Synthesis and antiplasmodial activity of lycorine derivatives

Article abstract of DOI:10.1016/j.bmc.2010.05.023

Twenty seven lycorine derivatives were prepared and evaluated for their in vitro antimalarial activity against chloroquine-sensitive strains of Plasmodium falciparum. The best antiplasmodial activities were achieved with lycorine derivatives that present free hydroxyl groups at C-1 and C-2 or esterified as acetates or isobutyrates. The double bond C-2-C-3 is also important for the activity. Concerning to the antiplasmodial activity of the secolycorines, the higher values were obtained with the replacement of the methylenedioxy moiety by hydroxyl or acetate groups and with methyl substituent attached to the nitrogen atom.

Full text of DOI:10.1016/j.bmc.2010.05.023

Bioorganic & Medicinal Chemistry 18 (2010) 4694–4701
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis and antiplasmodial activity of lycorine derivatives
a,b,
Juan C. Cedrón a,b, David Gutiérrez c, Ninoska Flores c, Ángel G. Ravelo a,b, , Ana Estévez-Braun
*
*
a Instituto Universitario de Bio-Orgánica ‘Antonio González’, Av. Astrofísico Francisco Sánchez 2, 38206 La Laguna—Tenerife, Spain
b Instituto Canario de Investigación del Cáncer (ICIC), http://www.icic.es
c 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:
Twenty seven lycorine derivatives were prepared and evaluated for their in vitro antimalarial activity
against chloroquine-sensitive strains of Plasmodium falciparum. The best antiplasmodial activities were
achieved with lycorine derivatives that present free hydroxyl groups at C-1 and C-2 or esterified as ace-
tates or isobutyrates. The double bond C-2–C-3 is also important for the activity. Concerning to the anti-
plasmodial activity of the secolycorines, the higher values were obtained with the replacement of the
methylenedioxy moiety by hydroxyl or acetate groups and with methyl substituent attached to the nitro-
gen atom.
Received 15 March 2010
Revised 4 May 2010
Accepted 6 May 2010
Available online 11 May 2010
Keywords:
Alkaloids
Amaryllidaceae
Lycorine
Ó 2010 Elsevier Ltd. All rights reserved.
Plasmodium falciparum
1. Introduction
alkaloids’, isolated from plants of all genera of this family. Since the
isolation of lycorine (1) from Narcissus pseudonarcissus in 1877,
Half of the world’s population is at risk of malaria, and an esti-
mated 243 million cases led to nearly 863,000 deaths in 2008.1 The
World Health organization (WHO) estimates that 3 billion people
live in areas where malaria transmission occurs. Indeed, it is ende-
mic in 109 countries and territories in tropical and subtropical re-
gions, particularly in sub-Saharan Africa.1 Plasmodium falciparum is
responsible for the most severe form of the disease, and resistant
strains have emerged to many currently used antimalarial agents.2
Historically, natural products have played a major role in the
treatment of this infectious disease.3 For centuries, the indigenous
people from South America have used the bark from the ‘fever
tree’, Cinchona succirubra, for the treatment of malaria.3 The Chi-
nese medicinal plant, Artemisia annua, has likewise been used as
an antimalarial herbal remedy for hundreds of years.3 Chemical
investigations of C. succirubra and A. annua, identified the major ac-
tive metabolites to be quinine and artemisinin, respectively.3c This
research has subsequently led to the development of numerous
antimalarial drugs based on these two important plant natural
products.3c Unfortunately, resistance of the malarial parasite to
current small molecule therapies and subsequent lack of efficacy
makes necessary the development of new antimalarial agents that
are structurally different from the existing drugs.4
over 300 alkaloids have been isolated from plants of this family,5
including the recently isolated from Pancratium canariense.6 Ama-
ryllidaceae alkaloids exhibit a wide range of biological activities
including cytotoxic,7 antiviral,8 antitumour,9 anticholinergic10
and anti-inflammatory.11 For example, galanthamine is used in
the treatment of Alzheimer’s disease.12 Some of these alkaloids
are of particular interest because of their potential antiprotozoal
activity.13 Thus, lycorine (1), augustine and crinamine were found
to be the principal antimalarial constituents in Crinum amabile
bulbs.14 Several lycorine type-alkaloids were examined for their
inhibitory activity against Trypanosoma brucei and P. falciparum.
Among them, 2-O-acetyllycorine showed the most potent activity
against parasitic T. brucei, and 1-O-(3R)-hydroxybutanoyllycorine,
1,2-di-O-butanoyllycorine, and 1-O-propanoyllycorine showed sig-
nificant activity against P. falciparum.15 The antiplasmodial activity
of other Amaryllidaceae type-alkaloids have been summarized in a
recent review on alkaloids with antiprotozoal activity.12 Structure–
antiplasmodial activity relationships have not been studied in
Amaryllidaceae alkaloids. Some results suggest that the methyl-
enedioxy group and a tertiary non-methylated nitrogen contribute
to a higher activity in these alkaloids.16 Additional investigation is
required to specify the necessary structural requirements for anti-
parasitic activity, and, in particular, the possible mode of action.
With these antecedents, in the present study we report the
preparation of 27 lycorine derivatives, their inhibitory activity
against P. falciparum and some preliminary conclusions about
structure–activity relationships.
Plants belonging to the Amaryllidaceae family are known by
producing an exclusive group of alkaloids, named ‘Amaryllidaceae
* Corresponding authors. Tel.: +34 922 318576; fax: +34 922 318571.
E-mail addresses: agravelo@ull.es (Á.G. Ravelo), aestebra@ull.es (A. Estévez-
Braun).
0968-0896/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2010.05.023

J. C. Cedrón et al. / Bioorg. Med. Chem. 18 (2010) 4694–4701
4695
2. Results and discussion
2.1. Chemistry
14–17 were formed by Hofmann elimination.21 In order to gener-
ate diversity on the structure of the secolycorines formed (14–
17), some modifications were achieved. First, the methylenedioxy
group was removed with BBr3 and the corresponding compounds
18 and 19 were formed. Secolycorines 14, 15, and 16 were con-
verted into the corresponding lactams 20, 21, and 22 when treated
with 3 equiv of iodosylbenzene. Hydrogenation of the double bond
of 14 and 16 yielded derivatives 23 and 24, respectively. The cate-
chol group on the structure of 18 and 19 was also modified. Thus,
acetylation, acylation with undecyl chloride and methoxylation
employing trimethylsilyldiazomethane were performed on 23,
yielding the corresponding derivatives 25, 26, and 27, respectively.
Acetylation of 19 was also performed yielding compound 28.
Lycorine (1) was obtained as the main alkaloid from the bulbs of
P. canariense.6 Due to its low solubility in most solvents, many
derivatives were obtained from lycorine diacetate 2, as it is shown
in Scheme 1.
Compounds 2–4 were obtained by acylation of lycorine with
anhydrides of different sizes, in the presence of pyridine. Treatment
of 1 with the Jones reagent yielded the
a,b-unsaturated ketone 5.
Compound 6 was obtained by hydrogenation of the double bond
of 2 in the presence of 10% Pd/C.17 Reaction of 2 with BBr3 followed
by acetylation led to compound 7 which does not have the methyl-
enedioxy group and the acetyl group at C-11. Derivatives 8–10 pres-
ent the ring B as a lactam and they were obtained in low yield by
oxidation of 2 with potassium permanganate.18 Compound 9
showed also the ring C aromatized, while 10 possess a cis-diol in-
stead of the double bond. When iodosylbenzene was used as oxi-
dizer,19 only the lactam 9 was formed quantitatively. Compound 2
was heated with diluted HCl to afford selectively the monoacetylat-
ed derivative 11.20 Two compounds, the deacetylated 12 and the
monoacetylated 13, were obtained when 8 was treated with HCl un-
der the same conditions followed for 2.
2.2. Biological assay and SAR
Results of the antiplasmodial evaluation are summarized in
Table 1. Lycorine (1) resulted be the most active alkaloid, with an
IC50 value of 0.13
lM. Compounds 2, 4, 11, 25, and 28 showed also
important antiplasmodial activity, with IC50 values less than 1
l
M.
From the obtained results we can establish some structure–
activity relationships. The presence of the hydroxyl groups at C-1
and C-2 in the lycorine skeleton seems important for the activity.
For example, acylation of the hydroxyl groups of lycorine 1
produced a decrease in the activity (i.e., 1 vs 2, 1 vs 3, 1 vs 4).
When 2 was reacted with different alkyl halides followed by
treatment with t-BuOK/t-BuOH the corresponding secolycorines
Scheme 1. Reagents and conditions: (a) Ac2O, py; (b) R2O, py; (c) Jones reagent, acetone; (d) H2, 10% Pd/C, THF; (e) 10% HCl, 50 °C, 30 min; (f) (1) BBr3, DCM, 0 °C; (2) Ac2O, py;
(g) KMnO4, acetone, 1 h; (h) 10% HCl, 50 °C, 30 min; (i) (1) RX, CH3CN, 24 h; (2) t-BuOK/t-BuOH, reflux, 4 h; (j) BBr3, DCM, 0 °C; (k) PhIO, NBu4I, CH3CN/H2O 9:1; (l) H2, 10% Pd/
C, THF; (m) Ac2O, py; (n) C11H23COCl, NEt3, DCM; (o) Me3SiCHN2, DCM/MeOH 1:1.

4696
J. C. Cedrón et al. / Bioorg. Med. Chem. 18 (2010) 4694–4701
Table 1
Reactions were monitored by TLC (on silica gel POLYGRAM SIL G/
UV
foils). IR spectra were obtained using a Bruker IFS28/55
In vitro activity against Plasmodium falciparum F32
254
spectrophotometer. Optical rotations were measured with a Per-
kin–Elmer 241 automatic polarimeter. 1H and 13C NMR spectra
were recorded in CDCl3 or MeOD at 300 and 75 MHz respectively
using a Bruker AMX300. 2D NMR experiments were conducted
on a Bruker AVANCE 400 NMR spectrometer. MS and HRMS were
obtained on a VG Autospec spectrometer. Analtech Silica Gel GF
preparative layer with UV254 was used for preparative-TLC purifi-
cation. Silica gel (0.2–0.63 mm) was employed for column chroma-
tography. Silica gel 60 (Merck) was used on a Harrison Research
7924T Chromatotron.
Compound
IC50
(
l
M)
Compound
IC50 (lM)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
0.13
0.26
2.7
15
16
17
18
19
20
21
22
23
24
25
26
27
28
86.0
9.7
7.4
0.6
1.1
14.7
34.8
8.4
>100
9.2
>100
0.9
No tested
>100
>100
>100
>100
>100
>100
7.4
0.9
Lycorine 1 was isolated from the bulbs of P. canariense as de-
scribed in Ref. 6.
47.0
12.4
0.8
11.3
Chloroquine
0.04
3.2. General procedure for acylation of 1
Lycorine 1 (20–30 mg) was dissolved in 1 mL of pyridine and an
excess of the corresponding anhydride was added. After stirring at
rt for 16 h the solvent was removed under reduced pressure and
the residue was purified by preparative-TLC using DCM/MeOH
9:1, to yield the corresponding esters 2–4.
The oxidation of the hydroxyl group at C-2 also led to a less active
compound (5). Comparison of the activity of compounds 2 and 6
indicated that the presence of the double bond C-3–C-4 plays an
important role for the activity. In addition, oxidation of the carbon
C-6 to the corresponding lactam led to inactive compounds (i.e., 2
vs 8, 1 vs 12, 11 vs 13). Compound 9 having the D ring aromatized
3.2.1. 1,2-Diacetyllycorine (2)
and a lactam moiety presented an IC50 = 9.2 lM. With respect to
Following the procedure described above, 30 mg (0.105 mmol) of
1 was treated with 0.3 mL (3.18 mmol) of acetic anhydride. After
purification, 39 mg of 2 (100%) were obtained as an amorphous
white solid. 1H NMR (CDCl3) d: 6.73 (1H, s, H-10), 6.56 (1H, s, H-7),
5.89 (2H, br s, OCH2O), 5.71 (1H, s, H-1), 5.51 (1H, s, H-3), 5.23
(1H, s, H-2), 4.14 (1H, d, J = 14.1 Hz, H-6), 3.51 (1H, d, J = 14.1 Hz,
H-6), 3.35 (1H, dd, J = 4.1 Hz, J = 8.4 Hz, H-12), 2.86 (1H, d,
J = 10.1 Hz, H-10b), 2.75 (1H, d, J = 10.2 Hz, H-4a), 2.62 (2H, br s, H-
11), 2.39 (1H, dd, J = 8.6 Hz, J = 17.4 Hz, H-12), 2.05 (3H, s, OCOCH3),
1.93 (3H, s, OCOCH3) ppm. 13C NMR (CDCl3) d: 169.7 (s, OCOCH3),
169.5 (s, OCOCH3), 146.1 (s, C-8), 146.0 (s, C-9), 145.8 (s, C-4),
129.1 (s, C-6a), 126.3 (s, C-10a), 113.5 (d, C-3), 107.0 (d, C-7),
104.8 (d, C-10), 100.7 (t, OCH2O), 70.6 (d, C-2), 68.9 (d, C-1), 60.9
(d, C-4a), 56.6 (t, C-6), 53.3 (t, C-12), 40.2 (d, C-10b), 28.4 (t, C-11),
20.9 (q, OCOCH3), 20.7 (q, OCOCH3). EIMS m/z (%): 371 ([M]+, 17);
311 (16); 268 (13); 252 (100); 238 (4); 226 (31); 222 (9); 192 (4).
HREIMSm/z 371.1383(calcd for C20H21NO6 [M]+ 371.1369). IR (neat)
the secolycorine series (14–28), the most potent compounds were
compounds 16, 17, 18, 24, 25, and 28. The role of the alkyl group
attached to the nitrogen is not too clear. When we compared the
antiplasmodial activity of compounds 14–17, we obtain similar
values of activity except for compound 15 with a N-ethyl group
which was inactive. In the case of compound 18 (R = Me) and 19
(R = C4H9) which present a catechol moiety, 19 was inactive while
18 showed good activity. Compound 25 (R = Me) and 28 (R = C4H9)
with two acetates showed the same good activity. As it happened
with the lycorine series, the oxidation at C-6 yielded inactive com-
pounds (20–22). When compound 14 (R = Me) was hydrogenated
the inactive derivative 23 was obtained, while in the case of 16
(R = Bu) the corresponding hydrogenated derivative (24) showed
similar activity. We also analyzed the replacement of the methyl-
enedioxy moiety at the aromatic ring A by other groups. Thus,
the best activity was achieved with the hydroxyl groups (i.e., 18
vs 14), the presence of two acetyl groups or two methoxy groups
led to similar activity (i.e., 25 vs 14, 27 vs 14), while the replace-
ment by two lauroyl groups produced a drastic loss of activity
(i.e., 18 vs 26).
m
max 2925, 1734, 1645, 1485, 1370, 1316, 1234, 1132, 1035, 965, 900,
736 cmꢀ1. ½a 2D0
ꢁ
= +3.9 (c 0.1, MeOH).
3.2.2. 1,2-Dipropionyllycorine (3)
In conclusion, we have prepared several lycorines and secolyc-
orine derivatives. The best antiplasmodial activities were achieved
with lycorine derivatives that present free hydroxyl groups at C-1
and C-2 or esterified as acetates or isobutyrates. The double bond
C-2–C-3 is also important for the activity. Concerning to the anti-
plasmodial activity of the secolycorines, the higher values were ob-
tained with the replacement of the methylenedioxy moiety by
hydroxyl or acetate groups and with methyl substituent attached
to the nitrogen atom.
Following the procedure described above, 20 mg (0.7 mmol) of
1 was reacted with 0.5 mL (3.9 mmol) of propionic anhydride to
yield after purification, 17.8 mg of 3 (65%) as an amorphous white
solid. 1H NMR (CDCl3) d: 6.73 (1H, s, H-10), 6.56 (1H, s, H-7), 5.90
(2H, br s, OCH2O), 5.73 (1H, s, H-1), 5.52 (1H, s, H-3), 5.24 (1H, s,
H-2), 4.15 (1H, d, J = 14.1 Hz, H-6), 3.52 (1H, d, J = 14.1 Hz, H-6),
3.36 (1H, ddd, J = 4.7 Hz, J = 9.0 Hz, J = 9.0 Hz, H-12), 2.88 (1H, d,
J = 10.2 Hz, H-10b), 2.78 (1H, J = 10.4 Hz, H-4a), 2.63 (2H, br s, H-
11), 2.41 (1H, m, H-12), 2.33 (2H, q, J = 7.5 Hz, CH2CH3), 2.19 (2H,
q, J = 7.5 Hz, CH2CH3), 1.14 (3H, t, J = 7.5 Hz, CH2CH3), 1.00 (3H, t,
J = 7.5 Hz, CH2CH3). 13C NMR (CDCl3) d: 173.2 (s, C@O), 172.9 (s,
C@O), 146.1 (s, C-8), 146.0 (s, C-9), 145.6 (s, C-4), 129.0 (s, C-6a),
126.4 (s, C-10a), 113.7 (d, C-3), 107.0 (d, C-7), 104.8 (d, C-10),
100.7 (t, OCH2O), 70.5 (d, C-2), 68.8 (d, C-1), 61.0 (d, C-4a), 56.6
(t, C-6), 53.4 (t, C-12), 40.3 (d, C-10b), 28.4 (t, C-11), 27.3
(t, CH2CH3), 27.2 (t, CH2CH3), 8.7 (q, CH2CH3), 8.7 (q, CH2CH3). EIMS
m/z (%): 399 (M+, 7); 325 (13); 268 (11); 252 (100); 226 (19); 194
(5). HREIMS m/z 399.1704 (calcd for C22H25NO6 [M]+ 399.1682). IR
Our results represent a starting point for the preparation of a
new series of lycorine and secolycorine derivatives with the aim
of improving the antiplasmodial activity.
3. Experimental
3.1. General
All solvents and reagents were purified by standard techniques
reported in Perrin, D. D.; Amarego, W. L. F. Purification of Labora-
tory Chemicals, third edition, Pergamon Press, Oxford, 1988 or
used as supplied from commercial sources as appropriate.
(neat) mmax 2980, 2939, 1740, 1621, 1485, 1349, 1318, 1265, 1236,
1176, 1079, 1037, 936, 855, 807, 736 cmꢀ1. ½a D20
ꢁ
= +111.2 (c 0.16,
MeOH).

J. C. Cedrón et al. / Bioorg. Med. Chem. 18 (2010) 4694–4701
4697
3.2.3. 1,2-Bis(2-methylbutyryl)lycorine (4)
92); 314 (27); 254 (100); 226 (5); 212 (6); 187 (4). HREIMS m/z
373.1511 (calcd for C20H23NO6 [M]+ 373.1525). IR (neat) mmax
2923, 1738, 1649, 1485, 1372, 1244, 1118, 1035, 934, 855, 735,
Following the procedure described above, 20 mg (0.7 mmol) of
1 was treated with 0.5 mL (2.51 mmol) of (+)-(R)-2-metylbutyric
anhydride. After purification, 7.1 mg of 4 (23%) was obtained as
an amorphous white solid. 1H NMR (CDCl3) d 6.73 (1H, s, H-10),
6.57 (1H, s, H-7), 5.90 (2H, br s, OCH2O), 5.72 (1H, s, H-1), 5.52
(1H, s, H-3), 5.23 (1H, s, H-2), 4.15 (1H, d, J = 14.1 Hz, H-6), 3.53
(1H, d, J = 13.9 Hz, H-6), 3.38 (1H, br s, H-12), 2.89 (1H, d,
J = 10.3 Hz, H-10b), 2.81 (1H, br s, H-4a), 2.65 (2H, br s, H-11),
2.39 (2H, m, H-12, CHMeCH2CH3), 2.23 (1H, m, CHMeCH2CH3),
1.69 (2H, m, CHMeCH2CH3), 1.56 (2H, m, CHMeCH2CH3), 1.14
(3H, d, J = 6.9 Hz, CHMeCH2CH3), 0.96 (3H, d, J = 6.9 Hz,
CHMeCH2CH3), 0.92 (3H, t, J = 7.4 Hz, CHMeCH2CH3), 0.75 (3H, t,
J = 7.4 Hz, CHMeCH2CH3). 13C NMR (CDCl3) d 175.2 (s, C@O),
175.1 (s, C@O), 146.1 (s, C-8), 145.9 (s, C-9), 145.5 (s, C-4), 129.1
(s, C-6a), 126.4 (s, C-10a), 113.7 (d, C-3), 107.0 (d, C-7), 105.0 (d,
C-10), 100.6 (t, OCH2O), 70.4 (d, C-2), 68.6 (d, C-1), 61.2 (d, C-4a),
56.6 (t, C-6), 53.4 (t, C-12), 40.7 (d, CHMeCH2CH3), 40.7 (d,
CHMeCH2CH3), 28.4 (t, C-11), 26.5 (t, CHMeCH2CH3), 26.3 (t,
CHMeCH2CH3), 16.3 (q, CHMeCH2CH3), 16.2 (q, CHMeCH2CH3),
11.3 (q, CHMeCH2CH3), 11.1 (q, CHMeCH2CH3). EIMS m/z (%): 455
(M+, 5); 353 (9); 268 (10); 252 (100); 226 (9); 194 (3). HREIMS
605 cmꢀ1. ½a 2D0
= ꢀ66.9 (c 0.16, MeOH).
ꢁ
3.2.6. 8,9-Nor-2,8,9-triacetyllycorine (7)
A solution of 20 mg (0.054 mmol) of 2 in 2 mL of DCM at 0 °C
was treated with 0.11 mL (2 equiv) of a solution 2 M BBr3 in
DCM. The reaction mixture was stirred for 4 h until disappearance
of the starting material. Then it was treated with 2 mL of MeOH
and the solvent removed. The residue was dissolved in 1 mL of pyr-
idine and reacted with 0.3 mL (3.18 mmol) of acetic anhydride for
24 h. After evaporation of the solvent and purification by prepara-
tive-TLC using DCM/MeOH (19:1), 7.6 mg of 7 (35%) were obtained
as an pale yellow amorphous solid. 1H NMR (CDCl3) d: 7.04 (1H, s,
H-10), 6.96 (1H, s, H-7), 6.02 (1H, d, J = 4.7 Hz, H-3), 5.50 (1H, s, H-
2), 4.70 (1H, s, H-1), 4.19 (1H, br d, J = 14.0 Hz, H-6), 3.66 (2H, m, H-
6, H-12), 3.02 (2H, br s, H-4a, H-10b), 2.66 (3H, br s, H-11, H-12),
2.22 (6H, s, OCOCH3), 2.03 (3H, s, OCOCH3). 13C NMR (CDCl3) d:
171.7 (s, OCOCH3), 168.1 (s, OCOCH3), 168.1 (s, OCOCH3), 143.7
(s, C-8), 141.9 (s, C-9), 140.5 (s, C-4), 131.8 (s, C-6a), 122.0 (s, C-
10a), 119.4 (d, C-3), 112.2 (s, C-7), 108.8 (d, C-10), 69.8 (d, C-2),
67.3 (d, C-1), 60.9 (d, C-4a), 56.3 (t, C-6), 53.5 (t, C-12), 43.4 (d,
C-10b), 29.4 (t, C-11), 20.7 (q, OCOCH3), 20.4 (q, OCOCH3), 20.4
(q, OCOCH3). EIMS m/z (%): 401 (M+, 5); 359 (2); 339 (8); 323
(10); 297 (11); 282 (22); 254 (27); 238 (100); 210 (15). HREIMS
m/z 401.1461 (calcd for C21H23NO7 [M]+ 401.1475). IR (neat) mmax
3398, 2922, 2852, 1737, 1619, 1560, 1460, 1370, 1238, 1117,
m/z 455.2293 (calcd for C26H33NO6 [M]+ 455.2308). ½a D20
ꢁ
= +11.9
(c 0.32, MeOH). IR (neat) mmax 2968, 2928, 1736, 1650, 1544,
1462, 1368, 1263, 1178, 1139, 1036, 738 cmꢀ1
.
3.2.4. 2-Oxolycorine (5)
To a solution of 50 mg (0.17 mmol) of 1 in acetone (2 mL) at
0 °C, was added the Jones reagent dropwise, until the solution
turned orange. The reaction was stirred for 30 min and then was
filtered through Florisil. The residue was concentrated and purified
by preparative-TLC using DCM/MeOH (9:1) to yield 5 mg of 5 (11%)
as an amorphous yellow solid. 1H NMR (CDCl3) d: 6.77 (1H, s, H-
10), 6.59 (1H, s, H-7), 5.96 (2H, br s, OCH2O), 5.93 (1H, d,
J = 1.2 Hz, H-3), 4.55 (1H, d, J = 3 Hz, H-1), 4.16 (1H, d, J = 14.1 Hz,
H-6), 3.60 (1H, d, J = 14.4 Hz; H-6), 3.45 (1H, m, H-12), 3.24 (1H,
d, J = 9.6 Hz, H-10b), 3.12 (1H, d, J = 9.8 Hz, H-4a), 2.85 (2H, m,
H-11), 2.52 (1H, dd, J = 8.6 Hz, J = 17.2 Hz, H-12). 13C NMR (CDCl3)
1034, 918, 883, 664 cmꢀ1. ½a D20
= ꢀ34.4 (c 0.18, MeOH).
ꢁ
3.3. Oxidation of 2 with potassium permanganate to obtain
derivatives 8, 9, and 10
100 mg (0.27 mmol) of 2 dissolved in 3 mL of acetone were
treated with a solution of 0.25 g of KMnO4 in 1 mL of water. The
reaction mixture was stirred for 4 h. Then H2O was added and
the aqueous phase was extracted several times with DCM. The or-
ganic phases were collected and dried over anhydrous MgSO4, fil-
tered and concentrated. The resulting residue was purified using
DCM/MeOH (9:1) to yield 10.1 mg of 8 (10%), 6.2 mg of 9 (8%)
and 10 mg of 10 (9%) as white amorphous solids.
d: 197.1 (s, C-2), 147.8 (s, C-8), 147.7 (s, C-9), 146.4 (s, C-4), 128.9
(s, C-6a), 125.6 (s, C-10a), 119.4 (d, C-3), 107.3 (d, C-7), 104.7 (d, C-
10), 100.8 (t, OCH2O), 70.0 (d, C-1), 61.5 (d, C-4a), 56.1 (t, C-6), 53.1
(t, C-12), 45.6 (d, C-10b), 29.4 (t, C-11). EIMS m/z (%):285 (M+, 18);
266 (100); 240 (8); 226 (16); 208 (4); 180 (3). HREIMS m/z
285.0999 (calcd for C16H15NO4 [M]+ 285.1001). IR (neat) mmax
2920, 2851, 1661, 1469, 1360, 1318, 1232, 1146, 1071, 1030,
3.3.1. 1,2-Diacetyl-6-oxolycorine (8)
1H NMR (CDCl3) d: 7.55 (1H, s, H-7), 6.67 (1H, s, H-10), 6.01 (2H,
br s, OCH2O), 5.74 (1H, s, H-1), 5.61 (1H, s, H-3), 5.28 (1H, s, H-2),
4.23 (1H, d, J = 12.3 Hz, H-12), 3.82 (2H, m, H-4a, H-10b), 3.04 (1H,
d, J = 12.6 Hz, H-12), 2.81 (2H, m, H-11), 2.09 (3H, s, OCOCH3), 2.03
(3H, s, OCOCH3). 13C NMR (CDCl3) d 169.6 (s, OCOCH3), 169.2
(OCOCH3), 162.3 (s, C-6), 150.5 (s, C-4), 146.8 (s, C-8), 143.4 (s, C-
9), 131.6 (s, C-6a), 126.0 (s, C-10a), 115.2 (d, C-3), 108.7 (d, C-7),
103.3 (d, C-10), 101.5 (t, OCH2O), 69.9 (d, C-2), 67.1 (d, C-1), 54.9
(d, C-4a), 43.3 (t, C-12), 40.2 (d, C-10b), 28.3 (t, C-11), 20.8 (q,
OCOCH3), 20.6 (q, OCOCH3). EIMS m/z (%): 385 (M+, 17); 370 (2);
325 (34); 283 (56); 266 (100); 241 (11); 208 (9); 191 (6); 180
(5). HREIMS m/z 385.1175 (calcd for C20H19NO7 [M]+ 385.1162).
IR (neat) mmax 3056, 2914, 1741, 1651, 1612, 1482, 1416, 1371,
925, 895, 845, 796, 733 cmꢀ1. ½a D20
= ꢀ20.5 (c 0.4, MeOH).
ꢁ
3.2.5. 1,2-Diacetyl-3,4S-dihydrolycorine (6)
24 mg (0.065 mmol) of compound 2 dissolved in 3 mL of dry
THF were hydrogenated in the presence of catalytic amounts of
Pd/C (10%). The reaction mixture was left at room temperature
for 24 h until disappearance of the starting material. Then the mix-
ture was filtered through Celite and the solvent was evaporated.
After purification by preparative-TLC using DCM/MeOH (9:1),
7.7 mg of 6 (32%) was obtained as an amorphous white solid. 1H
NMR (CDCl3) d: 6.64 (1H, s, H-10), 6.57 (1H, s, H-7), 5.90 (2H, br
s, OCH2O), 5.67 (1H, s, H-1), 4.93 (1H, m, H-2), 4.00 (1H, d,
J = 14,6 Hz, H-6), 3.82 (1H, d, J = 14.6 Hz, H-6), 3.07 (2H, m,
H-12), 2.68 (2H, m, H-4a, H-10b), 2.38 (1H, dd, J = 8.9 Hz,
J = 14.6 Hz, H-4), 2.14 (2H, m, H-11), 2.10 (3H, s, OCOCH3), 1.96
(3H, s, OCOCH3), 1.66 (2H, m, H-3). 13C NMR (CDCl3) d: 170.0 (s,
OCOCH3), 169.6 (s, OCOCH3), 146.2 (s, C-8), 145.9 (s, C-9), 131.8
(s, C-6a), 127.9 (s, C-10a), 106.9 (d, C-7), 104.8 (d, C-10), 100.6 (t,
OCH2O), 74.1 (d, C-2), 70.7 (d, C-1), 59.2 (d, C-4a), 54.7 (t, C-6),
53.2 (t, C-12), 37.1 (d, C-4), 32.7 (d, C-10b), 30.7 (t, C-11), 29.4 (t,
C-3), 20.9 (q, OCOCH3), 20.7 (q, OCOCH3). EIMS m/z (%):373 (M+,
1235, 1039, 967, 933, 735, 702 cmꢀ1. ½a D20
ꢁ
= +73.3 (c 0.18, MeOH).
3.3.2. 2-Acetyl-1-deoxy-1,2,4a,10b-tetradehydro-6-oxolycorine
(9)
1H NMR (CDCl3) d: 7.90 (1H, s, H-7), 7.43 (2H, s, H-1, H-3), 7.03
(1H, s, H-10), 6.13 (2H, br s, OCH2O), 4.97 (2H, t, J = 8.0 Hz, H-12),
3.43 (2H, t, J = 8.1 Hz, H-11), 2.35 (3H, s, OCOCH3). 13C NMR (CDCl3)
d: 170.1 (s, OCOCH3), 159.1 (s, C-6), 151.7 (s, C-2), 148.6 (s, C-9),
146.8 (s, C-8), 137.0 (s, C-4), 132.1 (s, C-4a), 130.0 (s, C-10a),
123.0 (s, C-6a), 118.0 (d, C-3), 116.7 (s, C-10b), 112.1 (d, C-1),

4698
J. C. Cedrón et al. / Bioorg. Med. Chem. 18 (2010) 4694–4701
106.6 (d, C-10), 101.9 (d, C-7), 100.7 (t, OCH2O), 46.5 (t, C-12), 27.1
(t, C-11), 20.8 (q, OCOCH3). EIMS m/z (%): 323 (M+, 26); 281 (100);
250 (3); 222 (10); 194 (6); 166 (3). HREIMS m/z 323.0804 (calcd for
C18H13NO5 [M]+ 323.0794). IR (neat) mmax 3042, 2917, 1752, 1647,
1616, 1496, 1469, 1365, 1256, 1206, 1136, 1095, 1035, 956, 935,
C-10b), 27.8 (t, C-11). EIMS m/z (%): 301 (M+, 41); 283 (29); 265
(74); 257 (29); 241 (100); 226 (14); 206 (9); 191 (13); 178 (9).
HREIMS m/z 301.0949 (calcd for C16H15NO5 [M]+ 301.0950) IR mmax
(neat) 3394, 2923, 2856, 1632, 1596, 1460, 1419, 1373, 1266, 1118,
1036, 817, 564 cmꢀ1. ½a D20
ꢁ
= +25.9 (c 0.58, MeOH).
908 cmꢀ1
.
3.5.2. 1-Acetyl-6-oxolycorine (13)
3.3.3. 1,2-Diacetyl-3,4-dihydroxy-6-oxolycorine (10)
1H NMR (CDCl3, 400 MHz) d 7.56 (1H, s, H-7), 6.61 (1H, s, H-10),
6.03 (2H, s, OCH2O), 5.68 (1H, s, H-1), 5.63 (1H, s, H-3), 4.32 (1H, s,
H-2), 4.20 (1H, d, J = 12.9 Hz, H-12), 3.80 (2H, m, H-4a, H-10b), 3.02
(1H, d, J = 12.9 Hz, H-12), 2.82 (2H, s, H-11), 2.05 (3H, s, OCOCH3).
13C NMR (CDCl3, 100 MHz) d 170.6 (s, OCOCH3), 162.7 (s, C-6),
150.7 (s, C-4), 147.0 (s, C-8), 141.9 (s, C-9), 132.3 (s, C-6a), 128.2
(s, C-10a), 118.6 (d, C-3), 108.9 (d, C-7), 103.3 (d, C-10), 101.7 (t,
OCH2O), 70.6 (d, C-2), 69.3 (d, C-1), 55.3 (d, C-4a), 43.6 (t, C-12),
39.4 (d, C-10b), 28.5 (t, C-11), 20.9 (q, OCOCH3). EIMS m/z (%):
343 (M+, 36); 325 (2); 283 (20); 266 (44); 254 (9); 241 (100);
226 (9); 208 (4). HREIMS m/z 343.1059 (calcd for C18H17NO6 [M]+
343.1056) IR (neat) mmax 3280, 2921, 1738, 1640, 1598, 1463,
1H NMR (CDCl3) d: 7.53 (1H, s, H-7), 6.45 (1H, s, H-10), 6.02 (2H,
br s, OCH2O), 5.32 (1H, s, H-1), 5.23 (1H, d, J = 10.5 Hz, H-2), 4.21
(1H, d, J = 7.5 Hz, H-3), 4.06 (1H, d, J = 10.1 Hz, H-4a), 3.91 (1H, d,
J = 17.9 Hz, H-12), 3.47 (1H, m, H-10b), 3.32 (1H, d, J = 14.4 Hz,
H-12), 2.21 (3H, s, OCOCH3), 2.09 (3H, s, OCOCH3), 2.02 (2H, m,
H-11). 13C NMR (CDCl3) d: 170.9 (s, OCOCH3), 170.3 (s, OCOCH3),
161.3 (s, C-6), 151.0 (s, C-9), 147.2 (s, C-8), 131.1 (s, C-10a),
124.7 (s, C-6a), 108.7 (d, C-7), 104.4 (d, C-10), 101.8 (t, OCH2O),
79.5 (s, C-4), 77.6 (d, C-2), 74.1 (d, C-3), 71.2 (d, C-1), 63.6 (d, C-
4a), 43.6 (t, C-12), 40.0 (t, C-11), 38.1 (d, C-10b), 21.0 (q, OCOCH3),
20.8 (q, OCOCH3). EIMS m/z (%): 419 (M+, 1); 383 (2); 341 (20); 299
(53); 282 (35); 257 (100); 228 (6); 190 (10). HREIMS m/z 419.1216
1420, 1373, 1270, 1227, 1172, 1123, 1031, 929, 780 cmꢀ1
= +17.1 (c 0.14, MeOH).
.
(calcd for C20H21NO9 [M]+ 419.1216). ½a D20
ꢁ
= ꢀ115.2 (c 0.21, MeOH).
½ ꢁ
a 2D0
IR (neat) mmax 3401, 2916, 1737, 1641, 1606, 1466, 1421, 1368,
1245, 1037, 932, 880, 736 cmꢀ1
.
3.6. Preparation of secolycorines 14–17
3.4. General procedure for deacetylation
Compounds 14–17 were prepared from 2 according to the pro-
cedure described in Ref. 21. Spectroscopic data for 14–16 resulted
identical to those published.21
A solution of the corresponding acetylated compound (20–
30 mg) in 5 mL of 10% HCl is heated at 50 °C for 30 min. Then the
reaction mixture is treated with 20% NH4OH solution until basic
pH is reached, and extracted several times with DCM. The organic
phases are dried over MgSO4, concentrated and purified by pre-
parative-TLC using DCM/MeOH (9:1).
3.6.1. 5-Methyl-8,9-methylenedioxy-4-vinyl-5,6-dihydrophena
ntridine (14)
Compound 14 was obtained as a pale yellow amorphous solid in
73% yield. HRMS m/z 264.1021 (calcd for C17H14NO2 [Mꢀ1]+
264.1025). IR (neat) mmax 3058, 2909, 1731, 1641, 1501, 1466,
3.4.1. 1-Acetyllycorine (11)
1380, 1332, 1247, 1175, 1121, 1082, 1038, 934, 809, 772, 736 cmꢀ1
.
Following the general procedure described above, 30 mg
(0.08 mmol) of 2 yielded 12.2 mg of the derivative 11 (46%) as an
amorphous white solid.
3.6.2. 5-Ethyl-8,9-methylenedioxy-4-vinyl-5,6-dihydrophena
ntridine (15)
1H NMR (CDCl3) d: 6.63 (1H, s, H-10), 6.56 (1H, s, H-7), 5.91 (2H,
s, OCH2O), 5.58 (1H, s, H-1), 5.53 (1H, s, H-3), 4.17 (1H, s, H-2), 4.14
(1H, d, J = 13.9 Hz, H-6), 3.50 (1H, d, J = 14.0 Hz, H-6), 3.34 (1H, m,
H-12), 2.85 (1H, d, J = 10.3 Hz, H-10b), 2.75 (1H, d, J = 10.3 Hz, H-
4a), 2.61 (2H, s, H-11), 2.40 (1H, m, H-12), 1.93 (3H, s, OCOCH3).
13C NMR (CDCl3) d: 170.5 (s, OCOCH3), 146.2 (s, C-8), 145.9 (s, C-
9), 143.4 (s, C-4), 128.9 (s, C-6a), 126.7 (s, C-10a), 117.1 (d, C-3),
107.0 (d, C-7), 104.5 (d, C-10), 100.7 (t, OCH2O), 72.3 (d, C-2),
69.1 (d, C-1), 61.2 (d, C-4a), 56.4 (t, C-6), 53.4 (t, C-12), 38.8 (d,
C-10b), 28.3 (t, C-11), 20.8 (q, OCOCH3). EIMS m/z (%): 329 (M+,
52); 268 (37); 250 (24); 240 (9); 226 (100); 192 (3). HRMS m/z
329.1260 (calcd for C18H19NO5 [M]+ 329.1263). IR (neat) mmax
3393, 2893, 1735, 1650, 1485, 1371, 1239, 1179, 1153, 1130,
Compound 15 was obtained as a pale yellow amorphous solid in
70% yield. HRMS m/z 278.1172 (calcd for C18H16NO2 [M]+
278.1181). IR (neat) mmax 3060, 2969, 1731, 1653, 1502, 1468,
1380, 1239, 1176, 1116, 1038, 935, 811, 736, 612 cmꢀ1
.
3.6.3. 5-Butyl-8,9-methylenedioxy-4-vinyl-5,6-dihydrophena
ntridine (16)
Compound 16 was obtained as a pale yellow amorphous solid in
77% yield. HREIMS m/z 307.1574 (calcd for C20H21NO2 [M]+
307.1572). IR (neat) mmax 2959, 2874, 1731, 1651, 1467, 1381,
1239, 1176, 1038, 935, 865, 812, 737, 700 cmꢀ1
.
3.6.4. 8,9-Methylenedioxy-5-undecyl-4-vinyl-5,6-dihydrophena
ntridine (17)
1037, 995, 933, 867, 735 cmꢀ1. ½a D20
= ꢀ118.9 (c 0.09, MeOH).
ꢁ
Compound 17 was obtained as a pale yellow amorphous solid in
28% yield. 1H NMR (CDCl3) d: 7.55 (1H, d, J = 7.5 Hz, H-1), 7.44 (1H,
d, J = 7.6 Hz, H-3), 7.20 (2H, m, H-10, H-11), 7.12 (1H, t, J = 7.7 Hz,
H-2), 6.68 (1H, s, H-7), 5.97 (2H, s, OCH2O), 5.70 (1H, d, J = 17.8 Hz,
H-12), 5.26 (1H, d, J = 11.1 Hz, H-12), 4.02 (2H, s, H-6), 2.63 (2H, t,
J = 7.3 Hz, NCH2(C9H18)CH3), 1.21 (18H, br s, NCH2(C9H18)CH3), 0.86
(3H, t, J = 6.9 Hz, NCH2(C9H18)CH3). 13C NMR (CDCl3) d: 147.0 (s, C-
9), 146.9 (s, C-8), 145.2 (s, C-4a), 133.5 (d, C-11), 132.9 (s, C-6a),
129.3 (s, C-10a), 126.9 (s, C-4), 126.2 (s, C-10b), 124.7 (d, C-1),
123.6 (d, C-3), 122.3 (d, C-2), 113.7 (t, C-12), 106.6 (d, C-7), 103.4
(d, C-10), 100.7 (t, OCH2O), 52.8 (t, C-6), 49.8 (t, NCH2(C9H18)CH3),
31.6, 29.3, 29.2, 29.0, 27.9, 26.7, 22.4 (t, NCH2(C9H18)CH3), 13.8 (q,
NCH2(C9H18)CH3). EIMS m/z (%): 405 ([M]+, 51); 292 (3); 264 (92);
250 (100); 234 (10); 220 (4); 206 (9); 191 (6). HREIMS m/z
405.2643 (calcd for C27H35NO2 [M]+ 405.2668). IR (neat) mmax
3.5. Reaction of 8 to obtain derivatives 12 and 13
Following the general procedure described above, 26.3 mg
(0.068 mmol) of 8 afforded 4.8 mg of compound 12 (20%) and
9.7 mg of compound 13 (48%) as amorphous white solids.
3.5.1. 6-Oxolycorine (12)
1H NMR (400 MHz, MeOD,) d: 7.37 (1H, s, H-7), 6.93 (1H, s, H-
10), 6.03 (2H, s, OCH2O), 5.63 (1H, s, H-3), 4.47 (1H, s, H-2), 4.21
(2H, s, H-1, H-12), 3.74 (2H, m, H-4a, H-12), 2.83 (3H, m, H-10b,
H-11). 13C NMR (100 MHz, MeOD) d: 163.5 (s, C-6), 151.0 (s, C-
8), 146.7 (s, C-9), 140.4 (s, C-4), 134.8 (s, C-6a), 125.5 (s, C-10a),
119.0 (d, C-3), 107.4 (d, C-7), 103.8 (d, C-10), 101.8 (t, OCH2O),
71.3 (d, C-2), 68.4 (d, C-1), 54.9 (d, C-4a), 43.4 (t, C-12), 40.2 (d,

J. C. Cedrón et al. / Bioorg. Med. Chem. 18 (2010) 4694–4701
4699
2925, 2854, 1733, 1650, 1502, 1466, 1382, 1239, 1175, 1037, 936,
811, 768 cmꢀ1
purification 4.8 mg of 20 (25%) as an amorphous white solid. 1H
NMR (CDCl3) d: 7.97 (1H, d, J = 7.6 Hz, H-1), 7.85 (1H, s, H-10),
7.57 (1H, s, H-7), 7.46 (1H, d, J = 7.1 Hz, H-3), 7.25 (1H, br s, H-2),
7.08 (1H, dd, J = 10.9 Hz, J = 16.1 Hz, H-11), 6.12 (2H, br s, OCH2O),
5.62 (1H, d, J = 16.9 Hz, H-12), 5.37 (1H, d, J = 10.7 Hz, H-12), 3.78
(3H, s, NMe). 13C NMR (CDCl3) d: 162.9 (s, C-6), 152.0 (s, C-9),
148.1 (s, C-8), 137.6 (d, C-11), 136.9 (s, C-4a), 130.3 (s, C-6a),
130.0 (d, C-1), 128.3 (s, C-10a), 122.4 (d, C-3), 121.9 (d, C-2),
120.9 (s, C-4), 120.7 (s, C-10b), 114.0 (t, C-12), 106.3 (d, C-7),
101.7 (t, OCH2O), 100.4 (d, C-10), 39.0 (q, NMe). EIMS m/z (%):
279 ([M]+, 92); 264 (100); 250 (6); 234 (8); 220 (7); 206 (22);
191 (8). HREIMS m/z 279.0886 (calcd for C17H13NO3 [M]+
279.0895). IR (neat) mmax 2981, 2912, 1641, 1501, 1461, 1380,
.
3.7. General procedure for preparation of derivatives 18 and 19
To a solution of the corresponding compound in 5 mL of dry DCM
at 0 °C, was added dropwise 2 equiv of a solution 1 M of in DCM. The
reaction mixture was stirred for ꢂ4 h until disappearance of the
starting material. Then, the solvent was evaporated and the residue
was purified by preparative-TLC using DCM/MeOH (19:1).
3.7.1. 8,9-Dihydroxy-5-methyl-4-vinyl-5,6-dihydrophenantridine
(18)
According to the procedure described above, 30.9 mg (0.12
mmol) of compound 14 was reacted with 0.25 mL of a solution
1 M of BBr3 in DCM. After purification, 11.8 mg of 23 (40%) was ob-
tained as an amorphous pale yellow solid. 1H NMR (CDCl3) d: 7.55
(1H, d, J = 7.7 Hz, H-1), 7.44 (1H, d, J = 7.7 Hz, H-3), 7.21 (2H, m, H-
10, H-11), 7.13 (1H, t, J = 7.7 Hz, H-2), 6.73 (1H, s, H-7), 5.72 (1H, d,
J = 17.7 Hz, H-12), 5.30 (1H, d, J = 10.9 Hz, H-12), 3.99 (2H, s, H-6),
2.49 (3H, s, NMe). 13C NMR (CDCl3) d: 145.0 (s, C-9), 143.4 (s, C-8),
142.7 (s, C-4a), 133.2 (d, C-11), 133.0 (s, C-6a), 128.7 (s, C-10a),
125.5 (s, C-4), 124.8 (s, C-10b), 124.6 (d, C-1), 124.1 (d, C-3), 122.4
(d, C-2), 114.2 (t, C-12), 113.4 (d, C-7), 110.1 (d, C-10), 54.0 (t, C-6),
41.5 (q, NMe). EIMS m/z (%): 253 ([M]+, 27); 252 (59); 251 (100);
236 (10); 223 (34); 208 (24); 191 (11); 178 (14). HRMS m/z
253.1096 (calcd for C16H15NO2 [M]+ 253.1103). IR (neat) mmax
3367, 2924, 2853, 1733, 1653, 1619, 1543, 1461, 1115, 1038,
1331, 1249, 1122, 1082, 1037, 935, 881, 774, 739, 669 cmꢀ1
.
3.8.2. 5-Ethyl-8,9-methylenedioxy-6-oxo-4-vinyl-5,6-
dihydrophenantridine (21)
Following the general procedure, 13.3 mg (0.048 mmol) of 15
was treated with 4 mg of TBAI and 33 mg of iodosylbenzene. After
purification, 6.8 mg of 21 (49%) was obtained as an amorphous
white solid. 1H NMR (CDCl3) d 7.99 (1H, d, J = 7.8 Hz, H-1), 7.85
(1H, s, H-10), 7.57 (1H, s, H-7), 7.43 (1H, d, J = 7.3 Hz, H-3), 7.23
(1H, m, H-2), 7.15 (1H, dd, J = 10.7 Hz, J = 17.1 Hz, H-11), 6.10
(2H, br s, OCH2O), 5.62 (1H, d, J = 17.1 Hz, H-12), 5.36 (1H, d,
J = 10.7 Hz, H-12), 4.53 (2H, q, J = 6.8 Hz, NCH2CH3), 1.30 (3H, t,
J = 6.8 Hz, NCH2CH3). 13C NMR (CDCl3) d: 162.6 (s, C-6), 152.0 (s,
C-9), 148.1 (s, C-8), 137.7 (d, C-11), 135.8 (s, C-4a), 130.8 (d, C-1),
130.3 (s, C-6a), 128.4 (s, C-10a), 122.3 (d, C-3), 122.2 (d, C-2),
121.1 (s, C-4), 120.9 (s, C-10b), 114.9 (t, C-12), 106.4 (d, C-7),
101.6 (t, OCH2O), 100.4 (d, C-10), 42.7 (t, NCH2CH3), 14.4 (q,
NCH2CH3). EIMS m/z (%):293 ([M]+, 75); 278 (77); 264 (100); 248
(7); 234 (7); 220 (10); 206 (19); 191 (7).HREIMS m/z 293.1052
(calcd for C18H15NO3 [M]+ 293.1052). IR (neat) mmax 2962, 2916,
1732, 1643, 1501, 1461, 1382, 1299, 1247, 1163, 1037, 935, 843,
813 cmꢀ1
.
3.7.2. 5-Butyl-8,9-dihydroxy-4-vinyl-5,6-dihydrophenantridine
(19)
According to the procedure described above, 36 mg (0.12 mmol)
of compound 16 was reacted with 0.25 mL of a solution 1 M of BBr3
in DCM. After purification, 11.8 mg of 24 (40%) was obtained as an
amorphous pale yellow solid. 1H NMR (CDCl3) d: 7.51 (1H, br s, H-
1), 7.43 (1H, d, J = 7.3 Hz, H-3), 7.17 (3H, m, H-2, H-10, H-11), 6.74
(1H, s, H-7), 5.69 (1H, d, J = 17.6 Hz, H-12), 5.27 (1H, d, J = 10.9 Hz,
H-12), 4.00 (2H, s, H-6), 2.64 (2H, t, J = 7.5 Hz, NCH2CH2CH2CH3),
1.46 (2H, m, NCH2CH2CH2CH3), 1.20 (2H, m, NCH2CH2CH2CH3),
0.83 (3H, t, J = 7.1 Hz, NCH2CH2CH2CH3). 13C NMR (CDCl3) d:
144.8 (s, C-4a), 143.6 (s, C-9), 143.0 (s, C-8), 133.4 (d, C-11),
132.9 (s, C-6a), 129.0 (d, C-1), 125.2 (s, C-10a), 124.7 (d, C-3),
124.0 (s, C-4), 123.9 (s, C-10b), 122.3 (d, C-2), 113.9 (t, C-12),
113.3 (d, C-7), 110.1 (d, C-10), 52.9 (t, C-6), 49.4 (t,
774, 739 cmꢀ1
.
3.8.3. 5-Butyl-8,9-methylenedioxy-6-oxo-4-vinyl-5,6-
dihydrophenantridine (22)
Following the general procedure, 15.1 mg (0.049 mmol) of 16
was treated with 4 mg of TBAI and 33 mg of iodosylbenzene. After
purification, 10.2 mg of 22 (65%) was obtained as an amorphous
white solid. 1H NMR (CDCl3) d: 7.98 (1H, d, J = 7.9 Hz, H-1), 7.84
(1H, s, H-10), 7.56 (1H, s, H-7), 7.41 (1H, d, J = 7.3 Hz, H-3), 7.22
(1H, m, H-2), 7.10 (1H, dd, J = 10.7 Hz, J = 17.2 Hz, H-11), 6.10
(2H, br s, OCH2O), 5.62 (1H, d, J = 17.2 Hz, H-12), 5.36 (1H, d,
J = 10.7 H-12), 4.49 (2H, t, J = 7.3 Hz, NCH2CH2CH2CH3), 1.62 (2H,
q, J = 7.3 Hz, NCH2CH2CH2CH3), 1.23 (2H, sext, J = 7.3 Hz,
NCH2CH2CH2CH3), 0.85 (3H, t, J = 7.3 Hz, NCH2CH2CH2CH3). 13C
NMR (CDCl3) d: 162.8 (s, C-6), 152.0 (s, C-9), 148.1 (s, C-8), 137.7
(d, C-11), 135.9 (s, C-4a), 130.6 (d, C-1), 130.2 (s, C-6a), 128.6 (s,
C-10a), 122.3 (d, C-3), 122.2 (d, C-2), 121.1 (s, C-4), 120.9 (s, C-
10b), 114.7 (t, C-12), 106.5 (d, C-7), 101.6 (t, OCH2O), 100.4 (d, C-
10), 47.4 (t, NCH2CH2CH2CH3), 30.6 (t, NCH2CH2CH2CH3), 19.5 (t,
NCH2CH2CH2CH3), 13.5 (q, NCH2CH2CH2CH3). EIMS m/z (%):321
([M]+, 48); 304 (22); 292 (32); 278 (39); 264 (100); 234 (4); 220
(7); 206 (12); 191 (7). HREIMS m/z 321.1357 (calcd for
C20H19NO3 [M]+ 321.1365). IR (neat) mmax 2959, 2929, 1732,
1644, 1500, 1461, 1382, 1247, 1204, 1162, 1087, 1038, 934, 882,
NCH2CH2CH2CH3),
28.9
(t,
NCH2CH2CH2CH3),
19.9
(t,
NCH2CH2CH2CH3), 13.7 (q, NCH2CH2CH2CH3). EIMS m/z (%): 295
([M]+, 56); 252 (100); 238 (94); 220 (7); 209 (9); 191 (7); 178
(8). HREIMS m/z 295.1563 (calcd for C19H21NO2 [M]+ 295.1572).
IR (neat) mmax 3395, 2958, 2929, 1667, 1609, 1511, 1393, 1336,
1300, 1250, 1196, 1056, 907, 858, 809, 739 cmꢀ1
.
3.8. General procedure for preparation of the lactam derivatives
20–22
To a suspension of the corresponding compound (10–20 mg) in
5 mL of CH3CN/H2O (9:1) were added 0.2 equiv of tetrabutylam-
monium iodide (TBAI) and 3 equiv of iodosylbenzene. The reaction
mixture was stirred for ꢂ4 h until disappearance of the starting
material. The solvent was evaporated and the residue was purified
by preparative-TLC using DCM as eluent.
845, 775, 739 cmꢀ1
.
3.9. Preparation of dihydrosecolycorines 23 and 24
3.8.1. 5-Methyl-8,9-methylenedioxy-6-oxo-4-vinyl-5,6-
dihydrophenantridine (20)
Following the general procedure, 18.2 mg (0.07 mmol) of 14
was treated with 6 mg of TBAI and 46 mg of iodosylbenzene. After
Derivatives 23 and 24 were prepared by hydrogenation accord-
ing to the method described in Ref. 21. Compounds 23 and 24
showed identical spectroscopic data to those published.21

4700
J. C. Cedrón et al. / Bioorg. Med. Chem. 18 (2010) 4694–4701
3.9.1. 4-Ethyl-5-methyl-8,9-methylenedioxy-5,6-
dihydrophenantridine (23)
tion 2 M of trimethylsilyldiazomethane in ethyl ether. The reaction
mixture was stirred for 24 h, then the solvent was evaporated and
the residue was purified by preparative-TLC using DCM as eluent,
to yield 4 mg of 27 (60%) as a pale yellow solid. 1H NMR (CDCl3)
d: 7.63 (1H, d, J = 7.7 Hz, H-1), 7.45 (1H, d, J = 7.7 Hz, H-3), 7.23
(2H, m, H-10, H-11), 7.16 (1H, t, J = 7.7 Hz, H-2), 6.73 (1H, s, H-7),
5.74 (1H, d, J = 17.7 Hz, H-12), 5.31 (1H, d, J = 11.0 Hz, H-12), 4.06
(2H, s, H-6), 3.96 (3H, s, OMe), 3.93 (3H, s, OMe), 2.52 (3H, s,
NMe). 13C NMR (CDCl3) d: 148.7 (s, C-9), 148.2 (s, C-8), 144.8 (s,
C-4a), 133.2 (d, C-11), 133.1 (s, C-6a), 128.9 (s, C-10a), 124.8 (s,
C-4), 124.8 (d, C-1), 124.5 (s, C-10b), 124.2 (d, C-3), 122.2 (d, C-
2), 114.1 (t, C-12), 109.5 (d, C-7), 106.1 (d, C-10), 55.8 (q, OMe),
55.7 (q, OMe), 54.2 (t, C-6), 41.6 (q, NMe). EIMS m/z (%): 280
([Mꢀ1]+, 100); 264 (21); 250 (4); 235 (6); 222 (3); 207 (4); 191
(5). HREIMS m/z 280.1341 (calcd for C18H18NO2 [Mꢀ1]+
280.1338). IR (neat) mmax 2929, 1640, 1610, 1515, 1466, 1380,
Compound 23 was isolated as a pale yellow solid in 35% yield.
HREIMS m/z 267.1248 (calcd for C17H17NO2 [M]+ 267.1259). IR
(neat) mmax 2965, 2932, 1644, 1620, 1501, 1467, 1380, 1298,
1237, 1167, 1080, 1038, 934, 861, 809, 760, 737 cmꢀ1
.
3.9.2. 5-Butyl-4-ethyl-8,9-methylenedioxy-5,6-
dihydrophenantridine (24)
Compound 24 was isolated as a pale yellow solid in 65% yield. IR
(neat) mmax 2961, 2930, 1731, 1651, 1467, 1377, 1238, 1176, 1095,
1038, 937, 861, 806, 737 cmꢀ1. HREIMS m/z 309.1720 (calcd for
C20H23NO2 [M]+ 309.1729).
3.9.3. 8,9-Diacetyl-5-methyl-4-vinyl-5,6-dihydrophenantridine
(25)
To a solution of 9.3 mg (0.037 mmol) of compound 18 in 1 mL of
pyridine, was added 0.3 mL (3.18 mmol) of acetic anhydride. The
reaction mixture was stirred at room temperature for 24 h. Then
the solvent was removed and the crude purified by preparative-
TLC using DCM as eluent to yield 8 mg of 25 (65%) as a pale yellow
solid. 1H NMR (CDCl3) d: 7.60 (1H, d, J = 7.7 Hz, H-1), 7.53 (1H, s, H-
10), 7.50 (1H, d, J = 7.7 Hz, H-3), 7.19 (2H, m, H-2, H-11), 7.08 (1H,
s, H-7), 5.74 (1H, d, J = 17.7 Hz, H-12), 5.32 (1H, d, J = 11.0 Hz, H-
12), 4.09 (2H, s, H-6), 2.53 (3H, s, NMe), 2.32 (3H, s, OCOCH3),
2.30 (3H, s, OCOCH3). 13C NMR (CDCl3) d: 168.2 (s, OCOCH3),
168.1 (s, OCOCH3), 145.3 (s, C-4a), 145.3 (s, C-8), 141.1 (s, C-9),
133.1 (s, C-6a), 133.0 (d, C-11), 130.7 (s, C-10b), 130.5 (s, C-10a),
127.6 (s, C-4), 125.9 (d, C-2), 124.1 (d, C-1), 123.1 (d, C-3), 121.2
(d, C-10), 117.7 (d, C-7), 114.4 (t, C-12), 53.9 (t, C-6), 41.8 (q,
NMe), 20.5 (q, OCOCH3), 20.4 (q, OCOCH3). EIMS m/z (%): 337
([M]+, 53); 322 (7); 294 (26); 280 (18); 252 (100); 238 (23); 224
(12); 208 (10). HREIMS m/z 337.1308 (calcd for C20H19NO4 [M]+
337.1314). IR (neat) mmax 2939, 1768, 1672, 1616, 1504, 1465,
1273, 1211, 1064, 1025, 809, 772, 734 cmꢀ1
.
3.9.6. 5-Butyl-8,9-diacetyl-4-vinyl-5,6-dihydrophenantridine
(28)
To a solution of 5.9 mg (0.02 mmol) of compound 19 in 1 mL of
pyridine, was added 0.3 mL (3.18 mmol) of acetic anhydride. The
reaction mixture was stirred for 24 h at room temperature, then
the solvent was eliminated and the residue was purified by prepara-
tive-TLC using DCM as eluent, to yield 5.4 mg of 28 (72%) as a pale
yellow solid. 1H NMR (CDCl3) d: 7.60 (1H, d, J = 7.6 Hz, H-1), 7.52
(1H, s, H-10), 7.50 (1H, d, J = 9.6 Hz, H-3), 7.14 (2H, m, H-2, H-11),
7.07 (1H, s, H-7), 5.72 (1H, d, J = 17.7 Hz, H-12), 5.30 (1H, d,
J = 11 Hz, H-12), 4.11 (2H, s, H-6), 2.68 (2H, t, J = 7.1 Hz,
NCH2CH2CH2CH3), 2.32 (3H, s, OCOCH3), 2.31 (3H, s, OCOCH3), 1.49
(2H, q, J = 7.5 Hz, NCH2CH2CH2CH3), 1.25 (2H, m, NCH2CH2CH2CH3),
0.86 (3H, t, J = 7.2 Hz, NCH2CH2CH2CH3). 13C NMR (CDCl3) d: 168.2 (s,
OCOCH3), 168.1 (s, OCOCH3), 145.9 (s, C-4a), 145.6 (s, C-8), 141.1 (s,
C-9), 133.3 (s, C-6a), 133.1 (d, C-11), 131.5 (s, C-10a), 131.0 (s,
C-10b), 127.8 (s, C-4), 126.1 (d, C-2), 123.7 (d, C-1), 123.0 (d, C-3),
120.9 (d, C-10), 117.7 (d, C-7), 114.0 (t, C-12), 52.9 (t, C-6), 49.2 (t,
NCH2CH2CH2CH3), 30.2 (t, NCH2CH2CH2CH3), 20.5 (q, OCOCH3),
20.4 (q, OCOCH3), 19.8 (t, NCH2CH2CH2CH3), 13.7 (q,
NCH2CH2CH2CH3). EIMS m/z (%): 379 ([M]+, 62); 336 (86); 322
(84); 294 (100); 280 (54); 252 (60); 238 (34); 210 (13). HREIMS m/
z 379.1779 (calcd for C23H25NO4 [M]+ 379.1784). IR (neat) mmax
2959, 2931, 1766, 1667, 1613, 1504, 1466, 1394, 1208, 1128, 1055,
1372, 1210, 1122, 1042, 1011, 919, 812, 760, 735 cmꢀ1
.
3.9.4. 8,9-Dilauroyl-5-methyl-4-vinyl-5,6-dihydrophenantridine
(26)
To a solution of 9.5 mg (0.038 mmol) of compound 18 in 3 mL of
DCM, were added 16 lL (3 equiv) of triethylamine and 27 lL
(3 equiv) of lauroyl chloride. The reaction mixture was stirred for
18 h stirring at room temperature. Then the solvent was elimi-
nated and the residue was the mixture was purified by prepara-
tive-TLC using DCM as eluent, to yield 17.7 mg of 26 (77%) as a
pale yellow solid. 1H NMR (CDCl3) d: 7.61 (1H, d, J = 7.7 Hz, H-1),
7.51 (1H, s, H-10), 7.49 (1H, d, J = 8.3 Hz, H-3), 7.19 (2H, m, H-2,
H-11), 7.07 (1H, s, H-7), 5.74 (1H, d, J = 17.7 Hz, H-12), 5.31 (1H,
d, J = 11.0 Hz, H-12), 4.08 (2H, s, H-6), 2.56 (4H, t, J = 7.0 Hz,
COCH2(C9H18)CH3), 2.52 (3H, s, NMe), 1.26 (36H, s,
COCH2(C9H18)CH3), 0.87 (6H, t, J = 5.2 Hz, COCH2(C9H18)CH3). 13C
NMR (CDCl3) d: 171.0 (s, C@O), 170.9 (s, C@O), 146.1 (s, C-4a),
141.3 (s, C-8), 141.3 (s, C-9), 133.1 (s, C-6a), 133.0 (d, C-11),
130.5 (s, C-10b), 130.3 (s, C-10a), 127.6 (s, C-4), 125.8 (d, C-2),
124.1 (d, C-1), 123.1 (d, C-3), 121.2 (d, C-10), 117.7 (d, C-7),
114.3 (t, C-12), 54.0 (t, C-6), 41.7 (q, NMe), 33.8 (t,
COCH2(C9H18)CH3), 31.6, 29.2, 29.1, 29.0, 29.0, 28.9, 28.9, 24.7,
22.4 (t, COCH2(C9H18)CH3), 13.8 (q, COCH2(C9H18)CH3). EIMS m/z
(%):617 ([M]+, 92); 435 (81); 252 (100); 238 (17); 224 (19); 208
(5). HREIMS m/z 617.4471 (calcd for C40H59NO4 [M]+ 617.4444).
IR (neat) mmax 2917, 2851, 1747, 1502, 1466, 1390, 1312, 1240,
921, 811, 737 cmꢀ1
.
3.10. Antiplasmodial assay
F-32 Tanzania (chloroquine-sensitive) strains of P. falciparum
were cultured according to Trager and Jensen22 on glucose-en-
riched RPMI 1640 medium, supplemented with 10% human serum
at 37 °C. After 24 h of incubation at 37 °C, the medium was re-
placed by fresh medium supplemented with the compound to be
evaluated at three different concentrations (0.1, 1, 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 parasite-
mia was calculated for each concentration of sample compared
to the control. IC50 values were determined graphically by plotting
concentrations versus percent inhibition. Chloroquine (0.04 lM)
was used as a positive control. All tests were performed in
triplicate.
1149, 1122, 1085, 909, 814, 760, 718 cmꢀ1
.
Acknowledgments
3.9.5. 5-Methyl-8,9-dimethoxy-4-vinyl-5,6-
dihydrophenantridine (27)
To a solution of 6.1 mg (0.024 mmol) of compound 18 in 5 mL of
a mixture DCM/MeOH 1:1, was added 0.5 mL (42 equiv) of a solu-
This work has been partly funded by the Spanish MEC (SAF
2006-06720 and SAF 2009-13296-C02-01) and by the ICIC (Institu-
to Canario de Investigación del Cáncer). J.C.C. thanks Gobierno
Autónomo de Canarias for a predoctoral fellowship.

J. C. Cedrón et al. / Bioorg. Med. Chem. 18 (2010) 4694–4701
4701
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