Short-acting 5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one derivatives as orally-active calcium-sensing receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2009.07.004

Synthesis and structure-activity relationship (SAR) studies on 5-trifluoromethylpyrido[4,3-d]pyrimidin-4(3H)-ones, a novel class of calcium receptor antagonists is described with particular emphasis on optimization of the pharmacokinetic/pharmacodynamic parameters required for a short duration of action compound. Orally-active compounds were identified which displayed the desired animal pharmacology (rapid and transient stimulation of parathyroid hormone) essential for bone anabolic effects.

Full text of DOI:10.1016/j.bmcl.2009.07.004

Bioorganic & Medicinal Chemistry Letters 19 (2009) 4555–4559
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Short-acting 5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one
derivatives as orally-active calcium-sensing receptor antagonists
*
Mary T. Didiuk , David A. Griffith, John W. Benbow, Kevin K. C. Liu, Daniel P. Walker, F. Christopher Bi,
Joel Morris, Angel Guzman-Perez, Hua Gao, Bruce M. Bechle, Ryan M. Kelley, Xiaojing Yang,
Kenneth Dirico, Syed Ahmed, William Hungerford, Joseph DiBrinno, Michael P. Zawistoski,
Scott W. Bagley, Jianke Li, Yuan Zeng, Stephanie Santucci, Robert Oliver, Matthew Corbett,
Thanh Olson, Chiliu Chen, Mei Li, Vishwas M. Paralkar, Keith A. Riccardi, David R. Healy,
Amit S. Kalgutkar, Tristan S. Maurer, Hang T. Nguyen, Kosea S. Frederick
Pfizer Global Research and Development, 558 Eastern Point Road, Groton, CT 06340, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Synthesis and structure–activity relationship (SAR) studies on 5-trifluoromethylpyrido[4,3-d]pyrimidin-
4(3H)-ones, a novel class of calcium receptor antagonists is described with particular emphasis on opti-
mization of the pharmacokinetic/pharmacodynamic parameters required for a short duration of action
compound. Orally-active compounds were identified which displayed the desired animal pharmacology
(rapid and transient stimulation of parathyroid hormone) essential for bone anabolic effects.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 20 March 2009
Revised 25 June 2009
Accepted 2 July 2009
Available online 8 July 2009
Keywords:
Osteoporosis
Human parathyroid hormone
Calcium receptor antagonists
Pharmacokinetics
SAR exploration
Osteoporosis is a life-debilitating and prevalent disease associ-
ated with significant mortality and morbidity, particularly after
hip fracture.1 In the osteoporotic population, there is an imbalance
between bone resorption and bone formation which results in pro-
gressive loss of bone mass and structure. Current treatment op-
tions involve anti-resorptive agents such as bisphosphonates,
estrogen, and selective estrogen receptor modulators, which slow
progression of the disease; however, bone which is lost is not re-
stored. In contrast, Teriparatide (ForteoÒ), a synthetic 1–34 amino
acid peptide fragment of human parathyroid hormone (PTH) is the
only FDA-approved anabolic agent that, upon daily subcutaneous
administration, has been shown to increase bone mineral density
and reduce fracture rates in humans.2–5 As a viable alternative to
subcutaneous PTH therapy, one can envision stimulating secretion
of endogenous PTH from the parathyroid glands, which is regu-
lated by the calcium receptor (CaR).6 Proof-of-concept in vivo stud-
ies in osteopenic, ovariectomized rats with the aminoalcohol
derivative and CaR antagonist NPS 2143 have demonstrated that
blockade of CaR results in transient PTH release and stimulation
of new bone formation.7–9
Key hurdles that preclude clinical studies with NPS 2143 in-
clude potent inhibition of human ether-a-go-go (hERG) channel
and a long pharmacokinetic half-life (T1/2 > 8 h) in animal pharma-
cology studies that results in significant compound accumulation
upon repeated oral dosing. A consequence of the latter is sustained
elevation of plasma PTH and a concurrent increase in bone turn-
over without a net change in bone mineral density.7,10 This is not
unexpected considering that chronically high PTH levels are asso-
ciated with bone loss (i.e., a catabolic response).11 While CaR
antagonists, structurally diverse from NPS 2143, have been dis-
closed in the literature, detailed understanding of their in vivo
pharmacology in preclinical species, especially in terms of
improvement in PTH profile, remains unclear.10,12 Based upon the
studies with NPS 2143, it has been proposed that a rapidly ab-
sorbed orally-active agent with a short half-life should evoke the
desired transient increase in plasma PTH levels, translating into a
bone anabolic response.10
* Corresponding author. Tel.: +1 860 715 1698.
E-mail address: mary.didiuk@pfizer.com (M.T. Didiuk).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.07.004

4556
M. T. Didiuk et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4555–4559
ously described 3H-quinazolinones class of CaR antagonists.12a
While potency and predicted human CL for 2 were less than opti-
mal (Table 1), an attractive feature of this compound and chemical
series in general was the absence of hERG channel inhibition asso-
ciated with the amino alcohol series.10 Herein, we describe our
efforts to achieve potency and stringent PK goals for the pyr-
ido[4,3-d]pyrimidin-4(3H)-ones while seeking to identify multiple
compounds suitable for clinical development.
Three major areas were examined to improve upon the pharma-
cology and ADME properties of the pyridopyrimidone series repre-
sented by 2: the C-5 substituent (R1) with special focus on
replacing the potentially electrophilic 2-chloropyridine motif, the
C-2 substituent (R2), and the side chain (R3). The synthesis of 2
and its analogs is shown in Scheme 1.
The halogen in 2-chloro-4-aminonicotinic acid (1) provided a
convenient handle for introducing substituents at C-5 and for fur-
ther SAR exploration. Amidation of 1 with appropriate amines and
reaction with either methyl- or benzyl-protected salicylaldehyde
analogs afforded 2,3-dihydropyrimidinone derivatives that were
oxidized to generate the corresponding pyrido[4,3-d]pyrimidin-
4(3H)-one scaffold. The 5-chloro-analog could be further elabo-
rated with nucleophiles to provide diverse C-5 substituents or
O-deprotected to afford 2. The preparation of 5-trifluoromethyl-
pyrido[4,3-d]pyrimidin-4(3H)-one derivatives was achieved from
2-trifluoromethyl-3-bromopyridine (3). Grignard formation from
3 followed by reaction with CO2 afforded a nicotinic acid deriva-
tive, which upon lithiation and treatment with hexachloroethane,
afforded 4 in a good yield. Esterification of 4 with diazomethane
yielded methyl ester 5, which was converted to the corresponding
azido ester 6 following nucleophilic displacement of the chloride
group with sodium azide. Treatment of 6 with concentrated HI
afforded a 1:1 mixture of the desired product, 4-amino-2-trifluoro-
methyl-nicotinic acid (7) and its amino ester derivative 8. The mix-
ture was readily separated via acid–base extraction. Subsequent
saponification of 8 with lithium hydroxide provided additional
quantities of 7 in 95% yield.
As a prelude to our discovery efforts, we felt that it was crucial to
identify the pharmacokinetic/pharmacodynamic (PK/PD) require-
ments of a short-acting, orally bioavailable CaR antagonist. Quanti-
tative PK/PD studies were undertaken in rats with a series of
literature CaR antagonists (including NPS 2143) to establish a rela-
tionship between PTH release and unbound systemic exposures
corrected for the corresponding in vitro CaR antagonist potencies
(IC50). PTH profiles discerned with small molecule antagonists were
then compared with those of ForteoÒ and PreosÒ (PTH 1-84, full-
length recombinant human PTH) at their respective efficacious
doses in the rat, which then allowed an insight into the potency
requirements for a small molecule agent.13,14 Assuming a 1:1 quan-
titative pharmacology translation between rat and human, simula-
tions were then performed to derive human PK parameters for an
orally-active CaR antagonist that would yield PTH profiles similar
to the ones discerned with efficacious doses of Forteo and Preos
in humans.15,16 The results of the in-house PK/PD analysis sug-
gested that in order to achieve a Forteo-/Preos-like profile, an oral-
ly-active CaR antagonist needs to fulfill the following criteria: (a)
in vitro CaR antagonist potency (IC50) 6 50 nM, (b) rapid and com-
plete oral absorption, (c) short half-life (T1/2) of ꢀ1 h (ideally
achieved via a blood clearance (CLb) of 10 mL/min/kg and steady
state volume (Vdss) of 1 L/kg).17,18
Given the degree of difficulty in achieving the narrow window
of human PK properties with any given agent, an overarching goal
in this exercise was the identification of multiple candidates with a
complementary range of human clearance predictions that would
maximize our chances of ‘hitting the target’ PK range (especially
CL and T1/2).19
For the purposes of pharmacologic and PK optimization, we
focused our attention on lead compound
2 (Scheme 1), a
pyrido[4,3-d]pyrimidin-4(3H)-one derivative, related to the previ-
Cl
Cl
O
N
R3
5
N
COOH
NH2
a-c
N
d
N
Pyrido[4,3-d]pyrimidin-4(3H)-ones were evaluated in vitro for
human CaR antagonism.20 Introduction of a range of small alkyl,
amino, and ether substituents resulted in compounds with dimin-
ished potency when compared with 2 (Table 1). The trifluoro-
methyl group at C-5 proved ideal, particularly in terms of its
X
2
O
PG = CH3, Bn
1
PG
R1
O
R1
O
N
R3
R3
N
N
O
N
N
e or f
X
X
N
Table 1
SAR on the C-5 substituent in pyrido[4,3-d]pyrimidin-4(3H)-ones
HO
R1
O
PG
compound 2 : R1 = Cl
R1 = Cl, and/or O- and N-alkyl
X = CH
N
N
R3= (CH2)2C6 H5
N
CF3
CF3
CF3
Br
COOH
Cl
COOMe
Cl
HO
g, h
i
N
N
N
Compound
R1
Cl
CaR IC50 (nM)
Log Db
Predicted human CLb
(mL/min/kg)
a
c
3
4
5
2
106
3.76
3.77
4.5
CF3
CF3
COOMe
N3
COOR
NH2
j
k
N
2a
5320
N.D.
N
N
O
2b
435
4.86
N.D.
6
7: R = H
l
8: R = Me
2c
2d
2e
(CH3)2CHO–
CH3
CF3
224
2990
50
4.81
3.99
4.89
5.8
N.D.
4.4
Scheme 1. Reagents and conditions: (a) H2NR3, HBTU, Et3N, CH2Cl2/DMF; (b)
CHOArOCH3 or CHOArOBn, TsOH, PhCH3, heat; (c) DDQ, CH2Cl2 or MnO2, CH2Cl2; (d)
O-alkyl: ROH, NaH, THF/DMF; N-alkyl: R1NH2, CH3OH, 50 °C; (e) BCl3, CH2Cl2; (f)
H2SO4, AcOH; (g) Mg, THF, reflux, 2 h; CO2 gas (74%); (h) n-BuLi (1.0 equiv), LTMP
(3.0 equiv), THF, ꢁ78 °C to ꢁ50 °C, 1.5 h; C2Cl6 (94%); (i) CH2N2, EtOAc (99%); (j)
NaN3 (8.0 equiv), DMF, 45–50 °C, 4 h, (98%); (k) HI, 0 °C, 1 h, 7 (48%), 8 (48%); (l)
LiOH (1.7 equiv), THF/dioxane/H2O (3:2:1), 85 °C, 3 h (95%).
a
Values are means of three experiments.
Values were calculated using ACD/Labs version 9.03.
Human CLb values were scaled from free CLint data from liver microsomes using
b
c
the well-stirred model (incorporating unbound fraction in plasma/microsomes) as
previously described, Ref. 21.

M. T. Didiuk et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4555–4559
4557
pharmacology and chemical stability, and was used extensively for
Table 2 (continued)
Compound C-2 (R2)
R3
CaR IC50 Log Db Predicted
further SAR exploration.
a
c
The influence of R2 and R3 functionalities on potency and micro-
somal clearance was investigated simultaneously (Table 2). Free
intrinsic clearance (CLint) predictions for pyridopyrimidinones
and related quinazolinones12a obtained from in silico modeling re-
vealed a good correlation ( 2-fold error) with experimental values
measured in human liver microsomes as shown in Figure 1, a fea-
ture which also appeared to be closely governed by Log D.21,22 The
(nM)
human CLb
(mL/min/kg)
N
9a
19
5.73
4.45
2.0
H3COCHN
N
9b
226
64
N.D.
6.0
H3C
Table 2
SAR on the R2 and R3 substituents in pyrido[4,3-d]pyrimidin-4(3H)-ones
CF3
O
CF3
O
N
R3
R3
R2
N
N
N
N
9c
5.36
N
F3C
2
2
N
N
S
2f-n and 9a-f
10a and 10b
Compound C-2 (R2)
R3
CaR IC50 Log Db Predicted
a
9d
1070
152
79
4.80
5.24
4.41
15
c
(nM)
610
human CLb
Cl
(mL/min/kg)
2f
4.58
4.94
5.23
5.23
4.93
3.81
3.52
3.38
3.83
4.40
N.D.
HO
9e
N.D.
6.7
F
Cl
F
N
2g
132
41
7.3
12
9f
HO
HO
Cl
(R)-2h
(S)-2h
2i
N
10a
656
216
3.38
4.43
N.D.
15
S
158
25
N.D.
4.0
9.0
4.0
7.5
7.4
2.0
HO
HO
10b
N.D. not determined.
a
Values are means of three experiments.
b
c
Values were calculated using ACD/Labs version 9.03.
Protocols for measuring half-lives in human liver microsomes and subsequent
F
scaling of half-life data to intrinsic clearance (CLint) and CLb have been published,
Ref. 21.
N
2j
22
HO
HO
HO
HO
HO
N
N
N
N
F
2k
151
76
H3CO
2l
F
F
2m
2n
8
36
Figure 1. Plot of experimental versus predicted intrinsic liver microsomal clearance
(gray dots: training set compounds; red dots: test set compounds).

4558
M. T. Didiuk et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4555–4559
Table 3
Pharmacokinetic data for selected 5-trifluoropyridopyrimidinones in the rata
b
c
Compound
Dose (mg/kg)
Route
RLM CLp
25
Cmax (ng/mL)
Tmax (h)
CLp (mL/min/kg)
32.2 0.92
Vdss (L/kg)
1.4 0.04
T1/2 (h)
AUC (ng h/mL)
518 15
(R)-2h
1
10
1
1
10
1
iv
po
iv
iv
po
125 23
350 34
0.5 0.3
0.6 0.07
2i
2m
13
28
31.6
46.5
3.60
1.53
3.90
528.0
364.0
133 56
165 68
0.3 0.1
1.3 0.5
8.60c
2n
9c
33
56
35.9
3.20
0.62
489.5
1
iv
100 50
17 4.0
2.9 0.8
0.8 0.06
1200 570
10
1
po
iv
450 170
9f
29
21 3.8
6.0 3.8
0.95 0.03
810 160
a
Pharmacokinetic studies were conducted in male Sprague-Dawley rats (n = 2–5). Compounds were administered in glycerol formal containing 2% DMSO (iv) or as spray
dried dispersion (po).
b
Blood clearance predicted using rat liver microsomes was converted into plasma clearance values by multiplying the blood/plasma partition ratio measured for the
individual compounds.
c
Half-life values represent terminal elimination (b) phase; the effective half-lives (
a
) were much shorter.
CLint values depicted in Figure 1 are obtained by dividing the
apparent liver microsomal CLint values by the unbound fraction
of compounds to liver microsomes.23 The availability of the in sil-
ico tool to predict CL of virtual compounds greatly facilitated our
efforts toward the design of analogs for SAR purposes.
As indicated in Table 2, subtle changes in the R2 and R3 substit-
uents in 2e affected the balance between potency and CL. For
example, incorporation of aromatic fluorine on the phenethyl ring
in 2e generated 2g with a projected human CL value approaching
the target range, albeit with a threefold decrease in CaR potency.
Likewise, introduction of a 60-fluoro group on the phenol substitu-
ent in 2e resulted in 2f with diminished potency. In the case of 2f,
C-2 furan derivative as a CaR antagonist.10 As observed earlier,
a-methylation of the phenethyl side chain led to a 3–10-fold
increase in antagonist activity of the resulting compounds (e.g.,
9d/9e and 10a/10b).
Having identified several potent antagonists with a complimen-
tary range of predicted human CL values near the target of 10 mL/
min/kg, we examined their in vivo disposition in rats. The purpose
of these studies was to establish an in vitro/in vivo correlation for CL
to increase confidence in our scaled human CL projections, and to
demonstrate PTH release, in vivo. Intravenous (iv) rat PK studies
on selected compounds (e.g., (R)-2h, 2m, 2n, 9f) revealed a good
correlation ( 2-fold) between observed in vivo CL and the corre-
sponding CL value estimated from rat liver microsomes (Table 3).
Pretreatment of rats with the P450 inactivator 1-aminobenzotriazole
led to a ꢀ4-fold decrease in clearance of compound (R)-2h
(32.2 ? 7.8 mL/min/kg), ꢀ4-fold increase in AUC and a sevenfold
increase in half-life, suggesting that oxidative metabolism was
the principal elimination pathway in these compounds. Metabolite
identification studies on (R)-2h and 2m in human and rat liver
microsomes and hepatocytes revealed that the rate-limiting step
in the metabolism was P450-catalyzed oxidations on the phenol/
3-hydroxypyridine motif; glucuronidation of the phenolic OH
group in starting material was a very minor component of overall
metabolism.26 Collectively, these observations strengthen the level
of confidence level in using human liver microsomes to predict CL
of pyridopyrimidinones.
introduction of a
a-methyl group on the 3-phenethyl substituent
(compound 2i) led to a significant boost in potency, wherein the
(R)-configuration was preferred.
While the introduction of the 60-fluorine as illustrated in 2f was
detrimental for activity, we were pleased to find that a nitrogen
atom at the 30-position of the C-2 phenol ring was generally well
tolerated. When coupled with an appropriate
a-methylarylethyl
substituent, the change resulted in several compounds with the
desired optimal potency and human CL range as highlighted in Ta-
ble 2. While not extensively investigated in this analysis, the find-
ing that replacement of the pendant arylalkyl group with a
cyclohexylethyl moiety (compound 2n) preserved CaR activity
suggests a potential exists for additional SAR work around this re-
gion of the molecule. Examination of the influence of Log D on po-
tency and clearance predictions on the phenols/3-hydroxypyridine
indicated that increased Log D values in general correlated with in-
creased potency and higher predicted/measured CL.
The role that the C-2 phenolic hydroxyl group plays in receptor
binding remains unclear. Likely hypotheses include hydrogen
bonding of the phenol with a complimentary amino acid residue(s)
on the receptor in addition to a role in electrostatic interactions with
the receptor. The hydrogen bonding contribution was explored by
incorporating mildly acidic functionalities (e.g., NHCOCH3) in place
of the phenolic OH. Thus, replacement of the OH group in 2j with
the acetamide led to 9a, which demonstrated comparable CaR
potency. The electrostatic component was probed by introducing
polarizable functional groups (e.g., Cl or CF3) in place of the
phenolic OH group or by replacing the phenol/3-hydroxypyridine
ring system with small heterocycles like thiazole (Table 2).24,25
In general, replacement of the phenol OH group with small neutral
groups/polarizable atoms resulted in compounds with decreased
antagonist activity (e.g., 9b and 9f vs 2j). Likewise, replacement
of the C-2 phenol/3-hydroxypyridine with the thiazole heterocycle
(compound 10a) also led to a 10-fold loss in potency. A similar
finding has been discerned with SAR studies on quinazolinon-
es where the C-2 phenolic compound was far superior to the
Consistent with previous studies on amino alcohol and quinaz-
olinone-based CaR antagonists,8,10,12 iv administration of selected
compounds (R)-2h and 2m at 1 mg/kg (Table 4) to rats resulted
in a rapid increase in plasma PTH levels (10–20-fold higher than
baseline levels).27 More importantly, however, were the observa-
tions of rapid and transient PTH increases following single po dose
Table 4
PTH stimulation following iv and po administration of 5-trifluoropyridopyrimidinones
in the rata
Compound
Dose (mg/kg)
Route
PTHb,c (pg/mL)
(R)-2h
1.0
10
iv
po
921
620
2m
1.0
10
iv
po
1303
599
Corresponding levels of the hormone were ꢀ4–6-fold greater than basal levels after
po administration.
a
Studies conducted in male Sprague-Dawley rats (n = 5/6).
PTH levels peaked at ꢀ2 min (earliest sampling point) and at 5 ꢁ 15 min in the
b
iv and po studies, respectively.
c
PTH levels after iv administration were 10–20-fold higher than baseline levels
in vehicle treated animals.

M. T. Didiuk et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4555–4559
4559
14. (a) The experimental data was modeled using an indirect response precursor
pool PK/PD model, commonly applied to pharmacological mechanisms that
result in the stimulation of hormone release into plasma. This modeling
effort provided estimates for in vitro potency (IC50) and the maximal fold
PTH stimulation above baseline (Emax), which would be required for bone
anabolism.; (b) Sharma, A.; Jusko, W. J. Br. J. Clin. Pharmacol. 1998, 45,
229.
15. Schwietert, H. R.; Groen, E. W. J.; Sollie, F. A. E.; Jonkman, J. H. G. Clin.
Pharmacol. Ther. 1997, 61, 360.
16. Hodsman, A. B.; Hanley, D. A.; Ettinger, M. P.; Bolognese, M. A.; Fox, J.; Metcalfe,
A. J.; Lindsay, R. J. Clin. Endocrinol. Metab. 2003, 88, 5212.
administration of (R)-2h and 2m at 10 mg/kg. Consistent with the
short effective half-lives of the test compounds, PTH elevation was
transient and returned to baseline within 60 min following iv or po
administration. It is interesting to point out that some compounds
(e.g., 2m and 9f) exhibited pronounced biphasic kinetics (rapid
decline in concentration in the
a-phase followed by a prolonged
b-phase), leading to higher estimated distribution volumes (>1.0–
2.0 L/kg) and longer terminal elimination half-lives. However, this
attribute does not result in significant compound accumulation
and/or sustained PTH elevation in a sub-chronic setting. For in-
stance, consecutive daily po dosing (10 mg/kg) of (R)-2h and 2m
in rats for 5 days led to the anticipated transient stimulation of
the hormone on days 1 and 5; sustained PTH elevation was not ob-
served on day 5 (comparison with pre-bleed samples with days 1
and 5).
In conclusion, orally-active 5-trifluoromethylpyrido[4,3-d]pyr-
imidin-4(3H)-one CaR antagonists with a short duration of action
have been identified using a combination of PK/PD and in silico
modeling of microsomal stability data, which greatly facilitated de-
sign of analogs. Additional safety and ADME profiling is currently
underway for analogs (R)-2h and 2m in support of potential clini-
cal studies.
17. Half-life (T1/2) is calculated as 0.693 ꢂ Vdss/CLb.
18. Assuming complete oral absorption (Fa = 1) and insignificant gut metabolism
(Fg = 1), a theoretical oral bioavailability (F) of 50% is possible with a CLb of
10 mL/min/kg. Oral F is expressed as a sum of the components: Fa ꢂ Fg ꢂ Fh
where Fh is 1 ꢁ CLb/Q. Q is the human hepatic blood flow at 20 mL/min/kg.
19. Retrospective in-house analysis of success rates for human clearance and half-
life predictions using human liver microsomes have revealed 2-fold error in
the predictions.
20. Human embryonic kidney 293 (HEK 293) cells expressing human calcium
receptor were used to detect in vitro calcilytic activity using Fluorometric
imaging plate reader (FLIPR) methodology. Receptor activation by extracellular
Ca2+ results in the release of Ca2+ from intracellular stores into the cytosol. A
fluorescent indicator (Fluo-4) is internalized by the cells from growth media
and interacts with Ca2+ released into the cytosol to provide means of
quantifying intracellular Ca2+ levels and receptor agonism/antagonism.
Potential antagonists were identified by their ability to decrease this
fluorescent response. The IC50 values were based on the ability of the cells to
inhibit the Ca2+ induced increase in intracellular Ca2+. Fluorescence signal was
read 42 s after the stimulation of the calcium receptor by the addition of
1.7 mM Ca2+ (EC95 for calcium).
References and notes
21. Obach, R. S. Drug Metab. Dispos. 1999, 27, 1350.
22. In silico model for human microsomal CL was developed based on >500 data
points (400 data points for training set and 96 data points for test set). The
descriptors used to build the model were: MOE descriptors E-state,
1. Ray, N. F.; Chan, J. K.; Thamer, M.; Melton, L. J., III J. Bone Miner. Res. 1997, 12, 24.
2. Nemeth, E. F. J. Mol. Endocrinol. 2002, 29, 15.
3. Deal, C. Nat. Clin. Pract. Rheumatol. 2009, 5, 20.
lipophilicity and structural fragments coded in MOE.
A model describing
4. Blick, S. K.; Dhillon, S.; Keam, S. J. Drugs 2008, 68, 2709.
non-specific microsomal binding using similar descriptors has been published
by us. See— Gao, H.; Yao, L.; Mathieu, H. W.; Zhang, Y.; Maurer, T. S.;
Troutman, M. D.; Scott, D. O.; Ruggeri, R. B.; Lin, J. Drug Metab. Dispos. 2008,
36, 2130.
5. Stroup, J.; Kane, M. P.; Abu-Baker, A. M. Am. J. Health Syst. Pharm. 2008, 23, 1076.
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25. Title compounds were prepared using the appropriate arylaldehyde derivatives
according to the general protocol outlined in Scheme 1.
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OH group may be due to the formation of a stable internal H-bond as shown.
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