Synthesis and antibacterial assay of 9-substituted aryl-1,8-dioxo-octahydroxanthenes

Article abstract of DOI:10.14233/ajchem.2014.16128

The present report highlights the heterogeneous catalytic activity of nano copper ferrite for the one pot synthesis of 9-substituted aryl-1,8- dioxo-octahydroxanthenes when dimedone reacts with various aromatic aldehydes under solvent free conditions, cat

Full text of DOI:10.14233/ajchem.2014.16128

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Asian Journal of Chemistry; Vol. 26, No. 15 (2014), 4594-4598
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.16128
Synthesis and Antibacterial Assay of 9-Substituted Aryl-1,8-dioxo-octahydroxanthenes
1,*
1,2
2
1
1
YELLAJYOSULA LAKSHMI NARASIMHA MURTHY , PALLA MAHESH , BHOOMIREDDY RAMA DEVI , L.K. DURGESWARAI and PALLA MANI
1Deptartment of Organic Chemistry, Andhra University, Visakhapatnam-530 003, India
2Deptartment of Chemistry, Jawaharlal Technological University, Kukatpally, Hyderabad-500 085, India
*Corresponding author: E-mail: murthyyln@gmail.com
Received: 1 August 2013;
Accepted: 15 October 2013;
Published online: 16 July 2014;
AJC-15531
The present report highlights the heterogeneous catalytic activity of nano copper ferrite for the one pot synthesis of 9-substituted aryl-1,8-
dioxo-octahydroxanthenes when dimedone reacts with various aromatic aldehydes under solvent free conditions, catalyzed by nano
catalyst. The main advantageous of this protocol includes excellent yields, mild reaction conditions and short reaction times.
Keywords: Nano copper ferrite, One-pot synthesis, Solvent free conditions, Xanthenes, Antibacterial assay, Docking.
sulfonic acid on silica gel21, Dowex-50 W ion exchange resin
under solvent-free conditions22, HClO4-SiO223, ZnO and ZnO-
acetyl chloride24 and heteropoly acid supported MCM-4125.
However, the methods reported, serve their best but still
suffer from certain drawbacks such as long reaction times,
low yields, use of toxic transition metals as catalysts, use of
hazardous organic solvents and tedious workup procedures.
Recently, because of the unique properties of nano particles,
synthetic chemists focused on nano-catalysts. Therefore,
synthesis and characterization of catalysts with lower dimen-
sions have become the most interesting topic of research.
Moreover, due to quantum size effects, nanometer-sized particles
may exhibit unique properties for a wide range of applications.
Keeping the above facts and as a part of our ongoing research,
herein we report, first time, use of nano copper ferrite as hetero-
geneous support for the synthesis of 9-substituted aryl-1,8-
dioxo-octahydroxanthenes. This method offers advantageous
such as short reaction time, recyclability of the catalyst and
easy to work-up procedure.
INTRODUCTION
Xanthene and its derivatives are an important class of
organic molecules because they have wide range of biological
and pharmaceutical properties such as antibacterial1, antiviral2
and these are being utilized as antagonists for paralyzing action
of zoxazolamine3 and in photodynamic therapy4,5. Further-
more, these compounds can be used as dyes in laser techno-
logies and pH sensitive fluorescent materials for visualization
of bio-molecules6. In particular, xanthenediones constitute a
key structural motif in a number of natural products7-9 and
have been used as versatile synthons because of the inherent
reactivity of inbuilt pyran ring10. Synthesis of xanthenediones
is a continuing hot topic because these moieties are active
pharmaceutical ingredients (API's) and also valuable reactive
intermediates for both synthetic and medicinal chemists.
A survey of the literature reveals that various methods
have been reported for preparation of xanthene derivatives.
The classical method for the synthesis of 9-substituted aryl-
1,8-dioxo-octahydroxanthenes involves the condensation of
appropriate active methylene compounds with various substi-
tuted aromatic aldehydes. For this purpose, two molecules of
dimedone (5,5-dimethyl-1,3-cyclohexane) was reacted with
various aromatic aldehydes11 by using different Lewis acid
catalysts such as triethylbenzyl ammonium chloride12, p-
dodecyl benzenesulfonic acid13, diammonium hydrogen phos-
phate14 under various conditions, sulfonic acid under ultrasonic
irradiation15, ionic liquids16, Ambedrlyst-1s17, NaHSO4-SiO2
or silica chloride18, phosphomolybdic acid supported on silica
gel19, man-sized MCM-41-SO3H under ultrasonic irradiation20,
EXPERIMENTAL
Preparation of nano copper ferrite: The catalyst was
synthesized26 by citrate gel precursor method. Copper(II)
nitrate and iron(III) nitrate were taken in stoichiometric propor-
tions and minimum amount of deionized water was added to
produce clear cationic solution. Citric acid solution was then
prepared in stoichiometric ratio.Aqueous solutions with molar
ratio of metal iron solutions were mixed and citric acid was
added in equimolar ratio to the above mixed metal iron solution.
pH was adjusted to 7 by adding ammonia solution. The aqueous

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Vol. 26, No. 15 (2014)
Synthesis and Antibacterial Assay of 9-Substituted Aryl-1,8-dioxo-octahydroxanthenes 4595
mixture was heated up to 90 °C to evolve reddish brown gases
and became dried gel, which was finally treated at 350 °C for
1 h to observe whether the dry gel burnt out in self propagating
manner to form loose powder. The finely powdered particles
were calcinated at 600 °C. The powder was then characterized.
General method of synthesis of 9-substituted aryl-1,8-
dioxo-octahydroxanthenes: A mixture of 5,5-dimethyl-1,3-
cyclohexanedione (2eq) (1), substituted aromatic aldehydes
(1 eq) (2) and CuFe2O4 nano particles (15 mol %) were stirred
at 120 °C in an oil bath for the time indicated in Table-1. The
completion of the reaction was monitored by TLC.After comp-
letion of the reaction, the reaction was cooled to room tempe-
rature and a solid product was obtained. The product was
dissolved in methanol and the catalyst was recovered by
magnetization. The crude products were further purified by
recrystallization from ethanol. All the synthesized products
were characterized by IR, NMR and Mass spectroscopic data
and their melting points were compared with authentic samples.
The reaction times, percentage of yield and m.p.’s were presented
in Table-1. The spectral data of the synthesized compounds
(3a-3j) are given below.
126.93, 128.91,129.12, 129.88, 131.03, 131.23, 131.58,
143.98, 148.65; MS (m/e, %) 437 (20), 281 (100), 252 (40),
75 (15).
Compound(3i): 9-(4-Nitrophenyl)-3,3,6,6-tetramethyl-
1,2,3,4,5,6,7,8-octahydroxanthene-1,8-dione m.p. 219-221 °C.
IR (KBr, νmax, cm-1): 2958, 1670, 1650, 1520, 1362, 1206,
870. 1H NMR (400 MHz, CDCl3): δ 8.09 (d, J = 8.0 Hz, 2H,
ArH), 7.46 (d, J = 8.0 Hz, 2H, ArH), 4.82 (s, 1H, CH), 2.49
(s, 4H, 2CH2), 2.21 (q, J = 16.2 Hz, 4H, 2CH2), 1.12 (s, 6H,
2CH3), 0.99 (s, 6H, 2CH3). 13C NMR (75 MHz, CDCl3): δ
196.1,162.9, 151.3, 146.6, 129.4, 123.5, 114.5, 50.5, 40.8,
32.3, 32.1, 29.6,29.2, 27.2. MS (m/e): 395 (M+). Anal. Calcd
for C23H25NO5: C, 69.85; H, 6.37; N, 3.54. Found: C, 69.96; H
6.49; N, 3.43.
Antibacterial assay: Antibacterial studies were carried
out on human pathogenic bacteria. Salmonella typhi, Vibrio
cholerae, Shigella dysenteriae and Enterococcus faecalis,
which were clinical isolates collected at King George Hospital,
Visakhapatnam, India. S. typhi, V. cholerae, S. dysenteriae and
E. faecalis are gastrointestinal pathogens.Antibacterial activity
was performed by agar well diffusion method and minimum
inhibitory concentration (MIC)27,28.Agar well diffusion method
was performed to determine the inhibitory zones in millimeter
(mm). MIC was determined by broth dilution assay and the
experiment was conducted between 1-1000 µg/mL of compound
concentration. Ciprofloxacin (antibiotic) and DMSO were used
as positive control and negative control respectively29.
Molecular docking studies: X-ray crystal structures of
proteins used in docking studies are obtained from Protein
Data Bank. Topoisomerase I (PDB ID 1T8I) was used in docking
studies. Co-cystalized ligands and water molecules are removed
from target protein usingArgus lab. Ligands are prepared using
Chemoffice (Cambridge). Energy minimization was done
using molecular mechanics. The minimized was executed until
root mean square value reached smaller than 0.001 Kcal/mol.
Such energy minimized ligands and receptor used for docking
studies using GEMDOCK (Generic Evolutionary Method for
molecular docking) is a generic evolutionary method with an
empirical scoring function for the protein-ligand docking,
which is a problem of paramount importance in structure-based
drug design, combines both continuous and discrete search
mechanisms. A population size of 300 with 70 generations
Spectral data for selected compounds
Compound (3a): 9-Phenyl-3,3,6,6-tetramethyl-1,2,3,4,5,
6,7,8-octahydroxanthene-1,8-dione m.p. 204-205 °C. IR (KBr,
1
ν
max, cm-1): 2954,1664,1364,1199. H NMR (400 MHz,
CDCl3): δ 7.27-7.09 (m, 5H, ArH), 4.74 (s, 1H, C9-H), 2.46
(s, 4H, 2CH2), 2.19 (q, J = 16.5 Hz, 4H, 2CH2), 1.10 (s, 6H,
13
2CH3), 0.98 (s, 6H, 2CH3). C NMR (100 MHz, CDCl3): δ
196.2, 162.3, 143.8, 128.4, 127.6, 115.2, 50.6, 40.7, 32.0, 31.6,
29.3, 27.2. MS (m/e): 350 (M+). Anal. Calcd for C23H26O3:
C, 78.83; H, 7.47. Found: C, 78.96; H, 7.40.
Compound (3b): 9-(4-Methylphenyl)-3,3,6,6-tetramethyl-
1,2,3,4,5,6,7,8-octahydroxanthene-1,8-dione. m.p. 215-
217 °C. IR (KBr, νmax, cm-1): 3030, 2980, 1685, 1660, 1620,
1490, 1365, 1200, 1135, 1000, 850, 840. 1H NMR (400 MHz,
CDCl3): δ 7.16 (d, J = 8.0Hz, 2H, Ar H), 7.01 (d, J = 8.0 Hz,
2H, ArH), 4.70 (s, 1H, CH), 2.45 (s, 4H, 2CH2), 2.23 (s, 3H,
CH3), 2.19 (q, J = 16.3 Hz, 4H, 2CH2), 1.09 (s, 6H, 2CH3),
0.99 (s, 6H, 2CH3).13C NMR (100 MHz, CDCl3): δ 196.4,
162.1, 141.1, 135.7, 128.7, 128.1,115.7, 50.7, 40.8, 32.1, 31.3,
29.2, 27.3, 20.9. MS (m/e): 364 (M+).Anal.Calcd for C24H28O3:
C, 79.09; H, 7.74. Found: C, 79.16; H 7.49.
and three solutions were used, in docking accuracy setting30,31
.
Compound (3c): 9-(4-Hydroxyphenyl)-3,3,6,6-tetra-
methyl-1,2,3,4,5,6,7,8-octahydroxanthene-1,8-dione. m.p.
220-222 °C. IR (KBr, νmax, cm-1): 3324, 2959, 1652, 1617,
1363. 1H NMR (400 MHz, CDCl3): δ 7.10 (d, J = 8.4 Hz, 2H,
Ar H), 6.60 (d, J = 8.4 Hz, 2H, Ar H), 5.72 (s, 1H, OH, D2O
exchangeable), 4.67 (s, 1H, CH), 2.45 (s, 4H, 2CH2), 2.20 (q,
J = 16.2 Hz, 4H, 2CH2), 1.09 (s, 6H, 2CH3), 0.99 (s, 6H, 2CH3).
13C NMR (75 MHz, CDCl3): δ 195.8, 162.5, 140.7, 135.5,
128.2, 128.0,115.2, 50.6, 40.1, 32.4, 31.2, 29.1, 27.2. MS
(m/e): 366 (M+). Anal.Calcd for C23H26O4: C, 75.38; H, 7.15.
Found: C, 75.16; H 7.29.
RESULTS AND DISCUSSION
In continuation of our interest in the area of clean synthesis,
under solvent-free conditions, for the development of new
synthetic methodologies herein, we report a simple, efficient
and one-pot reaction of dimedone and aldehydes using nano
copper ferrite at 120 °C for the preparation of 9-substituted
aryl-1,8-dioxo-octahydroxanthenes (3a-3j) in high yields
(Scheme-I) and the results were presented in Table-1.
Initially, a blank reaction using benzaldehyde and dimedone
(mole rate 1:2) at 120 °C without nano copper ferrite was per-
formed in order to establish the real effectiveness of the catalyst
and the results showed that desired product was not formed
even after 12 h of heating. We then focused to optimize catalyst
loading percentage. In order to evaluate the most appropriate
Compound (3g): 9-(4-Bromophenyl)-3,3,6,6-tetramethyl-
1,2,3,4,5,6,7,8-octahydroxanthene-1, 8-dione. m.p. 230-232 °C;
IR (KBr, νmax, cm-1): 3030, 1624, 1586; 1H NMR (400 MHz,
CDCl3): δ 6.47 (1H, s, CH),7.25-8.34 (m, 4H,ArH.); 13C NMR
(CDCl3): δC 37.46,116.64, 118.02, 120.21, 122.39, 124.38,

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4596 Murthy et al.
Asian J. Chem.
TABLE-1
SYNTHESIS OF 9-ARYL-1,8-DIOXO-OCTAHYDROXANTHENES USING NANO COPPER FERRITE
Product
R
-H
Time (min)
Yield (%)
m.p. (°C)
202-204
215-217
238-239
243-245
230-232
224-226
228-230
223-225
230-232
219-221
Lit. m.p. (°C)
202-20423
217-21823
236-23932
246-24812
242-24423
226-22823
–
3a
3b
3c
3d
3e
3f
5
95
85
88
90
80
90
88
91
92
95
-CH3
-CH(CH3)2
-OH
15
25
30
30
15
17
14
12
10
-OCH3
-NMe2
-NEt2
-F
3g
3h
3i
224-22633
234-23633
226-22823
-Br
3j
-NO2
R
Under the optimized conditions, aromatic aldehyde (2a-2j)
containing electron donating as well as electron withdrawing
groups with different substitution patterns were effectively
cyclized to give 9-aryl substituted 1,8-dioxo-octahydroxanthenes
(Table-1).
CHO
O
O
O
+
120oC, solvent free
O
O
R
2
From Table-1, it is observed that the presence of electron
withdrawing groups on benzaldehyde (compounds 3f and 3j)
require less reaction times and produce high yields than electron
donating groups on benzaldehyde ( compounds 3b, 3c, 3e, 3f
and 3g). The presence of electron withdrawing group acce-
lerates the formation of carbocation at the carbonyl carbon of
benzaldehyde. Interestingly, the basic molecule itself, without
any substitution, reacts in presence of catalyst leading to the
formation of the product in good yield (90 %). The formation
of xanthene moiety is confirmed by spectroscopic methods.
In IR spectra stretching frequencies between 1670-1624 cm-1
= copper ferrite
nanoparticles
3a-3j
1
R: a = H; b = -CH3; c = -CH(CH3)2; d = -OH; e = -OMe;
f = -NMe2; g = -NEt2; h = -Br; i = -F; j = -NO2
Scheme-I:Synthesis of 9-substituted aryl-1,8-Dioxo-octahydroxanthenes
employing reusable Nano copper ferrite as catalyst
catalyst percentage, a model reaction using benzaldehyde and
dimedone (mole ratio1:2) was carried out using 0, 5, 10, 15
and 20 mol % of Nano copper ferrite at different temperatures
under solvent-free conditions (Table-2). It was found that 15
mol % of Nano copper ferrite showed high yield in lesser
reaction time at 120 °C (Table-2).
1
correspond to the carbonyl group of xanthenes. In H NMR
spectra, chemical shift at δ 4.82-4.67 corresponds to the -CH
proton of tertiary carbon which confirms the formation of target
molecule.
TABLE- 2
OPTIMIZED CONDITIONS FOR CATALYST LOADING AT120 oC
Antimicrobial activity: To explore the bioactive lead
molecules, the above synthesized compounds were evaluated
for their antibacterial activity on human pathogens viz., S. typhi,
V. cholerae, S. dysentriae, E. faecalis at Department of Organic
Chemistry, Microbial Laboratories, A.U, adopting well
diffusion method and the results are tabulated in Table-4.
Xanthene derivatives (3a-3j) showed significant antibac-
terial activity on human pathogens. Zone of inhibitions were
observed between 6-15 mm. Among the series of compounds,
compound 3f showed highest zone of inhibition (15 mm) and
low MIC (1 µg/mL) on Vibrio cholerae. Compound 3f (N,N-
diethyl) showed good activity on both gram positive and gram
negative bacteria. The pathogens S. typhi, S. dysenteria, E.
faecalis showed resistance to synthesized xanthenes analogues
compared to V. cholerae. Some of the analogues showed com-
parable activity with ciprofloxacin. Further molecular docking
studies performed on X ray crystal structure of topoisomerase,
which is one of the target sites for cytotoxic activity. The results
were depicted in Table-5. In silico studies were correlated with
in vitro studies. The binding energies or dock energies of
Xanthene derivatives (3a-3j) found to be between 119.8-138.5
Kcal/mol. Binding energy is inversely proportional to binding
affinity. Compound 3f binds with high affinity than other
synthesized compounds and its binding interactions with
glutamic acid494, threonine501, lysine493 residues of topoisomerase
Product
R
Catalyst (mol %)
Yield
0
Time (min)
0
12 (h)
5
92
8
6
5
7
O
O
10
15
20
93
95
O
94
After completion of the reaction, the catalyst was recov-
ered by magnetization and washed with diethyl ether and the
recovered catalyst was reused for few more cycles. During
washing with the solvent, it was clearly evident that there was
no leaching of catalyst and was confirmed by performing the
reaction with the filtrate. The leaching of metal after three
cycles was found to be 0.17 %. From our investigations, we
observe that nano catalyst shows excellent to good reactivity
with promising yields even for the next three cycles in the
same reaction. Since, there was no observable loss in the yield
percentage; further reusability of nano catalyst was not needed.
The results are listed in Table-3.
TABLE- 3
REUSABILITY OF NANO CATALYST
S. No.
Catalyst recovery (%)
Yield (%)
1
2
3
4
–
95
89
82
78
97
86
80

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Vol. 26, No. 15 (2014)
Synthesis and Antibacterial Assay of 9-Substituted Aryl-1,8-dioxo-octahydroxanthenes 4597
TABLE-4
ANTI-MICROBIAL ACTIVITIES OF 9-ARYL-1,8-DIOXO-OCTAHYDROXANTHENES
DERIVATIVES AGAINST VARIOUS HUMAN PATHOGENS
S.No
1
Compound
S. typhi
9/100
V. Cholerae
8/100
S. dysenteriae
11/100
10/>1000
09/100
11/100
10/1000
14/10
E. faecalis
9/1000
9/>1000
9/1000
8/100
3a
2
9/1000
10/100
9/10
9/1000
10/100
10/100
11/100
15/1
3b
3
3c
4
3d
5
10/100
14/10
10/>1000
13/100
6/1000
10/1000
ND
3e
6
3f
7
10/1000
10/100
9/1000
13/10
11/1000
10/100
10/1000
10/100
18/1
11/1000
9/100
3g
8
3h
9
8/100
3i
3j
10
11
10/100
16/10
10/100
15/10
Antibiotic
17/10
Ciprofloxacin for bacteria; * 50 µg compound per well; ND: Not Determined
TABLE-5
MOLECULAR DOCKING STUDIES OF XANTHENE
DERIVATIVES ON TOPOISOMERASE I
Binding energy
(-Kcal/mol)
Interacted
amino acids
Compound
LYS-493
GLU-494
ARG-508
-123.5
-128.8
-127.3
-119.8
-133.1
-138.5
-129.0
-128.1
-138.0
-131.9
3a
ARG-488
TYR-537
LYS-532
LEU-602
GLN-599
LYS-603
ARG-590
THR-591
THR-718
3b
3c
3d
3e
3f
Fig. 1. Molecular docking of synthesized xanthone (3f) on topoisomerase I
ARG-375
ASN-419
GLU-418
was obviously revealed. Further the microbial investigations
confirm that the N,N- dimethyl analogue (3f) is a promising
lead molecule.
GLU-494
THR-501
LYS-493
ACKNOWLEDGEMENTS
LYS-532
TYR-537
LYS-532
3g
3j
The authors are thankful to Defense Research and Develo-
pment Organization, New Delhi for providing financial
assistance. The authors are also grateful to the Committee
on strengthening infrastructure for Science & Technology
(COSIST) Labs, Andhra University for providing spectral
data.
PHE-529
GLY-531
ARG-488
LEU-487
GLY-531
TYR-537
LYS-734
PRO-739
VAL-738
3h
3i
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