Synthesis and antimalarial activity of new haemanthamine-type derivatives

Article abstract of DOI:10.1016/j.bmc.2012.07.036

Thirty one derivatives were prepared from the natural alkaloids haemanthamine (1), haemanthidine (2) and 11-hydroxyvittatine (3). They were evaluated for their in vitro antimalarial activity against chloroquine-sensitive strains of Plasmodium falciparum and some structure-activity relationships were outlined. For haemanthamine derivatives having a methoxy group at C-3, the presence of a free hydroxyl group at C-11 is important for the activity. The double bond at C-1-C-2 plays also an important role to achieve good inhibitory activity. Compound 35 with two nicotinate groups at C-3 and at C-11 was the most active compound with a IC₅₀ = 0.8 ± 0.06 μM.

Full text of DOI:10.1016/j.bmc.2012.07.036

Bioorganic & Medicinal Chemistry 20 (2012) 5464–5472
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis and antimalarial activity of new haemanthamine-type derivatives
Juan C. Cedrón a,b,c, David Gutiérrez d, Ninoska Flores d, Ángel G. Ravelo a,b, , Ana Estévez-Braun a,b,
⇑
⇑
a Instituto Universitario de Bio-Orgánica ‘Antonio González’, Av. Astrofísico Francisco Sánchez 2, 38206, Departamento de Química Orgánica, Universidad de La Laguna, Tenerife, Spain
b Instituto Canario de Investigación del Cáncer (ICIC), Spain
c Pontificia Universidad Católica del Perú, Sección Química. Av. Universitaria 1801 San Miguel, Lima 32, Peru
d Instituto de Investigaciones Fármaco Bioquímicas, Facultad de Ciencias Farmacéuticas y Bioquímicas, Universidad Mayor de San Andrés, Av. Saavedra 2024, 2° piso, Miraflores, La
Paz, Bolivia
a r t i c l e i n f o
a b s t r a c t
Article history:
Thirty one derivatives were prepared from the natural alkaloids haemanthamine (1), haemanthidine (2)
and 11-hydroxyvittatine (3). They were evaluated for their in vitro antimalarial activity against chloro-
quine-sensitive strains of Plasmodium falciparum and some structure–activity relationships were out-
lined. For haemanthamine derivatives having a methoxy group at C-3, the presence of a free hydroxyl
group at C-11 is important for the activity. The double bond at C-1–C-2 plays also an important role to
achieve good inhibitory activity. Compound 35 with two nicotinate groups at C-3 and at C-11 was the
Received 15 May 2012
Revised 13 July 2012
Accepted 21 July 2012
Available online 31 July 2012
Keywords:
Haemanthamine
Antiplasmodial activity
Amaryllidaceae alkaloids
most active compound with a IC50 = 0.8 0.06 lM.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
narciclasine has shown anticancer activity,13 and galantamine is a
worldwide distributed drug for the treatment of Alzheimer0s dis-
ease.14 Some of the Amaryllidaceae alkaloids are also of particular
interest because of their potential antimalarial activity: lycorine,
haemanthamine, haemanthidine and crinamine possess important
activity against several strains of Plasmodium falciparum.15–17
In the present work we have carried out selective modifications
on the structures of three haemanthamine-type alkaloids: hae-
manthamine (1), haemanthidine (2) and 11-hydroxyvittatine (3).
These alkaloids were isolated in large amounts from the bulbs of
Pancratium canariense.18,19 The 31 obtained derivatives were eval-
uated as antimalarial agents against P. falciparum and some preli-
minary structure-activity relationships were established for the
haemanthamine skeleton.
AIDS, malaria and tuberculosis cause together more than five
million deaths per year, especially in developing countries.1
Although the development of vaccines for these diseases is in pro-
gress, treatment for patients depends on the use of specific drugs.
Natural products have made and continue to make an immense con-
tribution to malaria chemotherapy either directly as antimalarial
agents or as important lead compounds for the discovery of more
potent antimalarials.2 Chloroquine, and other quinoline antimalari-
als such as primaquine, mepacrine and mefloquine have been main-
stays of antimalarial chemotherapy for more than past 40 years.3
Artemisinin isolated from the Chinese plant Artemesia annua has
been used successfully against chloroquine-resistant malarial para-
sites.4 But, the poor solubility of artemisinin, coupled with its short
plasma half life led to a high rate of parasite recrudescence. The
development of semi-synthetic analogues through the reduced lac-
tone dihydroxyartemisinin gave rise to the oil-soluble derivatives
artemether and arteether as well as the water-soluble sodium
artesunate. However, the rapid spread of drug resistant malarial
strains all over the world forces the search for more selective and
effective antimalarial drugs.5,6 Isolation of new lead compounds
from plants is one of the strategies that can be in the search for
new drugs.7–9 Alkaloids of the Amaryllidaceae family exhibit a wide
and important range of biological activities.10–12 For example,
2. Results and discussion
2.1. Chemistry
Alkaloids haemanthamine 1, haemanthidine 2, 11-hydroxyvit-
tatine 3, vittatine 4, 8-O-demethylmaritidine 5 and 6-O-methylma-
ritidine 6 were isolated from Pancratium canariense as published
(Fig 1).18,19
Modifications achieved on the structure of haemanthamine 1 are
shown in Schemes 1 and 2. For the most part, the transformations
were carried out on the hydroxyl group at C-11 or on the double
bond presents in ring D in order to study their role in the antiplas-
modial activity. Compound 7 was obtained quantitatively by acety-
lation with acetic anhydride. Esterification with p-vinylbenzoic acid
⇑
Corresponding authors.
E-mail address: aestebra@ull.es (A. Estévez-Braun).
http://www.icic.es
0968-0896/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmc.2012.07.036

J. C. Cedrón et al. / Bioorg. Med. Chem. 20 (2012) 5464–5472
5465
R4
2
OR3
1
3
haemanthamine (1): R1+R2=-CH2-, R3=Me, R4=OH, R5=H
haemanthidine (2): R1+R2=-CH2-, R3=Me, R4=R5=OH
11-hydroxyvittatine (3): R1+R2=-CH2-, R3=R5=H, R4=OH
vittatine (4): R1+R2=-CH2-, R3=R4=R5=H
8-O-demethylmaritidine (5): R1=Me, R2=R3=R4=R5=H
6-O-methylmaritidine (6): R1+R2=-CH2-, R3=Me, R4=OH, R5=OMe
11
10
7
R1O
10a
6a
9
4
10b
H
6
12
4a
R2O 8
N
R5
Figure 1. Structures of haemanthamine-type alkaloids.
O
2'
3'
4'
1'
6'
O
AcO
OMe
OR
9: R=Nic (48%)
OMe
OMe
O
5'
OMe
OMe
10: R=p-BrBz (60%)
O
O
O
O
O
11: R=COCH(CH3)2 (65%)
12: R=COCH=CH2 (28%)
H
H
H
N
N
O
N
8 (73%)
7 (100%)
a
c
b
HON
OMe
OH
O
OMe
D
O
O
O
O
O
d
e
f
O
C
H
H
H
A
B
N
N
N
N
O
O
O
15 (26%)
14 (40%)
13 (85%)
1
g
i
h
OH
OMe
OH
OH
O
O
O
HO
HO
H
N
H
N
O
H
O
N
16 (33%)
17 (55%)
18 (50%)
Scheme 1. Reagents and conditions: (a) Ac2O, py; (b) p-vinylbenzoic acid, DCC, DCM; (c) RCl, NEt3, DCM; (d) NBS, DCM; (e) Jones reagent, acetone; (f) NH3OHCl, NaOAc, EtOH,
reflux, 15 h; (g) 6 M HCl, 100 °C, 4 h; (h) BBr3, DCM, 0 °C; (j) 30% H2O2, MeOH, 24 h.
Br
N
OH
OMe
OH
HO
OMe
O
O
O
O
H
H
N
a
c
19 (52%)
21 (51%)
OH
OMe
O
O
H
N
HO
Br
OH
OMe
Br
OH
OMe
d
b
Br
1
O
O
H
N
H
N
O
O
20 (25%)
22 (69%)
2
OH
1
OH
3
4
10
10a
OAc
9
8
O
O
10b
4a
e
O
6
6a
H
7
N
O
N
H
R
7
O
23: R=Me (33%)
24: R=Et (47%)
Scheme 2. Reagents and conditions: (a) H2, 10% Pd/C, THF; (b) Br2, DCM, 24 h; (c) CH3CONHBr, SnCl4, H2O, CH3CN, 0 °C; (d) CH3CONHBr, SnCl4, CH3CN, 0 °C; (e) (1) RX, CH3CN,
24 h; (2) t-BuOK/t-BuOH, reflux, 4 h.

5466
J. C. Cedrón et al. / Bioorg. Med. Chem. 20 (2012) 5464–5472
produced derivative 8, which possesses a terminal vinyl group. The
hydroxyl group was also acylated with several acyl chlorides of dif-
ferent size, lipophilicity and stereoelectronic properties (nicotyl, p-
bromobenzoyl, isobutyryl and acryloyl chloride), to yield the corre-
sponding esters 9–12. When 1 was treated with NBS one product
was obtained in good yield, being identified as the epoxide 13. Since
the absolute configuration of haemanthamine is known the stereo-
chemistry of the epoxy ring was established as 11S, 12R on the basis
of the following NOEs observed in the Roesy spectrum H-4a/H-6b,
H-12/H-4a, H-12/H-6a. Oxidation of the hydroxyl group to the cor-
responding ketone 14 was achieved by using the Jones reagent and
treatment of 14 with hydroxylamine hydrochloride led to the oxime
15. The treatment of 1 with concentrated HCl under reflux condi-
tions yielded derivative 16, which was identified as apohaemanth-
amine, a natural alkaloid isolated from Eucharis amazonica.20 The
polyhydroxylated compound 17 was obtained by treatment of 1
with BBr3. The reaction of 1 with H2O2 afforded the corresponding
N-oxide derivative 18.
The double bond at C-1–C-2 of haemanthamine was modified as
shown in Scheme 2: Hydrogenation and bromination led to deriv-
atives 19 and 20, respectively. Treatment of 1 with N-bromoacet-
amide according to the published conditions for haloamidation21
produced compound 21. However, when this reaction was per-
formed under anhydrous conditions only one product, after
work-up, was obtained, being identified as 22. Thus, the presence
or absence of water allowed us the regioselective preparation of
the corresponding bromohydrines. Hofmann elimination22 was
performed on 11-acetylhaemanthamine. Thus, the reaction of 7
with different alkyl halides followed by treatment with t-BuOK/t-
BuOH yielded the corresponding new biphenyl derivatives 23
and 24. The formation of these compounds occurred with aromati-
zation of ring C and ring D opening, and they were obtained as a
mixture of anti and syn formamide conformers.
Modifications carried out on the hydroxyl groups of 11-
hydroxyvittatine (3) are shown in Scheme 4. Acetylation of 3
yielded compound 33. The derivative 34 was obtained by esterifi-
cation using (R)-(ꢀ)-methoxyphenylacetic acid (MPA), while acyl-
ation of 3 with different acyl chlorides led the corresponding
compounds 35–37.
2.2. Biological assay and SAR
Results of the antiplasmodial evaluation are summarized in Ta-
ble 1, indicating that haemanthamine (1) and haemanthidine (2)
are the most active natural alkaloids, with IC50 values of 1.3 and
1.2
l
M, respectively. However, derivative 35 presented the best
M.
antiplasmodial activity, with an IC50 value under 1
l
From the obtained results presented in Table 1, we can establish
some structure–activity relationships for the haemanthamine skel-
eton. When 1 was converted into the corresponding acyl deriva-
tives 7–10 and 12, a dramatic decrease in the activity was
observed (i.e., 1 vs 7, 1 vs 8, 1 vs 9, 1 vs 10, 1 vs 12). These results
indicated that a hydrogen-bond-donor (HBD) at C-11 is an impor-
tant requirement for the antiplasmodial activity. Only in the case of
compound 12 which presents an acryloyl moiety, a 6-fold lower
activity than 1, was detected. Probably, in this case the acryloyl
moiety at C-11 could act as a Michael acceptor.
The oxidation of the hydroxyl group at C-11 also led to a less ac-
tive compound (1 vs 14). The replacement of the methoxy group at
C-3 by a hydroxyl group produced a decrease in the activity (1 vs
17). The N-oxide derivative 18 obtained by oxidation of 1 with
H2O2 was inactive. The epoxy derivative 13 showed similar anti-
plasmodial activity than compound 1, while the derivative 16
was inactive. The similar antiplasmodial activity of compounds 1
and 13 could be attributed to a possible hydrolysis of the oxirane
ring.
The structure of haemanthidine (2) was also modified as shown
in Scheme 3. Acetylation with Ac2O/py and acylation with different
acyl chlorides afforded derivatives 25–28. When 2 reacted with the
Jones reagent only the hydroxyl group at C-11 was chemoselec-
tively oxidized, yielding compound 29. With the aim of oxidizing
the hydroxyl group at C-6, TEMPO (2,2,6,6-tetramethyl-1-piperid-
inyloxy)23 was employed, but derivative 30 was obtained instead
of the desired lactam. The structure of 30 was unequivocally estab-
lished on the basis of the correlations observed in the HMBC spec-
trum. The derivatives 31 and 32 were prepared from 2 using BBr3
and HCl, respectively in a similar way to that followed for
haemanthamine.
Concerning the modifications on the double bond at C-1–C-2 of
the ring D, derivatives 19–22 were less active than 1, indicating
that this double bond seems to play an important role in the activ-
ity. A simplification of the haemanthamine skeleton achieved by
the formation of the biphenyl compounds 23 and 24 produced a
drastic loss of activity.
With respect to the haemanthidine series (2, 25–32), the pres-
ence of a hydroxyl group at C-6 produces similar antiplasmodial
activity (i.e., 1 vs 2). The diacetylated compounds were less active
than compound 2 (i.e., 2 vs 25, 2 vs 27, 2 vs 28). In this case, the
introduction of two nicotinates (26) or two p-bromo benzoates
(27) produced a lower loss of activity than the introduction of
OAc
OR
1
OH
OMe
OMe
OMe
26: R1=H, R2=Nic (81%)
27: R1=R2=p-BrBz (40%)
28: R1=R2=COCH(CH3)2 (65%)
a
b
O
O
O
O
O
O
H
H
H
N
N
N
OAc
25 (100%)
OH
2
OR
2
c
f
e
d
O
OH
O
OMe
O
OMe
OH
HO
HO
H
N
O
O
O
HO
HO
H
H
H
N
N
O
N
OH
CHO
OH
OH
31 (62%)
29 (46%)
30 (76%)
32 (67%)
Scheme 3. Reagents and conditions: (a) Ac2O, py; (b) RCl, NEt3, DCM; (c) Jones reagent, acetone; (d) TEMPO, NBu4I, m-CPBA, DCM, 24 h; (e) BBr3, DCM, 0 °C; (f) 6 M HCl,
100 °C, 4 h.

J. C. Cedrón et al. / Bioorg. Med. Chem. 20 (2012) 5464–5472
5467
since they are present in the most active compounds. From the re-
sults obtained in the acylation of haemanthamine (7–12), haeman-
thidine (25–28) and 11-hydroxy vittatine (33–37), we can
conclude that the free hydroxyl at C-11 is essential in the hae-
manthamine series with only one hydroxyl group at C-11. In the
haemanthidine series with hydroxyl groups at C-11 and at C-6 or
in the 11-hydroxy vittatine series with hydroxyl groups at C-3
and at C-11, the nature of the acyl groups at C-6 or at C-3 modulate
the loss of antiplasmodial activity associated with the acylation of
the OH at C-11. The presence of two aromatic ester groups at C-3
and at C-11 produces good inhibitory activity. The findings of the
present study suggest that some haemantamine derivatives are
good inhibitors of P. falciparum and provided a useful starting point
for the preparation of new haemanthamine-type derivatives with
improved antiplasmodial activity.
OAc
OAc
OH
OH
O
O
O
O
a
H
H
N
N
33 (100%)
3
c
b
OMPA
OMPA
OR
OR
O
O
O
H
H
N
N
O
35: R=Nic (47%)
36: R=p-BrBz (56%)
37: R=COCH(CH3)2 (63%)
34 (74%)
4. Experimental
4.1. Chemistry
Scheme 4. Reagents and conditions: (a) Ac2O, py; (b) (R)-(ꢀ)-MPA, DCC, DCM; (c)
RCl, NEt3, DCM.
IR spectra were obtained using a Bruker IFS28/55 spectropho-
tometer. Optical rotations were measured with a Perkin-Elmer
241 automatic polarimeter. 1H and 13C NMR spectra were re-
corded, unless any other indication, in CDCl3 or MeOD at 300 and
75 MHz respectively. 2D NMR experiments were conducted on a
Bruker WP-400 SY NMR spectrometer at 400 MHz. High- and
low-resolution mass spectra were obtained on a VG Autospec spec-
trometer. Analtech Silica Gel GF preparative layer with UV254 was
used for TLC. Silica gel (0.2–0.63 mm) was employed for column
chromatography. Silica gel 60 (Merck) was used on a Harrison Re-
search 7924T Chromatotron.
Table 1
In vitro activity against Plasmodium falciparum F32
Compound
IC50
(
l
M)a
Compound
IC50 (lM)
1
2
3
4
5
6
7
8
1.3 0.2
1.2 0.09
13.2 1.4
7.3 0.1
91.5 10.4
75.5 9.0
75.8 8.7
>100
51.7 4.9
43.3 4.1
56.6 8.1
8.4 1.7
1.6 0.1
73.5 10.0
95.5 9.5
92.9 14.8
13.4 1.8
>100
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
6.5 0.9
62.6 7.5
72.6 5.0
73.4 10.5
>100
52.3 7.5
7.1 0.9
2.9 0.6
52.5 6.6
85.7 9.5
76.6 9.6
72.1 10.0
84.2 10.5
>100
9
Alkaloids 1–6 were extracted from the bulbs of Pancratium
10
11
12
13
14
15
16
17
18
19
canariense as described in Reference15
.
4.1.1. 11-Acetylhaemanthamine (7)
To 14 mg (0.046 mmol) of 1 in 1 mL of pyridine was added
0.3 mL (3.18 mmol) of acetic anhydride. After 3 h stirring, the sol-
vent was evaporated and the residue was purified by preparative
TLC using DCM/MeOH 19:1 as eluent to yield 15 mg (99%) of 7 as
5.1 0.7
0.8 0.06
3.0 0.6
7.0 1.2
0.04
36
37
9.9 1.3
Chloroquine
an amorphous white solid. ½a D20
ꢁ
ꢀ5.6 (c 0.98, EtOH). 1H NMR
a
Data are expressed as mean standard deviation of three determinations.
(CDCl3) d: 4.97 (1H, t, J = 5.0 Hz, H-11), 1.96 (3H, s, OCOCH3), for
the rest of the signals see Supplementary data. 13C NMR (CDCl3)
d 169.8 (s, OCOCH3), 79.9 (d, C-11), 21.0 (q, OCOCH3), for the rest
of the signals see Supplementary data. IR (neat, cmꢀ1): 2933,
1735, 1648, 1483, 1373, 1240, 1086, 1036, 933, 847, 755, 662. EIMS
m/z (%): 343 (M+, 100); 300 (4); 284 (17); 268 (12); 252 (16); 224
(28); 211 (16); 188 (11); 181 (19). HRMS m/z 343.1410 (calcd for
two acetates (25), or two isobutiryl groups (28). These results indi-
cate that the presence of an aromatic moiety at C-6 favours the
antiplasmodial activity (i.e., 9 vs 26, 10 vs 27).The replacement of
the methylenedioxy moiety at the aromatic ring A by other groups
led to a decreased activity (i.e., 1 vs 5, 1 vs 17 and 2 vs 31). The for-
mation of compounds 29, 30, 31, and 32 led to similar results that
those obtained from haemanthamine (1). Regarding to the deriva-
tives (33–37) obtained from 11-hydroxyvittatine (3), the acylation
of the hydroxyl groups led to different results depending on the
type of esters at C-3 and C-11. Thus, the diacetate compound 33
was inactive (i.e., 3 vs 33), the introduction of isobutyrates pro-
duced a slight improved activity (i.e., 3 vs 37) and the best activity
was achieved with the presence of two nicotinates (i.e., 3 vs 35).
C
19H21NO5 [M]+ 343.1420).
4.1.2. 11-(p-Vinylbenzoyl)-haemanthamine (8)
To a solution of 23.4 mg (0.08 mmol) of 1 in 3 mL of DCM were
added 33 mg (2 equiv) of 1,3-dicyclohexylcarbodiimide (DCC) and
19 mg (2 equiv) of p-vinylbenzoic acid. The mixture was stirred for
24 h. Then, the solvent was evaporated and the residue was puri-
fied by preparative TLC using DCM/MeOH 9:1 to yield 24.4 mg
(73%) of compound 8 as an amorphous white solid. ½a D20
ꢁ
+46.2 (c
1
0.08, MeOH). H NMR (CDCl3) d 7.86 (2H, d, J = 8.0 Hz, H-20), 7.45
(2H, d, J = 8.0 Hz, H-30), 6.74 (1H, dd, J = 10.8 Hz, J = 17.5 Hz, H-50),
5.86 (1H, d, J = 19.9 Hz, H-60), 5.39 (1H, d, J = 10.8 Hz, H-60), 5.20
(1H, br s, H-11) for the rest of the signals see Supplementary data.
13C NMR (CDCl3) d 164.9 (s, C@O), 141.9 (s, C-10), 135.6 (d, C-50),
129.4 (d, C-20), 127.3 (s, C-40), 125.9 (d, C-30), 116.4 (t, C-60), 80.5
(d, C-11), for the rest of the signals see Supplementary data. IR
(neat, cmꢀ1): 2922, 2848, 1710, 1621, 1481, 1270, 1239, 1178,
1097, 1020, 930, 848, 783, 683. EIMS m/z (%): 432 ([M+1]+, 100);
3. Conclusion
We have prepared 31 derivatives from the natural alkaloids
haemanthamine (1), haemanthidine (2) and 11-hydroxyvittatine
(3) with the aim of identifying the structural requirements to
achieve good inhibitory activity against P. falciparum. The presence
of the double bond at C-1–C-2 of the ring D and the methylenedioxi
group at the ring A seem to play an important role in the activity

5468
J. C. Cedrón et al. / Bioorg. Med. Chem. 20 (2012) 5464–5472
356 (4); 342 (5); 315 (4); 288 (11); 277 (3). HREIMS m/z 432.1814
NMR (CDCl3) d 6.30 (1H, d, J = 8.6 Hz, OCOCHCH2), 6.03 (1H, dd,
J = 10.4 Hz, J = 17.2 Hz, OCOCHCH2), 5.81 (1H, d, J = 10.4 Hz,
OCOCHCH2), 5.06 (1H, t, J = 5.1 Hz, H-11), for the rest of the signals
see Supplementary data. 13C NMR (CDCl3) d 164.8 (s, C@O), 130.6
(t, OCOCHCH2), 128.1 (d, OCOCHCH2), 80.0 (d, C-11), for the rest
of the signals see Supplementary data. IR (neat, cmꢀ1): 3036,
2929, 1722, 1619, 1483, 1405, 1326, 1267, 1239, 1086, 1041,
932, 849, 808, 733. EIMS m/z (%): 355 ([M]+, 100); 340 (3); 324
(4); 300 (8); 283 (18); 268 (14); 252 (17); 225 (26); 210 (16),
(calcd for C26H26NO5 [M+1]+ 432.1811).
4.1.3. General procedure for acylation of 1
To a solution of haemanthamine (1) in 3 mL of dry DCM were
added Et3N (2.5 equiv) and 1.5 equiv of the corresponding acyl
chloride. The mixture was stirred at room temperature until disap-
pearance of the starting material. Then, the solvent was evaporated
and the residue was purified by preparative TLC using DCM/MeOH
9:1 to afford the corresponding esters 9–12.
185 (5). HREIMS m/z 355.1414 (calcd for
C
20H21NO6 [M]+
355.1420).
4.1.4. 11-Nicotylhaemanthamine (9)
Following the procedure described above, 17.6 mg (0.06 mmol)
4.1.8. 11,12-Epoxyhaemanthamine (13)
of 1 was treated with 21
l
L (2.5 equiv) of Et3N and 16 mg
To 20 mg (0.066 mmol) of 1 dissolved in DCM (3 mL) were
added 24 mg (2 equiv) of N-bromosuccinimide (NBS). The reaction
was stirred for 12 h and then the solvent was evaporated. The res-
idue was purified by preparative TLC using DCM/MeOH 9:1 to yield
(0.09 mmol) of nicotinoyl chloride. After purification, 11 mg
(48%) of 9 were obtained as an amorphous white solid. ½a D20
ꢁ
+30.0 (c 0.95, EtOH). 1H NMR (CDCl3) d 9.10 (1H, s, CCHN), 8.78
(1H, d, J = 3.5 Hz, NCHCHCHC), 8.20 (1H, d, J = 7.9 Hz, NCHCHCHC),
7.41 (1H, dd, J = 2.9 Hz, J = 7.8 Hz, NCHCHCHC), 5.22 (1H, dd,
J = 2.2 Hz, J = 3.9 Hz, H-11), for the rest of the signals see Supple-
mentary data. 13C NMR (CDCl3) d 163.9 (s, C@O), 153.3 (d, CCHN),
150.3 (d, NCHCHCHC), 136.9 (d, NCHCHCHC), 125.9 (s, CCHN),
123.3 (d, NCHCHCH), 81.0 (d, C-11), for the rest of the signals see
Supplementary data. IR (neat, cmꢀ1): 2927, 1721, 1591, 1482,
1328, 1283, 1239, 1115, 1039, 935, 848, 754, 701, 664. EIMS m/z
(%): 406 (M+, 100); 375 (5); 300 (8); 283 (27); 268 (18); 252
(20); 224 (38); 181 (14). HREIMS m/z 406.1562 (calcd for
19 mg (85%) of compound 13 as an amorphous white solid. ½a D20
ꢁ
+2.8 (c 1.2, EtOH). 1H NMR (CDCl3) d 4.27 (1H, br s, H-11), 3.78
(2H, m, H-4a, H-12), for the rest of the signals see Supplementary
data. 13C NMR (CDCl3) d 76.7 (d, C-12), 64.7 (d, C-11), for the rest
of the signals see Supplementary data. IR (neat, cmꢀ1): 2928,
1643, 1485, 1244, 1035, 929, 855, 733, 591. EIMS m/z (%): 300
([M+1]+, 8); 269 (75); 257 (60); 240 (31); 227 (100); 211 (43);
181 (84). HREIMS m/z 300.1235 (calcd for C17H18NO4 [M+1]+
300.1236).
C
23H22N2O5 [M]+ 406.1529).
4.1.9. 11-Oxohaemanthamine (14)
To a solution of 20 mg (0.066 mmol) of 1 in acetone (2 mL) at
0 °C, was added the Jones reagent dropwise, until the solution
turned orange. The reaction mixture was stirred for 30 min and
then isopropanol was added. The solution was filtered through
Florisil and the filtrate was concentrated and purified by prepara-
tive TLC using DCM/MeOH 9:1 to yield 8 mg (40%) of compound 14
4.1.5. 11-(p-Bromobenzoyl)-haemanthamine (10)
Following the procedure described above, 20.6 mg (0.7 mmol)
of 1 was reacted with 24 lL (2.5 equiv) of Et3N and 23 mg
(1.05 mmol) of p-bromobenzoyl chloride to yield, after purifica-
tion, 19 mg (60%) of 10 as an amorphous white solid. ½a D20
ꢁ
+27.3
(c 0.9, EtOH). H NMR (CDCl3) d 7.77 (2H, d, J = 8.4 Hz, H-20), 7.57
(2H, d, J = 8.4 Hz, H-30), 5.91 (2H, s, OCH2O), 5.21 (1H, br s, H-11),
for the rest of the signals see Supplementary data. 13C NMR (CDCl3)
d 163.8 (s, C@O), 131.6 (d, C-20), 130.6 (d, C-30), 126.2 (s, C-10),
123.0 (s, C-40), 106.5 (d, C-7), 103.7 (d, C-10), 100.8 (t, OCH2O),
80.9 (d, C-11), for the rest of the signals see Supplementary data.
IR (neat, cmꢀ1): 3443, 2928, 1721, 1645, 1483, 1270, 1240, 1173,
1100, 1039, 936, 847, 755. EIMS m/z (%): 485 ([M+1]+, 100); 483
([M-1]+, 99); 456 (5); 441 (7); 371 (9); 300 (20); 283 (65); 268
(52); 252 (37); 224 (61); 184 (54). HREIMS m/z 485.0672 (calcd
for C24H22NO5Br [M]+ 485.0661).
as an amorphous white solid. ½a D20
ꢁ
+38.3 (c 0.6, EtOH). 1H NMR
1
(CDCl3) d 3.52 (4H, m, H-6, H-12, H-4a), for the rest of the signals
see Supplementary data. 13C NMR (CDCl3) d 205.2 (s, C-11), 58.7
(t, C-12), for the rest of the signals see Supplementary data. IR
(neat, cmꢀ1): 2925, 1734, 1646, 1482, 1239, 1085, 1038, 932,
849, 758, 666. EIMS m/z (%): 299 (M+, 2); 271 (100); 211 (25);
181 (65). HREIMS m/z 299.1140 (calcd for C17H17NO4 [M]+
299.1158).
4.1.10. 11-Oxohaemanthamine oxime (15)
To a solution of 17 mg (0.057 mmol) of 14 in 2 mL of EtOH were
added 12 mg (3 equiv) of hydroxylamine hydrochloride and a solu-
tion of 10 mg (2 equiv) of sodium acetate in 0.5 mL of H2O. The
mixture was refluxed for 15 h. Then, the solvent was evaporated
and water was added to the residue. The mixture was extracted
with DCM and the organic phase was then dried over anhydrous
magnesium sulphate, filtered and concentrated. Further purifica-
tion by preparative TLC using DCM/MeOH 9:1 yielded 4.6 mg
4.1.6. 11-Isobutyrylhaemanthamine (11)
Following the procedure described above, 16.5 mg
(0.055 mmol) of 1 was treated with 20 lL (2.5 equiv) of Et3N and
9 lL (0.17 mmol) of isobutyryl chloride. After purification, 13 mg
(65%) of 11 were obtained as an amorphous white solid. ½a D20
ꢁ
+3.8 (c 1.3, EtOH). 1H NMR (CDCl3) d 4.97 (1H, t, J = 5.0 Hz, H-11),
2.44 (1H, m, CH(CH3)2), 1.10 (6H, d, J = 7.0 Hz, CH(CH3)2), for the
rest of the signals see Supplementary data. 13C NMR (CDCl3) d
175.6 (s, C@O), 79.0 (d, C-11), 33.7 (d, CH(CH3)2), 18.8 (q,
CH(CH3)2), 18.4 (q, CH(CH3)2), for the rest of the signals see Supple-
mentary data. IR (neat, cmꢀ1): 2973, 2932, 1731, 1483, 1325, 1240,
1155, 1086, 1039, 934, 850, 755, 663. EIMS m/z (%): 371 (M+, 100);
342 (6); 300 (12); 283 (30); 268 (35); 252 (20); 224 (53); 181 (24).
HREIMS m/z 371.1748 (calcd for C21H25NO5 [M]+ 371.1733).
(26%) of compound 15 as an amorphous white solid. ½a D20
ꢀ7.4 (c
ꢁ
0.23, EtOH). 1H NMR (CDCl3) d 3.84 (2H, m, H-12), for the rest of
the signals see Supplementary data. 13C NMR (CDCl3) d 168.0 (s,
C-11), 53.1 (t, C-12), for the rest of the signals see Supplementary
data. IR (neat, cmꢀ1): 3421, 2926, 1645, 1483, 1329, 1240, 1086,
1038, 932, 854, 796, 736. EIMS m/z (%): 314 (M+, 19); 297 (8);
266 (21); 238 (12); 224 (100); 210 (12); 181 (5). HREIMS m/z
314.1266 (calcd for C17H18N2O4 [M]+ 314.1267).
4.1.7. 11-Acryloylhaemanthamine (12)
4.1.11. Apohaemanthamine (16)
Following the procedure described above, 30 mg (0.1 mmol) of
1 were treated with 28 lL (2 equiv) of Et3N and 13 lL (0.15 mmol)
A solution of 20 mg (0.066 mmol) of 1 in 5 mL of a solution 6 M
HCl was heated at 100 °C for 4 h. Then, a 20% NH4OH solution was
added until basic pH and the mixture was extracted with DCM. The
organic phase was dried over anhydrous magnesium sulphate and
of acryloyl chloride. After purification, 9.6 mg (28%) of 12 were ob-
tained as an amorphous white solid. ½a D20
ꢁ
+13.9 (c 0.18, MeOH). 1H

J. C. Cedrón et al. / Bioorg. Med. Chem. 20 (2012) 5464–5472
5469
concentrated. After purification by preparative TLC, using DCM/
rest of the signals see Supplementary data. 13C NMR (CDCl3) d 63.8
(d, C-2), 60.1 (t, C-1), for the rest of the signals see Supplementary
data. IR (neat, cmꢀ1): 3440, 2927, 1644, 1503, 1483, 1241, 1037,
933, 734, 600. EIMS m/z (%): 460 (M+, 3); 459 (2); 382 (29); 380
(29); 331 (5); 300 (100); 270 (11); 245 (34); 238 (18); 181 (21).
HREIMS m/z 460.9663 (calcd for C17H19NO4Br2 [M]+ 460.9660).
MeOH 22:3, 5.8 mg (33%) of compound 16 was obtained as an
amorphous white solid. ½a D20
ꢁ
+91.5 (c 0.6, MeOH). 1H NMR (MeOD)
d 4.40 (1H, br s, H-3), 3.69 (1H, s, H-11), 3.21 (2H, s, H-12), for the
rest of the signals see Supplementary data. 13C NMR (MeOD) d 80.2
(d, C-11), 64.6 (d, C-3), 60.5 (t, C-12), for the rest of the signals see
Supplementary data. IR (neat, cmꢀ1): 3055, 2927, 1645, 1482,
1384, 1264, 1233, 1037, 936, 870, 738, 703. EIMS m/z (%): 269
(M+, 100); 240 (21); 224 (10); 214 (24); 186 (22); 181 (34); 152
(15); 128 (16). HREIMS m/z 269.1058 (calcd for C16H15NO3 [M]+
269.1052).
4.1.16. 2-Bromo-1-hydroxyhaemanthamine (21)
20 mg (0.066 mmol) of 1 was added to a cold (0 °C) mixture of
10 mg (1.2 equiv) of N-bromoacetamide, 27
lL (0.4 equiv) of a 1 M
solution of tin chloride (SnCl4) in DCM, and 1.5
l
L (1.2 equiv) of
H2O in 5 mL of MeCN. After 12 h stirring, water was added and
the mixture was extracted with DCM. The organic phase was dried
over anhydrous MgSO4, filtered, concentrated and purified by pre-
parative TLC using DCM/MeOH 9:1 to yield 13.5 mg (51%) of com-
4.1.12. 12 8,9-Nor-11-hydroxyvittatine (17)
To a solution of 22 mg (0.073 mmol) of 1 in 5 mL of dry DCM, at
0 °C, was added dropwise 0.22 mL (3 equiv) of a 1 M BBr3 solution
in DCM. The reaction mixture was stirred for 7 h, then the solvent
was removed and the residue was chromatographied with pre-
parative TLC using DCM/MeOH 9:1. 15.5 mg (55%) of compound
pound 21 as an amorphous white solid. ½a D20
ꢁ
+135.0 (c 0.6, MeOH).
1H NMR (MeOD) d 4.90 (1H, m, H-2), 4.39 (1H, d, J = 5.4 Hz, H-1),
for the rest of the signals see Supplementarydata. 13C NMR (MeOD)
d 76.8 (d, C-1), 41.0 (d, C-2), for the rest of the signals see Supple-
mentary data. IR (neat, cmꢀ1): 3422, 2930, 1670, 1484, 1378, 1330,
1236, 1095, 1034, 935, 839, 768, 740, 670. FABMS m/z (%): 399 (M+,
4); 382 (46); 380 (48); 350 (7); 289 (17); 273 (4); 241 (8); 181 (6);
176 (11), 154 (100). HRMS m/z 399.0486 (calcd for C17H20NO5Br
[M]+ 399.0500).
17 was obtained as an amorphous white solid. ½a D20
ꢁ
+50.5 (c 1.55,
EtOH). 1H NMR (MeOD) d 4.53 (1H, br s, H-3), for the rest of the sig-
nals see Supplementary data. 13C NMR (MeOD) d 145.5 (s, C-9),
145.3 (s, C-8), 63.7 (d, C-3), for the rest of the signals see Supple-
mentary data. IR (neat, cmꢀ1): 3437, 2928, 1644, 1250, 613. EIMS
m/z (%): 275 (M+, 4); 257 (100); 228 (26); 214 (11); 199 (22);
181 (43). HREIMS m/z 275.1139 (calcd for
C
15H17NO4 [M]+
275.1158).
4.1.17. 1-Bromo-2-hydroxyhaemanthamine (22)
A solution of 20 mg (0.066 mmol) of 1 in 5 mL of dry MeCN, at
4.1.13. Haemanthamine N-oxide (18)
0 °C, was added to a mixture of 10 mg (1.2 equiv) of N-bromoacet-
To a solution of 24.4 mg (0.083 mmol) of 1 in 2 mL of MeOH, at
0 °C, was added dropwise 0.1 mL (11 equiv) of 30% H2O2. The reac-
tion mixture was stirred at room temperature for 24 h. Then, an ex-
cess of manganese dioxide was added and the resulting mixture
was filtered through Celite. After evaporation of the solvent,
13 mg (50%) of compound 18 were obtained as an amorphous
amide and 27 lL (0.4 equiv) of a 1 M solution of tin chloride (SnCl4)
in DCM. The reaction mixture was stirred for 5 h. After that period,
water was added and the mixture was extracted with DCM. The or-
ganic phase was concentrated and purified by preparative TLC,
using DCM/MeOH 9:1 to yield 18 mg (69%) of compound 22 as
an amorphous white solid. ½a D20
ꢁ
+88.0 (c 0.9, MeOH). 1H NMR
white solid. ½a 2D0
ꢁ
+2.8 (c 0.91, EtOH). 1H NMR (MeOD) d 4.68 (2H,
(MeOD) d 6.77 (1H, s, H-10), 6.60 (1H, s, H-7), 5.92 (1H, br s,
OCH2O), 5.90 (1H, br s, OCH2O), 4.91 (1H, d, J = 5.3 Hz, H-1), 4.45
(1H, d, J = 17.1 Hz, H-6), 4,.42 (1H, d, J = 5.3 Hz, H-2), 4.19 (1H,
dd, J = 2.9 Hz, J = 6.3 Hz, H-11), 3.89 (1H, d, J = 17.1 Hz, H-6), 3.63
(1H, m, H-3), 3.54 (2H, m, H-12), 3.39 (3H, s, OMe), 3.30 (1H, m,
H-4a), 2.40 (1H, m, H-4), 2.27 (1H, d, J = 9.3 Hz, H-4). 13C NMR
(MeOD) d 147.0 (s, C-8), 146.6 (s, C-9), 129.7 (s, C-10a), 125.2 (s,
C-6a), 106.1 (d, C-7), 101.8 (d, C-10), 100.8 (t, OCH2O), 87.5 (d, C-
11), 79.4 (d, C-3), 76.9 (d, C-2), 63.7 (d, C-4a), 62.9 (t, C-12), 59.5
(t, C-6), 55.6 (q, OMe), 54.9 (s, C-10b), 40.6 (d, C-1), 28.8 (t, C-4).
IR (neat, cmꢀ1): 3458, 2932, 1730, 1503, 1484, 1385, 1236, 1100,
1035, 935, 845, 735, 671. FABMS m/z (%): 398 ([M-1]+, 8); 382
(18); 380 (16); 350 (7); 289 (14); 273 (6); 242 (5); 226 (3); 176
(14), 154 (100). HRMS m/z 398.0444 (calcd for C17H19NO5Br [M-
1]+ 398.0422).
d, J = 4.5 Hz, H-6), 3.67 (2H, dd, J = 4.5 Hz, J = 8.6 Hz, H-12), for
the rest of the signals see Supplementary data. 13C NMR (MeOD)
d 75.4 (t, C-12), 74.0 (t, C-6), for the rest of the signals see Supple-
mentary data. IR (neat, cmꢀ1): 3430, 2925, 1725, 1645, 1487, 1249,
1038, 930. EIMS m/z (%): 317 ([M]+, 5); 301 (85); 269 (61); 257
864); 240 (34); 227 (100); 211 (45); 181 (83). HREIMS m/z
317.1263 (calcd for C17H21NO5 [M]+ 317.1259).
4.1.14. 1,2-Dihydrohaemanthamine (19)
15.3 mg (0.047 mmol) of compound 1 dissolved in 3 mL of THF
were hydrogenated in the presence of catalytic amounts of Pd/C.
The reaction mixture was stirred for 5 days. The solution was fil-
tered through Celite and the solvent was evaporated. After purifi-
cation by preparative TLC with DCM/MeOH 9:1, 8 mg (52%) of
compound 19 was obtained as an amorphous white solid. ½a D20
ꢁ
+39.8 (c 0.6, EtOH). 1H NMR (CDCl3) d 1.88 (4H, m, H-1, H-2), for
the rest of the signals see Supplementary data. 13C NMR (CDCl3)
d 26.5 (t, C-2), 22.5 (t, C-1), for the rest of the signals see Supple-
mentary data. IR (neat, cmꢀ1): 3441, 2926, 2857, 1720, 1644,
1487, 1354, 1245, 1087, 1041, 939, 852, 758, 670. EIMS m/z (%):
303 (M+, 100); 287 (18); 272 (20); 259 (41); 244 (12); 226 (33);
211 (38); 186 (50). HREIMS m/z 303.1454 (calcd for C17H21NO4
[M]+ 303.1471).
4.1.18. General procedure for the preparation of formamides 23
and 24
A solution of compound 7 in 5 mL of CH3CN was treated with an
excess of the corresponding alkyl halide. The reaction mixture was
refluxed for 24 h. Then, the solvent was evaporated and the residue
was dissolved in 5 mL of t-butanol. An excess of potassium t-
butoxide (7 equiv) was added and the mixture was refluxed for
4 h. After this period, a saturated solution of NH4Cl was added
and the mixture was extracted with DCM. The organic phase was
dried over anhydrous MgSO4, filtered, concentrated and purified
by preparative TLC using DCM/MeOH 99:1 as eluent.
4.1.15. 1,2-Dibromohaemanthamine (20)
A solution of 22 mg (0.073 mmol) of 1 in 4 mL of dry DCM was
treated with 5 lL (1 equiv) of Br2. The reaction mixture was stirred
at room temperature for 24 h. Then, the solvent was evaporated
4.1.19. N-{[6-(4-Hydroxyphenyl)-1,3-benzodioxol-5-yl]methyl}-
N-methylformamide (23)
Following the general procedure, 19 mg (0.055 mmol) of 1 were
treated with 0.5 mL (8 mmol) of methyl iodide, to yield 5.1 mg
and the residue was purified by preparative TLC using DCM/MeOH
17:3 to afford 8 mg (25%) of compound 20 as an orange solid. ½a D20
ꢁ
+4.3 (c 0.8, EtOH). 1H NMR (CDCl3) d 4.87 (2H, s, H-1, H-2), for the

5470
J. C. Cedrón et al. / Bioorg. Med. Chem. 20 (2012) 5464–5472
(33%) of compound 23 as an amorphous pale yellow solid. 1H NMR
(CDCl3) d 8.01 (1H, s, CHO), 7.48 (1H, s, CHO), 7.08 (2H, d, J = 8.4 Hz,
H-1, H-4a), 7.02 (2H, d, J = 8.4 Hz, H-1, H-4a), 6.88 (2H, d, J = 8.4 Hz,
H-2, H-4), 6.85 (2H, d, J = 8.3 Hz, H-2, H-4), 6.74 (1H, s, H-7), 6.72
(2H, s, H-7, H-10), 6.70 (1H, s, H-10), 6.00 (2H, s, OCH2O), 5.97
(2H, s, OCH2O), 4.44 (2H, s, H-6), 4.23 (2H, s, H-6), 2.63 (3H, s,
NMe), 2.61 (3H, s, NMe). 13C NMR (CDCl3) d 162.5 (d, CHO),
162.4 (d, CHO), 155.7 (s, C-3), 155.0 (s, C-3), 147.0 (s, C-9), 146.9
(s. C-9), 146.6 (s, C-8), 146.5 (s. C-8), 136.2 (s, C-10a), 135.6 (s. C-
10a), 132.1 (s, C-10b), 131.3 (s, C-10b), 130.2 (d, C-1, C-4a), 129.9
(d, C-1, C-4a), 126.3 (s, C-6a), 125.8 (s, C-6a), 115.3 (d, C-2, C-4),
115.0 (d, C-2, C-4), 110.7 (d, C-10), 110.0 (d, C-10), 108.8 (d, C-7),
107.9 (d, C-7), 101.1 (t, OCH2O), 100.9 (t, OCH2O), 51.5 (t, C-6),
44.7 (t, C-6), 33.6 (q, NMe), 28.7 (q, NMe). IR (neat, cmꢀ1): 3272,
2923, 1720, 1612, 1502, 1447, 1394, 1268, 1171, 1090, 1038,
930, 834, 735, 666. EIMS m/z (%): 285 ([M]+, 66); 254 (4); 226
(100); 214 (6); 197 (27); 168 (21); 139 (11). HREIMS m/z
285.1002 (calcd for C16H15NO4 [M]+ 285.1001).
4.1.23. 6-Nicotylhaemanthidine (26)
Following the procedure described above, 15 mg (0.047 mmol)
of 2 were treated with 33 lL (0.235 mmol) of Et3N and 25.2 mg
(0.141 mmol) of nicotinoyl chloride. After purification, 16 mg
(81%) of compound 26 were obtained as an amorphous white solid.
½
a 2D0 +22.2 (c 0.09, MeOH). 1H NMR (CDCl3) d 9.29 (1H, s, CCHN),
ꢁ
9.22 (1H, s, CCHN), 8.80 (1H, d, J = 3.8 Hz, NCHCHCHC), 8.76 (1H,
d, J = 4.6 Hz, NCHCHCHC), 8.37 (1H, d, J = 7.8 Hz, NCHCHCHC),
8.30 (1H, d, J = 7.9 Hz, NCHCHCHC), 7.42 (1H, dd, J = 4.8 Hz,
J = 7.7 Hz, NCHCHCHC), 7.37 (1H, dd, J = 5.0 Hz, J = 7.8 Hz,
NCHCHCHC), 6.86 (1H, s, H-6), 3.98 (1H, s, H-11), for the rest of
the signals see Supplementary data. 13C NMR (CDCl3) d 164.0 (s,
C@O), 153.6 (d, CCHN), 153.3 (d, CCHN), 150.9 (d, NCHCHCHC),
150.8 (d, NCHCHCHC), 137.2 (d, NCHCHCHC), 137.2 (d,
NCHCHCHC), 125.5 (s, CCHN), 123.2 (d, NCHCHCHC), 123,0 (d,
NCHCHCHC), 86.8 (d, C-6), 78.0 (d, C-11), for the rest of the signals
see Supplementary data. IR (neat, cmꢀ1): 3399, 2925, 2855, 1724,
1603, 1483, 1387, 1249, 1195, 1098, 1036, 933, 870, 737, 700,
663. EIMS m/z (%): 422 (M+, 2); 406 (3); 323 (10); 284 (7); 257
(18); 248 (31); 225 (63); 166 (12); 123 (100). HREIMS m/z
422.1469 (calcd for C23H22N2O6 [M]+ 422.1478).
4.1.20. N-Ethyl-N-{[6-(4-Hydroxyphenyl)-1,3-benzodioxol-5-
yl]methyl}formamide (24)
Following the general procedure described above, 37.7 mg
(0.11 mmol) of 1 were treated with 0.5 mL (6.7 mmol) of ethyl bro-
mide, to yield 15.4 mg (47%) of compound 24 as an amorphous pale
yellow solid. 1H NMR (CDCl3) d 8.10 (1H, s, CHO), 7.72 (1H, s, CHO),
7.38 (4H, m, H-1, H-4a), 7.22 (4H, m, H-2, H-4), 6.81 (1H, s, H-7), 6.73
(2H, s, H-7, H-10), 6.71 (1H, s, H-10), 6.00 (2H, s, OCH2O), 5.97 (2H, s,
OCH2O), 4.44 (2H, s, H-6), 4.22 (2H, s, H-6), 3.12 (2H, q, J = 7.1 Hz,
NCH2CH3), 2.98 (2H, q, J = 7.1 Hz, NCH2CH3), 0.83 (3H, t, J = 7.1 Hz,
NCH2CH3), 0.77 (3H, t, J = 7.1 Hz, NCH2CH3). 13C NMR (CDCl3) d
162.3 (d, CHO), 162.0 (d, CHO), 154.2 (s, C-3), 154.0 (s, C-3), 147.2
(s, C-9), 146.8 (s, C-8), 136.0 (s, C-10a), 135.5 (s, C-10a), 129.2 (d,
C-1, C-4a), 128.9 (d, C-1, C-4a), 128.2 (d, C-2, C-4), 128.1 (C-2, C-
4), 127.2 (s, C-10b), 127.2 (s, C-10b), 126.9 (s, C-6a), 126.5 (s, C-
6a), 110.2 (d, C-10), 109.5 (d, C-10), 108.1 (d, C-7), 108.0 (d, C-7),
101.1 (t, OCH2O), 100.9 (t, OCH2O), 48.0 (t, C-6), 41.2 (t, NCH2CH3),
41.0 (t, NCH2CH3), 36.0 (t, C-6), 13.7 (q, NCH2CH3), 11.7 (q,
NCH2CH3). IR (neat, cmꢀ1): 3445, 3057, 2975, 2893, 1699, 1503,
1481, 1443, 1398, 1375, 1224, 1100, 1037, 930, 872, 769, 704. EIMS
m/z (%): 299 ([M]+, 6); 283 (54); 254 (5); 224 (3); 210 (100); 181
(26); 167 (5); 152 (31); 139 (6). HREIMS m/z 299.1158 (calcd for
4.1.24. 6,11-Bis(p-bromobenzoyl)-haemanthidine (27)
Following the procedure described above, 15.6 mg
(0.049 mmol) of 2 was reacted with 33 lL (0.245 mmol) of NEt3
and 31.1 mg of p-bromobenzoyl chloride (0.147 mmol) to yield,
after purification, 13 mg (40%) of compound 27 as an amorphous
white solid. ½a 2D0
ꢁ
+25.0 (c 0.22, MeOH). 1H NMR (CDCl3) d 7.98
(2H, d, J = 8.4 Hz, H-20), 7.75 (2H, d, J = 8.4 Hz, H-20), 7.61 (2H, d,
J = 8.6 Hz, H-30), 7.57 (2H, d, J = 8.4 Hz, H-30), 6.91 (1H, s, H-6),
5.18 (1H ,d, J = 4.4 Hz, H-11), for the rest of the signals see Supple-
mentary data. 13C NMR (CDCl3) d 164.9 (s, C@O), 164.6 (s, C@O),
164,5 (s, C@O), 164,5 (s, C@O), 131.7 (d, C-20), 131.6 (d, C-20),
131.5 (d, C-20), 131.2 (d, C-30), 130.5 (d, C-30), 128.7 (s, C-10),
128.5 (s, C-10), 128.5 (s, C-10), 128.2 (s, C-10), 128.2 (s, C-40), 128.1
(s, C-40), 87.7 (d, C-6), 80.3 (d, C-11), 76.9 (d, C-11), for the rest
of the signals see Supplementary data. IR (neat, cmꢀ1): 2926,
1720, 1589, 1482, 1398, 1262, 1173, 1092, 1010, 935, 848, 754.
EIMS m/z (%): 682 (M+, 7); 680 (4); 500 (30); 482 (37); 457 (10);
299 (52); 284 (63); 266 (40); 254 (29); 182 (100). HREIMS m/z
682.9946 (calcd for C31H25NO7Br2 [M]+ 682.9977).
C
17H17NO4 [M]+ 299.1153).
4.1.25. 6,11-Diisobutyrylhaemanthidine (28)
4.1.21. 6,11-Diacetylhaemanthidine (25)
Following the procedure described above, 15 mg (0.047 mmol)
To 13.8 mg (0.044 mmol) of compound 2 dissolved in 1 mL of
pyridine, 0.3 mL (3.18 mmol) of acetic anhydride were added.
The reaction mixture was stirred at room temperature for 3 h, then
the solvent was evaporated and the residue was purified by pre-
parative TLC with DCM/MeOH 19:1 to yield 17 mg (99%) of com-
of 2 were treated with 33 lL of Et3N (0.245 mmol) and 15 lL of iso-
butyryl chloride (0.147 mmol). After purification, 14 mg (65%) of
compound 28 were obtained as an amorphous white solid. ½a D20
ꢁ
+51.2 (c 0.16, MeOH). 1H NMR (CDCl3) d 6.57 (1H, s, H-6), 4.88
(1H, br s, H-11), 2.64 (1H, m, CH(CH3)2), 2.44 (1H, m, CH(CH3)2),
1.25 (6H, d, J = 6.8 Hz, CH(CH3)2), 1.09 (6H, d, J = 6.9 Hz, CH(CH3)2),
for the rest of the signals see Supplementary data. 13C NMR (CDCl3)
d 176.1 (s, C@O), 175.8 (s, C@O), 175.7 (s, C@O), 175.4 (s, C@O),
86.6 (d, C-6), 85.2 (d, C-6), 78.9 (d, C-11), 78.0 (d, C-11), 34.0
(d, CH(CH3)2), 33.8 (d, CH(CH3)2), 33.6 (d, CH(CH3)2), 33.6 (d,
CH(CH3)2), 18.8 (q, CH(CH3)2), 18.7 (q, CH(CH3)2), 18.6 (q,
CH(CH3)2), 18.5 (q, CH(CH3)2), for the rest of the signals see Supple-
mentary data. IR (neat, cmꢀ1): 2974, 2935, 1734, 1647, 1483, 1387,
1335, 1248, 1190, 1150, 1094, 1023, 934, 858, 808, 736. EIMS m/z
(%): 457 (M+, 31); 442 (18); 386 (41); 370 (78); 343 (6); 299 (74);
284 (100); 273 (11); 254 (40); 209 (27). HREIMS m/z 457.2111
(calcd for C25H31NO7 [M]+ 457.2101).
pound 25 as an amorphous white solid. ½a D20
ꢀ.7 (c 1.19, EtOH).
ꢁ
1H NMR (CDCl3) d 6.12 (1H, s, H-6), 4.90 (1H, t, J = 6.6 Hz, H-11),
for the rest of the signals see Supplementary data. 13C NMR (CDCl3)
d 170.1 (s, OCOCH3), 169.9 (s, OCOCH3), 86.3 (d, C-6), 78.5 (d, C-11),
21.2 (q, OCOCH3), 20.9 (q, OCOCH3) for the rest of the signals see
Supplementary data. IR (neat, cmꢀ1): 3055, 2932, 1737, 1483,
1370, 1245, 1089, 1036, 936, 864, 815, 737. EIMS m/z (%): 401
(M+, 32); 386 (20); 359 (19); 342 (47); 327 (16); 299 (36); 284
(100); 268 (37); 254 (27); 224 (49); 209 (66); 181 (18). HREIMS
m/z 401.1461 (calcd for C21H23NO7 [M]+ 401.1475).
4.1.22. General procedure for acylation of 2
To a solution of haemanthidine 2 in 3 mL of dry DCM were
added 5 equiv of Et3N and 3 equiv of the corresponding acyl chlo-
ride. After stirring at rt for 18 h, the solvent was evaporated and
the residue was purified by preparative TLC using DCM/MeOH
92:8 yielding the corresponding esters 26–28.
4.1.26. 11-Oxohaemanthidine (29)
To a solution of 20 mg (0.063 mmol) of compound 2 in 2 mL of
acetone at 0 °C, the Jones reagent was added dropwise, until the
solution turned orange. The reaction mixture was stirred for

J. C. Cedrón et al. / Bioorg. Med. Chem. 20 (2012) 5464–5472
5471
30 min and then isopropanol was added. The solution was filtered
through Florisil and the residue was concentrated and purified by
preparative TLC using DCM/MeOH 9:1 as eluant, to yield 9 mg
using DCM/MeOH 22:3, 12 mg (67%) of compound 32 were ob-
tained as an amorphous white solid. ½a D20
ꢁ
+81.5 (c 0.4, MeOH). 1H
NMR (CDCl3) d 6.99 (1H, s, H-7), 6.82 (4H, d, J = 8.3 Hz, H-1), 6.79
(2H, s, H-10), 6.60 (2H, dd, J = 4.1 Hz, J = 8.3 Hz, H-2), 5.96 (2H, br
s, OCH2O), 5.95 (2H, br s, OCH2O), 5.81 (1H, s, H-6), 5.19 (1H, s,
H-6), 4.46 (2H, d, J = 3.6 Hz, H-3), 3.81 (1H, dd, J = 4.6 Hz,
J = 14.3 Hz, H-12), 3.65 (3H, m, H-4a, H-11), 3.41 (1H, d,
J = 9.7 Hz, H-12), 3.28 (1H, d, J = 13.6 Hz, H-12), 3.03 (2H, m, H-
4a, H-12), 1.90 (4H, m, H-4). 13C NMR (CDCl3) d 147.9 (s, C-9),
147.7 (s, C-9), 147.2 (s, C-8), 147.1 (s, C-8), 138.0 (d, C-2), 137.9
(d, C-2), 131.1 (s, C-10a), 128.2 (d, C-1), 128.1 (d, C-1), 126.1 (s,
C-6a), 108.7 (d, C-7), 107.6 (d, C-7), 105.4 (d, C-10), 105.3 (d, C-
10), 101.0 (t, OCH2O), 86.6 (d, C-6), 85.2 (d, C-6), 79.0 (d, C-11),
64.4 (d, C-3), 64.2 (d, C-3), 59.5 (d, C-4a), 56.8 (t, C-12), 53.0 (d,
C-4a), 52.1 (t, C-12), 47.4 (s, C-10b), 46.8 (s, C-10b), 33.6 (t, C-4),
29.4 (t, C-4). IR (neat, cmꢀ1): 3418, 3058, 2927, 1730, 1673,
1617, 1483, 1386, 1299, 1248, 1118, 1082, 1037, 932, 872, 817,
736, 700. EIMS m/z (%): 285 (M+, 99); 268 (100); 256 (11); 239
(10); 225 (11); 209 (31); 201 (28); 185 (15). HREIMS m/z
285.1009 (calcd for C16H15NO4 [M]+ 285.1001).
(46%) of compound 29 as an amorphous white solid. ½a D20
ꢁ
+51.4 (c
0.7, MeOH). 1H NMR (CDCl3) d 3.87 (3H, m, H-12, H-4a), 3.51 (1H,
d, J = 18.7 Hz, H-12), for the rest of the signals see Supplementary
data. 13C NMR (CDCl3) d 209.1 (s, C-11), 209.0 (s, C-11), 53.6 (t, C-
12), 49.1 (t, C-12), for the rest of the signals see Supplementarydata.
IR (neat, cmꢀ1): 3416, 2924, 1747, 1503, 1482, 1400, 1246, 1118,
1084, 1037, 935, 871, 736, 670. EIMS m/z (%): 315 (M+, 11); 300
(5); 287 (59); 258 (28); 225 (57); 209 (28); 200 (100); 141 (22).
HREIMS m/z 315.1091 (calcd for C17H17NO5 [M]+ 315.1107).
4.1.27. 6-(6-Methoxy-3-oxo-3,6,7,7a-tetrahydro-3aH-indol-3a-
yl)-1,3-benzodioxole-5-carbaldehyde (30)
To 20 mg (0.063 mmol) of 2 in 5 mL of DCM were added 5 mg
(0.2 equiv) of tetrabutylammonium iodide, 7 mg (0.7 equiv) of
TEMPO and 33 mg (3 equiv) of m-chloroperbenzoic acid. The reac-
tion mixture was stirred at room temperature for 24 h. Then, it was
treated with a saturated solution of sodium bicarbonate and the
mixture was extracted with DCM. The organic phase was dried
over MgSO4, filtered, concentrated and purified by preparative
TLC using DCM/MeOH 97:3 to yield 15 mg (76%) of compound 30
4.1.30. 3,11-Diacetyl-11-hydroxyvittatine (33)
To 14 mg (0.049 mmol) of compound 3 in 1 mL of pyridine were
added 0.3 mL (3.18 mmol) of acetic anhydride. The reaction mix-
ture was stirred for 3 h, then the solvent was evaporated and the
residue was purified by preparative TLC with DCM/MeOH 19:1 to
yield 18 mg (100%) of compound 33 as an amorphous white solid.
as an amorphous white solid. ½a D20
ꢁ
ꢀ4.0 (c 1.2, MeOH). 1H NMR
(CDCl3) d 9.68 (1H, s, CHO), 7.29 (1H, s, H-7), 7.26 (1H, s, H-12),
7.08 (1H, s, H-10), 6.31 (1H, d, J = 10.1 Hz, H-2), 6.12 (2H, s,
OCH2O), 5.63 (1H, d, J = 10.1 Hz, H-1), 4.60 (1H, t, J = 3.2 Hz, H-3),
3.90 (1H, m, H-4a), 3.45 (3H, s, OMe), 3.08 (1H, m, H-4), 1.51
(1H, dt, J = 2.5 Hz, J = 10.4 Hz, H-4). 13C NMR (CDCl3) d 193.9 (s,
C-11), 191.3 (d, CHO), 152.4 (s, C-9), 147.7 (s, C-8), 133.9 (C-12),
133.9 (d, C-2), 132.5 (s, C-6a), 127.7 (s, C-10a), 125.8 (d, C-1),
115.9 (d, C-7), 112.9 (d, C-10), 102.6 (t, OCH2O), 74.3 (d, C-3),
69.9 (d, C-4a), 57.2 (s, C-10b), 56.5 (q, OMe), 24.4 (t, C-4). IR (neat,
cmꢀ1): 2924, 1718, 1691, 1605, 1547, 1507, 1360, 1330, 1263,
1198, 1095, 1034, 926, 878, 788, 600. EIMS m/z (%): 313 (M+, 30);
294 (7); 268 (5); 256 (4); 225 (5); 200 (11); 178 (18); 125 (100).
HRMS m/z 313.0963 (calcd for C17H15NO5 [M]+ 313.0950).
½
a 2D0
ꢁ
ꢀ35.0 (c 0.06, MeOH). 1H NMR (CDCl3) d 5.36 (1H, br s, H-3),
4.96 (1H, m, H-11), 1.99 (3H, s, OCOCH3), 1.96 (3H, s, OCOCH3), for
the rest of the signals see Supplementary data. 13C NMR (CDCl3) d
170.2 (s, OCOCH3), 169.8 (s, OCOCH3), 80.0 (d, C-11), 66.1 (d, C-3),
20.9 (q, OCOCH3), 20.9 (q, OCOCH3), for the rest of the signals see
Supplementary data. IR (neat, cmꢀ1): 3048, 2927, 2720, 1650,
1503, 1437, 1372, 1323, 1100, 948, 854, 794, 735. EIMS m/z (%):
371 (M+, 100); 312 (29); 269 (47); 252 (36); 240 (35); 224 (83);
209 (67); 181 (54). HREIMS m/z 371.1357 (calcd for C20H21NO6
[M]+ 371.1369).
4.1.28. 8,9-Nor-6,11-dihydroxyvittatine (31)
4.1.31. 3,11-Bis(methoxyphenylacetyl)-11-hydroxyvittatine (34)
To a solution of 10 mg (0.035 mmol) of compound 3 in 5 mL of
DCM, 29 mg (4 equiv) of 1,3-dicyclohexylcarbodiimide (DCC) and
23 mg (4 equiv) of (R)-(ꢀ)-methoxyphenylacetic acid were added.
The reaction mixture was refluxed for 12 h. Then the solvent was
evaporated. Further purification of the residue by preparative TLC
using DCM/MeOH 19:1 yielded 15 mg (74%) of compound 34 as
an amorphous white solid. 1H NMR (CD3CN) d 7.35 (5H, s, Ph),
7.31 (5H, s, Ph), 5.21 (1H, br s, H-3), 4.83 (1H, m, H-11), 4.73 (1H,
s, CHOMe), 4.72 (1H, s, CHOMe), 4.13 (1H, d, J = 17.7 Hz, H-6), 3.70
(1H, d, J = 17.7 Hz, H-6), for the rest of the signals see Supplementary
data.13C NMR (CD3CN) d 169.7 (s, C@O), 169.3 (s, C@O), 135.5 (s,
Ph), 128,7 (s, Ph), 127.3 (d, Ph), 126.8 (d, Ph), 82.5 (d, CHOMe),
82.0 (d, CHOMe), 80.2 (d, C-11), 66.8 (d, C-3), for the rest of the sig-
nals see Supplementary data. IR (neat, cmꢀ1): 2924, 2849, 1742,
1621, 1574, 1482, 1238, 1171, 1104, 1023, 934, 732, 695. HRMS
m/z 583.2642 (calcd for C34H33NO8 [M]+ 583.2660).
To a solution of 22 mg (0.07 mmol) of compound 2 in 5 mL of dry
DCM at 0 °C, was added dropwise0.4 mL (6 equiv) of a 1 M BBr3 solu-
tion in DCM. After 5 h stirring, the solvent was removed and the res-
idue was purified by preparative TLC using DCM/MeOH 4:1. 13 mg
(62%) of compound 31 were obtained as an amorphous orange solid.
½
a 2D0 +27.9 (c 1.1, EtOH). 1H NMR (MeOD) d 6.98 (1H, m, H-2), 6.92
ꢁ
(1H, s, H-7), 6.91 (1H, s, H-10), 6.86 (1H, s, H-10), 6.82 (1H, s, H-7),
6.69 (1H, d, J = 8.5 Hz, H-1), 6.66 (1H, d, J = 8.5 Hz, H-1), 6.27 (1H,
s, H-6), 5.67 (1H, s, H-6), 4.56 (1H, br s, H-3), 3.99 (1H, m, H-12),
3.96 (1H, m, H-4a), 3.79 (1H, br s, H-11), 3.76 (1H, br s, H-11), 3.49
(1H, d, J = 5.8 Hz, H-12), 2.10 (2H, t, J = 5.1 Hz, H-4). 13C NMR (MeOD)
d 147.1 (s, C-9), 146.4 (s, C-9), 145.9 (s, C-8), 145.7 (s, C-8), 139.1 (d,
C-2), 139.0 (d, C-2), 126.0 (d, C-1), 125.8 (d, C-1), 122.0 (s, C-10a),
120.0 (s, C-6a), 115.0 (d, C-7), 113.7 (d, C-7), 111.9 (d, C-10), 111.6
(d, C-10), 86.3 (d, C-6), 85.7 (d, C-6), 77.1 (d, C-11), 76.3 (d, C-11),
63.4 (d, C-3), 60.9 (d, C-4a), 56.2 (t, C-12), 54.2 (d, C-4a), 51.8 (t, C-
12), 47.0 (s, C-10b), 32.0 (t, C-4), 30.4 (t, C-4). IR (neat, cmꢀ1):
3443, 2925, 1643, 1247, 668. EIMS m/z (%): 291 (M+, 4); 273 (48);
255 (100); 228 (17); 213 (10); 199 (31); 181 (28). HREIMS m/z
291.1084 (calcd for C15H17NO5 [M]+ 291.1103).
4.1.32. General procedure for acylation of compound 3
To a solution of 11-hydroxyvittatine (3) in 3 mL of dry DCM
were added 5 equiv of Et3N and 3 equiv of the corresponding acyl
chloride. After stirring at rt for 18 h, the solvent was evaporated
and the residue was purified by preparative TLC using DCM/MeOH
92:8 as eluent, to afford the corresponding esters 35–37.
4.1.29. Apohaemanthidine (32)
20 mg (0.063 mmol) of compound 2 in 5 mL of a 6 M HCl solu-
tion were heated at 100 °C for 4 h. Then a 20% NH4OH solution was
added until basic pH and the mixture was extracted with DCM. The
organic phase was dried over anhydrous magnesium sulphate
filtered and concentrated. After purification by preparative TLC,
4.1.33. 3,11-Dinicotyl-11-hydroxyvittatine (35)
Following the procedure described above, 16 mg (0.056 mmol)
of compound 3 were treated with 39 lL (0.28 mmol) of Et3N and

5472
J. C. Cedrón et al. / Bioorg. Med. Chem. 20 (2012) 5464–5472
30 mg (0.17 mmol) of nicotinoyl chloride. After purification, 13 mg
glucose-enriched RPMI 1640 medium, supplemented with 10% hu-
man serum at 37 °C. After 24 h of incubation at 37 °C, the medium
was replaced by fresh medium supplemented with the compound
to be evaluated in DMSO at three different concentrations (0.1, 1
(47%) of compound 35 were obtained as an amorphous white solid.
½
a 2D0
ꢁ
ꢀ50.0 (c 0.05, MeOH). 1H NMR (CDCl3) d 9.14 (2H, s, CCHN),
8.80 (1H, dd, J = 1.5 Hz, J = 4.8 Hz, NCHCHCHC), 8.73 (1H, dd,
J = 1.5 Hz, J = 4.8 Hz, NCHCHCHC), 8.23 (1H, d, J = 8.2 Hz,
NCHCHCHC), 8.19 (1H, d, J = 8.2 Hz, NCHCHCHC), 7.42 (1H, dd,
J = 5.0 Hz, J = 7.9 Hz, NCHCHCHC), 7.34 (1H, dd, J = 5.0 Hz, J = 7.9
Hz, NCHCHCHC), 5.66 (1H, br s, H-3), 5.26 (1H, dd, J = 3.5 Hz,
J = 6.5 Hz, H-11), 4.43 (1H, d, J = 17.0 Hz, H-6), 3.71 (1H, d,
J = 17.0 Hz, H-6), for the rest of the signals see Supplementary data.
13C NMR (CDCl3) d 164.3 (s, C@O), 163.9 (s, C@O), 153.5 (d, CCHN),
153.2 (d, CCHN), 150.7 (d, NCHCHCHC), 150.4 (d, NCHCHCHC),
136.9 (d, NCHCHCHC), 136.6 (d, NCHCHCHC), 125.8 (s, CCHN),
125.5 (s, CCHN), 123.2 (d, NCHCHCHC), 123.0 (d, NCHCHCHC),
80.8 (d, C-11), 67.1 (d, C-3), 60.7 (t, C-6), for the rest of the signals
see Supplementary data. IR (neat, cmꢀ1): 3050, 2925, 1719, 1591,
1482, 1421, 1329, 1278, 1239, 1114, 1023, 935, 852, 738, 701. EIMS
m/z (%): 497 (M+, 51); 374 (32); 268 (47); 252 (32); 238 (16); 224
(75); 209 (51); 181 (27). HREIMS m/z 497.1594 (calcd for
and 10 lg/mL) and incubation was continued for further 48 h. On
the third day of the test, a blood smear was taken from each well
and parasitemia was calculated for each concentration of sample
compared to the control. IC50 values were determined graphically
by plotting concentrations vs. percent inhibition. Chloroquine
(0.04 lM) was used as a positive control. All tests were performed
in triplicate.
Acknowledgments
This work has been partly funded by the Spanish MICINN (SAF
2009-13296-C02-01) and ICIC (Instituto Canario de Investigación
del Cáncer). J.C.C. thanks Gobierno Autónomo de Canarias for a pre-
doctoral fellowship.
C
28H23N3O6 [M]+ 497.1587).
Supplementary data
4.1.34. 3,11-Bis(p-bromobenzoyl)-11-hydroxyvittatine (36)
Following the procedure described above, 16 mg (0.056 mmol)
of compound 3 were treated with 39 lL (0.28 mmol) of Et3N and
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmc.2012.07.036.
37 mg (0.17 mmol) of p-bromobenzoyl chloride to yield, after puri-
fication, 20 mg (56%) of compound 36 as an amorphous white so-
References and notes
lid. ½a 2D0
ꢁ
+10.5 (c 0.19, MeOH). 1H NMR (CDCl3) d 7.82 (2H, d,
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J = 8.4 Hz, H-20), 7.78 (2H, d, J = 8.4 Hz, H-20), 7.59 (2H, d,
J = 8.4 Hz, H-30), 7.51 (2H, d, J = 8.4 Hz, H-30), 5.59 (1H, br s, H-3),
5.21 (1H, dd, J = 3.6 Hz, J = 6.3 Hz, H-11). 13C NMR (CDCl3) d 165.0
(s, C@O), 164.5 (s, C@O), 146.7 (s, C-9), 146.6 (s, C-8), 133.4 (s, C-
10a), 131.7 (d, C-20), 131.4 (d, C-20), 130.9 (d, C-30), 130.6 (d, C-
30), 128.8 (s, C-10), 128.5 (s, C-10), 128.2 (s, C-40), 127.9 (s, C-40),
80.7 (d, C-11), 66.9 (d, C-3). IR (neat, cmꢀ1): 3044, 2926, 1715,
1590, 1482, 1398, 1327, 1100, 1014, 936, 849, 737, 681. EIMS m/
z (%): 652 (M+, 17); 452 (20); 408 (3); 269 (70); 251 (39); 238
(18); 224 (82); 182 (100). HREIMS m/z 652.9899 (calcd for
C
30H23NO6Br2 [M]+ 652.9872).
4.1.35. 3,11-Diisobutyryl-11-hydrovittatine (37)
Following the procedure described above, 16 mg (0.056 mmol)
of compound 3 were treated with 39
lL (0.28 mmol) of Et3N and
18 (0.17 mmol) of isobutyryl chloride. After purification,
lL
15 mg (63%) of compound 37 were obtained as a white solid.
½
a 2D0
ꢁ
ꢀ118.9 (c 0.09, MeOH). 1H NMR (CDCl3) d 4.93 (1H, dd,
J = 3.3 Hz, J = 6.5 Hz, H-11), 4.35 (1H, d, J = 16.9 Hz, H-6), 3.72
(1H, d, J = 16.9 Hz, H-6), 2.44 (2H, dq, J = 2.4 Hz, J = 4.4 Hz,
CH(CH3)2), 1.09 (12H, d, J = 6.9 Hz, CH(CH3)2). 13C NMR (CDCl3) d
176.3 (s, C@O), 175.7 (s, C@O), 79.7 (d, C-11), 65.7 (d, C-3), 33.7
(d, CH(CH3)2), 33.6 (d, CH(CH3)2), 18.7 (q, CH(CH3)2), 18.7 (q,
CH(CH3)2), 18.6 (q, CH(CH3)2), 18.6 (q, CH(CH3)2). IR (neat, cmꢀ1):
2974, 2934, 1729, 1621, 1503, 1483, 1387, 1239, 1192, 1154,
1064, 1038, 992, 938, 852, 736. EIMS m/z (%): 427 (M+, 62); 398
(6); 340 (27); 269 (100); 252 (24); 238 (14); 224 (49); 181 (37).
HREIMS m/z 427.2011 (calcd for C24H29NO6 [M]+ 427.1995).
19. Cedrón, J. C.; Del Arco-Aguilar, M.; Estévez-Braun, A.; Ravelo, A. G. Chemistry
and biology of Pancratium alkaloids. In The Alkaloids; Cordell, G. A., Ed.;
Academic Press, 2010; pp 1–37.
20. Cabezas, F.; Ramírez, A.; Viladomat, F.; Codina, C.; Bastida, J. Chem. Pharm. Bull.
2003, 51, 315.
21. Yeung, Y.; Gao, X.; Corey, E. J. Am. Chem. Soc. 2006, 128, 9644.
22. Lee, S.; Venkatesham, U.; Rao, C.; Lam, S.; Lin, J. Bioorg. Med. Chem. 2007, 15,
1034.
23. Rychnovsky, S.; Vaidyanathan, R. J. Org. Chem. 1999, 64, 310.
24. Trager, W.; Jensen, J. Science 1976, 193, 673.
4.2. Antiplasmodial assay
F-32 Tanzania (chloroquine sensitive) strains of Plasmodium
falciparum were cultured according to Trager and Jensen24 on