Rational design of novel, potent piperazinone and imidazolidinone BACE1 inhibitors

Article abstract of DOI:10.1016/j.bmcl.2008.04.050

Guided by structure-based design, we synthesized two novel series of potent inhibitors of BACE1 and generated extensive SAR around both the prime and non-prime side binding pockets. The key feature of both series is a cyclic amine motif specifically crafted to achieve interactions with both the flap and with the S2′ pocket.

Full text of DOI:10.1016/j.bmcl.2008.04.050

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry Letters 18 (2008) 3236–3241
Rational design of novel, potent piperazinone
and imidazolidinone BACE1 inhibitors
b,
b
b
a
a
b
J. N. Cumming,a,* T. X. Le, S. Babu, C. Carroll, X. Chen, L. Favreau, P. Gaspari,
*
T. Guo,b D. W. Hobbs,b Y. Huang,a U. Iserloh,a M. E. Kennedy,a R. Kuvelkar,a G. Li,a
J. Lowrie,b N. A. McHugh,a L. Ozgur,b J. Pan,a E. M. Parker,a K. Saionz,b
A. W. Stamford,a C. Strickland,a D. Tadesse,b J. Voigt,a L. Wang,a Y. Wu,a
L. Zhanga and Q. Zhanga
aSchering-Plough Research Institute, 2015 Galloping Hill Road, Kenilworth, NJ 07033, USA
bPharmacopeia, Inc., PO BOX 5350, Princeton, NJ 08543, USA
Received 24 March 2008; revised 14 April 2008; accepted 21 April 2008
Available online 25 April 2008
Abstract—Guided by structure-based design, we synthesized two novel series of potent inhibitors of BACE1 and generated extensive
SAR around both the prime and non-prime side binding pockets. The key feature of both series is a cyclic amine motif specifically
crafted to achieve interactions with both the flap and with the S20 pocket.
Ó 2008 Elsevier Ltd. All rights reserved.
Alzheimer’s disease (AD)1 is a progressive, ultimately
BACE1
IC50 (nM) IC50 (nM)
Cell
fatal neurodegenerative disorder for which there is cur-
rently no disease modifying therapy. It affects more
than five million people in the United States, fifteen
million people worldwide, and has become the sev-
enth-leading cause of death in this country.1d A key
hallmark of AD is deposition of aggregated b-amyloid
peptides (Ab40,42) as plaques in the brain.2 These pep-
tides are formed through processing of amyloid precur-
sor protein (APP), initiated by b-secretase (BACE1).3,4
Given that BACE1 knockout mice are viable,5 and that
modest reduction in BACE1 activity produces a sharp
decline in AD-like pathology in transgenic mouse
models,6 this enzyme is an attractive therapeutic target
to slow or halt the progression of this devastating
disease.
OH
Cpd
R
H
H
N
H
N
Pr2N
S3
1a
1b Bn
1c OEt
130
14
7
240
522
106
O
O
Ar
R
S2
S1
S2'
OH
O
H
N
2 (n = 1), piperazinones
3 (n = 0), imidazolidinones
( )n
N
R
Thr72
NH
(flap)
S2'
Figure 1. BACE1 in vitro activity for initial lead piperidines 1
(Ar = 3,5-difluorophenyl)7a and design elements of novel piperazinone
and imidazolidinone cores 2 and 3.
As part of our BACE1 inhibitor program, we recently
reported a series of novel, potent peptidomimetic piper-
idines 17a (Fig. 1) and pyrrolidines.7 In the former series,
substitutions from the 4-position of the piperidine ring
improved inhibitor potency either by occupation of the
S20 subsite with large lipophilic groups, for example
1b, or by formation of a weak hydrogen bond (3.2 A)
to the flap Thr72 NH from a small alkoxy group, for
Keywords: Alzheimer’s disease; b-Secretase; BACE; Aspartyl protease
inhibitors; Peptidomimetics.
*
Corresponding authors. Tel.: +1 908 740 2515; fax: +1 908 740 7152
(J.N.C.); tel.: +1 609 452 3674; fax: +1 609 655 4187 (T.X.L.); e-mail
addresses: jared.cumming@spcorp.com; tle@pcop.com
˚
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.04.050

J. N. Cumming et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3236–3241
3237
achieve a hydrogen bond to Thr72 NH. From these
observations, and with the aid of molecular modeling,8
we designed both piperazinones 2 and imidazolidinones
39 (Fig. 1) as cyclic amine scaffolds that could achieve
both occupancy of S20 and a hydrogen bond to the flap
from the same ring system.
O
OH
Boc
N
Boc
N
Bn2N
F
Bn2N
Ar
H
a
F
+
O
N
Bn
5
O
N
Bn
4
6
OH
OH
O
Stereoselective synthesis of these new inhibitors begin-
ning from (S)-N,N-dibenzyl-3,5-difluorophenyl-alaninal
410 is summarized in Scheme 1 for piperazinone analog
2a. The stereochemistry of the hydroxyl group and
cyclic amine ring was set via chirality transfer from
the a-amino acid center in a non-chelation controlled
Aldol reaction enforced by the N,N-dibenzyl protecting
group.11 Thus, addition of the conjugate base of tert-
butyl 4-benzyl-piperazin-3-one-1-carboxylate 5 to alde-
hyde 4 gave Aldol product 6 with the desired absolute
and relative stereochemistry as the major isolable prod-
uct. Palladium-mediated debenzylation proceeded
smoothly to give primary amine 7 that was then cou-
pled to 5-methyl-N,N-dipropylisophthalic acid 812 in
the presence of EDCI/HOBt to give amide 9. Finally,
removal of the cyclic amine Boc group gave BACE1
inhibitor 2a.
Boc
Boc
N
H
N
H2N
Ar
N
Pr2N
c
b
d
O
O
O
N
Bn
N
Bn
Ar
7
9
OH
O
H
H
Pr2N
N
N
2a
O
O
N
Bn
Ar
Scheme 1. Synthesis of BACE1 inhibitor 2a as a representative
example for generation of both piperazinone and imidazolidinone
analogs 2 and 3 (Ar = 3,5-difluorophenyl): (a) LDA + 5 then 4,
ꢀ78 °C, 41%; (b) H2, Pd(OH)2, HOAc, EtOH, 91%; (c) 8, EDCI,
DIEA 81%; (d) TFA, 79%.
example 1c. Combining these features to achieve syner-
gistic improvements in potency proved challenging.
Imidazolidinone analogs 3 were made in similar overall
yield following the above route, simply substituting tert-
butyl 3-benzyl-imidazolidin-4-one-1-carboxylate 1013
for piperazinone core 5 in the Aldol step. The modifica-
tions of the S2–S3 motifs described in Tables 1 and 2
Examination of the X-ray crystal structure of piperidine
1b7a in the BACE1 active site strongly suggested that a
carbonyl introduced to the 3-position of the ring could
Table 1. SAR of piperazinone 2 and imidazolidinone 3 BACE1 inhibitors bearing variations of an isophthalamide group in S2/S3 (Ar = 3,5-
difluorophenyl)16
OH
H
N
H
N
R
( )n
O
O
N
Ar
Bn
Compound
n
R
BACE1 IC50 (nM)
Cell IC50 (nM)
ClogP17
2a
3a
1
0
3
5
300
1100
5.4
4.9
Pr2N
O
O
MeO
2b
3b
1
0
1
2
75
700
4.2
3.7
N
MeO
OMe
2c
2d
1
1
4
2
57
3.7
2.9
N
O
MeO
N
140
N
O

3238
J. N. Cumming et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3236–3241
Table 2. SAR of S2/S3 non-isophthalamide variations of piperazinone
phenyl)16
2
imidazolidinone 3 BACE1 inhibitors (Ar = 3,5-difluoro-
OH
H
N
H
N
R
( )n
O
O
N
Ar
Bn
Compound
n
R
BACE1 IC50 (nM)
Cell IC50 (nM)
O
2e
3e
1
0
9
905
510
11,000
PrN
O
2f
3f
1
0
5
140
180
21,500
BuN
O
2g
3g
1
0
3
88
240
12,000
BuN
Ph
O
2h
2i
2j
1
1
1
16
10
22
960
530
BuN
O
N
O
N
1400
Ph
O
MeO
2k
2l
1
1
1
1
13
1500
620
N
O
9
N
PrN
O
2m
2n
11
22
1100
790
N
PrN
Pr
O
N
PrN
were made employing appropriate replacements7b,14 of
acid 8 in the penultimate coupling step for both cyclic
amine series.
non-prime side groups. As Table 1 shows, all of these
analogs are potent BACE1 inhibitors. Comparison of
the activity of piperazinone 2a (BACE1 IC50 = 3 nM)
with the original lead piperidine 1b (BACE1 IC50
=
We first examined our novel piperazinone and imidazo-
lidinone cores derivatized with isophthalamide-type
14 nM) shows that additional potency has been gleaned
by introduction of the carbonyl group. Overlay of the X-

J. N. Cumming et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3236–3241
3239
may reflect intrinsically better binding imparted by the
combination of S20 occupation with additional hydro-
gen bonding to the flap.
S3
S2
In fact, the S20 binding moiety remains a significant
component of BACE1 potency in the piperazinone ser-
ies, as evidenced by the SAR of modifications to the 4-
position of the ring (Table 3).20 Close analogs of parent
2a that direct at least some lipophilicity into S20 (2s–2w)
showed good to excellent potency (BACE1 IC50 = 3–
27 nM). Interestingly, a phenyl group directly attached
to the lactam nitrogen 2x cannot attain the necessary
trajectory to occupy S20 and thus has a diminished po-
tency similar to small alkyl groups or no substitution
at all (2o–2q, BACE1 IC50 = 175–345 nM).
2.9Å
S2'
S1
Lead piperazinone 2a and imidazolidinone 3a were pro-
filed in vivo in 6-week-old, pre-plaque CRND8 mice
(Table 4).2c,21 Both compounds showed modest reduc-
tion of Ab40 in the plasma with a single 100 mg/kg sc
dose, but did not affect brain levels of the peptide. The
PK profiles from these experiments show low brain pen-
etration, which may be due to their being substrates for
P-pg as reflected in the Caco-2 efflux ratios. These com-
pounds were further profiled against other human
aspartyl proteases (Cathepsins D and E, Pepsin) and
generally showed low to modest selectivity (1–15-fold).
Figure 2. Overlay of BACE1 X-ray structures for piperidine 1b
˚
(yellow) and piperazinone 2a (green) and showing the 2.9A hydrogen
bond from the carbonyl of the piperazinone ring in 2a to Thr72 NH of
the flap (gray).
ray crystal structures of these two analogs (Fig. 2)15 con-
˚
firms that a hydrogen bond (2.9 A) to the flap Thr72 NH
was in fact achieved from the new carbonyl without per-
turbing the overall binding mode of the analog.
Another observation from Table 1 is that piperazinone
2a and imidazolidinone 3a have a larger decrease in cel-
lular activity (200–300-fold) relative to piperidine 1b (37-
fold). This increased shift may be due to the reduced ba-
sicity of the piperazinone and imidazol-idinone cores
(measured pKa = 6.0, 3.6, respectively). Given that the
BACE1 active site is displayed in an endosomal com-
partment that is slightly acidic (pH ꢁ5), more basic
compounds like piperidines 118 may accumulate inside
the compartment to a larger degree than less basic ana-
logs. The cellular shift of the piperazinone analogs could
be attenuated by lowering their ClogP via changes to
the isophthalamide moiety. In this way we achieved
excellent potency both in vitro and in the cell with ana-
logs 2b–d (cellular IC50 = 57–140 nM).
In conclusion, using X-ray crystallography in conjunc-
tion with molecular modeling, we have designed a series
of novel, potent piperazinone- and imidazolidinone-
based peptidomimetic inhibitors of BACE1. These novel
cyclic amine aspartyl protease binding motifs combine
potency enhancements from simultaneous occupation
of S20 and formation of an additional hydrogen bond
to the flap. Piperazinones 2 in particular are tolerant
of a wide diversity of modifications to their non-prime
side substituents, and we have identified many analogs
with BACE1 IC50 < 20 nM, a number of which have cel-
lular potency below 200 nM. Two of these new com-
pounds, piperazinone 2a and imidazolidinone analog
3a, produced modest inhibition of peripheral Ab40 in a
We next turned our attention to pyrrolidinone and cyc-
lic urea non-prime side derivatives (Table 2). Interest-
ingly, the piperazinone core was very tolerant of a
variety of these modifications, whereas the imidazolidi-
none core was not. Looking at the first two entries in
Table 2, piperazinone analogs 2e and 2f both have
BACE1 IC50 < 10 nM versus the imidazolidinone ana-
logs 3e and 3f with BACE1 IC50 > 100 nM. In the third
entry, introduction of additional substitution on the
pyrrolidinone ring restored some potency to the imi-
dazolidinone analog 3g, but it was still nearly 30-fold
less active than the corresponding piperazinone 2g.
Table 3. SAR of modification of the substituents in S20 from the 4-
position of the piperazinone ring (Ar = 3,5-difluorophenyl)16
OH
H
N
H
N
Pr2N
O
O
O
N
R
Ar
Compound
R
BACE1 IC50 (nM) Cell IC50 (nM)
2o
2p
2q
2r
H
264
235
175
44
13
10
3
7500
7000
Me
Et
Pr
Examination of a wider array of pyrrolidinones as well
as cyclic urea derivatives in the piperazinone series pro-
duced a set of analogs 2h–n that generally showed excel-
lent potency against BACE1 (IC50 = 9–22 nM). The
rightward shift in cellular potency remained high
(P40-fold) for these analogs. It is noteworthy that the
tolerance of the piperazinone series for non-prime side
variation was not seen in our piperidine series,19 and
4000
2000
915
2s
CH2i-Pr
CH2c-Pr
CH2Ph
2t
2a
2u
2v
2w
2x
300
550
CH2(o-MeOPh)
CH2(o-CNPh)
CH2(o-ClPh)
Ph
5
20
27
345
970
755
10,000

3240
J. N. Cumming et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3236–3241
Table 4. Detailed in vivo, in vitro, and ancillary profiles of piperaz-
inone 2a and imidazolidinone 3a (Ar = 3,5-difluorophenyl)
Pearson, J.; Strome, R.; Zuke, N.; Loukides, J.; French, J.;
Turner, S.; Lozza, G.; Grilli, M.; Kunicki, S.; Morissette,
C.; Paquette, J.; Gervais, F.; Bergeron, C.; Fraser, P.;
Carlson, G.; George-Hyslop, P. St.; Westaway, D. J. Biol.
Chem. 2001, 276, 21562; (d) Hock, C.; Konietzko, U.;
Streffer, J. R.; Tracy, J.; Signorell, A.; Muller-Tillmanns,
B.; Lemke, U.; Henke, K.; Moritz, E.; Garcia, E.;
Wollmer, M. A.; Umbricht, D.; de Quervain, D. J.;
Hofmann, M.; Maddalena, A.; Papassotiropoulos, A.;
Nitsch, R. M. Neuron 2003, 38, 547.
OH
H
N
H
N
Pr2N
( )n
O
O
O
N
Ar
Bn
Assay
CRND8 mouse plasma Ab40
Plasma concentration (ng/mL)
Brain concentration (ng/g)
B/P ratio
2a (n = 1)
3a (n = 0)
3. For an overview of BACE1 biology, see Vassar, R. J. Mol.
Neurosci. 2004, 23, 105.
a
ꢀ65 8%
4020
200
ꢀ43 6%
4660
120
4. Efforts towards BACE1 inhibitors have been reviewed: (a)
Ghosh, A. K.; Bilcer, G.; Hong, L.; Koelsch, G.; Tang, J.
Curr. Alzheimer Res. 2007, 4, 418; (b) Durham, T. B.;
Shepherd, T. A. Curr. Opin. Drug Discovery Dev. 2006, 9,
776; (c) Guo, T.; Hobbs, D. W. Curr. Med. Chem. 2006,
13, 1811; (d) Thompson, L. A.; Bronson, J. J.; Zusi, F. C.
Curr. Pharm. Design 2005, 11, 3383; (e) Cumming, J. N.;
Iserloh, U.; Kennedy, M. E. Curr. Opin. Drug Discovery
Dev. 2004, 7, 536.
5. Modest developmental phenotypes in BACE1 knockout
mice have recently been identified (a) Willem, M.; Garratt,
A. N.; Novak, B.; Citron, M.; Kaufmann, S.; Rittger, A.;
DeStrooper, B.; Saftig, P.; Birchmeier, C.; Haass, C.
Science 2006, 314, 664; (b) Dominguez, D.; Tournoy, J.;
Hartmann, D.; Huth, T.; Cryns, K.; Deforce, S.; Serneels,
L.; Camacho, I. E.; Marjaux, E.; Craessaerts, K.; Roeb-
roek, A. J. M.; Schwake, M.; D’Hooge, R.; Bach, P.;
Kalinke, U.; Moechars, D.; Alzheimer, C.; Reiss, K.;
Saftig, P.; De Strooper, B. J. Biol. Chem. 2005, 280, 30797.
6. McConlogue, L.; Buttini, M.; Anderson, J. P.; Brigham,
E. F.; Chen, K. S.; Freedman, S. B.; Games, D.; Johnson-
Wood, K.; Lee, M.; Zeller, M.; Liu, W.; Motter, R.; Sinha,
S. J. Biol. Chem. 2007, 282, 26326.
0.07
17
0.03
3
Caco-2 efflux ratio (A-B/B-A)
BACE1 IC50 (nM)
BACE2 IC50 (nM)
Cell IC50 (nM)
3
5
22
300
47
30
11
51
1100
32
2
Cathepsin D Ki (nM)
Cathepsin E Ki (nM)
Pepsin Ki (nM)
4
a Four animals per compound, 100 mg/kg sc dose, Ab40 measured at
3 h post-dose. Levels of Ab40 are expressed as mean standard error
as a percent of vehicle. For additional general experimental details,
see Ref. 21.
transgenic mouse model with a single dose. SAR around
other, related cyclic amine scaffolds that similarly
capture an additional hydrogen bond to the flap will
be reported in due course.
7. (a) Iserloh, U.; Wu, Y.; Cumming, J. N.; Pan, J.; Wang,
L. Y.; Stamford, A. W.; Kennedy, M. E.; Kuvelkar, R.;
Chen, X.; Parker, E. M.; Strickland, C.; Voigt, J.
Bioorg. Med. Chem. Lett. 2008, 18, 414; (b) Iserloh, U.;
Pan, J.; Stamford, A. W.; Kennedy, M. E.; Zhang, Q.;
Zhang, L.; Parker, E. M.; McHugh, N. A.; Favreau, L.;
Strickland, C.; Voigt, J. Bioorg. Med. Chem. Lett. 2008,
18, 418.
8. We employed both the de novo design method Allegrow
(v. 020802, Boston De Novo, Boston, MA) as well as
minimization using the Polak-Ribiere conjugated gradient
algorithm until convergence of 0.001, CFF91 force field,
Insight 2000/CDISCOVER (Accelrys Inc., San Diego,
CA).
Acknowledgments
The authors thank Dr. C. McNemar for pKa determina-
tions on analogs 2a and 3a and Dr. William Greenlee for
continued support. This work is based upon research
conducted at the Cornell High Energy Synchrotron
Source (CHESS), which is supported by the National
Science Foundation under award DMR 0225180, using
the Macromolecular Diffraction at CHESS (Mac-
CHESS) facility, which is supported by award RR-
01646 from the National Institutes of Health, through
its National Center for Research Resources.
9. During the preparation of this manuscript, another report
published of similar imidazolidinone peptido-mimetic
BACE1 inhibitors: Barrow, J. C.; Rittle, K. E.; Ngo, P.
L.; Selnick, H. G.; Graham, S. L.; Pitzenberger, S. M.;
McGaughey, G. B.; Colussi, D.; Lai, M.; Huang, Q.;
Tugusheva, K.; Espeseth, A. S.; Simon, A. J.; Munshi, S.
K.; Vacca, J. P. Chem Med Chem 2007, 2, 995.
10. Prepared from commercially available Boc-3,5-difluor-
ophenylalanine: Reetz, M. T.; Drewes, M. W.; Schwic-
kardi, R. Org. Synth. 1999, 76, 110.
11. (a) Reetz, M. T.; Drewes, M. W.; Schmitz, A. Angew.
Chem. Int. Ed. Engl. 1987, 26, 1141; For an extensive
review of this chemistry, see (b) Reetz, M. T. Chem. Rev.
1999, 99, 1121.
12. The 5-methyl-N,N-dipropylisophthalamide group has
been used extensively in the patent and journal literature:
Maillaird, M.; Hom, R.; Gailunas, A.; Jagodzinska, B.;
Fang, L. Y.; John, V.; Freskos, J. N.; Pulley, S. R.; Beck,
J. P.; Tenbrink, R. E. PCT Int. Appl. WO 2002002512,
2002.
References and notes
1. General reviews of Alzheimer’s Disease: (a) Nguyen, J.;
Yamani, A.; Kiso, Y. Curr. Pharm. Design 2006, 12, 4295;
(b) Zimmermann, M.; Gardoni, F.; Di Luca, M. Drugs
Aging 2005, 22, 27; (c) Citron, M. Nat. Rev. Neurosci.
2004, 5, 677; (d) For excellent online references to general
information and statistics about Alzheimer’s disease, as
well as ongoing research in the field, see http://www.
alz.org and http://www.ahaf.org.
2. An abundance of genetic and biochemical evidence has
been reported that link the etiology of AD to Ab-mediated
toxicity: (a) St. George-Hyslop, St. P. H. P. H. Biol.
Psychiatry 2000, 47, 183; (b) Patterson, D.; Gardiner, K.;
Kao, F. T.; Tanzi, R.; Watkins, P.; Gusella, J. F. Proc.
Natl. Acad. Sci. U.S.A. 1988, 85, 8266; (c) Chishti, M. A.;
Yang, D. S.; Janus, C.; Phinney, A. L.; Horne, P.;

J. N. Cumming et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3236–3241
3241
13. Made by treatment of 3-benzyl-imidazolidin-4-one (Pfeif-
fer, U.; Riccaboni, M. T.; Erba, R.; Pinza, M. Liebigs Ann.
Chem. 1988, 993) with Boc2O/Et3N, 83%.
were determined by incubating HEK293 cells, stably
transfected with the human APP cDNA containing both
Swedish and London FAD mutations, with increasing
concentrations of BACE inhibitors. Ab40 levels were
measured in the cell culture media using an Ab1ꢀ40
specific ELISA assay: (b) Zhang, L.; Song, L.; Terracina,
G.; Liu, Y.; Pramanik, B.; Parker, E. Biochemistry 2001,
40, 5049.
14. (a) The (2R)-methoxymethyl)pyrrolidine-5-methyl isoph-
thalamide moiety in analogs 2b and 3b (Table 1) was first
reported by Elan Pharmaceuticals and Pfizer: John, V.;
Maillard, M.; Jagodzinska, B.; Beck, J. P.; Gailunas, A.;
Fang, L.; Sealy, J.; Tenbrink, R.; Freskos, J.; Mickelson, J.;
Samala, L.; Hom, R. PCT Int. Appl. WO 2003040096,
2003.; (b) The requisite acids for the 5-methoxy isophthal-
amide analog 2c and the pyridine dicarboxamide analog 2d
(Table 1) were made by treatment of the corresponding
diacids with ((2R)-methoxymethyl)pyrroldine, EDCI,
HOBT (10–45%); (c) The requisite acids for the cyclic urea
derivatives 2l and 2m were made from (4S)-3-benzyloxy-
carbonyl-2-oxoimidazolidine-4-carboxylate (Hayashi, K.;
Nunami, K.; Kato, J.; Yoneda, N.; Kubo, M.; Ochiai, T.;
Ishida, R. J. Med. Chem. 1989, 32, 289): (i) NaH, alkyl
halide; (ii) H2, Pd(OH)2; (iii) NaH, alkyl halide.
15. Coordinates for the X-ray structure of inhibitors 1b, 1c, 2a
and 3a complexed with BACE1 with have been deposited
in the Protein Data Bank (www.rcsb.org), and can be
accessed under PDB ID 3CIB, 2QP8, 3CIC and 3CID.
16. Inhibition of BACE1 in vitro was determined using an
APP-derived peptide containing the Swedish mutant: (a)
Kennedy, M. E.; Wang, W.; Song, L.; Lee, J.; Zhang, L.;
Wong, G.; Wang, L.; Parker, E. Anal. Biochem. 2003, 319,
49; Cellular IC50 values for inhibition of Ab40 production
17. Calculated using CLOGP version 4.3 (BioByte Corpora-
tion, Claremont, CA).
18. Predicted pKa values for simple 4-benzylpiperidine and 4-
ethoxypiperidine are ꢁ10–11 (SciFinder 2007).
19. For example, the corresponding analog of 2f with the 4-
benzyl-piperazin-3-one core replaced by 4-ethoxy-piperi-
dine group, BACE1 IC50 = 250 nM (unpublished results).
20. To make the desired variations of the lactam nitrogen
substituents, the requisite piperazinone cores were made
from commercially-available piperazin-2-one: (i) Boc2O;
(ii) NaH, alkyl halide. The resulting 4-substituted pipera-
zinones were then substituted for core 5 in Scheme 1.
21. CRND8-APP mice are models for early onset (familial)
AD that express human APP containing both Swedish and
London mutations that enhance the rate of APP cleavage
by BACE1 and favor production of Ab42 over Ab40 in the
c-secretase cleavage step: Hyde, L. A.; Kazdoba, T. M.;
Grilli, M.; Lozza, G.; Brussa, R.; Zhang, Q.; Wong, G. T.;
McCool, M. F.; Zhang, L.; Parker, E. M.; Higgins, G. A.
Behav. Brain Res. 2005, 160, 344.