Electrophilic addition to the multiple bond of 1-carboxymethyl-5-fluorouracil

Article abstract of DOI:10.1007/s11172-020-2731-9

1-Carboxymethyl-5-fluoro-5-halogeno-6-hydroxy-5,6-dihydrouracils and 1-carboxymethyl- 5-fluoro-6-hydroxy-5-nitro-5,6-dihydrouracil were synthesized in high yields by oxidative halogenation or nitration of 1-carboxymethyl-5-fluorouracil. Oxidative halogenation or nitration of 5-fluoro-1-(methoxycarbonylmethyl)uracil in acidic media results in the addition of the corresponding groups at the C(5) atom of uracil and simultaneous hydrolysis of the ester group. Bimolecular ions of the obtained compounds were detected in the negative ion mass spectra.

Full text of DOI:10.1007/s11172-020-2731-9

Russian Chemical Bulletin, International Edition, Vol. 69, No. 1, pp. 114—117, January, 2020
114
Electrophilic addition to the multiple bond of 1-carboxymethyl-5-fluorouracil
I. B. Chernikova, М. S. Yunusov, and A. G. Mustaphin
Ufa Institute of Chemistry, Ufa Federal Research Centre, Russian Academy of Sciences,
71 prosp. Oktyabrya, 450054 Ufa, Russian Federation.
Е-mail: inna.b.chernikova@yandex.ru
1-Carboxymethyl-5-fluoro-5-halogeno-6-hydroxy-5,6-dihydrouracils and 1-carboxymeth-
yl-5-fluoro-6-hydroxy-5-nitro-5,6-dihydrouracil were synthesized in high yields by oxidative
halogenation or nitration of 1-carboxymethyl-5-fluorouracil. Oxidative halogenation or nitra-
tion of 5-fluoro-1-(methoxycarbonylmethyl)uracil in acidic media results in the addition of the
corresponding groups at the C(5) atom of uracil and simultaneous hydrolysis of the ester group.
Bimolecular ions of the obtained compounds were detected in the negative ion mass spectra.
Key words: 5-fluorouracil, electrophilic addition, halogenation.
A number of uracil derivatives have been shown to
exhibit antitumor1—6 and antiviral activity.7—10 At the
same time, the reported derivatives possessing an antiviral
activity differ considerably in their structures from 5-chloro-
5-fluoro-6-hydroxy-5,6-dihydrouracil, for which we for-
merly revealed a pronounced antiviral activity against
different strains of influenza virus.11 In the search for new
antiviral drugs among analogs of 5-chloro-5-fluoro-6-
hydroxy-5,6-dihydrouracil, compounds containing an
acetic acid residue at position 1 were synthesized.
1-Carboxymethyl-5-fluorouracil (2) was prepared from
5-fluorouracil (1) and chloroacetic acid according to
a described method.12 The corresponding methyl ester 3
was synthesized by boiling acid 2 in methanol in the pres-
ence of sulfuric acid (Scheme 1).13
Oxidative halogenation and nitration of compound 2
were carried out using previously developed methods.14
The mechanism of the electrophilic addition to uracil
derivatives was already discussed.14—15 Bromination of
compound 2 with a KBr—H2O2 mixture in 20% H2SO4
for 5 h gave bromohydrin 4 in 67% yield (Scheme 2).
A twofold prolongation of the reaction increased the
yield to 83%.
Scheme 2
Scheme 1
Compound
4, 4´
X
Br
Cl
Yield (%)
83
78
75
5, 5´
6, 6´
NO2
Reagents and conditions: i. KBr (2 eq.), 20% H2SO4, 33% H2O2
(3 eq.), ~20 C, 10 h, or ii. НCl (3 eq.), 33% H2O2 (4 eq.),
СН2Cl2, ~20 C, 5 h, or iii. H2SO4, 67% HNO3, 020 C, 5 h.
Chlorination of 2 using KCl under analogous con-
ditions did not result in the desired product substi-
tuted at position 5; only starting compound 2 was isolated.
However, chlorination of 2 in a two-phase medium16
gave chlorohydrin 5 in 78% yield. Nitration of uracil 2
with an H2SO4—HNO3 mixture at 0—10 C for 5 h pro-
duced the corresponding nitro compound in 75% yield
(see Scheme 2).
Reagents and conditions: i. ClCH2COOH (1.35 eq.), KOH (4 eq.),
H2O, ~20 C, 5 h; ii. MeOH, H2SO4 (cat.), 60 C, 3 h.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 0114—0117, January, 2020.
1066-5285/20/6901-0114 © 2020 Springer Science+Business Media, Inc.

1-Carboxymethyl-5-fluorouracil derivatives
Russ. Chem. Bull., Int. Ed., Vol. 69, No. 1, January, 2020
115
It is worth noting that methylene protons of the
The spatial structures of compounds 4—6 likely cor-
respond to those of analogous 5-fluorouracil derivatives
substituted at position 5, in which the ОН group at the
С(6) atom acquires an axial position due to anomeric effect,
whereas the F atom acquires an equatorial position.14
Formerly we showed that according to the calculations at the
B3LYP/6-311+G(d,p)//B3LYP/6-311G(d,p) + IEFPCM
level of theory, as well as the results of the GIAO model-
ling of the 13C NMR spectra, the equatorial orientation
of the fluorine atom and the axial orientation of the hydr-
oxyl group at the position 6 of the dihydrouracil ring are
characteristic of 5,6-substituted 5-fluorouracils.14
The proposed stereochemistry agrees with the influence
of the anomeric effect on α-substituted saturated N(O, S)-
heterocycles, in which, as shown in many examples, the
ОН group located in the α-position to the heteratom in
the heterocycle is usually axially oriented.17
Compounds 4—6 are amorphous, which precludes
their X-ray analysis. Taking into account the conditions,
under which the oxidative halogenation and nitration were
carried out, one may expect that the electrophilic additions
should proceed according to the monomolecular mecha-
nism via an intermediate С(6)-carbocation being planar
in the case of uracil derivatives, which determinates the
predominant role of the anomeric effect.17 Under the used
conditions, the orientation of the substituents at the С(5)
and С(6) atoms may vary and differ from the initial one.
In this case, the influence of the anomeric effect should
also predominate.
CH2COOH moieties in obtained compounds 4—6 are not
1
equivalent and appear in the Н NMR spectrum as two
doublets, whereas they are equivalent in starting 1-carb-
oxymethyl-5-fluorouracil (2). Nonequivalence of these
protons in compounds 4—6 is probably due to the presence
of the OH group in position 6 and the formation of a hydro-
gen bond between this OH group and the carboxyl group,
as well as due to the existence of the ring-chain tauto-
merism leading to the formation of equilibrium structures
4´—6´ (see Scheme 2). This is indicated by the preservation
1
of the proton nonequivalence in the Н NMR spectra at
70 С. Note that the nonequivalence of protons at the С(7)
atom is also observed for methyl ester 7. In the 13С NMR
1
and Н NMR spectra of compounds 4—6, the spin-spin
interactions of the F atom with the С(4), С(5) and С(6)
atoms, as well as with the proton at the С(6) atom
are observed. In the mass spectra of negative ions, the
[М – Н]– ion peaks with masses of 283 and 239 and iso-
topic distributions characteristic of monobromo or mono-
chloro derivatives, respectively, were observed for com-
pounds 4 and 5. Bimolecular ions with masses of 567 and
479, which contain two Br or Cl atoms, respectively, were
detected for these compounds in addition. A similar ob-
servation was made for nitro derivative 6 as well.
The presence of bimolecular negative ions in the mass
spectra of compounds 4—6 can be explained by the initial
formation of radical anions following by the formation
of anions [М – Н]– (Scheme 3). Probably, the formation
of radical anions III is more preferable because of their
capability to be stabilized by formation of equilibrium
structures IV and V. The latter can react with initial
molecules I, forming bimolecular anion [2 М – Н]–, e.g.,
of type VI.
Bromination of 5-fluoro-1-(methoxycarbonylmethyl)-
uracil (3) using the KBr—H2O2 system in 20% H2SO4 gave
5-bromo-1-carboxymethyl-5-fluoro-6-hydroxy-5,6-di-
hydrouracil (4) in 86% yield (Scheme 4). Simultaneously
with bromination at position C(5) of the uracil ring,
Scheme 3

116
Russ. Chem. Bull., Int. Ed., Vol. 69, No. 1, January, 2020
Chernikova et al.
as an eluent, flow rate of 0.1 mL min–1) operating in the positive
and negative ion modes at the capillary potentials of 4.5 and
–3.5 kV, respectively; the atmospheric-pressure chemical ioniza-
tion (APCI) was used as an ionization method, the APCI inter-
face, heater and vaporizer temperatures were 250, 200 and 230 C,
respectively, the interface capillary voltage was 25÷–25 V. The
hydrolysis of the ester group occurred in the acidic
medium. Similarly to chlorination of 2, chlorination of
compound 3 with the use of KCl for 5 h under the same
conditions leaved the starting compound intact. Chlorin-
ation in the two-phase system resulted in the formation
of two products, one of which is acid 5, while the other is
its methyl ester 7. 1-Carboxymethyl-5-fluoro-6-hydroxy-
5-nitro-5,6-dihydrouracil (6) was obtained in 84% yield
upon nitration of compound 3 with the H2SO4—HNO3
mixture at 0—10 С for 5 h (see Scheme 4).
flow rate of the nebulizing gas (nitrogen) was 2.5 L min–1
.
Elemental analysis was carried out using a EURO-3000 elemen-
tal analyzer.
5-Bromo-1-carboxymethyl-5-fluoro-6-hydroxy-5,6-dihydro-
uracil (4). To a mixture of 1-carboxymethyl-5-fluorouracil (2)
(0.10 g, 0.53 mmol) or 5-fluoro-1-(methoxycarbonyl)methyl-
uracil (3) (0.11 g, 0.53 mmol) and KBr (0.13 g, 1.06 mmol) in
20% H2SO4 (2.30 mL), 33% H2O2 (0.16 mL, 1.59 mmol) was
added dropwise, and the resulting mixture was stirred for 5 h at
room temperature. Then, the reaction mixture was diluted with
water and extracted with diethyl ether. The combined extracts
were washed with water, dried over Na2SO4, the solvent was
evaporated, the product was re-precipitated from an acetone-
hexane (1 : 7) mixture. A white powder was obtained. In the case
of substrate 2, the yield of 4 was 67% (0.10 g), upon the twofold
prolongation of the reaction, the yield increased to 83% (0.12 g).
In the case of substrate 3, the yield of 4 was 86% (0.13 g). 1H NMR
(DMSO-d6) δ: 3.97 (d, 1 Н, Ha(7), J = 17.40 Hz); 4.15 (d, 1 H,
Hb(7), J = 17.40 Hz); 5.45 (d, 1 H, H(6), J = 4.50 Hz); 7.35
(br.s, 1 H, OH); 11.25 (br.s, 1 H, H(3)). 13С NMR (DMSO-d6)
δ: 48.19 (s, C(7)); 83.77 (d, C(6), J = 26.40 Hz); 91.12 (d, C(5),
J = 199.95 Hz); 150.88 (s, C(2)); 163.84 (d, C(4), J = 18.90 Hz);
169.89 (s, C(8)). MS, m/z (Irel (%)): 283 [M – H]– (90), 285
(80); 567 [2 M – H]– (32), 569 (100), 571 (42). Found (%):
С, 24.54; Н, 2.07; Br, 29.03; N, 9.85. С6H6BrFN2O5. Calculat-
ed (%): С, 25.28; Н, 2.12; Br, 28.03; N, 9.83.
Scheme 4
Compound
X
Br
Cl
NO2
Cl
R
H
H
H
Me
Yield (%)
4
5
6
7
86
—
84
—
Reagents and conditions: i. KBr (2 eq.), 20% H2SO4, 33% H2O2
(3 eq.), ~20 C, 5 h, or ii. НCl (3 eq.), 33% H2O2 (4 eq.), СН2Cl2,
~20 C, 5 h, or iii. H2SO4, 67% HNO3, 020 C, 5 h.
1-Carboxymethyl-5-chloro-5-fluoro-6-hydroxy-5,6-dihydro-
uracil (5). To 1-carboxymethyl-5-fluorouracil (2) (0.10 g,
0.53 mmol) or 5-fluoro-1-(methoxycarbonyl)methyluracil (3)
(0.11 g, 0.53 mmol) in СН2Cl2 (1.00 mL), 34% HCl (0.15 mL,
1.60 mmol) was added under stirring at room temperature,
then, 33% H2O2 (0.21 mL, 2.12 mmol) was added dropwise,
and the reaction mixture was stirred at room temperature
for 5 h. Then, the reaction mixture was diluted with water
and extracted with diethyl ether. The combined extracts were
washed with water, dried over Na2SO4, the solvent was evapo-
rated, the product was re-precipitated from a mixture of ace-
tone with hexane (1 : 7). A white powder was obtained. In the
case of substrate 2, the yield of 5 was 78% (0.10 g). In the case
of substrate 3, the total yield of 5 and 7 (in the 7 : 3 ratio) was
0.13 g. 1H NMR (DMSO-d6) δ: 3.95 (d, 1 Н, Ha(7), J = 17.50 Hz);
4.10 (d, 1 H, Hb(7), J = 17.50 Hz); 5.35 (d, 1 H, H(6),
J = 1.70 Hz); 7.60 (br.s, 1 H, ОН); 11.90 (br.s, 1 H, H(3)).
13С NMR (DMSO-d6) δ: 48.44 (s, C(7)); 82.93 (d, C(6),
J = 27.67 Hz); 97.30 (d, C(5), J = 255.29 Hz); 150.84 (s, C(2));
163.04 (d, C(4), J = 27.66 Hz); 168.73 (s, C(8)). MS, m/z
(Irel (%)): 239 [M – H]– (100), 241 (30); 479 [2 M – H]– (84),
481 (58), 483 (5%). Found (%): С, 29.11; Н, 2.39; Cl, 30.01;
N, 14.81. С6H6ClFN2O5. Calculated (%): С, 29.96; Н, 2.51;
Cl, 14.74; N, 11.64.
In conclusion, 5-halogeno-6-hydroxy and 6-hydroxy-
5-nitro derivatives of uracil were synthesized for the first
time by oxidative halogenation and nitration of 1-carboxy-
methyl-5-fluorouracil and its methyl ester with the purpose
of their further involvement in a study of the dependence
between the structure and antiviral activity in the series of
uracil derivatives.
Experimental
The 1Н and 13С NMR spectra were recorded at a constant
temperature of 298 K using a Bruker Avance-III 500 pulsed
spectrometer operating at frequencies of 500.13 MHz (1H) and
125.76 MHz (13C) and equipped with a 5 mm broad-band mul-
tinuclear (PABBO) probe and the Z-axis gradient unit. Solvent
signals were used as references. The 13С NMR spectra with
proton decoupling were recorded using the following parameters:
the 29.8 kHz spectral window, the 3.2 s exciting pulse (30)
duration, the 2 s relaxation delay, the number of points was 64 K,
the number of scans was 512—2048. The DEPT-90 and
DEPT-135 experiments were performed to assist the interpreta-
tion of the 13С NMR spectra. Two-dimensional spectra were
obtained using the standard multipulse sequences available in
the spectrometer software. Mass spectra were recorded using
a Shimadzu LCMS-2010 EV spectrometer with quadrupole mass
analyzer (manual syringe injection, mixed acetonitrile-chloro-
form solutions of samples, the 95 : 5 acetonitrile-water mixture
5-Chloro-5-fluoro-6-hydroxy-1-(methoxycarbonyl)methyl-
5,6-dihydrouracil (7). 1H NMR (DMSO-d6) δ: 3.66 (s, 3 Н,
Н (9)); 3.99 (d, 1 Н, Ha(7), J = 17.50 Hz); 4.20 (d, 1 H, Hb(7),
J = 17.50 Hz); 5.36 (d, 1 H, H(6), J = 1.70 Hz); 7.65 (br.s, 1 H,
ОН); 11.38 (d, 1 H, H(3), J = 3.46 Hz). 13С NMR (DMSO-d6)

1-Carboxymethyl-5-fluorouracil derivatives
Russ. Chem. Bull., Int. Ed., Vol. 69, No. 1, January, 2020
117
δ: 48.02 (s, С(7)); 52.32 (s, С(9)); 83.05 (d, C(6), J = 26.56 Hz);
97.33 (d, C(5), J = 254.81 Hz); 150.86 (s, C(2)); 163.03 (d, C(4),
J = 27.22 Hz); 169.93 (s, C(8)).
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1-Carboxymethyl-5-fluoro-6-hydroxy-5-nitro-5,6-dihydro-
uracil (6). 1-Carboxymethyl-5-fluorouracil (2) (0.10 g, 0.53 mmol)
or 5-fluoro-1-(methoxycarbonylmethyl)uracil (3) (0.11 g,
0.53 mmol) was gradually dissolved under stirring in concen-
trated H2SO4 (0.30 mL, ρ = 1.8356 g mL–1). After complete
dissolution of the starting compound, the mixture was cooled to
0 C, 67% HNO3 (0.20 mL, ρ = 1.399 g mL–1) was added drop-
wise to the mixture, and the resulting mixture was kept at 0—10 C
for 5 h. The mixture was diluted with water, neutralized with
NaHCO3 to pH = 3 and extracted with diethyl ether. The com-
bined extracts were washed with water, dried over Na2SO4, the
solvent was evaporated, the product was re-precipitated from
a mixture of acetone with hexane (1 : 7). A white powder was
obtained. In the case of substrate 2, the yield of 6 was 75% (0.10 g);
in the case of substrate 3, the total yield of 6 was 84% (0.11 g).
1H NMR (DMSO-d6) δ: 3.90 (d, 1 Н, Ha(7), J = 17.75 Hz);
4.25 (d, 1 H, Hb(7), J = 17.75 Hz); 5.55 (d, 1 H, H(6),
J = 3.80 Hz); 7.90 (br.s, 1 H, OH); 11.65 (br.s, 1 H, H(3)).
13С NMR (DMSO-d6) δ: 46.55 (s, C(7)); 78.80 (d, C(6),
J = 25.20 Hz); 107.34 (d, C(5), J = 245.20 Hz); 150.47 (s, C(2));
158.68 (d, C(4), J = 26.40 Hz); 170.02 (s, C(8)). MS, m/z
(Irel (%): 250 [M – H]– (100); 501 [2 M – H]– (9). Found (%):
С, 28.63; Н, 2.33; N, 16.89. С6H6FN3O7. Calculated (%):
С, 28.70; Н, 2.41; N, 16.73.
This work was performed within the framework
of the state task of the Ministry of Education and
Science of the Russian Federation (Project No. АААА-
А17-117011910025-6) and under financial support of
the Russian Foundation for Basic Research (Project
No. 18-53-41004). The spectroscopic part of the study
was carried out using the equipment of the center of
Collective Usage "Chemistry" of the Ufa Institute of
Chemistry of the Ufa Federal Research Centre of
Russian Academy of Sciences.
17. A. J. Kirby, The Anomeric Effect and Related Stereoelectronic
Effects at Oxygen, Springer, Berlin, 1983, 149 pp.
References
Received October 4, 2019;
in revised form October 23, 2019;
accepted October 29, 2019
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