Synthesis and antimicrobial activity of 4-trifluoromethylpyridine nucleosides

Article abstract of DOI:10.1515/hc-2017-0019

4-Trifluoromethylpyridine derivatives 4-8 represent good candidates for the discovery of new antibacterial agents. Fluorinated pyridine nucleosides 4-7 and non-nucleoside analogues 8a,b were synthesized and evaluated for their antibacterial activities aga

Full text of DOI:10.1515/hc-2017-0019

Heterocycl. Commun. 2017; aop
SShyaiknhtahS.eAlsneiysadai, Annads Aa. Anbtduilmqadiecr,rAolaba Aia. SlalaemcatnidvIbirtayhim M. Abdou*
of 4-trifluoromethylpyridine nucleosides
DOI 10.1515/hc-2017-0019
with the transcription or replication processes required
for microbial survival. As there are no alternative path-
ways in the pathogens for these basic metabolic pro-
cesses, the nucleoside analogues, by inhibiting these
basic pathways, are effective antimicrobial agents [8].
For example, some nucleosides exhibit antibacterial
activity by specific inhibition of cell-wall peptidogly-
can biosynthesis [9], certain bacterial enzymes, such as
purine nucleoside phosphorylases [10] and DNA ligases
[11]. Adenosine analogues such as cordycepin [12], oxe-
tanocin [13], formycins [14], toyocamycin and its deriva-
tives [15] show biological activity including antibiotic
properties.
Received February 1, 2017; accepted February 2, 2017
Abstract: 4-Trifluoromethylpyridine derivatives 4–8 rep-
resent good candidates for the discovery of new antibac-
terial agents. Fluorinated pyridine nucleosides 4–7 and
non-nucleoside analogues 8a,b were synthesized and
evaluated for their antibacterial activities against Staph-
ylococcus aureus, Bacillus infantis, Escherichia coli and
Stenotrophomonas maltophilia. The minimum inhibitory
concentrations (MICs) of the new nucleosides 4–7 range
from 1.3 to 4.9 μg/mL and MICs of fluoroaryl derivatives
8a,b are in the range of 1.8–5.5 μg/mL. Activity of amoxi-
cillin, the reference drug, is 1.0–2.0 μg/mL under similar
conditions.
Designing expeditious routes to obtain nucleosides is
of paramount importance to organic and medicinal chem-
Keywords: antimicrobial; fluoropyridine; gHMBC; nucleo- ists. Three general glycosylation methods dominate in
sides; synthesis.
nucleoside synthesis. The Fischer approach [16] employs
nucleophilic displacement of an α-halogen by the metal
salt of a heterocycle to furnish the nucleoside. The fusion
method consists of heating a peracylated sugar with a
nucleobase. The mildest and most popular method is the
Vorbruggen variant [17, 18] of the Hilbert-Johnson reaction,
which makes use of a fully protected sugar and couples it
with a silylated nucleobase in the presence of Lewis acids,
typically tin tetrachloride (SnCl
4) or trimethylsilyl trif-
luoromethanesulfonate (TMSOTf), among others [19], to
provide the protected nucleoside.
In this paper, we describe synthesis of a new class of
4-trifluoromethylpyridine derivatives 4–8. The 4-trifluo-
romethylpyridine moiety is attached to a sugar moiety
(pentose or hexose) in nucleosides 4–7 and to a fluori-
nated aryl group in analogues 8a,b. These products were
evaluated as antibacterial agents.
Introduction
The increasing prevalence of life-threatening antibacte-
rial diseases and rapidly growing trend of antimicrobial
resistance necessitate the development of new and more
effective antimicrobial agents. The 2-pyridones represent
a unique class of pharmacophores present in various ther-
apeutic agents [1]. They exhibit antitumor [2], antimalarial
[3], analgesic [4] and anti-HIV properties [5] and inhibit
in-vitro and in-vivo the bacterial type II DNA topoisomer-
ases, which includes two highly homologous enzymes:
DNA gyrase and topoisomerase IV [6]. Fluorine substitu-
tion can bring substantial changes in the physical, chemi-
cal and biological properties [7] of bioactive molecules.
One important strategy in this respect is chemical
synthesis of nucleosides. The use of nucleoside ana-
logues can be considered a novel option as they are Results and discussion
expected to act at the genomic level, thereby interfering
Chemistry
*Corresponding author: Ibrahim M. Abdou, Department
3-Cyano-4-trifluoromethyl-6-(thiophen-2′-yl)-2-pyridone
of Chemistry, College of Science, UAEU Al-Ain 15551, UAE,
e-mail: i.abdou@uaeu.ac.ae; Imabdou@gmail.com
Shaikha S. Alneyadi, Anas A. Abdulqader and Alaa A. Salem:
Department of Chemistry, College of Science, UAEU Al-Ain
15551, UAE
3 was obtained in one-pot condensation of the 1,3-dicar-
bonyl substrate 1 with equimolar amount of cynoaceta-
mide 2 in refluxing ethanol. The reaction afforded a
single product 3 with an 89% yield (Scheme 1). The
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ꢁꢁꢁꢂ
2ꢀ
ꢀS.S. Alneyadi et al.: 4-Trifluoromethylpyridine nucleosides
O
O
CN
NC
HN
O
O
NH2
2
S
S
CF3
CF3
KOH, EtOH, ∆, 6–8 h
3
1
e
CF3
CN
CF3
N
CF3
N
CN
O
CN
S
S
S
N
O
OSi(CH3)3
K
O
c
a
R
S
S
8a: R = F; 88%
8b: R = CF3; 86%
CF3
CN
CF3
CN
N
N
O
O
O
O
OAc
AcO
AcO
AcO
AcO
OAc
AcO
5: 72%
4: 78%
b
d
S
S
CF3
CN
CF3
CN
N
N
O
O
O
O
HO
HO
HO
OH
HO
OH
HO
6: 73%
7: 74%
Scheme 1ꢁReagents and conditions: (a) HMDS, (NH4)2SO4, reflux, 2 h, then 1,2,3,5-tetra-O-acetyl-β-D-ribofuranose, TMSOTf/CH3CN, 0–25°C;
(b) TEA/MeOH/H2O; (c) aqueous KOH, 2 h, 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide, acetone; (d) TEA/MeOH/H2O; (e) aroyl chlo-
ride, pyridine, CH3CN.
nuclear magnetic resonance (NMR) spectra of 3 are fully band at 259 nm can be attributed to the n-σ* transition,
consistent with the assigned structure [20]. The gradi- while the band at 360 nm is apparently a combination of
ent heteronuclear multiple bond correlation (gHMBC) n-π* and π-π* transitions.
spectrum of 3 (Figure 1) shows a correlation between
The β-D-ribofuranosyl-2-pyridone 4 was prepared
the signal of thiophene-H3 (δ 8.15) and pyridone-C5 (δ in 68% yield by reaction between a silyl derivative of
105.9). The proton signal at δ 8.15 also correlates to the compound 3 and 1,2,3,5-tetra-O-acetyl-β-D-ribofuranose
C-6 signal of pyridone-C6 at δ 143.7. Another correlation (Scheme 1). The reaction of a nucleophilic base normally
is observed between the pyridone-H5 signal at δ 7.63 and takes place from the less sterically hindered β-face of the
the signals of C-2′ and C-3′ of the thiophene at δ 129.7 and intermediate cation to give the β-isomer. The structure of
140.7, respectively. The gHMBC spectrum does not show the obtained riboside 4 was confirmed using analytical
any correlation between the thiophene protons and the and spectroscopic data IR, NMR and elemental analysis.
carbon atom of the CN group at δ 120.5. Based on these The IR spectrum of 4 shows bands at 2215 and 1748 cm−1
observations, the CF3 group must be located at position indicating the presence of cyano and acetoxy groups,
4 and the thiophen-2′-yl group at position 6 of the 2-pyri- respectively. On the other hand, a sharp peak at 1652 cm−1
done moiety. The infrared (IR) spectrum of compound 3 for the carbonyl group of the 2-pyridone indicates that the
shows the most significant absorption band for the amide sugar is linked to the pyridine ring through the nitrogen
1
carbonyl group at 1661 cm−1. A strong band at 2230 cm−1 atom giving the N-riboside. In the H NMR spectrum of
corresponds to the CN group and a NH signal appears at 4, the anomeric proton H-1″ resonates as a doublet at δ
3419 cm−1. The UV-vis spectrum of compound 3 (Figure 2) 6.41 with a coupling constant JH1″−H2″ꢀ=ꢀ4.3 Hz, indicating
shows two absorption bands at 360 nm and 259 nm. The that the obtained product 4 is a β-isomer. The 13C-NMR
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S.S. Alneyadi et al.: 4-Trifluoromethylpyridine nucleosidesꢀ
ꢀ3
124
126
128
130
132
134
7.88, 130.3, 0.29
8.14, 132.77, 0.48
7.64, 132.91, 0.26
136
138
140
142
144
146
148
150
152
154
156
7.23, 134.47, 0.79
8.15, 140. 21, 0.24
7.88, 138.51, 0.18
8.6 8.5 8.4 8.3 8.2 8.1 8.0 7.9 7.8 7.7 7.6 7.5 7.4 7.3 7.2 7.1 7.0 6.9
F2 Chemical shift (ppm)
Figure 1ꢁThe gHMBC spectrum in DMSO-d6 of 2-pyridone 3.
0.8
without the formation of the N-nucleoside. Apparently,
α-acetobromoglucose undergoes a reaction with potas-
sium salt of 3 through a Walden inversion, to yield the
corresponding glucoside 5. Since Walden inversion
occurs in the halogen replacement reaction, the reac-
tion involving halide with the α-configuration yields
the β-isomer. The IR spectrum of 5 shows the presence
of acetoxy carbonyl groups at 1749 cm−1. A strong band
appears at 2231 cm−1 corresponding to the CN group.
0.6
0.4
0.2
0
240
340
440
Wavelength (nm)
Figure 2ꢁA UV-vis absorption of 3 in 0.01 m Tris–KCl buffer solu-
tion, pH 7.4. The buffer was prepared by dissolving 10.0 mm of
tris(hydroxymethyl)aminomethane hydrochloride (1.58 g), 1.0 mm
Na2EDTA (0.37 g) and 100.0 mm KCl (7.45 g) in 1.0 L of deionized
water.
1
The H-NMR spectrum of 5 shows the β-configuration.
The anomeric proton H-1″ appears as a doublet at a rela-
tively low field, δ 6.13. The spin-spin coupling constant,
JH1″−H2″ꢀ=ꢀ8.0 Hz, indicates that the protons H-1″ and H-2″
are in diaxial orientation. The H-2″ and H-3″ signals
spectrum shows a signal at δ 87.2 corresponding to the C-1″ appear as a multiplet at δ 5.37–5.45. The H-5″ and H-4″
atom of the β-configuration. signals appear as a multiplet at δ 5.15–5.24. The H2-6′,6″
The O-glucoside derivative 5 was prepared by the signals appear as a multiplet at δ 4.08–7.11. Protons of the
reaction of a potassium salt of 3 with an activated sugar four acetoxy groups appear as four singlets at δ 1.94, 2.03,
at room temperature. In principle, the ambident 2-pyri- 2.05 and 2.06. The pyridine H-5 proton resonates at δ 7.6 2
done anion contains two reactive nucleophilic centers, and this downfield position is consistent with the for-
the pyridine ring nitrogen and the carbonyl oxygen mation of O-glucoside [20]. The structure of compound
13
at C-2. A sole O-nucleoside product has been isolated 5 was further confirmed by the analysis of the C-NMR
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ꢀS.S. Alneyadi et al.: 4-Trifluoromethylpyridine nucleosides
4ꢀ
spectrum which shows a signal at δ 109.7 corresponding accounts for the Cꢀ=ꢀC stretch in the aromatic system. The
to the C-1″ atom of the β-configuration. The signals at δ strong band at 2231 cm−1 corresponds to the CN group at
154.7 and 141.5 are assigned to C-6 and C-4 of the pyridine C-3. The 1H NMR spectrum contains two doublets at δ 7.9 5
ring. Signals at δ 168.8, 169.3, 170.4 and 170.7 belong to and 8.35 with coupling constants Jꢀ=ꢀ5.0 Hz and 3.7 Hz for
the four acetoxy carbonyl carbons. Signals correspond- the thiophene protons H-5 and H-3 and the resonance for
ing to pyridine C-5 and C-3 resonate at δ 94.9 and 110.8, H-4 of the thiophene appears as a triplet at δ 7.29. The H-5
respectively. The signals at δ 72.7, 70.0, 68.0, 61.6 and of pyridine resonates in low field at δ 8.55, which confirms
13
60.4 can be assigned to C-2″, C-3″, C-4″, C-5″ and C-6″, the formation of O-benzoylated compound. The C NMR
respectively. On the other hand, the C-2 atom of pyridine spectrum of 8b is also fully consistent with the discussed
appears at δ 162.4 and the signal for the nitrile carbon is structure. A similar analysis confirmed the structure of 8a.
observed at δ 119.6.
Deacetylation of 3-cyano-1-(2″,3″,5″-tri-O-acetyl-β-
D-ribofuranosyl)-4-trifluoromethyl-6-(thiophen-2′-yl)- Antibacterial properties
2-pyridone 4 afforded nucleoside 6 in 73% yield. The IR
absorption spectrum of compound 6 shows a characteris- An agar-diffusion method was used for the determination
tic band at 3428 cm−1 for the sugar hydroxy groups. Another of the preliminary antimicrobial activity of compounds
band at 2206 cm−1 can be assigned to the nitrile group. A 3–8. Amoxicillin was used as a reference drug. The results
sharp absorption band at 1655 cm−1 is attributed to the were recorded for each tested compound as a diameter of
stretching vibration of the carbonyl group of 2-pyridone. an inhibition zone of microbial growth around the disk in
In addition, the furanoside ring system shows a broad mm. The minimum inhibitory concentration (MIC) values
1
band at 1050 cm−1. The H-NMR spectrum of compound 6 were also determined. The inhibition zones (mm) and MIC
shows a doublet at δ 5.89 corresponding to the anomeric values (μg/mL) are given in Tables 1 and 2, respectively. As
proton of the ribosyl moiety; a coupling constant of 4.0 Hz can be seen, the synthesized compounds show good anti-
is consistent with the diaxial orientation of the H-1″ and bacterial activity against all selected bacteria strains with
H-2″ protons and indicates the formation of the β-isomer. MIC values ranging from 1.3 to 5.5 μg/mL. Compounds 4
The 13C-NMR spectrum of 6 is characterized by a signal at and 5 are highly active against S. maltophilia with MIC
δ 83.5 corresponding to the C1″ atom of the ribosyl residue.
Hydrolysis, to remove the acetyl groups in compound
Table 1ꢁAntibacterial activity of compounds 4–8.
5 was carried out using triethylamine (TEA) in methanol
and produced the free nucleoside 7 in 74% yield. The IR
Compoundsꢁ
ꢁ
Zone of inhibition (diameter, mm)
spectrum of 7 shows a characteristic band at 3403 cm−1
due to the sugar four hydroxy groups. Another band at
2206 cm−1 can be assigned to the nitrile group. The IR
absorption of ether linkage of the glucopyranoside ring
B. infantisꢁ
E. coliꢁ
S. aureusꢁ
S. maltophilia
4
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
26ꢃ
32ꢃ
25ꢃ
30ꢃ
20ꢃ
28ꢃ
15ꢃ
28ꢃ
27ꢃ
23ꢃ
29ꢃ
20ꢃ
31ꢃ
16ꢃ
18ꢃ
25ꢃ
24ꢃ
26ꢃ
19ꢃ
26ꢃ
15ꢃ
30
29
23
23
18
24
14
5
6
7
8a
8b
1
system appears at 1036 cm−1. The H NMR spectrum of 7
shows a doublet at δ 7.24 corresponding to the anomeric
proton of the glucose moiety. The coupling constant of
8.0 Hz is consistent with the diaxial orientation of the Amoxicillin ꢃ
H-1′′ and H-2′′ protons indicating the formation of a single
β-isomer. There are four signals corresponding to four
13
hydroxy protons that are exchangeable with D2O. The C
NMR spectrum of 7 is characterized by a signal at δ 9 7. 3
corresponding to the C-1 atom of the glucose residue.
Non-nucleosides 8a,b were synthesized by the reac-
tion of 3 with an aroyl chloride. This reaction afforded the
corresponding products within 30 min in yields of 87%
and 85% (Scheme 1). Structures of 8a,b were confirmed by
elemental analysis and spectral data. The IR spectrum of
8b shows the presence of one carbonyl group at 1760 cm−1
corresponding to the ester group, which indicates the for-
mation of O-benzoylation product. The band at 1603 cm−1
Table 2ꢁMinimum inhibitory concentration for compounds 4–8.
Compoundsꢁ Concentration of compounds (μg/mL) to inhibit 105 cell/mL
ꢁ
B. infantisꢁ
E. coliꢁ
S. aureusꢁ
S. maltophilia
4
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
4.3ꢃ
3.5ꢃ
4.7ꢃ
3.8ꢃ
5.5ꢃ
3.2ꢃ
1ꢃ
2.7ꢃ
2.3ꢃ
3.1ꢃ
1.3ꢃ
3.5ꢃ
1.8ꢃ
1.5ꢃ
4.9ꢃ
2.4ꢃ
3.0ꢃ
2.5ꢃ
5.0ꢃ
2.8ꢃ
1.5ꢃ
1.7
1.5
2.3
2.0
3.6
2.8
2
5
6
7
8a
8b
Amoxicillin ꢃ
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ꢀ5
trimethylsilyl trifluoromethanesulfonate (TMSOTf) (0.015 mol,
2.71 mL) and stirred at room temperature for an additional 3 h until the
reaction was completed as observed by TLC analysis (ethyl acetate/
hexane, 1:1). The mixture was diluted with ethyl acetate (150 mL),
and the organic solution was washed with a saturated NaHCO3 solu-
tion (50 mL) and then water (2ꢀ×ꢀ50 mL). The organic layer was dried
with anhydrous Na2SO4, concentrated under a reduced pressure and
the residue of 3 was purified by silica gel chromatography using 1%
MeOH in ethyl acetate as an eluent to give the pure product as pale
brown powder: yield 78%; mp 218°C; IR: 1652 (Cꢀ=ꢀO), 1748 (acetoxy
values of 1.7 and 1.5 μg/mL, respectively. High antibacte-
rial activities of nucleoside 7 (MICꢀ=ꢀ1.3 μg/mL) and the
non-nucleoside derivative 8b (MICꢀ=ꢀ1.8 μg/mL) against E.
coli should be noted.
Conclusion
Four new pyridine nucleosides 4–7 and two non-nucleo-
side analogues 8a,b were synthesized. Pyridine ribosides
4, 5 and glucosides 6, 7 are potent antibacterial agents.
The antibacterial p-trifluoromethylbenzoate 8b is more
active than its p-fluorobenzoate analogue 8a.
1
carbonyl), 2215 cm−1 (CN); H NMR (CDCl3): δ 2.09, 2.11, 2.12 (3s, 9H,
3CH3), 4.32–4.37 (m, 3H, H-5″a, H-5″b, H-3″), 5.32–5.36 (m, 2H, H-2″,
H-4″), 6.41 (d, 1H, H-1″, Jꢀ=ꢀ4.3 Hz), 6.85 (s, 1H, pyridine H-5), 7.32 (m,
1H, thiophene-H4), 7.69 (d, 1H, thiophene-H-5, Jꢀ=ꢀ5.0 Hz), 8.24 (d, 1H,
thiophene-H3, Jꢀ=ꢀ3.7 Hz); 13C NMR (DMSO-d6): δ 21.1, 21.2, 21.6 (3CH3),
79.0 (C5″), 79.4 (C3″), 79.7 (C2″), 86.2 (C4″), 87.2 (C1″), 97.2 (pyridine-
C5), 111.6 (pyridine-C3), 118.2 (CN), 121.6 (CF3), 124.3 (thiophene-C3),
127.2 (thiophene-C4), 128.7 (thiophene-C5), 130.0 (pyridine-C4), 141.7
(thiophene-C2), 145.3 (pyridine-C6), 155.8 (pyridine-C2), 170.6 (ace-
toxy carbonyl carbons). Anal. Calcd for C22H19F3N2O8S: C, 50.00; H,
3.62; N, 5.30; S, 6.07. Found: C, 50.09; H, 3.73; N, 5.21; S, 6.87.
Experimental
All reagents and chemicals were purchased from Sigma-Aldrich and
used without further purification. Melting points were determined
using Pyrex capillaries on a Gallenkamp apparatus. IR spectra were
recorded with a Thermo Nicolet Nexus 470 FT-IR spectrometer using
3-Cyano-2-(2″,3″,4″,6″-tetra-O-acetyl-β-D-glucopyranosyloxy)-
4-trifluoromethyl-6-(thiophen-2′-yl)pyridine (5)ꢁTo a solution
of 2-pyridone 3 (0.01 mol, 2.70 g) in aqueous KOH (0.01 mol, 0.56
g) in 6.0 mL distilled water, a solution of 2,3,4,6-tetra-O-acetyl-α-D-
glycopyranosyl bromide (0.011 mol, 4.11 g) in acetone (30 mL) was
added. The mixture was stirred at room temperature until the reac-
tion was judged completed by TLC (4–6 h), then treated with CH2Cl2
(30 mL). The organic layer was dried over Na2SO4, filtered and con-
centrated under reduced pressure at room temperature. Crystalliza-
tion of the residue from ethanol gave the nucleoside 5 as pale yellow
powder: yield 72%; mp 134°C, IR: 1749 (acetoxy carbonyl), 2231 cm−1
(CN); 1H NMR (CDCl3): δ 1.94, 2.03, 2.05, 2.06 (4s, 12H, 4CH3), 4.08–4.13
(m, 2H, H-6″a, H-6″b), 5.15–5.24 (m, 2H, H-4″, H-5″), 5.37–5.45 (m, 2H,
H-2″,H-3″), 6.12, 6.14 (d, 1H, H-1″, Jꢀ=ꢀ8.0 Hz), 7.18 (m, 1H, thiophene-
H-4), 7.59 (d, 1H, thiophene-H-5, Jꢀ=ꢀ5.0 Hz), 7.62 (s, 1H, pyridine H-5),
7.75 (d, 1H, thiophene-H3, Jꢀ=ꢀ3.7 Hz); 13C NMR (CDCl3): δ 20.5, 20.6,
20.7, 21.1 (4CH3), 60.4 (C6″), 61.6 (C5″), 68.0 (C4″), 70.0 (C3″), 72.7
(C2″), 94.9 (pyridine-C5), 109.7 (C1″), 110.8 (C3), 119.6 (CN), 122.4 (CF3),
128.9 (thiophene-C3), 129.2 (thiophene-C4), 132.1 (thiophene-C5 ),
141.5 (pyridine-C4), 144.5 (thiophene-C2), 154.7 (pyridine-C6), 162.4
(pyridine-C2), 168.8, 169.3, 170.4, and 170.7 (four acetoxy carbonyl
carbon). Anal. Calcd for C25H23F3N2O10S: C, 50.00; H, 3.86; N, 4.66; S,
5.34. Found: C, 50.05; H, 3.97; N, 4.57; S, 5.42.
1
KBr disks. H NMR (400 MHz) and 13C NMR (100 MHz) spectra were
obtained on a Varian Gemini 400 spectrometer in CDCl3 or DMSO-d6.
All exchangeable protons were confirmed by addition of D2O. Thin-
layer chromatography (TLC) was carried out on Merck silica gel F254
plates and UV light was used for visualization. Column chromatogra-
phy was performed on a Merck silica gel. Absorption measurements
were carried out using an Agilent 8453 spectrophotometer and 1-cm
quartz cells. Elemental Analysis was performed on a Leco Model
CHN-600 elemental analyzer.
3-Cyano-4-trifluromethyl-6-(thiophen-2′-yl)-2-pyridone
(3)ꢁ
A
mixture of 4,4,4-trifluoro-1-(thiophen-2-yl)butane-1,3-dione
(10.0 mmol, 2.22 g), 2-cyanoacetamide (11.0 mmol, 0.92 g) and potas-
sium hydroxide (12.0 mmol, 0.67 g) in ethanol (50 mL) was heated
under reflux for 6 h. The mixture was cooled, acidified with 0.1 m
HCl and the resultant precipitate was crystallized from ethanol: yel-
low powder; yield 89%; mp 293–294°C; IR: 1661 (Cꢀ=ꢀO), 2230 (CN),
3419 cm−1 (NH); 1H NMR (DMSO-d6): δ 7.23 (m, 1H, thiophene-H4), 7.63
(bs, 1H, pyridone-H5), 7.88, 7.89 (dd, 1H, thiophene-H5, Jꢀ=ꢀ4.9 Hz),
8.15, 8.16 (dd,1H, thiophene-H3, Jꢀ=ꢀ3.7 Hz), 13.57 (bs, 1H, NH,
exchangeable with D2O); 13C NMR (DMSO-d6): δ 105.9 (pyridine-C5),
113.8 (pyridine-C3), 120.5 (CN), 129.7–140.5 (aromatic carbons), 143.7
(pyridine-C6), 154.1 (pyridine-C2), 164.8 (pyridine-C4). Anal. Calcd
for C11H5F3N2OS: C, 48.89; H, 1.86; N, 10.37; S, 11.87. Found: C, 48.94;
H, 1.97; N, 10.28; S, 11.95.
General procedure for deacetylation of nucleosides,
synthesis of 6 and 7
3-Cyano-1-(2″,3″,5″-tri-O-acetyl-β-D-ribofuranosyl)-4-trifluoro- TEA (1.0 mL) was added to a solution of protected nucleoside 4 or 5
methyl-6-(thiophen-2′-yl)-2-pyridone (4)ꢁA mixture of 2-pyridone (1.0 mmol) in methanol (10 mL) containing 3 drops of water and the
3 (0.01 mol, 2.70 g), 1,1,1,3,3,3 hexamethyldisilazane (HMDS, 60 mL), mixture was stirred overnight at room temperature. The reaction
ammonium sulfate (0.0009 mol, 0.125 g) and 2-3 drops of chlorotri- was monitored by TLC (2% methanol and 98% CH2Cl2) and stirring
methylsilane was heated under nitrogen for 2 h. Excess HMDS was was continued until completion. The solvent was removed under
removed by distillation, and the residue was dried under reduced reduced pressure, the residue was treated with methanol and
pressure for 6 h. The resulting silyl intermediate product was dis- the resultant solution was concentrated until TEA was removed.
solved in anhydrous MeCN (20 mL) and a solution of 1″,2″,3″,5″-tetra- The crude product 6 or 7 was purified by silica gel chromatogra-
O-acetyl-β-D-ribofuranose (0.01 mol, 3.18 g) in 20 mL of MeCN was phy eluting with chloroform/methanol (9:1) and crystallized from
added with stirring. The mixture was cooled to 5°C, treated with methanol.
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ꢀS.S. Alneyadi et al.: 4-Trifluoromethylpyridine nucleosides
6ꢀ
8.35 (d, 1H, thiophene-H3, Jꢀ=ꢀ3.7 Hz ), 8.55 (s, 1H, pyridine-H5); 13
C
3-Cyano-1-(β-D-ribofuranosyl)-4-trifluoromethyl-6-(thiophen-
2′-yl)-2-pyridone (6)ꢁPale yellow powder; yield 73%; mp 197°C; IR:
1655 (CO), 2206 (CN), 3428 cm−1 (-OH); 1H-NMR (DMSO-d6): δ 3.81–3.86
(m, 5 H, H-2″, H-3″, H-4″ and 2 H-5″), 4.81–4.84 (3 OH, exchangeable
with D2O), 5.89 (d, 1H, H-1″, Jꢀ=ꢀ4.0 Hz), 6.34 (s, 1H, pyridine H-5), 6.80
(m, 1H, thiophene-H4), 7.18–7.19 (d, 1H, thiophene-H5, Jꢀ=ꢀ5.0 Hz), 7.73
(d, 1H, thiophene-H3, Jꢀ=ꢀ3.7 Hz); 13C-NMR (DMSO-d6): δ 75.3 (C5″),
75.6 (C3″), 75.9 (C2″), 82.5 (C-4″), 83.5 (C1″), 93.4 (pyridine-C5), 114.5
(pyridine-C3), 117.8 (CN), 120.5 (CF3), 123.4 (thiophene-C3), 124.9
(thiophene-C4), 126.3 (thiophene-C5), 137.9 (thiophene-C2), 141.5
(pyridine-C6), 152.2 (pyridine-C2), 166.8 (pyridine-C4). Anal. Calcd
for C16H13F3N2O5S: C, 47.76; H, 3.26; N, 6.96; S, 7.97. Found: C, 47.81; H,
3.37; N, 6.87; S, 8.01.
NMR (CDCl3): δ 95.8 (pyridine C3), 112.1 (pyridine-C5), 113.8 (CN),
116.1 (CF3), 120.4 (CF3), 123.2, 127.7 (thiophene-C3), 129.7 (thiophene-
C4), 131.1 (thiophene-C5), 132.6, 133.3, 134.6 (aromatic carbons),
140.8 (pyridine-C4), 156.8 (thiophene-C2), 159.8 (pyridine-C6),
162.6 (Cꢀ=ꢀO), 166.8 (pyridine-C2). Anal. Calcd for C19H10F6N2O2S: C,
51.36; H, 2.27; N, 6.30; S, 7.22. Found: C, 51.41; H, 2.38; N, 6.21; S,
7. 3 0.
Antibacterial evaluations
Well diffusion assayꢁTwo Gram positive bacteria (Bacillus infantis
and Staphyloccus aureus) and two Gram negative bacteria (Escheri-
chia coli and Stenotrophomonas maltophilia) were used. A Mueller
Hinton agar (38.0 g of Mueller Hinton agar in 1000 mL of distilled
water) was prepared, autoclaved and poured into the Petri dishes. It
solidified at room temperature. The bacterial strains (106 cells/mL)
were introduced onto the plates using a pipette and hockey sticks to
spread them on the agar. All compounds were poured individually
into the wells (50 μL/well). The wells were then incubated at 37°C
for 24–48 h. The bacterial inhibition was determined by measuring
the diameter of the inhibition zone (mm) using a transparent scale.
Antibiotic amoxicillin (5 mg/mL) was used as a positive control at
50 μL/well.
3-Cyano-2-(β-D-glucopyranosyloxy)-4-trifluoromethyl-6-
(thiophen-2′-yl)pyridine (7)ꢁPale yellow powder; yield 74%; mp
1
134°C; IR: 2206 (CN), 3392 cm−1 (sugar-OH); H NMR (DMSO-d6): δ
3.14–3.19 (m, 6H, H-2″, H-3″, H-4″, H-5″, H-6″a, H-6″b), 4.63–4.93 (4
OH, exchangeable with D2O), 6.97 (d, 1H, H-1″, Jꢀ=ꢀ8.0 Hz), 7.11 (m, 1H,
thiophene-H4), 7.24 (s, 1H, pyridine-H5), 7.40 (d, 1H, thiophene-H5,
Jꢀ=ꢀ5.0 Hz), 7.60 (d, 1H, thiophene-H3, Jꢀ=ꢀ3.7 Hz); 13C NMR (DMSO-d6): δ
62.8 (C5″), 64.0 (C3″), 70.4 (C2″), 72.4 (C4″), 97.3 (C1″), 112.1 (pyridine-
C5), 113.2 (pyridine-C3), 122.0 (CN), 124.8 (CF3), 131.4 (thiophene-C3),
131.6 (thiophene-C4),134.6 (thiophene-C5), 143.9 (pyridine-C4), 146.9
(thiophene-C2), 157.2 (pyridine-C6), 164.8 (pyridine-C2). Anal. Calcd
for C17H15F3N2O6S: C, 47.22; H, 3.50; N, 6.48; S, 7.42. Found: C, 47.27; H,
3.61; N, 6.39; S, 7.50.
Minimum inhibitory concentration (MIC)ꢁThis is the lowest con-
centration of the antimicrobial compound that inhibits the bacterial
strain. Compounds were serially diluted with sterile distilled water
and examined from lower dilution to higher dilution to find the MIC.
Serially diluted compounds (100 μL) were added to a sterile nutrient
broth (900 μL) and the bacterial cultures were inoculated as 105 cells/
mL. Compounds and bacterial cultures in the nutrient broth were
incubated at 37°C for 18–24 h. Controls included a nutrient broth with
the compound only and another nutrient broth with the bacterial cul-
ture only. After incubation, the tubes were examined for turbidity,
compared with controls and to confirm the results, loops of culture
were inoculated in agar plates by streaking. The MIC was measured
as the lowest concentration (mg/mL) of the extract resulting in no
growth of the bacteria.
General procedure for synthesis of 8a,b
To a solution of 2-pyridone 3 (5.0 mmol) in a mixture of acetonitrile
(30 mL) and pyridine (2 mL), a solution of an aroyl chloride (10 mmol)
in acetonitrile (5.0 mL) was added gradually with stirring at room
temperature. The mixture was stirred at room temperature until
the reaction was completed as indicated by TLC analysis. The mix-
ture was concentrated under reduced pressure and the residue was
washed with water (2ꢀ×ꢀ20 mL) and crystallized from ethanol to give
the desired products 8a,b.
3-Cyano-6-(thiophen-2′-yl)-4-(trifluoromethyl)pyridin-2-yl
4′′-fluorobenzoate (8a)ꢁPale yellow crystals; yield 87%; mp
156°C; IR: 3089 (C-H, aromatic), 2235 (CN), 1754 (Cꢀ=ꢀO), 1603 (Cꢀ=ꢀC),
Acknowledgments: The authors wish to thank the Dean-
ship of Graduate Studies and the Department of Chemis-
try, UAE University for financial support (Research Grant
# 31S030).
1
1451 cm−1 (Cꢀ=ꢀN); H NMR (CDCl3): δ 7.29 (m, 1H, thiophene-H4), 7.64
(d, 2H, p-fluorobenzoyl, Jꢀ=ꢀ8.0 Hz ), 7.96–7.97 (d, 1H, thiophene-H5,
Jꢀ=ꢀ5.0 Hz), 8.33 (d, 2H, p-fluorobenzoyl, Jꢀ=ꢀ8.0 Hz ), 8.36 (d, 1H, thio-
phene-H3, Jꢀ=ꢀ3.7 Hz ), 8.56 (s, 1H, pyridine-H5); 13C NMR (CDCl3): δ
95.8 (pyridine-C3), 112.1 (pyridine-C5), 113.8 (CN), 115.4 (CF3), 121.8
(aromatic carbons), 125.6 (thiophene-C3), 130.2 (thiophene-C4),
132.5 (thiophene-C5), 133.5, 134.8, 140.8 (aromatic carbons), 143.0
(pyridine-C4), 153.8 (thiophene-C2), 156.9 (pyridine-C6), 159.7 (Cꢀ=ꢀO),
162.5 (C-F), 166.6 (pyridine-C2). Anal. Calcd for C18H10F4N2O2S: C,
54.82; H, 2.56; N, 7.10; S, 8.13. Found: C, 54.87; H, 2.67; N, 7.01; S, 8.21.
References
[1] Saiki, A. Y.; Shen, L. L.; Chen, C. M.; Baranowski, J.; Lerner, C.
G. DNA cleavage activities of Staphylococcus aureus gyrase and
topoisomerase IV stimulated by quinolones and 2-pyridones.
Antimicrob. Agents Chemother. 1999, 43, 1574–1577.
[2] Cocco, M. T. C.; Onnis, V. New bis(pyridyl)methane derivatives
from 4-hydroxy-2-pyridones: synthesis and antitumoral activity.
Eur. J. Med. Chem. 2003, 38, 37–47.
3-Cyano-6-(thiophen-2′-yl)-4-(trifluoromethyl)pyridin-2-yl
4′′-(trifluoromethyl) benzoate (8b)ꢁPale yellow crystals; yield
85%; mp 171°C; IR: 3085 (C-H, aromatic), 2231 (CN), 1760 (Cꢀ=ꢀO), 1603
1
(Cꢀ=ꢀC), 1421 cm−1 (Cꢀ=ꢀN); H NMR (CDCl3): δ 7.29 (m, 1H, thiophene-
H4), 7.48–7.52 (m, 2H, p-trifluoromethylbenzoyl), 7.95 (d, 1H, thio-
phene-H5, Jꢀ=ꢀ5.0 Hz), 8.26–8.29 (m, 2H, p-trifluoromethylbenzoyl),
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S.S. Alneyadi et al.: 4-Trifluoromethylpyridine nucleosidesꢀ
ꢀ7
[3] Abadi, A.; Al-Deeb, O.; Al-Afify, A.; El-Kashef, H. H. Synthesis
of 4-alkyl (aryl)-6-aryl-3-cyano-2(1H)-pyridinones and their
2-imino isosteres as nonsteroidal cardiotonic agents. Farmaco
1999, 54, 195–201.
[4] Oztürk, G.; Erol, D. D.; Uzbay, T.; Aytemir, M. D. Synthesis of
4(1H)-pyridinone derivatives and investigation of analgesic and
antiinflammatory activities. Farmaco 2001, 56, 251–256.
[5] Storck, P. A.; Grierson, D. S. Tosylation/mesylation of
4-hydroxy-3-nitro-2-pyridinones as an activation step in the
construction of dihydropyrido[3,4-b]benzo[f][1,4]thiazepin-
1-one based anti-HIV agents. Tetrahedron Lett. 2005, 46,
2919–2922.
[6] Li, Q. M. L.; Shen, L. L. The 2-pyridone antibacterial agents:
bacterial topoisomerase inhibitors. Med. Res. Rev. 2000, 20,
231–293.
[7] Pursor, S. M. P.; Swallow, S.; Gouverneur, V. Fluorine in medici-
nal chemistry. Chem. Soc. Rev. 2008, 37, 320–330.
[8] Isono, K. Nucleoside antibiotics: structure, biological
activity, and biosynthesis. J. Antibiot. (Tokyo) 1988, 41,
1711–1739.
[12] Ahn, Y. J.; Park, S. J.; Lee, S. G.; Shin, S. C.; Choi, D. H.
Cordycepin: selective growth inhibitor derived from liquid
culture of Cordyceps militaris against Clostridium spp. J. Agric.
Food Chem. 2000, 48, 2744–2748.
[13] Shimada, N.; Hasegawa, S.; Harada, T.; Tomisawa, T.; Fujii,
A.; Takita, T. Oxetanocin, a novel nucleoside from bacteria. J.
Antibiot. (Tokyo) 1986, 39, 1623–1625.
[14] Lee, R. T.; Lee, Y. C. Synthesis of 3-(2-aminoethylthio)propyl
glycosides. Carbohyd. Res. 1974, 37, 193–201.
[15] Kazimierczuk, Z.; Cottam, H. B.; Revankar, G. R.; Robins, R.; K.
Synthesis of 2-deoxynucleotides via a novel direct stereospe-
cific sodium salt glycosylation procedure. J. Am. Chem. Soc.
1984, 106, 6379–6382.
[16] Andrzejewska, M.; Kamiński, J.; Kazimierczuk, Z. Microwave
induced synthesis of ribonucleosides on solid support. Nucleo-
sides, Nucleotides, Nucleic Acids 2002, 21, 73–78.
[17] Vorbrüggen, H.; Bennua, B. New simple nucleoside synthesis.
Tetrahedron Lett. 1978, 19, 1339–1342
[18] Niedballa, U.; Vorbrueggen, H. Synthesis of nucleosides 17. A
general synthesis of N-glycosides. 6. On the mechanism of the
stannic chloride catalyzed silyl Hilbert-Johnson reaction. J. Org.
Chem.1976, 41, 2084–2086.
[19] Davoodnia, A.; Attar, P.; Morsali, A.; Eshghi, H.; Hoseini, N.
T.; Khadem, S. Experimental and theoretical studies on the
tautomerism in 2-aminopyridines and 2(1h)-pyridinones:
synthesis of 2-amino-4-aryl-3-cyano-6-(3,4-dimethoxyphenyl)
pyridines and 4-aryl-3-cyano-6-(3,4-dimethoxyphenyl)-2(1H)-
pyridinones. Bull. Korean Chem. Soc. 2011, 32, 1873–1878.
[20] Alneyadi, S. S.; Shehadi, I. A.; Abdou, I. M. Synthesis and anti-
proliferative activity of pyridine O-galactosides and 4-fluoroben-
zoyl analogues. Heterocycl. Commun. 2015, 21, 285–290.
[9] Kimuraa, K-I.; Buggb, T. D. H. Recent advances in antimicrobial
nucleoside antibiotics targeting cell wall biosynthesis. Nat.
Prod. Rep. 2003, 20, 252–273.
[10] Bzowska, A.; Kulikowska, E.; Shugar, D. Purine nucleoside
phosphorylases: properties, functions, and clinical aspects.
Pharmacol. Ther. 2000, 88, 349–425.
[11] Mills, S. D.; Eakin, A. E.; Buurman, E. T.; Newman, J. V.; Gao, N.;
Huynh, H.; Johnson, K. D.; Lahiri, S.; Shapiro, A. B.; Walkup, G.
+
K.; et al. Novel bacterial NAD -dependent DNA ligase inhibitors
with broad-spectrum activity and antibacterial efficacy in vivo.
Antimicrob Agents Chemother. 2010, 55, 1088–1096.
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