Synthesis of novel 6-substituted thymine ribonucleosides and their 3′-fluorinated analogues

Article abstract of DOI:10.1016/j.tet.2016.08.065

Nine novel 6-fluorothymine nucleoside analogues of both N(1)-α/β and N(3)-β-ribo series were prepared by the Vorbrüggen method starting from persilylated 6-fluorothymine and 1-O-acetyl-2,3,5-tri-O-benzoyl-β-D-ribofuranose, 1-O-acetyl-2,5-di-O-benzoyl-3-deoxy-3-fluoro-α,β-D-ribofuranose or 1,2,3,5-tetra-O-benzoyl-β-D-ribofuranose and its α-anomer. Protected N(3)-β-D-ribofuranosides were prepared as sole products in high yields at room temperature. A mixture of benzoylated N(1)-β- and α-anomeric ribonucleosides was obtained at lower temperatures. Yields of β-anomers and stereoselectivities (β:α=2.2/4.5:1) of the condensation reactions depended on reaction conditions and the structure of the glycosylating agent. Debenzoylation of 6-fluorothymine N(1)- or N(3)-β-D-ribofuranosides and their 3′-fluorodeoxy analogues by LiOH monohydrate in MeCN/H₂O resulted in the corresponding fluorinated nucleosides in good yields, whereas the deprotection of N(1)-α-ribofuranosides under the same conditions unexpectedly yielded 6,2′-O-α-D-anhydronucleosides. 6-Substituted (OMe, NH₂) thymine β-ribonucleosides were prepared by the treatment of protected N(1)-β-D-ribosides with nucleophilic agents.

Full text of DOI:10.1016/j.tet.2016.08.065

Accepted Manuscript
Synthesis of novel 6-substituted thymine ribonucleosides and their 3′-fluorinated
analogues
Tatyana S. Bozhok, Grigorii G. Sivets, Alexander V. Baranovsky, Elena N.
Kalinichenko
PII:
S0040-4020(16)30850-X
10.1016/j.tet.2016.08.065
TET 28046
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 25 March 2016
Revised Date: 11 August 2016
Accepted Date: 23 August 2016
Please cite this article as: Bozhok TS, Sivets GG, Baranovsky AV, Kalinichenko EN, Synthesis of novel
6-substituted thymine ribonucleosides and their 3′-fluorinated analogues, Tetrahedron (2016), doi:
10.1016/j.tet.2016.08.065.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
Graphical Abstract
To create your abstract, type over the instructions in the template box below.
Fonts or abstract dimensions should not be changed or altered.
Synthesis of novel 6-substituted thymine
Leave this area blank for abstract info.
ribonucleosides and their 3′-fluorinated analogues
Tatyana S. Bozhok, Grigorii G. Sivets, Alexander V. Baranovsky, Elena N. Kalinichenko*
Institute of Bioorganic Chemisrty, National Academy of Sciences of Belarus, Kuprevicha, 5/2, BY-220141
Minsk, Belarus

1
ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
Synthesis of novel 6-substituted thymine ribonucleosides and their 3′-fluorinated
analogues
Tatyana S. Bozhoka, Grigorii G. Sivetsa, Alexander V. Baranovskya, Elena N. Kalinichenkoa,
a Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, Kuprevicha, 5/2, BY-220141 Minsk, Belarus
ARTICLE INFO
ABSTRACT
Article history:
Received
Nine novel 6-fluorothymine nucleoside analogues of both N(1)-α/β and N(3)-β-ribo series were
prepared by the Vorbrüggen method starting from persilylated 6-fluorothymine and 1-O-acetyl-
Received in revised form
Accepted
Available online
2,3,5-tri-O-benzoyl-β-D-ribofuranose,
1-O-acetyl-2,5-di-O-benzoyl-3-deoxy-3-fluoro-α,β-D-
ribofuranose or 1,2,3,5-tetra-O-benzoyl-β-D-ribofuranose and its α-anomer. Protected N(3)-β-D-
ribofuranosides were prepared as sole products in high yields at room temperature. A mixture of
benzoylated N(1)-β- and α-anomeric ribonucleosides was obtained at lower temperatures.
Yields of β-anomers and stereoselectivities (β:α = 2.2/4.5:1) of the condensation reactions
depended on reaction conditions and the structure of the glycosylating agent. Debenzoylation of
6-fluorothymine N(1)- or N(3)-β-D-ribofuranosides and their 3′-fluorodeoxy analogues by LiOH
monohydrate in MeCN/H2O resulted in the corresponding fluorinated nucleosides in good
yields, whereas the deprotection of N(1)-α-ribofuranosides under the same conditions
unexpectedly yielded 6,2′-O-α-D-anhydronucleosides. 6-Substituted (OMe, NH2) thymine β-
ribonucleosides were prepared by the treatment of protected N(1)-β-D-ribosides with
nucleophilic agents.
Keywords:
6-fluorothymine
ribonucleosides
3′-fluorodeoxyribo analogues
anhydronucleosides
carbon-fluorine coupling
through-space coupling
2009 Elsevier Ltd. All rights reserved.
1. Introduction
used as anticancer drugs for the treatment of solid or
hematological malignancies.2,5,6 Unlike 5-fluoropyrimidines, 6-
fluorothymine nucleosides are little studied.
Fluorinated nucleosides have been shown to possess
interesting physicochemical and biological properties.1-3
Bioisosteric replacement of a hydroxyl group or hydrogen atom
by fluorine atom(s) is a classic approach in medicinal chemistry
to improve the pharmacological properties of a biologically
active molecule. As the most electronegative element, fluorine
can serve as an isopolar and isosteric mimic of a hydroxyl group
because the C-F bond length is close to the C-O bond length.
Moreover, fluorine is the second smallest atom, similar in size to
hydrogen and substitution of the latter by fluorine in small
molecule can cause significant electronic consequences without
much distortion of the geometry.4 Introduction of a fluorine atom
to a nucleoside molecule may change substrate metabolism due
to the higher strength of the C-F bond compared to that of the C-
H bond resulting in higher biological activity and chemical
stability of fluorinated derivatives.
There are only a few papers published on the synthesis and
antiviral activity of glycosides of this hard-to-reach fluorinated
pyrimidine or their analogues obtained by the substitution of the
C(6)-fluorine atom with different nucleophilic agents (Fig. 1).7,8
Fig. 1. Glycosides of 6-fluorothymine and their analogues.
All these factors along with the clinical importance of
nucleoside-based antiviral and anticancer drugs have determined
the historic interest to medicinal chemistry of fluorinated
nucleosides. C(5)-Fluoro substitution of the pyrimidine
nucleobase led to development of 5-fluorouracil, ftorafur
(tegafur) and nowadays capecitabine which are clinically
Synthesis of 6-fluoro-5-methyluridine was carried out by the
coupling of silylated 6-fluorothymine with peracetylated D-ribose
in the presence of SnCl4 in 1,2-dichloroethane followed by
deprotection of the intermediate nucleoside under acidic
treatment or with zinc acetate.8 Studentsov et al. described the
synthesis of 6-fluorothymine arabinonucleosides.9 It should be
noted that the 6-fluoro analogue of natural thymine arabinoside
———
 Corresponding author. Tel./fax: +375 17 2650611; е-mail address:
kalinichenko@iboch.bas-net.by

2
Tetrahedron
ACCEPTED MANUSCRIPT
(spongothymidine) inhibits development of viral infections and
Chlorination of 1 with gaseous HCl in methylene chloride
followed by hydrolysis of intermediate 3 and benzoylation of the
forming 2,3,5-tri-О-benzoyl-D-ribofuranose gave rise to 1,2,3,5-
displays antitumor activity. Langen and co-workers found that
the reaction of silylated 6-fluorothymine with α-
acetobromoglucose in the presence of SnC14 gives only the
acetylated N(1)-β-D-nucleoside in 75% yield.7,8 Deprotection of
the latter by HCl treatment in methanol resulted in 60% yield of
the target nucleoside.8
tetra-О-benzoyl-β-D-ribofuranose (5) and its α-anomer
6
(Scheme 1). In addition, the latter was also prepared via 1,3,5-tri-
О-benzoyl-α-D-ribofuranose13 from acetate 1.
2.2. Glycosylation reactions: regio- and stereo-selectivities of
D-ribose couplings under Vorbrüggen conditions
It is noteworthy that deacetylation of protected 6-
fluorothymine β-D-glucopyranoside or -ribofuranoside with
methanolic ammonia or sodium methoxide led to fluorine atom
replacement at the C(6)-position to afford the corresponding 6-
amino- and -methoxy-substituted thymine nucleosides.8
Treatment of the deacetylated 6-fluorothymine ribonucleoside by
different nucleophilic agents resulted in 6-substituted thymine
nucleosides.7 Some C(6)-modified pyrimidine nucleoside
analogues showed antiviral and anticancer activities.8-10
Condensation reactions of persilylated 6-fluorothymine (7)
with D-ribose derivatives 1, 2, 5 and 6 in the presence of
trimethylsilyl triflate (TMSOTf) under Vorbrüggen method14
conditions followed by deprotection of intermediate
ribonucleosides were investigated for the synthesis of fluorinated
nucleosides (Scheme 2).
Within our research program on the study of fluorinated
nucleosides we have investigated new aspects of the synthesis of
1-(β-D-ribofuranosyl)-6-fluorothymine and synthesized its novel
analogues with a fluorine atom at the C(3′)-position of the ribose
moiety starting from available carbohydrate precursors for
investigation of biological properties.
2. Results and discussion
2.1. Preparation of acylated D-ribose derivatives
Acylated derivatives of D-ribofuranose 1, 2, 5 and 6 (Scheme
1) were used as glycosylating agents in the coupling reactions
with 6-fluorothymine.9 1-O-Acetyl-2,3,5-tri-О-benzoyl-β-D-
ribofuranose (1) and 1-O-acetyl-2,5-di-О-benzoyl-3-deoxy-3-
fluoro-α,β-D-ribofuranose (2) were obtained from D-ribose11 and
D-xylose12 according to the known procedures. Perbenzoylated D-
ribofuranose derivatives 5 and 6 were prepared from readily
available 1-О-acetyl-2,3,5-tri-О-benzoyl-β-D-ribofuranose (1) in
50% and 24% yields, respectively.
Scheme 2. Reagents and conditions: a) HMDS, TMSCl, reflux, 8 h;
b) BSTFA, CH3CN, rt, 2 h; c) TMSOTf, MeCN, rt, 4 h; d) TMSOTf, MeCN,
0 oC→ -15 ºC, 4 h (Table 1, entries 1-9); e) LiOH·H2O, MeCN, H2O, rt, 5 h;
f) NH3/MeOH, rt, 24 h; g) MeONa/MeOH, rt, 2 h; h) BzCl, Py, rt, 20 h.
o
Scheme 1. Reagents and conditions: a) HCl, CH2Cl2, 0 C, 1.5 h; b) CH2Cl2,
MeOH, H2O, rt, 1 h; c) BzCl, Py/CH2Cl2, rt, 20 h; d) BzCl, Py, rt, 20 h.
Table 1. Preparation of benzoylated 6-fluorothymine ribonucleosides from acylated D-ribose derivatives 1, 2, 5 and 6
Yield
of β (%)c
Silylation conditions
of 6-fluorothymine
β/α
Entry
Sugar
Condensation conditionsa
Products
Ratiob
1
2
3
4
5
6
7
8
9
1
1
1
1
2
2
5
5
6
HMDS, TMSCl, reflux; 8 h
HMDS, TMSCl, reflux; 8 h
BSTFA, CH3CN, rt, 2 h
BSTFA, CH3CN, rt, 2 h
HMDS, TMSCl, reflux; 8 h
HMDS, TMSCl, reflux; 8 h
BSTFA, CH3CN, rt, 2 h
BSTFA, CH3CN, rt, 2 h
BSTFA, CH3CN, rt, 2 h
TMSOTf, MeCN, rt, 4 h
N(3)-β (8)
-
85
42
53
55
78
45
60
53
49
TMSOTf, MeCN, 0 oC→ -15 ºC, 4 h
TMSOTf, MeCN, 0 oC→ -15 ºC, 4 h
TMSOTf, MeCN/(CH2Cl)2, 0 oC→ -15 ºC, 4 h
TMSOTf, MeCN, rt, 4 h
N(1)-β/α (10/12)
N(1)-β/α (10/12)
N(1)-β/α (10/12)
N(3)-β (9)
3.0:1
2.2:1
3.2:1
-
TMSOTf, MeCN, 0 oC→ -15 ºC, 4 h
TMSOTf, MeCN, 0 oC→ -15 ºC, 4 h
TMSOTf, MeCN/(CH2Cl)2, 0 oC→ -15 ºC, 4 h
TMSOTf, MeCN, 0 oC→ -15 ºC, 4 h
N(1)-β/α (11/13)
N(1)-β/α (10/12)
N(1)-β/α (10/12)
N(1)-β/α (10/12)
3.7:1
4.3:1
4.5:1
2.4:1
a
b
c
Molar ratio sugar : pyrimidine base : TMSOTf – 1:1.2:1.1.
Ratio was determined by 1H NMR spectroscopic analysis of anomeric mixture in CDCl3 after isolation by column chromatography.
Isolated yield of benzoylated β-ribonucleoside by column chromatography.

3
ACCEPTED MANUSCRIPT
Firstly, we undertook a search for stereoselective reaction
conditions for the N-glycosylation of 2,4-bis-O-(trimethylsilyl)-
6-fluorothymine (7). This was prepared by treatment of 6-
without. On the whole, these findings, as well as the literature
data,7,8 provide evidence that the outcome of the glycosylation
reactions of 7 with different acyl D-ribose derivatives strongly
depends on the reaction conditions viz. Lewis acid, temperature,
the method used for preparing the silylated base, and the structure
and anomeric stereochemistry of the glycosylating agent.
fluorothymine
with
hexamethyldisilazane
(HMDS)
/
trimethylsilyl chloride (TMSCl) under reflux or with N,O-bis-
trimethylsilyl trifluoroacetamide15 (BSTFA) in CH3CN at room
temperature, in order to synthesise benzoylated 6-fluorothymine
β-nucleosides. Results of the investigation on condensation
reactions of 7 with four sugars under different conditions are
summarized in Table 1. Silyl derivative 7, prepared using
HMDS/TMSCl, was condensed with sugars 1 or 2 in anhydrous
MeCN in the presence of TMSOTf at room temperature to give
the unexpected protected N(3)-β-isomers 8 (85%) or 9 (78%),
respectively, as the only reaction products (Table 1, entries 1 and
5).
2.3. Deprotection of 6-fluorothymine β-ribosides and
intramolecular cyclization of α-ribosides
Secondly, deprotection of the benzoylated 6-fluorothymine
D-ribofuranosides 8-13 as in the case of acetylated 6-
fluorothymine glycosides,7 represented another task to be solved
for the efficient synthesis of target nucleosides. Standard
deprotection of individually protected nucleosides 10 and 11 with
methanolic ammonia resulted in the substitution of the fluorine
atom at the C(6)-position of the heterocycle by the amino group
with the formation of 6-aminothymine substituted nucleosides 18
and 19 in high yields (72-75%). The 6-methoxythymine
ribonucleoside 20 was isolated after treatment of 10 with NaOMe
in methanol at room temperature in 68% yield after
chromatographic purification on silica gel.
Similar coupling reactions of the silylated base 7 with acyl
o
o
derivatives 1 or 2 at low temperature (from 0 C to -15 C) in
anhydrous MeCN gave protected N(1)-β-ribonucleosides 10
(42%) or 11 (45%) as the main products, along with N(1)-α-
nucleosides 12 (14%) and 13 (11%). These isomeric products
were isolated by column chromatography on silica gel.
Formation of N(3)-isomeric derivatives 8 and 9 was not observed
under the reaction conditions stated (entries 2 and 6). These
findings on the glycosylation reactions of the silylated base 7 in
MeCN indicate that the regio- and stereo-selectivity of N-
glycosylation depends on temperature. The undesired exclusive
formation of a N(3)-glycoside bond took place at room
temperature. Felczak et al. noted also that the condensation of
uracil derivatives containing an electrophilic trifluoromethyl
substituent at C(6) with 1-O-acetyl-2,3,5-tri-O-benzoyl-β-D-
ribofuranose (1) led to formation of only the N(3)-ribosides
despite the use of various conditions.10 Probably, the size and
character of the C(6)-substituent in the pyrimidine heterocycle is
critical for its N-glycosylation. It was reported that condensation
We have found that the treatment of individually N(1)-β-
nucleosides 10 and 11 with LiOH monohydrate in a mixture of
acetonitrile-water (3:1.3, v/v) led to target nucleosides 16 and 17
in high yields (75-79%) compared to the previously described
methods for removal of the acetyl groups of 6-fluorothymine
nucleosides using zinc acetate or HCl in methanol.7,8 In a similar
way, the removal of the benzoyl groups in N(3)-β-
ribonucleosides 8 and 9 gave nucleoside analogues 14 and 15
with 57% and 63 % yield, respectively.
Deprotection of individually protected α-nucleosides of 6-
fluorothymine 12 and 13 with LiOH monohydrate in a mixture of
acetonitrile-water and subsequent chromatographic purification
unexpectedly gave pure 6,2′-O-α-D-anhydronucleosides 21 and
22 in 81% and 85% yields, respectively. One can assume that the
formation of anhydronucleosides 21 and 22 resulted from an
intramolecular substitution of the fluorine atom at the C(6)-
position of the heterocycle by the activated hydroxyl group at the
C(2′)-atom of the intermediate deprotected nucleoside during
removal of the protective groups of nucleosides 12 and 13 under
the basic conditions. The benzoylation of the prepared α-
cyclonucleosides 21 and 22 was carried out with benzoyl
chloride in pyridine. This led to tribenzoate 23 and dibenzoate 24
isolated by column chromatography on silica gel in 75% and
81% yields, respectively. In the case of compound 21, dibenzoate
25 (20%) was also isolated from the reaction mixture by column
chromatography.
of
a
silylated 6-chlorouracil with 2,3,5-tri-O-benzoyl-D-
ribofuranosyl chloride under heating gave only the N(3)-β-D-
riboside in low yield.16 The coupling reaction of silylated 6-
methylmercaptouracil with
1-bromo-2,3,5-tri-O-benzoyl-D-
ribofuranose in MeCN also gave the corresponding N(3)-β-D-
riboside of 6-substituted uracil.17
However, at lower temperatures the desired N(1)-β-anomers
10 and 11 were prepared as the main classical condensation
products along with α-anomers of riboside 12 and fluorodeoxy
nucleoside 13 (ratios β:α–3.0/3.7:1). Further, the coupling
reactions of the silylated base 7 prepared using BSTFA were
carried out with acyl derivate 1 in anhydrous MeCN or a mixture
of MeCN/(СH2Cl)2 in the presence of TMSOTf (Table 1, entries
3 and 4). The protected N(1)-β-ribonucleoside 10 was prepared in
53-55% yield after chromatographic isolation on silica gel. In a
continuation of this investigation, we also studied available
1,2,3,5-tetra-О-benzoyl-β-D-ribofuranose (5) and its α-anomer 6
in the condensation reactions with 7 (entries 7-9) and, as a result,
the N(1)-β-ribonucleoside 10 was obtained in 49-60% yield. It
should be noted that the best yield of the intermediate protected
nucleoside and good stereoselectivities (ratios β:α – 4.3/4.5:1) of
the condensation reactions were achieved at lower temperatures
using benzoate 5 as glycosylating agent (entries 7-8). These
results differ from the known approach,8 leading to exclusively
N(1)-β-glycoside of 6-fluorothymine with application of 1,2,3,5-
tetra-O-acetyl-β-D-ribofuranose and the silylated base 7 at room
temperature in dichloroethane in the presence of SnCl4.
According to previous communications,18,19 the formation of α-
anomers of ribonucleosides as by-products was observed during
the condensation of the D-ribofuranose derivative with
persilylated bases in few cases, e.g. the glycosylation of 5-
fluorouracil in dichloroethane in the presence of SnCl4 or
2.4. Structural analysis
The structures of all synthesized nucleosides were proved by
1
various spectroscopic methods. The assignment of H and 13C
NMR spectra was conducted with support from 2D NMR
spectroscopy (1H-1H COSY, NOESY and 1H-13C HMBC).
2.4.1. Regio- and stereoisomeric assignment. Comparison of
the UV absorption spectra of the isomeric pairs of 6-
fluorothymine nucleosides 14, 15 and 16, 17 in acidic, neutral
and alkaline aqueous solutions revealed
a
significant
bathochromic shift of the absorption maxima to 281 nm (lg ε 4.0
and 3.96) for N(3)-nucleosides 14 and 15 not only at pH 13,
which is typical for N(3)-nucleosides,20 but also at the neutral pH
(see experimental part). It should be noted that similar spectral
behavior have been described for 3-(β-D-ribofuranosyl)-6-
trifluoromethyluracil at neutral and alkaline pH as compared to
the spectrum at pH 1.10

4
Tetrahedron
ACCEPTED MANUSCRIPT
Table 2. Selected 13C, 19F, 1H NMR data for 6-fluorohymine ribonucleosides and their analogues [some JC,F, JHʹ,Hʹ, JHʹ,F values are
given in brackets]a
Chemical shift δ (ppm), in brackets J (Hz)
Com-
pound
H(3ʹ)
[ J3ʹ,4ʹ
6.16-6.13
C(2)
[ JC2,F6
C(4)
[ JC4,F6
C(6)
[ JC6,F6
C(1ʹ)
[JC1ʹ,F6
C(2ʹ)
C(4ʹ)
H(1ʹ)
H(2ʹ)
[ J2ʹ,3ʹ]
F-C(6)
F-C(3ʹ)
H(4ʹ)
]
]
]
]
]
[ JC2ʹ,F6
]
[ JC4ʹ,F6
]
[ J1ʹ,2ʹ
]
150.0
163.7
d [17.5]
163.7
d [17.1]
163.2
d [18.3]
163.4
d [18.2]
163.0
d [17.6]
163.1
d [17.4]
169.0
d [17.5]
169.6
157.1
d [267.5]
157.1
d [270.3]
157.7
d [271.3] d [4.8]
157.4 86.5
d [271.4] d [4.9]
158.4
d [272.7]
158.5
d [271.1]
167.4
d [242.8]
168.9
d [245.9]
157.9
87.2
br s
86.1
br s
74.1
s
73.0
d
79.2
s
79.5
d
79.4
s
79.9
d
-96.43
s
-95.82
s
-98.94
s
-99.36
s
-94.51
s
-94.12
s
-75.43
s
-74.23
s
-
6.60
br s
6.59
br s
6.26
br s
6.24
br s
7.04
d [5.7]
6.97
d [6.7]
6.40
d [4.1]
6.45
d [6.1]
5.87
d [4.3]
5.91
d [6.9]
6.14
d [4.8]
6.21
d [5.1]
4.72-4.65 m
(H-4ʹ, H-5ʹʹ)
4.61-4.55 m
(H-4ʹ, H-5ʹʹ)
4.69-4.66
m
4.62-4.55 m
(H-4ʹ, H-5ʹʹ)
4.98-4.95
m
4.95-4.90
dm
3.92-3.89
m
4.21-4.14
dm
3.71-3.68
m
8
d [9.1]
150.2
d [8.9]
147.7
d [4.5]
147.7
d [3.7]
147.9
d [4.7]
148.0
d [4.8]
156.8
d [31.5]
158.6
d [29.7]
148.3
d [3.9]
148.4
d [4.1]
146.5
s
m
-205.39
m
-
6.04
br s
5.72
br d
9
87.9
74.0
6.03
5.92
10
11
12
13
14
15
16
17
21
22
d [3.5]
72.8
d
70.6
s
70.5
d
72.8
s
dd [6.4]
5.97
t
-204.27
m
-
5.59
dd [6.3]
6.09
dt
5.79
85.8
s
84.8
s
90.0
s
88.7
s
88.5
s
86.8
s
85.8
s
86.5
d
79.7
d [5.4]
80.7
dd [3.8]
85.7
s
84.3
d
84.4
s
82.5
d
84.3
s
79.1
d
t
t
-202.96
m
-
5.84
5.41
dt
ddd [4.2]
4.39
4.72
dd [6.2]
5.05
t
71.2
d
-202.29
m
-
5.06
d [17.6]
163.3
d [17.9]
163.2
d [18.1]
165.3
dt [5.2]
4.32
ddd [3.0]
3.95-3.92
m
71.4
d [3.9]
69.5
dd [5.6]
80.2
s
-97.89
s
-98.24
s
-
d [269.7]
157.8
d [270.5]
159.0
t
-199.82
m
-
4.64
4.96
4.10-4.03
dm
3.56
ddd
4.03
dt [4.6]
5.19
ddd [2.3]
4.01
s
s
t [5.1]
5.49
dd [9.3]
5.17
146.5
s
165.4
s
159.1
s
81.6
d
-
-212.65
dd
dt [5.2]
ddd [7.3]
ddd
a8-13 – CDCl3; 14, 15 – CD3OD; 16, 17, 21 and 22 – DMSO-d6
13C NMR data presented in Table 2 provides additional
confirmation for the assigned structures of N(1)-β-, N(3)-β-
ribonucleoside derivatives 14-17. In the 13C NMR spectra of each
pair of isomeric nucleosides, downfield shift of the C(6)-atoms of
the N(3)-nucleosides 14 and 15 to 9-11 ppm was observed as
compared with N(1)-nucleosides 16 and 17.The magnitude of the
constant JC6,F6 for N(3)-isomers in comparison with their N(1)-
counterparts was reduced by 26 Hz and 24 Hz, respectively. It is
interesting to note a significant change in the vicinal coupling
constant between the C(2)-atom and fluorine atom at the C(6)-
The signal of the H(1′)-proton of N(3)-β-riboside 8 displayed
in the H NMR spectrum as a broad singlet at 6.60 ppm was
1
shifted to a lower field of 0.3 ppm compared to N(1)-β-riboside
1
10. The most informative feature in the H NMR spectra of α-
anomer 12 is the downfield shift of H(1′) and H(4′) resonances12
in comparison with the those of the corresponding β-nucleoside
10 (Table 2).
It should be noted that the described 1H NMR spectra features
observed for a number of 6-fluorothymine analogues 8, 10 and
12 are the same for 3′-deoxy-3′-fluoro-D-ribosides of 6-
fluorothymine 9, 11 and 13 and the corresponding deprotected
nucleosides 14-17 (Table 2). The signals of the 6-amino groups
as well as the 6-methoxy group are displayed as singlets at 6.51,
3
position: the magnitude of JC2,F6 is equal to 3.9 Hz for N(1)-
isomer 16, but for N(3)-nucleoside 14 the one comprises 31.5 Hz,
whereas the magnitudes of 3JC4,F6 vicinal couplings are similar for
the both regioisomers.
1
6.59 ppm, and 3.88 ppm in the H NMR spectra of 6-substituted
thymine nucleosides 18-20, respectively.
Configurations at the anomeric centers of prepared 6-
fluorothymine nucleosides 10-13 were determined on the basis of
NMR data. Long-range JC,F couplings of C(1′) to F(6) were
The configuration at the anomeric center of β-nucleoside 10
and its α-anomer 12 was also confirmed by 2D NMR
spectroscopy (Fig. 2). It is noteworthy that in the case of
nucleoside 10 an obvious cross-peak between H(4′) and H(1′)
observed in the NOESY spectrum provides evidence in favor of
its β-anomeric configuration. This cross-peak is the most
intensive and twice more stronger than the interaction between
H(1ʹ) and H(2ʹ). The NOE-effect involving protons of СH3 and
C(5′)-O-benzoyl (meta-proton, 7.42 ppm) groups found in the
spectrum of 10 are clearly missing in that of 12.
In the NOESY spectrum of the benzoylated α-riboside 12, a
weak cross-peak between H(4′) and H(1′) (10% of the intensity of
the H(1ʹ)-H(2ʹ) cross-peak and 30% of that of H(1ʹ)-H(3ʹ) was
found. The presence of such interaction can be explained by a
conformational flexibility of the molecule. The structure is not
rigid and, at a certain moment, the protons are getting closer to
raise a signal. In addition, a NOE-effect was also observed
between H(5′) and H(3′)-protons (Fig. 2). Slight interactions could
be also seen between the protons of the СH3 group (d at 1.75 ppm,
JCH3,F6 = 2.3 Hz) and the ortho- (7.85 ppm) and meta- (7.38 ppm)
protons of the C(2′)-O-benzoyl group.
3
observed in the 13C NMR spectra of β-nucleosides 10 and 11 (4.8
Hz and 4.9 Hz, respectively) (Table 2). Six-bonds couplings
between carbon C(4′) and F(6) were observed in spectra of the α-
isomers 12 and 13 (5.4 Hz and 3.8 Hz, respectively). These
confirm the accession of the pentofuranose to the N(1)-atom of 6-
fluorothymine in both condensation products and their α-
anomeric configurations. The latter couplings (6JC4′,F6) generally
indicate spatial proximities of the nuclei involved and favorable
non-bonded interactions between the fluorine of the heterocyclic
base and carbon atom C(4′) in ”through-space” C-F and C-H
couplings.21 Decrease of the ”through-space” C-F coupling
magnitude (6JC4′,F6 = 3.8 Hz) for 3′-fluororiboside 13 likely
reflects molecule conformational features caused by repulsion
taking place between the fluorine atoms of the heterobase and
carbohydrate moiety. Such repulsion leads to an increase in the
distance between the C(4′)- and F(6)-atoms. This observation
also confirms a major contributor to the carbon couplings to be
the direct ”through-space” carbon-fluorine couplings in contrast
to its ”through-bond” counterpart.21

5
ACCEPTED MANUSCRIPT
Fig. 2. 2D NOESY of β-riboside 10 (A) and α-riboside 12 (B) with 3D view of the molecules obtained using HyperChem 8.0.
The 19F NMR spectra of compounds 8-13, 16 and 17 exhibit
the characteristic peaks near -96.69 ppm assigned to the F(6)-
atom. The signal of the fluorine atom for deprotected N(3)-
nucleosides 14 and 15 is shifted upfield on 22-24 ppm compared
to N(1)-isomers 16 and 17 and observed at -75 ppm, which is
obviously due to the location of the D-ribofuranose.
It should be emphasized that synthesis of 6,2′-O-α-D-
anhydronucleosides has not been earlier described. However,
several processes was reported for the preparation of pyrimidine
6,2′-O-β-D-anhydronucleosides.22-25 Folkers et al. have
synthesized a series of C(5)-substituted 6,2′-anhydrouridines22 by
the treatment of β-ribofuranosyl barbiturate acid derivatives with
thiocarbonyldiimidazole under refluxing in toluene, among them
6,2′-anhydro-1-(β-D-arabinofuranosyl)-6-hydroxythymine (27)
(Fig. 3), an isomeric analogue of 21, which was prepared in 60%
yield.22 6,2′-Anhydro-1-(β-D-arabinofuranosyl)-6-hydroxyuridine
(28) was also prepared from the alkali treatment of 1-β-D-
arabinofuranosyl-5-halogenuracils with sodium methoxide in
methanol or sodium hydroxide.23,24 The structures of the 6,2′-
anhydrouridines were established by the 1H NMR and UV
absorption spectra.
2.4.2. Cyclization. The surprising structures of 6,2′-O-α-D-
anhydronucleosides 21 and 22 have been confirmed by NMR
spectroscopy, including 2D techniques, and by comparison with
the spectral data obtained for their benzoyl derivatives 23-25.
1
Analysis of the H NMR spectra of benzoylated α-nucleoside
derivatives 12 and 25 showed that chemical shifts of the H(1′),
H(2′), H(3′) and H(4′) protons of the α-cyclonucleoside 25 shifted
into the strong field (Δ = 0.5 ppm for H(1′) and H(3′); Δ = 0.4
ppm for H(2′) and H(4′). Chemical shifts of the H(5′) and H(5′′)
signals are not changed.
The most informative NMR spectra features of α-
cyclonucleosides are (i) shifts of the H(2′) resonance signal at
0.85-0.87 ppm to a lower field for compound 21 and fluoride 22
compared to β-ribosides 16 and 17 and (ii) absence of signals of
the 2′-OH groups, indicating the presence of 6,2′-anhydro
linkage. Furthermore, the fluorine at the C(6)-atom of the
heterocycle is absent in the 19F NMR spectra of compounds 21
and 22, and there is only a signal of fluorine at the C(3′)-atom
(dd, -212.65 ppm) for 3′-fluoro-cyclonucleoside 22.
Fig. 3. Structures of 6,2′-O-D-anhydrouridines.
It is worth noting that the change of anomeric configuration
from 6,2′-anhydro-1-(β-D-arabinofuranosyl)-6-hydroxythymine

6
Tetrahedron
ACCEPTED MANUSCRIPT
(27)22 to 6,2′-anhydro-1-(α-D-ribofuranosyl)-6-hydroxythymine
N(1)-β-ribonucleosides
and
stereoselectivities
of
the
(21) is accompanied by a shift of the signal Н(3′) (dd at 4.01
ppm) to a higher-field (Δ = 0.38 ppm) versus Н(3′) (s at 4.39
ppm)22 for β-nucleoside. However, differences in 1H NMR
chemical shifts of the H(1′) (Δ = 0.11 ppm) and H(2′) (Δ = 0.04
ppm) protons of the isomeric nucleosides are slight, and the J1′,2′
magnitudes (4.8 and 5.0 Hz) are very close for the both
nucleosides with 1,2-cis arrangements of H(1′)- and H(2′)-
protons. The coupling constant (J = 9.3 Hz) between H(3′)- and
condensation reactions (ratios β:α
–
2.2/4.5:1) at lower
temperatures depends on the silylation procedure of the
heterocyclic base and the structure of glycosylating agent. The
use of BSTFA instead of HMDS/TMSCl for the silylation of 6-
fluorothymine resulted in better total yields of protected 6-
fluorothymine N(1)-β- and -α-ribonucleosides in the
condensation reactions from acetate 1. Among four D-ribose
derivatives, good yields of the β-nucleoside and the best
stereoselectivities (ratios β:α – 4.3/4.5:1) of the coupling
reactions were achieved from β-benzoate 5. It was found that
mild deprotection of the benzoyl groups of intermediate 6-
fluorothymine β-nucleosides using LiOH monohydrate in a
mixture of acetonitrile-water resulted in the target nucleosides in
high yields. An effective method for the preparation of 6-
fluorothymine N(1)-β-ribonucleoside was devised in 47% overall
yield from 1,2,3,5-tetra-О-benzoyl-β-D-ribofuranose. A new
approach to the synthesis of 6,2′-O-α-D-anhydronucleosides has
been developed as a result of the intramolecular substitution
reaction of the fluorine atom at the C(6)-position of the
heterocycle by the C(2′)-hydroxyl group of an intermediate
deprotected nucleoside during removal of the protective groups
of 6-fluorothymine N(1)-α-ribonucleosides under the basic
reaction conditions. The anomeric configuration of the glycosidic
bonds was determined by 2D NMR spectroscopy. It is
1
H(4′)-protons is found in the H NMR spectrum of 21 while
clearly missing22 in the spectrum of the known
β-6,2′-
anhydronucleoside 27. The value of J3′,4′ (2.0 Hz)23 observed for
β-6,2′-anhydrouridine 28, the structural analogue of 27, is much
below that of α-cyclonucleoside 21. These data demonstrate the
extremely tense conformation of prepared novel α-
cyclonucleosides.
Conformationally
constrained
cyclic
pyrimidine nucleosides of this family are likely to be of interest
for preparation of modified oligonucleotides with interesting
antisense properties.26
It should be noted that in the CD-spectrum of 6,2′-O-α-
anhydronucleosides 21 and 22 we observed strongly pronounced
positive Cotton effects at 255 nm (bands B2u) with large
amplitudes (θ = 27103 and θ = 20103, respectively) as
compared to CD-spectral data prepared for 6-fluorothymine
β-ribofuranosides 14 and 16 under the same conditions (Fig. 4).
This phenomenon could likely be explained by the rigid
conformation of the obtained anhydronucleosides in comparison
with 6-fluorothymine β-ribonucleosides 14 and 16.
6
noteworthy that the couplings JC4′,F6 caused by spatial
proximities of the nuclei were detected for protected 6-
fluorothymine α-nucleosides and this fact possibly indicates the
preferable direct ”through-space” interaction between fluorine
atom of heterocyclic base and C(4′) carbon atom in contrast to its
”through-bond” counterpart.
4. Experimental
4.1. General
Organic solvents were purified and dried by standard methods
before use. UV absorption spectra were measured on a Varian
Cary 100 spectrometer. NMR spectra were registered on a Bruker
Avance 500 MHz spectrometer at 500 MHz (1H), 125 MHz (13C)
and 470 MHz (19F). Chemical shifts (δ) are given in ppm related
to internal SiMe4 and coupling constants (J) in Hz. IR spectra
were measured on
a Perkin Elmer Spectrum 100 FT-IR
spectrometer. High-resolution mass spectra (HRMS) were
recorded on an Agilent 6550 Q-ToF instrument using ESI
(electrospray ionization). Melting points were determined on an
electrically heated melting point apparatus and were uncorrected.
CD spectra were obtained on a Jasco J-20 spectropolarimeter.
Preparative column chromatography was performed on silica gel
Merck 60 (70-230 mesh). TLC analysis was carried out using
TLC Silica gel 60 F254 (aluminium-backed sheets, Merck). The
following solvent systems were used: hexane-EtOAc, 3:2, v/v
(А), CHCl3- MeOH, 4:1, v/v (B).
Fig. 4. CD-spectra of compounds 14, 16, 18, 20-22 in water.
From the CD-spectra of N(1)-ribosides 16, 18 and 20 bearing
different substituents at the C(6)-atom of the heterocycle and
N(3)-isomer 14, which has two carbonyl groups close to the
anomeric center, one can assume that the size of the substituent
as well its electronegativity causing change in the electronic
structure of the modified pyrimidine bases exerts significant
influence on the shape of the CD-spectra bands and amplitude of
Cotton effect.
4.2. Synthesis of perbenzoylated D-ribofuranose derivatives
4.2.1. 1,2,3,5-Tetra-O-benzoyl-β-D-ribofuranose (5) and its α-
isomer 6. Hydrogen chloride was bubbled into an ice-cold
solution of 1 (0.80 g, 1.58 mmol) in methylene chloride (15 mL)
for 1.5 h. After being kept at 2-8 °C for 5 h, the solution was
concentrated under vacuum. To the obtained crude 1-chloro
derivative 3 was added a mixture of CH2Cl2 (7 mL), MeOH (7
mL) and H2O (1.5 mL). The mixture was stirred for 1 h at
ambient temperature and diluted with CHCl3 (150 mL). The
organic phase was washed with 5% NaHCO3 (50 mL), dried over
Na2SO4 and evaporated to dryness. The obtained residue was
applied to a chromatographic column (silica gel, 80 cm3) and
3. Conclusion
New 6-substituted thymine ribonucleosides and their
3′-fluorinated analogues have been synthesized. It is shown that
the regio- and stereoselectivity of N-glycosylation of persilylated
6-fluorothymine with acyl derivatives of D-ribose in MeCN in the
presence of TMSOTf depends on temperature and leads to the
formation of N(1)-β- and N(1)-α-ribonucleosides or only N(3)-β-
-isomers. Yields (42-60%) of target benzoylated 6-fluorothymine

7
ACCEPTED MANUSCRIPT
eluted with a linear ethyl acetate gradient (20→30%, v/v, 400
mL). The fractions containing the product were collected and
evaporated to yield 0.61 g of colorless oil. To this ice-cooled
residue in a mixture of anhydrous pyridine (0.3 mL) and CH2Cl2
(10 mL) was added benzoyl chloride (300 mL, 2.58 mmol), the
reaction mixture was stirred for 20 h at room temperature. After
standard workup the obtained residue was applied to a
chromatographic column (silica gel, 100 cm3) and eluted with
CHCl3/hexane (5:1, v/v, 500 mL). The fractions containing the
products 5 and 6 were collected and evaporation to dryness under
vacuum. 5: Yield 50%; white solid; m.p. 120-121 oC (from
Et2O/hexane); Rf (A) 0.21; 1Н NMR (СDCl3): δ 8.08-7.30 (15Н,
m, Bz), 6.60 (1Н, br s, Н1′), 6.16-6.13 (2Н, m, Н2′, Н3′), 4.78
(1Н, dd, J = 2.8, J = 11.3, Н5′), 4.72-4.65 (2Н, m, Н4′, Н5′′),
1.84 (3H, d, J = 1.5, CH3); 13С NMR (СDCl3): δ 166.5, 165.7 and
165.4 (3С6Н5С=О), 163.7 (d, J = 17.5, C4), 157.1 (d, J = 267.5,
C6), 150.0 (d, J = 9.1, C2), 133.6-128.4 (18Сar), 90.9 (d, J =
13.0, C5), 87.2 (br s, C1ʹ), 79.2 (C4ʹ), 74.1 (C2ʹ), 71.2 (C3ʹ), 63.7
(C5ʹ), 6.7 (CH3); 19F NMR (СDCl3): δ -96.43 (s, FC6); IR (KBr,):
v 1725, 1664, 1602, 1452, 1315, 1271, 1177, 1123, 1071, 1027,
711 cm-1; HRMS [M+NH4]+ calcd for C31H29FN3O9: 606.1888,
found 606.1887.
EtOH), (lit.27 mp 120-121 C); Н NMR (СDCl3): δ 8.04-7.21
(20Н, m, Bz), 6.68 (1Н, s, Н1′), 6.02-5.98 (2Н, m, Н2′, Н3′),
4.89-4.86 (1Н, m, Н4′), 4.75 (1Н, dd, J = 3.9, J = 12.2, Н5′), 4.57
(1Н, dd, J = 4.5, Н5′′); 13С NMR (СDCl3): δ 166.1, 165.4, 165.0
and 164.7 (4С6Н5С=О), 133.7-128.3 (24Сar), 99.1 (C1′), 79.9
(C4ʹ), 75.1 (C2ʹ or C3ʹ), 71.4 (C2ʹ or C3ʹ), 63.7 (C5ʹ); IR (KBr,):
v 1725, 1601, 1585, 1451, 1316, 1268, 1178, 1115, 1067, 1026,
953, 710 cm-1; HRMS (M+Na)+: calcd. for C33H26NaO9:
589.1475; found 589.1471.
o
1
4.3.2. 3-(2,5-Di-О-benzoyl-3-deoxy-3-fluoro-β-D-ribofuranosyl)-
6-fluorothymine (9). Yield 78%; white solid, m.p. 167-169 C
(from Et2O/hexane); Rf (A) 0.20; Н NMR (СDCl3): δ 8.08-7.39
1
(10Н, m, Bz), 6.59 (1Н, br s, Н1′), 6.04 (1Н, br s, Н2′), 5.72 (1Н,
br d, J = 54.6, Н3′), 4.70 (1Н, d, J = 11.2, Н5′), 4.61-4.55 (2Н,
m, Н4′, Н5′′), 1.80 (3H, d, J = 1.1, CH3); 13С NMR (СDCl3): δ
166.3 and 165.7 (2С6Н5С=О), 163.7 (d, J = 17.1, C4), 157.1 (d,
J = 270.3, C6), 150.2 (d, J = 8.9, C2), 133.7-128.3 (12Сar), 90.7
(d, J = 15.8, C5), 88.0 (d, J = 193.9, C3ʹ), 86.1 (br s, C1ʹ), 79.5
(d, J = 25.7, C4ʹ), 73.0 (d, J = 7.5, C2ʹ), 63.1 (C5ʹ), 6.5 (CH3); 19F
NMR (СDCl3): δ -95.82 (s, FC6), -205.39 (m, FC′3); IR (KBr,): v
1725, 1664, 1602, 1452, 1315, 1271, 1177, 1110, 1071, 1027,
711 cm-1; HRMS [M+Na]+ calcd for C24H20F2N2O7Na: 509.1136,
found 509.1129.
1
6: Yield 24%; colorless oil, Н NMR (СDCl3): δ 8.13-7.28
(20Н, m, Bz), 6.95 (1Н, d, J = 4.4, Н1′), 5.92 (1Н, dd, J = 2.1,
J = 6.5, Н3′), 5.75-5.72 (1Н, m, Н2′), 4.93-4.91 (1Н, m, Н4′),
4.78 (1Н, dd, J = 3.0, J = 12.1, Н5′), 4.68 (1Н, dd, J = 3.5, Н5′′);
13С NMR (СDCl3):
δ 166.1, 165.7, 165.1 and 165.0
(4С6Н5С=О), 133.6-128.4 (24Сar), 95.0 (C1′), 82.9 (C4ʹ), 71.5
(C2ʹ or C3ʹ), 70.8 (C2ʹ or C3ʹ), 64.0 (C5ʹ); IR (KBr,): v 1725,
1601, 1585, 1451, 1316, 1268, 1178, 1136, 1112, 1067, 1023,
956, 708 cm-1; HRMS (M+Na)+: calcd. for C33H26NaO9:
589.1475; found 589.1473.
Method B: To 2,4-bis-O-(trimethylsilyl)-6-fluourothymine
(7), prepared as in method A, a solution of acetate 1 or 2 (2.11
mmol) in anhydrous MeCN (6.5 mL) was added. To this ice-
cooled mixture TMSOTf (0.42 mL, 2.32 mmol) was added under
stirring. Then the reaction mixture was stirred for 4 h from 0 С
to -15 C. After the standard workup, the obtained residue was
applied to a chromatographic column (silica gel, 150 cm3) and
eluted with a linear ethyl acetate gradient (15→35% v/v, 1600
ml) in hexane. The fractions containing the individual products
10 and 12 (or 11 and 13) were collected and evaporated to
dryness under vacuum.
4.2.2. 1,2,3,5-Tetra-O-benzoyl-α-D-ribofuranose (6). To a ice-
cooled solution of 1,3,5-tri-O-benzoyl-α-D-ribofuranose (4)
(0.50 g, 1.08 mmol) in anhydrous pyridine (10 mL) was added
benzoyl chloride (0.25 mL, 2.15 mmol) and the mixture was
stirred for 20 h at room temperature. After standard workup the
obtained residue was applied to a chromatographic column (silica
gel, 60 cm3) and eluted with a linear ethyl acetate gradient
(20→30% v/v, 300 mL) in hexane. The fractions containing the
product were collected and evaporation to yield 0.58 g (95%) of
6 as colorless oil. 6: similarly 4.2.1.
4.3.3. 1-(2,3,5-Tri-О-benzoyl-β-D-ribofuranosyl)-6-fluorothymine
(10). Yield 42%; white solid, m.p. 93-95 C (from Et2O/hexane);
Rf (A) 0.54; Н NMR (СDCl3): δ 8.81 (1Н, s, NН), 8.08-7.31
1
(15Н, m, Bz), 6.26 (1Н, br s, Н1′), 6.03 (1Н, dd, J = 2.6, J = 6.4,
Н2′), 5.92 (1Н, t, Н3′), 4.84 (1Н, dd, J = 3.1, J = 12.0, Н5′), 4.69-
4.66 (1Н, m, Н4′), 4.61 (1Н, dd, J = 5.1, Н5′′), 1.86 (3H, d, J =
2.3, CH3); 13С NMR (СDCl3): δ 166.3, 165.7 and 165.4
(3С6Н5С=О), 163.2 (d, J = 18.3, C4), 157.7 (d, J = 271.3, C6),
147.7 (d, J = 4.5, C2), 133.9-128.5 (18Сar), 92.8 (d, J = 16.7,
C5), 87.9 (d, J = 4.8, C1′), 79.4 (C4ʹ), 74.0 (d, J = 3.5, C2ʹ), 70.5
(C3ʹ), 63.3 (C5ʹ), 6.6 (CH3); 19F NMR (СDCl3): δ -98.94 (s,
FC6); IR (KBr,): v 1730, 1684, 1602, 1469, 1452, 1316, 1271,
1178, 1123, 1097, 1071, 1027, 712 cm-1; HRMS [M+NH4]+ calcd
for C31H29FN3O9: 606.1888, found 606.1883.
4.3. General
6-fluorothymine with acetates 1 and 2
procedure
for
the
glycosylation
of
Method A: A suspension of 6-fluorothymine (0.35 g, 2.43
mmol) in mixture of hexamethyldisilazane (7 mL) and
trimethylchlorosilane (0.02 mL, 0.16 mmol) was refluxed under
nitrogen for 8 h. The obtained homogeneous solution was
evaporated to dryness under vacuum, then the residue was
codistilled with anhydrous toluene (2 × 15 mL). To the obtained
2,4-bis-O-(trimethylsilyl)-6-fluourothymine (7), was added a
solution of acetates 1 or 2 (2.11 mmol) in anhydrous MeCN (6.5
mL). To this ice-cooled mixture TMSOTf (0.42 mL, 2.32 mmol)
was added, and the resulting solution was stirred for 5 min at +5
С. Then the reaction mixture was brought to room temperature
and stirred for 4 h, and diluted with CH2Cl2 (150 mL). The
organic phase was washed with 5% NaHCO3 (2 × 50 mL), dried
over Na2SO4 and evaporated to dryness. The obtained residue
was applied to a chromatographic column (silica gel, 100 cm3)
and eluted with a linear ethyl acetate gradient (15→50%, v/v,
1200 mL) in hexane. The fractions containing the individual
products 8 or 9 were collected and evaporated to dryness under
vacuum.
4.3.4. 1-(2,5-Di-О-benzoyl-3-deoxy-3-fluoro-β-D-ribofuranosyl)-
6-fluorothymine (11). Yield 45%; white solid, m.p. 82-84 C
(from Et2O/hexane); Rf (A) 0.53; 1Н NMR (СDCl3): δ 8.39 (s,
1Н, NН), 8.09-7.44 (10Н, m, Bz), 6.24 (1Н, br s, Н1′), 5.97 (1Н,
dd, J = 6.3, J = 10.4, Н2′), 5.59 (1Н, dt, J = 53.1, Н3′), 4.75 (1Н,
dt, J = 3.7, J = 11.8, Н5′), 4.62-4.55 (2Н, m, J = 5.0, Н4′, Н5′′),
1.85 (3H, d, J = 2.4, CH3); 13С NMR (СDCl3): δ 166.1 and 165.5
(2С6Н5С=О), 163.4 (d, J = 18.2, C4), 157.4 (d, J = 271.4, C6),
147.7 (d, J = 3.7, C2), 133.9-128.5 (12Сar), 92.7 (d, J = 16.5,
C5), 87.7 (d, J = 194.4, C3ʹ), 86.5 (d, J = 4.9, C1ʹ), 79.9 (d, J =
25.4, C4ʹ), 72.8 (d, J = 12.5, C2ʹ), 62.8 (d, J = 3.0, C5ʹ), 6.4
(CH3); 19F NMR (СDCl3): δ -99.36 (s, FC6), -204.27 (m, FC′3);
IR (KBr, cm-1): v 1730, 1684, 1602, 1469, 1452, 1316, 1271,
4.3.1. 3-(2,3,5-Tri-О-benzoyl-β-D-ribofuranosyl)-6-fluorothymine
(8). Yield 85%; white solid, m.p. 180-182 C (from

8
Tetrahedron
ACCEPTED MANUSCRIPT
1178, 1123, 1097, 1071, 1027, 712; HRMS [M+Na]+ calcd for
fractions containing the individual products 14-17 and 21, 22
C24H20F2N2O7Na: 509.1136, found 509.1130.
were collected and evaporated to dryness under vacuum.
4.3.5. 1-(2,3,5-Tri-О-benzoyl-α-D-ribofuranosyl)-6-
4.5.1. 3-(β-D-Ribofuranosyl)-6-fluorothymine (14). Yield 57%;
white solid, m.p. 179-181 C (from Et2O/hexane); Rf (В) 0.21;
UV λ, nm (lg ε): pH 1, λmax 257 (3.83), λmin 232 (3.43); pH 7, λmax
281 (4.0), λmin 247 (2.59); pH 13, λmax 281 (4.0), λmin 247 (3.18);
1Н NMR (СD3OD): δ 6.40 (1Н, d, J = 4.1, Н1′), 4.72 (1Н, dd, J =
6.2, Н2′), 4.39 (1Н, t, Н3′), 3.92-3.89 (1Н, m, Н4′), 3.81 (1Н, dd,
J = 2.6, J = 11.9, Н5′), 3.68 (1Н, dd, J = 4.8, Н5′′), 1.77 (3H, d, J
˂1, CH3); 13C NMR (СD3OD): δ 169.0 (d, J = 17.5, C4), 167.4
(d, J = 242.8, C6), 156.8 (d, J = 31.5, C2), 90.0 (C1′), 87.3 (d, J =
25.9, C5), 85.7 (C4′), 72.8 (C2′), 71.6 (C3′), 63.7 (C5′), 6.9
(CH3); 19F NMR (СD3OD): δ -75.43 (s, FC6); IR (KBr): v 1724,
1657, 1636, 1477, 1439, 1382, 1257, 1143, 1104, 1050, 859 cm-1;
HRMS [M+Na]+ calcd for C10H13FN2O6Na: 299.0655, found
299.0650.
fluorothymine (12). Yield 14%; white solid, m.p. 90-92 C (from
Et2O/hexane); Rf (A) 0.46; 1Н NMR (СDCl3): δ 8.61 (1Н, s, NН),
8.07-7.31 (15Н, m, Bz), 7.04 (1Н, d, J = 5.7, Н1′), 6.09 (1Н, t,
Н2′), 5.79 (1Н, t, Н3′), 4.98-4.95 (1Н, m, Н4′), 4.77 (1Н, dd, J =
3.1, J = 12.2, Н5′), 4.56 (1Н, dd, J = 4.0, Н5′′), 1.74 (3H, d, J =
2.3, CH3); 13С NMR (СDCl3): δ 166.2, 165.2 and 164.6
(3С6Н5С=О), 163.0 (d, J = 17.6, C4), 158.4 (d, J = 272.7, C6),
147.9 (d, J = 4.7, C2), 134.1-128.3 (18Сar), 92.5 (d, J = 16.6,
C5), 85.8 (C1ʹ), 79.7 (d, J = 5.4, C4ʹ), 71.4 (C3ʹ), 70.6 (C2ʹ), 63.6
(C5ʹ), 6.2 (CH3); 19F NMR (СDCl3): δ -94.51 (s, FC6); IR (KBr):
v 1730, 1679, 1602, 1475, 1452, 1417, 1316, 1270, 1178, 1135,
1096, 1069, 1026, 712 cm-1; HRMS [M+Na]+ calcd for
C31H25FN2O9Na: 611.1442, found 611.1449.
4.3.6. 1-(2,5-Di-О-benzoyl-3-deoxy-3-fluoro-α-D-ribofuranosyl)-
6-fluorothymine (13). Yield 11%; white solid, m.p. 78-80 C
4.5.2. 3-(3-Deoxy-3-fluoro-β-D-ribofuranosyl)-6-fluorothymine
(15). Yield 63%; colorless oil; UV λ, nm (lg ε): pH 1, λmax 258
(3.82), λmin 233 (3.42); pH 7, λmax 282 (3.96), λmin 248 (2.57); pH
13, λmax 282 (3.96), λmin 248 (3.05); NMR (СD3OD): δ 6.45 (1Н,
d, J = 6.1, Н1′), 5.06 (1Н, ddd, J = 3.0, J = 5.2, J = 56.1, Н3′),
5.05 (1Н, dt, J = 15.2, Н2′), 4.21-4.14 (1Н, dm, J = 25.0, Н4′),
3.74 (1Н, dd, Ј = 3.2, J = 12.1, Н5′), 3.66 (1Н, dd, J = 3.8, Н5′′),
1.74 (3Н, d, J ˂1, CH3); 13C NMR (СD3OD): δ 169.6 (d, J =
17.6, C4), 168.9 (d, J = 245.9, C6), 158.6 (d, J = 29.7, C2), 93.5
(d, J = 182.9, C3′), 88.7 (C1′), 87.4 (d, J = 26.5, C5), 84.3 (d, J =
23.4, C4′), 71.2 (d, J = 15.3, C2′), 63.3 (d, J = 8.3, C5′), 7.1
(CH3); 19F NMR (СD3OD): δ -74.23 (s, FC6), -202.29 (m, FC3′);
HRMS [M+Na]+ calcd for C10H12F2N2O5Na: 301.0612, found
301.0607.
1
(from Et2O/hexane); Rf (A) 0.43; Н NMR (СDCl3): δ 8.18 (1Н,
s, NН), 8.06-7.43 (10Н, m, Bz), 6.97 (1Н, d, J = 6.7, Н1′), 5.84
(1Н, dt, J = 12.8, Н2′), 5.41 (1Н, ddd, J = 4.2, J = 5.9, J = 52.7,
Н3′), 4.95-4.90 (1Н, dm, J = 18.5, Н4′), 4.65 (1Н, dd, J = 3.2, J =
12.3, Н5′), 4.53 (1Н, dd, J = 3.5, Н5′′), 1.85 (3H, d, J = 2.4,
CH3); 13С NMR (СDCl3): δ 166.0 and 164.6 (2С6Н5С=О), 163.1
(d, J = 17.4, C4), 158.5 (d, J = 271.1, C6), 148.0 (d, J = 4.8, C2),
134.1-128.6 (12Сar), 92.5 (d, J = 16.8, C5), 88.8 (d, J = 198.7,
C3ʹ), 84.8 (C1ʹ), 80.7 (dd, J = 3.8, J = 25.4, C4ʹ), 70.5 (d, J =
14.3, C2ʹ), 63.6 (d, J = 5.7, C5ʹ), 6.2 (CH3); 19F NMR (СDCl3): δ
-94.12 (s, FC6), -202.96 (m, FC3′); IR (KBr): v 1730, 1679,
1602, 1475, 1452, 1417, 1316, 1270, 1178, 1133, 1095, 1069,
1026, 712 cm-1; HRMS [M+Na]+ calcd for C24H20F2N2O7Na:
509.1136; found 509.1132.
4.5.3. 1-(β-D-Ribofuranosyl)-6-fluorothymine (16). Yield 79%;
white solid, m.p. 135-136 oC (from Et2O); Rf (В) 0.67; UV λ, nm
(lg ε): pH 1, λmax 255 (4.03), λmin 228 (3.53); pH 7, λmax 255
(4.03), λmin 228 (3.53); pH 13, λmax 258 (3.86), λmin 241 (3.68); 1Н
NMR (DMSO-d6): δ 11.63 (1Н, br s, NH), 5.87 (1Н, d, J = 4.3,
Н1′), 5.33 (1Н, d, J = 5.2, 2′ОН), 5.07 (1Н, d, J = 6.0, 3′ОН),
4.76 (1Н, t, J = 5.7, 5′ОН), 4.32 (1Н, t, Н2′), 3.95-3.92 (1Н, m,
Н3′), 3.71-3.68 (1Н, m, Н4′), 3.55 (1Н, dd, J = 3.7, J = 11.8,
Н5′), 3.45-3.40 (1Н, m, J = 5.7, Н5′′), 1.73 (3H, d, J = 2.4, CH3);
13C NMR (DMSO-d6): δ 163.3 (d, J = 17.9, C4), 157.9 (d, J =
269.7, C6), 148.3 (d, J = 3.9, C2), 90.9 (d, J = 15.6, C5), 88.5
(C1′), 84.4 (C4′), 71.4 (d, J = 3.9, C2′), 69.2 (C3′), 61.4 (C5′), 6.1
(CH3); 19F NMR (DMSO-d6): δ -97.89 (s, FC6); IR (KBr): v
1724, 1685, 1669, 1475, 1427, 1387, 1232, 1121, 1098, 1064,
1036, 857 cm-1; HRMS [M+Na]+ calcd for C10H13FN2O6Na:
299.065, found 299.0651.
4.4. General
procedure
for
the
glycosylation
of
6-fluorothymine with benzoates 5 and 6
To a suspension of 6-fluorothymine (0.10 g, 0.69 mmol) in
anhydrous MeCN (5.5 mL) was added BSTFA (0.55 mL, 2.07
mmol), the mixture was stirred for 2 h at room temperature and
the obtained homogeneous solution was evaporated to dryness
under vacuum. To the obtained 2,4-bis-O-(trimethylsilyl)-6-
fluourothymine (7) a solution of benzoate 5 or 6 (0.31 g, 0.55
mmol) in anhydrous MeCN (4.5 mL) was added. To this ice-
cooled mixture TMSOTf (1.1 mL, 0.61 mmol) was added under
stirring, then the reaction mixture was stirred for 4 h from 0 С to
-15 C. After the standard workup, the obtained residue was
applied to a chromatographic column (silica gel, 60 cm3) and
eluted with a linear ethyl acetate gradient (15→35% v/v, 600
mL) in hexane. The fractions containing the products 10 and 12
were collected and evaporated to yield β-anomer 0.19 g (60%),
α:β - 4.3:1 from 5 and 0.16 g (51%), α:β - 2.4:1 from 6.
4.5.4. 1-(3-Deoxy-3-fluoro-β-D-ribofuranosyl)-6-fluorothymine
(17). Yield 75%; colorless oil; Rf (В) 0.72; UV λ, nm (lg ε): pH
1, λmax 255 (3.95), λmin 228 (3.61); pH 7, λmax 255 (3.95), λmin 228
(3.61); pH 13, λmax 258 (3.84), λmin 241 (3.69); 1Н NMR (DMSO-
d6): δ 11.72 (1Н, br s, NH), 5.91 (1Н, d, J = 6.9, Н1′), 5.87 (1Н,
d, J = 5.8, 2′ОН), 4.98 (1Н, t, J = 5.4, 5′ОН), 4.96 (1Н, ddd, J =
2.3, J = 4.6, J = 54.4, Н3′), 4.64 (1Н, dt, J = 19.1, Н2′), 4.10-4.03
(1Н, dm, J = 25.2, Н4′), 3.52-3.50 (2Н, m, Н5′, Н5′′), 1.73 (3H,
d, J = 2.3, CH3); 13C NMR (DMSO-d6): δ 163.2 (d, J = 18.1, C4),
157.8 (d, J = 270.5, C6), 148.4 (d, J = 4.1, C2), 91.2 (d, J = 15.5,
C5), 91.0 (d, J = 183.3, C3′), 86.8 (C1′), 82.5 (d, J = 22.1, C4′),
69.5 (dd, J = 5.6, J = 15.8, C2′), 60.4 (d, J = 8.3, C5′), 6.1 (CH3);
19F NMR (DMSO-d6): δ -98.24 (s, FC6), -199.82 (m, FC3′).
HRMS [M+Na]+ calcd for C10H12F2N2O5Na: 301.0612, found
301.0604.
4.5. General procedure for the debenzoylation of
6-fluorothymine
monohydrate
ribonucleosides
8-13
with
LiOH
To a solution of benzoylated 6-fluorothymine nucleoside 8-13
(0.21 mmol) in MeCN (31 mL) and H2O (13 mL) was added
LiOHH2O (0.76 mmol for 8, 10, 12 and 0.52 mmol for 9, 11,
13). The reaction mixture was stirred for 5 h at room temperature,
neutralized by the addition of Amberlite IRG-5 (H+-form) ion-
exchange resin, then filtered, washed with methanol and
evaporated to dryness under vacuum. The obtained residue was
purified by column chromatography (silica gel, 50 cm3) using a
linear MeOH gradient (0→15% v/v, 600 mL) in CHCl3. The
4.5.5. 6,2′-Anhydro-1-(α-D-ribofuranosyl)-6-hydroxythymine
o
(21). Yield 81%; white solid, m.p. 234-236 C (from Et2O); Rf

9
ACCEPTED MANUSCRIPT
(В) 0.53; UV λ, nm (lg ε): pH 1, λmax 260 (4.08); pH 7, λmax 260
4.7. Procedure for the debenzoylation of 6-fluorothymine
ribonucleosides 10 with NaOMe in methanol
1
(4.14); pH 13, λmax 262 (3.97); Н NMR (DMSO-d6): δ 11.04
(1Н, br s, NH), 6.14 (1Н, d, J = 4.8, Н1ʹ), 5.72 (1Н, d, J = 5.7,
3′ОН), 5.19 (1Н, t, Н2′), 4.86 (1Н, t, J = 5.1, 5′ОН), 4.01 (1Н,
dd, J = 5.1, J = 9.3, Н3′), 3.68 (1Н, d, Н5′), 3.56 (1Н, ddd, J =
1.6, J = 4.2, J = 9.3, Н4′) 3.43 (1Н, dd, J = 12.4, Н5′′), 1.68 (3H,
s, CH3); 13C NMR (DMSO-d6): δ 165.3 (C4), 159.0 (C6), 146.5
(C2), 85.8 (C1′), 84.3 (C4′), 81.3 (C5), 80.2 (C2′), 69.6 (C3′),
59.2 (C5′), 6.7 (CH3); IR (KBr): v 1750, 1682, 1665, 1650, 1489,
1228, 1049, 1034, 1003, 1021, 772 cm-1; HRMS [M+H]+ calcd
for C10H13N2O6: 257.0774, found 257.0767.
Compound 10 (0.43 mmol) was dissolved in anhydrous
MeOH (20 mL). To this was added a methanolic solution of 1.25
M NaOMe (2 mL). The reaction mixture was stirred for 2 h at
room temperature and neutralized by glacial AcOH. The mixture
was evaporated to dryness under vacuum and the residue was
purified with column chromatography (silica gel, 40 cm3) using a
linear MeOH gradient (0→30% v/v, 400 mL) in CHCl3. The
fractions containing the product 20 were collected and
evaporated to dryness.
4.5.6. 6,2′-Anhydro-1-(3-deoxy-3-fluoro-α-D-ribofuranosyl)-6-
hydroxythymine (22). Yield 85%; white solid, m.p. 221-223 C
o
4.7.1. 1-(β-D-Ribofuranosyl)-6-methoxythymine (20). Yield 68%;
white solid, m.p. 172-174 oC (from Et2O); Rf (В) 0.64; UV λ, nm
(lg ε): pH 1, λmax 265 (4.02); pH 7, λmax 265 (4.02); pH 13, λmax
(from Et2O); Rf (В) 0.63; UV λ, nm (lg ε): pH 1, λmax 259 (4.06);
1
pH 7, λmax 259 (4.11); pH 13, λmax 261 (3.93); Н NMR (DMSO-
1
266 (3.89); Н NMR (DMSO-d6): δ 11.35 (1Н, br s, NH), 5.71
d6): δ 11.13 (1Н, s, NH), 6.21 (1Н, d, J = 5.1, Н1′), 5.49 (1Н, dt,
J = 1.7, Н2′), 5.22 (1Н, br s, 5′ОН), 5.17 (1Н, ddd, J = 5.2, J =
7.3, J = 50.5, Н3′), 4.03 (1Н, ddd, J = 7.3, J = 14.2, Н4′), 3.66
(1Н, dd, J = 2.6, J = 12.6, Н5′), 3.54 (1Н, dd, J = 3.6, Н5′′), 1.67
(3H, s, CH3); 13C NMR (DMSO-d6): δ 165.4 (C4), 159.1 (C6),
146.5 (C2), 88.2 (d, J = 192.8, C3′), 86.5 (d, J = 4.8, C1′), 81.8
(C5), 81.6 (d, J = 12.7, C2′), 79.1 (d, J = 22.8, C4′), 58.9 (C5′),
6.7 (CH3); 19F NMR (DMSO-d6): δ -212.65 (dd, FC3′); IR (KBr):
v 1734, 1673, 1662, 1619, 1489, 1226, 1105, 1053, 1034, 767
cm-1; HRMS [M+H]+ calcd for C10H12FN2O5: 259.0730, found
259.0726.
(1Н, br s, Н1′), 5.21 (1Н, br s, 2′ОН), 4.95 (1Н, br s, 3′ОН), 4.72
(1Н, t, 5′ОН), 4.41 (1Н, d, Н2′), 3.95 (1Н, t, Н3′), 3.88 (3H, s,
OCH3), 3.67-3.64 (1Н, m, Н4′), 3.60 (1Н, dd, J = 3.5, J = 11.8,
Н5′), 3.46 (1Н, dd, J = 6.1, Н5′′), 1.77 (3H, s, CH3); 13C NMR
(DMSO-d6): δ 164.1 (C4), 159.1 (C6), 149.4 (C2), 96.7 (C1′),
89.0 (C4′), 83.9 (C5), 70.9 (C2′), 69.3 (C3′), 62.6 (OCH3), 61.5
(C5′), 7.9 (CH3); IR (KBr): v 1707, 1698, 1670, 1623, 1476,
1246, 1133, 1100, 1044, 1021 cm-1; HRMS [M+Na]+ calcd for
C11H16N2O7Na: 311.0855, found 311.0849.
4.8. General
procedure
for
the
benzoylation
of
anhydronucleosides 21 and 22
4.6. General procedure for the debenzoylation of
6-fluorothymine ribonucleosides 10 and 11 with methanolic
ammonia
To a ice-cooled solution of 6,2′-anhydronucleosides 21 or 22
(0.07 mmol) in anhydrous pyridine (1 mL) was added benzoyl
chloride (0.42 mmol for 21 and 0.32 mmol for 22) and the
mixture was stirred for 20 h at room temperature. After standard
workup the obtained residue was applied to a chromatographic
column (silica gel, 30 cm3) and eluted with a linear ethyl acetate
gradient (0→30% v/v, 300 mL) in hexane. The fractions
containing the individual product 23, 24 or 25 were collected and
evaporated to dryness under vacuum.
Compound 10 or 11 (0.50 mmol) was dissolved in MeOH (15
mL) saturated with NH3 at 0 °C and stirred for 24 h at room
temperature. The reaction mixture was evaporated to dryness
under vacuum and the obtained residue was purified by column
chromatography (silica gel, 60 cm3) using a linear MeOH
gradient (0→30% v/v, 500 mL) in CHCl3. The fractions
containing the individual product 18 or 19 were collected and
evaporated to dryness under vacuum.
4.8.1. 6,2′-Anhydro-1-(3,5-di-О-benzoyl-α-D-ribofuranosyl)-N-3-
benzoyl-6-hydroxythymine (23). Yield 75%; colorless oil; 1Н
NMR (СDCl3): δ 8.05-7.38 (15Н, m, Bz), 6.54 (1Н, d, J = 4.9,
Н1ʹ), 5.72 (1Н, t, Н2ʹ), 5.31 (1Н, dd, J = 5.3, J = 8.9, Н3ʹ), 4.74
(1Н, dd, J = 3.5, J = 12.2, Н5ʹ), 4.64-4.57 (2Н, m, Н5ʹʹ, Н4ʹ),
1.75 (3H, s, CH3); HRMS [M+Na]+ calcd for C31H24N2O9Na:
591.1380, found 591.1377.
4.6.1. 1-(β-D-Ribofuranosyl)-6-aminothymine (18). Yield 72%;
white solid, m.p. 124-126 C (from EtOH); Rf (В) 0.23; UV λ,
nm (lg ε): pH 1, λmax 280 (4.26); pH 7, λmax 280 (4.26); pH 13,
1
λmax 281 (4.11); Н NMR (DMSO-d6): δ 10.57 (1Н, s, NH), 6.51
(2H, s, NH2), 6.24 (1Н, d, J = 7.3, Н1′), 5.48 (1Н, t, J = 4.6,
5′ОН), 5.24 (1Н, d, J = 6.4, 3′ОН), 5.04 (1Н, d, J = 4.9, 2′ОН),
4.41-4.37 (1Н, m, Н2′), 4.05-4.02 (1Н, m, Н3′), 3.81 (1Н, br s,
Н4′), 3.64-3.57 (2Н, m, J = 11.8, Н5′, Н5′′), 1.65 (3H, s, CH3);
13C NMR (DMSO-d6): δ 162.2 (C4), 151.7 (C2), 150.5 (C6), 87.9
(C1′), 84.7 (C4′), 82.17 (C5), 69.2 (C2′), 69.1 (C3′), 60.0 (C5′),
8.1 (CH3); IR (KBr): v 1715, 1693, 1627, 1572, 1505, 1293,
1191, 1117, 1072, 1044 cm-1; HRMS [M+Na]+ calcd for
C10H15N3O6Na: 296.0859, found 509.0845.
4.8.2. 6,2′-Anhydro-1-(5-О-benzoyl-3-deoxy-3-fluoro-α-D-
ribofuranosyl)-N-3-benzoyl-6-hydroxythymine (24). Yield 81%;
1
colorless oil; Н NMR (СDCl3): δ 8.05-7.45 (10Н, m, Bz), 6.45
(1Н, d, J = 4.9, Н1ʹ), 5.41 (1Н, t, Н2ʹ), 5.13 (1Н, ddd, J = 5.2, J =
8.2, J = 50.1, Н3ʹ), 4.71 (1Н, dd, J = 3.4, J = 12.5, Н5ʹ), 4.61
(1Н, dd, J = 4.0, Н5ʹʹ), 4.49-4.44 (1Н, m, Н4ʹ), 1.91 (3H, s, CH3);
HRMS [M+Na]+ calcd for C24H19FN2O7Na: 489.1074, found
489.1076.
4.6.2. 1-(3-Deoxy-3-fluoro-β-D-ribofuranosyl)-6-aminothymine
(19). Yield 75%; white solid; Rf (В) 0.42; UV λ, nm (lg ε): pH 1,
λmax 280 (4.23); pH 7, λmax 280 (4.23); pH 13, λmax 281 (4.03); 1Н
NMR (DMSO-d6): δ 10.64 (1Н, s, NH), 6.59 (2H, s, NH2), 6.33
(1Н, d, J = 8.9, Н1′), 5.80 (1Н, d, J = 6.3, 2′ОН), 5.70 (1Н, br s,
5′ОН), 4.96 (1Н, dd, J = 55.6, Н3′), 4.65 (1Н, dm, J = 22.1, Н2′),
4.21 (1Н, d, J = 30.4, Н4′), 3.75 (1Н, dd, J = 4.3, J = 11.8, Н5′),
3.57 (1Н, d, Н5′′), 1.66 (3H, s, CH3); 13C NMR (DMSO-d6): δ
162.2 (C4), 151.4 (C6), 150.6 (C2), 91.9 (d, J = 182.2, C3′), 86.2
(C1′), 82.6 (d, J = 24.1, C4′), 82.1 (C5), 67.9 (d, J = 15.2, C2′),
60.0 (d, J = 11.0, C5′), 8.2 (CH3); 19F NMR (DMSO-d6): δ -
195.54 (m, FC3′); HRMS [M+Na]+ calcd for C10H14FN3O5Na:
298.0815, found 298.0810.
4.8.3. 6,2′-Anhydro-1-(3,5-di-О-benzoyl-α-D-ribofuranosyl)-6-
hydroxythymine (25). Yield 20%; colorless oil; 1Н NMR
(СDCl3): δ 8.52 (s, 1Н, NH), 8.03-7.37 (10Н, m, Bz), 6.51 (1Н,
d, J = 5.0, Н1ʹ,), 5.68 (1Н, t, Н2’), 5.28 (1Н, dd, J = 5.4, J = 9.1,
Н3’), 4.73 (1Н, dd, J = 3.7, J = 12.4, Н-5ʹ), 4.60 (1Н, dd, J = 4.2,
Н5ʹʹ), 4.53-4.50 (1Н, m, Н4ʹ), 1.73 (3H, s, CH3); HRMS
[M+Na]+ calcd for C24H20N2O8Na: 487.1117, found 487.1125.

10
Tetrahedron
ACCEPTED MANUSCRIPT
Acknowledgments
This work was supported within the research project number
2.19 of ChemPharmSynthesis Program, National Academy of
Sciences of Belarus.
The authors are indebted to Dr. E.P. Studentsov
(St. Petersburg State Technological Institute, Russia) for a
sample of 6-fluorothymine without which the implementation of
this work would be impossible.
Supplementary material
Supplementary data Supplementary data related to this article can
be found in the online version.
Notes and references
1. Parker, W. B. Chem. Rev. 2009, 109, 2880-2893.
2. Begue, J. P.; Bonnet-Delpon, D. J. Fluorine Chem. 2006, 127,
992-1012.
3. Wojtowicz-Rajchel, H. J. Fluorine Chem. 2012, 143, 11-48.
4. O’Hagan, D. Chem. Soc. Rev. 2008, 37, 308–319.
5. Liu, P.; Sharon, A.; Chu, C. K. J. Fluorine Chem. 2008, 129, 743-
766.
6. Thomas, D. M.; Zalcberg, J. R. Clin. Exp. Pharmacol. Physiol.
1998, 25, 887-895.
7. Barwolff, D.; Kowollik, G.; Langen, P. Collect. Czech. Chem.
Commun. 1974, 39, 1494-1499.
8. Von Janta-Lipinski, M.; Langen, P. Nucleic Acids Res. Symposium
Series 1981, 9, 41-44.
9. (a) Studentsov, E. P. Bulletin of St PbSIT(TU) 2009, 5, 3-10; (b)
Studentsov, E. P.; Ivin, B. A.; Korableva, N. V.; Sochilin, E. G.
Patent № 537074 (RU), 1976.
10. Felczak, К.; Drabikowska, А. К.; Vilpo, J. А.; Kulikowski, T.;
Shugar, D. J. Med. Chem. 1996, 39, 1720-1728.
11. Kissman, H. M.; Pidacks, C.; Baker, B. R. J. Am. Chem. Soc.
1955, 77, 18-24.
12. Mikhailopulo, I. A.; Poopeiko, N. E.; Pricota, T. I.; Sivets, G. G.;
Kvasyuk, E. I.; Balzarini, J.; De Clercq, E. J. Med. Chem. 1991,
34, 2195-2202.
13. Howell, H. G.; Brodfuehrer, P. R.; Brundidge, S. P.; Benigni, D.
A.; Sapino, C. Jr. J. Org. Chem. 1988, 53, 85-88.
14. Vorbruggen, H.; Krolekevich, K.; Bennua, B. Chem. Ber. 1981,
114, 1234-1255.
15. Evershed, R. F. In Handbook of Derivatives for Chromatography,
2nd ed; Blau, K., Halket, J., Eds.; John Wiley and Sons: Chicheste,
New York, Brisbane, Toronto and Singapore, 1993; pp. 51-108.
16. Pichat, L.; Chatelain, G. Bull. Soc. Chim. Fr. 1970, 5, 1833-1837.
17. Winkley, M. W.; Robins, R. K. J. Chem. Soc. (C) 1969, 5, 791-
796.
18. Saneyoshi, M.; Inomata, M.; Fukuoka, F. Chem. Pharm. Bull.
1978, 26, 2990-2997.
19. Nedorezova, T. P.; Melnik S. Ya.; Preobrazhenskaya M. N. Russ.
J. Bioorg. Chem. 1976, 2, 1205-1208.
20. Prystas, M.; Sorm, F. Collect. Czech. Chem. Commun. 1969, 34,
2316-2347.
21. Hsee, Li C.; Sardellat, D. J. Magn. Reson. Chem. 1990, 28, 688-
692.
22. Folkers, G.; Junginger, G.; Muller, Ch. E.; Schlozb, U.; Eger, K.
Arch. Pharm. 1989, 322, 119-123.
23. Otter, B. A.; Falco, E. A.; Fox, J. J. J. Org. Chem. 1968, 33, 3593-
3600.
24. Honjo, M.; Furukawa, Y.; Nishikawa, M.; Kamiya, K.; Yoshioka,
Y. Chem. Pharm. Bull. 1967, 15, 1076-1079.
25. Harnden, M. R.; Jarvest, R. L. Nucleos. Nucleot. 1985, 4, 465-476.
26. Haziri, A. I.; Leuman, C. J. J. Org. Chem. 2012, 77, 5861-5869.
27. Ness, R. K.; Diehl, H. W.; Fletcher H. G. J. Am. Chem. Soc. 1954,
76, 763-767.