Xanthenones: Calixarenes-catalyzed syntheses, anticancer activity and QSAR studies

Article abstract of DOI:10.1039/c4ob02611j

An efficient method is proposed for obtaining tetrahydrobenzo[a]xanthene-11-ones and tetrahydro-[1,3]-dioxolo[4,5-b]xanthen-9-ones. The method is based on the use of p-sulfonic acid calix[n]arenes as catalysts under solvent-free conditions. The antiprolif

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FULL PAPER
Xanthenones: Calixarenes-catalyzed Syntheses, Anticancer Activity and QSAR Studies
Daniel Leite da Silva,a Bruna Silva Terra,a Mateus Ribeiro Lage,b Ana Lúcia Tasca Góis Ruiz,c Cameron
Capeletti da Silva,d João Ernesto de Carvalho,c José Walkimar de Mesquita Carneiro, b Felipe Terra
Martins,d Sergio Antonio Fernades,e and Ângelo de Fátima*a
5
Received (in XXX, XXX) XthXXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
An efficient method is proposed for obtaining tetrahydrobenzo[a]xantheneꢀ11ꢀones and tetrahydroꢀ[1,3]ꢀ
dioxolo[4,5ꢀb]xanthenꢀ9ꢀones. The method is based on the use of pꢀsulfonic acid calix[n]arenes as
10 catalysts under solventꢀfree condition.The antiproliferative activity of fitityꢀnine xanthenones against six
human cancer cells was studied. The capacity of all compounds to inhibit cancer cells growth was
dependent on the histological origin of cells. QSAR studies indicate that among compounds derived from
β
ꢀnaphtol the most efficient compounds against glioma (U251) and renal (NCIꢀH460) cancer cells are
those having higher hydrogen bonding donor ability.
15
Introduction
Cancer is an important public health concern and a leading cause
of death. It accounted for eight million deaths worldwide (ca.
15% of all deaths) in 2010 (38% more than in 1990).1,2 Many of
Xanthenones are important biologically active heterocyclic
compounds, with remarkable biological and medicinal properties,
such as antiviral4, antiꢀinflammatory5, antiproliferative6 and
20 current chemotherapy drugs have low specificity for tumor cancer 50 antibacterial activities.7 Furthermore these compounds are also
cells, and are also toxic to normal cells. Related to the
inefficiency of existing drugs against different types of cancer
issues, as well as the increasing emergence of strains resistant to
these drugs are also reported.3 Indeed, one of the biggest
25 challenges of combating cancer is the development of new
anticancer agents that are safe and effective.
used as dyes8, as probes for fluorescenceꢀbased detection of
biomolecules9 and in laser technologies.11 Xanthenones are also
investigated for agricultural purpose as bactericide agent7 and as
photosensitizers in photodynamic therapy.11
55 Multicomponent reaction (MCR) approaches, using a phenolic
compound, aldehydes and 1,3ꢀdicarbonyl compounds under acidꢀ
catalyst effect, are used for synthesis of xanthones.12ꢀ14 In the
recent years, use of calix[n]arenes as catalyst has received
considerable interest in organic synthesis, particularly in MCRs.15
aGrupo de Estudos em Química Orgânica e Biológica (GEQOB),
Departamento de Química, Instituto de Ciências Exatas, Universidade
30 Federal de Minas Gerais, Belo Horizonte, MG, 31270ꢀ901, Brazil. Fax:
+55ꢀ31ꢀ3409ꢀ5700;
adefatima@qui.ufmg.br
Tel:+55ꢀ31ꢀ3409ꢀ6373;
Eꢀmail: 60 Calix[n]arenes are macrocyclic compounds synthesized by the
ortoꢀcondensation of paraꢀsubstituted phenols and formaldehyde
bInstituto de Química, Universidade Federal Fluminense, Campus do
Valonguinho, Niterói, RJ, 24220ꢀ900, Brazil.
under base conditions. There are a large number of applications
involving calix[n]arenes due to their easy structural
modification.15ꢀ17 In the last two decades, chemical literature has
65 reported numerous applications of calix[n]arenes in
supramolecular chemistry.18 Among all calix[n]arenes known so
far, pꢀsulfonic acid calix[n]arenes showed to be the most efficient
35 cCentro Pluridisciplinar de Pesquisas Químicas, Biológicas e Agrícolas
(CPQBA), Universidade Estadual de Campinas, Paulínia, SP, 13081ꢀ970,
Brazil.
.dInstituto de Química, Universidade Federal de Goiás, Goiânia, GO,
74690ꢀ900, Brazil.
40 eGrupo de Quıímica Supramolecular
e
Biomimética (GQSB),
catalysts for Biginelli19, Povarov20,21
,
Mannichꢀtype22 and
Departamento de Química, Universidade Federal de Viçosa, Viçosa, MG,
36570ꢀ900, Brazil.
†CCDC reference numbers 945409ꢀ945410.See DOI: 10.1039/b000000x/
esterification23 reactions. Although the use of calix[n]arenes as
70 catalysts in various reactions, there is no report in the literature on
the use of these compounds as catalysts in the synthesis of
xanthenones.
45
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Table 1. Effect of the quantity of pꢀsulfonic acid calix[n]arenes
of xanthenone 4 based on the amount of catalyst.
The facilite synthesis based on MCR approaches and the diverse
biological profile exhibited by xanthenones brought new
perspectives for the development of new drugs based on this class
of compounds. Herein, we report the synthesis of fiftyꢀnine
xanthenones and their in vitro antiproliferative activity was
investigated on six human cancer cell types and some structure–
activity relationship (SAR) studies were conducted.
5
45
Entry
1
2
3
4
5
6
7
8
Catalyst (mol%)
ꢀꢀ
Yielda (%)
16
53
57
61
74
63
54
61
64
68
67
CX3 (0.15)
CX3 (0.5)
CX3 (1.0)
CX3 (1.5)
CX3 (2.0)
CX6 (0.15)
CX6 (0.5)
CX6 (1.0)
CX6 (1.5)
CX6 (2.0)
10 Results and Discussion
We report herein an easyꢀtoꢀdo and solventꢀfree threeꢀcomponent
synthesis of xanthenones in the presence of a catalytic quantity of
the calix[n]arenes CX1ꢀCX6 (Figure 1). Xanthenones were
synthesized using aldehydes, 1,3ꢀdicarbonyl compound, βꢀ
15 naphthol or sesamol as a starting material. First we focused on the
screening of a series of calix[n]arenes (Figure 1) as catalysts in
reactions containing βꢀnaphthol, 4ꢀfluoroꢀbenzaldehyde and
dimedone at 120 ºC under solventꢀfree conditions (Table 1).
Among the calix[n]arenes tested in the range of 0.15ꢀ2.0 mol%,
20 CX3 and CX6 were the most efficient catalysts. Both CX3 and
CX6 at 1.5 mol% furnished the xanthenone 4 in 74% and 68%
yields, respectively (Table 1; entries 5 and 10, respectively).
9
10
11
Reagents
and
conditions:
β
ꢀnaphthol/4ꢀfluoroꢀ
o
benzaldehyde/dimedone (molar ratio of 1.2:1.0:1.5), 120 C for 1
h. aIsolated yield.
100
CX3
CX6
t
n = 1 and R = Bu (CX1)
80
60
40
20
0
R
R
R
R
CX2
n = 1 and R = H (
)
n = 1 and R = SO3H (CX3)
Catalyst:
t
CX4
n = 3 and R = Bu (
)
n = 3 and R = H (CX5)
n = 3 and R = SO3H (CX6)
HO
OH
OH
OH
25 Figure 1. Struture of calix[n]arenes evaluated as catalyst.
Amounts of CX3 or CX6 lower than 1.0 mol% (Table 1; entries 2
and 3 for CX3, and entries 7 and 8 for CX6) or higher than 1.5
mol% (Table 1; entries 6 and 11, for CX3 and CX6, respectively)
30 provided 4 in poor to moderate yields. The yield of reactions in
the presence of 1.5 mol% calix[n]arenes CX1, CX2, CX4 or
CX5 was comparable to that of catalystꢀfree reactions (Table 1;
entry 1).
First
Second
Third
Run
Figure 2. Reuse of pꢀsulfonic acid calix[n]arenes CX3 and CX6
50 in the synthesis of xanthenone 4.
Considering that yields of reactions in the presence of either CX3
or CX6 were roughly the same (Table 1, entries 5 and 10,
respectively) we chose the former to evaluate the scope of pꢀ
55 sulfonic acid calix[4]arene for the synthesis of xanthenones.
Thus, a variety of aldehydes, 1,3ꢀdicarbonyls and two phenolic
compounds were used (Table 2). Fiftyꢀnine xanthenones (4-62)
were synthesized with yields in the range of 58 to 92%. The
reaction yields were not considerably affected by the presence of
60 electronꢀwithdrawing or electronꢀdonating groups in the
aldehydes (Table 2).
We also evaluated whether calix[n]arenes CX3 or CX6 could be
35 reused in such reactions. After completing the reaction, CHCl3
and water were added to the mixture for recovering CX3 or CX6
in the aqueous phase from the reaction medium. Once dried, the
residue was used in successive reactions in which the yields were
monitored. CX3 and CX6 were successfully used in three
40 successive reactions without significant loss of catalyst activity
(Figure 2).
65
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Table 2. Synthesis of xanthenones catalyzed by the pꢀsulfonic acid calix[4]arene CX3.
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Reagents and conditions: phenolic compound/aldehyde/1,3ꢀdicarbonyl compound (molar ratio of 1.2:1.0:1.5), 120 oC for 1 h. The yield
for obtaining each xanthenone is presented in parentheses.
5
Once synthesized, the structural characterizations of the 15 the crystal lattice. Therefore, crystal structure could not be solved
xanthenones were determined from the corresponding IR, NMR
(1H and 13C) and ESIꢀHRMS data. Crystals of 4 were also
obtained and its crystal structure was determined using singleꢀ
crystal Xꢀray diffractometry. Crystal data and refinement results
in the centrosymmetric triclinic space group with only one
molecule in the asymmetric unit. The xanthenone core, formed
with the four fused rings labeled as AꢀD in Figure 3, is
approximately planar, except for ring A which assumes a halfꢀ
10 are provided as supporting information (Table S1). Xanthenone 4 20 chair conformation with C3 deviating away from the leastꢀ
crystallizes in the triclinic system (space group P1). Both R and S
enantiomers are present in the chosen crystallographic
asymmetric unit (Figure 3). Their molecular conformation is
similar. Moreover, they can not be related by centrosymmetry in
squares plane calculated through the other five coplanar atoms of
this ring by ꢀ0.631(7) Å in the Rꢀenantiomer (atom labels ending
with suffix A) and 0.660(6) Å in the Sꢀenantiomer (atom labels
ending with suffix B) (r.m.s.d. of the C2ꢀC1ꢀC6ꢀC5ꢀC4 fitted
4
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atoms is 0.0292 Å in the Rꢀenantiomer and 0.0205 Å in the Sꢀ
Antiproliferative activity
enantiomer). Ring
B
is not completely planar in both
25
enantiomers, with C7 carbon deviating by ꢀ0.270(6) Å in the Rꢀ
enantiomer and 0.212(6) Å in the Sꢀenantiomer from the leastꢀ
square mean plane calculated through the C6ꢀC5ꢀO2ꢀC9ꢀC8
atoms (r.m.s.d. of the fitted atoms is 0.0431 Å in the Rꢀ
Although xanthenones are known as bioactive heterocyclic
compounds, only few works explored the potential of this class of
compounds against cancer cells. Based on this, the
antiproliferative effect of a series of synthesized xanthenones
5
enantiomer and 0.0270 Å in the Sꢀenantiomer). Taking the 30 were investigated on glioma (U251), breast (MCFꢀ7), multiple
xanthenone mean plane is taken as reference, the outꢀofꢀplane C3
and C7 carbons are on the same side of the fluorinated phenyl
10 ring in both enantiomers. Another intramolecular feature common
to both enantiomers is the substituted phenyl ring conformation.
Ring E is almost perpendicular to the xanthenone mean plane, 35 positive control.24
drugsꢀresistant ovarian (NCIꢀADR/RES), renal (786ꢀ0), lung nonꢀ
small cells (NCIꢀH460), colon (HTꢀ29), and keratinocyte
(HaCaT). Cell proliferation was determined by the
sulforhodamine B method and doxorubicin (Dox) used as a
forming an angle of 82.04(12)° in the Rꢀenantiomer and
84.33(17)° in the Sꢀenantiomer with the leastꢀsquare plane
15 calculated through the planar nonꢀhydrogen atoms of the four
fused rings AꢀD. Therefore, C3 and C7 were not included in this
mean plane calculation.
Initially the fiftyꢀnine xanthenones synthesized were subdivided
into two groups of compounds according to the precursor phenol
structure. Group was constituted of ꢀnaphtholꢀderived
xanthenones (4-32; Table 2) while 33-62 (Table 2), sesamol
40 derivatives, were included in Group 2. The concentration of the
most active xanthenones that elicited 50% cell growth inhibition
(GI50) is summarized in Table 3. The GI50 values for the
remainder compounds tested are provided as supporting
information (Table S2).
1
β
45 When analyzing the data obtained for compounds of Group 1
(Table 3) noted that the NCIꢀADR/RES cell line was the most
sensitive cancer cells as attested by the number of compounds
that negatively affected cells growth at GI50 ≤ 10 µg/mL (Table
3). NCIꢀH460 cells were the least sensitive to compounds of
50 Group 1 (Table 3).
For NCIꢀADR/RES nineteen compounds of Group 1 showed GI50
values lower than 10 ꢀg/mL. The active compounds of Group 1
for this strain showed GI50 values in the range of 0.027 to 9.8
ꢀg/mL. Among the active compounds of Group 1 for NCIꢀ
55 ADR/RES cell line compound 5 was the most potent, with an
GI50 value of 0.027 ꢀg/mL, its GI50 value was found to be in the
same order of magnitude of that for doxorubicin (GI50 = 0.047
ꢀg/mL) (Table 3). Indeed, xanthenone 5 showed high selectivity
index for NCIꢀADR/RES cancer cells, presenting weak
60 antiproliferative activity against nonꢀtumorogenic HaCat cells
(Table 3). Xanthenones 7, 9, 13, 15, 16, 23 and 29 were also
promising against NCIꢀADR/RES cells by exhibiting GI50 around
1 ꢀg/mL (Table 3). Xanthenones 13, 15, and 29 were the most
potent compounds against NCIꢀH460 cells; its GI50 value were
65 lower than 5.0 ꢀg/mL. MCF7 cells were highly sensitive to
xanthenones 8, 9, 13-15, 24 and 29 (Table 3). Compounds 13-15,
20 and 29 compromised U251 cells growth by 50% when used at
concentrations lower than 6.5 ꢀg/mL, while 786ꢀ0 cells were
sensitive to 4, 6, 8, and 29. For HTꢀ29 cells compounds 13ꢀ15,
70 and 29 were the most potent with GI50 values lower than
4.0 ꢀg/mL. Among the tested compounds of Group 1,
xanthenones 13, 15, 29 were those that exhibited the largest
20 Figura 3. The two crystallographically independent molecules of
compound 4. Ellipsoids of 30% probability and arbitrary radius
spheres represent nonꢀhydrogen and hydrogen atoms,
respectively. Rings are also arbitrarily labeled.
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spectrum of action. These xanthenones showed considerable
antiproliferative activity (GI50 < 10 µg/mL) against all the cancer
cell lines, except for kidney cancer cell line (786ꢀ0) in which
At first, a structural analysis of the studied compounds was
carried out. The geometries of the 59 synthesized compounds
xanthenones 13 and 15 presented GI50 values of 216.0 and 29.8 60 were obtained from AM1 semiempirical calculations, after a
5
µg/mL, respectively (Table 3).
conformational analysis using the conformer distribution
subroutine of the SPARTAN'06 software. The most stable
conformation of each derivative was then reoptimized with the
MOPAC software, again using the AM1 method. The outputs
The second group of xanthenones evaluated (Group 2) is related
with those compounds derived from sesamol (Table 3,
compounds 33-62). The antiproliferative activity of these
compounds was expressed as the concentration that produced 65 files from the MOPAC calculation were used to generate a set of
molecular descriptors by using the CODESSA software.
CODESSA may generate about 400 molecular descriptors
associated with molecular constitution, geometry, and topology
and with electrostatic, thermodynamic, and quantum chemical
70 parameters. The molecular descriptors generated by CODESSA
were correlated to the biological efficiency using the heuristic
method.25 Models based on a single molecular descriptor were
chosen to obtain statistically significant meanings. After
elimination of descriptors with low variance or high
75 intercorrelation, the best correlations were found with the
molecular descriptors for compounds of Group 1 to cell lines
U251 and NCIꢀH460. Compounds with GI50 > 250 µg/mL were
not considered in QSAR studies.
For U251 the best correlation was between experimental
80 biological activity of compounds of Group 1 and the calculated
efficiency based on the molecular descriptor HDCAꢀ1.
HDCAꢀ1 is a molecular descriptor that reports the hydrogen
bonding donor ability of the molecule. The values of this
descriptor are obtained as a sum of the accessible surface area of
85 Hꢀbonding donor H atoms, as described below.26,27
10 50% cell growth inhibition or a cytostatic effect (GI50, ꢀg/mL) for
each cell line (Table 3). Data obtained for compounds of Group 2
(Table 3) shows that MCF7 was the most sensitive cancer cells as
attested by the number of compounds that negatively affected
cells growth at GI50 ≤ 10 µg/mL. Nine compouds were active
15 agaist MCF7, and 48 was the most potent with GI50 of 0.7 µg/mL.
Compounds 48 also compromised U251, NCIꢀADR/RES, and
HTꢀ29 cells growth by 50% when used at concentrations lower
than 1.0 ꢀg/mL while NCIꢀADR/RES cells were sensitive to
other six compounds 36, 39, 41, 43 e 45, and 49. For HTꢀ29 cells
20 compounds 41, 45, 49 and 56 were the most potent with GI50
values lower than 4.0 ꢀg/mL. Kidney cells (786ꢀ0) was the less
sensitive strain to compounds of Group 2, for this line only
compounds 41, 48 and 49 were active, with GI50 values of 4.0,
2.2 and 7.1 µg/mL, respectively. For NCIꢀH460 strain
25 compounds 41, 48, 49 and 56 were active compounds of Group 2.
Compounds 48 (GI50 = 2.3 µg/mL) and 56 (GI50 = 3.1 µg/mL)
exhibited GI50 values lower than 4.0 µg/mL, thus showing potent
anticancer activity. Among compounds of Group 2, 41, 48 and 49
were that showing the highest spectrum of action, which were
30 active against the six cancer cell lines evaluated. Compound 48
showed GI50 values lower than 4.0 µg/mL for all tested strains
and can therefore be described as the most promising compound
among compounds of Group 2.
HDCA1 =
s
D ∈ HH −donor
∑
D
D
where
sD – solventꢀaccessible surface area of Hꢀbonding donor H atoms.
The selectivity index (SI) was calculated for each compound of
35 Group 1 and 2 (Table 3). Among evaluated xanthenones,
compound 5 showed the highest SI value for NCIꢀADR/RES
cells, which indicated the potential use of this compound for
future in vivo tests.
When compared the results obtained for compounds of Group 1
40 and 2, we can see that in general compounds of Group 1 were
more active than the compounds of Group 2. Among compounds
of Group 1 evaluated eight compounds showed no activity
against any of the tested strains, where eigheteen compounds of
Group 2 were inactive for all cell lines evaluated. Together these
45 results suggest that the naphthyl nucleus is important for the
antiproliferative activity of this class of compound. Overall, the
potency of xanthenones was dependent on the histological origin
of cancer cells.
90
The model obtained for U251 cells is given in Figure 4 with the
corresponding calculated versus measured efficiency plots.
This correlation indicates that the increasing the accessible
surface area of hydrogen bond donor atoms (HDCA1) leads to an
95 increase in biological activity of the compound. This model
shown to be consistent with the fact that compounds 13, 14, 15,
and 29 which have a hydroxyl group in the meta or para position
and have the highest values of HDCA1 molecular descriptor were
the most active against U251 cells. Although compounds 11 and
100 21 possess a hydroxyl group in the ortho position, this is less
accessible than the meta or para positions resulting in lower
values for the descriptor HDCA1 and experimental biological
activity.
105
50 QSAR Studies.
For a more careful analysis of the relationship between molecular
structure and biological activity, QSAR studies were performed.
To determine the correlation between molecular descriptors and
55 the efficiency of the set of xanthenones, we tested a set of models
as discussed below.
110
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Table 3. Selective index (SI)a and concentration of the most active xanthenones (GI50b in ꢀg/mL) that elicits cancer cellsc growth
inhibition by 50%.
U251
GI50
MCF7
NCI-ADR/RES
786-0
NCI-H460
HT-29
GI50 SI
HaCaT
Group
Xanthenone
SI
0.2
0.8
GI50
SI
0.2
0.5
GI50
2.0
0.03
>250
0.8
227.9
0.7
67.5
0.4
SI
16.1
1626
<0.4
70.3
0.1
33.3
0.8
GI50
SI
10.3
1.5
35.3
<0.2
15.1
0.9
GI50
36.3
85.8
81.7
50.5
28.7
31.4
>250
2.8
SI
0.9
0.5
GI50
32.1
43.9
98.9
54.1
25.7
23.3
52.9
6.1
1
1
4
5
6
7
8
186.6
56.8
>250
29.8
28.5
25.6
14.0
2.9
203.7
92.0
61.4
56.9
2.0
3.1
28.9
2.8
>250
1.7
27.1
225.4
216.0
>250
29.8
197.4
20.4
246.3
188.3
76.6
4.9
>250 <0.1
<0.2
0.4
<0.2
0.5
0.8
<0.2
1.9
1.8
5.9
ꢀ
1.8
<0.8
0.4
1.0
2.4
1.4
2.6
1.1
1.3
1.7
1.9
1.0
1.3
2.4
>250
>250
>250
48.2
29.9
>250
3.2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
-
<0.4
1.8
0.9
0.9
3.8
2.1
2.0
6.9
2.7
4.4
2.4
1.0
0.6
2.4
1.1
0.3
1.2
1.1
0.8
1.1
0.8
1.1
7.4
1.6
1.0
12.9
4.5
<0.2
2.3
2.1
5.2
2.5
1.3
1.6
0.4
1.8
2.5
1.1
2.3
1.3
1.2
1.3
1.1
1.3
1.2
3.4
1.2
1.1
0.9
0.7
<0,.2
2.2
0.4
7.7
2.1
1.4
<0.8
0.6
0.3
1.7
1.1
0.5
0.8
1.2
0.4
0.3
0.4
1.1
9
5.2
>250
2.6
0.2
11
13
14
15
16
20
21
23
24
29
36
39
41
43
45
48
49
56
Doxd
15.2
0.9
0.03
<0.02
0.7
1.3
1.4
0.8
0.2
0.2
1.4
2.9
2.9
2.7
3.9
6.7
13.1
2.6
3.2
3.4
5.8
67.0
625
3.2
0.3
0.4
8.9
20.1
>250
28.4
204.6
34.1
15.4
7.1
26.6
12.9
4.0
32.6
4.3
0.80
2.8
3.5
0.2
94.0
6.5
84.5
35.1
25.1
2.9
25.2
37.2
3.4
29.5
5.3
100.3
21.5
127.0
82.4
8.8
119.9
19.6
>250
60.3
44.2
4.3
24.3
27.8
5.0
26.1
10.5
2.3
7.3
3.1
>250
16.0
>250
95.9
16.2
2.9
19.4
4.9
3.5
25.1
2.6
0.43
2.7
2.7
0.08
3.9
341
3.5
51.9
0.1
4.4
17.8
2.9
2.8
24.4
5.7
0.4
9.3
1.0
0.1
1.0
26.2
110.3
4.0
1.8
7.2
0.8
3.0
26.3
3.2
4.9
3.8
1.1
0.1
0.4
8.6
28.5
25.0
2.2
0.8
5.4
1.6
0.7
3.3
3.3
0.03
0.7
2.2
2.9
0.06
0.5
1.8
0.4
1.6
7.1
0.3
<0.01
12.9
>250
4.0
5.3
15.4
b
0.05
0.04
0.01
aSelectivity index was determined as the ratio of the GI50 for HaCat to the GI50 for the cancer cell line. GI50 values were obtained from
two independent experiments, each done in triplicate. U251, glioma cells; MCF7, breast; NCIꢀADR/RES, multiple drugꢀresistant
c
5
ovarian cancer cells; 786ꢀ0, renal cancer cells; NCIꢀH460, nonꢀsmall lung cancer cells; HTꢀ29, colon cancer cells; HaCaT, keratinocyte.
dReference drug.
charges.26,27 HDAC2 descriptor can be calculated as described
1
Log (
) = 6.49e −1(±8.41e − 02)(HDCA1) − 2.46e + 00(±1.01e − 01)
IC
qD sD
Stot
50
below. HDCA2 =
D∈HH ꢀdonor
∑
2
2
2
D
n = 23; r = 0.764; F = 68.1; s = 0.1067; R
= 0.731
cv
20 where
sD ꢀ solventꢀaccessible surface area of Hꢀbonding donor H atoms
qD ꢀ partial charge on Hꢀbonding donor H atoms
Stot ꢀtotal solventꢀaccessible molecular surface area
25 The model obtained for NCIꢀH460 cells is given in Figure 5. This
relation indicates that the activity values increase when increasing
the value of the molecular descriptor HDCA2. This behavior is
similar to that shown for U251 cells and the HDCA1 molecular
descriptor. Again compounds 13, 14, 15, and 29 which have a
30 hydroxyl group in the meta or para positions and have the highest
values of HDCA2 molecular descriptor were the most active
against NCIꢀH460 cells and orto hidroxilated compounds 11 and
21were less activite than meta or para hidroxilated derivatives. In
summary these two models shows that the activity of compoouds
35 of Group 1 against U251 and NCIꢀH460 increased with the
increasing in accessible surface area of hydrogen bond donor
atoms.
10 Figure 4. Experimental versus calculated efficiency with the
HDCA1 descriptor.
The best correlation found for NCIꢀH460 cells was between the
experimental biological activity of compounds of Group 1 and
15 the calculated efficiency based on the molecular descriptor
HDCA2. HDCA2 is a molecular descriptor based on accessible
area of hydrogenꢀbond donor atoms and correspondes to partial
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d5. Coupling constants (J) are reported in Hertz (Hz). High
40 resolution mass spectra (HRMS) were recorded on Shimadzu LCꢀ
ITꢀTOF Prominence system. Low temperature Xꢀray diffraction
data were collected using an EnrafꢀNonius KappaꢀCCD
diffractometer equipped with a CCD camera of 95 mm and κꢀ
goniostat. No absorption correction was applied to the raw dataset
45 due to the negligible absorption coefficient using graphiteꢀ
monochromated Mo Kα beam (λ=0.71073 Å). The structure was
solved using the direct methods of phase retrieval and the model
was refined by fullꢀmatrix least squares method based on F2.
Positions of hydrogens have followed a riding model with bond
50 distances stereochemically constrained according to the bonded
carbon. The isotropic thermal displacement parameters of
hydrogens were either 20% (CꢀH hydrogens, except those in
methyl moieties) or 50% (hydrogens in methyl moieties) greater
than the equivalent isotropic parameter of the bonded carbon.
55
1
Log (
) = 4.00e + 00(±5.06e − 01)(HDCA2) −
IC
50
2.74e + 00(±1.39e − 01)
2
2
2
n = 22; r = 0.758; F = 62.5; s = 0.159; R
= 0.639
cv
General procedure for the synthesis of xanthenones
Figure 5. Experimental versus calculated efficiency with the
HDCA2 descriptor.
A mixture of an aromatic aldehyde (1 mmol), 1,3ꢀdicarbonyl
compound (1.5 mmol) and βꢀnaphthol or sesamol (1.2 mmol) and
60 pꢀsulfonic acid calix[n]arene CX3 or CX6 (1.5 mol%) was stirred
at 120 ºC for 1 h. After completion of the reaction, methanol and
was added to the mixture and stirred for 30 min. Then the solid
was filtered and washed with cold ethanol to afford the
xanthenones 4-62 in high purity (Table 3). All xanthenones were
5
Conclusions
An efficient method was described for the synthesis of fifty nine
xanthenones under mild conditions. The reaction yields
dramatically increased upon the use of pꢀsulfonic acid
calix[n]arenes as catalysts. Some advantages of the approach here
1
65 characterized by H, 13C NMR, IR, HRMS (ESI) and melting
point (see Supporting Information for reference).
10 described include absence of solvents and metal catalysts, short
reaction time, catalyst tolerance of a wide range of functional
groups and catalyst recycling as well. The ability to inhibit the
growth of cancer cells were also investigated for synthesized
compounds. Compound 5 was as potent as the reference drug
15 doxorubicin against NCIꢀADR/RES and present the greater value
of SI. Several compounds were shown to be active against
different cancer cell lines indicating that the capacity to inhibit
cancer cells growth of the xanthenones was dependent on the
Antiproliferative assay
Human tumor cell lines U251 (glioma), MCFꢀ7 (breast) NCIꢀ
70 ADR/RES (multiple drugsꢀresistant ovarian), 786ꢀ0 (renal), NCIꢀ
H460 (lung, nonꢀsmall cells), HTꢀ29 (colon), and HaCaT
(keratinocyte) were kindly provided by Frederick Cancer
Research & Development CenterꢀNational Cancer Instituteꢀ
Frederick, MA, USA. Stock cultures were grown in RPMI 1640
75 (GIBCO BRL, Life Technologies) supplemented with 5% of fetal
bovine serum and penicillin (final concentration of 1 mg/mL) and
streptomycin (final concentration of 200 U/mL).31,32 Cells in 96ꢀ
well plates (100 ꢀL cells/well) were exposed to Biginelli adducts
(0.25–250 ꢀg/mL) for 48 h at 37 ºC and 5% of CO2. Afterward
80 cells were fixed with 50% trichloroacetic acid, submitted to
sulforhodamine B assay for cell proliferation quantitation at 540
nm.24 The concentration of compound that inhibits cell growth by
50% (GI50) was determined through nonꢀlinear regression
analysis using software ORIGIN 7.5 (OriginLab Corporation).
85 Doxorubicin was used as a reference drug. Results presented are
from two independent experiments, each done in triplicate.
histological origin of cells. In gereral xanthenones derivates of βꢀ
20 naphtol were more active than derived from sesamol. A QSAR
study was performed and two QSAR models were obtained for
compounds of Group 1 against U251 and NCIꢀH460 cells and
indicated that the biological activity of compounds increased with
increasing accessible surface area of hydrogen bond donor atoms.
25 These results show some xanthenones as lead compounds for
obtaining new anticancer agents.
Experimental
General methods and materials
All starting materials were obtained from commercially available
30 sources with highꢀgrade purity and used without further
purification. Calix[n]arenes CX1ꢀCX6 were prepared according
to known procedures.28,29,30 Reactions did not require anhydrous
conditions. The melting points (uncorrected) of synthesized
xanthenones were determined on a Mettler FP 80 HT apparatus.
35 Infrared spectra were recorded on a Perkin Elmer Spectrum One
spectrophotometer (KBr). The 1H and 13CꢀNMR spectra were
recorded on a Bruker AVANCE DPXꢀ200 spectrometry at 200
Computations.
90 The conformational analysis of the 59 xanthenones was done
using the conformer distribution subroutine of the SPARTAN'06
software.33 The most stable conformation of each derivative was
selected for further calculations with the MOPAC code34, again
using the AM135 semiempirical method. In this new step the
95 geometry optimization was developed with the MOPAC code and
1
MHz to H and 50 MHz to 13C, in DMSOꢀd6, CDCl3 or pyridineꢀ
8
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all structures were confirmed as a local minimum by calculation
of the Hessian matrix force constant (no negative eigenvector).36
Two sets of output files were obtained with the MOPAC code. In
11. R. M. Ion, A. Planner, K. Wiktorowicz, D. Frackowiak, Acta
Biochim. Pol.1998, 45, 833ꢀ845.
12. M. M. Heravi, H. Alinejhad, K. Bakhtiari, M. Saeedi, H. A.
the first one the following keywords were used: AM1, PRECISE, 50 Oskooie, F. F. Bamoharram, Bull. Chem. Soc. Ethiop., 2011, 25,
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XYZ, EF, ENPART, VECTORS, BONDS, PI, and POLAR. In
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properties, the following keywords were used: AM1, PRECISE,
THERMO, ROT=1, and XYZ. These output files from MOPAC
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13. J. M. Khurana, D. P. Magoo, Tetrahedron Lett., 2009, 50,
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calculations were used to the development of the initial 55 für Chem., 2009, 140, 1481ꢀ1483.
10 CODESSA calculations, to generate set of molecular
a
descriptors used in the QSAR analysis, also developed by using
the CODESSA software.37 In the statistical analysis for the
QSAR study the following parameters were employed: maximum
15. J. B. Simões, D. L. da Silva, A. de Fátima, S. A. Fernandes,
Curr. Org. Chem. 2012, 16, 949ꢀ971.
16. A. de Fátima, S. A. Fernandes, A. A. Sabino, Curr. Drug.
number of descriptors per model, 1; criterion of significance of 60 Discov. Tech. 2009, 6, 151ꢀ170.
15 parameter, 0.01; level of high correlation, 0.99; level of
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17. E. V. V. Varejão, A. de Fátima, S. A. Fernandes. Curr.
Pharm. Des. 2013, 19, 6507ꢀ6521.
18. P. Jose, S. Menon, Bioinorg. Chem. Appl. 2007, 28, 1ꢀ16.
19. D. L. da Silva, S. A. Fernandes, A. A. Sabino, A. de Fátima.
65 Tetrahedron Lett. 2011, 52, 6328ꢀ6330.
20. J. B. Simões, A. de Fátima, A. A. Sabino, F. J. T. Aquino, D.
L. da Silva, L. C. A. Barbosa, S. A. Fernandes. Org. Biomol.
Chem. 2013, 11, 5069ꢀ5073.
21. J. B. Simões, A. de Fátima, A. A. Sabino, L. C. A. Barbosa,
70 S. A. Fernandes. RSC Adv. 2014, 4, 18612ꢀ18615.
22. S. Shimizu, N. Shimada, Y. Sasaki, Green Chem. 2006, 8,
608ꢀ614.
23. S. A. Fernandes, R. Natalino, P. A. R. Gazolla, M. J. da Silva,
G. N. Jham, Tetrahedron Lett. 2012, 53, 1630ꢀ1633.
75 24. A. Monks, D. Scudeiro, P. Skehan, R. Shoemaker, K. Paull,
D. Vistica, C. Hose, J. Langley, P. Cronise, A. VaigroꢀWolff, M.
GrayꢀGoodrich, H. Campbelli, J. Mayo, M. J. Boyd, J. Nat.
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Acknowledgements
We acknowledge the following Brazilian agencies: Conselho
Nacional de Desenvolvimento Cientifíco e Tecnológico (CNPq)
20 for research fellowships (A.D.F., J.W.M.C., S.A.F.) and financial
support; Fundação de Amparo à Pesquisa de Minas Gerais
(FAPEMIG), Coordenação de Aperfeiçoamento de Pessoal de
Nível Superior (Capes), and Fundação de Amparo à Pesquisa do
Estado do Rio de Janeiro (FAPERJ). Authors are also thankful to
25 Dr. C.M. da Silva and L.S. Neto for critical reading of the
manuscript.
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