), PTC (0.2 g) and product (4.5 g, 80% yield): mp
180e183 ꢁC; IR (KBr) ymax 3301, 2923, 1635, 1600, 1562,
7 (5 g,
20.8 mmol), PTC (0.2 g) and product (4.5 g, 67% yield): mp
153e155 ꢁC; IR (KBr) ymax 3413, 3313, 2927, 2854, 1627,
1
1512, 1365, 1292, 1215, 1172, 1126, 1033 cmꢃ1; H NMR
1600, 1550, 1504, 1431, 1373, 1242, 1137, 1103, 1029 cmꢃ1
;
1H NMR (CDCl3, 200 MHz) d 1.57 (3H, s), 1.81 (3H, s),
3.40 (2H, d, J ¼ 7.0 Hz), 5.33 (1H, m), 6.41 (1H, s), 6.42
(1H, m), 6.85 (1H, d, J ¼ 8.2 Hz), 7.42 (3H, m), 7.84 (2H,
m), 13.48 (1H, s); 13C NMR (DMSO-d6, 50 MHz) d 20.09,
27.88, 30.60, 104.95, 110.43, 115.36, 117.68, 119.44, 125.02,
128.06, 130.76, 131.20, 133.30, 133.71, 135.18, 147.00,
160.46, 167.27, 168.16, 193.85.
(CDCl3, 200 MHz) d 3.81 (3H, s), 6.38 (2H, m), 6.88 (2H, d,
J ¼ 8.8 Hz), 7.40 (1H, d, J ¼ 15.4 Hz), 7.55 (2H, d, J ¼
8.8 Hz), 7.73 (1H, d, J ¼ 9.4 Hz), 7.77 (1H, d, J ¼ 15.4 Hz),
9.78 (1H, s), 13.42 (1H, s); 13C NMR (DMSO-d6, 50 MHz)
d 55.88, 103.06, 108.62, 113.49, 114.92, 119.04, 127.75,
131.46, 133.45, 144.24, 161.95, 165.52, 166.28, 192.00.
3.4. General procedure for the preparation of
compounds 9aeg
3.3.4. 1-(2,4-Dihydroxyphenyl)-3-[4-methoxy-3-
(3-methylbut-2-enyl) phenyl]-prop-2-en-1-one (8d)
Compound 5d (5 g, 24.5 mmol), compound 7 (5 g,
20.8 mmol), PTC (0.2 g) and product (5 g, 71%yield): mp
150e154 ꢁC; IR (KBr) ymax 3163, 2916, 1624, 1593, 1542,
Chalcones 8aeg (10 mmol) and sodium acetate (20 mmol)
were taken in 10% aqueous ethanol and heated to reflux for
24e48 h. Evaporated ethanol under reduced pressure diluted
the reaction mass with cold water and extracted with MDC
(3 ꢂ 25 mL). The organic layer was dried over anhydrous
Na2SO4 and evaporated solvent under reduced pressure to get
the product. The product obtained mainly contains equal
amount of products and starting materials which were separated
by column chromatography on silica gel, eluting with 15e25%
ethyl acetate in hexane.
1
1500, 1373, 1261, 1226, 1141, 1029 cmꢃ1; H NMR (CDCl3,
200 MHz) d 1.74 (3H, s), 1.77 (1H, s), 3.34 (2H, d,
J ¼ 7.2 Hz), 3.89 (3H, s), 5.30 (1H, t, J ¼ 7.2 Hz), 6.37 (1H,
s), 6.44 (1H, dd, J ¼ 8.6, 2.0 Hz), 6.88 (1H, d, J ¼ 8.6 Hz),
7.45 (3H, m), 7.84 (1H, d, J ¼ 9.4 Hz), 7.86 (1H, d,
J ¼ 15.4 Hz); 13C NMR (CDCl3, 50 MHz) d 17.87, 25.86,
28.49, 55.60, 103.79, 107.58, 110.46, 114.74, 117.44, 121.84,

2244
G.V. Rao et al. / European Journal of Medicinal Chemistry 44 (2009) 2239e2245
3.4.1. 2-(20,20-Dimethyl chrom-30-en-60-yl)-7-hydroxy
chroman-4-one (9a)
6.51 (1H, d, J ¼ 8.6 Hz), 6.86 (1H, d, J ¼ 8.0 Hz), 7.12 (1H,
d, J ¼ 8.0 Hz), 7.60 (1H, s), 7.73 (1H, d, J ¼ 8.6 Hz), 8.92
(1H, s), 9.99 (1H, s); 13C NMR (DMSO-d6, 50 MHz)
d 20.03, 27.91, 30.49, 45.53, 81.49, 104.93, 112.81, 115.94,
117.03, 125.07, 127.81, 129.81, 130.53, 130.76, 131.63,
133.68, 157.56, 165.52, 166.96, 192.46.
Chalcone 8a (3 g, 9.2 mmol) and sodium acetate (1.5 g,
20 mmol) were taken in 10% aqueous ethanol and heated to
reflux for 24 h. Evaporated ethanol under reduced pressure
diluted the reaction mass with cold water and extracted with
MDC (3 ꢂ 25 mL). The organic layer was dried over anhy-
drous Na2SO4 and evaporated solvent under reduced pressure
to get the product. The product obtained mainly contains equal
amount of products and starting material which was separated
by column chromatography on silica gel, eluting with 15%
ethyl acetate in hexane (1.3 g, 43% yield): mp 161e165 ꢁC;
IR (KBr) ymax 3039, 2927, 2715, 1651, 1569, 1492, 1353,
3.4.4. 7-Hydroxy-2-[40-methoxy-30-(3-methylbut-2-enyl)
phenyl]chroman-4-one (9d)
Compound 9d (2.5 g, 7.4 mmol) and sodium acetate (1.2 g,
14.6 mmol), product (1.25 g, 50% yield): mp 135e139 ꢁC; IR
(KBr) ymax 3325, 2958, 2850, 1662, 1593, 1500, 1461, 1323,
1
1215, 1122, 1029 cmꢃ1; H NMR (CDCl3, 200 MHz) d 1.70
1
1245, 1164, 1118, 1060 cmꢃ1; H NMR (CDCl3, 200 MHz)
(3H, s), 1.74 (3H, s), 2.78 (1H, dd, J ¼ 3.0, 17.0 Hz), 3.07
(1H, dd, J ¼ 17.0, 13.2 Hz), 3.33 (2H, d, J ¼ 7.4 Hz), 3.85
(3H, s), 5.38 (1H, dd, J ¼ 3.0, 13.2 Hz), 5.79 (1H, br s),
6.44 (1H, d, J ¼ 2.2 Hz), 6.53 (1H, dd, J ¼ 2.2, 8.6 Hz), 6.88
(1H, d, J ¼ 8.2 Hz), 7.22 (1H, s), 7.27 (1H, d, J ¼ 8.2 Hz),
7.85 (1H, d, J ¼ 8.6 Hz); 13C NMR (CDCl3, 50 MHz)
d 17.82, 25.85, 28.50, 44.12, 55.56, 79.98, 103.49, 110.33,
110.44, 115.24, 122.02, 125.13, 127.63, 129.44, 130.39,
130.49, 130.76, 157.55, 162.61, 163.78, 191.22.
d 1.44 (6H, s), 2.79 (1H, dd, J ¼ 3.0, 17.0 Hz), 3.06 (1H, dd,
J ¼ 17.0, 13.2 Hz), 5.35 (1H, dd, J ¼ 3.0, 13.2 Hz), 5.65 (1H,
d, J ¼ 9.8 Hz), 6.07 (1H, br s), 6.33 (1H, d, J ¼ 9.8 Hz), 6.45
(1H, d, J ¼ 2.0 Hz), 6.54 (1H, dd, J ¼ 8.6, 2.0 Hz), 6.81 (1H,
d, J ¼ 8.2 Hz), 7.08 (1H, d, J ¼ 2.0 Hz), 7.19 (1H, dd,
J ¼ 2.0, 8.2 Hz), 7.85 (1H, d, J ¼ 8.6 Hz); 13C NMR (CDCl3,
50 MHz) d 28.15, 44.10, 77.82, 79.79, 103.48, 110.61,
115.09, 116.60, 121.49, 121.98, 124.48, 127.26, 129.46,
130.81, 131.41, 153.48, 162.89, 163.74, 191.24.
3.4.5. 7-Hydroxy-2-(40-hydroxyphenyl) chroman-4-one (9f)
Compound 8f (4 g, 15.6 mmol) and sodium acetate (2.5 g,
30.5 mmol), product (1.6 g, 40% yield): mp 169e170 ꢁC; IR
(KBr) ymax 3031, 2920, 2827, 1654, 1600, 1515, 1469, 1330,
3.4.2. 2-(20,20-Dimethyl chroman-60-yl)-7-hydroxy
chroman-4-one (9b)
Compound 8b (3 g, 9.2 mmol), sodium acetate (1.5 g,
18.2 mmol), product (1.35 g, 45% yield): mp 155 ꢁC; IR
(KBr) ymax 2927, 2854, 1651, 1573, 1500, 1353, 1330, 1242,
1234, 1164, 1118 cmꢃ1
;
1H NMR (CDCl3, 200 MHz)
d 2.52e2.95 (3H, m), 5.18 (1H, d, J ¼ 13 Hz), 6.27 (1H, s),
6.38 (1H, d, J ¼ 8.4 Hz), 6.73 (2H, dd, J ¼ 2.0, 7.2 Hz), 7.13
(2H, dd, J ¼ 2.0, 7.2 Hz), 7.60 (1H, dd, J ¼ 2.6, 8.4 Hz), 8.90
(1H, br s), 9.9 (1H, br s); 13C NMR (DMSO-d6, 50 MHz)
d 43.64, 79.44, 103.03, 110.96, 114.01, 115.59, 128.73,
128.87, 129.79, 158.08, 163.65, 165.08, 190.58.
1
1153, 1114, 1060 cmꢃ1; H NMR (CDCl3, 200 MHz) d 1.35
(6H, s), 1.83 (2H, t, J ¼ 6.6 Hz), 2.76 (3H, m), 3.06 (1H, dd,
J ¼ 17.0, 13.4 Hz), 5.35 (1H, dd, J ¼ 2.6, 13.4 Hz), 6.48
(1H, d, J ¼ 2.0 Hz), 6.57 (1H, dd, J ¼ 8.6, 2.0 Hz), 6.82 (1H,
d, J ¼ 9.0 Hz), 7.17 (1H, s), 7.30 (1H, d, J ¼ 8.0 Hz), 7.86
(1H, d, J ¼ 8.6 Hz); 13C NMR (CDCl3, 50 MHz) d 22.42,
26.77, 32.56, 43.86, 74.55, 79.82, 103.36, 110.68, 114.59,
114.45, 117.51, 121.16, 125.57, 127.69, 129.32, 154.50,
163.46, 163.89, 191.92.
3.4.6. 7-Hydroxy-2-(40-methoxyphenyl) chroman-4-one (9g)
Compound 8g (4 g, 14.8 mmol) and sodium acetate (2.4 g,
29.2 mmol), product (1.8 g, 45% yield): mp 155e163 ꢁC; IR
(KBr) ymax 3305, 2908, 1662, 1589, 1515, 1323, 1215, 1176,
1110, 1033 cmꢃ1; 1H NMR (CDCl3, 200 MHz) d 2.8 (1H, dd,
J ¼ 3.0, 16.8 Hz), 3.07 (1H, dd, J ¼ 16.8, 13.0 Hz), 3.85 (3H,
s), 5.41 (1H, dd, J ¼ 13.0, 3.0 Hz), 6.01 (1H, br s), 6.45 (2H,
m), 6.41 (1H, dd, J ¼ 2.2, 8.6 Hz), 6.95 (2H, d, J ¼ 8.6 Hz),
7.39 (2H, d, J ¼ 8.6 Hz), 7.86 (1H, d, J ¼ 8.8 Hz); 13C NMR
(DMSO-d6, 50 MHz) d 43.09, 55.06, 78.63, 102.49, 110.44,
113.47, 113.75, 128.07, 128.31, 130.98, 159.26, 162.99,
164.53, 189.85.
3.4.3. 7-Hydroxy-2-[40-hydroxy-30-(3-methylbut-2-
enyl)phenyl]chroman-4-one (9c)
Mixture of chalcone 8c (25 g, 77 mmol) and sodium acetate
(10 g, 120 mmol) was taken in aqueous ethanol (90:10 etha-
nol:water, 100 mL) and heated to reflux for 24 h. After that
ethanol was removed under reduced pressure, quenched the re-
action mass with ice-cold water (100 mL) and extracted with
ethyl acetate (4 ꢂ 100 mL). Ethyl acetate extract was washed
with water and dried over anhydrous sodium sulphate. On
evaporation of ethyl acetate a solid residue was obtained
which was subjected to silica gel column chromatography.
The pure product (14 g, 56% yield) thus obtained was crystal-
lized as pale yellow crystals from chloroform/n-hexane. mp
120e122 ꢁC; IR (KBr) ymax 3282, 2896, 2854, 1670, 1612,
4. Anti-oxidant assay
4.1. Reducing power assay
The reducing power assays of flavonoid compounds were
determined by the method of Oyaizu. Samples of respective
compounds (200 mg, 0.6e0.78 mM) in 1 mL of milli Q water
were mixed with phosphate buffer (2.5 mL, 0.2 mM, pH 6.6)
and potassium ferricyanide solution (2.5 mL, 1% w/v). The
1581, 1469, 1434, 1276, 1157, 1126 cmꢃ1
;
1H NMR
(CDCl3, 200 MHz) d 1.71 (3H, s), 1.74 (3H, s), 2.67 (1H,
dd, J ¼ 2.6, 16.8 Hz), 3.01 (1H, dd, J ¼ 16.8, 8.6 Hz), 3.32
(2H, d, J ¼ 7.0 Hz), 5.31 (2H, d, J ¼ 9.8 Hz), 6.41 (1H, s),

G.V. Rao et al. / European Journal of Medicinal Chemistry 44 (2009) 2239e2245
2245
mixture was incubated at 50 ꢁC for 20 min, followed by the
addition of aqueous trichloroacetic solution (2.5 mL, 10% w/
v). The mixture was then centrifuged at 5000 rpm for
10 min using refrigerated bench top centrifuge (Rotina-38R).
The upper layer of the solution (2.5 mL) was mixed with milli
Q water (2.5 mL) and ferric chloride solution (0.5 mL, 0.1%w/
v), and the absorbance was measured at 700 nm using UVevis
spectrophotometer (CARY 50 Bio). Increased absorbance of
the reaction mixture indicates the increased reducing power.
All experiments were performed in triplicate.
compounds 8ae8g, 9ae9d, 9f and 9g are available free of
charge via the Internet at http://www.sciencedirect.org.
Supplementary data associated with this article can also be
found in the online version, at doi: 10.1016/j.ejmech.2008.
05.032.
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Acknowledgement
We thank Dr. Anil Kush, CEO, Vittal Mallya Scientific
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1
The HNMR, 13C NMR and Mass spectroscopic data and
data supporting anti-oxidant and cytotoxic activities of