A comparative study of inclusion complexes of orthosubstituted [arylidenamino]-1,3,4-thiadiazino[6,5b] indole derivatives

Article abstract of DOI:10.1155/2012/156346

Some[Arylidenamino]-1,3,4-thiadiazino[6,5b] indoles have been synthesized starting from indole-2,3-dione, thiosemicarbazide and aromatic aldehydes with activating and deactivating groups. Inclusion complexes of these compounds have been prepared with β-cy

Full text of DOI:10.1155/2012/156346

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
http://www.ejchem.net
2012, 9(3), 1213-1222
A Comparative Study of Inclusion Complexes of
Orthosubstituted [Arylidenamino]-1,3,4-
thiadiazino[6,5b] Indole Derivatives
SUNAKAR PANDA AND JAGAT KRUSHNA TRIPATHY
P.G. Department of Chemistry
Berhampur University, Bhanja Bihar, Odisha
Sunakar_bu@yahoo.co.in
Jagat_luna_tripathy@yahoo.com
Received 09 August 2011; Accepted 04 October 2011
Abstract: Some[Arylidenamino]-1,3,4-thiadiazino[6,5b] indoles have been
synthesized starting from indole-2,3-dione, thiosemicarbazide and aromatic
aldehydes with activating and deactivating groups. Inclusion complexes of
these compounds have been prepared with β-cyclodextrin so as increase the
solubility and bioaccessibility. Thermodynamic properties like change in free
energy , change in enthalpy , change in entropy and stability constant of the
inclusion complexes have been determined to know whether the inclusion
complex formation is thermodynamically allowed or not. The compounds and
their inclusion complexes are also screened againt S.aureus and E.coli.to
know the antibacterial activity change after inclusion complex formation The
antioxidant activities are also studied.
Key Words: Substituted indoles, β-Cyclodextrin, Inclusion complex, antimicrobial activity,antioxidant
activity.
Introduction
Today bacterial resistance to antibiotics is a big challenge for mankind. A number of drugs
is no way helpful for the humanbody which had a wonderful effect for chronic and common
diseases. Indole and its derivatives are very good pharmacophores exhibiting wide spectrum
of pharmacological activities such as antidepressive, anti-inflammatory, anti-fungicidial,
anti-bactericidial and anti-tuberculostatic activities1-4. Azediones and thiazolidinones show
excellent antimicrobial activities5-8. There are also reports that compounds containing indole
or substituted indole coupled with azedinone or thiazolidinone units are acting as drugs for
treating a number of diseases7,8.Since the bio-accessibility of drugs depend upon their
solubility, the poor solubility of these compounds in aqueous medium may be a limiting
factor reducing pharmacological activities.The solubility and bio-accessibility of these
compounds can be enhanced significantly by forming inclusion complex with
cyclodextrins9.Out of all the known cyclodextrins, β-cyclodextrin is usually considered for

1214 Sunakar Panda
inclusion complex formation because it is cheaper, easily available and highly stable
towards heat and oxidation10-12
.
In the present work an attempt has been made to synthesize some 2-[arylidenamino]-
1,3,4-thiadiazino[6,5b]indoles in their purest forms starting from indole-2,3-dione. The aryl
aldehydes considered in the synthesis are of three types containing hydroxyl and chloro
group at ortho position. The inclusion complexes of the compounds have been prepared with
β-cyclodextrin . The formation of compounds and their inclusion complexes have been
ascertained from elemental analysis, melting point data and study of spectral characteristics.
Thermodynamics properties of the inclusion complexes are also studied to know
thermodynamic stability of inclusion complexes and the type of interaction in between the
host and guest.
Experimental
Apparatus and Materials
All the chemicals of acceptable standards were procured from local market. Double distilled
water to be used as solvent was prepared in the laboratory. Electronic spectra were recorded
on Shimadzu UV-1700 Spectrophotometer and IR spectra were recorded in KBr pellets in
Shimadzu 8400 FTIR Spectrophotometer. Melting points were recorded by open capillary
method.
Synthesis of 2-[Arylidenamino]-1, 3, 4-thiadiazino [6,5b] indoles
Three different 2-[arylidenamino]-1, 3, 4-thiadiazino [6,5b] indoles were synthesized
starting from indole -2,3--dione (as per the scheme-I) through the following intermediate
steps8.
i) Synthesis of 3-Thiosemicarbazideindole-2-one : A mixture of 2gm of indole-2, 3-dione
and 1.23gm of thiosemicarbazide in 50 ml of methanol was refluxed for one hour. The
completion of the reaction was checked by TLC. The excess of methanol was distilled out.
The content was cooled and poured into ice cold water. It was filtered, washed with water,
dried and recrystallised from ethanol to obtain 3-Thiosemicarbazideindole-2-one
ii) Synthesis of 2-Amino-1, 3, 4-thiadiazino [6, 5-b] indole: 3gm of
3-Thiosemicarbazideindole-2-one was mixed with small quantity of cold and concentrated
H2SO4. The reaction mixture was left at room temperature for 16 hours. The reaction
mixture was then poured into ice-cold water and neutralized with liquid NH3 to obtain a
solid mass. The solid mass was filtered by using Whatmann-42 filter paper. It was washed
with water, dried and recrystallised from ethanol to yield 2-Amino-1, 3, 4-thiadiazino [6, 5-
b] indole.
a) Synthesis of Benzylidenamino-1, 3, 4-thiadiazino [6,5b] indole (Compound-I): 1.06gm of
Benzaldehyde and 2.02gm of 2-Amino-1, 3, 4-thiadiazino [6, 5-b] indole were taken in 50ml
of methanol. The mixture was refluxed for 6 hours in presence of glacial acetic acid. The
completion of the reaction was checked by TLC and excess of methanol was distilled off.
The refluxed mixture was poured into ice-cold water, filtered , washed with water and dried.
b) Synthesis
of 2-[2-hydroxy benzylidenamino]-1, 3, 4-thiadiazino [6,5b] indole
(Compound-II) 1.22 gm of o-hydroxybenzaldehyde and 2.02gm of 2-Amino-1, 3, 4-
thiadiazino [6, 5-b] indole were taken in 50ml of methanol. The mixture was refluxed for 6
hours in presence of glacial acetic acid. The completion of the reaction was checked by TLC
and excess of methanol was distilled off. The refluxed mixture was poured into ice-cold
water, filtered and washed with water and dried. The dried mass was crystallized from
ethanol.

A comparative study of inclusion complexes of orthosubstituted 1215
Scheme-I
S
O
NH2NHCNH2
+
N
O
H
MeOH
N-NH
O
C-NH2
S
1
N
H
N-N
OH
C-NH2
SH
N
Cold Conc.
H2SO4
N
N
2
N
S
NH2
R
G1
CHO
CH3COOH
R
N
N
N
S
N
CH
R= H, o-OH and o-Cl.

1216 Sunakar Panda
c) Synthesis of 2-[2-chloro benzylidenamino]-1, 3, 4-thiadiazino [6,5b] indole
(Compound-II) :1.465 gm of o-chlorobenzaldehyde and 2.02gm of 2-Amino-1, 3, 4-
thiadiazino [6, 5-b] indole were taken in 50ml of methanol. The mixture was refluxed for 6
hours in presence of glacial acetic acid. The completion of the reaction was checked by TLC
and excess of methanol was distilled off. The refluxed mixture was poured into ice-cold
water, filtered and washed with water and dried. The dried mass was crystallized from
ethanol.
Phase Solubility Measurements:-
The aqueous phase solubility of the compound at various concentration. β -cyclodextrin (0-
10mMl) was studied by Higuchi-Corner method13. Accurately weighed sample of these
compounds was shaken in rotary flash shaker at room temperature in a series of conical flask
for a period of 48 hours till the attainment of equilibrium. The solutions were filtered
through whatmann-42 filter paper and were analyzed in a UV-visible spectrophotometer.
The various values of absorbance at λ-max were plotted against different concentrations of β
–cyclodextrin. The dried mass was recrystallized from ethanol.
Synthesis of inclusion complexes:-
The inclusion complexes of the compounds (I,II and III) with β –cyclodextrin were prepared
as per co-precipitation method14. The solutions of these compounds in required
concentrations were added drop by drop to β –cyclodextrin solution of the required
concentration. The mixtures were stirred for a period of 48 hours and filtered. The filtrate
was cooled for 24 hours in refrigerators. The precipitate obtained was filtered through G-4
crucible, washed with water and dried in air for 24 hours.
Study of thermodynamic properties:-
The thermodynamic stability constant of the complexes was calculated using Benesi-
Hilderband relation15. The stability constant K of each complex was calculated with
increasing temperature. From the slope of the linear plot of lnK vs. 1/T, ΔH was calculated.
Then ΔS was calculated from vant Hoff’s equation
ln K= ΔH/RT- ΔS/R
The value of ΔG was calculated at 298 K using the equation:
ΔG = -RT ln K
Antibacterial study
The antibacterial activity of compounds is studied as per cup-plate methode..The solutions
of the test compounds were prepared in dimethylsulfoxide (DMSO) at 500µg/ml. The
bacterial strains are inoculated into 100ml of the sterile nutrient broth and incubated at 37±1
oC for 24 hours. The density of the bacterial suspension is standardized by McFarland
method. Well of uniform diameter (6mm) are made on agar plates, after inoculating them
separately with the test organisms aseptically. The drug, control and the test compounds are
introduced with the help of micropipette and the plates are placed in the refrigerator at 8-
10oC for proper diffusion of drug into the media. After two hours of cold incubation, the
petriplates are transferred to incubator and maintained at 37±2oC for 18-24 hours.Then the
petriplates are observed for zone of inhibition by using vernier scale. The results are
reported by comparing the zone of inhibition shown by the test compounds with standard

A comparative study of inclusion complexes of orthosubstituted 1217
drug Tetracycline. The results are the mean value of zone of inhibition of three sets
measured in millimeter25.
Evaluation of Antioxidant activity
In the present study DPPH scavenging assay method was used for screening the antioxidant
activity of the synthesized compounds. The antioxidant activity using the DPPH assay was
assessed by the method of Tagashira and Ohtake. Test sample solution was prepared in
100µg/ml concentration in ethanolic DPPH. After vortexing, the mixture was incubated for
10 minutes at room temperature and the absorbance at 517 nm was measured. The difference
in absorbance between a test sample and a control was considered as activity. BHT was used
as reference substance27.
Results and Discussion
The synthesis of Compound-I (Benzylidenamino-1,3,4-thiadiazino[6,5b]indole), Compound-
II : 2-[2- Hydroxy Benzylidenamino]-1,3,4-thiadiazino[6,5b]indole Compound-III : 2-[2--
Chloro Benzylidenamino]-1,3,4-thiadiazino[6,5b]indole have been confirmed from
elemental analysis and IR data as shown in Table-1. The elemental composition matches
with theoretical data IR data of the compound-I show characteristic absorption at
672,1296,1611,1682 and 3141 cm-1 indicating the presence of C-S, C-C ,N-N, C=N and
benzene ring in the compound as expected. IR-data of the compound –II show characteristic
absorptions at 672,1294,1611,1683 and 3142 cm-1 indicating the presence of C-S, C-C,N-N,
C=N and benzene ring in the compound as expected. Similarly, the IR-data of the compound
–III show characteristic absorptions at 674, 1371, 1462, 1595,1674 and 3265 cm-1 indicating
the presence of C-S, C-C ,C-N, N-N, C=N and benzene ring in the compound. IR data of the
complex-I show characteristic absorption at 670,1290,1605,1679 and 3130 cm-1 indicating
the presence of C-S, C-C ,N-N, C=N and benzene ring in the compound as expected. IR-data
of the complex –II show characteristic absorptions at 669,1290,1610,1679 and 3130 cm-1
indicating the presence of C-S, C-C,N-N, C=N and benzene ring in the compound as
expected. Similarly, the IR-data of the complex –III show characteristic absorptions at 672,
1370,, 1460, 1594,1672 and 3262 cm-1 indicating the presence of C-S, C-C ,C-N, N-N, C=N
and benzene ring in the compound.
3
2.5
2
comp-I
1.5
comp-II
comp-III
1
0.5
0
0
0.002 0.004 0.006 0.008
Concentration in mM/L
Figure 1: Phase solubility plot of Compound I, II and III.

1218 Sunakar Panda
Table 1: Analytical data of Compounds with and without inclusion complex.
Compound-I : Benzylidenamino-1,3,4-thiadiazino[6,5b]indole.
Compound-II : 2-[2- Hydroxy Benzylidenamino]-1,3,4-thiadiazino[6,5b]indole.
Compound-III : 2-[2--Chloro Benzylidenamino]-1,3,4-thiadiazino[6,5b]indole.
Compound/ Melting Colour Elemental Analysis
λ
IR( KBr )
cm-1
Complex
Point
(First line indicates finding value & max
Sl.No.
1
second line indicates calculated value (A0)
)
Compound- 224
I
C
66.4
H
N
S
O
3550 672(C-S)
1296(C-C)
1611(N-N)
1682(-
3.45 19.4 1.0
Yellow
66.2
-
3.44 19.3 1.03
C=N)
3141(Ring)
3542 670(C-S)
1290(C-C)
1605(N-N)
1679(C=N)
3130()Ring)
3540 672 (C-S)
1294(C-C)
1611(N-N)
1683(-
2
3
Compound- 228
I- β- CD
-
-
-
-
Pale
Yellow
Compound- 239
II
62.8
3.3
18.4 10.5
5.0
Yellow 62.75 3.27 18.3 10.46 5.23
C=N)
3142(Ring)
3530 669 (C-S)
1290(C-C)
1610(N-N)
1679(-
4
5
Compound- 246
II- β- CD
-
-
-
-
-
Pale
Yellow
C=N)
3130(Ring)
3536 674 (C-S)
1371(C-C)
1462 (C-N)
1595(N-N)
1674(-
Compound- 243
III
59.0
2.61 17.2 9.0
Yellow 59.16 2.77 17.3 9.86
C=N)
3265(Ring)
3528 672 (C-S)
1370(C-C)
1460(C-N)
1594(N-N)
1672(-
6
Compound- 248
III -β- CD
-
-
-
-
-
Yellow
C=N)
3262(Ring)
The synthesis of inclusion complexes of
thiadiazino[6,5b] indole) Compound-II: 2-[2- Hydroxy Benzylidenamino]-1,3,4-
thiadiazino[6,5b] indole Compound-III: 2-[2--Chloro Benzylidenamino]-1,3,4-
compound I (Benzylidenamino-1,3,4-
thiadiazino[6,5b] indole were confirmed from changes in melting point, colour and spectral
characteristics (UV-Vis and IR). The melting point of compound I, II and III are found to be
s 2240C, 2390C and 2430C but their inclusion complexes have melting points 2280C, 2460C
and 2480C(Table-1). The colour of the compound I, II and III are found to be yellow but
their inclusion complexes have colours pale yellow, pale yellow and yellow respectively.

A comparative study of inclusion complexes of orthosubstituted 1219
The absorption maximum of the compounds I, II and III are found at 3550, 3540 and 3536
Ao but their but their inclusion complexes have absorption maximum at 3542, 3530 and 3528
Ao .The higher melting point of inclusion complexes than the compounds is due to the fact
that extra amount of thermal energy is required for the latter to bring it out of β-
cyclodextrin cavity.
1
0.9
0.8
0.7
0.6
0.5
comp-I
comp-II
0.4
comp-III
0.3
0.2
0.1
0
0
500
1000
1500
1/conc in mM-1L
Figure 2: Plot of 1/ O.D. vs. Conc. of Compound I, II and III.
It is quite interesting to note that the absorption maxima undergo a shift towards lower
wavelength after the formation of inclusion complex.(Table-I) .This may be attributed to the
transference of the compound from a more protic environment to a less protic environment
with in the cavity of β- cyclodextrin. This is further supported by IR data The IR stretching
frequencies due to different bonds undergo a downward shift towards low energy and the
peaks become broader, weaker and smoother. Such changes in spectral characteristics due to
inclusion complex formation may be due to the weak interaction like H-bonding,
vanderWaal’s forces, hydrophobic interactions etc. between the guest compound and the
host β- cyclodextrin16-17
.
The phase solubility plots of the compounds in β- cyclodextrin solution are shown in
Figure 1. In all the cases, it is seen that there is a linear increase in solubility of these
compounds with increasing concentration of β- cyclodextrin.Since the slopes of all the plots
are less than unity the stochiometry of these complexes may be 1:118.
The thermodynamic stability constants (KT) of inclusion complexes were determined by
using Benesi-Hilderband relation.
1.2
1
0.8
comp-I
0.6
comp-II
comp-III
0.4
0.2
0
0.0032
0.0033
0.0034
0.0035
1/T in K-1
Figure 3: Plot of ln K vs. 1/T of Compound I, II and III.

1220 Sunakar Panda
12
10
8
Compound
Complex
6
4
2
0
I
II
III
Figure 4A: Antimicrobial susceptibility test of Compound I, II and III against S.aureus.
25
20
15
Compound
Complex
10
5
0
I
II
III
Figure 4B: Antimicrobial susceptibility test of Compound I, II and III against E.coli.
The values of KT for all the complexes were calculated using the relation
KT = Intercept/Slope.
The KT values of the inclusion complexes of compounds I,II and III with β- cyclodextrin
are found to be 420.9,231.3,190.78 M-1 respectively (Table-2) The data obtained are within
100 to 1000 M-1(ideal values) indicating appreciable stabilities for the inclusion
complexes19.
Table 2: Thermodynamic data of inclusion complexes at 298 K.
Compound-I : Benzylidenamino-1,3,4-thiadiazino[6,5b]indole.
Compound-II : 2-[2- Hydroxy Benzylidenamino]-1,3,4-thiadiazino[6,5b]indole.
Compound-III : 2-[2--Chloro Benzylidenamino]-1,3,4-thiadiazino[6,5b]indole.
Complexes
Compound-I- β- CD
K(M-1)
420.9
∆G (kJ/MOLE)
-14.98
∆H (kJ/MOLE)
-12.105
∆S(kJ/MOLE)
0.00965
Compound-II- β- CD
231.3
-13.489
-13.012
-11.429
-11.429
0.0105
.0053
Compound-III- β- CD 190.78

A comparative study of inclusion complexes of orthosubstituted 1221
70
60
50
40
Compound
Complex
30
20
10
0
I
II
III
Figure 5: Anti-Oxidant activity of Compound I, II and III.
The thermodynamic parameters associated with the interaction of the compound with β-
cyclodextrin for 1:1 stochiometry have also been calculated by determining stability
constant (K- values) at different temperatures. The K- values are to found to decrease with
rise in temperature as expected for an exothermic process (deencapsulation)20-21. The plots of
ln K versus inverse absolute temperature produce linear plots Figure 3. From the slopes of
the curves, van’t Hoff’s reaction isotherm and van’tHoff equation, the values of ∆G (change
in free energy), ∆H (change in enthalpy) and ∆S (change in entropy) have been calculated
(Table-2). In Table-2, it is found that ∆G values are negative for all the inclusion complexes.
These data clearly demonstrates that formation of inclusion complexes of compounds I,
II and III with β- cyclodextrin is a spontaneous process. Further it is found that in case of all
three inclusion complexes, ∆H values are negative (Table-2). The negative value of enthalpy
change (∆H) indicates that all the three inclusion complex formation is exothermic and
energy allowed processes. That is, the compounds are getting stabilized within the cavity of
β- cyclodextrin by weak intermolecular forces as suggested earlier22-23 The antibacterial
activities of the compounds and their inclusion complexes against S.aureus and E.coli are
shown in fig. 4A and 4B. Both the compounds and their inclusion complexes are susceptible
to both the bacteria. However, the inclusion complexes increase the antibacterial activity
significantly as compared to their corresponding compounds. This may be attributed to
enhanced solubility of the compounds after the inclusion complex formation which becomes
more available to specific tissues leading to increased antibacterial activity.25-26
The antioxidant activities of the compounds and their inclusion complexes are shown in
Fig. 5. The radical scavenging activities of the compounds increase significantly after the
formation of inclusion complex. This can be correlated to the higher stability of the
compounds due to inclusion complex formation there by increasing the bioaccessibility27.
Conclusion
From the above results and discussion, it is clear that the formation of inclusion complexes
of compound-I, II and III is thermodynamically allowed which can be a very good analytical
tool for enhancing the bioaccessibility of the drugs. The study further reveals that non-
covalent intermolecular forces bind the host β- cyclodextrin and guest molecules. The ∆G,
∆S and ∆H values support the formation of such complexes.

1222 Sunakar Panda
Acknowledgement
The authors thank to Dr. U.L.Narayana, Principal, Indira Gandhi Institute of Pharmaceutical
science; Mr. Sanjay Tiwari and Mr. Dilip Kumar Pattnaik for carrying out the IR study. Also
the authors are thankful to Dr. J R Panda,Department of Pharmaceutical science, Roland
institute of Pharmaceutical Science, Berhampur University for carrying the antimicrobial
activity.
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