Synthesis, Evaluation and Molecular Docking of Thiazolopyrimidine Derivatives as Dipeptidyl Peptidase IV Inhibitors

Article abstract of DOI:10.1111/cbdd.12041

A series of thiazolopyrimidine derivatives was designed, synthesized and screened for in-vitro inhibition of Dipeptidyl Peptidase IV (DPP IV). The SAR study indicated the influence of substituted chemical modifications on thiazolopyrimidine scaffold. Comp

Full text of DOI:10.1111/cbdd.12041

ª 2012 John Wiley & Sons A/S
Chem Biol Drug Des 2012; 80: 918–928
doi: 10.1111/cbdd.12041
Research Article
Synthesis, Evaluation and Molecular Docking of
Thiazolopyrimidine Derivatives as Dipeptidyl
Peptidase IV Inhibitors
Mani Sharma1,*, Monica Gupta1,*, Divya
Singh1, Manoj Kumar2 and Punit Kaur2
the next 25 years and will affect 380 million people by 2025 (2).
Patients with diabetes experiences severe pancreatic ß-cell dysfunc-
tion and a progressive loss of insulin secretion ultimately leads to
hyperglycaemia (3). The treatment of diabetes includes modification
1Department of Pharmaceutical Chemistry, Delhi Institute of
Pharmaceutical Sciences and Research, Pushp Vihar, Sector-3, M B
Road, New Delhi 110017, India
in lifestyle and use of anti-hyperglycaemic agents to maintain the
adequate glucose level (4). Nevertheless, therapeutically available
anti-diabetic agents are associated with risks of adverse effects
such as gastrointestinal toxicities, hypoglycaemia and weight gain.
As a result, novel therapies having long-term efficacy and improved
tolerability are urgently required to attain glycemic control. Amongst
the various strategies of treatment, DPP IV inhibitor appears to be
novel class of antidiabetic drugs, as they are observed with
improved insulin secretion in type-2 diabetic patients (5).
2Department of Biophysics, All India Institute of Medical Sciences,
New Delhi 110029, India
*Corresponding authors: Mani Sharma, mani120484@gmail.com;
Monica Gupta, monicagupta35@gmail.com
A
series of thiazolopyrimidine derivatives was
designed, synthesized and screened for in-vitro
inhibition of Dipeptidyl Peptidase IV (DPP IV). The
SAR study indicated the influence of substituted
chemical modifications on thiazolopyrimidine
DPP IV is a 766-amino acid serine protease which belongs to prolyl
oligopeptidase family. It is highly specific enzyme, removes N-termi-
nal of dipeptide from amino terminus preferentially having proline
or alanine residues at penultimate position (6). DPP IV rapidly inacti-
vates incretin hormones (<2 min), secreted by intestinal endocrine
cells in response to meal intake (7,8). The incretin hormone includes
glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic
polypeptide responsible for 50–70% of postprandial insulin release
(9). GLP-1 is a naturally occurring peptide hormone and allows
regeneration of insulin stimulating pancreatic ß-cell function. It also
regulates glucose homoeostasis by potentiating glucose-induced
insulin secretion and reducing production of glucagon (10). The inhi-
bition of DPP IV will restore the level of endogenous incretin hor-
mones and might delay or prevent the onset of diabetes (11). DPP
IV inhibitors possess advantages over existing antidiabetic agents
as increase in weight gain and hypoglycaemia is not seen (5,12).
Therefore, DPP IV inhibitors have emerged as novel class of antidia-
betic drugs which prevent proteolytic degradation of incretin hor-
mones and stimulate glucose-dependent insulin secretion (5).
scaffold. Compound
9 (IC50 = 0.489 lM) and 10
(IC50 = 0.329 lM) having heterocyclic-substituted
piperazine with acetamide linker resulted as most
potent DPP IV inhibitors among all the compounds
screened. Single dose (10 mg ⁄ kg) of both the com-
pounds 9 and 10 significantly reduced glucose
excursion during oral glucose tolerance test in
streptozotocin induced diabetic rat model. Molec-
ular docking studies illustrated the probable bind-
ing mode and interactions of thiazolopyrimidine
nucleus and its derivatives at binding site of
receptor. The binding site for DPP IV is composed
of active site region (catalytic triad of Ser630,
Asp708 and His740) including S1 and S2 sub-
pocket. The aryl moiety of compounds 9, 10 and
11 were observed to occupy S2 binding pocket
and interacted with aromatic ring of Tyr662 and
Tyr666 acquired through p-p interaction. Thus, it is
indicated that occupancy of the highly hydropho-
bic S2 pocket is more important for DPP IV inhibi-
tory activity. The present study on substituted
thiazolopyrimidine derivatives shows good to
moderate inhibitory potential of DPP IV enzyme.
These findings encouraged us to explore targeted DPP IV inhibitors
which may serve as better approach to surmount the problems con-
sorted by clinically used antidiabetic agent. Earlier studies shows
that heterocyclic structures such as fused azolopyrimidines (13), thi-
enopyrimidine [14], benzimidazole (15), quinoxalinedione (16), imi-
dazopyrazinone (17), imidazopyridazinones (18) and xanthine (19)
have played a vital role in providing series of potent, selective and
novel DPP IV inhibitors. Taking the earlier consideration in fact,
maintaining cyclic integrity of the pharmacophore may prove to be
an attractive strategy for development of DPP IV inhibitors with
desirable activity.
Key words: diabetes, DPP IV, molecular docking, thaizolopyrimidine
Received 17 April 2012, revised 27 July 2012 and accepted for publica-
tion 21 August 2012
Diabetes mellitus (T2DM) is slowly but gradually growing metabolic
disorder affecting 90–95% of population worldwide (1). The contin-
ued global burden of diabetes is speculated to be double within
918

Thiazolopyrimidine Derivatives as Potent DPP IV Inhibitors
Figure 1: Dipeptidyl Peptidase
IV inhibitors.
The structural frame work of molecules was designed using thiazol-
opyrimidine ring as core bioactive scaffold. Accordingly, the chemi-
cal modifications were carried out on scaffold to increase its
affinity and selectivity towards DPP IV inhibition. However, the mod-
ified pharmacophore closely showed resemblance with the various
potent and selective DPP IV inhibitors (Figure 1) (20,21).
tion. White solid; Yield: 89%; mp: 104–110 ꢀC; Rf: 0.35; 1H NMR
(300MHz, DMSO-d6) d p.p.m.: 3.4 (s, 3H), 6.55 (s, 2H); FT-IR (mmax
⁄ cm, KBr) 3313 (N-H stretch), 3100 (C-H stretch), 1140 (C-N stretch),
1233 (C-S stretch); Anal. Calcd. For C6H6N4O2S: C, 36.36; H, 3.05; N,
28.27; Found: C, 36.31; H, 3.09; N, 28.25.
;
Thus, the present study discloses synthesis of series of thiazolopyr-
imidine derivatives, structure-activity relationship (SAR) and in-vitro
inhibitory activity against DPP IV enzyme. Among the synthesized
derivatives, two compounds 9 and 10 showed the most potent DPP
IV inhibition and excellent anti-hyperglycaemic activity in streptozo-
tocin induced diabetic rat model. Molecular docking study has been
carried out for the insight of binding mode and interaction pattern
of designed inhibitors of DPP IV using crystal structure of DPP IV.
Step II: general procedure for synthesis of N-
substituted chloracetamides (2–7)
Secondary amine (2.9 mol) was taken in 1, 4-dioxan (10 mL) main-
taining temperature 50–60 ꢀC. The solution of chloroacetyl chloride
(3.33 mol) in 1, 4-dioxan (2 mL) was added drop wise under contin-
uous stirring. After reflux of 2 h, cooled mixture to room tempera-
ture and stirred for 30 min. The completion of reaction was
monitored by thin-layer chromatography (TLC) using mobile phase,
chloroform:methanol (9.5:0.5). The reaction mixture was concen-
trated under reduced pressure and the resulting mixture was diluted
with water and neutralized using saturated bicarbonate solution.
The solution was further diluted and partitioned between water
and chloroform. The organic layer was washed twice with water,
brine and dried over anhydrous sodium sulphate. The organic layer
was evaporated to the dryness under reduced pressure and resul-
tant intermediates (2–7) were obtained in excellent yields.
Methods and Materials
Experimental
All commercial chemicals and solvents were purchased from Sigma-
Aldrich Chemical Company, St. Louis, MO, USA and Spectrochem Pvt.
Ltd. Chemicals, India and solvents were used as such without further
1
purification. H spectra were recorded on Bruker NMR spectrometer
operating at 300 MHz in CDCl3 or DMSO-d6 with tetramethylsilane as
an internal standard. Chemical shifts are expressed as parts per million
(p.p.m., d), and signals are reported as s (singlet), d (doublet), t (triplet), q
(quartet) and m (multiplet). All the Fourier Transform Infrared (FT-IR) spec-
tra were recorded on Jasco-410 spectrophotometer. Elemental analysis
was carried out using Vario EL III elemental analyser. Melting points of
compounds were determined in open capillary tubes using Hicon melting
point instrument and are uncorrected. All reactions were carried out
under dried condition and performed using oven-dried glassware.
1-(4-aminopiperidin-1-yl)-2-chloroethanone (2)
Yellow oil; Yield: 75%; Rf: 0.69; H NMR (300MHz, CDCl3) d p.p.m.:
2.00 (q, J = 12, 4H), 3.2 (t, J = 9, 4H), 4.46 (d, J = 12, 2H), 4.8 (s,
2H); FT-IR (mmax; ⁄ cm, neat): 2936 (C-H stretch), 1649 (C=O), 1169 (C-
1
N
stretch), 654 (C-Cl stretch); Anal. Calcd. For C7H13ClN2O: C, 47.60; H,
7.42; N, 15.86; Found: C, 47.62; H, 7.45; N, 15.89.
2-chloro-1-[4-(pyrimidin-2-yl) piperazin-1-
yl]ethanone (3)
1
Step I: synthesis of 2-amino-4-methyl-4H-
thiazolo [4,5-d]pyrimidine-5,7-dione (1)
The compound 1 is prepared by previously reported procedure (22).
The compound obtained was authenticated by further characteriza-
Yellow oil; Yield: 87%; Rf: 0.71; H NMR (300MHz, CDCl3) d p.p.m.:
3.70–3.64 (m, 4H), 3.91–3.73 (m, 4H), 4.28 (s, 2H), 6.66 (t, J = 9,
1H), 8.38 (d, J = 9, 2H); FT-IR (mmax; ⁄ cm, neat): 2931 (C-H stretch),
1629 (C=O), 1493 (C=N), 640 (C-Cl stretch); Anal. Calcd. For
Chem Biol Drug Des 2012; 80: 918–928
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Sharma et al.
C10H13ClN4O: C, 49.90; H, 5.44; N, 23.28; Found: C, 49.94; H, 5.39;
N, 23.24.
pressure to give the final compounds. Compounds obtained as solid
were recrystallized using appropriate solvent, and the oily com-
pounds were purified by column chromatography (5% MeOH in
DCM). The final synthetic compounds were obtained in considerable
yields.
2-chloro-1-[4-(pyridin-2-yl) piperazin-1-
yl]ethanone (4)
1
Brown oil; Yield: 87%; Rf: 0.70; H NMR (300MHz, CDCl3) d p.p.m.:
3.71–3.66 (m, 4H), 3.91–3.73 (m, 4H), 4.43 (s, 2H), 6.73 (t,
J = 12 Hz, 1H), 6.99 (d, J = 9, 1H), 7.71 (t, J = 15.3, 1H), 8.17 (s,
1H); FT-IR (mmax; ⁄ cm, neat): 3004 (C-H stretch), 2920 (C-H stretch),
1647 (C=O), 1541 (C=N), 775 (C-Cl stretch); Anal. Calcd. For
C11H14ClN3O: C, 55.12; H, 5.89; N, 17.53; Found: C, 55.17; H, 5.85;
N, 17.58.
2-amino-6-[2-(4-aminopiperidin-1-yl)-2-oxoethyl]-
4-methyl[1,3]thiazolo[4,5-d]pyrimidine-
5,7(4H,6H)-dione (8)
Yellow oil; Yield: 64%; Rf: 0.65; H NMR (300MHz, CDCl3) d p.p.m.:
2.00 (q, J = 12, 4H), 3.2 (t, J = 9, 4H), 3.55 (s, 3H), 4.46 (d, J = 12,
2H), 4.8 (s, 2H); FT-IR (mmax; ⁄ cm, neat): 3313 (N-H stretch), 1649
1
(C=O), 1233(C-S stretch), 1169 (C-N
) Anal. Calcd. For
stretch
C13H18N6O3S: C, 46.14; H, 5.36; N, 24.84; Found: C, 46.17; H, 5.31;
N, 24.83.
2-chloro-1-[4-(4-chlorophenyl) piperazin-1-
yl]ethanone (5)
Yellow solid; Yield: 84%; mp: 129–133 ꢀC; Rf: 0.71; 1H NMR
(300MHz, CDCl3) d p.p.m.: 3.23–3.15 (m, 4H), 3.72–3.68 (m, 4H),
4.12 (s, 2H), 6.88 (d, J = 6 Hz, 2H), 7.28 (d, J = 6 Hz, 2H); FT-IR
(mmax; ⁄ cm, KBr): 2917 (C-H stretch), 1594 (C=O), 1497 (C=C ring
stretch), 667 (Ar-Cl stretch), 624 (C-Clstretch); Anal. Calcd. For
C12H14Cl2N2O: C, 52.76; H, 5.17; N, 10.26; Found: C, 52.79; H, 5.19;
N, 10.29.
2-amino-6-{2-[4-(4-chlorophenyl)piperazin-1-yl]-
2-oxoethyl}-4-methyl[1,3]thiazolo[4,5-
d]pyrimidine-5,7(4H,6H)-dione (9)
Yellow solid; Yield: 67%; mp: 145–148ꢀC; Rf: 0.69; 1H NMR
(300MHz, CDCl3) d p.p.m.: 3.25–3.13 (m, 4H), 3.56 (s, 3H), 3.68–3.57
(m, 4H), 4.760 (s, 2H), 6.99 (d, J = 13.2 Hz, 2H), 7.269 (d, J = 8.7,
2H); FT-IR (mmax; ⁄ cm, KBr): 3446 (N-H stretch), 2917 (C-H stretch), 1653
(C=O), 1495 (C=C stretch), 1233 (C-S stretch), 669 (Ar-Cl stretch); Anal.
Calcd. For C18H19ClN6O3S: C, 49.71; H, 4.40; N, 19.32; Found: C,
49.69; H, 4.43; N, 19.37.
1-(azepan-1-yl)-2-chloroethanone (6)
1
Light brown oil; Yield: 78%; Rf: 0.69; H NMR (300MHz, CDCl3) d
p.p.m.: 1.79–1.73 (m, 4H), 1.87–1.82 (m, 4H), 3.58–3.42 (m, 4H),
4.11 (s, 2H); FT-IR (mmax; ⁄ cm, neat): 1647 (C=O), 1099 (C-N stretch),
651 (C-Cl stretch); Anal. Calcd. For C8H14ClNO: C, 54.70; H, 8.03; N,
7.97; Found: C, 54.74; H, 8.05; N, 7.99.
2-amino-4-methyl-6-{2-oxo-2-[4-(pyridin-2-
yl)piperazin-1-yl]ethyl}[1,3]thiazolo[4,5-
d]pyrimidine-5,7(4H,6H)-dione (10)
1
Yellow oil; Yield: 64%; Rf: 0.69; H NMR (300MHz, CDCl3) d p.p.m.:
2-chloro-1-(piperidin-1-yl) ethanone (7)
Yellow oil; Yield: 77%; Rf: 0.69; H NMR (300MHz, CDCl3) d p.p.m.:
3.56 (s, 3H), 3.70–3.64 (m, 4H), 3.91–3.73 (m, 4H), 4.85 (s, 2H), 6.73
(q, J = 6 Hz, 2H), 7.52 (d, J = 6 Hz, 1H), 8.20 (s, 1H); FT-IR (mmax;
1
2.00–1.89 (m, 4H), 3.48 (t, J = 18 Hz, 4H), 4.0 (s, 2H); FT-IR (mmax
;
⁄ cm, KBr): 3462 (N-H stretch), 2926 (C-H stretch), 1652 (C=O), 1479
(C=C stretch), 1234 (C-S stretch), Anal. Calcd. For C17H19N7O3S: C,
50.86; H, 4.77; N, 24.43; Found: C, 50.88; H, 4.73; N, 24.39.
⁄ cm, neat): 1647 (C=O), 1096 (C-N stretch), 802 (C-Cl stretch); Anal.
Calcd. For C7H12ClNO: C, 52.02; H, 7.48; N, 8.67; Found: C, 52.07;
H, 7.52; N, 8.71.
2-amino-4-methyl-6-{2-oxo-2-[4-(pyrimidin-2-
yl)piperazin-1-yl]ethyl}[1,3]thiazolo[4,5-
d]pyrimidine-5,7(4H,6H)-dione (11)
Step III: General procedure for synthesis of
compounds (8–13)
To a solution of 2-amino-4-methyl-4H-thiazolo [4, 5-d] pyrimidine-
5,7-dione (0.25 mmol) in dry DMF (1 ml), added anhydrous potas-
sium carbonate (0.75 mmol) and mixture was heated initially at
70 ꢀC for 2 h under continuous stirring. At 70 ꢀC drop wise added
the solution of N-substituted chloracetamide derivative (0.25 mmol)
in dry DMF to the reaction mixture. The reaction mixture was
heated at 70–80 ꢀC for 3 h, and completion of reaction was moni-
tored through TLC using mobile phase as chloroform:methanol
(9.5:0.5). The reaction mixture was brought to room temperature, fil-
tered to remove insoluble particulates. Filtrate was diluted with ice-
cold water and partitioned between water and ethyl acetate layer.
The extraction process was repeated twice, combined organic layers
were washed with water and brine. The organic layers were dried
over anhydrous sodium sulphate and concentrated under reduced
Yellow solid; Yield: 64%; mp: 134–140 ꢀC; Rf: 0.69; 1H NMR
(300MHz, CDCl3) d p.p.m.: 3.56 (s, 3H), 3.70–3.64 (m, 4H), 3.91–3.73
(m, 4H), 4.28 (s, 2H), 6.66 (t, J = 9 Hz, 1H), 8.41 (d, J = 9 Hz, 2H);
FT-IR (mmax; ⁄ cm, KBr): 3444(N-H stretch), 2924 (C-H stretch), 1493
(C=N), 1650 (C=O), 1236 (C-S stretch); Anal. Calcd. For C16H18N8O3S:
C, 47.75; H, 4.51; N, 27.84; Found: C, 47.78; H, 4.48; N, 27.89.
2-amino-6-[2-(azepan-1-yl)-2-oxoethyl]-4-
methyl[1,3]thiazolo[4,5-d]pyrimidine-5,7(4H,6H)-
dione (12)
1
Brown oil; Yield: 64%; Rf: 0.65; H NMR (300MHz, CDCl3) d p.p.m.:
1.62–1.47 (m, 4H), 1.85–1.74 (m, 4H), 3.55 (s, 3H), 4.15- 4.04 (m,
4H), 4.65 (s, 2H), 5.82 (s, 2H); FT-IR (mmax; ⁄ cm, KBr): 3312 (N-H
920
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Thiazolopyrimidine Derivatives as Potent DPP IV Inhibitors
stretch), 2925 (C-H stretch), 1651 (C=O); Anal. Calcd. For C14H19N5O3S:
2-amino-6-[2-(diethylamino)ethyl]-4-
C, 49.84; H, 5.68; N, 20.76; Found: C, 49.87; H, 5.62; N, 20.78.
methyl[1,3]thiazolo[4,5-d]pyrimidine-5,7(4H,6H)-
dione (17)
Yellow solid; Yield: 75%; mp: 147–150 ꢀC; Rf: 0.65; 1H NMR
(300MHz, CDCl3) d p.p.m.: 1.09 (t, J = 24 Hz, 6H), 2.70 (q,
J = 27 Hz, 4H), 3.56 (s, 3H), 4.13 (t, J = 15 Hz, 4H), 5.68 (s, 2H); FT-
IR (mmax; ⁄ cm, KBr): 3447 (N-Hstretch), 2925 (C-Hstretch), 1457 (C-N),
1648 (C=O); Anal. Calcd. For C12H19N5O2S: C, 48.47; H, 6.44; N,
23.55; Found: C, 48.43; H, 6.42; N, 23.58.
2-amino-4-methyl-6-[2-oxo-2-(piperidin-1-
yl)ethyl][1,3]thiazolo[4,5-d]pyrimidine-
5,7(4H,6H)-dione (13)
1
Yellow oil; Yield: 68%; Rf: 0.65; H NMR (300MHz, CDCl3) d p.p.m.:
1.28–1.25 (m, 2H), 2.65–2.52 (m, 4H), 3.55 (s, 3H), 3.70 (t,
J = 12 Hz, 4H), 4.17 (s, 2H), 6.55 (s, 2H); FT-IR (mmax; ⁄ cm, KBr):
3475 (N-H stretch), 2927 (C-H stretch), 1654 (C=O); Anal. Calcd. For
C13H17N5O3S: C, 48.28; H, 5.30; N, 21.66; Found: C, 48.23; H, 5.32;
N, 21.67.
2-amino-6-[2-(dimethylamino)ethyl]-4-
methyl[1,3]thiazolo[4,5-d]pyrimidine-5,7(4H,6H)-
dione (18)
White solid; Yield: 75%; mp:149–153 ꢀC; Rf: 0.65; 1H NMR
(300MHz, CDCl3) d p.p.m.: 1.25 (s, 6H), 3.56 (s, 3H), 4.17 (t,
J = 15 Hz, 4H), 5.69 (s, 2H); FT-IR (mmax; ⁄ cm, KBr): 3447(N-H stretch),
2925 (C-H stretch), 1457 (C-N), 1648 (C=O); Anal. Calcd. For
C10H15N5O2S: C, 44.60; H, 5.61; N, 26.00; Found: C, 44.63; H, 5.58;
N, 26.04.
General procedure for synthesis of compounds
(14–18)
To a solution of 2-amino-4-methyl-4H-thiazolo [4,5-d]pyrimidine-5,7-
dione (0.25 mmol) in dry DMF (1 ml) was added anhydrous potas-
sium carbonate (0.75 mmol) under vigorous stirring. A solution of
alkyl chloride (0.25 mmol) in dry DMF was added drop wise to the
reaction mixture. The reaction mixture was heated for 2 h at 70ꢀ C
and status of reaction was monitored by TLC using ethylacetate:
hexane as mobile phase (6:4). The reaction mixture was cooled to
room temperature. The product was filtered and washed twice with
cold water. The final compounds obtained were dried under vac-
uum. Recrystallization was carried out using appropriate solvent.
Pharmacological activity
The Institutional Animal Ethical Committee (IAEC) approved the
experiments for oral glucose tolerance test (OGTT). Healthy Wistar
rats used for the study were obtained from Animal House of Delhi
Institute of Pharmaceutical Sciences and Research. Rats were
housed in colony cages (3 female and 1 male rats per cage for
breeding), at an ambient temperature of 25 ꢀC with 12 h light: 12 h
dark cycle. Animals were kept in polypropylene cages and were fed
with rat food as pellets and water ad libitum unrestrictedly. All
experimental procedures were performed according to IAEC (Proto-
col No.1 ⁄ DIPSAR ⁄ IAEC ⁄ 2010) and CPCSEA guidelines.
2-amino-6-benzyl-4-methyl[1,3]thiazolo[4,5-
d]pyrimidine-5,7(4H,6H)-dione (14)
Yellow solid; Yield: 74%; mp: 142–146 ꢀC; Rf: 0.65; 1H NMR
(300MHz, CDCl3) d p.p.m.: 3.54 (s, 3H), 5.19 (s, 2H), 5.74 (s, 2H),
7.30–7.26 (m, 3H), 7.55 (t, J = 15, 2H); FT-IR (mmax; ⁄ cm, KBr): 3440
(N-Hstretch), 1643 (C=O), 1429 (C-N); Anal. Calcd. For C13H12N4O2S:
C, 54.15; H, 4.20; N, 19.43; Found: C, 54.17; H, 4.23; N, 19.47.
Induction of experimental diabetes (23,24)
Induction of diabetes was carried out using freshly prepared
solution of streptozotocin (STZ, Sigma-Aldrich) at the dose level of
90 mg ⁄ kg (I.P.) in 0.1 M freshly prepared citrated buffer pH 4.5
to 2 days old neonatal pups. A total of 24 diabetic and 6 non-
diabetic male rats were used in the study. After 6 weeks of
injection, animals were screened for fasting blood glucose level.
Diabetic rats were further divided into four groups with six rats
per group. Animals showing fasting glucose levels >150 mg ⁄ dL
were considered diabetic and selected for screening of
compounds.
2-amino-4-methyl-6-[2-(piperidin-1-
yl)ethyl][1,3]thiazolo[4,5-d]pyrimidine-
5,7(4H,6H)-dione (15)
Yellow solid; Yield: 78%; mp:145–147 ꢀC; Rf: 0.65; 1H NMR
(300MHz, CDCl3) d p.p.m.: 1.28–1.25 (m, 2H), 2.65–2.52 (m, 4H),
3.41 (s, 3H), 3.70 (t, J = 12 Hz, 4H), 4.17 (t, J = 12 Hz, 2H), 5.68 (s,
2H); FT-IR (mmax; ⁄ cm, KBr): 3321(N-H stretch), 2925 (C-H stretch), 1646
(C=O), 1440 (C-N); Anal. Calcd. For C13H19N5O2S: C, 50.47; H, 6.19;
N, 22.64; Found: C, 50.49; H, 6.22; N, 22.61.
Antihyperglycemic activity
2-amino-4-methyl-6-[2-(morpholin-4-
yl)ethyl][1,3]thiazolo[4,5-d]pyrimidine-
5,7(4H,6H)-dione (16)
Male Wistar rats weighing 150–200 g having blood glucose level
>150 mg ⁄ dL were selected for OGTT. Animals of diabetic control
group received vehicle (0.5% w ⁄ v methylcellulose) and standard
group received vildagliptin (10 mg ⁄ kg). Animals of experimental
group were administered single dose of test compounds (suspension
in 0.5% w ⁄ v methylcellulose) of 10 mg ⁄ kg body weight (25,26). A
glucose load (2 g ⁄ kg) was given orally to over night fasting rats
after 30 min prior to administration of the test compound ⁄ vehicle.
Blood samples were taken from tail vein at regular intervals of 0,
Light brown solid; Yield: 78%; mp:150–156 ꢀC; Rf: 0.65; 1H NMR
(300MHz, CDCl3) d p.p.m.: 2.65 (t, J = 18 Hz, 4H), 3.52 (s, 3H),
3.70–3.61 (m, 4H), 4.17 (t, J = 15 Hz, 4H), 5.68 (s, 2H); FT-IR (mmax
;
⁄ cm, KBr): 3475 (N-Hstretch), 2927 (C-Hstretch), 1654 (C=O), 1457 (C-N);
Anal. Calcd. For C12H17N5O3S: C, 46.29; H, 5.50; N, 22.49; Found: C,
46.31; H, 5.53; N, 22.50.
Chem Biol Drug Des 2012; 80: 918–928
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Sharma et al.
30, 60, 90, 120 min after glucose load. The blood glucose level
was monitored using glucometer (ACCU-CHEK, Active; Roche Diag-
onistics, Mannheim, Germany).
been taken as the most probable binding conformation of the
ligand. Discovery Studio (DS) 2.0 (Accelrys Inc., San Diego, CA,
USA) and the protocols available in it were used for this (32).
Statistical evaluation
Results and Discussion
The statistical data were expressed as mean € SEM IC50 values
were determined using non-linear regression analysis. Statistical
evaluation was performed by one-way ANOVA followed by Dunnett's
post-test. Statistical studies and data analyses were performed
using GRAPHPAD PRISM Version 5.0 (GraphPad Software Inc., San
Diego, CA, USA).
Chemistry
A series of 2-amino-4-methyl-4H-thiazolo [4,5-d]pyrimidine-5,7-dione
derivatives as DPP IV inhibitors were designed and synthetic strategy
followed is outlined in Scheme 1. The preparation of 2-amino-4-
methyl-4H-thiazolo [4,5-d]pyrimidine-5,7-dione (1) was easily synthe-
sized in two steps via 6-amino-1-methyl-2,4-dioxo-1,2,3,4-tetrahydro-
pyrimidin-5-yl-thiocyanate followed by cyclization, according to the
previously reported procedure (22). The other part of synthesis
involved preparation of N-substituted chloracetamides by nucleophilic
substitution reaction of amines and chloroacetyl chloride [20]. Start-
ing material used were various substituted secondary amines. These
were subsequently reacted with chloroacetyl chloride to provide N-
substituted chloracetamide intermediates in an excellent yield.
Resulting intermediates and few commercially available alkyl chlo-
rides were again condensed via N-3 alkylation of 2-amino-4-methyl-
4H-thiazolo [4,5-d] pyrimidine-5,7-dione using anhydrous potassium
carbonate as base at 70–80 ꢀC. The title analogues were obtained
in considerable yields after purification. The synthesis of proposed
structures was found in conformity with spectral analysis.
In-vitro DPP IV enzyme inhibition assay
All the synthesized compounds were evaluated for in-vitro DPP IV
enzyme inhibition. The enzyme assay was performed using DPP IV
drug discovery kit (BML-AK 499; Enzo Life Sciences, Plymouth Meet-
ing, PA, USA). The activity of test compounds was assayed using
human recombinant DPP IV enzyme, chromogenic substrate (H-Gly-
Pro-AMC, Km 114 lM), DPP IV inhibitor (P32 ⁄ 98), assay buffer and
calibration standard as provided in the kit. The assay was per-
formed using 96-well flat-bottomed microtiter plate followed by
addition of assay buffer, DPP IV enzyme and chromogenic substrate
(HGly-Pro-pNA). The assay principle and procedure was followed as
per manufacturer's guidelines. Solutions of the test compounds
were made in dimethyl sulfoxide (DMSO) at different concentrations
of 25, 50, 100, 200 lg ⁄ mL and 20 lL were added to each well
after further dilutions. The plate was incubated at 37 ꢀC for 10 min
to allow enzyme-inhibitor reaction and read continuously at A-
405 nm using Bio-Rad Elisa Plate Reader, Philadelphia, PA, USA.
In-vitro DPP IV activity
The synthesized thiazolopyrimidine derivatives (8–18) were evalu-
ated in-vitro for DPP IV enzyme inhibitory activity and results
obtained are reported as micromolar inhibitory concentration, IC50
(lM). The DPP IV inhibition was determined using human DPP IV,
and the inhibitory activity was obtained for various substitutions
around thiazolopyrimidine scaffold. The unsubstituted thiazolopyrimi-
dine 1 showed micromolar inhibition (IC50 = 11.87 lM). Further, we
focused our optimization strategy towards effect of chemical substi-
tutions on thiazolopyrimidine ring. The influence of three different
substitution patterns having methylene, ethylene and acetamide lin-
ker was studied against their specificity towards DPP IV inhibition.
Insertion of an acetamide linker produced potent inhibitors, which
might have allowed conformational changes and may be responsible
for increase in inhibitory effect (Table 1). The alkyl chlorides having
ethylene and methylene linker (14–18) caused considerably lower
potency than N-substituted chloracetamide (8–13) derivatives.
Modelling studies
The binding mode and molecular interactions of the selected thizol-
opyrimidine derivatives were analysed using computational model-
ling. The structures of designed inhibitors were built and minimized,
and subsequently simulated annealing was carried out to obtain the
probable three-dimensional (3-D) conformation for these compounds
with the help of CHARMm (27,28) force field parameters and partial
charges based on MMFF94 (29). The crystal structure of DPP IV
complexed with a structurally similar compound, a triazolopyridine
derivative, (PDB Id: 2FJP) was taken as the template model (30).
The binding site for docking studies was defined around the active
site region (catalytic triad of Ser630, Asp708 and His740) including
the S1 and S2 sub-pocket. The side chains of the binding site resi-
dues were kept flexible, during this analysis to allow for local per-
turbations in this region. The CHARMm force field parameters were
assigned to the protein atoms of DPP IV. The obtained structure of
thizolopyrimidine derivatives from above was docked into the
defined binding site using LigandFit (31) docking protocol. The Li-
gandFit docking algorithm combines a shape comparison filter with
a Monte Carlo conformational search to generate docked poses
consistent with the binding site shape. The docked poses have
been scored using Dock Score scoring function. It is a force field-
based scoring function that is combination of internal energy of the
ligand and interaction energy between ligand and receptor in the
docked complex. The docked pose with the highest Dock Score has
N-substituted chloracetamide derivatives (2–7) which were synthe-
sized from secondary amines and chloroacetyl chloride, have been
explored due to their substrate specificity for DPP IV inhibition (20).
An introduction of 4-aminopiperidine substituent 8 (IC50 = 0.98 lM)
showed higher inhibition against DPP IV enzyme. Further, effect of
substitutions on DPP IV inhibitory activity was evaluated using 6 or
7
membered cyclic amines. The azepanyl derivative 12
(IC50 = 38.27 lM) preserved the activity as compared to less bulky
group as piperidine 13 (IC50 = 91.18 lM). Among the cyclic ana-
logues, good correlation with variation in ring size was observed
indicating minimum activity for piperidine analogue. Comparison of
potency indicates that bulkier group can be well tolerated and
922
Chem Biol Drug Des 2012; 80: 918–928

Thiazolopyrimidine Derivatives as Potent DPP IV Inhibitors
O
O
N
O
N
S
SCN
NH2
a
HN
b
HN
HN
NH2
N
O
N
1
NH2
O
O
O
O
R1
- HCl
Cl
NHR1
(a - f)
Cl
Cl
NH
+
e
d
c
( 2 - 7 )
O
N
O
R
S
N
R1
S
N
N
N
NH2
NH2
O
O
O
N
, R1 =
, R1 =
, R1 =
14
15
16
17
18
benzyl
4 - aminopiperidinyl
azepanyl
piperidynyl
, R =
, R =
, R =
8
12
13
1
(piperidin-yl-)ethyl
9
(4-chlorophenyl)piperazin - 1 -yl
(pyridin-2-yl)piperazin -1-yl
(pyrimidyl-2-yl)piperazin-1-yl
, R =
, R1 =
(morpholin-4-yl)ethyl
10
11
, R1=
, R = N,N - diethylethanamino
, R =
N,N - dimethylethanamino
Scheme 1: (a) Br2 ⁄ KSCN, DMF, (b) DMF, 80–120 ꢀC, (c) NHR (a–h) secondary amines, diisopropylethylamine, 1,4-dioxan, reflux, 2 h, (d) 2–
7, anhydrous K2CO3, DMF, 70–80 ꢀC, (e) RCl (alkyl chlorides), anhydrous K2CO3, DMF, 70 ꢀC.
decrease in bulkiness may be responsible for diminished inhibitory
activity. Alternative approach for improving the inhibitory effect was
explored by using bicyclic analogues such as substituted piperazine
which offered highly potent compounds of series as 9, 10 and 11.
Dramatic rise in potency was seen with substitution of chlorophenyl
piperazine 9 (IC50 = 0.489 lM). It was observed that introduction of
electron withdrawing chlorine atom at 4-position of phenyl ring is
desirable for enhancement of activity. These results prompted us to
introduce pyridyl piperazine 10 (IC50 = 0.329 lM) having an electron
deficient aromatic pyridyl moiety which led the most potent com-
pound of series. Conversely, no beneficial modification was seen
with pyrimidyl piperazine 11 (IC50 = 1.494 lM) which showed weak
inhibition. However, pyrimidyl piperazine derivative provided an
inhibitor with rise in potency as compared to non-substituted scaf-
fold 1.
which suggest that decrease in alkyl chain length and replacement
by methyl group may lead to decrease in inhibitory activity.
In general, substantial decrease in potency was observed in few
cases with removal of ring strain and reduction in alkyl chain
length. Thus, we can say that incorporation of acetamide linker hav-
ing carboxyl group attached next to heteroatom can effectively con-
tribute to higher DPP IV enzyme inhibitory activity, which has
validated our rational of study design.
Antihyperglycemic activity
The most active compounds 9 and 10 were chosen for in-vivo
study on the basis of in-vitro DPP IV enzyme inhibitory activity.
These compounds were orally administered at the dose of
10 mg ⁄ kg. In single dose study, both the compounds lead to lower
plasma glucose levels beginning 30 min after glucose loading and
10 mg ⁄ kg dose significantly suppressed hyperglycaemia as com-
pared with control group. The results indicate that area under blood
glucose concentration-time curve (AUC) and OGTT significantly
reduced (<0.0001) glucose excursion during 0–2 h. Vildagliptin
showed 40.97% reduction of blood glucose at time of OGTT (at
1.5 h) at 10mg ⁄ kg. At the same time, compound 9 and 10 also
showed glucose lowering up to 32.81% and 31.27%, respectively,
at same dose. These results showed that the in-vivo efficacy of
both the compounds was comparable to vildagliptin at 10 mg ⁄ kg as
shown in Figure 2A,B.
The effect of alkyl chain length using methylene and ethylene linker
was assessed to understand the alterations in activity as a replace-
ment for acetamide linker (Table 2). The SAR revealed that benzylic
moiety having methylene linker 14 (IC50 = 34.61 lM) may be toler-
ated as substitution. The incorporation of ethylpiperidine 15
(IC50 = 32.69 lM) showed comparable potency with that of com-
pound 14. The potency was retained when N,N-diethylethamine 17
(IC50 = 2.46 lM) was introduced and replacement by ethylmorpho-
line analogue 16 (IC50 = 67.21 lM) leads to the drastic reduction in
inhibitory potency. Disappointingly, inhibition was decreased sharply
when N,N-dimethylethamine 18 (IC50 = 103.9 lM) was substituted,
Chem Biol Drug Des 2012; 80: 918–928
923

Sharma et al.
Table 1: DPP IV inhibitory effect of thiazolopyrimidine derivatives
1, 8–13
Table 2: DPP IV inhibitory effect of thiazolopyrimidine deriva-
tives, 14–18
O
O
R1
O
N
S
S
R
N
NH2
NH2
N
N
N
O
N
IC50 (lM)a
Compound
R1
IC50 (lM)a
Compound
R
1
8
11.87
0.98
14
34.61
H
H2N
N
15
16
17
32.69
67.21
2.42
N
N
O
N
9
0.489
Cl
N
O
N
O
18
103.9
2.5
10
11
0.329
1.49
N
N
N
P 32 ⁄ 98
O
N
N
S
O
NH2
N
aIC50 represents inhibitory concentration determined by non-linear regression
analysis using GRAPHPAD PRISM software.
N
N
N
O
12
13
38.27
91.18
18 were further evaluated for in silico studies. DPP IV molecule
consists of two domains, an eight stranded beta-propeller domain
at the N-terminus and a serine protease domain on the C-terminal
end. The active site is located in the serine protease domain and
comprises the catalytic triad Ser630, Asp708 and His740 which lies
in a cave-like pocket bounded by hydrophobic residues. The protein
around this active site comprises two subsites, a S1 pocket com-
prising residues Tyr631, Val656, Trp659, Tyr662, Tyr666 and Val711
and a S2 pocket lined by the side chains of residues Tyr547, Tyr631
and Pro550. The thiazolopyrimidine group of the derivatives docked
into the binding site pocket occupying a position akin to that
observed for triazolopyridine ring in biarylphenylalanine fluoropyrroli-
dine amide (compound 23) (PDB id: 2FJP) (28) (Figure S1). More-
over, the orientation of the thiazolopyrimidine nucleus in all the
derivatives is found to be oriented perpendicular to the triazolopyri-
dine ring of compound 23 (Figure 3). This orientation brings the
aromatic interactions with Phe357 in an edge to face rather than
parallel manner. Concurrently, it facilitates the formation of intermo-
lecular hydrogen bonds between the nitrogen atoms of the thiazolo-
pyrimidine ring and the hydroxyl group of Ser209 (Figure 4A–D)
which has been implicated to be essential for DPP IV inhibitors
(33).
N
O
N
O
O
P 32 ⁄ 98
2.5
N
S
NH2
a
IC50 represents inhibitory concentration determined by non-linear regres-
sion analysis using GRAPHPAD PRISM software.
Oral dosing of compounds 9 and 10 significantly decreased ele-
vated glucose challenge and possesses therapeutic efficacy, thus
improving glycemic control.
Modelling studies
Our concerned study is also focused to understand the binding
mode of thiazolopyrimidne moiety and to investigate the necessary
interactions required for DPP IV inhibition. On the basis of results
obtained from in-vitro screening, compounds 1, 8, 9, 10, 11 and
The compound 8 has a piperidine ring, which does not occupy the
S1 pocket. It lies near the catalytic triad which brings the primary
924
Chem Biol Drug Des 2012; 80: 918–928

Thiazolopyrimidine Derivatives as Potent DPP IV Inhibitors
Figure 2: Effect of compound 9
and 10 on blood glucose level in
an oral glucose tolerance test
(OGTT) using streptozotocin induced
diabetic rats: (A) time course of
changes in blood glucose level and
(B) area under the blood glucose
concentration-time curve (AUC) for
the period of 0–2 h during OGTT.
Data are expressed as mean € -
SEM for 6 animals in each group.
***p < 0.0001 versus diabetic
group.
comparison with compound 8, and consequently, the thiazolopyrimi-
dine ring moves towards Glu361 where it interacts both with the
carboxylate group of this residue together with Arg358 (Figure 4B).
However, the piperazine moiety in compound 9 unlike compound 8
lacks the capability to form hydrogen bonded interactions with the
protein. The chlorophenyl group in compound 9 lies in the S1
pocket and interacts with the aromatic ring side chains of Tyr662
and Tyr666 (Figure 4B). This leads to a twofold increase in inhibi-
tory activity of compound 9 as compared to compound 8 indicating
that the occupation of the hydrophobic S1 pocket plays an impor-
tant role in the inhibitory activity. This is also supported by a higher
steric interaction energy (more negative) of compound
9
()38.55 kcal ⁄ mol) in comparison with compound 8 ()29.21 kcal ⁄ -
mol) (Table 3).
In compounds 10 and 11, the aryl moiety (pyridine ⁄ pyrimidine) at
the piperazine ring also resides in the S1 pocket and results in aro-
matic interactions resembling the chlorophenyl group of compound
9 (Figure 4C,D). The nitrogen (N23) atom in the pyridine ⁄ pyrimidine
aryl moiety in compound 10 and 11 forms a hydrogen bond with
hydroxyl group of Tyr666 (Figure 4C,D). However, the other nitrogen
(N25) atom in pyrimidine aryl moiety of compound 11 results in a
nearly fourfold lower activity as compared to pyridine containing
compound 10. This is due to the resulting repulsive force existing
between the similarly charged N25 atom in the ring and Nz atom
Figure 3: The binding conformation of docked compounds in
stick rendering and DPP IV (GRASP surface rendering) along with
selected side chains in stick) (PDB id: 2FJP). The compound 1 is
shown in grey colour, 8 in green, 9 in cyan, 10 in magenta, 11 in
yellow and 17 in orange.
amino group of piperidine within hydrogen bonding distance from
the side chain atoms of the catalytic triad residues (Figure 4A). As
a result, compound 8 acts as a potent inhibitor. The compound 9
has is bulkier, having chlorophenyl substituent at piperazine ring, in
Chem Biol Drug Des 2012; 80: 918–928
925

Sharma et al.
A
B
C
D
Figure 4: The docked complex
of (A) compound 8, (B) compound
9, (C) compound 10 and (D) com-
pound 11 in the binding pocket of
DPP IV. The DPP IV is shown in
cartoon rendering with selected
binding site residues in (stick ren-
dering in green) and compounds in
(stick rendering in cyan).
Table 3: Docking results of compounds (1, 8–11, 17) with DPP IV
Docking energy (kcal ⁄ mol)
Ligand
Steric
Electrostatic
Total
Interacting residues with docked ligand (hydrogen-bonded residues are highlighted in bold)
Compound 8
Compound 9
Compound 10
Compound 11
Compound 17
Compound 1
)29.21
)38.55
)32.43
)33.19
)24.64
)15.83
)21.67
)13.04
)21.64
)15.74
)20.70
)15.84
)50.88
)51.59
)54.07
)48.93
)45.34
)31.67
R125, E205, E206, S209, F357, R358, Y547, S630, Y662, Y666, R669, N710, H740
R125, E205, E206, S209, F357, R358, E361, Y547, V656, S630, Y631, Y662, Y666, N710, V711
R125, E205, E206, S209, F357, R358, E361, Y547, S630, Y631, Y662, Y666, N710, H740
R125, E205, E206, S209, F357, R358, E361, Y547, S630, Y631, Y662, Y666, N710, H740
R125, E205, E206, V207, S209, F357, Y547, S630, Y631, Y662, Y666, R669
E205, E206, V207, S209, F357, R358
of Arg125 as reflected by decrease in electrostatic interaction
energy (less negative) (Table 3).
ric interaction energy (Table 3). The compound 17 has the same
thiazolopyrimidine nucleus but lacks piperazine ring. Its ethyl substi-
tuent lies in the S1 pocket and thiazolopyrimidine nucleus occupies
the adjacent pocket where it interacts with Arg125, Glu206 and
Ser209. This is less potent than compound 8, 9, 10 and 11 ethyl
substituent occupies S1 pocket less optimally as evident from lesser
steric interaction energy (Table 3). The compound 1, thiazolopyrimi-
dine nucleus, occupies the binding position similar to the other
compounds in the series but in the opposite orientation. It forms
strong face to face p-p interaction with aromatic ring of Phe357 in
addition to hydrogen bonded interactions with Glu206 and Arg358.
The compound 10 is more potent than compound 9 due to pres-
ence of an additional hydrogen bonded interaction between the
nitrogen atom of pyridyl group and the side chain of Tyr666 (Fig-
ure 4C). This is also corroborated by better electrostatic interaction
energy of compound 10 in comparison with compound 9, in spite
of compound 9 having higher steric interaction energy (Table 3).
However, compound 9 is more potent than compound 11 because
of greater occupancy of S1 pocket as evident from increase in ste-
926
Chem Biol Drug Des 2012; 80: 918–928

Thiazolopyrimidine Derivatives as Potent DPP IV Inhibitors
The identified potent inhibitors of DPP IV, compounds 8, 9, 10, 11
concept. Recent Pat Endocr Metab Immune Drug Discov;1:
15–24.
and 17, have predicted to have good ADMET property. All of these
satisfy four criteria of Lipinski's rule of five for drug like compound.
Their molecular weight ranges from 338 Da to 434 Da and calcu-
lated LogP value lies between 1.6 to )1.5. The maximum number
of hydrogen bond acceptor is 8 in compound 11 and the number of
hydrogen bond donor is either 1 or 2. Hence, it indicates that they
should have good oral bioavailability. They also have moderate to
good predicted score for blood–brain barrier penetration, CYP2D6
interactions and hepatotoxicity. Hence, they are very good drug like
compounds that can provide good drug candidate.
6. Wu J., Chen Y., Shi X., Gu W. (2009) Dipeptidyl peptidase IV
(DPP IV): a novel emerging target for the treatment of type 2
diabetes. J Nan Jing Med Univ;23:228–235.
7. Mest H.J., Mentlein R. (2005) Dipeptidyl peptidase inhibitors as
new drugs for the treatment of type 2 diabetes. Diabetolo-
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ways for novel therapies. Trends Endocrinol Metab;20:280–286.
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In conclusion, we synthesized series of thiazolopyrimidine deriva-
tives evaluated for inhibitory activity against DPP IV enzyme. Among
these, compounds 9 (IC50 = 0.489 lM) and 10 (IC50 = 0.329 lM)
showed excellent DPP IV inhibition and exhibited pronounced in-vivo
antihyperglycemic activity in streptozotocin induced diabetic rat
model. Furthermore, heterocyclic-substituted piperazines with an
acetamide linker were indicated to offer the best potent DPP IV
inhibitors. Molecular docking studies of active compounds displayed
the probable binding interactions in the binding site of DPP IV.
Thus, thiazolopyrimidine nucleus demonstrated a potential bioactive
core for design of DPP IV inhibitors with desirable bioactivity for
type 2 diabetes.
mantan-1-yl)amino]acetyl}-pyrrolidine-2-carbonitrile).
Pharmacol;70:134–143.
Biochem
13. Brigance R.P., Meng W., Fura A., Harrity T., Wang A., Zahler R.,
Kirby M.S., Hamann L.G. (2010) Synthesis and SAR of azolopyrimi-
dines as potent and selective dipeptidyl peptidase-4 (DPP4) inhibi-
tors for type 2 diabetes. Bioorg Med Chem Lett;20:4395–4398.
14. Deng J., Peng L., Zhang G., Lan X., Li C., Chen F., Zhou Y., Lin
Z., Chen L., Dai R., Xu H., Yang L., Zhang X., Hu W. (2011) The
highly potent and selective dipeptidyl peptidase IV inhibitors
bearing a thienopyrimidine scaffold effectively treat type 2 dia-
betes. Eur J Med Chem;46:71–76.
15. Wallace M.B., Feng J. (2008) Structure-based design and syn-
thesis of benzimidazole derivatives as dipeptidyl peptidase IV
inhibitors. Bioorg Med Chem Lett;18:2362–2367.
16. Cheon H.G., Lee C.M., Kim B.T., Hwang K.J. (2004) Lead discov-
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Acknowledgments
The funding of this study was supported by Government of NCT
Delhi, India. One of the author, MS is also pleased to acknowledge
Udaya P. Singh, SHIATS for his critical discussion and suggestions
on the manuscript. The support from the Indian council of Medical
Research in the form of the Bio-Medical Informatics Centre is grate-
fully acknowledged. The authors acknowledge Novartis Switzerland
for providing vildagliptin.
17. Zhu Y., Xia S., Zhu M., Yi W., Cheng J., Song G., Li Z., Lu P.
(2010) Synthesis, biological assay in-vitro and molecular docking
studies of new imidazopyrazinone derivatives as potential dip-
eptidyl peptidase IV inhibitors. Eur J Med Chem;45:4953–4962.
18. Eckhardt M., Hauel N., Himmelsbach F., Langkopf E., Nar H.,
Mark M., Tadayyon M., Thomas L., Guth B., Lotz R. (2008) 3,5-
Dihydro-imidazo[4,5-d]pyridazin-4-ones: a class of potent DPP-4
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19. Kurukulasuriya R., Rohde J.J., Szczepankiewicz B.G., Basha F.,
Lai C., Jae H.S., Winn M., Stewart K.D., Longenecker K.L., Lub-
ben T.W., Ballaron S.J., Sham H.L., Geldern T.W.V. (2006) Xan-
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Bioorg Med Chem Lett;16:6226–6230.
Conflict of Interest
None.
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Supporting Information
Additional Supporting Information may be found in the online ver-
sion of this article:
Figure S1. The binding conformation of docked compound 10
(stick rendering in cyan) superimposed on crystal structure of com-
pound 23 (stick rendering in orange) in DPP IV (GRASP surface ren-
dering) (PDB id: 2FJP).
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