Synthesis and antiviral evaluation of acyclic azanucleosides developed from sulfanilamide as a lead structure

Article abstract of DOI:10.1016/j.bmc.2008.08.041

The acyclic azanucleosides with 2-, 3-, or 4-aminobenzenesulfonyl function at the nitrogen atom of the sugar mimic were prepared by coupling of 2-, 3-, or 4-nitro-N-(2-pivaloyloxyethyl)-N-(pivaloyloxymethyl)benzenesulfonamide with the silylated pyrimidine nucleobases followed by the reduction of the nitro group with sodium dithionite in aqueous solution or the palladium-catalysed transfer hydrogenation. The azanucleosides were evaluated for, but found to be devoid of, activity against several RNA- and DNA-viruses in vitro.

Full text of DOI:10.1016/j.bmc.2008.08.041

Bioorganic & Medicinal Chemistry 16 (2008) 8379–8389
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis and antiviral evaluation of acyclic azanucleosides
developed from sulfanilamide as a lead structure
a
b
b
a,
*
´
Rafał Gawin , Erik De Clercq , Lieve Naesens , Mariola Koszytkowska-Stawinska
a Faculty of Chemistry, Warsaw University of Technology, ul. Noakowskiego 3, 00-664 Warszawa, Poland
b Rega Institute for Medical Research, Katholieke Universiteit Leuven, Minderbroedersstraat 10, B-3000 Leuven, Belgium
a r t i c l e i n f o
a b s t r a c t
Article history:
The acyclic azanucleosides with 2-, 3-, or 4-aminobenzenesulfonyl function at the nitrogen atom of the
sugar mimic were prepared by coupling of 2-, 3-, or 4-nitro-N-(2-pivaloyloxyethyl)-N-(pivaloyloxymeth-
yl)benzenesulfonamide with the silylated pyrimidine nucleobases followed by the reduction of the nitro
group with sodium dithionite in aqueous solution or the palladium-catalysed transfer hydrogenation. The
azanucleosides were evaluated for, but found to be devoid of, activity against several RNA- and DNA-
viruses in vitro.
Received 28 April 2008
Revised 6 August 2008
Accepted 20 August 2008
Available online 26 August 2008
Keywords:
Ó 2008 Elsevier Ltd. All rights reserved.
Azanucleosides
Nucleoside analogs
Antiviral agents
Sulfonamides
1. Introduction
determining the physiological activity of biologically active
compounds.10
Nucleoside analogs constitute a very important class of thera-
peutics used in the treatment of various diseases, mostly viral
infections and cancer.1 However, their clinical usefulness can be
sometimes limited by toxic side effects, poor oral bioavailability
or the emergence of drug resistance.2 Therefore, much attention
is still focused on the synthesis and biological activities of novel
nucleoside analogs, including acyclonucleosides.3 The introduction
of the sulfonamido group [R-SO2–N(H/R1)–] into a sugar4–6 or a
nucleobase7 moiety of the parent nucleoside is one of the reported
modifications. Among the sulfonamido nucleosides, however, only
a few derivatives with the sulfanilamido group (4-NH2–C6H4–SO2–
NH–) have been reported so far. This pharmacophore, found in
many biologically active compounds (such as an inhibitor of HIV-
1 protease amprenavir),8 is present in 50-deoxy-50-sulfanilamido-
furanosyl nucleosides A (Fig. 1).4b To the best of our knowledge,
their biological properties have not been examined.
2. Results and discussion
In view of the commercial availability of the nitro- or the acet-
amido-substituted benzenesulfonyl chlorides 2, we decided to pre-
pare the nitro and the acetamido precursors 5, 6, and 7 (Scheme 1,
R = NO2 or NHAc), and then to transform them into the correspond-
ing amino derivatives by reduction or hydrolysis, respectively.
The key substrates for the synthesis of 5, 6, and 7, that is, the
corresponding N-(pivaloyloxymethyl)sulfonamides 4, were ob-
tained from the reaction of 2-pivaloyloxyethylamine hydrochloride
1 with benzenesulfonyl chlorides 2 followed by the alkylation of 3
with chloromethyl pivalate (Scheme 1). N-(Pivaloyloxymethyl)sul-
O
N
NHR
H3C
SO2 N
Therefore, continuing our research program on azanucleosides,9
we decided to synthesize the pyrimidine aza-derivatives B with 2-,
3-, or 4-aminobenzenesulfonyl function at the nitrogen atom of the
sugar mimic (Fig. 1). These compounds can be considered as deriv-
atives of sulfanilamide (4-NH2–C6H4–SO2–NH2). We prepared aza-
nucleosides B in the form of the corresponding pivaloyl esters and/
or amides (R = acyl) in order to improve their lipophilicity
N
O
R1
O
SO2
H2N
O
N
N
NH
PivO
H
O
A
B
OR
(RH)N- = 2-, 3-, 4-
R1 = H, CH3, F
R = H, SO3H
Figure 1. Nucleoside analogs containing 2-, 3-, or 4-aminobenzenesulfonyl
* Corresponding author. Tel.: +48 22 234 5442; fax: +48 22 628 2741.
function.
E-mail address: mkoszyt@ch.pw.edu.pl (M. Koszytkowska-Stawin´ ska).
0968-0896/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2008.08.041

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R. Gawin et al. / Bioorg. Med. Chem. 16 (2008) 8379–8389
R
R
R
a, R = 4-NO2; b, R = 3-NO2;
c, R = 2-NO2; d, R = 4-NHAc
NH3+Cl-
ii
i
SO2
+
SO2
PivO
SO2Cl
N
N
OPiv
PivO
H
PivO
1
2a-d
3a-d (50-70)%)
4a-d (43-83%)
5-Fluorouracil,
iii or iv (R=4-NHAc)
Uracil, iii
Thymine, iii
R
R
R
F
CH3
O
NH
O
NH
O
SO2
SO2
SO2
N
N
N
N
N
NH
N
PivO
PivO
7a-d (52-70%)
PivO
5a-d (54-89%)
O
O
O
6a-d (54-76%)
Scheme 1. Reagents and conditions: (i) pyridine, dichloromethane, room temperature, overnight; (ii) PivOCH2Cl, K2CO3, DMF, room temperature, 5 days; (iii) a—nucleobase,
BSA, acetonitrile, room temperature, 1 h; b—TMSOTf, acetonitrile, room temperature, 2 days. (iv) a—5-fluorouracil, BSA, acetonitrile, room temperature, 1 h; b—SnCl4,
acetonitrile, dichloromethane, room temperature, 2 days.
fonamides 4 were transformed into 5, 6, or 7 by the one-pot base
silylation/nucleoside coupling methodology (Scheme 1).11 Deriva-
tives 4 reacted with the silylated thymine, uracil or 5-fluorouracil
in the presence of trimethylsilyl trifluoromethanesulfonate
(TMSOTf) to give the corresponding azanucleosides 5, 6, and 7 in
54–89% yields. The only exception was the coupling of the acetam-
ido derivative 4d with 5-fluorouracil; instead of the desired 7d, 4-
acetamido-N-(2-pivaloyloxyethyl)-N-(acetamidomethyl)benzene-
sulfonamide12 (not shown) was formed as the only product under
these conditions. This compound resulted from the reaction of 4d
with N-monosilylated or free acetamide, which are formed during
silylation of the nucleobase with N,O-bis(trimethylsilyl)acetamide
(BSA).13 Replacement of TMSOTf with tin(IV) chloride let us to pre-
pare 7d in 52% yield.
of palladium on charcoal, or with sodium borohydride/palladium
on charcoal mixture; unfortunately yields of the reaction products
have not been given.14g
Considering the presence of the 4-nitrobenzenesulfonamido
function in a molecule, the reduction conditions of 50-deoxy-50-
(4-nitrobenzenesulfonamido)thymidine (i.e., sodium dithionite
in alkaline medium) has attracted our considerable attention.4b
To the best of our knowledge, this reducing agent has not been
employed for the reduction of nucleoside nitro analogs being
derivatives of uracil or 5-fluorouracil so far. Therefore, we
decided to examine this method for the transformation of the ni-
tro derivatives 5, 6, and 7 into the amino azanucleosides B. Ini-
tially, the reduction of the thymine derivatives 5a–c was
examined (Scheme 2). Taking into account the NO2-isomerism
of 5a–c, the reaction was found to be not general. The reduction
of 5a (4-NO2) or 5b (3-NO2) with sodium dithionite in alkaline
solution at 90 °C was accompanied by hydrolysis of the ester
group to give the hydroxy derivatives 8a (59%) or 8b (52%),
respectively (Scheme 2, conditions (i). Reduction of the 2-NO2
isomer 5c under the same conditions afforded a complex mix-
ture, from which the amino derivative 8c was isolated in 5%
yield. Modification of the literature procedure by the use of
aqueous sodium dithionite at 90 °C resulted in the formation of
all isomers 9a–c as pivaloyl esters in yields exceeding 50%
(Scheme 2, conditions (ii). The 2-NH2 isomer 9c was treated with
ammonium hydroxide at 70 °C to obtain 8c in 79% yield (Scheme
2, conditions (iii)).
The 1H–13C HMBC correlations observed for 5a, and the 1H–1H
ROESY correlations for 5b or 5d confirmed the N-1 substitution
pattern of azanucleosides 5–7 (Fig. 2).
Nucleoside analogs with the nitro group in a sugar moiety14
(mostly derivatives of uracil14a–e) have been reduced to the corre-
sponding amino derivatives by the heterogeneous catalytic hydro-
genation (in the presence of Raney-Nickel,14a–c palladium on
charcoal,14f,14g or platinum(IV) oxide14h), or with the following
reducing agents: sodium dithionite,4b tin in acetic acid,14d or so-
dium borohydride (in the presence of nickel(II) chloride14e or pal-
ladium on charcoal14g).15 The number of reports on the reduction
of the 5-fluorouracil nitro nucleosides is limited. They have been
reduced by heterogeneous catalytic hydrogenation in the presence
NO2
NHAc
NO2
O
H
H
N
H
N
O
N
O
SO2
O
O
O
SO2
SO2
2
N
6
6
6
1'
1'
N
1'
N
N
N
N
CH3
CH3
CH3
PivO
PivO
PivO
H
H H
H
H H
H
H H
5a
δH(1') = 5.13 δC(1') = 60.32
5b
5d
δH(1') = 5.22
δH(6) = 7.45
δH(1') = 5.22
δH(6) = 7.34
δH(6) = 7.40
δC(6) = 139.92
δC(2) = 150.83
Figure 2. 1H–13C HMBC correlations observed for 5a, and 1H–1H ROESY correlations for 5b and 5d.

R. Gawin et al. / Bioorg. Med. Chem. 16 (2008) 8379–8389
8381
NO2
CH3
NH2
NH2
CH3
CH3
i
ii
O
O
O
SO2
SO2
N
SO2
NH
N
N
NH
N
N
N
NH
HO
PivO
PivO
O
O
O
9a (58%)
9b (54%)
9c (56%)
8a (59%)
8b (52%)
8c (5%)
5a, 4-NO2
5b, 3-NO2
5c, 2-NO2
CH3
CH3
iii
H2N
H2N
O
O
SO2
N
SO2
N
N
NH
N
NH
PivO
HO
O
O
8c (79%)
9c
Scheme 2. Reagents and conditions: (i) Na2S2O4, 4% NaOH aq, 90 °C, 1 h; (ii) Na2S2O4 aq, 90 °C, 1 h; (iii) NH3 aq, MeOH, 70 °C, 1 day.
Taking into account a kind of nucleobase present in the nitro
compounds tested, the dithionite reduction was not general as
well. In contrast to the thymine derivatives 5a–c, treating of the ni-
tro derivatives of uracil or 5-fluorouracil, that is, 6a or 7a, respec-
tively, with sodium dithionite in alkaline medium or in aqueous
solution did not afford the corresponding amino azanucleosides
at all.
Although the heterogeneous catalytic hydrogenation is one of
the most often used methods for the reduction of nucleoside nitro
analogs, the palladium-catalysed hydrogenation (H2, 10% Pd/C,
ambient pressure) of 6a–c or 7a–c did not give the expected
results; multi-component mixtures (by TLC) were produced.
Therefore, we applied the palladium-catalysed transfer hydrogena-
tion16 to achieve the amino analogs 10 and 11 (Schemes 3 and 4).
Treating of the uracil derivatives 6a–c with cyclohexene/10% Pd/C
mixture in ethanol at 60 °C gave the corresponding amino deriva-
tives 10a–c in 58–89% yields (Scheme 3).
NO2
SO2
NH2
SO2
i
O
NH
O
NH
N
N
N
N
PivO
PivO
O
O
6a, 4-NO2
6b, 3-NO2
6c, 2-NO2
10a (58%)
10b (62%)
10c (89%)
Scheme 3. Reagents and conditions: (i) cyclohexene, 10% Pd/C, EtOH, 60 °C, 1 day.
NH2
NH2
i
F
+
O
NH
O
NH
SO2
SO2
N
NO2
N
N
N
PivO
PivO
O
O
F
11a
10a
O
NH
SO2
N
N
PivO
NH(CH3)
N(CH3)2
O
7a
F
F
ii
11a (9%)
O
NH
+
+
O
NH
SO2
N
N
SO2
N
N
PivO
PivO
O
O
12 (45%)
13 (15%)
NO2
NH2
SO2
F
F
O
NH
O
SO2
iii
N
NH
N
N
N
PivO
PivO
O
O
11a (64%)
11b (57%)
11c (62%)
7a, 4-NO2
7b, 3-NO2
7c, 2-NO2
Scheme 4. Reagents and conditions: cyclohexene, 10% Pd/C, 60 °C, 1 day: (i) EtOH; 11a:10a = 3:2 (1H NMR); (ii) MeOH; (iii) 1,4-dioxane.

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R. Gawin et al. / Bioorg. Med. Chem. 16 (2008) 8379–8389
NH2
NHAc
R
NHAc
SO2
i
ii
CH3
R
O
O
O
NH
O
NH
(R = CH3)
(R = CH3 or H)
SO2
N
SO2
N
N
N
N
N
NH
HO
PivO
HO
O
O
8a (39%)
5d, R = CH3
6d, R = H
14a, R = CH3 (94%)
14b, R = H (85%)
Scheme 5. Reagents and conditions: (i) NH3 aq, MeOH, 70 °C, 1 day; (ii) NaOH aq (4%), 90 °C, 2 h.
The reduction of the 5-fluorouracil derivatives 7 by the palla-
dium-catalysed transfer hydrogenation was more complex and
its outcome depended on the solvent used (Scheme 4). The reduc-
tion of 7a in ethanol provided an inseparable mixture of the ex-
pected amino derivative 11a and the uracil derivative 10a in a
3:2 ratio17 (Scheme 4, conditions (i)); 10a was a product of hydrog-
enolysis of the carbon–fluorine bond.18 The formation of 10a was
not observed when the reaction was carried out in methanol at
60 °C (Scheme 4, conditions (ii)), but 11a was the minor product
(yield 9%); the N-methyl derivative 12 (45%) and the N,N-dimethyl
one 13 (15%) were also obtained. We assume that 12 and 13 were
formed from the reductive methylation of 11a or 12 with formal-
dehyde, respectively, which was produced from the catalytic dehy-
drogenation of methanol.16a All difficulties with the reduction of 7
were solved when 1,4-dioxane was used as the reaction medium
(Scheme 4, conditions (iii)); all isomers 11a–c were prepared in
the yields of 57–64%.
An alternative approach toward azanucleosides B consisted in
ammonolysis or an alkaline hydrolysis of the 4-acetamido deriva-
tives (Scheme 5). Ammonolysis of 5d or 6d with ammonium
hydroxide at 70 °C resulted in the selective cleavage of the pivaloyl
ester; azanucleosides 14a or 14b were obtained in 94% or 85%
yield, respectively. Both the O- and N-protecting groups were re-
moved when the thymine derivative 5d was treated with aqueous
sodium hydroxide at 90 °C to provide 8a in 39% yield. The latter
conversion was much less effective than the previously performed
reduction of the nitro derivative 5a with sodium dithionite under
alkaline conditions (Scheme 2).
cil, respectively) showed cytotoxicity against Vero cells at the con-
centration of 200 M; with the MCC value of 40 M, 14a (analog of
5d with the hydroxy group instead of the O-pivaloyloxy one at the
sugar mimic) was found to be much more cytotoxic than 5d, while
the cytotoxicity of 14b (the hydroxy analog of 6d) was not detected
l
l
at concentrations up to 100
showed no cytotoxicity for Vero cells at concentrations up to
100 M. The nitro azanucleosides, and among them mainly deriv-
lM. The remaining compounds
l
atives of 5-fluorouracil, proved cytotoxic for MDCK cells and CRFK
cells. The following cytotoxic concentration values were deter-
mined for the nitro derivatives of the 5-fluorouracil series: (i) 7a
(the 4-NO2 isomer): MCC = 20
(MDCK cells), CC50 = 44 M (CRFK cells); (ii) 7b (the 3-NO2 iso-
mer): MCC P 100 M (MDCK cells), CC50 > 100 M (MDCK cells),
CC50 = 95 (CRFK cells); and (iii) 7c (the 2-NO2 isomer):
(MDCK cells), CC50 > 100 (MDCK cells),
M (CRFK cells).21 The thymine 4-NO2 derivative 5a
M) and the uracil 4-NO2 derivative 6a (CC50 = 49 M)
lM (MDCK cells), CC50 = 69 lM
l
l
l
l
M
MCC = 4
lM
lM
CC50 = 14
l
(CC50 = 53
l
l
displayed cytotoxicity on CRFK cells. The remaining compounds
tested did not show cytotoxicity toward MDCK or CRFK cells at
concentrations up to 100 lM.
The antiviral activity was expressed as the 50% effective con-
centration, or concentration producing 50% inhibition of virus-in-
duced cytopathic effect, as determined by visual scoring of the
CPE, or by measuring the cell viability with the colorimetric forma-
zan-based MTS assay. Antiviral effect of the tested compounds was
examined at the following concentration values: assays (a), (i)
40
compounds; assays (b), (i) 20
for 7c, or (iii) 100 M for other compounds; and assays (c)–(e),
100 M for all tested compounds. In evaluations (a), both 5c (the
thymine 2-NO2 derivative) and 7b (the 5-fluorouracil 3-NO2 deriv-
ative) displayed EC50 = 100 M against Coxsackie B4 virus and Pun-
ta Toro virus; activity of the compounds in other viruses was not
detected at concentration of 100 M. No antiviral effects were de-
l
M for 5d and 6d, (ii) 8
lM for 14a, or (iii) 100
lM for other
lM for 5a, 6a, 7a, and 7b, (ii) 4
lM
l
3. Antiviral evaluation
l
All azanucleosides with nitro, amino, or acetamido group were
evaluated for activity against several RNA- and DNA-viruses, using
the following cell-based assays: (a) Vero cells infected with parain-
fluenza-3 virus, reovirus-1, Sindbis virus, Coxsackie B4 virus, or
Punta Toro virus; (b) Crandell-Rees Feline Kidney (CRFK) cells in-
fected with feline corona virus or feline herpes virus; (c) human
embryonic lung (HEL) fibroblasts infected with herpes simplex
virus-1 (KOS), herpes simplex virus-2 (G), acyclovir-resistant her-
pes simplex virus-1 (TKꢀ KOS ACVr), vaccinia virus, or vesicular
stomatitis virus; (d) HeLa cells infected with vesicular stomatitis
virus, coxsackie B4 virus or respiratory syncytial virus; and (e) Ma-
din Darby canine kidney (MDCK) cells infected with influenza
virus, subtype A/H1N1, A/H3N2 or B.
l
l
tected for any of the remaining compounds against any of the
viruses evaluated.
4. Conclusion
Acyclic azanucleosides with 2-, 3-, or 4-aminobenzene-sulfo-
nyl function at the nitrogen atom of the sugar mimic were ob-
tained via reduction of the corresponding nitro precursors;
depending on the nucleobase present in the molecule of the nitro
derivative, sodium dithionite or cyclohexene–10% Pd/C mixture
was employed as the reducing agent. The studies showed that ni-
tro analogs sensitive to reduction conditions, such as 5-fluoroura-
cil derivatives, could be transformed into the corresponding
amines by the palladium-catalysed transfer hydrogenation with
good yields. Generally, our findings on the reduction of the nucle-
oside nitro analogs by the heterogeneous transfer hydrogenation
may be of help in synthesizing of many amino nucleosides from
nitro precursors.
The cytotoxicity of the test compounds toward the uninfected
host cells was expressed as the minimal compound concentration
(MCC) that caused a microscopically detectable alteration of nor-
mal cell morphology, or 50% cytotoxic concentration (CC50), caus-
ing
a 50% decrease in cell viability, as determined by a
colorimetric formazan-based MTS assay.19,20 None of the tested
compounds displayed cytotoxicity on HEL cells or HeLa cells at
concentrations up to 100
lM. Among the tested compounds, 5d
and 6d (the O-pivaloylated 4-NHAc derivatives of thymine or ura-

R. Gawin et al. / Bioorg. Med. Chem. 16 (2008) 8379–8389
8383
30.3 mmol). Crystallization (hexane/ethyl acetate, 2:1, v/v) gave
3a (6.17 g, 68%) as a white solid; mp 134–135 °C. dH (400 MHz,
CDCl3) 1.17 (s, 9H), 3.29–3.33 (m, 2H), 4.12–4.15 (m, 2H), 5.03 (t,
3JH–H 6.0, 1H, NH), 8.04–8.09 (m, 2H), 8.36–8.40 (m, 2H). dC
(50 MHz, CDCl3) 27.11, 38.80, 42.74, 62.63, 124.56, 128.33,
145.93, 150.18, 178.62. mmax (KBr) 3248m (NH), 1702s (C@O),
1533s (NO2), 1350s (NO2), 1341s (SO2), 1174s (SO2). HRMS m/z
calcd for C13H18N2O6NaS (M+Na)+ 353.0778, found 353.0767.
5. Experimental
5.1. Materials and methods
Pre-coated Merck silica gel 60 F-254 plates were used for both
thin-layer chromatography (TLC, 0.2 mm), and the preparative
thin-layer chromatography (2 mm); the spots were detected under
UV light (254 nm). Column chromatography was performed using
silica gel (200–400 mesh, Merck). High Resolution Mass Spectra
(Electrospray Ionisation, ESI) were performed on a MarinerÒ spec-
trometer in positive ionization mode. The IR spectra were recorded
on a Perkin-Elmer System 2000 spectrometer in KBr disc; resolu-
5.3.2. 3-Nitro-N-(2-pivaloyloxyethyl)benzenesulfonamide (3b)
According to the general procedure, 3b was obtained from 1
(6.0 g, 33 mmol) and 3-nitrobenzenesulfonyl chloride 2b (8.04 g,
36.3 mmol). Crystallization (hexane/ethyl acetate, 2.5:1, v/v) gave
3b (6.87 g, 63%) as a white solid; mp 91–92 °C. dH (400 MHz, CDCl3)
1.17 (s, 9H), 3.30–3.34 (m, 2H), 4.13–4.15 (m, 2H), 5.02 (t, 3JH–H 6.0,
1H, NH), 7.74–7.79 (m, 1H), 8.19–8.22 (m, 1H), 8.44–8.46 (m, 1H),
8.70–8.73 (m, 1H). dC (50 MHz, CDCl3) 27.15, 38.86, 42.60, 62.61,
122.28, 127.37, 130.81, 132.61, 142.43, 148.47, 178.72. mmax (KBr)
3260m (NH), 1705s (C@O), 1527s (NO2), 1350s (NO2), 1345s
(SO2), 1165s (SO2). HRMS m/z calcd for C13H18N2O6NaS (M+Na)+
353.0778, found 353.0763.
tion was 2 cmꢀ1; absorption maxima ( max) are given in cmꢀ1
m
and quoted as ‘s’ strong, ‘m’ medium, ‘br’ broad. In the case of
highly overlapped IR bands deconvolution with Grams Research
software was preformed. The 1H NMR spectra were measured on
a Varian Gemini-200BB at 200 MHz or on a Varian Mercury-
400BB spectrometer at 400 MHz. The 13C NMR spectra were re-
corded on a Varian Gemini-200BB spectrometer at 50 MHz. 1H
and 13C chemical shifts (d) are reported in parts per million
(ppm) relative to the solvent signals: CDCl3, dH (residual CHCl3)
7.26 ppm, dC 77.16 ppm; or DMSO-d6, dH (residual DMSO-d5)
2.50 ppm, dC 39.52 ppm; signals are quoted as ‘s’ (singlet), ‘d’ (dou-
blet), ‘t’ (triplet), ‘m’ (multiplet), and ‘br s’ (broad singlet). Coupling
constants J are reported in Hertz. The 1H–13C HMBC (Heteronuclear
Multiple Bond Correlation) spectrum of 5a was measured on a Var-
ian Mercury-400BB spectrometer in DMSO-d6. The 1H–1H ROESY
(Rotating frame Overhause Effect Spectroscopy) spectra of 5b or
5d were measured on a Varian Mercury-400BB spectrometer in
CDCl3 or DMSO-d6, respectively. Anhydrous MgSO4 was employed
as a drying agent. Solvents were distilled off under reduced pres-
sure on a rotating evaporator.
5.3.3. 2-Nitro-N-(2-pivaloyloxyethyl)benzenesulfonamide (3c)
According to the general procedure, 3c was obtained from 1
(6.0 g, 33 mmol) and 2-nitrobenzenesulfonyl chloride 2c (8.04 g,
36.3 mmol). Chromatographic purification (chloroform/acetone,
98:2, v/v) gave 3c (7.58 g, 70%) as a colorless oil. dH (200 MHz, CDCl3)
1.14 (s, 9H), 3.33–3.42 (m, 2H), 4.09–4.15 (m, 2H), 5.77 (t, 3JH–H 5.8,
1H, NH), 7.70–7.77 (m, 2H), 7.84–7.87 (m, 1H), 8.10–8.15 (m, 1H). dC
(50 MHz, CDCl3) 27.16, 38.86, 42.94, 62.49, 125.60, 131.00, 133.14,
133.73, 133.95, 148.15, 178.31. mmax (KBr) 3242m (NH), 1704s
(C@O), 1536s (NO2), 1351s (NO2), 1344s (SO2), 1171s (SO2). HRMS
m/z calcd for C13H18N2O6NaS (M+Na)+, 353.0778, found 353.0794.
The methodology used for measuring the antiviral activity has
been described previously.22
5.3.4. 4-Acetamido-N-(2-pivaloyloxyethyl)benzenesulfonamide
(3d)
5.2. 2-Pivaloyloxyethylamine hydrochloride (1)
According to the general procedure, 3d was obtained from 1
(5.0 g, 27.5 mmol) and 4-acetamidobenzenesulfonyl chloride 2d
(7.07 g, 30.3 mmol). Chromatographic purification(chloroform/ace-
tone, 95:5, v/v) gave 3d (4.7 g, 50%) as a white solid; mp 90–91 °C. dH
(400 MHz, CDCl3) 1.17 (s, 9H), 2.22 (s, 3H), 3.20–3.24 (m, 2H), 4.08–
4.10 (m, 2H), 4.78 (t, 3JH–H 6.0, 1H, NH), 7.48 (br s, 1H, NH), 7.61–7.65
(m, 2H), 7.63–7.77 (m, 2H). dC (50 MHz, CDCl3) 24.80, 27.25, 38.92,
42.46, 62.84, 119.69, 128.30, 134.49, 142.30, 169.24, 178.72. mmax
(KBr) 3307m (NH), 3269m (NH), 1725s (C@O), 1676s (C@O),
1594s, 1533br s, 1327s (SO2), 1158s (SO2). HRMS m/z calcd for
A mixture of ethanolamine hydrochloride (10.30 g, 105 mmol)
and pivaloyl chloride (105 mmol, 13.0 mL) was heated on an oil
bath at 90 °C until the production of hydrogen chloride ceased (ca.
4 h); after this time the mixture solidified. The residual hydrogen
chloride was removed under reduced pressure. The residue was
kept at a vacuum desiccator over KOH overnight to give the crude
1 (18.26 g) as a pale yellow, amorphous solid. An analytical sample
was obtained by crystallization from dry acetone. dH (200 MHz;
DMSO-d6) 1.17 (s, 9H), 3.06 (m, 2H), 4.17 (t, 3JH–H 5.6, 2H), 8.29 (br
s, 3H, NH3þ). dH (50 MHz; DMSO-d6) 26.83, 37.65, 40.61, 60.79,
177.36. mmax (KBr) 2916–3112br s (NH3+), 1724s (C@O), 1575m
ðNH3þÞ, 1500 ðNH3þÞ. LRMS m/z calcd for C7H16NO2 (M+H)+ 146.1,
found 146.1.
C
15H22N2O5NaS (M+Na)+ 365.1142, found 365.1159.
5.4. General method for the synthesis of N-(2-pivaloyloxyethyl)
-N-(pivaloyloxymethyl)benzenesulfonamides (4)
5.3. General method for the synthesis of N-(2-
pivaloyloxyethyl)benzenesulfonamides (3)
Chloromethyl pivalate (15 mol) was added to a stirred mixture
of N-(2-pivaloyloxyethyl)benznenesulfonamide
3 (5 mol) and
anhydrous potassium carbonate (25 mmol) in dry DMF (10 mL)
at room temperature. The mixture was stirred for 5 days at room
temperature and then was poured into ice-cold water (50 mL).
The organic phase was extracted with dichloromethane (3ꢁ
50 mL). The extracts were combined and washed with water, and
dried. The solvent was distilled off. The residue was purified by col-
umn chromatography or crystallization to give 4; the solvents are
given in parentheses below.
A mixture of the crude 1, dry pyridine and dry dichloromethane,
in the ratio of 10 mmol/30 mmol/18 mL, respectively, was cooled in
an ice-water bath and the corresponding benzenesulfonyl chloride 2
(11 mmol) was added in one portion. The mixture was kept over-
night at room temperature and then washed with water, diluted
hydrochloric acid (5%), brine, and dried. The solvent was distilled
off. The residue was purified by column chromatography or crystal-
lization to afford 3; the solvents are given in parentheses below.
5.4.1. 4-Nitro-N-(2-pivaloyloxyethyl)-N-(pivaloyloxymethyl)
benzenesulfonamide (4a)
According to the general procedure, 4a was obtained from 3a
(5.0 g, 15 mmol). Crystallization (hexane/ethyl acetate, 3:1, v/v)
5.3.1. 4-Nitro-N-(2-pivaloyloxyethyl)benzenesulfonamide (3a)
According to the general procedure, 3a was obtained from 1
(5.0 g, 27.5 mmol) and 4-nitrobenzenesulfonyl chloride 2a (6.7 g,

8384
R. Gawin et al. / Bioorg. Med. Chem. 16 (2008) 8379–8389
afforded 4a (5.15 g, 76%) as a white solid; mp 105–107 °C. dH
to give the corresponding azanucleoside 5, 6, or 7; the solvents are
given in parentheses below.
3
(CDCl3, 400 MHz) 0.99 (s, 9H), 1.22 (s, 9H), 3.49 (t, JH–H 5.6, 2H),
3
4.29 (t, JH–H 5.6, 2H), 5.58 (s, 2H), 8.06–8.11 (m, 2H), 8.34–8.39
(m, 2H). dC (CDCl3, 50 MHz) 26.77, 27.15, 38.74, 45.59, 61.94,
71.76, 124.33, 128.89, 145.68, 150.23, 177.62, 178.20. mmax (KBr)
1735s (C@O), 1725s (C@O), 1533s (NO2), 1356s (NO2), 1352s
(SO2), 1152s (SO2). HRMS m/z calcd for C19H28N2O8NaS (M+Na)+
467.1459, found 467.1458.
5.5.1. 1-[N-(4-Nitrobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
aminomethyl]-5-methyl-1H,3H-pyrimidin-2,4-dione (5a)
According to the general procedure, 5a was obtained from 4a
(445 mg, 1 mmol) and thymine in the presence of TMSOTf. Chro-
matographic purification (chloroform/acetone, 9:1, v/v) gave 5a
(315 mg, 67%) as a white solid; mp 172–173 °C. dH (200 MHz,
DMSO-d6) 1.11 [s, 9H, –C(O)C(CH3)3], 1.72 [s, 3H, –CH@C(CH3)–],
3.74–3.79 (m, 2H, PivO–CH2–CH2–), 4.13–4.18 (m, 2H, PivO–CH2–
CH2–), 5.13 (s, 2H, –N–CH2–N–), 7.40 [br s, 1H, –CH@C(CH3)–],
8.06–8.10 (m, 2H), 8.35–8.39 (m, 2H), 11.26 [br s, 1H, NH]. dC
(50 MHz, DMSO-d6,) 11.83 [–CH@C(CH3)–], 26.69 [–C(O)C(CH3)3],
37.50 [–C(O)C(CH3)3], 48.09 (PivO–CH2–CH2–), 60.32 (–N–CH2–
N–), 61.61 (PivO–CH2–CH2–), 108.91 [–CH@C(CH3)–], 124.49 (Ar),
128.22 (Ar), 139.92 [–CH@C(CH3)–], 144.93 (Ar), 149.68 (Ar),
150.83 [–N–C(O)–NH–], 163.62 [–NH–C(O)–C(CH3)@], 177.03 [–
C(O)C(CH3)3]. mmax (KBr) 1722s (C@O), 1712s (C@O), 1683s
(C@O), 1533s (NO2), 1354s (NO2). HRMS m/z calcd for C19H24N4O8-
NaS (M+Na)+ 491.1207, found 491.1206.
5.4.2. 3-Nitro-N-(2-pivaloyloxyethyl)-N-(pivaloyloxymethyl)
benzenesulfonamide (4b)
According to the general procedure, 4b was obtained from 3b
(3.1 g, 9.2 mmol). Crystallization (hexane/ethyl acetate, 13:1, v/v)
afforded 4b (2.42 g, 59%) as a white solid; mp 84–85 °C. dH
3
(200 MHz, CDCl3) 0.96 (s, 9H), 1.20 (s, 9H), 3.48 (t, JH–H 5.4, 2H),
3
4.27 (t, JH–H 5.4, 2H), 5.57 (s, 2H), 7.71–7.79 (m, 1H), 8.20–8.24
(m, 1H), 8.43–8.47 (m, 1H), 8.69–8.71 (m, 1H). dC (50 MHz, CDCl3)
26.84, 27.29, 38.81, 38.89, 45.69, 62.11, 71.93, 122.86, 127.58,
130.68, 133.21, 142.34, 148.53, 177.83, 178.34. mmax (KBr) 1739s
(C@O), 1728s (C@O), 1537s (NO2), 1359s (NO2), 1353s (SO2),
1145s (SO2). HRMS m/z calcd for C19H28N2O8NaS (M+Na)+
467.1459, found 467.1454.
5.5.2. 1-[N-(3-Nitrobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
aminomethyl]-5-methyl-1H,3H-pyrimidin-2,4-dione (5b)
According to the general procedure, 5b was obtained from 4b
(445 mg, 1 mmol) and thymine in the presence of TMSOTf. Crystal-
lization (methanol/diethyl ether, 5:1, v/v) gave 5b (370 mg, 79%) as
a white solid; mp 160–162 °C. The filtrate was concentrated to dry-
ness, and the residue was purified by column chromatography
(chloroform/acetone, 95:5, v/v) to give the additional amount of
5b (49 mg, 10%) as a white solid. dH (DMSO-d6 200 MHz) 1.12 [s,
5.4.3. 2-Nitro-N-(2-pivaloyloxyethyl)-N-(pivaloyloxymethyl)
benzenesulfonamide (4c)
According to the general procedure, 4c was obtained from 3c
(3.1 g, 9.2 mmol). Chromatographic purification (dichloromethane)
gave 4c (1.77 g, 43%) as a white solid; mp 45–47 °C. dH (200 MHz,
CDCl3) 0.99 (s, 9H), 1.19 (s, 9H), 3.71 (t, 3JH–H 5.4, 2H), 4.24 (t, 3JH–H
5.4, 2H), 5.52 (s, 2H), 7.63–7.78 (m, 3H), 8.06–8.15 (m, 1H). dC
(50 MHz, CDCl3) 26.86, 27.26, 38.78, 38.85, 46.73, 62.22, 71.89,
124.43, 131.51, 132.04, 133.48, 134.24, 148.19, 177.81, 178.34.
mmax (KBr) 1733s (C@O), 1721s (C@O), 1540s (NO2), 1372s (NO2),
1349s (SO2), 1150s (SO2). HRMS m/z calcd for C19H28N2O8NaS
(M+Na)+, 467.1459, found 467.1458.
4
9H, –C(O)C(CH3)3], 1.71 [d, JH–H 1.0, 3H, –CH@C(CH3)], 3.76–3.82
(m, 2H, PivO–CH2–CH2– or PivO–CH2–CH2–), 4.14–4.19 (m, 2H,
PivO–CH2–CH2– or PivO–CH2–CH2–), 5.22 (s, 2H, –N–CH2–N–),
4
7.45 [q, JH–H 1.0, 1H, –CH@C(CH3)–], 7.85–7.93 (m, 1H, Ar-H),
8.25–8.29 (m, 1H, Ar-H), 8.43–8.53 (m, 2H, Ar-H), 11.23 (br s, 1H,
NH). dC (DMSO-d6, 50 MHz) 11.87, 26.82, 38.17, 48.32, 60.74,
61.95, 109.13, 121.36, 127.78, 131.62, 132.74, 140.23, 141.32,
147.74, 151.00, 163.74, 177.24. mmax (KBr) 1718s (C@O), 1710s
(C@O), 1681s (C@O), 1531s (NO2), 1351s (NO2). HRMS m/z calcd
for C19H24N4O8NaS (M+Na)+ 491.1207, found 491.1196.
5.4.4. 4-Acetamido-N-(2-pivaloyloxyethyl)-N-
(pivaloyloxymethyl)benzenesulfonamide (4d)
According to the general procedure, 4d was obtained from 3d
(2.0 g, 5.8 mmol). Chromatographic purification (chloroform/ace-
tone, 98:2, v/v) gave 4d (2.2 g, 83%) as a white solid; mp 73–
76 °C. dH (200 MHz, CDCl3) 1.00 (s, 9H), 1.19 (s, 9H), 2.19 (s, 3H),
3
3
3.41 (t, JH–H 5.6, 2H), 4.24 (t, JH–H 5.6, 2H), 5.52 (s, 2H), 7.64–
7.68 (m, 2H), 7.75–7.80 (m, 2H), 7.95 (br s, 1H, NH) dC (50 MHz,
CDCl3) 24.87, 26.98, 27.31, 38.87, 45.38, 62.53, 72.41, 119.39,
129.00, 134.51, 142.50, 168.77, 178.42, 178.47. mmax (KBr) 3336m
(NH), 1738s (C@O), 1709s (C@O), 1679s (C@O), 1593s, 1537br s,
1351s (SO2), 1158s (SO2). HRMS m/z calcd for C21H32N2O7NaS
(M+Na)+ 479.1822, found 479.1828.
5.5.3. 1-[N-(2-Nitrobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
aminomethyl]-5-methyl-1H,3H-pyrimidin-2,4-dione (5c)
According to the general procedure, 5c was obtained from 4c
(445 mg, 1 mmol) and thymine in the presence of TMSOTf. Chro-
matographic purification (chloroform/acetone, 95:5, v/v) gave 5c
(248 mg, 54%) as a white solid; mp 129–130 °C. dH (200 MHz,
DMSO-d6) 1.11 (s, 9H), 1.63 (br s, 3H), 3.83–8.87 (m, 2H), 4.13–
4.18 (m, 2H), 5.30 (s, 2H), 7.17 (br s, 1H), 7.76–8.03 (m, 4H),
11.30 (br s, 1H, NH). dC (50 MHz, DMSO-d6) 11.93, 26.81, 38.15,
48.06, 59.70, 61.44, 109.11, 124.66, 129.07, 132.34, 132.80,
134.88, 139.54, 147.44, 151.26, 163.72, 177.23. mmax (KBr) 1738s
(C@O), 1712s (C@O), 1674s (C@O), 1540s (NO2), 1366s (NO2).
5.5. General procedure for the coupling of 4 with thymine,
uracil, or 5-fluorouracil
A mixture of a nucleobase (thymine, uracil, or 5-fluorouracil)
(2.0 mmol) and N,O-bis-(trimethylsilyl)acetamide (BSA, 815 mg,
4.0 mmol, 1.0 mL) in dry acetonitrile (10 mL) was stirred at room
temperature for 1 h under an argon atmosphere. Then, a solution
of 4 (1.0 mmol) in dry acetonitrile (1 mL) and subsequently a Lewis
acid [TMSOTf (370 mg, 1.7 mmol, 0.3 mL), or 1 M solution of tin(IV)
chloride in dichloromethane (3 mL)] were added. The reaction
mixture was kept at room temperature for 2 days. Ethyl acetate
(50 mL) and a saturated aqueous solution of sodium bicarbonate
(1 mL) were added. The mixture was stirred for 1 h and then fil-
tered through a Celite pad. The organic phase was separated,
washed with brine, and dried. The volatiles was distilled off. The
residue was purified by column chromatography or crystallization
HRMS m/z calcd
C
19H24N4O8NaS (M+Na)+ 491.1207, found
491.1226.
5.5.4. 1-[N-(4-Acetamidobenzenesulfonyl)-N-(2-pivaloyloxye-thyl)
aminomethyl]-5-methyl-1H,3H-pyrimidin-2,4-dione (5d)
According to the general procedure, 5d was obtained from 4d
(228 mg, 0.5 mmol) and thymine in the presence of TMSOTf. Chro-
matographic purification (chloroform/acetone, 8:2, v/v) gave 5d
(152 mg, 63%) as a white solid; mp 115–117 °C. dH (200 MHz,
4
CDCl3) 1.18 [s, 9H, –C(O)C(CH3)3), 1.89 [d, JH–H 1.2, 3H, –
3
CH@C(CH3)–], 2.20 [s, 3H, –NH–C(O)CH3], 3.69 (t, JH–H 5.4, 2H,
3
PivO–CH2–CH2– or PivO–CH2–CH2–), 4.18 (t, JH–H 5.4, 2H, PivO–

R. Gawin et al. / Bioorg. Med. Chem. 16 (2008) 8379–8389
8385
CH2–CH2– or PivO–CH2–CH2–), 5.22 (s, 2H, –N–CH2–N–), 7.34 [q, 4J
5.5.9. 1-[N-(4-Nitrobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
H–H 1.2, 1H, –CH@C(CH3)–], 7.63–7.71 (m, 4H, Ar-H), 7.92 [br s, 1H,
–NH–C(O)CH3], 9.07 [br s, 1H, –C(O)–NH–C(O)–] dC (50 MHz,
CDCl3) 12.42, 24.82, 27.31, 38.88, 48.10, 60.94, 62.47, 111.37,
119.56, 128.14, 134.33, 139.83, 142.86, 151.37, 164.08, 168.99,
178.40. mmax (KBr) 3320m (NH), 1742s (C@O), 1735s (C@O),
1716s (C@O), 1685s (C@O), 1664m, 1592m, 1533m. HRMS m/z
calcd for C21H28N4O7NaS (M+Na)+ 503.1571, found 503. 1595.
aminomethyl]-5-fluoro-1H,3H-pyrimidin-2,4-dione (7a)
According to the general procedure, 7a was obtained from 4a
(445 mg, 1 mmol) and 5-fluorouracil in the presence of TMSOTf.
Crystallization (methanol) gave 7a (275 mg, 58%) as a white solid;
mp 154–155 °C. dH (200 MHz, DMSO-d6) 1.10 (s, 9H), 3.73–3.78
3
(m, 2H), 4.12–4.17 (m, 2H), 5.22 (s, 2H), 7.94 (d, JH–F 6.6, 1H),
8.10–8.15 (m, 2H), 8.38–8.42 (m, 2H), 11.84 (br s, 1H, NH). dC
(50 MHz, DMSO-d6) 26.82, 38.16, 48.34, 61.10, 61.56, 124.73,
2
1
5.5.5. 1-[N-(4-Nitrobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
aminomethyl]-1H,3H-pyrimidin-2,4-dione (6a)
128.44, 128.81 (d, JC–F 34.9), 139.47 (d, JC–F 229.9), 144.85,
2
149.74, 149.98, 157.15 (d, JC–F 25.8), 177.20. mmax (KBr) 1718s
According to the general procedure, 6a was obtained from 4a
(445 mg, 1 mmol) and uracil in the presence of TMSOTf. Chromato-
graphic purification (chloroform/acetone, 9:1, v/v) gave 6a (343 mg,
76%) as a white solid; mp 213–215 °C. dH (200 MHz, DMSO-d6) 1.11
(s, 9H), 3.75 (t, 3JH–H 5.2, 2H), 4.14 (t, 3JH–H 5.2, 2H), 5.25 (s, 2H), 5.61
(d, 3JH–H 8.0, 1H), 7.62 (d, 3JH–H 8.0, 1H), 8.07–8.12 (m, 2H), 8.34–8.40
(m, 2H), 11.26 (br s, 1H, NH). dC (50 MHz, DMSO-d6) 26.82, 38.13,
48.20, 60.85, 61.76, 101.59, 124.67, 128.32, 144.65, 144.93, 149.91,
151.04, 163.24, 177.20 mmax (KBr) 1731s (C@O), 1716s (C@O),
1707s (C@O), 1685s, 1533s (NO2), 1349s (NO2). HRMS m/z calcd for
(C@O), 1705s (C@O), 1666s (C@O), 1537s (NO2), 1349s (NO2). HRMS
m/z calcd for C18H21N4O8FNaS (M+Na)+ 495.0956, found 495.0937.
5.5.10. 1-[N-(3-Nitrobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
aminomethyl]-5-fluoro-1H,3H-pyrimidin-2,4-dione (7b)
According to the general procedure, 7b was obtained from 4b
(445 mg, 1 mmol) and 5-fluorouracil in the presence of TMSOTf.
Chromatographic purification (chloroform/acetone, 85:15, v/v) gave
7b (322 mg, 68%) as a white solid; mp 132–133 °C. dH (200 MHz,
CDCl3) 1.13 (s, 9H), 3.68–3.74 (m, 2H), 4.16–4.21 (m, 2H), 5.30 (s,
2H), 7.74–7.83 (m, 2H), 8.11–8.16 (m, 1H), 8.41–8.47 (m, 1H),
8.52–8.54 (m, 1H), 9.93 (br s, 1H, NH). dC (50 MHz, CDCl3) 27.17,
C
18H22N4O8NaS (M+Na)+ 477.1051, found 477.1068.
2
5.5.6. 1-[N-(3-Nitrobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
minomethyl]-1H,3H-pyrimidin-2,4-dione (6b)
38.79, 48.10, 61.34, 61.67, 121.94, 127.86 (d, JC–F 33.4), 128.02,
1
131.25, 132.54, 140.67 (d, JC–F 238.6), 141.60, 148.57, 150.21,
2
According to the general procedure, 6b was obtained from 4b
(1.25 g, 2.8 mmol) and uracil in the presence of TMSOTf. Chromato-
graphic purification (chloroform/acetone, 95:5, v/v) gave 6b
(971 mg, 76%) as a white solid; mp 142–143 °C. dH (200 MHz,
DMSO-d6) 1.11 (s, 9H), 3.77–3.79 (m, 2H), 4.12–4.17 (m, 2H),
157.19 (d, JC–F 26.6), 178.28. mmax (KBr) 1724s (C@O), 1703s
(C@O), 1676s (C@O), 1534s (NO2), 1353s (NO2). HRMS m/z calcd
for C18H21N4O8FNaS (M+Na)+, 495.0956, found 495.0974.
5.5.11. 1-[N-(2-Nitrobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
aminomethyl]-5-fluoro-1H,3H-pyrimidin-2,4-dione (7c)
3
3
5.27 (s, 2H), 5.60 (d, JH–H 8.0, 1H), 7.65 (d, JH–H 8.0, 1H), 7.86–
7.94 (m, 1H), 8.25–8.30 (m, 1H), 8.45–8.55 (m, 2H), 11.25 (br s,
1H, NH). dC (50 MHz, DMSO-d6) 26.82, 38.13, 48.24, 60.98, 61.91,
101.54, 121.46, 127.85, 131.62, 132.70, 141.11, 144.73, 147.86,
151.04, 163.17, 177.19. mmax (KBr) 1729s (C@O), 1715s (C@O),
1703s (C@O), 1683s, 1534s (NO2), 1355s (NO2,). HRMS m/z calcd
for C18H22N4O8NaS (M+Na)+ 477.1051, found 477.1065.
According to the general procedure, 7c was obtained from 4c
(445 mg, 1 mmol) and 5-fluorouracil in the presence of TMSOTf.
Chromatographic purification (chloroform/acetone, 95:5, v/v) gave
7c (329 mg, 70%) as a white solid; mp 162–163 °C. dH (200 MHz,
DMSO-d6) 1.10 (s, 9H), 3.80–3.86 (m, 2H), 4.12–4.17 (m, 2H),
5.32 (s, 2H), 7.69–7.72 (m, 1H), 7.78–7.95 (m, 2H), 8.01–8.05 (m,
2H), 11.84 (br s, 1H, NH). dC (50 MHz, DMSO-d6) 26.79, 38.15,
2
5.5.7. 1-[N-(2-Nitrobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
aminomethyl]-1H,3H-pyrimidin-2,4-dione (6c)
47.96, 60.25, 61.26, 124.79, 128.20 (d, JC–F 33.8), 129.32, 131.96,
1
132.86, 135.03, 139.38 (d, JC–F 230.3), 147.45, 149.95, 157.10 (d,
According to the general procedure, 6c was obtained from 4c
(445 mg, 1 mmol) and uracil in the presence of TMSOTf. Chromato-
graphic purification (chloroform/acetone, 95:5, v/v) gave 6c
(245 mg, 54%) as a white solid; mp 145–146 °C. dH (200 MHz,
DMSO-d6) 1.09 (s, 9H), 3.78–3.83 (m, 2H), 4.09–4.15 (m, 2H), 5.35
(s, 2H), 5.53 (d, 3JH–H 8.0, 1H), 7.44 (d, 3JH–H 8.0, 1H), 7.79–8.05 (m,
4H), 11.31 (br s, 1H, NH). dC (50 MHz, DMSO-d6) 26.80, 38.12,
47.71, 60.00, 61.39, 101.78, 124.85, 129.27, 131.96, 132.86, 135.01,
143.98, 147.46, 151.32, 163.18, 177.20. mmax (KBr) 1737s (C@O),
1704s (C@O), 1686s (C@O), 1656s, 1541s (NO2), 1367s (NO2). HRMS
m/z calcd for C18H22N4O8NaS (M+Na)+ 477.1051, found 477.1070.
2JC–F 25.8), 177.21. mmax (KBr) 1724s (C@O), 1694s (C@O), 1666s
(C@O), 1542s (NO2), 1368s (NO2). HRMS m/z calcd for
C18H21N4O8FNaS (M+Na)+ 495.0956, found 495.0970.
5.5.12. 1-[N-(4-Acetamidobenzenesulfonyl]-N-(2-pivaloyloxye-
thyl)aminomethyl]-5-fluoro-1H,3H-pyrimidin-2,4-dione (7d)
According to the general procedure, 7d was obtained from 4d
(228 mg, 0.5 mmol) and 5-fluorouracil in the presence of tin(IV)
chloride. Chromatographic purification (chloroform/methanol,
98:2, v/v) gave 7d (127 mg, 52%) as a white solid; mp 168 °C
(subl.). dH (200 MHz, DMSO-d6) 1.09 (s, 9H), 2.09 (s, 3H), 3.60–
3.65 (m, 2H), 4.07–4.12 (m, 2H), 5.16 (s, 2H), 7.71–7.77 (m, 4H),
3
5.5.8. 1-[N-4-(Acetamidobenzenesulfonyl)-N-(2-pivaloyloxye-
thyl)aminomethyl]-1H,3H-pyrimidin-2,4-dione (6d)
7.86 (d, JH–F 6.4, 1H), 10.38 (br s, 1H, NH), 11.89 (br s, 1H, NH).
dC (50 MHz, DMSO-d6) 24.18, 26.78, 47.78, 61.03, 61.70, 118.61,
2
1
According to the general procedure, 6d was obtained from 4d
(228 mg, 0.5 mmol) and uracil in the presence of TMSOTf. Chro-
matographic purification (chloroform/acetone, 8:2, v/v) gave 6d
(148 mg, 66%) as a white solid; mp > 121 °C (dec). dH (200 MHz,
127.97, 128.74 (d, JC–F 34.55), 132.60, 139.35 (d, JC–F 230.60),
2
143.66, 149.82, 157.19 (d, JC–F 25.45), 169.10, 177.14. mmax (KBr)
3383m (NH), 1742s (C@O), 1719s (C@O), 1705s (C@O), 1678s
(C@O), 1591m, 1533m. HRMS m/z calcd for C20H25N4O7FNaS
(M+Na)+ 507.1320, found 507.1342.
3
CDCl3) 1.19 (s, 9H), 2.21 (s, 3H), 3.68 (t, JH–H 5.6, 2H), 4.18 (t, 3J
3
3
5.6, 2H), 5.25 (s, 2H), 5.72 (d, JH–H 8.2, 1H), 7.60 (d, JH–H 8.2,
H–H
1H), 7.63–7.70 (m, 5H), 8.97 (br s, 1H, NH) dC (50 MHz, CDCl3)
24.88, 27.34, 38.87, 48.05, 61.23, 62.47, 102.85, 119.63, 128.20,
134.25, 142.80, 144.17, 151.12, 163.12, 168.85, 178.37. mmax (KBr)
3318m (NH), 1748s (C@O), 1731s (C@O), 1712s (C@O), 1681s
(C@O), 1632m, 1592m, 1533m. HRMS m/z calcd for C20H26N4O7NaS
(M+Na)+ 489.1414, found 489.1438.
5.6. General method for the reduction of the thymine
derivatives 5a–c with sodium dithionite in alkaline medium
A mixture of 5a–c (0.4 mmol), sodium dithionite (350 mg,
2 mmol) and 4% aqueous solution of sodium hydroxide (20 mL)
was heated at 90 °C for 1 h. Then, the mixture was cooled to

8386
R. Gawin et al. / Bioorg. Med. Chem. 16 (2008) 8379–8389
room temperature, neutralized with an aqueous hydrochloric
acid (5%), and extracted with ethyl acetate (5ꢁ 10 mL). The ex-
tracts were combined, washed with brine (5 mL) and dried.
The solvent was distilled off. The residue was purified by column
chromatography (chloroform/methanol/NH3 aq, 95:5:0.1, v/v/v)
to give 8a–c.
5.7. General method for the reduction of the thymine
derivatives 5a–c with sodium dithionite under neutral
conditions
A mixture of 5a–c (0.3 mmol), sodium dithionite (260 mg,
1.5 mmol) and water (15 mL) was heated at 90 °C for 1 h. The mix-
ture was cooled to room temperature and extracted with ethyl ace-
tate (5ꢁ 10 mL). The extracts were combined, washed with brine
(5 mL) and dried. The solvent was distilled off. The residue was
purified by column chromatography (chloroform/methanol, 95:5,
v/v) to yield 9a–c.
5.6.1. 1-[N-(4-Aminobenzenesulfonyl)-N-(2-hydroxyethyl)
aminomethyl]-5-methyl-1H,3H-pyrimidin-2,4-dione (8a)
Method A. According to the general procedure, 8a was ob-
tained from 5a (100 mg, 0.2 mmol). Chromatographic purification
afforded 8a (42 mg, 59%) as a white solid; mp 179–180 °C. dH
(DMSO-d6, 200 MHz) 1.75 (s, 3H), 3.19–3.28 (m, 2H), 3.39–3.45
5.7.1. 1-[N-(4-Aminobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
aminomethyl]-5-methyl-1H,3H-pyrimidin-2,4-dione (9a)
According to the general procedure, 9a was obtained from 5a
(140 mg, 0.3 mmol). Chromatographic purification afforded 9a
3
(m, 2H), 4.76 (t, JH–H 5.2, 1H, OH), 5.07 (s, 2H), 6.09 (br s, 2H,
NH2), 6.57–6.62 (m, 2H), 7.36–7.44 (m, 2H), 7.36 (br s, 1H),
11.29 (br s, 1H, NH). dC (DMSO-d6, 50 MHz) 11.89, 50.31,
59.53, 60.27, 108. 45, 112.56, 123.66, 128.58, 139.92, 150.89,
153.02, 163.81. mmax (KBr) 3435m (NH), 3374m (OH), 3335m
(NH), 1719 (C@O), 1687 (C@O), 1630m, 1361s (SO2), 1151s
(SO2). HRMS m/z calcd for C14H18N4O5NaS (M+Na)+ 377.0890,
found 377.0898.
Method B. (Scheme 5). A mixture of 5d (47 mg, 0.1 mmol) and an
aqueous sodium hydroxide (4%, 3 mL) was heated at 90 °C for 2 h.
Then, the mixture was cooled to room temperature, neutralized
with aqueous hydrochloric acid (5%), and extracted with ethyl ace-
tate (5ꢁ 5 mL). The extracts were combined, washed with brine
(5 mL) and dried. The solvent was distilled off. The residue was
purified by column chromatography (chloroform/methanol/NH3
aq, 95:5:0.1, v/v/v) to afford 8a (14 mg, 39%).
(70 mg, 58%) as
(200 MHz, CDCl3) 1.17 (s, 9H), 1.91 (d, JH–H 1.0, 3H), 3.62 (d, JH–
a white solid; mp 186–190 °C (dec). dH
4
3
4
5.4, 2H), 4.15 (d, JH–H 5.4, 2H), 4.26 (br s, 2H, NH2), 5.21 (s,
H
4
2H), 6.62–6.66 (m, 2H), 7.47–7.51 (m, 2H), 7.37 (d, JH–H 1.0, 1H),
9.88 (br s, 1H, NH). dC (50 MHz, CDCl3) 12.43, 22.27, 38.82, 47.59,
60.65, 62.41, 111.34, 114.21, 127.45, 129.11, 139.77, 151.31,
151.40, 164.08, 178.30. mmax (KBr) 3483m (NH), 3381m (NH),
1730s (C@O), 1717s (C@O), 1663s (C@O), 1630m, 1594m, 1314s
(SO2), 1142s (SO2). HRMS m/z calcd for C19H26N4O6NaS (M+Na)+
461.1465, found 461.1488.
5.7.2. 1-[N-(3-Aminobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
aminomethyl]-5-methyl-1H,3H-pyrimidin-2,4-dione (9b)
According to the general procedure, 9b was obtained from 5b
(141 mg, 0.3 mmol). Chromatographic purification afforded 9b
(71 mg, 54%) as a white solid; mp > 163 °C (dec). dH (200 MHz,
DMSO-d6) 1.11 (s, 9H), 1.72 (s, 3H), 3.56–3.61 (m, 2H), 4.08–4.13
(m, 2H), 5.16 (s, 2H), 5.62 (br s, 2H, NH2), 6.77–6.87 (m, 2H), 6.98
(br s, 1H), 7.14–7.26 (m, 2H), 11.34 (s, 1H, NH). dC (50 MHz,
DMSO-d6) 12.03, 26.81, 38.13, 47.29, 59.94, 61.70, 109.00,
110.87, 112.88, 117.96, 129.88, 139.82, 139.97, 149.72, 151.24,
163.88, 177.20. mmax (KBr) 3404m (NH), 3353m (NH), 1729s
(C@O), 1713s (C@O), 1686s (C@O), 1628m, 1599m, 1339s (SO2),
1157s (SO2). HRMS m/z calcd for C19H26N4O6NaS (M+Na)+
461.1465, found 461.1471.
5.6.2. 1-[N-(3-Aminobenzenesulfonyl)-N-(2-hydroxyethyl)
aminomethyl]-5-methyl-1H,3H-pyrimidin-2,4-dione (8b)
According to the general procedure, 8b was obtained from 5b
(143 mg, 0.3 mmol). Chromatographic purification afforded 8b
(74 mg, 52%) as a white solid; mp 168–169 °C. dH (200 MHz,
3
DMSO-d6) 1.74 (s, 3H), 3.28–3.47 (m, 4H), 4.82 (t, JH–H 5.0,
1H, OH), 5.12 (s, 2H), 5.61 (br s, 2H, NH2), 6.77–6.87 (m, 2H),
6.98 (s, 1H), 7.15–7.23 (m, 1H), 7.33 (m, 1H), 11.30 (br s, 1H,
NH). dC (50 MHz, DMSO-d6), 12.09, 50.76, 59.77, 60.45, 108.89,
110.98, 113.01, 117.89, 129.84, 139.95, 139.97, 149.66, 151.15,
164.02. mmax (KBr) 3471m (NH), 3405m (OH), 3362m (NH),
1716s (C@O), 1685s (C@O), 1640m, 1361s (SO2), 1151s (SO2).
HRMS m/z calcd for C14H18N4O5NaS (M+Na)+ 377.0890, found
377.0889.
5.7.3. 1-[N-(2-Aminobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
aminomethyl]-5-methyl-1H,3H-pyrimidin-2,4-dione (9c)
According to the general procedure, 9c was obtained from 5c
(187 mg, 0.4 mmol). Chromatographic purification afforded 9c
(97 mg, 56%) as a white solid; mp 137–138 °C. dH (200 MHz,
5.6.3. 1-[N-(2-Aminobenzenesulfonyl)-N-(2-hydroxyethyl)
aminomethyl]-5-methyl-1H,3H-pyrimidin-2,4-dione (8c)
Method A. According to the general procedure, 8c was obtained
from 5c (187 mg, 0.4 mmol). Chromatographic purification affor-
4
DMSO-d6) 1.11 (s, 9H), 1.68 (d, JH–H 1.0, 3H), 3.61–3.66 (m, 2H),
4.01–4.07 (m, 2H), 5.24 (s, 2H), 6.02 (br s, 2H, NH2), 6.59–6.66
4
(m, 1H), 6.82–6.86 (m, 1H), 7.20 (q, JH–H 1.0, 1H), 7.26–7.30 (m,
ded 8c (7 mg, 5%) as
a white solid; mp 138–139 °C. dH
1H), 7.46–7.50 (m, 1H), 11.26 (br s, 1H, NH). dC (50 MHz, DMSO-
d6) 12.01, 26.83, 38.12, 46.69, 59.63, 61.75, 108.82, 115.66,
117.54, 118.80, 129.15, 134.44, 139.78, 146.86, 151.33, 163.90,
177.22. mmax (KBr) 3475m (NH), 3369m (NH), 1733s (C@O),
1719s (C@O), 1691s (C@O), 1621m, 1599m, 1324s (SO2), 1144s
(SO2). HRMS m/z calcd for C19H26N4O6NaS (M+Na)+ 461.1465,
found 461.1471.
(200 MHz, DMSO-d6) 1.71 (s, 3H), 3.14–3.57 (m, 4H), 4.80 (br s,
1H, OH), 5.21 (s, 2H), 6.02 (br s, 2H, NH2), 6.58–6.66 (m, 1H),
6.82–6.86 (m, 1H), 7.26–7.31 (m, 2H), 7.46–7.50 (m, 1H), 11.00
(br s, 1H, NH). dC (50 MHz, DMSO-d6) 12.05, 49.94, 59.32, 59.97,
108.73, 115.54, 117.45, 118.74, 129.26, 134.33, 139.92, 146.89,
151.20, 164.00. mmax (KBr) 3471m (NH), 3406m (OH), 3351m
(NH), 1714s (C@O), 1386s (C@O), 1625m, 1361s (SO2), 1143s
(SO2). HRMS m/z calcd for C14H18N4O5NaS (M+Na)+ 377.0890,
found 377.0903.
5.8. General method for the palladium-catalysed transfer
hydrogenation of derivatives 6a–c or 7a–c
Method B. A mixture of 9c (107 mg, 0.24 mmol), concentrated
ammonium hydroxide (5 mL), and methanol (5 mL) was heated
in a sealed tube at 70 °C for 1 day. The volatiles were evaporated
to dryness under reduced pressure. The residue was purified by
column chromatography (chloroform/methanol, 95:5, v/v) to af-
ford 8c (68 mg, 79%).
A mixture of 6a–c or 7a–c (200 mg), cyclohexene (8 mL), palla-
dium on charcoal (10% Pd/C, 100 mg), and a solvent (ethanol,
methanol, or 1,4-dioxane; 15 mL) was heated in a sealed tube at
60 °C for 1 day under an argon atmosphere. The catalyst was fil-
tered off, and the filtrate was concentrated to dryness. The residue

R. Gawin et al. / Bioorg. Med. Chem. 16 (2008) 8379–8389
8387
was purified by column or preparative thin-layer chromatography
5.8.5. 1-[N-(3-Aminobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
to afford the corresponding products (see Schemes 3–5); the elut-
ing solvents are given in parentheses below.
aminomethyl]-5-fluoro-1H,3H-pyrimidin-2,4-dione (11b)
According to the general procedure, 11b was obtained from 7b
(50 mg, 0.11 mmol) in 1,4-dioxane. Preparative thin-layer chro-
matography (chloroform/acetone, 85:15, v/v) provided 11b
(27 mg, 57%) as a white solid; mp 151–152 °C. dH (200 MHz,
DMSO-d6) 1.11 (s, 9H), 3.58–3.62 (m, 2H), 4.07–4.12 (m, 2H),
5.16 (s, 2H), 5.63 (br s, 2H, NH2), 6.78–6.89 (m, 2H), 6.91–7.06
5.8.1. 1-[N-(4-Aminobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
aminomethyl]-1H,3H-pyrimidin-2,4-dione (10a)
According to the general procedure, 10a was obtained from
6a (100 mg, 0.22 mmol) in ethanol. Column chromatography
(chloroform/acetone, 95:5, v/v) provided 10a (54 mg, 58%) as a
white solid; mp 147–149 °C. dH (200 MHz, DMSO-d6) 1.18 (s,
9H), 3.59–3.65 (m, 2H), 4.13–4.18 (m, 2H), 4.24 (br s, 2H,
3
(m, 1H), 7.16–7.23 (m, 1H), 7.77 (d, JH–F 6.6, 1H), 11.89 (br s,
1H, NH). dC (50 MHz, DMSO-d6) 26.86, 38.19, 47.79, 60.86,
2
61.68, 110.85, 112.89, 118.10, 128.53 (d, JC–F 33.8), 129.98,
3
1
2
NH2), 5.24 (s, 2H), 5.73 (m, JH–H 8.0, 1H), 6.62–6.68 (m, 2H),
139.40 (d, JC–F 229.5), 139.74, 149.81, 149.89, 157.45 (d, JC–F
25.8), 177.24. mmax (KBr) 3365m (NH), 3315m (NH), 1738s
(C@O), 1710s (C@O), 1691s (C@O), 1669m, 1599m, 1355s (SO2),
1165s (SO2). HRMS m/z calcd for C18H23N4O6FNaS (M+Na)+
465.1215, found 465.1224.
3
7.46–7.54 (m, 2H), 7.64 (d, JH–H 8.0, 1H), 8.74 (br s, 1H, NH).
dC (50 MHz, DMSO-d6) 27.31, 38.83, 47.66, 61.02, 62.49, 102.81,
114.30, 127.29, 129.16, 144.17, 151.22, 151.34 163.24, 178.27.
mmax (KBr) 3483m (NH), 3389m (NH), 1723s (C@O), 1710s
(C@O), 1687s (C@O), 1629m, 1598m, 1324s (SO2), 1146s (SO2).
HRMS m/z calcd for C18H24N4O6NaS (M+Na)+ 447.1309, found
447.1330.
5.8.6. 1-[N-(2-Aminobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
aminomethyl]-5-fluoro-1H,3H-pyrimidin-2,4-dione (11c)
According to the general procedure, 11c was obtained from 7c
(50 mg, 0.11 mmol) in 1,4-dioxane. Preparative thin-layer chro-
matography (chloroform/acetone, 85:15, v/v) provided 11c
(29 mg, 62%) as a white solid; mp > 170 °C (dec). dH (400 MHz,
DMSO-d6) 1.09 (s, 9H), 3.64–3.66 (m, 2H), 3.99–4.01 (m, 2H),
5.8.2. 1-[N-(3-Aminobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
aminomethyl]-1H,3H-pyrimidin-2,4-dione (10b)
According to the general procedure, 10b was obtained from 6b
(200 mg, 0.44 mmol) in ethanol. Column chromatography (chlo-
roform/acetone, 98:2, v/v) provided 10b (117 mg, 62%) as a white
solid; mp 147–148 °C. dH (200 MHz, DMSO-d6) 1.11 (s, 9H), 3.55–
3.60 (m, 2H), 4.06–4.11 (m, 2H), 5.18 (s, 2H), 5.6–5.64 (m, 3H),
6.79–6.87 (m, 2H), 6.92–6.98 (m, 1H), 7.16–7.23 (m, 1H), 7.56
5.24 (s, 2H), 6.03 (br s, 2H, NH2), 6.60–6.64 (m, 1H), 6.83 (d, 3J
3
8.4, 1H), 7.27–7.31 (m, 1H), 7.48 (d, JH–H 8.0, 1H), 7.74 (d,
H–H
3JH–F 6.8, 1H), 11.89 (br s, 1H, NH). dC (100 MHz, DMSO-d6)
26.85, 38.14, 47.10, 60.60, 61.08, 115.75, 117.62, 118.69, 128.63,
3
2
1
(d, JH–H 7.8, 1H), 11.30 (br s, 1H, NH). dC (50 MHz, DMSO-d6)
(d, JC–F 33.4), 129.20, 134.58, 139.23 (d, JC–F 229.8), 146.92,
2
26.84, 38.14, 47.53, 60.63, 61.86, 101.47, 110.96, 112.85, 118.00,
129.93, 139.69, 144.45, 149.70, 151.26, 163.36, 177.19. mmax
(KBr) 3373m (NH), 3305m (NH), 1740s (C@O), 1696s (C@O),
1679s (C@O), 1633m, 1599m, 1356s (SO2), 1155s (SO2). HRMS
m/z calcd for C18H24N4O6NaS (M+Na)+ 447.1309, found 447.1330.
150.01, 157.27 (d, JC–F 25.8), 177.24. mmax (KBr) 3488m (NH),
3367m (NH), 1735s (C@O), 1720s (C@O), 1699s (C@O), 1664m,
1629m, 1599m, 1324s (SO2), 1141s (SO2). HRMS m/z calcd for
C
18H23N4O6FNaS (M+Na)+ 465.1215, found 465.1222.
5.8.7. 1-[N-(4-Methylaminobenzenesulfonyl)-N-(2-pivaloyloxy-
ethyl)aminomethyl]-5-fluoro-1H,3H-pyrimidin-2,4-dione (12)
According to the general procedure, 12 was obtained from 7a
(100 mg, 0.21 mmol in methanol. Column chromatography (chlo-
roform/acetone, 95:5, v/v) provided 12 (43 mg, 45%) as a white so-
lid; mp 157–158 °C. dH (200 MHz, DMSO-d6) 1.10 (s, 9H), 2.72 (d,
3JH–H 5.0, 3H), 3.50–3.56 (m, 2H), 4.04–4.10 (m, 2H), 5.10 (s, 2H),
5.8.3. 1-[N-(2-Aminobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
aminomethyl]-1H,3H-pyrimidin-2,4-dione (10c)
According to the general procedure, 10c was obtained from 6c
(200 mg, 0.44 mmol) in ethanol. Column chromatography (chlo-
roform/acetone, 95:5, v/v) provided 10c (168 mg, 89%) as a white
solid; mp 146–147 °C. dH (200 MHz, DMSO-d6) 1.10 (s, 9H), 3.57–
3
3.63 (m, 2H), 3.97–4.02 (m, 2H), 5.30 (s, 2H), 5.58 (d, JH–H 8.0,
3
6.56–6.61 (m, 2H), 7.48–7.52 (m, 2H), 6.71 (q, JH–H 5.0, 1H, NH),
1H), 6.03 (s, 2H, NH2), 6.59–6.66 (m, 1H), 6.8–6.87 (m, 1H),
3
7.82 (d, JH–F 6.8, 1H), 11.48 (br s, 1H, NH). dC (50 MHz, DMSO-
3
7.27–7.35 (m, 1H), 7.46–7.50 (m, 1H), 7.56 (d, JH–H 8.0, 1H),
d6) 26.81, 29.10, 38.11, 47.53, 60.98, 61.91, 110.80, 123.35,
11.32 (br s, 1H, NH). dC (50 MHz, DMSO-d6) 26.84, 38.10, 46.68,
60.31, 61.84, 101.39, 115.70, 117.65, 118.55, 129.13, 134.50,
144.43, 146.93, 151.39, 163.39, 177.18. mmax (KBr) 3471m (NH),
3373m (NH), 1717s (C@O), 1702s (C@O), 1695s (C@O), 1670m,
1618m, 1340s (SO2), 1155s (SO2). HRMS m/z calcd for C18H24N4O6-
NaS (M+Na)+ 447.1309, found 447.1287.
2
1
128.64, (d, JC–F 33.8), 128.69, 139.32 (d, JC–F 229.1), 149.88,
2
153.53, 157.27 (d, JC–F 25.4), 177.17. mmax (KBr) 3430m (NH),
1738s (C@O), 1722s (C@O), 1684s (C@O), 1664m, 1599m, 1319s
(SO2), 1150s (SO2). HRMS m/z calcd for C19H25N4O6FNaS (M+Na)+
479.1371, found 479.1367.
5.8.8. 1-[N-(4-Dimethylaminobenzenesulfonyl)-N-(2-pivaloyl-
oxyethyl)aminomethyl]-5-fluoro-1H,3H-pyrimidin-2,4-dione (13)
According to the general procedure, 13 was obtained from 7a
(100 mg, 0.21 mmol in methanol. Column chromatography (chlo-
roform/acetone, 95:5, v/v) provided 13 (15 mg, 15%) as a white
solid; mp 164–165 °C. dH (200 MHz, DMSO-d6) 1.09 (s, 9H),
2.99 (s, 6H), 3.53–3.59 (m, 2H), 4.05–4.10 (m, 2H), 5.11
5.8.4. 1-[N-(4-Aminobenzenesulfonyl)-N-(2-pivaloyloxyethyl)
aminomethyl]-5-fluoro-1H,3H-pyrimidin-2,4-dione (11a)
According to the general procedure, 11a was obtained from 7a
(50 mg, 0.11 mmol) in 1,4-dioxane. Preparative thin-layer chroma-
tography (chloroform/acetone, 85:15, v/v) provided 11a (30 mg,
64%) as a white solid; mp 153–155 °C. dH (200 MHz, DMSO-d6)
1.10 (s, 9H), 3.50–3.57 (m, 2H), 4.03–4.10 (m, 2H), 5.10 (s, 2H),
6.14 (s, 2H, NH2), 6.58–6.62 (m, 2H), 7.42–7.46 (m, 2H), 7.82 (d,
3JH–F 6.8, 1H), 11.67 (br s, 1H, NH). dC (50 MHz, DMSO-d6) 26.84,
3
(s, 2H), 6.72–6.77 (m, 2H), 7.54–7.59 (m, 2H), 7.82 (d, JH–F
6.8, 1H), 11.83 (br s, 1H, NH). dC (50 MHz, DMSO-d6) 26.84,
2
2
38.18, 39.64, 47.68, 60.99, 61.95, 111.10, 123.75, 128.65 (d, JC–
38.15, 47.53, 61.04, 61.92, 112.79, 123.45, 128.26, (d, JC–F 32.7),
1
1
2
33.6), 128.46, 139.33 (d, JC–F 229.5), 149.87, 153.02, 157.30
128.84, 138.83 (d, JC–F 228.8), 149.86, 153.50, 157.24 (d, JC–F
25.8), 177.21. mmax (KBr) 3478m (NH), 3364m (NH), 1731s (C@O),
1716s (C@O), 1691s (C@O), 1672m, 1619m, 1599m, 1330s (SO2),
1145s (SO2). HRMS m/z calcd for C18H23N4O6FNaS (M+Na)+
465.1215, found 465.1235.
F
2
(d, JC–F 27.2), 177.22. mmax (KBr) 1735s (C@O), 1715s (C@O),
1694s (C@O), 1671m, 1598m, 1319s (SO2), 1172s (SO2). HRMS
m/z calcd for
C
20H27N4O6FNaS (M+Na)+ 493.1528, found
493.1552.

8388
R. Gawin et al. / Bioorg. Med. Chem. 16 (2008) 8379–8389
Imbach, J.-L. Nucleosides Nucleotides 1995, 14, 1795; (h) Sharma, M.; Li, Y. X.;
Ledvina, M.; Bobek, M. Nucleosides Nucleotides 1995, 14, 1831; (i) Urjasz, W.;
Celewicz, L.; Golankiewicz, K. Nucleosides Nucleotides 1996, 15, 1189; (j) Martin,
J. A.; Thomas, G. J.; Merret, J. H.; Lambert, R. W.; Bushnel, D. J.; Dundson, S. J.;
Freeman, A. C.; Hopkins, R. A.; Johns, I. R.; Keech, E.; Simmonite, H.; Wong-Kai-
In, P.; Holland, M. Antiviral Chem. Chemother. 1998, 1, 1; (k) Scherman, M. S.;
Winans, K. A.; Stern, R. J.; Jones, V.; Bertozzi, C. R.; McNeil, M. R. Antimicrob.
Agents Chemother. 2003, 47, 378; (l) Vanada, J.; Bennet, E.; Wilson, D.; Bishoff,
H.; Barry, C.; Aldrich, C. Org. Lett. 2006, 8, 4707.
5.9. General procedure for the ammonolysis of 5d or 6d
A mixture of 5d or 6d, concentrated ammonium hydroxide, and
methanol in the ratio of 0.5 mmol/10 mL/10 mL, respectively, was
heated in a sealed tube at 70 °C for 1 day. The volatiles were evap-
orated to dryness under reduced pressure. The residue was purified
by column chromatography (chloroform/methanol, 95:5, v/v) to
give 14a or 14b, respectively.
5. For 30-deoxy-30-sulfonamidofuranosyl nucleosides, see: (a) Van Calenbergh, S.;
Van Den Eeckhout, E.; Herdewijn, P.; De Bruyn, A.; Verlinde, C.; Hol, W.;
Callens, M.; Van Aerschot, A.; Rozenski, J. Helv. Chim. Acta 1994, 77, 631; (b)
Yamana, K.; Ohashi, Y.; Nunota, K.; Nakano, H. Tetrahedron 1997, 53, 4265.
6. For N-(p-toluenesulfonyl)pyrrolidines, see: (a) Nair, V.; Walsh, R. H. J. Org.
Chem. 1974, 39, 3045; (b) Ng, K. E.; Orgel, L. E. J. Med. Chem. 1989, 32, 1754; (c)
Pickering, L.; Malhi, B. S.; Coe, P. L.; Walker, R. T. Nucleosides Nucleotides 1994,
13, 1493; (d) Westwood, N. B.; Walker, R. T. Tetrahedron 1998, 54, 13391; (e)
Negwer, M.; Scharmow, H.-G. In Organic-Chemical Drugs and their Synonyms;
Wiley-VCH Verlag GmbH, 2001, p 1454.
5.9.1. 1-[N-(4-Acetamidobenzenesulfonyl)-N-(2-hydroxyethyl)
aminomethyl]-5-methyl-1H,3H-pyrimidin-2,4-dione (14a)
According to the general procedure, 14a was obtained from 5d
(136 mg, 0.28 mmol). Chromatographic purification afforded 14a
(105 mg, 94%) as a white solid; mp > 219 °C (dec). dH (200 MHz,
DMSO-d6) 1.73 (br s, 3H), 2.10 (s, 3H), 3.17–3.72 (m, 4H), 4.82
(br s, 1H, OH), 5.13 (s, 2H), 7.41 (br s, 1H), 7.69–7.85 (m, 5H),
10.80 (br s, 1H, NH). dC (50 MHz, DMSO-d6) 12.06, 24.18, 50.72,
59.70, 60.53, 108.80, 118.63, 123.94, 132.89, 140.26, 143.68,
151.15, 164.06, 169.30. mmax (KBr) 3406s (OH), 3312m (NH),
1715s (C@O), 1698s (C@O), 1664s (C@O), 1594m, 1537m, 1336s
(SO2), 1155s (SO2). HRMS m/z calcd for C16H20N4O6NaS (M+Na)+
419.0996, found 419.0998.
ˇ
ˇ
7. Krizmanic´, I.; Višnjevac, A.; Luic´, M.; Glavaš-Obrovac, L.; Zinic´, M.; Zinic´, B.
Tetrahedron 2003, 59, 4947. and references cited therein.
8. (a) Scozzafava, A.; Owa, T.; Mastrolorenzo, A.; Supuran, C. T. Curr. Med. Chem.
2003, 10, 925; (b) Supuran, C. T.; Casini, A.; Scozzafava, A. Med. Res. Rev. 2003,
23, 535; (c) Supuran, C. T.; Innocenti, A.; Mastrolorenzo, A.; Scozzafava, A. Mini-
Rev. Med. Chem. 2004, 4, 189.
´
9. (a) Koszytkowska-Stawinska, M.; Sas, W. Tetrahedron Lett. 2004, 45, 5437; (b)
Koszytkowska-Stawin´ ska, M.; Sas, W.; De Clercq, E. Tetrahedron 2006, 62,
10325; (c) Koszytkowska-Stawin´ ska, M.; Kaleta, K.; Sas, W.; De Clercq, E.
´
Nucleosides Nucleotides Nucl. 2007, 26, 51; (d) Koszytkowska-Stawinska, M.;
Kołaczkowska, E.; Adamkiewicz, E.; De Clercq, E. Tetrahedron 2007, 63, 10587.
10. (a) Pitman, I. H. Med. Res. Rev. 1981, 1, 189; (b) Gao, H.; Mitra, A. Synthesis 2000,
329; (c) Anastasi, C.; Quelever, G.; Burlet, S.; Garino, C.; Souard, F.; Kraus, J.-L.
Curr. Med. Chem. 2003, 10, 1825; (d) Calogeropoulou, T.; Detsi, A.; Lekkas, E.;
Koufaki, M. Curr. Top. Med. Chem. 2003, 3, 1467; (e) De Clercq, E.; Field, H. J. Br. J.
Pharmacol. 2006, 147, 1.
5.9.2. 1-[N-(4-Acetamidobenzenesulfonyl)-N-(2-hydroxyethyl)
aminomethyl]-1H,3H-pyrimidin-2,4-dione (14b)
According to the general procedure, 14b was obtained from
6d (81 mg, 0.18 mmol). Chromatographic purification afforded
11. Vorbrüggen, H.; Ruh-Pohlenz, C. In Handbook of Nucleoside Synthesis; John
Wiley: New York, 2001; pp 29-33.
14b (69 mg, 85%) as
a white solid; mp > 212 °C (dec). dH
(200 MHz, DMSO-d6) 2.10 (s, 3H), 3.21–3.59 (m, 4H), 4.83 (br
12. 4-Acetamido-N-(2-pivaloyloxyethyl)-N-(acetamidomethyl)benzenesulfonamide:
(36% yield); dH (200 MHz, CDCl3) 1.17 (s, 9H), 1.95 (s, 3H), 2.20 (s, 3H), 3.52 (t,
3JH–H 5.6, 2H), 4.19 (t, 3JH–H 5.6, 2H), 4.72 (d, 3JH–H 6.2, 2H), 6.55 (t, 3JH–H 6.2, 1H,
NH), 7.62–7.68 (m, 2H), 7.70–7.74 (m, 2H), 8.12 (br s, 1H, NH). dC (50 MHz,
CDCl3) 23.26, 24.77, 38.86, 46.65, 53.26, 62.20, 119.67, 128.30, 134.40, 142.64,
169.13, 170.98, 178.66. HRMS m/z calcd for C18H27N3O6NaS (M+Na)+ 436.1513,
found 436.1528.
13. Such competition of N-monosilylated or free acetamide with persilylated
nucleobases for sugar cation upon the nucleosides synthesis has been
reported (a) Cristalli, G.; Volpini, R.; Vittorio, S.; Camaioni, E.; Rafaiani, G.;
Potenza, S.; Vita, A. Nucleosides Nucleotides 1996, 15, 1567; (b) Ochoa, C.;
Provensio, R.; Jimeno, M. L.; Balzarini, J.; De Clercq, E. Nucleosides Nucleotides
1998, 17, 901.
3
3
s, 1H, OH), 5.16 (s, 2H), 5.62 (d, JH–H 8.0, 1H), 7.65 (d, JH–H
8.0, 1H), 7.70–7.75 (m, 2H), 7.81–7.85 (m, 2H), 8.44 (br s, 1H,
NH), 10.75 (br s, 1H, NH). dC (50 MHz, DMSO-d6) 24.05, 50.61,
59.53, 60.75, 101.21, 118.45, 127.75, 132.52, 143.46, 144.66,
150.94, 163.30, 169.04. mmax (KBr) 3394s (OH), 3327m (NH),
1718s (C@O), 1698s (C@O), 1671s (C@O), 1591s, 1522s, 1154s
(SO2), 1342s (SO2). HRMS m/z calcd for C15H18N4O6NaS
(M+Na)+ 405.0839, found 405.0859.
14. (a) Watanabe, K. A.; Beránek, J.; Friedman, H. A.; Fox, J. J. J. Org. Chem. 1965, 30,
2735; (b) Friedman, H. A.; Watanabe, K. A.; Fox, J. J. J. Org. Chem. 1967, 32, 3775;
(c) Matsuda, A.; Watanabe, K. A. Nucleosides Nucleotides 1996, 15, 205; (d) Ohta,
N.; Minamoto, K.; Yamamoto, T.; Koide, N.; Naoya, S.; Sakodo, R. Nucleosides
Nucleotides 1996, 15, 833; (e) Rozens, E.; Katkevica, D.; Bizdena, E.; Stroemberg,
R. J. Am. Chem. Soc. 2003, 125, 12125; (f) Glinski, R. P.; Sporn, M. B. Biochemistry
1972, 11, 405; (g) Liu, B.; Hu, L. Bioorg. Med. Chem. 2003, 11, 3889; (h) Baer, H.
H.; Bayer, M. Can. J. Chem. 1971, 49, 568.
15. For the reduction of nucleoside analogues with the nitro group in a nucleobase
moiety, see: (a) Bigge, C. F.; Kalaritis, P.; Deck, J. R.; Mertes, M. P. J. Am. Chem.
Soc. 1980, 102, 2033; (b) Dziwiszek, K.; Schinazi, R. F.; Chou, T.-C.; Su, T.-L.;
Dzik, J. Nucleosides Nucleotides 1994, 13, 77; (c) De Riccardis, F.; Bonala, R. R.;
Johnson, F. J. Am. Chem. Soc. 1999, 121, 10453; (d) Chakraborti, D.; Colis, L.;
Schneider, R.; Bau, A. Org. Lett. 2003, 5, 2861; (e) Takamura-Enya, T.; Enomoto,
S.; Wakabayashi, K. J. Org. Chem. 2006, 71, 5599.
Acknowledgments
The synthetic part of this work was financially supported by
Warsaw University of Technology. We thank Dr. Wojciech Sas,
Warsaw University of Technology, for his support, and fruitful
discussions. We thank Leentje Persoons, Frieda De Meyer and
Vicky Broeckx for excellent technical help, and the International
Consortium for Antivirals (ICAV) and Fonds voor Wet-
enschappelijk Onderzoek Vlaanderen for financial support (Pro-
ject No. G.0188.07).
References and notes
16. For reviews, see: (a) Johnstone, R. A. W.; Wilby, A. H. Chem. Rev. 1985, 85, 129;
(b) Rylander, P.N. In Hydrogenation Methods; Academic Press, 1985; pp 16-17,
104–107, and 163.
1. (a) De Clercq, E. J. Clin. Virol. 2004, 30, 115; (b) Galmarini, C. M.; Mackey, J. R.;
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P. Nat. Rev. Drug Disc. 2005, 4, 535.
2. (a) Johnson, A. A.; Ray, A. S.; Hanes, J.; Suo, Z.; Colacino, J. M.; Anderson, K. S.;
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Chemother. 2003, 51, 1079; (c) Jeha, S.; Gandhi, V.; Chan, K. W.; McDonald, L.;
Ramirez, I.; Madden, R.; Rytting, M.; Brandt, M.; Keating, M.; Plunkett, W.;
Kantarjian, H. Blood 2004, 103, 784.
17. The 11a: 10a ratio was estimated from the 1H NMR spectrum of the mixture by
the comparison of the intensities of the signals corresponding to the H-6
3
3
proton of 10a [7.64 (d, JH–H 8.0 Hz)] and to the H-6 one of 11a [7.82 (d, JH–F
6.8 Hz)].
18. (a) Duschinsky, R.; Pleven, E. J. Am. Chem. Soc. 1957, 79, 4559; (b) Colla, L.;
Herdewijn, P.; De Clercq, E.; Balzarini, J.; Vanderhaeghe, H. Eur. J. Med. Chem.
Chim. Ther. 1985, 20, 295.
19. The reference antivirals displayed the following MCC values: (a) Vero cells:
3. Gumina, G.; Olgen, S.; Chu, C. K. In Antiviral Nucleosides: Chiral Synthesis and
Chemotherapy; Chu, C. K., Ed.; Elsevier B.V., 2003; pp 161–169.
brivudin, >250
brivudin, >250
>100 M; (c) HeLa cells: brivudin, >250
propyl)adenine [(S)-DHPA], >250 M; ribavirin, >250
oseltamivir carboxylate, >100 M; ribavirin, 100 M; amantadin, >100
rimantadin, >100 M.
20. The reference antivirals displayed the following CC50 values: (a) MDCK cells:
oseltamivir carboxylate, >100 M; ribavirin, >100 M; amantadin, >100 M;
rimantadin, >100 M; (b) CRFK cells: hippeastrum hybrid agglutinin (HHA),
>100 g/mL; urtica dioica agglutinin (UDA), >100 g/mL; ganciclovir, >100 M.
l
l
M; [(S)-DHPA], >250
M; ribavirin, >250
l
l
M; ribavirin, >250
M; acyclovir, >250
M; (S)-9-(2,3-dihydroxy-
M; (d) MDCK cells:
M;
l
M; (b) HEL cells:
4. For 50-deoxy-50-sulfonamidofuranosyl nucleosides, see: (a) Markham, A. F.;
Newton, C. R.; Porter, R. A.; Sim, I. S. Antiviral Res. 1982, 2, 319; (b) Cosstick, R.;
Jones, A. S.; Walker, R. T. Tetrahedron 1984, 40, 427; (c) Elliott, R. D.; Brockman,
R. W.; Montgomery, J. A. J. Med. Chem. 1986, 29, 1052; (d) Sim, I. S.; Picton, C.;
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1988, 7, 129; (e) Martin, J. A.; Duncan, I. B.; Hall, M. J.; Wong-Kai-In, P.;
Lambert, R. W.; Thomas, G. J. Nucleosides Nucleotides 1989, 8, 753; (f) Homma,
H.; Watanabe, Y.; Abiru, T.; Murayama, T.; Nomura, Y.; Matsuda, A. J. Med.
Chem. 1992, 35, 2881; (g) Criton, M.; Dewyntert, G.; Aouf, N.; Montero, J.-L.;
lM; ganciclovir,
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l

R. Gawin et al. / Bioorg. Med. Chem. 16 (2008) 8379–8389
8389
21. The estimated values indicate that in the case of both the host cell cultures,
cytotoxicity of the 5-fluorouracil nitro derivatives decreases in the following
order: 2-NO2 isomer > 4-NO2 isomer > 3-NO2 isomer. However, based on our
current knowledge, it is difficult to discuss on the relationship between NO2-
isomerism and cytotoxicity of the compounds.
22. (a) De Clercq, E.; Descamps, J.; Verhelst, G.; Walker, R. T.; Jones, A. S.;
Torrence, P. F.; Shugar, D. J. Infect. Dis. 1980, 141, 563; (b) De Clercq, E.;
Cools, M.; Balzarini, J.; Marquez, V. E.; Borcherding, D. R.; Borchardt, R. T.;
Drach, J. C.; Kitaoka, S.; Konno, T. Antimicrob. Agents Chemother. 1989, 33,
1291.