Simple structural modifications confer cytotoxicity to allobetulin

Article abstract of DOI:10.1016/j.bmc.2015.05.015

Abstract A variety of allobetulin derivatives was synthesized from allobetulin or allobetulone. These compounds were screened for their cytotoxic activity using a photometric SRB assay employing six different human tumor cell lines. In summary, opening of

Full text of DOI:10.1016/j.bmc.2015.05.015

Bioorganic & Medicinal Chemistry 23 (2015) 3002–3012
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Simple structural modifications confer cytotoxicity to allobetulin
⇑
Lucie Heller, Anja Obernauer, René 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 12 February 2015
Revised 4 May 2015
Accepted 5 May 2015
Available online 12 May 2015
A variety of allobetulin derivatives was synthesized from allobetulin or allobetulone. These compounds
were screened for their cytotoxic activity using a photometric SRB assay employing six different human
tumor cell lines. In summary, opening of ring A of allobetulin in general lowers the cytotoxicity, but the
2,3-seco diethyl ester was highly cytotoxic and remarkable selective for A549 lung carcinoma cells while
being significantly less cytotoxic for non-malignant mouse fibroblasts. The introduction of an amino
group at position C-3 in the allobetulin skeleton enhances cytotoxicity and furnishes highly cytotoxic
compounds. Their selectivity to distinguish between cancer cell and non-malignant cell depends on
the configuration at position C-3.
Keywords:
Allobetulin
Betulin
Cytotoxicity
SRB-assay
Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction
and screened. Interestingly enough, only a few reports have been
published concerning the biological activity of 1 and derivatives
Plant derived secondary metabolites have been exploited by
humankind for thousands of years to combat diseases. Over the
last decade, these natural products were subject to many biological
studies, and—in order to improve their biological activities—mis-
cellaneous chemical transformations have been performed, and
numerous new derivatives were obtained and screened for their
activity.1
thereof.18 Thus, allobetulin as well as some acetylated and phos-
phorylated analogs and some oxime-derived compounds have
been shown to exhibit moderate antiviral activity.18–20 In addition,
for several derivatives a moderate antiulcer activity21,22 was deter-
mined, and the cytotoxicity of some quinoxaline, pyrazine, azoles
or 2-hydroxymethylene derivatives of 1 was significantly lower
than those of the corresponding betulin derived analogs.23–25
Quite recently, a moderate activity was reported for an allobetulin
derived ozonide.26
The diminished cytotoxicity of allobetulin derivatives as com-
pared to their parent betulin analog is not unexpected at all. The
presence of a carbonyl or carboxyl group at C-28 of the betulin
skeleton seems mandatory for obtaining good cytotoxicity,
although there some exceptions to this rule of thumb.27 As previ-
ously shown for several pentacyclic triterpenoids, the presence of
an amino group at position C-3 seems favorable and enhances
cytotoxicity.28–30 Hence, we decided to investigate allobetulin
and derivatives thereof in more detail.
Natural triterpenoids2 have been used in traditional medicine
for their anticancer, antiviral/virostatic, anti-inflammatory and
hepatoprotective activity.3–11 These triterpenes are important for
the survival of the plant, and they form a wide family of com-
pounds. They are biosynthesized by numerous higher plants and
some higher fungi from 2,3-epoxy-squalene by a cyclization reac-
tion; by this way, most abundant betulin (Fig. 1) is formed. A re-ar-
rangement reaction, however, transforms betulin to allobetulin (1).
While betulin was first accessed as early as 178812 from the
sublimation of birch bark, and its oxidized product betulinic acid
(Fig. 1) was first described13 in 1902—albeit of uncertain struc-
ture—the structure of a ‘re-arranged’ betulin remained unclear
until 1922 when Schulze and Pieroh14 treated betulin with formic
2. Results and discussion
2.1. Chemistry
acid, and allobetulin (1), a (3b,18a,19b) 19,28-epoxy-18-olean-3-ol
was formed. The correct molecular formula was determined by
Dischendorfer,15 but it took almost another century to obtain a sin-
gle crystal X-ray structure.16
Allobetulin (1) can be obtained (Scheme 1) from betulin by a
Wagner–Meerwein re-arrangement, and many different conditions
have been applied including formic acid, sulfuric acid, hydrochloric
acid, or solid supported reagents as well as ferric chloride hydrate,
trifluoroacetic acid, orthophosphoric acid, bismuth triflate or p-
toluenesulfonic acid.18 In our hands, the reaction of betulin with
The cytotoxic activity of betulin and betulinic acid has been
investigated,17 and numerous derivatives have been prepared
⇑
Corresponding author. Tel.: +49 (0) 345 5525660; fax: +49 (0) 345 5527030.
E-mail address: rene.csuk@chemie.uni-halle.de (R. Csuk).
http://dx.doi.org/10.1016/j.bmc.2015.05.015
0968-0896/Ó 2015 Elsevier Ltd. All rights reserved.

L. Heller et al. / Bioorg. Med. Chem. 23 (2015) 3002–3012
3003
29
30
28
H
H
H
H
H
O
H
OH
OH
28
25
H
26 19
1
28
O
2
H
H
H
27
HO
HO
HO
3
H
H
24 23
Betulin
Betulinic acid
Allobetulin (1)
Figure 1. Structure of betulin, betulinic acid and allobetulin (1).
Scheme 1. Synthesis of allobetulin (1) and allobetulone (2) derived compounds 3–8: (a) Montmorillonit K10, DCM, 3 h reflux, 5 days 25 °C, 79%; (b) CrO3, H2SO4, acetone,
81%; (c) m-CPBA, NaHCO3, DCM, 25 °C, 3 h, 85%; (d) HONH2ÁHCl, pyridine, 60 °C, 3 h, 91.5%; (e) POCl3, pyridine, 25 °C, overnight, 46%; (f) NH+4CH3CO2À, MeOH, NaBH3CN, 25 °C,
24 h, 16% (of 6) and 46% (of 7); (g) Oxone,ÒMeOH, H2SO4, 25 °C, 7 days, 65%; (h) KOtBu, tBuOH, air, 40 °C, 1 h, 80%.
Montmorillonit K31 worked quite nicely, and 1 was obtained in 79%
yield. Jones oxidation of 1 gave 81% of allobetulone (2).32 This com-
pound is characterized in its IR spectrum by the presence of a sig-
nal at
m
= 1702 cmÀ1 being assigned to the C@O moiety. For this
carbonyl group in the 13C NMR spectrum
a
signal at
d = 218.2 ppm was detected. Reaction of 2 with m-CPBA33 in
DCM in the presence of NaHCO3 resulted in a Bayer–Villiger reac-
tion, and lactone 334–37 was obtained in 85% isolated yield.
From the reaction of 2 with hydroxylammonium chloride38 in
pyridine for 3 h at 60 °C oxime 437,39,40 was obtained, whose treat-
ment with POCl3 gave seco-5. Reductive amination of 2 with ammo-
nium acetate and sodium cyanoborohydride41 gave a mixture of
amines (3a)-6 and (3b)-7 that were easily separated by chromatog-
raphy and their absolute configuration with respect to C-3 was
established from their 1H NMR spectra. From the reaction of 2 with
potassium tert-butanolate in the presence of air compound 8 was
obtained by the process of an abnormal Beckmann rearrangement.42
A ring opening formation of an alkene occurred (as a consequence of
a Bayer–Villiger rearrangement followed by an elimination reaction
of the transient tertiary alcohol) also upon treatment of 2 with
oxoneÒ, and a yield of 65% of seco-9 was obtained.
Scheme 2. Synthesis of seco-10 and esters 9, 11–16: (a) MeOH, KOH, 25 °C, 7 d,
87%; (b) K2CO3, DMF, RX, 25 °C, 12 h.
different alkyl halides in the presence of potassium carbonate
yielded esters 11–16. Reaction of 1 with acetic acid and nitric acid
(Scheme 3) as previously reported by Tolstikov et al.43 gave 70% of
Treatment of
9 with potassium hydroxide in methanol
(Scheme 2) furnished acid 10. Esterification of 10 in DMF with

3004
L. Heller et al. / Bioorg. Med. Chem. 23 (2015) 3002–3012
2-nitro-substituted 17 and 8% of 2,2-dinitro-substituted 18. The
reaction of 17 with hydrogen peroxide in the presence of potas-
sium carbonate for 5 days resulted in the formation of diacid 19
in 78% yield whose esterification as described above gave diesters
20–26.
7000 (electrospray, voltage 4.1 kV, sheath gas nitrogen) instru-
ment, IR and spectra were taken as KBR pills on a Perkin-Elmer
Spectrum 1000 instrument. The optical rotation was measured
on a Perkin-Elmer polarimeter at 20 °C; TLC was performed on sil-
ica gel (Merck 5554); elemental analyses were performed on a
Vario EL (CHNS). The solvents were dried according to usual proce-
dures. The purity of the compounds were determined by HPLC and
found to be >98%. Betulinic acid was obtained from different com-
mercial suppliers in bulk quantities.
2.2. Biology
Many natural occurring triterpenes are cytotoxic, and usually
EC50 values between 10–80 lM have been reported. Performing
photometric SRB assays44 allowed exploring the cytotoxic activi-
ties of our compounds. The EC50 values from these tests employing
several different human cancer cell lines are compiled in Table 1.
As compared to betulin, allobetulin (1) lost all of its cytotoxicity
while some of the cytotoxicity is restored upon oxidation at posi-
tion C-3. No activity was found for the lactone 3 and the nitrile
5. Not unexpected but nevertheless disappointing was the perfor-
mance of esters 11–15 and most of the diesters 20–26. For most
4.2. General—biological screening
The SRB assay was performed as previously described.44,50–52
4.3. Syntheses
4.3.1. Allobetulin (1)
Following the procedure of Li et al.31 from betulin (3.0 g,
6.79 mmol) and Montmorillonit K10 (3.0 g) followed by chro-
matography (SiO2, hexane/ethyl acetate, 95:5) 1 (2.36 g, 79%)
was obtained as a colorless solid; Rf = 0.47 (hexane/ethyl acetate,
of these compounds EC50 values >30 lM (cut-off of the assay) were
determined. A somewhat higher cytotoxicity was observed for the
di-propargyl ester 24. Surprisingly enough, the di-ethyl ester 21
showed an excellent cytotoxicity for the A549 lung carcinoma cell
8:2); mp 268–273 °C (lit.: 266–268 °C31); [
a]D = +48.2° (c = 0.11,
line, and an EC50 = 5.9
lM was observed.
CHCl3) (lit.: [a]
D = +48° (c = 0.2, CHCl3)53); MS (ESI, MeOH):
Good cytotoxicity, however, was established for the (3
a
) 3-
m/z = 443.1 (60%, [M+H]+), 885.4 (100%, [2M+H]+), 907.4 (11%,
amino-derivative 6, and an even better result was obtained for
[2M+Na]+).
(3b) 3-amino 7 showing EC50 values ranging between 5.5 and
10.4
l
M. This parallels previous findings for other triterpenoids,
4.3.2. Allobetulone (2)
for example, glycyrrhetinic acid,28 boswellic acid,45,46 oleanolic47–49
or usolic acid,41 where the introduction of an amino group at
position C-3 led to highly increased cytotoxicity. High cytotoxicity
for tumor cells, however, is not sufficient to make a compound
ready for broader biological screening; a low cytotoxicity for
non-malignant cells is mandatory. Hence, compounds 6, 7 and 21
were screened in SRB assays employing non-malignant mouse
Jones oxidation of 1 (1.76 g, 3.98 mmol) in acetone (700 mL)
with a fresh prepared mixture of CrO3 (1.58 g, 15.8 mmol), water
(15.2 mL) and sulfuric acid (98%, 3.6 mL) followed by chromato-
graphic purification (SiO2, hexane/ethyl acetate, 95:5) gave 2
(1.42 g, 81%) as a colorless solid; Rf = 0.70 (hexane/ethyl acetate,
8:2); mp 235–238 °C (lit.: 235–238 °C32); [
a]D = +82.2° (c = 0.11,
CHCl3) (lit.:
[a]
D = +86° (c = 1.0, CHCl3)53); MS (ESI, MeOH):
fibroblasts NIH 3T3. For (3
was found; (3b)-configurated 7 showed increased cytotoxicity for
the fibroblasts, and an EC50 = 7.3 0.4 was determined.
Improved selectivity was found for 21, since NIH 3T3 cells gave
a
)-configurated 6 EC50 = 15.9 0.1
lM
m/z = 441.1 (100%, [M+H]+), 463.3 (6%, [M+Na]+), 472.7 (11%,
[M+H+MeOH]+), 494.7 (14%, [M+Na+MeOH]+), 881.5 (98%,
[2M+H]+), 903.3 (19%, [2M+Na]+).
lM
an EC50 = 25.0 1.0
lM.
4.3.3. (18a,19b) 19,28-Epoxy-A-homo-4-oxa-18-oleanan-3-one
(3)
To a solution of 2 (350 mg, 0.8 mmol) in DCM (20 mL), m-CPBA
(420 mg, 2.43 mmol) and NaHCO3 (420 mg, 5 mmol) were added,
and the mixture was stirred at 25 °C for 3 h. The mixture was
washed in succession with an aq solution of KI (10%, 20 mL), aq
NaHCO3 (satd, 20 mL), aq Na2S (1%, 20 mL), water (3 Â 200 mL),
and dried. The solvent was removed, and the residue subjected
to chromatography (SiO2, hexane/ethyl acetate, 7:3) to yield 3
(310 mg, 85%) as a colorless solid; Rf = 0.29 (hexane/ethyl acetate,
3. Conclusions
Several different seco-compounds derived from allobetulin or
allobetulone were synthesized in short sequences. Ring opening
of ring A led to products more or less not cytotoxic at all.
Reductive amination of allobetulone, however, yielded two epi-
meric amines 6 and 7 that showed rather low EC50 values in pho-
tometric SRB assays. Loss of a carboxyl at C-28 (as present in
betulinic acid) lowers cytotoxicity, but the introduction of an
amino moiety at C-3 compensates and increases the cytotoxicity
of the compounds towards human tumor cell lines. The configura-
tion at C-3 is important to obtain compounds of sufficient non-ma-
lignant/malignant selectivity. Screening of compounds using a
broad panel of tumor cell lines seems appropriate to find selective
compounds as exemplified for the seco-diester 21.
8:2); mp 227–230 °C (lit.: 246–248 °C35); [
CHCl3); IR (KBr): = 3416m, 2934s, 1720s, 1462s, 1373s, 1355s,
1328m, 1285s, 1264m, 1248s, 1215m, 1192s, 1152s, 1138s,
1113s, 1056m, 1031s, 1005s cmÀ1 1H NMR (500 MHz, CDCl3):
a]D = +90.8° (c 0.7,
m
;
d = 3.76 (d, J = 7.8 Hz, 1H, CHa (28)), 3.52 (s, 1H, CH (19)), 3.44 (d,
J = 7.8 Hz, 1H, CHb (28)), 2.63 (ddd, J = 14.1, 12.9, 4.6 Hz, 1H, CHa
(2)), 2.48 (ddd, J = 14.3, 5.9, 3.5 Hz, 1H, CHb (2)), 1.81 (ddd,
J = 14.3, 13.0, 3.4 Hz, 1H, CHa (1)), 1.74 (dd, J = 12.2, 2.8 Hz, 1H,
CH (9)), 1.70–1.59 (m, 2H, CHa (12) + CHa (11)), 1.58–1.45 (m, 6H,
CHb (1) + CHa (22) + CH (13) + CHa (6) + CHa (21) + CH (18)), 1.47
(s, 3H, CH3 (24)), 1.44–1.32 (m, 4H, CHa (7) + CH (5) + CHa
(16) + CHb (11)), 1.38 (s, 3H, CH3 (23)), 1.32–1.26 (m, 5H, CHb
(7) + CHb (6) + CHa (15) + CHb (22) + CHb (16)), 1.22 (dd, J = 13.4,
5.1 Hz, 1H, CHb (21)), 1.11 (ddd, J = 12.7, 4.0, 2.4 Hz, 1H, CHb
(15)), 1.07 (s, 3H, CH3 (25)), 1.01 (s, 3H, CH3 (26)), 0.95–0.88 (m,
1H, CHb (12)) 0.92 (s, 3H, CH3 (30)), 0.89 (s, 3H, CH3 (27)), 0.79
(s, 3H, CH3 (29)) ppm; 13C NMR (125 MHz, CDCl3): d = 175.1
(C@O, C3), 88.0 (CH, C19), 86.1 (Cquart, C4), 71.4 (CH2, C28), 53.1
4. Experimental
4.1. General—chemistry
Melting points are uncorrected (Leica hot stage microscope),
NMR spectra were recorded using the Varian spectrometers
Gemini 2000 or Unity 500 (d given in ppm, J in Hz, internal
Me4Si; typical experiments: H–H-COSY, HMBC, HMQC, NOESY
and DQF-COSY), MS spectra were taken on a Finnigan MAT LCQ

L. Heller et al. / Bioorg. Med. Chem. 23 (2015) 3002–3012
3005
Scheme 3. Synthesis of nitro-compounds 17 and 18, seco-diacid 19 and diesters 20–26: (a) HOAc, HNO3, 25 °C, 1 h, 70% (of 20) and 8% (of 21); (b) MeOH, H2O2, K2CO3, 25 °C,
5 days, 78%; (c) K2CO3, DMF, RX, 25 °C, 12 h.
Table 1
Cytotoxicity of selected compounds (EC50 values in
triplicate; confidence interval CI = 95%; cut-off 30
l
M from SRB assays after 96 h of treatment; the values are averaged from three independent experiments performed each in
l
M)
EC50
518A2
HT29
MCF7
A549
8505C
A2780
Betulin
1
2
28.8 1.9
>30
22.5 2.6
>30
>30
>30
26.8 2.5
>30
24.4 0.8
>30
>30
20.6 1.1
>30
20.8 2.7
>30
>30
>30
>30
>30
29.3 0.9
>30
18.5 1.7
>30
3
>30
4
n.s.
5
6
7
8
25.7 0.4
10.2 0.19
5.4 0.7
>30
>30
>30
21.5 2.2
12.6 0.6
7.3 0.1
23.3 3.8
>30
>30
>30
6.8 0.2
6.2 0.6
>30
15.2 0.1
10.4 0.3
>30
15.5 1.8
7.8 0.2
>30
12.9 1.4
6.6 0.1
>30
9
>30
>30
>30
>30
>30
10
11–15
16
19
20
21
22
23
24
25
26
n.s.
>30
n.s.
n.s.
29.4 2.8
26.1 1.4
>30
>30
17.4 1.8
>30
>30
>30
>30
>30
>30
17.5 1.7
17.6 1.7
27.0 2.9
29.2 4.0
15.7 0.6
>30
29.4 4.5
26.1 1.6
>30
>30
27.2 1.0
>30
>30
5.9 0.6
>30
>30
21.1 2.0
>30
27.1 4.0
24.6 2.5
>30
>30
18.7 2.4
>30
18.1 3.0
18.9 2.0
22.4 3.0
22.7 1.0
12.5 1.7
>30
n.s.
Human cancer cell lines: 518A2 (melanoma), HT29 (colorectal adenocarcinoma), MCF7 (breast adenocarcinoma), A2780 (ovarian adenocarcinoma); A549 (alveolar basal
epithelial adenocarcinoma) and 8505C (thyroid carcinoma); n.s. stands for not soluble.
(CH, C9), 51.8 (CH, C5), 46.8 (CH, C18), 41.6 (Cquart, C20), 40.9 (Cquart
C14), 40.6 (Cquart, C8), 40.4 (CH2, C1), 39.6 (Cquart, C10), 36.8 (CH2,
C16), 36.4 (Cquart, C17), 34.6 (CH, C13), 32.9 (CH2, C7), 32.8 (CH21
C21), 32.5 (CH2, C2), 31.1 (CH3, C24), 28.9 (CH3, C30), 26.9
(CH3, C23), 26.7 (CH2, C12), 26.5 (CH2, C15), 26.3 (CH2, C22), 24.7
(CH3, C29), 23.7 (CH2, C11), 22.4 (CH2, C6), 18.8 (CH3, C25),
15.5 (CH3, C26), 13.4 (CH3, C27) ppm; MS (ESI, MeOH):
m/z = 457.2 (100%, [M+H]+), 479.3 (22%, [M+Na]+), 489.1 (54%,
[M+H+MeOH]+), 510.8 (14%, [M+Na+MeOH]+).
,
Compound 4 (1.48 g, 91.5%) was obtained as an extremely insol-
uble off-white solid; Rf = 0.65 (hexane/ethyl acetate, 8:2); mp
,
285–287 °C; IR (KBr): m = 3268s, 2925s, 2879s, 1452m, 1388m,
1376m, 1263w, 1171w, 1140w, 1020w, 1005w, 924m cmÀ1; MS
(ESI, MeOH): m/z = 456.4 (100%, [M+H]+); analysis calcd for
C30H49NO2 (455.72): C 79.09, H 10.84, N 3.07; found: C 78.81, H
11.12, N 2.92.
4.3.5. (18a,19b) 19,28-Epoxy-3,4-seco-18-olean-4(23)-ene-3-
nitrile (5)
4.3.4. (18
a
,19b) 19,28-Epoxy-18-oleanan-3-one oxime (4)
To a solution of 4 (50 mg, 0.11 mmol) in dry pyridine (10 mL),
POCl3 (0.03 mL, 0.2 mmol) was added, and the mixture was stirred
overnight. Aqueous work-up (1% aq hydrochloric acid, 300 mL) fol-
lowed by extraction with chloroform (2 Â 50 mL), evaporation of
the solvent and chromatography (SiO2, hexane/ethyl acetate,
95:5) yielded 5 (20 mg, 46%) as a colorless solid; Rf = 0.80 (hex-
ane/ethyl acetate, 8:2); mp 267–269 °C (lit.: 266–267 °C38);
To a solution of 2 (1.56 g, 3.55 mmol) in pyridine (40 mL),
hydroxylammonium chloride (460 mg, 6.62 mmol) was added,
and the mixture was stirred at 60 °C for 3 h. The reaction was
quenched by adding hydrochloric acid (concd, aq, 5 mL). Aq
NaHCO3 (concd) was added until pH = 7.0, the mixture was diluted
with water (150 mL) and extracted with chloroform (3 Â 100 mL).
The organic phases were dried (Na2SO4) and concentrated.
[a]D = +43.5° (c = 0.78, CHCl3) (lit.: [a]
D = +61° (c = 2.6, CHCl3)54);

3006
L. Heller et al. / Bioorg. Med. Chem. 23 (2015) 3002–3012
IR (KBr):
m
= 3448br, 3079w, 3065m, 2930s, 2861s, 2245m, 1811w,
J = 13.2, 3.5 Hz, 1H, CHa (1)), 1.75–1.69 (m, 1H, CHa (2)), 1.69–
1.60 (m, 1H, CHa (15)), 1.60–1.55 (m, 2H, CHa (12) + CHa (6)),
1.54–1.47 (m, 2H, CHa (11) + CH (18)), 1.47–1.37 (m, 7H, CHa
(7) + CHa (16) + CH (13) + CHa (21) + CHa (22) + CHb (6) + CH (9)),
1.36–1.22 (m, 5H, CHb (7) + CHb (16) + CHb (22) + CHb (11) + CHb
(21)), 1.15–1.10 (m, 1H, CHb (12)), 1.03 (s, 3H, CH3 (23)), 1.00 (s,
3H, CH3 (24)), 1.02–0.96 (m, 1H, CHb (1)), 0.93 (s, 3H, CH3 (27)),
0.90 (s, 3H, CH3 (30)), 0.88 (s, 3H, CH3 (25)), 0.85 (s, 3H, CH3
(26)), 0.86–0.79 (m, 3H, CHb (15) + CH (5) + CHb (2)), 0.80 (s, 3H,
CH3 (29)) ppm; 13C NMR (125 MHz, CD3OD): d = 89.1 (CH, C19),
71.8 (CH2, C28), 61.0 (CH, C3), 56.5 (CH, C5), 51.7 (CH, C9), 47.5
(CH, C18), 42.2 (Cquart, C20), 41.4 (Cquart, C14), 41.2 (Cquart, C8),
1735w, 1636m, 1454s, 1387w, 1384s, 1297w, 1274m, 1255m,
1228w, 1203w, 1184w, 1165w, 1105w, 1085w, 1063 w, 1038s,
1006s cmÀ1 1H NMR (500 MHz, CDCl3): d = 4.87 (s, 1H, CHa (24)),
;
4.63 (s, 1H, CHb, (24)), 3.76 (d, J = 7.8 Hz, 1H, CHa (28)), 3.52 (s,
1H, CH (19)), 3.44 (d, J = 7.8 Hz, 1H, CHb (28)), 2.33 (ddd, J = 15.6,
7.6, 3.0 Hz, 1H, CHa (2)), 2.20 (ddd, J = 16.9, 9.7, 7.4 Hz, 1H, CHb
(2)), 1.91 (dd, J = 12.5, 2.3 Hz, 1H, CH (9)), 1.79–1.62 (m, 4H, CHa
(1) + CH2 (7) + CHa (22)), 1.71 (s, 3H, CH3 (23)), 1.61–1.50 (m, 2H,
CHa (12) + CHa (21)), 1.50–1.35 (m, 8H, CH (13) + CHa (15) + CH
(18) + CH (5) + CHa (11) + CHa (16) + CHb (1) + CHa (6)), 1.34–1.19
(m, 5H, CHb (11) + CHb (15) + CHb (6) + CHb (16) + CHb (21)), 1.15–
1.10 (m, 1H, CHb (12)), 1.02 (s, 3H, CH3 (26)), 0.95–0.91 (m, 1H,
CHb (22)), 0.93 (s, 3H, CH3 (30)), 0.92 (s, 3H, CH3 (27)), 0.85 (s,
3H, CH3 (25)), 0.79 (s, 3H, CH3 (29)) ppm; 13C NMR (125 MHz,
CDCl3): d = 147.1 (Cquart, C4), 120.3 (C„N, C3), 114.1 (CH2, C24),
88.0 (CH, C19), 71.4 (CH2, C28), 50.8 (CH, C9), 46.9 (CH, C18),
41.6 (Cquart, C20), 41.2 (Cquart, C14), 41.6 (CH, C5), 40.5 (Cquart, C8),
39.8 (Cquart, C10), 36.8 (CH2, C16), 36.4 (Cquart, C17), 34.6 (CH2,
C7), 34.3 (CH, C13), 32.8 (CH2, C2), 32.4 (CH2, C6), 28.9 (CH3,
C30), 26.5 (CH2, C12), 26.3 (CH2, C15), 26.1 (CH2, C22), 24.7 (CH3,
C29), 24.3 (CH2, C1), 22.9 (CH3, C23), 21.9 (CH2, C11), 20.3 (CH3,
C25), 15.9 (CH3, C26), 13.6 (CH3, C27), 11.5 (CH2, C2) ppm; MS
(ESI, CH2Cl2/MeOH): m/z = 438.2 (100%, [M+H]+), 460.3 (13%,
[M+Na]+), 491.9 (6 %, [M+Na+MeOH]+).
39.1 (CH2, C1), 37.8 (Cquart, C10), 37.2 (CH2, C16), 37.2 (Cquart
,
C17), 36.8 (Cquart, C4), 34.9 (CH, C13), 34.4 (CH2, C7), 33.3 (CH2,
C21), 29.1 (CH3, C30), 28.0 (CH3, C23), 27.0 (CH2, C12), 27.0 (CH2,
C15), 26.7 (CH2, C22), 24.8 (CH3, C29), 23.9 (CH2, C2), 21.7 (CH2,
C11), 18.8 (CH2, C6), 16.6 (CH3, C25), 16.1 (CH3, C26), 15.9 (CH3,
C24), 13.9 (CH3, C27) ppm; MS (ESI, MeOH): m/z = 442.3 (100%,
[M+H]+); analysis calcd for C30H51NO (441.73): C 81.57, H 11.64,
N 3.17; found: C 81.37, H 11.81, N 3.11.
4.3.7. (18a,19b) 19,28-Epoxy-2-hydroxy-18-olean-1-en-3-one
(8)
Air was bubbled at 40 °C through a mixture of 2 (100 mg,
0.22 mmol) and potassium tert butanolate (0.95 g, 8.47 mmol) in
tert. butanol (10 mL) for one hour. The crude product was precipi-
tated by the addition of dil. aq. hydrochloric acid (1%, 200 mL), fil-
tered off, washed with water (3 Â 50 mL) and purified by
4.3.6. (3
a
,18
a
,19b) 3-Amino-19,28-epoxy-18-oleanan (6) and
-oleanan (7)
(3b,18 ,19b) 3-amino-19,28-epoxy-18
a
a
A suspension of 2 (900 mg, 2.05 mmol) and ammonium acetate
(2.0 g) in methanol (400 ml) was stirred for 15 min at 25 °C.
Sodium cyanoborohydride (0.18 g) was added, and the mixture
was stirred at 25 °C for 24 h. Most of the solvents were removed
under diminished pressure, conc. aq. hydrochloric acid (30 mL)
was added, and the crude product was filtered off, washed with
water (3 Â 100 mL) and purified by chromatography (SiO2,
CHCl3/MeOH 9:1) to afford 6 (140 mg, 16%) and 7 (420 mg, 46%).
Data for 6: off-white solid; Rf = 0.79 (CHCl3/MeOH 9:1); mp
chromatography (SiO2, hexane/ethyl acetate, 4:1) to yield 8
(80 mg, 80%) as a colorless solid; Rf = 0.63 (hexane/ethyl acetate,
8:2); mp 122–125 °C; [ D = +65.4° (c = 0.74, CHCl3); IR (KBr):
= 3434m, 2928s, 2866s, 1724w, 1669m, 1455m, 1385m, 1234w,
1163w, 1140w, 1058m, 1036m cmÀ1; UV–vis (CHCl3): kmax (log
) = 271 (3.64) nm; 1H NMR (400 MHz, CDCl3) d = 6.48 (s, 1H, CH
a]
m
e
(1)), 5.91 (s, 1H, OH), 3.77 (d, J = 7.7 Hz, 1H, CHa (28)), 3.54 (s,
1H, CH (19)), 3.45 (d, J = 7.8 Hz, 1H, CHb (28)), 1.77–1.56 (m, 5H,
CHa (15) + CHa (11) + CH (9) + CH (5) + CHa (12)), 1.56–1.37 (m,
11H, CHa (21) + CH2 (7) + CH (13) + CH2 (6) + CH (18) + CHa
(28) + CHa (16) + CHa (22) + CHb (11)), 1.37–1.19 (m, 3H, CHb
(22) + CHb (16) + CHb (21)), 1.21 (s, 3H, CH3 (23)), 1.15 (s, 3H, CH3
(25)), 1.17–1.07 (m, 1H, CHb (12)), 1.11 (s, 3H, CH3 (24)), 1.04 (s,
3H, CH3 (26)), 1.02–0.90 (m, 1H, CHb (15)), 0.94 (s, 3H, CH3 (30)),
0.91 (s, 3H, CH3 (27)), 0.81 (s, 3H, CH3 (29)) ppm; 13C NMR
(100 MHz, CDCl3) d = 201.3 (C@O, C3), 144.1 (Cquart, C2), 129.1
(CH, C1), 88.0 (CH, C19), 71.4 (CH, C28), 54.4 (CH, C5), 46.9 (CH,
216–220 °C; [
a]D = +37.4° (c = 0.7, CHCl3); IR (KBr):
m
= 3442br,
2927s, 2867s, 1627w, 1532w, 1384s, 1039w, 1206w cmÀ1
;
1H
NMR (500 MHz, CDCl3): d = 3.77 (d, J = 7.8 Hz, 1H, CHa (28)), 3.53
(s, 1H, CH (19)), 3.44 (d, J = 7.8 Hz, 1H, CHb (28)), 3.17 (dd, J = 2.6,
2.6 Hz, 1H, CH (3)), 2.12–2.03 (m, 1H, CHa (2)), 1.94–1.88 (m, 1H,
CHb (2)), 1.71–1.62 (m, 2H, CH (5) + CHa (15)), 1.62–1.50 (m, 3H,
CHa (7) + CHa (21) + CHa (12)), 1.50–1.39 (m, 8H, CH (9) + CH
(18) + CH (13) + CHb (7) + CHa (1) + CHa (11) + CHa (6) + CHa (22)),
1.39–1.27 (m, 4H, CHa (16) + CHb (6) + CHb (22) + CHb (1)), 1.27–
1.19 (m, 3H, CHb (16) + CHb (11) + CHb (21)), 1.16–1.09 (m, 1H,
CHb (12)), 1.11 (s, 3H, (23)), 0.97 (s, 9H, CH3 (24) + CH3 (26) + CH3
(27)), 0.93 (s, 3H, CH3 (30)), 0.88 (s, 3H, CH3 (25)), 0.91–0.84 (m,
1H, CHb (15)), 0.78 (s, 3H, CH3 (29)) ppm; 13C NMR (125 MHz,
CDCl3): d = 88.0 (CH, C19), 71.5 (CH2, C28), 58.6 (CH, C3), 50.0
(CH, C5), 48.6 (CH, C9), 47.6 (CH, C18), 41.6 (Cquart, C20), (41.0
Cquart, C14), 40.8 (Cquart, C8), 37.3 (Cquart, C10), 36.9 (CH2, C16),
36.4 (Cquart, C17), 35.7 (Cquart, C4), 34.3 (CH, C13), 34.1 (CH2, C7),
32.9 (CH2, C21), 32.7 (CH2, C1), 28.9 (CH3, C30), 27.5 (CH3, C23),
26.8 (CH2, C12), 26.7 (CH2, C15), 26.4 (CH2, C22), 24.5 (CH3, C29),
22.7 (CH3, 24), 22.2 (CH2, C2), 21.0 (CH2, C11), 18.3 (CH2, C6),
16.6 (CH3, C25), 15.9 (CH3, C26), 13.8 (CH3, C27) ppm; MS (ESI,
MeOH): m/z = 442.3 (100%, [M+H]+); analysis calcd for C30H51NO
(441.73): C 81.57, H 11.64, N 3.17; found: C 81.42, H 11.76, N 3.02.
Data for 7: off-white solid; Rf = 0.88 (CHCl3/MeOH 9:1); mp
C18), 46.4 (CH, C9), 44.2 (Cquart, C4), 41.6 (Cquart, C20), 41.6 (Cquart
,
C14), 41.2 (Cquart, C8), 38.9 (Cquart, C10), 36.9 (CH2, C16), 36.4
(Cquart, C17), 34.4 (CH, C13), 33.7 (CH2, C7), 32.8 (CH2, C21), 29.0
(CH3, C30), 27.3 (CH3, C23), 26.5 (CH2, C12), 26.4 (CH2, C15), 26.4
(CH2, C22), 24.7 (CH4, C29), 21.7 (CH3, C24), 21.4 (CH2, C11), 20.7
(CH3, C25), 18.9 (CH2, C6), 16.4 (CH3, C26), 13.5 (CH3, C27) ppm;
MS (ESI, MeOH): m/z = 455.2 (100%, [M+H]+), 477.3 (30%,
[M+Na]+), 486.7 (14%, [M+H+MeOH]+), 493.0 (6%, [M+K]+), 508.7
(3%, [M+Na+MeOH]+), 909.3 (47%, [2 M+H]+), 928.9 (23%,
[4 M+K+H]2+); analysis calcd for C30H46O3 (454.68): C 79.25, H
10.20; found: C 79.01, H 10.42.
4.3.8. Methyl (18a,19b) 19,28-epoxy-3,4-seco-18-olean-4(23)-
ene-3-carboxylate (9)
To a solution of 2 (3.27 g 7.42 mmol) in methanol (155 mL)
oxoneÒ (460 mg, 21.47 mmol) and methanolic H2SO4 (98 mL,
0.05 mmol H2SO4) were added; the mixture was stirred at 25 °C
for a week and filtered. The solvents were removed under dimin-
ished pressure, and the residue subjected to chromatography to
afford 9 (2.26 g, 65 %) as a colorless solid; Rf = 0.57 (hexane/ethyl
234–238 °C; [
2947s, 2863s, 2344w, 1625w, 1528w, 1449m, 1384s, 1140w,
1036m, 1009w cmÀ1 1H NMR (500 MHz, CD3OD): d = 3.77 (d,
J = 7.6 Hz, 1H, CHa (28)), 3.53 (s, 1H, CH (19)), 3.46 (d, J = 7.8 Hz,
1H, CHb (28)), 2.83 (dd, J = 11.6, 5.3 Hz, 1H, CH (3)), 1.82 (ddd,
a]D = +29.6° (c = 0.78, DMSO); IR (KBr): m = 3442br,
;
acetate, 8:2); mp 146–150 °C (lit.: 146–147 °C54); [
a]D = +61.2°

L. Heller et al. / Bioorg. Med. Chem. 23 (2015) 3002–3012
3007
(c = 0.79, CHCl3) (lit.: [
= 3442br, 2948s, 2865s, 1740s, 1634w, 1455m, 1433m, 1382m,
1358w, 1290w, 1254m, 1174m, 1139w, 1114w, 1032m, 1008w
cmÀ1 1H NMR (500 MHz, CDCl3): d = 4.84 (s, 1H, CHa (24)), 4.64
a
]
D = +59.5° (c = 2.0, CHCl3)54); IR (KBr):
was stirred for 1 h at 25 °C; ethyl bromide (0.03 mL, 0.39 mmol)
was added, and stirring at 25 °C was continued for another 12 h.
Usual aqueous workup followed by chromatography (SiO2, hex-
ane/ethyl acetate, 9:1) yielded 11 (140 mg, 88%) as a colorless
solid; Rf = 0.83 (hexane/ethyl acetate, 8:2); mp 168–171 °C (lit.:
m
;
(s, 1H, CHb (24)), 3.76 (d, J = 7.8 Hz, 1H, CHa (28)), 3.65 (s, 3H,
CH3 (31)), 3.52 (s, 1H, CH (19)), 3.44 (d, J = 7.8 Hz, 1H, CHb (28)),
2.34 (ddd, J = 15.9, 11.0, 5.3 Hz, 1H, CHa (2)), 2.17 (ddd, J = 14.9,
11.2, 6.5 Hz, 1H, CHb (2)), 1.95 (dd, J = 12.7, 2.3 Hz, 1H, CH (9)),
1.80–1.73 (m, 1H, CHa (1)), 1.72 (s, 3H, CH3 (23)), 1.69–1.56 (m,
3H, CHa (22) + CH (13) + CHa (7)), 1.56–1.49 (m, 3H, CHb (22) + CH
(5) + CHa (6)), 1.49–1.45 (m, 2H, CHb (7) + CH (18)), 1.44–1.35 (m,
5H, CHa (11) + CHb (6) + CHa (21) + CHa (12) + CHa (16)), 1.35–1.26
(m, 3H, CHb (1) + CHb (16) + CHa (15)), 1.26–1.19 (m, 2H, CHb
(21) + CHb (11)), 1.12 (ddd, J = 13.1, 3.8, 2.3 Hz, 1H, CHb (12)),
1.01 (s, 3H, CH3 (26)), 0.92 (s, 3H, CH3 (30)), 0.92 (s, 3H, CH3
(27)), 0.91–0.84 (m, 1H, CHb (15)), 0.84 (s, 3H, CH3 (25)), 0.78 (s,
3H, CH3 (29)) ppm; 13C NMR (125 MHz, CDCl3): d = 174.7 (C@O,
C3), 147.5 (Cquart, C4), 113.6 (CH2, C24), 88.0 (CH, C19), 71.4 (CH2,
(28)), 51.7 (CH3, C31), 50.6 (CH, C9), 46.9 (CH, C18), 41.6 (CH2,
146–148 °C)35
;
[
a]
D = +60.8° (c = 0.81, CHCl3); IR (KBr):
= 3449w, 3067w, 2952s, 2865s, 1734s, 1636w, 1490m, 1451s,
1383s, 1338w, 1294m, 1253m, 1231w, 1175s, 1112m, 1094m,
1033s, 1007m cmÀ1 1H NMR (500 MHz, CDCl3): d = 4.84 (s, 1H,
m
;
CHa (24)), 4.66 (s, 1H, CHb (24)), 4.10 (q, J = 7.2 Hz, 2H, CH2 (31)),
3.77 (d, J = 7.7 Hz, 1H, CHa (28)), 3.52 (s, 1H, CH (19)), 3.44 (d,
J = 7.8 Hz, 1H, CHb (28)), 2.37–2.28 (m, 1H, CHa (2)), 2.15 (ddd,
J = 14.8, 11.2, 6.8 Hz, 1H, CHb (2)), 1.96 (dd, J = 12.7, 2.6 Hz, 1H,
(CH (9)), 1.81–1.73 (m, 1H, CHa (1)), 1.72 (s, 3H, CH3 (23)), 1.67–
1.57 (m, 3H, CHa (15) + CH2 (7)), 1.56–1.45 (m, 5H, CHa (21) + CHa
(12) + CH (5) + CH (18) + CH (13)), 1.45–1.34 (m, 6H, CHa
(22) + CHa (11) + CHa (16) + CH2 (6) + CHb (1)), 1.34–1.19 (m, 4H,
CHb (22) + CHb (16) + CHb (11) + CHb (21)), 1.24 (t, J = 7.1 Hz, 3H,
CH3 (32)), 1.13 (ddd, J = 13.0, 4.2, 2.3 Hz, 1H, CHb (12)), 1.01 (s,
3H, CH3 (26)), 0.93 (s, 3H, CH3 (30)), 0.92 (s, 3H, CH3 (27)), 0.96–
0.89 (m, 1H, CHb (15)), 0.84 (s, 3H, CH3 (25)), 0.79 (s, 3H, CH3
(29)) ppm; 13C NMR (125 MHz, CDCl3): d = 174.3 (C@O, C3),
147.7 (Cquart, C4), 113.6 (CH2, C24), 88.0 (CH, C19), 71.4 (CH2,
C20), 41.4 (CH, C5), 41.2 (Cquart, C20), 40.4 (Cquart, C8), 39.5 (Cquart
,
C10), 36.9 (CH2, C16), 36.4 (Cquart, C17), 34.4 (CH, C13), 34.4 (CH2,
C7), 32.9 (CH2, C21), 32.6 (CH2, C6), 28.9 (CH3, C30), 28.6 (CH2,
C2), 26.6 (CH2, C12), 26.5 (CH2, 15), 26.4 (CH2, C22), 24.7 (CH2,
C1), 24.7 (CH3, C29), 23.4 (CH3, C23), 21.7 (CH2, C11), 20.6 (CH3,
C25), 15.9 (CH3, C26), 13.6 (CH3, C27) ppm; MS (ESI, MeOH):
m/z = 471.1 (73%, [M+H]+), 493.3 (14%, [M+Na]+), 503.1 (46%,
[M+H+MeOH]+), 726.3 (11%, [3 M+K+H]2+), 941.3 (100%,
[2 M+H]+), 963.3 (35%, [2 M+Na]+).
C28), 60.4 (CH2, C31), 50.5 (CH, C9), 46.9 (CH, C18), 41.6 (Cquart
C20), 41.4 (CH, C5), 41.2 (Cquart, C14), 40.4 (Cquart, C8), 39.6 (Cquart
,
,
C10), 36.9 (CH2, C16), 36.4 (Cquart, C17), 34.4 (CH, C13), 34.4 (CH2,
C7), 32.9 (CH2, C21), 32.6 (CH2, C6), 29.0 (CH3, C30), 28.9 (CH2,
C2), 26.6 (CH2, C12), 26.5 (CH2, C15), 26.4 (CH2, C22), 24.7 (CH3,
C29), 24.7 (CH2, C1), 23.4 (CH3, C23), 21.7 (CH2, C11), 20.6 (CH3,
C25), 15.9 (CH3, C26), 14.4 (CH3, C32), 13.6 (CH3, C27) ppm; MS
(ESI, MeOH): m/z = 485.3 (100%, [M+H]+), 507.3 (8%, [M+Na]+),
517.1 (42%, [M+H+MeOH]+).
4.3.9. (18
carboxylic acid (10)
Compound (2.26 g, 4.81 mmol) was dissolved methanol
a,19b) 19,28-Epoxy-3,4-seco-18-olean-4(23)-ene-3-
9
(100 mL) containing finely powdered potassium hydroxide (3.77 g,
67.19 mmol), and the mixture was stirred at 25 °C for a week.
After pouring onto diluted aq. HCl (500 mL, 4%), the precipitate
was filtered off, washed with water (3 Â 100 mL) and purified by
chromatography (SiO2, hexane/ethyl acetate, 7:3) to yield 10
(1.90 g, 87 %) as a colorless solid; Rf = 0.44 (hexane/ethyl acetate,
4.3.11. Propyl (18a,19b) 19,28-epoxy-3,4-seco-18-olean-4(23)-
ene-3-carboxylate (12)
Following the procedure given for the synthesis of 11, from 10
(150 mg, 0.33 mmol), potassium carbonate, DMF (25 mL) and pro-
pyl bromide (0.04 mL, 0.39 mmol) followed by chromatography
(SiO2, hexane/ethyl acetate, 9:1) 12 (140 mg, 85%) was obtained
as a colorless solid; Rf = 0.83 (hexane/ethyl acetate, 8:2); mp
8:2); mp 237–241 °C (lit.: 238–240 °C55); [
CHCl3) (lit.: [
D = +60° (c 1.2, CHCl3)55); IR (KBr):
1638w, 1490w, 1455m, 1374m, 1246s, 1182m, 1142w, 1129w,
1021m, 1004m, 1008w cmÀ1 1H NMR (400 MHz, CDCl3): d = 4.85
a
]D = +63.2° (c = 1.03,
a]
m
= 2924s, 1718s,
168–171 °C; [
3082w, 2951s, 2862s, 1734s, 1636m, 1460s, 1420w, 1384s,
1338m, 1294s, 1253w, 1157s, 1070m, 1039s cmÀ1 1H NMR
a]D = +59.3° (c = 0.76, CHCl3); IR (KBr): m = 3468w,
;
(s, 1H, CHa (24)), 4.66 (s, 1H, CHb (24)), 3.78 (d, J = 7.7 Hz, 1H, CHa
(28)), 3.55 (s, 1H, CH (19)), 3.45 (d, J = 7.8 Hz, 1H, CHb (28)), 2.43–
2.32 (m, 1H, CHa (2)), 2.25–2.14 (m, 1H, CHb (2)), 2.00–1.92 (m, 1H,
CH (9)), 1.82–1.70 (m, 1H, CHa (1)), 1.73 (s, 3H, CH3 (23)), 1.70–
1.58 (m, 3H, CHa (15) + CH2 (7)), 1.58–1.43 (m, 5H, CHa (12) + CHa
(21) + CH (5) + CH (18) + CH (13)), 1.42–1.20 (m, 10H, CH2
(11) + CH2 (22) + CH2 (6) + CHb (21) + CHb (1) + CH2 (16)), 1.17–
1.10 (m, 1H, CHb (12)), 1.02 (s, 3H, CH3 (26)), 0.97–0.90 (m, 1H,
CHb (15)), 0.93 (s, 3H, CH3 (30)), 0.93 (s, 3H, CH3 (27)), 0.85 (s, 3H,
CH3 (25)), 0.80 (s, 3H, CH3 (29)) ppm; 13C NMR (100 MHz, CDCl3):
d = 179.9 (C@O, C3), 147.6 (Cquart, C4), 113.7 (CH2, C24), 88.1 (CH,
;
(500 MHz, CDCl3): d = 4.85 (s, 1H CHa (24)), 4.66 (s, 1H, CHb (24)),
4.05–3.97 (m, 2H, CH2 (31)), 3.77 (d, J = 7.7 Hz, 1H, CHa (28)),
3.53 (s, 1H, CH (19)), 3.44 (d, J = 7.8 Hz, 1H, CHb (28)), 2.38–2.30
(m, 1H, CHa (2)), 2.15 (ddd, J = 14.8, 11.2, 6.7 Hz, 1H, CHb (2)),
1.96 (dd, J = 12.7, 2.5 Hz, 1H, CH (9)), 1.81–1.74 (m, 1H, CHa (1)),
1.73 (s, 3H, CH3 (23)), 1.68–1.59 (m, 5H, CHa (15) + CH2
(32) + CH2 (7)), 1.59–1.47 (m, 5H, CHa (12) + CH (5) + CHa
(21) + CH (18) + CH (13)), 1.47–1.34 (m, 6H, CHa (11) + CHa
(22) + CHa (16) + CH2 (6) + CHb (1)), 1.34–1.25 (m, 3H, CHb
(22) + CHb (16) + CHb (11)), 1.26–1.19 (m, 1H, CHb (21)), 1.13
(ddd, J = 13.1, 4.2, 2.3 Hz, 1H, CHb (12)), 1.01 (s, 3H, CH3 (26)),
0.97–0.87 (m, 4H, CHb (15) + CH3 (33)), 0.93 (s, 3H, CH3 (30)),
0.92 (s, 3H, CH3 (27), 0.84 (s, 3H, CH3 (25)), 0.79 (s, 3H, CH3 (29))
ppm; 13C NMR (125 MHz, CDCl3): d = 174.4 (C@O, C3), 147.7
(Cquart, C4), 113.6 (CH2, C24), 88.0 (CH, C19), 71.4 (CH2, C28), 66.1
(CH2, C31), 50.5 (CH, C9), 46.9 (CH, C18), 41.6 (Cquart, C20), 41.4
(CH, C5), 41.2 (Cquart, C14), 40.4 (Cquart, C8), 39.6 (Cquart, C10), 36.9
(CH2, C16), 36.4 (Cquart, C17), 34.5 (CH2, C7), 34.4 (CH, C13), 32.9
(CH2, C21), 32.6 (CH2, C6), 28.9 (CH3, C30), 28.9 (CH2, C2), 26.6
(CH2, C12), 26.5 (CH2, C15), 26.4 (CH2, C22), 24.7 (CH3, C29), 24.7
(CH2, C1), 23.4 (CH3, C23), 22.1 (CH2, C32), 21.7 (CH2, C11), 20.6
(CH3, C25), 15.9 (CH3, C26), 13.6 (CH3, C27), 10.6 (CH3, C33) ppm;
MS (ESI, MeOH): m/z = 499.3 (100%, [M+H]+), 521.4 (8%,
C19), 71.4 (CH2, C28), 50.6 (CH, C9), 46.9 (CH, C18), 41.6 (Cquart
C20), 41.4 (CH, C5), 41.2 (Cquart, C14), 40.4 (Cquart, C8), 39.5 (Cquart
,
,
C10), 36.9 (CH2, C16), 36.4 (CH, C17), 34.4 (CH, C13), 34.2 (CH2,
C7), 32.9 (CH2, C21), 32.6 (CH2, C6), 28.9 (CH3, C30), 28.5 (CH2, C2),
26.6 (CH2, C12), 26.5 (CH2, C15), 26.4 (CH2, C22), 24.7 (CH3, C29),
24.7 (CH2, C1), 23.3 (CH3 C23), 21.7 (CH2, C11), 20.6 (CH3, C25),
15.9 (CH3, C26), 13.6 (CH3, C27) ppm; MS (ESI, MeOH): m/z = 455.6
(23%, [MÀH]À), 911.5 (100%, [2MÀH]À).
4.3.10. Ethyl (18a,19b) 19,28-epoxy-3,4-seco-18-olean-4(23)-
ene-3-carboxylate (11)
A suspension of 10 (150 mg, 0.33 mmol), freshly grounded
potassium carbonate (80 mg, 0.58 mmol) in dry DMF (15 mL)

3008
L. Heller et al. / Bioorg. Med. Chem. 23 (2015) 3002–3012
[M+Na]+), 531.1 (41%, [M+H+MeOH]+), analysis calcd for C33H54O3
(498.78): C 79.46, H 10.91; found: C 79.34, H 11.02.
36.9 (CH2, C16), 36.4 (Cquart, C17), 34.4 (CH, C13), 34.1 (CH2, C7),
32.9 (CH2, C21), 32.5 (CH2, C6), 28.9 (CH3, C30), 28.5 (CH2, C2), 26.6
(CH2, C12), 26.5 (CH2, C15), 26.4 (CH2, C21), 24.7 (CH3, C29), 24.6
(CH2, C1), 23.3 (CH3, C23), 21.7 (CH2, C11), 20.6 (CH3, C25), 15.9
(CH3, C26), 13.6 (CH3, C27) ppm; MS (ESI, MeOH): m/z = 495.3
4.3.12. Allyl (18a,19b) 19,28-epoxy-3,4-seco-18-olean-4(23)-ene-
3-carboxylate (13)
Following the procedure given for the synthesis of 11, from 10
(150 mg, 0.33 mmol), potassium carbonate (0.08 g, 0.58 mmol),
DMF (15 mL) and allyl iodide (0.04 mL, 0.39 mmol) followed by
chromatography (SiO2, hexane/ethyl acetate, 8:2) 13 (150 mg,
91 %) was obtained as a colorless solid; Rf = 0.68 (hexane/ethyl
(100%,
[M+H]+),
512.1
(6%,
[M+NH4]+),
527.1
(39%,
[M+H+MeOH]+); analysis calcd for C33H50O3 (494.75): C 80.11, H
10.19; found: C 79.89, H 10.31.
4.3.14. Butyl (18a,19b) 19,28-epoxy-3,4-seco-18-olean-4(23)-
acetate, 8:2); mp 152–154 °C; [
(KBr): = 3473w, 3082w, 2949s, 2862s, 1745s, 1636w, 1460m,
1419w, 1386s, 1360m, 1296m, 1253w, 1184m, 1154s, 1068w,
1039m, 1005m cmÀ1 1H NMR (500 MHz, CDCl3): d = 5.91 (ddt,
a
]
D = +58.3° (c = 0.74, CHCl3); IR
ene-carboxylate (15)
m
Following the procedure given for the synthesis of 11, from 10
(150 mg, 0.33 mmol), potassium carbonate (0.80 g, 0.58 mmol),
DMF (15 mL) and n-butylbromide (0.04 mL, 0.39 mmol) followed
by chromatography (SiO2, hexane/ethyl acetate, 8:2) 15 (160 mg,
95%) was obtained as a colorless solid; Rf = 0.84 (hexane/ethyl acet-
;
J = 16.6, 11.2, 5.7 Hz, 2H, CH2 (32)), 5.30 (d, J = 17.2 Hz, 1H, CHZ
(33)), 5.22 (d, J = 10.5 Hz, 1H, CHE (33)), 4.84 (s, 1H, CHa (24)),
4.65 (s, 1H, CHb (24)), 4.56 (d, J = 5.6 Hz, 2H, CH2 (31)), 3.77 (d,
J = 7.8 Hz, 1H, CHa (28)), 3.52 (s, 1H, CH (19)), 3.44 (d, J = 7.8 Hz,
1H, CHb (28)), 2.41–2.33 (m, 1H, CHa (2)), 2.24–2.15 (m, 1H, CHb
(2)), 1.98–1.93 (m, 1H, CH (9)), 1.82–1.74 (m, 1H, CHa (1)), 1.72
(s, 3H, CH3 (23)), 1.68–1.60 (m, 3H, CHa (15) + CH2 (7)), 1.60–1.45
(m, 5H, CHa (12) + CH (5) + CH (18) + CHa (21) + CH (13)), 1.45–
1.34 (m, 6H, CHa (22) + CHa (11) + CHa (16) + CH2 (6) + CHb (1)),
1.34–1.25 (m, 3H, CHb (22) + CHb (16) + CHb (11)), 1.25–1.19 (m,
1H, CHb (21)), 1.16–1.09 (m, 1H, CHb (12)), 1.01 (s, 3H, CH3 (26)),
0.97–0.87 (m, 1H, CHb (15)), 0.93 (s, 3H, CH3 (30)), 0.92 (s, 3H,
CH3 (27)), 0.84 (s, 3H, CH3 (25)), 0.79 (s, 3H, CH3 (29)) ppm; 13C
NMR (125 MHz, CDCl3): d = 173.9 (C@O, C3), 147.6 (Cquart, C4),
132.4 (CH, C32), 118.3 (CH2, C33), 113.6 (CH2, C24), 88.0 (CH,
C19), 71.4 (CH2, C28), 65.2 (CH2, C31), 50.6 (CH, C9), 46.9 (CH,
C18), 41.6 (Cquart, C20), 41.4 (CH, C5), 41.3 (Cquart, C14), 40.4
(Cquart, C8), 39.6 (Cquart, C10), 36.9 (CH2, C16), 36.4 (Cquart, C17),
34.4 (CH, C13), 34.4 (CH2, C7), 32.9 (CH2, C21), 32.6 (CH2, C6),
28.9 (CH3, C30), 28.8 (CH2, C2), 26.6 (CH2, C12), 26.5 (CH2, C15),
26.4 (CH2, C22), 24.7 (CH3, C29), 24.7 (CH2, C1), 23.4 (CH3, C23),
21.7 (CH2, C11), 20.6 (CH3, C25), 15.9 (CH3, C26), 13.6 (CH3, C27)
ppm; MS (ESI, MeOH): m/z = 497.3 (100%, [M+H]+), 519.3 (14%,
[M+Na]+), 545.1 (48%, [M+H+MeOH]+); analysis calcd for
ate, 8:2); mp 145–148 °C; [
= 3462w, 3083w, 2950s, 2863s, 1734s, 1638w, 1459m, 1420w,
1386m, 1358m, 1296m, 1253w, 1231w, 1157s, 1072w, 1037m,
1037m, 1003w cmÀ1 1H NMR (400 MHz, CDCl3): d = 4.84 (s, 1H,
a]D = +58.2° (c = 0.71, CHCl3); IR (KBr):
m
;
CHa (24)), 4.65 (s, 1H, CHb (24)), 4.05 (t, J = 6.6 Hz, 2H, CH2 (31)),
3.77 (d, J = 7.6 Hz, 1H, CHa (28)), 3.50 (d, J = 16.0 Hz, 1H, CH (19)),
3.44 (d, J = 7.7 Hz, 1H, CHb (28)), 2.42–2.27 (m, 1H, CHa (2)), 2.15
(ddd, J = 14.8, 11.0, 6.8 Hz, 1H, CHb (2)), 1.96 (dd, J = 12.6, 2.0 Hz,
1H, CH (9)), 1.84–1.75 (m, 1H, CHa (1)), 1.72 (s, 3H, CH3 (23)),
1.69–1.56 (m, 5H, CHa (15) + CH2 (7) + CH2 (32)), 1.56–1.44 (m,
5H, CHa (12) + CHa (21) + CH (18) + CH (5) + CH (13)), 1.44–1.26
(m, 11H, CHa (22) + CH2 (11) + CH2 (33) + CH2 (16) + CH2 (6) + CHb
(1) + CHb (21)), 1.25–1.18 (m, 1H, CHb (22)), 1.16–1.09 (m, 1H,
CHb (12), 1.01 (s, 3H, CH3 (26)), 0.97–0.89 (m, 3H, CHb (15) + CH2
(34)), 0.93 (s, 3H, CH3 (30)), 0.92 (s, 3H, CH3 (27)), 0.84 (s, 3H,
CH3 (25)), 0.79 (s, 3H, CH3 (29)) ppm; 13C NMR (100 MHz,
CDCl3): d = 174.4 (C@O, C3), 147.7 (Cquart, C4), 113.6 (CH2, C24),
88.0 (CH, C19), 71.4 (CH2, C28), 64.4 (CH2, C31), 50.5 (CH, C9),
46.9 (CH, C18), 41.6 (Cquart, C20), 41.4 (CH, C5), 41.2 (Cquart, C14),
40.4 (Cquart, C8), 39.6 (Cquart, C10), 36.9 (CH2, C16), 36.4 (Cquart
,
C17), 34.4 (CH2, C7), 34.4 (CH, C13), 32.9 (CH2, C21), 32.6 (CH2,
C6), 30.8 (CH2, C32), 28.9 (CH3, C30), 28.9 (CH2, C2), 26.6 (CH2,
C12), 26.5 (CH2, C15), 26.4 (CH2, C22), 24.7 (CH3, C29), 24.7 (CH2,
C1), 23.4 (CH3, C23), 21.7 (CH2, C11), 20.6(CH3, C25), 19.3 (CH2,
C33), 15.9 (CH3, C26), 13.9 (CH3, C27), 13.6 (CH3, C34) ppm; MS
(ESI, MeOH): m/z = 513.3 (100%, [M+H]+), 535.3 (5%, [M+Na]+),
545.1 (34%, [M+H+MeOH]+); analysis calcd for C34H56O3 (512.81):
C 79.63, H 11.01; found: C 79.57, H 11.18.
C33H52O3 (496.76): C 79.79, H 10.55; found: C 79.61, H 10.73.
4.3.13. Propargyl (18 ,19b) 19,28-epoxy-3,4-seco-18-olean-
a
4(23)-ene-3-carboxylate (14)
Following the procedure given for the synthesis of 11, from 10
(150 mg, 0.33 mmol), potassium carbonate (0.08 g, 0.58 mmol),
DMF (15 mL) and propargyl bromide (80% in toluene, 0.04 mL,
0.39 mmol) followed by chromatography (SiO2, hexane/ethyl acet-
ate, 8:2) 14 (150 mg, 92%) was obtained as a colorless solid;
4.3.15. Benzyl (18a,19b) 19,28-epoxy-3,4-seco-18-olean-4(23)-
ene-3-carboxylate (16)
Rf = 0.74 (hexane/ethyl acetate, 8:2); mp 122–124 °C; [
(c = 0.59, CHCl3); IR (KBr): = 3498w, 3289s, 3080w, 2949s, 2860s,
2130w, 1758s, 1636w, 1459m, 1418w, 1387s, 1296m, 1253w,
1228w, 1184w, 1139s, 1070w, 1039m, 1005m cmÀ1 1H NMR
a
]
D = +58.7°
Following the procedure given for the synthesis of 11, from 10
(150 mg, 0.33 mmol), potassium carbonate (0.08 g, 0.58 mmol),
DMF (15 mL) and benzylbromide (0.05 mL, 0.39 mmol) followed
by chromatography (SiO2, hexane/ethyl acetate, 8:2) 18 (160 mg,
88%) was obtained as a colorless solid; Rf = 0.73 (hexane/ethyl acet-
m
;
(400 MHz, CDCl3): d = 4.84 (s, 1H, CHa (24)), 4.69–4.62 (m, 3H, CHb
(24) + CH2 (31), 3.77 (d, J = 7.7 Hz, 1H, CHa (28)), 3.52 (s, 1H, CH
(19)), 3.44 (d, J = 7.8 Hz, 1H, CHb (28)), 2.46 (t, J = 2.3 Hz, 1H, CH
(33)), 2.44–2.34 (m, 1H, CHa (2)), 2.27–2.17 (m, 1H, CHb (2)), 1.94
(dd, J = 12.5, 1.9 Hz, 1H, CH (9)), 1.84–1.73 (m, 1H, CHa (1)), 1.72 (s,
3H, CH3 (23)), 1.68–1.57 (m, 3H, CHa (15) + CH2 (7)), 1.56–1.45 (m,
5H, CHa (12) + CHa (21) + CH (5) + CH (18) + CH (13)), 1.44–1.19
(m, 10H, CH2 (22) + CH2 (6) + CH2 (16) + CH2 (11) + CHb (1) + CHb
(21)), 1.16–1.09 (m, 1H, CHb (12)), 1.01 (s, 3H, CH3 (26)), 0.95–0.89
(m, 1H, CHb (15)), 0.93 (s, 3H, CH3 (30)), 0.92 (s, 3H, CH3 (27)), 0.85
(s, 3H, CH3 (25)), 0.79 (s, 3H, CH3 (29)) ppm; 13C NMR (100 MHz,
CDCl3): d = 173.3 (C@O, C3), 147.6 (Cquart, C4), 113.7 (Cquart, C24),
88.0 (CH, C19), 77.9 (Cquart, C32), 74.9 (CH, C33), 71.4 (CH, C28),
52.0 (CH2, C31), 50.6 (CH, C9), 46.9 (CH, C18), 41.6 (Cquart, C20),
41.4 (CH, C5), 41.2 (Cquart, C14), 40.4 (Cquart, C8), 39.6 (Cquart, C10),
ate, 8:2); mp 146–149 °C; [a]D = +56.1° (c = 0.87, CHCl3); IR (KBr):
m
= 3439w, 3086w, 3070w, 3035m, 2951s, 2869s, 2364w, 1960w,
1896w, 1803w, 1728s, 1687w, 1634m, 1454s, 1387s, 1387s,
1359m, 1336m, 1295s, 1256m, 1217s, 1196s, 1170s, 1156s,
1126s, 1112s, 1084w, 1062m, 1035s, 1004m cmÀ1
;
1H NMR
(500 MHz, CDCl3): d = 7.39–7.30 (m, 5H, CHaromat), 5.11 (d,
J = 12.7 Hz, 1H, CHa (31)), 5.09 (d, J = 12.7 Hz, 1H, CHb (31)), 4.84
(s, 1H, CHa (24)), 4.65 (s, 1H, CHb (24)), 3.77 (d, J = 7.8, 1H, CHa
(28)), 3.52 (s, 1H, CH (19)), 3.44 (d, J = 7.8 Hz, 1H, CHb (28)), 2.40
(ddd, J = 15.9, 10.3, 5.9 Hz, 1H, CHa (2)), 2.22 (ddd, J = 15.0, 10.7,
7.2 Hz, 1H, CHb (2)), 1.96 (dd, J = 12.6, 2.6 Hz, 1H, CH (9)), 1.81–
1.73 (m, 1H, CHa (1)), 1.72 (s, 3H, CH3 (23)), 1.69–1.60 (m, 3H,
CHa (15) + CH2 (7)), 1.58–1.45 (m, 5H, CHa (12) + CH (5) + CHa
(21) + CH (18) + CH (13)), 1.45–1.32 (m, 6H, CHa (22) + CHa

L. Heller et al. / Bioorg. Med. Chem. 23 (2015) 3002–3012
3009
(11) + CHa (16) + CH2 (6) + CHb (1)), 1.32–1.25 (m, 3H, CHb
(22) + CHb (16) + CHb (11)), 1.22 (dd, J = 13.5, 4.8 Hz, 1H, CHb
(21)), 1.12 (ddd, J = 12.9, 4.0, 2.2 Hz, 1H, CHb (12)), 1.01 (s, 3H,
CH3 (26)), 0.95–0.90 (m, 1H, CHb (15)), 0.93 (s, 3H, CH3 (30)),
0.91 (s, 3H, CH3 (27)), 0.85 (s, 3H, CH3 (CH3 (25)), 0.79 (s, 3H, CH3
(29)) ppm; 13C NMR (125 MHz, CDCl3): d = 174.1 (C@O, C3),
147.6 (Cquart, C4), 136.2 (Caromat, C32), 128.7 (CHaromat, C34), 128.3
(CHaromat, C35), 128.3 (CHaromat, C33), 113.6 (CH2, C24), 88.0 (CH,
C19), 71.4 (CH2, C28), 66.4 (CH2, C31), 50.5 (CH, C9), 46.9 (CH,
C18), 41.6 (Cquart, C20), 41.4 (CH, C5), 41.2 (Cquart, C14), 40.4
(Cquart, C8), 39.6 (Cquart, C10), 36.9 (CH2, C16), 36.4 (Cquart, C17),
34.4 (CH, C13), 34.3 (CH2, C7), 32.9 (CH2, C21), 32.6 (CH2, C6),
29.0 (CH3, C30), 28.8 (CH2, C2), 26.6 (CH2, C12), 26.5 (CH2, C15),
26.4 (CH2, C22), 24.7 (CH3, C29), 24.6 (CH2, C1), 23.3 (CH3, C23),
21.7 (CH2, C11), 20.6 (CH3, C25), 15.9 (CH3, C26), 13.6 (CH3, C27)
ppm; MS (ESI, MeOH): m/z = 547.3 (100%, [M+H]+), 569.5 (6%,
[M+Na]+), 614.9 (11%, [M+H+MeOH]+); analysis calcd for
CH3 (27) + CH3 (30)), 0.81 (s, 3H, CH3 (29)) ppm; 13C NMR
(100 MHz, CDCl3): d = 197.4 (C@O, C3), 119.4 (Cquart, C2), 88.0 (CH,
C19), 71.3 (CH2, C28), 52.5 (CH, C5), 50.2 (CH, C9), 48.9 (CH2, C1),
47.6 (Cquart, C4), 46.8 (CH, C18), 41.6 (Cquart, C20), 41.1 (Cquart, C14),
40.6 (Cquart, C8), 37.0 (CH2, C16), 36.8 (Cquart, C10), 36.4 (CH2, C17),
34.4 (CH, C13), 32.8 (CH2, C7), 32.3 (CH2, C21), 30.6 (CH3, C23),
28.9 (CH3, C30), 26.5 (CH3, C12), 26.3 (CH2, C15), 26.3 (CH2, C22),
24.7 (CH3, C29), 23.3 (CH3, C24), 22.1 (CH2, C11), 19.8 (CH2, C6),
17.9 (CH3, C25), 15.3 (CH3, C26), 13.6 (CH3, C27) ppm; MS (ESI,
MeOH): m/z = 531.1 (44%, [M+H]+), 548.2 (11%, [M+NH4]+), 553.2
(100%, [M+Na]+), 563.0 (17%, [M+H+MeOH]+), 571.3 (22%,
[M+Na+H2O]+), 584.8 (8%, [M+Na+MeOH]+).
4.3.17. (18a,19b) 19,28-Epoxy-2,3-seco-18-oleanan-2,3-
dicarboxylic acid (19)
To a suspension of 17 (100 mg, 0.21 mmol) in methanol (2 mL)
hydrogen peroxide (30%, 0.4 mL) and potassium carbonate (0.16 g,
1.16 mmol) were added. The mixture was diluted with methanol
(2 mL), and stirred for 5 days at 25 °C, neutralized by the careful
addition of diluted aq hydrochloric acid (10:1), diluted with water
(10 mL) and an aq. solution of sodium pyrosulfite (satd, 5 mL). The
precipitate was filtered off and purified by chromatography (SiO2,
CHCl3/MeOH 9:1) to afford 19 (80 mg, 78%) as a colorless solid;
Rf = 0.27 (hexane/ethyl acetate, 2:3); mp 301–304 °C (lit.: 305–
C37H54O3 (546.82): C 81.27, H 9.95; found: C 80.99, H 10.13.
4.3.16. (18a,19b) 19,28-Epoxy-2-nitro-olan-2-en-3-ol (17) and
(18 ,19b) 19,28-epoxy-2,2-dinitro-oleanan-3-one (18)
a
Acetic acid (2 mL) was warmed to 70 °C and 1 (100 mg,
0.23 mmol) was added. After cooling in an ice-bath, conc. nitric
acid (1 mL) was added, and stirring at 25 °C was continued for
another 5 h. The mixture was diluted with water (50 mL), and
the crude product was filtered off. Chromatographic purification
(SiO2, hexane/ethyl acetate, 9:1) gave 17 (80 mg, 70%) and 18
(10 mg, 8%).
306 °C)32; IR (KBr):
m = 2952s, 2362w, 1700s, 1457m, 1393m,
1239m, 1179m, 1037m, 1004w cm-1; MS (ESI, MeOH): m/z = 487.4
(100%, [M-H]-), 975.2 (86%, [2MÀH]À), 997.5 (79%, [2MÀ2H+Na]À).
Data for 17: colorless solid; Rf = 0.62 (hexane/ethyl acetate, 8:2);
4.3.18. Dimethyl (18
2,3-dicarboxylate (20)
a,19b) 19,28-epoxy-2,3-seco-18-oleanan-
mp 238–240 °C (lit.: 235.8 °C)43; [
a
]
D = +141.1° (c = 0.71, CHCl3); IR
= 3422br, 2929s, 2866s, 1736w, 1709w, 1602s, 1513s,
1456s, 1403s, 1376s, 1326m, 1295s, 1263m, 1232s, 1202s,
1160m, 1138m, 1103m, 1086m, 1060m, 1034s, 1008m cmÀ1 1H
(KBr):
m
Following the procedure given for the synthesis of 11, from 19
(200 mg, 0.41 mmol), potassium carbonate (0.22 g, 1.59 mmol),
DMF (25 mL) and methyl iodide (0.06 mL, 0.99 mmol) followed by
chromatography (SiO2, hexane/ethyl acetate, 8:2) 20 (120 mg,
56%) was obtained as a colorless solid; Rf = 0.63 (hexane/ethyl acet-
;
NMR (500 MHz, CDCl3): d = 3.76 (d, J = 7.8 Hz, 1H, CHa (28)), 3.53
(s, J = 9.8 Hz, 1H, CH (19)) 3.44 (d, J = 7.8 Hz, 1H, CHb (28)), 2.83
(d, J = 15.7 Hz, 1H, CHa (1)), 1.98 (d, J = 15.7 Hz, 1H, CHb (1)),
1.73–1.65 (m, 1H, CHa (15)), 1.63–1.53 (m, 2H, CHa (11) + CHa
(12)), 1.53–1.45 (m, 4H, CH2 (6) + CH (13) + CHa (7)), 1.45–1.27
(m, 5H, CH2 (16) + CH2 (21) + CHa (22)), 1.26 (s, 3H, CH3 (23)),
1.25–1.20 (m, 3H, CHb (22) + CHb (7) + CHb (11)), 1.18 (s, 3H, CH3
(24)), 1.18–1.09 (m, 1H, CHb (12)), 1.00 (s, 3H, CH3 (26)), 0.98–
0.90 (m, 1H, CHb (15)), 0.93 (s, 3H, CH3 (30)), 0.91 (s, 3H, CH3
(27)), 0.87 (s, 3H, CH3 (25)), 0.80 (s, 3H, CHa (29)) ppm; 13C NMR
(125 MHz, CDCl3): d = 178.6 (Cquart, C3), 123.0 (Cquart, C2), 88.0
(CH, C19), 71.4 (CH2, C28), 52.2 (CH, C5), 49.5 (CH, C9), 46.9 (CH,
C18), 41.6 (Cquart, C20), 40.9 (Cquart, C14), 40.6 (Cquart, C8), 40.4
(Cquart, C4), 40.3 (CH2, C1), 36.9 (CH2, C16), 36.6 (Cquart, C10), 36.4
(Cquart, C17), 34.4 (CH, C13), 32.8 (CH2, C7), 32.7 (CH2, C21), 28.9
(CH3, C30), 28.8 (CH3, C23), 26.5 (CH2, C12), 26.4 (CH2, C15), 26.3
(CH2, C22), 24.7 (CH3, C29), 21.7 (CH2, C11), 20.6 (CH3 (C24), 19.6
(CH2, C6), 16.6 (CH3, C25), 15.5 (CH3, C26), 13.6 (CH3, C27) ppm;
MS (ESI, MeOH): m/z = 486.2 (100%, [M+H]+), 503.1 (38%,
[M+NH4]+), 508.3 (46%, [M+Na]+), 540.1 (16%, [M+Na+MeOH]+).
Data for 18: colorless solid; Rf = 0.48 (hexane/ethyl acetate, 8:2);
ate, 8:2); mp 143–146 °C (lit.: 238–240 °C32); [
a]D = +40.8° (c = 0.80,
CHCl3) (lit.: [ m
a]
D = +30° (c = 1.10, CHCl3)32; IR (KBr):
= 3436w,
2947s, 2948s, 2290s, 1740s, 1438s, 1394m, 1374m, 1355m,
1283w, 1253m, 1234m, 1206m, 1154s, 1128s, 1058w, 1032m,
1015w cmÀ1; 1H NMR (400 MHz, CDCl3): d = 3.75 (d, J = 7.7 Hz, 1H,
CHa (28)), 3.64 (s, 3H, CH3 (31)), 3.60 (s, 3H, CH3 (32)), 3.51 (s, 1H,
CH (19)), 3.42 (d, J = 7.7 Hz, 1H, CHb (28)), 2.46 (d, J = 17.8 Hz, 1H,
CHa (1)), 2.41–2.33 (m, 2H, CH (5) + CH (9)), 2.30 (d, J = 17.9 Hz,
1H, CHb (1)), 1.71–1.58 (m, 2H, CHa (15) + CHa (12)), 1.57–1.34 (m,
9H, CHa (11) + CH (18) + CHa (22) + CHa (6) + CHa (16) + CHa
(17) + CH (13) + CHa (7) + CHa (21)), 1.33–1.15 (m, 5H, CHb
(22) + CHb (16) + CHb (17) + CHb (7) + CHb (21)), 1.23 (s, 6H, CH3
(23) + CH3 (24)), 1.15–1.06 (m, 3H, CHb (11) + CHb (12) + CHb (6)),
0.96 (s, 3H, CH3 (26)), 0.92 (s, 3H, CH3 (27)), 0.91 (s, 6H, CH3
(25) + CH3 (30)), 0.89–0.79 (m, 1H, CHb (15)), 0.77 (s, 3H, CH3 (29))
ppm; 13C NMR (100 MHz, CDCl3): d = 180.1 (C@O, C3), 172.2 (C@O,
C2), 88.0 (CH, C19), 71.4 (CH2, C28), 51.8 (CH3, C32), 51.0 (CH3,
C31), 48.6 (CH, C5), 46.8 (CH, C18), 46.6 (Cquart, C4), 42.9 (CH, C9),
42.3 (Cquart, C8), 42.1 (Cquart, C10), 41.6 (CH2, C1), 41.2 (Cquart, C20),
40.6 (Cquart, C14), 36.8 (CH2, C16), 36.4 (CH2, C17), 34.5 (CH, C13),
33.0 (CH2, C7), 32.9 (CH2, C21), 28.9 (CH3, C30), 27.7 (CH3, C23),
26.7 (CH2, C12), 26.6 (CH2, C15), 26.4 (CH2, C22), 24.7 (CH3, C29),
24.1 (CH3, C24), 22.1 (CH2, C11), 20.9 (CH2, C6), 20.2 (CH3, C25),
15.9 (CH3, C26), 13.6 (CH3, C27) ppm; MS (ESI, MeOH): m/z = 517.3
(100%, [M+H]+), 534.3 (22%, [M+NH4]+), 539.5 (6%, [M+Na]+), 795
(5%, [3M+K+H]2+), 1055.5 (100%, [2M+Na]+).
mp 217–220 °C (lit.: 202.4 °C43); [
(KBr): = 3434m, 2953s, 2870s, 1728m, 1574s, 1470w, 1387w,
1314w, 1254w, 1210w, 1140w, 1060w, 1028w cmÀ1 1H NMR
a]D = +64.0° (c = 0.92, CHCl3); IR
m
;
(400 MHz, CDCl3): d = 3.76 (d, J = 7.8 Hz, 1H, CHa (28)), 3.53 (s, 1H,
CH (19)), 3.46 (d, J = 7.8 Hz, 1H, CHb (28)), 3.10 (d, J = 16.2 Hz, 1H,
CHa (1)), 2.95 (d, J = 16.2 Hz, 1H, CHb (1)), 1.77–1.67 (m, 1H, CHa
(15)), 1.61–1.44 (m, 12H, CH (9) + CHa (7) + CH (5) + CH (18) + CHa
(6) + CH2 (21) + CHa (16) + CHa (12) + CHa (22) + CH2 (11)), 1.44–
1.39 (m, 1H, CH (13)), 1.39–1.35 (m, 1H, CHb (22)), 1.34–1.31 (m,
1H, CHb (16)), 1.30–1.19 (m, 2H, CHb (7) + CHb (6)), 1.24 (s, 3H, CH3
(23)), 1.24 (s, 3H, CH3 (24)), 1.16–1.06 (m, 1H, CHb (12)), 1.01 (s,
6H, CH3 (26) + CH3 (25)), 1.05–0.90 (m, 1H, CHb (15)), 0.94 (s, 6H,
4.3.19. Diethyl (18a,19b) 19,28-epoxy-2,3-seco-18-oleanan-2,3-
dicarboxylate (21)
Following the procedure given for the synthesis of 11, from 19
(200 mg, 0.41 mmol), potassium carbonate (0.22 g, 1.59 mmol),

3010
L. Heller et al. / Bioorg. Med. Chem. 23 (2015) 3002–3012
DMF (20 mL) and ethyl iodide (0.08 mL, 0.99 mmol)) followed by
chromatography (SiO2, hexane/ethyl acetate, 9:1) 21 (150 mg,
67%) was obtained as a colorless solid; Rf = 0.58 (hexane/ethyl acet-
[M+NH4]+), 1167.9 (100%, [2 M+Na]+); analysis calcd for C36H60O5
(572.86): C 75.48, H 10.56; found: C 75.39, H 10.71.
ate, 8:2); mp 103–107 °C; [
= 3421w, 2930s, 2867s, 1737s, 1452s, 1391s, 1373s, 1340m,
1283m, 1255s, 1236s, 1208s, 1148s, 1037s, 1008m cmÀ1 1H
a
]
D = +41.3° (c = 0.84, CHCl3); IR (KBr):
4.3.21. Diallyl (18
dicarboxylate (23)
a,19b) 19,28-epoxy-2,3-seco-18-oleanan-2,3-
m
;
Following the procedure given for the synthesis of 11, from 19
(200 mg, 0.41 mmol) potassium carbonate (0.22 g, 1.59 mmol),
DMF (15 mL) and allyl iodide (0.09 mL, 0.95 mmol) followed by
chromatography (SiO2, hexane/ethyl acetate, 9:1) 23 (150 mg,
64%) was obtained as a colorless solid; Rf = 0.64 (hexane/ethyl acet-
NMR (400 MHz, CDCl3): d = 4.21–4.11 (m, 1H, CHa (33)), 4.12 (q,
J = 7.2 Hz, 2H, CH2 (31)), 3.98 (dq, J = 10.8, 7.1 Hz, 1H, CHb (33)),
3.76 (d, J = 7.6 Hz, 1H, CHa (28)), 3.51 (s, 1H, CH (19)), 3.43 (d,
J = 7.7 Hz, 1H, CHb (28)), 2.48–2.41 (m, 2H, CH2 (1)), 2.40–2.37
(m, 1H, CH (5)), 2.24 (dd, J = 12.3, 2.0 Hz, 1H, CH (9)), 1.71–1.59
(m, 1H, CHa (15)), 1.58–1.44 (m, 7H, CHa (6) + CHa (11) + CHa
(7) + CH (18) + CH (13) + CHa (12) + CHa (22)), 1.43–1.34 (m, 4H,
CHa (16) + CHb (7) + CHa (21) + CHb (6)), 1.33–1.15 (m, 10H, CHb
(22) + CHb (16) + CHb (21) + CHb (11) + CH3 (32) + CH3 (34)), 1.25
(s, 3H, CH3 (23)), 1.23 (s, 3H, CH3 (24)), 1.15–1.07 (m, 1H, CHb
(12)), 0.96 (s, 3H, CH3 (26)), 0.93 (s, 3H, CH3 (25)), 0.91 (s, 3H,
CH3 (27)), 0.91 (s, 1H, CH3 (30)), 0.92–0.83 (m, 1H, CHb (15)),
0.78 (s, 3H, CH3 (29)) ppm; 13C NMR (100 MHz, CDCl3): d = 179.4
(C@O, C3), 171.9 (C@O, C2), 88.0 (CH, C19), 71.4 (CH2, C28), 60.4
(CH2, C33), 59.8 (CH2, C31), 48.4 (CH, C5), 47.0 (Cquart, C4), 46.8
(CH, C18), 43.3 (CH, C9), 42.9 (CH2, C1), 42.6 (Cquart, C8), 41.6
(Cquart, C10), 41.2 (Cquart, C20), 40.6 (Cquart, C14), 36.8 (CH2, C16),
36.4 (Cquart, C17), 34.5 (CH, C13), 33.0(CH2, C7), 32.9 (CH2, C21),
29.0 (CH3, C30), 26.8 (CH3, C23), 26.6 (CH2, C12), 26.6 (CH2, C15),
26.4 (CH2, C22), 24.9 (CH3, C29), 24.7 (CH3, C24), 22.1 (CH2, C11),
21.4 (CH2, C6), 20.3 (CH3, C25), 15.9 (CH3, C26), 14.5 (CH3, C34),
14.2 (CH3, C32), 13.6 (CH3, C27) ppm; MS (ESI, MeOH):
m/z = 545.2 (80%, [M+H]+), 562.0 (6%, [M+NH4]+), 1111.4 (100%,
[2M+Na]+); analysis calcd for C34H56O5 (544.81): C 74.96, H
10.36; found: C 74.73, H 10.41.
ate, 8:2); mp 115–120 °C; [
= 3096m, 2927s, 2862s, 1720s, 1648m, 1451s, 1374s, 1338m,
1284s, 1256s, 1235s, 1208s, 1133s, 1059m, 1038s, 1008s cmÀ1
a]D = +38.9° (c = 0.67, CHCl3); IR (KBr):
m
;
1H NMR (500 MHz, CDCl3): d = 5.98–5.85 (m, 4H, CH2 (32) + CH2
(35)), 5.34 (q, J = 1.5 Hz, 1H, CHa (33)), 5.30 (q, J = 1.5 Hz, 1H, CHb
(33)), 5.22 (ddd, J = 5.6, 2.6, 1.2 Hz, 1H, CHa (36)), 5.21–5.19 (m,
1H, CHb (36)), 4.63–4.58 (m, 2H, CHa (34)), 4.56 (ddt, J = 7.2, 6.0,
1.4 Hz, 2H, CH2 (31)), 4.43 (ddt, J = 13.4, 5.5, 1.4 Hz, 1H, CHb
(34)), 3.76 (d, J = 7.7 Hz, 1H, CHa (28)), 3.52 (s, 1H, CH (19)), 3.43
(d, J = 7.8 Hz, 1H, CHb (28)), 2.53–2.41 (m, 3H, CH2 (1) + CH (5)),
2.26 (dd, J = 12.5, 2.5 Hz, 1H, CH (9)), 1.66–1.60 (m, 1H, CHa (15)),
1.56–1.35 (m, 10H, CHa (11) + CHa (7) + CH (18) + CH (13) + CHa
(12) + CH2 (6) + CH2 (21) + CHa (16)), 1.33–1.25 (m, 3H, CHb
(16) + CH2 (22)), 1.29 (s, 3H, CH3 (24)), 1.27 (s, 3H, CH3 (23)),
1.25–1.18 (m, 2H, CHb (7) + CHb (11)), 1.15–1.10 (m, 1H, CHb
(12)), 0.96 (s, 3H, CH3 (26)), 0.94 (s, 3H, CH3 (25)), 0.92 (s, 3H,
CH3 (30)), 0.91 (s, 3H, CH3 (25)), 0.89–0.83 (m, 1H, CHb (15)),
0.78 (s, 3H, CH3 (29)) ppm; 13C NMR (125 MHz, CDCl3): d = 179.0
(C@O, C3), 171.5 (C@O, C2), 132.6 (CH, C35), 132.5 (CH, C32),
118.3 (CH2, C36), 117.9 (CH2, C33), 88.0 (CH, C19), 71.5 (CH2,
C28), 65.2 (CH2, C34), 64.8 (CH2, C31), 48.5 (CH, C5), 47.1 (Cquart
,
C4), 46.8 (CH, C18), 43.3 (CH, C9), 42.7 (Cquart, C8), 42.6 (CH2, C1),
41.6 (Cquart, C10), 41.2 (Cquart, C20), 40.6 (Cquart, C14), 36.8 (CH2,
C16), 36.4 (Cquart, C17), 34.5 (CH, C13), 32.9 (CH2, C7), 32.9 (CH2,
C21), 29.0 (CH3, C23), 27.0 (CH3, C23), 26.6 (CH2, C12), 26.6 (CH2,
C15), 26.4 (CH2, C22), 24.8 (CH3, C29), 24.7 (CH3, C24), 22.1 (CH2,
C11), 21.4 (CH2, C6), 20.2 (CH3, C25), 15.9 (CH2, C26), 13.6 (CH2,
C27) ppm; MS (ESI, MeOH): m/z = 569.3 (100%, [M+H]+), 595.9
(8%, [M+NH4]+), 1167.9 (9%, [M+Na]+); analysis calcd for C36H56O5
(568.83): C 76.01, H 9.92; found: C 75.79, H 10.05.
4.3.20. Dipropyl (18
dicarboxylate (22)
a,19b) 19,28-epoxy-2,3-seco-18-oleanan-2,3-
Following the procedure given for the synthesis of 11, from 19
(200 mg, 0.41 mmol), potassium carbonate (0.22 g, 1.59 mmol),
DMF (20 mL) and propyl bromide (0.09 mL, 0.98 mmol) followed
by chromatography (SiO2, hexane/ethyl acetate, 9:1) 22 (180 mg,
76%) was obtained as a colorless solid; Rf = 0.87 (hexane/ethyl acet-
ate, 8:2); mp 92–96 °C; [
= 3420w, 2967s, 2867s, 1739s,1717s, 1457m, 1387m, 1375m,
1338w,1305w, 1284m, 1255s, 1236m, 1208m, 1148s,
1134s,1059w, 1037s, 1008m cmÀ1 1H NMR (400 MHz, CDCl3):
a]D = +41.8° (c = 0.55, CHCl3); IR (KBr):
m
4.3.22. Dipropargyl (18a,19b) 19,28-epoxy-2,3-seco-18-oleanan-
;
2,3-dicarboxylate (24)
d = 4.09–4.02 (m, 1H, CHa (34)), 4.02 (t, J = 6.7 Hz, 2H, CH2 (31)),
3.88 (dt, J = 10.8, 6.5 Hz, 1H, CHb (34)), 3.76 (d, J = 7.6 Hz, 1H, CHa
(28)), 3.52 (s, 1H, CH (19)), 3.43 (d, J = 7.7 Hz, 1H, CHb (28)),
2.51–2.43 (m, 2H, CH2 (1)), 2.43–2.40 (m, 1H, CH (5)), 2.27–2.20
(m, 1H, CH (9)), 1.72–1.58 (m, 5H, CH2 (32) + CH2 (35) + CHa
(15)), 1.59–1.44 (m, 7H, CHa (11) + CHa (6) + CHa (7) + CH
(18) + CHa (12) + CHa (22) + CH (13)), 1.43–1.33 (m, 4H, CHa
(21) + CHb (7) + CHb (6) + CHa (16)), 1.34–1.17 (m, 4H, CHb
(22) + CHb (16) + CHb (7) + CHb (11)), 1.27 (s, 3H, CH3 (24)), 1.26
(s, 3H, CH3 (23)), 1.15–1.06 (m, 1H, CHb (12)), 1.00–0.84 (m, 7H,
CHb (15) + CH3 (33) + CH3 (36)), 0.96 (s, 3H, CH3 (26)), 0.94 (s, 3H,
CH3 (25)), 0.92 (s, 3H, CH3 (30)), 0.91 (s, 3H, CH3 (27)), 0.78 (s,
Following the procedure given for the synthesis of 11, from 19
(200 mg, 0.41 mmol), potassium carbonate (0.20 g, 1.45 mmol),
DMF (10 mL) and propargyl bromide (80% in toluene, 0.11 mL,
0.98 mmol) followed by chromatography (SiO2, hexane/ethyl acet-
ate, 9:1) 24 (130 mg, 56%) was obtained as a colorless solid;
Rf = 0.59
(hexane/ethyl
acetate,
8:2);
mp 102–108 °C;
[a]
D = +38.7° (c = 0.55, CHCl3); IR (KBr):
m
= 3287s, 2927s, 2868s,
2130w, 1744s, 1720s, 1451s, 1374s, 1338m, 1252s, 1214m,
1170s, 1119s, 1059w, 1038s, 1026s cmÀ1 1H NMR (400 MHz,
;
CDCl3): d = 4.71 (dd, J = 15.6, 2.2 Hz, 1H, CHa (34)), 4.69 (d,
J = 2.2 Hz, 2H, CH2 (31)), 4.59 (dd, J = 15.6, 2.3 Hz, 1H, CHb (34)),
3.76 (d, J = 7.6 Hz, 1H, CHa (28)), 3.52 (s, 1H, CH (19)), 3.43 (d,
J = 7.8 Hz, 1H, CHb (28)), 2.57–2.49 (m, 1H, CHa (1)), 2.47–2.36
(m, 4H, CHb (1) + CH (5) + CH (33) + CH (36)), 2.27–2.20 (m, 1H,
CH (9)), 1.68–1.60 (m, 1H, CHa (15)), 1.57–1.43 (m, 8H, CH2
(11) + CH2 (6) + CH (18) + CHa (12) + CH (13) + CHa (21)), 1.42–
1.34 (m, 3H, CH2 (7) + CHa (16)), 1.33–1.25 (m, 3H, CH2
(22) + CHb (16)), 1.29 (s, 3H, CH3 (24)), 1.28 (s, 3H, CH3 (23)),
1.25–1.16 (m, 1H, CHb (21)), 1.15–1.06 (m, 1H, CHb (12)), 0.99–
0.87 (m, 1H, CHb (15)), 0.96 (s, 3H, CH3 (26), 0.95 (s, 3H, CH3
(25)), 0.92 (s, 6H, CH3 (27) + CH3 (30)), 0.78 (s, 3H, CH3 (27))
ppm; 13C NMR (100 MHz, CDCl3): d = 178.5 (C@O, C3), 170.9
(C@O, C2), 88.0 (CH, C19), 78.1 (CH, C36), 77.9 (CH, C33), 74.8
3H, CH3 (29)) ppm; 13C NMR (100 MHz, CDCl3): d = 179.4 (Cquart
,
C3), 172.1 (Cquart, C2), 88.0 (CH, C19), 71.4 (CH2, C28), 66.2 (CH2,
C34), 65.7 (CH2, C31), 48.4 (CH, C5), 47.2 (Cquart, C4), 46.8 (CH,
C18), 43.4 (CH, C9), 43.0 (CH2, C1), 42.5 (Cquart, C8), 41.6 (Cquart
,
C10), 41.2 (Cquart, C20), 40.6 (Cquart, C14), 36.9 (CH2, C16), 36.4
(Cquart, C17), 34.5 (CH, C13), 33.0 (CH2, C7), 32.9 (CH2, C21), 29.0
(CH3, C30), 26.7 (CH3, C23), 26.6 (CH2, C12), 26.6 (CH2, C15), 26.4
(CH2, C22), 25.1 (CH3, C29), 24.7 (CH3, C24), 22.2 (CH2, C32), 22.1
(CH2, C35), 22.0 (CH2, C11), 21.5 (CH2, C6), 20.3 (CH3, C25), 15.9
(CH3, C26), 13.6 (CH3, C27), 10.7 (CH3, C36), 10.7 (CH3, C33) ppm;
MS (ESI, MeOH): m/z = 573.9 (28%, [M+H]+), 595.9 (3%,

L. Heller et al. / Bioorg. Med. Chem. 23 (2015) 3002–3012
3011
(Cquart, C35), 74.7 (Cquart, C32), 71.4 (CH2, C28), 52.2 (CH2, C34), 51.5
(CH2, C31), 48.5 (CH, C5), 47.0 (Cquart, C4), 46.8 (CH, C18), 43.3 (CH,
CH (9)), 1.56–1.45 (m, 3H, CHa (15) + CHa (11) + CHa (7)), 1.45–
1.32 (m, 7H, CHa (12) + CHa (22) + CH (13) + CH (18) + CHa
(16) + CH2 (6)), 1.32–1.26 (m, 3H, CHb (22) + CHb (16) + CHb (22)),
1.30 (s, 3H, CH3 (24)), 1.28 (s, 3H, CH3 (23)), 1.26–1.18 (m, 1H,
CHb (7)), 1.17–1.11 (m, 1H, CHb (11)), 1.11–1.06 (m, 1H, CHb
(12)), 0.93 (s, 9H, CH3 (30) + CH3 (25) + CH3 (26)), 0.80 (s, 3H, CH3
(29)), 0.78 (s, 3H, CH3 (27)), 0.74–0.62 (m, 1H, CHb (15)) ppm;
13C NMR (100 MHz, CDCl3): d = 179.1 (C@O, C3), 171.6 (C@O, C2),
136.4 (Caromat, C37), 136.3 (Caromat, C32), 128.8 (CHaromat, C39),
128.6 (CHaromat, C34), 128.5 (CHaromat, C40), 128.2 (CHaromat, C35),
128.0 (CHaromat, C38), 127.9 (CHaromat, C33), 87.9 (CH, C19), 71.4
(CH2, C28), 66.2 (CH2, C36), 65.9 (CH2, C31), 48.4 (CH, C5), 47.1
(Cquart, C4), 46.8 (CH, C18), 43.4 (CH, C9), 42.9 (Cquart, C8), 42.7
(CH2, C1), 41.6 (Cquart, C10), 41.1 (Cquart, C20), 40.5 (Cquart, C14),
36.8 (CH2, C16), 36.4 (Cquart, C17), 34.4 (CH, C13), 32.8 (CH2, C7),
32.8 (CH2, C21), 28.9 (CH3, C30), 26.7 (CH3, C23), 26.6 (CH2, C12),
26.4 (CH2, C15), 26.3 (CH2, C22), 24.9 (CH3, C29), 24.7 (CH3, C24),
22.0(CH2, C11), 21.4(CH2, C6), 20.2(CH3, C25), 15.8 (CH3, C26),
13.5 (CH3, C27) ppm; MS (ESI, MeOH): m/z = 669.3 (100%,
[M+H]+), 686.2 (8%, [M+NH4]+), 691.7 (6%, [M+Na]+); analysis calcd
for C44H60O5 (668.94): C 79.00, H 9.04; found: C 78.81, H 9.25.
C9), 42.7 (Cquart, C8), 42.6 (CH2, C1), 41.6 (Cquart, C10), 41.2 (Cquart
,
C20), 40.6 (Cquart, C14), 36.8 (CH2, C16), 36.4 (Cquart, C17), 34.5
(CH, C13), 32.9 (CH2, C7), 32.9 (CH2, C21), 28.9 (CH3, C30), 27.1
(CH3, C23), 26.6 (CH2, C12), 26.5 (CH2, C15), 26.4 (CH2, C22), 24.7
(CH3, C29), 24.6 (CH3, C24), 22.1 (CH2, C11), 21.2 (CH2, C6), 20.2
(CH3, C25), 15.9 (CH3, C26), 13.7 (CH3, C27) ppm; MS (ESI,
MeOH): m/z = 565.2 (100%, [M+H]+), 582.3 (58%, [M+NH4]+),
587.5 (16%, [M+Na]+); analysis calcd for C36H52O5 (564.80): C
76.56, H 9.28; found: C 76.44, H 9.37.
4.3.23. Dibutyl (18a,19b) 19,28-epoxy-2,3-seco-18-oleanan-2,3-
dicarboxylate (25)
Following the procedure given for the synthesis of 11, from 19
(200 mg, 0.41 mmol), potassium carbonate (0.20 g, 1.45 mmol),
DMF (25 mL) and butyl bromide (0.11 mL, 0.98 mmol)) followed
by chromatography (SiO2, hexane/ethyl acetate, 9:1) 25 (150 mg,
60 %) was obtained as an off-white solid; Rf = 0.72 (hexane/ethyl
acetate, 8:2); mp 54–57 °C; [
(KBr): = 3447br, 2959s, 2868s, 1739s, 1716s, 1457m, 1385m,
1284w, 1255m, 1236w, 1208w, 1148s, 1134s, 1060w, 1036m,
1008m cmÀ1 1H NMR (400 MHz, CDCl3): d = 4.16–4.07 (m, 1H,
a]D = +37.5° (c = 0.56, CHCl3); IR
m
;
Acknowledgements
CHa (35)), 4.07–4.00 (m, 2H, CH2 (31)), 3.91 (dt, J = 11.0, 6.5 Hz,
1H, CHb (35)), 3.76 (d, J = 7.6 Hz, 1H, CHa (28)), 3.52 (s, 1H, CH
(19)), 3.43 (d, J = 7.7 Hz, 1H, CHb (28)), 2.49–2.39 (m, 3H, CH2
(1) + CH (5)), 2.26–2.19 (m, 1H, CH (9)), 1.70–1.56 (m, 5H, CHa
(15) + CH2 (36) + CH2 (32)), 1.56–1.44 (m, 5H, CHa (11) + CHa
(12) + CHa (21) + CH (18) + CH (13)), 1.43–1.34 (m, 10H, CHa
(22) + CH2 (6) + CH2 (37) + CH2 (33) + CHa (16) + CH2 (7)), 1.33–
1.21 (m, 2H, CHb (22) + CHb (16)), 1.27 (s, 3H, CH3 (24)), 1.26 (s,
3H, CH3 (23)), 1.22–1.17 (m, 2H, CHb (11) + CHb (21)), 1.15–1.09
(m, 1H, CHb (12)), 0.99–0.89 (m, 6H, CH3 (38) + CH3 (34)), 0.96 (s,
3H, CH3 (26)), 0.93 (s, 3H, CH3 (25)), 0.91 (s, 3H, CH3 (30)), 0.89–
0.84 (m, 1H, CHb (15)), 0.78 (s, 3H, CH3 (29)) ppm; 13C NMR
(100 MHz, CDCl3): d = 179.4 (C@O, C3), 172.1 (C@O, C2), 88.0 (CH,
C19), 71.5 (CH2, C28), 64.4 (CH2, C35), 63.9 (CH2, C31), 48.4 (CH,
We are grateful to Dr. R. Kluge for the ESI-MS spectra and to
Dr. D. Ströhl for measurement of the NMR spectra. Many thanks
are due to Mrs J. Wiese for measuring the IR spectra and the
optical rotations. The cell lines were kindly provided by
Dr. Thomas Müller (Dept. of Haematology/Oncology, Martin-Luther
Universität Halle-Wittenberg). Support by the ‘Gründerwerkstatt—
Biowissenschaften’ is gratefully acknowledged.
References and notes
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C5), 47.2 (Cquart, C4), 46.9 (CH, C18), 43.4 (CH, C9), 43.0 (Cquart
,
C8), 42.6 (CH2, C1), 41.6 (Cquart, C10), 41.2 (Cquart, C20), 40.6
(Cquart, C14), 36.9 (CH2, C16), 36.4 (Cquart, C17), 34.5 (CH, C13),
33.0 (CH2, C7), 32.9 (CH2, C21), 31.0 (CH2, C36), 30.7 (CH2, C32),
29.0 (CH3, C30), 26.7 (CH3, C23), 26.6 (CH2, C12), 26.6 (CH2, C15),
26.4 (CH2, C22), 25.1 (CH3, C29), 24.7 (CH3, C24), 22.1 (CH2, C11),
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15.9 (CH3, C26), 13.9 (CH3, C27), 13.9 (CH3, C38), 13.6 (CH3, C34)
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acetate, 8:2); mp 122–124 °C; [
(KBr): = 3430w, 2950s, 2868s, 1739s,1723s, 1496w, 1456m,
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m
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