A convenient synthesis of new annelated pyrimidines and their biological importance

Article abstract of DOI:10.1002/jhet.1891

Several bicyclic/tricyclic-fused pyrimidines were synthesized from the reactions of amino esters and bifunctional nucleophiles such as 2-methylthio-thiazoline and 2-methylthio-imidazoline. The synthesized compounds were tested for their in vitro antimicrobial activities that revealed mild to moderate growth inhibitory potentials.

Full text of DOI:10.1002/jhet.1891

E216
A Convenient Synthesis of New Annelated Pyrimidines
and Their Biological Importance
Vol 51
a
a
a
b
b
*
M. Wahab Khan, Mohammed Kabir Uddin, Morshed Ali, Mohammad S. Rahman, Mohammad Abdur Rashid,
b
*
and Rasheduzzaman Chowdhury
aDepartment of Chemistry, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh
bDepartment of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Dhaka, Dhaka 1000, Bangladesh
*
E-mail: rashidma@univdhaka.edu or rzchowdhury@yahoo.com
Received May 29, 2012
DOI 10.1002/jhet.1891
Published online 25 April 2014 in Wiley Online Library (wileyonlinelibrary.com).
O
COOEt
N
Dry AcOH, reflux
N
+
MeS
X
X
NH2
N
Several bicyclic/tricyclic-fused pyrimidines were synthesized from the reactions of amino esters and bifunctional
nucleophiles such as 2-methylthio-thiazoline and 2-methylthio-imidazoline. The synthesized compounds were
tested for their in vitro antimicrobial activities that revealed mild to moderate growth inhibitory potentials.
J. Heterocyclic Chem., 51, E216 (2014).
INTRODUCTION
and facile method for the syntheses of a novel series of
linear/angular-fused pyrimidines. The current work describes
the syntheses of fused pyrimidines (9–15) on the basis of
SN—SN tandem reactions of amino esters and annelating
reagents. The ease and generality of the reactions coupled
with the simple work-up may merit their use in pharmaceuti-
cal industries for the syntheses of molecules with similar
scaffolds.
Fused heterocycles represent an important class of organic
compounds because of their structural diversity and potential
applications in medicinal chemistry [1–3]. Such heterocycles
frequently form part(s) of pharmacophores or fragments of
naturally occurring bioactive molecules. Perhaps the most
important of them are heterocyclic systems containing
pyrimidine skeleton. Fused pyrimidines have drawn consid-
erable interest over the last few years as reflected by the
recent number of articles describing their synthetic routes
and broad-spectrum activities. Compounds of this class have
been reported to block platelet aggregation [4–6], demonstrate
promising antihypertensive [7,8], antimalarial/antiparasitic
[9–11], anti-inflammatory [12], and anticancer [13,14]
activities. However, the macromolecular target-based inhibi-
tion studies on fused pyrimidines have lagged behind these
biological activity data. Substituted pyrazolopyrimidines
were found to inhibit signaling kinases such as glycogen
synthase kinase 3 and cyclin-dependent kinase 5 [15].
Whereas glycogen synthase kinase 3 has been implicated in a
number of diseases, including type II diabetes, Alzheimer’s
disease, inflammation, cancer, and bipolar disorder, cyclin-
dependent kinase 5 is involved in the processes of neuronal
maturation. Such a widespread use of fused pyrimidines in
the pharmaceutical, agrochemical, and veterinary industries
prompted an immense interest to develop new facile routes
for efficient and cost-effective syntheses.
RESULTS AND DISCUSSION
Chemistry. Several fused pyrimidines were synthesized
in the current study from annelated substrates and reagents.
The reaction progress was in general monitored by TLC
employing suitable solvent mixtures. The final products
were primarily characterized on the basis of their spectral
data interpretation and wherever appropriate, confirmed by
comparison with reported values.
The annelated substrates, ethyl esters of 5-amino-1-methyl-
1H-pyrazole-4-carboxylate (1), 3-amino-1-methyl-1H-pyrazole-
4-carboxylate (2), 2-amino-4,5-dimethyl-thiophene-
3-carboxylate (3), and 2-amino-4,5-diphenyl-furan-3-
carboxylate (4) were prepared from ethyl (ethoxymethylene)
cyanoacetate, ethoxymethylene malononitrile, butan-2-one,
and benzoin, respectively by Gewald procedure [21,22] in
57–84% yields (Scheme 1). The compounds were identified
by careful observation of their spectral data. NMR and IR
spectral characteristics for functional groups including —
COOEt and —NH2 were conserved in all annelated sub-
strates (1–4). 1 and 2 are isomeric, and hence their spectral
properties were similar but not identical. Apart from their
very different melting points (90 and 222ꢀC for 1 and 2),
certain features distinguished them. Notably, the UV absorp-
tion patterns were different for the two compounds; 1
Over the years, various methods for the synthesis of
fused pyrimidines have been developed and used in hetero-
cyclic chemistry [16–20]. However, some of these methods
suffer from undesired complexities such as longer reaction
time, use of expensive or hazardous reagents, and often
inconvenient work-up. As part of our ongoing interest in
medicinal chemistry, we attempted to develop a general
© 2014 HeteroCorporation

August 2014
Synthesis of Annelated Pyrimidines
E217
Scheme 1
11–13 from 2 to 4, respectively (Scheme 3). In brief, the
reactions were carried out in mixtures containing an amino
ester (1–4) and an annelating reagent (6 or 8) in dry acetic
acid at 100/160ꢀC under reflux for 1–8 h. The formed precip-
itate was filtered off, occasionally washed with water, and
recrystallized from ethanol to furnish products in reasonably
good yields (51–73%). The reactions likely proceed via a
conserved mechanism involving an initial nucleophilic
attack of the amino group of esters to the electron-deficient
alkenic carbon (C-2) of reagents (6 or 8). The intermediate
(s) thus formed then eliminates the leaving group (—SMe)
followed by ring closure in the next step by a second nucle-
ophilic attack of the heterocyclic nitrogen of the reagents to
the sp2-hybridized carbon of the ester (substrate). This results
in an elimination of ethanol to yield the final products via
intermolecular cyclization (Scheme 4).
COOEt
NH2
COOEt
CN
1. Me-NHNH2
2. MeOH
N
N
EtO
EtO
N
Me
1
COOEt
NH2
CN
CN
1. Me-NHNH2
2. EtOH
Me
N
2
Me
COOEt
NH2
Me
Me
O
1. NC-CH2-COOEt
2. Sulfur/ EtOH
3. Et2NH
Me
S
3
In addition, the annelating substrate (1) was also used in the
synthesis of 1-methyl-5-(4-methyl-benzoyl)-1,5-dihydro-
pyrazolo[3,4-d]pyrimidin-4-one (15) in a two-step route
as shown in Scheme 5. The target compound (15) was
synthesized from 1-methyl-1,5-dihydro-pyrazolo[3,4-d]
pyrimidin-4-one (14) and p-toluoyl chloride in dry ether
in approximately 65% yield.
In the present study, characterization of the reagents and
products employed various spectral techniques including
UV, IR, and high-field NMR analysis. Three of the synthe-
sized compounds, 9–11 contain thiazolo/imidazo pyrimidine
moiety (ring BC) fused with a pyrazole ring (A) that has an
N-methyl substituent. These three compounds had relatively
higher melting points (>250ꢀC) compared with the rest and
exhibited some common 1H-NMR features such as a down-
field 1H singlet at d 7.76 ppm for an unsubstituted pyrazole
ring proton, two 2H triplets around d 4.15 (t, 2H, J = 7.2–
7.8 Hz) and 3.26 (t, 2H, J = 7.2–7.8 Hz) for two methylenes
on ring C, and a sharp 3H singlet (d 2.5–3.0) for the
N-methyl group. The other compounds (12 and 13) had addi-
tional spectral characteristics for two methyl (12) or two
phenyl (13) groups.
Ph
Ph
Ph
O
COOEt
NH2
1. NC-CH2-COOEt
2. DMF
3. Et2NH
OH
Ph
O
4
absorbed at l 254, 226, and 206 nm, whereas 2 showed
1
bathochromic shift to l 268 and 210 nm. H-NMR spectra
for the two compounds were similar except for the broad
2H singlet for the ortho-amino group centered around d
5.28 and 4.38 ppm in 1 and 2, respectively.
The annelating reagents, 2-methylthio-thiazoline (6)
and 2-methylthio-imidazoline (8) were prepared starting
from ethanolamine and ethylene diamine, respectively
by Jensen method (Scheme 2) [23,24]. The final methyla-
tion step was carried out in methanol with equimolar
amounts of methyl iodide. The compounds were readily
identified by their spectral characteristics and by compa-
rison with literature values. Chemically, these annelating
agents are interesting because they contain a good leaving
group (—SMe) and show both nucleophilic and electro-
philic characters. In particular, 2-methylthio-thiazoline
(6) is widely used as a carbon—nitrogen double bond
fragment for the synthesis of heterocyclic compounds
having a thiazole ring.
The 13C-NMR spectra for the compounds were particu-
larly helpful in assigning the double bonded carbons and
were in good agreement with the structures. In addition,
DEPT 13C-NMR revealed different hydrocarbon status
(CH, CH2, or tertiary) that was also consistent with the
structures. The IR spectra were in general useful for
Fused pyrimidine derivatives (9) and (10) were synthe-
sized from annelated substrate, amino ester (1), whereas
Scheme 2
1. MeI
H2C NH2
H2C OH
HN
HN
N
N
N
CS2
2. MeOH, reflux
NaOH
S
S
HS
HS
MeS
MeS
S
S
S
5
7
6
1. MeI
2. MeOH, reflux
N
H2C NH2
H2C NH2
CS2
EtOH, conc.HCl
N
H
N
H
N
H
8
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

E218
M. Wahab Khan, M. K. Uddin, M. Ali, M. S. Rahman, M. A. Rashid, and R. Chowdhury
Vol 51
Scheme 3
[25]. The synthesized compounds demonstrated mild
growth inhibition (mean zone of inhibition, 6.5–12.0 mm)
at 200-mg dose against antibiotic-susceptible standard
strains of gram-positive and gram-negative bacteria as
well as human fungal pathogens (Table 1). The data
show that the annelated substrates (1, 2, and 4) and the
reagents (6 and 8) possess some degree of growth
inhibitory activity especially against the fungus such as
Candida albicans. Compound 3 appears to be mildly
active against gram-positive Bacillus and gram-negative
Escherichia coli and the fungus Aspergillus niger. In
contrast, such selectivity towards fungi was significantly
altered with the bigger tricyclic final products, as they
seemed to inhibit the growth (to variable degrees) of an
increased number of pathogens (Table 1).
When using living cells, restricted growth phenotypes
often depend on cell permeability of the small molecule
inhibitors. Log of calculated partition coefficient (CLogP)
for n-octanol/water is a calculated (by CSChemDraw
Ultra v8.03) lipophilicity index that often correlates with
biological activity and lipophilicity (and therefore perme-
ability) of compounds [25]. On the other hand, polar
functional groups are important for interacting with
biological macromolecules such as proteins and nucleic
acids. Protecting such functionality with acyl or alkyl
groups often allows a small molecule to cross the cell
membrane which then becomes active via metabolic
deprotection in cells. The standard antibiotic used in the
current study, kanamycin, is highly functionalized with
low ClogP value (À5.17), whereas 13 has the highest
CLogP value (3.76) amongst the tested compounds
because of the presence of aromatic rings. Although
lipophilicity index suggests that the compound 13 should
be cell permeable, but when tested for growth inhibition,
it did not show significant antimicrobial activity presum-
ably because of poor functionalization.
identifying —NH2 and —COOÀ groups in the amino
esters (starting material) and the carbonyl group in
1
the final product. Complete analysis of the UV, IR, H-
NMR, and 13C-NMR spectra were supported by the
molecular formula derived from the elemental analysis
and allowed unambiguous determination of the structures
presented here.
Biological. Antimicrobial activities of fused primidine
derivatives were evaluated by a standard in vitro bioassay
Scheme 4
O
N
O
N
O
N
O
OEt
N
OEt
N
N
-EtOH
N
-MeSH
+
MeS
X
X
X
X
N
H
H
H
Scheme 5
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

August 2014
Synthesis of Annelated Pyrimidines
E219
Table 1
Spectrum of antimicrobial activity of fused pyrimidines and reagents against gram-positive and gram-negative bacteria and fungi.
Diameters of mean zone of inhibition (MZI)
1
2
3
4
6
8
9
10
11
12
13
14
Kan
Gram positive
Bacillus cereus QL 29
Bacillus megaterium QL 38
Bacillus subtilis QL 40
-
-
-
-
-
-
8.1
7.5
-
-
-
6.5
-
-
-
-
-
-
7.4
9.4
-
7.2
8.6
-
7.6
10.1
8.6
7.6
10.1
8.6
8.5
9.8
8.6
7.2
8.5
8.1
31.9
34.2
30.1
Gram negative
Esherichia coli ATCC 25922
Pseudomonas aeruginosa ATCC 27853
Salmonella paratyphii A AM 16590
Shigella dysenteriae ATCC 26131
-
-
-
-
-
-
-
-
8.2
-
-
-
-
-
-
-
-
-
-
-
-
7.2
-
-
7.1
-
-
6.5
-
-
6.5
-
-
7.9
-
-
8.2
8.9
6.5
7.0
34.2
34.8
26.9
36.9
-
-
-
7.4
7.4
7.8
9.1
8.2
Fungi
Aspergillus niger
-
-
9.8
-
9.5
-
-
-
9.5
-
-
-
9.4
-
-
-
-
-
9.8
-
-
-
-
9.5
8.1
10.5
-
-
9.8
-
-
-
11.5
-
35.0
32.5
27.6
32.1
Candida albicans ATCC 10231
Rhizopus oryzae ATCC 20344
Saccharomyces cerevisiae AB 972
10.0
-
-
12.0
-
-
-
7.8
-
7.8
8.8
8.6
8.1
8.6
The word Kan means kanamycin, and “-” indicates no sensitivity or MZI lower than 6 mm.
Doses for kanamycin and the newly tested compounds were 30 and 200 micrograms per disk, respectively.
Compound 15 at 200 mg/disk was fully resistant to all the tested organisms and is therefore not included in the table.
monitored by TLC on Kieselgel gel 60F254 precoated sheets
(E. Merck, Darmstadt, Germany), and the spots were detected
under UV exposure at 254 nm. Column chromatography was
carried out on silica gel (60–120 mesh ASTM). The CLogP
values were determined by using the CS ChemDraw Ultra version
8.03, by Cambridge-Soft.com.
CONCLUSION
Overall, we described a convenient, general, and facile
method for the synthesis of fused heterocyclic compounds
via heteroannelations of amino ester substrates with annelat-
ing agents. The most important features of the syntheses are
that readily available, inexpensive starting materials were
used at relatively milder reaction conditions that furnished
products in reasonably good yields. In addition, no hazardous
compounds/effluents were generated via the procedure.
The method appears to be versatile in that it can be used to
introduce a variety of fused heterocycles at variable positions
for drug discovery. Although the compounds in this class
showed mild growth inhibitory activities in our bioassay, they
might be potent inhibitors of some of the biological targets
such as tyrosine kinase SRC, human heat shock protein 90,
and platelet-derived growth factor receptor kinase as sug-
gested by a structural search using Ligand Activity by Surface
Similarity Order descriptors in the ChemSpider server [26].
Ethyl-5-amino-1-methyl-1H-pyrazole-4-carboxylate (1). To
a
solution of ethyl (ethoxymethylene)cyanoacetate (10.00 g,
59 mmol) in methanol (35 mL) was added methyl hydrazine
(equivalent amount) dropwise whilst maintaining the temperature
below 60ꢀC. The mixture was then heated under reflux for 1 h,
filtered off, dried, and recrystallized from ethanol that afforded 1.
White crystals (yield: 8.39 g, 84%), mp 90–91ꢀC; UV (EtOH) l:
254, 226 nm; IR (KBr) n: 3401, 3284, 3115, 2986, 1679, 1562,
1385 cmÀ1 1H-NMR (CDCl3, 400 MHz): dH 7.59 (s, 1H, CH),
;
5.35–5.20 (br.s, 2H, NH2), 4.25 (q, 2H, J =7.1 Hz, CH2), 3.61
(s, 3H, NCH3), 1.33 (t, 3H, J =7.1Hz, CH3); 13C-NMR (CDCl3,
100 MHz): dC 164.31, 149.24, 138.86, 95.76, 59.29, 33.86, 14.25;
Anal. Calcd for C7H11N3O2: C, 49.52; H, 6.41; N, 24.65. Found:
C, 49.48; H, 6.38; N, 24.70%.
Ethyl-3-amino-1-methyl-1H-pyrazole-4-carboxylate (2)
[15,27].
Compound 2 was synthesized from a mixture of
ethoxymethylene malononitrile (10.85g, 89 mmol) in ethanol
(35 mL) and methyl hydrazine (3.60 g, 78mmol) by a similar
procedure described for 1. Yellowish crystals (yield: 7.61 g, 58%),
mp 222–223ꢀC; UV (EtOH) l: 268 nm; IR (KBr) n: 3433, 3285,
EXPERIMENTAL
General.
Sigma-Aldrich Company Ltd. (Dorset, UK) Melting points were
recorded on Gallenkamp melting point apparatus
Reagents were procured from Fluka, Merck, and
3198, 1692, 1576, 1261, 1105cmÀ1
;
1H-NMR (CDCl3,
a
400 MHz): dH 7.52 (s, 1H, CH), 4.38 (br.s, 2H, NH2), 4.25
(q, 2H, J = 7.1 Hz, CH2), 3.66 (s, 3H, NCH3), 1.28 (t, 3H,
J = 7.1Hz, CH3); 13C-NMR (CDCl3, 100MHz): dC 164.09,
156.38, 133.24, 99.10, 59.72, 38.90, 14.46.
(Loughborough, UK) and paraffin oil bath and are uncorrected.
UV and IR spectra were recorded on Shimadzu UV–VIS and
Shimadzu FTIR spectrophotometers, (Kyoto, Japan), respectively.
The H-NMR (400 MHz) and 13C-NMR (100 MHz) spectra were
1
Ethyl-2-amino-4,5-dimethyl-thiophene-3-carboxylate (3)
acquired in CDCl3/DMSO-d6 on an Ultra Shield Bruker DPX 400
spectrometer (Analytische Messtechnik, Karlsruhe, Germany); the
chemical shifts are reported in parts per million relative to the
residual nondeuterated solvent signals. The number of attached
protons for 13C signals was determined using the DEPT 135 pulse
sequence. The reaction progress and product homogeneity were
[28].
A
solution of butanone (8.9 mL, 100 mmol),
ethylcyanoacetate (11.31 g, 100 mmol), and sulfur (3.20 g,
100 mmol) in 95% ethanol (30 mL) was treated with diethylamine
(4 mL) whilst maintaining the temperature below 60ꢀC using an ice
bath. The reaction mixture was stirred for 2 h at RT before being
poured into ice water. This yielded precipitate that was filtered,
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

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M. Wahab Khan, M. K. Uddin, M. Ali, M. S. Rahman, M. A. Rashid, and R. Chowdhury
Vol 51
washed thoroughly with water, and recrystallized from ethanol to give
3. Yellowish crystals (yield: 15.16 g, 76%), mp 89–91ꢀC; UV (EtOH)
l: 240 nm; IR (KBr) n: 3433, 3285, 3197, 1648, 1502, 1452, 1314,
neutralized with 15% NaOH (2.4 mL). The final product (8) was
extracted with CHCl3 (30 mL Â 4) and dried over sodium sulfate,
and the solvent was evaporated to dryness under reduced pressure.
White crystals (yield: 1.51 g, 44%), mp 119–121ꢀC; UV (EtOH)
1261, 1026 cmÀ1 1H-NMR (CDCl3, 400 MHz): dH 5.27 (s, 2H,
;
1
l: 251nm; IR (KBr) n: 3393, 3150, 1604, 1582, 1107cmÀ1; H-
NH2), 4.29 (q, 2H, J=7.2Hz, CH2), 3.60 (s, 6H, 2 Â CH3), 1.39
(t, 3H, J=7.2Hz, CH3); 13C-NMR (CDCl3, 100 MHz): dC 164.31,
138.86, 113.96, 95.76, 59.29, 46.69, 33.87, 25.04, 14.26.
NMR (CDCl3, 400MHz): dH 7.29 (s, 1H, NH), 4.20
(d, J=7.9Hz, 2H, CH2), 3.39 (d, J= 7.9 Hz, 2H, CH2), 2.48 (s, 3H,
SCH3); 13C-NMR (CDCl3, 100 MHz): dC 164.85, 50.13, 13.25.
1-Methyl-6,7-dihydro-1H-pyrazolo[3,4-d]thiazolo[3,2-a]
pyrimidin-4-one (9) [12]. A solution of amino ester (1) (0.68 g,
4 mmol) and 2-methylthio-thiazoline (6) (0.52 g, 4 mmol) in dry
acetic acid (6 mL) was heated under reflux for 4 h. The reaction
progress was monitored by TLC (chloroform–methanol 13:1,
Rf = 0.86) that indicated conversion of the starting materials into
product (9). The reaction mixture was cooled at RT and stirred for an
hour before adding crushed ice (35 g) into it. Reddish crystals (yield:
0.45 g, 55%), mp >250ꢀC; UV (EtOH) l: 268nm; IR (KBr) n:
Ethyl-2-amino-4,5-diphenyl-furan-3-carboxylate (4) [19].
A
solution of ethylcyanoacetate (2.13g, 19mmol) and benzoin
(5.25 g, 25mmol) in DMF (7.5ml) was treated with diethylamine
(4mL). After 12h of stirring at RT, the mixture was poured into
water (60 mL), and the solid material was filtered and recrystallized
from ethanol. Yellowish crystals (yield: 3.51 g, 61%), mp 163–
165ꢀC; UV (EtOH) l: 253nm; IR (KBr) n: 3384, 3060, 2934, 1677,
1595, 1389, 1206, 977, 929, 755 cmÀ1; 1H-NMR (CDCl3, 400 MHz):
dH 9.26 (br.s, 2H, NH2), 7.62–7.64 (m, 2H, Ar—H), 7.45–7.49 (m,
1H, Ar—H), 7.45 (d, 2H, Ar—H), 7.36–7.40 (m, 5H, Ar—H), 4.27
(q, 2H, J=7.2Hz, CH2), 1.04 (t, 3H, J=7.2Hz, CH3); 13C-NMR
(CDCl3, 100 MHz): dC 164.87, 161.47, 136.05, 132.89, 132.56,
130.88, 128.97, 128.60, 128.50, 128.28, 117.32, 113.40, 100.73,
60.29, 42.24, 29.68, 11.13; DEPT 13C-NMR (CDCl3, 100 MHz): dC
132.89, 130.89, 128.97, 128.60, 128.50, 128.28, 42.25, 11.14.
1
3097, 3040, 2899, 1677, 1599, 1396, 927 cmÀ1; H-NMR (CDCl3,
400 MHz): dH 7.76 (s, 1H, CH), 4.14 (t, 2H, J=7.4Hz, CH2), 3.27
(t, 2H, J=7.4Hz, CH2), 2.47 (s, 3H, NCH3); 13C-NMR (CDCl3,
100 MHz): dC 164.40, 140.8, 136.8, 115.2, 72.1, 44.0, 42.9, 35.84.
1-Methyl-6,7-dihydro-1H-pyrazolo[3,4-d]imidazo[1,2-a]
pyrimidin-4(8H)-one (10) [29]. A solution of amino ester (1)
(0.68 g, 4 mmol) in dry acetic acid was treated with 2-methylthio-
imidazoline (8) (0.52 g, 4 mmol) at 160ꢀC under nitrogen
atmosphere for an hour. The reaction progress was monitored by
TLC (n-hexane–ethyl acetate, 9:1, Rf = 0.54), which indicated
formation of the product. After cooling at RT, crushed ice (35g)
was added, and the mixture was stirred for another hour. The
formed precipitate was collected and recrystallized from methanol
to give (10). Reddish crystals (yield: 0.56 g, 73%), mp >250ꢀC;
UV (EtOH) l: 275nm; IR (KBr) n: 3433, 3285, 3197, 2986,
2-Methylthio-thiazoline (6). To a mixture of ethanolamine
(3.66 g, 60 mmol) and sodium hydroxide (9.60 g) in water (26 mL),
carbon disulfide (158 mmol) was added at 30ꢀC with continuous
stirring. The mixture was heated under reflux for 7 h, and the
resulting solution was left to cool, which afforded solid deposits.
An addition of 200 mL of concentrated HCl to the reaction mixture
led to some more precipitates. The solid material was finally filtered
off, washed with water, dried, and recrystallized from water to give
2-mercaptothiazoline (5). Yellowish crystals (yield: 6.01 g, 84%),
mp 102–104ꢀC; UV (EtOH) l: 240 nm; IR (KBr) n: 3133, 1507,
1
1296, 1050 cmÀ1; H-NMR (CDCl3, 400 MHz): dH 8.16 (s, 1H,
1692, 1502, 1105cmÀ1 1H-NMR (CDCl3, 400 MHz): dH 7.76
;
SH), 3.98 (t, 2H, J=7.9Hz, CH2), 3.55 (t, 2H, J=7.9Hz, CH2,).
Methylation of 5 (6.01 g, 50 mmol) was carried out by standard
protocol using equimolar amount of methyl iodide in methanol
(30.3 mL). The reaction mixture was heated under reflux for an
hour before being cooled and diluted with ether. This afforded
white crystalline hydroiodide salts that were filtered. The product
salts were then dissolved in water and decomposed with 15%
NaOH to yield 6 that was finally extracted with CHCl3 and was
evaporated to dryness under reduced pressure in a vacuum
evaporator. Yellow oil (yield: 4.35 g, 65%), bp 70ꢀC; UV (EtOH)
l: 253 nm; IR (KBr) n: 2932, 2853, 1564, 1304, 1255, 1001, 920,
727 cmÀ1; 1H-NMR (CDCl3, 400 MHz): dH 4.2 (t, 2H, J = 7.9 Hz,
CH2), 3.39 (t, 3H, J = 7.9 Hz, CH2) 2.50 (s, 3H, SCH3); 13C-NMR
(CDCl3, 100MHz): dC 165.47, 63.74, 44.31, 35.26, 14.83.
(s, 1H, CH), 6.98 (s, 1H, NH), 4.15 (t, 2H, J = 7.8Hz, CH2), 3.25
(t, 2H, J = 7.8 Hz, CH2), 3.03 (s, 3H, NCH3); 13C-NMR (CDCl3,
100 MHz): dC 165.40, 137.32, 125.12, 110.25, 72.05, 39.32, 34.37.
2-Methyl-6,7-dihydro-2H-pyrazolo[3,4-d]thiazolo[3,2-a]
pyrimidin-4-one (11) [30,31].
A solution of amino ester (2)
(1.00 g, 6 mmol) and 2-methylthio-thiazoline (6) (0.79 g, 6 mmol)
in dry acetic acid (6 mL) was heated under reflux in a 100-mL
round-bottomed flask. The reaction was monitored by TLC
(chloroform–methanol, 11:1, Rf = 0.7). After completion, the
reaction mix was cooled at RT followed by adding crushed ice
(25 g) and stirring for an hour. The formed precipitate was filtered,
washed, and crystallized from methanol to give (11). Reddish
crystals (yield: 0.63 g, 51%), mp >250ꢀC; UV (EtOH) l: 280 nm;
IR (KBr) n: 3148, 3097, 3017, 2897, 2861, 1675, 1599, 1396,
2-Methylthio-imidazoline (8).
To a mixture of ethylene
928, 785 cmÀ1 1H-NMR (CDCl3, 400 MHz): dH 7.76 (s, 1H,
;
diamine (5.00 g, 83 mmol), rectified spirit (100 mL), and water
(100 mL) was added dropwise carbon disulfide (equimolar) with
occasional stirring for 2 h. The reaction mixture was heated with
reflux for an hour before adding concentrated HCl (15 mol) and
continued for another 9 h. The resulting solid on cooling was filtered,
washed with cold acetone (80 mL), and recrystallized from ethanol
to give 7. Yellowish crystals (yield: 3.98 g, 47%), mp 155–156ꢀC;
UV (EtOH) l: 245.6 nm; IR (KBr) n: 3249, 2880, 2571, 1499,
CH), 4.15 (t, 2H, J = 7.2 Hz, CH2), 3.26 (t, 2H, J = 7.2 Hz, CH2),
2.47 (s, 3H, NCH3); 13C-NMR (CDCl3, 100 MHz): dC 164.48,
149.23, 139.01, 96.13, 59.14, 46.78, 33.99, 14.43; DEPT
13C-NMR (CDCl3, 100 MHz): dC 139.01, 59.14, 33.99, 14.43.
6,7-Dimethyl-2,3-dihydro-thiazolo[3,2-a]thieno[2,3-d]
pyrimidin-5-one (12) [32,33]. The solution of ethyl-2-amino-
4,5-dimethyl-thiophene-3-carboxylate (3) (1.00 g, 5 mmol) and 2-
methylthio-thiazoline (6) (0.67 g, 5 mmol) in dry acetic acid
(6mL) was heated under reflux for 8 h. The reaction progress was
monitored by TLC (n-hexane–ethyl acetate, 9:1, Rf = 0.51) that
showed formation of 12. The mixture was then poured into ice
water, and the resulting precipitate was filtered off, washed with
water, and recrystallized from ethanol that afforded the final
product (12). Reddish crystals (yield: 0.66g, 55%), mp 171–
1
1492, 1275, 1196, 920 cmÀ1; H-NMR (CDCl3, 400 MHz): dH 6.0
(s, 2H, NH, NH/SH), 3.75–3.77 (m, 4H, 2 Â CH2). Methylation of 7
was carried out by adding methyl iodide (1.85 mL, 29 mmol) to a
solution of 7 in methanol (18 mL). The reaction mixture was heated
under reflux for 2 h with stirring. Methanol was then removed
under reduced pressure, and the solid white hydroiodide salt was
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

August 2014
Synthesis of Annelated Pyrimidines
E221
172ꢀC; UV (EtOH) l: 265nm; IR (KBr) n: 3097, 3018, 2970, 1675,
1534, 1396, 928 cmÀ1 1H-NMR (CDCl3, 400MHz): dH 4.22
(t, 2H, J = 7.5 Hz, CH2), 3.41 (t, 2H, J = 7.5 Hz, CH2), 2.53 (s, 6H,
2 Â CH3); 13C-NMR (CDCl3, 100 MHz): dC 178.33, 170.48,
138.87, 128.06, 61.49, 60.43, 46.91, 37.75, 25.39, 14.06.
Acknowledgment. Financial support from the Ministry of Science
and Information and Communication Technology, Government of
the Peoples’ Republic of Bangladesh, is gratefully acknowledged.
;
2,3-Diphenyl-5,6-dihydro-imidazo[3,2-a]furo[2,3-d]pyrimidin-
4(8H)-one (13). A solution of amino ester (4) (0.78g, 3 mmol)
and 2-methylthio-imidazoline (8) (0.52 g, 4 mmol) in dry acetic
acid (6mL) was heated under reflux for 6 h. The progress of the
reaction was monitored by TLC (chloroform–methanol, 13:1,
Rf = 0.45) that showed the conversion of the starting material into
product. After cooling the reaction mixture to RT, crushed ice was
added, and the mixture was stirred for an hour. The precipitate
was collected and crystallized from methanol to give (13). Light
yellow crystals (yield: 0.50g, 60%), mp 201–203ꢀC; UV (EtOH)
l: 288 nm; IR (KBr) n: 3393, 3335, 3149, 2207, 1667, 1580,
REFERENCES AND NOTES
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1452, 1199, 972 cmÀ1 1H-NMR (CDCl3, 400MHz): dH 8.76
;
(s, 1H, NH), 7.78–7.88 (m, 4H, Ar—H), 7.49 (t, 2H, J = 8.1 Hz,
Ar—H), 7.26 (t, 2H, J = 8.0 Hz, Ar—H), 7.11 (t, 2H, J = 7.6 Hz,
Ar—H), 3.77 (t, 2H; J = 7.8 Hz, CH2), 2.21 (t, 2H, J = 7.8 Hz,
CH2); 13C-NMR (CDCl3, 100 MHz): dC 172.47, 171.38, 142.74,
137.88, 131.00, 129.50, 128.26, 124.10, 123.93, 122.32, 118.68,
61.37, 60.62, 59.33, 37 .95; DEPT 13C-NMR (CDCl3, 100 MHz):
dC 130.81, 128.69, 128.06, 123.90, 122.12, 118.49, 60.42, 37.75.
1-Methyl-5-(4-methyl-benzoyl)-1,5-dihydro-pyrazolo[3,4-d]
pyrimidin-4-one (15).
A solution of amino ester (1) (1.00 g,
6 mmol) in formamide (4 mL) was refluxed at 180ꢀC for 4h. The
reaction progress was checked by TLC (n-hexane–ethylacetate, 1:2,
Rf = 0.35). The resulting mixture was poured into ice water and
stirred for an hour. The formed precipitate was filtered and
recrystallized from ethanol to give (14). White crystals (yield: 0.68 g,
77%), mp >250ꢀC; UV (EtOH) l: 253 nm; IR (KBr) n: 3148,
3097, 2897, 1675, 1396 cmÀ1 1H-NMR (DMSO-d6, 400 MHz):
;
dH 8.05 (s, 1H, CH), 8.00 (s, 1H, NH), 3.88 (s, 3H, NCH3), 2.58
(s, 1H, CH); 13C-NMR (DMSO-d6, 100MHz): dC 166.13, 157.18,
144.8, 132.02, 114.17, 36.23, 33.09. To a solution of 14 (0.25 g,
2 mmol), p-toluoyl chloride (0.32 g, 2 mmol), and diethyl ether
(6 mL) were added. Then, the mixture was heated under reflux for
about 6 h with continuous stirring. The reaction was monitored by
TLC (n-hexane–ethyl acetate, 1:3, Rf = 0.61). The mixture was
evaporated to dryness under reduced pressure in vacuum evaporator.
The resulting solid was recrystallized from ethanol to give 15. White
crystal (yield: 0.29 g, 65%); mp 220–222ꢀC; UV (EtOH): 263.0,
220.0 nm; IR (KBr) n: 2979, 1758, 1734, 1539, 1347, 1188 cmÀ1
;
1H-NMR (DMSO-d6, 400 MHz): dH 7.97 (d, 2H, J=8.0Hz, Ar—
H), 7.92 (d, 2H, J=8.0Hz, Ar—H), 7.58 (s, 1H, CH), 5.47 (s, 1H,
CH), 3.60 (s, 3H, NCH3), 2.49 (s, 3H, Ar—CH3); 13C-NMR
(DMSO-d6, 100 MHz): dC 173.61, 164.11, 151.53, 149.25, 136.63,
127.79, 127.60, 127.11, 126.71, 95.32, 59.12, 57.08, 42.93, 28.89.
Antimicrobial activity. Antimicrobial susceptibility testing
was performed by the standardized disk diffusion of the National
Committee for Clinical Laboratory Standards [25]. Inhibitory zone
diameters were measured on nutrient agar for bacteria and potato
dextrose agar (Difco Lab.) for fungi, with conventional metrical
filter paper disks (BBL, Cocksville, USA, 6 mm in diameter)
containing 200 mg of compounds. All experiments were
conducted twice and repeated if the results differed significantly.
The inhibitory zone diameters were read with a caliper. For each
tested strain, the growth conditions and the sterility of the medium
were checked in negative controls. The results obtained were
compared with standard antibiotic kanamycin (30mg/disk) disks
bought from Mast Diagnostics, UK.
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet