Discovery of substituted biphenyl oxazolidinone inhibitors of cholesteryl ester transfer protein

Article abstract of DOI:10.1021/ml100309n

Recently, there has been a strong interest in the ability to increase levels of high density lipoprotein-cholesterol (HDL-C). This interest stems from the hypothesis that such an elevation in HDL-C will decrease the likelihood of cardiovascular disease. I

Full text of DOI:10.1021/ml100309n

LETTER
pubs.acs.org/acsmedchemlett
Discovery of Substituted Biphenyl Oxazolidinone Inhibitors of
Cholesteryl Ester Transfer Protein
Christopher F. Thompson,*,† Amjad Ali,† Nazia Quraishi,† Zhijian Lu,† Milton L. Hammond,†
Peter J. Sinclair,† Matt S. Anderson,‡ Suzanne S. Eveland,‡ Qiu Guo,‡ Sheryl A. Hyland,‡ Denise P. Milot,‡
Carl P. Sparrow,‡ and Samuel D. Wright‡
Departments of †Medicinal Chemistry and ‡Cardiovascular Diseases, Merck Research Laboratories, Rahway, New Jersey 07065,
United States
S Supporting Information
b
ABSTRACT: Recently, there has been a strong interest in the ability to increase levels of high density
lipoprotein-cholesterol (HDL-C). This interest stems from the hypothesis that such an elevation in
HDL-C will decrease the likelihood of cardiovascular disease. Inhibition of cholesteryl ester transfer
protein (CETP) has been shown to elevate HDL-C levels in human subjects. This letter describes the
discovery of a novel and potent (<100 nM IC50 for the inhibition of CE transfer) CETP inhibitor
scaffold containing an oxazolidinone core.
KEYWORDS: Cholesteryl ester transfer protein, CETP, cardiovascular disease, high density lipopro-
tein, HDL, oxazolidinone
espite advances in treatment, cardiovascular disease (CVD)
remains a leading cause of death in developed countries.
D
Two key risk factors for CVD are low-density lipoprotein-
cholesterol (LDL-C) and high-density lipoprotein-cholesterol
(HDL-C). Lower levels of LDL-C correlate with a decrease in
deaths due to CVD. The opposite is true of HDL-C; CVD
decreases at higher levels of HDL-C.1À4 In recent decades, great
progress has been made in lowering LDL-C, particularly via
medicines such as statins and with lifestyle changes. While much
success has been achieved in decreasing LDL-C, increasing
HDL-C still presents a medical challenge.1À4 Even after 50 years
of use, niacin is still the leading therapy for raising HDL-C. How-
ever, the increase in HDL-C seen with niacin is modest (∼20%),
and side effects/toxicity prohibit some patients from taking this
drug.1À6 Thus, alternative avenues for raising HDL-C are being
investigated.
One target for raising HDL-C that has recently received great
attention in the scientific community is cholesteryl ester transfer
protein (CETP).1À4,7À10 CETP exchanges cholesteryl ester (CE)
and triglycerides between various lipoprotein particles. It has been
shown that inhibition of CETP dramatically increases HDL-C, both
in animal models and in the clinic.11,12 Unfortunately, the first
CETP inhibitor to reach phase III trials, torcetrapib (Figure 1),
failed to achieve the desired outcome of a reduction in coronary
events in patients receiving treatment.13 In fact, treatment with
torcetrapib increased the risk of death from both cardiovascular and
noncardiovascular causes.13 The reasons for this failure have been
the subject of intense debate, and further investigation of CETP
inhibitors is necessary.14À17 The CETP inhibitor anacetrapib
(Figure 1) has been shown to differ from torcetrapib in its off-target
Figure 1. Structures of torcetrapib, anacetrapib, and lead compound 1.
Received: January 4, 2011
Accepted: March 24, 2011
Published: March 24, 2011
r
2011 American Chemical Society
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dx.doi.org/10.1021/ml100309n ACS Med. Chem. Lett. 2011, 2, 424–427
|

ACS Medicinal Chemistry Letters
LETTER
Scheme 1. Retrosynthetic Analysis of Target Compound 2
Scheme 2. Regioselective Epoxide Openinga
a Reagents and conditions: (i) i-PrOH, reflux 12 h, 72% yield of 6.
Scheme 3. Synthesis of Compound 2a
a Reagents and conditions: (i) CH2Cl2, room temperature, 5 h, 25% yield. (ii) LiAlH4, Et2O, room temperature, 1 h, 52% yield. (iii) Phosgene, (i-
Pr)2EtN, CH2Cl2, room temperature, 10 min, 55% yield.
profile and is currently being studied in clinical trials.18,19 This letter
describes the discovery of a novel CETP inhibitor scaffold, closely
related to anacetrapib, which contains an oxazolidinone core.
In the investigation of CETP inhibitors conducted at Merck, lead
compound 1 (Figure 1) had emerged as a potent inhibitor of CE
transfer by CETP.20,21 It was hypothesized that the potency and/or
stability of 1 could be improved by constraining the acyclic carbamate
into an oxazolidinone ring. Retrosynthetically, it was anticipated that
the target molecule, 2, could be obtained by opening of epoxide 4
with amine 3 followed by closure of the resulting product to the
oxazolidinone (Scheme 1). Although a mixture of attack at the
terminal carbon and the benzylic position of epoxide 4 was expected,
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ACS Medicinal Chemistry Letters
LETTER
Table 1. IC50 Values for Inhibition of CE Transfera
Scheme 4. Synthesis of Compound 9a
a Reagents and conditions: (i) Triphosgene, (i-Pr)2EtN, CH2Cl2, 0 °C, 1
h, 98% yield.
Surprisingly, racemic 9 was shown to be a potent inhibitor of CETP
(Table 1). Separation of 9 into its two enantiomers (9A and 9B)
demonstrated that all of the activity resided in a single enantiomer
(9B).
To determine the stereochemistry of compound 9B, related
compounds 10 and 11 were synthesized following the route used
in the synthesis of 9 (Schemes 2 and 4) and starting by opening the
known, commercially available, S- and R-styrene oxides with amine
3.24 As in the case of compound 9, only one enantiomer (compound
11, R) was a potent inhibitor of CETP, and this observation forms the
basis of the stereochemical assignment of 9A and 9B.25 Although
compound 9B is only a slightly more potent inhibitor of CETP than
original lead compound 1, it is interesting to note that 11 is much
more potent than the comparable acyclic analogue, compound 12. It
is also worth mentioning that the addition of a ring constraint did not
improve phamacokinetics. Compound 1 has a clearance of 12.8 mL/
min/kg in mice, while the clearance of 9B is 31.6 mL/mg/kg.
Volumes of distribution (3.3 L/kg for 1 and 3.4 L/kg for 9B) and
oral bioavailability (5% for 1and 4% for 9B) in mice are similar for the
two compounds.
In summary, a new class of CETP inhibitors containing an
oxazolidinone core has been discovered. Surprisingly, the oxazoli-
dinone does not have the substitution pattern anticipated from an
earlier lead compound. Rather, it is an alternative regioisomer
discovered through a serendipitous, regioselective epoxide opening.
The novel molecule, 9B, is a potent inhibitor of CETP containing a
single chiral center. Further developments from this program
detailing the evolution of 9B into clinical candidate anacetrapib,
which also contains an oxazolidinone core, will be forthcoming.
a IC50 values were determined using a standard bioassay described in ref
22. The IC50 value for torcetrapib was been determined by this method
in ref 18 and was reported to be 13 nM. b Average of three or more 10
point titrations. c Result of a single 10 point titration. d Average of two 10
point titrations. e Inactive indicates <50% inhibition of CETP at a
concentration of 100 μM.
’ ASSOCIATED CONTENT
S
Supporting Information. Synthetic procedures and
b
spectral data for the preparation of intermediates 3À8 and final
compounds 2, 9, 11, and 12. This material is available free of
charge via the Internet at http://pubs.acs.org.
it was surprising to observe substitution exclusively at the less hind-
ered carbon, leading to undesired amino-alcohol 6 (Scheme 2). With
this first approach to compound 2 thwarted, an alternative synthesis
was undertaken (Scheme 3). Alkylation of amine 3 with bromide 7
led to intermediate 8, which was reduced to desired amino alcohol 5
with LiAlH4. Cyclization led to the racemic oxazolidinone 2. Dis-
appointingly, this constrained version of lead compound 1 was a very
weak (14 μM) inhibitor of CETP (Table 1).22
’ AUTHOR INFORMATION
Corresponding Author
*Tel: 617-992-2497. E-mail: christopher_thompson@merck.com.
In an effort to ensure the thorough investigation of constrained
analogues, amino alcohol 6 was also cyclized to the corresponding
oxazolidinone, although it was not anticipated that this regioisomer
would exhibit potent CETP inhibition.23 In the event, cyclization of 6
to 9 proceeded in good yield using triphosgene (Scheme 4).
Author Contributions
Compounds were synthesized by C.F.T. and N.Q. with guidance
and helpful suggestions from A.A. and Z.L. Biological studies
were done by S.S.E., Q.G., S.A.H., and D.P.M. Program guidance
was provided by M.L.H., P.J.S., M.S.A., C.P.S., and S.D.W.
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ACS Medicinal Chemistry Letters
LETTER
’ ACKNOWLEDGMENT
(19) Cannon, C. P.; Shah, S.; Dansky, H. M.; Davidson, M.; Brinton,
E. A.; Gotto, A. M.; Stephanavage, M.; Liu, S. X.; Gibbons, P.; Ashraf,
T. B.; Zafarino, J.; Mitchel, Y.; Barter, P. Safety of anacetrapib in patients
with or at high risk for coronary heart disease. N. Engl. J. Med. 2010,
363, 2046.
We acknowledge Cameron Smith for careful reading of this
manuscript and suggestions.
(20) Lu, Z.; Napolitano, J. B.; Theberge, A.; Ali, A.; Hammond,
M. L.; Tan, E.; Tong, X.; Xu, S. X.; Latham, M. J.; Peterson, L. B.;
Anderson, M. S.; Eveland, S. S.; Guo, Q.; Hyland, S. A.; Milot, D. P.;
Chen, Y.; Sparrow, C. P.; Wright, S. D.; Sinclair, P. J. Design of a novel
class of biphenyl CETP inhibitors. Bioorg. Med. Chem. Lett. 2010,
20, 7469.
(21) For a good overview of other approaches to CETP inhibitors,
see ref 8 and the following review article:Hunt, J. A.; Lu, Z. Cholesteryl
ester transfer protein (CETP) inhibitors. Curr. Top. Med. Chem. 2009,
9, 419.
(22) The ability of compounds to inhibit transfer of CE by CETP
(IC50 values in Table 1) was determined using a fluorescence transfer
assay that has been described in detail. See the following:Eveland, S. S.;
Milot, D. P.; Guo, Q.; Chen, Y.; Hyland, S. A.; Peterson, L. B.; Jezequel-
Sur, S.; O'Donnell, G. T.; Zuck, P. D.; Ferrer, M.; Strulovici, B.; Wagner,
J. A.; Tanaka, W. K.; Hilliard, D. A.; Laterza, O.; Wright, S. D.; Sparrow,
C. P.; Anderson, M. S. A high-precision fluorogenic cholestery ester
transfer protein assay compatible with animal serum and 3456-well assay
technology. Anal. Biochem. 2007, 368, 239.
(23) Amino alcohol 6 is a weak inhibitor of CE transfer (IC50 value
for the inhibition of CE transfer = 5.2 μM). Likewise, compound 5 has
little activity (IC50 value for the inhibition of CE transfer = 13.7 μM).
(24) In the cases of R- and S-styrene oxide, attack at both the
benzylic and the terminal positions of the epoxide was observed, as had
been originally anticipated for 4. Attack at the benzylic carbon resulted in
a less polar product (Rf = 0.32 in 25% ethyl acetate/hexanes) that was
readily separated using silica gel chromatography from the desired, more
polar product resulting from attack at the terminal carbon (Rf = 0.11 in
25% ethyl acetate/hexanes)
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