Coumarin versus Chromone Monoamine Oxidase B Inhibitors: Quo Vadis?

Article abstract of DOI:10.1021/acs.jmedchem.7b00918

Because of the lack of significant disease-modifying drugs for neurodegenerative disorders, a pressing need for new chemical entities endowed with IMAO-B still exists. Within this framework, and for the first time, a study was performed to compare coumari

Full text of DOI:10.1021/acs.jmedchem.7b00918

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Brief Article
Coumarin versus chromone monoamine oxidase B inhibi-tors: Quo vadis?
André Fonseca, Joana Reis, Tiago B. Silva, Maria João Matos, Donatella Bagetta,
Francesco Ortuso, Stefano Alcaro, Eugenio Uriarte, and Fernanda M. Borges
J. Med. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jmedchem.7b00918 • Publication Date (Web): 28 Jul 2017
Downloaded from http://pubs.acs.org on July 29, 2017
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Coumarin versus chromone monoamine oxidase B inhibitors:
Quo vadis?
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André Fonsecaa,b¥, Joana Reisa¥, Tiago Silvaa, Maria João Matosa,b, Donatella Bagettac, Francesco
Ortusoc, Stefano Alcaroc, Eugenio Uriarteb,d, and Fernanda Borgesa*
a CIQUP/Department of Chemistry and Biochemistry, Faculty of Sciences, University of Porto, 4169-007, Porto, Portu-
gal.
b Department of Organic Chemistry, Faculty of Pharmacy, Universidad of Santiago de Compostela, 15782, Santiago de
Compostela, Spain.
c Department of “Scienze della Salute”, University “Magna Græcia” of Catanzaro, Campus “Salvatore Venuta”, Viale
Europa, 88100, Catanzaro, Italy.
d
Applied Chemical Science Institute, Universidad Autonoma de Chile, 7500912, Santiago de Chile, Chile
KEYWORDS: benzopyrone; coumarin; chromone; monoamine oxidase B; mechanism; docking simulation
ABSTRACT: Due to the lack of significant disease-modifying drugs for neurodegenerative disorders, a pressing need for
new chemical entities endowed with IMAO-B still exists. Within this framework, and for the first time, a study was per-
formed to compare coumarin- and chomone-3-phenylcarboxamide scaffolds. Compounds 10a and 10b were the most po-
tent, selective and reversible non-competitive IMAO-B. The benzopyrone sp2 oxygen atom was found to be position inde-
pendent and a productive contributor for the ligand–enzyme complex stability.
INTRODUCTION
According to epidemiological studies, Parkinson’s (PD) and
Alzheimer’s diseases (AD) are the most prevalent neuro-
degenerative disorders, representing a heavy burden on
the patient, family, caregivers and society. Unfortunately,
the available therapies are only palliative, which makes the
design and development of new disease-modifying drugs
an unmet clinical need.1,2 Given the establishment of do-
paminergic loss as a pathological hallmark of PD, the ther-
apeutic strategies until now have been focused on boosting
the levels of dopamine in the brain. Monoamine oxidase B
(MAO-B), a flavin monoamine oxidase located in the outer
mitochondrial membrane, is a pharmacological target for
the treatment of PD, since its inhibition enhances DA lev-
els.3 Selective MAO-B inhibitors (IMAO-B) are generally a
valid asset in early PD therapy in combination with L-
Figure 1A. Coumarin (2H-benzopyran-2-one) and chromone
DOPA. The first selective and irreversible IMAO-B intro-
(4H-benzopyran-4-one)
phenylcarboxamide
scaffolds;
(1a)
B.
Coumarin-3-
chromone-3-
duced in the market were selegiline (L-deprenyl) and
rasagiline. Safinamide, a reversible IMAO-B, was recently
introduced. However, due to the lack of significant disease
modifying properties of these drugs, a pressing need for
new chemical entities endowed with selective and reversi-
ble IMAO-B still exists. Heterocycles play a key role in the
discovery of new pharmacologically active compounds.4
Benzopyrones, namely coumarin (α-benzopyrone) and
chromone (γ-benzopyrone) (Figure 1A), are currently
considered as valid templates for the design and develop-
ment of new chemical entities.5–7
and
phenylcarboxamide (1b) IMAO-B 8,9
.
Coumarins and chromones are ubiquitous in nature, and
have relevant pharmacological activities such as anti-
inflammatory, antioxidant, cardioprotective and antimi-
crobial properties.10–12 Our research group has shown that
coumarin-3-phenylcarboxamide (1a) and chromone-3-
phenylcarboxamide (1b) are privileged structures for the
rational discovery and development of new IMAO-B.8,9
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Figure 2. Best docking poses of compounds 1a and 1b into the hMAOs active sites. The most relevant interacting residues are
depicted in polytube CPK colored, FAD cofactor is shown as spacefill and ligands as green carbons polytube.
Focusing on the lead optimization, and guided by the data
obtained so far, we performed a comprehensive structure-
activity relationship (SAR) study between the two struc-
tural isomers. Firstly, target recognition of compounds 1a
and 1b (Figure 1B) was investigated at the molecular level
by means of docking simulations. Then, the benzopyrane-
3-phenylcarboxamide scaffolds were derivatized by intro-
ducing substituents on the benzopyrane and exocyclic
aromatic nucleus. A small library of new coumarin (8a-
21a) (Scheme 1A) and chromone (8b-21b) (Scheme 1B)
derivatives was synthesized and screened for MAO inhibi-
tion. The druglike properties, kinetics, and mechanism of
enzymatic inhibition were evaluated for the best IMAO-B.
Pan assay interference properties (PAINS) of the com-
pounds under study were theoretically investigated.
Asn181 side chain. On the other hand, the most stable 1a
and 1b poses into the hMAO-B active site were similar to
those previously reported, while head-tail orientations
were observed in less stabilised poses only. A remarkable
stabilizing contribution was due to a hydrogen bond (HB)
between the ligands’ oxygen atoms and the Cys172 side
chain. For both compounds, the best poses involved the
anilide sp2 oxygen whereas in less stable complexes such
an interaction occurred by means of HB acceptor atoms in
the benzopyrone ring. Since the other complexes stabiliz-
ing contribution were equivalent to the hMAO-A ones, and
taking into account that hMAO-B Cys172 is replaced by
Asn181 in hMAO-A, we could attribute the experimentally
observed hMAO-B selectivity to the ligands-Cys172 hydro-
gen bonding (Figure 2). Additionally, the 1a and 1b bind-
ing modes analysis confirmed that no relevant differences
can be observed between coumarin and chromone scaf-
folds with respect to the recognition of the same target,
and this was particularly evident as these structures
played a key role in isoform selectivity.
The role of the benzopyrane-3-phenylcarboxamide scaf-
folds was then investigated by the introduction of substit-
uents on the benzopyrane ring and on the exocyclic aro-
matic nucleus. The rational design strategy (Figure 3) was
mainly focused on the study of a) the effect of different
substituents (R1 = CH3; OCH3) on the benzopyrone ring; b)
the effect of different electron donating or withdrawing
substituents (R2 = H, CH3, Cl, OH) located at meta and para
positions (the most relevant positions found in previous
studies13) on the exocyclic aromatic ring, and on c) the
assessment of the impact of the position of the carbonyl
group on the benzopyrone isomeric structures on MAO
activity.
RESULTS AND DISCUSSION
The first studies on the ligand-target recognition were
performed with compounds 1a and 1b (Figure 2). The
results clearly indicated that 1a and 1b interact almost
equally with both MAOs (Supporting information, Table
S1). The docking geometries graphical examination
showed that 1a and 1b interacted with the active site of
hMAO-A by positioning the benzopyrone moiety towards
the FAD cofactor, whereas the anilide ring was located at
the entrance gorge. The benzopyrone and exocyclic aro-
matic rings played a main role in the stabilization of the
complexes. In fact, the benzopyrone cores of 1a and 1b
were involved in stacking to Tyr444 and Phe208 side
chains, respectively. Other productive interactions includ-
ed weak hydrophobic contacts with active site residues.
Notably, both inhibitors highlighted unfavorable electro-
static repulsion between the benzopyrone ring and
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Both systems preserve the carboxamide spacer located at pound 16a (IC50 = 47.24 nM) with a m-methyl group. The
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3-position of the pyrone ring (Figure 3).
presence of a hydroxyl group either in meta or para posi-
tion resulted in a decrease of activity. Although the benzo-
pyrone carbonyl group is important for MAO-B inhibition,
its position on the pyrone ring did not seem relevant (see
supporting information). All compounds under study were
selective towards MAO-B, since no significant activity was
found towards MAO-A (cut-off 10 µM, Table 1).
The interaction with the active sites of hMAO-A and
hMAO–B for coumarin and chromone-based derivatives 8-
21 was then evaluated by means of docking simulation
(Supporting information).
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Figure 3. Rational design strategy followed in this work
All compounds, excluding 10a with respect to hMAO-A,
were able to bind both MAO isoforms. Even if a linear cor-
relation between docking score and experimental data was
not observed (Supporting information, Table S2), the theo-
retical descriptor GScore clearly indicated that the com-
plexes between the studied molecules and hMAO-B are
more stable than the corresponding hMAO-A ones. After-
wards, molecular modeling studies were focused into the
role of R1 and R2 substituents. Regarding hMAO-A, the
most stable docking poses suggested a modest role of me-
thyl and methoxy substituents at R1, since they didn’t
significantly alter the ligand binding modes (see support-
ing information, Figures S1-S24). In hMAO-B, the best
poses of 8a and 8b reported a quite similar interaction
profile when compared to 1a and 1b. The most evident
difference concerned the opposite configuration of the
global minimum 8a complex with respect to the 1a one.
However, such a change was not observed in higher energy
poses. Even the most stable docking models of 15a
matched with the non-substituted compounds. In particu-
lar, the positioning of the coumarin scaffold overlapped
with 1a. Furthermore, the methoxy group of 15a accepted
one HB by Tyr188, which led to a greater complex stabili-
zation and enhanced theoretical affinity. Such an interac-
tion could also be addressed to 15b, even if its complex
geometry limited the HB energy contribution. The pres-
ence of a methoxy group at R1 allowed 15b to establish
one HB between the benzopyrone carbonyl oxygen and the
target’s Cys172. The anilide moiety was similarly located
when compared to the previously reported for 1b. Subse-
quently, we investigated the role of the different chemical
nature of substituents at R2 and their position (see sup-
porting information, Figures S25-S40). The top poses for
coumarins and chromones with R2 = m-methyl, m-
hydroxyl or m-chlorine (9-11, 16-18) showed the benzo-
pyrone moiety facing towards the FAD cofactor, except for
11a, which remarked the same binding mode of 8a. Theses
derivatives were mainly involved in stacking interactions
to Tyr398 and in HB to Cys172. Additionally, regarding
hMAO-B, no differences were found among higher affinity
poses of R2 para derivatives with respect to the corre-
sponding meta analogues. Since its chlorine substituent
was directed toward the FAD cofactor, 17b represented
the only exception to the previous observation.
The coumarin derivatives (Scheme 1A) were synthesized
starting from the appropriate salicylaldehyde to yield
coumarin-3-carboxylates (4a or 5a), which after hydroly-
sis yielded the corresponding coumarin carboxylic acids
6a and 7a.14 The coumarin-3-carboxamide derivatives 8a-
21a were synthesized via EDC-induced coupling of 6a and
7a with the appropriate phenylamines (see supporting
information).15
The chromone-based compounds (Scheme 1B) were syn-
thesized starting from the appropriate acetophenone to
yield chromon-3-carbaldehydes (4b or 5b).16 Afterwards,
the oxidation of the formyl group with sodium chlorite
yielded the chromone carboxylic acids 6b and 7b.17 The
chromone-3-carboxamide derivatives 8b-21b were ob-
tained through a reaction that encompassed the in situ
generation of an acyl chloride intermediate, and the subse-
quent addition of the appropriate phenylamine.13
The hMAO-A and -B in vitro inhibition (IC50) and selectivi-
ty, expressed as SI ([IC50 (MAO-A)]/[IC50 (MAO-B)]), of the
compounds under study and standard drugs (clorgyline for
MAO-A and (R)-(−)-deprenyl, rasagiline, safinamide for
MAO-B), are shown in Table 1.
Following the previous studies on coumarin-18 and chro-
mone-based13 compounds as MAO inhibitors, and to un-
derstand the effect of substituents located at similar posi-
tions on the isomeric scaffolds, a SAR study was per-
formed.
The introduction of 6-methyl or 6-methoxy substituents at
the benzopyrone-3-phenylcarboxamide scaffolds generally
resulted in potent and selective IMAO-B (Table 1). Never-
theless, 6-methylcoumarin derivatives (8a-14a) displayed
a higher potency than the 6-methoxy analogues (15a-21a).
With the exception of compound 8b (no substituents on
the chromone exocyclic ring), the introduction of a 6-
methyl (compounds 8b-14b) or a 6-methoxy (compounds
15a-21a) substituent on the chromone scaffold had no
noteworthy influence on MAO-B inhibitory activity.
For both series, a higher potency was observed for deriva-
tives bearing meta substituents on the exocyclic ring. In-
terestingly, the most active compounds of both series were
compounds 10a (IC50 = 5.07 nM), 10b (IC50 = 4.2 nM) and
17b (IC50 = 3.94 nM), all bearing a m-chlorine substituent.
The introduction of para substituents resulted in a de-
crease of activity, apart from compound 19a (IC50 = 19.43
nM), bearing a p-methyl group when compared to com-
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A
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O
O
O
O
O
O
R1
R1
R1
R1
c
a
b
OEt
H
OH
N
H
R2
O
OH
O
O
O
O
2a, 3a
4a, 5a
6a, 7a
8a-21a
B
O
O
O
O
O
O
8
9
R1
R1
R1
R1
d
e
f
CH3
H
OH
N
H
R2
10
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12
13
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OH
O
O
O
2b, 3b
4b, 5b
6b, 7b
8b-21b
15a/b
R1=OCH3; R2=H
8a/b
R1=CH3; R2=H
12a/b
13a/b
R1=CH3; R2=4'-CH3
19a/b
R1=OCH3; R2=4'-CH3
R1=OCH3; R2=4'-Cl
R1=CH3
16a/b
17a/b
18a/b
R1=OCH3; R2=3'-CH3
20a/b
21a/b
R1=CH3; R2=4'-Cl
R1=CH3; R2=4'-OH
9a/b
R1=CH3; R2=3'-CH3
R1=CH3; R2=3'-Cl
R1=OCH3
R1=OCH3; R2=3'-Cl
R1=OCH3; R2=3'-OH
14a/b
10a/b
R1=OCH3; R2=4'-OH
11a/b
R1=CH3; R2=3'-OH
Scheme 1. A- Synthetic strategy followed for the synthesis of the coumarin derivatives 8a-21a Reagents and conditions: (a) dieth-
yl malonate, EtOH, piperidine, reflux, overnight; (b) NaOH (0.5% aq./EtOH), reflux, 4h (c) EDC, DMAP, DCM, appropriate phenyla-
mine, 0º to r.t., 4h; B- Synthetic strategy followed for the synthesis of chromone-3-phenylcarboxamide 8b-21b. Reagents and con-
ditions: (d) POCl3, DMF, -10ºC, 15h; (e) H3NSO3, NaClO2, 0ºC, 12h (f) POCl3, DMF, appropriate phenylamine, r.t., 1-5h.
Subsequently, the kinetics and binding affinities of the
most promising compounds - coumarin 10a (6-methyl, m-
chloro) and chromone 10b (6-methyl; m-chloro) - were
evaluated on hMAO-B. From the Lineweaver-Burk plots
(Figure 4), we observed that both compounds operated by
a non-competitive inhibition mechanism (see supporting
information). The enzyme binding affinities, determined as
inhibition constants (Ki), were calculated from the corre-
sponding Dixon plots. Coumarin 10a (Figure 4A) and
chromone 10b (Figure 4B) displayed Ki values of 1.17 and
Figure 4. Kinetic studies on the mechanism of hMAO-B inhibi-
2.69 nM, respectively. The estimated Ki values correlated
tion by (A) coumarin 10a and (B) chromone 10b. Dixon plots
well with the experimental data (IC50): coumarin 10a (IC50
insets on the top right of each graphic.
= 5.07 nM) and chromone 10b (IC50 = 4.20 nM) displayed
slightly different IC50 and Ki values, but both within the low
nanomolar range.
Additionally, time-dependent inhibition studies with com-
pounds 10a and 10b were performed (see supporting
information). After the first 15 minutes of incubation, a
continuous decrease on enzymatic residual activity was
observed for irreversible IMAO-B ((R)-(-)-Deprenyl and
rasagiline, Figure 4A), while an enhancement on enzymatic
activity was observed across the analysis time for safina-
mide, a reversible IMAO-B (Figure 4A). For the compounds
10a and 10b (Figure 4B), the binding to the active site was
observed in the first 15 minutes, followed by an increase
on enzymatic activity over the following 60 minutes, point-
ing towards MAO-B reversible inhibition.13
Figure 5. Time-dependent inhibition of recombinant human
MAO-B by (A) standard drugs (R)-(−)-deprenyl (50 nM),
safinamide (40 nM) and rasagiline (200 nM) and (B) test
compounds 10a (12.5 nM), and 10b (12.5 nM). The residual
activity was expressed as % of control. Data are the mean ±
S.D. of three different experiments.
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Table 1. MAO inhibitory activities of benzopyrone derivatives 8a-21a and 8b-21b and standard inhibitors.
4
5
6
7
IC50 (nM)
hMAO-A
IC50 (nM)
hMAO-A
Compound
SI
Compound
SI
hMAO-B
15.32 ± 1.02
7.52 ± 1.05
5.07 ± 1.25
45.40 ± 1.30
13.90 ± 1.30
11.08 ± 1.20
621.70 ± 1.8
5.95 ± 1.28
47.24 ± 1.12
9.03 ± 1.07
228.6 ± 1.26
19.43 ± 1.19
18.90 ± 1.01
*
hMAO-B
21.35 ± 1.10
17.10 ± 1.17
4.20 ± 1.08
78.22 ± 1.30
151.6 ± 5.14
45.42 ± 2.32
512.6 ± 2.81
41.8 ± 2.2
8
9
8a
9a
*
>6527a
>13300a
>19724a
>2203a
>7194a
>9030a
>161a
8b
9b
*
>4684a
>5848a
>23810a
>1278a
>660a
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
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*
*
10a
*
10b
*
11a
*
11b
*
12a
*
12b
*
13a
*
13b
*
>2202a
>195a
14a
*
14b
*
15a
*
>16810a
>2120a
>11074a
>447a
15b
*
>2392a
>4590a
>25381a
>881a
16a
*
16b
*
21.80 ± 1.21
3.94 ± 1.08
113.5 ± 1.10
210.8 ± 8.1
10.31 ± 1.55
674.2 ± 1.72
23.07 ± 2.07
17a
*
17b
*
18a
*
18b
*
19a
*
>5150a
>5291a
n.a.
19b
*
>474a
20a
*
20b
*
>9699a
>148a
21a
*
21b
*
Deprenyl
Rasagiline
68730 ± 421
52974 ± 742
16.73 ± 1.48
49.66 ± 2.26
4108
Safinamide
Clorgyline
*
>4335a
>0.0446
1067
4.46 ± 0.32
*
a
(*) Inactive at 100 µM; n.a. non-applicable; SI: hMAO-B selectivity index = IC50(hMAO-A)/IC50(hMAO-B). Values obtained under the as-
sumption that the corresponding IC50 against MAO-A is 100 μM.
Overall, coumarin and chromone derivatives presented
druglike properties similar to those of the standard IMAO-
B safinamide (see supporting information, Table S1).19 All
compounds complied with the Lipinski’s rule of five20 and
the clogP and tPSA values were within the ideal parame-
ters for oral bioavailability. Furthermore, the blood (plas-
ma)−brain partitioning (log BB) complied with the re-
quirements for BBB permeability (log BB > -1).19 In gen-
eral, multiparameter score LLE21 values ranged from 3 to
5, with the exception of chromone 15b (LLE = 5.36) and
coumarin 17a (LLE = 5.08).
Taking into account the inhibition and selectivity observed
experimentally with respect to MAO isoforms and theoret-
ical results (see supporting information), we are confident
that our compounds, in particular the most promising
ones, cannot be considered PAINS.
(IC50 = 4.2 nM) and 17b (IC50 = 3.94 nM) were identified as
the most potent IMAO-B. In both series, the presence of a
m-chlorine substituent was favourable. Compounds 10a
and 10b showed drug-like properties and were potent
reversible and non-competitive IMAO-B. The data of mo-
lecular modeling indicated the existence of a Cys172 HB
involving the carboxamide spacer located at position 3 of
the pyrone ring. Considering that hMAO-B Cys172 is re-
placed by Asn181 in hMAO-A, the experimental hMAO-B
selectivity data of compounds 10a and 10b could be ad-
dressed to this feature. Additionally, it was observed that
the benzopyrone core, and in particular its sp2 oxygen
atom is a stabilizer of the complexes between our most
promising inhibitors and the target. Overall, no relevant
differences were observed between coumarin and chro-
mone-3-phenylcarboxamide derivatives with respect to
the recognition of the same target.
CONCLUSIONS
EXPERIMENTAL SECTION
Since coumarins and chromones are structural isomers, an
innovative project was developed involving molecular
modelling studies, synthesis of a small library of coumarin
(8a-21a) and chromone (8b-21b) derivatives and screen-
ing toward MAO-A and MAO-B inhibition. From the current
study, coumarin 10a (IC50 = 5.07 nM) and chromones 10b
Starting materials and reagents were obtained from com-
mercial suppliers and were used without further purifica-
tion (Sigma-Aldrich, Portugal). The purity of the final
products (>97% purity) was verified by high-performance
liquid chromatography (HPLC) equipped with a UV detec-
tor.
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Pharmacology. The evaluation of the monoamine oxidase
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Synthesis of coumarin derivatives
Synthesis of ethyl 6ꢀmethylcoumarinꢀ3ꢀcarboxylate (4a), ethyl 6ꢀ
methoxycoumarinꢀ3ꢀcarboxylate
carboxylic acid (6a) and 6ꢀmethoxycoumarinꢀ3ꢀcarboxylic acid
inhibitory activity of the compounds under study on both
hMAO isoforms was assessed following a previously de-
scribed method.13
To evaluate the mechanism of hMAO-B inhibition of cou-
marin 10a and chromone 10b, substrate-dependent kinet-
ic experiments and time-dependent reversibility studies
(5a),
6ꢀmethylcoumarinꢀ3ꢀ
(7a)
A
solution of 5ꢀmethylsalicylaldehyde (2a) or 5ꢀ
methoxysalicylaldehyde (3a) (1 mmol) and diethyl malonate (1
mmol) in ethanol (10 mL) was stirred at room temperature for 5
min. Pirimidine (15µL) was then added and the reaction was
maintained under reflux overnight. Afterwards, it was allowed to
cool at room temperature and the resulting suspension was filtered
off. The solid was washed with cold ethanol and diethyl ether and
recrystallized from ethanol. Then, to a solution of coumpound 4a
or 5a (2 mmol) in ethanol (25 mL), an aqueous solution of NaOH
(0.5%, 5mL) was added. The mixture was kept under reflux for
1h. Afterwards, an aqueous solution of HCl (10%) was added
dropwise until pH around 2. The resulting solid was filtered,
washed with water and recrystallized from ethanol.
were performed following
a
previously described
method.13 PAINS studies details were included in the sup-
porting information.
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ASSOCIATED CONTENT
Supporting Information. Chemistry: Detailed synthesis and
compound characterization; Pharmacology: Detailed biologi-
cal assays, inhibitory activity, kinetic and reversibility assays;
Theoretical drug-like properties determination; Molecular
modelling: Detailed procedures, docking scores and binding
poses od all derivatives; Molecular formula strings.
Synthesis of coumarin derivatives (8aꢀ21a)
To a solution of the appropriate coumarinꢀ3ꢀcarboxylic acid (6a or
7a, 1 mmol) in dichloromethane (DCM) (5 mL), 1ꢀethylꢀ3ꢀ(3ꢀ
dimethylaminopropyl)carbodiimide (EDC) (1.10 mmol) and 4ꢀ
dimethylaminopyridine (DMAP) (1.10 mmol) were added. The
mixture was kept with a flux of argon at 0ºC for ten minutes.
Shortly after, the aromatic amine (1 mmol) with the intended
substitution pattern was added in small portions. The reaction
mixture was stirred at room temperature. The solid obtained was
filtered and purified by column chromatography (hexane/ethyl
acetate 9:1) or by recrystallization from ethanol to give the deꢀ
sired products 8aꢀ21a.
AUTHOR INFORMATION
Corresponding Author
* E-mail address: fborges@fc.up.pt (F. Borges); Tel.: +351
220402560 (30560).
Author Contributions
The manuscript was written through contributions of all au-
thors. All authors have given approval to the final version of
the manuscript. ¥ Authors contribute equally.
Synthesis of chromone derivatives
ACKNOWLEDGMENT
Synthesis of 6ꢀmethylchromoneꢀ3ꢀcarbaldehyde (4b), 6ꢀ
methoxychromoneꢀ3ꢀcarbaldehyde (5b), 6ꢀmethylchromoneꢀ3ꢀ
carboxylic acid (6b) and 6ꢀmethoxychromoneꢀ3ꢀcarboxylic acid
(7b)
The authors would like to thank Fundação para a Ciência e
Tecnologia (FCT) - QUI/UI0081/2013, POCI-01-0145-FEDER-
006980 - for the financial support. Thanks are due to FCT,
POPH and FEDER/COMPETE for A. Fonseca, J Reis,T. Silva and
M. J. Matos grants. The authors also thank the COST action
CA15135 (Multi-Target Paradigm for Innovative Ligand Iden-
tification in the Drug Discovery Process, MuTaLig) for sup-
port.
A solution of 5ꢀmethylꢀ2ꢀhydroxyacetophenone (2b), or 5′ꢀ
methoxyꢀ2′ꢀhydroxyacetophenone (3b) (6 mmol), in anhydrous
N,Nꢀdimethylformamide (12 mL) was stirred at a temperature of ꢀ
10ºC for 30 minutes. Phosphoryl chloride (POCl3) (12 mmol) was
added dropwise at a temperature below ꢀ10ºC during 1 hour. The
mixture was stirred at room temperature for 15 h and poured into
water (40 mL).29 The product was filtered and washed with ethyl
ether. Then, asolution of sodium chlorite (NaClO2) (80 %, 32
mmol) in water (25 mL) was added dropwise to a mixture of 6ꢀ
methylꢀ4ꢀoxoꢀ4Hꢀchromeneꢀ3ꢀcarbaldehyde (4b) or 6ꢀmethoxyꢀ4ꢀ
oxoꢀ4Hꢀchromeneꢀ3ꢀcarbaldehyde (5b) (8 mmol) in dicloroꢀ
methane (50 mL) and sulfamic acid (NH2SO3H) (40 mmol) in
water (50 mL) at 0 ºC. After 15 hours, the reaction was extracted
with dicloromethane.30 The combined organic phases were dried
over Na2SO4, filtered and evaporated. The product was finally
washed with ethyl ether.
ABBREVIATIONS
AD, Alzheimer’s Disease, BBB, Blood-Brain Barrier, FAD, Fla-
vin Adenine Dinucleotide, HB, Hydrogen Bond; LLE, Lipophilic
Ligand Efficiency; MAO, monoamine oxidase; ND, Neuro-
degenerative Diseases; PD, Parkinson’s Disease; ROS, Reactive
Oxygen Species; PAINS, Pan Assay Interference Properties.
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Synthesis of chromone derivatives (8bꢀ21b)
POCl3 (2.6 mmol) was added to a solution of the correspondent
chromoneꢀ3ꢀcarboxylic acid (6b or 7b, 2.6 mmol) in DMF (4
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and/or crystallization.
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N-Substituted-2-Oxo-2H-1-Benzopyran-3-
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