S-(2-(Acylamino)phenyl) 2,2-dimethylpropanethioates as CETP inhibitors

Article abstract of DOI:10.1016/j.bmcl.2004.02.071

Studies on the relationship between the structure of the benzene moiety of S-(2-(acylamino)phenyl) 2,2-dimethylpropanethioates and CETP inhibitory activity were performed. Substituents on the benzene moiety influenced CETP inhibitory activity in a type an

Full text of DOI:10.1016/j.bmcl.2004.02.071

Bioorganic & Medicinal Chemistry Letters 14 (2004) 2589–2591
S-(2-(Acylamino)phenyl) 2,2-dimethylpropanethioates
as CETP inhibitors
Kimiya Maeda, Hiroshi Okamoto and Hisashi Shinkai*
Central Pharmaceutical Research Institute, JT Inc., 1-1 Murasaki-cho, Takatsuki, Osaka 569-1125, Japan
Received 9 February 2004; accepted 20 February 2004
Abstract—Studies on the relationship between the structure of the benzene moiety of S-(2-(acylamino)phenyl) 2,2-dimethylpro-
panethioates and CETP inhibitory activity were performed. Substituents on the benzene moiety influenced CETP inhibitory activity
in a type and position dependent manner, and electron-withdrawing groups at the 4- or 5-position increased the activity. The most
potent compound showed 50% inhibition of CETP activity in human plasma at a concentration of 2 lM.
Ó 2004 Elsevier Ltd. All rights reserved.
Me
O
O
A high level of low-density lipoprotein (LDL) choles-
terol is well known to be a major risk factor for
atherosclerosis and coronary heart disease, and 3-
hydroxy-3-methylglutaryl co-enzyme A (HMG-CoA)
reductase inhibitors (statins) are widely used to decrease
LDL cholesterol levels.1 On the other hand, a low level
of high-density lipoprotein (HDL) cholesterol is also an
important risk factor.2;3 HDL cholesterol plays a role in
the transfer of excess cholesterol from the peripheral
tissues to the liver (reverse cholesterol transport)4;5 and
in the inhibition of lipoprotein oxidation,6;7 so HDL
cholesterol is protective against atherosclerosis. There-
fore, convenient drugs that can significantly increase the
HDL cholesterol level would be useful.8;9 Cholesteryl
ester transfer protein (CETP) is a plasma glycoprotein
that plays a role in the exchange of cholesteryl esters
(CE) in HDL for triglycerides in very low-density lipo-
protein (VLDL).10;11 This process reduces the level of
antiatherogenic HDL cholesterol and increases the level
of proatherogenic VLDL and LDL cholesterol. Indeed,
the atherogenicity of CETP has been supported by many
studies,12–16 and we showed that a CETP inhibitor, JTT-
705, was able to inhibit the progression of atheroscle-
rosis in rabbits through marked elevation of HDL
cholesterol and slight reduction of non-HDL choles-
terol.17 The suggestion that CETP inhibitors are
potentially antiatherogenic agents has led to their
development as therapeutic drugs and two compounds,
JTT-705 and torcetrapib, have reached clinical studies
(Fig. 1).18
Me
CF3
N
N
Me
O
NH Me Me
S
F3C
Me
O
Me
CF3
O
O
JTT-705
torcetrapib
Figure 1. Structures of JTT-705 and torcetrapib.
We previously reported on the structure–activity rela-
tionships of S-(2-(acylamino)phenyl) alkanethioate
derivatives, which are CETP inhibitors.19 By performing
structural changes and modification of both the acyl-
amino moiety and the thioester moiety, the structural
requirements for inhibition of CETP have been
elucidated and the optimum compound, S-(2-((1-(2-
ethylbutyl)cyclohexane)carbonylamino)phenyl) 2-methyl-
propanethioate (JTT-705), has been developed that
shows 50% inhibition of CETP activity in human plas-
ma at a concentration of 6 lM and is currently in phase
II clinical studies.18 Here we describe new data on the
relationship between the structure of the central benzene
moiety and CETP inhibitory activity, as well as the
discovery of compound 18, which is more potent than
JTT-705.
The compounds for evaluation were synthesized from
2-aminothiophenols (Scheme 1) or 2-nitrophenols20
(Scheme 2). Diacylation at both nitrogen and sulfur
atoms of the 2-aminothiophenols with 2 equiv of the
corresponding acyl chlorides,21 followed by selective
* Corresponding author. Tel.: +81-72-681-9700; fax: +81-72-681-9725;
e-mail: hisashi.shinkai@ims.jti.co.jp
0960-894X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.02.071

2590
K. Maeda et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2589–2591
R5
R5
NH2
O
NH
O
NH
R1
R2
SH
R4
R1
SH
R4
R1
S
t-Bu
c
a,b
O
R2
R2
R4
R3
R3
R3
1, 7, 10, 13
Scheme 1. Reagents: (a) 1-methylcyclohexanecarbonyl chloride (R5¼Me) or 1-(3-methylbutyl)cyclohexanecarbonyl chloride (R5¼isopentyl), pyr-
idine, CHCl3; (b) KOH, THF–MeOH–H2O; (c) pivaloyl chloride, pyridine, CHCl3.
R5
R5
NO2
NO2
Me
N
O
NH
Me
N
O
NH
NH2
Me
N
R1
R2
OH
R4
R1
R2
S
R1
S
R1
S
t-Bu
R1
R2
S
a,b
e,f
c
Me
Me
Me
d
O
O
O
O
R4
R2
R2
R4
R4
R4
R3
R3
R3
R3
R3
2-6, 8, 9, 11, 12, 14-18
Scheme 2. Reagents and conditions: (a) N,N-dimethylthiocarbamoyl chloride, NaH, DMF; (b) diphenyl ether, 120–200 °C; (c) SnCl2Æ2H2O, AcOEt;
(d) 1-methylcyclohexanecarbonyl chloride (R5¼Me) or 1-(3-methylbutyl)cyclohexanecarbonyl chloride (R5¼isopentyl), pyridine; (e) KOH, THF–
MeOH–H2O; (f) pivaloyl chloride, pyridine, CHCl3.
Table 1. Inhibition of CETP activity by the 1-methylcyclohexanecar-
bonylamino compounds
hydrolysis of the thioester bond, yielded the acylamino-
thiophenols. Coupling between these thiophenols and
pivaloyl chloride gave the S-(2-(acylamino)phenyl) 2,2-
dimethylpropanethioates (Scheme 1). The 2-nitrophe-
nols were reacted with N,N-dimethylthiocarbamoyl
Me
O
NH
chloride to give O-aryl dimethylthiocarbamates, and
were subsequently transformed to S-aryl thiocarbamates
by Newman–Kwart rearrangement.22 After these nitro
compounds were converted to aniline derivatives by
reduction with tin(II) chloride, acylation was done with
the corresponding acyl chlorides. Hydrolysis of the
resulting S-acylaminophenyl dimethylthiocarbamates to
thiols and subsequent acylation with pivaloyl chloride
produced the S-(2-(acylamino)phenyl) 2,2-dimethylpro-
panethioates (Scheme 2).
R1
S
t-Bu
O
R2
R4
R3
Compounds
R1
R2
R3
R4
CETP inhibition
in human plasma
IC50 (lM)a
1
2
3
4
5
6
7
8
9
H
H
H
F
H
H
H
F
H
F
72
>300
78
H
H
H
H
H
H
H
H
H
H
F
>300
70
28
In vitro inhibition of CETP activity was assessed by
measuring the rate of [3H] cholesteryl ester transfer from
HDL to apoprotein B-containing lipoproteins in human
plasma, as described previously.17;19 The effect of each
substituent on the central benzene moiety of compounds
1 and 10 was investigated and the results are summa-
rized in Tables 1 and 2. For comparison, the inhibitory
activity of JTT-705 is also shown in Table 2.
H
H
H
H
H
F
Cl
H
H
H
H
H
CF3
CN
OMe
40
102
>300
a Concentration achieving 50% inhibition of CETP-mediated CE
transfer from HDL to VLDL and LDL.
First, the introduction of one or two fluoro groups into
the benzene moiety of compound 1 was tested. Although
the 5-fluoro compound 3 and the 4-fluoro compound 5
maintained CETP inhibitory activity, the 6-fluoro
compound 2 and the 3,5-difluoro compound 4 showed
loss of activity. Since the 4- and 5-positions tolerated the
introduction of a fluoro group, various groups were
introduced into the 4-position on the benzene moiety of
compounds 1 and 10. Although introduction of elec-
tron-donating groups (9, and 15–16) caused loss of
CETP inhibitory activity, introduction of electron-
withdrawing groups either maintained the inhibitory
activity (8, and 11) or caused it to increase (6, 7, and 12–
14) compared with that of the parent compounds (1 and
10). Among various electron-withdrawing groups, the
chloro group showed the greatest enhancement of
activity. The 4-chloro compound 12 was about 5-fold
more potent than the parent compound 10. Because the
active forms of this series are free thiols, as described
previously,19 the effect of electron-withdrawing groups,
especially at the 4-position, may be partly due to
acceleration of hydrolysis of the thioester. A chloro
group was also substituted at the 5-position on the

K. Maeda et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2589–2591
2591
Table 2. Inhibition of CETP activity by the 1-(3-methylbutyl)cyclo-
hexanecarbonylamino compounds
tration of 2 lM making it about three times more potent
than JTT-705.
Me
Me
O
NH
R3
Acknowledgements
R1
S
t-Bu
We would like to thank Shigeo Ishiguro, Jun-ichi
Haruta, Itsuo Uchida, Noriaki Shimoyama, Takao Ito,
and Takahiro Yamasaki for their helpful support.
O
R2
R4
Compounds
R1
R2
R3
R4
CETP inhibition
in human plasma
IC50 (lM)a
References and notes
10
11
12
13
14
15
16
17
18
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Cl
Cl
H
H
H
H
H
H
H
H
H
61
60
F
Cl
1. Knopp, R. H. N. Engl. J. Med. 1999, 341, 498.
2. Gordon, D. J.; Rifkind, B. M. N. Engl. J. Med. 1989, 321,
1311.
13
13
CF3
CN
OMe
Me
H
25
3. Lusis, A. J. Nature 2000, 407, 233.
>300
>300
10
4. Fielding, C. J.; Fielding, P. E. J. Lipid Res. 1995, 36, 211.
5. Barter, P. J.; Rye, K. A. Curr. Opin. Lipidol. 1996, 7, 82.
6. Hegele, R. A. Ann. Med. 1999, 31, 217.
Cl
2
7. Shih, D. M.; Xia, Y. R.; Wang, X. P.; Miller, E. J. Biol.
Chem. 1996, 271, 4396.
8. Shinkai, H. Exp. Opin. Ther. Patents 2001, 11, 739.
9. Shinkai, H. Mini Rev. Med. Chem. 2002, 2, 271.
10. Tall, A. R. J. Lipid Res. 1993, 34, 1255.
JTT-705
6
a Concentration achieving 50% inhibition of CETP-mediated CE
transfer from HDL to VLDL and LDL.
11. Lagrost, L. Biochem. Biophys. Acta 1994, 1215, 209.
12. Marotii, K. R.; Castle, C. K.; Boyle, T. P.; Lin, A. H.;
Murray, R. W.; Melchior, G. W. Nature 1993, 364, 73.
13. Quinet, E.; Tall, A. R.; Ramakrishnan, R.; Rudel, L.
J. Clin. Invest. 1991, 87, 1559.
benzene moiety of 10, which was another position tol-
erating the introduction of substituents. The 5-chloro
compound 17 showed markedly increased activity and
was about 6-fold more potent than 10. On the basis of
these results, we were able to obtain the 4,5-dichloro
compound 18 with the highest potency, which was about
30-fold more potent than 10. The effect of substituting
two chloro groups at the 4- and 5-positions on the
benzene moiety seemed to be synergistic (about 30-fold
enhancement of activity) compared with the effect of a
single chloro group at the 4- or 5-position (about 5- or 6-
fold enhancement).
14. Bhatnagar, D.; Durrington, P. N.; Chennon, K. M.; Prais,
H.; MacKness, M. I. Atherosclerosis 1993, 98, 25.
15. Foger, B.; Luef, G.; Ritsch, A. J. Mol. Med. 1995, 73, 369.
16. Kuivenhoven, J. A.; Jukema, J. W.; Zwinderman, A. H.;
Knijff, P.; McPherson, R.; Bruschke, A. V. G.; Lie, K. I.;
Kastelein, J. J. P. N. Engl. J. Med. 1998, 338, 86.
17. Okamoto, H.; Yonemori, F.; Wakitani, K.; Minowa, T.;
Maeda, K.; Shinkai, H. Nature 2000, 406, 203.
18. Grooth, G. J.; Kuivenhoven, J. A.; Stalenhoef, A. F. H.;
Graaf, J.; Zwinderman, A. H.; Posma, J. L.; Tol, A.;
Kastelein, J. J. P. Circulation 2002, 105, 2159.
19. Shinkai, H.; Maeda, K.; Yamasaki, T.; Okamoto, H.;
Uchida, I. J. Med. Chem. 2000, 43, 3566.
20. Commercially unavailable 2-nitrophenols, such as 3,5-
difluoro-2-nitrophenol and 4,5-dichloro-2-nitrophenol,
were prepared by the method reported in the following
literature; Ouertani, M.; Girard, P.; Kagan, H. B. Tetra-
hedron Lett. 1982, 23, 4315.
21. The acyl chlorides were prepared by the method reported
in Ref. 19.
22. (a) Kwart, H.; Evans, E. R. J. Org. Chem. 1966, 31, 410;
(b) Newman, M. S.; Karnes, H. A. J. Org. Chem. 1966, 31,
3980.
In summary, studies on the relationships between the
structure of the benzene moiety of S-(2-(acyl-
amino)phenyl) 2,2-dimethylpropanethioates and CETP
inhibitory activity revealed that the effect of each sub-
stituent depended on its nature and position. Although
electron-donating groups were not effective, substitution
of electron-withdrawing groups at the 4- or 5-positions
caused an increase in activity. Moreover, the introduc-
tion of chloro groups at both positions induced syner-
gistic enhancement of inhibitory activity, and the most
potent 4,5-dichloro compound 18 achieved 50% inhibi-
tion of CETP activity in human plasma at a concen-