Selectivity control in the reaction between 2-hydroxyarylaldehydes and 4-hydroxycoumarin. Antioxidant activities and computational studies of the formed products

Article abstract of DOI:10.1016/j.molstruc.2021.129936

A series of 6H,7H-7-(4-Hydroxy-3-coumarinyl)[1]benzopyrano[4,3-b][1]benzopyran-6-ones 4a-g and 3-(2-hydroxybenzoyl)-2H-chromen-2-ones 5a-g derivatives were synthesized by reaction of 4-hydroxycoumarin with 2-hydroxyarylaldehydes 2a-f or 2-hydroxynaphtalde

Full text of DOI:10.1016/j.molstruc.2021.129936

Journal of Molecular Structure 1231 (2021) 129936
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Selectivity control in the reaction between 2-hydroxyarylaldehydes
and 4-hydroxycoumarin. Antioxidant activities and computational
studies of the formed products
Kamilia Ould Lamaraa, Malika Makhloufi-Cheblia, Amina Benazzouz-Touamia,
Souhila Terrachet-Bouazizb,c, Nejla Hamdid,e, Artur M.S. Silvaf, Jean-Bernard Behrg,∗
a Laboratoire de Physique et Chimie des Matériaux LPCM, Faculté des Sciences, Université Mouloud Mammeri, 15000 Tizi Ouzou, Algeria
b Department of Chemistry, Faculty of Sciences, University Mohamed Bouguerra, Boumerdes, Algeria
c Laboratoire de Physico-Chimie Théorique et de Chimie Informatique, Faculté de Chimie, USTHB, BP 32 El Alia, 16111 Bab-Ezzouar, Algiers, Algeria
d Centre de Recherche Nucléaire de Draria (CRND), BP 43 Sebala, Draria, Algeria
e Département du Génie de l’environnement, Ecole Nationale Polytechnique, 10 Avenue des Frères Ouadek, Hassen Badi, BP 182, 16200 El Harrach, Algiers,
Algeria
f QOPNA & LAQV-REQUIMTE, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
g Université de Reims Champagne Ardenne, CNRS, ICMR UMR 7312, 51097 Reims, France
a r t i c l e i n f o
a b s t r a c t
Article history:
A
series of 6H,7H-7-(4-Hydroxy-3-coumarinyl)[1]benzopyrano[4,3-b][1]benzopyran-6-ones 4a-g and
Received 3 December 2020
Accepted 8 January 2021
Available online 15 January 2021
3-(2-hydroxybenzoyl)-2H-chromen-2-ones 5a-g derivatives were synthesized by reaction of 4-
hydroxycoumarin with 2-hydroxyarylaldehydes 2a-f or 2-hydroxynaphtaldehyde 2g using different sol-
vents and acid/base catalysts. The approach relies on a regioselective cascade reaction involving one/two
molar equiv of the 4-hydroxy coumarin iteratively acting as active methylene substrate in a Knoevenagel
condensation and in a Michael addition. The structures of all compounds were established by IR, mass
spectrometry, 1H-NMR and 13 C-NMR. Antioxidant activity of the synthesized compounds were determined
using the DPPH scavenging assay, best results being obtained with 5b (IC50 = 236 μg/mL). Computational
studies showed that the compounds bind in the ATP-binding site of p38 MAPK, in a same manner than
known polyaromatic potent inhibitors. The synthesized compounds might be considered further for can-
cer therapy.
Keywords:
Coumarin
Antioxidant activity
Molecular docking
Molecular dynamics
Cancer
P38 MAPK protein
© 2021 Elsevier B.V. All rights reserved.
1. Introduction
ber of cellular pathways and plays an important role in cell sur-
vival and apoptosis. This was confirmed by other studies reporting
Due to its versatile properties, the coumarinyl substructure is a
priviledged scaffold in the design of organic compounds. Notwith-
standing its particular physico-chemical behavior as a powerful flu-
orogenic conjugate, the 2-chromenone moiety is also found in nat-
ural products and highly bioactive compounds. Indeed, coumarin-
derived drugs exhibit broad biological activity with, for exam-
ple, antioxidant, anticoagulant, antifungal, anthelmintic, or hyp-
notic properties [1–10]. Anticancer properties of chromenones have
also been reported. Recently, Batran and collaborators demon-
strated that coumarin derivatives act as potent anti-breast and
anti-cervical cancer agents [11]. In this domain, one of the pos-
sible targets of coumarin-derived compounds is the p38 mitogen-
activated protein kinase (p38 MAPK) that regulates a large num-
the intervention of p38 MAPK inhibitors on cancer cell death [12].
Thus, coumarin appears as an attractive chemical scaffold for the
development of new anticancer agents, which would target p38
MAP-kinase as the biological receptor. Numerous methods have
been devised for the functionalization of coumarin, among which
the reaction with 2-hydroxybenzaldehydes appears of broad versa-
tility. Although very few number of investigations have been car-
ried out on the reactivity of 4-hydroxycoumarin 1 vis-a-vis ortho-
hydroxy arylaldehydes 2, the outome of the reaction seemed par-
ticularly dependent on the reaction conditions. In their pioneering
work in 1943 W. R. Sullivan and coworkers [13] reported the con-
densation of 4-hydroxycoumarin with o-hydroxybenzaldehyde in
refluxing ethanol affording two products, to which they attributed
the structures of the 1:1 adduct 3a and of the 2:1 adduct 4 as
shown on Scheme 1. However, the chemical structure of 3a was
unambiguously corrected in 1984 to its regioisomer 5. Formation of
∗
Corresponding author.
E-mail address: jb.behr@univ-reims.fr (J.-B. Behr).
https://doi.org/10.1016/j.molstruc.2021.129936
0022-2860/© 2021 Elsevier B.V. All rights reserved.

K.O. Lamara, M. Makhloufi-Chebli, A. Benazzouz-Touami et al.
Journal of Molecular Structure 1231 (2021) 129936
Scheme 1. Selectivity of the reaction of o-hydroxyaldehydes with the 4-hydroxycoumarin.
5 can be explained by a subsequent intramolecular translactoniza-
tion from unstable intermediate 3a, which occurs spontaneously in
absence of any catalyst. This translactonization has already been
revisited and described in our laboratory by M. Makhloufi and all
[14]. The authors used apolar medium (toluene) in the presence of
triethylamine (NEt3) or KF-Al2O3 (10%) to initiate the transforma-
tion.
docking and molecular dynamics studies were performed for com-
pounds 4a and 5a in order to evaluate their potential as p38 MAPK
inhibitors.
2. Experimental section
2.1. General
Years later, Xiang-Shan Wang and all [15] experienced the
condensation of o-hydroxyarylaldehydes with an excess of 4-
hydroxycoumarin (2:1) in ethanol, using KF-Al2O3 as a catalyst.
Surprisingly, in these conditions the 2:1 adduct 6 was obtained
almost exclusively, with no traces of the expected 2:1 adduct 4.
Whereas 4 results from intramolecular addition/elimination be-
tween OH from the salicylaldehyde moiety and coumarinyl C=O,
an identical reaction between both the coumarinyl moieties ac-
counts for the formation of 6. Even more astounding was the result
obtained in an aqueous medium when triethylbenzylammonium
chloride hydrate (TEBAC-H2O) was used as catalyst. In this case the
1:1 adduct 5 was obtained as a stable product in good yields (84%).
According to these results, the reaction of o-hydroxyaldehydes with
4-hydroxycoumarin appears as a highly versatile option to pre-
pare new series of coumarin-based conjugates. The variety of prod-
ucts which might be accessed under various conditions justifies
the idea of revisiting this reaction to probe chemico- and regio-
selectivity [16,17]. In this study, the reaction of 4-hydroxycoumarin
with a series of o-hydroxyarylaldehydes was performed under var-
ious solvent, catalyst or activation conditions to control the forma-
tion of the two possible poly-heterocyclic products. We also report
the evaluation of the antiradical activity of the synthesized com-
pounds using the DPPH scavenging assay. In addition, molecular
Melting points were determined on a Stuart scientific SPM3
apparatus fitted with a microscope and are uncorrected. 1H and
13C NMR spectra were recorded in DMSO-d6 solutions on Bruker
Avance 300 (300.13 MHz for 1H and 75.47 MHz for 13C) spectrom-
eter. Chemical shifts are reported in parts per million (δ, ppm) us-
ing TMS as internal reference and coupling constants (J) are given
in hertz (Hz). Mass spectra are obtained with ESI. Positive-ion ESI
mass spectra were acquired using a Q-TOF 2 instrument [diluting 1
mL of the sample chloroform solution (10−5 M) in 200 μL of 0.1%
trifluoroacetic acid/methanol solution. Nitrogen was used as neb-
ulizer gas and argon as collision gas. The needle voltage was set
at 3000 V, with the ion source at 80°C and desolvation tempera-
ture at 150°C. Cone voltage was 35 V]. The elemental microanalysis
(C, H, N) was carried out by the Truspec 630-200-200 Elementary
Analysis-Equipment.
2.2. Procedure for the synthesis of 5-iodosalicylaldehyde
To a dry 500 ml round bottom flask, 14 ml (0.134 mol) of saly-
cilaldehyde and 300 ml of methanol were added and stirred until
complete dissolution. While maintaining magnetic stirring 20.07 g
(0.134 mol) of sodium iodide (NaI) were added. After complete dis-
2

K.O. Lamara, M. Makhloufi-Chebli, A. Benazzouz-Touami et al.
Journal of Molecular Structure 1231 (2021) 129936
Table 1
Synthesis of 6H,7H-7-(4-Hydroxy-3-coumarinyl)[1]benzopyrano[4,3-b][1]benzopyran-6-one 4a and 3-(2-hydroxybenzoyl)-2H-
chromen-2-ones 5a under different reaction conditions.a
Entry
Solvent
Yields %
5a
4a
1
2
3
4
5
6
7
8
9
Ethanol
Methanol
Propanol
Isopropanol
Butan-2-ol
Isobutanol
ACN
40
5
33
21
25
11
26
-
35
-
34
11
7
2
THF
14
2
Toluene
No reaction
No reaction
a Reaction conditions: 4-hydroxycoumarin 1 (1 equiv), salicylaldehyde 2a (1 equiv), refluxing solvent, 1.5 hours.
b Isolated yields.
Table 2
Synthesis of 5a and 4a under different catalysts in ethanol and methanol.
Entry
Solvent
Catalyst (amount)
Yields (%)
5a
Time (min)
4a
1
Ethanol
H3PMo12O40 (1%)
H3PMo12O40 (2%)
H3PMo12O40 (5%)
H3PMo12O40 (8%)
Triethylamine
3
18
22
36
32
-
90
90
90
90
20
90
90
90
90
20
90
2
4
3
6
4
traces
5
53
6
Methanol
H3PMo12O40 (1%)
H3PMo12O40 (2%)
H3PMo12O40 (5%)
H3PMo12O40 (8%)
Triethylamine
5
38
39
40
40
-
7
2
8
traces
traces
78
9
10
11
c
H3PMo12O40 (5%)
-
65
c
Reaction conditions: 4-hydroxycoumarin 1 (2 equiv), salicylaldehyde 2a (1 equiv), refluxing methanol, H3PMo12 O40 (5%), 1.5 hours.
905, 866, 757 cm−1 1H NMR (DMSO-D6): δ 5.75 (s, 1H, H∗), 7.15–
,
solution of the NaI the beaker was placed on an ice/water bath.
Carefully 1eq of chloramine T was added to the reaction mixture,
magnetic stirring was maintained for 60 minutes keeping the tem-
perature at 0°C. After removal of the ice bath, 100 ml of a 10%
(w/w) aqueous solution of sodium thiosulfate was added while
stirring for further 5 minutes. Under magnetic stirring, acidification
of the reaction mixture was carried out with an HCl solution (2M,
about 10 ml) until a yellow precipitate formed (PH 3-4). The solid
obtained was filtered, washed with cold distilled water, dried and
then recrystallized from dilute ethanol (v/v) to obtain the iodosali-
cylaldehyde as light yellow crystals. Yield 60 %, mp 98°C, IR (KBr):
3220 (broad, OH), 2974 (CH aliphatic), 1668 (C=O), 1604 (C=C aro-
matic), 557 (C-I). 1H-NMR (DMSO-D6): δ 10.93 (s, 1H, OH), 10.16 (s,
1H, CHO), 7.87 (d, J=2.5, 1H, HAr), 7.77 (dd, J=9.0, J=2.5, 1H, HAr),
6.85 (d, J=9.0, 1H, ArH).
7.68 (m, 11H, ArH), 8.09–8.12 (d, J=8.1 Hz, 1H, ArH), 12.20 (br
s, OH-pyr); RMN 13C (DMSO-D6,): δ 28.7 (C∗), 100.6, 106.1, 113.9,
116.1, 116.2, 116.5, 122.2, 122.6, 123.9, 124.5, 125.3, 128.3, 128.6,
132.2, 132.5, 149.2, 151.7, 152.2, 156.3 160.4. ms (ESI): m/z (% rel-
ative intensity): 433.2 (100 %) (M+Na+). Elemental analysis: Calcd.
For C25H14 O6: C 73.17; H 3.44; Found: C 73.20; H 3.50.
10-Hydoxy-6H,7H-7-(4-Hydroxy-3-coumarinyl)[1]benzopyrano[4,3-
b][1]benzopyran-6-one (4b)
White powder, mp 265-267°C; 1H NMR (DMSO-D6): δ 5.71 (s,
1H, CH), 6.61 (d, J=6.63Hz, 1H, ArH) 6.82 (d, J= 6.8 Hz, 1H, ArH),
7.32-7.50 (m, 5H, ArH), 7.52 (t, 1H, ArH), 7.76 (t, 1H, ArH), 8.31 (d,
J=8.3 Hz, 1H, ArH), 9.85 (br s, OH-Ar), 12.20 (br s, OH-pyr.); RMN
13C (DMSO-D6): δ 28.7 (C∗), 107.3, 114.0, 115.5, 116.1,116.2,116.3,
118.3,123.2, 123.9, 124.4, 125.2, 132.2, 132.4, 145.1, 151.9, 152.1,
160.5. ms (ESI): m/z (% relative intensity): 449.2 (100%) (M+Na+).
Elemental analysis: Calcd. For: C25H14 O7: C 70.42; H 3.31; Found:
C 70.50; H 3.39.
2.3. General procedure for the synthesis of 6H,7H-7-(4-Hydroxy-3-
coumarinyl)[1]benzopyrano[4,3-b][1]benzopyran-6-ones (4a-g) and
3-(2-hydroxybenzoyl)-2H-chromen-2-ones (5a-g)
11-Hydoxy-6H,7H-7-(4-Hydroxy-3-coumarinyl)[1]benzopyrano[4,3-
b][1]benzopyran-6-one (4c)
Pink powder, mp 235-237°C; 1H NMR (DMSO-D6): δ 5.62 (s,
1H, CH), 6.57 (d, J=6.6 Hz, 1H, ArH), 6.71 (d, J= 6.7 Hz, 1H, ArH),
6.98 (d, J= 7.0 Hz, 1H, ArH), 7.31-7.73 (m, 7H, ArH), 8.08 (d, J=8.1
Hz, 1H, ArH), 9.79 (br s, OH-Ar), 12.12 (br s, OH-pyr); RMN 13C
(DMSO-D6): δ 28.1 (C∗), 102.7, 112.9, 113.8, 116.2, 116.4, 122.7,
123.9, 124.5, 129.1, 132.1, 132.4, 149.7, 151.9, 152.1, 157.3, 160.5. ms
(ESI): m/z (% relative intensity): 449.2 (100%) (M+Na+). Elemental
analysis: Calcd. For C25H14 O7: C 70.42; H 3.31; Found: C 70.50; H
3.39.
A dry flask was charged with 4-hydroxy-2H-chromen-2-one 1
[(1 equiv, 5 mmol) or (2 equiv, 0.1 mmol)], the appropriate salicy-
laldehyde derivative (and 2-hydroxynaphtaldehyde) 2a-g (1 equiv,
5 mmol) and in free or in the presence of an amount of catalyst
(see Tables 1 and 2), in solvent (20 mL). The mixture was stirred
and refluxed. The obtained solid was filtered off and washed with
hot methanol and was identified as compound 4a-g (solid not solu-
ble in hot methanol obtained by filtration before cooling) and 5a-g
(obtained from the filtrate after cooling).
9-Hydoxy-6H,7H-7-(4-Hydroxy-3-coumarinyl)[1]benzopyrano[4,3-
b][1]benzopyran-6-one (4d)
Gray powder, mp 292-294°C; 1H NMR (DMSO-D6): δ 5.67 (s,
1H, H∗), 6.60 (s, 1H, ArH) 6.68 (d, J= 6.70 Hz, 1H, ArH), 7.1 (d, J=
6H,7H-7-(4-Hydroxy-3-coumarinyl)[1]benzopyrano[4,3-
b][1]benzopyran-6-one (4a)
White powder, mp 241-243°C; IR υ (cm−1): 2972, 1699, 1645,
1610, 1567, 1488, 1455, 1390, 1276, 1242, 1221, 1106, 1044, 979,
3

K.O. Lamara, M. Makhloufi-Chebli, A. Benazzouz-Touami et al.
Journal of Molecular Structure 1231 (2021) 129936
7.17Hz, 1H, ArH), 7.33-7.48 (m, 5H, ArH), 7.59 (t, 1H, ArH), 7.67 (t,
1H, ArH), 8.05 (d, J= 8.06 Hz, 1H, ArH), 9.39 (br s, OH-Ar), 12.24
(br s, OH-pyr.); RMN 13C (DMSO-D6): δ 28.7 (C∗), 98.8, 113.9, 114.0,
115.2, 116.1, 116.4, 117.1, 122.6, 123.9, 124.5, 132.2, 132.4, 142.0,
142.1, 151.9, 152.2, 154.5, 160.5. ms (ESI): m/z (% relative intensity):
449.1 (100%) (M+Na+). Elemental analysis: Calcd. For C25H14 O7: C
70.42; H 3.31; Found: C 70.50; H 3.39.
(100). Elemental analysis: Calcd. for C16 H10O5: C 68.09; H 3.57
Found: C 68.22; H 3.50.
3-(2-hydroxybenzoyl)-6-iodo-2H-chromen-2-one (5f)
Yellow powder, mp 252-234°C; 1H NMR (DMSO-D6): δ 6.92-
6.96 (m, 2H, ArH), 7.29 (d, J=7.3 Hz, 1H, HAr), 7.47-7.52 (m, 1H,
ArH), 7.69 (d, J=7.7 Hz, 1H, HAr), 7.97 (d, J= 7.8 Hz, 1H, HAr),
8.26 (s, 1H, HAr), 8.27 (s, 1H, H-4), 10.74 (s, br, OH-11); 13C-
NMR (DMSO-D6): δ 117.4, 117.5, 119.0, 119.9, 121.1, 123.8, 127.0,
130.2, 131.3, 136.0, 138.0, 141.7, 153.9, 158.1, 159.2, 192.0, 160.89.
ms (ESI): m/z (% relative intensity): 414.9 (100) (M+Na)+. Elemen-
tal analysis: Calcd. for C16 H9IO4: C 49.01; H 2.31 Found: C 48.92;
H 2.40.
9-Nitro-6H,7H-7-(4-Hydroxy-3-coumarinyl)[1]benzopyrano[4,3-
b][1]benzopyran-6-one(4e)
White powder, mp 312-315°C; I.R υ (cm−1): 3309, 3072, 1703,
1670, 1646, 1629, 1609, 1523, 1496, 1455, 1392, 1337, 1286, 1243,
1218, 1185, 1111, 1090, 1059, 904, 848, 754. 1H NMR (DMSO-D6):
δ 6.20 (s, 1H, H∗), 6.79 (d, J=8.8 Hz, 1H, ArH) 7.22–7.26 (m, 4H,
ArH), 7.48–7.52 (m, 2H, ArH), 7.82 (d, J=7.2 Hz, 2H, ArH), 7.93 (dd,
J=8.8 Hz, J’=2.8 Hz, 1H, ArH), 8.04 (d, J=8.0 Hz, 1H, ArH); RMN 13C
(DMSO-D6): δ 28.6 (C∗), 102.5, 112.5, 113.3, 116.1, 116.6, 117.6, 122.7,
123.1, 124.3, 124.4, 124.7, 125.0, 132.5, 132.9, 133.3, 138.3, 144.2,
152.0, 152.3, 154.3, 159.7, 160.1. ms (ESI): m/z (% relative intensity):
478.1 (100%) (M+Na+). Elemental analysis: Calcd. for C25H13O8N: C
65.94, H 2.88, N 3.08, Found: C 66.02, H 2.96, N 3.04.
3-(2-hydroxybenzoyl)-2H-benzo[f]chromen-2-one (5g)
Yellow powder, mp 254-256°C; I.R (KBr): 3486 (OH), 1571
(C=C-aromatic); 1H-NMR (DMSO-D6): δ 6.93 (d, J=7.8 Hz, 2H,
HAr), 7.49 (t, 2H, HAr), 7.72 (t, 2H, HAr), 7.65 (d, J=7.8 Hz, 1H, HAr),
8.10 (d, J=7.7 Hz, 1H, HAr), 8.30 (d, J=7.6 Hz, 1H, HAr), 8.63 (d,
J=8.0 Hz, 1H, HAr), 9.13 (s, 1H, H-4), 10.78 (s, 1H, OH-11); 13C-NMR
(DMSO-D6): δ 112.3, 116.2, 116.9, 119.0, 122.1, 123.3, 126.0, 127.1,
128.4, 128.6, 128.9, 129.7, 131.1, 134.4, 135.3, 138.7, 153.9, 157.6,
159.0, 192.8; ms (ESI): m/z (% relative intensity): 339.09 (100)
(M+Na)+. Elemental analysis: Calculated for: C20H12O4: C 75.94;
H 3.82; Found: C 75.80; H 3.75.
9-Iodo-6H,7H-7-(4-Hydroxy-3-coumarinyl)[1]benzopyrano[4,3-
b][1]benzopyran-6-one(4f)
White powder, mp 295-297°C; 1H NMR (DMSO-d6, 300 MHz):
δ 5.69 (s, 1H, CH), 7.16 (d, J=7.19 Hz, 1H, ArH), 7.31-7.48 (m,
5H, ArH), 7.57-7.71 (m, 3H, ArH), 8.05 (dd, J=8.07 Hz, J’=2.1 Hz,
2H, ArH), 8.07 (d, J=8.09 Hz, 1H, ArH), 12.33 (s, br, OH-pyr.);
RMN 13C (DMSO-D6, 400MHz): δ 28.9, 102.80, 116.5, 116.6, 118.2,
118.9, 122.6, 124.5, 125.4, 126.3, 132.7, 132.8, 134.5, 137.4, 144.5,
152.4, 152.7, 152.8, 160.7. ms (ESI): m/z (% relative intensity): 558.9
(100%) (M+Na)+. Elemental analysis: Calcd. for C25H13IO6: C 55.99,
H 2.44, Found: C 56.02, H 2.56.
2.4. Evaluation of the free-radical scavenging properties of 4a-g and
5a-g
The DPPH radical scavenging capacity was measured from the
bleaching of purple coloured ethanol solution of DPPH. according
to the method described by L.L. Mensor et al, J.S. Lee et al [18,19].
DPPH. stock solution was prepared by dissolving 4 mg DPPH. in
100 mL ethanol. Compounds 4 and 5 were dissolved in DMSO to
obtain a solution of 10−1 M. Test compounds were diluted fur-
ther with DMSO to get final concentrations of 0.05, 0.025 and
0.0125 mol/l for all the compounds, whereas the standard (ascor-
bic acid) was diluted to 0.1, 0.05, 0.025, 0.0125, 0.00625, 0.003125,
0.0015625 mol/l solutions respectively. Wells were loaded with 40
μL of tested sample and then with 2 mL of DPPH solution, all as-
says being carried out in triplicate. Negative control wells were
loaded with 40 μL of DMSO and 2 mL of DPPH. solution. After
vortexing, the mixtures were incubated at room temperature for
1 h in darkness at 25°C, and then the absorbance of the plate was
recorded at 517 nm. Ascorbic acid (AA) was used as standard for
the antioxidant activity screening. A blank containing only ethanol
with DMSO was used as the control. Each measurement was per-
formed in triplicate.
6H,7H-7-(4-Hydroxy-3-coumarinyl)[1]benzo[f]benzopyrano[4,3-
b][1]benzopyran-6-one (4g)
Pink powder, mp 298-300°C; 1H NMR (DMSO-D6): δ 6.19 (s, 1H,
CH), 7.26 (t, J=7.7 Hz, 2H, ArH) 7.42-7.63 (m, 7H, ArH), 7.69-7.74
(m, 1H, ArH), 7.93-7.99 (t, J=8.0 Hz, 2H, ArH), 8.16 (dd, 1H, J=8.2
Hz, J’= 2.1 Hz), 12.66 (br s, OH-pyr.); RMN 13C (DMSO-D6): δ 27.0
(C∗), 101.3, 113.7, 115.8, 116.2, 116.5, 117.0, 122.7, 123.9, 124.5, 125.0,
127.2, 128.7, 129.2, 132.3, 132.6, 138.4, 152.0, 152.2, 160.5; ms (ESI):
m/z (% relative intensity): 483.2 (100%) (M+Na+). Elemental analy-
sis: Calcd. For: C29H16 O6: C 75.65; H 3.50; Found: C 75.86; H 3.65.
3-(2-hydroxybenzoyl)-2H-chromen-2-one (5a)
Yellow powder, mp 175-177°C; I.R υ (cm−1): 3403 (OH), 1716
(O=C-O); 1H-NMR (DMSO-D6): δ 6.90–6.97 (m, 2H, HAr), 7.40–7.50
(m, 3H, HAr), 7.67–7.74 (m, 2H, HAr), 7.86 (d, J=7.6 Hz, 1H, HAr),
8.34 (s, 1H, H-4), 10.69 (s, br, OH-11); 13C NMR (DMSO-D6): δ 116.1,
116.9, 118.3, 119.2, 123.4, 124.8, 128.1, 128.8, 129.7, 130.8, 133.2,
135.2, 142.7, 153.7, 158.5, 191.8. Ms (ESI): m/z (% relative inten-
sity): 267 (M+H)+ (100). Elemental analysis: Calcd. for C16 H10O4:
C 72.18; H 3.79; Found: C 72.02; H 3.60.
2.5. Molecular docking studies
Molecular docking studies were conducted next to evaluate the
potential of compounds 4a,5a to inhibit p38 MAPK, an anticancer
target enzyme. To this aim, 4a,5a as well as the known inhibitor
SB2, structurally belonging to the pyridinyl-imidazole family, were
docked in the p38 MAPK active site, using iGEMDOCK v 2.1 pro-
gram [20], to predict their binding mode, their interactions and
their binding energies with this protein. Structures were drawn us-
ing MarvinSketch software [21] and the corresponding PDB files
were imported in iGEMDOCK v2.1 software as ligands. The pro-
tein coordinates of p38 MAPK was downloaded from the Protein
Data Bank [22] (PDB: 1a9u with resolution of 2.50 Ǻ, correspond-
ing to p38 MAPK protein complexed with inhibitor SB2). The active
site was identified as a distance of 8 Ǻ from the center of bound
ligand SB2. All docking simulations were performed with standard
docking, population size of 200, 70 generations and number of so-
lutions of 2. Obtained binding modes and docking energies of 4a,5a
were compared with those of the potent inhibitor SB2.
8-hydroxy-3-(2-hydroxybenzoyl)-2H-chromen-2-one (5b)
Yellow powder, mp 252-254°C; 1H-NMR (DMSO-D6): δ 7.18 (d,
J=7.8 Hz, 1H, HAr), 7.20 (t, 1H, HAr), 7.34 (d, J=7.6 Hz, 1H, HAr),
8.34 (s, 1H, H-4), 10.40 (s, 1H, OH-8), 10.77 (s,1H, OH-11); 13C
NMR (DMSO-D6): δ 116.9, 118.3, 119.2, 123.4, 124.9, 128.1, 120.8,
129.7, 130.8, 133.2, 135.2, 144.4, 146.5, 153.7, 158.5, 191.8. Ms (ESI):
m/z (% relative intensity): 305 (M+Na)+ (100). Elemental analysis:
Calcd. for C16 H10O5: C 68.09; H 3.57; Found: C 68.12; H 3.60.
7-hydroxy-3-(2-hydroxybenzoyl)-2H-chromen-2-one (5c)
Yellow powder, mp 254-256°C; RMN 1H (DMSO-D6): δ 6.78 (s,
1H, HAr), 6.84 (d, J=7.6 Hz, 1H, HAr), 6.87 (d, J=8.0 Hz, 1H, HAr),
6.90 (t, 1H, HAr), 7.71 (d, J=7.8 Hz, 1H, HAr), 7.42 (t, 1H, HAr),7.59
(d, J=7.6 Hz, 1H, HAr), 8.28 (s, 1H, H-4), 9.93 (s, 1H, OH-7), 10.64
(s, 1H, OH-11); RMN 13C (DMSO-D6): δ 102.0, 110.9, 113.9, 116.8,
119.2, 123.5, 124.3, 130.9, 131.6, 134.7, 144.7, 156.4, 158.3, 158.5,
163.6, 192.5. Ms (ESI): m/z (% relative intensity): 305 (M+Na)+
4

K.O. Lamara, M. Makhloufi-Chebli, A. Benazzouz-Touami et al.
Journal of Molecular Structure 1231 (2021) 129936
Scheme 2. Synthesis of 3-acetoacetylcoumarins 8 [29] and pyranyl-pyranpchromene 9. [30].
Scheme 3. Synthesis of 6H,7H-7-(4-Hydroxy-3-coumarinyl)[1]benzopyrano[4,3-b][1]benzopyran-6-one 4a and 3-(2-hydroxybenzoyl)-2H-chromen-2-ones 5a.
2.6. Molecular dynamics studies
densation with 2, a first set of experiments was devoted to study
the influence of the solvent and of a catalyst in the reaction out-
come.
In order to evaluate the stability of docked complexes, 4a-p38
MAPK, 5a-p38 MAPK and SB2-p38 MAPK, we submitted them to
10 ns of molecular dynamics simulations, using the same proto-
col of molecular dynamics as in our previous work [23]. Thus, we
used the Nano Molecular Dynamics software NAMD 2.12 [24] with
CHARMM 36 force field. Ligands topologies were generated using
the CHARMM General Force Field (CGenFF) web server. All com-
plexes were solvated in a cubic water box of edge length 10 Ǻ
and then neutralized with NaCl. The particle mesh Ewald (PME)
method [25] was used with a 12 Ǻ nonbonded cutoff and a grid
spacing of 1 Ǻ to include the contribution of short/long-range
interactions. Periodic boundary conditions (PBCs) [26] were used
and temperature and pressure were maintained constant using
Langevin thermostat (310 K) and Langevin barostat (1 atm), respec-
tively. Then, the three systems underwent 5000 steps of steepest-
descent energy minimization to remove atomic overlaps or im-
proper geometries. After this, studied systems were equilibrated
for 100 ps under the constant number of particles, pressure and
temperature (NPT). Finally, the obtained systems were submitted
to 10 ns of molecular dynamics using 2 fs time steps. Obtained re-
sults were visualized and analyzed using VMD software [27] and
Discovery Studio visualizer [28].
We have started our work by revisiting the condensation of
equimolar amounts of 4-hydroxycoumarin 1 and salicylaldehyde 2a
in refluxing ethanol, for 1.5 hours in the absence of any catalyst.
This reaction led mainly to the formation of a yellowish solid af-
ter cooling and recristallisation from methanol, in moderate yield
though (entry 1 of Table 1). MS (m/z 267 [M+H]+) and 1H NMR
[10.69 ppm (br s, 1H, OH phenolic), 8.34 ppm (s, 1H, H-4), 6.90-
7.82 ppm (9H, Har)] analyses were consistent with the formation
of compound 5a, a 1:1 adduct of 1 and 2a (m/z 267 [M+H]+)
(Scheme 1). One can explain the formation of this compound by
a Knoevenagel condensation of 1 with 2a leading to compound 5a
after subsequent intramolecular translactonization (Scheme 3).
The reaction of salicylaldehyde 2a with 4-hydroxycoumarin
1 was used as a model and was studied in different solvents
(methanol, propanol, isopropanol, butan-2-ol, isobutanol, acetoni-
trile, THF and toluene) without any catalyst. Under these con-
ditions, the reaction yielded a mixture of dicoumarol 4a and
translactonised product 5a, which could be separated by simple re-
crystallisation in hot methanol. An optimized yield of 40 % was ob-
tained in the presence of ethanol (Table 1, entry 1), protic solvents
appearing as the most suitable for this transformation. In all these
assays, translactonized compound 5a was obtained as the major
product, and was even formed in an exclusive manner in iPrOH
or 2-butanol.
3. Results and discussion
To investigate the influence of a catalyst in the reaction out-
come, the same transformation was carried out under acid- (het-
eropolyacid, H3PMo12O40) and base-catalyzed conditions (triethy-
lamine) in refluxing ethanol/methanol. Under all these condi-
tions, the reaction afforded two products 4a and 5a (Table 2)
as well. However, acid catalysis mostly promotes the forma-
tion of dicoumarol 4a, whereas NEt3 affords exclusively the
translactonization product 5a. The formation of compound 4a
3.1. Chemistry
In our previous studies, we have shown that the condensation
of 4-hydroxy-6-methyl-2H-pyran-2-one (TAL) 7 with salicylalde-
hyde derivatives 2a, in a range of different solvents (reflux) and
using different catalysts, afforded 3-acetoacetylcoumarins 8 in ba-
sic medium [29] and 10-(4-Hydroxy-6-methyl-2-oxo-2H-pyran-3-
yl)-3-methyl-1H,10H-pyrano[4,3-b]chromen-1-ones 9 in the pres-
ence of heteropolyacids (HPA) [30] (Scheme 2). 4-hydroxycoumarin
(or 4-hydroxybenzopyran-2-one) 1 might react in the same man-
ner than its homologue 7, via the strongly nucleophilic carbon at
position C3. To investigate the reactivity of 1 in a Knoevenagel con-
can be explained by
ing an acid/base catalyzed Knoevenagel condensation of 1 with
2a leading to compound 3, which undergoes Michael ad-
dition in specific position (3a) of another molecule of 4-
a regioselective cascade reaction involv-
a
a
5

K.O. Lamara, M. Makhloufi-Chebli, A. Benazzouz-Touami et al.
Journal of Molecular Structure 1231 (2021) 129936
Scheme 4. Mechanism proposal for the synthesis of of 6H,7H-7-(4-Hydroxy-3-coumarinyl)[1]benzopyrano[4,3-b][1] benzopyran-6-one 4a and 3-(2-hydroxybenzoyl)-2H-
chromen-2-ones 5a.
hydroxycoumarin
1
affording intermediate 10.
A
further cy-
obtained when using 2eq of 4-hydroxycoumarin 1 and 1eq of
2-hydroxyarylaldehydes 2b-f and 2-hydroxy-naphthaldehyde 2g.
Unlike other salicyaldehyde derivatives, it was observed that
5-hydroxysalicylaldehyde 2d leads to the formation of the same
product 4d in the presence or absence of the catalyst.
An increase in reaction time (TLC monitoring), led to total se-
lectivity (towards compounds 4) with better yields than those ob-
served when the reaction time was 90 minutes and the best yield
was observed with 2-hydroxynaphthaldehyde 2g (4g: 83%) (see
Table 4).
clodehydration of 10 yielded the isolated 6H,7H-7-(4-Hydroxy-3-
coumarinyl)[1]benzopyrano[4,3-b][1]benzopyran-6-one 4a. Forma-
tion of 4a is sensitive to nature of the solvent used and to the
amount of HPA. The yield of 4a increases with the increasing
amount of H3PMo12O40 (Table 2), best yield being obtained in the
presence of 5 mol % catalyst in methanol.
When the reaction was performed using two equiv of 1 and
one equiv of salicylaldehyde 2a in the presence of 5 mol % of
H3PMo12O40 in methanol, 4a was obtained in good yield (65%)
(Table 2).
Subsequently,
hydroxyarylaldehydes
2g, which feature
the
reaction
2b-f and
range of electron-donating or electron-
was
applied
to
2-
2-hydroxynaphthaldehyde
3.2. Mechanism of reaction
a
withdrawing substituents (Table 3). The reactions were carried
out in MeOH or EtOH, without any catalyst or in the presence
of H3PMo12O40 (5 mol%). Alternatively, the molar ratio of both
reagents 1 and 2a-g was varied from 1:1 to 2:1 to study the im-
pact of an excess of 1 on ratio or yield. The transformation proved
efficient in all cases, yielding the expected benzoylchromenes
5b-g and fused chromeno-chromens 4b-4g. Better yields were
The first step of the proposal mechanism (Scheme 4) is a Kno-
evenagel condensation followed by dehydration, resulting in the
formation of a stable chromone 3, which might exist in two tau-
tomeric forms 3a and 3b. In the last step, the chromone conjugate
3 undergoes two types of reactions according to the conforma-
tion of the intermediate: intramolecular translactonisation, which
passes through the form 3b, gives the compounds 5 and a Michael
6

K.O. Lamara, M. Makhloufi-Chebli, A. Benazzouz-Touami et al.
Journal of Molecular Structure 1231 (2021) 129936
Table 3
Synthesis of 5a-g and/or 4a-g in the absence of catalyst (in ethanol) and in the presence of H3PMo12 O40 (5 mol %) (in methanol), 4-hydroxycoumarin 1/
2-hydroxyarylaldehydes 2b-f (and 2-hydroxy-naphthaldehyde 2g) (1:1 and 2:1 eq.), 1.5 hours.
(amount of
Entry
Solvent
products)
Aldehyde
Conditions
no catalyst
Yields (%)
5a-g
4a-g
1
2
3
4
Salicylaldehyde 2a
40
22
40
-
5
3-hydroxysalicylaldehyde 2b
4-hydroxysalicylaldehyde 2c
5-hydroxysalicylaldehyde 2d
10
-
(1:1)
Ethanol
24
5
6
7
5-nitrosalicylaldehyde 2e
5-Iodosalicylaldehyde 2f
2-hydroxynaphtaldehyde 2g
No reaction
No reaction
68
51
16
-
8
Salicylaldehyde 2a
H3PMo12O40 (5 mol %)
6
-
36
32
40
43
37
41
48
9
3-hydroxysalicylaldehyde 2b
4-hydroxysalicylaldehyde 2c
5-hydroxysalicylaldehyde 2d
5-nitrosalicylaldehyde 2e
5-Iodosalicylaldehyde 2f
10
11
12
13
14
15
(1:1)
-
-
-
10
-
Methanol
(2:1)
2-hydroxynaphtaldehyde 2g
16
17
18
19
20
21
Salicylaldehyde 2a
H3PMo12O40 (5 mol %)
traces
65
53
64
60
32
48
65
3-hydroxysalicylaldehyde 2b
4-hydroxysalicylaldehyde 2c
5-hydroxysalicylaldehyde 2d
5-nitrosalicylaldehyde 2e
5-Iodosalicylaldehyde 2f
2-hydroxynaphtaldehyde 2g
-
-
-
-
traces
-
Table 4
Synthesis of 4a-g in the presence of H3PMo12 O40 (5 mol %), methanol and ratio of
4-hydroxycoumarin 1/ 2a-g (2:1 eq).
Entry
Aldehydes
Compound
Time (h)
Yields (%)
1
2
3
4
5
6
7
Salicylaldehyde 2a
4a
4b
4c
4d
4e
4f
5
4
4
3
6
4
6
73
62
78
76
40
63
83
3-hydroxysalicylaldehyde 2b
4-hydroxysalicylaldehyde 2c
5-hydroxysalicylaldehyde 2d
5-nitrosalicylaldehyde 2e
5-Iodosalicylaldehyde 2f
2-hydroxynaphtaldehyde 2g
4g
addition of a second molecule of 4 –hydroxycoumarin on the form
3a, gives dicoumaroles 4.
In order to explain the formation of the two products, we car-
ried out the theoretical calculations of the formation enthalpies
ꢀHf and the electrostatic potential of the charges (Table 5) for
the two rotamers 3a and 3b at B3LYP/6-31G∗ level of theory us-
ing ORCA software [31,32].
Fig. 1. The variation of absorbance versus concentration of the different compounds
4, 5 and AA.
According to (Table 5), with almost all substrates (R=H, OH,
NO2, I) the endo-OH conformation 3b is of lower energy than its
exo-OH counterpart 3a. This result might account for the increas-
ing yield in product 5, which results from intramolecular attack of
proximal OH to coumarinyl carbonyl such as observed in structure
3a.
AA. Lower absorbance of the reaction mixture indicates higher free
radical scavenging activity. The IC50 of the most active compounds
are shown in Fig. 2 The capability to scavenge the DPPH. (or in-
hibition %) was calculated as follows: RSA (%) = [(Ac - As)/Ac] x
100
Where Ac is the absorbance of the control (absorbance of DPPH.
ethanol solution without sample), and As is the absorbance of the
tested compound after 60 min incubation.
On the other hand, if we look at the Mulliken charge values of
the carbon atom of the C=O bond in position 2 of the coumarin
nucleus, the latter is more positive in the 3b form than in the 3a,
which favors the approach of the polar solvent and facilitates the
translactonization unlike the apolar solvent.
These assays reveal that compound 5b has excellent antiox-
idant activity (IC50= 0.2357 mg/ml) followed by compound 4b
and 5f. However, the other coumarinyl derivatives 5a, 5g, 4e, 4g
do not show any significant activity. According to the results ob-
tained, we notice that the condensation of a second molecule of
4-hydroxycoumarin (compound 4b, 4f) leads to a decrease in an-
tioxidant activity (SAR (%) 5b > 4b, 5f > 4f).
3.3. Antioxidant activity assessment
The antioxidant activity (free radical scavenging activity) of
the synthesized 5 and 4 was evaluated using the 2,2-diphenyl-1-
picrylhydrazyl free radical (DPPH.) scavenging assay [18,19]. Fig. 1
shows the variation of absorbance versus concentration of the dif-
ferent compounds 4a-g, 5a-c, 5f-g and of the standard ascorbic acid
The results showed that the position of the hydroxyl groups has
a significant impact on antioxidant activity. The best inhibition was
7

K.O. Lamara, M. Makhloufi-Chebli, A. Benazzouz-Touami et al.
Journal of Molecular Structure 1231 (2021) 129936
Table 5
Calculated Gibbs energy of the two rotamers 3a and 3b.
R
Solvent
ꢀHf Kcal/mol x 10−3
3a
3b
H
Ethanol Methanol THF
Ethanol Methanol THF
Ethanol Methanol HF
Ethanol Methanol THF
Ethanol Methanol THF
Ethanol Methanol THF
Ethanol Methanol THF
-575.45 -576,93 -573,61
-622.78 -621,39 -620,59
-620.19 -617,63 -621,81
-620.99 -626,90 -624,96
-703.53 -708,40 -700,45
578.63 -578,33 -582,64
-670.28 -669,76 -670,23
-577.24 -579,05 -571,14
-624.46 -619,00 -618,07
-619.08 -622,61 -616,99
-618.48 -629,16 -624,79
-707,32 -708,22 -706,41
-579.52 -579,52 -577,72
-670.51 -669,99 -670,68
3-OH
4-OH
5-OH
5-NO2
5-I
Benzo[f]
Table 6
Interacting residues, hydrogen bonds, and binding energies of studied compounds as predicted by iGEMDOCK software.
Compound
Hydrogen bonds
Interacting residues
Binding energy
4a
Asp168 (2 Hbonds), Lys53
Ala51, Lys53
Asp168, Glu71, Leu167, Leu104, Lys53, Ala51, Met109,
Asp168, Leu167, Leu104, Lys53, Val38, Ala51
-104.37
-77.13
-98.80
5a
SB2
Met109, Lys53
Asp168, Met109, His107, Thr106, Val105, Ala51, Leu104, Lys53, Val38, Tyr35
in (Fig. 3C) and Table 6. It makes two hydrogen bonds with residue
Asp168 and one with Lys53. On the other hand, compound 5a
makes one hydrogen bond with residue Ala51 and one with Lys53
(Fig. 3C and Table 6).
In Table 6, we reported 4a and 5a binding energies, hydrogen
˚
bonds and interacting residues of the active site (< 4 A). The bind-
ing energies between synthesized compounds and p38 MAPK pro-
tein are negative. It is worth noting that, the negative value of
binding energy change reveals that the binding process is spon-
taneous and that the compound might be accepted as a drug.
On the other hand, the calculated binding energy of compound
4a is lower than that of experimental ligand SB2 (Table 6). Based
on this result, it can be assumed that the synthesized compound
4a shows higher affinities for p38 MAPK protein. In addition, inter-
acting residues namely Asp168, Leu104, Lys53 and Ala51 are pre-
dicted by our docking model to be conserved in three studied com-
pounds.
Fig. 2. IC50 values of the antioxidant activity for compounds 5b, 4b and the stan-
dard AA.
observed when the OH group is in the meta position. Compared
to the two compounds 5a and 4a, the introduction of an halogen
substituent (Iodine) in the compounds 5f, 4f has led to an increase
in activity.
3.5. Molecular dynamics studies
To confirm the binding mode and the stability of docked ligands
4a and 5a with p38 MAPK, molecular dynamics simulations were
conducted. The stability of studied systems was evaluated based on
change in RMSD of ligands in the protein active site and RMSD of
carbons α of protein backbone and compared to those of experi-
mental ligand SB2.
3.4. Molecular docking
In order to evaluate the potential of our synthesized com-
pounds against cancer pathology, we studied herein their bind-
ing mode, interaction and binding energies with p38 mitogen-
activated protein kinase (p38 MAPK). The results show that almost
all of the docked compounds bind at the same binding site in the
active site of p38 MAPK as determined experimentally. Our docking
method was first validated with the known ligand SB2, a potent in-
hibitor of p38 MAPK, by using the structure of protein-ligand com-
plex PDB: 1a9u. Satisfyingly, comparison between the calculated
and experimental positioning of SB2 into the protein shows that
the docked conformation was close to the crystal one (as shown
Calculated RMSD plots of protein backbone Cα atoms of stud-
ied systems (4a-p38 MAPK, 5a-p38 MAPK and SB2-p38 MAPK),
through the 10 ns of molecular dynamics are reported in (Fig. 4).
This figure shows that the backbone Cα of 5a-p38 and 4a-p38
complexes show small fluctuations until 5 ns, where the complex
˚
˚
reach stability at around 1.5 A and 2.2 A of RMSD, respectively,
until the end of simulation. The RMSD of backbone Cα of SB2-p38
˚
˚
increases until 8.3 A, after which it stabilizes at 2.8 A until the end
of simulation.
Calculated RMSD plots of the three studied ligands 4a, 5a and
SB2, through the 10 ns of molecular dynamics are reported in
(Fig. 5).
˚
in Fig. 3A). The RMSD between the two conformations was 0.75 A,
which is quite satisfactory as previously demonstrated [33].
Superposition of the docked conformations of synthesized com-
pounds 4a and 5a on the X-ray structure of SB2 shows that binding
modes of 4a and 5a are indeed most closely related to that ob-
served in the crystallographic complex 1a9u, as shown in (Fig. 3B).
Visualization of docked conformations of 4a and 5a shows that,
the synthesized compounds are involved in hydrogen bonds and
hydrophobic interactions with the residues of the protein active
site. Compound 4a interacted with different amino acids as shown
Analysis of results shows some differences between the three
curves indicating some movements of studied compounds in the
p38 active site. The calculated RMSD values of compound 4a de-
˚
˚
creases from 1 A to 0.5 A till 0.5 ns, and stays constant until the
end of simulation time. This result confirms that the compound 4a
reach equilibrium at 0.5 ns, revealing that it has converged during
the simulation. On the other hand, the RMSD curve shape calcu-
lated for compound 5a approaches a horizontal line during all the
8

K.O. Lamara, M. Makhloufi-Chebli, A. Benazzouz-Touami et al.
Journal of Molecular Structure 1231 (2021) 129936
Fig. 3. Superimposition of A- docked (green) and experimental (magenta) structures of SB2; B- compounds 4a (magenta), 5a (pink) and experimental (green) structures of
SB2); C and D- Hydrogen bond interactions between p38 MAPK active site residues and synthesized compounds C- 4a, D- 5a. The protein backbone was presented in blue
ribbon.
Fig. 5. RMSD plots of the studied compounds 4a (green), 5a (blue) and SB2 (red)
through the 10 ns of molecular dynamics simulations.
Fig. 4. RMSD plots of backbone Cα atoms of complexes 4a-p38 (green), 5a-p38
(blue) and SB2-p38 (red).
2
2
˚
˚
18926.0 A and 19018.58 A , respectively (Fig. 6A). The SASA of 4a-
p38 MAPK and 5a-p38 MAPK complexes exhibit similar behavior as
the experimental one up to 6 ns, following that a slight decrease
in SASA of 5a-p38 MAPK complex was observed.
˚
time of simulation, at the average value of RMSD of 1.4 A, indicat-
ing that the compound reaches equilibrium and its change of con-
formation is very little. In contrary, the experimental compound
SB2 is stable until 7 ns, after which some fluctuations were ob-
served.
The calculated radius of gyration (rGyr) for 4a-p38 MAPK, and
5a-p38 MAPK complexes exhibits lesser fluctuations relative to the
SB2-p38 MAPK revealing that the systems composed of our syn-
thesized compounds 4a and 5a and p38 MAPK protein arranged to
a more compact conformation.
The solvent accessible surface area (SASA) and the radius of gy-
ration (rGyr) were calculated for the three studied complexes dur-
ing the 10 ns of molecular dynamics simulation to illustrate the
structural change of the protein and reported in (Fig. 6). These two
parameters are widely used as the criterion of equilibrium [23,34].
4. Conclusion
The average values of total SASA calculated for SB2-p38 MAPK,
In this work, we have established
a simple and efficient
2
˚
4a-p38 MAPK, and 5a-p38 MAPK complexes are 19178.6 A ,
methodology to control the selectivity of the reaction of salicy-
9

K.O. Lamara, M. Makhloufi-Chebli, A. Benazzouz-Touami et al.
Journal of Molecular Structure 1231 (2021) 129936
Acknowledgments
Thanks are due to the Portuguese NMR Network. We thank
Hilário Tavares (Department of Chemistry, University of Aveiro,
3810-193 Aveiro, Portugal) for performing the mass and NMR spec-
tra.
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