Enzymatic resolution of a quaternary stereogenic centre as the key step in the synthesis of (S)-(+)-citalopram

Article abstract of DOI:10.1016/j.tetasy.2003.10.022

The enzymatic resolution of 4-[(4-dimethylamino)-1-(4′-fluorophenyl)- 1-hydroxy-1-butyl]-3-(hydroxymethyl)-benzonitrile, a useful intermediate in the synthesis of enantiomerically pure citalopram, has been studied. Candida antarctica lipase B (CAL-B) catalyzes the enzymatic acetylation of the primary benzylic alcohol with high enantioselectivity at the quaternary stereogenic centre. The enzymatic enantioselective hydrolysis of the 3-acetyloxymethyl derivative catalyzed by CAL-B is also possible.

Full text of DOI:10.1016/j.tetasy.2003.10.022

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 15 (2004) 341–345
Enzymatic resolution of a quaternary stereogenic centre as the
key step in the synthesis of (S)-(+)-citalopram
a
a
b
b
Laura F. Solares, Rosario Brieva, Margarita Quir oꢀ s, Isidro Llorente,
b
Miguel Bayod and Vicente Gotor
a,
*
a
Facultad de Qu ꢀı mica, Departamento de Qu ꢀı mica Org aꢀ nica e Inorg aꢀ nica, Universidad de Oviedo, 33071 Oviedo, Spain
Astur-Pharma S.A. Pol ꢀı gono Industrial de Silvota, parcela 23, 33192 Llanera (Asturias), Spain
b
Received 8 October 2003; accepted 23 October 2003
0
Abstract—The enzymatic resolution of 4-[(4-dimethylamino)-1-(4 -fluorophenyl)-1-hydroxy-1-butyl]-3-(hydroxymethyl)-benzo-
nitrile, a useful intermediate in the synthesis of enantiomerically pure citalopram, has been studied. Candida antarctica lipase
B (CAL-B) catalyzes the enzymatic acetylation of the primary benzylic alcohol with high enantioselectivity at the quaternary ste-
reogenic centre. The enzymatic enantioselective hydrolysis of the 3-acetyloxymethyl derivative catalyzed by CAL-B is also possible.
Ó 2003 Elsevier Ltd. All rights reserved.
1
. Introduction
esters with (+) and ())-a-methoxy-a-trifluoro-methyl-
phenylacetyl chloride and subsequent crystallization or
chromatographic separation by HPLC. The chromato-
graphic separation of the enantiomers of citalopram or
2
Citalopram, 1 is a very selective inhibitor of serotonin
5-HT) reuptake that has proved to be an efficient anti-
(
depressant in man. It was shown that almost the entire
1
the intermediate (±)-2 could also be carried out using a
TM
2
inhibition activity resides in the (S)-(+)-enantiomer.
chiral stationary phase such as Chiralpak
AD or
TM
4
Chiralcel OD. These routes involve consumption of
expensive enantiomerically pure reagents and, particu-
larly the crystallization methods, give relatively low
yields resulting in them being nonviable for industrial
production. Hence, there is a desire for the development
of new synthetic methods adequate to be carried out on a
large scale; among them, the use of enzymes as catalysts
OH
NC
NC
O
OH
N
N
5
is very suitable for this purpose.
F
F
Moreover, the resolution of the diol (±)-2 by enzymatic
methods is an interesting challenge from a theoretical
point of view. On the one hand, only a few hydrolases
were shown to be active on tertiary alcohols, because of
the adverse steric interactions caused by these sub-
(
S)-(+)-Citalopram, 1
(±)-2
0
The 4-[(4-dimethylamino)-1-(4 -fluorophenyl)-1-hydroxy-
-butyl]-3-(hydroxymethyl)-benzonitrile, (±)-2 is a useful
6
strates. On the other hand, the enantioselective recog-
1
nition at the primary hydroxyl group should be difficult
because this reaction site is four bonds removed from
the stereogenic centre.
3
intermediate in the synthesis of racemic citalopram. The
preparation of the single enantiomer has been carried out
by the stereoselective crystallization of the diastereo-
meric salts of the diol (±)-2 with (+)-di-p-toloyltartaric
acid or by the formation of the diastereomeric
2. Results and discussion
*
0
Corresponding author. Tel./fax: +34-985-103448; e-mail: vgs@
sauron.quimica.uniovi.es
Taking into account the structure of substrate (±)-2, in a
first approach we tested the capability of several lipases
957-4166/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2003.10.022

342
L. F. Solares et al. / Tetrahedron: Asymmetry 15 (2004) 341–345
OH
OH
O
O
NC
NC
NC
O
CAL-B
OH
OH
OH
N
+
N
+
N
O
organic solvent
30ºC
F
F
F
(±)-2
(S)-(-)-2
MsCl/Et
(R)-(+)-3
3
N
(
S)-(+)-Citalopram, 1
Scheme 1.
as catalysts in the acetylation process. In a first set of
experiments, vinyl acetate was chosen as the acyl donor
in dioxane. The enzymatic reactions were carried out at
30 °C (Scheme 1, Table 1). Only one of the tested en-
zymes catalyzed the acetylation of the primary alcohol:
enantioselectivity of E ¼ 27. In acetonitrile the process
is slower than in toluene but the enantioselectivity is
higher (E ¼ 66).
In order to improve the performance of the process, we
studied the influence of the substrate, enzyme and the
acylating agent concentrations. First, we increased the
concentration of substrate and enzyme from 5 to 10 mg/
mL in toluene (entry 5). Under these conditions we
observed a significative improvement of the reaction rate
but enantioselectivity decreased from E ¼ 27 to E ¼ 13.
Then, using these last conditions (10 mg/mL of enzyme
and substrate), we carried out the process using 5 or
1.5 equiv of vinyl acetate (entries 6 and 7). As one can
see from the table, decreasing the amount of acylating
agent increases the enantioselectivity of the enzymatic
reaction without a significative loss of reaction rate. The
best result (E ¼ 59) was obtained using 1.5 equiv of vinyl
acetate (entry 7). Even though one can expect that a
better enantioselectivity can be obtained using a con-
centration of enzyme and substrate of 5 mg/mL and
1.5 equiv of acylating agent (entry 8), under these con-
ditions, after 24 h, a 49% conversion was achieved, with
lower enantioselectivity (E ¼ 13).
lipase B from Candida antarctica (CAL-B) showed a
7
moderate enantioselectivity (E ¼ 17), at a low reaction
rate. It is noteworthy that the remaining substrate (S)-
(
))-2 has the correct configuration to complete the
synthesis of (+)-citalopram. In the processes catalyzed
by other lipases from C. antarctica (CAL-A and CAL-B-
L2), Pseudomonas cepacia, Candida rugosa or Mucor
miehei and the proteases from Aspergillus oryzae,
Streptomyces griseus or Savinase the unaltered starting
material was recovered.
In order to improve the rate of the CAL-B catalyzed
process we increased the concentration of the acylating
agent from 10 to 20 equiv. Under these conditions, the
reaction rate is moderated, 47% conversion is achieved
after 60 h of reaction, but the enantioselectivity slightly
decreased. Next we examined the effect of the organic
solvent; entries 3, 4 and 9 (Table 1) summarize the re-
sults of the experiments carried out in tert-butyl methyl
ether, toluene and acetonitrile, respectively. Under these
conditions, it is apparent that toluene and acetonitrile
are the best solvents for the CAL-B catalysis: after 24 h,
a 58% conversion was achieved in toluene, with an
A similar study was carried out in acetonitrile (entries 9–
13). It is apparent that the influence of the concentration
of the reagents and the enzyme is less dramatic in this
Table 1. CAL-B catalyzed acetylation of (±)-2 with vinyl acetate, at 30 °C
a
b
b
c
Entry Solvent
Substrate and Vinyl acetate
enzyme concn concn (equiv)
Time (h)
c (%)
Ee
s
(%)
Ee
p
(%)
E
(
mg/mL)
1
2
3
4
5
6
7
8
9
1
1
1
1
1,4-Dioxane
5
5
5
5
10
20
20
10
10
5
120
60
72
24
17
14
9
51
47
58
58
74
60
56
49
53
54
53
56
50
79
64
76
72
61
60
36
67
78
73
85
84
86
79
74
17
12
10
27
13
36
59
13
66
60
70
62
15
1,4-Dioxane
t-BuOMe
Toluene
84
>99
>99
>99
>99
71
Toluene
Toluene
10
10
10
5
Toluene
Toluene
1.5
1.5
10
24
39
17
21
21
26
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
5
99
0
1
2
3
10
10
20
5
5
>99
99
1.5
1.5
1.5
>99
75
a
b
c
Conversion, c ¼ ee
Determined by HPLC.
Enantiomeric ratio, E ¼ ln½ð1 ꢀ cÞð1 þ ee
s s p
/(ee + ee ).
7
p
Þꢁ= ln½ð1 ꢀ cÞð1 ꢀ ee Þꢁ.
p

L. F. Solares et al. / Tetrahedron: Asymmetry 15 (2004) 341–345
343
O
O
O
O
OH
NC
NC
NC
H
2
O, lipase
OH
OH
OH
N
N
+
N
organic solvent
F
F
F
(
±)-3
(S)-(-)-3
(R)-(+)-2
Scheme 2.
solvent compared to toluene. Again, we obtained the
best enantioselectivity using 10 mg/mL of enzyme and
substrate, and 1.5 equiv of acylating agent (E ¼ 70,
entry 11).
processes: the (R) enantiomer was preferentially hydro-
lyzed. The enantioselectivity of the CAL-B catalyzed
hydrolysis was similar to that of the acetylation in the
same solvent (entry 1, E ¼ 68) but the reaction rate was
much slower. The reaction catalyzed by CAL-B-L2 gave
poorer results.
Next, we examined the influence of the acyl donor in the
biocatalytic process. The reactions were carried out in
acetonitrile using a concentration of enzyme and sub-
strate 10 mg/mL and 1.5 equiv of acylating agent. Iso-
propenyl acetate or vinylpropionate led to lower
enantioselectivities in our system (E < 10). When vinyl
benzoate and methyl methoxyacetate were used the
unaltered starting material was recovered after 5 days of
reaction.
Next, we studied the effect of the reaction parameters on
the enantioselectivity of the enzymatic hydrolysis. We
observed a strong influence of the organic solvent
(entries 3–5). Acetonitrile is the best of the tested
solvents; when the processes were carried out in toluene,
1,4-dioxane or tert-butyl methyl ether the enantioselec-
tivity showed by the lipase dramatically decreased. The
attempt to improve the reaction rate increasing the
temperature resulted in low enantioselectivities. Taking
in account the influence of the pH of the aqueous
solution employed in a enzymatic hydrolysis, 4 equiv of
phosphate buffer 0.1 M, pH ¼ 7 were used instead of
Other suitable acyl donors are the anhydrides but, in
this case, all the attempts to use glutaric or succinic
anhydride gave the racemic product, probably because
of the significant amount of product formed through the
parallel chemical reaction.
2
H O (entry 8), but no improvement was observed in
these conditions.
Another common approach for the resolution of race-
mic alcohols is the enzymatic hydrolysis. In order to
study this reaction we prepared the racemic acetyl de-
rivative (±)-3 by treatment of the diol (±)-2 with acetic
anhydride. As in the case of acetylation, a first set of
experiments were examined in order to find the most
suitable enzyme for catalyzing the hydrolysis of the ac-
etyl derivative. As the hydrolysis in aqueous media
Finally, the reaction of enantiomerically pure substrate
(S)-())-2 with mesyl chloride and triethylamine was
carried out to obtain the (S)-(+)-citalopram 4 with a
yield higher than 90%.
(
phosphate buffer, pH 7) takes place spontaneously, we
3. Conclusions
carried out the process in acetonitrile with a small
amount of water (4 equiv) as nucleophile (Scheme 2,
Table 2). Only two of the tested enzymes catalyzed the
reaction, the lipases from C. antarctica, CAL-B and
CAL-B-L2. As expected, the stereochemical preferences
of these enzymes were the same as for the acetylation
0
The resolution of 4-[(4-dimethylamino)-1-(4 -fluorophe-
nyl)-1-hydroxy-1-butyl]-3-(hydroxymethyl)-benzonitrile
2 via a CAL-B catalyzed acetylation is described. Good
yields and high enantioselectivities can be achieved by
an appropriate selection of the reaction parameters. The
a
Table 2. Lipase catalyzed hydrolysis of (±)-3 in organic solvents
b
Entry
Lipase
Solvent
T (°C)
Time (h)
c (%)
Ee
s
(%)
Ee
p
(%)
E
1
2
3
4
5
6
7
8
CAL-B
Acetonitrile
Acetonitrile
Toluene
30
30
30
30
30
50
50
30
89
120
65
40
18
26
25
74
50
60
36
63
16
11
8
95
73
31
5
68
7
CAL-B-L2
CAL-B
CAL-B
2
1,4-Dioxane
t-BuOMe
65
48
1
CAL-B
CAL-B
73
67
87
44
28
67
56
78
4
Acetonitrile
Acetonitrile
145
145
120
10
10
13
CAL-B-L2
CAL-B
c
Acetonitrile
a
b
c
4
1
4
equiv of H
0 mg/mL.
2
O.
equiv of phosphate buffer 0.1 M, pH ¼ 7.

344
L. F. Solares et al. / Tetrahedron: Asymmetry 15 (2004) 341–345
best found conditions were the use of vinyl acetate as
acyl donor in acetonitrile, at 30 °C. In these processes,
the remaining alcohol (S)-())-2 has the correct config-
uration to complete the synthesis of (S)-(+)-citalopram.
On the other hand, the hydrolysis reaction catalyzed by
CAL-B also achieved good enantioselectivity and a
moderate reaction rate.
crude residue was purified by flash chromatography on
silica gel (ethyl acetate/Et N 10:1) to afford the acetyl-
ated product (+)-3 and the remaining substrate ())-2.
3
0
4
droxy-1-butyl]-3-(hydroxymethyl)-benzonitrile, (–)-2. Col-
.1.1. ())-4-[(4-Dimethylamino)-1-(4 -fluorophenyl)-1-hy-
2
D
0
1
ourless oil; ½aꢁ )98.5 (c 1, CHCl ), ee > 99%. H NMR
3
Taking into account the simplicity and easy scale-up of
lipase catalyzed reactions, the applicability of this
method to the industrial preparation of the antidepres-
(
CDCl
3
) d (ppm) 1.63 (br s, 2H, OH), 2.24 (s, 6H, CH
.38 (m, 6H, CH ), 4.30 (dd, 2H, CH ), 6.98 (t, 2H, CH),
.27 (m, 3H, CH), 7.59 (d, 2H, CH); C NMR (CDCl3)
), 43.8 (CH ), 44.6 (CH ), 59.8 (CH ),
), 111.3 (C), 114.6 (CH), 114.9 (CH), 118.5 (C),
3
),
2
7
2
2
13
8
sant (+)-citalopram is noteworthy.
d (ppm) 22.0 (CH
2
2
3
2
6
1
1
4.0 (CH
2
It is remarkable that the enzymatic catalyzed resolution
of a quaternary stereogenic centre is feasible by a
transesterification or hydrolysis reaction in organic sol-
vents. On the other hand, an enantioselective recogni-
tion can be achieved by the enzyme at a primary
hydroxyl group four bonds removed from the stereo-
genic centre.
27.0 (C), 127.4 (CH), 127.6 (CH), 128.1 (C), 128.9 (C),
þ
30.8 (CH), 135.8 (CH), 142.1 (C), 151.1 (C); MS (ESI ,
þ
þ
m=z): 365 (M+Na) , 343 (M+H) .
0
4.1.2. (+)-3-Acetyloxymethyl-4-[(4-dimethylamino)-1-(4 -
fluorophenyl)-1-hydroxy-1-butyl]-benzonitrile, (+)-3. Col-
2
0
1
ourless oil; ½aꢁ +36.5 (c 1.2, CHCl
3
), ee > 90%. H NMR
),
.18 (s, 6H, CH ), 2.45 (m, 6H, CH ), 5.19 (dd, 2H,
D
(
CDCl
3
) d (ppm) 1.56 (br s, 1H, OH), 2.02 (s, 3H, CH
3
4. Experimental
2
3
2
CH ), 6.96 (t, 2H, CH), 7.28 (m, 2H, CH), 7.65 (m, 3H,
2
13
Enzymatic reactions were carried out in a Gallenkamp
incubatory orbital shaker. Immobilized C. antarctica
lipase B Novozym 435 (CAL-B) was a gift from Novo
Nordisk. C. antarctica lipase B Chirazyme-L2, cf., lyo.
CH); C NMR (CDCl
3.2 (CH ), 44.6 (CH
3
) d (ppm) 20.8 (CH
3
), 22.1 (CH
2
),
4
2
3
), 59.7 (CH ), 63.5 (CH
2
2
), 110.9
C), 114.5 (CH), 114.8 (CH), 118.6 (C), 126.9 (CH), 127.6
(
(
1
CH), 127.7 (CH), 130.3 (CH), 132.2 (CH), 137.5 (C),
þ
(
CAL-B-L2) was purchased from Roche Diagnostics.
42.3 (C), 149.9 (C), 170.3 (CO); MS (ESI , m=z): 407
þ þ
M+Na) , 385 (M+H) .
(
Melting points were taken using a Gallenkamp appa-
ratus and were uncorrected. Optical rotations were
measured using a Perkin–Elmer 241 polarimeter and
4.1.2.1. Determination of the ee by HPLC analysis.
Two well resolved peaks were obtained for the racemic
ꢀ
1
2
specific rotations are quoted in units of 10 deg cm /g.
13
1
H and C NMR spectra were obtained with TMS
tetramethylsilane) as internal standard using a Bruker
compound (1 mg in 1 mL mobile phase; 20 lL sample) at
(
3
3
(
6 °C in hexane/i-propanol (98:2), 0.5 cm /min, Rs 1.5
1
13
AC-300 ( H 300 MHz and C 75.5 MHz) spectrometer.
Mass spectra were recorded on a Hewlett-Packard 1100
LC/MSD. All reagents were purchased from Aldrich
Chemie. Solvents were distilled over an adequate desic-
cant and stored under nitrogen. Flash chromatography
was performed using Merck silica gel 60 (230–400 mesh).
S)-())-3, t 36.03 min; (R)-(+)-3, t 40.38 min.
R
R
4
1
.2. Chemical acetylation of 4-[(4-dimethylamino)-
0
-(4 -fluorophenyl)-1-hydroxy-1-butyl]-3-(hydroxy-
methyl)-benzonitrile, (±)-2
The enantiomeric excesses were determined by chiral
HPLC analysis on a Shimadzu LC liquid chromato-
graph, using a CHIRALCEL OD for the acetyl deriv-
ative 3. The substrate (diol) 2 was first acetylated to
convert it into the ester 3 and then analyzed.
Acetic anhydride (0.11 mL, 1.17 mmol) was added
dropwise to a 0 °C solution of diol (±)-2 (0.2 g,
0
1
2 2 3
.58 mmol) in CH Cl (6 mL) and Et N (0.16 mL,
.17 mmol) and stirred for 8 h. The resulting mixture
was washed with 1 N HCl. The organic fraction was
dried over Na SO , filtered and evaporated under re-
duced pressure to afford the compound (±)-3 as a yellow
2
4
4
1
.1. Enzymatic acetylation of 4-[(4-dimethylamino)-
0
oil (189.5 mg, 85%).
-(4 -fluorophenyl)-1-hydroxy-1-butyl]-3-(hydroxy-
methyl)-benzonitrile, (±)-2
4
.3. Enzymatic hydrolysis of (±)-3-acetyloxymethyl-
0
The reaction mixture containing (±)-2 (0.2 g), vinyl ac-
etate and the lipase (0.2 g) in the corresponding organic
solvent (see concentration of enzyme and substrate in
Table 1) was shaken at 30 °C and 250 rpm in a rotatory
shaker. The progress of the reaction was monitored by
4-[(4-dimethylamino)-1-(4 -fluorophenyl)-1-hydroxy-
1-butyl]-benzonitrile, (±)-3
The reaction mixture containing (±)-3 (0.2 g), H O
2
(4 equiv) and the lipase (0.2 g) in the corresponding or-
ganic solvent (20 mL) was shaken at 30 °C and 250 rpm
in a rotatory shaker. The progress of the reaction was
monitored by TLC using the solvent system ethyl ace-
3
TLC using the solvent system ethyl acetate/Et N 10:1.
When the reaction was terminated the enzyme was re-
moved by filtration and washed with ethyl acetate. The
solvent was evaporated under reduced pressure and the
3
tate/Et N 10:1. When the reaction was terminated the

L. F. Solares et al. / Tetrahedron: Asymmetry 15 (2004) 341–345
345
enzyme was removed by filtration and washed with ethyl
acetate. The solvent was evaporated under reduced
pressure and the crude residue was purified by flash
chromatography on silica gel (ethyl acetate/Et N 10:1)
3
to afford the hydrolyzed product (+)-2 and the remain-
ing substrate ())-3.
Acknowledgements
This work was supported by the Principado de Asturias
(project CIS01-15). We express our appreciation to
Novo Nordisk Co. for the generous gift of the lipase
Novozym 435. L.F.S. was a recipient of a MCYT pre-
doctoral fellowship. We thank Luc ꢀı a Rodr ꢀı guez for her
technical assistance.
4
.4. Synthesis of (S)-(+)-1-[3-(dimethylamino)propyl]-
0
1-(4 -fluorophenyl)-1,3-dihydro-5-isobenzofurancarbo-
nitrile, (S)-(+)-citalopram, (S)-(+)-1
References and notes
0
To a suspension of 4-[(4-dimethylamino)-1-(4 -fluoro-
phenyl)-1-hydroxy-1-butyl]-3-(hydroxymethyl)-benzo-
nitrile, ())-2 (0.5 g, 1.46 mmol) in dry dichloromethane
1. Gravem, A.; Amthor, K. F.; Astrup, C.; Elgen, K.;
Gjessing, L. R.; Gunby, B.; Pettersen, R. D.; Kyrdalen,
L.; Vaadal, J.; Ofsti, E. Acta Psych. Scand. 1987, 75, 478–
(
5 mL), under nitrogen atmosphere and 0 °C, was added
dropwise a solution of mesyl chloride (0.14 mL,
.81 mmol), in 3 mL of dry dichloromethane. The re-
4
86.
. Boegeso, K. P. EP Patent 0347066, 1989; Chem. Abstr.
990, 113, 78150.
. Boegeso, K. P. U.S. Patent 4,650,884, 1987; EP 171943,
Chem. Abstr. 1986, 105, 42560.
. Bech Sommer, M.; Nielsen, O.; Pedersen, H.; Ahmadian,
H.; Pedersen, H.; Brosen, P.; Geiser, F.; Lee, J.; Cox, G.;
Dapremont, O.; Steu, C.; Assenza, S. P.; Hariharan, S.;
Nair, U. WO Patent 03/006449, 2003.
2
3
4
1
1
sulting mixture was allowed to warm up to 15 °C stirred
for 1 h. The progress of the reaction was monitored by
TLC using (ethyl acetate/Et
sulting mixture was washed with NaOH 1 N. The or-
ganic fraction was dried over Na SO , filtered and
3
N 10:1). After 1 h the re-
2
4
evaporated under reduced pressure. No further purifi-
cation was necessary to afford the compound (+)-cita-
5
. Schmid, A.; Dordick, J. S.; Hauer, B.; Kiener, A.; Wub-
bolts, M.; Witholt, B. Nature 2001, 409, 258–268.
. Hari Krishna, S.; Persson, M.; Bornscheuer, U. T. Tetra-
hedron: Asymmetry 2002, 13, 2693–2696; Henke, E.; Pleiss,
J.; Bornscheuer, U. T. Angew. Chem., Int. Ed. 2002, 41,
1
lopram as a yellow oil (426 mg, 90%). H NMR (CDCl )
3
6
d (ppm) 2.14 (s, 6H, CH
3
), 2.23 (m, 6H, CH
H, CH ), 6.99 (t, 2H, CH), 7.44 (m, 3H, CH), 7.58 (d,
2
), 5.16 (d,
2
2
2
13
H, CH); C NMR (CDCl ) d (ppm) 22.0 (CH ), 38.8
3
2
3
211–3213.
(
1
CH
2
), 45.2 (CH
3
), 59.3 (CH
2
), 71.2 (CH
2
), 91.0 (C),
11.6 (C), 115.1 (CH), 115.4 (CH), 118.5 (C), 122.7
7
. Chen, C. S.; Fujimoto, Y.; Girdaukas, G.; Sih, C. J. J. Am.
Chem. Soc. 1982, 104, 7294–7299.
(
1
(
CH), 125.1 (CH), 126.6 (CH), 126.7 (CH), 131.7 (CH),
þ
þ þ
M+Na) , 325 (M+H) .
8. Bayod, M.; Llorente, I.; Gotor, V.; Quir oꢀ s, M.; Fern ꢀa ndez-
Solares, L.; Brieva, R. ES Patent application P200302215 to
Astur Pharma.
39.5 (C), 140.2 (C), 149.4 (C); MS (ESI , m=z): 347