Structure based design of iminohydantoin BACE1 inhibitors: Identification of an orally available, centrally active BACE1 inhibitor

Article abstract of DOI:10.1016/j.bmcl.2012.02.013

From an initial lead 1, a structure-based design approach led to identification of a novel, high-affinity iminohydantoin BACE1 inhibitor that lowers CNS-derived Aβ following oral administration to rats. Herein we report SAR development in the S3 and F′ subsites of BACE1 for this series, the synthetic approaches employed in this effort, and in vivo data for the optimized compound.

Full text of DOI:10.1016/j.bmcl.2012.02.013

Bioorganic & Medicinal Chemistry Letters 22 (2012) 2444–2449
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Structure based design of iminohydantoin BACE1 inhibitors: Identification
of an orally available, centrally active BACE1 inhibitor
⇑
,
Jared N. Cumming , Elizabeth M. Smith, Lingyan Wang, Jeffrey Misiaszek, James Durkin, Jianping Pan,
Ulrich Iserloh, Yusheng Wu, Zhaoning Zhu, Corey Strickland, Johannes Voigt, Xia Chen, Matthew E.
Kennedy, Reshma Kuvelkar, Lynn A. Hyde, Kathleen Cox, Leonard Favreau, Michael F. Czarniecki, William
,à
⇑
J. Greenlee, Brian A. McKittrick, Eric M. Parker, Andrew W. Stamford
Merck Research Laboratories, 2000 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:
From an initial lead 1, a structure-based design approach led to identification of a novel, high-affinity
iminohydantoin BACE1 inhibitor that lowers CNS-derived Ab following oral administration to rats. Herein
we report SAR development in the S3 and F0 subsites of BACE1 for this series, the synthetic approaches
employed in this effort, and in vivo data for the optimized compound.
Received 11 January 2012
Revised 3 February 2012
Accepted 6 February 2012
Available online 16 February 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
BACE
b-Secretase
Alzheimer0s disease
Iminohydantoin
In vivo
Alzheimer0s disease (AD) is a chronic, progressive, ultimately
fatal neurodegenerative disease that occurs predominantly in the
elderly population. Current treatments, which consist of the acety-
lcholineesterase inhibitors and the NMDA receptor antagonist
memantine, temporarily slow the cognitive decline that is associ-
ated with the disease, but do not alter the underlying neurodegen-
erative process and therefore have no effect on disease progression.1
Given the devastating effects of AD on patients and their families as
well the increasing societal burden as a result of aging populations
worldwide, disease-modifying treatments are urgently needed.2,3
The characteristic neuropathological hallmarks of AD are the
presence of extracellular amyloid plaques comprised predomi-
nantly of the amyloid peptide Ab42 and intracellular tangles of
hyperphosphorylated protein tau in the cortex and hippocampus.
According to the amyloid hypothesis, accumulation of Ab, most
likely as soluble oligomeric and protofibrillar forms, is causative
of the disease.4,5 The amyloid peptides Ab40 and Ab42 are formed
by sequential cleavage of the amyloid precursor protein (APP), first
by the aspartyl protease b-APP cleaving enzyme 1 (BACE1)6–10
which yields the soluble APP N-terminal fragment sAPPb and the
membrane bound C-terminal fragment C100. C100 is subsequently
cleaved by c-secretase to yield the plaque-forming Ab40 and Ab42
peptides. Inhibition of BACE1 is highly attractive as a potential dis-
ease-modifying approach for AD. BACE1 knockout mice are viable
with no overt abnormalities, do not synthesize Ab and display only
a moderate peripheral nerve hypomyelination phenotype that is
due to the loss of BACE1-mediated processing of Type III Neuregu-
lin.11–15 Furthermore, BACE1 is a well-characterized aspartyl prote-
ase, and is amenable to structure-based drug design.16 However,
the identification of small molecule BACE inhibitors that penetrate
the CNS and lower CNS-derived Ab has proved to be exceptionally
challenging. This communication describes the evolution of novel
iminohydantoin BACE1 inhibitors resulting in the identification
of a potent inhibitor that lowers cerebrospinal fluid (CSF) Ab in rats
following oral administration.
We have previously described the design of a cyclic acylguani-
dine series of BACE1 inhibitors exemplified by the diphenyl imi-
nohydantoin 1, an inhibitor of BACE1 with low micromolar
affinity (Fig. 1).17,18 Based on its high ligand efficiency (LE), inher-
ent selectivity over the related aspartyl protease cathepsin D, and
favorable pharmacokinetic properties, 1 was considered to be an
ideal lead for further optimization. An X-ray crystal structure of
⇑
Corresponding authors. Tel.: +1 732 594 3049 (J.N.C.), tel.: +1 732 594 1960
(A.W.S.).
E-mail addresses: jared.cumming@merck.com (J.N. Cumming),
andrew.stamford@merck.com (A.W. Stamford).
Present address: Merck Research Laboratories, 126 E. Lincoln Ave., RY121-274,
Rahway, NJ 07065, USA
à
Present address: Merck Research Laboratories, 126 E. Lincoln Ave., PO Box 2000,
Rahway, NJ 07065, USA
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2012.02.013

J. N. Cumming et al. / Bioorg. Med. Chem. Lett. 22 (2012) 2444–2449
2445
N-phenyl-benzamide 2 was converted into the chloroimidate
which was then reacted with the appropriate benzaldehyde and
1,3-dimethylimidazolium iodide to afford the benzil derivative
3.22 Condensation of 3 with methylguanidine hydrochloride affor-
ded the desired targets 4. Alternatively, the benzil route was used
to prepare the bromophenyl iminohydantion 5. Suzuki coupling of
5 with the appropriate boronic acid gave the desired products 4.
Gratifyingly, several 3-biaryl modifications resulted in inhibi-
tors with improved BACE1 affinity (Table 1). Thus, derivatization
of the S1 phenyl group as an appropriately (30-substituted) biphe-
nyl-3-yl resulted in an order of magnitude improvement in affinity
with analogs 4b, 4d–4h displaying sub-micromolar Ki values. The
importance of the 30-substituent is highlighted by comparison to
the parent biphenyl analog 4a whereby incorporation of an unsub-
stituted phenyl group resulted in essentially no improvement of
affinity.
BACE1 X-ray crystal structures obtained with the racemic
3-methoxyphenyl and pyridin-3-yl analogs 4b and 4j revealed den-
sity only for the (R) enantiomers, confirming the predicted binding
modes with the biaryl motif occupying the S1 and S3 pockets.24
For the pyridin-3-yl analog, the pyridine nitrogen is presumed to
face the entrance of the S3 sub-pocket which was inferred by
the observation of a crystallographic water molecule at a distance
of 2.9 Å from the pyridine nitrogen (Fig. 2). In the case of the
HN
HN
1
N
Compound
cell Aβ40 IC50: 12 μM
O
MW: 265, cLogP: 1.9
ligand efficiency: 0.37
BACE1 Ki: 3.6 μM
rat AUC0-6h 10 mg/kg p.o.: 5 μM.h
b/p ratio: 1.8
Cath-D: 38% inhib. @ 50 μM
Figure 1. Profile and binding mode of iminohydantoin lead 1.
Table 1
BACE1 affinities of iminohydantoins 4a–p23
1 complexed to BACE1 revealed the following characteristics
(Fig. 1). The amidine motif of the iminohydantoin core participates
in an H-bond donor–acceptor complex with two Asp residues,
Asp32 and Asp228, at the active site of BACE1. The S1 pocket of
Compd
R
BACE1 Ki (
lM)
Method (Scheme 1)
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
Ph
3-MeOPh
4-MeOPh
3-EtOPh
3-F
3-Cl
3-Me
3-CN
Pyridin-2-yl
Pyridin-3-yl
Pyridin-4-yl
Pyrazin-5-yl
5-Methylpyridin-3-yl
5-Cyanopyridin-3-yl
5-Fluoropyridin-3-yl
5-Chloropyridin-3-yl
3.3
0.19
3.8
0.46
0.72
0.30
0.55
0.37
1.9
B
B
B
B
A
A
A
A
B
B
B
B
B
B
B
B
BACE1, defined by several hydrophobic residues including Leu30
,
Phe108, Trp115 and Ile118, is occupied by one of the phenyl groups
of 1. The other phenyl group of 1 occupies space near S20 that we
have termed F0. In the X-ray crystal structure of the peptidomimet-
ic inhibitor OM99-2 and BACE1, this region is occupied by Tyr71 of
the flap loop in its closed conformation.19 In the X-ray crystal
structure of 1,20 the flap loop is fairly well-ordered but more open
in comparison with the closed, substrate-bound form, with the
aromatic ring of Tyr71 engaged in a hydrophobic interaction with
the inhibitor. In this communication we report the optimization
of lead iminohydantoin 1 enabled by structure-based design to af-
ford a novel, high-affinity BACE1 inhibitor that lowers CNS-derived
Ab following oral administration to rats.
0.53
3.8
0.31
0.43
0.47
0.29
0.09
An attractive approach to gain affinity while maintaining the
high LE of 1 was to occupy the adjacent S3 pocket by substitution
on the phenyl group residing in S1. In silico docking experiments
indicated that 3-biaryl substitution offered the possibility of occu-
pying the contiguous S1–S3 pockets.21 To this end a series of biaryl
derivatives was prepared and evaluated as BACE1 inhibitors. The
synthesis of the biaryl derivatives is shown in Scheme 1.
R
NH
NH
Br
R
a
b
c
HN
N
HN
N
O
NH
O
O
R=Br
method B
O
O
2
3
5
4a-p
b
method A
Scheme 1. Reagents and conditions: (a) (i) SOCl2, toluene, reflux, (ii) aldehyde, 1,3-
dimethyl-imidazolium iodide, NaH, THF, (iii) 1 N HCl, THF; (b) N-methylguanidine
hydrochloride, Et3N, EtOH, reflux; (c) RB(OH)2, Pd(dppf)Cl2, K2CO3, toluene, H2O,
microwave, 150 °C.
Figure 2. X-ray crystal structure of 4j bound to BACE1.

2446
J. N. Cumming et al. / Bioorg. Med. Chem. Lett. 22 (2012) 2444–2449
Table 2
BACE1 Ki, cell IC50 and selectivity of 6a–b and 7a–b23
Compd
R
BACE1 Ki (
lM)
Cell Ab40 IC50
(lM)
Fold selectivity: BACE1 versus Cathepsin D
6a
6b
7a
7b
(R)-3-MeOPh
(S)-3-MeOPh
(R)-Pyridin-3-yl
(S)-Pyridin-3-yl
0.08
6.0
0.11
1.7
2.3
120
19
455
6
nda
0.63
nda
a
Not determined.
3-methoxyphenyl analog 4c, the methoxy group projects into the S3
subpocket displacing the aforementioned water molecule (Fig. 2).
The enantiomers of both the 3-methoxyphenyl (6a, 6b) and pyri-
din-3-yl analogs (7a, 7b) were prepared (Table 2)25 and in each case
the (R) absolute configuration was assigned to the more active enan-
tiomer of each pair. Compounds 6a and 7a possess LE values of 0.35
and 0.36 respectively, which compare favorably to that of 1. These
compounds were also active in a cellular assay of BACE1-mediated
processing of APP, with the less lipophilic pyridyl analog 7a showing
a smaller shift between the Ki and cell Ab40 IC50 in comparison to the
corresponding methoxyphenyl analog 6a.
Our attention next turned toward examining the effect of mod-
ifications of the phenyl group that resides in F0 with respect to
BACE1 affinity and cell activity, fixing the biaryl motif as a 30-
chloro-3-biphenyl moiety. Synthesis of these F0 modified analogs
is described in Scheme 2. The appropriate ketone starting material
8 was converted to the corresponding hydantoin 9 via Bucherer–
Berg conditions. Exploiting the relative acidity of the N3 proton,
the hydantoin was smoothly methylated at N3 using dimethyl-
formamide-dimethylacetal (DMF-DMA) in essentially quantitative
yield to give 10. Conversion of the more reactive C2 carbonyl to the
corresponding thiocarbonyl 11 with Lawesson0s reagent followed
by oxidative amination gave the iminohydantoin 12. Suzuki cou-
pling of 12 was conducted using polystyrene-immobilized triphen-
ylphosphine–palladium complex to install the 30-chlorophenyl
moiety directly without protection of the acyl guanidine moiety
yielding the desired products 13. The yields for this sequence were
generally good to excellent.
Table 3
BACE1 affinity and cell activity of 13a–o23
Compd R0
BACE1 Ki (nM) Ab40 IC50 (nM)
cLogP
(fold shift relative to Ki)
13a
13b
13c
13d
13e
13f
13g
13h
13i
13j
13k
13l
13m
13n
13o
Me
Et
i-Pr
720
450
320
47
110
470
470
4,800 (7ꢀ)
5,300 (12ꢀ)
4,600 (15ꢀ)
1,900 (40ꢀ)
2,800 (25ꢀ)
6,900 (15ꢀ)
11,000 (23ꢀ)
6,000 (31ꢀ)
9,500 (27ꢀ)
5,900 (7ꢀ)
4,400 (26ꢀ)
nda
3.4
3.9
4.3
3.8
4.3
4.9
5.4
4.3
4.4
3.0
3.0
3.0
2.0
2.0
2.8
c-Pr
c-Bu
c-Pn
c-Heꢀ
1-Methyl-c-Pr 190
c-Pr-methyl
Pyridin-2-yl
Pyridin-3-yl
Pyridin-4-yl
350
860
170
>10,000
Pyrmidin-5-yl 830
Pyrmidin-2-yl 1200
21,000 (25ꢀ)
>10,000
Thiazol-2-yl
1200
>10,000
a
Not determined.
ity and reducing the shift between the BACE1 Ki and cell IC50. To
this end a strategy of modifying the distal phenyl group was imple-
mented, with an emphasis on reduction of cLogP by replacing
chloro with more polar substituents and the distal phenyl group
with a pyridin-3-yl group. Synthesis and derivatization of the re-
quired cyclopropyl iminohydantoin core to enable this approach
is described in Scheme 3. Copper-mediated addition of cyclopro-
pylmagnesium chloride to 3-bromobenzoyl chloride 14 gave cyclo-
propyl ketone 15 that was converted to the iminohydantoin 16 in
four steps and 50% overall yield following procedures analogous to
those in Scheme 2. Suzuki coupling of 16 to form biaryl derivatives
17 proceeded directly without the need for protection of the imi-
nohydantoin. Complementarily, the bromophenyl intermediate
16 was also converted to its boronate ester 18, which underwent
Suzuki coupling with aryl bromides to give desired biaryl
derivatives.
As noted in Table 3, the majority of analogs in which the phenyl
was replaced by an alkyl (13a–c) or cycloalkyl group (13f–g) had
affinities similar to that of the phenyl analog 4f. Notably, the cyclo-
propyl analog 13d was about sixfold more potent than 4f (47 nM
vs 300 nM). Heterocyclic replacements resulted in analogs of
similar to somewhat reduced affinities (13j–k, 13m–o) with the
exception of the pyridine-4-yl analog 13l which was essentially
inactive. Cellular activity was generally in the micromolar range,
with potency shifts relative to Ki values ranging from about seven-
fold (13a and 13j) up to 40-fold (13d).
Inspection of the data in Table 4 reveals that reduction of the
cLogP value below 3 results in significantly reduced cellular po-
tency shifts (17c–i). In addition, where tested, the compounds
were of equal or higher affinity against BACE2, a peripherally
localized enzyme with significant homology to BACE1.26 While a
Having identified cyclopropyl as a substituent that confers
higher affinity than phenyl, further modifications to the biaryl
motif were conducted with an objective of improving BACE1 affin-
HN
HN
HN
HN
O
N
N
O
O
d
Br
b
O
O
N
NH
R'
9
X
O
O
N
HN
HN
O
O
Br
B
50%
c
a
b
Br
O
R'
R'
Br
Br
14 X = Cl
18
16
a
8
10
70%
e
15 X = c-Pr
S
HN
HN
HN
HN
HN
N
N
N
Cl
d
e
HN
O
HN
O
c
O
O
R'
11
R'
13a-o
Br
R'
12
Br
Ar
17a-i
Scheme 3. Reagents and conditions. (a) c-PrMgCl, CuCl, LiCl, ꢁ60 °C; (b) Steps a–d,
Scheme 2; (c) ArB(OH)2, PS-Ph3P-Pd, K2CO3, i-PrOH, microwave, 110 °C; (d)
Bis(pinacolato)diboron, PdCl2dppf, KOAc, DMSO, 120 °C; (e) ArBr, PS-Ph3P-Pd,
K2CO3, DMSO, 120 °C.
Scheme 2. Reagents and conditions. (a) (NH4)2CO3, KCN, 120 °C; (b) DMF-DMA,
100 °C; (c) Lawesson’s reagent, 100 °C; (d) t-BuOOH, NH4OH; (e) 3-ClPhB(OH)2, PS-
Ph3P-Pd, K2CO3, i-PrOH, microwave, 110 °C.

J. N. Cumming et al. / Bioorg. Med. Chem. Lett. 22 (2012) 2444–2449
2447
Table 4
O
O
HO
BACE1 affinity and cell Ab40 activity of 17a–i23
NH
a
b
H2N
O
H2N
O
HN
O
Br
Compd Ar
BACE1 Ki Ab40 IC50 (nM)
cLogP BACE2 Ki
Br
Br
91%
29%
(50%max.
theoretical)
(nM)
(fold shift relative
(nM)
to Ki)
20
21
22
17a
17b
17c
17d
17e
17f
17g
17h
17i
3,5-Cl2Ph
3-MeOPh
3-CNPh
Pyridin-3-yl
5-MeO-Pyridin-3-yl 100
5-CN-Pyridin-3-yl
5-F-Pyridin-3-yl
5-Cl-Pyridin-3-yl
30
99
130
270
2400 (80ꢀ)
1600 (16ꢀ)
940 (7ꢀ)
880 (3ꢀ)
390 (4ꢀ)
610 (2ꢀ)
800 (5ꢀ)
380 (6ꢀ)
640 (3ꢀ)
4.5
3.0
2.5
1.6
2.0
1.2
1.8
2.4
2.1
nda
7.8
30
360
11
170
139
nda
68
Cl
S
HN
19
N
N
e,f,g
68%
c,d
R=
N
N
HN
O
HN
R
O
94%
Br
24
R=
270
160
59
23
j
Br
Br
(HO)2B
h,i
39%
5-Me-Pyridin-3-yl 250
N
72%
N
a
Not determined.
Scheme 4. Reagents and conditions. (a) 1 N aq. KOH, 185 °C, 24 h; (b) (i) TMSCHN2,
(ii) Chiralpak AS column (Diacel, 5 ꢀ 50 cm, 20 mm), 0.5% i-PrOH/hexanes, 65 mL/
min), second eluting isomer; (c) Cl2C(S), DCM, sat. aq. NaHCO3; (d) MeNH2–HCl,
DIEA, 70 °C; (e) t-BuOOH, NH4OH; (f) bis-(pinacolato)diboron, PdCl2dppf, KOAc,
DMSO, 120 °C; (g) 3,5-dichloropyridine, PS-Ph3P-Pd, aq. K2CO3, DMSO, 120 °C; (h)
1-(trimethylsilyl)propyne, Pd(PPh3)4, CuI, Et3N, n-Bu4NF, PhMe, rt; (i) BuLi, B(Oi-
Pr)3, THF/PhMe, ꢁ40 to ꢁ10 °C then aq. NH4OH; (j) Product of step (e),
PdCl2(dppf)CH2Cl2, aq. K2CO3, dioxane, 65 °C.
number of groups have reported inhibitors with selectivity for
BACE1 over BACE2,27,28 the lack of any overt phenotype reported
for BACE2 knockout mice suggests that no liabilities are expected
to arise from BACE2 inhibition,29 and indeed recent reports suggest
there may be a benefit in glucose homeostasis.30
The chloropyridine analog 17h was among the most potent
compounds with respect to both Ki and cellular activity, and an
X-ray crystal structure of this compound with BACE1 was obtained
(Fig. 3).31 As was observed for 4b and 4j, only density for the 5-(R)
enantiomer was observed and the binding features of this analog
were highly conserved in comparison with the earlier compounds.
The cyclopropyl substituent resides in the F0 pocket and is engaged
in a hydrophobic interaction with Tyr71 of the well-ordered flap.
The chloropyridyl substituent resides in the S3 sub-pocket with
the chloro substituent positioned at the entrance of the S3 sub-
pocket.
The (R) enantiomer of the chloropyridine analog, 19 was pre-
pared and subjected to more detailed characterization. Synthesis
of 19 was achieved by hydrolysis of the racemic hydantoin inter-
mediate 20 to give amino acid 21 (Scheme 4). Conversion of 21
to its methyl ester followed by chiral HPLC gave the (R)-enantio-
mer 22. Treatment of 22 with thiophosgene afforded the thioisocy-
anate which upon reaction with methylamine cyclized to the
thiohydantoin 23. Elaboration of 23 to chloropyridine 19 was
achieved following procedures analogous to those outlined in
Scheme 2.
Compound 19 binds to BACE1 with good affinity, very high LE
(0.44) and is about 350-fold selective for BACE1 versus cathepsin
D (Table 5). In a rat oral pharmacokinetic screen, the compound
achieved good plasma exposure.32 Subsequent efforts focused on
further improving BACE1 affinity explored replacement of the
chloro by a propynyl group, which based on its linear trajectory
afforded the possibility of binding more deeply in the S3 sub-pock-
et. The resultant analog 24 (Ki 5.4 nM, Table 5), synthesized as out-
lined in Scheme 4, was about a fivefold more potent inhibitor of
BACE1 compared to the chloro analog 19. Cellular activity of 24
was also improved relative to 19, with 24 displaying a cell IC50 of
82 nM. Replacement of the chloro substituent by propynyl is also
beneficial for BACE1 selectivity versus cathepsin D, with selectivity
of 24 increasing to 7,500-fold. An X-ray crystal structure of 24 and
BACE1 was highly consistent with that observed for chloro ana-
log,23 with the major difference being protrusion of the propynyl
methyl group deep into the S3 sub-pocket where it is likely en-
gaged in
a
favorable hydrophobic interaction with Ala396
(Fig. 4).33 In a rat pharmacokinetic screen 24 showed excellent
plasma exposure following oral administration.32
Based on its favorable overall profile, the ability of compound
24 to lower Ab40 levels in rat plasma and CSF was evaluated
(Fig. 5). A single oral dose of 30 mg/kg elicited a 54% reduction of
CSF Ab40 three hours post dose relative to vehicle-treated control,
indicating inhibition of BACE1 localized in the CNS. In the same
experiment, plasma Ab40 was reduced by 85%. The plasma expo-
sure of 24 at that dose was 4.2 lM with a brain/plasma ratio of
0.2, a value that was in good agreement with the rat oral pharma-
cokinetic screen.
In summary, optimization of the iminohydantoin class of BACE1
inhibitors has afforded 24 as a potent, selective, brain penetrant
Table 5
Profiles of 19 and 2423
Compd BACE1 Cell Ab40 Fold selectivity: BACE1 Rat AUC0- Brain/ cLogP
Ki (nM) IC50 (nM) versus Cathepsin D
(l
M h)a plasma
6h
19
24
21
5.4
150
82
350
7,500
3.1
17.9
ndb
0.3
2.4
2.4
a
10 mg/kg orally administered as a hydroxypropyl-b-cyclodextrin solution in
20%.
b
Not determined.
Figure 3. X-ray crystal structure of 17h bound to BACE1.

2448
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Figure 4. X-ray crystal structure of 24 bound to BACE1.
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100
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p<0.05 vs. Vehicle
-54%
50
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-85%
0
17. (a) Zhu, Z.; Sun, Z.-Y.; Ye, Y.; Voigt, J.; Strickland, C.; Smith, E. M.; Cumming, J.;
Wang, L.; Wong, J.; Wang, Y.-S.; Wyss, D. F.; Chen, X.; Kuvelkar, R.; Kennedy, M.
E.; Favreau, L.; Parker, E.; McKittrick, B. A.; Stamford, A.; Czarniecki, M.;
Greenlee, W.; Hunter, J. C. J. Med. Chem. 2010, 53, 951. Other researchers
independently identified the same diphenyliminohydantoin structure, c.f.; (b)
Malamas, M. S.; Robichaud, A.; Erdei, J.; Quagliato, D.; Solvibile, W.; Zhou, P.;
Morris, K.; Turner, J.; Wagner, E.; Fan, K.; Olland, A.; Jacobsen, S.; Reinhart, P.;
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Compartment
Figure 5. Inhibition of CSF and plasma Ab40 in Sprague–Dawley rats 3 h after a
single oral 30 mg/kg dose of 24.
and orally active BACE1 inhibitor, demonstrating that inhibitors
from this class hold promise as potential disease-modifying agents
for AD. Subsequent reports will detail further optimization efforts
that resulted in inhibitors with improved cell and in vivo potency.
19. Hong, L.; Koelsch, G.; Lin, X.; Wu, S.; Terzyan, S.; Ghosh, A. K.; Zhang, X. C.;
Tang, J. Science 2000, 290, 150.
20. Coordinates for the X-ray structure of compound 1 complexed with BACE1
have been deposited in the Protein Data Bank (www.rcsb.org), and can be
accessed under PDB ID 4DJU.
Acknowledgements
21. Jaguar, version 5.5; Schrödinger LLC: New York.
Use of the IMCA-CAT beamline at the Advanced Photon Source
was supported by the companies of the Industrial Macromolecular
Crystallography Association through a contract with Hauptman-
Woodward Medical Research Institute. Use of the Advanced Pho-
ton Source was supported by the U.S. Department of Energy, Office
of Science, Office of Basic Energy Sciences, under Contract No. DE-
AC02-06CH11357.
22. Miyashita, A.; Matsuda, H.; Higashino, T. Chem. Pharm. Bull. 1992, 40, 2627.
23. Inhibitor Ki values at purified human BACE1, BACE2, and Cathepsin D (Cath-D)
were determined using a FRET-peptide substrate hydrolysis assay. Cellular
IC50 values for reduction of Ab40 production were determined in stably
transfected HEK293-APPswe/lon cells. The protocols for these assays have been
previously described in reference 17 (Zhu, et al.). All values reported are the
average of a minimum of two independent determinations.
24. Coordinates for the X-ray structures of compounds 4b and 4j complexed with
BACE1 have been deposited in the Protein Data Bank (www.rcsb.org), and can
be accessed under PDB IDs 4DJV and 4DJW, respectively.
25. Separation of 4b on a Chirocel Preparative OJ column eluted with isopropanol
(0.1% triethylamine): hexane (0.1% triethylamine) in a ratio of 1:3 gave 6a (tR
23.3 min) as the later eluting component. Separation of the 3-bromophenyl
intermediate 5 on a Chirocel Preparative OJ column eluted with isopropanol
(0.1% triethylamine): hexane (0.1% triethylamine) in a ratio of 3: 17 gave the
(R)-enantiomer of 5 (tR 38. 6 min.) as the later eluting component, which was
converted to 7a via Suzuki coupling with pyridin-3-ylboronic acid.
26. De Strooper, B.; Vasar, R.; Golde, T. Nat. Rev. Neurol. 2010, 6, 99.
27. Malamas, M. S.; Erdei, J.; Gunawan, I.; Barnes, K.; Hui, Y.; Johnson, M.;
Robichaud, A.; Zhou, P.; Yan, Y.; Solvibile, W.; Turner, J.; Fan, K. Y.; Chopra, R.;
Bard, J.; Pangalos, M. N. Bioorg. Med. Chem. Lett. 2011, 21, 5164.
28. Al-Tel, T. H.; Semreen, M. H.; Al-Qawasmeh, RA.; Schmidt, M. F.; El-Awadi, R.;
Ardah, M.; Zaarour, R.; Rao, S. N.; El-Agnaf, O. J. Med. Chem. 2011, 54, 8373.
References and notes
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be accessed under PDB ID 4DJX.
32. Korfmacher, W. A.; Cox, K. A.; Ng, K. J.; Veals, J.; Hsieh, Y.; Wainhaus, S.; Broske,
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33. Coordinates for the X-ray structure of compound 24 complexed with BACE1
have been deposited in the Protein Data Bank (http://www.rcsb.org), and can
be accessed under PDB ID 4DJY.