4-CF3-ezetimibe analogs: Design, synthesis, and biological evaluation of cholesterol absorption inhibitions

Article abstract of DOI:10.1016/j.tetlet.2013.08.027

On the purpose of looking for better cholesterol absorption inhibitors, several trifluoromethyl substituted ezetimibe analogs 1a-d were designed and synthesized. The key steps in the synthesis of these optically pure trans-4-CF₃-β-lactams inclu

Full text of DOI:10.1016/j.tetlet.2013.08.027

Tetrahedron Letters 54 (2013) 5541–5543
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
4-CF3-ezetimibe analogs: design, synthesis, and biological evaluation
of cholesterol absorption inhibitions
Yingle Liu a, Jun-Ling Chen a, Gai-Hong Wang c, Peng Sun c, Heyao Huang c, Feng-Ling Qing a,b,
⇑
a College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, 2999 North Renmin Lu, Shanghai 201620, China
b Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Science, 345 Lingling Lu, Shanghai 200032, China
c Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zucongzhi Lu, Shanghai 201203, China
a r t i c l e i n f o
a b s t r a c t
Article history:
On the purpose of looking for better cholesterol absorption inhibitors, several trifluoromethyl substituted
ezetimibe analogs 1a–d were designed and synthesized. The key steps in the synthesis of these optically
pure trans-4-CF3-b-lactams include chiral auxiliary induced asymmetric hydrogenation and substrate
controlled stereoselective alkylation. The inhibitory activities of these target compounds were evaluated
on the cholesterol absorption in Caco-2 cells. The result showed that the inhibitory activity of compound
1a was comparable to ezetimibe.
Received 13 June 2013
Revised 19 July 2013
Accepted 6 August 2013
Available online 13 August 2013
Keywords:
Ezetimibe
Ó 2013 Elsevier Ltd. All rights reserved.
Cholesterol
b-Lactam
Trifluoromethyl
Asymmetric hydrogention
Ezetimibe is a strong cholesterol absorption inhibitor that
reduces plasma low-density lipoprotein fraction (LDL-C). It was
approved as the first drug for the treatment of high cholesterol
in 2002.1 Last year, annual worldwide sales for ZETIA (ezetimibe)
were $2.57 billion, which puts ezetimibe high on the list of
valuable drugs. So the development of new synthetic methods
for ezetimibe has become interesting targets for many academic
and industrial laboratories.2 At the same time, a lot of research
interests have been put in the synthesis of new ezetimibe
derivatives,3 as the inhibition mechanism of ezetimibe was not
fully elucidated at a molecular level.4 The structure–activity
relationship (SAR) studies of ezetimibe analogs are still necessary
to develop new cholesterol absorption inhibitors, which might
ultimately be useful in preventing cardiovascular disease.5
It is well known that the incorporation of fluorine atom and/or
fluorine-containing groups into an organic molecule often changes
the chemical, physical, and biological properties of the parent com-
pound.6 Introduction of fluorine atom and/or fluorine-containing
groups into biologically active molecules has become an important
strategy in the design of pharmaceuticals and agrochemicals.7 For
example, the p-fluorine substitution in the N1-phenyl and C3-pen-
dent phenyl rings of ezetimibe was found to block the undesired
metabolic transformations,1b because of the higher strength of
the C–F bond compared to C–H bond. In continuity of our research
interest in fluorine-containing biologically active molecules,8 we
designed a series of new 4-CF3-ezetimibe analogs 1a–d (Scheme
1), mainly considering from two aspects. First, the C4-position of
ezetimibe is the most frequently modified position, and some
successful examples have been reported.3a,9 Secondly, the trifluo-
romethyl group (CF3) enjoys a privileged role in the realm of
medicinal chemistry because its incorporation into small
molecules often enhances the efficacy by promoting electrostatic
interactions with targets, improving cellular membrane permeabil-
ity, and increasing robustness toward oxidative metabolism of the
drug. It was also suggested in the literature that introducing the
trifluoromethyl group on the b-lactam ring would have a good
effect on antibacterial activity.10 We hope that our target mole-
cules 1 will contribute to the SAR studies of ezetimibe analogs.
What is more, the synthesis of 1 is the first example for preparing
optically pure 4-trifluormethyl substituted trans-b-lactams, which
R2
OH
CF3
OH
CF3
N
R1
O
N
F
O
1a: R1 = R3 = F, R2 = OH;
R3
1b: R1 = F, R2 = OH, R3 = OMe;
1c: R1 = H, R2 = H, R3 = F;
1d: R1 = H, R2 = H, R3 = OMe.
F
Ezetimibe
⇑
Corresponding author. Tel.: +86 21 54925187; fax: +86 21 64166128.
E-mail address: flq@mail.sioc.ac.cn (F.-L. Qing).
Scheme 1. Design of target molecules 1a–d.
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.08.027

5542
Y. Liu et al. / Tetrahedron Letters 54 (2013) 5541–5543
R
O
CF3
Ar
CF3
Ar
Ar
H '
OH
1
H1'
NH
O
O
H4
CF3
N
N
H
O
F3C
R*
R*
1
A
B
N
F
O
Ar
Cl
Ar
N
O
NH
F
1a
F3C
F3C
OH
F3C
TFA
D
C
Figure 1. NOE correlation of compound 1a.
Scheme 2. Retrosynthetic analysis of compound 1.
Table 1
Inhibitory effect on the cholesterol absorption in Caco-2 cells
Entry
Compound
Inhibitory rate of 3H cholesterol absorption (%)
25 50 100
might be important precursors to other chiral fluorinated
compounds.11
lM
l
M
lM
The retrosynthestic analysis of target molecules 1 is shown in
1
2
3
4
5
Ezetimibe
15.6 1.6
18.6 0.7
11.6 1.5
23.0 4.0
10.8 0.6
46.1 1.8
30.5 2.8
30.0 0.0
23.5 0.5
18.3 1.1
92.9 0.2
72.6 1.0
45.6 1.1
31.4 3.9
28.3 0.2
1a
1b
1c
1d
Scheme 2. Compounds
1 can be prepared by alkylation of
4-trifluormethylated b-lactams A. Although construction of chiral
4-trifluormethylated b-lactams have been reported by several
groups,11b,d,12 none of them were interested in N-aryl derivatives.
Herein we proposed a new synthetic route to intermediate A.
The key step is auxiliary induced asymmetric hydrogenation of
in compounds 5 was confirmed to be (S)-configuration, just the
same as our desired configuration. With these chiral -trifluoro-
enamine C to chiral a-trifluoromethyl amine B, which can be easily
a
converted to A by some transformations. Enamine C can be
prepared from a simple staring material trifluoroacetic acid (TFA)
via the intermediate D according to the reported work.13,14
methyl amines 5 in hand, the preparation of optically active
4-trifluormethylated b-lactams 7 was operated in general steps.
Removing the chiral auxiliary of compounds 5 by treatment with
hydrogen peroxide and lithium hydroxide, followed by esterifica-
tion, gave chiral b-trifluoromethyl-b-amino esters 6 in excellent
yields. The b-lactams 7 were obtained by intramolecular cycliza-
tion of esters 6 using methyl magnesium bromide as the base.12b
The final step was to assemble b-lactams 7 with alkyl chains.
Coupling of b-lactams 7a and 7b with alkyl iodides 8a3h under
the condition of LiHMDS/HMPA in THF gave the coupling products,
which were then deprotected to afford the final products 1a and
1b, respectively. The other two target molecules 1c and 1d were
obtained by coupling of b-lactams 7a and 7b with alkyl iodides
8b15 under the same coupling conditions. It was noteworthy that
all the coupling reactions exclusively produced the trans-isomers.
This trans/cis stereoselectivity is consistent with previous similar
alkylation reactions of b-lactams.16 The absolute configuration of
final products 1 was further confirmed by 2D NMR NOESY experi-
ment. As show in Figure 1, correlation between H4 and H01 was
clearly observed in compounds 1a.
The synthesis of target molecules 1 began with TFA, which
reacted with 4-substituted anilines in carbon tetrachloride in the
presence of triphenylphosphine and triethylamine to give N-aryl
trifluoroacetimidoyl chlorides 2, according to the Uneyama’s
method13 (Scheme 3). Then, treatment of commercially available
chiral amide 3 with lithium diisopropylamide (LDA, 2.0 equiv) at
ꢀ78 °C in THF generated the corresponding lithium enolate, which
reacted with imidoyl chlorides 2 to provide the enamines 4 in good
yields and high Z/E selectivities.14 After that, we turned our atten-
tion to the reduction of enamines 4, but no reduction product was
obtained under the reported reaction condition of ZnI2/NaBH4.14 To
our delight, Pd/C catalyzed hydrogenation of enamines 4a and 4b
gave the desired products 5a and 5b in high yields and good diaste-
reoselectives (5a: 87% yield, dr = 91:9; 5b: 94% yield, dr = 87:13),
respectively. What was more, enantiomerically pure compounds
5a and 5b (>99:1 dr) can be obtained in moderate yields via recrys-
tallization of the crude products. From the X-ray crystallographic
analysis of compound 5b (see ESI), the newly formed stereocenter
O
O
R
R
R
R
N
O
O
NH
O
Bn
O
NH
O
O
N
Pd/C, H2,
MeOH
H2N
Bn
3
F3C
N
O
F3C
N
F3C
TFA
OH
F3C
Cl
LDA, THF
PPh3, NEt3,
CCl4
Bn
2a
O
: R = F, 63%;
4a
: R = F, 82%, Z/E = 31:1;
5a
: R = F, 70%, >99:1 dr;
2b: R = OMe, 91%
4b
: R = OMe, 63%, Z/E = 27:1
5b: R = OMe, 73%, >99:1 dr
OH
OTBS
CF3
1. LiHMDS,
HMPA,
I
THF;
R
N
O
F
R
2. HF/pyridine,
+
+
F
THF
8a
8b
O
1a: R = F, 46%;
MeMgBr,
1. LiOH, H2O2,
THF/H2O;
NH
O
N
1b
: R = OMe, 29%
R
Et2O
2. SOCl2,
CF3
F3C
6a: R = F, 95%;
OMe
F3C
: R = F, 62%;
MeOH
LiHMDS,
7a
I
HMPA, THF
N
O
7b: R = OMe, 80%
6b: R = OMe, 93%
1c: R = F, 32%;
1d: R = OMe, 32%
R
Scheme 3. Synthesis of target molecules 1a–d.

Y. Liu et al. / Tetrahedron Letters 54 (2013) 5541–5543
5543
T. J. Am. Chem. Soc. 2010, 132, 12150–12154; (h) Limanto, J.; Krska, S. W.;
Dorner, B. T.; Vazquez, E.; Yoshikawa, N.; Tan, L. Org. Lett. 2010, 12, 512–515; (i)
Delpiccolo, C. M. L.; Testero, S. A.; Leyes, F. N.; Boggián, D. B.; Camacho, C. M.;
Mata, E. G. Tetrahedron 2012, 68, 10780–10786.
Finally, the new trifluoromethylated analogs 1a–d were sub-
jected to cholesterol absorption experiment in Caco-2 cells, with
ezetimibe as the reference. The results are summarized in Table
1. The inhibitory activity of compound 1a was close to ezetimibe
(entries 1 and 2). This result showed that the C4-aryl group of eze-
timibe could be replaced by trifluoromethyl group. However, the
changes of other position groups of ezetimibe resulted in lower
biological activities (entries 3–5).
In conclusion, several trifluoromethyl substituted ezetimibe
analogs, optically pure trans-4-CF3-b-lactams 1a–d, were synthe-
sized in convenient synthetic methods. The inhibitory activities
of these analogs were evaluated and compound 1a showed a good
inhibitory activity.
4. Altmann, S. W.; Davis, H. R.; Zhu, L. J.; Yao, X. R.; Hoos, L. M.; Tetzloff, G.; Iyer, S.
P. N.; Maguire, M.; Golovko, A.; Zeng, M.; Wang, L. Q.; Murgolo, N.; Graziano, M.
P. Science 2004, 303, 1201–1204.
5. (a) Sudhop, T.; von Bergmann, K. Drugs 2002, 62, 2333–2347; (b) Bruckert, E.
Cardiology 2002, 97, 59–66.
6. For recent books, see: (a) Kirsch, P. Modern Fluoroorganic Chemistry; Wiley-
VCH: Weinheim, 2004; (b) Chambers, R. D. Fluorine in Organic Chemistry;
Blackwell: Oxford, 2004; (c) Uneyama, K. Organofluorine Chemistry; Blackwell:
Oxford, 2006; (d) Bégué, J.-P.; Bonnet-Delpon, D. Bioorganic and Medicinal
Chemistry of Fluorine; Wiley: New York, 2008; (e) Ojima, I. Fluorine in Medicinal
Chemistry and Chemical Biology; Blackwell: Oxford, 2009.
7. For recent reviews, see: (a) Müller, K.; Faeh, C.; Diederich, F. Science 2007, 317,
1881–1886; (b) Purser, S.; Moore, P. R.; Swallow, S.; Gouverneur, V. Chem. Soc.
Rev. 2008, 37, 320–330; (c) Hagmann, W. K. J. Med. Chem. 2008, 51, 4359–4369.
8. For recent examples, see: (a) Qiu, X.-L.; Qing, F.-L. Eur. J. Org. Chem. 2011, 3261–
3278; (b) Yang, Y.; Zheng, F.; Bols, M.; Marinescu, L. G.; Qing, F.-L. J. Fluorine
Chem. 2011, 132, 838–845; (c) Chen, J.-L.; Zheng, F.; Huang, Y.; Qing, F.-L. J. Org.
Chem. 2011, 76, 6525–6533; (d) Qing, F.-L.; Zheng, F. Synlett 2011, 1052–1072;
(e) Yang, Y.; Zheng, F.; Qing, F.-L. Tetrahedron 2011, 67, 3388–3394; (f) Chen, Z.-
H.; Wang, B.-L.; Kale, A. J.; Moore, B. S.; Wang, R.-W.; Qing, F.-L. J. Fluorine Chem.
2012, 136, 12–19; (g) Yang, Y.; Jiang, X.; Qing, F.-L. J. Org. Chem. 2012, 77, 7538–
7547; (h) Chen, Z.-H.; Wang, R.-W.; Qing, F.-L. Tetrahedron Lett. 2012, 53, 2171–
2176.
9. (a) Vaccaro, W. D.; Davis, H. R. Bioorg. Med. Chem. Lett. 1998, 8, 313–318; (b)
van Heek, M.; Farley, C.; Compton, D. S.; Hoos, L.; Alton, K. B.; Sybertz, E. J.;
Davis, H. R. Br. J. Pharmacol. 2000, 129, 1748–1754; (c) Kværnø, L.; Ritter, T.;
Werder, M.; Hauser, H.; Carreira, E. M. Angew. Chem., Int. Ed. 2004, 43, 4653–
4656.
10. (a) Bevilacqua, P. F.; Keith, D. D.; Roberts, J. L. J. Org. Chem. 1984, 49, 1430–
1434; (b) Guanti, G.; Banfi, L.; Narisano, E.; Scolastico, C.; Bosone, E. Synthesis
1985, 609–611.
11. For recent examples, see: (a) Battaglia, A.; Bernacki, R. J.; Bertucci, C.;
Bombardelli, E.; Cimitan, S.; Ferlini, C.; Fontana, G.; Guerrini, A.; Riva, A. J.
Med. Chem. 2003, 46, 4822–4825; (b) Jiang, J.; Shan, H.; DeVita, R. J. Org. Lett.
2003, 5, 4101–4103; (c) Kuznetsova, L.; Ungureanu, I. M.; Pepe, A.; Zanardi, I.;
Wu, X.; Ojima, I. J. Fluorine Chem. 2004, 125, 487–500; (d) Huguenot, F.;
Brigaud, T. J. Org. Chem. 2006, 71, 2159–2162; (e) Kuznetsova, L. V.; Pepe, A.;
Ungureanu, I. M.; Pera, P.; Bernacki, R. J.; Ojima, I. J. Fluorine Chem. 2008, 129,
817–828; (f) Petrik, V.; Röschenthaler, G.-V.; Cahard, D. Tetrahedron 2011, 67,
3254–3259.
12. (a) Davoli, P.; Forni, A.; Franciosi, C.; Moretti, I.; Prati, F. Tetrahedron:
Asymmetry 1999, 10, 2361–2371; (b) Michaut, V.; Metz, F.; Paris, J.-M.;
Plaquevent, J.-C. J. Fluorine Chem. 2007, 128, 889–895.
13. Tamura, K.; Mizukami, H.; Maeda, K.; Watanabe, H.; Uneyama, K. J. Org. Chem.
1993, 58, 32–36.
Acknowledgments
We thank the National Natural Science Foundation of China
(21072028, 21272036) and the National Basic Research Program
of China (2012CB21600) for funding this work.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2013.08.
027.
References and notes
1. (a) Burnett, D. A.; Caplen, M. A.; Davis, H. R., Jr.; Burrier, R. E.; Clader, J. W. J.
Med. Chem. 1994, 37, 1733–1736; (b) Rosenblum, S. B.; Huynh, T.; Afonso, A.;
Davis, H. R., Jr.; Yumibe, N.; Clader, J. W.; Burnett, D. A. J. Med. Chem. 1998, 41,
973–980; (c) Clader, J. W. J. Med. Chem. 2004, 47, 1–9.
2. For recent examples, see: (a) Bertrand, B.; Durassier, S.; Frein, S.; Burgos, A.
Tetrahedron Lett. 2007, 48, 2123–2125; (b) Sasikala, C. H. V. A.; Padi, P. R.;
Sunkara, V.; Ramayya, P.; Dubey, P. K.; Uppala, V. B. R.; Praveen, C. Org. Process
Res. Dev. 2009, 13, 907–910; (c) Mothana, S.; Grassot, J.-M.; Hall, D. G. Angew.
Chem., Int. Ed. 2010, 49, 2883–2887; (d) Kyslíková, E.; Babiak, P.; Marešová, H.;
ˇ
Palyzová, A.; Hájícek, J.; Kyslík, P. J. Mol. Catal. B: Enzym. 2010, 67, 266–270; (e)
ˇ
ˇ
ˇ
Sova, M.; Mravljak, J.; Kovac, A.; Pecar, S.; Casar, Z.; Gobec, S. Synthesis 2010,
3433–3438; (f) Michalak, M.; Stodulski, M.; Stecko, S.; Mames, A.; Panfil, I.;
Soluch, M.; Furman, B.; Chmielewski, M. J. Org. Chem. 2011, 76, 6931–6936; (g)
Wang, X.; Meng, F.; Wang, Y.; Han, Z.; Chen, Y.-J.; Liu, L.; Wang, Z.; Ding, K.
Angew. Chem., Int. Ed. 2012, 51, 9276–9282.
14. Fustero, S.; Pina, B.; Salavert, E.; Navarro, A.; Arellano, M. C. R.; Fuentes, A. S. J.
Org. Chem. 2002, 67, 4667–4679.
15. Smith, S. M.; Takacs, J. M. J. Am. Chem. Soc. 2010, 132, 1740–1741.
16. For recent examples, see: (a) O’Dowd, H.; Lewis, J. G.; Trias, J.; Asano, R.; Blais,
J.; Lopez, S. L.; Park, C. K.; Wu, C.; Wang, W.; Gordeev, M. F. Bioorg. Med. Chem.
Lett. 2008, 18, 2645–2648; (b) Liang, G.-B.; Qian, X.; Biftu, T.; Singh, S.; Gao, Y.-
D.; Scapin, G.; Patel, S.; Leiting, B.; Patel, R.; Wu, J.; Zhang, X.; Thornberry, N. A.;
Weber, A. E. Bioorg. Med. Chem. Lett. 2008, 18, 3706–3710; (c) Meiries, S.;
Marquez, R. J. Org. Chem. 2008, 73, 5015–5021; Brain, C. T.; Chen, A.; Nelson, A.;
Tanikkul, N.; Thomas, E. J. Tetrahedron 2010, 66, 6613–6625.
3. For recent examples, see: (a) Kværnø, L.; Werder, M.; Hauser, H.; Carreira, E. M.
J. Med. Chem. 2005, 48, 6035–6053; (b) Kværnø, L.; Werder, M.; Hauser, H.;
Carreira, E. M. Org. Lett. 2005, 7, 1145–1148; (c) Figueiredo, R. M.; Fröhlich, R.;
Christmann, M. J. Org. Chem. 2006, 71, 4147–4154; (d) Xu, X.; Fu, R.; Chen, J.;
Chen, S.; Bai, X. Bioorg. Med. Chem. Lett. 2007, 17, 101–104; (e) Tiwari, D. K.;
Shaikh, A. Y.; Pavase, L. S.; Gumaste, V. K.; Deshmukh, A. R. A. S. Tetrahedron
2007, 63, 2524–2534; (f) Wang, Y.; Zhang, H.; Huang, W.; Kong, J.; Zhou, J.;
Zhang, B. Eur. J. Med. Chem. 2009, 44, 1638–1643; (g) Tang, P.; Furuya, T.; Ritter,