A novel and eco-friendly procedure for the synthesis of some pyrazolo-thiadiazolo-pyrimidinones and its in vitro anti-bacterial activity

Article abstract of DOI:10.1007/s00044-011-9769-z

A novel series of 2-substituted-aminomethyl-8-phenyl-pyrazolo[3,4-d][1,3,4] thiadiazolo[3,2-a]pyrimidin-4 (1H)-ones have been synthesized by treating 2-chloromethyl-8-phenyl-pyrazolo[3,4-d][1,3,4]thiadiazolo[3,2-a] pyrimidin-4(1H)-one with various nucleophiles. The chloromethyl derivative was prepared by treating 2-amino-3-mercapto pyrazolo[3,4-d]pyrimidine with one carbon donor, chloroacetic acid. The intermediate 2-amino-3-mercapto pyrazolo[3,4-d]pyrimidine was prepared by a novel, eco-friendly route starting from 2-amino-3-carbethoxy-1-phenyl-pyrazole. The target compounds exhibited broad-spectrum antibacterial activity (Kirby Bauer's Method). Springer Science+Business Media, LLC 2011.

Full text of DOI:10.1007/s00044-011-9769-z

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2012) 21:2458–2464
DOI 10.1007/s00044-011-9769-z
ORIGINAL RESEARCH
A novel and eco-friendly procedure for the synthesis of some
pyrazolo-thiadiazolo-pyrimidinones and its in vitro anti-bacterial
activity
•
Dhananjaya Ranganath Abhishek Mazumdar
•
•
Sirisha Mulukuri Raghava Doonaboina
•
•
Murty Devarakonda Mailavaram Raghu Prasad
Received: 17 January 2011 / Accepted: 27 July 2011 / Published online: 13 August 2011
Ó Springer Science+Business Media, LLC 2011
Abstract A novel series of 2-substituted-aminomethyl-8-
phenyl-pyrazolo[3,4-d][1,3,4]thiadiazolo[3,2-a]pyrimidin-4
(1H)-ones have been synthesized by treating 2-chlor-
omethyl-8-phenyl-pyrazolo[3,4-d][1,3,4]thiadiazolo[3,2-a]
pyrimidin-4(1H)-one with various nucleophiles. The chlo-
romethyl derivative was prepared by treating 2-amino-3-
mercapto pyrazolo[3,4-d]pyrimidine with one carbon
donor, chloroacetic acid. The intermediate 2-amino-3-
mercapto pyrazolo[3,4-d]pyrimidine was prepared by a
novel, eco-friendly route starting from 2-amino-3-car-
bethoxy-1-phenyl-pyrazole. The target compounds exhib-
ited broad-spectrum antibacterial activity (Kirby Bauer’s
Method).
stability, which is enough to be isolated, processed, and
stored for a reasonable period of time without deterioration
of potency, and should not produce undesirable side effects
in the host, such as sensitivity or allergic reactions, damage
or irritation to kidney or gastrointestinal tract; the rates of
elimination of the antibiotic should be low enough to allow
a convenient dosage form, yet rapid and complete enough
to facilitate removal of drugs and its metabolites from the
body soon after administration is discontinued, and more
than everything the antibiotic should prevent the ready
development of resistant forms of the parasite (John et al.,
2004). In order to overcome the resistance of strains,
researchers look into finding novel drugs using the tool,
bio-isosterism (http://www.cdc.gov/Drugresistance/community/
anitbiotic-resistance.htm, 21 Jan 2010).
Keywords Antibacterial activity Á
2-Amino-3-mercapto-pyrazolo[3,4-d]pyrimidines Á
Bioisosteres Á Eco-friendly route Á Kirby Bauer’s method Á
Thiadiazolopyrazolopyrimidines
Thiadiazoloquinazolines, the biological analogs of pur-
ines, exhibit antibacterial activity (Soliman et al., 1978).
Thiadiazolopyrimidines have been reported to possess
antibacterial (Robert et al., 1974; Metzner and Heydehn-
auss, 1979; Niedlein and Menche, 1972), antifungal
(Tokunaga et al., 1987; Yadav and Sandhya, 1995), and
herbicidal activities (Suiko and Mackawa, 1977; Kazayuki
et al., 1976). The concept of bio-isosterism has been
exploited to design new types of condensed thiadiazo-
lothienopyrimidines as isosteres of thiadiazoloquinazolines
from our laboratories and has shown encouraging results
(Raghu Prasad et al., 2000, 2007).
Introduction
As of the day, several hundred of compounds belonging to
various classes are available to combat bacterial infections.
However, very few such compounds have found applica-
tion in general medicinal practice, because in addition to
the ability to combat infections, an antibiotic must possess
other attributes like broad spectrum of activity, chemical
Literature survey revealed that pyrazolopyrimidines
possess various biological activities like antibacterial (Holla
et al., 2006; Shamourk et al., 2005), antifungal (Rajesh and
Leena, 2005; Wang Hong et al., 2004; Giori et al., 1985), and
antiviral (Jyh-Haur et al., 2004; El-Bendary and Badria,
2000) activities. However, few efforts have been made to
fuse pyrazolopyrimidine ring system with other heterocyclic
rings systems and test their efficacy on biological effect
D. Ranganath Á A. Mazumdar Á S. Mulukuri Á R. Doonaboina Á
M. Devarakonda Á M. Raghu Prasad (&)
Department of Pharmaceutical Chemistry, Shri Vishnu College
of Pharmacy, Affiliated to Andhra University, Visakhapatnam,
Bhimavaram-2, Vishnupur, Andhra Pradesh, India
e-mail: raghumrp@mailcity.com; raghumrp@rediffmail.com
123

Med Chem Res (2012) 21:2458–2464
2459
(Gatta et al., 1993; Russo et al., 1992, 1993; Gruccione et al.,
1996). This observation prompted us to fuse thiadiazole ring
system to pyrazolopyrimidines, which in turn are the bio-
isosteres of thiadiazolothienopyrimidines and thiadiazolo-
quinazolines. Herewith, we are reporting the synthesis of
some novel of 8-phenyl-2-substituted-aminomethyl-pyr-
azolo[3,4-d][1,3,4]thiadiazolo[3,2-a]pyrimidin-4(1H)-ones
5a–h as antibacterial agents.
mercapto hetero-fused pyrimidinones (Modica et al., 1997)
using thiophosgene as reagent. However, this was not an
attractive route as thiophosgene was non-eco-friendly and
also resulted in less yields. Thus, an alternate, simple,
eco-friendly route has been developed to synthesize the
intermediate 2-amino-3-mercapto-pyrazolo[3,4-d]pyrimi-
dine-4-ones 3 via dithio carbamate derivative 2. The
dithiocarbamate derivative 2 was obtained by reacting
o-amino ester of pyrazole 1 with CS2, NaOH, and dim-
ethylsulfate in dimethylsulphoxide. Dimethylsulphoxide is
a polar aprotic solvent, with high dielectric constant (high
insulating properties). A polar solvent has both positive and
negative ends and therefore can easily solvate anion or
cation. Thus, a single charge on o-amino ester of pyrazole
is surrounded by hundreds of solvent molecules; hence,
area of charged surface is increased by thousand folds and
the rate of reaction increased by million folds. Further, a
high concentration of alkali (20 mol NaOH) was used to
restrict amount of water, which otherwise would have
Results and discussion
The target compounds, 8-phenyl-2-substituted-amino-
methyl-pyrazolo[3,4-d][1,3,4] thiadiazolo[3,2-a]pyrimidin-
4(1H)-ones 5a–h, were synthesized by following the route
depicted in Scheme 1. The starting material, 5-amino-4-
carbethoxy-1-phenyl-pyrazole 1, was prepared as per the
reported method (James et al., 1987). A few reports are
available in the literature for the synthesis of 2-amino-3-
Scheme 1 Synthesis
of 8-phenyl-2-substituted-
aminomethyl-pyrazolo
[3,4-d][1,3,4] thiadiazolo
[3,2-a]pyrimidin-4(1H)-ones
5a–h
O
O
OEt
OEt
CS2/NaOH
N
N
DMS/DMSO
NH
NH2
N
N
Ph
[2]
SMe
Ph
[1]
S
EtOH
N2H4 (99%)
O
O
NH2
OEt
NH
N
N
In Situ
SH
N
N
N
N
Ph
NHNH2
Ph
S
[3]
ClCH2COOH
Conc. H2SO4
O
O
N
N
N
CH2-NHR
CH2Cl
N
S
S
N
N
N
N
R-NH2/ TEA
N
Ph
N
Ph
[5a-h]
[4]
Me
OMe
-N
O
-H2C
O
R = -CH3, -CH2CH3, -(CH2)5CH3,
,
,
,
,
123

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Med Chem Res (2012) 21:2458–2464
caused hydration of 1 and would have hindered the rate of
reaction. The other reason for using dimethylsulphoxide as
a solvent may be that it increases the rate of alkylation at
sulfur atoms.
cyclized compound. The NMR spectrum of the synthesized
compound showed –CH2Cl signal as singlet at around
d = 4.87 ppm, and the disappearance of –NH2 and –SH
signals at d = 4.9 and 4.2 ppm confirmed the formation of
cyclized product. The mass spectrum showed the M? peak at
m/z = 317 with a relative abundance of 100% and M?2 peak
at m/z = 319 (isotope effect due to the presence of chlorine)
with relative abundance of 20%, and the fragmentation
pattern was in agreement with the structure. The target
compounds, 2-substituted-aminomethyl-8-phenyl-pyrazolo
[3,4-d][1,3,4]thiadiazolo[3,2-a]pyrimidin-4(1H)-ones 5a–h,
were obtained by heating the mixture of 2-chloromethyl-8-
phenyl-pyrazolo[3,4-d][1,3,4]thiadiazolo[3,2-a]pyrimidin-4
(1H)-one 4, triethylamine and methylamine in dioxane.
Then, the reaction mixture was cooled to room temperature
and poured into ice-water mixture, and the excess amine was
neutralized by dilute hydrochloric acid (10%). The resultant
precipitate thus obtained was filtered, dried, and recrystal-
lised from benzene. The formations of these new amino
derivatives were confirmed by specific IR peaks, which
showed the absence of –CH2Cl peak and the presence of –NH
stretching and bending vibrations. The structure of the
To a vigorously stirred solution of 5-amino-4-car-
bethoxy-1-phenyl-pyrazole in dimethylsulphoxide, carbon
disulfide and aqueous sodium hydroxide was added drop
wise at room temperature. After two and half hours, dim-
ethylsulfate was added drop wise under cooling in an ice
bath. Stirring was continued for one and half hour. Then, the
reaction mixture was poured into ice-cold water mixture.
The precipitate obtained was filtered, dried, and recrystal-
lised from boiling ethanol. The IR data of this compound
showed characteristic –NH– vibration at 3398 cm-1 and
–C=N vibration at 1557.8 cm-1 and –C=O vibration at
1647.55 cm-1. This indicated the formation of the product.
1H NMR spectra of the synthesized compound also showed
SCH3 signals as singlet at around d = 2.67 ppm, which
clearly confirmed the formation of the product. The mass
spectra showed (M?–SMe) peak at m/z = 275 with a rela-
tive abundance of 35%, and the fragmentation pattern was
in agreement with the structure.
1
Solution of methyl-N-[4-carbethoxy-1-phenyl-pyrazolyl]
dithiocarbamate 2 in ethanol was treated with hydrazine
hydrate (99%) and heated to reflux on a water bath until the
methyl mercaptan evolution ceased. The solution was
immediately filtered under hot condition. The solid obtained
was collected, dried, and recrystallised from boiling ethanol
to yield 5-amino 6-mercapto-1-phenyl-pyrazolo[3,4-d]-
pyrimidine-4[3H]-one 4. The IR data of the synthesized
compound showed characteristic –NH2 vibration at
3333.3 cm-1 and 3204.5 cm-1, and –C=O vibration at
1655.94 cm-1 and =C–H vibration at 2929.97 cm-1. The
1HNMR spectra of the synthesized compound showed –NH2
and –SH signals as singlets at around d = 4.96 and
4.20 ppm, SMe signal at d = 2.67 disappeared, which
confirmed cyclization. The mass spectra showed (M?) peak
at m/z = 259 with a relative abundance of 90%, and the
fragmentation pattern was in agreement with the structure.
2-Chloromethyl-8-phenyl-pyrazolo[3,4-d][1,3,4]thi-
compounds has been further ascertained based on the H
NMR spectrum, which showed presence of –NH signal and
the disappearance of –CH2Cl signal followed by the presence
of molecular ion peak corresponding to their molecular
weights in mass spectra.
Antibacterial activity
The antibacterial activities of compounds 5a–h were tested
against one strain each of a Staphylococcus aureus
(Gram ?ve bacteria), Bacillus subtilis (Gram ?ve spore),
E. coli (Gram -ve bacteria), and Klebsiella (Gram -ve
capsule) using Ampicillin (0.005 mL, 50 lg) as a standard
drug using Kirby Bauer’s Method (Bauer et al., 1966)
(Table 1). The negative control did not show any zone of
inhibition in any of the bacterial strains used for the study.
Compounds 5e (14.5 1.414) and 5h (14.0 1.425) were
the most active compounds of the series against Klebsiella.
The same compound 5h (11.5 0.707) showed the best
activity against E. coli, but compounds 5c (20.5 0.707)
and 5d (20 1.421) showed selectivity toward B. subtilis
and S. aureus.
adiazolo[3,2-a]pyrimidin-4(1H)-one 4 was obtained by
fusion of 5-amino-6-mercapto-1-phenylpyrazolo[3,4-d]-
pyrimidine-4[3H]-one 3 with chloroacetic acid in presence
of concentrated sulfuric acid by heating the mixture on a
water bath for 5 h (neat reaction). The compound was puri-
fied using column chromatography by gradient elution
technique using chloroform and ethyl acetate as solvent
system. The IR data of the synthesized compound showed
characteristic =C–H aromatic vibrations at 3174.65 cm-1
and C=O vibrations at 1562.5 cm-1 and C=N vibrations at
Conclusions
Series of 2-substituted-aminomethyl-8-phenyl-pyrazolo[3,4-d]
[1,3,4]thiadiazolo[3,2-a] pyrimidin-4(1H)-ones 5a-h have
been synthesized by treating 2-chloromethyl-8-phenyl-
pyrazolo[3,4-d][1,3,4]thiadiazolo[3,2-a]pyrimidin-4(1H)-one
4 with various nucleophiles. The chloromethyl derivative
1519.32 cm-1, and –CH2–Cl vibrations at 1238.70 cm-1
.
The appearance of characteristic –CH2–Cl vibrations and
disappearance of NH2 peak indicated the formation of
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Med Chem Res (2012) 21:2458–2464
2461
Table 1 Antibacterial activity of preparation of 8-phenyl-2-substituted-aminomethyl- pyrazolo[3,4-d][1,3,4]thiadiazolo[3,2-a]pyrimidin-4(1H)-
ones 5a–h
Compounds
Klebsiella Gram (-ve)
E.coli Gram (-ve)
S. aureus Gram (?ve)
B. subtilis Gram (?ve)
5a
11.5 0.500
12 1.414
11 1.414
10.5 0.707
11 1.414
8.5 0.707
09 1.414
10.5 0.707
9.5 0.707
11.5 0.707
18.5 0.707
13.5 0.707
18.5 0.505
17.5 0.707
20 1.421
6.5 0.707
16 1.440
5b
5c
11.5 0.707
13 1.414
20.5 0.707
18.5 0.407
07 1.414
5d
5e
14.5 1.414
12.5 0.707
12 1.414
7.5 0.707
14.5 0.707
16.5 0.707
15.5 0.707
22.5 0.707
5f
14.0 1.414
17.0 1.414
15.5 0.707
23.3 2.001
5g
5h
14.0 1.425
24.5 0.707
Ampicillin
was prepared by treating 2-amino-3-mercapto pyrazolo[3,4-
d]pyrimidine 3 with one carbon donor, chloroacetic acid.
The intermediate 2-amino-3-mercapto pyrazolo[3,4-d]
pyrimidine 3 was prepared by a novel, eco-friendly route
starting from 2-amino-3-carbethoxy-1-phenyl-pyrazole 1.
All the tested compounds were found to possess activity
against all the microorganisms (broad-spectrum activity)
with potency lesser than the standard drug. This observa-
tion indicates that further lead optimization is necessary to
get compounds with better antibacterial activity. The
efforts are in progress toward reaching the goal.
(6.3 mL, 25 mmol) was added drop wise under cooling in
an ice bath. Stirring was continued for 1.5 h. Then, the
reaction mixture was poured into ice-cold water mixture.
The precipitate obtained was filtered and dried. The residue
was sticky semisolid and was triturated with petroleum
ether several times until the compound became free flow-
ing. The free flowing solid was recrystallised from boiling
ethanol to give white needle like compound.
Yield 50%, mp: 152–154°C; IR (KBr) mmax 3388 (–N–
H), 3182 (C–H aromatic), 1642 (C=O), 1552 (C=N), 748
1
(=C–H oop) cm-1. H NMR (CDCl3) d: 8.18 (s, 1H), 7.91
(m, 2H), 7.52 (m, 2H), 7.42 (m, 1H), 4.26 (t, J = 4.12 Hz,
2H), 2.67 (s, 3H), 1.78 (q, J = 4.14 Hz, 3H). MS m/z: 275
(M?). Anal. Calc. for C14H15N3O2S2: C, 52.33; H, 4.67; N,
13.08. Found: C, 52.55; H, 4.78; N, 13.10.
Experimental
General techniques
Synthesis of 5-amino 6-mercapto-1-phenyl-pyrazolo[3,4-
d]pyrimidine-4[3H]-one 3
Analytical TLC was performed on silica gel F254 plates
(Merck) with visualization by UV or iodine vapors. Melt-
ing points were determined in open capillaries on a Gal-
lenkemp melting point apparatus and are uncorrected. The
IR spectra (KBr, vMax, cm-1) were run on Perkin Elmer
FTIR spectrophotometer. 1H-NMR (d ppm CDCl3/DMSO-
d6) spectra were recorded using AMX-400 with TMS as
internal standard. MS spectra were recorded on Autospec.
Elemental analyses were performed on Carlo Erba 1108
analyzer and were within 0.4% of theoretical values. All
the chemicals used were of analytical grade.
Solution of methyl-N-[4-carbethoxy-1-phenyl-pyrazolyl]
dithiocarbamate 2 (2 g, 10 mmol) in ethanol (10 mL) was
treated with hydrazine hydrate (99%) (1.2 g/3.0 mL,
100 mmol) and heated to reflux on water bath until the
methyl mercaptan evolution ceased (8 h). The solution was
immediately filtered under hot condition. The solid obtained
was collected, dried, and recrystallised from boiling ethanol.
Yield 50%, mp: 259–260°C; IR (KBr) mmax 3333, 3204
(–NH2), 2957 (C–H aromatic), 1655 (–C=O), 1581 (C=C,
aromatic), 754 (=C–H oop) cm-1. 1H NMR (CDCl3) d: 8.14
(s, 1H), 8.02 (d, J = 4.06 Hz, 2H), 7.48 (t, J = 4.06 Hz,
2H), 7.30 (t, J = 4.06 Hz, 1H), 4.96 (s, 2H), 4.20 (s, 1H). MS
m/z: 259 (M?). Anal. Calc. for C11H9N5OS: C, 50.96; H,
3.47; N, 27.02. Found: C, 51.08; H, 3.75; N, 27.04.
Chemistry
Synthesis of methyl-n-[4-carbethoxy-1-phenyl-
pyrazolyl]dithiocarbamate 2
To a vigorously stirred solution of 5-amino-4-carbethoxy-
1-phenyl-pyrazole 1 (2 g, 20 mmol) in dimethylsulphoxide
(20 mL), carbon disulfide (3.2 mL, 26 mmol) and aqueous
sodium hydroxide (3 mL, 20 mmol) was added drop wise
at room temperature. After 2.5 h stirring, dimethylsulfate
Synthesis of 2-chloromethyl-8-phenyl-pyrazolo
[3,4-d][1,3,4]thiadiazolo[3,2-a]pyrimidin-4(1H)-one 4
Fusion of 5-amino 6-mercapto-1-phenyl-pyrazolo[3,4-d]
pyrimidine-4[3H]-one 3 (1 g, 10 mmol) with chloro acetic
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Med Chem Res (2012) 21:2458–2464
2-[{(Hexyl)amino}methyl]-8-phenyl-pyrazolo[3,4-d][1,3,4]
thiadiazolo[3,2-a]pyrimidin-4(1H)-one (5c) Yield 72%,
mp: 252–254°C; IR (KBr) mmax 3088 (C–H aromatic), 2918
(–C–H stretch), 1562 (–C=O), 1509 (C=N), 815 (aromatic
C–H oop), 705 (–C–S) cm-1. 1H NMR (CDCl3) d: 8.37 (s,
1H), 8.23 (s, 1H), 7.96 (d, J = 4.02 Hz, 2H), 7.52 (t,
J = 4.02 Hz, 2H), 7.37 (t, J = 4.04 Hz, 1H), 4.79 (s, 2H),
4.66 (t, J = 5.42 Hz, 2H), 2.24 (m, 11H). MS m/z: 382
(M?). Anal. Calc. for C19H22N6OS: C, 59.68; H, 5.75; N,
21.98. Found: C, 59.75; H, 5.96; N, 22.02.
acid (0.070 g, 10 mmol) was carried out in presence of
concentrated sulfuric acid by heating the mixture on a
water bath for 5 h. The reaction mixture was cooled and
poured into ice water. The resultant precipitate was filtered
and dried. The compound was purified using column
chromatography by gradient elution technique using chlo-
roform and ethyl acetate as solvent system, the extract was
subjected to rotary flash evaporator, and the pure com-
pound was isolated.
Yield 75%, mp: 220–221°C; IR (KBr) mmax 3174 (C–H
aromatic), 2931(–C–H stretch), 1562 (–C=O), 1519 (C=N),
1238 (–CH2Cl), 818 (aromatic C–H oop), 710 (–C–S)
.
cm-1 1H NMR (CDCl3) d: 8.4 (s, 1H), 8.03 (d, J =
4.16 Hz, 2H), 7.54 (t, J = 4.16, 2H), 7.40 (t, J = 4.26,
1H), 4.92 (s, 2H). MS m/z: 317 (M?). Anal. Calc. for
C13H8N5OSCl: C, 49.21; H, 2.52; N, 22.08. Found: C,
49.45; H, 2.70; N, 22.12.
2-[{(Furfuryl)amino}methyl]-8-phenyl-pyrazolo[3,4-d][1,3,4]
thiadiazolo[3,2-a] pyrimidin-4(1H)-one (5d) Yield 78%,
mp: 228–230°C; IR (KBr) mmax 3075 (C–H aromatic), 2922
(–C–H stretch), 1570 (C=O), 1509 (C=N), 744 (aromatic
C–H oop), 705 (–C–S) cm-1. 1H NMR (CDCl3) d: 8.36 (s,
1H), 8.22 (s, 1H), 7.95 (m, 3H), 7.50 (m, 3H), 7.35 (s, 2H),
4.79 (s, 2H), 4.65 (s, 2H). MS m/z: 378 (M?). Anal. Calc.
for C18H14N6O2S: C, 57.14; H, 3.70; N, 22.22. Found: C,
57.28; H, 3.88; N, 22.25.
General procedure for the synthesis of 2-alkyl/aryl/
hetroarylaminomethyl-8-phenyl-pyrazolo[3,4-d]
[1,3,4]thiadiazolo[3,2-a]pyrimidin-4(1H)-ones 5a–h
2-[(Morpholino)methyl]-8-phenyl-pyrazolo[3,4-d][1,3,4]
thiadiazolo[3,2-a]pyrimidin-4(1H)-one (5e) Yield 65%,
mp: 245–246°C; IR (KBr) mmax 3074 (C–H aromatic), 2978
(–C–H stretch), 1591 (C=O), 1504 (C=N), 746 (aromatic
C–H oop), 709 (–C–S) cm-1. 1H NMR (CDCl3) d: 8.26 (s,
1H), 8.24 (m, 1H), 7.97 (m, 2H), 7.52 (m, 2H), 4.78 (s,
2H), 4.15 (d, J = 6.72 Hz, 4H), 3.24 (d, J = 6.74 Hz, 4H).
MS m/z: 368 (M?). Anal. Calc. for C17H16N6O2S: C,
55.43; H, 4.34; N, 22.82. Found: C, 55.65; H, 4.62; N,
22.86.
A mixture of 8-phenyl-2-chloromethyl-pyrazolo[3,4-d][1,3,4]
thiadiazolo[3,2-a] pyrimidin-4(1H)-one 4 (3.17 g, 10 mmol),
triethylamine (1.01 mL, 12 mmol), and various amine
(12 mmol) in dioxan was heated to reflux for 8 h. Then, the
reaction mixture was cooled to room temperature and poured
into ice-water mixture, and the excess amine was neutralized
by dilute hydrochloric acid (10%). The resultant precipitate
thus obtained was filtered, dried, and recrystallised from
benzene.
2-[{(Phenyl)amino}methyl]-8-phenyl-pyrazolo[3,4-d][1,3,4]
thiadiazolo[3,2-a] pyrimidin-4(1H)-one (5f) Yield 62%,
mp: 233–234°C; IR (KBr) mmax 3355 (=C–H aromatic),
3204 (–NH– stretch), 2929 (–CH stretch), 1664 (–NH
bend), 1559 (C=O), 1504 (C=N), 817 (aromatic –CH oop)
2-[{(Methyl)amino}methyl]-8-phenyl-pyrazolo[3,4-d][1,3,4]
thiadiazolo[3,2-a] pyrimidin-4(1H)-one (5a) Yield 70%,
mp: 269–271°C; IR (KBr) mmax 3059 (C–H aromatic), 2926
(–C–H stretch), 1582 (–C=O), 1502 (C=N), 800 (aromatic
C–H oop), 704 (–C–S) cm-1. 1H NMR (CDCl3) d: 8.37 (s,
1H), 8.22 (s, 1H), 7.96 (d, J = 4.56 Hz, 2H), 7.50 (t,
J = 4.56 Hz, 2H), 7.37 (t, J = 4.56 Hz, 1H), 4.78 (s, 2H),
2.37 (s, 3H). MS m/z: 312 (M?). Anal. Calc. for
C14H12N6OS: C, 53.84; H, 3.84; N, 26.92. Found: C, 54.12;
H, 4.10; N, 26.95.
cm-1 1H NMR (CDCl3) d: 8.39 (s, 1H), 8.00 (d,
.
J = 4.25 Hz, 2H), 7.50 (t, J = 4.25 Hz, 2H), 7.34 (t,
J = 4.25 Hz, 1H), 7.12 (t, J = 7.10 Hz, 2H), 6.68 (d,
J = 6.95 Hz, 1H), 6.51(d, J = 7.05 Hz, 2H), 4.74 (d,
J = 6.72 Hz, 2H), 4.55 (t, J = 6.72 Hz, 1H). MS m/z: 374
(M?). Anal. Calc. for C19 H14 N6OS: C, 60.96; H, 3.74; N,
22.45. Found: C, 61.18; H, 3.86; N, 22.45.
2-[{(Ethyl)amino}methyl]-8-phenyl-pyrazolo[3,4-d][1,3,4]
thiadiazolo[3,2-a]pyrimidin-4(1H)-one (5b) Yield 75%,
mp: 238–240°C; IR (KBr) mmax 3059 (C–H aromatic), 2926
(–C–H stretch), 1582 (–C=O), 1502 (C=N), 800 (aromatic
C–H oop), 704 (–C–S) cm-1. 1H NMR (CDCl3) d: 8.38 (s,
1H), 8.23 (s, 1H), 7.96 (d, J = 4.12 Hz, 2H), 7.52 (m, 2H),
7.37 (t, J = 4.14 Hz 1H), 4.79 (s, 2H), 4.66 (q,
J = 5.02 Hz, 2H), 2.18 (t, J = 5.06 Hz, 3H). MS m/z: 326
(M?). Anal. Calc. for C15H14N6OS: C, 55.21; H, 4.29; N,
25.76. Found: C, 55.48; H, 4.62; N, 25.76.
2-[{(m-Tolyl)amino}methyl]-8-phenyl-pyrazolo[3,4-d][1,3,4]
thiadiazolo[3,2-a] pyrimidin-4(1H)-one (5g) Yield 70%,
mp: 240–242°C; IR (KBr) mmax 3378 (=C–H aromatic),
3081 (–NH– stretch), 2962 (–C–H stretch), 1684 (–NH
1
bend), 1590 (C=O), 1504 (C=N) cm-1. H NMR (CDCl3)
d: 8.39 (s, 1H), 8.03 (d, J = 4.72 Hz, 2H), 7.50 (t,
J = 4.72 Hz, 2H), 7.36 (t, J = 4.72 Hz, 1H), 7.24 (t,
J = 5.02 Hz, 2H), 6.74 (d, J = 5.02 Hz, 2H), 4.72 (d,
123

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Acknowledgments Dr. M. Raghu Prasad is thankful to All India
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