6-Aryl-4-methylsulfanyl-2H-pyran-2-one-3-carbonitriles as PPAR-γ activators

Article abstract of DOI:10.1016/j.bmcl.2005.05.031

Various 6-aryl-3-cyano/methoxycarbonyl-4-methylsulfanyl-2H-pyran-2-ones have been synthesized as a potential substitute of 2,4-thiazolidinedione head group to express potent PPAR-γ transactivation response. Some of the screened compounds have shown promis

Full text of DOI:10.1016/j.bmcl.2005.05.031

Bioorganic & Medicinal Chemistry Letters 15 (2005) 3356–3360
6-Aryl-4-methylsulfanyl-2H-pyran-2-one-3-carbonitriles as
PPAR-c activatorsq
Ashoke Sharon,a Ramendra Pratap,b Rit Vatsyayan,c Prakas R. Maulik,a Uma Roy,c
Atul Goelb and Vishnu Ji Ramb,*
aMolecular and Structural Biology Division, Central Drug Research Institute, Lucknow 226001, India
bMedicinal and Process Chemistry Division, Central Drug Research Institute, Lucknow 226001, India
cBiochemistry Division, Central Drug Research Institute, Lucknow 226001, India
Received 16 March 2005; revised 9 May 2005; accepted 10 May 2005
Abstract—Various 6-aryl-3-cyano/methoxycarbonyl-4-methylsulfanyl-2H-pyran-2-ones have been synthesized as a potential substi-
tute of 2,4-thiazolidinedione head group to express potent PPAR-c transactivation response. Some of the screened compounds have
shown promising PPAR-c agonistic activity.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
Diabetes is the fourth leading killer disease in the devel-
oped world. There are more than 200 million diabetics
worldwide, accounting for a huge economic and social
burden.1,2 Thus, the development of new effective thera-
Figure 1. Thiazolidinedione class of antidiabetic drugs.
peutic agents is the major thrust for research and is ger-
mane to both the national and international scenario.
Type 2 diabetes mellitus (T2DM) is the most important
type of diabetes, as more than 80% of diabetics are of
this class.
sensitizing properties of TZDs through PPARc with
minimum or no adverse side effects. This necessitated a
search for highly effective, safe, and orally active antihy-
perglycemic agents, particularly those that normalize
both insulin and glucose levels.
The peroxisome proliferator-activated receptors
(PPARs) are legitimate molecular targets for the devel-
opment of the antidiabetic agents. The reported synthet-
ic ligands such as rosiglitazone (I) and pioglitazone
(II)3,4 had high affinity for PPAR-c receptor, belong to
the thiazolidinedione class of antidiabetic agents (Fig.
1), and have significantly improved the clinical situation
of Type 2 diabetics with serious side effects of hepato-
toxicity, weight gain, and edema. This situation empha-
sized the need to identify strategies to develop new
antihyperglycemic agents that could retain the insulin
The PPARs play a significant role in regulating the stor-
age and catabolism of dietary fats, discovered5,6 in early
1990s. The X-ray analysis7 of PPAR-c bound with ros-
iglitazone reveals that carbonyl groups of the TZD form
hydrogen bonds with two histidine residues, H323 and
H449, of PPAR-c target receptor and Y473 in the
AF-2 helix forms a secondary hydrogen bond. The par-
tially negatively charged nitrogen of the TZD head group
is within hydrogen-bonding distance from the OH group
of the Y473 side chain. All of these primary and second-
ary hydrogen bonds result in a fixed conformation of the
TZD head group and of the participating amino acids.
Keywords: Diabetes; PPAR; Pyran-2-one; Transactivation.
q CDRI Communication No. 6724.
*
Based on the ligand–receptor binding knowledge, the
synthesis of new prototype structures 3 (Fig. 2) has been
Corresponding author. Tel.: +91 522 2612411; fax: +91 522 2623405/
2623938; e-mail: vjiram@yahoo.com
0960-894X/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.05.031

A. Sharon et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3356–3360
3357
Figure 2. Chemical structure of proposed prototype molecules (3) and
compound (3a).
initiated to develop a better drug candidate for treating
T2DM. Prototype 3 is a pyran-2-one-based derivative
and its importance is greatly realized due to its unique
structural features and diverse pharmacological proper-
ties.8–12 With careful structural analysis of pyran deriva-
tives, it was understood that the replacement of TZD
head group by pyran nucleus as a new chemical entity
may retain the antihyperglycemic activity.
Figure 4. Flexible alignment of I (red) and 3a (green) showing
significant molecular alignment.
complementarity with respect to all details of the recep-
torÕs steric constraints and interaction geometries.
A successful solution to the docking problem comprises
the generation of relevant binding modes (ÔposesÕ) of the
ligand and the correct ranking of each pose, and it is
essential for the success of virtual screening approaches
in structure-based drug design. It requires docking tools
that are able to generate suitable configuration and con-
formations of a ligand within a protein binding site and
energy measurements describing the quality of the
interactions.
A flexible alignment of the synthesized compounds with
rosiglitazone (I) was performed using the advanced pro-
gram MOE-Flex Align,13 to determine their conforma-
tional and pharmacophoric relation using I and II as a
template for the (virtual) superimposition (Fig. 3) and
scoring (Table 1). Each alignment is given a score that
quantifies the quality of the alignment in terms of both
internal strain (U) and overlap of molecular features (S).
The Lamarckian genetic algorithm AutoDock 3.0.514
has been implemented as a more efficient alternative
for docking. The X-ray conformation7 (green) and
AutoDock predicted structure (red) of rosiglitazone I
have been superimposed in Figure 5 to define the param-
eters of the program. The root mean square deviation
Figure 4 shows significant alignment indicated by super-
imposition of the middle phenoxy ring and similarities in
the head group pyran (3a) and thiazolidinedione ring of
rosiglitazone (I). The carbonyl oxygen of thiazolidine-
dione is considered as the most essential pharmacophore
for the binding with the PPAR. Projection of pyran ring
toward thiazolidinedione region of I as in Figure 4,
prompted to visualize its importance to act as a head
group.
˚
between these two conformations is ꢀ0.8 A, indicating
that the parameter set for the AutoDock simulation is
reasonable to reproduce the X-ray structure. Therefore,
the AutoDock method and the parameter set could be
extended to search the binding conformations for other
ligands accordingly. Table 2 shows the calculated ener-
gies and docked results from the compound 3a with
the comparison of docked rosiglitazone. Figure 6 shows
the 3D docked model of compound 3a with PPAR-c
and illustrates the probable binding conformational
alignment of this compound with comparison of I
(red). H-bonding is one of the important characteristics
of the ligand–receptor interaction. From these above
Further, we applied a receptor-based approach to the
validation of our hypothesis regarding the substitution
of the pyran ring in place of thiazolidinedione. This ap-
proach essentially searches for a ligand whose orienta-
tion and conformation achieve the highest degree of
Figure 3. Flexible overlay of compounds I and II showing high
similarities.
Table 1. Score for flexible alignment
Compounds
Strain energy (U)
Object function value (S)
Figure 5. Superimposition of the docked I (red) with crystallographic
rosiglitazone molecule (green) complexed in the binding cavity of
PPAR-c (gold).
I and II
I and 3a
30.93
41.34
169.9
228.63

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A. Sharon et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3356–3360
Table 2. Docking results
Compound
Cluster Final intermolecular Final docked
rank
energy (kcal/mol)
energy (kcal/mol)
I (rosiglitazone)
3a
I
I
ꢁ13.42
ꢁ11.39
ꢁ13.89
ꢁ10.72
Figure 6. Docked compound 3a (green) with rosiglitazone (I) (red) for
comparison in the binding cavity of PPAR, showing interaction with
neighboring residues through H-bonding.
silico analyses, we may consider pyran as a head group
in lieu of thiazolidinedione.
2. Chemistry
The ketene dithioacetals15,16 (2a–c) have been used as syn-
thon for the synthesis of various pyran derivatives by
reaction with aryl methyl ketones. Numerous highly func-
tionalized 2H-pyran-2-ones have been prepared from 4-
hydroxy acetophenone. The reaction of 1,2-dibromoe-
thane with 4-hydroxy acetophenone in the presence of
K2CO3 provided 1-[4-(2-bromoethoxy)phenyl]ethanone
(1) as a major product. Reaction of ketone 1 with methyl
2-substituted-3,3-bis-methylsulfanylacrylate (2) in the
presence of potassium hydroxide provided the corre-
sponding 2H-pyran-2-one derivatives (3).17 The interme-
diate 4, used for the preparation of 5, was obtained from
the reaction of 1 with secondary amine in DMF. Thus,
various 3,6-disubstituted-4-methylsulfanyl-2H-pyran-2-
ones (5) were synthesized by base-catalyzed condensa-
tion–cyclization of aryl methyl ketone (4) with 217
(Scheme 1).
Scheme 1. Synthetic scheme for the preparation of ketones 4, 6, and
various pyrans 3, 5, 7, and 8. Formation of 3 indicates the in situ
substitution of bromine atom by thioalkyl group.
The conformation of 3b along with the atom numbering
scheme is shown in Figure 7. X-ray crystal structure
showed that one molecule is in the asymmetric unit.
The co-planarity was found between pyran and phenoxy
ring; phenoxy ring is twisted with 7.88 (1)ꢁ from the
mean plane of the pyran ring. As expected, this planarity
can be attributed to weak intramolecular H-bond [C13–
˚
˚
H13ꢂ ꢂ ꢂO1; Hꢂ ꢂ ꢂA = 2.38 A, Dꢂ ꢂ ꢂA = 2.72 A (1) and
h(DHA) = 100.9ꢁ].
All the synthesized compounds were characterized by
their spectroscopic and elemental analyses.20 The IR
spectrum of one of the compound 3b showed two bands
at m 1706 and 2209 cmꢁ1 due to CO and CN groups,
1
respectively. H NMR spectrum of 3b showed two trip-
lets at d 1.27 and 1.46 ppm due to two methyl groups
and two quartets at d 2.61 and 3.19 for two methylene
protons of SCH2CH3 substituents. Two methylene
groups of linker resonated at d 2.91 and d 4.19 ppm as
triplet for SCH2 and OCH2, respectively. A singlet of
pyran ring proton appears at 6.6 ppm while peaks at d
6.97–7.9 ppm were attributed to the aromatic protons.
The FAB mass peak at 362 supported the proposed
structure. Finally, the structure of 3b was confirmed
by single crystal X-ray analysis.18
Figure 7. ORTEP diagram of 3b showing the X-ray molecular
structure in 50% probability level.

A. Sharon et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3356–3360
Table 3. In vitro PPAR-c transactivation assay19 for some synthesized
compounds of prototype I
3359
References and notes
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7
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3c
5a
5b
5c
4
6
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5d
5e
5
19
16
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5f
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a Compounds were tested in quadruple at concentrations ranging from
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3. Results and discussion
Our objective was to design pyran-based PPAR-c
ligands to identify lead structures through an in silico
approach to evaluate their transactivation response. It
is evident from the first series of designed and synthe-
sized compounds 3a–c that the compounds displayed
(Table 3) significant increases in activation response.
Oxidation of both the methylsulfanyl groups in 3a to
its corresponding sulfoxide 8 reduced the activity pro-
file of the compound. Exchange of methylsulfanyl
group by highly hydrophobic phenylsulfanyl substitu-
ent in 7 drastically reduced the activity. In attempts
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18. Crystal data of 3b: C18H19NO3S2, M = 361.46, mono-
4. Biological activity
clinic, space group P2(1)/n, a = 5.419 (0), b = 22.523
3
(1), c = 14.833 (2) A, V = 1804.9(3) A , T = 293 K, Z = 4,
˚
˚
Of various compounds evaluated in in vitro PPAR-
transactivation assay, only three compounds, 3a–c, dem-
onstrated significant transactivation responses. This
study made it possible to modify the structure of 3a to
obtain more compounds as potent PPAR-activators.
Thus, it was imperative to generate information through
computational analyses including docking and molecu-
lar simulations with iterative synthesis and biological
screening.
Dc = 1.330 g cmꢁ1
,
l(Mo-Ka) = 0.31 mmꢁ1
,
F(000) =
760, yellow rectangular crystal, size 0.42 · 0.22 ·
0.20 mm, 4496 reflections measured, 3187 unique,
Rw = 0.15 for all data, conventional R = 0.05 for 2031
Fo > 4r(Fo) and 0.0922 for all 3187 data, S = 1.004 for all
data and 219 parameters. Unit cell determination and
intensity data collection (2h = 50ꢁ) were performed on a
Bruker P4 diffractometer at 293(2) K. Structure solutions
by direct methods and refinements by full-matrix least-
squares methods on F2. Programs: XSCANS [(Siemens
Analytical X-ray Instruments: Madison, Wisconsin, USA
1996) used for data collection and data processing],
SHELXTL-NT [(Bruker AXS: Madison, Wisconsin,
USA 1997) used for structure determination, refinements
and molecular graphics]. (CCDC No of 3b: 273004).
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Spieglman, B. M.; Evans, R. M. Cell 1995, 83, 803–812.
20. Spectroscopic data of 4-methylsulfanyl-6-substituted-
phenyl-2-oxo-2H-pyran-3-carbonitrile 3a: yield: 48%;
Acknowledgments
V.J.R. and R.P.S. are thankful to ICMR for financial
support of the project. A.S. thanks CSIR for Senior Re-
search Fellowship. Authors are thankful to SAIF,
CDRI, Lucknow for providing spectroscopic data and
elemental analyses.

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A. Sharon et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3356–3360
mp: 165–168 ꢁC; MS (FAB): 334 (M+ + 1); 1H NMR
1H NMR (CDCl3, 200 MHz): d 1.31 (t, 3H, J = 7.4 Hz,
CH3), 1.49 (t, 3H, J = 7.4 Hz, CH3), 2.61–2.68 (q, 2H,
J = 7.3 Hz, CH3), 2.94 (t, 2H, J = 6.7 Hz, CH2), 3.19–
3.24 (q, 3H, J = 7.5 Hz, CH2), 4.22 (t, 2H, J = 6.8 Hz,
CH2), 6.60 (s, 1H, ArH), 7.0 (d, 2H, J = 8.9 Hz, ArH),
7.81 (d, 2H, J = 8.9 Hz, ArH); Anal. Calcd for
C18H19NO3S2: C, 59.81; H, 5.30; N, 3.87. Found: C,
59.91; H, 5.35; N, 3.89.
(CDCl3, 200 MHz): d 2.23 (s, 3H, SCH3), 2.70 (s, 3H,
SCH3), 2.91 (t, 2H, J = 5.8 Hz, CH2), 4.24 (t, 2H,
J = 5.8 Hz, CH2), 6.60 (s, 1H, ArH), 7.0 (d, 2H,
J = 8.8 Hz, ArH), 7.83 (d, 2H, J = 8.8 Hz, ArH); Anal.
Calcd for C16H15NO3S2: C, 57.64; H, 4.53; N, 4.20.
Found: C, 57.67; H, 4.63; N, 4.32. 3b: yield: 46%; mp:
181 ꢁC; MS (FAB): 362 (M+ + 1); IR : 1706.6 cmꢁ1 (CO);