Design of a potent, soluble glucokinase activator with increased pharmacokinetic half-life

Article abstract of DOI:10.1016/j.bmcl.2011.03.093

The continued optimization of a series of glucokinase activators is described, including attempts to understand the interplay between molecular structure and the composite parameter of unbound clearance. These studies resulted in the discovery of a new sc

Full text of DOI:10.1016/j.bmcl.2011.03.093

Bioorganic & Medicinal Chemistry Letters 21 (2011) 3467–3470
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design of a potent, soluble glucokinase activator with increased
pharmacokinetic half-life
⇑
Kurt G. Pike , Joanne V. Allen, Peter W. R. Caulkett, David S. Clarke, Craig S. Donald, Mark L. Fenwick,
Keith M. Johnson, Craig Johnstone, Darren McKerrecher, John W. Rayner, Rolf P. Walker, Ingrid Wilson
Cardiovascular and Gastrointestinal Research Area, AstraZeneca R&D, Mereside, Alderley Park, Macclesfield, Cheshire SK10 4TG, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
The continued optimization of a series of glucokinase activators is described, including attempts to
understand the interplay between molecular structure and the composite parameter of unbound clear-
ance. These studies resulted in the discovery of a new scaffold for glucokinase activators and further
exploration of this scaffold led to the identification of GKA60. GKA60 maintains an excellent balance
of potency and physical properties whilst possessing a significantly different, but complimentary, pre-
clinical pharmacokinetic profile compared with the previously disclosed compound GKA50.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 3 March 2011
Revised 21 March 2011
Accepted 22 March 2011
Available online 7 April 2011
Keywords:
Glucokinase activator
GKA
GKA50
GKA60
Type 2 diabetes
Bioavailability
Unbound clearance
Type 2 diabetes is a complex disease which affects 150 million
people worldwide, with its prevalence expected to double by the
year 2025.1 Current therapies do not achieve adequate glycaemic
control;2 consequently, there is an unmet need for therapeutic
agents which deliver superior glycaemic control.
Glucokinase (GK, also known as hexokinase IV or D) is ex-
pressed predominantly in the liver, pancreas, brain and gut where
its function is to catalyze the conversion of glucose to glucose-6-
phosphate. In both the liver, where the action of GK promotes gly-
cogen synthesis, and the pancreas, where the action of GK results
in glucose-sensitive insulin release,3 GK is the rate limiting enzyme
in glucose utilisation.4 Activation of GK is therefore expected to im-
prove glycaemic control by modulating hepatic glucose balance
and decreasing the threshold for insulin secretion.5–7
Several groups have described small molecule glucokinase acti-
vators (GKAs) which act by binding to an allosteric site.8 In previ-
ous letters we have described the identification, and subsequent
optimization, of our own series of pyridine acid containing
GKAs.9,10 This optimization required the breaking of an emerging
relationship between enzyme potency and binding to plasma pro-
teins in order to achieve the desired profile. The strategy of itera-
tive design, starting from a previously identified outlier to the
relationship (GKA22), and the use of the composite parameter of
unbound clearance (CLu)11 to measure progress, was disclosed.
These studies resulted in the identification of GKA50, which
showed excellent in vitro profiles, good pharmacokinetic parame-
ters and excellent in vivo efficacy (Fig. 1).
In addition, we have previously described how knowledge of
the plasma compound levels following an oral dose, together with
knowledge of the enzyme potency and the plasma protein binding
of that compound, can be used to predict in vivo efficacy in an
acute animal model.12 Understanding the importance of the phar-
macokinetic (PK) exposure of a compound in relation to in vivo
efficacy led us to consider how compounds with different PK pro-
files might complement each other. In particular we reasoned that
a compound with a significantly increased half-life would be wor-
thy of further investigation. Given the impact of plasma protein
binding on our in vivo efficacy models we were conscious of the
need to avoid driving an increase in half-life simply by increasing
plasma protein binding. As such we were keen to explore whether
CO2H
CO2H
O
O
O
O
N
N
O
N
H
N
H
O
O
S
GKA22
GKA50
⇑
Corresponding author. Tel.: +44 1625 512733.
E-mail address: kurt.pike@astrazeneca.com (K.G. Pike).
Figure 1. The structures of GKA22 and GKA50.
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.03.093

3468
K. G. Pike et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3467–3470
Table 3
targeting a further reduction in unbound clearance would be a
more optimal strategy to achieve our goal.
The effect of the linker group on CLu
CO2H
In this Letter we describe our continuing attempts to reduce un-
bound clearance and to better understand the structural features
which impact most on this composite parameter. The extremely
low in vitro and in vivo metabolic turnover of our pyridine acid
containing GKAs precluded the use of metabolite identification
studies to help direct chemistry efforts. Hence an iterative strategy
of modifying discrete parts of the molecule to examine the affect
on potency,13 plasma protein binding14 and rat in vivo clearance15
was adopted.
Our first step was to investigate modifications to the exposed
pendant phenyl ring. A range of substitution patterns incorporating
both electron withdrawing and electron donating groups was
examined and found to be tolerated, as illustrated in Table 1
(1–3). In each case any reduction in clearance observed was
accompanied with an increase in plasma protein binding, and vice
versa, resulting in no improvement in CLu. Heterocycles (4) and
saturated rings (5) were also tolerated but again no improvement
in CLu was observed.
O
O
R2
N
H
N
O
R1
Compd R1
R2
EC50
(l
M)
% Free (rat) Rat CL CLu
9
OMe 0.07
OMe 0.03
0.33
0.37
2.9
879
F
F
10
11
12
13
4.2
1.6
0.6
0.2
1135
1600
171
95
H
H
H
0.10 (n = 1) 0.10
0.15 (n = 1) 0.35
0.21 (n = 1) 0.21
Next we turned our attention to 5-position of the central ring,
Table 2. Whilst the isopropyl ether (6) is well tolerated this change
has a detrimental effect on the unbound clearance. Other modifica-
tions designed to reduce metabolism, such as 7 and 8, were not
well tolerated.
potency (12) a significant reduction in CLu was observed. A further
reduction in CLu was observed when the biphenyl ether moiety
was installed (13). These results perhaps suggest that metabolism
of the carbon chains linking the aromatic rings in this portion of
the molecule plays a significant part in the clearance of the com-
pounds. Compound 13 shows a significantly increased pharmaco-
kinetic half-life in rat compared with GKA50 (10.5 h compared to
4.5 h).
Turning our attention to the alkyl linker we discovered that
moving the methyl substituent to the b-carbon (9), or the introduc-
tion of fluorine atoms to that carbon (10), resulted in potent com-
pounds (Table 3). However, no reduction in CLu was observed.
Cyclisation of the linker to give an indane ring (11) was tolerated
but also failed to deliver a reduction in CLu. Whilst removal of a
methylene from the linker did result in a slight reduction of
The increased pharmacokinetic half-life observed with 13 com-
pared to GKA50 encouraged the team to further investigate this
novel biphenyl ether scaffold. Studies to understand the effects of
substitution on the biphenyl ether on both the potency, and the
properties, of the molecule were conducted (Table 4).
Table 1
Relationship of exposed aryl ring to CLu
CO2H
O
Combining the unsubstituted biphenyl ether with the more
optimal alkyl ether side chain (14) gave rise to a slight improve-
ment in potency and reduction in plasma protein binding; how-
ever, CLu remained largely unchanged. The introduction of a
methoxy substituent generally appeared to improve the potency
and reduce plasma protein binding; however, a concomitant in-
crease in clearance rates appears to negate any benefit to CLu
(15, 16). The introduction of a chlorine atom to the ring also re-
sulted in an increase in binding to plasma proteins that was not
O
N
O
N
H
O
R
Compd
R
EC50
(
lM)
% Free (rat)
Rat CL
CLu
475
400
1452
1100
640
GKA50
Ph
4-F-Ph
0.03
0.04
0.07
0.05
0.03
0.09
0.40
0.25
0.42
0.10
0.25
<0.03
1.9
1.0
6.1
1.1
1.6
0.4
1
2
3
4
5
2-MeO-Ph
3-F-5-F-Ph
2-Furanyl-5-Cl
c-Pn
>1333
Table 4
The effect of substitution on the biphenyl ether motif
CO2H
O
O
Table 2
N
O
N
H
The relationship between the 5-ether linked substituent and CLu
CO2H
O
O
R
O
5
N
R
N
H
Compd
R
EC50
(
l
M)
% Free (rat)
Rat CL
CLu
3
O
14
15
16
17
18
19
20
21
Ph
0.16 (n = 1)
0.04
0.06
0.11
0.10
0.18
0.40
0.06
0.55
0.66
0.69
0.16
0.12
0.21
1.22
7.38
0.4
2.8
3.2
0.8
0.9
0.2
—
73
424
464
500
750
95
3-MeO-Ph
4-MeO-Ph
3-Cl-Ph
4-Cl-Ph
3-F-Ph
Compd
R
EC50
0.02
>10
>10
(
l
M)
% Free (rat)
Rat CL
CLu
6
7
8
i-Pr
0.23
0.42
1.09
3.3
—
—
1435
—
—
3-NMe2-Ph
4-SO2Me-Ph
—
111
C(Me)2CH2OMe
4-THP
8.2

K. G. Pike et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3467–3470
3469
Table 5
compensated for by a sufficient reduction in clearance rates (17,
18); however, the introduction of fluorine to the 3-position did ap-
pear to offer a good balance of properties (19). The introduction of
more polar functionality resulted in a significant reduction of
plasma protein binding but was accompanied by either a reduction
in potency (20), or an increase in clearance which negated any
significant benefit to CLu (21). We have previously reported the
dependency of both potency and plasma protein binding on lipo-
philicity for our pyridine acid GKAs and highlighted the challenge
this posed for subsequent optimisation of the series.9,10 For the
subset of biphenyl ether containing compounds, such as 14–21
and additional closely related structural analogues, the binding
to plasma proteins also appears related to lipophilicity, as evalu-
ated by C log P.16 In contrast the potency of these compounds
appears to be largely independent of lipophilicity (Fig. 2).
Biphenyl ether compounds, such as 14–21, could be prepared
according to the route outlined in Scheme 1. A key feature of the
synthesis is the use of a copper mediated coupling of a phenol with
a phenylboronic acid to install the biphenyl ether motif.17 The syn-
thetic availability of a range of substituted phenylboronic acids al-
lowed the rapid exploration of the SAR outlined above.
To build on the promising profile of 19 the effect of disubstitu-
tion was investigated. These investigations resulted in the identifi-
cation of GKA60, a potent, soluble GKA possessing a further
The structure of GKA60 is shown along with a comparison of its properties compared
to GKA50
CO2H
O
O
N
O
N
H
F
O
F
Compd
EC50
Solubility (
% Free (rat, dog, human)
Rat clearance (mL/min/kg)
Rat half-life (h)
Rat bioavailability (%)
Dog clearance (mL/min/kg)
Dog half-life (h)
GKA50
GKA60
(
lM)
0.03
1350
0.40, 1.46, 0.44
1.9
4.5
99
4.4
1.4
0.09
841
0.23, 1.59, 0.55
0.1
15.8
97
5.2
4.9
>100
<1, <1, <1
lM)
Dog bioavailability (%)
100
<1, <1, <1
Hepatic Clint: rat, dog, human
L/min/106 cells)
CLu (rat, dog)
(l
475, 301
43, 327
reduction in unbound clearance. The profile of GKA60 compared
to that of GKA50 is summarized in Table 5.
As can be seen, both GKA50 and GKA60 possess excellent po-
tency, solubility and pharmacokinetic profiles in both rat and
dog. In particular, the significantly increased pharmacokinetic
half-life of GKA60 in rat results in a different shape of PK profile.
Following identical 3 mg/kg oral doses of GKA50 and GKA60 to
CR-Han Wistar rats maximal concentrations (Cmax) of 4.23
lg/mL
and 16.2 g/mL, respectively, were observed. When differences in
l
plasma protein binding and potency are taken into account these
Cmax levels would be anticipated to result in similar activation of
GK (Fig. 3). However, GKA60 retains significantly higher plasma
levels at later time-points (24 h post dose a concentration of
7.06
lg/mL of GKA60 is observed compared with a concentration
of 0.116
lg/mL for GKA50). As such we believe this compound pos-
sesses a significantly different, but complementary, pharmacoki-
netic profile to that of GKA50.
In summary, we have described our continued efforts to reduce
CLu within a series of GKAs in the absence of structural in vitro
metabolism data. We have outlined the systematic investigation
into the relationship between the molecular structure and CLu
which, in turn, highlighted the importance of the alkyl linker
Figure 2. Plots of (a) plasma protein binding (log K1app) and (b) enzyme potency
(pEC50) against lipophilicity (C log P) for a range of biphenyl ether compounds.
HO
CO2Me
CO2Me
O
CO2H
(i)
O
(ii)
MeO
MeO
OBn
OBn
OBn
po @ 3 mg/kg
10
(iii)
CO2Me
CO2Me
O
O
(iv)
O
O
N
N
N
MeO
MeO
N
MeO
H
H
1
0.1
OH
OBn
(v)
CO2Me
CO2H
O
O
(vi)
O
O
N
N
N
MeO
N
H
H
O
O
R
R
0.01
Scheme 1. General synthetic route to biphenyl ethers 14–21. Reagents and
conditions: (i) PS-PPh3, DIAD, (R)-1-methoxypropan-2-ol, THF; (ii) 2 M NaOH,
THF/MeOH/H2O (73% over two steps); (iii) (COCl)2, CH2Cl2, DMF (cat) followed by
methyl 6-aminonicotinate, THF, pyridine (50%); (iv) Pd/C, MeOH/THF, H2(g) (72%);
(v) RB(OH)2, Cu(OAc)2, Et3N, molecular sieves, CH2Cl2 (40–80%); (vi) 0.5 M NaOH,
THF/H2O (95%).
0
4
8
12
16
20
24
Time (hours)
Figure 3. Pharmacokinetic profiles, normalised for plasma protein binding and
enzyme potency, for GKA50 (grey squares) and GKA60 (black triangles).

3470
K. G. Pike et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3467–3470
6. Leighton, B.; Atkinson, A.; Coghlan, M. P. Biochem. Soc. Trans. 2005, 33, 371.
7. Zelent, D.; Najafi, H.; Odili, S.; Buettger, C.; Weik-Collins, H.; Li, C.; Doliba, N.;
Grimsby, J.; Matschinsky, F. M. Biochem. Soc. Trans. 2005, 33, 306.
8. For comprehensive reviews of GKAs see: (a) Fyfe, M. C. T.; Procter, M. P. Drugs
Future 2009, 34, 641; (b) Matschinsky, F. M. Nat. Rev. Drug Disc. 2009, 8, 399; (c)
Coghlan, M.; Leighton, B. Expert Opin. Invest. Drugs 2008, 17, 145.
9. McKerrecher, D.; Allen, J. V.; Bowker, S. S.; Boyd, S.; Caulkett, P. W. R.; Currie, G.
S.; Davies, C. D.; Fenwick, M. L.; Gaskin, H.; Grange, E.; Hargreaves, R. B.; Hayter,
B. R.; James, R.; Johnson, K. M.; Johnstone, C.; Jones, C. D.; Lackie, S.; Rayner, J.
W.; Walker, R. P. Bioorg. Med. Chem. Lett. 2005, 15, 2103.
moiety and resulted in the discovery of a novel biphenyl ether scaf-
fold. Compounds adhering to this scaffold have been identified that
possess a reasonable balance of potency and physicochemical
properties whilst also delivering an increased pharmacokinetic
half-life in rat. In particular, GKA60 has been identified as a potent,
soluble GKA displaying a significantly different, but complemen-
tary, pharmacokinetic profile to GKA50, in rat. Pleasingly GKA60
also shows significant activity in our animal models and was se-
lected for further pre-clinical evaluation.
10. McKerrecher, D.; Allen, J. V.; Caulkett, P. W. R.; Donald, C. S.; Fenwick, M. L.;
Grange, E.; Johnson, K. M.; Johnstone, C.; Jones, C. D.; Pike, K. G.; Rayner, J. W.;
Walker, R. P. Bioorg. Med. Chem. Lett. 2006, 16, 2705.
11. Chiou, W. L.; Robbiel, G.; Chung, S. M.; Wul, T.-C.; Mal, C. Pharm. Res. 1998, 15,
1474.
Acknowledgements
12. Coope, G. J.; Atkinson, A. M.; Allott, C.; McKerrecher, D.; Johnstone, C.; Pike, K.
G.; Holme, P. C.; Vertigan, H.; Gill, D.; Coghlan, M. P.; Leighton, B. Br. J.
Pharmacol. 2006, 149, 328.
The authors would like to acknowledge the contributions of col-
leagues in bioscience, physical chemistry and pharmacokinetics in
generating and interpreting the data reported in this communica-
tion. Dr. M. J. Waring is also thanked for helpful discussions and
assistance with the preparation of the manuscript.
13. EC50 values were determined at 10 mmol/L glucose, and are quoted as the
geometric mean of at least three independent experiments (unless otherwise
indicated). Assay to assay variability was within two fold based on the results
of a standard compound. All compounds in this series exhibited a negligible
effect on Vmax. Detailed in vitro studies and assay conditions are described in:
Brocklehurst, K. J.; Payne, V. A.; Davies, R. A.; Carroll, D.; Vertigan, H. L.;
Wightman, H. J.; Aiston, S.; Waddell, I. D.; Leighton, B.; Coghlan, M. P.; Agius, L.
Diabetes 2004, 53, 535.
References and notes
14. The plasma protein binding of compounds was measured using equilibrium
dialysis technique. More detailed description of the assay conditions are
1. Tadayyon, M.; Smith, S. A. Expert Opin. Invest. Drugs 2003, 12, 307.
2. Turner, R. C.; Cull, C. A.; Frighi, V.; Holmann, R. J. Am. Med. Assoc. 1999, 281,
2005.
described in Ref.11
.
15. Rat clearance values were obtained following an IV dose of 1 mg/kg to CR-Han
Wistar rats. The compounds were dosed as a solution and the clearance values
are quoted in mL/min/kg.
16. C log P values were calculated using the commercially available package C log P
v4.3 from BioByte Corp, 201 W. 4th St., #204 Claremont, CA 91711-4707.
17. Evans, D. A.; Katz, J. L.; West, T. R. Tetrahedron Lett. 1998, 39, 2937.
3. Matschinsky, F. M. Diabetes 2002, 51, S394.
4. Matschinsky, F. M., Magnuson, M. A., Eds.Frontiers in Diabetes; Matschinsky, F.
M., Magnuson, M. A., Eds.; Karger: Basel, 2004; Vol. 16, pp 1–17.
5. Gloyn, A. l.; Odili, S.; Zelent, D.; Buettger, C.; Castleden, H. A.; Steele, A. M.;
Stride, A.; Shiota, C.; Magnuson, M. A.; Lorini, R.; d’Annunzio, G.; Stanley, C. A.;
Kwagh, J.; van Schaftingen, E.; Veigha da Cunha, M.; Barbetti, F.; Dunten, P.;
Han, Y.; Grimsby, J.; Taub, R.; Ellard, S.; Hattersley, A. T.; Matschinsky, F. M. J.
Biol. Chem. 2005, 280, 14105.