Pilsicainide and its oxymethylene analog: Facile alternative syntheses and in vitro testing on human skeletal muscle sodium channels

Article abstract of DOI:10.3987/com-07-11096

Facile, alternative synthetic routes gave access to both pilsicainide [N-(2,6-dimethylphenyl)-2-tetrahydro-lH-pyrrolizin-7a(5H)-ylacetamide, 1], a well-known I_c antiarrhythmic drug, and its oxymethylene analog 2. Both compounds were tested on human skeletal muscle voltage-gated sodium channels, hNavl.4, transfected in tsA201 cells. 7a-[2-(2,6-Dimethylphenoxy)ethyl]hexahydro-lH-pyrrolizine (2) behaved as a bioisostere of 1, exerting a 4-fold more potent use-dependent block.

Full text of DOI:10.3987/com-07-11096

HETEROCYCLES, Vol. 71, No. 9, 2007
2011
HETEROCYCLES, Vol. 71, No. 9, 2007, pp. 2011 - 2026. © The Japan Institute of Heterocyclic Chemistry
Received, 1st May, 2007, Accepted, 14th June, 2007, Published online, 15th June, 2007. COM-07-11096
PILSICAINIDE AND ITS OXYMETHYLENE ANALOG: FACILE
ALTERNATIVE SYNTHESES AND IN VITRO TESTING ON HUMAN
SKELETAL MUSCLE SODIUM CHANNELS
Claudio Bruno, Alessia Catalano, Jean-Francois Desaphy,† Maria M.
Cavalluzzi, Alessia Carocci, Antonella Dipalma,† Carlo Franchini, Giovanni
Lentini,* Diana Conte Camerino,† and Vincenzo Tortorella
†
Medicinal Chemistry Department − Unit of Pharmacology, Department of
Pharmacobiology − Campus, University of Studies − Faculty of Pharmacy, via E.
Orabona 4, 70125 Bari, Italy
glentini@farmchim.uniba.it
Abstract – Facile, alternative synthetic routes gave access to both pilsicainide [N-
(2,6-dimethylphenyl)-2-tetrahydro-1H-pyrrolizin-7a(5H)-ylacetamide, 1], a well-
known IC antiarrhythmic drug, and its oxymethylene analog 2. Both compounds
were tested on human skeletal muscle voltage-gated sodium channels, hNav1.4,
transfected in tsA201 cells. 7a-[2-(2,6-Dimethylphenoxy)ethyl]hexahydro-1H-
pyrrolizine (2) behaved as a bioisostere of 1, exerting a 4-fold more potent use-
dependent block.
INTRODUCTION
Pilsicainide [N-(2,6-dimethylphenyl)-2-tetrahydro-1H-pyrrolizin-7a(5H)-ylacetamide] (1, Figure 1) is a
synthetic drug available in Japan endowed with class IC antiarrhythmic properties1 related to the
inhibition of cardiac muscle sodium channels. Like other IC antiarrhythmic drugs, pilsicainide may cause
serious side effects such as ventricular fibrillation and tachycardia.2,3 Ozeki at al.4 reported the first case
of pilsicainide intoxication associated with dehydration. The authors speculated the reason was
pilsicainide rapid absorption from the gastrointestinal tract and its resistance to metabolic
transformations which cause accumulation in patients with impaired renal function induced by

2012
HETEROCYCLES, Vol. 71, No. 9, 2007
dehydration. Severe side effects occurred also when pilsicainide was administered to elderly patients
affected by renal disfunctions.5,6
Figure 1
N
H2N
1, 3: X = CONH
2, 4: X = CH2O
X
X
1, 2
3, 4
Thus, close blood level monitoring and dosage adjustment are required whenever pilsicainide is
administered to patients with impaired renal function due to ageing or dehydration.7 These findings
prompted us to look for a pilsicainide-like drug whose liver metabolization might be favoured resulting
in a safer use in the above reported clinical cases. In the domain of IB antiarrhythmic drugs, a well-
known bioisosteric relationship holds between tocainide (3) and its oxymethylene analog mexiletine (4),
the latter being endowed with a more favorable toxicological profile.8 Furthermore, mexiletine is
subjected to extensive metabolization.9 Thus, we decided to investigate the pilsicainide oxymethylene
analog (2) as a possible bioisostere of 1. To verify our design, we needed (a) a facile access to 2 and (b)
clues in favor of its sodium channel blocking activity. Herein we present how both goals were pursued:
facile, alternative synthetic routes to 1 and 2 were developed and 2 was proved to be at least four times
more potent than its prototype 1 when the blocking activity on human skeletal muscle voltage-gated
sodium channels, hNav1.4, transfected in tsA201 cells was tested.
RESULTS AND DISCUSSION
The key intermediate for the synthesis of both compounds 1 and 2 is 4-(2-oxopyrrolidin-1-yl)butanoic
acid (12, Scheme 1). It was obtained following different synthetic routes, all of which use freely
purchasable compounds as starting materials, in this resulting more convenient than those previously
reported, both starting from γ-butyrolactone,10,11 which is a regulated chemical. Both literature

HETEROCYCLES, Vol. 71, No. 9, 2007
2013
procedures has the advantage to give 12 in a single step. However the first one, consisting in the reaction
of γ-butyrolactone with potassium cyanate,10 in our hands gave 12 only in low yield (20%), while the
second one, using the sodium salt of 2-pyrrolidone as a reactant, is tainted by the hazard of explosions.12
Scheme 1
O
O
N
N
H
5
13
OH
iii 41%
73% viii
i
78%
O
O
O
O
N
ii
78%
iv
N
v
N
N
71%
91%
CN
I
O
OEt
OH
6
7
8
9
ix
73%
47% iii
O
O
O
N
N
N
O
N
vi, x
84%a
vi, vii
iv
71%
39%
O
O
O
O
OEt
CN
OEt
OEt
OH
14
12
11
10
Reagents and conditions: (i) I2, 1,2-bis(diphenylphosphino)ethane, anhyd toluene, 130 °C; (ii) NaCN, anhyd DMF, 50 °C; (iii)
Me2C(OH)CN, DEAD, Ph3P, anhyd Et2O, –20 °C; (iv) Me3SiCl, abs EtOH, 50 °C; (v) LiAlH4, anhyd THF, rt; (vi) KOH, EtOH, 60 °C;
(vii) 2 N HCl; (viii) CH2CHCO2Et, CsF, Si(OEt)4, rt; (ix) CH2(CO2Et)2, EtONa, anhyd THF, 60 °C; (x) 6 N HCl, 60 °C, then 220 °C.
aYields refer to crystallized product.
The first entry starts with the replacement of the hydroxy group of 1-(2-hydroxyethyl)pyrrolidin-2-one
(5) by iodine which was easily performed modifying a literature procedure:13 the use of 1,2-
bis(diphenylphosphino)ethane in lieu of triphenylphosphine allowed the easy isolation of 6. In fact, the
bis(phosphine oxide) by-product formed in the reaction, being more polar than triphenylphosphine oxide,
may be precipitated treating the crude product with EtOAc and then removed by filtration.14 After
concentration, flash chromatography on the filtrate gave pure 6. The cyanoderivative 7, which is now

2014
HETEROCYCLES, Vol. 71, No. 9, 2007
commercially available, was obtained via two alternative routes, starting from 515 and 616 respectively,
and was fully characterized. The transformation of nitrile 7 into the corresponding ethyl ester 8 was
obtained following a literature procedure17 and reduction of 8 with LiAlH4 gave alcohol 9. Nitrile 10 and
ethyl ester 11 were obtained starting from 9 via the same reactions that had led to the inferior homologs
7 and 8. Alkaline hydrolysis of the ethyl ester 11, followed by treatment with acid, gave the key
intermediate 12. This route may be more conveniently entered submitting γ-butyrolactame 13 to
conjugate addition to ethyl acrylate, extending a modified Michael addition procedure previously
reported for 13 superior cyclohomologs and acetamides.18
The intermediate 12 can be more directly accessed by submitting to hydrolysis and decarboxylation the
diester 14, which was, in turn, obtained by submitting the iodide 6 to malonic ester synthesis.
The acid 12 represents the key intermediate for the synthesis of 2 (Scheme 2). Pyrrolizine derivatives 15,
16, and 1 (pilsicainide) were prepared as previously described.19,20 The free amine 1 was converted into
its hydrochloride salt (1.HCl) by treatment with 2 N HCl. Perhydropyrrolizineethanol 17 was obtained
by reduction of 16 following the procedure reported in the literature for the corresponding methyl
ester.21 7a-[2-(2,6-Dimethylphenoxy)ethyl]hexahydro-1H-pyrrolizine (2), the oxymethylene analog of 1,
was obtained by condensating the alcohol 17 with 2,6-dimethylphenol under Mitsunobu conditions.22 As
an alternative, 2 was obtained by a Williamson-type etherification of 18, the mesyl derivative of 17, with
2,6-dimethylphenol.23 The free amine 2 was converted into its hydrochloride salt (2.HCl) by treatment
with 2 N HCl.
The activity of the hydrochloride salts of 1 and 2 (1.HCl and 2.HCl, respectively) was tested in vitro on
voltage-gated sodium currents recorded in tsA201 cells transfected with the human skeletal muscle
sodium channel, hNav1.4, using the whole-cell patch-clamp method. Sodium currents were elicited by

HETEROCYCLES, Vol. 71, No. 9, 2007
2015
depolarizing the cell from the holding potential of −120 mV to −30 mV at two stimulation frequency,
0.1 Hz for determination of tonic block and 10 Hz for use-dependent block determination.
Scheme 2
O
O
O
S
OEt
OH
O
O
i, ii
iii
iv
vii
viii
ix
N+
ClO4
15
2.HCl
12
N
N
N
18
vi
N
72%
84%
95%
-
78%
28%
50%
16
17
2
v, ix
31%
20%
1.HCl
Reagents and conditions: (i) soda lime, 170 °C; (ii) HClO4, EtOH; (iii) EtOCOCH2CO2K, abs EtOH, reflux; (iv) LiAlH4, anhyd THF, rt;
(v) 2,6-dimethylaniline, NaH, anhyd dioxane, 100 °C; (vi) 2,6-dimethylphenol, PPh3, DIAD, anhyd THF, rt; (vii) MeSO2Cl, Et3N, anhyd
CH2Cl2, 0 °C; (viii) 2,6-dimethylphenol, EtONa, anhyd THF/anhyd CH2Cl2, 60 °C; (ix) HCl.
The IC50 values (Table 1) were calculated by fitting the concentration/effect relationships with a first-
order binding function, and are reported with the S.E. of the fit.24
Table 1. In vitro blocking activity of the hydrochloride salts of pilsicainide (1.HCl) and its
oxymethylene analog 2.HCl on voltage-gated sodium currents recorded in tsA201 cells transfected with
the human skeletal muscle sodium channel, hNav1.4 (see experimental section for details).
Compound
Pilsicainide hydrochloride (1.HCl)
2.HCl
IC50 at 0.1 Hz (µM)
189 ± 10
IC50 at 10 Hz (µM)
76 ± 7
76 ± 6
18 ± 2
CONCLUSIONS
Alternative entries to 12, a key intermediate in the synthesis of pilsicainide (1), have been proposed.
They all start from commercially available compounds which are not included in the regulated substance
lists and avoid erratic10 or hazardous11,12 reactions. The same routes gave access to the oxymethylene
analog of 1 — 7a-[2-(2,6-dimethylphenoxy)ethyl]hexahydro-1H-pyrrolizine (2). The route that passes

2016
HETEROCYCLES, Vol. 71, No. 9, 2007
through the malonic synthesis of 14 was the most efficient in our hands and is to be preferred when
considering also the hazard accompanying the reaction between γ-butyrolactone and the sodium salt of
13.11,12 Finally, the route starting from either alcohol 5 or lactame 13, passes through several
pyrrolidinone intermediates which are possibly useful for the preparation of cognition enhancers, smart
drugs generally referred to as “racetams”.25,26
When tested in vitro on voltage-gated sodium currents recorded in tsA201 cells transfected with the
human skeletal muscle sodium channel, hNav1.4, using the whole-cell patch-clamp method, both 1.HCl
and 2.HCl displayed both tonic and phasic blocking activities. However, 2.HCl was more potent than its
prototype 1.HCl in both protocols used. In particular, it was four times more potent than 1.HCl under
use-dependent block conditions. On the basis of these preliminar results, 2 may be considered as a
bioisostere of pilsicainide. Further pharmacological investigations will explore its therapeutical potential
usefulness.
EXPERIMENTAL
General. Yields refer to purified products and were not optimized. The structures of the compounds
were confirmed by routine spectrometric analyses. Only spectra for compounds not previously described
are given. Melting points were determined on a Gallenkamp apparatus in open glass capillary tubes and
are uncorrected. Infrared spectra were recorded on a Perkin-Elmer (Norwalk, CT) Spectrum One FT
1
spectrophotometer and band positions are given in reciprocal centimeters (cm−1). H NMR and 13C
NMR spectra were recorded on a Bruker 300-MHz spectrometer (ASPECT 3000), operating at 300 and
1
13
75 MHz for H and C, respectively, using CDCl3 as solvent unless otherwise indicated. Chemical
shifts are reported in parts per million (ppm) relative to solvent resonance: CDCl3, δ 7.26 (1H NMR) and
δ 77.3 (13C NMR); DMSO-d6, δ 2.50 (1H NMR); CD3OD, δ 3.30 (1H NMR) and δ 47.8 (13C NMR). J
values are given in Hz. EIMS spectra were recorded on a Hewlett-Packard 6890-5973 MSD gas

HETEROCYCLES, Vol. 71, No. 9, 2007
2017
chromatograph/mass spectrometer at low resolution. Elemental analyses were performed on a
Eurovector Euro EA 3000 analyzer. GC was performed on a Varian 3800 gas chromatograph equipped
with a flame ionization detector and a Jew Scientific DB-5 capillary column (30 m, 0.25 mm i. d., 0.25
µm film thickness). Chromatographic separations were performed on silica gel columns by flash
chromatography (Kieselgel 60, 0.040−0.063 mm, Merck, Darmstadt, Germany) as described by Still et
al.27 TLC analyses were performed on precoated silica gel on aluminium sheets (Kieselgel 60 F254,
Merck).
In vitro testing. In vitro testing was performed as previously described.24 Briefly, the tsA201 cells, a
subclone of HEK293 cells, were transiently transfected with the full-length hNav1.4 cDNA, encoding a
human skeletal muscle sodium channel, using the calcium-phosphate precipitation method. The cells
were co-transfected with a lower amount of cDNA encoding the plasma membrane receptor CD8. For
patch-clamp recordings, 36−72 h after transfection, successfully transfected cells were recognized using
Dynal microbeads coated with anti-CD8 antibody (Dynal A.S., Oslo, Norway).
Whole-cell sodium currents were recorded at rt (20−22 °C) using an Axopatch 1D amplifier (Axon
Instruments, Union City, CA, USA). Voltage-clamp protocols and data acquisition were performed with
pClamp 6.0 software (Axon Instruments) through a 12-bit A-D/D-A Digidata 1200 interface (axon
Instruments). The external solution contained (mM): 150 NaCl, 4 KCl, 2 CaCl2, 1 MgCl2, 5 Hepes and 5
glucose; the pH was set to 7.4 with NaOH. The pipette solution contained (mM): 120 CsF, 10 CsCl, 10
NaCl, 5 EGTA, and 5 Hepes; The pH was set to 7.2 with CsOH. Currents were low-pass filtered at 2
kHz (−3dB) by the four pole Bessel filter of the amplifier and digitized at 10−20 kHz.
After rupturing the patch membrane, sodium currents were elicited by a 25 ms-long test pulse to −30
mV from a holding potential of −120 mV applied at 0.1 Hz frequency, until stabilization of current
amplitude was achieved (typically 5 min). Then the drug was applied at the desired concentration around
the cell through a plastic capillary, and effects of drug on sodium currents was measured first at 0.1 Hz

2018
HETEROCYCLES, Vol. 71, No. 9, 2007
stimulation frequency then at 10 Hz. Blocking effects were fully reversed upon drug wash-out. Little or
no run-down was observed during the experiments.
Analysis was performed off-line. The mean ratio IDRUG/ICTRL calculated from at least 3 cells was
reported as a function of drug concentration and the relationship was fitted by a first-order binding
function, IDRUG/ICTRL = 1/(1 + ([DRUG]/IC50), allowing the calculation of half-maximum inhibitory
concentration values.
1-(2-Iodoethyl)pyrrolidin-2-one (6). This compound had been previously obtained by means of a
Finkelstein reaction on the corresponding chloride but attempts to isolate it by distillation had given
samples analyzed only closely to the theoretical composition at the best (bp 125–127.5 °C, 0.5
mmHg).28 To a stirred solution of compound 5 (2.00 g, 15.5 mmol) in dry toluene (40 mL) under N2
atmosphere, 4.00 g (10.0 mmol) of 1,2-bis(diphenylphosphino) ethane were added. The reaction mixture
was brought to 130 °C and then 5.12 g (20.2 mmol) of iodine were added portionwise. The mixture was
refluxed for 1 h, then absolute EtOH (1 mL) was added in two portions at ca. 30 min intervals. After
evaporation of the solvent, the residue was taken up with CHCl3 and washed twice with saturated
Na2S2O3 and then twice with H2O. The organic layer was dried (Na2SO4) and concentrated under
vacuum, then EtOAc was added, and the precipitate formed was filtered off. The filtrate was evaporated
and the residue was purified by flash chromatography (EtOAc) to give 2.90 g of 6 as a colorless oil
(78%): bp 160 °C, 1 mmHg; IR (neat): 1685 (C=O) cm–1; 1H NMR (300 MHz): δ 2.08 (apparent quintet,
J = 7.6 Hz; t upon irradiation at 2.45, J = 6.9 Hz; t upon irradiation at 3.49, J = 8.1 Hz, 2H,
CH2CH2CH2), 2.45 (t, J = 8.1 Hz; s upon irradiation at 2.08, 2H, CH2CO), 3.25 (t, J = 7.1 Hz; s upon
irradiation at 3.67, 2H, CH2I), 3.50 (t, J = 7.0 Hz; s upon irradiation at 2.08, 2H, CH2CH2CH2N), 3.67 (t,
J = 7.0 Hz; s upon irradiation at 3.25, 2H, CH2CH2I); 13C NMR (75 MHz): δ 1.02 (1C), 18.3 (1C), 31.0
(1C), 45.3 (1C), 47.7 (1C), 175.5 (1C); MS (70 eV) m/z (%) 239 (M+, 7), 112 (100).

HETEROCYCLES, Vol. 71, No. 9, 2007
2019
3-(2-Oxopyrrolidin-1-yl)propanenitrile (7). Method A. To a stirred solution of triphenylphosphine
(3.04 g, 11.6 mmol) in anhydrous Et2O (15 mL) at –20 °C, under nitrogen atmosphere, a solution of
diethyl azodicarboxylate (1.83 mL, 11.6 mmol) in anhydrous Et2O (15 mL) was added dropwise. The
reaction was stirred for 20 min under cooling, then a solution of 5 (3 g, 23.2 mmol) in 10 mL of
anhydrous Et2O and anhydrous THF (1:1) was added dropwise. After stirring for 30 min at the same
temperature, a solution of acetone cyanohydrin (1.06 mL, 11.6 mmol) in anhydrous Et2O (20 mL) was
added and the mixture was stirred overnight at rt, then the precipitate formed was filtered off. The
filtrate was evaporated and the residue was purified by flash chromatography (EtOAc) to give 0.44 g of
7 as a pale yellow oil (41%). Method B. To a stirred solution of 6 (5.70 g, 23.8 mmol) in anhydrous
DMF (50 mL), NaCN (2.34 g, 47.7 mmol) was added. The reaction was heated to 50 °C and stirred for 5
h. The solvent was then evaporated under vacuum, taken up with CH2Cl2 and then washed with water.
The organic layer was dried (Na2SO4) and concentrated under vacuum. Purification of the crude oil
residue by flash chromatography (EtOAc) gave 2.60 g of 7 as a pale yellow oil (78%): IR (neat): 2249
(C≡N), 1681 (C=O) cm–1; 1H NMR (300 MHz): δ 2.06 (apparent quintet, J = 7.6 Hz, 2H, CH2CH2CH2),
2.38 (t, J = 8.0 Hz, 2H, CH2CO), 2.60 (t, J = 6.5 Hz, 2H, CH2CN), 3.54 (apparent t, J = 7.0 Hz, 4H,
13
CH2NCH2); C NMR (75 MHz): δ 16.7 (1C), 18.3 (1C), 30.8 (1C), 39.1 (1C), 48.1 (1C), 118.3 (1C),
175.7 (1C); MS (70 eV) m/z (%) 138 (M+, 41), 98 (100).
Ethyl 3-(2-oxopyrrolidin-1-yl)propanoate (8). Method A: To a stirred solution of 7 (1.46 g, 10.6
mmol) in absolute EtOH (4.10 mL, 70.4 mmol), under nitrogen atmosphere, chlorotrimethylsilane (4.10
mL, 32.3 mmol) was added. The reaction mixture was heated at 50 °C for 16 h. After being cooled to rt,
water (0.40 mL, 23.3 mmol) was added to the mixture and followed by the addition of Na2CO3 (1.12 g,
10.6 mmol) and CH2Cl2 (15 mL). The mixture was dried (Na2SO4) and evaporated. Purification of the
crude oil residue by flash chromatography (EtOAc) gave 1.40 g of 8 as a slightly yellowish oil (71%).
Method B: To a suspension of CsF (0.18 g, 1.17 mmol) in 13 (0.89 mL, 11.7 mmol), tetraethyl

2020
HETEROCYCLES, Vol. 71, No. 9, 2007
orthosilicate (2.61 mL, 11.7 mmol) was added, then ethyl acrylate (1.40 mL, 12.9 mmol) was added
dropwise. The reaction mixture was stirred for 4h at rt. Purification of the crude oil by flash
chromatography (EtOAc/petroleum ether 1:1) gave 1.57 g of 8 as a colorless oil (73%): IR (neat): 1732
(C=O, ester), 1683 (C=O, amide) cm–1; 1H NMR (300 MHz COSY): δ 1.25 (t, J = 7.1 Hz, 3H, CH3),
2.00 (apparent quintet, J = 7.6 Hz, 2H, CH2CH2CH2), 2.35 (t, J = 8.1 Hz, 2H, CH2CON), 2.55 (t, J = 6.9
Hz, 2H, CH2COO), 3.41 (t, J = 7.0 Hz, 2H, CH2CH2CH2N), 3.57 (t, J = 6.9 Hz, 2H, CH2CH2COO), 4.13
13
(q, J = 7.1 Hz, 2H, CH3CH2); C NMR (75 MHz): δ 14.4 (1C), 18.2 (1C), 31.0 (1C), 32.9 (1C), 38.8
(1C), 47.8 (1C), 60.9 (1C), 171.9 (1C), 175.3 (1C); MS (70 eV) m/z (%) 185 (M+, 36), 98 (100).
1-(3-Hydroxypropyl)pyrrolidin-2-one (9). To a stirred solution of 8 (0.20 g, 1.08 mmol) in dry THF
(10 mL) LiAlH4 (0.04 g, 1.08 mmol) under N2 atmosphere was added. The mixture was stirred at rt for 1
h. The reaction was quenched by the careful addition of few drops of water until the end of gas evolution.
The residue was removed by filtration and the filtrate was dried over anhydrous Na2SO4 and
concentrated under vacuum to give 0.14 g (91%) of a colorless oil: full characterization of this
compound can be found in the literature29 and our data are in agreement all but 1H NMR signals relative
to H2C-4 and H2C-2’. On the basis of a COSY experiment on 3’,3’-D2-9 (obtained by reduction of 8
with LiAlD4), m at 1.68–1.74 and t at 2.05 (J = 7.7 Hz) are to be assigned to H2C-2’ and H2C-4,
respectively.
4-(2-Oxopyrrolidin-1-yl)butanenitrile (10). Prepared as above described for 7 (Method A) starting
from 9. IR (neat): 2246 (C≡N), 1666 (C=O) cm–1; 1H NMR (300 MHz COSY; signals unambiguously
assigned on the basis of a COSY experiment on 2,2-D2-10 obtained from 3’,3’-D2-9): δ 1.88 (apparent
quintet, J = 7.0 Hz, 2H, CH2CH2CN), 2.0–2.1 (m, 2H, CH2CH2CO), 2.35 (t overlapping t at 2.37, J = 7.2
Hz, 2H, CH2CN), 2.37 (t overlapping t at 2.35, J = 8.1 Hz, 2H, CH2CO), 3.36 (t overlapping t at 3.39, J
= 6.8 Hz, 2H, CH2CH2CH2CN), 3.39 (t overlapping t at 3.36, J = 7.0 Hz, 2H, CH2NCO); 13C NMR (75

HETEROCYCLES, Vol. 71, No. 9, 2007
2021
MHz): δ 15.1 (1C), 18.1 (1C), 23.7 (1C), 31.0 (1C), 41.8 (1C), 47.6 (1C), 119.4 (1C), 175.9 (1C); MS
(70 eV) m/z (%) 152 (M+, 27), 98 (100).
Ethyl 4-(2-oxopyrrolidin-1-yl)butanoate (11). Prepared as above described for 8 starting from 10. IR
1
(neat): 1734 (C=O, ester), 1685 (C=O, amide) cm–1; H NMR (300 MHz; signals unambiguously
assigned on the basis of a COSY experiment on 2,2-D2-11 obtained from 2,2-D2-10): δ 1.22 (t, J = 7.2
Hz, 3H, CH3), 1.82 (apparent quintet, J = 7.4 Hz, 2H, CH2CH2COO), 1.99 (apparent quintet, J = 7.6 Hz,
2H, CH2CH2CON), 2.28 (t overlapping t at 2.34, J = 7.5 Hz, 2H, CH2COO), 2.34 (t overlapping t at 2.28,
J = 8.1 Hz, 2H, CH2CON), 3.28 (t, J = 7.2 Hz, 2H, CH2CH2CH2COO), 3.36 (t, J = 7.0 Hz, 2H,
13
CH2NCO), 4.10 (q, J = 7.2 Hz, 2H, CH2CH3); C NMR (75 MHz): δ 14.5 (1C), 18.2 (1C), 22.9 (1C),
31.2 (1C), 31.9 (1C), 42.2 (1C), 47.3 (1C), 60.7 (1C), 173.3 (1C), 175.4 (1C); MS (70 eV) m/z (%) 199
(M+, 35), 112 (100).
4-(2-Oxopyrrolidin-1-yl)butanoic acid (12). Method A: To an alcoholic stirred solution of 15 % KOH
(10 mL), compound 11 (0.15 g, 0.75 mmol) and H2O (0.2 mL) were added. The reaction mixture was
heated at 60 °C for 1 h. The solvent was removed under vacuum and the residue taken with 6 N HCl and
extracted five times with CH2Cl2. The combined organic phases were dried and evaporated to give 0.05
g (39%) of a slightly yellowish solid. Method B: To an alcoholic stirred solution of 15 % KOH (30 mL),
compound 14 (2.70 g, 9.96 mmol) and H2O (0.5 mL) were added. The reaction mixture was heated at
60 °C for 1 h and then acidified with 37% HCl. The solvent was removed under vacuum and the residue
was heated at 220 °C for 20 min. The crude residue was taken up three times with hot acetone. The
combined organic phases were evaporated and the residue was taken up with CHCl3, dried (Na2SO4) and
evaporated to give a yellow solid which was recrystallized from EtOAc to give 1.43 g (84%) of a
slightly yellowish solid: mp 86–87 °C (EtOAc); IR (KBr): 3200–2400 (OH), 1718 (C=O, carboxylic
acid), 1644 (C=O, amide) cm–1; 1H NMR (300 MHz COSY, DMSO-d6): δ 1.64 (apparent quintet, J =

2022
HETEROCYCLES, Vol. 71, No. 9, 2007
7.2 Hz, 2H, CH2CH2COO; 0.03 ppm upfield shifted upon treatment with NaOD), 1.88 (apparent quintet,
J = 7.4 Hz, 2H, CH2CH2CON), 2.15 (t overlapping t at 2.18, J = 7.5 Hz, 2H, CH2COO; 0.07 ppm
upfield shifted upon treatment with NaOD), 2.18 (t overlapping t at 2.15, J = 7.5 Hz, 2H, CH2CON),
3.14 (t, J = 7.1 Hz, 2H, CH2CH2CH2COO), 3.28 (t, J = 7.1 Hz; 2H, CH2NCO), 12.04 (s, 1H, COOH); 1H
NMR (300 MHz): δ 1.84 (apparent quintet, J = 7.2 Hz, 2H, CH2CH2COO), 2.01 (apparent quintet, J =
7.6 Hz, 2H, CH2CH2CON), 2.33 (t, J = 7.2 Hz, 2H, CH2COO), 2.41 (t, J = 8.1 Hz; s upon irradiation at
2.01, 2H, CH2CON), 3.32 (t, J = 7.1 Hz, 2H, CH2CH2CH2COO), 3.40 (t, J = 7.1 Hz; s upon irradiation
at 2.01, 2H, CH2NCO), 10.2 (br s, 1H, COOH); 13C NMR (75 MHz): δ 18.0 (1C), 22.7 (1C), 31.1 (1C),
31.6 (1C), 42.2 (1C), 47.6 (1C), 176.3 (1C), 176.8 (1C); MS (70 eV) m/z (%) 171 (M+, 24), 98 (100).
Anal. Calcd for C8H13NO3 (171.19): C, 56.13; H, 7.65; N, 8.18. Found C, 56.01; H, 7.68; N, 8.09.
Diethyl [2-(2-oxopyrrolidin-1-yl)ethyl]malonate (14). To a suspension of NaOEt (0.63 g, 9.26 mmol)
in anhydrous THF (5 mL), diethyl malonate (1.4 mL, 9.22 mmol) was added and the mixture was heated
at 60 °C. Then, a solution of 6 (2.00 g, 8.37 mmol) in anhydrous THF (10 mL) was added dropwise.
After 1.5 h the solvent was removed under vacuum and the residue was taken up with EtOAc, washed
with 0.3 N HCl, H2O and 5% NaHCO3. The organic layer was dried (Na2SO4) and concentrated under
vacuum. Purification of the residue by flash chromatography (EtOAc) gave 1.64 g (73%) of a colorless
oil: IR (neat): 1731 (C=O, ester), 1685 (C=O, amide) cm–1; 1H NMR (300 MHz COSY): δ 1.26 (t, J =
7.1 Hz, 6H, CH2CH3), 2.00 (apparent quintet, J = 7.6 Hz, 2H, CH2CH2CH2), 2.11 (apparent q, J = 7.2
Hz, 2H, CH2CH), 2.35 (t, J = 8.1 Hz, 2H, CH2CO), 3.25–3.35 (m, 3H, NCH2CH2CH), 3.38 (t, J = 7.2
Hz, 2H, CH2NCO), 4.10–4.25 (m, 4H, CH2CH3); 13C NMR (75 MHz): δ 14.2 (2C), 18.1 (1C), 26.6 (1C),
31.1 (1C), 40.8 (1C), 47.3 (1C), 49.8 (1C), 61.8 (2C), 169.2 (2C), 175.4 (1C); MS (70 eV) m/z (%) 271
(M+, 4), 112 (100).

HETEROCYCLES, Vol. 71, No. 9, 2007
2023
2-Tetrahydro-1H-pyrrolizin-7a(5H)-ylethanol (17). It was prepared by reduction of compound 16 and
obtained as a pure, colorless oil after distillation (bp 70 °C, 2 mmHg); yield: 95%; IR (neat): 3361 (OH)
cm–1; 1H NMR (300 MHz COSY): δ 1.56–1.69 (m, 4H, CCH2CH2O + CCHHCH2CH2), 1.72–1.86 (m,
6H, CH2CH2CH2 + CCHHCH2CH2), 2.50–2.62 (m, 2H, CHHN), 2.98–3.10 (m, 2H, CHHN), 3.76–3.85
(m, 2H, CH2O), 7.41 (br s, 1H, OH); 13C NMR (75 MHz): δ 25.0 (2C), 38.5 (2C), 40.1 (1C), 55.3 (2C),
60.6 (1C), 74.2 (1C); MS (70 eV) m/z (%) 154 (M+ – 1, 5), 110 (100).
2-[Tetrahydro-1H-pyrrolizin-7a(5H)-yl]ethyl methanesulfonate (18). To a stirred solution of 17
(0.30 g, 1.93 mmol) in dry CH2Cl2 (10 mL) under N2 atmosphere at 0 °C, 0.33 mL (2.89 mmol) of Et3N
were added. Then a solution of 0.21 mL (2.13 mmol) of MeSO2Cl in dry CH2Cl2 (8 mL) was added
dropwise. The reaction mixture was kept at 0 °C for 3 h, then a saturated aqueous NaHCO3 (10 mL) was
added. The aqueous solution was azeotropically evaporated and the white solid obtained was washed
four times with hot acetone (15 mL x 4) and filtrated. The combined organic phases were evaporated
and the residue was taken up with CHCl3, dried (Na2SO4), and concentrated in vacuo to give 0.35 g
1
(78%) of the title compound as a yellow oil: H NMR (300 MHz COSY): δ 2.08 (ddd, J = 13.2, 11.2,
6.3 Hz, 2H, CCHHCH2CH2), 2.23 (br ddd, J = 13.2, 6.3, 2.2 Hz, 2H, CCHHCH2CH2), 2.34 (t, J = 9.2
Hz, 2H, CCH2CH2O), 2.40–2.60 (m, 2H, CH2CHHCH2), 2.68 (s overlapping m at 2.65–2.90, 3H, CH3),
2.65–2.90 (m overlapping s at 2.68, 2H, CH2CHHCH2), 3.36 (apparent dt, J = 11.8, 5.8 Hz, 2H, CHHN),
396 (br ddd, J = 12.0, 6.4, 2.0 Hz, 2H, CHHN), 4.22 (t, J = 9.2 Hz, 2H, CH2O); 13C NMR (75 MHz): δ
26.0 (1C), 29.7 (2C), 36.7 (2C), 39.8 (1C), 57.4 (1C), 62.0 (2C), 92.9 (1C); MS (70 eV) m/z (%) 138
(M+ – 95, 6), 110 (100).
7a-[2-(2,6-Dimethylphenoxy)ethyl]hexahydro-1H-pyrrolizine (2). Method A: To a stirred solution of
triphenylphosphine (0.76 g, 2.90 mmol) in dry THF (20 mL) under N2 atmosphere, a solution of
compound 17 (0.30 g, 1.93 mmol) in dry THF (10 mL) was added, and then 2,6-dimethylphenol (0.35 g,

2024
HETEROCYCLES, Vol. 71, No. 9, 2007
2.90 mmol). A solution of DIAD (0.57 mL, 2.90 mmol) in dry THF (20 mL) was then added dropwise.
The mixture was stirred at rt for 24 h. The solvent was then evaporated under reduced pressure, then the
residue was taken up with EtOAc and extracted three times with 2 N HCl. The aqueous phases were
made alkaline with 6 N NaOH and extracted with CHCl3. The organic layer was dried (Na2SO4) and
concentrated under vacuum and the residue was purified by flash chromatography using silica gel
(CHCl3/MeOH 9:1) to give 0.10 g of a colorless oil (20%). Method B: To a solution of NaOEt (0.13 g,
1.91 mmol) in anhydrous THF (5 mL), 2,6-dimethylphenol (0.20 g, 1.64 mmol) was added and the
mixture was heated at 60 °C. Then, a solution of 18 (0.35 g, 1.50 mmol) in 10 mL of anhydrous THF
and anhydrous CH2Cl2 (1:1) was added dropwise. After 1.5 h the solvent was removed under vacuum
and the residue was taken up with 2 N HCl and washed with EtOAc. The aqueous phase was made
alkaline with 2 N NaOH and extracted with EtOAc to give a mixture of the free amine 2 and the parent
1
alchol 17 (0.155 g, 70:30, 28% yield of the desired product 2 as stated by GC analysis). H NMR (300
MHz COSY): δ 1.50–1.65 (m, 2H, CCHHCH2CH2), 1.65–1.92 (m, 6H, CCHHCH2CH2 + CH2CH2CH2),
1.99 (t, J = 7.3 Hz, 2H, CCH2CH2O), 2.28 (s, 6H, CH3), 2.54–2.65 (m, 2H, CHHN), 2.95–3.05 (m, 2H,
CHHN), 3.84 (t, J = 7.3 Hz, 2H, CH2O), 6.86–6.94 (m, 1H, Ar HC-4) 6.95–7.04 (m, 2H, Ar HC-3,5);
13C NMR (75 MHz): δ 16.7 (2C), 25.2 (2C), 37.9 (2C), 42.3 (1C), 55.5 (2C), 70.5 (1C), 72.0 (1C), 123.7
(1C), 128.9 (2C), 131.1 (2C), 156.7 (1C); MS (70 eV) m/z (%) 259 (M+, 5), 110 (100).
7a-[2-(2,6-Dimethylphenoxy)ethyl]hexahydro-1H-pyrrolizine Hydrochloride (2.HCl). It was
obtained by treating the free amine with a few drops of 2 N HCl and azeotropically removing water.
1
Yield: 50%; mp 147–149 °C (THF); H NMR (300 MHz COSY, CD3OD): δ 2.05–2.40 (m, 8H,
CCH2CH2CH2), 2.27 (s overlapping m at 2.05–2.40, 6H, CH3), 2.34 (t overlapping m at 2.05–2.40, J =
6.2 Hz, 2H, CCH2CH2O), 3.16–3.28 (m, 2H, CHHN), 3.58–3.72 (m, 2H, CHHN), 3.96 (t, J = 6.1 Hz,
2H, CH2O), 6.86–6.96 (m, 1H, Ar HC-4), 6.96–7.05 (m, 2H, Ar HC-3,5); 13C NMR (75 MHz, CD3OD):
δ 15.4 (2C), 24.0 (2C), 35.9 (2C), 37.4 (1C), 55.0 (2C), 68.0 (1C), 81.5 (1C), 124.2 (1C), 128.8 (2C),

HETEROCYCLES, Vol. 71, No. 9, 2007
2025
130.5 (2C), 155.7 (1C). Anal. Calcd for C17H25NO.HCl.0.33H2O (301.86): C, 67.64; H, 8.90; N, 4.64.
Found C, 67.63; H, 8.90; N, 4.91.
ACKNOWLEDGEMENTS
This work was accomplished thanks to the financial support of the Ministero dell’Istruzione,
dell’Università e della Ricerca (MIUR 2003033405).
REFERENCES AND NOTES
1. K. Okishige, M. Nishizaki, K. Azegami, M. Igawa, N. Yamawaki, and K. Aonuma, Am. Heart J.,
2000, 140, 437.
2. J. Morganroth, J. L. Anderson, and G. D. Gentzkow, J. Am. Coll. Cardiol., 1986, 8, 607.
3. M. Kawabata, K. Hirao, T. Horikawa, K. Suzuki, K. Motokawa, F. Suzuki, K. Azegami, and K.
Hiejima, J. Electrocardiol., 2001, 34, 65.
4. S. Ozeki, T. Utsunomiya, S. Matsuo, and K. Yano, Jpn. Circ. J., 1999, 63, 219.
5. T. Toeda, R. Susa, T. Saigawa, T. Abe, Y. Yamaguchi, K. Fuse, and H. Murooka, Jpn. Heart J.,
2000, 41, 405.
6. G. Hiasa, H. Okayama, K. Nishimura, and T. Sumimoto, Internal Medicine, 2005, 44, 55.
7. T. Kitahashi and I. Furuta, J. Pharm. Biomed. Anal., 2002, 29, 625.
8. B. Herweg and J. S. Steinberg, Card. Electrophysiol. Rev., 2000, 4, 255.
9. L. Labbé and J. Turgeon, Clin. Pharmacokinet., 1999, 37, 361.
10. W. Reppe and co-workers Justus Liebigs Ann. Chem., 1955, 596, 199.
11. S. Miyano, S. Fujii, O. Yamashita, N. Toraishi, and K. Sumoto, J. Heterocycl. Chem., 1982, 19,
1465.
12. M. Oka, T. Suzuki, and Y. Baba, E. P. Patent 0703233, 1996 (Chem. Abstr., 1996, 125, 10610).
13. M. D. Rozwadowska, Tetrahedron: Asymmetry, 1993, 4, 1619.
14. I. A. O’Neil, S. Thompson, C. L. Murray, and S. B. Kalindjian, Tetrahedron Lett., 1998, 39, 7787.
15. M. C. Aesa, G. Baán, L. Novák, and C. Szántay, Synth. Commun., 1996, 26, 909.
16. L. Friedman and H. Shechter, J. Org. Chem., 1960, 25, 877.
17. F.-T. Luo and A. Jeevanandam, Tetrahedron Lett., 1998, 39, 9455.
18. K. H. Ahn and S. J. Lee, Tetrahedron Lett., 1994, 35, 1875.
19. S. Miyano, T. Somehara, M. Nakao, and K. Sumoto, Synthesis, 1978, 701. CAUTION: warming of
solid hexahydropyrrolizinium perchlorate must be avoided because traces of chlorates, always to be

2026
HETEROCYCLES, Vol. 71, No. 9, 2007
feared when working with perchlorates, may cause explosions.
20. S. Miyano, K. Sumoto, F. Satoh, K. Shima, M. Hayashimatsu, M. Morita, K. Aisaka, and T.
Noguchi, J. Med. Chem., 1985, 28, 714.
21. S. Miyano, O. Yamashita, S. Fujii, T. Somehara, and K. Sumoto, Heterocycles, 1981, 16, 755.
22. O. Mitsunobu, Synthesis, 1981, 1.
23. S. Miyano, K. Sumotu, F. Satoh, and M. Hayashimatsu, J. P. Patent 59184178, 1984 (Chem. Abstr.,
1985, 102, 45772).
24. J.-F. Desaphy, A. De Luca, M. P. Didonna, A. L. George Jr., and D. Camerino Conte,
J. Physiol., 2004, 554, 321.
25. D. E. Butler, I. C. Nordin, Y. J. L’Italien, L. Zweisler, P. H. Poschel, and J. G. Marriott, J. Med.
Chem., 1984, 27, 684.
26. A. H. Gouliaev, J. B. Mønster, M. Vedsø, and A. Senning, Org. Prep. Proced. Int., 1995, 27, 273.
27. W. C. Still, M. Kahn, and A. Mitra, J. Org. Chem., 1978, 43, 2923.
28. B. Puetzer, L. Katz, and L. Horwitz, J. Am. Chem. Soc., 1952, 74, 4959.
29. D. J. Bergmann, E. M. Campi, W. R. Jackson, and A. F. Patti, Aust. J. Chem., 1999, 52, 1131.