Synthesis of the cytotoxic gitogenin 3β-O-[2-O-(α-L- rhamnopyranosyl)-β-D-galactopyranoside] and its congeners

Article abstract of DOI:10.1055/s-2006-926316

(25R)-5a-Spirostan-2a,3b-diol (gitogenin) 3β-O-[2-O-(α-L- rhamnopyranosyl)-β-D-galactopyranoside] (1), a cytotoxic spirostan saponin isolated from the underground parts of Hosta longipes (Liliaceae), was concisely synthesized. In this context, its congeners 2-4 were also prepared. All four compounds showed comparable potency to dioscin in inhibition against the growth of tumor cells. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-926316

PAPER
775
Synthesis of the Cytotoxic Gitogenin 3b-O-[2-O-(a-L-Rhamnopyranosyl)-b-D-
galactopyranoside] and its Congeners
G
a
itogenin
3
b
-
O
-[2
i
-
O
-(
a
-
L
n
-
Rhamnopy
g
b
-
D
x
-galactopyra
i
noside]a Li,*a Yichun Zhang,a Tiantian Guo,a Huashi Guan,a Yan Hao,b Biao Yu*b
Key Laboratory of Marine Drugs, The Ministry of Education of China, Marine Drug and Food Institute, Ocean University of China,
Qingdao 266003, P. R. of China
E-mail: liyx417@ouc.edu.cn; E-mail: byu@mail.sioc.ac.cn
State Key Laboratory of Bio-organic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, Shanghai 200032, P. R. of China
b
Received 20 July 2005; revised 3 October 2005
O
Abstract: (25R)-5a-Spirostan-2a,3b-diol (gitogenin) 3b-O-[2-O-
(a-L-rhamnopyranosyl)-b-D-galactopyranoside] (1), a cytotoxic
spirostan saponin isolated from the underground parts of Hosta lon-
gipes (Liliaceae), was concisely synthesized. In this context, its
congeners 2–4 were also prepared. All four compounds showed
comparable potency to dioscin in inhibition against the growth of
tumor cells.
O
HO
O
OR
O
OH
O
HO
H
1: R = H
O
2: R = α−L-Rha
HO
O
Key words: gitogenin 3b-O-[2-O-(a-L-rhamnopyranosyl)-b-D-ga-
lactopyranoside], saponin, chacotrioside, synthesis, antitumor
HO
OH
O
R
OH
O
HO
O
O
(25R)-5a-Spirostan-2a,3b-diol (gitogenin) 3b-O-[2-O-(a-
L-rhamnopyranosyl)-b-D-galactopyranoside] (1) was iso-
lated by Mimaki et al. from the underground parts of Hos-
ta longipes and H. sieboldii (Liliaceae),1,2 and showed
remarkable inhibition activity against the growth of hu-
man promyelocytic leukaemia HL-60 cells with an IC50
value of 3.0 mg/mL.2 In continuation of our research on
antitumor saponins,3,4 here we chose saponin 1 as a target
to develop an approach to the first synthesis of gitogenin
glycosides, which constitute a rare group of steroidal sa-
ponins in nature. In this context, gitogenin 3b-O-[2,4-di-
O-(a-L-rhamnopyranosyl)-b-D-galactopyranoside] (2),
gitogenin 3b-O-[2,4-di-O-(a-L-rhamnopyranosyl)-b-D-
glucopyranoside] (chacotrioside) (3) (namely introduc-
tion of the b-chacotriosyl sugar residue of the most active
spirostan saponins5 onto the 3-OH of gitogenin), and tigo-
genin 3b-O-chacotrioside (4), were also prepared. This
enabled us to compare the antitumor activities of these
congeners with diosgenin 3b-O-chacotrioside (dioscin),
which represents one of the most potent antitumor
spirostan saponins.4,5
HO
O
H
HO
HO
O
O
3: R = OH
4: R = H
Dioscin: R = H, ∆5,6
HO
HO
OH
Figure 1 Saponins 1–4
To convert diosgenin into gitogenin, a 2a-hydroxyl group
needs to be introduced and the C-5,6 double bond to be
stereoselectively saturated. Thus, hydrogenation of dios-
genin in the presence of Pd/C provided tigogenin 9 ste-
reoselectively in 93% yield7 (Scheme 2). Tosylation of 9
with p-toluenesulfonyl chloride in pyridine at room tem-
O
O
O
O
a
b
HO
O
Diosgenin
5
O
O
O
The rare steroid gitogenin has been prepared from the
abundant diosgenin by Sondheimer et al. using a five-step
sequence as depicted in Scheme 1.6 We first attempted to
follow this synthetic approach. But the low yield in the
transformation of the bromide 6 to the 2-acetoxy-3-one 7
(ca. 20%, the literature yield was 25%) and the difficulty
associated with the purification of 6 and 7 prompted us to
seek for a new procedure for the preparation of gitogenin.
O
d
c
AcO
O
O
7
6
Br
O
O
O
O
e
HO
HO
AcO
O
Gitogenin
8
H
H
SYNTHESIS 2006, No. 5, pp 0775–0782
x
x
.
x
x
.2
0
0
6
Advanced online publication: 07.02.2006
DOI: 10.1055/s-2006-926316; Art ID: F12205SS
© Georg Thieme Verlag Stuttgart · New York
Scheme 1 Reagents: a) cyclohexanone, Al(i-OPr)3; b) NBS, CCl4;
c) KOAc, AcOH; d) Pd/C, H2; e) LiAlH4.

776
Y. Li et al.
PAPER
O
O
a
c
O
O
Diosgenin
RO
9 R = H
10 R = Ts
b
11
13
H
H
O
NOE
CH3
O
O
H
d
BnO
HO
e
O
HO
H
12
14
OH
O
O
CH3
H
O
O
g
BnO
O
f
BnO
HO
+
13
H
15
H
Scheme 2 Reagents and conditions: a) H2, Pd/C, CH2Cl2–MeOH, r.t., 93%; b) TsCl, pyridine, 0 °C then r.t.; c) silica gel, EtOAc–PE, r.t., 73%
(for two steps); d) OsO4, NMO, t-BuOH–THF–H2O (10:8:1), r.t., 77; e) Bu2SnO, toluene, reflux, 6 h; then BnBr, Bu4N+Br–, reflux, 2 h, 98%;
f) Dess–Martin periodinane, CH2Cl2, r.t.; g) NaBH4, CeCl3·7H2O, MeOH, –40 °C, 55% (two steps for 15), 28% (two steps for 13).
perature led to a single product, conceivably the corre- synthesized from diosgenin in total seven steps and in a
sponding 3-OTs derivative 10, as detected in TLC. remarkable 28% overall yield.
Surprisingly, a less polar compound 11 was obtained from
We then focused our attention on the incorporation of the
silica gel column chromatography of the crude 10. In fact,
2-O-benzylgitogenin 15 with sugar residues. To this end,
elution after loading the crude 10 onto silica gel for 48
glycosylation of 2-O-benzylgitogenin 15 with 2,3,4,6-tet-
hours provided 11 in a good 73% yield (from 9). Stirring
ra-O-benzoyl-D-galactopyranosyl
trichloroacetimidate
the crude 10 overnight in the presence of silica gel in
CH2Cl2 at r.t. converted it completely into 11. The struc-
ture of compound 11 was confirmed by 2D NMR analysis,
i.e., COSY, HMQC, HMBC, and DEPT spectra, to be the
desired D2,3 intermediate. Elimination of the 3-O-tosyl es-
ter under such mild conditions was unexpected.8 Oxida-
tion of olefin 11 with a catalytic amount of OsO4 in the
presence of NMO afford the 2a,3a-diol 12 in 77% yield.9
The stereochemistry of the nascent 2-OH in 12 was con-
firmed by the NOE correlation observed between H-2 and
H-19 and the chemical shifts of 2-axial proton (d = 3.76,
br d, J = 11.3 Hz) and 3-equatorial proton (d = 3.96, br s).
Selective protection of the equatorial 2a-OH of diol 12
was examined via the organotin-mediated regioselective
benzylation.9 Thus, treatment of the 2,3-diol 12 with
Bu2SnO in anhydrous toluene under azeotropic conditions
followed with BnBr and Bu4N+I– at reflux led to the de-
sired 2-O-benzylated product 13 in an excellent 98%
(16) under the action of a catalytic amount of TMSOTf af-
forded the 3-O-b-galactopyranoside 17 in quantitative
yield12 (Scheme 3). Removal of the benzoyl groups with
NaOMe in MeOH readily gave 18, which was subjected
to 1-BBTZ [1-(benzoyloxy)benzotriazole] in the presence
of Et3N in CH2Cl2 to selectively protect the 3,6-OHs on
the b-galactopyranosyl residue, leading to 2,4-diol 19 in a
good 68% yield.13 Regioselective glycosylation of diol 19
has been investigated using two rhamnopyranosyl donors.
Coupling of 19 with 2,3,4-tri-O-acetyl-L-rhamnopyrano-
syl trichloroacetimidate (30, 1.1 → 3.0 equiv) under the
promotion of a catalytic amount of TMSOTf or BF3·OEt2
gave poor regioselectivity and low yield of the desired 2-
O-glycosylated product 21. The reaction results were very
different from those for diosgenin.14 Apparently, the poor
reactive selectivity of 2¢-OH in 19 resulted from its dimin-
ished reactivity due to the presence of 2a-OBn in the sa-
pogenin. To address this problem, a larger and lower
reactive glycosyl donor should be adopted. Fortunately,
by using the 2,3,4-tri-O-benzoyl-a-L-rhamnopyranosyl
bromide (20, 1.1 equiv) as the donor, selective glycosyla-
tion of 2¢-OH in 19 was carried out smoothly under the ac-
tion of AgOTf to obtain the desired product 21 in a
satisfactory 62% yield; in the mean time, the 2,4-di-O-
glycosylated product 22 was isolated in 17% yield. This
protocol has previously been used for the selective rham-
nosylation of the 2-OH of a 3,6-di-O-pivaloyl-b-D-glu-
copyranoside.15 Removal of the 2-O-benzyl group on 21
by hydrogenolysis in the presence of Pd/C, followed by
removal of the benzoyl groups on the sugar residue with
NaOMe in MeOH afforded the desired natural saponin 1
in good yield (76% for two steps). The analytical data for
the synthetic compound 1 were in well agreement with
1
yield. H NMR spectra of 13 showed that the chemical
shift of 2-H moved upfield (d = 3.63, ddd, J = 12.1, 2.9,
1.8 Hz). The final inversion of the 3a-OH of 13 into the b-
configuration was attempted by an oxidation-reduction
sequence. Treatment of 13 with Dess–Martin
periodinane10 gave the 3-ketone 14, which was directly
subjected to reduction with NaBH4 in the presence of
CeCl3⋅7H2O at –40 °C.11 The desired 3b-OH product 15
was obtained as the major product in 55% yield (over two
steps), meanwhile, the 3a-OH epimer 13 was also isolated
in 28%. The chemical shift and peak shape of the 3-H
1
(d = 3.94–3.89, m) for 15 on the H NMR spectra, strik-
ingly different from those of the 3-equatorial proton (d =
4.41 ppm, br s) for 13, confirmed the b-configuration of
3-OH. Thus, 2-O-benzylgitogenin 15 was conveniently
Synthesis 2006, No. 5, 775–782 © Thieme Stuttgart · New York

PAPER
Gitogenin 3b-O-[2-O-(a-L-Rhamnopyranosyl)-b-D-galactopyranoside]
777
OBz
O
OBz
O
OBz
O
O
CCl3
15
+
O
BzO
BzO
BzO
CCl3
O
R
OBz
NH
16
+
a
O
OBz
NH
15 R = OBn
9 R = H
HO
23
O
a
O
OBz
BnO
O
OBz
O
O
17
BzO
R
OBz
O
OBz
b
O
BzO
BzO
O
24: R = OBn
25: R = H
O
OBz
b
O
OR
BnO
O
OR1
O
O
18 R = R1 = H
19 R = H, R1 = Bzm
R1O
OR2
O
c
R
O
OR
R1O
R2O
Br
O
OR1
26 R = OBn, R1 = R2 = H
27 R = H, R1 = R2 = H
28 R = OBn, R1 = H, R2 = Bz
29 R = H, R1 = H, R2 = Bz
d
BzO
O
O
BzO
OBz
c
20
NH
CCl3
BnO
O
OR
OBz
O
O
d
O
BzO
O
AcO
30
21 R = H
22 R = Bz3-α-L-Rha
O
AcO
OAc
O
O
R
e
OBz
O
BzO
AcO
BzO
O
OBz
O
1 and 2
BzO
O
31 R = OBn
32 R = H
3 R = OH
4 R = H
AcO
AcO
O
e, then f
or f
Scheme 3 Reagents and conditions: a) 16 (1.3 equiv), TMSOTf (0.1
equiv), CH2Cl2, 0 °C, quant.; b) NaOMe, MeOH, r.t., 99%; c) BBTZ,
Et3N, CH2Cl2, r.t., 68%; d) 20 (1.1 equiv), AgOTf (1.2 equiv),
CH2Cl2, –20 °C, 62% (for 21), 17% (for 22); e) H2, 10% Pd/C,
CH2Cl2–MeOH, r.t., overnight; then NaOMe, MeOH–CH2Cl2, r.t.,
overnight, 76% (two steps for 1), 83% (two steps for 2).
O
AcO
AcO
OAc
Scheme 4 Reagents and conditions: a) 23 (1.3 equiv), TMSOTf (0.1
equiv), CH2Cl2, 0 °C, quant. (for 24); 97% (for 25); b) NaOMe, Me-
OH, r.t., 85% (for 26); 91% (for 27); c) BBTZ, Et3N, CH2Cl2, r.t.,
55% (for 28); 40% (for 29); d) 30 (5 equiv), TMSOTf (0.2 equiv),
CH2Cl2, –20 °C; e) H2, 10% Pd/C, CH2Cl2–MeOH, r.t.; f) NaOMe,
MeOH–CH2Cl2, r.t., 61% (three steps for 3); 52% (two steps for 4).
those reported for the natural product.1 Employing the
similar deprotection procedure, gitogenin trisaccharide 2
was obtained in 83% from 22.
carcinoma cell), BGC-823 (human gastric cancer cell),
and HGC-27 (human gastric carcinoma cell), were evalu-
ated following a standard MTT assay with dioscin as a
positive control.17 The IC50 values are listed in Table 1.
The tigogenin 3-O-chacotrioside 4 showed similar poten-
cy as dioscin against the three tumor cell lines; while the
gitogenin glycosides 1–3 were slightly less potent.
The next task was to introduce the chacotriosyl residue
onto gitogenin 15 and tigogenin 9 to prepare saponins 3
and 4. The procedure was straightforward as shown in
Scheme 4, adopting modification of the previous proce-
dure for the preparation of dioscin and its derivatives.4
Thus, glycosylation of 15 and 9 with 2,3,4,6-tetra-O-ben-
zoyl-D-glucopyranosyl trichloroacetimidate 23 under the
action of a catalytic amount of TMSOTf afforded the 3-O-
b-glucopyranosides 24 and 25, respectively, in excellent
yields. Removal of the benzoyl groups from the b-glu- Table 1 Inhibition Activities of Compounds 1–4 against the Growth
of Tumor Cells
copyranosyl residue with NaOMe in methanol, followed
by selective protection of the 3,6-OHs with BBTZ in the
presence of Et3N, provided the corresponding 3,6-di-O-
Tumor cells IC50 (mM)
1
2
3
4
Dioscin
0.52
2.0
benzoyl derivatives 28 and 29 in moderate yields. Glyco-
sylation of the diols 28 and 29 with 2,3,4-tri-O-acetyl-L-
rhamnopyranosyl trichloroacetimidate (30) under the pro-
motion of TMSOTf afforded the desired trisaccharides 31
and 32, respectively, which were directly subjected to
deprotection to provide the desired chacotriosyl saponins
3 and 4 in good yields. The 13C NMR data for the synthetic
compound 4 were in well agreement with those reported
for the metabolic product.16
A549
2.5
2.6
2.1
3.9
2.2
4.2
2.3
4.0
2.7
0.81
1.2
2.2
BGC-823
HGC-27
1.4
Solvents were purified in the usual way. Petroleum ether (PE) refers
to the fraction boiling in the range 60–90 °C. TLC was performed
The inhibition activities of saponins 1–4 against the
growth of three tumor cell lines, i.e., A549 (human lung on precoated Merck silica gel 60 F254 plates. Flash column chroma-
Synthesis 2006, No. 5, 775–782 © Thieme Stuttgart · New York

778
Y. Li et al.
PAPER
tography was performed on silica gel (200–300 mesh, Qingdao,
China). Optical rotations were determined with a JASCO P-1020
polarimeter. Melting points were determined with a Yanaco appara-
tus and are uncorrected. 1H NMR and 13C NMR spectra were taken
on a Jeol JNM-ECP 600 MHz spectrometer with TMS as an internal
standard, and chemical shifts recorded in d values. Mass spectra
were obtained on a Q-TOF GlOBAL mass spectrometer.
J = 7.0 Hz, 3 H), 0.81 (s, 3 H), 0.79 (d, J = 6.6 Hz, 3 H), 0.76 (s, 3
H).
13C NMR (pyridine-d5): d = 109.2, 81.1, 69.8, 69.1, 66.8, 63.0, 56.5,
54.6, 42.0, 41.9, 40.8, 40.1, 38.7, 37.2, 35.6, 34.7, 32.5, 32.1, 31.8,
30.6, 29.2, 28.2, 21.1, 17.3, 16.7, 15.0, 12.8.
ESI-HRMS: m/z calcd for [M + H]+ C27H45O4: 433.3318; found:
433.3306.
(25R)-5a-Spirostan-3b-ol (9)
(25R)-5a-Spirostan-2a-O-benzyloxy-3a-ol (13)
A suspension of diosgenin (2.0 g, 4.8 mmol) and Pd/C (10%, cat.)
in CH2Cl2–EtOH (1:1, 60 mL) in the presence of AcOH (2 drops)
was stirred under 1 atm H2 for 12 h, and then filtered and concen-
trated. The residue was purified by recrystallization from hexane to
A mixture of 12 (6.50 g, 15.0 mmol) and Bu2SnO (6.73 g, 27.0
mmol) in anhyd toluene (300 mL) was stirred at reflux for 6 h with
the azeotropic removal of H2O (Dean–Stark trap). The resulting so-
lution was cooled to r.t., and then BnBr (5.35 mL, 45.1 mmol) and
Bu4N+I– (6.09 g, 16.5 mmol) were added. The mixture was refluxed
for 2.5 h. TLC indicated that the reaction was complete. The mix-
ture was evaporated to a syrup which was dissolved in CH2Cl2 (350
mL), then washed successively with 5% Na2S2O3 (3 × 80 mL), H2O
(2 × 80 mL), and brine (80 mL). The organic layer was dried
(Na2SO4) and then filtered and concentrated. The residue was puri-
fied by silica gel column chromatography (1:15 EtOAc–PE) to af-
ford 13 as a white solid (9.86 g, 98%); mp 166.5–169 °C; Rf 0.29
(1:6 EtOAc–PE); [a]D20 –67.8 (c = 0.20, CHCl3).
20
give 9 (1.87 g, 93%) as a white solid; mp 189.0–194.0 °C; [a]D
–67.9 (c = 0.20, CHCl3); Rf 0.23 (CHCl3).
1H NMR (CDCl3): d = 4.39 (q, J = 7.3 Hz, 1 H, H-16), 3.59 (m, 1
H), 3.47 (m, 1 H), 3.37 (t, J = 11.0 Hz, 1 H,), 1.98 (m, 1 H), 0.96 (d,
J = 7.3 Hz, 3 H), 0.82 (s, 3 H), 0.79 (d, J = 6.4 Hz, 3 H), 0.76 (s, 3
H).
13C NMR (CDCl3): d = 109.3, 80.6, 71.3, 66.8, 62.2, 56.3, 54.4,
44.9, 41.6, 40.6, 40.1, 38.2, 37.0, 35.6, 35.1, 32.3, 31.8, 31.5, 31.4,
30.3, 28.8, 28.6, 21.1, 17.1, 16.5, 14.5, 12.4.
ESI-HRMS: m/z calcd for [M + H]+ C27H45O3: 417.3369; found:
417.3387.
1H NMR (pyridine-d5): d = 7.52–7.29 (m, 5 H, ArH), 4.73 (d, 1 H,
J = 11.7 Hz, CH2Ph), 4.64 (d, J = 11.8 Hz, 1 H, CH2Ph), 4.53 (q,
J = 6.6 Hz, 1 H, H-16), 4.41 (br s, 1 H, H-3), 3.63 (ddd, J = 1.8, 2.9,
12.1 Hz, 1 H, H-2), 3.57 (br d, J = 12.8 Hz, 1 H, H-26), 3.49 (t,
J = 10.3 Hz, 1 H, H-26), 1.12 (d, J = 7.0 Hz, 3 H), 0.84 (s, 3 H),
0.79 (s, 3 H), 0.67 (d, J = 4.4 Hz, 3 H).
13C NMR (pyridine-d5): d = 140.1, 128.6 (2 C), 128.0 (2 C), 127.7,
109.2, 81.1, 77.8, 70.1, 66.8, 66.3, 63.0, 56.4, 54.6, 42.0, 40.8, 40.1,
38.8, 38.6, 37.2, 35.3, 34.7, 32.4, 32.1, 31.8, 30.6, 29.3, 28.1, 21.1,
17.3, 16.7, 15.0, 12.9.
(25R)-5a-Spirostan-2-ene (11)
An ice-cold solution of 9 (10.2 g, 24.5 mmol) in anhyd pyridine (90
mL) was treated in portions with p-toluenesulfonyl chloride (14.0 g,
73.5 mmol) and then permitted to stir overnight at r.t. The solution
was concentrated to afford a residue, which was dissolved in EtOAc
(350 mL) and then washed successively with 5% HCl (3 × 70 mL),
aq sat. NaHCO3 solution (3 × 70 mL) and brine (70 mL). The organ-
ic layer was dried (Na2SO4) and then filtered and concentrated. The
residue was loaded onto a silica gel column with CHCl3–PE (1:5),
and was eluted after 48 h (1:5 to 1:3 CHCl3–PE) to afford 11 as a
white solid (7.12 g, 73%); mp 171.0–173.0 °C; Rf 0.56 (1:20
EtOAc–PE); [a]D20 –32.2 (c = 0.20, CHCl3).
ESI-HRMS: m/z calcd for [M + H]+ C34H51O4: 523.3787; found:
523.3787.
(25R)-5a-Spirostan-2a-O-benzyloxy-3b-ol (15)
A solution of 13 (8.46 g, 15.3 mmol) in CH2Cl2 (140 mL) was added
to Dess–Martin periodinane reagent (24.0 g, 56.6 mmol). After stir-
ring at r.t. for 12 h, the solution was washed with aq NaHCO3–10%
Na2S2O3 (3 × 30 mL), 5% HCl (80 mL), and brine (80 mL). The or-
ganic layer was dried (Na2SO4), filtered and concentrated to afford
the corresponding crude 3-ketone 14, which was directly subjected
to the next reaction. Part of the crude product was purified by a sil-
ica gel column chromatography (1:10 EtOAc–PE) to afford pure 14
for analysis.
1H NMR (CDCl3): d = 5.59 (m, 2 H, H-2, H-3), 4.39 (q, J = 7.4 Hz,
1 H, H-16), 3.47 (ddd, J = 1.9, 4.0, 10.6 Hz, 1 H, H-26), 3.38 (t,
J = 10.6 Hz, 1 H, H-26), 2.01–0.69 (m, 26 H), 0.96 (d, J = 7.0 Hz,
3 H, H-21), 0.80–0.77 (m, 9 H, H-18, H-19, H-27).
13C NMR (CDCl3): d = 125.8 (2 C, C-2, C-3), 109.2 (C-22), 80.8
(C-16), 66.8 (C-26), 62.2 (C-17), 56.3 (C-14), 54.0 (C-9), 41.6 (C-
20), 41.4 (C-5), 40.4 (C-13), 40.0 (C-12), 39.7 (C-1), 35.2 (C-8),
34.7 (C-10), 32.0, 31.7, 31.4, 30.3 (2 C, C-4, C-25), 28.8, 28.6, 20.7
(C-11), 17.1 (C-27), 16.4 (C-18), 14.5 (C-21), 11.7 (C-19).
14
ESI-HRMS: m/z calcd for [M + H]+ C27H43O2: 399.3263; found:
399.3265.
Rf 0.29 (1:6 EtOAc–PE); [a]D20 –9.1 (c = 0.20, CHCl3).
1H NMR (CDCl3): d = 7.38–7.26 (m, 5 H, ArH), 4.88 (d, J = 11.5
Hz, 1 H, CH2Ph), 4.48 (d, J = 11.9 Hz, 1 H, CH2Ph), 4.39 (q,
J = 7.4 Hz, 1 H, H-16), 4.03 (dd, J = 6.8, 12.4 Hz, 1 H, H-2), 3.47
(ddd, 1 H, J = 2.3, 4.1, 10.6 Hz, H-26), 3.36 (t, J = 11.0 Hz, 1 H, H-
26), 2.37–2.30 (m, 2 H), 2.16 (dd, J = 3.2, 13.7 Hz, 1 H), 1.04 (s, 3
H), 0.96 (d, J = 6.8 Hz, 3 H), 0.79 (d, J = 6.4 Hz, 3 H), 0.78 (s, 3 H).
13C NMR (CDCl3): d = 209.0 (C=O), 138.0, 128.4 (2 C), 127.7 (3
C), 109.2, 80.7, 79.2, 72.1, 66.8, 62.1, 55.8, 53.8, 48.1, 46.7, 44.1,
41.6, 40.6, 39.7, 37.2, 34.3, 31.7, 31.3, 30.3, 28.8, 28.3, 21.4, 17.1,
16.4, 14.5, 13.0.
(25R)-5a-Spirostan-2a,3a-diol (12)
A solution of 11 (10.5 g, 26.0 mmol) in THF (20 mL) was added
dropwise to a solution of OsO4 (catalyst) in tert-butyl alcohol–
THF–H2O (10:8:1, 190 mL) containing NMO (N-methylmorpho-
line N-oxide, 10.67 g, 79.0 mmol). After stirring the mixture at r.t.
for 2 h, aq sat. NaHS solution (60 mL) was added, and stirring con-
tinued for 30 min. The resulting mixture was extracted with CH2Cl2
(3 × 250 mL). The organic layer was washed with water (3 × 100
mL) and brine (100 mL), and dried (Na2SO4) and then filtered and
concentrated. The residue was applied to a silica gel column chro-
matography (1:3 EtOAc–PE) to afford 12 (8.37 g, 74%) as a white
solid; Rf 0.23 (1:2 EtOAc–PE); [a]D20 –61.2 (c = 0.20, CHCl3).
ESI-HRMS: m/z calcd for [M + H]+ C34H49O4: 521.3631; found:
521.3616.
1H NMR (CDCl3): d = 4.39 (q, J = 7.7 Hz, 1 H, H-16), 3.96 (br s, 1
H, H-3), 3.76 (br d, J = 11.3 Hz, 1 H, H-2), 3.47 (ddd, J = 1.5, 3.7,
11.0 Hz, 1 H, H-26), 3.37 (t, J = 11.0 Hz, 1 H, H-26), 0.96 (d,
To a solution of the crude 14 in THF–MeOH (10:4, 140 mL) con-
taining CeCl3·7H2O (2.0 g) at –40 °C was added a solution of
NaBH4 (2.0 g) in MeOH (10 mL) dropwise. After stirring at –40 °C
for 2 h, the resulting mixture was concentrated and then dissolved
Synthesis 2006, No. 5, 775–782 © Thieme Stuttgart · New York

PAPER
Gitogenin 3b-O-[2-O-(a-L-Rhamnopyranosyl)-b-D-galactopyranoside]
779
in CH2Cl2 (350 mL). The solution was then washed with 5% HCl
(2 × 70 mL), aq sat NaHCO3 solution (70 mL), and brine (70 mL).
The organic layer was dried (Na2SO4) then filtered and concentrat-
ed. The residue was applied to a silica gel column chromatography
(1:12 to 1:5 EtOAc–PE) to afford 15 (4.61 g, 55%) and 13 (2.37 g,
28%) as white solids.
J = 8.4, 9.9 Hz, 1 H, H-2¢), 3.91 (t, J = 7.0 Hz, 1 H, H-5¢), 3.85 (m,
1 H), 3.56 (m, 1 H), 3.48 (m, 1 H), 3.37 (t, J = 11.0 Hz, 1 H, H-26),
3.06 (br s, 1 H, OH), 2.48 (br s, 1 H, OH), 0.97 (d, J = 7.0 Hz, 3 H),
0.81 (s, 3 H), 0.79 (d, J = 6.2 Hz, 3 H), 0.76 (s, 3 H).
ESI-HRMS: m/z calcd for [M + Na]+ C54H68O11Na: 915.4659;
found: 915.4654.
15
Gitotenin 2a-O-Benzyl-3b-O-[2-O-(2,3,4-tri-O-benzoyl-a-L-
rhamnopyranosyl)-3,6-di -O-benzoyl-b-D-galactopyranoside]
(21) and Gitotenin 2a-O-Benzyl-3b-O-[2,4 -di-O-(2,3,4-tri-O-
benzoyl-a-L-rhamnopyranosyl)-3,6-di-O-benzoyl-b-D-galacto-
pyranoside] (22)
To a mixture of 19 (1.22 g, 1.37 mmol), 20 (813 mg, 1.51 mmol),
and powdered 4Å molecular sieves in anhyd CH2Cl2 (60 mL) at –40
°C was added a solution of AgOTf (422 mg, 1.64 mmol) in toluene
(5 mL). After stirring at –40 °C for 0.5 h and then at 0 °C for 1 h,
the reaction was quenched with Et3N. The solid was then filtered
off, and the filtrate was concentrated under vacuum to give a yellow
oil which was subjected to silica gel column chromatography (1:20
EtOAc–toluene) to give 21 (1.14 g, 62%) and 22 (0.41 g, 17%) as
white solids.
Carbonization point 290 °C; Rf 0.19 (1:6 EtOAc–PE); [a]D20 –96.0
(c = 0.40, CHCl3).
1H NMR (pyridine-d5): d = 7.58–7.28 (m, 5 H, ArH), 6.22 (br s, 1
H), 4.92 (d, J = 11.8 Hz, 1 H, CH2Ph), 4.90 (d, J = 11.8 Hz, 1 H,
CH2Ph), 4.56 (q, J = 7.7 Hz, 1 H, H-16), 3.94–3.89 (m, 1 H, H-3),
3.72–3.68 (m, 1 H, H-2), 3.58 (br d, 1 H, J = 10.3 Hz, H-26), 3.49
(t, J = 10.6 Hz, 1 H, H-26), 1.12 (d, J = 6.9 Hz, 3 H), 0.84 (s, 3 H),
0.82 (s, 3 H), 0.68 (d, J = 5.5 Hz, 3 H).
13C NMR (pyridine-d5): d = 140.5, 128.6 (2 C), 128.1 (2 C), 127.5,
109.2, 81.7, 81.1, 75.0, 72.0, 66.9, 63.0, 56.4, 54.5, 44.8, 43.0, 42.0,
40.8, 40.2, 37.4 (2 C), 34.7, 32.4, 32.2, 31.8, 30.6, 29.3, 28.3, 21.5,
17.3, 16.7, 15.0, 13.5.
ESI-HRMS: m/z calcd for [M + Na]+ C34H50O4Na: 545.3607; found:
545.3610.
21
20
Mp 183–185.5 °C; Rf 0.24 (1:20 EtOAc–toluene); [a]D +41.5
(c = 0.40, CHCl3).
Gitotenin 2a-O-Benzyl-3b-O-(2,3,4,6-tetra-O-benzoyl-b-D-
galactopyranoside) (17)
1H NMR(CDCl3): d = 8.04–7.05 (m, 30 H, ArH), 5.76 (dd, J = 3.7,
10.3 Hz, 1 H, Rha-3), 5.60 (t, J = 10.3 Hz, 1 H, Rha-4), 5.48 (dd,
J = 1.4, 3.3 Hz, 1 H, Rha-2), 5.32 (d, J = 1.4 Hz, 1 H, Rha-1), 5.30
(dd, J = 3.3, 9.9 Hz, 1 H, H-3¢), 4.93 (d, J = 11.0 Hz, 1 H, CH2Ph),
4.83 (d, 1 H, J = 7.3 Hz, H-1¢), 4.70–4.63 (m, 3 H, Rha-5, H-6¢,
CH2Ph), 4.45 (dd, J = 5.5, 11.4 Hz, 1 H, H-6¢), 4.41 (q, J = 7.0 Hz,
1 H, H-16), 4.29 (dd, J = 7.7, 9.9 Hz, 1 H, H-2¢), 4.25 (d, J = 2.9
Hz, 1 H, H-4¢), 3.96 (ddd, J = 5.9, 9.2, 14.7 Hz, 1 H), 3.93 (t, J = 6.6
Hz, 1 H), 3.56 (ddd, 1 H, J = 5.2, 9.2, 13.9 Hz), 3.48 (ddd, J = 2.0,
4.2, 10.6 Hz, 1 H, H-26), 3.38 (t, J = 11.0 Hz, 1 H, H-26), 1.34 (d,
J = 6.2 Hz, 3 H, Rha-CH3), 0.96 (d, J = 7.0 Hz, 3 H), 0.79 (d,
J = 6.2 Hz, 3 H), 0.73 (s, 3 H), 0.70 (s, 3 H).
13C NMR (CDCl3): d = 166.5. 165.8, 165.6, 165.2, 164.8, 139.3,
133.3–133.0, 129.8–127.3, 109.2, 98.7 (C-1¢), 98.1 (Rha-1), 81.1,
80.8, 78.0, 76.7 (C-3¢), 73.9 (C-2¢), 72.7, 71.9, 71.7 (C-5¢, Rha-4),
70.9 (Rha-2), 69.5 (Rha-3), 67.0, 66.8 (C-4¢, C-26), 62.1 (2 C), 56.0,
54.1, 43.9, 43.5, 41.6, 40.5, 39.8, 36.7, 34.4, 32.8, 32.0, 31.9, 31.8,
31.4, 30.3, 29.7, 29.4, 28.8, 28.0, 22.7, 21.1, 19.2, 17.6, 17.1, 16.4,
14.5, 14.1, 13.1.
To a mixture of 15 (1.80 g, 3.44 mmol), 16 (3.82 g, 5.16 mmol) and
powdered 4Å molecular sieves in anhyd CH2Cl2 (70 mL) at 0 °C
was added TMSOTf (59 mL, 0.34 mmol). After stirring at 0 °C for
0.5 h and then at r.t. for 0.5 h, the reaction was quenched with Et3N.
The solid was then filtered off. The filtrate was concentrated and pu-
rified by silica gel column chromatography (1:10:2 EtOAc–PE–
CHCl3) to give 17 (quant.) as a white solid; mp 211–212.5 °C;
Rf 0.21 (1:5 EtOAc–PE); [a]D20 +11.8 (c = 0.20, CHCl3).
1H NMR (CDCl3): d = 8.04–7.19 (m, 25 H, ArH), 5.97 (d, J = 2.3
Hz, 1 H, H-4¢), 5.79 (dd, J = 8.2, 10.5 Hz, 1 H, H-2¢), 5.58 (dd,
J = 3.7, 10.6 Hz, 1 H, H-3¢), 5.06 (d, 1 H, J = 8.2 Hz, H-1¢), 4.93 (d,
J = 11.5 Hz, 1 H, CH2Ph), 4.67 (d, J = 11.5 Hz, 1 H, CH2Ph), 4.57
(dd, J = 6.0, 11.0 Hz, 1 H, H-6¢), 4.39–4.34 (m, 2 H, H-16, H-6¢),
4.22–4.20 (m, 1 H, H-5¢), 3.76–3.80 (m, 1 H, H-3), 3.53–3.56 (m, 1
H, H-2), 3.46 (ddd, J = 1.9, 3.7, 10.6 Hz, 1 H, H-26), 3.36 (t,
J = 11.0 Hz, 1 H, H-26), 0.95 (d, J = 6.8 Hz, 3 H), 0.78 (d, J = 6.4
Hz, 3 H), 0.72 (s, 3 H), 0.70 (s, 3 H).
ESI-HRMS: m/z calcd for [M + H]+ C68H77O13: 1101.5364; found:
1101.5378.
22
20
Gitotenin 2a-O-Benzyl-3b-O-(3,6-di-O-benzoyl-b-D-galactopy-
ranoside) (19)
Mp 106.0–108.0 °C; Rf 0.43 (1:20 EtOAc–toluene); [a]D +68.7
(c = 0.32, CHCl3).
Compound 17 was dissolved in MeOH–CHCl3 (1:1, 80 mL), and
then NaOMe (catalyst) was added. After stirring at r.t. for 2 h, the
resulting solution was neutralized with ion-exchange resin (H+), and
then filtered and concentrated. The residue was purified by silica gel
column chromatography (30:1 to 6:1 CHCl3–MeOH) to afford the
corresponding gitotenin 2a-O-benzyl-3b-O-(b-D-galactopyrano-
side) (18) as a white solid (2.34 g, 99%); Rf 0.38 (10:1 CHCl3–
MeOH). To a stirred solution of 18 (2.00 g, 2.92 mmol) and 1-
BBTZ (2.80 g, 11.68 mmol) in CH2Cl2 (60 mL) was added Et3N
(2.42 mL, 17.25 mmol). The mixture was stirred at r.t. for 12 h. Re-
moval of the solvent afforded a residue, which was subjected to sil-
ica gel column chromatography (1:5:2 EtOAc–PE–CHCl3) to give
19 (1.78 g, 68%) as a white solid; mp 162.0–163.0 °C; Rf 0.23 (1:3
EtOAc–PE); [a]D20 –47.1 (c = 0.36, CHCl3).
1H NMR (CDCl3): d = 8.05–7.04 (m, 45 H, ArH), 5.89 (dd, J = 1.1,
2.9 Hz, 1 H, H-3¢), 5.81 (dd, J = 9.9, 12.3 Hz, 1 H, Rha-3), 5.79 (dd,
J = 3.3, 10.3 Hz, 1 H, Rha-3), 5.60 (t, J = 10.3 Hz, 1 H, Rha-4),
5.55 (t, J = 9.8 Hz, 1 H, Rha-4), 5.49 (m, 2 H, 2 × Rha-2), 5.39 (d,
1 H, J = <1 Hz, Rha-1), 5.18 (d, 1 H, J = <1 Hz, Rha-1), 5.07 (d,
J = 11.7 Hz, 1 H, CH2Ph), 4.92 (d, J = 7.7 Hz, 1 H, H-1¢), 4.80 (d,
J = 11.7 Hz, 1 H, CH2Ph), 4.73 (m, 1 H, Rha-5), 4.63 (dd, J = 5.5,
11.0 Hz, 1 H), 4.53 (dd, J = 8.4, 11.0 Hz, 1 H), 4.49 (d, J = 2.6 Hz,
1 H), 4.46 (dd, J = 2.6, 10.3 Hz, 1 H), 4.42 (q, J = 7.3 Hz, 1 H), 4.24
(m, 1 H, Rha-5), 4.02 (m, 2 H), 3.64 (ddd, J = 5.1, 8.8, 13.6 Hz, 1
H), 3.49 (m, 1 H, H-26), 3.39 (t, J = 11.0 Hz, 1 H, H-26), 1.38 (d,
J = 6.2 Hz, 3 H), 1.17 (d, J = 6.2 Hz, 3 H), 0.97 (d, J = 7.0 Hz, 3
H), 0.80 (d, J = 6.6 H z, 3 H), 0.74 (s, 3 H), 0.71 (s, 3 H).
13C NMR (CDCl3): d = 166.0, 165.8 (2 C), 165.7, 165.3, 165.0,
164.9, 164.6, 139.5, 133.2–132.8, 130.9, 129.8–128.1, 127.4,
127.1, 109.2, 99.5, 99.3, 98.3, 81.7, 80.8, 77.7, 76.6, 74.8, 74.0,
72.6, 72.1, 71.8, 71.5, 71.3, 70.6, 70.4, 69.9, 69.7, 68.1, 67.0, 66.9,
1H NMR (CDCl3): d = 8.09–7.22 (m, 15 H, ArH), 5.12 (dd, J = 3.3,
9.9 Hz,1 H, H-3¢), 4.69–4.63 (m, 3 H, CH2Ph, H-6¢), 4.62 (d, J = 7.7
Hz, 1 H, H-1¢), 4.45 (dd, J = 6.2, 11.3 Hz, 1 H, H-6¢), 4.40 (q,
J = 7.0 Hz, 1 H, H-16), 4.20 (d, J = 3.0 Hz, 1 H, H-4¢), 4.13 (dd,
Synthesis 2006, No. 5, 775–782 © Thieme Stuttgart · New York

780
Y. Li et al.
PAPER
62.4, 62.2, 56.0, 54.1, 44.0, 43.7, 41.6, 40.6, 39.8, 36.7, 34.5, 33.0,
32.0, 31.9, 31.8, 31.4, 30.3, 29.7, 29.6, 29.4, 28.8, 28.0, 27.7, 22.7,
21.1, 19.1, 17.5, 17.1, 16.4, 14.5, 14.1, 13.1.
1H NMR (CDCl3): d = 7.99–7.16 (m, 25 H, ArH), 5.87 (t, J = 9.7
Hz, 1 H, H-3¢), 5.71 (t, J = 9.6 Hz, 1 H, H-4¢), 5.54 (dd, J = 7.8, 9.7
Hz, 1 H, H-2¢), 5.05 (d, J = 7.8 Hz, 1 H, H-1¢), 4.88 (d, J = 11.5 Hz,
1 H, CH2Ph), 4.60 (d, J = 11.5 Hz, 1 H, CH2Ph), 4.53 (dd, J = 3.2,
12.4 Hz, 1 H, H-6¢), 4.42 (dd, J = 4.6, 12.4 Hz, 1 H, H-6¢), 4.37 (q,
J = 7.8 Hz, 1 H, H-16), 4.04 (m, 1 H), 3.73 (m, 1 H), 3.48 (m, 2 H),
3.36 (t, J = 11.0 Hz, 1 H, H-26), 0.95 (d, J = 6.9 Hz, 3 H), 0.79 (d,
J = 6.4 Hz, 3 H), 0.71 (s, 3 H), 0.66 (s, 3 H).
Gitogenin 3b-O-[2-O-(a-L-Rhamnopyranosyl)-b-D-galactopyra-
noside] (1)
A suspension of 21 (120 mg, 0.089 mmol) and Pd/C (10%, catalyst)
in CH2Cl2–MeOH (1:1, 16 mL) in the presence of AcOH (2 drops)
was stirred under 1 atm of H2 for 12 h, then filtered and concentrat-
ed. The residue was subjected to silica gel column chromatography
(1:4 to 1:2, EtOAc–PE) to give a white solid, which was dissolved
in MeOH–CHCl3 (1:1, 16 mL), and then NaOMe (100 mg) was add-
ed. After stirring at r.t. for 12 h, the solution was neutralized with
ion-exchange resin (H+), then filtered and concentrated. The residue
was purified by silica gel column chromatography (6:1 to 4:1
CHCl3–MeOH) to afford 1 as a white solid (50.2 mg, 76% for two
ESI-HRMS: m/z calcd for [M + Na]+ C68H76O13Na: 1123.5184;
found: 1123.5205.
Tigogenin 3b-O-(2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranoside)
(25)
A procedure similar to that described for the preparation of 17 was
employed for the preparation of 25 from tigogenin 9 (1.00 g, 2.4
mmol) and 2,3,4,6-tetra-O-benzoyl-b-D-glucopyranosyl trichloro-
acetimidate 23 (2.31 g, 3.12 mmol); yield: 2.32 g (97%); white sol-
id; Rf 0.32 (1:4 EtOAc–PE); [a]D20 +43.0 (c = 0.20, CHCl3).
1H NMR (CDCl3): d = 8.02–7.26 (m, 20 H, ArH), 5.89 (t, J = 9.5
Hz, 1 H), 5.62 (t, 1 H, J = 9.5 Hz), 5.49 (dd, 1 H, J = 7.7, 9.5 Hz),
4.94 (d, 1 H, J = 7.7 Hz, H-1¢), 4.60 (dd, J = 3.3, 12.1 Hz, 1 H), 4.52
(dd, J = 6.2, 12.1 Hz, 1 H), 4.38 (q, J = 7.0 Hz, 1 H, H-16), 4.16 (m,
1 H), 3.59 (m, 1 H, H-3), 3.47 (ddd, J = 1.8, 4.1, 10.6 Hz, 1 H, H-
26), 3.37 (t, J = 11.0 Hz, 1 H, H-26), 0.96 (d, J = 7.0 Hz, 3 H), 0.79
(d, J = 6.2 Hz, 3 H), 0.73 (s, 3 H), 0.69 (s, 3 H).
20
steps); mp 235.0–237.0 °C; Rf 0.35 (2:1 CHCl3–MeOH); [a]D
–67.2 (c = 0.10, 1:1 CHCl3–MeOH) {Lit.1[a]D –70, (c = 0.10, 1:1
CHCl3–MeOH)}.
1H NMR (pyridine-d5): d = 6.32 (s, 1 H, Rha-1), 5.03 (d, J = 7.8 Hz,
1 H, H-1¢), 4.87 (m, 1 H), 4.83 (dd, J = 1.9, 3.7 Hz, 1 H), 4.68 (dd,
J = 7.8, 9.6 Hz, 1 H), 4.63 (dd, J = 3.7, 9.6 Hz, 1 H), 4.53 (q,
J = 7.8 Hz, 1 H), 4.47 (m, 2 H), 4.39 (dd, J = 5.5, 11.0 Hz, 1 H),
4.29 (m, 2 H), 4.12 (m, 2 H), 3.90 (m, 1 H), 3.56 (dd, J = 11.0 Hz,
1 H, H-26), 3.48 (t, J = 10.6 Hz, 1 H, H-26), 1.59 (d, J = 6.4 Hz, 3
H), 1.11 (d, J = 6.9 Hz, 3 H), 0.88 (s, 3 H), 0.78 (s, 3 H), 0.67 (d,
J = 5.5 Hz, 3 H).
13C NMR (pyridine-d5): d = 109.2, 102.1, 101.6, 85.4, 81.1, 77.0,
76.6, 76.1, 74.1, 72.8, 72.5, 70.8, 70.6, 69.4, 66.8, 63.0, 62.2, 56.3,
54.3, 45.8, 44.6, 41.9, 40.7, 40.0, 36.8, 34.6, 33.6, 32.2, 32.1, 31.8,
30.6, 29.2, 28.1, 21.4, 18.5, 17.3, 16.6, 15.0, 13.5.
ESI-HRMS: m/z calcd for [M + H]+ C61H71O12: 995.4946; found:
995.4985.
Tigogenin 3b-O-(b-D-Glucopyranoside) (27)
A procedure similar to that for the preparation of 18 was used for
the preparation of 27 from 25 (1.67 g); yield: 879 mg (91%); white
20
ESI-HRMS: m/z calcd for [M + K]+ C39H64O13K: 779.3984; found:
779.3989.
solid; Rf 0.26 (8:1 CHCl3–MeOH); [a]D –70.1 (c = 0.28, 1:1
CHCl3–MeOH).
1H NMR (DMSO-d6): d = 4.90 (d, J = 4.7 Hz, 1 H, OH), 4.87 (d,
J = 5.1 Hz, 1 H, OH), 4.85 (d, J = 4.7 Hz, 1 H, OH), 4.44 (t, J = 5.9
Hz, 1 H, 6¢-OH), 4.26 (q, J = 7.3 Hz, 1 H, H-16), 4.21 (d, J = 8.0
Hz, 1 H, H-1¢), 3.64 (m, 1 H), 3.56 (m, 1 H), 3.42 (m, 2 H), 3.20 (t,
J = 11.0 Hz, 1 H), 3.11 (td, J = 4.4, 8.8 Hz, 1 H), 3.07–2.99 (m, 2
H), 2.88 (td, J = 4.8, 8.0 Hz, 1 H), 0.89 (d, J = 7.0 Hz, 3 H), 0.77 (s,
3 H), 0.73 (d, J = 6.2 Hz, 3 H), 0.71 (s, 3 H).
Gitogenin 3b-O-[2,4-Di-O-(a-L-rhamnopyranosyl)-b-D-galacto-
pyranoside] (2)
A procedure similar to that described for the preparation of 1 from
21 was employed for the preparation of 2 from 22 (230 mg); yield:
94 mg (83% for two steps); white solid; mp 191.0–194.0 °C; Rf 0.28
(2:1 CHCl3–MeOH); [a]D20 –80.6 (c = 0.20, 1:1 CHCl3–MeOH).
1H NMR (CD3OD): d = 5.25 (d, J = 1.8 Hz, 1 H, Rha-1), 5.15 (d,
J = 1.9 Hz, 1 H, Rha-1), 4.43 (d, J = 7.3 Hz, 1 H, H-1¢), 4.37 (q,
J = 7.3 Hz, 1 H, H-16), 4.11 (m, 1 H), 4.01 (dd, J = 1.4, 3.2 Hz, 1
H), 3.90 (m, 2 H), 3.77 (dd, J = 7.8, 11.0 Hz, 1 H), 3.75 (dd, J = 2.8,
9.6 Hz, 1 H), 3.69–3.57 (m, 6 H), 3.50 (ddd, J = 5.5, 9.2, 14.2 Hz,
1 H), 3.43 (ddd, J = 2.3, 4.1, 11.0 Hz, 1 H, H-26), 3.37 (td, J = 5.5,
9.6 Hz, 2 H), 3.34 (s, 1 H), 1.25 (d, J = 6.4 Hz, 3 H), 1.22 (d, J = 5.9
Hz, 3 H), 0.94 (d, J = 7.3 Hz, 3 H), 0.88 (s, 3 H), 0.78 (d, J = 6.4
Hz, 3 H), 0.78 (s, 3 H).
13C NMR (CD3OD): d = 110.5, 103.3, 102.6, 101.5, 85.0, 82.2,
77.2, 77.1, 76.8, 76.6, 73.9, 73.8, 72.4, 72.3, 72.2, 72.1, 71.6, 70.6,
69.8, 67.8, 63.8, 63.1, 57.4, 55.7, 46.1, 45.8, 42.9, 41.7, 41.1, 37.9,
35.8, 33.9, 33.3, 32.6, 32.4, 31.4, 29.9, 29.0, 22.3, 18.0, 17.9, 17.5,
17.0, 14.9, 13.7.
ESI-HRMS: m/z calcd for [M + H]+ C33H55O8: 579.3897; found:
579.3889.
Gitogenin 2a-O-Benzyl-3b-O-(3,6-di-O-benzoyl-b-D-glucopyra-
noside) (28)
Compound 26 (780 mg, 85%) was synthesized from 24 (1.48 g) by
a procedure similar to that used for 18.
26
Yield: 780 mg (85%); white solid; Rf 0.51 (8:1 CHCl3–MeOH);
[a]D20 –64.1 (c = 0.20, 1:1 CHCl3–MeOH).
ESI-HRMS: m/z calcd for [M + H]+ C40H61O9: 685.4316; found:
685.4320.
Then a procedure similar to that used in the preparation of 19 was
employed for the preparation of 28 from 26 (780 mg, 1.14 mmol).
ESI-HRMS: m/z calcd for [M + H]+ C45H75O17: 887.5004; found:
887.5017.
28
Gitogenin 2a-O-Benzyl-3b-O-(2,3,4,6-tetra-O-benzoyl-b-D-glu-
copyranoside) (24)
20
Yield: 556 mg (55%); white solid; Rf 0.20 (1:3 EtOAc–PE); [a]D
–38.1 (c = 0.19, CHCl3).
A procedure similar to that described for the preparation of 17 was
employed for the preparation of 24 from 2a-O-benzylgitotenin 15
(600 mg, 1.15 mmol) and 2,3,4,6-tetra-O-benzoyl-b-D-glucopyra-
nosyl trichloroacetimidate 23 (1.28 g, 1.725 mmol); yield: 1.27 g
(ca. 100%); white solid: Rf 0.21 (1: 5 EtOAc–PE); [a]D20 –14.6 (c =
0.20, CHCl3).
1H NMR (CDCl3): d = 8.08–7.20 (m, 15 H, ArH), 5.19 (t, J = 9.5
Hz, 1 H, H-3¢), 4.72 (dd, J = 5.9, 12.1 Hz, 1 H, H-6¢), 4.71 (d,
J = 11.3 Hz, 1 H, CH2Ph), 4.65 (d, J = 8.1 Hz, 1 H, H-1¢), 4.62 (d,
J = 11.3 Hz, 1 H, CH2Ph), 4.60 (dd, J = 2.2, 11.3 Hz, 1 H, H-6¢),
4.40 (q, J = 7.7 Hz, 1 H, H-16), 3.78 (m, 1 H), 3.74 (m, 2 H, H-2¢,
Synthesis 2006, No. 5, 775–782 © Thieme Stuttgart · New York

PAPER
Gitogenin 3b-O-[2-O-(a-L-Rhamnopyranosyl)-b-D-galactopyranoside]
781
H-4¢), 3.66 (ddd, J = 2.2, 4.0, 9.5 Hz, 1 H, H-5¢), 3.56 (m, 1 H), 3.48
(m, 1 H, H-26), 3.37 (t, J = 11.0 Hz, 1 H, H-26), 0.96 (d, J = 7.0 Hz,
3 H), 0.80 (s, 3 H), 0.80 (d, J = 6.6 Hz, 3 H), 0.75 (s, 3 H).
ESI-HRMS: m/z calcd for [M + H] + C54H69O11: 893.4840; found:
The above product (440 mg, 0.327 mmol) was dissolved in MeOH–
CHCl3 (1:1, 20 mL), and NaOMe (200 mg) was added. After stir-
ring at r.t. for 20 h, the solution was neutralized with ion-exchange
resin (H+), then filtered and concentrated. The residue was purified
by silica gel column chromatography (6:1 to 4:1 CHCl3–MeOH) to
afford 3.
893.4810.
Tigogenin 3b-O-(3,6-Di-O-benzoyl-b-D-glucopyranoside) (29)
Compound 29 was synthesized as a white solid from 27 (860 mg,
1.09 mmol) by a procedure similar to that used for 19; yield: 472 mg
(40%); Rf 0.14 (1:3 EtOAc–PE); [a]D20 –32.3 (c = 0.2, CHCl3).
1H NMR (DMSO-d6): d = 8.01–7.52 (m, 10 H, ArH), 5.58 (d,
J = 6.2 Hz, 1 H, OH), 5.34 (d, J = 5.5 Hz, 1 H, OH), 5.08 (t, J = 9.5
Hz, 1 H, H-3¢), 4.52 (dd, J = 2.2, 11.7 Hz, 1 H, H-6¢), 4.50 (d,
J = 8.1 Hz, 1 H, H-1¢), 4.43 (dd, J = 7.3, 11.7 Hz, 1 H, H-6¢), 4.27
(q, J = 7.0 Hz, 1 H, H-16), 3.72 (m, 1 H), 3.57–3.40 (m, 3 H), 3.31
(m, 1 H), 3.20 (t, J = 11.0 Hz, 1 H), 0.90 (d, J = 7.0 Hz, 3 H), 0.73
(d, J = 6.5 Hz, 3 H), 0.70 (s, 6 H).
3
Yield: 267 mg (92%); white solid; mp 232.4–232.5 °C; Rf 0.38 (3:1
CHCl3–MeOH); [a]D20 –84.9 (c = 0.20, 1:1 CHCl3–MeOH).
1H NMR (DMSO-d6): d = 5.02 (br s, 1 H, Rha-1), 4.98 (d, J = 7.0
Hz, 1 H, 3¢-OH), 4.78 (t, J = 5.5 Hz, 1 H, 6¢-OH), 4.73 (d, J = 4.4
Hz, 1 H, Rha-2-OH), 4.68 (d, J = 5.1 Hz, 1 H, Rha-4-OH), 4.66 (d,
J <1 Hz, 1 H, Rha-1), 4.64 (d, 1 H, J = 4.4 Hz, Rha-4-OH), 4.59 (d,
1 H, J = 4.4 Hz, Rha-2-OH), 4.52 (d, J = 5.8 Hz, 1 H, Rha-3-OH),
4.48 (d, J = 5.9 Hz, 1 H, Rha-3-OH), 4.40 (d, 1 H, J = 8.1 Hz, H-
1¢), 4.26 (q, 1 H, J = 7.0 Hz, H-16), 4.22 (d, 1 H, J = 3.3 Hz, 2-OH),
3.92–3.83 (m, 2 H, 2 × Rha-5), 3.69 (m, 1 H, Rha-2), 3.59 (m, 2 H,
Rha-2, H-6¢), 3.44–3.16 (m, 13 H), 1.10 (d, J = 6.2 Hz, 3 H), 1.08
(d, J = 6.2 Hz, 3 H), 0.89 (d, J = 7.0 Hz, 3 H), 0.77 (s, 3 H), 0.73 (d,
J = 6.6 Hz, 3 H), 0.71 (s, 3 H).
13C NMR (DMSO-d6): d = 108.4, 100.5 (2 C), 99.0, 83.1, 80.2,
77.3, 76.7, 75.9, 75.3, 71.9 (2 C), 70.7, 70.6 (2 C), 70.4, 69.3, 68.7,
68.0, 65.9, 61.9, 60.1, 55.5, 53.6, 54.3, 45.3, 43.8, 41.1, 40.1, 36.2,
33.9, 32.3, 31.7, 31.4, 30.9, 29.8, 28.5, 27.5, 20.7, 17.8, 17.7, 17.1,
16.2, 14.6, 12.9.
ESI-HRMS: m/z calcd for [M + H] + C47H63O10: 787.4421; found:
787.4427.
Gitogenin 3b-O-[2,4-Di-O-(a-L-rhamnopyranosyl)-b-D-gluco-
pyranoside] (3)
To a mixture of 28 (0.558 g, 0.625 mmol) and powdered 4Å molec-
ular sieves in anhyd CH2Cl2 (25 mL) at –30 °C was added BF3⋅OEt2
(97 mL, 0.747 mmol), followed by a solution of 30 (1.36 g, 3.12
mmol) in CH2Cl2 (5 mL). After stirring at –30 °C for 0.5 h and then
at 0 °C for 1 h, the reaction was quenched with Et3N. The solid was
filtered off, and the filtrate was concentrated under vacuum to give
a yellow oil. The oil was subjected to silica gel column chromatog-
raphy (1:3 to 1:2 EtOAc–PE) to afford the crude 31, which was di-
rectly subjected to the next reaction; R 0.26 (2:3 EtOAc–PE). A
suspension of the crude 31 and 10% Pd/C (catalyst) in CH2Cl2–
MeOH (1:1, 30 mL) was stirred in the presence of AcOH (2 drops)
under 1 atm of H2 for 12 h, then filtered and concentrated. The res-
idue was subjected to silica gel column chromatography (1:10
EtOAc–CHCl3 to 1:7 EtOAc–CHCl3) to give gitogenin 3b-O-[2,4-
di-O-(2,3,4-tri-O-acetyl-a-L-rhamnopyranosyl)-3,6-di-O-benzoyl-
b-D-glucopyranoside]; yield: 0.556 g (66%); white solid; Rf 0.12
(1:8 EtOAc–CHCl3); [a]D20 –50.4 (c = 0.30, CHCl3).
ESI-HRMS: m/z calcd for [M + K]+ C45H74O17K: 925.4563; found:
925.4532.
Tigogenin 3b-O-[2,4-Di-O-(a-L-rhamnopyranosyl)-b-D-gluco-
pyranoside] (4)
To a mixture of 29 (0.452 g, 0.574 mmol) and powdered 4Å molec-
ular sieves in anhyd CH2Cl2 (25 mL) at –30 °C was added TMSOTf
(23 mL, 0.132 mmol), followed by a solution of 30 (1.25 g, 2.87
mmol) in CH2Cl2 (5 mL). After stirring at –30 °C for 0.5 h and then
at 0 °C for 1 h, the reaction was quenched with Et3N. The solid was
filtered off, and the filtrate was concentrated under vacuum to give
a yellow oil. The oil was subjected to silica gel column chromatog-
raphy (1:3 to 1:2 EtOAc–PE) to afford the crude 32, which was di-
rectly subjected to the next reaction; Rf 0.26 (1:2 EtOAc–PE).
Compound 4 was synthesized as a white solid from 32 using a pro-
cedure similar to that used for 3. Compound 4; yield: 52% (for two
Gitogenin 3b-O-[2,4-Di-O-(2,3,4-tri-O-acetyl-a-L-rhamnopyra-
nosyl)-3,6-di-O-benzoyl-b-D-glucopyranoside]
1H NMR (CDCl3): d = 8.11–7.42 (m, 10 H, ArH), 5.62 (t, J = 9.2
Hz, 1 H, H-3¢), 5.16 (m, 3 H, 2 × Rha-3, Rha-2), 4.98 (m, 2 H, H-
6¢, Rha-2), 4.92–4.88 (m, 3 H, Rha-1, 2 × Rha-4), 4.78 (d, J = 1.1
Hz, 1 H, Rha-1), 4.64 (d, J = 7.7 Hz, 1 H, H-1¢), 4.44 (dd, J = 4.0,
12.4 Hz, 1 H, H-6¢), 4.40 (q, J = 7.3 Hz, 1 H, H-16), 4.32 (m, 1 H,
Rha-5), 3.99 (t, J = 9.5 Hz, 1 H, H-4¢), 3.87 (ddd, J = 2.2, 4.0, 9.8
Hz, 1 H, H-5¢), 3.79 (t, J = 8.8 Hz, 1 H, H-2¢), 3.72 (m, 1 H, Rha-
5), 3.62 (m, 1 H), 3.53 (br s, 1 H, OH), 3.47 (m, 2 H), 3.37 (t,
J = 11.0 Hz, 1 H, H-26), 2.03, 1.98, 1.96, 1.92, 1.88, 1.75 (s, 3 H
each, 6 × OCOCH3), 1.14 (d, J = 6.2 Hz, 3 H), 0.97 (d, J = 6.9 Hz,
3 H), 0.81 (s, 3 H), 0.79 (d, J = 6.6 Hz, 3 H), 0.75 (s, 3 H), 0.69 (d,
J = 6.2 Hz, 3 H).
steps); mp 228.3–229.4 °C; Rf 0.21 (8:1 CHCl3–MeOH); [a]D
–88.4 (c = 0.20, 1:1 CHCl3–MeOH);
20
1H NMR (DMSO-d6): d = 4.99 (s, 1 H, Rha-1), 4.92 (d, J = 6.6 Hz,
1 H, OH), 4.72 (t, J = 6.2 Hz, 1 H, 6¢-OH), 4.71 (d, J = 4.4 Hz, 1 H,
OH), 4.68 (s, 1 H, Rha-1), 4.66 (d, J = 5.2 Hz, 1 H), 4.64 (d, J = 4.4
Hz, 1 H), 4.58 (d, J = 4.4 Hz, 1 H), 4.51 (d, J = 5.9 Hz, 1 H), 4.48
(d, J = 5.9 Hz, 1 H), 4.39 (d, J = 7.7 Hz, 1 H, H-1¢), 4.26 (q, J = 7.0
Hz, 1 H, H-16), 3.96–3.16 (m, 17 H), 1.10 (d, J = 6.2 Hz, 3 H), 1.07
(d, J = 6.2 Hz, 3 H), 0.90 (d, J = 7.0 Hz, 3 H), 0.76 (s, 3 H), 0.73 (d,
J = 6.6 Hz, 3 H), 0.71 (s, 3 H).
13C NMR (pyridine-d5): d = 109.2, 102.9, 102.1, 99.8, 81.1, 78.6,
78.0, 77.9, 77.1, 77.0, 74.1, 73.9, 72.8, 72.7, 72.5 (2 C), 70.4, 69.5,
66.8, 63.0, 61.4, 56.4, 54.4, 44.5, 42.0, 40.8, 40.1, 37.2, 35.9, 35.2,
34.4, 32.4, 32.1, 31.8, 30.6, 29.9, 29.2, 28.9, 21.2, 18.6, 18.5, 17.3,
16.6, 15.0, 12.4.
13C NMR (CDCl3): d = 170.1, 169.9 (3 C), 169.6, 169.0, 165.8,
165.0, 133.4, 133.2, 130.1 (2 C), 130.0 (2 C), 129.6, 129.0, 128.4 (4
C), 109.3, 100.6, 99.1, 97.9, 86.9, 80.8, 76.7, 75.6, 73.5, 71.0, 70.5,
70.1, 70.0, 69.1, 68.6, 68.5, 67.6, 66.8, 66.5, 62.1, 62.0, 56.0, 54.1,
44.5, 44.3, 41.6, 40.6, 39.9, 36.6, 34.4, 33.4, 32.0, 31.7, 31.3, 30.3,
28.8, 27.8, 21.1, 20.8, 20.7, 20.6, 20.3, 17.1, 17.0, 16.9, 16.5, 14.5,
13.2.
ESI-HRMS: m/z [M + H]+ C45H75O16: 871.5055; found: 871.5028.
Acknowledgment
ESI-HRMS: m/z [M + H]+ C71H95O25: 1347.6162; found:
1347.6199.
This work was supported by the National Basic Research Program
of China (2003CB716400) and the Chinese Academy of Sciences
(KGCX2-SW-213-05).
Synthesis 2006, No. 5, 775–782 © Thieme Stuttgart · New York

782
Y. Li et al.
PAPER
(8) (a) Schröder, M. Chem. Rev. 1980, 80, 187. (b) Kametani,
T.; Katoh, T.; Fujio, J.; Nogiwa, I.; Tsubuki, M.; Honda, T.
J. Org. Chem. 1988, 53, 1982. (c) Kametani, T.; Katoh, T.;
Tsubuki, M.; Honda, T. J. Am. Chem. Soc. 1986, 108, 7055.
(d) Khripach, V. A.; Zhabinskii, V. N.; Antonchick, A. P.;
Konstantinova, O. V.; Schneider, B. Steroids 2002, 67,
1101.
(9) (a) David, S.; Hanessian, S. Tetrahedron 1985, 41, 643.
(b) Simas, A. B. C.; Pais, K. C.; Desilva, A. A. T. J. Org.
Chem. 2003, 68, 5426.
(10) (a) Ireland, R. E.; Liu, L. J. Org. Chem. 1993, 58, 2899.
(b) Boeckman, J. R. K.; Shao, P.; Mulins, J. J. Org. Synth.
1999, 77, 141.
(11) Molander, G. A. Chem. Rev. 1992, 92, 29.
(12) Deng, S.; Yu, B.; Xie, J.; Hui, Y. J. Org. Chem. 1999, 64,
7265.
(13) (a) Lu, J.; Chan, T. H. J. Org. Chem. 1998, 63, 6035.
(b) Kim, S.; Chang, H.; Kim, W. J. J. Org. Chem. 1985, 50,
1751.
(14) Du, Y.; Gu, G.; Wei, G.; Hua, Y.; Linhard, R. J. Org. Lett.
2003, 5, 3627.
(15) Li, B.; Yu, B.; Hui, Y.; Li, M.; Han, X.; Fung, K. P.
Carbohydr. Res. 2001, 331, 1.
References
(1) Mimaki, Y.; Kanmoto, T.; Kuroda, M.; Sashida, Y.; Satomi,
Y.; Nishino, A. Phytochemistry 1996, 42, 1065.
(2) Mimaki, Y.; Kuroda, M.; Kameyama, A.; Yokosuka, A.;
Sashida, Y. Phytochemistry 1998, 48, 1361.
(3) Yu, B.; Hui, Y. Chemical Synthesis of Bioactive Steroidal
Saponins, In Glycochemistry: Principles, Synthesis, and
Application; Wang, P. G.; Bertozzi, C. R., Eds.; Marcel
Dekker Inc: New York, 2001, 163–174.
(4) (a) Li, M.; Han, X.; Yu, B. Carbohydr. Res. 2003, 338, 117.
(b) Zhang, Y.; Li, Y.; Zhu, S.; Guan, H.; Lin, F.; Yu, B.
Carbohydr. Res. 2004, 339, 1753. (c) Zhang, Y.; Li, Y.;
Guo, T.; Guan, H.; Shi, J.; Yu, Q.; Yu, B. Carbohydr. Res.
2005, 340, 1453.
(5) (a) Nakamura, T.; Komori, C.; Lee, Y. Y.; Hashimoto, F.;
Yahara, S.; Nohara, T.; Ejima, A. Biol. Pharm. Bull. 1996,
19, 564. (b) Liu, M. J.; Wang, Z.; Ju, Y.; Zhou, J. B.; Wang,
Y.; Wong, R. N. S. Biol. Pharm. Bull. 2004, 27, 1059.
(6) Herran, J.; Rosenkranz, G.; Sondheimer, F. J. Am. Chem.
Soc. 1954, 76, 5531.
(7) Williams, J. R.; Gong, H.; Hoff, N.; Olubodun, O. I.; Carroll,
P. J. Org. Lett. 2004, 6, 269.
(16) Ikeda, T.; Tsumagari, H.; Okawa, M.; Nohara, T. Chem.
Pharm. Bull. 2004, 52, 142.
(17) Liu, X.; Cui, Y.; Yu, Q.; Yu, B. Phytochemistry 2005, 66,
1671.
Synthesis 2006, No. 5, 775–782 © Thieme Stuttgart · New York