Design, synthesis and antiviral activity of 2-(3-amino-4-piperazinylphenyl) chromone derivatives

Article abstract of DOI:10.1248/cpb.c12-01050

Previously, we have confirmed that the antiviral activities of the chromone derivatives were controlled by the type as well as the position of the substituents attached to the chromone core structure. In the course of our ongoing efforts to optimize the antiviral activity of the chromone derivatives, we have been attempting to derivatize the chromone scaffold via introduction of various substituents. In this proof-of-concept study, we introduced a 3-amino-4-piperazinylphenyl functionality to the chromone scaffold and evaluated the antiviral activities of the resulting chromone derivatives. The synthesized 2-(3-amino-4-piperazinylphenyl)- chromones showed severe acute respiratory syndrome-corona virus (SARS-CoV)-specific antiviral activity. In particular, the 2-pyridinylpiperazinylphenyl substituents provided the resulting chromone derivatives with selective antiviral activity. Taken together, this result indicates the possible pharmacophoric role of the 2-pyridinylpiperazine functionality attached to the chromone scaffold, which warrants further in-depth structure-activity relationship study.

Full text of DOI:10.1248/cpb.c12-01050

486
Note
Chem. Pharm. Bull. 61(4) 486–488 (2013)
Vol. 61, No. 4
Design, Synthesis and Antiviral Activity of 2-(3-Amino-4-
piperazinylphenyl)chromone Derivatives
,a
Mi Kyoung Kim,a Hyunjun Yoon,a Dale Lynn Barnard,b and Youhoon Chong*
a Department of Bioscience and Biotechnology, Bio/Molecular Informatics Center, Konkuk University; Hwayang-
b
dong, Gwangjin-gu, Seoul 143–701, Korea: and Institute for Antiviral Research, Department of Animal, Dairy and
Veterinary Science, Utah State University; 5600 Old Main Hill, Logan, UT 84322, U.S.A.
Received December 7, 2012; accepted January 23, 2013
Previously, we have confirmed that the antiviral activities of the chromone derivatives were controlled
by the type as well as the position of the substituents attached to the chromone core structure. In the course
of our ongoing efforts to optimize the antiviral activity of the chromone derivatives, we have been attempt-
ing to derivatize the chromone scaffold via introduction of various substituents. In this proof-of-concept
study, we introduced a 3-amino-4-piperazinylphenyl functionality to the chromone scaffold and evaluated the
antiviral activities of the resulting chromone derivatives. The synthesized 2-(3-amino-4-piperazinylphenyl)-
chromones showed severe acute respiratory syndrome-corona virus (SARS-CoV)-specific antiviral activity.
In particular, the 2-pyridinylpiperazinylphenyl substituents provided the resulting chromone derivatives
with selective antiviral activity. Taken together, this result indicates the possible pharmacophoric role of
the 2-pyridinylpiperazine functionality attached to the chromone scaffold, which warrants further in-depth
structure–activity relationship study.
Key words piperazinylphenylchromone; antiviral activity; hepatitis C virus; severe acute respiratory syn-
drome (SARS); SARS-corona virus
1,3-Diketoacid (DKA) (Fig. 1) is one of the well-known which smoothly underwent nucleophilic substitution reaction.
antiviral scaffold with anti-human immunodeficiency virus Treatment of the resulting tert-butyl piperazinylbenzoate with
(HIV),1) anti-hepatitis B virus (HBV),2) and anti-severe acute trifluoroacetic acid (TFA) provided the desired piperazinylben-
respiratory syndrome-corona virus (SARS-CoV)3) activity. zoic acids 9a–d as white powder, which was used for the next
Previously, we discovered a chromone scaffold (Fig. 1) as a step without further purification. On the other hand, the two
novel pharmacophore for antiviral agents against HCV4) as phenolic hydroxyl groups of 2,4,6-trihydroxyacetophenone 10
well as SARS-CoV,5) and reported structure–activity relation- were protected with either methyl or benzyl group to give the
ship studies on a series of chromone derivatives.6–8) Interest- corresponding 2-hydroxy-4,6-dialkoxy acetophenone 11a or
ing antiviral activities against HCV and/or SARS-CoV were b in 88% and 94% yield, respectively. 1-Ethyl-3-(3-dimethyl-
observed from various chromone derivatives.6–8) Also, through aminopropyl)carbodiimide (EDC)-mediated coupling of 9 with
structure–activity relationship study, we confirmed that a 11 provided the corresponding ester which underwent cycliza-
substituent could play a key role in controlling the antiviral tion followed by dehydration upon sequential treatment with
activity of the chromone derivatives against HCV and SARS- tert-BuOK and sulfuric acid to give the chromone scaffold.
CoV.9) Thus, in the course of our ongoing efforts to optimize Finally, reduction of the nitro functionality to the amino group
the antiviral activity of the chromone derivatives, we have was accomplished upon treatment with H2 in the presence of
been attempting to derivatize the chromone scaffold via intro- Pd(OH)2–C with concomitant removal of the benzyl protect-
duction of various substituents. In this context, a 2-pyridinyl- ing groups to furnish the desired compounds 1, 4, 5, and 6, in
piperazine moiety which was used to potentiate the anti-HCV 84%, 83%, 84%, and 88% yield, respectively. Deprotection of
activity of the acridone scaffold10) (Fig. 1) drew our attention.
In particular, structural similarity between the chromone and
the acridone scaffold led us to design novel chromone deriva-
tives with a piperazinylphenyl substituent (Fig. 1).
Herein, we report synthesis and antiviral evaluation
of 2-(3-amino-4-piperazin-1-yl-phenyl)chromone derivatives
(Fig. 1).
Chemistry The chromone scaffold was constructed by
condensation of 3-nitro-4-piperazinylbenzoic acid 9 and 2-hy-
droxyacetophenone 11 followed by ring closure (Chart 1). The
piperazinylbenzoic acid 9a–d were prepared by nucleophilic
aromatic substitution reaction of the commercially available
4-chloro-3-nitrobenzoic acid 7 with variously substituted pi-
perazines. However, direct substitution of 7 with piperazine
did not work due to the acidic nature of 7. Thus, 7 was tran-
siently converted to the corresponding tert-butyl ester 8a–d,
Fig. 1. Structures of DKA, Chromone, Piperazinylacridone, and the
Title Compound (Piperazinylphenylchromone)
The authors declare no conflict of interest.
Bold lines indicate structural similarities between these structures.
© 2013 The Pharmaceutical Society of Japan
*To whom correspondence should be addressed. e-mail: chongy@konkuk.ac.kr

April 2013
487
Chart 1. Synthesis of the Title Compounds 1–6
the methyl group of 1 was attempted with BBr3 to give a mix- was also evaluated. Using a modified protocol of Barnard et
ture of 2 (28% yield) and 3 (43% yield), which were readily al.,13) cytopathic effect (CPE) reduction assays were performed
separated by column chromatography on silica gel.
in Vero 76 cells, which were visually assessed (visual assay,
Anti-HCV Activity The synthesized compounds 1–6 Table 1) and then verified spectrophotometrically by neutral
were evaluated for their antiviral activity in the Huh-Luc/neo red (NR) uptake assay14,15) (neutral red assay, Table 1) in the
cell line harboring a genotype 1b/strain Con-1 HCV subge- same plate.
nomic replicon.11,12) The level of HCV RNA replication was
In the visual assay, three compounds (1, 3, 4) showed
quantified with luciferase reporter assay, and the results were moderate but selective antiviral activity (EC50=34–42µm,
summarized in Table 1. Except compound 4, no other com- CC50>100 µm). However, in the NR uptake assay only com-
pound prepared in this study showed antiviral activity against pound 1 maintained antiviral activity. In comparison, com-
HCV. The compound 4 with a piperazinylbenzoxazole sub- pound 2 showed improved activity and selectivity in the NR
stituent showed significant anti HCV-activity (EC50=1.5 µm) uptake assay compared to those values obtained in the visual
but with low selectivity (CC50=3.8 µm, SI=2.6).
assay. The activity/selectivity profiles of 5 and 6 were similar
Anti-SARS-CoV Activity The potential for all the syn- in both assays in that 5 showed moderate antiviral activity
thesized compounds to inhibit the SARS-CoV in cell culture with low selectivity while 6 was neither active nor cytotoxic.
Table 1. Antiviral Activity of the Synthesized Compounds against HCV and SARS-CoV
Anti-SARS-CoV activity (µm)
Anti-HCV activity (µm)
Compound
Visual assay
Neutral red assay
a)
b)
EC50
CC50
SIc)
EC50
CC50
SI
EC50
CC50
SI
1
2
3
4
5
6
>20
>20
>20
1.5
>20
>20
0.07
>20
>20
>20
3.8
13.8
>20
1.0
1.0
1.0
2.6
<0.7
1.0
34
68
38
42
32
>100
68
>100
>100
42
>100
—
>100
>2.9
1.0
>2.6
>2.4
1.3
1.0
—
>150
52
51
>45
>100
38
>100
>100
45
>100
38
89
—
>100
>1.9
>2.0
<1.0
1.0
1.0
<1.0
—
>100
—
>89
—
rIFNα-2bd)
M128553e)
>2
—
>28.6
—
—
0.7
0.58
>170
a) EC50: compound concentration that reduces viral replication by 50%. b) CC50: compound concentration that reduces cell viability by 50%. c) SI=CC50/EC50. d) Recombi-
nant human interferon α-2b was used as a positive control for anti-HCV activity assay. e) SARS-CoV M(pro) protease inhibitor (Maxim Pharmaceuticals) was used as a posi-
tive control for the anti-SARS-CoV activity assay.

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Vol. 61, No. 4
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In this proof-of-concept study, we introduced a 3-amino-
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Acknowledgments This research was supported by Basic
Science Research Program through the National Research
Foundation of Korea (NRF) funded by the Ministry of Edu-
cation, Science and Technology (2010-0008260), by a Grant
of the Korea Healthcare Technology R&D Project, Ministry
for Health, Welfare & Family Affairs, Republic of Korea
(A08-4628-AA2023-08N1-00010A), by Priority Research
Centers Program through the National Research Foundation
of Korea (NRF) funded by the Ministry of Education, Science
and Technology (2009-0093824), and by a Grant from Next
Generation Bio-Green 21 PJ007982 (Korea Rural Develop-
ment Administration). This project has been funded in part
with Federal Funds from the Division of Microbiology and
Infectious Diseases, National Institute of Allergy and Infec-
tious Diseases, National Institute of Health, Department of
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