Synthesis and evaluation of four hederagenin glycosides as α-glucosidase inhibitor

Article abstract of DOI:10.1002/hlca.201200128

The four hederagenin glycosides 1-4 were efficiently synthesized through one-pot sequential glycosylations with glycose 1-(trichloroacetimidate)s as donors, resulting in a significantly simplified synthetic procedure without isolation of glycosylation intermediates. The activity of the synthetic hederagenin glycosides 1-4 against α-glucosidase type IV was evaluated; hederagenin glycoside 4 containing an α-L-rhamnopyranosyl unit showed the best activity with an IC₅₀ value of 47.9 μM. Copyright

Full text of DOI:10.1002/hlca.201200128

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Helvetica Chimica Acta – Vol. 96 (2013)
Synthesis and Evaluation of Four Hederagenin Glycosides as a-Glucosidase
Inhibitor
by Qing-Chao Liu*a), Tian-Tian Guob), Shou-Dong Guoc), Wen-Hong Lia), Dong Lia)
a) Department of Pharmaceutical Engineering, Northwest University, Xiꢀan 710069, P. R. China
(fax: þ 86-29-88305682; e-mail: liuqc21@nwu.edu.cn)
b) Department of Chemical Medicine, Xiꢀan Institute for Food and Drug Control, Xiꢀan 710054,
P. R. China
c) Key Laboratory of Atherosclerosis of Shandong Provincial Universities, Institute of Atherosclerosis,
Taishan Medical University, Taian, 271000, P. R. China
The four hederagenin glycosides 1 – 4 were efficiently synthesized through one-pot sequential
glycosylations with glycose 1-(trichloroacetimidate)s as donors, resulting in a significantly simplified
synthetic procedure without isolation of glycosylation intermediates. The activity of the synthetic
hederagenin glycosides 1 – 4 against a-glucosidase type IV was evaluated; hederagenin glycoside 4
containing an a-l-rhamnopyranosyl unit showed the best activity with an IC50 value of 47.9 mm.
Introduction. – a-Glucosidase is a membrane-bound enzyme at the epithelium of
the small intestine, that cleaves glucose from disaccharides and oligosaccharides by
hydrolysis. a-Glucosidase inhibitors are a class of compounds that inhibit the
breakdown of oligo- and disaccharides from complex dietary carbohydrates, slow
down the absorption of absorbable monosaccharides available, and reduce the
postprandial insulin and glucose peak [1][2]. In fact, a-glucosidase inhibitors like
acarbose, voglibose, and miglitol effectively compensate for defective early-phase
insulin release by inhibiting postprandial absorption of monosaccharides, and have
been approached for clinical use of the management of type-2 diabetes [3 – 5].
Hederagenin saponins are largely represented in nature and possess many
biological activities such as hemolytic, antiviral, antimicrobial, fungicidal, molluscici-
dal, feeding deterrent, antimutagenic, or cytotoxic activity [6 – 19] (hederagenin ¼
(3b,4a)-3,23-dihydroxyolean-12-en-28-oic acid). However, few researchers focus on
the a-glucosidase activities of these hederagenin saponins. One of the reason is that the
extraction of this kind of saponins from natural sources can be long and tedious and
results in very small quantities of the desired saponin. Chemical synthesis and
modification is known to be a powerful tool for the preparation of novel compounds
with diverse structures for pharmacology studies and for the development of new
chemical entities. In fact, the synthesis of hederagenin glycosides has attracted some
attention [20 – 22]. Nevertheless, a more concise and efficient synthetic strategy
towards hederagenin saponins require further investigations. Based on our experience
in triterpenoid saponin synthesis [23 – 27], we developed a highly efficient synthesis of
the four hederagenin glycosides 1 – 4 (Fig.), which were subsequently evaluated for a-
glucosidase activity.
ꢁ 2013 Verlag Helvetica Chimica Acta AG, Zꢂrich

Helvetica Chimica Acta – Vol. 96 (2013)
143
Figure. Synhtesized hederagenin glycosides 1 – 4
Results and Discussion. – Construction of the glycosidic linkage with the aglycone is
critical and difficult in the synthesis of saponins. Fortunately, the development of
glycosylation procedures by one-pot protocols has made the synthesis of oligosacchar-
ides and glycoconjugates bearing a complicated sugar moiety available or even easier
[28 – 40]. Recently, by applying the ꢃone-pot sequential glycosylationꢀ procedure, we
have successfully completed the synthesis of several bidesmosidic oleanolic acid
saponins [23 – 25][27]. Encouraged by these accomplishments, we decided to adopt this
strategy with two glycose 1-(trichloroacetimidate)s as donors to achieve the synthesis
of the hederagenin glycosides 1 – 4. Such an approach would allow us to rapidly access a
variety of structural analogs of hederagenin glycosides.
As shown in Scheme 1, hederagenin acceptor 6 was easily prepared in 71% yield
from hederagenin (5), triphenylmethyl chloride (TrCl), and 1,8-diazabicyclo[5.4.0]un-
dec-7-ene (DBU) in refluxing tetrahedrofuran (THF), and then benzoyl chloride
(BzCl) in pyridine at 08 [40]. Monosaccharide 1-(trichloroacetimidate) donors 7 – 10
were synthesized in a straightforward manner. Firstly, commercial monosaccharides (d-
glucose, d-xylose, l-arabinose, and l-rhamnose (¼6-deoxy-l-mannose) were perben-
zoylated with BzCl in pyridine. Then regioselective removal of the benzoyl group at the
anomeric position with MeNH2 in MeOH, followed by treatment with trichloroace-
tonitrile (Cl3CCN) and DBU in dry CH2Cl2, afforded the corresponding imidates 7 – 10
in yields of 60 – 70% over three steps [26].
With hederagenin acceptor 6 and glycosyl donors 7 – 10 in hand, we then set about
assembling the target hederagenin glycosides 1 – 4 in a concise way a by one-pot
sequential glycosylation with two glycose 1-(trichloroacetimidate) donors (Scheme 2).
Thus, first the coupling of hederagenin acceptor 6 with monosaccharide donor 7, 8, 9, or
10 in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate
(Me3SiOSO2CF3; 0.3 equiv) at ꢀ 788 provided within 30 min the desired glycoside 11,
12, 13, or 14, which was then transformed into the key intermediate 11’, 12’, 13’, or 14’ by
warming to room temperature for 30 min. After addition of a CH2Cl2 solution of the
glucose 1-(trichloroacetmidate) 7 to the above mixture at 08, the desired product 15, 16,
17, or 18 was obtained. Removal of all protecting benzoyl groups with MeONa in
CH2Cl2/MeOH afforded the target hederagenin glycosides 1 – 4 in satisfactory yields.

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Helvetica Chimica Acta – Vol. 96 (2013)
Scheme 1
The activity of the synthetic hederagenin glycosides 1 – 4 against a-glucosidase type
IV was evaluated, and the results are summarized in the Table. The data indicate that
the synthetic hederagenin glycosides 1 – 4 were active. Among them, hederagenin
glycoside 4 containing the a-l-rhamnopyranosyl unit showed the best activity with a
IC50 value of 47.9 mm.
Table. a-Glucosidase Inhibition by the Synthetic Hederagenin Glycosides 1 – 4
1
2
3
4
Deoxynojirimycinb)
IC50 [mm]a)
87.5 ꢁ 3.5
98.3 ꢁ 1.9
78.2 ꢁ 6.3
47.9 ꢁ 2.6
342.1 ꢁ 8.9
a) The IC50 value was calculated from the dose-response curve of six concentrations of each test
compound in triplicate. b) Standard
Conclusions. – In summary, a highly concise and practical strategy was developed
for the synthesis of hederagenin glycosides 1 – 4. The key to this approach is the use of a

Helvetica Chimica Acta – Vol. 96 (2013)
145
Scheme 2
a) Me3SiOSO2CF3 (0.3 equiv.), CH2Cl2, 4 ꢄ molecular sieves, ꢀ 788, 30 min. b) R.t., 30 min. c) 7
(1.5 equiv.), Me3SiOSO2CF3 (0.1 equiv.), CH2Cl2, 4 ꢄ molecular sieves, 08, 30 min; 68% for 15 (3 steps),
62% for 16 (3 steps), 60% for 17 (3 steps), 64% for 18 (3 steps). d) MeONa, CH2Cl2/MeOH 1:2; 87%
for 1, 83% for 2, 89% for 3, 87% for 4.
one-pot sequential glycosylation, resulting in a significantly simplified synthetic
procedure without isolation of the glycosylation intermediates. The hederagenin
glycosides 1 – 4 were moderately active against a-glucosidase type IV. Further
investigations on the preparation and bioactivity evaluation of hederagenin glycosides
is currently under way in our research group.
This work was financially supported by the Scientific Research Foundation of Northwest University
(NG10003), the Postdoctoral Science Foundation of Northwest University (BSH11012), and the
Foundation of Shaanxi Educational Committee (11JK0676).
Experimental Part
General. Commercial reagents were used without further purification unless specified. Solvents were
dried and redistilled in the usual way prior to use. TLC: precoated silica gel 60 F254 plates (SiO2; E.
Merck). Flash column chromatography (FC): silica gel (SiO2; 200 – 300 mesh). Optical rotations:
1
PerkinꢀElmer-241-MC polarimeter. H- and 13C-NMR Spectra: Jeol-JNM-ECP-600 spectrometer; d in
ppm rel. to Me4Si as internal standard, J in Hz. MS: Q-TOF-Global mass spectrometer; in m/z.

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Helvetica Chimica Acta – Vol. 96 (2013)
Triphenylmethyl (3b,4a)-23-(Benzoyloxy)-3-hydroxyolean-12-en-28-oate (6). A soln. of hederagenin
(5; 500 mg, 1.06 mmol), TrCl (363 mg, 1.27 mmol), and DBU (0.26 ml, 1.70 mmol) in dry THF (15 ml)
was refluxed for 10 h. The solvent was evaporated and the residue dissolved in pyridine (8 ml) and
CH2Cl2 (12 ml), and then benzoyl chloride (0.17 ml, 1.48 mmol) was slowly added at 08. After stirring for
1 h, the reaction was quenched by addition of MeOH, the mixture concentrated, the residue taken up
with CH2Cl2, the CH2Cl2 phase washed with H2O and brine, dried (Na2SO4), and concentrated, and the
27
residue purified by CC SiO2, petroleum ether/AcOEt 12 :1: 6 (616 mg, 71%). White solid. [a]D ¼ þ16.7
(c ¼ 0.85, CHCl3). 1H-NMR (CDCl3, 600 MHz): 7.27 – 8.03 (m, 20 arom. H); 5.32 (t, J ¼ 3.3, HꢀC(12));
4.53 (d, J ¼ 11.3, 1 H, CH2(23)); 4.03 (d, J ¼ 11.3, 1 H, CH2(23)); 3.49 (dd, J ¼ 13.7, 4.4, HꢀC(3)); 2.89 (dd,
J ¼ 13.5, 4.0, HꢀC(18)); 1.13, 0.99, 0.95, 0.90, 0.83, 0.74 (s each, 3 H each, 6 Me). 13C-NMR (CDCl3,
150 MHz): 179.1 (C(28)); 166.8; 143.7 (C(13)); 137.7; 137.5; 136.5; 132.4; 130.1; 129.6; 129.1; 128.4; 122.3
(C(12)); 72.5 (C(3)); 66.8 (C(23)); 48.3; 47.9; 46.9; 42.4; 41.5; 39.2; 38.4; 36.9; 33.1; 31.8; 27.8; 26.7; 25.8;
24.3; 23.3; 17.9; 17.1; 15.7; 12.1. HR-ESI-MS: 841.4831 ([M þ Na]þ, C56H66NaO5þ ; calc. 841.4803).
Compounds 15 – 18: Typical Procedure. A mixture of 6 (100 mg, 0.11 mmol), trichloroacetimidate 7,
8, 9, or 10 (0.14 mmol, 1.2 equiv.), and powdered 4-ꢄ molecular sieves in dry CH2Cl2 (5 ml) was stirred
for 30 min at r.t. and then cooled to 08. Me3SiOSO2CF3 (15 ml, 0.09 mmol, 0.3 equiv.) was added slowly at
ꢀ 788. After 30 min stirring at ꢀ 788, the mixture was warmed up to r.t. within 30 min, and then cooled
again to 08. A soln. of 7 (122 mg, 0.17 mmol, 1.5 equiv.) in dry CH2Cl2 (5 ml) was injected slowly. The
mixture was stirred at 08 for 30 min, and then warmed up to r.t. within another 30 min. The reaction was
quenched by addition of Et3N and then the mixture filtered. The filtrate was concentrated and purified by
a CC SiO2, petroleum ether/AcOEt) to afford the products 15 – 18.
2,3,4,6-Tetra-O-benzoyl-b-d-glucopyranosyl (3b,4a)-23-(Benzoyloxy)-3-[(2,3,4,6-tetra-O-benzoyl-b-
d-glucopyranosyl)oxy]okan-12-en-28-oate (15): Yield 68%. [a]2D3 ¼ þ20.6 (c ¼ 1.01, CHCl3). 1H-NMR
(CDCl3, 600 MHz): 7.31 – 8.05 (m, 45 arom. H); 5.97 (t, J ¼ 9.7, 1 H, HꢀC(3’’)); 5.93 (d, J ¼ 8.3, HꢀC(1’’));
5.91 (t, J ¼ 9.6, HꢀC(3’)); 5.57 – 5.71 (m, HꢀC(2’), HꢀC(2’’), HꢀC(4’), HꢀC(4’’)); 5.27 (t, J ¼ 3.1,
HꢀC(12)); 4.85 (d, J ¼ 7.9, HꢀC(1’)); 4.61 (dd, J ¼ 11.9, 3.2, 1 H, CH2(6’)); 4.57 (dd, J ¼ 11.9, 6.9, 1 H,
CH2(6’)); 4.51 (dd, J ¼ 11.5, 2.8, 1 H, CH2(6’’)); 4.47 (dd, J ¼ 11.5, 5.0, 1 H, CH2(6’’)); 4.35 (d, J ¼ 11.3, 1 H,
CH2(23)); 4.27 – 4.31 (m, 2 H, HꢀC(5’’), CH2(23)); 4.15 (m, HꢀC(5’)); 3.69 (dd, J ¼ 11.7, 3.7, HꢀC(3));
3.19 (dd, J ¼ 13.7, 4.0, HꢀC(18)); 1.07, 0.97, 0.95, 0.91, 0.77, 0.73 (s each, 3 H each, 6 Me). 13C-NMR
(CDCl3, 150 MHz): 177.3 (C(28)); 165.9; 165.7; 165.4; 163.9; 163.4; 143.7 (C(13)); 138.3; 138.1; 137.8;
137.5; 136.5; 136.1; 133.5; 133.1; 132.9; 129.8; 129.6; 128.5; 128.1; 122.4 (C(12)); 105.4 (C(1’)); 96.7
(C(1’’)); 89.3 (C(3)); 78.3; 77.5; 71.9; 70.5; 70.1; 67.1; 66.9; 66.2; 65.8; 62.6; 55.9; 47.9; 46.9; 41.7; 39.2; 36.7;
33.3; 31.9; 27.8; 26.7; 25.8; 24.6; 17.6; 17.1; 15.6. HR-MALDI-MS: 1755.6883 ([M þ Na]þ, C105H104NaO2þ3
;
calc. 1755.6862).
2,3,4,6-Tetra-O-benzoyl-b-d-glucopyranosyl (3b,4a)-23-(Benzoyloxy)-3-[(2,3,4-tri-O-benzoyl-b-d-
xylopyranosyl)oxy]olean-12-en-28-oate (16): Yield 62%. [a]2D3 ¼ þ23.1 (c ¼ 0.96, CHCl3). 1H-NMR
(CDCl3, 600 MHz): 7.33 – 8.03 (m, 40 arom. H); 5.97 (t, J ¼ 9.6, HꢀC(3’’)); 5.93 (d, J ¼ 8.7, HꢀC(1’’)); 5.78
(t, J ¼ 8.5, HꢀC(3’)); 5.71 – 5.74 (m, HꢀC(2’’), HꢀC(4’’)); 5.44 (dd, J ¼ 8.2, 6.4, HꢀC(2’)); 5.30 (dt, J ¼ 8.7,
4.6, HꢀC(4’)); 5.27 (t, J ¼ 3.7, HꢀC(12)); 4.81 (d, J ¼ 6.4, HꢀC(1’)); 4.53 (dd, J ¼ 11.5, 2.8, 1 H, CH2(6’’));
4.47 (dd, J ¼ 11.0, 5.0, 1 H, CH2(6’’)); 4.43 (dd, J ¼ 11.9, 4.6, 1 H, CH2(5’); 4.37 (d, J ¼ 11.5, 1 H, CH2(23));
4.29 (d, J ¼ 11.5, 1 H, CH2(23)); 4.26 (m, HꢀC(5’’)); 3.67 (dd, J ¼ 13.7, 3.7, HꢀC(3)); 3.61 (dd, J ¼ 11.9, 7.8,
1 H, CH2(5’)); 3.13 (dd, J ¼ 14.3, 4.0, HꢀC(18)); 1.05, 0.97, 0.94, 0.89, 0.76, 0.73 (s each, 3 H each, 6 Me).
13C-NMR (CDCl3, 150 MHz): 177.5 (C(28)); 165.9; 165.6; 165.3; 163.9; 163.2; 143.6 (C(13)); 138.7; 138.0;
137.6; 136.4; 136.1; 133.5; 132.7; 129.8; 129.5; 128.3; 128.1; 122.5 (C(12); 104.3 (C(1’)); 96.7 (C(1’’)); 89.5
(C(3)); 77.9; 77.1; 70.8; 70.5; 69.9; 67.1; 66.3; 65.7; 62.6; 56.0; 47.7; 46.5; 42.3; 39.1; 36.7; 33.5; 31.9; 27.8;
26.7; 25.9; 24.7; 17.6; 15.3. HR-MALDI-MS: 1621.6509 ([M þ Na]þ, C97H98NaO2þ1 ; calc. 1621.6493).
2,3,4,6-Tetra-O-benzoyl-b-d-glucopyranosyl (3b,4a)-23-Benzoyloxy)-3-[(2,3,4-tri-O-benzoyl-a-l-
1
arabinopyranosyl)oxy]olean-12-en-28-oate (17): Yield 60%. [a]2D3 ¼ þ30.6 (c ¼ 1.03, CHCl3). H-NMR
(CDCl3, 600 MHz): 7.25 – 8.07 (m, 40 arom. H); 5.96 (t, J ¼ 9.7, HꢀC(3’’)); 5.93 (d, J ¼ 8.3, HꢀC(1’’));
5.67 – 5.78 (m, HꢀC(2’), HꢀC(3’), HꢀC(2’’), HꢀC(4’’)); 5.58 (dd, J ¼ 8.8, 3.4, HꢀC(4’)); 5.27 (t, J ¼ 3.3,
HꢀC(12)); 4.76 (d, J ¼ 6.5, HꢀC(1’)); 4.43 – 4.56 (m, 3 H, CH2(5’), CH2(6’’), CH2(6’’)); 4.36 (d, J ¼ 11.7,
1 H, CH2(23)); 4.27 (m, HꢀC(5’’)); 4.23 (d, J ¼ 11.5, 1 H, CH2(23)); 3.85 (dd, J ¼ 11.6, 6.3, 1 H, CH2(5’));
3.61 (dd, J ¼ 14.3, 3.7, HꢀC(3)); 3.11 (dd, J ¼ 13.9, 4.1, HꢀC(18)); 1.01, 0.95, 0.93, 0.89, 0.75, 0.73 (s each,

Helvetica Chimica Acta – Vol. 96 (2013)
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3 H each, 6 Me). 13C-NMR (CDCl3, 150 MHz): 177.3 (C(28)); 165.7; 165.6; 165.3; 163.5; 162.9; 143.5
(C(13)); 137.9; 137.6; 137.1; 136.4; 136.0; 133.7; 132.9; 129.8; 129.3; 128.1; 127.9; 122.5 (C(12)); 103.7
(C(1’)); 96.5 (C(1’’)); 88.9 (C(3)); 78.1; 76.9; 70.3; 70.1; 69.3; 66.9; 66.3; 65.5; 61.9; 56.3; 47.9; 45.7; 43.7;
39.5; 36.7; 33.6; 31.9; 27.9; 25.6; 24.7; 17.3; 14.9. HR-MALDI-MS: 1621.6511 ([M þ Na]þ, C97H98NaO2þ1
;
calc. 1621.6491).
2,3,4,6-Tetra-O-benzoyl-b-d-glucopyranosyl (3b,4a)-2,3-(Benzoyloxy)-3-[(2,3,4-tri-O-benzoyl-6-de-
oxy-a-l-mannopyranosyl)oxy]olean-12-en-28-oate (18): Yield 64%. [a]2D3 ¼ þ16.9 (c ¼ 0.85, CHCl3).
1H-NMR (CDCl3, 600 MHz): 7.24 – 8.11 (m, 40 arom. H); 5.95 (t, J ¼ 9.7, 1 H, HꢀC(3’’)); 5.91 (d, J ¼ 8.5,
HꢀC(1’’)); 5.83 (dd, J ¼ 10.2, 3.3, HꢀC(3’)); 5.65 – 5.72 (m, HꢀC(2’), HꢀC(4’), HꢀC(4’’)); 5.56 (dd, J ¼
9.9, 8.0, HꢀC(2’’)); 5.26 (t, J ¼ 3.7, HꢀC(12)); 5.09 (d, J ¼ 1.3, HꢀC(1’)); 4.47 – 4.53 (m, 2 H, CH2(5’),
CH2(6’’)); 4.41 (dd, J ¼ 11.9, 5.1, 1 H, CH2(6’’)); 4.33 (d, J ¼ 11.5, 1 H, CH2(23)); 4.21 (d, J ¼ 11.5, 1 H,
CH2(23)); 4.19 (ddd, J ¼ 10.9, 5.4, 3.3, HꢀC(5’’)); 3.93 (m, 1 H, CH2(5’)); 3.63 (dd, J ¼ 14.5, 4.0, HꢀC(3));
3.15 (dd, J ¼ 13.7, 3.9, HꢀC(18)); 1.35 (d, J ¼ 6.2, Me(6’)); 1.03, 0.97, 0.95, 0.90, 0.75, 0.71 (s each, 3 H each,
6 Me). 13C-NMR (CDCl3, 150 MHz): 177.3 (C(28)); 166.1; 165.7; 165.4; 163.9; 163.1; 163.0; 143.3
(C(13)); 136.9; 136.7; 136.3; 136.0; 134.8; 133.7; 132.9; 129.6; 128.0; 127.5; 122.7 (C(12)); 98.1 (C(1’));
96.7 (C(1’’)); 88.7 (C(3)); 77.9; 76.7; 71.6; 69.7; 69.3; 66.5; 66.1; 63.2; 61.9; 56.7; 48.1; 45.7; 43.6; 39.5; 36.7;
33.7; 32.1; 27.9; 25.7; 23.8; 17.5; 15.1. HR-MALDI-MS: 1635.6671 ([M þ Na]þ, C98H100NaO2þ1 ; calc.
1635.6650).
Hederagenin Glycosides 1 – 4: Typical Procedure. To a soln. of one of the fully protected hederagenin
glycosides 15 – 18 (50 mg) in dry CH2Cl2/MeOH 1:2 (10 ml) was added a freshly prepared MeONa/
MeOH soln. (1.0 mol/l, 0.20 ml). The mixture was stirred at r.t. for 5 h and neutralized with Dowex Hþ
resin to pH 7 and then filtered. The filtrate was concentrated and the resulting residue subjected to CC
(SiO2): hederagenin glycosides 1 – 4 as white amorphous solids.
b-d-Glucopyranosyl (3b,4a)-3-b-d-Glucopyranosyloxy)olean-12-en-28-oate (1): Yield 87%. [a]D23
¼
þ13.9 (c ¼ 0.85, MeOH). 1H-NMR (C5D5N, 600 MHz): 6.34 (d, J ¼ 8.1, HꢀC(1’’)); 5.45 (t, J ¼ 3.8,
HꢀC(12)); 5.14 (d, J ¼ 7.7, HꢀC(1’)); 4.55 – 4.58 (m, HꢀC(3’), HꢀC(3’’)); 4.43 (m, HꢀC(2’), HꢀC(4’));
4.25 – 4.29 (m, 4 H, HꢀC(2’’), HꢀC(4’’), CH2(6’), CH2(6’’)); 4.23 (d, J ¼ 11.5, 1 H, CH2(23)); 4.01 – 4.07
(m, 4 H, HꢀC(5’), HꢀC(5’’), CH2(6’), CH2(6’’)); 3.73 (d, J ¼ 11.5, 1 H, CH2(23)); 3.63 (dd, J ¼ 11.5, 4.5,
HꢀC(3)); 3.21 (dd, J ¼ 13.8, 3.7, HꢀC(18)); 1.22, 1.13, 0.99, 0.94, 0.89, 0.87 (s each, 3 H each, 6 Me).
13C-NMR (C5D5N, 150 MHz): 176.4 (C(28)); 144.3 (C(13)); 123.1 (C(12)); 105.7 (C(1’)); 95.8 (C(1’’));
82.7 (C(3)); 79.3; 78.8; 78.6; 78.4; 76.0; 74.3; 71.8; 71.5; 65.3; 63.1; 62.6; 48.3; 48.1; 47.1; 46.5; 43.4; 42.3;
41.7; 40.0; 39.0; 37.2; 34.3; 33.4; 32.7; 30.9; 28.5; 26.3; 25.9; 24.1; 23.8; 18.5; 17.6; 16.3. HR-ESI-MS:
797.4701 ([M þ H]þ, C42H69O1þ4 ; calc. 797.4681).
b-d-Glucopyranosyl (3b,4a)-3-b-d-Xylopyranosyloxy)olean-12-en-28-oate (2): Yield 83%. [a]D23
¼
þ14.3 (c ¼ 0.71, MeOH). 1H-NMR (C5D5N, 600 MHz): 6.33 (d, J ¼ 8.3, HꢀC(1’’)); 5.41 (t, J ¼ 3.3,
HꢀC(12)); 4.86 (d, J ¼ 7.1, HꢀC(1’)); 4.49 – 4.57 (m, HꢀC(3’), HꢀC(3’’)); 4.38 – 4.43 (m, HꢀC(2’),
HꢀC(2’’), HꢀC(4’’), HꢀC(4’)); 4.25 – 4.29 (m, 3 H, CH2(5’), CH2(5’), CH2(6’’)); 4.21 (d, J ¼ 11.3, 1 H,
CH2(23)); 4.01 – 4.07 (m, 2 H, HꢀC(5’’), CH2(6’’)); 3.69 (d, J ¼ 11.3, 1 H, CH2(23)); 3.57 (dd, J ¼ 13.7, 4.0,
HꢀC(3)); 3.19 (dd, J ¼ 14.3, 3.7, HꢀC(18)); 1.20, 1.11, 0.99, 0.97, 0.91, 0.88 (s each, 3 H each, 6 Me).
13C-NMR (C5D5N, 150 MHz): 176.5 (C(28)); 144.5 (C(13)); 123.3 (C(12)); 106.3 (C(1’)); 95.6 (C(1’’));
82.3 (C(3)); 79.2; 75.0; 74.5; 73.1; 71.7; 69.9; 66.7; 64.7; 62.3; 48.5; 47.6; 43.7; 42.3; 41.9; 40.1; 39.0; 37.5;
34.6; 33.5; 32.7; 31.1; 28.5; 26.3; 26.0; 24.3; 23.7; 23.3; 18.4; 17.3; 16.1. HR-ESI-MS: 767.4593 ([M þ H]þ,
C41H67Oþ13 ; calc. 767.4574).
b-d-Glucopyranosyl (3b-4a)-(a-l-Arabinopyranosyloxy)olean-12-en-28-oate (3): Yield 89%.
[a]2D3 ¼ þ48.7 (c ¼ 0.85, MeOH). 1H-NMR (C5D5N, 600 MHz): 6.31 (d, J ¼ 7.6 Hz, HꢀC(1’’)); 5.43 (t,
J ¼ 3.3, HꢀC(12)); 4.99 (d, J ¼ 6.9, HꢀC(1’)); 4.59 (d, J ¼ 3.6, HꢀC(4’)); 4.42 – 4.52 (m, HꢀC(2’),
HꢀC(2’’), HꢀC(3’), HꢀC(3’’), HꢀC(4’’)); 4.25 – 4.37 (m, 3 H, CH2(5’), CH2(5’), CH2(6’’)); 4.23 (d, J ¼
11.5, 1 H, CH2(23)); 4.15 – 4.21 (m, 2 H, HꢀC(5’’), CH2(6’’)); 3.75 (d, J ¼ 11.3, 1 H, CH2(23)); 3.59 (dd,
J ¼ 11.7, 4.0, HꢀC(3)); 3.23 (dd, J ¼ 14.3, 3.7, HꢀC(18)); 1.20, 1.13, 0.98, 0.91, 0.90, 0.89 (s each, 3 H each, 6
Me). 13C-NMR (C5D5N, 150 MHz): 176.7 (C(28)); 144.2 (C(13)); 123.1 (C(12)); 106.7 (C(1’)); 95.8
(C(1’’)); 82.2 (C(3)); 79.3; 74.9; 74.3; 73.3; 71.4; 69.9; 66.7; 64.6; 62.4; 48.3; 47.6; 43.4; 42.2; 41.9; 40.2;
39.0; 37.2; 34.2; 33.4; 32.7; 30.9; 28.5; 26.3; 26.0; 24.1; 23.7; 23.5; 18.4; 17.6; 16.3. HR-ESI-MS: 767.4589
([M þ H]þ, C41H67O1þ3 ; calc. 767.4573).

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Helvetica Chimica Acta – Vol. 96 (2013)
b-d-Glucopyranosyl (3b,4a)-[(6-Deoxy-a-l-mannopyranosyl)oxy]olean-12-en-28-oate (4): Yield
87%. [a]2D3 ¼ þ15.7 (c ¼ 0.63, MeOH). 1H-NMR (CDCl3, 600 MHz): 6.32 (t, J ¼ 7.9, HꢀC(1’’)); 6.01
(br. s, HꢀC(1’)); 5.67 (t, J ¼ 9.3, HꢀC(4’’)); 5.53 (dd, J ¼ 9.7, 8.0, HꢀC(2’’)); 5.27 (t, J ¼ 3.7, HꢀC(12)); 5.03
(br. s, HꢀC(2’)); 4.45 – 4.56 (m, HꢀC(3’), HꢀC(4’), HꢀC(5’), CH2(6’’)); 4.39 (dd, J ¼ 12.3, 5.3, 1 H,
CH2(6’’)); 4.37 (d, J ¼ 11.3, 1 H, CH2(23)); 4.17 (d, J ¼ 11.3, 1 H, CH2(23)); 4.10 (m, HꢀC(5’’)); 3.67 (dd,
J ¼ 13.8, 4.1, HꢀC(3)); 3.19 (dd, J ¼ 14.1, 3.7, HꢀC(18)); 1.67 (d, J ¼ 5.9, Me(6’)); 1.19, 1.11, 0.99, 0.90,
0.88, 0.87 (s each, 3 H each, 6 Me). 13C-NMR (CDCl3, 150 MHz): 177.2 (C(28)); 165.9; 165.7; 165.3;
163.7; 163.1; 162.9; 143.5 (C(13)); 137.0; 136.7; 136.5; 136.1; 134.5; 133.7; 132.9; 129.3; 127.9; 127.6; 122.6
(C(12)); 103.1 (C(1’)); 96.6 (C(1’’)); 88.3 (C(3)); 78.0; 76.7; 71.9; 69.5; 69.1; 66.5; 66.0; 63.2; 61.5; 57.0;
48.1; 45.9; 43.5; 39.4; 36.5; 33.9; 32.8; 28.1; 25.3; 23.7; 17.5; 15.3. HR-ESI-MS: 7781.4751 ([M þ H]þ,
C42H69Oþ13 ; calc. 781.4733).
a-Glucosidase Inhibition. The inhibitory activity of all samples against a-glucosidase type VI (Sigma
G6136) was measured spectrophotometrically at pH 6.8 and at 378, with 0.7 mm 4-nitrophenyl a-d-
glucopyranoside (PNP-G) as a substrate and 0.017 units/ml of enzyme, in 50 mm sodium phosphate
buffer containing 100 mm NaCl. As a positive control, 1-deoxynojirimycin (0.3 mm) was used, for which
the same IC50 as given in [41] was determined. The increment in absorption at 400 nm due to the
hydrolysis of PNP-G by a-glucosidase was monitored continuously with the spectrophotometer.
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Received March 13, 2012