Synthesis and antiviral activities of some heteroaryl-substituted triarylmethanes

Article abstract of DOI:10.1002/jhet.457

Some molecular modifications were attempted to find antiviral active compounds in the class of triarylmethanes against herpes simplex virus type 1 (HSV-1). All the synthesized compounds were evaluated for antiviral activity with HSV-1 by a plaque reductio

Full text of DOI:10.1002/jhet.457

1434
Synthesis and Antiviral Activities of Some Heteroaryl-Substituted
Triarylmethanes
Vol 47
Nobuko Mibu,a Kazumi Yokomizo,b Takeshi Miyata,b and Kunihiro Sumotoa*
aFaculty of Pharmaceutical Sciences,
Fukuoka University, 8-19-1 Nanakuma, Jonan-Ku, Fukuoka 814-0180, Japan
bFaculty of Pharmaceutical Sciences, Sojo University, 4-22-1 Ikeda, Kumamoto 862-0082, Japan
*E-mail: kunihiro@adm.fukuoka-u.ac.jp
Received October 16, 2009
DOI 10.1002/jhet.457
Published online 24 August 2010 in Wiley Online Library (wileyonlinelibrary.com).
Some molecular modifications were attempted to find antiviral active compounds in the class of triar-
ylmethanes against herpes simplex virus type 1 (HSV-1). All the synthesized compounds were evaluated
for antiviral activity with HSV-1 by a plaque reduction assay. Some of the compounds showed signifi-
cant antiviral activities.
J. Heterocyclic Chem., 47, 1434 (2010).
INTRODUCTION
ring to other heterocycles or the introduction of phos-
phoryl ester functionalities into the products has
attracted our attention as a potential approach to find
new antiviral active compounds.
In our synthetic studies on antiviral compounds, we
found that some triarylmethane derivatives showed signifi-
cant activity against herpes simplex virus type 1 (HSV-1)
in a plaque reduction assay [1–3]. Most of the compounds,
which were synthesized previously, showed a wide range
of activities against the HSV-1 virus. Molecular modifica-
tions of this class of compounds seemed interesting, and
we therefore carried out further synthetic investigation and
evaluation of this new class of derivatives.
We describe here, the preparation of some new hetero-
aryl (pyridine or pyrrole ring)-substituted triarylmethane
derivatives. For the purpose of structural comparison non-
heterocyclic 4,40,400-trihydroxytriphenylmethane 4a was
chosen. We also attempted the transformation of hydroxyl
groups of products to phosphoryl ester functionalities.
Results of plaque reduction assays to assess the anti-HSV-
1 activities of these compounds are also presented.
In this series, we recently reported that the triaryl-
methane scaffold derivative 1a showed a higher level of
antiviral activity (EC50 ¼ 2.1 lM) and lower cytotoxic-
ity (IC50 ¼ 79.3 lM) than those of the corresponding
4,40-dihydroxytriphenylmethane derivative 2, showing
antiviral activity (EC50 ¼ 5.5 lM, IC50 ¼ 38.1 lM) [1].
Compound 1a is composed of a heterocyclic methylene-
dioxy group instead of the 4-methoxyphenyl group in 2.
Phosphorylated aciclovir and many nucleoside phos-
phates have also shown significant antiviral activity [4–
6]. A methane-based symmetrical tri-indolemethane 3
for enhancement of chemically induced HL-60 cell dif-
ferentiation has recently been reported [7]. The corre-
sponding tri-indolemethyl cation (turbomycin A) was
isolated from soil microbial DNA, and it exhibited broad
antibiotic activity against gram-negative and gram-posi-
tive organisms [8]. Therefore, the alteration of a phenyl
RESULTS AND DISCUSSION
Chemistry. We have already reported [1] the proce-
dure for synthesis of compound 1a by condensation of
phenol and aldehyde using various Brønsted acids. The
reaction of phenol and aldehyde (piperonal) with sulfu-
ric acid in the shade for 1a improved the yield to 93%.
Heteroaryl-substituted triarylmethane derivatives 5a
or 7 containing pyridine or pyrrole rings were easily
synthesized in excellent yield by the reaction of phenol
and nicotinaldehyde or the reaction of pyrrole and vanil-
lin using trifluoroacetic acid (TFA) as a Brønsted acid.
For compound 6a, the reaction of bromomagnesium
phenolate of sesamol with nicotinaldehyde at a reaction
C
V
2010 HeteroCorporation

November 2010
Synthesis and Antiviral Activities of Some Heteroaryl-Substituted
Triarylmethanes
1435
Table 1
Physical data of triarylmethane derivatives (1 and 4–7)
Analysis (%) Calcd
(Found)
mp (ꢀC) (Recryst solvent)
Appearance
Formula, HR-MS
m/z Calcd (Found)
Compound
Formula
C
H
N
IR (cmꢁ1) (KBr)
1b
Pale yellow oil
C28H34O10P2
ꢂ 1.5H2O
54.28
(54.36
6.02
6.29
0.00
0.00)
C28H35O10P2 (M þ H)þ
593.1705
(593.1705)
3490 (OH)
1275 (P¼O)
1030 (PAO)
3500 (OH)
1270 (P¼O)
1025 (PAO)
3240 (OH)
1260 (CAO)
1105 (CAO)
3500 (OH)
1275 (P¼O)
1030 (PAO)
3495 (OH)
1275 (P¼O)
1025 (PAO)
3420 (OH)
3320 (NH)
1230 (CAO)
4b
5a
Pale yellow oil
C31H43O12P3
ꢂ 2.5H2O
49.94
(49.95
6.49
6.43
0.00
0.00)
C31H44O12P3 (M þ H)þ
701.2046
(701.2046)
239–244 (CH3CN-H2O)
colorless powder
C18H15NO2
ꢂ 0.2H2O
76.96
(77.03
5.53
5.56
4.99
5.16)
C18H16NO2 (M þ H)þ
278.1181
(278.1182)
5b
6b
7
Pale yellow viscous solida
C26H33NO8P2
ꢂ 0.3H2O
56.28
(56.27
6.10
6.18
2.52
2.50)
C26H34NO8P2 (M þ H)þ
550.1760
(550.1757)
Yellow oil
C28H33NO12P2
ꢂ 0.8H2O
51.59
(51.63
5.35
5.34
2.15
2.11)
C28H34NO12P2 (M þ H)þ
638.1556
(638.1557)
117-120 (iso-PrOH)
pale purple crystals
C16H16N2O2
71.62
(71.64
6.01
6.09
10.44
10.43)
C16H16N2O2 (Mþ)
268.1212
(268.1214)
a Consistent and correct mp could not be obtained because this compound is a viscous material.
temperature of 30ꢀC and a long reaction time (2 d) gave
an excellent result (84% yield).
DMF to improve the solubility of the reaction solvent
resulted in better yields of the corresponding phosphorylated
products (see experimental).
The phosphorylation of hydroxyl groups of tri- or di-
hydroxytriarylmethanes 1a and 4–6b gave tris- or bis- phos-
phoryl esters (1b and 4–6a) by the reported procedures
[9,10]. Thus, the phosphorylation of hydroxygroups was
accomplished by a slight excess of (EtO)2POH in the pres-
ence of Et3N in CCl4 from 0ꢀC to room temperature over-
night to give the products 1b and 4–6b in 11–89% yields.
Compounds 5b and 6b were obtained under the conditions
of a slight excess of (EtO)2POCl in the presence of NaH at
room temperature for 1 h in 43% and 66% yields, respec-
tively. In both methods, the yields of phosphorylated prod-
ucts depend on the solubility of the starting tri- or di-
hydroxytriarylmethanes. In fact, the addition of THF or
All of the structures of the new compounds synthesized
were determined by using spectroscopic data and elemental
analyses, and the signal assignments were confirmed by
2D-NMR analyses (Tables 1 and 2).
Biological activities
Antiviral activities. The anti-HSV-1 activities of the
synthesized compounds were estimated by using plaque
reduction assays in Vero cells [11]. The results of the
assays are summarized in Table 3 together with the data
for the original compounds 1a [1] and 6a [1].
Substitution with a pyridine ring (compound 5a)
resulted in antiviral activity (EC50 ¼ 6.8 lM, IC50
¼
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

November 2010
Synthesis and Antiviral Activities of Some Heteroaryl-Substituted
Triarylmethanes
1437
Table 3
Antiviral activity (EC50) and cytotoxicity (IC50) against HSV-1.
the molecule. To elucidate these phenomena, further
molecular modifications of triarylmethanes and evalua-
tion of their activity against HSV-1 are underway.
EC50 (lM)
I C50 (lM)
IC50/EC50
1aa
1b
4a
4b
5a
5b
6aa
6b
7
2.1
>16
22.6
8.6
79.3
21.3
127
19.8
54.1
39.6
>135
87.6
190
38.2
<1.3
5.6
2.3
7.9
EXPERIMENTAL
Melting points were determined using a micro melting point
apparatus (Yanagimoto MP-S3) without correction. IR spectra
were measured by a Shimadzu FTIR-8100 IR spectrophotome-
ter. Low- and high-resolution mass spectra (LR-MS and HR-
MS) were obtained by a JEOL JMS HX-110 double-focusing
model equipped with a FAB ion source interfaced with a JEOL
6.8
>36
7.3
<1.1
>18.5
1.8
49.1
>150
<1.3
a The data of the compounds from [1].
l
JMA-DA 7000 data system. H- and 13C-NMR spectra were
obtained by JEOL JNM A-500. Chemical shifts were expressed
in d ppm downfield from an internal tetramethylsilane signal for
lH-NMR and the carbon signal of the corresponding solvent
[CDCl3 (77.00 ppm), CD3OD (39.50 ppm), and dimethyl sulfox-
ide (DMSO)-d6 (39.50 ppm)] for 13C-NMR. Microanalyses were
performed with a Yanaco MT-6 CHN corder. Routine monitor-
ing of reactions was carried out using precoated Kieselgel
60F254 plates (E. Merck). Centrifugal or flash column chroma-
tography was performed on silica gel (Able-Biott or Fuji Silysia
FL60B, respectively) with a UV detector. Preparation of com-
pounds (1a [1], 4a [1], and 6a [4]) have already been reported.
Commercially available starting materials including 4a were
used without further purification.
4,40-(1,3-Benzodioxol-5-ylmethylene)bisphenol (1a) [1]. To
a solution of phenol (755 mg, 8.0 mmol) and 3,4-methylene-
dioxybenzaldehyde (600 mg, 4.0 mmol) in AcOH (2.3 mL)
was added conc. H2SO4 (0.43 mL, 8.0 mmol). In the shade,
the solution was stirred for 20 h at room temperature. The
reaction mixture was poured into ice water (50 mL) and
extracted from AcOEt (100 mL ꢃ 3). The organic layer was
washed with brine and dried over MgSO4. After evaporation,
the residue was purified by centrifugal chromatography on
silica gel (1% EtOH/CH2Cl2) to give 1a (1.192 g, 3.7 mmol,
93% yield). Recrystallization from water/isoPrOH gave pale
reddish crystals.
54.1 lM) similar to that of compound 6a (EC50 ¼ 7.3
lM, IC50 > 135 lM) previously reported [1]; however,
its cytotoxicity was increased to that of 2,20-dihydroxy-
triarylmethane 6a. The introduction of two pyrrole rings
with an NAH group (compound 7) resulted in no signifi-
cant antiviral activity at a concentration of 150 lM.
Thus, two hydroxyl groups on the triphenylmethane
scaffold might be necessary to show significant antiviral
potency.
The phosphorylation of hydroxyl groups of 1a, 5a,
and 6a resulted in increased cytotoxicity in both trans-
formations into 1b, 5b, and 6b, respectively. Transfor-
mation of nonheterocyclic derivative 4a into 4b also
showed a similar tendency. Phosphorylated triphenyl-
methane derivative 4b showed a higher level of anti-
viral activity than that of original compound 4a, but
antiviral activities of both heteroaryl-substituted deriv-
atives 5b and 6b were lower than those of the corre-
sponding 5a and 6a, respectively. With reference to
the phosphorylated hetero-ring substituted derivative
1b, its antiviral activity was also lower than that of
the corresponding nonphosphorylated original com-
pound 1a. Compounds synthesized in this study
showed inhibitory concentrations (EC50) ranging from
6.8 to > 150 lM. Among these compounds, we found
that 5a has the highest level of activity against HSV-
1 (EC50 ¼ 6.8 lM), but its selectivity index was 7.9.
In this study on modification of triarylmethanes by
alteration of heteroaryl rings and transformation into
phosphorylated derivatives, unfortunately, we could
not find more potent antiviral compounds than the 4,40-
dihydroxytriarylmethane 1a reported previously [1].
Throughout this work, however, it is notable that com-
pounds 5a and 6a containing a heteroaryl group (pyri-
dine) showed higher levels of antiviral activity than that
of C3 symmetrical 4,40,400-trihydroxytriphenylmethane
4a (EC50 ¼ 22.6 lM), and the C3 symmetry structure of
both compounds (a prochiral symmetrical molecule) was
destroyed by introducing a different heteroaryl ring in
General procedure of phosphorylation for preparation of
4,40-(1,3-benzodioxol-5-ylmethylene)bisphenylphosphoric
acid tetraethyl ester (1b). This compound was prepared
according to the method reported by Huffman et al. [9].
Thus, diethyl phosphite (3.6 mmol) was added to a stirred
solution of 1a (1.5 mmol) in CCl4 (5 mL) at 0ꢀC, followed
by the addition of Et3N (4.2 mmol) dropwise. The reaction
mixture was stirred overnight at 0ꢀC to room temperature
for 18 h. After dilution with CH2Cl2, the resulting mixture
was washed with water, 10% aqueous HCl, and brine and
then dried over MgSO4. After filtration and evaporation, the
residue was purified by centrifugal chromatography (SiO2:
30–40% AcOEt in n-hexane), which gave 1b (0.281 mmol,
19% yield) as a pale yellow oil.
4,40,400-Methylidynetriphenyl-phosphoric acid hexaethyl
ester (4b). In a manner similar to that for the preparation of
1b, after reaction of 4a (2.0 mmol) in CCl4 (3 mL), diethyl
phosphite (7.4 mmol) and Et3N (8.2 mmol) at temperatures in
the range of 0ꢀC to room temperature for 17 h, purification by
flash chromatography (SiO2: 2–10% EtOH in CH2Cl2) gave 4b
(1.78 mmol, 89% yield) as a pale yellow oil.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

1438
N. Mibu, K. Yokomizo, T. Miyata, and K. Sumoto
Vol 47
4,40-(3-Pyridinylmethylene)bisphenol (5a). A mixture of
DMF (3, 3, 2 mL) and 60% NaH (2.6 mmol) with diethyl
chlorophosphate (2.4 mmol) in dry CH2Cl2 (2 mL) for 1.5 h,
the reaction mixture was poured into a saturated NaHCO3 so-
lution (50 mL) and extracted with AcOEt (40 mL ꢃ 3). Cen-
trifugal chromatography (SiO2: 70–100% AcOEt in n-hexane)
gave 6b (0.663 mmol, 66% yield) as a yellow oil.
2,20-[(4-Hydroxy-3-methoxy-phenyl)methylene]bis-1H-pyrrol
(7). A mixture of pyrrole (16.4 mL, 240 mmol) and vanillin
(912 mg, 6.0 mmol) and TFA (94 lL, 1.2 mmol) was stirred
in the shade at room temperature for 20 h. After evaporation,
purification by flash chromatography (5% AcOEt in CHCl3)
gave 7 (1.288 g, 4.8 mmol) as a colorless solid in 80% yield.
Recrystallization from iso-PrOH gave analytically pure pale
violet crystals 7.
phenol (941 mg, 10.0 mmol) and nicotinaldehyde (536 mg, 5.0
mmol) and TFA (3.85 mL, 50 mmol) was stirred in the shade
at room temperature for 20 h. After evaporation, purification
by centrifugal chromatography (50–70% AcOEt in n-hexane)
gave 5a (1.380 g, 5.0 mmol) as a colorless solid quantitatively.
Recrystallization from CH3CNAH2O gave an analytically pure
colorless powder 5a.
4,40-(3-Pyridinylmethylene)bisphenylphosphoric acid tet-
raethyl ester (5b)
[Method A]. In a manner similar to that for the preparation
of 1b, after the reaction of 5a (1.0 mmol) in CCl4 (3 mL),
diethyl phosphate (3.7 mmol), and Et3N (4.1 mmol) in the
range of 0ꢀC to room temperature for 18 h, purification by
centrifugal chromatography (SiO2: 3–5% EtOH in CH2Cl2)
gave 5b (0.281 mmol, 11% yield) as a pale yellow viscous
solid.
Antiviral activity assay and cytotoxicity of target
compounds. The antiviral activities of synthesized compounds
were measured using
a plaque reduction assay [11] as
described in our previous article [1]. Results of antiviral activ-
ity (EC50) and cytotoxicity values (IC50) with Vero cells are
summarized in Table 3.
[Method B]. According to the method reported by Asaad et
al [10], NaH (60% in oil, 10 mmol) was added to a stirred so-
lution of 5a (1.0 mmol) in dry THF-CH2Cl2 (1, 3 mL) at room
temperature under an N2 atmosphere. After stirring for 0.5 h,
diethyl chlorophosphate (3.0 mmol) in dry CH2Cl2 (2 mL) was
added to the reaction mixture dropwise for 20 min and then
stirred for more 1 h. The reaction mixture was then poured
into a saturated NaHCO3 solution (40 mL) and extracted with
CH2Cl2 (30 mL ꢃ 2), and its organic layer was washed with
water, dried over MgSO4, and evaporated. The resulting prod-
ucts were purified by centrifugal chromatography (SiO2: 5%
EtOH in CH2Cl2) to give 5b (0.432 mmol, 43% yield).
6,60-(3-Pyridinylmethylene)bis-1,3-benzodioxol-5-ol (6a)
[1]. Under N2 atmosphere, a solution of sesamol (2.76 g, 20.0
mmol) in dry ether (Et2O; 50 mL) was added dropwise to a
solution of 3 M EtMgBr (6.7 mL, 20 mmol) in dry Et2O (60
mL) with stirring at room temperature, and the mixture was
kept for 10 min, then the solvent was removed in vacuo. After
addition of dry CH2Cl2 (300 mL) to the residue, a solution of
nicotinaldehyde (536 mg, 5.0 mmol) in dry CH2Cl2 (50 mL)
was added with stirring under N2 atmosphere. The resulting
mixture was sonicated at 30ꢀC for 2 days. The reaction was
quenched with saturated aqueous NH4Cl (100 mL), and the
mixture was extracted with AcOEt (100 mL ꢃ 3). The organic
layer was dried over MgSO4 and concentrated in vacuo to give
the solid. The residue was recrystallized from MeOH to give
6a as a pale green powder (1.53 g, 4.2 mmol) in 84% yield.
Preparation of 6,60-(3-pyridinylmethylene)bis-1,3-benzo-
dioxol-5-ylphosphoric acid tetraethyl ester (6b)
Acknowledgments. The authors would like to thank Mr. Masa-
hiko Ishii, Mr. Junya Ueno, and Ms Yoko Tomioka for their valu-
able technical assistance.
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[Method A]. In a manner similar to that of the preparation
of 1b, after reaction of 6a (1.0 mmol) in CCl4 (3 mL), diethyl
phosphite (3.7 mmol), and Et3N (4.1 mmol) at temperatures in
the range of 0ꢀC to room temperature for 18 h, purification by
centrifugal chromatography (SiO2: 3–5% EtOH in CH2Cl2)
gave 6b (0.505 mmol, 51% yield) as a yellow oil.
[10] Asaad, N.; Kirby, A. J. J Chem Soc Perkin Trans 2 2002,
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[Method B]. In a manner similar to that for the preparation
of 5b, after the reaction of 6a (1.0 mmol) in dry THF-CH2Cl2-
[11] Schinazi, R. F.; Peters, J.; Williams, C.; Chance, D.; Nah-
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet