New syntheses of rac-Huperzine A and its rac-7-ethyl-derivative. Evaluation of several Huperzine A analogues as acetylcholinesterase inhibitors

Article abstract of DOI:10.1016/S0040-4020(00)00363-X

rac-Huperzine A, its rac-7-ethyl-derivative and two regioisomeric analogue have been prepared though synthetic sequences involving the elaboration of the pyridisne ring in a late stage, by reaction of an intermidiate pyrrolidine enamine with propiolamide, which gave mixtures of regioisomeric pyridone derivatives. The acetylcholinesterase inhibitory activity of these and two other recently described 11-unsubstituted huperzine A analogues was determined, the rac-7-ethyl analogue of huperzine A being the most active compound, although it is about 12-fold less active than (-)- huperzine A. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00363-X

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 4541±4553
New Syntheses of rac-Huperzine A and its rac-7-Ethyl-Derivative.
Evaluation of Several Huperzine A Analogues as
Acetylcholinesterase Inhibitors
a
a
a
a
Pelayo Camps,a, Joan Contreras, Rachid El Achab, Jordi Morral, Diego Munoz-Torrero,
*
Ä
Merce Font-Bardia, Xavier Solans, Albert Badia and Nuria M. Vivas
b
b
c
c
Á
a
 Á Á
Laboratori de Quõmica Farmaceutica, Facultat de Farmacia, Universitat de Barcelona, Av. Diagonal 643; E-08028 Barcelona, Spain
b
Á
Departament de Cristal.logra®a, Mineralogia i Diposits Minerals, Facultat de Geologia,
Â
Universitat de Barcelona, Av. Martõ Franques s/n; E-08028 Barcelona, Spain
c
Á
Á
Departament de Farmacologia i Terapeutica, Facultat de Medicina,
Á
Universitat Autonoma de Barcelona; E-08193 Bellaterra, Barcelona, Spain
Received 6 March 2000; revised 3 April 2000; accepted 20 April 2000
AbstractÐrac-Huperzine A, its rac-7-ethyl-derivative and two regioisomeric analogues have been prepared through synthetic sequences
involving the elaboration of the pyridone ring in a late stage, by reaction of an intermediate pyrrolidine enamine with propiolamide, which
gave mixtures of regioisomeric pyridone derivatives. The acetylcholinesterase inhibitory activity of these and two other recently described
11-unsubstituted huperzine A analogues was determined, the rac-7-ethyl analogue of huperzine A being the most active compound, although
it is about 12-fold less active than (2)-huperzine A. q 2000 Elsevier Science Ltd. All rights reserved.
Cholinergic neurotransmission is specially affected in
patients with Alzheimer's disease.1±5 Experimental
evidence has shown that inhibitors of acetylcholinesterase
(AChE) might elevate levels of acetylcholine in the brains
of these patients and reverse the cognitive decline.6±8 The
®rst, and thus far the only, two drugs approved in the USA
for the treatment of the cognitive de®cit in Alzheimer's
disease, i.e. tacrine, 3 (Cognexw) and donepezil (Ariceptw),
are both reversible inhibitors of AChE. (2)-Huperzine A
(1), a lycopodium alkaloid isolated from the club moss
Huperzia serrata (Thunb.) Trev.ˆLycopodium serratum
Thunb. and a Chinese traditional medicine,9±12 is another
potent and selective reversible inhibitor of AChE, which
appears to be superior to other AChE inhibitors such as
tacrine, physostigmine or galanthamine, because of its
comparatively longer duration of action and higher
therapeutic index13 (Fig. 1).
2-fold more potent than tacrine, being selected as the lead
compound of a more restricted series. Recently we have
published the synthesis, pharmacological evaluation, and
molecular modeling, of new potent huperzine A-tacrine
hybrid compounds resulting from the modi®cation of the
parent structure 5.15 The more active hybrid compounds of
the new series contain a 9-ethyl group and a 3-¯uorine atom,
or still better a 3-chlorine atom (6)16 (Fig. 1).
When we started this work, we did not have the molecular
modeling information and we assumed that our hybrid
Some time ago, we published the synthesis and pharmaco-
logical evaluation of a series of huperzine A-tacrine hybrid
compounds.14 The sole compound of the series which incor-
porated the ethylidene group characteristic of huperzine A
(4) was 2.5-fold less potent than tacrine as AChE inhibitor,
while compound 5, lacking the ethylidene substituent, was
Keywords: biologically active compounds; polycyclic heterocyclic
compounds; pyridones; acetylcholinesterase inhibitory activity.
* Corresponding author. Tel.: 134-93402-4536; fax: 134-93403-5941;
e-mail: camps@farmacia.far.ub.es
Figure 1. Structures of several acetylcholinesterase inhibitors.
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00363-X

4542
P. Camps et al. / Tetrahedron 56 (2000) 4541±4553
Scheme 1. Synthesis of rac-huperzine A, 1, its rac-7-ethyl-derivative, 2, and their regioisomers 20a and 20b.
compounds were placed in the active site of AChE in a
similar environment to that of huperzine A in such a way
that their carbobicyclic substructures would occupy roughly
the same position and that the 4-aminoquinoline sub-
structure of the hybrid compounds would partly occupy
the same position of the 2-pyridone subunit of huperzine
A. Taking into account the pharmacological data of the
hybrid compounds, we planned the synthesis of two huper-
zine A analogues, which could be more active than huper-
zine A: one of them lacking the ethylidene substituent at
position 11 (7) (Fig. 1) and the other one having a 7-ethyl
instead of a 7-methyl group (2). Although compound 2 was
protected in a patent17 and it has been recently cited,18 to the
best of our knowledge, its synthesis and activity data have
not been published yet.
analogues of huperzine A by elaboration of the heterocyclic
ring from the ketone functionality of 17a followed by depro-
tection of the bridgehead amino group.
When we had prepared keto acid 16a, precursor of 17a,
Kozikowski et al. published the synthesis of a 2-amino-
thiazole analogue of huperzine A from keto carbamate
17a.19 They had prepared the last compound through a
synthetic sequence parallel to the one we were developing.
This fact prompted us to publish our improved conversion of
keto ester 10 into the bicyclic compound 14a,20 the only part
of our synthetic sequence that was somewhat different from
the published one. Worthy of note, the attempted conversion
of 17a to the 2-aminothiazole analogue of huperzine A by
Kozikowski's group did not give the desired product but a
regioisomeric derivative, in which ring closure had taken
place from the less hindered a-carbonyl position.19
Our initial work on the synthesis of new analogues of huper-
zine A had been directed to the preparation of analogues
modi®ed at the heterocyclic moiety. At that moment, all the
described syntheses of huperzine A and its analogues started
from compounds containing a protected 2-pyridone ring.
We envisioned a route to a common advanced intermediate,
such as keto carbamate 17a (Scheme 1), from which we
could gain easy access to different modi®ed heterocyclic
In spite of the above discouraging results, we completed the
conversion of 17a to rac-huperzine A and applied the new
methodology to the synthesis of the rac-7-ethyl-derivative
of huperzine A, 2, which is herein described. The synthesis
of the 11-deethylidene analogue 7 and its regioisomer 8
(Fig. 1) using a similar methodology, has been recently

P. Camps et al. / Tetrahedron 56 (2000) 4541±4553
4543
b-lactone, followed by silica gel-promoted stereospeci®c
[212]-retrocycloaddition of this b-lactone with evolution
of CO2.22 However, treatment of 14a with the enolate
derived from S-phenyl thiopropionate did not lead to the
desired b-lactone, but to a product of retro-Dieckmann
reaction, 22, as a diastereomeric mixture, which was
isolated in 69% yield after column chromatography
(Scheme 2).
Elaboration of the pyridone ring from keto carbamate 17a
was carried out by using a modi®cation of a procedure
described by Kozikowski et al.23 Reaction of 17a with
Ê
pyrrolidine in re¯uxing benzene in the presence of 4 A
molecular sieves, gave the corresponding enamine, for
which Kozikowski's group had established an anti-arrange-
ment for the endocyclic CvC double bonds.19 Reaction of
this enamine with freshly prepared propiolamide (from
ethyl propiolate and concentrated ammonium hydroxide)24
in benzene under re¯ux afforded a mixture of regioisomeric
pyridones 18a and 19a, in which the ®rst one was the major
regioisomer. These pyridones were ef®ciently separated by
column chromatography through silica gel, a signi®cant
amount of starting 17a (32%) being recovered (40% yield
of 18a and 26% yield of 19a, taking into account the
recovered starting keto carbamate). Pyridone 18a is a
known product which had been obtained in low yield by
Kozikowski's group as a by-product in the ®rst synthesis
of huperzine A,25,26 while 19a is a new product, which was
fully characterized through its spectroscopic data and
elemental analysis.
Scheme 2. Attempted stereoselective synthesis of (E)-15a from 14a via 21.
i) S-phenyl thiopropionate, LDA, THF, 2788C, 30 min; ii) 14a, THF
2788C, 30 min, then 1.5 h from 278 to 08C; 69% yield of 22 as a 55:45
diastereomeric mixture.
published.21 Also, we report herein the AChE inhibitory
activity of all of the different huperzine A analogues
prepared in our group.
Results and Discussion
Keto carbamate 17a was obtained in 22% overall yield from
commercially available 1,4-cyclohexanedione monoethyl-
ene ketal, 9 (Scheme 1) as described by Kozikowski et
al.,19 except for the conversion of the stereoisomeric
mixture of alcohols 11a and 12a to compound 14a, which
was carried out as previously described by our group.20
Cleavage of the methyl carbamate function of 18a was
carried out by reaction with lithium 1-propanethiolate in
hexamethylphosphoric triamide (HMPA),27 obtaining
huperzine A, 1, in 66% yield, after twofold column chro-
matography. According to our experience in a related
case,21 the cleavage of the carbamate group of 19a was
not attempted under the above conditions and was carried
out directly by reaction with trimethylsilyl iodide (TMSI)
followed by reaction with MeOH under re¯ux,28 obtaining
in quantitative yield the new huperzine A analogue 20a,
resulting from the hydrolysis of the carbamate function
and the HI-promoted isomerization of the endocyclic
Although compound (E)-15a had been obtained in high
yield and high diastereomeric purity from 14a by Wittig
ole®nation to a 85:15 mixture of (Z)-15a and (E)-15a,
followed by isomerization of the exocyclic CvC double
bond, alternatively we attempted the stereoselective con-
version of 14a to (E)-15a, through a two-step protocol
that had been successfully used for this purpose in the
synthesis of other huperzine A analogues. This involved
the diastereoselective formation of an intermediate
Figure 2. Crystal structure (ORTEP) of alcohol 13b.

4544
P. Camps et al. / Tetrahedron 56 (2000) 4541±4553
Table 1. AChE inhibitory activity of (2)-huperzine A and its analogues 2,
7, 8, 20a, and 20b. Values are expressed as mean^standard error of the
mean of at least four experiments. IC50, 50% inhibitory concentration of
AChE (from bovine erithrocytes) activity
Wittig reaction of 14b with ethylidenetriphenylphosphorane
afforded a mixture of (Z)-15b and (E)-15b in the approxi-
mate ratio of 85:15, in 89% yield. Different attempts to
obtain pure (Z)-15b by column chromatography or by
distillation were fruitless. However, we could obtain pure
(Z)-15b by preferential saponi®cation of (E)-15b from the
above mixture by using excess of aqueous NaOH in a 1:1
mixture of tetrahydrofuran (THF) and methanol (MeOH).
Compound
IC50 (mM)
Tacrine, 3
(2)-Huperzine A, (2)-1
2
7
8
0.130^0.010
0.074^0.0055
0.870^0.081
9.05^0.40
.100
Isomerization of the mixture of (Z)-15b and (E)-15b in the
approximate ratio of 85:15 by reaction with thiophenol cata-
lyzed by azobisisobutyronitrile (AIBN) afforded in good
yield a mixture of (E)-15b and (Z)-15b in the approximate
ratio of 95:5, from which pure (E)-15b could not be
obtained by distillation.
20a
20b
25.1^0.4
97.1^5.8
CvC double bond to a neighboring position, what re¯ects
the greater stability of the anti-arrangement for the endo-
cyclic CvC double bond and the heterocyclic ring in this
kind of bicyclo[3.3.1]nonadiene derivatives.19
Saponi®cation of the mixture of (E)-15b and (Z)-15b in the
ratio of 95:5 by reaction with 20% aqueous NaOH in a
mixture of THF/MeOH in the ratio of 1:1 under re¯ux,28
followed by hydrolysis of the ketal function with 2 N HCl
in dioxane, afforded pure keto acid 16b in 75% yield, after
column chromatography. A modi®ed Curtius rearrangement
of this keto acid 16b by reaction with diphenylphosphoryl
azide in the presence of Et3N, followed by methanolysis of
the resulting isocyanate,27 afforded keto carbamate 17b in
83% overall yield.
For the synthesis of the rac-7-ethyl analogue of huperzine
A, through the above methodology, compound 10 was
reacted with a-ethylacrolein in the presence of N,N,N0,N0-
tetramethylguanidine (TMG) as the base catalyst. The
product thus obtained (probably a mixture of alcohols 11b
and 12b according to our previous results in the correspond-
ing reaction with methacrolein20) was used as such in the
next step. Reaction with p-tolyl chlorothionoformate,
followed by pyrolysis of the resulting mixture of thiocarbo-
nates at 2508C/2±4 Torr led to the ole®n 14b in 28% overall
yield. When the reaction of 10 with a-ethylacrolein was
carried out in the presence of 1,8-diazabicyclo[5.4.0]-
undec-7-ene (DBU) as the base catalyst, a crude product
containing mainly alcohols 12b and 13b was obtained
(13C NMR). Column chromatography of this crude product
gave in order of elution an impure mixture of 12b and 13b in
an approximate ratio of 2:1 and pure alcohol 13b.
Elaboration of the 2-pyridone ring from 17b was carried out
in a similar way to that described before for the preparation
of pyridones 18a and 19a. After a tedious chromatographic
puri®cation of the resulting crude product, the expected
regioisomeric pure pyridones 18b and 19b were isolated
in 28% and 19% yield, respectively, taking into account
the amount of recovered keto carbamate 17b (19%).
The higher yield observed for the cleavage of the carbamate
group of 19a with TMSI in comparison with that obtained in
the cleavage of 18a with lithium 1-propanethiolate led us to
carry out the cleavage of the methyl carbamate of pyridones
18b and 19b under the former reaction conditions. Thus,
reaction of 18b and 19b with TMSI in re¯uxing chloroform
for 8 h, followed by treatment with methanol under re¯ux
for 14 h, afforded crude products containing the expected
amines 2 and 20b, respectively. Again, the puri®cation of
the reaction products proved to be a dif®cult task, as a
consequence of their high polarity, due to the presence of
the pyridone ring and the amino group. After successive
puri®cations by column chromatography, the 7-ethyl
analogues of huperzine A 2 and 20b were obtained in
61% and 85% yield, respectively.
The relative con®guration and the solid state conformation
of 13b were determined by X-ray diffraction analysis
(Fig. 2). The hydroxy- and ethyl-bearing cyclohexane ring
in 13b adopts a chair conformation, in which these sub-
stituents are in a relative cis-arrangement with an axial-
hydroxy group and an equatorial ethyl group, while the
other cyclohexane ring adopts a boat conformation to
avoid the steric interaction between the 3-endo and 7-endo
substituents. Worthy of note, a similar compound (13a) had
not been previously observed in the corresponding reaction
with methacrolein, in which a mixture of 11a and 12a was
mainly obtained when TMG was used as the base catalyst,
while mainly 12a was obtained by using DBU. Since in both
11a and 12a, the hydroxy and methyl groups are in a trans-
arrangement, a pyrolytic syn elimination of the correspond-
ing thiocarbonates was used to carry out the dehydration
of these alcohols to 14a, instead of using an elimination
reaction via the corresponding mesylates.
All of the new huperzine A analogues prepared in this work,
i.e. the regioisomeric huperzine A 20a and the 7-ethyl
analogues 2 and 20b, as well as the 11-unsubstituted
analogues 7 and 8, described in a previous work,21 were
tested for their ability to inhibit AChE from bovine erythro-
cytes by the method of Ellman et al.29 The IC50 values for
AChE inhibition by these compounds are displayed in Table
1, together with the IC50 of tacrine and natural (2)-huper-
zine A. The sole huperzine A analogue with a signi®cant
AChE inhibitory activity is the 7-ethyl analogue 2, which is
12-fold less potent than (2)-huperzine A. Taking into account
the racemic nature of 2 and the fact that rac-huperzine A is
Taking advantage of the trans-diaxial relationship of the
hydroxy group and the proton at position 7 in alcohol 13b,
this compound was transformed into the ole®n 14b by base-
induced (DBU) elimination of the corresponding mesylate,
although the global yield of 14b from 13b was very low
(21%). On the other hand, conversion of the mixture of 12b
and 13b into the corresponding mixture of thiocarbonates,
followed by pyrolysis gave 14b in 27% overall yield from 10.

P. Camps et al. / Tetrahedron 56 (2000) 4541±4553
4545
Table 2. 1H NMR chemical shifts (all of these spectra were taken at
500 MHz in CDCl3) and coupling constants of compounds 14b, (Z)-15b,
(E)-15b, 16b, and 17b
In conclusion, structural changes on the carbobicyclic
substructure that lead to hybrid compound 6 from 4 with
improved AChE inhibitory activity (i.e. removal of the
ethylidene group at position 11 and substitution of the
9-methyl by a 9-ethyl group), when carried out on the corre-
sponding subunit of huperzine A do not have the same
effect. Thus, the removal of the ethylidene group of
huperzine A leads to an important decrease of the AChE
inhibitory activity, showing clearly that this exocyclic
ole®nic appendage is one of the essential features for high
AChE inhibitory activity,26,30±34 while the substitution of the
7-methyl group of huperzine A by a 7-ethyl group has a
small but negative effect on the AChE inhibitory activity.
14b
(Z)-15b
(E)-15b
16b
17b
2-Hexo
2-Hendo
4-H
3.30
2.68
5.40
2.87
2.27
2.13
2.79
2.20
2.06
1.07
2.94
2.16
5.40
2.79
1.91
1.82
2.39
1.88
1.95
0.99
5.41
1.42
3.84
2.92
2.16
5.38
3.33
1.81
1.86
2.36
1.91
1.95
0.99
4.93
1.61
3.83
3.00
2.12
5.39
3.60
2.50
2.45
3.11
2.42
1.92
0.95
5.41
1.75
2.32
2.32
5.35
3.58
2.48
2.39
3.43
2.48
1.88
0.93
5.43
1.73
5-H
6-Hexo
6-Hendo
8-Hexo
8-Hendo
10-Ha
20-Ha
100-Hb
200-Hb
OCH2CH2O
The recently published results15,35 on the molecular
modeling of hybrid compounds such as 5 with AChE from
Torpedo californica (TcAChE) have shown them to interact
with the active site of the enzyme as truly huperzine
A-tacrine hybrids, but in a different way from that we had
assumed. Thus, the 4-aminoquinoline subunit of the
more active enantiomer (eutomer) of these compounds
[(2)-enantiomer] is placed in the active site of the enzyme
in the same position of the corresponding subunit in tacrine,
while their unsaturated methyl-substituted three-carbon
bridge roughly occupies the same position of the corre-
sponding moiety of natural (2)-huperzine A, in agreement
with their absolute con®gurations,36 which are opposed, in
spite of being all of them levorotatory. The 2-pyridone sub-
unit of (2)-huperzine A occupies a position opposed to that
occupied by the 4-aminoquinoline substructure of the
hybrid compounds and similarly the ethylidene-substituted
3.89
4.02
3.82
OCH3
COOH
NHCOO
3.72
3.73
3.65
4.73
9.00±13.4
J (Hz)
2-Hexo/2-Hendo
2-Hexo/8-Hexo
4-H/5-H
17.5
1.0
6.0
5.5
2.5
14.0
3.0
17.5
1.0
6.0
5.0
2.5
13.0
2.5
14.0
7.5
7.5
17.5
1.5
6.0
4.5
2.5
13.0
2.5
14.0
7.5
7.0
18.0
2.0
5.5
4.5
2.5
14.5
2.0
15.5
7.5
6.5
5.5
4.5
2.5
14.5
2.5
13.5
7.5
5-H/6-Hexo
5-H/6-Hendo
6-Hexo/6-Hendo
6-Hendo/8-Hendo
8-Hexo/8-Hendo
10-H/20-Ha
14.5
7.5
100-H/200-Hb
7.0
a 10-H and 20-H correspond to the a and b protons of the C3-substituent.
b 100-H and 200-H correspond to the a and b protons of the C9-substituent.
Table 4. 1H NMR chemical shifts (except where otherwise stated, these
spectra were taken at 500 MHz in CD3OD; the values indicated with *
within a column can be interchanged) and coupling constants of compounds
1, 2, 18a, and 18b
about one-half as potent as (2)-huperzine A, the acetylcho-
linesterase inhibitory activity of 2 is only about 6-fold lower
than that of rac-huperzine A. The 11-unsubstituted huper-
zine A analogue 7 is 122-fold less potent than (2)-huper-
zine A, while the regioisomeric analogues 8, 20a, and 20b
are still less potent, about 300±1300-fold less potent than
(2)-huperzine A.
1a
2
18ab
18b
1-H
3-H
4-H
6-Hexo
6-Hendo
8-H
12.38
6.39
7.88
2.14*
2.09*
5.39
3.58
2.87
2.71
1.52
4.87
6.38
7.88
2.31
2.21
5.46
3.70
2.82
2.61
1.87
0.88
5.54
1.72
4.87
4.84
6.34
7.54
2.39
2.13
5.46
3.64
2.87
2.57
1.55
4.84
6.34
7.54
2.40
2.16
5.46
3.66
2.89
2.58
1.85
0.86
5.32
1.67
4.84
3.57
Table 3. 13C NMR chemical shifts (all of these spectra were taken at
75.4 MHz in CDCl3) of compounds 14b, (Z)-15b, (E)-15b, 16b, and 17b
9-H
14b
(Z)-15b
(E)-15b
16b
17b
10-Hexo
10-Hendo
10-Hc
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
56.1
42.0
140.3
120.0
44.4
41.1
106.4
44.5
209.8
29.0
12.0
47.0
40.1
138.5
122.2
43.4
41.0
108.3
45.1
137.8
29.3
12.0
115.2
12.4
176.7
52.1
62.9
50.6
39.7
139.2
120.9
32.0
40.2
108.5
45.3
139.2
29.4
12.0
113.3
13.1
175.6
52.0
62.9
52.2
40.7
138.0
121.9
33.2
46.9
209.1
51.6
136.3
29.2
12.1
57.9
46.1
137.6
122.9
32.9
46.2
208.8
53.2
136.4
28.9
12.1
20-Hc
100-Hd
200-Hd
5-NH/5-NH2
OCH3
5.46
1.65
1.58
5.31
1.66
4.84
3.57
J (Hz)
3-H/4-H
6-Hexo/6-Hendo
8-H/9-H
9.5
17.0
5.5
9.2
16.5
4.0
9.0
16.0
5.0
9.5
16.0
4.0
a
a
C2000
b
b
C1
C200
COO
OCH3
OCH2CH2O
116.7
13.2
179.7
113.9
12.9
155.1
51.9
9-H/10-Hexo
9-H/10-Hendo
10-Hexo/10-Hendo
10-H/20-Hc
100-H/200-Hd
5.2
1.5
17.0
5.0
1.5
17.0
7.5
5.0
2.0
17.0
5.0
1.5
17.0
7.5
171.8
52.6
63.3
64.6
6.7
6.5
7.0
7.0
64.5
62.9
a This spectrum was recorded in CDCl3.
a C10 and C20 correspond to the a and b carbon atoms of the C3-sub-
stituent.
b The following coupling constant was also observed: 8-H/10-Hˆ0.5 Hz.
c 10-H and 20-H correspond to the a and b protons of the C7-substituent.
d 100-H and 200-H correspond to the a and b protons of the C11-sub-
stituent.
b C100 and C200 correspond to the a and b carbon atoms of the C9-sub-
stituent.

4546
P. Camps et al. / Tetrahedron 56 (2000) 4541±4553
Table 5. 13C NMR chemical shifts (except where otherwise stated, these
spectra were taken at 75.4 MHz in CD3OD; the values indicated with *
within a column can be interchanged) of compounds 1, 2, 18a, and 18b
methane-bridge of (2)-huperzine A occupies a position
opposed to that occupied by the corresponding bridge of
the hybrid compounds. Thus, no structure-activity parallel-
ism should be expected for modi®cations carried out at C11
of huperzine A and at C13 of the hybrid compounds.
However, a certain parallelism might be expected for substi-
tutions at C7 of huperzine A and at C9 of the hybrid
compounds, as really observed.
1a
2
18a
18b
C2
C3
C4
C4a
C5
165.4
117.0
140.2
122.8
54.3
165.7
117.9
141.4
124.3
55.4
165.9
117.9
141.1
122.7
58.3
165.8
117.9
141.1
122.6
58.4
C6
C7
C8
C9
49.1
47.9
48.6
47.0
134.1
124.2
32.8
140.8
123.6
33.9
134.1
125.9
34.1
139.8
124.3
34.0
Experimental
C10
C10a
C11
35.2
36.4
35.1
35.2
General
143.1
142.5
22.6
144.5
141.5
30.3
12.6*
113.1
12.7*
144.3
136.6
22.6
144.1
136.8
30.2
12.6
113.4
12.5
Melting points were determined with a MFB 595010 M
Gallenkamp melting point apparatus. 500 MHz H NMR
b
C10
1
b
C2000
C200
COO
c
spectra were performed on a Varian VXR 500 spectrometer,
and 75.4 MHz 13C NMR spectra on a Varian Gemini 300.
Chemical shifts (d) are reported in ppm related to internal
tetramethylsilane (TMS). Assignments given for the NMR
spectra are based on DEPT, 1H/1H and 1H/13C COSY experi-
C1
111.2
12.3
113.4
12.5
157.2
52.3
c
157.2
52.3
OCH3
a This spectrum was recorded in CDCl3.
ments (HMQC sequence). The H and 13C NMR data of
1
b C10 and C20 correspond to the a and b carbon atoms of the C7-sub-
stituent.
compounds 14b, (Z)-15b, (E)-15b, 16b, and 17b are
c C100 and C200 correspond to the a and b carbon atoms of the C11-
substituent.
collected in Tables 2 and 3, respectively, the H and 13C
NMR data of compounds 1, 2, 18a, and 18b are collected in
1
Tables 4 and 5, the H and 13C NMR data of compounds
1
19a, 19b, 20a, and 20b are collected in Tables 6 and 7,
respectively, while those of compounds 12b, 13b, and 22
are described in the experimental. IR spectra were recorded
on a FT/IR Perkin±Elmer spectrometer, model 1600.
Routine MS spectra were taken on a Hewlett±Packard
5988A spectrometer using the electron impact technique
(70 eV): only signi®cant ions are given. Unless otherwise
stated, silica gel SDS 60 (60±200 mm) was utilized for the
column chromatography. Elemental analyses and high
resolution mass spectra were carried out, respectively, at
the Microanalysis Service and the Mass Spectrometry
Table 6. 1H NMR chemical shifts (all of these spectra were taken at
500 MHz in CD3OD; the values indicated with * within a column can be
interchanged) and coupling constants of compounds 19a, b and 20a, b
19a
19b
20a
20b
1-H
3-H
4-H
5-H
4.85
6.29
7.42
4.11
5.58
4.85
6.29
7.43
4.14
5.57
4.84
6.37
7.48
3.99
4.87
6.39
7.50
4.05
Â
Laboratory of the Centro de Investigacion y Desarrollo
(C.I.D.), C.S.I.C., Barcelona, Spain. All new compounds
6-H
6-Hexo
6-Hendo
8-H
2.43
2.02
5.30
2.49
2.11
5.34
Table 7. 13C NMR chemical shifts (all of these spectra were taken at
75.4 MHz in CD3OD) of compounds 19a, b and 20a, b
8-Hexo
8-Hendo
10-Hexo
10-Hendo
10-Ha
2.42
2.37
2.88
3.49
1.63
2.42
2.37
2.84
3.49
1.95
0.96
5.20
1.67
4.85
3.61
19a
19b
20a
20b
2.59*
2.74*
1.57
2.74*
2.84*
1.91
0.91
5.47
1.76
4.87
C2
C3
C4
C4a
C5
C6
C7
165.5
116.9
142.7
122.2
38.5
126.5
132.7
49.9
56.5
41.9
145.3
137.0
22.6
165.5
116.9
142.6
122.2
38.4
124.8
138.2
48.3
56.6
41.9
145.4
137.3
30.2
165.6
118.1
144.4
120.7
36.4
165.5
118.4
144.3
120.4
36.3
20-Ha
100-Hb
200-Hb
9-NH/9-NH2
OCH3
5.22
1.68
4.85
3.62
5.52
1.72
4.84
40.8
39.1
135.1
130.6
54.1
141.7
127.4
54.7
C8
C9
J (Hz)
3-H/4-H
5-H/6-H
9.5
5.5
9.0
6.0
9.2
9.2
C10
C10a
C11
44.2
43.6
143.4
141.0
22.8
142.8
139.9
30.3
12.4
113.5
12.6
5-H/6-Hexo
5-H/6-Hendo
6-Hexo/6-Hendo
8-Hexo/8-Hendo
8-Hexo/10-Hexo
10-Hexo/10-Hendo
10-H/20-Ha
100-H/200-Hb
4.7
1.7
17.0
5.0
1.5
17.5
a
C10
C20ab
12.6
112.3
12.9
157.8
52.2
b
16.0
18.5
6.5
16.0
C100
112.5
13.0
157.8
52.3
113.1
12.6
b
C200
COO
18.0
7.5
7.0
17.0
6.7
16.5
7.5
7.0
OCH3
a C10 and C20 correspond to the a and b carbon atoms of the C7-sub-
stituent.
a 10-H and 20-H correspond to the a and b protons of the C7-substituent.
b 100-H and 200-H correspond to the a and b protons of the C11-sub-
stituent.
b C100 and C200 correspond to the a and b carbon atoms of the C11-
substituent.

P. Camps et al. / Tetrahedron 56 (2000) 4541±4553
4547
herein described are racemic, although this is not indicated
either in their names or in their numbering.
a colorless gummy mixture (34.5 g) was ®rst isolated,
containing alcohols 12b and 13b in an approximate ratio
of 2:1 (13C NMR), as the main components, which was
used as such in the next step. On further elution with
AcOEt, pure alcohol 13b (10.0 g, 30% yield) was isolated,
as a crystalline white solid. The analytical sample of 13b
was obtained by recrystallization from AcOEt.
(E)-5-Amino-11-ethylidene-5,6,9,10-tetrahydro-7-methyl-
5,9-methano-1H-cycloocta[b]pyridin-2-one, rac-huper-
zine A, (1). A mixture of carbamate 18a (150 mg, 0.50
mmol), anhydrous HMPA (0.9 mL) and freshly prepared
lithium 1-propanethiolate (ca. 0.5 M solution in anhydrous
HMPA,37 6.7 mL, ca. 3.35 mmol) was stirred at 408C for
24 h. The mixture was allowed to cool to room temperature,
was poured into crushed ice (50 g) and was concentrated to
dryness in vacuo. The resulting brown residue (660 mg) was
submitted to column chromatography (40±60 mm-silica gel,
220 g, mixtures of CHCl3/MeOH). On elution with CHCl3/
MeOH in the ratio of 95:5, slightly impure 1 (105 mg) was
obtained. This product was submitted again to column
chromatography (40±60 mm-silica gel, 10 g) under the
same conditions, obtaining pure 1 (80 mg, 66% yield), as
a white solid, mp 217±2198C (AcOEt). IR (KBr) n 3358,
3293, 2917, 2894, 1651, 1617, 1554, 1459, 1435, 1405,
1378, 1351, 1309, 1170, 1119, 1087, 959, 926, 910, 841,
13b: mp 158±1598C. IR (KBr) n 3518, 2959, 2932, 2898,
1730, 1703, 1458, 1436, 1301, 1250, 1193, 1172, 1146,
1118, 1093, 1022, 989, 949, 923 cm21
.
1H NMR
(500 MHz, CDCl3) d 0.97 (t, Jˆ7.0 Hz, 3H, CH2CH3),
1.41 (ddq, Jˆ14.0 Hz, J0ˆJ00ˆ7.0 Hz, 1H) and 1.53 (ddq,
Jˆ14.0 Hz, J0ˆJ00ˆ7.0 Hz, 1H) (CH2CH3), 1.72 (d, Jˆ
3.5 Hz, 1H, OH), 1.83 (ddd, Jˆ13.5 Hz, J0ˆ4.5 Hz, J00ˆ
2.0 Hz, 1H, 8-Hendo), 2.13 (dd, Jˆ14.0 Hz, J0ˆ3.5 Hz, 1H,
4-Hendo), 2.19 (d, Jˆ14.0 Hz, 1H, 2-Hendo), 2.22 (ddd, Jˆ
14.0 Hz, J0ˆ11.0 Hz, J00ˆ3.5 Hz, 1H, 4-Hexo), super-
imposed ca. 2.19±2.26 (m, 1H, 7-H), 2.38 (dd, JvJ0ˆ
13.5 Hz, 1H, 8-Hexo), 2.69 (ddd, Jˆ11.0 Hz, J0ˆJ00ˆ3.5 Hz,
1H, 5-H), 2.89 (dd, Jˆ14.0 Hz, J0ˆ3.5 Hz, 1H, 2-Hexo), 3.76
(s, 3H, COOCH3), 3.88±4.10 (complex signal, 5H, 6-H and
OCH2CH2O). 13C NMR (75.4 MHz, CDCl3) d 11.9 (CH3,
CH2CH3), 23.6 (CH2, CH2CH3), 33.7 (CH, C7), 37.0 (CH2,
C4), 38.8 (CH2, C8), 40.9 (CH2, C2), 50.7 (CH, C5), 52.6
(CH3, COOCH3), 56.4 (C, C1), 64.2 (CH2) and 65.2 (CH2)
(OCH2CH2O), 77.0 (CH, C6), 105.4 (C, C3), 172.5 (C,
COOCH3), 210.3 (C, C9). MS, m/z (%): 298 (Mz1, 13),
280 [(M2H2O)z1, 4], 266 [(M2CH3OH)z1, 5], 239
[(M2COOCH3)1, 15], 227 (10), 214 [(M2C5H8O)z1, 15],
211 (11), 99 [(C5H7O2)1, 69], 87 (47), 86 [(C5H10O)z1, 100],
55 (85). Anal. calcd for C15H22O6: C, 60.39; H, 7.44. Found:
C, 60.34; H, 7.64.
771, 720, 659 cm21
.
(E)-5-Amino-7-ethyl-11-ethylidene-5,6,9,10-tetrahydro-
5,9-methano-1H-cycloocta[b]pyridin-2-one (2). To
a
suspension of carbamate 18b (118 mg, 0.38 mmol) in
CHCl3 (14 mL), TMSI (0.54 mL, 0.76 g, 3.8 mmol) was
added dropwise and the mixture was heated under re¯ux
for 8 h. MeOH (14 mL) was then added and the reaction
mixture was heated under re¯ux for 14 h. Evaporation of
the solvents at reduced pressure gave a brown residue
(230 mg), which was submitted to column chromatography
(40±60 mm-silica gel, 20 g, mixtures of CHCl3/MeOH). On
elution with a mixture of CHCl3/MeOH in the ratio of 96:4,
impure amine 2 (130 mg) was obtained as a yellowish solid.
This product was again submitted to column chroma-
tography (40±60 mm-silica gel, 20 g, mixtures of hexane/
AcOEt and then AcOEt/MeOH). On elution with a mixture
of AcOEt/MeOH in the ratio of 91:9, almost pure 2 (59 mg,
61% yield) was obtained as a white solid. The analytical
sample of 2 was obtained by recrystallization from MeOH,
mp 102±1048C. IR (KBr) n 3430, 3271, 3142, 2959, 2925,
2863, 1657, 1629, 1609, 1552, 1449, 1427, 1408, 1382,
1350, 1303, 1176, 1120, 972, 929, 902, 835, 773, 717,
662 cm21. MS, m/z (%): 257 [(M1H)1, 22], 256 (Mz1,
72), 255 [(M2H)1, 12], 242 (15), 241 [(M2CH3)1, 83],
228 (19), 227 [(M2CH2CH3)1, 100], 187 [(M2C5H9)1,
81], 173 [(M2C6H11)1, 31], 55 (36). Exact mass calcd for
C16H20N2O 256.1576, obsd 256.1567.
13C NMR data of 12b, deduced from the spectrum of the
mixture 12b/13b in the approximate ratio of 2:1 (assignment
carried out by comparison with the known 7-methyl-derivative
12a20). 13C NMR (75.4 MHz, CDCl3) d 10.9 (CH3,
CH2CH3), 23.6 (CH2, CH2CH3), 33.8 (CH2, C4), 36.0
(CH, C7), 37.3 (CH2, C8), 40.5 (CH2, C2), 51.2 (CH, C5),
52.6 (CH3, COOCH3), 56.5 (C, C1), 64.1 (CH2) and 65.1
(CH2) (OCH2CH2O), 76.2 (CH, C6), 105.2 (C, C3), 172.3
(C, COOCH3), 208.7 (C, C9).
Methyl 3-ethyl-7,7-ethylenedioxy-9-oxobicyclo[3.3.1]-
non-3-ene-1-carboxylate (14b). A solution of 10 (10.0 g,
46.7 mmol) and TMG (1.14 mL, 1.04 g, 9.04 mmol) in
anhydrous CH2Cl2 (200 mL) was cooled to 2788C and
treated dropwise with a solution of a-ethylacrolein
(18.3 mL, 15.7 g, 187 mmol) in anhydrous CH2Cl2
(50 mL). The reaction mixture was stirred at 2788C for
30 min, was allowed to warm to room temperature for 3 h,
and was stirred at room temperature for 2 h. The reaction
mixture was evaporated at reduced pressure, the resulting
brown gummy residue (15.8 g) was submitted to column
chromatography (silica gel, 180 g, AcOEt), to give a color-
less gummy residue (13.8 g) which was used as such in the
following step.
Methyl 7exo-ethyl-3,3-ethylenedioxy-6exo-hydroxy-9-
oxobicyclo[3.3.1]nonane-1-carboxylate (13b) and stereo-
isomeric mixture of methyl 7exo-ethyl-3,3-ethylene-
dioxy-6endo-hydroxy-9-oxobicyclo[3.3.1]nonane-1-carb-
oxylate (12b) and 13b. A solution of 10 (24.0 g, 112 mmol)
and DBU (19.6 mL, 20.0 g, 131 mmol) in anhydrous aceto-
nitrile (450 mL) was treated dropwise with a solution of
a-ethylacrolein (43.1 mL, 37.0 g, 441 mmol) in anhydrous
acetonitrile (200 mL). The reaction mixture was stirred at
room temperature for 30 min and was evaporated at reduced
pressure. The resulting reddish gummy residue (62.0 g) was
submitted to column chromatography (40±60 mm-silica gel,
450 g, mixtures of hexane/AcOEt). On elution with AcOEt,
A solution of the above residue (13.8 g) in anhydrous
pyridine (85 mL) was cooled in an ice-water bath, and
was treated dropwise with p-tolyl chlorothionoformate
(8.5 mL, 97% content, 10.4 g, 54.1 mmol). The resulting

4548
P. Camps et al. / Tetrahedron 56 (2000) 4541±4553
reddish mixture was allowed to warm to room temperature,
was stirred at room temperature for 3 h, was poured into
cold water (250 mL) and was extracted with toluene
(5£100 mL). The combined organic extracts were washed
successively with 5% aqueous HCl (5£100 mL), water
(3£100 mL), and brine (3£100 mL), were dried with
anhydrous Na2SO4, and evaporated at reduced pressure, to
give a brown gummy residue (24.2 g), which was taken up
in CH2Cl2 (100 mL), treated with active charcoal, and
®ltered through a short pad of Celitew. Evaporation of the
solvent gave a brown oily residue (21.3 g) of the corre-
sponding stereoisomeric mixture of thiocarbonates, which
was pyrolyzed without further puri®cation.
give a brown oily residue (930 mg), which was submitted to
column chromatography (silica gel, 65 g, mixtures of
hexane/AcOEt). On elution with a mixture of hexane/
AcOEt in the ratio of 80:20, keto ester 14b (200 mg, 21%
overall yield from alcohol 13b) was isolated. On elution
with a mixture of hexane/AcOEt in the ratio of 30:70,
unchanged mesylate was recovered (75 mg).
Methyl
cyclo[3.3.1]non-3-ene-1-carboxylate, [(Z)-15b]. To
(Z)-3-ethyl-7,7-ethylenedioxy-9-ethylidenebi-
a
stirred mixture of ethyltriphenylphosphonium bromide
(26.1 g, 70.3 mmol) and anhydrous THF (260 mL),
n-BuLi (1.6 M solution in hexane, 37.5 mL, 60.0 mmol)
was added dropwise at room temperature over 10 min.
The resulting orange suspension was stirred at room
temperature for 1.25 h, cooled to 08C, and treated dropwise
for 15 min, with a solution of keto ester 14b (3.75 g,
13.4 mmol) in anhydrous THF (65 mL). The reaction
mixture was allowed to warm to room temperature, stirred
at room temperature for 4 h, and poured into water
(270 mL). The organic solvents were evaporated at reduced
pressure and the resulting aqueous phase was extracted with
AcOEt (4£100 mL). The combined organic extracts were
washed with brine (100 mL), dried with anhydrous Na2SO4,
and evaporated at reduced pressure. Column chroma-
tography of the resulting oily residue (14.5 g) (40±60 mm-
silica gel, 200 g, mixtures of hexane/AcOEt in the ratio of
80:20) afforded a mixture of esters (Z)-15b and (E)-15b in
an approximate ratio of 85:15 (1H NMR) (3.50 g, 89%
yield), as a white solid. Puri®cation of (Z)-15b from this
diastereomeric mixture by a second column chroma-
tography under the above conditions or by distillation at
1108C/1 Torr or 1608C/2 Torr was fruitless.
The above residue was heated at 2508C/2±4 Torr in two
portions (11.4 g19 90 g) in a rotary microdistillation appa-
ratus. A yellow oil (7.10 g15.30 g, respectively) distilled,
which was taken up altogether in CH2Cl2 (100 mL). The
resulting solution was washed with 2 N NaOH (3£60 mL),
dried with anhydrous Na2SO4, and evaporated at reduced
pressure to give a yellowish oil (8.20 g), which was
submitted to column chromatography (40±60 mm-silica
gel, 120 g, mixtures of hexane/AcOEt). On elution with a
mixture of hexane/AcOEt in the ratio of 80:20, keto ester
14b (3.70 g, 28% overall yield from 10) was isolated as a
colorless oil, which solidi®ed on standing.
Note: A similar yield of 14b (27% overall yield from 10)
was obtained using the above procedure except for the use
of DBU as the base catalyst instead of TMG.
The analytical sample of 14b was obtained by recrystalli-
zation from CH2Cl2: white crystals, mp 70±718C. IR (KBr)
n 2967, 2929, 2906, 2880, 2848, 1746, 1715, 1456, 1436,
1350, 1304, 1251, 1230, 1167, 1144, 1110, 1070, 1048,
1002, 952, 934, 836 cm21. MS, m/z (%): 280 (Mz1, 39),
249 [(M2CH3O)1, 11], 248 [(M2CH3OH)z1, 37], 221
[(M2COOCH3)1, 44], 177 [(M2COOCH3±C2H4O)1,
38], 149 [(M2COOCH3±C2H4O±CO)1, 30], 99
[(C5H7O2)1, 68], 91 (100), 87 (93), 86 [(C5H10O)z1, 98],
79 (68), 77 (60), 55 (51). Anal. calcd for C15H20O5: C,
64.27; H, 7.20. Found: C, 64.44; H, 7.21.
Pure (Z)-15b by partial hydrolysis of the mixture of (Z)-15b/
(E)-15b in the ratio of 85:15. A mixture of (Z)-15b/(E)-15b
in the ratio of 85:15 (169 mg, 0.58 mmol), 20% aqueous
NaOH (12 mL, 60 mmol), THF (12 mL) and MeOH
(12 mL) was stirred under re¯ux for 6 h. The organic
solvents were evaporated in vacuo and the remaining
aqueous mixture was extracted with CH2Cl2 (2£25 mL).
The combined organic extracts were dried with anhydrous
Na2SO4 and evaporated at reduced pressure to afford pure
(Z)-15b [130 mg, 90% of recovered (Z)-15b], as a colorless
oil. The analytical sample of (Z)-15b was obtained by distil-
lation at 1508C/1 Torr. IR (NaCl) n 2962, 2938, 2920, 2874,
1729, 1458, 1434, 1237, 1200, 1167, 1148, 1129, 1100, 1055,
996, 951, 925, 834, 702 cm21. MS, m/z (%): 292 (Mz1, 0.4),
248 [(M2C2H4O)z1, 2], 216 [(M2C2H4O±CH3OH)z1, 27],
191 [(M2C5H9O2)1, 40], 189 [(M2C5H11O2)1, 27], 159
[(M2C5H9O2±CH3OH)1, 100], 131 [(M2C5H9O2±
HCOOCH3)1, 37], 119 [(C9H11)1, 71], 91 (62). Anal. calcd
for C17H24O4: C, 69.83; H, 8.28. Found: C, 70.07; H, 8.44.
Alkene 14b from alcohol 13b via its mesylate. A stirred
solution of alcohol 13b (2.00 g, 6.71 mmol), Et3N (9.7 mL,
7.0 g, 70 mmol) and 4-(dimethylamino)pyridine (DMAP)
(20.5 mg, 0.17 mmol) in anhydrous CH2Cl2 (60 mL) was
treated, dropwise, with methanesulfonyl chloride (2.1 mL,
3.1 g, 27 mmol), and the reaction mixture was stirred at
room temperature for 6 h. The resulting solution was diluted
with CH2Cl2 (50 mL), washed with saturated aqueous
NH4Cl (4£50 mL) and dried with anhydrous Na2SO4.
Evaporation of the solvent at reduced pressure afforded a
brown solid residue (1.95 g), which contained the corre-
sponding mesylate impuri®ed with other products (1H
NMR). A solution of this crude mesylate (1.00 g) and
DBU (0.85 mL, 0.87 g, 97% content, 5.5 mmol) in
anhydrous toluene (45 mL) was heated under re¯ux for
24 h. After cooling in an ice-water bath, and made acidic
with 0.1 N HCl (18 mL), the organic phase was separated
and the aqueous one was extracted with CH2Cl2 (3£30 mL).
The combined organic phase and extracts were dried with
anhydrous Na2SO4, and evaporated at reduced pressure to
Methyl
(E)-3-ethyl-7,7-ethylenedioxy-9-ethylidenebi-
cyclo[3.3.1]non-3-ene-1-carboxylate [(E)-15b]. A solution
of a mixture of (Z)-15b/(E)-15b in the ratio of 85:15
(640 mg, 2.19 mmol), AIBN (256 mg, 1.56 mmol) and thio-
phenol (0.35 mL, 376 mg, 3.41 mmol) in anhydrous toluene
(7 mL) was heated at 858C for 22 h. The mixture was
concentrated in vacuo and the resulting residue was taken
up in CH2Cl2 (20 mL). The organic solution was washed
successively with 2 N NaOH (2£15 mL) and brine

P. Camps et al. / Tetrahedron 56 (2000) 4541±4553
4549
(30 mL), dried with anhydrous Na2SO4, and evaporated at
reduced pressure to give a yellow oil (780 mg), which was
submitted to column chromatography (silica gel, 50 g,
mixtures of hexane/AcOEt). On elution with a mixture of
hexane/AcOEt in the ratio of 80:20, a mixture of esters (E)-
15b and (Z)-15b in an approximate ratio of 95:5 (1H NMR)
(550 mg, 86% yield) was obtained. An analytical sample of
the above mixture was obtained by distillation at 1258C/
1.5 Torr. IR (NaCl) n 2963, 2928, 2901, 2878, 1729,
1457, 1433, 1238, 1158, 1130, 1092, 1052, 996, 951, 927,
839, 703 cm21. MS, m/z (%): 292 (Mz1, 10), 233
[(M2COOCH3)1, 23], 231 (10), 230 (11), 224
[(M2C5H8)z1, 24], 191 [(M2C5H9O2)1, 68], 159
[(M2C5H9O2±CH3OH)1, 95], 131 [(M2C5H9O2±
HCOOCH3)1, 40], 119 [(C9H11)1, 52], 91 (94), 87
[(C4H7O2)1, 100], 86 (76). Anal. calcd for C17H24O4: C,
69.83; H, 8.28. Found: C, 69.35; H, 8.37.
of 75:25). On elution with CH2Cl2/AcOEt in the ratio of
75:25, keto carbamate 17b (800 mg, 83% yield) was
isolated, as a white solid. The analytical sample of 17b
was obtained by recrystallization from a mixture of
CH2Cl2/hexane in the ratio of 1:3, mp 80±828C. IR (KBr)
n 3317, 3058, 2964, 2924, 2889, 1702, 1542, 1436, 1381,
1320, 1270, 1221, 1193, 1079, 1039, 956, 864, 780,
701 cm21. MS, m/z (%): 263 (Mz1, 3), 248 [(M2CH3)1, 2],
234 [(M2CH2CH3)1, 4], 231 [(M2CH3OH)z1, 8], 206
[(M2C3H5O)1, 100], 188 [(M2NH2COOCH3)z1, 35], 174
[(M2C3H5O±CH3OH)1,
98],
146
[(M2C3H5O±
HCOOCH3)1, 73], 131 [(M2C3H5O±NH2COOCH3)1, 57],
117 [(C9H9)1, 31], 91 (55). Anal. calcd for C15H21NO3: C,
68.41; H, 8.04; N, 5.32. Found: C, 68.41; H, 8.17; N, 5.41.
(E)-11-Ethylidene-5,6,9,10-tetrahydro-5-(methoxycar-
bonylamino)-7-methyl-5,9-methano-1H-cycloocta[b]-
pyridin-2-one (18a), and (E)-11-ethylidene-5,8,9,10-
tetrahydro-9-(methoxycarbonylamino)-7-methyl-5,9-
methano-1H-cycloocta[b]pyridin-2-one (19a). A mixture
of keto carbamate 17a (1.90 g, 7.63 mmol), pyrrolidine
(E)-3-Ethyl-9-ethylidene-7-oxobicyclo[3.3.1]non-3-ene-
1-carboxylic acid (16b). A mixture (E)-15b/(Z)-15b in the
ratio of 95:5 (580 mg, 1.99 mmol), 20% aqueous NaOH
(38 mL, 0.19 mol), THF (38 mL) and MeOH (38 mL) was
stirred under re¯ux for 48 h. The organic solvents were
evaporated in vacuo and the remaining aqueous mixture
was washed with CH2Cl2 (2£50 mL), made acidic with
5 N HCl (50 mL), and extracted with CH2Cl2 (3£30 mL).
The combined organic extracts were washed with brine
(2£40 mL), dried with anhydrous Na2SO4, and evaporated
at reduced pressure. The resulting yellow oily residue
(0.48 g) was taken up in dioxane (10 mL), treated with
2 N HCl (10 mL), and the mixture was stirred at room
temperature for 4 h. The organic solvent was evaporated
in vacuo and the remaining aqueous mixture was extracted
with CH2Cl2 (3£40 mL). The combined organic extracts
were dried with anhydrous Na2SO4, and evaporated at
reduced pressure to give a yellowish solid residue
(455 mg), which was submitted to column chromatography
(silica gel, 60 g, mixtures of hexane/AcOEt). On elution
with a mixture of hexane/AcOEt in the ratio of 50:50,
pure (E)-16b (350 mg, 75% yield) was isolated as a white
solid. The analytical sample of 16b was obtained by sub-
limation at 908C/1 Torr, mp 166±1688C. IR (KBr) n 3650±
2300 (max. at 3437, 2955, 2920, 2862, 2756, 2591), 1728,
1680, 1442, 1381, 1327, 1225, 1164, 1088, 1037, 943, 829,
786, 712, 658 cm21. MS, m/z (%): 234 (Mz1, 5), 216
[(M2H2O)z1, 11], 189 [(M2COOH)1, 31], 188
[(M2HCOOH)z1, 11], 177 [(M2C3H5O)1, 45], 159
[(M2C3H5O±H2O)1, 100], 147 (44), 131 [(M2C3H5O±
HCOOH)1, 36], 119 [(C9H11)1, 81], 117 [(C9H9)1, 33],
105 [(C8H9)1, 39], 91 (66). Anal. calcd for C14H18O3: C,
71.77; H, 7.75. Found: C, 71.45; H, 7.89.
Ê
(0.80 mL, 0.69 g, 9.7 mmol), 4 A molecular sieves (5 g)
and anhydrous benzene (95 mL) was heated under re¯ux
for 5 h. The mixture was allowed to cool to room tempera-
ture and was ®ltered under argon. The ®ltrate was treated
with freshly prepared propiolamide24 (1.40 g, 20.3 mmol)
and the reaction mixture was heated under re¯ux for 21 h.
The resulting orange suspension was allowed to cool to
room temperature and ®ltered. The ®ltrate was evaporated
at reduced pressure to give a reddish residue (2.80 g), which
was submitted to column chromatography (40±
60 mm-silica gel, 350 g, mixtures of hexane/AcOEt and
then mixtures of AcOEt/MeOH). On elution with a mixture
of hexane/AcOEt in the ratio of 30:70, starting keto carba-
mate 17a (600 mg) was recovered. On elution with AcOEt,
19a slightly contaminated with 18a (407 mg, 18% yield,
26% yield taking into account the recovered 17a) was
isolated. On elution with a mixture of AcOEt/MeOH in
the ratio of 90:10, pure 18a (620 mg, 27% yield, 40%
yield taking into account the recovered 17a) was isolated.
The analytical samples of pyridones 18a and 19a were
obtained by recrystallization from MeOH and from a
mixture of AcOEt/MeOH in the ratio of 1:2, respectively.
18a: mp 284±284.58C (dec.). IR (KBr) n 3321, 3248, 3001,
2932, 1714, 1654, 1619, 1555, 1537, 1459, 1308, 1273,
1249, 1180, 1107, 1070, 1040, 933, 836, 752 cm21
.
19a: mp 266±2678C (dec.). IR (KBr) n 3279, 3236, 3025,
2931, 1724, 1651, 1617, 1555, 1457, 1256, 1223, 1192,
1109, 1068, 1045, 830, 755, 663, 636 cm21. MS, m/z (%):
300 (Mz1, 27), 299 [(M2H)1, 10], 285 [(M2CH3)1, 4], 268
[(M2CH3OH)z1, 4], 253 [(M2H±HCOOH)1, 10], 239
[(M2H±HCOOCH3)1, 8], 226 (34), 225 [(M2
NH2COOCH3)z1, 100], 224 (49), 210 [(M2 NH2COOCH3±
CH3)1, 88]. Anal. calcd for C17H20N2O3´1/5H2O: C, 67.17;
H, 6.77; N, 9.22. Found: C, 67.18; H, 6.96; N, 9.18.
Methyl (E)-N-{3-ethyl-9-ethylidene-7-oxobicyclo[3.3.1]-
non-3-en-1-yl}carbamate (17b). A solution of keto acid
16b (860 mg, 3.68 mmol), Et3N (0.52 mL, 378 mg,
3.73 mmol) and diphenylphosphoryl azide (0.86 mL,
1.09 g, 97% content, 3.87 mmol) in anhydrous chloro-
benzene (17 mL) was heated at 908C for 3.5 h. Anhydrous
MeOH (25 mL) was added and the resulting mixture was
heated under re¯ux for 17 h. The solvent was evaporated at
reduced pressure to give a residue (1.90 g), which was
submitted to column chromatography (silica gel, 85 g,
CH2Cl2 and then mixtures of CH2Cl2/AcOEt in the ratio
(E)-7-Ethyl-11-ethylidene-5,6,9,10-tetrahydro-5-(methoxy-
carbonylamino)-5,9-methano-1H-cycloocta[b]pyridin-2-
one (18b), and (E)-7-ethyl-11-ethylidene-5,8,9,10-tetra-
hydro-9-(methoxycarbonylamino)-5,9-methano-1H-cyclo-
octa[b]pyridin-2-one (19b). A mixture of keto carbamate

4550
P. Camps et al. / Tetrahedron 56 (2000) 4541±4553
17b (673 mg, 2.56 mmol), pyrrolidine (0.27 mL, 232 mg,
Ê
3.26 mmol), 4 A molecular sieves (1.50 g) and anhydrous
19b: mp 236±2388C (dec.). IR (KBr) n 3428, 3317, 3235,
3045, 2962, 2927, 1707, 1652, 1619, 1557, 1526, 1458,
1276, 1250, 1188, 1107, 1043, 827, 779, 639 cm21. MS,
m/z (%): 315 [(M1H)1, 5], 314 (Mz1, 25), 313 [(M2H)1,
10], 299 [(M2CH3)1, 3], 285 [(M2CH2CH3)1, 5], 282
[(M2CH3OH)z1, 4], 281 (3), 267 [(M2CH3OH±CH3)1,
5], 240 (31), 239 [(M2NH2COOCH3)z1, 100], 238 (43),
224 [(M2NH2COOCH3±CH3)1, 55], 210 [(M2
benzene (30 mL) was heated under re¯ux for 5 h. The
mixture was allowed to cool to room temperature and was
®ltered under argon. The ®ltrate was treated with freshly
prepared propiolamide24 (530 mg, 7.68 mmol) and the reac-
tion mixture was heated under re¯ux for 15 h. The resulting
orange suspension was allowed to cool to room temperature,
was diluted with MeOH (120 mL) and was ®ltered. The
®ltrate was evaporated at reduced pressure to give an orange
residue (1.40 g), which was taken up in AcOEt (450 mL)
and was extracted with 1 N NaOH (6£100 mL). The
combined aqueous extracts were neutralized with 0.75 N
HCl (ca. 800 mL) and extracted successively with CH2Cl2
(5£100 mL) and AcOEt (5£100 mL). The combined
organic extracts were washed with saturated aqueous
NaHCO3 (2£50 mL), dried with anhydrous Na2SO4, and
evaporated at reduced pressure, to give a yellow-green
solid residue (520 mg), which was submitted to column
chromatography (40±60 mm-silica gel, 52 g, mixtures of
hexane/AcOEt, and then AcOEt/MeOH). On elution with
a mixture of AcOEt/MeOH in the ratio of 97:3, pure 19b
(66 mg), a mixture of 19b and 18b in the ratio of 2:5 (1H
NMR) (72 mg), and pure 18b (99 mg) were consecutively
obtained. The mixture 19b/18b in the ratio of 2:5 (72 mg)
was submitted again to column chromatography (silica gel,
14 g) under the same conditions. On elution with a mixture
of AcOEt/MeOH in the ratio of 98:2, pure 19b (10 mg) and
pure 18b (50 mg), were consecutively eluted.
NH2COOCH3±CH2CH3)1,
70].
Anal.
calcd
for
C18H22N2O3´1/2H2O: C, 66.85; H, 7.17; N, 8.66. Found:
C, 66.86; H, 7.08; N, 8.57.
(E)-9-Amino-11-ethylidene-5,6,9,10-tetrahydro-7-methyl-
5,9-methano-1H-cycloocta[b]pyridin-2-one (20a). It was
prepared in a similar manner to that described for compound
2, starting from a suspension of carbamate 19a (105 mg,
0.35 mmol) in CHCl3 (13 mL), TMSI (0.50 mL, 0.70 g,
3.5 mmol), and MeOH (13 mL). The resulting brown
residue (320 mg) was submitted to column chromatography
(ammonia-saturated silica gel, 25 g, mixtures of CHCl3/
MeOH). On elution with a mixture of CHCl3/MeOH in
the ratio of 85:15, impure amine 20a was obtained
(230 mg) as a white solid. This product was again submitted
to column chromatography (ammonia-saturated silica gel,
20 g, mixtures of hexane/AcOEt, and then mixtures of
AcOEt/MeOH). On elution with a mixture of AcOEt/
MeOH in the ratio of 90:10, pure 20a (85 mg, quantitative
yield) was isolated as a white solid. The analytical sample of
20a was obtained by recrystallization from MeOH, mp
187±1938C (dec.). IR (KBr) n 3507, 3353, 3315, 3116,
2954, 2930, 2889, 2839, 2825, 2504, 2452, 2348, 2337,
2184, 2138, 1650, 1559, 1457, 1428, 1407, 1382, 1204,
1178, 1117, 972, 941, 833, 790, 656, 631, 608 cm21. MS,
m/z (%): 243 [(M1H)1, 17], 242 (Mz1, 81), 241 [(M2H)1,
35], 228 (19), 227 [(M2CH3)1, 100], 226 [(M2NH2)1, 13],
225 [(M2NH3)z1, 16], 214 [(M2CO)z1, 44], 213 [(M2H±
CO)1, 61], 212 (30), 210 (35). Exact mass calcd for
C15H18N2O 242.1419, obsd 242.1412.
On the other hand, the initial AcOEt solution was dried with
anhydrous Na2SO4 and evaporated at reduced pressure to
give an orange residue (1.40 g), which was submitted to
column chromatography (silica gel, 100 g, mixtures of
hexane/AcOEt and then, mixtures of AcOEt/MeOH). On
elution with a mixture of hexane/AcOEt in the ratio of
75:25, starting keto carbamate 17b (130 mg) was recovered.
On elution with a mixture of AcOEt/MeOH in the ratio of
95:5, a mixture of pyridones 19b/18b in an approximate
ratio of 2:3 (150 mg) was obtained. This mixture was
again submitted to column chromatography (silica gel,
15 g) under the same conditions. On elution with a mixture
of AcOEt/MeOH in the ratio of 97:3, pure (E)-19b (50 mg),
a mixture 19b/18b in a ratio of 1:4 (1H NMR) (40 mg), and
pure 18b (30 mg) were consecutively eluted [22% total
yield of 18b and 16% total yield of 19b, 28 and
19%, respectively, taking into account the amount of
recovered 17b]. The analytical samples of pyridones
18b and 19b were obtained by recrystallization from a
mixture of AcOEt/MeOH in the ratio of 8:1 and from
AcOEt, respectively.
(E)-9-Amino-7-ethyl-11-ethylidene-5,6,9,10-tetrahydro-
5,9-methano-1H-cycloocta[b]pyridin-2-one (20b). It was
prepared in a similar manner to that described for compound
2, starting from a suspension of carbamate 19b (86 mg,
0.27 mmol) in CHCl3 (10 mL), TMSI (0.39 mL, 0.55 g,
2.7 mmol), and MeOH (10 mL). The resulting brown
residue (160 mg) was submitted to column chromatography
(40±60 mm-silica gel, 8 g, mixtures of CHCl3/MeOH). On
elution with a mixture of CHCl3/MeOH in the ratio of 96:4,
impure amine 20b was obtained (134 mg) as a yellowish
solid. This product was again submitted to column chroma-
tography (40±60 mm-silica gel, 27 g, mixtures of hexane/
AcOEt, and then mixtures of AcOEt/MeOH). On elution
with a mixture of AcOEt/MeOH in the ratio of 80:20, almost
pure 20b (59 mg, 85% yield) was isolated as a white solid.
The analytical sample of 20b was obtained after twofold
chromatography (silica gel) under the same conditions
followed by recrystallization from a mixture of hexane/
AcOEt in the ratio of 2:1, mp 190±1918C (dec.). IR (KBr)
n 3426, 3359, 3256, 3097, 2954, 2930, 2883, 1653, 1622,
1553, 1458, 1409, 1384, 1205, 1111, 938, 824, 707, 655,
626 cm21. MS, m/z (%): 257 [(M1H)1, 13], 256 (Mz1, 56),
255 [(M2H)1, 21], 242 (10), 241 [(M2CH3)1, 47], 239
[(M2NH3)z1, 12], 228 (38), 227 [(M2CH2CH3)1, 100],
18b: mp 237±2398C. IR (KBr) n 3591, 3514, 3360, 3120,
2971, 2956, 2880, 2832, 2796, 1717, 1650, 1619, 1553,
1523, 1458, 1308, 1251, 1186, 1111, 1047, 959, 934, 833,
779, 640, 619 cm21. MS, m/z (%): 315 [(M1H)1, 7], 314
(Mz1, 31), 313 [(M2H)1, 2], 299 [(M2CH3)1, 6], 285
[(M2CH2CH3)1, 15], 282 [(M2CH3OH)z1, 7], 267
[(M2CH3OH±CH3)1, 5], 253 [(M2H±HCOOCH3)1, 35],
239 [(M2NH2COOCH3)z1, 66], 224 [(M2NH2COOCH3±
CH3)1, 53], 210 [(M2NH2COOCH3±CH2CH3)1, 100].
Anal. calcd for C18H22N2O3.2/3H2O: C, 66.23; H, 7.21; N,
8.58. Found: C, 66.23; H, 7.02; N, 8.49.

P. Camps et al. / Tetrahedron 56 (2000) 4541±4553
Table 8. Experimental data of the X-ray crystal structure determination of 13b
4551
Molecular formula
Molecular mass
Temperature
C15H22O6
298.33
293(2)K
F(000)
d (calcd) [Mg m23
Size of crystal [mm]
Measured re¯ections
Independent re¯ections
1280
1.331
0.1£0.1£0.2
5778
]
Crystal system
Space group
Cell parameters
Orthorhombic
Pcab
3415
2663
a
Observed re¯ections
m(Mo-Ka) [mm21
b
Ê
a [A]
10.147(6)
14.550(3)
20.172(4)
90
90
90
]
0.100
0.058
0.121
0.299
20.175
279
Ê
b [A]
R
Rw
Ê
c [A]
c
Ê -3
Ê -3
a [8]
b [8]
g [8]
Drmax (eA )
Drmin (eA )
d
Re®ned parameters
Max. shift/e.s.d.
Ê 3
V [A ]
Z
2978(2)
8
0.00
a Determined by automatic centering of 25 re¯ections (12#u#218).
b
Ê
m(Mo-Ka), Linear absorption coef®cient. Radiation Mo-Ka (lˆ0.71069 A).
c Maximum peaks in ®nal difference synthesis.
d Minimum peaks in ®nal difference synthesis.
212 (31). Exact mass calcd for C16H20N2O 256.1576, obsd
256.1567.
Anal. calcd for C14H20O6´H2O: C, 55.62; H, 7.34. Found: C,
55.83; H, 7.69.
Attempted synthesis of (E)-15a from keto ester 14a:
Obtention of 7,7-ethylenedioxy-5-(methoxycarbonyl)-3-
methylcyclooct-2-enecarboxylic acid (22). A solution of
lithium diisopropylamide (LDA) (2 M solution in heptane/
THF/ethylbenzene, 1.90 mL, 3.80 mmol) in anhydrous THF
(25 mL) was cooled to 2788C. To this stirred solution was
added dropwise over 5 min, S-phenyl thiopropionate
(0.58 mL, 0.63 g, 3.80 mmol). The mixture was stirred at
2788C for 30 min, and was treated dropwise with a solution
of keto ester 14a (1.00 g, 3.76 mmol) in anhydrous THF
(10 mL). The reaction mixture was stirred at 2788C for
30 min, was allowed to warm slowly to 08C during 1.5 h,
and was treated with saturated aqueous NH4Cl (20 mL). To
this mixture, water (50 mL) and diethyl ether (50 mL) were
added. The aqueous phase was separated and the organic
one was washed with 10% aqueous K2CO3 (2£50 mL) and
brine (50 mL), was dried with anhydrous Na2SO4, and was
evaporated at reduced pressure, to give starting keto ester
14a (90 mg). The initial aqueous phase was treated with
cold 2 N HCl (20 mL) and extracted with CH2Cl2
(3£50 mL). The combined organic extracts were washed
with brine (2£40 mL), dried with anhydrous Na2SO4, and
evaporated at reduced pressure, to give a mixture of dia-
stereomers of 22 in an approximate ratio of 55:45 (1H NMR)
(0.70 g, 69% yield) as a yellowish oil. The analytical sample
was obtained by column chromatography (silica gel, 40 g,
mixtures of hexane/AcOEt) of a portion of this crude
(200 mg). On elution with a mixture of hexane/AcOEt in
the ratio of 55:45, pure diastereomeric mixture 22 (118 mg)
was isolated.
NMR data of the main stereoisomer deduced from the
spectra of the mixture 22. H NMR (500 MHz, CDCl3) d
1
1.64 (d, Jˆ1.0 Hz, 3H, 3-CH3), 1.82 (dd, Jˆ13.5 Hz,
J0ˆ12.5 Hz, 1H, 8-Ha), 2.00±2.13 (complex signal, 3H,
6-Ha, 6-Hb and 8-Hb), superimposed in part 2.40 (dd,
Jˆ13.5 Hz, J0ˆ1.5 Hz, 1H, 4-Ha), 2.77 (dd, Jˆ13.5 Hz,
J0ˆ8.0 Hz, 1H, 4-Hb), superimposed in part 2.82 (m, 1H,
5-H), 3.40 (broad dd, Jˆ11.5 Hz, J0ˆ8.0 Hz, 1H, 1-H), 3.65
(s, 3H, COOCH3), 3.64±3.96 (complex signal, 4H,
OCH2CH2O), 5.64 (dm, Jˆ8.0 Hz, 1H, 2-H), 7.40±10.40
(broad signal, 1H, COOH). 13C NMR (75.4 MHz, CDCl3)
d 24.3 (CH3, 3-CH3), 32.1 (CH2, C4), 36.5 (CH2, C6), 38.55
(CH, C5), 40.23 (CH, C1), 42.5 (CH2, C8), 51.82 (CH3,
COOCH3), 63.7 (CH2) and 65.1 (CH2) (OCH2CH2O),
109.1 (C, C7), 124.0 (CH, C2), 135.6 (C, C3), 176.0 (C,
COOCH3), 180.43 (C, COOH).
NMR data of the minor stereoisomer deduced from the
spectra of the mixture 22. H NMR (500 MHz, CDCl3) d
1
1.72 (d, Jˆ1.0 Hz, 3H, 3-CH3), 1.78 (dd, Jˆ13.5 Hz,
J0ˆ12.5 Hz, 1H, 8-Ha), 2.00±2.13 (complex signal, 2H,
6-Ha and 8-Hb), 2.24 (dd, Jˆ13.0 Hz, J0ˆ5.0 Hz, 1H,
4-Ha), superimposed in part 2.38 (dd, Jˆ14.0 Hz,
J0ˆ3.5 Hz, 1H, 6-Hb), 2.53 (dddd, Jˆ12.5 Hz, J0ˆJ00ˆ
5.0 Hz, J000ˆ3.5 Hz, 1H, 5-H), 2.73 (dd, JˆJ0ˆ13.0 Hz,
1H, 4-Hb), 3.53 (ddd, Jˆ12.5 Hz, J0ˆ8.5 Hz, J00ˆ2.0 Hz,
1H, 1-H), 3.68 (s, 3H, COOCH3), 3.64±3.96 (complex
signal, 4H, OCH2CH2O), 5.59 (boad d, Jˆ8.5 Hz, 1H,
2-H), 7.40±10.40 (broad signal, 1H, COOH). 13C NMR
(75.4 MHz, CDCl3) d 23.1 (CH3, 3-CH3), 31.6 (CH2, C4),
37.5 (CH2, C6), 38.47 (CH, C5), 40.19 (CH, C1), 43.3 (CH2,
C8), 51.75 (CH3, COOCH3), 63.9 (CH2) and 65.2 (CH2)
(OCH2CH2O), 109.5 (C, C7), 123.3 (CH, C2), 137.2 (C,
C3), 175.2 (C, COOCH3), 180.37 (C, COOH).
Spectroscopic and analytical data of the diastereomeric
mixture 22. IR (NaCl) n 3500±2500 (max. at 3464, 3190,
2642), 2949, 2883, 1733, 1708, 1437, 1345, 1288, 1200,
1170, 1129, 1096, 1047, 1001, 949, 921, 896, 827,
732 cm21. MS, m/z (%): 284 (Mz1, 1), 266 [(M2H2O)z1,
6], 253 [(M2CH3O)1, 1], 252 [(M2CH3OH)z1, 1], 239
[(M2COOH)1, 4], 238 [(M2HCOOH)z1, 3], 225
[(M2COOCH3)1, 3], 222 [(M2H2O±C2H4O)z1, 4], 157
[(C7H9O4)1, 22], 86 [(C4H6O2)z1, 100], 55 [(C3H3O)1, 22].
X-Ray crystal-structure determination of 13b38
A prismatic crystal was selected and mounted on a Enraf-
Nonius CAD4 four-circle diffractometer. Unit-cell para-
meters were determined by automatic centering of 25

4552
P. Camps et al. / Tetrahedron 56 (2000) 4541±4553
re¯ections (12,u,218) and re®ned by the least-squares
method. Intensities were collected with graphite-monochro-
matized Mo-Ka radiation, using v/2u scan technique
(Table 8). 5778 re¯ections were measured in the range
2.02#u#30.07, 3415 of which were non-equivalent by
symmetry [Rint (on I)ˆ0.052]. 2663 re¯ections were
assumed as observed by applying the condition I.2s(I).
Three re¯ections were measured every two hours as orien-
tation and intensity control; signi®cant intensity decay was
not observed. Lorentz polarization but no absorption correc-
tions were made. The structure was solved by Direct
methods, using the shelxs computer program39 and re®ned
by the full-matrix least-squares method with the shelx-93
computer program40 using 3365 re¯ections (very negative
References
1. Davies, P.; Malony, A. J. F. Lancet 1976, 2, 1403.
2. Perry, E. K.; Perry, R. H.; Blessed, G.; Tomlinson, B. E. Lancet
1977, 1, 189.
3. White, P.; Goodhard, M. J.; Keet, J. K.; Hiley, C. R.; Carrasio,
L. H.; William, I. E. I. Lancet 1977, 1, 668±671.
4. Reisine, T. D.; Yamamura, H. I.; Bird, E. D.; Spokes, E.; Enna,
S. J. Brain Res. 1978, 159, 477±481.
5. Davies, P. Brain Res. 1979, 171, 319±327.
6. Muramoto, O.; Sugishita, M.; Sugita, H.; Toyokura, Y. Arch.
Neurol. 1979, 36, 501±503.
7. Hollander, E.; Mohs, R. C.; Davis, K. L. Br. Med. Bull. 1986,
42, 97±100.
intensities were not assumed). The function minimized was
8. Hershenson, F. M.; Moos, W. H. J. Med. Chem. 1986, 29,
1125±1130.
P
w(uFou22uFcu2)2, where wˆ[s2(I)1(0.0585P)210.2945P]21,
and Pˆ(uFou212uFcu2)/3. f, f0 and f00 were taken from Inter-
national Tables of X-ray Crystallography.41 All H atoms
were located from a difference synthesis and re®ned with
an overall isotropic temperature factor. Goodness of ®t on
F2ˆ1.137 for all observed re¯ections. Mean shift/
e.s.d.ˆ0.00.
9. Liu, J.-S.; Zhu, Y.-L.; Yu, C.-M.; Zhou, Y.-Z.; Han, Y.-Y.; Wu,
F.-W.; Qi, B.-F. Can. J. Chem. 1986, 64, 837±839.
10. Ayer, W. A.; Kasitu, G. C. Can. J. Chem. 1989, 67, 1077±
1086.
11. Ayer, W. A.; Browne, L. M.; Orszanska, H.; Valenta, Z.; Liu,
J.-S. Can. J. Chem. 1989, 67, 1538±1540.
12. Kozikowski, A. P.; Thiels, E.; Tang, X.-C.; Hanin, I. Adv.
Med. Chem. 1992, 1, 175±205.
Determination of AChE inhibitory activity
13. Hanin, I.; Tang, X. C.; Kozikowski, A. P. Clinical and Pre-
clinical Studies with Huperzine. Cholinergic Basis for Alzheimer
È
Therapy; Becker, R., Giacobini, E., Eds.; Birkhauser: Boston,
AChE inhibitory activity was evaluated spectrophoto-
metrically at 258C by the method of Ellman,29 using
AChE from bovine erythrocytes and acetylthiocholine
iodide (0.53 mM) as substrate. The reaction took place in
a ®nal volume of 3 mL of 0.1 M phosphate-buffered solu-
tion pH 8.0, containing 0.025 units of AChE and 333 mM
5,50-dithiobis(2-nitrobenzoic) acid (DTNB) solution used to
produce the yellow anion of 5-thio-2-nitrobenzoic acid.
Inhibition curves with different derivatives were performed
in triplicate by incubating with at least 12 concentrations of
inhibitor for 15 min. One triplicate sample without inhibitor
was always present to yield the 100% of AChE activity. The
reaction was stopped by the addition of 100 mL 1 mM
eserine, and the color production was measured at
412 nm. The drug concentration producing 50% of AChE
activity inhibition (IC50) was calculated. Results are
expressed as mean^S.E.M. of at least four experiments.
DTNB, acetylthiocholine and the enzyme were purchased
from Sigma and eserine from Fluka.
1991, pp 305±313.
14. Badia, A.; BanÄos, J. E.; Camps, P.; Contreras, J.; Gorbig,
È
D. M.; MunÄoz-Torrero, D.; Simon, M.; Vivas, N. M. Bioorg.
Med. Chem. 1998, 6, 427±440.
È
Ä
15. Camps, P.; El Achab, R.; Gorbig, D. M.; Morral, J.; Munoz-
Torrero, D.; Badia, A.; BanÄos, J. E.; Vivas, N. M.; Barril, X.;
Orozco, M.; Luque, F. J. J. Med. Chem. 1999, 42, 3227±3242.
16. Camps, P.; Cusack, B.; Mallender, W. D.; El Achab, R.;
Morral, J.; MunÄoz-Torrero, D.; Rosenberry, T. L. Mol. Pharmacol.
2000, 57, 409±417.
17. Kozikowski, A. P. U.S. Patent 5,104,880, 1992.
18. Kozikowski, A. P.; TuÈckmantel, W. Acc. Chem. Res. 1999, 32,
641±650.
19. Kozikowski, A. P.; Campiani, G.; TuÈckmantel, W. Hetero-
cycles 1994, 39, 101±116.
20. Camps, P.; Contreras, J. Synth. Commun. 1996, 26, 9±18.
21. Camps, P.; Contreras, J.; Morral, J.; MunÄoz-Torrero, D.; Font-
Bardia, M.; Solans, X. Tetrahedron 1999, 55, 8481±8496.
22. Kozikowski, A. P.; Campiani, G.; Saxena, A.; Doctor, B. P.
J. Chem. Soc., Chem. Commun. 1995, 283±285.
23. Kozikowski, A. P.; Reddy, E. R.; Miller, C. P. J. Chem. Soc.,
Perkin Trans. 1 1990, 195±197.
Acknowledgements
24. Saggiomo, A. J. J. Org. Chem. 1957, 22, 1171±1175.
25. Xia, Y.; Kozikowski, A. P. J. Am. Chem. Soc. 1989, 111,
4116±4117.
Â
A fellowship from Agencia EspanÄola de Cooperacion
Internacional (Instituto de Cooperacion con el Mundo
Â
Â
Â
Arabe, Mediterraneo y Paõses en Desarrollo) to R. El
Achab and ®nancial support from Fundacio La Marato de
Â
26. Kozikowski, A. P.; Xia, Y.; Reddy, E. R.; Tu
Èckmantel, W.;
Â
Â
Hanin, I.; Tang, X. C. J. Org. Chem. 1991, 56, 4636±4645.
27. Method: see Ref. 19.
28. Method: see Ref. 26.
TV3 (project 3004/97) are gratefully acknowledged. We
Â
also thank the Serveis Cientõ®co-Tecnics of the University
of Barcelona and particularly Dr M. Feliz and Dr A. Linares
Á
29. Ellman, G. L.; Courtney, K. D.; Andres Jr, B.; Featherstone,
R. M. Biochem. Pharmacol. 1961, 7, 88±95.
Á
for recording the NMR spectra, Ms P. Domenech from the
Centro de Investigacion y Desarrollo (C.I.D.) (Barcelona,
Â
30. Campiani, G.; Sun, L. -Q.; Kozikowski, A. P.; Aagaard, P.;
McKinney, M. J. Org. Chem. 1993, 58, 7660±7669.
31. Kozikowski, A. P.; Yamada, F.; Tang, X. C.; Hanin, I.
Tetrahedron Lett. 1990, 31, 6159±6162.
Spain) for carrying out the elemental analyses, and Prof. Dr
A. Kozikowski of the Georgetown University Medical
Center, Washington, USA, for a generous gift of a sample
of natural (2)-huperzine A.
32. Bai, D. Pure Appl. Chem. 1993, 65, 1103±1112.

P. Camps et al. / Tetrahedron 56 (2000) 4541±4553
4553
33. Kaneko, S.; Shikano, M.; Katoh, T.; Terashima, S. Synlett
1997, 447±448.
structure reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre. Copies of the data can
be obtained free of charge on application to The Director, CCDC,
12 Union Road, Cambridge CB2 1EZ, UK (fax: 11223-336-033;
e-mail: deposit@chemcrys.cam.ac.uk).
34. Kaneko, S.; Nakajima, N.; Shikano, M.; Katoh, T.; Terashima,
S. Tetrahedron 1998, 54, 5485±5506.
35. Barril, X.; Orozco, M.; Luque, F. J. J. Med. Chem. 1999, 42,
5110±5119.
39. Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467±473.
40. Sheldrick, G. M. shelx-93: Program for Crystal Structure
È È
Determinations; University of Gottingen: Gottingen, Germany,
36. Camps, P.; Contreras, J.; Font-Bardia, M.; Morral, J.; MunÄoz-
Torrero, D.; Solans, X. Tetrahedron: Asymmetry 1998, 9, 835±
849.
1994.
41. International Tables of X-ray Crystallography; Kynock Press:
Birmingham, 1974; Vol. IV, pp 99, 100 and 149.
37. Kayser, R. H.; Brault, M.; Pollack, R. M.; Bantia, S.; Sadoff,
S. F. Preparation of n-PrSLi. J. Org. Chem. 1983, 48, 4497±4502.
38. Crystallographic data (excluding structure factors) for the