An efficient and green synthesis of fluorine containing benzo[a]xanthen-11(12H)-ones and evaluation of their anticancer activity

Article abstract of DOI:10.14233/ajchem.2020.22503

A facile and an efficient procedure has been developed by one-pot condensation of naphthalene-diols, fluoro substituted benzaldehydes and cyclic 1,3-dicarbonyl compounds for the synthesis of fluorine containing benzo[a]xanthen-11(12H)-ones under the catal

Full text of DOI:10.14233/ajchem.2020.22503

Asian Journal of Chemistry; Vol. 32, No. 4 (2020), 923-929
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2020.22503
An Efficient and Green Synthesis of Fluorine Containing
Benzo[a]xanthen-11(12H)-ones and Evaluation of their Anticancer Activity
1,
1,*,
2,
J. SUMALATHA , A. SREEDEVI
and C. RADHA RANI
1Division of Pharmaceutical Chemistry, Institute of Pharmaceutical Technology, Sri Padmavathi Mahila Visvavidyalayam, Tirupati-517502,
India
2Department of Chemistry, Sri Venkateswara College of Engineering, Tirupati-517507, India
*Corresponding author: E-mail: sridevitirupati@rediffmail.com
Received: 8 October 2019;
Accepted: 11 December 2019;
Published online: 25 February 2020;
AJC-19813
A facile and an efficient procedure has been developed by one-pot condensation of naphthalene-diols, fluoro substituted benzaldehydes
and cyclic 1,3-dicarbonyl compounds for the synthesis of fluorine containing benzo[a]xanthen-11(12H)-ones under the catalyst and
solvent-free conditions. All the synthesized compounds were characterized by IR, NMR (1H & 13C) and mass spectrometry. Several
advantages offer the present approach, such as, shorter reaction time, low cost, anticipation of toxic solvents and catalyst, higher yield of
products and durability of substrate range. On the other hand, anticancer activity was also performed for the title compounds which
demonstrated a significant activity on selected cancer cell lines.
Keywords: Fluorine, Benzo[a]xanthen-11(12H)-ones, Naphthalene-diols, Anticancer activity.
received significant attention since last two decades [9-13].
Many xanthene derivatives with excellent anticancer activity
have been obtained [14-21]. Therefore, a numeral quantity of
synthetic modifications have been reported with either by solid
or polymer-based catalysts under solvent or solvent-free thermal/
ultrasound/microwaves reaction conditions [22-30]. Some of
the disadvantages, like, requirement of excess reagents/catalysts,
prolonged reaction times, toxic organic solvent usages and
lower yields even with harsh conditions influence these metho-
dologies. Therefore, for the better synthesis of benzoxanthene
derivatives, there is a requirement of an advanced and environ-
mentally benign simple and efficient technique.
Further, on account of multi-component reactions (MCRs)
exceptional practical and synthetic efficiency have attracted
considerable attention in synthetic organic chemistry. Moreover
they can form the new product in a single flask by involving
three or more substrate molecules reacting together. In addition
they offer greater potential for molecular assortment by mini-
mum synthetic time per step. Synthesis of heterocyclic comp-
ounds is the primary goal of MCRs research, which is crucial
in various fields, like, natural products, pharmaceutical drug
molecules and agrochemicals [31]. In addition, in the formation
INTRODUCTION
Nowadays across the world, the most serious health issue
is cancer and its leading cause of death with various types of
cancer in many high-developed countries [1]. One out of three
persons become victims of cancer during their life period. In
general, males are more prone to develop cancer than females
and also the mortality rate was more in male community. But,
increase in female mortality rate owing to cancer has been recor-
ded, whereas in infants cancers are mostly seen during their
first year of age. For the treatment of cancer, one of the most
widely applied modalities is chemotherapy. However, drug
resistance is one of the major obstacles in this standard chemo-
therapy for successful treatment of cancer patients. Herein,
anticancer drug is one of the alterations that is developed during
the treatment of patients [2-5]. However, treatment by anticancer
drugs didn’t adequately increase the success rate [6-8]. There-
fore, more effective anticancer drugs are urgently required in
order to increase the effectiveness of cancer treatment.
On the other hand, in view of the broad spectrum of pharma-
ceutical and biological properties of low-cost available xanthene
and benzoxanthene compounds from plant sources, they have
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924 Sumalatha et al.
Asian J. Chem.
of green chemical carbon-heteroatom bond solvent-free
conditions have significantly drawn the attention of chemists
[32-35].
6.40 (m, 1H), 5.48 (s, 1H), 2.74-2.52 (m, 2H), 2.33 (dd, J =
16.0, 3.2 Hz, 1H), 2.10 (d, J = 16.5 Hz, 1H), 1.07 (s, 3H), 0.90
(s, 3H) ppm; 13C NMR (100 MHz, DMSO-d6): δ 195.7, 164.4,
156.5, 147.8, 132.9, 132.5, 130.3, 129.8, 129.0, 128.2, 125.3,
117.1, 116.8, 113.8, 113.5, 111.4, 105.6, 104.4, 103.6, 50.0,
40.3, 31.8, 28.8, 28.4, 26.1 ppm. LCMS (m/z): 407 (M+.).
Anal. calcd. (%) for C25H20O3F2: C, 73.88; H, 4.96; F, 9.35;
found (%): C, 73.45; H, 4.79; F, 9.07.
12-(2-Fluorophenyl)-6-hydroxy-9,10-dihydro-8H-
benzo[a]xanthen-11(12H)-one (4c): Pale yellow solid;Yield:
89 %; m.p.: 212-213 °C; IR (KBr, νmax, cm–1): 3435.2 (OH,
str.), 2958.8-2871.4 (CH2, str.), 1677.2 (C=O), 1622.0,
1481.8& 1422.6 (CH2, bend.), 1357.9, 1227.5 (C-F, str.),
1113.2, 963.9, 815.6, 616.2; 1H NMR (400 MHz, DMSO-d6)
δ 10.13 (s, 1H), 8.11 (dd, J = 14.4, 6.2 Hz, 1H), 7.62 (t, J =
7.3 Hz, 1H), 7.32-7.12 (m, 3H), 6.99-6.82 (m, 2H), 6.70 (d, J
= 7.3 Hz, 1H), 6.66-6.55 (m, 1H), 5.73 (s, 1H), 2.83-2.70 (m,
2H), 2.43-2.25 (m, 2H), 2.06-1.79 (m, 2H) ppm; 13C NMR
(100 MHz, DMSO-d6): δ 196.8, 166.1, 153.4, 153.4, 145.1,
139.4, 131.8, 131.2, 129.7, 127.2, 126.3, 125.2, 124.9, 123.4,
123.1, 119.5, 119.4, 115.8, 114.1, 109.2, 36.4, 28.3, 27.0, 20.0
ppm. Anal. calcd. (%) for C23H17O3F: C, 76.65; H, 4.75; F,
5.27; found (%): C, 76.49; H, 4.64; F, 5.04.
12-(4-Bromo-2-fluorophenyl)-6-hydroxy-9,10-dihydro-
8H-benzo[a]xanthen-11(12H)-one (4d): Yellow solid;Yield:
88 %; m.p.: 201-202 °C; IR (KBr, νmax, cm–1): 3426.1 (OH, str.),
2958.8-2875.3 (CH2, str.), 1598.0 (C=O), 1502.2, 1459.2 &
1422.4 (CH2, bend.), 1384.9, 1222.9, 1218.6 (C-F, str.), 1125.7,
968.0, 852.8, 746.3 (C-Br, str.); 1H NMR (400 MHz, DMSO-
d6) δ 10.16 (s, 1H), 7.71-7.58 (m, 1H), 7.46-7.19 (m, 5H),
7.01-6.78 (m, 2H), 5.69 (s, 1H), 2.77 (d, J = 5.0 Hz, 2H), 2.40-
2.17 (m, 2H), 2.05-1.80 (m, 2H) ppm; 13C NMR (100 MHz,
DMSO-d6): δ 196.4, 166.1, 154.8, 145.1, 139.4, 131.8, 131.2,
126.4, 125.0, 123.5, 122.9, 122.0, 119.2, 118.1, 109.3, 36.5,
28.4, 27.0, 20.0 ppm. LCMS (m/z): 439 (M+.), 441 (M+2).
Anal. calcd. (%) for C23H16O3BrF: C, 62.89; H, 3.67; Br, 18.19;
F, 4.32; found (%): C, 62.68; H, 3.52; Br, 18.03; F, 4.20.
12-(2,4-Difluorophenyl)-6-hydroxy-9,10-dihydro-8H-
benzo[a]xanthen-11(12H)-one (4e): Pale yellow solid;Yield:
86 %; m.p.: 215-217 °C; IR (KBr, νmax, cm–1): 3440.5 (OH,
str.), 2963.2-2861.6 (CH2, str.), 1657.8 (C=O), 1505.2, 1454.7
& 1422.4 (CH2, bend.), 1361.4, 1232.3, 1177.6 (C-F, str.),
1130.1, 963.7, 838.4, 616.7; 1H NMR (400 MHz, DMSO-d6)
δ 10.14 (s, 1H), 8.07 (d, J = 8.2 Hz, 1H), 7.63 (d, J = 7.3 Hz,
1H), 7.34-7.20 (m, 2H), 7.17 (s, 1H), 6.97 (t, J = 7.6 Hz, 1H),
6.50-6.41 (m, 2H), 5.69 (s, 1H), 2.82-2.69 (m, 2H), 2.43-2.25
(m, 2H), 2.06-1.80 (m, 2H) ppm; 13C NMR (100 MHz, DMSO-
d6): δ 196.6, 166.1, 154.9, 145.1, 139.4, 131.2, 131.1, 126.3,
125.1, 124.9, 124.9, 123.5, 123.0, 119.2, 113.9, 109.2, 106.0,
105.8, 102.3, 36.5, 28.0, 27.0, 20.0 ppm. Anal. calcd. (%) for
C23H16O3F2: C, 73.01; H, 4.26; F, 10.04; found (%): C, 72.88;
H, 4.04; F, 09.89.
The literature survey at this stage revealed that there are
no reports on the synthesis of fluorine containing benzo[a]-
xanthen-11(12H)-ones under catalyst and solvent-free condi-
tions at 60 °C. Therefore, herein, a cleaner and relatively faster
green one-pot synthetic methodology is reported for the fluorine
containing benzo[a]xanthen-11(12H)-ones via three-compo-
nent coupling of naphthalenediols, fluoro/bromo substituted
benzaldehydes and various cyclohexane-1,3-dione under catalyst
and solvent-free conditions at 60 °C and tested their cytotoxic
activity.
EXPERIMENTAL
Chemicals were obtained from Sd-fine chemicals, Merck,
SRL,Aldrich andAlfaaesar chemical companies.All procured
chemicals are of analytical grade and the reported melting
points were determined in open capillaries using “Stuart
Melting PointApparatus” in °C and are uncorrected. Systronics
UV-visible spectrometer was used to record the UV spectra
and Perkin-Elmer Spectrum BX-I infrared spectrophotometer
was used to record the IR spectra using KBr pellet. The NMR
data are collected using the NMR-400 MHz, Jeol, Model: JNM-
ECS400. To check the purity of the titled compounds used the
glass plates coated by silica gel G and the sample spots were
observed by iodine vapour.
General procedure for the preparation of fluorine con-
taining benzo[a]xanthen-11(12H)-ones (4a-j): The mixture
of naphthalenediol (1a-b, 1 mmol), fluoro substituted benzal-
dehyde (2a-e, 1 mmol) and 1,3-dicarbonyl compound (3a-b,
1 mmol) was stirred in a round bottom flask at 60 °C under
catalyst and solvent-free conditions for 20 min.After comple-
tion of the reaction (TLC) resulted solid was dissolved in THF,
filtered and evaporated the solvent using rotary evaporator.
After recrystallization by ethanol we obtained the pure products
as white solids (4a-j).
12-(3-Flurophenyl)-6-hydroxy-9,10-dihydro-8H-benzo-
[a]xanthen-11(12H)-one (4a): Pale yellow solid;Yield: 91 %;
m.p.: 230-231 °C; IR (KBr, νmax, cm–1): 3444.8 (OH, str.),
2963.2-2875.3 (CH2, str.), 1653.5 (C=O), 1588.7, 1482.2 &
1449.8 (CH2, bend.), 1371.4, 1237.3 (C-F, str.), 1190.5, 1125.7,
954.4, 820.4, 621.4; 1H NMR (400 MHz, DMSO-d6) δ 10.25
(s, 1H), 7.21 (q, J = 7.3 Hz, 3H), 6.99 (d, J = 7.8 Hz, 1H),
6.94-6.87 (m, 5H), 5.56 (s, 1H), 2.67-2.56 (m, 2H), 2.24 (t, J
= 2.7 Hz, 2H), 1.93-1.79 (m, 2H) ppm; 13C NMR (100 MHz,
DMSO-d6): δ 196.8, 166.1, 153.4, 153.4, 145.1, 139.4, 131.8,
131.2, 129.7, 127.2, 126.3, 125.2, 124.9, 123.4, 123.1, 119.5,
119.4, 115.8, 114.1, 109.2, 36.4, 28.3, 27.0, 20.0 ppm. Anal.
calcd. (%) for C23H17O3F: C, 76.65; H, 4.75; F, 5.27; found
(%): C, 76.44; H, 4.69; F, 5.05.
12-(2,4-Difluorophenyl)-2-hydroxy-9,9-dimethyl-9,10-
dihyro-8H-benzo[a]xanthen-11(12H)-one (4b): Pale yellow
solid; Yield: 89 %; m.p.: 231-232 °C; IR (KBr, νmax, cm–1):
3435.5 (OH, str.), 2958.88-2871.0 (CH2, str.), 1676.5 (C=O),
1621.1, 1482.3 & 1422.4 (CH2, bend.), 1357.6, 1227.2 (C-F,
str.), 1112.8, 963.7, 815.4, 616.7; 1H NMR (400 MHz, DMSO-
d6): δ 9.94 (s, 1H), 7.80-7.67 (m, 2H), 7.24-6.84 (m, 5H), 6.54-
12-(2-Fluorophenyl)-6-hydroxy-9,9-dimethyl-9,10-
dihydro-8H-benzo[a]xanthen-11(12H)-one (4f): Pale yellow
solid; Yield: 90 %; m.p.: 209-211 °C; IR (KBr, νmax, cm–1):
3431.2 (OH, str.), 2954.5-2861.6 (CH2, str.), 1610.8 (C=O),
1510.2, 1449.7 & 1421.6 (CH2, bend.), 1380.6, 1228.0 (C-F,
str.), 1176.8, 1121.4, 1065.2, 838.5, 538.2; 1H NMR (400 MHz,

Vol. 32, No. 4 (2020)
An Efficient and Green Synthesis of Fluorine Containing Benzo[a]xanthen-11(12H)-ones 925
DMSO-d6) δ 10.13 (s, 1H), 7.69-7.60 (m, 1H), 7.49-6.82 (m,
8H), 5.71 (d, J = 9.2 Hz, 1H), 2.78-2.57 (m, 2H), 2.35 (dd,
J = 16.0, 4.1 Hz, 1H), 2.10 (d, J = 15.6 Hz, 1H), 1.07 (d, J =
7.8 Hz, 3H), 0.92 (d, J = 6.9 Hz, 3H) ppm; 13C NMR (100
MHz, DMSO-d6): δ 196.2, 164.2, 153.4, 145.2, 139.4, 131.0,
130.7, 129.8, 128.5, 127.2, 126.6, 125.1, 124.8, 123.4, 122.1,
119.4, 117.4, 115.8, 112.8, 109.2, 50.0, 40.2, 31.9, 28.8, 28.5,
26.2 ppm. Anal. calcd. (%) for C25H21O3F: C, 77.30; H, 5.45;
F, 4.89; found (%): C, 77.18; H, 5.29; F, 4.73.
1028.5, 829.8, 750.6; 1H NMR (400 MHz, DMSO-d6) δ 9.88
(s, 1H), 7.80-7.69 (m, 3H), 7.26-7.17 (m, 3H), 7.05-6.94 (m,
3H), 5.37 (s, 1H), 2.71-2.60 (m, 2H), 2.34-2.23 (m, 2H), 2.02-
1.82 (m, 2H) ppm; 13C NMR (100 MHz, DMSO-d6): δ 196.2,
165.2, 156.6, 147.6, 133.2, 132.4, 131.3, 131.2, 130.3, 129.2,
125.3, 117.7, 115.9, 11.34, 112.2, 104.4, 36.2, 29.2, 26.3, 19.8
ppm. Anal. calcd. (%) for C23H17O3F: C, 76.65; H, 4.75; F,
5.27; found (%): C, 76.53; H, 4.62; F, 5.16.
Biological assay
12-(3-Fluorophenyl)-6-hydroxy-9,9-dimethyl-9,10-
dihyrdo-8H-benzo[a]xanthen-11(12H)-one (4g): Pale yellow
solid; Yield: 91 %; m.p.: 210-215 °C; IR (KBr, νmax, cm–1):
3421.8 (OH, str.),2963.2-2866.0 (CH2, str.), 1593.0 (C=O),
1523.9, 1482.1 & 1459.0 (CH2, bend.), 1380.6, 1223.6 (C-F,
str.), 1186.2, 1112.0, 1074.6, 889.6, 746.3; 1H NMR (400 MHz,
DMSO-d6) δ 10.30 (s, 1H), 7.90 (d, J = 8.2 Hz, 1H), 7.67 (d,
J = 7.8 Hz, 1H), 7.35-7.19 (m, 4H), 7.16-7.02 (m, 2H), 6.90
(t, J = 8.5 Hz, 1H), 5.59 (s, 1H), 2.74-2.48 (m, 2H), 2.36 (d, J
= 15.6 Hz, 1H), 2.15 (d, J = 16.5 Hz, 1H), 1.07 (s, 3H), 0.89
(s, 3H) ppm; 13C NMR (100 MHz, DMSO-d6): δ 195.9, 161.5,
145.2, 140.1, 132.6, 131.9, 126.5, 125.2, 123.9, 123.0, 118.5,
115.2, 111.6, 109.9, 50.0, 40.5, 33.9, 31.9, 28.7, 26.1 ppm.
Anal. calcd. (%) for C25H21O3F: C, 77.30; H, 5.45; F, 4.89;
found (%): C, 77.19; H, 5.32; F, 4.73.
12-(4-Fluorophenyl)-2-hydroxy-9,9-dimethyl-9,10-
dihydro-8H-benzo[a]xanthen-11(12H)-one (4h): Pale yellow
solid; Yield: 90 %; m.p.: 218-220 °C; IR (KBr, νmax, cm–1):
3435.5 (OH, str.), 2926.4-2852.3 (CH2, str.), 1649.5 (C=O),
1588.8, 1482.2 & 1449.7 (CH2, bend.), 1380.6, 1241.7, 1191.3
(C-F, str.), 1107.0, 940.2, 872.6; 1H NMR (400 MHz, DMSO-
d6) δ 9.88 (s, 1H), 7.79-7.72 (m, 2H), 7.30-7.09 (m, 5H), 7.06-
6.94 (m, 2H), 5.35 (s, 1H), 2.72-2.48 (m, 2H), 2.33 (d, J = 16.0
Hz, 1H), 2.12 (d, J = 16.0 Hz, 1H), 1.05 (s, 3H), 0.86 (s, 3H)
ppm; 13C NMR (100 MHz, DMSO-d6): δ 195.9, 163.9, 161.2
(d, J = 251.2Hz), 156.4, 147.6, 140.8, 132.3, 130.2, 129.8,
129.7, 128.9, 125.4, 117.1, 115.1, 114.9, 114.7, 113.5, 113.1,
105.0, 50.0, 40.1, 33.4, 31.8, 28.7, 26.1 ppm. Anal. calcd. (%)
for C25H21O3F: C, 77.30; H, 5.45; F, 4.89; found (%): 77.16;
H, 5.31; F, 4.76.
12-(2-Fluorophenyl)-2-hydroxy-9,10-dihydro-8H-
benzo[a]xanthen-11(12H)-one (4i): Yellow solid;Yield: 90 %;
m.p.: 210-212 °C; IR (KBr, νmax, cm–1): 3444.8 (OH, str.), 2954.5-
2866.0 (CH2, str.), 1657.8 (C=O), 1510.2, 1449.7 & 1426.4
(CH2, bend.), 1366.2, 1213.6, 1177.6 (C-F, str.), 1130.0, 959.4,
834.1, 607.8; 1H NMR (400 MHz, DMSO-d6) δ 9.56 (s, 1H),
7.68 (dd, J = 14.9, 8.9 Hz, 2H), 7.44 (d, J = 14.7 Hz, 1H),
7.19-7.08 (m, 2H), 7.04-6.94 (m, 3H), 6.74-6.59 (m, 1H), 5.55
(s, 1H), 2.72 (s, 2H), 2.42-2.25 (m, 2H), 2.04-1.64 (m, 2H)
ppm; 13C NMR (100 MHz, DMSO-d6): δ 197.2, 166.7, 156.2,
153.8, 149.8, 147.8, 132.9, 131.4, 128.2, 127.5, 127.2, 126.9,
125.4, 124.5, 119.3, 116.9, 116.1, 115.1, 114.1, 113.4, 105.7,
36.4, 28.7, 27.0, 19.9 ppm. Anal. calcd. (%) for C23H17O3F: C,
76.65; H, 4.75; F, 5.27; found (%): C, 76.52; H, 4.62; F, 5.14.
12-(4-Fluorophenyl)-2-hydroxy-9,10-dihydro-8H-
benzo[a]xanthen-11(12H)-one (4j): Pale yellow solid;Yield:
92 %; m.p.: 217-219 °C; IR (KBr, νmax, cm–1): 3426.2 (OH,
str.), 2958.8-2852.3 (CH2, str.), 1625.4 (C=O), 1588.7, 1482.1
& 1449.7 (CH2, bend.), 1384.9, 1233.0 (C-F, str.), 1139.5,
Culture conditions of cell lines: The cancerous cell lines
(HepG2/HeLa) and non-cancerous cell lines (HEK 293) are
obtained from National Center for Cell Sciences, Pune, India.
Then the procured cell lines were grown in Eagle’s minimum
essential medium, supplemented with 10 % FBS. The cell
cultures were maintained with 5 % CO2 at 37 °C in a humidified
atmosphere. The cell lines were subcultured twice in each week,
with seeding at a density of about 5 × 103 cells/mL. Before
evaluation of activity of synthesized compounds, fresh medium
was added for cells which were washed with PBS previously.
For the final evaluation, exponentially cells grown were collected
and re-suspended in fresh culture with 10 % FBS.
MTT assay: The title compounds (4a-j) were evaluated
for cytotoxic activity against human hepato cellular carcinoma
cell lines (HepG2) and human cervical cancer (HeLa) cells.
3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide
(MTT) is a pale yellow substrate that is cleaved by living cells
to yield a dark blue formazan product. This process requires
active mitochondria and even freshly dead cells do not cleave
significant amount of MTT. Thus the amount of MTT cleaved
is directly proportional to the number of viable cells present,
which is quantified by colorimetric methods. The compounds
were dissolved in DMSO and serially diluted with MEM (mini-
mum essential medium) complete medium to get the concen-
trations for a range of test concentration. DMSO concentration
was kept < 0.1 % in all the compounds. HePG2 hepatocellular
carcinoma and human cervical cancer HeLa cells maintained
in appropriate conditions were seeded in 96 well plates and
treated with different concentrations of the test compounds
and incubated in 5 % CO2 at 37 °C for 96 h. MTT reagent was
added to the wells and incubated for 4 h; the dark blue formazan
product formed by the cells was dissolved in DMSO under a
safety cabinet and read at 550 nm. Percentage inhibitions were
calculated and plotted with the concentrations for calculating
the IC50 values.
RESULTS AND DISCUSSION
To develop the optimal reaction conditions, we carried
out a model reaction (Scheme-I) for the development of optimal
reaction conditions with naphthalene-2,3-diol (1a, 1 mmol),
3-fluorobenzaldehyde (2a, 1 mmol) and cyclohexane-1,3-dione
(3a, 1 mmol) under different experimental conditions such as
various solvent and catalyst conditions, optimized reaction
times and temperatures for an effective reaction completion
(Table-1). With these overall results was demonstrated that
under catalyst and solvent-free conditions with shorter reaction
time at 60 °C are optimal conditions for 4a synthesis at high
yield (Table-1, entry 5). This higher yield could be elucidated

926 Sumalatha et al.
Asian J. Chem.
F
R1
O
X
X
R
OH
+
CHO
Neat
60 o
R
R1 CHO
(2a-e)
+
O
O
X
OH
OH
O
O
C
O
O
X
+
+
(3a-b)
(1a-b)
(4a-j)
F
O
Scheme-II: Synthesis of fluorinated benzo[a]xanthen-11(12H)-ones (4a-j)
OH
(1a)
(2a)
(3a)
(4a)
Scheme-I: Synthesis of 12-(3-fluorophenyl)-6-hydroxy-9,10-dihydro-8H-
benzo[a]xanthen-11(12H)-one (4a)
by sequential connection of substrates through the formation
of ortho-quinone methides intermediate formed by the
nucleophilic addition of naphthalene diols (1a-b) to aldehydes
(2a-e). This ortho-quinone methides intermediate was proce-
ssed by a Michael addition with enolic form of cyclic 1,3-
dicarbonyls (3a-b) and subsequent intramolecular addition of
phenolic moiety with carbonyl group of diketone resulted in
cyclic hemiketal and later dehydration of it afforded the title
compounds (4a-j).
After that, titled compounds (4a-j) were screened for in
vitro cytotoxic activity and which was measured after 96 h by
exposure against human hepatocellular carcinoma cell lines
(HepG2) and cervical cancer cells of human (HeLa) at 0.001
to 10 µM concentrations. Herein, two independent experiments
were performed with duplicates and determined the mean
values. The average values of these two determinations are
reported by 8-10 % or lesser difference in all cases.
The cell viability graphic method was used to measure
the IC50 values of titled compounds by plotting the concentra-
tions on X-axis and percentage of inhibition on Y-axis. The
obtained linear graph was intersected at 50 % inhibition and
then collected the concentration value on X-axis at correlated
point of it was recorded and considered as IC50 values in µM
(Table-3). Table-3 revealed that based on structural differences
the compounds showed dissimilar range of substantial IC50
values varying from > 10 to 0.6 µM. As evident that the com-
pounds 4g, 4a, 4j and 4f exhibited maximum activity (Fig. 1)
compared to that of HepG2 cell lines (IC50 of 0.8, 2.0, 4.0 and
6.0 µM, respectively). Similarly the compounds 4g, 4j, 4f and
4a exhibited high cytotoxicity against HeLa cell lines with
IC50 of 0.6, 2.0, 2.0 and 3.0 µM, respectively (Fig. 1). The 4g
compound showed high activity (0.6 µM) against HeLa cell
lines when compared to HepG2 cell lines. The compound 4g
exhibited highest inhibition of cellular proliferation at 10 µM
in both the cell lines.
TABLE-1
OPTIMIZATION OF REACTION
CONDITIONS FOR THE SYNTHESIS 4aa
Catalyst
(10 mol %)
Temp.
(°C)
Time
(min)
Yieldb
(%)
Entry
Solvent
1
2
3
4
5
6
7
8
9
Neat
Neat
Neat
Neat
Neat
InF3
p-TSA
K-10
GaCl3
MSA
PSA
Ethanol
THF
DMF
Water
Neat
Neat
Neat
Neat
Neat
80
60
120
100
60
60
60
60
60
120
120
80
130
20
20
60
40
35
86
70
80
60
91
78
75
78
85
77
58
80
10
11
12
Toluene
CH2Cl2
Ethanol
60
75
80
40
20
20
SSA
aReaction of naphthalene-2,3-diol (1a, 1 mmol), 3-fluorobenzaldehyde
(2a, 1 mmol) and cyclohexane-1,3-dione (3a, 1 mmol) using either
neat or various catalysts in 10 mol %; bIsolated yields.
by the uniform distribution of reactant’s eutectic mixture being
in close proximity to react together in solvent-free condition
than solvent condition.
In order to extend the above reaction conditions for a
library system (Table-2), various kinds of aldehydes (2b-e),
naphthalene diols (1a & 1b) and cyclohexane-1,3-diones (3a
& 3b) were exposed to react (Scheme-II) for corresponding
fluorine containing benzo[a]xanthen-11(12H)-ones (4a-j).All
of the aldehydes gave expected product at high yields regard-
less of their substitutions under the similar reaction condition.
In this procedure, the pure products were isolated by simple
filtration using a little amount of THF without chromatography
or a cumbersome work-up procedure.All the titled compounds
were characterized by IR, NMR (1H & 13C) and mass spectro-
metry (for related spectra see supplementary material).
To support the higher product yields of the titled comp-
ounds a schematic mechanism (Scheme-III) was employed
On the other hand, the normal cells (HEK 293) were un-
affected by the treated compounds suggesting that the non-
toxic nature of the compounds for healthy cells. Therefore, this
study discovered a new family of fluorine containing benzo[a]-
TABLE-2
SYNTHESIS OF OXYGEN AND FLUORINE CONTAINING BENZO[a]XANTHEN-11(12H)-ONE DERIVATIVES (4a-j)
Compd.
4a
4b
4c
4d
4e
4f
4g
4h
4i
R
R1
X
H
CH3
H
H
H
CH3
CH3
CH3
H
Time (min)
Yield (%)
m.p. (°C)
230-231
231-232
212-213
201-202
215-217
209-211
210-215
218-220
210-212
217-219
3-OH
7-OH
3-OH
3-OH
3-OH
3-OH
3-OH
7-OH
7-OH
7-OH
3-F-C6H4
2,4-F-C6H3
2-F-C6H4
4-Br, 2-F-C6H3
2,4-F-C6H3
2-F-C6H4
3-F-C6H4
4-F-C6H4
2-F-C6H4
4-F-C6H4
20
23
26
25
23
26
19
18
22
20
91
89
89
88
86
90
91
90
90
92
H
4j

Vol. 32, No. 4 (2020)
An Efficient and Green Synthesis of Fluorine Containing Benzo[a]xanthen-11(12H)-ones 927
X
X
X
X
K.E.T
H
O
O
O
O
O
(3a-b)
R1
OH
H
R1
R1
H
(2a-e)
OH
O
O
–H2O
R
R
R
(1a-b)
o-Quinone methides
X
X
O
H
O
X
R1
O
X
H
R
R1
R1
O
OH
O
X
OH
–H2O
O
X
(4a-j)
R
R
Scheme-III: Plausible mechanisms of benzo[a]xanthen-11(12H)-one derivatives (4a-j)
100
100
4a
4g
50
50
0
0.001
0
0.01
0.1
1
10
0.001
0.01
0.1
1
10
100
100
50
0
4f
4g
50
0
0.001
0.01
0.1
1
10
0.001
0.01
0.1
1
10
Concentration
Fig. 1. Cytotoxic activity of compounds 4a and 4g against HepG2 (top) and 4f and 4g against HeLa (bottom) cell lines using MTT assay on
a 96 h culture with an IC50 values of 2.0, 0.8 and 2.0 ,0.6 µM, respectively

928 Sumalatha et al.
Asian J. Chem.
presence of –OH substituent at position 6 exhibited significant
in vitro cytotoxic activity on both cancer cell lines. Most of
the titled compounds (4a-j) structure has stereogenic centers,
due to keto-enol tautomerism possibility they show racemization
readily (Fig. 2a). Delocalization of non-bonding electrons of
the oxygen into various parts of benzo[a]xanthen-11(12H)-
one create nucleophilic and electrophilic centers and facilitate
its attack on enzymes and proteins sites with vice-versa.
As shown in Fig. 2a the basic core unit of titled compounds
have one -OH group on hydrophobic heterocyclic moiety at
various positions, which favours the hydrogen bond donation
for enzyme or protein of receptor. On the other hand, there are
also two oxygen and one fluorine sites ready for hydrogen bond
acceptance with enzyme or protein. More electron withdrawing
group of fluorine at meta position on phenyl ring at C12 position,
-OH group at C6 position and an extra hydrophobic methyl
groups at C9 of 4g showing higher in vitro cytotoxic activity
on both cancer cell lines. Excitingly, without these methyl
groups at C9 of 4a have shown little bit lower activity on HepG2
and moderately on HeLa cell lines. It indicates that decrease
of an organic moiety on basic core unit results in lowering the
hydrophobic interaction with the residues of enzymes/proteins
sites (Fig. 2b).
TABLE-3
in vitro CYTOTOXIC ACTIVITY OF TITLE COMPOUNDS
(4a-j) AGAINST HepG2 AND HeLa CELL LINESa
IC50 (µM)b
IC50 (µM)b
Compd.
Compd.
HepG2
HeLa
3.0
>10
>10
>10
>10
HepG2
HeLa
2.0
0.6
2.0
>10
>10
>10
>10
6.0
0.8
4a
4b
4c
4d
4e
4f
4g
4h
4i
>10
>10
4.0
>10
>10
2.0
4j
aIC50 values were determined from growth inhibition curves (0.001-10
µM); bThe reported values are the average of two determinations that
in all cases differed by 8-10 % or less.
xanthen-11(12H)-one derivatives (4a-j) with noteworthy target
specific cytotoxic activity.
Structure-activity relationship (SAR): The oxygenated
tricyclic hydro benzo[a]xanthene derivatives are an outstanding
class of compounds with diverse captivating pharmacological
properties [36-38]. Many natural and synthetic xanthene analo-
gous have been reported in literature and several of them showed
antitumor activity [39,40]. In recent years, in the fields of
medicinal chemistry and material science, synthesis of this
class of compounds gained considerable attention as the number
of its applications have increased.
In this work, the antitumor activity of the target molecules
with two kinds of human cancer cell lines was tested and the
activity probably is attributed to several factors. Therefore,
the SAR study of the titled compounds is explained as below.
Mostly the SAR studies were carried out at C2, C6 and C12 posi-
tions of the titled compounds (4a-j), which revealed that the
In this connection, the structure, configuration, steric size
and nature of attached groups on benzo[a]xanthen-11(12H)-
one ring have critically governed the ease and effectiveness of
interaction with enzymes/proteins in living organisms leading
to normal metabolic biochemical processes. Therefore, analogue
compounds of 4a, 4j and 4f effectively check the abnormal
cell metabolic disorders with their necessary steric and elec-
Electron withdrawing/ donating
(a)
groups of F and/or Br at various
R
m
p
positions on phenyl ring
R
Hydrogen bond donor and accepter group;
Ancaring carbonyl group
R
Hydrogen bond donor and accepter group;
open for substitution
2
o
1
17
HO 3
O
O
O
HO
tautomerization
4
HO
13
16
15
tautomerization
12
11
10
9
18
X
X
X
5
14
O
6
8
7
O
X
O
X
X
These groups are also responsible for the
biological activity
(4a-j)
Hydrophobic 4H-chromene;
Heterocyclic schaffold extending with phenyl
Guest and hosting or hydrogen bond donating/accepting
nature of the compounds at various centres of titled
compounds with enzyme/protein (E/P)
E/P
R
(b)
E/P
Lipinski rule of five (for 4g):
E/P
HO
Molecular weight
Hydrogen bond donor
: 388.44 Dalton
: 1
O
R = F/Br
X = H/Me
Hydrogen bond acceptor : 3
X
Calculated log P
: 5.13+/- 0.49
(from ACD Lab)
O
X
E/P
(4a-j)
Fig. 2. Illustration of SAR of the titled compounds (4a-j), (a) the possible tautomerisation and probable active interactive groups on the basic
core unit and (b) the possible interactions of titled compounds with protein/enzyme-ligand in two dimensional view. The calculated
Lipinski’s properties of 4g are displayed and log P value is measured by using ACD/Chem Sketch

Vol. 32, No. 4 (2020)
An Efficient and Green Synthesis of Fluorine Containing Benzo[a]xanthen-11(12H)-ones 929
15. R. Giri, J.R. Goodell, C. Xing, A. Benoit, H. Kaur, H. Hiasa and D.M.
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In conclusion, a green and facile synthetic methodology
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cancer activity also showed the titled compounds combating
two human cancer cell lines, hepatocellular carcinoma (HepG2)
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The authors declare that there is no conflict of interests
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