Studies on some glitazones having pyridine as the linker unit

Article abstract of DOI:10.1016/j.bmc.2003.11.027

Molecular modeling on various well-known glitazones carrying a pyridine ring instead of benzene ring as the middle linker unit showed conformational rigidity as compared to their parent molecules. Blocking the lone pair of electrons on the pyridine N, made them flexible once again. A few representatives of these analogues were synthesized and their efficacy as PPARγ agonists evaluated.

Full text of DOI:10.1016/j.bmc.2003.11.027

Bioorganic & Medicinal Chemistry 12 (2004) 655–662
Studies on some glitazones having pyridine as the linker unit§
Uma Ramachandran,a,* Alka Mital,a Prasad V. Bharatam,b Smriti Khanna,b
Poduri Rama Rao,c Krishnamoorthy Srinivasan,c Rakesh Kumar,a
Harmander Pal Singh Chawla,a Chaman Lal Kaul,a Suryaprakash Raichurd and
Ranjan Chakrabartid
aDepartment of Pharmaceutical Technology, National Institute of Pharmaceutical Education and Research (NIPER),
Sector 67, S.A.S. Nagar-160 062, India
bDepartment of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER),
Sector 67, S.A.S. Nagar-160 062, India
cDepartment of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER),
Sector 67, S.A.S. Nagar-160 062, India
dDr.Reddy’s Laboratories-Discovery Research, Bollaram Road, Miyapur, Hyderabad 500 050, India
Received 2 June 2003; accepted 26 November 2003
Abstract—Molecular modelingon various well-known glitazones carryinga pyridine ringinstead of benzene ringas the middle linker
unit showed conformational rigidity as compared to their parent molecules. Blocking the lone pair of electrons on the pyridine N, made
them flexible once again. A few representatives of these analogues were synthesized and their efficacy as PPARg agonists evaluated.
# 2003 Elsevier Ltd. All rights reserved.
1. Introduction
A series of 5-(4-alkoxybenzyl) 2,4-thiazolidinediones
were reported by Sohda et al.10 as antihyperglycemic
agents. The representative agent ciglitazone lowered
elevated glucose plasma insulin and triglyceride levels in
insulin resistant animals but showed no hypoglycemic
effect in non-diabetic or streptozotocin induced diabetic
rats.11 Because of the several attractive features, such as
improvement of insulin sensitivity and lack of hypogly-
cemia, the last few years have seen development of
many agents of this type such as troglitazone, pioglita-
zone, and rosiglitazone. Although troglitazone was
withdrawn in the early 2000 on the basis of idiosyncratic
hepatotoxicity, several more are progressing through
clinical development.12,13 The medical needs drivingthis
investment are the desire for greater degree of glucose
lowering, and also the potential reductions in plasma
triglycerides which is now known to increase not only
insulin sensitivity but leptin sensitivity as well.14
Type 2 diabetes (non-insulin dependent diabetes melli-
tus-NIDDM) is a complex metabolic disorder char-
acterized by hyperglycemia and/or insulin resistance,
and is often associated with other disorders such as
obesity, hypertension and hyperlipidemia.1À4 The type 2
diabetes is the most common type and accounts for
more than 90% of the diagnosed cases of diabetes.
The discovery of nuclear receptor peroxisome pro-
liferator activated receptors, PPARg and PPARa as
molecular targets5,6 for antidiabetic thiazolidinediones
(TZDs) has heralded a new era in the approach to under-
standingthe patho-physiology of insulin resistance and
its relationship to cardiovascular diseases.7À9 The thiazo-
lidinediones which are high affinity agonists for PPARg
led to the proposal that ligand-dependent modulation of
gene transcription through PPARg is an important phar-
macological target for treating type 2 diabetes.9
The compounds of this class have a few essential phar-
macophore elements. These comprise of an acidic group
linked to a central flat ringand a large lipophilic sub-
structure. Various structural modifications containing
these essential features have been reported. But there
are very few reports where the central phenyl linker
Keywords: Type 2 diabetes; AM1 calculations; Pyridine analogues of
TZDs; Conformational rigidity; Transactivitaion; PPARg agonists.
* Correspondingauthor. Tel.: +91-01-7221-4682; fax: +91-01-7221-
4692; e-mail: umaram54@yahoo.com
§NIPER communication number 238.
0968-0896/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2003.11.027

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U.Ramachandran et al./ Bioorg.Med.Chem.12 (2004) 655–662
fragment is replaced. Those reported are with thio-
phene,15 naphthalene,16 benzofuran,17 benzoxazole18
and pyridine.10,19,20,21 This central linker is essentially a
planar, aromatic ring and has been suggested to have
hydrophobic and p–p stackinginteractions while bind-
that 2a conformation should be the preferred con-
formation of the pyridine derivative of pioglitazone. A
Boltzman population estimate indicates that 2a struc-
ture is much more populated than 2, in the ratio 1:2353
(Table 1). Similar rotational process in 1 shows an
energy difference of only 0.04 kcal/mol with a barrier of
only 1.77 kcal/mol at AM1 level. This suggests that
there is an inherent conformational rigidity to the pyri-
dine derivative of pioglitazone, originating because of
the lone-pair repulsions on N and O. This observation
was also confirmed by the ab initio28 HF/3-21G*//AM1
calculations performed on 2 and 2a, which show an
energy difference (ÁE) of 5.17 kcal/mol and a rotational
barrier of about 6.50 kcal/mol. This is further supported
by the same study in the solvent phase usingthe Self-
consistent Reaction Field (SCRF)29 with water
(e=78.39) as solvent, which shows ÁE value of 5.07
kcal/mol and rotational barrier of 6.89 kcal/mol. Fig. 2a
and 2b shows the 3-D structures of 1 and 2a.
22
ingto the receptor. It also restricts the conformations
of terminal lipophilic fragment. There is some con-
troversy regarding the antidiabetic activity when this
central linker fragment is substituted by pyridine. Some
TZDs havinga pyridine ringinstead of the benzene ring
in the 4-oxyaryl position were reported to have weaker
activities.10 However, pyridyl analogues of some other
thiazolidinediones,19 2,4-oxazolidinediones20 and tetra-
zoles23 exhibited potent glucose and lipid-lowering
activities.
We carried out semi-empirical AM1 calculations to
understand the electronic features, which control the
conformational preferences of a series of glitazones with
pyridine as the central ring. This was followed up by the
synthesis of some of them and checkingtheir PPAR
agonist activity.
The AM1 studies on the pyridine derivatives of rosigli-
tazone 6, troglitazone 7, bromo derivative of rosiglita-
zone 8, and indole derivative of glitazone 9 (Fig. 1),
showed large rotational barriers, 4.84, 5.30, 4.93 and
5.40 kcal/mol respectively, which amounts the Boltzman
ratios of 1:3404, 1:2016, 1:3946 and 1:4606 respectively.
This suggests that the replacement of the central ben-
zene ringin well-known glitazones with a pyridine ring
2. Molecular modeling and chemistry
Semi-empirical AM1 calculations24 were performed on
pioglitazone 1 (Fig. 1) to identify the most stable con-
formation. Complete optimizations on 1 showed that
the most stable conformation has an almost planar
arrangement, except that the thiazolidinedione ring
(ringA) is on a slightly elevated plane to the rest of the
molecule. The C1–C2–O3–C4 and C2–O3–C4–C5 tor-
sional angles are about 180ꢀ (Fig. 1). This gas phase
optimized structure is slightly different from the bioac-
tive conformation which gives U-shape as in rosiglita-
zone,25 the energy difference between the global
minimum and the bioactive conformation is only about
0.2 kcal/mol at AM1 level. A U-shaped conformation is
required for the drugto be an effective agonist because
the PPAR homodimer and PPAR-RXR heterodimer
possesses a Y-shaped active site, such that the U-shaped
glitazone can fit in two arms of the Y-shaped active
site.26,27 The modelingstudies reported here are based
on the bioactive (U-shaped) conformation of glitazones
and their derivatives.
AM1 calculations were then carried out on 2, where the
central benzene ringof 1 is replaced by pyridine. Com-
plete optimizations of 2 lead to a local minimum struc-
ture, conformational analysis on 2 showed that 2a,
which is more stable by about 4.62 kcal/mol, is the glo-
bal minimum on the potential energy (PE) surface of 2.
The differences in the structures 2 and 2a are due to the
torsional angle N1–C2–O3–C4 being 180ꢀ in 2 and 0ꢀ in
2a. This change in the conformation of the most stable
structure of 2 indicates that the replacement of benzene
with pyridine in 1 leads to some instability, which can
be attributed to the repulsive interactions between the
lone pairs of electrons on N1 and O3 in 2. The AM1
calculated rotation barrier for the rotation across the
C2–O3 bond in 2 is ꢁ0.32 kcal/mol and that in 2a is
4.94 kcal/mol. This C2–O3 rotational process indicates
Figure 1. Structures of pyridine derivatives of some glitazones.

U.Ramachandran et al./ Bioorg.Med.Chem.12 (2004) 655–662
657
Table 1. Heats of formation (Hf) and relative energuies (kcal/mol) of various conformers across C2–O3 rotational path of Pioglitazone and i9ts
derivatives
Compd
Hf-180ꢀ
Hf-0ꢀ
Hf-TS
ÁHf
Rotational barrier
Population ratio
1
2
3
4
5
À57.77
À42.44
À35.11
102.16
106.16
À57.73
À47.06
À35.06
103.08
107.06
À55.99
À42.12
À34.73
106.70
109.70
0.04
4.62
0.05
0.45
1.00
1.77
4.94
0.38
3.86
3.53
1:1
1:2353
1:1
2:1
5:1
Figure 3. The PE surface for the rotation across C2–O3 bond in the
derivatives of pioglitazone.
The above molecular modelingstudies indicate that
substitution of benzene ringin glitazones with pyridine
as a linker unit brings in conformational rigidity in gli-
tazones (Fig. 2b), which may be removed by converting
them to their correspondingN-oxides, protonated salts,
and methoiodide salts.
Figure 2. (a) 3-D structure of 1; (b) 3-D structure of 2a.
would lead to an increase in the conformational rigidity
of these systems, and the preferred conformation in
these systems is opposite to that of the parent glita-
zones.
To explore the effect of these novel pyridine analogues
on their biological action, we synthesized the pyridine
analogue of pioglitazone, 2; its HCl salt, 4 and N-oxide,
3 and N-oxide as its HCl salt, 3a (Scheme 1). We also
made pyridine analogue of troglitazone, 7, its N-oxide
22 and HCl salt 23 (Scheme 2). To our knowledge,
compounds havingN-oxides have never been tested for
antidiabetic activity.
Methods to eliminate the conformational rigidity in 2 in
order to make the pyridine derivatives as flexible as
pioglitazone, were explored. Ideally, it can be done by
converting 2 to its HCl salt. We carried out AM1 cal-
culations on 2 with protonation at various possibilities
and found that the most favored protonation site is N1
(Fig. 1) hence the HCl salt of 2 is expected to have a
structure 4. The C2–O3 rotational barrier in 4 is 3.86
kcal/mol and the ÁE between the rotamers is 0.45 kcal/
mol. Boltzman population analysis suggests that the
ratio of population of 4 and 4a are 2:1, indicatingthat
the relative preferences are much less pronounced and
conformational rigidity disappears in the HCl salt of 2.
Similarly the N-oxide derivative 3 and the methoiodide
salt 5 of 2, also showed a much reduced conformational
rigidity. Comparison of the relative energies and the
rotation barriers of the various conformations of these
derivatives is given in Table 1 and Figure 3. Similar
results have been observed in the protonated salts, N-
oxides and methoiodide salts of 6, 7, 8 and 9.
The thiazolidinediones represented by formulas 2 and 7
were synthesized accordingto the Schemes 1 and 2. The
pioglitazone analogue 5-[2-[2-(5-ethyl-2-pyridyl) ethoxy]
pyridyl methyl]-2,4-thiazolidinedione 2 was synthesized
by known procedures, startingfrom 5-ethyl-2-(2-
hydroxy-ethyl) pyridine, 10.30 Base mediated coupling
with 2-chloro-5-cyanopyridine, 11 followed by treat-
ment with Raney-nickel alloy in aqueous formic acid
furnished the aldehyde 13. Knoevenagel condensation
between 13 and thiazolidine-2,4-dione in the presence of
piperidinium acetate catalyst afforded pyridyl methylene
thiazolidinedione analogue 14. The olefinic bond in 14
was hydrogenated in 1,4-dioxane using 10% Pd-C in
equivalent amounts to give 2. In an alternative method
to prepare 2, 10 was coupled with 2-chloro-5-nitropyr-
idine, followed by hydrogenation to afford the amine

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U.Ramachandran et al./ Bioorg.Med.Chem.12 (2004) 655–662
Table 2. Activation of PPARw. HEK 293T cells were transfected
with Gal4-PPARw1LBD, pGL2(Gal 4Â5)-SV 40-Luc reporter and
pAdvantage constructs. These values are an average of three experi-
ments conducted in triplicate
PPARg—Fold Activation
Compd
Conc.
Rosiglitazone
2
3
3a
4
7
22
23
Scheme 1. Reagents: (i) NaH, THF (ii) Raney Ni, HCOOH (iii) 2,4-
TZD, piperidinium acetate toluene (iv) 10% Pd/C (v) MCPBA.
1 mM
10 mM
50 mM
21.7
28.3
34.7
1.6 0.6
3.3 2.7 10.1 10.2 18.8 19.8
1.8
2.3
3.0
4.0
1.3
9.6
*
*
17.8 20.1 23.7 25.4 28.1
*Compounds precipitated
vator, rosiglitazone. Activity of pioglitazone derivatives,
2 and 3 (both non-salt forms) could not be assessed due
to solubility problem. However, the N-oxide as its HCl
salt, 3a showed significant activity.
None of these compounds show any PPARa activation
even at 100 mM concentration, when tested with respective
plasmid. This is in keepingwith the fact that glitazones are
selective for PPARg over PPARa.
Scheme 2. Reagents: (i) NaH, MOMCl, DMF; (ii) 11, NaH, THF; (iii)
Raney Ni, HCOOH; (iv) TZD, Piperidinium acetate, toluene; (v) 10%
Pd/C, dioxane; (vi) gl. acetic acid, 10% H2SO4; (vii) MCPBA; (viii)
HCl.
4. Conclusions
derivative. The product of Meerwein arylation of
methyl acrylate and amine in the presence of cuprous
oxide could not be isolated in pure form. Oxidation of 2
with m-chloroperbenzoic acid gave N-oxide, 3; that the
pyridine ring of the linker fragment is the one to get
oxidized was confirmed by NMR studies. We failed to
obtain methoiodide salt in pure form.
Molecular modelingstudies on some well-known glita-
zones containingpyridine ringas the linker unit were
carried out. These studies showed that the pyridine
analogues by themselves suffer from restricted rotation,
which could be set right by suitable derivatization. This
led to the synthesis of some novel N-oxide glitazones.
Functional assay showed that they are PPARg agonists.
The troglitazone analogue 7 was synthesized according
to Scheme 2. Reduction of 6-hydroxy-2,5,7,8-tetra-
methyl chroman-2-carboxylic acid 15 gave the corres-
pondingalcohol 16. The phenolic group of 16 was
protected by the methoxymethyl (MOM) group and
coupled with 2-chloro-5-cyanopyridine to afford 18. The
other synthetic steps after this couplingwere similar to
the pioglitazone analogue 2.
5. Experimental
5.1. General experimental details
Semi-empirical AM1 calculations have been performed
33
usingGaussian 98 package
on pioglitazone, rosiglita-
zone, troglitazone, bromo derivative of rosiglitazone
and indole glitazone and their pyridine derivatives.
Complete optimisations have been performed on all
conformations considered in this work, at AM1 level.
Heats of formation values of various conformations
have been compared to estimate the relative energies of
the various conformations alongwith their rotation
barriers. The rotational barriers in 2 in gas phase and
solution phase have been estimated usingabsolute
energy estimates at HF/3-21G* level using AM1
optimised geometries.
3. Biological screening
3.1. PPAR transactivation
The conformational insights of some of these novel
pyridine analogues (2, 7) though interesting, will be dif-
ficult to test in actual biological systems, be it in binding
affinity or functional assays since these assays are done
in buffered system.
Thin layer chromatography analyses were performed on
precoated silica gel plates (F254, Merck). Chromato-
graphy was performed on flash silica gel (230–400
mesh). Meltingpoints were recorded on a Buchi capil-
lary meltingpoint apparatus and are uncorrected.
Infrared (IR) spectra were recorded on a Nicolet
Impact-410 FTIR spectrometer. Proton magnetic reso-
nance (NMR) spectra were recorded on a Bruker
300 MHz spectrometer in CDCl3 or DMSO-d6 solution.
However, we tested their PPAR agonist competence by
assayingtheir cells in cells transfected with a GAL4-
PPAR ligand binding domain chimer expression vector
and a luciferase reporter plasmid as described by Chak-
rabarti et al.31 The results of the PPARg transcriptional
activity by the compounds given in Table 2. As seen
from the study, 432, 7, 22 and 23 show significant but
less activity as compared to the known PPARg acti-

U.Ramachandran et al./ Bioorg.Med.Chem.12 (2004) 655–662
659
The chemical shifts are reported in d (ppm) relative to
internal standard tetramethylsilane (TMS) and coupling
constants J are given in Hz. Mass spectroscopy was
conducted usingShimadzu QP5000 mass spectrometer.
extracted with ethyl acetate. The organic extract was
washed with water, dried over sodium sulphate and
evaporated in vacuum to give 17.6g (92%) of crude 5-[2-
(5-ethyl-2-pyridyl) ethoxy] pyridonitrile, 12. The crude
product was purified by column chromatography to
yield 12.32 g(64.5%) of pure 12 as white solid (mp 88–
90 ꢀC). IR (cmÀ1) 3430, 2223, 1608, 1562, 1491, 1300,
996. MS (M+1)+ 254. 1H NMR (CDCl3) d 8.47 (1H, d,
J=1.9 Hz), 8.40 (1H, d, J=1.63 Hz), 7.75 (1H, dd,
J=2.3, 6.4 Hz), 7.45 (1H, dd, J=2.1, 5.8 Hz), 7.15 (1H,
d, J=7.85 Hz), 6.78 (1H, d, J=8.7 Hz), 4.75 (2H, t,
J=6.78 Hz), 3.24 (2H, t, J=6.77 Hz), 2.63 (2H, q,
J=7.57 Hz), 1.24 (3H, t, J=7.60 Hz). Anal. calcd for
C15H15N3O: C, 71.15; H, 5.93; N, 16.60. found C, 69.79;
H, 5.89; N, 16.06.
5.2. Biological study
The response element (UASGAL4X5) was cloned
upstream of the Pgl2-sv 40-Luc reporter (Promega,
Madison. WI, USA), which contains the Simian virus
early promoter for luciferase assay. GAL4 fusions were
made by fusinghuman PPAR g1 or PPARa ligand-
bindingdomain (amino acids: 174–475) to the C-term-
inal end of the yeast GAL4 DNA- bindingdomain
(amino acids: 1–147) of the pM1 vector. pAdVantage
(Promega, Madison, WI, USA) vector was used to
enhance luciferase expression.
5.2.3. 5-[2-(5-ethyl-2-pyridyl) ethoxy] pyridoxaldehyde
(13). A mixture of 5-[2-(5-ethyl-2-pyridyl) ethoxy]
5-pyridonitrile 12 (8 g, 31.6 mol), Raney-Ni alloy (16 g)
and formic acid (100 mL, 98-100%) was refluxed for 5
h. After filtration, the filtrate was diluted with water,
made alkaline with 4N KOH and extracted with diethyl
ether. The organic extract was washed with water, dried
over sodium sulphate and concentrated in vacuum to
give 5.48 g (68%) of 13. The crude product was purified by
chromatography using ethyl acetate/hexane (20/80 v/v) to
yield 2.85 g(35%) of 13 as white crystalline solid. (mp
64–67 ꢀC). IR (cmÀ1) 2967, 1683, 1605, 1565, 1493,
1357, 1292. MS (M+1)+ 257. 1H NMR (CDCl3) d 9.94
(1H, s), 8.61 (1H, s), 8.41 (1H, s,), 8.04 (1H, dd, J=2.26,
6.4 Hz), 7.45 (1H, dd, J=2.0, 5.9 Hz) 7.16 (1H, d,
J=7.89 Hz), 6.8 (1H, d, J=8.66 Hz), 4.79 (2H, t, J=6.78
Hz), 3.26 (2H, t, J=6.78 Hz) 2.63 (2H, q, J=7.59 Hz)
1.24 (3H, t, J=7.60 Hz) Anal. calcd for C15H16N2O2 : C,
70.31H, 6.25; N, 10.94; found C, 69.10; H, 6.46; N, 10.11.
HEK 293T cells were grown in Dulbecco’s modified
Eagle’s medium supplemented with 10% foetal bovine
serum (DMEM-FBS) at 37 ꢀC in 5% CO2Á. At 1 day
prior to transfection, cells were plated to 50–60% con-
fluence in DMEM containing10% delipidated FBS
(DMEM-DFBS). Cells were transfected by Superfect as
per the manufacturer’s protocol. At 3 h after transfec-
tion, the reagent was removed and cells maintained in
DMEM-DFBS. At 42 h after transfection, the cells were
placed in phenol red-free DMEM-DFBS, and treated
for 18 h with the test compounds or vehicle alone. The
cells were lysed and assayed for luciferase activity.
Luciferase activity was determined by usingLuclite kit
(Packard, CT, USA) in a Packard Top-count and
expressed as fold activation relative to untreated cells.
5.2.1. 2-Chloro-5-cyano pyridine (11). A mixture of 6-
chloro nicotinic acid (10 g, 0.064 mol) and thionyl
chloride (9.26 mL, 0.127 mol) were refluxed for 4 h. The
excess thionyl chloride removed by addingtoluene and
distillingunder vacuum. The resultingugm was dis-
solved in ether and dry ammonia gas was passed into
the solution; a white solid begins to precipitate. The
solution was filtered and the precipitate was leached
with hot acetone. The acetone layer was collected, dis-
tilled under vacuum to give 9 g (90.5%) of 6-chloro-
nicotinamide. (mp 208 ꢀC).
5.2.4. 5-[2-[2-(5-ethyl-2-pyridyl) ethoxy] pyridylmethy-
lene]-2,4 thiazolidinedione (14). A solution of pyridox-
aldehyde 13 (2.5 g, 9.8 mmol) and 2,4-thiazolidinedione
(1.26 g, 10.74 mmol) in toluene containing piperidinium
acetate (0.620 g, 4.9 mmol) was boiled under reflux in a
Dean–Stark water trap for 5 h. The solution was cooled
and filtered. The precipitate was washed with toluene.
The toluene layer was concentrated and cooled to give
1.38 g(40%) of 14 as a yellow solid. (mp 165–168 ꢀC).
1
IR (cmÀ1) 3433, 2960, 1702, 1596. MS 355.7. H NMR
The amide was refluxed with phosphrous oxychloride
(21.4 mL, 0.23 mol) and chloroform (60 mL) for 2.5 h.
The reaction mixture was concentrated and then poured
into ice water. The reaction mixture was extracted with
dichloromethane, washed with saturated sodium bicar-
bonate solution, water, dried and concentrated to give 7
g(88%) of 11 as white solid (mp 117–118 ꢀC). [lit. mp
117–118 ꢀC].
(DMSO-d6) d 8.47 (1H,d), 8.36 (1H, d), 7.85 (1H, dd,
J=2.45, 6.3 Hz), 7.76 (1H, s), 7.56 (1H, dd, J=2.05,
5.82 Hz), 7.25 (1H, d), 6.92 (1H, d), 4.68 (2H, t, J=6.66
Hz), 3.16 (2H, t, J=6.63 Hz), 2.58 (2H, q, J=7.54 Hz),
1.17 (3H, t, J=7.58 Hz). Anal. calcd for C18H17N3O3S:
C, 60.85; H, 4.79; N, 11.83; S, 9.02; found C, 59.96; H,
4.58; N, 11.45; S, 9.0.
5.2.5. 5-[2-[2-(5 ethyl-2-pyridyl) ethoxy] pyridyl methyl]-
2-4, thiazolidinedione (2). A mixture of 14 (1.35 g, 3.8
mmol), 10% palladium on carbon (1.35 g) in 1,4-diox-
ane (30 mL) was hydrogenated under 50 kg/cm2 at
50 ꢀC for 24 h. After removal of the catalyst by fil-
tration, the filtrate was concentrated in vacuum to give
5.2.2. 5-[2-(5-ethyl-2-pyridyl) ethoxy] 5-pyridonitrile
(12). To a stirred suspension of sodium hydride (5.45 g,
227.4 mol, 60% w/w dispersion) in dry THF was added
5-ethyl-2-(2-hydroxyethyl) pyridine, 10 (4 g, 75.8 mol) in
dry THF (20 mL), and the mixture was stirred for 30
min. A solution of 11 (10.5 g, 75.8 mol) in dry THF (20
mL) was added dropwise at 0 ꢀC. The reaction was stir-
red at 0 ꢀC for 2 h and then poured into ice water and
1.29 g(95%) crystals of 2 (mp 128–131 ꢀC). IR (cmÀ1
)
3430, 2965, 1739, 1706, 1605. MS (M+1)+ 358. 1H
NMR (DMSO-d6) d 8.28 (1H, s), 7.93 (1H,s), 7.49 (2H,

660
U.Ramachandran et al./ Bioorg.Med.Chem.12 (2004) 655–662
d), 7.17 (1H,d), 6.65 (1H, d), 4.83 (1H, m), 4.50 (2H, t,
J=6.65 Hz), 3.05 (4H, m), 2.52 (2H, q, J=7.5 Hz), 1.13
(3H, t, J=7.48 Hz) Anal. calcd for C18H19N3O3S: C,
60.59; H, 5.32; N, 11.76; S, 8.96; found C, 60.45; H,
5.10; N, 11.54; S, 8.90.
calcd for C16H24O4: C, 68.57; H, 8.57; found C, 67.88;
H, 8.45.
5.2.9.
[2-(6-(methoxymethoxy)-2,5,7,8-tetramethyl)-5-
pyrido-nitrile] methoxychroman (18). To a well stirred
and cooled mixture of 17 (1.5 g, 5.36 mmol) and 2-
chloro-5-cyano pyridine 11 (0.742 g, 5.36 mmol) in dry
THF (30 mL), sodium hydride 0.386 g(16.07 mmol)
was added gradually. The resultant mixture was stirred
for 2 h at room temperature, and then poured into ice
water and extracted with ethyl acetate. The extract was
washed with water, dried and concentrated to give 1.84
g(90%) of 18 as an oil. IR (cmÀ1) 3019, 1602, 1486,
5.2.6. 5-[2-[2-(5-ethyl-2-pyridyl) ethoxy pyridyl N-oxide
methyl]-2,4 thiazolidinedione (3). To a mixture of 2
(0.100 g, 0.28 mmol) in chloroform (1 mL) and metha-
nol (0.5 mL) was added m-chloroperbenzoic acid (60%,
0.056 g, 0.32 mmol) in one portion. The mixture was
allowed to stir overnight at room temperature and then
worked up by washingsubsequently with saturated
aqueous NaHCO3, aqueous sodium sulfite and with
brine. The organic layer was dried and concentrated in
vacuum to afford the product as an oil. IR (cmÀ1) 3345,
1
1396, 1292, 1254, 1215. MS (M+1)+ 383. H NMR
(CDCl3) d 8.45 (1H, s), 7.78 (1H, d) J=2.3, 6.4 Hz),
6.84 (1H, d), 4.85 (2H, s), 4.40 (2H, q), 3.61 (3H, s), 2.64
(2H, brt), 2.17 (3H, d), 2.02 (3H, s), 1.88 (2H, m), 1.38
(3H, s), 1.26 (3H, s). Anal. calcd for C22H26N2O4: C,
69.11; H, 6.81; N, 7.33; found C, 68.5; H, 6.5; N, 7.00.
1
2967, 1752, 1689, 788. MS 373. H NMR (DMSO-d6) d
8.37 (1H, d), 8.0 (1H, s), 7.41 (2H, d), 7.16 (1H, d) 6.66
(1H, d), 4.35 (1H, m), 3.95 (2H, t, J=7.22 Hz), 3.05
(4H, m), 2.62 (2H, q, J=7.5 Hz), 1.22 (3H, t, J=7.5
Hz). Anal. calcd for C18H19N3O4S; C, 57.91; H, 5.09; N,
11.26; S,8.58; found C, 57.55; H, 4.90; N, 11.01; S, 8.5.
5.2.10. [2-(6-(methoxymethoxy)-2,5,7,8-tetramethyl)-5-
pyridox -aldehyde] methoxychroman (19). A mixture of
18 (1.5 g, 3.9 mmol), Raney-Ni alloy (39 g) and formic
acid (20 mL, 98–100%) were refluxed for 5 h. After
removal of the alloy by filtration, the filtrate was diluted
with water, made alkaline with 4N KOH and extracted
with diethyl ether. The extract was washed with water,
dried and concentrated to give 1.36 g (90%) of crude
product which was purified by column chromatography
to give 0.272 g (20%) of pure aldehyde 19 as a viscous
oil. MS (M+1)+ 386. 1H NMR (CDCl3) d 9.95 (1H, s),
8.59 (1H, d), 8.07 (1H, dd, J=2.2, 6.5 Hz), 6.84 (1H, d),
5.30 (2H, s), 4.48 (2H, q), 4.28 (3H, s), 2.67 (2H, brt),
2.13 (3H, d), 2.06 (3H, s), 1.88 (2H, m), 1.58 (3H, s),
1.40 (3H, s). Anal. calcd for C22H27NO5: C, 68.57; H,
7.01; N, 3.64; found C, 67.4; H, 6.5; N, 3.5.
5.2.7. 6-hydroxy-2,5,7,8-tetramethylchroman-2-yl metha-
nol40 (16).
A mixture of 6-hydroxy-2,5,7,8-tetra-
methylchroman-2-carboxylic acid 15 (5 g, 0.02 mol),
absolute ethanol (25 mL) and concd sulfuric acid (1 mL)
refluxed for 5 h. The excess ethanol was concentrated,
residue was diluted with water and extracted with die-
thyl ether. The ether layer washed with brine, dried and
concentrated to give 5.56 g (100%) of the ethyl ester. IR
(cmÀ1) 3527, 2986, 1734, 1448, 1187. To a well stirred
mixture of lithium aluminium hydride (2.28 g, 0.06 mol
in dry THF (100 mL) was added this ethyl ester (5.56 g,
0.02 mol) in THF (25 mL) dropwise. After stirringfor
2 h at room temperature, the reaction mixture was
poured into ice water, acidified with diluted HCl and
extracted with diethyl ether. The extract was dried and
concentrated to give 6-hydroxy-2,5,7,8-tetra-methyl
chroman-2-yl methanol 16 as an oil (4.48 g, 95%). IR
5.2.11. 5-[2-(2-(6-(methoxymethoxy)-2,5,7,8-tetramethyl-
chroman-2-yl)methoxy)-2-pyridylmethylene]-2,4-thiazoli-
dinedione (20). A solution of 19 (0.250 g, 0.65 mmol)
and 2,4-thiazolidinedione (0.076 g, 0.65 mmol) in tolu-
ene containingpiperidinium acetate (0.042 ,g 0.33
mmol) was boiled under reflux in a Dean–Stark water
trap for 5 h. The solution was cooled and filtered. The
filtrate was concentrated to give 0.30 g (95%) of yellow
oil, purified by column chromatography to give 0.075 g
(25%) of pure 20. MS 484. 1H NMR (DMSO-d6) d 8.43
(1H, d), 8.01 (1H, d), 7.76 (1H, S), 6.86 (1H, d), 4.40
(2H, s), 4.28 (3H, s), 4.02 (2H, q), 2.57 (2H, brt), 2.02
(3H, d), 1.99 (3H, s), 1.88 (2H,m), 1.70 (3H, s), 1.30
(3H, s). Anal. calcd for C25H28N2O6S: C, 61.98; H, 5.79;
N, 5.79; S, 6.61; found C, 60.55; H, 5.00; N, 5.01; S, 6.0.
1
(cmÀ1) 3379, 2926, 1461, 1416, 1259, 1058. MS 236. H
NMR (CDCl3) d 3.61 (2H, t), 2.67 (2H, brt), 2.17 (3H,
s), 2.12 (3H, d), 1.94 (2H, m), 1.59 (3H, s), 1.22 (3H, s).
5.2.8. [6-(methoxymethoxy)-2,5,7,8-tetramethylchroman-
2-yl] methanol (17). Compound 16 (2 g, 8.5 mmol) was
dissolved in dry DMF (20 mL) and cooled to 5–10 ꢀC.
Sodium hydride (0.610 g, 25.4 mmol) was added gradu-
ally to the resultingsolution with stirringat 5–10 ꢀC.
The mixture was reacted for 1 h at room temperature
and then cooled to 3–5 ꢀC, and 0.682 g(8.5 mmol) of
chloro-methylmethyl ether dissolved in dry benzene (20
mL) was added drop wise. After the addition was com-
pleted the solution was stirred for 1 h at room tem-
perature. The reaction mixture was then poured into ice
water and extracted with cyclohexane. The extract was
washed with 5% aqueous NaOH solution and then with
water. It was then dried (Na2SO4) and the solvent was
evaporated, giving 1.97 g (83%) of 17 as a white solid.
(mp 56–59 ꢀC). IR (cmÀ1) 3435, 2924, 1593, 1455, 1396,
5.2.12. 5-[2-(2(6-(methoxymethoxy)-2,5,7,8-tetramethyl-
chroman -2-yl) methoxy)-2-pyridylmethyl]-2,4-thiazolidi-
nedione (21). A mixture of 20 (0.500 g, 10.33 mmol),
10% palladium on carbon (0.500 g) in 1,4-dioxane
(10 mL) was hydrogenated under 50 kg/cm2 at 50 ꢀC for
20 h. After removal of the catalyst by filtration, the fil-
trate was concentrated in vacuum to get 0.502 g (95%)
1
1
1055, MS 280. H NMR (CDCl3) d 5.32 (2H, s), 4.87
(2H, s), 3.61 (3H, s), 2.61 (2H, brt), 2.18 (3H, d), 2.09
(3H, s), 1.73 (2H, m), 1.59 (3H, s), 1.22 (3H, s). Anal.
of the oily hydrogenated product. H NMR (CDCl3) d
8.03 (1H,d), 7.58 (1H,d), 6.85 (1H, d) 4.62 (2H, s), 4.50
(1H, m), 4.30 (2H, q), 3.18 (2H, m), 2.67 (2H, brt), 2.13

U.Ramachandran et al./ Bioorg.Med.Chem.12 (2004) 655–662
661
(3H, d), 2.06 (3H, s), 1.88 (2H, m), 1.62 (3H, s), 1.38
(3H, s), 3.45 (3H, brs). MS 486. Anal. calcd for
C25H30N2O6S: C, 61.73; H, 6.17; N, 5.76; S, 6.58; found;
C, 60.5; H, 5.50; N, 5.5; S, 6.5.
10. Sohda, T.; Mizuno, K.; Imamiya, E.; Sugiyama, Y.;
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5.2.13. 5-[2-[2-(6-hydroxy-2,5,7,8-tetramethyl chroman-
2-yl) methoxy]-2 pyridyl methyl]-2,4-thiazolidinedione
(7). The product 21 was dissolved in gl. acetic acid (15
13. Rami, H. K.; Smith, S. A.Exp.Opin.Ther.Patents
10, 623.
2000,
mL) containing10% H SO4 (30 mL) and the mixture
2
heated at 90 ꢀC for 20 h. The reaction mixture cooled
and poured into a mixture of cold aq NaHCO3 solution
and extracted with diethyl ether. The extract was
washed with water, dried and concentrated to give 0.456
14. Chen, H. C.; Smith, S. J.; Ladha, Z.; Jensen, D. R.; Fer-
reira, L. D.; Pulawa, L. K.; McGuire, J. G.; Pitas, R. E.;
Eckel, R. H.; Farese, R. V. J.Clin.Invest. 2002, 109, 1049.
15. Hulin, B.; Clark, D. A.; Goldstein, S. W.; McDermott,
R. E.; Dambek, P. J.; Kappeler, W. H.; Lamphere, C. H.;
Lewis, D. M.; Rizzi, J. P. J.Med.Chem. 1992, 35, 1853.
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Gibbs, E. M.; Clark, D. A. J.Med.Chem. 1996, 39, 3897.
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1
g(85%) of 7 as an oil. MS (M+1)+ 443. H NMR
(CDCl3) d 7.99 (1H, s), 7.45 (1H, dd), 6.73 (1H, d), 4.51
(1H, m), 4,30 (2H, q), 3.18 (2H, m), 2.64 (2H, brt), 2.18
(3H, d), 2.07 (3H, s), 1.88 (2H, m), 1.38 (3H, s), 1.25
(3H, s). Anal. calcd for C23H26N2O5S: C, 62.44; H, 5.88;
N, 6.33; S, 7.24; found C, 61.40; H, 5.00; N, 6.20; S,
7.20.
19. Sohda, T.; Ikeda, H.; Imai, S.; Momose, Y. EP
0605228A1, 1994.
20. Momose, Y.; Maekawa, T.; Yamano, T.; Kawada, M.;
Odaka, H.; Ikeda, H.; Sohda, T. J.Med.Chem. 2002, 45,
1518.
21. Tetsuya, K.; Takashi, Y.; Takeshi, N.; Suke, O. K.; Kat-
suhiro, K.; Yoshio, O.; Mikio, S.; Nobuhide, M.; Chi, S.
K. WO 9526347, 1995.
22. Kulkarni, S. S.; Gediya, L. K.; Kulkarni, V. M. Bioorg.
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5.2.14. 5-[2-[2-(6-hydroxy-2,5,7,8-tetramethylchroman-2-
yl) methoxy]-2-pyridyl N-oxide methyl]-2,4-thiazolidine-
dione (22). To a mixture of 7(0.055 g, 0.12 mmol)in
chloroform (1 mL) and methanol (0.5 mL) was added
m-chloroperbenzonic acid (0.025 g, 0.143 mmol) in one
portion. The mixture was allowed to stir overnight at
room temperature and then worked up. Extracted with
methylene chloride and washed subsequently with satu-
rated aqueous NaHCO3, sodium sulfite and brine. The
organic layer dried and concentrated to give an oily
product 22. 1H NMR (CDCl3) d 8.05 (1H, d), 7.53 (1H,
dd), 6.75 (1H, d), 4.52 (1H, m), 4.30 (2H, q), 3.18 (2H,
m), 2.64 (2H, brt), 2.20 (3H, d), 2.07 (3H, s), 1.87 (2H,
m), 1.38 (3H, s), 1.25 (3H, s). Anal. calcd for
C23H26N2O6S: C, 60.26; H, 5.68; N, 6.11; S, 6.99;.
found; C, 60.00; H, 5.00; N, 6.0; S, 7.00.
23. Momose, Y.; Maekawa, T.; Odaka, H.; Ikeda, H.; Sohda,
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Acknowledgements
We thank Dr. C. S. Dey for his helpful discussions.
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