Design, synthesis and biological evaluation of oxindole-based chalcones as small-molecule inhibitors of melanogenic tyrosinase

Article abstract of DOI:10.1248/cpb.c17-00301

The enzyme tyrosinase regulates melanogenesis and skin hyperpigmentation by converting L-3,4-dihy-droxyphenylalanine (L-DOPA) into dopaquinone, a key step in the melanin biosynthesis. The present work deals with design and synthesis of various oxindole-ba

Full text of DOI:10.1248/cpb.c17-00301

Vol. 65, No. 9
Chem. Pharm. Bull. 65, 833–839 (2017)
833
Regular Article
Design, Synthesis and Biological Evaluation of Oxindole-Based
Chalcones as Small-Molecule Inhibitors of Melanogenic Tyrosinase
Sharad Kumar Suthar,a Sumit Bansal,a Niteen Narkhede,a Manju Guleria,b
,a
Angel Treasa Alex,c and Alex Joseph*
a Department of Pharmaceutical Chemistry, Manipal College of Pharmaceutical Sciences; Manipal-576104, India:
c
b School of Pharmaceutical Sciences, Jaipur National University; Jaipur-302017, India: and Department of
Pharmaceutical Biotechnology, Manipal College of Pharmaceutical Sciences; Manipal-576104, India.
Received April 11, 2017; accepted June 2, 2017
The enzyme tyrosinase regulates melanogenesis and skin hyperpigmentation by converting L-3,4-dihy-
droxyphenylalanine (L-DOPA) into dopaquinone, a key step in the melanin biosynthesis. The present work
deals with design and synthesis of various oxindole-based chalcones as monophenolase and diphenolase activ-
ity inhibitors of tyrosinase. Among the screened compounds, 4-hydroxy-3-methoxybenzylidene moiety bear-
ing chalcone (7) prepared by one pot reaction of oxindole and vanillin displayed the highest activity against
tyrosinase with IC50s of 63.37 and 59.71µM in monophenolase and diphenolase activity assays, respectively.
In molecular docking studies, chalcone 7 also showed the highest binding affinity towards the enzyme tyrosi-
nase while exhibiting the lowest estimated free energy of binding, among all the ligands docked.
Key words tyrosinase inhibitor; oxindole-based chalcone; melanogenesis; molecular docking
Tyrosinase is a major enzyme of melanogenic cascade, ac- firmed the tyrosinase inhibitory potential of chalcones, which
countable for hydroxylation of L-tyrosine to L-3,4-dihydroxy- can be attributed to their antioxidant capability suppressing
phenylalanine (L-DOPA) and subsequent oxidation of L-DOPA the pigmentation resulting from auto-oxidative process.27,28)
to dopaquinone, the significant steps in melanin production.1,2) Furthermore, Okombi et al.29) published the report of benzyl-
Melanogenesis is a major defence mechanism of human skin idenebenzofuran-3(2H)-ones as inhibitors of tyrosinase from
against UV radiations. However, abnormal production and human melanocytes. The lead compound (Z)-4,6-dihydroxy-2-
accumulation of melanin in the skin are a serious aesthetic (4-hydroxybenzylidene)benzofuran-3(2H)-one displayed an
problem, which can cause melasma, freckles, ephelide, and IC50 of 38 2.9µM, emerging as the remarkably potent inhibi-
senile lentigines.3) In the food industry, melanin is responsible tor of tyrosinase when compared with the reference compound
for browning reactions in fruits and vegetables, resulting in kojic acid. The pharmacophoric similarity between the lead
the nutritional as well as market value loss. Therefore, the de- tyrosinase inhibitor (Z)-4,6-dihydroxy-2-(4-hydroxybenzyli-
velopment of tyrosinase inhibitors has gradually become more dene) benzofuran-3(2H)-one and our synthesized compounds
important as skin whitening agents and preservatives in cos- (3–10) has been presented in Fig. 2. Based on these remarks,
metic and food industry, respectively,4,5) and research in this we synthesized oxindole-based chalcones to investigate their
area is continuously growing.6–13) Many tyrosinase inhibitors tyrosinase inhibitory potential for their applications as skin
have already been reported from both synthetic and natural whitening agents in cosmetics and as preservatives in food
sources, for example hydroquinone, kojic acid, arbutin, retinol, industry.
linoleic acid, galangin, and numerous botanical products.14)
However, due to undesirable side effects, many of them are
Results and Discussion
Chemistry The synthesis of oxindole-based chalcones
banned in several countries.15,16)
The indole moiety is considered as a promising scaffold for (3–10) was carried out by Claisen–Schmidt condensation re-
tyrosinase inhibition17) and many indole group bearing com- action of a ketone with various aldehydes. Oxindole (indolin-
pounds, such as N-p-coumaroyl serotonin, N-feruloyl sero- 2-one) (1) was stirred with appropriate aldehydes (2) in the
tonin, and N-caffeoyl serotonin have been described as poten- presence of ethanolic NaOH to yield the title compounds
tial tyrosinase inhibitors.18) Likewise, octapeptide containing (3–10) (Chart 1). All the compounds were synthesized in fairly
indole scaffold has also been reported as a strong inhibitor of good yields (75–94%) and their structures were established by
1
tyrosinase.19) The role of indole moiety and tyrosinase in mela- using UV, IR, H-NMR, and mass spectroscopic techniques.
nogenesis has been depicted in Fig. 1. In the similar vein, α,β- The UV spectra of compounds (3–10) demonstrated two
unsaturated carbonyl compounds, the chalcones are known typical chalcone bands, the band-I at 441.50–347.00nm and
to possess diverse biological activities, e.g. antioxidant,20) band-II at 270.50–239.50nm. The IR spectra of compounds
anticancer,21) anti-inflammatory,22) antidepressive,23) antimicro- (3–10) displayed peaks at 3143.97–3192.19, 1616.35–1699.29,
bial,24) and anti-tyrosinase.25,26) Isoliquiritigenin chalcone as a and 1564.27–1614.42cm−1 distinctive to N–H group and α,β-
potent inhibitor of tyrosinase was reported by Nerya et al.25) unsaturated carbonyl system, i.e. C=O and C=C groups,
1
Recently, we reported (Z)-3-(2,4,6-trihydroxybenzylidene)- respectively. The H-NMR spectra of synthesized compounds
indolinone that suppressed the tyrosinase activity in a double- showed two singlets at 9.0202–11.8558 and 7.2566–8.3317ppm
digit micro-molar range.26) Many other studies have also con- characteristic to NH and=CH (vinylic) protons, respectively.
*To whom correspondence should be addressed. e-mail: alex.joseph@manipal.edu
© 2017 The Pharmaceutical Society of Japan

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Chem. Pharm. Bull.
Vol. 65, No. 9 (2017)
Fig. 1. Role of Indole Moiety and Tyrosinase in Melanogenic Pathway
α-MSH; α-melanocyte-stimulating harmone, MC1R; melanocortin 1 receptor, MITF; microphthalamia-associated transcription factor, ROS; reactive oxygen species,
TRP; tyrosinse-related proteins.
Table 1. Tyrosinase Inhibition Activity of Oxindole-Based Chalcones
(3–10)
IC50 (µM)
Compound
L-Tyrosine
L-DOPA
3
77.07
152.88
256.70
182.46
63.37
85.33
145.17
241.89
180.25
59.71
4
5
6
7
Fig. 2. Pharmacophoric Similarity between the Lead Tyrosinase Inhibi-
tor (Z)-4,6-Dihydroxy-2-(4-hydroxybenzylidene)benzofuran-3(2H)-one of
Aurone Class and Synthesized Oxindole-Based Chalcones
8
223.56
95.98
232.32
99.10
9
10
110.77
22.52
107.26
29.74
Kojic acid
a doublet due to the presence of neighbouring Ar-CH=CH-
1
group. The total number of protons in the H-NMR spectra
of compounds were consistent with their respective protons
of molecular formulas. The high resolution (HR)-MS electro-
spray ionization (ESI)-MS spectra of compounds displayed
molecular ion peaks distinctive to their molecular masses.
Taken together, the structures of synthesized α,β-unsaturated
carbonyl compounds (3–10) were confirmed by the presence
of IR and NMR peaks characteristic to α,β-unsaturation,
along with the presence of molecular ion peaks corresponding
to the molecular masses of the synthesized compounds.
Tyrosinase Inhibition Activity The tyrosinase inhibi-
tory activity of oxindole-based chalcones (3–10) and reference
compound kojic acid was investigated by using L-tyrosine and
L-DOPA as the substrates in monophenolase and diphenolase
activity assays, respectively. The results obtained in these as-
says are shown in Table 1 and Fig. 3.
(a) Ethanolic NaOH; (b) Stir 2h.
Chart 1. Synthesis of New Oxindole-Based Chalcones (3–10)
However, in the 1H-NMR spectrum of 3-phenylallylidene
Among the chalcones evaluated, compound 3 (4-hydroxy
substituted compound 8, =CH proton appeared upfield and as substituted) and 7 (4-hydroxy-3-methoxy substituted) ex-

Vol. 65, No. 9 (2017)
Chem. Pharm. Bull.
835
Fig. 3. IC50 (µM) Plot of Oxindole-Based Chalcones and Reference Compound Kojic Acid for Tyrosinase Inhibition
Results presented are mean S.E.M. of three values.
hibited the most potent tyrosinase inhibitory activity with 5,6-dihydroxyindole, we can accept that these compounds will
IC50s of 77.07 and 63.37µM in monophenolase and 85.33 and act as competitive inhibitors of tyrosinase. Moreover, many
59.71 µM in diphenolase activity assays, respectively. At the previous studies have already reported that chalcones which
same time, the reference compound kojic acid demonstrated bear the structural similarity with tyrosinase substrates act as
50% of tyrosinase inhibition at concentrations of 22.52 and the competitive inhibitors of the enzyme.28,30)
29.74 µM in monophenolase and diphenolase activity assays,
Molecular Docking Analysis Before performing molecu-
correspondingly. It is evident from the results that the hydrox- lar docking studies, all the designed chalcones were assessed
yl group bearing compounds 3 and 7 displayed IC50s much against the Lipinski’s Rule of Five31) and other drug-likeness
comparable to that of the reference compound kojic acid. On parameters. The Lipinski’s Rule of Five states that for a chem-
the other hand, compounds 4 and 6 lacking a hydroxyl group ical compound to be a successful oral drug, it should not vio-
at position-4 of benzylidene moiety, showed moderate to poor late more than one of the following parameters; i) Number of
activity (IC50s of 152.88 and 182.46µM in monophenolase and hydrogen bond donors (sum of OHs and NHs) should be ≤5,
145.17 and 180.25µM in diphenolase activity assays, respec- ii) Number of hydrogen bond acceptors (sum of Os and Ns)
tively). These results indicate the importance of a hydroxyl should be ≤10, iii) Its LogP value should be ≤5, iv) Its mo-
group at position 4 of benzylidene moiety for tyrosinase inhi- lecular weight should be ≤500. The calculation of Lipinski’s
bition. However, a complete loss of activity was observed in Rule of Five along with molar refractivity and polar surface
4-dimethylamino substituted compound 5 (neither hydroxylat- area parameters revealed that none of the designed chalcones
ed nor methoxylated at position 4). Upon comparison between violated these drug-likeness parameters. Moreover, all the
the inhibitory potential of compounds 3 and 7, we found that compounds demonstrated the values well within the proposed
the methoxy group at position 3 of the benzylidene ring in limits of parameters as shown in Table 2.
compound 7 augments the tyrosinase inhibition. In addition,
In order to predict the possible binding interactions that
3-phenylallylidene substituted compound 8 (chalcone prepared might take place between the oxindole-based chalcones and
by reaction of cinnamaldehyde with oxindole) showed the least tyrosinase enzyme, all the designed compounds were docked
activity against tyrosinase; and thus, it may be assumed that into the active site of tyrosinase. These docked compounds
this modification is not useful for the inhibition of tyrosinase. showed estimated free energy of binding in the range of
On the contrary, chalcone prepared from heterocyclic alde- –7.09 to −1.18kcal/mol (Table S1). Among them, 4-hydroxy-
hydes, such as 9 (2-pyridinecarboxaldehyde) and 10 (5-ethyl- 3-methoxybenzylidene moiety bearing compound 7 showed
furfural) exhibited moderate tyrosinase inhibitory potential the lowest estimated free energy of binding, whereas 4-di-
with IC50s of 95.98 and 110.77µM in monophenolase and 99.10 methylaminobenzylidene moiety possessing compound
5
and 107.26µM in diphenolase activity assays, respectively. exhibited the highest estimated free energy of binding. Closer
These results indicated that the replacement of benzylidene analysis of the docked complex formed between compound 7
scaffold with 5 or 6 membered heterocyclic counterparts may and tyrosinase indicated the presence of three strong hydrogen
retain the tyrosinase inhibitory potential of oxindole-based bonds; where, two bondings were of 1.8Å each, while another
chalcones.
one was of 2.2Å (Figs. 4, 5). The hydroxyl oxygen of benzyli-
While discussing the mode of tyrosinase inhibition by dene scaffold was hydrogen bonded with the histidine (His)-60
our lead compound 7 or other chalcones, since our designed (H–O…H–N, 1.8Å), while carbonyl oxygen of oxindole moi-
compounds are based on mimicking the structural part of ety was interacting with the valine (Val)-218 (C=O…H–N,
tyrosinase substrates (Fig. 1); (i) L-tyrosinse, (ii) L-DOPA, and 1.8Å) residue of tyrosinase. Additionally, the hydroxyl oxygen

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Chem. Pharm. Bull.
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Table 2. Calculation of Lipinski’s Rule of Five and Other Descriptors for Synthesized Oxindole-Based Chalcones
No. of H-bond No. of H-bond
Molar refractivity Polar surface area
Lipinski’s &
other violations
Compd.
LogP
Molecular weight
donors
acceptors
(cm3)
(Å2)
3
4
2
1
1
1
2
1
1
1
2
2
2
3
3
1
2
1
2.96
3.11
3.37
2.95
2.80
3.79
2.28
3.05
237.25
251.28
264.32
281.31
267.28
247.29
222.24
239.27
71.71
76.19
84.16
82.66
78.18
80.05
67.13
71.80
49.33
38.33
32.34
47.56
58.56
29.10
41.99
42.24
0
0
0
0
0
0
0
0
5
6
7
8
9
10
No. of H-bond donors ≤5. No. of H-bond acceptors ≤10. LogP ≤5. Molecular weight ≤500. Molar refractivity 30–140cm3. Polar surface area ≤140Å2.
Fig. 4. Molecular Docking of the Lead Compound 7 in the Active Site
of Tyrosinase
Fig. 5. 3D Binding Orientation of the Lead Compound 7 in the Active
The amino acids His-42, His-60, and Val-218 involved in hydrogen bond interac-
tions with the compound 7 are highlighted.
Site of Tyrosinase
of benzylidene also formed a hydrogen bond with the His-42
residue (H–O…H–N, 2.2Å) of the target protein. Apart from
hydrogen bondings, the oxindole scaffold of compound 7
was positioned in the hydrophobic cavity created by Val-217,
Val-218, and proline (Pro)-219 residues of tyrosinase (Fig. 6).
Further analyses of the docked complex indicated hydrophobic
and van der Waals contacts between the benzylidene part of
compound 7 and methionine (Met)-61, phenylalanine (Phe)-65,
leucine (Leu)-66, Phe-197 residues of tyrosinase (Fig. 6).
Taken together, the formation of three strong hydrogen
bonds between compound 7 and tyrosinase (His-42, His-60,
and Val-218 residues were involved) and deep positioning
of oxindole scaffold in the hydrophobic pocket of Val-217,
Val-218, and Pro-219 residues might have played a central
role in the tyrosinase inhibitory activity of the lead compound
7. Furthermore, the lead compound 7 has the highest polar
surface area and second least LogP value among all the com-
pounds synthesized. The compound 7 was further analysed
for absorption, distribution, metabolism, excretion, and toxic-
ity (ADMET) parameters and results of this study have been
summarized in Table 3.
Fig. 6. Molecular Docking of the Lead Compound 7 in the Active Site
of Tyrosinase
The amino acids involved in hydrogen, hydrophobic, and van der Waals interac-
tions and present in the surroundings of compound 7 are highlighted.
Conclusion In the present study, we report for the first inhibitory activity. Among the synthesized chalcones, com-
time, the potential of oxindole-based chalcones as tyrosinase pound 7 was emerged as the most potent tyrosinase inhibitor
inhibitors. The results of this study concluded that the type that possessed a hydroxyl group at position 4 and a methoxy
and position of substitutions on benzylidene moiety are funda- group at position 3 of benzylidene moiety. In conclusion, this
mental for the oxindole-based chalcones to impart tyrosinase work offers an oxindole-based new scaffold for the develop-

Vol. 65, No. 9 (2017)
Chem. Pharm. Bull.
837
Table 3. Prediction of ADMET Profile of the Lead Compound 7
hyde (0.1mol) (2) in an ethanolic solution (80%, 25mL) con-
taining 2% sodium hydroxide were stirred in ice-cold condi-
tions for about 2h (Chart 1). The reaction mixture was kept in
the refrigerator for about 10–12h followed by neutralized with
20% HCl solution with continuous stirring. The solid product
precipitated out was filtered off, washed with ample water, and
dried to yield a final purified product.
Parameter
Compound 7 (Most active)
Absorption
Result
BBB+
Probability
0.7717
1.0000
0.6196
0.5596
0.7554
0.8349
Blood–Brain Barrier
Human Intestinal Absorption
HIA+
Caco-2 Permeability (LogPapp, cm/s)
P-Glycoprotein Substrate
Caco-2+
(Z)-3-(4-Hydroxybenzylidene)indolin-2-one (3) Light-
yellow solid; Yield: 87%; mp: 285–286°C; UV λmax (MeOH)
nm: 351.50, 246.50. IR (KBr) cm−1: 3234.62 (broad, O–H &
N–H stretch), 3022.45, 2819.93 (C–H stretch), 1683.86 (C=O
Substrate
Non-inhibitor
Non-inhibitor
P-Glycoprotein Inhibitor
Renal Organic Cation Transporter
1
Distribution and Metabolism
stretch), 1585.49 (C=C stretch). H-NMR (mixture of CDCl3
CYP450 2C9 Substrate
CYP450 2D6 Substrate
CYP450 3A4 Substrate
CYP450 1A2 Inhibitor
CYP450 2C9 Inhibitor
CYP450 2D6 Inhibitor
CYP450 2C19 Inhibitor
CYP450 3A4 Inhibitor
CYP Inhibitory Promiscuity
Non-substrate
Non-substrate
Substrate
0.7888
0.7348
0.6051
0.9099
0.7704
0.7813
0.7095
0.7457
0.8324
& dimethyl sulfoxide (DMSO)-d6, 400MHz) δ: 10.4766 (s,
1H, NH), 10.0758 (1H, s, OH), 7.5457 (s, 1H, =CH (C-11-H)),
6.8406–7.7174 (8H, Ar-H). HR-MS (ESI) m/z: 238.0860
(M+1)+ (Calcd for C15H11NO2: 237.0784). Anal. Calcd for
C15H11NO2: C, 75.94; H, 4.67; N, 5.90. Found: C, 75.99; H,
4.68; N, 5.87.
Inhibitor
Inhibitor
Non-inhibitor
Non-inhibitor
Inhibitor
(Z)-3-(4-Methoxybenzylidene)indolin-2-one (4) Orange-
red solid; Yield: 93%; mp: 99–100°C; UV λmax (MeOH)
nm: 347.00, 247.00. IR (KBr) cm−1: 3192.19 (N–H stretch),
3072.60, 2962.66, 2837.29 (C–H stretch), 1697.36 (C=O
High
Excretion and Toxicity
AMES Toxicity
Toxic
Non-carcinogens
III
0. 8277
0.9422
0.4339
—
1
stretch), 1606.70 (C=C stretch). H-NMR (CDCl3, 400MHz)
Carcinogens
δ: 9.0202 (s, 1H, NH), 7.2598 (s, 1H, =CH (C-11-H)),
6.8674–7.7537 (8H, Ar-H), 3.8849 (s, 3H, OCH3 (C-19-H)).
HR-MS (ESI) m/z: 252.1027 (M+1)+, 274.0844 (M+Na)+
(Calcd for C16H13NO2: 251.0941). Anal. Calcd for C16H13NO2:
C, 76.48; H, 5.21; N, 5.57. Found: C, 76.54; H, 5.19; N, 5.60.
(Z)-3-(4-(Dimethylamino)benzylidene)indolin-2-one (5)
Acute Oral Toxicity
Rat Acute Toxicity (LD50, mol/kg)
2.6961
Acute Oral Toxicity: Category III includes compounds with LD50 values greater
than 500mg/kg but less than 5000mg/kg. Probability indicates scale between 0 and 1.
ment of effective skin whitening agents. However, further
research is required to optimize the lead and to understand the Orange-red solid; Yield: 82%; mp: 155–157°C; UV λmax
detailed molecular mechanism behind the tyrosinase inhibi- (MeOH) nm: 441.50, 270.50. IR (KBr) cm−1: 3155.54 (N–H
tory activity of these chalcones.
stretch), 3024.38, 2900.94, 2825.72, 2735.06 (C–H stretch),
1666.50 (C=O stretch), 1564.27 (C=C stretch). 1H-NMR
(mixture of CDCl3 & DMSO-d6, 400MHz) δ: 10.3115 (s,
Experimental
Chemistry All the chemicals and reagents were purchased 1H, NH), 7.4850 (s, 1H,=CH (C-11-H)), 6.7063–8.4245 (8H,
from Sigma-Aldrich, Aldrich, Merck, Ranbaxy Fine Chemi- Ar-H), 3.0795 & 3.0719 (singlet each, 6H, N(CH3)2). HR-MS
cals Ltd., Sulabh Laboratories, and Spectrochem, India, and (ESI) m/z: 265.1312 (M+1)+, 287.1133 (M+Na)+ (Calcd for
were used without further purification. Tyrosinase, L-tyrosine, C17H16N2O: 264.1257). Anal. Calcd for C17H16N2O: C, 77.25; H,
L-DOPA, and kojic acid were purchased from Sigma Life Sci- 6.10; N, 10.60; Found: C, 77.21; H, 6.11; N, 10.62.
ence, India. Melting points were recorded on a capillary melt-
(Z)-3-(3,4-Dimethoxybenzylidene)indolin-2-one (6) Or-
ing point apparatus (Shital Scientific Industries, India) and ange-yellow solid; Yield: 91%; mp: 179–180°C; UV λmax
are uncorrected. The UV-visible spectra were obtained with (MeOH) nm: 366.00, 261.50nm. IR (KBr) cm−1: 3167.12 (N–H
a Shimadzu UV-2450 spectrophotometer (Shimadzu, Japan). stretch), 3026.31, 2962.66, 2899.01, 2839.22 (C–H stretch),
The IR spectra were recorded on a Shimadzu FTIR-8310 1695.43 (C=O stretch), 1579.70 (C=C stretch). 1H-NMR
(Shimadzu) using potassium bromide discs. The proton NMR (mixture of CDCl3 & DMSO-d6, 400MHz) δ: 10.4926 (s, 1H,
spectra were recorded on a Bruker AVANCE II 400MHz NH), 7.6571 (s, 1H,=CH (C-11-H)), 6.8177–8.7319 (7H, Ar-H),
spectrophotometer (Bruker, Germany) and chemical shifts are 3.8771 (s, 3H, OCH3), 3.8727 (s, 3H, OCH3). HR-MS (ESI)
reported in parts per million (δ). The proton NMR spectra in m/z: 282.1106 (M+1)+ (Calcd for C17H15NO3: 281.1046). Anal.
the supplementary data file were prepared with Mnova 8.1.1 Calcd for C17H15NO3: C, 72.58; H, 5.37; N, 4.98; Found: C,
program of Mastrelab Research, Spain by processing flame 72.62; H, 5.40; N, 4.97.
ionization detecter (FID) files of earlier mentioned Bruker
(Z)-3-(4-Hydroxy-3-methoxybenzylidene)indolin-2-one
NMR instrument. The mass spectra (ESI-HR-MS) were ob- (7) Light-brown solid; Yield: 90%; mp: 220–221°C; UV
tained with a Bruker, Compact, Qq-TOF LC-MS/MS mass λmax (MeOH) nm: 371.00, 252.50. IR (KBr) cm−1: 3396.64
spectrometer (Bruker, Germany). Elemental analysis was per- (O–H stretch), 3174.83 (N–H stretch), 3072.60, 2835.36
formed on a 2400 CHN analyzer (PerkinElmer, Inc., U.S.A.). (C–H stretch), 1685.79 (C=O stretch), 1587.42 (C=C stretch).
The purity of all the compounds was established by a single 1H-NMR (mixture of CDCl3 & DMSO-d6, 400MHz) δ:
spot on the TLC silica gel 60F254 plates (Merck, Germany). 10.4926 (s, 1H, NH), 9.7266 (1H, s, OH), 7.5506 (s, 1H, =CH
The n-hexane: ethyl acetate (7:3) solvent system was used a (C-11-H)), 6.8597–7.7796 (m, 7H, Ar-H), 3.8290 (s, 3H, OCH3).
mobile phase in TLC.
HR-MS (ESI) m/z: 268.0968 (M+1)+, 290.0796 (M+Na)+
General Procedure for the Synthesis of Compounds (Calcd for C16H13NO3: 267.0890). Anal. Calcd for C16H13NO3:
(3–10) Oxindole (0.1mol, 1.33g) (1) and appropriate alde- C, 71.90; H, 4.90; N, 5.24; Found: C, 71.96; H, 4.89; N, 5.23.

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Chem. Pharm. Bull.
Vol. 65, No. 9 (2017)
(3Z)-3-((E)-3-Phenylallylidene)indolin-2-one
(8) Or- point spacing of 0.375Å. The Lamarckian Genetic Algorithm
ange-yellow solid; Yield: 94%; mp: 168–170°C; UV λmax (LGA) was applied to search conformers with lowest binding
(MeOH) nm: 360.00, 239.50. IR (KBr) cm−1: 3174.83 (N–H energy. Results of molecular docking studies are presented as
stretch), 3066.82, 3028.24, 2899.01, 2837.29 (C–H stretch), estimated free energy of binding in kcal/mol (docking score).
1699.29 (C=O stretch), 1614.42, 1462.04 (C=C stretch). For visualization and analysis of docking results, PyMOL
1H-NMR (mixture of CDCl3 & DMSO-d6, 400MHz) δ: molecular viewer version 1.6 was used. For the prediction of
10.4200 (s, 1H, NH), 7.1097–8.5353 (10H, Ar-H &=CH (C- ADMET parameters, automated online program admetSAR
11-H)), 6.9865–7.0242 (t, 1H, J=7.54Hz, Ar-CHCH (C-12-H)), was used.32)
6.8514–6.8706 (d, 1H, J=7.68Hz, Ar-CHCH (C-13-H)).
HR-MS (ESI) m/z: 248.1063 (M+1)+, 270.0890 (M+Na)+
Acknowledgment The authors are thankful to Mr. Shri
(Calcd for C17H13NO: 247.0992). Anal. Calcd for C17H13NO: C, Manish Ji, NMR department, Sophisticated Analytical In-
82.57; H, 5.30; N, 5.66; Found: C, 82.55; H, 5.28; N, 5.65. strumentation Facility (SAIF), Panjab University, Chandigarh,
(Z)-3-((Pyridin-2-yl)methylene)indolin-2-one (9) Red India for recording NMR spectra of the samples.
solid; Yield: 75%; mp: 192–195°C; UV λmax (MeOH) nm:
358.00, 260.00. IR (KBr) cm−1: 3433.29 (N–H stretch),
Conflict of Interest The authors declare no conflict of
3057.17, 2953.02, 2810.28, 2684.91 (C–H stretch), 1616.35 interest.
1
(C=O stretch), 1583.56 (C=C stretch). H-NMR (mixture of
CDCl3 & DMSO-d6, 400MHz) δ: 11.8558 (s, 1H, NH), 8.3317
Supplementary Materials UV, FT-IR, 1H-NMR, and
(s, 1H,=CH (C-11-H)), 7.0204–9.2271 (8H, Ar-H). HR-MS HR-MS spectra of all the compounds (3–10) are provided as
(ESI) m/z: 223.0843 (M+1)+ (Calcd for C14H10N2O: 222.0788). supplementary material.
Anal. Calcd for C14H10N2O: C, 75.66; H, 4.54; N, 12.60; Found:
C, 75.71; H, 4.55; N, 12.58.
(Z)-3-((5-Ethylfuran-2-yl)methylene)indolin-2-one
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