Potential inhibitors of plasmodial heme oxygenase; an innovative approach for combating chloroquine resistant malaria

Article abstract of DOI:10.1016/S0968-0896(97)10013-X

Syntheses of imidazo-pyridines and substituted prolines and their effect on heme oxygenase activity of Plasmodium yoelii and corresponding infected host have been studied. Six compounds in vitro and one in vivo showed selective inhibition of parasite enzy

Full text of DOI:10.1016/S0968-0896(97)10013-X

BIOORGANIC &
MEDICINAL
CHEMISTRY
Bioorganic & Medicinal Chemistry 6 (1998) 181±187
Potential inhibitors of plasmodial heme oxygenase; an innovative
approach for combating chloroquine resistant malaria
Pratima Srivastavaa, Vikash Chandra Pandeya, Anju Prabha Misrab, Preeti Guptab,
Kanwal Rajb, Amiya Prasad Bhadurib
aBiochemistry Division, Central Drug Research Institute, Lucknow, 226001, India
bMedicinal Chemistry Division, Central Drug Research Institute, Lucknow, 226001, India
Received 27 May 1997; accepted 10 September 1997
Abstract
Syntheses of imidazo-pyridines and substituted prolines and their e€ect on heme oxygenase activity of Plasmodium
yoelii and corresponding infected host have been studied. Six compounds in vitro and one in vivo showed selective
inhibition of parasite enzyme which may be further exploited in the development of resistant reversal agents. # 1998
Elsevier Science Ltd. All rights reserved.
1. Introduction
oquine it is more lethal to parasites [4]. This clearly
indicates that if the heme milieu is minimised, there will
be less opportunity for chloroquine to impart its lethal
e€ect on the parasite, and compounds capable of inhi-
biting heme degradation will help to combat chlor-
oquine resistance if given in conjugation with
chloroquine. In continuation of our earlier studies [5,6]
in this direction the need arose to identify new mole-
cular structures associated with selective inhibition of
parasite heme oxygenase. This led to the evaluation of
imidazo [1,2-a]pyridines and substituted prolines as
selective inhibitors of cell-free malarial parasites heme
oxygenase. The details are presented here.
Malaria caused by the protozoan parasite plasmodia
is still an unconquered disease for mankind. The main
reason is the emergence of plasmodial resistance
towards the routinely used antimalarials like chlor-
oquine. This has resulted in a resurgence in malaria and
has thrown up challenges for innovating a remedy to
combat the situation. E€orts being made in this direc-
tion include biochemical and immunological approa-
ches. Some encouraging experimental observations like
increased vacuolar pH, permease, protease, or plasmodial
glycoprotein levels have been analysed [1] to determine
reasons for drug resistance in plasmodia. However, no
speci®c and conclusive biochemical change(s) could be
speci®ed for explaining chloroquine resistance in plas-
modia. Compared to the chloroquine-sensitive parasite,
our observation on the enhanced heme oxygenase and
decreased heme/hemozoin levels in chloroquine-resis-
tant plasmodia [2] have projected the possibility for
combating chloro-quine-resistant malarial parasite.
Heme oxygenase is responsible for heme and hemozoin
degradation generated during the intraerythrocytic
development of malarial parasites of di€erent species,
viz P. falciparum, P. knowlesi, P. yoelii and P. berghei
[3]. Heme itself is toxic but in conjugation with chlor-
2. Chemistry
The strategy for the syntheses of substituted imi-
dazo[1,2-a]pyridines involves the condensation of
2-aminopyridine and substituted phenacyl bromides
to yield the 2-(substituted)phenylimidazo[1,2-a]pyr-
idines(1±7) (Scheme 1, Table 1) [7,8]. Compounds 3±5
on O-alkylation with dialkylamino alkylchlorides/alkyl
halide in the presence of sodium hydride yielded 8, 9,
10±16 and 17, respectively. Selective nitrosation at posi-
tion 3 in compound 2 and 6 gave the nitroso derivatives
0968-0896/98/$19.00 # 1998 Elsevier Science Ltd. All rights reserved
PII: S0968-0896(97)10013-X

182
P. Srivastava et al./Bioorg. Med. Chem. 6 (1998) 181±187
18, 19, respectively. Reduction of compound 19 with
Zn/CH3COOH furnished the amine 20 (Scheme 1). The
substituted prolines (21±29) were prepared by following
the method reported in the literature [9]. Structures of
all new compounds were in full agreement with their
mass, NMR, IR and elemental analysis data.
di€erent extents of inhibition, while the host enzyme
remained una€ected or there was negligible e€ect of the
compounds on the same for compounds 8, 14, 15, 16, 24
and 25.
The compounds which showed their inhibitory e€ect
at lower concentration seem to be better inhibitors of
the enzyme. However, compound 20 remained ine€ec-
tive in arresting the parasite as well as the host enzyme.
Compounds 21, 22, 23 and 26 equally inhibited the host
and the parasite enzyme to almost the same extent.
The e€ect of three compounds, 8, 14 and 25, which
showed selective or potential inhibitory e€ects on HO
activity of the parasite in vitro, were also tested in vivo
for the inhibition of the enzyme. The results obtained
show that out of the three compounds only 25 com-
pletely inhibited the HO activity of the parasite in vivo
(Table 2).
3. Results
The compounds belonging to imidazopyridine and
substituted prolines were taken in order to monitor their
e€ect on heme oxygenase activity of the cell-free para-
site Plasmodium yoelii as well as for control measures
infected hepatic host enzymes. For compounds which
were water insoluble, a proper control of the corre-
sponding solvent was introduced and their e€ect pre-
determined on the enzyme to neutralize the alteration (if
any). Almost all the compounds were DMSO-soluble
except compound 23 which was soluble in water.
4. Discussion
The data obtained showed that the compounds tested
at di€erent concentrations displayed inhibition of the
parasite as well as the corresponding host enzyme
(Table 1). Further, it was also observed that some com-
pounds selectively inhibited the parasite enzyme with
Heme plays a crucial role in controlling the physio-
logical function as well as resistance property of the
malarial parasite. The lethal e€ect of the chloroquine±
heme adduct depends upon the action of the key
Scheme 1.

P. Srivastava et al./Bioorg. Med. Chem. 6 (1998) 181±187
183
Table 1
In vitro e€ect of di€erent compounds on heme oxygenase activity of cell free parasite P. yoelii and corresponding infected host
Compound no.
R
R1
R2
Concentration (ꢀM)
% inhibition in HO
Parasite
Host
1
H
H
Cl
H
H
10
50
Nil
Nil
20
Nil
Nil
12
100
10
2
Br
Nil
Nil
Nil
20
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
15
50
100
10
3
H
OH
H
50
30
80
100
10
4.
H
H
OH
Nil
Nil
Nil
12
50
100
10
5.
CH3
H
OH
H
CH(CH3)2
OCH3
50
33
72
59
60
100
10
6.
Nil
Nil
52
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
15
50
100
10
7.
H
OCH3
H
Nil
20
50
100
10
20
8.
H
O(CH2)2N Et2
O(CH2)2Pipa
H
H
100
100
100
Nil
20
50
100
10
9.
H
H
50
100
10
20
10.
11.
12.
13.
14.
15.
16.
17.
18.
H
O(CH2)2NMe2
O(CH2)2NEt2
O(CH2)2Pipa
CH(CH3)2
CH(CH3)2
CH(CH3)2
CH(CH3)2
CH(CH3)2
H
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
100
100
100
100
100
100
100
100
12
50
100
10
H
H
50
100
10
H
H
50
47
100
10
100
Nil
Nil
Nil
Nil
Nil
CH3
CH3
CH3
CH3
CH3
H
O(CH2)2NMe2
O(CH2)2NEt2
O(CH2)2Pyrb
OCH2)2Pipa
OCH3
50
100
10
50
100
10
5.9
Nil
Nil
10.4
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
Nil
50
100
10
50
60
100
10
100
Nil
Nil
Nil
Nil
Nil
Nil
50
100
10
Br
50
100

184
P. Srivastava et al./Bioorg. Med. Chem. 6 (1998) 181±187
Table 1Ðcontd
Compound no.
R
R1
R2
Concentration (ꢀM)
% inhibition in HO
Parasite
Host
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
H
H
H
H
OCH3
OCH3
H
10
50
15
75
Nil
Nil
Nil
Nil
Nil
Nil
Nil
100
100
Nil
31
100
10
100
Nil
Nil
Nil
Nil
100
100
12
50
100
10
CH2CH3
CH3
OH
OH
OH
OH
H
50
100
10
H
50
50
70
100
10
60
CH2CH3
CH3
5-NO2
5-NO2
H
Nil
15
Nil
10
50
100
10
34
71
20
Nil
5
50
100
100
100
100
100
Nil
34
100
10
6
CH3
Nil
Nil
4
50
100
10
CH3
OCH3
H
H
Nil
Nil
41
50
100
10
60
CH3
3-NO2
5-OCH3
5-OCH3
Nil
Nil
50
Nil
Nil
Nil
Nil
Nil
Nil
Nil
5
50
100
10
CH3
OCH3
OH
Nil
35
50
100
10
70
12
CH3
50
100
29
50
6
aPip=piperdin-1-yl.
bPyr=pyrrolidin-1-yl.
enzyme, heme oxygenase, which regulates the heme
milieu of the parasite. Another possible pathway has
been discussed by Slater et al. (1992) [12] which was
later modi®ed by Dorn et al. (1995) [13] stating the form-
ation of hemozoin which was responsible for showing
the resistant property of the parasite. Srivastava et al.
(1995) [14] also reported that even the preformed
hemozoin can be acted upon by heme oxygenase.
The e€ective compounds having the selective inhibition
of parasite enzyme open further avenues for develop-
ment of resistant reversal agents based on the above-
mentioned concept.
Table 2
In vivoa e€ect of potential compounds on heme oxygenase
activity of the cell free P. yoelii
Compounds 8, 14, 15, 16, 24 and 25, which selectively
block the parasite heme oxygenase activity in vitro (and,
with compound 25, in vivo), indicate that they can
intercept the intraerythrocytic heme catabolism and
provide ample toxic heme environment for e€ective
chloroquine-heme adduct formation which can make
the resistant strain of the parasite susceptible. It is likely
that if such compounds are administered with chlor-
oquine, it may act as a resistant reversal agent [12].
S. no.
Compound
no.
% inhibition in heme
oxygenase activity
1.
2.
3.
8
14
25
Nil
57
100
aCompounds were fed at the dose of 15 mg/kg b.wt Â5 days to
P. yoelii infected mice and the parasites isolated from the
animals were subjected to Heme oxygenase assay.

P. Srivastava et al./Bioorg. Med. Chem. 6 (1998) 181±187
185
5. Conclusion
2-aminopyridine in dry chloroform (100 ml) was
re¯uxed for 8 h. The solvent was removed under reduced
pressure, and the residual solid was kept at 100ꢀC under
vacuum for 1 h. The solid obtained after neutralisation
with sodium bicarbonate solution was ®ltered and
recrystallised from methanol±chloroform. Yield, 80%;
In conclusion, the present study con®rms that imi-
dazo [1,2-a] pyridines and substituted prolines as classes
of compounds are the new molecular structures which
selectively inhibit the parasite heme oxygenase in vitro
and in vivo, thereby opening new avenues for the
syntheses of di€erent classes of potential resistant
reversal agents, helpful in reversing the resistance prop-
erty of the malarial parasites which when given in com-
bination with chloroquine or other antimalarial(s) may
eradicate the resistant parasites.
m.p. 214ꢀC; MS; m/z 266 (M+); H NMR (CD3OD): ꢁ
1
1.12 (d, J ˆ 9Hz,6H, HC(CH3)2), 2.36 (s, 3H, CH3),
3.28 (m, 1H, HC(CH3)2), 6.65 (s, 1H, H-30), 6.9 (dde,
1H, H-6), 7.3 (dde, 1H, H-7), 7.48 (s, 1H, H-60), 7.52 (d,
J ˆ 9 Hz, 1H, H-8), 7.85 (s, 1H, H-3), 8.4 (d, J ˆ 8 Hz,
1H, H-5). Anal. calcd. for C17H18N2O.1/2 H2O: C,
74.18; H, 6.90; N, 10.18; Found: C, 74.15; H, 6.98; N,
10.22%.
6. Biological evaluation
Compounds (1±4) and (6,7) were prepared following
the same procedure.
6.1 Materials and methods
Plasmodium yoelii nigeriensis (multidrug-resistant)
infection was maintained in Swiss albino mice having
chloroquine tolerance up to 120 mg/kg b.wt. Infection/
parasitaemia was ascertained by monitoring the giemsa-
stained blood smears of infected animals micro-
scopically. The isolation of parasites was carried out
from infected animals' blood through density gradient
centrifugation and saponin lysis as described earlier [2].
Heme oxygenase activity was assayed following the
bilirubin formation [10] in the post-mitochondrial frac-
tion. Di€erent concentrations (10±100 ꢀM) of tested
compounds were supplemented in an assay system of
heme oxygenase before starting the enzymatic reaction.
For the evaluation of the ecacy of the compounds in
vivo, the compounds which selectively inhibited the
heme oxygenase activity of the parasite were orally admi-
nistered (15 mg/kg b.wt for 5 days) to P. yoelii infected
mice. The parasites from each compound-treated infected
animals were isolated and used for enzyme assay [2,10].
7.1.1 2-(3-Methoxy phenyl)imidazo[1,2-a]pyridine (7)
Yield, 72%; m.p. 72ꢀC [CHCl3]; MS; m/z 224 (M+);
1H NMR (CDCl3): ꢁ 3.92 (s, 3H, OCH3), 6.78±7.65 (m,
6H, Ar±H), 7.52 (bs, 1H, H-20), 7.88 (s, 1H, H-3), 8.12
(d, J ˆ 9 Hz, 1H, H-5). Anal. calcd. for C14H12N2O: C,
75.00; H, 5.35; N, 12.5; Found: C, 74.87; H, 5.31; N,
12.68%.
7.1.2 2-[4-(2-N,N-Diethylamino)ethoxyphenyl]imidazo
[1,2-a]pyridine (8)
A mixture of 3.2 g (9.52 mmol), 2-N,N-diethylamino-
ethylchloride hydrochloride 1.63 g (9.52 mmol) and
sodium hydride 0.68 g (28.57 mmol) in dry THF (50 ml)
was heated under re¯ux for 10 h. Then the solvent was
distilled o€. The residual oil was taken up in chloro-
form, washed with water till neutral and dried over
Na2SO4. The solvent was distilled o€ to give the pro-
duct. Recrystallised from chloroform±methanol, yield
(64%); m.p. 80ꢀC; MS; m/z 309 (M+); 1H NMR
(CDCl3): ꢁ 1.10 (t, J ˆ 8 Hz, 6H, N(CH2CH3)2), 2.4±
3.0 (m, 6H, 3ÂNCH2), 4.15 (t, J ˆ 6:5 Hz, 2H,
OCH2), 6.66±8.2 (m, 9H, Ar-H). Anal. calcd. for
C19H23N3O.H2O: C, 69.72; H, 7.64; N, 12.84; Found: C,
69.73; H, 7.50; N, 12.87%.
7. Experimental
All reagents and starting materials were from com-
mercial sources and used without further puri®cation.
All melting points were recorded on hot stage apparatus
and are uncorrected. 1H-NMR was measured on a
Perkin±Elmer R-32 or Bruker 400 FT or Bruker 300 FT
NMR instrument using TMS as a standard and mass
spectra on a JEOL- JMS-D-300 or JEOL SX 102/DA-
6000 mass spectrometer. Chemical analyses were carried
out on Carlo Erbo 1103 analyzer.
7.1.3 2-[4-(2-Piperidin-1-yl)ethoxyphenyl]imidazo
[1,2-a]pyridine (9)
Yield, 80%; m.p. 116ꢀC [CHCl3-MeOH]; MS: m/z
321 (M+); 1H NMR (CDCl3): ꢁ 1.5 (m, 6H, 3ÂCH2),
2.5 (m, 4H, 2ÂNCH2), 2.8 (t, J ˆ 6 Hz, CH2N), 4.1(t,
J ˆ 6 Hz, OCH2), 6.6±8.05 (m, 9H, Ar-H). Anal.
calcd. for C20H23N3O.H2O: C, 70.79; H, 7.3; N, 12.3;
Found: C, 70.92; H, 7.58; N, 12.35%.
Representative procedure for the preparation of imi-
dazo [1,2-a]pyridines:
7.1 2-[(4-Hydroxy-5-isopropyl-2-methyl)phenyl]
imidazo[1,2-a]pyridine (5)
7.1.4 2-[3-(2-N,N-Dimethylamino)ethoxyphenyl]
imidazo[1,2-a]pyridine (10)
Yield, 80%; m.p. 172ꢀC (oxalate)[MeOH-Ether];
MS: m/z 281 (M+); 1H NMR (CDCl3): ꢁ 2.5 (s, 6H,
A solution of 1 g (3.89 mmol) of 4-hydroxy-3-isopropyl-
6-methyl phenacyl bromide and 0.36 g (3.89 mmol) of
N(CH3)2), 2.7(t, J ˆ 6 Hz, 2H,
CH2N), 4.1(t,

186
P. Srivastava et al./Bioorg. Med. Chem. 6 (1998) 181±187
J ˆ 6 Hz, 2H, OCH2), 6.6±8.0 (m, 9H, Ar-H). Anal.
calcd. for C17H19N3O.(COOH)2.3H2O: C, 53.64; H,
6.35; N, 9.88; Found: C, 53.52; H, 6.37; N, 9.92%.
C23H29N3O.H2O: C, 72.44; H, 8.13; N, 11.02; Found: C,
72.66; H, 8.18; N, 11.12%.
7.1.10 2-[4-(Piperidin-1-yl)ethoxy-5-isopropyl-2-
methylphenyl]imidazo[1,2-a]pyridine (16)
7.1.5 2-[3-(2-N,N-Diethylamino)ethoxyphenyl]imidazo
[1,2-a]pyridine (11)
Yield , 56%; m.p. 216ꢀC (oxalate)[MeOH-Ether]; MS:
Yield, 80%; m.p. 165ꢀC (oxalate)[MeOH-Ether]; MS:
m/z 377 (M+); 1H NMR (CDCl3):
ꢁ 1.15 (d,
1
m/z 309 (M+); H NMR (CDCl3): ꢁ 1.02 (t, J ˆ 7 Hz,
J ˆ 9 Hz, 6H, HC(CH3)2, 1.5 (m, 6H, 3ÂCH2), 2.36
(s, 3H, CH3), 2.5 (m, 4H, 2ÂNCH2), 2.85 (t, J ˆ 6 Hz,
CH2N), 3.3 (m, 1H, HC(CH3)2), 4.1 (t, J ˆ 6 Hz, 2H,
OCH2), 6.6 (s, 1H, H-30), 6.78 (dde, 1H, H-6), 7.2 (dde,
1H, H-7), 7.45 (d, J ˆ 9 Hz, 1H, H-8), 7.5 (s, 1H,
H-60), 7.76 (s, 1H, H-3), 8.4 (d, J ˆ 6 Hz, 1H, H-5).
Anal. calcd. for C24H31N3O.(COOH)2.2H2O: C,
62.02; H, 6.9; N, 8.34; Found: C, 61.93; H, 6.88; N,
8.36%.
6H, 2ÂCH3), 2.6 (me, 4H, 2ÂNCH2), 2.85 (t, J ˆ 7 Hz,
2H, CH2N), 4.08 (t, J ˆ 7 Hz, 2H, OCH2), 6.6±8.0
(m, 9H, Ar-H). Anal. calcd. for C19H23N3O.
(COOH)2.3H2O: C, 53.50; H, 6.58; N, 8.91; Found: C,
53.52; H,6.69; N, 8.98%.
7.1.6 2-[3-(2-Piperidin-1-yl)ethoxyphenyl]imidazo
[1,2-a]pyridine (12)
Yield , 80%; m.p. 148ꢀC (oxalate)[MeOH-Ether]; MS:
m/z 321 (M+); 1H NMR (CDCl3): ꢁ 1.5 (m, 6H,
3ÂCH2), 2.5 (m, 4H, 2ÂNCH2), 2.75 (t, J ˆ 6 Hz, 2H,
CH2N), 4.15 (t, J ˆ 6 Hz, 2H, OCH2), 6.6±8.0 (m,
7.1.11 2-[5-Isopropyl-4-methoxy-2-methylphenyl]
imidazo [1,2-a]pyridine (17)
Yield, 48%; Viscous mass; MS : m/z 280 (M+); 1H
NMR (CDCl3): ꢁ 1.26 (d, J ˆ 7 Hz, 6H, HC(CH3)2, 2.53
(s, 3H, CH3), 3.30 (m, 1H, HC(CH3)2), 3.86 (s, 3H,
OCH3), 6.75 (s, 1H, H-30), 6.80 (dde, 1H, H-6), 7.19
(dde, 1H, H-7), 7.63 (s, 1H, H-60), 7.70 (s, 1H, H-3), 7.75
(d, J ˆ 9 Hz, H-8), 8.14 (d, J ˆ 7 Hz, 1H, H-5). Anal.
calcd. for C18H20N2O: C, 77.14; H, 7.14; N, 10.0;
Found: C, 77.12; H, 7.12; N, 9.89%.
9H,
Ar-H).
Anal.
calcd.
for
C20H23N3O
(COOH)2.3H2O: C, 56.77; H, 6.6; N, 9.03; Found: C,
56.98; H, 6.38; N, 9.16%.
7.1.7 2-[4-(2-N,N-Dimethylamino)ethoxy-5-isopropyl-
2-methylphenyl]imidazo[1,2-a]pyridine (13)
Yield, 76%; m.p. 111ꢀC (oxalate)[MeOH-Ether]; MS:
1
m/z 337 (M+); H NMR (CD3OD+CDCl3): ꢁ 1.15(d,
J ˆ 9:2 Hz, 6H, HC(CH3)2), 2.25 (s, 6H, N(CH3)2, 2.36
(s, 3H, CH3), 2.72 (t, J ˆ 6 Hz, CH2N), 3.25 (m, 1H,
HC(CH3)2), 4.05 (t, J ˆ 6 Hz, 2H, OCH2), 6.7 (s, 1H,
H-30), 6.78 (dde, 1H, H-6), 7.2 (dde, 1H, H-7), 7.45 (d,
J ˆ 9 Hz, 1H, H-8), 7.5 (s, 1H, H-60), 7.76 (s, 1H, H-3),
8.3 (d, J ˆ 7 Hz, 1H, H-5). Anal. calcd. for C21H27N3O.
(COOH)2.3H2O: C, 57.38; H, 7.27; N, 8.73; Found: C,
57.39; H, 7.37; N, 8.78%.
7.1.12 2-(3-Methoxyphenyl)-3-nitrosoimidazo[1,2-
a]pyridine (19)
To the solution of 7 (1.0 g (4.46 mmol)), in glacial
acetic acid (10 ml), aqueous solution of sodium nitrite
0.3 g (4.46 mmol) was added dropwise maintaining tem-
perature at 0ꢀC. Stirring was continued at room tem-
perature for another 3 h. Green solid separated was
®ltered and washed with chilled water, crystallised from
methanol-chloroform (73%), m.p. 160ꢀC: MS; m/z 253
1
7.1.8 2-[4-(2-N,N-Diethylamino)ethoxy-5-isopropyl-2-
methylphenyl]im idazo[1,2-a]pyridine (14)
(M+); H NMR (CDCl3) ꢁ 3.92 (s, 3H,OCH3), 7.15±
9.95 (m, 8H, Ar-H) Anal. calcd. for C14H11N3O2: C,
66.40; H, 4.34; N, 16.60; Found: C, 66.43; H, 4.50; N,
16.61%.
Yield, 77%; m.p. 67ꢀC (oxalate)[MeOH-Ether]; MS :
m/z 365 (M+); 1H NMR (D2O): ꢁ 0.90 (de, 6H,
CH(CH3)2), 1.15 (te, 6H, 2ÂCH2CH3), 2.0 (s, 3H, CH3),
2.85 (m, 1H, HC(CH3)2), 3.1 (qe, 4H, 2ÂNCH2CH3),
3.35 (bs, 2H, CH2N), 3.95 (bs, 2H, O-CH2), 4.05 (t,
J ˆ 6 Hz, 2H, OCH2), 6.6±8.0 (m, 7H, Ar-H). Anal.
calcd. for C23H31N3O. (COOH)2.H2O: C, 63.42; H,
7.38; N, 8.87; Found: C, 63.55; H, 7.42 ; N, 9.09%.
7.1.13 3-Amino-2-(3-methoxyphenyl)imidazo[1,2-a]
pyridine (20)
To the solution of 19 (1.0 g (3.95 mmol)) in acetic
acid-water (150:75 ml) mixture, zinc powder 2.31 g
(35.5 mmol) was added in portions maintaining tem-
perature at 0ꢀC. Stirring was continued at room tem-
perature for another 4 h. Zn dust was ®ltered and solid
obtained after neutralisation with aq. ammonia was ®l-
tered, dried and crystallised from ethyl acetate (40%)
7.1.9 2-[4-(2-Pyrrolidin-1-yl)ethoxy-5-isopropyl-2-
methylphenyl]imidazo[1,2-a]pyridine (15)
Yield, 75%; m.p. 120ꢀC [CHCl3-MeOH]; MS: m/z
363 (M+) ; H NMR (CDCl3): ꢁ 1.25 (d, J ˆ 8 Hz, 6H,
m.p. 120ꢀC: MS: m/z 239 (M+); H NMR (CDCl3): ꢁ
1
1
HC(CH3)2, 1.75 (m, 4H(CH2)2, 2.46 (s, 3H, CH3), 2.6
(m, 4H, 2ÂN-CH2), 2.90 (t, 2H, J ˆ 6:5 Hz, CH2N),
3.3 (m, 1H, HC(CH3)2), 4.1 (t, J ˆ 6:5 Hz, 2H,
OCH2), 6.6±8.0 (m, 7H, Ar-H). Anal. calcd. for
3.45 (bs, 2H, NH2), 3.89 (s, 3H, OCH3), 6.78±7.6 (m,
7H, Ar-H), 8.0 (d, J ˆ 9 Hz, 1H, H-5) Anal. calcd. for
C14H13N3O: C, 70.29; H, 5.4; N, 17.57; Found: C,
70.49; H, 5.5; N, 17.72%.

P. Srivastava et al./Bioorg. Med. Chem. 6 (1998) 181±187
187
7.1.14 Dimethyl/ethyl-2-methyl-c-5-(2-substituted-
phenyl)-pyrrolidine -c-3,t-4- dicarboxylate-r-2-carboxylic
acid (21±29)
7.26±8.62 (m, 3H, ArH). Anal. calcd. For C18H23NO8:
C, 56.69; H, 6.08; N, 3.89; Found: C, 3.67; H, 5,90,
N, 3.80%.
These compounds were prepared by the method
reported in literature [9], and spectral data for new
compounds are given below:
7.1.14.6 Compound 29. Yield, 62%; m.p. 202±4ꢀC
[MeOH]; MS: m/z 368 (M++1); 1H NMR (Pyd5): ꢁ
2.10 (s, 3H, CH3), 3.61 (s, 3H, OCH3), 3.64 (s, 3H,
OCH3), 3.68 (s, 3H, OCH3), 3.86 (d, J ˆ 11 Hz, 1H, H-3),
4.34 (t, 1H, H-4), 4.92 (d, J ˆ 10 Hz, 1H, H-5), 6.90±7.34
(m, 4H, ArH). Anal. calcd. For C17H21NO8: C, 55.58;
H, 5.71; N, 3.81; Found: C, 55.67; H, 5.63; N, 3.83%.
7.1.14.1 Compound 21. Yield, 60%; m.p. 217ꢀC [MeOH];
1
MS: m/z 366 (M++1); H NMR (Py.d5): ꢁ 1.04 (t, 3H,
CH2CH3), 1.14 (t, 3H, CH2CH3), 3.92 (d, J ˆ 11 Hz,
1H, H-3), 4.14 (q, 2H, CH2CH3), 4.24 (q, 2H,
CH2CH3), 4.31 (t, 1H, H-4), 5.15 (d, J ˆ 10 Hz, 1H,
H-5), 6.88±7.46 (m, 4H, ArH). Anal calcd. for
C18H23NO7: C, 59.17; H, 6.30; N, 3.86 Found: C, 59.28;
H, 6.50; N, 3.80.
Acknowledgements
Thanks are due to the Council of Scienti®c and Indus-
trial Research, New Delhi for providing Sr Research
Associateship to PS and PG, and to Zymogenetics, USA
for providing Research Assistantship to APM.
7.1.14.2 Compound 23. Yield, 60%; m.p. 205±7ꢀC
[MeOH]; MS: m/z 411 (M++1); 1H NMR (Pyd5): ꢁ
1.10 (t, 3H, CH2CH3), 1.16 (t, 3H, CH2CH3), 2.12 (s,
3H, CH3), 3.86 (d, J ˆ 11 Hz, 1H, H-3), 4.12 (q, 2H,
CH2CH3), 4.16 (q, 2H, CH2CH3), 4.22 (t, 1H, H-4), 5.32
(d, J ˆ 10 Hz, 1H, H-5), 7.10±8.14 (m, 3H, ArH). Anal.
calcd. for: C18H22N2O9: C, 52.68; H, 5.36; N, 6.82;
Found: C, 52.70 ; H, 5.47 ; N, 6.78%.
References
[1] Slater AFG. Pharmacol Therap 1993;57:203.
[2] Srivastava P, Pandey VC. Int J Parasitol 1995;25:1061.
[3] Srivastava P, Puri SK, Dutta GP, Pandey VC. Med Sci
Res 1992;20:321.
[4] Fitch CD. Parasitol Today 1986;2:330.
[5] Walter RD, Seth M, Bhaduri AP, Trop Med Parasitol
1993;44:5.
7.1.14.3 Compound 24. Yield, 60%; m.p. 188±90ꢀC
[MeOH]; MS: m/z 383 (M++1), 1H NMR (Py.d5): ꢁ
2.10 (s, 3H, CH3), 3.68 (s,6H, (OCH3)2), 3.88 (d,
J ˆ 11 Hz, 1H, H-3), 4.24 (t, 1H, H-4), 5.40 (d,
J ˆ 10 Hz, 1H, H-5), 7.10±8.88 (m, 3H, Ar-H); Anal.
calcd: For C16H18N2O9: C, 50.26; H, 4.69; N, 7.28;
Found: C, 50.30; H, 4.60; N, 7.28%.
[6] De D, Bhaduri AP, Milhous WK. Am J Trop Hyg
1993;41:113.
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1949;68:441, (b) Buu-Hoi Ng Ph, Jacquignon P, Xuong
Ng D, Lavit D. J Org Chem 1954;19:1370. (c) Schmid L,
Grundig K. Monatsh, 1953;84:491. (d) Ito Y,
Kato H, Ogawa N, Etsuche E, Kunata S, Jpn Kokai
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1994;50(10):3159.
[10] Tenhunen R, Marver HS, Schmid R. Proc Natl Acad Sci
1968;61:748.
7.1.14.4 Compound 27. Yield, 50%; m.p. 230±35ꢀC
[MeOH]; MS : m/z 367 (M++1); 1H NMR (Pyd5): ꢁ
2.10 (s, 3H, CH3), 3.66 (s, 3H, OCH3), 3.68 (s, 3H,
OCH3), 3.95 (d, J ˆ 11 Hz, 1H, H-3), 4.22 (t, 1H, H-4),
4.98 (d, J ˆ 10 Hz, 1H, H-5), 7.38±8.86 (m, 4H, ArH).
Anal. calcd. For C16H18N2O8: C, 52.48; H, 4.91; N,
7.62; Found: C, 52.38; H, 4.82; N, 7.60%.
[11] Lowry OH, Rosebrough NJ, Farr AL, Randall RJ. J Biol
Chem 1951;193:265.
[12] Slater AFG, Cerami A. Nature 1992;355:167.
[13] Dorn A, Sto€el R, Matile H, Bubendorf A, Ridley RG.
Nature 1995;374:269.
7.1.14.5 Compound 28. Yield, 68%; m.p. 210ꢀC
1
[MeOH]; MS : m/z 381 (M++1); H NMR (Py.d5) : ꢁ
2.93 (s, 3H, CH3), 4.48 (s, 3H, OCH3), 4.52 (s, 3H,
OCH3), 4.58 (s, 6H, OCH3)2), 4.81 (d, J ˆ 11 Hz, 1H,
H-3), 5.01 (t, 1H, H-4), 6.22 (d, J ˆ 10 Hz, 1H, H-5),
[14] Srivastava P, Pandey VC, Bhaduri AP. Trop Med Para-
sitol 1995;46:83.