Straightforward partial synthesis of four diastereomeric 2,3-dihydroxy-olean-12-en-28-oic acids from oleanolic acid

Article abstract of DOI:10.1016/j.tet.2015.09.037

The four diastereomeric 2,3-dihydroxy-olean-12-en-28-oic acids (maslinic, augustic, bredemolic and 3-epi-maslinic acid) were easily accessed from one single starting material, oleanolic acid. The procedures allow the medium-to-large scale preparation of these valuable starting materials. Except for maslinic acid, the triterpenoic acids showed only a low cytotoxicity towards several human tumor cell lines.

Full text of DOI:10.1016/j.tet.2015.09.037

Tetrahedron 71 (2015) 8528e8534
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Straightforward partial synthesis of four diastereomeric
2,3-dihydroxy-olean-12-en-28-oic acids from oleanolic acid
*
ꢀ
Sven Sommerwerk, Lucie Heller, Immo Serbian, Rene Csuk
Martin-Luther-University Halle-Wittenberg, Organic Chemistry, Kurt-Mothes-Str. 2, D-06120 Halle (Saale), Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 20 July 2015
Received in revised form 11 September 2015
Accepted 15 September 2015
Available online 16 September 2015
The four diastereomeric 2,3-dihydroxy-olean-12-en-28-oic acids (maslinic, augustic, bredemolic and 3-
epi-maslinic acid) were easily accessed from one single starting material, oleanolic acid. The procedures
allow the medium-to-large scale preparation of these valuable starting materials. Except for maslinic
acid, the triterpenoic acids showed only a low cytotoxicity towards several human tumor cell lines.
Ó 2015 Elsevier Ltd. All rights reserved.
Keywords:
Maslinic acid
Augustic acid
Bredemolic acid
3-epi-Maslinic acid
Cytotoxicity
1. Introduction
partial synthesis of all four diastereomers from one single pre-
cursor, oleanolic acid.
Secondary plant metabolites are an inexhaustible reservoir for
isolation, modification, and finally their biological testing. Among
other secondary plant metabolites, more than 20.000 triterpenes
have been isolated so far. Pentacyclic triterpenes are among the
most abundant, many of these compounds are bioactive, and they
show antitumor, antiviral, anti-inflammatory as well as antidiabetic
activities. Only a few compounds (e.g., corosolic acid (1, Fig. 1) as
a dietary supplement for the treatment of diabetes mellitus) are
already on the market, while several of them are regarded as
suitable candidates for an extended biological screening including
initial preclinical and clinical trials. This seems especially be true for
derivatives of betulinic acid (2) and of maslinic acid (3). Recently,
we were able to show that a maslinic acid derivative (‘EM2’)1 shows
high cytotoxicity for several human tumor cell lines while being
significantly less toxic for non-malignant human fibroblasts. In the
course of a more detailed look at analogs of this compound, we
became interested to access the four diastereomeric 2,3-dihydroxy-
olean-12-en-28-oic acids, i.e., maslinic acid (3), augustic acid (4),
bredemolic acid (5) and 3-epi-maslinic acid (6) in significant
amount, and we outlined syntheses of maslinic acid (3) from ole-
anolic acid (7) with augustic acid (4) being a side product of this
preparation. In this contribution we extend our strategy to the
Fig. 1. Structure of corosolic acid (1), betulinic acid (2), maslinic acid (3), augustic acid
(4), bredemolic acid (5), 3-epi-maslinic acid (6) and oleanolic acid (7).
2. Results and discussion
Maslinic acid (3) (showing a 2a, 3b-configuration in ring A,
Fig. 1) can easily be obtained in large amounts either by extractive
work-up of solid wastes of the olive oil pressing or from green or
black olives1e4 being easily bought in almost unlimited quantity
* Corresponding author. Tel.: þ49 345 55 025660; fax: þ49 345 55 27030; e-mail
anddas an alternativedby
a
short partial synthesis5 from
address: rene.csuk@chemie.uni-halle.de (R. Csuk).
http://dx.doi.org/10.1016/j.tet.2015.09.037
0040-4020/Ó 2015 Elsevier Ltd. All rights reserved.

S. Sommerwerk et al. / Tetrahedron 71 (2015) 8528e8534
8529
reasonably priced oleanolic acid (7). This approach allowed the
partial synthesis of maslinic acid by convenient and
acetone in the presence of sulfuric acid at 0 ꢀC for 30 min led to the
formation of the (2 ,3
) acetonide 12.26 This acetonide was cleaved
a
a a
chromatography-free four-step synthesis in an over-all yield of 41%
from oleanolic acid. Accessing the C2/C3 epimers of maslinic acid,
however, seemed more challenging.
by dilute acids, by treatment with an ion exchange resin or even by
prolonged contact with silica gel.
The bromides 9/10 also served as a suitable starting material for
the partial synthesis (Scheme 3) of augustic acid (4). Thus, treat-
ment of 9/10 with sodium hydroxide in DMF at 60 ꢀC27 under access
of air gave a 95% yield of 13 whose treatment with sodium boro-
hydride gave augustic acid (4) in 76% isolated yield.
Augustic acid (4), being epimeric to maslinic acid with respect to
position C-2 has previously been isolated in small amounts from the
leaves6 of Perilla frutescense (L.), from Byrsonima crassifolia,7 from the
roots of Ambroma augusta8 and from Rosmarinus officinals (L.).9 Dur-
ing our expedient partial synthesis of 3 [5], 4 has been obtained as
a by-product. Augustic acid, however, seems of special interest to
pharmaceutical chemists, since this compound induces apoptosis10
in murine melanoma B16-F10 cells, and it is an inhibitor of the ty-
rosine phosphatase 1B GST fusion protein as well as of the glycogen
phosphorylase (rabbit).11 In addition, it is vasodilative in rats,12
antiproliferative (Raji-cells)13 and anti-inflammatory (ICR mouse).13
Bredemolic acid (5) was first described by Tschesche et al.14 as
early as 1960, and has been isolated14 from Bredemeyera floribunda
in small amounts; a lengthy partial synthesis has been described by
the same group15 in 1963 and more recently by Cheng et al.16
Bredemolic acid also is an inhibitor16 of the muscle glycogen
phosphorylase in rabbit. Nothing is known, however, of its cyto-
toxicity for human tumor cells.
Scheme 3. Partial synthesis of augustic acid (4): a) NaOH, DMF, 0 ꢀC, 20 min then 60 ꢀ
C
under access of air, 1 h, 95%; b) NaBH4, MeOH, 25 ꢀC, 76%.
Our partial synthesis (Scheme 4) of bredemolic acid (5) started
from, oleanolic acid (7) whose mesylation afforded a mesylate 14 in
almost quantitative yield. Treatment of 14 with lithium carbonate
in dry DMF furnished alkene 1528 whose epoxidation29 with m-
CPBA yielded compound 16. Ring opening of this epoxide in the
presence of aqueous perchloric acid yielded the target compound,
bredemolic acid (5).
Finally, 3-epi-maslinic acid (6) has previously been iso-
lateddamong other triterpenoidsdfrom Potentilla chinensis,17
Centella asiatica,18 Prunella vulgaris19,20 and Salvia officinalis.21
A
lengthy partial synthesis11 of this inhibitor of the muscle glycogen
phosphorylase has been described.
The partial synthesis (Scheme 1) of maslinic acid (3) started
from oleanolic acid (7) that was oxidized with silica gel supported
Jones reagent22 to yield 3-oxo 8,23 whose bromination with pyr-
idiniumtribromide in acetic acid24,25 gave a 7:3 mixture of bro-
mides 9/10 in quantitative yield. These epimeric bromides can be
obtained in analytical pure form by chromatographydbut their
separation is not necessary for the synthesis of 3. Thus, this mixture
of bromides was treated with sodium hydroxide in DMF under inert
gas to yield (2a) configurated 11 whose reduction with NaBH4 gave
a mixture of maslinic acid (3) and 3-epi-maslinic acid (6).
Scheme 4. Partial Synthesis of bredemolic acid (5): a) MsCl, pyridine, 80 ꢀC, 1 h, 99%;
b) Li2CO3, DMF, reflux, 1 h, 85%; c) mCPBA, DCM, 25 ꢀC, 2 h, 85%; d) HClO4, THF, H2O,
25 ꢀC, 30 min, 71%.
Thus, all four diastereomeric 2,3-dihydroxylated triterpenoic
acids 3e6 were readily available in good yields and significant
amounts from a single starting material, oleanolic acid (7). These
compounds can be identified using their physico-chemical prop-
Scheme 1. a) SiO2, Jones reagent, acetone, 30 min, 0 ꢀC, 98%; b) pyridiniumtribromide,
erties (mp, mmp, 1H and 13C NMR, [
a]D) while their identification
AcOH, 2 h, 25 ꢀC, quant.; c) NaOH, DMF, inert gas, 0 ꢀC, quant.; d) NaBH4, MeOH, THF,
using TLC by comparing their Rf values with authentic samples
remains still a problem. Applying ‘usual’ eluents and mixtures
thereof (e.g., hexanes, chloroform, ethyl acetate, THF, DCM, toluene,
benzene, methanol, isopropanol) allows a distinction between 3
and 5. Unambiguous identification of 3 (Rf¼0.29), 5 (Rf¼0.31) and 6
(Rf¼0.37)/4 (Rf¼0.38) was found for a four component system
0
ꢀC, 1 h, 48% (of 3) and 45% (of 6).
Mixtures of these two triterpenoic acids can be separated quite
easily (Scheme 2). Thus, treatment of mixtures of 3 and 6 with
consisting
of
toluene/ethyl
acetate/heptane/formic
acid
(80:20:30:4).
No problem was the identification of the compounds using 1H
NMR spectroscopy.30 Identification of these triterpenoic acids as
well as a proof for the absolute configuration at centers C-2/C-3 can
be obtained from their respective 1H NMR data (Table 1).
Thus, the signal for H-3ax is detected (as in 3 and 4) at lower
frequencies than H-2eq (as in 5 and 6), and the same applies for H-2.
3
The coupling constant JH-2,H-3 is large for 3 and 5 (reflecting an
axial/axial or an equatorial/equatorial configuration) while being
small for 4 and 6.
Scheme 2. Separation of maslinic acid (3)/3-epi-maslinic acid (6) mixtþures by acetali-
zation and de-acetalization [(a) acetone, H2SO4, 0 ꢀC, 30 min; b) IR 120H , MeOH, 25 ꢀC,
95% ].

8530
S. Sommerwerk et al. / Tetrahedron 71 (2015) 8528e8534
Table 1
LCQ 7000 (electrospray, voltage 4.1 kV, sheath gas nitrogen) in-
strument. The optical rotation was measured on a PerkineElmer
polarimeter at 20 ꢀC; TLC was performed on silica gel (Merck
5554); elemental analyses were performed on a Vario EL (CHNS).
The solvents were dried according to usual procedures. The purity
of the compounds was determined by HPLC and found to be >98%.
Oleanolic acid was obtained from different commercial suppliers
in bulk quantities.
Selected NMR spectroscopic data for triterpenoic acids 3e6 (500 MHz (for 1H) or
13
125 MHz (for C), pyridine-d5, 25 ꢀC)
Maslinic
acid (3)
Augustic
acid (4)
Bredemolic
acid (5)
3-epi-Maslinic
acid (6)
d
d
H-2
H-3
4.11ax
3.41ax
9.4
4.41eq
3.44ax
4.0
4.36eq
4.00eq
7.5
4.21ax
3.77eq
2.6
J (H-2, H-3)
J (H-2, H-1ax
J (H-2, H-1eq
)
)
11.2
4.4
2.8
4.0
6.6
6.6
11.6
4.5
d
C-2
C-3
69.0
84.3
71.8
78.7
71.1
78.7
66.5
79.7
4.2. Generaldbiological screening
d
The SRB assay was performed as previously described.31,37
4.3. Synthesis of maslinic acid (3)
Performing photometric SRB assays31 for compounds 3e6
allowed exploring their cytotoxic activities. The EC50 values from
these tests employing several different human cancer cell lines and
mouse fibroblasts NIH 3T3 are compiled in Table 2.
4.3.1. 3-Oxoolean-12-en-28-oic acid (8). A suspension of oleanolic
acid (7, 19.72 g, 43.18 mmol) and silica gel (150 mL) in acetone
(1000 mL) was refluxed for 30 min. The mixture was cooled to 0 ꢀC
and Jones reagent was added [freshly prepared from CrO3 (5.18 g,
51.82 mmol), water (16.8 mL) and concentrated H2SO4 (5 mL)].
After stirring for 30 min at 0 ꢀC, MeOH (4 mL) was added, and
stirring was continued for 1 h before evaporating to dryness. The
resulting solid was subjected to a Soxhlet extraction with diethyl
ether for 6 h; the solvent was removed and 8 (19.31 g, 98%) was
obtained as a slightly yellowish solid; an analytical sample showed
mp: 225e227 ꢀC (lit.: 226e229 ꢀC).23
Table 2
Cytotoxicity of selected compounds (EC50 values in
treatment; the values are averaged from three independent experiments performed
M). Human cancer cell
mM from SRB assays after 96 h of
each in triplicate; confidence interval CI¼95%; cut-off 30
m
lines: 518A2 (melanoma), FaDu (hypopharyngeal carcinoma), HT29 (colorectal ad-
enocarcinoma), MCF7 (breast adenocarcinoma), A549 (lung adenocarcinoma); NIH
3T3: nonmalignant mouse fibroblasts
EC50
518A2
FaDu
HT29
MCF7
A549
NIH 3T3
3
5
6
10
13.7ꢂ0.9
25.7ꢂ0.7
29.6ꢂ1.9
27.9ꢂ1.4
24.9ꢂ1.1
29.1ꢂ1.0
>30
28.8ꢂ0.5
>30
>30
>30
23.4ꢂ0.5
26.4ꢂ1.0
>30
21.1ꢂ0.2
>30
>30
4.3.2. (2
a
)-Bromo-3-oxoolean-12-en-28-oic acid (9) and (2
b
)-
8
25.1ꢂ2.1
bromo-3-oxoolean-12-en-28-oic acid (10). To
a
solution of
>30
>30
>30
27.1ꢂ0.9
>30
>30
(19.25 g, 42.34 mmol) in acetic acid (500 mL) pyridiniumtribromide
(90%, 15.35 g, 43.18 mmol) was added at 25 ꢀC in several portions
within 1 h. After stirring for 2 h, the mixture was cooled (0 ꢀC) and
diluted with ice-cold water (1.5 L). The precipitate was filtered off
and thoroughly washed with water. After drying (CaCl2) a mixture
of compounds 9 and 10 (22.57 g, 100%) was obtained as an off white
solid. The mixture was used for the next steps. Separation of 9 from
10 was accomplished by chromatography (silica gel, hexane/ethyl
acetate 8:1), and gave analytical samples.
The effect of 3 onto cancer cell lines has been investigated by
several groups. Thus, Reyes et al.32e35 demonstrated that 3 is able
inducing apoptotic cell death in colon cancer cell lines HT29 and
Caco-2. It was cytotoxic for the breast cancer cell line MCF7 [12].
But compound 3 also exhibits some selectivity between non-
malignant and cancer cells.36 For example, its cytotoxicity for ma-
lignant 518A2 melanoma cells was twice as for non-malignant
mouse fibroblasts. The highest cytotoxicity was established for 3
and the human melanoma cell line 518A2 while being significantly
less cytotoxic for other human tumor cell lines and for non-
malignant mouse fibroblasts.
Data for (9): mp 155e158 ꢀC; Rf¼0.15 (silica gel, hexane/ethyl
acetate, 8:2); [
a
]D¼þ43.88ꢀ (c¼0.35, CHCl3); IR (KBr):
¼3422v,
n
2949s, 2866s, 1724s, 1697s, 1461s, 1387s, 1365m, 1305w, 1270m,
1187m, 1163m, 1065m, 1012m, 763s, 727m, 646s, 603s cmꢁ1
;
1H
NMR (500 MHz, CDCl3):
d
¼5.28 (dd, J¼3.6, 3.6 Hz, 1H, H-12), 5.06
(dd, J¼13.4, 6.1 Hz, 1H, H-2), 2.82 (dd, J¼13.8, 4.3 Hz, 1H, H-18), 2.56
(dd, J¼13.0, 6.1 Hz, 1H, H-1a), 2.14e1.88 (m, 4H, H-1bþH-16aþH-
11aþH-11b), 1.88e1.54 (m, 8H, H-5þH-9þH-19aþH-7aþH-7bþH-
15aþH-16aþH-16b), 1.54e1.40 (m, 3H, H-6aþH-6bþH-22a),
1.39e1.01 (m, 6H, H-2þH-19bþH-22bþH-21aþH-21bþH-15b), 1.21
(s, 3H, H-25), 1.20 (s, 3H, H-27), 1.12 (s, 3H, H-23), 1.09 (s, 3H, H-24),
0.93 (s, 3H, H-29), 0.90 (s, 3H, H-30), 0.80 (s, 3H, H-26) ppm; 13C
3. Conclusion
All four diastereomeric 2,3-dihydroxy-olean-12-en-28-oic acids
3e6 were semi-synthesized in short sequence from commercially
available oleanolic acid (7). These procedures allow the medium-
to-large scale production in a very straightforward way. For most
steps no purification or simple re-crystallization affords sufficiently
pure material. The cytotoxicity of the triterpenoic acids was eval-
uated in photometric SRB assays. These experiments showed acid 3
slightly higher cytotoxic than acids 4e6 for 518A2 human mela-
noma cells.
NMR (125 MHz, CDCl3):
d¼206.9 (C-3), 184.3 (C-28), 144.0 (C-13),
122.0 (C-12), 56.7 (C-2), 52.4 (C-1), 52.3 (C-5), 49.5 (C-4), 47.1 (C-9),
46.7 (C-17), 45.9 (C-19), 41.9 (C-14), 41.1 (C-18), 40.0 (C-8), 39.5 (C-
10), 33.9 (C-21), 33.2 (C-30), 32.5 (C-7), 32,3 (C-22), 30.8 (C-20),
27.8 (C-15), 26.5 (C-27), 26.0 (C-23), 23.7 (C-29), 23.6 (C-11), 22.8
(C-16), 22.1 (C-24), 19.4 (C-6), 17.3 (C-26), 15.4 (C-25) ppm; MS
79
81
(ESI): m/z (%)¼531.3 ([C
H
BrO3ꢁH]ꢁ, 48), 533.3 ([C30H45
30 45
79
4. Experimental section
BrO3ꢁH]ꢁ, 52), 1063.1 ([2C30H4579BrO3ꢁH]ꢁ, 92), 1065.1 ([C30H45
BrO3þC30H4581BrO3ꢁH]ꢁ, 100); Anal. Calcd for C30H45BrO3
(533.58): C 67.53, H 8.50; found: C 67.31, H 8.74.
4.1. GeneraldChemistry
Data for (10): mp 148e151 ꢀC; Rf¼0.22 (silica gel, hexane/ethyl
Melting points are uncorrected (Leica hot stage microscope),
acetate 8:2); [
a
]D¼þ120.03ꢀ (c¼0.25, CHCl3); IR (KBr):
¼3425m,
n
NMR spectra were recorded using the Varian spectrometers
Gemini 2000 or Unity 500 (
typical experiments: HeH-COSY, HMBC, HMQC, NOESY, DQF-
COSY, INADEQUATE), MS spectra were taken on a Finnigan MAT
2949s, 1731s, 1697s, 1636w, 1459s, 1388s, 1365m, 1305m, 1268m,
d
given in ppm, J in Hz, internal Me4Si;
1208m, 1162m, 1062m, 774s, 709m, 646m, 606m cmꢁ1
(500 MHz, CDCl3):
¼5.30 (dd, J¼3.4, 3.4 Hz, 1H, H-12), 5.08 (dd,
J¼11.0, 9.5 Hz, 1H, H-2), 2.84 (dd, J¼13.9, 3.9 Hz, 1H, H-18), 2.50 (dd,
;
1H NMR
d

S. Sommerwerk et al. / Tetrahedron 71 (2015) 8528e8534
8531
2
3
J¼13.6, 11.3 Hz, 1H, H-1a), 2.10e1.91 (m, 3H, H-11aþH-16aþH-1b),
1.92e1.44 (m, 10H, H-16bþH-5þH-9þH-22aþH-22bþH-15aþH-
19aþH-11bþH-7aþH-6a), 1.44e1.30 (m, 3H, H-6bþH-7bþH-21a),
1.30e1.02 (m, 3H, H-21bþH-19bþH-15b), 1.17 (s, 3H, H-27), 1.14 (s,
3H, H-23), 1.13 (s, 3H, H-29), 0.93 (s, 3H, H-24), 0.91 (s, 3H, H-30),
0.88 (s, 3H, H-25), 0.76 (s, 3H, H-26) ppm; 13C NMR (125 MHz,
11b), 1.96 (ddd, 1H, JH,H¼18.5 Hz, JH,H¼7.5, 3.3 Hz, H-11a), 1.94
2 3
(ddd, 1H, JH,H¼13.2 Hz, JH,H¼4.4, 2.5 Hz, H-16b), 1.80 (ddd, 1H,
2JH,H¼13.9 Hz, JH,H¼14.5, 4.3 Hz, H-22a), 1.79 (dd, 1H,
3
3JH,H¼10.6 Hz, 7.5 Hz, H-9), 1.77 (dd, 1H, JH,H¼14.0 Hz,
2
3JH,H¼13.6 Hz, H-19a), 1.56 (dddd, 1H, 2JH,H¼13.1 Hz, 3JH,H¼4.4, 2.9,
2
3
1.6, H-6a), 1.51 (ddd, 1H, JH,H¼13.0 Hz, JH,H¼11.8, 4.4 Hz, H-7a),
2
3
CDCl3):
d¼209.2 (C-3), 183.1 (C-28), 143.6 (C-13), 122.4 (C-12), 53.5
1.43 (ddd, 1H, JH,H¼13.2 Hz, JH,H¼4.3, 2.6 Hz, H-21a), 1.38 (dddd,
2 3
(C-1), 52.7 (C-5), 51.2 (C-2), 47.7 (C-4), 46.9 (C-9), 46.8 (C-17), 45.9
(C-19), 42.1 (C-14), 41.4 (C-18), 39.6 (C-8), 39.3 (C-10), 34.0 (C-21),
33.2 (C-30), 32.5 (C-22), 31,7 (C-7), 30.8 (C-20), 29.6 (C-23), 27.8 (C-
15), 25.9 (C-27), 23.7 (C-29), 23.6 (C-11), 23.1 (C-16), 20.4 (C-24),
20.1 (C-6), 18.3 (C-25), 16.6 (C-26) ppm; MS (ESI): m/z (%)¼531.3
([C30H4579BrO3ꢁH]ꢁ, 100), 533.3 ([C30H4581BrO3ꢁH]ꢁ, 92), 1063.1
([2C30H4579BrO3ꢁH]ꢁ, 54), 1065.1 ([C30H4579BrO3þC30H4581BrO3
ꢁH]ꢁ, 60); Anal. Calcd for C30H45BrO3 (533.58): C 67.53, H 8.50;
found: C 67.39, H 8.72.
1H, JH,H¼13.1 Hz, JH,H¼13.1, 11.8, 4.9, H-6b), 1.31 (ddd, 1H,
2JH,H¼13.0 Hz, 3JH,H¼4.9 Hz, 2.9, H-7b), 1.27 (dd, 1H, JH,H¼12.5 Hz,
2
3JH,H¼11.4 Hz, H-1a), 1.26 (dd, 1H, JH,H¼14.0 Hz, JH,H¼4.5 Hz, H-
2
3
19b), 1.25 (s, 3H, CH3 (24)), 1.24 (s, 3H, CH3 (27)), 1.19 (ddd, 1H,
2JH,H¼13.2 Hz, JH,H¼14.5, 4.1 Hz, H-21b), 1.17 (ddd, 1H,
3
2JH,H¼13.6 Hz, JH,H¼4.0, 2.5 Hz, H-15a), 1.05 (s, 3H, CH3 (23)), 1.02
3
3
(dd, 1H, JH,H¼13.1, 1.6 Hz, H-5), 1.00 (s, 3H, CH3 (25)), 0.98 (s, 3H,
CH3 (29)), 0.97 (s, 3H, CH3 (26)), 0.92 (s, 3H, CH3 (30)) ppm; 13C NMR
(125 MHz, pyridine-d5):
d
¼180.2 (C-28, 1JC,C¼54.2 Hz), 144.9 (C-13,
1JC,C¼41.3 Hz), 122.5 (C-12, CH]C, 1JC,H¼154 Hz, 1JC,C¼41.3 Hz), 83.9
1
1
1
4.3.3. (2
a
)-Hydroxy-3-oxoolean-12-en-28-oic acid (11). To a solu-
(C-3, JC,H¼142 Hz, JC,C¼39.5, 36.9 Hz), 68.6 (C-2, JC,H¼141 Hz,
1 1
tion of 9/10 (11.28 g, 21.14 mmol) in DMF (130 mL) at 0 ꢀC under
inert gas 2M NaOH (22.20 mL, 44.39 mmol) was added, and 20 min
later, the resulting suspension was re-dissolved by adding MeOH
(250 mL), then acidified with 2 M HCl (25 mL) and finally treated
with water (1.5 L) at 0 ꢀC. The resulting solid was collected and
thoroughly washed with water, dried (CaCl2) and 11 (9.95 g, 100%)
was obtained as an off white solid; mp 143e146 ꢀC; Rf¼0.41 (silica
1JC,C¼39.5, 37.2 Hz), 56.0 (C-5, JC,H¼125 Hz, JC,C¼35.2, 34.2,
32.9 Hz), 48.2 (C-9, 1JC,H¼120 Hz, 1JC,C¼35.0, 33.8, 32.9 Hz), 47.8 (C-
1, 1JC,H¼128 Hz, 1JC,C¼37.2, 31.7 Hz), 46.7 (C-17, Cq, 1JC,C¼54.2, 34.9,
34.5, 31.2 Hz), 46.5 (C-19, 1JC,H¼127 Hz, 1JC,C¼33.1, 32.3 Hz), 42.3 (C-
1
1
14, Cq, JC,C¼41.3, 35.6, 35.0, 33.6 Hz), 42.0 (C-18, JC,H¼130 Hz,
1JC,C¼39.4, 34.9, 32.3 Hz), 39.9 (C-4, Cq, 1JC,C¼36.9, 36.8, 36.6, 34.2),
1
39.9 (C-8, Cq, JC,C¼35.5, 35.2, 33.6, 32.9 Hz), 38.6 (C-10, Cq,
gel, hexane/ethyl acetate, 6:4); [
a
]D¼þ64.23ꢀ (c¼0.35, CHCl3); IR
1JC,C¼35.8, 33.8, 33.7, 32.9 Hz), 34.3 (C-21, 1JC,H¼127 Hz, 1JC,C¼34.3,
1
1
(KBr):
n
¼3446v, 2944s, 1700s, 1636m, 1559w, 1540w, 1507w, 1458m,
34.1 Hz), 33.3 (C-7, JC,H¼128 Hz, JC,C¼35.2, 33.1 Hz), 33.3 (C-30,
1 1 1
1388s, 1268m, 1162m, 1101m, 1056m, 1029s, 994m, 646m cmꢁ1; 1H
NMR (500 MHz, CDCl3):
1JC,H¼122 Hz, JC,C¼36.4 Hz), 33.2 (C-22, JC,H¼128 Hz, JC,C¼34.1,
31.2 Hz), 31.0 (C-20, Cq, 1JC,C¼36.4, 35.9, 34.3, 33.1 Hz), 29.4 (C-24,
d
¼5.28 (dd, J¼3.6, 3.6 Hz, 1H, H-12), 4.54
1
1
1
(dd, J¼12.6, 6.6 Hz, 1H, H-2), 2.83 (dd, J¼13.7, 4.3 Hz, 1H, H-18), 2.40
(dd, J¼12.6, 6.6 Hz, 1H, H-1a), 2.03e1.89 (m, 2H, H-11aþH-11b),
1.82e1.65 (m, 2H, H-22aþH-15a),1.66e1.40 (m, 9H, H-9þH-19aþH-
7aþH-7bþH-22bþH-16aþH-16bþH-6aþH-6b), 1.40e1.04 (m, 6H,
H-1bþH-5þH-19bþH-21aþH-21bþH-15b), 1.26 (s, 3H, H-25), 1.16
(s, 3H, H-23), 1.10 (s, 3H, H-24), 0.93 (s, 3H, H-29), 0.93 (s, 3H, H-30),
1JC,H¼125 Hz, JC,C¼36.6 Hz), 28.3 (C-15, JC,H¼128 Hz, JC,C¼35.0,
1
1
33.5 Hz), 26.2 (C-27, JC,H¼126 Hz, JC,C¼35.6 Hz), 24.0 (C-11,
1JC,H¼129 Hz, JC,C¼41.3, 35.0 Hz), 23.8 (C-16, JC,H¼124 Hz,
1
1
1JC,C¼34.5, 33.5 Hz), 23.8 (C-29, JC,H¼126 Hz, JC,C¼35.9 Hz), 18.9
1
1
1
1
1
(C-6, JC,H¼126 Hz, JC,C¼35.2, 33.1 Hz), 17.7 (C-23), JC,H¼125 Hz,
1JC,C¼36.8 Hz), 17.5 (C-25, 1JC,H¼125 Hz, 1JC,C¼35.5 Hz), 16.9 (C-26,
0.81 (s, 3H, H-26) ppm; 13C NMR (125 MHz, CDCl3):
d¼216.7 (C-3),
1JC,H¼125 Hz, JC,C¼35.8 Hz) ppm; MS (ESI, MeOH, C30H48O4): m/
1
183.9 (C-28), 143.9 (C-13), 122.3 (C-12), 69.3 (C-2), 57.8 (C-5), 49.5
(C-1), 47.9 (C-4), 47.5 (C-9), 46.6 (C-17), 45.9 (C-19), 41.8 (C-14), 41.1
(C-18), 39.6 (C-8), 37.9 (C-10), 33.9 (C-21), 33.2 (C-30), 32.6 (C-7),
32,5 (C-22), 30.8 (C-20), 27.8 (C-15), 26.1 (C-27), 24.9 (C-23), 23.8
(C-29), 23.7 (C-11), 23.0 (C-16), 21.7 (C-24), 19.3 (C-6), 17.4 (C-26),
16.2 (C-25) ppm; MS (ESI): m/z (%)¼469.5 ([MꢁH]ꢁ, 100), 939.2
([2MꢁH]ꢁ, 66), 961.7 ([2Mꢁ2HþNa]ꢁ, 28); Anal. Calcd for C30H46O4
(470.68): C 76.55, H 9.85; found: 76.32, H 9.98.
z¼471.6 ([MꢁH]ꢁ, 63%), 517.2 ([MþHCO2]ꢁ, 72%), 943.3 ([2MꢁH]ꢁ,
100%); Anal. Calcd for C30H48O4: C 76.23, H 10.24; found: C 76.11, H
10.39.
4.4. Synthesis of 3-epi-maslinic acid (6)
4.4.1. (2
a,3
a
)-Dihydroxyolean-12-en-28-oic acid [3-epi-maslinic
acid (6)] and (2
a
,3 )-(isopropylidenedioxy)-olean-12-en-28-oic acid
a
(12). Crude mixtures of 3 and 6 (obtained as described above, 10 g)
were dissolved in acetone (200 mL) at 60 ꢀC. The solution was fil-
tered, and at 0 ꢀC a freshly prepared solution of conc. H2SO4 (4 mL,
98%) in acetone (80 mL) was slowly added. The mixture was stirred
for 30 min, water (1.5 L) was added, and the precipitate was filtered
off, dried (CaCl2) and recrystallized from ethanol to yield pure 3.
The filtrate was evaporated; flash chromatography (silica gel, hex-
aneeethyl acetate, 7:3) furnished crude 12. An analytical sample
was obtained by re-crystallization from acetone. A solution of 12
(5.13 g, 10 mmol) in methanol (100 mL) was stirred with ion ex-
change resin (IR 120Hþ) for 2 h. The resin was filtered off, the sol-
vents were evaporated, and 6 (4.49 g, 95%) was obtained as
a colorless solid (being pure enough for the next transformations).
An analytical sample was obtained by re-crystallization from
ethanol.
4.3.4. (2a,3b)-Dihydroxyolean-12-en-28-oic acid (maslinic acid)
(3). To a solution of 11 (9.95 g, 21.14 mmol) in THF (120 mL) and
MeOH (20 mL) NaBH4 (0.40 g, 10.57 mmol) was added at 0 ꢀC. The
mixture was stirred for 1 h. An aqueous solution of HCl (2 m, 20 mL)
and water (1.5 L) were added, the precipitate was filtered off and
dried (CaCl2). This mixture (consisting of 5 and 6) was dissolved in
acetone (200 mL) at 60 ꢀC. It was cooled to 0 ꢀC, H2SO4 (concen-
trated, 4 mL) in acetone (80 mL) was added, and the mixture was
stirred for 30 min. After adding water (1.5 L), the precipitate was
filtered off, dried (CaCl2) and 3 (4.84 g, 48%) was obtained as white
solid [recrystallized once from EtOAc (150 mL)]; mp 265e267 ꢀC
(lit.:11 266e269 ꢀC); Rf¼0.22 (hexane/ethyl acetate, 6:4);
[
a
]D¼þ55.52ꢀ (c¼0.5, CHCl3).; [(lit.:38
[
a
]D¼34ꢀ, c¼0.2, MeOH; IR
(KBr):
n
¼3424m, 2944s, 1697m, 1462m, 1385m, 1050m cmꢁ1
;
1H
NMR (800 MHz, pyridine-d5):
d
¼5.46 (dd, 1H, 3JH,H¼3.7, 3.4, H-12),
Data for 6: mp 289e293 ꢀC (lit.:11 295e297 ꢀC); Rf¼0.40 (silica
4.07 (ddd, 1H, 3JH,H¼11.4, 9.4, 4.4 Hz, H-2), 3.37 (d, 1H, 3JH,H¼9.4 Hz,
gel, hexane/ethyl acetate, 1:1); [
a
]D¼55.34ꢀ (c¼0.11, pyridine); IR
3
H-3), 3.28 (dd, 1H, JH,H¼13.6, 4.5 Hz, H-18), 2.23 (dd, 1H,
(KBr):
n
¼2946vs, 2876s, 1698s, 1462m, 1388m, 1366m, 1266m,
2JH,H¼ꢁ12.5 Hz, JH,H¼4.4 Hz, H-1b), 2.16 (ddd, JH,H¼13.6 Hz,
1234m, 1184m, 1162m, 1034m, 994m cmꢁ1
pyridine-d5):
;
1H NMR (500 MHz,
3
2
3JH,H¼14.3, 4.4 Hz, 1H, H-15b), 2.09 (ddd, 1H, JH,H¼13.2 Hz,
d¼5.48 (dd, 1H, J¼3.4, 3.4 Hz, H-12), 4.31 (ddd, 1H,
2
3JH,H¼14.3, 4.0 Hz, H-16a), 2.02 (ddd, 1H, JH,H¼13.9 Hz, JH,H¼4.1,
J¼11.6, 4.1, 3.4 Hz, H-2), 3.77 (d, 1H, J¼2.6 Hz, H-3), 3.30 (dd, 1H,
J¼14.0, 4.2 Hz, H-18), 2.23e1.89 (m, 8H, H-15aþH-
2
3
2.6 Hz, H-22b), 2.00 (ddd, 1H, 2JH,H¼18.5 Hz, 3JH,H¼10.6, 3.7 Hz, H-

8532
S. Sommerwerk et al. / Tetrahedron 71 (2015) 8528e8534
11aþH11bþH16aþH16bþH-22aþH-1aþH-9a), 1.86e1.63 (m, 4H,
H-22bþH-1bþH-19aþH-5), 1.60e1.15 (m, 8H, H-7aþH-7bþH-
6aþH-6bþH-21aþH-21bþH-19bþH-15b), 1.28 (s, 3H, CH3 (24)),
1.19 (s, 3H, CH3 (27)), 1.04 (s, 3H, CH3 (26)), 1.00 (s, 3H, CH3 (29)),
0.98 (s, 3H, CH3 (25)), 0.93 (s, 3H, CH3 (30)), 0.91 (s, 3H, CH3 (23))
26.0 (C-27), 23.7 (C-29), 23.6 (C-11), 23.0 (C-16), 21.9 (C-24),19.3 (C-
26), 18.8 (C-6), 17.7 (C-25) ppm; MS (ESI): m/z (%)¼467.3 ([MꢁH]ꢁ,
54), 935.3 ([2MꢁH]ꢁ, 28), 958.6 ([2Mꢁ2HþNa]ꢁ, 24); Anal. Calcd
for C30H44O4 (468.67): C 76.88, H 9.46; found: C 76.61, H 9.83.
ppm; 13C NMR (125 MHz, pyridine-d5):
d¼180.5 (C-28), 145.2 (C-
4.5.2. (2b,3b)-Dihydroxyolean-12-en-28-oic acid (augustic acid)
13), 122.9 (C-12), 79.7 (C-3), 66.5 (C-2), 49.2 (C-5), 48.4 (C-9), 47.0
(C-17), 46.8 (C-19), 43.2 (C-1), 42.6 (C-14), 42.4 (C-18), 40.4 (C-8),
39.2 (C-4), 39.1 (C-10), 34.6 (C-21), 33.6 (C-30), 33.6 (C-22), 33.6 (C-
7), 31.3 (C-20), 29.9 (C-24), 28.7 (C-15), 26.5 (C-27), 24.3 (C-11), 24.1
(C-29), 24.1 (C-16), 22.7 (C-23), 18.9 (C-6), 17.9 (C-26), 17.0 (C-25)
ppm; MS (ESI): m/z (%)¼471.4 ([MꢁH]ꢁ, 100), 943.2 ([2MꢁH]ꢁ, 68),
965.7 ([2Mꢁ2HþNa]ꢁ, 18); Anal. Calcd for C30H48O4: C 76.23, H
10.24; found: C 76.01, H 10.29.
(4). To a solution of 13 (9.43 g, 20.12 mmol) in THF (120 mL) and
MeOH (20 mL) NaBH4 (0.76 g, 20.12 mmol) was added at room
temperature. The mixture was stirred for 1 h, an aqueous solution
of HCl (2M, 20 mL) and water (1.5 L) were added. The precipitate
was filtered off, dried (CaCl2), and 4 (7.22 g, 76%) was obtained as
a
colorless solid [recrystallized from EtOAc (500 mL)]; mp
310e314 ꢀC (decomp.; (lit.:11 308e310 ꢀC)); Rf¼0.49 (silica gel,
hexane/ethyl acetate, 1:1); [
a
]D¼þ88.05ꢀ (c¼0.31, THF) (lit.:16
Data for 12: colorless solid; mp 158e161 ꢀC; Rf¼0.63 (silica gel,
[a
]D¼þ93.5ꢀ (c¼0.17, pyridine); IR (KBr):
n
¼2946vs, 1704vs,
hexane/ethyl acetate, 7:3); [
a
]D¼þ83.74ꢀ (c 0.29, CHCl3); IR (ATR):
1464m, 1388m, 1378m, 1362m, 1322m, 1304m, 1264s, 1188s, 1162m,
n
¼2949s, 2871w, 1695m, 1642m, 1366m, 1217m, 1166w, 1127m,
1150m, 1060m, 1024s, 988m, 932m cmꢁ1
;
1H NMR (500 MHz, pyr-
1048vs, 938m, 861m, 759m, 497s cmꢁ1; 1H NMR (500 MHz, CDCl3):
¼5.29 (dd, J¼3.6, 3.6 Hz, 1H, H-12), 4.17 (ddd, J¼10.6, 6.1, 4.5 Hz,
idine-d5):
d
¼5.47 (dd, J¼3.6, 3.6 Hz, 1H, H-12), 4.12e4.40 (m, 1H, H-
d
2), 3.44 (d, J¼4.0 Hz, 1H, H-3), 3.33 (dd, J¼13.8, 4.5 Hz, 1H, H-18),
2.32 (dd, J¼14.1, 2.8 Hz, 1H, H-1a), 2.26e1.95 (m, 6H, H-15aþH-
16aþH-16bþH-22aþH-11aþH-11b), 1.88e1.80 (m, 2H, H-22bþH-
19a), 1.73e1.43 (m, 5H, H-9þH-6aþH-6bþH-7aþH-21a), 1.53 (s, 3H,
H-25), 1.42e1.18 (m, 5H, H-7bþH-19bþH-1bþH-21bþH-15b), 1.37
(s, 3H, H-23), 1.32 (s, 3H, H-27), 1.28 (s, 3H, H-24), 1.09 (s, 3H, H-26),
1.05e1.00 (m, 1H, H-5), 1.02 (s, 3H, H-29), 0.96 (s, 3H, H-30) ppm;
1H, H-2), 3.69 (d, J¼4.3 Hz, 1H, H-3), 2.83 (dd, J¼13.6, 4.3 Hz, 1H, H-
18), 1.98 (ddd, J¼13.5, 13.5 4.0 Hz, 1H, H-16a), 1.93e1.89 (m, 2H, H-
11a, H11-b), 1.83e1.66 (m, 3H, H-1aþH-22aþH-15a), 1.66e1.54 (m,
4H, H-19aþH-22bþH-16bþH-9), 1.53e1.45 (m, 2H, H-6aþH-7a),
1.47 (s, 3H, CH3 (32)), 1.38e1.27 (m, 3H, H-21aþH-7bþH-6b), 1.32 (s,
3H, CH3 (33)), 1.24e1.06 (m, 4H, H-21bþH-5þH-19bþH-15b), 1.15
(s, 3H, CH3 (27)), 1.07 (s, 3H, CH3 (24)), 1.04e0.97 (m, 1H, H-1b), 0.92
(s, 3H, CH3 (29)), 0.90 (s, 3H, CH3 (30)), 0.89 (s, 3H, CH3 (23)), 0.88 (s,
3H, CH3 (25)), 0.73 (s, 3H, CH3 (26)) ppm; 13C NMR (125 MHz,
13C NMR (125 MHz, pyridine-d5):
d
¼180.5 (C-28), 145.2 (C-13),
123.1 (C-12), 78.7 (C-3), 71.8 (C-2), 56.4 (C-5), 48.9 (C-9), 47.1 (C-17),
46.9 (C-19), 45.3 (C-1), 42.7 (C-14), 42.4 (C-18), 40.3 (C-8), 39.2 (C-
4), 37.8 (C-10), 34.6 (C-21), 33.7 (C-7), 33.7 (C-30), 33.6 (C-22), 31.4
(C-20), 30.6 (C-24), 28.6 (C-15), 26.6 (C-27), 24.4 (C-11), 24.2 (C-29),
24.1 (C-16), 19.0 (C-6), 18.5 (C-23), 17.9 (C-26), 17.0 (C-25) ppm; MS
(ESI): m/z (%)¼471.3 ([MꢁH]ꢁ, 100), 943.3 ([2MꢁH]ꢁ, 30); Anal.
Calcd for C30H48O4: C 76.23, H 10.24; found: C 76.15, H 10.31.
CDCl3):
d
¼183.5 (C-28), 143.6 (C-13), 122.8 (C-12), 107.2 (C-31), 83.0
(C-3), 72.0 (C-2), 49.8 (C-5), 47.2 (C-9), 46.7 (C-17), 46.1 (C-19), 42.4
(C-1), 41.9 (C-14), 41.2 (C-18), 39.5 (C-8), 38.3 (C-10), 35.6 (C-4), 34.0
(C-21), 33.2 (C-30), 32.6 (C-22), 32.4 (C-7), 30.8 (C-20), 29.0 (C-32),
28.5 (C-24), 27.8 (C-15), 26.7 (C-33), 26.1 (C-27), 24.0 (C-23), 23.7
(C-29), 23.4 (C-11), 23.1 (C-16), 18.5 (C-6), 17.2 (C-26), 15.6 (C-25)
ppm; MS (ESI): m/z (%)¼511.5 ([MꢁH]ꢁ, 59),1023.3 ([2MꢁH]ꢁ,100),
1045.6 ([2M-2HþNa]ꢁ, 38); Anal. Calcd for C33H52O4: C 77.30, H
10.22; found: C 77.11, H 10.34.
4.6. Synthesis bredemolic acid
4.6.1. (3b)-Methylsulfonyloxy-olean-12-en-28-oic acid (14). To a so-
4.5. Synthesis of augustic acid (4)
lution of oleanolic acid (7, 5.00 g, 10.95 mmol) in pyridine (40 mL),
methanesulfonyl chloride (2.51 g, 21.92 mmol) was added, and the
mixture was stirred for 1 h at 80 ꢀC. The mixture was poured into
ice cold aq HCl (1 M, 600 mL) and extracted with DCM (500 mL).
The organic layer was washed with water (3ꢃ500 mL) and brine
(1ꢃ500 mL), dried (MgSO4), filtrated, and the filtrate was concen-
trated under reduced pressure to yield 14 (5.78 g, 99%) being suf-
ficiently pure for the next synthetic step. An analytical sample was
obtained by flash chromatography (florisil, hexane/ethyl acetate,
8:2) as a colorless solid; mp 135 ꢀC; Rf¼0.16 (silica gel, hexane/ethyl
4.5.1. 2-Hydroxy-3-oxoolean-1,12-dien-28-oic acid (13). To a solu-
tion of 9/10 (11.28 g, 21.14 mmol) in DMF (130 mL) 2 M NaOH
(22.20 mL, 44.39 mmol) was added at 0 ꢀC, and the mixture was
stirred for 20 min. The suspension was heated to 60 ꢀC and 2M
NaOH (22.30 mL, 44.39 mmol) was added under access of air.
Stirring was continued for 1 h, the mixture was cooled to 0 ꢀC, di-
luted with methanol MeOH (250 mL), acidified with 2M HCl
(50 mL), and finally water (1.5 L) was added. The precipitate was
collected and thoroughly washed with water, dried (CaCl2), and 13
(9.43 g, 95%) was obtained as an off white solid; mp 138e141 ꢀC;
acetate, 8:2); [
a
]D¼þ59.56ꢀ (c¼1.02, CHCl3); IR (KBr):
¼2948vs,
n
2880s, 1728m, 1698s, 1466m, 1356s, 1332s, 1268m, 1176vs, 1110m,
Rf¼0.50 (silica gel, hexane/ethyl acetate 6:4);
(c¼0.31, CHCl3); UVevis (CHCl3): lmax (log
(KBr):
1385s, 1234m, 1149m, 1123s, 1056s, 803m, 458s cmꢁ1
(500 MHz, CDCl3):
¼6.34 (s, 1H, H-1), 5.94 (s, 1H, OH-2), 5.34 (dd,
[
a
]D¼þ100.97ꢀ
;
978m, 934s, 910vs, 876s, 836m, 532m cmꢁ1 1H NMR (500 MHz,
3
)¼272 nm (4.31); IR
CDCl3):
d¼5.26 (dd, J¼3.7, 3.7 Hz, 1H, H-12), 4.35 (dd, J¼10.9, 5.8 Hz,
n
¼3441s, 2947s, 1713s, 1697s, 1652m, 1463s, 1429m, 1396s,
1H, H-3), 3.01 (s, 3H, CH3 (31)), 2.82 (dd, J¼13.9, 4.6 Hz, 1H, H-18),
2.02e1.81 (m, 5H, H-16aþH-11aþH-11bþH-2aþH-2b), 1.81e1.52
(m, 8H, H-22aþH-22bþH-15aþH-1aþH-19aþH-16bþH-6aþH-9),
1.48e1.11 (m, 6H, H-7aþH-7bþH-6bþH-21aþH-21bþH-19b), 1.12
(s, 3H, CH3 (27)), 1.10e1.01 (m, 2H, H-15bþH-1b), 1.02 (s, 3H, CH3
(24)), 0.94 (s, 3H, CH3 (25)), 0.92 (s, 3H, CH3 (29)), 0.90 (s, 3H, CH3
(30)), 0.87e0.82 (m, 1H, H-5), 0.85 (s, 3H, CH3 (23)), 0.74 (s, 3H, CH3
;
1H NMR
d
J¼3.6, 3.6 Hz, 1H, H-12), 2.85 (dd, J¼13.7, 4.3 Hz, 1H, H-18),
2.20e1.92 (m, 3H, H-16aþH-11aþH-11b), 1.91e1.85 (m, 1H, H-9),
1.84e1.67 (m, 2H, H-15aþH-22a), 1.67e1.43 (m, 6H, H-6aþH-
16bþH-22bþH-7aþH-19aþH-5), 1.43e1.06 (m, 6H, H-6bþH-
15bþH-7bþH-21aþH-21bþH-19b),1.22 (s, 3H, H-26),1.22 (s, 3H, H-
23), 1.13 (s, 3H, H-27), 1.10 (s, 3H, H-24), 0.94 (s, 3H, H-29), 0.91 (s,
3H, H-30), 0.83 (s, 3H, H-25) ppm; 13C NMR (125 MHz, CDCl3):
(26)) ppm; 13C NMR (125 MHz, CDCl3):
d
¼184.3 (C-28), 143.8 (C-
13), 122.5 (C-12), 90.6 (C-3), 55.6 (C-5), 47.9 (C-9), 46.7 (C-17), 46.0
(C-19), 41.7 (C-14), 41.1 (C-18), 39.4 (C-8), 39.0 (C-31), 38.7 (C-4),
38.3 (C-1), 37.0 (C-10), 33.9 (C-21), 33.2 (C-30), 32.6 (C-22), 32.6 (C-
7), 30.8 (C-20), 28.4 (C-24), 27.8 (C-15), 26.0 (C-27), 25.3 (C-2), 23.7
(C-29), 23.5 (C-11), 23.0 (C-16), 18.5 (C-6), 17.3 (C-26), 16.5 (C-23),
15.5 (C-25) ppm; MS (ESI): m/z (%)¼533.2 ([MꢁH]ꢁ, 100), 1067.3
d
¼201.2 (C-3), 183.5 (C-28), 144.0 (C-2), 143.9 (C-13), 128.3 (C-1),
122.2 (C-12), 54.0 (C-5), 46.7 (C-4), 45.8 (C-19), 44.0 (C-17), 43.2 (C-
9), 42.1 (C-14), 41.3 (C-18), 40.1 (C-8), 38.6 (C-10), 34.0 (C-21), 33.2
(C-30), 32.6 (C-7), 32,5 (C-22), 30.8 (C-20), 27.8 (C-15), 27.4 (C-23),

S. Sommerwerk et al. / Tetrahedron 71 (2015) 8528e8534
8533
([2MꢁH]ꢁ, 16), 1089.3 ([2M-2HþNa]ꢁ, 12); Anal. Calcd for
added, and the mixture was stirred at room temperature for
30 min. Et2O (200 mL) was added, and the mixture was washed
with saturated aq NaHCO3 solution (2ꢃ100 mL), water (2ꢃ100 mL)
and brine (1ꢃ100 mL), dried (MgSO4), filtrated, and the filtrate was
evaporated under reduced pressure. The residue was subjected to
column chromatography (silica gel, hexane/ethyl acetate, 1:1) to
C
31H50SO5: C 69.62, H 9.42, S 6.00; found: C 69.57, H 9.51, S 5.87.
4.6.2. Olean-2,12-dien-28-oic acid (15). A suspension of compound
14 (5.78 g, 10.81 mmol) and Li2CO3 (4.79 g, 64.86 mmol) in dry DMF
(50 mL) was heated under reflux for 1 h. The mixture was poured
into ice cold aq HCl (0.2 M, 500 mL) and extracted with Et2O
(500 mL). The organic layer was washed with water (4ꢃ500 mL)
and brine (1ꢃ500 mL); dried (MgSO4), filtrated and concentrated
under reduced pressure. The residue was subjected to column
chromatography (silica gel, hexane/ethyl acetate, 8:2) to yield
compound 15 (4.03 g, 85%) as a colorless solid; mp 144e146 ꢀC;
yield compound
6 (370 mg, 71%) as a colorless solid; mp
234e237 ꢀC (lit.:14 288e292 ꢀC); Rf¼0.31 (silica gel, hexane/ethyl
acetate, 1:1);
[
a
]D¼þ91.13ꢀ (c¼0.29, pyridine) (lit.:14 þ93.5ꢀ
(c¼0.17, pyridine); IR (KBr): ¼2946vs, 2868s, 1696s, 1462m, 1386m,
n
1366m, 1304m,1268m, 1240m, 1210m,1182m,1164w, 1112w,1064m,
1010m cmꢁ1 1H NMR (500 MHz, pyridine-d5):
¼5.53 (dd, J¼3.4,
;
d
Rf¼0.53 (silica gel, hexane/ethyl acetate, 8:2); [
a
]D¼þ107.58ꢀ
3.4 Hz, 1H, H-12), 4.36 (ddd, J¼7.2, 6.6, 6.6 Hz, 1H, H-2), 4.00 (d,
J¼7.5 Hz, 1H, H-3), 3.32 (dd, J¼13.6, 4.2 Hz, 1H, H-18), 2.22e1.99 (m,
6H, H-15aþH-16aþH-1aþH-11aþH-11bþH-22a), 1.99e1.75 (m, 5H,
H-16bþH-1bþH-9þH-22bþH-19a), 1.61e1.39 (m, 5H, H-7a)þH-
5þH-6aþH-6bþH-21a), 1.38e1.15 (m, 4H, H-7bþH-19bþH-15bþH-
21b), 1.32 (s, 3H, CH3 (25)), 1.31 (s, 3H, CH3 (23)), 1.29 (s, 3H, CH3
(24)), 1.26 (s, 3H, CH3 (27)), 1.08 (s, 3H, CH3 (26)), 1.01 (s, 3H, CH3
(29)), 0.94 (s, 3H, CH3 (30)) ppm; 13C NMR (125 MHz, pyridine-d5):
(c¼0.90, CHCl3), lit.:28
[
a
]D¼þ74ꢀ (c¼1, CHCl3); IR (KBr):
¼2950vs,
n
2886s,1696vs,1462m,1384m,1364m,1304m, 1270m,1208w,1162w,
1032w, 1018w cmꢁ1
;
1H NMR (500 MHz, CDCl3):
d
¼5.44e5.28 (m,
3H, H-2þH-3þH-12), 2.84 (dd, J¼13.6, 4.2 Hz, 1H, H-18), 2.04e1.68
(m, 6H, H-16aþH-11aþH-11bþH-1aþH-22aþH-15a), 1.68e1.54 (m,
5H, H-19aþH-16bþH-9þH-1bþH-22b), 1.54e1.08 (m, 9H, H-6aþH-
6bþH-7aþH-7bþH-21aþH-21bþH-19bþH-5þH-15b), 1.15 (s, 3H,
CH3 (27)), 0.96 (s, 3H, CH3 (24)), 0.95 (s, 3H, CH3 (25)), 0.94 (s, 3H,
CH3 (29)), 0.91 (s, 3H, CH3 (30)), 0.88 (s, 3H, CH3 (23)), 0.80 (s, 3H,
d
¼180.6 (C-28), 145.2 (C-13), 123.1 (C-12), 78.7 (C-3), 71.1 (C-2), 51.2
(C-5), 49.0 (C-9), 47.1 (C-17), 46.8 (C-19), 46.1 (C-1), 42.8 (C-14), 42.5
(C-18), 40.4 (C-8), 38.3 (C-4), 38.1 (C-10), 34.6 (C-21), 33.6 (C-30),
33.6 (C-22), 33.4 (C-7), 31.3 (C-20), 28.6 (C-15), 27.5 (C-24), 26.5 (C-
27), 24.3 (C-11), 24.1 (C-29), 24.1 (C-16), 23.8 (C-23), 20.1 (C-6), 20.0
(C-25), 17.7 (C-26) ppm. MS (ESI): m/z (%)¼471.4 ([MꢁH]ꢁ, 100);
Anal. Calcd for C30H48O4: C 76.23, H 10.24; found: C 76.17, H 10.38.
CH3 (26)) ppm; 13C NMR (125 MHz, CDCl3):
d¼184.5 (C-28), 143.6
(C-13), 138.1 (C-3), 123.0 (C-12), 121.6 (C-2), 52.2 (C-5), 46.8 (C-17),
46.3 (C-9), 46.0 (C-19), 41.9 (C-14), 41.2 (C-18), 40.9 (C-1), 39.6 (C-8),
36.4 (C-4), 34.6 (C-10), 34.0 (C-21), 33.2 (C-30), 32.6 (C-22), 32.2 (C-
7), 32.0 (C-24), 30.8 (C-20), 27.8 (C-15), 26.0 (C-27), 23.7 (C-29),
23.4 (C-11), 23.1 (C-16), 22.9 (C-23), 19.6 (C-6), 17.3 (C-26), 15.7 (C-
25) ppm; MS (ESI): m/z (%)¼437.5 ([MꢁH]ꢁ, 100), 875.4 ([2MꢁH]ꢁ,
20), 898.6 ([2M-2HþNa]ꢁ, 38); Anal. Calcd for C30H46O2: C 82.14, H
10.57; found C 82.02, H 10.65.
Acknowledgements
€
Thanks are due to Dr. D. Strohl for the NMR spectra, to Dr. R.
Kluge for numerous ESI-MS measurements, and to Mrs. J. Wiese
for measuring the IR spectra and optical rotations. The cell lines
4.6.3. (2a,3a)-Epoxy-olean-12-en-28-oic acid (16). To a solution of
compound 15 (570 mg, 1.30 mmol) in dry DCM (30 mL) m-CPBA
(250 mg, 1.45 mmol) was added, and the mixture was stirred at
room temperature for 2 h. Further DCM (50 mL) was added, and the
mixture was washed with saturated aq NaHCO3 solution
(2ꢃ50 mL), water (2ꢃ50 mL) and brine (1ꢃ50 mL), dried (MgSO4),
filtrated, and the filtrate was concentrated in vacuo. The residue
was subjected to column chromatography (silica gel, hexane/ethyl
acetate, 8:2) to yield compound 16 (502 mg, 85%) as a colorless
solid; mp 176e177 ꢀC; Rf¼0.44 (silica gel, hexane/ethyl acetate,
€
were kindly provided by Dr. Thomas Muller (Dept. of Haematol-
€
ogy/Oncology, Martin-Luther Universitat Halle-Wittenberg). Sup-
€
port by the ‘GrunderwerkstattdBiowissenschaften’ is gratefully
acknowledged. We also thank Mr. S. Ludwig for his valuable help in
the synthesis of some compounds and initial studies as well as
Prof. Dr. J. Balbach for his allowance to use his 800 MHz NMR
spectrometer.
Supplementary data
8:2); [
a
]D¼þ74.33ꢀ (c¼0.87, CHCl3); IR (KBr):
¼2942vs, 2866s,
n
1698vs, 1462s, 1386s, 1364s, 1304s, 1280s, 1238s, 1162s, 1122m,
Supplementary data related to this article can be found in the
online version, at http://dx.doi.org/10.1016/j.tet.2015.09.037
1064m, 1012m, 942m, 828s cmꢁ1
¼5.28 (dd, J¼3.6, 3.6 Hz, 1H, H-12), 3.20e3.17 (m, 1H, H-2),
2.84e2.79 (m, 1H, H-18), 2.79 (d, J¼3.8 Hz, 1H, H-3), 2.00e1.47 (m,
10H,
;
1H NMR (500 MHz, CDCl3):
d
References and notes
H-16aþH-16bþH-1aþH-11aþH-11bþH-22aþH-22bþH-
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H-21aþ H-1bþH-6bþH-7b), 1.23e1.05 (m, 3H, H-21bþH-19bþH-
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0.96e0.91 (m, 1H, H-5), 0.92 (s, 3H, CH3 (29)), 0.91 (s, 3H, CH3 (25)),
0.89 (s, 3H, CH3 (30)), 0.71 (s, 3H, CH3 (26)) ppm; 13C NMR
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