Novel substituted hydrazono indolo[2,1-b]quinazoline-6,12-dione analogues as cytostatic agents: Synthesis, crystal structure, biological evaluation and molecular docking studies

Article abstract of DOI:10.1016/j.bmcl.2016.10.006

A series of novel substituted hydrazono indolo[2,1-b]quinazoline-6,12-dione analogues have been synthesized and screened for their in vitro cytotoxic and antimicrobial activities. Among all the target compounds, 3c exhibited the most potent inhibitory act

Full text of DOI:10.1016/j.bmcl.2016.10.006

Accepted Manuscript
Novel substituted hydrazono indolo[2,1-b]quinazoline-6,12-dione analogues as
cytostatic agents: Synthesis, crystal structure, biological evaluation and molec-
ular docking studies
Ramu Guda, Sirassu Narsimha, Ramavath Babu, Srujana Muthadi, Harikiran
Lingabathula, Rambabu Palabindela, Narsimha Reddy Yellu, Girijesh Kumar,
Mamatha Kasula
PII:
S0960-894X(16)31034-4
DOI:
http://dx.doi.org/10.1016/j.bmcl.2016.10.006
BMCL 24309
Reference:
To appear in:
Bioorganic & Medicinal Chemistry Letters
Received Date:
Revised Date:
Accepted Date:
16 June 2016
16 September 2016
5 October 2016
Please cite this article as: Guda, R., Narsimha, S., Babu, R., Muthadi, S., Lingabathula, H., Palabindela, R., Yellu,
N.R., Kumar, G., Kasula, M., Novel substituted hydrazono indolo[2,1-b]quinazoline-6,12-dione analogues as
cytostatic agents: Synthesis, crystal structure, biological evaluation and molecular docking studies, Bioorganic &
Medicinal Chemistry Letters (2016), doi: http://dx.doi.org/10.1016/j.bmcl.2016.10.006
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Novel substituted hydrazono indolo[2,1-b]quinazoline-6,12-dione analogues as
cytostatic agents: Synthesis, crystal structure, biological evaluation and
molecular docking studies
a
a
b
c
Ramu Guda, Sirassu Narsimha, Ramavath Babu, Srujana Muthadi, Harikiran
c
a
c
d
Lingabathula, Rambabu Palabindela, Narsimha Reddy Yellu, Girijesh Kumar, *
a
Mamatha Kasula *
a
Department of Chemistry, Kakatiya University, Warangal, India -506009.
b
School of Chemistry, University of Hyderabad, Hyderabad-500046, India.
c
University College of Pharmaceutical Sciences, Kakatiya University, Warangal, 506009-India.
d
Department of Chemistry, Panjab University, Chandigarh- 160014, India.
*
Corresponding Author
E-mail address: mamathakasula2016@gmail.com (K. Mamatha)
*
Co-Corresponding Author
E-mail address: girijeshchem@gmail.com (Girijesh Kumar)
1

Abstract
A series of novel substituted hydrazono indolo[2,1-b]quinazoline-6,12-dione analogues have
been synthesized and screened for their in vitro cytotoxic and antimicrobial activities. Among all
the target compounds, 3c exhibited the most potent inhibitory activity against three cancer cell
lines MCF-7, A549, HeLa with IC50 values 07.14± 1.285 µM, 09.18± 0.968 µM and 10.57 ±
0
.581 µM respectively, while maintaining low toxicity towards non-cancer originated cell line,
HEK-293. The detailed studies about molecular interactions with probable target protein
indoleamine 2, 3-dioxygenase (IDO1) were done by using docking simulations. The results from
docking models are in consistent with the experimental in vitro cytotoxic activity conclusions i.e
3
c shows the highest binding energy -11.25Kcal/mol. Furthermore, antimicrobial studies
revealed that the compound 3e has shown excellent anti bacterial activity against four tested
strains and the compounds 3b, 3e and 3f have shown good anti fungal activity against two tested
organisms as compared with their standard drugs.
Keywords: tryptanthrin, cytotoxicity, antibacterial activity, antifungal activity, molecular
docking, IDO1.
2

Globally nowadays greater number of population was affected by the cancer. In 2012, 14.2
million new cancer cases and 8.2 million deaths were registered, and up to 2030 it is expected to
1
increase to about 19 million. About 22% of cancer deaths are due to the usage of tobacco, 10%
2
of cancer deaths due to lack of physical activities, junk diet, and devouring of alcohol. Several
times, conventional treatments like radiation and surgical are not suitable because of the
improper location of tumor in the body. In most of the times these methods fail completely to
remove tumors. So, for cell devastation without harming to other parts, chemotherapy is the
systematic method and the best source for cancer treatment. But most of the drugs available in
market for the treatment of cancer (chemotherapy) are having the undesirable side effects. Thus,
it is a great challenge for the people working in the domain of medicinal chemistry to design and
develop such an efficient, safe, suitable and potent anti cancer drug having the greater resistance
without causing any adverse side effects and also which could be able to suppress the high
4
–6
cancer mortality rate in the world is the need of the contemporary research.
On the other hand the most common infectious diseases in human beings are caused by the
pathogens include bacteria and fungi. These infectious agents enter into the body produce a
variety of manifestations and increases at an alarming rate causing deadly diseases. The
treatment of infectious diseases remains as an important issue because of the rapid increase in
7
multi-drug resistant microbial pathogens, encourages as in developing a new class of drugs.
Polygonum tinctorium and Isatis tincoria (Chinese wood) are the natural products of Chinese
medicinal plants, which are the main source for the indolo[2,1-b]quinazolin-6,12-dione
8
9,10
(
tryptanthrin). The literature reveals that tryptanthrin shows anti microbial activity. In 1998,
Mitscher Baker reported that tryptanthrin and its analogues act as anti tubercular agents such as
1
1
12,13
PA-505, PA-510 and exhibits potent anti inflammatory activities.
It also has structural
1
4
similarity with batracyclin, which is a known cytotoxic agent. These structural resemblances of
tryptanthrin leads to develop their analogs as excellent therapeutic agents. Presently, studies on
1
5
anti cancer activity of tryptanthrin are getting more and more popular. Recent studies report
1
6–18
that tryptanthrin induces apoptosis and differentiation of leukemia cells
and inhibits the drug
It also reduces the activity of
cyclooxygenase-2 (COX-2) and reduces the expression of nitric oxide synthase and
1
9,20
resistant related gene in breast and colon cancer cells.
2
1–23
prostogladine (E2) in cells.
Some of the biologically active tryptanthrin analogues were
shown in Fig. 1.
3

O
O
O
N
O
N
O
N
O
N
N
N
N
N
F
8-fluoro tryptanthrin
PA-505
PA-510
(IDO-1 inhibitor)
anti tubercular agent
anti tubercular agent
O
O
N
NH2
N
N
N
N
N
N
Br
O
O
batracylin
8
-bromo tryptanthrin
luotonin
(T. gondi Inhibitor)
anti cancer agent
O
N
O
3
2
N
12
tryptanthrin
Figure 1. Some biologically potent tryptanthrin derivatives.
In the due course, to diagnose the various novel anti cancer agents, we were particularly
interested on the parent molecule tryptanthrin, due to their distinct and wide range of biological
2
4–26
properties.
The targeted compounds 1a-f, 2a-f, 3a-f and 4a were synthesized by well established
methods outlined in scheme 1. The key intermediates were synthesized from condensation of
isatin and isotoic anhydride in toluene in presence of triethylamine as a base. Hydrazine
derivatives of tryptanthrin were synthesized by condensation of intermediate A with hydrazine in
2
7
THF solvent for 12 h by using reported synthetic protocol. The titled compounds were
synthesized by refluxing intermediate B with 1,3–diketones in acetic acid for 6–8 h with good
1
13
yields. The newly synthesized compounds were characterized by H and C NMR, IR, Mass
spectrometry, elemental analysis and single crystal X-ray analysis (Fig. S1–S27, Supporting
Information (SI) and Fig.2). The IR spectrum of the targeted compound 3c showed the
-1
-1
-1
prominent absorption bands at 3648 cm (enolic-OH), 1678 cm (C=O), 1544 cm (C=N) and
-1
1
480 cm (C=C). The synthesized molecules may exists in two forms i.e. keto (in crystalline
state) and enol (in solution state) due to the probability of the shifting of enolic-OH hydrogen
1
atom towards the adjacent nitrogen (Scheme 1). The H NMR spectra of compounds 1a-f, 2a-f,
3
a-f and 4a, shows singlet at the region δ 15.89–13.24 ppm, which corresponds to the presence
of enolic-OH; however, we did not observed any signals related to N–H proton. The appearance
4

of methine proton of 1,3-diketone at the region 6.25 ppm to 5.72 ppm are evidence for the
predominance of enol form over the keto form in solution state. However, signal at 197.6 ppm
1
3
and 159.8 ppm in C NMR, shows presence of enolic carbon and carbonyl group of quinazoline
ring and further strengthens the above mentioned statement. The LCMS of 3c showed [M+1] ion
peak at m/z 437, whereas, elemental analysis data suggested the purity of the bulk sample of 3c.
NH2
O
N
O
O
R1
N
N
(b)
O
(a)
O
N
N
R1
R1
N
H
N
H
O
R2
R2
O
O
R2
A
B
O
O
R3
R4
(c)
R4
4
R4
R
R3
R3
R3
O
CDCl3
or
O
N
O
N
H
H
N
N
H
N
N
N
DMSO-d6
N
N
N
N
R1
R1
N
Proton Shift
R1
O
O
R2
R2
O
R2
In Solution state
In solid state
1
a-f, 2a-f, 3a-f, 4a
1
2
3
R4 = H
d : R3 , R4
e : R3 , R4
O
f : R3 , R4
O O
1
2
3
4
: R = H,
R = H
a : R = H,
1
2
3
4
O
O
: R = -OCH3 R = H
,
b : R = CH R = -OC H
3,
2
5
1
2
3
4
: R = Br,
R = H
c : R = H,
R = Ph
H C CH3
3
O
1
2
: R = CH , R = CH3
3
Scheme 1. Synthesis of titled compounds 1a-f, 2a-f, 3a-f, 4a. (a) Et
NH .H O, 12 h, THF, reflux. (c) Acetic acid, reflux, 1,3-diketones (acetyl acetone, ethyl acetoacetate,
benzoyl acetone, dimedone, indanedione,1,3-cyclohexanedione).
3
N, 2-4 h, toluene, reflux. (b) NH -
2
2
2
5

The single crystal X-ray data confirms that the keto form predominates over enol form in the
solid state with good R-factor 0.0476 and 0.0527 for 1a and 3c, respectively (Fig. 2 and Table
S1, SI). In both, 1a and 3c the bond lengths of C17–O2 are found to be 1.236 Å and 1.243 Å,
respectively (Table S2, SI), which are in between the standard bond lengths of C=O (1.21 Å)
and C–O (1.43 Å). Similarly, the bond lengths of N14–C15 are found to be 1.375 Å and 1.370 Å
for the compounds 1a and 3c, respectively (Table S2, SI), which is in between the standard bond
lengths of C–N (1.47 Å) and C=N (1.25 Å). A deep observation concludes that delocalization of
π–electrons and proton shifting takes place in between N and O atom as shown in the Scheme 1.
Crystallographic data and structure refinement parameters are presented in Table S1. Both
compounds 1a and 3c crystallize in monoclinic crystal system with the space group P2
1
/n (for
1
a) and P2 /c (for 3c). The labeled ORTEP diagram (30% probability level) of 1a and 3c are
1
depicted in Fig. 2. The selected bond distances of compounds 1a and 3c are listed in Table S2.
Compound 1a contains inter molecular interactions (C–H···O, C–H···π and C···N). Compound
3
c also includes the similar types of inter molecular interactions(C–H···O, C–H···π and C···N)
and forms a one dimensional infinite chain, which is finally transformed into a 2D hydrogen
bonded structure having the hexagonal channels. However, for clarity we have shown only C–
H···π interactions (Fig. S28 and S29; SI). The CCDC numbers for the compounds 1a and 3c is
1
474666 and 1474667, respectively.
(
a)
(
b)
Figure 2. (a) ORTEP diagram of compound 1a. (b) ORTEP diagram of compound 3c. In both case the thermal
ellipsoids are drawn at 30% probability level; ring hydrogen atoms have been omitted for clarity.
6

In vitro cytotoxic bioassay: The newly synthesized tryptanthrin derivatives were evaluated
for their in vitro cytotoxic activities against three human cancer cell lines, according to the
2
8,29
procedures described in literature.
The tumor cell line panel consists of MCF-7, A549 and
HeLa cell lines. Cisplatin was used as the reference drug. The relationship between surviving
fraction and drug concentration was plotted to obtain the survival curves of MCF-7, A549 and
HeLa (Fig. 3a, b, c). The response parameter calculated was the IC50 value, which corresponds
to the concentration required for 50% inhibition of cell viability (Table 1). The structure of most
potent tryptanthrin derivative is shown in Fig. 4.
(
a) Anticancer activity(MCF-7)
(b) Anticancer activity(A549)
(c) Anti cancer activity (HeLa)
Figure 3. (a), (b), (c) Survival curves of MCF-7, A549, HeLa cell lines.
7

As shown in Table 1, some of the tryptanthrin derivatives exhibited excellent activity against the
three tumor cells. Remaining compounds showed moderate to good anti cancer activity.
Aromatic and aliphatic units
H C
3
for liphophilic control
N
O
N
H
N
Bromo substituent enhances
anticancer activity
Br
N
Tryptanthrin backbone as a
potent Molecule
O
Figure 4. Structure of most potent tryptanthrin analogue 3c.
Among all the compounds derived from tryptanthrin, 3c (Fig. 3) has exhibited excellent
activity against three cancer cell lines MCF-7, A549, HeLa with IC50 values 07.14± 1.285µM,
0
9.18± 0.968µM and 10.57 ± 0.581µM compared with the standard drug cisplatin. The
compounds, 3e has shown good activity against MCF-7, HeLa with IC50 values 15.88 ± 0.889
µM, 17.02 ± 1.201µM and 1c shown against A549 cell line with IC50 value 17.59 ± 0.686 µM.
Remaining compounds have exhibited promising activity with IC50 values ranging from 22.13 ±
1
.028 to 68.75 ± 0.498 µM against MCF-7, A549 and HeLa cancer cell lines. We also screened
for their cytotoxicity of active compounds against HEK-293 (Human Embryonic Kidney 293)
using MTT-micro cultured tetrazolium assay, IC50 values of 1c, 3c, 3e were 68.09±1.654µM,
4
6.10±1.453µM and 55.21±1.711µM. The results are presented in Table 1.
A deep observation into the structure activity relationship demonstrates that, the cytotoxic
proficiency was highly dependent on the type and position of the pharmacophoric substituent on
the indole and quinazoline ring of tryptanthrin. Various substituents at C2, C8 position of indole
2
5
and quinazolone rings in tryptanthrin change the cytotoxic activity against different cell lines.
However, in particular the substituents like electron donating or electron withdrawing groups
replace the hydrogen atom at C8 position of indole shows completely dissimilar results. Electron
withdrawing group Br at C8 position enhances the cytotoxic activity appreciably and electron
donating groups -CH
3
, -OCH groups reduces the cytotoxic activity against three cancer cell lines
3
MCF-7, A549 and HeLa compared with non substituted tryptanthrin derivatives.
8

Table 1. Cytotoxic activities of newly synthesized tryptanthrin derivatives on human cancer cell
a
lines MCF-7, A549 and HeLa [in vitro (IC50 µM)] .
HEK293
ND
S.No. Compound
MCF-7
A549
HeLa
1
1
2
3
4
5
6
7
8
9
B
B
B
25.24 ± 0.791 28.74 ± 0.142
32.29 ± 1.314 31.20 ± 0.219
23.18 ± 0.339 23.09 ± 1.688
42.08 ± 1.025 43.85 ± 0.393
25.59 ± 0.537
29.22 ± 1.025
22.13 ± 1.028
44.76 ± 0.031
42.86 ± 1.796
25.22 ± 1.686
59.29 ± 0.545
49.40 ± 0.573
23.89 ± 0.743
49.15 ± 0.851
58.23 ± 1.091
33.66 ± 1.389
56.93 ± 0.726
62.29 ± 0.779
32.10 ± 0.445
31.25 ± 1.567
36.68 ± 0.630
10.57 ± 0.581
39.81 ± 0.845
17.02 ± 1.201
35.81 ± 0.504
42.02 ± 1.267
3.88± 0.354
2
3
ND
ND
ND
1a
1b
ND
50.65 ± 0.977
26.22 ± 0.556 17.59 ± 0.686
68.75 ± 0.498 66.17 ± 1.283
51.05 ± 1.507
6
8.09±1.654
1c
ND
1d
ND
1e
50.29 ± 1.545 56.36 ± 1.726
27.92 ± 1.125 29.84 ± 1.251
47.93 ± 0.750 46.67 ± 1.368
54.53 ± 1.307 56.22 ± 0.280
31.08 ± 1.024 29.33 ± 1.178
68.69 ± 1.230 67.83 ± 0.388
60.87 ± 0.431 63.49 ± 0.532
32.68 ± 1.104 35.99 ± 0.700
33.00 ± 0.562 31.11 ± 0.975
36.56 ± 0.712 40.04 ± 0.573
ND
1f
ND
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
2a
ND
1
1
1
1
1
1
1
1
1
2
2
2
2
2b
ND
2c
ND
2d
ND
2e
ND
2f
ND
3a
ND
3b
4
6.10±1.453
ND
3c
07.14± 1.285
40.02 ± 0.980 46.33 ± 1.466
15.88 ± 0.889 20.36± 0.832
09.18± 0.968
3d
5
5.21±1.711
ND
3e
3f
43.87 ± 0.712 41.67 ± 1.412
44.54 ± 1.193 46.56 ± 1.321
ND
4a
ND
Cisplatin
4.28± 0.355
5.14± 0.421
a
Values are expressed as mean ± SEM. Cytotoxicity as IC50 for each cell line, is the concentration of compound
which is reduced by 50% the optical density of treated cell with respect to untreated cell using the MTT assay.
Anti bacterial activity: All the synthesized compounds were screened for their in vitro anti
bacterial activity against two gram-positive bacteria such as Staphylococcus aureus and Bacillus
subtilis and two gram-negative bacteria such as Klebsiella pneumoniae and Escherichia coli
3
0
using broth dilution method. The standard pathogenic microbial cultures were procured from
the Microbial Type Culture Collection (MTCC), Chandigarh, India. Minimum inhibitory
concentration (MIC) values for the tested compounds, as well as standards were measured in
9

µg/mL. The results of in vitro anti bacterial screening reveals that, most of the compounds
exhibit equipotent activity. The compound 3e exhibited excellent anti bacterial activity against
four tested strains S. aureus (1.562µg/mL), B. subtilis (1.562µg/mL), K. pneumonia (3.125
µg/mL) and E. coli (3.125 µg/mL) subtilis with respect to the standard drug streptomycin.
Similarly the compounds 2e, 3b exhibited good activity against S. aureus (1.562 µg/mL), B.
subtilis (3.125µg/mL) and E. coli (6.25µg/mL). The compound 1e also has shown good to
moderate activity against S. aureus (3.125µg/mL), B. subtilis (6.25µg/mL), K. pneumonia (1.562
µg/mL) and E. coli (12.5 µg/mL). The Compounds 1f, 2f and 3f have shown good activity
against S. aureus, B. subtilis. The enhanced activity of 3e against all the strains may be due to the
presence of indane ring. The minimum inhibitory concentrations (MIC) of the compounds are
presented in Table 2.
Table 2. Anti bacterial activity of newly synthesized tryptanthrin derivatives (MIC).
MIC (µg/mL)
Compound
1
S. Aureus
50
B. Subtilis
>100
>100
50
K.pneumoniae
50
E. Coli
>100
>100
>100
50
B
2
B
>100
>100
25
>100
25
12.5
3
B
1
a
25
1
1
1
b
c
d
6.25
>100
50
6.25
>100
50
12.5
>100
12.5
12.5
>100
50
1
1
2
e
f
a
3.125
6.25
12.5
6.25
>100
>100
1.562
3.125
50
6.25
3.125
50
6.25
>100
>100
3.125
6.25
50
1.562
12.5
50
3.125
>100
>100
12.5
12.5
6.25
50
12.5
>100
>100
6.25
12.5
50
2
b
2
c
2
d
2
2
3
e
f
a
6.25
>100
3
3
3
3
b
c
d
e
f
a
1.562
>100
>100
1.562
6.25
12.5
6.25
3.125
>100
>100
1.562
3.125
12.5
3.125
12.5
6.25
>100
>100
3.125
12.5
25
>100
>100
3.125
6.25
6.25
1.562
3
4
Streptomycin
6.25
10

Anti fungal activity: All the synthesized compounds were investigated for their in vitro anti
fungal activity against the fungal strains Aspergillus niger and Pencillium notatum comparing
with standard drug Ketoconazole with minimum inhibitory concentration (MIC) values. The
results of the in vitro anti fungal activity in MIC of tested compounds (Table 3) revealed that the
compounds 3b, 3e and 3f exhibited excellent anti fungal activity against Aspergillus niger and
Pencillium notatum with values for 3b (6.25 µg/mL, 3.125 µg/mL), for 3e (3.125 µg/mL, 6.25
µg/mL) and for 3f (3.125 µg/mL, 6.25 µg/mL). Compounds 1b, 1e and 1f exhibited moderate to
good activity against Aspergillus niger strains with values 12.5 µg/mL, 6.5 µg/mL, and 12.5
µg/mL. Furthermore, compound 2f registered moderate activity against Pencillium notatum
organism with 12.5 µg/mL. Remaining compounds are moderate to poor in anti fungal activity
against the tested fungal strains.
Table 3. Anti fungal activity of newly synthesized tryptanthrin derivatives (MIC).
Minimum Inhibitory Concentration MIC (µg/mL)
Compound
1
Asperegillus niger Pencillium notatum
B
50
>100
50
>100
50
50
2
B
3
B
1
a
>100
12.5
25
>100
25
25
1
b
1
c
1
1
1
2
d
e
f
a
100
6.25
12.5
>100
50
100
12.5
25
100
50
2
b
2
c
25
50
2
2
d
e
100
50
>100
50
2
f
100
>100
6.25
25
12.5
>100
3.125
25
3
a
3
b
3
c
3
3
3
d
e
f
a
100
3.125
6.25
100
3.125
>100
6.25
6.25
100
3.125
4
Ketoconazole
Standard = Ketoconazole ; Strains: Asperegillus niger, pencillium notatum
11

Molecular docking studies: To illustrate the interaction mechanism of most active tryptanthrin
derivatives with enzyme and to correlate with its docking score with the experimental cytotoxic
activity results, we have chosen a computer aided experimental method that is molecular
docking. The 2D structures of synthesized target compounds were drawn in Chem Draw Ultra
3
1
1
2.0 and structures have been fully optimized with small hf/3-21g*
basic set by using
3
2
Guassian 09.
Table 4. Binding energies of tryptanthrin inhibitors against IDO1 receptor.
S.No
Compound
1
Binding Energy ( K cal/mol )
1
2
3
4
5
6
7
8
9
B
-8.57
-8.88
-8.27
-9.60
-9.70
2
B
3
B
1a
1b
1c
1d
1e
1f
2a
2b
2c
2d
2e
2f
3a
3b
3c
3d
3e
3f
-10.99
-10.64
-10.71
-10.18
-10.30
-9.22
-10.91
-10.81
-11.03
-10.56
-10.02
-9.78
-11.25
-10.77
-11.04
-10.13
-9.17
1
1
1
1
1
1
1
1
1
1
2
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
4a
The crystallographic 3D structure of IDO1 enzyme was extracted from RSC PDB (an
information portal to biological macromolecular structure) PDB ID: 2d0U. It is an attractive
target in the cancer disease and it catalyzes essential amino acid L-tryptophan to N-
3
3
formylkynurenine. Indoleamine 2,3-dioxygenase is the first and rate-limiting enzyme
of tryptophan catabolism through kynurenine pathway, thus causing depletion of tryptophan
3
4
which can cause halted growth of microbes as well as T cells. Protein structure was cleaned by
12

removing water molecules, ligands using UCSF chimera 1.10.1 software. Such energy
minimized compounds and receptors are used for docking.
The inhibitors 1c, 2e, 3c and 3e bind strongly to receptor as inferred by their minimum
binding energies -10.99, -11.03, -11.25 and -11.04 K cal/mol respectively. The docking results
were in good coincidence with experimental IC50 values (Table 4). The Fig. 5, shows the best
conformations of 1c, 3c and 3e forming a cluster into the binding pocket of receptor. Molecular
docking results reveal that in IDO1 enzyme complex, all the interactions of 1c are hydrophobic
interactions with amino acids and there were no hydrogen bonding interactions. In Ic, the phenyl
ring of 1,3-diketone interacts with amino acid Phen270 through π- π stacking, in tryptanthrin
skeleton indole-6-membered aromatic ring with amino acids Phen214, Ile217, Val166, Val170
and indole 5-membered ring with amino acids Phe163, Phe214 through π–π stacking.
Quinazoline 6-membered ring in tryptanthrin interacts with amino acids Ala264, Phen163,
Phen214, Ile349 and aromatic ring with amino acid Val350 through hydrophobic interactions.
(
a)
(b)
(c)
Figures 5. (a), (b), (c) shows the binding poses and interactions of tryptanthrin analogues 1c, 3c and 3e to the
binding sites of IDO1 enzyme.
3c has only one hydrogen bonding interaction with His346 by N-atom, hydrophobic interactions
with the phenyl ring of di-ketone with amino acids Phen163, Ile217 and Ile349 through π–π
stacking. Indole-6-membered ring with amino acids Phe270, Ala264 and indole 5-membered
aromatic ring with Ala264, His346 interacts through π–π stacking. Quinazolone 6-membered
13

ring in tryptanthrin with amino acids Ala264, Phen214 and aromatic ring with amino acids
Phen214, Val166 and Val170 through hydrophobic interactions. Compound 3e has two hydrogen
bonding interactions with His346 by N-atom, and another by keto group of indane ring with
Ser263 amino acid. The remaining all are hydrophobic interactions through π–π stacking. Indole
6
-membered aromatic ring with amino acids Phen214, Ala264, Val170 and indole 5-membered
ring with amino acids Phen214, Ala263 through π–π stacking interaction. Quinazolone 6-
membered ring in tryptanthrin with following amino acids Phen163, phen214 and aromatic ring
with amino acids Phen163, Ile217 and Ile349 through hydrophobic interactions.
In summary, we have synthesized novel 1,3-diketone substituted hydrazono tryptanthrin
derivatives. These compounds were evaluated for their in vitro anti cancer activity against three
cancer cell lines MCF-7, A549 and HeLa. The molecular docking studies of these inhibitors
against target IDO 1gave the highest binding energies -11.25kcal/mol,-11.04 kcal/mol for 3c and
3
e. The binding energies and H-bonding interactions to the amino acids of active sites of the
target enzyme well supported the experimental in vitro cytotoxicity (IC50) results. Furthermore,
e has exhibited the excellent anti bacterial activity against two gram-positive bacteria such as
3
Staphylococcus aureus and Bacillus subtilis, two gram-negative bacteria such as Escherichia coli
and Klebsiella pneumonia. The compounds 3b, 3e and 3f have shown most promising anti fungal
activity against Pencillium notatum and Aspergillus niger strains. These encouraging results are
useful in designing and developing new drugs from these derivatives.
Acknowledgements
The Authors are grateful to Prof. Samar K. Das and UGC-Networking Resource Center of
the School of Chemistry, University of Hyderabad, for providing the lab space and
instrumentation facilities. Useful suggestions and specific comments by the anonymous referees
at the revision stage are gratefully acknowledged. The financial assistance from the University
Grant Commission (UGC), New Delhi, is also thankfully acknowledged.
Supporting information
Supplementary data associated with this article can be found, in the online version, at
http://dx.doi.org...............
14

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16

Graphical Abstract
Novel substituted hydrazono indolo[2,1-b]quinazoline-
,12-dione analogues as cytostatic agents: Synthesis,
Leave this area blank for abstract info.
6
crystal structure, biological evaluation and molecular
docking studies
a
a
b
c
c
Ramu Guda, Sirassu Narsimha, Ramavath Babu, Srujana Muthadi, Harikiran Lingabathula,
Rambabu
a
c
d
a
Palabindela, Narsimha Reddy Yellu, Girijesh Kumar, * Mamatha Kasula *
New tryptanthrin derivatives have shown moderate to excellent anti cancer activity against three
human cancer cell lines MCF-7, A549 and HeLa.
17

Research Highlights
•
•
Keto form predominates in the solid state of hydrazono-tryptanthrin analogues.
Compound with highest binding energy -11.25Kcal/mol shown excellent
cytotoxicity.
•
Anti-bacterial activity for indane substituted hydrazono-tryptanthrin was
outstanding.
•
•
Three 8-bromotryptanthrin analogues shown promising anti-fungal activity.
IDO1 protein: a potential target for tryptanthrin analogues.
18