Received: October 21, 2014 | Accepted: November 7, 2014 | Web Released: November 18, 2014
CL-140965
5-Iodo-4-thio-2¤-deoxyuridine: Synthesis, Structure, and Cytotoxic Activity
1
1
2
3
3
Xiao-Hui Zhang,* Hong-Yan Yin, Giuseppe Trigiante, Reto Brem, Peter Karran,
4
4
2
Mateusz B. Pitak, Simon J. Coles, and Yao-Zhong Xu*
College of Environment and Chemical Engineering, Dalian University, Dalian 116622, P. R. China
1
2
Department of Life, Health and Chemical Sciences, the Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
3
Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Herts. EN6 3LD, UK
4
UK National Crystallography Service, Chemistry, Faculty of Natural and Environmental Sciences,
University of Southampton, Highfield Campus, Southampton, SO17 1BJ, UK
(
E-mail: y.z.xu@open.ac.uk)
The novel nucleoside 5-iodo-4-thio-2¤-deoxyuridine (4) was
synthesized and fully characterized by IR, NMR, and MS. Its
structure was determined by single-crystal X-ray diffraction.
Compound 4 absorbs strongly at 346 nm and is minimally toxic
to human tumour cells, but its cytotoxicity is substantially
enhanced by low dose UVA radiation. The combined use of 4
and UVA offers a promising route to selectively and effectively
kill proliferating cells.
O
4
S
I
I
HN
O
HN
O
4
O
N
(i), (ii), (iii)
O
N
RO
RO
1: R = H
2: R = Ac
3: R = Ac
4: R = H
OR
OR
Scheme 1. Synthesis of 5-iodo-4-thio-2¤-deoxyuridine (4).
i) Ac2O/pyridine (91% for 2); (ii) P4S10/1,4-dioxane (74%
for 3); (iii) NH3(g)/MeOH (68% for 4).
Nucleic acids (DNA and RNA) direct the flow of genetic
information. In addition to the four canonical bases, structurally
similar base analogues can be incorporated into DNA. These
alter its properties and facilitate basic studies of DNA-related
processes such as its interaction with proteins, replication, and
transcription. Site-specifically modified bases and nucleosides
are particularly useful in this regard, and thiobases, in which
an oxygen atom in the base is replaced by sulfur,1 have
proved invaluable in studies of DNA duplex stability, protein
recognition, and replication.4 We have been exploring the
photochemical properties of thiobases and their derivatives,
particularly 6-thioguanine (6-TG) and 4-thiothymidine (4-
thioTdR). Unlike canonical DNA bases, both are strong UVA
chromophores and are extremely sensitive to wavelengths of
(
Table 1. Key spectral data of compounds 1 and 4
UV
max/nm)
IR
/cm
1H NMR
(N3H)/ppm (C4)/ppm
13C NMR
Cpd
¹
1
(
3
1
4
290
346
1677 (C4=O)
1088 (C4=S)
11.66
12.99
160.48
189.31
6
The synthetic route is shown in Scheme 1 in which the
starting material 1 was first acetylated at its 3¤- and 5¤-positions
to give the acetylated nucleoside 2, followed by a thiolation at
the 4-postion to give the protected 4-thio-nucleoside 3. This was
then deprotected to afford the target product 4. Previously we
315400 nm (UVA range). Upon exposure to UVA radiation,
DNA-embedded 6-thioguanine is oxidized to guanine-6-
sulfinate and guanine-6-sulfonate in an oxygen-dependent
1
7a
used triazole/POCl and thioacetic acid to produce 3. The
3
79
reaction. UVA irradiation of cells containing DNA 6-TG also
current synthesis is straightforward and proceeds with good
yields (see ESI for details). The intermediates 2 and 3 and
the product 4 were fully characterized by MS, UV, IR spectra,
1
0
induces DNA strand breakage and interstrand crosslinking.
These DNA lesions block replication and transcription and
11
1
13
cause cell death. DNA 4-thioTdR also displays synergistic
lethality with UVA radiation. It undergoes UVA-mediated
conversion to potentially cytotoxic lesions including inter- and
intrastrand DNA crosslinks.12 In the absence of UVA, cells can
H NMR and C NMR measurements (see ESI for details).
Some key spectral data of 1 and 4 are summarized in Table 1 for
comparison.
The spectral characterization provides a good confirmation
for the structure of 4. High-resolution MS analysis of 4 gave
accumulate significant levels of 4-thioTdR without detrimental
effects on proliferation.1
3,14
The combined use of 4-thioTdR
an ion at 392.9382 for the molecular fragment (M + Na ), the
+
and UVA offers a novel approach to selectively kill rapidly
proliferating cells, such as cancer cells, while causing minimal
damage to normal tissues.15 The advantage this synergistic
photoactivation of DNA thiobases has over conventional
therapies is that it can target proliferating cells more selective-
ly. We have therefore explored the properties of additional 4-
thioTdR analogues and have previously reported the synthesis
m/z being within 1 ppm of the calculated m/z (392.9378) for
C9H11IN2NaO4S. 4 absorbs strongly at 346 nm, substantially
shifted from the 290 nm maximum of 1 (Figure S1, see ESI).
1
6
This red shift reflects the presence of the sulfur atom. The
¹
1
observed band at 1088 cm in the infrared spectrum is within
¹
1
the characteristic range (10701150 cm ) assigned to the C=S
1
8
stretching mode of the thioamide group in 4-thiouridine,
1
6
and chemical properties of 5-bromo-4-thio-2¤-deoxyuridine.
indicating the presence of the C4=S group in 4. NMR data
offer further support. D2O exchange experiments readily identify
Here we report a synthetic route for 5-iodo-4-thio-2¤-deoxy-
uridine. We also describe its crystal structure and initial studies
of its cytotoxicity.
the signal in ¤ 12.99 ppm as proton N3H. The presence of the
H
thioamide in 4 is also evident from the substantial NMR
© 2015 The Chemical Society of Japan | 147