Synthesis and biological evaluation of ticagrelor derivatives as novel antiplatelet agents

Article abstract of DOI:10.1016/j.bmcl.2012.04.050

Ticagrelor (1) is the first reversible P2Y12 receptor antagonist blocking adenine diphosphate (ADP)-induced platelet aggregation with rapid onset and offset of effects. In this study, synthesis of ticagrelor and its derivatives has been accomplished in a convergent way. The compound design was based on modifications of ticagrelor and its major metabolite (33) in order to ameliorate their pharmacokinetic properties and dosing profile. The final compounds (1a-g, 35a-g) were evaluated for their inhibitory effect on ADP-induced platelet aggregation in rats. The assay results showed that some compounds (e.g., 1b, 1d, 33, 35b, 35f) exhibited comparable potency with that of ticagrelor.

Full text of DOI:10.1016/j.bmcl.2012.04.050

Bioorganic & Medicinal Chemistry Letters 22 (2012) 3598–3602
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and biological evaluation of ticagrelor derivatives as novel
antiplatelet agents
Hao Zhang a,b, Jun Liu b,c, Luyong Zhang b,c, Lingyi Kong b, Hequan Yao b, Hongbin Sun a,b,
⇑
a Center of Drug Discovery, College of Pharmacy, China Pharmaceutical University, 24 Tongjia Xiang, Nanjing 210009, China
b State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing 210009, China
c Jiangsu Center for Drug Screening, China Pharmaceutical University, Nanjing 210038, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Ticagrelor (1) is the first reversible P2Y12 receptor antagonist blocking adenine diphosphate (ADP)-
induced platelet aggregation with rapid onset and offset of effects. In this study, synthesis of ticagrelor
and its derivatives has been accomplished in a convergent way. The compound design was based on mod-
ifications of ticagrelor and its major metabolite (33) in order to ameliorate their pharmacokinetic prop-
erties and dosing profile. The final compounds (1a–g, 35a–g) were evaluated for their inhibitory effect on
ADP-induced platelet aggregation in rats. The assay results showed that some compounds (e.g., 1b, 1d,
33, 35b, 35f) exhibited comparable potency with that of ticagrelor.
Received 27 February 2012
Revised 16 March 2012
Accepted 10 April 2012
Available online 16 April 2012
Keywords:
Ticagrelor
Metabolite
Ó 2012 Elsevier Ltd. All rights reserved.
Antiplatelet activity
Derivatives
Synthesis
Platelet activation is critical in atherothrombosis, leading to
heart attacks, myocardial infarction, and unstable angina.1 In the
past decades, increasing evidence demonstrates that ADP initiates
platelet aggregation by simultaneous activating G protein-coupled
receptors P2Y12. Because of its central role in the formation and
stabilization of a thrombus, the P2Y12 receptor is now a well-
established target of antithrombotic drugs, especially the thieno-
pyridines such as clopidogrel and prasugrel that are irreversible
P2Y12 inhibitors. Currently, dual treatment with aspirin and clop-
idogrel is the cornerstone of antiplatelet therapy for patients with
acute coronary syndromes (ACS) and prevention of thrombotic
events after percutaneous coronary intervention (PCI) with stent-
ing.2 However, a major disadvantage of clopidogrel is its reduced
antiplatelet function (referring to ‘clopidogrel resistance’) in 30–
55% patients with a loss-of-function polymorphism in the gene
encoding cytochrome P450 2C19 (CYP2C19), which is responsible
for its hepatic transformation into the active metabolite.3 For over-
coming drug resistance in ACS patients, prasugrel has been devel-
oped and launched, albeit with suffering from a high bleeding risk.
In contrast to irreversible P2Y12 inhibitors, ticagrelor (1) is the first
reversible P2Y12 inhibitor approved by FDA for the prevention of
thrombotic events such as stroke or heart attack in patients with
ACS or myocardial infarction with ST elevation. Through its direct
and reversible mode of action, ticagrelor exhibits rapid onset and
offset of effects, making it more suitable for patients who are going
to take surgery. In addition, unlike the thienopyridines, ticagrelor
does not require metabolic activation,4 indicating a less variability
related to genetic polymorphisms.5 However, the bleeding risk of
ticagrelor still exists, and patient compliance is also of concern
since ticagrelor has to be taken twice daily. That is, there are still
unmet medical needs for the treatment of ACS and its complica-
F
HN
F
N
N
N
HO
N
O
N
S
1
HO
OH
retrosynthetic analysis
HO
O
NH2
Cl
H2N
Cl
F
N
NH2
O
O
N
S
F
⇑
Corresponding author. Tel./fax: +86 25 83271198.
E-mail address: hbsun2000@yahoo.com (H. Sun).
4
3
2
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.04.050

H. Zhang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 3598–3602
Cl
3599
H2N
HO
N
HO
NH2
O
Cl
N
HN
O
N
S
H2N
Cl
N
a
b
+
O
O
S
O
O
5
2
3
F
F
Cl
HN
N
N
N
N
O
N
HO
N
O
HO
c
N
O
N
S
N
O
N
S
O
6
7
O
F
F
HN
N
N
N
HO
d
N
O
N
S
1
HO
OH
Scheme 1. Reagents and conditions: (a) TEA, NaI, 1,4-dioxane, 120 °C; (b) NaNO2, acetic acid, H2O, EtOAc; (c) 4, DIPEA, DCM; (d) concd HCl, methanol.
OH
OH
OH
N
N
c
a, b
N
N
N
N
HO
N
S
HO
N
SH
HO
S
8
9
2-Thiobarbituric acid
d
Cl
N
Cl
Cl
f
H
e
H2N
N
N
N
N
H
N
N
N
Cl
N
S
Cl
N
S
Cl
S
10
2
11
Scheme 2. Reagents and conditions: (a) CH3CH2CH2I, NMP, NaOH, H2O; (b) HCl; (c) p-toluidine, NaNO2, H2SO4, ethanol, H2O, 0 °C; (d) POCl3, pyridine, toluene, 90 °C; (e) Zn,
HCOONH4, methanol; (f) Raney-Ni, H2, methanol.
tions, and novel antiplatelet agents with fast onset of action, less
interindividual variability, and low risk of bleeding are desirably
needed.
The current Letter describes the design, synthesis and biologi-
cally evaluation of ticagrelor derivatives, especially the prodrugs
of ticagrelor or its active metabolite, in order to find more potent
and safer antiplatelet agents. The compounds were evaluated for
their antiplatelet effects in rats. To the best of our knowledge, this
Letter is among the first to report synthesis and biological evalua-
tion of ticagrelor derivatives.
Ticagrelor was synthesized convergently as depicted in Schemes
1–4.6–11 As shown in Scheme 1, reaction of pyrimido dichloride 2
and amino alcohol 3 gave amino pyrimidine 5, which was converted
to the triazolopyrimidine 6 under diazotization conditions. Reac-
tion of 6 with amine 4 followed by deprotection afforded 1.6
Preparation of pyrimido dichloride 2 is outlined in Scheme 2.
Reaction of 2-thiobarbituric acid with 1-iodopropane under basic
condition, followed by acidification, gave pyrimidine 8.7 Azo
coupling reaction of 8 with p-toluene diazonium salt yielded azo
compound 9. Chlorination of 9 by phosphorus oxychloride afforded
dichloride 10. Reduction of 10 by active zinc powders/ammonium
formate and Raney’s nickel/hydrogen gas in sequence provided
amino pyrimidine 2.
Synthesis of amino alcohol 3 is depicted in Scheme 3. Amino
alcohol 18 was prepared following the reference method starting
with D
-ribose.8,9 N-protection of 18 with Cbz-Cl yielded alcohol
19, which was alkylated with ethyl bromoacetate in the presence
of NaH (60%) at À30 °C to give ester 20. Reduction of 20 with LiBH4
provided alcohol 21, which was hydrogenated in the presence of
Pd/C to form amino alcohol 3.10
Synthesis of amine 4 is summarized in Scheme 4. Following ref-
erence method,11 reaction of chloroacetyl chloride with 1,2-difluo-
robenzene by Friedel–Crafts acylation yielded ketone 22, which
was stereoselectively reduced by borane dimethylsulfide in the

3600
H. Zhang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 3598–3602
HO
HO
O
TsO
OMe
OMe
O
c
O
b
a
OH
OH
HO
O
O
O
O
D-ribose
12
13
O
N
O
N
I
OMe
O
O
Bn
d
e
f
Bn
O
O
O
O
O
O
O
O
17
15
16
EtO2C
14
HN Cbz
HO
HO
NH2
O
HN Cbz
h
j
i
g
O
O
O
O
O
O
20
19
18
HO
HO
O
HN
Cbz
O
NH2
k
O
O
O
O
21
3
Scheme 3. Reagents and conditions: (a) concd HCl, methanol, acetone; (b) pyridine, p-toluenesulfonyl chloride, DCM; (c) NaI, DMF, 120 °C; (d) activated zinc, ethanol, 60 °C;
(e) N-benzylhydroxylamine, ethanol; (f) DMF, 130 °C; (g) Pd/C (10%), H2, methanol; (h) Cbz-Cl, DIPEA, MIBK; (i) NaH (60%), ethyl bromoacetate, THF, À30 °C; (j) LiBH4, THF,
0 °C; (k) Pd/C (10%), H2, methanol.
OH
O
F
F
Cl
F
F
F
F
Cl
O
a
b
Cl
+
Cl
23
22
c
O
F
F
F
F
e
d
CO2Et
COOH
26
f
25
F
F
24
F
F
F
F
F
g
h
NH2
COCl
CONH2
F
28
27
4
Scheme 4. Reagents and conditions: (a) AlCl3, 60 °C; (b) BH3-Me2S, (S)-DPPM, B(OCH3)3, toluene; (c) NaOH, H2O, toluene, 40 °C, (d) t-BuOK, triethyl phosphonoacetate,
toluene, 60–80 °C; (e) NaOH, methanol, H2O, 65 °C; (f) SOCl2, 35 °C; (g) ammonia, H2O; (h) NaOH, NaOCl, H2O, 40 °C.
presence of (S)-diphenylprolinol to afford optically pure alcohol 23
with S-configuration. Treatment of 23 with NaOH gave epoxide 24.
Wadsworth–Emmons cyclopropanation of 24 with triethyl phos-
phonoacetate in the presence of potassium tert-butoxide afforded
ester 25, which was hydrolyzed to afford carboxylic acid 26. Con-
version of 26 to amide 28, followed by Hofmann degradation fur-
nished amine 4.
As mentioned above, patients have to take ticagrelor twice a
day, thus posing a challenge to compliance. In order to prolong
drug action time, a series of ester and carbonic ester derivatives
of ticagrelor (1a–g) were synthesized as shown in Scheme 5. Reac-
tion of 7 with acyl anhydrides, acyl chlorides, or chlorocarbonic
acid esters in the presence of triethylamine gave esters 29a–g.
We encountered some difficulties in selective removal of the iso-
propylidene protecting group during the preparation of 1a–g, with
the ester groups being susceptible to hydrolysis. Finally, we found
that 1.0% iodine in methanol (w/v)12 worked well to selectively re-
move the isopropylidene group, giving rise to 1a–g in good yields.
AR-C124910XX (33), the major metabolite of ticagrelor, is rap-
idly formed by cytochrome P450 3A (CYP3A)-mediated metabo-
lism.13 It is worth noting that 33 and its parent compound have
a similar potency in inhibiting the P2Y12 receptor,14 implying that
a prodrug approach based on 33 might lead to novel antiplatelet
agents. Therefore, 33 and its ester and carbonic ester derivatives
(35a–g) were synthesized as outlined in Scheme 6. Reaction of
pyrimido dichloride 2 with amino alcohol 18 afforded amino
pyrimidine 30, which was converted to the triazolopyrimidine 31
under diazotization conditions. Chloro displacement of 31 with
amine 4 yielded triazolo-pyrimidine 32. Reaction of 32 with acyl
anhydrides, acyl chlorides, or chlorocarbonic acid esters in the
presence of triethylamine, followed by selective deprotection, gave
esters 35a–g.

H. Zhang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 3598–3602
3601
F
F
F
HN
HN
N
F
O
N
N
N
N
N
O
HO
R
N
O
O
a
N
O
N
N
S
O
S
O
O
29a-g
7
F
F
HN
O
N
N
b
R
N
O
N
O
N
S
HO
OH
1a-g
Scheme 5. Reagents and conditions: (a) ROCl, ROCOCl or anhydrides, TEA, acetonitrile; (b) 1.0% iodine in methanol (w/v), 60 °C.
Cl
N
Cl
N
H2N
HN
N
N
N
N
N
S
a
S
HO
HO
b
2
+ 18
O
O
O
O
31
30
F
F
F
F
HN
HN
N
N
N
N
N
N
N
c
d
N
HO
HO
N
S
N
S
O
O
HO
OH
33
32
e
F
F
F
HN
N
F
HN
O
N
O
N
N
N
O
N
f
N
N
O
R
S
N
R
O
N
S
O
HO
OH
35a-g
34a-g
Scheme 6. Reagents and conditions: (a) TEA, NaI, 1,4-dioxane, 120 °C; (b) NaNO2, acetic acid, H2O, EtOAc; (c) 4, DIPEA, DCM; (d) concd HCl, methanol; (e) ROCl, ROCOCl or
anhydrides, TEA, acetonitrile; (f) 1.0% iodine in methanol (w/v), 60 °C.
The synthesized ticagrelor derivatives were evaluated for their
inhibitory effect on ADP-induced platelet aggregation in rats at
dose of 5 mg/kg. Ticagrelor (1) was used as a positive control.
ADP-induced platelet aggregation was determined by Born’s
method.15 The assay results are summarized in Table 1. The results
demonstrate a variable degree of antiplatelet activity for the test
compounds. As expected, ticagrelor exhibited very strong inhibi-
tory activity, while its major metabolite (33) was slightly less

3602
H. Zhang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 3598–3602
Table 1
Inhibitory effect of ticagrelor derivatives (1a–g and 35a–g) on ADP-induced platelet aggregation in rats at dose of 5 mg/kga
F
F
F
HN
N
HN
N
F
O
N
N
O
N
N
N
R
N
O
N
N
R
O
O
S
S
HO
OH
HO
OH
35a-g
1a-g
Compd
R
Inhibition of platelet aggregation (%)
1
1a
1b
1c
1d
1e
—
Propyl
tert-Butyl
Phenyl
Ethoxy
66.27⁄⁄⁄
NAb
46.12⁄
NA
47.68⁄⁄
Isobutoxy
NDc
1f
1g
Pyridine-3-yl
Styryl
NA
ND
33
—
45.72⁄⁄
ND
44.53
28.49
NA
20.10
42.55⁄⁄
13.23
—
35a
35b
35c
35d
35e
35f
35g
Vehicle
Methyl
Ethyl
Propyl
tert-Butyl
Phenyl
Ethoxy
Isobutoxy
—
a
b
c
Inhibition data refer to ex-vivo measurements 0.5 h after oral administration. ⁄P <0.05, ⁄⁄P <0.01, ⁄⁄⁄P <0.001 versus vehicle.
NA: Not Active.
ND: Not Determined.
potent than its parent compound. Carbonic ester derivatives with
small steric hindrance exhibit potent inhibitory effect (e.g., 1d,
35f vs 35g), indicating that the steric hindrance at the ester groups
might reduce their hydrolysis rates and thus result in lower concen-
trations of the active drugs. The same tendency was also observed
with ester derivatives of 33 (e.g., 35b, 35c), while large substituents
led to significant decreases in potency (e.g., 35d), or even complete
loss of potency (e.g., 1c, 1f). However, two pivalic acid esters 1b and
35d showed entirely opposite effects: while 1b had a similar po-
tency to that of the active metabolite 33, 35d exhibited no activity
at all. Further exploration on SAR studies is needed.
In summary, 15 ticagrelor derivatives were synthesized and
evaluated for their inhibitory effect on ADP-induced platelet aggre-
gation in rats. The assay results showed that some compounds (e.g.,
1b, 1d, 33, 35b, 35f) exhibited comparable potency with that of
ticagrelor. Further investigation aimed at improving the pharmaco-
kinetic properties and dosing profile of ticagrelor is warranted.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2012.04.
050.
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Acknowledgements
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This work was supported in part by the ‘111 Project’ from the
Ministry of Education of China and the State Administration of
Foreign Expert Affairs of China (No. 111-2-07).