Synthesis, quantum chemical study, AIM simulation, in silico ADMET profile analysis, molecular docking and antioxidant activity assessment of aminofuran derivatives

Article abstract of DOI:10.1016/j.molstruc.2019.127285

Quantum computational investigations and in silico biological evaluation of substituted aminofuran derivatives are described in this study. The synthesized compounds were characterized by ¹H NMR, ¹³C NMR, FTIR, UV–Vis and ESI-MS spec

Full text of DOI:10.1016/j.molstruc.2019.127285

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Synthesis, quantum chemical study, AIM simulation, in silico ADMET profile analysis,
molecular docking and antioxidant activity assessment of aminofuran derivatives
Iqbal Azad, Yusuf Akhter, Tahmeena Khan, Mohammad Irfan Azad, Subhash
Chandra, Praveer Singh, Durgesh Kumar, Malik Nasibullah
PII:
S0022-2860(19)31394-8
DOI:
https://doi.org/10.1016/j.molstruc.2019.127285
MOLSTR 127285
Reference:
To appear in: Journal of Molecular Structure
Received Date: 20 April 2019
Revised Date: 22 October 2019
Accepted Date: 23 October 2019
Please cite this article as: I. Azad, Y. Akhter, T. Khan, M.I. Azad, S. Chandra, P. Singh, D. Kumar,
M. Nasibullah, Synthesis, quantum chemical study, AIM simulation, in silico ADMET profile analysis,
molecular docking and antioxidant activity assessment of aminofuran derivatives, Journal of Molecular
Structure (2019), doi: https://doi.org/10.1016/j.molstruc.2019.127285.
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2019 Published by Elsevier B.V.

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Synthesis, quantum chemical study, AIM simulation, in silico ADMET profile
analysis, molecular docking and antioxidant activity assessment of
aminofuran derivatives
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Iqbal Azad , Yusuf Akhter , Tahmeena Khan , Mohammad Irfan Azad , Subhash
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Chandra , Praveer Singh , Durgesh Kumar , Malik Nasibullah
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Department of Chemistry, Integral University, Dasauli, P.O. Bas-ha, Kursi Road, Lucknow-226026, U.P., India.
Department of Biotechnology, Babasaheb Bhimrao Ambedkar University, Vidya Vihar, Raebareli Road, Lucknow,
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Uttar Pradesh 226025, India.
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Department of Chemistry, Jamia Millia Islamia, Jamia Nagar, New Delhi 110025, India.
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Department of Chemistry, IIT BHU, Varanasi 221005, India.
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Department of Chemistry, University of Lucknow, Lucknow 226007, India.
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Department of Chemistry, University of Delhi, New Delhi 110007, India.
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*malik7860@gmail.com, malik@iul.ac.in
Abstract
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Quantum computational investigations and in silico biological evaluation of substituted
aminofuran derivatives are described in this study. The synthesized compounds were
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characterized by H NMR, C NMR, FTIR, UV-Vis and ESI-MS spectroscopic techniques.
Experimental observations were compared with the theoretical data generated by quantum
chemical calculations. Computational quantum chemical evaluations were done through ab-initio
density function theory (DFT) using Becke’s three parameters hybrid functional (B3LYP) with
6-311++G(d,p) level of theory, to study the molecular structural properties, thermodynamic
properties, nonlinear optical properties (NLO) and natural bond order (NBO). NBO exploration
was also done to study the intermolecular interactions and their stabilization energies with the
help of a molecular electrostatic potential map (MEP). Mulliken population and NBO correlated
the charge distributions within the molecule. Topological parameters at the bond critical point
(BCP) were studied by the quantum theory of atoms in molecules (QTAIM). VEDA4 program
was used to evaluate the potential energy distribution (PED). The molecular docking
investigation was done with three human targets viz. coronin 1C (Cor1C), eukaryotic elongation
factor 1A (eEF1A) and villin found in various carcinoma cells. The molecular docking
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interactions of the compounds revealed a good interaction profile with cytoskeletal targets
Furthermore, pharmacological absorption, distribution, metabolism, excretion and toxicity
(ADMET) properties along with druglikeness were also assessed. The synthesized compounds
were also evaluated for their antioxidant activity and were shown to possess potential antioxidant
activity.
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Keyword: Synthesis; Quantum analysis; Chemical reactivity; Molecular Docking; Molecular
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Dynamic
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Highlights:
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Synthesis and characterization of aminofuran derivatives by H NMR, C NMR, FTIR,
UV-Vis and Mass spectroscopic techniques was done.
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Computational quantum chemical studies were performed to evaluate NPO, NLO, NBO,
FMO, MEP and global reactivity descriptors.
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in silico pharmacological and druglikeness evaluation was also perfomed.
QTAIM methods were used to evaluate intramolecular interaction.
Molecular docking was done to explore the biological significance.
1. Introduction
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Substituted furans are widely distributed in a large number of natural products and synthetic
compounds of biological and synthetic importance [1]. The utilization of furan-based moieties in
electronic devices especially optoelectronic and their applications in conductive polymers has
increased their importance [2,3]. In this paper, two tetra-substituted aminofuran derivatives
(dimethyl 2-(cyclohexyl-amino)-5-phenylfuran-3,4-dicarboxylate (I) and dimethyl 2-(tert-butyl-
amino)-5-phenylfuran-3,4-dicarboxylate (II) have been synthesized following a one-step
isocyanide based multi-component strategy and characterized by various spectroscopic
techniques. Density functional theory (DFT) was used for the evaluation and validation of
molecular descriptors, AIM simulation and for molecular dynamic analysis [4]. Nonlinear
optical (NLO) materials are important for diverse optical phenomena such as the generation of
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innovative light frequencies. Many organic molecules possess NLO properties in the presence of
the π-conjugated system [5,6]. The synthesized aminofuran derivatives were subjected to the
evaluation of spectroscopic parameters. Obtained experimental data were correlated with the
theoretically generated data. The NBO analysis was also carried out for interpreting the
molecular wave-function in relation to charge, bond order, bond type, hybridization, resonance,
and donor-acceptor interactions etc. [7,8]. In eukaryotic cells the cytoskeleton is involved in the
longitudinal association of the cells and dynamic relations with other cell types as well as their
aptitude to develop, split, and adapt to altering situations. The cytoskeleton also has an acute
function in mitotic assembly and disassembly, cell division, cytokinesis and apoptosis [9,10].
However these cytoskeletal fibers function on their own and necessitate the occurrence of a huge
quantity of accessory and regulatory proteins. It is assumed that the transformation of actin
cytoskeleton may assist cancer cells in eluding apoptotic signaling [11,12]. Coronin 1C (Cor1C),
eukaryotic elongation factor 1A (eEF1A) and villin are some cytoskeletal fibers involved in
various types of cancers [13,14]. Coronins have been evolved as regulatory protein for actin
dependant processes such as cell motility. Cor1C is a transcriptionally dynamic gene that is up-
regulated in several aggressive cancers. Cor1C has also been found to meditate miR-206
regulatory mechanism. Cor1C belongs to the coronin family of actin-binding proteins which are
imperative for the control and remodeling of the actin filaments network [15,16]. It has been
found to reduce cell invasion and metastasis in many rapidly dividing cancer cells [17,18]. The
elongation factor eEF1A has a vital role in protein synthesis. eEF1A is associated with transfer
of tRNAs to ribosomes [19,20]. Two isomeric forms are known viz. eEF1A1 and eEF1A2 which
are approximately 92% similar in their respective amino acid sequencing and have similar
functions [21,22]. It was found to be overexpressed in 30% of ovarian, 30-60% of breast and
80% of pancreatic cancers [23,24]. In non-small cell lung cancer eEF1A2 was overexpressed in
28% of the observed cases [25]. eEF1A2 is also involved in cell multiplication, migration and
invasion with the help of actin remodeling [26] and phosphatidylinositol signaling [27]. Villin is
also a cytoskeletal protein that is necessary for the development of brush‐border microvilli in
small intestine and colon epithelium [28].
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2. Experimental and computational methods
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Synthesis
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The synthetic route of the target compounds I and II and the proposed synthetic mechanism is
presented as scheme I and II. A mixture of Ph P 3 (0.33g, 1.25 mM) and cyclohexyl isocyanide 2
3
(0.14 g, 1.25 mM) in dry dichloromethane (DCM) (5 ml) was added drop wise in the solution of
benzoic acid 1 (0.12 g, 1 mM) and dimethyl acetylenedicarboxylate 4 (DMAD) (0.14 g, 1 mM)
in dry DCM (10 ml) at room temperature. The contents were refluxed for 16 h and the reaction
was monitored with the help of TLC. The solvent was removed under reduced pressure and the
viscous filtrate was purified by column chromatography using ethyl acetate (EtOAc) and hexane
(2:8) mixtures as eluent to give I and II in appreciable yield.
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dimethyl 2-(cyclohexylamino)-5-phenylfuran-3,4-dicarboxylate (I): Viscous pale yellow oil,
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67% yield. IR (KBr) (vmax/cm ): 3364 (-NH), 1736 (C=O), 1670 (C=O), 1557, 1446 (Ph), 1251,
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1180, 1153, 1037; H-NMR (400 MHz, CDCl ): δ 1.41-1.68 (m, 10H, 5xCH c-hex), 3.15 (m,
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2,
1H, CHNH), 3.92 (s, 3H, OCH ), 3.93 (s, 3H,OCH ), 6.79 (d, J = 8.1 Hz, 1H, NH) 7.46-7.83 (m,
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5H, ArH); C-NMR (300 MHz, CDCl
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2 2
): δ 19.92 (C24H , c-hex), 19.92(C23H , c-hex),
24.81(C25H , c-hex), 31.16(C22H , c-hex), 33.53(C26H , c-hex), 51.44 (OC13H ), 52.45
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(OC14H ), 52.94 (C21HN), 88.98 (C2Furan), 113.45 (C3Furan), 121.94 (o-C16HPh), 125.32 (o-
C20H ), 129.58 (m-C18H ), 129.58 (m-C17H ), 130.21 (p-C19H ), 138.01 (C15ipso),
Ph
Ph
Ph
Ph
155.22 (C4Furan), 161.87 (C1Furan), 163.99 (C6OOCH ), 165.20 (C7OOCH ); ESI-HRMS calcd
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+
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for C20H23NO (M + H ): 358.21. Found: 357.42; Anal. Calc. C, 67.21; H, 6.49; N, 3.92.
dimethyl 2-(tert-butylamino)-5-phenylfuran-3,4-dicarboxylate (II): Viscous colorless oil,
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52% yield. IR (KBr) (vmax/cm ): 3326 (-NH), 1701 (C=O), 1665 (C=O), 1567, 1433 (Ph), 1271,
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1194, 1151, 1099, 1021; H-NMR (400 MHz, CDCl ): δ 1.48 (s, 9H, 3xCH t-but), 3.85 (s, 3H,
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3 3
OCH ), 3.96 (s, 3H, OCH ), 7.11 (s, 1H, NH) 7.37-7.39 (t, 1H, ArH), 7.62-7.64 (d, J = 8.1 Hz,
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2H, ArH), 7.80-7.82 (t, 2H, ArH); C-NMR (300 MHz, CDCl ): δ 29.87 (C(CH ) ), 50.29
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3 3
3 3 3 3
(C(CH ) ), 50.89 (OCH ), 52.42 (OCH ), 84.38 (C2Furan), 117.36 (C3Furan), 124.60 (o-C16HPh),
126.37 (o-C20H ), 127.08 (m-C18H ), 129.38 (m-C17H ), 130.20 (p-C19H ), 132.51
Ph
Ph
Ph
Ph
(C15ipso), 138.22 (C4Furan), 162.10(C1Furan), 165.13 (C6OOCH ), 167.38 (C7OOCH ); ESI-
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HRMS calcd for C20
4.23.
H23NO
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(M + H ): 332.15. Found: 331.14; Anal. Calc. C, 65.24; H, 6.39; N,
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Scheme I. Synthesis scheme of aminofuran derviratives I and II
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Scheme II. Proposed Mechanistic pathway
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2.1. Experimental details
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All the reagents were purchased from Sigma-Aldrich and utilized without further purification.
The progress of the reaction was monitored with the help of thin layer chromatography (TLC).
TLC plates were prepared using silica Gel ‘G' (Merck, India). Electro-thermal melting point
apparatus was used to assess the melting points (°C) by open capillary method and were
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uncorrected. The FT-IR spectra (4000-450 cm ) of the compounds were recorded using KBr
pellets method on Agilent Cary 630 FT-IR spectrometer. UV-Visible spectra (200-400 nm) were
recorded on ELICO SL-160 double beam, UV-Visible spectrophotometer equipped with a 10
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mm quartz cell in ethanol. H-NMR and C-NMR spectra were recorded on Bruker Avance (FT-
NMR) instrument (400 MHz) in CDCl using TMS as an internal reference. Mass spectrometric
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analysis was performed on Agilent 6520 Q-TOF mass spectrometer with electro spray ionization
(ESI) probe.
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2.2. Density Functional Theory (DFT) Calculations
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The geometry optimization of the molecules and all other calculations (vibrational frequencies,
nuclear magnetic resonance, electronic absorption, optimized geometric parameters, natural bond
orbital, global reactivity and etc) were done by GaussView and Gaussian 09W program package.
The quantum calculations were done with the help of IA32W-G09RevD.01 program. GaussView
was used to define the primary atomic coordinates and for the optimization of the molecular
structure. In the ground state (gaseous and solvent phase) the molecular structure was optimized
using DFT/HF with B3LYP method with STO-3G, 6-31G, 6-31+G(d), 6-31G(d,p), 6-31+G(d,p),
6-311G(d,p) and 6-311++G(d,p) basis set. The calculated vibrational frequencies were scaled by
a factor of 0.9679 for 6-311++G(d,p) level. VEDA4 program was used to analyze the calculated
vibrational frequencies by potential energy distribution (PED). The energies and the strengths of
the lowest energy spin permitted electronic excitations were calculated with the help of time-
dependent DFT (TD-DFT) using B3LYP method in vacuum and solvent phase by polarized
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continuum model (PCM). H-NMR and C-NMR analyses were carried out using the Gauge
independent atomic orbital (GIAO) method. QTAIM methods have been used to achieve a
deeper understanding of the intra and intermolecular interactions as well as to assess the strength
of hydrogen bonding.
The energy of highest occupied molecular orbital (EHOMO), lowest unoccupied molecular orbital
(ELUMO), the band gap energy (EGAP or ELUMO-HOMO), chemical softness (σ), global softness (S),
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absolute electronegativity (ꢀ), chemical potential (CP), chemical hardness (η), electrophilicity
index (ω), nucleophilicity index (N), additional electronic charges (∆N) and optical softness (σ˳)
were calculated with the help of Eq. (1)-(12) and the scale factor (ꢁAverage) between the observed
and the theoretical frequencies was calculated by Eq. (13)-(14). Furthermore, DFT/B3LYP 6-
311++G(d,p) level theory was used to perform the natural bond order (NBO) and non-linear
optical (NLO) calculation. NBO 3.0 program was used to recognize the inter and intramolecular
delocalization or hyperconjugation and strength of delocalization interaction with the help of Eq.
(26). NLO parameters such as static dipole movement (µ), mean polarizability (α), anisotropy of
polarizability (∆α) and first hyperpolarizability (β) were calculated with the help of Eq. (15)-(18)
[29,30]. Molecular electrostatic potential surfaces (MEP) of the compounds were analyzed with
the help of GaussView tool.
ꢂꢃ =ꢄ−ꢅꢆꢇꢈꢇ
(1)
(2)
(3)
ꢅꢉ = −ꢅꢊꢋꢈꢇ
ꢅꢌꢍꢎ =ꢄꢅꢊꢋꢈꢇ −ꢄꢅꢆꢇꢈꢇ
ꢐ
|ꢒꢓꢉ|
ꢑ
|ꢔꢅꢆꢇꢈꢇꢔꢅꢊꢋꢈꢇꢄ|
ꢑ
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ꢏ =ꢄ− (ꢅ
+ꢄꢅꢊꢋꢈꢇ) =ꢄ
=
(4)
(5)
(6)
(7)
(8)
ꢆꢇꢈꢇ
ꢐ
ꢑꢄ
ꢕꢖ = −ꢏ =ꢄ (ꢅ
+ꢄꢅꢊꢋꢈꢇ)
ꢆꢇꢈꢇ
ꢑꢄ
ꢐ
ꢒꢔꢉ
ꢅꢆꢇꢈꢇꢔꢅꢊꢋꢈꢇ
ꢗ =ꢄꢄ (ꢅ
−ꢄꢅꢊꢋꢈꢇ) =
=ꢄ
ꢑ
ꢆꢇꢈꢇ
ꢑꢄ
ꢑ
ꢐ
ꢘ =ꢄ
ꢗ
ꢐ
ꢙ =ꢄ
ꢑꢗ
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ꢛꢃꢑ
1
1
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ꢚ =ꢄ ꢑꢗ
(9)
ꢐ
ꢜ =ꢄ
ꢚ
(10)
ꢛꢃ
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1
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∆ꢜꢝꢍꢞ =ꢄ− ꢟ
(11)
(12)
(13)
ꢐ
ꢘꢠ =
ꢅꢌꢉꢃ
ꢢꢅꢞꢎ.
ꢡ = ꢢ
ꢛꢍꢣꢤ.
ꢡ ꢓꢡ ꢓꢡ ꢓ⋯ꢓꢡ
ꢜ
ꢐ
ꢑ
ꢩ
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ꢡꢉꢥꢦꢧꢍꢨꢦ =ꢄ
(14)
ꢜ
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ꢐ
ꢑ
ꢑ
ꢑ
ꢑ
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ꢪ = (ꢪ + ꢪ ꢄ+ꢄꢪ )
(15)
(16)
ꢞ
ꢫ
ꢬ
ꢐ
1
ꢭ =ꢄ ꢄ(ꢭ +ꢄꢭꢫꢫ +ꢄꢭꢬꢬ)
ꢞꢞ
ꢩ
ꢐ
ꢑ
ꢐ
ꢑ
ꢑ
ꢑ
ꢑ
ꢑ
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∆ꢭ =ꢄ√ꢑꢄꢮ(ꢭꢞꢞ −ꢄꢭ ) +ꢄ(ꢭ −ꢄꢭ ) +ꢄ(ꢭ −ꢄꢭ ) + ꢯꢭ + ꢄꢯꢭꢑ + ꢯꢭ ꢰ
(17)
(18)
ꢫꢫ
ꢫꢫ
ꢬꢬ
ꢬꢬ
ꢞꢞ
ꢞꢬ
ꢞꢫ
ꢫꢬ
ꢑ
ꢑ
ꢑ ꢐ/ꢑ
1
ꢱ = (ꢱ + ꢱ + ꢱ )
ꢞ
ꢫ
ꢬ
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Whereꢄꢄꢄβ
x
ꢄ=ꢄβxxxꢄ+ꢄβxyyꢄ+ꢄβxzz,ꢄβ ꢄ=ꢄβyyyꢄ+ꢄβyzzꢄ+ꢄβyxx,ꢄβzꢄ=ꢄβzzzꢄ+ꢄβzxxꢄ+ꢄβzyyꢄ
y
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2.3. Molecular docking simulation
2.3.1. Ligand preparation
The 2D structures of compound I and II were drawn in ChemDraw Professionals (Perkin Elmer
15.1) and ChemDraw 3D was used to prepare .mol files. Structure optimization was done using
the MMFF94 method. For greater accuracy, the optimized structure was further subjected to
energy minimization using the DFT/B3LYP/6-311++G(d,p) basis set through Gaussian 09W and
Gauss View v6.0. Optimized structures of the compounds are presented in Figure 1.
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Figure 1. Optimized structure of compound I and II with DFT-B3LYP/6-311++G(d,p) level
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2.3.2. Homology modeling
The crystal structure of villin was available (PDB ID: 3FG7). Homology modeling is a potential
tool to prepare the 3D structure models of the protein molecule, required for the interaction
analysis. Since the 3D structures of human eukaryotic elongation factor 1A2 (eEF1A2) and
coronin-1C (Cor1C) could not be retrieved from the Protein Data Bank (http://www.rcsb.org),
they were generated with the help of homology modeling. The sequences of amino acids of
human eEF1A2 and Cor1C were obtained from universal protein knowledge database
(UniProtKB) having IDs Q05639 and Q9ULV4, respectively. ExPASy Molecular Biology
Server was used to set the amino acid sequence into FASTA format to build homology models.
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Phyre2 (Protein homology/analog recognition engine 2.0) server was used to generate the 3D
structure of query proteins with the help of FASTA sequence. The server used 1G7C and 2AQ5
as a template to produce a working model of human eEF1A2 and Cor1C through one-to-one
threading method. The query proteins contained 442 and 394 amino acids. The pockets and
cavities were attained by CASTp server. BDSV 2017R was used to visualize the protein’s
structure.
2.3.3. Verification of homology modeling
The model generated with the help of 3D modeling was validated with the help of Molprobity
(http://molprobity.biochem.duke.edu/) which is an online server used for the structure evaluation.
The confirmation was done with the calculation of H atoms, total atoms, Ramachandran,
interaction analysis, rotamer analysis and covalent-geometry analysis.
2.3.4. Receptor preparation
The target proteins were exposed to structural optimization. Polar hydrogen atoms, non-polar
hydrogen atoms and Kollman charges were added. The receptor macromolecule was subjected to
energy minimization through the default RMSD and AMBER force field 14SB with the help of
Chimera 1.12. Energy predictions were completed after structural procurement and eliminating
structural conflicts. Optimization was executed by MMTK which is encompassed with Chimera
and visualized by BDS visualizer 2017R (Figure 2).
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Figure 2. Electrostatic potential surface structure and pocket sites of eEF1A2 (I), Cor1C (II) and
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villin (III) with the amino acid sequence.
2.3.5. AutoDock
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Molecular docking is used to calculate the binding energy upon protein-ligand interaction and to
detect the probable ligand binding sites. The docking investigations were accomplished by
AutoDock 4.2 and AutoDock Tools (ADT) through the Lamarckian Genetic Algorithm (LGA).
The scoring function in AutoDock is based on the hydrogen bonding, van der Waals interaction,
electrostatic interaction, entropy change upon ligand binding and solvation [31]. The grid
parameter file (GPF) was set at 32×32×32 Å, 30×30×30 Å and 30×30×30 Å along, x, y, z axes
with grid arrangement and grid center which was set at 28.10, 35.10 and 48.10 Å for eEF1A2,
4.70, 41.10 and 21.10 Å for Cor1C and 14.93, 16.47 and 13.91 Å for villin respectively. Firstly
.gpf was run to produce the grid map of the protein and ligand complex. Flexible docking
simulation was executed through 500 runs, 27000 generations, 50 GA populations and 2.5×106
energy evaluations. RMS cluster tolerance was set to 2.0 Å per run and 10 most stable
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conformations were selected on the basis of scoring and position. Confirmation of the ligand
having the minimum energy was selected for the docking evaluation. AutoDock estimated free
binding energy scoring function as presented by Eq. (19)–(20):
ꢲꢧꢦꢦꢄꢳꢴꢵꢶꢴꢵꢨꢄꢦꢵꢧꢨꢫ = ꢲꢒꢈ + ꢲꢷꢒ + ꢷꢲ − ꢋꢸꢄ
ꢲꢒꢈ = ꢄꢥꢶꢹ + ꢄꢆꢄꢳꢺꢵꢶꢄ + ꢄꢅꢣꢦꢤ. +ꢄꢅꢶꢦꢻꢺꢣꢥ.
(19)
(20)
Where FIM = Final inter molecular energy, FTI = Final total internal energy, TF =
Torsional free energy, US = Unbound system’s energy, vdW = van der Waals energy, H bond =
Hydrogen bonding energy, Elec = Electrostatic energy, Edesolv = Disolvation energy
2.3.6. AutoDock Vina
Molecular docking validation was performed with the help of AutoDock Vina which runs the
PDBQT file that is prepared through MGL tools. Protein and ligand files were prepared using
AutoDock tools and grid box size was set at 32×32×32 Å, 30×30×30 Å and 30×30×30 Å along
the x, y, and z axes respectively. The grid center was set at 28.10, 35.10 and 48.10 Å for eEF1A2,
4.70, 41.10 and 21.10 Å for Cor1C and 14.93, 16.47 and 13.91 Å for villin respectively. The
docking calculations produced ten poses. The identification of the final pose was done on the
basis of interaction profile of the protein ligand complex. AutoDock Vina estimated scoring
function as given by Eq. (21):
∆ꢌ(ꢳꢴꢵꢶꢴꢵꢨ) =ꢄ∆ꢌ(ꢥꢶꢹ) +ꢄ∆ꢌ(ꢆꢄꢳꢺꢵꢶ)ꢄ+ꢄ∆ꢌ(ꢅꢣꢦꢤ. )ꢄ+ꢄ∆ꢌ(ꢅꢶꢦꢻꢺꢣꢥ. )ꢄ+ꢄ∆ꢌ(ꢼꢺꢧꢻ) (21)
Where ∆ꢽ = Gibbs’s free energy, ∆G (tors) = Torsional free energy
2.3.7. iGEMDOCK
2
2
2
2
2
2
2
2
2
69
70
71
72
73
74
75
76
77
iGEMDOCK is a graphical docking, screening and post-screening evaluation tool. During
docking simulation by iGEMDOCK, accurate docking parameters were set as, numbers of runs:
80, maximum interactions: 8000, population size: 800 with an energy threshold of 100. Docking
outcome was obtained in the form of the lowest binding energy confirmation [32,33]. The
hydrophobic and electrostatic preferences were set at 1.00. The binding site of the receptor was
recognized at a distance of 8 Å. iGEMDOCK empirical scoring function is given by Eq. (22):
ꢾꢿꣀꣁꣂꣃꣃꢄ = ꢄ꣄ꣅ꣆ꢄ + ꢄ꣇ꢄ꣈꣉ꣁꣅꢄ + ꢄ꣊꣋ꣂ꣌.
(22)
1
1

2
2
2
2
2
2
2
2
2
2
2
2
2
78
79
80
81
82
83
84
85
86
87
88
89
90
2.4. PreADMET
PreADMET is a web-based tool for evaluating the ADMET properties. The input of PreADMET
is .mol file. Synthesized compounds were assessed for blood brain barrier penetrability (BBB),
Caco-2 cell permeability, human intestinal absorption, Madin-Darby, canine kidney cell
permeability, plasma protein binding distribution and skin permeability [34] using PreADMET.
2.5. Druglikeness
The druglikeness was assessed on Lipinski's, Veber’s and Ghose filters [35-37].
Free radical scavenging or antioxidant activity by DPPH Assay
Antioxidant activity was assessed through (diphenylpicrylhydrazide) DPPH method at different
concentrations viz. 25, 50, 75 and 100 ꢀL in freshly prepared DPPH as described earlier [38].
The scavenging the DPPH radical was measured by the following Eq. (23):
ꢉꢛꢔꢉꢸ
2
91
꣍ꢃꢃꢆꢄꢻꢤꢍꢥꢦꢵꢨꢴꢵꢨꢄꢦ꣎꣎ꢦꢤꢼꢄ(%ꢄꢴꢵ꣏ꢴꢳꢴꢼꢴꢺꢵ) = ꣐
꣑ × ꢐꢠꢠ
(23)
ꢉꢛ
꣒
ℎ꣓꣔꣓;ꢄ꣕ = ꢄ꣕꣗꣘꣙꣔꣗꣚꣛꣜꣓ꢄ꣙꣝ꢄ꣞ℎ꣓ꢄ꣜꣙꣛꣞꣔꣙꣟ꢄ꣔꣓꣚꣜꣞꣠꣙꣛ꢄ(꣡꣢꣢꣣ꢄ꣘꣙꣟꣤꣞꣠꣙꣛)
꣖
꣕꣥
= ꣕꣗꣘꣙꣔꣗꣚꣛꣜꣓ꢄ꣙꣝ꢄ꣞ℎ꣓ꢄ꣜꣙꣦꣧꣙꣤꣛꣨꣘ꢄ
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
3. Results and discussion
3.1. Geometry optimization
The target molecules, C20
H
5 5
23NO (I) and C18H21NO (II) were exposed to geometry optimization
using DFT/B3LYP/6-311++G(d,p) method. Geometry optimization involves the calculation of
wave-function, energy of the molecule and works to find the most stable conformation of the
molecule having minimum energy. The calculated bond lengths, bond angles and dihedral angles
are given in Table 1 and optimized molecular structures of the compounds are given as Figure 1.
The calculated bond lengths for C1-C2, C2-C3, C3-C4, C4-O5 and O5-C1 were 1.390, 1.448,
1.364 1.402 and 1.347 Å in compound I and 1.391, 1.447, 1.364 1.402 and 1.347 Å in compound
II for the furan ring, out of which C1-C2 and C3-C4 possessed double bond character. For the
carboxylate group, C2-C6, C6-O9, C6-O10, O10-C13 and C3-C7, C7-O11, C1-O12, O12-C14
bond lengths were calculated to be 1.447, 1.212, 1.378, 1.438 and 1.487, 1.210, 1.342, 1.439 Å
in compound I whereas 1.448, 1.212, 1.378, 1.478 and 1.488, 1.210, 1.342 and 1.439 Å in
compound II. Due to the presence of double bond character the contraction in the bond length
1
2

3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
was found between C6-O9 and C7-O11 in both the compounds. Calculated bond lengths of the
amine group, C1-N8, N8-C21 were 1.346 and 1.465 Å in compound I whereas 1.347 and 1.485
Å in compound II. Within the aromatic group, bond lengths have been calculated between 1.390-
1.407 Å for I and between 1.390-1.407 Å for compound II, respectively. The ring size in both the
compounds showed that substitution changes do not influence the aromatic ring system. The
bond length of C-C for the cyclohexyl group was found between 1.535-1.540 Å in compound I
and the bond length of C-C for the tertbutyl group was between 1.536-1.540 Å in compound II.
The bond angle of phenyl ring system was found approximately near ~120.3° and the bond angle
of cyclohexyl group was found near ~111.5°. The bond angles of C1-N8-C21, N8-C21-C22 of
compounds I and II were 125°, 109.5° and 128°, 105.5° respectively. These variations in the
bond angles were due to the substitutions at C21 position. Cyclohexyl substitution (C21, tertiary)
enhanced the strain in the bond angle as compared to the tertbutyl substitution (C21, quaternary).
In furan region, the bond angles of C1-C2-C3, C2-C3-C4, C3-C4-O5, C4-O5-C1 and O5-C1-C2
were 105.3°, 107.8°, 108.6° and 110.2°, respectively for compound I and 105.4°, 107.8°, 108.2°,
108.7° and 110.0°, respectively for compound II.
The dihedral angles in furan region viz. C1-C2-C3-C4, C2-C3-C4-O5, C3-C4-O5-C1, C4-O5-
C1-C2 and O5-C1-C2-C3 displayed low bond angles viz. 0.1°, -0.8°, 1.2°, -1.2° and 0.7° in
compound I and 1.6°, -1.1°, 1.1°, -0.7° and 0.04°, respectively in compound II. The major
variations between the dihedral angles of C1-N8-C21-C22, C2-C1-N8-C21 and O5-C1-N8-C21
were observed to be -150.6°, -175.2° and 8.0° in compound I and -173.8°, 166.5° and -13.8° in
compound II respectively. C21 quaternary carbon was more stable as compared to the tertiary
carbon leading to the distortion in the dihedral angles of the ring system. Some minor variations
were also observed between the dihedral angles of C3-C2-C1-N8, C4-O5-C1-N8 and C6-C2-C1-
N8 viz. -176.3°, 176.3° and 177.6° in compound I and 179.8°, 179.5° and -7.2° in compound II
respectively. These variations were observed due to the weak internal hydrogen bonding between
N8-H----O10-C6 influencing the C21 position. The calculated geometrical parameters were in
good agreement with the single-crystal X-ray analyses reported by the researchers [39,40] (Table
1).
1
3

3
38
Table 1. Selected optimized geometrical parameters using DFT-B3LYP/6-311++G(d,p)
Bond length (Å) Comp. I Comp. II Bond angle (°) Comp. I Comp. II Dihedral angle (°) Comp. I Comp. II
C1-C2
C2-C3
1.390
1.448
1.364
1.402
1.347
1.447
1.212
1.378
1.438
1.487
1.210
1.342
1.439
1.346
1.465
1.535
1.536
1.535
1.535
1.536
1.540
1.458
1.407
1.390
1.394
1.394
1.391
1.406
-
1.391
1.447
1.364
1.402
1.347
1.448
1.212
1.378
1.438
1.488
1.210
1.342
1.439
1.347
1.485
1.536
-
C1-C2-C3
C2-C3-C4
C3-C4-O5
C4-O5-C1
O5-C1-C2
C2-C6-O9
C2-C6-O10
C6-O10-C13
C6-C2-C3
C6-C2-C1
C2-C3-C7
C2-C1-N8
C3-C7-O11
C3-C7-O12
C7-O12-C14
C7-C3-C4
C3-C4-C15
C3-C4-O5
C4-O5-C1
C4-C15-C16
C4-C15-C20
105.285 105.401
107.803 107.782
108.151 108.165
108.571 108.651
110.175 109.989
126.649 126.513
111.600 111.781
115.371 115.417
126.921 126.489
127.422 127.707
125.112 125.107
132.233 131.271
125.437 125.414
110.724 110.710
115.972 115.981
126.899 126.952
136.785 136.647
108.151 108.165
108.571 108.651
119.895 120.003
121.502 121.404
C1-C2-C3-C4
C2-C3-C4-O5
C3-C4-O5-C1
C4-O5-C1-C2
O5-C1-C2-C3
C1-C2-C6-O10
C1-C2-C6-O9
C1-C2-C3-C7
C1-O5-C4-C15
C1-N8-C21-C22
C1-N8-C21-C23
C1-N8-C21-C24
C1-N8-C21-C26
C2-C3-C7-O11
C2-C3-C7-O12
C2-C3-C4-C15
C2-C6-O10-C13
C2-C1-N8-C21
C3-C7-O12-C14
C3-C2-C6-O9
C3-C2-C6-O10
C3-C2-C1-N8
C3-C4-C15-C20
C3-C4-C15-C16
C4-C3-C7-O11
C4-C3-C7-O12
C4-C3-C2-C6
C4-O5-C1-N8
0.094
-0.797
1.236
0.638
-1.057
1.101
C3-C4
C4-O5
-1.191
0.682
-0.693
0.043
O5-C1
C2-C6
10.822
10.790
C6-O9
-168.279 -168.213
-175.219 -175.034
178.000 178.080
-150.630 -173.836
C6-O10
O10-C13
C3-C7
C7-O11
C7-O12
O12-C14
C1-N8
-
-
-55.078
68.030
-
85.506
-125.150 -125.133
55.145 55.730
N8-C21
C21-C22
C22-C23
C23-C24
C24-C25
C25-C26
C26-C21
C4-C15
C15-C16
C16-C17
C17-C18
C18-C19
C19-C20
C20-C15
C21-C23
C21-C24
-176.511 -177.070
-178.650 -178.625
-175.197 166.482
-170.257 -173.641
-
-
-
3.271
3.410
-
-177.630 -177.587
-176.301 179.821
1.458 C15-C16-C17 120.672 120.685
1.407 C16-C17-C18 120.340 120.329
1.390 C17-C18-C19 119.389 119.398
1.394 C18-C19-C20 120.735 120.721
1.394 C19-C20-C15 120.258 120.270
1.391 C20-C15-C16 118.598 118.590
-27.441
153. 394 152.397
62.381 60.026
-28.323
-119.271 -119.112
-173.285 -172.496
176. 290 179.497
1.406
1.540
1.539
C1-N8-C21
N8-C21-C22
N8-C21-C26
125.045 128.099
109.463 105.472
C4-C15-C16-C17 179.809 179.828
-
112.272
-
-
-
-
-
C4-C15-C20-C19
O5-C1-C2-C6
179.753 179.704
174.017 173.065
C21-C22-C23 111.496
C22-C23-C24 111.816
C23-C24-C25 111.321
C24-C25-C26 111.531
O5-C1-N8-C21
O5-C4-C15-C16
O5-C4-C15-C20
7.996
-13.756
-22. 114 -23.420
157.051 155.860
1
4

C25-C26-C21 111.396
-
O5-C4-C3-C7
C6-C2-C3-C7
C6-C2-C1-N8
C6-C2-C1-O5
C7-C3-C4-C15
174.408 174.512
N8-C21-C23
N8-C21-C24
-
-
110.910
110.301
11.402
11.832
-7.157
177.573
174.017 173.065
-1.306
-1.501
N8-C21-C22-C23 -179.406
N8-C21-C26-C25 178.150
-
-
0.185
0.781
-0.426
-1.005
-0.056
0.528
-
C15-C16-C17-C18
C15-C20-C19-C18
C16-C17-C18-C19
C16-C15-C20-C19
C17-C18-C19-C20
C17-C16-C15-C20
C21-C22-C23-C24
0.153
0.761
-0.481
-1.071
0.024
0.620
54.689
C21-C26-C25-C24 -55.201
C22-C23-C24-C25 -54.349
-
-
C22-C21-C26-C25
55.201
-
3
3
39
40
3.2. Infrared Spectroscopy
3
3
3
3
3
3
3
3
3
3
3
3
3
3
41
42
43
44
45
46
47
48
49
50
51
52
53
54
The experimental FT-IR spectra of compound I and II were compared with the calculated spectra
as presented in Table 2. Scaled (calculated) harmonic vibrational frequencies using DFT-B3LYP
method and observed vibrational frequencies with comprehensive detailed PED assignments are
given in Supplementary Table 4 using vibrational energy distribution analysis (VEDA) program
[41]. The experimental and theoretical vibrational analyses were performed between 4000-450
-1
cm and represented graphically in Figure 4. The harmonic frequencies were calculated in the
gaseous phase. However, the experimental values were obtained in the solid phase. The
calculated vibrations were scaled down through a single scaling factor 0.9679 to discard any
harmonicity found in the real system [42]. Compounds I and II consisted of 49 and 45 atoms, and
had 141 and 129 fundamental vibrations modes. The optimized molecular structures of the
compounds were subjected to energy and harmonic vibrational frequencies calculation through
DFT/B3LYP/6-311++G(d,p) method. The correlation graph showed good agreement between
2
experimental and theoretical vibrational spectra (r = 0.9996) for both the compounds as shown in
Figure 3 and 4.
1
5

3
55
56
3
Figure 3. Observed and calculated IR spectra of compound I and II
3
57
58
3
N-H group vibrations
The N–H stretching vibrations commonly occur in the region 3500-3300 cm [43]. Secondary
-1
359
360
361
362
363
364
365
-1
-1
amines give a broad band at ~1500 cm and an out of plane bending at ~800 cm . The N–H
-1
stretching vibrations of compounds I/II were calculated at 3480/3476 cm and observed at
-1
3349/3326 cm . Stretching (N–H), in-plane (N–H) and out-plane (N–H) deformation bands were
-1
observed at 3480, 1588, 678/ 3476, 1580, 679 cm and calculated at 3349, 1606, 677/ 3326,
-1
1567, 675 cm for the two derivatives. The experimental values were in good agreement with the
theoretical values.
366
Carbonyl group (C=O) vibrations
367
368
369
370
371
The stretching vibration of ester C=O group with conjugated arene ring has been reported as a
-1
strong band between 1740-1715 cm . The calculated C=O stretching vibration was observed as a
-1
strong band at 1710 and 1702 cm for compounds I/II. The calculated peaks were observed at
-1
-1
1736 and 1670 cm for compound I and 1701 and 1665 cm for compound II. The vibrational
-1
frequency of C–O bands was found between 1300-1000 cm . The stretching vibrations for ester
1
6

-
1
3
3
3
72
73
74
C–O group for compound I and II were calculated at 1186, 1052, 868, 817 cm and 1166, 1013,
-1
-1
825, 792 cm showing correlation with the observed vibrations at 1181, 1053, 856, 804 cm for
-1
compound I and 1161, 1020, 804, 787 cm for compound II.
3
75
CH group vibrations
3
-
1
3
3
3
3
3
76
77
78
79
80
The C-H stretching vibrations generally lie between 3000-3100 cm . The stretching vibrations of
-1
C–H, linked with OCH groups were observed at 2983 and 2942 cm for compound I/II while
3
-1
the calculated values were found at 2973 and 2954 cm . The in-plane deformations of OCH
3
-1
were observed at 1446 and 1433 cm for compound I and II whereas the calculated bands were
-1
found at 1447 and 1432 cm respectively.
3
81
CH group vibrations
2
-
1
3
3
3
3
3
82
83
84
85
86
Methylene group has its characteristic bending absorption at ~1465 cm . Scissoring vibration of
-1
the CH
2
group was observed at 1461 cm which was in good agreement with the calculated
-1
value at 1460 cm . The stretching symmetric and anti-symmetric vibrations for C–H were
-1
observed at 2933 and 2910 cm for compound I, whereas the calculated values were 2951 and
-1
2913 cm .
3
87
C–N vibrations
-
1
3
3
3
3
3
3
88
89
90
91
92
93
The amine (C–N) stretching vibrations are observed between 1350-1000 cm [44] as medium to
strong intensity bands. Due to the conjugation of the aromatic ring and the attached nitrogen
-1
atom of the amine group, aromatic amines absorb at a higher frequency between 1350-1250 cm .
-1
The experimental spectra showed only two bands at 1606, 1557 and 1601, 1469 cm for
compound I and II respectively corresponding to the C–N symmetrical and anti-symmetrical
stretching.
3
3
3
3
3
3
4
94
95
96
97
98
99
00
Phenyl ring vibrations
-1
The C-H stretching vibrations in the phenyl ring occur between 3100-3000 cm [45]. The
experimental spectra showed four medium-weak intensity bands at 3119, 3078, 3069 and 2968
-1
-1
cm for compound I and 3083, 3081 and 3060 cm for compound II which were in agreement
with the C-H stretching of the phenyl ring. Theoretically these bands were observed between
-1
-1
3097-3061 cm for compound I and 3096-3061 cm for compound II. The in-plane aromatic C-
-1
H bending vibrations are found in the range 1465-1000 cm [43,44]. These bands were
1
7

-
1
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
observed at 1475, 1461, 1369, 1306, 1091 and 996 cm for compound I and 1433, 1313, 1271,
-1
1099, 999 cm for compound II. The calculated bands were found at 1462, 1460, 1351, 1209,
-1
-1
1165, 1138, 1020, 1013 and 981 cm for compound I and 1432, 1319, 1288, 1076 and 982 cm
for compound II showing good agreement with the experimental data. The in-plane bending
vibrations were mixed with ring C-C stretching vibrations. The C-H out-of-plane deformations
-1
-1
were observed at 947, 799, 759 and 712 cm and calculated at 960, 792, 758 and 740 cm for
-1
compoundI and for compound II, they were observed at 999, 908, 787, 755 and 743 cm and
-1
calculated at 982, 910, 792, 751 and 748 cm , respectively. The most prominent C-C stretching
-1
bands of furan ring were observed at 1621, 1606, 1572 and 1557 cm for compound I. While for
-1
compound II they were observed at 1601, 1567 and 1469 cm . C-C stretching bands of the
-1
hetero-ring were found at 1602, 1588, 1579 and 1555 cm for compound I and 1595, 1580 and
-1
1465 cm for compound II. The characteristic C-C stretching of phenyl ring is expected in the
-1
-
range 1650-1200 cm . Experimentally these bands were observed at 1602, 1579, 1475, 1432 cm
1
-1
for compound I and 1595, 1588, 1555, 1319 cm for compound II. Generally these bands
overlap with the C-H in-plane deformation. Theoretically calculated bands were obtained at
-1
-1
1621, 1572, 1486, 1428 cm for compound I and 1601, 1582, 1513, 1313 cm for compound II
representing a good agreement between the theoretical and experimental data.
-1
4
4
19
20
Table 2. Experimental and calculated vibrational wave numbers (cm ) at B3LYP/6-311
G++(d,p) level
Comp. I
Comp. II
Vibration Modes (I/ II)
IRUnscale IRScale IRObserv IRUnscale IRScale IRObserv
3
596
214
3480
3110
3349
3119
3591
3213
3476
3110
3326
3083
[STRE-(N8H27)]/ [STRE-(N8H25)]
[STRE-(C20H38)]/ [STRE-(C20H36)]
3
[
STRE-(C17H35), (C18H36) and (C19H37)]/ [STRE-
3186
3172
3071
3010
3084
3071
2973
2913
3078
3069
2983
2910
3186
3162
3052
3026
3084
3061
2954
2928
3081
3060
2942
2901
(
C16H32), (C17H33) and (C18H34)]
STRE-(C17H35) and (C19H37)]/ [STRE-(C17H33),
C16H32), (C18H34) and (C19H35)]
STRE-C13H28) and (C13H30)]/ [STRE-(C14H29),
C14H30) and (C14H31)(49)]
STRE-(C22H41) and (C24H44)]/ [STRE-(C22H37),
C22H38), (C22H39) and (C23H42)]
[
(
[
(
[
(
1
8

1
767
759
1710
1702
1736
1670
1767
1758
1710
1702
1701
1665
[STRE-(O11C7)]/ [STRE-(O11C7)]
[STRE-(O9C6)]/ [STRE-(-(O9C6)]
1
[
STRE-(C16C17), (C20C19) and (C3C4)]/ (BEND-
1656
1602
1621
1641
1588
1582
H32C16C17), (H33C17C18), (H34C18C19)-(H35C19C20),
H36C20C15)]
(
1
641
632
1588
1579
1606
1572
1632
1607
1580
1555
1567
1513
[STRE-(C2C1) and (N8C1)]/ [STRE-( (C3C4), (C4C15)]
STRE-(C3C4), (C19C18) and (C15C20)]/ [STRE-C3C4),
[
1
(
C4C15), (C16C17), (C20C19) and (C15C20)]
BEND-(H34C16C17), (H35C17C18), (H37C19C20) and
H38C20C19)]/ [STRE-H37C22)(17), (H38C22),
H39C22), (H40C23), (H41C23), (H42C23), (H43C24),
H44C24) and (H45C24)]
BEND-(H43C23H42), (H45C24H44), (H47C25H46) and
H49C26H48)]/-
BEND-(H32C14H31), (H33C14H32) and TORS-
H32C14O12C7)]/ [BEND-H27C14H26), (H28C14H27)]
BEND-(H29C13H28) and (H30C13H29)]/ [BEND-
H26C13H28) and (H31C14H30)]
BEND-(H39C21C26) and (C2C1O5)]/ [BEND-
H36C20C15), (H32C16C15) and (H34C18C19)]
[
(
1524
1475
1486
1527
1478
1483
(
(
[
1511
1495
1475
1462
1451
1462
1447
1427
1415
1405
1475
1446
1426
1412
1393
-
-
-
(
[
1480
1475
1363
1262
1432
1428
1319
1221
1433
1426
1313
1227
(
[
(
[
[
BEND-(H39C21C26) and (C2C1O5)]/ [STRE-(N8C21),
BEND-(H25N8C21) and (H40C23C21)]
[
BEND-(H44C24C25), TORS-H42C23C24C25),
H43C23C24C25) and (H44C24C25C26)]/ [BEND-
H44C24C21), (H45C24C21), (H43C24C21) and (TORE-
H41C23C21C24)]
STRE-(C4C15) and (O5C4)]/ [STRE-(O10C6) and TORE-
H26C13O10C6)]
(
1
395
289
1351
1248
1369
1251
1233
1205
1194
1166
1194
1161
(
(
[
1
(
1
273
226
1232
1186
1230
1181
-
-
-
[STRE-(O12C7)]/-
1
1167
1130
1110
[TORE-(H45C24C25C26)]/ [BEND-(H31C14H30)]
[
STRE-(O5C1), (N8C21) and BEND-(C16C17C18)]/
[BEND-(H44C24C21), TORE-(H41C21N8C1),
1117
1081
1091
1092
1057
1070
(
H26C13O10C6)]
STRE-(O5C4)]/ [STRE-(O5C4), (O10C13), TORE-
C17C18C19C20)]
[STRE-(O12C14)]/-
[v-(C23C24)(11)-v-(C22C23)(12)-v-(C25C26)(15)]/-
[
1
087
073
1052
1053
1046
1013
1020
(
1
1039
921
1038
930
-
-
-
-
-
-
9
52
1
9

[
STRE-(O10C6), (O12C7), BEND-(O9C6O10) and
O11C7O12)]/ [STRE-(O10C13), (O12C14)]
(TORE-(O9C2O10C6) and (C6C1C3C2)]/ [STRE-(
(O11C7), TORE-(H34C16C17C18), (H36C18C19C20) and
H38C20C19C18)(10)]
TORE-(O9C2O10C6) and (O11C3O12C7)]/ [TORE-
O10C6C2C3)]
8
8
7
7
97
45
98
64
868
817
772
740
856
804
777
712
852
818
787
759
825
792
761
735
804
787
763
718
(
[
(
[
(
[
BEND-(C19C18C17), (C2C1O5C4) and (N8C2O5C1)]/
[TORE-(H45C24C21CN8), (H26C13O10C6) and
(
H42C23C21N8)]
7
6
00
83
678
661
677
650
701
-
679
-
675
-
[TORE-(H27N8C1C2)]/ [STRE-(C2C1)(17) and (C1N8)]
[BEND-(C23C24C25) and (C25C26C21)]/-
421
4
22
23
4
Figure 4. The correlation graph between experimental and calculated wave numbers for
424
425
426
compound I and II
1
13
3.3. H and C NMR spectra
427
428
429
430
431
432
The chemical shifts for the optimized structure have been computed with the help of DFT-
B3LYP method with 6-311++G(d,p) as a basis set, using the GIAO approach. The IEFPCM
model with chloroform solvent (relative permittivity (ε) 46.7) was used to study the solvent-
induced and temperature effects. Linear scaling approach is most applicable, the slope and
intercept from the fittest line agrees for the direct calculation of the empirically scaled chemical
shifts (Eq. 24) [46].
(
ꢴꢵꢼꢦꢧꢤꢦꢎꢼꢄꢔꢄꢘ)
ꢻ
ꢤꢍꢣꢦꢶ
433
꣩
=ꢄ
(24)
ꢤꢍꢣꢤ
ꢻ
ꢣꢺꢎꢦ
4
34
35
Where σ is the calculated isotropic shielding value for a particular nucleus or the average of
4
several symmetry associated nuclei.
2
0

1
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
The experimental and calculated chemical shifts are shown in Table 3. In the H NMR spectrum
of compound I, a multiplet for ten protons of the cyclohexyl group was observed between 1.25-
1.67 ppm and a singlet for nine protons of the tertbutyl group was observed 1.48 ppm,
respectively. A doublet for NH proton was observed at 2.17 ppm for compound I and singlet was
observed at 7.11 ppm for compound II while a one proton multiplet for the CHNH proton was
observed at 3.15 ppm for compound I, this peak was absent in the compound II, due to the
presence of quaternary tertbutyl carbon, directly attached with the NH group. A singlet for three
methyl protons of the –COOCH groups was observed at 3.92 and 3.93 ppm for compound I and
3
3.85 and 3.96 ppm for compound II, respectively. Furthermore, additional support for the
1
3
characterization of the structure of aminofuran derivatives was obtained by their C NMR
spectra. The peaks of the carboxylate carbon (-COO; C6=O9 and C7=O11) were observed at
163.99 and 165.20 ppm for compound I and 165.73 and 167.38 ppm for compound II,
respectively. The peak due to the carbon attached to the amine nitrogen, C1-N8 was found at
161.87 and 162.10 ppm for compound I and compound II, respectively, as reported in the
literature (Table 3; Figure 5 and 6).
4
51
52
1
4
Figure 5. H NMR spectra of compound I and II
2
1

4
53
54
1
3
4
Figure 6. C NMR spectra of compound I and II
455
456
457
458
459
460
461
462
463
1
2
13
The correlation coefficient for H NMR (r =0.970 and 0.983) for compound I and II and C
2
NMR (r =0.998 and 0.998) exhibited sufficient agreement between the experimental and
calculated findings (Figure 7). The radar graphs were also prepared to explore the correlation of
1
3
C NMR values and interesting agreement was obtained between the experimental and
1
13
calculated values (Figure 8). The H and C NMR results were supported by the presence of a
molecular ion peak at 357.21 and 332.15 in the mass spectra of the two derivatives I and II
confirming the molecular formula of the two compounds to be C20
respectively.
5 5
H23NO and C18H21NO ,
464
2
2

1
13
4
4
65
66
Figure 7. Correlation between the experimental and calculated H and C chemical shifts at
DFT-B3LYP/6-311G++(d,p) level
1
13
4
67
Table 3. Calculated and experimental H and C NMR chemical shift (꣪/꣧꣧꣦) in CDCl3
Comp. I
Comp. II
Atoms
Position
Exp. value Calc. value
∆
ꢁ
Exp. value Calc. value
∆
ꢁ
C1
C2
161.87
88.98
113.45
155.22
163.99
165.20
51.44
52.76
138.01
121.94
129.58
130.21
129.58
125.32
52.94
33.53
-
162.52
91.72
121.10
148.84
165.90
171.18
50.10
51.97
134.10
127.76
131.20
130.22
131.47
129.67
53.15
34.08
-
-0.65 0.996
-2.74 0.970
-7.65 0.937
6.38 1.043
-1.91 0.988
-5.98 0.965
1.34 1.027
0.79 1.015
3.91 1.029
-5.82 0.954
-1.62 0.988
-0.01 0.999
-1.89 0.986
-4.35 0.966
-0.21 0.996
-0.55 0.984
162.10
84.38
117.36
138.22
165.13
167.38
50.29
50.89
132.51
124.60
129.38
127.08
130.20
126.37
52.42
-
163.59
92.90
120.85
149.71
165.73
171.30
50.15
52.00
134.01
128.32
131.15
130.37
131.47
130.06
56.09
-
-1.49 0.991 IC, Furan C-NH
-8.52 0.908 IC, Furan C-CO
-3.49 0.971 IC, Furan C-CO
-11.49 0.923 IC, Furan C-Ph
C3
C4
C6
-0.6
-3.92 0.977 IC, COOCH
0.14 1.003 IC,OCH
0.996 IC, COOCH3
C7
3
C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
3
-1.11 0.979 IC,OCH3
-1.51 0.989 IC, Ph C
-3.72 0.971 IC, Ph CH
-1.77 0.987 IC, Ph CH
-3.29 0.975 IC, Ph CH
-1.27 0.990 IC, Ph CH
-3.69 0.972 IC, Ph CH
-3.67 0.935 IC, c-hex CHN
-
-
IC, c-hex CH2
1.012 IC, t-but CH3
IC, c-hex CH
1.213 IC, t-but CH
IC, c-hex CH2
1.115 IC, t-but CH3
-
-
29.87
-
29.53
-
0.34
C23
C24
24.81
-
27.17
-
-2.36 0.913
-
-
2
-
-
29.87
-
24.62
-
5.25
3
19.92
-
26.36
-
-6.44 0.756
-
-
-
-
29.87
-
26.80
-
3.07
C25
C26
19.92
31.16
26.50
35.81
-6.58 0.752
-4.65 0.870
-
-
-
-
IC, c-hex CH2
IC, c-hex CH2
-
-
2
R
0.998
0.957
5.61
0.998
0.995
6.03
ꢁ꣫꣬꣭꣮꣯꣰꣭
H1
6.88
3.92
3.93
1.27
0.39
0.29
-
1.226
1.110
1.080
7.11
3.85
3.96
1.08
0.3
0.31
-
1.179 s, 1H, N-H
1.085 s, 3H, OCH
3
H2, H3, H4
H5, H6 H7
H8, H9,
3.53
3.64
3.55
3.65
1.085 s, 3H, OCH3
0.968 m, 5H, ArH
7.46-7.83 7.23-8.33
0.983 7.37-7.82 7.25-8.35
H10, H11,
2
3

H12
H13
3.15
3.53
-0.38 0.892
-
-
-
-
-
-
-
-
m, 1H, NCH
m, 10H, CH2
H14, H15, 1.41-1.68 1.02-1.94
-
1.047
H16, H17,
H18, H19,
H20, H21,
H22, H23
H13, H14,
H15, H16,
H17, H18,
H19, H20,
H21
-
-
-
1.48
1.01
0.47
1.465 s, 9H, C(CH3)3
2
R
0.970
1.057
0.983
1.156
ꢁ꣫꣬꣭꣮꣯꣰꣭
468
4
69
70
1
3
4
Figure 8. C NMR values of synthesized compounds in the form of radar presentation to
471
472
473
showing a correlation between experimental and calculated values
3.4. Electronic absorption spectra
474
475
476
477
478
The electronic spectra were computed and TD-DFT excitations were calculated in the gaseous
phase. The PCM model was used to observe the transitions in the solvent phase. The predicted
UV-Vis spectra and electronic transitions of high oscillatory strength in gaseous phase, ethanol
and chloroform are shown in Table 4 and displayed good agreement with the observed spectra in
ethanol [47]. The weak and broad absorption bands were obtained at 359 and 282 nm for
2
4

4
4
4
4
4
79
80
81
82
83
compound I and at 353 and 271 nm for II showed satisfactory correlation with the TD-DFT
calculated transitions at 361 and 287 nm, with oscillator strength (f) of 0.3367 and 0.2285 for I
and II, 350 and 266 nm with 0.4423 and 0.0035 oscillator strength (f). These excitations
generally correspond to H→L and H→L+2 for compound I whereas H→L and H→L+4
electronic transitions for compound II (Table 4).
4
4
84
85
Table 4. Electronic transition calculated by TDDFT using B3LYP/CPCM method in gaseous
phase, ethanol and chloroform solvents
EExcitation Osc. strength Calc. ꢁExcitation
Major
Cont.*
%
Name
Phase
Coefficient
Assignment
(
eV)
.6099
4.1476
(f)
(nm)
transition
3
0.3152
0.0032
0.0015
0.3367
0.0064
0.2285
0.3635
0.2387
0.0008
0.4037
0.0639
0.0011
0.4423
0.0035
0.0037
0.4735
0.0206
0.0002
343.45
298.93
286.79
360.83
295.56
286.92
357.84
286.36
256.87
333.20
264.43
259.04
350.40
266.45
245.94
348.08
269.89
248.94
0.70156
0.67088
0.67414
0.70186
0.63200
0.64353
0.70252
0.60674
0.68096
0.69937
0.66459
0.67751
0.70042
0.65014
0.64291
0.70127
0.58210
0.69402
H(95) → L(96)
H(95) → L(97)
H(95) → L(99)
H(95) → L(96)
H(95) → L(98)
H(95) → L(97)
H(95) → L(96)
H(95) → L(97)
H(95) → L(101)
H(88) → L(89)
H(88) → L(95)
H(88) → L(93)
H(88) → L(89)
H(88) → L(93)
H(88) → L(94)
H(88) → L(89)
H(88) → L(92)
H(88) → L(94)
π → π*
π → π*
π → π*
π → π*
π → π*
π → π*
π → π*
π → π*
π → π*
π → π*
π → π*
π → π*
π → π*
π → π*
π → π*
π → π*
π → π*
π → π*
98.44
90.02
90.89
98.52
79.88
82.83
98.71
73.63
92.74
97.82
88.34
91.80
98.12
84.54
82.67
98.36
67.78
96.33
Gas
4
.3231
.4361
3
Comp. I EtOH
4.1948
4
.3213
.4648
3
CHCl
Gas
3
4.3296
4
.8267
.7210
3
4.6887
4
.7864
.5384
3
Comp. II EtOH
4.6532
5
.0412
.5620
3
CHCl3
4.5938
.9806
4
4
4
86
87
3.5. FMO (Frontier Molecular Orbital)
4
4
4
4
88
89
90
91
The HOMO and LUMO are involved in the chemical stability of the molecule [43,45]. The
HOMO signifies the aptitude to donate an electron and LUMO signifies the tendency to gain
electron. The HOMO and LUMO energies have been computed using TD-DFT/B3LYP/6-
311++G(d,p) method. In the favor of the chemical hardness, the large HOMO-LUMO difference
2
5

4
4
4
4
4
4
4
4
5
5
5
5
5
5
92
93
94
95
96
97
98
99
00
01
02
03
04
05
represents a hard molecule and small HOMO-LUMO difference signifies a soft molecule. The
molecule with least HOMO-LUMO variations indicates its high reactivity. The HOMO-LUMO
energy difference was calculated in gaseous phase, in EtOH and CHCl respectively to present
3
the reactivity and kinetic stability of the molecules. The calculated energies were predicted by
the PCM model by TD-DFT/B3LYP method with 6-311++G(d,p) level. The HOMO-LUMO
energy difference computed by quantum chemical analysis revealed the chemical reactivity of
the compounds and defined the combined charge transfer interaction within the molecule, which
is necessary for the biological activity of a molecule. The positive and negative phases are
denoted by red and green colors respectively. HOMO-LUMO plots are shown in Figure 9. The
HOMO was delocalized on the furan and phenyl rings, carboxylate and amine group, whereas
the LUMO in compound II was mainly localized on the furan and phenyl rings and on the
carboxylate group (Table 5; Figure 9).
Table 5. HOMO-LUMO energies with HOMO-LUMO energy gap
Comp. I (eV)
Solvent
Comp. II (eV)
Activity ranking
(in Gas phase,
Gaseous
phase
Solvent Gaseous Solvent Solvent
(EtOH) (CHCl
3
)
phase
(EtOH) (CHCl
3
)
3
EtOH and CHCl )
EHOMO
ELUMO
EGAP
-5.3746
-1.3281
4.0464
-5.5676
-1.6361
3.9315
-5.5117
-5.4230 -5.5944 -5.5380
-1.2971 -1.5876 -1.4100
II > I
I > II
II > I
-1.5450
3.9667
4.1328
4.0069
4.0380
5
06
2
6

5
07
08
5
Figure 9. Atomic orbital composition of the FMOs and their energy gap obtained from TD-
509
510
511
512
513
514
515
516
517
518
519
520
521
DFT/B3LYP/6-311++G(d,p) level in ethanol using PCM model
3.6. MEP (Molecular electrostatic potential) and MR (Molar refractivity)
The MEP recognizes the electrophilic and nucleophilic sites in a molecule and explains the
charge distribution on the basis of polarity in the molecular system depicted by the color
variations and offers findings in a pictorial form describing the virtual polarity of the molecule
[46]. The red and blue colors depict electrophilic and nucleophilic sites as displayed in the Figure
11. The color code was found in the range -9.812 (red) to +9.812 a.u. (blue) and -9.394 (red) to
+9.394 a.u. (blue) for compounds I and II. Electrostatic potential decreased in the order; blue >
green > yellow > orange > red. A high electropositive potential was observed in the vicinity of
the –COO group and a low electropositive potential was found near the nitrogen atom. The MEP
findings confirmed the occurrence of an intramolecular hydrogen bond between N8-H27ꢁꢁꢁꢁO10
in compound I and N8-H25ꢁꢁꢁꢁO10 in II (Figure 10).
2
7

5
22
23
5
Figure 10. MEP plot (A = 3D surface, B = transparent 3D surface and C = contour map) of the
524
525
526
527
528
529
synthesized compounds showing total density mapped with ESP
MR is another essential parameter used to analyze the polarizability of a material. It is
determined by molecular weight, refractive index, and density of the substance and represents
the interaction profile and lipophilicity of the system [7]. It is a constitutive-chemical parameter
and presented by the Lorenz-Lorentz Eq. (25).
n2
n2
1
2
MW
ρ
MR =
π α
= 1.333 N
530
531
532
533
534
535
536
537
538
539
540
541
542
�
(25)
where n is the refractive index; ρ is the density; MW is the molecular weight; (MW/ρ) is the
molar volume; N is the Avogadro number; α is the polarizability of the molecular system
depending on the wavelength of the light used to measure n. The values of MR were found to be
97.93 (I) and 88.98 (II) esu respectively.
Mulliken population analysis (MPA)
Mulliken atomic charge is a vital parameter for the theoretical prediction of the effect of atomic
charge in the molecular coordination, which is responsible for regulating structural confirmation
and bonding aptitudes. Mulliken atomic charge values were analyzed with the help of MPA
which was calculated with the help of DFT- B3LYP method using 6-311++G(d,p) as the basis
set and presented in Supplementary Table 1. All the carbon atoms were negatively charged
except C1 (0.17942), C2 (0.106861), C3 (0.286459), C15 (0.758823), C16 (0.116305) and C26
2
8