Development of a Novel and Scalable Process for the Synthesis of a Key Cangrelor Intermediate

Full text of DOI:10.1080/00304948.2019.1677442

Organic Preparations and Procedures International
The New Journal for Organic Synthesis
ISSN: 0030-4948 (Print) 1945-5453 (Online) Journal homepage: https://www.tandfonline.com/loi/uopp20
Development of a Novel and Scalable Process for
the Synthesis of a Key Cangrelor Intermediate
Vinodh Guvvala, Venkatesan Chidambaram Subramanian & Jayashree
Anireddy
To cite this article: Vinodh Guvvala, Venkatesan Chidambaram Subramanian & Jayashree
Anireddy (2019): Development of a Novel and Scalable Process for the Synthesis of a
Key Cangrelor Intermediate, Organic Preparations and Procedures International, DOI:
10.1080/00304948.2019.1677442
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Organic Preparations and Procedures International, 0:1–7, 2019
# 2019 Taylor & Francis Group, LLC
ISSN: 0030-4948 print / 1945-5453 online
DOI: 10.1080/00304948.2019.1677442
Development of a Novel and Scalable Process for
the Synthesis of a Key Cangrelor Intermediate
Vinodh Guvvala,1,2 , Venkatesan Chidambaram Subramanian,2
and Jayashree Anireddy1
1Centre for Chemical Science & Technology, Institute of Science &
Technology, Jawaharlal Nehru Technological University Hyderabad,
Kukatpally, Hyderabad 500 085, India
2Gland Pharma Ltd, Research and Development, D. P. Pally, Hyderabad 500
043, India
Cangrelor (Figure 1) is a parenteral drug that reversibly inhibits the P2Y12 receptor;
like ticagrelor, it does not require metabolic activation. It has a rather short half-life of
3 to 4 minutes;1,2 and, with an infusion of 4 mg/kg per minute, peak inhibition occurs
after 15 minutes. Cangrelor also has a rapid offset, with normal levels of platelet aggre-
gation returning after 60 minutes. Inhibitors of platelet activation and aggregation are
substances that are useful during percutaneous coronary intervention and other catheter-
ization techniques in order to reduce bleeding complications and in the treatment of
acute coronary syndromes and clotting disorders in general. One class of antiplatelet
agents includes the inhibitors of the P2Y12 receptor, a G-protein coupled purinergic
receptor which is an important component of platelet activation.3 Cangrelor (trade name
kengreal in the US and kengrexal in Europe) was approved by the United States Food
and Drug Administration in 2015.
In continuation of our ongoing research to improve the process and identify impur-
ities4–6 we now report a novel, convenient, and readily scalable approach for the synthe-
sis of the key intermediate of cangrelor. A detailed study has been undertaken to
identify, synthesize and characterize the cangrelor intermediates using up-to-date spec-
tral techniques (IR, NMR, and HRMS).
The synthesis of cangrelor has been reported in the literature starting from 2-
mercaptoadenosine7,8 (Scheme 1). The synthesis involves seven stages and additional
purifications to get cangrelor. During the synthesis, compound 5 serves as a key precur-
sor. This material is highly expensive. The reported preparation of this compound
involves four steps. However, the preparation suffers from certain drawbacks, most
importantly the availability of the starting material as being difficult to access. A lot of
purification procedures were involved in each stage, and these present difficulties in
scale-up. Therefore, a synthetic route starting from more readily available and cheaper
substrates was sought. The synthetic process reported in the literature7–11 shows that the
Received August 31, 2018; in final form July 3, 2019.
Address correspondence to Vinodh Guvvala, Gland Pharma Ltd, Research and Development, D.
P. Pally, Hyderabad 500 043, India. E-mail: vinodh.guvvala@glandpharma.com
1

2
Guvvala et al.
Figure 1. Cangrelor.
Reagents and conditions: i) CF CH CH I, NaOH, H O; ii) Ac O, NaOAc; iii) NaH, DMF, ClCH CH SMe; iv)
3
2
2
2
2
2
2
MeO-, MeOH, heat.
Scheme 1. Synthesis of cangrelor key intermediate 5 from 2-mercaptoadenosine (1).
2-mercaptoadenosine (1) was S-alkylated with 1-iodo-3,3,3-trifluoropropane in the pres-
ence of NaOH to give trifluoropropyl sulfide (2). This was followed by acetylation of 2
using acetic anhydride in the presence of anhydrous sodium acetate at 80 ꢀC to provide
3. In our hands, during the acetate formation, we observed penta-acetate and tri-acetates
along with the required tetra-acetate (3), to the extent of about 20–30% (LC-MS ana-
lysis). These materials are difficult to remove. Further N-alkylation with methyl-
thioethyl chloride in the presence of NaH yielded 4. Hydrolysis of the resulting 4 with
0.1M NaOH in refluxing MeOH furnished the 2,6-difunctionalized adenosine derivative
of cangrelor, the desired key intermediate 5 (Scheme 1).
To avoid such drastic conditions as the use of sodium hydride in DMF, we starting
from the easily and commercially available 2,6-dichloropurine. Halide substituents on
the purine system display a leaving group ability which decreases in the series C-6 >
C-2.12 We envisioned that, if the difference in reactivity is sufficiently large, 2,6-
dichloropurine (7) could also be used as the starting material to construct the key inter-
mediate 5. With the protocol described above, the synthesis is started from 7 which can
be directly synthesized from xanthine (6). The later compound was prepared according
to the literature procedure.13 Then, 7 was subjected to the Hilbert ꢁ Johnson glycosyla-
tion reaction14–18 with fully protected ribose in the presence of Lewis acid TMSOTf to

Key Cangrelor Intermediate
3
Reagents and conditions: i) POCl , Base; ii) DBU, TMSOTf, ACN, 75-80oC; iii) Et N, Ethanol ,70-75oC, 4 h;
3
3
iv) NaSH H O, DMF, NaI, 120oC; v) NaOH, MeOH/H O, r.t.
2
2
Scheme 2. Synthesis of cangrelor key intermediate 5 from xanthine (6).
give the b-anomer (8) in good yield without any additional purification. The HPLC pur-
ity of the isolated compound was >98%. The IR spectrum of compound 8 showed a
band at 1728 cmꢁ1 attributed to the ester groups of the benzoate. In addition other sig-
nals at 1558 and 1267 cmꢁ1 confirmed the C ¼ N and C-O of the purine and ribose
1
functionalities. Besides, the H NMR spectrum of compound 8 showed two doublets of
doublets at d 4.73 (H-5'), 4.88 (H-5''), a multiplet at d 6.12-6.20 (H1' & H2') and a
doublet at 6.48 (H4') attributed to the ribose ring. Other signals were observed in the
aromatic region due to the purine ring. Subsequently, introduction of the amine group
on the C-6 position was successfully accomplished by treatment of compound 8 with
(methylthio)ethan-1-amine hydrochloride in the presence of triethylamine in ethanol at
70-75 ꢀC. This cleanly produced the C-6 amination compound only. The hydrochloride
salt of (methylthio)ethan-1-amine had been prepared in three steps from 2-chloroethane-
amine hydrochloride (8a) by the literature procedure.19 The IR spectrum of the com-
pound 9 displayed a band at 3372 (NH) cmꢁ1 to confirm that the amination took place.
The structure of the compound was further confirmed by NMR and HRMS analysis.
After successful introduction of the amino alkyl group on the C-6 position of pyr-
imidine, our attention turned towards introduction of the SH group on C-2. For that
compound 9 was treated with 60% sodium hydrogen sulfide in the presence of dimethyl
formamide at 120 ꢀC for 44–48 hours to give thiol (10). During the course of the reac-
tion in addition to the expected thiol formation we found that the benzoate groups also
got deprotected due to the highly basic nature (pH 9.5–10.00) of the reaction medium.
The structure was confirmed by the absence of ester bands in the IR spectrum. This
1
was further evidenced by the absence of peaks in the aromatic region in the H NMR
associated with the benzoyl group. The structure was additionally supported by 13C
NMR and HRMS analysis (see Experimental Section).
After successful introduction of the thiol group at the C-2 position, further S-alkyl-
ation20 was performed by coupling with trifluoropropyl iodide (10a) in the presence of

4
Guvvala et al.
sodium hydroxide in methanol at room temperature to give the final nucleoside ana-
1
logue (5) in good yield (Scheme 2). The H and 13C NMR data are in good agreement
with the reported values.7 Finally the cangrelor core is synthesized in five linear steps
in a simple methodology without any additional purification techniques. The compound
is isolated in good yield with greater than 99.6% of purity (HPLC analysis).
In conclusion, an alternative efficient and novel synthetic route to cangrelor key
intermediate 5 was developed. The target was obtained with >99.5% purity without
any additional purifications. This improved method involves five steps starting from
readily and cheaply available xanthine. The developed process is scalable, cost effect-
ive, with simplified reaction workup, and avoids the use of costly metal catalysts or
chromatography. It may be commercially viable for synthesis in large quantities com-
pared to previous methods discussed above.
Experimental Section
General
The starting material 2,6-dichloro-9H-purine was prepared by using a literature proced-
ure from xanthine.13 Other materials, solvents, and reagents were of commercial origin
and used without additional operations. The HPLC analysis was performed on an
Agilent model no. 1200 series (Chemstation software) using the Inertsil ODS column
C-18, 100 ꢂ 2.1 mm, 3.5 mm with gradient elution mobile phases A (5 mM of ammo-
nium carbonate adjusted with acetic acid to pH 3.2) and B (acetonitrile:methanol
70:30). The gradient profile was as follows: 10% of B in 3 min, 10–60% B in 12 min,
60–85% B in 20 min, 85% B in 38 min and re-equilibration of the column from 38 to
45 min with 10% of B with 45 min runtime using 10 mL injection volumes with 0.3 mL
flow rate under 272 nm. All stages and intermediate core samples were neutralized and
diluted with the mobile phase and filtered through a 0.22 micron membrane filter before
injection.
The IR spectra were recorded on
a Shimadzu FTIR Spectrophotometer
(PRESTIGE-21) using the KBr disc technique. The H and 13C NMR spectral analyses
were carried out on a Bruker instrument (300 MHz). The samples were dissolved in
DMSO-d6, CDCl3 and the NMR spectrum was measured by using tetramethylsilane
(TMS) as an internal standard. HRMS ESI-TOF positive ion ꢀmass spectra were
recorded on an Agilent Q-TOF 6530 instrument. Melting points in C were recorded on
DSC-60 Shimadzu instrument and were uncorrected.
1
(2R,3R,4R,5R)-2-((Benzoyloxy)methyl)-5-(2,6-dichloro-9H-purin-9-
yl)tetrahydrofuran-3,4-diyl dibenzoate (8)
A mixture of 2,6-dichlorpurine (7) (50 g, 0.2645 mol) and 1-O-acetyl-2,3,5-tri-O-ben-
zoyl-[3-D-ribofuranose 7a (146.7 g, 0.291 mol) was dried by co-evaporation with
anhydrous acetonitrile (2 x 250 mL). The resultant mixture was taken in anhydrous
acetonitrile (500 mL), DBU (118.4 mL, 0.7936 mol) was added followed by dropwise
addition of trimethylsilyl trifuoromethylsulfonate (191.52 mL, 1.058 mol) over a period
of 30 minutes under an argon atmosphere. After completion of the addition, the reaction
temperature was raised to 70–80 ꢀC and was stirred at the same temperature for about
4 h. The reaction mixture was then diluted with dichloromethane (1.0 L) and washed

Key Cangrelor Intermediate
5
with saturated sodium bicarbonate solution (1.0 L x 2) followed by brine (2 x 500 mL).
The organic layer was concentrated under reduced pressure and the resultant solid
obtained was recrystallized from 10% v/v DMSO/water and gave a white solid (Yield:
1
150 g, (89%); HPLC purity: 98.6%), mp 82–85 ꢀC; H NMR (300 MHz, CDCl3) d 4.73
(dd, 1H, H5', J ¼ 12.0 & 3.6 Hz), 4.88 (dd, 1H, H5'', J ¼ 12.3 & 3.6 Hz,), 6.12–6.20 (m,
2H, H1' & H2'), 6.48 (d, 1H, H4', J ¼ 6.0 Hz), 4.91–4.96 (m, 1H, H3'), 8.30 (s, 1H,
H8), 7.35-8.08 (m, 15H, phenyl ring protons); 13C NMR (CDCl3, 75 MHz) d 152.48,
130.05, 130.01, 153.62, 152.48, 81.66, 74.44, 71.69, 87.12, 63.62, 165.10, 165.28,
165.43, 128.22, 128.74, 128.77, 128.89, 129.18, 129.76; HRMS (ESI) m/z: [M þ Na]þ
calcd for C31H22Cl2N4O7 655.07632, found 655.07653; IR (KBr, cmꢁ1): 1728, 2925,
2956, 1595, 1558, 1267.
Anal. Calcd for C31H22Cl2N4O7: C, 58.78; H, 3.50; Cl, 11.19; N, 8.85. Found: C,
58.82; H, 3.48; Cl, 11.22; N, 8.89.
(2R,3R,4R,5R)-2-((Benzoyloxy)methyl)-5-(2-chloro-6-((2-(methylthio)ethyl)amino)-
9H-purin-9-yl)tetrahydrofuran-3,4-diyl dibenzoate (9)
To a mixture of glucosylated 2,6-dichlorpurine 8 (40 g, 0.0631mol) and (methylthio)e-
than-1-amine hydrochloride 8a (11.28 g, 0.088 mol) in ethanol (1.0 L), triethylamine
(26.62 mL, 0.1894 mol) was added. The reaction mixture was heated to 70–75 ꢀC for
about 4 hours. Then the reaction mixture was cooled to 0 ꢀC. The resultant solid was fil-
tered and washed with cold ethanol (200 mL) and gave a white solid (Yield: 37.36 g
1
(86%); HPLC purity: 97.99%), mp 79–82 ꢀC; H NMR (300 MHz, CDCl3) d 3.83 (brs,
2H, H1''), 2.79 (t, 2H, H2''), 2.14 (s, 3H, H3''), 5.06-5.07 (m, 1H, H1'), 6.16 (t, 1H, H2',
J ¼ 5.4 Hz), 5.99 (t, 1H, H3', J ¼ 5.1 Hz), 6.85 (d, 1H, H4', J ¼ 5.4 Hz), 4.65 (dd, 1H,
H5', J ¼ 12.0 & 3.3 Hz), 4.77 (dd, 1H, H5', J ¼ 12.6 & 2.4 Hz), 7.29-8.15 (m, 16H, phe-
nyl ring protons & H8); 13C NMR (CDCl3, 75 MHz) d 161.40, 138.31, 86.99, 84.77,
74.42, 70.40, 62.04, 32.47, 14.53; HRMS (ESI) m/z: [M þ H]þ calcd for
C34H31ClN5O7S 688.16327, found 688.16319; IR (KBr, cmꢁ1): 3372, 1728, 2919,
2954, 1616, 1601.
Anal. Calcd for C34H31ClN5O7S: C, 59.34; H, 4.39; Cl, 5.15; N, 10.18; S, 4.66.
Found: C, 59.30; H, 4.37; Cl, 5.18; N, 10.14; S, 4.71.
(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(2-mercapto-6-((2-(methylthio)ethyl)amino)-9H-
purin-9-yl)tetrahydrofuran-3,4-diol (10)
To a stirred solution of compound 9 (35 g, 0.05086 mol), in N,N-dimethyl formamide
(525 mL), 60% sodium hydrogen sulfide hydrate (22.58 g, 0.3051 mol) was added fol-
lowed by NaI (3.81 g, 0.0254 mol). The resultant reaction mixture was heated to 120 ꢀC
for 62 hours. After completion of the reaction as monitored by HPLC, the reaction mix-
ture was concentrated to one-third and poured into water. The precipitated salts were
filtered off and the filtrate was washed with dichloromethane (3 x 350 mL). Then, the
aqueous layer pH was adjusted to 4.5 using acetic acid. The solid obtained was filtered
and washed with water. The resultant solid was recrystallized from aqueous ethanol
(525 mL) and dried under reduced pressure to give a pale yellow solid (Yield: 17.0 g,
1
(90%), HPLC purity: 99.52%), mp 139–141 ꢀC; H NMR (300 MHz, DMSO-d6) d 2.12
(s, 3H, H3''), 2.72 (t, 2H, H2''), 3.65-3.67 (m, 2H, H1''), 8.00 (s, 1H, H8), 3.41 (dd, 1H,

6
Guvvala et al.
H5'a, J ¼ 5.1 & 11.7 Hz), 3.50 (dd, 1H, H5'b, J ¼ 3.9 & 11.7 Hz), 3.95 (t, 1H, H1',
J ¼ 5.1 Hz), 4.02 (t, 1H, H2', J ¼ 4.8 Hz) 3.78 (t, 1H, H3', J ¼ 4.5 Hz), 5.92 (d, 1H, H4',
J ¼ 4.2 Hz); 13C NMR (DMSO-d6, 75 MHz) d 154.98, 152.9, 145.01, 118.21, 97.21,
89.20, 72.97, 71.20, 61.50, 53.10, 34.91, 15.20; HRMS (ESI) m/z: (M þ H]þ calcd for
C13H20N5O4S2 374.09567, found 374.09695; IR (KBr, cmꢁ1): 3365, 3305, 2924, 2956,
1618, 1596.
Anal. Calcd for C13H20N5O4S2: C, 41.81; H, 5.13; N, 18.75; S, 17.17. Found: C,
41.78; H, 5.11; N, 18.69; S, 17.21.
(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(6-((2-(methylthio)ethyl)amino)-2-((3,3,3-
trifluoropropyl)thio)-9H-purin-9-yl)tetrahydrofuran-3,4-diol (5)
To a stirred solution of compound 10 (20 g, 0.0536 mol), in methanol: water (360 mL:
120 mL), 1M sodium hydroxide solution (132 mL) was added. The resultant solution
was cooled to 0 ꢀC then 1,1,1-trifluoro-3-iodopropane 10a (9.14 mL, 0.0803 mol) was
added slowly at the same temperature. Then the reaction mixture was stirred at room
temperature for 8-9 hours. After completion of the reaction as monitored by HPLC, the
reaction mass was concentrated to remove methanol and filtered and washed with cold
methanol (200 mL) to give an off-white solid (Yield: 24.0 g, (95%), HPLC purity:
99.5%), mp 175–177 ꢀC; 1H NMR (300 MHz, DMSO-d6) d 2.10 (s, 3H, SCH3),
2.65–2.81 (m, 4H, NCH2CH2 þ SCH2CH2CF3), 3.27 (m, 2H, SCH2), 3.51–3.70 (m,
4H, NCH2 þ H-5'a þ H-5'b), 3.92 (m, 1H, H-4'), 4.11 (m, 1H, H-3'), 4.56 (m, 1H, H-
2'), 5.09 (t, 1H, J ¼ 5.0 Hz, OH), 5.21 (d, 1H, J ¼ 4.8 Hz, OH) 5.46 (d, 1H, J ¼ 6.3 Hz,
OH), 5.83 (d, 1H, J ¼ 6.3 Hz, H-1'), 8.14 (brs, 1H, NH), 8.28 (s, 1H, H-8); 13C NMR
(DMSO-d6, 75 MHz) d 14.63, 22.90, 32.77, 39.07, 33.16, 33.53, 33.88, 34.25, 61.62,
70.57, 73.58, 85.71, 87. 51, 138.95, 117.56, 121.24, 124.92, 128.60, 132.28, 149.58.07,
154.03, 162.57; HRMS (ESI) m/z: [M þ H]þ calcd for C16H23F3N5O4S2 470.11436,
found 470.11606; IR (KBr, cmꢁ1): 3339, 3270, 2928, 2980, 1623, 1584.
Acknowledgments
The authors are grateful to Gland Pharma Limited, Hyderabad, for providing facilities
to carry out the work. We thank the Synthesis R&D team of Gland Pharma for fruitful
discussions in the prediction of the structure.
ORCID
Vinodh Guvvala
Venkatesan Chidambaram Subramanian
Jayashree Anireddy
http://orcid.org/0000-0002-7643-4433
http://orcid.org/0000-0002-6235-0765
http://orcid.org/0000-0002-4714-2044
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