Optimisation of 2-cyano-pyrimidine inhibitors of cathepsin K: Improving selectivity over hERG

Article abstract of DOI:10.1016/j.bmcl.2010.08.101

Several structure-guided optimisation strategies were explored in order to improve the hERG selectivity profile of cathepsin K inhibitor 1, whilst maintaining its otherwise excellent in vitro and in vivo profile. Ultimately, attenuation of c log P and pK<

Full text of DOI:10.1016/j.bmcl.2010.08.101

Bioorganic & Medicinal Chemistry Letters 20 (2010) 6237–6241
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Optimisation of 2-cyano-pyrimidine inhibitors of cathepsin K: Improving
selectivity over hERG
Zoran Rankovic a, , Jiaqiang Cai a, Jennifer Kerr a, Xavier Fradera a, John Robinson a, Ashvin Mistry a,
⇑
William Finlay a, George McGarry a, Fiona Andrews a, Wilson Caulfield a, Iain Cumming a,
Maureen Dempster a, John Waller a, Wullie Arbuckle a, Mark Anderson a, Iain Martin a,
Ann Mitchell a, Clive Long a, Mark Baugh a, Paul Westwood a, Emma Kinghorn a, Phil Jones a,
Joost C. M. Uitdehaag b, Mario van Zeeland b, Dominique Potin c, Laurent Saniere c, Andre Fouquet c,
François Chevallier c, Hortense Deronzier c, Cecile Dorleans c, Eric Nicolai c
a Merck Research Laboratories, MSD, Newhouse, Lanarkshire, ML1 5SH, Scotland, United Kingdom
b Merck Research Laboratories, MSD, 5340BH Oss, The Netherlands
c Cerep, 19 avenue du Quebec, 91951 Courtaboeuf cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Several structure-guided optimisation strategies were explored in order to improve the hERG selectivity
profile of cathepsin K inhibitor 1, whilst maintaining its otherwise excellent in vitro and in vivo profile.
Ultimately, attenuation of c log P and pKa properties proved a successful approach and led to the discov-
ery of a potent analogue 23, which, in addition to the desired selectivity over hERG (>1000-fold), dis-
played a highly attractive overall profile.
Received 6 August 2010
Revised 18 August 2010
Accepted 19 August 2010
Available online 24 August 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Cathepsin K
Cysteine protease
Osteoporosis
Osteoporosis is the most common bone disorder which pre-
dominately affects postmenopausal women, but also occurs in pre-
menopausal women as well as in men. It is a skeletal disorder
which is characterised by low bone mass and an accompanying mi-
cro-architectural deterioration that results in skeletal fragility and
an increased risk of fracture.1 Bone tissue is renewed every
5–7 years throughout the skeleton by a dynamic process involving
balanced bone resorption and formation in which osteoclasts and
bone-forming osteoblasts play a critical role. The bone loss associ-
ated with osteoporosis is attributed to an imbalance between these
two processes. Cathepsin K (catK) is one of 11 lysosomal cysteine
proteases from the papain family expressed in the human genome,
and is highly expressed in osteoclasts, which suggests an impor-
tant role in bone remodelling.2
Despite attractive in vitro and in vivo profiles of several com-
pounds in this series, their further progression was precluded by
a prohibitively high hERG potency (e.g., 1 hERG IC50 = 160 nM).
Blockade of the hERG channel is associated with QT interval pro-
longation which, in turn, can cause a life threatening cardiac
arrhythmia torsades de points (TdP).5 Therefore, we endeavoured
to improve hERG selectivity, whilst retaining the desirable
in vitro and in vivo properties of compounds in this series.
Our aim was to achieve a minimum 100-fold separation be-
tween activity in the functional bone resorption (rabbit osteoclast,
ROC6) and hERG ([3H]-Dofetilide binding) assays. This margin
translated into a >1000-fold catK/hERG selectivity requirement in
order to take into account up to a 10-fold lower potency of our
compounds in the ROC assay when compared to the catK
A large body of evidence accumulated over the last decade indi-
cates that inhibition of catK is an important therapeutic approach
in the treatment of osteoporosis.3
CN
CN
N
N
N
N
We recently disclosed a novel series of 2-cyano-pyrimidines as
F3C
N
N
potent inhibitors of cathepsin K, typified by compound 1 (Fig. 1).4
1
2
⇑
Corresponding author. Tel./fax: +44 (0)1698736157.
E-mail address: zoran.rankovic@merck.com (Z. Rankovic).
Figure 1. Lead compound 1 and its P2-aliphatic analogue 2.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.08.101

6238
Z. Rankovic et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6237–6241
Table 1
Optimisation of the P3 group
enzymatic assay. This selectivity profile was expected to ensure at
least a 30-fold safety window in vivo between the plasma free frac-
tion Cmax values for a therapeutic dose, and maximum dose devoid
of any changes in the QT interval.7
Basing our rationale on reported mutation studies and homol-
ogy models, we postulated that the CF3-phenyl moiety of 1 partic-
CN
CN
N
N
N
N
F3C
F3C
3
6
ipates in hydrophobic/
the amine group may form a cation-
p
-stacking interactions with Phe656, whilst
interaction with Tyr652,
CONMe2
6
R5
p
4 catK IC50 = 427 nM
another aromatic residue in the hERG S6 domain that forms the
channel’s large intracellular cavity.8 Discrete modification of sub-
stitution around the aromatic ring or its replacement by a non-aro-
matic group, which aims to disrupt the interaction of a ligand with
the above mentioned aromatic residues in the hERG S6 domain, are
reportedly successful medicinal chemistry strategies for removing
hERG block.9 Unfortunately, in this series, non-aromatic P2 deriva-
tives such as the cyclohepthyl 2 retained high hERG binding whilst
displaying markedly reduced catK potency (2 catK IC50 = 100 nM,
Compds
R
catKa IC50 (nM)
hERGb Ki (
lM)
3
5
6
7
8
H
33
12
4
<1
9
ND
CONMe2
>10
0.71
0.12
0.37
CONMeCH2CH2NMe2
CONBnCH2CH2NMe2
CONMeBn
a
Inhibition of recombinant human cathepsin
K in a fluorescence assay,
employing Z-Phe-Arg-MCA as synthetic substrates. Data represent means of two
experiments performed in duplicate.
Inhibition of [3H]-Dofetilide binding to hERG K+ channel in HEK293 cells fol-
b
hERG = 0.7 lM).
lowing a 10 lM dose of test compound. Data represent means of two experiments
An alternative strand of the above strategy, which was adopted
to further explore SAR around this series as well as to improve
selectivity over hERG, was born out of the biostructural informa-
tion derived from the crystal structure of 1 bound to cathepsin
K.4 The structure indicated the possibility of transferring the amine
moiety from the solvent-exposed prime side into the S3 pocket,
where it may form favourable interactions with residues such as
Asp61 or Tyr67 (Fig. 2). It was hypothesised that the new structural
arrangement may improve selectivity by favoring catK over hERG
binding. The solvent-exposed portion of the CF3-phenyl group bur-
ied into the S2 pocket was considered to be the most suitable posi-
tion for linking such an amino group (i.e., from C-5 or C-6). Since
the phenyl ring was in a perpendicular orientation with respect
to the S3 pocket, an appropriate ‘bend’ had to be incorporated into
the linker in order to provide optimal directionality. As such, we
opted to utilise an amide linker as the point of attachment to the
phenyl ring; a tertiary amide would also provide an out of plane
‘twist’ which would be required to direct the P3-amine group into
the pocket (Fig. 2).
performed in duplicate.
tion in 4 (Table 1), compared to the 20°–30° angle required for
positioning of the nitrile warhead and P2 group for optimal inter-
action with the Cys25 and S2 pocket in the cathepsin K active site.
Gratifyingly, attachment of the dimethylcarbamide group onto
the adjacent C5 position proved more successful. The resulting
5-dimethylcarbamide analogue 5 displayed a threefold improve-
ment in catK potency compared to 3 (Table 1). The crystal structure
of 5 co-crystallized with catK suggested a ‘face-to-face’ interaction
between the amide group and Tyr67 at the entrance to the S3
pocket, which may account for the observed improvement in catK
potency (Fig. 3).
Encouraged by this result, amide 6, with a dimethyl amine
group linked through an ethyl spacer, was prepared.10 As initially
hypothesised, the P3-amine-containing analogue 6 displayed a
low nanomolar catK potency, similar to that of the lead compound
1 which featured the amine group in the prime side of the mole-
cule. Unfortunately, this compound also proved to be a potent
In order to establish if such changes around the P2 group were
tolerated, 6- and 5-dimethylcarbamide analogues 4 and 5 were ini-
tially synthesized (Table 1).10 6-Dimethylcarbamide 4 displayed a
10-fold lower catK potency (427 nM) compared to the parent
compound 3, making it an unsuitable starting point for extension
into the S3 pocket. This was attributed to a greater torsion angle
between the two aromatic moieties induced by the ortho-substitu-
hERG blocker (0.71 lM). Further attempts to optimise interactions
within the S3 pocket were successful only when lipophilic
aromatic groups were incorporated, such as the benzyl group in
compound 7. The co-crystal structure of 7 with catK provided a
rationale for this observation (Fig. 4). In this case, the benzyl group
Figure 2. Co-crystal structure of pyrimidine 1 with cathepsin K (1.9 Å resolution;
PDB 3KWZ). The sulphate molecule in the prime side is an artefact of the
crystallization.
Figure 3. Co-crystal structure of 5 with cathepsin K (1.8 Å resolution; PDB 3O0U).
The amide group is at an angle of approx. 90° with respect to the phenyl ring,
positioned in parallel to Tyr67, and pointing into the S3 pocket.

Z. Rankovic et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6237–6241
6239
amino group was also close to Tyr67, either interacting with the
hydroxyl group from Tyr67 or simply exposed to solvent (this part
of the molecule was too disordered to allow for more precise in-
sight). Unfortunately, the improved catK potency of 7 was accom-
panied with a similar increase in hERG block and, indeed, this
proved to be an unbreakable pattern as more analogues were syn-
thesized in the P3-amine series. High lipophilicity of these com-
pounds was considered to be the main contributing factor to
their potent hERG block, as well as the presence of the basic amine
functionality. However, it is important to note that basic amine
group presence is not an absolute requirement for hERG block,
especially for highly lipophilic compounds.11 For example, com-
pound 8 (c log P = 4.8) retained the high hERG potency (Ki = 370
nM) exhibited by its amine-containing analogue 7 (Ki = 120 nM).
In summary, despite the success achieved in making significant
structural changes whilst maintaining high catK potency, this
approach ultimately failed to deliver the desired hERG selectivity
profile, providing further evidence of the channel’s binding
promiscuity.9
Figure 4. Co-crystal structure of 7 with cathepsin K (1.65 Å resolution; PDB 3O1G).
A conserved water is in contact with Gly66 and the ligand pyrimidine ring, and has
been modelled in the unprimed side.
Consequently, we focused our optimisation efforts on an alter-
native approach which, up to this point, had been pursued in
parallel to the above: since lead compound 1 was lipophilic and
contained a relatively basic amine (c log P = 4, pKa = 9.2), we
aimed to attenuate these properties. Such an approach has
been employed successfully in a number of hERG optimisation
was found to form extensive interactions with the floor of the S3
pocket (made up of the Gly65-Gly66-Tyr67 backbone), and
engaged in an edge-to-face interaction with Tyr67. The dimethyl-
S
O
S
HI
O
O
O
N
N
O
OH H2N NH
F3C
F3C
F3C
OH
b
a
9c
9a
9b
CN
N
CN
N
e, f
N
d, c
N
NRR1
F3C
OH
F3C
9e
9d
Scheme 1. Reagents and conditions: (a) NaH/EtOH (cat), Et2O, 0 °C; (b) iPrOH, 100 °C, 4 h, Et3N, MeOH, reflux, 6 h; (c) oxone, CH3CN/H2O, 20 °C, 18 h; (d) NaCN, DMSO, 20 °C,
3 h; (e) Dess–Martin, CH2Cl2, 20 °C, 3 h; (f) amine, NaBH(OAc)3, CH2Cl2, 20 °C, 18 h.
Table 2
Analogues of 1 containing alternative solubilising groups
CN
N
N
R
F3C
X
catKa IC50 (nM)
hERGb Ki (
lM)
c log Pc
pKa
d
Compds
X
R
1
9d
10
H2
H2
O
–Piperidine
–OH
–OH
4
8
166
0.16
31
>10
4
2
2.2
9.2
NA
4.1e
H
N
11
O
389
3.16
3.2
NA
a
Inhibition of recombinant human cathepsin K in a fluorescence assay, employing Z-Phe-Arg-MCA as synthetic substrates. Data
represent means of two experiments performed in duplicate.
b
Inhibition of [3H]-Dofetilide binding to hERG K+ channel in HEK293 cells following a 10
lM dose of test compound. Data represent
means of two experiments performed in duplicate.
C
Calculated log P.17
d
e
18
Calculated pKa of conjugated base.
18
Calculated pKa of acid.

6240
Z. Rankovic et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6237–6241
campaigns reported in the literature.11 Furthermore, reduction in
log P and pKa is undoubtedly a sensible strategy to adopt as it often
confers beneficial effects on wider selectivity, pharmacokinetic and
safety properties.12 Inspection of the available SAR and crystal
structure of 1 bound to catK (Fig. 2), led to the conclusion that
the region around the solvent-exposed propyl-piperidine was most
suitable for modulation of the compound’s physicochemical prop-
erties. Incorporation of polar and electron withdrawing groups in
this region of the molecule was not expected to perturb the key
interactions believed to be providing the main contribution to
the inhibitor’s overall binding energy, such as the reversible cova-
lent bond formation between the nitrile warhead and Cys25, and
the CF3-phenyl group interaction with the S2 pocket. To explore
the above hypothesis, a range of analogues of 1 were synthesized
according to the general route depicted in Scheme 1.
Diketone 9b, obtained in one step from commercially available
acetophenone 9a and -butyrolactone in the presence of sodium
c
hydride, was heated with S-methyl-isothiourea hydroiodide13 in
iso-propanol at 100 °C for 4 h. After cooling to room temperature,
triethylamine and methanol were added, and the resulting reaction
mixture was refluxed for another 6 h to yield pyrimidine 9c. The
methylsulfide of 9c was oxidised using ozone to the corresponding
sulphone, which was then displaced by cyanide to afford the de-
sired 6-cyanopyrimidine 9d. A high yielding oxidation of 9d with
Dess–Martin reagent afforded the corresponding aldehyde, which
was then subjected to a standard reductive amination procedure
using sodium triacetoxyborohydride and the relevant amine to ob-
tain desired product 9e. The synthetic route was designed to allow
the final step to be carried out in a high throughput fashion, which
enabled a rapid and efficient exploration of the SAR in this region.
Table 3
Attenuation of c log P and pKa to improve catK/hERG profile
CN
N
N
R
F3C
catKa IC50 (nM)
hERGb Ki (
lM)
c log Pc
pKa
d
Compds
R
H
N
12
4
0.32
4.1
10.4
13
14
15
16
17
18
–NHMe
–NHCH2CF3
–N-Methyl piperazine
–Morpholine
–NHCH2CH2OMe
4-Hydroxy piperidine
6
30
10
9
10
9
0.63
0.5
1.0
0.32
0.56
1.12
2.2
3
2
2.9
3
1.9
10.1
4.9
7.6
7.0
9.3
8.4
H
N
N
19
20
3
9
0.4
3.8
6.4
–NH2CH2COOH
>10
–0.4
9.6 (2.3)e
N
N
H
N
21
22
23
11
8
>10
2.1
1.2
1.8
9.4 (3.5)e
7.4
N
N
H
–NH2CH2CONH2
3.98
3.16
H
N
O
3
7.4
NH2
H
N
O
O
24
25
12
4
1.58
2.51
1.5
2.0
6.1
7.7
NH2
NH2
H
N
O
H
N
NH2
NH2
26
27
5
>10
>10
0.7
1.9
6.6
5.3
O
O
N
13
O
a
Inhibition of recombinant human cathepsin K in a fluorescence assay, employing Z-Phe-Arg-MCA as synthetic substrates. Data represent
means of two experiments performed in duplicate.
b
Inhibition of [3H]-Dofetilide binding to hERG K+ channel in HEK293 cells following a 10
lM dose of test compound. Data represent means of
two experiments performed in duplicate.
c
Calculated log P.17
d
e
18
Calculated pKa of conjugated base.
18
Calculated pKa of acid.

Z. Rankovic et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6237–6241
6241
We started by replacing the amine group in 1 with a range of
alternative solubilising groups, such as the OH in 9d. This com-
pound displayed catK potency similar to that of lead compound
1, and acceptable solubility (60 mg/L). Importantly, the less lipo-
philic 9d (Table 2) was found to be practically devoid of hERG bind-
nent (IC50 = 16 nM) was not considered detrimental, but poten-
tially beneficial for this programme. We hypothesised that
inhibition of cathepsin S, recently linked to the reversal of neuro-
pathic pain15, may prove beneficial for the management of chronic
pain associated with osteoporosis.16
ing (Ki = 31
l
M). Disappointingly, however, the compound
In cardiovascular safety studies in conscious pig 23 produced no
significant electrocardiographic or hemodynamic effect when
dosed orally up to 40 mg/kg (Cmax = 2650 nM). The compound
was clean in the Ames test at concentrations of up to and including
100 lM in both the absence and presence of rat liver S9 fraction,
and showed no significant adverse reaction in a 2-week safety
displayed poor inhibition in the ROC assay (IC50 = 686 nM), proba-
bly due to poor permeability (Caco-2, AB <20 nm/s), as well as poor
pharmacokinetic properties, all of which proved difficult to opti-
mise. Alternative replacements such as the carboxylic and amide
groups in 10 and 11 (Table 2), led to reduction in both catK and
hERG potency. Interestingly, amide 11 retained a moderate hERG
block (c log P = 3.2). Its direct analogue 12 further demonstrated
the importance of the basic amine for binding to both hERG and
catK (Table 3).
Compounds 13–19 indicated that significant attenuation of only
one of the two parameters, c log P or pKa, is unlikely to be sufficient
to exert the desired effect on hERG binding. In fact, an analysis of
all hERG data within this series suggested that the targeted hERG
study in rats (po up to 100 mg/kg).
In summary, several crystal structure-guided optimisation
strategies were explored in order to improve the hERG selectivity
profile of lead compound 1 (ꢁ40-fold). Ultimately, attenuation of
c log P and pKa properties proved a successful approach and led
to the discovery of a potent catK inhibitor 23, which, in addition
to the desired selectivity over hERG (>1000-fold), displayed an
attractive overall in vitro and in vivo profile. More detailed pre-
clinical data discussing the efficacy of this compound on bone
resorption markers in primates will be reported elsewhere.
potency (Ki >3 lM) is most likely to be achieved for compounds
with c log P <2 and pKa <7.5. This afforded a very narrow window
of opportunity, particularly since pushing these parameters a little
further below these levels would start impacting on cellular per-
meability and, consequently, on potency in the functional assay
and, in addition, on pharmacokinetic properties. For example, gly-
cine analogue 20 (c log P = À0.4) displayed a good catK/hERG selec-
tivity margin, but showed poor permeability (Papp <22 nm/s) and,
inevitably, it proved inactive in the ROC assay. Still, encouraged
by the selectivity profile of this compound, we synthesized a num-
ber of closely related analogues designed to yield improved perme-
ability. Bioisosteric replacements such as the tetrazole in 21
maintained the favourable selectivity profile of 20, but showed lit-
tle improvement in the ROC assay (IC50 = 1640 nM). A break-
through in our efforts came with the synthesis of primary amide
22, which demonstrated a fitting c log P/pKa profile (1.2 and 7.4,
Acknowledgement
We thank Han Kok and Wim Koot for running fermentors to
produce cathepsin K protein.
References and notes
1. (a) Bonnick, S. L. Clin. Cornerstone 2006, 8, 28; (b) Rosen, C. J.; Klibanski, A. Am. J.
Med 2009, 122, 409.
2. For recent reviews see: (a) Grabowska, U. B.; Chambers, T. J.; Shiroo, M. Curr.
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2009, 122, 409; (c) Cai, J.; Jamieson, C.; Moir, J.; Rankovic, Z. Expert Opin. Ther.
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Hwang, S.-M.; Tomaszek, T.; Yamashita, D. S.; Marquis, R. W.; Oh, H.; Jeong, J.
U.; Veber, D. F.; Gowen, M.; Lark, M. W.; Stroup, G. Bone 2007, 40, 122; (b)
Stoch, S. A.; Zajic, S.; Stone, J.; Miller, D. L.; Van Dyck, K.; Gutierrez, M. J.; De
Decker, M.; Liu, L.; Liu, Q.; Scott, B. B.; Panebianco, D.; Jin, B.; Duong, L. T.;
Gottesdiener, K.; Wagner, J. A. Clin. Pharmacol. Ther. 2009, 86, 175.
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McGarry, G.; Andrews, F.; Caulfield, W.; Cumming, I.; Dempster, M.; Waller, J.;
Scullion, P.; Martin, I.; Mitchell, A.; Long, C.; Baugh, M.; Westwood, P.;
Kinghorn, E.; Bruin, J.; Hamilton, W.; Uitdehaag, J.; van Zeeland, M.; Potin, D.;
Saniere, L.; Fouquet, A.; Chevallier, F.; Deronzier, H.; Dorleans, C.; Nicolai, E.
Bioorg. Med. Chem. Lett. 2010, 20, 1524.
respectively). This compound yielded not only
a catK/hERG
selectivity margin of 500-fold, but also showed a high potency in
the ROC assay (IC50 = 49 nM). Further progression of 22 was, how-
ever, prevented by its poor plasma stability—a consequence of
rapid hydrolysis of the amide group by plasma peptidases
(t1/2 = 65 min). Introduction of alpha substitution in compounds
23–27 markedly improved plasma stability without affecting the
desired catK/hERG/ROC profile (plasma t1/2 ꢀ150 min). The most
promising overall profile was displayed by gem-dimethyl analogue
23 (Table 4).
5. Redfern, W. S.; Carlsson, L.; Davis, A. S.; Lynch, W. G.; MacKenzie, I.; Palethorpe,
S.; Siegl, P. K. S.; Strang, I.; Sullivan, A. T.; Wallis, R.; Camm, A. J.; Hammond, T.
G. Cardiovasc. Res. 2003, 58, 32.
6. Frith, J. C.; Rogers, M. J. J. Bone Miner. Res. 2003, 18, 204.
This compound showed high selectivity over closely related
cathepsins B and L, and no significant interactions at a concentra-
tion of 10 lM in a broader selectivity panel of 65 receptors, ion
7. Redfern, W. S.; Carlsson, L.; Davis, A. S.; Lynch, W. G.; MacKenzie, I.; Palethorpe,
S.; Sieglf, P. K. S.; Stranga, I.; Sullivang, A. T.; Wallish, R.; Cammi, A. J.;
Hammonda, T. G. Cardiovasc. Res. 2003, 58, 32.
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Sanguinetti, M. C. J. Biol. Chem. 2004, 279, 10120.
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route described in Ref. 4.
Table 4
Potency, selectivity and pharmacokinetic data for 23
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et al., Bioorg. Med. Chem. Lett. 2008, 18, 4872.
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Hecker, L. R.; Nortey, S. O.; Hanslin, A.; Costanzo, M. J.; Howse, R. M.; Molinari,
A. J. Synthesis 1988, 460.
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Malcangio, M. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 10655.
Parameter
Valuea
catK; catS; catB; catL IC50 (nM)
ROC; HOCc IC50 (nM)
3; 16; 2512; >10,000
30; 39
3.0
90; 140
393
>35
75–87
29
29
hERGb Ki (
lM)
Papp (Caco-2) AB; BA (nm/s)
Solubility of the HCl salt in PBS, pH 7.4 (mg/L)
CYP inhibition: 1A2; 2C9; 2C19; 3A4; IC50
PPB: human, rat, dog, pig, cyno (% bound)
Rat F (%); wistar, iv 2 mg/kg; po 10 mg/kg
Dog F (%); beagle, iv 0.78 mg/kg; po 1.96 mg/kg
Cyno F (%); iv 2 mg/kg; po 4.63 mg/kg
(l
M)
57
16. Ringe, J.; Faber, H.; Bock, O.; Valentine, S.; Felsenberg, D.; Pfeifer, M.; Minne, H.;
Schwalen, S. Rheumatol. Int. 2002, 22, 199.
17. c log P 4.10, BioByte Corp., 201 W. 4th St. #204 Claremont, CA 91711-4707, USA.
18. pKa’s calculated with ACD PhysChem Batch, version 4.76; Advanced Chemistry
Development: Toronto, ON, Canada.
a
Values represent means of at least two experiments performed in duplicate.
Manual patch clamp recordings in HEK293 cells stably expressing hERG
b
channel.
c
Human osteoclasts assay (HOC).14