Improved synthesis, X-ray structure, and antifungal activity of a sugar-psoralen conjugate: 4,4′-Dimethylxanthotoxol 2,3,4,6-tetra-O-Acetyl-β-D-glucoside

Article abstract of DOI:10.1080/07328303.2019.1609018

An improved synthesis for 4,4′-dimethylxanthotoxol 2,3,4,6-tetra-O-acetyl-β-D-glucoside (1) starting from resorcinol was developed. Crystallographic analysis of glucoside 1 indicated that the dihedral angles between the mean planes of the tricyclic ring system of adjacent molecules was 54.820(22)° probably due to the steric hindrance caused by the bulky O-glucoside moiety, which prevents the molecules from packing via π···π stacking between the tricyclic cores. The antifungal screening data revealed that glucoside 1 had higher inhibition than its parent compound 4,4′-dimethylxanthotoxol and azoxystrobin against Rhizoctonia solani, Pyricularia grisea, and Alternaria alternate Japanese pear pathotype, with the inhibitory rates of 75.4, 65.7 and 70.1%, respectively, at the 50 μg/mL concentration.

Full text of DOI:10.1080/07328303.2019.1609018

Journal of Carbohydrate Chemistry
ISSN: 0732-8303 (Print) 1532-2327 (Online) Journal homepage: https://www.tandfonline.com/loi/lcar20
Improved synthesis, X-ray structure, and
antifungal activity of a sugar-psoralen conjugate:
4,4′-Dimethylxanthotoxol 2,3,4,6-tetra-O-
Acetyl-β-D-glucoside
Chao-Yue Chen, Ting-Hai Yang, Chang-Duo Pan & Xin Wang
To cite this article: Chao-Yue Chen, Ting-Hai Yang, Chang-Duo Pan & Xin Wang (2019)
Improved synthesis, X-ray structure, and antifungal activity of a sugar-psoralen conjugate: 4,4′-
Dimethylxanthotoxol 2,3,4,6-tetra-O-Acetyl-β-D-glucoside, Journal of Carbohydrate Chemistry,
38:3, 179-191, DOI: 10.1080/07328303.2019.1609018
To link to this article: https://doi.org/10.1080/07328303.2019.1609018
Published online: 06 May 2019.
Submit your article to this journal
Article views: 15
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=lcar20

JOURNAL OF CARBOHYDRATE CHEMISTRY
2019, VOL. 38, NO. 3, 179–191
https://doi.org/10.1080/07328303.2019.1609018
Improved synthesis, X-ray structure, and
antifungal activity of a sugar-psoralen conjugate:
4,40-Dimethylxanthotoxol 2,3,4,6-tetra-O-Acetyl-
b-D-glucoside
Chao-Yue Chen, Ting-Hai Yang, Chang-Duo Pan, and Xin Wang
School of Chemistry and Environmental Engineering, Jiangsu University of Technology,
Changzhou, PR China
ABSTRACT
ARTICLE HISTORY
An improved synthesis for 4,40-dimethylxanthotoxol 2,3,4,6-
tetra-O-acetyl-b-D-glucoside (1) starting from resorcinol was
developed. Crystallographic analysis of glucoside 1 indicated
that the dihedral angles between the mean planes of the
tricyclic ring system of adjacent molecules was 54.820(22)ꢀ
probably due to the steric hindrance caused by the bulky
O-glucoside moiety, which prevents the molecules from pack-
ing via pꢁꢁꢁp stacking between the tricyclic cores. The antifun-
gal screening data revealed that glucoside 1 had higher
inhibition than its parent compound 4,40-dimethylxanthotoxol
and azoxystrobin against Rhizoctonia solani, Pyricularia grisea,
and Alternaria alternate Japanese pear pathotype, with the
inhibitory rates of 75.4, 65.7 and 70.1%, respectively, at the
50 mg/mL concentration.
Received 7 October 2018
Accepted 10 April 2019
KEYWORDS
Antifungal activity;
crystallographic
analysis; glucoside;
psoralen; synthesis
GRAPHICAL ABSTRACT
Introduction
Psoralens, also known as linear furocoumarins, are a group of compounds
that are widely distributed in many plants. They possess a wide spectrum
of biological activities, including cytotoxic, phytotoxic, photosensitizing,
insecticidal, to antibacterial effects.[1–3] Furthermore, some of them have
been applied as therapeutics against diseases such as skin disorders,
CONTACT Chao-Yue Chen
njuchaoyuechen@163.com
School of Chemistry and Environmental
Engineering, Jiangsu University of Technology, Changzhou, PR China
ß 2019 Taylor & Francis Group, LLC

180
C.-Y. CHEN ET AL.
O
O
O
Cl
HO
O
O
HO
OH
O
O
O
H
H
3C
3C
OEt
K
2CO3, acetone,
reflux, 85%
H
2SO4, 0 °C - r.t.
89%
O
CH3
CH3
CH3
3
2
OAc
O
AcO
AcO
OH
O
O
O
O
O
O
AcO
1M NaOH
[RuCl2(p-cymene)]2
PhI(TFA)2, DCM, 59%
Br
TBAB, NaOH, reflux
73%
reflux, 82%
H
3C
H
3C
CH3
CH3
4
5
O
O
O
CH3
OAc
O
AcO
AcO
O
AcO
CH3
1
Scheme 1. Improved synthetic approach for glucoside 1.
autoimmune diseases, cutaneous T-cell lymphoma, and several other types
of cancer.[1–3] Recently, another biological effect of psoralens, i.e., antifun-
gal activity, has attracted increasing interest from agricultural chemists,
because a series of structure-activity relationship (SAR) studies demon-
strated that linear furanocoumarin cores could also be promising lead
structures for exploiting new pesticides for the treatment of agricultural
diseases.[4–10]
We have synthesized a range of glycosylated psoralen derivatives and
investigated their antiproliferative effects and antioxidant activities.[3]
Among those compounds, 4,40-dimethylxanthotoxol 2,3,4,6-tetra-O-acetyl-
b-D-glucoside (1, see Scheme 1) showed antiproliferative effects against
three kinds of human tumor cell lines under UV light. The present paper
is a continuation of our research on biologically active sugar-psoralen con-
jugate derivatives. Specifically, we developed an improved synthetic method
for glucoside 1 and performed X-ray crystallographic analysis of glucoside
1 to obtain deeper insight into its structure. Furthermore, considering that
both the furanocoumarin core[4–10] and the glycosyl moiety[11–14] have
been reported as effective pharmacophores for fungicidal inhibition, the
antifungal activity of glucoside 1 was further investigated to explore its
potential as antifungal agent.
Results and discussion
Our previously described synthesis of glucoside 1 starting from pyrogallol
took four steps to reach the key intermediate 4,40-dimethylxanthotoxol (5
in Scheme 1) in a 31% overall yield.[3] That method required laborious

JOURNAL OF CARBOHYDRATE CHEMISTRY
181
protection/deprotection steps to restore the hydroxyl groups and suffered
from unwanted side-reaction of intramolecular aldol condensation. In this
work, we planned to develop a facile and more efficient procedure.
Recently, direct oxidative hydroxylation of C-H bonds by transition met-
als has emerged as a straight-forward and powerful strategy for generating
phenols.[15–19] Prompted by this development, we envisioned a new syn-
thetic approach for 5 starting from resorcinol and taking advantage of
ruthenium(II)-catalyzed ortho C-H hydroxylation in order to avoid the
above mentioned problems.
The modified synthetic pathway is described in Scheme 1. The
preparation of key intermediate 5 began from a reaction of resorcinol with
ethylacetoacetate in concentrated sulfuric acid to give 4-methyl-7-hydroxy-
coumarin 2 in and excellent yield (89%). This coumarin derivative
was then alkylated with 1-chloroacetone in the presence of K2CO3 to afford
4-methyl-7-(2-oxopropoxy)-2H-chromen-2-one
3
in an 85% yield.
Compound 3 was converted into 4,4’-dimethylpsoralen 4 after heating with
1 M NaOH in aqueous solution. In order to introduce a hydroxyl group at
the 8-position of 4 regioselectively, an ortho C-H hydroxylation reaction
was examined using transition metal catalysts such as Pd(OAc)2, Cu(OAc)2
and [RuCl2(p-cymene)]2 under various conditions. After reaction optimiza-
tion, [RuCl2(p-cymene)]2 was identified as the best catalyst for ortho-select-
ive hydroxylation of 4 to be converted into 4,40-dimethylxanthotoxol 5 with
PhI(TFA)2 as the oxidant (59%).[17] Substituents on 7- and 9-positions may
bind to the Ru catalyst and act as directing groups to enhance both the
reactivity and the selectivity for adjacent C-H bond activation. As a result,
the intermediate 5 was obtained in an overall 37% yield, as opposed to the
originally reported overall yield of 31%.[3] Although only a 6% overall yield
increase was achieved, it should be noted that the new and old routes
employed different starting materials and synthetic methodologies. The pre-
vious route started from pyrogallol and a protection-deprotection strategy
was necessary to reach 5,[3] while in the new synthesis, cheaper resorcinol
as starting material was employed and the key reaction was a direct
oxidative hydroxylation, which avoided both the deprotection step and
side-reaction of intramolecular aldol condensation in the original route.
Furthermore, this new synthetic approach has the potential to be used for
the synthesis of other xanthotoxols from resorcinol via C-H hydroxylation.
The target glucoside 1 was finally obtained in a 73% yield via direct O-gly-
cosylation of 5 with per-acetylglycosyl bromide in a biphasic media using
tetrabutylammonium bromide (TBAB) as a phase transfer catalyst and
NaOH as the base.
In order to obtain a better understanding of the structures of glycosy-
lated psoralen derivatives, we further performed X-ray crystallographic

182
C.-Y. CHEN ET AL.
Figure 1. Molecule structure and ORTEP drawing of glucoside 1.
analysis of glucoside 1. The molecular structure of glucoside 1 is depicted
in Figure 1. The crystallographic data are summarized in Table 1, while
the selected bond lengths, bond angles, and torsion angles are given in
Tables 2–4, respectively. The hydrogen bonding geometries for 1 are shown
in Table 5.
As depicted in Figure 1, glucoside 1 consists of four rings in which three of
them (furan, benzene, and pyrone) are fused together into a tricyclic nucleus,
with a terminal glucoside ring attached to it. The dihedral angles between the
furan (C8–C9–C11–O10–C12) and phenyl (C5–C6–C7–C8–C12–C13) rings,
phenyl and pyrone (C2–C3–C4–O12–C5–C6) rings are 1.899(76)ꢀ and
4.032(69)ꢀ, respectively, indicating the close-to-planar structure of the tricyclic
nucleus of the psoralen moiety. The two carbon atoms of the two methyl
groups, C(1) and C(10), are deviated from the furan ring by 0.1172ꢀ, and
from the pyrone ring by 0.0233ꢀ, respectively. It is clear that, except for the
glucoside moiety, all other atoms in glucoside 1 are almost located in one big
plane of p-conjugated system.
The six-membered glucoside ring (C14–C15–C16–C17–C18–O1) which
attached at C13 of the aglycone is oriented approximately 45ꢀ to the plane
of the psoralen ring with dihedral angle of 42.952(77)ꢀ. The Glc moiety
adopts the relaxed 4C1 chair conformation as expected, with ring-puckering
parameters of Q ¼ 0.587(2) Å, h ¼ 11.3(2)ꢀ, and w ¼ 338.3(12)ꢀ. All of the

JOURNAL OF CARBOHYDRATE CHEMISTRY
183
Table 1. Crystal data and structure refinement for glucoside 1.
Compound
1
Empirical formula
Chemical formula weight (Mr)
C27H28O13
560.49
Crystal system
Space group
Orthorhombic
P212121
Unit cell dimensions
a (Å)
b (Å)
8.4807(4)
15.9662(8)
19.8840(9)
90
90
90
c (Å)
a (ꢀ)
b (ꢀ)
c (ꢀ)
Volume (Å3)
2692.4(2)
Z
4
Density (calcd.) g/cm3)
1.383
0.111
1176
Absorption coefficient (mmꢂ1
F(000)
)
Temperature (K)
Radiation (Å)
h Min, max (ꢀ)
Data set
Total., Uniq. Data
R (int)
296
Mo Ka 0.71073
2.4, 27.6
limiting indices ꢂ11 < h < 11; ꢂ19 < k < 20; ꢂ20 < l < 25
24354, 6195
0.039
Nref, Npar
6195, 367
R, wR2, S
CCDC number
0.0405, 0.0940, 1.05
1854605
Table 2. Selected bond lengths for glucoside 1.
Bond Lengths
(Å)
Bond Lengths
(Å)
O1–C14
O1–C18
O10–C11
O10–C12
O11–C13
O11–C14
O12–C4
O12–C5
O13–C4
C2–C3
1.407(3)
1.430(3)
1.390(3)
1.365(3)
1.376(3)
1.407(3)
1.384(3)
1.376(3)
1.210(3)
1.338(4)
1.460(4)
1.443(4)
1.404(3)
C5-C13
C6-C7
C7-C8
1.395(3)
1.398(4)
1.385(3)
1.443(3)
1.403(3)
1.499(4)
1.336(4)
1.387(3)
1.521(3)
1.521(3)
1.514(3)
1.527(3)
0.9800
C8-C9
C8-C12
C9-C10
C9-C11
C12-C13
C14-C15
C15-C16
C16-C17
C17-C18
C14-H14
C2–C6
C3–C4
C5–C6
non-H substituents on the glucoside ring are situated in equatorial posi-
tions. H-14 and H-15 in the pyranose ring bear a trans-diaxial relationship
to each other with torsion angle of 168.927(207)ꢀ. The glycosidic torsion
angle (v) defined by O1–C1–O11–C13 is ꢂ61.175(246)ꢀ. Based on the
above analysis, it is easily observed that the glucoside moiety has the b-con-
figuration and is the pyranose isomer. The X-ray structure determination
on 1 confirms the structure proposed on the basis of the method of prepar-
1
ation and the H NMR data.
A series of X-ray crystal structure analysis[20–24] of psoralens indicated
that pꢁꢁꢁp interactions between rings of the planar tricyclic systems are a
common feature in the crystal packing, thus the adjacent molecules are

184
C.-Y. CHEN ET AL.
Table 3. Selected bond angles for glucoside 1.
Bond Angles
(ꢀ)
Bond Angles
(ꢀ)
C14–O1–C18
C11–O10–C12
C13–O11–C14
C4–O12–C5
C3–C2–C6
111.33(16)
105.28(18)
120.55(17)
121.3(2)
118.9(2)
123.1(2)
116.2(3)
117.1(2)
126.7(2)
121.7(2)
115.0(2)
123.2(2)
117.6(2)
123.1(2)
119.3(2)
118.4(2)
133.3(2)
121.0(2)
105.7(2)
O10–C11–C9
O10–C12–C8
O10–C12–C13
C8–C12–C13
O11–C13–C5
O11–C13–C12
C5–C13–C12
O1–C14–O11
O1–C14–C15
O11–C14–C15
C14–C15–C16
C15–C16–C17
C16–C17–C18
O1–C18–C17
C8–C9–C11
112.8(2)
110.3(2)
127.5(2)
122.2(2)
115.4(2)
128.7(2)
115.9(2)
108.11(18)
108.82(18)
105.18(17)
111.23(18)
112.03(19)
109.89(18)
106.64(17)
105.8(2)
111.00
C2–C3–C4
O12–C4–O13
O12–C4–C3
O13–C4–C3
O12–C5–C6
O12–C5–C13
C6–C5–C13
C2–C6–C5
C2–C6–C7
C5–C6–C7
C6–C7–C8
C7–C8–C9
O1–C14–H14
O11–C14–H14
C15–C14–H14
112.00
111.00
C7–C8–C12
C9–C8–C12
Table 4. Selected torsion angles for glucoside 1.
Torsion Angles
(ꢀ)
Torsion Angles
(ꢀ)
C18–O1–C14–O11
C12–O10–C11–C9
C13–O11–C14–C15
C14–O11–C13–C12
C5–O12–C4–C3
C5–O12–C4–O13
C3–C2–C6–C7
C2–C3–C4–O13
O12–C5–C6–C7
C13–C5–C6–C7
178.94(16)
0.2(3)
C11–O10-C12-C8
C11–O10-C12-C13
C13–O11-C14-O1
C14–O11-C13-C5
C4–O12-C5-C13
C4–O12-C5-C6
C6–C2-C3-C4
ꢂ0.7(3)
178.1(2)
ꢂ61.2(3)
168.6(2)
ꢂ177.9(2)
2.4(3)
ꢂ177.3(2)
ꢂ12.5(4)
ꢂ4.2(3)
176.3(2)
173.3(2)
ꢂ179.4(3)
ꢂ176.2(2)
4.1(4)
ꢂ4.4(3)
176.5(2)
ꢂ179.3(2)
ꢂ2.6(4)
ꢂ178.0(2)
ꢂ0.7(3)
0.3(3)
3.5(4)
C3–C2-C6-C5
ꢂ5.3(4)
C2–C3-C4-O12
O12–C5-C6-C2
C6–C5-C13-C12
C6–C5-C13-O11
C13–C5-C6-C2
C5–C6-C7-C8
1.2(4)
2.4(4)
O12–C5–C13–O11
O12–C5–C13–C12
C2–C6–C7–C8
ꢂ3.8(4)
175.3(2)
ꢂ177.3(2)
ꢂ0.8(4)
178.6(3)
178.3(3)
0.9(3)
C6–C7–C8–C12
C9–C8–C12–C13
C12–C8–C9–C11
C8–C9–C11–O10
C8–C12–C13–C5
C8–C12–C13–O11
O1–C14–C15–C16
O11–C14–C15–C16
C15–C16–C17–C18
C18–O1–C14–C15
C14–O1–C18–C17
C6–C7-C8-C9
C7–C8-C9-C11
C9–C8-C12-O10
C7–C8-C12-C13
C7–C8-C12-O10
O10–C12-C13-O11
O10–C12-C13-C5
C14–C15–C16–C17
C16–C17–C18–O1
0.2(4)
2.9(4)
ꢂ178.7(2)
ꢂ178.3(2)
53.6(3)
2.7(4)
169.22(19)
49.7(3)
ꢂ178.4(2)
ꢂ46.6(3)
ꢂ59.2(2)
ꢂ67.3(2)
70.1(2)
usually packed in near parallel arrangements across centers the of
tricyclic moieties. However, the crystallographic data of glucoside 1 indicate
that the molecules are stabilized only by weak C–HꢁꢁꢁO interactions
(Table 5), and no pꢁꢁꢁp stacking between rings of the tricyclic systems in
adjacent molecules is observed in it (Figure 2). In fact, the dihedral angles
between the mean planes of the tricyclic ring system of adjacent molecules
is 54.820(22)ꢀ. It is obvious that the steric hindrance caused by the bulky

JOURNAL OF CARBOHYDRATE CHEMISTRY
185
Table 5. Geometry for hydrogen bonds in the crystal structure of glucoside 1.
D—HꢁꢁꢁA
D—H
HꢁꢁꢁA
DꢁꢁꢁA
D—HꢁꢁꢁA
C1—H1BꢁꢁꢁO4
0.9600
0.9800
0.9800
0.9800
0.9800
0.9600
0.9600
0.9600
2.5300
2.5400
2.2800
2.2700
2.3300
2.4200
2.3200
2.5400
3.250(3)
2.912(3)
2.721(3)
2.706(3)
2.714(3)
3.286(4)
3.134(4)
3.484(4)
132.00
102.00
106.00
106.00
102.00
150.00
142.00
169.00
C14— H14ꢁꢁꢁO10
C15—H15ꢁꢁꢁO9
C16—H16ꢁꢁꢁO7
C17—H17ꢁꢁꢁO5
C20—H20BꢁꢁꢁO13
C23—H23CꢁꢁꢁO3
C25—H25CꢁꢁꢁO5
Figure 2. Molecular packing of glucoside 1.
O-glucoside moiety may be responsible for the disruption of pꢁꢁꢁp stacking
interactions between the tricyclic ring aglycones in glucoside 1.
We also evaluated the in vitro antifungal activities of glucoside 1 and
compared it to the parent compound 5 by mycelium growth rate method[5]
against the six most common plant pathogenic fungi in China, including
Rhizoctonia solani, Pyricularia grisea, Gibberella zeae, Alternaria solani,
Alternaria alternate, and Fusarium oxysporum f. sp. Niveum. The positive
control used was azoxystrobin, and the results are presented in Table 6.
Both 1 and 5 were more active than the positive control against
Rhizoctonia solani, Pyricularia grisea, and Alternaria alternata Japanese
pear pathotype, and both displayed equivalent antifungal activity as the
positive control against Fusarium oxysporum f. sp. niveum but showed
poorer activity than the positive control against Gibberella zeae and
Alternaria solani. In addition, glucoside 1 revealed higher inhibition than

186
C.-Y. CHEN ET AL.
Table 6. Antifungal activities of compounds 1 and 5 against six fungus species in vitroa.
Speciesb/ Inhibitory Rate (%)c
Compound number
RHS
PYG
GIZ
ALS
AAJPP
FON
1
5
75.4
67.3
61.2
65.7
59.2
52.8
18.7
20.2
59.3
12.6
10.3
30.4
70.1
66.5
62.0
31.7
30.4
32.2
Azoxystrobin
aRHS: Rhizoctonia solani; PYG: Pyricularia grisea; GIZ: Gibberella zeae; ALS: Alternaria solani; AAJPP: Alternaria alter-
nata Japanese pear pathotype; FON: Fusarium oxysporum f. sp. Niveum.
bCompound concentration: 50 mg/mL.
cAll data were presented as the average of three replications.
its parent compound 5 against Rhizoctonia solani, Pyricularia grisea, and
Alternaria alternata Japanese pear pathotype under the same conditions,
suggesting that the introduction of a glycoside moiety[11–14] is helpful to
improve the antifungal activity of furancoumarins for these fungi. These
preliminary results indicate the potential of using glycosylated psoralen
derivatives for new furancoumarin fungicide design, and further investiga-
tions are currently underway in our lab.
Conclusion
4,40-Dimethylxanthotoxol 2,3,4,6-tetra-O-acetyl-b-D-glucoside 1 was synthe-
sized via a C-H hydroxylation methodology starting from resorcinol.
Crystal structure analysis of 1 revealed that probably owning to the steric
effect of the bulky terminal O-glucoside moiety, this molecule does not
have pꢁꢁꢁp stacking interactions between the tricyclic nucleus of the agly-
cone in adjacent molecules. We have also shown that among the six kinds
of phytopathogenic fungi tested, glucoside 1 was particularly effective
against Rhizoctonia solani, Pyricularia grisea, and Alternaria alternata
Japanese pear pathotype with the inhibitory rates of 75.4, 65.7 and 70.1%,
vs 61.2, 52.8 and 62.0% for the positive control of azoxystrobin, respect-
ively, at the concentration of 50 mg/mL.
Experimental section
General methods
Chemicals were purchased as reagent grade and used without further puri-
fication. Thin-layer chromatography (TLC) was carried out on glass plates
coated with silica gel (Qingdao Haiyang Chemical Co., Gel 60 F-254) and
visualized by UV light (254 nm and 365 nm). Melting points were deter-
mined on an electrically heated RK-Z melting point apparatus (Analytical
1
instrument factory in Tianjin, China) and were uncorrected. H and 13C
NMR spectra were determined on Brucker ARX-300 (300 MHz, Bruker,
Rheinstetten/Karlsruhe, Germany) with TMS as internal standard.

JOURNAL OF CARBOHYDRATE CHEMISTRY
187
Synthesis of 7-hydroxy-4-methylcoumarin (2)
To a concentrated H2SO4 (80.0 mL) at 0 ꢀC, a solution of resorcinol (7.71 g,
70.0 mmol) in freshly distilled ethyl acetoacetate (9.11 g, 70.0 mmol) was
added dropwise. The reaction mixture was allowed to warm to room tem-
perature and stirred over night. Then, the mixture was poured with vigor-
ous stirring into ice water (100.0 mL). The solid was collected by filtration,
washed with ice-cold water, and recrystallized from ethanol to afford pure
7-hydroxy-4-methylcoumarin 2 as a white solid. Yield 89%, m.p.
1
182–184 ꢀC (Lit. 188 ꢀC[25]). H NMR (300 MHz, DMSO-d6) d(ppm): 10.50
(s, 1 H), 7.58 (d, J ¼ 6.0 Hz, 1 H), 6.79 (d, J ¼ 6.0 Hz, 1 H), 6.69 (s, 1 H),
6.11 (s, 1 H), 2.35 (s, 3 H).
Synthesis of 7-(2-oxo-propoxy)-4-methyl-2H-chromen-2-one (3)
To the mixture of 7-hydroxy-4-methylcoumarin 2 (5.46 g, 31.0 mmol),
anhydrous K2CO3 (8.55 g, 62.0 mmol), and catalytic amount of KI in dry
acetone (50.0 mL), chloroacetone (4.16 g, 45.0 mmol) was added dropwise
with vigorous stirring at room temperature. After the addition was com-
plete, the reaction mixture was refluxed for 24 h (monitored by TLC).
Then, the mixture was cooled and filtered. The filtrate was evaporated
under reduced pressure and the residue was crystallized from MeOH to
give 7-(2-oxo-propoxy)-4-methyl-2H-chromen-2-one 3 as a white solid.
1
Yield 85%, m.p. 160 – 163 ꢀC (Lit. 155–158 ꢀC[26]). H NMR (300 MHz,
CDCl3) d (ppm): 7.53 (d, J ¼ 9.0 Hz, 1 H), 6.88 (dd, J ¼ 9.0, 3.0 Hz, 1 H),
6.74 (d, J ¼ 3.0 Hz, 1 H), 6.15 (s, 1 H), 4.64 (s, 2 H), 2.39 (s, 3 H), 2.30
(s, 3 H).
Synthesis of 4,4’-dimethylpsoralen (4)
7-(2-Oxo-propoxy)-4-methyl-2H-chromen-2-one 3 (5.81 g, 25.0 mmol) was
dissolved in aqueous NaOH (1.0 M, 100.0 mL) and refluxed for 24 h under
nitrogen atmosphere. The mixture was cooled to 0 ꢀC and then acidified
with 2.0 M HCl. The precipitation formed was collected, washed with cold
water. The crude product was purified by silica gel chromatography with
petroleum ether/ethyl acetate (1:1) to give 4,4’-dimethylpsoralen 4 as a
1
white solid. Yield 82%, m.p. 219–221 ꢀC (Lit. 220–222 ꢀC[27]). H NMR
(300 MHz, CDCl3) d (ppm): 7.67 (s, 1 H), 7.46 (s, 1 H), 7.39 (s, 1 H), 6.25
(s, 1 H), 2.52 (s, 3 H), 2.29 (s, 3 H). 13C NMR (75 MHz, CDCl3) d (ppm):
161.3, 156.7, 152.9, 151.7, 143.2, 126.5, 116.2, 115.7, 114.8, 113.3, 99.8,
19.3, 8.0.

188
C.-Y. CHEN ET AL.
Synthesis of 4,40-dimethylxanthotoxol (5)
4,4’-Dimethylpsoralen 4 (0.107 g, 0.50 mmol), [RuCl2(p-cymene)]2(7.7 mg,
2.5 mol %), PhI(TFA)2 (0.43 g, 1.0 mmol) and DCE (15.0 mL) were placed
into a 50.0 mL schlenk tube equipped with a septum under N2. The tube
was then placed into an oil bath and the reaction mixture was stirred at
reflux for 24 h. At ambient temperature, the reaction mixture was diluted
with H2O (15.0 mL) and extracted with EtOAc (3 x 15.0 mL). The com-
bined organic layer was concentrated under reduced pressure. The crude
products were purified by column chromatography (n-hexane/EtOAc) on
silica gel to afford the desired product. Yield 59%, m.p. > 250 ꢀC (Lit.
1
>300 ꢀC[28]). H NMR (300 MHz, DMSO-d6) d(ppm): 10.49 (s, 1 H), 7.82
(s, 1 H), 7.40 (s, 1 H), 6.30 (s, 1 H), 2.48 (s, 3 H), 2.22 (s, 3 H). 13C NMR
(75 MHz, DMSO-d6) d(ppm): 160.4, 154.7, 145.8, 143.9, 140.1, 130.4, 126.9,
117.2, 116.3, 112.8, 105.8,19.3, 8.0.
Synthesis of 4,40-Dimethyl-8-O-(200,300,400,600-tetra-O-acetyl-b-D-
glucopyranosyl)xanthotoxol (1)
4,40-Dimethylxanthotoxol 5 (1.38 g, 6.0 mmol), tetra-acetylglucosyl bromide
(3.08 g, 7.5 mmol), and TBAB (2.58 g, 8.0 mmol) were dissolved in DCM
(30.0 mL) and warmed to 35 ꢀC. A solution of NaOH (5%, 10.0 mL) was
added, and the reaction mixture was refluxed for 8 h. The mixture was
cooled to room temperature and diluted with CHCl3 (30.0 mL), which was
then washed with cold 1.0 N HCl solution and brine, dried over anhydrous
Na2SO4, and concentrated. The residue was purified by column chromatog-
raphy (silica gel, EtOAc:hexane ¼ 1:2 as eluent) to afford glycosylated psor-
alen derivative 1. Yield 73%, white solid, m.p. 118 – 120 ꢀC (Lit. 118-120 ꢀC
1
[3]). H NMR (300 MHz, CDCl3) d(ppm): 7.48(d, J ¼ 1.2 Hz, 1 H), 7.47 (s,
1 H), 6.25 (d, J ¼ 1.2 Hz, 1 H), 5.45 – 5.21 (m, 4 H), 4.26 (dd, J ¼ 12.0,
4.5 Hz, 1 H), 4.08 (dd, J ¼ 12.0, 3.9 Hz, 1 H), 3.75 (ddd, J ¼ 9.9, 4.8, 2.1 Hz,
1 H), 2.51 (d, J ¼ 0.9 Hz, 3 H), 2.27 (d, J ¼ 1.2 Hz, 3 H), 2.19 (s, 3 H), 2.05
(s, 3 H), 2.02 (s, 3 H), 1.97 (s, 3 H). 13C NMR (75 MHz, CDCl3) d(ppm):
170.6, 170.2, 169.8, 169.4, 159.9, 152.7, 148.6, 143.4, 128.5, 127.2, 117.2,
115.9, 113.5, 110.3, 101.6, 72.7, 72.1, 71.4, 68.4, 61.7, 30.9, 20.7, 20.62,
20.58, 19.4, 7.7.
X-ray crystallography
X-Ray crystallography measurements were made on a Bruker Apperx II dif-
fractometer with graphite-monochromated Mo-Ka radiation (k ¼ 0.71073 Å).
An analytical crystalline sample of glucoside (1) was obtained by recrystal-
lization from n-hexane/ethyl acetate mixture.

JOURNAL OF CARBOHYDRATE CHEMISTRY
189
The structure was solved by direct methods, and the non-hydrogen
atoms were located from the trial structure and then refined anisotropically
with SHELXTL using full-matrix least-squares procedures based on F2 val-
ues. Hydrogen atoms positions were fixed geometrically at calculated dis-
tances and allowed to ride on the parent atoms. CCDC reference number
1854605 contains the supplementary crystallographic data reported in this
paper as CIF files. These data sets can be obtained free of charge from The
Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/data_
request/cif, and are also available as supporting information.
Antifungal assay
The antifungal activities of the glucoside 1 and its parent compound 5
were evaluated in vitro against six plants pathogenic fungi (Rhizoctonia sol-
ani, Pyricularia grisea, Gibberella zeae, Alternaria solani, Alternaria alter-
nata Japanese pear pathotype, Fusarium oxysporum f. sp. niveum), using the
mycelium growth inhibitory rate method[5] on PDA (a kind of culture
medium which was prepared with 200 g of potato, 20 g of agar, and 20 g of
Dextrose per liter of distilled water). The commercially available azoxystro-
bin, a broad spectrum fungicide used for protecting plants and food crops
from fungal diseases, was used as positive control. The tested compounds
were dissolved in dimethyl formamide (DMF) to generate the stock solu-
tion before mixing with molten agar below 55 ꢀC. The medium containing
compounds at a concentration of 50 mg/mL for the preliminary screening
was poured into sterilized petri dishes. Mycelia disks (5 mm in diameter)
were then inoculated in the center of the Petri dishes and incubated at
25 ꢀC for 3 to 5 days. A negative control was maintained with sterile water
mixed with PDA medium. Each treatment had three replicates. The diam-
eter of colony growth was measured when the fungal growth in the control
had completely covered the Petri dishes. The inhibition percentage of
mycelia growth was calculated using the following formula:
Da ꢂ Db
ð Þ
Mycelia growth inhibition %
¼
ꢃ 100
Da
Where Da represents control colony diameter and Db represents treated
colony diameter. The colony diameter is in millimeters. The colony diam-
eter of each strain was measured by cross bracketing method.
Funding
This work was supported in parts by the Natural Science Foundation of China (grant num-
ber 21602086) and the Changzhou Sci&Tech Program (grant number CJ20179015).

190
C.-Y. CHEN ET AL.
References
[1] Melough, M. M.; Cho, E.; Chun, O. K. Furocoumarins: a review of biochemical
activities, dietary sources and intake, and potential health risks. Food Chem. Toxicol.
2018, 113, 99–107. doi:10.1016/j.fct.2018.01.030.
[2] Francisco, C. S.; Rodrigues, L. R.; Cerqueira, N. M. F. S. A.; Oliveira-Campos,
A. M. F.; Rodrigues, L. M.; Esteves, A. P. Synthesis of novel psoralen analogues and
their in vitro antitumor activity. Bioorg. Med. Chem. 2013, 21, 5047–5053. doi:
10.1016/j.bmc.2013.06.049.
[3] Chen, C. Y.; Sun, J. G.; Liu, F. Y.; Fung, K. P.; Wu, P.; Huang, Z. Z. Synthesis and
biological evaluation of glycosylated psoralen derivatives. Tetrahedron 2012, 68,
2598–2606. doi:10.1016/j.tet.2012.01.090.
[4] Sardari, S.; Nishibe, S.; Daneshtalab, M. Coumarins, the bioactive structures with
antifungal property. Stud. Nat. Prod. Chem. 2000, 23, 335–393.
[5] Yu, X.; Wen, Y.; Liang, C. G.; Liu, J.; Ding, Y. B.; Zhang, W. H. Design, synthesis
and antifungal activity of psoralen derivatives. Molecules 2017, 22, 1672. doi:
10.3390/molecules22101672.
[6] Zhang, M. Z.; Zhang, R. R.; Wang, J. Q.; Eur, J. Microwave-assisted synthesis and
antifungal activity of novel fused Osthole derivatives. Eur. J. Med. Chem. 2016, 97,
275–279. doi:10.21037/atm.2016.05.14.
[7] Xiao, L.; Zhou, Y. M.; Zhang, X. F.; Du, F. Y. Notopterygium incisum extract and
associated secondary metabolites inhibit apple fruit fungal pathogens. Pestic.
Biochem. Physiol. 2018, 150, 59–65.
[8] Song, P. P.; Zhao, J.; Liu, Z. L.; Duan, Y. B.; Hou, Y. P.; Zhao, C. Q.; Wu, M.; Wei,
M.; Wang, N. H.; Lv, Y.; Zhao, J. H. Evaluation of antifungal activities and struc-
ture-activity relationships of coumarin derivatives. Pest Manag. Sci. 2017, 73,
94–101. doi:10.1002/ps.4422.
[9] Xie, Q.; Li, S. X.; Liao, D. F.; Wang, W.; Tekwani, B.; Huang, H. Y.; Ali, A.;
Rehman, J.; Schrader, K. K.; Duke, S. O.; et al. Bio-pesticidal and Antimicrobial
Coumarins from Angelica dahurica (Fisch. Ex Hoffm). Rec. Nat. Prod 2016, 10,
294–306.
[10] Nam, V. D.; Teruhisa, F.; Hirofumi, T.; Hiroshi, K.; Khoi, N. M.; Dung, L. V.; Ha,
D. T.; Hiroshi, H. Chemical composition of clausena lansium (lour.) skeels leaves
and antifungal activity. Nat. Prod. Sci. 2016, 22, 35–40. doi:10.20307/
nps.2016.22.1.35.
ꢀ
[11] Hipolito, T. M. M.; Bastos, G. T. L.; Barbosa, T. W. L.; de Souza, T. B.; Coelho,
ꢀ
L. F. L.; Dias, A. L. T.; Rodrıguez, I. C.; dos Santos, M. H.; Dias, D. F.; Franco,
L. L.; Carvalho, D. T. Synthesis, activity, and docking studies of eugenol-based glu-
cosides as new agents against Candida sp. Chem. Biol. Drug Des. 2018, 92,
1514–1524. doi:10.1111/cbdd.13318.
[12] de Souza, T. B.; Orlandi, M.; Coelho, L. F. L.; Malaquias, L. C. C.; Dias, A. L. T.;
Carvalho, R. R.; Silva, N. C.; Carvalho, D. T. Synthesis and in vitro evaluation of
antifungal and cytotoxic activities of eugenol glycosides. Med. Chem. Res. 2014, 23,
496–502. doi:10.1007/s00044-013-0669-2.
ꢀ
[13] de Souza, T. B.; Raimundo, P. O. B.; Andrade, S. F.; Hipolito, T. M. M.; Silva,
N. C.; Dias, A. L. T.; Ikegaki, M.; Rocha, R. P.; Coelho, L. F. L.; Veloso, M. P.; et al.
Synthesis and antimicrobial activity of 6-triazolo-6-deoxy eugenol glucosides.
Carbohydr. Res. 2015, 410, 1–8. doi:10.1016/j.carres.2015.04.002.

JOURNAL OF CARBOHYDRATE CHEMISTRY
191
[14] Vudhgiri, S.; Koude, D.; Veeragoni, D. K.; Misra, S.; Prasad, R. B. N.; Jala, R. C. R.
Synthesis and biological evaluation of 5-fatty-acylamido-1, 3, 4-thiadiazole-2-thiogly-
cosides. Bioorg. Med. Chem. Lett. 2017, 27, 3370–3373. doi:10.1016/
j.bmcl.2017.06.004.
[15] Li, X.; Liu, Y. H.; Gu, W. J.; Li, B.; Chen, F. J.; Shi, B. F. Copper-mediated hydroxyl-
ation of arenes and heteroarenes directed by a removable bidentate auxiliary. Org.
Lett. 2014, 16, 3904–3907. doi:10.1021/ol5016064.
[16] Mo, F.; Trzepkowski, L. J.; Dong, G. Synthesis of ortho-acylphenols through the pal-
ladium-catalyzed ketone-directed hydroxylation of arenes. Angew. Chem. Int. Ed.
Engl. 2012, 51, 13075–13079. doi:10.1002/anie.201207479.
[17] Liu, W.; Ackermann, L. Ortho- and para-selective ruthenium-catalyzed C(sp2)-H
oxygenations of phenol derivatives. Org. Lett. 2013, 15, 3484–3486. doi:10.1021/
ol401535k.
[18] Alonso, D. A.; Najera, C.; Pastor, I. M.; Yus, M. Transition-metal-catalyzed synthesis
of hydroxylated arenes. Chemistry 2010, 16, 5274–5284. doi:10.1002/
chem.201000470.
[19] Yang, F.; Zhang, H.; Liu, X.; Wang, B.; Ackermann, L. Transition metal-catalyzed
regio-selective aromatic C—H bond oxidation for C—O bond formation. Chin. J.
Org. Chem. 2019, 39, 59–73. doi:10.6023/cjoc201808017.
[20] Lei, L.; Xue, Y. B.; Liu, Z.; Peng, S. S.; He, Y.; Zhang, Y.; Fang, R.; Wang, J. P.; Luo,
Z. W.; Yao, G. M.; et al. Coumarin derivatives from Ainsliaea fragrans and their
anticoagulant activity. Sci. Rep 2015, 5, 13544.
[21] Cox, P. J.; Jaspars, M.; Kumarasamy, Y.; Nahar, L.; Sarker, S. D.; Shoeb, M. A mixed
crystal of imperatorin and phellopterin, with C–H.O, C–H.pi and pi-pi Interactions.
Acta Cryst. 2003, 59, o520–o522.
[22] Bauri, A. K.; Foro, S.; Nhu Do, Q. N. Crystal structure of bergapten: a photomuta-
genic and photobiologically active furanocoumarin. Acta Crystallogr. E Cryst.
Commun. 2016, E72, 1194–1196. doi:10.1107/S2056989016011221.
[23] Magotra, D. K.; Gupta, V. K.; Goswami, K. N.; Thappa, R. K. Archangelin. Acta
Cryst 1995, C51, 2196–2198.
[24] Brisse, F.; Simard, M. G.; Dugas, H.; Basak, A. Structure of a psoralen derivative of
a monosubstituted 18-crown-6 ether. Acta Crystallogr. C Cryst. Struct. Commun.
1991, C47, 1683–1687. doi:10.1107/S0108270190013725.
[25] Lingaraju, G. S.; Balaji, K. S.; Jayarama, S.; Anil, S. M.; Kiran, K. R.; Sadashiva,
M. P. Synthesis of new coumarin tethered isoxazolines as potential anticancer
agents. Bioorg. Med. Chem. Lett. 2018, 28, 3606–3612. doi:10.1016/
j.bmcl.2018.10.046.
[26] Soni, J. N.; Soman, S. S. Synthesis and antimicrobial evaluation of amide derivatives
of benzodifuran-2-carboxylic acid. Eur. J. Med. Chem. 2014, 75, 77–81. doi:10.1016/
j.ejmech.2014.01.026.
[27] Shen, Q.; Peng, Q.; Shao, J.; Liu, X.; Huang, Z.; Pu, X.; Ma, L.; Li, Y. M.; Chan,
A. S.; Gu, L. Synthesis and biological evaluation of functionalized coumarins as
acetylcholinesterase inhibitors. Eur. J. Med. Chem. 2005, 40, 1307–1315. doi:10.1016/
j.ejmech.2005.07.014.
[28] Marzaro, G.; Gandin, V.; Marzano, C.; Guiotto, A.; Chilin, A. Psoralenquinones as a
novel class of proteasome inhibitors: design, synthesis and biological evaluation.
ChemMedChem 2011, 6, 996–1000. doi:10.1002/cmdc.201100041.