Synthesis, characterization, crystal structure and anticancer activity of tetrahydro-quinolines using silica iodide as a heterogeneous catalyst

Article abstract of DOI:10.1016/j.molstruc.2020.128790

An efficient synthesis of tetrahydroquinolines using silica iodide as heterogeneous catalyst. Ethyl acetoacetate, dimedone, ammonium acetate with suitable aromatic aldehydes in ethanol was reported. Silica iodide (SiO₂–I) acts as an efficient h

Full text of DOI:10.1016/j.molstruc.2020.128790

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Synthesis, characterization, crystal structure and anticancer activity of tetrahydro-
quinolines using silica iodide as a heterogeneous catalyst
K.B. Ramesh, B.M. Omkaramurthy, M. Srinivas
PII:
S0022-2860(20)31115-7
DOI:
https://doi.org/10.1016/j.molstruc.2020.128790
MOLSTR 128790
Reference:
To appear in: Journal of Molecular Structure
Received Date: 29 April 2020
Revised Date: 19 June 2020
Accepted Date: 27 June 2020
Please cite this article as: K.B. Ramesh, B.M. Omkaramurthy, M. Srinivas, Synthesis, characterization,
crystal structure and anticancer activity of tetrahydro-quinolines using silica iodide as a heterogeneous
catalyst, Journal of Molecular Structure (2020), doi: https://doi.org/10.1016/j.molstruc.2020.128790.
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Authors Contribution
Dr. Ramesh K B
Conceptualization, Methodology, Validation, Writing and Formal analysis
Omkarmurthy B M
Resources, Software and Crystal structure interpretation
Dr. Srinivas M
Visualization, Verification, Data Curation, Supervision and Investigation

Synthesis, characterization, crystal structure and anticancer activity of Tetrahydro-
quinolines using Silica Iodide as a heterogeneous catalyst
Ramesh K Ba*, Omkaramurthy B. Mb, Srinivas Mc
aDepartment of Chemistry, Sharanabasaveshwar College of science,
Kalaburagi-585103, India
bDepartment of Studies in Chemistry, Jnana Bharathi campus, Bangalore University,
Bangalore-560006, India
cDepartment of Chemistry, REVA University, Kattigenahalli, Yelahanka,
Bangalore-560064, India
Abstract
An efficient synthesis of tetrahydroquinolines using silica iodide as heterogeneous catalyst.
Ethyl acetoacetate, dimedone, ammonium acetate with suitable aromatic aldehydes in ethanol
was reported. Silica iodide (SiO2-I) acts as an efficient heterogeneous catalyst to afford the prod-
ucts in excellent yield in short reaction duration and reusable catalyst. The synthesized 4d and 4h
compounds were characterized by the single crystal X-ray diffraction method. Further, the pre-
pared quinoline derivatives showed potent anti-cancer activity against HepG2 and MCF-7 cell
lines. Docking study was carried out to evaluate the binding affinity of the synthesized com-
pounds and the standard drug doxorubicin with Estrogen Receptor (ER).
Keywords: Synthesis: Tetrahydroquinolines, Silica iodide, crystal structure, anti-cancer
activity, docking study.
1. INTRODUCTION
In recent years, the advanced research on development of “one-pot reactions” represents a great
1

challenge in organic synthesis predominantly in the development of modern drugs [1]. Quino-
line is a heterocyclic structural unit which is found to occur in many natural alkaloids, therapeu-
tics and in other synthetic analogues [1]. Quinolines show a wide spectrum of biological activi-
ties such as antiproliferative, antiplasmodial, antimalarial, antibacterial, and anticancer activities
due to the variety of pharmacological properties [3]. Quinolines represent a large family of het-
erocyclic compounds which find application in the design of various medicinally important
compounds and hence, much attention has been focused on the synthesis of a variety of quino-
line derivatives [4]. There are few methods reported on the synthesis of the polyhydroquinolines
(a, b and c) in the literature [5]. The reported methods have significant drawbacks such as use
of relatively expensive and
HOH2C
H
N
O2
N
N
H
O
H
C l
N
N
H
OH
N
H
N
O
O
C l
N
H
C O 2H
N
hazardous reagents, low yields and involve drastic reaction conditions. Preparation of quinoline
derivatives by a one-pot multi-component strategies is a challenging and is in great demand.
Hence, moreover there is scope for investigations on such reactions in order to improve the
yields by use of mild and less harsh reaction conditions. Recently, heterogeneous catalysis has
gained much attention in the various fields of science including the synthetic organic chemistry
compared to homogeneous catalysis. Heterogeneous catalysts have many advantages since it ex-
2

hibits the high atom efficiency, recovery and recyclability. This research article deals with syn-
thesis of one-pot multi-component quinoline derivatives by the use of SiO2-I as a novel heteroge-
neous catalyst [6-8]. Further, an attempt is made to study the Crystal structure of the synthesized
4d and 4h compounds were characterized by the single crystal X-ray diffraction method. Applica-
tions for anticancer activity and molecular docking of synthesized compounds and their behavior.
To the best of our knowledge here we report SiO2-I heterogeneous catalyst is simple, environment
friendly and efficient method for the one-pot four-component synthesis of tetrahydroquinoline de-
rivatives were presented. Crystal structure of 4d and 4h and analyzed and correlated with anti-
cancer activity and docking. Synthesized compounds are evaluated with reference to the standard
drug doxorubicin (Scheme 1).
Scheme 1: SiO2- I catalyzed synthesis of Tetrahydroquinolines
3

The Plausible mechanisms for the synthesis of Tetrahydroquinolines
2. EXPERIMENTAL
2.1. Materials and methods
All the chemicals were commercially available and used without further purification, except liq-
uid aldehydes which were distilled before use. All yields refer to yield of the isolated products
1
after purification. All the products were characterized by the IR, HNMR, 13CNMR, Mass spec-
tral and CHN analyses. Melting points were determined on a RAAGA make melting point appa-
4

ratus. Nuclear magnetic resonance spectra were obtained from Bruker AMX instruments in
CDCl3 using TMS as an internal standard [400 MHz and 100 MHz for 1HNMR for 13CNMR re-
spectively]. ESI-MS analysis was carried out using ESI-Q TOF instrument. The crystal data were
collected at Xcalibur, Eos, Nova diffractometer. The crystal was kept at 293(2) K during data
collection. Using Olex2, the structure was solved with the ShelXT structure solution program
using Intrinsic Phasing and refined with the ShelXL refinement package using CGLS minimiza-
tion [9-10]. For biological assays, the HepG2 and MCF-7 cell lines were obtained from National
Centre for Cell Sciences (NCCS), Pune, INDIA.
3. RESULTS AND DISCUSSION
Primarily, one pot four-component reaction of 4-methoxybenzaldehyde (1 mmol), dimedone (1
mmol), ethyl acetoacetate (1 mmol), ammonium acetate (1.5 mmol) in EtOH (5 mL) was carried
out with different catalysts are Amberlite IR-120H, CeCl3, SnCl2, Na2CO3 and A4 size H+ mo-
lecular sieves at reflux temperature of the solvent and were found that, SiO2-I is best in terms of
yield and duration of the reaction (Entry 9 Table 1).
Entry
Catalyst
Time(h)
Yieldd (%)
b
Na2CO3
6
6
30
60
50
40
20
30
60
70
1
2
b
Ba(OH)2
b
3
4
5
6
7
8
SnCl2
8
Acidic Molecular sieves A4c
Amberlite IR120c
9
13
12
4
b
CeCl3
c
SiO2
SiO2-Clc
3.5
5

9
SiO2-Ic
2.5
90
a
Table 1. Effect of various catalysts on the synthesis of 4c
aReaction condition: 4-methoxybenzaldehyde (1 mmol), dimedone (1 mmol), ethyl acetoace-
b
tate (1 mmol), ammonium acetate (1.5 mmol) and EtOH (mL); 10 mol%; c0.1g; disolated yield.
3.1 Chemistry
We started the research work by examining the reaction of 4-methoxybenzaldehyde with dim-
edone, ethyl acetoacetate and ammonium acetate to get 4-(4'-methoxyphenyl)-2,7,7-trimethyl-5-
oxo-1,4,6,8-tetrahydroquinoline-3-carboxylic acid ethyl ester (4c) in EtOH in the presence of
catalytic SiO2-I as a heterogeneous catalyst refluxed around 2‒3h and yields 90 %. To under-
stand the importance of this method, performed further all the reactions using SiO2-I (0.1g) in
EtOH at reflux, and it was found that, SiO2-I can efficiently catalyze the reaction between dim-
edone, ethyl acetoacetate, ammonium acetate, and different aromatic aldehydes to give excellent
yield of the desired products within 2-3 h respectively. The data presented in the Table 2, it is
clear that, the method is effective for both electron withdrawing and electron donating aromatic
aldehydes [11-12]. Then, we carried out the reaction using aliphatic aldehydes (Table 2, entries
10 and 11), and it was found that, there was no product formation even after 15 h.
Prod Time Yielda
Mp (°C)
Entry
Aldehydes
uct
(h)
(%)
Found
Reported
1
2
2,3,4-MeOC6H2CHO
3-Br,4-MeOC6H3CHO
2.5
2.5
90
87
180−182†
250–251†
–
–
4a
4b
6

3
4
4-MeOC6H4CHO
2-IC6H4CHO
2.5
3.0
90
86
145–147
181–183†
199–201
255–257†
216–218
220–222†
238–240
–
145−147 9
4c
4d
4e
4f
–
5
3-HO,4-MeOC6H3CHO
3,5-BrC6H3CHO
3,4- ClC6H3CHO
3-F,4-ClC6H3CHO
4-HOC6H4CHO
HCHO
2.3
85
199–20110
6
2.4
82
–
7
2.8
80
216−21810
4g
4h
4i
8
2.6
89
–
9
3.0
87
238−24010
10
11
4j
15.0
15.0
ND
ND
–
–
CH3CHO
–
4k
aIsolated yield; †Novel compounds
Table 2. Synthesis of the Tetrahydroquinolines (4a–k)
3.2 Typical experimental procedure for the synthesis of Tetrahydroquinolines:
A mixture of aldehyde (1 mmol), dimedone (1 mmol), ethyl acetoacetate (1 mmol) and ammo-
nium acetate (1.5 mmol) was taken in EtOH (5 mL) mixed well and then SiO2-I (1.7 mmol) was
refluxed for 2-3h at 80°C. The course of the reaction was monitored by TLC [EtOAc: Hexane
(3:7)]. After the completion of the reaction mixture was cooled and poured onto crushed ice.
The obtained solid product was filtered along with the catalyst the residue was dissolved in etha-
nol and filtered to separate the catalyst. Catalyst was kept aside for further use. The crude prod-
uct obtained after the removal of the solvent under vacuum. Further the crude product was crys-
tallized from ethanol to get the pure products. The spectral and analytical data for some of the
prepared compounds is presented in the Table 2.
3.3 Spectral and analytical data of selected synthesized compounds
3.3.1 2,7,7-Trimethyl-5-oxo-4-(2',3',4'trimethoxyphenyl)-1,4,6,8-tetrahydroquinoline-3-
carboxylic acid ethyl ester (4a):
7

Colorless solid, Mp: 180–182 °C; IR (KBr): ν 3350 (N-H), 1712 (C=O); 1700, 1642, 1611, 1499,
1
1422, 1305, 1214, 1053, 1011 cm-1; H NMR (400 MHz, CDCl3): δ 0.95 (s, 3H, CH3,C(11) H),
1.06 (s, 3H, CH3,C(12)H), 1.95 (t, J = 6.8Hz, 3H,C(21) H), 2.21(m, 4H, 2CH2, C(6) C(8) H), 2.35
(s, 3H,CH3, C(1) H), 3.76–3.89 (s, 9H, 3 × OCH3, C(22)C(23)C(24) H), 4.04–4.06 (q, J = 2.4
Hz, 2H,C(20) H), 5.11 (s, 1H, CH,C(4) H), 6.52 (d, J = 8.8 Hz, 1H,C(14) H), 6.97 (d, J = 6.8 Hz,
1H,C(15) H), 10.24 (s, 1H, N-H) ppm; 13CNMR (100MHz, CDCl3): δ 14.30 (C-21), 19.42(C-1),
27.03(C-11, C-12), 29.54 (C-4), 32.62 (C-7), 50.95 (C-8), 55.84 (C-6,C-24), 59.73 (C-22), 60.41
(C-24), 60.50 (C-23),100.10 (C-10) 105.50 (C-3), 106.28 (C-15), 111.12 (C-13), 125.70 (C-14),
132.46 (C-17), 142.10 (C-2), 142.94 (C-9),149.44 (C-16), 152.11 (C-18), 168.10 (C-19,C=O),
195.72 (C-5, C=O) ppm; ESI-MS:[M] 429.5; Anal. Calcd. C24H31NO6 (%): C, 67.11; H, 7.27; N,
3.26; Found C, 66.01; H, 7.07; N, 3.21.
3.3.2 4-(3'-Bromo-4'-methoxyphenyl)-2,7,7-trimethyl-5-oxo-1,4,6,8-tetrahydroquinoline-3-
carboxylicacid ethyl ester (4b):
Colorless solid, Mp: 250–251 °C; IR (KBr): ν 3346 (N-H), 1716 (C=O); 1708, 1609, 1521, 1489,
1
1410, 1300, 1207, 1063, 1020 cm-1; HNMR (400 MHz, CDCl3): δ 0.96 (s, 3H, CH3, C(11) H),
1.07 (s, 3H, CH3, C(12) H), 1.21 (t, J = 7.2 Hz, 3H, C(21) H), 2.36–2.44 (m, 4H, 2CH2, C(6)
C(8) H), 2.70 (s, 3H, CH3, C(1) H), 3.80 (s, 3H, OCH3, C(22) H), 4.05–4.10 (q, J = 7.2 Hz, 2H,
C(20) H), 4.96 (s, 1H, CH, C(4) H), 6.66 (d, J = 8.0 Hz, 3H, C(14) H), 6.78 (d, J = 8.0 Hz, 1H,
C(15) H), 10.28 (s, 1H, NH) ppm; 13CNMR (100MHz,CDCl3): δ 14.25 (C-21) , 17.09 (C-7),
18.90 (C-1), 26.80 (C-11,C-12), 29.83 (C-4), 48.15 (C-8),54.17 (C-22), 58.07 (C-6), 59.37 (C-
20), 85.82 (C-10), 108.08 (C-17), 122.67 (C-3), 123.52 (C-15), 128.08 (C-14), 131.43 (C-13),
137.19 (C-18), 145.35 (C-2), 148.98 (C-9), 156.92 (C-16), 164.25 (C-19,C=O),197.64 (C-
8

5,C=O) ppm. ESI-MS:[M+1]448.1; Anal.Calcd for C22H26BrNO4 : C, 58.94; H, 5.85; N, 3.12.
Found: C, 57.33; H, 5.05; N, 3.10.
3.3.3 4-(2'-Iodophenyl)-2,7,7-trimethyl-5-oxo-1,4,6,8-tetrahydroquinoline-3-carboxylic acid
ethyl ester (4d):
Colorless solid, Mp: 181–183 °C; IR (KBr): ν 3339 (N-H), 1723 (C=O); 1709, 1600, 1545, 1408,
1
1400, 1299, 1207, 1083, 1030 cm-1; HNMR (400 MHz, CDCl3): δ 0.93 (s, 3H, CH3, C(11) H),
1.06 (s, 3H, CH3 C(12) H,), 1.18 (t, J = 6.4 Hz, 3H, C(21) H), 2.18–2.22 (m, 4H, 2CH2,
C(6)C(8) H), 2.38 (s, 3H, CH3, C(1) H), 4.03−4.08 (q, J = 6.8 Hz, 2H, C(20) H ), 4.97 (s, 1H,
CH, C(4) H), 6.71 (d, J = 8.0 Hz, 2H, Ar-H, C(18) H), 7.18 (d, J = 8.0 Hz, 2H, Ar-H, C(15) H),
13
9.51 (s, 1H, NH) ppm; CNMR (100MHz, CDCl3): δ 14.71 (C-21), 19.71 (C-1), 27.57(C-11,C-
12), 29.96(C-4), 50.99(C-6,C-8),60.26 (C-20), 98.74 (C-14), 102.20 (C-3),106.92 (C-
10),112.1(C-17),113.6(C-16), 129.4(C-18), 140.0(C-2,C-15), 143.9(C-9), 150.4(C-13), 168.0 (C-
19, C=O), 196.3(C-5, C=O) ppm; ESI-MS: [M+1] 466.08; Anal.Calcd for C21H24 INO3 : C,
54.20; H, 5.20; N, 3.01. Found: C, 53.22; H, 5.12; N, 2.73.
3.3.4 4-(3'-Hydroxy-4'-methoxy-phenyl)-2,7,7-trimethyl-5-oxo-1,4,6,8-tetrahydroquinoline-
3-carboxylic acid ethyl ester (4e):
Colorless solid, Mp: 199–201°C; IR (KBr): ν 3310 (N-H), 1746 (C=O); 1699, 1602, 1525, 1412,
1
1401, 1229, 1203, 1023, 998 cm-1; HNMR (400 MHz, CDCl3): δ 0.96 (s, 3H, CH3, C(11) H),
1.07 (s, 3H, CH3, C(12) H), 1.21 (t, J = 7.2 Hz, 3H, C(21) H), 2.31 (m, 4H, 2CH2, C(6) C(8) H),
2.40 (s, 3H, CH3, C(1) H), 2.62 (s, 1H, C(15) OH), 3.80 (s, 3H, OCH3, C(22) H), 4.05−4.10 (q, J
= 7.2 Hz, 2H, C(20) H), 4.95 (s, 1H, CH, C(4) H), 6.66–6.80 (m, 3H, Ar-H, C(14,17,18) H), 8.50
13
(s, 1H, NH) ppm; CNMR (100MHz, CDCl3): δ 13.90 (C-21), 17.29 (C-7), 18.20 (C-1), 27.81
(C-11, C-12), 29.72 (C-4), 47.51 (C-8), 51.19 (C-6), 55.54 (C-22), 59.64 (C-20), 100.23 (C-3),
9

108.23 (C-10), 113.90, 114.08 (C-17), 116.23 (C-14), 128.23 (C-18), 130.26 (C-13), 136.91 (C-
9), 142.50 (C-2,C-15), 145.02 (C-16), 160.26 (C-19,C=O), 196.94 (C-5, C=O) ppm; ESI-MS:
[M+1] 386.19; Anal.Calcd for C22H27NO5: C, 68.55; H, 7.06; N, 3.63. Found: C, 67.91; H, 6.78;
N, 3.61.
3.3.5 4-(3',5'-Dibromo-phenyl)-2,7,7-trimethyl-5-oxo-1,4,6,8-tetrahydroquinoline-3-
carboxylic acid ethyl ester (4f):
Colorless solid, Mp: 255–257 °C; IR (KBr): ν 3300 (N-H), 1796 (C=O); 1599, 1501, 1435, 1400,
1399, 1209, 1200, 1013, 910 cm-1; 1HNMR (400 MHz, CDCl3): δ 0.96 (s, 6H, 2 CH3 ,C(11)(12)
H), 1.08 (t, J = 7.6 Hz, 3H, CH3, C(21) H), 2.23 (m, 4H, 2CH2, C(6)C(8) H), 2.33 (s, 3H, CH3,
C(1) H), 4.06−4.08 (q, J = 4.0 Hz, 2H, C(20) H), 4.96 (s, 1H, CH, C(4) H), 6.72‒6.75 (d, J =
12.0 Hz, 2H, Ar-H, C(16)C(14) H), 7.39 (s, 1H, Ar-H, C(18) H) 9.69 (s, 1H, NH) ppm; 13CNMR
(100MHz, CDCl3): δ 13.30 (C-21), 17.70 (C-7), 18.90 (C-1), 26.80 (C-11,C-12), 30.91 (C-4),
55.82 (C-6), 59.95 (C-20), 100.10 (C-3), 108.02 (C-10), 122.47 (C-15), 128.45 (C-18), 128.52
(C-17), 129.75 (C-16), 130.14 (C-14), 137.51 (C-13), 145.66 (C-9), 153.06 (C-2), 160.15 (C-19,
C=O), 194.24 (C-5, C=O) ppm; ESI-MS: [M] 495.00; Anal.Calcd for C21H23Br2NO3: C, 50.73;
H, 4.66; N, 2.82. Found: C, 50.32; H, 4.02; N, 2.32.
3.3.6
4-(3',4'-Dichloro-phenyl)-2,7,7-trimethyl-5-oxo-1,4,6,8-tetrahydroquinoline-3-
carboxylic acid ethyl ester (4g):
Colorless solid, Mp: 216–218 °C; IR (KBr): ν 3386 (N-H), 1711 (C=O), 1704, 1662, 1615, 1509,
1
1438, 1365, 1234, 1153, 1044 cm-1; HNMR (400 MHz, CDCl3): δ 0.91 (s, 6H, 2CH3 C(11)
C(12) H), 1.02 (t, J = 7.6 Hz, 3H, CH3, C(21) H), 2.16 (m, 4H, 2CH2, C(6)C(8) H), 2.25 (s, 3H,
CH3, C(1) H), 3.99−4.01 (q, J = 6.8Hz, 2H, C(20) H), 5.05 (s, 1H, CH, C(4) H), 6.94−7.26 (m,
3H, Ar-H, C(14)C(17)C(18) H), 10.49 (s,1H,NH) ppm; 13CNMR (100MHz, CDCl3): δ 14.25 (C-
10

21), 16.08 (C-7), 19.48 (C-1), 27.65 (C-11, C-12), 29.28 (C-4), 50.90 (C-8), 54.20 (C-6), 59.76
(C-20), 102.61 (C-3), 109.08 (C-10), 127.29 (C-18), 130.10 (C-17), 132.16 (C-16, C-14), 138.11
(C-13, C-15) ppm, 139.32 (C-2), 145.10 (C-9), 167.55 (C-19, C=O), 195.64 (C-5, C=O) ppm.
ESI-MS: [M] 407.1; Anal.Calcd for C21H23Cl2NO3: C, 61.77; H, 5.68; N, 3.43. Found: C, 60.32;
H, 5.02; N, 3.32.
3.3.7
4-(4'-Chloro-3'-fluoro-phenyl)-2,7,7-trimethyl-5-oxo-1,4,6,8-tetrahydroquinoline-3-
carboxylicacid ethyl ester (4h):
Colorless solid, Mp: 220–222 °C; IR (KBr): ν 3429 (N-H), 1709 (C=O), 1649, 1644, 1408, 1336,
1
1287, 1129, 1010,810 cm-1; HNMR (400 MHz, CDCl3): δ 0.93 (s, 3H, CH3, C(11) H), 1.08 (s,
3H, CH3, C(12) H), 1.17 (t, J = 7.2 Hz, 3H, C(21) H), 2.20‒2.23 (m, 4H, 2CH2, C(6)C(8) H),
2.40 (s, 3H, CH3, C(1) H), 3.31 (s, 1H, NH), 4.05‒4.07 (q, J = 7.2 Hz, 2H, C(20) H), 5.02 (s,
1H, CH, C(4) H), 7.04–7.07 (m, 2H, Ar-H C(14) H), 7.21−7.23 (m, 2H, Ar-H, C(17) C(18) H)
ppm; 13CNMR (100MHz, CDCl3): δ 14.32 (C-21),17.04 (C-7), 19.48 (C-1), 27.24 (C-11, C-12),
29.48 (C-4), 50.76 (C-8), 54.71 (C-6), 60.10 (C-20), 105.28 (C-3), 111.49 (C-10), 116.32 (C-16),
118.18 (C-14), 124.70 (C-18), 129.85 (C-17), 144.27 (C-2), 148.25 (C-13), 148.69 (C-9), 156.71
(C-15), 167.18 (C-19, C=O), 195.62 (C-5, C=O) ppm; ESI-MS: [M+1] 391.2; Anal.Calcd for
C21H23ClFNO3: C, 64.37;H,5.92; N, 3.57. Found:C,63.21;H,5.31;N,3.20.
4. Single crystal X-ray diffraction
The crystal structures of compounds 4d and 4h was determined by single crystal X-ray diffrac-
tion. The crystal data of 4d and 4h structure refinement parameters and selected bond parameters
(Table 3). Refinement carried was full matrix least-squares on F2. The hydrogen atoms were
placed at calculated positions in the riding model approximation, their temperature factors were
set to 1.2 times those of the equivalent isotropic temperature factors of the present atoms. All
11

other non-hydrogen atoms were refined anisotropically. The molecular structures, packing mole-
cules and orientation of the planes containing the ring structures for 4d compound (Figure A, B
and C) and 4h compound (Figure D, E and F). The SXRD study of 4d has revealed that tetrahy-
droquinoline-3-carboxylic acid ethyl ester is connected with iodide to form. The Molecular for-
mula is C43 H51 I2 N2 O6; Analysis made at 293.71 K: triclinic, space group P-1 with Z = 2, T =
293(2) K, μ(MoKα) = 1.519 mm−1 and Dcalc = 1.473 g/ cm−3. The structure was solved by direct
methods and refined to a standard discrepancy index of R = 0.0688 and Rw = 0.1433 for 2437
reflections with F 2σ (F) and a goodness of fit on F2 = 1.010 (Table 4). Anisotropic displacement
parameters can be visualized with a displacement ellipsoid plot (ORTEP) drawn at 30% proba-
bility level, indicates that the chance of finding the atomic nucleus within the plotted ellipsoid is
30%.
The SXRD study of 4h as revealed that tetrahydroquinoline-3-carboxylic acid ethyl ester is con-
nected with fluorine and chlorine to form. The molecular formula is C21H23ClFNO3; Analysis
made at 293.71 K: orthorhombic, space group Pbcn with Z = 8, T = 293(2) K, μ (MoKα) =
0.217mm−1 and Dcalc = 1.281 g/ cm−3. The structure was solved by direct methods and refined
to a standard discrepancy index of R = 0.1133 and Rw = 0.2585 for 3716 reflections with F 2σ
(F) and a goodness of fit on F2 = 1.093 (Table 5). Hydrogen bonding interaction of C-H-N, N-H-
O and N-H-N (4d and 4h) are 0.97, 0.85 and 0.86 respectively (Table 4 and Table 5).
Empirical formula
C43 H51 I2 N2 O6
C21 H23 Cl F N O3
Formula weight
Temperature/K
945.65
293(2)
391.85
293(2)
12

Triclinic
P-1
Orthorhombic
Pbcn
Crystal system
Space group
13.281(2)
13.524(2)
14.772(2)
90
18.414(2)
15.599(2)
14.143(2)
90
a/Å
b/Å
c/Å
α/°
65
90
β/°
64
90
γ/°
Volume/Å3
Z
2135.0(6)
2
4062.4(9)
8
ρcalcg/cm3
1.471
1.519
954
1.281
0.217
1648
μ/mm-1
F(000)
Crystal size/mm3
0.480 x 0.060 x 0.020 0.260 x 0.140 x 0.140
MoKα (λ = 0.71073) MoKα (λ = 0.71073)
Radiation
2.835 to 25.348°.
2.881 to 25.350°.
2θ range for data collection/°
-16<=h<=22, -
18<=k<=16, -
12<=l<=17
-15<=h<=15, -
16<=k<=16, -
17<=l<=15
Index ranges
14092
15119
Reflections collected
7785 [R(int) = 0.0421]
1356 [Rint = 0.0188,
Rsigma = 0.0333]
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
7785 / 71 / 510
1.017
3716 / 31 / 245
1.010
R1 = 0.0656, wR2 =
0.1146
R1 = 0.0559, wR2 =
0.1691
Final R indexes [I>=2σ (I)]
R1 = 0.1464, wR2 = R1 = 0.2585, wR2 =
Final R indexes [all data]
0.1369
0.861 and -0.394
1993485
0.3607
0.474 and -0.382
1993402
Largest diff. peak/hole / e Å-3
CCDC
Table 3. Crystal data and structure refinement for 4d and 4h
13

___________________________________________________________________________
D-H...A d(D-H) d(H...A) d(D...A) <(DHA)
___________________________________________________________________________
N(1)-H(1N)...O(1)#1 0.86 1.99 2.845(6) 174.3
___________________________________________________________________________
Table 4. Hydrogen bonds for 4d: Symmetry transformations used to generate equivalent atoms:
#1 x,-y, z+1/2
__________________________________________________________________________
D-H...A
d(D-H)
d(H...A)
d(D...A)
<(DHA)
___________________________________________________________________________
N(1)-H(1N)...O(4)#2
N(2)-H(2N)...O(1)
0.85(2)
0.86(2)
2.01(2)
2.01(3)
2.59
2.860(8)
2.846(7)
3.28(3)
173(7)
165(7)
128.5
C(38')-H(38D)...N(2)#3 0.97
____________________________________________________________________________
Table 5. Hydrogen bonds for 4h: Symmetry transformations used to generate equivalent atoms:
#1 -x+1,-y+1,-z+1 #2 x+1,y-1,z #3 -x,-y+1,-z+1
14

Figure A: Molecular structure and space filled diagram of 4d
Figure B. Orientation and interactions of 4d
15

Figure C. Views of the coordination environment of 4d with different axis X, Y, Z (symmetry
transformations used to generate equivalent atoms: #1 -x+1,-y+1,-z+1
Figure D. Molecular structure and space filled diagram of 4h
Orientation
tions of 4h
Figure E.
and interac-
16

Figure F. Views of the coordination environment of 4h with different axis X, Y, Z (symmetry
transformations used to generate equivalent atoms: #1 -x+1,-y+1,-z+1 #2 x+1,y-1,z #3 -x,-
y+1,-z+1
The anisotropic thermal parameters of tetrahydroquinoline-3-carboxylic acid ethyl ester (4d and
4h) have been refined for all non-hydrogen atoms. Some of the hydrogen atoms could not be
solved, so the analysis was not included. The complete characterization of 4d and 4h crystallo-
graphically indicates the formation of the products regioselectively. For the first instance of time,
we at this moment report the complete unambiguous characterization of the products. To best of
our knowledge there is no precedent for the complete characterization of tetrahydroquinoline-3-
carboxylic acid ethyl ester (4d and 4h).
17

4.1 Crystallographic parameters: bond lengths, bond angles, and torsion angles
In 4d compound, C(1)-C(21), N-H, C-O, C-N, C-Cl, and C-F. Bond lengths are in the range of
1.536(9) and 1.356(8), 1.380(8) and 0.8600, 1.241(7) and 1.458(9), 1.241(7) and 1.458(9),
1.741(11) and 1.332(11) respectively. The bond angles are in the range of C(1)-C(21), 126.7(7)–
107.7(5), N-H, 118.3 (5) O(2)-C(16)-C(1), 128.6(8), N(1)-C(3)-C(8) 119.4(6), C(12)-C(13)-
Cl(1) 120.3(10) and F(1)-C(12)-C(13)119.6(10). The torsion angles are in the range of C(16)-
C(1)-C(2)-C(19 0.3(11), C(9)-C(1)-C(2)-N(1)
F(1)-C(12)-C(13)-Cl(1)
5.4(10), C(5)-C(6)-C(7)-O(1) -157.6(6),
-174.9(9). Therefore, these
2.1(13), F(1)-C(12)-C(13)-C(14)
interactions each comprising of C(1-21) chains form a two dimensional (2D) sheet Inter molecu-
lar hydrogen bonding interaction of D-H...A is N(1)-H(1N)...O(1) 174.3 with respect to the
Symmetry #1 x,-y,z+1/2.
In 4h compound, C (1)-C (21), N-H, C-O, C-N, and C-I. Bond lengths are in the range of
1.352(9) and 1.527(11), 0.85(2) and 0.86(2), 1.206(8) and 1.458(10), 1.368(8) and 1.380(9), I
(1)-C (11) 2.109(7) respectively. The bond angles are in the range of C(2)-C(1)-C(16)119.2(7),
C(3)-N(1)-C(2)123.3(6), C(16)-O(3)-C(17) 114.2(7), C(7)-C(6)-H(6B) 108.7 and C(10)-C(11)-
I(1)123.4(5). The torsion angles are in the range of C(16)-C(1)-C(2)-C(19)0.3(12),
C(9)-C(1)-
C(2)-N(1) 5.4(11), C(5)-C(6)-C(7)-O(1)-148.4(7) , I(1)-C(11)-C(12)-C(13)178.2(6). Hence, the-
se interactions each comprising of C(1-21) chains form a two dimensional (2D) sheet. Inter mo-
lecular hydrogen bonding interaction of D-H...A were N(1)-H(1N)...O(4)#2, N(2)-H(2N)...O(1)
and C(38')-H(38D)...N(2)#3, 173(7), 163(7) and 128.5 with respect to the Symmetry #1 -x+1,-
y+1,-z+1 #2 x+1,y-1,z #3 -x,-y+1,-z+1
18

5. BIOLOGY
5.1 MTT assay
Cell lines used: HepG-2 (Hepatocellular carcinoma cells) and MCF-7 (Human breast adenocar-
cinoma cells). The anti-cancer activity was tested against the two cell lines- HepG2 and MCF-7.
Minimum essential medium (MEM) growth medium augmented with 10% heat inactivated fetal
bovine serum (FBS), penicillin (100 IU/ml), streptomycin (100 μg/ml) and amphotericin-B (5
μg/ml) were used to grow the cells in a humidified atmosphere of 5% CO2 at 37 °C until conflu-
ent [13-14]. The cells were trypsinized with TPVG solution (0.2% trypsin, 0.02% EDTA, 0.05%
glucose in PBS). The stock cultures were maintained in 25 mL flat bottles. To determine the an-
tiproliferative effect of the test sample, the cells were seeded in 96-well flat bottom microtitre
plates with a density of 1 × 104 cells per well and incubated for 24 h at 37 °C in 5 % CO2 atmos-
phere to allow cell adhesion. After 24 h, the medium was removed when partial monolayer was
formed. The cells were treated with different concentrations of standard drug (Doxorubicin) and
sample compounds for 48 h. Microscopic examination was carried out and observations were
recorded at every 24 h. After the treatment, the solutions in the wells were discarded. The wells
were then treated with 50 μl of freshly prepared MTT reagent (2 mg/mL prepared in PBS). The
plates were shaken gently and incubated for 3 h at 37 °C in 5% CO2 atmosphere. After 3 h, the
supernatant liquid was removed to get the formazan crystals in the wells. Addition of 50 μl of
iso-propanol to each well dissolved the formazan crystals. Finally, the optical density was rec-
orded at a wavelength of 540 nm using a Micro-plate reader (Bio-Tek, ELX-800 MS).
The percentage growth was calculated using the following formula:
test absorbance-blank absorbance
% Growth inhibition
X 100
=
control absorbance-blank absorbance
19

The percentage growth concentration from IC50 , Concentration of drug required to kill 50% of
cells in exponentially growing cultures after a 48 h exposure to the drug for the HepG2, and
MCF-7 cell lines. In this study the standard drug was Doxorubicin, the values are obtained and
comparable with the values of the compounds 4e and 4i which displayed considerable activity
(Table 6).
Drug/Product
IC50 value (µg/ml) Drug/Product IC50 value (µg/ml)
on HepG2 cells
on MCF-7 cells
1.21 ± 0.05
4.40 ± 0.22
4.80 ± 0.12
4.60 ± 0.25
12.50 ± 0.28
3.40 ± 0.21
3.20 ± 0.11
5.50 ± 0.24
10.50 ± 0.35
3.80 ± 0.09
1.09 ± 0.03
4.80 ± 0.16
3.40 ± 0.17
3.20 ± 0.14
10.20 ± 0.34
2.80 ± 0.07
3.60 ± 0.21
4.60 ± 0.22
7.20 ± 0.80
2.60 ± 0.07
Doxorubicin
Doxorubicin
4a
4b
4c
4a
4b†
4c†
4d
4e†
4f†
4g
4d
4e†
4f†
4g
4h
4i†
4h
4i†
†active
Table 6. In vitro anticancer activity of quinolines 4a−4i on HepG2 and MCF-7
Human cancer cell lines
5.1.1 Protein preparation
X-ray crystal structure of ER (PDBID:2IOK) was retrieved from the RCSB protein data bank.
Atomic overlaps from the X-ray structure was removed. Auto dock tools were used to prepare
20

the ER by removing ligand, water molecules, non standard residues and alternate residues. Later
polar hydrogens were added to the ER in standard orientation without optimization and Gasteiger
charges were added using MGL tools (http://mgltools.scripps.edu/).
5.1.2 Ligand preparation
All the synthesized 3D structures were drawn by Chem Draw software. Drug doxorubicin was
retrieved from the complex PDBID 1I1E. Using Argus lab all the drawn structures including
doxorubicin were subjected to geometric cleaning and geometry optimization [15]. Gasteiger
charges were added and nonpolar hydrogens were merged and rotatable bonds were determined
based on the nature of the ligand by using MGL tools.
5.1.3 Grid map generation
After preparing the protein and ligands, the grid maps were generated; spacing was adjusted to
0.500Å to enable ligand binding. Grid dimension is adjusted to 42×64×64 points. AUTODOCK
interaction maps were used for docking protocol. Prior to the actual docking run, these maps
were calculated by AUTOGRID. For each ligand atom type, the interaction energy between the
ligand atom and the receptor was calculated for the entire binding site which is discretized
through a grid [16]. The protein was embedded in a 3D grid and a probe was placed at each grid
point. Interaction energy of the protein was assigned at each grid point and the affinity grid and
electrostatic potential for each atom of the ligand was calculated. Electrostatic interactions were
evaluated by interpolation [17].
5.1.4 Docking
Autodock Vina, a docking program was used to evaluate binding affinity of synthesized mole-
cules and doxorubicin with ER [18]. Vina was used to dock the receptor and ligand molecules.
21

Binding energy of docked complex ER-ligands were evaluated by using empirical free-energy
functions and Lamarckian genetic algorithm. The calculated binding free energy (ΔG) is based
on the electrostatic, van der Waal’s forces, hydrogen bonding and desolvation effects. Finally
Vina results were analyzed using the MGL tools.
5.1.5 Results
To know the inhibition interaction of ER by the prepared compounds, the docking tools were
used through autodock vina. The binding free energy (ΔG) concept is used to evaluate the bind-
ing affinity of protein-ligand complex using docking studies. The negative or low value of bind-
ing free energy (ΔG) indicates the strong binding affinity between protein-ligand complex and
the ligand in the docking complex is in the most favorable conformation [19-20]. In the present
study, comparing the binding affinity between prepared structures and the standard drug using
binding free energy (ΔG) in Kcal/mol. Lowest binding free energy (ΔG) docked complex, ER-4e
is shown in Figure G and ER-doxorubicin complex is shown in Figure H. Interaction of ER with
4e is shown in the Figure I and J. The binding free energy (ΔG) results are presented in the Table
7, which reflects the binding affinity of the standard and the prepared compound 4e with ER .
ER-4e and ER-doxorubicin complexes show binding free energy (ΔG) of −7.9 and −7.3
Kcal/mol respectively. Docking interactions revealed that, doxorubicin interacts with Gln 506
through a hydrogen bond, other amino acids present in the docking sites are: Asn 439, Gln 441,
Glu 444, Ala 493, Leu 495 and Arg 503 which plays vital role in binding. Ligand 4e interacts
with Thr 347 through hydrogen bond, other amino acids present in the docking site for 4e are:
Leu 346, Trp 383, Leu 384, Leu 387, Phe 404, Met 421, Leu 525 and His 524. The analyzed re-
sults predict that, 4e has greater binding affinity among the seven prepared structures and is
found to be greater than the drug doxorubicin (Entries 1 and 5).
22

Entry
Complex
Binding free energy
(ΔG) Kcal/mol
1
2
3
4
5
6
7
8
Doxorubicin
-7.3
-6.1
-6.4
-6.3
-7.9
-6.5
-6.5
-6.9
4a
4b
4d
4e
4f
4g
4h
Table 7. Docking results of the synthesized compounds and doxorubicin drug with ER binding
free energy (ΔG) in Kcal/mol
Figure: G
Figure: H
Figure G and H: Stick and wire model of docked complex; 4e ligand binding at ER docking site
and
Stick model showing the hydrogen interaction of doxorubicin with ER.
23

Fig. I: Interaction of 4e with threonine which is present at the docking site ER. Wire: ER; Stick: 4e.
Figure J: Ribbon model of ER-4e docked complex showing 4e present at
the docking site of ER. Red ribbon: ER; Magenta stick: 4e
CONCLUSION
Developed a new green protocol for the synthesis of 4-aryl-2,7,7-trimethyl-5-oxo-1,4,6,8-
tetrahydroquinoline 3-carboxylic acid ethyl esters by one-pot four-component cyclization reac-
tion of aromatic aldehydes, dimedone, ethyl acetoacetate and ammonium acetate in the presence
of a SiO2-I heterogeneous catalyst using ethanol as a solvent. The reactions are environmentally
benign, efficient and mild as it involves the use of a heterogeneous catalyst.
24

The crystal structures of 4d and 4h were determined by single crystal X-ray diffraction com-
pounds were held by moderate to strong hydrogen bonding interaction of C-H-N, N-H-O and N-
H-N respectively and also found that, newly synthesized quinoline derivatives 4e, 4f and 4i
showed excellent in vitro anticancer activity towards HepG2 cell lines and 4b, 4c, 4e, 4f and 4i
indicated reasonably good activity towards MCF-7 human cancer cell lines, which can be used as
lead compounds for developing new potential class of anticancer drugs. Docking results revealed
that, 4e compound has more binding affinity towards ER when compared to other seven prepared
molecules which is greater than the standard drug: doxorubicin. The obtained in vitro results
were correlated with the docking studies.
ACKNOWLEDGEMENTS
The Authors gratefully acknowledge the Dr.S.G.Dollegoudar, Principal Sharana-
basaveshwar College of science, Kalaburagi for his continuous support and also the
Department of Chemistry, Sharanabasaveshwar College of science, Kalaburagi.
CCDC number for 4d and 4h compounds were found to be 1993485 and 1993402.
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27

Highlights
‹ Present research work deals with synthesis of one-pot four component
route
‹ Reactions completion is very short time with high yields
‹ Docking results revealed that, 4e compound has more binding affinity
towards ER.
‹ Structural analysis of synthesized compounds (4d and 4h) by Single
Crystal X-ray Diffraction