Greener synthesis of indolizine analogues using water as a base and solvent: study for larvicidal activity against Anopheles arabiensis

Article abstract of DOI:10.1111/cbdd.12823

Greener synthesis of a series of novel indolizine analogues have been achieved by the cyclization of aromatic cycloimmonium ylides with electron-deficient alkynes in the presence of water as the base and solvent at 80?°C. Yield of the title compounds was

Full text of DOI:10.1111/cbdd.12823

Received Date : 26-Mar-2016
Revised Date : 19-May-2016
Accepted Date : 06-Jul-2016
Article type : Research Article
Greener synthesis of indolizine analogues using water as a base and
solvent: study for larvicidal activity against Anopheles arabiensis
1
2,*
3
2
Sandeep C , Katharigatta N. Venugopala , Raquel M. Gleiser , Abeen Chetram , Basavaraj
4
,5, *
6
7
2
Padmashali
, Rashmi S. Kulkarni , Rashmi Venugopala , Bharti Odhav
1
Institute for Stem Cell Biology and Regenerative Medicine, NCBS, TIFR, GKVK, Bellary Road,
Bangalore-560 065, India
2
Department of Biotechnology and Food Technology, Durban University of Technology, Durban
4
001, South Africa
3
CREAN-IMBIV (CONICET-UNC), Av. Valparaíso s.n., and FCEFyN, Av. Sársfield 299,
Universidad Nacional de Córdoba, Córdoba (5000), Argentina
4
Department of Chemistry, Sahyadri Science College (Autonomous), Shimoga 577 203, India
5
Department of Studies and Research in Chemistry, School of Basic Sciences, Rani Channamma
University, Belagavi 591 156, Karnataka, India
6
Department of Chemistry, Jain University, Bangalore 560 019, India
7
Department of Public Health Medicine, University of KwaZulu-Natal, Howard College Campus,
Durban 4001, South Africa
*
Corresponding authors
Tel. +27 31 373 4887; Fax: +27 86 242 3534; E-mail: katharigattav@dut.ac.za (Katharigatta N. Venugopala)
Tel. +91 98 4421 8894. E-mail: basavarajpadmashali@yahoo.com (Basavaraj Padmashali)
This article has been accepted for publication and undergone full peer review but has not
been through the copyediting, typesetting, pagination and proofreading process, which may
lead to differences between this version and the Version of Record. Please cite this article as
doi: 10.1111/cbdd.12823
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ABSTRACT
Greener synthesis of a series of novel indolizine analogues have been achieved by the
cyclization of aromatic cycloimmoniumylides with electron deficient alkynes in presence of
water as the base and solvent at 80 °C. Yield of the title compounds was good and reactions
performed were eco-friendly. The structures of these newly synthesized compounds have
been confirmed by spectroscopic techniques such as FTIR, NMR, LC-MS and elemental
analysis. Characterized title compounds were evaluated for larvicidal activity against
Anopheles arabiensis by standard WHO larvicidal assay using Temephos as standard at 4
μg/mL. Title compounds 2e, 2f and 2g emerged as promising larvicidal agents.
Keywords:
Indolizine analogues, synthesis, characterization, larvicidal activity.
Introduction
Indolizines are bicyclic heterocyclic compounds containing condensed five and six
membered rings with bridging nitrogen. They are isoelectronic with indole and represent a
group of heterocyclic compounds structurally related to purines. Indolizine skeletons with
different degrees of unsaturation are present in a wide variety of natural and unnatural
azacyclic compounds. Most of the naturally occurring indolizines have been isolated from
species of genus Dendrobates (Anura: Dendrobatidae) poison-arrow frogs (1, 2),
Monomorium (Hymenoptera: Formicidae) ants (3), Dendrobium (Asparagales: Orchidaceae)
orchids (4), Tylophora (Gentianales: Apocynaceae) vines (5) and plants of Leguminosae
(
Fabaceae) family (6). Indolizine alkaloids display broad spectrum of biological activities (4-
). Polyhydroxylated indolizine alkaloids are excellent inhibitors of biologically important
7
pathways. These include the binding and processing of glycoproteins (8), potent glycosidase
inhibitor activities (6, 9, 10), activity against HIV (11, 12) as well as against other important
pathogens (13). The 1-azabicyclo[4,3,0]nonane (indolizine) framework occupies a special
place in heterocyclic systems due to the presence of this structural assembly in a number of
natural products of biological importance such as tubersonine (14), (-)-strychnine (15), (+)-
vinblastine (16), (-)-monomorine (17), (-)-gephyrotoxin (18), etc. On the other hand,
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synthetic indolizine derivatives have been reported as calcium channel blockers (19),
3
phospholipase A inhibitors (20), histamine H -receptors antagonist (21), 5-HT -receptors
2
3
antagonists (22), anti-inflammatory (23, 24), anti-tumour agents (25-27), oral hypoglycaemic
28) and CNS activity (29-31). In continuation of our studies on synthesis of promising
heterocyclic compounds for anti-TB (32), anticancer (33, 34) and anti-mosquito properties
35, 36) and screening them for polymorphism behavior (37-39) herewith we undertake
(
(
design and synthesis of novel indolizine scaffolds (scheme 1) to be screened for larvicidal
activity against Anopheles arabiensis by standard WHO larvicidal assay using standard
substance (40).
Materials and Methods
Chemistry
All the reactions were carried out in hot-air dried glass wares under nitrogen atmosphere
using dry solvents. NMR (400 MHz) spectra were recorded at ambient temperature using
CDCl , DMSO-d as a solvent using Bruker-400 spectrometer. Chemical shift values are
3
6
measured in δ ppm and were referenced with TMS. The peak multiplicities were given as
follows; s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet. LC-MS analysis was
performed on Agilent LC-1200 series coupled with 6140 single quad mass spectrometer with
ESI +ve and –ve mode, MS range 100-2000. Elemental analyses were recorded using Perkin
Elmer CHNS analyser. All the commercially available chemicals were purchased from
Sigma-Aldrich Chemicals Company.
General procedure for the preparation of 1-(2-(substituted phenyl)-2-oxoethyl)pyridin-
1-ium bromide (1a-f)
To a stirred solution of pyridine (0.012 mol) in dry acetone (10 mL), was added substituted
phenacylbromide (0.012 mol). Stirring was continued for 5 h at room temperature. Solid
product separated was filtered and dried under vacuum to afford intermediates 1-(2-
(
substituted phenyl)-2-oxoethyl)pyridin-1-ium bromide (1a-f) at 96-99% yield.
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General procedure for the preparation of ethyl 3-(substituted benzoyl)-2-
methylindolizine-1-carboxylate (2a-j)
To a stirred solution of 1-(2-(substituted phenyl)-2-oxoethyl)pyridiniumbromide (0.0016
mol), in water (10 mL), was added ethyl propiolate / ethyl 2-butynoate (0.0016 mol), stirred
at 80 °C for 3h. Completion of reaction was monitored on TLC. The reaction mixture was
diluted with ethyl acetate. Organic layer was separated, washed with brine and dried under
sodium sulphate. The crude compound was purified by recrystallization method using hexane
and ethyl acetate to afford 69-83% yield of ethyl 3-(substituted benzoyl)-2-methylindolizine-
1-carboxylates. The physicochemical constants of the title compounds 2a-j are tabulated in
Table 3.
Ethyl 3-(4-nitrobenzoyl)indolizine-1-carboxylate (2a)
-1
1
FTIR (KBr) (cm ): 1679, 1620, 1595; H NMR (400 MHz, CDCl ) δ = 9.99-9.97 (m, 1H),
3
8
4
1
1
.45-8.36 (m, 3H), 7.97-7.93 (m, 2H), 7.74 (s, 1H), 7.56-7.51 (m, 1H), 7.19-7.15 (m, 1H),
13
.42-4.35 (q, J = 7.2Hz, 2H), 1.42-1.37 (t, J = 7.2, 3H); C NMR (300 MHz, CDCl ) = δ
3
82.86, 163.66, 149.37, 145.34, 140.38, 129.70, 129.31, 129.16, 128.56, 123.66, 121.85,
+
19.70, 115.94, 107.24, 60.30, 14.49; LC-MS (ESI, Positive): m/z: (M+H) : 339.2; Anal.
calculated for: C H N O ; C, 63.90; H, 4.17; N, 8.28; Found: C, 63.87; H, 4.10; N, 8.22.
1
8
14
2
5
Ethyl 2-methyl-3-(4-nitrobenzoyl)indolizine-1-carboxylate (2b)
-1
1
FTIR (KBr) (cm ): 1681, 1618, 1595; H NMR(400 MHz, CDCl ) δ = 9.78-9.76 (m, 1H),
3
8.40-8.32 (m, 3H), 7.83-7.79 (m, 2H), 7.47-7.41 (m, 1H), 7.07-7.06 (m, 1H), 4.43-4.36 (q, J
1
3
=
7.2Hz, 2H), 2.18 (s, 3H), 1.44-1.40 (t, J = 8Hz, 3H); C NMR (400 MHz, DMSO-d ) δ =
6
1
1
84.67, 163.74, 148.96, 146.17, 138.89, 137.45, 129.68, 128.55, 128.12, 123.87, 121.81,
+
18.66, 115.34, 104.88, 59.55, 14.38, 14.24; LC-MS (ESI, Positive): m/z: (M+H) : 353.2;
Anal. calculated for: C H N O ; C, 64.77; H, 4.58; N, 7.95; Found: C, 64.70; H, 4.48; N,
1
9
16
2
5
7
.88.
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Ethyl 3-(4-chlorobenzoyl)indolizine-1-carboxylate (2c)
-1
1
FTIR (KBr) (cm ): 1699, 1614, 1523; H NMR (400 MHz, CDCl ) δ = 9.93-9.91 (m, 1H),
3
8.42-8.39 (m, 1H), 7.78-7.75 (m, 3H), 7.51-7.45 (m, 3H), 7.12-7.08 (m, 1H), 4.41-4.35 (q, J
13
=
7.2Hz, 2H), 1.42-1.38 (t, J = 7.2Hz, 3H); C NMR (300 MHz, DMSO-d ) δ = 183.16,
6
1
1
62.89, 139.06, 137.95, 136.43, 130.47, 128.81, 128.73, 128.59, 127.72, 121.71, 118.77,
+
16.09, 105.39, 59.73, 14.27; LC-MS (ESI, Positive): m/z: (M+H) : 328.2; Anal. calculated
for: C H ClNO ; C, 65.96; H, 4.31; N, 4.27; Found: C, 65.91; H, 4.30; N, 4.31.
1
8
14
3
Ethyl 3-(4-chlorobenzoyl)-2-methylindolizine-1-carboxylate (2d)
-1
1
FTIR (KBr) (cm ): 1687, 1620, 1510; H NMR (400 MHz, CDCl ) δ = δ 9.53-9.50 (m, 1H),
3
8
1
3
1
.36-8.33 (m, 1H), 7.65-7.63 (d, J=8.0 Hz, 2H), 7.47-7.45 (d, J = 8.0 Hz, 2H), 7.38-7.34 (m,
H), 6.98-6.94 (m, 1H), 4.42-4.36 (q, J = 7.2Hz, 2H), 2.23 (s, 3H), 1.44-1.40 (t, J = 7.2Hz,
1
3
H); C NMR (400 MHz, CDCl ) δ = 186.3, 164.8, 139.6, 139.4, 138.21, 137.75, 130.33,
3
28.88, 127.96, 127.20, 122.51, 119.3, 114.4, 105.4, 59.84, 15.07, 14.52; LC-MS (ESI,
+
Positive): m/z: (M+H) : 342.2; Anal. calculated for: C H ClNO ; C, 66.77; H, 4.72; N,
19
16
3
4
.10; Found: C, 66.83; H, 4.71; N, 3.99.
Ethyl 3-(4-bromobenzoyl)indolizine-1-carboxylate (2e)
-1
1
FTIR (KBr) (cm ): 1699, 1612, 1521; H NMR (400 MHz, CDCl ) δ = 9.97-9.87 (m, 1H),
3
8.41-8.39 (m, 1H), 7.77 (s, 1H), 7.71-7.64 (m, 4H), 7.49-7.46 (m, 1H), 7.12-7.08 (m, 1H),
13
4
.40-4.35 (q, J = 7.2Hz, 2H), 1.42-1.38 (t, J = 7.2Hz, 3H); C NMR (400 MHz, DMSO-d ) δ
6
=
183.27, 162.86, 139.05, 138.28, 131.50, 130.61, 128.82, 128.72, 127.72, 125.34, 121.66,
+
1
18.76, 116.09, 105.39, 59.71, 14.25; LC-MS (ESI, Positive): m/z: (M+H) : 372.2; Anal.
calculated for: C H BrNO ; C, 58.08; H, 3.79; N, 3.76; Found; C, 57.98; H, 3.83; N, 3.68.
1
8
14
3
Ethyl 3-(4-bromobenzoyl)-2-methylindolizine-1-carboxylate (2f)
-1
1
FTIR (KBr) (cm ): 1687, 1622, 1618; H NMR (400 MHz, CDCl ) δ = 9.51-9.49 (m, 1H),
3
8
1
3
5
.36-8.33 (m, 1H), 7.63-7.61 (d, J = 10.4Hz, 2H), 7.57-7.55 (d, J = 9Hz, 2H), 7.38-7.36 (m,
H), 6.98-6.96 (m, 1H), 4.42-4.36 (q, J = 7.2Hz, 2H) , 2.23 (s, 3H), 1.44-1.40 (t, J = 7.2Hz,
+
H). LC-MS (ESI, Positive): m/z: (M+H) : 386.2; Anal. calculated for: C H BrNO ; C,
1
9
16
3
9.08; H, 4.18; N, 3.63; Found; C, 59.13; H, 4.06; N, 3.65.
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Ethyl 3-(4-fluorobenzoyl)indolizine-1-carboxylate (2g)
-1
1
FTIR (KBr) (cm ): 1699, 1618, 1522; H NMR (400 MHz, CDCl ) δ = 9.97-9.55 (m, 1H),
3
8.38-8.37 (m, 1H), 7.87-7.82 (m, 2H), 7.78 (s, 1H), 7.47-7.43 (m, 1H), 7.25-7.21 (t, J = 8.4
Hz, 2H) , 7.19-7.16 (m, 1H), 4.40-4.35 (q, J = 7.2Hz, 2H), 1.42-1.38 (t, J = 7.2Hz, 3H). LC-
+
MS (ESI, Positive): m/z: (M+H) : 312.2: Anal. calculated for: C H FNO ; C, 69.45; H,
18
14
3
4
.53; N, 4.50; Found; C, 69.41; H, 4.50; N, 4.55.
Ethyl 3-(4-fluorobenzoyl)-2-methylindolizine-1-carboxylate (2h)
-1
1
FTIR (KBr) (cm ): 1681, 1600, 1510; H NMR (400 MHz, CDCl ) δ = 9.43-9.42 (m, 1H),
3
8.35-8.33 (m, 1H), 7.74-7.70 (m, 2H), 7.36-7.33 (m, 1H), 7.18-7.15 (t, J = 8.4Hz, 2H),
6.96-6.93 (m, 1H), 4.42-4.36 (q, J = 7.2Hz, 2H), 2.23 (s, 3H), 1.44-1.40 (t, J = 7.2Hz, 3H);
1
3
C NMR (400 MHz, CDCl ) δ = 186.28, 166.38, 164.94, 163.87, 139.53, 137.48, 137.25,
3
1
5
37.22, 131.48, 131.39, 127.90, 127.02, 122.61, 119.36, 115.83, 115.62, 114.35, 105.36,
+
9.82, 14.99, 14.54; LC-MS (ESI, Positive): m/z: (M+H) : 326.2: Anal. calculated for:
C H FNO ; C, 70.14; H, 4.96; N, 4.31; Found; C, 70.15; H, 4.91; N, 4.33.
19
16
3
Ethyl 3-(4-methylbenzoyl)indolizine-1-carboxylate (2i)
-1
1
FTIR (KBr) (cm ): 1685, 1604, 1521; H NMR (400 MHz, CDCl ) δ = 9.96-9.94 (m, 1H),
3
8.40-8.38 (m, 1H), 7.83 (s, 1H), 7.75-7.73 (d, J = 8 Hz, 2H), 7.46-7.43 (m, 1H), 7.33-7.31 (d,
J = 8Hz, 2H), 7.09-7.07 (m, 1H), 4.40-4.35 (q, J = 7.2Hz, 2H), 2.46 (s, 3H), 1.41-1.38 (t, J =
13
7
.2Hz, 3H); C NMR (400 MHz, CDCl ) δ = 185.48, 164.15, 142.10, 139.81, 137.18,
3
1
29.16, 129.08, 128.75, 127.50, 122.66, 119.49, 115.15, 106.11, 60.07, 21.58, 14.56; LC-MS
+
(
ESI, Positive): m/z: (M+H) : 308.2: Anal. calculated for: C H NO ; 74.25; H, 5.58; N,
1
9
17
3
4
.56; Found; 74.28; H, 5.57; N, 4.51.
Ethyl 3-(4-cyanobenzoyl)indolizine-1-carboxylate (2j)
-1
1
FTIR (KBr) (cm ): 2227, 1683, 1616; H NMR (400 MHz, CDCl ) δ = 9.96-9.95 (m, 1H),
3
8
7
3
1
.44-8.42 (m, 1H), 7.90-7.88 (d, J = 8.4 Hz, 2H), 7.83-7.81 (d, J = 8.4Hz, 2H), 7.73 (s, 1H),
.54-7.52 (m, 1H), 7.17-7.14 (m, 1H), 4.41-4.36 (q, J = 7.2Hz, 2H), 1.42-1.38 (t, J = 7.2Hz,
1
3
H); C NMR (300 MHz, CDCl ) δ = 183.13, 163.66, 143.61, 140.24, 132.22, 129.27,
3
29.22, 129.04, 128.41, 121.78, 119.62, 118.06, 115.81, 114.79, 107.06, 60.25, 14.45; LC-
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+
MS (ESI, Positive): m/z: (M+H) : 319.2; Anal. calculated for: C H N O ; C, 71.69; H, 4.43;
1
9
14
2
3
N, 8.80; Found; C, 71.58; H, 4.47; N, 8.76.
Larvicidal Activity
The Anopheles arabiensis used were from a colonized strain from Zimbabwe which had been
reared according to the WHO (1975) guidelines (40) in an insectary simulating the
temperature (27.5 °C), humidity (70%), and lighting (12/12) of a malaria endemic
environment. One mL of test compound (1 mg/mL) was added to distilled water (250 mL)
rd
producing a final concentration of 4 ߤg/mL. Thirty 3 instar larvae were placed in the
container. A negative control was set up using a solvent (acetone) and distilled water and a
positive control included Temephos (Mostop; Agrivo), an effective emulsifiable
organophosphate larvicidal used by the malaria control program. Each container was
monitored for larval mortality at 24 h intervals for a period of three days and fed specially
made cat food with reduced oil/fat content at regular intervals. Bioassays were triplicated.
The percentage mortality was calculated relative to the initial number of exposed larvae. The
larvicidal results are tabulated in Table 4.
Data analysis
General linear mixed models (41) were used to determine differences between treatments
registered in larval mortality (larvicide assays). Dependent variables were A. arabiensis
mortality, fixed effects were test compound (test compounds 2a-j, acetone, and Temephos)
and observation period (24 and 48 h). Random effects were mosquito groups (i.e., container
in larvicide tests). Bonferroni-Hom test was used for post hoc analyses. In all cases, a value
of p < 0.05 was considered statistically significant. Throughout the text, the results are
presented as the adjusted mean plus/minus the standard error.
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Results and Discussion
Chemistry
The synthesis of biologically active indolizines (42) continues to attract the attention of
organic chemists (43-46). The indolizines are most commonly synthesized by sequential N-
quarterisation and intramolecular cyclocondensation reactions (47) or the cycloaddition
reaction (48, 49) of N-acyl/alkyl pyridinium salts. Another stereo selective route is based on
the iron-catalyzed cyclization of N-substituted pyrrolotrienes (50). A similar strategy was
reported for the synthesis of indolizines via intramolecular 1,5-dipolar cyclization of 2-vinyl
pyridiniumylide in the presence of tetrakis[pyrido]cobalt(II)-dichromate (51). A new pathway
to chiral indolizines was accomplished from proline via the Pauson Khand reaction (52)
involving an intramolecular cyclization reaction.
In the present research, synthesis of intermediates N-heterocyclicylides (1a-f) were prepared
by stirring substituted pyridines with substituted phenacyl bromides separately in the
presence of acetone at room temperature. The products obtained were filtered, dried under
vacuum and recrystallized using ethanol solvent. The yields of ylides (1a-f) obtained were
96-99%. Anticipated indolizines have been prepared by the 1,3-dipolar cycloaddition reaction
of N-heterocyclic ylides with electron deficient alkynes in the presence of water as a base and
solvent at 80 °C in good yields. The completion of reaction was monitored on TLC. The
reaction mixture was diluted with ethyl acetate, the organic layer was separated and washed
with brine and dried with anhydrous sodium sulphate and recrystallized with mixture of
hexane-ethyl acetate as a solvent to obtain title compounds at 69-83% yield.
Synthesis of title compound 2a was attempted using different solvents (DMF, MeCN, DMF,
THF, water) and bases such as K CO TEA, NaHCO and water at different temperatures as
2
3,
3
tabulated in Table 1. However, the synthesis of compound 2a was achieved with water as
base and solvent with remarkable increase in yield as well as reduced reaction time compare
to other solvents such as DMF, MeCN, and THF (Table 2).
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Table 1: Reaction condition for product 2a with different bases and solvents at various
temperatures
Entry
Base
Solvent
Temp (°C)
Yield (%)
1
2
3
4
5
6
K CO
DMF
MeCN
DMF
THF
RT
70
68
43
62
45
56
83
2
3
K CO
2
3
TEA
TEA
RT
60
NaHCO3
Water
DMF
Water
RT
80
RT = room temperature
Table 2: Reaction condition for product 2a with different solvents at various temperatures
Entry
Solvent/base ratio
Temperature (°C)
Yield (%)
1
2
3
4
5
Water:MeCN (1:1)
Water:THF (1:1)
Water:DMF (1:1)
Water:DMF (2:1)
Water
70
70
80
80
80
74
78
77
79
83
Scheme 1: Synthesis of indolizine analogues 2a-j: Reagents and conditions (a) pyridine, dry
acetone, stir at room temperature, 5 h; (b) water, stir, 80 °C, 3h.
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Table 3: Physicochemical constants of ethyl 3-(substituted benzoyl)-2-substituted indolizine-
1-carboxylate analogues 2a-j
c
Mol formulae
Compound
Yield
m.p (°C)
cLogP
1
2
R
R
a,b
(
Mol mass)
(%)
C H N O (338)
158-159
134-135
122-123
127-128
126-127
130-131
121-122
124-125
145-146
151-152
4.1470
4.6460
5.0722
5.5712
5.2222
5.7212
4.5022
5.0012
4.8504
3.8505
18
14
2
5
2
a
NO
NO
Cl
Cl
Br
Br
F
2
H
83
76
73
69
79
75
80
77
77
79
C H N O (352)
19
16
2
5
2
b
2
CH
H
3
3
3
3
C H ClNO (327)
18
14
3
2
c
C H ClNO (341)
19
16
3
2
d
CH
H
C H BrNO (371)
18
14
3
2
e
C H BrNO (385)
19
16
3
2
f
CH
H
C H FNO ( 311)
18
14
3
2
g
C H FNO (325)
19
16
3
2
h
F
CH
H
C H NO (307)
19
17
3
2
i
CH
3
C H N O (318)
19
14
2
3
2
j
CN
H
a
b
c
All of the products were characterized by spectral and physical data.
Yields after purification by recrystallization method.
cLogP was calculated using ChemBioDraw Ultra 13.0v.
All the compounds have been purified by recrystallization method using appropriate solvents.
The structures of all the synthesized compounds have been confirmed by various
1
13
spectroscopic techniques such as LC-MS, H-NMR, C-NMR, FTIR and elemental analysis.
1
2
In the H-NMR of title compounds 2b, 2d, 2f and 2h methyl protons as R on indolazine
1
3
nucleus are observed as singlet in the range of δ 2.18-2.23. In C-NMR carbonyl carbon is
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observed in the range of δ 182.86-186.3 for compounds 2a-e and 2h-j. Molecular mass of the
compounds was in compliance with the molecular ion peak.
Pharmacology
Even though indolizines have potent inhibitor activities of biologically important pathways,
as was illustrated in the introduction section, their potential as insecticide sources against
mosquitoes, to the best of our knowledge, has not been published. Table 4 summarises results
of larvicidal activity assessments. There were significant effects of treatment (p < 0.0001)
and exposure time (p < 0.0001) but not their interaction (p = 0.88) on larval mortality.
Overall mortality was slightly but significantly higher at 48 h (60.9 ± 0.8) compared to 24 h
(58.8 ± 0.8). All compounds tested except indolizine 2a resulted in mortalities higher than the
negative control. Compounds 2e and 2g were as effective (93 % and 95% mortality,
respectively) as the positive control Temephos (98 % mortality), followed by compound 2f
(81 %). The remaining compounds exerted moderate mortalities, ranging from 42 to 64 %.
Compound 2e having election withdrawing bromine at fourth positon of phenyl ring
exhibited 93% larvicidal activity whereas compound 2g having election withdrawing fluorine
atom at fourth positon of phenyl ring exhibited larvicidal activity at 95%. However,
analogous 2a, 2i and 2j with nitro, methyl, nitrile group, respectively did not show much
promising activity when compared to positive control Temephos. Compound 2f with election
2
withdrawing bromine at para positon of phenyl ring and methyl as R on indolazine nucleus
exhibited activity at 81%.
These results indicate that indolizine 2e and 2g emerged as promising larvicidal agents that
merit further research and development for mosquito control.
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Table 4: Mortality of Anopheles arabiensis larvae exposed to test compounds 2a-j
indolizines at 4 µg/mL (1 mg/250 mL) and their negative (acetone) and positive (Temephos)
controls. Adjusted means are shown. Adjusted standard errors were 2.7.
Mortality
Compound
24 h
18.9
61.1
55.6
58.9
92.2
77.8
94.4
40.0
60.0
41.1
7.8
48 h
20.0
64.4
58.9
61.0
93.0
81.1
95.6
42.2
62.2
43.3
10.0
98.9
A
2
2
2
2
2
2
2
2
2
2
a
b
c
d
e
f
B
B
B
DE
E
D
g
h
i
C
B
C
j
A
Acetone
D
Temephos
97.8
A-E
Compounds not sharing a letter differ significantly (p < 0.05).
Conclusions
The research work is focused on the efficient synthesis of indolizine analogous (2a-j) with
greener chemistry, which provides new method for the synthesis of indolizines. The reactions
performed were eco-friendly and yield of the products were very good at less reaction time
with least formation of by-product. All the indolizine analogous were toxic for A. arabiensis
larvae, and out of the title compounds tested for larvicidal activity, compounds 2e, 2f and 2g
emerged as potent agents comparable to standard compound Temephos.
Acknowledgement
Authors are thankful to Sahyadri Science College, Shimoga, National Research Foundation
(96807), South Africa and Durban University of Technology for support and facilities.
Medical Research council for facilities to screen the compounds for larvicidal activity.
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Supplementary data
Supplementary data related to this article can be found as attachment.
Competing interests
The authors declare that they have no competing interests.
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