Design and synthesis of novel substituted quinazoline derivatives as antileishmanial agents

Article abstract of DOI:10.1016/j.bmcl.2009.07.081

4-(Substituted-benzylidine)-2-substituted-5,6-dihydrobenzo[h]quinazoline (5a-p) and 4-(substituted-benzylidine)-2-substituted-3, 4, 5, 6-tetrahydrobenzo[h]quinazoline (6a-p) have been synthesized from 2-(substituted-benzylidine)tetralone-1(3a-d) and sever

Full text of DOI:10.1016/j.bmcl.2009.07.081

Bioorganic & Medicinal Chemistry Letters 19 (2009) 5474–5477
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design and synthesis of novel substituted quinazoline derivatives
as antileishmanial agents
a
b
b
K. C. Agarwal a, , Vidisha Sharma , Nishi Shakya , Suman Gupta
*
a Division of Medicinal & Process Chemistry, Central Drug Research Institute, Lucknow 226001, India
b Division of Parasitology, Central Drug Research Institute, Lucknow 226001, India
a r t i c l e i n f o
a b s t r a c t
Article history:
4-(Substituted-benzylidine)-2-substituted-5,6-dihydrobenzo[h]quinazoline (5a–p) and 4-(substituted-
benzylidine)-2-substituted-3, 4, 5, 6-tetrahydrobenzo[h]quinazoline (6a–p) have been synthesized from
2-(substituted-benzylidine)tetralone-1(3a–d) and several substituted guanidine sulfates(4a–d).These
compounds were tested for their in vitro antileishmanial activity. The compounds 6i, 6f, 6g show prom-
ising antileishmanial activity against Leishmania donovani.
Received 6 January 2009
Revised 4 June 2009
Accepted 16 July 2009
Available online 19 July 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Quinazolines
Pyrimidines
Antileishmanial agents
Leishmaniasis is a parasitic disease caused by different species
of genus Leishmania, protozoan which is transmitted by an insect
vector phleobotomine sandfly to humans. Leishmania has been
classically divided into cutaneous (CL), mucocutaneous (MCL)
and visceral leishmaniasis (VL), which can be fatal when untreated.
The disease is endemic in many tropical and subtropical regions of
the world, with 350 million people at risk.1 Around 12 million peo-
ple are affected by the disease in which 1.0–1.5 million cases per
annum of cutaneous leishmaniasis, 0.5 million cases of the fatal
visceral leishmaniasis.2
being explored to generate new leads in the chemotherapy of
leishmaniasis.5 Compounds of both synthetic and natural origin
comprising a diverse group of chemical structures have been re-
ported as antileishmanial agents. These include mostly the nitro-
gen heterocycles such as quinolines,6 acridines,7 phenothiazines,8
pyrimidines,9 purines,10 bis-benzamidines,11 pyrazolo[3,4b]pyri-
dine,12 benzothiazoles13 and imidazolidine.14 Other classes of com-
pounds include buparvaquone-oxime,15 bisbenzamidines,16
chalcones,17 quinines,18 amino acid esters and amides,19 amino
With the spread of HIV, visceral leishmaniasis has become
increasingly prevalent. Reactivation of asymptomatic or previously
healed leishmaniasis is common when there is co infection of AIDS
with leishmaniasis. There is still no effective vaccine for Kala-azar
and chemotherapy remains the most effective control measure.
Meglumine antimoniate (Glucantine) and sodium stibogluconate
(Pentostam) are the first line drugs for the treatment of leishman-
iasis. Pentamidine and Amphotericin B lipid complex3 are the sec-
ond line drugs in which Amphotericin B and its lipid complex are
quiet effective. Miltefosine,4 newly developed first oral drug is
effective but can not be given to pregnant women. Although new
drugs have been available in recent years for the treatment of vis-
ceral leishmaniasis, treatment of leishmaniasis suffers from prob-
lems of drug resistance and severe toxicity. In view of the above,
the search for the new molecular structures which would have
high tolerance limit as well as no toxicity, constitutes the major
thrust area of research on leishmaniasis. Natural products are
O
CHO
R'
O
R'
a
+
R
R
2
3
1
3a, R=H, R'=H
2a, R=H, R'=H
2b, R=Cl, R'=H
2c, R=F, R'=H
2d, R=Cl, R'=Cl
3b, R=Cl, R'=H
3c, R=F, R'=H
3d, R=Cl, R'=Cl
R1
b
NH2.H2SO4
R1
HN
4
R1
N
NH
N
N
R
+
R
R'
R'
6
5
* Corresponding author. Tel.: +91 522 2612411x4319; fax: +91 522 2623405.
E-mail address: kcagarwal@rediffmail.com (K.C. Agarwal).
Scheme 1. Reagents and conditions: (a) 5% alcoholic KOH, ethanol, 0 °C, rt, 2 h; (b)
substituted guanidine sulfates 4, t-BuOK, methanol, reflux, 24 h.
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.07.081

K. C. Agarwal et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5474–5477
5475
Table 1
Antileishmanial in vitro activity against luciferase–promastigote system of dihydroquinazolines 5a–p and tetrahydroquinazolines 6a–p against L. donovani
R
R0
R1
Compd 5
Mean % inhibition (at 10
l
g/ml) S.D.
Compd 6
Mean % inhibition (at 10
lg/ml) S.D.
(n = 2) promastigote
(n = 2) promastigote
H
H
5a
71.5 0.84
91.8 1.48
74.7 1.20
62.2 .70
6a
99.9 0.07
99.8 0.14
99.8 0.28
99.4 0.49
99.6 0.21
99.9 0.07
99.9 0.14
68.2 0.98
98.7 0.49
99.6 0.42
96.3 0.70
99.9 0.07
99.7 0.42
99.7 0.35
99.8 0.21
99.9 0.14
N
O
H
H
H
F
H
H
H
H
H
H
H
H
H
H
H
Cl
Cl
Cl
Cl
5b
5c
5d
5e
5f
6b
6c
6d
6e
6f
N
N
N
N
N
N
N
N
N
O
64.8 0.49
47.8 1.48
61.8 1.55
44.9 1.34
74.8 0.84
53.5 1.62
58.3 1.06
51.4 1.13
93.1 3.11
95.2 0.77
77.9 0.84
15.7 1.62
F
N
N
F
5g
5h
5i
6g
6h
6i
F
N
N
N
O
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
5j
6j
N
N
5k
5l
6k
6l
N
N
N
O
5m
5n
5°
6m
6n
6o
6p
N
N
N
5p
N
a
SSG
Pentamidine
b
a
SSG (sodium stilbogluconate) shows no inhibition in promastigotes at 10
l
g/ml.
b
Pentamidine shows 100% inhibition in promastigotes at 10
lg/ml, All compounds were confirmed by MS (ES+) analysis.
alcohols,20 alkyl phospholipids,21 ether phospholipids22 sulfanila-
mides,23 artemisinin24 and certain platinum complexes.
(pyrimethamine, cycloguanil), antibacterial (trimethoprim) and
anticancer (methotrexate). number of compounds having
pteridine, quinazoline and pyrimidine moieties are reported to be
potent inhibitors of DHFR in Leishmania. Based on these observa-
tions we hypothesized to synthesize dihydro and tetrahydroqui-
A
Biochemical targets are also under investigation25 in which
Dihydrofolate reductase (DHFR)26 is being used to design the novel
compounds. DHFR has been a successful target for antimalarials

5476
K. C. Agarwal et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5474–5477
Table 2
nazolines and screen them for their antileishmanial activity. Coo-
mbs group27,28 investigated some 5-substituted 2,4-diaminopyr-
imidines that were good inhibitors of Leishmania mexicana DHFR
in vitro model. However, in a mouse study, the compounds were
found toxic. In this communication, we report the quinazoline
based novel compounds having antileishmanial activity.
The synthetic strategy for the quinazoline-based compounds
has been depicted in Scheme 1. Tetralone-1, on reaction with var-
ious aldehydes 2a–d in alcoholic solution in the presence of so-
dium or potassium hydroxide furnished benzylidenes29 3a–d.
These benzylidenes 3a–d were then subjected to cyclization by
treating them with guanidine sulfates30 4a–d(R1 = cyclic amines)
in the presence of potassium tertiary butoxide in methanol under
reflux for 24 h. As confirmed by HPLC and TLC analysis, the crude
products were the mixture of two classes of compounds.
Antileishmanial in vitro activity against luciferase–amastigote system
Compd
IC50 (lg/ml)
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
6o
ND*
3.48
ND
ND
ND
3.22
4.07
3.58
5.20
ND
8.95
2.65
ND
ND
ND
6.33
53.62
12.11
Of these two types of product, tetrahydroquinazolines 6 had
moderate stability. After purification it had a tendency to undergo
slow oxidation when kept in methanolic solution to dihydroqui-
nazoline 5 on exposure to air and high temperature. This led us
to treat the crude product mixtures comprising 5 and 6 with DDQ
aiming to exclusively get dihydroquinazolines 5. However, addition
of oxidizing agent failed to facilitate the conversion of 6 to 5. All
the synthesized compounds were well characterized by spectro-
scopic methods such as IR, mass, NMR and elemental analysis.
The in vitro efficacy of the synthesized compounds on promastig-
otes and amastigotes of Leishmania donovani were assessed by a pre-
viously described method.31 The antileishmanial activity of dihydro
(5a–p) and tetrahydro (6a–p) quinazoline derivatives against a clin-
ically derived strain of L. donovani is shown in Table 1 while com-
pounds having promastigote inhibition more than 80% were
screened against amastigotes and their IC50 was calculated as shown
in Table 2. The Data suggests that tetrahydroquinazoline derivatives
represent interesting leads as antileishmanial agents. All the tetra-
hydroquinazoline (6a–p) derivatives showed close or equal to
100% inhibition against promastigotes except 6h (68.9%). However,
the corresponding dihydroqinazoline derivatives (5a–p) generally
showed significantly lower inhibition (14.7–94.7%) with 5n being
the most active compound. It was observed that the compounds
having R1 as pyridyl piperazinyl group 5d, 5h, 5l, 5p, 6d and 6h
possessed comparatively poor activities in both dihyro and tetrahy-
droquinazolines. This observation shows that when R and R0 are
identical, the bigger ortho- substituent R1 led to less active
compounds 5d, 5p (as compared 1-pyridin-2-yl-piperazine with
other cyclic amino groups) indicating that cyclic amino group R1
have impact on the activity. It was also noticed that when the
para-substituent R is a Cl moiety, the e-withdrawing ortho-substitu-
ent (R0 = Cl) resulted in more active compounds than the corre-
sponding unsubstituted analogs (comparing 5m–o with 5i–k)
suggesting the ortho-position R0 group can also impact the activity
of the products. In the absence of ortho-substituent (R0 = H), the ones
without para-substituent (R = H) were more active than the ones
with e-withdrawing para-substituents (R = F or Cl) (comparing
5a–d with 5e–h or 5i–l) demonstrating the importance of the impact
of para-substituent on activity. Overall, for the dihydroquinazoline
derivatives (5a–p), R, R0 and R1 all have impact on the activity of
the products.
6p
SSG
Pentamidine
*
ND = not done.
derivatives 6a–p, 6l with R1 as pyridyl piperazinyl group and R
as chloro substituent, exhibited least IC50 value of 2.65 g/ml.
Replacement of chloro group with more electronegative fluoro
group as in 6h led to increase in IC50 value to 3.58 g/ml. Introduc-
tion of another chloro group at ortho position in 6l decreased the
activity by approximately 2.5-fold as in 6p. Replacement of pyridyl
piperazine group with piperidinyl group led to decrease in activity.
The compound having no substitution as R and R0 6b gave IC50 va-
l
l
lue of 3.48 lg/ml. Introduction of fluoro group as ortho-substituent
in 6f led to slight decrease in IC50 value (3.22 lg/ml) .Introducing
five-membered pyrolidinyl substituent at R1 led to increase in
IC50 values. Compound 6g having fluoro substituent as R0 showed
IC50 value of 4.07
substituent chloro as in 6k resulted in abruptly high IC50 value of
8.95 g/ml. Replacement of pyrolidinyl group with morpholinyl
l
g/ml and surprisingly lesser electronegative R0
l
substituent in 6k again decreased the IC50 value to 5.20 lg/ml for
6i. From this data it can be observed that R1 and R0 both have con-
siderable effect on the IC50 values. All the compounds exhibited
higher activities against L. donovani as compared to reference drugs
Sodium Stibogluconate (IC50 = 53.62
lg/ml) and pentamidine
(IC50 = 12.11 g/ml) as representing the interesting leads as antile-
l
ishmanial compounds.
In conclusion, we have identified a new series of quinazoline
derivatives as inhibitors of L. donovani.The preliminary investiga-
tions revealed that these quinazolines has potential as antileish-
manial agents and has opened
exploration.
a new avenue for further
Acknowledgments
We are thankful to the Director, CDRI, Lucknow, India for con-
stant encouragement to the drug development programme. We
also acknowledge SAIF Division, CDRI, Lucknow for providing spec-
troscopic data. CDRI Communication No. 7639.
Among dihydroquinazolines compounds 5b, 5h, 5m and all of
the tetrahydroquinazolines 6a–p were screened against amastig-
otes and gave 45–100% inhibition Among them the compounds
giving >80% inhibition against amastigotes were selected for the
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2009.07.081.
calculation of IC50. All these compounds gave IC50 <10 lg/ml with
6l being the most active one. Among the tetrahydroquinazoline
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