Candida antarctica lipase B-catalyzed ring opening of 4-arylalkyl-substituted β-lactams

Article abstract of DOI:10.1016/j.tetasy.2007.11.016

The Lipolase-catalyzed ring opening of racemic 4-benzyl- 3 and 4-phenylethyl-2-azetidinone 4 was performed with 0.5 equiv of H₂O in diisopropyl ether at 45 °C. The resulting (S)-β-amino acid 5 or 6 (ee ≥ 87%) and (R)-β-lactam 7 or 8 (ee >99%) enantiomers could easily be separated. The ring opening of enantiomeric β-lactams with 18% aqueous HCl afforded the corresponding enantiopure β-amino acid hydrochlorides 9 and 10 (ee >99%).

Full text of DOI:10.1016/j.tetasy.2007.11.016

Available online at www.sciencedirect.com
Tetrahedron: Asymmetry 18 (2007) 2841–2844
Candida antarctica lipase B-catalyzed ring opening of
4
-arylalkyl-substituted b-lactams
a
a,
a,b
*
G a´ bor Tasn a´ di, Enik o} Forr o´ and Ferenc F u¨ l o¨ p
a
Institute of Pharmaceutical Chemistry, Academy of Sciences, University of Szeged, H-6720 Szeged E o¨ tv o¨ s utca 6, Hungary
Research Group of Stereochemistry of the Hungarian, Academy of Sciences, University of Szeged, H-6720 Szeged E o¨ tv o¨ s utca 6, Hungary
b
Received 30 October 2007; accepted 13 November 2007
Abstract—The Lipolase-catalyzed ring opening of racemic 4-benzyl- 3 and 4-phenylethyl-2-azetidinone 4 was performed with 0.5 equiv
of H
2
O in diisopropyl ether at 45 ꢀC. The resulting (S)-b-amino acid 5 or 6 (ee P 87%) and (R)-b-lactam 7 or 8 (ee >99%) enantiomers
could easily be separated. The ring opening of enantiomeric b-lactams with 18% aqueous HCl afforded the corresponding enantiopure
b-amino acid hydrochlorides 9 and 10 (ee >99%).
ꢁ
2007 Elsevier Ltd. All rights reserved.
1. Introduction
ing ester derivatives, followed by ring opening to give the
desired b-amino acids. We recently discovered a simple
1
3
In recent years, b-amino acids have aroused considerable
interest as potentially biologically active compounds.
and efficient direct enzymatic method for the enantioselec-
tive (E >200) ring cleavage of b-lactams. Later, the enan-
1
14
(
S)-Homo-b-phenylalanine increases the l-type opioid
tioselective (E >200) ring opening of several 4-aryl-
substituted b-lactams was reported.
2
15
receptor affinity and is a valuable building block for two
tripeptidomimics exhibiting angiotensin-converting enzyme
inhibitor activity and an optically active poly(b-peptide).
3
4
Herein, we report the lipase-catalyzed ring cleavage of 4-
It has been tested as a catalyst in intra- and intermolecular
aldol reactions. (R)-Homo-b-phenylalanine derivatized
benzyl- and 4-phenylethyl-2-azetidinones (± )-3 and (± )-4.
5
with a thiazolidine is a potent inhibitor of dipeptidyl pepti-
dase IV, which allows a novel therapeutic approach to the
2
. Results and discussion
6
treatment of diabetes type 2. A photochemical application
7
is also known. b-Phenylethyl-b-alanine has been applied
The starting racemic b-lactams 3 and 4 were prepared by
the addition of chlorosulfonyl isocyanate to allylbenzene
or 4-phenyl-1-butene 2, according to a literature meth-
8
as a model compound in analytical studies and its antisei-
9
10
zure activity has also been studied. Valuable antiplatelet
1
od
1
1
and antiviral agents have been synthesized from the title
10,13d
(Scheme 1).
b-lactams.
O
Since their widespread investigation, over the last few years
a number of new enzymatic and asymmetric syntheses of b-
amino acids and b-lactams have been published most of
which have been reviewed. An important indirect enzy-
matic method for the preparation of b-amino acid enantio-
mers is the lipase-catalyzed asymmetric acylation of the
primary hydroxy group of the N-hydroxymethylated b-lac-
tams, or the lipase-catalyzed hydrolysis of the correspond-
1. CSI
. Na SO or NaHSO3
NH
2
2
3
n
n
1
2
1
2
, n = 1
, n = 2
(±)-3, n = 1
(±)-4, n = 2
Scheme 1.
The earlier results on the lipase-catalyzed enantioselective
1
5
hydrolysis of 4-aryl-substituted b-lactams suggested the
possibility of the enantioselective ring opening of (± )-3
and (± )-4. Relatively low enantioselectivity (E = 12) was
*
Corresponding author. Tel.: +36 62 544964; fax: +36 62 545705; e-mail:
forro@pharm.u-szeged.hu
0957-4166/$ - see front matter ꢁ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2007.11.016

2842
G. Tasn a´ di et al. / Tetrahedron: Asymmetry 18 (2007) 2841–2844
H O
Lipolase
2
O
COOH
O
+
NH
DIPE
HN
n
NH
2
n
n
(
(
±)-3, n = 1
±)-4, n = 2
5, n = 1
6, n = 2
7, n = 1
8, n = 2
Scheme 2.
observed when the ring in (± )-4 was opened with H O in
diisopropyl ether (DIPE), with Lipolase (30 mg/mL) as a
catalyst at 60 ꢀC (Scheme 2).
drofuran or acetone. The reaction proceeded more slowly
in toluene (conv. = 19% after 24 h) and much more slowly
in 1,4-dioxane (conv. = 4% after 24 h) than in DIPE
2
(conv. = 58% after 24 h), tert-butyl methyl ether
To increase the enantioselectivity, several further enzymes
were tested. In addition to Lipolase (lipase B from Candida
antarctica, produced by submerged fermentation of a
genetically modified Aspergillus oryzae microorganism
and adsorbed on a macroporous resin), Chyrazyme L-2
and Novozym 435 (both lipase B from C. antarctica) also
proved to be promising catalysts, directing the hydrolysis
of (± )-4 with similar enantioselectivities (E ꢀ 12). Lipase
A from C. antarctica, lipase AY from Candida rugosa
and Lecitase did not show any reactivity at 45 ꢀC (no con-
version after 24 h), while PPL (porcine pancreas lipase) and
lipase AK from Pseudomonas fluorescens catalyzed the
reaction at 45 ꢀC, although the reaction rates and the
enantioselectivities were low (after 24 h, conv. ꢀ 3%,
E ꢀ 2). Therefore Lipolase was chosen as the enzyme for
further studies.
(conv. = 60% after 24 h), diethyl ether (conv. = 49% after
24 h) or n-hexane (conv. = 69% after 24 h). So we chose
to continue our studies in DIPE.
Certain additives can have a beneficial influence by increas-
1
6
ing the enantioselectivity and/or the reaction rate. As an
attempt, 1 equiv of triethylamine, 2-octanol and N,N-diiso-
propylethylamine were added to the reaction mixture.
However, no significant changes in the reaction rate or
enantioselectivity were observed (conv. ꢀ 57% after 24 h,
E ꢀ 10).
Since the enantioselective ring cleavage of some N-Boc-
1
7
protected cyclic b-lactams has been described, we synthe-
sized N-Boc-protected-(± )-4. Unfortunately, the Lipolase
(50 mg/mL)-catalyzed ring opening of N-Boc-(± )-4 at
4
5 ꢀC did not give a better result (conv. = 94% after 24 h,
Next, we tested the ring-cleavage reactions of (± )-4 at dif-
ferent temperatures: 60, 50, 45, 40 and 30 ꢀC. Decreasing
the reaction temperature also caused the reaction rate to
decrease as well, but without an increase in enantioselectiv-
ity (after 7 h, conv. = 41% at 60 ꢀC; 24% at 50 ꢀC; 20% at
E = 3).
On the basis of the preliminary results, we decided to per-
form the gram-scale resolutions of (± )-3 and (± )-4 in DIPE
with Lipolase as catalyst and H O (0.5 equiv) as the nucleo-
2
4
5 ꢀC; and 15% at 40 ꢀC; after 5 days, conv. = 61% at
0 ꢀC). Thus, 45 ꢀC was chosen as the optimal temperature.
phile at 45 ꢀC. We planned to stop the reactions at about
25% conversion [ee(b-amino acids) ꢀ60%], and then per-
form the reactions until about 85% conversion [ee(b-lac-
tams) ꢀ90%], following recrystallization of the crude b-
amino acid and b-lactam enantiomers. The results are
shown in Table 1 and in Section 4.
3
Several solvents were also tested. No reaction was observed
after 24 h when the Lipolase (50 mg/mL)-catalyzed ring
cleavage of (± )-4 was performed in chloroform, tetrahy-
Table 1. Lipolase-catalyzed ring opening of (± )-3 and (± )-4
a
25
Time (h)
Conv. at workup (%)
Enantiomer
Yield (%)
Isomer
ee (%)
½aꢁD
c
b,e
(
(
± )-3
± )-4
13
24
81
29
89
b-Amino acid 5
b-Lactam 7
b-Amino acid 6
b-Lactam 8
27
36
31
30
(S)
(R)
(S)
(R)
89
>99
87
>99
+7
d
b,f
88
+38.8
+24
+19
c
b,g
11
d
b,h
22
a
b
c
After recrystallization.
Specific rotations were measured with a Perkin–Elmer 341 polarimeter.
According to HPLC [APEX Octadecyl 5 l column (0.04 cm · 25 cm); precolumn derivatization with (S)-NIFE according to the literature; the mobile
phases were H O (A) and MeCN (B), both of which contained 0.1% TFA; the gradient slopes were 95% A + 5% B at 0 min, increased to 25% A + 75% B
within 60 min.; flow rate: 0.8 mL/min; room temperature; detection at 205 nm; retention times (min): 5, 38.69 (antipode: 39.67); 6, 40.00 (antipode:
0.90)].
18
2
4
d
According to GC [Chrompack Chirasil-L-Val column (25 m · 0.25 mm); 90 ꢀC for 20 min (3) and 10 min (4) ! 140 ꢀC; temperature rise 5 ꢀC/min;
1
40 kPa; retention times (min): 7, 35.77 (antipode: 36.66); 8, 38.52 (antipode: 39.27)].
e
f
19
25
c 0.2; H
c 0.65; CHCl
2
O lit. ½aꢁ ¼ ꢂ8:5 (c 0.2, H
2
O) for (R)-5, ee = 95%.
D
13d
25
D
3
3
lit. ½aꢁ ¼ þ30:1 (c 0.65, CHCl ), ee = 98%.
g
h
20
25
c 0.28 lit. ½aꢁ ¼ ꢂ28:4 (c 0.56, H
2 2
O) for (R)-6, ee >99%; H O.
D
3
c 0.21; CHCl .

G. Tasn a´ di et al. / Tetrahedron: Asymmetry 18 (2007) 2841–2844
2843
25
D
The transformations involving the ring opening of b-lac-
tams 7 and 8 with 18% aqueous HCl afforded b-amino acid
hydrochlorides 9 and 10 (Scheme 3), while treatment of
amino acids 5 and 6 with 18% aqueous HCl resulted in
the corresponding b-amino acid hydrochlorides 5ÆHCl
and 6ÆHCl.
acetone); ee = 89%; lit.19 ½aꢁ ¼ ꢂ8:5 (c 0.2, H O) for
2
(R)-5; mp = 222–225 ꢀC; ee = 95%}.
To obtain b-lactam 7 with high ee, the above unreacted lac-
tam (0.85 g) was dissolved in DIPE (30 mL). Lipolase
(0.8 g, 27 mg/mL) and H O (47 lL, 2.64 mmol) were
2
added. The mixture was stirred at 45 ꢀC for 88 h. The reac-
tion was stopped by filtering off the enzyme at 81% conver-
sion. The solvent was evaporated off, affording (R)-b-
O
COOH
1
8% HCl
reflux
2
5
lactam 7 {0.43 g, 36%; ½aꢁ ¼ þ38:8 (c 0.65; CHCl );
D
3
NH
NH2. HCl
1
3d
n
mp = 67–69 ꢀC (recrystallized from DIPE); ee >99%; lit.
n
2
D
5
½
aꢁ ¼ þ30:1 (c 0.65, CHCl ); ee = 98%}. When 5 (36 mg)
3
7
8
, n = 1
, n = 2
9, n = 1
10, n = 2
was treated with 18% HCl (5 mL), 5ÆHCl was obtained {38
25
mg, 88%; ½aꢁ ¼ þ6 (c 0.21; H O); mp = 172–175 ꢀC;
D
2
1
3d
ee = 89%; lit.
mp = 176–178 ꢀC}.
Scheme 3.
1
H NMR (D O, 400 MHz) d (ppm) for 5: 2.40–2.46 (dd,
2
The absolute configurations were proven by comparing the
J = 16.8, 8.2 Hz, 1H, CH CO H), 2.52–2.57 (dd, J =
2
2
1
3d,19,20
specific rotations with the literature data
Thus, the absolute configuration for 5 and 6 is (S), and for
and 8 it is (R).
(Table 1).
1
3
6.8, 4.9 Hz, 1H, CH CO H), 2.91–3.04 (m, 2H, CH Ph),
.73–3.76 (m, 1H, CH), 7.30–7.43 (m, 5H, Ph).
2 2 2
7
1
H NMR (D O, 400 MHz) d (ppm) for 5ÆHCl: 2.66–2.82
2
(
(
m, 2H, CH CO), 3.03–3.05 (m, 2H, CH Ph), 3.90–3.93
m, 1H, CH), 7.32–7.45 (m, 5H, Ph).
2
2
3. Conclusion
1
In conclusion, 4-benzyl- and 4-phenylethyl-2-azetidinones
± )-3 and (± )-4 were resolved via opening of the b-lactam
ring in an organic medium. The Lipolase-catalyzed reac-
H NMR (CDCl , 400 MHz) d (ppm) for 7: 2.68–2.72 (d,
3
(
J = 14.8 Hz, 1H), 2.82–2.87 (dd, J = 13.6, 8.0 Hz, 1H),
.95–3.00 (dd, J = 13.7, 5.7 Hz, 1H), 3.05–3.10 (m, 1H),
3.83–3.86 (m, 1H), 5.83 (br s, 1H), 7.17–7.35 (m, 5H).
2
tions when H O (0.5 equiv) was used as nucleophile in
2
DIPE at 45 ꢀC led to (S)-b-amino acids 5 and 6
(
ee P 87%) and (R)-b-lactams 7 and 8 (ee >99%). The
products could be separated with ease. Transformations
of b-lactams 7 and 8 by ring opening with 18% aqueous
HCl gave the corresponding enantiomers of the b-amino
acid hydrochlorides 9 and 10 (ee >99%).
4.3. Gram-scale resolution of racemic 4-phenylethyl-2-aze-
tidinone (± ±-4
With the procedure described above, the ring cleavage of
racemic 4 (0.8 g, 4.57 mmol) in DIPE (30 mL) in the pres-
4. Experimental
ence of Lipolase (0.8 g, 27 mg/mL) and H O (41 lL,
2
2
.29 mmol) afforded (S)-b-amino acid 6 [0.27 g, 31%;
25
4
.1. Small-scale resolutions
½aꢁ ¼ þ24 (c 0.28; H O); mp = 215–219 ꢀC (recrystallized
D
2
2
0
25
D
from H O/acetone); ee = 87%; lit. ½aꢁ ¼ ꢂ28:4 (c 0.56,
2
In a small-scale experiment, (± )-4 (0.05 M solution) in
DIPE (1 mL) was added to Lipolase (30 or 50 mg/mL).
H O (0.5 equiv) was added. The mixture was shaken at
H O) for (R)-6; mp = 215–217 ꢀC; ee >99%] in 11 h and
2
25
(R)-b-lactam 8 [0.24 g, 30%; ½aꢁ ¼ þ19 (c 0.21; CHCl );
D
3
2
mp = 46–48 ꢀC (recrystallized from DIPE); ee >99%] in
3
0, 40, 45, 50 or 60 ꢀC. The progress of the reaction was
22 h. When 6 (30 mg) was treated with 18% HCl (5 mL),
2
5
followed by taking samples from the mixture at intervals
and analyzing them by gas chromatography and HPLC
6ÆHCl was obtained [33 mg, 92%; ½aꢁ ¼ þ12 (c 0.21;
D
H O); mp = 150–152 ꢀC; ee = 87%].
2
(
Table 1).
1
H NMR (D O, 400 MHz) d (ppm) for 6: 1.96–2.02 (m,
2
4
(
.2. Gram-scale resolution of racemic 4-benzyl-2-azetidinone
± ±-3
2H), 2.45–2.52 (dd, J = 16.8, 8.4 Hz, 1H), 2.61–2.67 (dd,
J = 16.8, 4.6 Hz, 1H), 2.72–2.79 (m, 2H), 3.48–3.53 (m,
1H), 7.29–7.42 (m, 5H).
Racemic 3 (1.2 g, 7.44 mmol) was dissolved in DIPE
40 mL). Lipolase (1.2 g, 30 mg/mL) and H O (67 lL,
1
(
H NMR (D O, 400 MHz) d (ppm) for 6ÆHCl: 2.00–2.05
2
2
3
.72 mmol) were added. The mixture was stirred at 45 ꢀC
(m, 2H), 2.69–2.86 (m, 4H), 3.62 (m, 1H), 7.28–7.41 (m,
5H).
for 13 h. The reaction was stopped by filtering off the en-
zyme at 24% conversion. The solvent was evaporated off,
affording the unreacted b-lactam 7 (0.85 g, 5.27 mmol,
ee = 18%). The filtered enzyme was washed with distilled
H O (3 · 20 mL), and the H O was evaporated off, yielding
1
H NMR (CDCl , 400 MHz) d (ppm) for 8: 1.94–2.00 (dd,
3
J = 14.5, 7.5 Hz, 2H, CH Ph), 2.55–2.59 (d, J = 14.8 Hz,
1H, CHH), 2.64–2.73 (m, 2H, CH ), 3.02–3.08 (m, 1H,
CHH), 3.61–3.65 (m, 1H, CH), 5.67 (br s, 1H, NH),
7.16–7.32 (m, 5H, Ph).
2
2
2
2
2
D
5
the crystalline (S)-b-amino acid 5 {0.36 g, 27%; ½aꢁ ¼ þ7
(
c 0.2; H O); mp = 207–210 ꢀC (recrystallized from H O/
2
2

2844
G. Tasn a´ di et al. / Tetrahedron: Asymmetry 18 (2007) 2841–2844
4
.4. Ring opening of b-lactam enantiomers 7 and 8
8. (a) Hyun, M. H.; Han, S. C.; Whangbo, S. H. J. Chromatogr.,
´
A 2003, 992, 47–56; (b) Arki, A.; Tourw e´ , D.; Solym a´ r, M.;
F u¨ l o¨ p, F.; Armstrong, D. W.; P e´ ter, A. Chromatographia
Compounds 7 (50 mg) or 8 (25 mg) were refluxed in 18%
2
004, 60, S43–S54.
HCl (10 mL) for 3 h. The solvent was evaporated off to af-
25
9. Tan, C. Y. K.; Wainman, D.; Weaver, D. F. Bioorg. Med.
Chem. 2003, 11, 113–121.
ford 9 [60 mg, 90%; ½aꢁ ¼ ꢂ8 (c 0.11; H O); mp = 182–
D
2
2
5
1
85 ꢀC; ee >99%] or 10 {26 mg, 79%; ½aꢁ ¼ ꢂ15 (c 0.21;
D
1
1
0. Zablocki, J. A.; Tjoeng, F. S.; Bovy, P. R.; Miyano, M.;
Garland, R. B.; Williams, K.; Schretzman, L.; Zupec, M. E.;
Rico, J. G.; Lindmark, R. J.; Toth, M. V.; McMackins, D. E.;
Adams, S. P.; Panzer-Knodle, S. G.; Nicholson, N. S.; Taite,
B. B.; Salyers, A. K.; King, L. W.; Campion, J. G.; Feigen, L.
P. Bioorg. Med. Chem. 1995, 5, 539–551.
H O); mp = 146–148 ꢀC; ee >99%}. The H NMR (H O,
2
2
4
00 MHz) d (ppm) data for 9 and 10 are similar to those
for 5ÆHCl and 6ÆHCl.
1
1
1. Yoakim, C.; Ogilvie, W. W.; Cameron, D. R.; Chabot, C.;
Guse, I.; Hach e´ , B.; Naud, J.; O’Meara, J. A.; Plante, R.;
D e´ ziel, R. J. Med. Chem. 1998, 41, 2882–2891.
2. (a) Liu, M.; Sibi, M. P. Tetrahedron 2002, 58, 7991–8035; (b)
Liljeblad, A.; Kanerva, L. T. Tetrahedron 2006, 62, 5831–
Acknowledgements
The authors acknowledge the receipt of OTKA Grants T
46440 and T 049407, GVOP-3.1.1.-2004-05-0255/3.0 and
a Bolyai Fellowship for E.F.
0
5
854; (c) F u¨ l o¨ p, F. Chem. Rev. 2001, 101, 2181–2204; (d)
F u¨ l o¨ p, F.; Martinek, T. A.; T o´ th, G. K. Chem. Soc. Rev.
006, 35, 323–334.
13. (a) Forr o´ , E.; A´ rva, J.; F u¨ l o¨ p, F. Tetrahedron: Asymmetry
001, 12, 643–649; (b) Forr o´ , E.; F u¨ l o¨ p, F. Tetrahedron:
2
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