Synthesis and antiviral activity of 7-deazaneplanocin a against orthopoxviruses (vaccinia and cowpox virus)

Article abstract of DOI:10.1016/j.bmcl.2005.10.007

An efficient method for the synthesis of 7-deazaneplanocin A (2) has been accomplished by the condensation of cyclopentenol 3 with 6-chloro-7-deazapurine followed by subsequent functional group manipulations. The synthesized 7-deazaneplanocin A (2) exhibi

Full text of DOI:10.1016/j.bmcl.2005.10.007

Bioorganic & Medicinal Chemistry Letters 16 (2006) 285–287
Synthesis and antiviral activity of 7-deazaneplanocin A against
orthopoxviruses (vaccinia and cowpox virus)
Balakumar Arumugham,a Hyo-Joong Kim,a Mark N. Prichard,b
Earl R. Kernb and Chung K. Chua,*
aUniversity of Georgia College of Pharmacy, Athens, GA 30602, USA
bUniversity of Alabama School of Medicine, Birmingham, AL 35294, USA
Received 1 September 2005; revised 4 October 2005; accepted 4 October 2005
Available online 3 November 2005
Abstract—An efficient method for the synthesis of 7-deazaneplanocin A (2) has been accomplished by the condensation of cyclo-
pentenol 3 with 6-chloro-7-deazapurine followed by subsequent functional group manipulations. The synthesized 7-deazaneplanocin
A (2) exhibited potent antiviral activity against cowpox and vaccinia viruses without cytotoxicity in HFF cells.
Ó 2005 Elsevier Ltd. All rights reserved.
Neplanocin A (NPA)1 (1) is a naturally occurring carbo-
cyclic nucleoside, which has a cyclopentenyl sugar-substi-
tuted moiety. NPA has attracted much attention because
it showed interesting biological activities including antitu-
mor and broad spectrum antiviral activities.2 NPAꢀs bio-
logical activity may be explained in part by the inhibition
of S-adenosyl-L-homocysteine (AdoHcy) hydrolase,
which is essential for viral mRNA capping methylation.3
Structural modifications of NPA have yielded a number
of biologically active compounds. Among them, modifi-
cation on the C60-position of NPA has produced potent
analogues against malaria, hepatitis B virus, and hepatitis
C virus.4,5 Base (adenine) modified NPA analogues such
as 2-fluoro-6 and 3-deaza-7 derivatives showed potent
antiviral activity. Recently, 7-deazaadenine moiety was
introduced in place of adenine in 20-C-ribonucleoside.8
According to the report, the introduction of 7-deazaade-
nine moiety resulted in good enzymatic stability as well as
a significant anti-HCV activity. These results prompted us
to pursue the synthesis and biological evaluation of a 7-
deazaneplanocin A analogue (2), which has not been
reported so far.
virus and smallpox was responsible for serious illness
and death until the development of a successful vaccine.
The need for the therapeutic agent for the treatment of
orthopoxvirus infections was not urgent since the erad-
ication of smallpox from the world in 1980. However,
recent concern on bioterrorism rekindled the interest
on the treatment of patients, who were infected with
the orthopoxviruses, including variola virus. The antivi-
ral activities of neplanocin A and its analogues (nepla-
nocin C, neplanocin D, 20-deoxy NPA, 3-deaza NPA,
and 50-nor NPA) against surrogate vaccinia virus infec-
tions were reported in the literature.2,10 Recently, several
carbocyclic analogues also showed antiviral activity
against orthopoxviruses.11
In order to investigate the structure–activity relation-
ships of NPA, a more convenient and facile synthetic
methodology for key intermediates is required. During
the course of drug discovery program for carbocyclic
nucleosides, we developed a convergent method for the
synthesis of cyclopentenyl carbocyclic nucleosides.12
The synthetic strategy employed was the coupling of
cyclopentenol and heterocyclic bases to afford various
enantiomerically pure carbocyclic nucleosides. Herein,
we report the synthesis and antiviral activity of
7-deazaneplanocin A (2) (Fig. 1).
Variola, monkeypox, cowpox, and vaccinia viruses are
orthopoxviruses, which can infect humans.9 Among
orthopoxviruses, variola virus is the most dangerous
The preparation of 7-deazaneplanocin A (2) is shown in
Scheme 1. The cyclopentenol 3, which was prepared
according to the literature with slight modifications of
reported method,12 was coupled with 6-chloro-7-dea-
Keywords: 7-Deazaneplanocin A; Vaccinia; Cowpox; Orthopoxviruses.
*
Corresponding author. Tel.: +1 706 542 5379; fax: +1 706 542
5381; e-mail: dchu@rx.uga.edu
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.10.007

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B. Arumugham et al. / Bioorg. Med. Chem. Lett. 16 (2006) 285–287
NH
NH
2
known to be one of the most potent agents against
orthopoxviruses.16
2
N
N
N
N
N
HO
HO
N
N
In summary, we have synthesized 7-deazaneplanocin A
(2) by the coupling of functionalized cyclopentenol (3)
with 7-deazapurine. The synthesized 7-deazaneplanocin
A (2) showed potent antiviral activity against ortho-
poxviruses (cowpox and vaccinia) without any signifi-
cant cytotoxicity. Further biological evaluation to
delineate the mode of action as well as study of animal
models to assess the full potential of 7-deazaneplanocin
A is warranted.
OH OH
OH OH
2
1
Neplanocin A (NPA)
7-Deaza NPA
Figure 1. Structures of NPA and 7-deaza NPA.
Cl
N
N
N
TBDPSO
TBDPSO
HO
Ref. 12
O
a
OH
OH
Acknowledgment
O
O
O
O
b
OH OH
D-Ribose
3
4
This research was supported by grants and contracts
from National Institute of Allergy and Infectious Dis-
eases (U019 AI 056540, N01 AI30049).
NH
2
NH
2
N
N
N
TBDPSO
N
c
N
HO
N
References and notes
O
O
OH OH
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2
5
Scheme 1. Synthesis of 7-deazaneplanocin
A (2). Reagents and
conditions: (a) 6-chloro-7-deazapurine, PPh3, DIAD, THF, 81%; (b)
NH3, MeOH, 100 °C, 12 h, 83%; (c) 1—HCl, MeOH, 2—NaHCO3
63%.
zapurine13 under the Mitsunobu reaction conditions to
give compound 4 in 81% yield. Treatment of 4 with
methanolic ammonia at 100 °C for 12 h provided com-
pound 5 in 83% yield. Deprotection in acidic conditions
of 5 in 10% HCl in methanol followed by neutralization
with NaHCO3 gave 7-deazaneplanocin A (2)14 in 63%
yield.
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The antiviral activity of 7-deazaneplanocin A (2) was
evaluated against a wide variety of viruses, including
cowpox, vaccinia, yellow fever, dengue type 2, Punta
Toro A, SARSCoV, Tacaribe, VEE, and West Nile.
Among the tested viruses, 7-deazaneplanocin A exhibit-
ed potent activity against cowpox and vaccinia viruses in
a CPE reduction assay without any significant cytotox-
icity in HFF cells as shown in Table 1.
Although Neplanocin A has potent broad spectrum
antiviral activity including orthopoxviruses,2 significant
cytotoxicity of NPA limited its usefulness as an antiviral
agent.15 However, 7-deaza NPA (2) did not show any
cytotoxicity up to 300 lM in HFF cells in a neutral
red assay. Furthermore, 7-deaza NPA was more potent
than that of cidofovir in this assay, which has been
Table 1. Antiviral activity of 7-deazaneplanocin A (2) against cowpox
and vaccinia viruses
Virus
Cell line
EC50 EC90 Cytotoxicity Cidofovira
13. 6-Chloro-7-deazapurine is commercially available at
Toronto Research Chemicals, Inc.
(lM) (lM) CC50 (lM)
EC50 (lM)
23
14. Data for compound 2: mp 196–198 °C; ½aꢀD ꢁ43.80 (c
Cowpox HFF cells 1.2
Vaccinia HFF cells 3.4
4.6
21.5
>300
>300
5.0
4.8
0.10, MeOH); 1H NMR (500 Hz, DMSO-d6) d 8.04 (s,
1H), 7.00 (d, 3.5 Hz, 1H), 6.94 (br s, 2H), 6.54 (d, 3.5 Hz,
1H), 5.58 (m, 1H), 5.52 (m, 1H), 4.99 (br s, 1H), 4.88 (br s,
a Positive control.

B. Arumugham et al. / Bioorg. Med. Chem. Lett. 16 (2006) 285–287
287
2H), 4.40 (d, 4.5 Hz, 1H), 4.05–4.15 (m, 3H); 13C NMR
(125 MHz, DMSO-d6) 157.9, 151.9, 150.4, 2150.2, 124.9,
121.8, 103.2, 99.4, 77.6, 72.9, 64.2, 59.0; UV (H2O) kmax
273.0 nm (e 9281, pH 2), 272.0 nm (e 9068, pH 7),
272.0 nm (e 9244, pH 11); Anal. Calcd for C12H14N4O3Æ-
H2O: C, 51.42; H, 5.75; N, 19.99. Found: C, 51.85; H,
5.22; N, 19.67.
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