Synthesis of a phenylpropanoid glycoside, Osmanthuside B6

Article abstract of DOI:10.1016/S0008-6215(98)00092-5

2-Ac-Osmanthuside B6 [2-(4-hydroxyphenyl)ethyl 2-O-acetyl-3-O-(α-L-rhamnopyranosyl)-6-O (4-hydroxycinnamoyl)-β-D-glucopyranoside, 8], a derivative of Osmanthuside B 6, was synthesized in 7 steps with the goal of preparing Osmanthuside B6. Surprisingly, it

Full text of DOI:10.1016/S0008-6215(98)00092-5

Carbohydrate Research 308 (1998) 281±285
Synthesis of a phenylpropanoid glycoside,
Osmanthuside B61
San-Qi Zhanga, Zhong-Jun Lia, An-Bang Wanga, Meng-Shen Caia,*,
Rui Fengb
a Department of Bioorganic Chemistry, Beijing Medical University, Beijing 100083, P.R. China
b Instrumental Analysis Center, Academy of Military Medical Sciences, Beijing 100850, P.R. China
Received 31 July 1997; accepted 20 March 1998
Abstract
2-Ac-Osmanthuside B6 [2-(4-hydroxyphenyl)ethyl 2-O-acetyl-3-O-(ꢀ-l-rhamnopyranosyl)-6-O-
(4-hydroxycinnamoyl)-ꢁ-d-glucopyranoside, 8], a derivative of Osmanthuside B6, was synthesized
in 7 steps with the goal of preparing Osmanthuside B6. Surprisingly, it was found that the 2-acetyl
group in the glucose ring of the compound 7, 1-O-[2-(4-allyloxyphenyl)ethyl]-2-O-acetyl-3-O-
(2,3,4-tri-O-acetyl-ꢀ-l-rhamnopyranosyl)-6-O-(4-acetoxycinnamoyl)-ꢁ-d-glucopyranoside, could
not be removed by conventional deacetylation procedures. # 1998 Elsevier Science Ltd. All rights
reserved
Keywords: Phenylpropanoid glycosides; Osmanthuside B6; Synthesis
1. Introduction
phenylpropanoid glycoside having a disaccharide
residue, Osmanthuside B6 [7] (Fig. 1).
Phenylpropanoid glycosides are natural glyco-
sides acylated with a substituted cinnamoyl residue
and having a substituted phenylethyl group as
aglycon [1]. Many of them possess potent biologi-
cal activities such as antiviral, antitumor, antifugal,
and immunomodulatary agents [1±5]. To date,
about one hundred of these glycosides have been
isolated and identi®ed by spectra and chemical
conversions, but total syntheses have not yet been
reported. In our previous paper [6], the total
synthesis of a phenylpropanoid glycoside with a
monosaccharide residue, Grayanoside A was repor-
ted. This present paper deals with the synthesis of a
The designed synthetic route for Osmanthuside
B6 was as shown in Scheme 1.
2. Results and discussion
Allyl 4,6-O-benzylidene-ꢀ-d-glucopyranoside (1)
was prepared as previously described [8] and Eby's
[9] new method for selective acylation of the 2-OH
group in methyl 4,6-O-benzylidene-ꢀ-d-glucopyr-
anoside by forming a mercury complex was used
to acetylate selectively the 2-OH group in com-
pound 1. Because the 2-OH group is more acidic
than 3-OH, the reaction of the mercury complex
with acetic anhydride favored regioselective 2-
acetylation. In order to increase the selectivity and
* Corresponding author.
1
Studies on Glycosides XXIV.
0008-6215/98/$19.00 # 1998 Elsevier Science Ltd. All rights reserved
PII S0008-6215(98)00092-5

282
S.-Q. Zhang et al./Carbohydrate Research 308 (1998) 281±285
to prepare certain glycosides and oligosaccharides
[10±13]. Protected Osmanthuside B6 was also pre-
pared by this method. By using an improved
deprotection method [14], the allyl group in 5 was
removed to give compound 6 in 94% yield. Com-
pound 6 was converted into the syrupy tri-
chloroacetate according to the previously reported
procedure [11] in nearly quantitative yield. Without
further puri®cation, the trichloroacetate was trea-
ted with 4-allyloxyphenylethanol to give the pro-
tected disaccharide phenylpropanoid glycoside
Osmanthuside B6 (7) with use of Me3SiOTf as the
glycosylation catalyst.
Fig. 1. The structure of Osmanthuside B6.
yield, the procedure was improveꢀd as follows: the
reaction mixture was cooled to 0 C, and after the
mercury complex had been formed, acetic anhy-
dride diluted with THF (ꢁ1:3, v/v) was added
dropwise to a€ord compound 2 in 84% yield. The
reaction of tri-O-acetyl-l-rhamnopyranosyl bro-
mide with 2, catalyzed by mercuric cyanide, gave
disaccharide 3 in 80% yield. Removal of the ben-
zylidene group from compound 3 was readily
accomplished by re¯uxing 3 with catalytic amount
of p-toluenesulfonic acid in re¯uxing methanol±
water and 4 was obtained in 78%ꢀ yield. Cinna-
moylation of 4 was performed at 0 C by using 4-
acetoxycinnamoyl chloride as the acylation agent.
The presence of a cinnamoyl group in compound 5
The allyl group on the aglycon in 7 was removed
with the aid of PdCl2/CuCl, reagents that do not
need the presence of acid or base, and other func-
tional groups in the glycosides were not a€ected.
Compound 7 was dissolved in (10:1) THF±water,
and one molar equivalent of PdCl2/CuCl was
added. The mixture was stirred vigorously. When
TLC showed the disappearance of 7, the crude
product isolated was used directly for the attemp-
ted removal of acetyl groups by ammonia±metha-
ꢀ
nol at 5±10 C. The deacetylation product was
1
was con®rmed by IR (1760,1631 cm ).
The trichloroacetoxy group, a new leaving
group, has been used successfully in our laboratory
puri®ed by column chromatography to a€ord
compound 8 in 53% yield (two steps). NMR showed
that one acetyl group still remained, by comparison
Scheme 1. (a) NaH/HgCl2, Ac2O; (b) Tri-O-acetyl-l-rhamnopyranosyl bromide/Hg(CN)2, anhydrous toluene, 4 h re¯ux; ꢀ(c)
MeOH-H2O, p-TsOH, 2 h re¯ux; (d) 4-Acetoxycinnamoyl chloride/pyridine, THF, rt, 6 h; (e) PdCl2/CuCl/H2O, THF, 25±30 C,
2 h; (f) (Cl3CCO)2O/Cl3CCO2Na, anhydrous CHCl3, 5 h re¯uꢀx; (g) 2-(4-Allyloxyphenyl)ethanol, DBMP, Me3SiOTf, anhydrous
CH2Cl2, -15 ꢀC ! rt, 48 ;h. (h) PdCl2/CuCl/H2O, THF, 25±30 C, 6 h; (I) NH3±MeOH (15%), 5±10 ꢀC, 5 h.

S.-Q. Zhang et al./Carbohydrate Research 308 (1998) 281±285
283
of the 13C NMR data of 8 with those of Osman-
thuside B6 [7].
(dd, 1 H, H-2), 4.36±3.50 (m, 7 H, H±3(6, -OCH2-),
2.16 (s, 3 H, CH3CO-).
Allyl 2-O-acetyl-3-O-(2,3,4-tri-O-acetyl-a-l-
rhamnopyranosyl)-4,6-O-benzylidene-a-d-glucopyr-
anoside (3).ÐA mixture of 2 (5.25 g, 15 mmol), tri-
3. Experimental
O-acetyl-l-rhamnopyranosyl
bromide
(8.8 g,
General methods.ÐMelting points are uncor-
rected. Spectra were recorded with the following
instruments: 1H and 13C NMR, Jeol FX-90Q
(90 MHz) and Jeol GX-400 (400 MHz), 1H-1H
COSY, HETCOR, NOESY, Jeol GX-400; mass
spectra, VG 20-250 GLC±MS and VG ZAB GC
25 mmol), Hg(CN)2 (6.3 g, 25 mmol) in anhydrous
toluene (100 mL) was re¯uxed for 4 h. After cool-
ing, the solid was removed by ®ltration and thor-
oughly washed with toluene. The ®ltrate and
washings were combined and evaporated to dry-
ness in vacuo. The residue was stirred in 80 mL of
CHCl3, the solid material that separated was ®l-
tered o€, and the ®ltrate was evaporated to dry-
ness. The residue was recrystallized from MeOH
(60 mL) to give 3 (6.7 g) as a white needles. The
®ltrate was chromatographed on coꢀlumn of silica
gel with 4:1 petroleum ether (60±90 C)±EtOAc as
eluent to give more 3 (0.8 g), yield 80.4%; mp
1
GLC±MS. The H NMR spectra were recorded
with Me4Si as the internal standard and 13C NMR
with CDCl3 as solvent and internal standard.
Optical rotatioꢀns in CHCl3 solutions were mea-
sured at 22±25 C with a Perkin±Elmer 243 polari-
meter. The progress of reactions was monitored by
TLC on GF254 (Hai Yang Chemical Factory,
Qingdao, Shandong, P. R. China). Column chro-
matography was performed on silica gel H (10±
40 ꢂm) (Hai Yang Chemical Factory, Qingdao,
Shandong , P. R. China). The solvent system indi-
cated are volume volume ratios. Components were
detected by spraying the plates with 20% concd.
H2SO4 in EtOH and heating. Elemental analyses
were performed on Perkin±Elmer 240C instrument.
Allyl 2-O-acetyl-4,6-O-benzylidene-a-d-glucopyr-
anoside (2).ÐTo a dry THF solution of allyl 4,6-
O-benzylidene-ꢀ-d-glucopyranoside (1) [8] (12.32 g,
40 mmol) (200 mL) was added NaH (2.4 g, 80 %,
80 mmol). The mixture was stirred at room tem-
perature for 20 min. Anhydrous HgCl2 (10.88 g,
40 mmol) was added, the mixture was stirred at
room temperature for another 20 min. and then
ꢀ
183.0±185.0 C, [ꢀ]d+29.4ꢀ (c 0.51, CHCl3); IR:
1
1
1741, 1642 cm ; H NMR (400 MHz, CDCl3), ꢃH
(ppm): Glc: 5.28 (d, 1 H, J 3.6 Hz, H-1), 4.80 (dd, 1
H, H-2), 4.24 (t, 1 H, H-3), 3.63 (t, 1 H, H-4), 4.12
(m, 1 H, H-5), 3.76 (m, 1 H, H-6a), 4.30 (m, 1 H, H-
6e); Rha: 4.98 (s, 1 H, H-1'), 4.96 (dd, 1 H, H-2'),
5.22 (t, 1 H, H-3'), 5.07 (t, 1 H, H-4'), 3.98 (dd, 1 H,
H-5'), 0.71 (d, 3 H, CH3-6'), 1.96 (s, 3 H), 1.99 (s, 3
H), 2.11 (s, 3 H), 2.14 (s, 3 H) (4ÂCH3CO-), 3.96
(dd,1 H), 4.16 (dd, 1 H), 5.81 (m, 1 H), 5.32 (m, 1 H),
5.11 (m, 1 H) (-OCH2CH=CH2), 5.56 (s, 1 H, -CH-,
benzylidene), 7.33±7.48 (m, 5 H, Ar-H); 13NMR
(100 MHz, CDCl3): ꢃc (ppm) Glc: 95.7 (C-1), 73.5
(C-2), 74.0 (C-3), 79.5 (C-4), 62.8 (C-5), 68.6 (C-6),
Rha.: 97.4 (C-1'), 71.2 (C-2'), 68.6 (C-3'), 70.2 (C-4'),
66.1 (C-5'), 16.5 (C-6'), aglycon: 68.8,133.3, 117.8;
benzylidene: 101.9 (O-C-O) 137.0, 128.0, 126.3,
129.0 (Ar-C), 20.3, 20.5, 20.7, 20.8 (4ÂCH3CO),
169.7, 169.8, 170.2, 171.0 (4ÂCH3CO-). MS, m/z:
623 (M+1)+, 563, 273; Anal. Calcd for C30H38O14:
C, 57.87; H, 6.15. Found: C, 57.62, H, 6.08.
ꢀ
cooled to 0 C in an ice±water bath. Acetic anhy-
dride (6 mL, diluted with 20 mL THF ) was added
and the mixture was stirred for 2 h. Water (2 mL)
and AcOH (2 drops) were added. The solvent was
then evaporated o€ in vacuo. The residue was dis-
solved in the CHCl3 (100 mL) and the solution was
successively washed with water and brine, dried,
and evaporated to syrup. The syrup was dissolved
in EtOAc (15 mL), and petroleum ether (60 mL)
was added. The solid (9.5 g) was collected by suction
and further evaporation. Flash chromatography
(15:1 benzene±ethyl acetate) of the ®ltrate gave
additional 2 (2.2 g); yield: 83.6%, mp 96.0±97.0 ꢀC;
Allyl 2-O-acetyl-3-O-(2,3,4-tri-O-acetyl-a-l-
rhamnopyranosyl)-a-d-glucopyranoside
(4).ÐA
mixture of 3 (0.9 g, 1.45 mmol), MeOH (30 mL),
water (30 mL) and p-toluenesufonic acid (60 mg)
was re¯uxed for 2 h and the solvent was evaporated
under diminished pressure. The residue was dis-
solved in CHCl3 (30 mL), and the solution was
washed with saturated aqueous NaCl (30 mL),
dried with Na2SO4, and concentrated. Puri®cation
of the residue by VLC (vacuum liquidꢀ chromato-
graphy) [eluent: petrolum ether (60±90 C)±EtOAc
1:1!1:2 gave 4 (0.5 g, 78.1%) as a white amorphous
ꢀ
1
[ꢀ]d +131.9 (c 0.27, CHCl3); H NMR (90 MHz,
CDCl3); ꢃH (ppm): 7.60±7.80 (m, 5 H, ArH), 5.90
(m, 1 H, CH=C), 5.56 (s, 1 H, O-CHO), 5.30 (d, 1
H), 5.20 (d, 1 H, C=CH2), 5.16 (d, 1 H, H-1), 4.82

284
S.-Q. Zhang et al./Carbohydrate Research 308 (1998) 281±285
powder and 3 (0.15 g, recovered). IR (KBr): 3485,
1
2-O-Acetyl-1-O[2-(4-allyloxyphenyl)ethyl]-6-O-
(4-acetoxycinnamoyl)-3-O-(2,3,4-tri-O-acetyl-a-l-
rhamnopyranosyl)b-d-glucopyranoside (7).ÐTo a
solution of 6 (2.3 g, 3.3 mmol) in CHCl3 (15 mL)
were added sodium trichloroacetate (0.6 g,
3.3 mmol) and trichloroacetic anhydride (1.35 g,
4.4 mmol). The solution was re¯uxed for 5 h.
Chloroform (20 mL) was added after the mixture
had been cooled to room temperature. The CHCl3
solution was washed with ice±water (3Â20 mL)
and dried with anhydrous Na2SO4. Evaporation
of the solvent gave a syrup (one spot on TLC).
The syrup was dissolved in dry CH2Cl2 (50 mL)
and 2-(4-allyloxyphenyl)ethanol (1.0 g) and 2,6-di-
tert-butyl-4-methylpyridine (DBMP, 0.5 g) were
1734, 1640 cm .
Allyl 6-O-(4-O-acetoxycinnamoyl)-2-O-acetyl-3-
O-(2,3,4-tri-O-acetyl-a-l-rhamnopyranosyl)-a-d-
glucopyranoside (5).ÐTo a mixture of 4 (1.4 g,
2.62 mmol), dry THF (20 mL) and dry pyridine
ꢀ
(2 mL) cooled to 0 C was added during 20 min a
THF (10 mL) solution of 4-acetoxycinnamoyl
chloride (0.62 g, 2.76 mmol). The mixture was stirred
for 6 h (warming gradually to room temperature).
After removal of THF from the mixture, CHCl3
(30 mL) was added. The solution formed was
washed with brine (2Â30 mL), dried with anhydrous
Na2SO4 and concentrated in vacuo. Puri®cation of
the residue by VLC (eluent:5:1 benzene±EtOAc)
ꢀ
ꢀ
gave 5 (1.7 g, 89.9%), mp 89.0±91.0 C, [ꢀ]d+
added. The solution was cooled to 15 C, and
45.6 d (c 0.32, CHCl3); IR (KBr): 3474, 1741, 1706,
1631 cm ; H NMR (400 MHz, CDCl3), ꢃH (ppm):
stirred for 48 h in the presence of Me3SiOTf (10
drops) as catalyst, during which time the tempera-
ture was raised to room temperature. This mixture
was diluted with CHCl3 (50 mL), washed with water
(50 mL), aqeous NaHCO3 (5%, 50 mL) and water
(50 mL), dried with Na2SO4 and concentrated.
Flash chromatography (4:1 benzene±EtOAc) gave
a white amorphous solid (1.85 g, 61% from 5). mp
88.0±90.0 ꢀC, [ꢀ]d 35.0 ꢀ (c 0.2, CHCl3); IR(KBr):
1 1
Glc 5.24 (d, 1 H, J 3.4 Hz, H-1), 4.84 (dd, 1 H, H-2),
4.23 (t, 1 H, H-3), 3.53 (t, 1 H, H-4), 3.88 (t, 1 H, H-
5), 4.37 (t, 1 H, H-6a), 4.68 (dd, 1 H, H-6e); Rha
4.96 (d, 1 H, J 2.20 Hz, H-1'), 5.07 (dd, 1 H, H-2'),
5.23 (dd, 1 H, H-3'), 5.09 (t, 1 H, H-4'), 4.03 (dd, 1
H, H-5'), 1.22 (d, 3 H, CH3-6'), 4.17 (dd, 1 H), 3.98
(dd, 1 H), 5.87 (m, 1 H), 5.30 (m, 1 H), 5.15 (m, 1 H)
(-OCH2CH=CH2), 6.48 (d, 1 H, J 16.1 Hz), 7.75 (d,
1 H, J 16.1 Hz) (Ar-CH=CH-CO-), 7.14±7.58 (m, 4
H, Ar-H), 1.95 (s, 3 H), 1.99 (s, 3 H), 2.11 (s, 3 H),
2.14 (s, 3 H), 2.21 (s, 3 H) (5ÂCH3CO-); 13CNMR
(100 MHz, CDCl3): ꢃc (ppm) Glc. 95.2 (C-1), 72.0
(C-2), 80.0 (C-3), 69.2 (C-4), 70.0 (C-5), 62.9 (C-6);
Rha: 98.8 (C-1'), 70.8 (C-2'), 68.5 (C-3'), 69.9 (C-4'),
67.3 (C-5'), 17.3 (C-6'); cinnamoyl: 131.9, 129.4
(2C), 122.1 (2C), 152.3 [Ar-C], 144.9, 118.0, 167.4
[CH2=CH-CH2-O], 20.3, 20.4, 20.8, 21.0, 21.7
(5ÂCH3CO), 168.9, 169.0, 169.8, 170.0, 171.7
(5ÂCH3CO); aglycon: 68.7, 133.2, 117.3; MS, m/z:
723 (M+1)+, 655, 273, 189. Anal. Calcd for
C34H42O17: C, 56.50; H, 5.86. Found: C, 56.90; H,
5.81.
6-O-(4-Acetoxycinnamoyl)-2-O-acetyl-3-O-(2,3,4-
tri-O-acetyl-a-l-rhamnopyranosyl)-b-d-glucopyr-
anose (6).ÐTo a THF (15 mL) solution of 5 (2.6 g,
3.6 mmol) were added PdCl2 (0.64 g, 3.6 mmol),
CuCl (0.35 g, 3.6 mol) and water (1.5 mL), and the
solution was stirred vigorously for 2 h at 25±30 ꢀC.
The mixture was then diluted with CHcl3 (40 mL),
and ®ltered through a bed of Celite. The CHcl3
solution was washed with water and brine, dried
over anhydrous Na2SO4, and concentrated. Flash
chromatography (3:1 benzene±EtOAc) of the resi-
due gave 6 as a syrup (2.3 g, 93.5%).
1
1
3474, 1743, 1710, 1628 cm ; H NMR (400 MHz,
CDCl3), ꢃH (ppm): Glc 4.39 (d, 1 H, J7.93 Hz, H-
1), 4.99 (dd, 1 H, H-2), 3.61 (t, 1 H, H-3), 3.55 (t, 1
H, H-4), 3.51 (m, 1 H, H-5), 4.62 (dd, 1 H, H-6a),
4.44 (t, 1 H, H-6e); Rha 4.87 (d, 1 H, J1.8 Hz, H-
1'), 5.07 (dd, 1 H, H-2'), 5.26 (dd, 1 H, H-3'), 5.07
(t, 1 H, H-4'), 4.21 (dd, 1 H, H-5'), 1.21 (d, 3 H,
CH3-6'); 4.07 (m,1 H), 3.62 (m, 1 H) (-OCH2-
CH2Ar), 2.82 (t, 2 H, -OCH2CH2Ar), 4.49 (m, 2
H), 6.04 (m, 1 H) , 5.42 (m, 1 H), 5.27 (m, 1 H)
(-OCH2CH=CH2), 6.47 (d, 1 H, J 16.0 Hz), 7.73
(d, 1 H, J 16.0 Hz) (Ar-CH=CH-CO-), 6.81- 7.56
(m, 8 H, Ar-H), 1.95 (s, 3 H), 1.98 (s, 3 H), 2.11
(s, 3 H), 2.14 (s, 3 H), 2.21 (s, 3 H) (5ÂCH3CO-);
13C NMR (100 MHz, CDCl3): ꢃc (ppm) Glc.:
100.8 (C-1), 74.1 (C-2), 76.7 (C-3), 69.0 (C-4),
70.0 (C-5), 63.0 (C-6); Rha: 98.6 (C-1'), 71.7 (C-
2'), 68.5 (C-3'), 70.8 (C-4'), 67.4 (C-5'), 17.3 (C-6');
cinnamoyl: 131.9, 129.4 (2C), 122.1 (2C), 152.3
[Ar-C], 144.8, 117.3, 67.0 [C=C-C=O]; aglycon:
70.7, 35.1 (O-C-C), 130.7, 129.9 (2C) 114.6 (2C),
157.1 [Ar-C], 68.8, 133.4, 117.5 (O-CH2-CH
=CH2), 20.6, 20.7, 20.7, 20.8, 21.5 (5ÂCH3CO),
169.0, 169.9, 170.0, 170.5, 172.0 (5 ( CH3CO). MS,
m/z: 834 (M+1)+, 655, 273, 189, 161. Anal. Calcd
for C42H50O18: C, 59.85; H, 5.98. Found: C, 60.07;
H, 5.68.

S.-Q. Zhang et al./Carbohydrate Research 308 (1998) 281±285
2-(4-Hydroxyphenyl)ethyl-2-O-acetyl-6-O-(4-hy- References
285
droxycinnamoyl)-3-O-(a-l-rhamnopyranosyl)-b-d-
glucopyranoside (8, 2-OAc Osmanthuside B6).ÐTo
a THF (4 mL) solution of 7 (560 mg, 0.665 mmol)
were added PdCl2 (120 mg, 0.667 mmol), CuCl
(66 mg, 0.667 mmol) and water (8 drops). The
solution was stirred vigorously for 6 h at 25±30 ꢀC.
The mixture was then diluted with CHCl3 (15 mL),
and ®ltered on a bed of Celite. The ®ltrate was
washed with water (10 mLÂ4) and dried over
Na2SO4. Evaporation of the solvent gave a solid.
To the solid was added an NH4OH±MeOH mix-
ture (15 mL, 15%, w/w) and the mixture was stirred
for 5 h at 5±10 ꢀC and refrigerated overnight. After
evaporation of solvent, ¯ash chromatography
(10:5:1 EtOAc±benzene±MeOH) of the residue gave
8 (210 mg, 53.3%). 13CNMR (100 MHz, DOCD3),
ꢃc (ppm) Glc: 101.7 (C-1), 74.8 (C-2), 82.8 (C-3), 70.6
(C-4), 75.3 (C-5), 64.6 (C-6); Rha: 102.8 (C-1'), 72.4
(C-2'), 72.1 (C-3'), 73.9 (C-4'), 70.3 (C-5'), 17.6 (C-
6'); cinnamoyl: 127.1,130.9 (2C), 116.9 (2C), 161.0
[Ar-C], 146.8, 115.0, 169.0 [C=C-C=O]; aglycon:
131.0, 116.2 (2C), 131.2 (2C), 156.5 [Ar-C], 36.1, 71.8
[O-CH2-CH2-Ar], 20.1 (CH3CO-), 170.2 (CH3CO-).
MS, m/z: 843 (M+K)+, 497, 147,121.
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