Furofuran lignans as a new series of antidiabetic agents exerting α-glucosidase inhibition and radical scarvenging: Semisynthesis, kinetic study and molecular modeling

Article abstract of DOI:10.1016/j.bioorg.2019.03.077

A new series of furofuran lignans containing catechol moiety were prepared from the reactions between lignans and a variety of phenolics. All 22 products obtained were evaluated against three different α-glucosidases (maltase, sucrase and Baker's yeast glucosidase) and DPPH radical. Of furofuran lignans evaluated, β-14, having two catechol moieties and one acetoxy group, was the most potent inhibitor against Baker's yeast, maltase, and sucrase with IC₅₀ values of 5.3, 25.7, and 12.9 μM, respectively. Of interest, its inhibitory potency toward Baker's yeast was 28 times greater than standard drug, acarbose and its DPPH radical scavenging (SC₅₀ 11.2 μM) was 130 times higher than commercial antioxidant BHT. Subsequent investigation on mechanism underlying the inhibitory effect of β-14 revealed that it blocked Baker's yeast and sucrase functions by mixed-type inhibition while it exerted non-competitive inhibition toward maltase. Molecular dynamics simulation of the most potent furofuran lignans (4, α-8b, α-14, and β-14) with the homology rat intestinal maltase at the binding site revealed that the hydrogen bond interactions from catechol, acetoxy, and quinone moieties of furofuran lignans were the key interaction to bind tightly to α-glucosidase. The results indicated that β-14 possessed promising antidiabetic activity through simultaneously inhibiting α-glucosidases and free radicals.

Full text of DOI:10.1016/j.bioorg.2019.03.077

BioorganicChemistry87(2019)783–793
Contents lists available at ScienceDirect
Bioorganic Chemistry
journal homepage: www.elsevier.com/locate/bioorg
Furofuran lignans as a new series of antidiabetic agents exerting α-
glucosidase inhibition and radical scarvenging: Semisynthesis, kinetic study
and molecular modeling
Wisuttaya Worawalaia, Titiruetai Doungwichitrkula, Warin Rangubpitb, Panyakorn Taweechatb,
⁎
Pornthep Sompornpisutb, Preecha Phuwapraisirisana,
a Center of Excellence in Natural Product, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
b Center of Excellence in Computational Chemistry, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
A R T I C L E I N F O
A B S T R A C T
Keywords:
A new series of furofuran lignans containing catechol moiety were prepared from the reactions between lignans
and a variety of phenolics. All 22 products obtained were evaluated against three different α-glucosidases
(maltase, sucrase and Baker’s yeast glucosidase) and DPPH radical. Of furofuran lignans evaluated, β-14, having
two catechol moieties and one acetoxy group, was the most potent inhibitor against Baker’s yeast, maltase, and
sucrase with IC50 values of 5.3, 25.7, and 12.9 µM, respectively. Of interest, its inhibitory potency toward Baker’s
yeast was 28 times greater than standard drug, acarbose and its DPPH radical scavenging (SC50 11.2 µM) was
130 times higher than commercial antioxidant BHT. Subsequent investigation on mechanism underlying the
inhibitory effect of β-14 revealed that it blocked Baker’s yeast and sucrase functions by mixed-type inhibition
while it exerted non-competitive inhibition toward maltase. Molecular dynamics simulation of the most potent
furofuran lignans (4, α-8b, α-14, and β-14) with the homology rat intestinal maltase at the binding site revealed
that the hydrogen bond interactions from catechol, acetoxy, and quinone moieties of furofuran lignans were the
key interaction to bind tightly to α-glucosidase. The results indicated that β-14 possessed promising antidiabetic
activity through simultaneously inhibiting α-glucosidases and free radicals.
Diabetes mellitus
Glucosidase
Antioxidant
Furofuran lignan
Catechol
1. Introduction
quercitylcinnamates [7], N-arylmethylaminoquercitols [8], and fur-
ofuran lignans containing one free hydroxy group [9]. Of natural de-
Type 2 diabetes is a chronic disease in which there are high blood
sugar levels over a prolonged period [1]. Uncontrolled hyperglycemia
can impair many vital organs in the body, thus resulting in the devel-
opment of microangiopathic complications such as nephropathy, re-
tinopathy, and neuropathy [2]. One potential approach to alleviate
diabetes is suppressing postprandial glucose concentration by inhibiting
the α-glucosidase located in the brush border of the small intestine.
Moreover, current evidences demonstrate that oxidative damage and
the elevated generation of free radicals have been implicated in diabetic
complications [3,4]. Thus, considerable efforts have been made to de-
velop an antidiabetic drug that possesses both hypoglycemic and anti-
oxidant properties [5].
rived antidiabetic agents synthesized in our laboratory, a furofuran
lignan named sesamolin is considered as a versatile starter to facilely
produce a variety of antidiabetic agents possessing dual functions in
few steps. This approach was recently applied to synthesize a series of
flavonolignans by the coupling between this lignan and various flavo-
noids [10]. Of flavonolignans synthesized, epicatechinosamin (1) en-
compassing catechol moiety (Fig. 1) displayed more potent inhibition
against α-glucosidase and free radical than the other flavonolignans
having no catechol moiety. This result suggests that the catechol moiety
plays an important role in enhancing antidiabetic activity. A similar
observation was also reported by Nakai [11] and Moazzami [12]. The
catechol containing lignans 3 and 4 (Fig. 1) obtained via enzymatic
oxidation of sesamin (2) showed dramatically enhanced radical
scavenging over their starter 2.
In the course of our research for new antidiabetic agents having dual
functions through inhibiting α-glucosidase and scavenging free radi-
cals, we discovered arylalkanones from natural sources [6] together
To further explore more potent antidiabetic agents and gain insight
into the role of catechol moiety on inhibiting α-glucosidases and free
with
quercitol
derivatives
via
semisynthesis
such
as
⁎ Corresponding author.
E-mail address: peecha.p@chula.ac.th (P. Phuwapraisirisan).
https://doi.org/10.1016/j.bioorg.2019.03.077
Received 24 January 2019; Received in revised form 21 March 2019; Accepted 30 March 2019
Availableonline05April2019
0045-2068/©2019PublishedbyElsevierInc.

W. Worawalai, et al.
BioorganicChemistry87(2019)783–793
OH
OH
HO
O
O
O
O
O
O
OH
H
H
H
H
OH
O
O
O
sesamin
epicatechinosamin
O
O
2
1
OH
OH
OH
OH
O
O
H
H
H
H
O
O
HO
O
3
4
OH
O
Fig. 1. Structures of lignans encompassing catechol moiety.
radicals, we herein demonstrate the efficient synthesis of a new series of
furofuran lignans having multiphenolic and catechol moieties and re-
port on α-glucosidase inhibitory effect and antioxidant activity of them.
We also describe the mechanism underlying enzymatic inhibition and
the molecular modeling of the most active furofuran lignans.
furofuran lignans (7a-7c) having one free phenolic hydroxy group were
also oxidized by Pb(OAc)4 to generate para-quinone moiety in 8.
Moreover, α-9a was obtained by only oxidation reaction. In contrast,
treatment of 7d-7e, containing two phenolic hydroxy groups, with Pb
(OAc)4 followed by acid hydrolysis affording the undesired product.
To solve this problem, protection of phenolic hydroxy group is re-
quired. Silylation of α-7c with tert-butyldimethylsilylchloride
(TBDMSCl) gave α-10c in 51% yield. In addition, monosilylated pro-
ducts were observed in the case of furofuran lignans having two phe-
nolic hydroxy groups (7d and 7e). Subsequently, the methylenedioxy
cleavage of α-10c was carried out under the similar conditions men-
tioned above using Pb(OAc)4 followed by deprotection of TBS group
concomitant with hydrolysis of the orthoester by using TBAF, affording
α-11c in a fair yield. Unfortunately, the methylenedioxy cleavage of
10d and 10e, the lignans containing one free hydroxy group, failed to
afford expected products.
2. Results and discussion
2.1. Chemistry
Starting samin (6) was obtained from sesamolin, a naturally abun-
dant lignan isolated from sesame (Sesamum indicum) seed oil, via acid
hydrolysis (Scheme 1).
With the starter samin (6) in hand, furofuran lignans (7a-7e) were
first synthesized via Friedel-Crafts reaction as showed in Scheme 2.
Samin (6) reacted with a variety of electron-rich phenolics a-e in an
acidic solution (Amberlyst-15, CH3CN) at 70 °C to produce the dia-
stereomeric furofuran lignans (α-7a - α-7e and β-7a - β-7e) in excellent
yields. In this step, addition of a molecular sieve 4 Å to remove H2O
generated from the reaction was required.
Alternatively, furofuran lignans 14, 3, and 4 were also synthesized
starting from sesamolin and sesamin, respectively (Scheme 3). Silylation of
12 gave 13 in excellent yields. The methylenedioxy cleavage and depro-
tection of 13 produced 14 in good yields. In addition, sesamin (2) was
directly reacted with Pb(OAc)4 and then hydrolyzed by amberlyst-15 to
afford mono-catechol (3) and di-catechol (4) structures in excellent yields.
The relative configuration of the newly generated chiral center C-2
on the furan moiety of compounds 7a-7e, and 12 was determined based
on coupling constant analysis [9]. The α–isomer showed doublet of
doublet (dd) for both H-4ax and H-4 eq while the β–isomer displayed the
dd pattern for H-4ax but a unique doublet (d) for H-4 eq (Fig. 2). In
addition, the structures of the synthesized compounds (3, 4, 8, 11, and
14) were characterized by 1H NMR spectra which displayed no me-
thylenedioxy singlet signal at δ ≈ 5.90 ppm (see Supplementary in-
formation).
Oxidative cleavage of the aromatic methylenedioxy moiety in fur-
ofuran lignans 7 was the critical step to afford the desired products
containing catechol residue. The use of phosphorus pentachloride
(PCl5) in benzene yielded complex mixtures and starting material re-
covery. However, treatment of 7 with 3 equiv of lead tetraacetate (Pb
(OAc)4) [13] in toluene at 90 °C followed by acid hydrolysis in the
presence of amberlyst-15 provide furofuran lignans 8 in a good yield
(Scheme 2). The above result suggested that the reaction might proceed
via displacement of a proton of the methylenedioxy moiety by an
acetoxy group called orthoester type structure, which was then hy-
drolyzed by acid to obtain a catechol moiety [14]. Under this reaction,
Scheme 1. Synthesis of samin (6).
784

W. Worawalai, et al.
BioorganicChemistry87(2019)783–793
Scheme 2. Synthesis of furofuran lignans starting from samin. Reagents and conditions: (i) phenolics, amberlyst-15, CH3CN, 4 Å MS, 70 °C, 8 h; (ii) Pb(OAc)4,
toluene, 90 °C, 2 h; (iii) amberlyst-15, CH3CN-H2O (8:2), 70 °C, 3 h; (iv) TBDMSCl, imidazole, DCM, rt, 12 h; (v) TBAF, THF, rt, 3 h.
2.2. α-Glucosidase inhibition
Interestingly, the inhibitory activity of furofuran lignans dramatically
increased when encompassed catechol moiety (3, 4, 8b, 8c, α-11c, and
14). The furofuran lignans 8b and 8c, whose structures containing para-
quinone and catechol moieties, displayed inhibitory effects in range of
14.6–23.4 µM, which is 30–50 times more potent than their furofuran
starters (7b and 7c). Similarly, 14, having two catechol moieties,
showed higher inhibition (IC50 5.3–7.7 µM) than their starters 12 (IC50
205.8–210.3 µM). These results were also observed in furofuran lignans
3 and 4. Compound 4, bearing two catechol moieties, exhibited
stronger inhibition than 3 containing one catechol moiety, whereas
All furofuran lignans were evaluated for α-glucosidase inhibitory
activity using enzymes from two different sources; baker’s yeast (type I)
and rat intestine (type II), and the results are shown in Table 1. As for
Baker’s yeast α–glucosidase, 7a-7c, containing one phenolic hydroxy
group, showed weak inhibition (IC50 685.4-729.3 µM) whereas 7d and
7e, having two phenolic hydroxy groups, revealed higher inhibition
(IC50 25.4–56.4 µM). This result suggested that the inhibitory effect
increased according to the number of phenolic hydroxy group.
Scheme 3. Synthesis of furofuran lignans starting from sesamolin and sesamin. Reagents and conditions: (i) amberlyst-15, CH3CN, 70 °C, 8 h; (ii) TBDMSCl, imi-
dazole, DCM, rt, 12 h; (iii) Pb(OAc)4, toluene, 90 °C, 2 h; (iv) TBAF, THF, rt, 3 h; (v) amberlyst-15, CH3CN-H2O (8:2), 70 °C, 3 h.
785

W. Worawalai, et al.
BioorganicChemistry87(2019)783–793
Fig. 2. 1H NMR spectra of α-7e (top) and β-7e (bottom). For clarity, particular atoms are omitted.
Table 1
which is 28 times more active than the standard drug acarbose (IC50
147.2 µM).
α-Glucosidase inhibitory effect and radical scavenging activity of furofuran
lignans.
Further inspection of para-quinone moiety on inhibitory effect re-
vealed that this moiety possibly worked together with catechol residue
to inhibite the enzymes. Furofuran lignan α-8a, containing para-qui-
none and catechol moieties, showed the inhibition with an IC50 value of
23.4 µM, whereas α-9a, having no catechol moiety, was not active. In
addition, α-11c (IC50 17.8 µM) displayed the slightly higher inhibition
than α-8a (IC50 23.4 µM). This result suggested that phenolic hydroxy
group might contribute major effect on the inhibition when compared
with para-quinone moiety.
Compound
α-Glucosidase inhibitory effect (IC50, µM)a
DPPH radical
scavenging
(SC50, µM)a
Baker’s yeast
Maltase
Sucrase
α-7a
β-7a
α-7b
β-7b
α-7c
β-7c
α-7d
β-7d
α-7e
β-7e
700
698
729
716
692
685
32.2
25.4
56.4
42.9
4.0
3.8
5.2
3.7
2.4
2.1
1.5
1.4
1.0
1.7
1.2
1.9
1.0
0.7
> 1000
> 1000
> 1000
> 1000
> 1000
> 1000
> 1000
> 1000
> 1000
> 1000
> 1000
> 1000
340
171
410
220
5.7
4.6
5.4
3.8
> 1000
> 1000
41.4
As for type II α–glucosidases (Table 1), most furofuran lignans in-
hibited sucrase more selectively than maltase. Generally, the inhibitory
effect increased according to the number of phenolic hydroxy group,
which was similar to the results observed in type I α–glucosidase. The
remarkably increased inhibition was observed in a series of furofuran
lignans having catechol moiety, when compared with their parents
(weak inhibition). Of the synthesized lignans, β-14 was the most potent
inhibitor against maltase and sucrase with IC50 values of 25.7 and
12.9 µM, respectively. Moreover, para-quinone moiety also played an
important role in inhibiting type II α-glucosidases. Lignan α-8a, bearing
para-quinone residue, displayed the stronger inhibition against maltase
and sucrase with IC50 values of 96.5 and 110.2 µM, respectively, when
compared with α-11c having phenolic hydroxy group (IC50 173.6 and
136.4 µM against maltase and sucrase, respectively). Noticeably, the β-
isomer of all synthesized furofuran lignans exhibited higher inhibition
than its epimer (α-isomer) in all bioactivities examined.
151
110
380
260
96.5
63.3
97.0
47.0
0.9
180
170
340
231
110
61.1
46.6
33.0
1.1
1.1
1.3
1.1
3.5
1.6
1.4
1.6
1.2
1.1
1.7
1.9
2.4
1.0
1.8
1.3
0.2
39.0
> 1000
> 1000
82.6
α-8a or α-8c 23.4
β-8a or β-8c 19.8
1.3
0.9
1.4
1.2
79.5
α-8b
β-8b
α-9a
α-11c
α-12
β-12
α-14
β-14
3
15.9
14.6
76.4
67.8
> 1000
17.8
> 1000
> 1000
> 1000
72.6
1.8
174
3.7
136
3.2
0.9
210
206
7.70
5.30
21.6
10.0
147
ND
1.2
1.1
0.6
0.6
1.4
1.0
0.5
> 1000
> 1000
38.8
> 1000
> 1000
18.7
650
6.2
4.3
0.6
0.8
1.5
0.6
420
1.0
1.0
0.3
0.4
12.3
11.2
90.3
14.7
NDb
25.7
12.9
170
42.6
1.40
ND
1.9
1.1
0.2
191
29.2
3.20
ND
3.7
1.2
0.4
4
acarbose®
BHT
> 1000
a
b
IC50 or SC50 values represent as mean
Not determined.
SD of three determinations.
2.3. Evaluation of antioxidant activity
their starter (sesamin) was not active. These results revealed that the
presence of the catechol moiety might participate in chelation with
enzymes, thus enhancing inhibitory activity [15]. Among furofuran
lignans examined, β-14, bearing two catechol moieties and an acetoxy
group, was the most potent inhibitor with an IC50 value of 5.3 µM,
All synthesized furofuran lignans were also evaluated for anti-
oxidation against DPPH radical (Table 1). This approach measures the
hydrogen donating ability of the compound being studied. Furofuran
lignans 7a, 7b and 12 (except 7c, SC50 > 1000 µM), which have one
free hydroxy group on phenolic moiety with an activating group such as
786

W. Worawalai, et al.
BioorganicChemistry87(2019)783–793
methoxy group at ortho or para position, showed weak DPPH radical
scavenging activity in the range of 170.9–650.0 µM. In addition, fur-
ofuran lignans (7d, 8a-8c, α-11c, and 3), which contain one catechol
moiety, displayed moderate DPPH radical scavenging activity in the
range of 39.0–90.3 µM. However, 7e, bearing two free hydroxy groups
at meta position, did not reveal DPPH radical scavenging activity
(SC50 > 1000 µM). These observations suggest that the presence of
catechol moiety plays a critical role in trapping the radical. Re-
markably, furofuran lignans 14 and 4, containing two catechol moi-
eties, revealed strong DPPH radical scavenging activity in the range of
11.2–14.7 µM, which is approximately 100 times more active than the
standard BHT (SC50 1560 µM).
initial structure at 1.9
0.05, 1.9
0.08, 1.8
0.07, and
2.0 0.1 Å. Moreover, hydrogen bond analysis using VMD version 1.9
found the possibilities bonding around 1–4 hydrogen bond (Fig. S17)
along trajectories calculations. The criteria for a hydrogen bond for-
mation defined an atom between donor (D) and acceptor (A) atoms
using cut-off distance is less than 3.0 Å and the angle of D-H-A is less
than 20°. The interaction between the ligand and the enzyme formed
between the hydroxy groups on aromatic ring of ligand or oxygen atom
on furofuran core structure and the polar or charged residues of the
enzyme at binding site I (Fig. 4). Surprisingly, the binding mode of two
hydroxy groups on aromatic ring (catechol moiety) established the
hydrogen bonds more than quinone part of α-5b. The detailed binding
mode of 4 showed that two OH groups on aromatic ring (catechol
moiety) established the strong hydrogen bonds with amino acid residue
Arg580 whereas one OH group at para position from the other side
formed a hydrogen bond to Asp837 (Fig. 4D, Table 4). In the case of β-
14, two OH groups from catechol moiety formed hydrogen bonds with
Arg343 and His705 while oxygen atom of furofuran core structure
formed a hydrogen bond with Lys594 (Fig. 4C, Table 4). Furthermore,
acetoxy group also created a hydrogen bond interaction with Lys836.
As depicted in Fig. 4B, two OH groups from catechol moiety of α-14
interacted with residues Arg580 and Phe595 while one OH group on
aromatic ring at the meta position from the other side formed a hy-
drogen bond with Arg343. In addition, acetoxy group also interacted
with residue Leu346. Compound α-8b showed the hydrogen bond in-
teraction of oxygen atoms from p-quinone unit with amino acid residues
Lys573 and Lys594. Moreover, OH groups from catechol moiety also
formed hydrogen bonds with Arg580 (Fig. 4A, Table 4). Meanwhile, the
complex was entering to equilibration state that each system was carry
out free energy calculation of α-8b, α-14, β-14, and 4 complexes at
−15.5, −14.7, −20.5, and −16.4 kcal/mol, respectively.
2.4. Enzyme kinetic study
To evaluate the mechanisms of both type I and II α-glucosidase
inhibitions of the furofuran lignans having catechol moiety, kinetic
analysis was performed on the most potent inhibitors 4, α-8b, α-14,
and β-14. The Lineweaver-Burk plot of the active inhibitors (4, α-8b, α-
14, and β-14) against Baker’s yeast α-glucosidase displayed a series of
straight lines; all of which intersected in the second quadrant (Fig. 3a
for β-14 and Figs. S1a, S2a and S3a for 4, α-8b, and α-14, respectively).
Kinetic analysis showed that Vmax decreased with elevated Km in the
presence of increasing concentrations of the inhibitors. This behaviour
suggested that 4, α-8b, α-14, and β-14 inhibited yeast α-glucosidase in
a mixed-type manner comprising two different pathways, competitive
and noncompetitive. The Ki and K′i values were calculated directly by
the secondary plots (Figs. S4–S7). All active compounds showed the Ki
values less than the Ki′ values (Table 2), indicating that all active
compounds were predominantly bound to yeast α-glucosidase (EI) ra-
ther than forming ESI complex.
The binding free energy (ΔGbind) for α-8b, α-14, β-14 and 4 were
−10.33, −11.17, −11.28 and −11.65 kcal/mol (Table 4), respec-
tively. These results were consistent with the experimental results (Ki,
Table 2) showing that compound 4 exhibit the highest binding affinity
for rat maltase in pocket site I.
The inhibitory mechanisms of four active compounds against rat
intestinal maltase and sucrase were also examined using the above
methodology. The Lineweaver-Burk plots of α-14 and β-14 against
maltase and sucrase (Fig. 3b and c for β-14 and Figs. S3b and S3c for α-
14) showed a series of straight lines; all of which intersected on the X-
axis. Kinetic analysis showed that Vmax decreased with unchanged Km in
the presence of increasing concentrations of inhibitors. This behaviour
suggested that α-14 and β-14 were a non-competitive inhibitor against
maltase and sucrase. The kinetic parameters of the active compounds
are summarized in Table 2.
3. Conclusions
In summary, a new series of furofuran lignans containing catechol
moiety were obtained by Friedel-Crafts reaction between samin and
phenolics followed by the cleavage of the aromatic methylenedioxy
moiety. This synthetic design was implemented in the hope that ca-
techol part of the synthesized furofuran lignans would promote both α-
glucosidase inhibition and antioxidant activity. Furofuran lignans 3, 4,
7d, 8a-8c, α-11c, and 14, whose structures containing catechol moiety,
showed remarkable inhibitory activity against rat intestinal maltase
and sucrase as well as baker’s yeast. Among them, β-14, having two
catechol moieties and one acetoxy group, was the most potent inhibitor
against α-glucosidases. In addition, furofuran lignans 8a-8c, containing
para-quinone and catechol moieties, displayed α-glucosidase inhibition
more potent than α-11c, whose structure having one free hydroxy
group instead of quinone moiety. This result suggests that para-quinone
part might work together with catechol moiety to improve the activity.
Further investigation of kinetic study indicated that the most active
compounds α-8b, α-14, β-14, and 4 inhibited α-glucosidases (Baker’s
yeast, maltase, and sucrase) by mixed-type and non-competitive in-
hibition. This suggests that these inhibitors may bind to either the α-
glucosidase or α-glucosidase-substrate complex at the binding site.
Furthermore, the MD simulation of the most active compounds (α-8b,
α-14, β-14, and 4) towards maltase revealed that the hydrogen bonding
from catechol, acetoxy, and quinone moieties was the key interaction to
bind tightly to α-glucosidase. Moreover, DPPH radical scavenging ac-
tivity revealed that furofuran lignans possessing catechol moiety also
showed remarkable antioxidant property. Taken together, our results
suggest that furofuran lignan β-14 is promising candidate for the
2.5. Cavities validation and molecular docking
We applied a homology model of the rat intestinal N-terminal do-
main of maltase-glucoamylase (rat-ntMGAM) which was reported in
our previous study [16], and the active site of the model was inferred
from the template structure (PDB: 3L4W). We further applied Meta-
Pocket 2.0 (MPK2), a consensus method, to identify pocket for protein-
ligand binding site prediction. The six metaPocket clusters probable
binding sites of the rat intestinal maltase indicated using z-score from
the biggest to smallest, 22.42, 8.48, 5.32, 2.62, 2.42, and 1.13, re-
spectively as shown in Fig. S15.
The crude docking show the top three sites from the best three
pockets. From the pocket area of site I and the docking results (Table 3)
are in good agreement with previous study [15] as shown in Fig. S16.
Therefore, systems were performed the molecular dynamics (MD) si-
mulation.
2.6. Molecular dynamics simulation
The superimposition of the homology rat maltase-glucoamylase re-
presented 91.6% similarities and 81.9% identities of Human Maltase-
Glucoamylase (PDB:2QMJ) [17]. MD simulation of α-8b, α-14, β-14,
and 4 complexes with rat maltase-glucoamylase approximately found
the root mean square displacement (RMSD) of complexes compare to
787

W. Worawalai, et al.
BioorganicChemistry87(2019)783–793
Fig. 3. Lineweaver-Burk plots for inhibitory activity of β-14 against baker’s yeast (a), maltase (b) and sucrase (c).
788

W. Worawalai, et al.
BioorganicChemistry87(2019)783–793
Table 2
Kinetic parameters of α-8b, α-14, β-14, and 4 on α-glucosidases.
Compound
Baker’s yeast
Maltase
Sucrase
Ki (µM)
Ki′ (µM)
Inhibition type
Ki (µM)
Ki′ (µM)
Inhibition type
Ki (µM)
Ki′ (µM)
Inhibition type
α-8b
α-14
β-14
4
15.6
10.1
6.9
0.5
1.3
59.7
19.6
10.4
16.5
1.2
1.3
0.5
0.6
Mixed
Mixed
Mixed
Mixed
67.8
31.6
28.4
19.9
1.7
1.1
0.9
0.8
93.7
–
1.1
1.5
Mixed
34.2
18.6
11.6
15.1
0.9
0.7
0.8
0.7
62.7
–
1.0
Mixed
Non-competitive
Non-competitive
Mixed
Non-competitive
Mixed
0.8
–
18.5
39.9
1.0
1.1
9.1
0.6
40.1
Mixed
silica gel column and Preparative TLC to afford furofuran lignans 7a-7e.
Table 3
Binding glide scores of α-8b, α-14, β-14, and 4 on the homology rat intestinal
4.1.3.1. α-7a. Yield: 36%, yellow oil; 1H NMR (400 MHz, CDCl3) δ
6.89–6.73 (m, 4H), 6.62 (d, J = 8.6 Hz, 1H), 5.94 (s, 2H), 5.05 (d,
J = 4.0 Hz, 1H), 4.68 (d, J = 4.0 Hz, 1H), 4.31 (dd, J = 9.1, 7.3 Hz,
1H), 4.22 (dd, J = 9.1, 6.6 Hz, 1H), 4.01 (dd, J = 9.2, 4.7 Hz, 1H), 3.92
(d, J = 4.3 Hz, 4H), 3.89 (d, J = 7.1 Hz, 4H), 3.10–3.02 (m, 1H),
3.01–2.93 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 148.1, 147.4,
144.6, 138.7, 135.4, 128.3, 119.6, 115.9, 108.3, 106.7, 105.9, 101.2,
85.6, 82.4, 73.1, 71.6, 60.6, 56.4, 54.8, 54.2; HRMS m/z 409.1260 [M
+Na]+ (calcd for C21H22NaO7, 409.1263).
maltase.
Evaluations
Compounds
Binding Sites
I
II
III
Blind Docking glide score (kcal/mol)
α-8b
α-14
β-14
4
−8.4
−8.5
−8.9
−8.6
−8.9
−8.5
−8.5
−9.0
−7.5
−8.1
−7.6
−8.8
CDOCKER interaction (kcal/mol)
α-8b
α-14
β-14
4
−43.0
−47.0
−48.7
−42.1
−43.7
−47.4
−50.3
−46.2
−39.5
−44.6
−44.0
−43.2
4.1.3.2. β-7a. Yield: 28%, yellow oil; 1H NMR (400 MHz, CDCl3) δ 7.02
(d, J = 8.5 Hz, 1H), 6.89–6.73 (m, 3H), 6.65 (d, J = 8.4 Hz, 1H), 5.95
(s, 2H), 4.95 (d, J = 5.9 Hz, 1H), 4.36 (d, J = 8.0 Hz, 1H), 4.09 (d,
J = 9.4 Hz, 1H), 3.97–3.84 (m, 7H), 3.86–3.74 (m, 2H), 3.51–3.40 (m,
1H), 3.24 (t, J = 8.6 Hz, 1H), 2.86 (dd, J = 15.4, 7.2 Hz, 1H); 13C NMR
(100 MHz, CDCl3) δ 148.1, 147.3, 147.2, 138.2, 135.5, 129.9, 124.6,
119.7, 116.8, 108.3, 106.8, 105.8, 101.2, 87.7, 78.7, 70.6, 69.9, 60.3,
56.4, 54.9, 49.2; HRMS m/z 409.1261 [M+Na]+ (calcd for
further development of diabetes treatment.
4. Experimental section
4.1. Chemistry
C21H22NaO7, 409.1263).
4.1.1. General procedure
4.1.3.3. α-7b. Yield: 42%, white powder; 1H NMR (400 MHz, CDCl3) δ
7.71 (brs, 1H, eOH), 6.84–6.79 (m, 3H), 6.54 (s, 1H), 6.49 (s, 1H), 5.96
(s, 2H), 4.82 (d, J = 8.0 Hz, 1H), 4.78 (d, J = 8.0 Hz, 1H), 4.36 (dd,
J = 8.8, 7.2 Hz, 1H), 4.16 (dd, J = 9.6, 6.4 Hz, 1H), 3.92–3.86 (m, 2H),
3.84 (s, 3H, eOCH3), 3.82 (s, 3H, eOCH3), 3.21–3.14 (m, 2H); 13C NMR
(100 MHz, CDCl3) δ 150.3, 150.1, 148.2, 147.4, 142.6, 134.8, 125.2,
119.5, 111.2, 108.4, 106.7, 102.1, 101.3, 86.7, 85.6, 72.6, 70.8, 57.2,
56.1, 53.6, 53.2; HRMS m/z 409.1286 [M+Na]+ (calcd for
All moisture-sensitive reactions were carried out under a nitrogen
atmosphere. All solvents were distilled prior to use. High resolution
electrospray ionisation mass spectra (HRESIMS) was recorded with a
Bruker microTof spectrometer. 1H and 13C NMR spectra were recorded
(CDCl3 and CD3OD as solvents) at 400 and 100 MHz, respectively, on a
Varian Mercury+ 400 NMR and a Bruker (Avance) 400 NMR spectro-
meter. Chemical shifts are reported in ppm downfield from TMS or
solvent residue. Thin layer chromatography (TLC) was performed on
pre-coated Merck silica gel 60 F254 plates (0.25 mm thick layer) and
visualized by p-anisaldehyde reagent. Column chromatography was
performed using Merck silica gel 60 (70–230 mesh) and Sephadex LH-
20.
C21H22NaO7, 409.1263).
4.1.3.4. β-7b. Yield: 33%, white powder; 1H NMR (400 MHz, CDCl3) δ
8.05 (brs, 1H, eOH), 6.87–6.77 (m, 3H), 6.46 (s, 1H), 6.42 (s, 1H), 5.95
(s, 2H), 5.01 (d, J = 8.0 Hz, 1H), 4.44 (d, J = 6.8 Hz, 1H), 4.19 (d,
J = 9.6 Hz, 1H), 3.98 (t, J = 8.8 Hz, 1H), 3.88 (m, 1H), 3.85 (s, 3H,
eOCH3), 3.80 (s, 3H, eOCH3), 3.49 (dd, J = 8.4, 9.2 Hz, 1H), 3.40 (m,
1H), 2.91 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 150.1, 149.8, 148.2,
147.5, 142.7, 134.8, 125.2, 119.8, 110.5, 108.4, 106.7, 101.9, 101.2,
87.7, 84.6, 71.9, 70.1, 57.0, 56.0, 53.7, 50.8; HRMS m/z 409.1275 [M
+Na]+ (calcd for C21H22NaO7, 409.1263).
4.1.2. Hydrolysis of sesamolin (5)
To a solution of sesamolin (5, 0.27 mmol) in a mixture of acetoni-
trile/H2O (9:1, 10 mL) was treated with acidic resin Amberlyst-15
(1 mg/0.005 mmol of 5). After stirring at 70 °C for 8 h, the reaction
mixture was evaporated to dryness and purified by silica gel column
(50%EtOAc-hexane) to give samin 6 (60 mg, 90%) as a colorless oil.
4.1.3.5. α-7c. Yield: 41%, colorless oil; 1H NMR (400 MHz, CDCl3) δ
8.58 (brs, 1H, eOH), 6.82–6.77 (m, 3H), 6.22 (s, 1H), 5.95 (s, 2H), 5.12
(d, J = 8.0 Hz, 1H), 4.83 (d, J = 8.0 Hz, 1H), 4.49 (dd, J = 8.4, 8.4 Hz,
1H), 4.13 (dd, J = 9.6, 2.8 Hz, 1H), 4.04 (dd, J = 9.2, 6.8 Hz, 1H), 3.90
(s, 3H, eOCH3), 3.81 (s, 3H, eOCH3), 3.80 (m, 1H), 3.79 (s, 3H,
4.1.3. General coupling reaction between samin and phenolics
To a solution of samin 6 (1 equiv) in acetonitrile (1.0 mL/0.1 mmol
of 6) was treated with phenolics (1.5–2 equiv), Amberlyst-15 (1 mg/
0.005 mmol of 6) and a 4 Å molecular sieve. After stirring at 70 °C for
8 h, the reaction mixture was evaporated to dryness and purified by
789

W. Worawalai, et al.
BioorganicChemistry87(2019)783–793
Fig. 4. Molecular dynamics analysis of four active lignans to the binding site 1 of homology rat intestinal maltase. Last snapshot of (A) α-8b, (B) α-14, (C) β-14 and
(D) 4 in 5 ns MD simulations.
Table 4
Molecular interaction results of the homology rat intestinal maltase at the binding site I with the active lignans α-8b, α-14, β-14, and 4.
Compound
Binding free energy (ΔGbind , kcal/mol)
H-bond interacting residue
α-8b
α-14
β-14
4
−10.33
−11.17
−11.28
−11.65
LYS573, LYS594
ARG343, ARG580, LEU346, PHE595
ARG343, LYS594, LYS836, HIS705
ASP837, ARG580
eOCH3), 3.22 (m, 1H), 3.03 (m, 1H); 13C NMR (100 MHz, CDCl3) δ
153.9, 152.1, 150.9, 148.2, 147.3, 135.2, 134.7, 119.5, 109.1, 108.4,
106.8, 101.2, 97.0, 84.4, 84.2, 72.9, 70.8, 61.1, 60.9, 56.0, 54.7, 53.7;
HRMS m/z 439.1366 [M+Na]+ (calcd for C22H24NaO8, 439.1369).
4.1.3.7. α-7d. Yield: 41%, brown oil; 1H NMR (400 MHz, CDCl3) δ 6.84
(s, 1H, H-6′), 6.77 (m, 2H, H-2′ and H-5′), 6.67 (d, J = 8.4 Hz, 1H, H-
6″), 6.43 (d, J = 8.5 Hz, 1H, H-5″), 5.94 (s, 2H, H-7′), 4.97 (d,
J = 5.4 Hz, 1H, H-2), 4.71 (d, J = 4.9 Hz, 1H, H-6), 4.25 (dt,
J = 12.6, 8.4 Hz, 2H, H-4 and H-8), 3.94 (dd, J = 9.0, 3.8 Hz, 1H, H-
8), 3.89 (m, 1H, H-4), 3.85 (s, 3H, -OMe), 3.18 (m, 1H, H-1), 3.05 (m,
1H, H-5); 13C NMR (100 MHz, CDCl3) δ 148.1, 147.2, 147.1, 142.5,
135.1, 133.6, 119.6, 119.5, 116.6, 108.3, 106.7, 103.0, 101.2, 85.6,
84.4, 72.0, 56.3, 54.1, 53.0.
4.1.3.6. β-7c. Yield: 39%, colorless oil; 1H NMR (400 MHz, CDCl3) δ
8.87 (brs, 1H, eOH), 6.87 (s, 1H), 6.83–6.77 (m, 2H), 6.21 (s, 1H), 5.95
(s, 2H), 5.15 (d, J = 8.0 Hz, 1H), 4.40 (d, J = 4.0 Hz, 1H), 4.18 (d,
J = 10.0 Hz, 1H), 3.92 (m, 1H), 3.90 (s, 3H, eOCH3), 3.82 (s, 3H,
eOCH3), 3.79 (m, 1H), 3.78 (s, 3H, eOCH3), 3.48–3.43 (m, 2H), 2.90
(m, 1H); 13C NMR (100 MHz, CDCl3) δ 153.8, 152.6, 150.2, 148.2,
147.5, 135.0, 134.8, 119.8, 108.3, 106.7, 105.7, 101.2, 96.8, 87.5,
82.0, 71.4, 70.3, 61.1, 60.9, 55.9, 53.8, 50.2; HRMS m/z 439.1366 [M
+Na]+ (calcd for C22H24NaO8, 439.1369).
4.1.3.8. β-7d. Yield: 21%, brown oil; 1H NMR (400 MHz, CDCl3) δ 6.86
(s, 1H, H-6′), 6.82–6.72 (m, 3H, H-2′, H-5′ and H-6″), 6.45 (d,
J = 8.3 Hz, 1H, H-5″), 5.93 (s, 2H, H-7′), 5.00 (d, J = 5.8 Hz, 1H, H-
2), 4.39 (d, J = 7.0 Hz, 1H, H-6), 4.12 (dd, J = 8.3, 5.4 Hz, 1H, H-4),
3.90 (m, 1H, H-8), 3.85 (s, 3H, -OMe), 3.81 (s, 1H, H-4), 3.45 (m, 1H,
790

W. Worawalai, et al.
BioorganicChemistry87(2019)783–793
70 °C for 3 h, the resulting mixture was evaporated to dryness and
purified by silica gel column to give the target products 8a–8c, 9a, 3
and 4.
H-1), 3.35 (m, 1H, H-8), 2.87 (dd, J = 15.3, 6.9 Hz, 1H, H-5); 13C NMR
(100 MHz, CDCl3) δ 148.0, 147.3, 146.6, 142.0, 135.1, 133.1, 119.7,
118.9, 116.9, 108.2, 106.7, 103.1, 101.1, 87.6, 81.3, 71.2, 70.0, 56.2,
54.2, 49.5; HRMS m/z 395.1110 [M+Na]+ (calcd for C20H20NaO7,
395.1107).
4.1.5.1. α-8a and α-8c. Yield: 81%, yellow oil; 1H NMR (400 MHz,
CDCl3) δ 6.81–6.73 (m, 3H, H-2′, H-5′, and H-6′), 5.82 (s, 1H, H-3″),
5.15 (d, J = 5.6 Hz, 1H, H-2), 4.61 (d, J = 6.4 Hz, 1H, H-6), 4.26–4.17
(m, 2H, H-4 and H-8), 4.01 (s, 3H, H-8″), 3.89–3.83 (m, 2H, H-4 and H-
8), 3.79 (s, 3H, H-7″), 3.23 (m, 1H, H-1), 3.12 (m, 1H, H-5); 13C NMR
(100 MHz, CDCl3) δ 187.0, 178.6, 157.4, 155.4, 144.1, 143.9, 133.6,
130.3, 118.8, 115.5, 113.6, 107.6, 85.5, 78.3, 72.8, 72.7, 61.9, 56.6,
55.5, 52.0; HRESIMS m/z 411.1067 [M+Na]+ (calcd for C20H20NaO8,
411.1056).
4.1.3.9. α-7e. Yield: 5%, brown oil; 1H NMR (400 MHz, CDCl3) δ 6.98
(brs, 2H), 6.82 (s, 1H, H-6′), 6.77 (s, 2H, H-2′ and H-4′), 5.95 (d,
J = 3.1 Hz, 2H, H-7′), 5.23 (d, J = 7.7 Hz, 1H, H-2), 4.83 (d,
J = 3.9 Hz, 1H, H-6), 4.52–4.46 (m, 1H, H-4), 4.20 (dd, J = 9.4,
2.7 Hz, 1H, H-8), 4.03 (dd, J = 9.3, 6.7 Hz, 1H, H-8), 3.83–3.77 (m,
1H, H-4), 3.72 (s, 3H, -OMe), 3.25–3.17 (m, 1H, H-5), 3.10–3.02 (m,
1H, H-1); 13C NMR (100 MHz, CDCl3) δ 160.7, 156.0, 148.2, 147.3,
134.9, 119.5, 108.4, 106.8, 104.1, 101.2, 94.8, 84.4, 83.7, 72.9, 70.7,
55.4, 54.6, 53.7.
4.1.5.2. β-8a and β-8c. Yield: 70%, yellow oil; 1H NMR (400 MHz,
CDCl3) δ 6.79–6.73 (m, 3H), 5.83 (s, 1H), 4.90 (d, J = 6.6 Hz, 1H), 4.40
(d, J = 7.4 Hz, 1H), 4.03–4.01 (m, 2H), 3.99 (s, 3H), 3.80 (s, 3H), 3.70
(dd, J = 9.4, 6.0 Hz, 1H), 3.53 (dd, J = 8.3, 8.3 Hz, 1H), 3.36 (m, 1H),
2.85 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 187.2, 178.4, 157.6, 155.7,
144.1, 144.1, 133.1, 128.7, 119.0, 115.5, 113.7, 107.4, 86.7, 77.9,
70.8, 70.0, 62.2, 56.7, 54.3, 49.9; HRESIMS m/z 411.1067 [M+Na]+
(calcd for C20H20NaO8, 411.1056).
4.1.3.10. β-7e. Yield: 13%, brown oil; 1H NMR (400 MHz, CDCl3) δ
6.88–6.78 (m, 3H, H-2′, H-5′ and H-6′), 5.95 (s, 4H, H-7′, H-3″ and H-
5″), 5.20 (d, J = 5.8 Hz, 1H, H-2), 4.42 (d, J = 7.1 Hz, 1H, H-6), 4.18
(d, J = 9.7 Hz, 1H, H-4), 3.96 (t, J = 8.3 Hz, 1H, H-8), 3.82 (dd,
J = 9.7, 6.3 Hz, 1H, H-4), 3.73 (s, 3H, -OMe), 3.55 (m, 1H, H-1), 3.48
(m, 1H, H-8), 2.89 (m, 1H, H-5); 13C NMR (100 MHz, CDCl3) δ 160.7,
156.0, 148.2, 147.5, 134.8, 119.9, 108.3, 106.8, 101.2, 101.0, 94.5,
87.6, 81.7, 71.5, 70.3, 55.4, 53.6, 49.6; HRMS m/z 395.1111 [M+Na]+
(calcd for C20H20NaO7, 395.1107).
4.1.5.3. α-8b. Yield: 68%, yellow oil; 1H NMR (400 MHz, CD3OD) δ
6.79 (d, J = 2.0 Hz, 1H, H-2′), 6.73 (d, J = 8.1 Hz, 1H, H-5′), 6.67 (dd,
J = 8.1, 2.0 Hz, 1H, H-6′), 6.63 (s, 1H, H-6′′), 6.02 (s, 1H, H-3′′), 4.77
(d, J = 2.8 Hz, 1H, H-2), 4.56 (d, J = 5.4 Hz, 1H, H-6), 4.29 (dd,
J = 9.3, 6.7 Hz, 1H, H-8), 4.14 (dd, J = 9.1, 5.8 Hz, 1H, H-4), 4.05 (dd,
J = 9.3, 4.0 Hz, 1H, H-8), 3.89 (dd, J = 9.1, 3.2 Hz, 1H, H-4), 3.82 (s,
3H, H-7′′), 2.98–2.95 (m, 2H, H-1 and H-5); 13C NMR (100 MHz,
CD3OD) δ 189.0, 183.5, 160.5, 150.6, 146.5, 146.1, 133.6, 128.6,
118.9, 116.3, 114.5, 108.7, 86.7, 82.6, 74.2, 72.6, 57.0, 55.2, 54.3;
HRESIMS m/z 381.0949 [M+Na]+ (calcd for C19H18NaO7, 381.0950).
4.1.4. General protection of phenolic groups
To a solution of α-7c, α-12, and β-12 (1 eq), imidazole (5 eq) in
dichloromethane (DCM, 1.0 mL/0.1 mmol of starting material) was
added tert-butyldimethylsilyl chloride (TBDMSCl) (5 eq). The mixture
was stirred at room temperature for 12 h. The reaction mixture was
washed with water and extracted with DCM (3 × 5 mL). The organic
layer was washed with saturated aqueous NaCl, followed by dried over
Na2SO4. After filtration and removal of the solvent under reduced
pressure, the crude product was purified by silica gel column to obtain
α-10c, α-13, and β-13 in 51%, 70%, and 66% yield, respectively.
4.1.5.4. β-8b. Yield: 64%, yellow oil; 1H NMR (400 MHz, CD3OD) δ
6.80 (d, J = 1.9 Hz, 1H, H-2′), 6.78 (s, 1H, H-6′′), 6.73 (d, J = 8.1 Hz,
1H, H-5′), 6.68 (dd, J = 8.1, 2.0 Hz, 1H, H-6′), 6.03 (s, 1H, H-3′′), 4.70
(d, J = 6.7 Hz, 1H, H-2), 4.26 (d, J = 7.4 Hz, 1H, H-6), 4.04 (d,
J = 9.4 Hz, 1H, H-4), 3.87 (m, 1H, H-8), 3.84 (s, 3H, H-7′′), 3.81 (m,
1H, H-4), 3.49 (m, 1H, H-1), 3.28 (m, 1H, H-8), 2.92 (m, 1H, H-5); 13C
NMR (100 MHz, CD3OD) δ 188.2, 183.0, 160.6, 148.1, 146.5, 146.3,
133.5, 131.1, 119.0, 116.2, 114.5, 108.4, 89.0, 78.6, 71.5, 70.3, 57.0,
55.8, 50.3; HRESIMS m/z 381.0949 [M+Na]+ (calcd for C19H18NaO7,
381.0950).
4.1.4.1. α-10c. Yield: 51%, pale yellow oil; 1H NMR (400 MHz, CDCl3)
δ 6.86–6.77 (m, 3H), 6.16 (s, 1H), 5.95 (s, 2H), 5.18 (d, J = 7.0 Hz,
1H), 4.78 (d, J = 4.8 Hz, 1H), 4.35 (dd, J = 8.0, 8.0 Hz, 1H), 4.05 (m,
1H), 3.90 (s, 3H), 3.87–3.84 (m, 2H), 3.80 (s, 6H), 3.37 (m, 1H), 3.15
(m, 1H), 1.02 (s, 9H), 0.25 (s, 6H).
4.1.4.2. α-13. Yield: 70%, colorless oil; 1H NMR (400 MHz, CDCl3) δ
6.84–6.78 (m, 4H), 6.38 (s, 1H), 5.94 (s, 2H), 5.89 (d, J = 2.6 Hz, 2H),
5.06 (d, J = 3.6 Hz, 1H), 4.69 (d, J = 3.9 Hz, 1H), 4.29–4.23 (m, 2H),
3.93 (dd, J = 9.2, 3.8 Hz, 1H), 3.87 (dd, J = 9.2, 3.4 Hz, 1H), 2.99 (m,
2H), 1.01 (s, 9H), 0.24 (s, 3H), 0.24 (s, 3H).
4.1.5.5. α-9a. Yield: 20%, yellow oil; 1H NMR (400 MHz, CDCl3) δ 6.84
(d, J = 0.8 Hz, 1H, H-6′), 6.79–6.75 (m, 2H, H-2′ and H-5′), 5.93 (s, 2H,
H-7′), 5.82 (s, 1H, H-5″), 5.13 (d, J = 5.5 Hz, 1H, H-2), 4.62 (d,
J = 6.6 Hz, 1H, H-6), 4.21 (m, 2H, H-4 and H-8), 4.00 (s, 3H, -OMe),
3.87–3.82 (m, 2H, H-4 and H-8), 3.78 (s, 3H, -OMe), 3.24–3.19 (m, 1H,
H-1), 3.10–3.05 (m, 1H, H-5); 13C NMR (100 MHz, CDCl3) δ 186.8,
178.6, 157.3, 155.3, 148.1, 147.3, 135.3, 130.6, 119.6, 108.3, 107.6,
107.5, 106.6, 101.2, 85.5, 78.2, 72.9, 72.6, 61.8, 56.6, 55.9, 52.1;
HRMS m/z 423.1057 [M+Na]+ (calcd for C21H20NaO8, 423.1056).
4.1.4.3. β-13. Yield: 66%, colorless oil; 1H NMR (400 MHz, CDCl3) δ
7.05 (s, 1H), 6.88 (s, 1H), 6.84–6.76 (m, 2H), 6.37 (s, 1H), 5.94 (s, 2H),
5.91 (s, 2H), 4.88 (d, J = 6.2 Hz, 1H), 4.34 (d, J = 7.4 Hz, 1H), 4.08 (d,
J = 9.4 Hz, 1H), 3.82–3.76 (m, 2H), 3.42 (m, 1H), 3.27 (m, 1H), 2.83
(m, 1H), 1.00 (s, 9H), 0.27 (s, 3H), 0.22 (s, 3H).
4.1.5. General procedure for the preparation of compounds 8a–8c, 9a, 3
and 4
4.1.5.6. 3. Yield: 15%, brown oil; 1H NMR (400 MHz, CD3OD) δ
7.26–7.12 (m, 5H), 7.08 (dd, J = 8.1, 1.7 Hz, 1H), 6.31 (s, 2H), 5.25
(brs, 2H), 5.07 (d, J = 4.7 Hz, 1H), 5.03 (d, J = 4.6 Hz, 1H), 4.59 (dd,
J = 6.4, 2.6 Hz, 1H), 4.23–4.18 (m, 2H), 3.72–3.70 (m, 1H), 3.46 (t,
J = 11.0 Hz, 2H). The data were consistent with previous report [13].
A mixture of 7a–7c and 2 (1 eq) and lead tetraacetate (3 eq) in to-
luene (1.0 mL/0.1 mmol of starting material) was stirred at 90 °C for
2 h. After being cooled to rt, the reaction mixture was diluted with
toluene and filtered through a Celite pad. The filtrate was evaporated
until dryness, washed with water and extracted with EtOAc (×3). The
organic layer was dried with anhydrous sodium sulfate, and con-
centrated under reduced pressure to give a mixture of crude reaction.
This mixture was then treated with amberlyst-15 (1 mg/0.005 mmol of
starting material) in a mixture of MeCN-H2O (8:2). After stirring at
4.1.5.7. 4. Yield: 71%, dark brown oil; 1H NMR (400 MHz, CD3OD) δ
6.82–6.68 (m, 6H), 4.63 (d, J = 4.3, 2H), 4.21 (dd, J = 9.0, 7.1 Hz,
2H), 3.80 (dd, J = 9.0, 3.5 Hz, 2H), 3.07 (m, 2H); 13C NMR (100 MHz,
CD3OD) δ 145.0, 144.5, 132.4, 116.9, 115.2, 113.5. 84.9, 70.7, 53.5.
The data were consistent with previous report [13].
791

W. Worawalai, et al.
BioorganicChemistry87(2019)783–793
4.1.6. General procedure for the preparation of compounds α-11c and 14
A mixture of α-10c and 13 (1 eq) and lead tetraacetate (5 eq) in
toluene (1.0 mL/0.1 mmol of starting material) was stirred at 90 °C for
2 h. After being cooled to rt, the reaction mixture was diluted with
toluene and filtered through a Celite pad. The filtrate was evaporated
until dryness, washed with water and extracted with EtOAc (×3). The
organic layer was dried with anhydrous sodium sulfate, and con-
centrated under reduced pressure to give a mixture of crude reaction.
This mixture was then treated with tetrabutylammonium fluoride hy-
drate (TBAF, 5 eq) in THF (1.0 mL/0.1 mmol of starting material) at rt
for 3 h. After being quenched with water, the resulting mixture was
extracted with EtOAc (×3). The extracts were washed with saturated
aqueous NaCl, followed by dried over Na2SO4. After filtration and re-
moval of the solvent under reduced pressure, the crude product was
purified by Sephadex LH-20 column (100% MeOH) to afford α-11c and
14.
St. Louis) was used as a source of maltase and sucrase. Rat intestinal
acetone powder (1 g) was homogenized in 30 mL of 0.9% NaCl solution.
After centrifugation (12,000 g × 30 min), the aliquot was subjected to
assay. The synthesized compounds (1 mg/mL in DMSO, 10 µL) were
added with 30 µL of the 0.1 M phosphate buffer (pH 6.9), 20 µL of the
substrate solution (maltose: 2 mM; sucrose: 20 mM) in 0.1 M phosphate
buffer, 80 µL of glucose assay kit (SU-GLLQ2, Human), and 20 µL of the
crude enzyme solution. The reaction mixture was then incubated at
37 °C for 10 min (for maltose) and 40 min (for sucrose). Enzymatic ac-
tivity was quantified by measuring the absorbance of quinoneimine
formed (500 nm) using Bio-Rad 3550 microplate reader. The percen-
tage inhibition was calculated using the above expression.
4.3. Kinetic study of α-glucosidase inhibition
For kinetic analysis of the active compound, α-glucosidases and
active compounds were incubated with increasing concentrations of
pNPG (0.2–1 mM), maltose (0.5–8 mM), and sucrose (5–80 mM). The
type of inhibition was determined by the Lineweaver-Burk plot. For
calculation of Ki and Ki′ values, slope and intercept from the
Lineweaver-Burk plot were replotted vs. [I], which provided the sec-
ondary plot.
4.1.6.1. α-11c. Yield: 70%, brown oil; 1H NMR (400 MHz, CDCl3) δ
8.60 (s, 1H, eOH), 6.87–6.81 (m, 2H, H-5′ and H-6′), 6.73 (s, 1H, H-2′),
6.22 (s, 1H, H-3″), 5.60 (brs, 1H, eOH), 5.46 (brs, 1H, eOH), 5.11 (d,
J = 7.4 Hz, 1H, H-2), 4.82 (d, J = 3.3 Hz, 1H, H-6), 4.49 (t, J = 8.5 Hz,
1H, H-4), 4.12 (d, J = 7.5 Hz, 1H, H-8), 4.02 (m, 1H, H-8), 3.90 (s, 3H,
-OMe), 3.81 (s, 3H, -OMe), 3.79 (m, 1H, H-4), 3.78 (s, 3H, -OMe), 3.23
(m, 1H, H-5), 3.02 (m, 1H, H-1); 13C NMR (100 MHz, CDCl3) δ 153.9,
152.1, 143.9, 143.3, 135.4, 133.8, 125.2, 118.9, 115.5, 113.5, 109.2,
97.0, 84.4, 83.9, 73.0, 70.7, 61.1, 61.0, 56.0, 54.7, 53.4.
4.4. DPPH radical scavenging
Radical scavenging activity was validated using DPPH colorimetric
method. Briefly, The synthesized compounds (20 μL) were added to
0.1 mM methanolic solution of DPPH (100 μL). The mixture was kept
dark at room temperature in an incubator shaker for 15 min. The ab-
sorbance of the resulting solution was measured at 517 nm with a 96-
well microplate reader. The percentage inhibition was calculated by
[(A0-A1)/A0] × 100, where A0 is the absorbance without the sample,
and A1 is the absorbance with the sample. The SC50 value was deduced
from a plot of percentage inhibition versus sample concentration.
Butylated hydroxytoluene (BHT) was used as the standard control and
the experiment was performed in triplicate.
4.1.6.2. α-14. Yield: 36%, dark brown oil; 1H NMR (400 MHz, CD3OD)
δ 6.85 (s, 1H, H-6″), 6.80 (s, 1H, H-6′), 6.75 (d, J = 8.1 Hz, 1H, H-5′),
6.68 (d, J = 7.6 Hz, 1H, H-2′), 6.52 (s, 1H, H-3″), 4.75 (d, J = 4.3 Hz,
1H, H-2), 4.61 (d, J = 4.3 Hz, 1H, H-6), 4.20 (dd, J = 16.1, 9.4 Hz, 2H,
H-4 and H-8), 3.81 (dd, J = 8.8, 3.2 Hz, 2H, H-4 and H-8), 3.05 (s, 2H,
H-1 and H-5), 2.27 (s, 3H, H-8″); 13C NMR (100 MHz, CD3OD) δ 171.59,
146.42, 146.22, 146.07, 144.49, 141.90, 133.77, 125.36, 118.90,
116.28, 114.48, 113.75, 111.03, 87.07, 82.89, 73.08, 72.79, 55.36,
55.03, 54.77, 20.83; HRMS m/z 411.1058 [M+Na]+ (calcd for
C
20H20NaO8, 411.1056).
4.5. Modeling studies
4.1.6.3. β-14. Yield: 45%, yellow oil; 1H NMR (400 MHz, CD3OD) δ
7.02 (s, 1H, H-6″), 6.80 (s, 1H, H-2′), 6.74 (d, J = 8.3 Hz, 1H, H-5′),
6.69 (d, J = 7.9 Hz, 1H, H-6′), 6.50 (s, 1H, H-3′′), 4.75 (d, J = 5.3 Hz,
1H, H-2), 4.30 (d, J = 7.3 Hz, 1H, H-6), 4.03 (d, J = 9.3 Hz, 1H, H-4),
3.78–3.74 (m, 2H, H-4 and H-8), 3.25–3.23 (m, 2H, H-1 and H-8), 2.88
(m, 1H, H-5), 2.28 (s, 3H, H-8′′); 13C NMR (100 MHz, CD3OD) δ 171.6,
146.4, 146.1, 145.8, 144.1, 140.9, 133.7, 122.6, 119.0, 116.3, 114.5,
114.4, 110.7, 89.1, 79.2, 71.4, 70.3, 55.6, 50.2, 20.8; HRESIMS m/z
411.1053 [M+Na]+ (calcd for C20H20NaO8, 411.1056).
4.5.1. Pocket verification and docking methods
A homology model of the rat intestinal N-terminal domain of mal-
tase-glucoamylase (rat-ntMGAM) used in this experiment came from
our previous study [16]. Crude protein pocket or cavity using Fpocket
[18], the detection algorithm based on Voronoi tessellation [19], and
Metapocket [20], the protocol consensus among eight different method,
seek the biggest cavities. Additionally, the Achilles Blind docking server
[21] use to validate overlap area with seeking pocket programs, which
explore the ligand template match orientations and cavities to identify
putative ligand binding sites. However, each compound was in-
dividually docked into the best candidate cavity of maltase-glucoamy-
lase (α-glucosidases) using the CDOCKER [22] implemented in Dis-
covery Studio 3.0 (Accelrys Inc). According to the docking procedure
using the CHARMM force field that is simulated annealing search al-
gorithm and energy minimization [23]. The ∼9 Å radius sphere around
ligand was defined to docking site. The docked 100 random orienta-
tions were chosen the lowest CDOCKER interaction energy.
4.2. α-Glucosidase inhibitory activity
α-Glucosidase inhibitory activity against baker’s yeast was de-
termined according to our previous report [7]. The synthesized com-
pounds (1 mg/mL in DMSO, 10 µL) were pre-incubated with 40 µL of α-
glucosidase (0.1 U/mL in 0.1 M phosphate buffer, pH 6.9) at 37 °C for
10 min. The mixture was added with 50 µL of substrate solution (1 mM
p-nitrophenyl-α-D-glucopyranoside, pNPG) and incubated for 20 min.
The resulting mixture was quenched by adding 100 µL of 1 M Na2CO3.
p-Nitrophenoxide ion liberated from the enzymatic reaction was mon-
itored at 405 nm by Bio-Rad 3550 microplate reader. The percentage
inhibitionwas calculated by [(A0 - A1)/A0] × 100, where A1 and A0 are
the absorbance with and without the sample, respectively. The IC50
value was deduced from a plot of percentage inhibition versus sample
concentration and acarbose was used as a positive control.
4.5.2. Molecular dynamics simulation
MD simulations were carried out under the periodic boundary
condition (PBC) using the NAMD program package [24]. The CHRAMM
36 [25–28] force field and CHARMM General Force Field (CGENFF)
were used to treat protein and ligand, respectively. Each complex was
embedded in a three dimensional box of 130 × 130 × 130 Å3 con-
sisting of ∼10 000 (9260) TIP3P [29] water molecules. After neu-
tralization by Na+ and Cl- ions, the all-atom simulation box model
consists of ∼200 000 atoms (204 675). In addition, the solvent was
α-Glucosidase inhibitory activity against rat intestinal maltase and
sucrase was determined according to our previous report [6]. The crude
enzyme solution prepared from rat intestinal acetone powder (Sigma,
792

W. Worawalai, et al.
BioorganicChemistry87(2019)783–793
energetically relaxed by 5000 steps of energy minimization and 50 000
steps of solute-restrained MD simulations. Subsequently, every 100 000
steps were applied to system with whole protein-ligand, protein back-
bone-ligand, and ligand, respectively, restrained. The particle mesh
Ewald (PME) summation method [30,31] was used to calculate the
long-range electrostatic interactions. System was heated from 0 to
298 K with the NPT ensemble using the Nosé-Hoover Langevin piston
pressure control [32]. For each system, unrestrained MD simulations
were conducted for 5 ns.
[10] W. Worawalai, P. Phuwapraisirisan, Samin-derived flavonolignans, a new series of
antidiabetic agents having dual inhibition against α-glucosidase and free radicals,
Nat. Prod. Res. (2018), https://doi.org/10.1080/14786419.2018.1553169 inpress.
[11] M. Nakai, M. Harada, K. Nakahara, K. Akimoto, H. Shibata, W. Miki, Y. Kiso, Novel
antioxidative metabolites in rat liver with ingested sesamin, J. Agric. Food Chem.
51 (2003) 1666–1670.
[12] A.A. Moazzami, R.E. Andersson, A. Kamal-Eldin, Quantitative NMR analysis of a
sesamin catechol metabolite in human urine, J. Nutr. 137 (2007) 940–944.
[13] H. Urata, Y. Nishioka, T. Tobashi, Y. Matsumura, N. Tomimori, Y. Ono, Y. Kiso,
S. Wada, First chemical synthesis of antioxidative metabolites of sesamin, Chem.
Pharm. Bull. 56 (2008) 1611–1612.
[14] Y.Q. Ye, H. Koshino, J.I. Onose, K. Yoshikawa, N. Abe, S. Takahashi, First total
synthesis of vialinin A, a novel and extremely potent inhibitor of TNF-α production,
Org. Lett. 9 (2007) 4131–4134.
Acknowledgements
[15] B.W. Zhang, X. Li, W.L. Sun, Y. Xing, Z.L. Xiu, C.L. Zhuang, Y.S. Dong, Dietary
flavonoids and acarbose synergistically inhibit α-glucosidase and lower post-
prandial blood glucose, J. Agric. Food Chem. 65 (2017) 8319–8330.
[16] W. Worawalai, P. Sompornpisut, S. Wacharasindhu, P. Phuwapraisirisan,
Voglibose-inspired synthesis of new potent α-glucosidase inhibitors N-1,3-dihy-
droxypropylaminocyclitols, Carbohydr. Res. 429 (2016) 155–162.
[17] L. Sim, R. Quezada-Calvillo, E.E. Sterchi, B.L. Nichols, D.R. Rose, Human intestinal
maltase-glucoamylase: crystal structure of the N-terminal catalytic subunit and
basis of inhibition and substrate specificity, J. Mol. Biol. 375 (2008) 782–792.
[18] V.L. Guilloux, P. Schmidtke, P. Tuffery, Fpocket: an open source platform for ligand
pocket detection, BMC Bioinformatics 10 (2009) 168.
This project was financially supported by the Thailand Research
Fund (RSA5880027) and Faculty of Science, Chulalongkorn University
(Sci-Super IV_61_003). W.W. and W.R. are grateful to the Graduate
School of Chulalongkorn University for a Postdoctoral Fellowship
(Ratchadaphisek Sompot Fund) and a PhD Scholarship (Dusadi Phipat),
respectively. The Centers of Excellent in Natural Products (CENP) and
Computational Chemistry (CECC) were subsidized by Chulalongkorn
University.
[19] M. Tanemura, T. Ogawa, N. Ogita, A new algorithm for three-dimensional voronoi
tessellation, J. Comput. Phys. 51 (1983) 191–207.
[20] Z. Zhang, Y. Li, B. Lin, M. Schroeder, B. Huang, Identification of cavities on protein
surface using multiple computational approaches for drug binding site prediction,
Bioinformatics 27 (2011) 2083–2088.
Appendix A. Supplementary material
[21] B.A.H.P.C.B.-H.R. group. Achilles blind docking server, 2017. Available from: <
https://bio-hpc.ucam.edu/achilles/ > .
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.bioorg.2019.03.077.
[22] G. Wu, D.H. Robertson, C.L. Brooks 3rd, M. Vieth, Detailed analysis of grid-based
molecular docking: a case study of CDOCKER-A CHARMm-based MD docking al-
gorithm, J. Comput. Chem. 24 (2003) 1549–1562.
References
[23] F.A. Momany, R. Rone, Validation of the general purpose QUANTA 3.2/CHARMm
force field, J. Comput. Chem. 13 (1992) 888–900.
[1] C.Y. Cai, L. Rao, Y. Rao, J.X. Guo, Z.Z. Xiao, J.Y. Cao, Z.S. Huang, B. Wang,
Analogues of xanthones–chalcones and bis-chalcones as α-glucosidase inhibitors
and anti-diabetes candidates, Eur. J. Med. Chem. 130 (2017) 51–59.
[2] G. Wang, Z. Peng, J. Wang, X. Li, J. Li, Synthesis, in vitro evaluation and molecular
docking studies of novel triazine-triazole derivatives as potential α-glucosidase
inhibitors, Eur. J. Med. Chem. 125 (2017) 423–429.
[24] J.C. Phillips, R. Braun, W. Wang, J. Gumbart, E. Tajkhorshid, E. Villa, C. Chipot,
R.D. Skeel, L. Kale, K. Schulten, Scalable molecular dynamics with NAMD, J.
Comput. Chem. 26 (2005) 21.
[25] K. Vanommeslaeghe, E. Hatcher, C. Acharya, S. Kundu, S. Zhong, J. Shim, E. Darian,
O. Guvench, P. Lopes, I. Vorobyov, CHARMM general force field: a force field for
drug-like molecules compatible with the CHARMM all-atom additive biological
force fields, J. Comput. Chem. 31 (2010) 671–690.
[3] M. Brownlee, Biochemistry and molecular cell biology of diabetic complications,
Nature 414 (2001) 813–820.
[26] K. Vanommeslaeghe, A.D. MacKerell Jr, Automation of the CHARMM general force
field (CGenFF) I: bond perception and atom typing, J. Chem. Inf. Model. 52 (2012)
3144–3154.
[4] A.C. Maritim, R.A. Sanders, J.B. Watkins III, Diabetes, oxidative stress, and anti-
oxidants: a review, J. Biochem. Mol. Toxicol. 17 (2003) 24–38.
[5] E. Ladopoulou, A.N. Matralis, A.P. Kourounakis, New multifunctional di-tert-bu-
tylphenoloctahydro(pyrido/benz)oxazine derivatives with antioxidant, anti-
hyperlipidemic, and antidiabetic action, J. Med. Chem. 56 (2013) 3330–3338.
[6] R. Ramadhan, P. Phuwapraisirisan, New arylalkanones from Horsfieldia macro-
botrys, effective antidiabetic agents concomitantly inhibiting α-glucosidase and free
radicals, Bioorg. Med. Chem. Lett. 25 (2015) 4529–4533.
[27] W. Yu, X. He, K. Vanommeslaeghe, A.D. MacKerell Jr, Extension of the CHARMM
general force field to sulfonyl-containing compounds and its utility in biomolecular
simulations, J. Comput. Chem. 33 (2012) 2451–2468.
[28] I.S. Gutiérrez, F.-Y. Lin, K. Vanommeslaeghe, J.A. Lemkul, K.A. Armacost,
C.L. Brooks III, A.D. MacKerell Jr., Parametrization of halogen bonds in the
CHARMM general force field: improved treatment of ligand–protein interactions,
Bioorg. Med. Chem. 24 (2016) 4812–4825.
[7] E. Rattanangkool, P. Kittikhunnatham, T. Damsud, S. Wacharasindhu,
P. Phuwapraisirisan, Quercitylcinnamates, a new series of antidiabetic bioconju-
gates possessing α-glucosidase inhibition and antioxidant, Eur. J. Med. Chem. 66
(2013) 296–304.
[29] W.L. Jorgensen, J. Chandrasekhar, J.D. Madura, R.W. Impey, M.L. Klein,
Comparison of simple potential functions for simulating liquid water, J. Chem.
Phys. 79 (1983) 926–935.
[8] W. Worawalai, S. Wacharasindhu, P. Phuwapraisirisan, N-ar-
ylmethylaminoquercitols, a new series of effective antidiabetic agents having α-
glucosidase inhibition and antioxidant activity, Bioorg. Med. Chem. Lett. 25 (2015)
2570–2573.
[30] T. Darden, D. York, L. Pedersen, Particle mesh Ewald: An N⋅ log (N) method for
Ewald sums in large systems, J. Chem. Phys. 98 (1993) 10089–10092.
[31] U. Essmann, L. Perera, M.L. Berkowitz, T. Darden, H. Lee, L.G. Pedersen, A smooth
particle mesh Ewald method, J. Chem. Phys. 103 (1995) 8577–8593.
[32] G.J. Martyna, D.J. Tobias, M.L. Klein, Constant pressure molecular dynamics al-
gorithms, J. Chem. Phys. 101 (1994) 4177–4189.
[9] W. Worawalai, P. Khongchai, N. Surachaitanawat, P. Phuwapraisirisan, Synthesis of
furofuran lignans as antidiabetic agents simultaneously achieved by inhibiting α-
glucosidase and free radical, Arch. Pharm. Res. 39 (2016) 1370–1381.
793