Novel glitazones: Design, synthesis, glucose uptake and structure-activity relationships

Article abstract of DOI:10.1016/j.bmcl.2010.01.125

Glitazones are known to exhibit antihyperglycemic activity by decreasing peripheral insulin resistance. In the present study, we have designed some novel glitazones based on the structure-activity relationships as possible PPAR-γ agonists. The manually designed glitazones were synthesized by using the appropriate synthetic schemes and screened for their in vitro antihyperglycemic activity by estimating glucose uptake by rat hemi-diaphragm, both in the absence and in the presence of external insulin. Some of the glitazones exhibited good antihyperglycemic activity in presence of insulin. Illustration about their design, synthesis, evaluation, and structure-activity relationships is described.

Full text of DOI:10.1016/j.bmcl.2010.01.125

Bioorganic & Medicinal Chemistry Letters 20 (2010) 1953–1956
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Novel glitazones: Design, synthesis, glucose uptake and structure–activity
relationships
B. R. Prashantha Kumar a, M. J. Nanjan b,
*
a Department of Pharmaceutical Chemistry, J.S.S. College of Pharmacy, Ootacamund 643 001, Tamilnadu, India
b TIFAC CORE, J.S.S. College of Pharmacy, Ootacamund 643 001, Tamilnadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Glitazones are known to exhibit antihyperglycemic activity by decreasing peripheral insulin resistance. In
the present study, we have designed some novel glitazones based on the structure–activity relationships
as possible PPAR-c agonists. The manually designed glitazones were synthesized by using the appropri-
ate synthetic schemes and screened for their in vitro antihyperglycemic activity by estimating glucose
uptake by rat hemi-diaphragm, both in the absence and in the presence of external insulin. Some of
the glitazones exhibited good antihyperglycemic activity in presence of insulin. Illustration about their
design, synthesis, evaluation, and structure–activity relationships is described.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 25 October 2009
Revised 22 January 2010
Accepted 25 January 2010
Available online 1 February 2010
Keywords:
Glitazones
Glucose uptake
Diabetes
PPAR-
c
Antidiabetic activity
Type-2 diabetes mellitus is a chronic metabolic disorder that re-
sults from defects in both insulin secretion and insulin action.
Although it has been primarily regarded as a disorder of glucose
metabolism and homeostasis, more recently it has been viewed
as a constellation of metabolic disturbances.1 Diabetes is a global
burden and is rising all over the world due to various reasons.2
Thiazolidinediones or glitazones, specifically targeted to combat
insulin resistance, offered a new approach to the treatment of
type-2 diabetes as ‘insulin sensitizers’.3 In December 1997, the first
drug from this class, troglitazone4 was suspended from marketing
in the UK due to concerns of drug-induced hepatotoxicity. In June
1998, the National Institute of Health terminated a study investi-
gating troglitazone’s potential for preventing type-2 diabetes due
to documented cases of fatal hepatotoxicity.
In 1999, two new thiazolidinediones, pioglitazone and rosiglit-
azone, were approved by the US FDA for the treatment of type-2
diabetes. To date, the incidence of hepatotoxicity appears to be
minor with both pioglitazone and rosiglitazone. There are, how-
ever, other factors that limit the use of these drugs such as weight
gain, congestive heart failure etc. There is, therefore, a need for the
development of newer and safer drugs from this class.5
tisers are currently under investigation. Some of these belong to
the glitazone class, but others have different chemical structures.7,8
In recent years, we have been engaged in a research program di-
rected towards the development of novel glitazones. We have
made efforts to elucidate quantitative structure–activity relation-
ships,9,10 developed methods to synthesize glitazones efficiently11
and screened them for their antihyperglycemic activity.12 In the
present communication we describe results on designing some no-
vel glitazones, their synthesis, glucose uptake activity, and their
structure–activity relationships.
From our previous studies we have learnt that glitazones nor-
mally need to possess a polar thiazolidinedione ring system as a
head followed by hydrophobic benzyloxy moiety as trunk linked
by a two carbon atom linker and a hydrophobic ring as a tail for
better antihyperglycemic activity (Fig. 1).13
Keeping these structural features in mind, we have designed
newer glitazones having structures similar to this template phar-
macophore structure. The synthetic scheme adopted is shown in
Scheme 1. The tail part was first designed and synthesized, by con-
Glitazones are agonists for the peroxisome proliferator-acti-
vated receptor, PPAR-c, which regulates the transcription of insu-
S
O
HN
lin-responsive genes involved in the control of glucose
O
O
production, transport, and utilization.6 Several new insulin sensi-
Polar head
Hydrophobic
trunk
Two carbon
linker
Hydrophobic
ring tail
* Corresponding author. Tel./fax: +91 423 2447135.
E-mail address: mjnanjan@gmail.com (M.J. Nanjan).
Figure 1. Simplified, typical pharmacophore structure of PPAR agonists.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.01.125

1954
B. R. Prashantha Kumar, M. J. Nanjan / Bioorg. Med. Chem. Lett. 20 (2010) 1953–1956
Table 1
O
O
List of glitazones synthesized and their effect on glucose uptake by the isolated rat
hemi-diaphragm
[a]
O
Cl
Cl
N
H
R
NH2
R
Cl
Compd
R
X
Glucose uptake (mg/g/45 min)
1
No insulin
With insulin
[b]
N
N
H
**
4
5
O
S
12.25 1.37
32.00 0.91
30.00 0.81
O
N
R
O
H
2
*
9.75 1.25
O
[c]
6
O
S
9.50 1.32
11.75 1.03
12.00 1.29
8.0 1.08
27.25 1.10
30.00 0.91*
28.50 1.19
24.75 0.85
31.75 1.31**
26.75 0.85
O
O
7
N
H
R
O
S
O
4-16
O
8
O
S
HN
HN
X
X
[d]
O
9
10
11
12
13
O
S
10.50 0.64
10.25 1.10
10.75 0.85
9.75 0.47
CH2
CH2
N
H
R
O
S
O
17,18
**
36.25 1.10
O
S
O
O
Scheme 1. Synthesis of glitazones. Reagents and conditions: (a) CHCl3, triethyl-
amine, 0–5 °C to rt, stirred for 6 h, 90–99%. (b) Acetone, vanillin, K2CO3, stirred at rt
for 36 h, 65–80%. (c) Toluene, 3 or rhodanine, piperidine, acetic acid, molecular
sieves, reflux, 110 °C for 15 h or MW irradiation 700 W, 30 min, 70–81%. (d) Acetic
acid, 5% Pd on charcoal, H2 at 50 Psi, 14 h, 85–87%.
33.50 1.19**
29.00 0.91
O
14
15
O
10.00 0.70
9.75 0.85
NH2
necting various aromatic/alicyclic amines with the two carbon lin-
ker. The acylated amines 1 were then connected to the p-hydroxy
group of vanillin to obtain 2. Vanillin, instead of p-hydroxy benzal-
dehyde, was used because vanillin is a natural product. There are
no reports so far about glitazones which are incorporated with a
natural substrate like vanillin as part of their trunk. The trunk
which is connected with the hydrophobic tail via the two carbon
linker was then connected to the head group thiazolidinedione 3
or its bioisoster, that is, 2-thiaxo-thiazolidine-4-one or rhodanine
ring system to obtain 4–16. Compounds 12 and 13 were further
subjected to hydrogenation to reduce C@C using 5% Pd on charcoal
to get the compounds 17 and 18 (Table 1).
NO2
NO2
O
S
26.25 1.03
25.50 0.64
16
17
9.00 0.70
O
S
11.25 0.85
30.25 0.85*
28.25 0.85
O
O
18
9.50 0.64
**
35.25 1.25
Std
Rosiglitazone
11.25 0.47
Thiazolidinedione
3 was prepared by reacting equimolar
*
**
Group 1: 8.75 0.75, Group 2: 25.25 1.1. P <0.05, P <0.01, Std: standard drug.
amounts of chloroacetic acid and thiourea under ice cold condi-
tions. The white precipitate of 2-imino thiazolidine-4-one obtained
was then acidified and refluxed with HCl for 12 h to get white crys-
tals of thiazolidinedione (Scheme 2).11 All the compounds were
analyzed using IR, 1H NMR, 13C NMR, and HRMS analytical
methods.14
O
S
O
[a]
Cl
H2N
NH2
NH
NH
OH
S
The antidiabetic activities of compounds 4–18 were measured
using glucose uptake by rat hemi-diaphragm according to the
methods described by Walaas15 and Chattopadhyay.16 The institu-
tional animal Ethics Committee (IAEC) of JSS College of Pharmacy
approved the proposal. Rat diaphragm was selected because stri-
ated muscle is quantitatively the most important tissue for glucose
disposal in the animal body. The glucose content was measured17
and the glucose uptake was calculated as the difference between
the initial and final glucose content. Data were expressed as
mean standard error of mean (SEM) and shown in Table 1.18
Statistical comparisons between the groups were performed in
two sets using one-way ANOVA followed by Dunnet’s multiple
comparison post-test using graphPad Prism 4.0 software for Win-
dows (San Diego, California, USA). In the first set, group 1 that
served as a control was compared with groups 3–18 including
the analogous standard drug (rosiglitazone). In the second set
group 2 that served as control was compared with groups 19–34.
[b]
O
NH
S
3
O
Scheme 2. Preparation of thiazolidine-2,4-dione. Reagents and conditions: (a) 0–
5 °C, water, stirring for 15 min. (b) HCl, reflux 12 h, 89%.
We neither compared set one versus set two groups nor all the
groups with each other, as it is well known biologically that insulin
enhances the glucose uptake. The focus was, therefore, turned to
comparing the differences made by the presence of compounds.
There is a reasonable correlation between the groups 3–18 ver-
sus groups 19–34 with a correlation coefficient value of 0.2982

B. R. Prashantha Kumar, M. J. Nanjan / Bioorg. Med. Chem. Lett. 20 (2010) 1953–1956
1955
doing extremely good as many of the compounds in the series con-
tain the same. Two carbon linker in the form of amide (CH2CONH)
which is the common structural moiety in all the compounds ap-
pears to be a requirement for the activity.
The hydrophobic tail part which differs in most of the com-
pounds is of major interest. Compound 12 with anisidine moiety
is the most active compound from this series, even when compared
with the standard drug (rosiglitazone). Compound 13 with a simi-
lar tail and rhodanine as a head also show equally good activity.
This prompted us to go one step ahead with these compounds.
Hence, we reduced the C@C of compounds 12 and 13 to yield com-
pounds 17 and 18. Compounds 17 and 18, however, failed to meet
the expectations.
40
30
20
R2 = 0.2982
5
10
15
Absence of insulin
Figure 2. Correlation between the groups 3–18 versus groups 19–34.
In conclusion, we have found a new series of glitazones with
different body make up having promising levels of glucose uptake
activity. Compound 12 seems to be the candidate compound to
investigate further for its safety and efficacy. The in vitro and
in vivo studies on the title compounds will be reported in due
course.
(Fig. 2). This indicates some degree of correlation for the com-
pounds with respect to their glucose uptake enhancement in the
absence and the presence of insulin.
The results of the in vitro glucose uptake study indicate that all
the compounds enhance the glucose uptake by the tissue except
compound 9 (groups 8 and 24). The compounds exhibit from weak
to moderate and from moderate to significant glucose uptake. The
results also reveal one key aspect, namely, the compounds signifi-
cantly enhance the glucose uptake in the presence of the insulin
rather in the absence of external insulin. It is quite evident, there-
fore, that this class of compounds tends to sensitize the tissue to
take up insulin which later enhances the glucose utilization by
the tissue cells.19 Out of the 15 compounds, compounds 12 (group
27), 13 (group 28), 4 (group 19), and 10 (group 25) including ros-
iglitazone significantly enhance the glucose uptake in the presence
of insulin. Compound 12 is seen to be the most active compound
even when compared to rosiglitazone. It is, therefore, a candidate
compound to investigate further. Compounds 17 (group 32), 5
(group 20), and 7 (group 22) exhibit reasonably good glucose up-
take in the presence of insulin.
Acknowledgments
Mr. Prashantha Kumar would like to thank Dr. S. Chandrashek-
aran, Chairman, Department of Organic Chemistry, IISc, Bangalore,
India, for allowing him to work in his laboratory. The authors
would like to thank Mr. Kuldeep Singh, Mr. Mohan Patil and Mr.
Vadivelan, Department Pharmacology, JSS College of Pharmacy,
Ooty for their help in pharmacological screening.
References and notes
1. (a) Turner, N. C. Drug Discovery Today 1996, 1, 109; (b) Viberti, G. J. Diabetes
Complications 2005, 19, 168.
2. (a) Wild, S.; Roglic, G.; Green, A.; Sicree, R.; King, H. Diabetes Care 2004, 27,
1047; (b) Alan, R. S. Cell 2001, 104, 517.
We have also investigated the structure–activity relationships
based on the results obtained. In doing so, we defined the pharma-
cophore part of the structure by aligning energy minimized and
conformationally analyzed structures against common substruc-
ture and the most active compound 12 by atom fit method using
Sybyl 6.7 software (Tripos, USA).20 The superimposed common
part of the structure, namely, polar thiazolidinedione or its bioisos-
teric rhodanine head followed by hydrophobic benzyloxy trunk
which in turn is connected with two carbon linker in association
with the amide bond, seems to be the pharmacophore (Fig. 3). If
we disconnect and analyze individually the different parts of the
structures, it seems that compounds with thiazolidinedione moiety
as a head group shows better activity when compared to its bioiso-
stere rhodanine. Compound 7 alone is an exception to this state-
ment. This indicates the necessity of a relatively more polar
head. Regarding the hydrophobic trunk part, it appears vanillin is
3. (a) Olefsky, J. M.; Saltiel, A. R. Diabetes 1996, 45, 1661; (b) Benardeau, A.; Benz,
J.; Binggeli, A.; Blum, D.; Boehringer, M.; Grether, U.; Hilpert, H.; Kuhn, B.;
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Bioorg. Med. Chem. Lett. 2009, 19, 2468; (c) Maccari, R.; Ottanà, R.; Ciurleo, R.;
Rakowitz, D.; Matuszczak, B.; Laggner, C.; Langer, T. Bioorg. Med. Chem. 2008,
16, 5840.
4. Janine, C.; Menciu, C.; Rakotoarisoa, H.; Kahn, P. H.; Desmurs, J. R. Bioorg. Med.
Chem. Lett. 1999, 9, 3439.
5. (a) Helen, D. B.; James, S. K.; Linda, A. J. Diabetes Res. Clin. Pract. 2007, 76, 279;
(b) Nissen, S. E.; Wolski, K. N. N. Eng. J. Med. 2007, 356, 2457; (c) Peraza, M. A.;
Burdick, A. D.; Marin, H. E.; Gonzalez, F. J.; Peters, J. M. Toxicol. Sci. 2006, 90,
269.
6. Michaael, L.; Mitchell, A. L. Cell 2005, 123, 993.
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Hagmann, Ed.; Academic Press: USA, 1999; vol. 35, pp 211–220; (b) Kuhn, B.;
Hilpert, H.; Benz, J.; Binggeli, A.; Grether, U.; Humm, R.; Maerki, H. P.; Meyer,
M.; Mohr, P. Bioorg. Med. Chem. Lett. 2006, 16, 4016; (c) Sundriyal, S.; Viswanad,
B.; Bharathy, E.; Ramarao, P.; Chakraborti, A. K.; Bharatam, P. V. Bioorg. Med.
Chem. Lett. 2008, 18, 3192.
9. Prashantha Kumar, B. R.; Nanjan, M. J. Indian J. Pharm. Sci. 2008, 705, 565.
10. Prashantha Kumar, B. R.; Desai, B. J.; Vergheese, J.; Praveen, T. K.; Suresh, B.;
Nanjan, M. J. Lett. Drug Design Discovery 2008, 5, 79.
11. Prashantha Kumar, B. R.; Karvekar, M. D.; Adhikary, L.; Nanjan, M. J.; Suresh, B.
J. Heterocycl. Chem. 2006, 43, 897.
12. Prashantha Kumar, B. R.; Praveen, T. K.; Nanjan, M. J.; Karvekar, M. D.; Suresh,
B. Indian J. Pharmacol. 2007, 39, 299.
13. Prashantha Kumar, B. R.; Nanjan, M. J. Med. Chem. Res. 2009, 18 (doi:10.1007/
s00044-009-9246-0).
14. Structural data for some representative molecules (12): IR (KBr) 3369, 3200,
3072, 3005, 1697, 1676, 1514, 1271, 1151, 1037, 829; 1H NMR (400 MHz,
DMSO-d6) d 3.70 (s, 3H, CH3), 3.85 (s, 3H, CH3), 4.74 (s, 2H, CH2), 6.88 (d,
J = 9.02 Hz, 2H, ArH), 7.06–7.25 (m, 3H, ArH), 7.50(d, J = 9.02 Hz, 2H, ArH), 7.74
(s, 1H, @CH), 9.93 (s, 1H, NH), 12.50 (bs, 1H, NH); 13C NMR (400 MHz, DMSO-
d6) d 55.12, 55.64, 67.90, 113.87, 121.02, 123.35, 126.62, 131.42, 131.93,
149.17, 149.38, 155.51, 165.53, 167.33; HRMS (ES-TOF) m/z found 437.0013
(M+Na)+, calcd 437.0 (M+Na)+. (13) IR (KBr) 3367, 3198, 3072, 3001, 1708,
1678, 1512, 1442, 1209, 1037, 831; 1H NMR (400 MHz, DMSO-d6) d 3.71 (s, 3H,
CH3), 3.86 (s, 3H, CH3), 4.75 (s, 2H, CH2), 6.87 (d, J = 9.04 Hz, 2H, ArH), 6.89–
7.22 (m, 3H, ArH), 7.51(d, J = 9.04 Hz, 2H, ArH), 7.59 (s, 1H, @CH), 9.97 (s, 1H,
NH), 13.73 (bs, 1H, NH); 13C NMR (400 MHz, DMSO-d6) 55.12, 55.66, 67.79,
Figure 3. Energy minimized, aligned image of all the synthesized and screened
glitazones.

1956
B. R. Prashantha Kumar, M. J. Nanjan / Bioorg. Med. Chem. Lett. 20 (2010) 1953–1956
113.86, 120.97, 123.24, 124.09, 126.58, 131.40, 131.70, 149.23, 149.72, 155.46,
Group 18: 2 ml of Tyrode solution with 2000 mg/l glucose and 2 mg of
rosiglitazone (standard). Groups 19–33: 2 ml of Tyrode solution with 2000 mg/
165.41, 195.69; HRMS (ES-TOF) m/z found 453.0118 (M+Na)+, calcd 453.0
(M+Na)+. (17) 1H NMR (500 MHz, DMSO-d6) d 3.03 (dd, J = 14.5, 5.0 Hz, 1H,
CH2), 3.35 (dd, J = 14.5, 5.0 Hz, 1H, CH2), 3.73 (s, 3H, CH3), 3.79 (s, 3H, CH3), 4.61
(s, 2H, CH2), 4.88 (dd, J = 9.5, 4.0 Hz, 1H, CH), 6.75 (d, J = 8.5 Hz, 1H, ArH), 6.89
(d, J = 9.0 Hz, 2H, ArH), 6.90 (s, 1H, ArH), 6.93 (d, J = 8.5 Hz, 1H, ArH), 7.52 (d,
J = 9.0 Hz, 2H, ArH), 9.86 (s, 1H, NH), 12.04 (bs, 1H, NH); 13C NMR (400 MHz,
DMSO-d6) 36.97, 52.92, 55.11, 55.59, 68.67, 113.36, 113.82, 114.49, 121.11,
130.76, 131.37, 146.46, 148.99, 155.45, 166.08, 171.69, 175.82; HRMS (ES-TOF)
m/z found 439.0026 (M+Na)+, calcd 439.0 (M+Na)+.
l glucose, regular insulin 5
test compound 4–18. Group 34: 2 ml of Tyrode solution with 2000 mg/l
glucose, regular insulin containing 0.2 units of insulin and 2 mg of
ll containing 0.2 units of insulin and 2 mg of the
5 ll
rosiglitazone (standard). 68 Wistar rats of either sex were maintained on a
standard pellet diet, water ad libitum, and fasted overnight. The animals were
killed by decapitation and diaphragms were taken out swiftly avoiding trauma
and divided into two halves. The hemi-diaphragms 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 incubated 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 kit and Merck-Microlab 200
analyser.
15. Walaas, E.; Walaas, O. J. Biol. Chem. 1952, 195, 367.
16. Chattopadhyay, R. R.; Sarkar, S. K.; Ganguly, S.; Banerjee, R. N.; Basu, T. K. Indian
J. Physiol. Pharmacol. 1992, 36, 137.
17. (a) Trinder, P. Ann. Clin. Biochem. 1964, 6, 24; (b) Scand J. Clin. Lab. Invest. 1960,
12, 402.
18. (a) Glucose uptake measurement: Six well microtitre plates were selected for the
study with each well capacity of 5 ml (n = 4). Plates were divided into following
groups; Group 1: 2 ml of Tyrode solution with 2000 mg/l glucose. Group 2:
2 ml of Tyrode solution with 2000 mg/l glucose and regular insulin (Nova
19. (a) Feige, J. N.; Gelman, L.; Michalik, L.; Desvergne, B.; Wahli, W. Prog. Lipid Res.
2006, 45, 120; (b) Sohda, T.; Mizuno, K.; Imamiya, E.; Sugiyama, Y.; Fujita, T.;
Kawamatsu, Y. Chem. Pharm. Bull. 1982, 30, 3580; (c) Rose, D. P.; Connolly, J. M.
Pharmacol. Ther. 1999, 83, 217.
Nardisk, 40 IU/ml) 5
Tyrode solution with 2000 mg/l glucose and 2 mg of the test compound 4–18.
l
l containing 0.2 units of insulin. Groups 3–17: 2 ml of
20. SYBYL 6.7, Tripos Inc., 1699 South Hanley Road, St. Louis, MO 631444, USA.
www.tripos.com.