Bicyclic nucleoside inhibitors of varicella-zoster virus (VZV): The effect of a terminal halogen substitution in the side-chain

Article abstract of DOI:10.1016/S0960-894X(00)00193-1

Preliminary SAR studies on the side chain of a new class of antiviral nucleosides have shown that terminal substitution in the side-chain, with a halogen atom, lead to potent and highly specific anti-VZV agents. (C) 2000 Elsevier Science Ltd. All rights reserved.

Full text of DOI:10.1016/S0960-894X(00)00193-1

Bioorganic & Medicinal Chemistry Letters 10 (2000) 1215±1217
Bicyclic Nucleoside Inhibitors of Varicella-Zoster Virus (VZV):
The E€ect of a Terminal Halogen Substitution in the Side-Chain
Andrea Brancale, a Christopher McGuigan, a,* Graciela Andrei, b Robert Snoeck, b
Erik De Clercq b and Jan Balzarini b
aWelsh School of Pharmacy, Cardi€ University, King Edward VII Avenue, Cardi€ CF10 3XF, UK
bRega Institute for Medical Research, Katholieke Universiteit Leuven, B-3000, Leuven, Belgium
Received 21 January 2000; accepted 27 March 2000
AbstractÐPreliminary SAR studies on the side chain of a new class of antiviral nucleosides have shown that terminal substitution in the
side-chain, with a halogen atom, lead to potent and highly speci®c anti-VZV agents. # 2000 Elsevier Science Ltd. All rights reserved.
We have recently reported1 the discovery of an entirely
new category of potent anti-VZV agents based on novel
deoxynucleoside analogues with an unusual ¯uorescent
bicyclic base bearing a long alkyl side-chain, with an
optimum length of C8±C10 for antiviral activity (1). The
role of this peculiar structural feature for the antiviral
activity is still not clear and our groups are carrying out
several structure±activity relationship studies, which
involve modi®cations of the lipophilic chain of this new
class of anti-VZV nucleosides.
atom in the terminal position of the side chain. All the
compounds of this new class of anti-VZV nucleosides
were prepared by a Pd-catalysed coupling reaction of 5-
iodo-20-deoxyuridine with terminal alkynes, followed by
treatment of the 5-alkynyl nucleosides thus obtained,
with copper (I) iodide, leading to the desired ¯uorescent
derivatives.1,2 These two steps (coupling and cyclisation)
can be conducted in one ¯ask without isolating the 5-
alkynyl derivatives but, in the present case, the inter-
mediates were isolated and biologically evaluated.
The preparation of the appropriate terminal alkyne
precursors was achieved by converting 10-undecyn-1-ol
(2) into the desired halides 3a±d (Scheme 1). The ¯uoro-
alkyne 3a was obtained by treatment of the alcohol 2
with DAST,3 while 3b was prepared by reaction with
thionyl chloride, in the presence of pyridine.4
Carbon tetrabromide and triphenylphosphine5 were
used to obtain the bromo-alkyne 3c, and the reaction of
2 with iodine, in the presence of triphenylphosphine and
imidazole,6 gave the iodo derivative 3d. All of these
terminal alkynes (3a±d) were prepared in quantitative
yields and were successfully coupled to 5-iodo-20-deoxy-
uridine, leading to the 5-alkynyl nucleosides 4a±d7 which,
after the cyclisation step, gave the desired nucleosides
5a±d8,9 (Scheme 2). Compounds 4a±d and 5a±d were
characterized by high-®eld heteronuclear NMR and
mass spectrometry.
The fact that a minimum length of eight carbon atoms
in the side chain is fundamental for potent anti-VZV
activity,1 suggests the presence of a lipophilic pocket in
relation to that position, potentially either in the thy-
midine kinase or the DNA polymerase of VZV. In order
to probe this, we planned to prepare several analogues
bearing di€erent groups at the end of the chain. We
report here the synthesis and the biological evaluation
of several new compounds, which contain a halogen
Compounds 4a±d and 5a±d were evaluated as inhibitors
of a variety of herpes viruses in vitro, including herpes
simplex virus type 1 (HSV-1) and type 2 (HSV-2), var-
icella-zoster virus, cytomegalovirus and HIV-1. Data
*Corresponding author. Tel.: +44-29-20874537; fax: +44-29-
20874537; e-mail: mcguigan@cardi€.ac.uk
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00193-1

1216
A. Brancale et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1215±1217
for VZV in human embryonic lung (HEL) cells are
shown in Table 1. The antiviral activity (EC50) was
measured as the e€ective concentration required to
reduce virus plaque formation by 50%. In Table 1 the
activity of these new nucleosides is compared with that
of the lead compound 1 and the reference compound
acyclovir (ACV).
The target compounds 5a±d did not prove signi®cantly
di€erent from the lead compound 1 in their anti-VZV
potency. No cytotoxicity was observed for these com-
pounds at the highest concentration tested, while the 5-
alkynyl nucleosides 4a±d showed some cytotoxicity, with
a markedly lower anti-VZV activity, but still in the same
order as that of ACV. It cannot be excluded that some
Scheme 1. (i) DAST, DCM; 78 ꢀC to rt 1 h; (ii) SOCl2, pyridine, CH2Cl2; rt 1 h; (iii) CBr4, PPh3, Et2O; rt 2 h; (iv) I2, PPh3, imidazole, THF; rt 1 h.
Scheme 2.
Table 1.
Compound
EC50 (mM)a
VZV YS Strain
EC50 (mM)a
VZV OKA Strain
EC50 (mM)a
EC50 (mM)a
MCC (mM)b
CC50 (mM)c
TK VZVd 07/1 Strain
TK VZVd YS/R Strain
4a
4b
4c
4d
5a
5b
5c
5d
1
ACV
22
2.8
0.8
26
3.6
1.1
33
10
16
36
>20
15
>50
>50
>50
74
23
9.6
2.5
31
>20
13
200
200
50
>50
>50
>200
>200
50
116
74
97
68
200
200
>50
>200
>50
>200
6
13
0.014
0.012
0.031
0.034
0.008
1.0
0.022
0.007
0.026
0.061
0.015
2.9
50
>50
>50
125
>50
>200
aEC50, 50% e€ective concentration, required to reduce virus plaque formation 50%.
bMCC, minimal cytotoxic concentration, required to alter microscopically detectable cell morphology.
cCC50, 50% cytotoxic concentration, required to inhibit Hel cell growth by 50%
dTK , thymidine kinase-de®cient.

A. Brancale et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1215±1217
1217
of the observed activity of the alkynyl precursors arises
from in situ cyclisation to the corresponding bicyclic
system. As all the other compounds of this class,1 the
nucleosides 5a±d displayed no signi®cant activity against
thymidine kinase de®cient-VZV strains assays con®rm-
ing their dependence on VZV thymidine kinase-mediated
activation, for their biological activity, and did not show
activity against HSV-1, HSV-2, CMV or HIV-1 (data
not shown). The results obtained with these new
nucleosides are extremely encouraging and more exten-
sive work is currently in progress in our laboratories to
delineate the e€ect of side-chain modi®cations.
tered and the solvent removed in vacuo, yielding to the
product 2b as a colourless oil in quantitative yield.
5. Danishefsky, S.; Berman, E. M.; Ciufolini, M.; Etheredge,
S. J.; Segmuller, B. E. J. Am. Chem. Soc. 1985, 107, 3891.
6. Corey, E. J.; Pyne, S. G.; Su, W. Tetrahedron. Lett. 1983,
24, 4883.
7. Preparation of 4b: To a stirred solution of 5-iodo-20-deox-
yuridine (800 mg, 2.26 mmol) in dry dimethylformamide (8
mL), at room temperature under a nitrogen atmosphere, was
added diisopropylethylamine (584 mg, 0.80 mL, 4.52 mmol), 2b
(1.26 g, 6.78 mmol), tetrakis(triphenylphosphine)palladium(0)
(261 mg, 0.226 mmol) and copper (I) iodide (86 mg, 0.452
mmol). The reaction mixture was stirred at room temperature
for 19 h, after which time the solvent was removed in vacuo. The
resulting residue was dissolved in dichloromethane:methanol
(1:1) (6 mL) and an excess of Amberlite IRA-400 (HCO3
form) was added and the mixture was stirred for 30 min. The
resin was then ®ltered, washed with methanol and the com-
bined ®ltrate was evaporated to dryness. The crude product
was puri®ed by silica gel column chromatography using ethyl
acetate as eluent. The appropriate fractions were combined
and the solvent removed in vacuo to yield 4b as a white solid
(540 mg, 58% yield).
Acknowledgements
The authors are grateful to Mrs. Ann Absillis, Mrs.
Anita Camps, Mrs. Frieda De Meyer, Miss Lies Van-
denheurck and Mrs Anita Van Lierde for excellent
technical assistance. The research was supported by
grants from Therapeutic Developments Ltd. Cardi€, the
Belgian Fonds voor Wetenschappelijk Onderzoek
Vlaanderen and the Belgian Geconcerteerde Onder-
zoeksacties Vlaamse Gemeenschap. We also thank
Helen Murphy for excellent secretarial assistance.
8. Preparation of 5b: to a stirred solution of 4b (200 mg) in
methanol:triethylamine (7:3) (20 mL), at room temperature
under a nitrogen atmosphere, was added copper (I) iodide (20
mg). The reaction mixture was then heated to re¯ux and stir-
red for 4 h. The solvent was removed in vacuo and the crude
product puri®ed by silica column chromatography, using an
initial eluent of ethyl acetate, followed by an eluent of ethyl
acetate:methanol (9:1). The appropriate fractions were com-
bined and the solvent removed in vacuo yielding the pure
product 5b (140 mg, 70% yield).
References and Notes
1
9. Signi®cant spectroscopic data for 5b: H NMR (d6-DMSO;
300 MHz): 8.68 (1H, s, H-4), 6.44 (1H, s, H-5), 6.17 (1H, dd,
1. McGuigan, C.; Yarnold, C. J.; Jones, G.; Velazquez, S.;
Barucki, H.; Brancale, A.; Andrei, G.; Snoeck, R.; De Clercq,
E.; Balzarini, J. J. Med. Chem. 1999, 42, 4479.
3J=6.1 Hz, H-10), 5.29 (1H, d, J=4.3 Hz, 30-OH), 5.13 (1H,
3
t, J=5.3 Hz, 50-OH), 4.24 (1H, m, H-30), 3.92 (1H, m, H-40),
3
2. Robins, M. J.; Barr, P. J. J. Org. Chem. 1983, 48, 1854.
3. Middleton, J. J. Org. Chem. 1975, 40, 574.
3.65 (4H, m, H-50, CH2Cl), 2.65 (2H, t, 3J=7.2 Hz, base-
CH2), 2.38, 2.05 (2H, m, H-20), 1.74±1.30 (14H, m, 7ÂCH2).
13C NMR (d6-DMSO; 75 MHz): 26.6, 26.7, 27.7, 28.5, 28.7,
28.9, 29.1, 32.4 (8ÂCH2), 41.6 (C-20), 45.8 (CH2Cl), 61.1 (C-
50), 70.0 (C-30), 87.7, 88.4 (C-10, C-40), 100.1 (C-5), 106.7 (C-
4a), 137.1 (C-4), 154.1 (C-2), 158.7 (C-6), 171.5 (C-7a). Mass
spectrum (ES±MS (+ve) MNOBA matrix); m/z 435 (10%,
[MNa]+), 413 (50%, [MH]+), 297 (100%, [baseH]+). FAB
m/e 435.1680 (MNa+ C20H23Cl N2O5Na requires 435.1663).
4. Preparation of 3b: To a stirred solution 10-undecyn-1-ol (2.0
g, 11.88 mmol) in dichloromethane (10 mL) was added thionyl
chloride (20.7 mmol, 2.46 g, 1.5 mL) and pyridine (11.88 mmol,
0.94 g, 0.96 mL). The reaction was then left stirred for 1 h at
room temperature. The solvent was evaporated, water was
added to the reaction mixture and then extracted with di-
chloromethane. The organic layer was dried on MgSO4, ®l-