Synthesis of enantiopure 1,4-ethyl- and 1,4-ethylene-bridged cispentacin by lipase-catalyzed enantioselective ring opening of β-lactams

Article abstract of DOI:10.1016/j.tetasy.2003.12.034

1,4-Ethyl- and 1,4-ethylene-bridged cispentacin enantiomers 1a, 1c and 2a, 2c were prepared through the lipase-catalyzed enantioselective ring opening of racemic exo-3-azatricyclo[4.2.1.0^2.5]nonan-4-one, (±)-1, and exo-3-azatricyclo[4.2.1.0^2.5]non-7-en-4-one, (±)-2. High enantioselectivity (E >200) was observed when the Lipolase-catalyzed reactions were performed with 1equiv of H₂O in diisopropyl ether at 70°C. The resolved β-amino acids 1a and 2a (yield 46%) and β-lactams 1b and 2b (yield≥40%) could be easily separated. The ring opening of lactam enantiomers with 18% HCl afforded the corresponding β-amino acid hydrochloride enantiomers (ee ≥98%).

Full text of DOI:10.1016/j.tetasy.2003.12.034

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 15 (2004) 573–575
Synthesis of enantiopure 1,4-ethyl- and 1,4-ethylene-bridged
cispentacin by lipase-catalyzed enantioselective ring opening of
b-lactams
*
}
Eniko Forro and Ferenc Fulop
ꢀ
€
€
Institute of Pharmaceutical Chemistry, University of Szeged, H-6701 Szeged, PO Box 121, Hungary
Received 4 November 2003; revised 18 December 2003; accepted 22 December 2003
Abstract—1,4-Ethyl- and 1,4-ethylene-bridged cispentacin enantiomers 1a, 1c and 2a, 2c were prepared through the lipase-catalyzed
enantioselective ring opening of racemic exo-3-azatricyclo[4.2.1.02:5]nonan-4-one, ( ))1, and exo-3-azatricyclo[4.2.1.02:5]non-7-en-4-
one, ( ))2. High enantioselectivity (E >200) was observed when the Lipolase-catalyzed reactions were performed with 1 equiv of
H2O in diisopropyl ether at 70 ꢀC. The resolved b-amino acids 1a and 2a (yield 46%) and b-lactams 1b and 2b (yield P40%) could be
easily separated. The ring opening of lactam enantiomers with 18% HCl afforded the corresponding b-amino acid hydrochloride
enantiomers (ee P98%).
ꢁ 2004 Elsevier Ltd. All rights reserved.
1. Introduction
diene 4 by 1,2-dipolar cycloaddition of chlorosulfonyl
isocyanate (O@C@N–SO2Cl; CSI) (Scheme 1).11
A number of new enzymatic and asymmetric syntheses
of b-amino acids or their derivatives and b-lactams in
enantiomerically pure form have been elaborated over
recent years, and most of them have been reviewed.1–3 An
important indirect enzymatic route to enantiopure b-
amino acids or esters proceeds through the lipase-cata-
lyzed asymmetric acylation of the primary OH group of
N-hydroxymethylated b-lactams, or the lipase-catalyzed
hydrolysis of the corresponding ester derivatives, fol-
lowed by ring opening to the corresponding b-amino
acid or ester.4–8 We have recently published a direct
enzymatic method to enantiopure valuable b-amino
acids (e.g., cispentacin with strong antibiotic and anti-
fungal activities) through the lipase-catalyzed enantio-
selective hydrolysis of b-lactams in an organic solvent.9;10
O
1. CSI
2. Na2SO3
NH
( )-1
3
4
O
1. CSI
2. Na2SO3
NH
( )-2
Scheme 1.
In an earlier study, Lipolase (lipase B from Candida
antarctica, produced by submerged fermentation of a
genetically modified Aspergillus oryzae microorganism
and adsorbed on a macroporous resin) proved to
be applicable for the enantioselective ring opening of
6-azabicyclo[3.2.0]heptan-7-one, 7-azabicyclo[4.2.0]octan-
8-one, 8-azabicyclo[5.2.0]nonan-9-one and 9-azabicy-
Herein, we report the enantioselective ring opening of
racemic exo-3-azatricyclo[4.2.1.02:5]nonan-4-one, ( )-1,
and exo-3-azatricyclo[4.2.1.02:5]non-7-en-4-one, ( )-2.
clo[6.2.0]decan-10-one.10
High
enantioselectivities
2. Results and discussion
(E >200) were observed when the reactions were per-
formed with H2O (1 equiv) in diisopropyl ether at 60 ꢀC.
These results10 on the lipase-catalyzed enantioselective
hydrolysis of b-lactams suggested the possibility of
the enantioselective ring opening of ( )-1 and ( )-2
(Scheme 2).
The racemic b-lactams 1 and 2 were prepared from
bicyclo[2.2.1]hept-2-ene 3 and bicyclo[2.2.1]hepta-2,5-
* Corresponding author. Tel.: +36-62-545564; fax: +36-62-545705;
e-mail: fulop@pharma.szote.u-szeged.hu
0957-4166/$ - see front matter ꢁ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2003.12.034

574
E. Forrꢀo, F. F€ul€op / Tetrahedron: Asymmetry 15 (2004) 573–575
O
O
O
H2O
HOOC
HCl H2N
COOH
NH2
Lipolase
18% HCl
2
2
5
5
+
.
.
3
3
2
2
HN
NH
( )-1
HN
iPr2O
70 °C
(1S,2R,5S,6R)-1b
(1R,2S,3R,4S)-1c • HCl
(1S,2R,3S,4R)-1a (1S,2R,5S,6R)-1b
O
O
O
H2O
Lipolase
iPr2O
COOH
NH2
HOOC
HCl H2N
2
18% HCl
5
2
5
+
.
.
3
3
2
2
NH
( )-2
Scheme 2.
HN
HN
70 °C
(1R,2R,5S,6S)-2b
(1S,2S,3R,4R)-2c • HCl
(1R,2R,3S,4S)-2a (1R,2R,5S,6S)-2b
Scheme 3.
Even though the E value in the Lipolase-catalyzed ring
opening is excellent, the reaction rate for the ring
opening in the case of 2 clearly increases with increasing
temperature (after 96 h, 1 equiv of H2O, 50 mg mLꢀ1
Lipolase, 60 ꢀC: conv. ¼ 22%, ees ¼ 27%, eep >95%; after
96 h, 1 equiv of H2O, 50 mg mLꢀ1 Lipolase, 65 ꢀC: conv. ¼
26%, ees ¼ 33%, eep >95%; after 93 h, 1 equiv of H2O,
50 mg mLꢀ1 Lipolase, 70 ꢀC: conv. ¼ 30%, ees ¼ 41%,
eep >95%).12
Table 2. Specific rotation of the enantiomers prepared
25
D
a
Amino acid hydrochloride
Ee (%)
½aꢁ
1S,2R,3S,4R-1aÆHCl16
1R,2S,3R,4S-1cÆHCl17
1R,2R,3S,4S-2aÆHCl16
99
99
99
+3.8 (c ¼ 0:4, MeOH)b
)3.8 (c ¼ 0:3, MeOH)
)13.2 (c ¼ 0:5; MeOH)
)10.8 (c ¼ 0:5; H2O)
+13.4 (c ¼ 0:4; MeOH)
+10.6 (c ¼ 0:4; H2O)
1S,2S,3R,4R-2cÆHCl17
99
a Optical rotations were measured with a Perkin–Elmer 341 polari-
meter.
b [a]2D0 ¼ +3.9 (c 2, MeOH).18
On the basis of the preliminary results, the gram-scale
resolutions of ( )-1 and ( )-2 were performed with
1 equiv of water in the presence of Lipolase in diiso-
propyl ether at 70 ꢀC. In spite of the long reaction times,
the products had an excellent enantiomeric excess at
50% conversion. The results are reported in Table 1.
catalytically in the presence of cyclohexene as a hydro-
gen donor,7 the analyzed chromatogram peaks indicated
that the 1S,2R,5S,6R-3-azatricyclo[4.2.1.02:5]nonan-4-
one 1b was formed. The specific rotation value for the
25
D
The transformations involving the ring opening of
b-lactams 1b and 2b with 18% aqueous HCl resulted in
the enantiomers of the b-amino acid hydrochlorides
1cÆHCl and 2cÆHCl (Scheme 3). Treatment of amino
acids 1a and 2a with 18% aqueous HCl resulted in
enantiopure hydrochlorides 1aÆHCl and 2aÆHCl. The
specific rotations for the enantiomers prepared are
reported in Table 2.
isolated crude product: ½aꢁ ¼ +61.2 (c 0.3, CHCl3) is
close to the ½a2D5 ¼ +64.1 (c 0.5, CHCl3) reported for 1b.
Therefore, the absolute configuration for 2b is
(1R,2R,5S,6S) and that for 2a is (1R,2R,3S,4S).
In conclusion, a very efficient and simple direct enzy-
matic synthesis of 1,4-ethyl- and 1,4-ethylene-bridged
cispentacin enantiomers in an organic medium has been
developed. The products (b-lactam and b-amino acid)
could be easily separated. Transformations by ring
opening of the b-lactams 1b and 2b with 18% aqueous
HCl gave the enantiomers of the b-amino acid hydro-
chlorides 1cÆHCl and 2cÆHCl (ee >99%).
The absolute configuration in the case of 1 was proved
by comparing the specific rotation values with the lit-
erature data (Tables 1 and 2). When (1R,2R,5S,6S)-3-
azatricyclo[4.2.1.02:5]non-7-en-4-one 2b was reduced
Table 1. Lipolase-catalyzed ring opening of ( )-113 and ( )-214
Time
(day)
Conver-
sion (%)
E
b-Lactam(1b–2b)
b-Amino acid(1a–2a)
25
D
25
D
Yielda (%)
Isomer
Eeb (%) ½aꢁ
Yielda (%)
Isomer
Eed (%)
½aꢁ
c
d
( )-1
( )-2
11
8
50
50
>200
>200
40
47
1S,2R,5S,6R 99
1R,2R,5S,6S 99
+64.1e 46
+123.7e 46
1S,2R,3S,4R 99
1R,2R,3S,4S 98
+9.1f ;g
)12.2h
a Yield 100% at 50% conversion.
b According to GC [CP-Chirasil-Dex CB column, 120 ꢀC for 4 min fi 170 ꢀC (temperature rise 10 ꢀC/min; 140 kPa) retention times (min): 1b: 10.95
(antipode: 10.77); 2b: 10.23 (antipode: 10.09)].
c Optical rotations were measured with a Perkin–Elmer 341 polarimeter.
d Determined by GC [after double derivatization (i) diazomethane; (ii) acetic anhydride in the presence of 4-dimethylaminopyridine and pyridine (CP-
Chirasil-Dex CB column, 120 ꢀC for 5 min fi 170 ꢀC (temperature rise 10 ꢀC/min; 70 kPa) retention times (min): 1a: 14.01 (antipode: 14.20); 2a: 12.96
(antipode: 13.11)].
e c ¼ 0:5; CHCl3.
f c ¼ 0:5; H2O.
g [a]D20 ¼ )8 (c 1.4, H2O) for (1R,2S,3R,4S)-1c15
h c ¼ 0:4; H2O.
.

E. Forrꢀo, F. F€ul€op / Tetrahedron: Asymmetry 15 (2004) 573–575
575
d, J ¼ 1:4, H-5), 3.38 (1H, d, J ¼ 3:1, H-2), 5.85 (1H, br s,
NH). 13C NMR (100.62 MHz, CDCl3) d (ppm) 25.3, 27.2,
31.2, 34.2, 38.5, 53.8, 58.9, 170.7. Anal. Calcd for
C8H11NO: C, 70.04; H, 8.08; N, 10.21. Found: C, 69.89;
H, 8.15; N, 10.46.
Acknowledgements
The authors acknowledge receipt of OTKA grants T
034901 and TS 040888, FKFP grant 0115/2001 and a
ꢀ ꢀ
Bekesy Fellowship for EF (grant no. 181/2002).
14. With the procedure described above, the reaction of
racemic 211 (1 g, 7.39 mmol) in iPr2O (40 mL) in the
presence of Lipolase (2 g, 50 mg mLꢀ1
)
the
and water
b-lactam
(0.13 mL,
7.39 mmol)
afforded
25
D
(1R,2R,5S,6S)-2b [0.47 g, 47%; ½aꢁ ¼ +123.7 (c 0.5;
CHCl3); mp 89–91 ꢀC (recrystallized from diisopropyl
ether); ee 99%] and b-amino acid (1R,2R,3S,4S)-2a [0.52 g,
25
D
References and notes
46%; ½aꢁ ¼ )12.2 (c 0.4; H2O); mp >260 ꢀC (recrystallized
from water/acetone); ee ¼ 98%] in 8 days.
1H NMR (400 MHz, D2O) d (ppm) for 2a: 1.6 (1H, d,
J ¼ 7:8, CHAHB), 1.87 (1H, d, J ¼ 7:8, CHAHB), 2.49
(1H, d, J ¼ 6:3, H-2) 3.01, 3.07 (2H, br s, 2 · CH), 3.29
(1H, d, J ¼ 6:2, H-3) 6.19–6.39 (2H, m, CH@CH). 13C
NMR (100.62 MHz, D2O) d (ppm) 43.6, 46.7, 46.9, 47.6,
51.9, 135.1, 140.5, 180.2. Anal. Calcd for C8H11NO2: C,
62.73; H, 7.24; N, 9.14. Found: C, 62.6; H, 7.19; N, 9.14.
1H NMR (400 MHz, CDCl3) d (ppm) for 2b: 1.65 (1H, d,
J ¼ 9:7, CHAHB), 1.81 (1H, d, J ¼ 9:7, CHAHB), 2.88,
2.93 (2H, br s, 2 · CH), 3.05 (1H, d, J ¼ 1:6, H-2), 3.51
(1H, d, J ¼ 3:4, H-3), 5.96 (1H, br s, NH), 6.13–6.25 (2H,
m, CH@CH).13C NMR (100.62 MHz, D2O) d (ppm) 39.3,
41.4, 44.3, 53.7, 58.8, 136.6, 138.8, 171.4. Anal. Calcd for
C8H9NO: C, 71.09; H, 6.71; N, 10.36. Found: C, 70.98; H,
6.69; N, 10.36.
€ €
1. Fulop, F. Chem. Rev. 2001, 101, 2181–2204.
2. Park, K.; Kurth, M. J. Tetrahedron 2002, 58, 8629–8659.
3. (a) Palomo, C.; Oiarbide, M.; Landa, A.; Esnal, A.; Linden,
A. J. Org. Chem. 2001, 66, 4180; (b) Palomo, C.; Aizpurua,
J. M.; Ganboa, I.; Oiarbide, M. Synlett 2001, 1813.
ꢀ
ꢀ
€ €
4. Csomos, P.; Kanerva, L. T.; Bernath, G.; Fulop, F.
Tetrahedron: Asymmetry 1996, 7, 1789.
ꢀ
ꢀ
ꢀ
€ €
5. Kaman, J.; Forro, E.; Fulop, F. Tetrahedron: Asymmetry
2000, 11, 1593.
€ €
Tetrahedron: Asymmetry 2000, 11, 4179.
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€€
6. Fulop, F.; Palko, M.; Kaman, J.; Lazar, L.; Sillanpaa, R.
ꢀ
7. Forro, E.; Arva, J.; Fulop, F. Tetrahedron: Asymmetry
ꢀ
2001, 12, 643.
€ €
ꢀ
8. Forro, E.; Fulop, F. Tetrahedron: Asymmetry 2001, 12, 2351.
9. Park, S.; Forro, E.; Grewal, H.; Fulop, F.; Kazlauskas, R.
€ €
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€ €
J. Adv. Synth. Catal. 2003, 345, 986.
15. Bolm, C.; Schiffers, I.; Atodiresei, I.; Hackenberger, C. P.
R. Tetrahedron: Asymmetry 2003, 14, 3455.
16. When 1a or 2a (0.2 g) was treated with 18% HCl (7 mL),
ꢀ
€ €
10. Forro, E.; Fulop, F. Org. Lett. 2003, 5, 1209.
11. Moriconi, E. J.; Crawford, W. C. J. Org. Chem. 1967, 32,
370.
(1S,2R,3S,4R)-1aÆHCl [0.21 g, 85%; [a]2D5 ¼ +3.8 (c 0.4;
12. In a typical small-scale experiment, racemic b-lactam
(0.05 M solution) in iPr2O (2 mL) was added to Lipolase
(50 mg mLꢀ1). Water (1 equiv) was added. The mixture
was shaken at 60, 65 or 70 ꢀC. The progress of the reaction
was followed by taking samples from the reaction mixture
at intervals and analyzing them by gas chromatography.
The ee values for the unreacted b-lactam enantiomers were
determined by gas chromatography on a Chromopak
Chiralsil-Dex CB column (25 m), while the ees for the ring-
opened amino acids produced (during preliminary exper-
iments) were calculated by using hexadecane [CP-Chirasil-
Dex CB column, 120 ꢀC for 4 min fi 170 ꢀC (temperature
rise 10 ꢀC/min; 140 kPa) retention time 8.19 min] as an
internal standard.10
MeOH); mp 196–199 ꢀC (H2O); ee ¼ 99%] and
25
(1R,2R,3S,4S)-2aÆHCl [0.23 g, 96%; ½aꢁ ¼ )10.8 (c 0.5;
D
H2O), )13.2 (c ¼ 0:5; MeOH); mp 206–210 ꢀC (H2O);
ee ¼ 99%] were obtained.
1H NMR (400 MHz, D2O) d (ppm) for 1aÆHCl: 1.29–1.82
(6H, m, 3 · CH2), 2.42, 2.62 (2H, br s, 2 · CH), 2.85 (1H,
d, J ¼ 8:1, H-2), 3.47 (1H, d, J ¼ 8:1, H-3). 13C NMR
(100.62 MHz, D2O) d (ppm) 26.2, 28.3, 33.9, 41.4, 42.4,
50.7, 55.3, 177.7. Anal. Calcd for C8H13NO2ÆHCl: C,
50.14; H, 7.36; N, 7.31. Found: C, 50.16; H, 7.52; N, 7.48.
1H NMR (400 MHz, D2O) d (ppm) for 2aÆHCl: 1.66 (1H,
d, J ¼ 9:2, CHAHB), 1.92 (1H, d, J ¼ 9:4, CHAHB), 2.56
(1H, d, J ¼ 5:9, H-2) 3.04, 3.21 (2H, br s, 2 · CH), 3.39
(1H, d, J ¼ 5:8, H-3) 6.24–6.39 (2H, m, CH@CH). 13C
NMR (100.62 MHz, D2O) d (ppm) 43.6, 44.7, 46.7, 47.5,
52.8, 136.1, 139.6, 176.3. Anal. Calcd for C8H11NO2ÆHCl:
C, 50.67; H, 6.38; N, 7.39. Found: C, 50.76; H, 6.16; N,
7.24.
13. Racemic 111 (1 g, 7.28 mmol) was dissolved in iPr2O
(40 mL). Lipolase (2 g, 50 mg mLꢀ1) and water (0.13 mL,
7.28 mmol) were added and the mixture was shaken in an
incubator shaker at 70 ꢀC for 11 days. The reaction was
stopped by filtering off the enzyme at 50% conversion. The
17. 1b or 2b (0.2 g) was refluxed in 18% HCl (7 mL) for 3 h.
The solvent was evaporated off, and the products were
recrystallized from water, which afforded white crystals of
solvent was evaporated and the residue of (1S,2R,5S,6R)-
25
D
1b crystallized [0.4 g, 40%; ½aꢁ ¼ +64.1 (c 0.5; CHCl3); mp
25
58–60 ꢀC (recrystallized from diisopropyl ether); ee 99%].
The filtered enzyme was washed with distilled water
(3 · 20 mL), and the water was evaporated, yielding the
(1R,2S,3R,4S)-1cÆHCl [0.21 g, 77%, ½aꢁ ¼ )3.8 (c 0.3;
25
D
MeOH); mp 198–207 ꢀC (H2O); ee 99%] or (1S,2S,3R,4R)-
2cÆHCl [0.23 g, 84%, ½aꢁ ¼ +10.6 (c 0.4; H2O), +13.4
D
crystalline b-amino acid (1S,2R,3S,4R)-1a [0.52 g, 46%;
(c ¼ 0:4; MeOH); mp 196–210 ꢀC (H2O); ee 99%], respec-
25
D
½aꢁ ¼ +9.1 (c 0.5; H2O); slow melting (229–242 ꢀC,
tively.
recrystallized from water/acetone), ee ¼ 99%].
The 1H NMR (400 MHz, D2O) and 13C NMR
(100.62 MHz, D2O) d (ppm) data for (1R,2S,3R,4S)-
1cÆHCl or (1S,2S,3R,4R)-2cÆHCl are similar to those for
(1S,2R,3S,4R)-1aÆHCl and (1R,2R,3S,4S)-2aÆHCl. Anal.
found for (1R,2S,3R,4S)-1cÆHCl: C, 49.88; H, 7.33; N,
7.24. Anal. found for (1S,2S,3R,4R)-2cÆHCl: C, 50.67; H,
6.22; N, 7.45.
1H NMR (400 MHz, D2O) d (ppm) for 1a: 1.26–1.76 (6H,
m, 3 · CH2), 2.4, 2.51 (2H, br s, 2 · CH), 2.59 (1H, d,
J ¼ 8:1, H-2), 3.38 (1H, d, J ¼ 8:1, H-3). 13C NMR
(100.62 MHz, D2O) d (ppm) 26.2, 28.5, 33.9, 41.6, 42.4,
52.1, 55.1, 180.1. Anal. Calcd for C8H13NO2: C, 61.91; H,
8.44; N, 9.03. Found: C, 62.06; H, 8.51; N, 10.14.
1H NMR (400 MHz, CDCl3) d (ppm) for 1b: 1.02–1.69
(6H, m, 3 · CH2), 2.35, 2.41 (2H, br s, 2 · CH), 2.97 (1H,
18. Kanerva, L. T.; Csomos, P.; Sundholm, O.; Bernath, G.;
€ €
ꢀ
Fulop, F. Tetrahedron: Asymmetry 1996, 7, 1705–1716.
ꢀ