NMR and UV studies of 4-thio-2′-deoxyuridine and its derivatives

Article abstract of DOI:10.3390/molecules16075655

5-Substituted-4-thio-2'-deoxyuridine nucleosides have been chemically synthesized and studied by NMR and UV spectroscopy. The results have been analyzed and discussed in connection with the previous data. The imino proton signal and the carbon signal of the thiocarbonyl group in the 5-substituted-4-thio-2'-deoxyuridines were found to be at much lower field, offering a potential for monitoring these modified bases at the DNA level. All 4-thionucleosides have strong absorptions at around 340 nm and consequently would be useful as potential UVA-induced anticancer agents.

Full text of DOI:10.3390/molecules16075655

Molecules 2011, 16, 5655-5664; doi:10.3390/molecules16075655
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Communication
NMR and UV Studies of 4-Thio-2′-deoxyuridine and
Its Derivatives
1
,
2
Xiaohui Zhang * and Yao-Zhong Xu
1
College of Environment and Chemical Engineering, Dalian University, Dalian 116622, China
Department of Chemistry, the Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
2
*
Author to whom correspondence should be addressed; E-Mail: xiaohui99@hotmail.co.uk;
Tel.: +86-411-8740-2378; Fax: +86-411-8740-2299.
Received: 30 May 2011 / Accepted: 10 June 2011 / Published: 1 July 2011
Abstract: 5-Substituted-4-thio-2’-deoxyuridine nucleosides have been chemically
synthesized and studied by NMR and UV spectroscopy. The results have been analyzed
and discussed in connection with the previous data. The imino proton signal and the carbon
signal of the thiocarbonyl group in the 5-substituted-4-thio-2’-deoxyuridines were found
to be at much lower field, offering a potential for monitoring these modified bases at
the DNA level. All 4-thionucleosides have strong absorptions at around 340 nm and
consequently would be useful as potential UVA-induced anticancer agents.
Keywords: NMR; UV; 4-thiothymidine; DNA
1
. Introduction
Cancer is one of major killers in modern society. The fundamental cause for cancer incidence is
DNA damage and mutation [1]. An agent or treatment that can cause DNA damage can also be used
as a therapeutic means by destroying cancerous cells. This, in fact, is the principle underlying
chemotherapy and radiotherapy. However, often such treatments are either too toxic (in the case of
chemotherapy) or too powerful (in the case of radiotherapy) and thus indiscriminate, also causing harm
to normal cells. Clearly, improved treatments for cancer patients are urgently required. Recently we
reported that 4-thiothymidine (thioT), an analogue of the naturally occurring nucleoside thymidine, can
be incorporated into cellular DNA and activated by UVA light to kill cells [2,3]. These findings
offered a new therapeutic approach to cancer treatment. This mild and synergistic approach has
the advantage over conventional therapies, that it can target proliferating cells more selectively.

5
656
Molecules 2011, 16
As a part of our ongoing work, several 5-substituted-4-thio-2’-deoxyuridine derivatives (including
-bromo-4-thio-2’-deoxyuridine [4] and 5-iodo-4-thio-2-deoxyuridine) were synthesized and their
physico-chemical properties explored by NMR and UV spectroscopy. Interestingly, a great number of
-substituted-2’-deoxyuridines have been synthesized and tested for anti-viral or anti-cancer activity [5,6].
5
5
However, to our surprise, only very few 5-substituted-4-thio-2’-deoxyuridines have been prepared [7-11]
and little biological exploitation carried out [8]. Here we present our main findings on this topic and
review their useful properties in relation with other thio-analogues.
2
. Results and Discussion
Previously we reported a simple method for preparation of 4-thiothymidine by replacing the
-oxygen of thymidine with sulfur [10]. More recently we extended the method to preparation
4
of 5-bromo-4-thio-2’-deoxyuridine [4] and others. A general scheme for the preparation of
-substituted-4-thio-2’-deoxyuridines is shown in Scheme 1. 2’-Deoxyuridine (1a) and its 5-substituted
5
compounds (1b–1f) were converted to their 4-thio-analogues (2a–2f) by simply replacing oxygen atom
at the 4-position with sulfur. These conversions are minimal modifications of 5-substituted-
2
’-deoxyuridine, thus possessing a good chance for the 4-thioanalogues to be incorporated into cellular
DNA. Interestingly, the replacement of oxygen atom with sulfur shifts the UV spectra of the
corresponding nucleosides to longer wavelengths with maxima at around 330–340 nm (the UVA range)
as shown in Figure 1. The substituent at the 5-position also influences UV maxima: H (262 nm in
H O) [12], CH (267 nm in H O) [12], F (265 nm in CH CN) [13], Cl (277 nm in MeOH) [14], Br
2
3
2
3
(
279 nm in MeOH) [14] and I (285 nm in CH
3
OH) [14] for 5-substituted-2’-deoxyuridine. A red shift
around 60–70 nm was found for 5-substituted-4-thiouridines and increased along with the conjugation
capability of the substituents from H (332 nm in CH CN), CH (336 nm in CH CN), F (336.4 nm in
O) [15], Cl (339 nm in H O) [16], Br (340 nm in CH CN) to I (345 nm in CH CN). Clearly all these
3
3
3
H
2
2
3
3
4-thioanalogues (2) are sensitive to UVA light, offering therapeutic potential as UVA-induced drugs [2,3].
Scheme 1. Chemical transformation of 5-substituted nucleosides to its 4-thioanalogues.
O
S
a)
b) X= CH3
c) X= F
d) X= Cl
X= H
X
X
4
4
5
6
NH
2
5
6
NH
2
N
O
N
O
e)
f)
X=Br
X=I
HO
HO
5
'
5'
O
O
1
'
1'
4
' 3'
2'
4' 3'
2'
OH
OH
1
2
Reaction conditions: (i) ClSi(Me)
3
/TEA; (ii) Triazole/POCl
3
/TEA; (iii) CH
3
COSH; (iv) 1N HCl.

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Molecules 2011, 16
Figure 1. UV spectra of 5-substituted-2’-deoxyuridines (in CH
3
OH) and their
4
3
-thioanalogues (in CH CN).
2
T
BrdU
IdU
1.6
1.2
0.8
0.4
0
thio-T
thio-Br-dU
thio-I-dU
200
220
240
260
280
300
320
340
360
380
400
-0.4
1
1
H-NMR: Table 1 lists the H-NMR chemical shifts of the 5-substituted 2’-deoxyuridines and their
-thioanalogues synthesized in our lab and some related compounds from the literature. Nucleosides
4
consist of a sugar (deoxyribose) and a base. Since the modification is made on the base, chemical
shifts of the base protons are substantially different, in particular, the 3-position imino group (NH).
On the other hand, the chemical shifts of the sugar moieties are little changed.
1
Table 1. H-NMR of 5-Substituted-2’deoxyuridines and their 4-thioanalogues (in DMSO-d
6
).
CH3
5.67(5-H) 6.12
1’-H
2’-H
2.47
2.49
2.10
2.13
2.12
2.10
2.11
2.14
3’-H 4’-H
4.21 3.76
4.22 3.74
4.25 3.78
4.25 3.80
4.22 3.78
4.22 3.78
4.22 3.81
4.24 3.79
5’-H 3’-OH 5’-OH 6-H
NH
1
a
3.54
3.55
3.62
3.61
3.58
3.58
3.56
3.59
5.24
5.21
5.25
5.25
5.25
5.23
5.26
5.27
5.01 7.84 11.28
5.01 7.68 11.25
5.15 8.21 11.82
5.16 8.32 11.83
5.17 8.38 11.78
5.14 8.38 11.65
1b
1.79
6.15
6.12
6.11
6.08
6.08
1
c [13]
1
d [14]
1
e
1
f
2
a
6.30(5-H) 6.07
1.96 6.10
5.03
5.10
7.78 12.68
7.89 12.69
2b
2
2
c [15]
d [16]
6.11 2.6-2.2 4.30 3.87 3.8-3.6 5.3-3.4 5.3-3.4 8.33 12.80
5.81
6.02
6.01
4.16
2.21
2.17
3.95 4.27
4.22 4.09
4.23 3.81
3.54
3.61
3.59
5.47
5.26
5.25
5.03
5.21
5.18
8.05 13.10
8.52 13.08
8.55 12.99
2
e
2
f
Data for 5-fluoro-2’-deoxyuridine (1c), 5-chloro-2’-deoxyuridine (1d), 5-fluoro-4-thio-
’-deoxyuridine (2c) and 5-chloro-4-thiouridine (2d) are from references [13-16], respectively.
2
The presence of a thiocarbonyl group in 2 is evident from the appearance of NH and thiocarbonyl
1
13
carbon signals in the H and C-NMR spectra respectively. Exchangeable signals in the δ
1
1
2.68–13.10 ppm range in the low-field part of H-NMR spectra, attributable to the N–H protons,
suffort the structures of molecules 2. The appearance of only one carbon signal in the
185.30–190.70 ppm region (characteristic for a thiocarbonyl group) together with an intense
δ
C

5
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Molecules 2011, 16
absorption band at 332–344 nm in the UV spectra (Figure 1), confirm the presence of the thiocarbonyl
moieties in compounds 2.
1
It is interesting to note that the H chemical shifts of the imino proton (NH) in all the
thionucleosides 2 are substantially higher (at around 13 ppm) than those of the parent nucleosides 1
that resonate at δ 11.2–11.83 ppm (Table 1). This difference offers a valuable NMR window to detect
the imino proton of thionucleosides, as in general there are no signals from normal nucleosides
appearing at such a low field. In addition these NH-proton signals are exchangeable and readily
identifiable by D O exchange experiments. Therefore these would also be a good marker in NMR
2
studies of 4-thionucleosides and their corresponding DNAs.
1
3
13
C-NMR: All the C signals were assigned using the standard procedure or DEPT protocols or
13
2
-D NMR spectroscopy where necessary. A careful inspection of the C-NMR data (Table 2) provides
1
3
useful structural information. As the modification occurs on the base, this is also reflected in the C
chemical shifts of the base. There are four carbons on the base. The carbon at C-2- position (i.e., 2-C)
is substantially away from the modified positions (4 and 5), thus the chemical shifts of C-2 vary little.
1
3
The most notable differences between the C-NMR spectra of 1 and 2 are the chemical shifts of the
carbon at the 4-position (i.e., 4-C), and a characteristic downfield shift (from δ around 160 to
around 190 ppm) was observed. This could be due to increased conjugation by the replacement of
C
δ
C
oxygen with sulfur at the 4-position. Interestingly, 2-thio-2’-deoxynucleosides differ only slightly
while 4-thio-2’-deoxynucleosides exhibit somewhat large differences [8]. As shown in Figure 1, the
introduction of a sulfur atom at the 4-position in the nucleosides shifts their UV spectra towards longer
wavelength with maxima at 330 to 340 nm. In contrast, the UV spectra of 2-thio-2’-deoxyuridine
analogues are similar to those of their un-modified nucleosides. For instance the UV λmax of
2
2-thio-2’-deoxyuridine is at 273 nm (in H O) [17] which is only slightly changed from that of its parent
compound 1a (UV λmax at 262 nm). Due to the energy level of lone pair electrons of 3p in sulfur is
*
higher than that of lone pair electrons of 2p in oxygen, the requied energy of the n→π transition for a
thiocarbonyl is lower than that for a carbonyl. Although the spectra of 2-thionucleosides containing
C=S bonds would be expected to shift to longer wavelengths relative to those containing C=O bonds,
the thiocarbonyl in 2-position is attached to two nitrogens, so the UV absorption wavelength should
also move back to shorter wavelengths. Overall, in the end there is a little change in the UV absorption
maxima for the 2-thionucleoside analogues. This is also one of the reasons why 2-thionucleoside
analogues are not exploited as useful agents for UVA-induced DNA damage.
1
3
6
Table 2. C-NMR of 5-Substituted uridine derivatives and their 4-thioanalogues (in DMSO-d ).
CH
3
1’-C 2’-C 3’-C 4’-C 5’-C
2-C
4-C
5-C
6-C
1
a
--
84.11 39.63 70.43 87.40 61.29 150.45 163.14 101.76 140.53
1b
12.26 83.73 39.40 70.43 87.24 61.33 150.46 163.75 109.36 136.12
1
c [18]
--
--
--
--
86.99 42.05 72.15 89.04 62.83 151.03 159.90 142.03 126.44
91.18 N/A 74.78 87.55 61.12 149.51 158.93 106.63 138.53
84.90 40.18 70.01 87.61 60.85 149.82 159.28 95.76 140.37
84.65 40.19. 70.01 87.52 60.82 150.12 160.51 69.27 145.05
1
d [16]
1
e
1
f

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Molecules 2011, 16
Table 2. Cont.
CH
3
1’-C 2’-C 3’-C 4’-C 5’-C
2-C
4-C
5-C
6-C
2
a
--
85.00 N/A 70.10 87.70 61.00 147.70 190.00 112.60 135.90
2b
17.00 84.70 39.90 70.10 87.70 61.00 147.80 190.70 117.70 133.50
2
c [23]
--
--
--
--
87.66 80.22 72.97 69.82 62.76 146.39 179.86 147.23 118.16
92.27 79.51 75.04 88.78 61.18 147.03 185.30 116.37 135.45
85.63 39.23 69.43 87.78 60.40 147.19 186.39 106.63 137.29
85.39 39.50 69.50 87.74 60.41 147.63 189.31 82.99 140.15
2d [16]
2
e
2
f
Data for 5-Fluoro-2’-deoxyuridine (1c), 5-Chloro-2’-deoxyuridine (1d), 5-Fluoro-4-thiouridine (2c)
and 5-Chloro-4-thiouridine (2d) are from references [16,18] respectively).
1
3
As the major factor in C chemical shift is paramagnetic shielding, that is different from
1
13
diamagnetic shielding in H chemical shift, thus the shielding constant σ for C spectrum is generally
expressed as below [19]:
2
2
−1
−3
2
2
p B
σ = −e h (ΔE) {r }2p[QAA + Σ QAB] / 2m C
−
1
−3
or σ ∝ −(ΔE) {r }
p
2p
where C is the light speed; m and e are respectively for the mass of atom and number of electron; the
−3
term {r }2p is the mean inverse cube of the distance from the nucleus for the carbon 2p atomic orbit;
This term accounts for the charge density effect in the paramagnetic term since increasing charge
density leads to an expansion of the orbital and thereby a reduction in σ
p
; ΔE represents the excitation
energy of average electron to the low lying excited state; Σ goes over all atoms; Q is bond order; QAA
B
is contribution of electron density of 2p orbital in nucleus; QAB is bond order between nucleus and
bond which relate to nucleus.
Comparing the carbonyl oxygen group in a nucleoside with the thiocarbonyl sulfur group in a
−3
thionucleoside would lead to the prediction that σ
p
should be more for the latter if the {r }2p term
dominates since there is a less contribution from electronegativity on sulfur, the deshielding of carbon
1
3
atom is strong and the signal carbon resonate moves to lower field such as the C-NMR spectra of
δ = 159.28–163.75 ppm for C=O in compound 1 and δ = 179.86–190.70 ppm for C=S in compound 2.
C
C
Obviously, the equation shows that the ׀σ
p
׀ dependence is mainly affected by the excitation energy
of an average electron ΔE to paramagnetic shielding under consideration; that is, the bigger ׀σ
stronger paramagnetic shielding, and the atom will resonate at lower field. Therefore, σ depends upon
ΔE. In addition, it has been shown by Figgis et al. [20] that organic carbonyl oxygen shieldings
p
׀, the
p
n→π*
correlate approximately with λmax
electronic transition). For C=O, it is n→π absorption, the absorption of UV is 280 nm, (ΔE) which is
values (i.e., the inverse of the excitation energy for the lowest
*
−1
bigger makes ׀σ
p
׀ bigger, the deshielding of the carbon atom is stronger, and the signal carbon
*
resonance moves to lower field. For C=S, it is also n→π , the absorption of UV moves towards longer
wavelength, approaching to 400 nm, the intensity of absorption in C=S is bigger than that in C=O, so
1
3
the wave of absorption is longer. For C-NMR, the C=S resonance is downfield in comparison with
that in a C=O.
Since the C=C double bond carries a polar group, the electron distribution is thus displaced. This
displacement is usually understood as a combination of inductive effects and conjugative effects.

5
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Molecules 2011, 16
There is the electron excited state as n-π* or π-π* in molecules where C=C double bond attached a
polar group when highly electronegative atoms like halogen are near these sigma σ electrons. The
highly electronegative atoms attract these sigma σ electrons toward themselves and away from the
spinning nuclei. These would affect on the deshielding and an NMR signal to be generated would
move further downfield.
Table 2 shows that the 5-C signals of the fluorine-modified deoxyuridine 1c and its thioanalogue
2
c are substantially different from other halogen-modified compounds 1d, 1e, 1f and their
1
3
4
-thioanalogues 2d, 2e, 2f respectively. Figure 2 plots C chemical shifts of C-5 against with the
electronegativity of the 5-substitutents. The greater the electronegativity of atom or group, the lower
the electron density around C–X and the further downfield the chemical shift. When linked with
fluorine atom, the 5-C has the highest values, namely 142.03 ppm (for 1c) and 147.23 ppm (for 2c).
This could be ascribed to the extremely high electronegativity of fluorine. F, Cl, Br and I are each
more electronegative than the H atom, it could be anticipated that, when the H atom of C-5 are
1
3
replaced by these substituents, the C resonance would be progressively shiftded to much lower field.
Obviously, the electron-withdrawing inductive effects of the 5-substituent do play an important role
for F, Cl and methyl group. However when a substituent at the 5-position is I or Br, the chemical shift
1
3
of the 5-C is even lower than that of those 5-C bearing H- or CH group. The C resonance of C-5
3
for BrdU (5-bromo-2’-deoxyuridine) and IdU (5-iodo-2’-deoxyuridine) is displaced to higher field
relative to that of dU (2’-doxyuridine) by 6 ppm for BrdU and by 32.49 ppm for IdU. Clearly the
electron-withdrawing effect alone is not enough to explain those. This unusual effect could be
explained by “heavy atom effect” which invariably cause shifts upfield [21]. When a carbon atom is
attached by heavy halogen atom (such as Br or I), the diamagnetic interactions arising from more
1
3
electron charge within Br or I atoms may exhibit an abnormally high C shielding and cause the
1
3
chemical shift of C resonance to upfield.
On the other hand, the circulating π electrons are in the delocalized pyrimidine ring. These π
electrons create a magnetic field that is parallel to the lines of force of the external magnetic field. This
will aid the external field (a deshielding effect) and allow the NMR signal generation to occur at a
lower magnetic field strength setting. For example, the carbons at the 6-position of 1c and 2c have
C C
reduced values (δ 126.44 ppm for 1c and δ 118.16 ppm for 2c). These results can be explained by
the conjugative effects which operate in the π-system and have π-donor group for p orbital in Cl, Br, I,
causing an upfield shift. Therefore, as the conjugation to p orbital of Cl and Br elements usually has a
smaller effect on C=C than that to p orbital of I element, so the signal of C-6 of iodo-substituted
nucleosides (1f and 2f) have high values than other halogen-substituted analogues.
Such a shift suggests possible changes of base-pairing properties compared with their parent
nucleosides. The cause of this lower field shift may also reflect the longer conjugation of the ring
system of thio-nucleosides. This is further evidenced from their longer wavelength absorption in their
UV spectra (Figure 1). In general, deoxyuridine nucleosides have absorption maxima at 260–285 nm
*
arising from their π→π transitions. Although several deoxyuridines containing an X group are found
to have increased UV maxima and 4-thioanalogues have further increased UV maxima, there is still a
need for new compounds absorbing at even long-wavelengths. We developed a method by replacing
the oxygen atom by sulfur to produce UVA-sensitive thio-analogues as shown in Scheme 1 (above).

5
661
Molecules 2011, 16
1
3
Figure 2. C chemical shift of the atom (group) at 5-C plotted against its electro negativity.
The replacement of an oxygen atom at the 4-position by selenium in uridine derivatives
produces UVA-sensitive 4-seleno-uridine and its analogues [22]. The UV absorption spectrum for
4
-seleno-2’-deoxyuridine was compared to that of 2’-deoxyuridine and 4-thio-2’-deoxyuridine. As
expected, its absorption maximum was found at longer wavelength [368 nm (in H O)] than those of
2
2’-deoxyuridine and 4-thio-2’-deoxyuridine. This is due to the fact the energy level of the lone pair on
selenium is higher than those on a sulfur atom or an oxygen atom, (ΔE) which is smaller, leads to
longer wavelength absorption. Therefore the 4-selenonucleosides would be more sensitive toward
UVA light than 4-oxy- and 4-thio-nucleosides. This UVA absorption property should provide a
potential to specially target molecules of seleno-modified DNA with UVA light at 368 nm.
Recently, much effort was directed to study the photophysical and photochemical properties of
uridine derivatives that contain both C=O and C=S fragments. In the series of 4-thio-2’-deoxyuridines,
it was found that the presence of the C=S function in the molecules dominated their photochemistry in
aqueous solution [2,8,23,24]. According to the idea, 4-selenouridine derivatives that contain X groups
(
where X = halogen) will shift to much longer UV wavelengths than that of thiocarbonyl groups and
could be particularly useful as potential UVA-induced anticancer agents.
In summary, the thiation of nucleosides and related compounds has been extensively studied in the
past, the UVA-sensitive 4-thio-2’deoxyuridine and its derivatives have never been studied in detail by
NMR and UV spectroscopy. We have now established the identities of the thio products derived from
carbonyl products in NMR and UV spectroscopy.
3. Experimental
3.1. General
1
13
H-Nuclear magnetic resonance (NMR) spectra and C-NMR spectra were recorded using a
1
13
JEOL LA300 spectrometer at 300 and 75 MHz, respectively. H-NMR and C-NMR spectra were
determined in DMSO-d solution and chemical shifts are quoted in parts per million (p.p.m.) from
tetramethylsilane as internal standard. Ultraviolet spectra were recorded with a Philips PU 8700
UV/Vis spectrophotometer for 5-substituted 4-thio-2’-deoxyuridine derivative (50 mM in CH CN).
6
3

5
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Molecules 2011, 16
3
.2. Typical Thiation Chemical Preparation of 5-Substituted-4-thiouridine Derivatives
A general procedure is described for the chemical synthesis of 4-thio-2’-deoxyuridine (2a),
-thiothymidine (2b), 5-bromo-4-thio-2’-deoxyuridine (2e) and 5-iodo-4-thio-2’-deoxyridine (2f). The
4
appropriate 5-substituted-deoxyuridine derivative (16 mmol, ca. 3.9~5.7 g) was dissolved in dry THF
150 mL). Triethylamine (63.4 mL, 0.454 mol) was added, followed by trimethylchlorosilane (6.34 mL,
1.2 mmol). The reaction mixture was stirred in an ice bath for 2.5 h after all the materials were added.
(
8
TLC showed no residual starting material at this time. The reaction mixture was diluted with 50%
ethyl acetate in hexane (250 mL), washed with water (2 × 100 mL) and saturated aqueous NaCl (80 mL).
The aqueous phase was back extracted with 50% ethyl acetate in hexane (1 × 150 mL). The combined
organic phase was dried (Na SO ), and evaporated to give crude product which was used directly in the
2
4
next step.
,2,4-Triazole (6.8 g, 98.4 mmol) was suspended in anhydrous CH
then triethylamine (16 mL) were added slowly. After 1 h, the 3’,5’-bis-(trimethylsilyl)-5-substituted-
’-deoxyuridine derivative (6.7 mmol) in CH CN (30 mL) was added over 30 min. Then the solution
1
3 3
CN (80 mL) at 0 °C. POCl (2.1 mL),
2
3
was stirred for 16 h at room temperature and the reaction was monitored by TLC (solvent: 50:50
n-pentane/diethyl ether). After the starting material was converted into a new compound with lower Rf,
the reaction mixture was filtered, diluted with ethyl acetate (160 mL) and washed with saturated
aqueous NaHCO
3
(150 mL), then twice with 150 mL of saturated aqueous NaCl. The organic layer
SO and the solvent evaporated. The residue was dried by repeated
was dried over anhydrous Na
2
4
evaporation of a toluene solution to give product, then used in the next step.
To a solution of 3’,5’-O-(trimethylsilyl)-5-substituted-2’-deoxy-4-triazolyuridine derivative (6.0 mmol)
in CH
mixture was left stirring overnight and monitored with TLC (5% CH
starting material was completely converted into a new spot. The reaction solution was diluted with
CH Cl (250 mL), washed with saturated NaHCO (2 × 250 mL), then with saturated aqueous NaCl
250 mL). The organic layer was dried (Na SO ) and evaporated under reduced pressure to give crude
3
CN (120 mL) was added thioacetic acid (6 mL, 6.39 g, 83.9 mol) in an ice bath. The reaction
3
OH in CHCl as eluent) until the
3
2
2
3
(
2
4
product, which was taken up in THF and acidified with 1 N HCl (pH = 3). The mixture was stirred at
room temperature for 20 h and the reaction monitored by TLC. The desilylated 4-thio-2’-deoxyuridine
3 3
product was purified by column chromatography on silica gel (eluting with 5% CH OH in CHCl ) to
afford the corresponding products 2a, 2b, 2e or 2f (1.39 g, 38%;, 1.69 g, 36%; 1.62 g, 31; 1.59 g, 27%
overall yield from 5-substituted-2’-deoxyuridine derivatives, respectively).
4
. Conclusions
-Substituted-4-thio-2’-deoxyuridines can be effectively prepared from its parent nucleosides and
5
have distinctive NMR and UV properties that can be used for easy monitoring and exploited as
potential UVA-induced anticancer agents.

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Molecules 2011, 16
Acknowledgements
The Project Sponsored by the Open University, UK and the Scientific Research Foundation for the
Returned Overseas Chinese Scholars, State Education Ministry, China. We are grateful to John Joule,
The Manchester University, UK for his critical reading of earlier versions of the manuscript.
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