Microwave assisted synthesis and
antifungal studies of 5-amino thiadiazole substituted
pyrimidine compounds
Karthic R1*,
Andrews B2, Subramani K1
1PG & Research
Department of Chemistry, Islamiah College,
Vaniyambadi-635751, India
(Affiliated to Thiruvalluvar University, Vellore, Tamil Nadu, India)
2Department of
Chemistry, Priyadarshini Engineering College, Vaniyambadi, India
(Affiliated to Anna
University, Chennai, Tamil Nadu, India)
*Corresponding Author E-mail: karthicrm@gmail.com
ABSTRACT:
Simple synthetic methods of
5-(5-amino-1,3,4-thiadiazol-2yl)-3,4-dihydro-6-methyl-4-phenylpyrimidin-2(1H)-thione
(3f-j) are described. Compound 1 is converted to carbothiamide 2 by reacting compound 1 with thiosemicarbazide in catalytic amount of acetone is
irradiated with help of domestic microwave oven (200W) for 2 minutes.
Compound 2 is act as a key intermediate for the final compounds. The
compound 2 is converted to corresponding thiadiazole
3 by treatment with conc.H2SO4 and NH3.
Structural elucidation is accomplished by IR, 1H and 13CNMR,
Elemental analysis and GC-Mass spectral data of the synthesized compounds. Few
of these Pyrimidine derivatives have been evaluated
for their possible antifungal activity. Most of the tested compounds show
significant antifungal activity.
KEYWORDS: Pyrimidine, thiadiazole, carbothiamide, thiosemicarbazide,
antifungal activity.
Literature survey has revealed
the importance of pyrimidine derivatives and
antimicrobial agent1, which are found to be associated with variety
of biological activities such as insecticidal, antimicrobial, antiviral etc, pyrimidine derivatives2-8 are powerful C-C bond
formation process has wide applications for the preparation of diverse amino
alkyl derivatives. It involves the condensation of a compound capable of
supplying one or more active hydrogen atom with aldehyde
and primary or secondary amine. Mannich bases
are physiologically reactive because of the basic function rendering the
molecule soluble in aqueous solvent when it is transformed into ammonium salt.
Several medicinally useful Mannich bases have been reviewed by Tromontini
and Angiolini9. Besides this, considerable work has been reported on
synthesis and pharmacological activities of various Mannich
bases for analogies, antispasmodic, anesthetic and antimalarial
as well as intermediates in drug synthesis. Antiviral properties of
certain thiourea and urea derivatives have been
reported in which the antiviral effect is attributed to the presence of an
intact NH-(C=S)-NH and NH-(C=O)-NH grouping10. In this
direction the synthesis and pharmacological study of Mannich
bases of 3-and 5-mercapto derivatives of 1,3,4-thiadiazole have been reported
in literature11-16. Further, pyrimidine,
fused heterocyclic pyrimidine derivatives and dihydropyrimidones are well known for their potential
biological activity such as antiviral, antitumor, antimicrobial fungicide,
algaecide and as antibiotics17-26. Moreover, the presences
of different interacted functional groups determine their great synthetic
potential. In continuation of this work, herein is reported that the synthesis
and in vitro study of antibacterial activity of heterocyclic N-Mannich bases of 5-(5-amino-1,3,4-thiadiazol-2yl)-3,4-dihydro-6-methyl-4-phenylpyrimidin-2(1H)-thione
(3f-j) against the species of Candida tropicalis, Aspergillus terreus and Penicillium sps. Amphotericin-B
is
used as standard drug. For this purpose, heterocyclic precursors DHPMs
(1f-j) are synthesized by microwave irradiation of aromatic aldehydes,
ethylacetoacetate and thiourea
according to the literature procedure27,28. Subsequently, these
DHPMs are used to synthesis compounds (2f-j). All the synthesized
compounds are characterized by using elemental analysis, mass spectra, 1H&
13CNMR spectral studies.
MATERIALS AND METHODS:
Melting points are determined
using open capillary method and are uncorrected. The compounds are checked for
homogeneity by TLC on silica gel-G. The IR spectra are recorded on FT-IR
Thermo Nicolet Avatar 370 spectrophotometer using KBr
disc method. The 1H and 13C-NMR are recorded on Bruker Avance-III 400MHz FTNMR
spectrometer using DMSO-d6. Elemental analyses are
recorded on Elemental Vario EL III instrument.
The mass spectrums are recorded on Joel GC-mate spectrometer. All compounds
given satisfactory micro analytical results. Pyrimidine
(1) is prepared by reported method27.
GENERAL PROCEDURE:
Synthesis of 5-(hydrazine
carbothioamide)-3,4-dihydro-6-methyl-4-phenylpyrimidin-2(1H)-thione
(2f). An equimolar mixture of compound1 (0.01mol)
and thiosemicarbazide (0.01mol) with catalytic amount
of acetone is irradiated in a domestic microwave oven (200W) for 2 minutes. The
reaction mixture is allowed to cool and the obtained solid is recrystallized from ethanol. The compounds prepared in this
manner (2f-j) are listed in Table 1. Melting point of the compound is 1430C,
yield 65%. 1HNMR (400MHz, DMSO-d6)
δ2.292(s,3H,CH3), 5.176(J= 3.6Hz,d,1H,CH), 6.681(s,2H,NH2),
7.211-7.366(m,5H,Ar-H), 7.981 (J=4Hz,d,2H,NHx2), 9.887 (J=1.2Hz,d,1H,NH),
10.308(s,1H,NH). 13CNMR(400MHz,DMSO-d6)
δ17.47, 59.54, 100.75, 126.35, 127.62, 128.50, 143.47, 144.95,
165.10, 178.47, 183.94. FT-IR(KBr) 3328, 3172, 3106
(NH), 2999(Ar-H), 2936(CH), 1669(C=O), 1573(C=N),
1327(C-N), 1283(C=S), 1117(N-N)cm-1. GCMS:m/z
[321M+].
General procedure for
Synthesis of
5-(5-amino-1,3,4-thiadiazole-2-yl)-3,4-dihydro-6-methyl-4-phenylpyrimidin-2(1H)-thione
3f. The
compound 2 (0.01mol) is dissolved with cooling in 4ml conc.H2SO4
and kept at room temperature for overnight, stirred it occasionally and then
poured onto crushed ice then resulting suspension is kept in ammonical solution for 2hrs, filtered and recrystallized from ethanol as white crystals. The
compounds prepared (3f-j) are listed in Table 2. Melting point 1850C,
Yield 75%. 1HNMR(400MHz,DMSO-d6)
δ2.301
(s,3H,CH3), 4.030(s,2H,NH2), 5.189(J=4Hz,d,1H,CH),
7.222-7.372(m,4H,Ar-H), 9.634(J=1.6 Hz,d,1H,NH), 9.074(s,1H,NH). 13CNMR(400MHz,DMSO-d6)
δ17.12, 59.57, 100.75, 126.35, 127.65, 128.51, 143.44, 144.95, 165.12,
174.23. FT-IR(KBr) 3328, 3174, 3106(NH), 3033(Ar-H), 2979(CH), 1574(C=N), 1384(C-N), 1282(C=S),
1195(C-S), 1001(N-N)cm-1. GCMS:m/z
[303M+].
Synthesis of
5-(5-amino-1,3,4-thiadiazole-2-yl)-4-(4-chlorophenyl)-3,4-dihydro-6-methyl
pyrimidin-2(1H)-thione 3g.1HNMR(400MHz,DMSO-d6)
δ2.301(s,3H,CH3), 4.027(s,2H,NH2), 5.179(J=3.6Hz,
d,1H,CH), 7.227-7.254(dd,2H,Ar-H), 7.419-7.440(dd,2H,Ar-H), 9.653(J=2Hz,
d,1H,NH), 10.369(s,1H,NH). 13CNMR(400MHz,DMSO-d6)
δ17.14, 59.62, 100.30, 128.28, 128.54, 132.24, 142.34, 145.32, 164.97,
174.24. FT-IR(KBr) 3327, 3174, 3104(NH), 3030(Ar-H), 2982(CH), 1573(C=N), 1380(C-N), 1281(C=S),
1196(C-S), 1092(N-N)cm-1. GCMS:m/z
[337M+].
Synthesis of
5-(5-amino-1,3,4-thiadiazole-2-yl)-4-(4-(dimethylamino)phenyl)-3,4-dihydro-6-methyl
pyrimidin-2(1H)-thione 3h. 1HNMR(400MHz,DMSO-d6)
δ2.284(s,3H,CH3), 2.864(s,6H,N(CH3)2),
4.018(s,2H,NH2), 5.059(J=2.8Hz,d,1H,CH), 6.671(J=9.2
Hz,d,2H,Ar-H), 7.024(J=8.8Hz,d,2H,Ar-H), 9.515(J=3.2 Hz,d,1H,NH),
10.202(s,1H,NH). 13CNMR(400MHz, DMSO-d6)
δ17.07, 53.48, 59.43, 101.25, 112.16, 127.08, 131.18, 144.24, 149.93,
165.25,173.84. FT-IR(KBr) 3326, 3164(NH), 2982(Ar-H), 2882(CH), 1593(C=N), 1360(C-N), 1281(C=S),
1191(C-S), 1100(N-N)cm-1. GCMS:m/z
[346M+].
Synthesis of
5-(5-amino-1,3,4-thiadiazole-2-yl)-4-(3-nitrophenyl)-3,4-dihydro-6-methyl
pyrimidin-2(1H)-thione 3i. 1HNMR(400MHz,DMSO-d6)
δ2.301(s,3H,CH3), 4.027(s,2H,NH2), 5.342(J=2.8Hz,d,
1H,CH), 7.236(J=8.4Hz,d,2H,Ar-H), 7.429(J=8.4Hz, d,2H,Ar-H),
7.682-7.856 (dd,2H,Ar-H), 8.165(J=2.4Hz, d,1H,NH), 9.655(s,1H,NH). 13CNMR(400MHz,DMSO-d6)δ17.83,
59.35, 99.35, 123.87, 130.07, 133.04, 134.40, 136.16, 149.38, 151.06, 165.83,
178.39. FT-IR(KBr) 3424, 3326, 3176(NH), 3016(Ar-H), 2986(CH), 1593(C=N), 1343(C-N), 1296(C=S),
1193(C-S), 1102(N-N)cm-1. GCMS: m/z [348M+].
Synthesis of
5-(5-amino-1,3,4-thiadiazole-2-yl)-4-(4-hydroxyphenyl)-3,4-dihydro-6-methyl
pyrimidin-2(1H)-thione 3j. 1HNMR(400MHz,DMSO-d6)
δ2.229(s,3H,CH3), 4.014(s,2H,NH2), 5.075(J=8.4Hz,d,
1H,CH), 7.386-8.051(m,4H,Ar-H), 8.562(J=5.2Hz,d, 1H,NH), 10.224(s,1H,
NH), 11.221(s,1H,OH). 13CNMR(400MHz,DMSO-d6)
δ17.06, 59.32, 90.20, 115.11, 115.51, 125.42, 127.86, 129.00, 134.36,
152.51, 164.92. FT-IR(KBr) 3545, 3187, 3134(NH),
3080(Ar-H), 2980(CH), 1511(C=N), 1329(C-N),
1285(C=S), 1186(C-S), 1113(N-N)cm-1. GCMS:m/z
[319M+].
RESULTS AND DISCUSSION:
Compounds (3f-j) are
synthesized as per the scheme 1 and 2. The compound 3f is prepared by
reacting hydrazine carbothioamide compound 2f
with conc.H2SO4 and NH3. Hydrazine carbothioamide compound 2f is synthesized by
reacting pyrimidine ethyl ester 1 with thiosemicarbazide is irradiated in a domestic microwave
oven (200W) for 2 minutes29. The reaction mixture is allowed to cool
and the obtained solid is recrystallized from
ethanol.
The pyrimidine
ethyl ester compound 1f prepared by a mixture of aromatic aldehyde (0.01mol), ethylacetoacetate
(0.01mol) and urea (0.01mol) is mixed thoroughly with 0.15 mole of tin (II)
chloride as catalyst in a conical flask. The content of the flask is irradiated
in a domestic microwave oven (400W) for 6 minutes. The completion of the reaction
is monitored by TLC.
The structures of the
synthesized compounds are confirmed by IR, 1H and 13C-NMR,
GC-MS and CHN analysis. Formation of compound 2f is confirmed by
the presence of N-H stretching peaks at 3328, 3172 cm-1 and
3106 cm-1 and C=S stretching peaks at 1669 cm-1 in IR and
singlet at 6.68 for NH2
group in 1HNMR spectra.
Treatment of compound 2f with
conc.H2SO4 and NH3, furnished
5-(5-amino-1,3,4-thiadiazol-2-yl)-3,4-dihydro-6-methyl-4-phenylpyrimidin-2(1H)-one(3f-j).
The structure of 3f is elucidated on the basis of C-S linkage in the thiadiazole ring, which causes sharp absorption band at
1195 cm-1 in its IR spectrum. 1HNMR spectrum shows a
singlet at δ4.03 due to NH2 functional group of 3f.
The IR spectral data reveals
the carbonyl absorption band at 1282 cm-1 of NH-CS-NH group, N-N
stretching band at1001 cm-1 aliphatic C-H and aromatic C-H
stretching at 2979 cm-1 and 3033 cm‑1 group of pyrimidine moiety 3f. Mass spectrum also supported
the proposed structure by viewing molecular ion peak at m/z 303 M+.
Table 1: Physical and
analytical data of compounds (2f-j)
|
Compd. |
Mol. Formula |
R |
R1 |
X |
Mol. Wt |
Yield (%) |
m.p (0C) |
Calcd. /Found (%) |
||||
|
C |
N |
H |
S |
|||||||||
|
2f |
C13H15N5OS2 |
H |
H |
S |
321 |
65 |
143 |
48.63 (48.46 |
21.80 21.97 |
4.70 4.55 |
19.91 20.10) |
|
|
2g |
C13H14N5OS2Cl |
N(CH3)2 |
H |
S |
355 |
72 |
110 |
43.90 (43.41 |
19.72 19.42 |
3.97 4.09 |
18.00 18.06) |
|
|
2h |
C15H20N6OS2 |
Cl |
H |
S |
364 |
75 |
148 |
49.47 (49.00 |
23.08 23.26 |
5.49 5.22 |
17.56 17.69) |
|
|
2i |
C13H14N6O3S2 |
H |
NO2 |
S |
366 |
70 |
125 |
42.65 (42.59 |
22.95 23.00 |
3.85 3.54 |
17.46 17.72) |
|
|
2j |
C13H15N5O2S2 |
OH |
H |
S |
337 |
78 |
118 |
46.32 (46.53 |
20.77 21.03 |
4.47 4.70 |
18.96 19.06) |
|
Table 2: Physical and
analytical data of compounds (3f-j)
|
Compd. |
Mol. Formula |
R |
R1 |
X |
Mol. Wt |
Yield (%) |
m.p (0C) |
Calcd. /Found (%) |
|||
|
C |
N |
H |
S |
||||||||
|
3f |
C13H13N5S2 |
H |
H |
S |
303 |
75 |
185 |
51.52 (51.45 |
23.10 23.95 |
4.32 4.35 |
21.09 21.15) |
|
3g |
C15H18N6S2 |
N(CH3)2 |
H |
S |
346 |
85 |
188 |
52.05 (52.44 |
24.28 24.84 |
5.24 5.39 |
18.47 18.54) |
|
3h |
C13H12N5S2Cl |
Cl |
H |
S |
337 |
70 |
161 |
46.32 (46.15 |
20.77 20.44 |
3.58 3.31 |
18.97 18.40) |
|
3i |
C13H12N6O2S2 |
H |
NO2 |
S |
348 |
72 |
150 |
44.86 (44.64 |
24.14 24.57 |
3.47 3.51 |
18.37 18.39) |
|
3j |
C13H13N5OS2 |
OH |
H |
S |
319 |
82 |
130 |
48.93 (48.53 |
22.06 22.50 |
4.10 4.01 |
20.04 20.28) |
Antifungal studies
Among the newly synthesized pyrimidine derivatives are screened for their antifungal
activity in vitro against the species of Candida tropicalis, Aspergillus terreus and Penicillium sps using agar well disk diffusion method. The
test compounds are dissolved in DMSO to get a solution of 50µg/ml
concentration. The inhibition zones are measured in millimeters at the end of
an incubation period of 18 hrs at 370C. Amphotericin-B
is used as a standard and the results are shown in Table 3. Most of the
tested compounds show moderate to good inhibition.
Table 3: Antifungal activities
of compounds (3f-j)
|
Compd. |
Candida tropicalis |
Aspergillus terreus |
Penicillium sps |
|
Control |
0 |
0 |
0 |
|
3f |
10 |
26 |
8 |
|
3g |
9 |
13 |
10 |
|
3h |
8 |
12 |
5 |
|
3i |
7 |
5 |
- |
|
3j |
6 |
9 |
8 |
CONCLUSION:
The investigation of
antifungal screening data reveals that, all the tested compounds show moderate
to good inhibition at 50µg/ml concentration. Especially the compound 3f, 3g and
3h shows very good activity than the others. However the activity of compounds
3f, 3g and 3h against the Aspergillus terreus inhibition is more compared to the standard drug.
ACKNOWLEDGEMENT:
The authors are thankful to
Principal and Research Department of chemistry, Islamiah
College, Vaniyambadi, Vellore district, Tamilnadu for constant encouragement and providing
necessary facilities.
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Received on
21.01.2017 Modified on
05.02.2017
Accepted on
21.02.2017 © AJRC All right
reserved
Asian J. Research Chem. 2017;
10(2):119-123.
DOI:
10.5958/0974-4150.2017.00018.9