3
4
5
6
7
K3PO4
K3PO4
K3PO4
K3PO4
Pd(PPh3)4
THF
THF
THF
THF
reflux
reflux
reflux
reflux
8
74.3
90.0
57.9
6.0
Pd(dppf)2Cl2
Pd(PPh3)2Cl2
Pd(OAc)2
2
8
10
a The reaction was conducted with N2 protected.
b The concentration of the base is 2 M; the equivalent of the base is 2.0 eq to compound 8.
c Isolated yield.
The final chemical stage required the debenzylation and
hydrolyzation of 9. The reaction proved to be more efficient
using H2, Pd/C and 1 M aqueous LiOH in THF in one pot. When
the reaction completed, removed the organic phase by distillation.
And the concentrated mixture was neutralized by diluted
hydrochloric acid (3 M) and then the product 2 was conveniently
obtained by simple filtration in 85.5% yield.
6. Tetsuhiro T., Masaomi N., J. Pharmacol. Sci. 2009,
109, 24.
7. PCT Int. Appl. (2007), US 0299086 A1.
8. Michael H. R., J. Med. Chem. 2013, 56, 9369.
9. Yoshiki, H., Tetsuhiro, T., Masaomi, N., Expert. Opin.
Drug. Discov, 2013, 8, 965.
10. 3-(Benzyloxy)-5-bromopicolinonitrile (6). A mixture
of THF (1.8 L) and benzyl alcohol (59 mL, 114 mmol)
With the optimized route in hand, we next began to extend
the scope of this synthetic strategy to a variety of PHD2
inhibitors from the patent.7 We have tried different substrates in
the Suzuki coupling and the following deprotection to provide
five more PHD2 inhibitors with different substitutions on the
benzyl ring in 37.3-39.3% total yields (see supporting
information). This showed that the synthetic route is an efficient
way to obtain various PHD2 inhibitors with high efficiency.
o
was cooled to 0 C. NaH was added slowly to the
mixture at 0 oC. After addition, the mixture was stirred
at room temperature for 1 h and 35oC for another 0.5 h.
The resultant solution was added to the solution of 5-
bromo-3-nitropicolinonitrile (5, 100 g, 438 mmol) in
THF (1.3 L) and the mixture was stirred at room
temperature for 24 h. The reaction mixture was
quenched with H2O (200 mL). After quenched, the
mixture was concentrated to a volume of about 200 mL.
Dichloromethane (1.5 L) was added, and the higher
aqueous phase was removed. The organic phase was
wash with saturated aqueous NaHCO3 (1.0 L×1), water
(1.0 L×3), saturated aqueous NaCl (1.0 L×1). The
organic phase was concentrated, and dried under
vacuum at 55oC to give 6 (110.0 g, 87.3% yield, 99.5%
purity by HPLC) as a brown solid.
In summary, we have developed a facile and high yielding
method to synthesize 2, involving a non-chromatography five-
step synthesis in 37.6% overall yield. This synthesis route has
several advantages, including a simple experimental procedure,
mild reaction conditions and high yields of the products. The
procedure allows rapid scale-up for the large-scale synthesis of
N-(5-(4-cyanophenyl)-3-hydroxypicolinoyl)glycine (2) and other
PHD2 inhibitors that are similar in chemical structure.
11. 3-(Benzyloxy)-5-bromopicolinic
acid
(7).
A
suspension of 6 (53.3 g, 184 mmol), methanol (1.0 L)
and 30% NaOH (1.0 L) was heated to 100 oC for 2 h.
The mixture was cooled to room temperature, and the
resultant solution was concentrated to a volume of
about 1.0 L. The concentrated mixture was neutralized
by aqueous HCl (3 M). The formed precipitate was
filtered off, washed with water, and dried to give 7
(49.3 g, yield 87.0%, 98.2% purity by HPLC) as a faint
yellow solid.
Acknowledgments
We are thankful for the financial support of the National
Natural Science Foundation of China (No.81302636), the Natural
Science Foundation of Jiangsu Province of China
(No.BK20130656) and the Priority Academic Program
Development of Jiangsu Higher Education Institutions (PAPD).
12. Methyl N-(5-bromo-3-hydroxypicolinoyl)glycine (8).
To a solution of 7 (49.3 g, 160 mmol) and glycine
methyl ester hydrochloride (24 g, 192 mmol) in
dichloromethane (500 mL) was added EDCI (45.9 g,
240 mmol), HOBT (32.6 g, 24 mmol) and Et3N (73
mL). The mixture was stirred at room temperature for 6
h under nitrogen atmosphere. The resultant solution was
added saturated aqueous NaHCO3 (1.0 L), and the
higher aqueous phase was removed. The organic phase
was washed with water (1.0 L×3) and saturated aqueous
NaCl (1.0 L×1), and dried with anhydrous MgSO4. The
solution was filtrated by silica gel, washed with
petroleum ether: EtOAc = 3:1 and concentrated to give
an oily product, which was recrystallized by
petroleum ether: EtOAc = 3:1, the solids were isolated
by filtration, washed with cold EtOAc and dried to give
8 (28.2 g, yield 64.5%, 99.6% purity by HPLC) of white
crystal.
Supplementary data
Supplementary data associate with this article is available.
References and notes
1. Tarhonskaya H., Chowdhury R., Leung I. K., Loik N.
D., McCullagh J. S., Claridge T. D., Schofield C. J.,
Flashman E. Biochem. J. 2014, 463, 363.
2. McDonough M. A, McNeill L. A., Tilliet M., Qiuyun
Chen, Papamicael C. A., Banerji B., Hewitson K. S.,
and Schofield C. J. J. Am. Chem. Soc. 2005, 127, 7680.
3. Berra, E., Benizri, E., Ginouves, A., Volmat, V., Roux,
D. and Pouyssegur J., EMBO J. 2003, 22, 4082.
4. Chowdhury R., Candela-Lena J. I., Chan M. C.,
Greenald D. J., Yeoh K. K., Tian Y. M., McDonough M.
A., Tumber A., Rose N. R., Conejo-Garcia A.,
Demetriades M., Mathavan S., Kawamura A., Lee M.
K., van Eeden F., Pugh C. W., Ratcliffe P. J., Schofield
C. J. Chem. Biol. 2013, 8, 1488.
13. Methyl
N-(5-(4-cyanophenyl)-3-
hydroxypicolinoyl)glycine (9). A suspension of 8 (7.26
g, 20 mmol), 4-cyanophenylboronic acid (3.0 g, 20
mmol) and THF (300 mL) was added K3PO4 (2M, 30
mL) and Pd(dppf)2Cl2 (1.0 g). The resultant solution
was stirred at 75 oC for 2 h under nitrogen atmosphere.
5. William A. D. J. Med. Chem. 2012, 55, 2943.