Total synthesis of viscumneoside III of Viscum coloratum

Article abstract of DOI:10.1016/j.tet.2018.03.057

The first total synthesis of viscumneoside III, a promising anti-angina pectoris dihydroflavone O-glycoside isolated from Viscum coloratum was described here. Trichloroaceti-midate was employed as the apiofuranosyl donor to construct the key building block of homoeriodictyol-7-O-β-D-apiosyl-(1 → 2)-β-D-glycoside (1). The longest linear sequence (from 2 to 1) in the synthetic route required thirteen steps and afforded the final product 1 with an overall yield of 6.3%.

Full text of DOI:10.1016/j.tet.2018.03.057

Accepted Manuscript
Total synthesis of viscumneoside III of Viscum coloratum
Lei Zou, Zixue Zhang, Xiaowen Chen, Hua Chen, Yi Zhang, Jianqi Li, Yu Liu
PII:
S0040-4020(18)30330-2
10.1016/j.tet.2018.03.057
TET 29397
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 7 February 2018
Revised Date: 23 March 2018
Accepted Date: 27 March 2018
Please cite this article as: Zou L, Zhang Z, Chen X, Chen H, Zhang Y, Li J, Liu Y, Total synthesis of
viscumneoside III of Viscum coloratum, Tetrahedron (2018), doi: 10.1016/j.tet.2018.03.057.
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ACCEPTED MANUSCRIPT
Graphical Abstract
Total synthesis of viscumneoside Ⅲ of
Viscum coloratum
Lei Zou, Zixue Zhang, Xiaowen Chen,Hua Chen, Yi Zhang, Jianqi Li, Yu Liu*

ACCEPTED MANUSCRIPT
Total synthesis of viscumneoside III of
Viscum coloratum
Lei Zou[a, b], Zixue Zhang[a, b, c], Xiaowen Chen[a, b], Hua Chen[a, b], Yi Zhang[a, b], Jianqi
Li[a, b], Yu Liu*[a, b]
aNovel Technology Center of Pharmaceutical Chemistry, Shanghai Institute of Pharmaceutical
Industry, China State Institute of Pharmaceutical Industry, Shanghai 201203, China;
bShanghai Engineering Research Center of Pharmaceutical Process, Shanghai Institute of
Pharmaceutical Industry, Shanghai 201203, China
cSchool of Pharmacy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240,
China
Abstract: The first total synthesis of viscumneoside III, a promising anti-angina pectoris
dihydroflavone O-glycoside isolated from Viscum coloratum was described here. Trichloroaceti-
midate was employed as the apiofuranosyl donor to construct the key building block of
homoeriodictyol-7-O-β-D-apiosyl-(1→2)-β-D-glycoside (1). The longest linear sequence (from 2
to 1) in the synthetic route required thirteen steps and afforded the final product 1 with an overall
yield of 6.3%.
Keywords: dihydroflavone O-glycoside; anti-angina pectoris; apiofuranosyl donor
1. Introduction
Viscum coloratum (Kom.) Nakai (V. coloratum) is a semi-parasitic plant which grows on
branches or stems of deciduous trees. It is known as Hujisheng in Chinese [1-2]. V. coloratum is an
important medicinal herb that has been used widely in traditional Chinese medicine for treatment
of various diseases [3-4], including coronary heart disease with angina pectoris, cancer, hepatitis
and hemorrhage [5-6]. Studies have shown that the dihydroflavones from V. coloratum are
responsible for the anti-angina pectoris activity [7-8]
.
Viscumneosides I-IV (Fig.1) are the major components of V. coloratum that are responsible
for its anti-coagulant, anti-inflammatory, antioxidant, anti-tumor and anti-fungal activities [7-9]. Our
team has reported the total synthesis of viscumneoside II previously [10], but the total synthesis of
viscumneoside III has not been reported so far. Viscumneoside III (Scheme 1, 1) possesses a
β-D-apiofuranosyl-(1→2) - β-D-glucopyranose sugar chain, apiofuranose-containing glycosides,
such as saponins, cucurbitosides or phenolic glycosides, play a crucial role in the biochemistry of
plants. However, the synthesis of apiofuranose-containing glycosides carrying flavanone
O-glycosides is still a challenge, the synthetic route requires delicate protective manipulation of
the hydroxyl groups on the aglycone and sugars because of regioselective construction of two
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glycosidic linkages. The promising anti-angina pectoris activity and limited availability from
natural sources makes viscumneoside III a suitable target for which to develop synthetic strategies
[11-12]. This is of great importance for establishing the structure-activity relationships (SARs) of
viscumneosides, which will in turn promote further understanding of the molecular mechanism of
its bioactivities and clinical effects.
Herein, we report our work on the first total synthesis of viscumneoside III. Compound 15, as
shown in the retrosynthetic analysis, is the key intermediate for the synthesis of the target
compound 1, which can be built by glycosylation of glycosyl bromides 12 with the partially
protected homoeriodictyol 7. The protecting groups on 12 will ensure the formation of a
β-glucosyl linkage in 15 through the neighboring group participation effect of the acetyl at C-2
position. We assume the glycosylation of 7 and 12 will occur only at C-7 of 7, since the free 5-OH
is less reactive due to the chelating effect with the carbonyl at C-4. Also, this study has addressed
issues associated with the inherent chemical reactivity of apiose.
viscumneoside I：R = H
II：R = β-D-Glc
III：R = β-D-Api-(1→2)-β-D-Glc
IV: R = β-D-Api-(1→5)-β-D-Api-
(1→2)- β-D-Glc
Figure 1. The structures of viscumneosides I- IV
Scheme 1. Retrosynthetic analysis of viscumneoside III (1)
2. Results and discussion
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2.1. Synthesis of homoeriodictyol-7-O-β-D-glucopyranoside acceptor 15
The synthesis started from commercially available material 1,3,5-trihydroxybenzene (2).
2-Hydroxy-4,6-bis(methoxymethoxy)-acetophenone (4) was prepared from 2 by a Friedel-Crafts
acylation followed by a MOM (methoxymethyl) protection. Then a base catalyzed aldol
condensation of 4 with 4-benzyloxy-3-methoxybenzaldehyde 5 gave chalcone 6 in 85% yield.
After cyclization in the presence of sodium acetate and followed by acidification, chalcone 6 was
converted to benzyl-protected dihydroflavone 7 in high yield [10, 13] (Scheme 2).
To
prepare
2,4,6-tri-O-acetyl-3-O-benzyl-α-D-glucopyranosyl
bromide
12,
1,2:5,6-di-O-isopropylidene-α-D-glucofuranose 8 was employed as the starting material. The
3-OH benzylation of 8 was accomplished by using benzyl bromide in the presence of sodium
hydride in THF to afford 9. Removal of the isopropylidene groups on 9 with 50% trifluoroacetic
acid provided 10. Subsequently acetylation of 10 in acetic anhydride and pyridine afforded
1,2,4,6-tetra-O-acetyl-3-O-benzyl-α/β-D-glucopyranose 11 with an overall yield of 40% from 8.
Bromination of 11 with 33% hydrogen bromide in acetic acid gave 12[14] (Scheme 3).
Scheme 2. (a) AlCl3, DCM, CH3NO2, AcCl, rt, 19 h, 60%; (b) DIPEA, DCM, MOMCl, rt, 10 h,
64%; (c) EtOH, 20% NaOH, rt, 7 h, 85%; (d) NaOAc, EtOH, reflux, 7h (e) MeOH, 10% HCl,
reflux, 1 h, 58% for two steps
Scheme 3. (a) NaH, THF, BnBr, 50 °C , 6 h; (b) 50% CF3COOH, r.t., overnight, 44% for two
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steps; (c) Ac2O, pyridine, r.t., 8 h, 90%; (d) 33% HBr/CH3COOH, DCM, 30 min.85%.
Scheme 4. (a) K2CO3, CHCl3, Bu4N+Br-, 45 , 14 h; (b) MeONa, MeOH, reflux, 8 h, 73% for
two steps; (c) benzaldehyde dimethylacetal, p-TsOH.H2O, CH2Cl2, 60 , 83%.
With the glycosyl donor 12 and acceptor 7 in hand, the next step is to construct the key building
block glycoside 13. The glycosylation of α-bromide 12 and homoeriodictyol derivative 7 was
performed in 0.25 M potassium carbonate aqueous solution in the presence of TBAB
(tetrabutylammonium bromide) at 45 , which gave the desired 7-O-β-D-glycoside 13 smoothly
(Scheme 4). Deacetylation of 13 with sodium methoxide in methanol afforded the
homoeriodictyol glycoside 14. Compound 14 was reacted with benzaldehyde dimethylacetal in the
presence of p-toluenesulfonic acid in dicloromethane at 60
glucopyranoside 15, which has a free 2-OH for the subsequent reaction.
2.2. Synthesis of apiofuranosyl donor 22
to get homoeriodictyol
β-D-Apiofuranose derivatives are not readily available, because of the rare natural occurrence
of this branched-chain sugar and its ability to exist in four different cyclic tautomers, which
complicates apiofuranose derivatization[15]. In our work, the desired form of apiofuranose has a
(3R)-stereochemistry, as present in natural apiofuranosides. Such apiofuranose derivatives can be
synthesized in forms of compounds with fixed 2,3-cis-configuration, for instance,
O-isopropylidene derivative 16. Compound 16 can be prepared from diacetone-D-mannose in 60%
overall yield according to published procedures [16]. After a 3-steps protecting group manipulation
[14], acetate 17 was prepared.
As known, although anomeric acetates are often less reactive than many other donors, in fact
they can sometimes be used as effective glycosyl donors, offering certain strategic advantages.
Thus initially we tried the glycosylation of accepter 15 with the anomeric acetate donor 17.
However, TLC (thin layer chromatography) analysis showed decomposition of the accepter, which
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resulted in low yield of the expected glycoside. Therefore glycosyl bromide 18 was considered as
an alternative glycosyl donor. But unfortunately, this kind of apiofuranosyl bromide 18 seemed to
be very unstable, since significant decomposition was detected by TLC analysis of the reaction
mixture when treating of the 17 with HBr in AcOH (Scheme 5) .
Scheme 5. (a) TMSOTf, DCM, 4 Å MS, (b) BF3.OEt2, DCM, 4 Å MS (c) 33% HBr-CH3COOH,
DCM
Scheme 6. (a) BzCl (1.1 equiv ), DCM, Py (3 equiv), 0 , 5 min, 45%; (b) CCl3CN (5 equiv),
DBU (0.3 equiv), DCM, -20 , 10 min, 75%; (c) 15 (0.7 equiv), TMSOTf (0.2 equiv), MS-4
Å, -20 , 2 h, 86%;
Therefore, other types of apiofuranosyl donors needed to be reasonable designed.
Trichloroacetimidate was selected due to its high reactivity and reliability. The primary hydroxyl
of compound 16 was selectively benzoylated with benzoyl chloride in the presence of pyridine to
afford 19. By reacting 19 with excess of trichloroacetonitrile catalyzed by DBU,
trichloroacetimidate 20 was prepared.
As expected, reaction of 15 with trichloroacetimidate donor 20 in the presence of TMSOTf
(trimethylsilyl trifluoromethanesulfonate) in anhydrous dichloromethane at -20
(Scheme 5)
provided the homoeriodictyol disaccharide derivative 21 in 86% isolated yield[19] (Scheme 6).
2.3. Total synthesis of viscumneoside III (1)
Finally, the final target 1 was obtained by removing all the protecting groups III. Removal of
the benzoyls from 21 using sodium methoxide, followed by hydrolysis of the isopropylidene and
benzylidene groups using acidic resin beads, and finally hydrogenolysis of the benzyls by 10%
Pd/C afforded the deprotected product 1 in high yield (Scheme 7). NOE difference spectroscopy
experiments were carried out to fully assign the structure of 1. Selective irradiation of H-1 (δ
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5.08 ppm) showed NOE enhancement of H-6 and H-8 (δ 6.20 ppm), while selective irradiation of
H-1II (δ 4.89 ppm) showed NOE enhancements of H-2I (δ 3.55 ppm). This NOE result confirms
the structure of 1. Diastereomers of compound 1 were separated on AD-H chiral column to get
two peaks with area ratio of 1:1.All the spectroscopic data recorded for 1 are in accordance with
those of its naturally-derived equivalent [7,9]
.
Scheme 7. (a) MeONa (1.5 eq), DCM/MeOH, reflux, 2 h, 85%; (b) Amberlyst 15 (H+),
MeOH-EtOAc, 70 , 4 h ; (c) 10% Pd/C, MeOH-EtOAc, r.t., 1 h, 60% for two steps.
3. Conclusion
The total synthesis of a promising anti-angina pectoris component of the viscumneosides was
reported here for the first time. The longest linear sequence (from 2 to 1) in the synthetic route
required thirteen steps and afforded an overall yield of 6.3%. The study addressed issues
associated with the inherent chemical reactivity of apiose. Trichloroacetimidate was employed as
the
apiofuranosyl
donor
to
construct
the
key
building
block
of
Homoeriodictyol-7-O-β-D-apiosyl-(1→2)-β-D-glycoside (1). It is anticipated that the developed
strategy will pave the way for the synthesis of other natural and novel viscumneosides to allow
biological investigation as additional promising anti-angina pectoris agents.
4. Experimental section
4.1. General
1
All solvents were distilled before used by standard methods. H NMR and 13C NMR were
recorded on Bruker 400 with TMS as internal standard at room temperature and chemical shifts
were quoted in parts per million (ppm) downfield from tetramethylsilane. HRMS was obtained on
Agilent 1946BESI-MS spectrometer. Flash column chromatography was carried out on silica gel
(200-300 mesh). Commercial reagents from TCI (Shanghai) Development Co., Ltd., Alfa Aesar
and Sigma Aldrich were without further purification.
4.2.
Synthesis
of
4'-Benzyloxy-
homoeriodictyol-7-O-3-benzyloxy-4,5-benzylidene-β-D- glycoside 15
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4.2.1 2-Hydroxy-4,6-bis(methoxymethoxy)-Acetophenone (3). 1,3,5-Trihydroxy (200.0 g, 1.59
mol) and AlCl3 (845.1 g, 6.34 mol) was dissolved in dichloromethane (1000.0 ml), followed by
drop addition of nitromethane (1000.0 ml) in 30 min. After the reaction mixture was stirred at
room temperature for 6 h, acetyl chloride (149.2 g, 1.90 mol) was added dropwise and then poured
into water (4000.0 ml). The mixture was extracted with ethyl acetate (2000.0 ml *3).The organic
layer was concentrated to dryness and recrystallized with water to get faint yellow solid 3 (161.3 g,
1
60%). H NMR (600 MHz, DMSO) δ: 12.20 (s, 2H, OH), 10.34 (s, 1H, OH), 5.79 (s, 2H, ArH),
2.53 (s, 3H, COCH3); 13C NMR (150 MHz, DMSO) δ: 202.92, 165.22, 164.76, 104.50, 94.99,
32.79. HRMS calcd for C8H8O4 m/z [M+H]+ 169.0495, found 169.0490.
4.2.2 2,4,6-Trihydroxyacetophenone (4). Compound 2 (110.1 g, 0.76 mol) was dissolved in
dichloromethane. The mixture was cooled to 0 and N-Ethyldiisopropylamine (293 g, 2.27 mol)
was added slowly followed by the addition of chloromethyl methyl ether (137.1 g, 1.96 mol)
dropwise. After being stirred at room temperature overnight, the reaction was quenched with
ammonium chloride saturated aqueous solution (1300.0 ml) and washed with brine (1300.0 ml).
The organic layer was concentrated and purified by column chromatography to give white solid 3
(111.6 g, 64%).1H NMR (600 MHz, CDCl3) δ: 13.69 (s, 1H, OH), 6.22 (d, J = 2.3 Hz, 2H, ArH),
5.23 (s, 2H, O-CH2-O), 5.14 (s, 2H, O-CH2-O), 3.50 (s, 3H, OCH3), 3.44 (s, 3H, OCH3), 2.62 (s,
3H, COCH3); 13C NMR (100 MHz, CDCl3) δ: 203.18 , 166.81 , 163.46 , 160.37 , 106.91 , 97.12 ,
94.50 , 94.00 , 56.68 , 56.39 , 32.94. HRMS calcd for C12H16O6 m/z [M+Na]+: 279.0839; found:
279.0843.
4.2.3 2-Hydroxy-4,6-bis(methoxymethoxy)-Acetophenone (6). A mixture of compound 4 (90.1 g,
0.35 mol) and 4-benzyloxy-3-methoxybenzaldehyde 5 (85.1 g, 0.35 mol) was dissolved in ethanol
(900.0 ml). To this solution was added 20% NaOH aqueous solution (540.0 ml). After being
stirred under room temperature overnight, the solution was adjusted to pH 6 with 20% HCl
aqueous solution and filtrated to get the crude product 6. The crude product was dried in vacuum
at 50 for 2 hours and recrystallized by ethanol (1200.0 ml) to afford yellow solid 6 (143.4 g,
85%).1H NMR (600 MHz, CDCl3) δ: 13.89 (s, 1H, OH), 7.83 (d, J = 15.5 Hz, 1H, β-CH=), 7.75 (d,
J = 15.5 Hz, 1H, α-CH=), 7.44 (d, J = 7.4 Hz, 2H, ArH), 7.38 (t, J = 7.5 Hz, 2H, ArH), 7.32 (t, J =
7.3 Hz, 1H, ArH), 7.16 (d, J = 1.8 Hz,1H, ArH), 7.14 (dd, J = 8.3, 1.9 Hz, 1H, ArH), 6.90 (d, J =
8.3 Hz, 1H, ArH), 6.32 (d, J = 2.3 Hz, 1H, ArH), 6.22 (d, J =2.3 Hz, 1H, ArH), 5.28 (s, 2H,
O-CH2-O), 5.21 (s, 2H, O-CH2-O), 5.19 (s, 2H, O-CH2-Ar), 3.93 (s, 3H, OCH3), 3.53 (s,3H,
OCH3), 3.48 (s, 3H, OCH3); 13C NMR (150 MHz, CDCl3) δ: 192.74 , 167.34 , 163.34 , 159.79 ,
150.37 , 149.80 ,142.81 , 136.62 , 128.89 , 128.66 , 128.05 , 127.22 , 125.40 , 122.60 , 97.60 ,
95.33 , 94.75 , 94.10 , 70.93 , 56.97 , 56.47 ,55.96. HRMS calcd for C27H28O8 m/z [M+H]+:
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480.1857, found 480.1856.
4.2.4 2-(4-(Benzyloxy)-3-methoxyphenyl)-5,7-dihydroxychroman-4-one (7). Compound 6 (62.1
g, 0.13 mol) and sodium acetate (42.4 g.0.52 mol) was added to the mixtures of ethanol (2480.0
ml) and water (248.0 ml), and then the reaction was stirred for 8 hours under reflux condition. The
suspension was cooled to room temperature and filtrated. The filtrate was concentrated to dryness.
The residue was dissolved in methanol and added 20% HCl aqueous solution (90.0ml) dropwise
under reflux condition. The reaction was stirred for 2 hours under reflux condition. The reaction
1
then cooled to room temperature and filtrated to afford yellow solid 7 (29.4 g, 58%). H NMR
(CDCl3, 400 MHz) δ: 12.05 (s, 1H, OH), 7.44 (d, J = 7.3 Hz, 2H, ArH), 7.37 (t, J = 7.3 Hz, 2H,
ArH), 7.31 (t, J = 7.2 Hz, 1H, ArH), 7.00 (s, 1H, ArH), 6.90 (d, J = 0.9 Hz, 2H, ArH), 6.00 (d, J =
2.3 Hz, 1H, ArH), 5.98 (d, J = 2.3 Hz, 1H, ArH), 5.54 (s, 1H, OH), 5.34 (dd, J = 13.0, 2.9 Hz, 1H,
2-H), 5.18 (s, 2H, O-CH2-Ar), 3.93 (s, 3H, OCH3), 3.10 (dd, J = 17.2, 13.1 Hz, 1H, 3-H), 2.79
(dd, J = 17.2, 3.0 Hz, 1H, 3-H); 13C NMR (CDCl3, 150 MHz) δ 195.91 , 164.47 , 164.39, 163.18 ,
149.96 , 148.72 , 136.87 , 131.23 , 128.61 , 127.96 , 127.24 , 118.82 , 113.92 , 110.03 , 103.23 ,
96.74 , 95.45 , 79.22 , 71.08 , 56.15 , 43.28 . HRMS calcd for C23H20O6 m/z [M+H]+: 392.1333,
found 392.1328
4.2.5 3-O-(Phenylmethyl)-α/β-D-glucopyranose (10). A mixture of 60% sodium-hydrogen ( 20.8
g, 0.52 mol) and TBAI (7.4 g, 0.02 mol) in tetrahydrofuran (300.0 ml) was stirred in ice bath for
30 minutes. A solution of Diacetone-D-Glucose 8 (104.1 g, 0.40 mol) in tetrahydrofuran (300.0 ml)
and Benzyl Bromide (82.1 g, 0.48 mol) was added dropwise to the reaction successively. The
reaction was stirred for 8 h at 50 and quenched with methanol (20.0 ml) and filtrated through
Celite, The filtrate was concentrated to get rude product 9. Compound 9 in the mixture of
trifluoroacetic acid (150.0 ml) and water (150.0 ml) was stirred overnight. The reaction was
diluted with brine (300.0 ml), washed with mixture of ether (80.0 ml) and ethyl acetate (400.0 ml).
The water layer was concentrated and purified by crystallization from ethyl acetate to give
derivative 10 (51.6 g, 44%). 1H NMR (400 MHz, DMSO) δ 7.42-7.24 (m, 5H, -ArH), 6.67 (d, J =
6.4 Hz, 1H, 1-CH), 5.05 (dd, J = 5.4, 3.7 Hz, 2H, 2-OH and 4-OH), 4.85 – 4.73 (m, 2H, OCH2Ar),
4.51 (t, J = 5.8 Hz, 1H, 1-OH), 4.39 – 4.25 (m, 1H, 6-OH), 3.69 (m, 1H, 2-CH), 3.46 (m, 1H,
4-CH), 3.26 – 3.03 (m, 4H, 3-CH ,5-CH and 6-CH2).
13C NMR (150MHz, DMSO) δ 139.68,
127.88, 127.40, 126.96, 96.90, 85.30, 76.70, 74.75, 73.61, 69.86, 61.05. HRMS calcd for
C13H18O6 m/z [M+Na]+: 293.0996, found 293.1001
4.2.6 1,2,4,6-Tetra-O-acetyl-3-O-benzyl-β-D-glucopyranose (11). A mixture of 10 (50.0 g, 0.17
mol) in acetic anhydride (200.0 ml) and pyridine (200.0 ml) was stirred overnight at room
temperature, then it was diluted with ethyl acetate and washed with 2M HCl and saturated
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NaHCO3 aqueous solution. Purification of the residue by crystallization from ethanol to give 11
(71.3 g, 90%).1H NMR (400 MHz, CDCl3) δ 7.40 - 7.14 (m, 5H, Ar), 5.63 (t, J = 9.2 Hz, 1H,
CH-1), 5.22 - 5.03 (m, 2H, CH-2 and CH-4), 4.61 (m, 2H, ArCH2), 4.21(m, 1H, α-CH2), 4.11 (m,
1H, β-CH), 3.84 - 3.62 (m, 2H, CH-3 and CH-3), 2.09 - 1.97 (m, 12H, 4CH3). 13C NMR (150
MHz, CDCl3) δ 170.84, 169.39, 169.35, 169.18, 137.69, 128.62, 128.08, 127.92, 92.12, 80.10,
74.32, 73.14, 71.68, 69.19, 61.93, 20.98, 20.85, 20.84, 20.81. HRMS calcd for C21H26O10 m/z
[M+Na]+: 461.1418, found 461.1420.
4.2.7 4'-Benzyloxy-homoeriodictyol-7-O-3-benzyloxy-β-D-glycoside (14). A mixture of 11
( 45.0 g, 0.10 mol) and 45% HBr/AcOH (180.0 ml) in dichlormethane (450.0 ml) was stirred for
20 minutes at 0 The reaction was diluted with dichlormethane and washed with brine and
saturated NaHCO3 aqueous solution, the organic phase was separated and concentrated. The
residue was purified by column chromatography to afford glycosyl donor 12, used directly to the
next step for its instability at room temperature. A mixture of 12 (29 g, 0.05mol), 7 (14.9 g, 0.04
mol) and TBAB(3.7 g, 0.01 mol) in 0.25M K2CO3 (500.0 ml) aqueous solution and chloroform
(500.0 ml) was stirred overnight at 45 . The organic layer was concentrated and purified by
column chromatography to give rude product 13 (26.0 g). A solution of rude product 13 (26.0 g) in
30% sodium methylate (3.0 ml) in methanol (520.0 ml) was stirred for 3 h under reflux condition.
The reaction was quenched with water (250.0 ml) and filtered to afford 14 (17.8 g, 73% for two
steps). [α]2D0 -9.0°(c 0.1, C3H6O); 1H NMR (400 MHz, DMSO) δ 12.09 (s, 1H, OH-5), 7.52 – 6.99
(m, 13H, Ar), 6.18 (m, 2H, H-6 and H-8), 5.67 (s, 1H, OH-4 ), 5.55 (dd, 1H, J = 12.8, 2.5 Hz,
H-2), 5.32 (d, 1H, J = 25.1 Hz, OH-2 ), 5.13 (d, 2H, J = 11.2 Hz, ArCH2O-4’), 5.07 (dd, 1H, J =
9.5, 7.5 Hz, H-1 ), 4.90 – 4.82 (m, 2H, ArCH2O-3 ), 4.68 – 4.56 (m, 1H, H-2 ), 3.82 (d, 3H, J =
8.2 Hz, CH3O-5’), 3.71 (d, 1H, J = 10.2 Hz, OH-6 ), 3.48 (m, 6H, H-3 , H-4 , H-5 ,H-6 and
H-3a), 2.79 (dd, J = 17.0, 2.5 Hz, 1H, H-3b). 13C NMR (150 MHz, DMSO) δ 197.16, 165.22,
163.02, 162.73, 149.15, 148.10, 139.50, 137.08, 131.13, 128.48, 127.99, 127.91, 127.80, 127.54,
127.14, 119.41, 113.30, 111.15, 103.27, 99.53, 96.68, 95.77, 84.89, 78.78, 77.10, 73.79, 72.90,
69.99, 69.03, 60.33, 55.81, 42.18. HRMS calcd for C36H36O11 [M+H]+ 667.2150, found 667.2149.
4.3.
Preparation
of
4'-Benzyloxy-homoeriodictyol-7-O-(5-O-Benzoyl-2,3-O-isopropylidene)-β-D-apiose
(1→2)-(3-benzyloxy-4,5-benzylidene)-β-D-glycoside 21
4.3.1 4'-Benzyloxy- homoeriodictyol-7-O-3-benzyloxy-4,5-benzylidene-β-D-glycoside (15). 14
(4.0 g, 6.20 mmol) was dissolved in acetone (48.0 ml), PhCH(OMe)2 (17.0 g,111.69 mmol) and
TsOH.H2O (1.8 g, 9.31 mmol) and the mixture was stirred for 2 h at room temperature. The
reaction was quenched with Et3N and diluted with ethyl acetate and washed with brine. The
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residue was purified by chromatography to afford 15 (3.8 g, 83%).1H NMR (400 MHz, CDCl3) δ
12.07 (d, J = 16.1 Hz, 1H, OH-5), 7.75 – 6.84 (m, 18H, Ar), 6.47 – 6.09 (m, 2H, H-6 and H-8),
5.56 (d, J = 17.5 Hz, 1H, ArCHO2), 5.34 (t, J = 15.2 Hz, 1H, H-1 ), 5.20 (s, 2H, ArCH2O-4’),
5.11–4.96 (m, 3H, H-2 and ArCH2O-3 ), 4.87 (t, J = 14.5 Hz, 1H, H-2 ), 4.39 (dd, J = 10.4, 4.9
Ⅰ
Ⅰ
Hz, 1H, H-4 ), 3.96 (d, J = 17.8 Hz, 3H, OCH3-3’), 3.88 – 3.69 (m, 4H, H-6 ，H-3 and OH-2 ),
Ⅰ
3.59 (m, 1H, H-3a), 3.21 – 3.00 (m, 1H, H-5 ), 2.87 (m, 1H, H-3b). 13C NMR (150 MHz, CDCl3)
δ 196.54, 164.87, 163.95, 162.93, 149.99, 148.81, 138.30, 137.19, 136.94, 131.14, 129.17, 128.69,
128.56, 128.38, 128.14, 128.05, 127.99, 127.55, 127.36, 126.16, 118.97, 113.94, 110.15, 104.31,
101.39, 97.52, 96.20, 80.91, 80.35, 79.40, 74.84, 73.69, 71.08, 68.52, 66.65, 56.21, 43.24. HRMS
calcd for C21H26O10 m/z [M+Na]+: 755.2463, found 755.2471.
4.3.2 3'-O-Benzoyl-2,3-O-isopropylidene-α/β-D-apiofuranoside (19). To a stirred solution of 16
(3.6 g, 18.67 mmol) and pyridine (4.4 g, 56.0 mmol) in anhydrous dichloromethane (71.0 ml) was
added benzoyl chloride (2.8 g, 19.60 mmol) dropwise at 0°C and the mixture was stirred at 0°C
for 2 h and partitioned between CH2Cl2/H2O. The organic layer was washed with 20% HCl
aqueous solution and brine, dried over MgSO4, filtrated and evaporated. The residue was purified
by column chromatography to give 19 (2.5 g, 45%).1H NMR (400 MHz, CDCl3) δ 8.11 – 8.09 (m,
2H, Ar), 7.61 - 7.45 (m, 3H, Ar), 5.52 (s, 1H, H-1), 4.67 - 4.51 (m, 3H, H-5 and H-2), 4.22 – 4.11
(m, 2H, H-4), 1.61 – 1.43 (m, 6H, OCH3). 13C NMR (150 MHz, CDCl3) δ 166.45, 133.74, 133.48,
130.00, 129.85, 128.82, 128.67, 114.11, 102.41, 90.45, 87.41, 74.66, 66.04, 27.63. HRMS calcd
for C15H18O6 m/z [M+Na]+: 317.0996, found 317.0999.
4.3.3
4'-Benzyloxy-homoeriodictyol-7-O-(5-O-Benzoyl-2,3-O-isopropylidene)-β-D-apiose
(1→2)-(3-benzyloxy-4,5-benzylidene)-β-D-glycoside (21). To a solution of hemiacetal 19 (2.6 g,
8.84 mmol)in dry dichloromethane (26.0 mL) was added trichloroacetonitrile (7.7 g, 53.04 mmol)
and1,8-Diazabicyclo[5.4.0]undec-7-ene (0.4 g, 2.6 mmol) at -20℃under nitrogen. After stirring
for 10 min, the mixture was concentrated and purified by column chromatography to afford
glycosyl donor 20, used directly to the next step for its instability at room temperature. A mixture
of 15 (3.1 g, 4.2 mmol), 20 (2.7 g, 6.3 mmol) and molecular sieves 4 Å (6.0 g) in anhydrous
dichloromethane (120.0 ml) was stirred for 30 min at 22℃, then the mixture was cooled to -20 ℃
and TMSOTf (0.3 g,1.3 mmol) was added by syringe. The stirring continued for 2 h at -20 ℃. The
mixture was quenched with Et3N (0.2 ml) and concentrated. The residue was purified by column
chromatography to afford homoeriodictyol disaccharide derivative 21 (3.1 g, 86%). [α]2D0 -37.8°(c
0.1, C3H6O); 1H NMR (400 MHz, CDCl3) δ 11.87 (s, 1H, OH-5), 8.10-7.28 (m, 25H, Ar), 6.99 (d,
Ⅱ
Ⅰ
1H, J =1.8Hz, H-1 ), 6.91 (m, 2H, ArCHO2 and H-1 ), 6.08 (m, 3H, H-2 and ArCH2O-4’), 5.60 (d,
Ⅰ
Ⅱ
Ⅰ
Ⅰ
2H, J = 3.2 Hz, ArCH2O-3 ), 5.20 (m, 2H, H-4Ⅰand H-2 ), 4.98-4.79 (m, 3H, H-2 , H-6α , and
10

ACCEPTED MANUSCRIPT
H-4α ), 4.44 – 4.35 (m, 4H, H-3 , H-6β , H-4β and H-5α ), 4.05 (m, 1H, H-5β ), 3.95 (s, 3H,
OCH3-3’), 3.79-3.77 (m, 1H, H-5 ), 3.10-3.02 (m, 1H, H-3a), 2.77-2.72 (m, 1H, H-3b), 1.31-1.28
(m, 6H, 2CH3). 13C NMR (150 MHz, CDCl3) δ 196.39, 166.14, 164.61, 163.95, 162.99, 150.11,
148.90, 137.90, 137.22, 136.98, 133.37, 131.29, 131.16, 129.82, 129.31, 128.82, 128.77, 128.65,
128.58, 128.51, 128.21, 127.50, 126.19, 119.03, 114.09, 110.16, 108.08, 104.28, 102.35, 98.52,
96.98, 90.44, 90.09, 87.43, 86.87, 81.46, 76.14, 74.94, 74.37, 71.24, 68.66, 66.53, 56.32, 43.55,
30.04, 27.68.
4.4. Total synthesis of viscumneoside III (1)
4.4.1
4'-Benzyloxy-homoeriodictyol-7-O-(5-O-Benzoyl-2,3-O-isopropylidene)-β-D-apiose
(1→2)- (4,5-benzylidene)-β-D-glycoside (22). A mixture of 21 (2.8 g, 2.80 mmol) and sodium
methylate (0.2 g, 4.21 mmol) in dichloromethane (28.0 ml) and methanol (28.0 ml) was stirred for
2 h at 45 and concentrated. The residue was redissolved in methanol (40.0 ml) and filtered to
afford 22 ( 2.2 g, 85%).1H NMR (400 MHz, DMSO) δ 7.80 – 6.76 (m, 20H, Ar), 5.71 (m, 1H,
H-1 ), 5.44 (m, 1H, ArCHO2), 5.16-5.10 (m, 4H, H-2, ArCH2O-4’ and H-1 ), 4.87-4.72 (m, 2H,
H-4 and H-2 ), 4.23(m, 2H, ArCH2O-3 ), 3.93-3.40 (m, 11H, H-2 , H-3 , H-5 , H-6 , H-5 ,
OH-5 and CH3O-3’), 2.50 (m, 2H, H-3), 1.34 (t, J = 9.2 Hz, 6H, 2CH3). 13C NMR (150 MHz,
DMSO) δ 189.71, 166.17, 163.42, 149.17, 148.42, 138.22, 137.54, 136.94, 133.36, 129.71, 129.15,
128.81, 128.45, 128.30, 128.19, 127.93, 127.76, 125.96, 121.33, 113.54, 112.11, 110.86, 109.78,
107.07, 100.09, 96.93, 92.88, 85.24, 80.91, 79.28, 74.90, 74.25, 73.77, 69.89, 67.82, 65.20, 55.38,
27.98. HRMS calcd for C51H52O15 [M+Na]+ 927.3198, found 927.3197.
4.4.2 Homoeriodictyol-7-O-β-D-apiose (1→2)-β-D-glycoside (1). A mixture of 22 (1.2 g, 1.32
mmol) and Amberlyst 15(H+) in methanol (23.0 ml) and ethyl acetate (23.0 ml) was stirred for 4 h
at 70 , filtered and the filtrate was diluted with methanol (75.0 ml) and ethyl acetate (75.0 ml).
The residue and 10% Pd/C (0.2 g) was stirred for 1 h at 22 under hydrogen. The mixture was
filtered and the filtrate was concentrated to give crude product. Purification of the crude product
was performed by pre-HPLC on Luna C18 eluted with acetonitrile furnished the target molecule 1
(0.5 g, 60% for two steps). [α]2D0 -108.0°(c 0.1, C3H6O); 1H NMR (400 MHz, MeOD) δ7.12 (d, 1H,
J = 1.5 Hz, H-2’), 6.95 (dd, 1H, J = 8.1, 1.7 Hz, H-6’), 6.86 (d, 1H, J = 8.1 Hz, H-5’), 6.21-6.19
(dd, 2H, J = 11.8, 2.1 Hz, H-6 and H-8), 5.60 (d, J = 14.8 Hz ,1H, H-1 ), 5.44-5.41 (dd, 1H, J =
12.8, 2.5 Hz, H-2), 5.08 (d, 1H, J = 7.4 Hz, H-1 ), 4.39 (s, 1H, H-2 ), 4.10-3.87 (m, 6H, H-2 ,
H-3 , H-4 and H-5 ), 3.72–3.36 (m, 7H, H-4 , H-5 , H-6 and CH3O-3’), 3.23 (m, 1H, H-3b),
2.83 (m, 1H. H-3a). 13C NMR (150 MHz, MeOD) δ 198.69, 166.73, 165.17, 164.82, 149.34,
148.37, 131.53, 120.83, 116.27, 111.60, 108.87, 105.09, 99.61, 97.88, 96.81, 94.12, 87.35, 81.06,
78.89, 78.35, 77.41, 75.88, 71.35, 65.01, 62.44, 56.67, 44.22. LC-MS (m/z): 619.2 [M+Na]+. Anal.
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Calcd for C27H32O15: C, 54.36; H, 5.41; Found: C, 54.33; H, 5.42.
Acknowledgments
We are grateful for the financial support from the Shanghai Science and Technology
Commission (No. 15431902700 ), Shanghai Science and Technology Star Project (Class B) (No.
15QB1404400) and National Natural Science Foundation Project (No. 81502930).
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