Synthesis of some novel pyrano[2,3-f]chromenone derivatives

Article abstract of DOI:10.1007/s13738-014-0518-3

A new series of pyrano[2,3-f]chromenone derivatives were synthesized starting from resorcinol. Resorcinol reacted with 3-chloropropanoic acid to give 7-hydroxychroman-4-one and reaction of the later compound with 2-methylbut-3-yn-2-ol led to the formation of 7-((2-methylbut-3-yn-2-yl)oxy)chroman-4-one. The obtained compound tolerated the cyclization reaction through Claisen rearrangement by heating in DMF to afford 8,8-dimethyl-2,3-dihydro-4H,8H-pyrano[2,3-f]chromen-4-one. Reaction of the later compound with various aromatic aldehydes gave the title compounds in good yields. All products were evaluated for their cytotoxic activity on the blood tumor cell line K562 and compared to reference drug, etoposide. Most of them exhibited low inhibitory activity against tumor cell line and among them, the compound possessing three methoxy groups on aromatic ring showed better cytotoxic effect.

Full text of DOI:10.1007/s13738-014-0518-3

J IRAN CHEM SOC
DOI 10.1007/s13738-014-0518-3
ORIgINAl PAPER
Synthesis of some novel pyrano[2,3‑f]chromenone derivatives
Babak Heidary Alizadeh · Mina Saeedi ·
Gholamreza Dehghan · Alireza Foroumadi ·
Abbas Shafiee
Received: 17 July 2014 / Accepted: 24 July 2014
© Iranian Chemical Society 2014
Abstract A new series of pyrano[2,3-f]chromenone
derivatives were synthesized starting from resorcinol.
Resorcinol reacted with 3-chloropropanoic acid to give
7-hydroxychroman-4-one and reaction of the later com-
pound with 2-methylbut-3-yn-2-ol led to the formation
of 7-((2-methylbut-3-yn-2-yl)oxy)chroman-4-one. The
obtained compound tolerated the cyclization reaction
through Claisen rearrangement by heating in DMF to afford
8,8-dimethyl-2,3-dihydro-4H,8H-pyrano[2,3-f]chromen-
4-one. Reaction of the later compound with various aro-
matic aldehydes gave the title compounds in good yields.
All products were evaluated for their cytotoxic activity on
the blood tumor cell line K562 and compared to reference
drug, etoposide. Most of them exhibited low inhibitory
activity against tumor cell line and among them, the com-
pound possessing three methoxy groups on aromatic ring
showed better cytotoxic effect.
Introduction
Pyranochromenes or pyranobenzopyrans are one of the
most important class of heterocycles attracting consider-
able interest in organic and natural product synthesis [1].
At this juncture, promising biological properties such
as antitubercular [2], BACE1 inhibitory [3], anticancer
(in human leukemia) [4], and antimicrobial activities
[5] of pyranochromenes have attracted medicinal chem-
ists attention. Also, they are widely present in naturally
occurring compounds such as deguelin (a), glyinflanin
K (b), and glyasperin M (c) (Fig. 1) possessing a wide
range of biological and pharmacological properties
[6–8].
For example, deguelin (a, Fig. 1) was originally iso-
lated from African plant Mundulea sericea and has
depicted strong anticancer activity in various in vitro and
in vivo studies for a number of cancers [9–11] includ-
ing prostate [12], lung [13, 14], and breast [15, 16]. It
is believed that it induces apoptosis in premalignant and
malignant human bronchial epithelial (HBE) cells with
no effect on the growth of normal HBE cells. Thus, it is
an attractive candidate agent for chemoprevention of can-
cer [13].
Keywords Pyranochromenone · Resorcinol ·
Claisen rearrangement
Brilliant results connected to exclusive antitumor activ-
ity of deguelin have inspired researchers to develop its
application and investigate more details [11, 17]. Herein, in
continuation of our research on the synthesis of chromene
derivatives [18–20], we report an efficient method for the
preparation of novel pyrano[2,3-f]chromenone 3 via the
reaction of 8,8-dimethyl-2,3-dihydro-4H,8H-pyrano[2,3-
f]chromen-4-one 1 and various aromatic aldehydes 2
in the presence of lDA and HMPA in THF at −78 °C
(Scheme 1).
B. H. Alizadeh
Iranian Research Institute of Plant Protection (IRIPP), Shahid
Chamran Avenue, Yaman St. No 1, PO. Box: 1454, Tehran, Iran
M. Saeedi · A. Foroumadi · A. Shafiee (*)
Department of Medicinal Chemistry, Faculty of Pharmacy
and Pharmaceutical Sciences Research Center, Tehran University
of Medical Sciences, 14176 Tehran, Iran
e-mail: ashafiee@ams.ac.ir; shafieea@tums.ac.ir
g. Dehghan
Department of Biology, Faculty of Natural Science, University
of Tabriz, Tabriz, Iran
1 3

J IRAN CHEM SOC
Fig. 1 Structure of deguelin (a)
and glyinflanin K (b)
amount of water was added to the reaction mixture and the
solution was concentrated under reduced pressure and the
residue was extracted with EtOAc (3 × 5 ml), washed with
1 N HCl, saturated NaHCO3, and brine. After drying over
Na2SO4, the solvent was removed under reduced pressure
and the residue was purified by column chromatography
using silicagel and hexane/ethyl acetate (4:1) as eluent to
obtain 7-((2-methylbut-3-yn-2-yl)oxy)chroman-4-one 8.
Pale yellow oil; yield: 97 %. 1H-NMR (500 MHz,
CDCl3) δ 1.72 (s, 6H, 2 × CH3), 2.67 (s, 1H, C≡CH),
2.78 (t, J = 6.3 Hz, 2H, H3), 4.53 (t, J = 6.3 Hz, 2H, H2),
6.80 (dd, J = 8.8, 2.3 Hz, 1H, H6), 6.88 (d, J = 2.3 Hz,
1H, H8), 7.84 (d, J = 8.8 Hz, 1H, H5). IR (film) ν 1,650
(C=O) cm−1. Anal. Calcd for C14H14O3: C, 73.03; H, 6.13.
Found: C, 73.19; H, 6.29.
Scheme 1 Synthesis of pyrano[2,3-f]chromenone derivatives 3
Experimental section
Chemistry
1H-NMR spectra were measured using a Bruker 500 spec-
trometer (germany) and chemical shifts were expressed
as δ (ppm) with tetramethylsilane as internal standard.
The IR spectra were obtained on a Shimadzu IR pres-
tige-21. Mass spectra were recorded on Agilent 6410 Tri-
ple Quad. lC/MS and Finnigan MAT TSQ-70. The purity
of all compounds was confirmed by TlC using differ-
ent mobile phases. The elemental analysis was performed
with an Elementar Analysensystem gmbH VarioEL CHNS
mode which were within 0.4 % of theoretical values for
C, H, and N. All chemicals were obtained from Merck
and Aldrich and 7-hydroxychroman-4-one 6 was prepared
according to our previous report through the reaction of
resorcinol 3 and 3-chloroacetic acid 4 [21].
7‑((2‑Methylbut‑3‑yn‑2‑yl)oxy)chroman‑4‑ol (9)
A solution of compound 8 (0.15 g, 0.65 mmol) in MeOH
(5 ml) was added to a stirred suspension of NaBH4
(45.4 mg, 1.2 mmol) in MeOH (1 ml) and the mixture was
stirred at room temperature for 2 h. Then, small amount
of water was added to the reaction mixture, MeOH was
removed under reduce pressure and the pH of solution was
adjusted to pH = 3 using 1 N HCl. Next, the crude product
was extracted with EtOAc (3 × 5 ml), washed with water,
saturated NaHCO3, and brine. After drying over Na2SO4,
the solvent was removed under reduced pressure to give
the product which was purified by column chromatography
using silicagel and hexane/ethyl acetate (3:1) as eluent to
give pure 7-((2-methylbut-3-yn-2-yl)oxy)chroman-4-ol 9.
Pale yellow oil; yield: 85 %. IR (film) ν 3,300
7‑((2‑Methylbut‑3‑yn‑2‑yl)oxy)chroman‑4‑one (8)
DBU (0.31 ml, 2.08 mmol) was added drop wise to a solu-
tion of 2-methylbut-3-yn-2-ol 7 (0.53 ml, 5.44 mmol) in
anhydrous CH3CN (13 ml) under argon at −5 °C. Then,
trifluoroacetic anhydride (0.76 ml, 5.44 mmol) was added
to the above-mentioned mixture over 30 min while keeping
the temperature just below 0 °C. Then, it was allowed to stir
at 0 °C for 1 h to form 2-methyl-3-butyn-2-triflate. Sepa-
rately, DBU (0.31 ml, 2.08 mmol) and CuCl2·2H2O (0.02 g,
0.10 mmol) was added to a solution of 7-hydroxychroman-
4-one 6 (0.22 g, 1.34 mmol) in CH3CN (2 ml) under argon
at −5 °C and allowed to be stirred for 30 min. Then, it was
added to the freshly prepared 2-methyl-3-butyn-2-triflate
solution over 50 min while keeping the temperature below
0 °C and allowed to be stirred for 30 min at 0 °C. Next, small
(OH) cm−1
.
4‑((8,8‑Dimethyl‑3,4‑dihydro‑2H,8H‑pyrano[2,3‑f]chro
men‑4‑yl)oxy)‑N,N‑dimethylaniline (10) and 8,8‑dime‑
thyl‑2H,8H‑pyrano[2,3‑f]chromene (11)
A solution of compound 9 (0.46 g, 0.2 mmol) in anhydrous
N,N-dimethylaniline (0.5 ml) was heated at 170 °C under
argon for 2 h. After cooling to room temperature, water was
added to the reaction mixture and extracted with ethyl ace-
tate (3 × 15 ml). The combined organic phase was dried
1 3

J IRAN CHEM SOC
Scheme 2 Investigation of various routes for the preparation of 8,8-dimethyl-2,3-dihydro-4H,8H-pyrano[2,3-f]chromen-4-one 1
over Na2SO4 and solvent was evaporated under reduced
pressure to obtain crude oil which was purified by column
chromatography using silicagel and hexane/ethyl acetate
(7:1) as eluent to separate two compounds 10 and 11.
8,8‑Dimethyl‑2H,8H‑pyrano[2,3‑f]chromene (11)
1
Pale yellow oil; yield: 15 %. H-NMR (500 MHz, CDCl3)
δ 1.43 (s, 6H, 2 × CH3), 4.82 (dd, J = 3.6, 1.7 Hz, 2H, H2),
5.60 (d, J = 10.0 Hz, 1H, H9), 5.63 (dt, J = 10.0, 3.6 Hz,
1H, H3), 6.34 (d, 1H, J = 8.3 Hz, H6), 6.36 (dt, J = 10.0,
1.7 Hz, 1H, H4), 6.60 (d, 1H, J = 10.0 Hz, H10), 6.73 (d,
1H, J = 8.3 Hz, H5). ESI-Mass m/z 237 (M++23). Anal.
Calcd for C14H14O2: C, 78.48; H, 6.59. Found: C, 78.29;
H, 6.69.
4‑((8,8‑Dimethyl‑3,4‑dihydro‑2H,8H‑pyrano[2,3‑f]chrome
n‑4‑yl)oxy)‑N,N‑dimethylaniline (10)
Pale yellow oil; yield: 65 %. 1H-NMR (500 MHz, CDCl3) δ
1.43 (s, 3H, CH3), 1.45 (s, 3H, CH3), 2.04 (m, 1H, H3), 2.23
(m, 1H, H3), 2.93 (s, 6H, N(CH3)2), 4.01 (t, J = 6.3 Hz, 1H,
H2), 4.16 (m, 1H, H4), 4.21 (t, J = 5.1 Hz, 1H, H2), 5.59 (d,
J = 9.9 Hz, 1H, H9), 6.30 (d, J = 8.3, Hz, 1H, H6), 6.63 (d,
J = 8.3 Hz, 1H, H5), 6.69 (d, J = 9.9 Hz, 1H, H10), 6.70 (d,
J = 8.6 Hz, 2H, N–Ar), 7.03 (d, J = 8.6 Hz, 2H, N–Ar).
ESI-Mass m/z 374 (M++23). Anal. Calcd for C22H25NO3: C,
75.19; H, 7.17; N, 3.99. Found: C, 75.38; H, 7.09; N, 4.18.
7‑((2‑Methylbut‑3‑yn‑2‑yl)oxy)‑2H‑chromene (15)
A mixture of compound 9 (0.46 g, 0.2 mmol) and catalytic
amount of p-TsOH in THF (5 ml) was heated at refluxed
for 2 h. Then, small amount of saturated NaHCO3 was
added to the reaction mixture and solvent was removed
1 3

J IRAN CHEM SOC
under reduce pressure at room temperature. The crude
product was extracted with ethyl acetate (3 × 15 ml)
and the combined organic phase was washed with brine.
After drying over Na2SO4, the solvent was removed under
reduced pressure to give the residue which was purified by
column chromatography using silicagel and hexane/ethyl
acetate (8:1) as eluent to obtain compound 15.
3‑(Hydroxy(phenyl)methyl)‑8,8‑dimethyl‑2,3‑dihydro‑4H,8
H‑pyrano[2,3‑f]chromen‑4‑one (3a)
Yield: 50 % as a mixture of diastereomers (anti/syn: 40/60).
1H-NMR (CDCl3) δ 1.44 (s, 6H, 2 × CH3), 1.47 (s, 6H,
2 × CH3), 2.98 (m, 1H, H3), 3.14 (m, 1H, H3), 3.95 (m,
1H, H2), 4.01 (d, J = 7.9 Hz, 1H, H2), 4.29 (dd, J = 11.5,
5.2 Hz, 1H, H2), 4.52 (t, J = 11.5 Hz, 1H, H2), 5.12anti
(d, J = 9.1 Hz, 1H, CH), 5.59 (d, J = 10.0 Hz, 1H, H9),
5.77syn (s, 1H, CH), 6.48 (d, J = 8.5 Hz, 1H, H6), 6.50 (d,
J = 8.6 Hz, 1H, H6), 6.53 (d, J = 10.0 Hz, 1H, H9), 6.83
(d, J = 10.0 Hz, 1H, H10),7.57 (m, 3H, H10, Ar), 7.62 (d,
J = 8.5 Hz, 2H, Ar), 7.72syn (d, J = 8.6 Hz, 1H, H5), 7.72 (m,
1H, Ar), 7.76anti (d, J = 8.7 Hz, 1H, H5), 8.26 (m, 4H, Ar),
8.32 (d, J = 8.5 Hz, 1H, Ar). IR (film) ν 3,500 (OH), 1,675
(C=O) cm−1; ESI-Mass m/z 359 (M++23); Anal. Calcd for
C21H20O4: C, 74.98; H, 5.99. Found: C, 74.76; H, 6.13.
Pale yellow oil; yield: 75 %. 1H-NMR (500 MHz,
CDCl3) δ 1.65 (s, 6H, 2 × CH3), 2.59 (s, 1H, C≡CH), 4.81
(dd, J = 3.6, 1.5 Hz, 2H, H2), 5.68 (dt, J = 9.8, 3.6 Hz, 1H,
H3), 6.41 (dt, J = 9.8, 1.5 Hz, 1H, H4), 6.73 (d, J = 2.4,
1H, H8), 6.71 (dd, J = 8.8, 2.4 Hz, 1H, H6), 6.86 (d,
J = 8.8 Hz, 1H, H5). ESI-Mass m/z 237 (M++23). Anal.
Calcd for C14H14O2: C, 78.48; H, 6.59. Found: C, 78.27;
H, 6.72.
8,8‑Dimethyl‑2,3‑dihydro‑4H,8H‑pyrano[2,3‑f]chromen‑4
‑one (1)
3‑(Hydroxy(4‑methoxyphenyl)methyl)‑8,8‑dimethyl‑2,3‑di‑
A solution of compound 8 (0.05 g, 0.22 mmol) in DMF
(3 ml) was heated at reflux for 6 h. After completion of
reaction, water was added to the reaction mixture and the
crude was extracted with dichloromethane (3 × 10 ml).
After drying over Na2SO4, the organic layers were evapo-
rated under reduced pressure and the pure compound 1 was
obtained by flash chromatography using silicagel and hex-
ane/ethyl acetate (5:1) as eluent.
hydro‑4H,8H‑pyrano[2,3‑f]chromen‑4‑one (3b)
Yield: 63 % as a mixture of diastereomers (anti/syn: 76/24).
1H-NMR (500 MHz, CDCl3) δ 1.45 (s, 6H, 2 × CH3), 1.47
(s, 6H, 2 × CH3), 2.98 (m, 1H, H3), 3.07 (m, 1H, H3), 3.82
(s, 3H, OCH3), 3.84 (s, 3H, OCH3), 4.04 (t, J = 11.5 Hz,
1H, H2), 4.09 (dd, J = 11.5, 5.4 Hz, 1H, H2), 4.40 (dd,
J = 11.5, 5.4 Hz, 1H, H2), 4.52 (m, 1H, H2), 4.93syn (d,
J = 9.0 Hz, 1H, CH), 5.57anti (d, J = 10.0 Hz, 1H, CH),
5.59 (d, J = 10.0 Hz, 1H, H9), 6.51 (m, 3H, H9, H10, H10),
6.48 (d, 1H, J = 8.7 Hz, H6), 6.51 (m, 1H, H6), 6.91 (d,
J = 9.0 Hz, 2H, Ar), 6.94 (d, J = 8.5 Hz, 2H, Ar), 7.28 (d,
J = 9.0 Hz, 2H, Ar), 7.34 (d, J = 8.5 Hz, 2H, Ar), 7.73syn
(d, J = 8.6 Hz, 1H, H5), 7.77anti (d, J = 8.7 Hz, 1H, H5). IR
(film) ν 500 (OH), 1,675 (C=O) cm−1; ESI-Mass m/z 389
(M++23). Anal. Calcd for C22H22O5: C, 72.12; H, 6.05.
Found: C, 72.23; H, 6.26.
1
Pale yellow solid; yield: 80 %, mp 120–122 °C. H-
NMR (CDCl3) δ 1.46 (s, 6H, 2 × CH3), 2.78 (t, J = 6.4 Hz,
2H, H3), 4.57 (t, J = 6.4 Hz, 2H, H2), 5.62 (d, J = 10.0 Hz,
1H, H9), 6.47 (d, J = 8.7 Hz, 1H, H6), 6.63 (d, J = 10.0 Hz,
1H, H10), 7.74 (d, J = 8.7 Hz, 1H, H5). IR (film) ν 1,760
(C=O) cm−1. MS m/z (%) 230 (M+, 19), 192 (33),
177 (100), 137 (54), 107 (32), 67 (53). Anal. Calcd for
C14H14O3: C, 73.03; H, 6.13. Found: C, 73.22; H, 6.28.
Procedure for the synthesis of pyrano[2,3-f]chromenone
derivatives (3)
3‑(Hydroxy(3‑methoxyphenyl)methyl)‑8,8‑dimethyl‑2,3‑di‑
hydro‑4H,8H‑pyrano[2,3‑f]chromen‑4‑one (3c)
A solution of compound 1 (0.17 mmol) in dry THF
(0.1 ml) was added to a solution of lDA (0.7 ml,
0.5 mmol) in the mixture of THF:Hex (2:1) at −78 °C and
stirred for 30 min. Then, aromatic aldehyde 2 (0.24 mmol)
and HMPA (0.1 ml) was added to the above-mentioned
solution and the reaction mixture was stirred for 2 h.
Next, it was quenched with saturated aq. NH4Cl (1 ml)
and extracted with EtOAc (3 × 20 ml). The extract was
washed successively with water (1 ml), 10 % HCl (1 ml),
water, saturated aq. NaHCO3 and brine. Organic phase was
dried over Na2SO4 and solvent was evaporated in vacuo to
give an oily product which was purified by TlC chroma-
tography (silica gel, hexane/EtOAc: 5/1) to give pure com-
pound 3 as mixture of diastereomers.
Yield: 60 % as a mixture of diastereomers (anti/syn: 66/35).
1H-NMR (500 MHz, CDCl3) δ 1.45 (s, 6H, 2 × CH3), 1.47
(s, 6H, 2 × CH3), 3.02anti (ddd, J = 10.0, 9.1, 5.7 Hz, 1H,
H3), 3.12syn (ddd, J = 10.0, 8.5, 3.0 Hz, 1H, H3), 3.83 (s,
3H, OCH3), 3.84 (s, 3H, OCH3), 4.02 (m, 1H, H2), 4.07
(dd, J = 11.0, 5.8 Hz, 1H, H2), 4.36 (dd, J = 11.0, 5.2 Hz,
1H, H2), 4.50 (dd, J = 11.0, 7.4 Hz, 1H, H2), 4.95anti (d,
J = 9.1 Hz, 1H, CH), 5.56syn (d, J = 3.0 Hz, 1H, CH), 5.57
(d, J = 8.1 Hz, 1H, H9), 5.59 (d, J = 10.0 Hz, 1H, H9),
6.46 (d, J = 8.7 Hz, 1H, H6), 6.51 (d, J = 8.7 Hz, 1H, H6),
6.52 (d, J = 10.0 Hz, 1H, H10), 6.54 (d, J = 10.0 Hz, 1H,
H10), 6.51 (s, 1H, Ar), 6.52 (s, 1H, Ar), 6.82–6.99 (m, 4H,
Ar), 7.29 7.31 (m, 2H, Ar), 7.73 (d, J = 8.7 Hz, 1H, H5),
1 3

J IRAN CHEM SOC
7.77 (d, J = 8.7 Hz, 1H, H5). IR (film) ν 3,450 (OH), 1,760
(C=O) cm−1. ESI-Mass m/z 389 (M++23), Anal. Calcd for
C22H22O5: C, 72.12; H, 6.05. Found: C, 72.25; H, 5.88.
1H, CH), 6.51 (d, J = 8.7 Hz, 1H, H9), 5.65 (d, J = 9.9 Hz,
1H, H9), 6.51 (d, J = 8.7 Hz, 1H, H10), 6.54 (d, J = 9.9 Hz,
1H, H10), 6.82 (d, J = 7.5 Hz, 1H, H6), 6.85 (d, J = 7.5 Hz,
1H, H6), 7.55 (d, J = 7.5 Hz, 1H, H5), 7.57 (d, J = 8.5 Hz,
2H, Ar), 7.72 (d, J = 7.5 Hz, 1H, H5), 7.74 (d, J = 8.7 Hz,
2H, Ar), 8.27 (d, J = 8.5 Hz, 2H, Ar), 8.32 (d, J = 8.7 Hz,
2H, Ar). IR (film) ν 3,500 (OH), 1,760 (C=O) cm−1. ESI-
Mass m/z 404 (M++ 23); Anal. Calcd for C21H19NO6: C,
66.14; H, 5.02; N, 3.67. Found: C, 66.27; H, 4.87; N, 3.43.
3‑((3,4‑Dimethoxyphenyl)(hydroxy)methyl)‑8,8‑dime‑
thyl‑2,3‑dihydro‑4H,8H‑pyrano[2,3‑f]chromen‑4‑one (3)
Yield: 65 % as a mixture of diastereomers (anti/syn: 55/45).
1H-NMR (500 MHz, CDCl3) δ 1.44 (s, 6H, 2 × CH3), 1.47
(s, 6H, 2 × CH3), 3.01 (m, 1H, H3), 3.09 (m, 1H, H3),
3.89 (s, 6H, 2 × OCH3), 3.91 (s, 6H, 2 × OCH3), 3.99
(dd, J = 10.7, 5.6 Hz, 1H, H2), 4.07 (dd, J = 10.7, 8.2 Hz,
1H, H2), 4.41 (dd, 1H, J = 11.3, 4.9 Hz, H2), 4.63 (t,
J = 7.2 Hz, 1H, H2), 4.92 (d, J = 9.4 Hz, 1H, CH), 5.57 (d,
J = 9.4 Hz, 1H, CH), 5.60 (d, J = 10.0 Hz, 1H, H6), 6.48
(d, J = 8.7 Hz, 1H, H6), 6.48 (d, J = 10.1 Hz, 1H, H9), 6.51
(d, J = 8.6 Hz, 1H, H9), 6.53 (d, J = 8.6 Hz, 1H, H10), 6.55
(d, J = 10.1 Hz, 1H, H10), 6.85 (m, 2H, Ar), 6.91 (m, 4H,
Ar), 7.74 (d, J = 8.6 Hz, 1H, H5), 7.78 (d, J = 8.7 Hz, 1H,
H5). IR (film) ν 3,500 (OH), 1,760 (C=O) cm−1. ESI-Mass
m/z 419 (M++23); Anal. Calcd for C23H24O6: C, 69.68; H,
6.10. Found: C, 69.52; H, 6.31.
Biology
Reagents and chemicals
RPMI 1640 and fetal bovine serum (FBS) were purchased
from gibco BRl (grand Island, NY). 3-(4,5-Dimethylthia-
zol-2-yl)-2,5 diphenyltetrazolium bromide (MTT), trypsin–
EDTA solution and dimethyl sulphoxide (DMSO) were
obtained from Sigma (Saint louis, MO, USA). Penicillin/
streptomycin was purchased from Invitrogen (San Diego,
CA, USA).
Cell lines and cell culture
3‑(Hydroxy(3,4,5‑trimethoxyphenyl)methyl)‑8,8‑dime‑
thyl‑2,3‑dihydro‑4H,8H‑pyrano[2,3‑f]chromen‑4‑one (3e)
Human blood cancer cell line K562 was obtained from the
National Cell Bank of Iran, Pasteur Institute, Tehran, Iran
and cultured at a density of 3–5 × 10 4/ml RPMI 1640
medium supplemented with FBS (10 %, v/v), streptomycin
(100 µg/ml), and penicillin (100 U/ml) and kept at 37 °C
in a 5 % CO2 humidified atmosphere. Drug treatments were
usually done 24 h after ceding the cells.
Yield: 70 % as a mixture of diastereomers (anti/syn: 31/69).
1H-NMR (500 MHz, CDCl3) δ 1.44 (s, 6H, 2 × CH3),
1.47 (s, 6H, 2 × CH3), 3.01anti (m, 1H, H3), 3.10syn (ddd,
J = 11.0, 5.5, 3.6 Hz, 1H, H3), 3.86 (s, 6H, 2 × OCH3), 3.87
(s, 6H, 2 × OCH3), 3.89 (s, 6H, 2 × OCH3), 4.05 (m, 1H,
H2), 4.12 (dd, J = 11.0, 5.5 Hz, 1H, H2), 4.41 (dd, J = 11.0,
5.2 Hz, 1H, H2), 4.53 (t, 1H, J = 11.5 Hz, H2), 4.90anti (d,
J = 9.1 Hz, 1H, CH), 5.59 (d, J = 10.1 Hz, 1H, H9), 5.60
(d, 1H, J = 10.1 Hz, H9), 5.61syn (d, J = 3.2 Hz, 1H, CH),
6.49 (d, J = 7.5 Hz, 1H, H6), 6.50 (d, J = 8.7 Hz, 1H, H6),
6.56 (d, J = 10.1 Hz, 1H, H10), 6.59(d, J = 10.1 Hz, 1H,
H10), 6.64 (s, 1H, Ar), 6.81 (s, 1H, Ar), 6.85 (s, 1H, Ar),
7.15 (s, 1H, Ar), 7.74 (d, 1H, J = 7.5 Hz, H5), 7.76 (d, 1H,
Cytotoxicity assay
The in vitro cytotoxic activity of all synthesized compounds
was determined against human blood cancer cell line K562
using MTT colorimetric assay [22]. Exponentially growing
cells (4 × 104 cells/well) were seeded in 96 well plates in
RPMI with 10 % FBS and incubated for 24 h. After treat-
ment of cells with different concentrations of test com-
pounds for 24 and 48 h at 37 °C, the medium was removed
and phenol red-free medium with FBS was added to cells.
Then, MTT solution was added to each well (2 mg/ml)
and incubated for 4 h. The viable cell number is directly
proportional to the formation of formazan. After that, they
were dissolved in isopropyl alcohol and the absorbance
of each well was measured using a microplate reader at
492 nm. In each plate, there were control wells (cells with-
out test compounds) and blank wells (the medium only
or 0.1 % DMSO). The percentage of cell viability versus
controls was assessed by the formula [1 − (absorbance of
treated cells/absorbance of control cells)] × 100.
J = 8.7 Hz, H5). IR (film) ν 3,350 (OH), 1,760 (C=O) cm−1
.
ESI-Mass m/z 449 (M++ 23). Anal. Calcd for C24H26O7: C,
67.59; H, 6.15. Found: C, 67.40; H, 6.29.
3‑(Hydroxy(4‑nitrophenyl)methyl)‑8,8‑dimethyl‑2,3‑dihy‑
dro‑4H,8H‑pyrano[2,3‑f]chromen‑4‑one (3f)
Yield: 31 % as a mixture of diastereomers (anti/syn: 55/45).
1H-NMR (500 MHZ, CDCl3) δ 1.44 (s, 6H, 2 × CH3), 1.47
(s, 6H, 2 × CH3), 2.36 (m, 1H, H3), 3.02 (m, 1H, H3),
3.95 (m, 1H, H2), 4.10 (d, J = 7.7 Hz, 1H, H2), 4.29 (dd,
J = 11.5, 5.0 Hz, 1H, H2), 4.54 (t, J = 11.5 Hz, 1H, H2),
5.60anti (d, J = 10.1 Hz, 1H, CH), 5.78syn (d, J = 3.7 Hz,
1 3

J IRAN CHEM SOC
Scheme 3 The formation of compound 10
Results and discussion
Chemistry
To achieve our goal, we tried to establish the best condition
for the preparation of 8,8-dimethyl-2,3-dihydro-4H,8H-
pyrano[2,3-f]chromen-4-one 1 and based on our previous
experience [21], resorcinol 4 was found as a versatile start-
ing material (Scheme 2).
Scheme
pyrano[2,3-f]chromen-4-one 1
4 Synthesis
of
8,8-dimethyl-2,3-dihydro-4H,8H-
Accordingly, 7-hydroxychroman-4-one 6 was prepared
by the condensation reaction of resorcinol 4 and 3-chloro-
propanoic acid 5 [21]. Then, focusing on the godfrey et al.
report on alkylation of phenolic hydroxyl [23], 7-((2-meth-
ylbut-3-yn-2-yl)oxy)chroman-4-one 8 was prepared via the
reaction of 6 and 2-methyl-3-butyn-2-ol 7 in the presence
of DBU, (CF3CO)2O, and CuCl2 in acetonitrile at 0 °C
in good yield (85 %). Compound 8 was heated in N,N-
dimethylaniline and polyethelene glycol 200 at 200–220 °C
to give the cyclized product 1, but no rearrangement was
occurred.
Alternatively, we changed our route and reacted com-
pound 8 with NaBH4 in MeOH to obtain 7-((2-methylbut-3-
yn-2-yl)oxy)chroman-4-ol 9 and heated the later compound
in boiling N,N-dimethylaniline which afforded cyclized
products 4-((8,8-dimethyl-3,4-dihydro-2H,8H-pyrano[2,3-
f]chromen-4-yl)oxy)-N,N-dimethylaniline 10 and 8,8-dime-
thyl-2H,8H-pyrano[2,3-f]chromene 11 as major and minor
products, respectively. Obviously, this route could not direct
us to compound 1. The formation of compound 10 has been
depicted in Scheme 3. It is presumed that heating 9 led to
[3]—sigmatropic rearrangement and intermediates 12 and
13 were formed. Finally, [1,5-H] shift gave 14 following
with cyclization to obtain the related compound 10.
Another effort directed us to dehydration reaction of 9
in the presence of p-TSA to obtain compound 15 which
was heated in N,N-dimethylaniline leading to no cyclized
product 11.
Finally, after examination of several procedures, we per-
ceived that 8,8-dimethyl-2,3-dihydro-4H,8H-pyrano[2,3-
f]chromen-4-one 1 could be prepared in high yield by heat-
ing 7-((2-methylbut-3-yn-2-yl)oxy)chroman-4-one 8 in
DMF at reflux (Scheme 4). It seems that Claisen rearrange-
ment easily took place in DMF to produce 1.
Next, different pyrano[2,3-f]chromenone derivatives 3a–
f (Table 1), bearing hydroxyl group at benzylic position,
were prepared by treatment of 1 and aromatic aldehydes 2
1 3

J IRAN CHEM SOC
Table 1 Synthesis and
percentage growth inhibition
values of products 3a–f
against K562 tumor cell line
at the concentrations of 50 and
100 μg/ml for 48 and 72 h
Entry
1.
Product 3
48 h
72 h
50 µg/ml
100 µg/ml
50 µg/ml
100 µg/ml
O
OH
OH
OH
OH
OH
OH
4.7 0.3
30 5.6
11.6 1.6
31.8 2.6
O
O
O
O
O
O
O
3a
2.
3.
4.
5.
6.
7.
7
1.5
6.7 0.5
12.1 1.7
32.3 5.3
42.9 7.2
17.6 3.1
45.3 6.7
20 3.5
32 3.4
9.3 1.3
22.2 3.6
54 5.8
O
O
OMe
OMe
3b
7.8 2.1
16.4 2.4
7.5 1.2
7.3 0.8
30 4.6
O
O
3c
5.9 1.1
O
OMe
OMe
O
3d
6
0.8
O
OMe
OMe
O
OMe
3e
7.1 0.6
37.6 4.1
O
Percent growth inhibition values
of cell proliferation at different
concentrations; mean SD
values of three independent
experiments are reported
O
NO2
3f
Etoposide (10 µg/ml)
68 8.3
in the presence of lDA and HMPA at −78 °C in THF. It
is worth mentioning that all reactions proceeded either
with electron-withdrawing or electron-donating para- and
meta-substituted benzaldehydes and desired products were
obtained in good yields.
All products 3a‑f were obtained as a mixture of two
syn/anti diastereomers based on the S-configuration or
R-configuration of C11 benzylic hydroxyl group (Fig. 2)
and the corresponding configuration at C11 was distin-
guished by the chemical shift of proton H11 which was
shifted downfield in syn-isomer. Also, H11–H3 coupling
constant was smaller in comparison to similar coupling in
anti-isomer. Because of the formation of hydrogen bond
between hydroxyl group at C11 and oxygen of carbonyl
group (Fig. 2), the H11–H3 relationship of the syn-isomer
is axial-equatorial and that of the anti-isomer is di-axial.
Thus, the observed coupling constant between H11 and
H3 of syn-isomer was lower than that of anti-isomer in
accordance with the data reported in the literature [24].
Fig. 2 Syn/anti diastereomers of compound 3
Biological investigation
The in vitro cytotoxic activity of all pyrano[2,3-
f]chromenones 3a–f were evaluated against blood cancer
human cell line K562 according to the literature [22] and
1 3

J IRAN CHEM SOC
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compared with the reference drug etoposide (Table 1).
According to percentage growth inhibition values of com-
pounds 3a–f, most of the compounds have no effect on
the cell line. Our results revealed that the cytotoxicity is
improved by increasing the number of methoxy groups in
aromatic ring. Hence, compound 3e showed better activ-
ity against blood cancer human cell line K562 (Entry 5,
Table 1).
Conclusion
13. K.H. Chun, J.W. Kosmeder II, S. Sun, J.M. Pezzuto, R. lotan,
W.K. Hong, H.Y. lee, J. Natl. Cancer Inst. 95, 291 (2003)
14. H.Y. lee, S.H. Oh, J.K. Woo, W.Y. Kim, C.S.V. Pelt, R.E. Price,
D. Cody, H. Tran, J.M. Pezzuto, R.M. Moriarty, W.K. Hong, J.
Natl. Cancer Inst. 97, 1695 (2005)
In summary, we have developed an efficient syn-
thetic approach for the synthesis of novel pyrano[2,3-
f]chromenone derivatives as analogues of deguelin, starting
from resorcinol. All products were obtained as a mixture of
syn/anti diastereomers which were demonstrated from their
1H NMR spectra.
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2, 942 (2009)
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H.J. lee, H.Y. Min, Y.g. Suh, K.W. Kim, H.Y. lee, Cancer lett.
332, 102 (2013)
17. W.Y. Kim, D.J. Chang, B. Hennessy, H.J. Kang, J. Yoo, S.H. Han,
Y.S. Kim, H.J. Park, S.Y. Seo, g. Mills, K.W. Kim, W.K. Hong,
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S. Heydari, S.K. Ardestani, F. Poorrajab, A. Shafiee, Chem. Biol.
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Acknowledgments The authors gratefully acknowledge the
Research Council of Tehran University of Medical Sciences and Iran
National Science Foundation (INSF).
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1 3