A novel class of apical sodium co-dependent bile acid transporter inhibitors: The 2,3-disubstituted-4-phenylquinolines

Article abstract of DOI:10.1016/S0960-894X(99)00683-6

A series of 2,3-disubstituted-4-phenylquinolines were prepared and were found to inhibit the apical sodium co-dependent bile acid transporter (ASBT). Alkyl and ester substitution at the 3-position showed comparable activities while substitution at the 2-position was much more sensitive to the nature of the substituent. The synthesis and in vitro potency data are presented for this novel class of compounds. (C) 2000 Elsevier Science Ltd. All rights reserved.

Full text of DOI:10.1016/S0960-894X(99)00683-6

Bioorganic & Medicinal Chemistry Letters 10 (2000) 277±279
A Novel Class of Apical Sodium Co-Dependent Bile Acid
Transporter Inhibitors: The 2,3-Disubstituted-4-Phenylquinolines
Michael B. Tollefson,* William F. Vernier, Horng-Chih Huang, Fang Ping Chen,
Emily J. Reinhard, Judith Beaudry, Bradley T. Keller and David B. Reitz
Searle Discovery, Monsanto Life Sciences, 700 Chester®eld Parkway N, St. Louis, MO 63198, USA
Received 11 October 1999; accepted 1 December 1999
AbstractÐA series of 2,3-disubstituted-4-phenylquinolines were prepared and were found to inhibit the apical sodium co-dependent
bile acid transporter (ASBT). Alkyl and ester substitution at the 3-position showed comparable activities while substitution at the
2-position was much more sensitive to the nature of the substituent. The synthesis and in vitro potency data are presented for this
novel class of compounds. # 2000 Elsevier Science Ltd. All rights reserved.
Bile acids are synthesized from cholesterol in the liver
and are excreted in the bile. The apical sodium co-
dependent bile acid transporter (ASBT) promotes re-
absorption of bile acids from the intestinal tract into the
enterohepatic circulation. Prevention of bile acid re-
absorption has been implicated in the lowering of chol-
esterol levels. Elevated plasma low density lipoprotein
(LDL) cholesterol levels are a major risk factor for
arteriosclerosis and coronary heart disease.1,2
the keto ester substituted naphthol 1 as an ASBT
inhibitor.5,6 Kondo and co-workers reported the struc-
turally similar diester naphthol 2 was e€ective at low-
ering total serum cholesterol levels.7,8 Based upon these
reports we sought to prepare the isoelectronic quino-
lines 3 and quinoline N-oxides 4 in an e€ort to prepare a
more potent therapeutically useful ASBT inhibitor.
Current therapies to treat hyperlipidemia include the
use of bile acid sequestrants to prevent absorption of
bile acids into the circulation and statins acting as
HMG-CoA reductase inhibitors. Sequestrants su€er
from poor patient compliance due to their large doses
and non-palatability.3
Partial surgical removal of the ileum was reported to
cause a lowering of plasma LDL cholesterol levels indi-
cating an ASBT inhibitor may be an e€ective therapy to
reduce serum cholesterol levels.4 An ASBT inhibitor
would lower plasma cholesterol levels by raising the
amount of bile acids excreted in the feces creating a
de®ciency of bile acids causing the further conversion of
cholesterol to bile acids. An ASBT inhibitor would have
a physiological response similar to a bile acid seques-
trant while eliminating its non-palatability.
The benzophenone 6 was used as a common inter-
mediate for all analogues prepared below (Scheme 1).
3,4,5-Trimethoxyaniline was protected as the carbamate
5. Treatment of carbamate 5 with 2 equiv of t-butyl
lithium in THF followed by trapping with the appro-
priate ester followed by removal of the Boc group with
tri¯uoroacetic acid a€orded benzophenone 6.
A number of substituted aryl naphthols have been
reported to inhibit ASBT. Hara and co-workers reported
*Corresponding author. Tel.: +1-847-982-8585; fax: +1-847-982-4714.
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(99)00683-6

278
M. B. Tollefson et al. / Bioorg. Med. Chem. Lett. 10 (2000) 277±279
Scheme 1. Preparation of ketone 6.
It was ®rst sought to synthesize compounds 4a and 4b
as the quinoline N-oxide isoelectronic equivalents to the
aryl naphthols 1 and 2 (Scheme 2). Reaction of 6 with
dimethyl acetylenedicarboxylate a€orded the diester
quinoline 3a. Oxidation of 3a with m-CPBA a€orded
the diester quinoline N-oxide 4a. To prepare the quino-
line similar to 1 we treated 3a with the appropriate
Grignard and obtained selective addition to the more
electron de®cient ester to a€ord the quinoline keto ester
3b. Treatment of 3b with mCPBA was not successful;
however, the use of sodium perborate in acetic acid
a€orded the quinoline N-oxide 4b.
Scheme 3. Preparation of quinolines 3 and quinoline N-oxides 4.
isoelectronic quinolines 3a, 3b, 4a and 4b showed little
to no inhibition of ASBT (see Table 1).
It was decided to make a series of ester, ketone, alcohol,
alkyl and aryl substituted quinolines. Preparation of the
remaining quinoline analogues (3) involved the
straightforward condensation of a number of ketones,
keto esters and diesters with the keto aniline 6 (Scheme
3). Treatment of 3 with m-CPBA or sodium perborate
a€orded the respective quinoline N-oxides (4).
The in vitro activity was determined by measuring the
uptake of [14C]-taurocholate in baby hamster kidney
cells transfected with the cDNA of human ASBT
(H14 cells).9 Naphthol 1 had an IC50=2.55 mM. The
The a-hydroxy quinoline 3d and lactone 3e were pre-
pared from the quinoline N-oxide 4c (Scheme 4). Treat-
ment of 4c with acetic anhydride transfers the N-oxide
Scheme 2. Preparation of diester 3a and 4a and ketoester 3b and 4b.
Table 1. In vitro assay of quinolines that inhibit ASBT-mediated uptake of [14C]-taurocholate
Compound
R1
R2
X
IC50 (mM)
% Inhibition @ 50 mM
ꢀ ꢀ
3a
4a
3b
4b
3c
4c
3d
3e
3f
3g
4g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
CO2Me
CO2Me
CO2Me
CO2Me
CO2Me
CO2Me
CO2Et
CO2Et
CO2Et
0
22
35
0
O
ꢀ ꢀ
C(O)CH2CHEt2
C(O)CH2CHEt2
CH2CH2CHEt2
CH2CH2CHEt2
CH(OH)CH2CHEt2
O
ꢀ ꢀ
13.3
O
ꢀ ꢀ
32
0
34
ꢀ ꢀ
ꢀ ꢀ
ꢀ ꢀ
-CH(CH2CHEt2)O2C-
i-Pr
Et
CO2Et
Me
Me
H
H
Me
4.4
7.1
Et
CH2CH2CHMe2
i-Pr
O
ꢀ ꢀ
36
9.2
10.8
21.4
ꢀ ꢀ
ꢀ ꢀ
ꢀ ꢀ
ꢀ ꢀ
ꢀ ꢀ
ꢀ ꢀ
ꢀ ꢀ
ꢀ ꢀ
ꢀ ꢀ
ꢀ ꢀ
i-Pr
-CH2CH2CH2CH2-
50
37
31
n-Bu
Me
Ph
p-NO2Ph
p-NH2Ph
p-FPh
p-FPh
Me
CH2CHMe2
Me
CO2Et
CO2Et
CO2Me
H
3.5
12
49
24.7
9.3

M. B. Tollefson et al. / Bioorg. Med. Chem. Lett. 10 (2000) 277±279
279
Scheme 4. Preparation of lacton 3e.
oxygen to the a-position on the alkyl side chain. The
acetate group was removed by treatment with sodium
methoxide to produce 3d. The lactone 3e can be formed
by subsequent treatment of 3d with 10% hydrochloric
acid.
References and Notes
1. Stark, R. M. Am. J. Cardiol. 1995, 78, 13.
2. Lipid Research Clinics Program. JAMA 1984, 251, 351.
3. Ast, M.; Frishman, W. H. J. Clin. Pharmacol. 1990, 30, 99.
4. Buchwald, H. et al. for the POSCH Group. New England J.
Medicine 1990, 323, 946.
The quinoline N-oxides (4c and 4g) exhibited a slight
loss of activity when compared to the corresponding
quinolines (3c and 3g). Placement of an oxygen at the
a-position, as in the alcohol 3d and the lactone 3e, also
resulted in the reduction of in vitro activity.
5. Hara, S.; Higaki, J.; Higashino, K.; Iwai, M.; Takasu, N.;
Miyata, K.; Tonda, K.; Nagata, K.; Goh, Y.; Mizui, T.
Pharm. Lett. 1997, 60, 365.
6. Mori, S.; Takechi, S.; Shimizu, S.; Kida, S.; Iwakura, H.;
Hajima, M. Tetrahedron Lett. 1999, 40, 1165.
7. Kuroda, T.; Kondo, K.; Iwasaki, T.; Ohtani, A.; Taka-
shima, K. Chem. Pharm. Bull. 1997, 45, 678.
8. Iwasaki, T.; Kondo, K.; Nishitani, T.; Kuroda, T.; Hir-
akoso, K.; Ohtani, A.; Takashima, K. Chem. Pharm. Bull.
1995, 43, 1701.
Alkyl and phenyl substituents are well tolerated at the
R1 position. Good activities were observed with i-propyl
(3f, i, j), ethyl (3g) and i-pentyl (3h). The 2-phenyl sub-
stituted quinoline 3n was found to be the most potent
compound with an IC50=3.5 mM. Some electronic
e€ects are apparent on the 2-phenyl ring where the
electron de®cient nitro group reduces potency with
respect to an amino substitution (3o versus 3p).
9. H-14 cells expressing functional human ASBT (H-14 cells)
were grown in T150 tissue culture ¯asks in DMEM (HG)
media. The cells were trypsinized and plated into opaque white
96-well tissue culture plates at a density of 6Â104 cells per well.
Naõve BHK cells were seeded at the same density and run in
the assay as a background control. After attaching and grow-
ing for 24 h, the culture media was decanted and the cells
washed with 200 mL/well assay bu€er consisting of Hanks'
balanced salt solution containing 25 mM HEPES, pH 7.4, and
0.1% bovine serum albumin (BSA). Test compounds were
prepared as a 50 mM stock solution in dimethyl sulfoxide
(DMSO) and diluted to the required concentration in assay
bu€er. A 100 mL of assay bu€er containing 5 mM [14C]tauro-
cholic acid and the indicated concentration of test compound
was added to each well. Each concentration was tested in
triplicate wells. Control wells contained 0.1% DMSO in assay
bu€er, the ®nal concentration of DMSO in the wells contain-
ing test compounds. The 96-well plate was incubated at 37 ꢁC
for 2 h in a humidi®ed incubator of 7.5% CO2. After the
incubation period, the plates were decanted and each well
washed twice with ice-cold phosphate-bu€ered saline (PBS)
containing 0.1% fatty-acid free BSA followed by one time
with straight PBS. Each well received 200 mL Microscint-20
and a clear plastic heat seal was placed over the top of the
plate. The radioactivity in each well was counted in a Packard
TopCount scintillation counter.
Substitution at the R2 group tolerated an ester, a methyl
or a proton. When R1=i-Pr the order of activity at R2
was 3f(CO2Et)>3i(H)>3j(Me) and when R1=p-FPh it
was 3q(CO2Me)>3r(H) indicating that an electron de®-
cient R2 substituent may be bene®cial.
It is evident that a number of substitutions at the R1
and R2 positions for this class of quinolines are well
tolerated for producing a potent ASBT inhibitor. The
oxygen substitution at the quinoline nitrogen or a-car-
bon of the 2-alkyl group is not tolerated and resulted in
a loss of activity. A variety of alkyl and aryl substituents
at the R1 position while substituting R2 with a hydro-
gen, methyl or ester produces 4-arylquinolines with
good in vitro potencies. This work is a positive step
toward the goal of producing a novel ASBT inhibitor to
lower plasma cholesterol levels and more work needs to
be done.