Concise synthesis of two trisaccharides related to the cytotoxic triterpenoid saponin isolated from Pithecellobium lucidum

Article abstract of DOI:10.1016/j.carres.2009.08.012

Convergent synthesis of two trisaccharides related to the cytotoxic triterpenoid saponin isolated from Pithecellobium lucidum is reported. The trisaccharides are synthesized in the form of their propargyl glycosides to leave the scope for further glycocon

Full text of DOI:10.1016/j.carres.2009.08.012

Carbohydrate Research 344 (2009) 2554–2558
Contents lists available at ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Note
Concise synthesis of two trisaccharides related to the cytotoxic triterpenoid
saponin isolated from Pithecellobium lucidum
*
Priya Verma, Balaram Mukhopadhyay
Indian Institute of Science Education and Research-Kolkata (IISER-K), Mohanpur Campus, BCKV Main Campus, Mohanpur, Nadia 741252, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 June 2009
Received in revised form 10 August 2009
Accepted 12 August 2009
Available online 15 August 2009
Convergent synthesis of two trisaccharides related to the cytotoxic triterpenoid saponin isolated from
Pithecellobium lucidum is reported. The trisaccharides are synthesized in the form of their propargyl
glycosides to leave the scope for further glycoconjugate formation through various multi-component
reactions. A simple protecting group manipulation is followed using commercially available monosaccha-
rides, D-glucose, D-xylose, D-fucose and L-rhamnose. H2SO4 immobilized on silica is used as the Brönsted
acid source for the N-iodosuccinimide-mediated thioglycoside activation for stereoselective glycosyla-
tions and proved to be a better choice over traditional Lewis acid catalysts such as TMSOTf and TfOH.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Saponin
Propargyl glycoside
H2SO4-silica
Oligosaccharide
Glyco-conjugate
During the routine programme of growth and development,
plants synthesize triterpenoid saponins which act as preformed
chemical barriers for fungal attack.1 Besides their important role
in plant growth, these glycosylated plant secondary metabolites
are often used as folk medicines for various diseases. Examples in-
clude plants that are exploited as sources of drugs, such as ginseng
and liquorice, and also crop plants, such as legumes and oats.2 One
common feature shared by all saponins is the presence of a sugar
chain at the C-3 of the aglycone moiety.3,4 These chains vary from
saponin to saponin but usually consist of glucose, arabinose, glucu-
ronic acid, xylose or rhamnose.5 Despite the commercial interest
related to this important class of bio-molecules, the biosynthetic
pathways for the formation of glycosides are largely unidentified.
To get a clear understanding and to exploit the potential use as
medicines, synthetic approach becomes necessary.
The leaves and stems of the plant Pithecellobium lucidum are
widely used as Chinese folk medicine for the treatment of rheuma-
talgia and wounds.6 Recently Ma et al .7 reported the chemical
structures of three new triterpenoid saponins isolated from the
EtOH extract of the dried roots of P. lucidum which exhibited signif-
icant in vitro inhibitory activity against three cultured human
tumour cell lines (HCT-8, Bel-7402 and A2780) with IC50 values
Synthesis of the trisaccharide 1 was commenced with propar-
gyl b- -glucopyranoside (3). The choice of propargyl group at the
reducing end was driven by the fact that it can be converted into
D
OR2
O
OH
O
HO
HO
O
OH
O
O
HO
O
O
O
O
OH
O
HO
OH
O
O
O
Me
HO
HO
OH
OH
OH
HO
HO
OH OH
HO
OH
HO
HO
O
O
HO
O
O
O
ranging from 17.48 to 37.26 lg/mL. Here we report concise synthe-
O
Me
O
sis of two trisaccharides (Fig. 1, 1 and 2) related to the triterpenoid
saponin isolated from the roots of P. lucidum as their propargyl
glycosides.
HO
O
O HO
O
O
O
HO
HO
HO
HO
OH
OH
OH
OH
2
OH
1
* Corresponding author. Fax: +91 33 23348092.
E-mail address: sugarnet73@hotmail.com (B. Mukhopadhyay).
Figure 1. Structure of the saponin and the target trisaccharides.
0008-6215/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2009.08.012

P. Verma, B. Mukhopadhyay / Carbohydrate Research 344 (2009) 2554–2558
2555
various glycoconjugates via dipolar cycloaddition8–15 and different
multi-component reactions16–21 or it can be converted into the
corresponding hemiacetal22 for further conjugation. Compound 3
was allowed to react with trityl chloride in pyridine followed by
benzoyl chloride affording propargyl 2,3,4-tri-O-benzoyl-6-O-tri-
the purification was not completely successful till preparative
TLC. Finally, global deprotection using NaOMe in MeOH afforded
the target trisaccharide, propargyl b-
D
-xylopyranosyl-(1?2)-b-
D-
fucopyranosyl-(1?6)-b-
D-glucopyranoside (1) in 87% yield
(Scheme 1).
tyl-b-
D
-glucopyranoside (4). Subsequently the trityl group was
Synthesis of the trisaccharide 2 commenced with glycosylation
between the known donor, p-tolyl 4-O-chloroacetyl-2,3-isopropyl-
selectively removed using 90% aqueous TFA23 to afford the desired
acceptor 5 in 79% overall yield. It was glycosylated with the known
trichloroacetimidate disaccharide donor 624 using H2SO4-silica25–31
to form the protected trisaccharide 7 in 91% yield. Use of H2SO4-
silica instead of traditional TMSOTf or TfOH was found to be
particularly beneficial as the reaction was clean and excellently
productive. The same reaction when carried out in the presence
of TMSOTf or TfOH, the yields were 78% and 73%, respectively.
Moreover, in most of the cases it becomes necessary to dilute
TMSOTf or TfOH before use. However, H2SO4-silica can be weighed
easily. After the completion of the reaction, just a filtration through
Celite removes the catalyst. It is worth noting that, a trehalose type
of compound was formed due to the self-coupling of two xylose
moieties. Although it was <3% as anticipated from 1H NMR, but
idene-1-thio-
3-O-benzoyl-4,6-O-benzylidene-b-
a-L
-rhamnopyranoside (8)32 and acceptor, propargyl
D
-glucopyranoside (9)33 using
NIS in the presence of H2SO4-silica to afford disaccharide 10 in
87% yield. Subsequently, the chloroacetate group was selectively
cleaved using thiourea34 to furnish the required disaccharide
acceptor 11 in 86% yield. Further glycosylation of the known donor,
p-tolyl 2,3,4-tri-O-benzoyl-1-thio-a-D
-arabinofuranoside (12)24
with disaccharide acceptor 11 using NIS in conjunction with
H2SO4-silica afforded the protected trisaccharide 13 in 83% yield.
Global deprotection of the trisaccharide was accomplished by
treating trisaccharide 13 with 80% AcOH at 80 °C followed by
NaOMe in MeOH to get the target trisaccharide 2 in 78% overall
yield (Scheme 2).
OH
OTr
OH
O
O
i. TrCl, Py
ii. BzCl, Py
O
90% TFA
HO
HO
O
BzO
BzO
BzO
BzO
O
O
OH
OBz
OBz
3
4
5
AcO
AcO
O
O
O
O
5
AcO
AcO
O
H2SO4-silica
O
O
BzO
O
AcO
O
AcO
BzO
O
CCl3
NH
AcO
AcO
OBz
OAc
OAc
7
6
HO
HO
O
O
NaOMe
MeOH
O
O
O HO
HO
HO
O
HO
OH
OH
1
Scheme 1. Synthesis of the trisaccharide 1.
O
O
Ph
O
Ph
STol
Ph
+
O
O
O
O
O
O
O
O
BzO
BzO
O
NIS
H2SO4-silica
Me
cAcO
O
O
O
Thiourea
BzO
OH
Me
O
O
Me
O
O
HO
cAcO
9
8
O
O
O
11
O
10
STol
BzO
HO
HO
HO
O
O
O
O
BzO
O
Ph
O
O
O
O
BzO
i. 80% AcOH,80 o
ii. NaOMe, MeOH
C
Me
OBz
12
O
O
Me
O
HO
O
O
NIS, H2SO4-silica
BzO
HO
O
OH
O
O
HO
2
BzO
OH
OBz
13
Scheme 2. Synthesis of the trisaccharide 2.

2556
P. Verma, B. Mukhopadhyay / Carbohydrate Research 344 (2009) 2554–2558
new compound (TLC: n-hexane–EtOAc; 2:1). The mixture was neu-
1. Experimental
1.1. General methods
tralized with Et3N, filtered through a pad of Celite, washed with
CH2Cl2 and the combined filtrate was evaporated. The residue
was purified by flash chromatography using n-hexane–EtOAc
(3:1) as eluent to afford pure trisaccharide 7 (1.7 g, 91%) as white
All reagents and solvents were dried prior to use according to
standard methods.35 Commercial reagents were used without fur-
ther purification unless otherwise stated. Analytical TLC was per-
formed on Silica Gel 60-F254 (Merck or Whatman) with detection
by fluorescence and/or by charring following immersion in a 10%
ethanolic solution of sulfuric acid. An orcinol dip, prepared by
the careful addition of concentrated sulfuric acid (20 cm3) to an
ice-cold solution of 3,5-dihydroxytoluene (360 mg) in EtOH
(150 cm3) and water (10 cm3), was used to detect deprotected
compounds by charring. Flash chromatography was performed
with silica gel 230–400 mesh (Qualigens, India). Optical rotations
were measured at the sodium D-line at ambient temperature, with
a Perkin Elmer 141 polarimeter. 1H NMR and 13C NMR spectra were
recorded on a Bruker Avance spectrometer using Me4Si or CH3OH
as internal standard, as appropriate.
foam. ½a 2D5
ꢁ
+97 (c 1.3, CHCl3). 1H NMR (CDCl3, 500 MHz) d: 7.97–
7.27 (m, 15H, ArH), 5.90 (t, 1H, J2,3 = J3,4 = 9.5 Hz, H-3), 5.51 (t,
1H, J3,4 = J4,5 = 9.5 Hz, H-4), 5.48 (m, 1H, H-2), 5.36 (dd, 1H,
J3 ,4 = 3.5 Hz, J2 ,3 = 11.0 Hz, H-30), 5.19 (br d, 1H, H-40), 5.13–5.04
0
0
0
0
(m, 2H, H-200, H-300), 4.95 (d, 1H, J1 ,2 = 7.5 Hz, H-100), 4.87 (m, 2H,
00 00
H-10, H-400), 4.64 (d, 1H, J1,2 = 7.5 Hz, H-1), 4.43 (m, 2H, CH2–
C„CH), 4.20–4.09 (m, 3H, H-20, H-5a00, H-5b00), 3.89 (m, 2H, H-5,
H-6ª), 3.66 (br d, 1H, J6a,6b = 11.0 Hz, H-6b), 3.37 (m, 1H, H-50),
2.54 (t, 1H, J = 2.5 Hz, CH2–C„CH), 2.15, 2.09, 2.03, 2.02, 2.01,
1.96 (5s, 15H, 5 ꢀ COCH3), 1.02 (d, 3H, J5 ,6 = 6.5 Hz, C–CH3). 13C
NMR (CDCl3, 125 MHz) d: 170.5, 170.4, 170.1, 169.8, 169.7
(5 ꢀ COCH3), 165.8, 165.2, 165.1 (3 ꢀ COPh), 133.5, 133.2, 133.1,
129.9 (2), 129.8 (2), 129.7 (2), 129.4, 128.9, 128.8, 128.5 (2),
128.2 (4) (ArC), 101.2 (C-1), 98.5 (C-100), 98.4 (C-10), 78.2, 75.8,
74.6, 73.5, 73.2, 71.7, 71.6, 70.9, 70.4, 69.9, 69.5, 69.1, 66.9, 64.5,
61.3, 60.4, 56.3, 20.7 (2), 20.6 (2), 20.4 (5 ꢀ COCH3), 15.7 (C–CH3).
HRMS calcd for C51H54O22Na (M+Na)+: 1041.3004, found:
1041.3006.
0
0
1.2. Propargyl 2,3,4-tri-O-benzoyl-b-D-glucopyranoside (5)
Trityl chloride (3.3 g, 12 mmol) was added to a solution of com-
pound 3 (2 g, 9.2 mmol) in dry pyridine (30 mL) and the mixture
was allowed to stir at 70 °C for 3 h when TLC (n-hexane–EtOAc,
2:1) showed complete conversion of the starting material. The
solution was allowed to attain room temperature and benzoyl
chloride (3.8 mL, 33 mmol) was added and the solution was al-
lowed to stir for another 2 h at room temperature. MeOH (2 mL)
was added to destroy excess benzoyl chloride and the solvents
were removed in vacuo and co-evaporated with toluene to remove
residual pyridine. The resulting syrup thus obtained was dissolved
in CH2Cl2 (40 mL) and washed with H2O (2 ꢀ 50 mL) and brine
(50 mL). Organic layer was separated, dried (Na2SO4) and evapo-
rated in vacuo. Resulting thick syrup was dissolved in CH2Cl2
(30 mL) followed by the addition of 90% aq TFA (10 mL) and the
solution was allowed to stir for 30 min at room temperature. Then
the solution was poured into a separating funnel and washed
successively with water (50 mL), saturated NaHCO3 (2 ꢀ 50 mL)
and brine (50 mL). The organic layer was collected, dried (Na2SO4)
and filtered. Solvents were evaporated and the resulting crude
material was purified by flash chromatography using n-hexane–
EtOAc (3:1) as eluent to afford pure compound 5 (3.8 g, 79%) as
1.4. Propargyl b-
D-xylopyranosyl-(1?2)-b-D-fucopyranosyl-
(1?6)-b- -glucopyranoside (1)
D
To a solution of compound 7 (1.5 g, 1.5 mmol) in MeOH (15 mL),
NaOMe in MeOH (0.5M, 1.5 mL) was added and the solution was al-
lowed to stir at room temperature for 3 h. The solution was then
neutralized with DOWEX 50W H+ resin and filtered through a plug
of cotton. The filtrate was evaporated and the sticky residue was
washed with CH2Cl2 to afford pure trisaccharide 1 (635 mg, 87%)
as white amorphous solid. ½a D25
ꢁ
+121 (c 1.1, H2O). 1H NMR (D2O,
0
300 MHz) d: 5.00 (d, 1H, J1 ,2 = 3.5 Hz, H-10), 4.55 (d, 1H,
0
J1 ,2 = 8.0 Hz, H-100), 4.50 (d, 1H, J1,2 = 7.5 Hz, H-1), 4.38 (m, 2H,
00 00
CH2–C„CH), 4.04 (m, 1H, H-50), 3.95 (dd, 1H, J5a ,4 = 3.5 Hz,
00 00
J5a ,5b = 10.5 Hz, H-5a00), 3.88 (dd, 1H, J5b ,4 = 5.0 Hz, J5a ,5b
=
00
00
00 00
00
00
10.5 Hz, H-5b00), 3.79 (dd, 1H, J3 ,4 = 3.5 Hz, J2 ,3 = 10.5 Hz, H-30),
3.78 (m, 1H, H-40), 3.73 (m, 2H, H-20, H-200), 3.58 (m, 2H, H-5, H-
50), 3.41 (t, 1H, J2,3 = J3,4 = 9.5 Hz, H-3), 3.38 (m, 2H, H-6a, H-6b),
3.29–3.21 (m, 3H, H-2, H-300, H-4), 2.85 (t, 1H, J = 2.0 Hz, CH2–
0
0
0
0
C„CH), 1.15 (d, 3H, J5 ,6 = 6.5 Hz, C–CH3). 13C NMR (D2O, 75 MHz)
d: 104.9 (C-1), 100.7 (C-100), 97.5 (C-10), 78.9, 78.1, 76.3, 75.9, 75.6,
74.3, 73.2, 72.9, 71.9, 69.8, 69.3, 68.5, 66.5, 65.9, 65.1, 56.7, 15.2
(C–CH3). HRMS calcd for C20H32O14Na (M+Na)+: 519.1690, found:
519.1687.
0
0
light yellow syrup. ½a D25
ꢁ
+110 (c 1.0, CHCl3). 1H NMR (CDCl3,
500 MHz) d: 7.98–7.26 (m, 15H, ArH), 5.97 (t, 1H, J3,4 = J4,5
=
9.5 Hz, H-4), 5.53 (dd, 1H, J1,2 = 8.0 Hz, J2,3 = 9.5 Hz, H-2), 5.50 (t,
1H, J2,3 = J3,4 = 9.5 Hz, H-3), 5.13 (d, 1H, J1,2 = 8.0 Hz, H-1), 4.49,
4.39 (2dd, J = 16.0 Hz, 1.5 Hz, OCH2–C„CH), 3.88 (dd, 1H,
J = 2.0 Hz, 13.0 Hz, H-6a), 3.82 (m, 1H, H-5), 3.75 (dd, 1H,
J = 4.0 Hz, 13.0 Hz, H-6b), 2.43 (t, 1H, J = 1.5 Hz, OCH2–C„CH). 13C
NMR (CDCl3, 125 MHz) d: 166.1 (COPh), 165.8 (COPh), 165.1
(COPh), 133.7, 133.2, 133.1, 129.9(2), 129.8(2), 129.7(2), 128.5(2),
128.3(2), 127.8(2) (ArC), 98.7 (C-1), 78.3, 75.5, 74.7, 72.8, 71.6,
69.5, 61.2, 56.2. HRMS calcd for C30H26O9Na (M+Na)+: 553.1475,
found: 553.1477.
1.5. Propargyl 4-O-chloroacetyl-2,3-O-isopropylidene-a-L-
rhamnopyranosyl-(1?2)-3-O-benzoyl-4,6-O-benzylidene-b-D-
glucopyranoside (10)
A mixture of compound 8 (1.2 g, 3.1 mmol), compound 9 (1 g,
2.4 mmol) and MS 4 Å (1.5 g) in dry CH2Cl2 (20 mL) was stirred un-
der nitrogen for 30 min. NIS (900 mg, 4 mmol) was added followed
by H2SO4-silica (50 mg) and the mixture was stirred at ambient
temperature for 30 min when TLC (n-hexane–EtOAc, 3:1) showed
complete conversion of the starting materials. The mixture was fil-
tered through a pad of Celite, washed with CH2Cl2 and the com-
bined filtrate was washed successively with aq Na2S2O3
(2 ꢀ 30 mL), satd NaHCO3 (2 ꢀ 30 mL) and brine (30 mL). The or-
ganic layer was collected, dried (Na2SO4) and filtered, and the sol-
vents were evaporated in vacuo. The crude residue was purified by
flash chromatography using n-hexane–EtOAc (3:1) to afford pure
1.3. Propargyl 2,3,4-tri-O-acetyl-b-
di-O-acetyl-b- -fucopyranosyl-(1?6)-2,3,4-tri-O-benzoyl-b-
glucopyranoside (7)
D-xylopyranosyl-(1?2)-3,4-
D
D-
A mixture of compound 5 (1 g, 1.9 mmol), compound 6 (1.5 g,
2.3 mmol) and MS 4 Å (2 g) in dry CH2Cl2 (25 mL) was stirred un-
der nitrogen atmosphere for 30 min and then H2SO4-silica
(50 mg) was added and the mixture was stirred at room tempera-
ture till the starting materials were completely consumed to form a
disaccharide 10 (1.4 g, 87%) as white foam. ½a D25
ꢁ
+113 (c 1.1, CHCl3).
1H NMR (CDCl3, 300 MHz) d: 8.06–7.30 (m, 10H, ArH), 5.64 (t, 1H,

P. Verma, B. Mukhopadhyay / Carbohydrate Research 344 (2009) 2554–2558
2557
J2,3 = J3,4 = 9.5 Hz, H-3), 5.51 (s, 1H, CHPh), 5.11 (s, 1H, H-10), 4.82
J1,2 = 7.5 Hz, H-1), 4.76 (dd, 1H, J4 ,5a = 3.5 Hz, J5a ,5b = 12.0 Hz, H-
00
00
00
00
(dd, 1H, J3 ,4 = 8.0 Hz, J4 ,5 = 10.5 Hz, H-40), 4.80 (d, 1H,
J1,2 = 7.5 Hz, H-1), 4.42 (m, 2H, CH2–C„CH), 4.40 (dd, 1H,
J5,6a = 5.0 Hz, J6a,6b = 11.0 Hz, H-6a), 3.96 (m, 4H, COCH2Cl, H-20,
H-6b), 3.91 (m, 1H, H-50), 3.90 (dd, 1H, J1,2 = 7.5 Hz, J2,3 = 9.5 Hz,
H-2), 3.82 (m, 2H, H-30, H-4), 3.63 (m, 1H, H-5), 2.50 (t, 1H,
J = 2.5 Hz, CH2–C„CH), 1.39, 1.05 (2s, 6H, 2 ꢀ isopropylidene-
5a00), 4.65 (dd, 1H, J4 ,5a = 5.5 Hz, J5a ,5b = 12.0 Hz, H-5b00), 4.54
(m, 1H, H-400), 4.41 (m, 3H, H-6a, CH2–C„CH), 4.19 (m, 1H, H-
6b), 4.01 (m, 1H, H-50), 3.90 (m, 2H, H-20, H-30), 3.81 (t, 2H,
J = 9.5 Hz, H-4, H-40), 3.59 (m, 2H, H-2, H-5), 2.44 (m, 1H, CH2–
C„CH), 1.58, 1.37 (2s, 6H, 2 ꢀ isopropylidene-CH3), 1.26 (d, 3H,
0
0
0
0
00
00
00
00
J5 ,6 = 6.0 Hz, C–CH3). 13C NMR (CDCl3, 75 MHz) d: 166.3, 165.7,
165.6, 165.4 (4 ꢀ COPh), 136.8, 133.6, 133.5, 133.3, 133.0, 130.0
(2), 129.9 (2), 129.8 (2), 129.7 (2), 129.4, 129.2, 129.1, 129.0,
128.5 (7), 128.3 (2), 128.2 (2), 126.2 (2) (ArC), 109.3 (isopropyli-
dene-C), 104.2 (C-100), 101.4 (CHPh), 99.9 (C-1), 98.8 (C-10), 81.9,
81.6, 78.5, 78.4, 78.1, 77.9, 76.4, 75.8, 75.7, 74.4, 68.7, 66.4, 64.9,
64.2, 60.4, 56.3, 27.8, 26.0 (isopropylidene-CH3), 17.6 (C–CH3).
HRMS calcd for C58H56O18Na (M+Na)+: 1063.3364, found:
1063.3360.
0
0
CH3), 1.16 (d, 3H, J5 ,6 = 6.0 Hz, C–CH3). 13C NMR (CDCl3, 75 MHz)
d: 166.6 (COCH2Cl), 165.7 (COPh), 136.8, 133.4, 129.8 (2), 129.3,
129.1, 128.6 (2), 128.2 (2), 126.1 (2) (ArC), 109.7 (isopropylidene-
C), 101.4 (CHPh), 99.8 (C-1), 98.5 (C-10), 78.4, 78.1, 78.0, 76.5,
75.8, 75.6, 75.2, 74.3, 68.6, 66.4, 64.3, 56.3, 40.9 (COCH2Cl), 27.5,
26.0 (isopropylidene-CH3), 16.6 (C–CH3). HRMS calcd for
C34H37O12ClNa (M+Na)+: 695.1871, found: 695.1869.
0
0
1.6. Propargyl 2,3-O-isopropylidene-
a-
L-rhamnopyranosyl-
(1?2)-3-O-benzoyl-4,6-O-benzylidene-b-
D
-glucopyranoside
1.8. Propargyl
a-
D
-arabinofuranosyl-(1?4)-
a-L-
(11)
rhamnopyranosyl-(1?2)-b-
D
-glucopyranoside (2)
To a solution of compound 10 (1.2 g, 1.8 mmol) in CH2Cl2–
MeOH (2:3, 15 mL) was added thiourea (685 mg, 9 mmol) followed
by collidine (210 lL, 1.8 mmol) and the solution was stirred under
reflux for 12 h till TLC showed complete conversion of the starting
material to a slower moving spot. After cooling to room tempera-
ture, the solution was diluted with CH2Cl2 (10 mL) and washed
successively with saturated aq NaHCO3 (2 ꢀ 30 mL) and brine
(30 mL). The organic layer was separated, dried (Na2SO4) and
evaporated in vacuo. The residue was purified by flash chromatog-
raphy using 3:1 n-hexane–EtOAc to afford pure compound 11
A suspension of compound 13 (1.1 g, 1.0 mmol) in AcOH–H2O
(9:1, 20 mL) was stirred at 80 °C for 2 h. Then the solvents were
evaporated, co-evaporated with toluene for complete removal of
AcOH. The residue thus obtained was dissolved in MeOH (10 mL)
followed by the addition of NaOMe in MeOH (0.5M, 1 mL) and
the solution was stirred at room temperature for 4 h. Solvents were
evaporated in vacuo to afford pure trisaccharide 2 (410 mg, 78%) as
white amorphous solid. ½a D25
ꢁ
+77 (c 1.2, H2O). 1H NMR (D2O,
300 MHz) d: 5.23 (s, 1H, H-100), 4.94 (s, 1H, H-10), 4.59 (d, 1H,
J1,2 = 8.0 Hz, H-1), 4.38 (m, 2H, CH2–C„CH), 4.03 (m, 3H, H-200, H-
300, H-400), 3.95 (br s, 1H, H-20), 3.84 (m, 3H, H-30, H-40, H-50), 3.73
(920 mg, 86%) as colourless foam. ½a D25
ꢁ
+82 (c 1.4, CHCl3). 1H
(dd, 1H, J4 ,5a = 3.0 Hz, J5a ,5b = 12.0 Hz, H-5a00), 3.63 (m, 2H, H-5,
00
00
00
00
NMR (CDCl3, 300 MHz) d: 8.06–7.29 (m, 10H, ArH), 5.63 (t, 1H,
J2,3 = J3,4 = 9.5 Hz, H-3), 5.50 (s, 1H, CHPh), 5.09 (s, 1H, H-10), 4.80
(d, 1H, J1,2 = 7.5 Hz, H-1), 4.42 (m, 2H, CH2–C„CH), 4.39 (dd, 1H,
J5,6a = 5.0 Hz, J6a,6b = 10.5 Hz, H-6a), 3.96–3.90 (m, 4H, H-2, H-20,
H-5b00), 3.50 (m, 2H, H-6a, H-6b), 3.34 (m, 2H, H-3, H-4), 3.28 (m,
1H, H-2), 2.70 (t, 1H, J = 2.5 Hz, CH2–C„CH), 1.24 (d, 3H,
13
J5 ,6 = 6.0 Hz, C–CH3). C NMR (D2O, 75 MHz) d: 113.7 (C-100),
106.5 (C-1), 104.6 (C-10), 89.1, 86.6, 84.8, 83.4, 81.7, 81.6, 81.4,
81.0, 75.8, 75.7, 74.6, 72.6, 66.4, 65.9, 61.8, 54.1, 22.2 (C–CH3).
HRMS calcd for C20H32O14Na (M+Na)+: 519.1690, found: 519.1688.
0
0
H-30, H-6b), 3.81 (t, 1H, J3 ,4 = J4 ,5 = 9.5 Hz, H-40), 3.82 (t, 1H,
J3,4 = J4,5 =9.5 Hz, H-4), 3.63 (m, 1H, H-50), 3.30 (m, 1H, H-5), 2.50
(t, 1H, J = 2.5 Hz, CH2–C„CH), 1.36, 1.10 (2s, 6H, 2 ꢀ isopropyli-
0
0
0
0
dene-CH3), 1.27 (d, 3H, J5 ,6 = 6.0 Hz, C–CH3). 13C NMR (CDCl3,
75 MHz) d: 165.7 (COCH2Cl), 136.8, 133.3, 129.8 (2), 129.4, 129.0,
128.5 (2), 128.2 (2), 126.1 (2) (ArC), 109.1 (isopropylidene-C),
101.4 (CHPh), 99.8 (C-1), 98.7 (C-10), 78.5, 78.3, 78.1, 77.8, 75.7,
75.6, 74.6, 74.4, 68.7, 66.3, 66.2, 56.2, 27.9, 25.9 (isopropylidene-
CH3), 17.0 (C–CH3). HRMS calcd for C32H36O11Na (M+Na)+:
619.2155, found: 619.2157.
0
0
2. Conclusion
In conclusion, we have successfully completed the syntheses of
two trisaccharide related to the cytotoxic triterpenoid saponin iso-
lated from P. lucidum. These trisaccharides were prepared in the
form of their propargyl glycosides which can be utilized further
to generate different types of glycoconjugates by using Huisgen
cycloaddition reaction or various multi-component reactions.
1.7. Propargyl 2,3,4-tri-O-benzoyl-
2,3-O-isopropylidene- -rhamnopyranosyl-(1?2)-3-O-
benzoyl-4,6-O-benzylidene-b- -glucopyranoside (13)
a-D-arabinofuranosyl-(1?4)-
a-L
D
Acknowledgements
A mixture of compound 11 (900 mg, 1.5 mmol), compound 12
(1.1 g, 2 mmol) and MS 4 Å (g) in dry CH2Cl2 (15 mL) was stirred
under nitrogen for 30 min. Then NIS (585 mg, 2.6 mmol) was
added followed by H2SO4-silica (50 mg) and the mixture was stir-
red at room temperature for 45 min when TLC (n-hexane–EtOAc,
2:1) showed complete conversion of the starting materials to form
a new compound. The mixture was filtered through a pad of Celite,
washed with CH2Cl2 and the combined filtrate was washed succes-
sively with aq Na2S2O3 (2 ꢀ 25 mL), satd NaHCO3 (2 ꢀ 25mL) and
brine (25 mL). The organic layer was collected, dried (Na2SO4)
and filtered, and the solvents were evaporated in vacuo. The crude
residue was purified by flash chromatography using n-hexane–
EtOAc (3:1) to afford pure trisaccharide 13 (1.3 g, 83%) as white
P.V. is thankful to UGC, New Delhi, India for fellowship. The
work is funded by DST, New Delhi, India through SERC Fast-Track
Grant SR/FTP/CS-110/2005.
Supplementary data
Supplementary data (copies of 1H and 13C spectra of all
compounds) associated with this article can be found, in the online
version, at doi:10.1016/j.carres.2009.08.012.
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