Synthesis and Antiviral Evaluation of Some 3′-Fluoro Bicyclic Nucleoside Analogues

Article abstract of DOI:10.1081/NCN-120027813

The synthesis of 3′-fluoro analogues of recently discovered highly potent anti-VZV furanopyrimidine deoxynucleosides (BCNAs) is herein reported, for both the alkyl and alkylphenyl series. The compounds are tested against a range of herpes viruses and disp

Full text of DOI:10.1081/NCN-120027813

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Synthesis and Antiviral Evaluation of Some 3′‐Fluoro
Bicyclic Nucleoside Analogues
Christopher McGuigan a , Antonella Carangio a , Robert Snoeck b , Graciela Andrei b , Erik
De Clercq b & Jan Balzarini b
a Welsh School of Pharmacy , Cardiff University , King Edward VII Avenue, Cardiff, CF10
3XF, UK
b Rega Institute for Medical Research , Katholieke Universiteit Leuven , Leuven, B‐3000,
Belgium
Published online: 01 Jun 2007.
To cite this article: Christopher McGuigan , Antonella Carangio , Robert Snoeck , Graciela Andrei , Erik De Clercq &
Jan Balzarini (2004) Synthesis and Antiviral Evaluation of Some 3′‐Fluoro Bicyclic Nucleoside Analogues , Nucleosides,
Nucleotides and Nucleic Acids, 23:1-2, 1-5, DOI: 10.1081/NCN-120027813
To link to this article: http://dx.doi.org/10.1081/NCN-120027813
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NUCLEOSIDES, NUCLEOTIDES & NUCLEIC ACIDS
Vol. 23, Nos. 1 & 2, pp. 1–5, 2004
Synthesis and Antiviral Evaluation of Some 3’-Fluoro
Bicyclic Nucleoside Analoguesy
1
2
Christopher McGuigan,1, Antonella Carangio, Robert Snoeck,
*
Graciela Andrei,2 Erik De Clercq,2 and Jan Balzarini2
1Welsh School of Pharmacy, Cardiff University, Cardiff, UK
2Rega Institute for Medical Research, Katholieke Universiteit Leuven,
Leuven, Belgium
ABSTRACT
The synthesis of 3’-fluoro analogues of recently discovered highly potent anti-VZV
furanopyrimidine deoxynucleosides (BCNAs) is herein reported, for both the alkyl
and alkylphenyl series. The compounds are tested against a range of herpes viruses
and display poor activity, strongly supporting the notion of the importance of the
presence of a 3’-OH for antiviral activity.
Key Words: VZV; Bicyclic nucleoside analogues; 3’-OH.
INTRODUCTION
We have reported[1] the potent and selective anti-VZV (Varicella Zoster Virus)
activity for bicyclic furanopyrimidine deoxynucleosides such as 1 (Figure 1). The
corresponding alkylphenyl analogues 2 are even more potent, with EC50 values vs.
yIn honor and celebration of the 70th birthday of Professor Leroy B. Townsend.
*
Correspondence: Christopher McGuigan, Welsh School of Pharmacy, Cardiff University, King
Edward VII Avenue, Cardiff, CF10 3XF, UK; Fax: + 44-29-2087-4537; E-mail: mcguigan@
cardiff.ac.uk.
1
DOI: 10.1081/NCN-120027813
1525-7770 (Print); 1532-2335 (Online)
www.dekker.com
Copyright D 2004 by Marcel Dekker, Inc.

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McGuigan et al.
Figure 1. Structures of potent anti-VZV bicyclic furanopyrimidines (BCNAs). For optimal
activity R is C8H17 and R’ is C5H11.
VZV in vitro in the higher picomolar range.[2] The compounds exhibit complete
specificity for VZV with no activity detectable against any other DNA or RNA viruses
studied. We have now prepared a moderate series of compounds of this general family
and recently reviewed the SAR[3,4] and biochemistry[5,6] of these agents.
Whilst we have carried out fairly extensive studies in the base region of these
compounds, we have to date reported little variation in the sugar. We did note[4] that
the 3’-methoxy analogue of (1), in fact with a C10 alkyl side chain, was > 10,000 times
less active than the parent 2’-deoxy nucleoside. This indicated little tolerance for
modification at the 3’-position.
The introduction of fluorine atoms in the sugar ring of nucleosides is well es-
tablished both as a means of stabilising the glycosidic bond, as in FMAU[7] or indeed
as to afford an antiviral effect, as in FLT.[8–10]
Scheme 1.

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3
Table 1.
EC50/mM
Compound
VZV OKA
VZV YS
VZV TKꢀ07
VZV TKꢀYS
CC50/mM
3a
3b
1
> 20
> 2
> 20
> 2
> 20
> 2
> 200
> 2
> 200
5.2
0.008
0.0003
0.024
0.0001
> 50
> 5
> 50
> 5
> 50
> 200
2
Thus, we sought the synthesis of analogues 3 of 1 and 2 with a 3’-fluorine sub-
stituent. The key synthon required for this preparation, following our established
procedures[1,2] was 5-iodo-2’,3’-dideoxy-3’-fluorouridine. This type of compound has
been prepared previously[10,11] for the synthesis of 3’-fluoro analogues of thymidine and
uridine, and we closely followed these published procedures (Scheme 1).
Thus, selective 5’-protection of 5-iodo-2’-deoxyuridine (IDU, 4) with trityl chloride
followed by treatment with mesyl chloride gave 5 in 94% yield. Following the
published procedure[11] the configuration of the 3’-group was readily inverted to give
the xylo compound 6 in 64% using refluxing ethanic sodium hydroxide. The 3’-b
configuration of 6 was confirmed by a positive NOESY experiment (data not shown).
Treatment of 6 with DAST[12] in dry THF at ambient temperature gave the 5’-trityl-
3’-fluoro nucleoside 7 in moderate yield, and the 5’-trityl group was removed under
standard acidic conditions to yield 8 as the key synthon. The successful introduction of
a fluorine into 8 was confirmed by 19F-NMR, with a signal at d—174 which showed a
large doublet splitting (J = ca. 50Hz) to the 3’-H in the 1H-NMR and to the 3’-C
(J = ca. 175 Hz) in the 13C NMR. All of these data are consistent with literature values
on close analogues.[11] The stereochemistry of the fluorine atom in 7 (and thus 8) was
fully confirmed as alpha by a NOESY experiment. Thus a clear cross peak between
H-1’ and H-2’ (alpha) distinguished the two H2’ protons, with the beta proton being more
upfield (ca. 2.6, 2.4 ppm). A clear cross peak is hence noted between H-2’ (beta) and the
H-3’ proton, proving the orientation of the 3’-fluorine as alpha.
Following our established procedures[1,2] synthon 8 was readily converted into the
octyl (3a) and p-pentylphenyl (3b) BCNAs using a two-step Pd- and Cu-catalysed process
(Scheme 1).a Full spectroscopic, spectrometric and analytical data completely supported
the structure and purity of 3a–b and confirmed the retention of a 3’-alpha-F Substituent.
Thus, compounds 3a–b were evaluated as inhibitors of VZV in vitro following our
established procedures, and using standard compounds 1 and 2 as positive biological
controls,[1,2] with data being presented in the Table 1.
As noted in the Table 1 compounds 3a–b display no detectable anti-VZV activity
at the highest concentration tested; 3a is thus > 1000 times less active than its parent
deoxynucleoside 1 and 3b is > 10,000 times less active than 2. Interestingly, 3b does
display some cytotoxicity, at ca. 5 mM. This is unusual for compounds of the BCNA
family which are in general non-cytotoxic, although some long chain analogues of 2
did display toxicity at ca. 20 mM.[2]
aSelected experimental procedures and data for 3a–b: 3-(2,3-Dideoxy-3-fluoro-b-D-ribofurano-
syl)-6-(octyl)-2,3-dihydrofuro-[2,3-d]pyrimidin-2-one (3a).

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McGuigan et al.
These data clearly show that the 3’-fluoro analogues of 1 and 2 are not active
against VZV, and that the 3’-OH appears to be essential for antiviral activity. This
confirms our earlier conclusion, based on the 3’-methyl ether[4] and implies little
tolerance in general for 3’-modification. Most likely, it may be that a free 3’-OH is
necessary for (VZV) thymidine kinase-mediated activation of those agents, which is
thought to be pre-requisite for anti-VZV activity,[5] or that a subsequent metabolic step
depends on the presence of a free 3’-OH, or both. We are currently pursuing a number
of strategies to address these questions.
To a stirred solution of 5-iodo-2’,3’-dideoxy-3’-fluorouridine (200 mg, 0.562 mmol)
in dry dimethylformamide (5 ml) at room temperature under a nitrogen atmosphere,
1-decyne (0.3 ml, 1.68 mmol), tetrakis(triphenylphosphine) palladium (0) (65 mg,
0.0562 mmol), copper (I) iodide (21 mg, 0.112 mmol) and diisopropylethylamine
(0.2 ml, 1.12 mmol) were added. The reaction mixture was stirred at room temperature
for 19 hours, after which time TLC (chloroform/methanol 95:5) showed complete
conversion of the starting material. Copper(I) iodide (21 mg, 0.112 mmol), and
triethylamine (8 ml) were added to the mixture which was subsequently refluxed for
8 hours. The reaction mixture was then concentrated in vacuo, and the resulting residue
was dissolved inꢀdichloromethane/methanol (1:1) (6 ml), and an excess of Amberlite
IRA-400 (HCO3 form) was added and stirred at room temperature for 30 minutes.
Then the resin was filtered, washed with methanol and the combined filtrate was
evaporated to dryness. The crude product was purified by silica column chromatog-
raphy, using an eluent of chloroform/methanol (95:5). The appropriate fractions were
combined and the solvent was removed in vacuo to yield the product, which was
further purified by trituration with methanol, yielding the pure product (178 mg, 86%)
as a white solid. Mp: > 240°C (decomposes).
1
IR (KBr): 3338.0 (OH), 2921.9 (aliphatic), 1671.9 (CO amide), 1112.5 (C–F). H-
nmr (d6-DMSO; 300 MHz): 8.57 (1H, s, H-4), 6.53 (1H, s, H-5), 6.20 (1H, dd, J = 5.6
and 8.3 Hz, H-1’), 5.36 (1H, dm, J = 49.3 Hz H-3’), 5.22 (1H, t, J = 5.2 Hz, 5’-OH),
4.33 (1H, dm, J = 26.2 Hz, H-4’), 3.64 (2H, m, H-5’), 2.74 (1H, m, H-2a’), 2.63 (2H, t,
J = 7.3 Hz, a-CH2), 2.31–2.08 (1H, m, H-2b’), 1.59 (2H, m, CH2), 1.23 (10H, m,
5 ꢁ CH2), 0.84 (3H, t, J = 6.6 Hz, o-CH3). 13C-nmr (d6-DMSO; 75 MHz): 14.3 (CH3),
22.4, 26.7, 27.7, 28.7, 28.9, 29.0, 31.6 (7 ꢁ CH2), 39.5 (d, J = 20.2 Hz, C-2’), 61.0 (d,
J = 11.1 Hz, C-5’), 86.5 (d, J = 22.5 Hz, C-4’), 88.0 (C-1’), 95.2 (d, J = 174.2 Hz, C-
3’), 100.1 (C-5) 107.0 (C-4a), 136.9 (C-4), 154.1 (C-6), 158.9 (C-2), 171.7 (C-7a). MS
(ES+) m/e 389 (MNa+, 100%), 271 (baseNa+, 10%). Accurate mass: C19H27N2O4FNa
requires : 389.1853; found: 389.1847.
3-(2,3-Dideoxy-3-fluoro- -D-ribofuranosyl)-6-(4-pentylphenyl)-2,3,-dihydro-
furo-[2,3-d]pyrimidin-2-one (3b). This was prepared entirely as outlined for
(3a) above, but using 4-n-pentylphenylacetylene, to yield the product (235 mg, 60%)
as a white solid. Mp: > 240°C (decomposes).
1
IR (KBr): 3354.9 (OH), 2921.3 (aliphatic), 1668.7 (CO amide), 1112.2 (C–F). H-
nmr (d6-DMSO; 300 MHz): 7.99 (1H, s, H-4), 7.74 (2H, Ha)—7.33 (2H, Hb) (AA’BB’
system, J = 8.1 Hz), 7.22 (1H, s, H-5), 6.25 (1H, dd, J = 5.7 and 7.9 Hz, H-1’), 5.39
(1H, dm, J = 50.1 Hz, H-3’), 5.28 (1H, t, J = 5.1 Hz, 5’-OH), 4.38 (1H, dm, J = 25.9
Hz, H-4’), 3.70 (2H, m, H-5’), 2.79 (1H, m, H-2a’), 2.61 (2H, t, J = 7.5 Hz, a-CH2),
2.39–2.16 (1H, m, H-2b’), 1.65 (2H, m, CH2), 1.30 (4H, m, 2 ꢁ CH2), 0.86 (3H, t,
J = 6.7 Hz, CH3). 13C-nmr (d6-DMSO; 75 MHz): 14.3 (CH3), 22.3, 30.8, 31.2, 35.3

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3’-Fluoro Bicyclic Nucleoside Analogues
5
(4 ꢁ CH2), 39.2 (d, J = 19.8 Hz, C-2’), 61.0 (d, J = 11.1 Hz, C-5’), 86.6 (d, J = 22.6
Hz, C-4’), 88.2 (C-1’), 95.1 (d, J = 174.3 Hz, C-3’), 99.0 (C-5) 107.5 (C-4a), 124.9 (C-
Hb), 126.1, (C-ipso), 129.4 (C-Ha) 138.0 (C-4), 144.5 (C-para), 154.11 (C-6), 154.4 (C-
2), 171.5 (C-7a). MS (ES+) m/e 423 (MNa+, 100%). Accurate mass: C22H25N2O4FNa
requires : 423.1696; found: 423.1700. Anal. Calcd for C22H25N2O4F: C, 65.99%; H,
6.29%; N, 7.00%. Found: C, 66.19%; H, 6.05%; N, 6.87%.
ACKNOWLEDGMENTS
The authors are grateful to Mrs. Anita Camps, Mr. Steven Carmans, and Ms. Lies
Vandenheurck for excellent technical assistance. This research was supported by grants
from the Belgian Fonds voor Geneeskundig Wetenschappelijk Onderzoek, the Belgian
Geconcerteerde Onderzoeksacties and The Leverhulme Trust. We also thank Helen
Murphy for excellent secretarial assistance.
REFERENCES
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4484.
2. McGuigan, C.; Barucki, H.; Blewett, S.; Carangio, A.; Erichsen, J.T.; Andrei, G.;
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Received August 8, 2003
Accepted September 15, 2003

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