Enzyme-catalyzed kinetic resolution of piperidine hydroxy esters

Article abstract of DOI:10.1016/j.tetasy.2004.08.018

Enantiomers of N-protected piperidine-based cis- and trans-4-hydroxy-3- carboxylates and cis-3-hydroxy-4-carboxylates were prepared through kinetic resolution utilizing lipase AK from Pseudomonas fluorescens and Candida antarctica lipase A. The highly enantioselective (E >200) kinetic resolution of (±)-ethyl cis-(±)-4 and trans-1-(tert-butoxycarbonyl)-4- hydroxypiperidine-3-carboxylate (±)-5 was achieved by Pseudomonas fluorescens lipase-catalyzed asymmetric acylation with vinyl acetate in diisopropyl ether at room temperature. Candida antarctica lipase A-catalyzed asymmetric acylation of (±)-ethyl cis-1-benzyl-3-hydroxypiperidine-4- carboxylate (±)-11 was performed with vinyl propanoate in diisopropyl ether at 3°C, with good enantioselectivity (E = 75).

Full text of DOI:10.1016/j.tetasy.2004.08.018

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 15 (2004) 3281–3287
Enzyme-catalyzed kinetic resolution of piperidine hydroxy esters
Magdolna Solym a´ r, Enik o} Forr o´ and Ferenc F u¨ l o¨ p*
Institute of Pharmaceutical Chemistry, University of Szeged, H-6701 Szeged, POBox 121, Hungary
Received 27 July 2004; accepted 10 August 2004
Available online 2 October 2004
Abstract—The highly enantioselective (E >200) kinetic resolution of (±)ꢀethyl cisꢀ(±)ꢀ4 and transꢀ1ꢀ(tertꢀbutoxycarbonyl)ꢀ4ꢀhydroxyꢀ
piperidineꢀ3ꢀcarboxylate (±)ꢀ5 was achieved by Pseudomonas fluorescens lipaseꢀcatalyzed asymmetric acylation with vinyl acetate
in diisopropyl ether at room temperature. Candida antarctica lipase Aꢀcatalyzed asymmetric acylation of (±)ꢀethyl cisꢀ1ꢀbenzylꢀ3ꢀ
hydroxypiperidineꢀ4ꢀcarboxylate (±)ꢀ11 was performed with vinyl propanoate in diisopropyl ether at 3ꢀC, with good enantioselecꢀ
tivity (E = 75).
ꢁ
2004 Elsevier Ltd. All rights reserved.
1. Introduction
The enantioselective synthesis of variably substituted
1
piperidine compounds has been widely investigated.
1
Among the alkaloids and their analogues, esters and
hydroxy esters containing a piperidine ring can modify
neurotransmission, resulting in wideꢀranging effects on
the central nervous system. Piperidineꢀbased comꢀ
pounds, such as nipecotic acid and its hydroxyꢀ or
aminoꢀsubstituted derivatives, have therefore been
BakerÕs yeast has been utilized with moderate to good
diastereoselectivities for the reduction of ethyl 1ꢀ(tertꢀ
butoxycarbonyl)ꢀ4ꢀoxopiperidineꢀ3ꢀcarboxylate 3 under
fermenting and nonfermenting conditions, when the
8
a,12,13
(3R,4S)ꢀenantiomer was obtained.
This absolute
configuration is identical with that of the corresponding
stereogenic carbons of natural (ꢀ)ꢀcocaine. The absolute
configuration of the resulting hydroxy ester has been
1
synthetized and investigated for their GABAꢀagonist
2
activity, their binding capability to the cocaine receptor
3
12a
on the dopamine transporter and their potential choꢀ
4
proved, but the specific rotation data on the products
5
linergic and anticonvulsant activities. The binding sites
involved in these effects exhibit stereoselectivity, as (R)ꢀ
with different enantiomeric excesses remain unclear.
Enzymatic kinetic resolution has been successfully used
in the cases of the Nꢀmethyl and Nꢀisopropyl analogues
(
GABAꢀuptake inhibitor and the affinity of (R)ꢀcocaine
ꢀ)ꢀnipecotic acid has proved to be a more effective
2
d
14
of 4 and 5, as earlier for the resolution of racemic
15
6
is higher for the cocaine receptor. Hydroxylated and
polyhydroxylated piperidines have been found to be
cocaine,
through the pig liver esteraseꢀcatalyzed
(R)ꢀselective hydrolysis of the phenylacetyl group.
BakerÕs yeast also catalyzes the reduction of ethyl 1ꢀbenzꢀ
ylꢀ3ꢀoxopiperidineꢀ4ꢀcarboxylate (the base of 6) in an
7
effective glucosidase inhibitors and have been used in
8
the synthesis of oligosaccharide mimetics. The transꢀ
1
6
4
ꢀhydroxy ester 5 is of importance as a potential interꢀ
mediate in the synthesis of the first reported selective
(R)ꢀselective manner.
9
ORL1ꢀreceptor antagonist. Orthogonally protected
transꢀ4ꢀaminopiperidineꢀ3ꢀcarboxylic acid has been utiꢀ
In order to prepare the enantiomers of piperidineꢀbased
4ꢀhydroxy and 3ꢀhydroxy esters, we set out to investiꢀ
gate the Oꢀacylation reactions of NꢀBocꢀprotected
4ꢀhydroxy esters 4 and 5, and their 3ꢀhydroxy ester regꢀ
ioisomers 9 and 10, in organic media by lipase catalysis.
lized as a conformationally restricted bꢀamino acid
1
0
building block in foldamer research. These facts highꢀ
light the significance of the syntheses of chiral piperꢀ
idines as synthetic building blocks and members of the
chiral pool.
2
. Results and discussion
.1. Synthesis of model racemic hydroxy esters
NꢀBenzylꢀsubstituted oxo esters 1 and 6 were syntheꢀ
2
*
0
Corresponding author. Tel.: +36 62 545564; fax: +36 62 545705;
eꢀmail: fulop@pharma.szote.uꢀszeged.hu
1
7
sized by Dieckmann condensation
from ethyl
957ꢀ4166/$ ꢀ see front matter ꢁ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2004.08.018

3282
M. Solym a´ r et al. / Tetrahedron: Asymmetry 15 (2004) 3281–3287
1
8
3ꢀ(NꢀbenzylꢀNꢀcarbethoxyethyl)aminopropanoate and
ethyl 4ꢀ(NꢀbenzylꢀNꢀcarbethoxymethyl)aminobutanoꢀ
ate (VP), the reaction became slower (after 144h,
c = 48%, or after 116h, c = 50%), but the enantioselecꢀ
tivity was not affected (E >200). Increase of the temperꢀ
ature was accompanied by a slight decrease in
enantioselectivity (entries 10–12). As the lipase concenꢀ
tration was increased from 20mg/mL (entry 10) to
30mg/mL (after 10h, c = 37%, E >200), the reaction rate
increased considerably, buta fur ht er increase ot 40mg/
mL (after 10h, c = 41%, E = 86) resulted in a drop in
enantioselectivity.
1
7
ate, respectively, which were debenzylated to give
hydrochlorides 2 and 7. Bocꢀprotected oxo esters 3
and 8 were subjected to reduction with NaBH to give
4
hydroxy esters 4, 5 and 9, 10, which were isolated by colꢀ
umn chromatography. Compounds 9 and 10 were
formed in a ratio of 7:3 in the reduction step; 9 could
be isolated with de = 96%, and 10 with de = 90%, but
in a very low (2%) yield. The diastereomeric mixture
of Nꢀbenzylꢀsubstituted hydroxy esters 11 and 12 was
prepared directly from the liberated base of 6 under
the same reduction conditions. Pure 11 was isolated by
column chromatography, whereas pure 12 could not
be isolated; it was obtained only in a 1:1 diastereomeric
mixture (Scheme 1).
In the smallꢀscale acylation of (±)ꢀ5 under the conꢀ
ditions optimized for (±)ꢀ4 (Table 1, entry 10), a
higher reaction rate (about five times) was observed,
with excellent enantioselectivity (after 2h, c = 41%,
E >200). This observation is in accordance with the litꢀ
erature data concerning the Oꢀacylation of the cisꢀ and
1
9
2
.2. Lipase-catalyzed acylation of (± ±-4 and (± ±-5
transꢀcyclohexaneꢀbased analogues by lipase PS and
the hydrolysis of the Oꢀacetates by P. fluorescens
2
0
After a lipase screening for the acylation of (±)ꢀ4 at
room temperature, the effects of solvent, acyl donor,
temperature and enzyme concentration were studied
lipase.
2.3. Lipase-catalyzed acylation of (± ±-11
(
Table 1).
Since the Oꢀacylated derivatives of the 3ꢀhydroxy regioꢀ
isomer 9 could notbe separa et d by chiral gas chromaꢀ
tography on either a bꢀcyclodextrin, an Lꢀvaline or a
cꢀcyclodextrin column (Chrompack CPꢀChirasilꢀDEXꢀ
CB, ChirasilꢀLꢀVal and GAMMA DEX 120), we
decided to continue with the Nꢀbenzyl analogue 11,
the enantiomers of which could be easily analyzed
through baseline separation of the acylated derivatives.
In an enzyme screening, with 0.2M VA as acyl donor
With vinyl acetate (VA) as acyl donor in diisopropyl
ether (iꢀPr O) at room temperature, Candida antarctica
2
lipase A (CALꢀA) catalyzed the acylation with moderate
enantioselectivity (entry 1). Lipolase (immobilized C.
antarctica lipase B preparation), lipase PS (from P. cepa-
cia), CALꢀB (C. antarctica lipase B, Novozym 435) and
lipase AK (from P. fluorescens) demonstrated excellent
enantioselectivities, but lower catalytic activity, under
the same conditions (entries 2–5). The best combination
of enantioselectivity and reaction rate was observed for
immobilized lipase AK catalysis. In an effort to increase
the reaction rate, different solvents were tested: low reacꢀ
tion rates and low enantioselectivities were observed in
CH Cl , THF and acetone (entries 6, 7 and 9), whereas
in iꢀPr O at 0.1M substrate concentration, with 70mg/
2
mL enzyme at45 ꢀC, lipase AK, lipase PS and Chiraꢀ
zyme Lꢀ2 were found not to catalyze the Oꢀacylation
of (±)ꢀ11; only CALꢀA displayed considerable catalytic
activity, but low enantioselectivity (Table 2, entry 1).
To increase the enantioselectivity, the effects of solvent,
acyl donor, temperature and enzyme concentration were
tested (Table 2). The enantioselectivity increased with
decreasing temperature, but the reaction rate decreased
(entries 1–3). As the reaction rate did not decrease at
2
2
the reaction rate was considerably higher in iꢀPr O and
2
in hexane (entries 5 and 8), with excellent enantioselecꢀ
tivities, iꢀPr O giving the best results. On change of
the acyl donor to isopropenyl acetate or vinyl propanoꢀ
2
O
N
OH
N
O
N
O
COOEt
COOEt
COOEt
.HCl
i
COOEt
ii
iii
N
H
.HCl
t
t
COO Bu
COO Bu
CH C H
5
2
6
1
2
3
cis (± ±)ꢁ
trans (± ±)5
COOEt
OH
COOEt
COOEt
COOEt
COOEt
O
O
OH
O
iv, iii
i
ii
iii
N
N
.HCl
N
N
N
H
.HCl
CH C H
CH C H
COO Bu
t
COO Bu
t
2
6
5
2
6
5
cis (± ±)11
trans (± ±)12
6
7
8
cis (± ±)-
trans (± ±)1ꢀ
Scheme 1. Reagents and conditions: (i) Pd/C, EtOH, H
2
atm; (ii) Boc
2
O, Et
3
2 2 4 3 2 2
N, CH Cl ; (iii) NaBH , abs EtOH; (iv) Et N, CH Cl .

M. Solym a´ r et al. / Tetrahedron: Asymmetry 15 (2004) 3281–3287
3283
Table 1. Enzymatic Oꢀacylation (20mg/mL enzyme) of (±)ꢀ4 and (±)ꢀ5 (0.1M) with vinyl acetate (VA) (0.2M)
OH
N
OH
OCOMe
COOEt
COOEt
COOEt
VA
+
lipase
N
N
t
t
t
COO Bu
COO Bu
COO Bu
(
(
± ±-4 cis
± ±-5trans
4a
5a
4b
5b
a
b
E
Entry
Enzyme
T (ꢀC)
SolventTime (h)
Conv.
(%)
Ee
s
(%)
Ee
p
(%)
c
1
2
3
4
5
6
7
8
9
CALꢀA
rt
iꢀPr
iꢀPr
iꢀPr
iꢀPr
iꢀPr
2
2
2
2
2
O
O
O
O
O
Cl
3.6
72
51
33
39
43
49
2
89
97
61
72
95
2
85
48
97
98
98
93
37
122
131
c
Lipase PS
CALꢀB
Lipolase
rt
rt
72
70
rt
>200
>200
27
c
c
c
c
c
Lipase AK
Lipase AK
Lipase AK
Lipase AK
rt
72
180
rtCH
rtTHF
rtHexane
rtAce 1t 80
45
2
2
180
180
13
50
11
99
76
98
8
>200
Lipase AK one
8
2
19
1
c
10
11
12
Lipase AK
Lipase AK
Lipase AK
iꢀPr
iꢀPr
iꢀPr
2
2
2
O
O
O
11
43
28
27
49
41
37
96
67
>99
>200
>200
100
c
55
60
99
96
c
d
a
b
c
Conv. = ee
s
/(ee
s p
+ ee ).
21
E = ln[(1 ꢀ ee /ee
Contains 20% (w/w) of lipase adsorbed on Celite in the presence of sucrose.
The reaction stopped at this conversion.
s
)/(1 ꢀ ee
s
p
)]/ln[(1 ꢀ ee
s s p
)/(1 + ee /ee )].
22
d
Table 2. CALꢀAꢀcatalyzed Oꢀacylation of (±)ꢀ11 (0.1M) with different acyl donors (0.2M) in organic solvents
COOEt
OH
COOEt
OH
COOEt
OCOR
acyl donor
lipase
+
N
N
N
CH Ph
CH Ph
CH Ph
2
2
2
(± ±)11 cis
11a
11b
R = Me, Et, n)Pr
a
b
Entry
CALꢀA (mg/mL)
T (ꢀC)
SolventAcyl donor
Time (h)
Conv.
(%)
Ee
s
(%)
Ee
p
(%)
E
1
2
3
4
5
6
7
8
9
70
70
70
40
40
40
40
40
40
40
40
rt
rt
3
iꢀPr
iꢀPr
iꢀPr
iꢀPr
2
2
2
2
O
O
O
O
VA
VA
VA
VA
5
10
50
38
40
43
60
50
57
60
60
83
86
79
7
18
23
15
145
9
rt
rtToluene
rtMeCN
VA
c
166
40
47
69
9
VA
VP
VP
VB
166
4
29
48
27
48
36
10
21
71
36
63
45
52
77
96
69
79
4
16
75
10
13
rt
3
iꢀPr
iꢀPr
iꢀPr
iꢀPr
2
O
O
O
O
2
2
2
4
rt
rt
45
3
50
1
1
0
1
Isopropenyl acetate
Et128
PrCO
2
EtPrCO
2
21
38
2
a
b
c
Conv. = ee
E = ln[(1 ꢀ ee
Opposite enantioselectivity.
s
/(ee
s p
+ ee ).
21
s
)/(1 ꢀ ee
s
/ee
p
s s p
)]/ln[(1 ꢀ ee )/(1 + ee /ee )].
4
0mg/mL enzyme concentration (entry 4 vs entry 2),
in the acyl donor from VA to VP, the reaction rate inꢀ
creased without a loss in enantioselectivity at room temꢀ
perature (entries 4 and 7), but when vinyl butanoate
(VB) was used, the enantioselectivity did decrease (entry
9). The application of isopropenyl acetate, possessing a
bulkier sideꢀchain in the alcohol part of the ester,
decreased both the enantioselectivity and the reaction
rate (entry 10 vs entry 4).
from economic considerations 40mg/mL enzyme was
used in the further reactions. On change of the solvent
to toluene or MeCN, the enantioselectivity and the reacꢀ
tion rate decreased (entries 5 and 6 vs entry 4). The
enzyme exhibited the opposite enantiopreference in
MeCN, but low enantioselectivity and a low reaction
rate (entry 6). With increase of the acid sideꢀchain length

3284
M. Solym a´ r et al. / Tetrahedron: Asymmetry 15 (2004) 3281–3287
Table 3. Gramꢀscale resolution of (±)ꢀ4, (±)ꢀ5 and (±)ꢀ11
c
Time (h) Conv. (%)
Substrate
4a–11a
4b–11b
2
5
d
25
d
Yield (%)
Abs. config. Ee (%) ½aŠD
Yield (%) Abs. config. Ee (%) ½aŠD
a
e
f
e
g
i
(
(
(
±)ꢀ4
41.5
14
50
50
3R,4S
3S,4S
3S,4S
>99
99
+57.9
ꢀ24.4
+37.7
30
41
28
3S,4R
3R,4R
3R,4R
99
>99
91
ꢀ41.0
47
39
33
a
±)ꢀ5
+6.5
b
h
±)ꢀ11 R@CH
2
CH
3
Resolution in two
steps
92
ꢀ24.0
a
b
c
d
e
f
0
.1M substrate, 0.2M VA in iꢀPr
.1M substrate, 0.2M VP in iꢀPr
Conv. = ee /(ee + ee ).
Total yield starting from racemic substrate.
c 1, CH Cl
c 0.91, CH
2
O, 30mg/mL lipase AK at45 ꢀC.
O, 40mg/mL CALꢀA at3 ꢀC.
0
2
s
s
p
2
2
.
2
Cl
Cl
c 0.77, CHCl
c 1, CHCl
2
.
g
h
i
c 1.01, CH
2
2
.
3
.
3
.
For the isolation of enantiomeric compounds, resoluꢀ
tion could be achieved in two consecutive steps, under
the same conditions (entry 8).
oxypiperidineꢀ4ꢀcarboxylate 11b (ee = 91%) were preꢀ
pared by CALꢀAꢀcatalyzed (R)ꢀselective Oꢀacylation
with VP in iꢀPr O at 3ꢀC. The isolated enantiomeric
2
compounds were characterized, and the previously
described literature data for 4a were clarified. Enantioꢀ
merically pure 5a, 5b and 11b had notbeen repor te d in
the literature previously. All the enantiomerically pure
compounds isolated are of great pharmaceutical interest
for further investigations.
As a result of the above smallꢀscale experiments, the preꢀ
parativeꢀscale resolution of (±)ꢀ4 and (±)ꢀ5 was perꢀ
formed through Oꢀacetylation by lipase AK with VA
in iꢀPr O at 45ꢀC (Table 1, conditions of entry 10), while
2
(
±)ꢀ11 was resolved through Oꢀacylation by CALꢀA
with VP in iꢀPr O at 3ꢀC (Table 2, entry 8), and the
2
enantiomers were isolated (Table 3).
4. Experimental
2
.4. Determination of absolute configuration
In a typical smallꢀscale experiment, the substrate (0.1M)
was dissolved in an organic solvent, and a lipase or a
lipase preparation, 20% (w/w) immobilized on Celite in
When the specific rotation data on 4a are compared with
8
a,12,13
literature values,
we can conclude from the sign of
rotation that lipase AK exhibited (R) selectivity in the
2
2
the presence of sucrose, and 2equiv of an acyl donor
were added. The progress of the reactions and the ee valꢀ
ues were followed by taking samples at intervals and
analyzing them by gas chromatography on a Chromꢀ
pack CPꢀChirasilꢀDEXꢀCB (25m). For good baseline
separation, the unreacted hydroxy group in the sample
was derivatized with acetic or propanoic anhydride in
the presence of pyridine containing 1% 4ꢀN,Nꢀdimethylꢀ
aminopyridine before injections.
25
Oꢀacylation. Our results reveal ½aŠ ¼ þ57:9 (c 1,
D
CH Cl ) for the hydroxy ester 4a (ee >99%), which is
2
2
2
D
5
in accordance with the literature values of ½aŠ ¼ þ15
8
a
25
D
(
CH Cl , ee = 41%) for the (3R,4S) enantiomer. For
c 0.75, CH Cl , ee = 24%) and ½aŠ ¼ þ23 (c 0.75,
2 2
2
2
1
3
determination of the absolute configuration, 11b was
transformed to its methyl ester and NꢀBocꢀprotected
analogue, which is known in the literature. Comparison
25
of the specific rotation ½aŠ ¼ ꢀ27 (c 0.12, CHCl ) with
D
3
25
that given in the literature, ½aŠ ¼ ꢀ32:7 (c 1, CHCl , ee
Melting points were determined with a Kofler apparatus
D
proved the absolute configuration (3R,4R)
3
1
2b
1
notgiven)
for the product.
at a heating rate of 4ꢀC/min. H NMR spectra were reꢀ
corded in CDCl at ambient temperature on a Bruker
DRX400 spectrometer. Chemical shifts are given in d
3
(
ppm) relative to TMS as internal standard; multipliciꢀ
ties were recorded as s (singlet), br s (broad singlet), d
doublet), dd (double doublet), ddd (double double douꢀ
3. Conclusions
(
The resolution of highly valuable Nꢀprotected piperidineꢀ
based hydroxy esters has been achieved by (R)ꢀselective
lipase catalysis. Enantiomerically pure (ee P 99%)
blet), t (triplet), dt (double triplet), ddt (double double
triplet), q (quartet) or m (multiplet). MS spectra were reꢀ
corded on a Finnigan MAT 95 S instrument. Elemental
analyses were performed with a Perkin–Elmer CHNSꢀ
2400 Ser II Elemental Analyzer. Optical rotations were
measured with a Perkin–Elmer 341 polarimeter.
(
3R,4S)ꢀethyl cisꢀ4a and (3S,4S)ꢀethyl transꢀ1ꢀ(tertꢀbutꢀ
oxycarbonyl)ꢀ4ꢀhydroxypiperidineꢀ3ꢀcarboxylate 5a and
3S,4R)ꢀethyl cisꢀ4b and (3R,4R)ꢀethyl transꢀ1ꢀ(tertꢀbutꢀ
oxycarbonyl)ꢀ4ꢀacetyloxypiperidineꢀ3ꢀcarboxylate 5b
(
were prepared by lipase AKꢀcatalyzed (R)ꢀselective
Oꢀacetylation with VA in iꢀPr O at 45ꢀC. (3S,4S)ꢀEthyl
4.1. Ethyl 4-oxopiperidine-3-carboxylate hydrochloride, 2
2
cisꢀ1ꢀbenzylꢀ3ꢀhydroxypiperidineꢀ4ꢀcarboxylate 11a
(ee = 92%) and (3R,4R)ꢀethyl cisꢀ1ꢀbenzylꢀ3ꢀpropanoylꢀ
Ethyl 1ꢀbenzylꢀ4ꢀoxopiperidineꢀ3ꢀcarboxylate hydroꢀ
1
chloride 1 (2.5g, 8.40mmol) was hydrogenated in the
8

M. Solym a´ r et al. / Tetrahedron: Asymmetry 15 (2004) 3281–3287
3285
presence of 10% Pd/C catalyst at atmospheric pressure
in abs EtOH (250mL) for 8h until the hydrogen uptake
was over. The catalyst was then filtered off and the solꢀ
ventwas evapora et d off. The residue was recrys at llized
C H NO : C, 57.13; H, 8.48; N, 5.12. Found: C,
13 23 5
57.22; H, 8.98; N, 5.26%.
1
(±)ꢀ5. de = 90%: lightꢀyellow oil, H NMR (DMSOꢀd ,
6
from EtOH/Et O to give lightꢀbrown crystals (1.64g,
2
400MHz, 333K) d 1.19 (3H, t, J = 7.1Hz, CH CH ),
2
3
2
3
1
9
4%), mp 159–162ꢀC, lit. mp 164–166ꢀC. H NMR
1.22–1.32 (1H, m, 5ꢀH), 1.39 (9H, s, tBu), 1.81 (1H,
ddd, J = 4.3, 7.6, 12.6Hz, 5ꢀH), 2.23 (1H, ddd, J = 4.0,
9.1, 9.8Hz, 3ꢀH), 2.72–3.13 (2H, m, 2ꢀH, 6ꢀH), 3.73–
3.80 (2H, m, 2ꢀH, 6ꢀH), 3.89 (1H, dd, J = 2.3, 13.4Hz,
4ꢀH), 4.08 (2H, q, J = 7.0Hz, OCH CH ), 4.79 (1H, d,
d 1.31 (3H, t, J = 7.1Hz, CH CH ), 2.77 (2H, t,
2
3
J = 5.7, 6ꢀCH ), 3.37 (2H, d, J = 5.2Hz, 5ꢀCH ), 3.87
2
2
(
(
2H, s, 2ꢀCH ), 4.23 (2H, q, J = 7.1Hz, OCH ), 10.12
2 2
þ
ꢀ
2H, s, NH Cl ), 12.16 (1H, br s, OH). Anal. Calcd
2
2
3
1
3
for C H ClNO : C, 46.27; H, 6.80; N, 6.75. Found:
C, 46.64; H, 6.99; N, 6.27%.
J = 5.5, OH). C NMR d 13.7, 27.7, 32.5, 41.3, 43.5,
49.7, 59.6, 67.59, 78.6, 153.5, 171.5. MS (m/z, EI) (rel.
abund.) 273 (4, [M ]), 216 (67), 200 (32), 172 (66), 154
8
14
3
+
4.2. Ethyl 1-(tert-butoxycarbonyl±-4-oxopiperidine-3-
carboxylate, 3
(37), 126 (72), 100 (65), 82 (82), 57 (100), 41 (51). Anal.
Calcd for C H NO : C, 57.13; H, 8.48; N, 5.12.
Found: C, 57.25; H, 8.64; N, 5.20%.
1
3
23
5
Ethyl 4ꢀoxopiperidineꢀ3ꢀcarboxylate hydrochloride 2
(6.05g, 29.23mmol) was dissolved in CH Cl , and
Et N (11.86g, 117.21mmol) was added. The mixture
4.4. Preparative-scale resolution of (± ±-4
2
2
3
was stirred for 2h and diꢀtertꢀbutyl dicarbonate
(
Five hundred milligrams (1.83mmol) of (±)ꢀ4 was disꢀ
solved in 18mL of iꢀPr O, and 540mg (30mg/mL) of
7.04g, 32.22mmol) was then added to the mixture,
2
which was next stirred overnight. The solvent was evapꢀ
orated off and the product was purified by silica gel colꢀ
umn chromatography, using EtOAc/hexane = 1:3 as
eluent, to give colourless crystals (7.06g, 89%), mp 64–
20% lipase AK preparation and 340lL (3.67mmol) of
VA were added. The reaction mixture was shaken at
45ꢀC for 41.5h. The reaction was stopped at 50%
conversion by filtering off the enzyme. After evaporaꢀ
tion of the solvent, the crude mixture was purified by
column chromatography, using EtOAc/hexane = 1:3 as
eluent.
1
2b
1
6
5ꢀC (crystallized from hexane), lit. mp
62ꢀC. H
NMR d 1.31 (3H, t, J = 6.6Hz, CH CH ), 1.48 (9H, s,
2
3
tBu), 2.32–2.40 (2H, m, 5ꢀCH2), 3.56 (2H, t,
J = 5.8Hz, 6ꢀCH ), 4.06 (2H, s, 2ꢀCH ), 4.23 (2H, q,
J = 6.8Hz, OCH ), 12.05 (1H, br s, OH). Anal. Calcd
2
2
(3R,4S)ꢀ4a (150mg, 30%), a slowly crystallizing oil,
2
2
5
1
for C H NO : C, 57.55; H, 7.80; N, 5.16. Found: C,
1
ee >99%, ½aŠ ¼ þ57:9 (c 1, CH Cl ). The H NMR,
3
21
5
D
2
2
1
3
5
7.06; H, 8.00; N, 4.72%.
C NMR and MS data were identical with those for
±)ꢀ4. HRMS (EI): 273.15839 (calcd 273.15762). Anal.
Calcd for C H NO : C, 57.13; H; 8.48; N, 5.12.
(
4.3. (± ±-Ethyl cis- and trans-1-(tert-butoxycarbonyl±-4-
hydroxypiperidine-3-carboxylate, (± ±-4 and (± ±-5
1
3
23
5
Found: C, 56.77; H, 7.93; N, 4.73%.
Ethyl 1ꢀ(tertꢀbutoxycarbonyl)ꢀ4ꢀoxopiperidineꢀ3ꢀcarbꢀ
oxylate (3g, 11.06mmol) was dissolved in abs EtOH
(3S,4R)ꢀ4b 25(160mg, 47%),
a
colourless oil,
1
ee = 99%, ½aŠ ¼ ꢀ41:0 (c 1, CH Cl ). H NMR d 1.23
D
2
2
(
in small portions during 30min at room temperature.
ca. 100mL), and NaBH (0.25g, 6.61mmol) was added
2
(3H, t, J = 7.0Hz, CH CH ), 1.46 (9H, s, tBu), 1.64–
2 3
1.75 (1H, m, 5ꢀH ), 1.95 (1H, ddd, J = 3.0, 7.3,
ax
4
g
The mixture was stirred overnight, and the solvent was
then evaporated off. The residue was dissolved in water
and extracted with EtOAc (3 · 25mL). The combined
organic layer was dried on Na SO and concentrated.
NMR indicated that the crude product was a mixture
of 87% cis and 13% trans isomers. The diastereomers
were separated by column chromatography, using
EtOAc/hexane = 1:3 as eluent.
12.1Hz, 5ꢀH ), 2.04 (3H, s, OCOCH ), 2.66 (1H,
eq
ddd, J = 3.3, 4.3, 11.1Hz, 3ꢀH ), 3.05 (1H, t, J = 12.3,
ax
3
6ꢀH ), 3.31 (1H, t, J = 12.6, 2ꢀH ), 3.86 (1H, d,
ax
ax
J = 10.3Hz, 6ꢀH ), 4.05–4.21 (3H, m, 2ꢀH , CH CH ),
3
2
4
eq
eq
2
1
3
5.46 (1H, dd, J = 3.0, 6.3Hz, 4ꢀH). C NMR d 14.8,
21.6, 29.1, 29.8, 39.6, 41.4, 45.0, 61.4, 68.8, 80.7, 155.6,
+
171.1, 170.6. MS (m/z, EI) (rel. abund.) 315 (3, [M ]),
258 (68), 242 (15), 214 (65), 199 (70), 182 (26), 170
(25), 154 (88), 126 (87), 110 (29), 82 (92), 57 (100), 43
(
±)ꢀ4. Firstꢀeluting isomer, de = 98%: colourless crysꢀ
1
(43). HRMS (EI): 315.17090 (calcd 315.16818). Anal.
Calcd for C H NO : C, 57.13; H, 7.99; N, 4.44.
Found: C, 57.63; H, 8.23; N, 4.74%.
2b
tals, mp 62–63ꢀC (crystallized from hexane), lit. mp
1
5
25
6
1
5
1
1
1
3
8–60ꢀC. H NMR (DMSOꢀd , 400MHz, 333K) d
6
.19 (3H, t, J = 7.3Hz, CH CH ), 1.39 (9H, s, tBu),
.49–1.59 (1H, m, 5ꢀH ), 1.67 (1H, ddd, J = 3.8,
2
3
4.5. Preparative-scale resolution of (± ±-5
ax
3.6Hz, 5ꢀH ), 2.46 (1H, dd, J = 3.3, 4.3Hz, 3ꢀH ),
eq
ax
.06–3.26 (2H, m, 6ꢀH , 2ꢀH ), 3.58 (1H, ddt,
ax
Compound (±)ꢀ5 [168mg (0.61mmol)] was dissolved in
6mL of iꢀPr O, and 180mg (30mg/mL) of 20% lipase
ax
J = 1.3, 4.8, 13.1Hz, 6ꢀH ), 3.77 (1H, dd, J = 4.0,
eq
2
1
3.4Hz, 2ꢀH ), 4.02–4.12 (2H, m, CH CH ), 4.19 (1H,
eq
AK preparation and 114lL (1.23mmol) of VA were
added. The reaction mixture was shaken at 45ꢀC for
14h. The reaction was stopped at 50% conversion by filꢀ
tering off the enzyme. After evaporation of the solvent,
the crude mixture was purified by column chromatograꢀ
phy, using EtOAc/hexane = 1:3 as eluent.
2
3
1
3
dd, J = 3.5, 6.0Hz, 4ꢀH), 4.70 (1H, br s, OH).
NMR d 13.7, 27.8, 31.5, 38.0, 39.6, 45.4, 59.4, 64.1,
8.3, 154.4, 170.8. MS (m/z, EI) (rel. abund.) 273 (2,
C
7
+
[
1
M ]), 216 (32), 200 (13), 172 (23), 154 (37), 126 (50),
00 (24), 82 (79), 57 (100), 41 (21). Anal. Calcd for

3286
M. Solym a´ r et al. / Tetrahedron: Asymmetry 15 (2004) 3281–3287
(
3S,4S)ꢀ5a (68mg, 41%), a lightꢀyellow oil, ee = 99%,
preparation and 137lL (1.26mmol) of VA were added.
The reaction mixture was stirred in a cold room for 5h.
The reaction was stopped at 36% conversion by filtering
off the enzyme. After evaporation of the solvent, the
crude mixture was purified by column chromatography,
using EtOAc as eluent, to afford (3S,4S)ꢀ11a (100.4mg,
25
1
13
½
aŠ ¼ ꢀ24:4 (c 0.91, CH Cl ). The H NMR, C
D
2
2
NMR and MS data were identical with those for (±)ꢀ
. HRMS (EI): 273.15965 (calcd 273.15762). Anal.
Calcd for C H NO : C: 57.13, H: 8.48, N: 5.12.
5
1
3
23
5
Found: C: 56.64, H: 8.06, N: 4.96%.
6
1%), ee = 51%, and (3R,4R)ꢀ11b (66.9mg, 33%),
25
D
(
3R,4R)ꢀ5b 25(67mg, 39%),
a
lightꢀyellow oil,
ee = 91%, ½aŠ ¼ ꢀ24:0 (c 1, CHCl3).
1
ee >99%, ½aŠD ¼ þ6:5 (c 1.01, CH Cl ). H NMR
2
2
1
d 1.25 (3H, t, J = 7.1Hz, CH CH ), 1.46 (9H, s, tBu),
H NMR data for 11b: d 1.13 (3H, t, J = 7.6Hz,
2
3
1
2
3
3
6
.50–1.70 (1H, m, 5ꢀH ), 2.03 (3H, s, OCH ), 2.04–
.10 (1H, m, 5ꢀH ), 2.60 (1H, ddd, J = 4.3, 9.8Hz,
OCOCH CH ), 1.21 (3H, t, J = 7.0Hz, CH CH ),
1.81–1.88 (1H, m, 4ꢀH), 2.06–2.23 (3H, m, 1ꢀH, 4ꢀH,
5ꢀH), 2.28–2.36 (2H, m, OCOCH CH ), 2.47–2.54
ax
3
2
3
2
3
eq
ꢀH ), 3.01 (1H, ddd, J = 3.3, 11.1, 13.9Hz, 6ꢀH ),
ax
ax
2
3
.14 (1H, br s, 2ꢀH ), 3.91 (1H, dt, J = 4.0, 13.9Hz,
ax
(1H, m, 3ꢀH), 2.94–3.00 (1H, m, 5ꢀH), 3.07 (1H,
dd, J = 3.0, 12.6Hz, 1ꢀH), 3.50 (1H, d, J = 13.4Hz,
6ꢀH), 3.60 (1H, d, J = 13.4Hz, 6ꢀH), 4.04–4.19 (2H,
m, CH CH ), 5.32 (1H, dd, J = 3.0, 5.3Hz, 2ꢀH),
ꢀH ), 4.12 (3H, q, J = 7.1Hz, 2ꢀH, CH CH ), 5.14
3
eq
2
1
3
(
1H, ddd, J = 4.3, 9.6Hz, 4ꢀH). C NMR d 14.8,
21.7, 29.0, 30.3, 42.3, 44.7, 47.6, 61.6, 71.7, 80.9, 155.0,
170.6, 171.5. MS (m/z, EI) (rel. abund.) 315 (3, [M ]),
256 (16), 242 (15), 214 (42), 198 (77), 182 (42), 170
2
3
+
13
7.22–7.32 (5H, m, aromatic). C NMR d 9.9, 14.8,
23.9, 28.4, 44.5, 52.4, 55.9, 61.2, 62.9, 127.9, 128.9,
129.6, 138.2, 172.5, 174.4. MS (m/z, EI) (rel. abund.)
(
(
26), 154 (88), 126 (87), 110 (32), 82 (93), 57 (100), 43
46). HRMS (EI): 315.16915 calcd 315.16818). Anal.
+
319 (6, [M ]), 290 (2), 274 (30), 256 (8), 245 (80),
228 (8), 218 (28), 190 (4), 172 (100), 149 (12), 118 (16),
97 (10), 91 (96). HRMS (EI): 319.17810 (calcd 319.17835).
Calcd for C H NO : C, 57.13; H, 7.99; N, 4.44.
6
Found: C, 57.08; H, 7.88; N, 4.22%.
1
5
25
4.6. (± ±-Ethyl cis-1-benzyl-3-hydroxypiperidine-4-carb-
oxylate, (± ±-11
Enantiomerically enriched 11a [90mg (0.34mmol)] was
dissolved in 3mL of iꢀPr O, and 120mg (40mg/mL) of
2
2
0% CALꢀA preparation and 75lL (0.68mmol) of VA
1
mmol) (liberated from 6 with Et N and purified by
silica gel column chromatography, using EtOAc/hexꢀ
ane = 1:3 as eluent) was dissolved in abs EtOH (ca.
ꢀBenzylꢀ3ꢀoxopiperidineꢀ4ꢀcarboxylate (1.5g, 5.74
1
were added. The reaction mixture was stirred at 3ꢀC
for 7.5h. The reaction was stopped at 23% conversion
by filtering off the enzyme. After evaporation of the solꢀ
vent, the crude mixture was purified by column chromaꢀ
7
3
1
small portions during 30min at room temperature.
00mL), and NaBH (0.25g, 6.61mmol) was added in
2
tography, using EtOAc as eluent, to afford (3S,4S)ꢀ11a
4
g
25
D
and (3R,4R)ꢀ11b (24.5mg, 23%), ee = 62%.
(41.6mg, 46%), ee = 92%, ½aŠ ¼ þ37:7 (c 0.77, CHCl ),
3
The mixture was stirred overnight, and the solvent was
then evaporated off. The residue was dissolved in water
and extracted with EtOAc (3 · 20mL). The combined
organic layer was dried on Na SO and concentrated.
1
13
The H NMR, C NMR and MS data for 11a were
identical with those for (±)ꢀ11. HRMS (EI): 263.15261
(calcd 263.15214).
2
4
NMR indicated that the crude product was a mixture
of 74% cis and 26% trans isomers. The cis isomer was
isolated after silica gel column chromatography, using
EtOAc/hexane = 1:3 as eluent; the trans isomer could
be obtained only in a 1:1 diastereomeric mixture.
Acknowledgements
The authors acknowledge receipt of OTKA grants
T034901 and TS 040888.
(
±)ꢀ11. Firstꢀeluting isomer, de = 98%: a lightꢀbrown oil,
H NMR (DMSOꢀd , 400MHz) d 1.16 (3H, t,
1
6
J = 7.09Hz, CH CH ), 1.48–1.60 (1H, m, 5ꢀH), 1.92
2
3
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(
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