Design, synthesis and evaluation of acridin-9-yl hydrazide derivatives as BACE-1 inhibitors

Article abstract of DOI:10.1007/s00044-016-1581-3

BACE-1, an aspartyl protease is implicated in Alzheimer’s disease. In this paper, we report BACE-1 inhibitory potential of acridin-9-yl hydrazide derivatives, known to inhibit other aspartyl proteases. The derivatives were designed based on the docking st

Full text of DOI:10.1007/s00044-016-1581-3

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res
DOI 10.1007/s00044-016-1581-3
ORIGINAL RESEARCH
Design, synthesis and evaluation of acridin-9-yl hydrazide
derivatives as BACE-1 inhibitors
Priti Jain1,2 Pankaj K. Wadhwa1 Hemant R. Jadhav1,2
•
•
Received: 18 November 2015 / Accepted: 11 April 2016
Ó Springer Science+Business Media New York 2016
Abstract BACE-1, an aspartyl protease is implicated in
Alzheimer’s disease. In this paper, we report BACE-1
inhibitory potential of acridin-9-yl hydrazide derivatives,
known to inhibit other aspartyl proteases. The derivatives
were designed based on the docking study, synthesized and
assessed for BACE-1 inhibition in vitro. Docking simula-
tion predicted the binding of prototype acridin-9-yl
hydrazide at BACE-1 active site. The enzyme–inhibitor
complex was primarily stabilized by hydrogen bonds
between the hydrazide part of the inhibitor and side chain
of Gly11, which is important amino acid of 10s loop. The
acridinyl moiety showed p–p stacking with Tyr71 while
the phenyl ring was buried in S1 cavity. Enzyme inhibition
experiments showed that the synthesized compounds had
moderate activity with compound AA-13 having 54.54 %
inhibition at 10 lM concentration.
Introduction
Aspartyl proteases are proteolytic enzymes belonging to the
family of endonucleases. These are widely distributed and
play important role in overall health and physiology (e.g.,
renin, chymosin, pepsin, napsin-A) as well as pathophysi-
ology of various diseases. Their role is established in malaria
(plasmepsins) (Azim et al., 2008), AIDS (HIV protease)
(Debouck, 1992), neoplastic disorders (cathepsin) (Fusek
and Vetvicka, 1995) and neurodegenerative disorders
(BACE-1 in Alzheimer’s) (Jain and Jadhav, 2011).
Alzheimer’s disease (AD) is a neurological disorder
leading to memory loss and cognitive decline. So far, the
drugs approved for AD, such as cholinesterase inhibitors
(donepezil, rivastigmine, galantamine, tacrine) and NMDA
receptor antagonist (memantine), are symptomatic and do
not stop the progression of disease (Cumming, 1998).
Hence, there are no drugs that stop or slow down the dis-
ease progression. Amyloid plaques and neurofibrillary
tangles (NFTs) proposed in amyloid cascade hypothesis are
the pathological hallmark for AD. As per this hypothesis,
when amyloid precursor protein (APP) gets cleaved by
secretases (b and c) in a sequential fashion, it generates b-
amyloid, i.e., Ab-42, which is hydrophobic and fibrillo-
genic (Jain and Jadhav, 2013). It aggregates to form oli-
gomers, accumulates in the brain and initiates a cascade of
events that lead to neuronal dysfunctioning, neurodegen-
eration and neuronal fatality. Since, BACE-1 or b-secretase
leads to the catalytic cleavage of APP, its inhibition can
lead to reduction in Ab-42 production (Suzuki et al., 1994;
Asami et al., 1995; Shimizu et al., 2008). BACE-1
knockout mice lacked Ab expression and had no ill health
effects (Asami et al., 1995).
Keywords Acridin-9-yl hydrazides Á BACE-1 inhibition Á
Alzheimer’s disease Á Docking study
& Hemant R. Jadhav
hemantrj@pilani.bits-pilani.ac.in
Priti Jain
pritijain@pilani.bits-pilani.ac.in
Pankaj K. Wadhwa
pankaj.wadhwa@pilani.bits-pilani.ac.in
1
Computational Chemistry Laboratory, Department of
Pharmacy, Birla Institute of Technology and Science Pilani,
Pilani Campus, Pilani, Rajasthan 333 031, India
2
Medicinal Chemistry Laboratory, Department of Pharmacy,
Birla Institute of Technology and Science Pilani, Pilani
Campus, Pilani, Rajasthan 333 031, India
The 3D crystal structure of BACE-1 co-crystallized with
different ligands reveals the basic requirements and the key
123

Med Chem Res
features needed for enzyme inhibition. BACE-1 has a cat-
alytic aspartate dyad and three hydrophobic pockets S1, S20
and S3. The inhibitor must have: (1) a group that acts as
H-bond donor to form H-bonding interactions with catalytic
Asp228 and Asp32, (2) hydrophobic groups to occupy S1
cavity (formed by the side chains of Tyr71, Phe108, Trp115,
Ile118 and Leu30) and S3 (formed by side chains of Trp115
and Ile110, as well as main chains of Gln12, Gly11, Gly230,
Thr231, Thr232 and Ser35), (3) polar groups to bind in S20
cavity having Ile126, Trp76, Val69, Arg128, Tyr198 amino
acid residues (Jain et al., 2016).
the inhibitor and Asp32. The acridinyl moiety showed p–p
stacking with Tyr71, occupied the S20 region while the
phenyl ring was buried in S1 cavity. It showed significant
interactions, accommodation of substrate-binding clefts and
a good docking score which was better than the standard
ligand 6IP-389. Based on these observations, a library of
derivatives with various electron-donating and electron-
withdrawing substituents was synthesized (Scheme 1) to
study the effect of substituents on BACE-1 inhibition.
Azim et al. have reported acridinyl hydrazides as potent
inhibitors of cathepsin-D and plasmepsin-II (Azim et al.,
2008). However, inhibition of BACE-1 by these compounds
is hitherto not been studied. Hence, in this study, we have
tried to explore acridin-9-yl hydrazide derivatives as BACE-
1 inhibitors for the treatment of Alzheimer’s disease.
Materials and methods
General
Reaction progress was monitored by TLC using precoated
silica gel G plates (Keiselgel 60F254, Merck) and visualized
using UV light. Melting points were measured with Buchi
530 melting point apparatus and were uncorrected. 1H NMR
spectra were recorded on a Bruker Avance 400 MHz system
using DMSO as solvent. Chemical shifts (d) are reported in
parts per millions (ppm) relative to TMS as internal stan-
dard. FTIR spectra were performed on IR Prestige 21 Shi-
madzu using KBr as standard. Mass spectra were recorded
on Waters Acquity instrument in electrospray mode. Unless
otherwise stated, all reagents were obtained from commer-
cial suppliers and used without further purification. Com-
pounds were named as per ChemDraw Ultra 11.0 software.
Design
In the last decade, several drug discovery strategies have
been exploited in search of BACE-1 inhibitors. The inhi-
bitors with therapeutic potential would require, besides
good potency and pharmacokinetic properties, low
molecular weight (\500 daltons) and high lipophilicity in
order to penetrate the blood–brain barrier. Keeping this in
mind and knowing that acridine derivatives are reported to
inhibit aspartyl proteases, we attempted to design acridin-
9-yl hydrazide derivatives for BACE-1 inhibition.
General procedure for the synthesis of 9-hydrazinyl
acridine (1)
Compound AA-11 (Fig. 1) was conceived as prototype
and was docked in BACE-1 protein (PDB id: 2OHP). It was
observed that the enzyme–inhibitor complex was primarily
stabilized by hydrogen bonds between the hydrazide part of
9-aminoacridine was dissolved in concentrated hydrochlo-
ric acid (HCl) and cooled to about 0 °C. Cooled solution of
Fig. 1 a Chemical structure of AA-11, b 2D interaction plot of AA-11
123

Med Chem Res
Scheme 1 Reagents and
conditions: a NaNO2, HCl, -5
to 0 °C, 1 h; SnCl2, HCl,
b HOBt, EDC HCl, THF, TEA,
substituted carboxylic acids,
0 °C, 12 h
N0-(Acridin-9-yl)-3-fluorobenzohydrazide (AA-12) Yield:
72.42 %, mp 290 °C, IR (cm-1): 3390.49 (sec. N–H
stretching), 3235.14 (Amide N–H stretch), 1631.78 (C=O
sodium nitrite in water (1.1 equivalent) was slowly added to
the above maintaining temperature at about 0 °C for about
1 h till the reaction was over. To the diazotized product,
acidified stannous chloride was slowly added till completion
of the reaction. The reduced product was then worked up
with sodium hydroxide (NaOH) and extracted with ethyl
acetate. The solvent was distilled under reduced pressure,
and crude compound was crystallized to get pure 9-hy-
drazinyl acridine.
1
stretching), 1588.42–1516.07 (Aromatic C=C stretch), H
NMR (400 MHz, DMSO, dppm): 4.18 (s, 1H, –NH),
7.22–8.02 (m, 13H, 12Ar–H and 1 –NH).
N0-(Acridin-9-yl)-2-fluorobenzohydrazide (AA-13) Yield:
80.40 %, mp 270 °C, IR (cm-1): 3275.13 (Amide N–H
stretch), 3028.24 (Aromatic C–H stretching), 1680.00
(C=O stretching), 1641.42–1504.48 (Aromatic C=C
General procedure for the synthesis of substituted
benzoic acid N0-acridin-9-yl hydrazide (AA-11
to AA-112)
1
stretch), H NMR (400 MHz, DMSO, dppm): 4.09 (s, 1H,
–NH), 7.15–8.06 (m, 13H, 12Ar–H and 1 –NH).
N0-(Acridin-9-yl)-4-fluorobenzohydrazide (AA-14) Yield:
52.35 %, mp 310 °C, IR (cm-1): 3361.49 (sec. N–H
stretching), 3292.31 (Amide N–H stretch), 3097.68 (Aro-
matic C–H stretching), 1692.65 (C=O stretching),
1587.42–1438.90 (Aromatic C=C stretch), 1H NMR
(400 MHz, DMSO, dppm): 4.06 (s, 1H, –NH), 7.11–8.10
(m, 13H, 12Ar–H and 1 –NH).
1.5 equivalents of substituted carboxylic acid was added to
tetrahydrofuran (THF) and allowed to stir till complete dis-
solution. To it was added 1.5 equivalent of hydroxy-O-
benzotriazole (HOBt) and N-(3-dimethylaminopropyl)-N0-
ethylcarbodiimideÁHCl (EDCÁHCl) and stirred for
15–20 min at ice-cold condition. To this solution were added
triethylamine (TEA) and 1.5 equivalent of 9-hydrazinyl
acridine. The reaction was run at ice-cold condition till
completion and worked up with dichloromethane (DCM),
washed with dil HCl and sodium bicarbonate (NaHCO3).
DCM layer was collected, and solvent was evaporated under
reduced pressure. The final solid product was crystallized.
The characterization details are given below:
N0-(Acridin-9-yl)-4-chlorobenzohydrazide (AA-15) Yield:
79.89 %, mp 298 °C, IR (cm-1): 3415.93 (sec. N–H
stretching), 1651.07 (C=O stretching), 1562.65–1497.01
(Aromatic C=C stretch), 1H NMR (400 MHz, DMSO,
dppm): 4.06 (s, 1H, –NH), 7.15–8.18 (m, 13H, 12Ar–H and
1 –NH).
N0-(Acridin-9-yl)-2-bromobenzohydrazide (AA-16) Yield:
68.97 %, mp 277 °C, IR (cm-1): 3361.49 (sec. N–H
stretching), 3292.31 (Amide N–H stretch), 3097.68 (Aro-
matic C–H stretching), 1692.65 (C=O stretching),
1587.42–1438.90 (Aromatic C=C stretch); 1H NMR
(400 MHz,: DMSO, dppm): 3.63 (br, 1H, –NH), 7.09–8.58
(m, 13H, 12 Ar–H and 1 –NH).
9-Hydrazinyl acridine (1) IR (cm-1): 3410.58 (sec. N–H
stretching), 3319.49 (sec. N–H stretching), 3217.31 (Aro-
matic C–H stretching), 2864.29 (Aliphatic C–H stretching),
1716.65 (C=O), 1587.42–1438.90 (Aromatic C=C stretch);
1H NMR (400 MHz, DMSO, dppm): 1.91 (s, –NH2), 3.60
(br, 1H, –NH), 7.27 (dd, 2H, Ar–H), 7.60 (dd, 2H, Ar–H),
7.82 (d, 2H, Ar–H), 8.37 (d, 2H, Ar–H).
N0-(Acridin-9-yl)-2,4-dichlorobenzohydrazide (AA-17) Yield:
76.29 %, mp 288 °C, IR (cm-1): 3372.20 (sec. N–H
stretching), 3102–3010 (Aromatic C–H stretching), 1648.27
(C=O stretching), 1525.06–1412.64(Aromatic C=C stretch),
1H NMR (400 MHz, DMSO, dppm): 4.15 (s, 1H, –NH),
7.42–8.15 (m, 12H, 11Ar–H and 1 –NH).
N0-(Acridin-9-yl)-2-nitrobenzohydrazide (AA-11) Yield:
59.74 %, mp 279 °C, IR (cm-1): 3331.07 (sec. N–H
stretching), 3275.13 (Amide N–H stretch), 1641.42 (C=O
1
stretching), 1588.42–1504.48 (Aromatic C=C stretch), H
NMR (400 MHz, DMSO, dppm): 4.11 (s, 1H, –NH),
7.02–8.10 (m, 13H, 12Ar–H and 1 –NH).
123

Med Chem Res
N0-(4-(2-(Acridin-9-yl)hydrazinecarbonyl)phenyl)acetamide
(AA-18) Yield: 68.92 %, mp 285 °C, IR (cm-1): 3356.14
(sec. N–H stretching), 3251.98 (Amide N–H stretch),
1645.28 (C=O), 1588.42–1427.42 (Aromatic C=C stretch),
1H NMR (400 MHz, DMSO, dppm): 2.04 (s, 3H, –CH3),
4.10 (s, 1H, –NH), 7.46–8.12 (m, 14H, 12Ar–H and 2 –NH).
compounds can be governed from the reduced fluorescence
quantum yield. The assay was conducted in 50 mM sodium
acetate buffer (pH 4.5) using 3X BACE-1 enzyme (1U/ml).
The screening of test compounds was performed at 10 lM
concentration. The test compounds were diluted with DMSO
to prepare the stock solution of 10 mM and further diluted
with buffer to achieve desired concentration of 10 lM. The
incubation time was kept 60 min following which the fluo-
rescence was read on Tecan multiwell spectrofluorometer
(excitation: 545 nm; emission: 590 nm). Oral bioavailability
prediction was done using JChem for Excel. It helps in
identifying the compounds with good oral bioavailability and
also CNS penetration; the crucial parameter needed for the
design of BACE-1 inhibitors.
N0-(Acridin-9-yl)-3-methoxybenzohydrazide (AA-19) Yield:
65.40 %, mp 285 °C, IR (cm-1): 3390.49 (sec. N–H
stretching), 3235.55 (Amide N–H stretch), 3040–3018
(Aromatic C–H stretching), 2894 (Aliphatic C–H stretch-
ing), 1621.45 (C=O stretching), 1582.42–1518.05 (Aromatic
C=C stretch), 1H NMR (400 MHz, DMSO, dppm): 3.86 (s,
3H, OCH3), 4.13 (s, 1H, –NH), 6.95–8.28 (m, 13H, 12 Ar–H
and 1 –NH).
N0-(Acridin-9-yl)-3,4-dimethoxybenzohydrazide
(AA-
Docking simulation and in silico physicochemical
properties prediction
110) Yield: 83.26 %, mp 286 °C, IR (cm-1): 3390.49
(sec. N–H stretching), 3277.06 (Amide N–H stretch),
1639.49 (C=O stretching), 1591.27–1516.05 (Aromatic
C=C stretch), 1H NMR (400 MHz, DMSO, dppm):
3.73–3.78 (s, 6H, 2OCH3), 4.15 (s, 1H, –NH), 6.84–8.12
(m, 12H, 11Ar–H and 1 –NH).
X-ray crystal structure of human BACE-1 (pdb code—
2OHP) in complex with aminopyridine derivative was
retrieved from Brookhaven protein database for docking
study. It was prepared formissing charges, missing bonds and
flexibility. Its model was then constructed through grid gen-
eration on Maestro by removing all the water molecules.
Ligands were prepared using LigPrep module of Schrodinger
Suite 2013. All possible ionization states at pH 7.0 2.0
were enumerated using Epik and minimized. Docking sim-
ulations were performed using Glide (Friesner et al., 2004).
Validation of docking protocol was done to govern the reli-
ability and reproducibility of the docking parameters used for
the study. The docking strategy revealed that the docked
ligand superimposed well with the reference ligands (co-
N0-(Acridin-9-yl)-3-amino-4-methylbenzohydrazide (AA-
111) Yield: 57.24 %, mp 275 °C, IR (cm-1): 3334.92
(sec. N–H stretching), 2925 (Aliphatic C–H stretching),
1639.49 (C=O stretching), 1586.39–1516.30 (Aromatic
C=C stretch), 1H NMR (400 MHz, DMSO, dppm): 2.35 (s,
3H, –CH3), 4.05–4.61 (hump, 3H), 6.99–7.98 (m, 12H, 11
Ar–H and 1 –NH).
N0-(Acridin-9-yl)isonicotinohydrazide (AA-112) Yield:
74.57 %, mp 301 °C, IR (cm-1): 3277.06 (Amide N–H
stretch), 3026.31 (Aromatic C–H stretch), 1641.42 (C=O
˚
crystallized ligand) with RMSD value of 0.385 A.
1
stretching), 1565.42–1504.05 (Aromatic C=C stretch), H
Oral bioavailability of the synthesized compounds was
predicted using JChem for Excel, and blood–brain barrier
(BBB) was predicted using online BBB permeation pre-
dictor software available at http://www.cbligand.org/BBB/.
These data help in identifying the compounds with good
oral bioavailability and central nervous system (CNS)
penetration; the crucial parameter needed for the design of
BACE-1 inhibitors. It is proposed that reducing the pep-
tidic nature molecular weight and logP, along with polar
surface area (PSA), could result in highly potent BACE-1
inhibitor with enhanced brain permeation. The physico-
chemical properties for the synthesized compounds are
shown in Table 1.
NMR (400 MHz, DMSO, dppm): 3.98 (s, 1H, –NH),
7.42–9.06 (m, 13H, 12Ar–H and 1 –NH).
In vitro evaluations
BACE-1 in vitro assay was carried out using fluorescence
resonance energy transfer (FRET) technique. The BACE-1
FRET assay kit was purchased from Pan Vera, Life Tech-
nologies (kit no P2985, Madison, WI, USA), and the assay
was carried out according to the protocol provided by the
supplier. The measure of inhibitory activity of compounds is
based upon the reduction in the fluorescence quantum yield
due to inhibition of BACE-1 enzymatic activity. The protease
substrate (APP-based peptide) consists of a fluorescence
donor (rhodamine) connected to a quenching acceptor
through a peptide sequence (EVNLDAEFK). The fluores-
cence is weak intrinsically due to resonance energy transfer,
but upon enzymatic cleavage, the quantum yield of donor
molecule increases. Inhibitory potential of the designed
Results and discussion
Total of 12 acridin-9-yl hydrazide derivatives having
electron-donating as well as electron-withdrawing groups
were synthesized. Synthesized derivatives were tested for
123

Med Chem Res
Table 1 Physicochemical properties and in vitro data of Acridin-9-yl hydrazide derivatives
Code
–Ar
Glide score
MW
HBA
HBD
PSA
LogP
BBB score
% Inhibitiona
AA-11
AA-12
AA-13
AA-14
AA-15
AA-16
AA-17
AA-18
AA-19
AA-110
AA-111
AA-112
o-NO2-Ph
-4.48
-6.73
-5.85
-5.64
-5.92
-6.45
-6.90
-7.95
-5.68
-6.31
-7.96
-5.68
358.10
331.12
331.11
331.11
347.08
391.03
381.04
370.14
343.38
373.14
342.14
314.11
5
3
3
3
3
3
3
4
4
5
4
4
2
2
2
2
2
2
2
3
2
2
3
2
98.41
55.27
55.27
55.27
55.27
55.27
55.27
84.37
64.5
4.39
4.60
4.60
4.60
5.06
5.22
5.66
3.69
4.30
4.14
4.14
3.24
0.041
0.091
0.070
0.090
0.080
0.080
0.062
0.097
0.065
0.022
0.070
0.094
41.80
34.54
24.18
27.90
32.18
31.45
32.00
52.72
43.54
53.27
54.45
37.18
m-F-Ph
o-F-Ph
p-F-Ph
p-Cl-Ph
o-Br-Ph
(o,p-di-Cl)-Ph
(p-NHCOCH3)-Ph
m-OCH3-Ph
(m,p-di-OCH3)-Ph
(m-NH2, p-CH3)-Ph
–C5H4N (Isonicotinic acid)
73.73
81.29
68.16
MW molecular weight, HBA hydrogen bond acceptor, HBD hydrogen bond donor, PSA polar surface area
a
% Inhibition at 10 lM concentration, values are mean of triplicate experiments performed independently
BACE-1 inhibition at 10 lM concentration, docking was
performed using Glide (Schrodinger suite), and the docking
scores and % BACE-1 inhibition values are given in
Table 1. Overall, the acridin-9-yl hydrazide derivatives
displayed consistent BACE-1 inhibition profile. Visual
analysis of docking poses (Fig. 2) was done to correlate
with % inhibition values. The docking studies revealed
occupance of substrate-binding cavities and interactions
with active site amino acids.
formed key interaction with 10s loop amino acid Gly11. As
compared to other deactivating groups like nitro (AA-11)
and bromo (AA-16) at ortho position, fluorine was found to
be least active. This can be explained from docking study
whereby it is observed that fluorine being highly elec-
tronegative gets solvent exposed, changing the conforma-
tion in such a way that interaction of amide nitrogen with
Asp32 does not occur. Since this is not the case with
bromine- and nitro-substituted compounds, these com-
pounds show interaction with Asp32. Placing o,p-dichloro
(compound AA-17) promoted interactions with Asp32,
Tyr71, placed the acridine ring in S20 cavity while phenyl
ring occupied S1 pocket and had better docking score as
compared to other electron-withdrawing substituted
derivatives. However, it did not show any advantage in %
inhibition studies.
It was observed that compound AA-12 substituted with
m-fluoro group on the phenyl ring displayed interaction
with Asp32. The acridine nitrogen formed hydrogen bond
with the main chain of Gly230. Acridine ring had p–p
stacking with Trp115 covering the S20 cavity and phenyl
ring occupied the S1 pocket. Placing the fluoro group at
ortho and para position (AA-13, AA-14) further affected
the activity negatively. Compound AA-12 showed 34.54 %
inhibition while AA-13 and AA-14 had 24.18 % and
27.90 % inhibition, respectively. The in vitro results were
supported by docking study where AA-12 scored higher
than AA-13 and AA-14. It was observed that placing an o-
fluoro or p-fluoro group (AA-13, AA-14) instead of m-
fluoro diminished the aspartate interactions though AA-13
Comparatively, compound AA-18 having p-acetamido
substitution formed contacts with Asp32, showed p–p
stacking with Tyr71 and Phe108 and had 52.72 % BACE-1
inhibition. Compound AA-19 bearing m-methoxy substi-
tution indicated that the enzyme–inhibitor complex was
primarily stabilized by hydrogen bonds between the
hydrazide part of the inhibitor and side chain of Gly11,
123

Med Chem Res
Fig. 2 Docking poses of few Acridin-9-yl hydrazide derivatives. a Docked pose of AA-18, b 2D interaction plot of AA 18, c 2D interaction plot
of AA-111, d 2D interaction plot of AA-19
which is important amino acid of 10s loop. The acridinyl
moiety showed p–p stacking with Tyr71 while the phenyl
ring was buried in S1 cavity. It failed to interact with the
aspartate dyad nevertheless. AA-110 with m,p-dimethoxy
phenyl group also showed similar interactions viz: hydro-
gen bonding interaction with Asp32, amine group of phe-
nyl ring formed interaction with Phe108 and p–p stacking
of both the rings with Tyr71. However, it showed 53.27 %
BACE-1 inhibition in vitro. Most active compound AA-
111, having m-amino and p-methyl phenyl group, showed
that NH of hydrazine formed hydrogen bonding interaction
with Asp32, amine group of phenyl ring formed interaction
with Phe108 and p–p stacking of both the rings with Tyr71.
The electron-donating substitution appears to increase the
potency, but it also makes the compounds polar and may
reduce brain permeation. Both, AA-18 and AA-111, dis-
played highest docking score in the series, and this result
was concurrent with BACE-1 inhibition (52.72 and
54.54 %, respectively).
It was observed that replacing benzoyl on hydrazine
with isonicotinoyl, as in compound AA-112, reduced the
interactions as well as BACE-1 inhibition.
Considering in vitro–in silico results and to substantiate
their lead-like nature, in silico prediction of oral bioavail-
ability and BBB permeation was made. The log p values
for all derivatives were within range of 3.24–5.66, hydro-
gen bond donor count between 2 and 3 and hydrogen bond
acceptor count from 3 to 5. It is reported that BBB per-
meability is affected by polar surface area (PSA), and PSA
2
˚
should be below 90 A for CNS active agents (Pajouhesh
123

Med Chem Res
and Lenz, 2005). Except AA-11, all compounds had polar
2
surface area less than or near to 70 A and, hence, BBB
References
˚
Asami OA, Ishibashi Y, Kikuchi T, Kitada C, Suzuki N (1995) Long
amyloid b protein secreted from wild type human neuroblastoma
IMR-32 cells. Biochemistry 34:10272–10278
Azim MK, Ahmed W, Ishtiaq AK, Nosheen AR, Khalid MK (2008)
Identification of acridinyl hydrazides as potent aspartic protease
inhibitors. Bioorg Med Chem Lett 18:3011–3015
Cumming JL (1998) Alzheimer’s disease: etiologies, pathophysiol-
ogy, cognitive reserve and treatment opportunities. Neurology
51:512–517
Debouck C (1992) The HIV-1 protease as a therapeutic target for
AIDS. AIDS Res Hum Retroviruses 8:153–164
permeability for the series was predicted to be good. Fur-
ther, using online BBB permeation prediction software,
BBB permeability was predicted, wherein any compound
having SVM_MACCSFP BBB score of more than 0.02
will be able to cross BBB. It was found that all the com-
pounds had score above 0.02 and hence were predicted to
cross BBB. All these parameters indicate that these
derivatives will have good oral bioavailability and will
cross blood–brain barrier.
Friesner RA, Banks JL, Murphy RB, Halgren TA, Klicic JJ, Mainz
DT, Repasky MP, Knoll EH, Shelley M, Perry JK, Shaw DE,
Francis P, Shenkin PS (2004) Glide: a new approach for rapid,
accurate docking and scoring. 1. Method and assessment of
docking accuracy. J Med Chem 47:1739–1749
Conclusion
Fusek M, Vetvicka V (1995) Aspartic Proteinases Physiology and
Pathology. CRC Press, Boca Raton
Jain P, Jadhav HR (2011) Therapeutic advances in the treatment of
Alzheimer’s disease: present and future. Curr Drug Ther
6:175–185
Jain P, Jadhav HR (2013) Quantitative structure activity relationship
analysis of aminoimidazoles as BACE-I inhibitors. Med Chem
Res 22:1740–1746
Jain P, Wadhwa PK, Rohilla S, Jadhav HR (2016) Rational design,
synthesis and in vitro evaluation of allylidene hydrazinecarbox-
imidamide derivatives as BACE-1 inhibitors. Bioorg Med Chem
Lett 26:33–37
Pajouhesh H, Lenz GR (2005) Medicinal chemical properties of
successful central nervous system drugs. NeuroRx 2:541–553
Shimizu H, Tosaki A, Kaneko K, Hisano H, Sakurai T, Nukina N
(2008) Crystal structure of an active form of BACE-I, an enzyme
responsible for amyloid protein production. Mol Cell Biol
28:3663–3671
Suzuki N, Cheung TT, Cai XD, Odaka A, Otvos L, Eckman C, Golde
TE, Younkin SG (1994) An increased percentage of long
amyloid b protein secreted by familial amyloid b-protein
precursor (bAPP717) mutants. Science 264:1336–1340
Acridin-9-yl hydrazide derivatives, reported to inhibit other
aspartyl proteases, were explored as BACE-1 inhibitors. As
indicated by docking scores as well as in vitro BACE-1
inhibition, it was observed that electron-donating substi-
tution on benzoyl moiety is preferred over electron-with-
drawing substituents. All the compounds showed
occupance of S1 and S20 cavity and except compounds
AA-13 and AA-19, and all derivatives had interaction with
Asp32, which is essential for activity. The designed
derivatives were also predicted to be orally bioavailable
and BBB penetrant. Further modification with respect to
inclusion of groups to enhance binding with catalytic
aspartate dyad (Asp32 and Asp228) and substitution of
electron-donating groups on benzoyl moiety may lead to
enhanced binding and potency.
Compliance with ethical standards
Conflict of interest The authors confirm that this article content has
no conflict of interest.
123