Synthesis of some new pyrido[2,3-d]pyrimidines and their ribofuranosides as possible antimicrobial agents

Article abstract of DOI:10.1002/1098-1071(2001)12:1<52::AID-HC11>3.0.CO;2-0

The ribofuranosides, namely, 4-amino-5,7-disubstituted-1-[2′,3′,5′- tri-O-benzoyl-α-D-ribofuranosyl]pyrido-[2,3-d] pyrimidine-2(1H)-thiones, have been synthesized by the condensation of trimethylsilyl derivatives of 5,7-disubstituted pyrido[2,3-d]pyrimidine-2(1H)-thiones with β-D-ribofuranose-1-acetate-2,3,5-tribenzoate in the presence of SnCl₄. The heterocyclic bases, namely, 4-amino-5,7-disubstituted pyrido[2,3-d]pyrimidine-2(1H)-thiones, were synthesized by the treatment of 2-amino-3-cyano-4,6-disubstituted pyridines with thiourea. The structures of all the synthesized ribofuranosides and their precursors have been established by elemental analysis, IR, and ¹H NMR spectral data. The ¹³C NMR data of ribofuranosides has also been presented. All the synthesized heterocyclic bases and their ribofuranosides have been screened for their antibacterial and antifungal activities.

Full text of DOI:10.1002/1098-1071(2001)12:1<52::AID-HC11>3.0.CO;2-0

Heteroatom Chemistry
Volume 12, Number 1, 2001
Synthesis of Some New Pyrido[2,3-
d]pyrimidines and Their Ribofuranosides as
Possible Antimicrobial Agents
Neeraj Kumar, Gajendra Singh, and Ashok K. Yadav
Department of Chemistry, University of Rajasthan, Jaipur-302004, India; Kudiwal@datainfosys.net
Received 27 March 2000; revised 28 September 2000
fungal [3,4], antitumor [5], antiinflammatory [6],
anticancer [7], and phosphodiesterase inhibitor
compounds [8].
ABSTRACT: The ribofuranosides, namely, 4-amino-
5,7-disubstituted-1-[2Ј,3Ј,5Ј-tri-O-benzoyl-␣-D-ribofur-
anosyl]pyrido-[2,3-d] pyrimidine-2(1H)-thiones, have
been synthesized by the condensation of trimethylsilyl
derivatives of 5,7-disubstituted pyrido[2,3-d]pyr-
In recent years, there has been significant inter-
est in the synthesis of nucleosides of various heter-
ocyclic bases as antiherpes [9], antifungal [10], an-
tibacterial [11], and antiviral [12] agents. Motoo et
al. [13] reported the anticancer activity of dioxo de-
rivatives of pyrido[2,3-d]pyrimidine. The impor-
tance of various heterocyclic bases such as purines,
pyrimidines, and pteridinones as intermediates for
the synthesis of biologically active nucleosides and
the utility of pyrido[2,3-d]pyrimidines as promising
drugs prompted our interest in exploring some new
pyrido[2,3-d]pyrimidines and their nucleoside ana-
logues, with the attempt to discover some potential
compounds of medicinal importance.
imidine-2(1H)-thiones with b-D-ribofuranose-1-ace-
tate-2,3,5-tribenzoate in the presence of SnCl4. The het-
erocyclic bases, namely, 4-amino-5,7-disubstituted
pyrido[2,3-d]pyrimidine-2(1H)-thiones, were synthe-
sized by the treatment of 2-amino-3-cyano-4,6-disub-
stituted pyridines with thiourea. The structures of all
the synthesized ribofuranosides and their precursors
have been established by elemental analysis, IR, and
1H NMR spectral data. The 13C NMR data of ribofur-
anosides has also been presented. All the synthesized
heterocyclic bases and their ribofuranosides have been
screened for their antibacterial and antifungal activi-
ties. ᭧ 2001 John Wiley & Sons, Inc. Heteroatom
Chem 12:52–56, 2001
RESULTS AND DISCUSSION
2-Amino-3-cyano-4,6-disubstituted pyridines II were
prepared from chalcones I [14] on treatment with
ammonium acetate in ethanol via Michael-type con-
densation. Compounds II, upon condensation with
thiourea, gave 4-amino-5,7-disubstituted pyrido[2,3-
d]pyrimidine-2(1H)-thiones III [15]. The ribofura-
nosides, namely, 4-amino-5,7-disubstituted-1-[2Ј,3Ј,
5Ј-tri-O-benzoyl-␣-D-ribofuranosyl]pyrido[2,3-d]py-
rimidine-2(1H)-thiones VI [16] were prepared by the
condensation of trimethylsilyl derivatives of pyr-
INTRODUCTION
The importance of the pyrido[2,3-d]pyrimidine nu-
cleus has been well proved and is illustrated by the
large number of patents of it. Perusal of the litera-
ture on pharmacological studies reported for the
pyrido[2,3-d]pyrimidines class of compounds re-
veals that these compounds have immense chemo-
therapeutic importance as antibacterial, [1,2] anti-
ido[2,3-d]pyrimidines IV with a sugar, that is, b-D-
ribofuranose-1-acetate-2,3,5-tribenzoate V, in pres-
ence of tin tetrachloride at 0ЊC. The proposed
Correspondence to: Ashok K. Yadav.
᭧ 2001 John Wiley & Sons, Inc.
52

Synthesis of Some New Pyrido[2,3-d]pyrimidines and Their Ribofuranosides as Possible Antimicrobial Agents
1H NMR Spectra
1
The H NMR data for the compounds are given in
Table 2. In the 1H NMR spectra of compounds III, a
multiplet due to aromatic protons appeared in the
region d 6.87–8.02. Signals due to מNH2 protons
were found to be merged with aromatic protons. The
ϾNH proton in compounds III appeared as a singlet
at d 7.62–8.13.
1
In the H NMR spectra of ribofuranosides VI, a
multiplet due to aromatic protons appeared in the
region d 6.95–8.18. A peak due to ϾNH was found to
be absent, indicating the site of attachment of the
sugar V. The ␣-configuration of the ribofuranosides
was confirmed by a doublet at d 6.40–6.53 (J ס 8Hz)
[17] due to CЈ1-H. CЈ-H and CЈ5-2H protons of the
4
sugar moiety causing a multiplet in the region d
4.37–4.84, and protons at CЈ and CЈ appeared in the
2
3
region d 5.71–5.93 as a multiplet. A sharp singlet due
to מCH3 protons in compounds IIIa and VIa was
observed at d 2.01 and d 2.06, respectively, while a
singlet due to the מOH proton in compounds IIId
and VId was noticed at d 9.96 and 10.02, respectively.
The 13C NMR data for compounds VIa–d are pre-
sented in Table 3 and these data are in reasonable
agreement for their values.
ANTIMICROBIAL ACTIVITY
The compounds III and ribofuranosides VI were
screened for their antimicrobial activity following
the paper disc method of Varma and Nobles [18].
The concentration applied was 100 lg per disk.
Streptomycin and mycostatin were used as reference
compounds while testing antibacterial and antifun-
gal activity, respectively.
SCHEME 1
structures of the synthesized compounds are well
supported by spectroscopic and elemental analysis
data (Table 1).
All the compounds were found to be moderately
active against various bacteria, such as Escherichia
coli (gram negative) and Staphylococcus aureus
(gram positive) and fungi (Aspergillus niger, Aspergil-
lus flavus). The comparison of activity indices of ri-
bofuranosides with the activity indices of their par-
ent bases reveal that the ribosylation enhances the
activity in almost all the cases, except in the case of
ribofuranoside VId against E. coli. Against A. niger,
compound VIb showed a remarkable increase in
activity.
SPECTRAL STUDIES
IR Spectra
The characteristic IR bands of compounds are given
in Table 2. In the IR spectra of compounds II, bands
due to מCN and NH2 groups appeared in the region
מ1
2210–2200 cm and 3450–3300 cmמ1, respectively.
The disappearance of a band due to מCN and ap-
pearance of a new band due to ϾCסS in the region
מ1
1250–1200 cm indicated the formation of com-
pounds III from II. In compounds III, bands due to
מNH2 and ϾNH groups appeared in the region
3460–3300 cmמ1 and 3200–3150 cmמ1, respectively.
Disappearance of a band due to ϾNH in com-
pounds VI and appearance of a new band at 1750–
These results have been tabulated in the form of
inhibition zone and activity indices (Table 4).
EXPERIMENTAL
מ1
1730 cm due to ϾCסO confirms the ribosilation
Melting points were determined in open capillary
tubes and are uncorrected. The IR spectra were re-
corded in KBr disks on a NICOLET-MEGNA FT-IR
by the substitution of the ϾNH proton. The sym-
metric and asymmetric stretching vibrations due to
the C–O–C linkage in compounds VI appeared in the
1
550 spectrometer. The H NMR spectra were ob-
מ1
region 1070–1030 cm
tained from an FX 90 Q JEOL type spectrophotom-

54 Kumar, Singh, and Yadav
TABLE 1 Characterization Data of Pyrido[2,3-d]pyrimidines and Their Ribofuranosides
Elemental Analysis %
Found (Calcd.)
Compound
R1
R2
Molecular Formula Molecular Weight Yield (%) M.P. (ЊC)
C
H
N
IIIa
IIIb
IIIc
IIId
VIa
VIb
VIc
VId
C4H3O 4-CH3–C6H4 C18H14N4 OS
334
338
399
336
778
782
843
780
75
73
69
67
71
68
72
63
105
178
116
138
75
64.70
4.21
16.75
(64.67) (4.19) (16.77)
60.39 3.28 16.54
(60.35) (3.25) (16.57)
51.15 2.78 14.01
(51.13) (2.76) (14.03)
60.75 3.60 16.63
(60.71) (3.57) (16.67)
67.90
(67.87) (4.37)
66.03 3.99
(65.98) (3.96)
61.23 3.72
(61.21) (3.68)
66.19 4.12
C4H3O 2-F–C6H4
C4H3O 4-Br–C6H4
C17H11 N4OSF
C17H11 N4OSBr
C4H3O 2-OH–C6H4 C17H12 N4O2S
C4H3O 4-CH3–C6H4 C44H34 N4O8S
4.42
7.18
(7.20)
7.13
(7.16)
6.62
(6.64)
7.15
(7.18)
C4H3O 2-F–C6H4
C4H3O 4-Br–C6H4
C43H31 N4O8SF
C43H31 N4O8SBr
73
148
105
C4H3O 2-OH–C6H4 C43H32 N4O9S
(66.15) (4.10)
TABLE 2 The IR and 1H NMR Spectral Data of Synthesized Compounds
1H NMR (d ppm from TMS)
מ1
IR (KBr: mmax cm
)
Compound ϾNH Ar-H (multiplet) -CH3
-OH
CЈ-H (doublet) ϾNH
1
-NH2 ϾCסS ϾCסO C–O–C
IIIa
IIIb
IIIc
IIId
VIa
8.09
7.62
8.13
7.92
—
7.15–8.00
6.87–7.56
6.93–8.02
6.97–7.69
7.03–8.08
2.01
—
—
—
2.06
—
—
—
9.96
—
—
—
—
—
6.42
3180 3460–3340
3150 3455–3320
3200 3450–3335
3170 3445–3320
1250
1230
1225
1230
1235
—
—
—
—
1745
—
—
—
—
1030
—
—
—
—
3450–3335
3430–3300
3445–3325
3440–3310
(J ס 8Hz)
6.53
(J ס 8Hz)
6.43
(J ס 8Hz)
6.40
VIb
VIc
VId
—
—
—
7.06–8.09
6.95–8.18
7.11–8.06
—
—
—
—
—
1200
1220
1215
1730
1750
1730
1070
1040
1035
10.02
(J ס 8Hz)
eter in CDCl3/DMSO-d6, and 13C NMR spectra were
recorded in CH3OH solution, using tetramethylsi-
lane as an internal standard. The purity of each com-
pound was checked by thin-layer chromatography
(TLC) using silica gel “G” as adsorbent, and visuali-
zation was accomplished by UV light or iodine. Chal-
cones were synthesized by reported methods [14].
the flask were poured onto crushed ice with constant
stirring to obtain a solid mass, which was washed
with water and cold ethanol. The residue was re-
crystallized from ethanol.
Synthesis of 4-Amino-5,7-disubstituted
pyrido[2,3-d]pyrimidine-2(1H)-thiones III
A mixture of II (0.01 mol) and thiourea (0.02 mol)
was refluxed on an oil bath at 120–130ЊC for 2 hours
with constant stirring. The temperature of the reac-
tion mixture was raised gradually (2 hours) to 180ЊC,
and finally the mixture was heated at 210–220ЊC for
2 hours. The product so obtained was washed with
water, saturated sodium bicarbonate solution, and
Synthesis of 2-Amino-3-cyano-4,6-disubstituted
Pyrimidines II
A mixture of the appropriate chalcone (0.045 mol),
malononitrile (0.045 mol), and ammonium acetate
(0.36 mol) in ethanol (80 mL) was refluxed in a water
bath for 8–10 hours. After cooling, the contents of

Synthesis of Some New Pyrido[2,3-d]pyrimidines and Their Ribofuranosides as Possible Antimicrobial Agents
TABLE 3 13C NMR Spectral Data of Ribofuranosides VIa–VId in CH3OH (d ppm from TMS)
Compound
C2
C4
C5
C6
C7
C9
C10
Furan–C5
Ar–C7
CH3–Ar at C7
VIa
VIb
VIc
VId
159.76 158.83 134.87 130.70 134.17 134.01 133.85 146.41, 109.15 128.05–134.44
21.3
—
115.36, 143.30
160.12 158.92 134.97 131.21 134.85 134.50 134.10 148.67, 110.36 130.27–153.62
116.28, 144.31
160.04 158.79 134.77 130.55 134.26 134.36 134.05 148.37, 110.21 126.85–135.67
116.21, 144.17
159.68 158.71 134.81 130.85 134.57 134.21 133.81 147.36, 109.26 134.21–150.67
116.13, 144.36
—
—
O
C1Ј
C2Ј
C3Ј
C4Ј
C5Ј
࿣
Ar (OBz)
–C–
VIa
VIb
VIc
VId
100.80
103.65
102.93
100.67
78.45
78.63
79.41
78.96
77.07
77.51
77.83
76.85
73.55
74.85
73.97
73.86
65.05
66.15
66.10
65.45
167.52, 166.35
167.21, 166.38
167.64, 166.21
167.83, 166.47
126.82–136.02
125.21–136.71
125.38–136.53
127.09–136.82
TABLE 4 Antimicrobial Activity of Synthesized Pyrido[2,3-d]pyrimidines and Ribofuranosides
Bacteria
Fungi
Compound
Escherichia coli
Staphylococcus aureus
Aspergillus niger
Aspergillus flavus.
IIIa
IIIb
IIIc
IIId
VIa
VIb
VIc
VId
14.1
(0.97)
13.4
(0.92)
13.2
(0.91)
18
(1.24)
14.5
(1.0)
16.2
(1.12)
16
19.3
(0.92)
18
(0.86)
22
(1.05)
21.5
(1.02)
24.8
(1.18)
23.7
(1.13)
24
9.9
(1.02)
9.6
(0.99)
11.0
(1.13)
10.2
(1.05)
11.8
(1.22)
12.1
(1.25)
11.5
(1.18)
11.2
9.5
(0.96)
9.8
(0.99)
10.6
(1.07)
10.0
(1.01)
11.1
(1.12)
11.7
(1.18)
11.5
(1.16)
10.8
(1.10)
15.3
(1.05)
(1.14)
22.5
(1.07)
(1.15)
(1.09)
Note: Values in parenthesis represent activity index; activity index ס inhibition area of sample/inhibition area of the standard.
finally, with cold ethanol, and was recrystallized
from DMF-ethanol (1:2).
methylsilylated pyrido[2,3-d]pyrimidines V were
dissolved in anhydrous acetonitrile (40 mL), and a
solution of b-D-ribofuranose-1-acetate-2,3,5-triben-
zoate (0.011 mol) in dry acetonitrile (20 mL) was
then added with stirring. The mixture was cooled to
0ЊC, a solution of SnCl4 (1.6 mL) in anhydrous ace-
tonitrile 5 mL was added dropwise, the mixture was
stirred until the reaction was determined complete
by TLC (2–3 hr) and then poured into saturated
NaHCO3 solution and extracted with CHCl3. The or-
ganic layer was dried over anhydrous MgSO4 and
concentrated to give the crude nucleosides, which
Synthesis of 4-Amino-5,7-disubstituted-1-
[2Ј,3Ј,5Ј-tri-O-benzoyl-␣- -ribofuranosyl]pyrido-
[2,3-d]pyrimidine-2(1H)-thiones VI
D
Compounds III (0.01 mol) were refluxed by stirring
under anhydrous conditions for 24 hours with hex-
amethyldisilazane (HMDS) (60 mL) and (NH4)2SO4
(0.02 g). The clear solution obtained was cooled, and
the solvent was removed in vacuo. The resulting tri-

56 Kumar, Singh, and Yadav
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ACKNOWLEDGMENT
Authors are thankful to the Head, Department of
Chemistry, University of Rajasthan Jaipur, for pro-
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