Microwave induced dry-media synthesis of spiro[indole-thiazolidinones/ thiazinones] as potential antifungal and antitubercular agents and study of their reactions

Article abstract of DOI:10.1080/10426500490422209

A series of new spiro[3H-indole-3,2′-thiazolidine]-2,4′(1H.)- diones (IV) and spiro[3H-indole-3,2′-tetrahydro-1,3-thiazine]-2, 4′(1H)-diones (V) have been synthesized in 85-93% yield by the one-pot environmentally benign microwave induced technique involving the cyclocondensation of 3-arylimino-2H-indol-2-ones (III) with thioacids viz. mercapto aceticacid (a) / 3-mercapto propionicacid (b) using montmorillonite KSF as inorganic solid support. Intermediates (III) were synthesized in situ by the reaction of indole-2,3-diones (I) and substituted anilines (II). The spiro compounds have been further subjected to solvent-free acetylation, aminoalkylation and thiation under microwave irradiation using solid supports. The synthesized compounds have been screened in vitro for antifungal activity against Rhizoctonia solani, Fusarium oxysporum, and Collectotrichum capsici, and antitubercular acivity against Mycobacterium tuberculosis.

Full text of DOI:10.1080/10426500490422209

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Phosphorus, Sulfur, and Silicon and the Related
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MICROWAVE INDUCED DRY-MEDIA SYNTHESIS OF
SPIRO[INDOLE-THIAZOLIDINONES/ THIAZINONES]
AS POTENTIAL ANTIFUNGAL AND ANTITUBERCULAR
AGENTS AND STUDY OF THEIR REACTIONS
Anshu Dandia a , Ruby Singh a & Kapil Arya a
a University of Rajasthan, Jaipur, India
Version of record first published: 12 Aug 2010
To cite this article: Anshu Dandia, Ruby Singh & Kapil Arya (2004): MICROWAVE INDUCED DRY-MEDIA SYNTHESIS OF
SPIRO[INDOLE-THIAZOLIDINONES/ THIAZINONES] AS POTENTIAL ANTIFUNGAL AND ANTITUBERCULAR AGENTS AND STUDY OF
THEIR REACTIONS, Phosphorus, Sulfur, and Silicon and the Related Elements, 179:3, 551-564
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Phosphorus, Sulfur, and Silicon, 179:551–564, 2004
ꢀC
Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500490422209
MICROWAVE INDUCED DRY-MEDIA SYNTHESIS
OF SPIRO[INDOLE-THIAZOLIDINONES/
THIAZINONES] AS POTENTIAL ANTIFUNGAL
AND ANTITUBERCULAR AGENTS AND STUDY
OF THEIR REACTIONS
Anshu Dandia, Ruby Singh, and Kapil Arya
University of Rajasthan, Jaipur, India
(Received December 2, 2002; accepted September 17, 2003)
A series of new spiro[3H-indole-3,2ꢁ-thiazolidine]-2,4ꢁ(1H)-diones (IV)
and spiro[3H-indole-3,2ꢁ-tetrahydro-1,3-thiazine]-2,4ꢁ(1H)-diones (V)
have been synthesized in 85–93% yield by the one-pot environmentally
benign microwave induced technique involving the cyclocondensation
of 3-arylimino-2H-indol-2-ones (III) with thioacids viz. mercapto aceti-
cacid (a)/3-mercapto propionicacid (b) using montmorillonite KSF as
inorganic solid support. Intermediates (III) were synthesized in situ by
the reaction of indole-2,3-diones (I) and substituted anilines (II). The
spiro compounds have been further subjected to solvent-free acetyla-
tion, aminoalkylation and thiation under microwave irradiation using
solid supports. The synthesized compounds have been screened in vitro
for antifungal activity against Rhizoctonia solani, Fusarium oxyspo-
rum, and Collectotrichum capsici, and antitubercular acivity against
Mycobacterium tuberculosis.
Keywords: Dry media; microwave irradiation; montmorillonite KSF;
spiro-indoles; thiazinone; thiazolidinone
Microwave heating has already gained importance in synthetic organic
chemistry in a short span of only a decade.1–3 However, the use of
solvents in microwave ovens gives rise to elevated temperatures and
consequently high pressures. These problems have been overcome to
a large extent by carrying out the reactions in dry conditions using
Financial assistance from UGC, New Delhi is gratefully acknowledged. R.S. thanks
CSIR, New Delhi for the award of SRF. We are also thankful to Tuberculosis Antimi-
crobial Acquisition and Coordinating Facility (TAACF), USA for antitubercular activity
and Department of Pathology, Durgapura, Jaipur for antifungal screening. We also are
grateful to the Director, RSIC, CDRI, Lucknow, India for providing mass spectra and
elemental analyses.
Address correspondence to Anshu Dandia, Department of Chemistry, University
of Rajasthan, Jaipur, 302004, India. E-mail: dranshudandia@eth.net
551

552
A. Dandia et al.
SCHEME 1
solid supports. Microwave enhanced chemical reactions on inorganic
solid supports under solvent-free conditions have attracted attention
recently.4−6 The advantages of this method are enhanced reaction rates,
less or no formation of side products, higher yields of pure products, and
reactions can be carried on a preparative scale in open vessels.

Spiro[Indole-Thiazolidinones/Thiazinones]
553
Thiazolidin-4-ones have exhibited a long history of biological
activity.7,8 The presence of N C S linkage is believed to account for
the fungicidal, antibacterial and antiviral activities.9–11 They also are
known to possess amoebicidal and anticonvulsant activities.
The recent literature survey reveals a wide range of pharmacological
properties associated with spiro[indole-thiazolidine]-diones.12–13 The
significance of these compounds can be judged from the fact that most of
the references of spiro-indoles in the literature are patents. Spiro[3H-
indole-3,2ꢁ-tetrahydro-1,3-thiazines]-2(1H)-ones also are reported to
possess anti-inflammatory, analgesic and anticonvulsant activities.14
The spiro[indole-thiazolidinone] system has been synthesized earlier
conventionally by a two-step procedure in 40–60% yield using isatin-3-
imines as key intermediate, which were synthesized from substituted
isatins and aromatic amines. The classical methods involving either
the azeotropic removal of water15 or reaction in presence of dehydrating
agent16 and use of large amount of volatile and toxic solvents at elevated
temperature for several hours heating were of some utility. Further, the
products are generally purified by crystallization or column chromatog-
raphy with further need of solvent. Spiro[indole-thiazinones] also have
been synthesized thermally in two steps by the azeotropic removal of
water.17
Keeping in view the various biological activities associated with spiro
indolines and in continuation of our ongoing program to develop benign
and expeditious methods for organic transformation under solvent-
free conditions using microwave irradiation and the interest in “green
chemistry” theme with growing emphasis on pollution prevention,18
we report here in one-pot environmentally desirable dry media syn-
thesis of a series of new spiro[indole-thiazolidinones] and spiro-
[indole-thiazinones] under microwave irradiation, where in not only the
reaction time has been brought down from hours to minutes in compar-
ison to conventional heating but also with improved yield. Crystalline
products in reasonable purity (TLC) were isolated with no need of fur-
ther purification.
RESULTS AND DISCUSSION
The cyclocondensation of III with thioacids (a/b) yielding exclusively
spiro compounds (IV/V) was studied using different types of inorganic
solid supports, e.g., montmorillonite KSF, alumina (acidic, basic, neu-
tral), and silica gel. Since, montmorillonite KSF efficiently catalyzed
the reaction, giving maximum yield (85–93%) with shortest period (6–
7 min) and easier work up, all compounds listed in Table I have been

554

555

556

Spiro[Indole-Thiazolidinones/Thiazinones]
557
synthesized in one pot using montmorillonite KSF as inorganic solid
support. Intermediate (III) were synthesized in situ by the reaction
indole-2,3-diones (I) with substituted anilines (II). One hundred per-
cent conversion was observed on TLC which also showed a formation
of single product.
The structure of the both spiro systems IV/V were assigned on the
basis of their elemental analyses, 1H NMR, 13C NMR and mass spectral
data (see Table I).
Finally, to check the possible intervention of specific (non-thermal)
microwave effects on reactivity, the reactions (in case of compounds IVa,
IVb, and Va, Table II) have been carried out using preheated oil-both
at the same time and at the same final temperature (134–138◦C) as
measured at the end of exposure during the microwave experiment.
It has been found that only traces of products (8–10%) were detected
on TLC. Lower yields were obtained under conventional heating, even
after one hour, indicating that effect of microwave irradiation is not
purely thermal.19
The noticeable rate enhancement due to a specific microwave effect is
consistent with the reaction mechanism,20 if we admit that the kinetic
rate determining step consists the nucleophilic attack of thiol group
on carbon-nitrogen double bond of imines (III). As the transition state
is more polar than the ground state due to development of a dipole, a
greater stabilization results with microwave as dipole-dipole interac-
tions are increased and favoured.
TABLE II Comparative Results for the Synthesis of Spiro
Compounds Using Microwave Activation (A) and Conventional
Heating (B) Indicating Existence of Specific Microwave Effect
Compd
no.
Reaction
time (min)
Final∗ temp
(◦C)
Isolated yield
(%)
Method
IVa
IVb
Va
A
MW
ꢀ
1 + 5
1 + 5
5 + 5
5 + 60
1 + 6
1 + 6
7 + 6
7 + 60
1 + 5
1 + 5
6 + 5
6 + 60
134–136
134–136
134–136
134–136
136–138
136–138
136–138
136–138
136–138
136–138
136–138
136–138
91
traces
traces
61
B (i)
B (ii)
B (iii)
A
(i) B
(ii) B
(iii) B
A
ꢀ
ꢀ
MW
ꢀ
92
traces
traces
58
ꢀ
ꢀ
MW
ꢀ
90
B (i)
B (ii)
B (iii)
traces
traces
60
ꢀ
ꢀ
∗Final temperature is measured by introducing a glass thermometer in
the reaction mixture at the end of exposure to microwave irradiation.

558
A. Dandia et al.
Further, in view to improve bioactivity, certain pharmacophores are
introduced in to spiro system and acetylation, thiation and amino alky-
lation of these compounds were carried out using solvent-free conditions
under microwave irradiation.
Thiation of heterocycles for the conversion of oxo group to thio group
provides precursors for fused heterocyclic systems.21 In these conver-
sions usually use of larger amounts of P2S5 in toxic pyridine22 and
benzene23 is required, the time of reaction is long and the yields are
moderate to low especially in an scale up.24 Amino alkylation and acety-
lation of organic compounds also requires several hours heating using
toxic and environmentally hazardous organic solvents. Faced with this
dilemma, we explored more effective and much faster routes for the im-
plementation of thiation, acetylation and aminoalkylation of the spiro
compounds in solvent free conditions using different types of inorganic
solid supports under microwave irradiation in few minutes. Acetyla-
tion of spiro compound was tried using different types of inorganic solid
supports, i.e., aluminas (neutral or basic) and montmorillonite KSF. It
has been observed that reaction did not occur using neutral alumina or
montmorillonite KSF. However, acetylation of spiro compound occurred
successfully when two or three drops of piperidine and neutral alumina
were used. Further, for the aminoalkylation, also different types of inor-
ganic solid supports were tried such as aluminas (basic, acidic, neutral),
montmorillonite KSF, silica gel. Acidic alumina was found to be the best
solid support for this conversion giving maximum yield with shorter
time as shown in Table III. Successful thiation of spiro compound was
carried out using silica gel.
It is noteworthy to mention here that the thiation occur at both car-
bonyl groups when spiro compound and P2S5 in 1:2 molar ratio adsorbed
on silica gel has been irradiated. Dithiation of the spiro compound has
been confirmed by the disappearance of both carbonyl groups in the
IR spectrum. Acetylation and aminoalkylation occur exclusively at in-
dole nitrogen. The formation of N-acetylated spiro compound has been

Spiro[Indole-Thiazolidinones/Thiazinones]
559
TABLE III Effect of Solid Supports in Dry Media Aminoalkylation
of Spiro[indole-thiazolidinone] (IVh, Table IIIa) and Acetylation
of Spiro[indole-thiazine] (Vj, Table IIIb) Under Microwave Irradiation
IIIA
Basic
alumina alumina
Neutral
Acidic
alumina
Montmorillonite
KSF
Support
Silica gel
Yield (%)
Time (min)
76
11
74
9
92
6
72
10
67
9
IIIB
Basic
alumina
Montmorillonite
KSF
Neutral alumina +
Support
piperidine
Yield (%)
Time (min)
Nil
15
Nil
12
85
7
confirmed on the basis of complete disappearance of NH absorption in
IR and 1H NMR spectrum and the appearance of a new C O absorption
band in IR spectrum and additional signals at δ 2.38 (s, 3H, COCH3) in
1H NMR spectrum. Formation of Mannich base from the corresponding
spiro compound has been confirmed by complete disappearance of NH
absorption in IR and 1H NMR spectrum and by the appearance of new
1
resonance signals centered at δ 2.78, 3.91, and 5.01 ppm in H NMR
spectrum due to morpholino group.
Evaluation of Antifungal Activity
The synthesized compounds were screened for antifungal activity
against three pathogenic fungi, namely Rhizoctonia solani, causing root
rot of okra, Fusarium oxysporum, causing wilt of mustard, and Col-
letotrichum capsici causing leaf spot and fruit rot of chilli. It was done
by two methods.
(i) Poison Plate Technique25
The compounds synthesized were dissolved in acetone and com-
pounds were prepared in 1000 and 500 ppm concentrations. Potato
dextrose-agar (PDA) medium was prepared in flasks and sterilized.
To this medium, a requisite quantity of solution was added and then
the medium was poured into petriplates in three replication. A culture
of test fungus was grown on PDA for 6–7 days. Small disc (4 mm) of
the fungus culture was cut with a sterile corkborer and transferred
asceptically, upside-down in the center of petridishes containing the
medium and fungicides. Plates were incubated at 25◦C 1◦C for 6 days.
Colony diameter were measured and data was statistically analysed.

560
A. Dandia et al.
TABLE IV Effect of Concentration of Different Chemicals on the Mean
Radial Growth (cms) of Fungus in vitro (Poison Plate Technique)
Rhizoctonia solani
Fusarium oxysporum
Colletorichum capsici
Compd.
no.
1000 ppm
500 ppm
1000 ppm
500 ppm 1000 ppm 500 ppm
IVa
IVb
3.52
3.10
3.91
4.58
4.72
3.75
4.50
5.17
4.77
4.07
6.77
6.46
IVc
IVd
IVe
IVf
IVg
IVh
Va
5.98
6.92
8.58
4.55
5.10
7.92
9.00
9.01
8.43
7.35
8.30
9.00
7.25
9.00
9.00
7.92
1.54
2.16
4.00
3.67
3.68
1.98
2.10
1.83
3.50
4.17
5.17
3.67
5.28
2.83
4.17
2.75
3.77
3.25
1.83
2.31
3.58
3.58
3.42
1.87
4.21
4.58
2.92
3.56
5.98
5.51
5.00
3.65
Vb
Vc
6.15
8.64
1.40
2.67
2.67
3.25
Vd
Ve
Vf
Vg
Vh
Vi
1.38
7.02
7.92
6.52
8.30
9.00
2.25
9.00
8.68
6.54
9.00
9.00
3.42
3.58
3.25
3.17
3.00
3.75
5.37
5.58
4.33
3.58
4.00
4.25
3.83
3.00
3.25
1.55
3.00
2.67
6.43
4.95
4.35
2.95
4.81
3.79
Vj
Vk
Vl
1.75
7.33
9.00
1.92
2.75
8.02
9.00
9.00
4.25
2.50
3.08
3.25
4.33
4.25
3.75
4.58
1.35
2.83
4.17
1.67
2.08
4.33
4.25
3.00
Vm
VI
3.33
8.74
1.33
6.50
3.50
6.33
VII
Check
CD%
5.08
9.00
0.78
5.08
9.00
1.21
2.50
8.67
0.91
2.88
8.67
0.92
1.83
7.67
1.06
3.67
7.67
1.28
Min value.
At par with min value.
The fungicidal data (Table IV) indicates that some of the compounds
were found significantly superior over check (9.0 cm) in controlling the
radial growth (1.30–6.00 cm) of all the there pathogens. Rest were at
par with check.
It was found that the compound Vd (X = H, Y = 4-COOH), Vj (X =
5-Br, Y = 2-Cl), Vm (X = 5-NO2, Y = 4-F) were most effective against
R. Solani (1.38–1.92 cm), compound IVc (X = 5,7-diCH3, Y = 2-COOH),
IVd (X = 5,7-diCH3, Y = 3-Cl), IVh (X = 5-CH3, Y = 4-CH3), Va (X =
H, Y = 4-Cl), Vb (X = H, Y = 3-Cl), Vc (X = H, Y = 2-Cl) and VI
(X = 5,7-diCH3, Y = H) were most effective against F. oxysporum (1.33–
2.16 cm) and the IVe (X = 5-Br, Y = 4-COOH), Vb (X = 4, X = 3-Cl),
Vg (X = 5,7-diCH3, Y = 4-COOH), Vj (X = 5-Br, Y = 2-Cl) and VII

Spiro[Indole-Thiazolidinones/Thiazinones]
561
(X = 5-CH3, Y = 4-CH3) were also found to be most effective against C.
capsici (1.25–1.87 cm). Compound IVa, IVb, IVg, Ve, Vf, Vh, Vi, and Ve
have shown moderate activity (2.50–3.92 cm) against these pathogens.
(ii) Pot Trial Method26
White seeded sorghum grains were soaked in water for about 12 h.
Of the soaked kernels 160 gm were placed in 500 ml flasks and 20
ml of water was added to each. The material was autoclaved twice on
successive days before inoculation. After sterilization, fungus bits were
inoculated in each flask and flasks were kept for 10 days at 25–27◦C.
One hundred seeds of okra were taken for one treatment of each com-
pound. Inoculum was added @ 2g/kg of soil, 3-days prior to sowing.
Sowing was done after 3 days, and germination data were recorded af-
ter 7,15,25 days of sowing. Suitable checks were maintained and the
data was statistically analysed (Table V). It was found that IVb hav-
ing two-CH3 and COOH groups showed maximum germination (63%).
“Baynate” and “Thiram,” standard fungicides also are having N C S
linkage, similar to the synthesized compounds. “Baynate” was found
best in reducing the plant mortality.
Evaluation of Antitubercular Activity
The antitubercular evaluation of the compunds was carried out at
“Tuberculosis Antimicrobial Acquisition and Coordinating Facility”
(TAACF) USA. Primary screening of the compounds for antitubercular
TABLE V Evaluation of Spiro[indole-thiazolidinone/thiazinone]
Derivatives as Seed Dressers Against Rhizoctonia solani Causing
Root Rot of Okra (in Pot Trial)
Compd
no.
Percent
germination 7 DAS
Plant stand
25 DAS
IVa
IVb
IVe
IVh
Va
Vf
VI
Vm
61.00
63.00
55.00
58.00
28.00
59.00
51.00
29.00
98.00
79.00
12.00
95.00
48.00
45.00
42.00
41.00
21.00
40.00
39.00
19.00
64.00
68.00
4.00
Baynate (0.2%)
Thiram (0.3%)
Check with inoculum
Check without inoculum
90.00
DAS—Days after sowing.

562
A. Dandia et al.
TABLE VI In vitro Evaluation of Anti Tuberculosis
Activity Against Mycobacterium tuberculosis
Compd
no.
Antitubercular activity
(H37Rv) MIC (µg/ml)
% Inhibition
IVa
IVb
IVc
IVd
IVe
IVf
IVg
IVh
Va
Vb
Vd
Ve
Vh
VI
<12.5
<12.5
<12.5
<12.5
>12.5
>12.5
>12.5
<12.5
>12.5
>12.5
>12.5
>12.5
<12.5
>12.5
<12.5
<12.5
93
94
95
92
72
45
68
95
32
50
35
88
94
25
93
90
VI
VII
MIC—Minimum inhibition concentration in µg/ml.
activity has been conducted at 12.5 µg/ml against mycobacterium tu-
berculosis H37Rv, in BACTEC 12B medium using BACTEC 460 ra-
diometric system. Antitubercular activity data were compared with
standard drug Rifampin at 0.25 µg/ml concentrations, which showed
98% inhibition. The results are presented in Table VI compounds IVa,
IVb, IVc, IVd, IVh, Vh, Vl, and VII were must effective against M.
tuberculosis at 12.5 µg/ml concentration and showed 90–95% inhibition
while the other compounds showed moderate activity against Mycobac-
terium tuberculosis.
EXPERIMENTAL
Melting points were determined in open glass capillaries and were un-
corrected. IR spectra were recorded on a Perkin-Elmer (model 577) in
1
KBr pellets. H NMR and 13C NMR were recorded on a Jeol model
FX90Q, using CDCl3 and TFA as solvent at 89.55 and 22.4 MHz,
respectively using TMS as internal reference. All compounds were
found homogenous on TLC in various solvent systems. The induced
microwave convection system used has microwave generated at a fre-
quency of 2450 MHz. The oven has a range of microwave output energy
of 700 watts. Montmorillonite KSF and anilines were Aldrich products
and were used as received.

Spiro[Indole-Thiazolidinones/Thiazinones]
563
Spiro[indole-3,2ꢀ-thiazolidine]-2,4ꢀ(1H)-diones (IVa–h)
and Spiro[3H-indole-3,2ꢀ-tetrahydro-1,3-thiazine]-
2,4ꢀ(1H)-diones (Va–m)
Spiro compounds IV/V have been synthesized in one-step without
isolating the intermediate anil (III) using montmorillonite KSF under
microwave irradiation.
An equimolar mixture of appropriate indole-2,3-dione (I) and substi-
tuted aniline (II) (0.005 mmol) was adsorbed on montmorillonite KSF
(4 gm) and irradiated for 30–90 s at 640 watt under microwave irradi-
ation. As the reactants disappeared (TLC) thioacids (a/b) (0.005 mmol)
was added to the reaction mixture, mixed thoroughly and again ir-
radiation at 640 watt for the specificed time (Table I). The product
was obtained by desorption with methanol and found to be pure by
TLC.
Synthesis of 5,7-Dimethyl-3ꢀ-phenyl-spiro[3H-indole-3,2ꢀ-
thiazolidine]-2,4ꢀ-(1H)-dithione (VI)
Spiro compound IVa and P2S5 in 1:2 molar ratio was adsorbed on
silica gel with the help of methanol. After removal of methanol, the
dry reaction mixture thus obtained was irradiated at 640 watt until
the completion of reaction (7 min, monitored by TLC). The product was
extracted into ethylacetate and further purified by methanol.
Synthesis of 1-Morpholinomethyl-5-methyl-3ꢀ-
(4-methylphenyl) spiro [3H-indole-3,2ꢀ-tetrahydro]-1,3-
thiazine]-2,4ꢀ (1H)-dione (VII)
A mixture of spiro compound IVh (1 mmol), formaldehyde solution
(1.5 mmol, 40%, aqueous solution) and morpholine (1 mmol) were mixed
and ground with acidic alumina (3 g) in a mortar. The dry powder thus
obtained was irradiated in a microwave oven at 640 watt for (6 min). The
inorganic support was separated by filtration after eluting the product
with ethyl acetate and product obtained after removal of solvent was
found to be pure by TLC.
1-Acetyl-5-bromo-3ꢀ-(2-chlorophenyl)-spiro[3H-indole-3,2ꢀ-
tetrahydro-1,3-thiazine)-2,4ꢀ-(1H)-diones (VIII)
A mixture of spiro compound Vj (1 mmol) and acetic anhydride
(1.5 mmol) was adsorbed on neutral alumina (3 g). To this mixture
two drops of piperidine was added, mixed thoroughly and irradiated at
640 watt for 6 min (monitored by TLC). The product was extracted into
ethylacetate and found to be pure by TLC.

564
A. Dandia et al.
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