Design, synthesis and glucose uptake activity of some novel glitazones

Article abstract of DOI:10.1016/j.bioorg.2014.05.006

Herein, we report a library consisting of some novel glitazones containing thiazolidinedione and its bioisosteres, rhodanine and oxadiazolidine ring structures as their basic scaffold for their antidiabetic activity. Twelve novel glitazones with diverse chemical structures were designed and synthesized by adopting appropriate synthetic schemes and analyzed. Later, subjected to in vitro glucose uptake assay in the absence and presence of insulin to confirm their antidiabetic activity using rat hemi-diaphragm. The titled compounds exhibited glucose uptake activity ranging weak to significant activity. Compounds 4, 5, 9, 11, 15, 16, 19 and 20 showed considerable glucose uptake activity apart from rosiglitazone, a standard drug. Compound 16 happens to be the candidate compound from this study to investigate further. The illustration about their design, synthesis, analysis and glucose uptake activity is reported here along with the in vitro and in silico study based structure-activity relationships.

Full text of DOI:10.1016/j.bioorg.2014.05.006

Bioorganic Chemistry 56 (2014) 27–33
Contents lists available at ScienceDirect
Bioorganic Chemistry
journal homepage: www.elsevier.com/locate/bioorg
Design, synthesis and glucose uptake activity of some novel glitazones
⇑
Koyel Kar, Uma Krithika, Mithuna, Prabhuddha Basu, S. Santhosh Kumar, Anu Reji, B.R. Prashantha Kumar
Department of Pharmaceutical Chemistry, JSS College of Pharmacy, Mysore, India
Department of Pharmaceutical Chemistry, JSS College of Pharmacy, Ootacamund 643 001, India1
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 September 2013
Available online 24 May 2014
Herein, we report a library consisting of some novel glitazones containing thiazolidinedione and its bio-
isosteres, rhodanine and oxadiazolidine ring structures as their basic scaffold for their antidiabetic activ-
ity. Twelve novel glitazones with diverse chemical structures were designed and synthesized by adopting
appropriate synthetic schemes and analyzed. Later, subjected to in vitro glucose uptake assay in the
absence and presence of insulin to confirm their antidiabetic activity using rat hemi-diaphragm. The
titled compounds exhibited glucose uptake activity ranging weak to significant activity. Compounds 4,
5, 9, 11, 15, 16, 19 and 20 showed considerable glucose uptake activity apart from rosiglitazone, a stan-
dard drug. Compound 16 happens to be the candidate compound from this study to investigate further.
The illustration about their design, synthesis, analysis and glucose uptake activity is reported here along
with the in vitro and in silico study based structure–activity relationships.
Keywords:
Thiazolidinediones
Glitazones
Glucose uptake activity
Rat hemi-diaphragm
Ó 2014 Elsevier Inc. All rights reserved.
1. Introduction
new classes of antidiabetic drugs to the market especially glitaz-
ones [9]. The pioneering discovery of ciglitazone by the group of
Diabetes mellitus is a metabolic disease characterized by hyper-
glycemia arises as a consequence of relative or absolute deficiency
of insulin secretion or resistance to insulin action or in combina-
tion of many factors [1]. Insulin is a hormone necessary for normal
carbohydrate, protein and fat metabolism in mammals. Insulin
resistance is one of key characteristic features of non-insulin
dependent diabetes mellitus (NIDDM) [2]. Patients with NIDDM
often suffer from dyslipidemia in the form of high plasma triglyc-
erides and low HDL cholesterol levels these factors are considered
as major risk factors for coronary heart diseases [3]. The primary
therapy for NIDDM is caloric restriction of diet and regulated aer-
obic exercises. When lifestyle modifications do not result in nor-
malization or near normalization of metabolic abnormalities,
pharmacologic therapy is unavoidable [4]. Before 1990, sulfonylu-
reas and biguanides were the oral antidiabetic agents available for
the treatment of type 2 diabetes to enhance the insulin secretion
and action [5,6]. Many drawbacks associated with these drugs
restrict their use and creates opportunity to develop some novel
insulin sensitizers to reduce insulin resistance [7,8]. Fortunately,
since from 1990, there is an explosion with the introduction of
scientists at Takeda Co., Japan, for insulin resistance by potentiat-
ing insulin action in genetically diabetic and or, obese animals lead
to the development of new glitazones or thiazolidine-2,4-diones
(TZDs) [10–12]. Among these TZDs, troglitazone was the first
approved by USFDA (United States Food and Drug Administration)
in late 1990s for the treatment of NIDDM followed by pioglitaz-
one and rosiglitazone [13–15]. These agents share a common par-
tial chemical structure, TZD, and are commonly called as
glitazones. These glitazones correct hyperglycemia by enhancing
insulin sensitivity at adipose, hepatic and skeletal muscle tis-
sues. Recently, rosiglitazone has been recalled from the market
due to its cardiovascular concerns and on the other hand this
has created an opportunity to develop some newer glitazones.
The major molecular target for these glitazones happens to be
the peroxisome proliferator activated receptor-gamma (PPAR-c)
which regulates the gene expression mainly in the adipose tissues
[16].
PPAR-c and its modulators are well known to play key role
in treating NIDDM, gastrointestinal diseases, and genetic disor-
ders associated with glucose homeostasis and lipid uptake
[17–20].
In the past we have reported the design, synthesis and eval-
uation of some novel TZDs [21–23]. In continuation, the present
interest on TZDs is mainly due to their structural diver-
sity based on structure–activity relationships learnt in the
past.
⇑
Corresponding author at: Department of Pharmaceutical Chemistry, JSS College
of Pharmacy, JSS University, Mysore 570 015, India. Fax: +91 821 2548359.
E-mail address: brprashanthkumar@jssuni.edu.in (B.R. Prashantha Kumar).
A Constituent Colleges of JSS University, Mysore 570 015, India.
1
http://dx.doi.org/10.1016/j.bioorg.2014.05.006
0045-2068/Ó 2014 Elsevier Inc. All rights reserved.

28
K. Kar et al. / Bioorganic Chemistry 56 (2014) 27–33
Knoevenagel condensation reactions were performed both
2. Results and discussion
under microwave and conventional methods. However, microwave
method happens to be the easy and efficient method over the con-
ventional method as it showed better results in terms of time and
yields when compared to the conventional method. All the synthe-
sized compounds were analyzed by IR, NMR and Mass spectral
studies to confirm their structures. All the compounds exhibit only
the Z configuration as expected from our previous studies because
in 1H NMR spectra, peak for @CH was found unusually at about 7.7
d ppm. 13C NMR spectra showed signal for @CH in Knoevenagel
condensed products at about 133 d ppm. The reason for this desh-
ielding is attributed to the cis position of the carbonyl function of
highly electronegative TZD or 2-thioxo-thiazolidine-4-one ring to
the @CH and hence the Z configuration [19,20].
2.1. Chemistry
Relationship between the structure and antihyperglycemic
activity of the substituted TZDs and related compounds has been
a subject of intensive investigation. TZDs with significant antihy-
perglycemic activity are known for their common structural fea-
tures, namely, acidic head group connected to a lipophilic tail by
a phenoxyalkyl linker (Fig. 1).
The structure–activity relationships drawn from our previously
generated CoMSIA model are [21], the superimposed common part
of the structures, namely, polar rhodanine head followed by polar
tyrosine or phenylalanine moiety at the third position and benzyl-
idene moiety at the fifth position of the rhodanine ring seems to be
the pharmacophore, as most of the compounds possessed this
common substructure. This indicated the necessity of relatively
more polar acidic groups nearer the thiazolidine head. The hydro-
phobic benzyloxy trunk, which in turn connected to the two car-
bon acyl linker in association with the amide bond, also
identified as the important structural components for the com-
pounds to exhibit significant antidiabetic activity. Regarding the
hydrophobic trunk part, vanillin was found to be extremely good
as many of the active compounds in the series contain the same.
In light of this back ground and considering all these pharmaco-
phore features we have used three synthetic schemes to design and
synthesize some novel glitazones. First, following Scheme 1, we
have synthesized the basic nucleus TZD 1 which happens to be
the head part of glitazones by reacting chloroacetic acid and thio-
urea. Vanillin, which happens to be the trunk portion of glitazones,
is connected to a two carbon linker to get 2. Further, it is connected
to the hydrophobic morpholine, which happens to be the hydro-
phobic tail part of glitazones to yield 3. At last, 1 is subjected to
the Knoevenagel condensation reaction with 3 to get glitazone 4.
Similarly, we used rhodanine which happens to be the one of the
bioisosteres of TZD to get 5.
Para amino benzoic acid (PABA) substituted TZDs were
designed to enhance the acidity near the TZD ring system was
prepared by adopting Scheme 2. First, PABA is connected to the
two carbon linker using chloroacetyl chloride to form 6 and later
reacted with the prepared potassium salt of TZD 7 using DMF as
solvent to obtain 8 in moderate yields. Later, compound 8 was
condensed with various substituted aldehydes using Knoevenagel
condensation reaction to get 9–16. Since, oxadiazole ring system
also happens to be bioisosteric with the TZD ring system, attempt
has been made to synthesise some novel oxadiazole based glitaz-
ones by adopting Scheme 3. Here, we first reacted ethylacetoace-
tate and hydrazine hydrate under neat condition to form
hydrazide 17, instantly at 100% yields. Later, we converted 17
to the substituted oxadiazole 18 by reacting with carbon disulfide
under basic conditions. The NH group of 18 is subjected to the
Mannich reaction with aniline and benzyl amine to get 23 and
24, respectively, having quite similar structural frame as that of
a usual glitazones.
2.2. Glucose uptake by rat hemi diaphragm
Antidiabetic activities for the twelve compounds were mea-
sured using glucose uptake by rat hemi-diaphragm method
according to the previously reported protocols and the procedure
that we had reported earlier [19–22]. Rat diaphragm was selected
because the striated muscle is quantitatively the most important
tissue for glucose disposal in the animal body. The glucose content
was measured and the glucose uptake was calculated as the differ-
ence between the initial and final glucose content at 2 mg of opti-
mized drug concentration [21–23]. The glucose uptake by rat
hemi-diaphragm was measured in mg/dl. Data was expressed as
mean standard error of mean (SEM) and are shown in Table 1.
Statistical comparisons between the groups were performed in
two sets against the respective control in one-way ANOVA fol-
lowed by Dunnet’s multiple comparison post-test using graphPad
Prism 4.0 software for Windows (San Diego, California, USA).
The results of the in vitro glucose uptake study indicate that the
compounds 4, 5, 9, 11, 15, 19 and 20 (p < 0.05) enhance the glucose
uptake significantly by the tissue cells. Compound 16 happens to
be the most potent compound amongst all the glitazones studied
here by enhancing the glucose uptake significantly (p < 0.01).
However, rosiglitazone, being a standard drug demonstrated its
superiority over all the glitazones studied here. Rest of the com-
pounds exhibit weak to moderate glucose uptake activity.
However, glitazones 13 and 14 failed to produce the glucose
uptake activity especially in the presence of insulin.
We have investigated the structure–activity relationships based
on the results obtained. To define the pharmacophore we aligned
energy minimized and conformationally analyzed structures of 4,
5, 9–16 against common atoms by atom fit method using Schro-
dinger 9.2 software (Fig. 2). The superimposed common substruc-
ture that contains polar thiazolidinedione or its bioisosteres,
rhodanine or oxadiazole-2-thione ring as head group followed by
hydrophobic benzyloxy trunk happens to be the pharmacophore.
The acidic TZD ring is extended with PABA via two carbon acyl lin-
ker and perhaps this could also be the one of the important reasons
for compounds 9, 11, 15 and 16 to exhibit significant glucose
uptake activity. Compound 16, the most active compound contains
para bromo benzylidene moiety at the fifth position of TZD scaf-
fold. Surprisingly, compounds 19 and 20 with oxadiazolidine-2-
thione scaffold also exhibited good glucose uptake activity.
Furthermore, we have docked all the reported glitazones here
against PPAR-c protein (PDB ID: 2PRG) [23] using regular protocol
S
using the Glide molecular docking tool implemented in the Schro-
dinger software (Schrödinger, L.L.C.) [24]. The binding conforma-
tions of the standard drug rosiglitazone and compound 16 at the
O
N
HN
O
active site of PPAR-c is as shown in Fig. 3. Key aspect here is that,
O
carboxyl group of PABA is superimposed over the TZD ring and this
indicates that they are bioisosteric with one another. However, the
binding mode of tail part of the structures differs considerably. The
Liphophilic tail
Phenoxyalkyl linker
Acidic head group
Fig. 1. Pharmacophore structural components of glitazones.

K. Kar et al. / Bioorganic Chemistry 56 (2014) 27–33
29
H
O
S
O
N
S
a, b
Cl
O
OH
OCH3
H2N
NH2
1
OCH3
O
S
O
e
N
O
OHC
Br
OCH3
OHC
X
OHC
OCH3
N
H
O
d
c
X = O, 4
X = S, 5
N
O
OH
O
2
3
Scheme 1. Reagents and conditions: (a) water, 0–5 °C, stir for 30 min, (b) HCl, reflux for 12 h, (c) dibromoethane, dry acetone, anhydrous K2CO3, stir at 50 °C, 48 h, (d)
morpholine, dry acetone, anhydrous K2CO3, stir under at rt for 48 h and (e) thiazolidine-2,4-dione or rhodanine, dry toluene, piperidine, acetic acid, molecular sieves, MW
irradiation; 420 W, 30–45 min, conventional; reflux at 110 °C for 12–15 h with stirring.
O
K
N
O
O
S
b
a
O
Cl
N
HOOC
R
NH2
HOOC
N
H
HOOC
N
H
O
O
S
8
6
7
R
c
R
O
9 -p-OCH3-C6H4
10 - C6H5
O
13
15
O
O
O
11 - p-OH-m-OCH3-C6H3
12 - p-OH-C6H4
S
N
HOOC
N
O
14 - p-NO2-C6H4
16 - p-Br-C6H4
H
N
O
O
9-16
Scheme 2. Reagents and conditions: (a) triethylamine, chloroacetylchloride, dry chloroform, 0–5 °C, stir for 24–30 h, (b) DMF, stir at 50–70 °C for 48 h and (c) aryl aldehyde,
dry toluene, piperidine, glacial acetic acid, MW irradiation; 420 W, 30–45 min, conventional; reflux at 110 °C for 12–15 h with stirring.
O
O
O
O
b
H
N
O
a
HN
N
c
O
S
O
NHNH2
S
O
17
N
O
NH
18
c
19
H
N
O
S
O
N
NH
20
Scheme 3. Reagents and conditions: (a) hydrazine hydrate, neat, stir at 0–5 °C for 3 min, (b) ethanol (50 ml), CS2, 0–5 °C, stir for 30 min and reflux for 6 h and (c) 37%
formaldehyde, aniline/benzylamine, ethanol, stir at rt for 2 h.
rosiglitazone also makes the same interactions at almost same dis-
Table 1
tances [25–27].
In vitro glucose uptake study for the glitazones by isolated rat hemi-diaphragm.
Compound/
group
In absence of insulin (mg/dl/ In presence of insulin (mg/dl/
3. Experimental methods
g/45 min)
g/45 min)
Mean SEM
Mean SEM
The melting points of the synthesized compounds were deter-
mined in open capillaries using Veego VMP-1 apparatus and are
expressed in °C and are uncorrected. The IR-spectra of compounds
were recorded on Shimadzu FT-IR spectrometer using KBr pellets
Control
4
5
20.89 1.41
29.31 2.36*
29.06 0.44*
29.05 1.64*
18.90 1.40
28.79 2.21
19.48 1.40
23.93 1.07
15.27 1.23
25.41 1.41
34.71 3.29**
28.50 1.50
30.40 1.62*
33.55 1.00
40.36 2.40*
38.29 0.71
39.15 2.57
35.33 1.33
42.02 3.53*
34.05 1.55
33.88 1.67
34.00 1.00
40.33 2.33*
47.65 2.87**
41.44 1.56*
40.36 1.49*
50.50 1.50**
9
technique and are expressed in cmÀ1 1H NMR, 13C NMR spectra
.
10
11
12
13
14
15
16
19
20
was recorded on AV-III 400 MHz spectrometer using DMSO-d6
as solvent and TMS as internal standard. The chemical shifts
were reported in d ppm. Mass spectra were obtained using JEOL
GC mate mass spectrometer under EI+ ionization technique/mode.
Microwave assisted synthesis was performed using microwave
system CATA R from Catalyst system (Pune, India). Auto analyzer
(Merck) was used for the glucose estimation during in vitro glucose
uptake study by rat hemi-diaphragm method. TLC were performed
to monitor the reactions and to determine purity of the products.
Compounds were purified by re-crystallization using suitable
solvents.
Rosiglitazone 36.00 1.00**
Statistics: Values are mean of triplicate SEM.
p < 0.05 compared to the respective control, one way-ANOVA followed by Dun-
nett’s post-test.
p < 0.01 compared to the respective control, one way-ANOVA followed by Dun-
nett’s post-test.
*
**
3.1. Procedure for the preparation of thiazolidine-2,4-dione [1]
carboxyl group of PABA has made hydrogen bonding interactions
at a distance of 1.503, 1.617 and 2.402 Å with residues His323,
His449 and Tyr473, respectively (Fig. 4), whereas TZD ring of
Thiazolidine-2,4-dione [3] was prepared according to the
Scheme 1. Equimolar amount of thiourea (0.3 M) and chloroacetic

30
K. Kar et al. / Bioorganic Chemistry 56 (2014) 27–33
Fig. 2. Aligned glitazones by the atom fit method depicting pharmacophore.
acid (0.3 M) was taken separately in 30 ml of water and mixed
under ice cold condition (0–5 °C) with stirring for 20 min to form
white precipitate of 2-imino-thiazolidine-4-one. Concentrated
HCl (30 ml) was added and refluxed for 12 h. Reaction was moni-
tored through TLC (ethyl acetate:pet ether, 2:3). The white crystal-
line solid obtained after cooling was filtered, washed with water
and dried. The yield was found to be 80%.
3.2. Thiazolidine-2,4-dione [1]
White crystalline solid, Yield 80%, M.P. 123–125 °C, IR (KBr,
cmÀ1): 3126.7 (NAH, broad peak, stretch), 1735.9 (C@O, stretch),
1849.8 (C@O, stretch), 1163.1 (C@S, stretch).
1H NMR (d ppm, DMSO-d6) d: 4.4 (s, 2H, CH2), 12.5 (s, 1H, NH).
3.3. Procedure for the preparation of 4-(2-bromoethoxy)-3-
methoxybenzaldehyde [2]
One equivalent of vanillin, 2.5 equivalent of dibromoethane
along with 1.2 equivalent of anhydrous K2CO3 and 70 ml of dry
acetone were transferred to a flask. Then it was refluxed at 50 °C
for 48 h. Reaction was monitored through TLC (ethyl acetate:pet
ether, 2:3). After completion of the reaction, solvent was evapo-
rated and the reaction mixture was transferred to the beaker con-
taining 200–300 ml of water and stirred for 20–30 min. Resulting
suspension was filtered. The solid obtained was then dissolved in
10% NaOH solution, stirred for 10 min and then filtered. The solid
obtained was washed with plain water and dried. The white crys-
tals of the pure product was taken forward for connecting it to the
morpholine.
Fig. 3. The binding conformations of rosiglitazone (antialias representation) and
compound 16 (ball and stick representation).
3.4. Procedure for connecting 2 to morpholine [3]
4-(2-Bromoethoxy) benzaldehyde (1 eq) was connected to mor-
pholine (1.5 eq) by stirring with anhydrous K2CO3 (1.1 eq) in dry
acetone for 48 h. Reaction was monitored through TLC (ethyl ace-
tate:pet ether, 2:3). After completion of the reaction the solvent
was evaporated and the reaction mixture was transferred to the
beaker containing 200–300 ml of water and stirred for 20–
30 min. Resulting suspension was filtered. The solid obtained was
then dissolved in 10% NaOH solution, stirred for 10 min and then
filtered. The solid obtained was washed with plain water and dried.
Later, it was subjected to the Knoevenagel condensation to get the
final compounds.
Fig. 4. Binding mode of compound 16 at the active site of the PPAR-c.

K. Kar et al. / Bioorganic Chemistry 56 (2014) 27–33
31
3.5. General procedure for Knovenagel condensation
The crude product obtained was washed with water and dried to
get the 4-(2-chloroacetamido) benzoic acid. It was taken directly
for the next step without any further purification. The yield was
found to be 85%.
The morpholine incorporated vanillin was subjected to the
Knoevenagel condensation reaction to get the final compounds [4
and 5].
Conventional method: Rhodanine (0.01 M) and thiazolidin-2,4-
dione (0.01 M) in dry toluene was transferred to flask. Then
morpholine incorporated vanillin (0.012 M), piperidine (3 drops),
glacial acetic acid (2–3 drops) and molecular sieves were added.
The reaction mixture was refluxed at 110 °C with occasional stir-
ring for 12–15 h. The reaction was monitored through TLC. Upon
completion of the reaction, reaction mixture was allowed to cool
and precipitated solid was filtered off. The corresponding product
was re-crystallized from ethyl acetate.
3.9. Synthesis of potassium salt of thiazolidine-2,4-dione [7]
Thiazolidine-2,4-dione (8 g) was dissolved in 12.5 ml of ethanol.
To this solution, KOH (4.2 g) in ethanol (10 ml) was added. The
mixture was stirred for 2 h. The white crystalline solid was
collected after filtration, washed with ethanol and dried under
vacuum to get potassium salt of thiazolidinedione.
3.10. Synthesis of 4-(2-(2,4-dioxothiazolidin-3-yl)acetamido)benzoic
Microwave method: Rhodanine (0.01 M) and thiazolidin-2,4-
dione (0.01 M) in dry toluene was transferred to flask. Then
morpholine incorporated vanillin (0.012 M), piperidine (3 drops),
glacial acetic acid (2–3 drops) and molecular sieves were added.
The reaction mixture was irradiated with microwaves at 700 W
for 30–45 min. The reaction was monitored through TLC. Upon
completion of the reaction, reaction mixture was allowed to cool
and precipitated solid was filtered off and washed with cold chlo-
roform. The corresponding product was re-crystallized with ethyl
acetate.
acid [8]
Potassium salt of 2,4-thiazolidinediones (2 eq) in DMF was
taken into flask. Then 4-(2-chloroacetamido) benzoic acid was
added slowly with stirring. After the addition was complete, the
mixture was allowed to stir and heated at 50–60 °C under reflux
for 24 h. Reaction was monitored through TLC. After completion
of the reaction, the solvent was evaporated and the mixture was
poured in water (500 ml) and product precipitated as a solid col-
lected on a filter and dried. The yield was found to be 60%.
3.6. (Z)-5-(4-(2-morpholinoethoxy)-benzylidene)-thiazolidine-2,
3.11. 4-(2-(2,4-Dioxothiazolidin-3-yl)acetamido)benzoic acid [8]
4-dione [4]
Cream amorphous solid, Yield 89%, M.P. 240–265 °C IUPAC: 4-
(2-(2,5-dioxothiazolidin-3-yl)acetamido)benzoic acid. IR (KBr,
cmÀ1): 3353.0 (NAH, broad peak, stretch), 3012.9 (Aromatic
CAH, stretch), 2941.5 (Aliphatic CAH, stretch), 1674.2 (C@O,
stretch), 1593.2 (Aromatic C@C, stretch), 1271.1 (C@S, stretch),
1246.0 (CAO, stretch), 1182.4 (CAN, stretch).
Yellow amorphous solid, Yield 85%, M.P. 280–285 °C, IR (KBr,
cmÀ1): 3236.6 (NAH, broad peak, stretch), 2877.8 (Aliphatic CAH,
stretch), 1697.4 (C@O, stretch), 1589.4 (Aromatic C@C, stretch),
1396.5 (CAO, stretch), 1265.3 (C@S, stretch), 1138.0 (CAN, stretch).
1H NMR (d ppm, DMSO-d6) d: 2.05 (t, 4H, 2CH2), 3.20 (t, 2H, CH2),
3.80 (s, 3H, OCH3), 3.85 (t, 4H, 2CH2), 4.41 (t, 2H, CH2), 7.20 (d, 1H,
ArH), 7.41 (d, 1H, ArH), 7.70 (s, 1H, @CH), 12.51 (bs, 1H, NH). Mass
(m/z): Molecular ion peak found, 364.4198 (peak calculated,
364.4201 for C17H20N2O5S), 52.34 (base peak). Mass fragment
(m/z): 321.25, 278.97 and 219.65.
3.12. General procedure for Knoevenagel condensation [9–16]
The resultant solid was subjected to the Knoevenagel condensa-
tion reaction to get the final compounds (9–16).
Conventional method: 4-(2-(2,4-Dioxothiazolidin-3-yl)acetam-
ido)benzoic acid (0.01 M) in dry toluene was transferred in flask.
Then aldehydes (0.01 M), piperidine (3 drops), acetic acid (2–3
drops) and molecular sieves were added. The reaction mixture
was stirred for 5 min and then refluxed at 110 °C with occasional
stirring for 2 h. The reaction was monitored through TLC. Upon
completion of the reaction, reaction mixture was allowed to cool
and precipitated solid was filtered off. The resultant solid was re-
crystallized with methanol.
Microwave method: 4-(2-(2,4-Dioxothiazolidin-3-yl)acetam-
ido)benzoic acid (0.01 M) in dry toluene was transferred in flask.
Then aldehydes (0.01 M), piperidine (3 drops), acetic acid (2–3
drops) and molecular sieves were added. The reaction mixture
was stirred for 5 min and then heated under microwave irradiation
(420 W) for 20–40 min. The reaction was monitored through TLC.
Upon completion of the reaction, reaction mixture was allowed
to cool and precipitated solid was filtered off. The resultant solid
was re-crystallized with methanol.
3.7. (Z)-5-(4-(2-morpholinoethoxy)-3-methoxybenzylidene)-2-
thioxothiazolidin-4-one [5]
Yellow amorphous solid, Yield 90%, M.P. 300–305 °C IR (KBr,
cmÀ1): 3140.2 (NAH, broad peak, stretch), 1685.8 (C@O, stretch),
1579.7 (Aromatic C@C, stretch), 1246.0 (CAO, stretch), 1271.1
(C@S, stretch), 1168.9 (CAN, stretch). 1H NMR (d ppm, DMSO-d6)
d: 1.80 (t, 4H, 2CH2), 3.02(t, 2H, CH2), 3.79 (s, 3H, OCH3), 3.82 (t,
4H, 2CH2), 4.44 (t, 2H, CH2), 7.20 (d, 1H, ArH), 7.41 (d, 1H, ArH),
7.69 (s, 1H, @CH), 13.78 (bs, 1H, NH). 13C NMR (d ppm, DMSO-
d6) d: 43.63 (2C, CH2), 43.64 (1C, CH2), 55.48 (2C, CH2), 55.49
(1C, CH3), 113.76 (1C, @C), 122.59 (2C, ArC), 125.85, 129.91 (2C,
ArC), 132.13 (2C, ArC), 133.12 (1C, @CH), 169.32 (1C, C@O),
191.45 (1C, C@S). Mass (m/z): peak found, 380.4789 (peak calcu-
lated, 380.4796 for C17H20N2O4S2), 68.58 (base peak). Mass frag-
ment (m/z): 337.19, 294.60, 250.85, and 235.82.
3.8. Synthesis of 4-(2-chloroacetamido) benzoic acid [6]
3.13. 4-(2-((E)-5-(4-Methoxy benzylidene)-2,4-dioxothiazolidin-3-
In Scheme 2, PABA (1 eq) and triethylamine (1.7 eq) along with
dry chloroform (50 ml) was transferred to flask fitted with guard
tube. The mixture was allowed to stir under room temperature
to form a uniform mixture. Chloroacetyl chloride (1.5 eq) was
added drop wise under ice cold condition with continuous stirring.
The reaction mixture was allowed to stir for about 24–30 h.
Reaction was monitored through TLC (ethyl acetate:pet ether,
2:3). After the reaction was completed the solvent was evaporated.
yl)acetamido)benzoic acid [9]
Light yellow amorphous solid, Yield 85%, M.P. 220–228 °C, IR
(KBr, cmÀ1): 3319.6 (NAH, broad peak, stretch), 3061.1 (Aromatic
CAH, stretch), 2951.1 (Aliphatic CAH, stretch), 1680.0 (C@O,
stretch), 1539.2 (Aromatic C@C, stretch), 1413.8 (CAN, stretch),
1386.8 (CAO, stretch), 1176.6 (C@S, stretch). 1H NMR (d ppm,
DMSO-d6) d: 4.04 (s, 3H, OCH3), 4.91 (s, 2H, CH2), 7.59 (d, 2H,

32
K. Kar et al. / Bioorganic Chemistry 56 (2014) 27–33
ArH), 7.62 (d, 2H, ArH), 7.80 (s, 1H, @CH), 7.88 (d, J = 7.2 Hz, 2H,
ArH), 7.92 (d, J = 7.6 Hz, 2H, ArH), 12.30 (bs, 1H, NH). 13C NMR (d
ppm, DMSO-d6) d: 43.54 (1C, CH2), 63.03 (1C, CH3), 118.43 (2C,
ArC), 118.68 (1C,@C), 123.72 (2C, ArC), 130.70 (2C, ArC), 134.02
(1C,@CH), 141.90 (3C, ArC), 143.16 (3C, ArC), 164.94 (1C, C@O),
165.88 (1C, C@O), 171.59 (1C, C@O), 171.96 (1C, C@O). MS (m/z):
peak found, 412.4209 (peak calculated, 412.4215 for C20H16N2O6S).
Mass fragments (m/z): 397.63, 387.35, 332.80, 293.48, 178.12,
164.16, 150.25, 137.29, 120.36 (base peak).
2H, ArH), 7.61 (d, J = 7.5 Hz, 2H, ArH), 7.68 (d, 2H, ArH), 7.93 (s,
1H, @CH), 7.94 (d, 2H, ArH), 8.08 (bs, 1H, NH). 13C NMR (d ppm,
DMSO-d6) d: 45.23 (1C, CH2), 120.53 (2C, ArC), 120.57 (2C, ArC),
120.69 (1C, @C), 130.58 (2C, ArC), 132.80 (1C, @CH), 143.29 (3C,
ArC), 144.76 (3C, ArC), 167.08 (1C, C@O), 168.83 (1C, C@O),
173.71 (1C, C@O). MS (m/z): peak found, 427.3908 (peak calcu-
lated, 427.3914 for C19H13N3O7S). Mass fragments (m/z): 412.45,
398.36, 351.36, 298.39, 187.07, 120.25 (base peak).
3.14. 4-(2-((E)-5-Benzylidene-2,4-dioxothiazolidin-3-yl)
3.19. 4-(2-((E)-5-(3-(2-morpholinoethoxy)-4-methoxybenzylidene)-
acetamido)benzoic acid [10]
2,4-dioxothiazolidin-3-yl)acetamido)benzoic acid [15]
Yellow amorphous solid, Yield 80%, M.P. 201–205 °C, IR (KBr,
cmÀ1): 3140.2 (NAH, broad peak, stretch), 3003.2 (Aromatic
CAH, stretch), 2847.0 (Aliphatic CAH, stretch), 1685.8 (C@O,
stretch), 1467.8 (Aromatic C@C, stretch), 1423.5 (CAN, stretch),
1354.0 (CAO, stretch), 1168.9 (C@S, stretch). 1H NMR (d ppm,
DMSO-d6) d: 4.90 (s, 2H, CH2), 7.07–7.55 (m, 5H, ArH), 7.78 (s,
1H, @CH), 7.80 (d, J = 7.6 Hz, 2H, ArH), 7.88 (d, J = 7.1 Hz, 2H,
ArH), 10.4 (bs, 1H, NH). MS (m/z): peak found, 382.3979 (peak cal-
culated, 382.3986 for C19H14N2O5S). Mass fragments (m/z): 350.12,
287.39, 167.47 and 120.36 (base peak).
Yellow amorphous solid, Yield 85%, M.P. 214–220 °C. 1H NMR (d
ppm, DMSO-d6) d: 4.43 (t, 3H, OCH3), 4.92 (s, 2H, CH2), 7.61 (d,
J = 7.3 Hz, 2H, ArH), 7.63 (d, J = 7.7 Hz, 2H, ArH), 7.65 (d, 2H,
@CH), 7.68 (d, J = 8.2 Hz, 2H, ArH), 7.71 (d, J = 8.0 Hz, 2H, ArH),
7.93 (d, 2H, ArH), 7.96 (d, 2H, ArH), 8.08 (bs, 1H, NH). MS (m/z):
peak found, 541.5721 (peak calculated, 541.5723 for C26H27N3O8S).
Mass fragments (m/z): 523.34, 480.34, 445.36, 436.32, 267.89,
265.43, 120.25 (base peak).
3.20. 4-(2-((E)-5-(4-bromobenzylidene)-2,4-dioxothiazolidin-3-yl)
3.15. 4-(2-((E)-5-(4-hydroxy-3-methoxybenzylidene)-2,
acetamido)benzoic acid [16]
4-dioxothiazolidin-3-yl)acetamido)benzoic acid [11]
Cream amorphous solid, Yield 84%, M.P. 260–265 °C. 1H NMR (d
ppm, DMSO-d6) d: 4.91 (s, 2H, CH2), 7.57 (d, J = 7.1 Hz, 2H, ArH),
7.60 (d, J = 7.2 Hz, 2H, ArH), 7.64 (d, J = 7.5 Hz, 2H, ArH), 7.77 (s,
1H, @CH), 7.86 (d, J = 7.8 Hz, 2H, ArH), 10.6 (bs, 1H, NH). 13C
NMR (d ppm, DMSO-d6) d: 43.82 (1C, CH2), 118.20 (2C, ArC),
118.59 (1C,@C), 123.72 (2C, ArC), 130.15 (2C, ArC), 132.85
(1C,@CH), 141.46 (3C, ArC), 143.04 (3C, ArC), 165.76 (1C, C@O),
167.59 (1C, C@O), 171.55 (1C, C@O), 173.62 (1C, C@O). MS (m/z):
peak found, 461.2926 (peak calculated, 461.2934 for C19H13BrN2-
O5S). Mass fragments (m/z): 445.69, 412.11, 398.34, 299.69,
211.46, 120.25 (base peak).
Brown amorphous solid, Yield 88%, M.P. 235–240 °C. 1H NMR (d
ppm, DMSO-d6) d: 4.09 (s, 3H, OCH3), 4.93 (s, 2H, CH2), 7.61 (m, 2H,
ArH), 7.63 (d, J = 7.4 Hz, 2H, ArH), 7.74 (d, J = 7.7 Hz, 2H, ArH), 7.79
(s, 1H, @CH), 10.5 (bs, 1H, NH). 13C NMR (d ppm, DMSO-d6) d: 43.47
(1C, CH2), 63.01 (1C, CH3), 118.66 (1C,@C), 118.85 (2C, ArC), 123.84
(2C, ArC), 130.67 (2C, ArC), 132.98 (1C, @CH), 143.02 (3C, ArC),
143.13 (3C, ArC), 164.56 (1C, C@O), 165.79 (1C, C@O), 171.54
(1C, C@O), 171.91 (1C, C@O). MS (m/z): peak found, 428.4211 (peak
calculated, 428.4206 for C20H16N2O7S). Mass fragments (m/z):
414.04, 334.96, 294.32, 178.92, 163.98, 121.19 (base peak), 93.32.
3.16. 4-(2-((E)-5-(4-hydroxybenzylidene)-2,4-dioxothiazolidin-3-yl)
acetamido benzoic acid [12]
3.21. Synthesis of 3-oxobutanehydrazide [17]
Deep brown amorphous solid, Yield 90%, M.P. 195–202 °C. 1H
NMR (d ppm, DMSO-d6) d: 4.91 (s, 2H, CH2), 7.59 (d, 2H, ArH),
7.61 (d, J = 7.5 Hz, 2H, ArH), 7.74 (d, J = 7.2 Hz, 2H, ArH), 7.78 (s,
1H, @CH), 7.89 (d, J = 8.1 Hz, 2H, ArH), 10.90 (bs, 1H, OH). MS (m/
z): peak found, 398.3918 (peak calculated, 398.3924 for C19H14N2-
O6S). Mass fragments (m/z): 377.64, 343.69, 276.50, 187.36, 120.25
(base peak).
According to Scheme 3, ethylacetoacetate (0.002 M) was taken
in flask. Hydrazine hydrate (0.002 M) was added drop wise under
ice cold condition with constant stirring for 5 min. The reaction
completes quickly and the resultant solid was re-crystallized with
alcohol to get white crystals of corresponding hydrazide.
3.22. 3-Oxobutanehydrazide [17]
3.17. 4-(2-((E)-5-(4-benzyloxy)-3-methoxybenzylidene)-2,
4-dioxothiazolidin-3-yl)acetamido)benzoic acid [13]
White crystalline solid, Yield 90%, M.P. 267–273 °C.
IR (KBr, cmÀ1): 3128.6 (NAH, broad peak, stretch), 2885.5
(Aliphatic CAH, stretch), 1776.5 (C@O, stretch).
Deep brown amorphous solid, Yield 86%, M.P. 250–255 °C. 1H
NMR (d ppm, DMSO-d6) d: 4.08 (t, 3H, OCH3), 4.92 (t, 2H, CH2),
7.60 (d, J = 7.2 Hz, 2H, ArH), 7.67 (d, J = 7.6 Hz, 2H, ArH), 7.75 (s,
1H, @CH), 7.88 (d, J = 8.0 Hz, 2H, ArH), 7.90 (d, J = 7.9 Hz, 2H,
ArH), 7.94 (d, 2H, ArH), 7.99 (d, 2H, ArH), 10.5 (bs, 1H, NH). MS
(m/z): peak found, 518.5379 (peak calculated, 518.5398 for
3.23. Synthesis of 1-(4,5-dihydro-5-thioxo-1,3,4-oxadiazol-2-yl)
propan-2-one [18]
C
27H22N2O7S). Mass fragments (m/z): 503.34, 478.54, 436.32,
3-Oxobutanehydrazide (0.01 M) was taken in flask. Ethanol of
50 ml was added along with KOH (0.015 M) and CS2 (0.015 M).
The reaction mixture was refluxed for 6 h. The reaction mixture
was monitored through TLC (ethyl acetate:pet ether, 10:1). Upon
completion of the reaction, the reaction mixture was allowed to
cool and ethanol was distilled off. The residue left was acidified
with dil.HCl. Then it was kept in the refrigerator for one day. The
precipitated solid was filtered off to get red crystals.
357.40, 276.50, 185.44 (base peak).
3.18. 4-(2-((E)-5-(4-nitrobenzylidene)-2,4-dioxothiazolidin-3-yl)
acetamido)benzoic acid [14]
Light brown amorphous solid, Yield 80%, M.P. 225–230 °C. 1H
NMR (d ppm, DMSO-d6) d: 4.92 (s, 2H, CH2), 7.59 (d, J = 7.0 Hz,

K. Kar et al. / Bioorganic Chemistry 56 (2014) 27–33
33
3.24. 1-(4,5-Dihydro-5-thioxo-1,3,4-oxadiazol-2-yl)propan-2-one
[18]
taken out swiftly avoiding trauma and divided into two halves.
The hemidiaphragms were then rinsed in cold Tyrode solution
(without glucose) to remove any blood clots and transferred to
the respective wells. The plates were closed with the lids and incu-
bated for 45 min at 21 °C with shaking at 60 cycles per min.
Following the incubation, the glucose content of the incubated
wells was measured by GOD/POD enzymatic method using
Merckotest glucose.
Red amorphous solid, Yield 80%, M.P. 280–285 °C. 1H NMR (d
ppm, CDCl3) d: 2.27 (s, 3H, CH3), 2.58 (s, 2H, CH2), 7.36 (bs, 1H,
NH). MS (m/z): Molecular ion peak found, 158.1810 (peak calcu-
lated, 158.1804 for C5H6N2O2S), 75.19 (base peak). Mass fragments
(m/z): 132.23, 104.26, 72.29.
3.25. General procedure for Mannich reaction [19,20]
4. Conclusion
1-(4,5-Dihydro-5-thioxo-1,3,4-oxadiazol-2-yl)propan-2-one
(18) was taken in flask. To this solution, primary aromatic amine
(benzylamine/aniline) and 37% formaldehyde solution were added.
Then the reaction mixture was stirred at room temperature for 2 h.
and allowed to stand overnight. The reaction mixture was moni-
tored through TLC (ethyl acetate:pet ether, 10:1). Upon completion
of the reaction, the separated solid was filtered, washed with cold
ethanol, dried and recrystallized from aqueous ethanol to get the
product (19, 20).
We have designed and synthesized some novel glitazones by
adopting three synthetic schemes and confirmed their structures.
Compound 16 was found to be the candidate compound to inves-
tigate further for its antidiabetic activity. For the first time we
are reporting some novel glitazones kind of structures containing
oxadiazolidine ring instead of TZD.
Acknowledgment
We acknowledge AICTE, New Delhi, India for funding this pro-
ject and for providing Schrodinger molecular modeling tools under
the RPS Scheme during the year 2011.
3.26. 1-(4-((Anilino)methyl)-4,5-dihydro-5-thioxo-1,3,4-oxadiazol-2-
yl)propan-2-one [19]
Orange amorphous solid, Yield 85%, M.P. 270–275 °C. 1H NMR (d
ppm, CDCl3) d: 2.27 (s, 2H, CH2), 2.95 (t, 2H, CH2), 4.48 (t, 2H, CH2),
4.93 (bs, 1H, NH), 6.60–7.10 (m, 5H, ArH), 7.90 (bs, 1H, NH/SH). MS
(m/z): Molecular ion peak found, 263.0703 (peak calculated,
263.0714 for C12H13N3O2S), 75.89 (base peak). Mass fragments
(m/z): 244.25, 132, 23121.21, 78.33.
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