Through scaffold modification to 3,5-diaryl-4,5-dihydroisoxazoles: new potent and selective inhibitors of monoamine oxidase B

Article abstract of DOI:10.1080/14756366.2016.1247061

3,5-Diaryl-4,5-dihydroisoxazoles were synthesized and evaluated as monoamine oxidase (MAO) enzyme inhibitors and iron chelators. All compounds exhibited selective inhibitory activity towards the B isoform of MAO in the nanomolar concentration range. The b

Full text of DOI:10.1080/14756366.2016.1247061

Journal of Enzyme Inhibition and Medicinal Chemistry
ISSN: 1475-6366 (Print) 1475-6374 (Online) Journal homepage: http://www.tandfonline.com/loi/ienz20
Through scaffold modification to 3,5-diaryl-4,5-
dihydroisoxazoles: new potent and selective
inhibitors of monoamine oxidase B
Rita Meleddu, Simona Distinto, Roberto Cirilli, Stefano Alcaro, Matilde
Yanez, Maria Luisa Sanna, Angela Corona, Claudia Melis, Giulia Bianco, Peter
Matyus, Filippo Cottiglia & Elias Maccioni
To cite this article: Rita Meleddu, Simona Distinto, Roberto Cirilli, Stefano Alcaro,
Matilde Yanez, Maria Luisa Sanna, Angela Corona, Claudia Melis, Giulia Bianco, Peter
Matyus, Filippo Cottiglia & Elias Maccioni (2017) Through scaffold modification to
3,5-diaryl-4,5-dihydroisoxazoles: new potent and selective inhibitors of monoamine
oxidase B, Journal of Enzyme Inhibition and Medicinal Chemistry, 32:1, 264-270, DOI:
10.1080/14756366.2016.1247061
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Date: 19 January 2017, At: 03:10

JOURNAL OF ENZYME INHIBITION AND MEDICINAL CHEMISTRY, 2017
VOL. 32, NO. 1, 264–270
http://dx.doi.org/10.1080/14756366.2016.1247061
RESEARCH ARTICLE
Through scaffold modification to 3,5-diaryl-4,5-dihydroisoxazoles: new potent and
selective inhibitors of monoamine oxidase B
Rita Meleddua, Simona Distintoa, Roberto Cirillib, Stefano Alcaroc, Matilde Yanezd, Maria Luisa Sannaa,
Angela Coronaa, Claudia Melisa, Giulia Biancoa, Peter Matyuse, Filippo Cottigliaa and Elias Maccionia
a
b
ꢀ
Department of Life and Environmental Sciences, University of Cagliari, Cagliari, Italy; Dipartimento del Farmaco, Istituto Superiore di Sanita,
c
d
ꢀ
ꢁ
Rome, Italy; Dipartimento di Scienze della Salute, Universita Magna Græcia di Catanzaro, Catanzaro, Italy; Departamento de Farmacologıa and
Instituto de Farmacia Industrial, Universidad de Santiago de Compostela, Campus Universitario Sur, Santiago de Compostela, Spain;
eDepartment of Organic Chemistry, Semmelweis University, Budapest, Hungary
ABSTRACT
ARTICLE HISTORY
Received 4 August 2016
Revised 5 September 2016
Accepted 5 September 2016
3,5-Diaryl-4,5-dihydroisoxazoles were synthesized and evaluated as monoamine oxidase (MAO) enzyme
inhibitors and iron chelators. All compounds exhibited selective inhibitory activity towards the B isoform of
MAO in the nanomolar concentration range. The best performing compound was preliminarily evaluated
for its ability to bind iron II and III cations, indicating that neither iron II nor iron III is coordinated. The
best compounds racemic mixtures were separated and single enantiomers inhibitory activity evaluated.
Furthermore, none of the synthesised compounds exhibited activity towards MAO A. Overall, these data
support our hypothesis that 3,5-diaryl-4,5-dihydroisoxazoles are promising scaffolds for the design of neu-
roprotective agents.
KEYWORDS
3,5-diaryl-dihydroisoxazoles;
MAO B selective inhibitors;
neuroprotective agents
Introduction
oxygen atom, we have designed and synthesised two series of 2,3-
dihydro-oxadiazoles20–22 that exhibited high selectivity and activity
towards MAO B. Moreover, we observed that the introduction of a
3,4-dichlorophenyl substituent in the position 2 of the dihydro-oxa-
diazole core is crucial for both selectivity and potency21. According
to these structural information and with the aim of setting new hit
structures for MAO B inhibition, we have devised a synthetic path-
way to obtain 3,5-diaryl-4,5-dihydroisoxazoles as bio-isosters of
both the previously reported 3,5-diaryl-4,5-dihydro-(1H)-pyrazoles
and 2,5-diaryl-2,3-dihydro-1,3,4-oxadiazoles.
Amine oxidase is a widely diffused family of enzymes responsible
for the oxidative deamination of both endogenous and exogenous
monoamines, diamines and polyamines. These enzymes are divided
into two classes, flavin adenine dinucleotide amino oxidase (FAD-
AO) (EC 1.4.3.4)1 and copper topaquinone amino oxidase (Cu/TPQ-
AO)2. The former, named monoamine oxidase (MAO), contains fla-
vin adenin dinucleotide (FAD) as a cofactor while the latter contains
2,4,5-trihydroxyphenylalanine quinone as cofactor (TPQ-Cu) and are
inhibited by semicarbazide. Regarding FAD-AO, two isoforms, MAO-
A and MAO-B, have been isolated, differing from central nervous
system (CNS) location, substrate specificity and sensitivity to inhibi-
tors3,4. MAO enzymes5 play a key role in the metabolism of mono-
amine neurotransmitters, and have been therefore studied in a
number of psychiatric and neurological diseases6. Moreover, the
MAO catalysed oxidative deamination of amines leads to the forma-
tion of hydrogen peroxide which is co-responsible for neurodegen-
eration7. Not surprisingly a number of MAO inhibitors have been
investigated as neuroprotective agents in the treatment of
Parkinson and Alzheimer diseases3,4,6,8–10. We have previously iden-
tified highly potent and selective MAO B inhibitors characterised by
a 3,5-diaryl-4,5-dihydro-(1H)-pyrazole scaffold11 and investigated on
the structural requirements for the enzyme inhibition (Figure 1). In
particular, the presence of two aryl substituents on the dihydro-
(1H)-pyrazole nucleus appeared as essential for MAO B selectivity
and inhibition potency activity12–15. Hence, we designed and
studied 2-thiazolylhydrazones derivatives, ideally originated by
removing C4 and C5 from the dihydropyrazole ring. These deriva-
Methods
Materials and apparatus
Starting materials and reagents were obtained from commercial
suppliers and were used without purification. All melting points
were determined on a Stuart SMP11 melting points apparatus and
are uncorrected (East Yorkshire, UK). Electron ionization mass spec-
tra were obtained by a Fisons QMD 1000 mass spectrometer
(70 eV, 200 mA, ion source temperature 200 ꢀC) (Loughborough,
UK). Samples were directly introduced into the ion source. Found
mass values are in agreement with theoretical ones. Melting
points, yield of reactions and the analytical and descriptive data of
derivatives are reported in Table 1.
1H-NMR (Table 2) were registered on a Bruker AMX 300 MHz
spectrometer (Billerica, MA). All samples were measured in CDCl3.
Chemical shifts are reported referenced to the solvent in which
they were measured. Coupling constants J are expressed in Hz.
Elemental analyses were obtained on a Perkin-Elmer 240 B micro-
tives exhibited high potency and selectivity towards MAO B16–19
.
More recently, through the isosteric replacement of the carbon 4 of analyser (Waltham, MA). Analytical data of the synthesised com-
the previously reported dihydropyrazole derivatives11 with an pounds are in agreement within 0.4% of the theoretical values.
CONTACT Elias Maccioni
maccione@unica.it
Department of Life and Environmental Sciences, University of Cagliari, Via Ospedale 72, Cagliari 09124, Italy
ß 2017 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distri-
bution, and reproduction in any medium, provided the original work is properly cited.

JOURNAL OF ENZYME INHIBITION AND MEDICINAL CHEMISTRY
265
Figure 1. Scaffold evolution of MAO B inhibitors: from dihydro-pyrazoles to dihydro-isoxazoles.
Table 1. Chemical, analytical, and physical data of derivatives EMAC II (i–m).
H3
C
R
N
O
C–H–N
Compound
R
Cryst. solvent
Calc.
Found
M.P. (ꢀC)
Yield %
E.I. 70 eV mass spectra m/z (rel. ab.)
EMAC II i
EMAC II j
EMAC II k
EMAC II l
EMAC II m
4-Cl
4-CH3
4-F
3,4-Cl
4-OCH3
Ethanol
Ethanol
Ethanol
Water/ethanol
ethanol
70.72, 5.19, 5.15
81.24, 6.82, 5.57
75.28, 5.53, 5.49
62.76, 4.28, 4.57
76.38, 6.41, 5.24
70.67, 5.17, 5.12
81.27, 6.83, 5.54
75.31, 5.54, 5.43
62.72, 4.31, 4.54
76.33, 6.40, 5.22
134-5
103-4
132-4
134-5
131-3
42
46
41
65
44
271 (100); 240 (78); 139 (17)
251 (100); 220 (83); 119 (13)
255 (100); 224 (75); 123 (19)
305 (100); 274 (81); 173 (22)
267 (100); 236 (71); 135 (9)
Table 2. 1H NMR data and main fragments in E.I. mass spectrometry of derivatives EMAC II (i–m).
Compound
1H NMR d (ppm)
EMAC II i
1H-NMR: (300 MHz, CDCl3) dH 2.38 (s, 3H, CH3), 3.23 (dd, 1H, Jab 16.5, Jax 7.8, CH2, isoxazole), 3.76 (dd, 1H, Jab 16.5, Jbx 10.1, CH2, isoxa-
zole), 5.59 (dd, 1H, Jbx 10.8, Jax 8.1, CH, isoxazole), 7.21 (d, 2H, J 7.8, CH, arom.), 7.33 (m, 4H, CH, arom.), 7.57 (2H, d, J 8.1, CH, arom.).
1H-NMR: (300 MHz, CDCl3) dH 2.37 (s, 3H, CH3), 2.43 (s, 3H, CH3), 3.30 (dd, 1H, Jab 16.5, Jax 8.3, CH2, isoxazole), 3.72 (dd, 1H, Jab 16.5, Jbx
10.8, CH2, isoxazole), 5.66 (dd, 1H, Jbx 10.8, Jax 8.3, CH, isoxazole), 7.16–7.29 (m, 6H, CH, arom.), 7.57 (d, 2H, J 8.3, CH, arom.).
1H-NMR: (300 MHz, CDCl3) dH 2.35 (s, 3H, CH3), 3.27 (dd, 1H, Jab 16.7, Jax 8.0, CH2, isoxazole), 3.74 (dd, 1H, Jab 16.5, Jbx 10.7, CH2, isoxa-
zole), 5.69 (dd, 1H, Jbx 10.7, Jax 8.3, CH, isoxazole), 7.04 (t, 2H, J 8.3, CH, arom.), 7.21 (d, 2H, J 8.1, CH, 4-CH3-phenyl), 7.36 (dd, 2H, CH,
J 8.3/5.3, arom.), 7.56 (d, 2H, J 8.2, CH, 4-CH3-phenyl).
EMAC II j
EMAC II k
EMAC II l
1H-NMR: (300 MHz, CDCl3) dH 2.38 (s, 3H, CH3), 3.27 (dd, 1H, Jab 16.7, Jax 7.8, CH2, isoxazole), 3.78 (dd, 1H, Jab 16.4, Jbx 10.8, CH2, isoxa-
zole), 5.67 (dd, 1H, Jbx 10.8, Jax 7.8, CH, isoxazole), 7.21 (m, 3H, CH, arom.), 7.44 (d, 1H, J 8.2, CH, arom.), m, 7.49 (d, 1H, J 1.2, CH,
arom.), 7.56 (d, 2H, J 8.1, CH, arom.).
EMAC II m
1H-NMR: (300 MHz, CDCl3) dH 2.38 (s, 3H, CH3), 3.30 (dd, 1H, Jab 16.7, Jax 7.8, CH2, isoxazole), 3.71 (dd, 1H, Jab 16.5, Jbx 10.6, CH2, isoxa-
zole), 3.80 (s, 3H, OCH3), 5.66 (dd, 1H, Jbx 10.5, Jax 8.6, CH, isoxazole), 6.89 (d, 2H, J 8.3, CH, arom.), 7.21 (d, 2H, J 8.2, CH, 4-CH3-phe-
nyl), 7.31 (d, 2H, J 8.7, CH, arom.), 7.58 (d, 2H, J 8.2, CH, 4-CH3-phenyl).
TLC chromatography was performed using silica gel plates (Merck hydroxylamine hydrochloride (0.0057 mol) and potassium hydrox-
F 254, Kenilworth, NJ), spots were visualised by UV light.
ide (0.013 mol) water solution are added dropwise. The solution
becomes progressively orange and the reaction is monitored by
thin layer chromatography (TLC) (CH2Cl2/n-hexane: 20/1). By cool-
ing the reaction, the formation of a precipitate is observed which
General procedure for the synthesis of compound derivatives
In
a,b-unsaturated ketone is dissolved in 30 ml of boiling absolute
ethanol. On this solution, 10 ml of freshly prepared
a
typical experiment, 0.0038 mol of the appropriate was filtered and crystallised from ethanol.
By this procedure (Scheme 1), compounds EMAC II (i–m) were
synthesised.
a

266
R. MELEDDU ET AL.
Scheme 1. Synthesis of EMAC II (i–m) compounds. Reagents and conditions: (i) ethanol, NaOH; (ii) ethanol, hydroxylamine hydrochloride, potassium hydroxide, reflux.
Figure 2. An ORTEP view of the molecular structure of (R)-(ꢁ)-EMAC II i enantiomer.
HPLC enantioseparations and stereochemical characterisation
since they were unable to directly react with the Amplex Red
reagent. The kinetic parameters of hMAO-A and hMAO-B were
evaluated in the presence of different tyramine concentrations. In
our experiments, hMAO-A displayed a Michaelis constant (Km) of
Direct separation of the enantiomers of EMAC II (i–m) was
achieved by HPLC using pure dichloromethane as the eluent. The
resolving power of the immobilized-type was sufficiently high to
achieve a baseline enantioseparation of all compounds in a short-
time analysis. The optimized analytical conditions were easily
scaled up to semipreparative level employing a 1 cm i.d. IA col-
umn. An amount of <20 mg of racemic samples was resolved for
each chromatographic run, and both enantiomers were collected
with high enantiomeric purity. The stereochemical characterization
of compounds EMAC II (i–m) was performed by CD correlation
comparing the maximum and minimum of ellitipticity of the CD
spectra of the isolated enantiomers of compound EMAC II i of
known stereochemistry (Figure 2), as previously described by
some of us23. Single enantiomers were resubmitted to biological
assay.
514 46.8 mM and
a maximum reaction velocity (Vmax) of
301.4 27.9 nmol/min/mg protein, whereas hMAO-B showed a Km
of 104.7 16.3 mM and a Vmax of 28.9 6.3 nmol/min/mg protein
(n ¼ 5). Active compounds showed reversible behaviour according
to the method proposed by Cer et al.24 Hence, reported IC50 is a
useful tool to determine the relative activity of the compounds
within the series as well as to determine substituent and key posi-
tions in the scaffold. All the tested compounds exhibited inhibitory
activity towards hMAO-B at nM concentration. Single enantiomers
activity was evaluated indicating that stereochemistry plays a rele-
vant role in determining inhibitory concentrations. None of the
tested compounds exhibited activity towards the A isoform of the
enzyme at the tested concentration of 100 mM.
Biological assay
Coordination studies
The interaction between EMAC II l and the Fe2þ or Fe3þ ions was
evaluated by recording the UV/VIS absorbance spectra of EMAC II
l (Figure 3) in absence and in presence either of FeCl3 or FeSO4.
The inhibitory activities of compounds EMAC II (i–m) on human
recombinant MAO A and B isoforms, expressed in baculovirus
infected BTI infected cells, as IC50, are reported in Table 1. Tested
compounds demonstrated no interference with the measurements, EMAC II l was solubilised in DMSO then diluted to 1 mM in

JOURNAL OF ENZYME INHIBITION AND MEDICINAL CHEMISTRY
267
Figure 3. Effect of Fe2þ or Fe3þ ions on the spectrum of absorbance of EMAC II l. UV/vis spectrum was measured with 100lM of compound alone (unbroken line) or
in the presence of 10 mM FeCl3 or FeSO4 (dotted line).
Table 3. Inhibitory activities towards hMAO-A and hMAO-B of EMAC II (i–m) derivatives.
Compound
Structure
MAO-A (IC50
)
MAO-B (IC50
)
Ratioe
>961d
b
EMAC II i
104.04 3.69 nM
41.05 1.52 nM
320.22 13.61 nM
11.97 0.37 nM
449.57 18.02 nM
H3C
H3C
H3C
H3C
H3C
Cl
CH3
F
N
O
b
b
b
b
EMAC II j
EMAC II k
EMAC II l
EMAC II m
>2436d
>312d
>8354d
>222d
N
O
N
N
O
O
Cl
Cl
OCH3
N
O
Clorgiline
4.46 0.32 nMc
67.25 1.02 lMc
6.56 0.76 lM
61.35 1.13 lM
19.60 0.86 nM
0.000073
3431.12
0.87
L-Deprenyl
Iproniazide
Moclobemide
7.54 0.36 lM
a
361.38 19.37 lM
<0.36e
aInactive at 1 mM (highest concentration tested).
bInactive at 100 lM (highest concentration tested). At higher concentration, the compounds precipitate.
c
cResults are mean SEM from five experiments. Level of statistical significance: P <0.01 versus the corresponding IC50 values obtained against MAO-B, as determined
by ANOVA/Dunnett’s.
dValues obtained under the assumption that the corresponding IC50 against MAO-A is the highest concentration tested (100 lM).
eSelectivity ratios [IC50(MAO-A)]/[IC50(MAO-B)].
50%DMSO solution. The UV/vis spectrum of the solution was Gradient (PRCG) method and a convergence criterion of 0.05 kcal/
recorded before and after addition of 10 mM final concentration (mol Å).
either of FeCl3 or FeSO4. The spectra were recorded with a
Docking experiments. Previous reported and validated QMPL
Ultrospec 2100 pro (Amersham Biosciences, Little Chalfont, UK) docking protocol was applied using default settings21,31. In order
and analysed with SWIFT II-METHOD software (GE Healthcare, to better take into account the induced fit phenomena, the most
Little Chalfont, UK).
energy favoured generated complexes were fully optimized with
the AMBER united atoms force field32 in GB/SA implicit water,30
ꢂ
setting 5000 steps iterations analysis with PRCG method and a
convergence criterion of 0.1 kcal/(mol Å). Analysis of the results of
the complex minimization was carried out taking into account the
state equations (free energy of complex formation) computed at
300 K, applying molecular mechanics and continuum solvation
models with the molecular mechanics generalized Born33. The
resulting complexes were considered for the binding modes
graphical analysis with Pymol34 and Maestro27.
Molecular modelling studies
Protein preparation. Three-dimensional coordinates of the recep-
tor25 were obtained from the Protein Data Bank (PDB).26 The pro-
tein was processed and the internal hydrogen bonding network of
the receptor was optimized using the algorithm implemented in
Protein Preparation wizard.27
Ligand preparation. The ligands were built using Maestro GUI27.
The lowest energy conformer was considered for the subsequent
computational studies. This was obtained with MacroModel ver-
sion 7.228, considering MMFFs29 as force field and solvent effects
Results and discussion
by adopting the implicit solvation model Generalized Born/Surface Pursuing in our research on the design and synthesis of new
Area (GB/SA) water30. The simulation was performed allowing agents for the selective inhibition of MAO B, we have synthesised
1000 steps Monte Carlo analysis with Polak-Ribier Conjugate a series of 3,5-diaryl-4,5-dihydro-isoxazoles EMAC II (i–m). All the

268
R. MELEDDU ET AL.
compounds were submitted to biological evaluation to investigate enzyme up to 100 mM concentration. Considering the presence of
their ability to inhibit both MAO isoforms. The structure and the an asymmetric carbon at the position 5 of the dihydro-isoxazole
nucleus we performed, semipreparative chromatographic enantio-
separation of all the new derivatives EMAC II (i–m). The separated
enantiomers were then submitted to biological evaluation (Table
4). The obtained data pointed out the importance of enantiomeric
separation for both potency and selectivity. In particular, in the
case of compound R-(ꢁ)-EMAC II l, the IC50 value towards MAO B,
drops from 11.97 nM to 1.89 nM, while the selectivity towards
MAO B is increased by more than six folds. Moreover, considering
the growing interest in the development of iron chelators for the
treatment of neurodegenerative disorders35–37, we have prelimin-
arily investigated our best compound able to bind iron II and iron
III cations following a previously reported procedure38. According
to our preliminary results (Figure 3), compound EMAC II l do not
have the ability to bind neither iron II nor iron III cations.
MAO A and MAO B IC50 values and selectivity ratios of the new
derivatives are reported in Table 3. All the compounds inhibit
MAO B isozyme with IC50 values ranging from higher to lower
nanomolar range. Accordingly to what is observed in our previous
report on similar derivatives21, compound EMAC II l, bearing a
3,4-dichlorophenyl moiety in the position 5 of the dihydro-
isoxazole ring resulted, the most active within all the tested
compounds. Based on this observation we assumed that, in the
formation of the enzyme–ligand complex, this portion of the
inhibitor is, in all probability, oriented similarly with respect to our
previously reported compounds. Interestingly, none of the new
compounds exhibited activity towards the MAO A isoform of the
Table 4. Inhibitory activities towards hMAO-A and hMAO-B of EMAC II (i–m) sin-
In order to explore the nature of the ligand–receptor interac-
tions, we have carried out docking experiments considering the
MAO B active site by means of QMPL docking protocol31,39,40. We
have focused our attention on the most active compound R-
(ꢁ)-EMAC II l, which shows the lowest IC50 value and the highest
selectivity towards MAO-B.
It should be pointed out that MAO-B cavity is rather narrow,
therefore, small changes are reflected in the biological activity. In
this respect, the best compound shows remarkable difference of
activity between the R and the S enantiomers. An analogous
behaviour was observed in the previous series11,20. According to
docking and post docking best scored pose, the most stable com-
plex configurations of both R and S enantiomers are depicted in
Figure 4(a,b).
gle enantiomers.
Compound
MAO-A (IC50
)
MAO-B (IC50
)
Ratio
6549b
a
a
a
a
a
a
a
a
a
a
R-(2) EMAC II i
S-(1) EMAC II i
R-(2) EMAC II j
S-(1) EMAC II j
R-(2) EMAC II k
S-(1) EMAC II k
R-(2) EMAC II l
S-(1) EMAC II l
R-(2) EMAC II m
S-(1) EMAC II m
15.27 0.95 nM
a
2.55 0.11 nM
31.37 1.67 lM
299.86 12.04 nM
33.82 1.12 lM
1.89 0.16 nM
10.96 0.83 lM
126.16 8.44 nM
291.82 13.45 nM
39 216b
3188b
333.5b
2956b
52 910b
9124
792.6b
342.6
IC50 values are the mean SEM from five experiments.
aInactive at 100 lM (highest concentration tested).
bValues obtained under the assumption that the corresponding IC50 against
MAO-B is the highest concentration tested (100 lM).
Figure 4. Putative binding mode of compound EMAC II l. (a) R-(ꢁ)-EMAC II l/MAO-B complex; (c) S-(1)-EMAC II l/MAO-B complex; (b, d) compound 2D representation and
binding pocket interacting residues: green, hydrophobic; cyan, polar residues. Green arrows indicate pꢁp interactions.

JOURNAL OF ENZYME INHIBITION AND MEDICINAL CHEMISTRY
269
Figure 5. Binding mode of previously published compounds and approved inhibitors. (a) 4f-(R) MAO-B complex21; (c) safinamide MAO-B complex (pdb code 4v5z)25;
(b, d) compound 2D representation and binding pocket interacting residues: in green, hydrophobic; cyan, polar residues. Green arrows indicate pꢁp interactions,
magenta arrow indicates H bonds.
The R enantiomer is stabilized by pꢁp interactions with Trp119,
Disclosure statement
Phe103, Phe343, Tyr326 and some hydrophobic interactions with
The authors have no declarations of interest to report.
several residues in the binding pocket: Leu 164, Leu 167, Phe 168,
Ile 316, Ile 199, Ile198, Leu 171 and the Tyr of the aromatic cage
435, 298, 188.
References
Conversely, the S enantiomer is oriented in the opposite way:
with the dichlorophenyl substituent in the entrance cavity and the
4-methylphenyl substituent in the catalytic cavity toward the FAD.
The complex results in less stability and gives rise only to a single
pꢁp interaction with Tyr 435 and several hydrophobic interactions
(Figure 4(c,d)).
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Compared with previous series21, the absence of acetyl group
allows a better accommodation in the cavity (Figures 4(a) and
5(a)). Once again, the importance in crossing both entrance and
catalytic cavity, in order to achieve the MAO-B isoform selective
activity is confirmed. This essential requisite has been reported by
several studies25,41,42 and can be observed in co-crystallized select-
ive MAO B inhibitors. A typical example is the inhibitor safinamide
(Figure 5(c,d))25,43
.
Conclusions
In summary, a small library of 3,5-diaryl-4,5-dihydroisoxazoles have
been designed and synthesized on the basis of previously
reported MAO inhibitors. Our finding highlighted the capability of
3,5-diaryl-4,5-dihydroisoxazoles to exert specific recognition and
inhibition against the isoform B of MAO. The stereochemical char-
acterization of R/S enantiomers confirms an enantioselective effect
against MAO B isoform. This scaffold is definitively interesting for
the development of novel selective neuroprotective agents.
7. Jha SK, Jha NK, Kumar D, et al. Linking mitochondrial dysfunc-
tion, metabolic syndrome and stress signaling in neurodegen-
eration. Biochim Biophys Acta Mol Basis Dis 2016 [Epub ahead
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