Novel orally active morpholine N-arylsulfonamides γ-secretase inhibitors with low CYP 3A4 liability

Article abstract of DOI:10.1016/j.bmcl.2009.09.055

A new class of 2,6-disubstituted morpholine N-arylsulfonamide γ-secretase inhibitors was designed based on the introduction of a morpholine core in lieu or piperidine in our lead series. This resulted in compounds with improved CYP 3A4 profiles. Several a

Full text of DOI:10.1016/j.bmcl.2009.09.055

Bioorganic & Medicinal Chemistry Letters 19 (2009) 6032–6037
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Novel orally active morpholine N-arylsulfonamides
c-secretase inhibitors
with low CYP 3A4 liability
a
a
a
a
Hubert Josien a, , Thomas Bara , Murali Rajagopalan , John W. Clader , William J. Greenlee ,
Leonard Favreau c, Lynn A. Hyde b, Amin A. Nomeir c, Eric M. Parker b, Lixin Song b,
Lili Zhang b, Qi Zhang b
*
a Department of CV and CNS Medicinal Chemistry, Schering-Plough Research Institute, 2015 Galloping Hill Road, Kenilworth, NJ 07033, USA
b Department of Neurobiology, Schering-Plough Research Institute, 2015 Galloping Hill Road, Kenilworth, NJ 07033, USA
c Department of Drug Safety and Metabolism, Schering-Plough Research Institute, 2015 Galloping Hill Road, Kenilworth, NJ 07033, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A new class of 2,6-disubstituted morpholine N-arylsulfonamide
c-secretase inhibitors was designed
Received 5 August 2009
Accepted 14 September 2009
Available online 19 September 2009
based on the introduction of a morpholine core in lieu or piperidine in our lead series. This resulted in
compounds with improved CYP 3A4 profiles. Several analogs that were active at lowering Ab levels in
Tg CRND8 mice upon oral administration were identified.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Alzheimer’s disease
c
-Secretase
Inhibitor
CYP 3A4
Sulfonamide
Morpholine
Alzheimer’s disease (AD), a neurodegenerative disease that af-
While the initial series typified by compound 1a had potential
drug–drug interaction due to high CYP 3A4 liability,7 lowering
the molecular weight and crowding the basic amine led to com-
pounds (e.g., 2) that showed better CYP profiles while retaining
in vitro and in vivo Ab40 lowering capability (Fig. 1).10b
Further analysis however indicated that compound 2 has a rel-
atively short half-life in human hepatocytes due to metabolism
occurring at the ethyl side chain and potentially at the piperidine
core. Reengineering of the core especially at position 4 of the piper-
idine was therefore attempted and we pursued small molecule
morpholine analogs (I) while others explored potential metabo-
lites.10c One attractive feature of the morpholine core was its im-
pact on lipophilicity that was shown to be a contributing factor
to CYP 3A4 liability in our previous series.10b
fects mostly the elderly, remains at the top of the healthcare agen-
da due to its growing patient population, attached socioeconomic
costs, and the limited therapeutic options that are currently avail-
able.1 AD main histological features are the appearance of b-amy-
loid (Ab) plaques and tau tangles in the brain of patients.2 This has
led many research groups to concentrate on the secretases3 and
tau kinases4 believed to be responsible for their generation. Several
drug candidates have recently entered in the clinic,5 although
many other areas remain under investigation in light of the com-
plexity of the disease.6 Among the secretases,
c-secretase remains
an attractive target, due to the breadth of inhibitors and modula-
tors,7,8 that have been discovered so far and the fact that, despite
c
-secretase involvement in other regulatory pathways such as
Notch processing, early clinical results seem to indicate that a ther-
apeutic window can be attained across several classes of
compounds.9
We initially decided to introduce the morpholine core in the
higher molecular weight aryl piperidine series that contained the
worst CYP 3A4 offenders, to more clearly test the impact of such
modification. For ease of synthesis, the des-cyclopropyl carbamate
series was selected.10a Our initial synthetic scheme relied on the
Our previous investigations in the
c-secretase inhibitor field led
us to report several series of piperidine sulfonamides
c-secretase
inhibitors that were efficacious at lowering Ab levels in Tg CRND8
preparation of alcohol 4 from L-serine methyl ester, followed by
mice.7,10
condensation with a diazo ketone in the presence of indium(III) tri-
flate.11 Reduction followed by intramolecular Mitsunobu led to
intermediate 6 that was converted to the carbamate used previ-
ously reported methods (Scheme 1).10a To our delight, the resulting
compound 7 showed an improved CYP 3A4 profile and minimal
* Corresponding author. Tel.: +1 908 740 6557; fax: +1 908 25 2492.
E-mail address: hubert.josien@spcorp.com (H. Josien).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.09.055

H. Josien et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6032–6037
6033
OH
N
OH
N
F
O
N
O
N
N
S
N
S
R1 R2
O
O
O
O
O
O
F
2
Memb Aβ40 IC50 = 6.9 nM
Cell Aβ40 IC50 = 8.3 nM
CYP 3A4 = 2.2 uM
Cl
O
Cl
1a (R1, R2 = cyclopropyl)
Memb Aβ40 IC50 = 2.5 nM
Cell Aβ40 IC50 = 5.0 nM
CYP 3A4 = 0.06 uM
R2
O
N
R1
N
S
R3
1b (R1 = R2 = H)
Memb Aβ40 IC50 = 41 nM
Cell Aβ40 IC50 = 167 nM
CYP 3A4 < 0.3 uM
O
O
O
(I)
Cl
Figure 1. Compounds 1–2 and strategy for removing CYP 3A4 liability.
O
HO
F
O
O
O
a,b,c
OTBDPS
d
OTPDPS
HN
S
OH
HN
S
H2N
F
5
O
O
4
3
O
O
Cl
Cl
OH
O
N
O
N
F
F
OTPDPS
g,h,i
N
O
N
S
e,f
O
S
O
O
O
O
F
6
F
7
Memb Aβ40 IC50 = 76 nM
Cell Aβ40 IC50 = 95 nM
CYP 3A4 = 3.0 μM
Cl
Cl
Scheme 1. Reagents: (a) 4-ClPhSO2Cl, Et3N; (b) TBDPSCl, imidazole; (c) LAH; (d) 2-diazo-1-(3,5-difluoro-phenyl)-ethanone, In(OTf)3; (e) NaBH4; (f) PPh3, DEAD; (g) TBAF; (h)
p-NO2PhOC(O)Cl, pyridine; (i) 2-piperazin-1-yl-ethanol.
shift in cell versus membrane Ab40 assay as compared to parent
1b. Compound 7 also showed improved blood levels in rat follow-
ing oral administration at 10 mg/kg (AUC0–6h = 4908 h ng/mL vs
826 h ng/mL for 1b).
This result led us to refocus our efforts to the morpholine core.
Due to a modest yield obtained in the conversion of 4 to 5, an im-
proved synthesis amenable to cyclopropyl carbamates was envi-
sioned (Scheme 2). This methodology implied the condensation
We first assessed high and low molecular weight morpholine
analogs using standard carbamates identified in our earlier
work.10b Compounds were evaluated for their in vitro
c-secretase
inhibitory potency, CYP 3A4 liability and preliminary in vivo effi-
cacy in our transgenic pre-plaque Tg CRND8 mice model of AD (Ta-
ble 1). The standard 3,5-difluorophenyl was used at R1 in the high
molecular weight series while the cyclopropyl moiety was ex-
plored as a more metabolically stable but still potent alternative
to the labile ethyl from compound 2 at R1 for lower molecular
weight analogs.
As shown in the table, both series showed comparable and
modest CYP 3A4 liability. The 3,5-difluorophenyl series was
slightly favored in terms of in vitro potency as compared to the
cyclopropyl series, following a trend observed in the piperidine
series. However, the cyclopropyl series seemed to have a slight
advantage in vivo (compound 14 vs 13), a feature attributed to
the lower molecular weight. The later series was thus progressed
further.
of a Boc-L-Serine carboxylate derivative with a a-bromo or a-hy-
droxy ketone to generate 9.12 Stereoselective intramolecular
reductive amination then gave 10 that was opened and ring-closed
to the morpholine core 11 under Mitsunobu conditions. Elabora-
tion into ester 12 set the stage for the Kulinkovich reaction10b,13
and derivatization into the final carbamates (I). This methodology
allowed for the preparation of highly functionalized morpholine
sulfonamides analogs. An alternative to the Kulinkovich strategy
was also used involving reacting 12 with Tebbe’s reagent followed
by Simmons–Smith cyclopropanation and demethylation.14

6034
H. Josien et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6032–6037
R3
R2
O
O
O
N
HO
O
a,b
R1
c,d,e
OTBDPS
O
OTBDPS
O
R1
OH
R2
R3
BocHN
BocHN
S
O
O
8
Ar
10
9
R3
R3
R2
O
N
O
N
R2
f,g
h,i,j
OTBDPS
R1
R1
COOMe
S
S
O
O
O
O
Ar
Ar
11
12
R3
R2
R1
O
R4
k,l,m
O
N
R5
N
S
O
O
O
Ar
(I)
Scheme 2. Reagents: (a) TBDPSCl, imidazole; (b) R1C(O)C(R2)(R3)Br, KOH; or R1C(O)C(R2)(R3)OH, DCC; (c) TFA; (d) NaBH(OAc)3; (e) 4-ClPhSO2Cl, Et3N; (f) NaBH4; (g) PPh3,
DEAD; (h) TBAF; (i) RuCl3, NaIO4; (j) SOCl2, MeOH; (k) EtMgBr, Ti(OiPr)4; (l) p-NO2PhOC(O)Cl, pyridine; (m) NHR4R5.
Table 1
Membrane
c
-secretase inhibition, CYP 3A4 profile and preliminary in vivo profile for core morpholine analogs (I) (Ar = 4-ClPh)
O
R2
NR2R3 =
O
N
R1
N
S
R3
N
N
N
N
N
O
O
O
OH
OH
OH
Ar
A
B
C
(I)
NR2R3
R1
Memb Ab40 IC50 (nM)
CYP 3A4b
(lM)
Tg CRND8 mice Ab40 reductionc (%)
a
Compd
13
14
15
16
17
18
A
A
B
B
C
C
3,5-F2Ph
cPr
3,5-F2Ph
cPr
3,5-F2Ph
cPr
1.4
9.5
5.5
37
12
27
4.1
2.5
3.8
4.1
9.6
>30
À68
À78
À87
+21
a
Values are mean of two experiments.
Values determined after 30 min pre-incubation with compound.
Reduction in plasma Ab40 at 3 h time point, following 30 mg/kg sub-cutaneous dosing.
b
c
A variety of cyclopropyl analogs were evaluated for their pri-
of CYP 3A4 selectivity. As reported before, candidates devoid of ba-
sic amine functionality usually have much reduced rat PK levels
and this was certainly observed with compound 32. However, we
were pleased to observe that acid variants 29 and 30 showed
excellent CYP 3A4 profile and average to excellent rat AUCs. This
was unfortunately accompanied by a drop in brain penetration
and, as a consequence, the compounds were not progressed further
in CNRD8 mice.
Armed with this data, we further explored modification at the
morpholine core (Table 3). Introduction of an extra methyl resulted
in improved potency for both cis and trans series but CYP 3A4 lia-
bility resurfaced, probably related to the increased lipophilic envi-
ronment at the morpholine oxygen location. Rat blood levels also
dropped substantially. In another attempt at trimming the scaffold
at R1 to lower CYP 3A4 liability, trimethyl morpholines analogs
(e.g., 38, 39) were prepared but, while the gem-dimethyl substitu-
tion contributed in gaining potency, it was accompanied again by a
drop in CYP 3A4 selectivity and/or rat blood levels.
mary in vitro
c-secretase potency and CYP 3A4 liability, and rat
pharmacokinetic (PK) data were obtained following 10 mg/kg oral
administration when appropriate (Table 2). The best candidates
were evaluated in the Tg CRND8 mice after acute oral administra-
tion. Following our exploration of CYP 3A4 mitigating approaches
in the small molecule piperidine sulfonamides series,10b we direc-
ted our efforts towards candidates featuring hindered basic amines
or non-basic amines at the right-hand side.
The best results were obtained using previously reported
bridged piperazines.10b Compound 22 in particular showed good
potency, excellent CYP3 A4 profile, good blood levels in rat and it
greatly lowered plasma Ab40 in CRND8 mice. Other basic amines
variants in the series, for example, 19–21, also featured excellent
plasma Ab40 efficacies and good to excellent rat PK levels albeit
more modest CYP 3A4 profiles. Removing the basic amine led to
reduction in either rat PK level (amides 23, 24) or potency (25).
Moving the bridge away from the basic amine also resulted in loss

H. Josien et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6032–6037
6035
Table 2
In vitro and AUC data in rat for series (I)
O
R1
O
N
R2
N
S
O
O
O
(I)
Cl
NR1R2
Memb Ab40
IC50 (nM)
Cell Ab40
CYP 3A4b
(lM)
Rat AUC0–6h (h ng/mL)
Tg CRND8 mice
reduction in plasma Ab40 (30 mg/kg po, 3 h)
c
Compd
IC50 (nM)a
a
N
N
14
9.5
7.1
4.6
10
9.0
25
20
25
15
25
31
2.5
446
À78%d
OH
NH
N
19
20
21
22
23
24
25
26
27
28
29
2.2
3.2
3.4
20
4365
939
À90%
À88%
N
N
N
N
1099
1916
871
N
N
7.9
15
À93%
N
N
OH
>30
>30
16
O
N
N
N
8.9
41
567
O
S
N
N
N
O O
17
72
17
27
<0.3
0.5
1.0
>30
4662
2908
1276
2463e
NH
N
N
2.4
15
N
N
OH
N
24
COOH
30
31
32
33
N
N
30
14
20
49
>30
15
703e
35
COOH
41
31
CONH2
N
N
>30
11
11
OH
O
O
S
O
870
N
H
CF3
a
b
c
Values are mean of two experiments.
Values determined after 30 min pre-incubation with compound.
Measured over 0–6 h after 10 mg/kg oral dosing in rat.
Sub-cutaneous administration.
d
e
Brain concentration <10 ng/mL at 6 h.

6036
H. Josien et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6032–6037
Table 3
Impact of morpholine core modification
R3
O
R2
R1
R4
N
NR4R5
=
O
R5
N
S
N
N
O
N
N
O
O
OH
Ar
O
A
B
(I)
NR4R5
Memb Ab40 IC50 (nM)
CYP 3A4b
(lM)
Rat AUC0–6h (h ng/mL)
a
c
Compd
Core
O
N
34
35
36
37
38
39
A
B
A
B
A
B
1.5
5.4
0.9
4.0
1.1
4.6
<0.3
4.8
0.5
178
O
N
24
23
1372
6
O
N
<0.3
6.7
a
b
c
Values are mean of two experiments.
Values determined after 30 min pre-incubation with compound.
Measured over 0–6 h after 10 mg/kg oral dosing in rat.
Plasma Aβ40
Brain Aβ40
8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
4
0
Vehicle
3
10
30
100
Vehicle
3
10
30
100
Figure 2. Reduction in Ab40 production in CRND8 mice following 5 days oral administration with compound 22.
Our best compound 22 was dosed orally once a day in Tg CRND8
Acknowledgments
mice at various doses ranging from 3 to 100 mg/kg and over a per-
iod of 5 days. Plasma and brain Ab40 levels were collected at the
end of the experiment (Fig. 2). This compound again showed a ro-
bust reduction in plasma Ab40 with an ED50 = 10 mg/kg. Reduction
in brain A40 required higher dose however, with an ED50 estimated
at 100 mg/kg. The compound had an IC50 = 194 nM for Notch pro-
cessing in whole cells, indicative of a ꢀ13-fold selectivity for inhi-
bition of Ab40 formation versus this process.
In summary, replacement of the core piperidine into morpho-
line in our lead series resulted in compounds with improved CYP
3A4 profile. Further modification of the core to optimize brain pen-
etration and potency will be reported in due course.
The authors wish to thanks Drs. A. Buevich, T.-M. Chan, and A.
Evans for their help in confirming many structures by NMR as well
as for many helpful discussions.
References and notes
1. (a) McDowell, I. Aging 2001, 13, 143; (b) Debaggio, T. Losing my Mind: an
Intimate Look at Life with Alzheimer’s; Free Press: Simon and Schuster, 2002.
2. (a) Pallas, M.; Camins, A. Curr. Pharmacol. Des. 2006, 12, 4389; (b) Hardy, J.;
Selkoe, D. J. Science 2002, 297, 353.
3. (a) Wolfe, M. S. Curr. Top. Med. Chem. 2008, 8, 2; (b) Hills, I. D.; Vacca, J. P. Curr.
Opin. Drug Discov. Dev. 2007, 10, 383.

H. Josien et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6032–6037
6037
4. (a) Churcher, I. Curr. Top. Med. Chem. 2006, 6, 579; (b) Vila, J. J. Cell. Mol. Med.
13. Kulinkovich, O.; Sviridov, S. V.; Vasilevski, D. A. Synthesis 1991, 234.
2008, 12, 258; (c) Run, X.; Liang, Z.; Zhang, L.; Iqbal, K.; Grundke-Iqbal, I.; Gong,
C. X. J. Alzheimer Dis. 2009, 16, 619.
5. Williams, M. Curr. Opin. Invest. Drugs 2009, 10, 23.
6. Gotz, J.; Ittner, L. M.; Lim, Y. A. Cell. Mol. Life Sci. 2009, 66, 1321.
7. Wolfe, M. S. Curr. Alzheimer Res. 2008, 5, 158.
8. (a) Imbimbo, B. P.; Hutter-Paier, B.; Villetti, G.; Facchinetti, F.; Cenacchi, V.;
Volta, R.; Lanzillotta, A.; Pizzi, M.; Windisch, M. Br. J. Pharmacol. 2009, 15, 982;
(b) Pissarnitski, D. Curr. Opin. Drug Discov. Dev. 2007, 10, 392.
9. (a) Imbimbo, B. P. Curr. Top. Med. Chem. 2008, 8, 54; (b) Hyde, L. A.; McHugh, N. A.;
Chen, J.; Zhang, Q.; Manfra, D.; Nomeir, A. A.; Josien, H.; Bara, T.; Clader, J. W.;
Zhang, L.; Parker, E. M.; Higgins, G. A. J. Pharmacol. Exp. Ther. 2006, 319, 1133.
10. (a) Pissarnitski, D. A.; Asberom, T. A.; Bara, T. A.; Buevich, A. V.; Clader, J. W.;
Greenlee, W. J.; Gusik, H. S.; Josien, H. B.; Li, W.; McEwan, M.; McKittrick, B. A.;
Nechuta, T. L.; Parker, E. M.; Sinning, L.; Smith, E. M.; Song, L.; Vaccaro, H. A.;
Voigt, J. H.; Zhang, L.; Zhang, Q.; Zhao, Z. Bioorg. Med. Chem. Lett. 2007, 17, 57;
(b) Josien, H.; Bara, T.; Rajagopalan, M.; Asberom, T.; Clader, J. W.; Favreau, L.;
Greenlee, W. J.; Hyde, L. A.; Nomeir, A. A.; Parker, E. M.; Pissarnitski, D. A.; Song,
L.; Zhang, L.; Zhang, Q.; Zhao, Z. Bioorg. Med. Chem. Lett. 2007, 17, 5330; (c) Li,
H.; Asberom, T.; Bara, T. A.; Clader, J. W.; Greenlee, W. J.; Josien, H. B.; McBriar,
M. D.; Nomeir, A.; Pissarnitski, D. A.; Rajagopalan, M.; Xu, R.; Zhao, Z.; Song, L.;
Zhang, L. Bioorg. Med. Chem. Lett. 2007, 17, 6290.
14. The following route was used prior to steps l-m of Scheme 2:
R3
R2
R3
R2
O
N
O
N
Tebbe
O
R1
R1
COOMe
S
S
O
O
O
O
Ar
Ar
12
R3
R2
R3
R2
O
O
N
ClCH2I
Et2Zn
BBr3
O
OH
R1
N
S
R1
S
O
O
O
O
Ar
Ar
This route used processes derived from: Pine, S. H. Org. React. 1993, 43, 1;
Denmark, S. E.; Beutner, G. In Cycloaddition Reactions in Organic Synthesis;
Kobayashi, S., Jorgensen, K. A., Eds; Wiley-VCH Verlag GmbH & Co KGaA:
Weinheim, Germany, 2002; p 85.
11. Muthusamy, S.; Babu, S. A.; Gunanathan, C. Tetrahedron Lett. 2002, 43, 3133.
12. (a) Caplar, V.; Lisini, A.; Kajfez, F.; Kolbah, D.; Sunjic, V. J. Org. Chem. 1978, 43,
1355; (b) Calmes, M.; Daunis, J.; Escale, F.; Jacquier, R.; Roumestant, M.-L.
Tetrahedron: Asymmetry 1994, 1643, 5.