Synthesis of an unusual quinazoline alkaloid: Theoretical and experimental investigations of its structural, electronic, molecular and biological properties

Article abstract of DOI:10.1039/c8ra00138c

An unusual quinazoline alkaloid (1) was obtained when 2-aminobenzaldehyde was refluxed with pyrrolidine in ethanol for 12 h. The synthesized compound was characterized using spectral data analysis augmented with X-ray and literature precedent. Single crys

Full text of DOI:10.1039/c8ra00138c

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PAPER
Synthesis of an unusual quinazoline alkaloid:
theoretical and experimental investigations of its
structural, electronic, molecular and biological
properties†
Cite this: RSC Adv., 2018, 8, 8259
a
*
Shabir H. Lone,
Salman Jameel,‡b Muzzaffar A. Bhat,‡c Rayees A. Lone,b
d
b
*
Ray J. Butcher and Khursheed A. Bhat
An unusual quinazoline alkaloid (1) was obtained when 2-aminobenzaldehyde was refluxed with pyrrolidine
in ethanol for 12 h. The synthesized compound was characterized using spectral data analysis augmented
with X-ray and literature precedent. Single crystal analysis depicted four conformations differing slightly in
ꢀ
bond angles and bond lengths. Compound 1 crystallizes in a triclinic crystal system with a P1 space group
having two molecules within the unit cell. The experimentally obtained parameters were compared to those
obtained theoretically, which depicted a good agreement. Using the DFT/B3LYP/6-31G (d,p) level of theory,
HOMO–LUMO energy gap, molecular electrostatic potential (MEP), vibrational (IR) and NMR analyses were
carried out. The HOMO–LUMO energy gap allowed the calculation of chemical hardness, chemical
inertness, electronegativity and the electrophilicity index of the molecule, which depicted its potential
kinetic stability and reactivity. Prediction of activity spectra of the target compound revealed that
compound 1 possesses notable antineoplastic activity with Pa ¼ 0.884. The molecule was therefore
evaluated against various cancerous cell lines in an in vitro SRB assay which depicted that compound 1
possesses the highest growth inhibition activity against THP-1 cell lines with an IC50 of 7 mM.
Received 6th January 2018
Accepted 16th February 2018
DOI: 10.1039/c8ra00138c
rsc.li/rsc-advances
agents of human leukemia cells, effects on the CNS, estrogenic
effects etc.10–24 Based on these literature reports of alkaloids and
Introduction
our previous work on the isolation, and synthesis of bioactive
compounds,25–37 we carried out the synthesis of an unusual self-
condensation product of 2-aminobenzaldehyde by a method
reported by Seidal and coworkers.38 In order to get deeper
insights in to the molecular, structural and biological properties
of the synthesized compound, we resorted to spectral, X-ray and
DFT analysis. The experimentally obtained parameters were in
close agreement to those obtained theoretically. Molecular
electrostatic potential and frontier molecular orbital analysis
were performed which permitted the calculation of HOMO–
LUMO energy gap and related parameters. Based on PASS
results, the molecule was evaluated against four different
human cancer cell lines to explore its biological potential.
Alkaloids are a very important class of compounds as far as their
role in metabolism and activity is concerned.1 They are among
the oldest drugs used for the treatment of diseases2 and are still
used as promising therapeutic agents.3,4 Deep sea environments
are nowadays the focus of research for discovering newer alka-
loids with potential therapeutic activities.5–7 New alkaloids are
also being produced via chemical synthesis and natural product
modications with some of them being more active than the
naturally obtained ones.8,9 In general alkaloids possess a range
of biological activities which include analgesic, antiviral, anti-
malarial, antineoplastic, antimicrobial, anti-inammatory,
antioxidant antifungal, antibacterial, hemoglobinization
aDepartment of Chemistry, Govt Degree College, Anantnag, Kashmir, 192101, India.
E-mail: lone.shabir480@gmail.com
bBioorganic Chemistry Division, Indian Institute of Integrative Medicine, Sanatnagar,
Srinagar, Kashmir, India 190005. E-mail: kabhat@iiim.ac.in
cDepartment of Chemistry, Islamic University of Science and Technology, Awantipora,
Kashmir, 192122, India
dDepartment of Chemistry, Howard University, Washington, DC 20059, USA
† Electronic supplementary information (ESI) available. CCDC 1814904 contains
the supplementary crystallographic data for 1. For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/c8ra00138c
‡ Both the authors contributed equally.
Results and discussion
Reduction of 2-nitrobenzaldehyde using iron powder in glacial
acetic acid : ethanol : water system (2 : 2 : 1) under ultrasonic
irradiation conditions for 1.5 h at 30 ꢀC yielded the corre-
sponding
2-aminobenzaldehyde.
Reuxing
2-amino-
benzaldehyde in ethanol with pyrrolidine yielded a reaction
mixture containing an unusual self-condensation quinazoline
alkaloid (1) (Fig. 1).
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Fig. 1 Synthesis of an unusual quinazoline alkaloid (1).
Pure 1 was obtained when the reaction mixture was subjected aminobenzaldehyde to yield compound 1 (Fig. 2). The product
to normal phase silica gel column chromatography. It's structure was characterized using LC-MS, IR and NMR data analysis. LC-
was elucidated while analyzing the spectral data in light of MS depicted m/z at 381 assignable to [M + H]+ corresponding
1
literature. The reaction proceeds via a series of nucleophilic to its molecular formula C25H24N4. H NMR depicted the pres-
additions of basic nitrogen of pyrrolidine ring on the highly ence of 12 aromatic protons assignable to three aromatic rings in
electrophilic aldehyde group of 2-aminobenzaldehyde to give an the molecule whose presence was further supported by the
intermediate which again condenses with two molecules of 2- appearance of 18 13C signals in the aromatic region of the
Fig. 2 Mechanism involved in the formation of quinazoline (1).
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Fig. 3 Four different conformations (a–d) of compound 1 as shown by single crystal X-ray analysis.
1
molecule. Three downeld H NMR singlets at d 5.96, 5.29 and
4.52 ppm correspond to 3 CH groups present in the molecule
which was supported by three carbon NMR resonances at d 84,
71 and 64 ppm in its DEPT-NMR. Presence of upeld resonances
at 51 and 23 ppm on the downside in DEPT NMR were assign-
able to four CH2 groups of the pyrrolidine moiety which was
supported by upeld resonances corresponding to 8 protons in
1H NMR (see ESI†). The actual structure was however arrived at
using single crystal X-ray analysis (Fig. 3). Pure crystals of 1 were
obtained by its crystallization from chloroform and ethanol at
room temperature. The molecule crystallizes in a triclinic system
Table 1 Crystal data and structure refinement of compound 1
Identication code
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
Shelx
C
101H97Cl3N16
1641.29
153 (2) K
1.54184 A
Triclinic
ꢀ
P1
˚
˚
Unit cell dimensions
a ¼ 12.8967 (4) A
˚
b ¼ 13.9278 (3) A
˚
c ¼ 23.2246 (7) A
3
˚
Volume
4093.1 (2) A
ꢀ
with P1 space group having 2-units in one unit cell. An X-ray
Z
2
ortep structure of compound 1 depicted four different confor-
mations as shown in (Fig. 3). The crystal renement of the
molecule is shown in Table 1. The four conformers have slight
variations among bond lengths and bond angles. Only a few
signicant differences with regard to bond lengths have been
mentioned in Table 2. The characteristic feature of crystal
packing view (Fig. 4) is the hydrogen bonding network in the
form of N/H–N, Cl/H–C. The molecules are interconnected by
means of these hydrogen bonds. Another interesting hydrogen
bond is the one involving Cl/H–C (Table 3). Since crystallization
of the molecule has been carried out in CHCl3:EtOH solvent, it is
likely that one of CHCl3 molecule per unit cell has intruded
inside during the process of crystallization providing additional
stability to the unit cell.
Density (calculated)
Absorption coefficient
F(000)
1.332 mg mꢁ3
1.497 mmꢁ1
1732
Crystal size
Theta range for data collection
Index ranges
0.345 ꢂ 0.275 ꢂ 0.233 mm3
3.492 to 76.684ꢀ
ꢁ16 # h # 16, ꢁ11 # k # 17,
ꢁ29 # l # 28
29 828
Reections collected
Independent reections
Completeness to theta ¼ 67.684ꢀ
Absorption correction
16 636 [R(int) ¼ 0.0333]
99.8%
Gaussian
Max. and min. transmission
Renement method
1.000 and 0.322
Full-matrix least-squares on F2
16 636/12/1111
1.045
Data/restraints/parameters
Goodness-of-t on F2
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Table 2 Comparative analysis of experimentally obtained bond lengths of four conformers with that obtained theoretically (notable ones have
been shown, for all refer to ESI file)
Exp. bond length
(A) of Conf. A
Exp. bond length
(A) of Conf. B
Exp. bond length
(A) of Conf. C
Exp. bond length
(A) of Conf. D
Theo. bond length
(A)
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
Bond
N(4)–H(4)
C(2)–C(3)
C(3)–C(4)
C(6)–C(7)
C(11)–C(12)
C(21)–C(22)
0.80
0.88
0.86
0.96
1.0138
1.5385
1.5335
1.420
1.487
1.398
1.496
1.518
1.399
1.525
1.388
1.531
1.520
1.383
1.514
1.385
1.527
1.523
1.511
1.399
1.377
1.566
1.485
1.512
1.399
1.386
Fig. 4 A perspective view of the crystal packing in the compound 1.
obtained X-ray data. Table 2 summarizes the selected experi-
mentally obtained (single crystal X-ray analysis) and theoreti-
cally calculated parameters (selected bond lengths) using DFT
methods. A good approximation of bond lengths while doing
optimization using DFT was observed to the experimentally
obtained values.
DFT studies
Theoretical calculations using DFT were performed. This
computational method is emerging as an important quantum,
chemical tool for studying various chemical problems and is
because this versatile method determines energy based on
electron density instead of wave-function. The DFT calculations
were carried out with a hybrid functional B3LYP (Becke's three
parameter hybrid functional) at 6-31G (d,p) level of theory using
Gaussian 09 package. The geometries were optimized without
imposing any molecular symmetry constraints.
Molecular electrostatic potential surface analysis
MEPS is a plot of electrostatic potential mapped on to constant
potential electron density surface. These surfaces help in pre-
dicting reactivity sites towards positively and negatively charged
reactants, in studies of biological recognition of one molecule by
another as in drug receptor and enzyme substrate interactions as
Optimized structures
The computational chemistry studies in this work aimed at well as hydrogen-bonding interactions. MEP surfaces reveal the
determination of geometric parameters for compound 1 and size shape and variation of electron density, electronegativity,
the same were compared with that of the experimentally partial charges and the sites of chemical reactivity with in the
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molecule.39–43 Fig. 5 shows MEP surface for compound 1, calcu- electron density (positive potential) which allow nucleophiles to
lated using DFT/B3LYP/6-31G (d,p) level of theory. The pictorial approach easily. As can be seen in the MEP for compound 1 the
representation with rainbow colour scheme of electrostatic region surrounding the secondary N-atom seems to the darkest
potential for compound 1 lies in the range of ꢁ5.422 a.u to 5.422 blue that is one with lowest electron density, a site more
a.u. The darkest red regions indicate regions with high electron vulnerable to nucleophilic attack. A plausible explanation in this
density (negative potential) which invite electrophilic attacks regard is that the lone pair of electrons on N-atom enters in
while as the darkest blue regions indicate regions with low conjugation with the phenyl moiety thereby decreasing the
electron density around that N-atom.
Frontier orbital analysis
Frontier molecular orbitals play important role in the determi-
nation of electric and optical properties electronic transitions,
kinetic stability.44 FMO's of compound 1 were calculated using
the Gaussian 09 package at the B3LYP/6-31G (d,p) level of
theory. The results are shown in Fig. 6. As can be seen from the
gures HOMO and LUMO are located or spread over the regions
containing the N-atoms and delocalised over one of the benzene
ring with adjacent NH moiety. In the target compound 1,
HOMO–LUMO energy gap is 0.094 eV. Using HOMO–LUMO
energy gap important relative reactivity descriptors like hard-
ness (h), chemical potential (m), electronegativity (c), ionization
energy (I) and electron affinity (A) were calculated and are
dened as follows:45–49
ðI ꢁ AÞ
ꢁðI þ AÞ
ðI þ AÞ
h ¼
;
m ¼
;
c ¼
2
2
2
where A and I represent electron affinity and ionization potential
Fig. 5 MEP plot of compound 1 calculated using DFT/B3LYP/6-31G
(d,p) level of theory.
of the molecule, which are in turn obtained from HOMO and
Fig. 6 HOMO–LUMO plots of compound 1.
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Table 3 Hydrogen bonds for compound 1 [A˚ and ꢀ
]
Table 5 Comparsion of theoretical and experimental NMR data of
compound 1
D–H/A
d(D–H)
d(H/A)
d(D/A)
:(DHA)
1H NMR
13C NMR
N(4B)–H(4B)/N(3A)
N(4D)–H(4D)/N(3C)
C(5D)–H(5DA)/Cl(1T)
0.88(5)
0.96(6)
1.00
2.34(5)
2.25(6)
2.96
3.143(4)
3.125(4)
3.718(7)
153(4)
151(4)
133.1
Experimental
(d ppm)
Experimental (d ppm)
Theoretical
Theoretical
7.30–6.70 (m, 12H)
5.96 (s, 1H)
5.28 (d, J ¼ 1.5 Hz, 1H)
4.82 (br s, 1H)
4.52 (s, 1H)
3.32 (m, 2H)
2.85 (m, 2H)
2.05–1.92 (m 4H)
8.10 (s, 1H)
7.60 (s, 1H)
7.38 (s, 2H)
7.19 (s, 2H)
7.10 (s, 2H)
6.98 (s, 1H)
6.78 (s, 1H)
6.72 (s, 1H)
6.65 (s, 1H)
6.59 (s, 1H)
6.17 (s, 1H)
5.83 (s, 1H)
5.39 (s, 1H)
4.10 (s, 1H)
3.53 (s, 1H)
3.06 (s, 1H)
2.62 (s, 1H)
1.89 (s, 1H)
1.71 (s, 1H)
1.66 (s, 1H)
1.38 (s, 1H)
146.08
144.23
140.08
130.20
129.59
129.12
128.73
128.48
128.31
127.88
124.97
124.74
124.56
123.93
123.32
123.09
119.98
117.44
84
133.86
132.90
118.62
114.61
113.18
112.86
112.63
111.98
110.86
110.58
109.86
108.72
108.11
107.89
106.40
105.42
104.73
97.81
LUMO energies as I ¼ ꢁEHOMO and A ¼ ꢁELUMO as per Janak
theorem50 and Perdew et al.51 As can be seen the HOMO–LUMO
energy gap in compound 1 is just 0.094 eV which indicates its
highly reactive nature. Another important factor is the global
electrophilicity index (u), a global reactivity index that is related
to chemical hardness and chemical potential, introduced by Parr
et al.49 represented as u ¼ m2/2h and was found to be 0.012 eV
indicating a poor electrophilic nature of 1. All the above
parameters have been calculated for compound 1 using B3LYP/
6-31G (d,p) level of theory and are presented in Table 4 as shown:
NMR analysis
Experimentally 1H and 13C NMR of the title compound was
evaluated in CDCl3 solvent using TMS as an internal standard.
Theoretically it was calculated in polarisable continuum model
with CHCl3 as solvent using GIAO method52 involving B3LYP/6-
31 G (d,p) level of theory. Both theoretical and experimental 1H
and 13C NMR spectral data are presented in Table 5. Experi-
mental 13C NMR of 1 revealed the presence of 23 resonances
assignable to its 25 carbons atoms because of symmetrical
nature of pyrrolidine ring. However its theoretical 13C NMR
spectrum displayed all the 25 resonances for 25 carbon atoms.
Similarly 1H NMR revealed the presence of 24 protons out of
which 12 correspond to aromatic protons of three phenyl rings,
three protons as CH groups, one as NH and 8 protons assignable
to the pyrrolidine moiety. In 1H NMR three CH protons appeared
at 4.52, 5.29 and 5.96 ppm and calculated using DFT at 5.4, 5.8
and 6.2 ppm respectively. Similarly eight protons of the pyrroli-
dine ring were observed in the range 1.25–3.32 ppm and calcu-
lated at 1.37–4.1 ppm for DFT which again revealed a fair
agreement. The remaining 12 aromatic protons observed in the
range 6.6–7.30 ppm were calculated at 6.6–8.2 ppm for DFT.
94.84
88.20
76.45
45.55
36.62
19.07
18.70
71.04
64.12
51.43
51.43
23.76
23.76
IR analysis
Theoretically a total of 153 normal modes of vibration were ob-
tained for compound 1. However in the desired region between
500 and 4000 cmꢁ1 only 130 such modes were observed. The
calculations have been performed within the harmonic approx-
imation for vibrations. Comparision of selected theoretical and
experimental modes is presented in Table 6. A ar agreement is
observed between theoretical and experimental IR data. Experi-
mental FT-IR displayed bands in the region 3400–2800 cmꢁ1
,
1700–1000 and 1000–500 cmꢁ1. Bands in the region 3400–
2800 cmꢁ1 were assignable to N–H stretchings, C–H stretchings
of all the aromatic rings, C–H stretchings in which C-atoms are
connected to N-atoms and CH2 stretchings of the pyrrolidine
moiety. The bands between 1620–1000 cmꢁ1 were assignable to
C]C stretching vibrations in aromatic rings, H–C]C aromatic
ring bend modes, CH2 scissorings, CH2 twistings and N–C
stretching vibrations. However bands between 900-500 mostly
correspond to the torsion modes i.e. distortions in dihedral
angles mostly of HCCC, CCCC, NCCC and CNCC type.
Table 4 Calculated energy values for compound 1 using B3LYP/6-
31G (d,p) level of theory
Parameter
Compound 1
Energy (au)
Dipole moment (debye)
EHOMO (eV)
ꢁ1186.014
3.499
ꢁ0.139
ꢁ0.045
0.094
ꢁ0.175
ꢁ0.005
0.169
ELUMO (eV)
EHOMO–LUMO (eV)
EHOMOꢁ1 (eV)
ELUMO+1 (eV)
E(HOMOꢁ1)–(LUMO+1) (eV)
Hardness (h)
PASS and biological evaluation
Aer having successfully optimized and calculated various
reactivity descriptors for compound 1, using DFT employing the
well-known B3LYP/6-31G (d,p) level of theory, we next studied
its bioevaluation against various human cancer cell lines.
Before carrying out the actual analysis, it was envisaged to
0.047
Chemical potential (m)
Electronegativity (c)
Electrophilicity index (u)
0.092
ꢁ0.092
0.012
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Table 6 Comparsion of theoretical and experimental IR (cmꢁ1) data of compound 1 (selected modes only)
Experimental
Theoretical
Experimental
Theoretical
Experimental
Theoretical
(cmꢁ1
)
(cmꢁ1
)
(cmꢁ1
)
(cmꢁ1
)
(cmꢁ1
)
(cmꢁ1
)
3401
3062
2980
2830
2800
1620
1560
1500
1490
3224
3061
3028
3006
2986
1613
1555
1501
1475
1465
1341
1301
1253
1222
1120
1036
1000
982
1472
1336
1314
1257
1225
1126
1031
987
960
856
795
750
685
620
580
534
512
967
857
792
753
689
617
577
535
521
979
predict the pharmacological properties of the target compound notable is the antineoplastic activity with Pa of 0.884. To validate
(1), using an available online PASS.53 PASS is an important tool the pass results, the title compound was evaluated using sul-
that evaluates the biological activity of a molecule in relation to phorhodamine B (SRB) assay against human-leukemia (THP-1),
its structure. It assesses the druglikeness and toxicities of colon (HCT-116), prostate (PC-3) and lung (A-549) cancer cell
molecules like teratogenicity, carcinogenicity embryogenecity lines. It was observed that the title compound possesses a broad
etc. The average accuracy of prediction is about 95% according spectrum anticancer effect on the cancerous cells with THP-1
to leave-one-out-cross validation (LOOCV) estimation and the cell line as its most easy and so target. Compound 1 dis-
probabilities, Pa (probable activity) and Pi (probable inactivity), played IC50 of 07, 12, 10, and 17 mM against THP-1, colon (HCT-
are values that vary from 0.000 to 1.000, and generally Pa + Pi s 116), prostate (PC-3) and human lung (A-549) cancer cell lines
1 as these probabilities are calculated independently.54 PASS respectively. Since the lowest IC50 is observed against human
analysis results for the title compound 1 have been enlisted in leukemia cell lines (THP-1) cell-lines, it implies that the usual
Table 7. Among the range of activities predicted, the most target of this compound may be leukemia cell lines. However it
is equally true that leukemia cell lines are more-sensitive.
Table 7 PASS prediction for the activity spectrum of compound 1 with
Pa > 0.5
Conclusion
An unusual quinazoline alkaloid (1) was synthesized and char-
Pa
Pi
Activity name
acterized using IR and NMR spectral techniques. Single crystal
analysis depicted four conformations differing slightly in bond
angles and bond lengths. Compound 1 crystallizes in the triclinic
crystal system with P-1 space group having two molecules within
the unit cell. The experimentally obtained parameters were
compared to that obtained theoretically which depicted a good
agreement. Using DFT/B3LYP/6-31G (d,p) level of theory, HOMO–
LUMO energy gap, molecular electrostatic potential surface
(MEPS), vibrational and NMR analysis were carried out. HOMO–
LUMO energy gap was established to carry out the calculation of
chemical hardness, chemical inertness, electronegativity and
electrophilicity index of the molecule, which depicted the poten-
tial kinetic stability and reactivity of the molecule. Prediction of
activity spectra of the target compound was carried out which
revealed that compound 1 possesses notable antineoplastic
activity. The pass results were validated by evaluating the mole-
cule against colon (HCT-116), leukemia (THP-1), prostate (PC-3)
and human lung (A-549) cancer cell lines respectively in an SRB
assay. It was observed that compound 1 possesses remarkable
potency against THP-1 cell lines with IC50 of 7 mM.
0.884
0.851
0.769
0.728
0.003
0.009
0.014
0.026
Antineoplastic enhancer
5 Hydroxytryptamine release stimulant
Nicotinic alpha-2-beta-2-receptor antagonist
Nicotinic alpha-6-beta-3-beta-4-alpha-5-receptor
antagonist
0.707
0.676
0.690
0.605
0.637
0.591
0.585
0.576
0.617
0.576
0.567
0.559
0.563
0.579
0.589
0.007
0.014
0.080
0.003
0.052
0.009
0.007
0.010
0.065
0.027
0.021
0.030
0.034
0.054
0.068
Antihypoxic
Thioredoxin inhibitor
Phobic disorders treatment
Poly(ADP-ribose) polymerase inhibitor
Fibrinolytic
Atherosclerosis treatment
Stroke treatment
Octopamine antagonist
Antineurotic
(R)-6-Hydroxynicotine oxidase inhibitor
(S)-6-Hydroxynicotine oxidase inhibitor
1,4-Lactonase inhibitor
Chloride peroxidase inhibitor
Pseudolysin inhibitor
Glycosylphosphatidylinositol
phospholipase D inhibitor
Alopecia treatment
Antieczematic
Testosterone 17 beta-dehydrogenase
(NADP+) inhibitor
Calcium channel (voltage-sensitive) activator
Nootropic
Phthalate 4,5-dioxygenase inhibitor
Kidney function stimulant
0.550
0.594
0.580
0.033
0.089
0.098
Experimental
General considerations
0.503
0.528
0.516
0.526
0.077
0.114
0.065
0.081
2-Nitrobenzaldehyde, iron powder, pyrrolidine etc were
procured from Sigma-Aldrich (USA) and used as received. The
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FT-IR spectra of the compound was recorded on Agilent FT-IR on a Bruker AXS SMART Apex CCD diffractometer using Mo-Ka
spectrometer in KBr discs (4000–400 cmꢁ1). 1H, 13C NMR (0.71073 A) radiations at 298 K. The soware SADABS56 was used
˚
spectra were recorded on a Bruker Spectrospin DPX-400 NMR for absorption correction and SHELXTL for space group,
spectrometer at 400.13 and 100.47 respectively using TMS as an structure determination and renements.57,58 All non-hydrogen
internal standard. Mass analysis was carried out using Nexera atoms were rened anisotropically.
UHPLC at 130 MPa with SIL-30 AC Nexera autosampler coupled
to an LC-MS 8030 tandem mass spectrometer manufactured by
Shimadzu Corporation, Kyoto, Japan. The soware SADABS was
used for absorption correction and SHELXTL for space group,
structure determination and renements. All non-hydrogen
atoms were rened anisotropically. All the computations have
been carried out at DFT/B3LYP/6-31G (d,p) level of theory using
GAUSSIAN 09 soware.
Density functional theory study
All the computations are carried out using GAUSSIAN 09 so-
ware.59 The DFT modeling method, using the hybrid B3LYP60
functional was used to calculate theoretical parameters for
compound 1 with the basis set combination 6-31 G (d,p).61
Geometry optimization was carried out until global minima
were achieved. The results of the optimized structure for
compound 1 are reported in Table 3 and are compared with X-
ray diffraction results.
Synthesis of 2-aminobenzaldehyde
2-Aminobenzaldehyde was synthesized by a procedure reported
by Gamble et al.55 To a suspension of 2-nitrobenzaldehyde
(0.200 g, 1.32 mmol) in a mixture of glacial acetic acid (2 mL),
SRB cytotoxic assay
SRB cytotoxic assay was used to screen the compounds for cell
cytotoxicity as per the reported procedures.62,63 Various human
cancer cell lines, human leukemia (THP-1, at a density of 7 ꢂ
103), human lung carcinoma cell line (A-549, at a density of 8 ꢂ
103 cells per mL per 100 mL per well), human prostate cancer cell
line (PC-3, at a density of 8 ꢂ 103 cells per mL per 100 mL per
well) and human colon cancer cell line (HCT-116, at a density of
1 ꢂ 104 cells per mL per 100 mL per well) used in this study were
purchased from European collection of cell culture (ECACC)
(USA) and seeded in at-bottomed 96-well plates.
ethanol (2 mL) and water (1 mL), reduced iron powder (0.280 g,
5.00 mmol) was added. The reaction mixture was exposed to
ultrasonic irradiation for 1–2 h at room temperature with
continuous TLC monitoring for the completion of reaction. The
mixture was ltered to remove the iron residue. The ltrate was
partitioned with 2 M KOH and the basic layer was further
extracted with ethyl acetate (3 ꢂ 25 mL). The combined organic
extracts were washed with brine and water and dried under
reduced pressure. The crude residue was then chromato-
graphed over silica gel column chromatography using 30%
EtOAc : Hexane as eluent to give 2-aminobenzaldehyde in 80%
yield.
Conflicts of interest
Synthesis of 1
The authors declare no conict of interest.
A 100 mL round bottomed ask was charged with 2-amino-
benzaldehyde (120 mg, 1 mmol),ethanol (2.5 mL) and pyrroli-
dine (0.027 mL, 0.33 mmol) and stirred under reux conditions
and the reaction monitored using TLC analysis till it was
complete. Aer the completion of reaction the solvent of the
mixture was evaporated under reduced pressure. The solid
residue so obtained, was subjected to silica gel column chro-
matography and puried using 65 : 45 ethyl acetate : hexane as
eluent. Compound 1 was obtained as pure yellowish solid.
Yield: 60%, mp: 183 ꢀC, IR (KBr cmꢁ1): 3401, 3062, 2980,
2830, 2800, 1620, 1560, 1500, 1490, 1465, 1380, 1341, 1301,
1253, 1222, 1120, 1036, 1000, 982, 960, 856, 795, 750, 685, 620,
580, 534, 512, 500. 1H NMR (400 MHz, CDCl3) 7.30–6.70 (m,
12H), 5.96 (s, 1H), 5.28 (d, J ¼ 1.5 Hz, 1H), 4.82 (br s, 1H), 4.52 (s,
1H), 3.32 (m, 2H), 2.85 (m, 2H), 2.05–1.92 (m 4H), 13C NMR (100
MHz, CDCl3) d 146.08, 144.23, 140.08, 130.20, 129.59, 129.12,
128.73, 128.48, 128.31, 127.88, 124.97, 124.74, 124.56, 123.93,
123.32, 123.09, 119.98, 117.44, 84.00, 71.04, 64.12, 51.43 (2C),
23.76 (2C). (ESI-MS) at m/z ¼ 381 for [M + H]+.
Acknowledgements
SHL thanks SERB India for the nancial support under NPDF
scheme (File no: PDF/2016/001690/CS). Salman Jameel thanks
CSIR for the Gate Fellowship (Budget Head: P-81101).
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