Novel peptidomimetics as BACE-1 inhibitors: Synthesis, molecular modeling, and biological studies

Article abstract of DOI:10.1016/j.bmcl.2012.11.011

Aiming at identifying new scaffolds for BACE-1 inhibition devoid of the pharmacokinetic drawbacks of peptide-like structures, we investigated a series of novel peptidomimetics based on a 1,4-benzodiazepine (BDZ) core 1a-h and their seco-analogues 2a-d. We herein discuss synthesis, molecular modeling and in vitro studies which, starting from 1a, led to the seco-analogues (R)-2c and (S)-2d endowed with BACE-1 inhibition properties in the micromolar range both on the isolated enzyme and in cellular studies. These data can encourage to pursue these analogues as hits for the development of a new series of BACE-1 inhibitors active on whole-cells.

Full text of DOI:10.1016/j.bmcl.2012.11.011

Bioorganic & Medicinal Chemistry Letters 23 (2013) 85–89
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Novel peptidomimetics as BACE-1 inhibitors: Synthesis, molecular
modeling, and biological studies
Stefania Butini a, Emanuele Gabellieri a, Margherita Brindisi a, Alice Casagni a, Egeria Guarino a,
Paul B. Huleatt a, Nicola Relitti a, Valeria La Pietra a,b, Luciana Marinelli a,b, Mariateresa Giustiniano a,b
,
a
Ettore Novellino a,b, Giuseppe Campiani a, , Sandra Gemma
⇑
a European Research Centre for Drug Discovery and Development (NatSynDrugs), Università degli Studi di Siena, Via Aldo Moro 2, 53100 Siena, Italy
b Dipartimento di Chimica Farmaceutica e Tossicologica, Università degli Studi di Napoli ‘Federico II’, Via D. Montesano 49, I-80131 Napoli, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Aiming at identifying new scaffolds for BACE-1 inhibition devoid of the pharmacokinetic drawbacks of
peptide-like structures, we investigated a series of novel peptidomimetics based on a 1,4-benzodiazepine
(BDZ) core 1a–h and their seco-analogues 2a–d. We herein discuss synthesis, molecular modeling and
in vitro studies which, starting from 1a, led to the seco-analogues (R)-2c and (S)-2d endowed with
BACE-1 inhibition properties in the micromolar range both on the isolated enzyme and in cellular studies.
These data can encourage to pursue these analogues as hits for the development of a new series of BACE-
1 inhibitors active on whole-cells.
Received 11 September 2012
Revised 31 October 2012
Accepted 6 November 2012
Available online 14 November 2012
Keywords:
BACE-1
Benzodiazepines
Alzheimer’s disease
Memapsin 2
b-Secretase
Ó 2012 Elsevier Ltd. All rights reserved.
Alzheimer’s disease (AD), one of the most prevalent neurode-
generative disorders among the elderly, is pathologically charac-
terized by the extracellular accumulation of amyloid-b (Ab)
plaques and by intracellular neurofibrillary tangles. Considerable
evidence indicates a central role of the Ab peptide and its aggrega-
tion in the pathogenesis of AD.1 High levels of soluble Ab peptides
correlate to cognitive decline in AD2,3 and the original amyloid cas-
cade hypothesis has evolved to propose that soluble oligomeric Ab
assemblies precede deposition and are the proximal cause of syn-
aptic dysfunction and early impairment in AD.4 Ab40 and Ab425
are the two major isoforms of Ab found in AD brains. Although
the Ab40 is the most abundant isoform, Ab42 is enriched in AD
brains as it progressively accumulates into extracellular senile pla-
ques.4 The proteolytic enzyme b-secretase (BACE-1) catalyzes the
rate-limiting step of the Ab generation by cleaving the Met671–
Asp672 peptide bond of amyloid precursor protein (APP) at the
extracellular space.6,7 Currently available therapies for AD only
treat disease symptoms and do not address the underlying disease
processes.8 On the basis of a number of seminal in vitro and in vivo
studies the aspartic protease BACE-1 has been recognized as a rel-
evant drug target for the development of AD disease-modifying
therapies.9 BACE-1 potent inhibitors have been produced by aca-
demic and industrial research.10 However very few of them fulfill
the requirements for in vivo biological and clinical studies and only
recently, orally available highly efficient BACE-1 inhibitors became
available.11 To identify new scaffolds for BACE-1 inhibition to over-
come the well-known pharmacokinetic drawbacks of peptide-like
structures, we decided to search for novel peptidomimetic com-
pounds based on the C8/C9-substituted 1,4-benzodiazepine (BDZ)
structural system or on the seco-1,4-BDZ scaffold, represented by
the core structures 1 and 2 depicted in Figure 1.
The BDZ system has not been explored to date for developing
BACE-1 inhibitors, and the BDZ system is one of the most impor-
tant privileged pharmacogenic structures for drug discovery en-
dowed with a high degree of druggability. This prompted us to
develop compounds 1a–h. Furthermore, we recently discovered a
versatile synthetic protocol for the synthesis of C8 and C9 modified
R1
O
H
N
O
R
*
NHCbz
R
R1
NH
*
N
O
* = (R) or (S) config
R and R1 as defined
in Table 1
1a-h
2a-d
⇑
Corresponding author. Tel.: +39 0577 234172; fax: +39 0577 234333.
E-mail address: campiani@unisi.it (G. Campiani).
Figure 1. Title compounds: benzodiazepines 1a–h and seco-analogues 2a–d.
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.11.011

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S. Butini et al. / Bioorg. Med. Chem. Lett. 23 (2013) 85–89
Table 1
1,4-BDZs which gave us the opportunity to investigate BDZs bear-
ing at these positions protonatable and non-protonatable func-
tions.12 Thus, we started our research program with the
synthesis and evaluation of a series of BDZs and their seco-ana-
logues (1 and 2, Fig. 1). In particular the compounds were function-
BACE-1 inhibition activity of compounds 1a–h and 2a–d as IC50 (l
M)a
R1
*
O
O
O
N
H
O
H
9
R
R
4
N
3
NH
8
R1
*
alized with
a
piperazine group at C9 and/or with the
N 3
O
hydroxyethylamine (HEA) moiety introduced at various positions
of the BDZ scaffold of 1 and of the seco-BDZs 2 (see Table 1).
Compounds 1a,b were prepared as described in Scheme 1 fol-
lowing a synthetic procedure previously described for the prepara-
A
B
R1
IC50
43
(lM)
b
Compd
A/B
A
R
tion of analogues 1c,d.12 The
L- or D-Cbz-protected phenylglycines
Boc
were activated by means of hexachloroacetone (HCA) and triphen-
ylphosphine, and then treated with the piperazino-substituted
aminobenzophenone 312 to give compound 2a. After deprotection
and cyclization (R)- and (S)-1a were obtained. Treatment of (S)-1a
with HCl gave the amine (S)-1b.
N
(R)-1a
N
C9
Boc
N
The synthesis of the BDZ scaffold necessary for the preparation
of the C8-hydroxyethylamino-BDZs was performed starting from
the benzophenone 412 (Scheme 2) which was coupled with Cbz
or Fmoc protected phenylglycine and successively exposed to trib-
utylvinyl tin13 to give 5a,b. These latter compounds were oxidized
in the presence of m-chloroperbenzoic acid (m-CPBA). The epoxide
ring 6a (obtained as a mixture of two diasteroeisomers) was sub-
jected to a nucleophilic ring opening reaction by exposure to N-
Boc-piperazine. The resulting hydroxyethylamino-derivative 2b
was obtained in good yield. When 6a was treated with benzyl-
amine in the presence of lithium perchlorate14 both regioisomers
were obtained (2c and 2d). Deprotection of N-Cbz 2b followed by
cyclization furnished compound 1e. Starting from 2c,d, deprotec-
tion of the N-Cbz under different reaction conditions was unsuc-
cessful, so the corresponding N-Fmoc protected derivatives 2e,f
were prepared. Deprotection of the Fmoc-group in the presence
of diethylamine was achieved and the intermediates were cyclized
to 1f,g. Scheme 3 reports the synthesis of 1h. Starting from the
(S)-1a
(S)-1b
(S)-1c
A
A
A
35
N
C9
H
N
NAc
NAc
N
C9
Boc
N
N
C9
Boc
N
(S)-1d
(R)-1e
A
A
NAc
N
C9
commercially available aminobenzophenone 7, coupling with L-
Boc
N
Cbz-Met followed by a m-CPBA oxidation provided the sulfoxide
(S)-8. The sulfoxide was then submitted to a thermal elimination
reaction by refluxing in xylene ((S)-9). The olefin 9 was oxidized
to the corresponding epoxide 10 (mixture of two diastereoisomers)
which was reacted with N-Boc-piperazine. After N-Cbz and N-Boc
deprotection and cyclization, 1h was obtained.
NAc
NAc
OH
C8
N
H
OH
C8
OH
(R)-1f
(R)-1g
(S)-1h
A
A
A
N
The BDZs 1a–h and the seco-analogues 2a–d, bearing or not the
HEA substructure, were tested against the isolated BACE-1 enzyme
in fluorescence-based assays (Table 1). Analytical data for the
tested compounds are given as Supplementary Information (SI).
HEA fragment is a peptide cleavage transition state mimetic, which
found multiple applications in targeting aspartyl proteases.15 Con-
sequently, to improve solubility, the piperazine moiety, present in
1a–d (1a, LogS = ꢀ4.77, 1b, LogS = ꢀ1.83, calculated at pH 7, ACD/
Labs V12.0, Toronto, Canada), was combined to the HEA fragment
(1e,h) (1e, LogS = ꢀ4.37, 1h, LogS = 0.44). To evaluate the effect
of the piperazine ring we synthesized analogues 1f,g exclusively
bearing the HEA moiety. In the BDZs series only 1a, 1g and 1h
showed inhibition of BACE-1 in the micromolar range (Table 1).
Starting from 1a we also investigated the stereoselectivity of inter-
action and we observed that (R)-1a and (S)-1a showed a compara-
ble potency. Removal of the carbamoyl moiety from 1a
dramatically reduced potency (1b). Moreover, tethering the phenyl
ring at C3 of 1a by one or two methylenes led to inactive analogues
(1c and 1d). The BDZ core structure was also decorated at C8 or C3
with HEA functionalities bearing or not the piperazine system (1e–
h). Compounds 1e,f present a substitution at the HEA-carbon atom
bearing the OH, while the HEA fragment of 1g,h was substituted on
the carbon atom close to the nitrogen. As regard to 1b and 1f, when
only the piperazine (1b) or the HEA group (1f) is present, neither
10.9
12.5
N
H
C8
OH
—
NH
N
Boc
N
(S)-2a
(R)-2b
B
B
NAc
4.9
N
C3
Boc
N
OH
C4
N
H
OH
C4
(S)-2c
(R)-2c
B
B
2.4
2.6
N
H
N
OH
C4

S. Butini et al. / Bioorg. Med. Chem. Lett. 23 (2013) 85–89
87
MeOS
Table 1 (continued)
Cbz
NH2
H
b
R1
IC50
4.1
(lM)
N
H
Cbz
Compd
A/B
R
N
H
N
a, b
c
O
N
H
O
O
OH
OH
O
O
(S)-2d
B
N
H
C4
7
(R)-2d
B
4.2
N
H
b
C4
9
8
O
a
Tests were performed on the isolated BACE-1 enzyme as previously described,16
Cbz
O
H
H
N
experimental details are given as SI.
N
N
NH
N
H
b
*
d,e,f,g
Each value is the mean of at least three experiments (all SD are within 10% of
O
O
the mean).
OH
N
c
NA not active at 100 lM.
1h
10
R
N
Boc
N
-Cbz-Met, HCA, PPh3, DCM, ꢀ10 °C, 300,
Boc
N
Scheme 3. Reagents and conditions: (a)
L
then rt, 50, 56%; (b) m-CPBA, DCM, 0 °C, 2 h, 62% for 8, 87% (76:24 dr) for 10; (c)
xylene, 200 °C, sealed tube, 3 h, 45%; (d) N-Boc-piperazine, EtOH, reflux, 24 h, 56%;
(e) Pd/C 10%, 1,4-cyclohexadiene, EtOH, reflux, 24 h, 99%; (f) AcCl, dry MeOH, 60 °C,
300, 99%; (g) EtOH, reflux, 24 h, 57%.
Cbz
b
N
N
N
H
H
O
N
*
N
N
NH2
a
O
H
*
O
N
O
the configuration at the aminoacidic carbon did not influence
activity ((R)-2c,d vs (S)-2c,d). The seco-analogue 2d again proved
to be more potent than the BDZs counterpart 1g.
3
2a
R = Boc, (
R)- and (S)-1a
c
R = H, ( )-1b
S
This structure–activity relationship (SAR) analysis was rational-
ized at the molecular level by means of docking studies (Auto-
Dock4.2 program) performed with our ligands into the BACE-1
active site. BACE-1 is a structurally challenging protein target,
which displays a pronounced induced-fit upon ligand interaction.
Indeed, a detailed comparison of the available X-ray structures
suggests that the flap region (residues 68–74) of the enzyme
undergoes a massive rearrangement upon ligand binding, as well
as the 10s-loop (residues 9–14).17,18 Thus, we selected for docking
studies five X-ray structures representative for the enzyme flexibil-
ity. Particularly, we chose 1XN3 (PDB code) as representative of the
flap region open conformation, while 1FKN, 1W51 and 1TQF were
chosen to represent the closed, the open and the outlier conforma-
tion of the 10s-loop.17,18 These four structures, together with the
2G94, also account for side chains flexibility of key active site res-
idues (L30, R128, K224, R235, R307). Docking of our ligands using
each of the five BACE-1 X-ray structures provided similar results.
However, results obtained using 1W51 and 1FKN better suited
with the experimentally determined IC50. Thus, we will herein dis-
cuss the poses found in 1W51 (highly similar to those found in
1FKN).
Scheme 1. Reagents and conditions: (a) L- or D-Cbz-Phenyl-Gly, HCA, PPh3, DCM,
ꢀ10 °C, 300 then rt, 50, 95%; (b) Pd/C 10%, 1,4-cyclohexadiene, EtOH, reflux, 24 h,
93%; (c) AcCl, MeOH, 60 °C, 300, 99%.
Br
NH2
O
P
P
H
H
N
N
O
*
N
N
*
H
H
O
O
O
O
c
a, b
4
d
6a,b
5a,b
P = Cbz, Fmoc
P
H
N
H
N
O
N
*
R
H
R
O
O
e/f, g
N
Analysis of the docking structure of (S)-1a into the BACE-1 en-
zyme revealed that the BDZ scaffold lies under the flap region
(Fig. 2, and SI for experimental details). The R substituent present
on the BDZ core (N-Boc piperazine) occupies the S20 pocket with
no H-bonding to the Asp residues (D32 and D228) at the catalytic
2b-d, P = Cbz, R and
1e-g
configuration as in Table 1
R as in Table 1
(
R
)-2e,f, P = Fmoc, R as for 1f,g
Scheme 2. Reagents and conditions: (a)
L
- or
D
-Cbz or Fmoc-Phenyl-Gly, HCA, PPh3,
DCM, ꢀ10 °C, 300, then rt, 50, 83% for Cbz-derivative and 88% for Fmoc-derivative;
(b) Pd(PPh3)4, tributyl(vinyl)tin, dry toluene, reflux, 1 h, 55% for 5a, 60% for 5b; (c)
m-CPBA, DCM, 0 °C, 2 h, 28% for 6a, 53% for 6b; (d) N-Boc-piperazine, EtOH, reflux
24 h, 64% for 2b, LiClO4, benzylamine, MeCN, rt, 1 h, 21–42% for 2c–f; (e) Pd/C 10%,
1,4-cyclohexadiene, EtOH, reflux, 24 h, 99%; (f) Et2NH, DCM, rt, 5 h, 99%; (g) EtOH,
reflux, 24 h, 20–70%.
the protonated nitrogen nor the hydroxyl group are suitably close
to any of the catalytic aspartic residues to engage an interaction, in
contrast with 1g and 1h which regain a certain activity against the
enzyme (with IC50 values of about 10 lM). Several seco-analogues
of BDZs (2a–d, Table 1) were also tested for activity and, with the
exception of (S)-2a, they were found more potent inhibitors than
their BDZ counterparts. Accordingly, the intermediates 2b and 2c
showed a micromolar activity against the enzyme, being more po-
tent than the BDZs 1e,f. Furthermore, as already observed with 1a,
Figure 2. Docked structure of (S)-1a into the BACE-1 (PDB code: 1W51). Ligands
carbon atoms are displayed in golden, and key binding site residues as cyan sticks.

88
S. Butini et al. / Bioorg. Med. Chem. Lett. 23 (2013) 85–89
site. The two phenyl rings at C3 (R1, Table 1) and C5 positions lean
forward the S1 and the S3 cavities, respectively, establishing
hydrophobic contacts with L30, I110 and W115 side chains. These
interactions may account for the micromolar inhibitory potency of
(S)-1a. In line with the experimentally determined IC50, a similar
docking outcome was obtained with the isomer (R)-1a. Consistent
with the binding pose of 1a, and in line with the IC50, the tethering
of the phenyl ring at C3 by one or two methylenes (1c and 1d) and
the introduction of an hydroxyethyl group (1e), resulted in a severe
clash with the S1 pocket wall (due to the BDZ scaffold rigidity), and
in a clash in the S20 pocket respectively. It must be noted that in
compounds 1b and 1f, neither the protonated nitrogen (1b) nor
the hydroxyl group (1f) lay close enough to any of the Asp residues
at the catalytic site for engaging productive interactions. Contras-
tingly, for 1g and 1h a more favorable spatial arrangement of the
HEA portion may account for the micromolar BACE-1 inhibition
potency. In line with the experimental IC50 values docking results
obtained with 1a suggested that the major flexibility of the seco-
analogues, would allow the molecules to better fit within BACE-1
active site. Accordingly, when the most active compound (S)-2c
was docked within the enzyme (Fig. 3a), H-bonding interactions
with the catalytic Asp residues were detected (Fig. 3b). Further-
more, the benzylamine group of (S)-2c occupies the S20 pocket,
establishing a T-shaped interaction with the Y198 side chain and
hydrophobic contacts with I226, T329, S35, and Y71. The o-disub-
a modified BACE cleavage sequence, NFEV and a K612V mutation
which prevents processing by
-secretase.19 The other assay em-
ploys SHSY5Y cells expressing APP NFEV and the wild-type
cleavage site. The compounds were tested to determine their IC50
against the generation of sAPPb (direct functional read out for
a
a-
BACE-1 activity). The determined IC50 values ranged from 2.6
to >22 M in HEK293 cells and from 1.2 M to >22 M in the
SHSY5Y cell line. In more detail, (S)-1g (IC50 >22 M in HEK293,
and IC50 >11 M in SHSY5Y) was in general less potent than the
lM
l
l
l
l
l
seco-compounds. Indeed (R)-2c and (S)-2d were found the most
interesting of the series showing IC50 values in both cell lines rang-
ing from 1.2 lM to 2.6 lM. Activities on cell based assays are in
line with the observed potencies on the isolated enzyme thus sug-
gesting that these scaffolds could be new hits for the development
BACE-1 inhibitors active on whole-cell assays.
In summary, we described a new series of BACE-1 inhibitors
based on a BDZ or a seco-BDZ structure. These compounds repre-
sent the first benzodiazepine compounds disclosed as BACE-1
inhibitors. As shown in Table 1, the seco-analogues proved to be
slightly more potent than BDZs and through docking studies we
have been able to clarify why the BDZ system opening led to an
improvement of the inhibitory potency. Nevertheless, optimization
of the inhibitors is necessary to obtain IC50s in the nanomolar
range and rational modifications of the BDZ scaffold will be guided
by the docking studies here presented. Taken together our molec-
ular modeling studies traced out the experimentally determined
SAR data, explained the higher potency of the seco-BDZs interme-
diates, and highlighted the optimization strategy which is cur-
rently ongoing in our laboratories.
stituted phenyl ring, lying under the flap region, establishes a p–p
stacking with Y71 side chain and hydrophobic contacts with F108
and I118. The phenone moiety of (S)-2c enters the S1 cavity, sur-
rounded by a L30 and I110, engaging a T-shaped interaction with
W115, while the R1 substituent (phenyl ring) plunges into the S3
pocket where no tight interactions are visible. The benzylcarba-
mate branch stretches out over the S3 pocket where an H-bond
is detected between T232 backbone NH and the carbamate car-
Acknowledgments
The Authors thank the European Research Centre for Drug Dis-
covery and Development (NatSynDrugs), MIUR Prin and Regione
Campania L.R. 05/02 grant for financial support. The Authors thank
Dr. Joseph P. Vacca at Merck-USA.
bonyl oxygen; R235 side chain establishes a cation-
p interaction
with the aromatic ring. The experimentally observed lack of stere-
oselectivity of interaction ((S)-2c vs (R)-2c, Table 1) was justified
by the superimposable binding poses obtained for both enantio-
mers. Also the seco-analogues (R)-2b, (R)- and (S)-2d share the
binding mode and enzyme inhibition potency in the low micromo-
lar range with compound 2c (as already observed in the BDZ ser-
ies). Our proposed binding mode could also explain the loss of
activity of compound (S)-2a, where the piperazine moiety at the
C3 faces the active site floor and gives a massive clash.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2012.11.
011.
BACE-1 is a transmembrane protein anchored to the luminal
side of the intracellular compartment. Since some BACE-1 inhibi-
tors active in isolated enzyme-assays fail when tested in cellular
assays, we engaged the most interesting analogues of the series
((S)-1g, (S)-2c, (R)-2c, and (S)-2d) in functional cell-based assays.
One assay used HEK293 cells expressing APP construct containing
References and notes
1. Citron, M. Nat. Rev. Drug Discov. 2010, 9, 387.
2. McLean, C. A.; Cherny, R. A.; Fraser, F. W.; Fuller, S. J.; Smith, M. J.; Beyreuther,
K.; Bush, A. I.; Masters, C. L. Ann. Neurol. 1999, 46, 860.
3. Naslund, J.; Haroutunian, V.; Mohs, R.; Davis, K. L.; Davies, P.; Greengard, P.;
Buxbaum, J. D. JAMA 2000, 283, 1571.
4. Walsh, D. M.; Selkoe, D. J. J. Neurochem. 2007, 101, 1172.
5. Haass, C.; Hung, A. Y.; Schlossmacher, M. G.; Oltersdorf, T.; Teplow, D. B.;
Selkoe, D. J. Ann. N.Y. Acad. Sci. 1993, 695, 109.
6. Yan, R.; Bienkowski, M. J.; Shuck, M. E.; Miao, H.; Tory, M. C.; Pauley, A. M.;
Brashier, J. R.; Stratman, N. C.; Mathews, W. R.; Buhl, A. E.; Carter, D. B.;
Tomasselli, A. G.; Parodi, L. A.; Heinrikson, R. L.; Gurney, M. E. Nature 1999, 402,
533.
7. Vassar, R.; Bennett, B. D.; Babu-Khan, S.; Kahn, S.; Mendiaz, E. A.; Denis, P.;
Teplow, D. B.; Ross, S.; Amarante, P.; Loeloff, R.; Luo, Y.; Fisher, S.; Fuller, J.;
Edenson, S.; Lile, J.; Jarosinski, M. A.; Biere, A. L.; Curran, E.; Burgess, T.; Louis, J.
C.; Collins, F.; Treanor, J.; Rogers, G.; Citron, M. Science 1999, 286, 735.
8. Sadowski, M.; Wisniewski, T. Curr. Pharm. Des. 1943, 2007, 13.
9. De Strooper, B. Physiol. Rev. 2010, 90, 465.
10. Ghosh, A. K.; Brindisi, M.; Tang, J. J. Neurochem. 2012, 120, 71.
11. Sankaranarayanan, S.; Holahan, M. A.; Colussi, D.; Crouthamel, M. C.;
Devanarayan, V.; Ellis, J.; Espeseth, A.; Gates, A. T.; Graham, S. L.; Gregro, A.
R.; Hazuda, D.; Hochman, J. H.; Holloway, K.; Jin, L.; Kahana, J.; Lai, M. T.;
Lineberger, J.; McGaughey, G.; Moore, K. P.; Nantermet, P.; Pietrak, B.; Price, E.
A.; Rajapakse, H.; Stauffer, S.; Steinbeiser, M. A.; Seabrook, G.; Selnick, H. G.;
Shi, X. P.; Stanton, M. G.; Swestock, J.; Tugusheva, K.; Tyler, K. X.; Vacca, J. P.;
Wong, J.; Wu, G.; Xu, M.; Cook, J. J.; Simon, A. J. J. Pharmacol. Exp. Ther. 2009,
328, 131.
Figure 3. Docked structure of (S)-2c into the BACE-1 (PDB code: 1W51), where a
portion of the binding site is visible as cornflower surface. (a) Detailed interaction
mode of (S)-2c with BACE-1 active site residues; (b) ligands carbon atoms are
displayed in golden, and key binding site residues as cyan sticks. H-Bonds are
shown as dark-blue dotted lines.

S. Butini et al. / Bioorg. Med. Chem. Lett. 23 (2013) 85–89
89
12. Butini, S.; Gabellieri, E.; Huleatt, P. B.; Campiani, G.; Franceschini, S.; Brindisi,
M.; Ros, S.; Coccone, S. S.; Fiorini, I.; Novellino, E.; Giorgi, G.; Gemma, S. J. Org.
Chem. 2008, 73, 8458.
17. Cosconati, S.; Marinelli, L.; Di Leva, F. S.; La Pietra, V.; De Simone, A.; Mancini,
F.; Andrisano, V.; Novellino, E.; Goodsell, D. S.; Olson, A. J. J. Chem. Inf. Model.
2012.
13. Krolski, M. E.; Renaldo, A. F.; Rudisill, D. E.; Stille, J. K. J. Org. Chem. 1988, 53,
1170.
18. Limongelli, V.; Marinelli, L.; Cosconati, S.; Braun, H. A.; Schmidt, B.; Novellino,
E. ChemMedChem 2007, 2, 667.
14. Chini, M.; Crotti, P.; Macchia, F. J. Org. Chem. 1991, 56, 5939.
15. Zhu, Z. Trends Pharmacol. Sci. 2012.
16. Porcari, V.; Magnoni, L.; Terstappen, G. C.; Fecke, W. Assay Drug Dev. Technol.
2005, 3, 287.
19. Pietrak, B. L.; Crouthamel, M. C.; Tugusheva, K.; Lineberger, J. E.; Xu, M.;
DiMuzio, J. M.; Steele, T.; Espeseth, A. S.; Stachel, S. J.; Coburn, C. A.; Graham, S.
L.; Vacca, J. P.; Shi, X. P.; Simon, A. J.; Hazuda, D. J.; Lai, M. T. Anal. Biochem.
2005, 342, 144.