Synthesis and crystal structures of ring A modified glycyrrhetinic acid derivatives derived from 2,3-oxirane and 2,3-thiirane intermediates

Article abstract of DOI:10.1016/j.tet.2010.03.098

A general method for the introduction of thiol groups at positions 1, 2, and 3 of glycyrrhetinic acid has been developed starting from a protected 2α,3α-oxido-derivative. Conversion into the corresponding 2β,3β-epithio-derivative was followed by ring-opening leading to either 2- or 3-substituted thio derivatives. Conversely, 3α-configured allylic alcohol intermediates derived from the 2,3-epoxide provided efficient access to both diastereoisomeric 3-thio derivatives as well as 1α-thio derivatives. The stereochemistry of the newly formed stereogenic centers was rigorously proven using X-ray crystallography.

Full text of DOI:10.1016/j.tet.2010.03.098

Tetrahedron 66 (2010) 4390e4402
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and crystal structures of ring A modified glycyrrhetinic acid derivatives
derived from 2,3-oxirane and 2,3-thiirane intermediates
Hassan Amer a, Kurt Mereiter b, Christian Stanettya, Andreas Hofingera, Laszlo Czollner c, Igor Beseda c,
,
Ulrich Jordis c, Bernhard Kueenburg d, Dirk Claßen-Houben d, Paul Kosma a
*
a Department of Chemistry, University of Natural Resources and Applied Life Sciences, Muthgasse 18, A-1190 Vienna, Austria
b Institute of Chemical Technologies and Analytics, University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria
c Institute of Applied Synthetic Chemistry, University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria
d
€
Onepharm Research and Development GmbH, Veterinarplatz 1, A-1210 Austria
a r t i c l e i n f o
a b s t r a c t
Article history:
A general method for the introduction of thiol groups at positions 1, 2, and 3 of glycyrrhetinic acid has
Received 12 February 2010
Received in revised form 23 March 2010
Accepted 26 March 2010
been developed starting from a protected 2
,3 -epithio-derivative was followed by ring-opening leading to either 2- or 3-substituted thio de-
rivatives. Conversely, 3 -configured allylic alcohol intermediates derived from the 2,3-epoxide provided
efficient access to both diastereoisomeric 3-thio derivatives as well as 1 -thio derivatives. The stereo-
a,3a-oxido-derivative. Conversion into the corresponding
2b b
a
Available online 14 April 2010
a
chemistry of the newly formed stereogenic centers was rigorously proven using X-ray crystallography.
Keywords:
Ó 2010 Elsevier Ltd. All rights reserved.
Terpenoids
Glycyrrhetinic acid
Rearrangement
Thiirane
Oxirane
1. Introduction
of glycyrrhetinic acid modified at positions 1, 2, and 3 of ring A, to be
used as versatile educts for further modification by alkylation, acyl-
The major bioactive compounds extracted from licorice roots
(Glycyrrhizae glabra) are glycyrrhizin and its natural metabolite gly-
cyrrhetinic acid (GA), which have been used for a long time in tradi-
tional medicines for the treatment of allergic, pulmonary, and hepatic
ailments.1e4 The broad spectrum of activities comprises antiin-
flammatory, cytotoxic, antiulcer, antiproliferative, antioxidative, and
endocrine activities.5e9 GA as well as the hemisuccinate ester carbe-
ation as well as glycosylation protocols. The major approaches
described herein utilize the known 2,3-oxido derivative of GA as the
central intermediate as well as the novel 2b,3b-epithio compounds
followed by allylic rearrangement reactions and full deprotection.
2. Results and discussion
noxolone are potent inhibitors of 11b-hydroxysteroid dehydrogenase
The previously described20 diphenylmethyl ester derivative 1
was converted into the crystalline 3-O-p-toluenesulfonyl derivative
2 in 99% yield by reaction with p-toluenesulfonyl chloride in pyri-
dine. Subsequent elimination was effected by treatment of 2 with
tetrabutyl ammonium iodide in DMF at 100 ꢀC, which afforded the
2,3-diene derivative 3 as crystalline material in 91% yield. In addi-
tion, a small amount of the fully deprotected diene 4, formed
during the reaction, was isolated by silica gel chromatography. The
NMR spectral characteristics of 4 are consistent with previously
published data of the 2,3-dehydro methyl ester of glycyrrhetinic
acid and also agree with the data of the free acid derivative.17,21
Reaction of the diene derivative 3 with m-chloroperbenzoic acid
was performed in a multigram scale and furnished the crystalline
1 and 2.10e13 Numerous modifications in the ring skeleton of the
oleanolic acid backbone have been performed.14 With respect to ring
A modification, most approaches have focussed on the modification
of position 3 of GA by oxidation, followed by reductive amination, as
well on utilization of the 2,3-dehydro derivative.15e17 These studies
succeeded in introducing O-, N-, and C-linked appendices into ring
A as well as affording halide-substituted derivatives.5,6,18 Further-
more, sulfone and phosphonate moieties have been installed in
ring A of GA.19 Within the framework of ongoing studies aimed at
the development of selective inhibitors of 11b-hydroxysteroid
dehydrogenase 1 and 2 we have set out to synthesize thio derivatives
2
a a-oxido derivative 5 (Scheme 1). The crystal structure of the
,3
* Corresponding author. Tel.: þ43 147654 6055; fax: þ43 1 47654 6059; e-mail
address: paul.kosma@boku.ac.at (P. Kosma).
epoxide 5 (Fig. 1) unambiguously established the stereochemistry
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.03.098

H. Amer et al. / Tetrahedron 66 (2010) 4390e4402
4391
29
30
19
CO2CH(Ph)2
CO2R
CO2R
20
21
22
H
H
H
O
O
O
d)
b)
c)
18
15
12
26
17
16
11
25
13
14
28
9
1
4
10
8
2
3
O
27
5
7
6
CO2H
RO
23
24
H
1 R = H
2 R = Ts
5 R = CH(Ph)2
6 R = H
3 R = CH(Ph)2
4 R = H
a)
O
CO2R
CO2R
f)
h)
11
H
H
O
O
AcO
13
I
CO2H
CO2H
AcO
e)
R'O
H
H
e), h)
O
O
7 R = CH(Ph)2
8 R = H
9 R = CH(Ph)2, R' = Ac
OH
OH
g)
g)
f)
10 R = CH(Ph)2, R' = H
11 R = H, R' = Ac
12 R = R' = H
i)
14
Scheme 1. Synthesis of 5 and 6 and 1a- and 3a
-hydroxy derivatives. Reagents and conditions: (a) TsCl, Pyr., 0 ꢀC/rt, 15 h, 99%; (b) Bu4NI, NaI, DMF, 100 ꢀC, 15 h, 91% for 3, 4.8% for
15
4; (c) mCPBA, CH2Cl2, 4 ꢀC/8 ꢀC, 15 h, 73% for 5, 53.5% for 6; (d) Ph3P, I2, CH2Cl2, ꢁ30 ꢀC, 0.5 h, Ac2O, pyr., DMAP, rt, 15 h, 85% for 7; (e) anisole, TFA, CH2Cl2, 8 ꢀC, 15 h, 72.5% for 8; (f)
DBU, toluene, 100 ꢀC, 15 h, 83% for 9; DBU, MeCN, 80 ꢀC, 15 h, 72% for 11; (g) 1 M KOH, EtOH, rt, 15 h, 90% for 10, 87% for 12; (h) 0.1 M NaOMe, 4 h, rt, 82% for 14; (i) 10% PdeC, H2,
MeOH, rt, 15 h, 80% for 13, 85% for 15.
ꢀ
ꢀ
ꢀ
Figure 1. Crystal structure of epoxide 5. H-atoms omitted for clarity. C2eO1¼1.451(3) A, C3eO1¼1.437(3) A, C2eC3¼1.471(4) A.
at C-2 and C-3, thereby confirming the previously reported
A of glycyrrhetinic acid. Thus, the diphenylmethyl ester derivative 5
was reacted with triphenylphosphine and iodine in dichloro-
methane followed by acetylation with acetic anhydride/pyridine/
DMAP.22 The resulting acetylated iodohydrin 7 was isolated in 85%
yield and its crystal and molecular structure was determined. The
structure of 7 (Fig. 2) revealed the presence of a twist boat con-
formation for ring A, which was also reflected in a large value of the
coupling constant of J2,3 (12.6 Hz). Removal of the diphenylmethyl
ester group from 7 was accomplished using trifluoroacetic acid to
generate the benzylium cation, which was trapped by anisole to
afford the acid derivative 8, isolated by silica gel chromatography in
72.5% yield. The elimination reaction of 7 in the presence of 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU) afforded the 1,2-dehydro
derivative 9 in 83% yield. Removal of the 3-O-acetyl group under
alkaline conditions furnished the allylic alcohol 10 in 90% yield.
assignment of an epoxide generated from the methyl ester of
glycyrrhetinic acid.17 The NMR data of 5 also confirm the previous
assignments of 2
which had been based on B3LYP/631G
a
,3
a
- and 2
b
,3
b
-oxido triterpenoid derivatives,
*
//MMþ and DFT calcula-
tions.22 Since the 1H NMR chemical shift values as well as the ho-
monuclear coupling constants are similar for both configurations,
13C NMR chemical shift arguments had been employed to assign
the epoxide configuration. Indeed, the 13C NMR chemical shift
values for C-1 (
,3 -epoxide 5 were in very close agreement with the published
values for a related 2 ,3
-epoxide triterpene derivative.22 Using the
d 41.02), C-2 (d 52.51, Table 1) and C-5 (d 46.51) of the
2
a a
a
a
free acid derivative 4 in a similar reaction gave the epoxide
derivative 6 in 53.5% isolated yield. The epoxide 5 provided a ver-
satile starting material for numerous chemical modifications of ring

4392
H. Amer et al. / Tetrahedron 66 (2010) 4390e4402
Table 1
13C NMR data (ppm) of compounds 4e16a
Carbon atom
4
5
6
7
8
9
10
11
12
13
34.09
14
70.50
15
70.89
16
49.46
1
2
3
4
5
6
7
8
41.47
40.58
52.51
61.25
31.64b
46.51
17.78c
31.75b
44.99
60.27
35.82
40.62
52.69
61.40
31.85
46.63
17.88
31.85
45.22
60.41
35.95
54.63
29.23
77.28
39.16b
49.94
19.11
31.51c
45.17
62.63
39.67b
56.43
30.26
79.03
40.25
50.54
20.15
32.45
46.55
63.77
40.99
143.61
119.39
74.72
35.71
48.09b
16.65
31.09
45.51
57.85
37.42
199.68
128.10
169.42
43.94
26.42c
26.29c
32.83
48.38b
41.05
43.30
32.83
38.25
26.07c
23.37d
19.21
18.73
23.53d
28.24e
175.15
28.18e
142.29
123.27
73.40
37.39
47.63
16.87
32.98
45.44
58.17
38.39
199.77
128.08
169.42
43.91
26.44b
26.35b
31.06
48.15
41.08
43.26
31.16
36.74
26.49b
23.59c
18.64
19.24
23.63c
28.31d
175.12
28.24d
143.64
119.48
74.81
141.35
123.70
73.03
36.80
47.86
16.93
33.02
45.86
58.31
38.52
201.63
127.76
172.14
43.80b
26.55c
26.37c
31.91
47.86
41.23
43.68b
31.03
37.84
26.21c
23.50d
18.30
19.10
23.25d
28.16e
179.38
28.40e
121.95
136.99
34.36
51.79
18.67
31.86b
45.38
60.47
36.16
200.46
128.54
169.72
43.81c
26.44d
26.42d
30.86
48.21
40.92
43.35c
31.91b
37.72
32.01
23.05e
18.26
16.10
23.29e
28.46f
182.19
28.57f
22.72
78.03
36.66
49.68
17.27
32.58
45.64
61.61
37.03
200.59
128.44
169.42
43.78b
26.63c
26.46c
31.86
48.27
40.95
43.26b
30.91
37.71
28.44d
21.95
16.22
18.71
23.54
28.53d
181.42
27.98
124.62
141.25
35.60
45.47
19.57
32.57
46.10
53.09
41.80
203.10
129.11
172.89
44.89b
27.64c
27.45c
32.96
49.87
42.52
45.06b
32.00
39.05
31.63
23.31
17.10
19.16
23.77
29.28
180.37
28.77
24.67
34.07
31.92
47.22
17.22
32.83
45.10
53.32
41.39
202.56
127.89
171.16
43.48b
26.24c
26.16c
31.56
48.23
41.01
43.48b
30.77
37.52
32.87
21.19
17.29
18.67
23.07
28.28d
179.18
28.10d
68.98
77.79
35.78
37.83b
50.36
48.33b
16.70
19.11
32.90
45.69
57.94
38.36
31.74c
45.29
9
63.10
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
37.71b
199.47
128.33
170.27
43.35d
26.44e
26.38e
31.83c
48.23
199.52
128.37
169.28
43.87
26.28d
26.23d
32.49
47.94
41.02
43.13
31.03
37.37
28.13e
21.98
18.18
17.84c
23.09
28.13e
175.08
28.24e
200.00
128.48
169.88
43.75
26.41b
26.38b
32.59
48.20
40.88
43.28
30.88
37.70
28.22
22.06
18.27
17.88
23.24
28.41
181.48
28.56
198.29
128.22
169.77
43.97
26.39d
26.29d
31.68
47.98
41.19
43.32
31.14c
37.46
23.98
23.27e
21.92
18.11
23.37e
28.23f
175.17
28.33f
201.16
128.66
173.88
44.79b
27.57c
27.32c
32.90
49.90
42.52
44.87b
31.95
38.99
23.81d
23.75d
22.56
18.66
24.11
29.22
180.23
28.70
200.06
128.17
169.88
43.77c
26.51d
26.37d
31.85
48.48b
40.86
41.04
43.40c
30.89
43.74d
30.93
37.68
36.97
26.09d
23.39e
18.74
23.47f
23.21f
21.92
19.28
18.20
23.61e
28.50f
181.51
28.40f
23.73f
28.57g
180.75
28.42g
a
Assignments were based on cosy, hsqc and hmbc measurements.
Assignments within a column may have to be reversed
beg
ꢀ
Figure 2. Crystal structure of iodohydrin 7 as 7$H2O. H-atoms omitted for clarity except for the hydrogen bonded water molecule on upper left. C2eI1¼2.166(2) A, C3eO1¼1.454
ꢀ
ꢀ
(2) A, I1eC2eC3eO1 46.1(2) .
For the synthesis of the corresponding C-29 acid derivative 12,
the 2-iodo derivative 8 was subjected to the elimination step to
provide the 3-O-acetyl derivative 11 (72% yield), which was sub-
sequently deacetylated under alkaline conditions to give the acid
derivative 12 in 87% yield. Hydrogenation of the allylic 3-O-acetyl
acid/anisole followed by transesterification with methanolic
NaOMe afforded compound 14 in 82% yield. The -configuration of
C-1 was substantiated following hydrogenation of the double bond
in ring A, which furnished the 1 -hydroxy isomer of glycyrrhetinic
a
a
acid 15 in 85% yield. The 1H NMR signal of H-1 of 15 appeared as
a broadened triplet with coupling constants of 2.8 Hz, again pro-
ving its equatorial arrangement. The migration of the hydroxy
group to position 1 was further inferred from the observed HMBC-
correlations of the low-field shifted C-1 13C NMR signal to the
signals of the methyl group at position 25 and H-9, respectively. The
derivative 9 in the presence of PdeC afforded the 3
a-acetyl
derivative 13 of 18 -glycyrrhetinic acid. The low-field shifted signal
b
of H-3 of 13 showed small homonuclear coupling constants to the
neighboring H-2 protons being diagnostic for the equatorial posi-
tion of H-3 thereby verifying the configurational assignment for
compounds 9e12. The allylic system present in ring A of this series
introduction of the 1
field shift of H-9 seen in the 1H NMR spectrum as well as a
the 13C NMR signal of C-9 in compound 14 (
53.09) and 15 (
Table 1), respectively. The 1 -hydroxylation of 4,4-dimethyl-2-ene
a
-hydroxy group also led to a substantial low-
-shift of
53.32,
provides also a versatile entry into the corresponding 1
a
-series via
b
an allylic rearrangement reaction. Thus, deprotection of the
diphenylmethyl ester group of compound 9 using trifluoroacetic
d
d
a

H. Amer et al. / Tetrahedron 66 (2010) 4390e4402
4393
triterpene derivatives has previously been accomplished via SeO2
oxidation of the corresponding 2-ene derivatives.23
configuration at C-2 and C-3 in contrast to the epoxide 5 (Fig. 3).
The use of higher temperatures (80 ꢀC) gave an increased amount of
the ring-opened derivatives 18 and 19 (30% and 35%, respectively)
in addition to the thiirane 17 (20%). Acetolysis of the thiirane de-
rivative 17 using a 1:1 mixture of acetic acid-acetic anhydride
produced the diacetate 20 in 70% yield, whereas treatment of 17
with acetic anhydride in pyridine afforded compound 20 in 92%
Acid-catalyzed ring-opening of the 2,3-oxide derivative 5 with
concomitant removal of the diphenylmethyl ester group gave the
known diol derivative 16 in 70% yield (Scheme 2).24,25 The 2,3-
epoxide 5 was used as starting material for the introduction of thiol
groups at positions 1, 2 and 3 of ring A, respectively (Scheme 2).
Reaction of 5 with N,N-dimethylthioformamide in toluene at 45 ꢀC
in the presence of TFA produced the crystalline 2,3-epithio de-
rivative 17 in 80% yield.26 The crystal and molecular structure of the
epithio compound 17 could be solved and revealed the inverted
yield. The stereochemical features of the resulting 2b-S-acetyl-3a-
O-acetyl product were unambiguously proven by the crystal
structure of 20 (Fig. 4). Similar to the crystal structure of the 2-iodo-
3-O-acetyl derivative 7, ring A was present in a twist boat
CO2CH(Ph)2
CO2CH(Ph)2
CO2H
a)
b)
5
H
H
H
O
O
O
RS
HO
HO
S
R'O
18 R = H, R' = CHO
19 R = R' = H
c)
17
16
17
20 R = R' = Ac
d)
21 R = H, R' = Ac
h) or i)
20
CO2H
CO2H
CO2R'
e)
H
g)
H
H
f)
O
O
O
6
AcS
RO
R
S
AcS
22 R = Ac
23 R = H
25 R = Cl, R' = CH(Ph)2
26 R = Br, R' = CH(Ph)2
27 R = Br, R' = H
24
Scheme 2. Synthesis of 2,3-epithio derivatives 17 and 24 and 2- and 3-thio-substituted derivatives. Reagents and conditions: (a) TFA, toluene, 40 ꢀC, 2 h, then 0.1 M NaOMe, MeOH,
rt, 2 h, then 10% PdeC, MeOH, rt 15 h, 70% for 16; (b) A: TFA, DMTF, toluene, 45 ꢀC, 4 h, 80% for 17; B: TFA, DMTF, toluene, 80 ꢀC, 2 h, 20% for 17, 35% for 18, 30% for 19; (c) pTsOH, 1:1
Ac2O/AcOH, rt, 2 h, 70%, or Ac2O/pyr, rt, 15 h, 92% for 20; (d) H2NNH2$H2O, THFecyclohexeneeEtOH, rt, 0.5 h, 94% for 21; (e) TFA, anisole, CH2Cl2, 8 ꢀC, 15 h, 93% for 22; (f) 0.2 M
NaOH, rt, 12 h, 80% for 24, (g) TFA, DMTF, toluene, 40 ꢀC, 15 h, 40% for 24; (h) AcCl, CoCl2, CH2Cl2, 0 ꢀC/rt, 83% for 25; (i) AcBr, CoCl2, CH2Cl2, 0 ꢀC, 0.5 h, 33% for 26, 43% for 27.
ꢀ
ꢀ
ꢀ
Figure 3. Crystal structure of epithioderivative 17. H-atoms omitted for clarity. C2eS1¼1.832(2) A, C3eS1¼1.838(2) A, C2eC3¼1.482(2) A.

4394
H. Amer et al. / Tetrahedron 66 (2010) 4390e4402
ꢀ
ꢀ
ꢀ
Figure 4. Crystal structure of 20. H-atoms omitted for clarity. C2eS1¼1.820(1) A, S1eC31¼1.767(1) A, C31eS1eC2¼101.1(1) .
10
conformation, thereby leading to a deceptive, large homonuclear
coupling constant for H-2 and H-3 (J2,3 11.7 Hz). Selective deace-
tylation of the 2-S-acetyl group of 20 was effected by reaction with
a)
hydrazine hydrate to give the 2b-thiol derivative 21 in 94% yield.
CO2R'
CO2R'
Deprotection of the diphenylmethyl ester group using TFAe
anisole furnished the acid derivative 22 in 93% yield. Attempted
de-O-acetylation of 22 under alkaline conditions, however, was
unsuccessful and resulted in reformation of the thiirane ring giving
24 in 80% yield. The epithio compound 24 was also prepar-
eddalthough in lower yield (40%)dby direct conversion of the 2,3-
epoxide derivative 6 by treatment with DMTF/TFA.
H
H
O
O
SR
Finally, the epithio compound 17 also served as the educt for
producing a series of 3-thio substituted derivatives with inverted
configuration at C-2. Reaction of 17 with CoCl2/acetyl chloride or
RS
32 R = Ac, R' = CH(Ph)2
33 R = H, R' = CH(Ph)2
34 R = Ac, R' = H
28 R = Ac, R' = CH(Ph)2
29 R = H, R' = CH(Ph)2
30 R = Ac, R' = H
b)
b)
b)
b)
CoCl2/acetyl bromide gave the corresponding 2a-halo-3b-thio-
c)
c)
acetyl derivatives 25 and 26 in 43% and 33% yield, respectively.27 In
the former reaction, a small portion of the elimination product 3
was isolated (10%), whereas in the latter reaction the major product
isolated had resulted from cleavage of the diphenylmethyl ester
group under the acidic conditions giving the 2-bromo acid 27.
Again, the configurational assignments were corroborated from the
solved crystal structure of compound 27 (Fig. 5), which revealed the
presence of the chair conformation of ring A in accordance with the
observed 1H NMR spectral characteristics of trans-oriented vicinal
protons (J2,3¼12.0 Hz). The allylic alcohol 10 was used as educt for
35 R = R' = H
31 R = R' = H
Scheme 3. Synthesis of 1- and 3-thio-substituted compounds 31 and 35. Reagents and
conditions: (a) CH3COSH, DMFedineopentylacetal, CH2Cl2, 40 ꢀC, 40 min, 30% for 28;
40.6% for 32; (b) H2NNH2$H2O, cyclohexene/THF/EtOH, rt, 0.5 h, 92.5% for 29; 70% for
31; 95% for 33; 90.5% for 35; (c) TFA, anisole, CH2Cl2, 8 ꢀC, 15 h, 86% for 30; 85% for 34.
the presence of the 3b substitutionproduct as the major isomer (ratio
w7:3). TheconfigurationatC-3of theminorisomerwasinferredfrom
the value of the homonuclear coupling constant J2,3, which was in
a similar range (5.4 Hz) as observed for the 3a-derivatives 9e12
ꢀ
ꢀ
ꢀ
Figure 5. Crystal structure of 27. C2eBr1¼1.969(4) A, C3eS1¼1.829(5) A, S1eC31¼1.758(6), Br1eC2eC3eS1¼ꢁ57.4(4) .
the installment of thiol groups at positions 1 and 3, respectively
(Scheme 3). Reaction of 10 with DMFedineopentylacetal and
thioacetic acid28 in dichloromethane at elevated temperature
(4.8e6.2 Hz), whereas the corresponding values were smaller for the
-isomeric forms (w2 Hz), being indicative of a pseudoaxial orien-
tation of H-3 in a half-chair conformation in the latter case (Fig. 6).
Treatment of 32 with hydrazine hydrate afforded the 1 -thiol
compound 33 in 95% yield. Similarly, the 3-S-acetyl derivative 28
was converted into the 3 ,3 -thiol derivative 29 in 90% yield. Fi-
b
afforded the 3-epimeric S-acetyl derivative 28 and the 1
a
-S-acetyl
a
derivative 32 in yields of 35% and 50%, respectively, after chro-
matographic separation.
a
b
The structural assignments of the regioisomers 28 and 32 was
based upon the identification of the thio-substituted carbons at
nally, the diphenylmethyl ester groups were cleaved without af-
fecting the S-acetyl groups using TFAeanisole to give the free acid
derivatives 30 and 34 in 90% and 85% yield, respectively. Eventually,
the fully deprotected compounds 31 and 35 were generated from
30 and 34 by hydrazinolysis in yields of 70% and 90%, respectively.
The 13C NMR data (Tables 1 and 2) closely match previous assign-
ments made for glycyrrhizin.29 Major chemical shift deviations are
observed for ring A carbons and the neighboring Me-groups at
d
54.00 and
correlation to either the methyl groups at position 23 and 24 or the C-
25 methyl group, respectively. Formation of the 1 -thioisomer is
presumed to occur via a similar pathwayas observed for the 1 -allylic
d 50.91 (Table 2), respectively, followed by their HMBC-
a
a
alcohol 14. The epimeric mixture of the 3-thio compounds, however,
could not be resolved by chromatography. The 1H NMR data indicated

H. Amer et al. / Tetrahedron 66 (2010) 4390e4402
4395
Table 2
13C NMR data (ppm) of compounds 17e35a
Carbon atom
17
39.20
18
51.81
19
20
47.37
21
52.14
22
46.88
24
39.00
25
51.53
26
52.67
1
2
3
4
5
6
7
8
52.99
38.08
48.41
32.45
52.67
19.00
32.01
45.23
62.94
36.96
199.34
128.48
169.06
43.19
26.29c
26.26c
31.62
47.88
41.14
43.91
31.09
37.42
34.40
26.38
17.61
18.53
23.28
28.26d
175.10
28.17d
36.40
80.01
38.31c
50.65
19.22
31.72d
45.22
62.83
37.51
198.46
128.27
169.76
43.36e
26.35f
26.44f
31.62d
48.03
41.28
43.99e
31.18d
37.45c
24.18
22.96
21.87
18.14
23.28
28.35g
175.16
28.23g
41.09c
77.57
40.54
76.11
38.28
50.23
19.04
31.73c
45.25
62.77
37.24
198.66
128.28
169.69
43.39
26.44d
26.37d
31.67c
48.05
41.26
44.00
31.19
37.52
24.31
22.89
21.40
18.17
23.48
28.36e
175.19
28.24e
36.99
79.21
38.37
50.65
19.23
31.73c
45.23
62.86
37.53
198.53
128.31
169.66
43.35
26.45d
26.37d
31.65c
48.03
41.28
44.00
31.19
37.53
24.08
23.07
21.89
18.16
23.40
28.35e
175.18
28.24e
40.15
76.15
37.90c
49.85
18.59
31.47d
45.11
62.50
36.94
199.62
127.49
171.09
43.23e
26.12f
25.99f
31.26d
48.10
40.95
43.37e
30.65
37.39c
23.84
23.02
20.91
17.75
22.40
28.17g
178.93
27.94g
38.03
48.09
32.29
52.51
18.80
31.84c
45.29
62.85
36.85
200.40
127.95
170.84
43.21d
26.14
26.14
31.58c
48.44
41.01
43.47d
30.78
37.49
34.16
26.14
17.39
18.35
23.08
28.28e
179.07
28.14e
59.43
61.89
41.11
55.65
18.70
32.50
45.27
61.10
38.65
199.12
128.29
169.23
43.26c
26.38d
26.33d
31.74
48.10
40.44
43.99c
31.16
37.45
29.77
19.38
16.81
18.61
23.30
28.29e
175.15
28.22e
53.53
62.03
41.11
55.59
18.76
32.48
45.28
61.06
39.54
199.10
128.30
169.25
43.27
26.38c
26.33c
31.75
48.10
40.89
44.00
31.16
37.45
30.02
19.22
16.59
18.59
23.29
28.29d
175.16
28.23d
38.32
51.77
18.66
31.72d
45.35
9
63.01
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
37.73e
198.85
128.27
169.84
43.35f
26.41g
26.34g
31.67d
48.06
41.24c
43.99f
31.16
37.62e
23.28h
22.84
22.18
18.15
23.38h
28.35i
175.18
28.22i
Carbon atom
27
28 (3
b)
28 (3
a
)
30b
31b
32
33
34
35
1
2
3
4
5
6
7
8
53.37
54.77
62.66
41.52
55.97
19.51
31.72
45.83
61.53
40.43
198.32
128.86
169.37
43.99c
27.22d
27.10d
32.46
48.95
41.97
44.09c
33.00
38.68
30.44
19.29
16.59
18.85
23.59
28.88e
177.62
28.42e
139.88
123.73
54.00
35.88
54.39
17.48
33.04
45.53
58.40
38.09
199.74
128.55
169.25
43.33
26.33c
26.29c
30.78
48.10
40.98
43.98
31.72
37.44
28.22d
20.72
19.23
19.23
23.48
28.44d
175.21
28.26d
139.71
121.57
52.33
35.88
50.66
16.68
33.04
45.57
58.46
38.26
199.74
128.55
169.34
43.27
26.42c
26.42c
30.78
48.10
40.98
43.98
31.72
37.44
24.85
20.72
19.40
18.76
23.40
28.26d
175.21
27.90d
139.60
123.70
53.88
35.71
54.28
17.28
32.86
45.56
58.31
37.97
200.65
127.66
171.01
43.51c
26.22d
26.13d
31.65
48.30
40.86
43.32c
30.80
37.49
28.18e
20.50
19.01
19.15
23.25
28.27e
179.13
28.18e
138.56
126.55
50.45
36.58
54.78
17.86
33.14
45.73
58.58
38.31
200.11
128.25
169.272
43.78
26.48c
26.43c
31.87
48.30
40.80
43.38
30.89
37.69
28.71d
19.48e
19.28e
19.42
23.53
28.52d
181.71
28.44d
50.91
124.09
136.74
34.55
48.79
18.93
31.22c
45.00
54.84
39.27
198.63
128.55
169.04
43.85
26.45
26.45
31.13d
47.75
41.26
44.00
31.65c
37.57
31.32d
23.35
16.85
18.34
23.73
28.35e
175.22
28.26e
46.89
125.64
136.21
34.38
44.19
18.68
31.15
44.71
55.36
39.86
200.39
128.44
170.10
43.99
26.48c
26.40c
31.66
47.88
41.32
43.99
31.15
37.54
31.53
23.07
17.05
18.18
23.86
28.38d
175.22
28.19d
50.75
124.02
136.65
34.49
48.76
18.89
31.19
45.12
54.86
39.21
199.28
128.37
169.73
43.77c
26.49d
26.36d
31.78
48.16
40.97
43.84c
30.78
37.65
31.32
23.32
16.84
18.26
23.68
28.53e
182.10
28.42e
46.85
125.66
136.24
34.39
44.04
18.69
31.17
44.85
55.38
39.90
200.96
128.37
170.87
43.85
26.54c
26.42c
31.82
48.16
41.10
44.04
30.88
37.76
31.55
23.09
17.06
18.20
23.89
28.64d
182.22
28.45d
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
a
Assignments were based on cosy, hsqc and hmbc measurements.
Data are listed for the major isomer.
Assignments within a column may be reversed.
b
cei
positions 23, 24, and 25, respectively. Biological data obtained with
the compounds will be reported elsewhere.
well the acidic 2,3-oxido derivative as educts. Conversion into the
corresponding 2,3-epithio derivatives with inverted configura-
tion was followed by ring-opening to provide either 2
well as 3 -thio- equipped derivatives. Finally, an allylic 3
droxy intermediatedagain conveniently accessible from the 2,3-
oxido intermediatedmay be transformed into 1 -configured as
well as 3 ,3 -thio analogs.
b
-thio- as
3. Conclusion
b
a
-hy-
Introduction of thiol groups into ring A of glycyrrhetinic acid
has been achieved in gram-scale utilizing the ester protected as
a
a
b

4396
H. Amer et al. / Tetrahedron 66 (2010) 4390e4402
ꢀ
ꢀ
Figure 6. Crystal structure of 33. C1eS1¼1.853(1) A, C2eC3¼1.330(2) A.
4. Experimental section
4.1. General methods
J1a,1b 12.2 Hz,1H,1a-H), 2.43 (s, 3H, CH3), 2.27 (s,1H, 9-H), 2.06e0.94
(m, 17H, 18-H, 15a-H, 16a-H, 19a-H, 21a-H, 6a-H, 7a-H, 19b-H, 6b-H,
7b-H, 21b-H, 22a-H, 22b-H, 5-H,16b-H,1b-H,15b-H),1.34 (s, 3H, 27-
CH3),1.17 (s, 3H),1.10 (s, 3H),1.06 (s, 3H), 0.89 (s, 3H), and 0.83 (s, 3H,
25-CH3, 30-CH3, 26-CH3, 23-CH3, 24-CH3 and 28-CH3). ESI-TOFMS:
m/z¼791.4345 [MþH]þ; calcd for C50H62O6S: 791.4926.
Glycyrrhetinic acid ester derivative 1 was prepared according to
published procedures.20 Concentration of solutions was performed
at reduced pressure at temperatures<40 ꢀC. Dichloromethane was
dried by stirring with CaH2 (5 g per L) for 16 h, then distilled and
stored under Ar over molecular sieves 0.4 nm. Column chroma-
tography was performed on silica gel 60 (230e400 mesh, Merck).
Analytical TLC was performed using silica gel 60 F254 HPTLC plates
with 2.5 cm concentration zone (Merck). Spots were detected by
treatment with anisaldehydeeH2SO4. Ion exchange treatment was
performed on Dowex 50 WX8 resin, Hþ form, 50e100 mesh.
Melting points were determined on a Kofler hot stage microscope
and are uncorrected. Optical rotations were measured with a Per-
kineElmer 243 B polarimeter. NMR spectra were recorded at 297 K
in CD3OD and CDCl3 with a Bruker DPX 300 or Avance 400 spec-
trometer (1H at 300.13 MHz, 13C at 75.47 MHz or 1H at 400.13 MHz,
13C at 100.62 MHz, respectively) using standard Bruker NMR soft-
ware. 1H NMR and 13C NMR spectra were referenced to internal
4.1.2. Diphenylmethyl 11-oxo-18
b-olean-2,12-dien-29-oate (3) and
11-oxo-18 -olean-2,12-dien-29-oic acid (4). Tetra-n-butylammo-
b
nium iodide (910 mg, 2.47 mmol) was added to a solution of 2
(4.0 g, 5.06 mmol) and sodium iodide (3.26 g, 21.74 mmol) in DMF
(40 mL) and the reaction mixture was stirred overnight at 100 ꢀC.
After cooling to rt, the reaction mixture was diluted with
dichloromethane (100 mL) and washed with 5% aq Na2S2O3,
NaHCO3, and brine. The aqueous layer was washed once more with
EtOAc, the organic phases were combined, dried (Na2SO4) and
concentrated. The residue was coevaporated three times with
toluene and purified by flash chromatography (6:1 n-hexane/
20
EtOAc) to afford 3 (2.85 g, 91%) as a colorless solid. Mp 235 ꢀC. [
a]
D
þ19 (c 0.7, CHCl3). 1H NMR (400 MHz, CDCl3):
¼7.41e7.26 (m, 10H,
d
arom. H), 6.93 (s, 1H, CH(Ph)2), 5.55 (s, 1H,12-H), 5.44 (ddd, J3,2 10.0,
J2,1a 6.0, J2,1b 1.6 Hz, 1H, 2-H), 2.40 (s, 1H, 9-H), 2.07e1.98 (m, 4H,
21a-H, 16a-H, 19a-H, 18-H), 1.80 (dt, J15a,15b 13.6, J15a,16 4.4 Hz, 1H,
15a-H), 1.73e1.63 (m, 2H, 7a-H, 19b-H), 1.63e1.50 (m, 2H, 6a-H, 6b-
H), 1.48e1.18 (m, 5H, 7b-H, 21b-H, 22a-H, 22b-H, 15b-H), 1.11 (dd,
1H, 5-H), 0.98 (m, 1H, 16b-H), 1.36 (s, 3H, 27-CH3), 1.19 (s, 3H, 30-
CH3), 1.17 (s, 3H), 1.12 (s, 3H), 0.97 (s, 3H), and 0.91 (s, 3H, 25-CH3,
26-CH3, 23-CH3, 24-CH3) and 0.68 (s, 3H, 28-CH3). ESI-TOFMS:
m/z¼619.3989 [MþH]þ; calcd for C43H54O3: 619.4151. Further
elution of the column with (1:1 n-hexane/EtOAc) afforded 4
tetramethylsilane (
scaffold are compiled in Tables 1 and 2. For MS analyses, samples
d
¼0). 13C NMR signals of the glycyrrhetinic acid
were dissolved in MeCN (w1 nmol/
was diluted in 50% aq MeCN containing 0.1% formic acid to give
a final concentration of w10 pmol/ L. This solution was subjected
to offline ESI Q-TOF MS on a Waters Micromass Q-TOF Ultima
Global. Capillary voltage was adjusted to obtain approx. 200
counts/s. The MS had been previously tuned with [Glu1]-fibrino-
peptide B to give the highest sensitivity and a resolution of ca.
10.000 (FWHM). Mass tuning of the TOF analyzer was done in the
tandem MS mode using again [Glu1]-fibrinopeptide B.
mL). An aliquot of the sample
m
(110 mg, 4.8%) as a colorless solid, which was crystallized from
20
dichloromethane/n-hexane. Mp 253e258 ꢀC. [
a]
þ210 (c 0.6,
D
CHCl3). 1H NMR (CDCl3, 400 MHz):
d 5.75 (s, 1H, 12-H), 5.43 (ddd,
4.1.1. Diphenylmethyl
3
b
-p-toluonesulfonyloxy-11-oxo-18
b
-olean-
JAB 10.8, JBX 6.0, JAX 1.5 Hz, 1H, 2-H), 5.36 (dd, J 2.2, J 10.8 Hz, 1H,
3-H), 3.04 (ddd, J1a,1b 17.0 Hz, 1H, 1a-H), 2.40 (s, 1H, 9-H), 2.20 (dd, J
13.4, J 4.4 Hz, 1H, 18-H), 2.07e1.90 (m, 3H, 16a-H, 21a-H, 19a-H),
1.85 (dt, J15a,15b 12.5 Hz, 1H, 15a-H), 1.75e1.20 (m, 10H, 7a-H, 1b-H,
19b-H, 6a-H, 6b-H, 7b-H, 22a-H, 22b-H, 21b-H, 15b-H), 1.11 (dd, 1H,
5-H), 1.03 (dddd, 1H, 16b-H), 1.37 (s, 3H, 27-CH3), 1.25 (s, 3H, 30-
CH3), 1.16 (2 s, 6H, 25-CH3, 26-CH3), 0.96 (s, 3H, 23-CH3), 0.91 (s, 3H,
24-CH3), and 0.86 (s, 3H, 28-CH3). ESI-TOFMS: m/z¼453.3367
[MþH]þ; calcd for C30H44O3: 453.336.
12-en-29-oate (2). A cooled solution of p-toluenesulfonyl chloride
(31.4 g, 0.165 mol) in dry pyridine (65 mL) was added dropwise at
0 ꢀC to a solution of 1 (30 g, 47.1 mmol) in dry pyridine (150 mL). The
reaction mixturewas stirred at rtovernight. Thesolutionwaspoured
onto ice-water, stirred for 30 min and diluted with dichloromethane
(200 mL). The organic layer was washed with 0.1 M HCl, water, and
satd aq NaHCO3 and brine. The organic phase was dried (Na2SO4)
and concentrated. Purification of the residue by MPLC (5:1 toluene/
EtOAc) afforded 2 as a colorless solid. Yield: 37 g (99%). Crystalliza-
20
tion from 10:1 EtOH/EtOAc gave colorless crystals. Mp 173 ꢀC. [
a
]
4.1.3. Diphenylmethyl 2a,3a-oxido-11-oxo-18b-olean-12-en-29-oate
D
þ102 (c 1.0, CHCl3). 1H NMR (300 MHz, CDCl3):
d
7.79 (d, 2H, arom.
(5). NaHCO3 (8.8 g, 105 mmol) and m-chloroperbenzoic acid (22 g,
89.25 mmol) was added portionwise to a stirred solution of 3
(36.2 g, 58.49 mmol) in dry dichloromethane (0.5 L) at 4 ꢀC under
H), 7.40e7.25 (m,12H, arom. H), 6.93 (s,1H, CH(Ph)2), 5.49 (s,1H,12-
H), 4.28 (dd, J3,2a 4.7, J3,2b 12.0 Hz, 1H, 3-H), 2.76 (dt, J1a,2a¼J1a,2b 3.5,

H. Amer et al. / Tetrahedron 66 (2010) 4390e4402
4397
Ar. The suspension was stirred at 8 ꢀC overnight, diluted with Et2O
(300 mL) and filtered over Celite. The filtrate was washed with
water and brine. The organic layer was dried (Na2SO4) and con-
centrated. The crude product was purified by flash chromatography
(1:5/1:3 Et2O/n-hexane) to afford 5 (27 g, 73%). Crystallization
23-CH3, 24-CH3), and 0.66 (s, 3H, 28-CH3). 13C NMR (CDCl3,
75.47 MHz):
d 140.09, 139.98, 128.24, 128.18, 127.85, 127.28, 126.93
(arom. C), 76.65 (CHPh2). ESI-TOFMS: m/z¼805.3813 [MþH]þ; calcd
for C45H57IO5: 805.3320.
was achieved by dissolving the material in dry EtOH at 50 ꢀC and
4.1.6. 3
b
-Acetyloxy-2
a
-iodo-11-oxo-18
b
-olean-12-en-29-oic
acid
20
gradual cooling to þ4 ꢀC. Mp 178 ꢀC. [
a
]
D
þ126 (c 0.9, CHCl3). 1H
(8). Anisole (0.4 mL) was added to a solution of 7 (200 mg,
0.249 mmol) in dry dichloromethane (5 mL) followed by addition of
trifluoroacetic acid (0.4 mL) at þ8 ꢀC. The solution was stirred
overnight at þ8 ꢀC. The solution was diluted with toluene (50 mL)
and evaporated. The residue was purified by silica gel chromatog-
raphy using first 2:1 n-hexane/EtOAc to remove anisole followed by
NMR (CDCl3, 400 MHz):
d 7.41e7.26 (m, 10H, arom. H), 6.93 (s, 1H,
CH(Ph)2), 5.54 (s, 1H, 12-H), 3.22 (ddd, J2,3 3.7, J2,1a 6.4 Hz, 1H, 2-H),
3.16 (dd, J1a,1b 14.9 Hz, 1H, 1a-H), 2.82 (d, 1H, 3-H), 2.30 (s, 1H, 9-H),
2.08e1.96 (m, 4H, 16a-H, 21a-H, 18-H, 19a-H), 1.76 (dt, J15a,15b
13.6 Hz, 1H, 15a-H), 1.73e1.20 (m, 10H, 19b-H, 7a-H, 6a-H, 6b-H, 7b-
H, 1b-H, 22a-H, 22b-H, 21b-H, 15b-H), 1.11e0.90 (m, 2H, 16b-H, 5-
H), 1.315 (s, 3H, 27-CH3), 1.17 (s, 3H, 30-CH3), 1.15 (s, 3H, 25-CH3),
1.11 (s, 3H, 23-CH3), 1.06 (s, 3H, 26-CH3), 1.04 (s, 3H, 24-CH3), and
50:1 CH2Cl2/EtOH to afford 8 as colorless solid. Yield: 115 mg,
20
(72.5%). [
400 MHz):
a
]
þ136 (c 0.7, 5:1 CHCl3/MeOH). 1H NMR (CDCl3,
D
d
5.64 (s, 1H, 12-H), 5.35 (d, J2,3 12.8 Hz, 1H, 3-H), 4.57
0.66 (s, 3H, 28-CH3). 13C NMR (CDCl3, 75.47 MHz):
d
140.03, 139.45,
(ddd, J1a,2 11.2, J1b,2 8.0 Hz,1H, 2-H), 3.00 (dd, J1a,1b 14.8 Hz, 1H, 1a-H),
2.70 (s, 1H, 9-H), 2.34 (dd, 1H, 1b-H), 2.225 (br dd, J18,19b 13.2, J18,19a
4.5 Hz, 1H, 18-H), 2.15 (ddd, J16a,16b¼J16a,15b 13.2, J16a,15a 4.4 Hz, 1H,
16a-H), 2.11 (s, 3H, CH3CO), 1.97e1.83 (m, 3H, 21a-H, 19a-H, 15a-H),
1.72 (ddd, 1H, 7a-H), 1.67(t, J19b,19a 13.2 Hz, 1H, 19b-H), 1.56e1.52 (m,
2H, 6a-H, 6b-H),1.46e1.14 (m, 6H, 7b-H, 22a-H, 22b-H, 21b-H,15b-H,
5-H), 1.06 (ddd, 1H, 16b-H), 1.43 (s, 3H, 27-CH3), 1.36 (s, 3H, 25-CH3),
1.17 (s, 3H, 30-CH3), 1.11 (s, 3H, 26-CH3), 1.06 (ddd, 1H, 16b-H), 0.97
and 0.96 (2 s, 6H, 23-CH3, 24-CH3), 0.84 (s, 3H, 28-CH3). 13C NMR
128.53, 128.02, 127.74, 127.15, 126.85 (arom. C), 76.50 (CHPh2). ESI-
TOFMS: m/z¼635.3943 [MþH]þ; calcd for C43H54O4: 635.4000.
4.1.4. 2
a
,3a
-Oxido-11-oxo-18
b
-olean-12-en-29-oic
acid
(6).
NaHCO3 (1.5 g, 18.67 mmol) and m-chloroperbenzoic acid (3.72 g,
0.268 mmol) were added portionwise to a stirred solution of 4
(6.5 g, 14.36 mmol) in dry dichloromethane (100 mL) at 4 ꢀC under
Ar. The suspension was stirred at 8 ꢀC overnight, diluted with EtOAc
(300 mL) and filtered over Celite. The filtrate was washed with
water and brine. The organic layer was dried (Na2SO4) and con-
centrated. The crude product was purified by flash chromatography
(50:1/20:1 CH2Cl2/EtOH) and was finally purified by crystalliza-
tion from DMSO. Crystals were washed with n-hexane and dried to
(CDCl3/CD3OD, 75.47 MHz):
ESI-TOFMS: m/z¼639.2054 [MþH]þ; calcd for C32H47IO5: 639.2546.
d
¼172.22 (CH3CO) and 21.36 (CH3CO).
4.1.7. Diphenylmethyl 3 -acetyloxy-11-oxo-18 -olean-1,12-dien-29-
a
b
oate (9). DBU (1.0 mL, 7.213 mmol) was added to a solution of 7
(1.0 g, 1.242 mmol) in dry toluene (20 mL) and the solution was
stirred at 100 ꢀC overnight. After cooling to rt, the solution was
diluted with dichloromethane (100 mL) and washed with aq NH4Cl,
satd aq NaHCO3, and brine. The organic layer was dried (Na2SO4)
and concentrated. The residue was submitted to chromatography
give 3.6 g (53.5%) of 6 as crystals. Mp 260 ꢀC. [
a
]
D
20 þ144 (c 0.9, 5:1
CHCl3/MeOH). 1H NMR (CD3OD/CDCl3, 400 MHz):
d 5.73 (s, 1H, 12-
H), 3.23 (dd, J2,1a 6.0, J2,3 3.6 Hz, 1H, 2-H), 3.16 (ddd, J1a,1b 14.8 Hz,
1H, 1a-H), 2.83 (d, 1H, 3-H), 2.33 (s, 1H, 9-H), 2.20 (dd, J 13.2, J
3.0 Hz, 1H, 18-H), 2.07e1.90 (m, 3H, 16a-H, 21a-H, 19a-H), 1.81 (dt,
J15a,15b 12.5, J15a,16a 3.6 Hz,1H,15a-H),1.69e1.01 (m,11H, 7a-H,1b-H,
19b-H, 6a-H, 6b H, 7b-H, 22a-H, 22b-H, 21b-H, 16b-H, 15b-H), 0.96
(dd, 1H, 5-H), 1.33 (s, 3H, 27-CH3), 1.23 (s,3H, 30-CH3), 1.16 (s, 3H,
25-CH3), 1.11 (s, 3H, 23-CH3), 1.10 (s, 3H, 26-CH3), 1.04 (s, 3H, 24-
CH3), and 0.84 (s, 3H, 28-CH3). ESI-TOFMS: m/z¼469.3318 [MþH]þ;
calcd for C30H44O4: 469.308.
on silica gel (10:1/1:3 n-hexane/EtOAc) to afford 9 as a colorless
20
solid (700 mg, 83.2%). [
400 MHz):
a
]
þ54 (c 1.0, CHCl3). 1H NMR (CDCl3,
D
d
7.32e7.18 (m, 10H, arom. H), 6.86 (s, 1H, CH(Ph)2), 6.82
(d, J1,2 10.0 Hz,1H,1-H), 5.47 (s,1H,12-H), 5.39 (dd, J2,3 4.8 Hz,1H, 2-
H), 4.79 (d, 1H, 3-H), 3.135 (dd, J1a,1b 15.2 Hz, 1H, 1a-H), 2.52 (s, 1H,
9-H), 1.98 (s, 3H, CH3CO), 2.01e1.89 (m, 4H, 16a-H, 21a-H,18-H, 19a-
H), 1.74 (dt, J15a,15b 13.5 Hz, J15a,16a 4.5 Hz, 1H, 15a-H), 1.65 (ddd, 1H,
7a-H), 1.59 (t, J19a,19b¼J19b,18 14.4 Hz, 1H, 19b-H), 1.43e1.08 (m, 8H,
6a-H, 6b-H, 21b-H, 5-H, 7b-H, 22a-H, 22b-H, 15b-H), 0.92 (ddd, 1H,
16b-H),1.32 (s, 3H, 27-CH3),1.19 (s, 3H, 25-CH3),1.10 (s, 3H, 30-CH3),
1.04 (s, 3H, 26-CH3), 0.85 and 0.84 (2 s, 6H, 23-CH3, 24-CH3), and
4.1.5. Diphenylmethyl
3a-acetyloxy-2b-iodo-11-oxo-18b-olean-12-
en-29-oate (7). A solution of 5 (10.2 g, 16.19 mmol) in dry CH2Cl2
(30 mL) was added at ꢁ25 ꢀC to a solution of triphenylphosphine
(6.58 g, 25.1 mmol) and I2 (6.16 g, 24.3 mmol) in dry CH2Cl2
(100 mL) under Ar and the mixture was stirred at ꢁ30 ꢀC for
30 min. The reaction mixture was diluted with dichloromethane
(200 mL) and washed with aq 5% Na2S2O3, satd aq NaHCO3, and
brine. The organic phase was dried (Na2SO4) and concentrated. The
residue and a catalytic amount of 4-N,N-dimethylaminopyridine
were dissolved in pyridine (40 mL) at rt. The solution was cooled to
0 ꢀC and acetic anhydride (20 mL) was added dropwise. The re-
action mixture was stirred overnight at rt. MeOH (5 mL) was added
and the solution was coevaporated four times with the addition of
toluene and concentrated in vacuo. The residue was submitted to
flash column chromatography (10:1/8:1 n-hexane/EtOAc) to give
0.60 (s, 3H, 28-CH3). 13C NMR (CDCl3, 75.47 MHz):
d 170.71 (CH3CO),
140.06, 140.02, 128.59, 128.10, 127.81, 127.19, 126.93 (arom. C), 76.59
(CHPh2), and 21.25 (CH3CO). ESI-TOFMS: m/z¼677.4206 [MþH]þ;
calcd for C45H56O5: 677.4708.
4.1.8. Diphenylmethyl
3a-hydroxy-11-oxo-18b-olean-1,12-dien-29-
oate (10). A 1.0 M KOH solution (2 mL) was added to a solution of 9
(650 mg, 0.96 mmol) in EtOH (10 mL). The reaction mixture was
stirred at rt overnight. The solution was made neutral by addition of
Dowex 50Hþ cation exchange resin and filtered. The filtrate was
concentrated and the residue was purified on a column of silica gel
7 as colorless crystals. Mp 168 ꢀC (n-hexane/EtOAc). Yield: 11.0 g,
(4:1/2:1 n-hexane/EtOAc) to give 10 as colorless solid (550 mg,
þ129 (c 0.8, CHCl3). 1H NMR (CDCl3, 400 MHz):
90.2%). [
a
]
þ111 (c 0.9, CHCl3). 1H NMR (CDCl3, 400 MHz):
20
20
(85%). [
d
a
]
D
D
7.42e7.27 (m, 10H, arom. H), 6.935 (s, 1H, CH(Ph)2), 5.55 (s, 1H, 12-
d 7.34e7.19 (m, 10H, arom. H), 6.86 (s, 1H, CH(Ph)2), 6.72 (d, J1,2
H), 5.38 (d, J2,3 12.6 Hz, 1H, 3-H), 4.39 (ddd, J1a,2 11.5, J1b,2 7.5 Hz, 1H,
2-H), 3.135 (dd, J1a,1b 15.2 Hz, 1H, H-1a), 2.48 (s, 1H, 9-H), 2.29 (dd,
1H, 1b-H), 2.14 (s, 3H, CH3CO), 2.07e1.96 (m, 4H, 16a-H, 21a-H, 18-
H, 19a-H), 1.78 (dt, J15a,15b 13.4 Hz, 1H, 15a-H), 1.69e1.23 (m, 9H,
19b-H, 7a-H, 6a-H, 6b-H, 7b-H, 22a-H, 22b-H, 21b-H, 15b-H),
1.15e0.98 (m, 2H, 16b-H, 5-H), 1.375 (s, 3H, 25-CH3), 1.35 (s, 3H, 27-
CH3),1.18 (s, 3H, 30-CH3),1.05 (s, 3H, 26-CH3), 0.96 and 0.93 (2 s, 6H,
10.0 Hz,1H,1-H), 5.51 (dd, J2,3 4.8 Hz,1H, 2-H), 5.47 (s,1H,12-H), 3.48
(br d, 1H, 3-H), 2.49 (s, 1H, 9-H), 2.01e1.91 (m, 4H, 16a-H, 21a-H, 18-
H,19a-H),1.74 (dt, J15a,15b 14.0 Hz, J15a,16a 4.8 Hz,1H,15a-H),1.63 (ddd,
1H, 7a-H), 1.59 (t, J19a,19b¼J19b,18 14.4 Hz, 1H, 19b-H), 1.43e1.08 (m,
9H, 6a-H, 6b-H, 21b-H, 5-H, 7b-H, 22a-H, 22b-H, 16b-H, 15b-H), 1.29
(s, 3H, 27-CH3), 1.18 (s, 3H, 25-CH3), 1.11 (s, 3H, 30-CH3), 1.03 (s, 3H,
26-CH3), 0.92 (s, 3H, 23-CH3), 0.79 (s, 3H, 24-CH3), and 0.60 (s, 3H,

4398
H. Amer et al. / Tetrahedron 66 (2010) 4390e4402
28-CH3). 13C NMR (CDCl3, 100.62 MHz):
d
140.03, 139.98, 128.55,
400 MHz): d 5.63 (s, 1H, 12-H), 5.62 (dd, J3,2 10.4, J1,2 6.0 Hz, 1H, 2-
128.38, 128.06, 127.76, 127.17, 126.90 (arom. C), and 76.54 (CHPh2).
H), 5.51 (d, 1H, 3-H), 4.55 (dd, 1H, 1-H), 3.47 (s, 1H, 9-H), 2.225 (br
dd, J18,19b 13.0, J18,19a 4.5 Hz, 1H, 18-H), 2.155 (dt, J16a,16b 13.6, J16a,15a
13.6, J16a,15b 4.8 Hz, 1H, 16a-H), 1.97e1.86 (m, 2H, 21a-H, 15a-H),
1.865 (ddd, J19a,19b 13.5, J18,19a 4.5 Hz, 1H, 19a-H), 1.76 (ddd,
J7a,7b¼J7a,6a 13.0, J7a,6b 4.5 Hz, 1H, 7a-H), 1.72 (t, 1H, 19b-H),
1.65e1.38 (m, 7H, 6a-H, 6b-H, 7b-H, 22a-H, 22b-H, 5-H, 21b-H),1.28
(ddd, 1H, 15b-H), 1.05 (ddd, 1H, 16b-H), 1.45 (s, 3H, 27-CH3), 1.20 (s,
3H, 26-CH3), 1.16 (s, 3H, 30-CH3), 1.115 (s, 3H, 25-CH3), 1.01(s, 3H,
23-CH3), 0.91 (s, 3H, 24-CH3), and 0.85 (s, 3H, 28-CH3). ESI-TOFMS:
m/z¼469.3313 [MþH]þ; calcd for C30H44O4: 469.3318.
ESI-TOFMS: m/z¼635.4459 [MþH]þ; calcd for C43H54O4: 635.4100.
4.1.9. 3a-Acetyloxy-11-oxo-18b-olean-1,12-dien-29-oic acid (11). A
solution of 8 (500 mg, 0.294 mmol) in dry MeCN (15 mL) was stirred
with DBU (0.375 mL, 2.463 mmol) at 80 ꢀC overnight. The solution
was concentrated and the residue was purified by silica gel chroma-
tography (50:1 CH2Cl2/EtOH) to furnish 11 as colorless solid. Yield:
20
287.5 mg (72%). [
a
]
þ34 (c 0.9, CHCl3). 1H NMR (CD3OD/CDCl3,
D
400 MHz):
d
6.90 (d, J1,2 10.2 Hz, 1H, 1-H), 5.75 (s, 1H, 12-H), 5.47 (dd,
J2,3 4.8 Hz, 1H, 2-H), 4.87 (d, 1H, 3-H), 2.63 (s, 1H, 9-H), 2.21 (br dd,
J18,19b 13.6, J18,19a 4.0 Hz, 1H, 18-H), 2.06 (s, 3H, CH3CO), 2.12e1.84 (m,
4H, 16a-H, 21a-H, 19a-H, 15a-H), 1.77 (ddd, 1H, 7a-H), 1.64 (t, J19a,19b
13.6 Hz,1H,19b-H),1.67e1.19 (m, 8H, 6a-H, 6b-H, 7b-H, 22a-H, 22b-H,
21b-H, 5-H, 15b-H),1.05 (ddd, 1H, 16b-H),1.41 (s, 3H, 27-CH3),1.28 (s,
3H, 25-CH3),1.23 (s, 3H, 30-CH3),1.16 (s, 3H, 26-CH3), 0.93 and 0.92 (2
s, 6H, 23-CH3, 24-CH3), and 0.86 (s, 3H, 28-CH3). 13C NMR (CDCl3,
4.1.13. 1a-Hydroxy-11-oxo-18b-olean-12-en-29-oic acid (15). A so-
lution of 14 (100 mg, 0.213 mmol) in dry MeOH (10 mL) was stirred
with 10% Pd/C (100 mg) under hydrogen overnight at rt. The catalyst
was filtered off on Celite and the filtrate was concentrated. Chroma-
tographyof the residue onsilicagel (20:1 CH2Cl2/EtOH) afforded 15 as
a colorless solid (85 mg, 85%). [
NMR (5:1 CDCl3/CD3OD, 400 MHz): d 5.66 (s, 1H, 12-H), 4.55 (dd,
a
]
20 þ144 (c 0.5, 5:1 CHCl3/MeOH). 1H
D
75.47 MHz):
d
¼170.80 (CH3CO) and 21.25 (CH3CO). ESI-TOFMS: m/
z¼511.3285 [MþH]þ; calcd for C32H46O5: 511.3423.
J1,2a¼J1,2b 2.8 Hz, 1H, 1-H), 3.33 (s, 1H, 9-H), 2.20 (br dd, J18,19b 12.5,
J18,19a 4.5 Hz, 1H, 18-H), 2.11e1.94 (m, 3H, 2a-H, 16a-H, 21a-H), 1.88
(ddd, J19a,19b 13.6 Hz, 1H, 19a-H), 1.84 (dt, J15a,15b 13.6, J15a,16a 4.0 Hz,1H,
15a-H), 1.71e1.58 (m, 4H, 6a-H, 7a-H, 19b-H, 3a-H), 1.47 (ddd, J2b,2a
14.4 Hz, 1H, 2b-H), 1.43e1.29 (m, 5H, 6b-H, 22a-H, 22b-H, 21b-H, 7b-
H),1.24e1.14 (m, 3H,15b-H, 5-H, 3b-H),1.04 (ddd,1H,16b-H),1.415 (s,
3H, 27-CH3), 1.18 (s, 3H, 30-CH3), 1.15 (s, 3H, 26-CH3), 1.14 (s, 3H, 25-
CH3), 0.91(s, 3H23-CH3), 0.86(s, 3H, 24-CH3), and 0.83(s, 3H, 28-CH3).
ESI-TOFMS: m/z¼471.2991 [MþH]þ; calcd for C30H46O4: 471.3747.
4.1.10. 3a-Hydroxy-11-oxo-18b-olean-1,12-dien-29-oic acid (12). A
solution of 11 (250 mg, 0.489 mmol) in EtOH (8 mL) was stirred
with 1 M KOH (2 mL) overnight at rt. The solution was concentrated
and the residue was purified by silica gel chromatography
(50:1/25:1 CH2Cl2/EtOH) to furnish 12 as colorless solid. Yield:
20
200 mg, (87%). [
a
]
þ144 (c 0.9, 5:1 CHCl3/MeOH). 1H NMR
D
(CD3OD/CDCl3, 300 MHz): d 6.67 (d, J1,2 13.7 Hz,1H,1-H), 5.68 (s,1H,
12-H), 5.53 (dd, J2,3 6.2 Hz, 1H, 2-H), 3.52 (d, 1H, 3-H), 2.71 (s, 1H, 9-
H), 2.23 (br dd, J18,19b 13.6, J18,19a 4.2 Hz, 1H, 18-H), 2.16e1.61 (m, 7H,
16a-H, 21a-H, 19a-H, 15a-H, 7a-H, 6a-H, 19b-H), 1.55e1.19 (m, 7H,
6b-H, 7b-H, 22a-H, 22b-H, 21b-H, 5-H, 15b-H), 1.06 (ddd, 1H, 16b-
H),1.42 (s, 3H, 27-CH3),1.24 (s, 3H, 25-CH3),1.19 (s, 3H, 30-CH3),1.16
(s, 3H, 26-CH3), 0.98, and 0.87 (2 s, 6H, 23-CH3, 24-CH3) and 0.85 (s,
3H, 28-CH3). ESI-TOFMS: m/z¼469.2889 [MþH]þ; calcd for
C30H44O4: 469.3318.
4.1.14. 2
Compound 5 (150 mg, 0.236 mmol) was dissolved in toluene (5 mL)
and a solution of TFA (200 L, 2.481 mmol) in toluene (2 mL) was
b,3a-Dihydroxy-11-oxo-18b-olean-12-en-29-oic acid (16).
m
added dropwise at rt. The mixture was stirred at 40 ꢀC for 2 h. The
reaction mixturewas coevaporatedwith toluenethreetimes and the
residue was dissolved in dry MeOH (5 mL). 0.1 M Methanolic NaOMe
(0.1 mL) was added and the reaction mixture was stirred at rt for 2 h.
Dowex 50Hþ cation exchange resin was added until neutral pH, the
resin was filtered off and the filtrate was concentrated. A solution of
the residue in MeOH (5 mL) was stirred at rt with 10% PdeC (50 mg)
under hydrogen at atmospheric pressure. The catalyst was filtered
over Celite and the filtrate was concentrated. Chromatography (10:1
4.1.11. Hydrogenation of 9. A solution of 9 (30 mg, 0.044 mmol) in
dry methanol (4 mL) was hydrogenated in the presence of 10%
PdeC (30 mg) at rt and atmospheric pressure for 15 h. The catalyst
was filtered over a layer of Celite and the filtrate was concentrated.
Purification of the residue on silica gel (50:1 CH2Cl2/EtOH) gave 13
as amorphous solid. Yield: 18 mg (80%). 1H NMR (CDCl3, 400 MHz):
CH2Cl2/MeOH) of the residue on a column of silica gel afforded 16 as
20
acolorless crystallinesolid. Yield: 80 mg(70%). Mp182e184 ꢀC. [
a]
D
d
5.72 (s, 1H, 12-H), 4.64 (dd, J3,2a¼J3,2b 3.2 Hz, 1H, 3-H), 2.56 (ddd,
þ147 (c 0.6, MeOH). 1H NMR (5:1 CD3OD/CDCl3, 400 MHz):
d 5.74 (s,
J1a,b 13.2, J1a,2 3.6 Hz, 1H, 1a-H), 2.47 (s, 1H, 9-H), 2.19 (br dd, J18,19b
13.6, J18,19a 3.2 Hz, 1H, 18-H), 2.07e1.81 (m, 5H, 16a-H, 21a-H, 2a-H,
19a-H, 15a-H), 1.72 (ddd, 1H, 7a-H), 1.645 (t, J19a,19b 13.6 Hz, 1H, 19b-
H), 1.56 (dddd, 1H, 2b-H), 1.50e1.16 (m, 9H, 6a-H, 6b-H, 7b-H, 22a-
H, 22b-H, 21b-H, 1b-H, 5-H, 15b-H), 1.04 (ddd, 1H, 16b-H), 1.43 (s,
3H, 27-CH3), 1.23 (s, 3H, 30-CH3), 1.17 (s, 3H, 25-CH3), 1.14 (s, 3H, 26-
CH3), 0.92 (s, 3H, 23-CH3), 0.86 (s, 3H, 24-CH3), and 0.84 (s, 3H, 28-
1H, 12-H), 3.75e3.65 (m, 2H, 2-H, 3-H), 2.54 (s, 1H, 9-H), 2.21 and
2.19 (m, 2H,18-H,1a-H), 2.08e1.10 (m,16H,15a-H,16a-H,19a-H, 21a-
H, 6a-H, 7a-H, 19b-H, 6b-H, 7b-H, 15b-H, 21b-H, 22a-H, 22b-H, 5-H,
16b-H,1b-H),1.37 (s, 3H, 27-CH3),1.31 (s, 3H, 25-CH3),1.23 (s, 3H, 30-
CH3), 1.10 (s, 3H, 26-CH3), 1.05 (s, 3H, 23-CH3), 0.94 (s, 3H, 24-CH3),
and 0.84 (s, 3H, 28-CH3). ESI-TOFMS: m/z¼487.3375 [MþH]þ; calcd
for C30H46O5: 487.3318.
CH3). 13C NMR (CDCl3/CD3OD, 100.62 MHz):
21.36 (CH3CO).
d¼170.74 (CH3CO) and
4.1.15. Diphenylmethyl
oate (17), diphenylmethyl 3
olean-12-en-29-oate (18), and diphenylmethyl 3
capto-11-oxo-18 -olean-12-en-29-oate (19). Method A. A solution of
trifluoroacetic acid (0.135 mL, 1.18 mmol) in dry toluene (10 mL)
was added dropwise to an ice-cooled solution of (5.0 g,
2
b
,3
a
b
-epithio-11-oxo-18
-formyloxy-2 -mercapto-11-oxo-18
-hydroxy-2 -mer-
b-olean-12-en-29-
b
b-
4.1.12. 1
a
-Hydroxy-11-oxo-18
b
-olean-2,12-dien-29-oic acid (14). A
a
b
solution of 9 (100 mg, 0.158 mmol) in dichloromethane (5 mL) was
stirred with trifluoroacetic acid (0.2 mL) and anisole (0.1 mL) at rt
for 12 h. The solution was concentrated and the residue was puri-
fied by silica gel chromatography (1:1 n-hexane/EtOAc). Product-
containing fractions were pooled and concentrated. The residue
was dissolved in dry MeOH (5 mL) and treated with 0.1 M meth-
anolic NaOMe (0.1 mL) for 4 h at rt. The solution was made neutral
by addition of Dowex 50Hþ cation exchange resin and filtered. The
filtrate was concentrated and purified by silica gel chromatography
b
5
7.88 mmol) and dimethylthioformamide (1.4 mL, 16.5 mmol) in dry
toluene (150 mL) under Ar. The reaction mixture was stirred at
45 ꢀC for 4 h, then coevaporated with toluene three times and
concentrated. The residue was submitted to silica gel chromatog-
raphy (15:1/10:1 CH2Cl2/EtOH) to afford 17 as the major product
20
(4.1 g, 80%) as colorless crystals. Mp 169 ꢀC. [
a
]
D
þ163 (c 0.9,
(1:1 n-hexane/EtOAc) to afford 14 as colorless amorphous solid.
CHCl3). 1H NMR (CDCl3, 400 MHz):
6.93 (s, 1H, CH(Ph)2), 5.54 (s, 1H, 12-H), 3.54 (dd, J1a,2 1.2, J1a,1b
d 7.41e7.26 (m, 10H, arom. H),
20
Yield: 60 mg (82%). [
a
]
þ197 (c 0.75, MeOH). 1H NMR (CD3OD,
D

H. Amer et al. / Tetrahedron 66 (2010) 4390e4402
4399
16.0 Hz, 1H, 1a-H), 3.36 (ddd, J2,1b 4.0 Hz, 1H, 2-H), 3.15 (d, J2,3
7.2 Hz, 1H, 3-H), 2.21 (s, 1H, 9-H), 2.07e1.96 (m, 4H, 21a-H, 16a-H
18-H, 19a-H), 1.77 (dt, J15a,15b 13.6, J15a,16a 4.8 Hz, 1H, 15a-H),
1.68e1.42 (m, 5H, 1b-H, 19b-H, 7a-H, 6a-H, 6b-H), 1.39e1.12 (m, 5H,
7b-H, 22a-H, 22b-H, 21b-H, 15b-H), 0.98 (ddd, 1H, 16b-H), 0.81 (br
dd, J5,6a 2.4, J5,6b 11.6 Hz, 1H, 5-H), 1.36 (s, 3H, 25-CH3), 1.33 (s, 3H,
27-CH3), 1.28 (s, 3H, 23-CH3), 1.17 (s, 3H, 30-CH3), 1.10 (s, 3H, 24-
CH3), 1.07 (s, 3H, 26-CH3), and 0.66 (s, 3H, 28-CH3). 13C NMR (CDCl3,
C), 76.67 (CHPh2), 30.59 [SC(O)CH3], 20.90 (OCCH3). ESI-TOFMS:
m/z¼753.4758 [MþH]þ; calcd for C47H60O6S: 753.4189.
Method B. A solution of 17 (300 mg, 0.45 mol) in dry pyridine
(4 mL) was cooled to 0 ꢀC. Acetic anhydride (2 mL) was added and
the solution was stirred at rt for 15 h. The solution was diluted with
dichloromethane (50 mL) and washed with ice-cold 10% HCl, water,
satd aq NaHCO3 and brine. Processing as described for method A
afforded 20 (310 mg, 92%).
100.62 MHz):
d 140.05, 139.99, 128.96, 128.59, 128.40, 128.08,
127.78, 127.42, 127.19, 126.91 (arom. C), and 76.56 (CHPh2). ESI-
TOFMS: m/z¼651.3872 [MþH]þ; calcd for C43H54O3S: 651.3746.
Method B. Trifluoroacetic acid (0.45 mL, 5.88 mmol) was added
dropwise to an ice-cooled solution of 6 (5.0 g, 7.88 mmol) and
dimethylthioformamide (1.4 mL, 16.5 mmol) in dry toluene (150 mL)
under Ar. The reaction mixture was stirred at 80 ꢀC for 2 h. Workup
and chromatography of the material as described for method A
afforded 17 as the higher running product (1.0 g, 20%). Elution of the
4.1.17. Diphenylmethyl 2b-mercapto-3a-acetyloxy-11-oxo-18b-olean-
12-en-29-oate (21). A solution of 20 (900 mg, 1.195 mmol) and hy-
drazine hydrate (120 mg, 2.39 mmol) in 5:1:1 THF/cyclohexene/
EtOH was stirred for 30 min at rt. The solution was diluted with
EtOAc(100 mL) and washed with ice-cold 0.1 M HCl, satd aq NaHCO3
and brine. The organic phase was dried (Na2SO4) and concentrated.
Purification of the residue by silica gel chromatography (6:1 n-
hexane/EtOAc) afforded 21 as a colorless solid. Yield: 800 mg (94%).
column using 10:1/3:1 n-hexane/EtOAc as eluant furnished com-
Mp 121e123 ꢀC. [
d 7.37e7.27 (m,10H, arom. H), 6.94 (s,1H, CH(Ph)2), 5.56 (s,1H,12-H),
a
]
20 þ135 (c 0.8, CHCl3).1H NMR (CDCl3, 300 MHz):
D
20
pound 18 as a colorless solid. Yield: 1.9 g (35%). [
a
]
þ144 (c 1.0,
D
CHCl3). 1H NMR (CDCl3, 400 MHz):
d
8.25 (s, 1H, CHO), 7.41e7.25 (m,
5.12 (d, J2,3 12.0 Hz,1H, 3-H), 3.08 (ddd, J2,1a 12.6, J2,1b 7.9 Hz,1H, 2-H),
2.50 (s, 1H, 9-H), 2.32 (dd, J1a,1b 13.6 Hz, 1H, 1a-H), 2.13 (s, 3H,
CH3CO), 2.12e1.98 (m, 5H, 21a-H, 16a-H, 18-H, 19a-H, 1b-H),
1.85e0.98 (m, 13H, 15a-H, 19b-H, 7a-H, 6a-H, 6b-H, 7b-H, 22a-H,
22b-H, SH, 21b-H,15b-H, 5-H,16b-H),1.36 (s, 3H, 27 CH3),1.33 (s, 3H,
25-CH3), 1.18 (s, 3H, 30-CH3), 1.06 (s, 3H, 26 CH3), 0.94 and 0.92 (2 s,
6H, 23-CH3, 24-CH3), and 0.67 (s, 3H, 28-CH3). 13C NMR (CDCl3,
10H, arom. H), 6.93 (s, 1H, CH(Ph)2), 5.56 (s, 1H, 12-H), 5.14 (d, J2,3
11.9 Hz,1H, 3-H), 3.13 (dddd, J2,1a 11.5, J2,1b 7.2 Hz,1H, 2-H), 2.50 (s,1H,
9-H), 2.32 (dd, J1a,1b 15.1 Hz, 1H, 1a-H), 2.10 (dd, 1H, 1b-H), 2.09e1.96
(m, 4H, 21a-H,16a-H,18-H,19a-H),1.79 (dt, J15a,15b 13.4, J15a,16a 4.3 Hz,
1H, 15a-H), 1.65 (t, J19a,19b¼J18,19b 14.3 Hz, 1H, 19b-H), 1.62e0.96 (m,
11H, 7a-H, 6a-H, 6b-H, SH, 7b-H, 22a-H, 22b-H, 21b-H, 15b-H, 5-H,
16b-H), 1.35 (s, 3H, 27-CH3), 1.33 (s, 3H, 25-CH3), 1.16 (s, 3H, 30-CH3),
1.06 (s, 3H, 26-CH3), 0.97 and 0.94 (2 s, 6H, 24-CH3, 23-CH3), and 0.65
75.47 MHz): d 170.89 (OC]O), 140.13, 140.05, 128.65, 128.31, 128.17,
127.845, 127.29,126.98 (arom. C), 76.69 (CHPh2), and 21.03 (OCCH3).
(s, 3H, 28-CH3). 13C NMR (CDCl3,100.62 MHz):
d 161.03 (CHO), 140.13,
ESI-TOFMS: m/z¼711.4276 [MþH]þ; calcd for C45H58O5S: 711.0830.
140.03, 128.64, 128.27, 128.16, 127.85, 127.28, 126.97 (arom. C), 76.68
(CHPh2). ESI-TOFMS: m/z¼697.4388 [MþH]þ; calcd for C44H56O5S:
4.1.18. 2b-S-Acetylthio-3a-acetyloxy-11-oxo-18b-olean-12-en-29-oic
697.3926. Further elution of the column finally gave compound 19 as
acid (22). Compound 20 (900 mg, 1.2 mmol) was dissolved in dry
CH2Cl2 (10 mL). Anisole (0.9 mL) was added followed by dropwise
addition of trifluoroacetic acid (0.9 mL). The solution was stirred
overnight at 8 ꢀC, diluted with toluene (50 mL) and concentrated.
Purification of the residue by silica gel chromatography (50:1
20
a colorless crystalline solid. Yield: 1.6 g (30%). Mp 124e125 ꢀC. [
a]
D
þ164 (c 0.9, CHCl3). 1H NMR (CDCl3, 400 MHz):
d 7.38e7.24 (m, 10H,
arom. H), 6.93 (s, 1H, CH(Ph)2), 5.56 (s, 1H, 12-H), 3.52 (d, J2,3 11.2 Hz,
1H, 3-H), 2.92 (dddd, J2,1a 11.4, J2,1b 8.1 Hz, 1H, 2-H), 2.51 (s, 1H, 9-H),
2.20(dd, J1a,1b 15.1 Hz,1H,1a-H), 2.12 (dd,1H,1b-H), 2.10e1.98 (m, 4H,
21a-H,16a-H,18-H,19a-H),1.80 (dt, J15a,15b 13.7, J15a,16a 4.4 Hz,1H,15a-
H), 1.66 (t, J19a,19b¼J18,19b 14.2 Hz, 1H, 19b-H), 1.65e1.45 (m, 3H, 7a-H,
6a-H, 6b-H),1.40e0.95 (m, 8H, 7b-H, 22a-H, 22b-H, SH, 21b-H,15b-H,
5-H, 16b-H), 1.35 (s, 3H, 27-CH3), 1.26 (s, 3H, 25-CH3), 1.21 (s, 3H, 30-
CH3),1.08(s, 3H, 23-CH3),1.07 (s, 3H, 26-CH3),0.90(s, 3H, 24-CH3), and
CH2Cl2/CH2Cl2/EtOH) afforded 22 as a colorless solid. Yield:
20
650 mg (93%). [
a]
þ129 (c 0.7, 5:1 CHCl3/MeOH). 1H NMR (3:1
D
CDCl3/CD3OD, 400 MHz): d 5.69 (s, 1H, 12-H), 5.11 (d, J2,311.6 Hz, 1H,
3-H), 3.90 (ddd, J2,1a 11.2, J2,1b 7.6 Hz, 1H, 2-H), 2.59 (s, 1H, 9-H), 2.41
(dd, J1a,1b 14.8 Hz, 1H, 1a-H), 2.30 (s, 3H, CH3COS), 2.23 (br dd, J18,19b
13.2, J18,19a 4.8 Hz, 1H, 18-H), 2.11e1.83 (m, 5H, 16a-H, 21a-H, 1b-H,
19a-H, 15a-H), 2.06 (s, 3H, CH3COO), 1.71 (dt, J7a,7b 11.8, J7a,6a 5.0 Hz,
1H, 7a-H), 1.63 (t, J19a,19b 13.5 Hz, 1H, 19b-H), 1.57e1.08 (m, 9H, 6a-
H, 6b-H, 7b-H, 22a-H, 22b-H, 21b-H, 5-H, 15b-H, 16b-H), 1.42 (s, 3H,
27-CH3), 1.32 (s, 3H, 25-CH3), 1.23 (s, 3H, 30-CH3), 1.12 (s, 3H, 26-
CH3), 1.03 (s, 3H, 23-CH3), 0.95 (s, 3H, 24-CH3), and 0.84 (s, 3H, 28-
0.67 (s, 3H, 28-CH3). 13C NMR (CDCl3, 100.62 MHz):
d 140.12, 140.04,
128.64, 128.51, 128.27, 128.14, 127.84, 127.26, 126.96 (arom. C), and
76.65 (CHPh2). ESI-TOFMS: m/z¼669.3704 [MþH]þ; calcd for
C43H56O4S: 669.3977.
4.1.16. 2
b
-S-acetylthio-3
a
-acetyloxy-11-oxo-18
b
-olean-12-en-29-
CH3). 13C NMR (CDCl3/CD3OD, 100.62 MHz):
d 195.91 (O]CS),
oate (20). Method A. A solution of episulfide 17 (100 mg, 0.15 mmol)
and p-toluenesulfonic acid (10 mg, 0.05 mmol) in 1:1 AcOH/Ac2O
(3 mL) was stirred for 2 h at rt. The solution was diluted with diethyl
ether (50 mL) and extracted with ice-water. The organic layer was
dried (Na2SO4) and concentrated. Purification of the residue by silica
gel chromatography (5:1 n-hexane/EtOAc) afforded unreacted 17
171.06 (O]CO), 30.01 [SC(O)CH3], 20.34 (OCCH3). ESI-TOFMS:
m/z¼587.2231 [MþH]þ; calcd for C34H50O6S: 587.3406.
4.1.19. 2b,3b-Epithio-11-oxo-18b-olean-12-en-29-oic acid (24).
Method A. A solution of 22 (190 mg, 0.324 mmol) and 0.2 M aq NaOH
(2 mL) in methanol (6 mL) was stirred for 12 h at rt. The solutionwas
diluted with EtOAc (100 mL) and washed twice with ice-cold 0.1 M
HCl and water. The organic phase was dried (Na2SO4) and concen-
trated. Purification of the residue by silica gel chromatography
(50:1/25:1 CH2Cl2/EtOH) furnished 24 as a colorless solid. Yield:
(20 mg, 18%) followed by 20 (90 mg, 70%) as colorless solid. Mp
20
214 ꢀC. [
d
a
]
þ124 (c 0.8, CHCl3). 1H NMR (CDCl3, 300 MHz):
D
7.41e7.24 (m,10H, arom. H), 6.93 (s,1H, CH(Ph)2), 5.54 (s,1H,12-H),
5.13 (d, J2,3 11.7 Hz, 1H, 3-H), 3.90 (dt, J2,1a 11.2, J2,1b 7.8 Hz, 1H, 2-H),
2.51 (s, 1H, 9-H), 2.45 (dd, J1a,1b 14.9 Hz, 1H, 1a-H), 2.29 (s, 3H, CH3C
(O)S), 2.04 (s, 3H, CH3CO), 2.08e1.96 (m, 4H, 21a-H,16a-H,18-H,19a-
H), 1.95 (dd, 1H, 1b-H), 1.85e0.98 (m, 12H, 15a-H, 19b-H, 7a-H, 6a-H,
6b-H, 7b-H, 22a-H, 22b-H, 21b-H,15b-H, 5-H,16b-H),1.38 (s, 3H, 27-
CH3), 1.31 (s, 3H, 25-CH3), 1.18 (s, 3H, 30-CH3), 1.06 (s, 3H, 26-CH3),
130 mg, (80%). [
a
]
20 þ169 (c 0.7, 5:1 CHCl3/MeOH). 1H NMR (CDCl3,
D
400 MHz):
d
5.68 (s,1H,12-H), 3.50 (dd, J1a,1b 16.0, J2,1a 0.8 Hz,1H,1a-
H), 3.37 (ddd, 1H, 2-H), 3.17 (d, J2,3 7.2 Hz, 1H, 3-H), 2.27 (s, 1H, 9-H),
2.20 (br dd, J18,19b 13.2, J18,19a 4.0 Hz, 1H, 18-H), 2.05 (dd,
J16a,16b¼J16a,15a 13.2, J16a,15b 4.2 Hz,1H,16a-H),1.97 (ddd, J21a,21b 13.0, J
3.2, J 6.0 Hz,1H, 21a-H),1.90 (ddd, 1H,19a-H),1.83 (ddd, J15a,15b 13.6,
J15a,16b 4.8 Hz, 1H, 15a-H), 1.64 (m, 2H, 1b-H, 7a-H), 1.60 (t, J19a,19b
13.2 Hz,1H,19b-H),1.52e1.16 (m, 8H, 6a-H, 6b-H, 7b-H, 22a-H, 22b-
1.01 (s, 3H, 24-CH3), 0.94 (s, 3H, 23-CH3), and 0.67 (s, 3H, 28-CH3).13
NMR (CDCl3, 75.47 MHz): 195.35 (SC]O), 170.65 (OC]O), 140.15,
140.06, 128.64, 128.48, 128.28, 128.15, 127.84, 127.28, 126.96 (arom.
C
d

4400
H. Amer et al. / Tetrahedron 66 (2010) 4390e4402
H, 21b-H, 5-H,15b-H),1.04 (ddd,1H,16b-H),1.36 (s, 3H, 27-CH3),1.36
(s, 3H, 25-CH3), 1.30 (s, 3H, 23-CH3), 1.18 (s, 3H, 30-CH3), 1.11 (s, 3H,
26-CH3), 1.11 (s, 3H, 24-CH3), and 0.82 (s, 3H, 28-CH3). ESI-TOFMS:
m/z¼485.2656 [MþH]þ; calcd for C30H44O3S: 485.3089.
25-CH3), 1.15 (s, 3H, 30-CH3), 1.13 (s, 3H, 26-CH3), 1.03 (s, 3H, 23-
CH3), 0.89 (s, 3H, 24-CH3), and 0.83 (s, 3H, 28-CH3). 13C NMR
(CD3OD/CDCl3, 100.62 MHz):
d 193.15 (SC]O) and 30.17 [SC(O)
CH3]. ESI-TOFMS: m/z¼607.2012 [MþH]þ; calcd for C32H47BrO4S:
Method B. Trifluoroacetic acid (0.050 mL) was added to a solu-
tion of 6 (1.0 g, 2.134 mmol) and dimethylthioformamide (0.28 mL,
4.267 mmol) in dichloromethane (10 mL) and the solution was
stirred overnight at 40 ꢀC. Toluene (50 mL) was added and the so-
lution was concentrated. The residue was purified by silica gel
chromatography (50:1/20:1 CH2Cl2/EtOH) to furnish 24 as a col-
orless solid. Yield: 420 mg, (40%).
607.2456.
4.1.22. Diphenylmethyl
3
a,3
b-S-acetylthio-11-oxo-18b-olean-1,12-
dien-29-oate (28) and diphenylmethyl 1
a-S-acetylthio-11-oxo-18b-
olean-2,12-dien-29-oate (32). Thioacetic acid (4.2 mL, 55.1 mmol)
was added dropwise during 30 min to a solution of 10 (7.0 g,
11.0 mmol) and DMF$dineopentylacetal (3.82 mL, 16.51 mmol) in
dry CH2Cl2 (100 mL) at rt. The reaction mixture was stirred at 40 ꢀC
for 2 h and concentrated The residue was purified by flash chro-
matography on silica gel (15:1/10:1 n-hexane/EtOAc) to afford first
28asa colorless solid(2.3 g, 30%).1HNMR (CDCl3, 300 MHz)of major
4.1.20. Diphenylmethyl
3b-S-acetylthio-2a-chloro-11-oxo-18b-olean-
12-en-29-oate (25). A solution of 17 (300 mg, 0.461 mmol) and CoCl2
(6 mg, 0.046 mmol) in CH2Cl2 (5 mL) was cooled to 0 ꢀC. Acetyl
chloride (72
mL, 0.922 mmol) was added and the suspension was
3b-isomer (70%): d 7.42e7.26 (m,10H, arom. H), 6.93 (s,1H, CH(Ph)2),
stirred for 15 h at rt. The reaction mixture was diluted with CH2Cl2
(100 mL) and then washed twice with satd aq NaHCO3, water, and
brine and dried (Na2SO4). The organic layer was concentrated and the
residue was purified by flash chromatography on silica gel (6:1 n-
hexane/EtOAc) to afford 3 (29 mg,10%) followed by 25 (278 mg, 83%)
6.65 (dd, J2,1 10.4, J3,1 2.8 Hz, 1H, 1-H), 5.53 (s, 1H, 12-H), 5.19 (dd, J3,2
2.0 Hz,1H, 2-H), 4.13 (t,1H, 3-H), 2.57 (s,1H, 9-H), 2.36 (s, 3H, CH3C]
OS), 2.07e1.96 (m, 4H, 21a-H, 16a-H, 18-H, 19a-H), 1.79 (ddd, J15a,15b
13.6, J15a,16b 3.9 Hz,1H,15a-H),1.72e0.95 (m,11H, 7a-H,19b-H, 6a-H,
6b-H, 7b-H, 22a-H, 22b-H, 21b-H, 5-H,15b-H,16b-H),1.37 (s, 3H, 27-
CH3), 1.30 (s, 3H, 25-CH3), 1.18 (s, 3H, 30-CH3), 1.10 (s, 3H, 26-CH3),
0.98 (s, 3H, 23-CH3), 0.89 (s, 3H, 24-CH3), and 0.66 (s, 3H, 28-CH3).
as colorless solid. [
a
]
20 þ106 (c 0.8, CHCl3).1H NMR (CDCl3, 300 MHz):
D
d
7.41e7.24 (m,10H, arom. H), 6.93 (s,1H, CH(Ph)2), 5.51 (s,1H,12-H),
4.15 (ddd, J2,1a 4.1 Hz,1H, 2-H), 3.59 (d, J3,2 11.8 Hz, 1H, 3-H), 3.55 (dd,
J1a,1b 13.3 Hz, 1H, 1a-H), 2.42 (s, 1H, 9-H), 2.39 (s, 3H, CH3C]OS),
2.07e1.96(m, 4H, 21a-H,16a-H,18-H,19a-H),1.84e1.59 (m, 4H, 15a-H,
7a-H,19b-H, 6a-H),1.52e0.88(m, 9H,1b-H, 6b-H, 7b-H, 22a-H,22b-H,
21b-H, 5-H, 15b-H, 16b-H), 1.38 (s, 3H, 27-CH3), 1.18 (s, 3H, 25-CH3),
1.18 (s, 3H, 30-CH3), 1.08 (s, 3H, 26-CH3), 1.04 (s, 3H, 23-CH3), 0.87 (s,
3H, 24-CH3), and 0.66 (s, 3H, 28-CH3). 13C NMR (CDCl3, 75.47 MHz):
Selected data for minor 3a-isomer (30%): d 6.69 (dd, J2,1 10.2,
J
3,1<1.0 Hz,1H, 1-H), 5.53 (s, 1H, 12-H), 5.43 (dd, J3,2 5.4 Hz, 1H, 2-H),
3.93 (dd, 1H, 3-H). ESI-TOFMS: m/z¼693.4413 [MþH]þ; calcd for
C45H56O4S: 693.977. Further elution gave 32 (3.1 g, 40.6%) as a col-
20
orless solid. Mp 100e101 ꢀC. [
a
]
þ271 (c 0.9, CHCl3). 1H NMR
D
(CDCl3, 300 MHz):
d 7.40e7.26 (m, 10H, arom. H), 6.94 (s, 1H, CH
(Ph)2), 5.75 (dd, 1H, J2,1 6.0 Hz, 2-H), 5.59 (s, 1H, 12-H), 5.36 (d, J3,2
9.6 Hz, 1H, 3-H), 5.01 (d, 1H, 1-H), 3.21 (s, 1H, 9-H), 2.29 (s, 3H,
CH3C]OS), 2.08e1.98 (m, 4H, 21a-H,16a-H,18-H,19a-H),1.80 (ddd,
J15a,15b 13.6, J15a,16b 4.4 Hz,1H,15a-H),1.68e1.46 (m, 4H, 7a-H,19b-H,
6a-H, 6b-H),1.42e1.14 (m, 6H, 7b-H, 22a-H, 22b-H, 21b-H, 5-H,15b-
H), 0.99 (ddd, 1H, 16b-H), 1.39 (s, 3H, 27-CH3), 1.33 (s, 3H, 25-CH3),
1.18 (s, 3H, 30-CH3),1.14 (s, 3H, 26-CH3), 0.98 (s, 3H, 23-CH3), 0.92 (s,
3H, 24-CH3), and 0.67 (s, 3H, 28-CH3). 13C NMR (CDCl3, 75.47 MHz):
d
194.73 (SC]O),140.14,140.06,128.65,128.47,128.15,127.83,127.28,
126.95(arom.C), 76.59(CHPh2), and30.58[SC(O)CH3].ESI-TOFMS:m/
z¼729.4123 [MþH]þ; calcd for C45H57ClO4S: 729.4497.
4.1.21. Diphenylmethyl 3b-S-acetylthio-2a-bromo-11-oxo-18b-olean-
12-en-29-oate (26) and
3b
-S-acetylthio-2
a-bromo-11-oxo-18b-
olean-12-en-29-oic acid (27). A solution of 17 (300 mg,
0.461 mmol) and CoCl2 (6 mg, 0.046 mmol) in CH2Cl2 (5 mL) was
d 193.27 (SC]O),140.05,128.59,128.46,128.09,127.87,127.28,127.15
cooled to 0 ꢀC. Acetyl bromide (72
mL, 0.922 mmol) was added and
(arom. C), 76.65 (CHPh2), and 31.13 [SC(O)CH3]. ESI-TOFMS:
the suspension was stirred for 30 min at 0 ꢀC. The reaction mixture
was diluted with CH2Cl2 (100 mL) and then washed twice with satd
aq NaHCO3, water, and brine and dried (Na2SO4). The organic layer
was concentrated and the residue was purified by flash chroma-
m/z¼693.3875 [MþH]þ; calcd for C45H56O4S: 693.977.
4.1.23. Diphenylmethyl 3a,3b-mercapto-11-oxo-18b-olean-1,12-dien-
29-oate (29). Hydrazine monohydrate (190 mg, 3.82 mmol) was
added to a solution of 28 (530 mg, 0.765 mmol) in 5:1:1 THF/
cyclohexene/EtOH (14 mL). The reaction mixture was stirred at rt
for 30 min and diluted with CH2Cl2 (100 mL). The organic phase
was washed with water, dried over cotton and concentrated. The
residue was purified by column chromatography (10:1 n-hexane/
EtOAc) to give 29 as amorphous solid (460 mg 92.5%). 1H NMR
tography on silica gel (6:1 n-hexane/EtOAc) to afford 26 (118 mg,
20
33%) as colorless solid. [
a]
þ124 (c 0.8, CHCl3). 1H NMR (CDCl3,
D
400 MHz):
d
7.41e7.23 (m, 10H, arom. H), 6.93 (s, 1H, CH(Ph)2), 5.51
(s, 1H, 12-H), 4.15 (ddd, J2,1a 4.4 Hz, 1H, 2-H), 3.69 (d, J3,2 12.0 Hz, 1H,
3-H), 3.69 (dd, J1a,1b 13.3 Hz, 1H, 1a-H), 2.42 (s, 1H, 9-H), 2.39 (s, 3H,
CH3C]OS), 2.08e1.96 (m, 4H, 21a-H,16a-H,18-H,19a-H),1.78 (ddd,
J15a,15b 13.2, J15a,16b 4.4 Hz, 1H, 15a-H), 1.73e1.57 (m, 4H, 1b-H, 7a-H,
19b-H, 6a-H), 1.48e0.88 (m, 8H, 6b-H, 7b-H, 22a-H, 22b-H, 21b-H,
5-H, 15b-H, 16b-H), 1.38 (s, 3H, 27-CH3), 1.18 (s, 3H, 25-CH3), 1.18 (s,
3H, 30-CH3), 1.07 (s, 3H, 26 CH3), 1.04 (s, 3H, 23-CH3), 0.87 (s, 3H,
24-CH3), and 0.66 (s, 3H, 28-CH3). 13C NMR (CDCl3, 100.62 MHz):
(CDCl3, 400 MHz) of major isomer:
d 7.39e7.26 (m, 10H, arom. H),
6.93 (s, 1H, CH(Ph)2), 6.59 (br d, J2,1 10.3 Hz, 1H, 1-H), 5.53 (s, 1H, 12-
H), 5.38 (dd, J2,3 2.0 Hz, 1H, 2-H), 3.30 (dt, J3,SH 10.2 Hz, 1H, 3-H),
2.53 (s, 1H, 9-H), 2.06e1.96 (m, 4H, 21a-H, 16a-H, 18-H, 19a-H),
1.85e1.10 (m, 13H, 15a-H, 7a-H, 19b-H, 6a-H, 6b-H, 7b-H, 22a-H,
22b-H, 21b-H, SH, 5-H, 15b-H, 16b-H), 1.36 (s, 3H, 27-CH3), 1.29 (s,
3H, 25-CH3), 1.17 (s, 3H, 30-CH3), 1.10 (s, 3H, 26-CH3), 1.03 (s, 3H, 23-
CH3), 0.90 (s, 3H, 24-CH3), and 0.66 (s, 3H, 28-CH3). ESI-TOFMS: m/
z¼651.3746 [MþH]þ; calcd for C43H54O3S: 651.872.
d
194.56 (SC]O), 140.14, 140.05, 128.65, 128.47, 128.15, 127.96,
127.29, 126.95 (arom. C), 76.64 (CHPh2), and 30.52 [SC(O)CH3]. ESI-
TOFMS: m/z¼773.3782 [MþH]þ; calcd for C45H57BrO4S: 773.239.
Elution of the column using 50:1 CH2Cl2/EtOH gave 27 (120 mg,
20
43%) as colorless crystals. Mp 228 ꢀC. [
a
]
þ106 (c 0.9, 5:1 CHCl3/
D
MeOH). 1H NMR (CD3OD, 400 MHz):
d
5.57 (s, 1H, 12-H), 4.49 (ddd,
4.1.24. 3a,3b-S-Acetylthio-11-oxo-18b-olean-1,12-dien-29-oic acid (30).
J2,1a 4.0 Hz, 1H, 2-H), 3.68 (d, J3,2 12.0 Hz, 1H, 3-H), 3.65 (dd, J1a,1b
13.2 Hz, 1H, 1a-H), 2.53 (s, 1H, 9-H), 2.31 (s, 3H, CH3C]OS), 2.25 (br
dd, J18,19b 12.4, J18,19a 3.6 Hz, 1H, 18-H), 2.14 (dd, J16a,16b¼J16a,15a 13.6,
J16a,15b 4.0 Hz, 1H, 16a-H), 1.97e1.60 (m, 7H, 21a-H, 15a-H, 19a-H,
7a-H, 1b-H, 19b-H, 6a-H), 1.54e0.92 (m, 8H, 6b-H, 7b-H, 22a-H,
22b-H, 21b-H, 5-H, 15b-H, 16b-H), 1.45 (s, 3H, 27-CH3), 1.19 (s, 3H,
Anisole (0.2 mL) and trifluoroacetic acid (0.2 mL) were added to an
ice-cold solution of 28 (160 mg, 0.231 mmol) in dry CH2Cl2 (8 mL)
and the reaction mixture was stirred at 8 ꢀC overnight. The solution
was coevaporated with toluene (50 mL) and concentrated. The
crude product was purified by column chromatography (3:1 n-
hexane/EtOAc) to remove the excess of anisole and was followed by

H. Amer et al. / Tetrahedron 66 (2010) 4390e4402
4401
20
50:1 CH2Cl2/EtOH to afford 30 as colorless solid (105 mg, 86.3%).
dioxane gave 34 as a colorless solid. [
a
]
þ324 (c 0.4, 5:1 CHCl3/
D
20
[
a]
þ114 (c 0.6, 5:1 CHCl3/MeOH). 1H NMR (CDCl3, 400 MHz) of
MeOH). 1H NMR (CDCl3, 300 MHz):
d 5.74 (s, 1H, 12-H), 5.73 (dd, J2,1
D
major 3
b
-isomer (70%):
d
6.64 (dd, J2,1 10.4, J3,1 2.8 Hz, 1H, 1-H), 5.68
6.2 Hz, 1H, 2-H), 5.36 (d, J3,2 9.8 Hz, 1H, 3-H), 5.06 (d, 1H, 1-H), 3.25
(s, 1H, 9-H), 2.28 (s, 3H, CH3C]OS), 2.20 (br dd, J18,19b 13.7, J18,19a
3.7 Hz, 1H, 18-H), 2.10e1.94 (m, 3H, 16a-H, 21a-H, 19a-H), 1.85 (ddd,
J15a,15b 13.8, J15a,16b 4.1 Hz, 1H, 15a-H), 1.75e1.14 (m, 10H, 7a-H, 19b-
H, 6a-H, 6b-H, 22a-H, 22b-H, 7b-H, 21b-H, 15b-H, 5-H), 1.04 (ddd,
J16a,16b 13.9 Hz, 1H, 16b-H), 1.41 (s, 3H, 27-CH3), 1.34 (s, 3H, 25-CH3),
1.23 (s, 3H, 30-CH3), 1.18 (s, 3H, 26-CH3), 0.97 (s, 3H, 23-CH3), 0.93
(s, 3H, 24-CH3), and 0.85 (s, 3H, 28-CH3). 13C NMR (CDCl3,
(s, 1H, 12-H), 5.19 (dd, J3,2 2.0 Hz, 1H, 2-H), 4.12 (t, 1H, 3-H), 2.61 (s,
1H, 9-H), 2.37 (s, 3H, CH3C]OS), 2.19 (br dd, J18,19b 12.4, J18,19a
4.4 Hz, 1H, 18-H), 2.05 (dd, J16a,16b¼J16a,15a 13.2, J16a,15b 4.4 Hz, 1H,
16a-H), 1.98 (ddd, J21a,21b 12.4, J 2.8, 1H, 21a-H), 1.90 (ddd, 1H, 19a-
H), 1.84 (ddd, 1H, 15a-H), 1.72e0.95 (m, 10H, 7a-H, 19b-H, 6a-H, 6b-
H, 7b-H, 22a-H, 22b-H, 21b-H, 5-H, 15b-H), 1.02 (ddd, 1H, 16b-H),
1.40 (s, 3H, 27-CH3), 1.31 (s, 3H, 25-CH3), 1.19 (s, 3H, 30-CH3), 1.14 (s,
3H, 26-CH3), 0.98 (s, 3H, 23-CH3), 0.88 (s, 3H, 24-CH3), and 0.82 (s,
75.47 MHz): d 193.24 (SC]O) and 31.07 [SC(O)CH3]. ESI-TOFMS: m/
3H, 28-CH3). 13C NMR (CD3OD/CDCl3, 100.62 MHz):
O) and 30.47 [SC(O)CH3]. Selected 1H NMR data for minor 3
mer (30%): 6.68 (dd, J2,110.4, J3,11.2 Hz, 1H, 1-H), 5.69 (s, 1H, 12-H),
d
196.13 (SC]
-iso-
z¼527.2200 [MþH]þ; calcd for C32H46O4S: 527.3195.
a
d
4.1.28. 1a-Mercapto-11-oxo-18b-olean-2,12-dien-29-oic acid (35). A
5.43 (dd, J3,2 5.6 Hz, 1H, 2-H), 3.92 (dd, 1H, 3-H). ESI-TOFMS: m/
z¼527.3195 [MþH]þ; calcd for C32H46O4S: 527.2593.
solution of 34 (1.8 g, 3.42 mmol) and NH2NH2$H2O (855 mg,
17.1 mmol) in 5:1:1 THF/cyclohexene/EtOH (12 mL) was stirred for
30 min at rt. The solution was diluted with EtOAc (100 mL) and
washed with ice-cold 0.1 M HCl, and water. The organic layer was
dried over cotton and was concentrated. The crude product was
4.1.25. 3a,3b-Mercapto-11-oxo-18b-olean-1,12-dien-29-oic acid (31).
A solution of 30 (150 mg, 0.285 mmol) and NH2NH2$H2O (143 mg,
0.284 mmol) in 5:1:1 THF/cyclohexene/EtOH (7.0 mL) was stirred
for 30 min at rt. The reaction mixture was diluted with EtOAc
(100 mL) and washed with ice-cold 0.1 M HCl and water. The or-
ganic layer was dried over cotton and concentrated. The crude
product was purified by column chromatography (50:1 CH2Cl2/
EtOH) to afford 31 (97 mg, 70%) as a syrup. 1H NMR (CD3OD/CDCl3,
purified by column chromatography (50:1 CH2Cl2/EtOH) to give 35
20
as colorless solid (510 mg, 90.5%). Mp 230e232 ꢀC. [
a
]
þ242 (c
D
0.6, 5:1 CHCl3/MeOH). 1H NMR (CDCl3, 400 MHz):
d 5.75 (s, 1H, 12-
H), 5.74 (dd, J3,2 9.8, J1,2 6.4 Hz, 1H, 2-H), 5.29 (d, 1H, 3-H), 4.44 (dd,
1H, 1-H), 3.73 (s, 1H, 9-H), 2.24 (br dd, J18,19b 13.4 Hz, 1H, 18-H), 2.06
(dt, J16a,16b 13.6, J16a,15a 13.6, J16a,15b 4.5 Hz, 1H, 16a-H), 2.00e1.95 (m,
2H, 21a-H, 19a-H), 1.86 (ddd, J15a,15b 13.6, J15a,16b 4.0 Hz, 1H, 15a-H),
1.73 (ddd, J7a,7b¼J7a,6a 12.8, J7a,6b 3.7 Hz, 1H, 7a-H), 1.64 (t, 1H, 19b-
H), 1.63e1.15 (m, 9H, 6a-H, 5-H, 6b-H, 22a-H, 22b-H, SH, 7b-H, 21b-
H, 15b-H), 1.06 (ddd, 1H, 16b-H), 1.45 (s, 3H, 27-CH3), 1.25 (s, 3H, 25-
CH3), 1.23 (s, 3H, 30-CH3), 1.19 (s, 3H, 26-CH3), 0.98 (s, 3H, 23-CH3),
0.90 (s, 3H, 24-CH3), and 0.88 (s, 3H, 28-CH3). ESI-TOFMS: m/
z¼485.2653 [MþH]þ; calcd for C30H44O3S: 485.3089.
400 MHz, major isomer):
d 6.55 (dd, J1,2 10.4, J1,3<1.0 Hz, 1H, 1-H),
5.68 (s, 1H, 12-H), 5.36 (dd, J3,2 2.0 Hz, 1H, 2-H), 3.31 (d, 1H, 3-H),
2.59 (s, 1H, 9-H), 2.21 (br dd, J18,19b 13.6 Hz, 1H, 18-H), 2.11e2.05 (m,
16H, 16a-H, 21a-H, 19a-H, 15a-H, 6a-H, 7a-H, 19b-H, 6b-H, 7b-H,
22a-H, 22b-H, SH, 21b-H, 15b-H, 5-H, 16b-H), 1.39 (s, 3H, 27-CH3),
1.30 (s, 3H, 25-CH3), 1.18 (s, 3H, 30-CH3), 1.15 (s, 3H, 26-CH3), 1.04 (s,
3H, 23-CH3), 0.91 (s, 3H, 24-CH3), and 0.83 (s, 3H, 28-CH3). ESI-
TOFMS: m/z¼485.2659 [MþH]þ; calcd for C30H44O3S: 485.3089.
4.1.29. X-ray structure determination of compounds 5, 7$H2O, 17, 20,
27, and 33. X-ray data were collected on a Bruker Smart APEX CCD
4.1.26. Diphenylmethyl
1a-mercapto-11-oxo-18b-olean-2,12-dien-
29-oate (33). A solution of 32 (1.0 g, 1.44 mmol), hydrazine hydrate
(217 mg, 4.33 mmol) in 5:1:1 THF/cyclohexene/EtOH (14 mL) was
stirred for 30 min at rt. The solution was diluted with EtOAc
(100 mL) and washed with ice-cold 0.1 M HCl and water. The or-
ganic layer was dried (Na2SO4) and concentrated. Purification of the
crude product on silica gel (10:1 n-hexane/EtOAc) afforded 33
area detector diffractometer using graphite-monochromated Mo K
a
ꢀ
ꢀ
radiation (
absorption (multi-scan method) and
l
¼0.71073 A) and 0.3
u
l
-scan frames. Corrections for
/2 effects were applied.30 After
structure solution with program SHELXS97 and direct methods,
refinement on F2 was carried out with the program SHELXL97.31 Non-
hydrogen atoms were refined anisotropically. All H-atoms were
placed in calculated positions and thereafter treated as riding. Except
for 5, the absolute structures could be unambiguously determined by
anomalous dispersion effects and the Flack absolute structure pa-
rameter (FASP). Important crystallographic data are given below,
crystallographic data for structures 5, 7$H2O, 17, 20, 27, and 33 have
been deposited with the Cambridge Crystallographic Data Centre as
supplementary publications CCDC 759592–759597.
(900 mg, 95%) as colorless crystals. Mp 197 ꢀC (EtOAc/n-hexane).
20
[
a]
þ235 (c 0.9, CHCl3). 1H NMR (400 MHz, CDCl3):
d 7.40e7.27
D
(m, 10H, arom. H), 6.95 (s, 1H, CH(Ph)2), 5.76 (dd, J2,1 6.0 Hz, 1H, 2-
H), 5.58 (s, 1H, 12-H), 5.305 (d, J3,2 10.0 Hz, 1H, 3-H), 4.455 (dd, 1H,
1-H), 3.70 (s,1H, 9-H), 2.11e2.01 (m, 4H, 21a-H,16a-H,18-H, 19a-H),
1.82 (ddd, J15a,15b 13.6, J15a,16b 4.4 Hz, 1H, H15a-H), 1.77e1.46 (m, 4H,
7a-H, 19b-H, 6a-H, 6b-H), 1.44e1.14 (m, 7H, 7b-H, 22a-H, 22b-H,
21b-H, SH, 5-H, 15b-H), 1.01 (ddd, 1H, 16b-H), 1.45 (s, 3H, 27-CH3),
1.25 (s, 3H, 25-CH3), 1.19 (s, 3H, 30-CH3),1.16 (s, 3H, 26-CH3), 0.99 (s,
3H, 23-CH3), 0.91 (s, 3H, 24-CH3), and 0.70 (s, 3H, 28-CH3). 13C NMR
Compound 5: C43H54O4, Mr¼634.86, colorless block from EtOAc/
hexane, 0.50ꢂ0.45ꢂ0.40 mm, monoclinic, space group P21 (no. 4),
ꢀ
ꢀ
ꢀ
a¼7.6234(8) A, b¼33.691(4) A, c¼13.9033(15) A,
b
¼90.309(2)ꢀ,
3
(CDCl3, 100.62 MHz):
d
194.56 (SC]O), 140.13, 140.05, 128.64,
V¼3570.8(7) A , Z¼4,
m
¼0.074 mmꢁ1, dx¼1.181 g cmꢁ3, T¼100 K.
ꢀ
128.45, 128.35, 127.92, 127.72, 126.84 (arom. C), 76.61 (CHPh2). ESI-
36,626 reflections collected (qmax¼30.0ꢀ) and merged to 20,209 in-
dependent data (Rint¼0.028); final R indices (all data): R1¼0.0570,
wR2¼0.1110, 862 parameters, FASP¼0.5(9). The structure contains
two independent molecules and is pseudosymmetric.
TOFMS: m/z¼651.3642 [MþH]þ; calcd for C43H54O3S: 651.3872.
4.1.27. 1a-S-Acetylthio-11-oxo-18b-olean-2,12-dien-29-oic acid (34).
Trifluoroacetic acid (0.5 m) was added dropwise to an ice-cold
solution of 32 (500 mg, 0.722 mmol) and anisole (0.5 mL) in dry
CH2Cl2 (20 mL) and the solution was stirred at 8 ꢀC for 15 h. The
solution was coevaporated with toluene (50 mL) and concentrated.
The crude product was purified by column chromatography using
first 3:1 n-hexane/EtOAc to remove the excess of anisole followed
by elution with 50:1 CH2Cl2/EtOH to afford 34 (194 mg, 85%). The
purified product was dissolved in EtOAc (100 mL) and washed with
ice-cold 0.1 M HCl and water. The organic layer was dried with
cotton and concentrated. Lyophilization of the residue from
Compound 7$H2O: C45H57IO5$H2O, Mr¼822.82, colorless prism
from wet EtOAc/hexane, 0.60ꢂ0.19ꢂ0.08 mm, orthorhombic, space
ꢀ
ꢀ
group P212121 (no. 19), a¼9.6240(4) A, b¼13.4522(6) A, c¼30.5377
3
ꢀ
(14) A, V¼3953.5(3) A , Z¼4,
m
¼0.858 mmꢁ1
,
dx¼1.382 g cmꢁ3
,
ꢀ
T¼100 K. 43,594 reflections collected (qmax¼30.0ꢀ) and merged to
11,452 independent data (Rint¼0.021); final R indices (all data):
R1¼0.0235, wR2¼0.0534, 480 parameters, FASP¼ꢁ0.019(7). The
compound contains a water molecule, which is hydrogen bonded to
the carbonyl oxygen atoms of the two COOR groups (O/O¼2.89
ꢀ
and 2.97 A).

4402
H. Amer et al. / Tetrahedron 66 (2010) 4390e4402
Compound 17: C43H54O3S, Mr¼714.45, colorless prism from eth-
anol, 0.59ꢂ0.44ꢂ0.42 mm, orthorhombic, space group P212121 (no.
References and notes
1. Kitagawa, I. Pure Appl. Chem. 2002, 74, 1189e1198.
ꢀ
ꢀ
ꢀ
19), a¼10.6918(6) A, b¼17.5747(9) A, c¼18.7998(10) A, V¼3532.6
2. Yu, B.; Hui, Y. In Glycochemistry: Principles, Synthesis, and Application;
Wang, P., Bertozzi, C. R., Eds.; Marcel Dekker: New York, NY, Basel, 2001;
pp 163e176.
3. Baran, J. S.; Langford, D. D.; Liang, C.; Pitzele, B. S. J. Med. Chem. 1974, 17,
184e191.
4. Asl, M. N.; Hosseinzadeh, H. Phytother. Res. 2008, 22, 709e724.
5. Rao, S. G. S. R.; Kondaiah, P.; Singh, S. K.; Ravanan, P.; Sporn, M. B. Tetrahedron
2008, 64, 11541e11548.
3
(3) A , Z¼4,
m
¼0.131 mmꢁ1, dx¼1.224 g cmꢁ3, T¼100 K. 52,033 re-
ꢀ
flections collected (qmax¼30.0ꢀ) and merged to 10,266 independent
data (Rint¼0.032); final R indices (all data): R1¼0.0448, wR2¼0.1018,
431 parameters, FASP¼ꢁ0.07(4).
Compound 20: C47H60O6S, Mr¼753.01, colorless block from
CH2Cl2/hexane, 0.48ꢂ0.37ꢂ0.25 mm, monoclinic, space group P21
6. Maitraie, D.; Hung, C.-F.; Tu, H.-Y.; Liou, Y.-T.; Wie, B.-L.; Yang, S.-C.; Wang, J.-P.;
Lin, C.-N. Bioorg. Med. Chem. 2009, 17, 2785e2792.
ꢀ
3
ꢀ
ꢀ
ꢀ
b
(no. 4), a¼11.9330(5) A, b¼16.2826(6) A, c¼11.9601(5) A, ¼116.530
(1)ꢀ, V¼2079.15(14) A , Z¼2,
m
¼0.126 mmꢁ1
,
dx¼1.203 g cmꢁ3
,
7. Chintharlapalli, S.; Papineni, S.; Jutooru, I.; McAlees, A.; Safe, S. Mol. Cancer Ther.
2007, 6, 1588e1598.
8. Papineni, S.; Chintharlapalli, S.; Safe, S. Mol. Pharmacol. 2008, 73, 553e565.
9. Liu, D.; Song, D.; Guo, G.; Wang, R.; Lv, J.; Jing, Y.; Zhao, L. Bioorg. Med. Chem.
2007, 15, 5432e5439.
10. Vicker, N.; Su, X.; Lawrence, H.; Cruttenden, A.; Purohit, A.; Reed, M. J.; Potter,
B. V. L. Bioorg. Med. Chem. Lett. 2004, 14, 3263e3267.
11. Classen-Houben, D.; Schuster, D.; Da Cunha, T.; Odermatt, A.; Wolber, G.; Jordis,
U.; Kueenburg, B. J. Steroid Biochem. Mol. Biol. 2009, 113, 248e252.
12. Walker, B. R.; Connacher, A. A.; Lindsay, R. M.; Webb, D. J.; Edwards, C. R. J. Clin.
Endocrinol. Metab. 1995, 80, 3155e3159.
13. Sandeep, T. C.; Yau, J. L.; MacLullich, A. M.; Noble, J.; Deary, I. J.; Walker, B. R.;
Seckl, J. R. Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 6734e6739.
14. Pellissier, H. Tetrahedron 2004, 60, 5123e5162.
15. Baltina, L. A. Curr. Med. Chem. 2003, 10, 155e171.
16. Aranda, G.; Lallemand, J.-Y.; Azerad, R.; Maurs, M.; Cortes, M.; Ramirez, H.;
T¼100 K. 27,869 reflections collected (qmax¼30.0ꢀ) and merged to
11,412 independent data (Rint¼0.019); final R indices (all data):
R1¼0.0346, wR2¼0.0875, 496 parameters, FASP¼ꢁ0.01(3).
Compound 27: C32H47BrO4S, Mr¼607.67, colorless blade from
EtOAc/hexane, 0.58ꢂ0.34ꢂ0.02 mm, monoclinic, space group P21
ꢀ
3
ꢀ
ꢀ
b
(no. 4), a¼7.9488(13) A, b¼11.3585(19) A, c¼16.754(3) A, ¼90.216
(3)ꢀ, V¼1512.7(4) A , Z¼2,
m
¼1.462 mmꢁ1
,
dx¼1.334 g cmꢁ3
,
ꢀ
T¼297 K. 6109 reflections collected (qmax¼28.3ꢀ) and merged to
4109 independent data (Rint¼0.052); final R indices (all data):
R1¼0.0695, wR2¼0.0865, 354 parameters, FASP¼0.001(10).
Compound 33: C43H54O3S, Mr¼650.92, colorless prism from
EtOAc/hexane, 0.58ꢂ0.20ꢂ0.20 mm, monoclinic, space group P21
Vernal, G. Synth. Commun. 1994, 24, 2525e2535.
ꢀ
ꢀ
ꢀ
b
(no. 4), a¼7.6070(4) A, b¼14.2467(7) A, c¼16.6541(8) A, ¼90.275
17. Teresawa, T.; Okada, T.; Hara, T.; Itoh, K. Eur. J. Med. Chem. 1992, 27, 345e351.
18. Honda, T.; Rounds, B. V.; Bore, L.; Finlay, H. J.; Favaloro, F. G., Jr.; Suh, N.; Wang,
Y.; Sporn, M. B.; Gribble, G. W. J. Med. Chem. 2000, 43, 4233e4246.
19. Chadalapaka, G.; Jutooru, I.; McAlees, A.; Stefanac, T.; Safe, S. Bioorg. Med. Chem.
Lett. 2008, 18, 2633e2639.
20. Beseda, I.; Czollner, L.; Shah, P. S.; Khunt, R.; Gaware, R.; Kosma, P.; Stanetty, C.;
del Ruiz Ruiz, M. C.; Amer, H.; Mereiter, K.; Da Cunha, T.; Odermatt, A.; Claßen-
Houben, D.; Jordis, U. Bioorg. Med. Chem. 2010, 18, 433e454.
21. Elgamal, M. H. A.; Fayez, M. B. E. Tetrahedron 1967, 23, 1633e1640.
22. García-Granados, A.; López, P. E.; Melguizo, E.; Moliz, J. N.; Parra, A.; Simeó, Y.
J. Org. Chem. 2003, 68, 4833e4844.
23. Aranda, G.; Bertranne-Delahaye, M.; Azerad, R.; Maurs, M.; Cortes, M.; Ramirez,
H.; Vernal, G.; Prangé, T. Synth. Commun. 1997, 27, 45e60.
24. Pitzele, B. S. J. Med. Chem. 1973, 17, 191e194.
25. Amr, A.; E-, G. E.; Ali, K. A.; Abdalla, M. M. Eur. J. Med. Chem. 2009, 44, 901e907.
26. Candela, K.; Fellous, R.; Joulain, D.; Faure, R. Flavour Fragrance J. 2003, 18,
52e56.
3
(1)ꢀ, V¼1804.86(16) A , Z¼2,
m
¼0.128 mmꢁ1
,
dx¼1.198 g cmꢁ3
,
ꢀ
T¼100 K. 18,728 reflections collected (qmax¼30.0ꢀ) and merged to
10,296 independent data (Rint¼0.014); final R indices (all data):
R1¼0.0317, wR2¼0.0812, 435 parameters, FASP¼0.03(3).
Acknowledgements
Authors are grateful to Daniel Kolarich and Martin Pabst for
providing the MS data and to David Baum and Maria Hobel for
technical assistance. Financial support by ZIT Zentrum für In-
novation und Technologie GmbH (Vienna Spot of Excellence:
182081) is gratefully acknowledged.
27. Iranpoor, N.; Firouzabadi, H.; Jafari, A. A. Synth. Commun. 2003, 33, 2321e2327.
28. Fuji, L.; Koreyuki, M.; Krematsu, K. Chem. Pharm. Bull. 1988, 36, 1750e1757.
29. Baltina, L. A.; Kunert, O.; Fatykhov, A. A.; Kondratenko, R. M.; Spirikhin, L. V.;
Baltina, L. A., Jr.; Galin, F. Z.; Tolstikov, G. A.; Haslinger, E. Chem. Nat. Compd.
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30. Bruker programs: SMART, version 5.629; SAINTþ, version 6.45; SADABS, version 2.
10; SHELXTL, version 6.14; Bruker AXS: Madison, WI, 2003.
31. Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112e122.
Supplementary data
Supplementary data associated with this article can be found in
online version at doi:10.1016/j.tet.2010.03.098. These data include
MOL files and InChIKeys of the most important compounds de-
scribed in this article.