Design, Synthesis and Biological Evaluation of Imidazo[1,2-a]pyridine Derivatives as Novel DPP-4 Inhibitors

Article abstract of DOI:10.1111/cbdd.12560

A new series of DPP-4 inhibitors with imidazo[1,2-a]pyridine scaffold were designed by exploiting scaffold hopping strategy and docking study. Based on docking binding model, structural modifications of 2-benzene ring and pyridine moieties of compound 5a led to the identification of compound 5d with 2, 4-dichlorophenyl group at the 2-position as a potent (IC₅₀ = 0.13 μm), selective (DPP-8/DPP-4 = 215 and DPP-9/DPP-4 = 192) and in vivo efficacious DPP-4 inhibitor. Further, molecular docking revealed that compound 5d could retain key binding features of DPP-4 with the pyridine moiety of imidazo[1,2-a]pyridine ring providing an additional π-π interaction with Phe357 of DPP-4. Compound 5d might be a promising lead for further development of novel DPP-4 inhibitor treating T2DM.

Full text of DOI:10.1111/cbdd.12560

Received Date : 20-Jan-2015
Revised Date : 06-Mar-2015
Accepted Date : 12-Mar-2015
Article type
: Research Article
Title page
Title:
Design, synthesis and biological evaluation of imidazo[1,2-a]pyridine derivatives as novel DPP-4
inhibitors
Authors:
a
a
a
a
b
Qing Li , Muxing Zhou , Li Han , Qing Cao , Xinning Wang a, LeiLei Zhao a, Jinpei Zhou ,
Huibin Zhang a,c,
Affiliation and Address:
a Center of Drug Discovery, China Pharmaceutical University, Nanjing 210009, PR China
b Department of Medicinal Chemistry, China Pharmaceutical University, 24 Tongjia Xiang, Nanjing
210009, PR China
c
Jiangsu Key Laboratory of Drug Discovery for Metabolic Disease, China Pharmaceutical
University, Nanjing 210009, PR China
*Corresponding author:
Huibin Zhang
Center of Drug Discovery, China Pharmaceutical University, 24 Tongjiaxiang, Nanjing 210009, China
 Corresponding author: Huibin Zhang, Center of Drug Discovery, China Pharmaceutical University, Nanjing 210009, PR
China. Tel: +86-25-83271302. Fax: +86-25-83271480. Email: zhanghb80@cpu.edu.cn (H. Z.).
This article has been accepted for publication and undergone full peer review but has not
been through the copyediting, typesetting, pagination and proofreading process which may
lead to differences between this version and the Version of Record. Please cite this article as
an 'Accepted Article', doi: 10.1111/cbdd.12560
This article is protected by copyright. All rights reserved.

Tel: +86-25-83271302; Fax: +86-25-83271480.
E-mail addresses: zhanghb80@cpu.edu.cn
This study was supported by the China National Key Hi-Tech Innovation Project for the R&D of
Novel Drugs (No. 2013ZX09301303-002) and supported by Natural Science Foundation of Jiangsu
Province (No. BK20141349).
Design, synthesis and biological evaluation of imidazo[1,2-a]pyridine derivatives as novel DPP-4
inhibitors
a
a
a
a
b
Qing Li , Muxing Zhou , Li Han , Qing Cao , Xinning Wang a, LeiLei Zhao a, Jinpei Zhou ,
Huibin Zhang a,c,
a Center of Drug Discovery, China Pharmaceutical University, Nanjing 210009, PR China
b Department of Medicinal Chemistry, China Pharmaceutical University, 24 Tongjia Xiang, Nanjing
210009, PR China
c
Jiangsu Key Laboratory of Drug Discovery for Metabolic Disease, China Pharmaceutical
University, Nanjing 210009, PR China
Abstract
A new series of DPP-4 inhibitors with imidazo[1,2-a]pyridine scaffold were designed by exploiting
scaffold hopping strategy and docking study. Based on docking binding model, structural
modifications of 2-benzene ring and pyridine moieties of compound 5a led to identification of
compound 5d with 2, 4-dichlorophenyl group at the 2-position as a potent (IC50 = 0.13μM), selective
(DPP-8/DPP-4=215 and DPP-9/DPP-4=192) and in vivo efficacious DPP-4 inhibitor. Further
molecular docking revealed that compound 5d could retain key binding features of DPP-4 with the
pyridine moiety of imidazo[1,2-a]pyridine ring providing an additional π−π interaction with Phe357
of DPP-4. Compound 5d might be a promising lead for further development of novel DPP-4 inhibitor
treating T2DM.
 Corresponding author: Huibin Zhang, Center of Drug Discovery, China Pharmaceutical University, Nanjing 210009, PR
China. Tel: +86-25-83271302. Fax: +86-25-83271480. Email: zhanghb80@cpu.edu.cn (H. Z.).
This article is protected by copyright. All rights reserved.

Keywords Type 2 diabetes mellitus, Dipeptidyl peptidase-4 inhibitor, imidazo[1,2-a]pyridine
derivatives, docking study.
Abbreviations: T2DM (Type 2 diabetes mellitus), DPP-4 (Dipeptidyl peptidase-4), GIP
(insulinotropic polypeptide), GLP-1 (glucagon-like peptide-1), OGTT (oral glucose tolerance test)
Type 2 diabetes mellitus (T2DM) is a chronic, progressive metabolic disease characterized by
hyperglycemia resulting from insulin deficiency and insulin resistance (1). T2DM affects more than
370 million people worldwide (2, 3), and is associated with harmful microvascular and macrovascular
complications such as retinopathy, nephropathy and coronary artery disease (4). Incretin hormones,
glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), play a key
role in the maintenance of normal glucose homeostasis (5). Both incretins can glucose-dependently
stimulate insulin secretion and inhibit glucagon release, and also delay gastric emptying and
suppresses appetite (6). In plasma, the active forms of these incretins are rapidly metabolized by
dipeptidyl peptidase-IV (DPP-4). Thus inhibition of DPP-4 can increase their plasma endogenous
levels of both incretins, and consequently improve glycaemic control of T2DM (7). DPP-4 inhibitors
such as sitagliptin(8), linagliptin(9), alogliptin(10) and teneligliptin(11) (Fig.1), have been approved
for the treatment of T2DM (12, 13). With comparable efficacy to sulfonylureas, DPP-4 inhibitors can
control hyperglycemia alone or in combination with other agents(14). They show a good safety and
tolerability profile, have no intrinsic risk of causing hypoglycemia, and are weight neutral (15).
However, these agents still do not meet clinic and commercial demands, especially for elderly patient
with T2DM (16). We report herein the design, synthesis and biological evaluation of
imidazo[1,2-a]pyridine derivatives as novel DPP-4 inhibitors.
Design
The design of new active hit compounds with novel scaffolds that are suitable for further hit-to-lead
optimization is a crucial step in the drug discovery process (17, 18). Scaffold hopping is one strategy
for discovering new molecules with novel scaffolds by modifying the core structure of template
molecules (19). Various DPP-4 inhibitors previously reported in literature provide many template
molecules for design novel scaffold compounds by using scaffold hopping approach (20). Among
them, a class of DPP-4 inhibitors with substituted bicyclic scaffolds (compound 1, 2 and 3) were
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discovered by Takeda and Bristol-Myers Squibb groups as potent, selective, and efficacious DPP-4
inhibitors(21-23), and were selected as template molecules. The aligned crystallographic structures of
DPP-4 complexed with compound 1, 2 and 3 (PDB ID: 3OPM 3NOX and 4JH0) (21-23) revealed that
the binding model of those compounds structurally overlapped well (Fig. 2). All of them incorporate
hydrophobic benzene ring to interact with S1 pocket; methylamine forms salt bridges with Glu205
and Glu206 and exhibits hydrogen binding interactions with Tyr662 (Fig.2). This type of salt bridge
interaction and hydrophobic binding between enzyme and ligand are two key features of DPP-4 (24).
Based on the results stated above, a novel bicyclic scaffold attached with hydrophobic benzene ring
and methylamine (Fig.2) was proposed to serve as novel DPP-4 inhibitors. This hypothesis was then
evaluated by computational docking study of imidazo[1,2-a]pyrimidin-3-yl)methanamine (compound
4, Fig. 3) to the DPP-4 receptor (PDB ID: 4JH0, Fig. 3). Docking study was carried out using Glide
5.9 (25, 26). The docking results revealed that benzene ring and methylamine moiety of the designed
compound 4 can retain two key features and show similar docking mode as compound 3 (Fig. 3).
Benzene ring interacts with S1 pocket, and methylamine forms salt bridges with Glu205 and Glu206.
However, a difference in the binding modes of the two compounds was observed in hydrogen binding
interactions where methylamine does not form hydrogen binding interactions with Tyr 662 (Fig. 3).
To explore a suitable central scaffold for investigation, eleven new core scaffolds B–L that can
preserve the benzene ring and methylamine of compound 4 in similar positions were evaluated by
docking study using Glide SP algorithm (25, 26). Glide search for possible locations of the ligand in
the active-site region of the receptor by using a series of hierarchical filters (25, 27). The pose of the
ligand were scored using GlideScore scoring function, which is based on ChemScore, but includes a
steric-clash term with other rewards and penalties (26). As shown in Figure 3, the GlideScore of
compounds incorporating scaffolds A, B, H and J are higher than that of the rest of scaffolds, in
which the scaffold B exhibits the highest GlideScore of -7.886 kcal/mol. Considering both the
synthetic feasibility for structural modification and the docking results, we decided to investigate the
imidazo[1,2-a]pyridine scaffold B. Thus imidazo[1,2-a]pyridine analogues 5a-q were synthesized and
evaluated for DPP-4 inhibitory activity (Fig. 4).
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Methods and Materials
General chemistry
All reagents were purchased from commercial sources and used without further purification.
Analytical thin-layer chromatography (TLC) was performed on the glass-backed silica gel sheets
(silica gel 60 Å GF 254). Melting points were measured on capillary tube and were uncorrected. IR
1
spectra (in KBr pellets) were taken using Shimadzu FT-IR-8400S spectrophotometer. H NMR and
13C NMR spectra (DMSO-d6, CDCl3) were recorded with a Bruker AV-300 spectrometer (Bruker
Instruments, Inc., Billerica, MA, USA) in the indicated solvents (TMS as internal standard): the
values of the chemical shifts are expressed in δ values (ppm) and the coupling constants (J) in Hz.
High-resolution mass spectra were recorded using an Agilent QTOF 6520 (Agilent, santa clara, CA,
USA); Element analysis was performed on CHN-O-Rapid instrument (Elementar, Hanau, Germany).
Detailed synthetic procedures and characterization data for all synthesized compounds are provided in
the Supporting Information of this article.
In vitro assay for inhibition of DPP-4, DPP-8 and DPP-9
The DPP-4 Drug Discovery Kit (Enzo Life Sciences International, Inc.) was used for the assay of
inhibition of DPP-4 activity. The assay is based on the cleavage of 7-amino-4-methylcoumarin (AMC)
moiety from the C-terminus of the peptide substrate (H-Gly-Pro-AMC), which increases its
fluorescence intensity at 460 nm. The DPP-4 inhibitor P32/98 was selected as a control. The substrate
and DPP-4 enzyme were diluted 1/50 with assay buffer (50mM Tris, pH=7.5). 25 μL of assay buffer,
15μL of enzyme solution and 10 μL of appropriately diluted solutions of the test compounds were
o
added sequently to 96-well microtiter plates. After incubation at 37 C for 10 min, 50 μL of diluted
substrate solution was added. Fluorescence was measured using an excitation wavelength of 380 nm
and an emission wavelength of 460 nm by a Synergy H1 Multi-Mode Reader (BioTek, USA). The
inhibitory rate relative to the control without inhibitor was calculated and IC50 values were determined
by nonlinear regression fitted by GraphPad Prism 5. The assays for inhibition of DPP-8 and DPP-9
activity were performed in similar procedure by using DPP4-Glo™ Assay kit (Promega,
Cat.No.G8531), DPP-8 and DPP-9 enzymes (BPS, Cat. NO. 80080 and 80080).
In vivo oral glucose tolerance test (OGTT) in ICR mice
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Male ICR mice aged 10 weeks (18–22 g) were purchased from Comparative Medicine Centre of
Yangzhou University. The mice were kept under conventional temperature and humidity conditions
(12 h/12 h light-dark cycle) and had free access to food and tap water for 1 week before the
experimental period. The male ICR mice were fasted overnight (12 h), weighted, and randomized into
groups (n = 8). Mice were dosed orally with vehicle (0.5% methylcellulose aqueous solution),
linagliptin (suspended in vehicle; 3 mg/kg) or compound 5d (suspended in vehicle; 3, 10 and 30
mg/kg) at -30 min. Two blood samples were collected at -30 and 0 min by tail bleeding for glucose
determinations. Glucose (20% aqueous glucose solution, 2.5 g/kg) was subsequently administered
orally (at 0 min). Additional blood samples were collected at 30, 60 and 120 min after glucose load
for glucose determinations. The blood glucose was measured by blood glucose test strips (SanNuo
ChangSha, ChangSha, China). All animal procedures were done in accordance with the applicable
institutional and governmental regulations concerning the ethical use of animals.
Molecular Docking
Docking studies were carried out using Glide 5.9 in Schrödinger 2013 suite (Schrödinger LLC, NY,
USA) (25, 26). The DPP-4 protein was extracted from RCSB Protein Data Bank (PDB ID: 4JH0)(21).
Protein structures were prepared using Maestro protein preparation wizard (Schrödinger LLC,
Maestro 9.4, NY, USA) applying the default parameters. Ligands were built using Maestro build panel
(Schrödinger LLC, Maestro9.4, NY, USA) and prepared by LigPrep application. A docking grid
was constructed by using the centroid of the bound ligand and a maximum size of 10 Å. Molecular
docking of all molecules into the generated grid was performed by using the standard precision (SP)
docking mode. To validate the docking procedure, a self-docking of 11 selected crystallized ligands
into their DPP-4 protein was carried out. The root mean square deviations (RMSD) between the
predicted conformation and the observed X-ray crystallographic conformation of all
compounds were below 2.00 Å (Sup. Table 1), which revealed Glide is successful in reproducing
the binding position. The Glide Scores were correlated well with the reported pIC50 values. (Sup.
Figure 1), thus it was found to be promising in predicting the potency of new DPP-4 inhibitors.
Results and discussion
1. Chemistry
The synthetic route adopted to obtain imidazo[1,2-a]pyridine 5a-q is diagrammed in Scheme 1.
According to reported procedure(28, 29), core imidazo[1,2-a]pyridine derivatives 8a-n were
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conveniently obtained by the reaction of 2-aminopyridine and substituted phenacyl bromides 7a-k
that were synthesized by bromination of acetophenones 6a-k with copper (II) bromide (30). Vilsmeier
formylation using N, N-dimethylformamide and phosphoryl chloride of these cyclic products 8a-n
produced imidazo[1,2-a]pyridine aldehydes 9a-n with good yield. These aldehydes were later
converted into oximes 10a-n by condensation with hydroxylamine hydrochloride in
pyridine/ethanol(31). Reduction of oxime 10a-n with Zn powder in acetic acid led to primary amine.
Primary amine was protected with Boc group to facilitate purification by column chromatography, and
deprotection of Boc group with HCl gas afforded target componds 5a-n. Boc-protected 5n was
hydrolyzed with NaOH to give the acid 11o. Coupling of 11o with appropriate amines followed by
deprotection of Boc group yielded the compounds 5o-q.
2. In vitro DPP-4 inhibition studies and structure–activity relationships
The synthesized compounds 5a–q were evaluated for inhibition of human recombinant DPP-4 in an in
vitro assay at 500 nM using linagliptin and aloglitptin as positive controls. Inhibitory potency was
measured by following the increase of fluorimetric intensity at 460 nm upon hydrolysis of
H-Gly-Pro-aminomethylcoumarin (H-Gly-Pro-AMC). The compounds with good inhibition rates at
500 nM were further selected to determine their IC50 values. The inhibitory activities are depicted in
Table 1.
Primary docking studies showed that 2-benzene ring was bound to DPP-4 in the S1 pocket (Fig. 4),
our SAR analysis started with substitutions on the benzene ring. 2-Phenyl derivative (5a) showed
moderate inhibitory activity (IC50 = 13.69 μM). Introducing substituents on the 3’-position of the
phenyl ring led to decrease of activity, regardless of electron-donating or withdrawing groups (5a vs
5b, 5g and 5i). Bromine and chlorine atoms substituted on the 4’-position of the phenyl ring group (5j,
IC50 = 0.94 μM, 5c, IC50 = 6.46 μM) improved activity compared with unsubstituted 5a. When the
chlorine and methyl were introduced into the 2’-position, the inhibitory activities of the resulting
compound 5d 5e and 5h were improved dramaticlly compared with that of unsubstituted 5a. The
activity of 2’-methyl substituted 5h (IC50 = 0.29 μM) was 47-fold more potent than that of compound
5a. 2’,4’-dichlorine atoms substituted phenyl imidazo[1,2-a]pyridine (5d) displayed the most potent
activity with IC50 values of 0.13 μM, which was 100-fold more than that of compound 5a. Meanwhile,
the effects of substitutions on the pyridine moiety of 2-phenylimidazo[1,2-a]pyridine were further
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explored. Introducing of small hydrophobic methyl group on 6, 7 and 8-position of
imidazo[1,2-a]pyridine (5k, 5l and 5m) retained inhibitory activities. However, hydrophilic groups
(5o, 5p and 5q) on 7-position of imidazo[1,2-a]pyridine led to losing inhibitory activities.
3. Docking study
To gain further insight into the observed SAR and the binding mode of the imidazo[1,2-a]pyridine
derivatives, a docking study was conducted. We used the molecular docking program GLIDE 5.9 (25)
to dock compounds into a DPP-4 crystal structure (PDB ID: 4JH0) (21). The docking results were
shown in Figure 5. Compound 5d fits in the enzyme pocket topologically very well. The overlay of
5d against compound 3 shows two molecules interact with DPP-4 in a similar way (Fig.5 C). The
primary amino group at the 3-position of the imidazo[1,2-a]pyridine ring can make salt bridges
interaction with the Glu205 and Glu206 and hydrogen bond with Tyr662. The 2, 4-dichlorophenyl
group at the 2-position of the imidazo[1,2-a]pyridine ring fits tightly into the hydrophobic S1 pocket
well (Fig.5 B). These two key binding interactions may explain the observed potency increase of
compound 5d compared to compound 5a and the decreasing activity of compound 5q. Compound 5a
and 5q may not form two key binding interactions efficiently, in which compound 5a forms salt
bridges to Glu205 and Glu206, and does not exhibit hydrogen bond with Tyr662 (Fig. 5 A), while
phenyl ring of compound 5q cannot fully occupy S1 pocket due to the strong hydrogen binding
interaction of trifluoromethyl of triazolo[4,3-a]pyrazine ring with Arg358 (Fig. 5 D), thus compound
5q lost inhibitory activity. In addition, the pyridine moiety of imidazo[1,2-a]pyridine ring of
compound 5d provides an additional π−π interactions with the Phe357 (Fig. 5 B). This result may
explain the significantly enhanced potency of compound 5d.
4. Selectivity for DPP-4 over DPP-8 and DPP-9
Compounds 5d and 5h were chosen for further evaluation of inhibition selectivity for DPP-4 over
DPP-8 and DPP-9. The inhibitory activities for DPP-8/9 are listed in Table 2, As shown in Table 2,
compounds 5d and 5h showed good selectivity against other serine proteases. The selectivity ratio of
compound 5d for DPP-4 over DPP-8 and DPP-9 were 215 and 192, respectively. The IC50 value of
compound 5h for DPP-8 and DPP-9 were more than 100 μM, with > 340-fold selectivity ratio.
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5. Effects of 5d on glucose excursion after an oral glucose tolerance test (OGTT) in ICR mice
Compound 5d was chosen for in vivo evaluation as it showed good in vitro potency and selectivity.
Compound 5d (3, 10, and 30 mg/kg), linagliptin (3 mg/kg) or vehicle (0.5% methylcellulose aqueous
solution) was orally administered to 12 h-fasted ICR mice (n = 8 in each group) 30 min prior to an
oral glucose challenge (2.5 g/kg). Blood glucose values in the mice were measured at -30, 0, 30, 60,
and 120 min. The results are shown in Figure 3. The results indicated that compound 5d produces a
dose-dependent improvement of glucose tolerance in ICR after oral administration. Compound 5d (30
mg/kg) reduced area under the curve from 0 to 120 min (AUC)0–120 min to 33.53% (5d, 748.66±88.56;
vehicle control, 1,125.49±92.25), which was similar to the hypoglycemic effect of linagliptin (3
mg/kg, 35.0%, 731.57±84.56).
Conclusion
In this article, we reported the design, synthesis and biological evaluation of new DPP-4 inhibitor with
imidazo[1,2-a]pyridine scaffold. First, novel imidazo[1,2-a]pyridine DPP-4 inhibitors were designed
by using scaffold hopping strategy combining with docking study. Then, based on docking binding
model, structure modifications and SAR studies of 2-benzene ring and pyridine moieties of
2-phenylimidazo[1,2-a]pyridine were performed, and compound 5d with 2,4-dichlorophenyl group at
the 2-position was identified as a potent, selective and in vivo efficacious DPP-4 inhibitor. Finally,
further molecular modeling revealed compound 5d can fit in the enzyme pocket topologically very
well with the pyridine moiety of imidazo[1,2-a]pyridine ring providing an additional π−π interactions
with the Phe357 of DPP-4. Based on these results, compound 5d might be a promising lead
compound for further optimization. Currently, further optimization is underway and will be published
in due course.
Acknowledgements
This study was supported by the China National Key Hi-Tech Innovation Project for the R&D of
Novel Drugs (No. 2013ZX09301303-002), and supported by Natural Science Foundation of Jiangsu
Province (No. BK20141349).
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Figures and schemes captions
Figure 1. Marketed DPP-4 inhibitors.
Figure 2 Design of novel bicyclic scaffold compounds. Strcutures and Supperposition of crystal
structure of compound 1 (maganta), 2 (green) and 3 (cyan).
Figure 3 Docking binding mode for compound 4 (yellow) and its overlay against compound 3, and
results of Glide scoring (kcal/mol) of designed scaffolds A-L.
Figure 4 Design of novel imidazo[1,2-a]pyridine derivatives and docking binding mode of compound
5a (light pink).
Figure 5. The binding mode of compounds 5a, 5d and 5q with DPP-4. The receptor was shown as
cartoon, and residue in the active site as lines (orange), and compounds 5a, 5d and 5q was shown as
stick, hydrogen bond as dash (black). 5a (light pink) compound 5d (maganta) and 5q (blue),
compound 3 (cyan).
Figure 6. Effect of compound 5d during an OGTT in male ICR mice. (A) show time-dependent
changes of blood glucose after oral administration of compounds, followed by 2.5 g/kg oral glucose
challenge. Date in (B) represent AUC0–120 min of blood glucose levels. Values are mean ± SEM (n = 8).
**P≤0.01 compared to vehicle-treated ICR mice by Student’s t test; ***P ≤0.001 compared to
vehicle-treated ICR mice by Student’s t test.
Scheme 1. Synthesis of compounds 5a-q. Reagents and conditions: (a) CuBr2, EA/CHCl3, reflux, 16 h;
(b) 2-aminopyridine, NaHCO3, EtOH, r.t.~80 °C, 12 h; (c) POCl3, DMF, 0~60oC, 2h; (d) NH2OH·HCl,
pyridine, EtOH, reflux; (e) i. Zn, NaOAc, AcOH, r.t, 10h; ii. Boc2O, NaOH, EtOH, r.t., 3h; iii.
HCl(gas), EA/ether, 0 oC. (f) NaOH, H2O, MeOH, r.t., 5h; (g) compound 5o (i) HCl (gas), EA, 0 oC,
8h; compounds 5p-q (i)amine, HBTU, DIEA, THF, r.t., 5h; (ii) HCl (gas), EA, 0 oC, 8h.
Table 1 In vitro activities of compounds 5a-q for DPP-4.
Table 2 The inhibitory activity of compounds 5d and 5h for DPP-8 and DPP-9.
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Table 1 In vitro activities of compounds 5a-q for DPP-4.
Compd
5a
R1
H
R2
H
%Inhibition at 0.50μM
8.33±1.06
IC50(μM) a
13.69±2.10
>50
3’-Cl
H
2.17±0.93
5b
5c
4’-Cl
H
10.46±1.19
75.33±3.43
42.98±2.13
-1.98±1.76
6.46±0.20
0.13±0.03
0.65±0.05
NT b
2’,4’-diCl
2’,5’-diCl
3’,4’-diF
3’-Me
2’-Me
3’-CF3
4’-Br
H
5d
5e
H
H
5f
H
-2.70±1.70
NT b
5g
H
59.27±2.22
-1.19±0.96
0.29±0.06
NT b
5h
5i
H
H
23.7±1.56
0.94±0.12
7.46±0.22
5j
4’-Me
6-Me
10.31±0.87
5k
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4’-Me
4’-Me
4’-Me
4’-Me
7-Me
8-Me
34.08±2.31
3.70±1.44
0.54±0.83
-3.40±0.90
0.84±0.12
>50
5l
5m
5n
5o
6-COOMe
6-COOH
>50
NT b
-
-4.65±1.35
NT b
NT b
5p
5q
-
-
-9.09±1.42
-
-
0.001
0.007
Linagliptin
Alogliptin
a Measured in three independent experiments.
b NT: not tested
Table 2 The inhibitory activity of compounds 5d and 5h for DPP-8 and DPP-9.
Compound
5d
DPP-4 IC50 (μM)
0.13
DPP-8 IC50 (μM)
28
DPP-9 IC50 (μM)
25
0.29
5h
＞100
＞100
＞100
0.007
Alogliptin
＞100
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This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.