Design, synthesis and structure-activity-relationship of 1,5-tetrahydronaphthyridines as CETP inhibitors

Article abstract of DOI:10.1016/j.bmcl.2012.03.075

This Letter describes the discovery and SAR optimization of 1,5-tetrahydronaphthyridines, a new class of potent CETP inhibitors. The effort led to the identification of 21b and 21d with in vitro human plasma CETP inhibitory activity in the nanomolar range (IC₅₀ = 23 and 22 nM, respectively). Both 21b and 21d exhibited robust HDL-c increase in hCETP/hApoA1 dual heterozygous mice model.

Full text of DOI:10.1016/j.bmcl.2012.03.075

Bioorganic & Medicinal Chemistry Letters 22 (2012) 3056–3062
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design, synthesis and structure–activity-relationship of
1,5-tetrahydronaphthyridines as CETP inhibitors
Maria-Carmen Fernandez a, , Ana Escribano a, Ana I. Mateo a, Saravanan Parthasarathy b,
⇑
Eva M. Martin de la Nava a, Xiaodong Wang c, Sandra L. Cockerham b, Thomas P. Beyer b,
Robert J. Schmidt b, Guoqing Cao d, Youyan Zhang b, Timothy M. Jones b, Anthony Borel b,
Stephanie A. Sweetana b, Ellen A. Cannady b, Gregory Stephenson b, Scott Frank b, Nathan B. Mantlo b
a Centro de Investigación Lilly, Avda. de la Industria, 30, 28108 Alcobendas, Madrid, Spain
b ELi Lilly and Co., Lilly Research Laboratories, Indianapolis, IN 46285, United States
c Loma Vista Drive, Burlingame, CA 94010, United States
d Hengrui Pharmaceutical, 279, Wenjing Road, Shanghai 200245, China
a r t i c l e i n f o
a b s t r a c t
Article history:
This Letter describes the discovery and SAR optimization of 1,5-tetrahydronaphthyridines, a new class of
potent CETP inhibitors. The effort led to the identification of 21b and 21d with in vitro human plasma
CETP inhibitory activity in the nanomolar range (IC50 = 23 and 22 nM, respectively). Both 21b and 21d
exhibited robust HDL-c increase in hCETP/hApoA1 dual heterozygous mice model.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 30 January 2012
Revised 20 March 2012
Accepted 21 March 2012
Available online 28 March 2012
Keywords:
CETP inhibitor
HDL-c
CVD
1,5-Tetrahydronaphthyridines
Cardiovascular disease (CVD) continues to be the leading cause
of mortality in the industrialized world. Often, patients who are
obese, have type 2 diabetes or metabolic syndrome, show abnor-
mal circulating lipid profiles including low levels of high-density
lipoprotein cholesterol (HDL-c) and elevated levels of LDL-c or
triglycerides. These individuals are at high risk of developing
CVD.2 Statins, alone or in combination with ezetimibe are the most
commonly used lipid-lowering therapies for cardiovascular risk
reduction.3,4 However two thirds of the statin-treated patients
continued to develop CVD. Several epidemiological studies have
demonstrated an inverse relation between HDL-c and coronary
heart disease,5 therefore, raising HDL-c represents a promising
therapeutic strategy for further reduction of cardiovascular
events.6 Current available HDL-c elevating drugs have limited
efficacy and undesirable side effects.7,8 Thus, there is significant
unmet medical need for a well tolerated plasma HDL-c enhancer.
The discovery that a genetic deficiency involving cholesterol ester
transfer protein (CETP) is associated with increased levels of HDL-c
provided the rational for its pharmacological inhibition.9 CETP is a
plasma glycoprotein that aids in the transfer of cholesteryl esters
from HDL to LDL and VLDL with a balanced exchanged of
triglycerides from apoB-containing lipoprotein particles to HDL.
The net result is a lowering of HDL-c and an increase in LDL-c.
Therefore, the inhibition of CETP would provide a therapeutically
beneficial plasma lipid profile. In the last years, many pharmaceu-
tical companies included us, have reported a wide variety of CETP
inhibitors.10
Torcetrapib, was the first CETP inhibitor to undergo large Phase
III trials but was withdrawn in 2006 after an increase in cardiovas-
cular events and mortality.11 These undesirable effects opened a
discussion with regards to the safety and efficacy of using CETP
inhibitors for prevention of cardiovascular disease. Post hoc analy-
sis of the study led to the conclusion that torcetrapib has com-
pound-specific and off-target effects, such as raising blood
pressure and aldosterone.12 Currently, clinical trials of other CETP
inhibitors, such as anacetrapib, dalcetrapib or evacetrapib (see
Fig. 1) with no reported off-target effects are ongoing.13,12b
In this Letter we describe the design and further optimization
through structure–activity relationship studies of a 1,5-tetra-
hydronaphthyridine series that led to the discovery of compounds
21b and 21d (see Fig. 1), potent in vitro inhibitors that exhibited
robust HDL-c elevation in vivo.
As an initial approach we studied the replacement of the aryl
moiety of the tetrahydroquinoline core by different heterocycles
with the aim to achieve CETP affinity and mitigate lipophylicity.
⇑
Corresponding author. Tel.: +34 91 663 3437; fax: +34 91 663 3411.
E-mail address: mc.fernandez@lilly.com (M.-C. Fernandez).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.03.075

M.-C. Fernandez et al. / Bioorg. Med. Chem. Lett. 22 (2012) 3056–3062
3057
F3C
F3C
O
F3 C
O
O
O
N
N
O
F3C
N
N
O
O
S
O
F3C
O
F3C
F
Dalcetrapib
CETP IC50 NT
Torcetrapib
CETP IC50 39 nM
Anacetrapib
CETP IC50 46 nM
F3C
F3C
O
N
O
N
N
N
CO2H
F3C
N
F3C
N
N
N
N
R
N
N
N
N
Evacetrapib
CETP IC50 26 nM
R= CF3, 21b
CETP IC50 23 nM
R= Me, 21d
CETP IC50 22 nM
Figure 1. Structure and human plasma CETP activity14 of CETP inhibitors.
F3C
F3C
F3C
CF3
CF3
N
CF3
N
O
O
N
N
N
O
N
O
O
O
O
O
O
N
S
N
MeO
2
1
(+/-)-3a
CETP IC50 0.49 uM
CETP IC50 46.0 uM
CETP IC50 44.1 uM
Figure 2. Structure and plasma CETP activity of the dihydro-5H-thieno[3,2-b]pyridine 1 and tetrahydro naphthyridines 2 and 3a.
F C
3
CO Et
2
CF
N
3
O
N
N
S
g, h
a, b, c, d
O
N
O
O
N
4a
X
Y
O
CO Et
2
S
X
e, f
1
R
g, h
R
Y
F C
3
O
O
b, c, d
O
O
CF
3
N
N
O
4b
6a,b
5a,b
N
N
N
O
O
5a, 6a, X = S, R = H, Y = bond
5b, 6b, X = CH, R = Me, Y = N
2
Scheme 1. Reagents and conditions: (a) NaOH, MeOH, 60 °C; (b) EtOCH@C(CO2Et)2, toluene, reflux; (c) PhOPh, reflux; (d) iPrOCOCl, Py, DCM, rt; (e) EtMgBr, CuI, THF, À78 to
À20 °C; (f) LiCl, DMSO, H2O, 160 °C; (g) [3,5-bis(trifluoromethyl) phenyl]methanamine, Ti(OiPr)4, NaBH4, MeOH; (h) Ac2O, Py, DCM.
Based on this hypothesis we prepared the dihydro-5H-thieno
[3,2-b]pyridine 1 and 1,8-tetrahydronaphthyridine 2 (see Fig. 2)
from the corresponding commercially available 2-aminothiophene
4a and 2-aminopyridine 4b, respectively. This approach, summa-
rized in Scheme 1, afforded both compounds as mixtures of four
isomers.
The first step of the synthesis involved the condensation of the
starting amines 4a,b with diethyloxymethylenmalonate followed
by thermal cyclization and subsequent carbamate formation to
produce adducts 5a,b. 1,4-Addition of ethyl magnesium bromide
in the presence of copper(I) iodide followed by decarboxylation
gave rise to the corresponding piperidones 6a,b that were

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M.-C. Fernandez et al. / Bioorg. Med. Chem. Lett. 22 (2012) 3056–3062
2
2
R
F C
3
R
2
H
N
R
O
O
NH
O
O
H2N
O
N
N
H
N
c, d
e
N
5
F C
3
N
5
N
5
R
R
(+/-)-10a-g
(+/-)-9a-g
R
(+/-)-8a-g
f
F C
3
a, b
2
R
O
5
N
N
R
N
F C
3
O
O
N
NH2
(+/-)-3a-g
(see Table 1)
5
7a-e
R
(+/-): Racemic mixture of cis isomers
Scheme 2. Reagents and conditions: (a) R2CHO, Na2SO4, DCM, À20 °C; (b) vinyl acetamide, BF3ÁOEt2, À20 to À10 °C; (c) iPrOCOCl, Py, 0 °C, rt; (d) 5 N HCl, 80 °C; (e) (3,5-bis-
CF3)PhCHO, NaBH(OAc)3, DCE, rt; (f) Ac2O, Py, rt.
converted to the compounds 1 and 2 via reductive amination with
bis(trifluoromethyl)phenyl methanamine and further acetamide
formation.
Continuing with the exploration of other pyridine regioisomers
we synthesized the 1,5-tetrahydronaphthyridine 3a (Fig. 2) ob-
tained as a racemic mixture of the cis isomers by a modification
of the Diels–Alder reaction (see Scheme 2).
treatment with vinyl acetamide in the presence of boron trifluoride
eterate.15 Subsequent acylation of 8a–g with isopropyl chlorofor-
mate and acetamide hydrolysis gave rise to the 4-amino deriva-
tives 9a–g that were derivatized to the N-benzyl amino
intermediates 10a–g by reductive amination with bis(trifluoro-
methyl)benzaldehyde. Further acetylation of 10a–g afforded the
corresponding 1,5-tetrahydronaphthyridines 3a–g.
The initial set of compounds was tested in the human CETP
plasma assay14 showing that ( )-1,5-tetrahydronaphthyridine 3a
inhibited CETP in a low micromolar range (see Fig. 2) and was sig-
nificantly more potent than the other analogs. Given this result we
focused our work on further optimization of 3a.
1,5-Tetrahydronaphthyridines substituted at positions 2 and 5
were prepared following the general procedure described in
Scheme 2. 3-Aminopyridines 7a–e were converted to intermedi-
ates 8a–g by reaction with the appropriate aldehyde followed by
Moreover, intermediate 10b can be further converted in more
elaborated derivatives following the procedures described in
Scheme 3. In this regard, reaction of 10b (R2 = Et, R5 = CF3) with
diketone and subsequent cyclization with hydroxylamine or
hydrazine gave pyrazole 14b and isoxazole 15b, respectively. Con-
densation of 11a–d with sodium azide in basic media produced the
tetrazoles 16a–d. Alternatively, reaction of 11b with hydroxyl-
amine followed by treatment with acetic anhydride afforded oxa-
diazole 12b.
F C
3
CF
3
F C
F C
3
F C
3
F C
3
3
O
O
CF
CF
CF
CF
3
3
3
3
N
N
N
N
N
O
O
O
O
O
O
O
O
N
5
a
N
N
N
N
N
O
d
e
m
N
N
N
N
H
N
(2R, 4S)-21b,d
N
N
R
N
N
N
O
N
5
N
5
N
R
F C
3
5
(+/-)-10a-g
(+/-)-11a-d
R
(+/-)-16a-d
(+/-)-16a-d (R = H)
(+/-)-18-d (R = Me)
F C
3
R
(+/-)-13b
(+/-)-14b
(+/-)-15b
R
b
c
CF
N
3
(+/-)-11b
f, g
i
(+/-)-12b
O
N
(See Table 2)
O
N
N
5
N
N
(2S, 4R)-22b,dR
N
F C
3
F C
3
F C
3
R
CF
3
CF
3
CF
3
O
O
h
O
O
O
O
j, k (R = NH2)
l (R = OH)
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
(+/-)-19b (R = NH2)
(+/-)-20b (R = OH)
F C
F C
3
3
(+/-)-16b
(+/-)-17b
R
F C
3
Scheme 3. Reagents and conditions: (a) Diketone, THF, DMAP, rt; (b) NH2OH, NaOAc, MeOH; (c) NH2NH2, EtOH, P2O5, 90 °C; (d) CNBr, THF, iPr2NEt, rt; (e) NaN3, Et3N, toluene,
110 °C; (f) NH2OH, EtOH, Et3N, 80 °C; (g) Ac2O, 80 °C; (h) K2CO3, IMe, ACN; (i) MeOH, PPh3, DEAD, DCM, rt; (j) 2-aminoethyl)carbamic acid tert-butyl ester, PPh3, DEAD, DCM,
rt; (k) TFA, DCM, rt; (l) 2-bromoethanol, CsCO3, DMF, 50 °C; (m) chiral separation on a Chiralpak AD (4.6 Â 150 mm).

M.-C. Fernandez et al. / Bioorg. Med. Chem. Lett. 22 (2012) 3056–3062
3059
Table 1
Deprotonation of 16b with potassium carbonate followed by
reaction with methyliodide allowed the preparation of the 1-meth-
yltetrazole derivative 17b. Alternatively, treatment of 16a–d with
methanol under Mitsunobu conditions afforded the 2-methyltet-
razole derivatives 18a–d. Applying the same methodology with
(2-aminoethyl)carbamic acid tert-butyl ester and further carba-
mate cleavage with trifluoroacetic acid produced 19b. 2-Hydroxy-
ethyl derivative 20b was prepared by alkylation of the tetrazole
intermediate 16b with 2-bromoethanol in dimethylformamide.
( )-cis-Methyl tetrazole derivatives 18b (R5 = CF3) and 18d
(R5 = Me) were separated by chiral chromatography on a Chiralpak
AD affording the corresponding enantiomers (2R, 4S)-21b,d and
(2S, 4R)-22b,d (see Scheme 3).
We began the optimization of our initial hit 3a for the search of
the best substitution at position 5 of the tetrahydronaphthyridine
core (see Table 1). It was found that while a donor and an acceptor
were allowed such as methoxy (3a) or trifluoromethyl (3b), a slight
reduction in potency was observed with bromo (3c), methyl (3d)
or dimethylamine (3e) substitutions. Keeping the trifluoromethyl
moiety at C-5, we explored the tolerability of other alkyl groups
at position 2. As a first attempt, we replaced ethyl (3b) by methyl
1,5-Tetrahydronaphthyridines substituted at C2 and C5
F C
3
2
R
O
O
N
N
F C
O
3
N
5
(+/-)-3a-g
R
aCompound
R2
R5
bCETP IC50 (nM)
3a
3b
3c
3d
3e
3f
Et
Et
Et
Et
Et
Me
cPr
OMe
CF3
Br
487
396
1297
980
948
1050
980
Me
NMe2
CF3
3g
CF3
a
Racemic mixtures.
Human plasma CETP IC50
b
.
Table 2
SAR study at exocyclic (Northern) nitrogen in conjunction with substitution on C-5
F C
3
O
N
O
N
F C
3
R
N
5
R
Compound R5
R
aCETP IC50
(nM)
Compound R5
R
aCETP IC50
(nM)
Compound R5
R
aCETP IC50
(nM)
N
N
N
N
N
N
b3b
CF3 COCH3
396
b18a
b18c
OMe
134
47
c22d
c21e
Me
50000
31
N
N
N
N
N
N
N
N
b11b
CF3 CN
>5000
Br
NMe2
NH2
N
N
N
N
N
N
N
N
N
b12b
b14b
b15b
CF3
74
b18d
b19b
b20b
Me
61
66
44
c21f
c21g
c21h
98
O
N
N
N
N
N
N
N
N
N
N
N
N
CF3
203
154
CF3
CF3
NHMe
142
591
N
N
N
N
N
O
N
N
N
N
N
CF3
NHEt
N
N
O
N
N
N
N
N
b16b
a17b
b18b
CF3
>50000
>50000
49
c21b
c22b
c21d
CF3
CF3
Me
23
7416
22
c21i
c21j
c21k
471
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
O
N
N
N
N
N
CF3
CF3
25000
>50000
N
N
N
N
N
N
N
N
N
N
N
N
N
N
a
b
c
Human plasma CETP activity.
Racemic mixtures.
Enantiomerically pure compounds.

3060
M.-C. Fernandez et al. / Bioorg. Med. Chem. Lett. 22 (2012) 3056–3062
Table 3
(3f) and cyclopropyl (3g) groups (Table 1). In both cases, a slight
reduction of the potency was observed compared to 3b.
To explore the nature of the acetamide region on the northern
nitrogen, a variety of compounds were prepared and screened
(Table 2). The replacement of acetyl group by cyano (11b), tetra-
zole (16b) and N-1-methyl tetrazole (17b) was detrimental for
activity. However, substitution with 3-methyl pyrazole (14b) or
3-methylisoxazole (15b) was tolerated. The best results were
obtained with 3-methyl-oxadiazole (12b) and N-2-substituted
tetrazole derivatives 18b, 19b and 20b.
Influence of substitution at positions 6 and 7
F C
3
O
R
N
N
O
F C
N
N
3
7
R
N
5
N
N
6
R
R
R5
R6
R7
R
aCETP IC50 (nM)
The relative stereochemistry of the chiral centers of 18b have
been established by X-ray.16 However, pure enantiomers, 21b
and 22b, obtained by chiral chromatography, were amorphous
and could not be crystallized, so the absolute configuration of the
most potent enantiomer (2R,4S)-21b, was determined by VCD
(vibrational circular dichroism).17 This result is in concordance
with what is described in the literature for the structurally related
tetrahydroquinolines.18
Compound
a18a
c21f
OMe
NH2
OMe
NH2
CF3
H
H
Me
Me
H
H
H
H
H
iPr
iPr
iPr
iPr
Et
134
98
38.4
106
24
b23a
b23c
b23d
Me
a
b
c
Human CETP plasma IC50
Racemic mixture.
Pure enantiomer.
.
Improvement on the CETP inhibition was also observed on the
2-methyltetrazole derivatives (18a,c–d) in comparison with the
corresponding acetyl derivatives. Methyl analogue 18d was sepa-
rated by chiral chromatography and isomer 21d showed a compa-
rable activity to the corresponding trifluoromethyl derivative 21b.
Since the 2-methyl tetrazole produced an important enhance-
ment in the potency compared to the acetamide analogs we recon-
sidered the initial idea of introducing polar groups at the
tetrahydronaphthyridine core to reduce the lipophilicity of this
scaffold. Analogs 21e–k (Table 2) were prepared and evaluated
as pure enantiomers. We were pleased to discover that amino
groups at position 5 were tolerated and good potency was achieved
in the case of methyl, dimethylamino or amino derivatives 21g,
21e and 21f, respectively. However, the scope of this activity is
limited to small amino groups since largest resulted in a loss of
potency.
After these encouraging results we decided to go one step further
and introduce an extra substituent in the tetrahydronaphthyridine
ring.19 We prepared the 5-methoxy-6-methyl-tetrahydronaph-
thyridine derivative 23a (Table 3) and 5-amino-6-methyl tetra-
hydronaphthyridine 23c. As it is shown in the table, methyl group
at 6-position slightly improved the activity of 23a compared to the
mono-substituted analog 18a while 23c was equipotent to 21f.
The introduction of a methyl group at the 7-position (23d) did not
reduce the potency despite the increase of steric hindrance that this
group confers to the molecule compared to 18b.
Table 4
Influence of the benzylic substitution in CETP inhibitors
3'
R
O
N
N
N
3''
O
R
N
N
N
5
N
R
(2R,4S)-24a-f)
aCompound
R5
R3’
R3’’
bCETP IC50 (nM)
21b
24a
24b
24c
24d
24e
CF3
CF3
Me
Me
Me
Me
CF3
CF3
CF3
CF3
CF3
Cl
CF3
23
20
12
21
30
24
Cl
Cl
CN
F
Cl
CF3
24f
CF3
207
N
a
Pure enantiomer.
Human CETP plasma IC50
b
.
Next, we turned our attention to the benzylic domain. It was
found that this region was highly lipophylic being only allowed
the exchange of trifluoromethyl groups by apolar substituents such
as chlorine (24a, 24b, 24f), fluorine (24d) or even cyano (24b) (Ta-
ble 4). However, 3-trifluoromethyl-methylpyridine 24f decreased
the potency of about 10-fold compared to 21b.20
Finally we investigated the substitution at the southern nitro-
gen with the preparation and further evaluation of a set of com-
pounds with different carbamates, amides and alkyl groups.19
Disappointedly, most of the modifications done to replace isopro-
pyl carbamate (21b) turned out in a loss of activity, especially
those derivatives containing polar functionalities (25c–j, Table 5).
Moreover, isopropyl amide (25k) was tolerated although larger
groups lose the potency. Alkyl groups were in detrimental of the
activity as well.
It is known that torcetrapib produced changes in electrolytes in
humans finding that the K+ and Na+ balance was changed most
likely due to the significant increase in plasma aldosterone.11a To
explore the safety profile of the 1,5-tetrahydronaphthyridine ser-
ies, we used the in vitro branched DNA method in a human adrenal
cell line (H295) previously developed by our group.13a This meth-
odology allowed us to demonstrate a potent and dramatic induc-
tion of cortisol and aldosterone synthase mRNA (Cyp11B1 and
Cyp11B2, respectively) by torcetrapib. These results correlate with
increase in aldosterone and cortisol levels in the culture medium
(data not shown). When 21b was tested in this assay, a 10-fold
induction of Cyp11B1 and Cyp11B2 mRNA was observed, which
was similar to the undesirable activity of torcetrapib.
In summary, we successfully modified our previous weakly
inhibitors 1 and 2 to afford the 1,5-tetrahydronapthyridine series
with improved potency. Key structural elements for maintaining
high potency have been identified through detailed structural–
activity relationship studies. This effort led to the identification
of the CETP inhibitors 21b and 21d with an in vitro human plasma
activity of 22 and 23 nM, respectively. Both 21b and 21d have
Compounds 21b and 21d displayed low to moderate clearance
across species (see Table 6) and low to moderate oral bioavailabil-
ity. At 30 mg/kg dose, 21b and 21d demonstrated robust HDL-c
elevation while ex vivo CETP inhibition in hCETP/hApoA1 hetero-
zygous dual transgenic mice was observed for both tetra-
hydronaphthyridines (Table 7).

M.-C. Fernandez et al. / Bioorg. Med. Chem. Lett. 22 (2012) 3056–3062
3061
Table 5
SAR study at the endocyclic (southern) nitrogen
F C
3
N
N
N
R
F C
3
N
N
N
N
F C
3
(2R,4S)-25-a-o)
Compound
R
aCETP IC50 (nM)
Compound
R
aCETP IC50 (nM)
N
O
N
N
21b
CO2iPr
23
25h
488
N
O
O
O
O
25a
25b
CO2Me
197
29
25i
25j
2111
5731
N
O
N
CO2Et
N
O
O
O
b25c
c25d
108
139
25k
25l
55
O
O
O
O
CO2H
114
O
O
O
N
25e
25f
572
25m
193
O
N
N
O
O
O
66
72
25n
25o
205
825
O
N
25g
O
a
b
c
Human CETP plasma IC50
Obtained from corresponding benzyl ether via hydrogenation.
Obtained from corresponding ester via saponification.
.
Table 6
Table 7
PK profile of 21b and 21d
Efficacy and CETP inhibition at 8 h time course and 30 mg/Kg dose in hCETP/hAPO-A1
tg micea
Compound
Species
CL (mL/min/Kg)
% F
Compound
b%CETPinh.
c%HDL-c Increase
21b
21b
21b
21d
21d
Rat
Monkey
Dog
Rat
Monkey
5.5
0.7
1.5
16.4
2.2
31
18
49
18
32
21b
21d
91.6
105
134
147.8
a
Formulation: Corn oil (79.5%), oleic acid (20%), labrafil (0.5%); Species: Male
CETP and ApoA1 heterozygote mice used for this experiment. Mice were orally
dosed with reference CETP compound and blood was taken from the mice at dif-
ferent time point. Serum will be aspirated off and tested for CETP activity.
Formulation: iv formulation: 20% solutol microemulsion/80% DI H2O; po formula-
tion: corn oil/oleic acid/labrafil 79.5:20:0.5; Species: Male Sprague Dawley can-
nualated rats; Female Cynomolgus Monkeys; Female Beagle Dogs Dose: 1 mg/Kg
and 3 mg/Kg. Time Course 0–72 h.
b
Ex vivo CETP inhibition.
In vivo serum HDLc.
c
shown the ability to significantly raise HDL-c in the hCETP/hApoA1
dual heterozygous mice model by inhibiting CETP.
References and notes
Acknowledgments
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14. Plasma CETP assay: A donor particle containing a fluorescent cholesterol ester
analog was prepared similarly to what was described by Bisgaier et al. (Bisgaier
et al. J. Lip. Res. 1993, 34, 1625). The donor particle (3%) was incubated with
human plasma (96%) and test compound in DMSO (1%), VLDL as an acceptor
particle. CETP inhibitory activity was recorded as reductions in fluorescent
intensity with increasing compound concentrations. IC50 values were
determined by non-linear regression.
15. Experimental procedure for the synthesis of 8a (R2 = Et, R5 = OMe): Dissolve 5-
aminopyridine-2-methoxy (1.05 g, 8.05 mmol) in anhydrous dichloromethane
(35 mL), add sodium sulfate (1.14 g) and cool the reaction mixture to À20 °C.
Add propionaldehyde (0.659 mL, 8.85 mmol) and stir the mixture from À20 to
0 °C for 1.5 h. Filter off the sodium sulfate and add N-vinyl acetamide (0.706 g,
85.11 mmol) to the filtrate at À20 °C followed by boron trifluoride diethyl
etherate (0.088 mL, 0.805 mmol). Stir the reaction mixture from À20 to À10 °C
for 2 h. Remove the solvent under vacuo and chromatograph the residue over
silica cartridge, eluting with hexanes/ethyl acetate to afford the title compound
(1.25 g, 63%).
16. See Supplementary data for crystallography details.
17. See Supplementary data for VCD analysis.
18. See WO03029220 A2 for crystallization details of (2R,4S)-4-[(3,5-bis-
trifluoromethyl-benzyl)-methoxycarbonyl-amino]-2-ethyl-6-trifluoromethyl-
3,4-dihydro-2H-quinoline-1-carboxylic acid ethyl ester.
19. General procedure for the synthesis of the 1,5-tetrahydronaphthyridines 23a,
c, d and 25a–o can be found in Supplementary data.
20. Compounds (2R,4S)-24a–f were prepared following the procedure described in
Scheme 2 from the 4-amino-tetrahydronaphthyridines 9d or 9d (see Scheme 2)
by reductive amination with the corresponding aldehyde and further
installation of the 2-methyl tetrazole followed by chiral separation.