Synthesis of 2-sulfanyl-6-methyl-1,4-dihydropyrimidines as a new class of antifilarial agents

Article abstract of DOI:10.1016/j.ejmech.2008.01.038

A series of 2-sulfanyl-6-methyl-1,4-dihydropyrimidines (8-21) were synthesized in good yields by alkylation of 5-methyl-6-phenyl-2-thioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid ethyl esters (2-7) with different alkyl or aralkyl halides in the pres

Full text of DOI:10.1016/j.ejmech.2008.01.038

Available online at www.sciencedirect.com
European Journal of Medicinal Chemistry 43 (2008) 2717e2723
http://www.elsevier.com/locate/ejmech
Original article
Synthesis of 2-sulfanyl-6-methyl-1,4-dihydropyrimidines
as a new class of antifilarial agents
B.K. Singh a, Mridul Mishra a, Nisha Saxena a, G.P. Yadav b, P.R. Maulik b,
a,
c,**
, R.P. Tripathi
*
M.K. Sahoo c, R.L. Gaur c, P.K. Murthy
a Medicinal and Process Chemistry Division, Central Drug Research Institute, Lucknow 226001, Uttar Pradesh, India
b Molecular and Structural Biology Division, Central Drug Research Institute, Lucknow 226001, Uttar Pradesh, India
c Parasitology Division, Central Drug Research Institute, Lucknow 226001, Uttar Pradesh, India
Received 19 October 2007; received in revised form 10 January 2008; accepted 18 January 2008
Available online 8 February 2008
Abstract
A series of 2-sulfanyl-6-methyl-1,4-dihydropyrimidines (8e21) were synthesized in good yields by alkylation of 5-methyl-6-phenyl-2-thi-
oxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid ethyl esters (2e7) with different alkyl or aralkyl halides in the presence of a combination
of anhydrous K2CO3 and catalytic amount of tetrabutyl ammonium bromide. The title compounds were evaluated for their antifilarial activity
against adult parasites of human lymphatic filarial parasite Brugia malayi (sub-periodic strain) in vitro and in vivo at various concentrations. One
of the compounds (18) showed promising antifilarial activity.
Ó 2008 Elsevier Masson SAS. All rights reserved.
Keywords: Dihydropyrimidines; 1,4-Dihydropyrimidines; Antifilarial; Brugia malayi; Tetrabutyl ammonium bromide
1. Introduction
morbidity and consequently the World Health Assembly has
adopted a resolution on the global elimination of lymphatic
filariasis as a public health problem [4e6].
Current global estimates suggest that around 80 countries
are endemic for lymphatic filariasis (LF) [1,2]. Of the three
parasites causing LF, Wuchereria bancrofti accounts for over
90% of the global burden. Brugia malayi is limited to Asia
and Brugia timori to a few islands in Indonesia. It has been
estimated that 1.1 billion people living in areas endemic for
this disease are exposed to the risk of infection, and that there
are about 120 million cases with either disease or infection
(microfilaria carriers) [3]. An estimated population of 22 mil-
lion is known to be the host for circulating microfilaria and 16
million people suffer from filarial manifestations like elephan-
tiasis of limbs, genitals and hydrocele. Low priority was given
to this disease, although it is responsible for significant
The available control strategies have significant limitations
as current drugs are principally microfilaricidal and require
annual repeated treatment for a number of years, thus there
is still a need for the development of a macrofilaricidal agent
or drug combination for the curative treatment or sustained
suppression of the microfilariae [7e10]. Drug resistance to
ivermectin appears to be another issue of concern, especially
in areas where diethylcarbamazine (DEC) cannot be given.
Besides, research is required on the progression and reversibil-
ity of disease manifestations.
A number of molecules from heterocycles are known as
good antifilarials [11]. Benzimidazoles [12] and triazines
[13,14] have recently been shown to possess very good antifi-
larial activity. In spite of tremendous medicinal chemistry in
dihydropyrimidines [15] and their derivatives only scanty
reports exist for their antifilarial activity. In recent years inter-
esting dihydropyrimidines are being looked as an important
class of molecules since many of them are clinical candidates
* Corresponding author. Tel.: þ91 522 2612412; fax: þ91 522 2623405/
2623938.
** Corresponding author.
E-mail addresses: drpkmurthy@gmail.com, drpkmurthy@yahoo.com (P.K.
Murthy), rpt.cdri@gmail.com, rpt.cdri@yahoo.co.in, rp_tripathi@cdri.res.in
(R.P. Tripathi).
0223-5234/$ - see front matter Ó 2008 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2008.01.038

2718
B.K. Singh et al. / European Journal of Medicinal Chemistry 43 (2008) 2717e2723
for different diseases [16e18]. S-DABO (Fig. 1) and many
other analogues have recently been shown to possess anti-
HIV activities [19,20]. We have recently shown that dihydro-
pyrimidinones show interesting antiparasitic activities [21]
via inhibition of crucial enzymes of parasite biochemistry.
Herein we have synthesized 2-sulfanyl-6-methyl-1,4-dihydro-
pyrimidines and evaluated them for the first time for their anti-
filarial activity both in vitro and in vivo. The method of
synthesis is simple and efficient and does not involve any
special apparatus or reagents.
signal H-4 was observed at around d 6.50 as singlet in all the
products. Further, the structure of one of such prototype (com-
pound 12) is established by X-ray crystallographic data
(Fig. 3). Interestingly out of the two enantiomers of dihydro-
pyridine 12 only one enantiomer crystallizes out and the other
remains in solution. Such a crystallization of single enantio-
mer from a racemic mixture has been reported earlier by dif-
ferent workers involving a process known as ‘‘chiral amnesia’’
[23e25].
Compounds 8e20 synthesized were evaluated in vitro for
their macrofilaricidal activity against B. malayi according to
the method of Murthy and Chatterjee [26]. Micro- and macro-
filaricidal activities were evaluated following the methods
described by Lammler and Wolf [27], Chatterjee et al. [28]
and Gaur et al. [29].
As evident from Table 2 compounds 8, 10e12, 14, 15, 18
and 19 resulted in complete loss of motility of adult worms
of B. malayi at 100 mM concentrations and they have shown
15.4e68.61% inhibition in MTT reduction assays while com-
pound 19 did not show any inhibition in MTT reduction assay.
Of these, three compounds (10, 15 and 18) affected both mo-
tility (irreversible loss) and MTT reduction (w50% inhibition
or more) and compounds 8, 11, 12, 14 and 19 either affected
motility with <50% MTT reduction or only motility. Further,
the compounds showing MTT reduction to the level of around
50% were screened at lower concentration also. Compound 10
at 50 mM concentration resulted in complete loss of motility of
filarial worms with no inhibition in MTT reduction assay,
while at 25 mM concentration it showed only sluggish motility
of filarial worm and displayed approximately 30% inhibition
in MTT reduction assay. Compound 15 on the other hand
displayed complete loss of motility in filarial worms at
50 mM concentration with 19% inhibition in MTT reduction
assay. Compounds 17 and 19 were not effective at lower con-
centrations. The best compound of the series was found to be
compound 18 which resulted in complete loss of motility at
two lower concentrations (50 and 25 mM) screened and good
inhibition (around 70%) in MTT reduction assay. DEC upto
200 mM was ineffective. However, at higher dose (400 mM),
DEC exerted irreversible paralysis of the worms i.e. the worms
failed to gain normal motility even after transferring the
treated worms in fresh medium without any drug at 37 ꢀC
for 30 min. The control vehicle did not display any activity
against the adult worms of B. malayi. Although no definite
conclusion on SAR can be drawn with this sizable number
of compounds, it is clear that 4-aryl-1,4-dihydropyridines
bearing less bulky electron-withdrawing substituent at the
4th position of phenyl ring (4-Fephenyl) compound 18 is
the best compound of the series.
2. Results and discussion
The starting 1,2,3,4-tetrahydropyrimidine-2-thione deriva-
tives were prepared in excellent yields by our earlier reported
protocol [22]. It involves a modified Biginelli three-component
reaction of aromatic aldehydes, ethyl acetoacetate and thiourea
in diethylene glycol at 120 ꢀC. The yields and characterization
of these tetrahydropyrimidine thiones were already described.
In the proposed reaction ethyl acetoacetate and thiourea were
kept constant while aromatic aldehydes were the variant.
The target molecules, 2-sulfanyl-6-methyl-1,4-dihydropyri-
midines, were synthesized from the respective tetrahydropyri-
midine-2-thiones by reaction with an alkyl or aralkyl halides
in anhydrous acetone in the presence of anhydrous K2CO3
and catalytic amount of tetrabutyl ammonium bromide
(Scheme 1 and Table 1). It is important to mention here that
this class was earlier synthesized by Atwal et al. [16] as
possible calcium channel blockers, however, our method of
synthesis is far better with respect to environmental consider-
ation, time and yields of the final product. Use of tetrabutyl
ammonium bromide as phase transfer catalyst not only
improves the yield of the sulfanyl derivatives but the reaction
time is also considerably reduced. The structures of all the
products were established on the basis of their spectral data
and analyses. In IR spectra of the compounds the carbonyl
frequency of the ester moiety was observed at around
1650 cmꢁ1 along with other usual characteristic frequencies.
All the compounds displayed [M þ H]þ corresponding to their
molecular formulae. In 1H NMR of the compounds three
protons of 6-methyl substituent appeared as singlets at around
d 2.45 along with other protons at their usual chemical shifts.
Out of the two possibilities of 1,4- and 3,4-dihydroisomers (A
and B) (Fig. 2) only the former prevailed as the characteristic
O
R2
HN
Only three compounds 10, 15 and 18 showing potent in vi-
tro antifilarial activity were screened in vivo against B. malayi
in Mastomys coucha model to see the effect of the compounds
on parasitological parameters and the results are depicted in
Table 3. As evident from Table 3 a significant effect on adult
worms (50%; P < 0.001) was shown by compound 18 at
100 mg/kg. In terms of embryostatic activity, it exerted signif-
icant (P < 0.01) efficacy by sterilizing about 68% of the
R
1
S
N
R3
Fig. 1. S-DABO.

B.K. Singh et al. / European Journal of Medicinal Chemistry 43 (2008) 2717e2723
2719
H
N
O
O
S
S
H3C
TBAHS/ DEG/120 °C
+
Ar-CHO
+
H3C
OC2H5
H3C
NH
O
O
H2N
NH2
1a-f
Ar
2-7
R'Br, K2CO3, TBAB
Acetone/ 30 °C
Napthyl, 3-nitrrophenyl, 4-methoxy phenyl,
4-fluorophenyl, 4-chlorophenyl, thiophen
Ar =
R' = Benzyl, Pentyl, Butyl,
Tetradecyl
H
H3C
N
SR'
H3C
O
N
O
Ar
8-21
Scheme 1. Synthesis of 6-methyl-2-sulfanyl-1,4-dihydropyrimidines.
surviving female worms compared to 20% observed in the
untreated controls. The efficacy of the compound was found
to be lower at 50 mg/kg as compared to 100 mg/kg. In normal
M. coucha at this dose the animals showed no mortality or
adverse effect on general and gross health of the animals dur-
ing the treatment and thereafter upto 15 days post-treatment.
Compound 15 at 100 mg/kg marginally (20%) exerted macro-
filaricidal effect. On the other hand, compounds 10 and 15 at
100 mg/kg affected the female reproductive potentials to the
tune of only 35 and 26%, respectively. None of the compounds
affected circulating mf. The control drug DEC at a dose of
25 mg/kg (i.p.) caused more than 65% (P < 0.001) reduction
in microfilaraemia and around 30% female sterilizing action.
Untreated control animals showed progressive rise in microfi-
laraemia till termination of the experiment. About 20% of live
female worms recovered from these animals were sterile.
As compound 18 with 4-flurophenyl and n-pentyl substitu-
ents was found to be the most potent antifilarial in the above
two experiments we were prompted to see its effect on the
adulticidal activity against filarial worms in B. malayi-jird
model. It is evident from the results (Table 4) the standard
antifilarial drug DEC (12.5 mg/kg, the effective dose of the
drug against animal filariid, Litomosoides carinii) did not
show any noticeable microfilaricidal activity and about 10%
adulticidal activity was observed only as compared to
untreated controls. However, the synthetic compound 18
displayed about 46% adulticidal (P < 0.01) activity and 34%
(P < 0.05) of the sterilized female worms were recovered. Un-
treated control animals showed no effect on mf of peritoneal
cavity of any of the animals. About 16% of live female worms
recovered from these animals was sterile. The results indicate
that compound 18 has potential for further optimization and
development of novel class of antifilarial agents.
In conclusion we have developed an efficient synthesis of
a series of 4-aryl-2-sulfanyl-6-methyl-1,4-dihydropyrimidines
Table 1
4-Aryl-6-methyl-2-sulfanyl-1,4-dihydropyrimidines (8e21) synthesized
Entry Compound Ar
R0
Time Yield (%)
1
1
1
8
1-Naphthyl
1-Naphthyl
Benzyl
n-Pentyl
n-Butyl
n-Tetradecyl
Benzyl
3
70
72
80
65
60
75
70
65
78
80
70
85
70
65
H
H3C
N
SR
SR
N
2
9
6
H3C
3
10
11
12
13
14
15
16
17
18
19
20
21
1-Naphthyl
1-Naphthyl
5
2
3
2
NH
3
4
6
N
5
3-Nitrophenyl
3-Nitrophenyl
3-Nitrophenyl
3
EtOOC
EtOOC
4
6
n-Pentyl
n-Butyl
5
4
7
4
8
4-Methoxyphenyl Benzyl
4-Methoxyphenyl n-Pentyl
4-Methoxyphenyl n-Tetradecyl
4-Fluorophenyl
4-Fluorophenyl
4-Chlorophenyl
Thiophenyl
3
9
3.5
5
10
11
12
13
14
n-Pentyl
n-Tetradecyl
n-Pentyl
Benzyl
6
7
A
B
4
3
Fig. 2. Two possible isomers of dihydropyrimidines.

2720
B.K. Singh et al. / European Journal of Medicinal Chemistry 43 (2008) 2717e2723
3. Experimental
3.1. General methods
Melting points were determined on a Buchi 510 apparatus
and are uncorrected. Commercially available reagent grade
chemicals were used as-received. All reactions were followed
by TLC on Merck Kieselgel 60 F254, with detection by UV
light and/or spraying 20% KMnO4 aqueous solution. Column
chromatography was performed on silica gel (230e400 mesh,
Merck). IR spectra were recorded as thin films or neat chloro-
form solution with a PerkineElmer Spectrum RX-1 (4000e
1
450 cmꢁ1) spectrophotometer. The H and 13C NMR spectra
were recorded on a Brucker DRX-300 in (D) chloroform
and chemical shift values expressed in parts per million rela-
tive to SiMe4 as internal reference, unless otherwise stated;
signals are reported as s (singlet), d (doublet), t (triplet), m
(multiplet); J in hertz. Fast atom bombardment mass spectra
(FABMS) were performed by the Mass Spectrometer Jeol
SX-102 (FAB). Elemental analyses were performed on a Per-
kineElmer 2400 II elemental analyzer.
Fig. 3. The ORTEP diagram (at 30% probability) of compound 12 showing the
molecular conformation along with atomic numbering scheme.
by simple alkylation of dihydropyrimidine thiones with alkyl
halides. One of the compounds (compound 18) displayed potent
activityinvitroandinvivoanditexertedadulticidalactivityalong
with female worms’ sterilization. Thus compound 18, found
active with no apparent signs of any toxicity in gross health of
treated and normal animals, may serve as a prototype lead for
further optimization and development of new antifilarial agents.
3.2. Typical experimental procedure for
compounds 8e21
To a magnetically stirred solution of compounds 2e7
(1 mmol) in acetone, K2CO3 (1 mmol) was added and the
reaction mixture was stirred for 10 min. After that alkyl
bromide (1 mmol) and tetrabutyl ammonium bromide
(20 mol%) were added and reaction mixture was stirred for
desired time at room temperature. After completion, reaction
mixture was evaporated and crude mass was extracted by ethyl
acetate and water. Organic layer was dried (anhydrous
Na2SO4) and evaporated under reduced pressure to get the
crude mass which was column chromatographed over silica
gel (60e120 mesh) using hexaneeEtOAc as eluent to give
compounds 8e21.
Table 2
In vitro macrofilaricidal activity of compounds on B. malayi
Compound
Concentration Motilitya Percent inhibition in MTT
(mM)
reduction over control
(means ꢂ SD)
8
100
100
100
50
0
3
0
0
1
0
0
3
0
18.95 ꢂ 1.77
9
10
NI
49.0 ꢂ 11.50
NI
25
30.41 ꢂ 8.7
24.34 ꢂ 3.13
43.14 ꢂ 5.11
15.41 ꢂ 2.82
25.74 ꢂ 3.44
11
12
13
14
100
100
100
100
3.2.1. 2-Benzylsulfanyl-6-methyl-4-naphthalen-1-yl-1,
4-dihydro-pyrimidine-5-carboxylic acid ethyl ester (8)
It was obtained by reaction of 2 (1.1 g, 3.37 mmol), K2CO3
(0.47 g, 3.37 mmol) and benzyl bromide (0.4 mL, 3.37 mmol)
15
100
50
0
0
1
2
2
3
3
0
0
0
0
3
3
1
2
3
3
3
52.11 ꢂ 26.92
19.29 ꢂ 9.49
25
NI
22.42 ꢂ 5.84
1
as a white solid (0.98 g, 70%); m.p. 132e133 ꢀC; H NMR
16
17
100
100
50
(200 MHz, CDCl3): d 0.99 (t, 3H, J ¼ 7.0 Hz), 2.42 (s, 3H),
3.87e4.16 (m, 4H), 6.57 (s, 1H), 6.83e7.05 (m, 4H), 7.33e
7.58 (m, 5H), 7.74e7.89 (m, 2H), 8.74 (d, 1H, J ¼ 8.2 Hz);
13C NMR (50 MHz, CDCl3): d 14.5, 19.0, 35.6, 56.6, 60.0,
99.6, 124.1, 125.8, 126.3, 127.4, 128.2, 128.8, 129.1, 131.6,
134.5, 138.2, 139.6, 167.0; IR (KBr) cmꢁ1: 3283, 2362,
1650, 1593; MS (FAB): m/z 417 (M þ H)þ.
NI
NI
25
NI
68.61 ꢂ 5.13
18
19
100
50
68.46 ꢂ 8.92
25
25.78 ꢂ 17.50
100
50
NI
NI
NI
NI
NI
NI
NI
NI
20
DEC (citrate)
100
400
200
100
50
3.2.2. 6-Methyl-4-naphthalen-1-yl-2-pentylsulfanyl-1,
4-dihydro-pyrimidine-5-carboxylic acid ethyl ester (9)
It was obtained by reaction of 2 (0.8 g, 2.45 mmol), K2CO3
(0.38 g, 2.45 mmol) and pentyl bromide (0.31 mL, 2.45 mmol)
as a white solid (0.7 g, 72%); m.p. 92e94 ꢀC; 1H NMR
(200 MHz, CDCl3): d 0.70 (t, 3H, J ¼ 6.7 Hz), 0.86e1.05
Untreated control Vehicle
a
Motility is expressed as highly motile (3), low (2), sluggish (1, irreversible)
and dead (0); NI ¼ no inhibition.

B.K. Singh et al. / European Journal of Medicinal Chemistry 43 (2008) 2717e2723
2721
Table 3
Antifilarial activity of synthetic compounds against B. malayi in M. coucha (values are means ꢂ SD)
Test compounds
(mg/kg, i.p. ꢃ 5
days)
No. of
animals
used
Mf count
before
treatment
Mf count on
day 8 post-initiation
of treatment
No. of live worms
Sterilized female worms
Number (%)
Male
Female
Totalb
10 (100)
15 (100)
6
6
9
6
6
6
38.00 ꢂ 14.18
40.67 ꢂ 2.31
83.00 ꢂ 45.48
45.0 ꢂ 7.07
47.33 ꢂ 20.01
89.67 ꢂ 71. 99
142.67 ꢂ 93.06
116.5 ꢂ 94.05
20.33 ꢂ 9.71#
106.71 ꢂ 51.45
13.00 ꢂ 7.21
5.67 ꢂ 1.16
3.25 ꢂ 1.89
7.0 ꢂ 1.41
7.33 ꢂ 0.58
7.0 ꢂ 3.58
15.33 ꢂ 5.69
10.0 ꢂ 1.00
6.5 ꢂ 1.91
28.33 ꢂ 12.5 (0.0)
15.57 ꢂ 2.08 (19.66)
9.75 ꢂ 3.3 (50.0)***
13.5 ꢂ 0.71 (30.77)
21.00 ꢂ 5.20 (0.0)
19.5 ꢂ 3.02
3.00 ꢂ 1.73 (25.77)
3.33 ꢂ 1.53 (34.58)
4.0 ꢂ 0.82 (67.71)**
2.5 ꢂ 0.71 (38.1)
18 (100)
18 (50)
DECa (25)
Untreated control
6.5 ꢂ 0.71
59.00 ꢂ 16.09
51.43 ꢂ 29.42
13.67 ꢂ 5.51
12.5 ꢂ 3.02
5.67 ꢂ 8.96 (29.7)
2.5 ꢂ 1.38 (20.18)
***P < 0.001, **P < 0.01 (over untreated control), #P < 0.001 (over pretreatment level).
a
Diethylcarbamazine citrate.
% Reduction in worm burden over control.
b
(m, 7H), 1.19e1.25 (m, 2H), 2.46 (s, 3H), 2.51e2.87 (m, 2H),
4.01 (q, 2H, J ¼ 7.0 Hz), 6.51 (s, 1H), 7.23e7.54 (m, 4H),
7.69e7.84 (m, 2H), 8.70 (d, 1H, J ¼ 8.2 Hz); 13C NMR
(50 MHz, CDCl3): d 14.2, 14.5, 19.1, 22.4, 29.7, 31.2, 31.6,
57.0, 60.0, 102.0, 123.8, 125.7, 126.1, 128.1, 128.7, 131.6,
134.5, 139.3, 167.1; IR (KBr) cmꢁ1: 3303, 2362, 1654; MS
(FAB): m/z 397 (M þ H)þ.
60.1, 99.5, 123.5, 125.7, 125.9, 126.0, 127.0, 128.0, 128.6,
129.5, 131.9, 134.5, 139.2, 146.0, 149.4, 167.3; IR (KBr)
cmꢁ1: 3302, 2363, 1650, 1597; MS (FAB): m/z 523 (M þ H)þ.
3.2.5. 2-Benzylsulfanyl-6-methyl-4-(3-nitro-phenyl)-1,
4-dihydro-pyrimidine-5-carboxylic acid ethyl ester (12)
It was obtained by reaction of 3 (1.0 g, 3.11 mmol), K2CO3
(0.43 g, 3.11 mmol) and benzyl bromide (0.37 mL,
3.11 mmol) as a greenish solid (0.76 g, 60%); m.p. 122e
123 ꢀC; 1H NMR (200 MHz, CDCl3): d 1.21 (t, 3H,
J ¼ 7.1 Hz), 2.31 (s, 3H), 4.06e4.16 (m, 3H), 4.28 (d, 1H,
J ¼ 13.6 Hz), 5.82 (s, 1H), 6.37 (s, 1H), 7.14e7.22 (m, 5H),
7.41 (t, 1H, J ¼ 7.8 Hz), 7.59 (d, 1H, J ¼ 7.6 Hz), 8.06e8.11
(m, 2H); 13C NMR (50 MHz, CDCl3): d 14.6, 19.1, 35.5,
59.8, 60.5, 100.3, 122.4, 122.5, 127.7, 128.8, 129.0, 129.2,
129.5, 133.9, 137.5, 137.5, 145.6, 147.2, 148.7, 150.4,
166.7; IR (KBr) cmꢁ1: 3326, 2364, 1678, 1653; MS (FAB):
m/z 411 (M þ H)þ.
3.2.3. 2-Butylsulfanyl-6-methyl-4-naphthalen-1-yl-1,
4-dihydro-pyrimidine-5-carboxylic acid ethyl ester (10)
It was obtained by reaction of 2 (1 g, 3.06 mmol), K2CO3
(0.42 g, 3.06 mmol) and butyl bromide (0.33 mL,
3.06 mmol) as a white solid (0.93 g, 80%); m.p. 97e98 ꢀC;
1H NMR (200 MHz, CDCl3): d 0.57 (t, 3H, J ¼ 6.9 Hz),
0.84e1.25 (m, 7H), 2.46 (s, 3H), 2.64e2.86 (m, 2H), 4.01
(q, 2H, J ¼ 7.0 Hz), 6.51 (s, 1H), 7.23e7.84 (m, 7H), 8.74
(d, 1H, J ¼ 8.1 Hz); 13C NMR (50 MHz, CDCl3): d 13.8,
14.5, 19.4, 22.2, 31.3, 32.0, 56.1, 60.0, 123.9, 125.7, 126.1,
128.1, 128.7, 131.7, 134.5, 139.3, 167.1; IR (KBr) cmꢁ1
3289, 2363, 1653; MS (FAB): m/z 383 (M þ H)þ.
:
3.2.6. 6-Methyl-4-(3-nitro-phenyl)-2-pentylsulfanyl-1,
4-dihydro-pyrimidine-5-carboxylic acid ethyl ester (13)
It was obtained by reaction of 3 (1.0 g, 3.11 mmol), K2CO3
(0.43 g, 3.11 mmol) and pentyl bromide (0.39 mL, 3.11 mmol)
3.2.4. 6-Methyl-4-naphthalen-1-yl-2-tetradecylsulfanyl-1,
4-dihydro-pyrimidine-5-carboxylic acid ethyl ester (11)
It was obtained by reaction of 2 (1.3 g, 3.98 mmol), K2CO3
(0.55 g, 3.98 mmol) and tetradecyl bromide (1 mL,
3.98 mmol) as a white solid (1.35 g, 65%); m.p. 86e87 ꢀC;
1H NMR (200 MHz, CDCl3): d 0.85e1.26 (m, 30H), 2.46
(s, 3H), 2.52e2.98 (m, 2H), 3.99 (q, 2H, J ¼ 7.0 Hz), 6.16
(s, 1H), 6.51 (s, 1H), 7.23e7.55 (m, 4H), 7.69e7.84 (m,
2H), 8.70 (d, 1H, J ¼ 8.2 Hz); 13C NMR (50 MHz, CDCl3):
d 14.5, 19.0, 23.1, 29.1, 29.4, 29.8, 30.1, 31.8, 32.3, 56.6,
1
as a white solid (0.91 g, 75%); m.p. 119e120 ꢀC; H NMR
(200 MHz, CDCl3): d 0.82 (t, 3H, J ¼ 7.1 Hz), 1.16e1.32
(m, 7H), 1.53e1.63 (m, 2H), 2.34 (s, 3H), 2.89e3.04 (m,
2H), 4.11 (q, 2H, J ¼ 7.0 Hz), 5.80 (s, 1H), 6.35 (s, 1H),
7.45 (t, 1H, J ¼ 7.8 Hz), 7.65 (d, 1H, J ¼ 7.8 Hz), 8.05e8.16
(m, 2H); 13C NMR (50 MHz, CDCl3): d 14.2, 14.6, 19.2,
22.5, 29.4, 31.1, 31.4, 59.5, 60.5, 100.1, 122.4, 129.5, 133.8,
Table 4
Antifilarial activity of compound 18 (100 mg/kg, i.p. ꢃ 5 days) and DEC against transplanted adult worms of B. malayi in Meriones unguiculatus (values are
means ꢂ SD)
Antifilarial agent
No. of
animals
Effect on microfilariae
in peritoneal cavity
No. of live worms
Sterilized female worms
Number (%)
(mg/kg, i.p. ꢃ 5 days)
Male
Female
Totalb
18 (100)
DECa (12.5)
Untreated control
5
5
5
No effect
No effect
No effect
2.40 ꢂ 0.55
4 ꢂ 0.71
4.40 ꢂ 2.97
7.60 ꢂ 1.14
8.60 ꢂ 0.89
6.80 ꢂ 3.11 (46.03)**
11.60 ꢂ 1.82
2.40 ꢂ 2.07 (34.31)*
0.80 ꢂ 0.84 (10.53)
1.40 ꢂ 1.14 (16.17)
4.00 ꢂ 1.00
12.60 ꢂ 1.67
**P < 0.01, *P < 0.05 (over untreated control).
a
Diethylcarbamazine citrate.
% Reduction in worm burden over control.
b

2722
B.K. Singh et al. / European Journal of Medicinal Chemistry 43 (2008) 2717e2723
145.7, 147.3, 148.6, 151.2, 166.8; IR (KBr) cmꢁ1: 3432, 2364,
3.2.11. 4-(4-Fluoro-phenyl)-6-methyl-2-pentylsulfanyl-1,
4-dihydro-pyrimidine-5-carboxylic acid ethyl ester (18)
It was obtained by reaction of 5 (1.5 g, 5.10 mmol), K2CO3
(0.70 g, 5.10 mmol) and pentyl bromide (0.63 mL, 5.10 mmol)
as an oil (1.3 g, 70%); 1H NMR (200 MHz, CDCl3): d 0.94 (t,
3H, J ¼ 6.6 Hz), 1.23e1.38 (m, 7H), 1.58e162 (m, 2H), 2.33
(s, 3H), 2.89e2.96 (m, 2H), 4.11 (q, 2H, J ¼ 7.0 Hz), 5.72 (s,
1H), 6.96e7.05 (m, 2H), 7.30e7.36 (m, 2H); 13C NMR
(50 MHz, CDCl3): d 14.3, 14.6, 20.3, 22.5, 29.5, 31.2, 31.3,
58.0, 60.1, 102.3, 115.2, 115.6, 116.1, 128.8, 128.9, 140.9,
159.9, 164.8, 166.9; IR (neat) cmꢁ1: 3293, 2365, 1653; MS
(FAB): m/z 365 (M þ H)þ.
1699, 1640; MS (FAB): m/z 392 (M þ H)þ.
3.2.7. 2-Butylsulfanyl-6-methyl-4-(3-nitro-phenyl)-1,
4-dihydro-pyrimidine-5-carboxylic acid ethyl ester (14)
It was obtained by reaction of 3 (0.9 g, 2.80 mmol), K2CO3
(0.39 g, 2.80 mmol) and butyl bromide (0.31 mL, 2.80 mmol)
as a white solid (0.74 g, 70%); m.p. 98e99 ꢀC; 1H NMR
(200 MHz, CDCl3): d 0.84 (t, 3H, J ¼ 7.0 Hz), 1.22 (t, 3H,
J ¼ 7.1 Hz), 1.27e1.39 (m, 2H), 1.52e1.68 (m, 2H), 2.35 (s,
3H), 2.91e3.08 (m, 2H), 4.07 (q, 2H, J ¼ 7.1 Hz), 5.81 (s,
1H), 6.36 (s, 1H), 7.45 (t, 1H, J ¼ 7.8 Hz), 7.66 (d, 1H,
J ¼ 7.7 Hz), 8.07e8.16 (m, 2H); 13C NMR (50 MHz,
CDCl3): d 13.9, 14.6, 19.1, 22.1, 31.1, 31.8, 59.4, 60.5,
3.2.12. 4-(4-Fluoro-phenyl)-6-methyl-2-tetradecylsulfanyl-
1,4-dihydro-pyrimidine-5-carboxylic acid ethyl ester (19)
It was obtained by reaction of 5 (1.5 g, 5.10 mmol), K2CO3
(0.70 g, 5.10 mmol) and tetradecyl bromide (1.39 mL,
5.10 mmol) as a light green solid (2.1 g, 85%); m.p. 50e
51 ꢀC; 1H NMR (200 MHz, CDCl3): d 0.88 (t, 3H,
J ¼ 6.7 Hz), 1.16e1.25 (m, 25H), 1.54e1.62 (m, 2H), 2.31
(s, 3H), 2.84e3.07 (m, 2H), 4.07 (q, 2H, J ¼ 7.0 Hz), 5.65
(s, 1H), 6.17 (s, 1H), 6.90e6.98 (m, 2H), 7.23e7.29 (m,
2H); 13C NMR (50 MHz, CDCl3): d 14.5, 14.6, 19.0, 23.1,
29.1, 29.5, 29.7, 29.8, 30.0, 31.4, 32.3, 59.2, 60.2, 101.2,
115.2, 115.6, 128.8, 128.9, 141.0, 159.9, 164.7, 167.2; IR
(neat) cmꢁ1: 3310, 1652, 1601; MS (FAB): m/z 491 (M þ H)þ.
122.4, 129.6, 133.7, 147.2, 148.6, 166.9; IR (KBr) cmꢁ1
3391, 1700, 1637; MS (FAB): m/z 377 (M þ H)þ.
:
3.2.8. 2-Benzylsulfanyl-4-(4-methoxy-phenyl)-6-methyl-1,
4-dihydro-pyrimidine-5-carboxylic acid ethyl ester (15)
It was obtained by reaction of 4 (1.5 g, 4.90 mmol), K2CO3
(0.67 g, 4.90 mmol) and benzyl bromide (0.58 mL,
4.90 mmol) as colorless oil (1.26 g, 65%); 1H NMR
(200 MHz, CDCl3): d 1.19 (t, 3H, J ¼ 7.0 Hz), 2.33 (s, 3H),
3.79 (s, 3H), 4.05e4.46 (m, 4H), 5.69 (s, 1H), 6.79e6.32
(m, 9H); 13C NMR (50 MHz, CDCl3): d 14.6, 19.6, 35.2,
55.6, 58.6, 60.2, 102.9, 114.1, 127.7, 128.5, 128.9, 129.4,
130.5, 137.5, 137.9, 159.2, 167.3; IR (neat) cmꢁ1: 3362,
2363, 1690, 1598; MS (FAB): m/z 397 (M þ H)þ.
3.2.13. 4-(4-Chloro-phenyl)-6-methyl-2-pentylsulfanyl-1,
4-dihydro-pyrimidine-5-carboxylic acid ethyl ester (20)
It was obtained by reaction of 6 (1.6 g, 5.16 mmol), K2CO3
(0.71 g, 5.16 mmol) and pentyl bromide (0.64 mL, 5.16 mmol)
as an oil (1.37 g, 70%); 1H NMR (200 MHz, CDCl3): d 0.86 (t,
3H, J ¼ 6.6 Hz), 1.10e1.33 (m, 7H), 1.53e1.60 (m, 2H), 2.32
(s, 3H), 2.89e3.03 (m, 2H), 4.04 (q, 2H, J ¼ 7.0 Hz), 5.58 (s,
1H), 7.12e7.33 (m, 4H); 13C NMR (50 MHz, CDCl3): d 14.2,
14.6, 19.1, 22.5, 23.0, 29.3, 29.4, 31.1, 31.4, 58.2, 60.5, 101.5,
128.4, 128.7, 129.0, 129.2, 133.2, 143.5, 167.0; IR (neat)
cmꢁ1: 3295, 2362, 1652; MS (FAB): m/z 381 (M þ H)þ.
3.2.9. 4-(4-Methoxy-phenyl)-6-methyl-2-pentylsulfanyl-1,
4-dihydro-pyrimidine-5-carboxylic acid ethyl ester (16)
It was obtained by reaction of 4 (1.3 g, 4.24 mmol), K2CO3
(0.59 g, 4.24 mmol) and pentyl bromide (0.53 mL, 4.24 mmol)
as an oil (0.82 g, 78%); 1H NMR (200 MHz, CDCl3): d 0.85 (t,
3H, J ¼ 6.7 Hz), 1.16e1.30 (m, 3H), 1.53e1.60 (m, 2H), 2.26
(s, 3H), 2.88e2.94 (m, 2H), 3.77 (s, 3H), 5.54 (s, 1H), 6.73e
6.83 (m, 2H), 7.14e7.21 (m, 2H); 13C NMR (50 MHz,
CDCl3): d 14.3, 14.7, 20.6, 22.5, 29.5, 31.2, 55.4, 57.8, 60.0,
102.0, 114.0, 128.3, 130.4, 137.6, 159.1, 167.1; IR (KBr)
cmꢁ1: 3298, 1680, 1653; MS (FAB): m/z 377 (M þ H)þ.
3.2.14. 2-Benzylsulfanyl-6-methyl-4-thiophen-2-yl-1,
4-dihydro-pyrimidine-5-carboxylic acid ethyl ester (21)
It was obtained by reaction of 7 (0.8 g, 2.83 mmol), K2CO3
(0.39 g, 2.83 mmol) and benzyl bromide (0.34 mL,
2.83 mmol) as a white solid (0.68 g, 65%); m.p. 89e90 ꢀC;
1H NMR (200 MHz, CDCl3): d 0.1.25 (t, 3H, J ¼ 7.0 Hz),
2.30 (s, 3H), 4.12e4.26 (m, 3H), 4.37 (d, 1H, J ¼ 13.3 Hz),
5.97 (s, 1H), 6.87e7.28 (m, 8H); 13C NMR (50 MHz,
CDCl3): d 14.7, 18.9, 35.8, 55.3, 60.4, 101.5, 123.9, 124.4,
126.8, 127.7, 128.9, 129.4, 137.7, 145.5, 149.2, 151.7,
167.0; IR (KBr) cmꢁ1: 3297, 2358, 1647; MS (ESI): m/z
373.1 (M þ H)þ.
3.2.10. 4-(4-Methoxy-phenyl)-6-methyl-2-tetradecylsulfanyl-
1,4-dihydro-pyrimidine-5-carboxylic acid ethyl ester (17)
It was obtained by reaction of 4 (1.5 g, 4.90 mmol), K2CO3
(0.67 g, 4.90 mmol) and tetradecyl bromide (1.34 mL,
1
4.90 mmol) as a foam (1.97 g, 80%); H NMR (200 MHz,
CDCl3): d 0.88 (t, 3H, J ¼ 6.6 Hz), 1.16e1.25 (m, 21H),
1.42e1.60 (m, 2H), 2.30 (s, 3H), 2.69e3.18 (m, 2H), 3.77
(s, 3H), 4.08 (q, 2H, J ¼ 7.0 Hz), 5.66 (s, 1H), 6.10 (s, 1H),
6.79 (d, 2H, J ¼ 8.6 Hz), 7.22 (d, 2H, J ¼ 8.7 Hz); 13C NMR
(50 MHz, CDCl3): d 14.5, 14.7, 23.1, 29.1, 29.5, 29.7, 29.9,
30.1, 31.3, 32.3, 55.4, 56.0, 60.0, 114.0, 114.6, 128.3, 132.3,
137.6, 159.1, 167.1; MS (FAB): m/z 503 (M þ H)þ.
Acknowledgements
This paper bears CDRI Communication No. 7347. Authors
thank SAIF Division for spectroscopic data. BKS, Nisha,

B.K. Singh et al. / European Journal of Medicinal Chemistry 43 (2008) 2717e2723
2723
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Appendix. Supplementary data
Supplementary data associated with this article can be found
in the online version, at doi:10.1016/j.ejmech.2008.01.038.
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