Ten new fawcettimine-related alkaloids from three species of Lycopodium

Article abstract of DOI:10.1016/j.tet.2011.05.107

Ten new fawcettimine-related alkaloids, i.e., lycopoclavamines, lycoposquarrosamine-A, and other hydroxylated fawcettimine derivatives, were isolated from three species of Lycopodium (Lycopodium clavatum, Lycopodium serratum, and Lycopodium squarrosum). The structures of the new alkaloids were elucidated by spectroscopic methods and chemical correlation.

Full text of DOI:10.1016/j.tet.2011.05.107

Tetrahedron 67 (2011) 6561e6567
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Ten new fawcettimine-related alkaloids from three species of Lycopodium
Kazuaki Katakawa a, Hiroko Mito b, Noriyuki Kogure b, Mariko Kitajima b, Sumphan Wongseripipatana c,
,
Munehisa Arisawa d, Hiromitsu Takayama b
*
a Department of Pharmaceutical Sciences, Musashino University, 1-1-20 Shinmachi, Nishitokyo-shi, Tokyo 202-8585, Japan
b Graduate School of Pharmaceutical Sciences, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
c Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok 10500, Thailand
d Department of Pharmaceutical Sciences, International University of Health and Welfare, 2600-1 Kitakanemaru, Ohtawara, Tochigi 324-8501, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 May 2011
Received in revised form 25 May 2011
Accepted 26 May 2011
Available online 31 May 2011
Ten new fawcettimine-related alkaloids, i.e., lycopoclavamines, lycoposquarrosamine-A, and other hy-
droxylated fawcettimine derivatives, were isolated from three species of Lycopodium (Lycopodium clav-
atum, Lycopodium serratum, and Lycopodium squarrosum). The structures of the new alkaloids were
elucidated by spectroscopic methods and chemical correlation.
Ó 2011 Elsevier Ltd. All rights reserved.
ꢀ
Dedicated to Professor Satoshi Omura on
the occasion of his being awarded the
Tetrahedron Prize
Keywords:
Lycopodium
Alkaloid
Structure elucidation
1. Introduction
Lycopoclavamine-A (1) was obtained as a colorless amorphous
solid and its molecular formula was deduced from HREIMS analysis
Lycopodium plants have sustained interest because they contain
alkaloids having complex polycyclic structures1 and biological ac-
tivities, such as acetylcholine esterase inhibitory activity.2 In the
course of our chemical studies on Lycopodium plants,3 we in-
vestigated the constituents in three species of Lycopodium, i.e.,
Lycopodium clavatum, Lycopodium serratum, and Lycopodium
squarrosum, and our effort resulted in the isolation of ten new
alkaloids having fawcettimine-related skeletons. In this paper, we
describe the structure elucidation of these new alkaloids (1e10)
(Fig. 1).
to be C16H23NO2. 1H and 13C NMR spectra (Table 1) showed the
presence of one carbonyl group (dC 206.6), one tri-substituted
olefinic function (dH 6.91, dC 136.3, 141.4), and one carbinolamine
moiety (dC 85.0). Particularly, the presence of the carbinolamine
moiety suggested that 1 had a fawcettimine-related skeleton.
1He1H COSY and HSQC analyses indicated the presence of three
carbon chains (aec) shown by the bold lines in Fig. 2. The existence
of 3,4-didehydrofawcettidane skeleton in 1 was elucidated by
HMBC spectroscopic analysis as follows. HMBC correlation between
the olefinic hydrogen [dH 6.91 (H-3)] and the carbonyl carbon [dC
206.6 (C-5)] as well as the correlation between the terminal hy-
drogen [dH 1.90 (H-6)] in fragment b and another olefinic carbon [dC
141.4 (C-4)] indicated that fragments a and b were connected by an
enone moiety. The presence of a cyclopentanone ring (C-4eC-7 and
C-12) was elucidated by HMBC correlations between the methylene
hydrogen [dH 1.90 (H-6)] in fragment b and the quaternary carbon
2. Results and discussion
L. clavatum was collected in Toyama Prefecture, Japan and the
alkaloid extract was prepared by following a conventional pro-
cedure. The alkaloid fraction was purified by repeated column
chromatography using silica gel, alumina, and amino-silica gel, and
two new alkaloids named lycopoclavamines-A (1) and -B (2) were
isolated together with fawcettimine (11).4
[dC 53.4 (C-12)] as well as between the methine hydrogen [dH 2.08
(H-7)] in fragment b and the olefinic carbon [dC 141.4 (C-4)]. Frag-
ment c should be connected to the quaternary carbon [dC 53.4 (C-
12)] described above based on the correlation between the methine
hydrogen [dH 2.08 (H-7)] in fragment b and the methylene carbon
* Corresponding author. Tel./fax: þ81 43 290 2901; e-mail address: takayama@
[dC 30.5 (C-11)]. Finally, the connectivity of the three fragments
p.chiba-u.ac.jp (H. Takayama).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.05.107

6562
K. Katakawa et al. / Tetrahedron 67 (2011) 6561e6567
through a carbinolamine moiety was elucidated by the correlations
R1
15
R3
between the four hydrogens located at the terminus of each frag-
ment [dH 2.93 (H-1), 2.72 (H-9), 1.91 (H-14), and 1.30 (H-14)] and
the carbinolamine carbon [dC 85.0 (C-13)], respectively. NOESY
correlation between H-1a and H-14a indicated a trans-decahy-
droquinoline ring system at the A/D-ring junction. This configura-
tion is enabled by taking an opposite configuration at the
hemiaminal carbon (C-13) relative to that in fawcettimine (11).
Furthermore, NOESY correlations H-16/H-8b and H-16/H-14a in-
R2
R5
A
8
7
14
5
6
H
13
R4
3
12
HO
4
2
N
1
D
9
10
1
2
3
4
: R1 = CH3, R2 = H, R3 = H2, R4 & R5 = carbonyl
: R1 = OH, R2 = CH3, R3 = H2, R4 & R5 = carbonyl
: R1 = CH3, R2 = H, R3 = H2, R4 = OH, R5 = H
: R1 = CH3, R2 = H, R3 = O, R4 = H, R5 = OH
dicated that 1 had a b-oriented methyl group at C-15, which differs
from that in common fawcettimine-type Lycopodium alkaloids.
Following lycovatin A isolated by Kobayashi and co-workers,5 this is
the second example of fawcettimine-related alkaloids possessing
a trans-decahydroquinoline ring system at the A/D-ring junction as
well as a b-oriented methyl group at C-15.
6
6
Lycopoclavamine-B (2) was obtained as a colorless amorphous
solid and its molecular formula was deduced from HREIMS analysis
to be C16H23NO3, which implied that 2 was an oxygenated de-
rivative of 1. The NMR spectra of 2 resembled those of 1 except that
the methyl group was detected as a singlet signal in the lower field
relative to that of 1, and one oxygenated quaternary carbon reso-
nance was observed instead of a methine signal corresponding to
C-15 in 1. These NMR data implied that 2 must be a 15-hydroxy
derivative of 1. 1He1H COSY and HSQC analysis of 2 indicated two
carbon chains ascribable to fragments a and c in 1 as well as
a snapped chain corresponding to fragment b (Fig. 3). HMBC cor-
relations between the singlet methyl hydrogen [dH 1.49 (H3-16)]
and three carbons [dC 46.1 (C-8), 46.8 (C-14), and 71.5 (C-15)]
showed the connectivity of the carbon chain corresponding to
fragment b in 1. NOESY correlations between H-7 and H-16 in-
dicated that the tertiary hydroxy group at C-15 should have
H
7
5
5
O
O
15R1
7
15
8O
8
16
16
3
H
4
H
H
13
A
H3C
H3C
3
13
4
14
12
12
2
1
O
R2
11
N
R
17
2
1
10
D
N
9
9
9
: R = OAc
10: R = H, N-oxide
12: R = H
5
: R1 = H, R2 = OAc
: R1 = H, R2 = OH
: R1 = OAc, R2 = H
: R1 = OH, R2 = H
6
7
8
13: R = OH
11: R1 = R2 = H
Fig. 1. Structures of new (1e10) and known (11e13) alkaloids.
a b-equatorial orientation. Other stereochemistry was elucidated
Table 1
based on NOESY correlations, such as H-1a/H-14a, H-6b/H-8b, and
H-8b/H-14a. Therefore, 2 was elucidated to be the 15-hydroxy de-
rivative of 1.
13C NMR data of 1e4 and 11
Position
1
2
3
4
11
1
2
3
4
5
6
7
8
46.7
29.9
46.9
29.7
47.3
29.8
47.4
29.4
50.0
22.6
35.9
60.2
220.4
41.9
43.2
31.9
53.4
28.8
28.2
48.2
88 (br)
44.4
23.7
21.8
OH
Ha
OH
136.3
141.4
206.6
43.2
37.3
40.5
46.0
23.0
30.5
53.4
85.0
43.1
27.3
22.3
136.6
140.7
205.7
42.8
36.2
46.1
45.6
22.8
29.9
53.3
86a
125.9
150.1
75.7
38.3
42.8
40.1
46.1
22.9
30.9
54.7
85.4
43.5
27.7
22.5
125.6
148.4
74.6
32.0
55.1
212.6
46.1
22.3
32.3
57.5
83.9
43.5
41.2
14.6
16
H3C
8
15
16
8
15
b
Hb
Hb
O
14
O
5
Hb
Ha
14
13
6
H
7
HO
6
4
Ha
HO
12
N
3
N
9
a
1
10
11
12
13
14
15
16
9
10
c
HSQC and
1H-1H COSY
HMBC
NOESY
46.8
71.5
29.2
a
Fig. 3. Selected 2D NMR data of lycopoclavamine-B (2).
Based on HMBC correlation.
L. serratum was collected in Chiba Prefecture, Japan. The alkaloid
fraction prepared in the previous study3f was purified by repeated
column chromatography to give one new alkaloid named
dihydrolycopoclavamine-A (3).
Dihydrolycopoclavamine-A (3) was obtained as a colorless
amorphous solid and its molecular formula was deduced from
HREIMS analysis to be C16H25NO2, which was two hydrogens more
than that of 1. The NMR spectra of 3 resembled those of 1 except for
the presence of an oxymethine signal instead of a carbonyl carbon
and an olefinic hydrogen signal that shifted to the higher field
relative to that of 1. This suggested that 3 was a dihydro derivative
16
H3C
Ha
8
b
H1b5
Hb
O
14
O
5
Hb
Ha
Ha
7
6
14
A
HO13
6
4
HO
12
13
N
3
N
1
a
1
11
D
9
c
HSQC and
1H-1H COSY
HMBC
NOESY
of 1. Extensive NMR analysis supported the a-orientation of a sec-
ondary hydroxy group at C-5, which was elucidated from the
NOESY correlation between H-5 and H-8b (Scheme 1). Oxidation of
Fig. 2. Selected 2D NMR data of lycopoclavamine-A (1).
3 with DesseMartin periodinane (DMP) afforded 1, whose

K. Katakawa et al. / Tetrahedron 67 (2011) 6561e6567
6563
Table 2
spectroscopic data were completely identical with those of the
natural product. Therefore, the structure of 3 was confirmed to be
13C NMR data of 5e8
dihydrolycopoclavamine-A.
Position
5
6
7
8
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
53.5
28.4
28.0
60.4
54.3
29.5
29.2
61.7
222.9 (br)
42.5
51.7
72.2
51.3
23.6
38.6
50.0
89.5
37.4
29.2
17.8
53.4
28.6
28.0
60.3
53.4
28.5
27.9
60.6
219.0
37.8
49.1
73.7
50.1
22.4
36.8
49.9
NOESY
H3C
H3C
HO
Ha
8
HbH
O
DMP
218.1
40.9
47.7
73.5
50.2
22.5
37.4
48.2
88.6
39.0
26.7
16.9
21.3
170.5
218.5
38.3
45.6
75.7
50.1
22.4
36.8
49.8
88.1
43.6
28.1
17.6
21.0
170.9
5
5
OH
HO
N
N
3
1
Scheme 1. Selected NOESY correlation of dihydrolycopoclavamine-A (3) and chemical
correlation of 3 and lycopoclavamine-A (1).
88 (br)
43.6
30.5
L. squarrosum was purchased at a flower market in Bangkok,
Thailand, and the alkaloid extract was obtained by following
a conventional procedure similar to that used for L. clavatum. The
alkaloid fraction was separated by column chromatography to af-
ford seven new alkaloids 4e10 together with fawcettimine (11) and
lycoflexine (12).6
17.8
CH3CO
CH3CO
analysis. NMR analysis (Table 2) indicated the presence of one
secondary acetoxy group (dH 2.11, 5.00; dC 21.3, 73.5, and 170.5)
besides the characteristic resonance for the fawcettimine-type
skeleton (eg. carbinolamine carbon resonated at dC 88.6) and im-
plied that 5 must be an acetoxy derivative of fawcettimine (11).
Extensive NMR analyses (particularly HMQC and 1He1H COSY) in-
dicated the presence of four fragment carbon chains [a:
eCH2CH2CH2CHe (C-1eC-4), b: eCH2CHCHe (C-6eC-8), c:
eCH2CH2CH2e (C-9eC-11), and d: eCH2CH(CH3)e (C-14eC-16)]
(Scheme 2). HMBC correlation between the secondary methyl hy-
drogen (dH 0.94, H3-16) and the oxymethine carbon (dC 73.5, C-8) as
well as HMBC correlations between the oxymethine hydrogen (dH
5.00, H-8) and the acetyl carbonyl carbon (dC 170.5) and between
the methylene hydrogen (dH 1.05, H-14) and the two quaternary
carbons [dC 48.2 (C-12) and 88.6 (C-13)] indicated that the acetoxy
Lycoposquarrosamine-A (4) was obtained as a colorless solid
and its molecular formula was established as C16H23NO3 by HREIMS
analysis, which was identical with that of 2. NMR data showed that
4 had a 3,4-didehydrofawcettidane skeleton with a trans-decahy-
droquinoline ring, one carbonyl group, and one secondary hydroxy
group, which was almost the same as that of 2 except for the
chemical shifts of the carbonyl and olefinic functions and the
presence of a secondary hydroxy group. Among them, the chemical
shift of the carbonyl carbon resonated at dC 212.6 (C-8), indicating
that this function did not constitute an a,b-unsaturated carbonyl
moiety present in 2. HMQC and 1He1H COSY analyses indicated the
presence of four partial structures [a: eCH2CH2CHe (C-1eC-3),
b: eCH(OH)CH2CHe (C-5eC-7), c: eCH2CH2CH2e (C-9eC-11), and
d: eCH2CH(CH3)e (C-14eC-16)] (Fig. 4). HMBC correlation between
the olefinic hydrogen [dH 5.87 (H-3)] located at the terminus of unit
a and the oxygenated methine carbon in unit b [dC 74.6 (C-5)] in-
dicated the presence of an allylic alcohol moiety. HMBC correlation
between the methyl hydrogen [dH 1.02 (H3-16)] and the ketonic
carbon [dC 212.6 (C-8)] as well as correlation between the central
methylene hydrogen in unit b [dH 1.61 (H-6)] and the same carbonyl
carbon implied that 4 had a carbonyl function at position 8. Fur-
thermore, the plane structure of 4 was elucidated by HMBC analysis
based on correlations H-3/C-12, H-9/C-13, H-11/C-4, H-11/C-7, and
group was located at C-8. The
a-orientation of the C-8 acetoxy
group was indicated from the enhancement of the signals for H-6
methylene hydrogens (dH 2.44, 2.33) by H-8 irradiation in the NOE
experiment. Thus, 5 was confirmed to be an 8a-acetoxy derivative
of fawcettimine, which was reported to be a synthetic intermediate
(acetylaposerratinine) in the literature,7 and this is the first iso-
lation from nature.
H-14/C-13. The b-orientation of the secondary hydroxy group was
H
O
elucidated from the NOE correlation H-5/H-7. The NOE correlation
between H-14b (dH 1.68) and H-15 (dH 3.11) as well as the large
coupling constant (13.2 Hz) between H-14a (dH 2.49) and H-15 in-
5
d
O 6
15
8
b
4
16
3
12
14
dicated the b-equatorial orientation of the C-16 methyl group. Thus,
N
O
a
11
4 was elucidated to be a 5-hydroxy-8-keto derivative of 1.
Compound 5 was obtained as a colorless amorphous solid and
its molecular formula was established as C18H27NO4 by HREIMS
HSQC and
1H-1H COSY
HMBC
9
c
O
5
NOE
16
H
CH3
O
O
6
15
H
O
H
O
d
H
H
OH
H
HO
8
O
14
O
Hb
14
b
5
7
7Ha
5
H
6
H
H
8
H
KOH
MeOH
H
H3C
H3C
H3C
13
H
HO
4
HO
12
N
N
O
O
N
N
3
H
11
a
9
O
c
5
6
HSQC and
1H-1H COSY
HMBC
NOE
Scheme 2. Selected NMR data of acetylaposerratinine (5) and chemical correlation of 5
and 8 -hydroxyfawcettimine (6).
a
Compound 6 was obtained as a colorless solid and its molecular
Fig. 4. Selected NMR data of lycoposquarrosamine-A (4).
formula was analyzed by HREIMS analysis to be C16H25NO3. 1H and

6564
K. Katakawa et al. / Tetrahedron 67 (2011) 6561e6567
13C NMR spectra resembled those of 5 except for the absence of an
acetoxy function and the existence of a higher-field-shifted oxy-
methine signal (dH 3.74, H-8). When 6 was dissolved in methanol-
d4, a methine signal ascribable to hydrogen at C-4 adjacent to the
carbonyl group disappeared and C-4 methine carbon was observed
as broad signal, which was caused by the protonedeuterium ex-
change. From the spectroscopic analysis, the structure of 6 was
deduced to be a deacetylated 5 and therefore, the hydrolysis of 5
was conducted. When 5 was treated with KOH/MeOH, a deacety-
lated product was obtained, the spectroscopic data of which were
completely identical with those of 6. Thus, 6 was elucidated to be
Compound 9 was obtained as a colorless amorphous solid and
its molecular formula was established as C19H27NO4 by HREIMS. 1H
and 13C NMR analysis implied the presence of two ketonic functions
[dC 216.1 (C-5) and 212.4 (C-13)] and one additional methylene
group [dH 3.18 and 2.62 (H2-17), dC 54.8 (C-17)], which indicated
that 9 had a lycoflexine-type skeleton. The NMR data of 9 well re-
sembled those of lycoposerramine-U (13),7 which was previously
isolated from L. serratum. In the 1H NMR spectra, 9 showed an acetyl
methyl signal (dH 2.13) and an oxymethine signal (dH 5.04, H-8) was
observed at a lower field than that of 13 (dH 3.86, H-8) (Scheme 4).
The same coupling pattern of the oxymethine signal in 9 and 13 (dd,
J¼2.4, 2.4 Hz) suggested that 9 was an acetylated 13. When 9 was
treated with KOH, the deacetylated derivative was obtained, the
spectroscopic properties, including the CD spectra, of which were
completely identical with those of 13. Thus, we concluded that 9
was acetyllycoposerramine-U.
8
a-hydroxyfawcettimine.
Compound 7 was obtained as a colorless solid. Its molecular
formula was established as C18H27NO4 by HREIMS analysis and was
identical with that of 5. Although the 1H and 13C NMR signals well
resembled those of 5, the coupling pattern of the oxymethine
resonance at dH 4.90 (dd, J¼10.7, 6.1 Hz, H-8) differed from that in 5
(dH 5.00, s). The plane structure was identical with that of 5, as
δH 5.04
δH 3.86
elucidated by extensive NMR analysis. The presence of three frag-
ments (aec) was inferred from 1H e 1H COSY and HMQC mea-
surements and the connectivities of the fragments were analyzed
from the results of HMBC (particularly H-6/C-5, H-9/C-13, H-11/C-7,
O
O
H
H
8
8
H
H
N
KOH
H3C
H3C
MeOH
O
17
O
O
O
H-11/C-12, and H-11/C-13) (Scheme 3). The
b-orientation of the
Ac
H
N
acetoxy function located at C-8 was elucidated based on the NOE
correlation between H-8 and H-11a. Thus, 7 was deduced to be 8b-
acetoxyfawcettimine.
9
lycoposerramine-U (13)
Scheme 4. Chemical correlation of acetyllycoposerramine-U (9) and lycoposerramine-
U (13).
O
H
O
Compound 10 was obtained as a colorless solid and its molecular
formula was elucidated by HRFABMS analysis to be C17H25NO3. The
NMR data of 10 and lycoflexine (12) very much resembled each
other except for the lower-field-shifted methylene signals around
nitrogen in 10. This fact, plus the mass spectral data, indicated that
10 was an N-oxide derivative of 12. To inspect this assumption, the
oxidation of 12 was examined (Scheme 5). When 12 was treated
with m-CPBA, an N-oxide derivative was obtained, the spectro-
scopic data of which were completely identical with those of 10.
Thus, 10 was elucidated to be lycoflexine N-oxide.
O
6
8 O
5
b
7
12
3
13
N
HSQC and
1H-1H COSY
HMBC
11
1
a
9
c
7
H3C
O
H
O
H
O
O
O
HO
O
16
H
H
O
O
H
H
8
8
KOH
H3C
H3C
H
H
H
N
H
N
MeOH
m-CPBA
N
N
H3C
H3C
Ha
11
O
O
7
8
NOE
lycoflexine (12)
10
O
Scheme 3. Selected NMR data of 8b-acetoxyfawcettimine (7) and chemical correlation
Scheme 5. Chemical conversion of lycoflexine (12) to lycoflexine N-oxide (10).
of 7 and 8 -hydroxyfawcettimine (8).
b
In conclusion, ten new fawcettimine-related alkaloids, i.e.,
lycopoclavamines (1e3), lycoposquarrosamine-A (4), and other
hydroxylated fawcettime derivatives (5e10), were isolated from
three species of Lycopodium (L. clavatum, L. serratum, and L. squar-
rosum). Lycopoclavamines (1e3) and lycoposquarrosamine-A (4)
are the second examples of fawcettimine-related alkaloids pos-
sessing a trans-decahydroquinoline ring system at the A/D-ring
Compound 8 was obtained as a colorless amorphous solid and
its molecular formula was analyzed by HREIMS analysis to be
C16H25NO5. 1H and 13C NMR data resembled those of 7 except for
the absence of the acetyl signal and the existence of a higher-field-
shifted oxymethine hydrogen signal (dH 3.71, H-8) compared to that
in 7 (dH 4.90). Intensive NMR analysis indicated that 8 had a faw-
cettimine skeleton that possessed a hydroxy group at C-8. NOE
correlation between the oxymethine hydrogen (H-8) and both H-11
junction as well as a b-oriented methyl group at C-15.
and H-14 indicated the C-8 hydroxy group must be
b-oriented.
Compound 7 was hydrolyzed with KOH/MeOH to give 8, which was
completely identical with the natural product. Thus, 8 was con-
3. Experimental
firmed to be 8
b
-hydroxyfawcettimine.
3.1. General experimental procedure
The absolute configurations of compounds 5e8 were identical
with that of fawcettimine (11), whose absolute configuration was
already established,4 based on comparison of the cotton curves in
the CD spectra.
1H and 13C NMR spectra: JEOL JNM ECP-600 at 600 MHz (1H) or
150 MHz (13C), JEOL JNM A-500 at 500 MHz (1H) or 125 MHz (13C),
and JEOL ECP-400 and JEOL JNM ECX-400 at 400 MHz (1H) or

K. Katakawa et al. / Tetrahedron 67 (2011) 6561e6567
6565
100 MHz (13C), respectively. EIMS and HREIMS: JEOL JMS-GC mate
and JEOL JMS-GC mate II (BU-25). FABMS: JEOL JMS-AX500.
HRFABMS: JEOL JMS-HX110. Optical rotation: JASCO P-1020 and
JASCO DIP-140. CD: JASCO J-720WI. TLC: Precoated silica gel 60 F254
plates (Merck, 0.25 mm thick), Precoated amino-silica gel plates
(Fuji Silysia Chemical), Aluminum oxide F254 (Merck, Type-E).
Column chromatography: Silica gel 60 (Merck, 70e230 mesh), Sil-
ica gel 60 N [Kanto Chemical, 40e50 mm (for flash chromatogra-
phy)], Chromatorex NH [Fuji Silysia Chemical, 100e200 mesh (for
amino-silica gel column chromatography)], Aluminum oxide 60
(Merck, 70e230 mesh).
(CDCl3, 100 MHz): see Table 1; EIMS m/z (%): 277 (Mþ, 100), 259
(36), 241 (41); HREIMS m/z 277.1680 (Mþ,
þ0.2 mmu).
D
3.4. Isolation of alkaloids from L. serratum
Alkaloid fraction E, which was prepared from L. serratum Thunb.
in the previous study,3f was purified over amino-silica gel using
50e100% CHCl3/n-hexane and then 1e10% MeOH/CHCl3 gradient to
give 3 (2.7 mg).
3.4.1. Dihydrolycopoclavamine-A (3). Colorless amorphous solid;
25
[a
]
þ34.7 (c 0.17, CHCl3); 1H NMR (CDCl3, 400 MHz): 5.94 (d, J
D
7.3 Hz, H-3), 4.55 (dd, J 7.8, 7.8 Hz, H-5), 3.68 (ddd, J 14.2, 14.2,
4.7 Hz, H-9), 3.50 (ddd, J 15.2, 13.0, 4.7 Hz, H-1), 2.88 (dd, J 15.1,
6.4 Hz, H-1), 2.71 (dd, J 14.2, 5.5 Hz, H-9), 2.67 (m, H-2), 2.14 (m, H-
11), 2.09 (m, H-2), 1.99 (m, H-15), 1.97 (m, H-14), 1.90 (m, H-7), 1.86
(m, H-10), 1.80 (2H, m, H2-6), 1.73 (m, H-11), 1.56 (m, H-8a), 1.47 (m,
H-10), 1.24 (m, H-14), 0.86 (3H, d, J 6.0 Hz, H3-16), 0.53 (ddd, J 12.5,
12.5, 12.5 Hz, H-8b); 13C NMR (CDCl3, 100 MHz): see Table 1; EIMS
3.2. Plant material
The club moss L. clavatum L. was collected in Toyama City,
Toyama Prefecture, Japan, and identified by one of the authors (M.
Arisawa). A voucher specimen was deposited at the Herbarium of
the Faculty of Pharmaceutical Sciences, International University of
Health and Welfare. The club moss L. squarrosum was purchased at
a flower market in Bangkok, Thailand. A voucher specimen was
deposited at the Herbarium of the Faculty of Pharmaceutical
Sciences, Chiba University.
m/z (%): 263 (Mþ, 100); HREIMS m/z 263.1885 (Mþ,
D 0 mmu).
3.4.2. DMP oxidation of compound 3. To a stirred solution of 3
(0.63 mg, 0.0024 mmol) in dry CH2Cl2 (0.2 mL) was added DMP
(1.2 mg, 0.0028 mmol) under argon atmosphere. After the reaction
mixture was stirred at room temperature for 1 h, it was poured into
saturated aqueous NaHCO3 and extracted with CHCl3. The combined
organic layer was dried over MgSO4 and evaporated. The residuewas
purified by silica gel column chromatography (0e15% MeOH/CHCl3)
to give semi-synthetic 1 (0.59 mg, 94%). All the spectroscopic data
3.3. Extraction and isolation of alkaloids from L. clavatum
The air-dried L. clavatum (219 g) was extracted with MeOH (1 L)
six times and the extracts were filtered. The combined filtrates
were concentrated under reduced pressure to give the crude ex-
tract (58.1 g), which was then suspended in 2% tartaric acid and
filtered. The aqueous filtrate was washed with AcOEt, rendered
basic with NaHCO3 (pH 9), and then exhaustively extracted with 5%
MeOH/CHCl3 (300 mL) five times. The organic layer was dried over
MgSO4 and evaporated to give the crude alkaloid fraction (1.03 g).
The crude alkaloid fraction was separated by silica gel flash column
chromatography using MeOH/CHCl3 (0e30%) gradient, MeOH/
CHCl3/aqueous ammonia (28%)¼4:7:1, and then MeOH to give five
fractions (AeE). The 5% MeOH/CHCl3 eluate (fraction C) was puri-
fied over amino-silica gel using CHCl3/n-hexane gradient (10e60%)
to give 1 (2.0 mg). The 15e30% MeOH/CHCl3 and MeOH/CHCl3/
aqueous ammonia (28%)¼4:7:1 eluate (fraction E) was rechroma-
tographed on silica gel using MeOH/AcOEt/aqueous ammonia
(28%)¼10:90:0 to 20:80:1 to give 2 (0.8 mg).
(1Hand 13C NMR, [
a]D, andMS) wereidentical withthoseof natural 1.
3.5. Isolation of alkaloids from L. squarrosum
The air-dried L. squarrosum (1.65 kg) was extracted with MeOH
(10 L) four times and the extracts were filtered. The combined fil-
trates were concentrated under reduced pressure to give the crude
extract (394 g), and the alkaloid extract (2.31 g) was obtained by
following a conventional procedure that was similar to the case of L.
clavatum. The crude alkaloid fraction was separated by silica gel
flash column chromatography using MeOH/CHCl3 (0e30%) gradi-
ent, 30% MeOH/CHCl3 saturated with ammonia, and then MeOH to
give six fractions (AeF). The 5e10% MeOH/CHCl3 eluate (fraction B)
was purified over silica gel using 8% MeOH/CHCl3 to give 9
(29.2 mg). The 15% MeOH/CHCl3 eluate (fraction C) was purified
over silica gel using 0e25% MeOH/AcOEt gradient to give six frac-
tions (C1eC6). The 8% MeOH/AcOEt eluate (fraction C4) was puri-
fied over amino-silica gel using 50e100% CHCl3/n-hexane to give 7
(3.2 mg). The 5e25% MeOH/AcOEt eluate (fraction C5) was purified
over silica gel using 3e20% CHCl3/n-hexane to give 5 (59.5 mg). The
20e30% MeOH/CHCl3 eluate (fraction D) was purified over silica gel
using 0e25% MeOH/AcOEt gradient to give seven fractions (D1eD7).
The 8% MeOH/AcOEt eluate (fraction D3) was purified over alumi-
num oxide using 0e100% CHCl3/n-hexane to give 4 (58.0 mg). The
MeOH eluate (fraction F) was purified over silica gel using 0e100%
MeOH/AcOEt gradient to give five fractions (F1eF5). The 50e70%
MeOH/AcOEt eluate (F4) was rechromatographed over amino-silica
gel using 80e100% CHCl3/n-hexane and then 1e10% MeOH/CHCl3 to
give seven sub-fractions. The 0e2% MeOH/CHCl3 eluate (F4E) was
purified over silica gel using 1e5% MeOH/CHCl3 saturated with
ammonia to give 6 (9.9 mg). The 2e5% MeOH/CHCl3 eluate (F4F) was
purified over silica gel using 0e20% MeOH/AcOEt to give 8 (5.9 mg).
The MeOH eluate (F5) was purified over silica gel using 10e50%
MeOH/CHCl3 saturated with ammonia to give 10 (6.1 mg).
25
3.3.1. Lycopoclavamine-A (1). Colorless amorphous solid; [a]
D
ꢀ48.8 (c 0.11, CHCl3); IR (CHCl3) nmax 1642, 1715 cmꢀ1
;
1H NMR
(CDCl3, 400 MHz): 6.91 (dd, J 7.4, 2.3 Hz, H-3), 3.73 (ddd, J 14.0, 14.0,
4.4 Hz, H-9), 3.52 (ddd, J 15.7, 11.8, 4.2 Hz, H-1a), 2.93 (dd, J 15.6,
6.9 Hz, H-1b), 2.78 (m, H-2), 2.72 (dd, J 14.2, 5.5 Hz, H-9), 2.55 (dd, J
17.6, 6.6 Hz, H-6a), 2.28 (m, H-2), 2.25 (m, H-11), 2.10 (m, H-15), 2.08
(m, H-7),1.91 (dd, J 12.1,12.1 Hz, H-14a),1.90 (d, J 17.9 Hz, H-6b),1.67
(2H, m, H-8a and 10),1.57 (m, H-11), 1.49 (m, H-10),1.30 (ddd, J 12.7,
2.4, 2.4 Hz, H-14b), 0.87 (3H, d, J 6.9 Hz, H3-16), 0.55 (ddd, J 13.7,12.4,
12.4 Hz, H-8b); 13C NMR (CDCl3,100 MHz):see Table 1; EIMSm/z (%):
261 (Mþ, 100), 243 (24); HREIMS m/z 261.1734 (Mþ,
D
þ0.5 mmu).
25
3.3.2. Lycopoclavamine-B (2). Colorless amorphous solid; [a]
D
ꢀ13.9 (c 0.06, CHCl3); IR (CHCl3) nmax 1645, 1718 cmꢀ1
;
1H NMR
(CDCl3, 400 MHz): 6.93 (dd, J 7.6, 2.1 Hz, H-3), 3.73 (ddd, J 13.8, 13.8,
4.4 Hz, H-9), 3.51 (ddd, J 16.3, 11.8, 4.5 Hz, H-1a), 2.96 (dd, J 15.4,
6.7 Hz, H-1b), 2.79 (m, H-2), 2.70 (dd, J 14.2, 5.5 Hz, H-9), 2.60 (dd, J
17.4, 6.4 Hz, H-6a), 2.51 (d, J 12.8 Hz, H-14a), 2.32 (m, H-2), 2.26 (m,
H-11), 2.13 (m, H-7), 1.93 (d, J 17.9 Hz, H-6b), 1.77 (ddd, J 13.5, 5.3,
2.5 Hz, H-8a), 1.67 (m, H-10), 1.56 (m, H-11), 1.52 (2H, m, H-10 and
14b), 1.49 (3H, s, H3-16), 1.10 (dd, J 13.3, 13.3 Hz, H-8b); 13C NMR
3.5.1. Lycoposquarrosamine-A (4). Colorless solid; CD (0.42 mM,
MeOH, 24 ꢁC)
l
nm (D3): 317 (0), 268 (þ0.6), 263 (0), 239 (þ1.0),

6566
K. Katakawa et al. / Tetrahedron 67 (2011) 6561e6567
222 (0), 227 (ꢀ0.9); 1H NMR (CDCl3, 600 MHz): 5.87 (d, J 7.7 Hz,
H-3), 4.30 (dd, J 8.3, 8.3 Hz, H-5), 3.72 (ddd, J 14.0, 14.0, 4.4 Hz, H-9),
3.41 (m, H-1), 3.11 (ddddd, J 13.2, 6.6, 6.6, 6.6, 5.2 Hz, H-15), 2.92
(dd, J 15.4, 6.0 Hz, H-1), 2.85 (dd, J 12.9, 8.0 Hz, H-6), 2.78 (dd, J 14.0,
5.5 Hz, H-9), 2.70 (m, H-2), 2.50 (d, J 6.9 Hz, H-7), 2.49 (dd, J 13.2,
13.2 Hz, H-14a), 2.41 (ddd, J 12.8, 4.4, 4.4 Hz, H-11), 2.07 (br ddd, J
18.1, 7.6, 4.8 Hz, H-2), 1.87 (m, H-10), 1.81 (m, H-11), 1.68 (dd, J 12.9,
5.2 Hz, H-14b), 1.61 (ddd, J 15.4, 8.5, 7.1 Hz, H-6), 1.51 (m, H-10), 1.02
(3H, d, J 6.6 Hz, H3-16); 13C NMR (CDCl3, 150 MHz): see Table 1;
EIMS m/z (%): 277 (Mþ, 100), 259 (55), 160 (39); HREIMS m/z
(m, H-10), 1.82 (m, H-2), 1.62 (br dd, J 14.0, 5.2 Hz, H-11), 1.45 (br d, J
13.7 Hz, H-10), 1.23 (dd, J 14.3, 3.4 Hz, H-14), 1.05 (3H, d, J 6.4 Hz,
H3-16); 13C NMR (CDCl3, 125 MHz): see Table 2; EIMS m/z (%): 279
(Mþ, 100), 261 (30), 236 (28), 193 (58), 151 (56), 123 (45), 70 (42);
HREIMS: m/z 279.1834 (Mþ,
D 0 mmu).
3.5.7. Hydrolysis of compound 7. To a stirred solution of 7 (1.3 mg,
0.0041 mmol) in MeOH (0.2 mL) was added aqueous 1 M KOH
(0.1 mL). After the reaction mixture was stirred at room temperature
for14.5 h, itwasdilutedwithwaterandthewholewasextractedwith
CHCl3. The combined organic layer was dried over Na2SO4 and
evaporated. The residue was purified by silica gel column chroma-
tography (MeOH/CHCl3/28% aqueous ammonia¼10:90:1 to 20:80:1)
to give semi-synthetic 8 (1.2 mg, quant.). All the spectroscopic data
(1H and 13C NMR and MS) were identical with those of natural 8.
277.1687 (Mþ,
D
þ0.9 mmu).
3.5.2. Acetylaposerratinine (5). Colorless amorphous solid; CD
(0.42 mM, MeOH, 24 ꢁC)
l
nm (D3): 334 (0), 289 (þ2.3), 243 (0); 1H
NMR (CDCl3, 500 MHz): 5.00 (s, H-8), 3.43 (ddd, J 14.6, 8.5, 4.3 Hz,
H-1), 3.26 (ddd, J 14.0, 14.0, 3.7 Hz, H-9), 2.88 (br dd, J 14.3, 4.6 Hz,
H-9), 2.71 (m, H-1), 2.53 (m, H-14), 2.48 (m, H-11), 2.44 (2H, m, H-6
and 15), 2.33 (dd, J 17.7, 8.9 Hz, H-6), 2.18 (m, H-3), 2.11 (3H, s,
H3-18), 2.06 (3H, m, H-3, 4, and 7), 1.92 (br s, H-2), 1.85 (m, H-2 and
10), 1.49 (dd, J 14.0, 4.9 Hz, H-11), 1.42 (br d, J 14.0 Hz, H-10), 1.05
(dd, J 13.4, 2.7 Hz, H-14), 0.94 (3H, d, J 6.7 Hz, H3-16); 13C NMR
(CDCl3, 150 MHz): see Table 2; EIMS m/z (%): 321 (Mþ, 100), 262
3.5.8. Acetyllycoposerramine-U (9). Colorless amorphous solid; CD
(0.20 mM, MeOH, 24 ꢁC)
l
nm (D3): 328 (0), 307 (ꢀ1.7), 281 (0), 243
(þ3.1), 208 (0); 1H NMR (CDCl3, 500 MHz): 5.04 (dd, J 2.4, 2.4 Hz, H-
8), 3.18 (br dd, J 14.3, 1.8 Hz, H-17), 3.07 (m, H-9), 2.94 (ddd, J 14.0,
14.0, 4.0 Hz, H-1), 2.89 (br d, J 4.0 Hz, H-1), 2.85 (m, H-9), 2.81 (ddd,
J 9.8, 9.8, 2.7 Hz, H-7), 2.62 (3H, m, H-6, 14, and 17), 2.33 (m, H-15),
2.28 (2H, m, H-11 and 14), 2.15 (3H, m, H-3, 10, and 11), 2.13 (3H, s,
H3-19), 2.06 (m, H-6), 1.99 (ddd, J 14.0, 14.0, 4.6 Hz, H-3), 1.82 (m,
(29), 123 (98); HREIMS m/z 321.1929 (Mþ,
D
ꢀ1.1 mmu).
3.5.3. Hydrolysis of compound 5. To a stirred solution of 5 (1.8 mg,
0.0056 mmol) in MeOH (0.2 mL) was added aqueous 1 M KOH
(0.1 mL). After the reaction mixture was stirred at room tempera-
ture for 6.5 h, it was diluted with water and extracted with CHCl3.
The combined organic layer was dried over Na2SO4, and evapo-
rated. The residue was purified by silica gel column chromatogra-
phy (MeOH/CHCl3/28% aqueous ammonia¼10:90:1 to 20:80:1) to
give semi-synthetic 6 (0.7 mg, 45%). All the spectroscopic data (1H
and 13C NMR and MS) were identical with those of natural 6.
H-2), 1.74 (m, H-10), 1.35 (m, H-2), 1.00 (3H, d, J 6.4 Hz, H3-16); 13
C
NMR (CDCl3, 125 MHz): 216.1 (C-5), 212.4 (C-13), 170.3 (C-18), 73.9
(C-8), 59.3 (C-12), 58.3 (C-4), 56.9 (C-9), 54.8 (C-17), 52.8 (C-1), 44.3
(C-7), 42.8 (C-14), 39.4 (C-11), 39.3 (C-6), 30.0 (C-15), 28.2 (C-3),
27.2 (C-10), 21.1 (C-19), 19.3 (C-2), 17.6 (C-16); FABMS (NBA): m/z
334 (MHþ); HRFABMS: m/z 333.1941 (Mþ,
D
ꢀ0.1 mmu).
3.5.9. Hydrolysis of compound 9. To a stirred solution of 9 (1.7 mg,
0.0051 mmol) in MeOH (0.5 mL) was added aqueous 1 M KOH
(0.1 mL). After the reaction mixture was stirred at room tempera-
ture for 1 h, it was evaporated to dryness. The residue was purified
by silica gel column chromatography (0e10% MeOH/CHCl3) to give
semi-synthetic 13 (1.5 mg, quant.). All the spectroscopic data (1H
and 13C NMR, CD, and MS) were identical with those of natural 13.
3.5.4. 8
a-Hydroxyfawcettimine (6). Colorless solid; CD (0.39 mM,
MeOH, 24 ꢁC)
l
nm (D3): 320 (0), 286 (þ3.0), 243 (0); 1H NMR
(CD3OD, 500 MHz) 3.74 (s, H-8), 3.45 (ddd, J 13.7, 8.9, 4.3 Hz, H-1),
3.22 (ddd, J 14.0,14.0, 4.0 Hz, H-9), 2.84 (dd, J 14.6, 4.9 Hz, H-9), 2.78
(ddd, J 15.0, 15.0, 6.4 Hz, H-11a), 2.67 (ddd, J 14.3, 4.9, 4.9 Hz, H-1),
2.47 (dd, J 12.8,12.8 Hz, H-14), 2.37 (dd, J 17.4,13.7 Hz, H-6), 2.27 (m,
H-15), 2.14 (2H, m, H-3 and 6), 2.08 (m, H-7), 2.02 (m, H-3), 1.93 (m,
H-2), 1.89 (m, H-10), 1.83 (m, H-2), 1.52 (br dd, J 14.3, 4.9 Hz, H-11b),
1.40 (br d, J 13.8 Hz, H-10), 1.04 (dd, J 13.7, 3.4 Hz, H-14), 1.04 (3H, d,
J 7.0 Hz, H3-16); 13C NMR (CD3OD, 125 MHz): see Table 2; EIMS m/z
(%): 279 (Mþ, 100), 221 (38), 193 (35), 152 (38), 83 (75); HREIMS: m/
3.5.10. Lycoflexine N-oxide (10). Colorless solid; CD (0.57 mM,
MeOH, 24 ꢁC)
l
nm (D3): 344 (0), 302 (þ2.1), 244 (þ0.2), 238 (þ0.4),
220 (0), 202 (ꢀ1.5); 1H NMR (CDCl3, 500 MHz): 3.70 (4H, m, H-1, 9, 9,
and17), 3.09(ddd,J13.1,13.1,3.4 Hz,H-1), 3.04(d,J14.0 Hz,H-17), 2.69
(m, H-7), 2.40 (dd, J 18.3, 7.9 Hz, H-6), 2.34 (2H, m, H2-14), 2.25 (3H, m,
H-2, 6, and 10), 2.17 (4H, m, H-3,11,11, and 15), 2.08 (m, H-3),1.99 (m,
H-2), 1.93 (m, H-10), 1.90 (m, H-8), 1.73 (ddd, J 14.6,12.5, 4.6 Hz, H-8),
1.07 (3H, d, J 6.4 Hz, H3-16); 13C NMR (CDCl3, 125 MHz): 213.1 (C-5),
211.8 (C-13), 75.2 (C-9), 70.7 (C-1), 68.1 (C-17), 60.1 (C-12), 57.6 (C-4),
46.8 (C-14), 41.3 (C-7), 39.6 (C-6), 34.2 (C-11), 30.8 (C-8), 28.2 (C-15),
27.0 (C-10), 22.0 (C-2), 21.9 (C-16), 21.2 (C-3); FABMS (NBA): m/z 292
z 279.1833 (Mþ,
D
ꢀ0.1 mmu).
3.5.5. 8
b-Acetoxyfawcettimine (7). Colorless solid; CD (0.36 mM,
MeOH, 24 ꢁC)
l
nm (D3): 334 (0), 289 (þ2.3), 243 (0); 1H NMR (CDCl3,
500 MHz): 4.90 (dd, J 10.7, 6.1 Hz, H-8), 3.42 (ddd, J 14.6, 8.9, 4.0 Hz,
H-1), 3.22 (ddd, J 14.0,14.0, 4.3 Hz, H-9), 2.89 (dd, J 14.6, 5.5 Hz, H-9),
2.72 (m, H-1), 2.68 (dd, J 18.3,13.4 Hz, H-6), 2.35 (3H, m, H-7,14, and
15), 2.29 (ddd, J 14.1, 14.1, 6.0 Hz, H-11), 2.19 (m, H-3), 2.07 (3H, m,
H-3, 4, and 6), 2.05 (3H, s, H3-18),1.91 (2H, m, H-2 and 10),1.82 (m, H-
2),1.62 (dd, J 14.3, 5.5 Hz, H-11),1.48 (brd, J 14.3 Hz, H-10),1.29(brd, J
11.0 Hz, H-14), 0.94 (3H, d, J 5.8 Hz, H3-16); 13C NMR (CDCl3,
125 MHz): see Table 2; EIMS m/z (%): 321 (Mþ, 100), 262 (39), 123
(MHþ); HRFABMS (NBA/PEG): m/z 292.1931 (MHþ,
D
þ1.8 mmu).
3.5.11. m-CPBA oxidation of lycoflexine (12). To a stirred solution of
12 (3.4 mg, 0.0124 mmol) in dry CH2Cl2 (0.6 mL) was added
m-CPBA (77%, 3.3 mg, 0.0147 mmol) under argon atmosphere. After
the reaction mixture was stirred at 0 ꢁC for 1 h, it was directly
subjected to aluminum oxide column chromatography (0e20%
MeOH/CHCl3) to give semi-synthetic 10 (2.5 mg, 69%). All the
spectroscopic data (1H and 13C NMR, CD, and MS) were identical
with those of natural 10.
(61), 83 (72); HREIMS m/z 321.1949 (Mþ,
D
þ0.9 mmu).
3.5.6. 8
b-Hydroxyfawcettimine (8). Colorless amorphous solid; CD
(0.41 mM, MeOH, 24 ꢁC)
l
nm (D3): 323 (0), 286 (þ2.4), 244 (0); 1H
NMR (CDCl3, 500 MHz): 3.71 (dd, J 10.1, 5.2 Hz, H-8), 3.41 (ddd, J
14.6, 9.2, 4.3 Hz, H-1), 3.20 (ddd, J 14.7, 14.7, 3.9 Hz, H-9), 2.87 (dd, J
14.9, 5.2 Hz, H-9), 2.69 (ddd, J 14.6, 6.4, 4.3 Hz, H-1), 2.64 (dd, J 16.5,
15.9 Hz, H-6), 2.43 (dd, J 14.0, 12.5 Hz, H-14), 2.22 (4H, m, H-3, 6, 7,
and 11), 2.14 (m, H-15), 2.07 (2H, m, H-3 and 4), 1.94 (m, H-2), 1.89
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific
Research from the Japan Society for the Promotion of Science, the
Takeda Science Foundation, and The Uehara Memorial Foundation.

K. Katakawa et al. / Tetrahedron 67 (2011) 6561e6567
6567
92, 445; (e) Nishikawa, Y.; Kitajima, M.; Takayama, H. Org. Lett. 2008, 10, 1987; (f)
Shigeyama, T.; Katakawa, K.; Kogure, N.; Kitajima, M.; Takayama, H. Org. Lett. 2007,
9, 4069; (g) Katakawa, K.; Nozoe, A.; Kogure, N.; Kitajima, M.; Hosokawa, M.; Ta-
kayama, H. J. Nat. Prod. 2007, 70, 1024 and references cited therein; (h) Katakawa,
K.; Kitajima, M.; Yamaguchi, K.; Takayama, H. Heterocycles 2006, 69, 223.
4. (a) Jung, M. E.; Chang, J. J. Org. Lett. 2010, 12, 2962 and references cited therein;
(b) Inubushi, Y.; Harayama, T. Chem. Pharm. Bull. 1981, 29, 3418.
5. Kubota, T.; Sunaura, T.; Morita, H.; Mikami, Y.; Hoshino, T.; Obara, Y.; Nakahata,
References and notes
1. For recent reviews, see: (a) Kitajima, M.; Takayama, H. Lycopodium alkaloids:
isolation and asymmetric synthesis In Topics in Current Chemistry; Knolker, H.-J.,
€
Ed.; Springer: Berlin, Heidelberg, 2011, doi:10.1007/128_2011_126; (b) Hirasawa,
Y; Kobayashi, J.; Morita, H. Heterocycles 2009, 77, 679; (c) Kobayashi, J.; Morita, H.
In The Alkaloids; Cordell, G. A., Ed.; Academic: New York, NY, 2005; Vol. 61, p 1;
(d) Ma, X.; Gang, D. R. Nat. Prod. Rep. 2004, 21, 752.
2. Malkova, L.; Kozikowski, A. P.; Gale, K. Neuropharmacology 2011, 60, 1262.
3. (a) Nakayama, A.; Kogure, N.; Kitajima, M.; Takayama, H. Org. Lett. 2009, 11, 5554;
(b) Tanaka, T.; Kogure, N.; Kitajima, M.; Takayama, H. J. Org. Chem. 2009, 74, 8675;
(c) Nishikawa, Y.; Kitajima, M.; Kogure, N.; Takayama, H. Tetrahedron 2009, 65,
1608; (d) Katakawa, K.; Nozoe, A.; Kitajima, M.; Takayama, H. Helv. Chim. Acta 2009,
N.; Kobayashi, J. Heterocycles 2006, 69, 469.
6. (a) Ramharter, J.; Weinstabl, H.; Mulzer, J. J. Am. Chem. Soc. 2010, 132, 14338; (b)
Ayer, W. A.; Fukazawa, Y.; Singer, P. P.; Altenkirk, B. Tetrahedron Lett. 1973, 5045.
7. Takayama, H.; Katakawa, K.; Kitajima, M.; Yamaguchi, K.; Aimi, N. Tetrahedron
Lett. 2002, 43, 8307.